This is /builds/ul11u3sru-gate/components/coreutils/coreutils-8.16/doc/coreutils.info, produced by makeinfo version 4.13 from /builds/ul11u3sru-gate/components/coreutils/coreutils-8.16/doc/coreutils.texi. INFO-DIR-SECTION Basics START-INFO-DIR-ENTRY * Coreutils: (coreutils). Core GNU (file, text, shell) utilities. * Common options: (coreutils)Common options. Common options. * File permissions: (coreutils)File permissions. Access modes. * Date input formats: (coreutils)Date input formats. END-INFO-DIR-ENTRY INFO-DIR-SECTION Individual utilities START-INFO-DIR-ENTRY * arch: (coreutils)arch invocation. Print machine hardware name. * base64: (coreutils)base64 invocation. Base64 encode/decode data. * basename: (coreutils)basename invocation. Strip directory and suffix. * cat: (coreutils)cat invocation. Concatenate and write files. * chcon: (coreutils)chcon invocation. Change SELinux CTX of files. * chgrp: (coreutils)chgrp invocation. Change file groups. * chmod: (coreutils)chmod invocation. Change file permissions. * chown: (coreutils)chown invocation. Change file owners/groups. * chroot: (coreutils)chroot invocation. Specify the root directory. * cksum: (coreutils)cksum invocation. Print POSIX CRC checksum. * comm: (coreutils)comm invocation. Compare sorted files by line. * cp: (coreutils)cp invocation. Copy files. * csplit: (coreutils)csplit invocation. Split by context. * cut: (coreutils)cut invocation. Print selected parts of lines. * date: (coreutils)date invocation. Print/set system date and time. * dd: (coreutils)dd invocation. Copy and convert a file. * df: (coreutils)df invocation. Report file system disk usage. * dir: (coreutils)dir invocation. List directories briefly. * dircolors: (coreutils)dircolors invocation. Color setup for ls. * dirname: (coreutils)dirname invocation. Strip last file name component. * du: (coreutils)du invocation. Report on disk usage. * echo: (coreutils)echo invocation. Print a line of text. * env: (coreutils)env invocation. Modify the environment. * expand: (coreutils)expand invocation. Convert tabs to spaces. * expr: (coreutils)expr invocation. Evaluate expressions. * factor: (coreutils)factor invocation. Print prime factors * false: (coreutils)false invocation. Do nothing, unsuccessfully. * fmt: (coreutils)fmt invocation. Reformat paragraph text. * fold: (coreutils)fold invocation. Wrap long input lines. * groups: (coreutils)groups invocation. Print group names a user is in. * head: (coreutils)head invocation. Output the first part of files. * hostid: (coreutils)hostid invocation. Print numeric host identifier. * hostname: (coreutils)hostname invocation. Print or set system name. * id: (coreutils)id invocation. Print user identity. * install: (coreutils)install invocation. Copy and change attributes. * join: (coreutils)join invocation. Join lines on a common field. * kill: (coreutils)kill invocation. Send a signal to processes. * link: (coreutils)link invocation. Make hard links between files. * ln: (coreutils)ln invocation. Make links between files. * logname: (coreutils)logname invocation. Print current login name. * ls: (coreutils)ls invocation. List directory contents. * md5sum: (coreutils)md5sum invocation. Print or check MD5 digests. * mkdir: (coreutils)mkdir invocation. Create directories. * mkfifo: (coreutils)mkfifo invocation. Create FIFOs (named pipes). * mknod: (coreutils)mknod invocation. Create special files. * mktemp: (coreutils)mktemp invocation. Create temporary files. * mv: (coreutils)mv invocation. Rename files. * nice: (coreutils)nice invocation. Modify niceness. * nl: (coreutils)nl invocation. Number lines and write files. * nohup: (coreutils)nohup invocation. Immunize to hangups. * nproc: (coreutils)nproc invocation. Print the number of processors. * od: (coreutils)od invocation. Dump files in octal, etc. * paste: (coreutils)paste invocation. Merge lines of files. * pathchk: (coreutils)pathchk invocation. Check file name portability. * pr: (coreutils)pr invocation. Paginate or columnate files. * printenv: (coreutils)printenv invocation. Print environment variables. * printf: (coreutils)printf invocation. Format and print data. * ptx: (coreutils)ptx invocation. Produce permuted indexes. * pwd: (coreutils)pwd invocation. Print working directory. * readlink: (coreutils)readlink invocation. Print referent of a symlink. * realpath: (coreutils)readpath invocation. Print resolved file names. * rm: (coreutils)rm invocation. Remove files. * rmdir: (coreutils)rmdir invocation. Remove empty directories. * runcon: (coreutils)runcon invocation. Run in specified SELinux CTX. * seq: (coreutils)seq invocation. Print numeric sequences * sha1sum: (coreutils)sha1sum invocation. Print or check SHA-1 digests. * sha2: (coreutils)sha2 utilities. Print or check SHA-2 digests. * shred: (coreutils)shred invocation. Remove files more securely. * shuf: (coreutils)shuf invocation. Shuffling text files. * sleep: (coreutils)sleep invocation. Delay for a specified time. * sort: (coreutils)sort invocation. Sort text files. * split: (coreutils)split invocation. Split into pieces. * stat: (coreutils)stat invocation. Report file(system) status. * stdbuf: (coreutils)stdbuf invocation. Modify stdio buffering. * stty: (coreutils)stty invocation. Print/change terminal settings. * su: (coreutils)su invocation. Modify user and group ID. * sum: (coreutils)sum invocation. Print traditional checksum. * sync: (coreutils)sync invocation. Synchronize memory and disk. * tac: (coreutils)tac invocation. Reverse files. * tail: (coreutils)tail invocation. Output the last part of files. * tee: (coreutils)tee invocation. Redirect to multiple files. * test: (coreutils)test invocation. File/string tests. * timeout: (coreutils)timeout invocation. Run with time limit. * touch: (coreutils)touch invocation. Change file timestamps. * tr: (coreutils)tr invocation. Translate characters. * true: (coreutils)true invocation. Do nothing, successfully. * truncate: (coreutils)truncate invocation. Shrink/extend size of a file. * tsort: (coreutils)tsort invocation. Topological sort. * tty: (coreutils)tty invocation. Print terminal name. * uname: (coreutils)uname invocation. Print system information. * unexpand: (coreutils)unexpand invocation. Convert spaces to tabs. * uniq: (coreutils)uniq invocation. Uniquify files. * unlink: (coreutils)unlink invocation. Removal via unlink(2). * uptime: (coreutils)uptime invocation. Print uptime and load. * users: (coreutils)users invocation. Print current user names. * vdir: (coreutils)vdir invocation. List directories verbosely. * wc: (coreutils)wc invocation. Line, word, and byte counts. * who: (coreutils)who invocation. Print who is logged in. * whoami: (coreutils)whoami invocation. Print effective user ID. * yes: (coreutils)yes invocation. Print a string indefinitely. END-INFO-DIR-ENTRY This manual documents version 8.16 of the GNU core utilities, including the standard programs for text and file manipulation. Copyright (C) 1994-2012 Free Software Foundation, Inc. Permission is granted to copy, distribute and/or modify this document under the terms of the GNU Free Documentation License, Version 1.3 or any later version published by the Free Software Foundation; with no Invariant Sections, with no Front-Cover Texts, and with no Back-Cover Texts. A copy of the license is included in the section entitled "GNU Free Documentation License".  File: coreutils.info, Node: Top, Next: Introduction, Up: (dir) GNU Coreutils ************* This manual documents version 8.16 of the GNU core utilities, including the standard programs for text and file manipulation. Copyright (C) 1994-2012 Free Software Foundation, Inc. Permission is granted to copy, distribute and/or modify this document under the terms of the GNU Free Documentation License, Version 1.3 or any later version published by the Free Software Foundation; with no Invariant Sections, with no Front-Cover Texts, and with no Back-Cover Texts. A copy of the license is included in the section entitled "GNU Free Documentation License". * Menu: * Introduction:: Caveats, overview, and authors * Common options:: Common options * Output of entire files:: cat tac nl od base64 * Formatting file contents:: fmt pr fold * Output of parts of files:: head tail split csplit * Summarizing files:: wc sum cksum md5sum sha1sum sha2 * Operating on sorted files:: sort shuf uniq comm ptx tsort * Operating on fields:: cut paste join * Operating on characters:: tr expand unexpand * Directory listing:: ls dir vdir dircolors * Basic operations:: cp dd install mv rm shred * Special file types:: mkdir rmdir unlink mkfifo mknod ln link readlink * Changing file attributes:: chgrp chmod chown touch * Disk usage:: df du stat sync truncate * Printing text:: echo printf yes * Conditions:: false true test expr * Redirection:: tee * File name manipulation:: dirname basename pathchk mktemp realpath * Working context:: pwd stty printenv tty * User information:: id logname whoami groups users who * System context:: date arch nproc uname hostname hostid uptime * SELinux context:: chcon runcon * Modified command invocation:: chroot env nice nohup stdbuf su timeout * Process control:: kill * Delaying:: sleep * Numeric operations:: factor seq * File permissions:: Access modes * Date input formats:: Specifying date strings * Opening the software toolbox:: The software tools philosophy * GNU Free Documentation License:: Copying and sharing this manual * Concept index:: General index --- The Detailed Node Listing --- Common Options * Exit status:: Indicating program success or failure * Backup options:: Backup options * Block size:: Block size * Floating point:: Floating point number representation * Signal specifications:: Specifying signals * Disambiguating names and IDs:: chgrp and chown owner and group syntax * Random sources:: Sources of random data * Target directory:: Target directory * Trailing slashes:: Trailing slashes * Traversing symlinks:: Traversing symlinks to directories * Treating / specially:: Treating / specially * Standards conformance:: Standards conformance Output of entire files * cat invocation:: Concatenate and write files * tac invocation:: Concatenate and write files in reverse * nl invocation:: Number lines and write files * od invocation:: Write files in octal or other formats * base64 invocation:: Transform data into printable data Formatting file contents * fmt invocation:: Reformat paragraph text * pr invocation:: Paginate or columnate files for printing * fold invocation:: Wrap input lines to fit in specified width Output of parts of files * head invocation:: Output the first part of files * tail invocation:: Output the last part of files * split invocation:: Split a file into fixed-size pieces * csplit invocation:: Split a file into context-determined pieces Summarizing files * wc invocation:: Print newline, word, and byte counts * sum invocation:: Print checksum and block counts * cksum invocation:: Print CRC checksum and byte counts * md5sum invocation:: Print or check MD5 digests * sha1sum invocation:: Print or check SHA-1 digests * sha2 utilities:: Print or check SHA-2 digests Operating on sorted files * sort invocation:: Sort text files * shuf invocation:: Shuffle text files * uniq invocation:: Uniquify files * comm invocation:: Compare two sorted files line by line * ptx invocation:: Produce a permuted index of file contents * tsort invocation:: Topological sort `ptx': Produce permuted indexes * General options in ptx:: Options which affect general program behavior * Charset selection in ptx:: Underlying character set considerations * Input processing in ptx:: Input fields, contexts, and keyword selection * Output formatting in ptx:: Types of output format, and sizing the fields * Compatibility in ptx:: The GNU extensions to `ptx' Operating on fields * cut invocation:: Print selected parts of lines * paste invocation:: Merge lines of files * join invocation:: Join lines on a common field Operating on characters * tr invocation:: Translate, squeeze, and/or delete characters * expand invocation:: Convert tabs to spaces * unexpand invocation:: Convert spaces to tabs `tr': Translate, squeeze, and/or delete characters * Character sets:: Specifying sets of characters * Translating:: Changing one set of characters to another * Squeezing:: Squeezing repeats and deleting Directory listing * ls invocation:: List directory contents * dir invocation:: Briefly list directory contents * vdir invocation:: Verbosely list directory contents * dircolors invocation:: Color setup for `ls' `ls': List directory contents * Which files are listed:: Which files are listed * What information is listed:: What information is listed * Sorting the output:: Sorting the output * Details about version sort:: More details about version sort * General output formatting:: General output formatting * Formatting the file names:: Formatting the file names Basic operations * cp invocation:: Copy files and directories * dd invocation:: Convert and copy a file * install invocation:: Copy files and set attributes * mv invocation:: Move (rename) files * rm invocation:: Remove files or directories * shred invocation:: Remove files more securely Special file types * link invocation:: Make a hard link via the link syscall * ln invocation:: Make links between files * mkdir invocation:: Make directories * mkfifo invocation:: Make FIFOs (named pipes) * mknod invocation:: Make block or character special files * readlink invocation:: Print value of a symlink or canonical file name * rmdir invocation:: Remove empty directories * unlink invocation:: Remove files via unlink syscall Changing file attributes * chown invocation:: Change file owner and group * chgrp invocation:: Change group ownership * chmod invocation:: Change access permissions * touch invocation:: Change file timestamps Disk usage * df invocation:: Report file system disk space usage * du invocation:: Estimate file space usage * stat invocation:: Report file or file system status * sync invocation:: Synchronize data on disk with memory * truncate invocation:: Shrink or extend the size of a file Printing text * echo invocation:: Print a line of text * printf invocation:: Format and print data * yes invocation:: Print a string until interrupted Conditions * false invocation:: Do nothing, unsuccessfully * true invocation:: Do nothing, successfully * test invocation:: Check file types and compare values * expr invocation:: Evaluate expressions `test': Check file types and compare values * File type tests:: File type tests * Access permission tests:: Access permission tests * File characteristic tests:: File characteristic tests * String tests:: String tests * Numeric tests:: Numeric tests `expr': Evaluate expression * String expressions:: + : match substr index length * Numeric expressions:: + - * / % * Relations for expr:: | & < <= = == != >= > * Examples of expr:: Examples of using `expr' Redirection * tee invocation:: Redirect output to multiple files or processes File name manipulation * basename invocation:: Strip directory and suffix from a file name * dirname invocation:: Strip last file name component * pathchk invocation:: Check file name validity and portability * mktemp invocation:: Create temporary file or directory * realpath invocation:: Print resolved file names Working context * pwd invocation:: Print working directory * stty invocation:: Print or change terminal characteristics * printenv invocation:: Print all or some environment variables * tty invocation:: Print file name of terminal on standard input `stty': Print or change terminal characteristics * Control:: Control settings * Input:: Input settings * Output:: Output settings * Local:: Local settings * Combination:: Combination settings * Characters:: Special characters * Special:: Special settings User information * id invocation:: Print user identity * logname invocation:: Print current login name * whoami invocation:: Print effective user ID * groups invocation:: Print group names a user is in * users invocation:: Print login names of users currently logged in * who invocation:: Print who is currently logged in System context * arch invocation:: Print machine hardware name * date invocation:: Print or set system date and time * nproc invocation:: Print the number of processors * uname invocation:: Print system information * hostname invocation:: Print or set system name * hostid invocation:: Print numeric host identifier * uptime invocation:: Print system uptime and load `date': Print or set system date and time * Time conversion specifiers:: %[HIklMNpPrRsSTXzZ] * Date conversion specifiers:: %[aAbBcCdDeFgGhjmuUVwWxyY] * Literal conversion specifiers:: %[%nt] * Padding and other flags:: Pad with zeros, spaces, etc. * Setting the time:: Changing the system clock * Options for date:: Instead of the current time * Date input formats:: Specifying date strings * Examples of date:: Examples SELinux context * chcon invocation:: Change SELinux context of file * runcon invocation:: Run a command in specified SELinux context Modified command invocation * chroot invocation:: Run a command with a different root directory * env invocation:: Run a command in a modified environment * nice invocation:: Run a command with modified niceness * nohup invocation:: Run a command immune to hangups * stdbuf invocation:: Run a command with modified I/O buffering * su invocation:: Run a command with substitute user and group ID * timeout invocation:: Run a command with a time limit Process control * kill invocation:: Sending a signal to processes. Delaying * sleep invocation:: Delay for a specified time Numeric operations * factor invocation:: Print prime factors * seq invocation:: Print numeric sequences File permissions * Mode Structure:: Structure of file mode bits * Symbolic Modes:: Mnemonic representation of file mode bits * Numeric Modes:: File mode bits as octal numbers * Directory Setuid and Setgid:: Set-user-ID and set-group-ID on directories Date input formats * General date syntax:: Common rules * Calendar date items:: 19 Dec 1994 * Time of day items:: 9:20pm * Time zone items:: EST, PDT, GMT * Day of week items:: Monday and others * Relative items in date strings:: next tuesday, 2 years ago * Pure numbers in date strings:: 19931219, 1440 * Seconds since the Epoch:: @1078100502 * Specifying time zone rules:: TZ="America/New_York", TZ="UTC0" * Authors of parse_datetime:: Bellovin, Eggert, Salz, Berets, et al Opening the software toolbox * Toolbox introduction:: Toolbox introduction * I/O redirection:: I/O redirection * The who command:: The `who' command * The cut command:: The `cut' command * The sort command:: The `sort' command * The uniq command:: The `uniq' command * Putting the tools together:: Putting the tools together Copying This Manual * GNU Free Documentation License:: Copying and sharing this manual  File: coreutils.info, Node: Introduction, Next: Common options, Prev: Top, Up: Top 1 Introduction ************** This manual is a work in progress: many sections make no attempt to explain basic concepts in a way suitable for novices. Thus, if you are interested, please get involved in improving this manual. The entire GNU community will benefit. The GNU utilities documented here are mostly compatible with the POSIX standard. Please report bugs to . Remember to include the version number, machine architecture, input files, and any other information needed to reproduce the bug: your input, what you expected, what you got, and why it is wrong. Diffs are welcome, but please include a description of the problem as well, since this is sometimes difficult to infer. *Note Bugs: (gcc)Bugs. This manual was originally derived from the Unix man pages in the distributions, which were written by David MacKenzie and updated by Jim Meyering. What you are reading now is the authoritative documentation for these utilities; the man pages are no longer being maintained. The original `fmt' man page was written by Ross Paterson. Franc,ois Pinard did the initial conversion to Texinfo format. Karl Berry did the indexing, some reorganization, and editing of the results. Brian Youmans of the Free Software Foundation office staff combined the manuals for textutils, fileutils, and sh-utils to produce the present omnibus manual. Richard Stallman contributed his usual invaluable insights to the overall process.  File: coreutils.info, Node: Common options, Next: Output of entire files, Prev: Introduction, Up: Top 2 Common options **************** Certain options are available in all of these programs. Rather than writing identical descriptions for each of the programs, they are described here. (In fact, every GNU program accepts (or should accept) these options.) Normally options and operands can appear in any order, and programs act as if all the options appear before any operands. For example, `sort -r passwd -t :' acts like `sort -r -t : passwd', since `:' is an option-argument of `-t'. However, if the `POSIXLY_CORRECT' environment variable is set, options must appear before operands, unless otherwise specified for a particular command. A few programs can usefully have trailing operands with leading `-'. With such a program, options must precede operands even if `POSIXLY_CORRECT' is not set, and this fact is noted in the program description. For example, the `env' command's options must appear before its operands, since in some cases the operands specify a command that itself contains options. Most programs that accept long options recognize unambiguous abbreviations of those options. For example, `rmdir --ignore-fail-on-non-empty' can be invoked as `rmdir --ignore-fail' or even `rmdir --i'. Ambiguous options, such as `ls --h', are identified as such. Some of these programs recognize the `--help' and `--version' options only when one of them is the sole command line argument. For these programs, abbreviations of the long options are not always recognized. `--help' Print a usage message listing all available options, then exit successfully. `--version' Print the version number, then exit successfully. `--' Delimit the option list. Later arguments, if any, are treated as operands even if they begin with `-'. For example, `sort -- -r' reads from the file named `-r'. A single `-' operand is not really an option, though it looks like one. It stands for standard input, or for standard output if that is clear from the context. For example, `sort -' reads from standard input, and is equivalent to plain `sort', and `tee -' writes an extra copy of its input to standard output. Unless otherwise specified, `-' can appear as any operand that requires a file name. * Menu: * Exit status:: Indicating program success or failure. * Backup options:: -b -S, in some programs. * Block size:: BLOCK_SIZE and --block-size, in some programs. * Floating point:: Floating point number representation. * Signal specifications:: Specifying signals using the --signal option. * Disambiguating names and IDs:: chgrp and chown owner and group syntax * Random sources:: --random-source, in some programs. * Target directory:: Specifying a target directory, in some programs. * Trailing slashes:: --strip-trailing-slashes, in some programs. * Traversing symlinks:: -H, -L, or -P, in some programs. * Treating / specially:: --preserve-root and --no-preserve-root. * Special built-in utilities:: `break', `:', ... * Standards conformance:: Conformance to the POSIX standard.  File: coreutils.info, Node: Exit status, Next: Backup options, Up: Common options 2.1 Exit status =============== Nearly every command invocation yields an integral "exit status" that can be used to change how other commands work. For the vast majority of commands, an exit status of zero indicates success. Failure is indicated by a nonzero value--typically `1', though it may differ on unusual platforms as POSIX requires only that it be nonzero. However, some of the programs documented here do produce other exit status values and a few associate different meanings with the values `0' and `1'. Here are some of the exceptions: `chroot', `env', `expr', `nice', `nohup', `printenv', `sort', `stdbuf', `su', `test', `timeout', `tty'.  File: coreutils.info, Node: Backup options, Next: Block size, Prev: Exit status, Up: Common options 2.2 Backup options ================== Some GNU programs (at least `cp', `install', `ln', and `mv') optionally make backups of files before writing new versions. These options control the details of these backups. The options are also briefly mentioned in the descriptions of the particular programs. `-b' `--backup[=METHOD]' Make a backup of each file that would otherwise be overwritten or removed. Without this option, the original versions are destroyed. Use METHOD to determine the type of backups to make. When this option is used but METHOD is not specified, then the value of the `VERSION_CONTROL' environment variable is used. And if `VERSION_CONTROL' is not set, the default backup type is `existing'. Note that the short form of this option, `-b' does not accept any argument. Using `-b' is equivalent to using `--backup=existing'. This option corresponds to the Emacs variable `version-control'; the values for METHOD are the same as those used in Emacs. This option also accepts more descriptive names. The valid METHODs are (unique abbreviations are accepted): `none' `off' Never make backups. `numbered' `t' Always make numbered backups. `existing' `nil' Make numbered backups of files that already have them, simple backups of the others. `simple' `never' Always make simple backups. Please note `never' is not to be confused with `none'. `-S SUFFIX' `--suffix=SUFFIX' Append SUFFIX to each backup file made with `-b'. If this option is not specified, the value of the `SIMPLE_BACKUP_SUFFIX' environment variable is used. And if `SIMPLE_BACKUP_SUFFIX' is not set, the default is `~', just as in Emacs.  File: coreutils.info, Node: Block size, Next: Floating point, Prev: Backup options, Up: Common options 2.3 Block size ============== Some GNU programs (at least `df', `du', and `ls') display sizes in "blocks". You can adjust the block size and method of display to make sizes easier to read. The block size used for display is independent of any file system block size. Fractional block counts are rounded up to the nearest integer. The default block size is chosen by examining the following environment variables in turn; the first one that is set determines the block size. `DF_BLOCK_SIZE' This specifies the default block size for the `df' command. Similarly, `DU_BLOCK_SIZE' specifies the default for `du' and `LS_BLOCK_SIZE' for `ls'. `BLOCK_SIZE' This specifies the default block size for all three commands, if the above command-specific environment variables are not set. `BLOCKSIZE' This specifies the default block size for all values that are normally printed as blocks, if neither `BLOCK_SIZE' nor the above command-specific environment variables are set. Unlike the other environment variables, `BLOCKSIZE' does not affect values that are normally printed as byte counts, e.g., the file sizes contained in `ls -l' output. `POSIXLY_CORRECT' If neither `COMMAND_BLOCK_SIZE', nor `BLOCK_SIZE', nor `BLOCKSIZE' is set, but this variable is set, the block size defaults to 512. If none of the above environment variables are set, the block size currently defaults to 1024 bytes in most contexts, but this number may change in the future. For `ls' file sizes, the block size defaults to 1 byte. A block size specification can be a positive integer specifying the number of bytes per block, or it can be `human-readable' or `si' to select a human-readable format. Integers may be followed by suffixes that are upward compatible with the SI prefixes (http://www.bipm.org/en/si/si_brochure/chapter3/prefixes.html) for decimal multiples and with the ISO/IEC 80000-13 (formerly IEC 60027-2) prefixes (http://physics.nist.gov/cuu/Units/binary.html) for binary multiples. With human-readable formats, output sizes are followed by a size letter such as `M' for megabytes. `BLOCK_SIZE=human-readable' uses powers of 1024; `M' stands for 1,048,576 bytes. `BLOCK_SIZE=si' is similar, but uses powers of 1000 and appends `B'; `MB' stands for 1,000,000 bytes. A block size specification preceded by `'' causes output sizes to be displayed with thousands separators. The `LC_NUMERIC' locale specifies the thousands separator and grouping. For example, in an American English locale, `--block-size="'1kB"' would cause a size of 1234000 bytes to be displayed as `1,234'. In the default C locale, there is no thousands separator so a leading `'' has no effect. An integer block size can be followed by a suffix to specify a multiple of that size. A bare size letter, or one followed by `iB', specifies a multiple using powers of 1024. A size letter followed by `B' specifies powers of 1000 instead. For example, `1M' and `1MiB' are equivalent to `1048576', whereas `1MB' is equivalent to `1000000'. A plain suffix without a preceding integer acts as if `1' were prepended, except that it causes a size indication to be appended to the output. For example, `--block-size="kB"' displays 3000 as `3kB'. The following suffixes are defined. Large sizes like `1Y' may be rejected by your computer due to limitations of its arithmetic. `kB' kilobyte: 10^3 = 1000. `k' `K' `KiB' kibibyte: 2^10 = 1024. `K' is special: the SI prefix is `k' and the ISO/IEC 80000-13 prefix is `Ki', but tradition and POSIX use `k' to mean `KiB'. `MB' megabyte: 10^6 = 1,000,000. `M' `MiB' mebibyte: 2^20 = 1,048,576. `GB' gigabyte: 10^9 = 1,000,000,000. `G' `GiB' gibibyte: 2^30 = 1,073,741,824. `TB' terabyte: 10^12 = 1,000,000,000,000. `T' `TiB' tebibyte: 2^40 = 1,099,511,627,776. `PB' petabyte: 10^15 = 1,000,000,000,000,000. `P' `PiB' pebibyte: 2^50 = 1,125,899,906,842,624. `EB' exabyte: 10^18 = 1,000,000,000,000,000,000. `E' `EiB' exbibyte: 2^60 = 1,152,921,504,606,846,976. `ZB' zettabyte: 10^21 = 1,000,000,000,000,000,000,000 `Z' `ZiB' 2^70 = 1,180,591,620,717,411,303,424. `YB' yottabyte: 10^24 = 1,000,000,000,000,000,000,000,000. `Y' `YiB' 2^80 = 1,208,925,819,614,629,174,706,176. Block size defaults can be overridden by an explicit `--block-size=SIZE' option. The `-k' option is equivalent to `--block-size=1K', which is the default unless the `POSIXLY_CORRECT' environment variable is set. The `-h' or `--human-readable' option is equivalent to `--block-size=human-readable'. The `--si' option is equivalent to `--block-size=si'.  File: coreutils.info, Node: Floating point, Next: Signal specifications, Prev: Block size, Up: Common options 2.4 Floating point numbers ========================== Commands that accept or produce floating point numbers employ the floating point representation of the underlying system, and suffer from rounding error, overflow, and similar floating-point issues. Almost all modern systems use IEEE-754 floating point, and it is typically portable to assume IEEE-754 behavior these days. IEEE-754 has positive and negative infinity, distinguishes positive from negative zero, and uses special values called NaNs to represent invalid computations such as dividing zero by itself. For more information, please see David Goldberg's paper What Every Computer Scientist Should Know About Floating-Point Arithmetic (http://www.validlab.com/goldberg/paper.pdf). Commands that accept floating point numbers as options, operands or input use the standard C functions `strtod' and `strtold' to convert from text to floating point numbers. These floating point numbers therefore can use scientific notation like `1.0e-34' and `-10e100'. Modern C implementations also accept hexadecimal floating point numbers such as `-0x.ep-3', which stands for -14/16 times 2^-3, which equals -0.109375. The `LC_NUMERIC' locale determines the decimal-point character. *Note Parsing of Floats: (libc)Parsing of Floats.  File: coreutils.info, Node: Signal specifications, Next: Disambiguating names and IDs, Prev: Floating point, Up: Common options 2.5 Signal specifications ========================= A SIGNAL may be a signal name like `HUP', or a signal number like `1', or an exit status of a process terminated by the signal. A signal name can be given in canonical form or prefixed by `SIG'. The case of the letters is ignored. The following signal names and numbers are supported on all POSIX compliant systems: `HUP' 1. Hangup. `INT' 2. Terminal interrupt. `QUIT' 3. Terminal quit. `ABRT' 6. Process abort. `KILL' 9. Kill (cannot be caught or ignored). `ALRM' 14. Alarm Clock. `TERM' 15. Termination. Other supported signal names have system-dependent corresponding numbers. All systems conforming to POSIX 1003.1-2001 also support the following signals: `BUS' Access to an undefined portion of a memory object. `CHLD' Child process terminated, stopped, or continued. `CONT' Continue executing, if stopped. `FPE' Erroneous arithmetic operation. `ILL' Illegal Instruction. `PIPE' Write on a pipe with no one to read it. `SEGV' Invalid memory reference. `STOP' Stop executing (cannot be caught or ignored). `TSTP' Terminal stop. `TTIN' Background process attempting read. `TTOU' Background process attempting write. `URG' High bandwidth data is available at a socket. `USR1' User-defined signal 1. `USR2' User-defined signal 2. POSIX 1003.1-2001 systems that support the XSI extension also support the following signals: `POLL' Pollable event. `PROF' Profiling timer expired. `SYS' Bad system call. `TRAP' Trace/breakpoint trap. `VTALRM' Virtual timer expired. `XCPU' CPU time limit exceeded. `XFSZ' File size limit exceeded. POSIX 1003.1-2001 systems that support the XRT extension also support at least eight real-time signals called `RTMIN', `RTMIN+1', ..., `RTMAX-1', `RTMAX'.  File: coreutils.info, Node: Disambiguating names and IDs, Next: Random sources, Prev: Signal specifications, Up: Common options 2.6 chown and chgrp: Disambiguating user names and IDs ====================================================== Since the OWNER and GROUP arguments to `chown' and `chgrp' may be specified as names or numeric IDs, there is an apparent ambiguity. What if a user or group _name_ is a string of digits? (1) Should the command interpret it as a user name or as an ID? POSIX requires that `chown' and `chgrp' first attempt to resolve the specified string as a name, and only once that fails, then try to interpret it as an ID. This is troublesome when you want to specify a numeric ID, say 42, and it must work even in a pathological situation where `42' is a user name that maps to some other user ID, say 1000. Simply invoking `chown 42 F', will set `F's owner ID to 1000--not what you intended. GNU `chown' and `chgrp' provide a way to work around this, that at the same time may result in a significant performance improvement by eliminating a database look-up. Simply precede each numeric user ID and/or group ID with a `+', in order to force its interpretation as an integer: chown +42 F chgrp +$numeric_group_id another-file chown +0:+0 / GNU `chown' and `chgrp' skip the name look-up process for each `+'-prefixed string, because a string containing `+' is never a valid user or group name. This syntax is accepted on most common Unix systems, but not on Solaris 10. ---------- Footnotes ---------- (1) Using a number as a user name is common in some environments.  File: coreutils.info, Node: Random sources, Next: Target directory, Prev: Disambiguating names and IDs, Up: Common options 2.7 Sources of random data ========================== The `shuf', `shred', and `sort' commands sometimes need random data to do their work. For example, `sort -R' must choose a hash function at random, and it needs random data to make this selection. By default these commands use an internal pseudorandom generator initialized by a small amount of entropy, but can be directed to use an external source with the `--random-source=FILE' option. An error is reported if FILE does not contain enough bytes. For example, the device file `/dev/urandom' could be used as the source of random data. Typically, this device gathers environmental noise from device drivers and other sources into an entropy pool, and uses the pool to generate random bits. If the pool is short of data, the device reuses the internal pool to produce more bits, using a cryptographically secure pseudorandom number generator. But be aware that this device is not designed for bulk random data generation and is relatively slow. `/dev/urandom' suffices for most practical uses, but applications requiring high-value or long-term protection of private data may require an alternate data source like `/dev/random' or `/dev/arandom'. The set of available sources depends on your operating system. To reproduce the results of an earlier invocation of a command, you can save some random data into a file and then use that file as the random source in earlier and later invocations of the command.  File: coreutils.info, Node: Target directory, Next: Trailing slashes, Prev: Random sources, Up: Common options 2.8 Target directory ==================== The `cp', `install', `ln', and `mv' commands normally treat the last operand specially when it is a directory or a symbolic link to a directory. For example, `cp source dest' is equivalent to `cp source dest/source' if `dest' is a directory. Sometimes this behavior is not exactly what is wanted, so these commands support the following options to allow more fine-grained control: `-T' `--no-target-directory' Do not treat the last operand specially when it is a directory or a symbolic link to a directory. This can help avoid race conditions in programs that operate in a shared area. For example, when the command `mv /tmp/source /tmp/dest' succeeds, there is no guarantee that `/tmp/source' was renamed to `/tmp/dest': it could have been renamed to `/tmp/dest/source' instead, if some other process created `/tmp/dest' as a directory. However, if `mv -T /tmp/source /tmp/dest' succeeds, there is no question that `/tmp/source' was renamed to `/tmp/dest'. In the opposite situation, where you want the last operand to be treated as a directory and want a diagnostic otherwise, you can use the `--target-directory' (`-t') option. `-t DIRECTORY' `--target-directory=DIRECTORY' Use DIRECTORY as the directory component of each destination file name. The interface for most programs is that after processing options and a finite (possibly zero) number of fixed-position arguments, the remaining argument list is either expected to be empty, or is a list of items (usually files) that will all be handled identically. The `xargs' program is designed to work well with this convention. The commands in the `mv'-family are unusual in that they take a variable number of arguments with a special case at the _end_ (namely, the target directory). This makes it nontrivial to perform some operations, e.g., "move all files from here to ../d/", because `mv * ../d/' might exhaust the argument space, and `ls | xargs ...' doesn't have a clean way to specify an extra final argument for each invocation of the subject command. (It can be done by going through a shell command, but that requires more human labor and brain power than it should.) The `--target-directory' (`-t') option allows the `cp', `install', `ln', and `mv' programs to be used conveniently with `xargs'. For example, you can move the files from the current directory to a sibling directory, `d' like this: ls | xargs mv -t ../d -- However, this doesn't move files whose names begin with `.'. If you use the GNU `find' program, you can move those files too, with this command: find . -mindepth 1 -maxdepth 1 \ | xargs mv -t ../d But both of the above approaches fail if there are no files in the current directory, or if any file has a name containing a blank or some other special characters. The following example removes those limitations and requires both GNU `find' and GNU `xargs': find . -mindepth 1 -maxdepth 1 -print0 \ | xargs --null --no-run-if-empty \ mv -t ../d The `--target-directory' (`-t') and `--no-target-directory' (`-T') options cannot be combined.  File: coreutils.info, Node: Trailing slashes, Next: Traversing symlinks, Prev: Target directory, Up: Common options 2.9 Trailing slashes ==================== Some GNU programs (at least `cp' and `mv') allow you to remove any trailing slashes from each SOURCE argument before operating on it. The `--strip-trailing-slashes' option enables this behavior. This is useful when a SOURCE argument may have a trailing slash and specify a symbolic link to a directory. This scenario is in fact rather common because some shells can automatically append a trailing slash when performing file name completion on such symbolic links. Without this option, `mv', for example, (via the system's rename function) must interpret a trailing slash as a request to dereference the symbolic link and so must rename the indirectly referenced _directory_ and not the symbolic link. Although it may seem surprising that such behavior be the default, it is required by POSIX and is consistent with other parts of that standard.  File: coreutils.info, Node: Traversing symlinks, Next: Treating / specially, Prev: Trailing slashes, Up: Common options 2.10 Traversing symlinks ======================== The following options modify how `chown' and `chgrp' traverse a hierarchy when the `--recursive' (`-R') option is also specified. If more than one of the following options is specified, only the final one takes effect. These options specify whether processing a symbolic link to a directory entails operating on just the symbolic link or on all files in the hierarchy rooted at that directory. These options are independent of `--dereference' and `--no-dereference' (`-h'), which control whether to modify a symlink or its referent. `-H' If `--recursive' (`-R') is specified and a command line argument is a symbolic link to a directory, traverse it. `-L' In a recursive traversal, traverse every symbolic link to a directory that is encountered. `-P' Do not traverse any symbolic links. This is the default if none of `-H', `-L', or `-P' is specified.  File: coreutils.info, Node: Treating / specially, Next: Special built-in utilities, Prev: Traversing symlinks, Up: Common options 2.11 Treating `/' specially =========================== Certain commands can operate destructively on entire hierarchies. For example, if a user with appropriate privileges mistakenly runs `rm -rf / tmp/junk', that may remove all files on the entire system. Since there are so few legitimate uses for such a command, GNU `rm' normally declines to operate on any directory that resolves to `/'. If you really want to try to remove all the files on your system, you can use the `--no-preserve-root' option, but the default behavior, specified by the `--preserve-option', is safer for most purposes. The commands `chgrp', `chmod' and `chown' can also operate destructively on entire hierarchies, so they too support these options. Although, unlike `rm', they don't actually unlink files, these commands are arguably more dangerous when operating recursively on `/', since they often work much more quickly, and hence damage more files before an alert user can interrupt them. Tradition and POSIX require these commands to operate recursively on `/', so they default to `--no-preserve-root', but using the `--preserve-root' option makes them safer for most purposes. For convenience you can specify `--preserve-root' in an alias or in a shell function. Note that the `--preserve-root' option also ensures that `chgrp' and `chown' do not modify `/' even when dereferencing a symlink pointing to `/'.  File: coreutils.info, Node: Special built-in utilities, Next: Standards conformance, Prev: Treating / specially, Up: Common options 2.12 Special built-in utilities =============================== Some programs like `nice' can invoke other programs; for example, the command `nice cat file' invokes the program `cat' by executing the command `cat file'. However, "special built-in utilities" like `exit' cannot be invoked this way. For example, the command `nice exit' does not have a well-defined behavior: it may generate an error message instead of exiting. Here is a list of the special built-in utilities that are standardized by POSIX 1003.1-2004. . : break continue eval exec exit export readonly return set shift times trap unset For example, because `.', `:', and `exec' are special, the commands `nice . foo.sh', `nice :', and `nice exec pwd' do not work as you might expect. Many shells extend this list. For example, Bash has several extra special built-in utilities like `history', and `suspend', and with Bash the command `nice suspend' generates an error message instead of suspending.  File: coreutils.info, Node: Standards conformance, Prev: Special built-in utilities, Up: Common options 2.13 Standards conformance ========================== In a few cases, the GNU utilities' default behavior is incompatible with the POSIX standard. To suppress these incompatibilities, define the `POSIXLY_CORRECT' environment variable. Unless you are checking for POSIX conformance, you probably do not need to define `POSIXLY_CORRECT'. Newer versions of POSIX are occasionally incompatible with older versions. For example, older versions of POSIX required the command `sort +1' to sort based on the second and succeeding fields in each input line, but starting with POSIX 1003.1-2001 the same command is required to sort the file named `+1', and you must instead use the command `sort -k 2' to get the field-based sort. The GNU utilities normally conform to the version of POSIX that is standard for your system. To cause them to conform to a different version of POSIX, define the `_POSIX2_VERSION' environment variable to a value of the form YYYYMM specifying the year and month the standard was adopted. Three values are currently supported for `_POSIX2_VERSION': `199209' stands for POSIX 1003.2-1992, `200112' stands for POSIX 1003.1-2001, and `200809' stands for POSIX 1003.1-2008. For example, if you have a newer system but are running software that assumes an older version of POSIX and uses `sort +1' or `tail +10', you can work around any compatibility problems by setting `_POSIX2_VERSION=199209' in your environment.  File: coreutils.info, Node: Output of entire files, Next: Formatting file contents, Prev: Common options, Up: Top 3 Output of entire files ************************ These commands read and write entire files, possibly transforming them in some way. * Menu: * cat invocation:: Concatenate and write files. * tac invocation:: Concatenate and write files in reverse. * nl invocation:: Number lines and write files. * od invocation:: Write files in octal or other formats. * base64 invocation:: Transform data into printable data.  File: coreutils.info, Node: cat invocation, Next: tac invocation, Up: Output of entire files 3.1 `cat': Concatenate and write files ====================================== `cat' copies each FILE (`-' means standard input), or standard input if none are given, to standard output. Synopsis: cat [OPTION] [FILE]... The program accepts the following options. Also see *note Common options::. `-A' `--show-all' Equivalent to `-vET'. `-b' `--number-nonblank' Number all nonempty output lines, starting with 1. `-e' Equivalent to `-vE'. `-E' `--show-ends' Display a `$' after the end of each line. `-n' `--number' Number all output lines, starting with 1. This option is ignored if `-b' is in effect. `-s' `--squeeze-blank' Suppress repeated adjacent empty lines; output just one empty line instead of several. `-t' Equivalent to `-vT'. `-T' `--show-tabs' Display TAB characters as `^I'. `-u' Ignored; for POSIX compatibility. `-v' `--show-nonprinting' Display control characters except for LFD and TAB using `^' notation and precede characters that have the high bit set with `M-'. On systems like MS-DOS that distinguish between text and binary files, `cat' normally reads and writes in binary mode. However, `cat' reads in text mode if one of the options `-bensAE' is used or if `cat' is reading from standard input and standard input is a terminal. Similarly, `cat' writes in text mode if one of the options `-bensAE' is used or if standard output is a terminal. An exit status of zero indicates success, and a nonzero value indicates failure. Examples: # Output f's contents, then standard input, then g's contents. cat f - g # Copy standard input to standard output. cat  File: coreutils.info, Node: tac invocation, Next: nl invocation, Prev: cat invocation, Up: Output of entire files 3.2 `tac': Concatenate and write files in reverse ================================================= `tac' copies each FILE (`-' means standard input), or standard input if none are given, to standard output, reversing the records (lines by default) in each separately. Synopsis: tac [OPTION]... [FILE]... "Records" are separated by instances of a string (newline by default). By default, this separator string is attached to the end of the record that it follows in the file. The program accepts the following options. Also see *note Common options::. `-b' `--before' The separator is attached to the beginning of the record that it precedes in the file. `-r' `--regex' Treat the separator string as a regular expression. Users of `tac' on MS-DOS/MS-Windows should note that, since `tac' reads files in binary mode, each line of a text file might end with a CR/LF pair instead of the Unix-style LF. `-s SEPARATOR' `--separator=SEPARATOR' Use SEPARATOR as the record separator, instead of newline. An exit status of zero indicates success, and a nonzero value indicates failure.  File: coreutils.info, Node: nl invocation, Next: od invocation, Prev: tac invocation, Up: Output of entire files 3.3 `nl': Number lines and write files ====================================== `nl' writes each FILE (`-' means standard input), or standard input if none are given, to standard output, with line numbers added to some or all of the lines. Synopsis: nl [OPTION]... [FILE]... `nl' decomposes its input into (logical) pages; by default, the line number is reset to 1 at the top of each logical page. `nl' treats all of the input files as a single document; it does not reset line numbers or logical pages between files. A logical page consists of three sections: header, body, and footer. Any of the sections can be empty. Each can be numbered in a different style from the others. The beginnings of the sections of logical pages are indicated in the input file by a line containing exactly one of these delimiter strings: `\:\:\:' start of header; `\:\:' start of body; `\:' start of footer. The two characters from which these strings are made can be changed from `\' and `:' via options (see below), but the pattern and length of each string cannot be changed. A section delimiter is replaced by an empty line on output. Any text that comes before the first section delimiter string in the input file is considered to be part of a body section, so `nl' treats a file that contains no section delimiters as a single body section. The program accepts the following options. Also see *note Common options::. `-b STYLE' `--body-numbering=STYLE' Select the numbering style for lines in the body section of each logical page. When a line is not numbered, the current line number is not incremented, but the line number separator character is still prepended to the line. The styles are: `a' number all lines, `t' number only nonempty lines (default for body), `n' do not number lines (default for header and footer), `pBRE' number only lines that contain a match for the basic regular expression BRE. *Note Regular Expressions: (grep)Regular Expressions. `-d CD' `--section-delimiter=CD' Set the section delimiter characters to CD; default is `\:'. If only C is given, the second remains `:'. (Remember to protect `\' or other metacharacters from shell expansion with quotes or extra backslashes.) `-f STYLE' `--footer-numbering=STYLE' Analogous to `--body-numbering'. `-h STYLE' `--header-numbering=STYLE' Analogous to `--body-numbering'. `-i NUMBER' `--line-increment=NUMBER' Increment line numbers by NUMBER (default 1). `-l NUMBER' `--join-blank-lines=NUMBER' Consider NUMBER (default 1) consecutive empty lines to be one logical line for numbering, and only number the last one. Where fewer than NUMBER consecutive empty lines occur, do not number them. An empty line is one that contains no characters, not even spaces or tabs. `-n FORMAT' `--number-format=FORMAT' Select the line numbering format (default is `rn'): `ln' left justified, no leading zeros; `rn' right justified, no leading zeros; `rz' right justified, leading zeros. `-p' `--no-renumber' Do not reset the line number at the start of a logical page. `-s STRING' `--number-separator=STRING' Separate the line number from the text line in the output with STRING (default is the TAB character). `-v NUMBER' `--starting-line-number=NUMBER' Set the initial line number on each logical page to NUMBER (default 1). `-w NUMBER' `--number-width=NUMBER' Use NUMBER characters for line numbers (default 6). An exit status of zero indicates success, and a nonzero value indicates failure.  File: coreutils.info, Node: od invocation, Next: base64 invocation, Prev: nl invocation, Up: Output of entire files 3.4 `od': Write files in octal or other formats =============================================== `od' writes an unambiguous representation of each FILE (`-' means standard input), or standard input if none are given. Synopses: od [OPTION]... [FILE]... od [-abcdfilosx]... [FILE] [[+]OFFSET[.][b]] od [OPTION]... --traditional [FILE] [[+]OFFSET[.][b] [[+]LABEL[.][b]]] Each line of output consists of the offset in the input, followed by groups of data from the file. By default, `od' prints the offset in octal, and each group of file data is a C `short int''s worth of input printed as a single octal number. If OFFSET is given, it specifies how many input bytes to skip before formatting and writing. By default, it is interpreted as an octal number, but the optional trailing decimal point causes it to be interpreted as decimal. If no decimal is specified and the offset begins with `0x' or `0X' it is interpreted as a hexadecimal number. If there is a trailing `b', the number of bytes skipped will be OFFSET multiplied by 512. If a command is of both the first and second forms, the second form is assumed if the last operand begins with `+' or (if there are two operands) a digit. For example, in `od foo 10' and `od +10' the `10' is an offset, whereas in `od 10' the `10' is a file name. The program accepts the following options. Also see *note Common options::. `-A RADIX' `--address-radix=RADIX' Select the base in which file offsets are printed. RADIX can be one of the following: `d' decimal; `o' octal; `x' hexadecimal; `n' none (do not print offsets). The default is octal. `-j BYTES' `--skip-bytes=BYTES' Skip BYTES input bytes before formatting and writing. If BYTES begins with `0x' or `0X', it is interpreted in hexadecimal; otherwise, if it begins with `0', in octal; otherwise, in decimal. BYTES may be, or may be an integer optionally followed by, one of the following multiplicative suffixes: `b' => 512 ("blocks") `KB' => 1000 (KiloBytes) `K' => 1024 (KibiBytes) `MB' => 1000*1000 (MegaBytes) `M' => 1024*1024 (MebiBytes) `GB' => 1000*1000*1000 (GigaBytes) `G' => 1024*1024*1024 (GibiBytes) and so on for `T', `P', `E', `Z', and `Y'. `-N BYTES' `--read-bytes=BYTES' Output at most BYTES bytes of the input. Prefixes and suffixes on `bytes' are interpreted as for the `-j' option. `-S BYTES' `--strings[=BYTES]' Instead of the normal output, output only "string constants": at least BYTES consecutive ASCII graphic characters, followed by a zero byte (ASCII NUL). Prefixes and suffixes on BYTES are interpreted as for the `-j' option. If N is omitted with `--strings', the default is 3. `-t TYPE' `--format=TYPE' Select the format in which to output the file data. TYPE is a string of one or more of the below type indicator characters. If you include more than one type indicator character in a single TYPE string, or use this option more than once, `od' writes one copy of each output line using each of the data types that you specified, in the order that you specified. Adding a trailing "z" to any type specification appends a display of the ASCII character representation of the printable characters to the output line generated by the type specification. `a' named character, ignoring high-order bit `c' ASCII character or backslash escape, `d' signed decimal `f' floating point (*note Floating point::) `o' octal `u' unsigned decimal `x' hexadecimal The type `a' outputs things like `sp' for space, `nl' for newline, and `nul' for a zero byte. Only the least significant seven bits of each byte is used; the high-order bit is ignored. Type `c' outputs ` ', `\n', and `\0', respectively. Except for types `a' and `c', you can specify the number of bytes to use in interpreting each number in the given data type by following the type indicator character with a decimal integer. Alternately, you can specify the size of one of the C compiler's built-in data types by following the type indicator character with one of the following characters. For integers (`d', `o', `u', `x'): `C' char `S' short `I' int `L' long For floating point (`f'): F float D double L long double `-v' `--output-duplicates' Output consecutive lines that are identical. By default, when two or more consecutive output lines would be identical, `od' outputs only the first line, and puts just an asterisk on the following line to indicate the elision. `-w[N]' `--width[=N]' Dump `n' input bytes per output line. This must be a multiple of the least common multiple of the sizes associated with the specified output types. If this option is not given at all, the default is 16. If N is omitted, the default is 32. The next several options are shorthands for format specifications. GNU `od' accepts any combination of shorthands and format specification options. These options accumulate. `-a' Output as named characters. Equivalent to `-t a'. `-b' Output as octal bytes. Equivalent to `-t o1'. `-c' Output as ASCII characters or backslash escapes. Equivalent to `-t c'. `-d' Output as unsigned decimal two-byte units. Equivalent to `-t u2'. `-f' Output as floats. Equivalent to `-t fF'. `-i' Output as decimal ints. Equivalent to `-t dI'. `-l' Output as decimal long ints. Equivalent to `-t dL'. `-o' Output as octal two-byte units. Equivalent to `-t o2'. `-s' Output as decimal two-byte units. Equivalent to `-t d2'. `-x' Output as hexadecimal two-byte units. Equivalent to `-t x2'. `--traditional' Recognize the non-option label argument that traditional `od' accepted. The following syntax: od --traditional [FILE] [[+]OFFSET[.][b] [[+]LABEL[.][b]]] can be used to specify at most one file and optional arguments specifying an offset and a pseudo-start address, LABEL. The LABEL argument is interpreted just like OFFSET, but it specifies an initial pseudo-address. The pseudo-addresses are displayed in parentheses following any normal address. An exit status of zero indicates success, and a nonzero value indicates failure.  File: coreutils.info, Node: base64 invocation, Prev: od invocation, Up: Output of entire files 3.5 `base64': Transform data into printable data ================================================ `base64' transforms data read from a file, or standard input, into (or from) base64 encoded form. The base64 encoded form uses printable ASCII characters to represent binary data. Synopses: base64 [OPTION]... [FILE] base64 --decode [OPTION]... [FILE] The base64 encoding expands data to roughly 133% of the original. The format conforms to RFC 4648 (ftp://ftp.rfc-editor.org/in-notes/rfc4648.txt). The program accepts the following options. Also see *note Common options::. `-w COLS' `--wrap=COLS' During encoding, wrap lines after COLS characters. This must be a positive number. The default is to wrap after 76 characters. Use the value 0 to disable line wrapping altogether. `-d' `--decode' Change the mode of operation, from the default of encoding data, to decoding data. Input is expected to be base64 encoded data, and the output will be the original data. `-i' `--ignore-garbage' When decoding, newlines are always accepted. During decoding, ignore unrecognized bytes, to permit distorted data to be decoded. An exit status of zero indicates success, and a nonzero value indicates failure.  File: coreutils.info, Node: Formatting file contents, Next: Output of parts of files, Prev: Output of entire files, Up: Top 4 Formatting file contents ************************** These commands reformat the contents of files. * Menu: * fmt invocation:: Reformat paragraph text. * pr invocation:: Paginate or columnate files for printing. * fold invocation:: Wrap input lines to fit in specified width.  File: coreutils.info, Node: fmt invocation, Next: pr invocation, Up: Formatting file contents 4.1 `fmt': Reformat paragraph text ================================== `fmt' fills and joins lines to produce output lines of (at most) a given number of characters (75 by default). Synopsis: fmt [OPTION]... [FILE]... `fmt' reads from the specified FILE arguments (or standard input if none are given), and writes to standard output. By default, blank lines, spaces between words, and indentation are preserved in the output; successive input lines with different indentation are not joined; tabs are expanded on input and introduced on output. `fmt' prefers breaking lines at the end of a sentence, and tries to avoid line breaks after the first word of a sentence or before the last word of a sentence. A "sentence break" is defined as either the end of a paragraph or a word ending in any of `.?!', followed by two spaces or end of line, ignoring any intervening parentheses or quotes. Like TeX, `fmt' reads entire "paragraphs" before choosing line breaks; the algorithm is a variant of that given by Donald E. Knuth and Michael F. Plass in "Breaking Paragraphs Into Lines", `Software--Practice & Experience' 11, 11 (November 1981), 1119-1184. The program accepts the following options. Also see *note Common options::. `-c' `--crown-margin' "Crown margin" mode: preserve the indentation of the first two lines within a paragraph, and align the left margin of each subsequent line with that of the second line. `-t' `--tagged-paragraph' "Tagged paragraph" mode: like crown margin mode, except that if indentation of the first line of a paragraph is the same as the indentation of the second, the first line is treated as a one-line paragraph. `-s' `--split-only' Split lines only. Do not join short lines to form longer ones. This prevents sample lines of code, and other such "formatted" text from being unduly combined. `-u' `--uniform-spacing' Uniform spacing. Reduce spacing between words to one space, and spacing between sentences to two spaces. `-WIDTH' `-w WIDTH' `--width=WIDTH' Fill output lines up to WIDTH characters (default 75). `fmt' initially tries to make lines about 7% shorter than this, to give it room to balance line lengths. `-p PREFIX' `--prefix=PREFIX' Only lines beginning with PREFIX (possibly preceded by whitespace) are subject to formatting. The prefix and any preceding whitespace are stripped for the formatting and then re-attached to each formatted output line. One use is to format certain kinds of program comments, while leaving the code unchanged. An exit status of zero indicates success, and a nonzero value indicates failure.  File: coreutils.info, Node: pr invocation, Next: fold invocation, Prev: fmt invocation, Up: Formatting file contents 4.2 `pr': Paginate or columnate files for printing ================================================== `pr' writes each FILE (`-' means standard input), or standard input if none are given, to standard output, paginating and optionally outputting in multicolumn format; optionally merges all FILEs, printing all in parallel, one per column. Synopsis: pr [OPTION]... [FILE]... By default, a 5-line header is printed at each page: two blank lines; a line with the date, the file name, and the page count; and two more blank lines. A footer of five blank lines is also printed. The default PAGE_LENGTH is 66 lines. The default number of text lines is therefore 56. The text line of the header takes the form `DATE STRING PAGE', with spaces inserted around STRING so that the line takes up the full PAGE_WIDTH. Here, DATE is the date (see the `-D' or `--date-format' option for details), STRING is the centered header string, and PAGE identifies the page number. The `LC_MESSAGES' locale category affects the spelling of PAGE; in the default C locale, it is `Page NUMBER' where NUMBER is the decimal page number. Form feeds in the input cause page breaks in the output. Multiple form feeds produce empty pages. Columns are of equal width, separated by an optional string (default is `space'). For multicolumn output, lines will always be truncated to PAGE_WIDTH (default 72), unless you use the `-J' option. For single column output no line truncation occurs by default. Use `-W' option to truncate lines in that case. The following changes were made in version 1.22i and apply to later versions of `pr': - Brian * Some small LETTER OPTIONS (`-s', `-w') have been redefined for better POSIX compliance. The output of some further cases has been adapted to other Unix systems. These changes are not compatible with earlier versions of the program. * Some NEW CAPITAL LETTER options (`-J', `-S', `-W') have been introduced to turn off unexpected interferences of small letter options. The `-N' option and the second argument LAST_PAGE of `+FIRST_PAGE' offer more flexibility. The detailed handling of form feeds set in the input files requires the `-T' option. * Capital letter options override small letter ones. * Some of the option-arguments (compare `-s', `-e', `-i', `-n') cannot be specified as separate arguments from the preceding option letter (already stated in the POSIX specification). The program accepts the following options. Also see *note Common options::. `+FIRST_PAGE[:LAST_PAGE]' `--pages=FIRST_PAGE[:LAST_PAGE]' Begin printing with page FIRST_PAGE and stop with LAST_PAGE. Missing `:LAST_PAGE' implies end of file. While estimating the number of skipped pages each form feed in the input file results in a new page. Page counting with and without `+FIRST_PAGE' is identical. By default, counting starts with the first page of input file (not first page printed). Line numbering may be altered by `-N' option. `-COLUMN' `--columns=COLUMN' With each single FILE, produce COLUMN columns of output (default is 1) and print columns down, unless `-a' is used. The column width is automatically decreased as COLUMN increases; unless you use the `-W/-w' option to increase PAGE_WIDTH as well. This option might well cause some lines to be truncated. The number of lines in the columns on each page are balanced. The options `-e' and `-i' are on for multiple text-column output. Together with `-J' option column alignment and line truncation is turned off. Lines of full length are joined in a free field format and `-S' option may set field separators. `-COLUMN' may not be used with `-m' option. `-a' `--across' With each single FILE, print columns across rather than down. The `-COLUMN' option must be given with COLUMN greater than one. If a line is too long to fit in a column, it is truncated. `-c' `--show-control-chars' Print control characters using hat notation (e.g., `^G'); print other nonprinting characters in octal backslash notation. By default, nonprinting characters are not changed. `-d' `--double-space' Double space the output. `-D FORMAT' `--date-format=FORMAT' Format header dates using FORMAT, using the same conventions as for the command `date +FORMAT'; *Note date invocation::. Except for directives, which start with `%', characters in FORMAT are printed unchanged. You can use this option to specify an arbitrary string in place of the header date, e.g., `--date-format="Monday morning"'. The default date format is `%Y-%m-%d %H:%M' (for example, `2001-12-04 23:59'); but if the `POSIXLY_CORRECT' environment variable is set and the `LC_TIME' locale category specifies the POSIX locale, the default is `%b %e %H:%M %Y' (for example, `Dec 4 23:59 2001'. Time stamps are listed according to the time zone rules specified by the `TZ' environment variable, or by the system default rules if `TZ' is not set. *Note Specifying the Time Zone with `TZ': (libc)TZ Variable. `-e[IN-TABCHAR[IN-TABWIDTH]]' `--expand-tabs[=IN-TABCHAR[IN-TABWIDTH]]' Expand TABs to spaces on input. Optional argument IN-TABCHAR is the input tab character (default is the TAB character). Second optional argument IN-TABWIDTH is the input tab character's width (default is 8). `-f' `-F' `--form-feed' Use a form feed instead of newlines to separate output pages. This does not alter the default page length of 66 lines. `-h HEADER' `--header=HEADER' Replace the file name in the header with the centered string HEADER. When using the shell, HEADER should be quoted and should be separated from `-h' by a space. `-i[OUT-TABCHAR[OUT-TABWIDTH]]' `--output-tabs[=OUT-TABCHAR[OUT-TABWIDTH]]' Replace spaces with TABs on output. Optional argument OUT-TABCHAR is the output tab character (default is the TAB character). Second optional argument OUT-TABWIDTH is the output tab character's width (default is 8). `-J' `--join-lines' Merge lines of full length. Used together with the column options `-COLUMN', `-a -COLUMN' or `-m'. Turns off `-W/-w' line truncation; no column alignment used; may be used with `--sep-string[=STRING]'. `-J' has been introduced (together with `-W' and `--sep-string') to disentangle the old (POSIX-compliant) options `-w' and `-s' along with the three column options. `-l PAGE_LENGTH' `--length=PAGE_LENGTH' Set the page length to PAGE_LENGTH (default 66) lines, including the lines of the header [and the footer]. If PAGE_LENGTH is less than or equal to 10, the header and footer are omitted, as if the `-t' option had been given. `-m' `--merge' Merge and print all FILEs in parallel, one in each column. If a line is too long to fit in a column, it is truncated, unless the `-J' option is used. `--sep-string[=STRING]' may be used. Empty pages in some FILEs (form feeds set) produce empty columns, still marked by STRING. The result is a continuous line numbering and column marking throughout the whole merged file. Completely empty merged pages show no separators or line numbers. The default header becomes `DATE PAGE' with spaces inserted in the middle; this may be used with the `-h' or `--header' option to fill up the middle blank part. `-n[NUMBER-SEPARATOR[DIGITS]]' `--number-lines[=NUMBER-SEPARATOR[DIGITS]]' Provide DIGITS digit line numbering (default for DIGITS is 5). With multicolumn output the number occupies the first DIGITS column positions of each text column or only each line of `-m' output. With single column output the number precedes each line just as `-m' does. Default counting of the line numbers starts with the first line of the input file (not the first line printed, compare the `--page' option and `-N' option). Optional argument NUMBER-SEPARATOR is the character appended to the line number to separate it from the text followed. The default separator is the TAB character. In a strict sense a TAB is always printed with single column output only. The TAB width varies with the TAB position, e.g., with the left MARGIN specified by `-o' option. With multicolumn output priority is given to `equal width of output columns' (a POSIX specification). The TAB width is fixed to the value of the first column and does not change with different values of left MARGIN. That means a fixed number of spaces is always printed in the place of the NUMBER-SEPARATOR TAB. The tabification depends upon the output position. `-N LINE_NUMBER' `--first-line-number=LINE_NUMBER' Start line counting with the number LINE_NUMBER at first line of first page printed (in most cases not the first line of the input file). `-o MARGIN' `--indent=MARGIN' Indent each line with a margin MARGIN spaces wide (default is zero). The total page width is the size of the margin plus the PAGE_WIDTH set with the `-W/-w' option. A limited overflow may occur with numbered single column output (compare `-n' option). `-r' `--no-file-warnings' Do not print a warning message when an argument FILE cannot be opened. (The exit status will still be nonzero, however.) `-s[CHAR]' `--separator[=CHAR]' Separate columns by a single character CHAR. The default for CHAR is the TAB character without `-w' and `no character' with `-w'. Without `-s' the default separator `space' is set. `-s[char]' turns off line truncation of all three column options (`-COLUMN'|`-a -COLUMN'|`-m') unless `-w' is set. This is a POSIX-compliant formulation. `-S[STRING]' `--sep-string[=STRING]' Use STRING to separate output columns. The `-S' option doesn't affect the `-W/-w' option, unlike the `-s' option which does. It does not affect line truncation or column alignment. Without `-S', and with `-J', `pr' uses the default output separator, TAB. Without `-S' or `-J', `pr' uses a `space' (same as `-S" "'). If no `STRING' argument is specified, `""' is assumed. `-t' `--omit-header' Do not print the usual header [and footer] on each page, and do not fill out the bottom of pages (with blank lines or a form feed). No page structure is produced, but form feeds set in the input files are retained. The predefined pagination is not changed. `-t' or `-T' may be useful together with other options; e.g.: `-t -e4', expand TAB characters in the input file to 4 spaces but don't make any other changes. Use of `-t' overrides `-h'. `-T' `--omit-pagination' Do not print header [and footer]. In addition eliminate all form feeds set in the input files. `-v' `--show-nonprinting' Print nonprinting characters in octal backslash notation. `-w PAGE_WIDTH' `--width=PAGE_WIDTH' Set page width to PAGE_WIDTH characters for multiple text-column output only (default for PAGE_WIDTH is 72). `-s[CHAR]' turns off the default page width and any line truncation and column alignment. Lines of full length are merged, regardless of the column options set. No PAGE_WIDTH setting is possible with single column output. A POSIX-compliant formulation. `-W PAGE_WIDTH' `--page_width=PAGE_WIDTH' Set the page width to PAGE_WIDTH characters. That's valid with and without a column option. Text lines are truncated, unless `-J' is used. Together with one of the three column options (`-COLUMN', `-a -COLUMN' or `-m') column alignment is always used. The separator options `-S' or `-s' don't affect the `-W' option. Default is 72 characters. Without `-W PAGE_WIDTH' and without any of the column options NO line truncation is used (defined to keep downward compatibility and to meet most frequent tasks). That's equivalent to `-W 72 -J'. The header line is never truncated. An exit status of zero indicates success, and a nonzero value indicates failure.  File: coreutils.info, Node: fold invocation, Prev: pr invocation, Up: Formatting file contents 4.3 `fold': Wrap input lines to fit in specified width ====================================================== `fold' writes each FILE (`-' means standard input), or standard input if none are given, to standard output, breaking long lines. Synopsis: fold [OPTION]... [FILE]... By default, `fold' breaks lines wider than 80 columns. The output is split into as many lines as necessary. `fold' counts screen columns by default; thus, a tab may count more than one column, backspace decreases the column count, and carriage return sets the column to zero. The program accepts the following options. Also see *note Common options::. `-b' `--bytes' Count bytes rather than columns, so that tabs, backspaces, and carriage returns are each counted as taking up one column, just like other characters. `-s' `--spaces' Break at word boundaries: the line is broken after the last blank before the maximum line length. If the line contains no such blanks, the line is broken at the maximum line length as usual. `-w WIDTH' `--width=WIDTH' Use a maximum line length of WIDTH columns instead of 80. For compatibility `fold' supports an obsolete option syntax `-WIDTH'. New scripts should use `-w WIDTH' instead. An exit status of zero indicates success, and a nonzero value indicates failure.  File: coreutils.info, Node: Output of parts of files, Next: Summarizing files, Prev: Formatting file contents, Up: Top 5 Output of parts of files ************************** These commands output pieces of the input. * Menu: * head invocation:: Output the first part of files. * tail invocation:: Output the last part of files. * split invocation:: Split a file into pieces. * csplit invocation:: Split a file into context-determined pieces.  File: coreutils.info, Node: head invocation, Next: tail invocation, Up: Output of parts of files 5.1 `head': Output the first part of files ========================================== `head' prints the first part (10 lines by default) of each FILE; it reads from standard input if no files are given or when given a FILE of `-'. Synopsis: head [OPTION]... [FILE]... If more than one FILE is specified, `head' prints a one-line header consisting of: ==> FILE NAME <== before the output for each FILE. The program accepts the following options. Also see *note Common options::. `-c K' `--bytes=K' Print the first K bytes, instead of initial lines. However, if K starts with a `-', print all but the last K bytes of each file. K may be, or may be an integer optionally followed by, one of the following multiplicative suffixes: `b' => 512 ("blocks") `KB' => 1000 (KiloBytes) `K' => 1024 (KibiBytes) `MB' => 1000*1000 (MegaBytes) `M' => 1024*1024 (MebiBytes) `GB' => 1000*1000*1000 (GigaBytes) `G' => 1024*1024*1024 (GibiBytes) and so on for `T', `P', `E', `Z', and `Y'. `-n K' `--lines=K' Output the first K lines. However, if K starts with a `-', print all but the last K lines of each file. Size multiplier suffixes are the same as with the `-c' option. `-q' `--quiet' `--silent' Never print file name headers. `-v' `--verbose' Always print file name headers. For compatibility `head' also supports an obsolete option syntax `-COUNTOPTIONS', which is recognized only if it is specified first. COUNT is a decimal number optionally followed by a size letter (`b', `k', `m') as in `-c', or `l' to mean count by lines, or other option letters (`cqv'). Scripts intended for standard hosts should use `-c COUNT' or `-n COUNT' instead. If your script must also run on hosts that support only the obsolete syntax, it is usually simpler to avoid `head', e.g., by using `sed 5q' instead of `head -5'. An exit status of zero indicates success, and a nonzero value indicates failure.  File: coreutils.info, Node: tail invocation, Next: split invocation, Prev: head invocation, Up: Output of parts of files 5.2 `tail': Output the last part of files ========================================= `tail' prints the last part (10 lines by default) of each FILE; it reads from standard input if no files are given or when given a FILE of `-'. Synopsis: tail [OPTION]... [FILE]... If more than one FILE is specified, `tail' prints a one-line header consisting of: ==> FILE NAME <== before the output for each FILE. GNU `tail' can output any amount of data (some other versions of `tail' cannot). It also has no `-r' option (print in reverse), since reversing a file is really a different job from printing the end of a file; BSD `tail' (which is the one with `-r') can only reverse files that are at most as large as its buffer, which is typically 32 KiB. A more reliable and versatile way to reverse files is the GNU `tac' command. The program accepts the following options. Also see *note Common options::. `-c K' `--bytes=K' Output the last K bytes, instead of final lines. However, if K starts with a `+', start printing with the Kth byte from the start of each file, instead of from the end. K may be, or may be an integer optionally followed by, one of the following multiplicative suffixes: `b' => 512 ("blocks") `KB' => 1000 (KiloBytes) `K' => 1024 (KibiBytes) `MB' => 1000*1000 (MegaBytes) `M' => 1024*1024 (MebiBytes) `GB' => 1000*1000*1000 (GigaBytes) `G' => 1024*1024*1024 (GibiBytes) and so on for `T', `P', `E', `Z', and `Y'. `-f' `--follow[=HOW]' Loop forever trying to read more characters at the end of the file, presumably because the file is growing. If more than one file is given, `tail' prints a header whenever it gets output from a different file, to indicate which file that output is from. There are two ways to specify how you'd like to track files with this option, but that difference is noticeable only when a followed file is removed or renamed. If you'd like to continue to track the end of a growing file even after it has been unlinked, use `--follow=descriptor'. This is the default behavior, but it is not useful if you're tracking a log file that may be rotated (removed or renamed, then reopened). In that case, use `--follow=name' to track the named file, perhaps by reopening it periodically to see if it has been removed and recreated by some other program. Note that the inotify-based implementation handles this case without the need for any periodic reopening. No matter which method you use, if the tracked file is determined to have shrunk, `tail' prints a message saying the file has been truncated and resumes tracking the end of the file from the newly-determined endpoint. When a file is removed, `tail''s behavior depends on whether it is following the name or the descriptor. When following by name, tail can detect that a file has been removed and gives a message to that effect, and if `--retry' has been specified it will continue checking periodically to see if the file reappears. When following a descriptor, tail does not detect that the file has been unlinked or renamed and issues no message; even though the file may no longer be accessible via its original name, it may still be growing. The option values `descriptor' and `name' may be specified only with the long form of the option, not with `-f'. The `-f' option is ignored if no FILE operand is specified and standard input is a FIFO or a pipe. Likewise, the `-f' option has no effect for any operand specified as `-', when standard input is a FIFO or a pipe. With kernel inotify support, output is triggered by file changes and is generally very prompt. Otherwise, `tail' sleeps for one second between checks-- use `--sleep-interval=N' to change that default--which can make the output appear slightly less responsive or bursty. When using tail without inotify support, you can make it more responsive by using a sub-second sleep interval, e.g., via an alias like this: alias tail='tail -s.1' `-F' This option is the same as `--follow=name --retry'. That is, tail will attempt to reopen a file when it is removed. Should this fail, tail will keep trying until it becomes accessible again. `--retry' This option is useful mainly when following by name (i.e., with `--follow=name'). Without this option, when tail encounters a file that doesn't exist or is otherwise inaccessible, it reports that fact and never checks it again. `--sleep-interval=NUMBER' Change the number of seconds to wait between iterations (the default is 1.0). During one iteration, every specified file is checked to see if it has changed size. Historical implementations of `tail' have required that NUMBER be an integer. However, GNU `tail' accepts an arbitrary floating point number. *Note Floating point::. When `tail' uses inotify, this polling-related option is usually ignored. However, if you also specify `--pid=P', `tail' checks whether process P is alive at least every NUMBER seconds. `--pid=PID' When following by name or by descriptor, you may specify the process ID, PID, of the sole writer of all FILE arguments. Then, shortly after that process terminates, tail will also terminate. This will work properly only if the writer and the tailing process are running on the same machine. For example, to save the output of a build in a file and to watch the file grow, if you invoke `make' and `tail' like this then the tail process will stop when your build completes. Without this option, you would have had to kill the `tail -f' process yourself. $ make >& makerr & tail --pid=$! -f makerr If you specify a PID that is not in use or that does not correspond to the process that is writing to the tailed files, then `tail' may terminate long before any FILEs stop growing or it may not terminate until long after the real writer has terminated. Note that `--pid' cannot be supported on some systems; `tail' will print a warning if this is the case. `--max-unchanged-stats=N' When tailing a file by name, if there have been N (default n=5) consecutive iterations for which the file has not changed, then `open'/`fstat' the file to determine if that file name is still associated with the same device/inode-number pair as before. When following a log file that is rotated, this is approximately the number of seconds between when tail prints the last pre-rotation lines and when it prints the lines that have accumulated in the new log file. This option is meaningful only when polling (i.e., without inotify) and when following by name. `-n K' `--lines=K' Output the last K lines. However, if K starts with a `+', start printing with the Kth line from the start of each file, instead of from the end. Size multiplier suffixes are the same as with the `-c' option. `-q' `--quiet' `--silent' Never print file name headers. `-v' `--verbose' Always print file name headers. For compatibility `tail' also supports an obsolete usage `tail -[COUNT][bcl][f] [FILE]', which is recognized only if it does not conflict with the usage described above. This obsolete form uses exactly one option and at most one file. In the option, COUNT is an optional decimal number optionally followed by a size letter (`b', `c', `l') to mean count by 512-byte blocks, bytes, or lines, optionally followed by `f' which has the same meaning as `-f'. On older systems, the leading `-' can be replaced by `+' in the obsolete option syntax with the same meaning as in counts, and obsolete usage overrides normal usage when the two conflict. This obsolete behavior can be enabled or disabled with the `_POSIX2_VERSION' environment variable (*note Standards conformance::). Scripts intended for use on standard hosts should avoid obsolete syntax and should use `-c COUNT[b]', `-n COUNT', and/or `-f' instead. If your script must also run on hosts that support only the obsolete syntax, you can often rewrite it to avoid problematic usages, e.g., by using `sed -n '$p'' rather than `tail -1'. If that's not possible, the script can use a test like `if tail -c +1 /dev/null 2>&1; then ...' to decide which syntax to use. Even if your script assumes the standard behavior, you should still beware usages whose behaviors differ depending on the POSIX version. For example, avoid `tail - main.c', since it might be interpreted as either `tail main.c' or as `tail -- - main.c'; avoid `tail -c 4', since it might mean either `tail -c4' or `tail -c 10 4'; and avoid `tail +4', since it might mean either `tail ./+4' or `tail -n +4'. An exit status of zero indicates success, and a nonzero value indicates failure.  File: coreutils.info, Node: split invocation, Next: csplit invocation, Prev: tail invocation, Up: Output of parts of files 5.3 `split': Split a file into pieces. ====================================== `split' creates output files containing consecutive or interleaved sections of INPUT (standard input if none is given or INPUT is `-'). Synopsis: split [OPTION] [INPUT [PREFIX]] By default, `split' puts 1000 lines of INPUT (or whatever is left over for the last section), into each output file. The output files' names consist of PREFIX (`x' by default) followed by a group of characters (`aa', `ab', ... by default), such that concatenating the output files in traditional sorted order by file name produces the original input file (except `-nr/N'). By default split will initially create files with two generated suffix characters, and will increase this width by two when the next most significant position reaches the last character. (`yz', `zaaa', `zaab', ...). In this way an arbitrary number of output files are supported, which sort as described above, even in the presence of an `--additional-suffix' option. If the `-a' option is specified and the output file names are exhausted, `split' reports an error without deleting the output files that it did create. The program accepts the following options. Also see *note Common options::. `-l LINES' `--lines=LINES' Put LINES lines of INPUT into each output file. For compatibility `split' also supports an obsolete option syntax `-LINES'. New scripts should use `-l LINES' instead. `-b SIZE' `--bytes=SIZE' Put SIZE bytes of INPUT into each output file. SIZE may be, or may be an integer optionally followed by, one of the following multiplicative suffixes: `b' => 512 ("blocks") `KB' => 1000 (KiloBytes) `K' => 1024 (KibiBytes) `MB' => 1000*1000 (MegaBytes) `M' => 1024*1024 (MebiBytes) `GB' => 1000*1000*1000 (GigaBytes) `G' => 1024*1024*1024 (GibiBytes) and so on for `T', `P', `E', `Z', and `Y'. `-C SIZE' `--line-bytes=SIZE' Put into each output file as many complete lines of INPUT as possible without exceeding SIZE bytes. Individual lines longer than SIZE bytes are broken into multiple files. SIZE has the same format as for the `--bytes' option. `--filter=COMMAND' With this option, rather than simply writing to each output file, write through a pipe to the specified shell COMMAND for each output file. COMMAND should use the $FILE environment variable, which is set to a different output file name for each invocation of the command. For example, imagine that you have a 1TiB compressed file that, if uncompressed, would be too large to reside on disk, yet you must split it into individually-compressed pieces of a more manageable size. To do that, you might run this command: xz -dc BIG.xz | split -b200G --filter='xz > $FILE.xz' - big- Assuming a 10:1 compression ratio, that would create about fifty 20GiB files with names `big-aa.xz', `big-ab.xz', `big-ac.xz', etc. `-n CHUNKS' `--number=CHUNKS' Split INPUT to CHUNKS output files where CHUNKS may be: N generate N files based on current size of INPUT K/N only output Kth of N to stdout l/N generate N files without splitting lines l/K/N likewise but only output Kth of N to stdout r/N like `l' but use round robin distribution r/K/N likewise but only output Kth of N to stdout Any excess bytes remaining after dividing the INPUT into N chunks, are assigned to the last chunk. Any excess bytes appearing after the initial calculation are discarded (except when using `r' mode). All N files are created even if there are fewer than N lines, or the INPUT is truncated. For `l' mode, chunks are approximately INPUT size / N. The INPUT is partitioned into N equal sized portions, with the last assigned any excess. If a line _starts_ within a partition it is written completely to the corresponding file. Since lines are not split even if they overlap a partition, the files written can be larger or smaller than the partition size, and even empty if a line is so long as to completely overlap the partition. For `r' mode, the size of INPUT is irrelevant, and so can be a pipe for example. `-a LENGTH' `--suffix-length=LENGTH' Use suffixes of length LENGTH. If a LENGTH of 0 is specified, this is the same as if (any previous) `-a' was not specified, and thus enables the default behavior, which starts the suffix length at 2, and unless `-n' or `--numeric-suffixes=FROM' are specified, will auto increase the length by 2 as required. `-d' `--numeric-suffixes[=FROM]' Use digits in suffixes rather than lower-case letters. The numerical suffix counts from FROM if specified, 0 otherwise. Note specifying a FROM value also disables the default auto suffix length expansion described above, and so you may also want to specify `-a' to allow suffixes beyond `99'. `--additional-suffix=SUFFIX' Append an additional SUFFIX to output file names. SUFFIX must not contain slash. `-e' `--elide-empty-files' Suppress the generation of zero-length output files. This can happen with the `--number' option if a file is (truncated to be) shorter than the number requested, or if a line is so long as to completely span a chunk. The output file sequence numbers, always run consecutively even when this option is specified. `-u' `--unbuffered' Immediately copy input to output in `--number r/...' mode, which is a much slower mode of operation. `--verbose' Write a diagnostic just before each output file is opened. An exit status of zero indicates success, and a nonzero value indicates failure. Here are a few examples to illustrate how the `--number' (`-n') option works: Notice how, by default, one line may be split onto two or more: $ seq -w 6 10 > k; split -n3 k; head xa? ==> xaa <== 06 07 ==> xab <== 08 0 ==> xac <== 9 10 Use the "l/" modifier to suppress that: $ seq -w 6 10 > k; split -nl/3 k; head xa? ==> xaa <== 06 07 ==> xab <== 08 09 ==> xac <== 10 Use the "r/" modifier to distribute lines in a round-robin fashion: $ seq -w 6 10 > k; split -nr/3 k; head xa? ==> xaa <== 06 09 ==> xab <== 07 10 ==> xac <== 08 You can also extract just the Kth chunk. This extracts and prints just the 7th "chunk" of 33: $ seq 100 > k; split -nl/7/33 k 20 21 22  File: coreutils.info, Node: csplit invocation, Prev: split invocation, Up: Output of parts of files 5.4 `csplit': Split a file into context-determined pieces ========================================================= `csplit' creates zero or more output files containing sections of INPUT (standard input if INPUT is `-'). Synopsis: csplit [OPTION]... INPUT PATTERN... The contents of the output files are determined by the PATTERN arguments, as detailed below. An error occurs if a PATTERN argument refers to a nonexistent line of the input file (e.g., if no remaining line matches a given regular expression). After every PATTERN has been matched, any remaining input is copied into one last output file. By default, `csplit' prints the number of bytes written to each output file after it has been created. The types of pattern arguments are: `N' Create an output file containing the input up to but not including line N (a positive integer). If followed by a repeat count, also create an output file containing the next N lines of the input file once for each repeat. `/REGEXP/[OFFSET]' Create an output file containing the current line up to (but not including) the next line of the input file that contains a match for REGEXP. The optional OFFSET is an integer. If it is given, the input up to (but not including) the matching line plus or minus OFFSET is put into the output file, and the line after that begins the next section of input. `%REGEXP%[OFFSET]' Like the previous type, except that it does not create an output file, so that section of the input file is effectively ignored. `{REPEAT-COUNT}' Repeat the previous pattern REPEAT-COUNT additional times. The REPEAT-COUNT can either be a positive integer or an asterisk, meaning repeat as many times as necessary until the input is exhausted. The output files' names consist of a prefix (`xx' by default) followed by a suffix. By default, the suffix is an ascending sequence of two-digit decimal numbers from `00' to `99'. In any case, concatenating the output files in sorted order by file name produces the original input file. By default, if `csplit' encounters an error or receives a hangup, interrupt, quit, or terminate signal, it removes any output files that it has created so far before it exits. The program accepts the following options. Also see *note Common options::. `-f PREFIX' `--prefix=PREFIX' Use PREFIX as the output file name prefix. `-b SUFFIX' `--suffix=SUFFIX' Use SUFFIX as the output file name suffix. When this option is specified, the suffix string must include exactly one `printf(3)'-style conversion specification, possibly including format specification flags, a field width, a precision specifications, or all of these kinds of modifiers. The format letter must convert a binary unsigned integer argument to readable form. The format letters `d' and `i' are aliases for `u', and the `u', `o', `x', and `X' conversions are allowed. The entire SUFFIX is given (with the current output file number) to `sprintf(3)' to form the file name suffixes for each of the individual output files in turn. If this option is used, the `--digits' option is ignored. `-n DIGITS' `--digits=DIGITS' Use output file names containing numbers that are DIGITS digits long instead of the default 2. `-k' `--keep-files' Do not remove output files when errors are encountered. `-z' `--elide-empty-files' Suppress the generation of zero-length output files. (In cases where the section delimiters of the input file are supposed to mark the first lines of each of the sections, the first output file will generally be a zero-length file unless you use this option.) The output file sequence numbers always run consecutively starting from 0, even when this option is specified. `-s' `-q' `--silent' `--quiet' Do not print counts of output file sizes. An exit status of zero indicates success, and a nonzero value indicates failure. Here is an example of its usage. First, create an empty directory for the exercise, and cd into it: $ mkdir d && cd d Now, split the sequence of 1..14 on lines that end with 0 or 5: $ seq 14 | csplit - '/[05]$/' '{*}' 8 10 15 Each number printed above is the size of an output file that csplit has just created. List the names of those output files: $ ls xx00 xx01 xx02 Use `head' to show their contents: $ head xx* ==> xx00 <== 1 2 3 4 ==> xx01 <== 5 6 7 8 9 ==> xx02 <== 10 11 12 13 14  File: coreutils.info, Node: Summarizing files, Next: Operating on sorted files, Prev: Output of parts of files, Up: Top 6 Summarizing files ******************* These commands generate just a few numbers representing entire contents of files. * Menu: * wc invocation:: Print newline, word, and byte counts. * sum invocation:: Print checksum and block counts. * cksum invocation:: Print CRC checksum and byte counts. * md5sum invocation:: Print or check MD5 digests. * sha1sum invocation:: Print or check SHA-1 digests. * sha2 utilities:: Print or check SHA-2 digests.  File: coreutils.info, Node: wc invocation, Next: sum invocation, Up: Summarizing files 6.1 `wc': Print newline, word, and byte counts ============================================== `wc' counts the number of bytes, characters, whitespace-separated words, and newlines in each given FILE, or standard input if none are given or for a FILE of `-'. Synopsis: wc [OPTION]... [FILE]... `wc' prints one line of counts for each file, and if the file was given as an argument, it prints the file name following the counts. If more than one FILE is given, `wc' prints a final line containing the cumulative counts, with the file name `total'. The counts are printed in this order: newlines, words, characters, bytes, maximum line length. Each count is printed right-justified in a field with at least one space between fields so that the numbers and file names normally line up nicely in columns. The width of the count fields varies depending on the inputs, so you should not depend on a particular field width. However, as a GNU extension, if only one count is printed, it is guaranteed to be printed without leading spaces. By default, `wc' prints three counts: the newline, words, and byte counts. Options can specify that only certain counts be printed. Options do not undo others previously given, so wc --bytes --words prints both the byte counts and the word counts. With the `--max-line-length' option, `wc' prints the length of the longest line per file, and if there is more than one file it prints the maximum (not the sum) of those lengths. The line lengths here are measured in screen columns, according to the current locale and assuming tab positions in every 8th column. The program accepts the following options. Also see *note Common options::. `-c' `--bytes' Print only the byte counts. `-m' `--chars' Print only the character counts. `-w' `--words' Print only the word counts. `-l' `--lines' Print only the newline counts. `-L' `--max-line-length' Print only the maximum line lengths. `--files0-from=FILE' Disallow processing files named on the command line, and instead process those named in file FILE; each name being terminated by a zero byte (ASCII NUL). This is useful when the list of file names is so long that it may exceed a command line length limitation. In such cases, running `wc' via `xargs' is undesirable because it splits the list into pieces and makes `wc' print a total for each sublist rather than for the entire list. One way to produce a list of ASCII NUL terminated file names is with GNU `find', using its `-print0' predicate. If FILE is `-' then the ASCII NUL terminated file names are read from standard input. For example, to find the length of the longest line in any `.c' or `.h' file in the current hierarchy, do this: find . -name '*.[ch]' -print0 | wc -L --files0-from=- | tail -n1 An exit status of zero indicates success, and a nonzero value indicates failure.  File: coreutils.info, Node: sum invocation, Next: cksum invocation, Prev: wc invocation, Up: Summarizing files 6.2 `sum': Print checksum and block counts ========================================== `sum' computes a 16-bit checksum for each given FILE, or standard input if none are given or for a FILE of `-'. Synopsis: sum [OPTION]... [FILE]... `sum' prints the checksum for each FILE followed by the number of blocks in the file (rounded up). If more than one FILE is given, file names are also printed (by default). (With the `--sysv' option, corresponding file names are printed when there is at least one file argument.) By default, GNU `sum' computes checksums using an algorithm compatible with BSD `sum' and prints file sizes in units of 1024-byte blocks. The program accepts the following options. Also see *note Common options::. `-r' Use the default (BSD compatible) algorithm. This option is included for compatibility with the System V `sum'. Unless `-s' was also given, it has no effect. `-s' `--sysv' Compute checksums using an algorithm compatible with System V `sum''s default, and print file sizes in units of 512-byte blocks. `sum' is provided for compatibility; the `cksum' program (see next section) is preferable in new applications. An exit status of zero indicates success, and a nonzero value indicates failure.  File: coreutils.info, Node: cksum invocation, Next: md5sum invocation, Prev: sum invocation, Up: Summarizing files 6.3 `cksum': Print CRC checksum and byte counts =============================================== `cksum' computes a cyclic redundancy check (CRC) checksum for each given FILE, or standard input if none are given or for a FILE of `-'. Synopsis: cksum [OPTION]... [FILE]... `cksum' prints the CRC checksum for each file along with the number of bytes in the file, and the file name unless no arguments were given. `cksum' is typically used to ensure that files transferred by unreliable means (e.g., netnews) have not been corrupted, by comparing the `cksum' output for the received files with the `cksum' output for the original files (typically given in the distribution). The CRC algorithm is specified by the POSIX standard. It is not compatible with the BSD or System V `sum' algorithms (see the previous section); it is more robust. The only options are `--help' and `--version'. *Note Common options::. An exit status of zero indicates success, and a nonzero value indicates failure.  File: coreutils.info, Node: md5sum invocation, Next: sha1sum invocation, Prev: cksum invocation, Up: Summarizing files 6.4 `md5sum': Print or check MD5 digests ======================================== `md5sum' computes a 128-bit checksum (or "fingerprint" or "message-digest") for each specified FILE. Note: The MD5 digest is more reliable than a simple CRC (provided by the `cksum' command) for detecting accidental file corruption, as the chances of accidentally having two files with identical MD5 are vanishingly small. However, it should not be considered secure against malicious tampering: although finding a file with a given MD5 fingerprint is considered infeasible at the moment, it is known how to modify certain files, including digital certificates, so that they appear valid when signed with an MD5 digest. For more secure hashes, consider using SHA-2. *Note sha2 utilities::. If a FILE is specified as `-' or if no files are given `md5sum' computes the checksum for the standard input. `md5sum' can also determine whether a file and checksum are consistent. Synopsis: md5sum [OPTION]... [FILE]... For each FILE, `md5sum' outputs the MD5 checksum, a flag indicating binary or text input mode, and the file name. If FILE contains a backslash or newline, the line is started with a backslash, and each problematic character in the file name is escaped with a backslash, making the output unambiguous even in the presence of arbitrary file names. If FILE is omitted or specified as `-', standard input is read. The program accepts the following options. Also see *note Common options::. `-b' `--binary' Treat each input file as binary, by reading it in binary mode and outputting a `*' flag. This is the inverse of `--text'. On systems like GNU that do not distinguish between binary and text files, this option merely flags each input mode as binary: the MD5 checksum is unaffected. This option is the default on systems like MS-DOS that distinguish between binary and text files, except for reading standard input when standard input is a terminal. `-c' `--check' Read file names and checksum information (not data) from each FILE (or from stdin if no FILE was specified) and report whether the checksums match the contents of the named files. The input to this mode of `md5sum' is usually the output of a prior, checksum-generating run of `md5sum'. Each valid line of input consists of an MD5 checksum, a binary/text flag, and then a file name. Binary mode is indicated with `*', text with ` ' (space). For each such line, `md5sum' reads the named file and computes its MD5 checksum. Then, if the computed message digest does not match the one on the line with the file name, the file is noted as having failed the test. Otherwise, the file passes the test. By default, for each valid line, one line is written to standard output indicating whether the named file passed the test. After all checks have been performed, if there were any failures, a warning is issued to standard error. Use the `--status' option to inhibit that output. If any listed file cannot be opened or read, if any valid line has an MD5 checksum inconsistent with the associated file, or if no valid line is found, `md5sum' exits with nonzero status. Otherwise, it exits successfully. `--quiet' This option is useful only when verifying checksums. When verifying checksums, don't generate an 'OK' message per successfully checked file. Files that fail the verification are reported in the default one-line-per-file format. If there is any checksum mismatch, print a warning summarizing the failures to standard error. `--status' This option is useful only when verifying checksums. When verifying checksums, don't generate the default one-line-per-file diagnostic and don't output the warning summarizing any failures. Failures to open or read a file still evoke individual diagnostics to standard error. If all listed files are readable and are consistent with the associated MD5 checksums, exit successfully. Otherwise exit with a status code indicating there was a failure. `-t' `--text' Treat each input file as text, by reading it in text mode and outputting a ` ' flag. This is the inverse of `--binary'. This option is the default on systems like GNU that do not distinguish between binary and text files. On other systems, it is the default for reading standard input when standard input is a terminal. `-w' `--warn' When verifying checksums, warn about improperly formatted MD5 checksum lines. This option is useful only if all but a few lines in the checked input are valid. `--strict' When verifying checksums, if one or more input line is invalid, exit nonzero after all warnings have been issued. An exit status of zero indicates success, and a nonzero value indicates failure.  File: coreutils.info, Node: sha1sum invocation, Next: sha2 utilities, Prev: md5sum invocation, Up: Summarizing files 6.5 `sha1sum': Print or check SHA-1 digests =========================================== `sha1sum' computes a 160-bit checksum for each specified FILE. The usage and options of this command are precisely the same as for `md5sum'. *Note md5sum invocation::. Note: The SHA-1 digest is more secure than MD5, and no collisions of it are known (different files having the same fingerprint). However, it is known that they can be produced with considerable, but not unreasonable, resources. For this reason, it is generally considered that SHA-1 should be gradually phased out in favor of the more secure SHA-2 hash algorithms. *Note sha2 utilities::.  File: coreutils.info, Node: sha2 utilities, Prev: sha1sum invocation, Up: Summarizing files 6.6 sha2 utilities: Print or check SHA-2 digests ================================================ The commands `sha224sum', `sha256sum', `sha384sum' and `sha512sum' compute checksums of various lengths (respectively 224, 256, 384 and 512 bits), collectively known as the SHA-2 hashes. The usage and options of these commands are precisely the same as for `md5sum'. *Note md5sum invocation::. Note: The SHA384 and SHA512 digests are considerably slower to compute, especially on 32-bit computers, than SHA224 or SHA256.  File: coreutils.info, Node: Operating on sorted files, Next: Operating on fields, Prev: Summarizing files, Up: Top 7 Operating on sorted files *************************** These commands work with (or produce) sorted files. * Menu: * sort invocation:: Sort text files. * shuf invocation:: Shuffle text files. * uniq invocation:: Uniquify files. * comm invocation:: Compare two sorted files line by line. * ptx invocation:: Produce a permuted index of file contents. * tsort invocation:: Topological sort.  File: coreutils.info, Node: sort invocation, Next: shuf invocation, Up: Operating on sorted files 7.1 `sort': Sort text files =========================== `sort' sorts, merges, or compares all the lines from the given files, or standard input if none are given or for a FILE of `-'. By default, `sort' writes the results to standard output. Synopsis: sort [OPTION]... [FILE]... `sort' has three modes of operation: sort (the default), merge, and check for sortedness. The following options change the operation mode: `-c' `--check' `--check=diagnose-first' Check whether the given file is already sorted: if it is not all sorted, print a diagnostic containing the first out-of-order line and exit with a status of 1. Otherwise, exit successfully. At most one input file can be given. `-C' `--check=quiet' `--check=silent' Exit successfully if the given file is already sorted, and exit with status 1 otherwise. At most one input file can be given. This is like `-c', except it does not print a diagnostic. `-m' `--merge' Merge the given files by sorting them as a group. Each input file must always be individually sorted. It always works to sort instead of merge; merging is provided because it is faster, in the case where it works. A pair of lines is compared as follows: `sort' compares each pair of fields, in the order specified on the command line, according to the associated ordering options, until a difference is found or no fields are left. If no key fields are specified, `sort' uses a default key of the entire line. Finally, as a last resort when all keys compare equal, `sort' compares entire lines as if no ordering options other than `--reverse' (`-r') were specified. The `--stable' (`-s') option disables this "last-resort comparison" so that lines in which all fields compare equal are left in their original relative order. The `--unique' (`-u') option also disables the last-resort comparison. Unless otherwise specified, all comparisons use the character collating sequence specified by the `LC_COLLATE' locale.(1) GNU `sort' (as specified for all GNU utilities) has no limit on input line length or restrictions on bytes allowed within lines. In addition, if the final byte of an input file is not a newline, GNU `sort' silently supplies one. A line's trailing newline is not part of the line for comparison purposes. Exit status: 0 if no error occurred 1 if invoked with `-c' or `-C' and the input is not sorted 2 if an error occurred If the environment variable `TMPDIR' is set, `sort' uses its value as the directory for temporary files instead of `/tmp'. The `--temporary-directory' (`-T') option in turn overrides the environment variable. The following options affect the ordering of output lines. They may be specified globally or as part of a specific key field. If no key fields are specified, global options apply to comparison of entire lines; otherwise the global options are inherited by key fields that do not specify any special options of their own. In pre-POSIX versions of `sort', global options affect only later key fields, so portable shell scripts should specify global options first. `-b' `--ignore-leading-blanks' Ignore leading blanks when finding sort keys in each line. By default a blank is a space or a tab, but the `LC_CTYPE' locale can change this. Note blanks may be ignored by your locale's collating rules, but without this option they will be significant for character positions specified in keys with the `-k' option. `-d' `--dictionary-order' Sort in "phone directory" order: ignore all characters except letters, digits and blanks when sorting. By default letters and digits are those of ASCII and a blank is a space or a tab, but the `LC_CTYPE' locale can change this. `-f' `--ignore-case' Fold lowercase characters into the equivalent uppercase characters when comparing so that, for example, `b' and `B' sort as equal. The `LC_CTYPE' locale determines character types. When used with `--unique' those lower case equivalent lines are thrown away. (There is currently no way to throw away the upper case equivalent instead. (Any `--reverse' given would only affect the final result, after the throwing away.)) `-g' `--general-numeric-sort' `--sort=general-numeric' Sort numerically, converting a prefix of each line to a long double-precision floating point number. *Note Floating point::. Do not report overflow, underflow, or conversion errors. Use the following collating sequence: * Lines that do not start with numbers (all considered to be equal). * NaNs ("Not a Number" values, in IEEE floating point arithmetic) in a consistent but machine-dependent order. * Minus infinity. * Finite numbers in ascending numeric order (with -0 and +0 equal). * Plus infinity. Use this option only if there is no alternative; it is much slower than `--numeric-sort' (`-n') and it can lose information when converting to floating point. `-h' `--human-numeric-sort' `--sort=human-numeric' Sort numerically, first by numeric sign (negative, zero, or positive); then by SI suffix (either empty, or `k' or `K', or one of `MGTPEZY', in that order; *note Block size::); and finally by numeric value. For example, `1023M' sorts before `1G' because `M' (mega) precedes `G' (giga) as an SI suffix. This option sorts values that are consistently scaled to the nearest suffix, regardless of whether suffixes denote powers of 1000 or 1024, and it therefore sorts the output of any single invocation of the `df', `du', or `ls' commands that are invoked with their `--human-readable' or `--si' options. The syntax for numbers is the same as for the `--numeric-sort' option; the SI suffix must immediately follow the number. `-i' `--ignore-nonprinting' Ignore nonprinting characters. The `LC_CTYPE' locale determines character types. This option has no effect if the stronger `--dictionary-order' (`-d') option is also given. `-M' `--month-sort' `--sort=month' An initial string, consisting of any amount of blanks, followed by a month name abbreviation, is folded to UPPER case and compared in the order `JAN' < `FEB' < ... < `DEC'. Invalid names compare low to valid names. The `LC_TIME' locale category determines the month spellings. By default a blank is a space or a tab, but the `LC_CTYPE' locale can change this. `-n' `--numeric-sort' `--sort=numeric' Sort numerically. The number begins each line and consists of optional blanks, an optional `-' sign, and zero or more digits possibly separated by thousands separators, optionally followed by a decimal-point character and zero or more digits. An empty number is treated as `0'. The `LC_NUMERIC' locale specifies the decimal-point character and thousands separator. By default a blank is a space or a tab, but the `LC_CTYPE' locale can change this. Comparison is exact; there is no rounding error. Neither a leading `+' nor exponential notation is recognized. To compare such strings numerically, use the `--general-numeric-sort' (`-g') option. `-V' `--version-sort' Sort by version name and number. It behaves like a standard sort, except that each sequence of decimal digits is treated numerically as an index/version number. (*Note Details about version sort::.) `-r' `--reverse' Reverse the result of comparison, so that lines with greater key values appear earlier in the output instead of later. `-R' `--random-sort' `--sort=random' Sort by hashing the input keys and then sorting the hash values. Choose the hash function at random, ensuring that it is free of collisions so that differing keys have differing hash values. This is like a random permutation of the inputs (*note shuf invocation::), except that keys with the same value sort together. If multiple random sort fields are specified, the same random hash function is used for all fields. To use different random hash functions for different fields, you can invoke `sort' more than once. The choice of hash function is affected by the `--random-source' option. Other options are: `--compress-program=PROG' Compress any temporary files with the program PROG. With no arguments, PROG must compress standard input to standard output, and when given the `-d' option it must decompress standard input to standard output. Terminate with an error if PROG exits with nonzero status. White space and the backslash character should not appear in PROG; they are reserved for future use. `--files0-from=FILE' Disallow processing files named on the command line, and instead process those named in file FILE; each name being terminated by a zero byte (ASCII NUL). This is useful when the list of file names is so long that it may exceed a command line length limitation. In such cases, running `sort' via `xargs' is undesirable because it splits the list into pieces and makes `sort' print sorted output for each sublist rather than for the entire list. One way to produce a list of ASCII NUL terminated file names is with GNU `find', using its `-print0' predicate. If FILE is `-' then the ASCII NUL terminated file names are read from standard input. `-k POS1[,POS2]' `--key=POS1[,POS2]' Specify a sort field that consists of the part of the line between POS1 and POS2 (or the end of the line, if POS2 is omitted), _inclusive_. Each POS has the form `F[.C][OPTS]', where F is the number of the field to use, and C is the number of the first character from the beginning of the field. Fields and character positions are numbered starting with 1; a character position of zero in POS2 indicates the field's last character. If `.C' is omitted from POS1, it defaults to 1 (the beginning of the field); if omitted from POS2, it defaults to 0 (the end of the field). OPTS are ordering options, allowing individual keys to be sorted according to different rules; see below for details. Keys can span multiple fields. Example: To sort on the second field, use `--key=2,2' (`-k 2,2'). See below for more notes on keys and more examples. See also the `--debug' option to help determine the part of the line being used in the sort. `--debug' Highlight the portion of each line used for sorting. Also issue warnings about questionable usage to stderr. `--batch-size=NMERGE' Merge at most NMERGE inputs at once. When `sort' has to merge more than NMERGE inputs, it merges them in groups of NMERGE, saving the result in a temporary file, which is then used as an input in a subsequent merge. A large value of NMERGE may improve merge performance and decrease temporary storage utilization at the expense of increased memory usage and I/O. Conversely a small value of NMERGE may reduce memory requirements and I/O at the expense of temporary storage consumption and merge performance. The value of NMERGE must be at least 2. The default value is currently 16, but this is implementation-dependent and may change in the future. The value of NMERGE may be bounded by a resource limit for open file descriptors. The commands `ulimit -n' or `getconf OPEN_MAX' may display limits for your systems; these limits may be modified further if your program already has some files open, or if the operating system has other limits on the number of open files. If the value of NMERGE exceeds the resource limit, `sort' silently uses a smaller value. `-o OUTPUT-FILE' `--output=OUTPUT-FILE' Write output to OUTPUT-FILE instead of standard output. Normally, `sort' reads all input before opening OUTPUT-FILE, so you can safely sort a file in place by using commands like `sort -o F F' and `cat F | sort -o F'. However, `sort' with `--merge' (`-m') can open the output file before reading all input, so a command like `cat F | sort -m -o F - G' is not safe as `sort' might start writing `F' before `cat' is done reading it. On newer systems, `-o' cannot appear after an input file if `POSIXLY_CORRECT' is set, e.g., `sort F -o F'. Portable scripts should specify `-o OUTPUT-FILE' before any input files. `--random-source=FILE' Use FILE as a source of random data used to determine which random hash function to use with the `-R' option. *Note Random sources::. `-s' `--stable' Make `sort' stable by disabling its last-resort comparison. This option has no effect if no fields or global ordering options other than `--reverse' (`-r') are specified. `-S SIZE' `--buffer-size=SIZE' Use a main-memory sort buffer of the given SIZE. By default, SIZE is in units of 1024 bytes. Appending `%' causes SIZE to be interpreted as a percentage of physical memory. Appending `K' multiplies SIZE by 1024 (the default), `M' by 1,048,576, `G' by 1,073,741,824, and so on for `T', `P', `E', `Z', and `Y'. Appending `b' causes SIZE to be interpreted as a byte count, with no multiplication. This option can improve the performance of `sort' by causing it to start with a larger or smaller sort buffer than the default. However, this option affects only the initial buffer size. The buffer grows beyond SIZE if `sort' encounters input lines larger than SIZE. `-t SEPARATOR' `--field-separator=SEPARATOR' Use character SEPARATOR as the field separator when finding the sort keys in each line. By default, fields are separated by the empty string between a non-blank character and a blank character. By default a blank is a space or a tab, but the `LC_CTYPE' locale can change this. That is, given the input line ` foo bar', `sort' breaks it into fields ` foo' and ` bar'. The field separator is not considered to be part of either the field preceding or the field following, so with `sort -t " "' the same input line has three fields: an empty field, `foo', and `bar'. However, fields that extend to the end of the line, as `-k 2', or fields consisting of a range, as `-k 2,3', retain the field separators present between the endpoints of the range. To specify ASCII NUL as the field separator, use the two-character string `\0', e.g., `sort -t '\0''. `-T TEMPDIR' `--temporary-directory=TEMPDIR' Use directory TEMPDIR to store temporary files, overriding the `TMPDIR' environment variable. If this option is given more than once, temporary files are stored in all the directories given. If you have a large sort or merge that is I/O-bound, you can often improve performance by using this option to specify directories on different disks and controllers. `--parallel=N' Set the number of sorts run in parallel to N. By default, N is set to the number of available processors, but limited to 8, as there are diminishing performance gains after that. Note also that using N threads increases the memory usage by a factor of log N. Also see *note nproc invocation::. `-u' `--unique' Normally, output only the first of a sequence of lines that compare equal. For the `--check' (`-c' or `-C') option, check that no pair of consecutive lines compares equal. This option also disables the default last-resort comparison. The commands `sort -u' and `sort | uniq' are equivalent, but this equivalence does not extend to arbitrary `sort' options. For example, `sort -n -u' inspects only the value of the initial numeric string when checking for uniqueness, whereas `sort -n | uniq' inspects the entire line. *Note uniq invocation::. `-z' `--zero-terminated' Delimit items with a zero byte rather than a newline (ASCII LF). I.E. treat input as items separated by ASCII NUL and terminate output items with ASCII NUL. This option can be useful in conjunction with `perl -0' or `find -print0' and `xargs -0' which do the same in order to reliably handle arbitrary file names (even those containing blanks or other special characters). Historical (BSD and System V) implementations of `sort' have differed in their interpretation of some options, particularly `-b', `-f', and `-n'. GNU sort follows the POSIX behavior, which is usually (but not always!) like the System V behavior. According to POSIX, `-n' no longer implies `-b'. For consistency, `-M' has been changed in the same way. This may affect the meaning of character positions in field specifications in obscure cases. The only fix is to add an explicit `-b'. A position in a sort field specified with `-k' may have any of the option letters `MbdfghinRrV' appended to it, in which case no global ordering options are inherited by that particular field. The `-b' option may be independently attached to either or both of the start and end positions of a field specification, and if it is inherited from the global options it will be attached to both. If input lines can contain leading or adjacent blanks and `-t' is not used, then `-k' is typically combined with `-b' or an option that implicitly ignores leading blanks (`Mghn') as otherwise the varying numbers of leading blanks in fields can cause confusing results. If the start position in a sort field specifier falls after the end of the line or after the end field, the field is empty. If the `-b' option was specified, the `.C' part of a field specification is counted from the first nonblank character of the field. On older systems, `sort' supports an obsolete origin-zero syntax `+POS1 [-POS2]' for specifying sort keys. The obsolete sequence `sort +A.X -B.Y' is equivalent to `sort -k A+1.X+1,B' if Y is `0' or absent, otherwise it is equivalent to `sort -k A+1.X+1,B+1.Y'. This obsolete behavior can be enabled or disabled with the `_POSIX2_VERSION' environment variable (*note Standards conformance::); it can also be enabled when `POSIXLY_CORRECT' is not set by using the obsolete syntax with `-POS2' present. Scripts intended for use on standard hosts should avoid obsolete syntax and should use `-k' instead. For example, avoid `sort +2', since it might be interpreted as either `sort ./+2' or `sort -k 3'. If your script must also run on hosts that support only the obsolete syntax, it can use a test like `if sort -k 1 /dev/null 2>&1; then ...' to decide which syntax to use. Here are some examples to illustrate various combinations of options. * Sort in descending (reverse) numeric order. sort -n -r * Run no more than 4 sorts concurrently, using a buffer size of 10M. sort --parallel=4 -S 10M * Sort alphabetically, omitting the first and second fields and the blanks at the start of the third field. This uses a single key composed of the characters beginning at the start of the first nonblank character in field three and extending to the end of each line. sort -k 3b * Sort numerically on the second field and resolve ties by sorting alphabetically on the third and fourth characters of field five. Use `:' as the field delimiter. sort -t : -k 2,2n -k 5.3,5.4 Note that if you had written `-k 2n' instead of `-k 2,2n' `sort' would have used all characters beginning in the second field and extending to the end of the line as the primary _numeric_ key. For the large majority of applications, treating keys spanning more than one field as numeric will not do what you expect. Also note that the `n' modifier was applied to the field-end specifier for the first key. It would have been equivalent to specify `-k 2n,2' or `-k 2n,2n'. All modifiers except `b' apply to the associated _field_, regardless of whether the modifier character is attached to the field-start and/or the field-end part of the key specifier. * Sort the password file on the fifth field and ignore any leading blanks. Sort lines with equal values in field five on the numeric user ID in field three. Fields are separated by `:'. sort -t : -k 5b,5 -k 3,3n /etc/passwd sort -t : -n -k 5b,5 -k 3,3 /etc/passwd sort -t : -b -k 5,5 -k 3,3n /etc/passwd These three commands have equivalent effect. The first specifies that the first key's start position ignores leading blanks and the second key is sorted numerically. The other two commands rely on global options being inherited by sort keys that lack modifiers. The inheritance works in this case because `-k 5b,5b' and `-k 5b,5' are equivalent, as the location of a field-end lacking a `.C' character position is not affected by whether initial blanks are skipped. * Sort a set of log files, primarily by IPv4 address and secondarily by time stamp. If two lines' primary and secondary keys are identical, output the lines in the same order that they were input. The log files contain lines that look like this: 4.150.156.3 - - [01/Apr/2004:06:31:51 +0000] message 1 211.24.3.231 - - [24/Apr/2004:20:17:39 +0000] message 2 Fields are separated by exactly one space. Sort IPv4 addresses lexicographically, e.g., 212.61.52.2 sorts before 212.129.233.201 because 61 is less than 129. sort -s -t ' ' -k 4.9n -k 4.5M -k 4.2n -k 4.14,4.21 file*.log | sort -s -t '.' -k 1,1n -k 2,2n -k 3,3n -k 4,4n This example cannot be done with a single `sort' invocation, since IPv4 address components are separated by `.' while dates come just after a space. So it is broken down into two invocations of `sort': the first sorts by time stamp and the second by IPv4 address. The time stamp is sorted by year, then month, then day, and finally by hour-minute-second field, using `-k' to isolate each field. Except for hour-minute-second there's no need to specify the end of each key field, since the `n' and `M' modifiers sort based on leading prefixes that cannot cross field boundaries. The IPv4 addresses are sorted lexicographically. The second sort uses `-s' so that ties in the primary key are broken by the secondary key; the first sort uses `-s' so that the combination of the two sorts is stable. * Generate a tags file in case-insensitive sorted order. find src -type f -print0 | sort -z -f | xargs -0 etags --append The use of `-print0', `-z', and `-0' in this case means that file names that contain blanks or other special characters are not broken up by the sort operation. * Use the common DSU (Decorate Sort Undecorate) idiom to sort lines according to their length. awk '{print length, $0}' /etc/passwd | sort -n | cut -f2- -d' ' In general this technique can be used to sort data that the `sort' command does not support, or is inefficient at, sorting directly. * Shuffle a list of directories, but preserve the order of files within each directory. For instance, one could use this to generate a music playlist in which albums are shuffled but the songs of each album are played in order. ls */* | sort -t / -k 1,1R -k 2,2 ---------- Footnotes ---------- (1) If you use a non-POSIX locale (e.g., by setting `LC_ALL' to `en_US'), then `sort' may produce output that is sorted differently than you're accustomed to. In that case, set the `LC_ALL' environment variable to `C'. Note that setting only `LC_COLLATE' has two problems. First, it is ineffective if `LC_ALL' is also set. Second, it has undefined behavior if `LC_CTYPE' (or `LANG', if `LC_CTYPE' is unset) is set to an incompatible value. For example, you get undefined behavior if `LC_CTYPE' is `ja_JP.PCK' but `LC_COLLATE' is `en_US.UTF-8'.  File: coreutils.info, Node: shuf invocation, Next: uniq invocation, Prev: sort invocation, Up: Operating on sorted files 7.2 `shuf': Shuffling text ========================== `shuf' shuffles its input by outputting a random permutation of its input lines. Each output permutation is equally likely. Synopses: shuf [OPTION]... [FILE] shuf -e [OPTION]... [ARG]... shuf -i LO-HI [OPTION]... `shuf' has three modes of operation that affect where it obtains its input lines. By default, it reads lines from standard input. The following options change the operation mode: `-e' `--echo' Treat each command-line operand as an input line. `-i LO-HI' `--input-range=LO-HI' Act as if input came from a file containing the range of unsigned decimal integers LO...HI, one per line. `shuf''s other options can affect its behavior in all operation modes: `-n LINES' `--head-count=COUNT' Output at most COUNT lines. By default, all input lines are output. `-o OUTPUT-FILE' `--output=OUTPUT-FILE' Write output to OUTPUT-FILE instead of standard output. `shuf' reads all input before opening OUTPUT-FILE, so you can safely shuffle a file in place by using commands like `shuf -o F out $ dd bs=1 skip=222 count=6 < out 2>/dev/null; echo deeper Note that although the listing above includes a trailing slash for the `deeper' entry, the offsets select the name without the trailing slash. However, if you invoke `ls' with `--dired' along with an option like `--escape' (aka `-b') and operate on a file whose name contains special characters, notice that the backslash _is_ included: $ touch 'a b' $ ls -blog --dired 'a b' -rw-r--r-- 1 0 Jun 10 12:28 a\ b //DIRED// 30 34 //DIRED-OPTIONS// --quoting-style=escape If you use a quoting style that adds quote marks (e.g., `--quoting-style=c'), then the offsets include the quote marks. So beware that the user may select the quoting style via the environment variable `QUOTING_STYLE'. Hence, applications using `--dired' should either specify an explicit `--quoting-style=literal' option (aka `-N' or `--literal') on the command line, or else be prepared to parse the escaped names. `--full-time' Produce long format directory listings, and list times in full. It is equivalent to using `--format=long' with `--time-style=full-iso' (*note Formatting file timestamps::). `-g' Produce long format directory listings, but don't display owner information. `-G' `--no-group' Inhibit display of group information in a long format directory listing. (This is the default in some non-GNU versions of `ls', so we provide this option for compatibility.) `-h' `--human-readable' Append a size letter to each size, such as `M' for mebibytes. Powers of 1024 are used, not 1000; `M' stands for 1,048,576 bytes. This option is equivalent to `--block-size=human-readable'. Use the `--si' option if you prefer powers of 1000. `-i' `--inode' Print the inode number (also called the file serial number and index number) of each file to the left of the file name. (This number uniquely identifies each file within a particular file system.) `-l' `--format=long' `--format=verbose' In addition to the name of each file, print the file type, file mode bits, number of hard links, owner name, group name, size, and timestamp (*note Formatting file timestamps::), normally the modification time. Print question marks for information that cannot be determined. Normally the size is printed as a byte count without punctuation, but this can be overridden (*note Block size::). For example, `-h' prints an abbreviated, human-readable count, and `--block-size="'1"' prints a byte count with the thousands separator of the current locale. For each directory that is listed, preface the files with a line `total BLOCKS', where BLOCKS is the total disk allocation for all files in that directory. The block size currently defaults to 1024 bytes, but this can be overridden (*note Block size::). The BLOCKS computed counts each hard link separately; this is arguably a deficiency. The file type is one of the following characters: `-' regular file `b' block special file `c' character special file `C' high performance ("contiguous data") file `d' directory `D' door (Solaris 2.5 and up) `l' symbolic link `M' off-line ("migrated") file (Cray DMF) `n' network special file (HP-UX) `p' FIFO (named pipe) `P' port (Solaris 10 and up) `s' socket `?' some other file type The file mode bits listed are similar to symbolic mode specifications (*note Symbolic Modes::). But `ls' combines multiple bits into the third character of each set of permissions as follows: `s' If the set-user-ID or set-group-ID bit and the corresponding executable bit are both set. `S' If the set-user-ID or set-group-ID bit is set but the corresponding executable bit is not set. `t' If the restricted deletion flag or sticky bit, and the other-executable bit, are both set. The restricted deletion flag is another name for the sticky bit. *Note Mode Structure::. `T' If the restricted deletion flag or sticky bit is set but the other-executable bit is not set. `x' If the executable bit is set and none of the above apply. `-' Otherwise. Following the file mode bits is a single character that specifies whether an alternate access method such as an access control list applies to the file. When the character following the file mode bits is a space, there is no alternate access method. When it is a printing character, then there is such a method. GNU `ls' uses a `.' character to indicate a file with an SELinux security context, but no other alternate access method. A file with any other combination of alternate access methods is marked with a `+' character. `-n' `--numeric-uid-gid' Produce long format directory listings, but display numeric user and group IDs instead of the owner and group names. `-o' Produce long format directory listings, but don't display group information. It is equivalent to using `--format=long' with `--no-group' . `-s' `--size' Print the disk allocation of each file to the left of the file name. This is the amount of disk space used by the file, which is usually a bit more than the file's size, but it can be less if the file has holes. Normally the disk allocation is printed in units of 1024 bytes, but this can be overridden (*note Block size::). For files that are NFS-mounted from an HP-UX system to a BSD system, this option reports sizes that are half the correct values. On HP-UX systems, it reports sizes that are twice the correct values for files that are NFS-mounted from BSD systems. This is due to a flaw in HP-UX; it also affects the HP-UX `ls' program. `--si' Append an SI-style abbreviation to each size, such as `M' for megabytes. Powers of 1000 are used, not 1024; `M' stands for 1,000,000 bytes. This option is equivalent to `--block-size=si'. Use the `-h' or `--human-readable' option if you prefer powers of 1024. `-Z' `--context' Display the SELinux security context or `?' if none is found. When used with the `-l' option, print the security context to the left of the size column.  File: coreutils.info, Node: Sorting the output, Next: Details about version sort, Prev: What information is listed, Up: ls invocation 10.1.3 Sorting the output ------------------------- These options change the order in which `ls' sorts the information it outputs. By default, sorting is done by character code (e.g., ASCII order). `-c' `--time=ctime' `--time=status' If the long listing format (e.g., `-l', `-o') is being used, print the status change time (the `ctime' in the inode) instead of the modification time. When explicitly sorting by time (`--sort=time' or `-t') or when not using a long listing format, sort according to the status change time. `-f' Primarily, like `-U'--do not sort; list the files in whatever order they are stored in the directory. But also enable `-a' (list all files) and disable `-l', `--color', and `-s' (if they were specified before the `-f'). `-r' `--reverse' Reverse whatever the sorting method is--e.g., list files in reverse alphabetical order, youngest first, smallest first, or whatever. `-S' `--sort=size' Sort by file size, largest first. `-t' `--sort=time' Sort by modification time (the `mtime' in the inode), newest first. `-u' `--time=atime' `--time=access' `--time=use' If the long listing format (e.g., `--format=long') is being used, print the last access time (the `atime' in the inode). When explicitly sorting by time (`--sort=time' or `-t') or when not using a long listing format, sort according to the access time. `-U' `--sort=none' Do not sort; list the files in whatever order they are stored in the directory. (Do not do any of the other unrelated things that `-f' does.) This is especially useful when listing very large directories, since not doing any sorting can be noticeably faster. `-v' `--sort=version' Sort by version name and number, lowest first. It behaves like a default sort, except that each sequence of decimal digits is treated numerically as an index/version number. (*Note Details about version sort::.) `-X' `--sort=extension' Sort directory contents alphabetically by file extension (characters after the last `.'); files with no extension are sorted first.  File: coreutils.info, Node: Details about version sort, Next: General output formatting, Prev: Sorting the output, Up: ls invocation 10.1.4 Details about version sort --------------------------------- Version sorting handles the fact that file names frequently include indices or version numbers. Standard sorting usually does not produce the order that one expects because comparisons are made on a character-by-character basis. Version sorting is especially useful when browsing directories that contain many files with indices/version numbers in their names: $ ls -1 $ ls -1v abc.zml-1.gz abc.zml-1.gz abc.zml-12.gz abc.zml-2.gz abc.zml-2.gz abc.zml-12.gz Version-sorted strings are compared such that if VER1 and VER2 are version numbers and PREFIX and SUFFIX (SUFFIX matching the regular expression `(\.[A-Za-z~][A-Za-z0-9~]*)*') are strings then VER1 < VER2 implies that the name composed of "PREFIX VER1 SUFFIX" sorts before "PREFIX VER2 SUFFIX". Note also that leading zeros of numeric parts are ignored: $ ls -1 $ ls -1v abc-1.007.tgz abc-1.01a.tgz abc-1.012b.tgz abc-1.007.tgz abc-1.01a.tgz abc-1.012b.tgz This functionality is implemented using gnulib's `filevercmp' function, which has some caveats worth noting. * `LC_COLLATE' is ignored, which means `ls -v' and `sort -V' will sort non-numeric prefixes as if the `LC_COLLATE' locale category was set to `C'. * Some suffixes will not be matched by the regular expression mentioned above. Consequently these examples may not sort as you expect: abc-1.2.3.4.7z abc-1.2.3.7z abc-1.2.3.4.x86_64.rpm abc-1.2.3.x86_64.rpm  File: coreutils.info, Node: General output formatting, Next: Formatting file timestamps, Prev: Details about version sort, Up: ls invocation 10.1.5 General output formatting -------------------------------- These options affect the appearance of the overall output. `-1' `--format=single-column' List one file per line. This is the default for `ls' when standard output is not a terminal. `-C' `--format=vertical' List files in columns, sorted vertically. This is the default for `ls' if standard output is a terminal. It is always the default for the `dir' program. GNU `ls' uses variable width columns to display as many files as possible in the fewest lines. `--color [=WHEN]' Specify whether to use color for distinguishing file types. WHEN may be omitted, or one of: * none - Do not use color at all. This is the default. * auto - Only use color if standard output is a terminal. * always - Always use color. Specifying `--color' and no WHEN is equivalent to `--color=always'. Piping a colorized listing through a pager like `more' or `less' usually produces unreadable results. However, using `more -f' does seem to work. Note that using the `--color' option may incur a noticeable performance penalty when run in a directory with very many entries, because the default settings require that `ls' `stat' every single file it lists. However, if you would like most of the file-type coloring but can live without the other coloring options (e.g., executable, orphan, sticky, other-writable, capability), use `dircolors' to set the `LS_COLORS' environment variable like this, eval $(dircolors -p | perl -pe \ 's/^((CAP|S[ET]|O[TR]|M|E)\w+).*/$1 00/' | dircolors -) and on a `dirent.d_type'-capable file system, `ls' will perform only one `stat' call per command line argument. `-F' `--classify' `--indicator-style=classify' Append a character to each file name indicating the file type. Also, for regular files that are executable, append `*'. The file type indicators are `/' for directories, `@' for symbolic links, `|' for FIFOs, `=' for sockets, `>' for doors, and nothing for regular files. Do not follow symbolic links listed on the command line unless the `--dereference-command-line' (`-H'), `--dereference' (`-L'), or `--dereference-command-line-symlink-to-dir' options are specified. `--file-type' `--indicator-style=file-type' Append a character to each file name indicating the file type. This is like `-F', except that executables are not marked. `--indicator-style=WORD' Append a character indicator with style WORD to entry names, as follows: `none' Do not append any character indicator; this is the default. `slash' Append `/' for directories. This is the same as the `-p' option. `file-type' Append `/' for directories, `@' for symbolic links, `|' for FIFOs, `=' for sockets, and nothing for regular files. This is the same as the `--file-type' option. `classify' Append `*' for executable regular files, otherwise behave as for `file-type'. This is the same as the `-F' or `--classify' option. `-k' `--kibibytes' Set the default block size to its normal value of 1024 bytes, overriding any contrary specification in environment variables (*note Block size::). This option is in turn overridden by the `--block-size', `-h' or `--human-readable', and `--si' options. The `-k' or `--kibibytes' option affects the per-directory block count written by the `-l' and similar options, and the size written by the `-s' or `--size' option. It does not affect the file size written by `-l'. `-m' `--format=commas' List files horizontally, with as many as will fit on each line, separated by `, ' (a comma and a space). `-p' `--indicator-style=slash' Append a `/' to directory names. `-x' `--format=across' `--format=horizontal' List the files in columns, sorted horizontally. `-T COLS' `--tabsize=COLS' Assume that each tab stop is COLS columns wide. The default is 8. `ls' uses tabs where possible in the output, for efficiency. If COLS is zero, do not use tabs at all. Some terminal emulators (at least Apple Terminal 1.5 (133) from Mac OS X 10.4.8) do not properly align columns to the right of a TAB following a non-ASCII byte. If you use such a terminal emulator, use the `-T0' option or put `TABSIZE=0' in your environment to tell `ls' to align using spaces, not tabs. `-w' `--width=COLS' Assume the screen is COLS columns wide. The default is taken from the terminal settings if possible; otherwise the environment variable `COLUMNS' is used if it is set; otherwise the default is 80.  File: coreutils.info, Node: Formatting file timestamps, Next: Formatting the file names, Prev: General output formatting, Up: ls invocation 10.1.6 Formatting file timestamps --------------------------------- By default, file timestamps are listed in abbreviated form, using a date like `Mar 30 2002' for non-recent timestamps, and a date-without-year and time like `Mar 30 23:45' for recent timestamps. This format can change depending on the current locale as detailed below. A timestamp is considered to be "recent" if it is less than six months old, and is not dated in the future. If a timestamp dated today is not listed in recent form, the timestamp is in the future, which means you probably have clock skew problems which may break programs like `make' that rely on file timestamps. Time stamps are listed according to the time zone rules specified by the `TZ' environment variable, or by the system default rules if `TZ' is not set. *Note Specifying the Time Zone with `TZ': (libc)TZ Variable. The following option changes how file timestamps are printed. `--time-style=STYLE' List timestamps in style STYLE. The STYLE should be one of the following: `+FORMAT' List timestamps using FORMAT, where FORMAT is interpreted like the format argument of `date' (*note date invocation::). For example, `--time-style="+%Y-%m-%d %H:%M:%S"' causes `ls' to list timestamps like `2002-03-30 23:45:56'. As with `date', FORMAT's interpretation is affected by the `LC_TIME' locale category. If FORMAT contains two format strings separated by a newline, the former is used for non-recent files and the latter for recent files; if you want output columns to line up, you may need to insert spaces in one of the two formats. `full-iso' List timestamps in full using ISO 8601 date, time, and time zone format with nanosecond precision, e.g., `2002-03-30 23:45:56.477817180 -0700'. This style is equivalent to `+%Y-%m-%d %H:%M:%S.%N %z'. This is useful because the time output includes all the information that is available from the operating system. For example, this can help explain `make''s behavior, since GNU `make' uses the full timestamp to determine whether a file is out of date. `long-iso' List ISO 8601 date and time in minutes, e.g., `2002-03-30 23:45'. These timestamps are shorter than `full-iso' timestamps, and are usually good enough for everyday work. This style is equivalent to `+%Y-%m-%d %H:%M'. `iso' List ISO 8601 dates for non-recent timestamps (e.g., `2002-03-30 '), and ISO 8601 month, day, hour, and minute for recent timestamps (e.g., `03-30 23:45'). These timestamps are uglier than `long-iso' timestamps, but they carry nearly the same information in a smaller space and their brevity helps `ls' output fit within traditional 80-column output lines. The following two `ls' invocations are equivalent: newline=' ' ls -l --time-style="+%Y-%m-%d $newline%m-%d %H:%M" ls -l --time-style="iso" `locale' List timestamps in a locale-dependent form. For example, a Finnish locale might list non-recent timestamps like `maalis 30 2002' and recent timestamps like `maalis 30 23:45'. Locale-dependent timestamps typically consume more space than `iso' timestamps and are harder for programs to parse because locale conventions vary so widely, but they are easier for many people to read. The `LC_TIME' locale category specifies the timestamp format. The default POSIX locale uses timestamps like `Mar 30 2002' and `Mar 30 23:45'; in this locale, the following two `ls' invocations are equivalent: newline=' ' ls -l --time-style="+%b %e %Y$newline%b %e %H:%M" ls -l --time-style="locale" Other locales behave differently. For example, in a German locale, `--time-style="locale"' might be equivalent to `--time-style="+%e. %b %Y $newline%e. %b %H:%M"' and might generate timestamps like `30. Ma"r 2002 ' and `30. Ma"r 23:45'. `posix-STYLE' List POSIX-locale timestamps if the `LC_TIME' locale category is POSIX, STYLE timestamps otherwise. For example, the `posix-long-iso' style lists timestamps like `Mar 30 2002' and `Mar 30 23:45' when in the POSIX locale, and like `2002-03-30 23:45' otherwise. You can specify the default value of the `--time-style' option with the environment variable `TIME_STYLE'; if `TIME_STYLE' is not set the default style is `locale'. GNU Emacs 21.3 and later use the `--dired' option and therefore can parse any date format, but if you are using Emacs 21.1 or 21.2 and specify a non-POSIX locale you may need to set `TIME_STYLE="posix-long-iso"'. To avoid certain denial-of-service attacks, timestamps that would be longer than 1000 bytes may be treated as errors.  File: coreutils.info, Node: Formatting the file names, Prev: Formatting file timestamps, Up: ls invocation 10.1.7 Formatting the file names -------------------------------- These options change how file names themselves are printed. `-b' `--escape' `--quoting-style=escape' Quote nongraphic characters in file names using alphabetic and octal backslash sequences like those used in C. `-N' `--literal' `--quoting-style=literal' Do not quote file names. However, with `ls' nongraphic characters are still printed as question marks if the output is a terminal and you do not specify the `--show-control-chars' option. `-q' `--hide-control-chars' Print question marks instead of nongraphic characters in file names. This is the default if the output is a terminal and the program is `ls'. `-Q' `--quote-name' `--quoting-style=c' Enclose file names in double quotes and quote nongraphic characters as in C. `--quoting-style=WORD' Use style WORD to quote file names and other strings that may contain arbitrary characters. The WORD should be one of the following: `literal' Output strings as-is; this is the same as the `-N' or `--literal' option. `shell' Quote strings for the shell if they contain shell metacharacters or would cause ambiguous output. The quoting is suitable for POSIX-compatible shells like `bash', but it does not always work for incompatible shells like `csh'. `shell-always' Quote strings for the shell, even if they would normally not require quoting. `c' Quote strings as for C character string literals, including the surrounding double-quote characters; this is the same as the `-Q' or `--quote-name' option. `escape' Quote strings as for C character string literals, except omit the surrounding double-quote characters; this is the same as the `-b' or `--escape' option. `clocale' Quote strings as for C character string literals, except use surrounding quotation marks appropriate for the locale. `locale' Quote strings as for C character string literals, except use surrounding quotation marks appropriate for the locale, and quote 'like this' instead of "like this" in the default C locale. This looks nicer on many displays. You can specify the default value of the `--quoting-style' option with the environment variable `QUOTING_STYLE'. If that environment variable is not set, the default value is `literal', but this default may change to `shell' in a future version of this package. `--show-control-chars' Print nongraphic characters as-is in file names. This is the default unless the output is a terminal and the program is `ls'.  File: coreutils.info, Node: dir invocation, Next: vdir invocation, Prev: ls invocation, Up: Directory listing 10.2 `dir': Briefly list directory contents =========================================== `dir' is equivalent to `ls -C -b'; that is, by default files are listed in columns, sorted vertically, and special characters are represented by backslash escape sequences. *Note `ls': ls invocation.  File: coreutils.info, Node: vdir invocation, Next: dircolors invocation, Prev: dir invocation, Up: Directory listing 10.3 `vdir': Verbosely list directory contents ============================================== `vdir' is equivalent to `ls -l -b'; that is, by default files are listed in long format and special characters are represented by backslash escape sequences.  File: coreutils.info, Node: dircolors invocation, Prev: vdir invocation, Up: Directory listing 10.4 `dircolors': Color setup for `ls' ====================================== `dircolors' outputs a sequence of shell commands to set up the terminal for color output from `ls' (and `dir', etc.). Typical usage: eval "$(dircolors [OPTION]... [FILE])" If FILE is specified, `dircolors' reads it to determine which colors to use for which file types and extensions. Otherwise, a precompiled database is used. For details on the format of these files, run `dircolors --print-database'. To make `dircolors' read a `~/.dircolors' file if it exists, you can put the following lines in your `~/.bashrc' (or adapt them to your favorite shell): d=.dircolors test -r $d && eval "$(dircolors $d)" The output is a shell command to set the `LS_COLORS' environment variable. You can specify the shell syntax to use on the command line, or `dircolors' will guess it from the value of the `SHELL' environment variable. The program accepts the following options. Also see *note Common options::. `-b' `--sh' `--bourne-shell' Output Bourne shell commands. This is the default if the `SHELL' environment variable is set and does not end with `csh' or `tcsh'. `-c' `--csh' `--c-shell' Output C shell commands. This is the default if `SHELL' ends with `csh' or `tcsh'. `-p' `--print-database' Print the (compiled-in) default color configuration database. This output is itself a valid configuration file, and is fairly descriptive of the possibilities. An exit status of zero indicates success, and a nonzero value indicates failure.  File: coreutils.info, Node: Basic operations, Next: Special file types, Prev: Directory listing, Up: Top 11 Basic operations ******************* This chapter describes the commands for basic file manipulation: copying, moving (renaming), and deleting (removing). * Menu: * cp invocation:: Copy files. * dd invocation:: Convert and copy a file. * install invocation:: Copy files and set attributes. * mv invocation:: Move (rename) files. * rm invocation:: Remove files or directories. * shred invocation:: Remove files more securely.  File: coreutils.info, Node: cp invocation, Next: dd invocation, Up: Basic operations 11.1 `cp': Copy files and directories ===================================== `cp' copies files (or, optionally, directories). The copy is completely independent of the original. You can either copy one file to another, or copy arbitrarily many files to a destination directory. Synopses: cp [OPTION]... [-T] SOURCE DEST cp [OPTION]... SOURCE... DIRECTORY cp [OPTION]... -t DIRECTORY SOURCE... * If two file names are given, `cp' copies the first file to the second. * If the `--target-directory' (`-t') option is given, or failing that if the last file is a directory and the `--no-target-directory' (`-T') option is not given, `cp' copies each SOURCE file to the specified directory, using the SOURCEs' names. Generally, files are written just as they are read. For exceptions, see the `--sparse' option below. By default, `cp' does not copy directories. However, the `-R', `-a', and `-r' options cause `cp' to copy recursively by descending into source directories and copying files to corresponding destination directories. When copying from a symbolic link, `cp' normally follows the link only when not copying recursively. This default can be overridden with the `--archive' (`-a'), `-d', `--dereference' (`-L'), `--no-dereference' (`-P'), and `-H' options. If more than one of these options is specified, the last one silently overrides the others. When copying to a symbolic link, `cp' follows the link only when it refers to an existing regular file. However, when copying to a dangling symbolic link, `cp' refuses by default, and fails with a diagnostic, since the operation is inherently dangerous. This behavior is contrary to historical practice and to POSIX. Set `POSIXLY_CORRECT' to make `cp' attempt to create the target of a dangling destination symlink, in spite of the possible risk. Also, when an option like `--backup' or `--link' acts to rename or remove the destination before copying, `cp' renames or removes the symbolic link rather than the file it points to. By default, `cp' copies the contents of special files only when not copying recursively. This default can be overridden with the `--copy-contents' option. `cp' generally refuses to copy a file onto itself, with the following exception: if `--force --backup' is specified with SOURCE and DEST identical, and referring to a regular file, `cp' will make a backup file, either regular or numbered, as specified in the usual ways (*note Backup options::). This is useful when you simply want to make a backup of an existing file before changing it. The program accepts the following options. Also see *note Common options::. `-a' `--archive' Preserve as much as possible of the structure and attributes of the original files in the copy (but do not attempt to preserve internal directory structure; i.e., `ls -U' may list the entries in a copied directory in a different order). Try to preserve SELinux security context and extended attributes (xattr), but ignore any failure to do that and print no corresponding diagnostic. Equivalent to `-dR --preserve=all' with the reduced diagnostics. `--attributes-only' Preserve the specified attributes of the original files in the copy, but do not copy any data. See the `--preserve' option for controlling which attributes to copy. `-b' `--backup[=METHOD]' *Note Backup options::. Make a backup of each file that would otherwise be overwritten or removed. As a special case, `cp' makes a backup of SOURCE when the force and backup options are given and SOURCE and DEST are the same name for an existing, regular file. One useful application of this combination of options is this tiny Bourne shell script: #!/bin/sh # Usage: backup FILE... # Create a GNU-style backup of each listed FILE. for i; do cp --backup --force -- "$i" "$i" done `--copy-contents' If copying recursively, copy the contents of any special files (e.g., FIFOs and device files) as if they were regular files. This means trying to read the data in each source file and writing it to the destination. It is usually a mistake to use this option, as it normally has undesirable effects on special files like FIFOs and the ones typically found in the `/dev' directory. In most cases, `cp -R --copy-contents' will hang indefinitely trying to read from FIFOs and special files like `/dev/console', and it will fill up your destination disk if you use it to copy `/dev/zero'. This option has no effect unless copying recursively, and it does not affect the copying of symbolic links. `-d' Copy symbolic links as symbolic links rather than copying the files that they point to, and preserve hard links between source files in the copies. Equivalent to `--no-dereference --preserve=links'. `-f' `--force' When copying without this option and an existing destination file cannot be opened for writing, the copy fails. However, with `--force'), when a destination file cannot be opened, `cp' then removes it and tries to open it again. Contrast this behavior with that enabled by `--link' and `--symbolic-link', whereby the destination file is never opened but rather is removed unconditionally. Also see the description of `--remove-destination'. This option is independent of the `--interactive' or `-i' option: neither cancels the effect of the other. This option is redundant if the `--no-clobber' or `-n' option is used. `-H' If a command line argument specifies a symbolic link, then copy the file it points to rather than the symbolic link itself. However, copy (preserving its nature) any symbolic link that is encountered via recursive traversal. `-i' `--interactive' When copying a file other than a directory, prompt whether to overwrite an existing destination file. The `-i' option overrides a previous `-n' option. `-l' `--link' Make hard links instead of copies of non-directories. `-L' `--dereference' Follow symbolic links when copying from them. With this option, `cp' cannot create a symbolic link. For example, a symlink (to regular file) in the source tree will be copied to a regular file in the destination tree. `-n' `--no-clobber' Do not overwrite an existing file. The `-n' option overrides a previous `-i' option. This option is mutually exclusive with `-b' or `--backup' option. `-P' `--no-dereference' Copy symbolic links as symbolic links rather than copying the files that they point to. This option affects only symbolic links in the source; symbolic links in the destination are always followed if possible. `-p' `--preserve[=ATTRIBUTE_LIST]' Preserve the specified attributes of the original files. If specified, the ATTRIBUTE_LIST must be a comma-separated list of one or more of the following strings: `mode' Preserve the file mode bits and access control lists. `ownership' Preserve the owner and group. On most modern systems, only users with appropriate privileges may change the owner of a file, and ordinary users may preserve the group ownership of a file only if they happen to be a member of the desired group. `timestamps' Preserve the times of last access and last modification, when possible. On older systems, it is not possible to preserve these attributes when the affected file is a symbolic link. However, many systems now provide the `utimensat' function, which makes it possible even for symbolic links. `links' Preserve in the destination files any links between corresponding source files. Note that with `-L' or `-H', this option can convert symbolic links to hard links. For example, $ mkdir c; : > a; ln -s a b; cp -aH a b c; ls -i1 c 74161745 a 74161745 b Note the inputs: `b' is a symlink to regular file `a', yet the files in destination directory, `c/', are hard-linked. Since `-a' implies `--preserve=links', and since `-H' tells `cp' to dereference command line arguments, it sees two files with the same inode number, and preserves the perceived hard link. Here is a similar example that exercises `cp''s `-L' option: $ mkdir b c; (cd b; : > a; ln -s a b); cp -aL b c; ls -i1 c/b 74163295 a 74163295 b `context' Preserve SELinux security context of the file, or fail with full diagnostics. `xattr' Preserve extended attributes of the file, or fail with full diagnostics. If `cp' is built without xattr support, ignore this option. If SELinux context, ACLs or Capabilities are implemented using xattrs, they are preserved by this option as well. `all' Preserve all file attributes. Equivalent to specifying all of the above, but with the difference that failure to preserve SELinux security context or extended attributes does not change `cp''s exit status. In contrast to `-a', all but `Operation not supported' warnings are output. Using `--preserve' with no ATTRIBUTE_LIST is equivalent to `--preserve=mode,ownership,timestamps'. In the absence of this option, each destination file is created with the mode bits of the corresponding source file, minus the bits set in the umask and minus the set-user-ID and set-group-ID bits. *Note File permissions::. `--no-preserve=ATTRIBUTE_LIST' Do not preserve the specified attributes. The ATTRIBUTE_LIST has the same form as for `--preserve'. `--parents' Form the name of each destination file by appending to the target directory a slash and the specified name of the source file. The last argument given to `cp' must be the name of an existing directory. For example, the command: cp --parents a/b/c existing_dir copies the file `a/b/c' to `existing_dir/a/b/c', creating any missing intermediate directories. `-R' `-r' `--recursive' Copy directories recursively. By default, do not follow symbolic links in the source; see the `--archive' (`-a'), `-d', `--dereference' (`-L'), `--no-dereference' (`-P'), and `-H' options. Special files are copied by creating a destination file of the same type as the source; see the `--copy-contents' option. It is not portable to use `-r' to copy symbolic links or special files. On some non-GNU systems, `-r' implies the equivalent of `-L' and `--copy-contents' for historical reasons. Also, it is not portable to use `-R' to copy symbolic links unless you also specify `-P', as POSIX allows implementations that dereference symbolic links by default. `--reflink[=WHEN]' Perform a lightweight, copy-on-write (COW) copy, if supported by the file system. Once it has succeeded, beware that the source and destination files share the same disk data blocks as long as they remain unmodified. Thus, if a disk I/O error affects data blocks of one of the files, the other suffers the same fate. The WHEN value can be one of the following: `always' The default behavior: if the copy-on-write operation is not supported then report the failure for each file and exit with a failure status. `auto' If the copy-on-write operation is not supported then fall back to the standard copy behaviour. This option is overridden by the `--link', `--symbolic-link' and `--attributes-only' options, thus allowing it to be used to configure the default data copying behavior for `cp'. For example, with the following alias, `cp' will use the minimum amount of space supported by the file system. alias cp='cp --reflink=auto --sparse=always' `--remove-destination' Remove each existing destination file before attempting to open it (contrast with `-f' above). `--sparse=WHEN' A "sparse file" contains "holes"--a sequence of zero bytes that does not occupy any physical disk blocks; the `read' system call reads these as zeros. This can both save considerable disk space and increase speed, since many binary files contain lots of consecutive zero bytes. By default, `cp' detects holes in input source files via a crude heuristic and makes the corresponding output file sparse as well. Only regular files may be sparse. The WHEN value can be one of the following: `auto' The default behavior: if the input file is sparse, attempt to make the output file sparse, too. However, if an output file exists but refers to a non-regular file, then do not attempt to make it sparse. `always' For each sufficiently long sequence of zero bytes in the input file, attempt to create a corresponding hole in the output file, even if the input file does not appear to be sparse. This is useful when the input file resides on a file system that does not support sparse files (for example, `efs' file systems in SGI IRIX 5.3 and earlier), but the output file is on a type of file system that does support them. Holes may be created only in regular files, so if the destination file is of some other type, `cp' does not even try to make it sparse. `never' Never make the output file sparse. This is useful in creating a file for use with the `mkswap' command, since such a file must not have any holes. `--strip-trailing-slashes' Remove any trailing slashes from each SOURCE argument. *Note Trailing slashes::. `-s' `--symbolic-link' Make symbolic links instead of copies of non-directories. All source file names must be absolute (starting with `/') unless the destination files are in the current directory. This option merely results in an error message on systems that do not support symbolic links. `-S SUFFIX' `--suffix=SUFFIX' Append SUFFIX to each backup file made with `-b'. *Note Backup options::. `-t DIRECTORY' `--target-directory=DIRECTORY' Specify the destination DIRECTORY. *Note Target directory::. `-T' `--no-target-directory' Do not treat the last operand specially when it is a directory or a symbolic link to a directory. *Note Target directory::. `-u' `--update' Do not copy a non-directory that has an existing destination with the same or newer modification time. If time stamps are being preserved, the comparison is to the source time stamp truncated to the resolutions of the destination file system and of the system calls used to update time stamps; this avoids duplicate work if several `cp -pu' commands are executed with the same source and destination. If `--preserve=links' is also specified (like with `cp -au' for example), that will take precedence. Consequently, depending on the order that files are processed from the source, newer files in the destination may be replaced, to mirror hard links in the source. `-v' `--verbose' Print the name of each file before copying it. `-x' `--one-file-system' Skip subdirectories that are on different file systems from the one that the copy started on. However, mount point directories _are_ copied. An exit status of zero indicates success, and a nonzero value indicates failure.  File: coreutils.info, Node: dd invocation, Next: install invocation, Prev: cp invocation, Up: Basic operations 11.2 `dd': Convert and copy a file ================================== `dd' copies a file (from standard input to standard output, by default) with a changeable I/O block size, while optionally performing conversions on it. Synopses: dd [OPERAND]... dd OPTION The only options are `--help' and `--version'. *Note Common options::. `dd' accepts the following operands. `if=FILE' Read from FILE instead of standard input. `of=FILE' Write to FILE instead of standard output. Unless `conv=notrunc' is given, `dd' truncates FILE to zero bytes (or the size specified with `seek='). `ibs=BYTES' Set the input block size to BYTES. This makes `dd' read BYTES per block. The default is 512 bytes. `obs=BYTES' Set the output block size to BYTES. This makes `dd' write BYTES per block. The default is 512 bytes. `bs=BYTES' Set both input and output block sizes to BYTES. This makes `dd' read and write BYTES per block, overriding any `ibs' and `obs' settings. In addition, if no data-transforming `conv' option is specified, input is copied to the output as soon as it's read, even if it is smaller than the block size. `cbs=BYTES' Set the conversion block size to BYTES. When converting variable-length records to fixed-length ones (`conv=block') or the reverse (`conv=unblock'), use BYTES as the fixed record length. `skip=N' Skip N `ibs'-byte blocks in the input file before copying. If `iflag=skip_bytes' is specified, N is interpreted as a byte count rather than a block count. `seek=N' Skip N `obs'-byte blocks in the output file before copying. if `oflag=seek_bytes' is specified, N is interpreted as a byte count rather than a block count. `count=N' Copy N `ibs'-byte blocks from the input file, instead of everything until the end of the file. if `iflag=count_bytes' is specified, N is interpreted as a byte count rather than a block count. `status=noxfer' Do not print the overall transfer rate and volume statistics that normally make up the third status line when `dd' exits. `conv=CONVERSION[,CONVERSION]...' Convert the file as specified by the CONVERSION argument(s). (No spaces around any comma(s).) Conversions: `ascii' Convert EBCDIC to ASCII, using the conversion table specified by POSIX. This provides a 1:1 translation for all 256 bytes. `ebcdic' Convert ASCII to EBCDIC. This is the inverse of the `ascii' conversion. `ibm' Convert ASCII to alternate EBCDIC, using the alternate conversion table specified by POSIX. This is not a 1:1 translation, but reflects common historical practice for `~', `[', and `]'. The `ascii', `ebcdic', and `ibm' conversions are mutually exclusive. `block' For each line in the input, output `cbs' bytes, replacing the input newline with a space and padding with spaces as necessary. `unblock' Remove any trailing spaces in each `cbs'-sized input block, and append a newline. The `block' and `unblock' conversions are mutually exclusive. `lcase' Change uppercase letters to lowercase. `ucase' Change lowercase letters to uppercase. The `lcase' and `ucase' conversions are mutually exclusive. `sparse' Try to seek rather than write NUL output blocks. On a file system that supports sparse files, this will create sparse output when extending the output file. Be careful when using this option in conjunction with `conv=notrunc' or `oflag=append'. With `conv=notrunc', existing data in the output corresponding to NUL blocks from the input, will be untouched. With `oflag=append' the seeks performed will be ineffective. `swab' Swap every pair of input bytes. GNU `dd', unlike others, works when an odd number of bytes are read--the last byte is simply copied (since there is nothing to swap it with). `sync' Pad every input block to size of `ibs' with trailing zero bytes. When used with `block' or `unblock', pad with spaces instead of zero bytes. The following "conversions" are really file flags and don't affect internal processing: `excl' Fail if the output file already exists; `dd' must create the output file itself. `nocreat' Do not create the output file; the output file must already exist. The `excl' and `nocreat' conversions are mutually exclusive. `notrunc' Do not truncate the output file. `noerror' Continue after read errors. `fdatasync' Synchronize output data just before finishing. This forces a physical write of output data. `fsync' Synchronize output data and metadata just before finishing. This forces a physical write of output data and metadata. `iflag=FLAG[,FLAG]...' Access the input file using the flags specified by the FLAG argument(s). (No spaces around any comma(s).) `oflag=FLAG[,FLAG]...' Access the output file using the flags specified by the FLAG argument(s). (No spaces around any comma(s).) Here are the flags. Not every flag is supported on every operating system. `append' Write in append mode, so that even if some other process is writing to this file, every `dd' write will append to the current contents of the file. This flag makes sense only for output. If you combine this flag with the `of=FILE' operand, you should also specify `conv=notrunc' unless you want the output file to be truncated before being appended to. `cio' Use concurrent I/O mode for data. This mode performs direct I/O and drops the POSIX requirement to serialize all I/O to the same file. A file cannot be opened in CIO mode and with a standard open at the same time. `direct' Use direct I/O for data, avoiding the buffer cache. Note that the kernel may impose restrictions on read or write buffer sizes. For example, with an ext4 destination file system and a linux-based kernel, using `oflag=direct' will cause writes to fail with `EINVAL' if the output buffer size is not a multiple of 512. `directory' Fail unless the file is a directory. Most operating systems do not allow I/O to a directory, so this flag has limited utility. `dsync' Use synchronized I/O for data. For the output file, this forces a physical write of output data on each write. For the input file, this flag can matter when reading from a remote file that has been written to synchronously by some other process. Metadata (e.g., last-access and last-modified time) is not necessarily synchronized. `sync' Use synchronized I/O for both data and metadata. `nocache' Discard the data cache for a file. When count=0 all cache is discarded, otherwise the cache is dropped for the processed portion of the file. Also when count=0 failure to discard the cache is diagnosed and reflected in the exit status. Here as some usage examples: # Advise to drop cache for whole file dd if=ifile iflag=nocache count=0 # Ensure drop cache for the whole file dd of=ofile oflag=nocache conv=notrunc,fdatasync count=0 # Drop cache for part of file dd if=ifile iflag=nocache skip=10 count=10 of=/dev/null # Stream data using just the read-ahead cache dd if=ifile of=ofile iflag=nocache oflag=nocache `nonblock' Use non-blocking I/O. `noatime' Do not update the file's access time. Some older file systems silently ignore this flag, so it is a good idea to test it on your files before relying on it. `noctty' Do not assign the file to be a controlling terminal for `dd'. This has no effect when the file is not a terminal. On many hosts (e.g., GNU/Linux hosts), this option has no effect at all. `nofollow' Do not follow symbolic links. `nolinks' Fail if the file has multiple hard links. `binary' Use binary I/O. This option has an effect only on nonstandard platforms that distinguish binary from text I/O. `text' Use text I/O. Like `binary', this option has no effect on standard platforms. `fullblock' Accumulate full blocks from input. The `read' system call may return early if a full block is not available. When that happens, continue calling `read' to fill the remainder of the block. This flag can be used only with `iflag'. `count_bytes' Interpret the `count=' operand as a byte count, rather than a block count, which allows specifying a length that is not a multiple of the I/O block size. This flag can be used only with `iflag'. `skip_bytes' Interpret the `skip=' operand as a byte count, rather than a block count, which allows specifying an offset that is not a multiple of the I/O block size. This flag can be used only with `iflag'. `seek_bytes' Interpret the `seek=' operand as a byte count, rather than a block count, which allows specifying an offset that is not a multiple of the I/O block size. This flag can be used only with `oflag'. These flags are not supported on all systems, and `dd' rejects attempts to use them when they are not supported. When reading from standard input or writing to standard output, the `nofollow' and `noctty' flags should not be specified, and the other flags (e.g., `nonblock') can affect how other processes behave with the affected file descriptors, even after `dd' exits. The numeric-valued strings above (BYTES and BLOCKS) can be followed by a multiplier: `b'=512, `c'=1, `w'=2, `xM'=M, or any of the standard block size suffixes like `k'=1024 (*note Block size::). Any block size you specify via `bs=', `ibs=', `obs=', `cbs=' should not be too large--values larger than a few megabytes are generally wasteful or (as in the gigabyte..exabyte case) downright counterproductive or error-inducing. To process data that is at an offset or size that is not a multiple of the I/O block size, you can use the `skip_bytes', `seek_bytes' and `count_bytes' flags. Alternatively the traditional method of separate `dd' invocations can be used. For example, the following shell commands copy data in 512 KiB blocks between a disk and a tape, but do not save or restore a 4 KiB label at the start of the disk: disk=/dev/rdsk/c0t1d0s2 tape=/dev/rmt/0 # Copy all but the label from disk to tape. (dd bs=4k skip=1 count=0 && dd bs=512k) <$disk >$tape # Copy from tape back to disk, but leave the disk label alone. (dd bs=4k seek=1 count=0 && dd bs=512k) <$tape >$disk Sending an `INFO' signal to a running `dd' process makes it print I/O statistics to standard error and then resume copying. In the example below, `dd' is run in the background to copy 10 million blocks. The `kill' command makes it output intermediate I/O statistics, and when `dd' completes normally or is killed by the `SIGINT' signal, it outputs the final statistics. $ dd if=/dev/zero of=/dev/null count=10MB & pid=$! $ kill -s INFO $pid; wait $pid 3385223+0 records in 3385223+0 records out 1733234176 bytes (1.7 GB) copied, 6.42173 seconds, 270 MB/s 10000000+0 records in 10000000+0 records out 5120000000 bytes (5.1 GB) copied, 18.913 seconds, 271 MB/s On systems lacking the `INFO' signal `dd' responds to the `USR1' signal instead, unless the `POSIXLY_CORRECT' environment variable is set. An exit status of zero indicates success, and a nonzero value indicates failure.  File: coreutils.info, Node: install invocation, Next: mv invocation, Prev: dd invocation, Up: Basic operations 11.3 `install': Copy files and set attributes ============================================= `install' copies files while setting their file mode bits and, if possible, their owner and group. Synopses: install [OPTION]... [-T] SOURCE DEST install [OPTION]... SOURCE... DIRECTORY install [OPTION]... -t DIRECTORY SOURCE... install [OPTION]... -d DIRECTORY... * If two file names are given, `install' copies the first file to the second. * If the `--target-directory' (`-t') option is given, or failing that if the last file is a directory and the `--no-target-directory' (`-T') option is not given, `install' copies each SOURCE file to the specified directory, using the SOURCEs' names. * If the `--directory' (`-d') option is given, `install' creates each DIRECTORY and any missing parent directories. Parent directories are created with mode `u=rwx,go=rx' (755), regardless of the `-m' option or the current umask. *Note Directory Setuid and Setgid::, for how the set-user-ID and set-group-ID bits of parent directories are inherited. `install' is similar to `cp', but allows you to control the attributes of destination files. It is typically used in Makefiles to copy programs into their destination directories. It refuses to copy files onto themselves. `install' never preserves extended attributes (xattr). The program accepts the following options. Also see *note Common options::. `-b' `--backup[=METHOD]' *Note Backup options::. Make a backup of each file that would otherwise be overwritten or removed. `-C' `--compare' Compare each pair of source and destination files, and if the destination has identical content and any specified owner, group, permissions, and possibly SELinux context, then do not modify the destination at all. `-c' Ignored; for compatibility with old Unix versions of `install'. `-D' Create any missing parent directories of DEST, then copy SOURCE to DEST. This option is ignored if a destination directory is specified via `--target-directory=DIR'. `-d' `--directory' Create any missing parent directories, giving them the default attributes. Then create each given directory, setting their owner, group and mode as given on the command line or to the defaults. `-g GROUP' `--group=GROUP' Set the group ownership of installed files or directories to GROUP. The default is the process's current group. GROUP may be either a group name or a numeric group ID. `-m MODE' `--mode=MODE' Set the file mode bits for the installed file or directory to MODE, which can be either an octal number, or a symbolic mode as in `chmod', with `a=' (no access allowed to anyone) as the point of departure (*note File permissions::). The default mode is `u=rwx,go=rx,a-s'--read, write, and execute for the owner, read and execute for group and other, and with set-user-ID and set-group-ID disabled. This default is not quite the same as `755', since it disables instead of preserving set-user-ID and set-group-ID on directories. *Note Directory Setuid and Setgid::. `-o OWNER' `--owner=OWNER' If `install' has appropriate privileges (is run as root), set the ownership of installed files or directories to OWNER. The default is `root'. OWNER may be either a user name or a numeric user ID. `--preserve-context' Preserve the SELinux security context of files and directories. Failure to preserve the context in all of the files or directories will result in an exit status of 1. If SELinux is disabled then print a warning and ignore the option. `-p' `--preserve-timestamps' Set the time of last access and the time of last modification of each installed file to match those of each corresponding original file. When a file is installed without this option, its last access and last modification times are both set to the time of installation. This option is useful if you want to use the last modification times of installed files to keep track of when they were last built as opposed to when they were last installed. `-s' `--strip' Strip the symbol tables from installed binary executables. `--strip-program=PROGRAM' Program used to strip binaries. `-S SUFFIX' `--suffix=SUFFIX' Append SUFFIX to each backup file made with `-b'. *Note Backup options::. `-t DIRECTORY' `--target-directory=DIRECTORY' Specify the destination DIRECTORY. *Note Target directory::. `-T' `--no-target-directory' Do not treat the last operand specially when it is a directory or a symbolic link to a directory. *Note Target directory::. `-v' `--verbose' Print the name of each file before copying it. `-Z CONTEXT' `--context=CONTEXT' Set the default SELinux security context to be used for any created files and directories. If SELinux is disabled then print a warning and ignore the option. An exit status of zero indicates success, and a nonzero value indicates failure.  File: coreutils.info, Node: mv invocation, Next: rm invocation, Prev: install invocation, Up: Basic operations 11.4 `mv': Move (rename) files ============================== `mv' moves or renames files (or directories). Synopses: mv [OPTION]... [-T] SOURCE DEST mv [OPTION]... SOURCE... DIRECTORY mv [OPTION]... -t DIRECTORY SOURCE... * If two file names are given, `mv' moves the first file to the second. * If the `--target-directory' (`-t') option is given, or failing that if the last file is a directory and the `--no-target-directory' (`-T') option is not given, `mv' moves each SOURCE file to the specified directory, using the SOURCEs' names. `mv' can move any type of file from one file system to another. Prior to version `4.0' of the fileutils, `mv' could move only regular files between file systems. For example, now `mv' can move an entire directory hierarchy including special device files from one partition to another. It first uses some of the same code that's used by `cp -a' to copy the requested directories and files, then (assuming the copy succeeded) it removes the originals. If the copy fails, then the part that was copied to the destination partition is removed. If you were to copy three directories from one partition to another and the copy of the first directory succeeded, but the second didn't, the first would be left on the destination partition and the second and third would be left on the original partition. `mv' always tries to copy extended attributes (xattr), which may include SELinux context, ACLs or Capabilities. Upon failure all but `Operation not supported' warnings are output. If a destination file exists but is normally unwritable, standard input is a terminal, and the `-f' or `--force' option is not given, `mv' prompts the user for whether to replace the file. (You might own the file, or have write permission on its directory.) If the response is not affirmative, the file is skipped. _Warning_: Avoid specifying a source name with a trailing slash, when it might be a symlink to a directory. Otherwise, `mv' may do something very surprising, since its behavior depends on the underlying rename system call. On a system with a modern Linux-based kernel, it fails with `errno=ENOTDIR'. However, on other systems (at least FreeBSD 6.1 and Solaris 10) it silently renames not the symlink but rather the directory referenced by the symlink. *Note Trailing slashes::. The program accepts the following options. Also see *note Common options::. `-b' `--backup[=METHOD]' *Note Backup options::. Make a backup of each file that would otherwise be overwritten or removed. `-f' `--force' Do not prompt the user before removing a destination file. If you specify more than one of the `-i', `-f', `-n' options, only the final one takes effect. `-i' `--interactive' Prompt whether to overwrite each existing destination file, regardless of its permissions. If the response is not affirmative, the file is skipped. If you specify more than one of the `-i', `-f', `-n' options, only the final one takes effect. `-n' `--no-clobber' Do not overwrite an existing file. If you specify more than one of the `-i', `-f', `-n' options, only the final one takes effect. This option is mutually exclusive with `-b' or `--backup' option. `-u' `--update' Do not move a non-directory that has an existing destination with the same or newer modification time. If the move is across file system boundaries, the comparison is to the source time stamp truncated to the resolutions of the destination file system and of the system calls used to update time stamps; this avoids duplicate work if several `mv -u' commands are executed with the same source and destination. `-v' `--verbose' Print the name of each file before moving it. `--strip-trailing-slashes' Remove any trailing slashes from each SOURCE argument. *Note Trailing slashes::. `-S SUFFIX' `--suffix=SUFFIX' Append SUFFIX to each backup file made with `-b'. *Note Backup options::. `-t DIRECTORY' `--target-directory=DIRECTORY' Specify the destination DIRECTORY. *Note Target directory::. `-T' `--no-target-directory' Do not treat the last operand specially when it is a directory or a symbolic link to a directory. *Note Target directory::. An exit status of zero indicates success, and a nonzero value indicates failure.  File: coreutils.info, Node: rm invocation, Next: shred invocation, Prev: mv invocation, Up: Basic operations 11.5 `rm': Remove files or directories ====================================== `rm' removes each given FILE. By default, it does not remove directories. Synopsis: rm [OPTION]... [FILE]... If the `-I' or `--interactive=once' option is given, and there are more than three files or the `-r', `-R', or `--recursive' are given, then `rm' prompts the user for whether to proceed with the entire operation. If the response is not affirmative, the entire command is aborted. Otherwise, if a file is unwritable, standard input is a terminal, and the `-f' or `--force' option is not given, or the `-i' or `--interactive=always' option _is_ given, `rm' prompts the user for whether to remove the file. If the response is not affirmative, the file is skipped. Any attempt to remove a file whose last file name component is `.' or `..' is rejected without any prompting. _Warning_: If you use `rm' to remove a file, it is usually possible to recover the contents of that file. If you want more assurance that the contents are truly unrecoverable, consider using `shred'. The program accepts the following options. Also see *note Common options::. `-f' `--force' Ignore nonexistent files and missing operands, and never prompt the user. Ignore any previous `--interactive' (`-i') option. `-i' Prompt whether to remove each file. If the response is not affirmative, the file is skipped. Ignore any previous `--force' (`-f') option. Equivalent to `--interactive=always'. `-I' Prompt once whether to proceed with the command, if more than three files are named or if a recursive removal is requested. Ignore any previous `--force' (`-f') option. Equivalent to `--interactive=once'. `--interactive [=WHEN]' Specify when to issue an interactive prompt. WHEN may be omitted, or one of: * never - Do not prompt at all. * once - Prompt once if more than three files are named or if a recursive removal is requested. Equivalent to `-I'. * always - Prompt for every file being removed. Equivalent to `-i'. `--interactive' with no WHEN is equivalent to `--interactive=always'. `--one-file-system' When removing a hierarchy recursively, skip any directory that is on a file system different from that of the corresponding command line argument. This option is useful when removing a build "chroot" hierarchy, which normally contains no valuable data. However, it is not uncommon to bind-mount `/home' into such a hierarchy, to make it easier to use one's start-up file. The catch is that it's easy to forget to unmount `/home'. Then, when you use `rm -rf' to remove your normally throw-away chroot, that command will remove everything under `/home', too. Use the `--one-file-system' option, and it will warn about and skip directories on other file systems. Of course, this will not save your `/home' if it and your chroot happen to be on the same file system. `--preserve-root' Fail upon any attempt to remove the root directory, `/', when used with the `--recursive' option. This is the default behavior. *Note Treating / specially::. `--no-preserve-root' Do not treat `/' specially when removing recursively. This option is not recommended unless you really want to remove all the files on your computer. *Note Treating / specially::. `-r' `-R' `--recursive' Remove the listed directories and their contents recursively. `-v' `--verbose' Print the name of each file before removing it. One common question is how to remove files whose names begin with a `-'. GNU `rm', like every program that uses the `getopt' function to parse its arguments, lets you use the `--' option to indicate that all following arguments are non-options. To remove a file called `-f' in the current directory, you could type either: rm -- -f or: rm ./-f The Unix `rm' program's use of a single `-' for this purpose predates the development of the getopt standard syntax. An exit status of zero indicates success, and a nonzero value indicates failure.  File: coreutils.info, Node: shred invocation, Prev: rm invocation, Up: Basic operations 11.6 `shred': Remove files more securely ======================================== `shred' overwrites devices or files, to help prevent even very expensive hardware from recovering the data. Ordinarily when you remove a file (*note rm invocation::), the data is not actually destroyed. Only the index listing where the file is stored is destroyed, and the storage is made available for reuse. There are undelete utilities that will attempt to reconstruct the index and can bring the file back if the parts were not reused. On a busy system with a nearly-full drive, space can get reused in a few seconds. But there is no way to know for sure. If you have sensitive data, you may want to be sure that recovery is not possible by actually overwriting the file with non-sensitive data. However, even after doing that, it is possible to take the disk back to a laboratory and use a lot of sensitive (and expensive) equipment to look for the faint "echoes" of the original data underneath the overwritten data. If the data has only been overwritten once, it's not even that hard. The best way to remove something irretrievably is to destroy the media it's on with acid, melt it down, or the like. For cheap removable media like floppy disks, this is the preferred method. However, hard drives are expensive and hard to melt, so the `shred' utility tries to achieve a similar effect non-destructively. This uses many overwrite passes, with the data patterns chosen to maximize the damage they do to the old data. While this will work on floppies, the patterns are designed for best effect on hard drives. For more details, see the source code and Peter Gutmann's paper `Secure Deletion of Data from Magnetic and Solid-State Memory' (http://www.cs.auckland.ac.nz/~pgut001/pubs/secure_del.html), from the proceedings of the Sixth USENIX Security Symposium (San Jose, California, July 22-25, 1996). *Please note* that `shred' relies on a very important assumption: that the file system overwrites data in place. This is the traditional way to do things, but many modern file system designs do not satisfy this assumption. Exceptions include: * Log-structured or journaled file systems, such as those supplied with AIX and Solaris, and JFS, ReiserFS, XFS, Ext3 (in `data=journal' mode), BFS, NTFS, etc. when they are configured to journal _data_. * File systems that write redundant data and carry on even if some writes fail, such as RAID-based file systems. * File systems that make snapshots, such as Network Appliance's NFS server. * File systems that cache in temporary locations, such as NFS version 3 clients. * Compressed file systems. In the particular case of ext3 file systems, the above disclaimer applies (and `shred' is thus of limited effectiveness) only in `data=journal' mode, which journals file data in addition to just metadata. In both the `data=ordered' (default) and `data=writeback' modes, `shred' works as usual. Ext3 journaling modes can be changed by adding the `data=something' option to the mount options for a particular file system in the `/etc/fstab' file, as documented in the mount man page (man mount). If you are not sure how your file system operates, then you should assume that it does not overwrite data in place, which means that shred cannot reliably operate on regular files in your file system. Generally speaking, it is more reliable to shred a device than a file, since this bypasses the problem of file system design mentioned above. However, even shredding devices is not always completely reliable. For example, most disks map out bad sectors invisibly to the application; if the bad sectors contain sensitive data, `shred' won't be able to destroy it. `shred' makes no attempt to detect or report this problem, just as it makes no attempt to do anything about backups. However, since it is more reliable to shred devices than files, `shred' by default does not truncate or remove the output file. This default is more suitable for devices, which typically cannot be truncated and should not be removed. Finally, consider the risk of backups and mirrors. File system backups and remote mirrors may contain copies of the file that cannot be removed, and that will allow a shredded file to be recovered later. So if you keep any data you may later want to destroy using `shred', be sure that it is not backed up or mirrored. shred [OPTION]... FILE[...] The program accepts the following options. Also see *note Common options::. `-f' `--force' Override file permissions if necessary to allow overwriting. `-NUMBER' `-n NUMBER' `--iterations=NUMBER' By default, `shred' uses 3 passes of overwrite. You can reduce this to save time, or increase it if you think it's appropriate. After 25 passes all of the internal overwrite patterns will have been used at least once. `--random-source=FILE' Use FILE as a source of random data used to overwrite and to choose pass ordering. *Note Random sources::. `-s BYTES' `--size=BYTES' Shred the first BYTES bytes of the file. The default is to shred the whole file. BYTES can be followed by a size specification like `K', `M', or `G' to specify a multiple. *Note Block size::. `-u' `--remove' After shredding a file, truncate it (if possible) and then remove it. If a file has multiple links, only the named links will be removed. `-v' `--verbose' Display to standard error all status updates as sterilization proceeds. `-x' `--exact' By default, `shred' rounds the size of a regular file up to the next multiple of the file system block size to fully erase the last block of the file. Use `--exact' to suppress that behavior. Thus, by default if you shred a 10-byte regular file on a system with 512-byte blocks, the resulting file will be 512 bytes long. With this option, shred does not increase the apparent size of the file. `-z' `--zero' Normally, the last pass that `shred' writes is made up of random data. If this would be conspicuous on your hard drive (for example, because it looks like encrypted data), or you just think it's tidier, the `--zero' option adds an additional overwrite pass with all zero bits. This is in addition to the number of passes specified by the `--iterations' option. You might use the following command to erase all trace of the file system you'd created on the floppy disk in your first drive. That command takes about 20 minutes to erase a "1.44MB" (actually 1440 KiB) floppy. shred --verbose /dev/fd0 Similarly, to erase all data on a selected partition of your hard disk, you could give a command like this: shred --verbose /dev/sda5 On modern disks, a single pass should be adequate, and it will take one third the time of the default three-pass approach. # 1 pass, write pseudo-random data; 3x faster than the default shred --verbose -n1 /dev/sda5 To be on the safe side, use at least one pass that overwrites using pseudo-random data. I.e., don't be tempted to use `-n0 --zero', in case some disk controller optimizes the process of writing blocks of all zeros, and thereby does not clear all bytes in a block. Some SSDs may do just that. A FILE of `-' denotes standard output. The intended use of this is to shred a removed temporary file. For example: i=$(mktemp) exec 3<>"$i" rm -- "$i" echo "Hello, world" >&3 shred - >&3 exec 3>- However, the command `shred - >file' does not shred the contents of FILE, since the shell truncates FILE before invoking `shred'. Use the command `shred file' or (if using a Bourne-compatible shell) the command `shred - 1<>file' instead. An exit status of zero indicates success, and a nonzero value indicates failure.  File: coreutils.info, Node: Special file types, Next: Changing file attributes, Prev: Basic operations, Up: Top 12 Special file types ********************* This chapter describes commands which create special types of files (and `rmdir', which removes directories, one special file type). Although Unix-like operating systems have markedly fewer special file types than others, not _everything_ can be treated only as the undifferentiated byte stream of "normal files". For example, when a file is created or removed, the system must record this information, which it does in a "directory"--a special type of file. Although you can read directories as normal files, if you're curious, in order for the system to do its job it must impose a structure, a certain order, on the bytes of the file. Thus it is a "special" type of file. Besides directories, other special file types include named pipes (FIFOs), symbolic links, sockets, and so-called "special files". * Menu: * link invocation:: Make a hard link via the link syscall * ln invocation:: Make links between files. * mkdir invocation:: Make directories. * mkfifo invocation:: Make FIFOs (named pipes). * mknod invocation:: Make block or character special files. * readlink invocation:: Print value of a symlink or canonical file name. * rmdir invocation:: Remove empty directories. * unlink invocation:: Remove files via the unlink syscall  File: coreutils.info, Node: link invocation, Next: ln invocation, Up: Special file types 12.1 `link': Make a hard link via the link syscall ================================================== `link' creates a single hard link at a time. It is a minimalist interface to the system-provided `link' function. *Note Hard Links: (libc)Hard Links. It avoids the bells and whistles of the more commonly-used `ln' command (*note ln invocation::). Synopsis: link FILENAME LINKNAME FILENAME must specify an existing file, and LINKNAME must specify a nonexistent entry in an existing directory. `link' simply calls `link (FILENAME, LINKNAME)' to create the link. On a GNU system, this command acts like `ln --directory --no-target-directory FILENAME LINKNAME'. However, the `--directory' and `--no-target-directory' options are not specified by POSIX, and the `link' command is more portable in practice. If FILENAME is a symbolic link, it is unspecified whether LINKNAME will be a hard link to the symbolic link or to the target of the symbolic link. Use `ln -P' or `ln -L' to specify which behavior is desired. An exit status of zero indicates success, and a nonzero value indicates failure.  File: coreutils.info, Node: ln invocation, Next: mkdir invocation, Prev: link invocation, Up: Special file types 12.2 `ln': Make links between files =================================== `ln' makes links between files. By default, it makes hard links; with the `-s' option, it makes symbolic (or "soft") links. Synopses: ln [OPTION]... [-T] TARGET LINKNAME ln [OPTION]... TARGET ln [OPTION]... TARGET... DIRECTORY ln [OPTION]... -t DIRECTORY TARGET... * If two file names are given, `ln' creates a link to the first file from the second. * If one TARGET is given, `ln' creates a link to that file in the current directory. * If the `--target-directory' (`-t') option is given, or failing that if the last file is a directory and the `--no-target-directory' (`-T') option is not given, `ln' creates a link to each TARGET file in the specified directory, using the TARGETs' names. Normally `ln' does not remove existing files. Use the `--force' (`-f') option to remove them unconditionally, the `--interactive' (`-i') option to remove them conditionally, and the `--backup' (`-b') option to rename them. A "hard link" is another name for an existing file; the link and the original are indistinguishable. Technically speaking, they share the same inode, and the inode contains all the information about a file--indeed, it is not incorrect to say that the inode _is_ the file. Most systems prohibit making a hard link to a directory; on those where it is allowed, only the super-user can do so (and with caution, since creating a cycle will cause problems to many other utilities). Hard links cannot cross file system boundaries. (These restrictions are not mandated by POSIX, however.) "Symbolic links" ("symlinks" for short), on the other hand, are a special file type (which not all kernels support: System V release 3 (and older) systems lack symlinks) in which the link file actually refers to a different file, by name. When most operations (opening, reading, writing, and so on) are passed the symbolic link file, the kernel automatically "dereferences" the link and operates on the target of the link. But some operations (e.g., removing) work on the link file itself, rather than on its target. The owner and group of a symlink are not significant to file access performed through the link, but do have implications on deleting a symbolic link from a directory with the restricted deletion bit set. On the GNU system, the mode of a symlink has no significance and cannot be changed, but on some BSD systems, the mode can be changed and will affect whether the symlink will be traversed in file name resolution. *Note Symbolic Links: (libc)Symbolic Links. Symbolic links can contain arbitrary strings; a "dangling symlink" occurs when the string in the symlink does not resolve to a file. There are no restrictions against creating dangling symbolic links. There are trade-offs to using absolute or relative symlinks. An absolute symlink always points to the same file, even if the directory containing the link is moved. However, if the symlink is visible from more than one machine (such as on a networked file system), the file pointed to might not always be the same. A relative symbolic link is resolved in relation to the directory that contains the link, and is often useful in referring to files on the same device without regards to what name that device is mounted on when accessed via networked machines. When creating a relative symlink in a different location than the current directory, the resolution of the symlink will be different than the resolution of the same string from the current directory. Therefore, many users prefer to first change directories to the location where the relative symlink will be created, so that tab-completion or other file resolution will find the same target as what will be placed in the symlink. The program accepts the following options. Also see *note Common options::. `-b' `--backup[=METHOD]' *Note Backup options::. Make a backup of each file that would otherwise be overwritten or removed. `-d' `-F' `--directory' Allow users with appropriate privileges to attempt to make hard links to directories. However, note that this will probably fail due to system restrictions, even for the super-user. `-f' `--force' Remove existing destination files. `-i' `--interactive' Prompt whether to remove existing destination files. `-L' `--logical' If `-s' is not in effect, and the source file is a symbolic link, create the hard link to the file referred to by the symbolic link, rather than the symbolic link itself. `-n' `--no-dereference' Do not treat the last operand specially when it is a symbolic link to a directory. Instead, treat it as if it were a normal file. When the destination is an actual directory (not a symlink to one), there is no ambiguity. The link is created in that directory. But when the specified destination is a symlink to a directory, there are two ways to treat the user's request. `ln' can treat the destination just as it would a normal directory and create the link in it. On the other hand, the destination can be viewed as a non-directory--as the symlink itself. In that case, `ln' must delete or backup that symlink before creating the new link. The default is to treat a destination that is a symlink to a directory just like a directory. This option is weaker than the `--no-target-directory' (`-T') option, so it has no effect if both options are given. `-P' `--physical' If `-s' is not in effect, and the source file is a symbolic link, create the hard link to the symbolic link itself. On platforms where this is not supported by the kernel, this option creates a symbolic link with identical contents; since symbolic link contents cannot be edited, any file name resolution performed through either link will be the same as if a hard link had been created. `-r' `--relative' Make symbolic links relative to the link location. Example: ln -srv /a/file /tmp '/tmp/file' -> '../a/file' *Note realpath invocation::, which gives greater control over relative file name generation. `-s' `--symbolic' Make symbolic links instead of hard links. This option merely produces an error message on systems that do not support symbolic links. `-S SUFFIX' `--suffix=SUFFIX' Append SUFFIX to each backup file made with `-b'. *Note Backup options::. `-t DIRECTORY' `--target-directory=DIRECTORY' Specify the destination DIRECTORY. *Note Target directory::. `-T' `--no-target-directory' Do not treat the last operand specially when it is a directory or a symbolic link to a directory. *Note Target directory::. `-v' `--verbose' Print the name of each file after linking it successfully. If `-L' and `-P' are both given, the last one takes precedence. If `-s' is also given, `-L' and `-P' are silently ignored. If neither option is given, then this implementation defaults to `-P' if the system `link' supports hard links to symbolic links (such as the GNU system), and `-L' if `link' follows symbolic links (such as on BSD). An exit status of zero indicates success, and a nonzero value indicates failure. Examples: Bad Example: # Create link ../a pointing to a in that directory. # Not really useful because it points to itself. ln -s a .. Better Example: # Change to the target before creating symlinks to avoid being confused. cd .. ln -s adir/a . Bad Example: # Hard coded file names don't move well. ln -s $(pwd)/a /some/dir/ Better Example: # Relative file names survive directory moves and also # work across networked file systems. ln -s afile anotherfile ln -s ../adir/afile yetanotherfile  File: coreutils.info, Node: mkdir invocation, Next: mkfifo invocation, Prev: ln invocation, Up: Special file types 12.3 `mkdir': Make directories ============================== `mkdir' creates directories with the specified names. Synopsis: mkdir [OPTION]... NAME... `mkdir' creates each directory NAME in the order given. It reports an error if NAME already exists, unless the `-p' option is given and NAME is a directory. The program accepts the following options. Also see *note Common options::. `-m MODE' `--mode=MODE' Set the file permission bits of created directories to MODE, which uses the same syntax as in `chmod' and uses `a=rwx' (read, write and execute allowed for everyone) for the point of the departure. *Note File permissions::. Normally the directory has the desired file mode bits at the moment it is created. As a GNU extension, MODE may also mention special mode bits, but in this case there may be a temporary window during which the directory exists but its special mode bits are incorrect. *Note Directory Setuid and Setgid::, for how the set-user-ID and set-group-ID bits of directories are inherited unless overridden in this way. `-p' `--parents' Make any missing parent directories for each argument, setting their file permission bits to the umask modified by `u+wx'. Ignore existing parent directories, and do not change their file permission bits. To set the file permission bits of any newly-created parent directories to a value that includes `u+wx', you can set the umask before invoking `mkdir'. For example, if the shell command `(umask u=rwx,go=rx; mkdir -p P/Q)' creates the parent `P' it sets the parent's permission bits to `u=rwx,go=rx'. To set a parent's special mode bits as well, you can invoke `chmod' after `mkdir'. *Note Directory Setuid and Setgid::, for how the set-user-ID and set-group-ID bits of newly-created parent directories are inherited. `-v' `--verbose' Print a message for each created directory. This is most useful with `--parents'. `-Z CONTEXT' `--context=CONTEXT' Set the default SELinux security context to be used for created directories. An exit status of zero indicates success, and a nonzero value indicates failure.  File: coreutils.info, Node: mkfifo invocation, Next: mknod invocation, Prev: mkdir invocation, Up: Special file types 12.4 `mkfifo': Make FIFOs (named pipes) ======================================= `mkfifo' creates FIFOs (also called "named pipes") with the specified names. Synopsis: mkfifo [OPTION] NAME... A "FIFO" is a special file type that permits independent processes to communicate. One process opens the FIFO file for writing, and another for reading, after which data can flow as with the usual anonymous pipe in shells or elsewhere. The program accepts the following option. Also see *note Common options::. `-m MODE' `--mode=MODE' Set the mode of created FIFOs to MODE, which is symbolic as in `chmod' and uses `a=rw' (read and write allowed for everyone) for the point of departure. MODE should specify only file permission bits. *Note File permissions::. `-Z CONTEXT' `--context=CONTEXT' Set the default SELinux security context to be used for created FIFOs. An exit status of zero indicates success, and a nonzero value indicates failure.  File: coreutils.info, Node: mknod invocation, Next: readlink invocation, Prev: mkfifo invocation, Up: Special file types 12.5 `mknod': Make block or character special files =================================================== `mknod' creates a FIFO, character special file, or block special file with the specified name. Synopsis: mknod [OPTION]... NAME TYPE [MAJOR MINOR] Unlike the phrase "special file type" above, the term "special file" has a technical meaning on Unix: something that can generate or receive data. Usually this corresponds to a physical piece of hardware, e.g., a printer or a disk. (These files are typically created at system-configuration time.) The `mknod' command is what creates files of this type. Such devices can be read either a character at a time or a "block" (many characters) at a time, hence we say there are "block special" files and "character special" files. Due to shell aliases and built-in `mknod' functions, using an unadorned `mknod' interactively or in a script may get you different functionality than that described here. Invoke it via `env' (i.e., `env mknod ...') to avoid interference from the shell. The arguments after NAME specify the type of file to make: `p' for a FIFO `b' for a block special file `c' for a character special file When making a block or character special file, the major and minor device numbers must be given after the file type. If a major or minor device number begins with `0x' or `0X', it is interpreted as hexadecimal; otherwise, if it begins with `0', as octal; otherwise, as decimal. The program accepts the following option. Also see *note Common options::. `-m MODE' `--mode=MODE' Set the mode of created files to MODE, which is symbolic as in `chmod' and uses `a=rw' as the point of departure. MODE should specify only file permission bits. *Note File permissions::. `-Z CONTEXT' `--context=CONTEXT' Set the default SELinux security context to be used for created files. An exit status of zero indicates success, and a nonzero value indicates failure.  File: coreutils.info, Node: readlink invocation, Next: rmdir invocation, Prev: mknod invocation, Up: Special file types 12.6 `readlink': Print value of a symlink or canonical file name ================================================================ `readlink' may work in one of two supported modes: `Readlink mode' `readlink' outputs the value of the given symbolic link. If `readlink' is invoked with an argument other than the name of a symbolic link, it produces no output and exits with a nonzero exit code. `Canonicalize mode' `readlink' outputs the absolute name of the given file which contains no `.', `..' components nor any repeated separators (`/') or symbolic links. readlink [OPTION] FILE By default, `readlink' operates in readlink mode. The program accepts the following options. Also see *note Common options::. `-f' `--canonicalize' Activate canonicalize mode. If any component of the file name except the last one is missing or unavailable, `readlink' produces no output and exits with a nonzero exit code. A trailing slash is ignored. `-e' `--canonicalize-existing' Activate canonicalize mode. If any component is missing or unavailable, `readlink' produces no output and exits with a nonzero exit code. A trailing slash requires that the name resolve to a directory. `-m' `--canonicalize-missing' Activate canonicalize mode. If any component is missing or unavailable, `readlink' treats it as a directory. `-n' `--no-newline' Do not output the trailing newline. `-s' `-q' `--silent' `--quiet' Suppress most error messages. `-v' `--verbose' Report error messages. The `readlink' utility first appeared in OpenBSD 2.1. The `realpath' command without options, operates like `readlink' in canonicalize mode. An exit status of zero indicates success, and a nonzero value indicates failure.  File: coreutils.info, Node: rmdir invocation, Next: unlink invocation, Prev: readlink invocation, Up: Special file types 12.7 `rmdir': Remove empty directories ====================================== `rmdir' removes empty directories. Synopsis: rmdir [OPTION]... DIRECTORY... If any DIRECTORY argument does not refer to an existing empty directory, it is an error. The program accepts the following options. Also see *note Common options::. `--ignore-fail-on-non-empty' Ignore each failure to remove a directory that is solely because the directory is non-empty. `-p' `--parents' Remove DIRECTORY, then try to remove each component of DIRECTORY. So, for example, `rmdir -p a/b/c' is similar to `rmdir a/b/c a/b a'. As such, it fails if any of those directories turns out not to be empty. Use the `--ignore-fail-on-non-empty' option to make it so such a failure does not evoke a diagnostic and does not cause `rmdir' to exit unsuccessfully. `-v' `--verbose' Give a diagnostic for each successful removal. DIRECTORY is removed. *Note rm invocation::, for how to remove non-empty directories (recursively). An exit status of zero indicates success, and a nonzero value indicates failure.  File: coreutils.info, Node: unlink invocation, Prev: rmdir invocation, Up: Special file types 12.8 `unlink': Remove files via the unlink syscall ================================================== `unlink' deletes a single specified file name. It is a minimalist interface to the system-provided `unlink' function. *Note Deleting Files: (libc)Deleting Files. Synopsis: It avoids the bells and whistles of the more commonly-used `rm' command (*note rm invocation::). unlink FILENAME On some systems `unlink' can be used to delete the name of a directory. On others, it can be used that way only by a privileged user. In the GNU system `unlink' can never delete the name of a directory. The `unlink' command honors the `--help' and `--version' options. To remove a file whose name begins with `-', prefix the name with `./', e.g., `unlink ./--help'. An exit status of zero indicates success, and a nonzero value indicates failure.  File: coreutils.info, Node: Changing file attributes, Next: Disk usage, Prev: Special file types, Up: Top 13 Changing file attributes *************************** A file is not merely its contents, a name, and a file type (*note Special file types::). A file also has an owner (a user ID), a group (a group ID), permissions (what the owner can do with the file, what people in the group can do, and what everyone else can do), various timestamps, and other information. Collectively, we call these a file's "attributes". These commands change file attributes. * Menu: * chgrp invocation:: Change file groups. * chmod invocation:: Change access permissions. * chown invocation:: Change file owners and groups. * touch invocation:: Change file timestamps.  File: coreutils.info, Node: chown invocation, Next: touch invocation, Prev: chmod invocation, Up: Changing file attributes 13.1 `chown': Change file owner and group ========================================= `chown' changes the user and/or group ownership of each given FILE to NEW-OWNER or to the user and group of an existing reference file. Synopsis: chown [OPTION]... {NEW-OWNER | --reference=REF_FILE} FILE... If used, NEW-OWNER specifies the new owner and/or group as follows (with no embedded white space): [OWNER] [ : [GROUP] ] Specifically: OWNER If only an OWNER (a user name or numeric user ID) is given, that user is made the owner of each given file, and the files' group is not changed. OWNER`:'GROUP If the OWNER is followed by a colon and a GROUP (a group name or numeric group ID), with no spaces between them, the group ownership of the files is changed as well (to GROUP). OWNER`:' If a colon but no group name follows OWNER, that user is made the owner of the files and the group of the files is changed to OWNER's login group. `:'GROUP If the colon and following GROUP are given, but the owner is omitted, only the group of the files is changed; in this case, `chown' performs the same function as `chgrp'. `:' If only a colon is given, or if NEW-OWNER is empty, neither the owner nor the group is changed. If OWNER or GROUP is intended to represent a numeric user or group ID, then you may specify it with a leading `+'. *Note Disambiguating names and IDs::. Some older scripts may still use `.' in place of the `:' separator. POSIX 1003.1-2001 (*note Standards conformance::) does not require support for that, but for backward compatibility GNU `chown' supports `.' so long as no ambiguity results. New scripts should avoid the use of `.' because it is not portable, and because it has undesirable results if the entire OWNER`.'GROUP happens to identify a user whose name contains `.'. The `chown' command sometimes clears the set-user-ID or set-group-ID permission bits. This behavior depends on the policy and functionality of the underlying `chown' system call, which may make system-dependent file mode modifications outside the control of the `chown' command. For example, the `chown' command might not affect those bits when invoked by a user with appropriate privileges, or when the bits signify some function other than executable permission (e.g., mandatory locking). When in doubt, check the underlying system behavior. The program accepts the following options. Also see *note Common options::. `-c' `--changes' Verbosely describe the action for each FILE whose ownership actually changes. `-f' `--silent' `--quiet' Do not print error messages about files whose ownership cannot be changed. `--from=OLD-OWNER' Change a FILE's ownership only if it has current attributes specified by OLD-OWNER. OLD-OWNER has the same form as NEW-OWNER described above. This option is useful primarily from a security standpoint in that it narrows considerably the window of potential abuse. For example, to reflect a user ID numbering change for one user's files without an option like this, `root' might run find / -owner OLDUSER -print0 | xargs -0 chown -h NEWUSER But that is dangerous because the interval between when the `find' tests the existing file's owner and when the `chown' is actually run may be quite large. One way to narrow the gap would be to invoke chown for each file as it is found: find / -owner OLDUSER -exec chown -h NEWUSER {} \; But that is very slow if there are many affected files. With this option, it is safer (the gap is narrower still) though still not perfect: chown -h -R --from=OLDUSER NEWUSER / `--dereference' Do not act on symbolic links themselves but rather on what they point to. This is the default. `-h' `--no-dereference' Act on symbolic links themselves instead of what they point to. This mode relies on the `lchown' system call. On systems that do not provide the `lchown' system call, `chown' fails when a file specified on the command line is a symbolic link. By default, no diagnostic is issued for symbolic links encountered during a recursive traversal, but see `--verbose'. `--preserve-root' Fail upon any attempt to recursively change the root directory, `/'. Without `--recursive', this option has no effect. *Note Treating / specially::. `--no-preserve-root' Cancel the effect of any preceding `--preserve-root' option. *Note Treating / specially::. `--reference=REF_FILE' Change the user and group of each FILE to be the same as those of REF_FILE. If REF_FILE is a symbolic link, do not use the user and group of the symbolic link, but rather those of the file it refers to. `-v' `--verbose' Output a diagnostic for every file processed. If a symbolic link is encountered during a recursive traversal on a system without the `lchown' system call, and `--no-dereference' is in effect, then issue a diagnostic saying neither the symbolic link nor its referent is being changed. `-R' `--recursive' Recursively change ownership of directories and their contents. `-H' If `--recursive' (`-R') is specified and a command line argument is a symbolic link to a directory, traverse it. *Note Traversing symlinks::. `-L' In a recursive traversal, traverse every symbolic link to a directory that is encountered. *Note Traversing symlinks::. `-P' Do not traverse any symbolic links. This is the default if none of `-H', `-L', or `-P' is specified. *Note Traversing symlinks::. An exit status of zero indicates success, and a nonzero value indicates failure. Examples: # Change the owner of /u to "root". chown root /u # Likewise, but also change its group to "staff". chown root:staff /u # Change the owner of /u and subfiles to "root". chown -hR root /u  File: coreutils.info, Node: chgrp invocation, Next: chmod invocation, Up: Changing file attributes 13.2 `chgrp': Change group ownership ==================================== `chgrp' changes the group ownership of each given FILE to GROUP (which can be either a group name or a numeric group ID) or to the group of an existing reference file. Synopsis: chgrp [OPTION]... {GROUP | --reference=REF_FILE} FILE... If GROUP is intended to represent a numeric group ID, then you may specify it with a leading `+'. *Note Disambiguating names and IDs::. The program accepts the following options. Also see *note Common options::. `-c' `--changes' Verbosely describe the action for each FILE whose group actually changes. `-f' `--silent' `--quiet' Do not print error messages about files whose group cannot be changed. `--dereference' Do not act on symbolic links themselves but rather on what they point to. This is the default. `-h' `--no-dereference' Act on symbolic links themselves instead of what they point to. This mode relies on the `lchown' system call. On systems that do not provide the `lchown' system call, `chgrp' fails when a file specified on the command line is a symbolic link. By default, no diagnostic is issued for symbolic links encountered during a recursive traversal, but see `--verbose'. `--preserve-root' Fail upon any attempt to recursively change the root directory, `/'. Without `--recursive', this option has no effect. *Note Treating / specially::. `--no-preserve-root' Cancel the effect of any preceding `--preserve-root' option. *Note Treating / specially::. `--reference=REF_FILE' Change the group of each FILE to be the same as that of REF_FILE. If REF_FILE is a symbolic link, do not use the group of the symbolic link, but rather that of the file it refers to. `-v' `--verbose' Output a diagnostic for every file processed. If a symbolic link is encountered during a recursive traversal on a system without the `lchown' system call, and `--no-dereference' is in effect, then issue a diagnostic saying neither the symbolic link nor its referent is being changed. `-R' `--recursive' Recursively change the group ownership of directories and their contents. `-H' If `--recursive' (`-R') is specified and a command line argument is a symbolic link to a directory, traverse it. *Note Traversing symlinks::. `-L' In a recursive traversal, traverse every symbolic link to a directory that is encountered. *Note Traversing symlinks::. `-P' Do not traverse any symbolic links. This is the default if none of `-H', `-L', or `-P' is specified. *Note Traversing symlinks::. An exit status of zero indicates success, and a nonzero value indicates failure. Examples: # Change the group of /u to "staff". chgrp staff /u # Change the group of /u and subfiles to "staff". chgrp -hR staff /u  File: coreutils.info, Node: chmod invocation, Next: chown invocation, Prev: chgrp invocation, Up: Changing file attributes 13.3 `chmod': Change access permissions ======================================= `chmod' changes the access permissions of the named files. Synopsis: chmod [OPTION]... {MODE | --reference=REF_FILE} FILE... `chmod' never changes the permissions of symbolic links, since the `chmod' system call cannot change their permissions. This is not a problem since the permissions of symbolic links are never used. However, for each symbolic link listed on the command line, `chmod' changes the permissions of the pointed-to file. In contrast, `chmod' ignores symbolic links encountered during recursive directory traversals. A successful use of `chmod' clears the set-group-ID bit of a regular file if the file's group ID does not match the user's effective group ID or one of the user's supplementary group IDs, unless the user has appropriate privileges. Additional restrictions may cause the set-user-ID and set-group-ID bits of MODE or REF_FILE to be ignored. This behavior depends on the policy and functionality of the underlying `chmod' system call. When in doubt, check the underlying system behavior. If used, MODE specifies the new file mode bits. For details, see the section on *note File permissions::. If you really want MODE to have a leading `-', you should use `--' first, e.g., `chmod -- -w file'. Typically, though, `chmod a-w file' is preferable, and `chmod -w file' (without the `--') complains if it behaves differently from what `chmod a-w file' would do. The program accepts the following options. Also see *note Common options::. `-c' `--changes' Verbosely describe the action for each FILE whose permissions actually changes. `-f' `--silent' `--quiet' Do not print error messages about files whose permissions cannot be changed. `--preserve-root' Fail upon any attempt to recursively change the root directory, `/'. Without `--recursive', this option has no effect. *Note Treating / specially::. `--no-preserve-root' Cancel the effect of any preceding `--preserve-root' option. *Note Treating / specially::. `-v' `--verbose' Verbosely describe the action or non-action taken for every FILE. `--reference=REF_FILE' Change the mode of each FILE to be the same as that of REF_FILE. *Note File permissions::. If REF_FILE is a symbolic link, do not use the mode of the symbolic link, but rather that of the file it refers to. `-R' `--recursive' Recursively change permissions of directories and their contents. An exit status of zero indicates success, and a nonzero value indicates failure.  File: coreutils.info, Node: touch invocation, Prev: chown invocation, Up: Changing file attributes 13.4 `touch': Change file timestamps ==================================== `touch' changes the access and/or modification times of the specified files. Synopsis: touch [OPTION]... FILE... Any FILE argument that does not exist is created empty, unless option `--no-create' (`-c') or `--no-dereference' (`-h') was in effect. A FILE argument string of `-' is handled specially and causes `touch' to change the times of the file associated with standard output. By default, `touch' sets file timestamps to the current time. Because `touch' acts on its operands left to right, the resulting timestamps of earlier and later operands may disagree. Also, the determination of what time is "current" depends on the platform. Platforms with network file systems often use different clocks for the operating system and for file systems; because `touch' typically uses file systems' clocks by default, clock skew can cause the resulting file timestamps to appear to be in a program's "future" or "past". The `touch' command sets the file's timestamp to the greatest representable value that is not greater than the requested time. This can differ from the requested time for several reasons. First, the requested time may have a higher resolution than supported. Second, a file system may use different resolutions for different types of times. Third, file timestamps may use a different resolution than operating system timestamps. Fourth, the operating system primitives used to update timestamps may employ yet a different resolution. For example, in theory a file system might use 10-microsecond resolution for access time and 100-nanosecond resolution for modification time, and the operating system might use nanosecond resolution for the current time and microsecond resolution for the primitive that `touch' uses to set a file's timestamp to an arbitrary value. When setting file timestamps to the current time, `touch' can change the timestamps for files that the user does not own but has write permission for. Otherwise, the user must own the files. Some older systems have a further restriction: the user must own the files unless both the access and modification times are being set to the current time. Although `touch' provides options for changing two of the times--the times of last access and modification--of a file, there is actually a standard third one as well: the inode change time. This is often referred to as a file's `ctime'. The inode change time represents the time when the file's meta-information last changed. One common example of this is when the permissions of a file change. Changing the permissions doesn't access the file, so the atime doesn't change, nor does it modify the file, so the mtime doesn't change. Yet, something about the file itself has changed, and this must be noted somewhere. This is the job of the ctime field. This is necessary, so that, for example, a backup program can make a fresh copy of the file, including the new permissions value. Another operation that modifies a file's ctime without affecting the others is renaming. In any case, it is not possible, in normal operations, for a user to change the ctime field to a user-specified value. Some operating systems and file systems support a fourth time: the birth time, when the file was first created; by definition, this timestamp never changes. Time stamps assume the time zone rules specified by the `TZ' environment variable, or by the system default rules if `TZ' is not set. *Note Specifying the Time Zone with `TZ': (libc)TZ Variable. You can avoid ambiguities during daylight saving transitions by using UTC time stamps. The program accepts the following options. Also see *note Common options::. `-a' `--time=atime' `--time=access' `--time=use' Change the access time only. `-c' `--no-create' Do not warn about or create files that do not exist. `-d' `--date=TIME' Use TIME instead of the current time. It can contain month names, time zones, `am' and `pm', `yesterday', etc. For example, `--date="2004-02-27 14:19:13.489392193 +0530"' specifies the instant of time that is 489,392,193 nanoseconds after February 27, 2004 at 2:19:13 PM in a time zone that is 5 hours and 30 minutes east of UTC. *Note Date input formats::. File systems that do not support high-resolution time stamps silently ignore any excess precision here. `-f' Ignored; for compatibility with BSD versions of `touch'. `-h' `--no-dereference' Attempt to change the timestamps of a symbolic link, rather than what the link refers to. When using this option, empty files are not created, but option `-c' must also be used to avoid warning about files that do not exist. Not all systems support changing the timestamps of symlinks, since underlying system support for this action was not required until POSIX 2008. Also, on some systems, the mere act of examining a symbolic link changes the access time, such that only changes to the modification time will persist long enough to be observable. When coupled with option `-r', a reference timestamp is taken from a symbolic link rather than the file it refers to. `-m' `--time=mtime' `--time=modify' Change the modification time only. `-r FILE' `--reference=FILE' Use the times of the reference FILE instead of the current time. If this option is combined with the `--date=TIME' (`-d TIME') option, the reference FILE's time is the origin for any relative TIMEs given, but is otherwise ignored. For example, `-r foo -d '-5 seconds'' specifies a time stamp equal to five seconds before the corresponding time stamp for `foo'. If FILE is a symbolic link, the reference timestamp is taken from the target of the symlink, unless `-h' was also in effect. `-t [[CC]YY]MMDDHHMM[.SS]' Use the argument (optional four-digit or two-digit years, months, days, hours, minutes, optional seconds) instead of the current time. If the year is specified with only two digits, then CC is 20 for years in the range 0 ... 68, and 19 for years in 69 ... 99. If no digits of the year are specified, the argument is interpreted as a date in the current year. Note that SS may be `60', to accommodate leap seconds. On older systems, `touch' supports an obsolete syntax, as follows. If no timestamp is given with any of the `-d', `-r', or `-t' options, and if there are two or more FILEs and the first FILE is of the form `MMDDHHMM[YY]' and this would be a valid argument to the `-t' option (if the YY, if any, were moved to the front), and if the represented year is in the range 1969-1999, that argument is interpreted as the time for the other files instead of as a file name. This obsolete behavior can be enabled or disabled with the `_POSIX2_VERSION' environment variable (*note Standards conformance::), but portable scripts should avoid commands whose behavior depends on this variable. For example, use `touch ./12312359 main.c' or `touch -t 12312359 main.c' rather than the ambiguous `touch 12312359 main.c'. An exit status of zero indicates success, and a nonzero value indicates failure.  File: coreutils.info, Node: Disk usage, Next: Printing text, Prev: Changing file attributes, Up: Top 14 Disk usage ************* No disk can hold an infinite amount of data. These commands report how much disk storage is in use or available, report other file and file status information, and write buffers to disk. * Menu: * df invocation:: Report file system disk space usage. * du invocation:: Estimate file space usage. * stat invocation:: Report file or file system status. * sync invocation:: Synchronize memory and disk. * truncate invocation:: Shrink or extend the size of a file.  File: coreutils.info, Node: df invocation, Next: du invocation, Up: Disk usage 14.1 `df': Report file system disk space usage ============================================== `df' reports the amount of disk space used and available on file systems. Synopsis: df [OPTION]... [FILE]... With no arguments, `df' reports the space used and available on all currently mounted file systems (of all types). Otherwise, `df' reports on the file system containing each argument FILE. Normally the disk space is printed in units of 1024 bytes, but this can be overridden (*note Block size::). Non-integer quantities are rounded up to the next higher unit. If an argument FILE is a disk device file containing a mounted file system, `df' shows the space available on that file system rather than on the file system containing the device node (i.e., the root file system). GNU `df' does not attempt to determine the disk usage on unmounted file systems, because on most kinds of systems doing so requires extremely nonportable intimate knowledge of file system structures. The program accepts the following options. Also see *note Common options::. `-a' `--all' Include in the listing dummy file systems, which are omitted by default. Such file systems are typically special-purpose pseudo-file-systems, such as automounter entries. `-B SIZE' `--block-size=SIZE' Scale sizes by SIZE before printing them (*note Block size::). For example, `-BG' prints sizes in units of 1,073,741,824 bytes. `--total' Print a grand total of all arguments after all arguments have been processed. This can be used to find out the total disk size, usage and available space of all listed devices. `-h' `--human-readable' Append a size letter to each size, such as `M' for mebibytes. Powers of 1024 are used, not 1000; `M' stands for 1,048,576 bytes. This option is equivalent to `--block-size=human-readable'. Use the `--si' option if you prefer powers of 1000. `-H' Equivalent to `--si'. `-i' `--inodes' List inode usage information instead of block usage. An inode (short for index node) contains information about a file such as its owner, permissions, timestamps, and location on the disk. `-k' Print sizes in 1024-byte blocks, overriding the default block size (*note Block size::). This option is equivalent to `--block-size=1K'. `-l' `--local' Limit the listing to local file systems. By default, remote file systems are also listed. `--no-sync' Do not invoke the `sync' system call before getting any usage data. This may make `df' run significantly faster on systems with many disks, but on some systems (notably SunOS) the results may be slightly out of date. This is the default. `-P' `--portability' Use the POSIX output format. This is like the default format except for the following: 1. The information about each file system is always printed on exactly one line; a mount device is never put on a line by itself. This means that if the mount device name is more than 20 characters long (e.g., for some network mounts), the columns are misaligned. 2. The labels in the header output line are changed to conform to POSIX. 3. The default block size and output format are unaffected by the `DF_BLOCK_SIZE', `BLOCK_SIZE' and `BLOCKSIZE' environment variables. However, the default block size is still affected by `POSIXLY_CORRECT': it is 512 if `POSIXLY_CORRECT' is set, 1024 otherwise. *Note Block size::. `--si' Append an SI-style abbreviation to each size, such as `M' for megabytes. Powers of 1000 are used, not 1024; `M' stands for 1,000,000 bytes. This option is equivalent to `--block-size=si'. Use the `-h' or `--human-readable' option if you prefer powers of 1024. `--sync' Invoke the `sync' system call before getting any usage data. On some systems (notably SunOS), doing this yields more up to date results, but in general this option makes `df' much slower, especially when there are many or very busy file systems. `-t FSTYPE' `--type=FSTYPE' Limit the listing to file systems of type FSTYPE. Multiple file system types can be specified by giving multiple `-t' options. By default, nothing is omitted. `-T' `--print-type' Print each file system's type. The types printed here are the same ones you can include or exclude with `-t' and `-x'. The particular types printed are whatever is supported by the system. Here are some of the common names (this list is certainly not exhaustive): `nfs' An NFS file system, i.e., one mounted over a network from another machine. This is the one type name which seems to be used uniformly by all systems. `4.2, ufs, efs...' A file system on a locally-mounted hard disk. (The system might even support more than one type here; Linux does.) `hsfs, cdfs' A file system on a CD-ROM drive. HP-UX uses `cdfs', most other systems use `hsfs' (`hs' for "High Sierra"). `pcfs' An MS-DOS file system, usually on a diskette. `-x FSTYPE' `--exclude-type=FSTYPE' Limit the listing to file systems not of type FSTYPE. Multiple file system types can be eliminated by giving multiple `-x' options. By default, no file system types are omitted. `-v' Ignored; for compatibility with System V versions of `df'. An exit status of zero indicates success, and a nonzero value indicates failure. Failure includes the case where no output is generated, so you can inspect the exit status of a command like `df -t ext3 -t reiserfs DIR' to test whether DIR is on a file system of type `ext3' or `reiserfs'.  File: coreutils.info, Node: du invocation, Next: stat invocation, Prev: df invocation, Up: Disk usage 14.2 `du': Estimate file space usage ==================================== `du' reports the amount of disk space used by the specified files and for each subdirectory (of directory arguments). Synopsis: du [OPTION]... [FILE]... With no arguments, `du' reports the disk space for the current directory. Normally the disk space is printed in units of 1024 bytes, but this can be overridden (*note Block size::). Non-integer quantities are rounded up to the next higher unit. If two or more hard links point to the same file, only one of the hard links is counted. The FILE argument order affects which links are counted, and changing the argument order may change the numbers that `du' outputs. The program accepts the following options. Also see *note Common options::. `-a' `--all' Show counts for all files, not just directories. `--apparent-size' Print apparent sizes, rather than disk usage. The apparent size of a file is the number of bytes reported by `wc -c' on regular files, or more generally, `ls -l --block-size=1' or `stat --format=%s'. For example, a file containing the word `zoo' with no newline would, of course, have an apparent size of 3. Such a small file may require anywhere from 0 to 16 KiB or more of disk space, depending on the type and configuration of the file system on which the file resides. However, a sparse file created with this command: dd bs=1 seek=2GiB if=/dev/null of=big has an apparent size of 2 GiB, yet on most modern systems, it actually uses almost no disk space. `-b' `--bytes' Equivalent to `--apparent-size --block-size=1'. `-B SIZE' `--block-size=SIZE' Scale sizes by SIZE before printing them (*note Block size::). For example, `-BG' prints sizes in units of 1,073,741,824 bytes. `-c' `--total' Print a grand total of all arguments after all arguments have been processed. This can be used to find out the total disk usage of a given set of files or directories. `-D' `--dereference-args' Dereference symbolic links that are command line arguments. Does not affect other symbolic links. This is helpful for finding out the disk usage of directories, such as `/usr/tmp', which are often symbolic links. `--files0-from=FILE' Disallow processing files named on the command line, and instead process those named in file FILE; each name being terminated by a zero byte (ASCII NUL). This is useful when the list of file names is so long that it may exceed a command line length limitation. In such cases, running `du' via `xargs' is undesirable because it splits the list into pieces and makes `du' print with the `--total' (`-c') option for each sublist rather than for the entire list. One way to produce a list of ASCII NUL terminated file names is with GNU `find', using its `-print0' predicate. If FILE is `-' then the ASCII NUL terminated file names are read from standard input. `-h' `--human-readable' Append a size letter to each size, such as `M' for mebibytes. Powers of 1024 are used, not 1000; `M' stands for 1,048,576 bytes. This option is equivalent to `--block-size=human-readable'. Use the `--si' option if you prefer powers of 1000. `-H' Equivalent to `--dereference-args' (`-D'). `-k' Print sizes in 1024-byte blocks, overriding the default block size (*note Block size::). This option is equivalent to `--block-size=1K'. `-l' `--count-links' Count the size of all files, even if they have appeared already (as a hard link). `-L' `--dereference' Dereference symbolic links (show the disk space used by the file or directory that the link points to instead of the space used by the link). `-m' Print sizes in 1,048,576-byte blocks, overriding the default block size (*note Block size::). This option is equivalent to `--block-size=1M'. `-P' `--no-dereference' For each symbolic links encountered by `du', consider the disk space used by the symbolic link. `-d DEPTH' `--max-depth=DEPTH' Show the total for each directory (and file if -all) that is at most MAX_DEPTH levels down from the root of the hierarchy. The root is at level 0, so `du --max-depth=0' is equivalent to `du -s'. `-0' `--null' Output a zero byte (ASCII NUL) at the end of each line, rather than a newline. This option enables other programs to parse the output of `du' even when that output would contain data with embedded newlines. `--si' Append an SI-style abbreviation to each size, such as `M' for megabytes. Powers of 1000 are used, not 1024; `M' stands for 1,000,000 bytes. This option is equivalent to `--block-size=si'. Use the `-h' or `--human-readable' option if you prefer powers of 1024. `-s' `--summarize' Display only a total for each argument. `-S' `--separate-dirs' Normally, in the output of `du' (when not using `--summarize'), the size listed next to a directory name, D, represents the sum of sizes of all entries beneath D as well as the size of D itself. With `--separate-dirs', the size reported for a directory name, D, is merely the `stat.st_size'-derived size of the directory entry, D. `--time' Show time of the most recent modification of any file in the directory, or any of its subdirectories. `--time=ctime' `--time=status' `--time=use' Show the most recent status change time (the `ctime' in the inode) of any file in the directory, instead of the modification time. `--time=atime' `--time=access' Show the most recent access time (the `atime' in the inode) of any file in the directory, instead of the modification time. `--time-style=STYLE' List timestamps in style STYLE. This option has an effect only if the `--time' option is also specified. The STYLE should be one of the following: `+FORMAT' List timestamps using FORMAT, where FORMAT is interpreted like the format argument of `date' (*note date invocation::). For example, `--time-style="+%Y-%m-%d %H:%M:%S"' causes `du' to list timestamps like `2002-03-30 23:45:56'. As with `date', FORMAT's interpretation is affected by the `LC_TIME' locale category. `full-iso' List timestamps in full using ISO 8601 date, time, and time zone format with nanosecond precision, e.g., `2002-03-30 23:45:56.477817180 -0700'. This style is equivalent to `+%Y-%m-%d %H:%M:%S.%N %z'. `long-iso' List ISO 8601 date and time in minutes, e.g., `2002-03-30 23:45'. These timestamps are shorter than `full-iso' timestamps, and are usually good enough for everyday work. This style is equivalent to `+%Y-%m-%d %H:%M'. `iso' List ISO 8601 dates for timestamps, e.g., `2002-03-30'. This style is equivalent to `+%Y-%m-%d'. You can specify the default value of the `--time-style' option with the environment variable `TIME_STYLE'; if `TIME_STYLE' is not set the default style is `long-iso'. For compatibility with `ls', if `TIME_STYLE' begins with `+' and contains a newline, the newline and any later characters are ignored; if `TIME_STYLE' begins with `posix-' the `posix-' is ignored; and if `TIME_STYLE' is `locale' it is ignored. `-x' `--one-file-system' Skip directories that are on different file systems from the one that the argument being processed is on. `--exclude=PATTERN' When recursing, skip subdirectories or files matching PATTERN. For example, `du --exclude='*.o'' excludes files whose names end in `.o'. `-X FILE' `--exclude-from=FILE' Like `--exclude', except take the patterns to exclude from FILE, one per line. If FILE is `-', take the patterns from standard input. On BSD systems, `du' reports sizes that are half the correct values for files that are NFS-mounted from HP-UX systems. On HP-UX systems, it reports sizes that are twice the correct values for files that are NFS-mounted from BSD systems. This is due to a flaw in HP-UX; it also affects the HP-UX `du' program. An exit status of zero indicates success, and a nonzero value indicates failure.  File: coreutils.info, Node: stat invocation, Next: sync invocation, Prev: du invocation, Up: Disk usage 14.3 `stat': Report file or file system status ============================================== `stat' displays information about the specified file(s). Synopsis: stat [OPTION]... [FILE]... With no option, `stat' reports all information about the given files. But it also can be used to report the information of the file systems the given files are located on. If the files are links, `stat' can also give information about the files the links point to. Due to shell aliases and built-in `stat' functions, using an unadorned `stat' interactively or in a script may get you different functionality than that described here. Invoke it via `env' (i.e., `env stat ...') to avoid interference from the shell. `-L' `--dereference' Change how `stat' treats symbolic links. With this option, `stat' acts on the file referenced by each symbolic link argument. Without it, `stat' acts on any symbolic link argument directly. `-f' `--file-system' Report information about the file systems where the given files are located instead of information about the files themselves. This option implies the `-L' option. `-c' `--format=FORMAT' Use FORMAT rather than the default format. FORMAT is automatically newline-terminated, so running a command like the following with two or more FILE operands produces a line of output for each operand: $ stat --format=%d:%i / /usr 2050:2 2057:2 `--printf=FORMAT' Use FORMAT rather than the default format. Like `--format', but interpret backslash escapes, and do not output a mandatory trailing newline. If you want a newline, include `\n' in the FORMAT. Here's how you would use `--printf' to print the device and inode numbers of `/' and `/usr': $ stat --printf='%d:%i\n' / /usr 2050:2 2057:2 `-t' `--terse' Print the information in terse form, suitable for parsing by other programs. The valid FORMAT directives for files with `--format' and `--printf' are: * %a - Access rights in octal * %A - Access rights in human readable form * %b - Number of blocks allocated (see `%B') * %B - The size in bytes of each block reported by `%b' * %C - The SELinux security context of a file, if available * %d - Device number in decimal * %D - Device number in hex * %f - Raw mode in hex * %F - File type * %g - Group ID of owner * %G - Group name of owner * %h - Number of hard links * %i - Inode number * %m - Mount point (See note below) * %n - File name * %N - Quoted file name with dereference if symbolic link * %o - Optimal I/O transfer size hint * %s - Total size, in bytes * %t - Major device type in hex * %T - Minor device type in hex * %u - User ID of owner * %U - User name of owner * %w - Time of file birth, or `-' if unknown * %W - Time of file birth as seconds since Epoch, or `0' * %x - Time of last access * %X - Time of last access as seconds since Epoch * %y - Time of last modification * %Y - Time of last modification as seconds since Epoch * %z - Time of last change * %Z - Time of last change as seconds since Epoch The `%W', `%X', `%Y', and `%Z' formats accept a precision preceded by a period to specify the number of digits to print after the decimal point. For example, `%.3X' outputs the last access time to millisecond precision. If a period is given but no precision, `stat' uses 9 digits, so `%.X' is equivalent to `%.9X'. When discarding excess precision, time stamps are truncated toward minus infinity. zero pad: $ stat -c '[%015Y]' /usr [000001288929712] space align: $ stat -c '[%15Y]' /usr [ 1288929712] $ stat -c '[%-15Y]' /usr [1288929712 ] precision: $ stat -c '[%.3Y]' /usr [1288929712.114] $ stat -c '[%.Y]' /usr [1288929712.114951834] The mount point printed by `%m' is similar to that output by `df', except that: * stat does not dereference symlinks by default (unless `-L' is specified) * stat does not search for specified device nodes in the file system list, instead operating on them directly * stat outputs the alias for a bind mounted file, rather than the initial mount point of its backing device. One can recursively call stat until there is no change in output, to get the current base mount point When listing file system information (`--file-system' (`-f')), you must use a different set of FORMAT directives: * %a - Free blocks available to non-super-user * %b - Total data blocks in file system * %c - Total file nodes in file system * %d - Free file nodes in file system * %f - Free blocks in file system * %i - File System ID in hex * %l - Maximum length of file names * %n - File name * %s - Block size (for faster transfers) * %S - Fundamental block size (for block counts) * %t - Type in hex * %T - Type in human readable form Time stamps are listed according to the time zone rules specified by the `TZ' environment variable, or by the system default rules if `TZ' is not set. *Note Specifying the Time Zone with `TZ': (libc)TZ Variable. An exit status of zero indicates success, and a nonzero value indicates failure.  File: coreutils.info, Node: sync invocation, Next: truncate invocation, Prev: stat invocation, Up: Disk usage 14.4 `sync': Synchronize data on disk with memory ================================================= `sync' writes any data buffered in memory out to disk. This can include (but is not limited to) modified superblocks, modified inodes, and delayed reads and writes. This must be implemented by the kernel; The `sync' program does nothing but exercise the `sync' system call. The kernel keeps data in memory to avoid doing (relatively slow) disk reads and writes. This improves performance, but if the computer crashes, data may be lost or the file system corrupted as a result. The `sync' command ensures everything in memory is written to disk. Any arguments are ignored, except for a lone `--help' or `--version' (*note Common options::). An exit status of zero indicates success, and a nonzero value indicates failure.  File: coreutils.info, Node: truncate invocation, Prev: sync invocation, Up: Disk usage 14.5 `truncate': Shrink or extend the size of a file ==================================================== `truncate' shrinks or extends the size of each FILE to the specified size. Synopsis: truncate OPTION... FILE... Any FILE that does not exist is created. If a FILE is larger than the specified size, the extra data is lost. If a FILE is shorter, it is extended and the extended part (or hole) reads as zero bytes. The program accepts the following options. Also see *note Common options::. `-c' `--no-create' Do not create files that do not exist. `-o' `--io-blocks' Treat SIZE as number of I/O blocks of the FILE rather than bytes. `-r RFILE' `--reference=RFILE' Base the size of each FILE on the size of RFILE. `-s SIZE' `--size=SIZE' Set or adjust the size of each FILE according to SIZE. SIZE may be, or may be an integer optionally followed by, one of the following multiplicative suffixes: `KB' => 1000 (KiloBytes) `K' => 1024 (KibiBytes) `MB' => 1000*1000 (MegaBytes) `M' => 1024*1024 (MebiBytes) `GB' => 1000*1000*1000 (GigaBytes) `G' => 1024*1024*1024 (GibiBytes) and so on for `T', `P', `E', `Z', and `Y'. SIZE may also be prefixed by one of the following to adjust the size of each FILE based on their current size: `+' => extend by `-' => reduce by `<' => at most `>' => at least `/' => round down to multiple of `%' => round up to multiple of An exit status of zero indicates success, and a nonzero value indicates failure.  File: coreutils.info, Node: Printing text, Next: Conditions, Prev: Disk usage, Up: Top 15 Printing text **************** This section describes commands that display text strings. * Menu: * echo invocation:: Print a line of text. * printf invocation:: Format and print data. * yes invocation:: Print a string until interrupted.  File: coreutils.info, Node: echo invocation, Next: printf invocation, Up: Printing text 15.1 `echo': Print a line of text ================================= `echo' writes each given STRING to standard output, with a space between each and a newline after the last one. Synopsis: echo [OPTION]... [STRING]... Due to shell aliases and built-in `echo' functions, using an unadorned `echo' interactively or in a script may get you different functionality than that described here. Invoke it via `env' (i.e., `env echo ...') to avoid interference from the shell. The program accepts the following options. Also see *note Common options::. Options must precede operands, and the normally-special argument `--' has no special meaning and is treated like any other STRING. `-n' Do not output the trailing newline. `-e' Enable interpretation of the following backslash-escaped characters in each STRING: `\a' alert (bell) `\b' backspace `\c' produce no further output `\e' escape `\f' form feed `\n' newline `\r' carriage return `\t' horizontal tab `\v' vertical tab `\\' backslash `\0NNN' the eight-bit value that is the octal number NNN (zero to three octal digits), if NNN is a nine-bit value, the ninth bit is ignored `\NNN' the eight-bit value that is the octal number NNN (one to three octal digits), if NNN is a nine-bit value, the ninth bit is ignored `\xHH' the eight-bit value that is the hexadecimal number HH (one or two hexadecimal digits) `-E' Disable interpretation of backslash escapes in each STRING. This is the default. If `-e' and `-E' are both specified, the last one given takes effect. If the `POSIXLY_CORRECT' environment variable is set, then when `echo''s first argument is not `-n' it outputs option-like arguments instead of treating them as options. For example, `echo -ne hello' outputs `-ne hello' instead of plain `hello'. POSIX does not require support for any options, and says that the behavior of `echo' is implementation-defined if any STRING contains a backslash or if the first argument is `-n'. Portable programs can use the `printf' command if they need to omit trailing newlines or output control characters or backslashes. *Note printf invocation::. An exit status of zero indicates success, and a nonzero value indicates failure.  File: coreutils.info, Node: printf invocation, Next: yes invocation, Prev: echo invocation, Up: Printing text 15.2 `printf': Format and print data ==================================== `printf' does formatted printing of text. Synopsis: printf FORMAT [ARGUMENT]... `printf' prints the FORMAT string, interpreting `%' directives and `\' escapes to format numeric and string arguments in a way that is mostly similar to the C `printf' function. *Note `printf' format directives: (libc)Output Conversion Syntax, for details. The differences are listed below. Due to shell aliases and built-in `printf' functions, using an unadorned `printf' interactively or in a script may get you different functionality than that described here. Invoke it via `env' (i.e., `env printf ...') to avoid interference from the shell. * The FORMAT argument is reused as necessary to convert all the given ARGUMENTs. For example, the command `printf %s a b' outputs `ab'. * Missing ARGUMENTs are treated as null strings or as zeros, depending on whether the context expects a string or a number. For example, the command `printf %sx%d' prints `x0'. * An additional escape, `\c', causes `printf' to produce no further output. For example, the command `printf 'A%sC\cD%sF' B E' prints `ABC'. * The hexadecimal escape sequence `\xHH' has at most two digits, as opposed to C where it can have an unlimited number of digits. For example, the command `printf '\x07e'' prints two bytes, whereas the C statement `printf ("\x07e")' prints just one. * `printf' has an additional directive, `%b', which prints its argument string with `\' escapes interpreted in the same way as in the FORMAT string, except that octal escapes are of the form `\0OOO' where OOO is 0 to 3 octal digits. If `\OOO' is nine-bit value, ignore the ninth bit. If a precision is also given, it limits the number of bytes printed from the converted string. * Numeric arguments must be single C constants, possibly with leading `+' or `-'. For example, `printf %.4d -3' outputs `-0003'. * If the leading character of a numeric argument is `"' or `'' then its value is the numeric value of the immediately following character. Any remaining characters are silently ignored if the `POSIXLY_CORRECT' environment variable is set; otherwise, a warning is printed. For example, `printf "%d" "'a"' outputs `97' on hosts that use the ASCII character set, since `a' has the numeric value 97 in ASCII. A floating-point argument must use a period before any fractional digits, but is printed according to the `LC_NUMERIC' category of the current locale. For example, in a locale whose radix character is a comma, the command `printf %g 3.14' outputs `3,14' whereas the command `printf %g 3,14' is an error. *Note Floating point::. `printf' interprets `\OOO' in FORMAT as an octal number (if OOO is 1 to 3 octal digits) specifying a byte to print, and `\xHH' as a hexadecimal number (if HH is 1 to 2 hex digits) specifying a character to print. Note however that when `\OOO' specifies a number larger than 255, `printf' ignores the ninth bit. For example, `printf '\400'' is equivalent to `printf '\0''. `printf' interprets two character syntaxes introduced in ISO C 99: `\u' for 16-bit Unicode (ISO/IEC 10646) characters, specified as four hexadecimal digits HHHH, and `\U' for 32-bit Unicode characters, specified as eight hexadecimal digits HHHHHHHH. `printf' outputs the Unicode characters according to the `LC_CTYPE' locale. Unicode characters in the ranges U+0000...U+009F, U+D800...U+DFFF cannot be specified by this syntax, except for U+0024 ($), U+0040 (@), and U+0060 ()`. The processing of `\u' and `\U' requires a full-featured `iconv' facility. It is activated on systems with glibc 2.2 (or newer), or when `libiconv' is installed prior to this package. Otherwise `\u' and `\U' will print as-is. The only options are a lone `--help' or `--version'. *Note Common options::. Options must precede operands. The Unicode character syntaxes are useful for writing strings in a locale independent way. For example, a string containing the Euro currency symbol $ env printf '\u20AC 14.95' will be output correctly in all locales supporting the Euro symbol (ISO-8859-15, UTF-8, and others). Similarly, a Chinese string $ env printf '\u4e2d\u6587' will be output correctly in all Chinese locales (GB2312, BIG5, UTF-8, etc). Note that in these examples, the `printf' command has been invoked via `env' to ensure that we run the program found via your shell's search path, and not a shell alias or a built-in function. For larger strings, you don't need to look up the hexadecimal code values of each character one by one. ASCII characters mixed with \u escape sequences is also known as the JAVA source file encoding. You can use GNU recode 3.5c (or newer) to convert strings to this encoding. Here is how to convert a piece of text into a shell script which will output this text in a locale-independent way: $ LC_CTYPE=zh_CN.big5 /usr/local/bin/printf \ '\u4e2d\u6587\n' > sample.txt $ recode BIG5..JAVA < sample.txt \ | sed -e "s|^|/usr/local/bin/printf '|" -e "s|$|\\\\n'|" \ > sample.sh An exit status of zero indicates success, and a nonzero value indicates failure.  File: coreutils.info, Node: yes invocation, Prev: printf invocation, Up: Printing text 15.3 `yes': Print a string until interrupted ============================================ `yes' prints the command line arguments, separated by spaces and followed by a newline, forever until it is killed. If no arguments are given, it prints `y' followed by a newline forever until killed. Upon a write error, `yes' exits with status `1'. The only options are a lone `--help' or `--version'. To output an argument that begins with `-', precede it with `--', e.g., `yes -- --help'. *Note Common options::.  File: coreutils.info, Node: Conditions, Next: Redirection, Prev: Printing text, Up: Top 16 Conditions ************* This section describes commands that are primarily useful for their exit status, rather than their output. Thus, they are often used as the condition of shell `if' statements, or as the last command in a pipeline. * Menu: * false invocation:: Do nothing, unsuccessfully. * true invocation:: Do nothing, successfully. * test invocation:: Check file types and compare values. * expr invocation:: Evaluate expressions.  File: coreutils.info, Node: false invocation, Next: true invocation, Up: Conditions 16.1 `false': Do nothing, unsuccessfully ======================================== `false' does nothing except return an exit status of 1, meaning "failure". It can be used as a place holder in shell scripts where an unsuccessful command is needed. In most modern shells, `false' is a built-in command, so when you use `false' in a script, you're probably using the built-in command, not the one documented here. `false' honors the `--help' and `--version' options. This version of `false' is implemented as a C program, and is thus more secure and faster than a shell script implementation, and may safely be used as a dummy shell for the purpose of disabling accounts. Note that `false' (unlike all other programs documented herein) exits unsuccessfully, even when invoked with `--help' or `--version'. Portable programs should not assume that the exit status of `false' is 1, as it is greater than 1 on some non-GNU hosts.  File: coreutils.info, Node: true invocation, Next: test invocation, Prev: false invocation, Up: Conditions 16.2 `true': Do nothing, successfully ===================================== `true' does nothing except return an exit status of 0, meaning "success". It can be used as a place holder in shell scripts where a successful command is needed, although the shell built-in command `:' (colon) may do the same thing faster. In most modern shells, `true' is a built-in command, so when you use `true' in a script, you're probably using the built-in command, not the one documented here. `true' honors the `--help' and `--version' options. Note, however, that it is possible to cause `true' to exit with nonzero status: with the `--help' or `--version' option, and with standard output already closed or redirected to a file that evokes an I/O error. For example, using a Bourne-compatible shell: $ ./true --version >&- ./true: write error: Bad file number $ ./true --version > /dev/full ./true: write error: No space left on device This version of `true' is implemented as a C program, and is thus more secure and faster than a shell script implementation, and may safely be used as a dummy shell for the purpose of disabling accounts.  File: coreutils.info, Node: test invocation, Next: expr invocation, Prev: true invocation, Up: Conditions 16.3 `test': Check file types and compare values ================================================ `test' returns a status of 0 (true) or 1 (false) depending on the evaluation of the conditional expression EXPR. Each part of the expression must be a separate argument. `test' has file status checks, string operators, and numeric comparison operators. `test' has an alternate form that uses opening and closing square brackets instead a leading `test'. For example, instead of `test -d /', you can write `[ -d / ]'. The square brackets must be separate arguments; for example, `[-d /]' does not have the desired effect. Since `test EXPR' and `[ EXPR ]' have the same meaning, only the former form is discussed below. Synopses: test EXPRESSION test [ EXPRESSION ] [ ] [ OPTION Due to shell aliases and built-in `test' functions, using an unadorned `test' interactively or in a script may get you different functionality than that described here. Invoke it via `env' (i.e., `env test ...') to avoid interference from the shell. If EXPRESSION is omitted, `test' returns false. If EXPRESSION is a single argument, `test' returns false if the argument is null and true otherwise. The argument can be any string, including strings like `-d', `-1', `--', `--help', and `--version' that most other programs would treat as options. To get help and version information, invoke the commands `[ --help' and `[ --version', without the usual closing brackets. *Note Common options::. Exit status: 0 if the expression is true, 1 if the expression is false, 2 if an error occurred. * Menu: * File type tests:: -[bcdfhLpSt] * Access permission tests:: -[gkruwxOG] * File characteristic tests:: -e -s -nt -ot -ef * String tests:: -z -n = == != * Numeric tests:: -eq -ne -lt -le -gt -ge * Connectives for test:: ! -a -o  File: coreutils.info, Node: File type tests, Next: Access permission tests, Up: test invocation 16.3.1 File type tests ---------------------- These options test for particular types of files. (Everything's a file, but not all files are the same!) `-b FILE' True if FILE exists and is a block special device. `-c FILE' True if FILE exists and is a character special device. `-d FILE' True if FILE exists and is a directory. `-f FILE' True if FILE exists and is a regular file. `-h FILE' `-L FILE' True if FILE exists and is a symbolic link. Unlike all other file-related tests, this test does not dereference FILE if it is a symbolic link. `-p FILE' True if FILE exists and is a named pipe. `-S FILE' True if FILE exists and is a socket. `-t FD' True if FD is a file descriptor that is associated with a terminal.  File: coreutils.info, Node: Access permission tests, Next: File characteristic tests, Prev: File type tests, Up: test invocation 16.3.2 Access permission tests ------------------------------ These options test for particular access permissions. `-g FILE' True if FILE exists and has its set-group-ID bit set. `-k FILE' True if FILE exists and has its "sticky" bit set. `-r FILE' True if FILE exists and read permission is granted. `-u FILE' True if FILE exists and has its set-user-ID bit set. `-w FILE' True if FILE exists and write permission is granted. `-x FILE' True if FILE exists and execute permission is granted (or search permission, if it is a directory). `-O FILE' True if FILE exists and is owned by the current effective user ID. `-G FILE' True if FILE exists and is owned by the current effective group ID.  File: coreutils.info, Node: File characteristic tests, Next: String tests, Prev: Access permission tests, Up: test invocation 16.3.3 File characteristic tests -------------------------------- These options test other file characteristics. `-e FILE' True if FILE exists. `-s FILE' True if FILE exists and has a size greater than zero. `FILE1 -nt FILE2' True if FILE1 is newer (according to modification date) than FILE2, or if FILE1 exists and FILE2 does not. `FILE1 -ot FILE2' True if FILE1 is older (according to modification date) than FILE2, or if FILE2 exists and FILE1 does not. `FILE1 -ef FILE2' True if FILE1 and FILE2 have the same device and inode numbers, i.e., if they are hard links to each other.  File: coreutils.info, Node: String tests, Next: Numeric tests, Prev: File characteristic tests, Up: test invocation 16.3.4 String tests ------------------- These options test string characteristics. You may need to quote STRING arguments for the shell. For example: test -n "$V" The quotes here prevent the wrong arguments from being passed to `test' if `$V' is empty or contains special characters. `-z STRING' True if the length of STRING is zero. `-n STRING' `STRING' True if the length of STRING is nonzero. `STRING1 = STRING2' True if the strings are equal. `STRING1 == STRING2' True if the strings are equal (synonym for =). `STRING1 != STRING2' True if the strings are not equal.  File: coreutils.info, Node: Numeric tests, Next: Connectives for test, Prev: String tests, Up: test invocation 16.3.5 Numeric tests -------------------- Numeric relational operators. The arguments must be entirely numeric (possibly negative), or the special expression `-l STRING', which evaluates to the length of STRING. `ARG1 -eq ARG2' `ARG1 -ne ARG2' `ARG1 -lt ARG2' `ARG1 -le ARG2' `ARG1 -gt ARG2' `ARG1 -ge ARG2' These arithmetic binary operators return true if ARG1 is equal, not-equal, less-than, less-than-or-equal, greater-than, or greater-than-or-equal than ARG2, respectively. For example: test -1 -gt -2 && echo yes => yes test -l abc -gt 1 && echo yes => yes test 0x100 -eq 1 error--> test: integer expression expected before -eq  File: coreutils.info, Node: Connectives for test, Prev: Numeric tests, Up: test invocation 16.3.6 Connectives for `test' ----------------------------- The usual logical connectives. `! EXPR' True if EXPR is false. `EXPR1 -a EXPR2' True if both EXPR1 and EXPR2 are true. `EXPR1 -o EXPR2' True if either EXPR1 or EXPR2 is true.  File: coreutils.info, Node: expr invocation, Prev: test invocation, Up: Conditions 16.4 `expr': Evaluate expressions ================================= `expr' evaluates an expression and writes the result on standard output. Each token of the expression must be a separate argument. Operands are either integers or strings. Integers consist of one or more decimal digits, with an optional leading `-'. `expr' converts anything appearing in an operand position to an integer or a string depending on the operation being applied to it. Strings are not quoted for `expr' itself, though you may need to quote them to protect characters with special meaning to the shell, e.g., spaces. However, regardless of whether it is quoted, a string operand should not be a parenthesis or any of `expr''s operators like `+', so you cannot safely pass an arbitrary string `$str' to expr merely by quoting it to the shell. One way to work around this is to use the GNU extension `+', (e.g., `+ "$str" = foo'); a more portable way is to use `" $str"' and to adjust the rest of the expression to take the leading space into account (e.g., `" $str" = " foo"'). You should not pass a negative integer or a string with leading `-' as `expr''s first argument, as it might be misinterpreted as an option; this can be avoided by parenthesization. Also, portable scripts should not use a string operand that happens to take the form of an integer; this can be worked around by inserting leading spaces as mentioned above. Operators may be given as infix symbols or prefix keywords. Parentheses may be used for grouping in the usual manner. You must quote parentheses and many operators to avoid the shell evaluating them, however. When built with support for the GNU MP library, `expr' uses arbitrary-precision arithmetic; otherwise, it uses native arithmetic types and may fail due to arithmetic overflow. The only options are `--help' and `--version'. *Note Common options::. Options must precede operands. Exit status: 0 if the expression is neither null nor 0, 1 if the expression is null or 0, 2 if the expression is invalid, 3 if an internal error occurred (e.g., arithmetic overflow). * Menu: * String expressions:: + : match substr index length * Numeric expressions:: + - * / % * Relations for expr:: | & < <= = == != >= > * Examples of expr:: Examples.  File: coreutils.info, Node: String expressions, Next: Numeric expressions, Up: expr invocation 16.4.1 String expressions ------------------------- `expr' supports pattern matching and other string operators. These have higher precedence than both the numeric and relational operators (in the next sections). `STRING : REGEX' Perform pattern matching. The arguments are converted to strings and the second is considered to be a (basic, a la GNU `grep') regular expression, with a `^' implicitly prepended. The first argument is then matched against this regular expression. If the match succeeds and REGEX uses `\(' and `\)', the `:' expression returns the part of STRING that matched the subexpression; otherwise, it returns the number of characters matched. If the match fails, the `:' operator returns the null string if `\(' and `\)' are used in REGEX, otherwise 0. Only the first `\( ... \)' pair is relevant to the return value; additional pairs are meaningful only for grouping the regular expression operators. In the regular expression, `\+', `\?', and `\|' are operators which respectively match one or more, zero or one, or separate alternatives. SunOS and other `expr''s treat these as regular characters. (POSIX allows either behavior.) *Note Regular Expression Library: (regex)Top, for details of regular expression syntax. Some examples are in *note Examples of expr::. `match STRING REGEX' An alternative way to do pattern matching. This is the same as `STRING : REGEX'. `substr STRING POSITION LENGTH' Returns the substring of STRING beginning at POSITION with length at most LENGTH. If either POSITION or LENGTH is negative, zero, or non-numeric, returns the null string. `index STRING CHARSET' Returns the first position in STRING where the first character in CHARSET was found. If no character in CHARSET is found in STRING, return 0. `length STRING' Returns the length of STRING. `+ TOKEN' Interpret TOKEN as a string, even if it is a keyword like MATCH or an operator like `/'. This makes it possible to test `expr length + "$x"' or `expr + "$x" : '.*/\(.\)'' and have it do the right thing even if the value of $X happens to be (for example) `/' or `index'. This operator is a GNU extension. Portable shell scripts should use `" $token" : ' \(.*\)'' instead of `+ "$token"'. To make `expr' interpret keywords as strings, you must use the `quote' operator.  File: coreutils.info, Node: Numeric expressions, Next: Relations for expr, Prev: String expressions, Up: expr invocation 16.4.2 Numeric expressions -------------------------- `expr' supports the usual numeric operators, in order of increasing precedence. These numeric operators have lower precedence than the string operators described in the previous section, and higher precedence than the connectives (next section). `+ -' Addition and subtraction. Both arguments are converted to integers; an error occurs if this cannot be done. `* / %' Multiplication, division, remainder. Both arguments are converted to integers; an error occurs if this cannot be done.  File: coreutils.info, Node: Relations for expr, Next: Examples of expr, Prev: Numeric expressions, Up: expr invocation 16.4.3 Relations for `expr' --------------------------- `expr' supports the usual logical connectives and relations. These have lower precedence than the string and numeric operators (previous sections). Here is the list, lowest-precedence operator first. `|' Returns its first argument if that is neither null nor zero, otherwise its second argument if it is neither null nor zero, otherwise 0. It does not evaluate its second argument if its first argument is neither null nor zero. `&' Return its first argument if neither argument is null or zero, otherwise 0. It does not evaluate its second argument if its first argument is null or zero. `< <= = == != >= >' Compare the arguments and return 1 if the relation is true, 0 otherwise. `==' is a synonym for `='. `expr' first tries to convert both arguments to integers and do a numeric comparison; if either conversion fails, it does a lexicographic comparison using the character collating sequence specified by the `LC_COLLATE' locale.  File: coreutils.info, Node: Examples of expr, Prev: Relations for expr, Up: expr invocation 16.4.4 Examples of using `expr' ------------------------------- Here are a few examples, including quoting for shell metacharacters. To add 1 to the shell variable `foo', in Bourne-compatible shells: foo=$(expr $foo + 1) To print the non-directory part of the file name stored in `$fname', which need not contain a `/': expr $fname : '.*/\(.*\)' '|' $fname An example showing that `\+' is an operator: expr aaa : 'a\+' => 3 expr abc : 'a\(.\)c' => b expr index abcdef cz => 3 expr index index a error--> expr: syntax error expr index + index a => 0  File: coreutils.info, Node: Redirection, Next: File name manipulation, Prev: Conditions, Up: Top 17 Redirection ************** Unix shells commonly provide several forms of "redirection"--ways to change the input source or output destination of a command. But one useful redirection is performed by a separate command, not by the shell; it's described here. * Menu: * tee invocation:: Redirect output to multiple files or processes.  File: coreutils.info, Node: tee invocation, Up: Redirection 17.1 `tee': Redirect output to multiple files or processes ========================================================== The `tee' command copies standard input to standard output and also to any files given as arguments. This is useful when you want not only to send some data down a pipe, but also to save a copy. Synopsis: tee [OPTION]... [FILE]... If a file being written to does not already exist, it is created. If a file being written to already exists, the data it previously contained is overwritten unless the `-a' option is used. A FILE of `-' causes `tee' to send another copy of input to standard output, but this is typically not that useful as the copies are interleaved. The program accepts the following options. Also see *note Common options::. `-a' `--append' Append standard input to the given files rather than overwriting them. `-i' `--ignore-interrupts' Ignore interrupt signals. The `tee' command is useful when you happen to be transferring a large amount of data and also want to summarize that data without reading it a second time. For example, when you are downloading a DVD image, you often want to verify its signature or checksum right away. The inefficient way to do it is simply: wget http://example.com/some.iso && sha1sum some.iso One problem with the above is that it makes you wait for the download to complete before starting the time-consuming SHA1 computation. Perhaps even more importantly, the above requires reading the DVD image a second time (the first was from the network). The efficient way to do it is to interleave the download and SHA1 computation. Then, you'll get the checksum for free, because the entire process parallelizes so well: # slightly contrived, to demonstrate process substitution wget -O - http://example.com/dvd.iso \ | tee >(sha1sum > dvd.sha1) > dvd.iso That makes `tee' write not just to the expected output file, but also to a pipe running `sha1sum' and saving the final checksum in a file named `dvd.sha1'. Note, however, that this example relies on a feature of modern shells called "process substitution" (the `>(command)' syntax, above; *Note Process Substitution: (bashref)Process Substitution.), so it works with `zsh', `bash', and `ksh', but not with `/bin/sh'. So if you write code like this in a shell script, be sure to start the script with `#!/bin/bash'. Since the above example writes to one file and one process, a more conventional and portable use of `tee' is even better: wget -O - http://example.com/dvd.iso \ | tee dvd.iso | sha1sum > dvd.sha1 You can extend this example to make `tee' write to two processes, computing MD5 and SHA1 checksums in parallel. In this case, process substitution is required: wget -O - http://example.com/dvd.iso \ | tee >(sha1sum > dvd.sha1) \ >(md5sum > dvd.md5) \ > dvd.iso This technique is also useful when you want to make a _compressed_ copy of the contents of a pipe. Consider a tool to graphically summarize disk usage data from `du -ak'. For a large hierarchy, `du -ak' can run for a long time, and can easily produce terabytes of data, so you won't want to rerun the command unnecessarily. Nor will you want to save the uncompressed output. Doing it the inefficient way, you can't even start the GUI until after you've compressed all of the `du' output: du -ak | gzip -9 > /tmp/du.gz gzip -d /tmp/du.gz | xdiskusage -a With `tee' and process substitution, you start the GUI right away and eliminate the decompression completely: du -ak | tee >(gzip -9 > /tmp/du.gz) | xdiskusage -a Finally, if you regularly create more than one type of compressed tarball at once, for example when `make dist' creates both `gzip'-compressed and `bzip2'-compressed tarballs, there may be a better way. Typical `automake'-generated `Makefile' rules create the two compressed tar archives with commands in sequence, like this (slightly simplified): tardir=your-pkg-M.N tar chof - "$tardir" | gzip -9 -c > your-pkg-M.N.tar.gz tar chof - "$tardir" | bzip2 -9 -c > your-pkg-M.N.tar.bz2 However, if the hierarchy you are archiving and compressing is larger than a couple megabytes, and especially if you are using a multi-processor system with plenty of memory, then you can do much better by reading the directory contents only once and running the compression programs in parallel: tardir=your-pkg-M.N tar chof - "$tardir" \ | tee >(gzip -9 -c > your-pkg-M.N.tar.gz) \ | bzip2 -9 -c > your-pkg-M.N.tar.bz2 An exit status of zero indicates success, and a nonzero value indicates failure.  File: coreutils.info, Node: File name manipulation, Next: Working context, Prev: Redirection, Up: Top 18 File name manipulation ************************* This section describes commands that manipulate file names. * Menu: * basename invocation:: Strip directory and suffix from a file name. * dirname invocation:: Strip last file name component. * pathchk invocation:: Check file name validity and portability. * mktemp invocation:: Create temporary file or directory. * realpath invocation:: Print resolved file names.  File: coreutils.info, Node: basename invocation, Next: dirname invocation, Up: File name manipulation 18.1 `basename': Strip directory and suffix from a file name ============================================================ `basename' removes any leading directory components from NAME. Synopsis: basename NAME [SUFFIX] basename OPTION... NAME... If SUFFIX is specified and is identical to the end of NAME, it is removed from NAME as well. Note that since trailing slashes are removed prior to suffix matching, SUFFIX will do nothing if it contains slashes. `basename' prints the result on standard output. Together, `basename' and `dirname' are designed such that if `ls "$name"' succeeds, then the command sequence `cd "$(dirname "$name")"; ls "$(basename "$name")"' will, too. This works for everything except file names containing a trailing newline. POSIX allows the implementation to define the results if NAME is empty or `//'. In the former case, GNU `basename' returns the empty string. In the latter case, the result is `//' on platforms where // is distinct from /, and `/' on platforms where there is no difference. The program accepts the following options. Also see *note Common options::. Options must precede operands. `-a' `--multiple' Support more than one argument. Treat every argument as a NAME. With this, an optional SUFFIX must be specified using the `-s' option. `-s SUFFIX' `--suffix=SUFFIX' Remove a trailing SUFFIX. This option implies the `-a' option. `-z' `--zero' Separate output items with NUL characters. An exit status of zero indicates success, and a nonzero value indicates failure. Examples: # Output "sort". basename /usr/bin/sort # Output "stdio". basename include/stdio.h .h # Output "stdio". basename -s .h include/stdio.h # Output "stdio" followed by "stdlib" basename -a -s .h include/stdio.h include/stdlib.h  File: coreutils.info, Node: dirname invocation, Next: pathchk invocation, Prev: basename invocation, Up: File name manipulation 18.2 `dirname': Strip last file name component ============================================== `dirname' prints all but the final slash-delimited component of each NAME. Slashes on either side of the final component are also removed. If the string contains no slash, `dirname' prints `.' (meaning the current directory). Synopsis: dirname [OPTION] NAME... NAME need not be a file name, but if it is, this operation effectively lists the directory that contains the final component, including the case when the final component is itself a directory. Together, `basename' and `dirname' are designed such that if `ls "$name"' succeeds, then the command sequence `cd "$(dirname "$name")"; ls "$(basename "$name")"' will, too. This works for everything except file names containing a trailing newline. POSIX allows the implementation to define the results if NAME is `//'. With GNU `dirname', the result is `//' on platforms where // is distinct from /, and `/' on platforms where there is no difference. The program accepts the following option. Also see *note Common options::. `-z' `--zero' Separate output items with NUL characters. An exit status of zero indicates success, and a nonzero value indicates failure. Examples: # Output "/usr/bin". dirname /usr/bin/sort dirname /usr/bin//.// # Output "dir1" followed by "dir2" dirname dir1/str dir2/str # Output ".". dirname stdio.h  File: coreutils.info, Node: pathchk invocation, Next: mktemp invocation, Prev: dirname invocation, Up: File name manipulation 18.3 `pathchk': Check file name validity and portability ======================================================== `pathchk' checks validity and portability of file names. Synopsis: pathchk [OPTION]... NAME... For each NAME, `pathchk' prints an error message if any of these conditions is true: 1. One of the existing directories in NAME does not have search (execute) permission, 2. The length of NAME is larger than the maximum supported by the operating system. 3. The length of one component of NAME is longer than its file system's maximum. A nonexistent NAME is not an error, so long a file with that name could be created under the above conditions. The program accepts the following options. Also see *note Common options::. Options must precede operands. `-p' Instead of performing checks based on the underlying file system, print an error message if any of these conditions is true: 1. A file name is empty. 2. A file name contains a character outside the POSIX portable file name character set, namely, the ASCII letters and digits, `.', `_', `-', and `/'. 3. The length of a file name or one of its components exceeds the POSIX minimum limits for portability. `-P' Print an error message if a file name is empty, or if it contains a component that begins with `-'. `--portability' Print an error message if a file name is not portable to all POSIX hosts. This option is equivalent to `-p -P'. Exit status: 0 if all specified file names passed all checks, 1 otherwise.  File: coreutils.info, Node: mktemp invocation, Next: realpath invocation, Prev: pathchk invocation, Up: File name manipulation 18.4 `mktemp': Create temporary file or directory ================================================= `mktemp' manages the creation of temporary files and directories. Synopsis: mktemp [OPTION]... [TEMPLATE] Safely create a temporary file or directory based on TEMPLATE, and print its name. If given, TEMPLATE must include at least three consecutive `X's in the last component. If omitted, the template `tmp.XXXXXXXXXX' is used, and option `--tmpdir' is implied. The final run of `X's in the TEMPLATE will be replaced by alpha-numeric characters; thus, on a case-sensitive file system, and with a TEMPLATE including a run of N instances of `X', there are `62**N' potential file names. Older scripts used to create temporary files by simply joining the name of the program with the process id (`$$') as a suffix. However, that naming scheme is easily predictable, and suffers from a race condition where the attacker can create an appropriately named symbolic link, such that when the script then opens a handle to what it thought was an unused file, it is instead modifying an existing file. Using the same scheme to create a directory is slightly safer, since the `mkdir' will fail if the target already exists, but it is still inferior because it allows for denial of service attacks. Therefore, modern scripts should use the `mktemp' command to guarantee that the generated name will be unpredictable, and that knowledge of the temporary file name implies that the file was created by the current script and cannot be modified by other users. When creating a file, the resulting file has read and write permissions for the current user, but no permissions for the group or others; these permissions are reduced if the current umask is more restrictive. Here are some examples (although note that if you repeat them, you will most likely get different file names): * Create a temporary file in the current directory. $ mktemp file.XXXX file.H47c * Create a temporary file with a known suffix. $ mktemp --suffix=.txt file-XXXX file-H08W.txt $ mktemp file-XXXX-XXXX.txt file-XXXX-eI9L.txt * Create a secure fifo relative to the user's choice of `TMPDIR', but falling back to the current directory rather than `/tmp'. Note that `mktemp' does not create fifos, but can create a secure directory in which the fifo can live. Exit the shell if the directory or fifo could not be created. $ dir=$(mktemp -p "${TMPDIR:-.}" -d dir-XXXX) || exit 1 $ fifo=$dir/fifo $ mkfifo "$fifo" || { rmdir "$dir"; exit 1; } * Create and use a temporary file if possible, but ignore failure. The file will reside in the directory named by `TMPDIR', if specified, or else in `/tmp'. $ file=$(mktemp -q) && { > # Safe to use $file only within this block. Use quotes, > # since $TMPDIR, and thus $file, may contain whitespace. > echo ... > "$file" > rm "$file" > } * Act as a semi-random character generator (it is not fully random, since it is impacted by the contents of the current directory). To avoid security holes, do not use the resulting names to create a file. $ mktemp -u XXX Gb9 $ mktemp -u XXX nzC The program accepts the following options. Also see *note Common options::. `-d' `--directory' Create a directory rather than a file. The directory will have read, write, and search permissions for the current user, but no permissions for the group or others; these permissions are reduced if the current umask is more restrictive. `-q' `--quiet' Suppress diagnostics about failure to create a file or directory. The exit status will still reflect whether a file was created. `-u' `--dry-run' Generate a temporary name that does not name an existing file, without changing the file system contents. Using the output of this command to create a new file is inherently unsafe, as there is a window of time between generating the name and using it where another process can create an object by the same name. `-p DIR' `--tmpdir[=DIR]' Treat TEMPLATE relative to the directory DIR. If DIR is not specified (only possible with the long option `--tmpdir') or is the empty string, use the value of `TMPDIR' if available, otherwise use `/tmp'. If this is specified, TEMPLATE must not be absolute. However, TEMPLATE can still contain slashes, although intermediate directories must already exist. `--suffix=SUFFIX' Append SUFFIX to the TEMPLATE. SUFFIX must not contain slash. If `--suffix' is specified, TEMPLATE must end in `X'; if it is not specified, then an appropriate `--suffix' is inferred by finding the last `X' in TEMPLATE. This option exists for use with the default TEMPLATE and for the creation of a SUFFIX that starts with `X'. `-t' Treat TEMPLATE as a single file relative to the value of `TMPDIR' if available, or to the directory specified by `-p', otherwise to `/tmp'. TEMPLATE must not contain slashes. This option is deprecated; the use of `-p' without `-t' offers better defaults (by favoring the command line over `TMPDIR') and more flexibility (by allowing intermediate directories). Exit status: 0 if the file was created, 1 otherwise.  File: coreutils.info, Node: realpath invocation, Prev: mktemp invocation, Up: File name manipulation 18.5 `realpath': Print the resolved file name. ============================================== `realpath' expands all symbolic links and resolves references to `/./', `/../' and extra `/' characters. By default, all but the last component of the specified files must exist. Synopsis: realpath [OPTION]... FILE... The program accepts the following options. Also see *note Common options::. `-e' `--canonicalize-existing' Ensure that all components of the specified file names exist. If any component is missing or unavailable, `realpath' will output a diagnostic unless the `-q' option is specified, and exit with a nonzero exit code. A trailing slash requires that the name resolve to a directory. `-m' `--canonicalize-missing' If any component of a specified file name is missing or unavailable, treat it as a directory. `-L' `--logical' Symbolic links are resolved in the specified file names, but they are resolved after any subsequent `..' components are processed. `-P' `--physical' Symbolic links are resolved in the specified file names, and they are resolved before any subsequent `..' components are processed. This is the default mode of operation. `-q' `--quiet' Suppress diagnostic messages for specified file names. `-s' `--strip' `--no-symlinks' Do not resolve symbolic links. Only resolve references to `/./', `/../' and remove extra `/' characters. When combined with the `-m' option, realpath operates only on the file name, and does not touch any actual file. `-z' `--zero' Separate output items with NUL characters. `--relative-to=FILE' Print the resolved file names relative to the specified file. Note this option honors the `-m' and `-e' options pertaining to file existence. `--relative-base=BASE' This option is valid when used with `--relative-to', and will restrict the output of `--relative-to' so that relative names are output, only when FILEs are descendants of BASE. Otherwise output the absolute file name. If `--relative-to' was not specified, then the descendants of BASE are printed relative to BASE. If `--relative-to' is specified, then that directory must be a descendant of BASE for this option to have an effect. Note: this option honors the `-m' and `-e' options pertaining to file existence. For example: realpath --relative-to=/usr /tmp /usr/bin => ../tmp => bin realpath --relative-base=/usr /tmp /usr/bin => /tmp => bin Exit status: 0 if all file names were printed without issue. 1 otherwise.  File: coreutils.info, Node: Working context, Next: User information, Prev: File name manipulation, Up: Top 19 Working context ****************** This section describes commands that display or alter the context in which you are working: the current directory, the terminal settings, and so forth. See also the user-related commands in the next section. * Menu: * pwd invocation:: Print working directory. * stty invocation:: Print or change terminal characteristics. * printenv invocation:: Print environment variables. * tty invocation:: Print file name of terminal on standard input.  File: coreutils.info, Node: pwd invocation, Next: stty invocation, Up: Working context 19.1 `pwd': Print working directory =================================== `pwd' prints the name of the current directory. Synopsis: pwd [OPTION]... The program accepts the following options. Also see *note Common options::. `-L' `--logical' If the contents of the environment variable `PWD' provide an absolute name of the current directory with no `.' or `..' components, but possibly with symbolic links, then output those contents. Otherwise, fall back to default `-P' handling. `-P' `--physical' Print a fully resolved name for the current directory. That is, all components of the printed name will be actual directory names--none will be symbolic links. If `-L' and `-P' are both given, the last one takes precedence. If neither option is given, then this implementation uses `-P' as the default unless the `POSIXLY_CORRECT' environment variable is set. Due to shell aliases and built-in `pwd' functions, using an unadorned `pwd' interactively or in a script may get you different functionality than that described here. Invoke it via `env' (i.e., `env pwd ...') to avoid interference from the shell. An exit status of zero indicates success, and a nonzero value indicates failure.  File: coreutils.info, Node: stty invocation, Next: printenv invocation, Prev: pwd invocation, Up: Working context 19.2 `stty': Print or change terminal characteristics ===================================================== `stty' prints or changes terminal characteristics, such as baud rate. Synopses: stty [OPTION] [SETTING]... stty [OPTION] If given no line settings, `stty' prints the baud rate, line discipline number (on systems that support it), and line settings that have been changed from the values set by `stty sane'. By default, mode reading and setting are performed on the tty line connected to standard input, although this can be modified by the `--file' option. `stty' accepts many non-option arguments that change aspects of the terminal line operation, as described below. The program accepts the following options. Also see *note Common options::. `-a' `--all' Print all current settings in human-readable form. This option may not be used in combination with any line settings. `-F DEVICE' `--file=DEVICE' Set the line opened by the file name specified in DEVICE instead of the tty line connected to standard input. This option is necessary because opening a POSIX tty requires use of the `O_NONDELAY' flag to prevent a POSIX tty from blocking until the carrier detect line is high if the `clocal' flag is not set. Hence, it is not always possible to allow the shell to open the device in the traditional manner. `-g' `--save' Print all current settings in a form that can be used as an argument to another `stty' command to restore the current settings. This option may not be used in combination with any line settings. Many settings can be turned off by preceding them with a `-'. Such arguments are marked below with "May be negated" in their description. The descriptions themselves refer to the positive case, that is, when _not_ negated (unless stated otherwise, of course). Some settings are not available on all POSIX systems, since they use extensions. Such arguments are marked below with "Non-POSIX" in their description. On non-POSIX systems, those or other settings also may not be available, but it's not feasible to document all the variations: just try it and see. An exit status of zero indicates success, and a nonzero value indicates failure. * Menu: * Control:: Control settings * Input:: Input settings * Output:: Output settings * Local:: Local settings * Combination:: Combination settings * Characters:: Special characters * Special:: Special settings  File: coreutils.info, Node: Control, Next: Input, Up: stty invocation 19.2.1 Control settings ----------------------- Control settings: `parenb' Generate parity bit in output and expect parity bit in input. May be negated. `parodd' Set odd parity (even if negated). May be negated. `cs5' `cs6' `cs7' `cs8' Set character size to 5, 6, 7, or 8 bits. `hup' `hupcl' Send a hangup signal when the last process closes the tty. May be negated. `cstopb' Use two stop bits per character (one if negated). May be negated. `cread' Allow input to be received. May be negated. `clocal' Disable modem control signals. May be negated. `crtscts' Enable RTS/CTS flow control. Non-POSIX. May be negated.  File: coreutils.info, Node: Input, Next: Output, Prev: Control, Up: stty invocation 19.2.2 Input settings --------------------- These settings control operations on data received from the terminal. `ignbrk' Ignore break characters. May be negated. `brkint' Make breaks cause an interrupt signal. May be negated. `ignpar' Ignore characters with parity errors. May be negated. `parmrk' Mark parity errors (with a 255-0-character sequence). May be negated. `inpck' Enable input parity checking. May be negated. `istrip' Clear high (8th) bit of input characters. May be negated. `inlcr' Translate newline to carriage return. May be negated. `igncr' Ignore carriage return. May be negated. `icrnl' Translate carriage return to newline. May be negated. `iutf8' Assume input characters are UTF-8 encoded. May be negated. `ixon' Enable XON/XOFF flow control (that is, `CTRL-S'/`CTRL-Q'). May be negated. `ixoff' `tandem' Enable sending of `stop' character when the system input buffer is almost full, and `start' character when it becomes almost empty again. May be negated. `iuclc' Translate uppercase characters to lowercase. Non-POSIX. May be negated. Note ilcuc is not implemented, as one would not be able to issue almost any (lowercase) Unix command, after invoking it. `ixany' Allow any character to restart output (only the start character if negated). Non-POSIX. May be negated. `imaxbel' Enable beeping and not flushing input buffer if a character arrives when the input buffer is full. Non-POSIX. May be negated.  File: coreutils.info, Node: Output, Next: Local, Prev: Input, Up: stty invocation 19.2.3 Output settings ---------------------- These settings control operations on data sent to the terminal. `opost' Postprocess output. May be negated. `olcuc' Translate lowercase characters to uppercase. Non-POSIX. May be negated. (Note ouclc is not currently implemented.) `ocrnl' Translate carriage return to newline. Non-POSIX. May be negated. `onlcr' Translate newline to carriage return-newline. Non-POSIX. May be negated. `onocr' Do not print carriage returns in the first column. Non-POSIX. May be negated. `onlret' Newline performs a carriage return. Non-POSIX. May be negated. `ofill' Use fill (padding) characters instead of timing for delays. Non-POSIX. May be negated. `ofdel' Use ASCII DEL characters for fill instead of ASCII NUL characters. Non-POSIX. May be negated. `nl1' `nl0' Newline delay style. Non-POSIX. `cr3' `cr2' `cr1' `cr0' Carriage return delay style. Non-POSIX. `tab3' `tab2' `tab1' `tab0' Horizontal tab delay style. Non-POSIX. `bs1' `bs0' Backspace delay style. Non-POSIX. `vt1' `vt0' Vertical tab delay style. Non-POSIX. `ff1' `ff0' Form feed delay style. Non-POSIX.  File: coreutils.info, Node: Local, Next: Combination, Prev: Output, Up: stty invocation 19.2.4 Local settings --------------------- `isig' Enable `interrupt', `quit', and `suspend' special characters. May be negated. `icanon' Enable `erase', `kill', `werase', and `rprnt' special characters. May be negated. `iexten' Enable non-POSIX special characters. May be negated. `echo' Echo input characters. May be negated. `echoe' `crterase' Echo `erase' characters as backspace-space-backspace. May be negated. `echok' Echo a newline after a `kill' character. May be negated. `echonl' Echo newline even if not echoing other characters. May be negated. `noflsh' Disable flushing after `interrupt' and `quit' special characters. May be negated. `xcase' Enable input and output of uppercase characters by preceding their lowercase equivalents with `\', when `icanon' is set. Non-POSIX. May be negated. `tostop' Stop background jobs that try to write to the terminal. Non-POSIX. May be negated. `echoprt' `prterase' Echo erased characters backward, between `\' and `/'. Non-POSIX. May be negated. `echoctl' `ctlecho' Echo control characters in hat notation (`^C') instead of literally. Non-POSIX. May be negated. `echoke' `crtkill' Echo the `kill' special character by erasing each character on the line as indicated by the `echoprt' and `echoe' settings, instead of by the `echoctl' and `echok' settings. Non-POSIX. May be negated.  File: coreutils.info, Node: Combination, Next: Characters, Prev: Local, Up: stty invocation 19.2.5 Combination settings --------------------------- Combination settings: `evenp' `parity' Same as `parenb -parodd cs7'. May be negated. If negated, same as `-parenb cs8'. `oddp' Same as `parenb parodd cs7'. May be negated. If negated, same as `-parenb cs8'. `nl' Same as `-icrnl -onlcr'. May be negated. If negated, same as `icrnl -inlcr -igncr onlcr -ocrnl -onlret'. `ek' Reset the `erase' and `kill' special characters to their default values. `sane' Same as: cread -ignbrk brkint -inlcr -igncr icrnl -ixoff -iuclc -ixany imaxbel opost -olcuc -ocrnl onlcr -onocr -onlret -ofill -ofdel nl0 cr0 tab0 bs0 vt0 ff0 isig icanon iexten echo echoe echok -echonl -noflsh -xcase -tostop -echoprt echoctl echoke and also sets all special characters to their default values. `cooked' Same as `brkint ignpar istrip icrnl ixon opost isig icanon', plus sets the `eof' and `eol' characters to their default values if they are the same as the `min' and `time' characters. May be negated. If negated, same as `raw'. `raw' Same as: -ignbrk -brkint -ignpar -parmrk -inpck -istrip -inlcr -igncr -icrnl -ixon -ixoff -iuclc -ixany -imaxbel -opost -isig -icanon -xcase min 1 time 0 May be negated. If negated, same as `cooked'. `cbreak' Same as `-icanon'. May be negated. If negated, same as `icanon'. `pass8' Same as `-parenb -istrip cs8'. May be negated. If negated, same as `parenb istrip cs7'. `litout' Same as `-parenb -istrip -opost cs8'. May be negated. If negated, same as `parenb istrip opost cs7'. `decctlq' Same as `-ixany'. Non-POSIX. May be negated. `tabs' Same as `tab0'. Non-POSIX. May be negated. If negated, same as `tab3'. `lcase' `LCASE' Same as `xcase iuclc olcuc'. Non-POSIX. May be negated. (Used for terminals with uppercase characters only.) `crt' Same as `echoe echoctl echoke'. `dec' Same as `echoe echoctl echoke -ixany intr ^C erase ^? kill C-u'.  File: coreutils.info, Node: Characters, Next: Special, Prev: Combination, Up: stty invocation 19.2.6 Special characters ------------------------- The special characters' default values vary from system to system. They are set with the syntax `name value', where the names are listed below and the value can be given either literally, in hat notation (`^C'), or as an integer which may start with `0x' to indicate hexadecimal, `0' to indicate octal, or any other digit to indicate decimal. For GNU stty, giving a value of `^-' or `undef' disables that special character. (This is incompatible with Ultrix `stty', which uses a value of `u' to disable a special character. GNU `stty' treats a value `u' like any other, namely to set that special character to .) `intr' Send an interrupt signal. `quit' Send a quit signal. `erase' Erase the last character typed. `kill' Erase the current line. `eof' Send an end of file (terminate the input). `eol' End the line. `eol2' Alternate character to end the line. Non-POSIX. `swtch' Switch to a different shell layer. Non-POSIX. `start' Restart the output after stopping it. `stop' Stop the output. `susp' Send a terminal stop signal. `dsusp' Send a terminal stop signal after flushing the input. Non-POSIX. `rprnt' Redraw the current line. Non-POSIX. `werase' Erase the last word typed. Non-POSIX. `lnext' Enter the next character typed literally, even if it is a special character. Non-POSIX.  File: coreutils.info, Node: Special, Prev: Characters, Up: stty invocation 19.2.7 Special settings ----------------------- `min N' Set the minimum number of characters that will satisfy a read until the time value has expired, when `-icanon' is set. `time N' Set the number of tenths of a second before reads time out if the minimum number of characters have not been read, when `-icanon' is set. `ispeed N' Set the input speed to N. `ospeed N' Set the output speed to N. `rows N' Tell the tty kernel driver that the terminal has N rows. Non-POSIX. `cols N' `columns N' Tell the kernel that the terminal has N columns. Non-POSIX. `size' Print the number of rows and columns that the kernel thinks the terminal has. (Systems that don't support rows and columns in the kernel typically use the environment variables `LINES' and `COLUMNS' instead; however, GNU `stty' does not know anything about them.) Non-POSIX. `line N' Use line discipline N. Non-POSIX. `speed' Print the terminal speed. `N' Set the input and output speeds to N. N can be one of: 0 50 75 110 134 134.5 150 200 300 600 1200 1800 2400 4800 9600 19200 38400 `exta' `extb'. `exta' is the same as 19200; `extb' is the same as 38400. Many systems, including GNU/Linux, support higher speeds. The `stty' command includes support for speeds of 57600, 115200, 230400, 460800, 500000, 576000, 921600, 1000000, 1152000, 1500000, 2000000, 2500000, 3000000, 3500000, or 4000000 where the system supports these. 0 hangs up the line if `-clocal' is set.  File: coreutils.info, Node: printenv invocation, Next: tty invocation, Prev: stty invocation, Up: Working context 19.3 `printenv': Print all or some environment variables ======================================================== `printenv' prints environment variable values. Synopsis: printenv [OPTION] [VARIABLE]... If no VARIABLEs are specified, `printenv' prints the value of every environment variable. Otherwise, it prints the value of each VARIABLE that is set, and nothing for those that are not set. The program accepts the following option. Also see *note Common options::. `-0' `--null' Output a zero byte (ASCII NUL) at the end of each line, rather than a newline. This option enables other programs to parse the output of `printenv' even when that output would contain data with embedded newlines. Exit status: 0 if all variables specified were found 1 if at least one specified variable was not found 2 if a write error occurred  File: coreutils.info, Node: tty invocation, Prev: printenv invocation, Up: Working context 19.4 `tty': Print file name of terminal on standard input ========================================================= `tty' prints the file name of the terminal connected to its standard input. It prints `not a tty' if standard input is not a terminal. Synopsis: tty [OPTION]... The program accepts the following option. Also see *note Common options::. `-s' `--silent' `--quiet' Print nothing; only return an exit status. Exit status: 0 if standard input is a terminal 1 if standard input is not a terminal 2 if given incorrect arguments 3 if a write error occurs  File: coreutils.info, Node: User information, Next: System context, Prev: Working context, Up: Top 20 User information ******************* This section describes commands that print user-related information: logins, groups, and so forth. * Menu: * id invocation:: Print user identity. * logname invocation:: Print current login name. * whoami invocation:: Print effective user ID. * groups invocation:: Print group names a user is in. * users invocation:: Print login names of users currently logged in. * who invocation:: Print who is currently logged in.  File: coreutils.info, Node: id invocation, Next: logname invocation, Up: User information 20.1 `id': Print user identity ============================== `id' prints information about the given user, or the process running it if no user is specified. Synopsis: id [OPTION]... [USERNAME] By default, it prints the real user ID, real group ID, effective user ID if different from the real user ID, effective group ID if different from the real group ID, and supplemental group IDs. In addition, if SELinux is enabled and the `POSIXLY_CORRECT' environment variable is not set, then print `context=C', where C is the security context. Each of these numeric values is preceded by an identifying string and followed by the corresponding user or group name in parentheses. The options cause `id' to print only part of the above information. Also see *note Common options::. `-g' `--group' Print only the group ID. `-G' `--groups' Print only the group ID and the supplementary groups. `-n' `--name' Print the user or group name instead of the ID number. Requires `-u', `-g', or `-G'. `-r' `--real' Print the real, instead of effective, user or group ID. Requires `-u', `-g', or `-G'. `-u' `--user' Print only the user ID. `-Z' `--context' Print only the security context of the current user. If SELinux is disabled then print a warning and set the exit status to 1. An exit status of zero indicates success, and a nonzero value indicates failure. Primary and supplementary groups for a process are normally inherited from its parent and are usually unchanged since login. This means that if you change the group database after logging in, `id' will not reflect your changes within your existing login session. Running `id' with a user argument causes the user and group database to be consulted afresh, and so will give a different result.  File: coreutils.info, Node: logname invocation, Next: whoami invocation, Prev: id invocation, Up: User information 20.2 `logname': Print current login name ======================================== `logname' prints the calling user's name, as found in a system-maintained file (often `/var/run/utmp' or `/etc/utmp'), and exits with a status of 0. If there is no entry for the calling process, `logname' prints an error message and exits with a status of 1. The only options are `--help' and `--version'. *Note Common options::. An exit status of zero indicates success, and a nonzero value indicates failure.  File: coreutils.info, Node: whoami invocation, Next: groups invocation, Prev: logname invocation, Up: User information 20.3 `whoami': Print effective user ID ====================================== `whoami' prints the user name associated with the current effective user ID. It is equivalent to the command `id -un'. The only options are `--help' and `--version'. *Note Common options::. An exit status of zero indicates success, and a nonzero value indicates failure.  File: coreutils.info, Node: groups invocation, Next: users invocation, Prev: whoami invocation, Up: User information 20.4 `groups': Print group names a user is in ============================================= `groups' prints the names of the primary and any supplementary groups for each given USERNAME, or the current process if no names are given. If more than one name is given, the name of each user is printed before the list of that user's groups and the user name is separated from the group list by a colon. Synopsis: groups [USERNAME]... The group lists are equivalent to the output of the command `id -Gn'. Primary and supplementary groups for a process are normally inherited from its parent and are usually unchanged since login. This means that if you change the group database after logging in, `groups' will not reflect your changes within your existing login session. Running `groups' with a list of users causes the user and group database to be consulted afresh, and so will give a different result. The only options are `--help' and `--version'. *Note Common options::. An exit status of zero indicates success, and a nonzero value indicates failure.  File: coreutils.info, Node: users invocation, Next: who invocation, Prev: groups invocation, Up: User information 20.5 `users': Print login names of users currently logged in ============================================================ `users' prints on a single line a blank-separated list of user names of users currently logged in to the current host. Each user name corresponds to a login session, so if a user has more than one login session, that user's name will appear the same number of times in the output. Synopsis: users [FILE] With no FILE argument, `users' extracts its information from a system-maintained file (often `/var/run/utmp' or `/etc/utmp'). If a file argument is given, `users' uses that file instead. A common choice is `/var/log/wtmp'. The only options are `--help' and `--version'. *Note Common options::. An exit status of zero indicates success, and a nonzero value indicates failure.  File: coreutils.info, Node: who invocation, Prev: users invocation, Up: User information 20.6 `who': Print who is currently logged in ============================================ `who' prints information about users who are currently logged on. Synopsis: `who' [OPTION] [FILE] [am i] If given no non-option arguments, `who' prints the following information for each user currently logged on: login name, terminal line, login time, and remote hostname or X display. If given one non-option argument, `who' uses that instead of a default system-maintained file (often `/var/run/utmp' or `/etc/utmp') as the name of the file containing the record of users logged on. `/var/log/wtmp' is commonly given as an argument to `who' to look at who has previously logged on. If given two non-option arguments, `who' prints only the entry for the user running it (determined from its standard input), preceded by the hostname. Traditionally, the two arguments given are `am i', as in `who am i'. Time stamps are listed according to the time zone rules specified by the `TZ' environment variable, or by the system default rules if `TZ' is not set. *Note Specifying the Time Zone with `TZ': (libc)TZ Variable. The program accepts the following options. Also see *note Common options::. `-a' `--all' Same as `-b -d --login -p -r -t -T -u'. `-b' `--boot' Print the date and time of last system boot. `-d' `--dead' Print information corresponding to dead processes. `-H' `--heading' Print a line of column headings. `-l' `--login' List only the entries that correspond to processes via which the system is waiting for a user to login. The user name is always `LOGIN'. `--lookup' Attempt to canonicalize hostnames found in utmp through a DNS lookup. This is not the default because it can cause significant delays on systems with automatic dial-up internet access. `-m' Same as `who am i'. `-p' `--process' List active processes spawned by init. `-q' `--count' Print only the login names and the number of users logged on. Overrides all other options. `-r' `--runlevel' Print the current (and maybe previous) run-level of the init process. `-s' Ignored; for compatibility with other versions of `who'. `-t' `--time' Print last system clock change. `-u' After the login time, print the number of hours and minutes that the user has been idle. `.' means the user was active in the last minute. `old' means the user has been idle for more than 24 hours. `-w' `-T' `--mesg' `--message' `--writable' After each login name print a character indicating the user's message status: `+' allowing `write' messages `-' disallowing `write' messages `?' cannot find terminal device An exit status of zero indicates success, and a nonzero value indicates failure.  File: coreutils.info, Node: System context, Next: SELinux context, Prev: User information, Up: Top 21 System context ***************** This section describes commands that print or change system-wide information. * Menu: * date invocation:: Print or set system date and time. * arch invocation:: Print machine hardware name. * nproc invocation:: Print the number of processors. * uname invocation:: Print system information. * hostname invocation:: Print or set system name. * hostid invocation:: Print numeric host identifier. * uptime invocation:: Print system uptime and load.  File: coreutils.info, Node: date invocation, Next: arch invocation, Up: System context 21.1 `date': Print or set system date and time ============================================== Synopses: date [OPTION]... [+FORMAT] date [-u|--utc|--universal] [ MMDDhhmm[[CC]YY][.ss] ] Invoking `date' with no FORMAT argument is equivalent to invoking it with a default format that depends on the `LC_TIME' locale category. In the default C locale, this format is `'+%a %b %e %H:%M:%S %Z %Y'', so the output looks like `Thu Mar 3 13:47:51 PST 2005'. Normally, `date' uses the time zone rules indicated by the `TZ' environment variable, or the system default rules if `TZ' is not set. *Note Specifying the Time Zone with `TZ': (libc)TZ Variable. If given an argument that starts with a `+', `date' prints the current date and time (or the date and time specified by the `--date' option, see below) in the format defined by that argument, which is similar to that of the `strftime' function. Except for conversion specifiers, which start with `%', characters in the format string are printed unchanged. The conversion specifiers are described below. An exit status of zero indicates success, and a nonzero value indicates failure. * Menu: * Time conversion specifiers:: %[HIklMNpPrRsSTXzZ] * Date conversion specifiers:: %[aAbBcCdDeFgGhjmuUVwWxyY] * Literal conversion specifiers:: %[%nt] * Padding and other flags:: Pad with zeros, spaces, etc. * Setting the time:: Changing the system clock. * Options for date:: Instead of the current time. * Date input formats:: Specifying date strings. * Examples of date:: Examples.  File: coreutils.info, Node: Time conversion specifiers, Next: Date conversion specifiers, Up: date invocation 21.1.1 Time conversion specifiers --------------------------------- `date' conversion specifiers related to times. `%H' hour (`00'...`23') `%I' hour (`01'...`12') `%k' hour, space padded (` 0'...`23'); equivalent to `%_H'. This is a GNU extension. `%l' hour, space padded (` 1'...`12'); equivalent to `%_I'. This is a GNU extension. `%M' minute (`00'...`59') `%N' nanoseconds (`000000000'...`999999999'). This is a GNU extension. `%p' locale's equivalent of either `AM' or `PM'; blank in many locales. Noon is treated as `PM' and midnight as `AM'. `%P' like `%p', except lower case. This is a GNU extension. `%r' locale's 12-hour clock time (e.g., `11:11:04 PM') `%R' 24-hour hour and minute. Same as `%H:%M'. `%s' seconds since the epoch, i.e., since 1970-01-01 00:00:00 UTC. Leap seconds are not counted unless leap second support is available. *Note %s-examples::, for examples. This is a GNU extension. `%S' second (`00'...`60'). This may be `60' if leap seconds are supported. `%T' 24-hour hour, minute, and second. Same as `%H:%M:%S'. `%X' locale's time representation (e.g., `23:13:48') `%z' RFC 2822/ISO 8601 style numeric time zone (e.g., `-0600' or `+0530'), or nothing if no time zone is determinable. This value reflects the numeric time zone appropriate for the current time, using the time zone rules specified by the `TZ' environment variable. The time (and optionally, the time zone rules) can be overridden by the `--date' option. `%:z' RFC 3339/ISO 8601 style numeric time zone with `:' (e.g., `-06:00' or `+05:30'), or nothing if no time zone is determinable. This is a GNU extension. `%::z' Numeric time zone to the nearest second with `:' (e.g., `-06:00:00' or `+05:30:00'), or nothing if no time zone is determinable. This is a GNU extension. `%:::z' Numeric time zone with `:' using the minimum necessary precision (e.g., `-06', `+05:30', or `-04:56:02'), or nothing if no time zone is determinable. This is a GNU extension. `%Z' alphabetic time zone abbreviation (e.g., `EDT'), or nothing if no time zone is determinable. See `%z' for how it is determined.  File: coreutils.info, Node: Date conversion specifiers, Next: Literal conversion specifiers, Prev: Time conversion specifiers, Up: date invocation 21.1.2 Date conversion specifiers --------------------------------- `date' conversion specifiers related to dates. `%a' locale's abbreviated weekday name (e.g., `Sun') `%A' locale's full weekday name, variable length (e.g., `Sunday') `%b' locale's abbreviated month name (e.g., `Jan') `%B' locale's full month name, variable length (e.g., `January') `%c' locale's date and time (e.g., `Thu Mar 3 23:05:25 2005') `%C' century. This is like `%Y', except the last two digits are omitted. For example, it is `20' if `%Y' is `2000', and is `-0' if `%Y' is `-001'. It is normally at least two characters, but it may be more. `%d' day of month (e.g., `01') `%D' date; same as `%m/%d/%y' `%e' day of month, space padded; same as `%_d' `%F' full date in ISO 8601 format; same as `%Y-%m-%d'. This is a good choice for a date format, as it is standard and is easy to sort in the usual case where years are in the range 0000...9999. `%g' year corresponding to the ISO week number, but without the century (range `00' through `99'). This has the same format and value as `%y', except that if the ISO week number (see `%V') belongs to the previous or next year, that year is used instead. `%G' year corresponding to the ISO week number. This has the same format and value as `%Y', except that if the ISO week number (see `%V') belongs to the previous or next year, that year is used instead. It is normally useful only if `%V' is also used; for example, the format `%G-%m-%d' is probably a mistake, since it combines the ISO week number year with the conventional month and day. `%h' same as `%b' `%j' day of year (`001'...`366') `%m' month (`01'...`12') `%u' day of week (`1'...`7') with `1' corresponding to Monday `%U' week number of year, with Sunday as the first day of the week (`00'...`53'). Days in a new year preceding the first Sunday are in week zero. `%V' ISO week number, that is, the week number of year, with Monday as the first day of the week (`01'...`53'). If the week containing January 1 has four or more days in the new year, then it is considered week 1; otherwise, it is week 53 of the previous year, and the next week is week 1. (See the ISO 8601 standard.) `%w' day of week (`0'...`6') with 0 corresponding to Sunday `%W' week number of year, with Monday as first day of week (`00'...`53'). Days in a new year preceding the first Monday are in week zero. `%x' locale's date representation (e.g., `12/31/99') `%y' last two digits of year (`00'...`99') `%Y' year. This is normally at least four characters, but it may be more. Year `0000' precedes year `0001', and year `-001' precedes year `0000'.  File: coreutils.info, Node: Literal conversion specifiers, Next: Padding and other flags, Prev: Date conversion specifiers, Up: date invocation 21.1.3 Literal conversion specifiers ------------------------------------ `date' conversion specifiers that produce literal strings. `%%' a literal % `%n' a newline `%t' a horizontal tab  File: coreutils.info, Node: Padding and other flags, Next: Setting the time, Prev: Literal conversion specifiers, Up: date invocation 21.1.4 Padding and other flags ------------------------------ Unless otherwise specified, `date' normally pads numeric fields with zeros, so that, for example, numeric months are always output as two digits. Seconds since the epoch are not padded, though, since there is no natural width for them. As a GNU extension, `date' recognizes any of the following optional flags after the `%': `-' (hyphen) Do not pad the field; useful if the output is intended for human consumption. `_' (underscore) Pad with spaces; useful if you need a fixed number of characters in the output, but zeros are too distracting. `0' (zero) Pad with zeros even if the conversion specifier would normally pad with spaces. `^' Use upper case characters if possible. `#' Use opposite case characters if possible. A field that is normally upper case becomes lower case, and vice versa. Here are some examples of padding: date +%d/%m -d "Feb 1" => 01/02 date +%-d/%-m -d "Feb 1" => 1/2 date +%_d/%_m -d "Feb 1" => 1/ 2 As a GNU extension, you can specify the field width (after any flag, if present) as a decimal number. If the natural size of the output of the field has less than the specified number of characters, the result is written right adjusted and padded to the given size. For example, `%9B' prints the right adjusted month name in a field of width 9. An optional modifier can follow the optional flag and width specification. The modifiers are: `E' Use the locale's alternate representation for date and time. This modifier applies to the `%c', `%C', `%x', `%X', `%y' and `%Y' conversion specifiers. In a Japanese locale, for example, `%Ex' might yield a date format based on the Japanese Emperors' reigns. `O' Use the locale's alternate numeric symbols for numbers. This modifier applies only to numeric conversion specifiers. If the format supports the modifier but no alternate representation is available, it is ignored.  File: coreutils.info, Node: Setting the time, Next: Options for date, Prev: Padding and other flags, Up: date invocation 21.1.5 Setting the time ----------------------- If given an argument that does not start with `+', `date' sets the system clock to the date and time specified by that argument (as described below). You must have appropriate privileges to set the system clock. Note for changes to persist across a reboot, the hardware clock may need to be updated from the system clock, which might not happen automatically on your system. The argument must consist entirely of digits, which have the following meaning: `MM' month `DD' day within month `hh' hour `mm' minute `CC' first two digits of year (optional) `YY' last two digits of year (optional) `ss' second (optional) Note, the `--date' and `--set' options may not be used with an argument in the above format. The `--universal' option may be used with such an argument to indicate that the specified date and time are relative to Coordinated Universal Time rather than to the local time zone.  File: coreutils.info, Node: Options for date, Prev: Setting the time, Up: date invocation 21.1.6 Options for `date' ------------------------- The program accepts the following options. Also see *note Common options::. `-d DATESTR' `--date=DATESTR' Display the date and time specified in DATESTR instead of the current date and time. DATESTR can be in almost any common format. It can contain month names, time zones, `am' and `pm', `yesterday', etc. For example, `--date="2004-02-27 14:19:13.489392193 +0530"' specifies the instant of time that is 489,392,193 nanoseconds after February 27, 2004 at 2:19:13 PM in a time zone that is 5 hours and 30 minutes east of UTC. Note: input currently must be in locale independent format. E.g., the LC_TIME=C below is needed to print back the correct date in many locales: date -d "$(LC_TIME=C date)" *Note Date input formats::. `-f DATEFILE' `--file=DATEFILE' Parse each line in DATEFILE as with `-d' and display the resulting date and time. If DATEFILE is `-', use standard input. This is useful when you have many dates to process, because the system overhead of starting up the `date' executable many times can be considerable. `-I[TIMESPEC]' `--iso-8601[=TIMESPEC]' Display the date using the ISO 8601 format, `%Y-%m-%d'. The argument TIMESPEC specifies the number of additional terms of the time to include. It can be one of the following: `auto' Print just the date. This is the default if TIMESPEC is omitted. `hours' Append the hour of the day to the date. `minutes' Append the hours and minutes. `seconds' Append the hours, minutes and seconds. `ns' Append the hours, minutes, seconds and nanoseconds. If showing any time terms, then include the time zone using the format `%z'. `-r FILE' `--reference=FILE' Display the date and time of the last modification of FILE, instead of the current date and time. `-R' `--rfc-822' `--rfc-2822' Display the date and time using the format `%a, %d %b %Y %H:%M:%S %z', evaluated in the C locale so abbreviations are always in English. For example: Fri, 09 Sep 2005 13:51:39 -0700 This format conforms to Internet RFCs 2822 (ftp://ftp.rfc-editor.org/in-notes/rfc2822.txt) and 822 (ftp://ftp.rfc-editor.org/in-notes/rfc822.txt), the current and previous standards for Internet email. `--rfc-3339=TIMESPEC' Display the date using a format specified by Internet RFC 3339 (ftp://ftp.rfc-editor.org/in-notes/rfc3339.txt). This is a subset of the ISO 8601 format, except that it also permits applications to use a space rather than a `T' to separate dates from times. Unlike the other standard formats, RFC 3339 format is always suitable as input for the `--date' (`-d') and `--file' (`-f') options, regardless of the current locale. The argument TIMESPEC specifies how much of the time to include. It can be one of the following: `date' Print just the full-date, e.g., `2005-09-14'. This is equivalent to the format `%Y-%m-%d'. `seconds' Print the full-date and full-time separated by a space, e.g., `2005-09-14 00:56:06+05:30'. The output ends with a numeric time-offset; here the `+05:30' means that local time is five hours and thirty minutes east of UTC. This is equivalent to the format `%Y-%m-%d %H:%M:%S%:z'. `ns' Like `seconds', but also print nanoseconds, e.g., `2005-09-14 00:56:06.998458565+05:30'. This is equivalent to the format `%Y-%m-%d %H:%M:%S.%N%:z'. `-s DATESTR' `--set=DATESTR' Set the date and time to DATESTR. See `-d' above. See also *note Setting the time::. `-u' `--utc' `--universal' Use Coordinated Universal Time (UTC) by operating as if the `TZ' environment variable were set to the string `UTC0'. Coordinated Universal Time is often called "Greenwich Mean Time" (GMT) for historical reasons.  File: coreutils.info, Node: Examples of date, Up: date invocation 21.1.7 Examples of `date' ------------------------- Here are a few examples. Also see the documentation for the `-d' option in the previous section. * To print the date of the day before yesterday: date --date='2 days ago' * To print the date of the day three months and one day hence: date --date='3 months 1 day' * To print the day of year of Christmas in the current year: date --date='25 Dec' +%j * To print the current full month name and the day of the month: date '+%B %d' But this may not be what you want because for the first nine days of the month, the `%d' expands to a zero-padded two-digit field, for example `date -d 1may '+%B %d'' will print `May 01'. * To print a date without the leading zero for one-digit days of the month, you can use the (GNU extension) `-' flag to suppress the padding altogether: date -d 1may '+%B %-d * To print the current date and time in the format required by many non-GNU versions of `date' when setting the system clock: date +%m%d%H%M%Y.%S * To set the system clock forward by two minutes: date --set='+2 minutes' * To print the date in RFC 2822 format, use `date --rfc-2822'. Here is some example output: Fri, 09 Sep 2005 13:51:39 -0700 * To convert a date string to the number of seconds since the epoch (which is 1970-01-01 00:00:00 UTC), use the `--date' option with the `%s' format. That can be useful in sorting and/or graphing and/or comparing data by date. The following command outputs the number of the seconds since the epoch for the time two minutes after the epoch: date --date='1970-01-01 00:02:00 +0000' +%s 120 If you do not specify time zone information in the date string, `date' uses your computer's idea of the time zone when interpreting the string. For example, if your computer's time zone is that of Cambridge, Massachusetts, which was then 5 hours (i.e., 18,000 seconds) behind UTC: # local time zone used date --date='1970-01-01 00:02:00' +%s 18120 * If you're sorting or graphing dated data, your raw date values may be represented as seconds since the epoch. But few people can look at the date `946684800' and casually note "Oh, that's the first second of the year 2000 in Greenwich, England." date --date='2000-01-01 UTC' +%s 946684800 An alternative is to use the `--utc' (`-u') option. Then you may omit `UTC' from the date string. Although this produces the same result for `%s' and many other format sequences, with a time zone offset different from zero, it would give a different result for zone-dependent formats like `%z'. date -u --date=2000-01-01 +%s 946684800 To convert such an unwieldy number of seconds back to a more readable form, use a command like this: # local time zone used date -d '1970-01-01 UTC 946684800 seconds' +"%Y-%m-%d %T %z" 1999-12-31 19:00:00 -0500 Or if you do not mind depending on the `@' feature present since coreutils 5.3.0, you could shorten this to: date -d @946684800 +"%F %T %z" 1999-12-31 19:00:00 -0500 Often it is better to output UTC-relative date and time: date -u -d '1970-01-01 946684800 seconds' +"%Y-%m-%d %T %z" 2000-01-01 00:00:00 +0000  File: coreutils.info, Node: arch invocation, Next: nproc invocation, Prev: date invocation, Up: System context 21.2 `arch': Print machine hardware name ======================================== `arch' prints the machine hardware name, and is equivalent to `uname -m'. Synopsis: arch [OPTION] The program accepts the *note Common options:: only. An exit status of zero indicates success, and a nonzero value indicates failure.  File: coreutils.info, Node: nproc invocation, Next: uname invocation, Prev: arch invocation, Up: System context 21.3 `nproc': Print the number of available processors ====================================================== Print the number of processing units available to the current process, which may be less than the number of online processors. If this information is not accessible, then print the number of processors installed. If the `OMP_NUM_THREADS' environment variable is set, then it will determine the returned value. The result is guaranteed to be greater than zero. Synopsis: nproc [OPTION] The program accepts the following options. Also see *note Common options::. `--all' Print the number of installed processors on the system, which may be greater than the number online or available to the current process. The `OMP_NUM_THREADS' environment variable is not honored in this case. `--ignore=NUMBER' If possible, exclude this NUMBER of processing units. An exit status of zero indicates success, and a nonzero value indicates failure.  File: coreutils.info, Node: uname invocation, Next: hostname invocation, Prev: nproc invocation, Up: System context 21.4 `uname': Print system information ====================================== `uname' prints information about the machine and operating system it is run on. If no options are given, `uname' acts as if the `-s' option were given. Synopsis: uname [OPTION]... If multiple options or `-a' are given, the selected information is printed in this order: KERNEL-NAME NODENAME KERNEL-RELEASE KERNEL-VERSION MACHINE PROCESSOR HARDWARE-PLATFORM OPERATING-SYSTEM The information may contain internal spaces, so such output cannot be parsed reliably. In the following example, RELEASE is `2.2.18ss.e820-bda652a #4 SMP Tue Jun 5 11:24:08 PDT 2001': uname -a => Linux dum 2.2.18 #4 SMP Tue Jun 5 11:24:08 PDT 2001 i686 unknown unknown GNU/Linux The program accepts the following options. Also see *note Common options::. `-a' `--all' Print all of the below information, except omit the processor type and the hardware platform name if they are unknown. `-i' `--hardware-platform' Print the hardware platform name (sometimes called the hardware implementation). Print `unknown' if the kernel does not make this information easily available, as is the case with Linux kernels. `-m' `--machine' Print the machine hardware name (sometimes called the hardware class or hardware type). `-n' `--nodename' Print the network node hostname. `-p' `--processor' Print the processor type (sometimes called the instruction set architecture or ISA). Print `unknown' if the kernel does not make this information easily available, as is the case with Linux kernels. `-o' `--operating-system' Print the name of the operating system. `-r' `--kernel-release' Print the kernel release. `-s' `--kernel-name' Print the kernel name. POSIX 1003.1-2001 (*note Standards conformance::) calls this "the implementation of the operating system", because the POSIX specification itself has no notion of "kernel". The kernel name might be the same as the operating system name printed by the `-o' or `--operating-system' option, but it might differ. Some operating systems (e.g., FreeBSD, HP-UX) have the same name as their underlying kernels; others (e.g., GNU/Linux, Solaris) do not. `-v' `--kernel-version' Print the kernel version. An exit status of zero indicates success, and a nonzero value indicates failure.  File: coreutils.info, Node: hostname invocation, Next: hostid invocation, Prev: uname invocation, Up: System context 21.5 `hostname': Print or set system name ========================================= With no arguments, `hostname' prints the name of the current host system. With one argument, it sets the current host name to the specified string. You must have appropriate privileges to set the host name. Synopsis: hostname [NAME] The only options are `--help' and `--version'. *Note Common options::. An exit status of zero indicates success, and a nonzero value indicates failure.  File: coreutils.info, Node: hostid invocation, Next: uptime invocation, Prev: hostname invocation, Up: System context 21.6 `hostid': Print numeric host identifier ============================================ `hostid' prints the numeric identifier of the current host in hexadecimal. This command accepts no arguments. The only options are `--help' and `--version'. *Note Common options::. For example, here's what it prints on one system I use: $ hostid 1bac013d On that system, the 32-bit quantity happens to be closely related to the system's Internet address, but that isn't always the case. An exit status of zero indicates success, and a nonzero value indicates failure.  File: coreutils.info, Node: uptime invocation, Prev: hostid invocation, Up: System context 21.7 `uptime': Print system uptime and load =========================================== `uptime' prints the current time, the system's uptime, the number of logged-in users and the current load average. If an argument is specified, it is used as the file to be read to discover how many users are logged in. If no argument is specified, a system default is used (`uptime --help' indicates the default setting). The only options are `--help' and `--version'. *Note Common options::. For example, here's what it prints right now on one system I use: $ uptime 14:07 up 3:35, 3 users, load average: 1.39, 1.15, 1.04 The precise method of calculation of load average varies somewhat between systems. Some systems calculate it as the average number of runnable processes over the last 1, 5 and 15 minutes, but some systems also include processes in the uninterruptible sleep state (that is, those processes which are waiting for disk I/O). The Linux kernel includes uninterruptible processes.  File: coreutils.info, Node: SELinux context, Next: Modified command invocation, Prev: System context, Up: Top 22 SELinux context ****************** This section describes commands for operations with SELinux contexts. * Menu: * chcon invocation:: Change SELinux context of file * runcon invocation:: Run a command in specified SELinux context  File: coreutils.info, Node: chcon invocation, Next: runcon invocation, Up: SELinux context 22.1 `chcon': Change SELinux context of file ============================================ `chcon' changes the SELinux security context of the selected files. Synopses: chcon [OPTION]... CONTEXT FILE... chcon [OPTION]... [-u USER] [-r ROLE] [-l RANGE] [-t TYPE] FILE... chcon [OPTION]... --reference=RFILE FILE... Change the SELinux security context of each FILE to CONTEXT. With `--reference', change the security context of each FILE to that of RFILE. The program accepts the following options. Also see *note Common options::. `-h' `--no-dereference' Affect symbolic links instead of any referenced file. `--reference=RFILE' Use RFILE's security context rather than specifying a CONTEXT value. `-R' `--recursive' Operate on files and directories recursively. `-H' If `--recursive' (`-R') is specified and a command line argument is a symbolic link to a directory, traverse it. *Note Traversing symlinks::. `-L' In a recursive traversal, traverse every symbolic link to a directory that is encountered. *Note Traversing symlinks::. `-P' Do not traverse any symbolic links. This is the default if none of `-H', `-L', or `-P' is specified. *Note Traversing symlinks::. `-v' `--verbose' Output a diagnostic for every file processed. `-u USER' `--user=USER' Set user USER in the target security context. `-r ROLE' `--role=ROLE' Set role ROLE in the target security context. `-t TYPE' `--type=TYPE' Set type TYPE in the target security context. `-l RANGE' `--range=RANGE' Set range RANGE in the target security context. An exit status of zero indicates success, and a nonzero value indicates failure.  File: coreutils.info, Node: runcon invocation, Prev: chcon invocation, Up: SELinux context 22.2 `runcon': Run a command in specified SELinux context ========================================================= `runcon' runs file in specified SELinux security context. Synopses: runcon CONTEXT COMMAND [ARGS] runcon [ -c ] [-u USER] [-r ROLE] [-t TYPE] [-l RANGE] COMMAND [ARGS] Run COMMAND with completely-specified CONTEXT, or with current or transitioned security context modified by one or more of LEVEL, ROLE, TYPE and USER. If none of `-c', `-t', `-u', `-r', or `-l' is specified, the first argument is used as the complete context. Any additional arguments after COMMAND are interpreted as arguments to the command. With neither CONTEXT nor COMMAND, print the current security context. The program accepts the following options. Also see *note Common options::. `-c' `--compute' Compute process transition context before modifying. `-u USER' `--user=USER' Set user USER in the target security context. `-r ROLE' `--role=ROLE' Set role ROLE in the target security context. `-t TYPE' `--type=TYPE' Set type TYPE in the target security context. `-l RANGE' `--range=RANGE' Set range RANGE in the target security context. Exit status: 126 if COMMAND is found but cannot be invoked 127 if `runcon' itself fails or if COMMAND cannot be found the exit status of COMMAND otherwise  File: coreutils.info, Node: Modified command invocation, Next: Process control, Prev: SELinux context, Up: Top 23 Modified command invocation ****************************** This section describes commands that run other commands in some context different than the current one: a modified environment, as a different user, etc. * Menu: * chroot invocation:: Modify the root directory. * env invocation:: Modify environment variables. * nice invocation:: Modify niceness. * nohup invocation:: Immunize to hangups. * stdbuf invocation:: Modify buffering of standard streams. * su invocation:: Modify user and group ID. * timeout invocation:: Run with time limit.  File: coreutils.info, Node: chroot invocation, Next: env invocation, Up: Modified command invocation 23.1 `chroot': Run a command with a different root directory ============================================================ `chroot' runs a command with a specified root directory. On many systems, only the super-user can do this.(1) Synopses: chroot OPTION NEWROOT [COMMAND [ARGS]...] chroot OPTION Ordinarily, file names are looked up starting at the root of the directory structure, i.e., `/'. `chroot' changes the root to the directory NEWROOT (which must exist) and then runs COMMAND with optional ARGS. If COMMAND is not specified, the default is the value of the `SHELL' environment variable or `/bin/sh' if not set, invoked with the `-i' option. COMMAND must not be a special built-in utility (*note Special built-in utilities::). The program accepts the following options. Also see *note Common options::. Options must precede operands. `--userspec=USER[:GROUP]' By default, COMMAND is run with the same credentials as the invoking process. Use this option to run it as a different USER and/or with a different primary GROUP. `--groups=GROUPS' Use this option to specify the supplementary GROUPS to be used by the new process. The items in the list (names or numeric IDs) must be separated by commas. Here are a few tips to help avoid common problems in using chroot. To start with a simple example, make COMMAND refer to a statically linked binary. If you were to use a dynamically linked executable, then you'd have to arrange to have the shared libraries in the right place under your new root directory. For example, if you create a statically linked `ls' executable, and put it in `/tmp/empty', you can run this command as root: $ chroot /tmp/empty /ls -Rl / Then you'll see output like this: /: total 1023 -rwxr-xr-x 1 0 0 1041745 Aug 16 11:17 ls If you want to use a dynamically linked executable, say `bash', then first run `ldd bash' to see what shared objects it needs. Then, in addition to copying the actual binary, also copy the listed files to the required positions under your intended new root directory. Finally, if the executable requires any other files (e.g., data, state, device files), copy them into place, too. Exit status: 125 if `chroot' itself fails 126 if COMMAND is found but cannot be invoked 127 if COMMAND cannot be found the exit status of COMMAND otherwise ---------- Footnotes ---------- (1) However, some systems (e.g., FreeBSD) can be configured to allow certain regular users to use the `chroot' system call, and hence to run this program. Also, on Cygwin, anyone can run the `chroot' command, because the underlying function is non-privileged due to lack of support in MS-Windows.  File: coreutils.info, Node: env invocation, Next: nice invocation, Prev: chroot invocation, Up: Modified command invocation 23.2 `env': Run a command in a modified environment =================================================== `env' runs a command with a modified environment. Synopses: env [OPTION]... [NAME=VALUE]... [COMMAND [ARGS]...] env Operands of the form `VARIABLE=VALUE' set the environment variable VARIABLE to value VALUE. VALUE may be empty (`VARIABLE='). Setting a variable to an empty value is different from unsetting it. These operands are evaluated left-to-right, so if two operands mention the same variable the earlier is ignored. Environment variable names can be empty, and can contain any characters other than `=' and ASCII NUL. However, it is wise to limit yourself to names that consist solely of underscores, digits, and ASCII letters, and that begin with a non-digit, as applications like the shell do not work well with other names. The first operand that does not contain the character `=' specifies the program to invoke; it is searched for according to the `PATH' environment variable. Any remaining arguments are passed as arguments to that program. The program should not be a special built-in utility (*note Special built-in utilities::). Modifications to `PATH' take effect prior to searching for COMMAND. Use caution when reducing `PATH'; behavior is not portable when `PATH' is undefined or omits key directories such as `/bin'. In the rare case that a utility contains a `=' in the name, the only way to disambiguate it from a variable assignment is to use an intermediate command for COMMAND, and pass the problematic program name via ARGS. For example, if `./prog=' is an executable in the current `PATH': env prog= true # runs 'true', with prog= in environment env ./prog= true # runs 'true', with ./prog= in environment env -- prog= true # runs 'true', with prog= in environment env sh -c '\prog= true' # runs 'prog=' with argument 'true' env sh -c 'exec "$@"' sh prog= true # also runs 'prog=' If no command name is specified following the environment specifications, the resulting environment is printed. This is like specifying the `printenv' program. For some examples, suppose the environment passed to `env' contains `LOGNAME=rms', `EDITOR=emacs', and `PATH=.:/gnubin:/hacks': * Output the current environment. $ env | LC_ALL=C sort EDITOR=emacs LOGNAME=rms PATH=.:/gnubin:/hacks * Run `foo' with a reduced environment, preserving only the original `PATH' to avoid problems in locating `foo'. env - PATH="$PATH" foo * Run `foo' with the environment containing `LOGNAME=rms', `EDITOR=emacs', and `PATH=.:/gnubin:/hacks', and guarantees that `foo' was found in the file system rather than as a shell built-in. env foo * Run `nemacs' with the environment containing `LOGNAME=foo', `EDITOR=emacs', `PATH=.:/gnubin:/hacks', and `DISPLAY=gnu:0'. env DISPLAY=gnu:0 LOGNAME=foo nemacs * Attempt to run the program `/energy/--' (as that is the only possible path search result); if the command exists, the environment will contain `LOGNAME=rms' and `PATH=/energy', and the arguments will be `e=mc2', `bar', and `baz'. env -u EDITOR PATH=/energy -- e=mc2 bar baz The program accepts the following options. Also see *note Common options::. Options must precede operands. `-0' `--null' Output a zero byte (ASCII NUL) at the end of each line, rather than a newline. This option enables other programs to parse the output of `env' even when that output would contain data with embedded newlines. `-u NAME' `--unset=NAME' Remove variable NAME from the environment, if it was in the environment. `-' `-i' `--ignore-environment' Start with an empty environment, ignoring the inherited environment. Exit status: 0 if no COMMAND is specified and the environment is output 125 if `env' itself fails 126 if COMMAND is found but cannot be invoked 127 if COMMAND cannot be found the exit status of COMMAND otherwise  File: coreutils.info, Node: nice invocation, Next: nohup invocation, Prev: env invocation, Up: Modified command invocation 23.3 `nice': Run a command with modified niceness ================================================= `nice' prints or modifies a process's "niceness", a parameter that affects whether the process is scheduled favorably. Synopsis: nice [OPTION]... [COMMAND [ARG]...] If no arguments are given, `nice' prints the current niceness. Otherwise, `nice' runs the given COMMAND with its niceness adjusted. By default, its niceness is incremented by 10. Niceness values range at least from -20 (process has high priority and gets more resources, thus slowing down other processes) through 19 (process has lower priority and runs slowly itself, but has less impact on the speed of other running processes). Some systems may have a wider range of nicenesses; conversely, other systems may enforce more restrictive limits. An attempt to set the niceness outside the supported range is treated as an attempt to use the minimum or maximum supported value. A niceness should not be confused with a scheduling priority, which lets applications determine the order in which threads are scheduled to run. Unlike a priority, a niceness is merely advice to the scheduler, which the scheduler is free to ignore. Also, as a point of terminology, POSIX defines the behavior of `nice' in terms of a "nice value", which is the nonnegative difference between a niceness and the minimum niceness. Though `nice' conforms to POSIX, its documentation and diagnostics use the term "niceness" for compatibility with historical practice. COMMAND must not be a special built-in utility (*note Special built-in utilities::). Due to shell aliases and built-in `nice' functions, using an unadorned `nice' interactively or in a script may get you different functionality than that described here. Invoke it via `env' (i.e., `env nice ...') to avoid interference from the shell. The program accepts the following option. Also see *note Common options::. Options must precede operands. `-n ADJUSTMENT' `--adjustment=ADJUSTMENT' Add ADJUSTMENT instead of 10 to the command's niceness. If ADJUSTMENT is negative and you lack appropriate privileges, `nice' issues a warning but otherwise acts as if you specified a zero adjustment. For compatibility `nice' also supports an obsolete option syntax `-ADJUSTMENT'. New scripts should use `-n ADJUSTMENT' instead. Exit status: 0 if no COMMAND is specified and the niceness is output 125 if `nice' itself fails 126 if COMMAND is found but cannot be invoked 127 if COMMAND cannot be found the exit status of COMMAND otherwise It is sometimes useful to run a non-interactive program with reduced niceness. $ nice factor 4611686018427387903 Since `nice' prints the current niceness, you can invoke it through itself to demonstrate how it works. The default behavior is to increase the niceness by `10': $ nice 0 $ nice nice 10 $ nice -n 10 nice 10 The ADJUSTMENT is relative to the current niceness. In the next example, the first `nice' invocation runs the second one with niceness 10, and it in turn runs the final one with a niceness that is 3 more: $ nice nice -n 3 nice 13 Specifying a niceness larger than the supported range is the same as specifying the maximum supported value: $ nice -n 10000000000 nice 19 Only a privileged user may run a process with lower niceness: $ nice -n -1 nice nice: cannot set niceness: Permission denied 0 $ sudo nice -n -1 nice -1  File: coreutils.info, Node: nohup invocation, Next: stdbuf invocation, Prev: nice invocation, Up: Modified command invocation 23.4 `nohup': Run a command immune to hangups ============================================= `nohup' runs the given COMMAND with hangup signals ignored, so that the command can continue running in the background after you log out. Synopsis: nohup COMMAND [ARG]... If standard input is a terminal, it is redirected from `/dev/null' so that terminal sessions do not mistakenly consider the terminal to be used by the command. This is a GNU extension; programs intended to be portable to non-GNU hosts should use `nohup COMMAND [ARG]... make.log `nohup' does not automatically put the command it runs in the background; you must do that explicitly, by ending the command line with an `&'. Also, `nohup' does not alter the niceness of COMMAND; use `nice' for that, e.g., `nohup nice COMMAND'. COMMAND must not be a special built-in utility (*note Special built-in utilities::). The only options are `--help' and `--version'. *Note Common options::. Options must precede operands. Exit status: 125 if `nohup' itself fails, and `POSIXLY_CORRECT' is not set 126 if COMMAND is found but cannot be invoked 127 if COMMAND cannot be found the exit status of COMMAND otherwise If `POSIXLY_CORRECT' is set, internal failures give status 127 instead of 125.  File: coreutils.info, Node: stdbuf invocation, Next: su invocation, Prev: nohup invocation, Up: Modified command invocation 23.5 `stdbuf': Run a command with modified I/O stream buffering =============================================================== `stdbuf' allows one to modify the buffering operations of the three standard I/O streams associated with a program. Synopsis: stdbuf OPTION... COMMAND COMMAND must start with the name of a program that 1. uses the ISO C `FILE' streams for input/output (note the programs `dd' and `cat' don't do that), 2. does not adjust the buffering of its standard streams (note the program `tee' is not in this category). Any additional ARGs are passed as additional arguments to the COMMAND. The program accepts the following options. Also see *note Common options::. `-i MODE' `--input=MODE' Adjust the standard input stream buffering. `-o MODE' `--output=MODE' Adjust the standard output stream buffering. `-e MODE' `--error=MODE' Adjust the standard error stream buffering. The MODE can be specified as follows: `L' Set the stream to line buffered mode. In this mode data is coalesced until a newline is output or input is read from any stream attached to a terminal device. This option is invalid with standard input. `0' Disable buffering of the selected stream. In this mode, data is output immediately and only the amount of data requested is read from input. Note the difference in function for input and output. Disabling buffering for input will not influence the responsiveness or blocking behavior of the stream input functions. For example `fread' will still block until `EOF' or error, even if the underlying `read' returns less data than requested. `SIZE' Specify the size of the buffer to use in fully buffered mode. SIZE may be, or may be an integer optionally followed by, one of the following multiplicative suffixes: `KB' => 1000 (KiloBytes) `K' => 1024 (KibiBytes) `MB' => 1000*1000 (MegaBytes) `M' => 1024*1024 (MebiBytes) `GB' => 1000*1000*1000 (GigaBytes) `G' => 1024*1024*1024 (GibiBytes) and so on for `T', `P', `E', `Z', and `Y'. Exit status: 125 if `stdbuf' itself fails 126 if COMMAND is found but cannot be invoked 127 if COMMAND cannot be found the exit status of COMMAND otherwise  File: coreutils.info, Node: su invocation, Next: timeout invocation, Prev: stdbuf invocation, Up: Modified command invocation 23.6 `su': Run a command with substitute user and group ID ========================================================== `su' allows one user to temporarily become another user. It runs a command (often an interactive shell) with the real and effective user ID, group ID, and supplemental groups of a given USER. Synopsis: su [OPTION]... [USER [ARG]...] If no USER is given, the default is `root', the super-user. The shell to use is taken from USER's `passwd' entry, or `/bin/sh' if none is specified there. If USER has a password, `su' prompts for the password unless run by a user with effective user ID of zero (the super-user). By default, `su' does not change the current directory. It sets the environment variables `HOME' and `SHELL' from the password entry for USER, and if USER is not the super-user, sets `USER' and `LOGNAME' to USER. By default, the shell is not a login shell. Any additional ARGs are passed as additional arguments to the shell. GNU `su' does not treat `/bin/sh' or any other shells specially (e.g., by setting `argv[0]' to `-su', passing `-c' only to certain shells, etc.). `su' can optionally be compiled to use `syslog' to report failed, and optionally successful, `su' attempts. (If the system supports `syslog'.) However, GNU `su' does not check if the user is a member of the `wheel' group; see below. The program accepts the following options. Also see *note Common options::. `-c COMMAND' `--command=COMMAND' Pass COMMAND, a single command line to run, to the shell with a `-c' option instead of starting an interactive shell. `-f' `--fast' Pass the `-f' option to the shell. This probably only makes sense if the shell run is `csh' or `tcsh', for which the `-f' option prevents reading the startup file (`.cshrc'). With Bourne-like shells, the `-f' option disables file name pattern expansion (globbing), which is not likely to be useful. `-' `-l' `--login' Make the shell a login shell. This means the following. Unset all environment variables except `TERM', `HOME', and `SHELL' (which are set as described above), and `USER' and `LOGNAME' (which are set, even for the super-user, as described above), and set `PATH' to a compiled-in default value. Change to USER's home directory. Prepend `-' to the shell's name, intended to make it read its login startup file(s). `-m' `-p' `--preserve-environment' Do not change the environment variables `HOME', `USER', `LOGNAME', or `SHELL'. Run the shell given in the environment variable `SHELL' instead of the shell from USER's passwd entry, unless the user running `su' is not the super-user and USER's shell is restricted. A "restricted shell" is one that is not listed in the file `/etc/shells', or in a compiled-in list if that file does not exist. Parts of what this option does can be overridden by `--login' and `--shell'. `-s SHELL' `--shell=SHELL' Run SHELL instead of the shell from USER's passwd entry, unless the user running `su' is not the super-user and USER's shell is restricted (see `-m' just above). Exit status: 125 if `su' itself fails 126 if subshell is found but cannot be invoked 127 if subshell cannot be found the exit status of the subshell otherwise 23.6.1 Why GNU `su' does not support the `wheel' group ------------------------------------------------------ (This section is by Richard Stallman.) Sometimes a few of the users try to hold total power over all the rest. For example, in 1984, a few users at the MIT AI lab decided to seize power by changing the operator password on the Twenex system and keeping it secret from everyone else. (I was able to thwart this coup and give power back to the users by patching the kernel, but I wouldn't know how to do that in Unix.) However, occasionally the rulers do tell someone. Under the usual `su' mechanism, once someone learns the root password who sympathizes with the ordinary users, he or she can tell the rest. The "wheel group" feature would make this impossible, and thus cement the power of the rulers. I'm on the side of the masses, not that of the rulers. If you are used to supporting the bosses and sysadmins in whatever they do, you might find this idea strange at first.  File: coreutils.info, Node: timeout invocation, Prev: su invocation, Up: Modified command invocation 23.7 `timeout': Run a command with a time limit =============================================== `timeout' runs the given COMMAND and kills it if it is still running after the specified time interval. Synopsis: timeout [OPTION] DURATION COMMAND [ARG]... COMMAND must not be a special built-in utility (*note Special built-in utilities::). The program accepts the following options. Also see *note Common options::. Options must precede operands. `--foreground' Don't create a separate background program group, so that the managed COMMAND can use the foreground TTY normally. This is needed to support timing out commands not started directly from an interactive shell, in two situations. 1. COMMAND is interactive and needs to read from the terminal for example 2. the user wants to support sending signals directly to COMMAND from the terminal (like Ctrl-C for example) Note in this mode of operation, any children of COMMAND will not be timed out. `-k DURATION' `--kill-after=DURATION' Ensure the monitored COMMAND is killed by also sending a `KILL' signal, after the specified DURATION. Without this option, if the selected signal proves not to be fatal, `timeout' does not kill the COMMAND. `-s SIGNAL' `--signal=SIGNAL' Send this SIGNAL to COMMAND on timeout, rather than the default `TERM' signal. SIGNAL may be a name like `HUP' or a number. Also see *Note Signal specifications::. DURATION is a floating point number followed by an optional unit: `s' for seconds (the default) `m' for minutes `h' for hours `d' for days A duration of 0 disables the associated timeout. Note that the actual timeout duration is dependent on system conditions, which should be especially considered when specifying sub-second timeouts. Exit status: 124 if COMMAND times out 125 if `timeout' itself fails 126 if COMMAND is found but cannot be invoked 127 if COMMAND cannot be found 137 if COMMAND is sent the KILL(9) signal (128+9) the exit status of COMMAND otherwise  File: coreutils.info, Node: Process control, Next: Delaying, Prev: Modified command invocation, Up: Top 24 Process control ****************** * Menu: * kill invocation:: Sending a signal to processes.  File: coreutils.info, Node: kill invocation, Up: Process control 24.1 `kill': Send a signal to processes ======================================= The `kill' command sends a signal to processes, causing them to terminate or otherwise act upon receiving the signal in some way. Alternatively, it lists information about signals. Synopses: kill [-s SIGNAL | --signal SIGNAL | -SIGNAL] PID... kill [-l | --list | -t | --table] [SIGNAL]... Due to shell aliases and built-in `kill' functions, using an unadorned `kill' interactively or in a script may get you different functionality than that described here. Invoke it via `env' (i.e., `env kill ...') to avoid interference from the shell. The first form of the `kill' command sends a signal to all PID arguments. The default signal to send if none is specified is `TERM'. The special signal number `0' does not denote a valid signal, but can be used to test whether the PID arguments specify processes to which a signal could be sent. If PID is positive, the signal is sent to the process with the process ID PID. If PID is zero, the signal is sent to all processes in the process group of the current process. If PID is -1, the signal is sent to all processes for which the user has permission to send a signal. If PID is less than -1, the signal is sent to all processes in the process group that equals the absolute value of PID. If PID is not positive, a system-dependent set of system processes is excluded from the list of processes to which the signal is sent. If a negative PID argument is desired as the first one, it should be preceded by `--'. However, as a common extension to POSIX, `--' is not required with `kill -SIGNAL -PID'. The following commands are equivalent: kill -15 -1 kill -TERM -1 kill -s TERM -- -1 kill -- -1 The first form of the `kill' command succeeds if every PID argument specifies at least one process that the signal was sent to. The second form of the `kill' command lists signal information. Either the `-l' or `--list' option, or the `-t' or `--table' option must be specified. Without any SIGNAL argument, all supported signals are listed. The output of `-l' or `--list' is a list of the signal names, one per line; if SIGNAL is already a name, the signal number is printed instead. The output of `-t' or `--table' is a table of signal numbers, names, and descriptions. This form of the `kill' command succeeds if all SIGNAL arguments are valid and if there is no output error. The `kill' command also supports the `--help' and `--version' options. *Note Common options::. A SIGNAL may be a signal name like `HUP', or a signal number like `1', or an exit status of a process terminated by the signal. A signal name can be given in canonical form or prefixed by `SIG'. The case of the letters is ignored, except for the `-SIGNAL' option which must use upper case to avoid ambiguity with lower case option letters. For a list of supported signal names and numbers see *Note Signal specifications::.  File: coreutils.info, Node: Delaying, Next: Numeric operations, Prev: Process control, Up: Top 25 Delaying *********** * Menu: * sleep invocation:: Delay for a specified time.  File: coreutils.info, Node: sleep invocation, Up: Delaying 25.1 `sleep': Delay for a specified time ======================================== `sleep' pauses for an amount of time specified by the sum of the values of the command line arguments. Synopsis: sleep NUMBER[smhd]... Each argument is a number followed by an optional unit; the default is seconds. The units are: `s' seconds `m' minutes `h' hours `d' days Historical implementations of `sleep' have required that NUMBER be an integer, and only accepted a single argument without a suffix. However, GNU `sleep' accepts arbitrary floating point numbers. *Note Floating point::. The only options are `--help' and `--version'. *Note Common options::. Due to shell aliases and built-in `sleep' functions, using an unadorned `sleep' interactively or in a script may get you different functionality than that described here. Invoke it via `env' (i.e., `env sleep ...') to avoid interference from the shell. An exit status of zero indicates success, and a nonzero value indicates failure.  File: coreutils.info, Node: Numeric operations, Next: File permissions, Prev: Delaying, Up: Top 26 Numeric operations ********************* These programs do numerically-related operations. * Menu: * factor invocation:: Show factors of numbers. * seq invocation:: Print sequences of numbers.  File: coreutils.info, Node: factor invocation, Next: seq invocation, Up: Numeric operations 26.1 `factor': Print prime factors ================================== `factor' prints prime factors. Synopses: factor [NUMBER]... factor OPTION If no NUMBER is specified on the command line, `factor' reads numbers from standard input, delimited by newlines, tabs, or spaces. The `factor' command supports only a small number of options: `--help' Print a short help on standard output, then exit without further processing. `--version' Print the program version on standard output, then exit without further processing. Factoring the product of the eighth and ninth Mersenne primes takes about 30 milliseconds of CPU time on a 2.2 GHz Athlon. M8=$(echo 2^31-1|bc) M9=$(echo 2^61-1|bc) n=$(echo "$M8 * $M9" | bc) /usr/bin/time -f %U factor $n 4951760154835678088235319297: 2147483647 2305843009213693951 0.03 Similarly, factoring the eighth Fermat number 2^256+1 takes about 20 seconds on the same machine. Factoring large numbers is, in general, hard. The Pollard Rho algorithm used by `factor' is particularly effective for numbers with relatively small factors. If you wish to factor large numbers which do not have small factors (for example, numbers which are the product of two large primes), other methods are far better. If `factor' is built without using GNU MP, only single-precision arithmetic is available, and so large numbers (typically 2^64 and above) will not be supported. The single-precision code uses an algorithm which is designed for factoring smaller numbers. An exit status of zero indicates success, and a nonzero value indicates failure.  File: coreutils.info, Node: seq invocation, Prev: factor invocation, Up: Numeric operations 26.2 `seq': Print numeric sequences =================================== `seq' prints a sequence of numbers to standard output. Synopses: seq [OPTION]... LAST seq [OPTION]... FIRST LAST seq [OPTION]... FIRST INCREMENT LAST `seq' prints the numbers from FIRST to LAST by INCREMENT. By default, each number is printed on a separate line. When INCREMENT is not specified, it defaults to `1', even when FIRST is larger than LAST. FIRST also defaults to `1'. So `seq 1' prints `1', but `seq 0' and `seq 10 5' produce no output. Floating-point numbers may be specified. *Note Floating point::. The program accepts the following options. Also see *note Common options::. Options must precede operands. `-f FORMAT' `--format=FORMAT' Print all numbers using FORMAT. FORMAT must contain exactly one of the `printf'-style floating point conversion specifications `%a', `%e', `%f', `%g', `%A', `%E', `%F', `%G'. The `%' may be followed by zero or more flags taken from the set `-+#0 '', then an optional width containing one or more digits, then an optional precision consisting of a `.' followed by zero or more digits. FORMAT may also contain any number of `%%' conversion specifications. All conversion specifications have the same meaning as with `printf'. The default format is derived from FIRST, STEP, and LAST. If these all use a fixed point decimal representation, the default format is `%.Pf', where P is the minimum precision that can represent the output numbers exactly. Otherwise, the default format is `%g'. `-s STRING' `--separator=STRING' Separate numbers with STRING; default is a newline. The output always terminates with a newline. `-w' `--equal-width' Print all numbers with the same width, by padding with leading zeros. FIRST, STEP, and LAST should all use a fixed point decimal representation. (To have other kinds of padding, use `--format'). You can get finer-grained control over output with `-f': $ seq -f '(%9.2E)' -9e5 1.1e6 1.3e6 (-9.00E+05) ( 2.00E+05) ( 1.30E+06) If you want hexadecimal integer output, you can use `printf' to perform the conversion: $ printf '%x\n' $(seq 1048575 1024 1050623) fffff 1003ff 1007ff For very long lists of numbers, use xargs to avoid system limitations on the length of an argument list: $ seq 1000000 | xargs printf '%x\n' | tail -n 3 f423e f423f f4240 To generate octal output, use the printf `%o' format instead of `%x'. On most systems, seq can produce whole-number output for values up to at least 2^53. Larger integers are approximated. The details differ depending on your floating-point implementation. *Note Floating point::. A common case is that `seq' works with integers through 2^64, and larger integers may not be numerically correct: $ seq 18446744073709551616 1 18446744073709551618 18446744073709551616 18446744073709551616 18446744073709551618 Be careful when using `seq' with outlandish values: otherwise you may see surprising results, as `seq' uses floating point internally. For example, on the x86 platform, where the internal representation uses a 64-bit fraction, the command: seq 1 0.0000000000000000001 1.0000000000000000009 outputs 1.0000000000000000007 twice and skips 1.0000000000000000008. An exit status of zero indicates success, and a nonzero value indicates failure.  File: coreutils.info, Node: File permissions, Next: Date input formats, Prev: Numeric operations, Up: Top 27 File permissions ******************* Each file has a set of "file mode bits" that control the kinds of access that users have to that file. They can be represented either in symbolic form or as an octal number. * Menu: * Mode Structure:: Structure of file mode bits. * Symbolic Modes:: Mnemonic representation of file mode bits. * Numeric Modes:: File mode bits as octal numbers. * Operator Numeric Modes:: ANDing, ORing, and setting modes octally. * Directory Setuid and Setgid:: Set-user-ID and set-group-ID on directories.  File: coreutils.info, Node: Mode Structure, Next: Symbolic Modes, Up: File permissions 27.1 Structure of File Mode Bits ================================ The file mode bits have two parts: the "file permission bits", which control ordinary access to the file, and "special mode bits", which affect only some files. There are three kinds of permissions that a user can have for a file: 1. permission to read the file. For directories, this means permission to list the contents of the directory. 2. permission to write to (change) the file. For directories, this means permission to create and remove files in the directory. 3. permission to execute the file (run it as a program). For directories, this means permission to access files in the directory. There are three categories of users who may have different permissions to perform any of the above operations on a file: 1. the file's owner; 2. other users who are in the file's group; 3. everyone else. Files are given an owner and group when they are created. Usually the owner is the current user and the group is the group of the directory the file is in, but this varies with the operating system, the file system the file is created on, and the way the file is created. You can change the owner and group of a file by using the `chown' and `chgrp' commands. In addition to the three sets of three permissions listed above, the file mode bits have three special components, which affect only executable files (programs) and, on most systems, directories: 1. Set the process's effective user ID to that of the file upon execution (called the "set-user-ID bit", or sometimes the "setuid bit"). For directories on a few systems, give files created in the directory the same owner as the directory, no matter who creates them, and set the set-user-ID bit of newly-created subdirectories. 2. Set the process's effective group ID to that of the file upon execution (called the "set-group-ID bit", or sometimes the "setgid bit"). For directories on most systems, give files created in the directory the same group as the directory, no matter what group the user who creates them is in, and set the set-group-ID bit of newly-created subdirectories. 3. Prevent unprivileged users from removing or renaming a file in a directory unless they own the file or the directory; this is called the "restricted deletion flag" for the directory, and is commonly found on world-writable directories like `/tmp'. For regular files on some older systems, save the program's text image on the swap device so it will load more quickly when run; this is called the "sticky bit". In addition to the file mode bits listed above, there may be file attributes specific to the file system, e.g., access control lists (ACLs), whether a file is compressed, whether a file can be modified (immutability), and whether a file can be dumped. These are usually set using programs specific to the file system. For example: ext2 On GNU and GNU/Linux the file attributes specific to the ext2 file system are set using `chattr'. FFS On FreeBSD the file flags specific to the FFS file system are set using `chflags'. Even if a file's mode bits allow an operation on that file, that operation may still fail, because: * the file-system-specific attributes or flags do not permit it; or * the file system is mounted as read-only. For example, if the immutable attribute is set on a file, it cannot be modified, regardless of the fact that you may have just run `chmod a+w FILE'.  File: coreutils.info, Node: Symbolic Modes, Next: Numeric Modes, Prev: Mode Structure, Up: File permissions 27.2 Symbolic Modes =================== "Symbolic modes" represent changes to files' mode bits as operations on single-character symbols. They allow you to modify either all or selected parts of files' mode bits, optionally based on their previous values, and perhaps on the current `umask' as well (*note Umask and Protection::). The format of symbolic modes is: [ugoa...][+-=]PERMS...[,...] where PERMS is either zero or more letters from the set `rwxXst', or a single letter from the set `ugo'. The following sections describe the operators and other details of symbolic modes. * Menu: * Setting Permissions:: Basic operations on permissions. * Copying Permissions:: Copying existing permissions. * Changing Special Mode Bits:: Special mode bits. * Conditional Executability:: Conditionally affecting executability. * Multiple Changes:: Making multiple changes. * Umask and Protection:: The effect of the umask.  File: coreutils.info, Node: Setting Permissions, Next: Copying Permissions, Up: Symbolic Modes 27.2.1 Setting Permissions -------------------------- The basic symbolic operations on a file's permissions are adding, removing, and setting the permission that certain users have to read, write, and execute or search the file. These operations have the following format: USERS OPERATION PERMISSIONS The spaces between the three parts above are shown for readability only; symbolic modes cannot contain spaces. The USERS part tells which users' access to the file is changed. It consists of one or more of the following letters (or it can be empty; *note Umask and Protection::, for a description of what happens then). When more than one of these letters is given, the order that they are in does not matter. `u' the user who owns the file; `g' other users who are in the file's group; `o' all other users; `a' all users; the same as `ugo'. The OPERATION part tells how to change the affected users' access to the file, and is one of the following symbols: `+' to add the PERMISSIONS to whatever permissions the USERS already have for the file; `-' to remove the PERMISSIONS from whatever permissions the USERS already have for the file; `=' to make the PERMISSIONS the only permissions that the USERS have for the file. The PERMISSIONS part tells what kind of access to the file should be changed; it is normally zero or more of the following letters. As with the USERS part, the order does not matter when more than one letter is given. Omitting the PERMISSIONS part is useful only with the `=' operation, where it gives the specified USERS no access at all to the file. `r' the permission the USERS have to read the file; `w' the permission the USERS have to write to the file; `x' the permission the USERS have to execute the file, or search it if it is a directory. For example, to give everyone permission to read and write a regular file, but not to execute it, use: a=rw To remove write permission for all users other than the file's owner, use: go-w The above command does not affect the access that the owner of the file has to it, nor does it affect whether other users can read or execute the file. To give everyone except a file's owner no permission to do anything with that file, use the mode below. Other users could still remove the file, if they have write permission on the directory it is in. go= Another way to specify the same thing is: og-rwx  File: coreutils.info, Node: Copying Permissions, Next: Changing Special Mode Bits, Prev: Setting Permissions, Up: Symbolic Modes 27.2.2 Copying Existing Permissions ----------------------------------- You can base a file's permissions on its existing permissions. To do this, instead of using a series of `r', `w', or `x' letters after the operator, you use the letter `u', `g', or `o'. For example, the mode o+g adds the permissions for users who are in a file's group to the permissions that other users have for the file. Thus, if the file started out as mode 664 (`rw-rw-r--'), the above mode would change it to mode 666 (`rw-rw-rw-'). If the file had started out as mode 741 (`rwxr----x'), the above mode would change it to mode 745 (`rwxr--r-x'). The `-' and `=' operations work analogously.  File: coreutils.info, Node: Changing Special Mode Bits, Next: Conditional Executability, Prev: Copying Permissions, Up: Symbolic Modes 27.2.3 Changing Special Mode Bits --------------------------------- In addition to changing a file's read, write, and execute/search permissions, you can change its special mode bits. *Note Mode Structure::, for a summary of these special mode bits. To change the file mode bits to set the user ID on execution, use `u' in the USERS part of the symbolic mode and `s' in the PERMISSIONS part. To change the file mode bits to set the group ID on execution, use `g' in the USERS part of the symbolic mode and `s' in the PERMISSIONS part. To set both user and group ID on execution, omit the USERS part of the symbolic mode (or use `a') and use `s' in the PERMISSIONS part. To change the file mode bits to set the restricted deletion flag or sticky bit, omit the USERS part of the symbolic mode (or use `a') and use `t' in the PERMISSIONS part. For example, to set the set-user-ID mode bit of a program, you can use the mode: u+s To remove both set-user-ID and set-group-ID mode bits from it, you can use the mode: a-s To set the restricted deletion flag or sticky bit, you can use the mode: +t The combination `o+s' has no effect. On GNU systems the combinations `u+t' and `g+t' have no effect, and `o+t' acts like plain `+t'. The `=' operator is not very useful with special mode bits. For example, the mode: o=t does set the restricted deletion flag or sticky bit, but it also removes all read, write, and execute/search permissions that users not in the file's group might have had for it. *Note Directory Setuid and Setgid::, for additional rules concerning set-user-ID and set-group-ID bits and directories.  File: coreutils.info, Node: Conditional Executability, Next: Multiple Changes, Prev: Changing Special Mode Bits, Up: Symbolic Modes 27.2.4 Conditional Executability -------------------------------- There is one more special type of symbolic permission: if you use `X' instead of `x', execute/search permission is affected only if the file is a directory or already had execute permission. For example, this mode: a+X gives all users permission to search directories, or to execute files if anyone could execute them before.  File: coreutils.info, Node: Multiple Changes, Next: Umask and Protection, Prev: Conditional Executability, Up: Symbolic Modes 27.2.5 Making Multiple Changes ------------------------------ The format of symbolic modes is actually more complex than described above (*note Setting Permissions::). It provides two ways to make multiple changes to files' mode bits. The first way is to specify multiple OPERATION and PERMISSIONS parts after a USERS part in the symbolic mode. For example, the mode: og+rX-w gives users other than the owner of the file read permission and, if it is a directory or if someone already had execute permission to it, gives them execute/search permission; and it also denies them write permission to the file. It does not affect the permission that the owner of the file has for it. The above mode is equivalent to the two modes: og+rX og-w The second way to make multiple changes is to specify more than one simple symbolic mode, separated by commas. For example, the mode: a+r,go-w gives everyone permission to read the file and removes write permission on it for all users except its owner. Another example: u=rwx,g=rx,o= sets all of the permission bits for the file explicitly. (It gives users who are not in the file's group no permission at all for it.) The two methods can be combined. The mode: a+r,g+x-w gives all users permission to read the file, and gives users who are in the file's group permission to execute/search it as well, but not permission to write to it. The above mode could be written in several different ways; another is: u+r,g+rx,o+r,g-w  File: coreutils.info, Node: Umask and Protection, Prev: Multiple Changes, Up: Symbolic Modes 27.2.6 The Umask and Protection ------------------------------- If the USERS part of a symbolic mode is omitted, it defaults to `a' (affect all users), except that any permissions that are _set_ in the system variable `umask' are _not affected_. The value of `umask' can be set using the `umask' command. Its default value varies from system to system. Omitting the USERS part of a symbolic mode is generally not useful with operations other than `+'. It is useful with `+' because it allows you to use `umask' as an easily customizable protection against giving away more permission to files than you intended to. As an example, if `umask' has the value 2, which removes write permission for users who are not in the file's group, then the mode: +w adds permission to write to the file to its owner and to other users who are in the file's group, but _not_ to other users. In contrast, the mode: a+w ignores `umask', and _does_ give write permission for the file to all users.  File: coreutils.info, Node: Numeric Modes, Next: Operator Numeric Modes, Prev: Symbolic Modes, Up: File permissions 27.3 Numeric Modes ================== As an alternative to giving a symbolic mode, you can give an octal (base 8) number that represents the mode. This number is always interpreted in octal; you do not have to add a leading `0', as you do in C. Mode `0055' is the same as mode `55'. (However, modes of five digits or more, such as `00055', are sometimes special. *Note Directory Setuid and Setgid::.) A numeric mode is usually shorter than the corresponding symbolic mode, but it is limited in that normally it cannot take into account the previous file mode bits; it can only set them absolutely. The set-user-ID and set-group-ID bits of directories are an exception to this general limitation; *Note Directory Setuid and Setgid::. Also, operator numeric modes can take previous file mode bits into account; *Note Operator Numeric Modes::. The permissions granted to the user, to other users in the file's group, and to other users not in the file's group each require three bits, which are represented as one octal digit. The three special mode bits also require one bit each, and they are as a group represented as another octal digit. Here is how the bits are arranged, starting with the lowest valued bit: Value in Corresponding Mode Mode Bit Other users not in the file's group: 1 Execute/search 2 Write 4 Read Other users in the file's group: 10 Execute/search 20 Write 40 Read The file's owner: 100 Execute/search 200 Write 400 Read Special mode bits: 1000 Restricted deletion flag or sticky bit 2000 Set group ID on execution 4000 Set user ID on execution For example, numeric mode `4755' corresponds to symbolic mode `u=rwxs,go=rx', and numeric mode `664' corresponds to symbolic mode `ug=rw,o=r'. Numeric mode `0' corresponds to symbolic mode `a='.  File: coreutils.info, Node: Operator Numeric Modes, Next: Directory Setuid and Setgid, Prev: Numeric Modes, Up: File permissions 27.4 Operator Numeric Modes =========================== An operator numeric mode is a numeric mode that is prefixed by a `-', `+', or `=' operator, which has the same interpretation as in symbolic modes. For example, `+440' enables read permission for the file's owner and group, `-1' disables execute permission for other users, and `=600' clears all permissions except for enabling read-write permissions for the file's owner. Operator numeric modes can be combined with symbolic modes by separating them with a comma; for example, `=0,u+r' clears all permissions except for enabling read permission for the file's owner. The commands `chmod =755 DIR' and `chmod 755 DIR' differ in that the former clears the directory DIR's setuid and setgid bits, whereas the latter preserves them. *Note Directory Setuid and Setgid::. Operator numeric modes are a GNU extension.  File: coreutils.info, Node: Directory Setuid and Setgid, Prev: Operator Numeric Modes, Up: File permissions 27.5 Directories and the Set-User-ID and Set-Group-ID Bits ========================================================== On most systems, if a directory's set-group-ID bit is set, newly created subfiles inherit the same group as the directory, and newly created subdirectories inherit the set-group-ID bit of the parent directory. On a few systems, a directory's set-user-ID bit has a similar effect on the ownership of new subfiles and the set-user-ID bits of new subdirectories. These mechanisms let users share files more easily, by lessening the need to use `chmod' or `chown' to share new files. These convenience mechanisms rely on the set-user-ID and set-group-ID bits of directories. If commands like `chmod' and `mkdir' routinely cleared these bits on directories, the mechanisms would be less convenient and it would be harder to share files. Therefore, a command like `chmod' does not affect the set-user-ID or set-group-ID bits of a directory unless the user specifically mentions them in a symbolic mode, or uses an operator numeric mode such as `=755', or sets them in a numeric mode, or clears them in a numeric mode that has five or more octal digits. For example, on systems that support set-group-ID inheritance: # These commands leave the set-user-ID and # set-group-ID bits of the subdirectories alone, # so that they retain their default values. mkdir A B C chmod 755 A chmod 0755 B chmod u=rwx,go=rx C mkdir -m 755 D mkdir -m 0755 E mkdir -m u=rwx,go=rx F If you want to try to set these bits, you must mention them explicitly in the symbolic or numeric modes, e.g.: # These commands try to set the set-user-ID # and set-group-ID bits of the subdirectories. mkdir G chmod 6755 G chmod +6000 G chmod u=rwx,go=rx,a+s G mkdir -m 6755 H mkdir -m +6000 I mkdir -m u=rwx,go=rx,a+s J If you want to try to clear these bits, you must mention them explicitly in a symbolic mode, or use an operator numeric mode, or specify a numeric mode with five or more octal digits, e.g.: # These commands try to clear the set-user-ID # and set-group-ID bits of the directory D. chmod a-s D chmod -6000 D chmod =755 D chmod 00755 D This behavior is a GNU extension. Portable scripts should not rely on requests to set or clear these bits on directories, as POSIX allows implementations to ignore these requests. The GNU behavior with numeric modes of four or fewer digits is intended for scripts portable to systems that preserve these bits; the behavior with numeric modes of five or more digits is for scripts portable to systems that do not preserve the bits.  File: coreutils.info, Node: Date input formats, Next: Opening the software toolbox, Prev: File permissions, Up: Top 28 Date input formats ********************* First, a quote: Our units of temporal measurement, from seconds on up to months, are so complicated, asymmetrical and disjunctive so as to make coherent mental reckoning in time all but impossible. Indeed, had some tyrannical god contrived to enslave our minds to time, to make it all but impossible for us to escape subjection to sodden routines and unpleasant surprises, he could hardly have done better than handing down our present system. It is like a set of trapezoidal building blocks, with no vertical or horizontal surfaces, like a language in which the simplest thought demands ornate constructions, useless particles and lengthy circumlocutions. Unlike the more successful patterns of language and science, which enable us to face experience boldly or at least level-headedly, our system of temporal calculation silently and persistently encourages our terror of time. ... It is as though architects had to measure length in feet, width in meters and height in ells; as though basic instruction manuals demanded a knowledge of five different languages. It is no wonder then that we often look into our own immediate past or future, last Tuesday or a week from Sunday, with feelings of helpless confusion. ... -- Robert Grudin, `Time and the Art of Living'. This section describes the textual date representations that GNU programs accept. These are the strings you, as a user, can supply as arguments to the various programs. The C interface (via the `parse_datetime' function) is not described here. * Menu: * General date syntax:: Common rules. * Calendar date items:: 19 Dec 1994. * Time of day items:: 9:20pm. * Time zone items:: EST, PDT, GMT. * Combined date and time of day items:: 1972-09-24T20:02:00,000000-0500 * Day of week items:: Monday and others. * Relative items in date strings:: next tuesday, 2 years ago. * Pure numbers in date strings:: 19931219, 1440. * Seconds since the Epoch:: @1078100502. * Specifying time zone rules:: TZ="America/New_York", TZ="UTC0". * Authors of parse_datetime:: Bellovin, Eggert, Salz, Berets, et al.  File: coreutils.info, Node: General date syntax, Next: Calendar date items, Up: Date input formats 28.1 General date syntax ======================== A "date" is a string, possibly empty, containing many items separated by whitespace. The whitespace may be omitted when no ambiguity arises. The empty string means the beginning of today (i.e., midnight). Order of the items is immaterial. A date string may contain many flavors of items: * calendar date items * time of day items * time zone items * combined date and time of day items * day of the week items * relative items * pure numbers. We describe each of these item types in turn, below. A few ordinal numbers may be written out in words in some contexts. This is most useful for specifying day of the week items or relative items (see below). Among the most commonly used ordinal numbers, the word `last' stands for -1, `this' stands for 0, and `first' and `next' both stand for 1. Because the word `second' stands for the unit of time there is no way to write the ordinal number 2, but for convenience `third' stands for 3, `fourth' for 4, `fifth' for 5, `sixth' for 6, `seventh' for 7, `eighth' for 8, `ninth' for 9, `tenth' for 10, `eleventh' for 11 and `twelfth' for 12. When a month is written this way, it is still considered to be written numerically, instead of being "spelled in full"; this changes the allowed strings. In the current implementation, only English is supported for words and abbreviations like `AM', `DST', `EST', `first', `January', `Sunday', `tomorrow', and `year'. The output of the `date' command is not always acceptable as a date string, not only because of the language problem, but also because there is no standard meaning for time zone items like `IST'. When using `date' to generate a date string intended to be parsed later, specify a date format that is independent of language and that does not use time zone items other than `UTC' and `Z'. Here are some ways to do this: $ LC_ALL=C TZ=UTC0 date Mon Mar 1 00:21:42 UTC 2004 $ TZ=UTC0 date +'%Y-%m-%d %H:%M:%SZ' 2004-03-01 00:21:42Z $ date --rfc-3339=ns # --rfc-3339 is a GNU extension. 2004-02-29 16:21:42.692722128-08:00 $ date --rfc-2822 # a GNU extension Sun, 29 Feb 2004 16:21:42 -0800 $ date +'%Y-%m-%d %H:%M:%S %z' # %z is a GNU extension. 2004-02-29 16:21:42 -0800 $ date +'@%s.%N' # %s and %N are GNU extensions. @1078100502.692722128 Alphabetic case is completely ignored in dates. Comments may be introduced between round parentheses, as long as included parentheses are properly nested. Hyphens not followed by a digit are currently ignored. Leading zeros on numbers are ignored. Invalid dates like `2005-02-29' or times like `24:00' are rejected. In the typical case of a host that does not support leap seconds, a time like `23:59:60' is rejected even if it corresponds to a valid leap second.  File: coreutils.info, Node: Calendar date items, Next: Time of day items, Prev: General date syntax, Up: Date input formats 28.2 Calendar date items ======================== A "calendar date item" specifies a day of the year. It is specified differently, depending on whether the month is specified numerically or literally. All these strings specify the same calendar date: 1972-09-24 # ISO 8601. 72-9-24 # Assume 19xx for 69 through 99, # 20xx for 00 through 68. 72-09-24 # Leading zeros are ignored. 9/24/72 # Common U.S. writing. 24 September 1972 24 Sept 72 # September has a special abbreviation. 24 Sep 72 # Three-letter abbreviations always allowed. Sep 24, 1972 24-sep-72 24sep72 The year can also be omitted. In this case, the last specified year is used, or the current year if none. For example: 9/24 sep 24 Here are the rules. For numeric months, the ISO 8601 format `YEAR-MONTH-DAY' is allowed, where YEAR is any positive number, MONTH is a number between 01 and 12, and DAY is a number between 01 and 31. A leading zero must be present if a number is less than ten. If YEAR is 68 or smaller, then 2000 is added to it; otherwise, if YEAR is less than 100, then 1900 is added to it. The construct `MONTH/DAY/YEAR', popular in the United States, is accepted. Also `MONTH/DAY', omitting the year. Literal months may be spelled out in full: `January', `February', `March', `April', `May', `June', `July', `August', `September', `October', `November' or `December'. Literal months may be abbreviated to their first three letters, possibly followed by an abbreviating dot. It is also permitted to write `Sept' instead of `September'. When months are written literally, the calendar date may be given as any of the following: DAY MONTH YEAR DAY MONTH MONTH DAY YEAR DAY-MONTH-YEAR Or, omitting the year: MONTH DAY  File: coreutils.info, Node: Time of day items, Next: Time zone items, Prev: Calendar date items, Up: Date input formats 28.3 Time of day items ====================== A "time of day item" in date strings specifies the time on a given day. Here are some examples, all of which represent the same time: 20:02:00.000000 20:02 8:02pm 20:02-0500 # In EST (U.S. Eastern Standard Time). More generally, the time of day may be given as `HOUR:MINUTE:SECOND', where HOUR is a number between 0 and 23, MINUTE is a number between 0 and 59, and SECOND is a number between 0 and 59 possibly followed by `.' or `,' and a fraction containing one or more digits. Alternatively, `:SECOND' can be omitted, in which case it is taken to be zero. On the rare hosts that support leap seconds, SECOND may be 60. If the time is followed by `am' or `pm' (or `a.m.' or `p.m.'), HOUR is restricted to run from 1 to 12, and `:MINUTE' may be omitted (taken to be zero). `am' indicates the first half of the day, `pm' indicates the second half of the day. In this notation, 12 is the predecessor of 1: midnight is `12am' while noon is `12pm'. (This is the zero-oriented interpretation of `12am' and `12pm', as opposed to the old tradition derived from Latin which uses `12m' for noon and `12pm' for midnight.) The time may alternatively be followed by a time zone correction, expressed as `SHHMM', where S is `+' or `-', HH is a number of zone hours and MM is a number of zone minutes. The zone minutes term, MM, may be omitted, in which case the one- or two-digit correction is interpreted as a number of hours. You can also separate HH from MM with a colon. When a time zone correction is given this way, it forces interpretation of the time relative to Coordinated Universal Time (UTC), overriding any previous specification for the time zone or the local time zone. For example, `+0530' and `+05:30' both stand for the time zone 5.5 hours ahead of UTC (e.g., India). This is the best way to specify a time zone correction by fractional parts of an hour. The maximum zone correction is 24 hours. Either `am'/`pm' or a time zone correction may be specified, but not both.  File: coreutils.info, Node: Time zone items, Next: Combined date and time of day items, Prev: Time of day items, Up: Date input formats 28.4 Time zone items ==================== A "time zone item" specifies an international time zone, indicated by a small set of letters, e.g., `UTC' or `Z' for Coordinated Universal Time. Any included periods are ignored. By following a non-daylight-saving time zone by the string `DST' in a separate word (that is, separated by some white space), the corresponding daylight saving time zone may be specified. Alternatively, a non-daylight-saving time zone can be followed by a time zone correction, to add the two values. This is normally done only for `UTC'; for example, `UTC+05:30' is equivalent to `+05:30'. Time zone items other than `UTC' and `Z' are obsolescent and are not recommended, because they are ambiguous; for example, `EST' has a different meaning in Australia than in the United States. Instead, it's better to use unambiguous numeric time zone corrections like `-0500', as described in the previous section. If neither a time zone item nor a time zone correction is supplied, time stamps are interpreted using the rules of the default time zone (*note Specifying time zone rules::).  File: coreutils.info, Node: Combined date and time of day items, Next: Day of week items, Prev: Time zone items, Up: Date input formats 28.5 Combined date and time of day items ======================================== A "combined date and time of day item" specifies the time on a specific day of the year. This type is needed for formats that cannot be represented by individual calendar date (*note Calendar date items::) and time of day (*note Time of day items::) items due to ambiguity. # ISO 8601 extended date and time of day format 1972-09-24T20:02:00,000000-0500 The ISO 8601 extended date and time of day format is an ISO 8601 date, a `T' character separator, followed by an ISO 8601 time of day.  File: coreutils.info, Node: Day of week items, Next: Relative items in date strings, Prev: Combined date and time of day items, Up: Date input formats 28.6 Day of week items ====================== The explicit mention of a day of the week will forward the date (only if necessary) to reach that day of the week in the future. Days of the week may be spelled out in full: `Sunday', `Monday', `Tuesday', `Wednesday', `Thursday', `Friday' or `Saturday'. Days may be abbreviated to their first three letters, optionally followed by a period. The special abbreviations `Tues' for `Tuesday', `Wednes' for `Wednesday' and `Thur' or `Thurs' for `Thursday' are also allowed. A number may precede a day of the week item to move forward supplementary weeks. It is best used in expression like `third monday'. In this context, `last DAY' or `next DAY' is also acceptable; they move one week before or after the day that DAY by itself would represent. A comma following a day of the week item is ignored.  File: coreutils.info, Node: Relative items in date strings, Next: Pure numbers in date strings, Prev: Day of week items, Up: Date input formats 28.7 Relative items in date strings =================================== "Relative items" adjust a date (or the current date if none) forward or backward. The effects of relative items accumulate. Here are some examples: 1 year 1 year ago 3 years 2 days The unit of time displacement may be selected by the string `year' or `month' for moving by whole years or months. These are fuzzy units, as years and months are not all of equal duration. More precise units are `fortnight' which is worth 14 days, `week' worth 7 days, `day' worth 24 hours, `hour' worth 60 minutes, `minute' or `min' worth 60 seconds, and `second' or `sec' worth one second. An `s' suffix on these units is accepted and ignored. The unit of time may be preceded by a multiplier, given as an optionally signed number. Unsigned numbers are taken as positively signed. No number at all implies 1 for a multiplier. Following a relative item by the string `ago' is equivalent to preceding the unit by a multiplier with value -1. The string `tomorrow' is worth one day in the future (equivalent to `day'), the string `yesterday' is worth one day in the past (equivalent to `day ago'). The strings `now' or `today' are relative items corresponding to zero-valued time displacement, these strings come from the fact a zero-valued time displacement represents the current time when not otherwise changed by previous items. They may be used to stress other items, like in `12:00 today'. The string `this' also has the meaning of a zero-valued time displacement, but is preferred in date strings like `this thursday'. When a relative item causes the resulting date to cross a boundary where the clocks were adjusted, typically for daylight saving time, the resulting date and time are adjusted accordingly. The fuzz in units can cause problems with relative items. For example, `2003-07-31 -1 month' might evaluate to 2003-07-01, because 2003-06-31 is an invalid date. To determine the previous month more reliably, you can ask for the month before the 15th of the current month. For example: $ date -R Thu, 31 Jul 2003 13:02:39 -0700 $ date --date='-1 month' +'Last month was %B?' Last month was July? $ date --date="$(date +%Y-%m-15) -1 month" +'Last month was %B!' Last month was June! Also, take care when manipulating dates around clock changes such as daylight saving leaps. In a few cases these have added or subtracted as much as 24 hours from the clock, so it is often wise to adopt universal time by setting the `TZ' environment variable to `UTC0' before embarking on calendrical calculations.  File: coreutils.info, Node: Pure numbers in date strings, Next: Seconds since the Epoch, Prev: Relative items in date strings, Up: Date input formats 28.8 Pure numbers in date strings ================================= The precise interpretation of a pure decimal number depends on the context in the date string. If the decimal number is of the form YYYYMMDD and no other calendar date item (*note Calendar date items::) appears before it in the date string, then YYYY is read as the year, MM as the month number and DD as the day of the month, for the specified calendar date. If the decimal number is of the form HHMM and no other time of day item appears before it in the date string, then HH is read as the hour of the day and MM as the minute of the hour, for the specified time of day. MM can also be omitted. If both a calendar date and a time of day appear to the left of a number in the date string, but no relative item, then the number overrides the year.  File: coreutils.info, Node: Seconds since the Epoch, Next: Specifying time zone rules, Prev: Pure numbers in date strings, Up: Date input formats 28.9 Seconds since the Epoch ============================ If you precede a number with `@', it represents an internal time stamp as a count of seconds. The number can contain an internal decimal point (either `.' or `,'); any excess precision not supported by the internal representation is truncated toward minus infinity. Such a number cannot be combined with any other date item, as it specifies a complete time stamp. Internally, computer times are represented as a count of seconds since an epoch--a well-defined point of time. On GNU and POSIX systems, the epoch is 1970-01-01 00:00:00 UTC, so `@0' represents this time, `@1' represents 1970-01-01 00:00:01 UTC, and so forth. GNU and most other POSIX-compliant systems support such times as an extension to POSIX, using negative counts, so that `@-1' represents 1969-12-31 23:59:59 UTC. Traditional Unix systems count seconds with 32-bit two's-complement integers and can represent times from 1901-12-13 20:45:52 through 2038-01-19 03:14:07 UTC. More modern systems use 64-bit counts of seconds with nanosecond subcounts, and can represent all the times in the known lifetime of the universe to a resolution of 1 nanosecond. On most hosts, these counts ignore the presence of leap seconds. For example, on most hosts `@915148799' represents 1998-12-31 23:59:59 UTC, `@915148800' represents 1999-01-01 00:00:00 UTC, and there is no way to represent the intervening leap second 1998-12-31 23:59:60 UTC.  File: coreutils.info, Node: Specifying time zone rules, Next: Authors of parse_datetime, Prev: Seconds since the Epoch, Up: Date input formats 28.10 Specifying time zone rules ================================ Normally, dates are interpreted using the rules of the current time zone, which in turn are specified by the `TZ' environment variable, or by a system default if `TZ' is not set. To specify a different set of default time zone rules that apply just to one date, start the date with a string of the form `TZ="RULE"'. The two quote characters (`"') must be present in the date, and any quotes or backslashes within RULE must be escaped by a backslash. For example, with the GNU `date' command you can answer the question "What time is it in New York when a Paris clock shows 6:30am on October 31, 2004?" by using a date beginning with `TZ="Europe/Paris"' as shown in the following shell transcript: $ export TZ="America/New_York" $ date --date='TZ="Europe/Paris" 2004-10-31 06:30' Sun Oct 31 01:30:00 EDT 2004 In this example, the `--date' operand begins with its own `TZ' setting, so the rest of that operand is processed according to `Europe/Paris' rules, treating the string `2004-10-31 06:30' as if it were in Paris. However, since the output of the `date' command is processed according to the overall time zone rules, it uses New York time. (Paris was normally six hours ahead of New York in 2004, but this example refers to a brief Halloween period when the gap was five hours.) A `TZ' value is a rule that typically names a location in the `tz' database (http://www.twinsun.com/tz/tz-link.htm). A recent catalog of location names appears in the TWiki Date and Time Gateway (http://twiki.org/cgi-bin/xtra/tzdate). A few non-GNU hosts require a colon before a location name in a `TZ' setting, e.g., `TZ=":America/New_York"'. The `tz' database includes a wide variety of locations ranging from `Arctic/Longyearbyen' to `Antarctica/South_Pole', but if you are at sea and have your own private time zone, or if you are using a non-GNU host that does not support the `tz' database, you may need to use a POSIX rule instead. Simple POSIX rules like `UTC0' specify a time zone without daylight saving time; other rules can specify simple daylight saving regimes. *Note Specifying the Time Zone with `TZ': (libc)TZ Variable.  File: coreutils.info, Node: Authors of parse_datetime, Prev: Specifying time zone rules, Up: Date input formats 28.11 Authors of `parse_datetime' ================================= `parse_datetime' started life as `getdate', as originally implemented by Steven M. Bellovin () while at the University of North Carolina at Chapel Hill. The code was later tweaked by a couple of people on Usenet, then completely overhauled by Rich $alz () and Jim Berets () in August, 1990. Various revisions for the GNU system were made by David MacKenzie, Jim Meyering, Paul Eggert and others, including renaming it to `get_date' to avoid a conflict with the alternative Posix function `getdate', and a later rename to `parse_datetime'. The Posix function `getdate' can parse more locale-specific dates using `strptime', but relies on an environment variable and external file, and lacks the thread-safety of `parse_datetime'. This chapter was originally produced by Franc,ois Pinard () from the `parse_datetime.y' source code, and then edited by K. Berry ().  File: coreutils.info, Node: Opening the software toolbox, Next: GNU Free Documentation License, Prev: Date input formats, Up: Top 29 Opening the Software Toolbox ******************************* An earlier version of this chapter appeared in the `What's GNU?' column of the June 1994 `Linux Journal' (http://www.linuxjournal.com/article.php?sid=2762). It was written by Arnold Robbins. * Menu: * Toolbox introduction:: Toolbox introduction * I/O redirection:: I/O redirection * The who command:: The `who' command * The cut command:: The `cut' command * The sort command:: The `sort' command * The uniq command:: The `uniq' command * Putting the tools together:: Putting the tools together  File: coreutils.info, Node: Toolbox introduction, Next: I/O redirection, Up: Opening the software toolbox Toolbox Introduction ==================== This month's column is only peripherally related to the GNU Project, in that it describes a number of the GNU tools on your GNU/Linux system and how they might be used. What it's really about is the "Software Tools" philosophy of program development and usage. The software tools philosophy was an important and integral concept in the initial design and development of Unix (of which Linux and GNU are essentially clones). Unfortunately, in the modern day press of Internetworking and flashy GUIs, it seems to have fallen by the wayside. This is a shame, since it provides a powerful mental model for solving many kinds of problems. Many people carry a Swiss Army knife around in their pants pockets (or purse). A Swiss Army knife is a handy tool to have: it has several knife blades, a screwdriver, tweezers, toothpick, nail file, corkscrew, and perhaps a number of other things on it. For the everyday, small miscellaneous jobs where you need a simple, general purpose tool, it's just the thing. On the other hand, an experienced carpenter doesn't build a house using a Swiss Army knife. Instead, he has a toolbox chock full of specialized tools--a saw, a hammer, a screwdriver, a plane, and so on. And he knows exactly when and where to use each tool; you won't catch him hammering nails with the handle of his screwdriver. The Unix developers at Bell Labs were all professional programmers and trained computer scientists. They had found that while a one-size-fits-all program might appeal to a user because there's only one program to use, in practice such programs are a. difficult to write, b. difficult to maintain and debug, and c. difficult to extend to meet new situations. Instead, they felt that programs should be specialized tools. In short, each program "should do one thing well." No more and no less. Such programs are simpler to design, write, and get right--they only do one thing. Furthermore, they found that with the right machinery for hooking programs together, that the whole was greater than the sum of the parts. By combining several special purpose programs, you could accomplish a specific task that none of the programs was designed for, and accomplish it much more quickly and easily than if you had to write a special purpose program. We will see some (classic) examples of this further on in the column. (An important additional point was that, if necessary, take a detour and build any software tools you may need first, if you don't already have something appropriate in the toolbox.)  File: coreutils.info, Node: I/O redirection, Next: The who command, Prev: Toolbox introduction, Up: Opening the software toolbox I/O Redirection =============== Hopefully, you are familiar with the basics of I/O redirection in the shell, in particular the concepts of "standard input," "standard output," and "standard error". Briefly, "standard input" is a data source, where data comes from. A program should not need to either know or care if the data source is a disk file, a keyboard, a magnetic tape, or even a punched card reader. Similarly, "standard output" is a data sink, where data goes to. The program should neither know nor care where this might be. Programs that only read their standard input, do something to the data, and then send it on, are called "filters", by analogy to filters in a water pipeline. With the Unix shell, it's very easy to set up data pipelines: program_to_create_data | filter1 | ... | filterN > final.pretty.data We start out by creating the raw data; each filter applies some successive transformation to the data, until by the time it comes out of the pipeline, it is in the desired form. This is fine and good for standard input and standard output. Where does the standard error come in to play? Well, think about `filter1' in the pipeline above. What happens if it encounters an error in the data it sees? If it writes an error message to standard output, it will just disappear down the pipeline into `filter2''s input, and the user will probably never see it. So programs need a place where they can send error messages so that the user will notice them. This is standard error, and it is usually connected to your console or window, even if you have redirected standard output of your program away from your screen. For filter programs to work together, the format of the data has to be agreed upon. The most straightforward and easiest format to use is simply lines of text. Unix data files are generally just streams of bytes, with lines delimited by the ASCII LF (Line Feed) character, conventionally called a "newline" in the Unix literature. (This is `'\n'' if you're a C programmer.) This is the format used by all the traditional filtering programs. (Many earlier operating systems had elaborate facilities and special purpose programs for managing binary data. Unix has always shied away from such things, under the philosophy that it's easiest to simply be able to view and edit your data with a text editor.) OK, enough introduction. Let's take a look at some of the tools, and then we'll see how to hook them together in interesting ways. In the following discussion, we will only present those command line options that interest us. As you should always do, double check your system documentation for the full story.  File: coreutils.info, Node: The who command, Next: The cut command, Prev: I/O redirection, Up: Opening the software toolbox The `who' Command ================= The first program is the `who' command. By itself, it generates a list of the users who are currently logged in. Although I'm writing this on a single-user system, we'll pretend that several people are logged in: $ who -| arnold console Jan 22 19:57 -| miriam ttyp0 Jan 23 14:19(:0.0) -| bill ttyp1 Jan 21 09:32(:0.0) -| arnold ttyp2 Jan 23 20:48(:0.0) Here, the `$' is the usual shell prompt, at which I typed `who'. There are three people logged in, and I am logged in twice. On traditional Unix systems, user names are never more than eight characters long. This little bit of trivia will be useful later. The output of `who' is nice, but the data is not all that exciting.  File: coreutils.info, Node: The cut command, Next: The sort command, Prev: The who command, Up: Opening the software toolbox The `cut' Command ================= The next program we'll look at is the `cut' command. This program cuts out columns or fields of input data. For example, we can tell it to print just the login name and full name from the `/etc/passwd' file. The `/etc/passwd' file has seven fields, separated by colons: arnold:xyzzy:2076:10:Arnold D. Robbins:/home/arnold:/bin/bash To get the first and fifth fields, we would use `cut' like this: $ cut -d: -f1,5 /etc/passwd -| root:Operator ... -| arnold:Arnold D. Robbins -| miriam:Miriam A. Robbins ... With the `-c' option, `cut' will cut out specific characters (i.e., columns) in the input lines. This is useful for input data that has fixed width fields, and does not have a field separator. For example, list the Monday dates for the current month: $ cal | cut -c 3-5 -|Mo -| -| 6 -| 13 -| 20 -| 27  File: coreutils.info, Node: The sort command, Next: The uniq command, Prev: The cut command, Up: Opening the software toolbox The `sort' Command ================== Next we'll look at the `sort' command. This is one of the most powerful commands on a Unix-style system; one that you will often find yourself using when setting up fancy data plumbing. The `sort' command reads and sorts each file named on the command line. It then merges the sorted data and writes it to standard output. It will read standard input if no files are given on the command line (thus making it into a filter). The sort is based on the character collating sequence or based on user-supplied ordering criteria.  File: coreutils.info, Node: The uniq command, Next: Putting the tools together, Prev: The sort command, Up: Opening the software toolbox The `uniq' Command ================== Finally (at least for now), we'll look at the `uniq' program. When sorting data, you will often end up with duplicate lines, lines that are identical. Usually, all you need is one instance of each line. This is where `uniq' comes in. The `uniq' program reads its standard input. It prints only one copy of each repeated line. It does have several options. Later on, we'll use the `-c' option, which prints each unique line, preceded by a count of the number of times that line occurred in the input.  File: coreutils.info, Node: Putting the tools together, Prev: The uniq command, Up: Opening the software toolbox Putting the Tools Together ========================== Now, let's suppose this is a large ISP server system with dozens of users logged in. The management wants the system administrator to write a program that will generate a sorted list of logged in users. Furthermore, even if a user is logged in multiple times, his or her name should only show up in the output once. The administrator could sit down with the system documentation and write a C program that did this. It would take perhaps a couple of hundred lines of code and about two hours to write it, test it, and debug it. However, knowing the software toolbox, the administrator can instead start out by generating just a list of logged on users: $ who | cut -c1-8 -| arnold -| miriam -| bill -| arnold Next, sort the list: $ who | cut -c1-8 | sort -| arnold -| arnold -| bill -| miriam Finally, run the sorted list through `uniq', to weed out duplicates: $ who | cut -c1-8 | sort | uniq -| arnold -| bill -| miriam The `sort' command actually has a `-u' option that does what `uniq' does. However, `uniq' has other uses for which one cannot substitute `sort -u'. The administrator puts this pipeline into a shell script, and makes it available for all the users on the system (`#' is the system administrator, or `root', prompt): # cat > /usr/local/bin/listusers who | cut -c1-8 | sort | uniq ^D # chmod +x /usr/local/bin/listusers There are four major points to note here. First, with just four programs, on one command line, the administrator was able to save about two hours worth of work. Furthermore, the shell pipeline is just about as efficient as the C program would be, and it is much more efficient in terms of programmer time. People time is much more expensive than computer time, and in our modern "there's never enough time to do everything" society, saving two hours of programmer time is no mean feat. Second, it is also important to emphasize that with the _combination_ of the tools, it is possible to do a special purpose job never imagined by the authors of the individual programs. Third, it is also valuable to build up your pipeline in stages, as we did here. This allows you to view the data at each stage in the pipeline, which helps you acquire the confidence that you are indeed using these tools correctly. Finally, by bundling the pipeline in a shell script, other users can use your command, without having to remember the fancy plumbing you set up for them. In terms of how you run them, shell scripts and compiled programs are indistinguishable. After the previous warm-up exercise, we'll look at two additional, more complicated pipelines. For them, we need to introduce two more tools. The first is the `tr' command, which stands for "transliterate." The `tr' command works on a character-by-character basis, changing characters. Normally it is used for things like mapping upper case to lower case: $ echo ThIs ExAmPlE HaS MIXED case! | tr '[:upper:]' '[:lower:]' -| this example has mixed case! There are several options of interest: `-c' work on the complement of the listed characters, i.e., operations apply to characters not in the given set `-d' delete characters in the first set from the output `-s' squeeze repeated characters in the output into just one character. We will be using all three options in a moment. The other command we'll look at is `comm'. The `comm' command takes two sorted input files as input data, and prints out the files' lines in three columns. The output columns are the data lines unique to the first file, the data lines unique to the second file, and the data lines that are common to both. The `-1', `-2', and `-3' command line options _omit_ the respective columns. (This is non-intuitive and takes a little getting used to.) For example: $ cat f1 -| 11111 -| 22222 -| 33333 -| 44444 $ cat f2 -| 00000 -| 22222 -| 33333 -| 55555 $ comm f1 f2 -| 00000 -| 11111 -| 22222 -| 33333 -| 44444 -| 55555 The file name `-' tells `comm' to read standard input instead of a regular file. Now we're ready to build a fancy pipeline. The first application is a word frequency counter. This helps an author determine if he or she is over-using certain words. The first step is to change the case of all the letters in our input file to one case. "The" and "the" are the same word when doing counting. $ tr '[:upper:]' '[:lower:]' < whats.gnu | ... The next step is to get rid of punctuation. Quoted words and unquoted words should be treated identically; it's easiest to just get the punctuation out of the way. $ tr '[:upper:]' '[:lower:]' < whats.gnu | tr -cd '[:alnum:]_ \n' | ... The second `tr' command operates on the complement of the listed characters, which are all the letters, the digits, the underscore, and the blank. The `\n' represents the newline character; it has to be left alone. (The ASCII tab character should also be included for good measure in a production script.) At this point, we have data consisting of words separated by blank space. The words only contain alphanumeric characters (and the underscore). The next step is break the data apart so that we have one word per line. This makes the counting operation much easier, as we will see shortly. $ tr '[:upper:]' '[:lower:]' < whats.gnu | tr -cd '[:alnum:]_ \n' | > tr -s ' ' '\n' | ... This command turns blanks into newlines. The `-s' option squeezes multiple newline characters in the output into just one. This helps us avoid blank lines. (The `>' is the shell's "secondary prompt." This is what the shell prints when it notices you haven't finished typing in all of a command.) We now have data consisting of one word per line, no punctuation, all one case. We're ready to count each word: $ tr '[:upper:]' '[:lower:]' < whats.gnu | tr -cd '[:alnum:]_ \n' | > tr -s ' ' '\n' | sort | uniq -c | ... At this point, the data might look something like this: 60 a 2 able 6 about 1 above 2 accomplish 1 acquire 1 actually 2 additional The output is sorted by word, not by count! What we want is the most frequently used words first. Fortunately, this is easy to accomplish, with the help of two more `sort' options: `-n' do a numeric sort, not a textual one `-r' reverse the order of the sort The final pipeline looks like this: $ tr '[:upper:]' '[:lower:]' < whats.gnu | tr -cd '[:alnum:]_ \n' | > tr -s ' ' '\n' | sort | uniq -c | sort -n -r -| 156 the -| 60 a -| 58 to -| 51 of -| 51 and ... Whew! That's a lot to digest. Yet, the same principles apply. With six commands, on two lines (really one long one split for convenience), we've created a program that does something interesting and useful, in much less time than we could have written a C program to do the same thing. A minor modification to the above pipeline can give us a simple spelling checker! To determine if you've spelled a word correctly, all you have to do is look it up in a dictionary. If it is not there, then chances are that your spelling is incorrect. So, we need a dictionary. The conventional location for a dictionary is `/usr/dict/words'. On my GNU/Linux system,(1) this is a sorted, 45,402 word dictionary. Now, how to compare our file with the dictionary? As before, we generate a sorted list of words, one per line: $ tr '[:upper:]' '[:lower:]' < whats.gnu | tr -cd '[:alnum:]_ \n' | > tr -s ' ' '\n' | sort -u | ... Now, all we need is a list of words that are _not_ in the dictionary. Here is where the `comm' command comes in. $ tr '[:upper:]' '[:lower:]' < whats.gnu | tr -cd '[:alnum:]_ \n' | > tr -s ' ' '\n' | sort -u | > comm -23 - /usr/dict/words The `-2' and `-3' options eliminate lines that are only in the dictionary (the second file), and lines that are in both files. Lines only in the first file (standard input, our stream of words), are words that are not in the dictionary. These are likely candidates for spelling errors. This pipeline was the first cut at a production spelling checker on Unix. There are some other tools that deserve brief mention. `grep' search files for text that matches a regular expression `wc' count lines, words, characters `tee' a T-fitting for data pipes, copies data to files and to standard output `sed' the stream editor, an advanced tool `awk' a data manipulation language, another advanced tool The software tools philosophy also espoused the following bit of advice: "Let someone else do the hard part." This means, take something that gives you most of what you need, and then massage it the rest of the way until it's in the form that you want. To summarize: 1. Each program should do one thing well. No more, no less. 2. Combining programs with appropriate plumbing leads to results where the whole is greater than the sum of the parts. It also leads to novel uses of programs that the authors might never have imagined. 3. Programs should never print extraneous header or trailer data, since these could get sent on down a pipeline. (A point we didn't mention earlier.) 4. Let someone else do the hard part. 5. Know your toolbox! Use each program appropriately. If you don't have an appropriate tool, build one. As of this writing, all the programs we've discussed are available via anonymous `ftp' from: `ftp://gnudist.gnu.org/textutils/textutils-1.22.tar.gz'. (There may be more recent versions available now.) None of what I have presented in this column is new. The Software Tools philosophy was first introduced in the book `Software Tools', by Brian Kernighan and P.J. Plauger (Addison-Wesley, ISBN 0-201-03669-X). This book showed how to write and use software tools. It was written in 1976, using a preprocessor for FORTRAN named `ratfor' (RATional FORtran). At the time, C was not as ubiquitous as it is now; FORTRAN was. The last chapter presented a `ratfor' to FORTRAN processor, written in `ratfor'. `ratfor' looks an awful lot like C; if you know C, you won't have any problem following the code. In 1981, the book was updated and made available as `Software Tools in Pascal' (Addison-Wesley, ISBN 0-201-10342-7). Both books are still in print and are well worth reading if you're a programmer. They certainly made a major change in how I view programming. The programs in both books are available from Brian Kernighan's home page (http://cm.bell-labs.com/who/bwk). For a number of years, there was an active Software Tools Users Group, whose members had ported the original `ratfor' programs to essentially every computer system with a FORTRAN compiler. The popularity of the group waned in the middle 1980s as Unix began to spread beyond universities. With the current proliferation of GNU code and other clones of Unix programs, these programs now receive little attention; modern C versions are much more efficient and do more than these programs do. Nevertheless, as exposition of good programming style, and evangelism for a still-valuable philosophy, these books are unparalleled, and I recommend them highly. Acknowledgment: I would like to express my gratitude to Brian Kernighan of Bell Labs, the original Software Toolsmith, for reviewing this column. ---------- Footnotes ---------- (1) Redhat Linux 6.1, for the November 2000 revision of this article.  File: coreutils.info, Node: GNU Free Documentation License, Next: Concept index, Prev: Opening the software toolbox, Up: Top Appendix A GNU Free Documentation License ***************************************** Version 1.3, 3 November 2008 Copyright (C) 2000, 2001, 2002, 2007, 2008 Free Software Foundation, Inc. `http://fsf.org/' Everyone is permitted to copy and distribute verbatim copies of this license document, but changing it is not allowed. 0. PREAMBLE The purpose of this License is to make a manual, textbook, or other functional and useful document "free" in the sense of freedom: to assure everyone the effective freedom to copy and redistribute it, with or without modifying it, either commercially or noncommercially. Secondarily, this License preserves for the author and publisher a way to get credit for their work, while not being considered responsible for modifications made by others. 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The combined work need only contain one copy of this License, and multiple identical Invariant Sections may be replaced with a single copy. If there are multiple Invariant Sections with the same name but different contents, make the title of each such section unique by adding at the end of it, in parentheses, the name of the original author or publisher of that section if known, or else a unique number. Make the same adjustment to the section titles in the list of Invariant Sections in the license notice of the combined work. In the combination, you must combine any sections Entitled "History" in the various original documents, forming one section Entitled "History"; likewise combine any sections Entitled "Acknowledgements", and any sections Entitled "Dedications". You must delete all sections Entitled "Endorsements." 6. COLLECTIONS OF DOCUMENTS You may make a collection consisting of the Document and other documents released under this License, and replace the individual copies of this License in the various documents with a single copy that is included in the collection, provided that you follow the rules of this License for verbatim copying of each of the documents in all other respects. You may extract a single document from such a collection, and distribute it individually under this License, provided you insert a copy of this License into the extracted document, and follow this License in all other respects regarding verbatim copying of that document. 7. AGGREGATION WITH INDEPENDENT WORKS A compilation of the Document or its derivatives with other separate and independent documents or works, in or on a volume of a storage or distribution medium, is called an "aggregate" if the copyright resulting from the compilation is not used to limit the legal rights of the compilation's users beyond what the individual works permit. When the Document is included in an aggregate, this License does not apply to the other works in the aggregate which are not themselves derivative works of the Document. If the Cover Text requirement of section 3 is applicable to these copies of the Document, then if the Document is less than one half of the entire aggregate, the Document's Cover Texts may be placed on covers that bracket the Document within the aggregate, or the electronic equivalent of covers if the Document is in electronic form. Otherwise they must appear on printed covers that bracket the whole aggregate. 8. TRANSLATION Translation is considered a kind of modification, so you may distribute translations of the Document under the terms of section 4. Replacing Invariant Sections with translations requires special permission from their copyright holders, but you may include translations of some or all Invariant Sections in addition to the original versions of these Invariant Sections. You may include a translation of this License, and all the license notices in the Document, and any Warranty Disclaimers, provided that you also include the original English version of this License and the original versions of those notices and disclaimers. In case of a disagreement between the translation and the original version of this License or a notice or disclaimer, the original version will prevail. If a section in the Document is Entitled "Acknowledgements", "Dedications", or "History", the requirement (section 4) to Preserve its Title (section 1) will typically require changing the actual title. 9. TERMINATION You may not copy, modify, sublicense, or distribute the Document except as expressly provided under this License. Any attempt otherwise to copy, modify, sublicense, or distribute it is void, and will automatically terminate your rights under this License. However, if you cease all violation of this License, then your license from a particular copyright holder is reinstated (a) provisionally, unless and until the copyright holder explicitly and finally terminates your license, and (b) permanently, if the copyright holder fails to notify you of the violation by some reasonable means prior to 60 days after the cessation. Moreover, your license from a particular copyright holder is reinstated permanently if the copyright holder notifies you of the violation by some reasonable means, this is the first time you have received notice of violation of this License (for any work) from that copyright holder, and you cure the violation prior to 30 days after your receipt of the notice. Termination of your rights under this section does not terminate the licenses of parties who have received copies or rights from you under this License. If your rights have been terminated and not permanently reinstated, receipt of a copy of some or all of the same material does not give you any rights to use it. 10. FUTURE REVISIONS OF THIS LICENSE The Free Software Foundation may publish new, revised versions of the GNU Free Documentation License from time to time. Such new versions will be similar in spirit to the present version, but may differ in detail to address new problems or concerns. See `http://www.gnu.org/copyleft/'. Each version of the License is given a distinguishing version number. If the Document specifies that a particular numbered version of this License "or any later version" applies to it, you have the option of following the terms and conditions either of that specified version or of any later version that has been published (not as a draft) by the Free Software Foundation. If the Document does not specify a version number of this License, you may choose any version ever published (not as a draft) by the Free Software Foundation. If the Document specifies that a proxy can decide which future versions of this License can be used, that proxy's public statement of acceptance of a version permanently authorizes you to choose that version for the Document. 11. RELICENSING "Massive Multiauthor Collaboration Site" (or "MMC Site") means any World Wide Web server that publishes copyrightable works and also provides prominent facilities for anybody to edit those works. A public wiki that anybody can edit is an example of such a server. A "Massive Multiauthor Collaboration" (or "MMC") contained in the site means any set of copyrightable works thus published on the MMC site. "CC-BY-SA" means the Creative Commons Attribution-Share Alike 3.0 license published by Creative Commons Corporation, a not-for-profit corporation with a principal place of business in San Francisco, California, as well as future copyleft versions of that license published by that same organization. "Incorporate" means to publish or republish a Document, in whole or in part, as part of another Document. An MMC is "eligible for relicensing" if it is licensed under this License, and if all works that were first published under this License somewhere other than this MMC, and subsequently incorporated in whole or in part into the MMC, (1) had no cover texts or invariant sections, and (2) were thus incorporated prior to November 1, 2008. The operator of an MMC Site may republish an MMC contained in the site under CC-BY-SA on the same site at any time before August 1, 2009, provided the MMC is eligible for relicensing. ADDENDUM: How to use this License for your documents ==================================================== To use this License in a document you have written, include a copy of the License in the document and put the following copyright and license notices just after the title page: Copyright (C) YEAR YOUR NAME. Permission is granted to copy, distribute and/or modify this document under the terms of the GNU Free Documentation License, Version 1.3 or any later version published by the Free Software Foundation; with no Invariant Sections, no Front-Cover Texts, and no Back-Cover Texts. A copy of the license is included in the section entitled ``GNU Free Documentation License''. If you have Invariant Sections, Front-Cover Texts and Back-Cover Texts, replace the "with...Texts." line with this: with the Invariant Sections being LIST THEIR TITLES, with the Front-Cover Texts being LIST, and with the Back-Cover Texts being LIST. If you have Invariant Sections without Cover Texts, or some other combination of the three, merge those two alternatives to suit the situation. If your document contains nontrivial examples of program code, we recommend releasing these examples in parallel under your choice of free software license, such as the GNU General Public License, to permit their use in free software.  File: coreutils.info, Node: Concept index, Prev: GNU Free Documentation License, Up: Top Index ***** [index] * Menu: * !: Connectives for test. (line 9) * !=: String tests. (line 28) * %: Numeric expressions. (line 16) * %b: printf invocation. (line 38) * &: Relations for expr. (line 17) * *: Numeric expressions. (line 16) * + <1>: Numeric expressions. (line 12) * +: String expressions. (line 53) * +PAGE_RANGE: pr invocation. (line 58) * - <1>: su invocation. (line 53) * - <2>: Numeric expressions. (line 12) * -: env invocation. (line 96) * - and Unix rm: rm invocation. (line 110) * -, removing files beginning with: rm invocation. (line 98) * --: Common options. (line 44) * --across: pr invocation. (line 82) * --additional-suffix: split invocation. (line 121) * --address-radix: od invocation. (line 36) * --adjustment: nice invocation. (line 47) * --all <1>: uname invocation. (line 30) * --all <2>: who invocation. (line 36) * --all <3>: nproc invocation. (line 19) * --all <4>: stty invocation. (line 26) * --all <5>: du invocation. (line 26) * --all <6>: df invocation. (line 32) * --all <7>: Which files are listed. (line 13) * --all: unexpand invocation. (line 37) * --all-repeated: uniq invocation. (line 69) * --almost-all: Which files are listed. (line 17) * --apparent-size: du invocation. (line 29) * --append: tee invocation. (line 25) * --archive: cp invocation. (line 65) * --attributes-only: cp invocation. (line 74) * --author: What information is listed. (line 10) * --backup <1>: ln invocation. (line 84) * --backup <2>: install invocation. (line 42) * --backup <3>: cp invocation. (line 80) * --backup <4>: mv invocation. (line 58) * --backup: Backup options. (line 13) * --batch-size: sort invocation. (line 259) * --before: tac invocation. (line 21) * --binary: md5sum invocation. (line 37) * --block-size <1>: Block size. (line 137) * --block-size <2>: df invocation. (line 38) * --block-size: du invocation. (line 50) * --block-size=SIZE: Block size. (line 12) * --body-numbering: nl invocation. (line 47) * --boot: who invocation. (line 40) * --bourne-shell: dircolors invocation. (line 34) * --buffer-size: sort invocation. (line 309) * --bytes <1>: du invocation. (line 46) * --bytes <2>: wc invocation. (line 43) * --bytes <3>: head invocation. (line 24) * --bytes <4>: tail invocation. (line 32) * --bytes <5>: cut invocation. (line 26) * --bytes <6>: fold invocation. (line 23) * --bytes: split invocation. (line 40) * --c-shell: dircolors invocation. (line 40) * --canonicalize: readlink invocation. (line 29) * --canonicalize-existing <1>: realpath invocation. (line 17) * --canonicalize-existing: readlink invocation. (line 36) * --canonicalize-missing <1>: readlink invocation. (line 43) * --canonicalize-missing: realpath invocation. (line 25) * --changes <1>: chgrp invocation. (line 20) * --changes <2>: chown invocation. (line 70) * --changes: chmod invocation. (line 39) * --characters: cut invocation. (line 34) * --chars: wc invocation. (line 47) * --check: sort invocation. (line 26) * --check-chars: uniq invocation. (line 106) * --classify: General output formatting. (line 48) * --color: General output formatting. (line 21) * --columns: pr invocation. (line 68) * --command: su invocation. (line 39) * --compare: install invocation. (line 47) * --complement: cut invocation. (line 83) * --compute: runcon invocation. (line 27) * --context <1>: id invocation. (line 48) * --context <2>: install invocation. (line 133) * --context <3>: mknod invocation. (line 54) * --context <4>: mkfifo invocation. (line 28) * --context <5>: What information is listed. (line 268) * --context: mkdir invocation. (line 56) * --count <1>: who invocation. (line 70) * --count: uniq invocation. (line 55) * --count-links: du invocation. (line 96) * --crown-margin: fmt invocation. (line 34) * --csh: dircolors invocation. (line 40) * --date <1>: touch invocation. (line 86) * --date: Options for date. (line 11) * --dead: who invocation. (line 44) * --decode: base64 invocation. (line 30) * --delimiter: cut invocation. (line 63) * --delimiters: paste invocation. (line 43) * --dereference <1>: chgrp invocation. (line 30) * --dereference <2>: Which files are listed. (line 84) * --dereference <3>: stat invocation. (line 22) * --dereference <4>: cp invocation. (line 148) * --dereference <5>: du invocation. (line 101) * --dereference: chown invocation. (line 103) * --dereference-args: du invocation. (line 61) * --dereference-command-line: Which files are listed. (line 36) * --dereference-command-line-symlink-to-dir: Which files are listed. (line 41) * --dictionary-order: sort invocation. (line 87) * --digits: csplit invocation. (line 81) * --directory <1>: ln invocation. (line 90) * --directory <2>: Which files are listed. (line 28) * --directory <3>: install invocation. (line 62) * --directory: mktemp invocation. (line 86) * --dired: What information is listed. (line 16) * --double-space: pr invocation. (line 94) * --dry-run: mktemp invocation. (line 98) * --echo: shuf invocation. (line 19) * --elide-empty-files <1>: split invocation. (line 126) * --elide-empty-files: csplit invocation. (line 90) * --error: stdbuf invocation. (line 34) * --escape: Formatting the file names. (line 11) * --exact: shred invocation. (line 134) * --exclude-from=FILE: du invocation. (line 213) * --exclude-type: df invocation. (line 144) * --exclude=PATTERN: du invocation. (line 207) * --expand-tabs: pr invocation. (line 118) * --fast: su invocation. (line 44) * --field-separator: sort invocation. (line 325) * --fields: cut invocation. (line 44) * --file <1>: stty invocation. (line 31) * --file: Options for date. (line 26) * --file-system: stat invocation. (line 28) * --file-type: General output formatting. (line 59) * --files0-from=FILE <1>: wc invocation. (line 62) * --files0-from=FILE <2>: du invocation. (line 67) * --files0-from=FILE: sort invocation. (line 221) * --filter: split invocation. (line 60) * --first-line-number: pr invocation. (line 194) * --follow: tail invocation. (line 48) * --footer-numbering: nl invocation. (line 75) * --force <1>: shred invocation. (line 101) * --force <2>: ln invocation. (line 96) * --force <3>: cp invocation. (line 115) * --force <4>: mv invocation. (line 63) * --force: rm invocation. (line 35) * --foreground: timeout invocation. (line 18) * --form-feed: pr invocation. (line 126) * --format <1>: General output formatting. (line 107) * --format <2>: What information is listed. (line 131) * --format <3>: General output formatting. (line 97) * --format: od invocation. (line 85) * --format=FORMAT <1>: seq invocation. (line 24) * --format=FORMAT: stat invocation. (line 34) * --from: chown invocation. (line 80) * --full-time: What information is listed. (line 100) * --general-numeric-sort: sort invocation. (line 105) * --group <1>: install invocation. (line 68) * --group: id invocation. (line 26) * --group-directories-first: Which files are listed. (line 50) * --groups <1>: id invocation. (line 30) * --groups: chroot invocation. (line 29) * --hardware-platform: uname invocation. (line 35) * --head-count: shuf invocation. (line 32) * --header <1>: pr invocation. (line 131) * --header: join invocation. (line 90) * --header-numbering: nl invocation. (line 79) * --heading: who invocation. (line 48) * --help: Common options. (line 37) * --hide-control-chars: Formatting the file names. (line 23) * --hide=PATTERN: Which files are listed. (line 57) * --human-numeric-sort: sort invocation. (line 130) * --human-readable <1>: Block size. (line 137) * --human-readable <2>: What information is listed. (line 116) * --human-readable <3>: du invocation. (line 81) * --human-readable: df invocation. (line 48) * --ignore: nproc invocation. (line 25) * --ignore-backups: Which files are listed. (line 23) * --ignore-case <1>: sort invocation. (line 94) * --ignore-case <2>: join invocation. (line 100) * --ignore-case: uniq invocation. (line 59) * --ignore-environment: env invocation. (line 96) * --ignore-fail-on-non-empty: rmdir invocation. (line 17) * --ignore-garbage: base64 invocation. (line 36) * --ignore-interrupts: tee invocation. (line 30) * --ignore-leading-blanks: sort invocation. (line 79) * --ignore-nonprinting: sort invocation. (line 145) * --ignore=PATTERN: Which files are listed. (line 70) * --indent: pr invocation. (line 200) * --indicator-style: General output formatting. (line 102) * --initial: expand invocation. (line 34) * --inode: What information is listed. (line 123) * --inodes: df invocation. (line 58) * --input: stdbuf invocation. (line 26) * --input-range: shuf invocation. (line 23) * --interactive <1>: ln invocation. (line 100) * --interactive <2>: rm invocation. (line 50) * --interactive <3>: cp invocation. (line 138) * --interactive: mv invocation. (line 69) * --io-blocks: truncate invocation. (line 26) * --iso-8601[=TIMESPEC]: Options for date. (line 34) * --iterations=NUMBER: shred invocation. (line 106) * --join-blank-lines: nl invocation. (line 87) * --join-lines: pr invocation. (line 144) * --keep-files: csplit invocation. (line 86) * --kernel-name: uname invocation. (line 65) * --kernel-release: uname invocation. (line 61) * --kernel-version: uname invocation. (line 76) * --key: sort invocation. (line 234) * --kibibytes: General output formatting. (line 85) * --kill-after: timeout invocation. (line 33) * --length: pr invocation. (line 153) * --line-bytes: split invocation. (line 54) * --line-increment: nl invocation. (line 83) * --lines <1>: tail invocation. (line 152) * --lines <2>: split invocation. (line 33) * --lines <3>: wc invocation. (line 55) * --lines: head invocation. (line 39) * --link: cp invocation. (line 144) * --literal: Formatting the file names. (line 17) * --local: df invocation. (line 69) * --logical <1>: pwd invocation. (line 15) * --logical <2>: ln invocation. (line 104) * --logical: realpath invocation. (line 30) * --login <1>: who invocation. (line 52) * --login: su invocation. (line 53) * --lookup: who invocation. (line 57) * --machine: uname invocation. (line 41) * --max-depth=DEPTH: du invocation. (line 118) * --max-line-length: wc invocation. (line 59) * --max-unchanged-stats: tail invocation. (line 140) * --merge <1>: sort invocation. (line 32) * --merge: pr invocation. (line 160) * --mesg: who invocation. (line 95) * --message: who invocation. (line 95) * --mode <1>: mkdir invocation. (line 19) * --mode <2>: install invocation. (line 74) * --mode <3>: mkfifo invocation. (line 21) * --mode: mknod invocation. (line 48) * --month-sort: sort invocation. (line 152) * --multiple: basename invocation. (line 32) * --name: id invocation. (line 34) * --no-clobber <1>: mv invocation. (line 76) * --no-clobber: cp invocation. (line 155) * --no-create <1>: truncate invocation. (line 22) * --no-create: touch invocation. (line 82) * --no-dereference <1>: cp invocation. (line 161) * --no-dereference <2>: ln invocation. (line 110) * --no-dereference <3>: chcon invocation. (line 22) * --no-dereference <4>: du invocation. (line 112) * --no-dereference <5>: chown invocation. (line 108) * --no-dereference <6>: chgrp invocation. (line 35) * --no-dereference: touch invocation. (line 100) * --no-file-warnings: pr invocation. (line 207) * --no-group: What information is listed. (line 110) * --no-newline: readlink invocation. (line 48) * --no-preserve-root <1>: rm invocation. (line 84) * --no-preserve-root <2>: chgrp invocation. (line 48) * --no-preserve-root <3>: chown invocation. (line 121) * --no-preserve-root: chmod invocation. (line 54) * --no-renumber: nl invocation. (line 108) * --no-symlinks: realpath invocation. (line 46) * --no-sync: df invocation. (line 73) * --no-target-directory <1>: ln invocation. (line 165) * --no-target-directory <2>: mv invocation. (line 109) * --no-target-directory <3>: cp invocation. (line 352) * --no-target-directory <4>: Target directory. (line 15) * --no-target-directory: install invocation. (line 124) * --nodename: uname invocation. (line 46) * --null <1>: printenv invocation. (line 19) * --null <2>: env invocation. (line 83) * --null: du invocation. (line 124) * --number <1>: cat invocation. (line 31) * --number: split invocation. (line 77) * --number-format: nl invocation. (line 95) * --number-lines: pr invocation. (line 173) * --number-nonblank: cat invocation. (line 20) * --number-separator: nl invocation. (line 112) * --number-width: nl invocation. (line 122) * --numeric-sort: sort invocation. (line 162) * --numeric-suffixes: split invocation. (line 114) * --numeric-uid-gid: What information is listed. (line 234) * --omit-header: pr invocation. (line 230) * --omit-pagination: pr invocation. (line 241) * --one-file-system <1>: cp invocation. (line 375) * --one-file-system <2>: du invocation. (line 203) * --one-file-system: rm invocation. (line 63) * --only-delimited: cut invocation. (line 71) * --operating-system: uname invocation. (line 57) * --output <1>: stdbuf invocation. (line 30) * --output <2>: shuf invocation. (line 37) * --output: sort invocation. (line 285) * --output-delimiter: cut invocation. (line 76) * --output-duplicates: od invocation. (line 155) * --output-tabs: pr invocation. (line 137) * --owner: install invocation. (line 86) * --page_width: pr invocation. (line 259) * --pages=PAGE_RANGE: pr invocation. (line 58) * --parallel: sort invocation. (line 353) * --parents <1>: mkdir invocation. (line 34) * --parents <2>: cp invocation. (line 240) * --parents: rmdir invocation. (line 22) * --physical <1>: pwd invocation. (line 22) * --physical <2>: ln invocation. (line 129) * --physical: realpath invocation. (line 35) * --pid: tail invocation. (line 120) * --portability <1>: pathchk invocation. (line 46) * --portability: df invocation. (line 80) * --prefix: csplit invocation. (line 62) * --preserve: cp invocation. (line 168) * --preserve-context: install invocation. (line 91) * --preserve-environment: su invocation. (line 64) * --preserve-root <1>: rm invocation. (line 79) * --preserve-root <2>: chown invocation. (line 116) * --preserve-root <3>: chgrp invocation. (line 43) * --preserve-root: chmod invocation. (line 49) * --preserve-timestamps: install invocation. (line 98) * --print-database: dircolors invocation. (line 45) * --print-type: df invocation. (line 119) * --printf=FORMAT: stat invocation. (line 43) * --process: who invocation. (line 66) * --processor: uname invocation. (line 50) * --quiet <1>: tty invocation. (line 18) * --quiet <2>: realpath invocation. (line 41) * --quiet <3>: csplit invocation. (line 101) * --quiet <4>: md5sum invocation. (line 68) * --quiet <5>: mktemp invocation. (line 93) * --quiet <6>: chown invocation. (line 76) * --quiet <7>: head invocation. (line 46) * --quiet <8>: tail invocation. (line 160) * --quiet <9>: readlink invocation. (line 54) * --quiet <10>: chgrp invocation. (line 26) * --quiet: chmod invocation. (line 45) * --quote-name: Formatting the file names. (line 30) * --quoting-style: Formatting the file names. (line 11) * --random-sort: sort invocation. (line 191) * --random-source <1>: shred invocation. (line 112) * --random-source <2>: sort invocation. (line 298) * --random-source: shuf invocation. (line 43) * --range <1>: runcon invocation. (line 43) * --range: chcon invocation. (line 63) * --read-bytes: od invocation. (line 71) * --real: id invocation. (line 39) * --recursive <1>: chown invocation. (line 140) * --recursive <2>: rm invocation. (line 91) * --recursive <3>: cp invocation. (line 253) * --recursive <4>: chcon invocation. (line 30) * --recursive <5>: Which files are listed. (line 91) * --recursive <6>: chgrp invocation. (line 66) * --recursive: chmod invocation. (line 69) * --reference <1>: touch invocation. (line 119) * --reference <2>: chgrp invocation. (line 52) * --reference <3>: truncate invocation. (line 30) * --reference <4>: chcon invocation. (line 25) * --reference <5>: Options for date. (line 59) * --reference <6>: chmod invocation. (line 62) * --reference: chown invocation. (line 125) * --reflink[=WHEN]: cp invocation. (line 266) * --regex: tac invocation. (line 26) * --relative: ln invocation. (line 138) * --relative-base: realpath invocation. (line 61) * --relative-to: realpath invocation. (line 56) * --remove: shred invocation. (line 123) * --remove-destination: cp invocation. (line 292) * --repeated: uniq invocation. (line 63) * --retry: tail invocation. (line 104) * --reverse <1>: sort invocation. (line 185) * --reverse: Sorting the output. (line 27) * --rfc-2822: Options for date. (line 65) * --rfc-3339=TIMESPEC: Options for date. (line 77) * --rfc-822: Options for date. (line 65) * --role <1>: runcon invocation. (line 35) * --role: chcon invocation. (line 55) * --runlevel: who invocation. (line 75) * --save: stty invocation. (line 41) * --section-delimiter: nl invocation. (line 68) * --sep-string: pr invocation. (line 221) * --separate-dirs: du invocation. (line 142) * --separator <1>: tac invocation. (line 33) * --separator: pr invocation. (line 212) * --serial: paste invocation. (line 34) * --set: Options for date. (line 107) * --sh: dircolors invocation. (line 34) * --shell: su invocation. (line 75) * --show-all: cat invocation. (line 16) * --show-control-chars <1>: pr invocation. (line 88) * --show-control-chars: Formatting the file names. (line 78) * --show-ends: cat invocation. (line 27) * --show-nonprinting <1>: pr invocation. (line 246) * --show-nonprinting: cat invocation. (line 51) * --show-tabs: cat invocation. (line 44) * --si <1>: Block size. (line 137) * --si <2>: What information is listed. (line 260) * --si <3>: df invocation. (line 99) * --si: du invocation. (line 130) * --signal: timeout invocation. (line 40) * --silent <1>: tail invocation. (line 160) * --silent <2>: readlink invocation. (line 54) * --silent <3>: csplit invocation. (line 101) * --silent <4>: chgrp invocation. (line 26) * --silent <5>: chown invocation. (line 76) * --silent <6>: chmod invocation. (line 45) * --silent <7>: tty invocation. (line 18) * --silent: head invocation. (line 46) * --size <1>: What information is listed. (line 244) * --size: truncate invocation. (line 34) * --size=BYTES: shred invocation. (line 117) * --skip-bytes: od invocation. (line 55) * --skip-chars: uniq invocation. (line 41) * --skip-fields: uniq invocation. (line 31) * --sleep-interval: tail invocation. (line 110) * --sort <1>: Sorting the output. (line 36) * --sort <2>: sort invocation. (line 191) * --sort <3>: Sorting the output. (line 56) * --sort <4>: sort invocation. (line 105) * --sort <5>: Sorting the output. (line 49) * --sort: sort invocation. (line 130) * --spaces: fold invocation. (line 29) * --sparse=WHEN: cp invocation. (line 296) * --split-only: fmt invocation. (line 47) * --squeeze-blank: cat invocation. (line 36) * --stable: sort invocation. (line 303) * --starting-line-number: nl invocation. (line 117) * --status: md5sum invocation. (line 76) * --strict: md5sum invocation. (line 100) * --strings: od invocation. (line 76) * --strip <1>: realpath invocation. (line 46) * --strip: install invocation. (line 108) * --strip-program: install invocation. (line 111) * --strip-trailing-slashes <1>: mv invocation. (line 95) * --strip-trailing-slashes: cp invocation. (line 330) * --suffix <1>: Backup options. (line 50) * --suffix <2>: csplit invocation. (line 66) * --suffix <3>: mv invocation. (line 100) * --suffix <4>: mktemp invocation. (line 114) * --suffix <5>: basename invocation. (line 38) * --suffix <6>: install invocation. (line 115) * --suffix <7>: ln invocation. (line 156) * --suffix: cp invocation. (line 343) * --suffix-length: split invocation. (line 106) * --summarize: du invocation. (line 138) * --symbolic: ln invocation. (line 150) * --symbolic-link: cp invocation. (line 335) * --sync: df invocation. (line 106) * --sysv: sum invocation. (line 31) * --tabs <1>: expand invocation. (line 22) * --tabs: unexpand invocation. (line 24) * --tabsize: General output formatting. (line 111) * --tagged-paragraph: fmt invocation. (line 40) * --target-directory <1>: install invocation. (line 120) * --target-directory <2>: ln invocation. (line 161) * --target-directory <3>: cp invocation. (line 348) * --target-directory <4>: mv invocation. (line 105) * --target-directory: Target directory. (line 31) * --temporary-directory: sort invocation. (line 345) * --terse: stat invocation. (line 54) * --text: md5sum invocation. (line 86) * --time <1>: du invocation. (line 161) * --time <2>: Sorting the output. (line 42) * --time <3>: who invocation. (line 83) * --time <4>: du invocation. (line 156) * --time <5>: touch invocation. (line 78) * --time <6>: du invocation. (line 150) * --time: Sorting the output. (line 13) * --time-style <1>: du invocation. (line 165) * --time-style: Formatting file timestamps. (line 26) * --tmpdir: mktemp invocation. (line 106) * --total <1>: df invocation. (line 42) * --total: du invocation. (line 55) * --traditional: od invocation. (line 206) * --type <1>: df invocation. (line 113) * --type <2>: runcon invocation. (line 39) * --type: chcon invocation. (line 59) * --unbuffered: split invocation. (line 134) * --uniform-spacing: fmt invocation. (line 53) * --unique <1>: sort invocation. (line 361) * --unique: uniq invocation. (line 101) * --universal: Options for date. (line 113) * --unset: env invocation. (line 90) * --update <1>: mv invocation. (line 82) * --update: cp invocation. (line 357) * --user <1>: runcon invocation. (line 31) * --user <2>: chcon invocation. (line 51) * --user: id invocation. (line 44) * --userspec: chroot invocation. (line 24) * --utc: Options for date. (line 113) * --verbose <1>: chcon invocation. (line 47) * --verbose <2>: rm invocation. (line 95) * --verbose <3>: head invocation. (line 50) * --verbose <4>: tail invocation. (line 164) * --verbose <5>: chgrp invocation. (line 58) * --verbose <6>: install invocation. (line 129) * --verbose <7>: cp invocation. (line 371) * --verbose <8>: shred invocation. (line 129) * --verbose <9>: readlink invocation. (line 58) * --verbose <10>: split invocation. (line 138) * --verbose <11>: chmod invocation. (line 59) * --verbose <12>: chown invocation. (line 132) * --verbose <13>: rmdir invocation. (line 31) * --verbose <14>: mv invocation. (line 92) * --verbose <15>: mkdir invocation. (line 51) * --verbose: ln invocation. (line 170) * --version: Common options. (line 41) * --version-sort: sort invocation. (line 179) * --warn: md5sum invocation. (line 95) * --width <1>: fmt invocation. (line 59) * --width <2>: fold invocation. (line 35) * --width <3>: General output formatting. (line 123) * --width <4>: od invocation. (line 162) * --width: pr invocation. (line 250) * --words: wc invocation. (line 51) * --wrap: base64 invocation. (line 22) * --writable: who invocation. (line 95) * --zero <1>: dirname invocation. (line 31) * --zero <2>: basename invocation. (line 42) * --zero <3>: realpath invocation. (line 53) * --zero: shred invocation. (line 144) * --zero-terminated <1>: sort invocation. (line 375) * --zero-terminated <2>: shuf invocation. (line 48) * --zero-terminated: uniq invocation. (line 112) * -0 <1>: printenv invocation. (line 18) * -0 <2>: env invocation. (line 82) * -0: du invocation. (line 123) * -1 <1>: General output formatting. (line 10) * -1 <2>: comm invocation. (line 23) * -1: join invocation. (line 105) * -2 <1>: join invocation. (line 108) * -2: comm invocation. (line 23) * -3: comm invocation. (line 23) * -a <1>: unexpand invocation. (line 37) * -a <2>: join invocation. (line 75) * -a: stty invocation. (line 26) * -A <1>: od invocation. (line 36) * -A: cat invocation. (line 16) * -a <1>: tee invocation. (line 25) * -a <2>: basename invocation. (line 32) * -a <3>: split invocation. (line 106) * -a <4>: od invocation. (line 175) * -a <5>: Connectives for test. (line 12) * -a <6>: du invocation. (line 26) * -a: who invocation. (line 36) * -A: Which files are listed. (line 17) * -a <1>: pr invocation. (line 82) * -a <2>: cp invocation. (line 65) * -a <3>: touch invocation. (line 78) * -a <4>: df invocation. (line 32) * -a <5>: Which files are listed. (line 13) * -a: uname invocation. (line 30) * -b <1>: md5sum invocation. (line 37) * -b <2>: who invocation. (line 40) * -b <3>: install invocation. (line 42) * -b <4>: File type tests. (line 10) * -b <5>: csplit invocation. (line 66) * -b <6>: sort invocation. (line 79) * -b <7>: split invocation. (line 40) * -b <8>: fold invocation. (line 23) * -b: Backup options. (line 13) * -B: du invocation. (line 50) * -b <1>: du invocation. (line 46) * -b <2>: ln invocation. (line 84) * -b <3>: cp invocation. (line 80) * -b <4>: mv invocation. (line 58) * -b: dircolors invocation. (line 34) * -B <1>: df invocation. (line 38) * -B: Which files are listed. (line 23) * -b <1>: cut invocation. (line 26) * -b <2>: od invocation. (line 178) * -b <3>: nl invocation. (line 47) * -b <4>: Formatting the file names. (line 11) * -b <5>: tac invocation. (line 21) * -b: cat invocation. (line 20) * -c <1>: od invocation. (line 181) * -c <2>: fmt invocation. (line 34) * -c <3>: touch invocation. (line 82) * -c <4>: dircolors invocation. (line 40) * -c <5>: wc invocation. (line 43) * -c <6>: truncate invocation. (line 22) * -c <7>: install invocation. (line 53) * -c: Sorting the output. (line 13) * -C: install invocation. (line 47) * -c <1>: su invocation. (line 39) * -c <2>: sort invocation. (line 18) * -c <3>: chgrp invocation. (line 20) * -c <4>: cut invocation. (line 34) * -c: sort invocation. (line 26) * -C: General output formatting. (line 15) * -c <1>: pr invocation. (line 88) * -c <2>: File type tests. (line 13) * -c <3>: stat invocation. (line 34) * -c: chown invocation. (line 70) * -C: split invocation. (line 54) * -c <1>: tail invocation. (line 32) * -c <2>: head invocation. (line 24) * -c <3>: runcon invocation. (line 27) * -c <4>: chmod invocation. (line 39) * -c <5>: uniq invocation. (line 55) * -c <6>: shuf invocation. (line 19) * -c: du invocation. (line 55) * -COLUMN: pr invocation. (line 68) * -D: du invocation. (line 61) * -d <1>: cp invocation. (line 108) * -d: uniq invocation. (line 63) * -D: uniq invocation. (line 69) * -d <1>: sort invocation. (line 87) * -d <2>: pr invocation. (line 94) * -d <3>: nl invocation. (line 68) * -d <4>: cut invocation. (line 63) * -d: paste invocation. (line 43) * -D: install invocation. (line 56) * -d <1>: who invocation. (line 44) * -d <2>: install invocation. (line 62) * -d: Options for date. (line 11) * -D: What information is listed. (line 16) * -d <1>: od invocation. (line 185) * -d <2>: touch invocation. (line 86) * -d <3>: Which files are listed. (line 28) * -d <4>: base64 invocation. (line 30) * -d <5>: ln invocation. (line 90) * -d <6>: mktemp invocation. (line 86) * -d <7>: split invocation. (line 114) * -d: File type tests. (line 16) * -d DEPTH: du invocation. (line 118) * -E: echo invocation. (line 73) * -e <1>: pr invocation. (line 118) * -e <2>: join invocation. (line 86) * -e <3>: split invocation. (line 126) * -e <4>: File characteristic tests. (line 9) * -e <5>: stdbuf invocation. (line 34) * -e: readlink invocation. (line 36) * -E: cat invocation. (line 27) * -e <1>: realpath invocation. (line 17) * -e <2>: cat invocation. (line 23) * -e: echo invocation. (line 25) * -ef: File characteristic tests. (line 23) * -eq: Numeric tests. (line 16) * -f <1>: nl invocation. (line 75) * -f <2>: od invocation. (line 188) * -f: su invocation. (line 44) * -F: pr invocation. (line 126) * -f <1>: pr invocation. (line 126) * -f: tail invocation. (line 48) * -F: tail invocation. (line 99) * -f <1>: csplit invocation. (line 62) * -f <2>: Options for date. (line 26) * -f <3>: sort invocation. (line 94) * -f <4>: uniq invocation. (line 31) * -f <5>: cut invocation. (line 44) * -f: Sorting the output. (line 20) * -F <1>: stty invocation. (line 31) * -F <2>: General output formatting. (line 48) * -F: ln invocation. (line 90) * -f <1>: cp invocation. (line 115) * -f <2>: File type tests. (line 19) * -f <3>: mv invocation. (line 63) * -f <4>: stat invocation. (line 28) * -f <5>: rm invocation. (line 35) * -f <6>: shred invocation. (line 101) * -f <7>: ln invocation. (line 96) * -f <8>: touch invocation. (line 96) * -f <9>: readlink invocation. (line 29) * -f <10>: chmod invocation. (line 45) * -f <11>: chgrp invocation. (line 26) * -f: chown invocation. (line 76) * -f FORMAT: seq invocation. (line 24) * -G: id invocation. (line 30) * -g: sort invocation. (line 105) * -G: Access permission tests. (line 31) * -g <1>: id invocation. (line 26) * -g <2>: stty invocation. (line 41) * -g <3>: Access permission tests. (line 9) * -g: install invocation. (line 68) * -G: What information is listed. (line 110) * -g: What information is listed. (line 105) * -ge: Numeric tests. (line 16) * -gt: Numeric tests. (line 16) * -h <1>: Block size. (line 137) * -h: chgrp invocation. (line 35) * -H: chown invocation. (line 143) * -h: chcon invocation. (line 22) * -H: df invocation. (line 54) * -h <1>: chown invocation. (line 108) * -h <2>: df invocation. (line 48) * -h <3>: pr invocation. (line 131) * -h: touch invocation. (line 100) * -H: Traversing symlinks. (line 18) * -h <1>: File type tests. (line 23) * -h: du invocation. (line 81) * -H <1>: Which files are listed. (line 36) * -H: chcon invocation. (line 33) * -h: nl invocation. (line 79) * -H <1>: du invocation. (line 87) * -H <2>: chgrp invocation. (line 70) * -H <3>: who invocation. (line 48) * -H: cp invocation. (line 131) * -h <1>: sort invocation. (line 130) * -h: What information is listed. (line 116) * -i <1>: stdbuf invocation. (line 26) * -i <2>: uname invocation. (line 35) * -i <3>: uniq invocation. (line 59) * -i: env invocation. (line 96) * -I: rm invocation. (line 44) * -i <1>: cp invocation. (line 138) * -i <2>: shuf invocation. (line 23) * -i <3>: nl invocation. (line 83) * -i <4>: sort invocation. (line 145) * -i <5>: rm invocation. (line 39) * -i <6>: What information is listed. (line 123) * -i: od invocation. (line 191) * -I: Which files are listed. (line 70) * -i <1>: tee invocation. (line 30) * -i <2>: expand invocation. (line 34) * -i <3>: base64 invocation. (line 36) * -i <4>: df invocation. (line 58) * -i <5>: ln invocation. (line 100) * -i <6>: pr invocation. (line 137) * -i <7>: join invocation. (line 100) * -i: mv invocation. (line 69) * -I[TIMESPEC]: Options for date. (line 34) * -J: pr invocation. (line 144) * -j: od invocation. (line 55) * -k <1>: sort invocation. (line 234) * -k <2>: General output formatting. (line 85) * -k <3>: Access permission tests. (line 12) * -k <4>: Block size. (line 137) * -k <5>: df invocation. (line 63) * -k <6>: du invocation. (line 90) * -k <7>: csplit invocation. (line 86) * -k: timeout invocation. (line 33) * -L <1>: cp invocation. (line 148) * -L <2>: chcon invocation. (line 38) * -L: Traversing symlinks. (line 22) * -l: who invocation. (line 52) * -L <1>: pwd invocation. (line 15) * -L: chgrp invocation. (line 75) * -l: nl invocation. (line 87) * -L: chown invocation. (line 148) * -l <1>: split invocation. (line 33) * -l: What information is listed. (line 131) * -L: wc invocation. (line 59) * -l: wc invocation. (line 55) * -L: Which files are listed. (line 84) * -l <1>: od invocation. (line 194) * -l <2>: df invocation. (line 69) * -l: su invocation. (line 53) * -L <1>: ln invocation. (line 104) * -L: realpath invocation. (line 30) * -l: pr invocation. (line 153) * -L: stat invocation. (line 22) * -l <1>: runcon invocation. (line 43) * -l: du invocation. (line 96) * -L: du invocation. (line 101) * -l: chcon invocation. (line 63) * -L: File type tests. (line 23) * -l: cp invocation. (line 144) * -le: Numeric tests. (line 16) * -lt: Numeric tests. (line 16) * -m <1>: sort invocation. (line 32) * -m <2>: General output formatting. (line 97) * -m <3>: readlink invocation. (line 43) * -m <4>: mknod invocation. (line 48) * -m <5>: mkfifo invocation. (line 21) * -m <6>: touch invocation. (line 115) * -m <7>: mkdir invocation. (line 19) * -m <8>: su invocation. (line 64) * -m <9>: realpath invocation. (line 25) * -m <10>: pr invocation. (line 160) * -m <11>: du invocation. (line 106) * -m: uname invocation. (line 41) * -M: sort invocation. (line 152) * -m <1>: wc invocation. (line 47) * -m <2>: install invocation. (line 74) * -m: who invocation. (line 62) * -N: od invocation. (line 71) * -n <1>: cp invocation. (line 155) * -n: uname invocation. (line 46) * -N: Formatting the file names. (line 17) * -n <1>: readlink invocation. (line 48) * -n <2>: echo invocation. (line 22) * -n <3>: What information is listed. (line 234) * -n <4>: split invocation. (line 77) * -n <5>: cat invocation. (line 31) * -n: nl invocation. (line 95) * -N: pr invocation. (line 194) * -n <1>: nice invocation. (line 47) * -n <2>: tail invocation. (line 152) * -n <3>: csplit invocation. (line 81) * -n <4>: sort invocation. (line 162) * -n <5>: pr invocation. (line 173) * -n <6>: String tests. (line 19) * -n <7>: cut invocation. (line 67) * -n <8>: shuf invocation. (line 32) * -n <9>: mv invocation. (line 76) * -n <10>: head invocation. (line 39) * -n <11>: ln invocation. (line 110) * -n: id invocation. (line 34) * -n NUMBER: shred invocation. (line 106) * -ne: Numeric tests. (line 16) * -nt: File characteristic tests. (line 15) * -o <1>: shuf invocation. (line 37) * -o <2>: pr invocation. (line 200) * -o <3>: What information is listed. (line 238) * -o <4>: stdbuf invocation. (line 30) * -o <5>: truncate invocation. (line 26) * -o: od invocation. (line 197) * -O: Access permission tests. (line 28) * -o <1>: install invocation. (line 86) * -o <2>: Connectives for test. (line 15) * -o <3>: uname invocation. (line 57) * -o: sort invocation. (line 285) * -ot: File characteristic tests. (line 19) * -p <1>: mktemp invocation. (line 106) * -p: General output formatting. (line 102) * -P: pathchk invocation. (line 42) * -p <1>: pathchk invocation. (line 29) * -p: dircolors invocation. (line 45) * -P: cp invocation. (line 161) * -p: cp invocation. (line 168) * -P: df invocation. (line 80) * -p <1>: File type tests. (line 28) * -p <2>: who invocation. (line 66) * -p <3>: install invocation. (line 98) * -p: uname invocation. (line 50) * -P <1>: chcon invocation. (line 42) * -P <2>: du invocation. (line 112) * -P <3>: chown invocation. (line 152) * -P: ln invocation. (line 129) * -p <1>: su invocation. (line 64) * -p <2>: mkdir invocation. (line 34) * -p: nl invocation. (line 108) * -P <1>: chgrp invocation. (line 79) * -P: Traversing symlinks. (line 26) * -p: rmdir invocation. (line 22) * -P <1>: realpath invocation. (line 35) * -P: pwd invocation. (line 22) * -q <1>: head invocation. (line 46) * -q <2>: realpath invocation. (line 41) * -q <3>: mktemp invocation. (line 93) * -q <4>: readlink invocation. (line 54) * -q: who invocation. (line 70) * -Q: Formatting the file names. (line 30) * -q <1>: Formatting the file names. (line 23) * -q <2>: csplit invocation. (line 101) * -q: tail invocation. (line 160) * -R: Options for date. (line 65) * -r: cp invocation. (line 253) * -R <1>: sort invocation. (line 191) * -R: chown invocation. (line 140) * -r: sort invocation. (line 185) * -R <1>: chmod invocation. (line 69) * -R: Which files are listed. (line 91) * -r <1>: tac invocation. (line 26) * -r <2>: touch invocation. (line 119) * -r <3>: who invocation. (line 75) * -r <4>: ln invocation. (line 138) * -r: Access permission tests. (line 15) * -R: chgrp invocation. (line 66) * -r <1>: Sorting the output. (line 27) * -r <2>: pr invocation. (line 207) * -r <3>: sum invocation. (line 25) * -r <4>: runcon invocation. (line 35) * -r <5>: id invocation. (line 39) * -r: chcon invocation. (line 55) * -R: chcon invocation. (line 30) * -r: truncate invocation. (line 30) * -R: rm invocation. (line 91) * -r <1>: rm invocation. (line 91) * -r: uname invocation. (line 61) * -R: cp invocation. (line 253) * -r: Options for date. (line 59) * -S: Sorting the output. (line 32) * -s <1>: readlink invocation. (line 54) * -s <2>: realpath invocation. (line 46) * -s <3>: sort invocation. (line 303) * -s <4>: Options for date. (line 107) * -s <5>: csplit invocation. (line 101) * -s <6>: tac invocation. (line 33) * -s <7>: paste invocation. (line 34) * -s <8>: cut invocation. (line 71) * -s <9>: cp invocation. (line 335) * -s <10>: pr invocation. (line 212) * -s <11>: sum invocation. (line 31) * -s: File characteristic tests. (line 12) * -S <1>: pr invocation. (line 221) * -S: sort invocation. (line 309) * -s: uniq invocation. (line 41) * -S: cp invocation. (line 343) * -s: fold invocation. (line 29) * -S: Backup options. (line 50) * -s <1>: tty invocation. (line 18) * -s <2>: uname invocation. (line 65) * -s <3>: du invocation. (line 138) * -s: truncate invocation. (line 34) * -S <1>: du invocation. (line 142) * -S: od invocation. (line 76) * -s: basename invocation. (line 38) * -S: mv invocation. (line 100) * -s <1>: nl invocation. (line 112) * -s <2>: od invocation. (line 200) * -s <3>: cat invocation. (line 36) * -s <4>: What information is listed. (line 244) * -s <5>: who invocation. (line 79) * -s: install invocation. (line 108) * -S: File type tests. (line 31) * -s: timeout invocation. (line 40) * -S: install invocation. (line 115) * -s: fmt invocation. (line 47) * -S: ln invocation. (line 156) * -s <1>: su invocation. (line 75) * -s: ln invocation. (line 150) * -s BYTES: shred invocation. (line 117) * -su: su invocation. (line 25) * -t <1>: who invocation. (line 83) * -t: install invocation. (line 120) * -T: who invocation. (line 95) * -t: md5sum invocation. (line 86) * -T <1>: install invocation. (line 124) * -T: cp invocation. (line 352) * -t <1>: cp invocation. (line 348) * -t: mv invocation. (line 105) * -T: mv invocation. (line 109) * -t <1>: stat invocation. (line 54) * -t: sort invocation. (line 325) * -T: sort invocation. (line 345) * -t <1>: chcon invocation. (line 59) * -t: runcon invocation. (line 39) * -T: pr invocation. (line 241) * -t: pr invocation. (line 230) * -T: df invocation. (line 119) * -t <1>: df invocation. (line 113) * -t <2>: ln invocation. (line 161) * -t: fmt invocation. (line 40) * -T: ln invocation. (line 165) * -t <1>: expand invocation. (line 22) * -t <2>: unexpand invocation. (line 24) * -t: od invocation. (line 85) * -T <1>: cat invocation. (line 44) * -T: General output formatting. (line 111) * -t <1>: cat invocation. (line 40) * -t <2>: Sorting the output. (line 36) * -t <3>: mktemp invocation. (line 122) * -t: File type tests. (line 34) * -u <1>: split invocation. (line 134) * -u <2>: shred invocation. (line 123) * -u <3>: id invocation. (line 44) * -u <4>: env invocation. (line 90) * -u <5>: Options for date. (line 113) * -u <6>: mv invocation. (line 82) * -u <7>: sort invocation. (line 361) * -u <8>: mktemp invocation. (line 98) * -u <9>: Sorting the output. (line 42) * -u <10>: fmt invocation. (line 53) * -u <11>: chcon invocation. (line 51) * -u <12>: uniq invocation. (line 101) * -u <13>: cp invocation. (line 357) * -u: runcon invocation. (line 31) * -U: Sorting the output. (line 49) * -u <1>: Access permission tests. (line 18) * -u <2>: cat invocation. (line 47) * -u: who invocation. (line 86) * -v <1>: chcon invocation. (line 47) * -v <2>: shred invocation. (line 129) * -v <3>: install invocation. (line 129) * -v <4>: chmod invocation. (line 59) * -v <5>: chown invocation. (line 132) * -v <6>: pr invocation. (line 246) * -v <7>: Sorting the output. (line 56) * -v <8>: cat invocation. (line 51) * -v <9>: mkdir invocation. (line 51) * -v <10>: mv invocation. (line 92) * -v <11>: rm invocation. (line 95) * -v <12>: tail invocation. (line 164) * -v <13>: head invocation. (line 50) * -v <14>: uname invocation. (line 76) * -v <15>: rmdir invocation. (line 31) * -v <16>: chgrp invocation. (line 58) * -v <17>: readlink invocation. (line 58) * -v: ln invocation. (line 170) * -V: sort invocation. (line 179) * -v <1>: nl invocation. (line 117) * -v <2>: cp invocation. (line 371) * -v: od invocation. (line 155) * -w <1>: fold invocation. (line 35) * -w: Access permission tests. (line 21) * -W: pr invocation. (line 259) * -w <1>: pr invocation. (line 250) * -w <2>: wc invocation. (line 51) * -w <3>: General output formatting. (line 123) * -w <4>: md5sum invocation. (line 95) * -w <5>: uniq invocation. (line 106) * -w <6>: nl invocation. (line 122) * -w <7>: od invocation. (line 162) * -w <8>: base64 invocation. (line 22) * -w <9>: fmt invocation. (line 59) * -w: who invocation. (line 95) * -WIDTH: fmt invocation. (line 59) * -x <1>: du invocation. (line 203) * -x <2>: od invocation. (line 203) * -x <3>: General output formatting. (line 107) * -x <4>: Access permission tests. (line 24) * -x <5>: cp invocation. (line 375) * -x <6>: shred invocation. (line 134) * -x: df invocation. (line 144) * -X: Sorting the output. (line 63) * -X FILE: du invocation. (line 213) * -z <1>: shuf invocation. (line 48) * -z <2>: shred invocation. (line 144) * -z: uniq invocation. (line 112) * -Z: mknod invocation. (line 54) * -z: csplit invocation. (line 90) * -Z <1>: install invocation. (line 133) * -Z: mkfifo invocation. (line 28) * -z <1>: dirname invocation. (line 31) * -z: realpath invocation. (line 53) * -Z: What information is listed. (line 268) * -z <1>: basename invocation. (line 42) * -z: sort invocation. (line 375) * -Z <1>: id invocation. (line 48) * -Z: mkdir invocation. (line 56) * -z: String tests. (line 15) * .cshrc: su invocation. (line 44) * /: Numeric expressions. (line 16) * /bin/sh: su invocation. (line 12) * /etc/passwd: su invocation. (line 12) * /etc/shells: su invocation. (line 64) * 128-bit checksum: md5sum invocation. (line 6) * 16-bit checksum: sum invocation. (line 6) * 160-bit checksum: sha1sum invocation. (line 6) * 224-bit checksum: sha2 utilities. (line 6) * 256-bit checksum: sha2 utilities. (line 6) * 384-bit checksum: sha2 utilities. (line 6) * 4.2 file system type: df invocation. (line 131) * 512-bit checksum: sha2 utilities. (line 6) * <: Relations for expr. (line 22) * <=: Relations for expr. (line 22) * = <1>: Relations for expr. (line 22) * =: String tests. (line 22) * == <1>: Relations for expr. (line 22) * ==: String tests. (line 25) * >: Relations for expr. (line 22) * >=: Relations for expr. (line 22) * \( regexp operator: String expressions. (line 24) * \+ regexp operator: String expressions. (line 28) * \? regexp operator: String expressions. (line 28) * \c: printf invocation. (line 29) * \OOO: printf invocation. (line 63) * \uhhhh: printf invocation. (line 70) * \Uhhhhhhhh: printf invocation. (line 70) * \xHH: printf invocation. (line 63) * \| regexp operator: String expressions. (line 28) * _POSIX2_VERSION <1>: sort invocation. (line 408) * _POSIX2_VERSION <2>: Standards conformance. (line 19) * _POSIX2_VERSION <3>: uniq invocation. (line 46) * _POSIX2_VERSION <4>: tail invocation. (line 175) * _POSIX2_VERSION: touch invocation. (line 138) * abbreviations for months: Calendar date items. (line 38) * access permission tests: Access permission tests. (line 6) * access permissions, changing: chmod invocation. (line 6) * access time: dd invocation. (line 227) * access time, changing: touch invocation. (line 78) * access time, printing or sorting files by: Sorting the output. (line 42) * access time, show the most recent: du invocation. (line 161) * across columns: pr invocation. (line 82) * across, listing files: General output formatting. (line 107) * adding permissions: Setting Permissions. (line 38) * addition: Numeric expressions. (line 12) * ago in date strings: Relative items in date strings. (line 23) * all repeated lines, outputting: uniq invocation. (line 69) * alnum: Character sets. (line 92) * alpha: Character sets. (line 95) * alternate ebcdic, converting to: dd invocation. (line 79) * always color option: General output formatting. (line 27) * always interactive option: rm invocation. (line 57) * am i: who invocation. (line 21) * am in date strings: Time of day items. (line 22) * and operator <1>: Connectives for test. (line 12) * and operator: Relations for expr. (line 17) * append: dd invocation. (line 167) * appending to the output file: dd invocation. (line 167) * appropriate privileges <1>: install invocation. (line 86) * appropriate privileges <2>: Setting the time. (line 6) * appropriate privileges <3>: hostname invocation. (line 6) * appropriate privileges: nice invocation. (line 6) * arbitrary date strings, parsing: Options for date. (line 11) * arbitrary text, displaying: echo invocation. (line 6) * arch: arch invocation. (line 6) * arithmetic tests: Numeric tests. (line 6) * ASCII dump of files: od invocation. (line 6) * ascii, converting to: dd invocation. (line 71) * atime, changing: touch invocation. (line 78) * atime, printing or sorting files by: Sorting the output. (line 42) * atime, show the most recent: du invocation. (line 161) * attributes, file: Changing file attributes. (line 6) * authors of parse_datetime: Authors of parse_datetime. (line 6) * auto color option: General output formatting. (line 25) * automounter file systems: df invocation. (line 32) * b for block special file: mknod invocation. (line 31) * background jobs, stopping at terminal write: Local. (line 41) * backslash escapes <1>: Character sets. (line 14) * backslash escapes: echo invocation. (line 25) * backslash sequences for file names: Formatting the file names. (line 11) * backup files, ignoring: Which files are listed. (line 23) * backup options: Backup options. (line 6) * backup suffix: Backup options. (line 50) * backups, making <1>: cp invocation. (line 80) * backups, making <2>: install invocation. (line 42) * backups, making <3>: ln invocation. (line 84) * backups, making <4>: mv invocation. (line 58) * backups, making: Backup options. (line 13) * backups, making only: cp invocation. (line 53) * base64: base64 invocation. (line 6) * Base64 decoding: base64 invocation. (line 30) * base64 encoding: base64 invocation. (line 6) * basename: basename invocation. (line 6) * baud rate, setting: Special. (line 43) * beeping at input buffer full: Input. (line 59) * beginning of time: Time conversion specifiers. (line 42) * beginning of time, for POSIX: Seconds since the Epoch. (line 13) * Bellovin, Steven M.: Authors of parse_datetime. (line 6) * Berets, Jim: Authors of parse_datetime. (line 6) * Berry, K. <1>: Authors of parse_datetime. (line 19) * Berry, K.: Introduction. (line 19) * binary: dd invocation. (line 244) * binary I/O: dd invocation. (line 244) * binary input files: md5sum invocation. (line 37) * bind mount <1>: stat invocation. (line 150) * bind mount: rm invocation. (line 67) * blank: Character sets. (line 98) * blank lines, numbering: nl invocation. (line 87) * blanks, ignoring leading: sort invocation. (line 79) * block (space-padding): dd invocation. (line 88) * block size <1>: Block size. (line 6) * block size: dd invocation. (line 33) * block size of conversion: dd invocation. (line 40) * block size of input: dd invocation. (line 25) * block size of output: dd invocation. (line 29) * block special check: File type tests. (line 10) * block special files: mknod invocation. (line 11) * block special files, creating: mknod invocation. (line 6) * BLOCK_SIZE: Block size. (line 12) * BLOCKSIZE: Block size. (line 12) * body, numbering: nl invocation. (line 17) * Bourne shell syntax for color setup: dircolors invocation. (line 34) * breaks, cause interrupts: Input. (line 12) * breaks, ignoring: Input. (line 9) * brkint: Input. (line 12) * bs: dd invocation. (line 33) * BSD sum: sum invocation. (line 25) * BSD tail: tail invocation. (line 19) * BSD touch compatibility: touch invocation. (line 96) * bsN: Output. (line 55) * bugs, reporting: Introduction. (line 12) * built-in shell commands, conflicts with <1>: sleep invocation. (line 34) * built-in shell commands, conflicts with <2>: kill invocation. (line 13) * built-in shell commands, conflicts with <3>: nice invocation. (line 37) * built-in shell commands, conflicts with <4>: pwd invocation. (line 30) * built-in shell commands, conflicts with <5>: test invocation. (line 28) * built-in shell commands, conflicts with <6>: printf invocation. (line 16) * built-in shell commands, conflicts with <7>: echo invocation. (line 11) * built-in shell commands, conflicts with <8>: stat invocation. (line 15) * built-in shell commands, conflicts with: mknod invocation. (line 20) * byte count: wc invocation. (line 6) * byte-swapping: dd invocation. (line 117) * c for character special file: mknod invocation. (line 34) * C shell syntax for color setup: dircolors invocation. (line 40) * C-s/C-q flow control: Input. (line 40) * calendar date item: Calendar date items. (line 6) * canonical file name <1>: readlink invocation. (line 6) * canonical file name: realpath invocation. (line 6) * canonicalize a file name <1>: realpath invocation. (line 6) * canonicalize a file name: readlink invocation. (line 6) * case folding: sort invocation. (line 94) * case translation: Local. (line 36) * case, ignored in dates: General date syntax. (line 66) * cat: cat invocation. (line 6) * cbreak: Combination. (line 52) * cbs: dd invocation. (line 40) * CD-ROM file system type: df invocation. (line 135) * cdfs file system type: df invocation. (line 135) * change or print terminal settings: stty invocation. (line 6) * change SELinux context: chcon invocation. (line 6) * changed files, verbosely describing: chgrp invocation. (line 20) * changed owners, verbosely describing: chown invocation. (line 70) * changing access permissions: chmod invocation. (line 6) * changing file attributes: Changing file attributes. (line 6) * changing file ownership: chown invocation. (line 6) * changing file timestamps: touch invocation. (line 6) * changing group ownership <1>: chgrp invocation. (line 6) * changing group ownership: chown invocation. (line 6) * changing security context: chcon invocation. (line 6) * changing special mode bits: Changing Special Mode Bits. (line 6) * character classes: Character sets. (line 79) * character count: wc invocation. (line 6) * character size: Control. (line 19) * character special check: File type tests. (line 13) * character special files: mknod invocation. (line 11) * character special files, creating: mknod invocation. (line 6) * characters, special: Characters. (line 6) * chcon: chcon invocation. (line 6) * check file types: test invocation. (line 6) * checking for sortedness: sort invocation. (line 26) * checksum, 128-bit: md5sum invocation. (line 6) * checksum, 16-bit: sum invocation. (line 6) * checksum, 160-bit: sha1sum invocation. (line 6) * checksum, 224-bit: sha2 utilities. (line 6) * checksum, 256-bit: sha2 utilities. (line 6) * checksum, 384-bit: sha2 utilities. (line 6) * checksum, 512-bit: sha2 utilities. (line 6) * chgrp: chgrp invocation. (line 6) * chmod: chmod invocation. (line 6) * chown: chown invocation. (line 6) * chroot: chroot invocation. (line 6) * cio: dd invocation. (line 175) * cksum: cksum invocation. (line 6) * clocal: Control. (line 33) * clock skew <1>: Formatting file timestamps. (line 12) * clock skew: touch invocation. (line 17) * clone: cp invocation. (line 266) * cntrl: Character sets. (line 101) * color database, printing: dircolors invocation. (line 45) * color setup: dircolors invocation. (line 6) * color, distinguishing file types with: General output formatting. (line 21) * cols: Special. (line 27) * column to wrap data after: base64 invocation. (line 22) * columns: Special. (line 27) * COLUMNS <1>: General output formatting. (line 123) * COLUMNS: Special. (line 30) * combination settings: Combination. (line 6) * combined date and time of day item: Combined date and time of day items. (line 6) * comm: comm invocation. (line 6) * command-line operands to shuffle: shuf invocation. (line 19) * commands for controlling processes: Process control. (line 6) * commands for delaying: Delaying. (line 6) * commands for exit status: Conditions. (line 6) * commands for file name manipulation: File name manipulation. (line 6) * commands for invoking other commands: Modified command invocation. (line 6) * commands for printing text: Printing text. (line 6) * commands for printing the working context: Working context. (line 6) * commands for printing user information: User information. (line 6) * commands for redirection: Redirection. (line 6) * commands for SELinux context: SELinux context. (line 6) * commands for system context: System context. (line 6) * commas, outputting between files: General output formatting. (line 97) * comments, in dates: General date syntax. (line 66) * common field, joining on: join invocation. (line 6) * common lines: comm invocation. (line 18) * common options: Common options. (line 6) * compare values: test invocation. (line 6) * comparing sorted files: comm invocation. (line 6) * comparison operators: Relations for expr. (line 22) * concatenate and write files: cat invocation. (line 6) * concurrent I/O: dd invocation. (line 175) * conditional executability: Conditional Executability. (line 6) * conditions: Conditions. (line 6) * conflicts with shell built-ins <1>: pwd invocation. (line 30) * conflicts with shell built-ins <2>: sleep invocation. (line 34) * conflicts with shell built-ins <3>: test invocation. (line 28) * conflicts with shell built-ins <4>: nice invocation. (line 37) * conflicts with shell built-ins <5>: mknod invocation. (line 20) * conflicts with shell built-ins <6>: stat invocation. (line 15) * conflicts with shell built-ins <7>: printf invocation. (line 16) * conflicts with shell built-ins <8>: echo invocation. (line 11) * conflicts with shell built-ins: kill invocation. (line 13) * connectives, logical <1>: Relations for expr. (line 6) * connectives, logical: Connectives for test. (line 6) * context splitting: csplit invocation. (line 6) * context, system: System context. (line 6) * control characters, using ^C: Local. (line 51) * control settings: Control. (line 6) * controlling terminal: dd invocation. (line 232) * conv: dd invocation. (line 65) * conversion block size: dd invocation. (line 40) * conversion specifiers, date: Date conversion specifiers. (line 6) * conversion specifiers, literal: Literal conversion specifiers. (line 6) * conversion specifiers, time: Time conversion specifiers. (line 6) * converting tabs to spaces: expand invocation. (line 6) * converting while copying a file: dd invocation. (line 6) * cooked: Combination. (line 37) * Coordinated Universal Time: Options for date. (line 113) * copy on write: cp invocation. (line 266) * copying directories recursively: cp invocation. (line 253) * copying existing permissions: Copying Permissions. (line 6) * copying files: cat invocation. (line 6) * copying files and directories: cp invocation. (line 6) * copying files and setting attributes: install invocation. (line 6) * core utilities: Top. (line 18) * count: dd invocation. (line 55) * count_bytes: dd invocation. (line 258) * COW: cp invocation. (line 266) * cp: cp invocation. (line 6) * crashes and corruption: sync invocation. (line 11) * CRC checksum: cksum invocation. (line 6) * cread: Control. (line 30) * creating directories: mkdir invocation. (line 6) * creating FIFOs (named pipes): mkfifo invocation. (line 6) * creating links (hard only): link invocation. (line 6) * creating links (hard or soft): ln invocation. (line 6) * creating output file, avoiding: dd invocation. (line 135) * creating output file, requiring: dd invocation. (line 131) * crN: Output. (line 45) * crown margin: fmt invocation. (line 34) * crt: Combination. (line 75) * crterase: Local. (line 22) * crtkill: Local. (line 56) * crtscts: Control. (line 36) * csh syntax for color setup: dircolors invocation. (line 40) * csN: Control. (line 19) * csplit: csplit invocation. (line 6) * cstopb: Control. (line 27) * ctime, printing or sorting by: Sorting the output. (line 13) * ctime, show the most recent: du invocation. (line 156) * ctlecho: Local. (line 51) * current working directory, printing: pwd invocation. (line 6) * cut: cut invocation. (line 6) * cyclic redundancy check: cksum invocation. (line 6) * data, erasing: shred invocation. (line 6) * database for color setup, printing: dircolors invocation. (line 45) * date: date invocation. (line 6) * date and time of day format, ISO 8601: Combined date and time of day items. (line 14) * date conversion specifiers: Date conversion specifiers. (line 6) * date format, ISO 8601: Calendar date items. (line 30) * date input formats: Date input formats. (line 6) * date options: Options for date. (line 6) * date strings, parsing: Options for date. (line 11) * day in date strings: Relative items in date strings. (line 15) * day of week item: Day of week items. (line 6) * dd: dd invocation. (line 6) * dec: Combination. (line 78) * decctlq: Combination. (line 63) * Decode base64 data: base64 invocation. (line 30) * delay for a specified time: sleep invocation. (line 6) * delaying commands: Delaying. (line 6) * deleting characters: Squeezing. (line 6) * dereferencing symbolic links: ln invocation. (line 42) * descriptor follow option: tail invocation. (line 48) * destination directory <1>: Target directory. (line 15) * destination directory <2>: install invocation. (line 124) * destination directory <3>: cp invocation. (line 348) * destination directory <4>: install invocation. (line 120) * destination directory <5>: cp invocation. (line 352) * destination directory <6>: ln invocation. (line 161) * destination directory <7>: mv invocation. (line 105) * destination directory: Target directory. (line 31) * destinations, multiple output: tee invocation. (line 6) * device file, disk: df invocation. (line 19) * df: df invocation. (line 6) * DF_BLOCK_SIZE: Block size. (line 12) * diagnostic: chcon invocation. (line 47) * dictionary order: sort invocation. (line 87) * differing lines: comm invocation. (line 18) * digit: Character sets. (line 104) * dir: dir invocation. (line 6) * dircolors: dircolors invocation. (line 6) * direct: dd invocation. (line 181) * direct I/O: dd invocation. (line 181) * directories, copying: cp invocation. (line 6) * directories, copying recursively: cp invocation. (line 253) * directories, creating: mkdir invocation. (line 6) * directories, creating with given attributes: install invocation. (line 62) * directories, removing (recursively): rm invocation. (line 91) * directories, removing empty: rmdir invocation. (line 6) * directory: dd invocation. (line 189) * directory check: File type tests. (line 16) * directory components, printing: dirname invocation. (line 6) * directory deletion, ignoring failures: rmdir invocation. (line 17) * directory deletion, reporting: rmdir invocation. (line 31) * directory I/O: dd invocation. (line 189) * directory listing: ls invocation. (line 6) * directory listing, brief: dir invocation. (line 6) * directory listing, recursive: Which files are listed. (line 91) * directory listing, verbose: vdir invocation. (line 6) * directory order, listing by: Sorting the output. (line 20) * directory, creating temporary: mktemp invocation. (line 6) * directory, stripping from file names: basename invocation. (line 6) * dired Emacs mode support: What information is listed. (line 16) * dirname: dirname invocation. (line 6) * disabling special characters: Characters. (line 13) * disambiguating group names and IDs: Disambiguating names and IDs. (line 6) * discarding file cache: dd invocation. (line 205) * disk allocation: What information is listed. (line 244) * disk device file: df invocation. (line 19) * disk usage: Disk usage. (line 6) * disk usage by file system: df invocation. (line 6) * disk usage for files: du invocation. (line 6) * diskette file system: df invocation. (line 139) * displacement of dates: Relative items in date strings. (line 6) * displaying text: echo invocation. (line 6) * displaying value of a symbolic link: readlink invocation. (line 6) * division: Numeric expressions. (line 16) * do nothing, successfully: true invocation. (line 6) * do nothing, unsuccessfully: false invocation. (line 6) * DOS file system: df invocation. (line 139) * double spacing: pr invocation. (line 94) * down columns: pr invocation. (line 68) * dsusp: Characters. (line 53) * dsync: dd invocation. (line 194) * du: du invocation. (line 6) * DU_BLOCK_SIZE: Block size. (line 12) * ebcdic, converting to: dd invocation. (line 75) * echo <1>: Local. (line 18) * echo: echo invocation. (line 6) * echoctl: Local. (line 51) * echoe: Local. (line 22) * echok: Local. (line 26) * echoke: Local. (line 56) * echonl: Local. (line 29) * echoprt: Local. (line 46) * effective user and group IDs, printing: id invocation. (line 6) * effective user ID, printing: whoami invocation. (line 6) * efs file system type: df invocation. (line 131) * Eggert, Paul: Authors of parse_datetime. (line 6) * eight-bit characters <1>: Control. (line 19) * eight-bit characters: Combination. (line 55) * eight-bit input: Input. (line 25) * ek: Combination. (line 22) * empty files, creating: touch invocation. (line 11) * empty lines, numbering: nl invocation. (line 87) * entire files, output of: Output of entire files. (line 6) * env: env invocation. (line 6) * environment variables, printing: printenv invocation. (line 6) * environment, preserving: su invocation. (line 64) * environment, printing: env invocation. (line 45) * environment, running a program in a modified: env invocation. (line 6) * eof: Characters. (line 32) * eol: Characters. (line 35) * eol2: Characters. (line 38) * epoch, for POSIX: Seconds since the Epoch. (line 13) * epoch, seconds since: Time conversion specifiers. (line 42) * equal string check: String tests. (line 25) * equivalence classes: Character sets. (line 128) * erase: Characters. (line 26) * erasing data: shred invocation. (line 6) * error messages, omitting <1>: chgrp invocation. (line 26) * error messages, omitting <2>: chown invocation. (line 76) * error messages, omitting: chmod invocation. (line 45) * evaluation of expressions: expr invocation. (line 6) * even parity: Control. (line 13) * evenp: Combination. (line 9) * exabyte, definition of: Block size. (line 117) * examples of date: Examples of date. (line 6) * examples of expr: Examples of expr. (line 6) * exbibyte, definition of: Block size. (line 121) * excl: dd invocation. (line 131) * excluding files from du: du invocation. (line 207) * executable file check: Access permission tests. (line 24) * executables and file type, marking: General output formatting. (line 48) * execute/search permission: Mode Structure. (line 18) * execute/search permission, symbolic: Setting Permissions. (line 63) * existence-of-file check: File characteristic tests. (line 9) * existing backup method: Backup options. (line 39) * exit status commands: Conditions. (line 6) * exit status of chroot: chroot invocation. (line 58) * exit status of env: env invocation. (line 100) * exit status of expr: expr invocation. (line 43) * exit status of false: false invocation. (line 6) * exit status of ls: ls invocation. (line 29) * exit status of mktemp: mktemp invocation. (line 130) * exit status of nice: nice invocation. (line 56) * exit status of nohup: nohup invocation. (line 47) * exit status of pathchk: pathchk invocation. (line 50) * exit status of printenv: printenv invocation. (line 25) * exit status of realpath: realpath invocation. (line 79) * exit status of runcon: runcon invocation. (line 46) * exit status of sort: sort invocation. (line 58) * exit status of stdbuf: stdbuf invocation. (line 67) * exit status of su: su invocation. (line 80) * exit status of test: test invocation. (line 41) * exit status of timeout: timeout invocation. (line 53) * exit status of true: true invocation. (line 6) * exit status of tty: tty invocation. (line 21) * expand: expand invocation. (line 6) * expr: expr invocation. (line 6) * expression evaluation <1>: expr invocation. (line 6) * expression evaluation: test invocation. (line 6) * expressions, numeric: Numeric expressions. (line 6) * expressions, string: String expressions. (line 6) * extended attributes, xattr <1>: install invocation. (line 35) * extended attributes, xattr: mv invocation. (line 34) * extension, sorting files by: Sorting the output. (line 63) * factor: factor invocation. (line 6) * failure exit status: false invocation. (line 6) * false: false invocation. (line 6) * fascism: su invocation. (line 87) * fdatasync: dd invocation. (line 147) * ffN: Output. (line 63) * field separator character: sort invocation. (line 325) * fields, padding numeric: Padding and other flags. (line 6) * FIFOs, creating: mkfifo invocation. (line 6) * file attributes, changing: Changing file attributes. (line 6) * file characteristic tests: File characteristic tests. (line 6) * file contents, dumping unambiguously: od invocation. (line 6) * file information, preserving: cp invocation. (line 236) * file information, preserving, extended attributes, xattr: cp invocation. (line 168) * file mode bits, numeric: Numeric Modes. (line 6) * file name manipulation: File name manipulation. (line 6) * file name pattern expansion, disabled: su invocation. (line 44) * file names, canonicalization: realpath invocation. (line 6) * file names, checking validity and portability: pathchk invocation. (line 6) * file names, creating temporary: mktemp invocation. (line 6) * file names, stripping directory and suffix: basename invocation. (line 6) * file offset radix: od invocation. (line 36) * file ownership, changing: chown invocation. (line 6) * file sizes: du invocation. (line 50) * file space usage: du invocation. (line 6) * file status: stat invocation. (line 6) * file system disk usage: df invocation. (line 6) * file system sizes: df invocation. (line 38) * file system space, retrieving current data more slowly: df invocation. (line 106) * file system space, retrieving old data more quickly: df invocation. (line 73) * file system status: stat invocation. (line 6) * file system types, limiting output to certain: df invocation. (line 69) * file system types, printing: df invocation. (line 119) * file systems: stat invocation. (line 28) * file systems and hard links: ln invocation. (line 6) * file systems, omitting copying to different: cp invocation. (line 375) * file timestamp resolution: touch invocation. (line 26) * file timestamps, changing: touch invocation. (line 6) * file type and executables, marking: General output formatting. (line 48) * file type tests: File type tests. (line 6) * file type, marking: General output formatting. (line 59) * file types: Special file types. (line 9) * file types, special: Special file types. (line 6) * file utilities: Top. (line 18) * files beginning with -, removing: rm invocation. (line 98) * files, copying: cp invocation. (line 6) * files, creating: truncate invocation. (line 11) * fingerprint, 128-bit: md5sum invocation. (line 6) * fingerprint, 160-bit: sha1sum invocation. (line 6) * fingerprint, 224-bit: sha2 utilities. (line 6) * fingerprint, 256-bit: sha2 utilities. (line 6) * fingerprint, 384-bit: sha2 utilities. (line 6) * fingerprint, 512-bit: sha2 utilities. (line 6) * first in date strings: General date syntax. (line 28) * first part of files, outputting: head invocation. (line 6) * fixed-length records, converting to variable-length: dd invocation. (line 40) * floating point: Floating point. (line 6) * flow control, hardware: Control. (line 36) * flow control, software: Input. (line 45) * flushing, disabling: Local. (line 32) * fmt: fmt invocation. (line 6) * fold: fold invocation. (line 6) * folding long input lines: fold invocation. (line 6) * footers, numbering: nl invocation. (line 17) * force deletion: shred invocation. (line 101) * formatting file contents: Formatting file contents. (line 6) * formatting of numbers in seq: seq invocation. (line 24) * formatting times <1>: date invocation. (line 20) * formatting times: pr invocation. (line 98) * fortnight in date strings: Relative items in date strings. (line 15) * fsync: dd invocation. (line 151) * fullblock: dd invocation. (line 252) * general date syntax: General date syntax. (line 6) * general numeric sort: sort invocation. (line 105) * gibibyte, definition of: Block size. (line 100) * gigabyte, definition of: Block size. (line 96) * giving away permissions: Umask and Protection. (line 12) * globbing, disabled: su invocation. (line 44) * GMT: Options for date. (line 113) * grand total of disk size, usage and available space: df invocation. (line 42) * grand total of disk space: du invocation. (line 55) * graph: Character sets. (line 107) * Greenwich Mean Time: Options for date. (line 113) * group IDs, disambiguating: Disambiguating names and IDs. (line 6) * group names, disambiguating: Disambiguating names and IDs. (line 6) * group owner, default: Mode Structure. (line 31) * group ownership of installed files, setting: install invocation. (line 68) * group ownership, changing <1>: chgrp invocation. (line 6) * group ownership, changing: chown invocation. (line 6) * group wheel, not supported: su invocation. (line 87) * group, permissions for: Setting Permissions. (line 26) * groups: groups invocation. (line 6) * growing files: tail invocation. (line 48) * hangups, immunity to: nohup invocation. (line 6) * hard link check: File characteristic tests. (line 23) * hard link, defined: ln invocation. (line 32) * hard links: dd invocation. (line 241) * hard links to directories: ln invocation. (line 90) * hard links to symbolic links: ln invocation. (line 173) * hard links, counting in du: du invocation. (line 96) * hard links, creating <1>: ln invocation. (line 6) * hard links, creating: link invocation. (line 6) * hard links, preserving: cp invocation. (line 108) * hardware class: uname invocation. (line 41) * hardware flow control: Control. (line 36) * hardware platform: uname invocation. (line 35) * hardware type: uname invocation. (line 41) * hat notation for control characters: Local. (line 51) * head: head invocation. (line 6) * head of output: shuf invocation. (line 32) * headers, numbering: nl invocation. (line 17) * help, online: Common options. (line 37) * hex dump of files: od invocation. (line 6) * High Sierra file system: df invocation. (line 135) * holes, copying files with: cp invocation. (line 296) * holes, creating files with: truncate invocation. (line 13) * HOME: su invocation. (line 18) * horizontal, listing files: General output formatting. (line 107) * host processor type: uname invocation. (line 50) * hostid: hostid invocation. (line 6) * hostname <1>: uname invocation. (line 46) * hostname: hostname invocation. (line 6) * hour in date strings: Relative items in date strings. (line 15) * hsfs file system type: df invocation. (line 135) * human numeric sort: sort invocation. (line 130) * human-readable output <1>: df invocation. (line 48) * human-readable output <2>: du invocation. (line 81) * human-readable output <3>: Block size. (line 43) * human-readable output: What information is listed. (line 116) * hup[cl]: Control. (line 23) * hurd, author, printing: What information is listed. (line 10) * ibs: dd invocation. (line 25) * icanon: Local. (line 11) * icrnl: Input. (line 34) * id: id invocation. (line 6) * idle time: who invocation. (line 86) * IEEE floating point: Floating point. (line 6) * iexten: Local. (line 15) * if: dd invocation. (line 17) * iflag: dd invocation. (line 156) * ignbrk: Input. (line 9) * igncr: Input. (line 31) * ignore file systems: df invocation. (line 32) * Ignore garbage in base64 stream: base64 invocation. (line 36) * ignoring case: sort invocation. (line 94) * ignpar: Input. (line 15) * imaxbel: Input. (line 59) * immunity to hangups: nohup invocation. (line 6) * implementation, hardware: uname invocation. (line 35) * indenting lines: pr invocation. (line 200) * index: String expressions. (line 45) * information, about current users: who invocation. (line 6) * initial part of files, outputting: head invocation. (line 6) * initial tabs, converting: expand invocation. (line 34) * inlcr: Input. (line 28) * inode number, printing: What information is listed. (line 123) * inode usage: df invocation. (line 58) * inode, and hard links: ln invocation. (line 32) * inodes, written buffered: sync invocation. (line 6) * inpck: Input. (line 22) * input block size: dd invocation. (line 25) * input encoding, UTF-8: Input. (line 37) * input range to shuffle: shuf invocation. (line 23) * input settings: Input. (line 6) * input tabs: pr invocation. (line 118) * install: install invocation. (line 6) * intr: Characters. (line 20) * invocation of commands, modified: Modified command invocation. (line 6) * isig: Local. (line 7) * ISO 8601 date and time of day format: Combined date and time of day items. (line 14) * ISO 8601 date format: Calendar date items. (line 30) * ISO/IEC 10646: printf invocation. (line 70) * ispeed: Special. (line 16) * istrip: Input. (line 25) * items in date strings: General date syntax. (line 6) * iterations, selecting the number of: shred invocation. (line 106) * iuclc: Input. (line 50) * iutf8: Input. (line 37) * ixany: Input. (line 55) * ixoff: Input. (line 45) * ixon: Input. (line 40) * join: join invocation. (line 6) * kernel name: uname invocation. (line 65) * kernel release: uname invocation. (line 61) * kernel version: uname invocation. (line 76) * kibibyte, definition of: Block size. (line 84) * kibibytes for file sizes: du invocation. (line 90) * kibibytes for file system sizes: df invocation. (line 63) * kill <1>: Characters. (line 29) * kill: kill invocation. (line 6) * kilobyte, definition of: Block size. (line 79) * Knuth, Donald E.: fmt invocation. (line 19) * language, in dates: General date syntax. (line 42) * last DAY <1>: Options for date. (line 11) * last DAY: Day of week items. (line 15) * last in date strings: General date syntax. (line 28) * last modified dates, displaying in du: du invocation. (line 150) * last part of files, outputting: tail invocation. (line 6) * LC_ALL <1>: sort invocation. (line 49) * LC_ALL: ls invocation. (line 17) * LC_COLLATE <1>: sort invocation. (line 49) * LC_COLLATE <2>: comm invocation. (line 12) * LC_COLLATE <3>: uniq invocation. (line 21) * LC_COLLATE <4>: join invocation. (line 14) * LC_COLLATE: Relations for expr. (line 22) * LC_CTYPE <1>: sort invocation. (line 79) * LC_CTYPE: printf invocation. (line 70) * LC_MESSAGES: pr invocation. (line 13) * LC_NUMERIC <1>: sort invocation. (line 105) * LC_NUMERIC <2>: printf invocation. (line 57) * LC_NUMERIC <3>: sort invocation. (line 162) * LC_NUMERIC <4>: Floating point. (line 17) * LC_NUMERIC: Block size. (line 58) * LC_TIME <1>: Formatting file timestamps. (line 30) * LC_TIME <2>: sort invocation. (line 152) * LC_TIME <3>: pr invocation. (line 105) * LC_TIME <4>: du invocation. (line 170) * LC_TIME: date invocation. (line 11) * LCASE: Combination. (line 71) * lcase: Combination. (line 71) * lcase, converting to: dd invocation. (line 99) * lchown <1>: chgrp invocation. (line 30) * lchown <2>: chown invocation. (line 103) * lchown <3>: chgrp invocation. (line 35) * lchown: chown invocation. (line 108) * leading directories, creating missing: install invocation. (line 62) * leading directory components, stripping: basename invocation. (line 6) * left margin: pr invocation. (line 200) * length: String expressions. (line 50) * limiting output of du: du invocation. (line 118) * line: Special. (line 37) * line buffered: stdbuf invocation. (line 6) * line count: wc invocation. (line 6) * line numbering: nl invocation. (line 6) * line settings of terminal: stty invocation. (line 6) * line-breaking: fmt invocation. (line 19) * line-by-line comparison: comm invocation. (line 6) * LINES: Special. (line 30) * link: link invocation. (line 6) * links, creating <1>: link invocation. (line 6) * links, creating: ln invocation. (line 6) * Linux file system types: df invocation. (line 131) * literal conversion specifiers: Literal conversion specifiers. (line 6) * litout: Combination. (line 59) * ln: ln invocation. (line 6) * ln format for nl: nl invocation. (line 98) * lnext: Characters. (line 62) * local file system types: df invocation. (line 131) * local settings: Local. (line 6) * logging out and continuing to run: nohup invocation. (line 6) * logical and operator <1>: Connectives for test. (line 12) * logical and operator: Relations for expr. (line 17) * logical connectives <1>: Relations for expr. (line 6) * logical connectives: Connectives for test. (line 6) * logical or operator <1>: Connectives for test. (line 15) * logical or operator: Relations for expr. (line 11) * logical pages, numbering on: nl invocation. (line 12) * login name, printing: logname invocation. (line 6) * login sessions, printing users with: users invocation. (line 6) * login shell: su invocation. (line 18) * login shell, creating: su invocation. (line 53) * login time: who invocation. (line 11) * logname: logname invocation. (line 6) * LOGNAME: su invocation. (line 18) * long ls format: What information is listed. (line 131) * lower: Character sets. (line 110) * lowercase, translating to output: Output. (line 12) * ls: ls invocation. (line 6) * LS_BLOCK_SIZE: Block size. (line 12) * LS_COLORS <1>: General output formatting. (line 33) * LS_COLORS: dircolors invocation. (line 23) * lutimes: touch invocation. (line 100) * machine type: uname invocation. (line 41) * machine-readable stty output: stty invocation. (line 41) * MacKenzie, D.: Introduction. (line 19) * MacKenzie, David: Authors of parse_datetime. (line 6) * Makefiles, installing programs in: install invocation. (line 30) * manipulating files: Basic operations. (line 6) * manipulation of file names: File name manipulation. (line 6) * match: String expressions. (line 36) * matching patterns: String expressions. (line 11) * MD5: md5sum invocation. (line 6) * md5sum: md5sum invocation. (line 6) * mebibyte, definition of: Block size. (line 93) * mebibytes for file sizes: du invocation. (line 106) * megabyte, definition of: Block size. (line 89) * merging files: paste invocation. (line 6) * merging files in parallel: pr invocation. (line 6) * merging sorted files: sort invocation. (line 32) * message status: who invocation. (line 95) * message-digest, 128-bit: md5sum invocation. (line 6) * message-digest, 160-bit: sha1sum invocation. (line 6) * message-digest, 224-bit: sha2 utilities. (line 6) * message-digest, 256-bit: sha2 utilities. (line 6) * message-digest, 384-bit: sha2 utilities. (line 6) * message-digest, 512-bit: sha2 utilities. (line 6) * Meyering, J.: Introduction. (line 19) * Meyering, Jim: Authors of parse_datetime. (line 6) * midnight in date strings: Time of day items. (line 22) * min: Special. (line 7) * minute in date strings: Relative items in date strings. (line 15) * minutes, time zone correction by: Time of day items. (line 30) * MIT AI lab: su invocation. (line 92) * mkdir: mkdir invocation. (line 6) * mkfifo: mkfifo invocation. (line 6) * mknod: mknod invocation. (line 6) * mktemp: mktemp invocation. (line 6) * modem control: Control. (line 33) * modes and umask: Umask and Protection. (line 6) * modes of created directories, setting: mkdir invocation. (line 19) * modes of created FIFOs, setting: mkfifo invocation. (line 21) * modification time, sorting files by: Sorting the output. (line 36) * modified command invocation: Modified command invocation. (line 6) * modified environment, running a program in a: env invocation. (line 6) * modify time, changing: touch invocation. (line 115) * month in date strings: Relative items in date strings. (line 15) * month names in date strings: Calendar date items. (line 38) * months, sorting by: sort invocation. (line 152) * months, written-out: General date syntax. (line 38) * MS-DOS file system: df invocation. (line 139) * mtime, changing: touch invocation. (line 115) * multicolumn output, generating: pr invocation. (line 6) * multiple changes to permissions: Multiple Changes. (line 6) * multiplication: Numeric expressions. (line 16) * multipliers after numbers: dd invocation. (line 284) * multithreaded sort: sort invocation. (line 353) * mv: mv invocation. (line 6) * name follow option: tail invocation. (line 48) * name of kernel: uname invocation. (line 65) * named pipe check: File type tests. (line 28) * named pipes, creating: mkfifo invocation. (line 6) * network node name: uname invocation. (line 46) * never interactive option: rm invocation. (line 52) * newer files, copying only: cp invocation. (line 357) * newer files, moving only: mv invocation. (line 82) * newer-than file check: File characteristic tests. (line 15) * newline echoing after kill: Local. (line 26) * newline, echoing: Local. (line 29) * newline, translating to crlf: Output. (line 19) * newline, translating to return: Input. (line 28) * next DAY <1>: Day of week items. (line 15) * next DAY: Options for date. (line 11) * next in date strings: General date syntax. (line 28) * NFS file system type: df invocation. (line 126) * NFS mounts from BSD to HP-UX <1>: What information is listed. (line 252) * NFS mounts from BSD to HP-UX: du invocation. (line 218) * nice: nice invocation. (line 6) * niceness: nice invocation. (line 6) * nl <1>: Combination. (line 18) * nl: nl invocation. (line 6) * nlN: Output. (line 39) * no dereference: chcon invocation. (line 22) * no-op: true invocation. (line 6) * noatime: dd invocation. (line 227) * nocache: dd invocation. (line 205) * nocreat: dd invocation. (line 135) * noctty: dd invocation. (line 232) * node name: uname invocation. (line 46) * noerror: dd invocation. (line 144) * noflsh: Local. (line 32) * nofollow: dd invocation. (line 238) * nohup: nohup invocation. (line 6) * nohup.out: nohup invocation. (line 18) * nolinks: dd invocation. (line 241) * non-directories, copying as special files: cp invocation. (line 95) * non-directory suffix, stripping: dirname invocation. (line 6) * nonblock: dd invocation. (line 224) * nonblocking I/O: dd invocation. (line 224) * none backup method: Backup options. (line 31) * none color option: General output formatting. (line 23) * none, sorting option for ls: Sorting the output. (line 49) * nonempty file check: File characteristic tests. (line 12) * nonprinting characters, ignoring: sort invocation. (line 145) * nonzero-length string check: String tests. (line 19) * noon in date strings: Time of day items. (line 22) * not-equal string check: String tests. (line 28) * notrunc: dd invocation. (line 141) * now in date strings: Relative items in date strings. (line 33) * nproc: nproc invocation. (line 6) * number of inputs to merge, nmerge: sort invocation. (line 259) * numbered backup method: Backup options. (line 35) * numbering lines: nl invocation. (line 6) * numbers, written-out: General date syntax. (line 28) * numeric expressions: Numeric expressions. (line 6) * numeric field padding: Padding and other flags. (line 6) * numeric modes: Numeric Modes. (line 6) * numeric operations: Numeric operations. (line 6) * numeric sequences: seq invocation. (line 6) * numeric sort: sort invocation. (line 162) * numeric tests: Numeric tests. (line 6) * numeric uid and gid: What information is listed. (line 234) * numeric user and group IDs: What information is listed. (line 234) * obs: dd invocation. (line 29) * ocrnl: Output. (line 16) * octal dump of files: od invocation. (line 6) * octal numbers for file modes: Numeric Modes. (line 6) * od: od invocation. (line 6) * odd parity: Control. (line 13) * oddp: Combination. (line 14) * of: dd invocation. (line 20) * ofdel: Output. (line 34) * ofill: Output. (line 30) * oflag: dd invocation. (line 160) * olcuc: Output. (line 12) * older-than file check: File characteristic tests. (line 19) * once interactive option: rm invocation. (line 54) * one file system, restricting du to: du invocation. (line 203) * one file system, restricting rm to: rm invocation. (line 63) * one-line output format: df invocation. (line 80) * onlcr: Output. (line 19) * onlret: Output. (line 27) * onocr: Output. (line 23) * operating on characters: Operating on characters. (line 6) * operating on sorted files: Operating on sorted files. (line 6) * operating system name: uname invocation. (line 57) * opost: Output. (line 9) * option delimiter: Common options. (line 44) * options for date: Options for date. (line 6) * or operator <1>: Connectives for test. (line 15) * or operator: Relations for expr. (line 11) * ordinal numbers: General date syntax. (line 28) * ospeed: Special. (line 19) * other permissions: Setting Permissions. (line 29) * output block size: dd invocation. (line 29) * output file name prefix <1>: split invocation. (line 15) * output file name prefix: csplit invocation. (line 62) * output file name suffix: csplit invocation. (line 66) * output format: stat invocation. (line 34) * output format, portable: df invocation. (line 80) * output NUL-byte-terminated lines <1>: printenv invocation. (line 19) * output NUL-byte-terminated lines <2>: du invocation. (line 124) * output NUL-byte-terminated lines: env invocation. (line 83) * output of entire files: Output of entire files. (line 6) * output of parts of files: Output of parts of files. (line 6) * output settings: Output. (line 6) * output tabs: pr invocation. (line 137) * overwriting of input, allowed <1>: sort invocation. (line 285) * overwriting of input, allowed: shuf invocation. (line 37) * owned by effective group ID check: Access permission tests. (line 31) * owned by effective user ID check: Access permission tests. (line 28) * owner of file, permissions for: Setting Permissions. (line 23) * owner, default: Mode Structure. (line 31) * ownership of installed files, setting: install invocation. (line 86) * p for FIFO file: mknod invocation. (line 28) * pad character: Output. (line 34) * pad instead of timing for delaying: Output. (line 30) * padding of numeric fields: Padding and other flags. (line 6) * paragraphs, reformatting: fmt invocation. (line 6) * parenb: Control. (line 9) * parent directories and cp: cp invocation. (line 240) * parent directories, creating: mkdir invocation. (line 34) * parent directories, creating missing: install invocation. (line 62) * parent directories, removing: rmdir invocation. (line 22) * parentheses for grouping: expr invocation. (line 31) * parity: Combination. (line 10) * parity errors, marking: Input. (line 18) * parity, ignoring: Input. (line 15) * parmrk: Input. (line 18) * parodd: Control. (line 13) * parse_datetime: Date input formats. (line 6) * parsing date strings: Options for date. (line 11) * parts of files, output of: Output of parts of files. (line 6) * pass8: Combination. (line 55) * passwd entry, and su shell: su invocation. (line 12) * paste: paste invocation. (line 6) * Paterson, R.: Introduction. (line 19) * PATH <1>: su invocation. (line 53) * PATH: env invocation. (line 23) * pathchk: pathchk invocation. (line 6) * pattern matching: String expressions. (line 11) * PC file system: df invocation. (line 139) * pcfs: df invocation. (line 139) * pebibyte, definition of: Block size. (line 114) * permission tests: Access permission tests. (line 6) * permissions of installed files, setting: install invocation. (line 74) * permissions, changing access: chmod invocation. (line 6) * permissions, copying existing: Copying Permissions. (line 6) * permissions, for changing file timestamps: touch invocation. (line 40) * permissions, output by ls: What information is listed. (line 191) * petabyte, definition of: Block size. (line 110) * phone directory order: sort invocation. (line 87) * pieces, splitting a file into: split invocation. (line 6) * Pinard, F. <1>: Introduction. (line 19) * Pinard, F.: Authors of parse_datetime. (line 19) * pipe fitting: tee invocation. (line 6) * Plass, Michael F.: fmt invocation. (line 19) * platform, hardware: uname invocation. (line 35) * pm in date strings: Time of day items. (line 22) * portable file names, checking for: pathchk invocation. (line 6) * portable output format: df invocation. (line 80) * POSIX: Introduction. (line 11) * POSIX output format: df invocation. (line 80) * POSIXLY_CORRECT <1>: sort invocation. (line 293) * POSIXLY_CORRECT <2>: id invocation. (line 11) * POSIXLY_CORRECT <3>: printf invocation. (line 48) * POSIXLY_CORRECT <4>: pr invocation. (line 105) * POSIXLY_CORRECT <5>: Standards conformance. (line 6) * POSIXLY_CORRECT <6>: echo invocation. (line 78) * POSIXLY_CORRECT <7>: Common options. (line 11) * POSIXLY_CORRECT: dd invocation. (line 325) * POSIXLY_CORRECT, and block size: Block size. (line 12) * pr: pr invocation. (line 6) * prime factors: factor invocation. (line 6) * print: Character sets. (line 113) * print machine hardware name: arch invocation. (line 6) * print name of current directory: pwd invocation. (line 6) * print system information: uname invocation. (line 6) * print terminal file name: tty invocation. (line 6) * Print the number of processors: nproc invocation. (line 6) * printenv: printenv invocation. (line 6) * printf: printf invocation. (line 6) * printing all or some environment variables: printenv invocation. (line 6) * printing color database: dircolors invocation. (line 45) * printing current user information: who invocation. (line 6) * printing current usernames: users invocation. (line 6) * printing groups a user is in: groups invocation. (line 6) * printing real and effective user and group IDs: id invocation. (line 6) * printing text: echo invocation. (line 6) * printing text, commands for: Printing text. (line 6) * printing the current time: date invocation. (line 6) * printing the effective user ID: whoami invocation. (line 6) * printing the host identifier: hostid invocation. (line 6) * printing the hostname: hostname invocation. (line 6) * printing the system uptime and load: uptime invocation. (line 6) * printing user's login name: logname invocation. (line 6) * printing, preparing files for: pr invocation. (line 6) * process zero-terminated items <1>: shuf invocation. (line 48) * process zero-terminated items <2>: sort invocation. (line 375) * process zero-terminated items: uniq invocation. (line 112) * processes, commands for controlling: Process control. (line 6) * prompting, and ln: ln invocation. (line 100) * prompting, and mv: mv invocation. (line 38) * prompting, and rm: rm invocation. (line 11) * prompts, forcing: mv invocation. (line 69) * prompts, omitting: mv invocation. (line 76) * prterase: Local. (line 46) * ptx: ptx invocation. (line 6) * punct: Character sets. (line 116) * pure numbers in date strings: Pure numbers in date strings. (line 6) * pwd: pwd invocation. (line 6) * quit: Characters. (line 23) * quoting style: Formatting the file names. (line 34) * radix for file offsets: od invocation. (line 36) * random sort: sort invocation. (line 191) * random source for shredding: shred invocation. (line 112) * random source for shuffling: shuf invocation. (line 43) * random source for sorting: sort invocation. (line 298) * random sources: Random sources. (line 6) * ranges: Character sets. (line 51) * raw: Combination. (line 43) * read errors, ignoring: dd invocation. (line 144) * read from stdin and write to stdout and files: tee invocation. (line 6) * read permission: Mode Structure. (line 12) * read permission, symbolic: Setting Permissions. (line 57) * read system call, and holes: cp invocation. (line 296) * readable file check: Access permission tests. (line 15) * readlink: readlink invocation. (line 6) * real user and group IDs, printing: id invocation. (line 6) * realpath <1>: readlink invocation. (line 6) * realpath: realpath invocation. (line 6) * recursive directory listing: Which files are listed. (line 91) * recursively changing access permissions: chmod invocation. (line 69) * recursively changing file ownership: chown invocation. (line 140) * recursively changing group ownership: chgrp invocation. (line 66) * recursively copying directories: cp invocation. (line 253) * redirection: Redirection. (line 6) * reference file: chcon invocation. (line 25) * reformatting paragraph text: fmt invocation. (line 6) * regular expression matching: String expressions. (line 11) * regular file check: File type tests. (line 19) * relations, numeric or string: Relations for expr. (line 6) * relative items in date strings: Relative items in date strings. (line 6) * release of kernel: uname invocation. (line 61) * relpath: realpath invocation. (line 56) * remainder: Numeric expressions. (line 16) * remote hostname: who invocation. (line 11) * removing empty directories: rmdir invocation. (line 6) * removing files after shredding: shred invocation. (line 123) * removing files or directories: rm invocation. (line 6) * removing files or directories (via the unlink syscall): unlink invocation. (line 6) * removing permissions: Setting Permissions. (line 42) * repeated characters: Character sets. (line 72) * repeated lines, outputting: uniq invocation. (line 63) * repeated output of a string: yes invocation. (line 6) * restricted deletion flag: Mode Structure. (line 56) * restricted shell: su invocation. (line 64) * return, ignoring: Input. (line 31) * return, translating to newline <1>: Input. (line 34) * return, translating to newline: Output. (line 16) * reverse sorting <1>: Sorting the output. (line 27) * reverse sorting: sort invocation. (line 185) * reversing files: tac invocation. (line 6) * rm: rm invocation. (line 6) * rmdir: rmdir invocation. (line 6) * rn format for nl: nl invocation. (line 101) * root as default owner: install invocation. (line 86) * root directory, allow recursive destruction: rm invocation. (line 84) * root directory, allow recursive modification <1>: chown invocation. (line 121) * root directory, allow recursive modification <2>: chmod invocation. (line 54) * root directory, allow recursive modification: chgrp invocation. (line 48) * root directory, disallow recursive destruction: rm invocation. (line 79) * root directory, disallow recursive modification <1>: chown invocation. (line 116) * root directory, disallow recursive modification <2>: chmod invocation. (line 49) * root directory, disallow recursive modification: chgrp invocation. (line 43) * root directory, running a program in a specified: chroot invocation. (line 6) * root, becoming: su invocation. (line 6) * rows: Special. (line 22) * rprnt: Characters. (line 56) * RTS/CTS flow control: Control. (line 36) * run commands with bounded time: timeout invocation. (line 6) * run with security context: runcon invocation. (line 6) * runcon: runcon invocation. (line 6) * running a program in a modified environment: env invocation. (line 6) * running a program in a specified root directory: chroot invocation. (line 6) * rz format for nl: nl invocation. (line 104) * Salz, Rich: Authors of parse_datetime. (line 6) * same file check: File characteristic tests. (line 23) * sane: Combination. (line 26) * scheduling, affecting: nice invocation. (line 6) * screen columns: fold invocation. (line 14) * seconds since the epoch: Time conversion specifiers. (line 42) * section delimiters of pages: nl invocation. (line 68) * security context <1>: mkdir invocation. (line 56) * security context <2>: mkfifo invocation. (line 28) * security context <3>: install invocation. (line 133) * security context <4>: id invocation. (line 48) * security context <5>: What information is listed. (line 268) * security context <6>: mknod invocation. (line 54) * security context: install invocation. (line 91) * seek: dd invocation. (line 50) * seek_bytes: dd invocation. (line 270) * self-backups: cp invocation. (line 53) * SELinux <1>: install invocation. (line 91) * SELinux <2>: id invocation. (line 48) * SELinux <3>: mkfifo invocation. (line 28) * SELinux <4>: What information is listed. (line 268) * SELinux <5>: mknod invocation. (line 54) * SELinux <6>: mkdir invocation. (line 56) * SELinux: install invocation. (line 133) * SELinux context: SELinux context. (line 6) * SELinux, context: SELinux context. (line 6) * send a signal to processes: kill invocation. (line 6) * sentences and line-breaking: fmt invocation. (line 19) * separator for numbers in seq: seq invocation. (line 42) * seq: seq invocation. (line 6) * sequence of numbers: seq invocation. (line 6) * set-group-ID: Mode Structure. (line 49) * set-group-ID check: Access permission tests. (line 9) * set-user-ID: Mode Structure. (line 42) * set-user-ID check: Access permission tests. (line 18) * setgid: Mode Structure. (line 49) * setting permissions: Setting Permissions. (line 46) * setting the hostname: hostname invocation. (line 6) * setting the time: Setting the time. (line 6) * setuid: Mode Structure. (line 42) * setup for color: dircolors invocation. (line 6) * sh syntax for color setup: dircolors invocation. (line 34) * SHA-1: sha1sum invocation. (line 6) * SHA-2: sha2 utilities. (line 6) * sha1sum: sha1sum invocation. (line 6) * sha224sum: sha2 utilities. (line 6) * sha256sum: sha2 utilities. (line 6) * sha384sum: sha2 utilities. (line 6) * sha512sum: sha2 utilities. (line 6) * SHELL: su invocation. (line 18) * SHELL environment variable, and color <1>: dircolors invocation. (line 23) * SHELL environment variable, and color: General output formatting. (line 33) * shell utilities: Top. (line 18) * shred: shred invocation. (line 6) * shuf: shuf invocation. (line 6) * shuffling files: shuf invocation. (line 6) * SI output <1>: df invocation. (line 99) * SI output <2>: What information is listed. (line 260) * SI output <3>: Block size. (line 43) * SI output: du invocation. (line 130) * signals, specifying: Signal specifications. (line 6) * simple backup method: Backup options. (line 44) * SIMPLE_BACKUP_SUFFIX: Backup options. (line 50) * single-column output of files: General output formatting. (line 10) * size: Special. (line 30) * size for main memory sorting: sort invocation. (line 309) * size of file to shred: shred invocation. (line 117) * size of files, reporting: What information is listed. (line 244) * size of files, sorting files by: Sorting the output. (line 32) * skip: dd invocation. (line 45) * skip_bytes: dd invocation. (line 264) * sleep: sleep invocation. (line 6) * socket check: File type tests. (line 31) * software flow control: Input. (line 45) * sort: sort invocation. (line 6) * sort field: sort invocation. (line 234) * sort stability: sort invocation. (line 303) * sort's last-resort comparison: sort invocation. (line 38) * sorted files, operations on: Operating on sorted files. (line 6) * sorting files: sort invocation. (line 6) * sorting ls output: Sorting the output. (line 6) * space: Character sets. (line 119) * sparse: dd invocation. (line 107) * sparse files, copying: cp invocation. (line 296) * sparse files, creating: truncate invocation. (line 13) * special characters: Characters. (line 6) * special file types: Special file types. (line 9) * special files: mknod invocation. (line 11) * special settings: Special. (line 6) * specifying sets of characters: Character sets. (line 6) * speed: Special. (line 40) * split: split invocation. (line 6) * splitting a file into pieces: split invocation. (line 6) * splitting a file into pieces by context: csplit invocation. (line 6) * squeezing empty lines: cat invocation. (line 36) * squeezing repeat characters: Squeezing. (line 6) * Stallman, R.: Introduction. (line 19) * standard input: Common options. (line 49) * standard output: Common options. (line 49) * standard streams, buffering: stdbuf invocation. (line 6) * start: Characters. (line 44) * stat: stat invocation. (line 6) * status: dd invocation. (line 61) * status time, printing or sorting by: Sorting the output. (line 13) * status time, show the most recent: du invocation. (line 156) * stdbuf: stdbuf invocation. (line 6) * sticky: Mode Structure. (line 56) * sticky bit check: Access permission tests. (line 12) * stop: Characters. (line 47) * stop bits: Control. (line 27) * strftime and date: date invocation. (line 20) * string constants, outputting: od invocation. (line 76) * string expressions: String expressions. (line 6) * string tests: String tests. (line 6) * strip directory and suffix from file names: basename invocation. (line 6) * stripping non-directory suffix: dirname invocation. (line 6) * stripping symbol table information: install invocation. (line 108) * stripping trailing slashes <1>: mv invocation. (line 95) * stripping trailing slashes: cp invocation. (line 330) * stty: stty invocation. (line 6) * su: su invocation. (line 6) * substitute user and group IDs: su invocation. (line 6) * substr: String expressions. (line 40) * subtracting permissions: Setting Permissions. (line 42) * subtraction: Numeric expressions. (line 12) * successful exit: true invocation. (line 6) * suffix, stripping from file names: basename invocation. (line 6) * sum: sum invocation. (line 6) * summarizing files: Summarizing files. (line 6) * super-user, becoming: su invocation. (line 6) * superblock, writing: sync invocation. (line 6) * supplementary groups, printing: groups invocation. (line 6) * susp: Characters. (line 50) * swab (byte-swapping): dd invocation. (line 117) * swap space, saving text image in: Mode Structure. (line 56) * swtch: Characters. (line 41) * symbol table information, stripping: install invocation. (line 108) * symbol table information, stripping, program: install invocation. (line 111) * symbolic (soft) links, creating: ln invocation. (line 6) * symbolic link check: File type tests. (line 23) * symbolic link to directory, controlling traversal of: Traversing symlinks. (line 6) * symbolic link to directory, never traverse <1>: Traversing symlinks. (line 26) * symbolic link to directory, never traverse <2>: chown invocation. (line 152) * symbolic link to directory, never traverse <3>: chgrp invocation. (line 79) * symbolic link to directory, never traverse: chcon invocation. (line 42) * symbolic link to directory, traverse each that is encountered <1>: chcon invocation. (line 38) * symbolic link to directory, traverse each that is encountered <2>: chgrp invocation. (line 75) * symbolic link to directory, traverse each that is encountered <3>: Traversing symlinks. (line 22) * symbolic link to directory, traverse each that is encountered: chown invocation. (line 148) * symbolic link to directory, traverse if on the command line <1>: chcon invocation. (line 33) * symbolic link to directory, traverse if on the command line <2>: chown invocation. (line 143) * symbolic link to directory, traverse if on the command line <3>: Traversing symlinks. (line 18) * symbolic link to directory, traverse if on the command line: chgrp invocation. (line 70) * symbolic link, defined: ln invocation. (line 42) * symbolic links and ln: ln invocation. (line 173) * symbolic links and pwd: pwd invocation. (line 26) * symbolic links, changing group: chgrp invocation. (line 35) * symbolic links, changing owner <1>: chown invocation. (line 80) * symbolic links, changing owner <2>: chgrp invocation. (line 30) * symbolic links, changing owner: chown invocation. (line 103) * symbolic links, changing time: touch invocation. (line 100) * symbolic links, copying: cp invocation. (line 161) * symbolic links, copying with: cp invocation. (line 335) * symbolic links, dereferencing: Which files are listed. (line 41) * symbolic links, dereferencing in du: du invocation. (line 101) * symbolic links, dereferencing in stat: stat invocation. (line 22) * symbolic links, following: dd invocation. (line 238) * symbolic links, permissions of: chmod invocation. (line 10) * symbolic modes: Symbolic Modes. (line 6) * symlinks, resolution: realpath invocation. (line 6) * sync <1>: sync invocation. (line 6) * sync: dd invocation. (line 202) * sync (padding with ASCII NULs): dd invocation. (line 122) * synchronize disk and memory: sync invocation. (line 6) * synchronized data and metadata I/O: dd invocation. (line 202) * synchronized data and metadata writes, before finishing: dd invocation. (line 151) * synchronized data reads: dd invocation. (line 194) * synchronized data writes, before finishing: dd invocation. (line 147) * syslog: su invocation. (line 29) * system context: System context. (line 6) * system information, printing <1>: uname invocation. (line 6) * system information, printing <2>: arch invocation. (line 6) * system information, printing: nproc invocation. (line 6) * system name, printing: hostname invocation. (line 6) * System V sum: sum invocation. (line 31) * tab stops, setting: expand invocation. (line 22) * tabN: Output. (line 51) * tabs: Combination. (line 66) * tabs to spaces, converting: expand invocation. (line 6) * tac: tac invocation. (line 6) * tagged paragraphs: fmt invocation. (line 40) * tail: tail invocation. (line 6) * tandem: Input. (line 45) * target directory <1>: Target directory. (line 31) * target directory <2>: install invocation. (line 120) * target directory <3>: Target directory. (line 15) * target directory <4>: mv invocation. (line 105) * target directory <5>: install invocation. (line 124) * target directory <6>: cp invocation. (line 352) * target directory <7>: ln invocation. (line 165) * target directory: mv invocation. (line 109) * tebibyte, definition of: Block size. (line 107) * tee: tee invocation. (line 6) * telephone directory order: sort invocation. (line 87) * temporary directory: sort invocation. (line 345) * temporary files and directories: mktemp invocation. (line 6) * terabyte, definition of: Block size. (line 103) * TERM: su invocation. (line 53) * terminal check: File type tests. (line 34) * terminal file name, printing: tty invocation. (line 6) * terminal lines, currently used: who invocation. (line 11) * terminal settings: stty invocation. (line 6) * terminal, using color iff: General output formatting. (line 25) * terse output: stat invocation. (line 54) * test: test invocation. (line 6) * text: dd invocation. (line 248) * text I/O: dd invocation. (line 248) * text image, saving in swap space: Mode Structure. (line 56) * text input files: md5sum invocation. (line 86) * text utilities: Top. (line 18) * text, displaying: echo invocation. (line 6) * text, reformatting: fmt invocation. (line 6) * this in date strings: Relative items in date strings. (line 33) * time <1>: Special. (line 11) * time: touch invocation. (line 86) * time conversion specifiers: Time conversion specifiers. (line 6) * time formats <1>: pr invocation. (line 98) * time formats: date invocation. (line 20) * time limit: timeout invocation. (line 6) * time of day item: Time of day items. (line 6) * time setting: Setting the time. (line 6) * time style <1>: du invocation. (line 165) * time style: Formatting file timestamps. (line 26) * time units <1>: sleep invocation. (line 11) * time units: timeout invocation. (line 44) * time zone correction: Time of day items. (line 30) * time zone item <1>: General date syntax. (line 46) * time zone item: Time zone items. (line 6) * time, printing or setting: date invocation. (line 6) * TIME_STYLE <1>: Formatting file timestamps. (line 106) * TIME_STYLE: du invocation. (line 193) * timeout: timeout invocation. (line 6) * timestamps of installed files, preserving: install invocation. (line 98) * timestamps, changing file: touch invocation. (line 6) * TMPDIR: sort invocation. (line 345) * today in date strings: Relative items in date strings. (line 33) * tomorrow: Options for date. (line 11) * tomorrow in date strings: Relative items in date strings. (line 29) * topological sort: tsort invocation. (line 6) * tostop: Local. (line 41) * total counts: wc invocation. (line 12) * touch: touch invocation. (line 6) * tr: tr invocation. (line 6) * trailing slashes: Trailing slashes. (line 6) * translating characters: Translating. (line 6) * true: true invocation. (line 6) * truncate: truncate invocation. (line 6) * truncating output file, avoiding: dd invocation. (line 141) * truncating, file sizes: truncate invocation. (line 6) * tsort: tsort invocation. (line 6) * tty: tty invocation. (line 6) * Twenex: su invocation. (line 92) * two-way parity: Control. (line 9) * type size: od invocation. (line 122) * TZ <1>: touch invocation. (line 65) * TZ <2>: Formatting file timestamps. (line 18) * TZ <3>: pr invocation. (line 111) * TZ <4>: who invocation. (line 26) * TZ <5>: date invocation. (line 16) * TZ <6>: Options for date. (line 113) * TZ <7>: Specifying time zone rules. (line 6) * TZ: stat invocation. (line 182) * u, and disabling special characters: Characters. (line 13) * ucase, converting to: dd invocation. (line 102) * ufs file system type: df invocation. (line 131) * umask and modes: Umask and Protection. (line 6) * uname: uname invocation. (line 6) * unblock: dd invocation. (line 93) * unexpand: unexpand invocation. (line 6) * Unicode: printf invocation. (line 70) * uniq: uniq invocation. (line 6) * unique lines, outputting: uniq invocation. (line 101) * uniquify files: uniq invocation. (line 6) * uniquifying output: sort invocation. (line 361) * unlink: unlink invocation. (line 6) * unprintable characters, ignoring: sort invocation. (line 145) * unsorted directory listing: Sorting the output. (line 20) * upper: Character sets. (line 122) * uppercase, translating to lowercase: Input. (line 50) * uptime: uptime invocation. (line 6) * use time, changing: touch invocation. (line 78) * use time, printing or sorting files by: Sorting the output. (line 42) * use time, show the most recent: du invocation. (line 156) * USER: su invocation. (line 18) * user ID, switching: su invocation. (line 6) * user IDs, disambiguating: Disambiguating names and IDs. (line 6) * user information, commands for: User information. (line 6) * user name, printing: logname invocation. (line 6) * user names, disambiguating: Disambiguating names and IDs. (line 6) * usernames, printing current: users invocation. (line 6) * users: users invocation. (line 6) * UTC: Options for date. (line 113) * utmp <1>: logname invocation. (line 6) * utmp <2>: users invocation. (line 14) * utmp: who invocation. (line 15) * valid file names, checking for: pathchk invocation. (line 6) * variable-length records, converting to fixed-length: dd invocation. (line 40) * vdir: vdir invocation. (line 6) * verbose ls format: What information is listed. (line 131) * verifying MD5 checksums: md5sum invocation. (line 68) * version number sort: sort invocation. (line 179) * version number, finding: Common options. (line 41) * version of kernel: uname invocation. (line 76) * version, sorting option for ls: Sorting the output. (line 56) * version-control Emacs variable: Backup options. (line 24) * VERSION_CONTROL <1>: install invocation. (line 42) * VERSION_CONTROL <2>: cp invocation. (line 80) * VERSION_CONTROL <3>: mv invocation. (line 58) * VERSION_CONTROL <4>: ln invocation. (line 84) * VERSION_CONTROL: Backup options. (line 13) * vertical sorted files in columns: General output formatting. (line 15) * vtN: Output. (line 59) * wc: wc invocation. (line 6) * week in date strings: Relative items in date strings. (line 15) * werase: Characters. (line 59) * wheel group, not supported: su invocation. (line 87) * who: who invocation. (line 6) * who am i: who invocation. (line 21) * whoami: whoami invocation. (line 6) * word count: wc invocation. (line 6) * working context: Working context. (line 6) * working directory, printing: pwd invocation. (line 6) * wrap data: base64 invocation. (line 22) * wrapping long input lines: fold invocation. (line 6) * writable file check: Access permission tests. (line 21) * write permission: Mode Structure. (line 15) * write permission, symbolic: Setting Permissions. (line 60) * write, allowed: who invocation. (line 95) * wtmp <1>: who invocation. (line 15) * wtmp: users invocation. (line 14) * xcase: Local. (line 36) * xdigit: Character sets. (line 125) * XON/XOFF flow control: Input. (line 40) * year in date strings: Relative items in date strings. (line 15) * yes: yes invocation. (line 6) * yesterday: Options for date. (line 11) * yesterday in date strings: Relative items in date strings. (line 29) * yottabyte, definition of: Block size. (line 131) * Youmans, B.: Introduction. (line 19) * zero-length string check: String tests. (line 15) * zettabyte, definition of: Block size. (line 124) * |: Relations for expr. (line 11)  Tag Table: Node: Top8539 Node: Introduction22434 Node: Common options23993 Node: Exit status27269 Node: Backup options28020 Node: Block size29944 Node: Floating point34798 Node: Signal specifications36208 Node: Disambiguating names and IDs38262 Ref: Disambiguating names and IDs-Footnote-139831 Node: Random sources39901 Node: Target directory41518 Node: Trailing slashes45003 Node: Traversing symlinks46024 Node: Treating / specially47097 Node: Special built-in utilities48644 Node: Standards conformance49779 Node: Output of entire files51335 Node: cat invocation51936 Node: tac invocation53743 Node: nl invocation55005 Node: od invocation58884 Node: base64 invocation65755 Node: Formatting file contents67134 Node: fmt invocation67585 Node: pr invocation70398 Node: fold invocation82839 Node: Output of parts of files84299 Node: head invocation84796 Node: tail invocation86981 Node: split invocation96281 Node: csplit invocation103202 Node: Summarizing files108007 Node: wc invocation108655 Node: sum invocation111729 Node: cksum invocation113134 Node: md5sum invocation114274 Node: sha1sum invocation119375 Node: sha2 utilities120155 Node: Operating on sorted files120779 Node: sort invocation121366 Ref: sort invocation-Footnote-1145294 Node: shuf invocation145846 Node: uniq invocation148425 Node: comm invocation153117 Node: ptx invocation155538 Node: General options in ptx158342 Node: Charset selection in ptx158923 Node: Input processing in ptx159825 Node: Output formatting in ptx165246 Node: Compatibility in ptx171812 Node: tsort invocation175045 Node: tsort background178204 Node: Operating on fields179852 Node: cut invocation180214 Node: paste invocation184171 Node: join invocation185485 Node: Operating on characters191836 Node: tr invocation192258 Node: Character sets193976 Node: Translating198494 Node: Squeezing200585 Node: expand invocation203652 Node: unexpand invocation205134 Node: Directory listing206952 Node: ls invocation207438 Ref: ls invocation-Footnote-1209534 Node: Which files are listed209756 Node: What information is listed213496 Node: Sorting the output222743 Node: Details about version sort225053 Node: General output formatting226821 Node: Formatting file timestamps231811 Node: Formatting the file names237137 Node: dir invocation240053 Node: vdir invocation240464 Node: dircolors invocation240842 Node: Basic operations242541 Node: cp invocation243161 Node: dd invocation259270 Node: install invocation271856 Node: mv invocation277131 Node: rm invocation281693 Node: shred invocation286019 Node: Special file types294052 Node: link invocation295558 Node: ln invocation296777 Node: mkdir invocation304832 Node: mkfifo invocation307203 Node: mknod invocation308323 Node: readlink invocation310455 Node: rmdir invocation312414 Node: unlink invocation313688 Node: Changing file attributes314647 Node: chown invocation315461 Node: chgrp invocation321647 Node: chmod invocation324697 Node: touch invocation327452 Node: Disk usage334844 Node: df invocation335505 Node: du invocation341447 Node: stat invocation349979 Node: sync invocation355492 Node: truncate invocation356447 Node: Printing text358217 Node: echo invocation358591 Node: printf invocation361177 Node: yes invocation366648 Node: Conditions367260 Node: false invocation367851 Node: true invocation368886 Node: test invocation370165 Node: File type tests372210 Node: Access permission tests373092 Node: File characteristic tests373977 Node: String tests374742 Node: Numeric tests375481 Node: Connectives for test376287 Node: expr invocation376640 Node: String expressions379081 Node: Numeric expressions381665 Node: Relations for expr382362 Node: Examples of expr383556 Node: Redirection384281 Node: tee invocation384739 Node: File name manipulation389529 Node: basename invocation390104 Node: dirname invocation392082 Node: pathchk invocation393677 Node: mktemp invocation395441 Node: realpath invocation401089 Node: Working context403894 Node: pwd invocation404538 Node: stty invocation405884 Node: Control408644 Node: Input409404 Node: Output411077 Node: Local412397 Node: Combination413979 Node: Characters416200 Node: Special417754 Node: printenv invocation419411 Node: tty invocation420421 Node: User information421127 Node: id invocation421762 Node: logname invocation423685 Node: whoami invocation424312 Node: groups invocation424799 Node: users invocation426004 Node: who invocation426951 Node: System context429887 Node: date invocation430552 Node: Time conversion specifiers432269 Node: Date conversion specifiers434692 Node: Literal conversion specifiers437728 Node: Padding and other flags438086 Node: Setting the time440277 Node: Options for date441398 Node: Examples of date445586 Ref: %s-examples447004 Node: arch invocation449189 Node: nproc invocation449638 Node: uname invocation450748 Node: hostname invocation453322 Node: hostid invocation453935 Node: uptime invocation454646 Node: SELinux context455769 Node: chcon invocation456144 Node: runcon invocation457966 Node: Modified command invocation459432 Node: chroot invocation460182 Ref: chroot invocation-Footnote-1462750 Node: env invocation463052 Node: nice invocation467296 Node: nohup invocation471012 Node: stdbuf invocation473295 Node: su invocation475817 Node: timeout invocation480318 Node: Process control482570 Node: kill invocation482793 Node: Delaying485866 Node: sleep invocation486063 Node: Numeric operations487164 Node: factor invocation487496 Node: seq invocation489254 Node: File permissions492875 Node: Mode Structure493567 Node: Symbolic Modes497262 Node: Setting Permissions498360 Node: Copying Permissions500973 Node: Changing Special Mode Bits501792 Node: Conditional Executability503614 Node: Multiple Changes504158 Node: Umask and Protection505825 Node: Numeric Modes506930 Node: Operator Numeric Modes509055 Node: Directory Setuid and Setgid510071 Node: Date input formats512898 Node: General date syntax515329 Node: Calendar date items518320 Node: Time of day items520325 Node: Time zone items522529 Node: Combined date and time of day items523789 Node: Day of week items524521 Node: Relative items in date strings525538 Node: Pure numbers in date strings528348 Node: Seconds since the Epoch529337 Node: Specifying time zone rules530966 Node: Authors of parse_datetime533346 Ref: Authors of get_date533533 Node: Opening the software toolbox534496 Node: Toolbox introduction535263 Node: I/O redirection537986 Node: The who command540820 Node: The cut command541717 Node: The sort command542780 Node: The uniq command543484 Node: Putting the tools together544174 Ref: Putting the tools together-Footnote-1556126 Node: GNU Free Documentation License556200 Node: Concept index581393  End Tag Table