3 @setfilename coreutils.info
4 @settitle @sc{gnu} Coreutils
9 @include constants.texi
11 @c Define new indices.
15 @c Put everything in one index (arbitrarily chosen to be the concept index).
25 * Coreutils: (coreutils). Core GNU (file, text, shell) utilities.
26 * Common options: (coreutils)Common options. Common options.
27 * File permissions: (coreutils)File permissions. Access modes.
28 * Date input formats: (coreutils)Date input formats.
31 @c FIXME: the following need documentation
32 @c * [: (coreutils)[ invocation. File/string tests.
33 @c * pinky: (coreutils)pinky invocation. FIXME.
35 @dircategory Individual utilities
37 * arch: (coreutils)arch invocation. Print machine hardware name.
38 * base64: (coreutils)base64 invocation. Base64 encode/decode data.
39 * basename: (coreutils)basename invocation. Strip directory and suffix.
40 * cat: (coreutils)cat invocation. Concatenate and write files.
41 * chcon: (coreutils)chcon invocation. Change SELinux CTX of files.
42 * chgrp: (coreutils)chgrp invocation. Change file groups.
43 * chmod: (coreutils)chmod invocation. Change file permissions.
44 * chown: (coreutils)chown invocation. Change file owners/groups.
45 * chroot: (coreutils)chroot invocation. Specify the root directory.
46 * cksum: (coreutils)cksum invocation. Print POSIX CRC checksum.
47 * comm: (coreutils)comm invocation. Compare sorted files by line.
48 * cp: (coreutils)cp invocation. Copy files.
49 * csplit: (coreutils)csplit invocation. Split by context.
50 * cut: (coreutils)cut invocation. Print selected parts of lines.
51 * date: (coreutils)date invocation. Print/set system date and time.
52 * dd: (coreutils)dd invocation. Copy and convert a file.
53 * df: (coreutils)df invocation. Report file system disk usage.
54 * dir: (coreutils)dir invocation. List directories briefly.
55 * dircolors: (coreutils)dircolors invocation. Color setup for ls.
56 * dirname: (coreutils)dirname invocation. Strip last file name component.
57 * du: (coreutils)du invocation. Report on disk usage.
58 * echo: (coreutils)echo invocation. Print a line of text.
59 * env: (coreutils)env invocation. Modify the environment.
60 * expand: (coreutils)expand invocation. Convert tabs to spaces.
61 * expr: (coreutils)expr invocation. Evaluate expressions.
62 * factor: (coreutils)factor invocation. Print prime factors
63 * false: (coreutils)false invocation. Do nothing, unsuccessfully.
64 * fmt: (coreutils)fmt invocation. Reformat paragraph text.
65 * fold: (coreutils)fold invocation. Wrap long input lines.
66 * groups: (coreutils)groups invocation. Print group names a user is in.
67 * head: (coreutils)head invocation. Output the first part of files.
68 * hostid: (coreutils)hostid invocation. Print numeric host identifier.
69 * hostname: (coreutils)hostname invocation. Print or set system name.
70 * id: (coreutils)id invocation. Print user identity.
71 * install: (coreutils)install invocation. Copy and change attributes.
72 * join: (coreutils)join invocation. Join lines on a common field.
73 * kill: (coreutils)kill invocation. Send a signal to processes.
74 * link: (coreutils)link invocation. Make hard links between files.
75 * ln: (coreutils)ln invocation. Make links between files.
76 * logname: (coreutils)logname invocation. Print current login name.
77 * ls: (coreutils)ls invocation. List directory contents.
78 * md5sum: (coreutils)md5sum invocation. Print or check MD5 digests.
79 * mkdir: (coreutils)mkdir invocation. Create directories.
80 * mkfifo: (coreutils)mkfifo invocation. Create FIFOs (named pipes).
81 * mknod: (coreutils)mknod invocation. Create special files.
82 * mktemp: (coreutils)mktemp invocation. Create temporary files.
83 * mv: (coreutils)mv invocation. Rename files.
84 * nice: (coreutils)nice invocation. Modify niceness.
85 * nl: (coreutils)nl invocation. Number lines and write files.
86 * nohup: (coreutils)nohup invocation. Immunize to hangups.
87 * nproc: (coreutils)nproc invocation. Print the number of processors.
88 * od: (coreutils)od invocation. Dump files in octal, etc.
89 * paste: (coreutils)paste invocation. Merge lines of files.
90 * pathchk: (coreutils)pathchk invocation. Check file name portability.
91 * pr: (coreutils)pr invocation. Paginate or columnate files.
92 * printenv: (coreutils)printenv invocation. Print environment variables.
93 * printf: (coreutils)printf invocation. Format and print data.
94 * ptx: (coreutils)ptx invocation. Produce permuted indexes.
95 * pwd: (coreutils)pwd invocation. Print working directory.
96 * readlink: (coreutils)readlink invocation. Print referent of a symlink.
97 * rm: (coreutils)rm invocation. Remove files.
98 * rmdir: (coreutils)rmdir invocation. Remove empty directories.
99 * runcon: (coreutils)runcon invocation. Run in specified SELinux CTX.
100 * seq: (coreutils)seq invocation. Print numeric sequences
101 * sha1sum: (coreutils)sha1sum invocation. Print or check SHA-1 digests.
102 * sha2: (coreutils)sha2 utilities. Print or check SHA-2 digests.
103 * shred: (coreutils)shred invocation. Remove files more securely.
104 * shuf: (coreutils)shuf invocation. Shuffling text files.
105 * sleep: (coreutils)sleep invocation. Delay for a specified time.
106 * sort: (coreutils)sort invocation. Sort text files.
107 * split: (coreutils)split invocation. Split into pieces.
108 * stat: (coreutils)stat invocation. Report file(system) status.
109 * stdbuf: (coreutils)stdbuf invocation. Modify stdio buffering.
110 * stty: (coreutils)stty invocation. Print/change terminal settings.
111 * su: (coreutils)su invocation. Modify user and group ID.
112 * sum: (coreutils)sum invocation. Print traditional checksum.
113 * sync: (coreutils)sync invocation. Synchronize memory and disk.
114 * tac: (coreutils)tac invocation. Reverse files.
115 * tail: (coreutils)tail invocation. Output the last part of files.
116 * tee: (coreutils)tee invocation. Redirect to multiple files.
117 * test: (coreutils)test invocation. File/string tests.
118 * timeout: (coreutils)timeout invocation. Run with time limit.
119 * touch: (coreutils)touch invocation. Change file timestamps.
120 * tr: (coreutils)tr invocation. Translate characters.
121 * true: (coreutils)true invocation. Do nothing, successfully.
122 * truncate: (coreutils)truncate invocation. Shrink/extend size of a file.
123 * tsort: (coreutils)tsort invocation. Topological sort.
124 * tty: (coreutils)tty invocation. Print terminal name.
125 * uname: (coreutils)uname invocation. Print system information.
126 * unexpand: (coreutils)unexpand invocation. Convert spaces to tabs.
127 * uniq: (coreutils)uniq invocation. Uniquify files.
128 * unlink: (coreutils)unlink invocation. Removal via unlink(2).
129 * uptime: (coreutils)uptime invocation. Print uptime and load.
130 * users: (coreutils)users invocation. Print current user names.
131 * vdir: (coreutils)vdir invocation. List directories verbosely.
132 * wc: (coreutils)wc invocation. Line, word, and byte counts.
133 * who: (coreutils)who invocation. Print who is logged in.
134 * whoami: (coreutils)whoami invocation. Print effective user ID.
135 * yes: (coreutils)yes invocation. Print a string indefinitely.
139 This manual documents version @value{VERSION} of the @sc{gnu} core
140 utilities, including the standard programs for text and file manipulation.
142 Copyright @copyright{} 1994-1996, 2000-2012 Free Software Foundation, Inc.
145 Permission is granted to copy, distribute and/or modify this document
146 under the terms of the GNU Free Documentation License, Version 1.3 or
147 any later version published by the Free Software Foundation; with no
148 Invariant Sections, with no Front-Cover Texts, and with no Back-Cover
149 Texts. A copy of the license is included in the section entitled ``GNU
150 Free Documentation License''.
155 @title @sc{gnu} @code{Coreutils}
156 @subtitle Core GNU utilities
157 @subtitle for version @value{VERSION}, @value{UPDATED}
158 @author David MacKenzie et al.
161 @vskip 0pt plus 1filll
174 @cindex core utilities
175 @cindex text utilities
176 @cindex shell utilities
177 @cindex file utilities
180 * Introduction:: Caveats, overview, and authors
181 * Common options:: Common options
182 * Output of entire files:: cat tac nl od base64
183 * Formatting file contents:: fmt pr fold
184 * Output of parts of files:: head tail split csplit
185 * Summarizing files:: wc sum cksum md5sum sha1sum sha2
186 * Operating on sorted files:: sort shuf uniq comm ptx tsort
187 * Operating on fields:: cut paste join
188 * Operating on characters:: tr expand unexpand
189 * Directory listing:: ls dir vdir dircolors
190 * Basic operations:: cp dd install mv rm shred
191 * Special file types:: mkdir rmdir unlink mkfifo mknod ln link readlink
192 * Changing file attributes:: chgrp chmod chown touch
193 * Disk usage:: df du stat sync truncate
194 * Printing text:: echo printf yes
195 * Conditions:: false true test expr
197 * File name manipulation:: dirname basename pathchk mktemp
198 * Working context:: pwd stty printenv tty
199 * User information:: id logname whoami groups users who
200 * System context:: date arch nproc uname hostname hostid uptime
201 * SELinux context:: chcon runcon
202 * Modified command invocation:: chroot env nice nohup stdbuf su timeout
203 * Process control:: kill
205 * Numeric operations:: factor seq
206 * File permissions:: Access modes
207 * Date input formats:: Specifying date strings
208 * Opening the software toolbox:: The software tools philosophy
209 * GNU Free Documentation License:: Copying and sharing this manual
210 * Concept index:: General index
213 --- The Detailed Node Listing ---
217 * Exit status:: Indicating program success or failure
218 * Backup options:: Backup options
219 * Block size:: Block size
220 * Floating point:: Floating point number representation
221 * Signal specifications:: Specifying signals
222 * Disambiguating names and IDs:: chgrp and chown owner and group syntax
223 * Random sources:: Sources of random data
224 * Target directory:: Target directory
225 * Trailing slashes:: Trailing slashes
226 * Traversing symlinks:: Traversing symlinks to directories
227 * Treating / specially:: Treating / specially
228 * Standards conformance:: Standards conformance
230 Output of entire files
232 * cat invocation:: Concatenate and write files
233 * tac invocation:: Concatenate and write files in reverse
234 * nl invocation:: Number lines and write files
235 * od invocation:: Write files in octal or other formats
236 * base64 invocation:: Transform data into printable data
238 Formatting file contents
240 * fmt invocation:: Reformat paragraph text
241 * pr invocation:: Paginate or columnate files for printing
242 * fold invocation:: Wrap input lines to fit in specified width
244 Output of parts of files
246 * head invocation:: Output the first part of files
247 * tail invocation:: Output the last part of files
248 * split invocation:: Split a file into fixed-size pieces
249 * csplit invocation:: Split a file into context-determined pieces
253 * wc invocation:: Print newline, word, and byte counts
254 * sum invocation:: Print checksum and block counts
255 * cksum invocation:: Print CRC checksum and byte counts
256 * md5sum invocation:: Print or check MD5 digests
257 * sha1sum invocation:: Print or check SHA-1 digests
258 * sha2 utilities:: Print or check SHA-2 digests
260 Operating on sorted files
262 * sort invocation:: Sort text files
263 * shuf invocation:: Shuffle text files
264 * uniq invocation:: Uniquify files
265 * comm invocation:: Compare two sorted files line by line
266 * ptx invocation:: Produce a permuted index of file contents
267 * tsort invocation:: Topological sort
269 @command{ptx}: Produce permuted indexes
271 * General options in ptx:: Options which affect general program behavior
272 * Charset selection in ptx:: Underlying character set considerations
273 * Input processing in ptx:: Input fields, contexts, and keyword selection
274 * Output formatting in ptx:: Types of output format, and sizing the fields
275 * Compatibility in ptx:: The @acronym{GNU} extensions to @command{ptx}
279 * cut invocation:: Print selected parts of lines
280 * paste invocation:: Merge lines of files
281 * join invocation:: Join lines on a common field
283 Operating on characters
285 * tr invocation:: Translate, squeeze, and/or delete characters
286 * expand invocation:: Convert tabs to spaces
287 * unexpand invocation:: Convert spaces to tabs
289 @command{tr}: Translate, squeeze, and/or delete characters
291 * Character sets:: Specifying sets of characters
292 * Translating:: Changing one set of characters to another
293 * Squeezing:: Squeezing repeats and deleting
297 * ls invocation:: List directory contents
298 * dir invocation:: Briefly list directory contents
299 * vdir invocation:: Verbosely list directory contents
300 * dircolors invocation:: Color setup for @command{ls}
302 @command{ls}: List directory contents
304 * Which files are listed:: Which files are listed
305 * What information is listed:: What information is listed
306 * Sorting the output:: Sorting the output
307 * Details about version sort:: More details about version sort
308 * General output formatting:: General output formatting
309 * Formatting the file names:: Formatting the file names
313 * cp invocation:: Copy files and directories
314 * dd invocation:: Convert and copy a file
315 * install invocation:: Copy files and set attributes
316 * mv invocation:: Move (rename) files
317 * rm invocation:: Remove files or directories
318 * shred invocation:: Remove files more securely
322 * link invocation:: Make a hard link via the link syscall
323 * ln invocation:: Make links between files
324 * mkdir invocation:: Make directories
325 * mkfifo invocation:: Make FIFOs (named pipes)
326 * mknod invocation:: Make block or character special files
327 * readlink invocation:: Print value of a symlink or canonical file name
328 * rmdir invocation:: Remove empty directories
329 * unlink invocation:: Remove files via unlink syscall
331 Changing file attributes
333 * chown invocation:: Change file owner and group
334 * chgrp invocation:: Change group ownership
335 * chmod invocation:: Change access permissions
336 * touch invocation:: Change file timestamps
340 * df invocation:: Report file system disk space usage
341 * du invocation:: Estimate file space usage
342 * stat invocation:: Report file or file system status
343 * sync invocation:: Synchronize data on disk with memory
344 * truncate invocation:: Shrink or extend the size of a file
348 * echo invocation:: Print a line of text
349 * printf invocation:: Format and print data
350 * yes invocation:: Print a string until interrupted
354 * false invocation:: Do nothing, unsuccessfully
355 * true invocation:: Do nothing, successfully
356 * test invocation:: Check file types and compare values
357 * expr invocation:: Evaluate expressions
359 @command{test}: Check file types and compare values
361 * File type tests:: File type tests
362 * Access permission tests:: Access permission tests
363 * File characteristic tests:: File characteristic tests
364 * String tests:: String tests
365 * Numeric tests:: Numeric tests
367 @command{expr}: Evaluate expression
369 * String expressions:: + : match substr index length
370 * Numeric expressions:: + - * / %
371 * Relations for expr:: | & < <= = == != >= >
372 * Examples of expr:: Examples of using @command{expr}
376 * tee invocation:: Redirect output to multiple files or processes
378 File name manipulation
380 * basename invocation:: Strip directory and suffix from a file name
381 * dirname invocation:: Strip last file name component
382 * pathchk invocation:: Check file name validity and portability
383 * mktemp invocation:: Create temporary file or directory
387 * pwd invocation:: Print working directory
388 * stty invocation:: Print or change terminal characteristics
389 * printenv invocation:: Print all or some environment variables
390 * tty invocation:: Print file name of terminal on standard input
392 @command{stty}: Print or change terminal characteristics
394 * Control:: Control settings
395 * Input:: Input settings
396 * Output:: Output settings
397 * Local:: Local settings
398 * Combination:: Combination settings
399 * Characters:: Special characters
400 * Special:: Special settings
404 * id invocation:: Print user identity
405 * logname invocation:: Print current login name
406 * whoami invocation:: Print effective user ID
407 * groups invocation:: Print group names a user is in
408 * users invocation:: Print login names of users currently logged in
409 * who invocation:: Print who is currently logged in
413 * arch invocation:: Print machine hardware name
414 * date invocation:: Print or set system date and time
415 * nproc invocation:: Print the number of processors
416 * uname invocation:: Print system information
417 * hostname invocation:: Print or set system name
418 * hostid invocation:: Print numeric host identifier
419 * uptime invocation:: Print system uptime and load
421 @command{date}: Print or set system date and time
423 * Time conversion specifiers:: %[HIklMNpPrRsSTXzZ]
424 * Date conversion specifiers:: %[aAbBcCdDeFgGhjmuUVwWxyY]
425 * Literal conversion specifiers:: %[%nt]
426 * Padding and other flags:: Pad with zeros, spaces, etc.
427 * Setting the time:: Changing the system clock
428 * Options for date:: Instead of the current time
429 * Date input formats:: Specifying date strings
430 * Examples of date:: Examples
434 * chcon invocation:: Change SELinux context of file
435 * runcon invocation:: Run a command in specified SELinux context
437 Modified command invocation
439 * chroot invocation:: Run a command with a different root directory
440 * env invocation:: Run a command in a modified environment
441 * nice invocation:: Run a command with modified niceness
442 * nohup invocation:: Run a command immune to hangups
443 * stdbuf invocation:: Run a command with modified I/O buffering
444 * su invocation:: Run a command with substitute user and group ID
445 * timeout invocation:: Run a command with a time limit
449 * kill invocation:: Sending a signal to processes.
453 * sleep invocation:: Delay for a specified time
457 * factor invocation:: Print prime factors
458 * seq invocation:: Print numeric sequences
462 * Mode Structure:: Structure of file mode bits
463 * Symbolic Modes:: Mnemonic representation of file mode bits
464 * Numeric Modes:: File mode bits as octal numbers
465 * Directory Setuid and Setgid:: Set-user-ID and set-group-ID on directories
469 * General date syntax:: Common rules
470 * Calendar date items:: 19 Dec 1994
471 * Time of day items:: 9:20pm
472 * Time zone items:: @sc{est}, @sc{pdt}, @sc{gmt}
473 * Day of week items:: Monday and others
474 * Relative items in date strings:: next tuesday, 2 years ago
475 * Pure numbers in date strings:: 19931219, 1440
476 * Seconds since the Epoch:: @@1078100502
477 * Specifying time zone rules:: TZ="America/New_York", TZ="UTC0"
478 * Authors of parse_datetime:: Bellovin, Eggert, Salz, Berets, et al
480 Opening the software toolbox
482 * Toolbox introduction:: Toolbox introduction
483 * I/O redirection:: I/O redirection
484 * The who command:: The @command{who} command
485 * The cut command:: The @command{cut} command
486 * The sort command:: The @command{sort} command
487 * The uniq command:: The @command{uniq} command
488 * Putting the tools together:: Putting the tools together
492 * GNU Free Documentation License:: Copying and sharing this manual
499 @chapter Introduction
501 This manual is a work in progress: many sections make no attempt to explain
502 basic concepts in a way suitable for novices. Thus, if you are interested,
503 please get involved in improving this manual. The entire @sc{gnu} community
506 @cindex @acronym{POSIX}
507 The @sc{gnu} utilities documented here are mostly compatible with the
508 @acronym{POSIX} standard.
509 @cindex bugs, reporting
510 Please report bugs to @email{bug-coreutils@@gnu.org}. Remember
511 to include the version number, machine architecture, input files, and
512 any other information needed to reproduce the bug: your input, what you
513 expected, what you got, and why it is wrong. Diffs are welcome, but
514 please include a description of the problem as well, since this is
515 sometimes difficult to infer. @xref{Bugs, , , gcc, Using and Porting GNU CC}.
521 @cindex MacKenzie, D.
524 This manual was originally derived from the Unix man pages in the
525 distributions, which were written by David MacKenzie and updated by Jim
526 Meyering. What you are reading now is the authoritative documentation
527 for these utilities; the man pages are no longer being maintained. The
528 original @command{fmt} man page was written by Ross Paterson. Fran@,{c}ois
529 Pinard did the initial conversion to Texinfo format. Karl Berry did the
530 indexing, some reorganization, and editing of the results. Brian
531 Youmans of the Free Software Foundation office staff combined the
532 manuals for textutils, fileutils, and sh-utils to produce the present
533 omnibus manual. Richard Stallman contributed his usual invaluable
534 insights to the overall process.
537 @chapter Common options
541 @itemx @w{@kbd{--backup}[=@var{method}]}
544 @vindex VERSION_CONTROL
545 @cindex backups, making
546 @xref{Backup options}.
547 Make a backup of each file that would otherwise be overwritten or removed.
550 @macro optBackupSuffix
551 @item -S @var{suffix}
552 @itemx --suffix=@var{suffix}
555 Append @var{suffix} to each backup file made with @option{-b}.
556 @xref{Backup options}.
559 @macro optTargetDirectory
560 @item -t @var{directory}
561 @itemx @w{@kbd{--target-directory}=@var{directory}}
563 @opindex --target-directory
564 @cindex target directory
565 @cindex destination directory
566 Specify the destination @var{directory}.
567 @xref{Target directory}.
570 @macro optNoTargetDirectory
572 @itemx --no-target-directory
574 @opindex --no-target-directory
575 @cindex target directory
576 @cindex destination directory
577 Do not treat the last operand specially when it is a directory or a
578 symbolic link to a directory. @xref{Target directory}.
586 @cindex output @sc{nul}-byte-terminated lines
587 Output a zero byte (@acronym{ASCII} @sc{nul}) at the end of each line,
588 rather than a newline. This option enables other programs to parse the
589 output of @command{\cmd\} even when that output would contain data
590 with embedded newlines.
597 Append an SI-style abbreviation to each size, such as @samp{M} for
598 megabytes. Powers of 1000 are used, not 1024; @samp{M} stands for
599 1,000,000 bytes. This option is equivalent to
600 @option{--block-size=si}. Use the @option{-h} or
601 @option{--human-readable} option if
602 you prefer powers of 1024.
605 @macro optHumanReadable
607 @itemx --human-readable
609 @opindex --human-readable
610 @cindex human-readable output
611 Append a size letter to each size, such as @samp{M} for mebibytes.
612 Powers of 1024 are used, not 1000; @samp{M} stands for 1,048,576 bytes.
613 This option is equivalent to @option{--block-size=human-readable}.
614 Use the @option{--si} option if you prefer powers of 1000.
617 @macro optStripTrailingSlashes
618 @itemx @w{@kbd{--strip-trailing-slashes}}
619 @opindex --strip-trailing-slashes
620 @cindex stripping trailing slashes
621 Remove any trailing slashes from each @var{source} argument.
622 @xref{Trailing slashes}.
625 @macro mayConflictWithShellBuiltIn{cmd}
626 @cindex conflicts with shell built-ins
627 @cindex built-in shell commands, conflicts with
628 Due to shell aliases and built-in @command{\cmd\} functions, using an
629 unadorned @command{\cmd\} interactively or in a script may get you
630 different functionality than that described here. Invoke it via
631 @command{env} (i.e., @code{env \cmd\ @dots{}}) to avoid interference
636 @macro multiplierSuffixes{varName}
637 @var{\varName\} may be, or may be an integer optionally followed by,
638 one of the following multiplicative suffixes:
640 @samp{b} => 512 ("blocks")
641 @samp{KB} => 1000 (KiloBytes)
642 @samp{K} => 1024 (KibiBytes)
643 @samp{MB} => 1000*1000 (MegaBytes)
644 @samp{M} => 1024*1024 (MebiBytes)
645 @samp{GB} => 1000*1000*1000 (GigaBytes)
646 @samp{G} => 1024*1024*1024 (GibiBytes)
648 and so on for @samp{T}, @samp{P}, @samp{E}, @samp{Z}, and @samp{Y}.
651 @c FIXME: same as above, but no ``blocks'' line.
652 @macro multiplierSuffixesNoBlocks{varName}
653 @var{\varName\} may be, or may be an integer optionally followed by,
654 one of the following multiplicative suffixes:
656 @samp{KB} => 1000 (KiloBytes)
657 @samp{K} => 1024 (KibiBytes)
658 @samp{MB} => 1000*1000 (MegaBytes)
659 @samp{M} => 1024*1024 (MebiBytes)
660 @samp{GB} => 1000*1000*1000 (GigaBytes)
661 @samp{G} => 1024*1024*1024 (GibiBytes)
663 and so on for @samp{T}, @samp{P}, @samp{E}, @samp{Z}, and @samp{Y}.
666 @cindex common options
668 Certain options are available in all of these programs. Rather than
669 writing identical descriptions for each of the programs, they are
670 described here. (In fact, every @sc{gnu} program accepts (or should accept)
673 @vindex POSIXLY_CORRECT
674 Normally options and operands can appear in any order, and programs act
675 as if all the options appear before any operands. For example,
676 @samp{sort -r passwd -t :} acts like @samp{sort -r -t : passwd}, since
677 @samp{:} is an option-argument of @option{-t}. However, if the
678 @env{POSIXLY_CORRECT} environment variable is set, options must appear
679 before operands, unless otherwise specified for a particular command.
681 A few programs can usefully have trailing operands with leading
682 @samp{-}. With such a program, options must precede operands even if
683 @env{POSIXLY_CORRECT} is not set, and this fact is noted in the
684 program description. For example, the @command{env} command's options
685 must appear before its operands, since in some cases the operands
686 specify a command that itself contains options.
688 Most programs that accept long options recognize unambiguous
689 abbreviations of those options. For example, @samp{rmdir
690 --ignore-fail-on-non-empty} can be invoked as @samp{rmdir
691 --ignore-fail} or even @samp{rmdir --i}. Ambiguous options, such as
692 @samp{ls --h}, are identified as such.
694 Some of these programs recognize the @option{--help} and @option{--version}
695 options only when one of them is the sole command line argument. For
696 these programs, abbreviations of the long options are not always recognized.
703 Print a usage message listing all available options, then exit successfully.
707 @cindex version number, finding
708 Print the version number, then exit successfully.
712 @cindex option delimiter
713 Delimit the option list. Later arguments, if any, are treated as
714 operands even if they begin with @samp{-}. For example, @samp{sort --
715 -r} reads from the file named @file{-r}.
719 @cindex standard input
720 @cindex standard output
721 A single @samp{-} operand is not really an option, though it looks like one. It
722 stands for standard input, or for standard output if that is clear from
723 the context. For example, @samp{sort -} reads from standard input,
724 and is equivalent to plain @samp{sort}, and @samp{tee -} writes an
725 extra copy of its input to standard output. Unless otherwise
726 specified, @samp{-} can appear as any operand that requires a file
730 * Exit status:: Indicating program success or failure.
731 * Backup options:: -b -S, in some programs.
732 * Block size:: BLOCK_SIZE and --block-size, in some programs.
733 * Floating point:: Floating point number representation.
734 * Signal specifications:: Specifying signals using the --signal option.
735 * Disambiguating names and IDs:: chgrp and chown owner and group syntax
736 * Random sources:: --random-source, in some programs.
737 * Target directory:: Specifying a target directory, in some programs.
738 * Trailing slashes:: --strip-trailing-slashes, in some programs.
739 * Traversing symlinks:: -H, -L, or -P, in some programs.
740 * Treating / specially:: --preserve-root and --no-preserve-root.
741 * Special built-in utilities:: @command{break}, @command{:}, @dots{}
742 * Standards conformance:: Conformance to the @acronym{POSIX} standard.
750 An exit status of zero indicates success,
751 and a nonzero value indicates failure.
754 Nearly every command invocation yields an integral @dfn{exit status}
755 that can be used to change how other commands work.
756 For the vast majority of commands, an exit status of zero indicates
757 success. Failure is indicated by a nonzero value---typically
758 @samp{1}, though it may differ on unusual platforms as @acronym{POSIX}
759 requires only that it be nonzero.
761 However, some of the programs documented here do produce
762 other exit status values and a few associate different
763 meanings with the values @samp{0} and @samp{1}.
764 Here are some of the exceptions:
765 @command{chroot}, @command{env}, @command{expr}, @command{nice},
766 @command{nohup}, @command{printenv}, @command{sort}, @command{stdbuf},
767 @command{su}, @command{test}, @command{timeout}, @command{tty}.
771 @section Backup options
773 @cindex backup options
775 Some @sc{gnu} programs (at least @command{cp}, @command{install},
776 @command{ln}, and @command{mv}) optionally make backups of files
777 before writing new versions.
778 These options control the details of these backups. The options are also
779 briefly mentioned in the descriptions of the particular programs.
784 @itemx @w{@kbd{--backup}[=@var{method}]}
787 @vindex VERSION_CONTROL
788 @cindex backups, making
789 Make a backup of each file that would otherwise be overwritten or removed.
790 Without this option, the original versions are destroyed.
791 Use @var{method} to determine the type of backups to make.
792 When this option is used but @var{method} is not specified,
793 then the value of the @env{VERSION_CONTROL}
794 environment variable is used. And if @env{VERSION_CONTROL} is not set,
795 the default backup type is @samp{existing}.
797 Note that the short form of this option, @option{-b} does not accept any
798 argument. Using @option{-b} is equivalent to using @option{--backup=existing}.
800 @vindex version-control @r{Emacs variable}
801 This option corresponds to the Emacs variable @samp{version-control};
802 the values for @var{method} are the same as those used in Emacs.
803 This option also accepts more descriptive names.
804 The valid @var{method}s are (unique abbreviations are accepted):
809 @opindex none @r{backup method}
814 @opindex numbered @r{backup method}
815 Always make numbered backups.
819 @opindex existing @r{backup method}
820 Make numbered backups of files that already have them, simple backups
825 @opindex simple @r{backup method}
826 Always make simple backups. Please note @samp{never} is not to be
827 confused with @samp{none}.
831 @item -S @var{suffix}
832 @itemx --suffix=@var{suffix}
835 @cindex backup suffix
836 @vindex SIMPLE_BACKUP_SUFFIX
837 Append @var{suffix} to each backup file made with @option{-b}. If this
838 option is not specified, the value of the @env{SIMPLE_BACKUP_SUFFIX}
839 environment variable is used. And if @env{SIMPLE_BACKUP_SUFFIX} is not
840 set, the default is @samp{~}, just as in Emacs.
849 Some @sc{gnu} programs (at least @command{df}, @command{du}, and
850 @command{ls}) display sizes in ``blocks''. You can adjust the block size
851 and method of display to make sizes easier to read. The block size
852 used for display is independent of any file system block size.
853 Fractional block counts are rounded up to the nearest integer.
855 @opindex --block-size=@var{size}
858 @vindex DF_BLOCK_SIZE
859 @vindex DU_BLOCK_SIZE
860 @vindex LS_BLOCK_SIZE
861 @vindex POSIXLY_CORRECT@r{, and block size}
863 The default block size is chosen by examining the following environment
864 variables in turn; the first one that is set determines the block size.
869 This specifies the default block size for the @command{df} command.
870 Similarly, @env{DU_BLOCK_SIZE} specifies the default for @command{du} and
871 @env{LS_BLOCK_SIZE} for @command{ls}.
874 This specifies the default block size for all three commands, if the
875 above command-specific environment variables are not set.
878 This specifies the default block size for all values that are normally
879 printed as blocks, if neither @env{BLOCK_SIZE} nor the above
880 command-specific environment variables are set. Unlike the other
881 environment variables, @env{BLOCKSIZE} does not affect values that are
882 normally printed as byte counts, e.g., the file sizes contained in
885 @item POSIXLY_CORRECT
886 If neither @env{@var{command}_BLOCK_SIZE}, nor @env{BLOCK_SIZE}, nor
887 @env{BLOCKSIZE} is set, but this variable is set, the block size
892 If none of the above environment variables are set, the block size
893 currently defaults to 1024 bytes in most contexts, but this number may
894 change in the future. For @command{ls} file sizes, the block size
897 @cindex human-readable output
900 A block size specification can be a positive integer specifying the number
901 of bytes per block, or it can be @code{human-readable} or @code{si} to
902 select a human-readable format. Integers may be followed by suffixes
903 that are upward compatible with the
904 @uref{http://www.bipm.org/en/si/si_brochure/chapter3/prefixes.html, SI prefixes}
905 for decimal multiples and with the
906 @uref{http://physics.nist.gov/cuu/Units/binary.html, ISO/IEC 80000-13
907 (formerly IEC 60027-2) prefixes} for binary multiples.
909 With human-readable formats, output sizes are followed by a size letter
910 such as @samp{M} for megabytes. @code{BLOCK_SIZE=human-readable} uses
911 powers of 1024; @samp{M} stands for 1,048,576 bytes.
912 @code{BLOCK_SIZE=si} is similar, but uses powers of 1000 and appends
913 @samp{B}; @samp{MB} stands for 1,000,000 bytes.
916 A block size specification preceded by @samp{'} causes output sizes to
917 be displayed with thousands separators. The @env{LC_NUMERIC} locale
918 specifies the thousands separator and grouping. For example, in an
919 American English locale, @samp{--block-size="'1kB"} would cause a size
920 of 1234000 bytes to be displayed as @samp{1,234}. In the default C
921 locale, there is no thousands separator so a leading @samp{'} has no
924 An integer block size can be followed by a suffix to specify a
925 multiple of that size. A bare size letter,
926 or one followed by @samp{iB}, specifies
927 a multiple using powers of 1024. A size letter followed by @samp{B}
928 specifies powers of 1000 instead. For example, @samp{1M} and
929 @samp{1MiB} are equivalent to @samp{1048576}, whereas @samp{1MB} is
930 equivalent to @samp{1000000}.
932 A plain suffix without a preceding integer acts as if @samp{1} were
933 prepended, except that it causes a size indication to be appended to
934 the output. For example, @samp{--block-size="kB"} displays 3000 as
937 The following suffixes are defined. Large sizes like @code{1Y}
938 may be rejected by your computer due to limitations of its arithmetic.
942 @cindex kilobyte, definition of
943 kilobyte: @math{10^3 = 1000}.
947 @cindex kibibyte, definition of
948 kibibyte: @math{2^{10} = 1024}. @samp{K} is special: the SI prefix is
949 @samp{k} and the ISO/IEC 80000-13 prefix is @samp{Ki}, but tradition and
950 @acronym{POSIX} use @samp{k} to mean @samp{KiB}.
952 @cindex megabyte, definition of
953 megabyte: @math{10^6 = 1,000,000}.
956 @cindex mebibyte, definition of
957 mebibyte: @math{2^{20} = 1,048,576}.
959 @cindex gigabyte, definition of
960 gigabyte: @math{10^9 = 1,000,000,000}.
963 @cindex gibibyte, definition of
964 gibibyte: @math{2^{30} = 1,073,741,824}.
966 @cindex terabyte, definition of
967 terabyte: @math{10^{12} = 1,000,000,000,000}.
970 @cindex tebibyte, definition of
971 tebibyte: @math{2^{40} = 1,099,511,627,776}.
973 @cindex petabyte, definition of
974 petabyte: @math{10^{15} = 1,000,000,000,000,000}.
977 @cindex pebibyte, definition of
978 pebibyte: @math{2^{50} = 1,125,899,906,842,624}.
980 @cindex exabyte, definition of
981 exabyte: @math{10^{18} = 1,000,000,000,000,000,000}.
984 @cindex exbibyte, definition of
985 exbibyte: @math{2^{60} = 1,152,921,504,606,846,976}.
987 @cindex zettabyte, definition of
988 zettabyte: @math{10^{21} = 1,000,000,000,000,000,000,000}
991 @math{2^{70} = 1,180,591,620,717,411,303,424}.
993 @cindex yottabyte, definition of
994 yottabyte: @math{10^{24} = 1,000,000,000,000,000,000,000,000}.
997 @math{2^{80} = 1,208,925,819,614,629,174,706,176}.
1002 @opindex --block-size
1003 @opindex --human-readable
1006 Block size defaults can be overridden by an explicit
1007 @option{--block-size=@var{size}} option. The @option{-k}
1008 option is equivalent to @option{--block-size=1K}, which
1009 is the default unless the @env{POSIXLY_CORRECT} environment variable is
1010 set. The @option{-h} or @option{--human-readable} option is equivalent to
1011 @option{--block-size=human-readable}. The @option{--si} option is
1012 equivalent to @option{--block-size=si}.
1014 @node Floating point
1015 @section Floating point numbers
1016 @cindex floating point
1017 @cindex IEEE floating point
1019 Commands that accept or produce floating point numbers employ the
1020 floating point representation of the underlying system, and suffer
1021 from rounding error, overflow, and similar floating-point issues.
1022 Almost all modern systems use IEEE-754 floating point, and it is
1023 typically portable to assume IEEE-754 behavior these days. IEEE-754
1024 has positive and negative infinity, distinguishes positive from
1025 negative zero, and uses special values called NaNs to represent
1026 invalid computations such as dividing zero by itself. For more
1027 information, please see David Goldberg's paper
1028 @uref{http://@/www.validlab.com/@/goldberg/@/paper.pdf, What Every
1029 Computer Scientist Should Know About Floating-Point Arithmetic}.
1032 Commands that accept floating point numbers as options, operands or
1033 input use the standard C functions @code{strtod} and @code{strtold} to
1034 convert from text to floating point numbers. These floating point
1035 numbers therefore can use scientific notation like @code{1.0e-34} and
1036 @code{-10e100}. Modern C implementations also accept hexadecimal
1037 floating point numbers such as @code{-0x.ep-3}, which stands for
1038 @minus{}14/16 times @math{2^-3}, which equals @minus{}0.109375. The
1039 @env{LC_NUMERIC} locale determines the decimal-point character.
1040 @xref{Parsing of Floats,,, libc, The GNU C Library Reference Manual}.
1042 @node Signal specifications
1043 @section Signal specifications
1044 @cindex signals, specifying
1046 A @var{signal} may be a signal name like @samp{HUP}, or a signal
1047 number like @samp{1}, or an exit status of a process terminated by the
1048 signal. A signal name can be given in canonical form or prefixed by
1049 @samp{SIG}. The case of the letters is ignored. The following signal names
1050 and numbers are supported on all @acronym{POSIX} compliant systems:
1056 2. Terminal interrupt.
1062 9. Kill (cannot be caught or ignored).
1070 Other supported signal names have system-dependent corresponding
1071 numbers. All systems conforming to @acronym{POSIX} 1003.1-2001 also
1072 support the following signals:
1076 Access to an undefined portion of a memory object.
1078 Child process terminated, stopped, or continued.
1080 Continue executing, if stopped.
1082 Erroneous arithmetic operation.
1084 Illegal Instruction.
1086 Write on a pipe with no one to read it.
1088 Invalid memory reference.
1090 Stop executing (cannot be caught or ignored).
1094 Background process attempting read.
1096 Background process attempting write.
1098 High bandwidth data is available at a socket.
1100 User-defined signal 1.
1102 User-defined signal 2.
1106 @acronym{POSIX} 1003.1-2001 systems that support the @acronym{XSI} extension
1107 also support the following signals:
1113 Profiling timer expired.
1117 Trace/breakpoint trap.
1119 Virtual timer expired.
1121 CPU time limit exceeded.
1123 File size limit exceeded.
1127 @acronym{POSIX} 1003.1-2001 systems that support the @acronym{XRT} extension
1128 also support at least eight real-time signals called @samp{RTMIN},
1129 @samp{RTMIN+1}, @dots{}, @samp{RTMAX-1}, @samp{RTMAX}.
1131 @node Disambiguating names and IDs
1132 @section chown and chgrp: Disambiguating user names and IDs
1133 @cindex user names, disambiguating
1134 @cindex user IDs, disambiguating
1135 @cindex group names, disambiguating
1136 @cindex group IDs, disambiguating
1137 @cindex disambiguating group names and IDs
1139 Since the @var{owner} and @var{group} arguments to @command{chown} and
1140 @command{chgrp} may be specified as names or numeric IDs, there is an
1142 What if a user or group @emph{name} is a string of digits?
1143 @footnote{Using a number as a user name is common in some environments.}
1144 Should the command interpret it as a user name or as an ID?
1145 @acronym{POSIX} requires that @command{chown} and @command{chgrp}
1146 first attempt to resolve the specified string as a name, and
1147 only once that fails, then try to interpret it as an ID.
1148 This is troublesome when you want to specify a numeric ID, say 42,
1149 and it must work even in a pathological situation where
1150 @samp{42} is a user name that maps to some other user ID, say 1000.
1151 Simply invoking @code{chown 42 F}, will set @file{F}s owner ID to
1152 1000---not what you intended.
1154 GNU @command{chown} and @command{chgrp} provide a way to work around this,
1155 that at the same time may result in a significant performance improvement
1156 by eliminating a database look-up.
1157 Simply precede each numeric user ID and/or group ID with a @samp{+},
1158 in order to force its interpretation as an integer:
1162 chgrp +$numeric_group_id another-file
1166 GNU @command{chown} and @command{chgrp}
1167 skip the name look-up process for each @samp{+}-prefixed string,
1168 because a string containing @samp{+} is never a valid user or group name.
1169 This syntax is accepted on most common Unix systems, but not on Solaris 10.
1171 @node Random sources
1172 @section Sources of random data
1174 @cindex random sources
1176 The @command{shuf}, @command{shred}, and @command{sort} commands
1177 sometimes need random data to do their work. For example, @samp{sort
1178 -R} must choose a hash function at random, and it needs random data to
1179 make this selection.
1181 By default these commands use an internal pseudorandom generator
1182 initialized by a small amount of entropy, but can be directed to use
1183 an external source with the @option{--random-source=@var{file}} option.
1184 An error is reported if @var{file} does not contain enough bytes.
1186 For example, the device file @file{/dev/urandom} could be used as the
1187 source of random data. Typically, this device gathers environmental
1188 noise from device drivers and other sources into an entropy pool, and
1189 uses the pool to generate random bits. If the pool is short of data,
1190 the device reuses the internal pool to produce more bits, using a
1191 cryptographically secure pseudorandom number generator. But be aware
1192 that this device is not designed for bulk random data generation
1193 and is relatively slow.
1195 @file{/dev/urandom} suffices for most practical uses, but applications
1196 requiring high-value or long-term protection of private data may
1197 require an alternate data source like @file{/dev/random} or
1198 @file{/dev/arandom}. The set of available sources depends on your
1201 To reproduce the results of an earlier invocation of a command, you
1202 can save some random data into a file and then use that file as the
1203 random source in earlier and later invocations of the command.
1205 @node Target directory
1206 @section Target directory
1208 @cindex target directory
1210 The @command{cp}, @command{install}, @command{ln}, and @command{mv}
1211 commands normally treat the last operand specially when it is a
1212 directory or a symbolic link to a directory. For example, @samp{cp
1213 source dest} is equivalent to @samp{cp source dest/source} if
1214 @file{dest} is a directory. Sometimes this behavior is not exactly
1215 what is wanted, so these commands support the following options to
1216 allow more fine-grained control:
1221 @itemx --no-target-directory
1222 @opindex --no-target-directory
1223 @cindex target directory
1224 @cindex destination directory
1225 Do not treat the last operand specially when it is a directory or a
1226 symbolic link to a directory. This can help avoid race conditions in
1227 programs that operate in a shared area. For example, when the command
1228 @samp{mv /tmp/source /tmp/dest} succeeds, there is no guarantee that
1229 @file{/tmp/source} was renamed to @file{/tmp/dest}: it could have been
1230 renamed to @file{/tmp/dest/source} instead, if some other process
1231 created @file{/tmp/dest} as a directory. However, if @file{mv
1232 -T /tmp/source /tmp/dest} succeeds, there is no
1233 question that @file{/tmp/source} was renamed to @file{/tmp/dest}.
1235 In the opposite situation, where you want the last operand to be
1236 treated as a directory and want a diagnostic otherwise, you can use
1237 the @option{--target-directory} (@option{-t}) option.
1239 @item -t @var{directory}
1240 @itemx @w{@kbd{--target-directory}=@var{directory}}
1241 @opindex --target-directory
1242 @cindex target directory
1243 @cindex destination directory
1244 Use @var{directory} as the directory component of each destination
1247 The interface for most programs is that after processing options and a
1248 finite (possibly zero) number of fixed-position arguments, the remaining
1249 argument list is either expected to be empty, or is a list of items
1250 (usually files) that will all be handled identically. The @command{xargs}
1251 program is designed to work well with this convention.
1253 The commands in the @command{mv}-family are unusual in that they take
1254 a variable number of arguments with a special case at the @emph{end}
1255 (namely, the target directory). This makes it nontrivial to perform some
1256 operations, e.g., ``move all files from here to ../d/'', because
1257 @code{mv * ../d/} might exhaust the argument space, and @code{ls | xargs ...}
1258 doesn't have a clean way to specify an extra final argument for each
1259 invocation of the subject command. (It can be done by going through a
1260 shell command, but that requires more human labor and brain power than
1263 The @w{@kbd{--target-directory}} (@option{-t}) option allows the @command{cp},
1264 @command{install}, @command{ln}, and @command{mv} programs to be used
1265 conveniently with @command{xargs}. For example, you can move the files
1266 from the current directory to a sibling directory, @code{d} like this:
1269 ls | xargs mv -t ../d --
1272 However, this doesn't move files whose names begin with @samp{.}.
1273 If you use the @sc{gnu} @command{find} program, you can move those
1274 files too, with this command:
1277 find . -mindepth 1 -maxdepth 1 \
1281 But both of the above approaches fail if there are no files in the
1282 current directory, or if any file has a name containing a blank or
1283 some other special characters.
1284 The following example removes those limitations and requires both
1285 @sc{gnu} @command{find} and @sc{gnu} @command{xargs}:
1288 find . -mindepth 1 -maxdepth 1 -print0 \
1289 | xargs --null --no-run-if-empty \
1296 The @option{--target-directory} (@option{-t}) and
1297 @option{--no-target-directory} (@option{-T})
1298 options cannot be combined.
1300 @node Trailing slashes
1301 @section Trailing slashes
1303 @cindex trailing slashes
1305 Some @sc{gnu} programs (at least @command{cp} and @command{mv}) allow you to
1306 remove any trailing slashes from each @var{source} argument before
1307 operating on it. The @w{@kbd{--strip-trailing-slashes}} option enables
1310 This is useful when a @var{source} argument may have a trailing slash and
1311 @c FIXME: mv's behavior in this case is system-dependent
1312 specify a symbolic link to a directory. This scenario is in fact rather
1313 common because some shells can automatically append a trailing slash when
1314 performing file name completion on such symbolic links. Without this
1315 option, @command{mv}, for example, (via the system's rename function) must
1316 interpret a trailing slash as a request to dereference the symbolic link
1317 and so must rename the indirectly referenced @emph{directory} and not
1318 the symbolic link. Although it may seem surprising that such behavior
1319 be the default, it is required by @acronym{POSIX} and is consistent with
1320 other parts of that standard.
1322 @node Traversing symlinks
1323 @section Traversing symlinks
1325 @cindex symbolic link to directory, controlling traversal of
1327 The following options modify how @command{chown} and @command{chgrp}
1328 @c FIXME: note that `du' has these options, too, but they have slightly
1329 @c different meaning.
1330 traverse a hierarchy when the @option{--recursive} (@option{-R})
1331 option is also specified.
1332 If more than one of the following options is specified, only the final
1334 These options specify whether processing a symbolic link to a directory
1335 entails operating on just the symbolic link or on all files in the
1336 hierarchy rooted at that directory.
1338 These options are independent of @option{--dereference} and
1339 @option{--no-dereference} (@option{-h}), which control whether to modify
1340 a symlink or its referent.
1347 @cindex symbolic link to directory, traverse if on the command line
1348 If @option{--recursive} (@option{-R}) is specified and
1349 a command line argument is a symbolic link to a directory, traverse it.
1356 @cindex symbolic link to directory, traverse each that is encountered
1357 In a recursive traversal, traverse every symbolic link to a directory
1358 that is encountered.
1365 @cindex symbolic link to directory, never traverse
1366 Do not traverse any symbolic links.
1367 This is the default if none of @option{-H}, @option{-L},
1368 or @option{-P} is specified.
1375 @node Treating / specially
1376 @section Treating @file{/} specially
1378 Certain commands can operate destructively on entire hierarchies.
1379 For example, if a user with appropriate privileges mistakenly runs
1380 @samp{rm -rf / tmp/junk}, that may remove
1381 all files on the entire system. Since there are so few
1382 legitimate uses for such a command,
1383 @sc{gnu} @command{rm} normally declines to operate on any directory
1384 that resolves to @file{/}. If you really want to try to remove all
1385 the files on your system, you can use the @option{--no-preserve-root}
1386 option, but the default behavior, specified by the
1387 @option{--preserve-option}, is safer for most purposes.
1389 The commands @command{chgrp}, @command{chmod} and @command{chown}
1390 can also operate destructively on entire hierarchies, so they too
1391 support these options. Although, unlike @command{rm}, they don't
1392 actually unlink files, these commands are arguably more dangerous
1393 when operating recursively on @file{/}, since they often work much
1394 more quickly, and hence damage more files before an alert user can
1395 interrupt them. Tradition and @acronym{POSIX} require these commands
1396 to operate recursively on @file{/}, so they default to
1397 @option{--no-preserve-root}, but using the @option{--preserve-root}
1398 option makes them safer for most purposes. For convenience you can
1399 specify @option{--preserve-root} in an alias or in a shell function.
1401 Note that the @option{--preserve-root} option also ensures
1402 that @command{chgrp} and @command{chown} do not modify @file{/}
1403 even when dereferencing a symlink pointing to @file{/}.
1405 @node Special built-in utilities
1406 @section Special built-in utilities
1408 Some programs like @command{nice} can invoke other programs; for
1409 example, the command @samp{nice cat file} invokes the program
1410 @command{cat} by executing the command @samp{cat file}. However,
1411 @dfn{special built-in utilities} like @command{exit} cannot be invoked
1412 this way. For example, the command @samp{nice exit} does not have a
1413 well-defined behavior: it may generate an error message instead of
1416 Here is a list of the special built-in utilities that are standardized
1417 by @acronym{POSIX} 1003.1-2004.
1420 @t{.@: : break continue eval exec exit export readonly
1421 return set shift times trap unset}
1424 For example, because @samp{.}, @samp{:}, and @samp{exec} are special,
1425 the commands @samp{nice . foo.sh}, @samp{nice :}, and @samp{nice exec
1426 pwd} do not work as you might expect.
1428 Many shells extend this list. For example, Bash has several extra
1429 special built-in utilities like @command{history}, and
1430 @command{suspend}, and with Bash the command @samp{nice suspend}
1431 generates an error message instead of suspending.
1433 @node Standards conformance
1434 @section Standards conformance
1436 @vindex POSIXLY_CORRECT
1437 In a few cases, the @sc{gnu} utilities' default behavior is
1438 incompatible with the @acronym{POSIX} standard. To suppress these
1439 incompatibilities, define the @env{POSIXLY_CORRECT} environment
1440 variable. Unless you are checking for @acronym{POSIX} conformance, you
1441 probably do not need to define @env{POSIXLY_CORRECT}.
1443 Newer versions of @acronym{POSIX} are occasionally incompatible with older
1444 versions. For example, older versions of @acronym{POSIX} required the
1445 command @samp{sort +1} to sort based on the second and succeeding
1446 fields in each input line, but starting with @acronym{POSIX} 1003.1-2001
1447 the same command is required to sort the file named @file{+1}, and you
1448 must instead use the command @samp{sort -k 2} to get the field-based
1451 @vindex _POSIX2_VERSION
1452 The @sc{gnu} utilities normally conform to the version of @acronym{POSIX}
1453 that is standard for your system. To cause them to conform to a
1454 different version of @acronym{POSIX}, define the @env{_POSIX2_VERSION}
1455 environment variable to a value of the form @var{yyyymm} specifying
1456 the year and month the standard was adopted. Three values are currently
1457 supported for @env{_POSIX2_VERSION}: @samp{199209} stands for
1458 @acronym{POSIX} 1003.2-1992, @samp{200112} stands for @acronym{POSIX}
1459 1003.1-2001, and @samp{200809} stands for @acronym{POSIX} 1003.1-2008.
1460 For example, if you have a newer system but are running software
1461 that assumes an older version of @acronym{POSIX} and uses @samp{sort +1}
1462 or @samp{tail +10}, you can work around any compatibility problems by setting
1463 @samp{_POSIX2_VERSION=199209} in your environment.
1465 @node Output of entire files
1466 @chapter Output of entire files
1468 @cindex output of entire files
1469 @cindex entire files, output of
1471 These commands read and write entire files, possibly transforming them
1475 * cat invocation:: Concatenate and write files.
1476 * tac invocation:: Concatenate and write files in reverse.
1477 * nl invocation:: Number lines and write files.
1478 * od invocation:: Write files in octal or other formats.
1479 * base64 invocation:: Transform data into printable data.
1482 @node cat invocation
1483 @section @command{cat}: Concatenate and write files
1486 @cindex concatenate and write files
1487 @cindex copying files
1489 @command{cat} copies each @var{file} (@samp{-} means standard input), or
1490 standard input if none are given, to standard output. Synopsis:
1493 cat [@var{option}] [@var{file}]@dots{}
1496 The program accepts the following options. Also see @ref{Common options}.
1504 Equivalent to @option{-vET}.
1507 @itemx --number-nonblank
1509 @opindex --number-nonblank
1510 Number all nonempty output lines, starting with 1.
1514 Equivalent to @option{-vE}.
1519 @opindex --show-ends
1520 Display a @samp{$} after the end of each line.
1526 Number all output lines, starting with 1. This option is ignored
1527 if @option{-b} is in effect.
1530 @itemx --squeeze-blank
1532 @opindex --squeeze-blank
1533 @cindex squeezing empty lines
1534 Suppress repeated adjacent empty lines; output just one empty line
1539 Equivalent to @option{-vT}.
1544 @opindex --show-tabs
1545 Display TAB characters as @samp{^I}.
1549 Ignored; for @acronym{POSIX} compatibility.
1552 @itemx --show-nonprinting
1554 @opindex --show-nonprinting
1555 Display control characters except for LFD and TAB using
1556 @samp{^} notation and precede characters that have the high bit set with
1561 On systems like MS-DOS that distinguish between text and binary files,
1562 @command{cat} normally reads and writes in binary mode. However,
1563 @command{cat} reads in text mode if one of the options
1564 @option{-bensAE} is used or if @command{cat} is reading from standard
1565 input and standard input is a terminal. Similarly, @command{cat}
1566 writes in text mode if one of the options @option{-bensAE} is used or
1567 if standard output is a terminal.
1574 # Output f's contents, then standard input, then g's contents.
1577 # Copy standard input to standard output.
1582 @node tac invocation
1583 @section @command{tac}: Concatenate and write files in reverse
1586 @cindex reversing files
1588 @command{tac} copies each @var{file} (@samp{-} means standard input), or
1589 standard input if none are given, to standard output, reversing the
1590 records (lines by default) in each separately. Synopsis:
1593 tac [@var{option}]@dots{} [@var{file}]@dots{}
1596 @dfn{Records} are separated by instances of a string (newline by
1597 default). By default, this separator string is attached to the end of
1598 the record that it follows in the file.
1600 The program accepts the following options. Also see @ref{Common options}.
1608 The separator is attached to the beginning of the record that it
1609 precedes in the file.
1615 Treat the separator string as a regular expression. Users of @command{tac}
1616 on MS-DOS/MS-Windows should note that, since @command{tac} reads files in
1617 binary mode, each line of a text file might end with a CR/LF pair
1618 instead of the Unix-style LF.
1620 @item -s @var{separator}
1621 @itemx --separator=@var{separator}
1623 @opindex --separator
1624 Use @var{separator} as the record separator, instead of newline.
1632 @section @command{nl}: Number lines and write files
1635 @cindex numbering lines
1636 @cindex line numbering
1638 @command{nl} writes each @var{file} (@samp{-} means standard input), or
1639 standard input if none are given, to standard output, with line numbers
1640 added to some or all of the lines. Synopsis:
1643 nl [@var{option}]@dots{} [@var{file}]@dots{}
1646 @cindex logical pages, numbering on
1647 @command{nl} decomposes its input into (logical) pages; by default, the
1648 line number is reset to 1 at the top of each logical page. @command{nl}
1649 treats all of the input files as a single document; it does not reset
1650 line numbers or logical pages between files.
1652 @cindex headers, numbering
1653 @cindex body, numbering
1654 @cindex footers, numbering
1655 A logical page consists of three sections: header, body, and footer.
1656 Any of the sections can be empty. Each can be numbered in a different
1657 style from the others.
1659 The beginnings of the sections of logical pages are indicated in the
1660 input file by a line containing exactly one of these delimiter strings:
1671 The two characters from which these strings are made can be changed from
1672 @samp{\} and @samp{:} via options (see below), but the pattern and
1673 length of each string cannot be changed.
1675 A section delimiter is replaced by an empty line on output. Any text
1676 that comes before the first section delimiter string in the input file
1677 is considered to be part of a body section, so @command{nl} treats a
1678 file that contains no section delimiters as a single body section.
1680 The program accepts the following options. Also see @ref{Common options}.
1684 @item -b @var{style}
1685 @itemx --body-numbering=@var{style}
1687 @opindex --body-numbering
1688 Select the numbering style for lines in the body section of each
1689 logical page. When a line is not numbered, the current line number
1690 is not incremented, but the line number separator character is still
1691 prepended to the line. The styles are:
1697 number only nonempty lines (default for body),
1699 do not number lines (default for header and footer),
1701 number only lines that contain a match for the basic regular
1702 expression @var{bre}.
1703 @xref{Regular Expressions, , Regular Expressions, grep, The GNU Grep Manual}.
1707 @itemx --section-delimiter=@var{cd}
1709 @opindex --section-delimiter
1710 @cindex section delimiters of pages
1711 Set the section delimiter characters to @var{cd}; default is
1712 @samp{\:}. If only @var{c} is given, the second remains @samp{:}.
1713 (Remember to protect @samp{\} or other metacharacters from shell
1714 expansion with quotes or extra backslashes.)
1716 @item -f @var{style}
1717 @itemx --footer-numbering=@var{style}
1719 @opindex --footer-numbering
1720 Analogous to @option{--body-numbering}.
1722 @item -h @var{style}
1723 @itemx --header-numbering=@var{style}
1725 @opindex --header-numbering
1726 Analogous to @option{--body-numbering}.
1728 @item -i @var{number}
1729 @itemx --line-increment=@var{number}
1731 @opindex --line-increment
1732 Increment line numbers by @var{number} (default 1).
1734 @item -l @var{number}
1735 @itemx --join-blank-lines=@var{number}
1737 @opindex --join-blank-lines
1738 @cindex empty lines, numbering
1739 @cindex blank lines, numbering
1740 Consider @var{number} (default 1) consecutive empty lines to be one
1741 logical line for numbering, and only number the last one. Where fewer
1742 than @var{number} consecutive empty lines occur, do not number them.
1743 An empty line is one that contains no characters, not even spaces
1746 @item -n @var{format}
1747 @itemx --number-format=@var{format}
1749 @opindex --number-format
1750 Select the line numbering format (default is @code{rn}):
1754 @opindex ln @r{format for @command{nl}}
1755 left justified, no leading zeros;
1757 @opindex rn @r{format for @command{nl}}
1758 right justified, no leading zeros;
1760 @opindex rz @r{format for @command{nl}}
1761 right justified, leading zeros.
1765 @itemx --no-renumber
1767 @opindex --no-renumber
1768 Do not reset the line number at the start of a logical page.
1770 @item -s @var{string}
1771 @itemx --number-separator=@var{string}
1773 @opindex --number-separator
1774 Separate the line number from the text line in the output with
1775 @var{string} (default is the TAB character).
1777 @item -v @var{number}
1778 @itemx --starting-line-number=@var{number}
1780 @opindex --starting-line-number
1781 Set the initial line number on each logical page to @var{number} (default 1).
1783 @item -w @var{number}
1784 @itemx --number-width=@var{number}
1786 @opindex --number-width
1787 Use @var{number} characters for line numbers (default 6).
1795 @section @command{od}: Write files in octal or other formats
1798 @cindex octal dump of files
1799 @cindex hex dump of files
1800 @cindex ASCII dump of files
1801 @cindex file contents, dumping unambiguously
1803 @command{od} writes an unambiguous representation of each @var{file}
1804 (@samp{-} means standard input), or standard input if none are given.
1808 od [@var{option}]@dots{} [@var{file}]@dots{}
1809 od [-abcdfilosx]@dots{} [@var{file}] [[+]@var{offset}[.][b]]
1810 od [@var{option}]@dots{} --traditional [@var{file}]@c
1811 [[+]@var{offset}[.][b] [[+]@var{label}[.][b]]]
1814 Each line of output consists of the offset in the input, followed by
1815 groups of data from the file. By default, @command{od} prints the offset in
1816 octal, and each group of file data is a C @code{short int}'s worth of input
1817 printed as a single octal number.
1819 If @var{offset} is given, it specifies how many input bytes to skip
1820 before formatting and writing. By default, it is interpreted as an
1821 octal number, but the optional trailing decimal point causes it to be
1822 interpreted as decimal. If no decimal is specified and the offset
1823 begins with @samp{0x} or @samp{0X} it is interpreted as a hexadecimal
1824 number. If there is a trailing @samp{b}, the number of bytes skipped
1825 will be @var{offset} multiplied by 512.
1827 If a command is of both the first and second forms, the second form is
1828 assumed if the last operand begins with @samp{+} or (if there are two
1829 operands) a digit. For example, in @samp{od foo 10} and @samp{od +10}
1830 the @samp{10} is an offset, whereas in @samp{od 10} the @samp{10} is a
1833 The program accepts the following options. Also see @ref{Common options}.
1837 @item -A @var{radix}
1838 @itemx --address-radix=@var{radix}
1840 @opindex --address-radix
1841 @cindex radix for file offsets
1842 @cindex file offset radix
1843 Select the base in which file offsets are printed. @var{radix} can
1844 be one of the following:
1854 none (do not print offsets).
1857 The default is octal.
1859 @item -j @var{bytes}
1860 @itemx --skip-bytes=@var{bytes}
1862 @opindex --skip-bytes
1863 Skip @var{bytes} input bytes before formatting and writing. If
1864 @var{bytes} begins with @samp{0x} or @samp{0X}, it is interpreted in
1865 hexadecimal; otherwise, if it begins with @samp{0}, in octal; otherwise,
1867 @multiplierSuffixes{bytes}
1869 @item -N @var{bytes}
1870 @itemx --read-bytes=@var{bytes}
1872 @opindex --read-bytes
1873 Output at most @var{bytes} bytes of the input. Prefixes and suffixes on
1874 @code{bytes} are interpreted as for the @option{-j} option.
1876 @item -S @var{bytes}
1877 @itemx --strings[=@var{bytes}]
1880 @cindex string constants, outputting
1881 Instead of the normal output, output only @dfn{string constants}: at
1882 least @var{bytes} consecutive @acronym{ASCII} graphic characters,
1883 followed by a zero byte (@acronym{ASCII} @sc{nul}).
1884 Prefixes and suffixes on @var{bytes} are interpreted as for the
1887 If @var{n} is omitted with @option{--strings}, the default is 3.
1890 @itemx --format=@var{type}
1893 Select the format in which to output the file data. @var{type} is a
1894 string of one or more of the below type indicator characters. If you
1895 include more than one type indicator character in a single @var{type}
1896 string, or use this option more than once, @command{od} writes one copy
1897 of each output line using each of the data types that you specified,
1898 in the order that you specified.
1900 Adding a trailing ``z'' to any type specification appends a display
1901 of the @acronym{ASCII} character representation of the printable characters
1902 to the output line generated by the type specification.
1906 named character, ignoring high-order bit
1908 @acronym{ASCII} character or backslash escape,
1912 floating point (@pxref{Floating point})
1921 The type @code{a} outputs things like @samp{sp} for space, @samp{nl} for
1922 newline, and @samp{nul} for a zero byte. Only the least significant
1923 seven bits of each byte is used; the high-order bit is ignored.
1924 Type @code{c} outputs
1925 @samp{ }, @samp{\n}, and @code{\0}, respectively.
1928 Except for types @samp{a} and @samp{c}, you can specify the number
1929 of bytes to use in interpreting each number in the given data type
1930 by following the type indicator character with a decimal integer.
1931 Alternately, you can specify the size of one of the C compiler's
1932 built-in data types by following the type indicator character with
1933 one of the following characters. For integers (@samp{d}, @samp{o},
1934 @samp{u}, @samp{x}):
1947 For floating point (@code{f}):
1959 @itemx --output-duplicates
1961 @opindex --output-duplicates
1962 Output consecutive lines that are identical. By default, when two or
1963 more consecutive output lines would be identical, @command{od} outputs only
1964 the first line, and puts just an asterisk on the following line to
1965 indicate the elision.
1968 @itemx --width[=@var{n}]
1971 Dump @code{n} input bytes per output line. This must be a multiple of
1972 the least common multiple of the sizes associated with the specified
1975 If this option is not given at all, the default is 16. If @var{n} is
1976 omitted, the default is 32.
1980 The next several options are shorthands for format specifications.
1981 @sc{gnu} @command{od} accepts any combination of shorthands and format
1982 specification options. These options accumulate.
1988 Output as named characters. Equivalent to @samp{-t a}.
1992 Output as octal bytes. Equivalent to @samp{-t o1}.
1996 Output as @acronym{ASCII} characters or backslash escapes. Equivalent to
2001 Output as unsigned decimal two-byte units. Equivalent to @samp{-t u2}.
2005 Output as floats. Equivalent to @samp{-t fF}.
2009 Output as decimal ints. Equivalent to @samp{-t dI}.
2013 Output as decimal long ints. Equivalent to @samp{-t dL}.
2017 Output as octal two-byte units. Equivalent to @option{-t o2}.
2021 Output as decimal two-byte units. Equivalent to @option{-t d2}.
2025 Output as hexadecimal two-byte units. Equivalent to @samp{-t x2}.
2028 @opindex --traditional
2029 Recognize the non-option label argument that traditional @command{od}
2030 accepted. The following syntax:
2033 od --traditional [@var{file}] [[+]@var{offset}[.][b] [[+]@var{label}[.][b]]]
2037 can be used to specify at most one file and optional arguments
2038 specifying an offset and a pseudo-start address, @var{label}.
2039 The @var{label} argument is interpreted
2040 just like @var{offset}, but it specifies an initial pseudo-address. The
2041 pseudo-addresses are displayed in parentheses following any normal
2048 @node base64 invocation
2049 @section @command{base64}: Transform data into printable data
2052 @cindex base64 encoding
2054 @command{base64} transforms data read from a file, or standard input,
2055 into (or from) base64 encoded form. The base64 encoded form uses
2056 printable @acronym{ASCII} characters to represent binary data.
2060 base64 [@var{option}]@dots{} [@var{file}]
2061 base64 --decode [@var{option}]@dots{} [@var{file}]
2064 The base64 encoding expands data to roughly 133% of the original.
2065 The format conforms to
2066 @uref{ftp://ftp.rfc-editor.org/in-notes/rfc4648.txt, RFC 4648}.
2068 The program accepts the following options. Also see @ref{Common options}.
2073 @itemx --wrap=@var{cols}
2077 @cindex column to wrap data after
2078 During encoding, wrap lines after @var{cols} characters. This must be
2081 The default is to wrap after 76 characters. Use the value 0 to
2082 disable line wrapping altogether.
2088 @cindex Decode base64 data
2089 @cindex Base64 decoding
2090 Change the mode of operation, from the default of encoding data, to
2091 decoding data. Input is expected to be base64 encoded data, and the
2092 output will be the original data.
2095 @itemx --ignore-garbage
2097 @opindex --ignore-garbage
2098 @cindex Ignore garbage in base64 stream
2099 When decoding, newlines are always accepted.
2100 During decoding, ignore unrecognized bytes,
2101 to permit distorted data to be decoded.
2108 @node Formatting file contents
2109 @chapter Formatting file contents
2111 @cindex formatting file contents
2113 These commands reformat the contents of files.
2116 * fmt invocation:: Reformat paragraph text.
2117 * pr invocation:: Paginate or columnate files for printing.
2118 * fold invocation:: Wrap input lines to fit in specified width.
2122 @node fmt invocation
2123 @section @command{fmt}: Reformat paragraph text
2126 @cindex reformatting paragraph text
2127 @cindex paragraphs, reformatting
2128 @cindex text, reformatting
2130 @command{fmt} fills and joins lines to produce output lines of (at most)
2131 a given number of characters (75 by default). Synopsis:
2134 fmt [@var{option}]@dots{} [@var{file}]@dots{}
2137 @command{fmt} reads from the specified @var{file} arguments (or standard
2138 input if none are given), and writes to standard output.
2140 By default, blank lines, spaces between words, and indentation are
2141 preserved in the output; successive input lines with different
2142 indentation are not joined; tabs are expanded on input and introduced on
2145 @cindex line-breaking
2146 @cindex sentences and line-breaking
2147 @cindex Knuth, Donald E.
2148 @cindex Plass, Michael F.
2149 @command{fmt} prefers breaking lines at the end of a sentence, and tries to
2150 avoid line breaks after the first word of a sentence or before the last
2151 word of a sentence. A @dfn{sentence break} is defined as either the end
2152 of a paragraph or a word ending in any of @samp{.?!}, followed by two
2153 spaces or end of line, ignoring any intervening parentheses or quotes.
2154 Like @TeX{}, @command{fmt} reads entire ``paragraphs'' before choosing line
2155 breaks; the algorithm is a variant of that given by Donald E. Knuth
2156 and Michael F. Plass in ``Breaking Paragraphs Into Lines'',
2157 @cite{Software---Practice & Experience} @b{11}, 11 (November 1981),
2160 The program accepts the following options. Also see @ref{Common options}.
2165 @itemx --crown-margin
2167 @opindex --crown-margin
2168 @cindex crown margin
2169 @dfn{Crown margin} mode: preserve the indentation of the first two
2170 lines within a paragraph, and align the left margin of each subsequent
2171 line with that of the second line.
2174 @itemx --tagged-paragraph
2176 @opindex --tagged-paragraph
2177 @cindex tagged paragraphs
2178 @dfn{Tagged paragraph} mode: like crown margin mode, except that if
2179 indentation of the first line of a paragraph is the same as the
2180 indentation of the second, the first line is treated as a one-line
2186 @opindex --split-only
2187 Split lines only. Do not join short lines to form longer ones. This
2188 prevents sample lines of code, and other such ``formatted'' text from
2189 being unduly combined.
2192 @itemx --uniform-spacing
2194 @opindex --uniform-spacing
2195 Uniform spacing. Reduce spacing between words to one space, and spacing
2196 between sentences to two spaces.
2199 @itemx -w @var{width}
2200 @itemx --width=@var{width}
2201 @opindex -@var{width}
2204 Fill output lines up to @var{width} characters (default 75). @command{fmt}
2205 initially tries to make lines about 7% shorter than this, to give it
2206 room to balance line lengths.
2208 @item -p @var{prefix}
2209 @itemx --prefix=@var{prefix}
2210 Only lines beginning with @var{prefix} (possibly preceded by whitespace)
2211 are subject to formatting. The prefix and any preceding whitespace are
2212 stripped for the formatting and then re-attached to each formatted output
2213 line. One use is to format certain kinds of program comments, while
2214 leaving the code unchanged.
2222 @section @command{pr}: Paginate or columnate files for printing
2225 @cindex printing, preparing files for
2226 @cindex multicolumn output, generating
2227 @cindex merging files in parallel
2229 @command{pr} writes each @var{file} (@samp{-} means standard input), or
2230 standard input if none are given, to standard output, paginating and
2231 optionally outputting in multicolumn format; optionally merges all
2232 @var{file}s, printing all in parallel, one per column. Synopsis:
2235 pr [@var{option}]@dots{} [@var{file}]@dots{}
2239 By default, a 5-line header is printed at each page: two blank lines;
2240 a line with the date, the file name, and the page count; and two more
2241 blank lines. A footer of five blank lines is also printed.
2242 The default @var{page_length} is 66
2243 lines. The default number of text lines is therefore 56.
2244 The text line of the header takes the form
2245 @samp{@var{date} @var{string} @var{page}}, with spaces inserted around
2246 @var{string} so that the line takes up the full @var{page_width}. Here,
2247 @var{date} is the date (see the @option{-D} or @option{--date-format}
2248 option for details), @var{string} is the centered header string, and
2249 @var{page} identifies the page number. The @env{LC_MESSAGES} locale
2250 category affects the spelling of @var{page}; in the default C locale, it
2251 is @samp{Page @var{number}} where @var{number} is the decimal page
2254 Form feeds in the input cause page breaks in the output. Multiple form
2255 feeds produce empty pages.
2257 Columns are of equal width, separated by an optional string (default
2258 is @samp{space}). For multicolumn output, lines will always be truncated to
2259 @var{page_width} (default 72), unless you use the @option{-J} option.
2261 column output no line truncation occurs by default. Use @option{-W} option to
2262 truncate lines in that case.
2264 The following changes were made in version 1.22i and apply to later
2265 versions of @command{pr}:
2266 @c FIXME: this whole section here sounds very awkward to me. I
2267 @c made a few small changes, but really it all needs to be redone. - Brian
2268 @c OK, I fixed another sentence or two, but some of it I just don't understand.
2273 Some small @var{letter options} (@option{-s}, @option{-w}) have been
2274 redefined for better @acronym{POSIX} compliance. The output of some further
2275 cases has been adapted to other Unix systems. These changes are not
2276 compatible with earlier versions of the program.
2279 Some @var{new capital letter} options (@option{-J}, @option{-S}, @option{-W})
2280 have been introduced to turn off unexpected interferences of small letter
2281 options. The @option{-N} option and the second argument @var{last_page}
2282 of @samp{+FIRST_PAGE} offer more flexibility. The detailed handling of
2283 form feeds set in the input files requires the @option{-T} option.
2286 Capital letter options override small letter ones.
2289 Some of the option-arguments (compare @option{-s}, @option{-e},
2290 @option{-i}, @option{-n}) cannot be specified as separate arguments from the
2291 preceding option letter (already stated in the @acronym{POSIX} specification).
2294 The program accepts the following options. Also see @ref{Common options}.
2298 @item +@var{first_page}[:@var{last_page}]
2299 @itemx --pages=@var{first_page}[:@var{last_page}]
2300 @c The two following @opindex lines evoke warnings because they contain `:'
2301 @c The `info' spec does not permit that. If we use those lines, we end
2302 @c up with truncated index entries that don't work.
2303 @c @opindex +@var{first_page}[:@var{last_page}]
2304 @c @opindex --pages=@var{first_page}[:@var{last_page}]
2305 @opindex +@var{page_range}
2306 @opindex --pages=@var{page_range}
2307 Begin printing with page @var{first_page} and stop with @var{last_page}.
2308 Missing @samp{:@var{last_page}} implies end of file. While estimating
2309 the number of skipped pages each form feed in the input file results
2310 in a new page. Page counting with and without @samp{+@var{first_page}}
2311 is identical. By default, counting starts with the first page of input
2312 file (not first page printed). Line numbering may be altered by @option{-N}
2316 @itemx --columns=@var{column}
2317 @opindex -@var{column}
2319 @cindex down columns
2320 With each single @var{file}, produce @var{column} columns of output
2321 (default is 1) and print columns down, unless @option{-a} is used. The
2322 column width is automatically decreased as @var{column} increases; unless
2323 you use the @option{-W/-w} option to increase @var{page_width} as well.
2324 This option might well cause some lines to be truncated. The number of
2325 lines in the columns on each page are balanced. The options @option{-e}
2326 and @option{-i} are on for multiple text-column output. Together with
2327 @option{-J} option column alignment and line truncation is turned off.
2328 Lines of full length are joined in a free field format and @option{-S}
2329 option may set field separators. @option{-@var{column}} may not be used
2330 with @option{-m} option.
2336 @cindex across columns
2337 With each single @var{file}, print columns across rather than down. The
2338 @option{-@var{column}} option must be given with @var{column} greater than one.
2339 If a line is too long to fit in a column, it is truncated.
2342 @itemx --show-control-chars
2344 @opindex --show-control-chars
2345 Print control characters using hat notation (e.g., @samp{^G}); print
2346 other nonprinting characters in octal backslash notation. By default,
2347 nonprinting characters are not changed.
2350 @itemx --double-space
2352 @opindex --double-space
2353 @cindex double spacing
2354 Double space the output.
2356 @item -D @var{format}
2357 @itemx --date-format=@var{format}
2358 @cindex time formats
2359 @cindex formatting times
2360 Format header dates using @var{format}, using the same conventions as
2361 for the command @samp{date +@var{format}}; @xref{date invocation}.
2362 Except for directives, which start with
2363 @samp{%}, characters in @var{format} are printed unchanged. You can use
2364 this option to specify an arbitrary string in place of the header date,
2365 e.g., @option{--date-format="Monday morning"}.
2367 @vindex POSIXLY_CORRECT
2369 The default date format is @samp{%Y-%m-%d %H:%M} (for example,
2370 @samp{2001-12-04 23:59});
2371 but if the @env{POSIXLY_CORRECT} environment variable is set
2372 and the @env{LC_TIME} locale category specifies the @acronym{POSIX}
2373 locale, the default is @samp{%b %e %H:%M %Y} (for example,
2374 @samp{Dec@ @ 4 23:59 2001}.
2377 Time stamps are listed according to the time zone rules specified by
2378 the @env{TZ} environment variable, or by the system default rules if
2379 @env{TZ} is not set. @xref{TZ Variable,, Specifying the Time Zone
2380 with @env{TZ}, libc, The GNU C Library Reference Manual}.
2382 @item -e[@var{in-tabchar}[@var{in-tabwidth}]]
2383 @itemx --expand-tabs[=@var{in-tabchar}[@var{in-tabwidth}]]
2385 @opindex --expand-tabs
2387 Expand @var{tab}s to spaces on input. Optional argument @var{in-tabchar} is
2388 the input tab character (default is the TAB character). Second optional
2389 argument @var{in-tabwidth} is the input tab character's width (default
2397 @opindex --form-feed
2398 Use a form feed instead of newlines to separate output pages. This does
2399 not alter the default page length of 66 lines.
2401 @item -h @var{header}
2402 @itemx --header=@var{header}
2405 Replace the file name in the header with the centered string @var{header}.
2406 When using the shell, @var{header} should be quoted and should be
2407 separated from @option{-h} by a space.
2409 @item -i[@var{out-tabchar}[@var{out-tabwidth}]]
2410 @itemx --output-tabs[=@var{out-tabchar}[@var{out-tabwidth}]]
2412 @opindex --output-tabs
2414 Replace spaces with @var{tab}s on output. Optional argument @var{out-tabchar}
2415 is the output tab character (default is the TAB character). Second optional
2416 argument @var{out-tabwidth} is the output tab character's width (default
2422 @opindex --join-lines
2423 Merge lines of full length. Used together with the column options
2424 @option{-@var{column}}, @option{-a -@var{column}} or @option{-m}. Turns off
2425 @option{-W/-w} line truncation;
2426 no column alignment used; may be used with
2427 @option{--sep-string[=@var{string}]}. @option{-J} has been introduced
2428 (together with @option{-W} and @option{--sep-string})
2429 to disentangle the old (@acronym{POSIX}-compliant) options @option{-w} and
2430 @option{-s} along with the three column options.
2433 @item -l @var{page_length}
2434 @itemx --length=@var{page_length}
2437 Set the page length to @var{page_length} (default 66) lines, including
2438 the lines of the header [and the footer]. If @var{page_length} is less
2439 than or equal to 10, the header and footer are omitted, as if the
2440 @option{-t} option had been given.
2446 Merge and print all @var{file}s in parallel, one in each column. If a
2447 line is too long to fit in a column, it is truncated, unless the @option{-J}
2448 option is used. @option{--sep-string[=@var{string}]} may be used.
2450 some @var{file}s (form feeds set) produce empty columns, still marked
2451 by @var{string}. The result is a continuous line numbering and column
2452 marking throughout the whole merged file. Completely empty merged pages
2453 show no separators or line numbers. The default header becomes
2454 @samp{@var{date} @var{page}} with spaces inserted in the middle; this
2455 may be used with the @option{-h} or @option{--header} option to fill up
2456 the middle blank part.
2458 @item -n[@var{number-separator}[@var{digits}]]
2459 @itemx --number-lines[=@var{number-separator}[@var{digits}]]
2461 @opindex --number-lines
2462 Provide @var{digits} digit line numbering (default for @var{digits} is
2463 5). With multicolumn output the number occupies the first @var{digits}
2464 column positions of each text column or only each line of @option{-m}
2465 output. With single column output the number precedes each line just as
2466 @option{-m} does. Default counting of the line numbers starts with the
2467 first line of the input file (not the first line printed, compare the
2468 @option{--page} option and @option{-N} option).
2469 Optional argument @var{number-separator} is the character appended to
2470 the line number to separate it from the text followed. The default
2471 separator is the TAB character. In a strict sense a TAB is always
2472 printed with single column output only. The TAB width varies
2473 with the TAB position, e.g., with the left @var{margin} specified
2474 by @option{-o} option. With multicolumn output priority is given to
2475 @samp{equal width of output columns} (a @acronym{POSIX} specification).
2476 The TAB width is fixed to the value of the first column and does
2477 not change with different values of left @var{margin}. That means a
2478 fixed number of spaces is always printed in the place of the
2479 @var{number-separator} TAB. The tabification depends upon the output
2482 @item -N @var{line_number}
2483 @itemx --first-line-number=@var{line_number}
2485 @opindex --first-line-number
2486 Start line counting with the number @var{line_number} at first line of
2487 first page printed (in most cases not the first line of the input file).
2489 @item -o @var{margin}
2490 @itemx --indent=@var{margin}
2493 @cindex indenting lines
2495 Indent each line with a margin @var{margin} spaces wide (default is zero).
2496 The total page width is the size of the margin plus the @var{page_width}
2497 set with the @option{-W/-w} option. A limited overflow may occur with
2498 numbered single column output (compare @option{-n} option).
2501 @itemx --no-file-warnings
2503 @opindex --no-file-warnings
2504 Do not print a warning message when an argument @var{file} cannot be
2505 opened. (The exit status will still be nonzero, however.)
2507 @item -s[@var{char}]
2508 @itemx --separator[=@var{char}]
2510 @opindex --separator
2511 Separate columns by a single character @var{char}. The default for
2512 @var{char} is the TAB character without @option{-w} and @samp{no
2513 character} with @option{-w}. Without @option{-s} the default separator
2514 @samp{space} is set. @option{-s[char]} turns off line truncation of all
2515 three column options (@option{-COLUMN}|@option{-a -COLUMN}|@option{-m}) unless
2516 @option{-w} is set. This is a @acronym{POSIX}-compliant formulation.
2519 @item -S@var{string}
2520 @itemx --sep-string[=@var{string}]
2522 @opindex --sep-string
2523 Use @var{string} to separate output columns. The @option{-S} option doesn't
2524 affect the @option{-W/-w} option, unlike the @option{-s} option which does. It
2525 does not affect line truncation or column alignment.
2526 Without @option{-S}, and with @option{-J}, @command{pr} uses the default output
2528 Without @option{-S} or @option{-J}, @command{pr} uses a @samp{space}
2529 (same as @option{-S"@w{ }"}). @option{--sep-string} with no
2530 @samp{=@var{string}} is equivalent to @option{--sep-string=""}.
2533 @itemx --omit-header
2535 @opindex --omit-header
2536 Do not print the usual header [and footer] on each page, and do not fill
2537 out the bottom of pages (with blank lines or a form feed). No page
2538 structure is produced, but form feeds set in the input files are retained.
2539 The predefined pagination is not changed. @option{-t} or @option{-T} may be
2540 useful together with other options; e.g.: @option{-t -e4}, expand TAB characters
2541 in the input file to 4 spaces but don't make any other changes. Use of
2542 @option{-t} overrides @option{-h}.
2545 @itemx --omit-pagination
2547 @opindex --omit-pagination
2548 Do not print header [and footer]. In addition eliminate all form feeds
2549 set in the input files.
2552 @itemx --show-nonprinting
2554 @opindex --show-nonprinting
2555 Print nonprinting characters in octal backslash notation.
2557 @item -w @var{page_width}
2558 @itemx --width=@var{page_width}
2561 Set page width to @var{page_width} characters for multiple text-column
2562 output only (default for @var{page_width} is 72). @option{-s[CHAR]} turns
2563 off the default page width and any line truncation and column alignment.
2564 Lines of full length are merged, regardless of the column options
2565 set. No @var{page_width} setting is possible with single column output.
2566 A @acronym{POSIX}-compliant formulation.
2568 @item -W @var{page_width}
2569 @itemx --page_width=@var{page_width}
2571 @opindex --page_width
2572 Set the page width to @var{page_width} characters. That's valid with and
2573 without a column option. Text lines are truncated, unless @option{-J}
2574 is used. Together with one of the three column options
2575 (@option{-@var{column}}, @option{-a -@var{column}} or @option{-m}) column
2576 alignment is always used. The separator options @option{-S} or @option{-s}
2577 don't affect the @option{-W} option. Default is 72 characters. Without
2578 @option{-W @var{page_width}} and without any of the column options NO line
2579 truncation is used (defined to keep downward compatibility and to meet
2580 most frequent tasks). That's equivalent to @option{-W 72 -J}. The header
2581 line is never truncated.
2588 @node fold invocation
2589 @section @command{fold}: Wrap input lines to fit in specified width
2592 @cindex wrapping long input lines
2593 @cindex folding long input lines
2595 @command{fold} writes each @var{file} (@option{-} means standard input), or
2596 standard input if none are given, to standard output, breaking long
2600 fold [@var{option}]@dots{} [@var{file}]@dots{}
2603 By default, @command{fold} breaks lines wider than 80 columns. The output
2604 is split into as many lines as necessary.
2606 @cindex screen columns
2607 @command{fold} counts screen columns by default; thus, a tab may count more
2608 than one column, backspace decreases the column count, and carriage
2609 return sets the column to zero.
2611 The program accepts the following options. Also see @ref{Common options}.
2619 Count bytes rather than columns, so that tabs, backspaces, and carriage
2620 returns are each counted as taking up one column, just like other
2627 Break at word boundaries: the line is broken after the last blank before
2628 the maximum line length. If the line contains no such blanks, the line
2629 is broken at the maximum line length as usual.
2631 @item -w @var{width}
2632 @itemx --width=@var{width}
2635 Use a maximum line length of @var{width} columns instead of 80.
2637 For compatibility @command{fold} supports an obsolete option syntax
2638 @option{-@var{width}}. New scripts should use @option{-w @var{width}}
2646 @node Output of parts of files
2647 @chapter Output of parts of files
2649 @cindex output of parts of files
2650 @cindex parts of files, output of
2652 These commands output pieces of the input.
2655 * head invocation:: Output the first part of files.
2656 * tail invocation:: Output the last part of files.
2657 * split invocation:: Split a file into pieces.
2658 * csplit invocation:: Split a file into context-determined pieces.
2661 @node head invocation
2662 @section @command{head}: Output the first part of files
2665 @cindex initial part of files, outputting
2666 @cindex first part of files, outputting
2668 @command{head} prints the first part (10 lines by default) of each
2669 @var{file}; it reads from standard input if no files are given or
2670 when given a @var{file} of @option{-}. Synopsis:
2673 head [@var{option}]@dots{} [@var{file}]@dots{}
2676 If more than one @var{file} is specified, @command{head} prints a
2677 one-line header consisting of:
2680 ==> @var{file name} <==
2684 before the output for each @var{file}.
2686 The program accepts the following options. Also see @ref{Common options}.
2691 @itemx --bytes=@var{k}
2694 Print the first @var{k} bytes, instead of initial lines.
2695 However, if @var{k} starts with a @samp{-},
2696 print all but the last @var{k} bytes of each file.
2697 @multiplierSuffixes{k}
2700 @itemx --lines=@var{k}
2703 Output the first @var{k} lines.
2704 However, if @var{k} starts with a @samp{-},
2705 print all but the last @var{k} lines of each file.
2706 Size multiplier suffixes are the same as with the @option{-c} option.
2714 Never print file name headers.
2720 Always print file name headers.
2724 For compatibility @command{head} also supports an obsolete option syntax
2725 @option{-@var{count}@var{options}}, which is recognized only if it is
2726 specified first. @var{count} is a decimal number optionally followed
2727 by a size letter (@samp{b}, @samp{k}, @samp{m}) as in @option{-c}, or
2728 @samp{l} to mean count by lines, or other option letters (@samp{cqv}).
2729 Scripts intended for standard hosts should use @option{-c @var{count}}
2730 or @option{-n @var{count}} instead. If your script must also run on
2731 hosts that support only the obsolete syntax, it is usually simpler to
2732 avoid @command{head}, e.g., by using @samp{sed 5q} instead of
2738 @node tail invocation
2739 @section @command{tail}: Output the last part of files
2742 @cindex last part of files, outputting
2744 @command{tail} prints the last part (10 lines by default) of each
2745 @var{file}; it reads from standard input if no files are given or
2746 when given a @var{file} of @samp{-}. Synopsis:
2749 tail [@var{option}]@dots{} [@var{file}]@dots{}
2752 If more than one @var{file} is specified, @command{tail} prints a
2753 one-line header consisting of:
2756 ==> @var{file name} <==
2760 before the output for each @var{file}.
2762 @cindex BSD @command{tail}
2763 @sc{gnu} @command{tail} can output any amount of data (some other versions of
2764 @command{tail} cannot). It also has no @option{-r} option (print in
2765 reverse), since reversing a file is really a different job from printing
2766 the end of a file; BSD @command{tail} (which is the one with @option{-r}) can
2767 only reverse files that are at most as large as its buffer, which is
2768 typically 32 KiB@. A more reliable and versatile way to reverse files is
2769 the @sc{gnu} @command{tac} command.
2771 The program accepts the following options. Also see @ref{Common options}.
2776 @itemx --bytes=@var{k}
2779 Output the last @var{k} bytes, instead of final lines.
2780 However, if @var{k} starts with a @samp{+}, start printing with the
2781 @var{k}th byte from the start of each file, instead of from the end.
2782 @multiplierSuffixes{k}
2785 @itemx --follow[=@var{how}]
2788 @cindex growing files
2789 @vindex name @r{follow option}
2790 @vindex descriptor @r{follow option}
2791 Loop forever trying to read more characters at the end of the file,
2792 presumably because the file is growing.
2793 If more than one file is given, @command{tail} prints a header whenever it
2794 gets output from a different file, to indicate which file that output is
2797 There are two ways to specify how you'd like to track files with this option,
2798 but that difference is noticeable only when a followed file is removed or
2800 If you'd like to continue to track the end of a growing file even after
2801 it has been unlinked, use @option{--follow=descriptor}. This is the default
2802 behavior, but it is not useful if you're tracking a log file that may be
2803 rotated (removed or renamed, then reopened). In that case, use
2804 @option{--follow=name} to track the named file, perhaps by reopening it
2805 periodically to see if it has been removed and recreated by some other program.
2806 Note that the inotify-based implementation handles this case without
2807 the need for any periodic reopening.
2809 No matter which method you use, if the tracked file is determined to have
2810 shrunk, @command{tail} prints a message saying the file has been truncated
2811 and resumes tracking the end of the file from the newly-determined endpoint.
2813 When a file is removed, @command{tail}'s behavior depends on whether it is
2814 following the name or the descriptor. When following by name, tail can
2815 detect that a file has been removed and gives a message to that effect,
2816 and if @option{--retry} has been specified it will continue checking
2817 periodically to see if the file reappears.
2818 When following a descriptor, tail does not detect that the file has
2819 been unlinked or renamed and issues no message; even though the file
2820 may no longer be accessible via its original name, it may still be
2823 The option values @samp{descriptor} and @samp{name} may be specified only
2824 with the long form of the option, not with @option{-f}.
2826 The @option{-f} option is ignored if
2827 no @var{file} operand is specified and standard input is a FIFO or a pipe.
2828 Likewise, the @option{-f} option has no effect for any
2829 operand specified as @samp{-}, when standard input is a FIFO or a pipe.
2831 With kernel inotify support, output is triggered by file changes
2832 and is generally very prompt.
2833 Otherwise, @command{tail} sleeps for one second between checks---
2834 use @option{--sleep-interval=@var{n}} to change that default---which can
2835 make the output appear slightly less responsive or bursty.
2836 When using tail without inotify support, you can make it more responsive
2837 by using a sub-second sleep interval, e.g., via an alias like this:
2840 alias tail='tail -s.1'
2845 This option is the same as @option{--follow=name --retry}. That is, tail
2846 will attempt to reopen a file when it is removed. Should this fail, tail
2847 will keep trying until it becomes accessible again.
2851 This option is useful mainly when following by name (i.e., with
2852 @option{--follow=name}).
2853 Without this option, when tail encounters a file that doesn't
2854 exist or is otherwise inaccessible, it reports that fact and
2855 never checks it again.
2857 @itemx --sleep-interval=@var{number}
2858 @opindex --sleep-interval
2859 Change the number of seconds to wait between iterations (the default is 1.0).
2860 During one iteration, every specified file is checked to see if it has
2862 Historical implementations of @command{tail} have required that
2863 @var{number} be an integer. However, GNU @command{tail} accepts
2864 an arbitrary floating point number. @xref{Floating point}.
2865 When @command{tail} uses inotify, this polling-related option
2866 is usually ignored. However, if you also specify @option{--pid=@var{p}},
2867 @command{tail} checks whether process @var{p} is alive at least
2868 every @var{number} seconds.
2870 @itemx --pid=@var{pid}
2872 When following by name or by descriptor, you may specify the process ID,
2873 @var{pid}, of the sole writer of all @var{file} arguments. Then, shortly
2874 after that process terminates, tail will also terminate. This will
2875 work properly only if the writer and the tailing process are running on
2876 the same machine. For example, to save the output of a build in a file
2877 and to watch the file grow, if you invoke @command{make} and @command{tail}
2878 like this then the tail process will stop when your build completes.
2879 Without this option, you would have had to kill the @code{tail -f}
2883 $ make >& makerr & tail --pid=$! -f makerr
2886 If you specify a @var{pid} that is not in use or that does not correspond
2887 to the process that is writing to the tailed files, then @command{tail}
2888 may terminate long before any @var{file}s stop growing or it may not
2889 terminate until long after the real writer has terminated.
2890 Note that @option{--pid} cannot be supported on some systems; @command{tail}
2891 will print a warning if this is the case.
2893 @itemx --max-unchanged-stats=@var{n}
2894 @opindex --max-unchanged-stats
2895 When tailing a file by name, if there have been @var{n} (default
2896 n=@value{DEFAULT_MAX_N_UNCHANGED_STATS_BETWEEN_OPENS}) consecutive
2897 iterations for which the file has not changed, then
2898 @code{open}/@code{fstat} the file to determine if that file name is
2899 still associated with the same device/inode-number pair as before.
2900 When following a log file that is rotated, this is approximately the
2901 number of seconds between when tail prints the last pre-rotation lines
2902 and when it prints the lines that have accumulated in the new log file.
2903 This option is meaningful only when polling (i.e., without inotify)
2904 and when following by name.
2907 @itemx --lines=@var{k}
2910 Output the last @var{k} lines.
2911 However, if @var{k} starts with a @samp{+}, start printing with the
2912 @var{k}th line from the start of each file, instead of from the end.
2913 Size multiplier suffixes are the same as with the @option{-c} option.
2921 Never print file name headers.
2927 Always print file name headers.
2931 For compatibility @command{tail} also supports an obsolete usage
2932 @samp{tail -[@var{count}][bcl][f] [@var{file}]}, which is recognized
2933 only if it does not conflict with the usage described
2934 above. This obsolete form uses exactly one option and at most one
2935 file. In the option, @var{count} is an optional decimal number optionally
2936 followed by a size letter (@samp{b}, @samp{c}, @samp{l}) to mean count
2937 by 512-byte blocks, bytes, or lines, optionally followed by @samp{f}
2938 which has the same meaning as @option{-f}.
2940 @vindex _POSIX2_VERSION
2941 On older systems, the leading @samp{-} can be replaced by @samp{+} in
2942 the obsolete option syntax with the same meaning as in counts, and
2943 obsolete usage overrides normal usage when the two conflict.
2944 This obsolete behavior can be enabled or disabled with the
2945 @env{_POSIX2_VERSION} environment variable (@pxref{Standards
2948 Scripts intended for use on standard hosts should avoid obsolete
2949 syntax and should use @option{-c @var{count}[b]}, @option{-n
2950 @var{count}}, and/or @option{-f} instead. If your script must also
2951 run on hosts that support only the obsolete syntax, you can often
2952 rewrite it to avoid problematic usages, e.g., by using @samp{sed -n
2953 '$p'} rather than @samp{tail -1}. If that's not possible, the script
2954 can use a test like @samp{if tail -c +1 </dev/null >/dev/null 2>&1;
2955 then @dots{}} to decide which syntax to use.
2957 Even if your script assumes the standard behavior, you should still
2958 beware usages whose behaviors differ depending on the @acronym{POSIX}
2959 version. For example, avoid @samp{tail - main.c}, since it might be
2960 interpreted as either @samp{tail main.c} or as @samp{tail -- -
2961 main.c}; avoid @samp{tail -c 4}, since it might mean either @samp{tail
2962 -c4} or @samp{tail -c 10 4}; and avoid @samp{tail +4}, since it might
2963 mean either @samp{tail ./+4} or @samp{tail -n +4}.
2968 @node split invocation
2969 @section @command{split}: Split a file into pieces.
2972 @cindex splitting a file into pieces
2973 @cindex pieces, splitting a file into
2975 @command{split} creates output files containing consecutive or interleaved
2976 sections of @var{input} (standard input if none is given or @var{input}
2977 is @samp{-}). Synopsis:
2980 split [@var{option}] [@var{input} [@var{prefix}]]
2983 By default, @command{split} puts 1000 lines of @var{input} (or whatever is
2984 left over for the last section), into each output file.
2986 @cindex output file name prefix
2987 The output files' names consist of @var{prefix} (@samp{x} by default)
2988 followed by a group of characters (@samp{aa}, @samp{ab}, @dots{} by
2989 default), such that concatenating the output files in traditional
2990 sorted order by file name produces the original input file (except
2991 @option{-r}). If the output file names are exhausted, @command{split}
2992 reports an error without deleting the output files that it did create.
2994 The program accepts the following options. Also see @ref{Common options}.
2998 @item -l @var{lines}
2999 @itemx --lines=@var{lines}
3002 Put @var{lines} lines of @var{input} into each output file.
3004 For compatibility @command{split} also supports an obsolete
3005 option syntax @option{-@var{lines}}. New scripts should use
3006 @option{-l @var{lines}} instead.
3009 @itemx --bytes=@var{size}
3012 Put @var{size} bytes of @var{input} into each output file.
3013 @multiplierSuffixes{size}
3016 @itemx --line-bytes=@var{size}
3018 @opindex --line-bytes
3019 Put into each output file as many complete lines of @var{input} as
3020 possible without exceeding @var{size} bytes. Individual lines longer than
3021 @var{size} bytes are broken into multiple files.
3022 @var{size} has the same format as for the @option{--bytes} option.
3024 @itemx --filter=@var{command}
3026 With this option, rather than simply writing to each output file,
3027 write through a pipe to the specified shell @var{command} for each output file.
3028 @var{command} should use the $FILE environment variable, which is set
3029 to a different output file name for each invocation of the command.
3030 For example, imagine that you have a 1TiB compressed file
3031 that, if uncompressed, would be too large to reside on disk,
3032 yet you must split it into individually-compressed pieces
3033 of a more manageable size.
3034 To do that, you might run this command:
3037 xz -dc BIG.xz | split -b200G --filter='xz > $FILE.xz' - big-
3040 Assuming a 10:1 compression ratio, that would create about fifty 20GiB files
3041 with names @file{big-xaa.xz}, @file{big-xab.xz}, @file{big-xac.xz}, etc.
3043 @item -n @var{chunks}
3044 @itemx --number=@var{chunks}
3048 Split @var{input} to @var{chunks} output files where @var{chunks} may be:
3051 @var{n} generate @var{n} files based on current size of @var{input}
3052 @var{k}/@var{n} only output @var{k}th of @var{n} to stdout
3053 l/@var{n} generate @var{n} files without splitting lines
3054 l/@var{k}/@var{n} likewise but only output @var{k}th of @var{n} to stdout
3055 r/@var{n} like @samp{l} but use round robin distribution
3056 r/@var{k}/@var{n} likewise but only output @var{k}th of @var{n} to stdout
3059 Any excess bytes remaining after dividing the @var{input}
3060 into @var{n} chunks, are assigned to the last chunk.
3061 Any excess bytes appearing after the initial calculation are discarded
3062 (except when using @samp{r} mode).
3064 All @var{n} files are created even if there are fewer than @var{n} lines,
3065 or the @var{input} is truncated.
3067 For @samp{l} mode, chunks are approximately @var{input} size / @var{n}.
3068 The @var{input} is partitioned into @var{n} equal sized portions, with
3069 the last assigned any excess. If a line @emph{starts} within a partition
3070 it is written completely to the corresponding file. Since lines
3071 are not split even if they overlap a partition, the files written
3072 can be larger or smaller than the partition size, and even empty
3073 if a line is so long as to completely overlap the partition.
3075 For @samp{r} mode, the size of @var{input} is irrelevant,
3076 and so can be a pipe for example.
3078 @item -a @var{length}
3079 @itemx --suffix-length=@var{length}
3081 @opindex --suffix-length
3082 Use suffixes of length @var{length}. The default @var{length} is 2.
3085 @itemx --numeric-suffixes
3087 @opindex --numeric-suffixes
3088 Use digits in suffixes rather than lower-case letters.
3091 @itemx --elide-empty-files
3093 @opindex --elide-empty-files
3094 Suppress the generation of zero-length output files. This can happen
3095 with the @option{--number} option if a file is (truncated to be) shorter
3096 than the number requested, or if a line is so long as to completely
3097 span a chunk. The output file sequence numbers, always run consecutively
3098 even when this option is specified.
3103 @opindex --unbuffered
3104 Immediately copy input to output in @option{--number r/...} mode,
3105 which is a much slower mode of operation.
3109 Write a diagnostic just before each output file is opened.
3115 Here are a few examples to illustrate how the
3116 @option{--number} (@option{-n}) option works:
3118 Notice how, by default, one line may be split onto two or more:
3121 $ seq -w 6 10 > k; split -n3 k; head xa?
3134 Use the "l/" modifier to suppress that:
3137 $ seq -w 6 10 > k; split -nl/3 k; head xa?
3150 Use the "r/" modifier to distribute lines in a round-robin fashion:
3153 $ seq -w 6 10 > k; split -nr/3 k; head xa?
3166 You can also extract just the Kth chunk.
3167 This extracts and prints just the 7th "chunk" of 33:
3170 $ seq 100 > k; split -nl/7/33 k
3177 @node csplit invocation
3178 @section @command{csplit}: Split a file into context-determined pieces
3181 @cindex context splitting
3182 @cindex splitting a file into pieces by context
3184 @command{csplit} creates zero or more output files containing sections of
3185 @var{input} (standard input if @var{input} is @samp{-}). Synopsis:
3188 csplit [@var{option}]@dots{} @var{input} @var{pattern}@dots{}
3191 The contents of the output files are determined by the @var{pattern}
3192 arguments, as detailed below. An error occurs if a @var{pattern}
3193 argument refers to a nonexistent line of the input file (e.g., if no
3194 remaining line matches a given regular expression). After every
3195 @var{pattern} has been matched, any remaining input is copied into one
3198 By default, @command{csplit} prints the number of bytes written to each
3199 output file after it has been created.
3201 The types of pattern arguments are:
3206 Create an output file containing the input up to but not including line
3207 @var{n} (a positive integer). If followed by a repeat count, also
3208 create an output file containing the next @var{n} lines of the input
3209 file once for each repeat.
3211 @item /@var{regexp}/[@var{offset}]
3212 Create an output file containing the current line up to (but not
3213 including) the next line of the input file that contains a match for
3214 @var{regexp}. The optional @var{offset} is an integer.
3215 If it is given, the input up to (but not including) the
3216 matching line plus or minus @var{offset} is put into the output file,
3217 and the line after that begins the next section of input.
3219 @item %@var{regexp}%[@var{offset}]
3220 Like the previous type, except that it does not create an output
3221 file, so that section of the input file is effectively ignored.
3223 @item @{@var{repeat-count}@}
3224 Repeat the previous pattern @var{repeat-count} additional
3225 times. The @var{repeat-count} can either be a positive integer or an
3226 asterisk, meaning repeat as many times as necessary until the input is
3231 The output files' names consist of a prefix (@samp{xx} by default)
3232 followed by a suffix. By default, the suffix is an ascending sequence
3233 of two-digit decimal numbers from @samp{00} to @samp{99}. In any case,
3234 concatenating the output files in sorted order by file name produces the
3235 original input file.
3237 By default, if @command{csplit} encounters an error or receives a hangup,
3238 interrupt, quit, or terminate signal, it removes any output files
3239 that it has created so far before it exits.
3241 The program accepts the following options. Also see @ref{Common options}.
3245 @item -f @var{prefix}
3246 @itemx --prefix=@var{prefix}
3249 @cindex output file name prefix
3250 Use @var{prefix} as the output file name prefix.
3252 @item -b @var{suffix}
3253 @itemx --suffix=@var{suffix}
3256 @cindex output file name suffix
3257 Use @var{suffix} as the output file name suffix. When this option is
3258 specified, the suffix string must include exactly one
3259 @code{printf(3)}-style conversion specification, possibly including
3260 format specification flags, a field width, a precision specifications,
3261 or all of these kinds of modifiers. The format letter must convert a
3262 binary unsigned integer argument to readable form. The format letters
3263 @samp{d} and @samp{i} are aliases for @samp{u}, and the
3264 @samp{u}, @samp{o}, @samp{x}, and @samp{X} conversions are allowed. The
3265 entire @var{suffix} is given (with the current output file number) to
3266 @code{sprintf(3)} to form the file name suffixes for each of the
3267 individual output files in turn. If this option is used, the
3268 @option{--digits} option is ignored.
3270 @item -n @var{digits}
3271 @itemx --digits=@var{digits}
3274 Use output file names containing numbers that are @var{digits} digits
3275 long instead of the default 2.
3280 @opindex --keep-files
3281 Do not remove output files when errors are encountered.
3284 @itemx --elide-empty-files
3286 @opindex --elide-empty-files
3287 Suppress the generation of zero-length output files. (In cases where
3288 the section delimiters of the input file are supposed to mark the first
3289 lines of each of the sections, the first output file will generally be a
3290 zero-length file unless you use this option.) The output file sequence
3291 numbers always run consecutively starting from 0, even when this option
3302 Do not print counts of output file sizes.
3308 Here is an example of its usage.
3309 First, create an empty directory for the exercise,
3316 Now, split the sequence of 1..14 on lines that end with 0 or 5:
3319 $ seq 14 | csplit - '/[05]$/' '@{*@}'
3325 Each number printed above is the size of an output
3326 file that csplit has just created.
3327 List the names of those output files:
3334 Use @command{head} to show their contents:
3359 @node Summarizing files
3360 @chapter Summarizing files
3362 @cindex summarizing files
3364 These commands generate just a few numbers representing entire
3368 * wc invocation:: Print newline, word, and byte counts.
3369 * sum invocation:: Print checksum and block counts.
3370 * cksum invocation:: Print CRC checksum and byte counts.
3371 * md5sum invocation:: Print or check MD5 digests.
3372 * sha1sum invocation:: Print or check SHA-1 digests.
3373 * sha2 utilities:: Print or check SHA-2 digests.
3378 @section @command{wc}: Print newline, word, and byte counts
3382 @cindex character count
3386 @command{wc} counts the number of bytes, characters, whitespace-separated
3387 words, and newlines in each given @var{file}, or standard input if none
3388 are given or for a @var{file} of @samp{-}. Synopsis:
3391 wc [@var{option}]@dots{} [@var{file}]@dots{}
3394 @cindex total counts
3395 @command{wc} prints one line of counts for each file, and if the file was
3396 given as an argument, it prints the file name following the counts. If
3397 more than one @var{file} is given, @command{wc} prints a final line
3398 containing the cumulative counts, with the file name @file{total}. The
3399 counts are printed in this order: newlines, words, characters, bytes,
3400 maximum line length.
3401 Each count is printed right-justified in a field with at least one
3402 space between fields so that the numbers and file names normally line
3403 up nicely in columns. The width of the count fields varies depending
3404 on the inputs, so you should not depend on a particular field width.
3405 However, as a @acronym{GNU} extension, if only one count is printed,
3406 it is guaranteed to be printed without leading spaces.
3408 By default, @command{wc} prints three counts: the newline, words, and byte
3409 counts. Options can specify that only certain counts be printed.
3410 Options do not undo others previously given, so
3417 prints both the byte counts and the word counts.
3419 With the @option{--max-line-length} option, @command{wc} prints the length
3420 of the longest line per file, and if there is more than one file it
3421 prints the maximum (not the sum) of those lengths. The line lengths here
3422 are measured in screen columns, according to the current locale and
3423 assuming tab positions in every 8th column.
3425 The program accepts the following options. Also see @ref{Common options}.
3433 Print only the byte counts.
3439 Print only the character counts.
3445 Print only the word counts.
3451 Print only the newline counts.
3454 @itemx --max-line-length
3456 @opindex --max-line-length
3457 Print only the maximum line lengths.
3459 @macro filesZeroFromOption{cmd,withTotalOption,subListOutput}
3460 @itemx --files0-from=@var{file}
3461 @opindex --files0-from=@var{file}
3462 @c This is commented out to avoid a texi2dvi failure.
3463 @c texi2dvi (GNU Texinfo 4.11) 1.104
3464 @c @cindex including files from @command{\cmd\}
3465 Disallow processing files named on the command line, and instead process
3466 those named in file @var{file}; each name being terminated by a zero byte
3467 (@acronym{ASCII} @sc{nul}).
3468 This is useful \withTotalOption\
3469 when the list of file names is so long that it may exceed a command line
3471 In such cases, running @command{\cmd\} via @command{xargs} is undesirable
3472 because it splits the list into pieces and makes @command{\cmd\} print
3473 \subListOutput\ for each sublist rather than for the entire list.
3474 One way to produce a list of @acronym{ASCII} @sc{nul} terminated file
3475 names is with @sc{gnu}
3476 @command{find}, using its @option{-print0} predicate.
3477 If @var{file} is @samp{-} then the @acronym{ASCII} @sc{nul} terminated
3478 file names are read from standard input.
3480 @filesZeroFromOption{wc,,a total}
3482 For example, to find the length of the longest line in any @file{.c} or
3483 @file{.h} file in the current hierarchy, do this:
3486 find . -name '*.[ch]' -print0 |
3487 wc -L --files0-from=- | tail -n1
3495 @node sum invocation
3496 @section @command{sum}: Print checksum and block counts
3499 @cindex 16-bit checksum
3500 @cindex checksum, 16-bit
3502 @command{sum} computes a 16-bit checksum for each given @var{file}, or
3503 standard input if none are given or for a @var{file} of @samp{-}. Synopsis:
3506 sum [@var{option}]@dots{} [@var{file}]@dots{}
3509 @command{sum} prints the checksum for each @var{file} followed by the
3510 number of blocks in the file (rounded up). If more than one @var{file}
3511 is given, file names are also printed (by default). (With the
3512 @option{--sysv} option, corresponding file names are printed when there is
3513 at least one file argument.)
3515 By default, @sc{gnu} @command{sum} computes checksums using an algorithm
3516 compatible with BSD @command{sum} and prints file sizes in units of
3519 The program accepts the following options. Also see @ref{Common options}.
3525 @cindex BSD @command{sum}
3526 Use the default (BSD compatible) algorithm. This option is included for
3527 compatibility with the System V @command{sum}. Unless @option{-s} was also
3528 given, it has no effect.
3534 @cindex System V @command{sum}
3535 Compute checksums using an algorithm compatible with System V
3536 @command{sum}'s default, and print file sizes in units of 512-byte blocks.
3540 @command{sum} is provided for compatibility; the @command{cksum} program (see
3541 next section) is preferable in new applications.
3546 @node cksum invocation
3547 @section @command{cksum}: Print CRC checksum and byte counts
3550 @cindex cyclic redundancy check
3551 @cindex CRC checksum
3553 @command{cksum} computes a cyclic redundancy check (CRC) checksum for each
3554 given @var{file}, or standard input if none are given or for a
3555 @var{file} of @samp{-}. Synopsis:
3558 cksum [@var{option}]@dots{} [@var{file}]@dots{}
3561 @command{cksum} prints the CRC checksum for each file along with the number
3562 of bytes in the file, and the file name unless no arguments were given.
3564 @command{cksum} is typically used to ensure that files
3565 transferred by unreliable means (e.g., netnews) have not been corrupted,
3566 by comparing the @command{cksum} output for the received files with the
3567 @command{cksum} output for the original files (typically given in the
3570 The CRC algorithm is specified by the @acronym{POSIX} standard. It is not
3571 compatible with the BSD or System V @command{sum} algorithms (see the
3572 previous section); it is more robust.
3574 The only options are @option{--help} and @option{--version}. @xref{Common
3580 @node md5sum invocation
3581 @section @command{md5sum}: Print or check MD5 digests
3585 @cindex 128-bit checksum
3586 @cindex checksum, 128-bit
3587 @cindex fingerprint, 128-bit
3588 @cindex message-digest, 128-bit
3590 @command{md5sum} computes a 128-bit checksum (or @dfn{fingerprint} or
3591 @dfn{message-digest}) for each specified @var{file}.
3593 Note: The MD5 digest is more reliable than a simple CRC (provided by
3594 the @command{cksum} command) for detecting accidental file corruption,
3595 as the chances of accidentally having two files with identical MD5
3596 are vanishingly small. However, it should not be considered secure
3597 against malicious tampering: although finding a file with a given MD5
3598 fingerprint is considered infeasible at the moment, it is known how
3599 to modify certain files, including digital certificates, so that they
3600 appear valid when signed with an MD5 digest.
3601 For more secure hashes, consider using SHA-2. @xref{sha2 utilities}.
3603 If a @var{file} is specified as @samp{-} or if no files are given
3604 @command{md5sum} computes the checksum for the standard input.
3605 @command{md5sum} can also determine whether a file and checksum are
3606 consistent. Synopsis:
3609 md5sum [@var{option}]@dots{} [@var{file}]@dots{}
3612 For each @var{file}, @samp{md5sum} outputs the MD5 checksum, a flag
3613 indicating binary or text input mode, and the file name.
3614 If @var{file} contains a backslash or newline, the
3615 line is started with a backslash, and each problematic character in
3616 the file name is escaped with a backslash, making the output
3617 unambiguous even in the presence of arbitrary file names.
3618 If @var{file} is omitted or specified as @samp{-}, standard input is read.
3620 The program accepts the following options. Also see @ref{Common options}.
3628 @cindex binary input files
3629 Treat each input file as binary, by reading it in binary mode and
3630 outputting a @samp{*} flag. This is the inverse of @option{--text}.
3631 On systems like @acronym{GNU} that do not distinguish between binary
3632 and text files, this option merely flags each input mode as binary:
3633 the MD5 checksum is unaffected. This option is the default on systems
3634 like MS-DOS that distinguish between binary and text files, except
3635 for reading standard input when standard input is a terminal.
3639 Read file names and checksum information (not data) from each
3640 @var{file} (or from stdin if no @var{file} was specified) and report
3641 whether the checksums match the contents of the named files.
3642 The input to this mode of @command{md5sum} is usually the output of
3643 a prior, checksum-generating run of @samp{md5sum}.
3644 Each valid line of input consists of an MD5 checksum, a binary/text
3645 flag, and then a file name.
3646 Binary mode is indicated with @samp{*}, text with @samp{ } (space).
3647 For each such line, @command{md5sum} reads the named file and computes its
3648 MD5 checksum. Then, if the computed message digest does not match the
3649 one on the line with the file name, the file is noted as having
3650 failed the test. Otherwise, the file passes the test.
3651 By default, for each valid line, one line is written to standard
3652 output indicating whether the named file passed the test.
3653 After all checks have been performed, if there were any failures,
3654 a warning is issued to standard error.
3655 Use the @option{--status} option to inhibit that output.
3656 If any listed file cannot be opened or read, if any valid line has
3657 an MD5 checksum inconsistent with the associated file, or if no valid
3658 line is found, @command{md5sum} exits with nonzero status. Otherwise,
3659 it exits successfully.
3663 @cindex verifying MD5 checksums
3664 This option is useful only when verifying checksums.
3665 When verifying checksums, don't generate an 'OK' message per successfully
3666 checked file. Files that fail the verification are reported in the
3667 default one-line-per-file format. If there is any checksum mismatch,
3668 print a warning summarizing the failures to standard error.
3672 @cindex verifying MD5 checksums
3673 This option is useful only when verifying checksums.
3674 When verifying checksums, don't generate the default one-line-per-file
3675 diagnostic and don't output the warning summarizing any failures.
3676 Failures to open or read a file still evoke individual diagnostics to
3678 If all listed files are readable and are consistent with the associated
3679 MD5 checksums, exit successfully. Otherwise exit with a status code
3680 indicating there was a failure.
3686 @cindex text input files
3687 Treat each input file as text, by reading it in text mode and
3688 outputting a @samp{ } flag. This is the inverse of @option{--binary}.
3689 This option is the default on systems like @acronym{GNU} that do not
3690 distinguish between binary and text files. On other systems, it is
3691 the default for reading standard input when standard input is a
3698 @cindex verifying MD5 checksums
3699 When verifying checksums, warn about improperly formatted MD5 checksum lines.
3700 This option is useful only if all but a few lines in the checked input
3705 @cindex verifying MD5 checksums
3706 When verifying checksums,
3707 if one or more input line is invalid,
3708 exit nonzero after all warnings have been issued.
3715 @node sha1sum invocation
3716 @section @command{sha1sum}: Print or check SHA-1 digests
3720 @cindex 160-bit checksum
3721 @cindex checksum, 160-bit
3722 @cindex fingerprint, 160-bit
3723 @cindex message-digest, 160-bit
3725 @command{sha1sum} computes a 160-bit checksum for each specified
3726 @var{file}. The usage and options of this command are precisely the
3727 same as for @command{md5sum}. @xref{md5sum invocation}.
3729 Note: The SHA-1 digest is more secure than MD5, and no collisions of
3730 it are known (different files having the same fingerprint). However,
3731 it is known that they can be produced with considerable, but not
3732 unreasonable, resources. For this reason, it is generally considered
3733 that SHA-1 should be gradually phased out in favor of the more secure
3734 SHA-2 hash algorithms. @xref{sha2 utilities}.
3737 @node sha2 utilities
3738 @section sha2 utilities: Print or check SHA-2 digests
3745 @cindex 224-bit checksum
3746 @cindex 256-bit checksum
3747 @cindex 384-bit checksum
3748 @cindex 512-bit checksum
3749 @cindex checksum, 224-bit
3750 @cindex checksum, 256-bit
3751 @cindex checksum, 384-bit
3752 @cindex checksum, 512-bit
3753 @cindex fingerprint, 224-bit
3754 @cindex fingerprint, 256-bit
3755 @cindex fingerprint, 384-bit
3756 @cindex fingerprint, 512-bit
3757 @cindex message-digest, 224-bit
3758 @cindex message-digest, 256-bit
3759 @cindex message-digest, 384-bit
3760 @cindex message-digest, 512-bit
3762 The commands @command{sha224sum}, @command{sha256sum},
3763 @command{sha384sum} and @command{sha512sum} compute checksums of
3764 various lengths (respectively 224, 256, 384 and 512 bits),
3765 collectively known as the SHA-2 hashes. The usage and options of
3766 these commands are precisely the same as for @command{md5sum}.
3767 @xref{md5sum invocation}.
3769 Note: The SHA384 and SHA512 digests are considerably slower to
3770 compute, especially on 32-bit computers, than SHA224 or SHA256.
3773 @node Operating on sorted files
3774 @chapter Operating on sorted files
3776 @cindex operating on sorted files
3777 @cindex sorted files, operations on
3779 These commands work with (or produce) sorted files.
3782 * sort invocation:: Sort text files.
3783 * shuf invocation:: Shuffle text files.
3784 * uniq invocation:: Uniquify files.
3785 * comm invocation:: Compare two sorted files line by line.
3786 * ptx invocation:: Produce a permuted index of file contents.
3787 * tsort invocation:: Topological sort.
3791 @node sort invocation
3792 @section @command{sort}: Sort text files
3795 @cindex sorting files
3797 @command{sort} sorts, merges, or compares all the lines from the given
3798 files, or standard input if none are given or for a @var{file} of
3799 @samp{-}. By default, @command{sort} writes the results to standard
3803 sort [@var{option}]@dots{} [@var{file}]@dots{}
3806 @command{sort} has three modes of operation: sort (the default), merge,
3807 and check for sortedness. The following options change the operation
3814 @itemx --check=diagnose-first
3817 @cindex checking for sortedness
3818 Check whether the given file is already sorted: if it is not all
3819 sorted, print a diagnostic containing the first out-of-order line and
3820 exit with a status of 1.
3821 Otherwise, exit successfully.
3822 At most one input file can be given.
3825 @itemx --check=quiet
3826 @itemx --check=silent
3829 @cindex checking for sortedness
3830 Exit successfully if the given file is already sorted, and
3831 exit with status 1 otherwise.
3832 At most one input file can be given.
3833 This is like @option{-c}, except it does not print a diagnostic.
3839 @cindex merging sorted files
3840 Merge the given files by sorting them as a group. Each input file must
3841 always be individually sorted. It always works to sort instead of
3842 merge; merging is provided because it is faster, in the case where it
3847 @cindex sort stability
3848 @cindex sort's last-resort comparison
3849 A pair of lines is compared as follows:
3850 @command{sort} compares each pair of fields, in the
3851 order specified on the command line, according to the associated
3852 ordering options, until a difference is found or no fields are left.
3853 If no key fields are specified, @command{sort} uses a default key of
3854 the entire line. Finally, as a last resort when all keys compare
3855 equal, @command{sort} compares entire lines as if no ordering options
3856 other than @option{--reverse} (@option{-r}) were specified. The
3857 @option{--stable} (@option{-s}) option disables this @dfn{last-resort
3858 comparison} so that lines in which all fields compare equal are left
3859 in their original relative order. The @option{--unique}
3860 (@option{-u}) option also disables the last-resort comparison.
3864 Unless otherwise specified, all comparisons use the character collating
3865 sequence specified by the @env{LC_COLLATE} locale.@footnote{If you
3866 use a non-@acronym{POSIX} locale (e.g., by setting @env{LC_ALL}
3867 to @samp{en_US}), then @command{sort} may produce output that is sorted
3868 differently than you're accustomed to. In that case, set the @env{LC_ALL}
3869 environment variable to @samp{C}. Note that setting only @env{LC_COLLATE}
3870 has two problems. First, it is ineffective if @env{LC_ALL} is also set.
3871 Second, it has undefined behavior if @env{LC_CTYPE} (or @env{LANG}, if
3872 @env{LC_CTYPE} is unset) is set to an incompatible value. For example,
3873 you get undefined behavior if @env{LC_CTYPE} is @code{ja_JP.PCK} but
3874 @env{LC_COLLATE} is @code{en_US.UTF-8}.}
3876 @sc{gnu} @command{sort} (as specified for all @sc{gnu} utilities) has no
3877 limit on input line length or restrictions on bytes allowed within lines.
3878 In addition, if the final byte of an input file is not a newline, @sc{gnu}
3879 @command{sort} silently supplies one. A line's trailing newline is not
3880 part of the line for comparison purposes.
3882 @cindex exit status of @command{sort}
3886 0 if no error occurred
3887 1 if invoked with @option{-c} or @option{-C} and the input is not sorted
3888 2 if an error occurred
3892 If the environment variable @env{TMPDIR} is set, @command{sort} uses its
3893 value as the directory for temporary files instead of @file{/tmp}. The
3894 @option{--temporary-directory} (@option{-T}) option in turn overrides
3895 the environment variable.
3897 The following options affect the ordering of output lines. They may be
3898 specified globally or as part of a specific key field. If no key
3899 fields are specified, global options apply to comparison of entire
3900 lines; otherwise the global options are inherited by key fields that do
3901 not specify any special options of their own. In pre-@acronym{POSIX}
3902 versions of @command{sort}, global options affect only later key fields,
3903 so portable shell scripts should specify global options first.
3908 @itemx --ignore-leading-blanks
3910 @opindex --ignore-leading-blanks
3911 @cindex blanks, ignoring leading
3913 Ignore leading blanks when finding sort keys in each line.
3914 By default a blank is a space or a tab, but the @env{LC_CTYPE} locale
3915 can change this. Note blanks may be ignored by your locale's collating
3916 rules, but without this option they will be significant for character
3917 positions specified in keys with the @option{-k} option.
3920 @itemx --dictionary-order
3922 @opindex --dictionary-order
3923 @cindex dictionary order
3924 @cindex phone directory order
3925 @cindex telephone directory order
3927 Sort in @dfn{phone directory} order: ignore all characters except
3928 letters, digits and blanks when sorting.
3929 By default letters and digits are those of @acronym{ASCII} and a blank
3930 is a space or a tab, but the @env{LC_CTYPE} locale can change this.
3933 @itemx --ignore-case
3935 @opindex --ignore-case
3936 @cindex ignoring case
3937 @cindex case folding
3939 Fold lowercase characters into the equivalent uppercase characters when
3940 comparing so that, for example, @samp{b} and @samp{B} sort as equal.
3941 The @env{LC_CTYPE} locale determines character types.
3942 When used with @option{--unique} those lower case equivalent lines are
3943 thrown away. (There is currently no way to throw away the upper case
3944 equivalent instead. (Any @option{--reverse} given would only affect
3945 the final result, after the throwing away.))
3948 @itemx --general-numeric-sort
3949 @itemx --sort=general-numeric
3951 @opindex --general-numeric-sort
3953 @cindex general numeric sort
3955 Sort numerically, converting a prefix of each line to a long
3956 double-precision floating point number. @xref{Floating point}.
3957 Do not report overflow, underflow, or conversion errors.
3958 Use the following collating sequence:
3962 Lines that do not start with numbers (all considered to be equal).
3964 NaNs (``Not a Number'' values, in IEEE floating point arithmetic)
3965 in a consistent but machine-dependent order.
3969 Finite numbers in ascending numeric order (with @math{-0} and @math{+0} equal).
3974 Use this option only if there is no alternative; it is much slower than
3975 @option{--numeric-sort} (@option{-n}) and it can lose information when
3976 converting to floating point.
3979 @itemx --human-numeric-sort
3980 @itemx --sort=human-numeric
3982 @opindex --human-numeric-sort
3984 @cindex human numeric sort
3986 Sort numerically, first by numeric sign (negative, zero, or positive);
3987 then by @acronym{SI} suffix (either empty, or @samp{k} or @samp{K}, or
3988 one of @samp{MGTPEZY}, in that order; @pxref{Block size}); and finally
3989 by numeric value. For example, @samp{1023M} sorts before @samp{1G}
3990 because @samp{M} (mega) precedes @samp{G} (giga) as an @acronym{SI}
3991 suffix. This option sorts values that are consistently scaled to the
3992 nearest suffix, regardless of whether suffixes denote powers of 1000
3993 or 1024, and it therefore sorts the output of any single invocation of
3994 the @command{df}, @command{du}, or @command{ls} commands that are
3995 invoked with their @option{--human-readable} or @option{--si} options.
3996 The syntax for numbers is the same as for the @option{--numeric-sort}
3997 option; the @acronym{SI} suffix must immediately follow the number.
4000 @itemx --ignore-nonprinting
4002 @opindex --ignore-nonprinting
4003 @cindex nonprinting characters, ignoring
4004 @cindex unprintable characters, ignoring
4006 Ignore nonprinting characters.
4007 The @env{LC_CTYPE} locale determines character types.
4008 This option has no effect if the stronger @option{--dictionary-order}
4009 (@option{-d}) option is also given.
4015 @opindex --month-sort
4017 @cindex months, sorting by
4019 An initial string, consisting of any amount of blanks, followed
4020 by a month name abbreviation, is folded to UPPER case and
4021 compared in the order @samp{JAN} < @samp{FEB} < @dots{} < @samp{DEC}.
4022 Invalid names compare low to valid names. The @env{LC_TIME} locale
4023 category determines the month spellings.
4024 By default a blank is a space or a tab, but the @env{LC_CTYPE} locale
4028 @itemx --numeric-sort
4029 @itemx --sort=numeric
4031 @opindex --numeric-sort
4033 @cindex numeric sort
4035 Sort numerically. The number begins each line and consists
4036 of optional blanks, an optional @samp{-} sign, and zero or more
4037 digits possibly separated by thousands separators, optionally followed
4038 by a decimal-point character and zero or more digits. An empty
4039 number is treated as @samp{0}. The @env{LC_NUMERIC}
4040 locale specifies the decimal-point character and thousands separator.
4041 By default a blank is a space or a tab, but the @env{LC_CTYPE} locale
4044 Comparison is exact; there is no rounding error.
4046 Neither a leading @samp{+} nor exponential notation is recognized.
4047 To compare such strings numerically, use the
4048 @option{--general-numeric-sort} (@option{-g}) option.
4051 @itemx --version-sort
4053 @opindex --version-sort
4054 @cindex version number sort
4055 Sort by version name and number. It behaves like a standard sort,
4056 except that each sequence of decimal digits is treated numerically
4057 as an index/version number. (@xref{Details about version sort}.)
4063 @cindex reverse sorting
4064 Reverse the result of comparison, so that lines with greater key values
4065 appear earlier in the output instead of later.
4068 @itemx --random-sort
4069 @itemx --sort=random
4071 @opindex --random-sort
4074 Sort by hashing the input keys and then sorting the hash values.
4075 Choose the hash function at random, ensuring that it is free of
4076 collisions so that differing keys have differing hash values. This is
4077 like a random permutation of the inputs (@pxref{shuf invocation}),
4078 except that keys with the same value sort together.
4080 If multiple random sort fields are specified, the same random hash
4081 function is used for all fields. To use different random hash
4082 functions for different fields, you can invoke @command{sort} more
4085 The choice of hash function is affected by the
4086 @option{--random-source} option.
4094 @item --compress-program=@var{prog}
4095 Compress any temporary files with the program @var{prog}.
4097 With no arguments, @var{prog} must compress standard input to standard
4098 output, and when given the @option{-d} option it must decompress
4099 standard input to standard output.
4101 Terminate with an error if @var{prog} exits with nonzero status.
4103 White space and the backslash character should not appear in
4104 @var{prog}; they are reserved for future use.
4106 @filesZeroFromOption{sort,,sorted output}
4108 @item -k @var{pos1}[,@var{pos2}]
4109 @itemx --key=@var{pos1}[,@var{pos2}]
4113 Specify a sort field that consists of the part of the line between
4114 @var{pos1} and @var{pos2} (or the end of the line, if @var{pos2} is
4115 omitted), @emph{inclusive}.
4117 Each @var{pos} has the form @samp{@var{f}[.@var{c}][@var{opts}]},
4118 where @var{f} is the number of the field to use, and @var{c} is the number
4119 of the first character from the beginning of the field. Fields and character
4120 positions are numbered starting with 1; a character position of zero in
4121 @var{pos2} indicates the field's last character. If @samp{.@var{c}} is
4122 omitted from @var{pos1}, it defaults to 1 (the beginning of the field);
4123 if omitted from @var{pos2}, it defaults to 0 (the end of the field).
4124 @var{opts} are ordering options, allowing individual keys to be sorted
4125 according to different rules; see below for details. Keys can span
4128 Example: To sort on the second field, use @option{--key=2,2}
4129 (@option{-k 2,2}). See below for more notes on keys and more examples.
4130 See also the @option{--debug} option to help determine the part
4131 of the line being used in the sort.
4134 Highlight the portion of each line used for sorting.
4135 Also issue warnings about questionable usage to stderr.
4137 @item --batch-size=@var{nmerge}
4138 @opindex --batch-size
4139 @cindex number of inputs to merge, nmerge
4140 Merge at most @var{nmerge} inputs at once.
4142 When @command{sort} has to merge more than @var{nmerge} inputs,
4143 it merges them in groups of @var{nmerge}, saving the result in
4144 a temporary file, which is then used as an input in a subsequent merge.
4146 A large value of @var{nmerge} may improve merge performance and decrease
4147 temporary storage utilization at the expense of increased memory usage
4148 and I/O. Conversely a small value of @var{nmerge} may reduce memory
4149 requirements and I/O at the expense of temporary storage consumption and
4152 The value of @var{nmerge} must be at least 2. The default value is
4153 currently 16, but this is implementation-dependent and may change in
4156 The value of @var{nmerge} may be bounded by a resource limit for open
4157 file descriptors. The commands @samp{ulimit -n} or @samp{getconf
4158 OPEN_MAX} may display limits for your systems; these limits may be
4159 modified further if your program already has some files open, or if
4160 the operating system has other limits on the number of open files. If
4161 the value of @var{nmerge} exceeds the resource limit, @command{sort}
4162 silently uses a smaller value.
4164 @item -o @var{output-file}
4165 @itemx --output=@var{output-file}
4168 @cindex overwriting of input, allowed
4169 Write output to @var{output-file} instead of standard output.
4170 Normally, @command{sort} reads all input before opening
4171 @var{output-file}, so you can safely sort a file in place by using
4172 commands like @code{sort -o F F} and @code{cat F | sort -o F}.
4173 However, @command{sort} with @option{--merge} (@option{-m}) can open
4174 the output file before reading all input, so a command like @code{cat
4175 F | sort -m -o F - G} is not safe as @command{sort} might start
4176 writing @file{F} before @command{cat} is done reading it.
4178 @vindex POSIXLY_CORRECT
4179 On newer systems, @option{-o} cannot appear after an input file if
4180 @env{POSIXLY_CORRECT} is set, e.g., @samp{sort F -o F}. Portable
4181 scripts should specify @option{-o @var{output-file}} before any input
4184 @item --random-source=@var{file}
4185 @opindex --random-source
4186 @cindex random source for sorting
4187 Use @var{file} as a source of random data used to determine which
4188 random hash function to use with the @option{-R} option. @xref{Random
4195 @cindex sort stability
4196 @cindex sort's last-resort comparison
4198 Make @command{sort} stable by disabling its last-resort comparison.
4199 This option has no effect if no fields or global ordering options
4200 other than @option{--reverse} (@option{-r}) are specified.
4203 @itemx --buffer-size=@var{size}
4205 @opindex --buffer-size
4206 @cindex size for main memory sorting
4207 Use a main-memory sort buffer of the given @var{size}. By default,
4208 @var{size} is in units of 1024 bytes. Appending @samp{%} causes
4209 @var{size} to be interpreted as a percentage of physical memory.
4210 Appending @samp{K} multiplies @var{size} by 1024 (the default),
4211 @samp{M} by 1,048,576, @samp{G} by 1,073,741,824, and so on for
4212 @samp{T}, @samp{P}, @samp{E}, @samp{Z}, and @samp{Y}. Appending
4213 @samp{b} causes @var{size} to be interpreted as a byte count, with no
4216 This option can improve the performance of @command{sort} by causing it
4217 to start with a larger or smaller sort buffer than the default.
4218 However, this option affects only the initial buffer size. The buffer
4219 grows beyond @var{size} if @command{sort} encounters input lines larger
4222 @item -t @var{separator}
4223 @itemx --field-separator=@var{separator}
4225 @opindex --field-separator
4226 @cindex field separator character
4227 Use character @var{separator} as the field separator when finding the
4228 sort keys in each line. By default, fields are separated by the empty
4229 string between a non-blank character and a blank character.
4230 By default a blank is a space or a tab, but the @env{LC_CTYPE} locale
4233 That is, given the input line @w{@samp{ foo bar}}, @command{sort} breaks it
4234 into fields @w{@samp{ foo}} and @w{@samp{ bar}}. The field separator is
4235 not considered to be part of either the field preceding or the field
4236 following, so with @samp{sort @w{-t " "}} the same input line has
4237 three fields: an empty field, @samp{foo}, and @samp{bar}.
4238 However, fields that extend to the end of the line,
4239 as @option{-k 2}, or fields consisting of a range, as @option{-k 2,3},
4240 retain the field separators present between the endpoints of the range.
4242 To specify @acronym{ASCII} @sc{nul} as the field separator,
4243 use the two-character string @samp{\0}, e.g., @samp{sort -t '\0'}.
4245 @item -T @var{tempdir}
4246 @itemx --temporary-directory=@var{tempdir}
4248 @opindex --temporary-directory
4249 @cindex temporary directory
4251 Use directory @var{tempdir} to store temporary files, overriding the
4252 @env{TMPDIR} environment variable. If this option is given more than
4253 once, temporary files are stored in all the directories given. If you
4254 have a large sort or merge that is I/O-bound, you can often improve
4255 performance by using this option to specify directories on different
4256 disks and controllers.
4258 @item --parallel=@var{n}
4260 @cindex multithreaded sort
4261 Set the number of sorts run in parallel to @var{n}. By default,
4262 @var{n} is set to the number of available processors, but limited
4263 to 8, as there are diminishing performance gains after that.
4264 Note also that using @var{n} threads increases the memory usage by
4265 a factor of log @var{n}. Also see @ref{nproc invocation}.
4271 @cindex uniquifying output
4273 Normally, output only the first of a sequence of lines that compare
4274 equal. For the @option{--check} (@option{-c} or @option{-C}) option,
4275 check that no pair of consecutive lines compares equal.
4277 This option also disables the default last-resort comparison.
4279 The commands @code{sort -u} and @code{sort | uniq} are equivalent, but
4280 this equivalence does not extend to arbitrary @command{sort} options.
4281 For example, @code{sort -n -u} inspects only the value of the initial
4282 numeric string when checking for uniqueness, whereas @code{sort -n |
4283 uniq} inspects the entire line. @xref{uniq invocation}.
4285 @macro zeroTerminatedOption
4287 @itemx --zero-terminated
4289 @opindex --zero-terminated
4290 @cindex process zero-terminated items
4291 Delimit items with a zero byte rather than a newline (@acronym{ASCII} @sc{lf}).
4292 I.E. treat input as items separated by @acronym{ASCII} @sc{nul}
4293 and terminate output items with @acronym{ASCII} @sc{nul}.
4294 This option can be useful in conjunction with @samp{perl -0} or
4295 @samp{find -print0} and @samp{xargs -0} which do the same in order to
4296 reliably handle arbitrary file names (even those containing blanks
4297 or other special characters).
4299 @zeroTerminatedOption
4303 Historical (BSD and System V) implementations of @command{sort} have
4304 differed in their interpretation of some options, particularly
4305 @option{-b}, @option{-f}, and @option{-n}.
4306 @sc{gnu} sort follows the @acronym{POSIX}
4307 behavior, which is usually (but not always!) like the System V behavior.
4308 According to @acronym{POSIX}, @option{-n} no longer implies @option{-b}. For
4309 consistency, @option{-M} has been changed in the same way. This may
4310 affect the meaning of character positions in field specifications in
4311 obscure cases. The only fix is to add an explicit @option{-b}.
4313 A position in a sort field specified with @option{-k} may have any
4314 of the option letters @samp{MbdfghinRrV} appended to it, in which case no
4315 global ordering options are inherited by that particular field. The
4316 @option{-b} option may be independently attached to either or both of
4317 the start and end positions of a field specification, and if it is
4318 inherited from the global options it will be attached to both.
4319 If input lines can contain leading or adjacent blanks and @option{-t}
4320 is not used, then @option{-k} is typically combined with @option{-b} or
4321 an option that implicitly ignores leading blanks (@samp{Mghn}) as otherwise
4322 the varying numbers of leading blanks in fields can cause confusing results.
4324 If the start position in a sort field specifier falls after the end of
4325 the line or after the end field, the field is empty. If the @option{-b}
4326 option was specified, the @samp{.@var{c}} part of a field specification
4327 is counted from the first nonblank character of the field.
4329 @vindex _POSIX2_VERSION
4330 @vindex POSIXLY_CORRECT
4331 On older systems, @command{sort} supports an obsolete origin-zero
4332 syntax @samp{+@var{pos1} [-@var{pos2}]} for specifying sort keys.
4333 The obsolete sequence @samp{sort +@var{a}.@var{x} -@var{b}.@var{y}}
4334 is equivalent to @samp{sort -k @var{a+1}.@var{x+1},@var{b}} if @var{y}
4335 is @samp{0} or absent, otherwise it is equivalent to @samp{sort -k
4336 @var{a+1}.@var{x+1},@var{b+1}.@var{y}}.
4338 This obsolete behavior can be enabled or disabled with the
4339 @env{_POSIX2_VERSION} environment variable (@pxref{Standards
4340 conformance}); it can also be enabled when @env{POSIXLY_CORRECT} is
4341 not set by using the obsolete syntax with @samp{-@var{pos2}} present.
4343 Scripts intended for use on standard hosts should avoid obsolete
4344 syntax and should use @option{-k} instead. For example, avoid
4345 @samp{sort +2}, since it might be interpreted as either @samp{sort
4346 ./+2} or @samp{sort -k 3}. If your script must also run on hosts that
4347 support only the obsolete syntax, it can use a test like @samp{if sort
4348 -k 1 </dev/null >/dev/null 2>&1; then @dots{}} to decide which syntax
4351 Here are some examples to illustrate various combinations of options.
4356 Sort in descending (reverse) numeric order.
4363 Run no more than 4 sorts concurrently, using a buffer size of 10M.
4366 sort --parallel=4 -S 10M
4370 Sort alphabetically, omitting the first and second fields
4371 and the blanks at the start of the third field.
4372 This uses a single key composed of the characters beginning
4373 at the start of the first nonblank character in field three
4374 and extending to the end of each line.
4381 Sort numerically on the second field and resolve ties by sorting
4382 alphabetically on the third and fourth characters of field five.
4383 Use @samp{:} as the field delimiter.
4386 sort -t : -k 2,2n -k 5.3,5.4
4389 Note that if you had written @option{-k 2n} instead of @option{-k 2,2n}
4390 @command{sort} would have used all characters beginning in the second field
4391 and extending to the end of the line as the primary @emph{numeric}
4392 key. For the large majority of applications, treating keys spanning
4393 more than one field as numeric will not do what you expect.
4395 Also note that the @samp{n} modifier was applied to the field-end
4396 specifier for the first key. It would have been equivalent to
4397 specify @option{-k 2n,2} or @option{-k 2n,2n}. All modifiers except
4398 @samp{b} apply to the associated @emph{field}, regardless of whether
4399 the modifier character is attached to the field-start and/or the
4400 field-end part of the key specifier.
4403 Sort the password file on the fifth field and ignore any
4404 leading blanks. Sort lines with equal values in field five
4405 on the numeric user ID in field three. Fields are separated
4409 sort -t : -k 5b,5 -k 3,3n /etc/passwd
4410 sort -t : -n -k 5b,5 -k 3,3 /etc/passwd
4411 sort -t : -b -k 5,5 -k 3,3n /etc/passwd
4414 These three commands have equivalent effect. The first specifies that
4415 the first key's start position ignores leading blanks and the second
4416 key is sorted numerically. The other two commands rely on global
4417 options being inherited by sort keys that lack modifiers. The inheritance
4418 works in this case because @option{-k 5b,5b} and @option{-k 5b,5} are
4419 equivalent, as the location of a field-end lacking a @samp{.@var{c}}
4420 character position is not affected by whether initial blanks are
4424 Sort a set of log files, primarily by IPv4 address and secondarily by
4425 time stamp. If two lines' primary and secondary keys are identical,
4426 output the lines in the same order that they were input. The log
4427 files contain lines that look like this:
4430 4.150.156.3 - - [01/Apr/2004:06:31:51 +0000] message 1
4431 211.24.3.231 - - [24/Apr/2004:20:17:39 +0000] message 2
4434 Fields are separated by exactly one space. Sort IPv4 addresses
4435 lexicographically, e.g., 212.61.52.2 sorts before 212.129.233.201
4436 because 61 is less than 129.
4439 sort -s -t ' ' -k 4.9n -k 4.5M -k 4.2n -k 4.14,4.21 file*.log |
4440 sort -s -t '.' -k 1,1n -k 2,2n -k 3,3n -k 4,4n
4443 This example cannot be done with a single @command{sort} invocation,
4444 since IPv4 address components are separated by @samp{.} while dates
4445 come just after a space. So it is broken down into two invocations of
4446 @command{sort}: the first sorts by time stamp and the second by IPv4
4447 address. The time stamp is sorted by year, then month, then day, and
4448 finally by hour-minute-second field, using @option{-k} to isolate each
4449 field. Except for hour-minute-second there's no need to specify the
4450 end of each key field, since the @samp{n} and @samp{M} modifiers sort
4451 based on leading prefixes that cannot cross field boundaries. The
4452 IPv4 addresses are sorted lexicographically. The second sort uses
4453 @samp{-s} so that ties in the primary key are broken by the secondary
4454 key; the first sort uses @samp{-s} so that the combination of the two
4458 Generate a tags file in case-insensitive sorted order.
4461 find src -type f -print0 | sort -z -f | xargs -0 etags --append
4464 The use of @option{-print0}, @option{-z}, and @option{-0} in this case means
4465 that file names that contain blanks or other special characters are
4467 by the sort operation.
4469 @c This example is a bit contrived and needs more explanation.
4471 @c Sort records separated by an arbitrary string by using a pipe to convert
4472 @c each record delimiter string to @samp{\0}, then using sort's -z option,
4473 @c and converting each @samp{\0} back to the original record delimiter.
4476 @c printf 'c\n\nb\n\na\n' |
4477 @c perl -0pe 's/\n\n/\n\0/g' |
4479 @c perl -0pe 's/\0/\n/g'
4483 Use the common @acronym{DSU, Decorate Sort Undecorate} idiom to
4484 sort lines according to their length.
4487 awk '@{print length, $0@}' /etc/passwd | sort -n | cut -f2- -d' '
4490 In general this technique can be used to sort data that the @command{sort}
4491 command does not support, or is inefficient at, sorting directly.
4494 Shuffle a list of directories, but preserve the order of files within
4495 each directory. For instance, one could use this to generate a music
4496 playlist in which albums are shuffled but the songs of each album are
4500 ls */* | sort -t / -k 1,1R -k 2,2
4506 @node shuf invocation
4507 @section @command{shuf}: Shuffling text
4510 @cindex shuffling files
4512 @command{shuf} shuffles its input by outputting a random permutation
4513 of its input lines. Each output permutation is equally likely.
4517 shuf [@var{option}]@dots{} [@var{file}]
4518 shuf -e [@var{option}]@dots{} [@var{arg}]@dots{}
4519 shuf -i @var{lo}-@var{hi} [@var{option}]@dots{}
4522 @command{shuf} has three modes of operation that affect where it
4523 obtains its input lines. By default, it reads lines from standard
4524 input. The following options change the operation mode:
4532 @cindex command-line operands to shuffle
4533 Treat each command-line operand as an input line.
4535 @item -i @var{lo}-@var{hi}
4536 @itemx --input-range=@var{lo}-@var{hi}
4538 @opindex --input-range
4539 @cindex input range to shuffle
4540 Act as if input came from a file containing the range of unsigned
4541 decimal integers @var{lo}@dots{}@var{hi}, one per line.
4545 @command{shuf}'s other options can affect its behavior in all
4550 @item -n @var{lines}
4551 @itemx --head-count=@var{count}
4553 @opindex --head-count
4554 @cindex head of output
4555 Output at most @var{count} lines. By default, all input lines are
4558 @item -o @var{output-file}
4559 @itemx --output=@var{output-file}
4562 @cindex overwriting of input, allowed
4563 Write output to @var{output-file} instead of standard output.
4564 @command{shuf} reads all input before opening
4565 @var{output-file}, so you can safely shuffle a file in place by using
4566 commands like @code{shuf -o F <F} and @code{cat F | shuf -o F}.
4568 @item --random-source=@var{file}
4569 @opindex --random-source
4570 @cindex random source for shuffling
4571 Use @var{file} as a source of random data used to determine which
4572 permutation to generate. @xref{Random sources}.
4574 @zeroTerminatedOption
4590 might produce the output
4600 Similarly, the command:
4603 shuf -e clubs hearts diamonds spades
4617 and the command @samp{shuf -i 1-4} might output:
4627 These examples all have four input lines, so @command{shuf} might
4628 produce any of the twenty-four possible permutations of the input. In
4629 general, if there are @var{n} input lines, there are @var{n}! (i.e.,
4630 @var{n} factorial, or @var{n} * (@var{n} - 1) * @dots{} * 1) possible
4631 output permutations.
4636 @node uniq invocation
4637 @section @command{uniq}: Uniquify files
4640 @cindex uniquify files
4642 @command{uniq} writes the unique lines in the given @file{input}, or
4643 standard input if nothing is given or for an @var{input} name of
4647 uniq [@var{option}]@dots{} [@var{input} [@var{output}]]
4650 By default, @command{uniq} prints its input lines, except that
4651 it discards all but the first of adjacent repeated lines, so that
4652 no output lines are repeated. Optionally, it can instead discard
4653 lines that are not repeated, or all repeated lines.
4655 The input need not be sorted, but repeated input lines are detected
4656 only if they are adjacent. If you want to discard non-adjacent
4657 duplicate lines, perhaps you want to use @code{sort -u}.
4658 @xref{sort invocation}.
4661 Comparisons honor the rules specified by the @env{LC_COLLATE}
4664 If no @var{output} file is specified, @command{uniq} writes to standard
4667 The program accepts the following options. Also see @ref{Common options}.
4672 @itemx --skip-fields=@var{n}
4674 @opindex --skip-fields
4675 Skip @var{n} fields on each line before checking for uniqueness. Use
4676 a null string for comparison if a line has fewer than @var{n} fields. Fields
4677 are sequences of non-space non-tab characters that are separated from
4678 each other by at least one space or tab.
4680 For compatibility @command{uniq} supports an obsolete option syntax
4681 @option{-@var{n}}. New scripts should use @option{-f @var{n}} instead.
4684 @itemx --skip-chars=@var{n}
4686 @opindex --skip-chars
4687 Skip @var{n} characters before checking for uniqueness. Use a null string
4688 for comparison if a line has fewer than @var{n} characters. If you use both
4689 the field and character skipping options, fields are skipped over first.
4691 @vindex _POSIX2_VERSION
4692 On older systems, @command{uniq} supports an obsolete option syntax
4694 This obsolete behavior can be enabled or disabled with the
4695 @env{_POSIX2_VERSION} environment variable (@pxref{Standards
4696 conformance}), but portable scripts should avoid commands whose
4697 behavior depends on this variable.
4698 For example, use @samp{uniq ./+10} or @samp{uniq -s 10} rather than
4699 the ambiguous @samp{uniq +10}.
4705 Print the number of times each line occurred along with the line.
4708 @itemx --ignore-case
4710 @opindex --ignore-case
4711 Ignore differences in case when comparing lines.
4717 @cindex repeated lines, outputting
4718 Discard lines that are not repeated. When used by itself, this option
4719 causes @command{uniq} to print the first copy of each repeated line,
4723 @itemx --all-repeated[=@var{delimit-method}]
4725 @opindex --all-repeated
4726 @cindex all repeated lines, outputting
4727 Do not discard the second and subsequent repeated input lines,
4728 but discard lines that are not repeated.
4729 This option is useful mainly in conjunction with other options e.g.,
4730 to ignore case or to compare only selected fields.
4731 The optional @var{delimit-method} tells how to delimit
4732 groups of repeated lines, and must be one of the following:
4737 Do not delimit groups of repeated lines.
4738 This is equivalent to @option{--all-repeated} (@option{-D}).
4741 Output a newline before each group of repeated lines.
4742 With @option{--zero-terminated} (@option{-z}), use a zero
4743 byte (@acronym{ASCII} @sc{nul}) instead of a newline.
4746 Separate groups of repeated lines with a single newline.
4747 With @option{--zero-terminated} (@option{-z}), use a zero
4748 byte (@acronym{ASCII} @sc{nul}) instead of a newline.
4749 This is the same as using @samp{prepend}, except that
4750 no delimiter is inserted before the first group, and hence
4751 may be better suited for output direct to users.
4754 Note that when groups are delimited and the input stream contains
4755 two or more consecutive blank lines, then the output is ambiguous.
4756 To avoid that, filter the input through @samp{tr -s '\n'} to replace
4757 each sequence of consecutive newlines with a single newline.
4759 This is a @sc{gnu} extension.
4760 @c FIXME: give an example showing *how* it's useful
4766 @cindex unique lines, outputting
4767 Discard the first repeated line. When used by itself, this option
4768 causes @command{uniq} to print unique lines, and nothing else.
4771 @itemx --check-chars=@var{n}
4773 @opindex --check-chars
4774 Compare at most @var{n} characters on each line (after skipping any specified
4775 fields and characters). By default the entire rest of the lines are
4778 @zeroTerminatedOption
4785 @node comm invocation
4786 @section @command{comm}: Compare two sorted files line by line
4789 @cindex line-by-line comparison
4790 @cindex comparing sorted files
4792 @command{comm} writes to standard output lines that are common, and lines
4793 that are unique, to two input files; a file name of @samp{-} means
4794 standard input. Synopsis:
4797 comm [@var{option}]@dots{} @var{file1} @var{file2}
4801 Before @command{comm} can be used, the input files must be sorted using the
4802 collating sequence specified by the @env{LC_COLLATE} locale.
4803 If an input file ends in a non-newline
4804 character, a newline is silently appended. The @command{sort} command with
4805 no options always outputs a file that is suitable input to @command{comm}.
4807 @cindex differing lines
4808 @cindex common lines
4809 With no options, @command{comm} produces three-column output. Column one
4810 contains lines unique to @var{file1}, column two contains lines unique
4811 to @var{file2}, and column three contains lines common to both files.
4812 Columns are separated by a single TAB character.
4813 @c FIXME: when there's an option to supply an alternative separator
4814 @c string, append `by default' to the above sentence.
4819 The options @option{-1}, @option{-2}, and @option{-3} suppress printing of
4820 the corresponding columns (and separators). Also see @ref{Common options}.
4822 Unlike some other comparison utilities, @command{comm} has an exit
4823 status that does not depend on the result of the comparison.
4824 Upon normal completion @command{comm} produces an exit code of zero.
4825 If there is an error it exits with nonzero status.
4827 @macro checkOrderOption{cmd}
4828 If the @option{--check-order} option is given, unsorted inputs will
4829 cause a fatal error message. If the option @option{--nocheck-order}
4830 is given, unsorted inputs will never cause an error message. If neither
4831 of these options is given, wrongly sorted inputs are diagnosed
4832 only if an input file is found to contain unpairable
4834 lines, and when both input files are non empty.
4836 @ifclear JOIN_COMMAND
4839 If an input file is diagnosed as being unsorted, the @command{\cmd\}
4840 command will exit with a nonzero status (and the output should not be used).
4842 Forcing @command{\cmd\} to process wrongly sorted input files
4843 containing unpairable lines by specifying @option{--nocheck-order} is
4844 not guaranteed to produce any particular output. The output will
4845 probably not correspond with whatever you hoped it would be.
4847 @checkOrderOption{comm}
4852 Fail with an error message if either input file is wrongly ordered.
4854 @item --nocheck-order
4855 Do not check that both input files are in sorted order.
4859 @item --output-delimiter=@var{str}
4860 Print @var{str} between adjacent output columns,
4861 rather than the default of a single TAB character.
4863 The delimiter @var{str} may not be empty.
4867 @node ptx invocation
4868 @section @command{ptx}: Produce permuted indexes
4872 @command{ptx} reads a text file and essentially produces a permuted index, with
4873 each keyword in its context. The calling sketch is either one of:
4876 ptx [@var{option} @dots{}] [@var{file} @dots{}]
4877 ptx -G [@var{option} @dots{}] [@var{input} [@var{output}]]
4880 The @option{-G} (or its equivalent: @option{--traditional}) option disables
4881 all @sc{gnu} extensions and reverts to traditional mode, thus introducing some
4882 limitations and changing several of the program's default option values.
4883 When @option{-G} is not specified, @sc{gnu} extensions are always enabled.
4884 @sc{gnu} extensions to @command{ptx} are documented wherever appropriate in this
4885 document. For the full list, see @xref{Compatibility in ptx}.
4887 Individual options are explained in the following sections.
4889 When @sc{gnu} extensions are enabled, there may be zero, one or several
4890 @var{file}s after the options. If there is no @var{file}, the program
4891 reads the standard input. If there is one or several @var{file}s, they
4892 give the name of input files which are all read in turn, as if all the
4893 input files were concatenated. However, there is a full contextual
4894 break between each file and, when automatic referencing is requested,
4895 file names and line numbers refer to individual text input files. In
4896 all cases, the program outputs the permuted index to the standard
4899 When @sc{gnu} extensions are @emph{not} enabled, that is, when the program
4900 operates in traditional mode, there may be zero, one or two parameters
4901 besides the options. If there are no parameters, the program reads the
4902 standard input and outputs the permuted index to the standard output.
4903 If there is only one parameter, it names the text @var{input} to be read
4904 instead of the standard input. If two parameters are given, they give
4905 respectively the name of the @var{input} file to read and the name of
4906 the @var{output} file to produce. @emph{Be very careful} to note that,
4907 in this case, the contents of file given by the second parameter is
4908 destroyed. This behavior is dictated by System V @command{ptx}
4909 compatibility; @sc{gnu} Standards normally discourage output parameters not
4910 introduced by an option.
4912 Note that for @emph{any} file named as the value of an option or as an
4913 input text file, a single dash @kbd{-} may be used, in which case
4914 standard input is assumed. However, it would not make sense to use this
4915 convention more than once per program invocation.
4918 * General options in ptx:: Options which affect general program behavior.
4919 * Charset selection in ptx:: Underlying character set considerations.
4920 * Input processing in ptx:: Input fields, contexts, and keyword selection.
4921 * Output formatting in ptx:: Types of output format, and sizing the fields.
4922 * Compatibility in ptx::
4926 @node General options in ptx
4927 @subsection General options
4932 @itemx --traditional
4933 As already explained, this option disables all @sc{gnu} extensions to
4934 @command{ptx} and switches to traditional mode.
4937 Print a short help on standard output, then exit without further
4941 Print the program version on standard output, then exit without further
4949 @node Charset selection in ptx
4950 @subsection Charset selection
4952 @c FIXME: People don't necessarily know what an IBM-PC was these days.
4953 As it is set up now, the program assumes that the input file is coded
4954 using 8-bit @acronym{ISO} 8859-1 code, also known as Latin-1 character set,
4955 @emph{unless} it is compiled for MS-DOS, in which case it uses the
4956 character set of the IBM-PC@. (@sc{gnu} @command{ptx} is not known to work on
4957 smaller MS-DOS machines anymore.) Compared to 7-bit @acronym{ASCII}, the set
4958 of characters which are letters is different; this alters the behavior
4959 of regular expression matching. Thus, the default regular expression
4960 for a keyword allows foreign or diacriticized letters. Keyword sorting,
4961 however, is still crude; it obeys the underlying character set ordering
4967 @itemx --ignore-case
4968 Fold lower case letters to upper case for sorting.
4973 @node Input processing in ptx
4974 @subsection Word selection and input processing
4979 @itemx --break-file=@var{file}
4981 This option provides an alternative (to @option{-W}) method of describing
4982 which characters make up words. It introduces the name of a
4983 file which contains a list of characters which can@emph{not} be part of
4984 one word; this file is called the @dfn{Break file}. Any character which
4985 is not part of the Break file is a word constituent. If both options
4986 @option{-b} and @option{-W} are specified, then @option{-W} has precedence and
4987 @option{-b} is ignored.
4989 When @sc{gnu} extensions are enabled, the only way to avoid newline as a
4990 break character is to write all the break characters in the file with no
4991 newline at all, not even at the end of the file. When @sc{gnu} extensions
4992 are disabled, spaces, tabs and newlines are always considered as break
4993 characters even if not included in the Break file.
4996 @itemx --ignore-file=@var{file}
4998 The file associated with this option contains a list of words which will
4999 never be taken as keywords in concordance output. It is called the
5000 @dfn{Ignore file}. The file contains exactly one word in each line; the
5001 end of line separation of words is not subject to the value of the
5005 @itemx --only-file=@var{file}
5007 The file associated with this option contains a list of words which will
5008 be retained in concordance output; any word not mentioned in this file
5009 is ignored. The file is called the @dfn{Only file}. The file contains
5010 exactly one word in each line; the end of line separation of words is
5011 not subject to the value of the @option{-S} option.
5013 There is no default for the Only file. When both an Only file and an
5014 Ignore file are specified, a word is considered a keyword only
5015 if it is listed in the Only file and not in the Ignore file.
5020 On each input line, the leading sequence of non-white space characters will be
5021 taken to be a reference that has the purpose of identifying this input
5022 line in the resulting permuted index. For more information about reference
5023 production, see @xref{Output formatting in ptx}.
5024 Using this option changes the default value for option @option{-S}.
5026 Using this option, the program does not try very hard to remove
5027 references from contexts in output, but it succeeds in doing so
5028 @emph{when} the context ends exactly at the newline. If option
5029 @option{-r} is used with @option{-S} default value, or when @sc{gnu} extensions
5030 are disabled, this condition is always met and references are completely
5031 excluded from the output contexts.
5033 @item -S @var{regexp}
5034 @itemx --sentence-regexp=@var{regexp}
5036 This option selects which regular expression will describe the end of a
5037 line or the end of a sentence. In fact, this regular expression is not
5038 the only distinction between end of lines or end of sentences, and input
5039 line boundaries have no special significance outside this option. By
5040 default, when @sc{gnu} extensions are enabled and if @option{-r} option is not
5041 used, end of sentences are used. In this case, this @var{regex} is
5042 imported from @sc{gnu} Emacs:
5045 [.?!][]\"')@}]*\\($\\|\t\\| \\)[ \t\n]*
5048 Whenever @sc{gnu} extensions are disabled or if @option{-r} option is used, end
5049 of lines are used; in this case, the default @var{regexp} is just:
5055 Using an empty @var{regexp} is equivalent to completely disabling end of
5056 line or end of sentence recognition. In this case, the whole file is
5057 considered to be a single big line or sentence. The user might want to
5058 disallow all truncation flag generation as well, through option @option{-F
5059 ""}. @xref{Regexps, , Syntax of Regular Expressions, emacs, The GNU Emacs
5062 When the keywords happen to be near the beginning of the input line or
5063 sentence, this often creates an unused area at the beginning of the
5064 output context line; when the keywords happen to be near the end of the
5065 input line or sentence, this often creates an unused area at the end of
5066 the output context line. The program tries to fill those unused areas
5067 by wrapping around context in them; the tail of the input line or
5068 sentence is used to fill the unused area on the left of the output line;
5069 the head of the input line or sentence is used to fill the unused area
5070 on the right of the output line.
5072 As a matter of convenience to the user, many usual backslashed escape
5073 sequences from the C language are recognized and converted to the
5074 corresponding characters by @command{ptx} itself.
5076 @item -W @var{regexp}
5077 @itemx --word-regexp=@var{regexp}
5079 This option selects which regular expression will describe each keyword.
5080 By default, if @sc{gnu} extensions are enabled, a word is a sequence of
5081 letters; the @var{regexp} used is @samp{\w+}. When @sc{gnu} extensions are
5082 disabled, a word is by default anything which ends with a space, a tab
5083 or a newline; the @var{regexp} used is @samp{[^ \t\n]+}.
5085 An empty @var{regexp} is equivalent to not using this option.
5086 @xref{Regexps, , Syntax of Regular Expressions, emacs, The GNU Emacs
5089 As a matter of convenience to the user, many usual backslashed escape
5090 sequences, as found in the C language, are recognized and converted to
5091 the corresponding characters by @command{ptx} itself.
5096 @node Output formatting in ptx
5097 @subsection Output formatting
5099 Output format is mainly controlled by the @option{-O} and @option{-T} options
5100 described in the table below. When neither @option{-O} nor @option{-T} are
5101 selected, and if @sc{gnu} extensions are enabled, the program chooses an
5102 output format suitable for a dumb terminal. Each keyword occurrence is
5103 output to the center of one line, surrounded by its left and right
5104 contexts. Each field is properly justified, so the concordance output
5105 can be readily observed. As a special feature, if automatic
5106 references are selected by option @option{-A} and are output before the
5107 left context, that is, if option @option{-R} is @emph{not} selected, then
5108 a colon is added after the reference; this nicely interfaces with @sc{gnu}
5109 Emacs @code{next-error} processing. In this default output format, each
5110 white space character, like newline and tab, is merely changed to
5111 exactly one space, with no special attempt to compress consecutive
5112 spaces. This might change in the future. Except for those white space
5113 characters, every other character of the underlying set of 256
5114 characters is transmitted verbatim.
5116 Output format is further controlled by the following options.
5120 @item -g @var{number}
5121 @itemx --gap-size=@var{number}
5123 Select the size of the minimum white space gap between the fields on the
5126 @item -w @var{number}
5127 @itemx --width=@var{number}
5129 Select the maximum output width of each final line. If references are
5130 used, they are included or excluded from the maximum output width
5131 depending on the value of option @option{-R}. If this option is not
5132 selected, that is, when references are output before the left context,
5133 the maximum output width takes into account the maximum length of all
5134 references. If this option is selected, that is, when references are
5135 output after the right context, the maximum output width does not take
5136 into account the space taken by references, nor the gap that precedes
5140 @itemx --auto-reference
5142 Select automatic references. Each input line will have an automatic
5143 reference made up of the file name and the line ordinal, with a single
5144 colon between them. However, the file name will be empty when standard
5145 input is being read. If both @option{-A} and @option{-r} are selected, then
5146 the input reference is still read and skipped, but the automatic
5147 reference is used at output time, overriding the input reference.
5150 @itemx --right-side-refs
5152 In the default output format, when option @option{-R} is not used, any
5153 references produced by the effect of options @option{-r} or @option{-A} are
5154 placed to the far right of output lines, after the right context. With
5155 default output format, when the @option{-R} option is specified, references
5156 are rather placed at the beginning of each output line, before the left
5157 context. For any other output format, option @option{-R} is
5158 ignored, with one exception: with @option{-R} the width of references
5159 is @emph{not} taken into account in total output width given by @option{-w}.
5161 This option is automatically selected whenever @sc{gnu} extensions are
5164 @item -F @var{string}
5165 @itemx --flac-truncation=@var{string}
5167 This option will request that any truncation in the output be reported
5168 using the string @var{string}. Most output fields theoretically extend
5169 towards the beginning or the end of the current line, or current
5170 sentence, as selected with option @option{-S}. But there is a maximum
5171 allowed output line width, changeable through option @option{-w}, which is
5172 further divided into space for various output fields. When a field has
5173 to be truncated because it cannot extend beyond the beginning or the end of
5174 the current line to fit in, then a truncation occurs. By default,
5175 the string used is a single slash, as in @option{-F /}.
5177 @var{string} may have more than one character, as in @option{-F ...}.
5178 Also, in the particular case when @var{string} is empty (@option{-F ""}),
5179 truncation flagging is disabled, and no truncation marks are appended in
5182 As a matter of convenience to the user, many usual backslashed escape
5183 sequences, as found in the C language, are recognized and converted to
5184 the corresponding characters by @command{ptx} itself.
5186 @item -M @var{string}
5187 @itemx --macro-name=@var{string}
5189 Select another @var{string} to be used instead of @samp{xx}, while
5190 generating output suitable for @command{nroff}, @command{troff} or @TeX{}.
5193 @itemx --format=roff
5195 Choose an output format suitable for @command{nroff} or @command{troff}
5196 processing. Each output line will look like:
5199 .xx "@var{tail}" "@var{before}" "@var{keyword_and_after}"@c
5200 "@var{head}" "@var{ref}"
5203 so it will be possible to write a @samp{.xx} roff macro to take care of
5204 the output typesetting. This is the default output format when @sc{gnu}
5205 extensions are disabled. Option @option{-M} can be used to change
5206 @samp{xx} to another macro name.
5208 In this output format, each non-graphical character, like newline and
5209 tab, is merely changed to exactly one space, with no special attempt to
5210 compress consecutive spaces. Each quote character: @kbd{"} is doubled
5211 so it will be correctly processed by @command{nroff} or @command{troff}.
5216 Choose an output format suitable for @TeX{} processing. Each output
5217 line will look like:
5220 \xx @{@var{tail}@}@{@var{before}@}@{@var{keyword}@}@c
5221 @{@var{after}@}@{@var{head}@}@{@var{ref}@}
5225 so it will be possible to write a @code{\xx} definition to take care of
5226 the output typesetting. Note that when references are not being
5227 produced, that is, neither option @option{-A} nor option @option{-r} is
5228 selected, the last parameter of each @code{\xx} call is inhibited.
5229 Option @option{-M} can be used to change @samp{xx} to another macro
5232 In this output format, some special characters, like @kbd{$}, @kbd{%},
5233 @kbd{&}, @kbd{#} and @kbd{_} are automatically protected with a
5234 backslash. Curly brackets @kbd{@{}, @kbd{@}} are protected with a
5235 backslash and a pair of dollar signs (to force mathematical mode). The
5236 backslash itself produces the sequence @code{\backslash@{@}}.
5237 Circumflex and tilde diacritical marks produce the sequence @code{^\@{ @}} and
5238 @code{~\@{ @}} respectively. Other diacriticized characters of the
5239 underlying character set produce an appropriate @TeX{} sequence as far
5240 as possible. The other non-graphical characters, like newline and tab,
5241 and all other characters which are not part of @acronym{ASCII}, are merely
5242 changed to exactly one space, with no special attempt to compress
5243 consecutive spaces. Let me know how to improve this special character
5244 processing for @TeX{}.
5249 @node Compatibility in ptx
5250 @subsection The @sc{gnu} extensions to @command{ptx}
5252 This version of @command{ptx} contains a few features which do not exist in
5253 System V @command{ptx}. These extra features are suppressed by using the
5254 @option{-G} command line option, unless overridden by other command line
5255 options. Some @sc{gnu} extensions cannot be recovered by overriding, so the
5256 simple rule is to avoid @option{-G} if you care about @sc{gnu} extensions.
5257 Here are the differences between this program and System V @command{ptx}.
5262 This program can read many input files at once, it always writes the
5263 resulting concordance on standard output. On the other hand, System V
5264 @command{ptx} reads only one file and sends the result to standard output
5265 or, if a second @var{file} parameter is given on the command, to that
5268 Having output parameters not introduced by options is a dangerous
5269 practice which @sc{gnu} avoids as far as possible. So, for using @command{ptx}
5270 portably between @sc{gnu} and System V, you should always use it with a
5271 single input file, and always expect the result on standard output. You
5272 might also want to automatically configure in a @option{-G} option to
5273 @command{ptx} calls in products using @command{ptx}, if the configurator finds
5274 that the installed @command{ptx} accepts @option{-G}.
5277 The only options available in System V @command{ptx} are options @option{-b},
5278 @option{-f}, @option{-g}, @option{-i}, @option{-o}, @option{-r}, @option{-t} and
5279 @option{-w}. All other options are @sc{gnu} extensions and are not repeated in
5280 this enumeration. Moreover, some options have a slightly different
5281 meaning when @sc{gnu} extensions are enabled, as explained below.
5284 By default, concordance output is not formatted for @command{troff} or
5285 @command{nroff}. It is rather formatted for a dumb terminal. @command{troff}
5286 or @command{nroff} output may still be selected through option @option{-O}.
5289 Unless @option{-R} option is used, the maximum reference width is
5290 subtracted from the total output line width. With @sc{gnu} extensions
5291 disabled, width of references is not taken into account in the output
5292 line width computations.
5295 All 256 bytes, even @acronym{ASCII} @sc{nul} bytes, are always read and
5296 processed from input file with no adverse effect, even if @sc{gnu} extensions
5297 are disabled. However, System V @command{ptx} does not accept 8-bit characters,
5298 a few control characters are rejected, and the tilde @kbd{~} is also rejected.
5301 Input line length is only limited by available memory, even if @sc{gnu}
5302 extensions are disabled. However, System V @command{ptx} processes only
5303 the first 200 characters in each line.
5306 The break (non-word) characters default to be every character except all
5307 letters of the underlying character set, diacriticized or not. When @sc{gnu}
5308 extensions are disabled, the break characters default to space, tab and
5312 The program makes better use of output line width. If @sc{gnu} extensions
5313 are disabled, the program rather tries to imitate System V @command{ptx},
5314 but still, there are some slight disposition glitches this program does
5315 not completely reproduce.
5318 The user can specify both an Ignore file and an Only file. This is not
5319 allowed with System V @command{ptx}.
5324 @node tsort invocation
5325 @section @command{tsort}: Topological sort
5328 @cindex topological sort
5330 @command{tsort} performs a topological sort on the given @var{file}, or
5331 standard input if no input file is given or for a @var{file} of
5332 @samp{-}. For more details and some history, see @ref{tsort background}.
5336 tsort [@var{option}] [@var{file}]
5339 @command{tsort} reads its input as pairs of strings, separated by blanks,
5340 indicating a partial ordering. The output is a total ordering that
5341 corresponds to the given partial ordering.
5355 will produce the output
5366 Consider a more realistic example.
5367 You have a large set of functions all in one file, and they may all be
5368 declared static except one. Currently that one (say @code{main}) is the
5369 first function defined in the file, and the ones it calls directly follow
5370 it, followed by those they call, etc. Let's say that you are determined
5371 to take advantage of prototypes, so you have to choose between declaring
5372 all of those functions (which means duplicating a lot of information from
5373 the definitions) and rearranging the functions so that as many as possible
5374 are defined before they are used. One way to automate the latter process
5375 is to get a list for each function of the functions it calls directly.
5376 Many programs can generate such lists. They describe a call graph.
5377 Consider the following list, in which a given line indicates that the
5378 function on the left calls the one on the right directly.
5384 tail_file pretty_name
5385 tail_file write_header
5387 tail_forever recheck
5388 tail_forever pretty_name
5389 tail_forever write_header
5390 tail_forever dump_remainder
5393 tail_lines start_lines
5394 tail_lines dump_remainder
5395 tail_lines file_lines
5396 tail_lines pipe_lines
5398 tail_bytes start_bytes
5399 tail_bytes dump_remainder
5400 tail_bytes pipe_bytes
5401 file_lines dump_remainder
5405 then you can use @command{tsort} to produce an ordering of those
5406 functions that satisfies your requirement.
5409 example$ tsort call-graph | tac
5429 @command{tsort} detects any cycles in the input and writes the first cycle
5430 encountered to standard error.
5432 Note that for a given partial ordering, generally there is no unique
5433 total ordering. In the context of the call graph above, the function
5434 @code{parse_options} may be placed anywhere in the list as long as it
5435 precedes @code{main}.
5437 The only options are @option{--help} and @option{--version}. @xref{Common
5443 * tsort background:: Where tsort came from.
5446 @node tsort background
5447 @subsection @command{tsort}: Background
5449 @command{tsort} exists because very early versions of the Unix linker processed
5450 an archive file exactly once, and in order. As @command{ld} read each object
5451 in the archive, it decided whether it was needed in the program based on
5452 whether it defined any symbols which were undefined at that point in
5455 This meant that dependencies within the archive had to be handled
5456 specially. For example, @code{scanf} probably calls @code{read}. That means
5457 that in a single pass through an archive, it was important for @code{scanf.o}
5458 to appear before read.o, because otherwise a program which calls
5459 @code{scanf} but not @code{read} might end up with an unexpected unresolved
5460 reference to @code{read}.
5462 The way to address this problem was to first generate a set of
5463 dependencies of one object file on another. This was done by a shell
5464 script called @command{lorder}. The GNU tools don't provide a version of
5465 lorder, as far as I know, but you can still find it in BSD
5468 Then you ran @command{tsort} over the @command{lorder} output, and you used the
5469 resulting sort to define the order in which you added objects to the archive.
5471 This whole procedure has been obsolete since about 1980, because
5472 Unix archives now contain a symbol table (traditionally built by
5473 @command{ranlib}, now generally built by @command{ar} itself), and the Unix
5474 linker uses the symbol table to effectively make multiple passes over
5477 Anyhow, that's where tsort came from. To solve an old problem with
5478 the way the linker handled archive files, which has since been solved
5482 @node Operating on fields
5483 @chapter Operating on fields
5486 * cut invocation:: Print selected parts of lines.
5487 * paste invocation:: Merge lines of files.
5488 * join invocation:: Join lines on a common field.
5492 @node cut invocation
5493 @section @command{cut}: Print selected parts of lines
5496 @command{cut} writes to standard output selected parts of each line of each
5497 input file, or standard input if no files are given or for a file name of
5501 cut @var{option}@dots{} [@var{file}]@dots{}
5504 In the table which follows, the @var{byte-list}, @var{character-list},
5505 and @var{field-list} are one or more numbers or ranges (two numbers
5506 separated by a dash) separated by commas. Bytes, characters, and
5507 fields are numbered starting at 1. Incomplete ranges may be
5508 given: @option{-@var{m}} means @samp{1-@var{m}}; @samp{@var{n}-} means
5509 @samp{@var{n}} through end of line or last field. The list elements
5510 can be repeated, can overlap, and can be specified in any order; but
5511 the selected input is written in the same order that it is read, and
5512 is written exactly once.
5514 The program accepts the following options. Also see @ref{Common
5519 @item -b @var{byte-list}
5520 @itemx --bytes=@var{byte-list}
5523 Select for printing only the bytes in positions listed in
5524 @var{byte-list}. Tabs and backspaces are treated like any other
5525 character; they take up 1 byte. If an output delimiter is specified,
5526 (see the description of @option{--output-delimiter}), then output that
5527 string between ranges of selected bytes.
5529 @item -c @var{character-list}
5530 @itemx --characters=@var{character-list}
5532 @opindex --characters
5533 Select for printing only the characters in positions listed in
5534 @var{character-list}. The same as @option{-b} for now, but
5535 internationalization will change that. Tabs and backspaces are
5536 treated like any other character; they take up 1 character. If an
5537 output delimiter is specified, (see the description of
5538 @option{--output-delimiter}), then output that string between ranges
5541 @item -f @var{field-list}
5542 @itemx --fields=@var{field-list}
5545 Select for printing only the fields listed in @var{field-list}.
5546 Fields are separated by a TAB character by default. Also print any
5547 line that contains no delimiter character, unless the
5548 @option{--only-delimited} (@option{-s}) option is specified.
5550 Note @command{awk} supports more sophisticated field processing,
5551 and by default will use (and discard) runs of blank characters to
5552 separate fields, and ignore leading and trailing blanks.
5555 awk '{print $2}' # print the second field
5556 awk '{print $NF-1}' # print the penultimate field
5557 awk '{print $2,$1}' # reorder the first two fields
5561 In the unlikely event that @command{awk} is unavailable,
5562 one can use the @command{join} command, to process blank
5563 characters as @command{awk} does above.
5566 join -a1 -o 1.2 - /dev/null # print the second field
5567 join -a1 -o 1.2,1.1 - /dev/null # reorder the first two fields
5571 @item -d @var{input_delim_byte}
5572 @itemx --delimiter=@var{input_delim_byte}
5574 @opindex --delimiter
5575 With @option{-f}, use the first byte of @var{input_delim_byte} as
5576 the input fields separator (default is TAB).
5580 Do not split multi-byte characters (no-op for now).
5583 @itemx --only-delimited
5585 @opindex --only-delimited
5586 For @option{-f}, do not print lines that do not contain the field separator
5587 character. Normally, any line without a field separator is printed verbatim.
5589 @item --output-delimiter=@var{output_delim_string}
5590 @opindex --output-delimiter
5591 With @option{-f}, output fields are separated by @var{output_delim_string}.
5592 The default with @option{-f} is to use the input delimiter.
5593 When using @option{-b} or @option{-c} to select ranges of byte or
5594 character offsets (as opposed to ranges of fields),
5595 output @var{output_delim_string} between non-overlapping
5596 ranges of selected bytes.
5599 @opindex --complement
5600 This option is a @acronym{GNU} extension.
5601 Select for printing the complement of the bytes, characters or fields
5602 selected with the @option{-b}, @option{-c} or @option{-f} options.
5603 In other words, do @emph{not} print the bytes, characters or fields
5604 specified via those options. This option is useful when you have
5605 many fields and want to print all but a few of them.
5612 @node paste invocation
5613 @section @command{paste}: Merge lines of files
5616 @cindex merging files
5618 @command{paste} writes to standard output lines consisting of sequentially
5619 corresponding lines of each given file, separated by a TAB character.
5620 Standard input is used for a file name of @samp{-} or if no input files
5642 paste [@var{option}]@dots{} [@var{file}]@dots{}
5645 The program accepts the following options. Also see @ref{Common options}.
5653 Paste the lines of one file at a time rather than one line from each
5654 file. Using the above example data:
5657 $ paste -s num2 let3
5662 @item -d @var{delim-list}
5663 @itemx --delimiters=@var{delim-list}
5665 @opindex --delimiters
5666 Consecutively use the characters in @var{delim-list} instead of
5667 TAB to separate merged lines. When @var{delim-list} is
5668 exhausted, start again at its beginning. Using the above example data:
5671 $ paste -d '%_' num2 let3 num2
5682 @node join invocation
5683 @section @command{join}: Join lines on a common field
5686 @cindex common field, joining on
5688 @command{join} writes to standard output a line for each pair of input
5689 lines that have identical join fields. Synopsis:
5692 join [@var{option}]@dots{} @var{file1} @var{file2}
5695 Either @var{file1} or @var{file2} (but not both) can be @samp{-},
5696 meaning standard input. @var{file1} and @var{file2} should be
5697 sorted on the join fields.
5700 Normally, the sort order is that of the
5701 collating sequence specified by the @env{LC_COLLATE} locale. Unless
5702 the @option{-t} option is given, the sort comparison ignores blanks at
5703 the start of the join field, as in @code{sort -b}. If the
5704 @option{--ignore-case} option is given, the sort comparison ignores
5705 the case of characters in the join field, as in @code{sort -f}.
5707 The @command{sort} and @command{join} commands should use consistent
5708 locales and options if the output of @command{sort} is fed to
5709 @command{join}. You can use a command like @samp{sort -k 1b,1} to
5710 sort a file on its default join field, but if you select a non-default
5711 locale, join field, separator, or comparison options, then you should
5712 do so consistently between @command{join} and @command{sort}.
5713 If @samp{join -t ''} is specified then the whole line is considered which
5714 matches the default operation of sort.
5716 If the input has no unpairable lines, a @acronym{GNU} extension is
5717 available; the sort order can be any order that considers two fields
5718 to be equal if and only if the sort comparison described above
5719 considers them to be equal. For example:
5737 @checkOrderOption{join}
5742 @item the join field is the first field in each line;
5743 @item fields in the input are separated by one or more blanks, with leading
5744 blanks on the line ignored;
5745 @item fields in the output are separated by a space;
5746 @item each output line consists of the join field, the remaining
5747 fields from @var{file1}, then the remaining fields from @var{file2}.
5750 The program accepts the following options. Also see @ref{Common options}.
5754 @item -a @var{file-number}
5756 Print a line for each unpairable line in file @var{file-number} (either
5757 @samp{1} or @samp{2}), in addition to the normal output.
5760 Fail with an error message if either input file is wrongly ordered.
5762 @item --nocheck-order
5763 Do not check that both input files are in sorted order. This is the default.
5765 @item -e @var{string}
5767 Replace those output fields that are missing in the input with @var{string}.
5768 I.E. missing fields specified with the @option{-12jo} options.
5772 Treat the first line of each input file as a header line. The header lines will
5773 be joined and printed as the first output line. If @option{-o} is used to
5774 specify output format, the header line will be printed according to the
5775 specified format. The header lines will not be checked for ordering even if
5776 @option{--check-order} is specified. Also if the header lines from each file
5777 do not match, the heading fields from the first file will be used.
5780 @itemx --ignore-case
5782 @opindex --ignore-case
5783 Ignore differences in case when comparing keys.
5784 With this option, the lines of the input files must be ordered in the same way.
5785 Use @samp{sort -f} to produce this ordering.
5787 @item -1 @var{field}
5789 Join on field @var{field} (a positive integer) of file 1.
5791 @item -2 @var{field}
5793 Join on field @var{field} (a positive integer) of file 2.
5795 @item -j @var{field}
5796 Equivalent to @option{-1 @var{field} -2 @var{field}}.
5798 @item -o @var{field-list}
5800 If the keyword @samp{auto} is specified, infer the output format from
5801 the first line in each file. This is the same as the default output format
5802 but also ensures the same number of fields are output for each line.
5803 Missing fields are replaced with the @option{-e} option and extra fields
5806 Otherwise, construct each output line according to the format in
5807 @var{field-list}. Each element in @var{field-list} is either the single
5808 character @samp{0} or has the form @var{m.n} where the file number, @var{m},
5809 is @samp{1} or @samp{2} and @var{n} is a positive field number.
5811 A field specification of @samp{0} denotes the join field.
5812 In most cases, the functionality of the @samp{0} field spec
5813 may be reproduced using the explicit @var{m.n} that corresponds
5814 to the join field. However, when printing unpairable lines
5815 (using either of the @option{-a} or @option{-v} options), there is no way
5816 to specify the join field using @var{m.n} in @var{field-list}
5817 if there are unpairable lines in both files.
5818 To give @command{join} that functionality, @acronym{POSIX} invented the @samp{0}
5819 field specification notation.
5821 The elements in @var{field-list}
5822 are separated by commas or blanks.
5823 Blank separators typically need to be quoted for the shell. For
5824 example, the commands @samp{join -o 1.2,2.2} and @samp{join -o '1.2
5825 2.2'} are equivalent.
5827 All output lines---including those printed because of any -a or -v
5828 option---are subject to the specified @var{field-list}.
5831 Use character @var{char} as the input and output field separator.
5832 Treat as significant each occurrence of @var{char} in the input file.
5833 Use @samp{sort -t @var{char}}, without the @option{-b} option of
5834 @samp{sort}, to produce this ordering. If @samp{join -t ''} is specified,
5835 the whole line is considered, matching the default operation of sort.
5836 If @samp{-t '\0'} is specified then the @acronym{ASCII} @sc{nul}
5837 character is used to delimit the fields.
5839 @item -v @var{file-number}
5840 Print a line for each unpairable line in file @var{file-number}
5841 (either @samp{1} or @samp{2}), instead of the normal output.
5848 @node Operating on characters
5849 @chapter Operating on characters
5851 @cindex operating on characters
5853 This commands operate on individual characters.
5856 * tr invocation:: Translate, squeeze, and/or delete characters.
5857 * expand invocation:: Convert tabs to spaces.
5858 * unexpand invocation:: Convert spaces to tabs.
5863 @section @command{tr}: Translate, squeeze, and/or delete characters
5870 tr [@var{option}]@dots{} @var{set1} [@var{set2}]
5873 @command{tr} copies standard input to standard output, performing
5874 one of the following operations:
5878 translate, and optionally squeeze repeated characters in the result,
5880 squeeze repeated characters,
5884 delete characters, then squeeze repeated characters from the result.
5887 The @var{set1} and (if given) @var{set2} arguments define ordered
5888 sets of characters, referred to below as @var{set1} and @var{set2}. These
5889 sets are the characters of the input that @command{tr} operates on.
5890 The @option{--complement} (@option{-c}, @option{-C}) option replaces
5892 complement (all of the characters that are not in @var{set1}).
5894 Currently @command{tr} fully supports only single-byte characters.
5895 Eventually it will support multibyte characters; when it does, the
5896 @option{-C} option will cause it to complement the set of characters,
5897 whereas @option{-c} will cause it to complement the set of values.
5898 This distinction will matter only when some values are not characters,
5899 and this is possible only in locales using multibyte encodings when
5900 the input contains encoding errors.
5902 The program accepts the @option{--help} and @option{--version}
5903 options. @xref{Common options}. Options must precede operands.
5908 * Character sets:: Specifying sets of characters.
5909 * Translating:: Changing one set of characters to another.
5910 * Squeezing:: Squeezing repeats and deleting.
5914 @node Character sets
5915 @subsection Specifying sets of characters
5917 @cindex specifying sets of characters
5919 The format of the @var{set1} and @var{set2} arguments resembles
5920 the format of regular expressions; however, they are not regular
5921 expressions, only lists of characters. Most characters simply
5922 represent themselves in these strings, but the strings can contain
5923 the shorthands listed below, for convenience. Some of them can be
5924 used only in @var{set1} or @var{set2}, as noted below.
5928 @item Backslash escapes
5929 @cindex backslash escapes
5931 The following backslash escape sequences are recognized:
5949 The 8-bit character with the value given by @var{ooo}, which is 1 to 3
5950 octal digits. Note that @samp{\400} is interpreted as the two-byte
5951 sequence, @samp{\040} @samp{0}.
5956 While a backslash followed by a character not listed above is
5957 interpreted as that character, the backslash also effectively
5958 removes any special significance, so it is useful to escape
5959 @samp{[}, @samp{]}, @samp{*}, and @samp{-}.
5964 The notation @samp{@var{m}-@var{n}} expands to all of the characters
5965 from @var{m} through @var{n}, in ascending order. @var{m} should
5966 collate before @var{n}; if it doesn't, an error results. As an example,
5967 @samp{0-9} is the same as @samp{0123456789}.
5969 @sc{gnu} @command{tr} does not support the System V syntax that uses square
5970 brackets to enclose ranges. Translations specified in that format
5971 sometimes work as expected, since the brackets are often transliterated
5972 to themselves. However, they should be avoided because they sometimes
5973 behave unexpectedly. For example, @samp{tr -d '[0-9]'} deletes brackets
5976 Many historically common and even accepted uses of ranges are not
5977 portable. For example, on @acronym{EBCDIC} hosts using the @samp{A-Z}
5978 range will not do what most would expect because @samp{A} through @samp{Z}
5979 are not contiguous as they are in @acronym{ASCII}.
5980 If you can rely on a @acronym{POSIX} compliant version of @command{tr}, then
5981 the best way to work around this is to use character classes (see below).
5982 Otherwise, it is most portable (and most ugly) to enumerate the members
5985 @item Repeated characters
5986 @cindex repeated characters
5988 The notation @samp{[@var{c}*@var{n}]} in @var{set2} expands to @var{n}
5989 copies of character @var{c}. Thus, @samp{[y*6]} is the same as
5990 @samp{yyyyyy}. The notation @samp{[@var{c}*]} in @var{string2} expands
5991 to as many copies of @var{c} as are needed to make @var{set2} as long as
5992 @var{set1}. If @var{n} begins with @samp{0}, it is interpreted in
5993 octal, otherwise in decimal.
5995 @item Character classes
5996 @cindex character classes
5998 The notation @samp{[:@var{class}:]} expands to all of the characters in
5999 the (predefined) class @var{class}. The characters expand in no
6000 particular order, except for the @code{upper} and @code{lower} classes,
6001 which expand in ascending order. When the @option{--delete} (@option{-d})
6002 and @option{--squeeze-repeats} (@option{-s}) options are both given, any
6003 character class can be used in @var{set2}. Otherwise, only the
6004 character classes @code{lower} and @code{upper} are accepted in
6005 @var{set2}, and then only if the corresponding character class
6006 (@code{upper} and @code{lower}, respectively) is specified in the same
6007 relative position in @var{set1}. Doing this specifies case conversion.
6008 The class names are given below; an error results when an invalid class
6020 Horizontal whitespace.
6029 Printable characters, not including space.
6035 Printable characters, including space.
6038 Punctuation characters.
6041 Horizontal or vertical whitespace.
6050 @item Equivalence classes
6051 @cindex equivalence classes
6053 The syntax @samp{[=@var{c}=]} expands to all of the characters that are
6054 equivalent to @var{c}, in no particular order. Equivalence classes are
6055 a relatively recent invention intended to support non-English alphabets.
6056 But there seems to be no standard way to define them or determine their
6057 contents. Therefore, they are not fully implemented in @sc{gnu} @command{tr};
6058 each character's equivalence class consists only of that character,
6059 which is of no particular use.
6065 @subsection Translating
6067 @cindex translating characters
6069 @command{tr} performs translation when @var{set1} and @var{set2} are
6070 both given and the @option{--delete} (@option{-d}) option is not given.
6071 @command{tr} translates each character of its input that is in @var{set1}
6072 to the corresponding character in @var{set2}. Characters not in
6073 @var{set1} are passed through unchanged. When a character appears more
6074 than once in @var{set1} and the corresponding characters in @var{set2}
6075 are not all the same, only the final one is used. For example, these
6076 two commands are equivalent:
6083 A common use of @command{tr} is to convert lowercase characters to
6084 uppercase. This can be done in many ways. Here are three of them:
6087 tr abcdefghijklmnopqrstuvwxyz ABCDEFGHIJKLMNOPQRSTUVWXYZ
6089 tr '[:lower:]' '[:upper:]'
6093 But note that using ranges like @code{a-z} above is not portable.
6095 When @command{tr} is performing translation, @var{set1} and @var{set2}
6096 typically have the same length. If @var{set1} is shorter than
6097 @var{set2}, the extra characters at the end of @var{set2} are ignored.
6099 On the other hand, making @var{set1} longer than @var{set2} is not
6100 portable; @acronym{POSIX} says that the result is undefined. In this situation,
6101 BSD @command{tr} pads @var{set2} to the length of @var{set1} by repeating
6102 the last character of @var{set2} as many times as necessary. System V
6103 @command{tr} truncates @var{set1} to the length of @var{set2}.
6105 By default, @sc{gnu} @command{tr} handles this case like BSD @command{tr}.
6106 When the @option{--truncate-set1} (@option{-t}) option is given,
6107 @sc{gnu} @command{tr} handles this case like the System V @command{tr}
6108 instead. This option is ignored for operations other than translation.
6110 Acting like System V @command{tr} in this case breaks the relatively common
6114 tr -cs A-Za-z0-9 '\012'
6118 because it converts only zero bytes (the first element in the
6119 complement of @var{set1}), rather than all non-alphanumerics, to
6123 By the way, the above idiom is not portable because it uses ranges, and
6124 it assumes that the octal code for newline is 012.
6125 Assuming a @acronym{POSIX} compliant @command{tr}, here is a better
6129 tr -cs '[:alnum:]' '[\n*]'
6134 @subsection Squeezing repeats and deleting
6136 @cindex squeezing repeat characters
6137 @cindex deleting characters
6139 When given just the @option{--delete} (@option{-d}) option, @command{tr}
6140 removes any input characters that are in @var{set1}.
6142 When given just the @option{--squeeze-repeats} (@option{-s}) option,
6143 @command{tr} replaces each input sequence of a repeated character that
6144 is in @var{set1} with a single occurrence of that character.
6146 When given both @option{--delete} and @option{--squeeze-repeats}, @command{tr}
6147 first performs any deletions using @var{set1}, then squeezes repeats
6148 from any remaining characters using @var{set2}.
6150 The @option{--squeeze-repeats} option may also be used when translating,
6151 in which case @command{tr} first performs translation, then squeezes
6152 repeats from any remaining characters using @var{set2}.
6154 Here are some examples to illustrate various combinations of options:
6159 Remove all zero bytes:
6166 Put all words on lines by themselves. This converts all
6167 non-alphanumeric characters to newlines, then squeezes each string
6168 of repeated newlines into a single newline:
6171 tr -cs '[:alnum:]' '[\n*]'
6175 Convert each sequence of repeated newlines to a single newline:
6182 Find doubled occurrences of words in a document.
6183 @c Separate the following two "the"s, so typo checkers don't complain.
6184 For example, people often write ``the @w{}the'' with the repeated words
6185 separated by a newline. The Bourne shell script below works first
6186 by converting each sequence of punctuation and blank characters to a
6187 single newline. That puts each ``word'' on a line by itself.
6188 Next it maps all uppercase characters to lower case, and finally it
6189 runs @command{uniq} with the @option{-d} option to print out only the words
6195 | tr -s '[:punct:][:blank:]' '[\n*]' \
6196 | tr '[:upper:]' '[:lower:]' \
6201 Deleting a small set of characters is usually straightforward. For example,
6202 to remove all @samp{a}s, @samp{x}s, and @samp{M}s you would do this:
6208 However, when @samp{-} is one of those characters, it can be tricky because
6209 @samp{-} has special meanings. Performing the same task as above but also
6210 removing all @samp{-} characters, we might try @code{tr -d -axM}, but
6211 that would fail because @command{tr} would try to interpret @option{-a} as
6212 a command-line option. Alternatively, we could try putting the hyphen
6213 inside the string, @code{tr -d a-xM}, but that wouldn't work either because
6214 it would make @command{tr} interpret @code{a-x} as the range of characters
6215 @samp{a}@dots{}@samp{x} rather than the three.
6216 One way to solve the problem is to put the hyphen at the end of the list
6223 Or you can use @samp{--} to terminate option processing:
6229 More generally, use the character class notation @code{[=c=]}
6230 with @samp{-} (or any other character) in place of the @samp{c}:
6236 Note how single quotes are used in the above example to protect the
6237 square brackets from interpretation by a shell.
6242 @node expand invocation
6243 @section @command{expand}: Convert tabs to spaces
6246 @cindex tabs to spaces, converting
6247 @cindex converting tabs to spaces
6249 @command{expand} writes the contents of each given @var{file}, or standard
6250 input if none are given or for a @var{file} of @samp{-}, to standard
6251 output, with tab characters converted to the appropriate number of
6255 expand [@var{option}]@dots{} [@var{file}]@dots{}
6258 By default, @command{expand} converts all tabs to spaces. It preserves
6259 backspace characters in the output; they decrement the column count for
6260 tab calculations. The default action is equivalent to @option{-t 8} (set
6261 tabs every 8 columns).
6263 The program accepts the following options. Also see @ref{Common options}.
6267 @item -t @var{tab1}[,@var{tab2}]@dots{}
6268 @itemx --tabs=@var{tab1}[,@var{tab2}]@dots{}
6271 @cindex tab stops, setting
6272 If only one tab stop is given, set the tabs @var{tab1} spaces apart
6273 (default is 8). Otherwise, set the tabs at columns @var{tab1},
6274 @var{tab2}, @dots{} (numbered from 0), and replace any tabs beyond the
6275 last tab stop given with single spaces. Tab stops can be separated by
6276 blanks as well as by commas.
6278 For compatibility, GNU @command{expand} also accepts the obsolete
6279 option syntax, @option{-@var{t1}[,@var{t2}]@dots{}}. New scripts
6280 should use @option{-t @var{t1}[,@var{t2}]@dots{}} instead.
6286 @cindex initial tabs, converting
6287 Only convert initial tabs (those that precede all non-space or non-tab
6288 characters) on each line to spaces.
6295 @node unexpand invocation
6296 @section @command{unexpand}: Convert spaces to tabs
6300 @command{unexpand} writes the contents of each given @var{file}, or
6301 standard input if none are given or for a @var{file} of @samp{-}, to
6302 standard output, converting blanks at the beginning of each line into
6303 as many tab characters as needed. In the default @acronym{POSIX}
6304 locale, a @dfn{blank} is a space or a tab; other locales may specify
6305 additional blank characters. Synopsis:
6308 unexpand [@var{option}]@dots{} [@var{file}]@dots{}
6311 By default, @command{unexpand} converts only initial blanks (those
6312 that precede all non-blank characters) on each line. It
6313 preserves backspace characters in the output; they decrement the column
6314 count for tab calculations. By default, tabs are set at every 8th
6317 The program accepts the following options. Also see @ref{Common options}.
6321 @item -t @var{tab1}[,@var{tab2}]@dots{}
6322 @itemx --tabs=@var{tab1}[,@var{tab2}]@dots{}
6325 If only one tab stop is given, set the tabs @var{tab1} columns apart
6326 instead of the default 8. Otherwise, set the tabs at columns
6327 @var{tab1}, @var{tab2}, @dots{} (numbered from 0), and leave blanks
6328 beyond the tab stops given unchanged. Tab stops can be separated by
6329 blanks as well as by commas. This option implies the @option{-a} option.
6331 For compatibility, GNU @command{unexpand} supports the obsolete option syntax,
6332 @option{-@var{tab1}[,@var{tab2}]@dots{}}, where tab stops must be
6333 separated by commas. (Unlike @option{-t}, this obsolete option does
6334 not imply @option{-a}.) New scripts should use @option{--first-only -t
6335 @var{tab1}[,@var{tab2}]@dots{}} instead.
6341 Also convert all sequences of two or more blanks just before a tab stop,
6342 even if they occur after non-blank characters in a line.
6349 @node Directory listing
6350 @chapter Directory listing
6352 This chapter describes the @command{ls} command and its variants @command{dir}
6353 and @command{vdir}, which list information about files.
6356 * ls invocation:: List directory contents.
6357 * dir invocation:: Briefly ls.
6358 * vdir invocation:: Verbosely ls.
6359 * dircolors invocation:: Color setup for ls, etc.
6364 @section @command{ls}: List directory contents
6367 @cindex directory listing
6369 The @command{ls} program lists information about files (of any type,
6370 including directories). Options and file arguments can be intermixed
6371 arbitrarily, as usual.
6373 For non-option command-line arguments that are directories, by default
6374 @command{ls} lists the contents of directories, not recursively, and
6375 omitting files with names beginning with @samp{.}. For other non-option
6376 arguments, by default @command{ls} lists just the file name. If no
6377 non-option argument is specified, @command{ls} operates on the current
6378 directory, acting as if it had been invoked with a single argument of @samp{.}.
6381 By default, the output is sorted alphabetically, according to the locale
6382 settings in effect.@footnote{If you use a non-@acronym{POSIX}
6383 locale (e.g., by setting @env{LC_ALL} to @samp{en_US}), then @command{ls} may
6384 produce output that is sorted differently than you're accustomed to.
6385 In that case, set the @env{LC_ALL} environment variable to @samp{C}.}
6386 If standard output is
6387 a terminal, the output is in columns (sorted vertically) and control
6388 characters are output as question marks; otherwise, the output is listed
6389 one per line and control characters are output as-is.
6391 Because @command{ls} is such a fundamental program, it has accumulated many
6392 options over the years. They are described in the subsections below;
6393 within each section, options are listed alphabetically (ignoring case).
6394 The division of options into the subsections is not absolute, since some
6395 options affect more than one aspect of @command{ls}'s operation.
6397 @cindex exit status of @command{ls}
6402 1 minor problems (e.g., failure to access a file or directory not
6403 specified as a command line argument. This happens when listing a
6404 directory in which entries are actively being removed or renamed.)
6405 2 serious trouble (e.g., memory exhausted, invalid option, failure
6406 to access a file or directory specified as a command line argument
6407 or a directory loop)
6410 Also see @ref{Common options}.
6413 * Which files are listed::
6414 * What information is listed::
6415 * Sorting the output::
6416 * Details about version sort::
6417 * General output formatting::
6418 * Formatting file timestamps::
6419 * Formatting the file names::
6423 @node Which files are listed
6424 @subsection Which files are listed
6426 These options determine which files @command{ls} lists information for.
6427 By default, @command{ls} lists files and the contents of any
6428 directories on the command line, except that in directories it ignores
6429 files whose names start with @samp{.}.
6437 In directories, do not ignore file names that start with @samp{.}.
6442 @opindex --almost-all
6443 In directories, do not ignore all file names that start with @samp{.};
6444 ignore only @file{.} and @file{..}. The @option{--all} (@option{-a})
6445 option overrides this option.
6448 @itemx --ignore-backups
6450 @opindex --ignore-backups
6451 @cindex backup files, ignoring
6452 In directories, ignore files that end with @samp{~}. This option is
6453 equivalent to @samp{--ignore='*~' --ignore='.*~'}.
6458 @opindex --directory
6459 List just the names of directories, as with other types of files, rather
6460 than listing their contents.
6461 @c The following sentence is the same as the one for -F.
6462 Do not follow symbolic links listed on the
6463 command line unless the @option{--dereference-command-line} (@option{-H}),
6464 @option{--dereference} (@option{-L}), or
6465 @option{--dereference-command-line-symlink-to-dir} options are specified.
6468 @itemx --dereference-command-line
6470 @opindex --dereference-command-line
6471 @cindex symbolic links, dereferencing
6472 If a command line argument specifies a symbolic link, show information
6473 for the file the link references rather than for the link itself.
6475 @itemx --dereference-command-line-symlink-to-dir
6476 @opindex --dereference-command-line-symlink-to-dir
6477 @cindex symbolic links, dereferencing
6478 Do not dereference symbolic links, with one exception:
6479 if a command line argument specifies a symbolic link that refers to
6480 a directory, show information for that directory rather than for the
6482 This is the default behavior when no other dereferencing-related
6483 option has been specified (@option{--classify} (@option{-F}),
6484 @option{--directory} (@option{-d}),
6486 @option{--dereference} (@option{-L}), or
6487 @option{--dereference-command-line} (@option{-H})).
6489 @item --group-directories-first
6490 @opindex --group-directories-first
6491 Group all the directories before the files and then sort the
6492 directories and the files separately using the selected sort key
6493 (see --sort option).
6494 That is, this option specifies a primary sort key,
6495 and the --sort option specifies a secondary key.
6496 However, any use of @option{--sort=none}
6497 (@option{-U}) disables this option altogether.
6499 @item --hide=PATTERN
6500 @opindex --hide=@var{pattern}
6501 In directories, ignore files whose names match the shell pattern
6502 @var{pattern}, unless the @option{--all} (@option{-a}) or
6503 @option{--almost-all} (@option{-A}) is also given. This
6504 option acts like @option{--ignore=@var{pattern}} except that it has no
6505 effect if @option{--all} (@option{-a}) or @option{--almost-all}
6506 (@option{-A}) is also given.
6508 This option can be useful in shell aliases. For example, if
6509 @command{lx} is an alias for @samp{ls --hide='*~'} and @command{ly} is
6510 an alias for @samp{ls --ignore='*~'}, then the command @samp{lx -A}
6511 lists the file @file{README~} even though @samp{ly -A} would not.
6513 @item -I @var{pattern}
6514 @itemx --ignore=@var{pattern}
6516 @opindex --ignore=@var{pattern}
6517 In directories, ignore files whose names match the shell pattern
6518 (not regular expression) @var{pattern}. As
6519 in the shell, an initial @samp{.} in a file name does not match a
6520 wildcard at the start of @var{pattern}. Sometimes it is useful
6521 to give this option several times. For example,
6524 $ ls --ignore='.??*' --ignore='.[^.]' --ignore='#*'
6527 The first option ignores names of length 3 or more that start with @samp{.},
6528 the second ignores all two-character names that start with @samp{.}
6529 except @samp{..}, and the third ignores names that start with @samp{#}.
6532 @itemx --dereference
6534 @opindex --dereference
6535 @cindex symbolic links, dereferencing
6536 When showing file information for a symbolic link, show information
6537 for the file the link references rather than the link itself.
6538 However, even with this option, @command{ls} still prints the name
6539 of the link itself, not the name of the file that the link points to.
6544 @opindex --recursive
6545 @cindex recursive directory listing
6546 @cindex directory listing, recursive
6547 List the contents of all directories recursively.
6552 @node What information is listed
6553 @subsection What information is listed
6555 These options affect the information that @command{ls} displays. By
6556 default, only file names are shown.
6562 @cindex hurd, author, printing
6563 List each file's author when producing long format directory listings.
6564 In GNU/Hurd, file authors can differ from their owners, but in other
6565 operating systems the two are the same.
6571 @cindex dired Emacs mode support
6572 With the long listing (@option{-l}) format, print an additional line after
6576 //DIRED// @var{beg1} @var{end1} @var{beg2} @var{end2} @dots{}
6580 The @var{begn} and @var{endn} are unsigned integers that record the
6581 byte position of the beginning and end of each file name in the output.
6582 This makes it easy for Emacs to find the names, even when they contain
6583 unusual characters such as space or newline, without fancy searching.
6585 If directories are being listed recursively (@option{-R}), output a similar
6586 line with offsets for each subdirectory name:
6589 //SUBDIRED// @var{beg1} @var{end1} @dots{}
6592 Finally, output a line of the form:
6595 //DIRED-OPTIONS// --quoting-style=@var{word}
6599 where @var{word} is the quoting style (@pxref{Formatting the file names}).
6601 Here is an actual example:
6604 $ mkdir -p a/sub/deeper a/sub2
6606 $ touch a/sub/deeper/file
6607 $ ls -gloRF --dired a
6610 -rw-r--r-- 1 0 Jun 10 12:27 f1
6611 -rw-r--r-- 1 0 Jun 10 12:27 f2
6612 drwxr-xr-x 3 4096 Jun 10 12:27 sub/
6613 drwxr-xr-x 2 4096 Jun 10 12:27 sub2/
6617 drwxr-xr-x 2 4096 Jun 10 12:27 deeper/
6621 -rw-r--r-- 1 0 Jun 10 12:27 file
6625 //DIRED// 48 50 84 86 120 123 158 162 217 223 282 286
6626 //SUBDIRED// 2 3 167 172 228 240 290 296
6627 //DIRED-OPTIONS// --quoting-style=literal
6630 Note that the pairs of offsets on the @samp{//DIRED//} line above delimit
6631 these names: @file{f1}, @file{f2}, @file{sub}, @file{sub2}, @file{deeper},
6633 The offsets on the @samp{//SUBDIRED//} line delimit the following
6634 directory names: @file{a}, @file{a/sub}, @file{a/sub/deeper}, @file{a/sub2}.
6636 Here is an example of how to extract the fifth entry name, @samp{deeper},
6637 corresponding to the pair of offsets, 222 and 228:
6640 $ ls -gloRF --dired a > out
6641 $ dd bs=1 skip=222 count=6 < out 2>/dev/null; echo
6645 Note that although the listing above includes a trailing slash
6646 for the @samp{deeper} entry, the offsets select the name without
6647 the trailing slash. However, if you invoke @command{ls} with @option{--dired}
6648 along with an option like @option{--escape} (aka @option{-b}) and operate
6649 on a file whose name contains special characters, notice that the backslash
6654 $ ls -blog --dired 'a b'
6655 -rw-r--r-- 1 0 Jun 10 12:28 a\ b
6657 //DIRED-OPTIONS// --quoting-style=escape
6660 If you use a quoting style that adds quote marks
6661 (e.g., @option{--quoting-style=c}), then the offsets include the quote marks.
6662 So beware that the user may select the quoting style via the environment
6663 variable @env{QUOTING_STYLE}. Hence, applications using @option{--dired}
6664 should either specify an explicit @option{--quoting-style=literal} option
6665 (aka @option{-N} or @option{--literal}) on the command line, or else be
6666 prepared to parse the escaped names.
6669 @opindex --full-time
6670 Produce long format directory listings, and list times in full. It is
6671 equivalent to using @option{--format=long} with
6672 @option{--time-style=full-iso} (@pxref{Formatting file timestamps}).
6676 Produce long format directory listings, but don't display owner information.
6682 Inhibit display of group information in a long format directory listing.
6683 (This is the default in some non-@sc{gnu} versions of @command{ls}, so we
6684 provide this option for compatibility.)
6692 @cindex inode number, printing
6693 Print the inode number (also called the file serial number and index
6694 number) of each file to the left of the file name. (This number
6695 uniquely identifies each file within a particular file system.)
6698 @itemx --format=long
6699 @itemx --format=verbose
6702 @opindex long ls @r{format}
6703 @opindex verbose ls @r{format}
6704 In addition to the name of each file, print the file type, file mode bits,
6705 number of hard links, owner name, group name, size, and
6706 timestamp (@pxref{Formatting file timestamps}), normally
6707 the modification time. Print question marks for information that
6708 cannot be determined.
6710 Normally the size is printed as a byte count without punctuation, but
6711 this can be overridden (@pxref{Block size}). For example, @option{-h}
6712 prints an abbreviated, human-readable count, and
6713 @samp{--block-size="'1"} prints a byte count with the thousands
6714 separator of the current locale.
6716 For each directory that is listed, preface the files with a line
6717 @samp{total @var{blocks}}, where @var{blocks} is the total disk allocation
6718 for all files in that directory. The block size currently defaults to 1024
6719 bytes, but this can be overridden (@pxref{Block size}).
6720 The @var{blocks} computed counts each hard link separately;
6721 this is arguably a deficiency.
6723 The file type is one of the following characters:
6725 @c The commented-out entries are ones we're not sure about.
6733 character special file
6735 high performance (``contiguous data'') file
6739 door (Solaris 2.5 and up)
6741 @c semaphore, if this is a distinct file type
6745 @c multiplexed file (7th edition Unix; obsolete)
6747 off-line (``migrated'') file (Cray DMF)
6749 network special file (HP-UX)
6753 port (Solaris 10 and up)
6755 @c message queue, if this is a distinct file type
6759 @c shared memory object, if this is a distinct file type
6761 @c typed memory object, if this is a distinct file type
6763 @c whiteout (4.4BSD; not implemented)
6765 some other file type
6768 @cindex permissions, output by @command{ls}
6769 The file mode bits listed are similar to symbolic mode specifications
6770 (@pxref{Symbolic Modes}). But @command{ls} combines multiple bits into the
6771 third character of each set of permissions as follows:
6775 If the set-user-ID or set-group-ID bit and the corresponding executable bit
6779 If the set-user-ID or set-group-ID bit is set but the corresponding
6780 executable bit is not set.
6783 If the restricted deletion flag or sticky bit, and the
6784 other-executable bit, are both set. The restricted deletion flag is
6785 another name for the sticky bit. @xref{Mode Structure}.
6788 If the restricted deletion flag or sticky bit is set but the
6789 other-executable bit is not set.
6792 If the executable bit is set and none of the above apply.
6798 Following the file mode bits is a single character that specifies
6799 whether an alternate access method such as an access control list
6800 applies to the file. When the character following the file mode bits is a
6801 space, there is no alternate access method. When it is a printing
6802 character, then there is such a method.
6804 GNU @command{ls} uses a @samp{.} character to indicate a file
6805 with an SELinux security context, but no other alternate access method.
6807 A file with any other combination of alternate access methods
6808 is marked with a @samp{+} character.
6811 @itemx --numeric-uid-gid
6813 @opindex --numeric-uid-gid
6814 @cindex numeric uid and gid
6815 @cindex numeric user and group IDs
6816 Produce long format directory listings, but
6817 display numeric user and group IDs instead of the owner and group names.
6821 Produce long format directory listings, but don't display group information.
6822 It is equivalent to using @option{--format=long} with @option{--no-group} .
6828 @cindex disk allocation
6829 @cindex size of files, reporting
6830 Print the disk allocation of each file to the left of the file name.
6831 This is the amount of disk space used by the file, which is usually a
6832 bit more than the file's size, but it can be less if the file has holes.
6834 Normally the disk allocation is printed in units of
6835 1024 bytes, but this can be overridden (@pxref{Block size}).
6837 @cindex NFS mounts from BSD to HP-UX
6838 For files that are NFS-mounted from an HP-UX system to a BSD system,
6839 this option reports sizes that are half the correct values. On HP-UX
6840 systems, it reports sizes that are twice the correct values for files
6841 that are NFS-mounted from BSD systems. This is due to a flaw in HP-UX;
6842 it also affects the HP-UX @command{ls} program.
6851 @cindex security context
6852 Display the SELinux security context or @samp{?} if none is found.
6853 When used with the @option{-l} option, print the security context
6854 to the left of the size column.
6859 @node Sorting the output
6860 @subsection Sorting the output
6862 @cindex sorting @command{ls} output
6863 These options change the order in which @command{ls} sorts the information
6864 it outputs. By default, sorting is done by character code
6865 (e.g., @acronym{ASCII} order).
6871 @itemx --time=status
6874 @opindex ctime@r{, printing or sorting by}
6875 @opindex status time@r{, printing or sorting by}
6876 @opindex use time@r{, printing or sorting files by}
6877 If the long listing format (e.g., @option{-l}, @option{-o}) is being used,
6878 print the status change time (the @samp{ctime} in the inode) instead of
6879 the modification time.
6880 When explicitly sorting by time (@option{--sort=time} or @option{-t})
6881 or when not using a long listing format,
6882 sort according to the status change time.
6886 @cindex unsorted directory listing
6887 @cindex directory order, listing by
6888 Primarily, like @option{-U}---do not sort; list the files in whatever
6889 order they are stored in the directory. But also enable @option{-a} (list
6890 all files) and disable @option{-l}, @option{--color}, and @option{-s} (if they
6891 were specified before the @option{-f}).
6897 @cindex reverse sorting
6898 Reverse whatever the sorting method is---e.g., list files in reverse
6899 alphabetical order, youngest first, smallest first, or whatever.
6905 @opindex size of files@r{, sorting files by}
6906 Sort by file size, largest first.
6912 @opindex modification time@r{, sorting files by}
6913 Sort by modification time (the @samp{mtime} in the inode), newest first.
6917 @itemx --time=access
6921 @opindex use time@r{, printing or sorting files by}
6922 @opindex atime@r{, printing or sorting files by}
6923 @opindex access time@r{, printing or sorting files by}
6924 If the long listing format (e.g., @option{--format=long}) is being used,
6925 print the last access time (the @samp{atime} in the inode).
6926 When explicitly sorting by time (@option{--sort=time} or @option{-t})
6927 or when not using a long listing format, sort according to the access time.
6933 @opindex none@r{, sorting option for @command{ls}}
6934 Do not sort; list the files in whatever order they are
6935 stored in the directory. (Do not do any of the other unrelated things
6936 that @option{-f} does.) This is especially useful when listing very large
6937 directories, since not doing any sorting can be noticeably faster.
6940 @itemx --sort=version
6943 @opindex version@r{, sorting option for @command{ls}}
6944 Sort by version name and number, lowest first. It behaves like a default
6945 sort, except that each sequence of decimal digits is treated numerically
6946 as an index/version number. (@xref{Details about version sort}.)
6949 @itemx --sort=extension
6952 @opindex extension@r{, sorting files by}
6953 Sort directory contents alphabetically by file extension (characters
6954 after the last @samp{.}); files with no extension are sorted first.
6959 @node Details about version sort
6960 @subsection Details about version sort
6962 Version sorting handles the fact that file names frequently include indices or
6963 version numbers. Standard sorting usually does not produce the order that one
6964 expects because comparisons are made on a character-by-character basis.
6965 Version sorting is especially useful when browsing directories that contain
6966 many files with indices/version numbers in their names:
6970 abc.zml-1.gz abc.zml-1.gz
6971 abc.zml-12.gz abc.zml-2.gz
6972 abc.zml-2.gz abc.zml-12.gz
6975 Version-sorted strings are compared such that if @var{ver1} and @var{ver2}
6976 are version numbers and @var{prefix} and @var{suffix} (@var{suffix} matching
6977 the regular expression @samp{(\.[A-Za-z~][A-Za-z0-9~]*)*}) are strings then
6978 @var{ver1} < @var{ver2} implies that the name composed of
6979 ``@var{prefix} @var{ver1} @var{suffix}'' sorts before
6980 ``@var{prefix} @var{ver2} @var{suffix}''.
6982 Note also that leading zeros of numeric parts are ignored:
6986 abc-1.007.tgz abc-1.01a.tgz
6987 abc-1.012b.tgz abc-1.007.tgz
6988 abc-1.01a.tgz abc-1.012b.tgz
6991 This functionality is implemented using gnulib's @code{filevercmp} function,
6992 which has some caveats worth noting.
6995 @item @env{LC_COLLATE} is ignored, which means @samp{ls -v} and @samp{sort -V}
6996 will sort non-numeric prefixes as if the @env{LC_COLLATE} locale category
6997 was set to @samp{C}.
6998 @item Some suffixes will not be matched by the regular
6999 expression mentioned above. Consequently these examples may
7000 not sort as you expect:
7008 abc-1.2.3.4.x86_64.rpm
7009 abc-1.2.3.x86_64.rpm
7013 @node General output formatting
7014 @subsection General output formatting
7016 These options affect the appearance of the overall output.
7021 @itemx --format=single-column
7024 @opindex single-column @r{output of files}
7025 List one file per line. This is the default for @command{ls} when standard
7026 output is not a terminal.
7029 @itemx --format=vertical
7032 @opindex vertical @r{sorted files in columns}
7033 List files in columns, sorted vertically. This is the default for
7034 @command{ls} if standard output is a terminal. It is always the default
7035 for the @command{dir} program.
7036 @sc{gnu} @command{ls} uses variable width columns to display as many files as
7037 possible in the fewest lines.
7039 @item --color [=@var{when}]
7041 @cindex color, distinguishing file types with
7042 Specify whether to use color for distinguishing file types. @var{when}
7043 may be omitted, or one of:
7046 @vindex none @r{color option}
7047 - Do not use color at all. This is the default.
7049 @vindex auto @r{color option}
7050 @cindex terminal, using color iff
7051 - Only use color if standard output is a terminal.
7053 @vindex always @r{color option}
7056 Specifying @option{--color} and no @var{when} is equivalent to
7057 @option{--color=always}.
7058 Piping a colorized listing through a pager like @command{more} or
7059 @command{less} usually produces unreadable results. However, using
7060 @code{more -f} does seem to work.
7063 @vindex SHELL @r{environment variable, and color}
7064 Note that using the @option{--color} option may incur a noticeable
7065 performance penalty when run in a directory with very many entries,
7066 because the default settings require that @command{ls} @code{stat} every
7067 single file it lists.
7068 However, if you would like most of the file-type coloring
7069 but can live without the other coloring options (e.g.,
7070 executable, orphan, sticky, other-writable, capability), use
7071 @command{dircolors} to set the @env{LS_COLORS} environment variable like this,
7073 eval $(dircolors -p | perl -pe \
7074 's/^((CAP|S[ET]|O[TR]|M|E)\w+).*/$1 00/' | dircolors -)
7076 and on a @code{dirent.d_type}-capable file system, @command{ls}
7077 will perform only one @code{stat} call per command line argument.
7081 @itemx --indicator-style=classify
7084 @opindex --indicator-style
7085 @cindex file type and executables, marking
7086 @cindex executables and file type, marking
7087 Append a character to each file name indicating the file type. Also,
7088 for regular files that are executable, append @samp{*}. The file type
7089 indicators are @samp{/} for directories, @samp{@@} for symbolic links,
7090 @samp{|} for FIFOs, @samp{=} for sockets, @samp{>} for doors,
7091 and nothing for regular files.
7092 @c The following sentence is the same as the one for -d.
7093 Do not follow symbolic links listed on the
7094 command line unless the @option{--dereference-command-line} (@option{-H}),
7095 @option{--dereference} (@option{-L}), or
7096 @option{--dereference-command-line-symlink-to-dir} options are specified.
7099 @itemx --indicator-style=file-type
7100 @opindex --file-type
7101 @opindex --indicator-style
7102 @cindex file type, marking
7103 Append a character to each file name indicating the file type. This is
7104 like @option{-F}, except that executables are not marked.
7106 @item --indicator-style=@var{word}
7107 @opindex --indicator-style
7108 Append a character indicator with style @var{word} to entry names,
7113 Do not append any character indicator; this is the default.
7115 Append @samp{/} for directories. This is the same as the @option{-p}
7118 Append @samp{/} for directories, @samp{@@} for symbolic links, @samp{|}
7119 for FIFOs, @samp{=} for sockets, and nothing for regular files. This is
7120 the same as the @option{--file-type} option.
7122 Append @samp{*} for executable regular files, otherwise behave as for
7123 @samp{file-type}. This is the same as the @option{-F} or
7124 @option{--classify} option.
7130 @opindex --kibibytes
7131 Set the default block size to its normal value of 1024 bytes,
7132 overriding any contrary specification in environment variables
7133 (@pxref{Block size}). This option is in turn overridden by the
7134 @option{--block-size}, @option{-h} or @option{--human-readable}, and
7135 @option{--si} options.
7137 The @option{-k} or @option{--kibibytes} option affects the
7138 per-directory block count written by the @option{-l} and similar
7139 options, and the size written by the @option{-s} or @option{--size}
7140 option. It does not affect the file size written by @option{-l}.
7143 @itemx --format=commas
7146 @opindex commas@r{, outputting between files}
7147 List files horizontally, with as many as will fit on each line,
7148 separated by @samp{, } (a comma and a space).
7151 @itemx --indicator-style=slash
7153 @opindex --indicator-style
7154 @cindex file type, marking
7155 Append a @samp{/} to directory names.
7158 @itemx --format=across
7159 @itemx --format=horizontal
7162 @opindex across@r{, listing files}
7163 @opindex horizontal@r{, listing files}
7164 List the files in columns, sorted horizontally.
7167 @itemx --tabsize=@var{cols}
7170 Assume that each tab stop is @var{cols} columns wide. The default is 8.
7171 @command{ls} uses tabs where possible in the output, for efficiency. If
7172 @var{cols} is zero, do not use tabs at all.
7174 @c FIXME: remove in 2009, if Apple Terminal has been fixed for long enough.
7175 Some terminal emulators (at least Apple Terminal 1.5 (133) from Mac OS X 10.4.8)
7176 do not properly align columns to the right of a TAB following a
7177 non-@acronym{ASCII} byte. If you use such a terminal emulator, use the
7178 @option{-T0} option or put @code{TABSIZE=0} in your environment to tell
7179 @command{ls} to align using spaces, not tabs.
7182 @itemx --width=@var{cols}
7186 Assume the screen is @var{cols} columns wide. The default is taken
7187 from the terminal settings if possible; otherwise the environment
7188 variable @env{COLUMNS} is used if it is set; otherwise the default
7194 @node Formatting file timestamps
7195 @subsection Formatting file timestamps
7197 By default, file timestamps are listed in abbreviated form, using
7198 a date like @samp{Mar 30@ @ 2002} for non-recent timestamps, and a
7199 date-without-year and time like @samp{Mar 30 23:45} for recent timestamps.
7200 This format can change depending on the current locale as detailed below.
7203 A timestamp is considered to be @dfn{recent} if it is less than six
7204 months old, and is not dated in the future. If a timestamp dated
7205 today is not listed in recent form, the timestamp is in the future,
7206 which means you probably have clock skew problems which may break
7207 programs like @command{make} that rely on file timestamps.
7210 Time stamps are listed according to the time zone rules specified by
7211 the @env{TZ} environment variable, or by the system default rules if
7212 @env{TZ} is not set. @xref{TZ Variable,, Specifying the Time Zone
7213 with @env{TZ}, libc, The GNU C Library Reference Manual}.
7215 The following option changes how file timestamps are printed.
7218 @item --time-style=@var{style}
7219 @opindex --time-style
7221 List timestamps in style @var{style}. The @var{style} should
7222 be one of the following:
7227 List timestamps using @var{format}, where @var{format} is interpreted
7228 like the format argument of @command{date} (@pxref{date invocation}).
7229 For example, @option{--time-style="+%Y-%m-%d %H:%M:%S"} causes
7230 @command{ls} to list timestamps like @samp{2002-03-30 23:45:56}. As
7231 with @command{date}, @var{format}'s interpretation is affected by the
7232 @env{LC_TIME} locale category.
7234 If @var{format} contains two format strings separated by a newline,
7235 the former is used for non-recent files and the latter for recent
7236 files; if you want output columns to line up, you may need to insert
7237 spaces in one of the two formats.
7240 List timestamps in full using @acronym{ISO} 8601 date, time, and time zone
7241 format with nanosecond precision, e.g., @samp{2002-03-30
7242 23:45:56.477817180 -0700}. This style is equivalent to
7243 @samp{+%Y-%m-%d %H:%M:%S.%N %z}.
7245 This is useful because the time output includes all the information that
7246 is available from the operating system. For example, this can help
7247 explain @command{make}'s behavior, since @acronym{GNU} @command{make}
7248 uses the full timestamp to determine whether a file is out of date.
7251 List @acronym{ISO} 8601 date and time in minutes, e.g.,
7252 @samp{2002-03-30 23:45}. These timestamps are shorter than
7253 @samp{full-iso} timestamps, and are usually good enough for everyday
7254 work. This style is equivalent to @samp{+%Y-%m-%d %H:%M}.
7257 List @acronym{ISO} 8601 dates for non-recent timestamps (e.g.,
7258 @samp{2002-03-30@ }), and @acronym{ISO} 8601 month, day, hour, and
7259 minute for recent timestamps (e.g., @samp{03-30 23:45}). These
7260 timestamps are uglier than @samp{long-iso} timestamps, but they carry
7261 nearly the same information in a smaller space and their brevity helps
7262 @command{ls} output fit within traditional 80-column output lines.
7263 The following two @command{ls} invocations are equivalent:
7268 ls -l --time-style="+%Y-%m-%d $newline%m-%d %H:%M"
7269 ls -l --time-style="iso"
7274 List timestamps in a locale-dependent form. For example, a Finnish
7275 locale might list non-recent timestamps like @samp{maalis 30@ @ 2002}
7276 and recent timestamps like @samp{maalis 30 23:45}. Locale-dependent
7277 timestamps typically consume more space than @samp{iso} timestamps and
7278 are harder for programs to parse because locale conventions vary so
7279 widely, but they are easier for many people to read.
7281 The @env{LC_TIME} locale category specifies the timestamp format. The
7282 default @acronym{POSIX} locale uses timestamps like @samp{Mar 30@
7283 @ 2002} and @samp{Mar 30 23:45}; in this locale, the following two
7284 @command{ls} invocations are equivalent:
7289 ls -l --time-style="+%b %e %Y$newline%b %e %H:%M"
7290 ls -l --time-style="locale"
7293 Other locales behave differently. For example, in a German locale,
7294 @option{--time-style="locale"} might be equivalent to
7295 @option{--time-style="+%e. %b %Y $newline%e. %b %H:%M"}
7296 and might generate timestamps like @samp{30. M@"ar 2002@ } and
7297 @samp{30. M@"ar 23:45}.
7299 @item posix-@var{style}
7301 List @acronym{POSIX}-locale timestamps if the @env{LC_TIME} locale
7302 category is @acronym{POSIX}, @var{style} timestamps otherwise. For
7303 example, the @samp{posix-long-iso} style lists
7304 timestamps like @samp{Mar 30@ @ 2002} and @samp{Mar 30 23:45} when in
7305 the @acronym{POSIX} locale, and like @samp{2002-03-30 23:45} otherwise.
7310 You can specify the default value of the @option{--time-style} option
7311 with the environment variable @env{TIME_STYLE}; if @env{TIME_STYLE} is not set
7312 the default style is @samp{locale}. @acronym{GNU} Emacs 21.3 and
7313 later use the @option{--dired} option and therefore can parse any date
7314 format, but if you are using Emacs 21.1 or 21.2 and specify a
7315 non-@acronym{POSIX} locale you may need to set
7316 @samp{TIME_STYLE="posix-long-iso"}.
7318 To avoid certain denial-of-service attacks, timestamps that would be
7319 longer than 1000 bytes may be treated as errors.
7322 @node Formatting the file names
7323 @subsection Formatting the file names
7325 These options change how file names themselves are printed.
7331 @itemx --quoting-style=escape
7334 @opindex --quoting-style
7335 @cindex backslash sequences for file names
7336 Quote nongraphic characters in file names using alphabetic and octal
7337 backslash sequences like those used in C.
7341 @itemx --quoting-style=literal
7344 @opindex --quoting-style
7345 Do not quote file names. However, with @command{ls} nongraphic
7346 characters are still printed as question marks if the output is a
7347 terminal and you do not specify the @option{--show-control-chars}
7351 @itemx --hide-control-chars
7353 @opindex --hide-control-chars
7354 Print question marks instead of nongraphic characters in file names.
7355 This is the default if the output is a terminal and the program is
7360 @itemx --quoting-style=c
7362 @opindex --quote-name
7363 @opindex --quoting-style
7364 Enclose file names in double quotes and quote nongraphic characters as
7367 @item --quoting-style=@var{word}
7368 @opindex --quoting-style
7369 @cindex quoting style
7370 Use style @var{word} to quote file names and other strings that may
7371 contain arbitrary characters. The @var{word} should
7372 be one of the following:
7376 Output strings as-is; this is the same as the @option{-N} or
7377 @option{--literal} option.
7379 Quote strings for the shell if they contain shell metacharacters or would
7380 cause ambiguous output.
7381 The quoting is suitable for @acronym{POSIX}-compatible shells like
7382 @command{bash}, but it does not always work for incompatible shells
7385 Quote strings for the shell, even if they would normally not require quoting.
7387 Quote strings as for C character string literals, including the
7388 surrounding double-quote characters; this is the same as the
7389 @option{-Q} or @option{--quote-name} option.
7391 Quote strings as for C character string literals, except omit the
7392 surrounding double-quote
7393 characters; this is the same as the @option{-b} or @option{--escape} option.
7395 Quote strings as for C character string literals, except use
7396 surrounding quotation marks appropriate for the
7399 @c Use @t instead of @samp to avoid duplicate quoting in some output styles.
7400 Quote strings as for C character string literals, except use
7401 surrounding quotation marks appropriate for the locale, and quote
7402 @t{`like this'} instead of @t{"like
7403 this"} in the default C locale. This looks nicer on many displays.
7406 You can specify the default value of the @option{--quoting-style} option
7407 with the environment variable @env{QUOTING_STYLE}. If that environment
7408 variable is not set, the default value is @samp{literal}, but this
7409 default may change to @samp{shell} in a future version of this package.
7411 @item --show-control-chars
7412 @opindex --show-control-chars
7413 Print nongraphic characters as-is in file names.
7414 This is the default unless the output is a terminal and the program is
7420 @node dir invocation
7421 @section @command{dir}: Briefly list directory contents
7424 @cindex directory listing, brief
7426 @command{dir} is equivalent to @code{ls -C
7427 -b}; that is, by default files are listed in columns, sorted vertically,
7428 and special characters are represented by backslash escape sequences.
7430 @xref{ls invocation, @command{ls}}.
7433 @node vdir invocation
7434 @section @command{vdir}: Verbosely list directory contents
7437 @cindex directory listing, verbose
7439 @command{vdir} is equivalent to @code{ls -l
7440 -b}; that is, by default files are listed in long format and special
7441 characters are represented by backslash escape sequences.
7443 @node dircolors invocation
7444 @section @command{dircolors}: Color setup for @command{ls}
7448 @cindex setup for color
7450 @command{dircolors} outputs a sequence of shell commands to set up the
7451 terminal for color output from @command{ls} (and @command{dir}, etc.).
7455 eval "`dircolors [@var{option}]@dots{} [@var{file}]`"
7458 If @var{file} is specified, @command{dircolors} reads it to determine which
7459 colors to use for which file types and extensions. Otherwise, a
7460 precompiled database is used. For details on the format of these files,
7461 run @samp{dircolors --print-database}.
7463 To make @command{dircolors} read a @file{~/.dircolors} file if it
7464 exists, you can put the following lines in your @file{~/.bashrc} (or
7465 adapt them to your favorite shell):
7469 test -r $d && eval "$(dircolors $d)"
7473 @vindex SHELL @r{environment variable, and color}
7474 The output is a shell command to set the @env{LS_COLORS} environment
7475 variable. You can specify the shell syntax to use on the command line,
7476 or @command{dircolors} will guess it from the value of the @env{SHELL}
7477 environment variable.
7479 The program accepts the following options. Also see @ref{Common options}.
7484 @itemx --bourne-shell
7487 @opindex --bourne-shell
7488 @cindex Bourne shell syntax for color setup
7489 @cindex @command{sh} syntax for color setup
7490 Output Bourne shell commands. This is the default if the @env{SHELL}
7491 environment variable is set and does not end with @samp{csh} or
7500 @cindex C shell syntax for color setup
7501 @cindex @command{csh} syntax for color setup
7502 Output C shell commands. This is the default if @code{SHELL} ends with
7503 @command{csh} or @command{tcsh}.
7506 @itemx --print-database
7508 @opindex --print-database
7509 @cindex color database, printing
7510 @cindex database for color setup, printing
7511 @cindex printing color database
7512 Print the (compiled-in) default color configuration database. This
7513 output is itself a valid configuration file, and is fairly descriptive
7514 of the possibilities.
7521 @node Basic operations
7522 @chapter Basic operations
7524 @cindex manipulating files
7526 This chapter describes the commands for basic file manipulation:
7527 copying, moving (renaming), and deleting (removing).
7530 * cp invocation:: Copy files.
7531 * dd invocation:: Convert and copy a file.
7532 * install invocation:: Copy files and set attributes.
7533 * mv invocation:: Move (rename) files.
7534 * rm invocation:: Remove files or directories.
7535 * shred invocation:: Remove files more securely.
7540 @section @command{cp}: Copy files and directories
7543 @cindex copying files and directories
7544 @cindex files, copying
7545 @cindex directories, copying
7547 @command{cp} copies files (or, optionally, directories). The copy is
7548 completely independent of the original. You can either copy one file to
7549 another, or copy arbitrarily many files to a destination directory.
7553 cp [@var{option}]@dots{} [-T] @var{source} @var{dest}
7554 cp [@var{option}]@dots{} @var{source}@dots{} @var{directory}
7555 cp [@var{option}]@dots{} -t @var{directory} @var{source}@dots{}
7560 If two file names are given, @command{cp} copies the first file to the
7564 If the @option{--target-directory} (@option{-t}) option is given, or
7565 failing that if the last file is a directory and the
7566 @option{--no-target-directory} (@option{-T}) option is not given,
7567 @command{cp} copies each @var{source} file to the specified directory,
7568 using the @var{source}s' names.
7571 Generally, files are written just as they are read. For exceptions,
7572 see the @option{--sparse} option below.
7574 By default, @command{cp} does not copy directories. However, the
7575 @option{-R}, @option{-a}, and @option{-r} options cause @command{cp} to
7576 copy recursively by descending into source directories and copying files
7577 to corresponding destination directories.
7579 When copying from a symbolic link, @command{cp} normally follows the
7580 link only when not copying
7581 recursively. This default can be overridden with the
7582 @option{--archive} (@option{-a}), @option{-d}, @option{--dereference}
7583 (@option{-L}), @option{--no-dereference} (@option{-P}), and
7584 @option{-H} options. If more than one of these options is specified,
7585 the last one silently overrides the others.
7587 When copying to a symbolic link, @command{cp} follows the
7588 link only when it refers to an existing regular file.
7589 However, when copying to a dangling symbolic link, @command{cp}
7590 refuses by default, and fails with a diagnostic, since the operation
7591 is inherently dangerous. This behavior is contrary to historical
7592 practice and to @acronym{POSIX}.
7593 Set @env{POSIXLY_CORRECT} to make @command{cp} attempt to create
7594 the target of a dangling destination symlink, in spite of the possible risk.
7595 Also, when an option like
7596 @option{--backup} or @option{--link} acts to rename or remove the
7597 destination before copying, @command{cp} renames or removes the
7598 symbolic link rather than the file it points to.
7600 By default, @command{cp} copies the contents of special files only
7601 when not copying recursively. This default can be overridden with the
7602 @option{--copy-contents} option.
7604 @cindex self-backups
7605 @cindex backups, making only
7606 @command{cp} generally refuses to copy a file onto itself, with the
7607 following exception: if @option{--force --backup} is specified with
7608 @var{source} and @var{dest} identical, and referring to a regular file,
7609 @command{cp} will make a backup file, either regular or numbered, as
7610 specified in the usual ways (@pxref{Backup options}). This is useful when
7611 you simply want to make a backup of an existing file before changing it.
7613 The program accepts the following options. Also see @ref{Common options}.
7620 Preserve as much as possible of the structure and attributes of the
7621 original files in the copy (but do not attempt to preserve internal
7622 directory structure; i.e., @samp{ls -U} may list the entries in a copied
7623 directory in a different order).
7624 Try to preserve SELinux security context and extended attributes (xattr),
7625 but ignore any failure to do that and print no corresponding diagnostic.
7626 Equivalent to @option{-dR --preserve=all} with the reduced diagnostics.
7628 @itemx --attributes-only
7629 @opindex --attributes-only
7630 Preserve the specified attributes of the original files in the copy,
7631 but do not copy any data. See the @option{--preserve} option for
7632 controlling which attributes to copy.
7635 @itemx @w{@kbd{--backup}[=@var{method}]}
7638 @vindex VERSION_CONTROL
7639 @cindex backups, making
7640 @xref{Backup options}.
7641 Make a backup of each file that would otherwise be overwritten or removed.
7642 As a special case, @command{cp} makes a backup of @var{source} when the force
7643 and backup options are given and @var{source} and @var{dest} are the same
7644 name for an existing, regular file. One useful application of this
7645 combination of options is this tiny Bourne shell script:
7649 # Usage: backup FILE...
7650 # Create a @sc{gnu}-style backup of each listed FILE.
7652 cp --backup --force -- "$i" "$i"
7656 @item --copy-contents
7657 @cindex directories, copying recursively
7658 @cindex copying directories recursively
7659 @cindex recursively copying directories
7660 @cindex non-directories, copying as special files
7661 If copying recursively, copy the contents of any special files (e.g.,
7662 FIFOs and device files) as if they were regular files. This means
7663 trying to read the data in each source file and writing it to the
7664 destination. It is usually a mistake to use this option, as it
7665 normally has undesirable effects on special files like FIFOs and the
7666 ones typically found in the @file{/dev} directory. In most cases,
7667 @code{cp -R --copy-contents} will hang indefinitely trying to read
7668 from FIFOs and special files like @file{/dev/console}, and it will
7669 fill up your destination disk if you use it to copy @file{/dev/zero}.
7670 This option has no effect unless copying recursively, and it does not
7671 affect the copying of symbolic links.
7675 @cindex symbolic links, copying
7676 @cindex hard links, preserving
7677 Copy symbolic links as symbolic links rather than copying the files that
7678 they point to, and preserve hard links between source files in the copies.
7679 Equivalent to @option{--no-dereference --preserve=links}.
7685 When copying without this option and an existing destination file cannot
7686 be opened for writing, the copy fails. However, with @option{--force}),
7687 when a destination file cannot be opened, @command{cp} then removes it and
7688 tries to open it again. Contrast this behavior with that enabled by
7689 @option{--link} and @option{--symbolic-link}, whereby the destination file
7690 is never opened but rather is removed unconditionally. Also see the
7691 description of @option{--remove-destination}.
7693 This option is independent of the @option{--interactive} or
7694 @option{-i} option: neither cancels the effect of the other.
7696 This option is redundant if the @option{--no-clobber} or @option{-n} option is
7701 If a command line argument specifies a symbolic link, then copy the
7702 file it points to rather than the symbolic link itself. However,
7703 copy (preserving its nature) any symbolic link that is encountered
7704 via recursive traversal.
7707 @itemx --interactive
7709 @opindex --interactive
7710 When copying a file other than a directory, prompt whether to
7711 overwrite an existing destination file. The @option{-i} option overrides
7712 a previous @option{-n} option.
7718 Make hard links instead of copies of non-directories.
7721 @itemx --dereference
7723 @opindex --dereference
7724 Follow symbolic links when copying from them.
7725 With this option, @command{cp} cannot create a symbolic link.
7726 For example, a symlink (to regular file) in the source tree will be copied to
7727 a regular file in the destination tree.
7732 @opindex --no-clobber
7733 Do not overwrite an existing file. The @option{-n} option overrides a previous
7734 @option{-i} option. This option is mutually exclusive with @option{-b} or
7735 @option{--backup} option.
7738 @itemx --no-dereference
7740 @opindex --no-dereference
7741 @cindex symbolic links, copying
7742 Copy symbolic links as symbolic links rather than copying the files that
7743 they point to. This option affects only symbolic links in the source;
7744 symbolic links in the destination are always followed if possible.
7747 @itemx @w{@kbd{--preserve}[=@var{attribute_list}]}
7750 @cindex file information, preserving, extended attributes, xattr
7751 Preserve the specified attributes of the original files.
7752 If specified, the @var{attribute_list} must be a comma-separated list
7753 of one or more of the following strings:
7757 Preserve the file mode bits and access control lists.
7759 Preserve the owner and group. On most modern systems,
7760 only users with appropriate privileges may change the owner of a file,
7762 may preserve the group ownership of a file only if they happen to be
7763 a member of the desired group.
7765 Preserve the times of last access and last modification, when possible.
7766 On older systems, it is not possible to preserve these attributes
7767 when the affected file is a symbolic link.
7768 However, many systems now provide the @code{utimensat} function,
7769 which makes it possible even for symbolic links.
7771 Preserve in the destination files
7772 any links between corresponding source files.
7773 Note that with @option{-L} or @option{-H}, this option can convert
7774 symbolic links to hard links. For example,
7776 $ mkdir c; : > a; ln -s a b; cp -aH a b c; ls -i1 c
7781 Note the inputs: @file{b} is a symlink to regular file @file{a},
7782 yet the files in destination directory, @file{c/}, are hard-linked.
7783 Since @option{-a} implies @option{--preserve=links}, and since @option{-H}
7784 tells @command{cp} to dereference command line arguments, it sees two files
7785 with the same inode number, and preserves the perceived hard link.
7787 Here is a similar example that exercises @command{cp}'s @option{-L} option:
7789 $ mkdir b c; (cd b; : > a; ln -s a b); cp -aL b c; ls -i1 c/b
7795 Preserve SELinux security context of the file, or fail with full diagnostics.
7797 Preserve extended attributes of the file, or fail with full diagnostics.
7798 If @command{cp} is built without xattr support, ignore this option.
7799 If SELinux context, ACLs or Capabilities are implemented using xattrs,
7800 they are preserved by this option as well.
7802 Preserve all file attributes.
7803 Equivalent to specifying all of the above, but with the difference
7804 that failure to preserve SELinux security context or extended attributes
7805 does not change @command{cp}'s exit status. In contrast to @option{-a},
7806 all but @samp{Operation not supported} warnings are output.
7809 Using @option{--preserve} with no @var{attribute_list} is equivalent
7810 to @option{--preserve=mode,ownership,timestamps}.
7812 In the absence of this option, each destination file is created with the
7813 mode bits of the corresponding source file, minus the bits set in the
7814 umask and minus the set-user-ID and set-group-ID bits.
7815 @xref{File permissions}.
7817 @itemx @w{@kbd{--no-preserve}=@var{attribute_list}}
7818 @cindex file information, preserving
7819 Do not preserve the specified attributes. The @var{attribute_list}
7820 has the same form as for @option{--preserve}.
7824 @cindex parent directories and @command{cp}
7825 Form the name of each destination file by appending to the target
7826 directory a slash and the specified name of the source file. The last
7827 argument given to @command{cp} must be the name of an existing directory.
7828 For example, the command:
7831 cp --parents a/b/c existing_dir
7835 copies the file @file{a/b/c} to @file{existing_dir/a/b/c}, creating
7836 any missing intermediate directories.
7843 @opindex --recursive
7844 @cindex directories, copying recursively
7845 @cindex copying directories recursively
7846 @cindex recursively copying directories
7847 @cindex non-directories, copying as special files
7848 Copy directories recursively. By default, do not follow symbolic
7849 links in the source; see the @option{--archive} (@option{-a}), @option{-d},
7850 @option{--dereference} (@option{-L}), @option{--no-dereference}
7851 (@option{-P}), and @option{-H} options. Special files are copied by
7852 creating a destination file of the same type as the source; see the
7853 @option{--copy-contents} option. It is not portable to use
7854 @option{-r} to copy symbolic links or special files. On some
7855 non-@sc{gnu} systems, @option{-r} implies the equivalent of
7856 @option{-L} and @option{--copy-contents} for historical reasons.
7857 Also, it is not portable to use @option{-R} to copy symbolic links
7858 unless you also specify @option{-P}, as @acronym{POSIX} allows
7859 implementations that dereference symbolic links by default.
7861 @item --reflink[=@var{when}]
7862 @opindex --reflink[=@var{when}]
7865 @cindex copy on write
7866 Perform a lightweight, copy-on-write (COW) copy, if supported by the
7867 file system. Once it has succeeded, beware that the source and destination
7868 files share the same disk data blocks as long as they remain unmodified.
7869 Thus, if a disk I/O error affects data blocks of one of the files,
7870 the other suffers the same fate.
7872 The @var{when} value can be one of the following:
7876 The default behavior: if the copy-on-write operation is not supported
7877 then report the failure for each file and exit with a failure status.
7880 If the copy-on-write operation is not supported then fall back
7881 to the standard copy behaviour.
7884 This option is overridden by the @option{--link}, @option{--symbolic-link}
7885 and @option{--attributes-only} options, thus allowing it to be used
7886 to configure the default data copying behavior for @command{cp}.
7887 For example, with the following alias, @command{cp} will use the
7888 minimum amount of space supported by the file system.
7891 alias cp='cp --reflink=auto --sparse=always'
7894 @item --remove-destination
7895 @opindex --remove-destination
7896 Remove each existing destination file before attempting to open it
7897 (contrast with @option{-f} above).
7899 @item --sparse=@var{when}
7900 @opindex --sparse=@var{when}
7901 @cindex sparse files, copying
7902 @cindex holes, copying files with
7903 @findex read @r{system call, and holes}
7904 A @dfn{sparse file} contains @dfn{holes}---a sequence of zero bytes that
7905 does not occupy any physical disk blocks; the @samp{read} system call
7906 reads these as zeros. This can both save considerable disk space and
7907 increase speed, since many binary files contain lots of consecutive zero
7908 bytes. By default, @command{cp} detects holes in input source files via a crude
7909 heuristic and makes the corresponding output file sparse as well.
7910 Only regular files may be sparse.
7912 The @var{when} value can be one of the following:
7916 The default behavior: if the input file is sparse, attempt to make
7917 the output file sparse, too. However, if an output file exists but
7918 refers to a non-regular file, then do not attempt to make it sparse.
7921 For each sufficiently long sequence of zero bytes in the input file,
7922 attempt to create a corresponding hole in the output file, even if the
7923 input file does not appear to be sparse.
7924 This is useful when the input file resides on a file system
7925 that does not support sparse files
7926 (for example, @samp{efs} file systems in SGI IRIX 5.3 and earlier),
7927 but the output file is on a type of file system that does support them.
7928 Holes may be created only in regular files, so if the destination file
7929 is of some other type, @command{cp} does not even try to make it sparse.
7932 Never make the output file sparse.
7933 This is useful in creating a file for use with the @command{mkswap} command,
7934 since such a file must not have any holes.
7937 @optStripTrailingSlashes
7940 @itemx --symbolic-link
7942 @opindex --symbolic-link
7943 @cindex symbolic links, copying with
7944 Make symbolic links instead of copies of non-directories. All source
7945 file names must be absolute (starting with @samp{/}) unless the
7946 destination files are in the current directory. This option merely
7947 results in an error message on systems that do not support symbolic links.
7953 @optNoTargetDirectory
7959 @cindex newer files, copying only
7960 Do not copy a non-directory that has an existing destination with the
7961 same or newer modification time. If time stamps are being preserved,
7962 the comparison is to the source time stamp truncated to the
7963 resolutions of the destination file system and of the system calls
7964 used to update time stamps; this avoids duplicate work if several
7965 @samp{cp -pu} commands are executed with the same source and destination.
7966 If @option{--preserve=links} is also specified (like with @samp{cp -au}
7967 for example), that will take precedence. Consequently, depending on the
7968 order that files are processed from the source, newer files in the destination
7969 may be replaced, to mirror hard links in the source.
7975 Print the name of each file before copying it.
7978 @itemx --one-file-system
7980 @opindex --one-file-system
7981 @cindex file systems, omitting copying to different
7982 Skip subdirectories that are on different file systems from the one that
7983 the copy started on.
7984 However, mount point directories @emph{are} copied.
7992 @section @command{dd}: Convert and copy a file
7995 @cindex converting while copying a file
7997 @command{dd} copies a file (from standard input to standard output, by
7998 default) with a changeable I/O block size, while optionally performing
7999 conversions on it. Synopses:
8002 dd [@var{operand}]@dots{}
8006 The only options are @option{--help} and @option{--version}.
8007 @xref{Common options}. @command{dd} accepts the following operands.
8013 Read from @var{file} instead of standard input.
8017 Write to @var{file} instead of standard output. Unless
8018 @samp{conv=notrunc} is given, @command{dd} truncates @var{file} to zero
8019 bytes (or the size specified with @samp{seek=}).
8021 @item ibs=@var{bytes}
8023 @cindex block size of input
8024 @cindex input block size
8025 Set the input block size to @var{bytes}.
8026 This makes @command{dd} read @var{bytes} per block.
8027 The default is 512 bytes.
8029 @item obs=@var{bytes}
8031 @cindex block size of output
8032 @cindex output block size
8033 Set the output block size to @var{bytes}.
8034 This makes @command{dd} write @var{bytes} per block.
8035 The default is 512 bytes.
8037 @item bs=@var{bytes}
8040 Set both input and output block sizes to @var{bytes}.
8041 This makes @command{dd} read and write @var{bytes} per block,
8042 overriding any @samp{ibs} and @samp{obs} settings.
8043 In addition, if no data-transforming @option{conv} option is specified,
8044 input is copied to the output as soon as it's read,
8045 even if it is smaller than the block size.
8047 @item cbs=@var{bytes}
8049 @cindex block size of conversion
8050 @cindex conversion block size
8051 @cindex fixed-length records, converting to variable-length
8052 @cindex variable-length records, converting to fixed-length
8053 Set the conversion block size to @var{bytes}.
8054 When converting variable-length records to fixed-length ones
8055 (@option{conv=block}) or the reverse (@option{conv=unblock}),
8056 use @var{bytes} as the fixed record length.
8058 @item skip=@var{blocks}
8060 Skip @var{blocks} @samp{ibs}-byte blocks in the input file before copying.
8062 @item seek=@var{blocks}
8064 Skip @var{blocks} @samp{obs}-byte blocks in the output file before copying.
8066 @item count=@var{blocks}
8068 Copy @var{blocks} @samp{ibs}-byte blocks from the input file, instead
8069 of everything until the end of the file.
8073 Do not print the overall transfer rate and volume statistics
8074 that normally make up the third status line when @command{dd} exits.
8076 @item conv=@var{conversion}[,@var{conversion}]@dots{}
8078 Convert the file as specified by the @var{conversion} argument(s).
8079 (No spaces around any comma(s).)
8086 @opindex ascii@r{, converting to}
8087 Convert @acronym{EBCDIC} to @acronym{ASCII},
8088 using the conversion table specified by @acronym{POSIX}.
8089 This provides a 1:1 translation for all 256 bytes.
8092 @opindex ebcdic@r{, converting to}
8093 Convert @acronym{ASCII} to @acronym{EBCDIC}.
8094 This is the inverse of the @samp{ascii} conversion.
8097 @opindex alternate ebcdic@r{, converting to}
8098 Convert @acronym{ASCII} to alternate @acronym{EBCDIC},
8099 using the alternate conversion table specified by @acronym{POSIX}.
8100 This is not a 1:1 translation, but reflects common historical practice
8101 for @samp{~}, @samp{[}, and @samp{]}.
8103 The @samp{ascii}, @samp{ebcdic}, and @samp{ibm} conversions are
8107 @opindex block @r{(space-padding)}
8108 For each line in the input, output @samp{cbs} bytes, replacing the
8109 input newline with a space and padding with spaces as necessary.
8113 Remove any trailing spaces in each @samp{cbs}-sized input block,
8114 and append a newline.
8116 The @samp{block} and @samp{unblock} conversions are mutually exclusive.
8119 @opindex lcase@r{, converting to}
8120 Change uppercase letters to lowercase.
8123 @opindex ucase@r{, converting to}
8124 Change lowercase letters to uppercase.
8126 The @samp{lcase} and @samp{ucase} conversions are mutually exclusive.
8129 @opindex swab @r{(byte-swapping)}
8130 @cindex byte-swapping
8131 Swap every pair of input bytes. @sc{gnu} @command{dd}, unlike others, works
8132 when an odd number of bytes are read---the last byte is simply copied
8133 (since there is nothing to swap it with).
8136 @opindex sync @r{(padding with @acronym{ASCII} @sc{nul}s)}
8137 Pad every input block to size of @samp{ibs} with trailing zero bytes.
8138 When used with @samp{block} or @samp{unblock}, pad with spaces instead of
8143 The following ``conversions'' are really file flags
8144 and don't affect internal processing:
8149 @cindex creating output file, requiring
8150 Fail if the output file already exists; @command{dd} must create the
8155 @cindex creating output file, avoiding
8156 Do not create the output file; the output file must already exist.
8158 The @samp{excl} and @samp{nocreat} conversions are mutually exclusive.
8162 @cindex truncating output file, avoiding
8163 Do not truncate the output file.
8167 @cindex read errors, ignoring
8168 Continue after read errors.
8172 @cindex synchronized data writes, before finishing
8173 Synchronize output data just before finishing. This forces a physical
8174 write of output data.
8178 @cindex synchronized data and metadata writes, before finishing
8179 Synchronize output data and metadata just before finishing. This
8180 forces a physical write of output data and metadata.
8184 @item iflag=@var{flag}[,@var{flag}]@dots{}
8186 Access the input file using the flags specified by the @var{flag}
8187 argument(s). (No spaces around any comma(s).)
8189 @item oflag=@var{flag}[,@var{flag}]@dots{}
8191 Access the output file using the flags specified by the @var{flag}
8192 argument(s). (No spaces around any comma(s).)
8194 Here are the flags. Not every flag is supported on every operating
8201 @cindex appending to the output file
8202 Write in append mode, so that even if some other process is writing to
8203 this file, every @command{dd} write will append to the current
8204 contents of the file. This flag makes sense only for output.
8205 If you combine this flag with the @samp{of=@var{file}} operand,
8206 you should also specify @samp{conv=notrunc} unless you want the
8207 output file to be truncated before being appended to.
8211 @cindex concurrent I/O
8212 Use concurrent I/O mode for data. This mode performs direct I/O
8213 and drops the @acronym{POSIX} requirement to serialize all I/O to the same file.
8214 A file cannot be opened in CIO mode and with a standard open at the
8220 Use direct I/O for data, avoiding the buffer cache.
8221 Note that the kernel may impose restrictions on read or write buffer sizes.
8222 For example, with an ext4 destination file system and a linux-based kernel,
8223 using @samp{oflag=direct} will cause writes to fail with @code{EINVAL} if the
8224 output buffer size is not a multiple of 512.
8228 @cindex directory I/O
8230 Fail unless the file is a directory. Most operating systems do not
8231 allow I/O to a directory, so this flag has limited utility.
8235 @cindex synchronized data reads
8236 Use synchronized I/O for data. For the output file, this forces a
8237 physical write of output data on each write. For the input file,
8238 this flag can matter when reading from a remote file that has been
8239 written to synchronously by some other process. Metadata (e.g.,
8240 last-access and last-modified time) is not necessarily synchronized.
8244 @cindex synchronized data and metadata I/O
8245 Use synchronized I/O for both data and metadata.
8249 @cindex discarding file cache
8250 Discard the data cache for a file.
8251 When count=0 all cache is discarded,
8252 otherwise the cache is dropped for the processed
8253 portion of the file. Also when count=0
8254 failure to discard the cache is diagnosed
8255 and reflected in the exit status.
8256 Here as some usage examples:
8259 # Advise to drop cache for whole file
8260 dd if=ifile iflag=nocache count=0
8262 # Ensure drop cache for the whole file
8263 dd of=ofile oflag=nocache conv=notrunc,fdatasync count=0
8265 # Drop cache for part of file
8266 dd if=ifile iflag=nocache skip=10 count=10 of=/dev/null
8268 # Stream data using just the read-ahead cache
8269 dd if=ifile of=ofile iflag=nocache oflag=nocache
8274 @cindex nonblocking I/O
8275 Use non-blocking I/O.
8280 Do not update the file's access time.
8281 Some older file systems silently ignore this flag, so it is a good
8282 idea to test it on your files before relying on it.
8286 @cindex controlling terminal
8287 Do not assign the file to be a controlling terminal for @command{dd}.
8288 This has no effect when the file is not a terminal.
8289 On many hosts (e.g., @acronym{GNU}/Linux hosts), this option has no effect
8294 @cindex symbolic links, following
8295 Do not follow symbolic links.
8300 Fail if the file has multiple hard links.
8305 Use binary I/O. This option has an effect only on nonstandard
8306 platforms that distinguish binary from text I/O.
8311 Use text I/O. Like @samp{binary}, this option has no effect on
8316 Accumulate full blocks from input. The @code{read} system call
8317 may return early if a full block is not available.
8318 When that happens, continue calling @code{read} to fill the remainder
8320 This flag can be used only with @code{iflag}.
8324 These flags are not supported on all systems, and @samp{dd} rejects
8325 attempts to use them when they are not supported. When reading from
8326 standard input or writing to standard output, the @samp{nofollow} and
8327 @samp{noctty} flags should not be specified, and the other flags
8328 (e.g., @samp{nonblock}) can affect how other processes behave with the
8329 affected file descriptors, even after @command{dd} exits.
8333 @cindex multipliers after numbers
8334 The numeric-valued strings above (@var{bytes} and @var{blocks}) can be
8335 followed by a multiplier: @samp{b}=512, @samp{c}=1,
8336 @samp{w}=2, @samp{x@var{m}}=@var{m}, or any of the
8337 standard block size suffixes like @samp{k}=1024 (@pxref{Block size}).
8339 Any block size you specify via @samp{bs=}, @samp{ibs=}, @samp{obs=}, @samp{cbs=}
8340 should not be too large---values larger than a few megabytes
8341 are generally wasteful or (as in the gigabyte..exabyte case) downright
8342 counterproductive or error-inducing.
8344 Use different @command{dd} invocations to use different block sizes for
8345 skipping and I/O@. For example, the following shell commands copy data
8346 in 512 KiB blocks between a disk and a tape, but do not save or restore a
8347 4 KiB label at the start of the disk:
8350 disk=/dev/rdsk/c0t1d0s2
8353 # Copy all but the label from disk to tape.
8354 (dd bs=4k skip=1 count=0 && dd bs=512k) <$disk >$tape
8356 # Copy from tape back to disk, but leave the disk label alone.
8357 (dd bs=4k seek=1 count=0 && dd bs=512k) <$tape >$disk
8360 Sending an @samp{INFO} signal to a running @command{dd}
8361 process makes it print I/O statistics to standard error
8362 and then resume copying. In the example below,
8363 @command{dd} is run in the background to copy 10 million blocks.
8364 The @command{kill} command makes it output intermediate I/O statistics,
8365 and when @command{dd} completes normally or is killed by the
8366 @code{SIGINT} signal, it outputs the final statistics.
8369 $ dd if=/dev/zero of=/dev/null count=10MB & pid=$!
8370 $ kill -s INFO $pid; wait $pid
8371 3385223+0 records in
8372 3385223+0 records out
8373 1733234176 bytes (1.7 GB) copied, 6.42173 seconds, 270 MB/s
8374 10000000+0 records in
8375 10000000+0 records out
8376 5120000000 bytes (5.1 GB) copied, 18.913 seconds, 271 MB/s
8379 @vindex POSIXLY_CORRECT
8380 On systems lacking the @samp{INFO} signal @command{dd} responds to the
8381 @samp{USR1} signal instead, unless the @env{POSIXLY_CORRECT}
8382 environment variable is set.
8387 @node install invocation
8388 @section @command{install}: Copy files and set attributes
8391 @cindex copying files and setting attributes
8393 @command{install} copies files while setting their file mode bits and, if
8394 possible, their owner and group. Synopses:
8397 install [@var{option}]@dots{} [-T] @var{source} @var{dest}
8398 install [@var{option}]@dots{} @var{source}@dots{} @var{directory}
8399 install [@var{option}]@dots{} -t @var{directory} @var{source}@dots{}
8400 install [@var{option}]@dots{} -d @var{directory}@dots{}
8405 If two file names are given, @command{install} copies the first file to the
8409 If the @option{--target-directory} (@option{-t}) option is given, or
8410 failing that if the last file is a directory and the
8411 @option{--no-target-directory} (@option{-T}) option is not given,
8412 @command{install} copies each @var{source} file to the specified
8413 directory, using the @var{source}s' names.
8416 If the @option{--directory} (@option{-d}) option is given,
8417 @command{install} creates each @var{directory} and any missing parent
8418 directories. Parent directories are created with mode
8419 @samp{u=rwx,go=rx} (755), regardless of the @option{-m} option or the
8420 current umask. @xref{Directory Setuid and Setgid}, for how the
8421 set-user-ID and set-group-ID bits of parent directories are inherited.
8424 @cindex Makefiles, installing programs in
8425 @command{install} is similar to @command{cp}, but allows you to control the
8426 attributes of destination files. It is typically used in Makefiles to
8427 copy programs into their destination directories. It refuses to copy
8428 files onto themselves.
8430 @cindex extended attributes, xattr
8431 @command{install} never preserves extended attributes (xattr).
8433 The program accepts the following options. Also see @ref{Common options}.
8443 Compare each pair of source and destination files, and if the destination has
8444 identical content and any specified owner, group, permissions, and possibly
8445 SELinux context, then do not modify the destination at all.
8449 Ignored; for compatibility with old Unix versions of @command{install}.
8453 Create any missing parent directories of @var{dest},
8454 then copy @var{source} to @var{dest}.
8455 This option is ignored if a destination directory is specified
8456 via @option{--target-directory=DIR}.
8461 @opindex --directory
8462 @cindex directories, creating with given attributes
8463 @cindex parent directories, creating missing
8464 @cindex leading directories, creating missing
8465 Create any missing parent directories, giving them the default
8466 attributes. Then create each given directory, setting their owner,
8467 group and mode as given on the command line or to the defaults.
8469 @item -g @var{group}
8470 @itemx --group=@var{group}
8473 @cindex group ownership of installed files, setting
8474 Set the group ownership of installed files or directories to
8475 @var{group}. The default is the process's current group. @var{group}
8476 may be either a group name or a numeric group ID.
8479 @itemx --mode=@var{mode}
8482 @cindex permissions of installed files, setting
8483 Set the file mode bits for the installed file or directory to @var{mode},
8484 which can be either an octal number, or a symbolic mode as in
8485 @command{chmod}, with @samp{a=} (no access allowed to anyone) as the
8486 point of departure (@pxref{File permissions}).
8487 The default mode is @samp{u=rwx,go=rx,a-s}---read, write, and
8488 execute for the owner, read and execute for group and other, and with
8489 set-user-ID and set-group-ID disabled.
8490 This default is not quite the same as @samp{755}, since it disables
8491 instead of preserving set-user-ID and set-group-ID on directories.
8492 @xref{Directory Setuid and Setgid}.
8494 @item -o @var{owner}
8495 @itemx --owner=@var{owner}
8498 @cindex ownership of installed files, setting
8499 @cindex appropriate privileges
8500 @vindex root @r{as default owner}
8501 If @command{install} has appropriate privileges (is run as root), set the
8502 ownership of installed files or directories to @var{owner}. The default
8503 is @code{root}. @var{owner} may be either a user name or a numeric user
8506 @item --preserve-context
8507 @opindex --preserve-context
8509 @cindex security context
8510 Preserve the SELinux security context of files and directories.
8511 Failure to preserve the context in all of the files or directories
8512 will result in an exit status of 1. If SELinux is disabled then
8513 print a warning and ignore the option.
8516 @itemx --preserve-timestamps
8518 @opindex --preserve-timestamps
8519 @cindex timestamps of installed files, preserving
8520 Set the time of last access and the time of last modification of each
8521 installed file to match those of each corresponding original file.
8522 When a file is installed without this option, its last access and
8523 last modification times are both set to the time of installation.
8524 This option is useful if you want to use the last modification times
8525 of installed files to keep track of when they were last built as opposed
8526 to when they were last installed.
8532 @cindex symbol table information, stripping
8533 @cindex stripping symbol table information
8534 Strip the symbol tables from installed binary executables.
8536 @itemx --strip-program=@var{program}
8537 @opindex --strip-program
8538 @cindex symbol table information, stripping, program
8539 Program used to strip binaries.
8545 @optNoTargetDirectory
8551 Print the name of each file before copying it.
8553 @item -Z @var{context}
8554 @itemx --context=@var{context}
8558 @cindex security context
8559 Set the default SELinux security context to be used for any
8560 created files and directories. If SELinux is disabled then
8561 print a warning and ignore the option.
8569 @section @command{mv}: Move (rename) files
8573 @command{mv} moves or renames files (or directories). Synopses:
8576 mv [@var{option}]@dots{} [-T] @var{source} @var{dest}
8577 mv [@var{option}]@dots{} @var{source}@dots{} @var{directory}
8578 mv [@var{option}]@dots{} -t @var{directory} @var{source}@dots{}
8583 If two file names are given, @command{mv} moves the first file to the
8587 If the @option{--target-directory} (@option{-t}) option is given, or
8588 failing that if the last file is a directory and the
8589 @option{--no-target-directory} (@option{-T}) option is not given,
8590 @command{mv} moves each @var{source} file to the specified
8591 directory, using the @var{source}s' names.
8594 @command{mv} can move any type of file from one file system to another.
8595 Prior to version @code{4.0} of the fileutils,
8596 @command{mv} could move only regular files between file systems.
8597 For example, now @command{mv} can move an entire directory hierarchy
8598 including special device files from one partition to another. It first
8599 uses some of the same code that's used by @code{cp -a} to copy the
8600 requested directories and files, then (assuming the copy succeeded)
8601 it removes the originals. If the copy fails, then the part that was
8602 copied to the destination partition is removed. If you were to copy
8603 three directories from one partition to another and the copy of the first
8604 directory succeeded, but the second didn't, the first would be left on
8605 the destination partition and the second and third would be left on the
8608 @cindex extended attributes, xattr
8609 @command{mv} always tries to copy extended attributes (xattr), which may
8610 include SELinux context, ACLs or Capabilities.
8611 Upon failure all but @samp{Operation not supported} warnings are output.
8613 @cindex prompting, and @command{mv}
8614 If a destination file exists but is normally unwritable, standard input
8615 is a terminal, and the @option{-f} or @option{--force} option is not given,
8616 @command{mv} prompts the user for whether to replace the file. (You might
8617 own the file, or have write permission on its directory.) If the
8618 response is not affirmative, the file is skipped.
8620 @emph{Warning}: Avoid specifying a source name with a trailing slash,
8621 when it might be a symlink to a directory.
8622 Otherwise, @command{mv} may do something very surprising, since
8623 its behavior depends on the underlying rename system call.
8624 On a system with a modern Linux-based kernel, it fails with
8625 @code{errno=ENOTDIR}.
8626 However, on other systems (at least FreeBSD 6.1 and Solaris 10) it silently
8627 renames not the symlink but rather the directory referenced by the symlink.
8628 @xref{Trailing slashes}.
8630 The program accepts the following options. Also see @ref{Common options}.
8640 @cindex prompts, omitting
8641 Do not prompt the user before removing a destination file.
8643 If you specify more than one of the @option{-i}, @option{-f}, @option{-n}
8644 options, only the final one takes effect.
8649 @itemx --interactive
8651 @opindex --interactive
8652 @cindex prompts, forcing
8653 Prompt whether to overwrite each existing destination file, regardless
8655 If the response is not affirmative, the file is skipped.
8661 @opindex --no-clobber
8662 @cindex prompts, omitting
8663 Do not overwrite an existing file.
8665 This option is mutually exclusive with @option{-b} or @option{--backup} option.
8671 @cindex newer files, moving only
8672 Do not move a non-directory that has an existing destination with the
8673 same or newer modification time.
8674 If the move is across file system boundaries, the comparison is to the
8675 source time stamp truncated to the resolutions of the destination file
8676 system and of the system calls used to update time stamps; this avoids
8677 duplicate work if several @samp{mv -u} commands are executed with the
8678 same source and destination.
8684 Print the name of each file before moving it.
8686 @optStripTrailingSlashes
8692 @optNoTargetDirectory
8700 @section @command{rm}: Remove files or directories
8703 @cindex removing files or directories
8705 @command{rm} removes each given @var{file}. By default, it does not remove
8706 directories. Synopsis:
8709 rm [@var{option}]@dots{} [@var{file}]@dots{}
8712 @cindex prompting, and @command{rm}
8713 If the @option{-I} or @option{--interactive=once} option is given,
8714 and there are more than three files or the @option{-r}, @option{-R},
8715 or @option{--recursive} are given, then @command{rm} prompts the user
8716 for whether to proceed with the entire operation. If the response is
8717 not affirmative, the entire command is aborted.
8719 Otherwise, if a file is unwritable, standard input is a terminal, and
8720 the @option{-f} or @option{--force} option is not given, or the
8721 @option{-i} or @option{--interactive=always} option @emph{is} given,
8722 @command{rm} prompts the user for whether to remove the file.
8723 If the response is not affirmative, the file is skipped.
8725 Any attempt to remove a file whose last file name component is
8726 @file{.} or @file{..} is rejected without any prompting.
8728 @emph{Warning}: If you use @command{rm} to remove a file, it is usually
8729 possible to recover the contents of that file. If you want more assurance
8730 that the contents are truly unrecoverable, consider using @command{shred}.
8732 The program accepts the following options. Also see @ref{Common options}.
8740 Ignore nonexistent files and never prompt the user.
8741 Ignore any previous @option{--interactive} (@option{-i}) option.
8745 Prompt whether to remove each file.
8746 If the response is not affirmative, the file is skipped.
8747 Ignore any previous @option{--force} (@option{-f}) option.
8748 Equivalent to @option{--interactive=always}.
8752 Prompt once whether to proceed with the command, if more than three
8753 files are named or if a recursive removal is requested. Ignore any
8754 previous @option{--force} (@option{-f}) option. Equivalent to
8755 @option{--interactive=once}.
8757 @itemx --interactive [=@var{when}]
8758 @opindex --interactive
8759 Specify when to issue an interactive prompt. @var{when} may be
8763 @vindex never @r{interactive option}
8764 - Do not prompt at all.
8766 @vindex once @r{interactive option}
8767 - Prompt once if more than three files are named or if a recursive
8768 removal is requested. Equivalent to @option{-I}.
8770 @vindex always @r{interactive option}
8771 - Prompt for every file being removed. Equivalent to @option{-i}.
8773 @option{--interactive} with no @var{when} is equivalent to
8774 @option{--interactive=always}.
8776 @itemx --one-file-system
8777 @opindex --one-file-system
8778 @cindex one file system, restricting @command{rm} to
8779 When removing a hierarchy recursively, skip any directory that is on a
8780 file system different from that of the corresponding command line argument.
8783 This option is useful when removing a build ``chroot'' hierarchy,
8784 which normally contains no valuable data. However, it is not uncommon
8785 to bind-mount @file{/home} into such a hierarchy, to make it easier to
8786 use one's start-up file. The catch is that it's easy to forget to
8787 unmount @file{/home}. Then, when you use @command{rm -rf} to remove
8788 your normally throw-away chroot, that command will remove everything
8789 under @file{/home}, too.
8790 Use the @option{--one-file-system} option, and it will
8791 warn about and skip directories on other file systems.
8792 Of course, this will not save your @file{/home} if it and your
8793 chroot happen to be on the same file system.
8795 @itemx --preserve-root
8796 @opindex --preserve-root
8797 @cindex root directory, disallow recursive destruction
8798 Fail upon any attempt to remove the root directory, @file{/},
8799 when used with the @option{--recursive} option.
8800 This is the default behavior.
8801 @xref{Treating / specially}.
8803 @itemx --no-preserve-root
8804 @opindex --no-preserve-root
8805 @cindex root directory, allow recursive destruction
8806 Do not treat @file{/} specially when removing recursively.
8807 This option is not recommended unless you really want to
8808 remove all the files on your computer.
8809 @xref{Treating / specially}.
8816 @opindex --recursive
8817 @cindex directories, removing (recursively)
8818 Remove the listed directories and their contents recursively.
8824 Print the name of each file before removing it.
8828 @cindex files beginning with @samp{-}, removing
8829 @cindex @samp{-}, removing files beginning with
8830 One common question is how to remove files whose names begin with a
8831 @samp{-}. @sc{gnu} @command{rm}, like every program that uses the @code{getopt}
8832 function to parse its arguments, lets you use the @samp{--} option to
8833 indicate that all following arguments are non-options. To remove a file
8834 called @file{-f} in the current directory, you could type either:
8847 @opindex - @r{and Unix @command{rm}}
8848 The Unix @command{rm} program's use of a single @samp{-} for this purpose
8849 predates the development of the getopt standard syntax.
8854 @node shred invocation
8855 @section @command{shred}: Remove files more securely
8858 @cindex data, erasing
8859 @cindex erasing data
8861 @command{shred} overwrites devices or files, to help prevent even
8862 very expensive hardware from recovering the data.
8864 Ordinarily when you remove a file (@pxref{rm invocation}), the data is
8865 not actually destroyed. Only the index listing where the file is
8866 stored is destroyed, and the storage is made available for reuse.
8867 There are undelete utilities that will attempt to reconstruct the index
8868 and can bring the file back if the parts were not reused.
8870 On a busy system with a nearly-full drive, space can get reused in a few
8871 seconds. But there is no way to know for sure. If you have sensitive
8872 data, you may want to be sure that recovery is not possible by actually
8873 overwriting the file with non-sensitive data.
8875 However, even after doing that, it is possible to take the disk back
8876 to a laboratory and use a lot of sensitive (and expensive) equipment
8877 to look for the faint ``echoes'' of the original data underneath the
8878 overwritten data. If the data has only been overwritten once, it's not
8881 The best way to remove something irretrievably is to destroy the media
8882 it's on with acid, melt it down, or the like. For cheap removable media
8883 like floppy disks, this is the preferred method. However, hard drives
8884 are expensive and hard to melt, so the @command{shred} utility tries
8885 to achieve a similar effect non-destructively.
8887 This uses many overwrite passes, with the data patterns chosen to
8888 maximize the damage they do to the old data. While this will work on
8889 floppies, the patterns are designed for best effect on hard drives.
8890 For more details, see the source code and Peter Gutmann's paper
8891 @uref{http://www.cs.auckland.ac.nz/~pgut001/pubs/secure_del.html,
8892 @cite{Secure Deletion of Data from Magnetic and Solid-State Memory}},
8893 from the proceedings of the Sixth @acronym{USENIX} Security Symposium (San Jose,
8894 California, July 22--25, 1996).
8896 @strong{Please note} that @command{shred} relies on a very important assumption:
8897 that the file system overwrites data in place. This is the traditional
8898 way to do things, but many modern file system designs do not satisfy this
8899 assumption. Exceptions include:
8904 Log-structured or journaled file systems, such as those supplied with
8905 AIX and Solaris, and JFS, ReiserFS, XFS, Ext3 (in @code{data=journal} mode),
8906 BFS, NTFS, etc.@: when they are configured to journal @emph{data}.
8909 File systems that write redundant data and carry on even if some writes
8910 fail, such as RAID-based file systems.
8913 File systems that make snapshots, such as Network Appliance's NFS server.
8916 File systems that cache in temporary locations, such as NFS version 3
8920 Compressed file systems.
8923 In the particular case of ext3 file systems, the above disclaimer applies (and
8924 @command{shred} is thus of limited effectiveness) only in @code{data=journal}
8925 mode, which journals file data in addition to just metadata. In both
8926 the @code{data=ordered} (default) and @code{data=writeback} modes,
8927 @command{shred} works as usual. Ext3 journaling modes can be changed
8928 by adding the @code{data=something} option to the mount options for a
8929 particular file system in the @file{/etc/fstab} file, as documented in
8930 the mount man page (man mount).
8932 If you are not sure how your file system operates, then you should assume
8933 that it does not overwrite data in place, which means that shred cannot
8934 reliably operate on regular files in your file system.
8936 Generally speaking, it is more reliable to shred a device than a file,
8937 since this bypasses the problem of file system design mentioned above.
8938 However, even shredding devices is not always completely reliable. For
8939 example, most disks map out bad sectors invisibly to the application; if
8940 the bad sectors contain sensitive data, @command{shred} won't be able to
8943 @command{shred} makes no attempt to detect or report this problem, just as
8944 it makes no attempt to do anything about backups. However, since it is
8945 more reliable to shred devices than files, @command{shred} by default does
8946 not truncate or remove the output file. This default is more suitable
8947 for devices, which typically cannot be truncated and should not be
8950 Finally, consider the risk of backups and mirrors.
8951 File system backups and remote mirrors may contain copies of the
8952 file that cannot be removed, and that will allow a shredded file
8953 to be recovered later. So if you keep any data you may later want
8954 to destroy using @command{shred}, be sure that it is not backed up or mirrored.
8957 shred [@var{option}]@dots{} @var{file}[@dots{}]
8960 The program accepts the following options. Also see @ref{Common options}.
8968 @cindex force deletion
8969 Override file permissions if necessary to allow overwriting.
8972 @itemx -n @var{number}
8973 @itemx --iterations=@var{number}
8974 @opindex -n @var{number}
8975 @opindex --iterations=@var{number}
8976 @cindex iterations, selecting the number of
8977 By default, @command{shred} uses @value{SHRED_DEFAULT_PASSES} passes of
8978 overwrite. You can reduce this to save time, or increase it if you think it's
8979 appropriate. After 25 passes all of the internal overwrite patterns will have
8980 been used at least once.
8982 @item --random-source=@var{file}
8983 @opindex --random-source
8984 @cindex random source for shredding
8985 Use @var{file} as a source of random data used to overwrite and to
8986 choose pass ordering. @xref{Random sources}.
8988 @item -s @var{bytes}
8989 @itemx --size=@var{bytes}
8990 @opindex -s @var{bytes}
8991 @opindex --size=@var{bytes}
8992 @cindex size of file to shred
8993 Shred the first @var{bytes} bytes of the file. The default is to shred
8994 the whole file. @var{bytes} can be followed by a size specification like
8995 @samp{K}, @samp{M}, or @samp{G} to specify a multiple. @xref{Block size}.
9001 @cindex removing files after shredding
9002 After shredding a file, truncate it (if possible) and then remove it.
9003 If a file has multiple links, only the named links will be removed.
9009 Display to standard error all status updates as sterilization proceeds.
9015 By default, @command{shred} rounds the size of a regular file up to the next
9016 multiple of the file system block size to fully erase the last block
9018 Use @option{--exact} to suppress that behavior.
9019 Thus, by default if you shred a 10-byte regular file on a system with 512-byte
9020 blocks, the resulting file will be 512 bytes long. With this option,
9021 shred does not increase the apparent size of the file.
9027 Normally, the last pass that @command{shred} writes is made up of
9028 random data. If this would be conspicuous on your hard drive (for
9029 example, because it looks like encrypted data), or you just think
9030 it's tidier, the @option{--zero} option adds an additional overwrite pass with
9031 all zero bits. This is in addition to the number of passes specified
9032 by the @option{--iterations} option.
9036 You might use the following command to erase all trace of the
9037 file system you'd created on the floppy disk in your first drive.
9038 That command takes about 20 minutes to erase a ``1.44MB'' (actually
9042 shred --verbose /dev/fd0
9045 Similarly, to erase all data on a selected partition of
9046 your hard disk, you could give a command like this:
9049 shred --verbose /dev/sda5
9052 On modern disks, a single pass should be adequate,
9053 and it will take one third the time of the default three-pass approach.
9056 # 1 pass, write pseudo-random data; 3x faster than the default
9057 shred --verbose -n1 /dev/sda5
9060 To be on the safe side, use at least one pass that overwrites using
9061 pseudo-random data. I.e., don't be tempted to use @samp{-n0 --zero},
9062 in case some disk controller optimizes the process of writing blocks
9063 of all zeros, and thereby does not clear all bytes in a block.
9064 Some SSDs may do just that.
9066 A @var{file} of @samp{-} denotes standard output.
9067 The intended use of this is to shred a removed temporary file.
9074 echo "Hello, world" >&3
9079 However, the command @samp{shred - >file} does not shred the contents
9080 of @var{file}, since the shell truncates @var{file} before invoking
9081 @command{shred}. Use the command @samp{shred file} or (if using a
9082 Bourne-compatible shell) the command @samp{shred - 1<>file} instead.
9087 @node Special file types
9088 @chapter Special file types
9090 @cindex special file types
9091 @cindex file types, special
9093 This chapter describes commands which create special types of files (and
9094 @command{rmdir}, which removes directories, one special file type).
9096 @cindex special file types
9098 Although Unix-like operating systems have markedly fewer special file
9099 types than others, not @emph{everything} can be treated only as the
9100 undifferentiated byte stream of @dfn{normal files}. For example, when a
9101 file is created or removed, the system must record this information,
9102 which it does in a @dfn{directory}---a special type of file. Although
9103 you can read directories as normal files, if you're curious, in order
9104 for the system to do its job it must impose a structure, a certain
9105 order, on the bytes of the file. Thus it is a ``special'' type of file.
9107 Besides directories, other special file types include named pipes
9108 (FIFOs), symbolic links, sockets, and so-called @dfn{special files}.
9111 * link invocation:: Make a hard link via the link syscall
9112 * ln invocation:: Make links between files.
9113 * mkdir invocation:: Make directories.
9114 * mkfifo invocation:: Make FIFOs (named pipes).
9115 * mknod invocation:: Make block or character special files.
9116 * readlink invocation:: Print value of a symlink or canonical file name.
9117 * rmdir invocation:: Remove empty directories.
9118 * unlink invocation:: Remove files via the unlink syscall
9122 @node link invocation
9123 @section @command{link}: Make a hard link via the link syscall
9126 @cindex links, creating
9127 @cindex hard links, creating
9128 @cindex creating links (hard only)
9130 @command{link} creates a single hard link at a time.
9131 It is a minimalist interface to the system-provided
9132 @code{link} function. @xref{Hard Links, , , libc,
9133 The GNU C Library Reference Manual}.
9134 It avoids the bells and whistles of the more commonly-used
9135 @command{ln} command (@pxref{ln invocation}).
9139 link @var{filename} @var{linkname}
9142 @var{filename} must specify an existing file, and @var{linkname}
9143 must specify a nonexistent entry in an existing directory.
9144 @command{link} simply calls @code{link (@var{filename}, @var{linkname})}
9147 On a @acronym{GNU} system, this command acts like @samp{ln --directory
9148 --no-target-directory @var{filename} @var{linkname}}. However, the
9149 @option{--directory} and @option{--no-target-directory} options are
9150 not specified by @acronym{POSIX}, and the @command{link} command is
9151 more portable in practice.
9153 If @var{filename} is a symbolic link, it is unspecified whether
9154 @var{linkname} will be a hard link to the symbolic link or to the
9155 target of the symbolic link. Use @command{ln -P} or @command{ln -L}
9156 to specify which behavior is desired.
9162 @section @command{ln}: Make links between files
9165 @cindex links, creating
9166 @cindex hard links, creating
9167 @cindex symbolic (soft) links, creating
9168 @cindex creating links (hard or soft)
9170 @cindex file systems and hard links
9171 @command{ln} makes links between files. By default, it makes hard links;
9172 with the @option{-s} option, it makes symbolic (or @dfn{soft}) links.
9176 ln [@var{option}]@dots{} [-T] @var{target} @var{linkname}
9177 ln [@var{option}]@dots{} @var{target}
9178 ln [@var{option}]@dots{} @var{target}@dots{} @var{directory}
9179 ln [@var{option}]@dots{} -t @var{directory} @var{target}@dots{}
9185 If two file names are given, @command{ln} creates a link to the first
9186 file from the second.
9189 If one @var{target} is given, @command{ln} creates a link to that file
9190 in the current directory.
9193 If the @option{--target-directory} (@option{-t}) option is given, or
9194 failing that if the last file is a directory and the
9195 @option{--no-target-directory} (@option{-T}) option is not given,
9196 @command{ln} creates a link to each @var{target} file in the specified
9197 directory, using the @var{target}s' names.
9201 Normally @command{ln} does not remove existing files. Use the
9202 @option{--force} (@option{-f}) option to remove them unconditionally,
9203 the @option{--interactive} (@option{-i}) option to remove them
9204 conditionally, and the @option{--backup} (@option{-b}) option to
9207 @cindex hard link, defined
9208 @cindex inode, and hard links
9209 A @dfn{hard link} is another name for an existing file; the link and the
9210 original are indistinguishable. Technically speaking, they share the
9211 same inode, and the inode contains all the information about a
9212 file---indeed, it is not incorrect to say that the inode @emph{is} the
9213 file. Most systems prohibit making a hard link to
9214 a directory; on those where it is allowed, only the super-user can do
9215 so (and with caution, since creating a cycle will cause problems to many
9216 other utilities). Hard links cannot cross file system boundaries. (These
9217 restrictions are not mandated by @acronym{POSIX}, however.)
9219 @cindex dereferencing symbolic links
9220 @cindex symbolic link, defined
9221 @dfn{Symbolic links} (@dfn{symlinks} for short), on the other hand, are
9222 a special file type (which not all kernels support: System V release 3
9223 (and older) systems lack symlinks) in which the link file actually
9224 refers to a different file, by name. When most operations (opening,
9225 reading, writing, and so on) are passed the symbolic link file, the
9226 kernel automatically @dfn{dereferences} the link and operates on the
9227 target of the link. But some operations (e.g., removing) work on the
9228 link file itself, rather than on its target. The owner and group of a
9229 symlink are not significant to file access performed through
9230 the link, but do have implications on deleting a symbolic link from a
9231 directory with the restricted deletion bit set. On the GNU system,
9232 the mode of a symlink has no significance and cannot be changed, but
9233 on some BSD systems, the mode can be changed and will affect whether
9234 the symlink will be traversed in file name resolution. @xref{Symbolic Links,,,
9235 libc, The GNU C Library Reference Manual}.
9237 Symbolic links can contain arbitrary strings; a @dfn{dangling symlink}
9238 occurs when the string in the symlink does not resolve to a file.
9239 There are no restrictions against creating dangling symbolic links.
9240 There are trade-offs to using absolute or relative symlinks. An
9241 absolute symlink always points to the same file, even if the directory
9242 containing the link is moved. However, if the symlink is visible from
9243 more than one machine (such as on a networked file system), the file
9244 pointed to might not always be the same. A relative symbolic link is
9245 resolved in relation to the directory that contains the link, and is
9246 often useful in referring to files on the same device without regards
9247 to what name that device is mounted on when accessed via networked
9250 When creating a relative symlink in a different location than the
9251 current directory, the resolution of the symlink will be different
9252 than the resolution of the same string from the current directory.
9253 Therefore, many users prefer to first change directories to the
9254 location where the relative symlink will be created, so that
9255 tab-completion or other file resolution will find the same target as
9256 what will be placed in the symlink.
9258 The program accepts the following options. Also see @ref{Common options}.
9269 @opindex --directory
9270 @cindex hard links to directories
9271 Allow users with appropriate privileges to attempt to make hard links
9273 However, note that this will probably fail due to
9274 system restrictions, even for the super-user.
9280 Remove existing destination files.
9283 @itemx --interactive
9285 @opindex --interactive
9286 @cindex prompting, and @command{ln}
9287 Prompt whether to remove existing destination files.
9293 If @option{-s} is not in effect, and the source file is a symbolic
9294 link, create the hard link to the file referred to by the symbolic
9295 link, rather than the symbolic link itself.
9298 @itemx --no-dereference
9300 @opindex --no-dereference
9301 Do not treat the last operand specially when it is a symbolic link to
9302 a directory. Instead, treat it as if it were a normal file.
9304 When the destination is an actual directory (not a symlink to one),
9305 there is no ambiguity. The link is created in that directory.
9306 But when the specified destination is a symlink to a directory,
9307 there are two ways to treat the user's request. @command{ln} can
9308 treat the destination just as it would a normal directory and create
9309 the link in it. On the other hand, the destination can be viewed as a
9310 non-directory---as the symlink itself. In that case, @command{ln}
9311 must delete or backup that symlink before creating the new link.
9312 The default is to treat a destination that is a symlink to a directory
9313 just like a directory.
9315 This option is weaker than the @option{--no-target-directory}
9316 (@option{-T}) option, so it has no effect if both options are given.
9322 If @option{-s} is not in effect, and the source file is a symbolic
9323 link, create the hard link to the symbolic link itself. On platforms
9324 where this is not supported by the kernel, this option creates a
9325 symbolic link with identical contents; since symbolic link contents
9326 cannot be edited, any file name resolution performed through either
9327 link will be the same as if a hard link had been created.
9333 Make symbolic links instead of hard links. This option merely produces
9334 an error message on systems that do not support symbolic links.
9340 @optNoTargetDirectory
9346 Print the name of each file after linking it successfully.
9350 @cindex hard links to symbolic links
9351 @cindex symbolic links and @command{ln}
9352 If @option{-L} and @option{-P} are both given, the last one takes
9353 precedence. If @option{-s} is also given, @option{-L} and @option{-P}
9354 are silently ignored. If neither option is given, then this
9355 implementation defaults to @option{-P} if the system @code{link} supports
9356 hard links to symbolic links (such as the GNU system), and @option{-L}
9357 if @code{link} follows symbolic links (such as on BSD).
9366 # Create link ../a pointing to a in that directory.
9367 # Not really useful because it points to itself.
9372 # Change to the target before creating symlinks to avoid being confused.
9378 # Hard coded file names don't move well.
9379 ln -s $(pwd)/a /some/dir/
9383 # Relative file names survive directory moves and also
9384 # work across networked file systems.
9385 ln -s afile anotherfile
9386 ln -s ../adir/afile yetanotherfile
9390 @node mkdir invocation
9391 @section @command{mkdir}: Make directories
9394 @cindex directories, creating
9395 @cindex creating directories
9397 @command{mkdir} creates directories with the specified names. Synopsis:
9400 mkdir [@var{option}]@dots{} @var{name}@dots{}
9403 @command{mkdir} creates each directory @var{name} in the order given.
9404 It reports an error if @var{name} already exists, unless the
9405 @option{-p} option is given and @var{name} is a directory.
9407 The program accepts the following options. Also see @ref{Common options}.
9412 @itemx --mode=@var{mode}
9415 @cindex modes of created directories, setting
9416 Set the file permission bits of created directories to @var{mode},
9417 which uses the same syntax as
9418 in @command{chmod} and uses @samp{a=rwx} (read, write and execute allowed for
9419 everyone) for the point of the departure. @xref{File permissions}.
9421 Normally the directory has the desired file mode bits at the moment it
9422 is created. As a @acronym{GNU} extension, @var{mode} may also mention
9423 special mode bits, but in this case there may be a temporary window
9424 during which the directory exists but its special mode bits are
9425 incorrect. @xref{Directory Setuid and Setgid}, for how the
9426 set-user-ID and set-group-ID bits of directories are inherited unless
9427 overridden in this way.
9433 @cindex parent directories, creating
9434 Make any missing parent directories for each argument, setting their
9435 file permission bits to the umask modified by @samp{u+wx}. Ignore
9436 existing parent directories, and do not change their file permission
9439 To set the file permission bits of any newly-created parent
9440 directories to a value that includes @samp{u+wx}, you can set the
9441 umask before invoking @command{mkdir}. For example, if the shell
9442 command @samp{(umask u=rwx,go=rx; mkdir -p P/Q)} creates the parent
9443 @file{P} it sets the parent's permission bits to @samp{u=rwx,go=rx}.
9444 To set a parent's special mode bits as well, you can invoke
9445 @command{chmod} after @command{mkdir}. @xref{Directory Setuid and
9446 Setgid}, for how the set-user-ID and set-group-ID bits of
9447 newly-created parent directories are inherited.
9453 Print a message for each created directory. This is most useful with
9456 @item -Z @var{context}
9457 @itemx --context=@var{context}
9461 @cindex security context
9462 Set the default SELinux security context to be used for created directories.
9469 @node mkfifo invocation
9470 @section @command{mkfifo}: Make FIFOs (named pipes)
9473 @cindex FIFOs, creating
9474 @cindex named pipes, creating
9475 @cindex creating FIFOs (named pipes)
9477 @command{mkfifo} creates FIFOs (also called @dfn{named pipes}) with the
9478 specified names. Synopsis:
9481 mkfifo [@var{option}] @var{name}@dots{}
9484 A @dfn{FIFO} is a special file type that permits independent processes
9485 to communicate. One process opens the FIFO file for writing, and
9486 another for reading, after which data can flow as with the usual
9487 anonymous pipe in shells or elsewhere.
9489 The program accepts the following option. Also see @ref{Common options}.
9494 @itemx --mode=@var{mode}
9497 @cindex modes of created FIFOs, setting
9498 Set the mode of created FIFOs to @var{mode}, which is symbolic as in
9499 @command{chmod} and uses @samp{a=rw} (read and write allowed for everyone)
9500 for the point of departure. @var{mode} should specify only file
9501 permission bits. @xref{File permissions}.
9503 @item -Z @var{context}
9504 @itemx --context=@var{context}
9508 @cindex security context
9509 Set the default SELinux security context to be used for created FIFOs.
9516 @node mknod invocation
9517 @section @command{mknod}: Make block or character special files
9520 @cindex block special files, creating
9521 @cindex character special files, creating
9523 @command{mknod} creates a FIFO, character special file, or block special
9524 file with the specified name. Synopsis:
9527 mknod [@var{option}]@dots{} @var{name} @var{type} [@var{major} @var{minor}]
9530 @cindex special files
9531 @cindex block special files
9532 @cindex character special files
9533 Unlike the phrase ``special file type'' above, the term @dfn{special
9534 file} has a technical meaning on Unix: something that can generate or
9535 receive data. Usually this corresponds to a physical piece of hardware,
9536 e.g., a printer or a disk. (These files are typically created at
9537 system-configuration time.) The @command{mknod} command is what creates
9538 files of this type. Such devices can be read either a character at a
9539 time or a ``block'' (many characters) at a time, hence we say there are
9540 @dfn{block special} files and @dfn{character special} files.
9542 @c mknod is a shell built-in at least with OpenBSD's /bin/sh
9543 @mayConflictWithShellBuiltIn{mknod}
9545 The arguments after @var{name} specify the type of file to make:
9550 @opindex p @r{for FIFO file}
9554 @opindex b @r{for block special file}
9555 for a block special file
9558 @c Don't document the `u' option -- it's just a synonym for `c'.
9559 @c Do *any* versions of mknod still use it?
9561 @opindex c @r{for character special file}
9562 @c @opindex u @r{for character special file}
9563 for a character special file
9567 When making a block or character special file, the major and minor
9568 device numbers must be given after the file type.
9569 If a major or minor device number begins with @samp{0x} or @samp{0X},
9570 it is interpreted as hexadecimal; otherwise, if it begins with @samp{0},
9571 as octal; otherwise, as decimal.
9573 The program accepts the following option. Also see @ref{Common options}.
9578 @itemx --mode=@var{mode}
9581 Set the mode of created files to @var{mode}, which is symbolic as in
9582 @command{chmod} and uses @samp{a=rw} as the point of departure.
9583 @var{mode} should specify only file permission bits.
9584 @xref{File permissions}.
9586 @item -Z @var{context}
9587 @itemx --context=@var{context}
9591 @cindex security context
9592 Set the default SELinux security context to be used for created files.
9599 @node readlink invocation
9600 @section @command{readlink}: Print value of a symlink or canonical file name
9603 @cindex displaying value of a symbolic link
9604 @cindex canonical file name
9605 @cindex canonicalize a file name
9609 @command{readlink} may work in one of two supported modes:
9615 @command{readlink} outputs the value of the given symbolic link.
9616 If @command{readlink} is invoked with an argument other than the name
9617 of a symbolic link, it produces no output and exits with a nonzero exit code.
9619 @item Canonicalize mode
9621 @command{readlink} outputs the absolute name of the given file which contains
9622 no @file{.}, @file{..} components nor any repeated separators
9623 (@file{/}) or symbolic links.
9628 readlink [@var{option}] @var{file}
9631 By default, @command{readlink} operates in readlink mode.
9633 The program accepts the following options. Also see @ref{Common options}.
9638 @itemx --canonicalize
9640 @opindex --canonicalize
9641 Activate canonicalize mode.
9642 If any component of the file name except the last one is missing or unavailable,
9643 @command{readlink} produces no output and exits with a nonzero exit
9644 code. A trailing slash is ignored.
9647 @itemx --canonicalize-existing
9649 @opindex --canonicalize-existing
9650 Activate canonicalize mode.
9651 If any component is missing or unavailable, @command{readlink} produces
9652 no output and exits with a nonzero exit code. A trailing slash
9653 requires that the name resolve to a directory.
9656 @itemx --canonicalize-missing
9658 @opindex --canonicalize-missing
9659 Activate canonicalize mode.
9660 If any component is missing or unavailable, @command{readlink} treats it
9666 @opindex --no-newline
9667 Do not output the trailing newline.
9677 Suppress most error messages.
9683 Report error messages.
9687 The @command{readlink} utility first appeared in OpenBSD 2.1.
9689 There is a @command{realpath} command on some systems
9690 which operates like @command{readlink} in canonicalize mode.
9695 @node rmdir invocation
9696 @section @command{rmdir}: Remove empty directories
9699 @cindex removing empty directories
9700 @cindex directories, removing empty
9702 @command{rmdir} removes empty directories. Synopsis:
9705 rmdir [@var{option}]@dots{} @var{directory}@dots{}
9708 If any @var{directory} argument does not refer to an existing empty
9709 directory, it is an error.
9711 The program accepts the following options. Also see @ref{Common options}.
9715 @item --ignore-fail-on-non-empty
9716 @opindex --ignore-fail-on-non-empty
9717 @cindex directory deletion, ignoring failures
9718 Ignore each failure to remove a directory that is solely because
9719 the directory is non-empty.
9725 @cindex parent directories, removing
9726 Remove @var{directory}, then try to remove each component of @var{directory}.
9727 So, for example, @samp{rmdir -p a/b/c} is similar to @samp{rmdir a/b/c a/b a}.
9728 As such, it fails if any of those directories turns out not to be empty.
9729 Use the @option{--ignore-fail-on-non-empty} option to make it so such
9730 a failure does not evoke a diagnostic and does not cause @command{rmdir} to
9731 exit unsuccessfully.
9737 @cindex directory deletion, reporting
9738 Give a diagnostic for each successful removal.
9739 @var{directory} is removed.
9743 @xref{rm invocation}, for how to remove non-empty directories (recursively).
9748 @node unlink invocation
9749 @section @command{unlink}: Remove files via the unlink syscall
9752 @cindex removing files or directories (via the unlink syscall)
9754 @command{unlink} deletes a single specified file name.
9755 It is a minimalist interface to the system-provided
9756 @code{unlink} function. @xref{Deleting Files, , , libc,
9757 The GNU C Library Reference Manual}. Synopsis:
9758 It avoids the bells and whistles of the more commonly-used
9759 @command{rm} command (@pxref{rm invocation}).
9762 unlink @var{filename}
9765 On some systems @code{unlink} can be used to delete the name of a
9766 directory. On others, it can be used that way only by a privileged user.
9767 In the GNU system @code{unlink} can never delete the name of a directory.
9769 The @command{unlink} command honors the @option{--help} and
9770 @option{--version} options. To remove a file whose name begins with
9771 @samp{-}, prefix the name with @samp{./}, e.g., @samp{unlink ./--help}.
9776 @node Changing file attributes
9777 @chapter Changing file attributes
9779 @cindex changing file attributes
9780 @cindex file attributes, changing
9781 @cindex attributes, file
9783 A file is not merely its contents, a name, and a file type
9784 (@pxref{Special file types}). A file also has an owner (a user ID), a
9785 group (a group ID), permissions (what the owner can do with the file,
9786 what people in the group can do, and what everyone else can do), various
9787 timestamps, and other information. Collectively, we call these a file's
9790 These commands change file attributes.
9793 * chgrp invocation:: Change file groups.
9794 * chmod invocation:: Change access permissions.
9795 * chown invocation:: Change file owners and groups.
9796 * touch invocation:: Change file timestamps.
9800 @node chown invocation
9801 @section @command{chown}: Change file owner and group
9804 @cindex file ownership, changing
9805 @cindex group ownership, changing
9806 @cindex changing file ownership
9807 @cindex changing group ownership
9809 @command{chown} changes the user and/or group ownership of each given @var{file}
9810 to @var{new-owner} or to the user and group of an existing reference file.
9814 chown [@var{option}]@dots{} @{@var{new-owner} | --reference=@var{ref_file}@}@c
9818 If used, @var{new-owner} specifies the new owner and/or group as follows
9819 (with no embedded white space):
9822 [@var{owner}] [ : [@var{group}] ]
9829 If only an @var{owner} (a user name or numeric user ID) is given, that
9830 user is made the owner of each given file, and the files' group is not
9833 @item owner@samp{:}group
9834 If the @var{owner} is followed by a colon and a @var{group} (a
9835 group name or numeric group ID), with no spaces between them, the group
9836 ownership of the files is changed as well (to @var{group}).
9839 If a colon but no group name follows @var{owner}, that user is
9840 made the owner of the files and the group of the files is changed to
9841 @var{owner}'s login group.
9844 If the colon and following @var{group} are given, but the owner
9845 is omitted, only the group of the files is changed; in this case,
9846 @command{chown} performs the same function as @command{chgrp}.
9849 If only a colon is given, or if @var{new-owner} is empty, neither the
9850 owner nor the group is changed.
9854 If @var{owner} or @var{group} is intended to represent a numeric user
9855 or group ID, then you may specify it with a leading @samp{+}.
9856 @xref{Disambiguating names and IDs}.
9858 Some older scripts may still use @samp{.} in place of the @samp{:} separator.
9859 @acronym{POSIX} 1003.1-2001 (@pxref{Standards conformance}) does not
9860 require support for that, but for backward compatibility @acronym{GNU}
9861 @command{chown} supports @samp{.} so long as no ambiguity results.
9862 New scripts should avoid the use of @samp{.} because it is not
9863 portable, and because it has undesirable results if the entire
9864 @var{owner@samp{.}group} happens to identify a user whose name
9867 The @command{chown} command sometimes clears the set-user-ID or
9868 set-group-ID permission bits. This behavior depends on the policy and
9869 functionality of the underlying @code{chown} system call, which may
9870 make system-dependent file mode modifications outside the control of
9871 the @command{chown} command. For example, the @command{chown} command
9872 might not affect those bits when invoked by a user with appropriate
9873 privileges, or when the
9874 bits signify some function other than executable permission (e.g.,
9876 When in doubt, check the underlying system behavior.
9878 The program accepts the following options. Also see @ref{Common options}.
9886 @cindex changed owners, verbosely describing
9887 Verbosely describe the action for each @var{file} whose ownership
9896 @cindex error messages, omitting
9897 Do not print error messages about files whose ownership cannot be
9900 @itemx @w{@kbd{--from}=@var{old-owner}}
9902 @cindex symbolic links, changing owner
9903 Change a @var{file}'s ownership only if it has current attributes specified
9904 by @var{old-owner}. @var{old-owner} has the same form as @var{new-owner}
9906 This option is useful primarily from a security standpoint in that
9907 it narrows considerably the window of potential abuse.
9908 For example, to reflect a user ID numbering change for one user's files
9909 without an option like this, @code{root} might run
9912 find / -owner OLDUSER -print0 | xargs -0 chown -h NEWUSER
9915 But that is dangerous because the interval between when the @command{find}
9916 tests the existing file's owner and when the @command{chown} is actually run
9918 One way to narrow the gap would be to invoke chown for each file
9922 find / -owner OLDUSER -exec chown -h NEWUSER @{@} \;
9925 But that is very slow if there are many affected files.
9926 With this option, it is safer (the gap is narrower still)
9927 though still not perfect:
9930 chown -h -R --from=OLDUSER NEWUSER /
9934 @opindex --dereference
9935 @cindex symbolic links, changing owner
9937 Do not act on symbolic links themselves but rather on what they point to.
9938 This is the default.
9941 @itemx --no-dereference
9943 @opindex --no-dereference
9944 @cindex symbolic links, changing owner
9946 Act on symbolic links themselves instead of what they point to.
9947 This mode relies on the @code{lchown} system call.
9948 On systems that do not provide the @code{lchown} system call,
9949 @command{chown} fails when a file specified on the command line
9951 By default, no diagnostic is issued for symbolic links encountered
9952 during a recursive traversal, but see @option{--verbose}.
9954 @itemx --preserve-root
9955 @opindex --preserve-root
9956 @cindex root directory, disallow recursive modification
9957 Fail upon any attempt to recursively change the root directory, @file{/}.
9958 Without @option{--recursive}, this option has no effect.
9959 @xref{Treating / specially}.
9961 @itemx --no-preserve-root
9962 @opindex --no-preserve-root
9963 @cindex root directory, allow recursive modification
9964 Cancel the effect of any preceding @option{--preserve-root} option.
9965 @xref{Treating / specially}.
9967 @item --reference=@var{ref_file}
9968 @opindex --reference
9969 Change the user and group of each @var{file} to be the same as those of
9970 @var{ref_file}. If @var{ref_file} is a symbolic link, do not use the
9971 user and group of the symbolic link, but rather those of the file it
9978 Output a diagnostic for every file processed.
9979 If a symbolic link is encountered during a recursive traversal
9980 on a system without the @code{lchown} system call, and @option{--no-dereference}
9981 is in effect, then issue a diagnostic saying neither the symbolic link nor
9982 its referent is being changed.
9987 @opindex --recursive
9988 @cindex recursively changing file ownership
9989 Recursively change ownership of directories and their contents.
9992 @xref{Traversing symlinks}.
9995 @xref{Traversing symlinks}.
9998 @xref{Traversing symlinks}.
10007 # Change the owner of /u to "root".
10010 # Likewise, but also change its group to "staff".
10011 chown root:staff /u
10013 # Change the owner of /u and subfiles to "root".
10018 @node chgrp invocation
10019 @section @command{chgrp}: Change group ownership
10022 @cindex group ownership, changing
10023 @cindex changing group ownership
10025 @command{chgrp} changes the group ownership of each given @var{file}
10026 to @var{group} (which can be either a group name or a numeric group ID)
10027 or to the group of an existing reference file. Synopsis:
10030 chgrp [@var{option}]@dots{} @{@var{group} | --reference=@var{ref_file}@}@c
10034 If @var{group} is intended to represent a
10035 numeric group ID, then you may specify it with a leading @samp{+}.
10036 @xref{Disambiguating names and IDs}.
10038 The program accepts the following options. Also see @ref{Common options}.
10046 @cindex changed files, verbosely describing
10047 Verbosely describe the action for each @var{file} whose group actually
10056 @cindex error messages, omitting
10057 Do not print error messages about files whose group cannot be
10060 @item --dereference
10061 @opindex --dereference
10062 @cindex symbolic links, changing owner
10064 Do not act on symbolic links themselves but rather on what they point to.
10065 This is the default.
10068 @itemx --no-dereference
10070 @opindex --no-dereference
10071 @cindex symbolic links, changing group
10073 Act on symbolic links themselves instead of what they point to.
10074 This mode relies on the @code{lchown} system call.
10075 On systems that do not provide the @code{lchown} system call,
10076 @command{chgrp} fails when a file specified on the command line
10077 is a symbolic link.
10078 By default, no diagnostic is issued for symbolic links encountered
10079 during a recursive traversal, but see @option{--verbose}.
10081 @itemx --preserve-root
10082 @opindex --preserve-root
10083 @cindex root directory, disallow recursive modification
10084 Fail upon any attempt to recursively change the root directory, @file{/}.
10085 Without @option{--recursive}, this option has no effect.
10086 @xref{Treating / specially}.
10088 @itemx --no-preserve-root
10089 @opindex --no-preserve-root
10090 @cindex root directory, allow recursive modification
10091 Cancel the effect of any preceding @option{--preserve-root} option.
10092 @xref{Treating / specially}.
10094 @item --reference=@var{ref_file}
10095 @opindex --reference
10096 Change the group of each @var{file} to be the same as that of
10097 @var{ref_file}. If @var{ref_file} is a symbolic link, do not use the
10098 group of the symbolic link, but rather that of the file it refers to.
10104 Output a diagnostic for every file processed.
10105 If a symbolic link is encountered during a recursive traversal
10106 on a system without the @code{lchown} system call, and @option{--no-dereference}
10107 is in effect, then issue a diagnostic saying neither the symbolic link nor
10108 its referent is being changed.
10113 @opindex --recursive
10114 @cindex recursively changing group ownership
10115 Recursively change the group ownership of directories and their contents.
10118 @xref{Traversing symlinks}.
10121 @xref{Traversing symlinks}.
10124 @xref{Traversing symlinks}.
10133 # Change the group of /u to "staff".
10136 # Change the group of /u and subfiles to "staff".
10141 @node chmod invocation
10142 @section @command{chmod}: Change access permissions
10145 @cindex changing access permissions
10146 @cindex access permissions, changing
10147 @cindex permissions, changing access
10149 @command{chmod} changes the access permissions of the named files. Synopsis:
10152 chmod [@var{option}]@dots{} @{@var{mode} | --reference=@var{ref_file}@}@c
10156 @cindex symbolic links, permissions of
10157 @command{chmod} never changes the permissions of symbolic links, since
10158 the @command{chmod} system call cannot change their permissions.
10159 This is not a problem since the permissions of symbolic links are
10160 never used. However, for each symbolic link listed on the command
10161 line, @command{chmod} changes the permissions of the pointed-to file.
10162 In contrast, @command{chmod} ignores symbolic links encountered during
10163 recursive directory traversals.
10165 A successful use of @command{chmod} clears the set-group-ID bit of a
10166 regular file if the file's group ID does not match the user's
10167 effective group ID or one of the user's supplementary group IDs,
10168 unless the user has appropriate privileges. Additional restrictions
10169 may cause the set-user-ID and set-group-ID bits of @var{mode} or
10170 @var{ref_file} to be ignored. This behavior depends on the policy and
10171 functionality of the underlying @code{chmod} system call. When in
10172 doubt, check the underlying system behavior.
10174 If used, @var{mode} specifies the new file mode bits.
10175 For details, see the section on @ref{File permissions}.
10176 If you really want @var{mode} to have a leading @samp{-}, you should
10177 use @option{--} first, e.g., @samp{chmod -- -w file}. Typically,
10178 though, @samp{chmod a-w file} is preferable, and @command{chmod -w
10179 file} (without the @option{--}) complains if it behaves differently
10180 from what @samp{chmod a-w file} would do.
10182 The program accepts the following options. Also see @ref{Common options}.
10190 Verbosely describe the action for each @var{file} whose permissions
10199 @cindex error messages, omitting
10200 Do not print error messages about files whose permissions cannot be
10203 @itemx --preserve-root
10204 @opindex --preserve-root
10205 @cindex root directory, disallow recursive modification
10206 Fail upon any attempt to recursively change the root directory, @file{/}.
10207 Without @option{--recursive}, this option has no effect.
10208 @xref{Treating / specially}.
10210 @itemx --no-preserve-root
10211 @opindex --no-preserve-root
10212 @cindex root directory, allow recursive modification
10213 Cancel the effect of any preceding @option{--preserve-root} option.
10214 @xref{Treating / specially}.
10220 Verbosely describe the action or non-action taken for every @var{file}.
10222 @item --reference=@var{ref_file}
10223 @opindex --reference
10224 Change the mode of each @var{file} to be the same as that of @var{ref_file}.
10225 @xref{File permissions}.
10226 If @var{ref_file} is a symbolic link, do not use the mode
10227 of the symbolic link, but rather that of the file it refers to.
10232 @opindex --recursive
10233 @cindex recursively changing access permissions
10234 Recursively change permissions of directories and their contents.
10241 @node touch invocation
10242 @section @command{touch}: Change file timestamps
10245 @cindex changing file timestamps
10246 @cindex file timestamps, changing
10247 @cindex timestamps, changing file
10249 @command{touch} changes the access and/or modification times of the
10250 specified files. Synopsis:
10253 touch [@var{option}]@dots{} @var{file}@dots{}
10256 @cindex empty files, creating
10257 Any @var{file} argument that does not exist is created empty, unless
10258 option @option{--no-create} (@option{-c}) or @option{--no-dereference}
10259 (@option{-h}) was in effect.
10261 A @var{file} argument string of @samp{-} is handled specially and
10262 causes @command{touch} to change the times of the file associated with
10266 By default, @command{touch} sets file timestamps to the current time.
10267 Because @command{touch} acts on its operands left to right, the
10268 resulting timestamps of earlier and later operands may disagree.
10269 Also, the determination of what time is ``current'' depends on the
10270 platform. Platforms with network file systems often use different
10271 clocks for the operating system and for file systems; because
10272 @command{touch} typically uses file systems' clocks by default, clock
10273 skew can cause the resulting file timestamps to appear to be in a
10274 program's ``future'' or ``past''.
10276 @cindex file timestamp resolution
10277 The @command{touch} command sets the file's timestamp to the greatest
10278 representable value that is not greater than the requested time. This
10279 can differ from the requested time for several reasons. First, the
10280 requested time may have a higher resolution than supported. Second, a
10281 file system may use different resolutions for different types of
10282 times. Third, file timestamps may use a different resolution than
10283 operating system timestamps. Fourth, the operating system primitives
10284 used to update timestamps may employ yet a different resolution. For
10285 example, in theory a file system might use 10-microsecond resolution
10286 for access time and 100-nanosecond resolution for modification time,
10287 and the operating system might use nanosecond resolution for the
10288 current time and microsecond resolution for the primitive that
10289 @command{touch} uses to set a file's timestamp to an arbitrary value.
10291 @cindex permissions, for changing file timestamps
10292 When setting file timestamps to the current time, @command{touch} can
10293 change the timestamps for files that the user does not own but has
10294 write permission for. Otherwise, the user must own the files. Some
10295 older systems have a further restriction: the user must own the files
10296 unless both the access and modification times are being set to the
10299 Although @command{touch} provides options for changing two of the times---the
10300 times of last access and modification---of a file, there is actually
10301 a standard third one as well: the inode change time. This is often
10302 referred to as a file's @code{ctime}.
10303 The inode change time represents the time when the file's meta-information
10304 last changed. One common example of this is when the permissions of a
10305 file change. Changing the permissions doesn't access the file, so
10306 the atime doesn't change, nor does it modify the file, so the mtime
10307 doesn't change. Yet, something about the file itself has changed,
10308 and this must be noted somewhere. This is the job of the ctime field.
10309 This is necessary, so that, for example, a backup program can make a
10310 fresh copy of the file, including the new permissions value.
10311 Another operation that modifies a file's ctime without affecting
10312 the others is renaming. In any case, it is not possible, in normal
10313 operations, for a user to change the ctime field to a user-specified value.
10314 Some operating systems and file systems support a fourth time: the
10315 birth time, when the file was first created; by definition, this
10316 timestamp never changes.
10319 Time stamps assume the time zone rules specified by the @env{TZ}
10320 environment variable, or by the system default rules if @env{TZ} is
10321 not set. @xref{TZ Variable,, Specifying the Time Zone with @env{TZ},
10322 libc, The GNU C Library Reference Manual}.
10323 You can avoid ambiguities during
10324 daylight saving transitions by using @sc{utc} time stamps.
10326 The program accepts the following options. Also see @ref{Common options}.
10331 @itemx --time=atime
10332 @itemx --time=access
10336 @opindex atime@r{, changing}
10337 @opindex access @r{time, changing}
10338 @opindex use @r{time, changing}
10339 Change the access time only.
10344 @opindex --no-create
10345 Do not warn about or create files that do not exist.
10348 @itemx --date=@var{time}
10352 Use @var{time} instead of the current time. It can contain month names,
10353 time zones, @samp{am} and @samp{pm}, @samp{yesterday}, etc. For
10354 example, @option{--date="2004-02-27 14:19:13.489392193 +0530"}
10355 specifies the instant of time that is 489,392,193 nanoseconds after
10356 February 27, 2004 at 2:19:13 PM in a time zone that is 5 hours and 30
10357 minutes east of @acronym{UTC}. @xref{Date input formats}.
10358 File systems that do not support high-resolution time stamps
10359 silently ignore any excess precision here.
10363 @cindex BSD @command{touch} compatibility
10364 Ignored; for compatibility with BSD versions of @command{touch}.
10367 @itemx --no-dereference
10369 @opindex --no-dereference
10370 @cindex symbolic links, changing time
10372 Attempt to change the timestamps of a symbolic link, rather than what
10373 the link refers to. When using this option, empty files are not
10374 created, but option @option{-c} must also be used to avoid warning
10375 about files that do not exist. Not all systems support changing the
10376 timestamps of symlinks, since underlying system support for this
10377 action was not required until @acronym{POSIX} 2008. Also, on some
10378 systems, the mere act of examining a symbolic link changes the access
10379 time, such that only changes to the modification time will persist
10380 long enough to be observable. When coupled with option @option{-r}, a
10381 reference timestamp is taken from a symbolic link rather than the file
10385 @itemx --time=mtime
10386 @itemx --time=modify
10389 @opindex mtime@r{, changing}
10390 @opindex modify @r{time, changing}
10391 Change the modification time only.
10393 @item -r @var{file}
10394 @itemx --reference=@var{file}
10396 @opindex --reference
10397 Use the times of the reference @var{file} instead of the current time.
10398 If this option is combined with the @option{--date=@var{time}}
10399 (@option{-d @var{time}}) option, the reference @var{file}'s time is
10400 the origin for any relative @var{time}s given, but is otherwise ignored.
10401 For example, @samp{-r foo -d '-5 seconds'} specifies a time stamp
10402 equal to five seconds before the corresponding time stamp for @file{foo}.
10403 If @var{file} is a symbolic link, the reference timestamp is taken
10404 from the target of the symlink, unless @option{-h} was also in effect.
10406 @item -t [[@var{cc}]@var{yy}]@var{mmddhhmm}[.@var{ss}]
10407 Use the argument (optional four-digit or two-digit years, months,
10408 days, hours, minutes, optional seconds) instead of the current time.
10409 If the year is specified with only two digits, then @var{cc}
10410 is 20 for years in the range 0 @dots{} 68, and 19 for years in
10411 69 @dots{} 99. If no digits of the year are specified,
10412 the argument is interpreted as a date in the current year.
10413 Note that @var{ss} may be @samp{60}, to accommodate leap seconds.
10417 @vindex _POSIX2_VERSION
10418 On older systems, @command{touch} supports an obsolete syntax, as follows.
10419 If no timestamp is given with any of the @option{-d}, @option{-r}, or
10420 @option{-t} options, and if there are two or more @var{file}s and the
10421 first @var{file} is of the form @samp{@var{mmddhhmm}[@var{yy}]} and this
10422 would be a valid argument to the @option{-t} option (if the @var{yy}, if
10423 any, were moved to the front), and if the represented year
10424 is in the range 1969--1999, that argument is interpreted as the time
10425 for the other files instead of as a file name.
10426 This obsolete behavior can be enabled or disabled with the
10427 @env{_POSIX2_VERSION} environment variable (@pxref{Standards
10428 conformance}), but portable scripts should avoid commands whose
10429 behavior depends on this variable.
10430 For example, use @samp{touch ./12312359 main.c} or @samp{touch -t
10431 12312359 main.c} rather than the ambiguous @samp{touch 12312359 main.c}.
10437 @chapter Disk usage
10441 No disk can hold an infinite amount of data. These commands report
10442 how much disk storage is in use or available, report other file and
10443 file status information, and write buffers to disk.
10446 * df invocation:: Report file system disk space usage.
10447 * du invocation:: Estimate file space usage.
10448 * stat invocation:: Report file or file system status.
10449 * sync invocation:: Synchronize memory and disk.
10450 * truncate invocation:: Shrink or extend the size of a file.
10454 @node df invocation
10455 @section @command{df}: Report file system disk space usage
10458 @cindex file system disk usage
10459 @cindex disk usage by file system
10461 @command{df} reports the amount of disk space used and available on
10462 file systems. Synopsis:
10465 df [@var{option}]@dots{} [@var{file}]@dots{}
10468 With no arguments, @command{df} reports the space used and available on all
10469 currently mounted file systems (of all types). Otherwise, @command{df}
10470 reports on the file system containing each argument @var{file}.
10472 Normally the disk space is printed in units of
10473 1024 bytes, but this can be overridden (@pxref{Block size}).
10474 Non-integer quantities are rounded up to the next higher unit.
10476 @cindex disk device file
10477 @cindex device file, disk
10478 If an argument @var{file} is a disk device file containing a mounted
10479 file system, @command{df} shows the space available on that file system
10480 rather than on the file system containing the device node (i.e., the root
10481 file system). @sc{gnu} @command{df} does not attempt to determine the
10483 on unmounted file systems, because on most kinds of systems doing so
10484 requires extremely nonportable intimate knowledge of file system
10487 The program accepts the following options. Also see @ref{Common options}.
10495 @cindex automounter file systems
10496 @cindex ignore file systems
10497 Include in the listing dummy file systems, which
10498 are omitted by default. Such file systems are typically special-purpose
10499 pseudo-file-systems, such as automounter entries.
10501 @item -B @var{size}
10502 @itemx --block-size=@var{size}
10504 @opindex --block-size
10505 @cindex file system sizes
10506 Scale sizes by @var{size} before printing them (@pxref{Block size}).
10507 For example, @option{-BG} prints sizes in units of 1,073,741,824 bytes.
10511 @cindex grand total of disk size, usage and available space
10512 Print a grand total of all arguments after all arguments have
10513 been processed. This can be used to find out the total disk size, usage
10514 and available space of all listed devices.
10520 Equivalent to @option{--si}.
10526 @cindex inode usage
10527 List inode usage information instead of block usage. An inode (short
10528 for index node) contains information about a file such as its owner,
10529 permissions, timestamps, and location on the disk.
10533 @cindex kibibytes for file system sizes
10534 Print sizes in 1024-byte blocks, overriding the default block size
10535 (@pxref{Block size}).
10536 This option is equivalent to @option{--block-size=1K}.
10542 @cindex file system types, limiting output to certain
10543 Limit the listing to local file systems. By default, remote file systems
10548 @cindex file system space, retrieving old data more quickly
10549 Do not invoke the @code{sync} system call before getting any usage data.
10550 This may make @command{df} run significantly faster on systems with many
10551 disks, but on some systems (notably SunOS) the results may be slightly
10552 out of date. This is the default.
10555 @itemx --portability
10557 @opindex --portability
10558 @cindex one-line output format
10559 @cindex @acronym{POSIX} output format
10560 @cindex portable output format
10561 @cindex output format, portable
10562 Use the @acronym{POSIX} output format. This is like the default format except
10567 The information about each file system is always printed on exactly
10568 one line; a mount device is never put on a line by itself. This means
10569 that if the mount device name is more than 20 characters long (e.g., for
10570 some network mounts), the columns are misaligned.
10573 The labels in the header output line are changed to conform to @acronym{POSIX}.
10576 The default block size and output format are unaffected by the
10577 @env{DF_BLOCK_SIZE}, @env{BLOCK_SIZE} and @env{BLOCKSIZE} environment
10578 variables. However, the default block size is still affected by
10579 @env{POSIXLY_CORRECT}: it is 512 if @env{POSIXLY_CORRECT} is set, 1024
10580 otherwise. @xref{Block size}.
10587 @cindex file system space, retrieving current data more slowly
10588 Invoke the @code{sync} system call before getting any usage data. On
10589 some systems (notably SunOS), doing this yields more up to date results,
10590 but in general this option makes @command{df} much slower, especially when
10591 there are many or very busy file systems.
10593 @item -t @var{fstype}
10594 @itemx --type=@var{fstype}
10597 @cindex file system types, limiting output to certain
10598 Limit the listing to file systems of type @var{fstype}. Multiple
10599 file system types can be specified by giving multiple @option{-t} options.
10600 By default, nothing is omitted.
10603 @itemx --print-type
10605 @opindex --print-type
10606 @cindex file system types, printing
10607 Print each file system's type. The types printed here are the same ones
10608 you can include or exclude with @option{-t} and @option{-x}. The particular
10609 types printed are whatever is supported by the system. Here are some of
10610 the common names (this list is certainly not exhaustive):
10615 @cindex @acronym{NFS} file system type
10616 An @acronym{NFS} file system, i.e., one mounted over a network from another
10617 machine. This is the one type name which seems to be used uniformly by
10620 @item 4.2@r{, }ufs@r{, }efs@dots{}
10621 @cindex Linux file system types
10622 @cindex local file system types
10623 @opindex 4.2 @r{file system type}
10624 @opindex ufs @r{file system type}
10625 @opindex efs @r{file system type}
10626 A file system on a locally-mounted hard disk. (The system might even
10627 support more than one type here; Linux does.)
10629 @item hsfs@r{, }cdfs
10630 @cindex CD-ROM file system type
10631 @cindex High Sierra file system
10632 @opindex hsfs @r{file system type}
10633 @opindex cdfs @r{file system type}
10634 A file system on a CD-ROM drive. HP-UX uses @samp{cdfs}, most other
10635 systems use @samp{hsfs} (@samp{hs} for ``High Sierra'').
10638 @cindex PC file system
10639 @cindex DOS file system
10640 @cindex MS-DOS file system
10641 @cindex diskette file system
10643 An MS-DOS file system, usually on a diskette.
10647 @item -x @var{fstype}
10648 @itemx --exclude-type=@var{fstype}
10650 @opindex --exclude-type
10651 Limit the listing to file systems not of type @var{fstype}.
10652 Multiple file system types can be eliminated by giving multiple
10653 @option{-x} options. By default, no file system types are omitted.
10656 Ignored; for compatibility with System V versions of @command{df}.
10661 Failure includes the case where no output is generated, so you can
10662 inspect the exit status of a command like @samp{df -t ext3 -t reiserfs
10663 @var{dir}} to test whether @var{dir} is on a file system of type
10664 @samp{ext3} or @samp{reiserfs}.
10667 @node du invocation
10668 @section @command{du}: Estimate file space usage
10671 @cindex file space usage
10672 @cindex disk usage for files
10674 @command{du} reports the amount of disk space used by the specified files
10675 and for each subdirectory (of directory arguments). Synopsis:
10678 du [@var{option}]@dots{} [@var{file}]@dots{}
10681 With no arguments, @command{du} reports the disk space for the current
10682 directory. Normally the disk space is printed in units of
10683 1024 bytes, but this can be overridden (@pxref{Block size}).
10684 Non-integer quantities are rounded up to the next higher unit.
10686 If two or more hard links point to the same file, only one of the hard
10687 links is counted. The @var{file} argument order affects which links
10688 are counted, and changing the argument order may change the numbers
10689 that @command{du} outputs.
10691 The program accepts the following options. Also see @ref{Common options}.
10699 Show counts for all files, not just directories.
10701 @itemx --apparent-size
10702 @opindex --apparent-size
10703 Print apparent sizes, rather than disk usage. The apparent size of a
10704 file is the number of bytes reported by @code{wc -c} on regular files,
10705 or more generally, @code{ls -l --block-size=1} or @code{stat --format=%s}.
10706 For example, a file containing the word @samp{zoo} with no newline would,
10707 of course, have an apparent size of 3. Such a small file may require
10708 anywhere from 0 to 16 KiB or more of disk space, depending on
10709 the type and configuration of the file system on which the file resides.
10710 However, a sparse file created with this command:
10713 dd bs=1 seek=2GiB if=/dev/null of=big
10717 has an apparent size of 2 GiB, yet on most modern
10718 systems, it actually uses almost no disk space.
10724 Equivalent to @code{--apparent-size --block-size=1}.
10726 @item -B @var{size}
10727 @itemx --block-size=@var{size}
10729 @opindex --block-size
10731 Scale sizes by @var{size} before printing them (@pxref{Block size}).
10732 For example, @option{-BG} prints sizes in units of 1,073,741,824 bytes.
10738 @cindex grand total of disk space
10739 Print a grand total of all arguments after all arguments have
10740 been processed. This can be used to find out the total disk usage of
10741 a given set of files or directories.
10744 @itemx --dereference-args
10746 @opindex --dereference-args
10747 Dereference symbolic links that are command line arguments.
10748 Does not affect other symbolic links. This is helpful for finding
10749 out the disk usage of directories, such as @file{/usr/tmp}, which
10750 are often symbolic links.
10752 @c --files0-from=FILE
10753 @filesZeroFromOption{du,, with the @option{--total} (@option{-c}) option}
10759 Equivalent to @option{--dereference-args} (@option{-D}).
10763 @cindex kibibytes for file sizes
10764 Print sizes in 1024-byte blocks, overriding the default block size
10765 (@pxref{Block size}).
10766 This option is equivalent to @option{--block-size=1K}.
10769 @itemx --count-links
10771 @opindex --count-links
10772 @cindex hard links, counting in @command{du}
10773 Count the size of all files, even if they have appeared already (as a
10777 @itemx --dereference
10779 @opindex --dereference
10780 @cindex symbolic links, dereferencing in @command{du}
10781 Dereference symbolic links (show the disk space used by the file
10782 or directory that the link points to instead of the space used by
10787 @cindex mebibytes for file sizes
10788 Print sizes in 1,048,576-byte blocks, overriding the default block size
10789 (@pxref{Block size}).
10790 This option is equivalent to @option{--block-size=1M}.
10793 @itemx --no-dereference
10795 @opindex --no-dereference
10796 @cindex symbolic links, dereferencing in @command{du}
10797 For each symbolic links encountered by @command{du},
10798 consider the disk space used by the symbolic link.
10800 @item -d @var{depth}
10801 @item --max-depth=@var{depth}
10802 @opindex -d @var{depth}
10803 @opindex --max-depth=@var{depth}
10804 @cindex limiting output of @command{du}
10805 Show the total for each directory (and file if --all) that is at
10806 most MAX_DEPTH levels down from the root of the hierarchy. The root
10807 is at level 0, so @code{du --max-depth=0} is equivalent to @code{du -s}.
10816 @opindex --summarize
10817 Display only a total for each argument.
10820 @itemx --separate-dirs
10822 @opindex --separate-dirs
10823 Normally, in the output of @command{du} (when not using @option{--summarize}),
10824 the size listed next to a directory name, @var{d}, represents the sum
10825 of sizes of all entries beneath @var{d} as well as the size of @var{d} itself.
10826 With @option{--separate-dirs}, the size reported for a directory name,
10827 @var{d}, is merely the @code{stat.st_size}-derived size of the directory
10832 @cindex last modified dates, displaying in @command{du}
10833 Show time of the most recent modification of any file in the directory,
10834 or any of its subdirectories.
10836 @itemx --time=ctime
10837 @itemx --time=status
10840 @opindex ctime@r{, show the most recent}
10841 @opindex status time@r{, show the most recent}
10842 @opindex use time@r{, show the most recent}
10843 Show the most recent status change time (the @samp{ctime} in the inode) of
10844 any file in the directory, instead of the modification time.
10846 @itemx --time=atime
10847 @itemx --time=access
10849 @opindex atime@r{, show the most recent}
10850 @opindex access time@r{, show the most recent}
10851 Show the most recent access time (the @samp{atime} in the inode) of
10852 any file in the directory, instead of the modification time.
10854 @item --time-style=@var{style}
10855 @opindex --time-style
10857 List timestamps in style @var{style}. This option has an effect only if
10858 the @option{--time} option is also specified. The @var{style} should
10859 be one of the following:
10862 @item +@var{format}
10864 List timestamps using @var{format}, where @var{format} is interpreted
10865 like the format argument of @command{date} (@pxref{date invocation}).
10866 For example, @option{--time-style="+%Y-%m-%d %H:%M:%S"} causes
10867 @command{du} to list timestamps like @samp{2002-03-30 23:45:56}. As
10868 with @command{date}, @var{format}'s interpretation is affected by the
10869 @env{LC_TIME} locale category.
10872 List timestamps in full using @acronym{ISO} 8601 date, time, and time zone
10873 format with nanosecond precision, e.g., @samp{2002-03-30
10874 23:45:56.477817180 -0700}. This style is equivalent to
10875 @samp{+%Y-%m-%d %H:%M:%S.%N %z}.
10878 List @acronym{ISO} 8601 date and time in minutes, e.g.,
10879 @samp{2002-03-30 23:45}. These timestamps are shorter than
10880 @samp{full-iso} timestamps, and are usually good enough for everyday
10881 work. This style is equivalent to @samp{+%Y-%m-%d %H:%M}.
10884 List @acronym{ISO} 8601 dates for timestamps, e.g., @samp{2002-03-30}.
10885 This style is equivalent to @samp{+%Y-%m-%d}.
10889 You can specify the default value of the @option{--time-style} option
10890 with the environment variable @env{TIME_STYLE}; if @env{TIME_STYLE} is not set
10891 the default style is @samp{long-iso}. For compatibility with @command{ls},
10892 if @env{TIME_STYLE} begins with @samp{+} and contains a newline,
10893 the newline and any later characters are ignored; if @env{TIME_STYLE}
10894 begins with @samp{posix-} the @samp{posix-} is ignored; and if
10895 @env{TIME_STYLE} is @samp{locale} it is ignored.
10898 @itemx --one-file-system
10900 @opindex --one-file-system
10901 @cindex one file system, restricting @command{du} to
10902 Skip directories that are on different file systems from the one that
10903 the argument being processed is on.
10905 @item --exclude=@var{pattern}
10906 @opindex --exclude=@var{pattern}
10907 @cindex excluding files from @command{du}
10908 When recursing, skip subdirectories or files matching @var{pattern}.
10909 For example, @code{du --exclude='*.o'} excludes files whose names
10912 @item -X @var{file}
10913 @itemx --exclude-from=@var{file}
10914 @opindex -X @var{file}
10915 @opindex --exclude-from=@var{file}
10916 @cindex excluding files from @command{du}
10917 Like @option{--exclude}, except take the patterns to exclude from @var{file},
10918 one per line. If @var{file} is @samp{-}, take the patterns from standard
10923 @cindex NFS mounts from BSD to HP-UX
10924 On BSD systems, @command{du} reports sizes that are half the correct
10925 values for files that are NFS-mounted from HP-UX systems. On HP-UX
10926 systems, it reports sizes that are twice the correct values for
10927 files that are NFS-mounted from BSD systems. This is due to a flaw
10928 in HP-UX; it also affects the HP-UX @command{du} program.
10933 @node stat invocation
10934 @section @command{stat}: Report file or file system status
10937 @cindex file status
10938 @cindex file system status
10940 @command{stat} displays information about the specified file(s). Synopsis:
10943 stat [@var{option}]@dots{} [@var{file}]@dots{}
10946 With no option, @command{stat} reports all information about the given files.
10947 But it also can be used to report the information of the file systems the
10948 given files are located on. If the files are links, @command{stat} can
10949 also give information about the files the links point to.
10951 @mayConflictWithShellBuiltIn{stat}
10956 @itemx --dereference
10958 @opindex --dereference
10959 @cindex symbolic links, dereferencing in @command{stat}
10960 Change how @command{stat} treats symbolic links.
10961 With this option, @command{stat} acts on the file referenced
10962 by each symbolic link argument.
10963 Without it, @command{stat} acts on any symbolic link argument directly.
10966 @itemx --file-system
10968 @opindex --file-system
10969 @cindex file systems
10970 Report information about the file systems where the given files are located
10971 instead of information about the files themselves.
10972 This option implies the @option{-L} option.
10975 @itemx --format=@var{format}
10977 @opindex --format=@var{format}
10978 @cindex output format
10979 Use @var{format} rather than the default format.
10980 @var{format} is automatically newline-terminated, so
10981 running a command like the following with two or more @var{file}
10982 operands produces a line of output for each operand:
10984 $ stat --format=%d:%i / /usr
10989 @itemx --printf=@var{format}
10990 @opindex --printf=@var{format}
10991 @cindex output format
10992 Use @var{format} rather than the default format.
10993 Like @option{--format}, but interpret backslash escapes,
10994 and do not output a mandatory trailing newline.
10995 If you want a newline, include @samp{\n} in the @var{format}.
10996 Here's how you would use @option{--printf} to print the device
10997 and inode numbers of @file{/} and @file{/usr}:
10999 $ stat --printf='%d:%i\n' / /usr
11008 @cindex terse output
11009 Print the information in terse form, suitable for parsing by other programs.
11013 The valid @var{format} directives for files with @option{--format} and
11014 @option{--printf} are:
11017 @item %a - Access rights in octal
11018 @item %A - Access rights in human readable form
11019 @item %b - Number of blocks allocated (see @samp{%B})
11020 @item %B - The size in bytes of each block reported by @samp{%b}
11021 @item %C - The SELinux security context of a file, if available
11022 @item %d - Device number in decimal
11023 @item %D - Device number in hex
11024 @item %f - Raw mode in hex
11025 @item %F - File type
11026 @item %g - Group ID of owner
11027 @item %G - Group name of owner
11028 @item %h - Number of hard links
11029 @item %i - Inode number
11030 @item %m - Mount point (See note below)
11031 @item %n - File name
11032 @item %N - Quoted file name with dereference if symbolic link
11033 @item %o - I/O block size
11034 @item %s - Total size, in bytes
11035 @item %t - Major device type in hex
11036 @item %T - Minor device type in hex
11037 @item %u - User ID of owner
11038 @item %U - User name of owner
11039 @item %w - Time of file birth, or @samp{-} if unknown
11040 @item %W - Time of file birth as seconds since Epoch, or @samp{0}
11041 @item %x - Time of last access
11042 @item %X - Time of last access as seconds since Epoch
11043 @item %y - Time of last modification
11044 @item %Y - Time of last modification as seconds since Epoch
11045 @item %z - Time of last change
11046 @item %Z - Time of last change as seconds since Epoch
11049 The @samp{%W}, @samp{%X}, @samp{%Y}, and @samp{%Z} formats accept a
11050 precision preceded by a period to specify the number of digits to
11051 print after the decimal point. For example, @samp{%.3X} outputs the
11052 last access time to millisecond precision. If a period is given but no
11053 precision, @command{stat} uses 9 digits, so @samp{%.X} is equivalent to
11054 @samp{%.9X}. When discarding excess precision, time stamps are truncated
11055 toward minus infinity.
11059 $ stat -c '[%015Y]' /usr
11062 $ stat -c '[%15Y]' /usr
11064 $ stat -c '[%-15Y]' /usr
11067 $ stat -c '[%.3Y]' /usr
11069 $ stat -c '[%.Y]' /usr
11070 [1288929712.114951834]
11073 The mount point printed by @samp{%m} is similar to that output
11074 by @command{df}, except that:
11077 stat does not dereference symlinks by default
11078 (unless @option{-L} is specified)
11080 stat does not search for specified device nodes in the
11081 file system list, instead operating on them directly
11084 stat outputs the alias for a bind mounted file, rather than
11085 the initial mount point of its backing device.
11086 One can recursively call stat until there is no change in output,
11087 to get the current base mount point
11090 When listing file system information (@option{--file-system} (@option{-f})),
11091 you must use a different set of @var{format} directives:
11094 @item %a - Free blocks available to non-super-user
11095 @item %b - Total data blocks in file system
11096 @item %c - Total file nodes in file system
11097 @item %d - Free file nodes in file system
11098 @item %f - Free blocks in file system
11099 @item %i - File System ID in hex
11100 @item %l - Maximum length of file names
11101 @item %n - File name
11102 @item %s - Block size (for faster transfers)
11103 @item %S - Fundamental block size (for block counts)
11104 @item %t - Type in hex
11105 @item %T - Type in human readable form
11109 Time stamps are listed according to the time zone rules specified by
11110 the @env{TZ} environment variable, or by the system default rules if
11111 @env{TZ} is not set. @xref{TZ Variable,, Specifying the Time Zone
11112 with @env{TZ}, libc, The GNU C Library Reference Manual}.
11117 @node sync invocation
11118 @section @command{sync}: Synchronize data on disk with memory
11121 @cindex synchronize disk and memory
11123 @cindex superblock, writing
11124 @cindex inodes, written buffered
11125 @command{sync} writes any data buffered in memory out to disk. This can
11126 include (but is not limited to) modified superblocks, modified inodes,
11127 and delayed reads and writes. This must be implemented by the kernel;
11128 The @command{sync} program does nothing but exercise the @code{sync} system
11131 @cindex crashes and corruption
11132 The kernel keeps data in memory to avoid doing (relatively slow) disk
11133 reads and writes. This improves performance, but if the computer
11134 crashes, data may be lost or the file system corrupted as a
11135 result. The @command{sync} command ensures everything in memory
11136 is written to disk.
11138 Any arguments are ignored, except for a lone @option{--help} or
11139 @option{--version} (@pxref{Common options}).
11144 @node truncate invocation
11145 @section @command{truncate}: Shrink or extend the size of a file
11148 @cindex truncating, file sizes
11150 @command{truncate} shrinks or extends the size of each @var{file} to the
11151 specified size. Synopsis:
11154 truncate @var{option}@dots{} @var{file}@dots{}
11157 @cindex files, creating
11158 Any @var{file} that does not exist is created.
11160 @cindex sparse files, creating
11161 @cindex holes, creating files with
11162 If a @var{file} is larger than the specified size, the extra data is lost.
11163 If a @var{file} is shorter, it is extended and the extended part (or hole)
11164 reads as zero bytes.
11166 The program accepts the following options. Also see @ref{Common options}.
11173 @opindex --no-create
11174 Do not create files that do not exist.
11179 @opindex --io-blocks
11180 Treat @var{size} as number of I/O blocks of the @var{file} rather than bytes.
11182 @item -r @var{rfile}
11183 @itemx --reference=@var{rfile}
11185 @opindex --reference
11186 Base the size of each @var{file} on the size of @var{rfile}.
11188 @item -s @var{size}
11189 @itemx --size=@var{size}
11192 Set or adjust the size of each @var{file} according to @var{size}.
11193 @multiplierSuffixesNoBlocks{size}
11195 @var{size} may also be prefixed by one of the following to adjust
11196 the size of each @var{file} based on their current size:
11198 @samp{+} => extend by
11199 @samp{-} => reduce by
11200 @samp{<} => at most
11201 @samp{>} => at least
11202 @samp{/} => round down to multiple of
11203 @samp{%} => round up to multiple of
11211 @node Printing text
11212 @chapter Printing text
11214 @cindex printing text, commands for
11215 @cindex commands for printing text
11217 This section describes commands that display text strings.
11220 * echo invocation:: Print a line of text.
11221 * printf invocation:: Format and print data.
11222 * yes invocation:: Print a string until interrupted.
11226 @node echo invocation
11227 @section @command{echo}: Print a line of text
11230 @cindex displaying text
11231 @cindex printing text
11232 @cindex text, displaying
11233 @cindex arbitrary text, displaying
11235 @command{echo} writes each given @var{string} to standard output, with a
11236 space between each and a newline after the last one. Synopsis:
11239 echo [@var{option}]@dots{} [@var{string}]@dots{}
11242 @mayConflictWithShellBuiltIn{echo}
11244 The program accepts the following options. Also see @ref{Common options}.
11245 Options must precede operands, and the normally-special argument
11246 @samp{--} has no special meaning and is treated like any other
11252 Do not output the trailing newline.
11256 @cindex backslash escapes
11257 Enable interpretation of the following backslash-escaped characters in
11266 produce no further output
11282 the eight-bit value that is the octal number @var{nnn}
11283 (zero to three octal digits), if @var{nnn} is
11284 a nine-bit value, the ninth bit is ignored
11286 the eight-bit value that is the octal number @var{nnn}
11287 (one to three octal digits), if @var{nnn} is
11288 a nine-bit value, the ninth bit is ignored
11290 the eight-bit value that is the hexadecimal number @var{hh}
11291 (one or two hexadecimal digits)
11296 @cindex backslash escapes
11297 Disable interpretation of backslash escapes in each @var{string}.
11298 This is the default. If @option{-e} and @option{-E} are both
11299 specified, the last one given takes effect.
11303 @vindex POSIXLY_CORRECT
11304 If the @env{POSIXLY_CORRECT} environment variable is set, then when
11305 @command{echo}'s first argument is not @option{-n} it outputs
11306 option-like arguments instead of treating them as options. For
11307 example, @code{echo -ne hello} outputs @samp{-ne hello} instead of
11308 plain @samp{hello}.
11310 @acronym{POSIX} does not require support for any options, and says
11311 that the behavior of @command{echo} is implementation-defined if any
11312 @var{string} contains a backslash or if the first argument is
11313 @option{-n}. Portable programs can use the @command{printf} command
11314 if they need to omit trailing newlines or output control characters or
11315 backslashes. @xref{printf invocation}.
11320 @node printf invocation
11321 @section @command{printf}: Format and print data
11324 @command{printf} does formatted printing of text. Synopsis:
11327 printf @var{format} [@var{argument}]@dots{}
11330 @command{printf} prints the @var{format} string, interpreting @samp{%}
11331 directives and @samp{\} escapes to format numeric and string arguments
11332 in a way that is mostly similar to the C @samp{printf} function.
11333 @xref{Output Conversion Syntax,, @command{printf} format directives,
11334 libc, The GNU C Library Reference Manual}, for details.
11335 The differences are listed below.
11337 @mayConflictWithShellBuiltIn{printf}
11342 The @var{format} argument is reused as necessary to convert all the
11343 given @var{argument}s. For example, the command @samp{printf %s a b}
11347 Missing @var{argument}s are treated as null strings or as zeros,
11348 depending on whether the context expects a string or a number. For
11349 example, the command @samp{printf %sx%d} prints @samp{x0}.
11353 An additional escape, @samp{\c}, causes @command{printf} to produce no
11354 further output. For example, the command @samp{printf 'A%sC\cD%sF' B
11355 E} prints @samp{ABC}.
11358 The hexadecimal escape sequence @samp{\x@var{hh}} has at most two
11359 digits, as opposed to C where it can have an unlimited number of
11360 digits. For example, the command @samp{printf '\x07e'} prints two
11361 bytes, whereas the C statement @samp{printf ("\x07e")} prints just
11366 @command{printf} has an additional directive, @samp{%b}, which prints its
11367 argument string with @samp{\} escapes interpreted in the same way as in
11368 the @var{format} string, except that octal escapes are of the form
11369 @samp{\0@var{ooo}} where @var{ooo} is 0 to 3 octal digits. If
11370 @samp{\@var{ooo}} is nine-bit value, ignore the ninth bit.
11371 If a precision is also given, it limits the number of bytes printed
11372 from the converted string.
11375 Numeric arguments must be single C constants, possibly with leading
11376 @samp{+} or @samp{-}. For example, @samp{printf %.4d -3} outputs
11380 @vindex POSIXLY_CORRECT
11381 If the leading character of a numeric argument is @samp{"} or @samp{'}
11382 then its value is the numeric value of the immediately following
11383 character. Any remaining characters are silently ignored if the
11384 @env{POSIXLY_CORRECT} environment variable is set; otherwise, a
11385 warning is printed. For example, @samp{printf "%d" "'a"} outputs
11386 @samp{97} on hosts that use the @acronym{ASCII} character set, since
11387 @samp{a} has the numeric value 97 in @acronym{ASCII}.
11392 A floating-point argument must use a period before any fractional
11393 digits, but is printed according to the @env{LC_NUMERIC} category of the
11394 current locale. For example, in a locale whose radix character is a
11395 comma, the command @samp{printf %g 3.14} outputs @samp{3,14} whereas
11396 the command @samp{printf %g 3,14} is an error.
11397 @xref{Floating point}.
11401 @command{printf} interprets @samp{\@var{ooo}} in @var{format} as an octal number
11402 (if @var{ooo} is 1 to 3 octal digits) specifying a byte to print,
11403 and @samp{\x@var{hh}} as a hexadecimal number (if @var{hh} is 1 to 2 hex
11404 digits) specifying a character to print.
11405 Note however that when @samp{\@var{ooo}} specifies a number larger than 255,
11406 @command{printf} ignores the ninth bit.
11407 For example, @samp{printf '\400'} is equivalent to @samp{printf '\0'}.
11412 @cindex ISO/IEC 10646
11414 @command{printf} interprets two character syntaxes introduced in
11415 @acronym{ISO} C 99:
11416 @samp{\u} for 16-bit Unicode (@acronym{ISO}/@acronym{IEC} 10646)
11417 characters, specified as
11418 four hexadecimal digits @var{hhhh}, and @samp{\U} for 32-bit Unicode
11419 characters, specified as eight hexadecimal digits @var{hhhhhhhh}.
11420 @command{printf} outputs the Unicode characters
11421 according to the @env{LC_CTYPE} locale. Unicode characters in the ranges
11422 U+0000...U+009F, U+D800...U+DFFF cannot be specified by this syntax, except
11423 for U+0024 ($), U+0040 (@@), and U+0060 (@`).
11425 The processing of @samp{\u} and @samp{\U} requires a full-featured
11426 @code{iconv} facility. It is activated on systems with glibc 2.2 (or newer),
11427 or when @code{libiconv} is installed prior to this package. Otherwise
11428 @samp{\u} and @samp{\U} will print as-is.
11430 The only options are a lone @option{--help} or
11431 @option{--version}. @xref{Common options}.
11432 Options must precede operands.
11434 The Unicode character syntaxes are useful for writing strings in a locale
11435 independent way. For example, a string containing the Euro currency symbol
11438 $ env printf '\u20AC 14.95'
11442 will be output correctly in all locales supporting the Euro symbol
11443 (@acronym{ISO}-8859-15, UTF-8, and others). Similarly, a Chinese string
11446 $ env printf '\u4e2d\u6587'
11450 will be output correctly in all Chinese locales (GB2312, BIG5, UTF-8, etc).
11452 Note that in these examples, the @command{printf} command has been
11453 invoked via @command{env} to ensure that we run the program found via
11454 your shell's search path, and not a shell alias or a built-in function.
11456 For larger strings, you don't need to look up the hexadecimal code
11457 values of each character one by one. @acronym{ASCII} characters mixed with \u
11458 escape sequences is also known as the JAVA source file encoding. You can
11459 use GNU recode 3.5c (or newer) to convert strings to this encoding. Here
11460 is how to convert a piece of text into a shell script which will output
11461 this text in a locale-independent way:
11464 $ LC_CTYPE=zh_CN.big5 /usr/local/bin/printf \
11465 '\u4e2d\u6587\n' > sample.txt
11466 $ recode BIG5..JAVA < sample.txt \
11467 | sed -e "s|^|/usr/local/bin/printf '|" -e "s|$|\\\\n'|" \
11474 @node yes invocation
11475 @section @command{yes}: Print a string until interrupted
11478 @cindex repeated output of a string
11480 @command{yes} prints the command line arguments, separated by spaces and
11481 followed by a newline, forever until it is killed. If no arguments are
11482 given, it prints @samp{y} followed by a newline forever until killed.
11484 Upon a write error, @command{yes} exits with status @samp{1}.
11486 The only options are a lone @option{--help} or @option{--version}.
11487 To output an argument that begins with
11488 @samp{-}, precede it with @option{--}, e.g., @samp{yes -- --help}.
11489 @xref{Common options}.
11493 @chapter Conditions
11496 @cindex commands for exit status
11497 @cindex exit status commands
11499 This section describes commands that are primarily useful for their exit
11500 status, rather than their output. Thus, they are often used as the
11501 condition of shell @code{if} statements, or as the last command in a
11505 * false invocation:: Do nothing, unsuccessfully.
11506 * true invocation:: Do nothing, successfully.
11507 * test invocation:: Check file types and compare values.
11508 * expr invocation:: Evaluate expressions.
11512 @node false invocation
11513 @section @command{false}: Do nothing, unsuccessfully
11516 @cindex do nothing, unsuccessfully
11517 @cindex failure exit status
11518 @cindex exit status of @command{false}
11520 @command{false} does nothing except return an exit status of 1, meaning
11521 @dfn{failure}. It can be used as a place holder in shell scripts
11522 where an unsuccessful command is needed.
11523 In most modern shells, @command{false} is a built-in command, so when
11524 you use @samp{false} in a script, you're probably using the built-in
11525 command, not the one documented here.
11527 @command{false} honors the @option{--help} and @option{--version} options.
11529 This version of @command{false} is implemented as a C program, and is thus
11530 more secure and faster than a shell script implementation, and may safely
11531 be used as a dummy shell for the purpose of disabling accounts.
11533 Note that @command{false} (unlike all other programs documented herein)
11534 exits unsuccessfully, even when invoked with
11535 @option{--help} or @option{--version}.
11537 Portable programs should not assume that the exit status of
11538 @command{false} is 1, as it is greater than 1 on some
11539 non-@acronym{GNU} hosts.
11542 @node true invocation
11543 @section @command{true}: Do nothing, successfully
11546 @cindex do nothing, successfully
11548 @cindex successful exit
11549 @cindex exit status of @command{true}
11551 @command{true} does nothing except return an exit status of 0, meaning
11552 @dfn{success}. It can be used as a place holder in shell scripts
11553 where a successful command is needed, although the shell built-in
11554 command @code{:} (colon) may do the same thing faster.
11555 In most modern shells, @command{true} is a built-in command, so when
11556 you use @samp{true} in a script, you're probably using the built-in
11557 command, not the one documented here.
11559 @command{true} honors the @option{--help} and @option{--version} options.
11561 Note, however, that it is possible to cause @command{true}
11562 to exit with nonzero status: with the @option{--help} or @option{--version}
11563 option, and with standard
11564 output already closed or redirected to a file that evokes an I/O error.
11565 For example, using a Bourne-compatible shell:
11568 $ ./true --version >&-
11569 ./true: write error: Bad file number
11570 $ ./true --version > /dev/full
11571 ./true: write error: No space left on device
11574 This version of @command{true} is implemented as a C program, and is thus
11575 more secure and faster than a shell script implementation, and may safely
11576 be used as a dummy shell for the purpose of disabling accounts.
11578 @node test invocation
11579 @section @command{test}: Check file types and compare values
11582 @cindex check file types
11583 @cindex compare values
11584 @cindex expression evaluation
11586 @command{test} returns a status of 0 (true) or 1 (false) depending on the
11587 evaluation of the conditional expression @var{expr}. Each part of the
11588 expression must be a separate argument.
11590 @command{test} has file status checks, string operators, and numeric
11591 comparison operators.
11593 @command{test} has an alternate form that uses opening and closing
11594 square brackets instead a leading @samp{test}. For example, instead
11595 of @samp{test -d /}, you can write @samp{[ -d / ]}. The square
11596 brackets must be separate arguments; for example, @samp{[-d /]} does
11597 not have the desired effect. Since @samp{test @var{expr}} and @samp{[
11598 @var{expr} ]} have the same meaning, only the former form is discussed
11604 test @var{expression}
11606 [ @var{expression} ]
11611 @mayConflictWithShellBuiltIn{test}
11613 If @var{expression} is omitted, @command{test} returns false.
11614 If @var{expression} is a single argument,
11615 @command{test} returns false if the argument is null and true
11616 otherwise. The argument
11617 can be any string, including strings like @samp{-d}, @samp{-1},
11618 @samp{--}, @samp{--help}, and @samp{--version} that most other
11619 programs would treat as options. To get help and version information,
11620 invoke the commands @samp{[ --help} and @samp{[ --version}, without
11621 the usual closing brackets. @xref{Common options}.
11623 @cindex exit status of @command{test}
11627 0 if the expression is true,
11628 1 if the expression is false,
11629 2 if an error occurred.
11633 * File type tests:: -[bcdfhLpSt]
11634 * Access permission tests:: -[gkruwxOG]
11635 * File characteristic tests:: -e -s -nt -ot -ef
11636 * String tests:: -z -n = == !=
11637 * Numeric tests:: -eq -ne -lt -le -gt -ge
11638 * Connectives for test:: ! -a -o
11642 @node File type tests
11643 @subsection File type tests
11645 @cindex file type tests
11647 These options test for particular types of files. (Everything's a file,
11648 but not all files are the same!)
11652 @item -b @var{file}
11654 @cindex block special check
11655 True if @var{file} exists and is a block special device.
11657 @item -c @var{file}
11659 @cindex character special check
11660 True if @var{file} exists and is a character special device.
11662 @item -d @var{file}
11664 @cindex directory check
11665 True if @var{file} exists and is a directory.
11667 @item -f @var{file}
11669 @cindex regular file check
11670 True if @var{file} exists and is a regular file.
11672 @item -h @var{file}
11673 @itemx -L @var{file}
11676 @cindex symbolic link check
11677 True if @var{file} exists and is a symbolic link.
11678 Unlike all other file-related tests, this test does not dereference
11679 @var{file} if it is a symbolic link.
11681 @item -p @var{file}
11683 @cindex named pipe check
11684 True if @var{file} exists and is a named pipe.
11686 @item -S @var{file}
11688 @cindex socket check
11689 True if @var{file} exists and is a socket.
11693 @cindex terminal check
11694 True if @var{fd} is a file descriptor that is associated with a
11700 @node Access permission tests
11701 @subsection Access permission tests
11703 @cindex access permission tests
11704 @cindex permission tests
11706 These options test for particular access permissions.
11710 @item -g @var{file}
11712 @cindex set-group-ID check
11713 True if @var{file} exists and has its set-group-ID bit set.
11715 @item -k @var{file}
11717 @cindex sticky bit check
11718 True if @var{file} exists and has its @dfn{sticky} bit set.
11720 @item -r @var{file}
11722 @cindex readable file check
11723 True if @var{file} exists and read permission is granted.
11725 @item -u @var{file}
11727 @cindex set-user-ID check
11728 True if @var{file} exists and has its set-user-ID bit set.
11730 @item -w @var{file}
11732 @cindex writable file check
11733 True if @var{file} exists and write permission is granted.
11735 @item -x @var{file}
11737 @cindex executable file check
11738 True if @var{file} exists and execute permission is granted
11739 (or search permission, if it is a directory).
11741 @item -O @var{file}
11743 @cindex owned by effective user ID check
11744 True if @var{file} exists and is owned by the current effective user ID.
11746 @item -G @var{file}
11748 @cindex owned by effective group ID check
11749 True if @var{file} exists and is owned by the current effective group ID.
11753 @node File characteristic tests
11754 @subsection File characteristic tests
11756 @cindex file characteristic tests
11758 These options test other file characteristics.
11762 @item -e @var{file}
11764 @cindex existence-of-file check
11765 True if @var{file} exists.
11767 @item -s @var{file}
11769 @cindex nonempty file check
11770 True if @var{file} exists and has a size greater than zero.
11772 @item @var{file1} -nt @var{file2}
11774 @cindex newer-than file check
11775 True if @var{file1} is newer (according to modification date) than
11776 @var{file2}, or if @var{file1} exists and @var{file2} does not.
11778 @item @var{file1} -ot @var{file2}
11780 @cindex older-than file check
11781 True if @var{file1} is older (according to modification date) than
11782 @var{file2}, or if @var{file2} exists and @var{file1} does not.
11784 @item @var{file1} -ef @var{file2}
11786 @cindex same file check
11787 @cindex hard link check
11788 True if @var{file1} and @var{file2} have the same device and inode
11789 numbers, i.e., if they are hard links to each other.
11795 @subsection String tests
11797 @cindex string tests
11799 These options test string characteristics. You may need to quote
11800 @var{string} arguments for the shell. For example:
11806 The quotes here prevent the wrong arguments from being passed to
11807 @command{test} if @samp{$V} is empty or contains special characters.
11811 @item -z @var{string}
11813 @cindex zero-length string check
11814 True if the length of @var{string} is zero.
11816 @item -n @var{string}
11817 @itemx @var{string}
11819 @cindex nonzero-length string check
11820 True if the length of @var{string} is nonzero.
11822 @item @var{string1} = @var{string2}
11824 @cindex equal string check
11825 True if the strings are equal.
11827 @item @var{string1} == @var{string2}
11829 @cindex equal string check
11830 True if the strings are equal (synonym for =).
11832 @item @var{string1} != @var{string2}
11834 @cindex not-equal string check
11835 True if the strings are not equal.
11840 @node Numeric tests
11841 @subsection Numeric tests
11843 @cindex numeric tests
11844 @cindex arithmetic tests
11846 Numeric relational operators. The arguments must be entirely numeric
11847 (possibly negative), or the special expression @w{@code{-l @var{string}}},
11848 which evaluates to the length of @var{string}.
11852 @item @var{arg1} -eq @var{arg2}
11853 @itemx @var{arg1} -ne @var{arg2}
11854 @itemx @var{arg1} -lt @var{arg2}
11855 @itemx @var{arg1} -le @var{arg2}
11856 @itemx @var{arg1} -gt @var{arg2}
11857 @itemx @var{arg1} -ge @var{arg2}
11864 These arithmetic binary operators return true if @var{arg1} is equal,
11865 not-equal, less-than, less-than-or-equal, greater-than, or
11866 greater-than-or-equal than @var{arg2}, respectively.
11873 test -1 -gt -2 && echo yes
11875 test -l abc -gt 1 && echo yes
11878 @error{} test: integer expression expected before -eq
11882 @node Connectives for test
11883 @subsection Connectives for @command{test}
11885 @cindex logical connectives
11886 @cindex connectives, logical
11888 The usual logical connectives.
11894 True if @var{expr} is false.
11896 @item @var{expr1} -a @var{expr2}
11898 @cindex logical and operator
11899 @cindex and operator
11900 True if both @var{expr1} and @var{expr2} are true.
11902 @item @var{expr1} -o @var{expr2}
11904 @cindex logical or operator
11905 @cindex or operator
11906 True if either @var{expr1} or @var{expr2} is true.
11911 @node expr invocation
11912 @section @command{expr}: Evaluate expressions
11915 @cindex expression evaluation
11916 @cindex evaluation of expressions
11918 @command{expr} evaluates an expression and writes the result on standard
11919 output. Each token of the expression must be a separate argument.
11921 Operands are either integers or strings. Integers consist of one or
11922 more decimal digits, with an optional leading @samp{-}.
11923 @command{expr} converts
11924 anything appearing in an operand position to an integer or a string
11925 depending on the operation being applied to it.
11927 Strings are not quoted for @command{expr} itself, though you may need to
11928 quote them to protect characters with special meaning to the shell,
11929 e.g., spaces. However, regardless of whether it is quoted, a string
11930 operand should not be a parenthesis or any of @command{expr}'s
11931 operators like @code{+}, so you cannot safely pass an arbitrary string
11932 @code{$str} to expr merely by quoting it to the shell. One way to
11933 work around this is to use the @sc{gnu} extension @code{+},
11934 (e.g., @code{+ "$str" = foo}); a more portable way is to use
11935 @code{@w{" $str"}} and to adjust the rest of the expression to take
11936 the leading space into account (e.g., @code{@w{" $str" = " foo"}}).
11938 You should not pass a negative integer or a string with leading
11939 @samp{-} as @command{expr}'s first argument, as it might be
11940 misinterpreted as an option; this can be avoided by parenthesization.
11941 Also, portable scripts should not use a string operand that happens to
11942 take the form of an integer; this can be worked around by inserting
11943 leading spaces as mentioned above.
11945 @cindex parentheses for grouping
11946 Operators may be given as infix symbols or prefix keywords. Parentheses
11947 may be used for grouping in the usual manner. You must quote
11948 parentheses and many operators to avoid the shell evaluating them,
11951 When built with support for the GNU MP library, @command{expr} uses
11952 arbitrary-precision arithmetic; otherwise, it uses native arithmetic
11953 types and may fail due to arithmetic overflow.
11955 The only options are @option{--help} and @option{--version}. @xref{Common
11956 options}. Options must precede operands.
11958 @cindex exit status of @command{expr}
11962 0 if the expression is neither null nor 0,
11963 1 if the expression is null or 0,
11964 2 if the expression is invalid,
11965 3 if an internal error occurred (e.g., arithmetic overflow).
11969 * String expressions:: + : match substr index length
11970 * Numeric expressions:: + - * / %
11971 * Relations for expr:: | & < <= = == != >= >
11972 * Examples of expr:: Examples.
11976 @node String expressions
11977 @subsection String expressions
11979 @cindex string expressions
11980 @cindex expressions, string
11982 @command{expr} supports pattern matching and other string operators. These
11983 have higher precedence than both the numeric and relational operators (in
11984 the next sections).
11988 @item @var{string} : @var{regex}
11989 @cindex pattern matching
11990 @cindex regular expression matching
11991 @cindex matching patterns
11992 Perform pattern matching. The arguments are converted to strings and the
11993 second is considered to be a (basic, a la GNU @code{grep}) regular
11994 expression, with a @code{^} implicitly prepended. The first argument is
11995 then matched against this regular expression.
11997 If the match succeeds and @var{regex} uses @samp{\(} and @samp{\)}, the
11998 @code{:} expression returns the part of @var{string} that matched the
11999 subexpression; otherwise, it returns the number of characters matched.
12001 If the match fails, the @code{:} operator returns the null string if
12002 @samp{\(} and @samp{\)} are used in @var{regex}, otherwise 0.
12004 @kindex \( @r{regexp operator}
12005 Only the first @samp{\( @dots{} \)} pair is relevant to the return
12006 value; additional pairs are meaningful only for grouping the regular
12007 expression operators.
12009 @kindex \+ @r{regexp operator}
12010 @kindex \? @r{regexp operator}
12011 @kindex \| @r{regexp operator}
12012 In the regular expression, @code{\+}, @code{\?}, and @code{\|} are
12013 operators which respectively match one or more, zero or one, or separate
12014 alternatives. SunOS and other @command{expr}'s treat these as regular
12015 characters. (@acronym{POSIX} allows either behavior.)
12016 @xref{Top, , Regular Expression Library, regex, Regex}, for details of
12017 regular expression syntax. Some examples are in @ref{Examples of expr}.
12019 @item match @var{string} @var{regex}
12021 An alternative way to do pattern matching. This is the same as
12022 @w{@samp{@var{string} : @var{regex}}}.
12024 @item substr @var{string} @var{position} @var{length}
12026 Returns the substring of @var{string} beginning at @var{position}
12027 with length at most @var{length}. If either @var{position} or
12028 @var{length} is negative, zero, or non-numeric, returns the null string.
12030 @item index @var{string} @var{charset}
12032 Returns the first position in @var{string} where the first character in
12033 @var{charset} was found. If no character in @var{charset} is found in
12034 @var{string}, return 0.
12036 @item length @var{string}
12038 Returns the length of @var{string}.
12040 @item + @var{token}
12042 Interpret @var{token} as a string, even if it is a keyword like @var{match}
12043 or an operator like @code{/}.
12044 This makes it possible to test @code{expr length + "$x"} or
12045 @code{expr + "$x" : '.*/\(.\)'} and have it do the right thing even if
12046 the value of @var{$x} happens to be (for example) @code{/} or @code{index}.
12047 This operator is a @acronym{GNU} extension. Portable shell scripts should use
12048 @code{@w{" $token"} : @w{' \(.*\)'}} instead of @code{+ "$token"}.
12052 To make @command{expr} interpret keywords as strings, you must use the
12053 @code{quote} operator.
12056 @node Numeric expressions
12057 @subsection Numeric expressions
12059 @cindex numeric expressions
12060 @cindex expressions, numeric
12062 @command{expr} supports the usual numeric operators, in order of increasing
12063 precedence. These numeric operators have lower precedence than the
12064 string operators described in the previous section, and higher precedence
12065 than the connectives (next section).
12073 @cindex subtraction
12074 Addition and subtraction. Both arguments are converted to integers;
12075 an error occurs if this cannot be done.
12081 @cindex multiplication
12084 Multiplication, division, remainder. Both arguments are converted to
12085 integers; an error occurs if this cannot be done.
12090 @node Relations for expr
12091 @subsection Relations for @command{expr}
12093 @cindex connectives, logical
12094 @cindex logical connectives
12095 @cindex relations, numeric or string
12097 @command{expr} supports the usual logical connectives and relations. These
12098 have lower precedence than the string and numeric operators
12099 (previous sections). Here is the list, lowest-precedence operator first.
12105 @cindex logical or operator
12106 @cindex or operator
12107 Returns its first argument if that is neither null nor zero, otherwise
12108 its second argument if it is neither null nor zero, otherwise 0. It
12109 does not evaluate its second argument if its first argument is neither
12114 @cindex logical and operator
12115 @cindex and operator
12116 Return its first argument if neither argument is null or zero, otherwise
12117 0. It does not evaluate its second argument if its first argument is
12120 @item < <= = == != >= >
12127 @cindex comparison operators
12129 Compare the arguments and return 1 if the relation is true, 0 otherwise.
12130 @code{==} is a synonym for @code{=}. @command{expr} first tries to convert
12131 both arguments to integers and do a numeric comparison; if either
12132 conversion fails, it does a lexicographic comparison using the character
12133 collating sequence specified by the @env{LC_COLLATE} locale.
12138 @node Examples of expr
12139 @subsection Examples of using @command{expr}
12141 @cindex examples of @command{expr}
12142 Here are a few examples, including quoting for shell metacharacters.
12144 To add 1 to the shell variable @code{foo}, in Bourne-compatible shells:
12147 foo=`expr $foo + 1`
12150 To print the non-directory part of the file name stored in
12151 @code{$fname}, which need not contain a @code{/}:
12154 expr $fname : '.*/\(.*\)' '|' $fname
12157 An example showing that @code{\+} is an operator:
12165 expr abc : 'a\(.\)c'
12167 expr index abcdef cz
12170 @error{} expr: syntax error
12171 expr index + index a
12177 @chapter Redirection
12179 @cindex redirection
12180 @cindex commands for redirection
12182 Unix shells commonly provide several forms of @dfn{redirection}---ways
12183 to change the input source or output destination of a command. But one
12184 useful redirection is performed by a separate command, not by the shell;
12185 it's described here.
12188 * tee invocation:: Redirect output to multiple files or processes.
12192 @node tee invocation
12193 @section @command{tee}: Redirect output to multiple files or processes
12196 @cindex pipe fitting
12197 @cindex destinations, multiple output
12198 @cindex read from stdin and write to stdout and files
12200 The @command{tee} command copies standard input to standard output and also
12201 to any files given as arguments. This is useful when you want not only
12202 to send some data down a pipe, but also to save a copy. Synopsis:
12205 tee [@var{option}]@dots{} [@var{file}]@dots{}
12208 If a file being written to does not already exist, it is created. If a
12209 file being written to already exists, the data it previously contained
12210 is overwritten unless the @option{-a} option is used.
12212 A @var{file} of @samp{-} causes @command{tee} to send another copy of
12213 input to standard output, but this is typically not that useful as the
12214 copies are interleaved.
12216 The program accepts the following options. Also see @ref{Common options}.
12223 Append standard input to the given files rather than overwriting
12227 @itemx --ignore-interrupts
12229 @opindex --ignore-interrupts
12230 Ignore interrupt signals.
12234 The @command{tee} command is useful when you happen to be transferring a large
12235 amount of data and also want to summarize that data without reading
12236 it a second time. For example, when you are downloading a DVD image,
12237 you often want to verify its signature or checksum right away.
12238 The inefficient way to do it is simply:
12241 wget http://example.com/some.iso && sha1sum some.iso
12244 One problem with the above is that it makes you wait for the
12245 download to complete before starting the time-consuming SHA1 computation.
12246 Perhaps even more importantly, the above requires reading
12247 the DVD image a second time (the first was from the network).
12249 The efficient way to do it is to interleave the download
12250 and SHA1 computation. Then, you'll get the checksum for
12251 free, because the entire process parallelizes so well:
12254 # slightly contrived, to demonstrate process substitution
12255 wget -O - http://example.com/dvd.iso \
12256 | tee >(sha1sum > dvd.sha1) > dvd.iso
12259 That makes @command{tee} write not just to the expected output file,
12260 but also to a pipe running @command{sha1sum} and saving the final
12261 checksum in a file named @file{dvd.sha1}.
12263 Note, however, that this example relies on a feature of modern shells
12264 called @dfn{process substitution}
12265 (the @samp{>(command)} syntax, above;
12266 @xref{Process Substitution,,Process Substitution, bashref,
12267 The Bash Reference Manual}.),
12268 so it works with @command{zsh}, @command{bash}, and @command{ksh},
12269 but not with @command{/bin/sh}. So if you write code like this
12270 in a shell script, be sure to start the script with @samp{#!/bin/bash}.
12272 Since the above example writes to one file and one process,
12273 a more conventional and portable use of @command{tee} is even better:
12276 wget -O - http://example.com/dvd.iso \
12277 | tee dvd.iso | sha1sum > dvd.sha1
12280 You can extend this example to make @command{tee} write to two processes,
12281 computing MD5 and SHA1 checksums in parallel. In this case,
12282 process substitution is required:
12285 wget -O - http://example.com/dvd.iso \
12286 | tee >(sha1sum > dvd.sha1) \
12287 >(md5sum > dvd.md5) \
12291 This technique is also useful when you want to make a @emph{compressed}
12292 copy of the contents of a pipe.
12293 Consider a tool to graphically summarize disk usage data from @samp{du -ak}.
12294 For a large hierarchy, @samp{du -ak} can run for a long time,
12295 and can easily produce terabytes of data, so you won't want to
12296 rerun the command unnecessarily. Nor will you want to save
12297 the uncompressed output.
12299 Doing it the inefficient way, you can't even start the GUI
12300 until after you've compressed all of the @command{du} output:
12303 du -ak | gzip -9 > /tmp/du.gz
12304 gzip -d /tmp/du.gz | xdiskusage -a
12307 With @command{tee} and process substitution, you start the GUI
12308 right away and eliminate the decompression completely:
12311 du -ak | tee >(gzip -9 > /tmp/du.gz) | xdiskusage -a
12314 Finally, if you regularly create more than one type of
12315 compressed tarball at once, for example when @code{make dist} creates
12316 both @command{gzip}-compressed and @command{bzip2}-compressed tarballs,
12317 there may be a better way.
12318 Typical @command{automake}-generated @file{Makefile} rules create
12319 the two compressed tar archives with commands in sequence, like this
12320 (slightly simplified):
12323 tardir=your-pkg-M.N
12324 tar chof - "$tardir" | gzip -9 -c > your-pkg-M.N.tar.gz
12325 tar chof - "$tardir" | bzip2 -9 -c > your-pkg-M.N.tar.bz2
12328 However, if the hierarchy you are archiving and compressing is larger
12329 than a couple megabytes, and especially if you are using a multi-processor
12330 system with plenty of memory, then you can do much better by reading the
12331 directory contents only once and running the compression programs in parallel:
12334 tardir=your-pkg-M.N
12335 tar chof - "$tardir" \
12336 | tee >(gzip -9 -c > your-pkg-M.N.tar.gz) \
12337 | bzip2 -9 -c > your-pkg-M.N.tar.bz2
12343 @node File name manipulation
12344 @chapter File name manipulation
12346 @cindex file name manipulation
12347 @cindex manipulation of file names
12348 @cindex commands for file name manipulation
12350 This section describes commands that manipulate file names.
12353 * basename invocation:: Strip directory and suffix from a file name.
12354 * dirname invocation:: Strip last file name component.
12355 * pathchk invocation:: Check file name validity and portability.
12356 * mktemp invocation:: Create temporary file or directory.
12360 @node basename invocation
12361 @section @command{basename}: Strip directory and suffix from a file name
12364 @cindex strip directory and suffix from file names
12365 @cindex directory, stripping from file names
12366 @cindex suffix, stripping from file names
12367 @cindex file names, stripping directory and suffix
12368 @cindex leading directory components, stripping
12370 @command{basename} removes any leading directory components from
12371 @var{name}. Synopsis:
12374 basename @var{name} [@var{suffix}]
12377 If @var{suffix} is specified and is identical to the end of @var{name},
12378 it is removed from @var{name} as well. Note that since trailing slashes
12379 are removed prior to suffix matching, @var{suffix} will do nothing if it
12380 contains slashes. @command{basename} prints the result on standard
12383 @c This test is used both here and in the section on dirname.
12384 @macro basenameAndDirname
12385 Together, @command{basename} and @command{dirname} are designed such
12386 that if @samp{ls "$name"} succeeds, then the command sequence @samp{cd
12387 "$(dirname "$name")"; ls "$(basename "$name")"} will, too. This works
12388 for everything except file names containing a trailing newline.
12390 @basenameAndDirname
12392 @acronym{POSIX} allows the implementation to define the results if
12393 @var{name} is empty or @samp{//}. In the former case, @acronym{GNU}
12394 @command{basename} returns the empty string. In the latter case, the
12395 result is @samp{//} on platforms where @var{//} is distinct from
12396 @var{/}, and @samp{/} on platforms where there is no difference.
12398 The only options are @option{--help} and @option{--version}. @xref{Common
12399 options}. Options must precede operands.
12407 basename /usr/bin/sort
12410 basename include/stdio.h .h
12414 @node dirname invocation
12415 @section @command{dirname}: Strip last file name component
12418 @cindex directory components, printing
12419 @cindex stripping non-directory suffix
12420 @cindex non-directory suffix, stripping
12422 @command{dirname} prints all but the final slash-delimited component of
12423 @var{name}. Slashes on either side of the final component are also
12424 removed. If the string contains no slash, @command{dirname} prints
12425 @samp{.} (meaning the current directory). Synopsis:
12431 @var{name} need not be a file name, but if it is, this operation
12432 effectively lists the directory that contains the final component,
12433 including the case when the final component is itself a directory.
12435 @basenameAndDirname
12437 @acronym{POSIX} allows the implementation to define the results if
12438 @var{name} is @samp{//}. With @acronym{GNU} @command{dirname}, the
12439 result is @samp{//} on platforms where @var{//} is distinct from
12440 @var{/}, and @samp{/} on platforms where there is no difference.
12442 The only options are @option{--help} and @option{--version}. @xref{Common
12450 # Output "/usr/bin".
12451 dirname /usr/bin/sort
12452 dirname /usr/bin//.//
12459 @node pathchk invocation
12460 @section @command{pathchk}: Check file name validity and portability
12463 @cindex file names, checking validity and portability
12464 @cindex valid file names, checking for
12465 @cindex portable file names, checking for
12467 @command{pathchk} checks validity and portability of file names. Synopsis:
12470 pathchk [@var{option}]@dots{} @var{name}@dots{}
12473 For each @var{name}, @command{pathchk} prints an error message if any of
12474 these conditions is true:
12478 One of the existing directories in @var{name} does not have search
12479 (execute) permission,
12481 The length of @var{name} is larger than the maximum supported by the
12484 The length of one component of @var{name} is longer than
12485 its file system's maximum.
12488 A nonexistent @var{name} is not an error, so long a file with that
12489 name could be created under the above conditions.
12491 The program accepts the following options. Also see @ref{Common options}.
12492 Options must precede operands.
12498 Instead of performing checks based on the underlying file system,
12499 print an error message if any of these conditions is true:
12503 A file name is empty.
12506 A file name contains a character outside the @acronym{POSIX} portable file
12507 name character set, namely, the ASCII letters and digits, @samp{.},
12508 @samp{_}, @samp{-}, and @samp{/}.
12511 The length of a file name or one of its components exceeds the
12512 @acronym{POSIX} minimum limits for portability.
12517 Print an error message if a file name is empty, or if it contains a component
12518 that begins with @samp{-}.
12520 @item --portability
12521 @opindex --portability
12522 Print an error message if a file name is not portable to all @acronym{POSIX}
12523 hosts. This option is equivalent to @samp{-p -P}.
12527 @cindex exit status of @command{pathchk}
12531 0 if all specified file names passed all checks,
12535 @node mktemp invocation
12536 @section @command{mktemp}: Create temporary file or directory
12539 @cindex file names, creating temporary
12540 @cindex directory, creating temporary
12541 @cindex temporary files and directories
12543 @command{mktemp} manages the creation of temporary files and
12544 directories. Synopsis:
12547 mktemp [@var{option}]@dots{} [@var{template}]
12550 Safely create a temporary file or directory based on @var{template},
12551 and print its name. If given, @var{template} must include at least
12552 three consecutive @samp{X}s in the last component. If omitted, the template
12553 @samp{tmp.XXXXXXXXXX} is used, and option @option{--tmpdir} is
12554 implied. The final run of @samp{X}s in the @var{template} will be replaced
12555 by alpha-numeric characters; thus, on a case-sensitive file system,
12556 and with a @var{template} including a run of @var{n} instances of @samp{X},
12557 there are @samp{62**@var{n}} potential file names.
12559 Older scripts used to create temporary files by simply joining the
12560 name of the program with the process id (@samp{$$}) as a suffix.
12561 However, that naming scheme is easily predictable, and suffers from a
12562 race condition where the attacker can create an appropriately named
12563 symbolic link, such that when the script then opens a handle to what
12564 it thought was an unused file, it is instead modifying an existing
12565 file. Using the same scheme to create a directory is slightly safer,
12566 since the @command{mkdir} will fail if the target already exists, but
12567 it is still inferior because it allows for denial of service attacks.
12568 Therefore, modern scripts should use the @command{mktemp} command to
12569 guarantee that the generated name will be unpredictable, and that
12570 knowledge of the temporary file name implies that the file was created
12571 by the current script and cannot be modified by other users.
12573 When creating a file, the resulting file has read and write
12574 permissions for the current user, but no permissions for the group or
12575 others; these permissions are reduced if the current umask is more
12578 Here are some examples (although note that if you repeat them, you
12579 will most likely get different file names):
12584 Create a temporary file in the current directory.
12591 Create a temporary file with a known suffix.
12593 $ mktemp --suffix=.txt file-XXXX
12595 $ mktemp file-XXXX-XXXX.txt
12600 Create a secure fifo relative to the user's choice of @env{TMPDIR},
12601 but falling back to the current directory rather than @file{/tmp}.
12602 Note that @command{mktemp} does not create fifos, but can create a
12603 secure directory in which the fifo can live. Exit the shell if the
12604 directory or fifo could not be created.
12606 $ dir=$(mktemp -p "$@{TMPDIR:-.@}" -d dir-XXXX) || exit 1
12608 $ mkfifo "$fifo" || @{ rmdir "$dir"; exit 1; @}
12612 Create and use a temporary file if possible, but ignore failure. The
12613 file will reside in the directory named by @env{TMPDIR}, if specified,
12614 or else in @file{/tmp}.
12616 $ file=$(mktemp -q) && @{
12617 > # Safe to use $file only within this block. Use quotes,
12618 > # since $TMPDIR, and thus $file, may contain whitespace.
12619 > echo ... > "$file"
12625 Act as a semi-random character generator (it is not fully random,
12626 since it is impacted by the contents of the current directory). To
12627 avoid security holes, do not use the resulting names to create a file.
12637 The program accepts the following options. Also see @ref{Common options}.
12644 @opindex --directory
12645 Create a directory rather than a file. The directory will have read,
12646 write, and search permissions for the current user, but no permissions
12647 for the group or others; these permissions are reduced if the current
12648 umask is more restrictive.
12654 Suppress diagnostics about failure to create a file or directory. The
12655 exit status will still reflect whether a file was created.
12661 Generate a temporary name that does not name an existing file, without
12662 changing the file system contents. Using the output of this command
12663 to create a new file is inherently unsafe, as there is a window of
12664 time between generating the name and using it where another process
12665 can create an object by the same name.
12668 @itemx --tmpdir[=@var{dir}]
12671 Treat @var{template} relative to the directory @var{dir}. If
12672 @var{dir} is not specified (only possible with the long option
12673 @option{--tmpdir}) or is the empty string, use the value of
12674 @env{TMPDIR} if available, otherwise use @samp{/tmp}. If this is
12675 specified, @var{template} must not be absolute. However,
12676 @var{template} can still contain slashes, although intermediate
12677 directories must already exist.
12679 @item --suffix=@var{suffix}
12681 Append @var{suffix} to the @var{template}. @var{suffix} must not
12682 contain slash. If @option{--suffix} is specified, @var{template} must
12683 end in @samp{X}; if it is not specified, then an appropriate
12684 @option{--suffix} is inferred by finding the last @samp{X} in
12685 @var{template}. This option exists for use with the default
12686 @var{template} and for the creation of a @var{suffix} that starts with
12691 Treat @var{template} as a single file relative to the value of
12692 @env{TMPDIR} if available, or to the directory specified by
12693 @option{-p}, otherwise to @samp{/tmp}. @var{template} must not
12694 contain slashes. This option is deprecated; the use of @option{-p}
12695 without @option{-t} offers better defaults (by favoring the command
12696 line over @env{TMPDIR}) and more flexibility (by allowing intermediate
12701 @cindex exit status of @command{mktemp}
12705 0 if the file was created,
12710 @node Working context
12711 @chapter Working context
12713 @cindex working context
12714 @cindex commands for printing the working context
12716 This section describes commands that display or alter the context in
12717 which you are working: the current directory, the terminal settings, and
12718 so forth. See also the user-related commands in the next section.
12721 * pwd invocation:: Print working directory.
12722 * stty invocation:: Print or change terminal characteristics.
12723 * printenv invocation:: Print environment variables.
12724 * tty invocation:: Print file name of terminal on standard input.
12728 @node pwd invocation
12729 @section @command{pwd}: Print working directory
12732 @cindex print name of current directory
12733 @cindex current working directory, printing
12734 @cindex working directory, printing
12737 @command{pwd} prints the name of the current directory. Synopsis:
12740 pwd [@var{option}]@dots{}
12743 The program accepts the following options. Also see @ref{Common options}.
12750 If the contents of the environment variable @env{PWD} provide an
12751 absolute name of the current directory with no @samp{.} or @samp{..}
12752 components, but possibly with symbolic links, then output those
12753 contents. Otherwise, fall back to default @option{-P} handling.
12758 @opindex --physical
12759 Print a fully resolved name for the current directory. That is, all
12760 components of the printed name will be actual directory names---none
12761 will be symbolic links.
12764 @cindex symbolic links and @command{pwd}
12765 If @option{-L} and @option{-P} are both given, the last one takes
12766 precedence. If neither option is given, then this implementation uses
12767 @option{-P} as the default unless the @env{POSIXLY_CORRECT}
12768 environment variable is set.
12770 @mayConflictWithShellBuiltIn{pwd}
12775 @node stty invocation
12776 @section @command{stty}: Print or change terminal characteristics
12779 @cindex change or print terminal settings
12780 @cindex terminal settings
12781 @cindex line settings of terminal
12783 @command{stty} prints or changes terminal characteristics, such as baud rate.
12787 stty [@var{option}] [@var{setting}]@dots{}
12788 stty [@var{option}]
12791 If given no line settings, @command{stty} prints the baud rate, line
12792 discipline number (on systems that support it), and line settings
12793 that have been changed from the values set by @samp{stty sane}.
12794 By default, mode reading and setting are performed on the tty line
12795 connected to standard input, although this can be modified by the
12796 @option{--file} option.
12798 @command{stty} accepts many non-option arguments that change aspects of
12799 the terminal line operation, as described below.
12801 The program accepts the following options. Also see @ref{Common options}.
12808 Print all current settings in human-readable form. This option may not
12809 be used in combination with any line settings.
12811 @item -F @var{device}
12812 @itemx --file=@var{device}
12815 Set the line opened by the file name specified in @var{device} instead of
12816 the tty line connected to standard input. This option is necessary
12817 because opening a @acronym{POSIX} tty requires use of the
12818 @code{O_NONDELAY} flag to prevent a @acronym{POSIX} tty from blocking
12819 until the carrier detect line is high if
12820 the @code{clocal} flag is not set. Hence, it is not always possible
12821 to allow the shell to open the device in the traditional manner.
12827 @cindex machine-readable @command{stty} output
12828 Print all current settings in a form that can be used as an argument to
12829 another @command{stty} command to restore the current settings. This option
12830 may not be used in combination with any line settings.
12834 Many settings can be turned off by preceding them with a @samp{-}.
12835 Such arguments are marked below with ``May be negated'' in their
12836 description. The descriptions themselves refer to the positive
12837 case, that is, when @emph{not} negated (unless stated otherwise,
12840 Some settings are not available on all @acronym{POSIX} systems, since they use
12841 extensions. Such arguments are marked below with
12842 ``Non-@acronym{POSIX}'' in their description. On non-@acronym{POSIX}
12843 systems, those or other settings also may not
12844 be available, but it's not feasible to document all the variations: just
12850 * Control:: Control settings
12851 * Input:: Input settings
12852 * Output:: Output settings
12853 * Local:: Local settings
12854 * Combination:: Combination settings
12855 * Characters:: Special characters
12856 * Special:: Special settings
12861 @subsection Control settings
12863 @cindex control settings
12869 @cindex two-way parity
12870 Generate parity bit in output and expect parity bit in input.
12876 @cindex even parity
12877 Set odd parity (even if negated). May be negated.
12884 @cindex character size
12885 @cindex eight-bit characters
12886 Set character size to 5, 6, 7, or 8 bits.
12891 Send a hangup signal when the last process closes the tty. May be
12897 Use two stop bits per character (one if negated). May be negated.
12901 Allow input to be received. May be negated.
12905 @cindex modem control
12906 Disable modem control signals. May be negated.
12910 @cindex hardware flow control
12911 @cindex flow control, hardware
12912 @cindex RTS/CTS flow control
12913 Enable RTS/CTS flow control. Non-@acronym{POSIX}. May be negated.
12918 @subsection Input settings
12920 @cindex input settings
12921 These settings control operations on data received from the terminal.
12926 @cindex breaks, ignoring
12927 Ignore break characters. May be negated.
12931 @cindex breaks, cause interrupts
12932 Make breaks cause an interrupt signal. May be negated.
12936 @cindex parity, ignoring
12937 Ignore characters with parity errors. May be negated.
12941 @cindex parity errors, marking
12942 Mark parity errors (with a 255-0-character sequence). May be negated.
12946 Enable input parity checking. May be negated.
12950 @cindex eight-bit input
12951 Clear high (8th) bit of input characters. May be negated.
12955 @cindex newline, translating to return
12956 Translate newline to carriage return. May be negated.
12960 @cindex return, ignoring
12961 Ignore carriage return. May be negated.
12965 @cindex return, translating to newline
12966 Translate carriage return to newline. May be negated.
12970 @cindex input encoding, UTF-8
12971 Assume input characters are UTF-8 encoded. May be negated.
12975 @kindex C-s/C-q flow control
12976 @cindex XON/XOFF flow control
12977 Enable XON/XOFF flow control (that is, @kbd{CTRL-S}/@kbd{CTRL-Q}). May
12984 @cindex software flow control
12985 @cindex flow control, software
12986 Enable sending of @code{stop} character when the system input buffer
12987 is almost full, and @code{start} character when it becomes almost
12988 empty again. May be negated.
12992 @cindex uppercase, translating to lowercase
12993 Translate uppercase characters to lowercase. Non-@acronym{POSIX}. May be
12994 negated. Note ilcuc is not implemented, as one would not be able to issue
12995 almost any (lowercase) Unix command, after invoking it.
12999 Allow any character to restart output (only the start character
13000 if negated). Non-@acronym{POSIX}. May be negated.
13004 @cindex beeping at input buffer full
13005 Enable beeping and not flushing input buffer if a character arrives
13006 when the input buffer is full. Non-@acronym{POSIX}. May be negated.
13011 @subsection Output settings
13013 @cindex output settings
13014 These settings control operations on data sent to the terminal.
13019 Postprocess output. May be negated.
13023 @cindex lowercase, translating to output
13024 Translate lowercase characters to uppercase. Non-@acronym{POSIX}. May be
13025 negated. (Note ouclc is not currently implemented.)
13029 @cindex return, translating to newline
13030 Translate carriage return to newline. Non-@acronym{POSIX}. May be negated.
13034 @cindex newline, translating to crlf
13035 Translate newline to carriage return-newline. Non-@acronym{POSIX}. May be
13040 Do not print carriage returns in the first column. Non-@acronym{POSIX}.
13045 Newline performs a carriage return. Non-@acronym{POSIX}. May be negated.
13049 @cindex pad instead of timing for delaying
13050 Use fill (padding) characters instead of timing for delays.
13051 Non-@acronym{POSIX}.
13056 @cindex pad character
13057 Use @acronym{ASCII} @sc{del} characters for fill instead of
13058 @acronym{ASCII} @sc{nul} characters. Non-@acronym{POSIX}.
13064 Newline delay style. Non-@acronym{POSIX}.
13071 Carriage return delay style. Non-@acronym{POSIX}.
13077 @opindex tab@var{n}
13078 Horizontal tab delay style. Non-@acronym{POSIX}.
13083 Backspace delay style. Non-@acronym{POSIX}.
13088 Vertical tab delay style. Non-@acronym{POSIX}.
13093 Form feed delay style. Non-@acronym{POSIX}.
13098 @subsection Local settings
13100 @cindex local settings
13105 Enable @code{interrupt}, @code{quit}, and @code{suspend} special
13106 characters. May be negated.
13110 Enable @code{erase}, @code{kill}, @code{werase}, and @code{rprnt}
13111 special characters. May be negated.
13115 Enable non-@acronym{POSIX} special characters. May be negated.
13119 Echo input characters. May be negated.
13125 Echo @code{erase} characters as backspace-space-backspace. May be
13130 @cindex newline echoing after @code{kill}
13131 Echo a newline after a @code{kill} character. May be negated.
13135 @cindex newline, echoing
13136 Echo newline even if not echoing other characters. May be negated.
13140 @cindex flushing, disabling
13141 Disable flushing after @code{interrupt} and @code{quit} special
13142 characters. May be negated.
13146 @cindex case translation
13147 Enable input and output of uppercase characters by preceding their
13148 lowercase equivalents with @samp{\}, when @code{icanon} is set.
13149 Non-@acronym{POSIX}. May be negated.
13153 @cindex background jobs, stopping at terminal write
13154 Stop background jobs that try to write to the terminal. Non-@acronym{POSIX}.
13161 Echo erased characters backward, between @samp{\} and @samp{/}.
13162 Non-@acronym{POSIX}. May be negated.
13168 @cindex control characters, using @samp{^@var{c}}
13169 @cindex hat notation for control characters
13170 Echo control characters in hat notation (@samp{^@var{c}}) instead
13171 of literally. Non-@acronym{POSIX}. May be negated.
13177 Echo the @code{kill} special character by erasing each character on
13178 the line as indicated by the @code{echoprt} and @code{echoe} settings,
13179 instead of by the @code{echoctl} and @code{echok} settings.
13180 Non-@acronym{POSIX}.
13186 @subsection Combination settings
13188 @cindex combination settings
13189 Combination settings:
13196 Same as @code{parenb -parodd cs7}. May be negated. If negated, same
13197 as @code{-parenb cs8}.
13201 Same as @code{parenb parodd cs7}. May be negated. If negated, same
13202 as @code{-parenb cs8}.
13206 Same as @code{-icrnl -onlcr}. May be negated. If negated, same as
13207 @code{icrnl -inlcr -igncr onlcr -ocrnl -onlret}.
13211 Reset the @code{erase} and @code{kill} special characters to their default
13218 @c This is too long to write inline.
13220 cread -ignbrk brkint -inlcr -igncr icrnl -ixoff
13221 -iuclc -ixany imaxbel opost -olcuc -ocrnl onlcr
13222 -onocr -onlret -ofill -ofdel nl0 cr0 tab0 bs0 vt0
13223 ff0 isig icanon iexten echo echoe echok -echonl
13224 -noflsh -xcase -tostop -echoprt echoctl echoke
13228 and also sets all special characters to their default values.
13232 Same as @code{brkint ignpar istrip icrnl ixon opost isig icanon}, plus
13233 sets the @code{eof} and @code{eol} characters to their default values
13234 if they are the same as the @code{min} and @code{time} characters.
13235 May be negated. If negated, same as @code{raw}.
13242 -ignbrk -brkint -ignpar -parmrk -inpck -istrip
13243 -inlcr -igncr -icrnl -ixon -ixoff -iuclc -ixany
13244 -imaxbel -opost -isig -icanon -xcase min 1 time 0
13248 May be negated. If negated, same as @code{cooked}.
13252 Same as @option{-icanon}. May be negated. If negated, same as
13257 @cindex eight-bit characters
13258 Same as @code{-parenb -istrip cs8}. May be negated. If negated,
13259 same as @code{parenb istrip cs7}.
13263 Same as @option{-parenb -istrip -opost cs8}. May be negated.
13264 If negated, same as @code{parenb istrip opost cs7}.
13268 Same as @option{-ixany}. Non-@acronym{POSIX}. May be negated.
13272 Same as @code{tab0}. Non-@acronym{POSIX}. May be negated. If negated, same
13279 Same as @code{xcase iuclc olcuc}. Non-@acronym{POSIX}. May be negated.
13280 (Used for terminals with uppercase characters only.)
13284 Same as @code{echoe echoctl echoke}.
13288 Same as @code{echoe echoctl echoke -ixany intr ^C erase ^? kill C-u}.
13293 @subsection Special characters
13295 @cindex special characters
13296 @cindex characters, special
13298 The special characters' default values vary from system to system.
13299 They are set with the syntax @samp{name value}, where the names are
13300 listed below and the value can be given either literally, in hat
13301 notation (@samp{^@var{c}}), or as an integer which may start with
13302 @samp{0x} to indicate hexadecimal, @samp{0} to indicate octal, or
13303 any other digit to indicate decimal.
13305 @cindex disabling special characters
13306 @kindex u@r{, and disabling special characters}
13307 For GNU stty, giving a value of @code{^-} or @code{undef} disables that
13308 special character. (This is incompatible with Ultrix @command{stty},
13309 which uses a value of @samp{u} to disable a special character. GNU
13310 @command{stty} treats a value @samp{u} like any other, namely to set that
13311 special character to @key{U}.)
13317 Send an interrupt signal.
13321 Send a quit signal.
13325 Erase the last character typed.
13329 Erase the current line.
13333 Send an end of file (terminate the input).
13341 Alternate character to end the line. Non-@acronym{POSIX}.
13345 Switch to a different shell layer. Non-@acronym{POSIX}.
13349 Restart the output after stopping it.
13357 Send a terminal stop signal.
13361 Send a terminal stop signal after flushing the input. Non-@acronym{POSIX}.
13365 Redraw the current line. Non-@acronym{POSIX}.
13369 Erase the last word typed. Non-@acronym{POSIX}.
13373 Enter the next character typed literally, even if it is a special
13374 character. Non-@acronym{POSIX}.
13379 @subsection Special settings
13381 @cindex special settings
13386 Set the minimum number of characters that will satisfy a read until
13387 the time value has expired, when @option{-icanon} is set.
13391 Set the number of tenths of a second before reads time out if the minimum
13392 number of characters have not been read, when @option{-icanon} is set.
13394 @item ispeed @var{n}
13396 Set the input speed to @var{n}.
13398 @item ospeed @var{n}
13400 Set the output speed to @var{n}.
13404 Tell the tty kernel driver that the terminal has @var{n} rows.
13405 Non-@acronym{POSIX}.
13408 @itemx columns @var{n}
13411 Tell the kernel that the terminal has @var{n} columns. Non-@acronym{POSIX}.
13417 Print the number of rows and columns that the kernel thinks the
13418 terminal has. (Systems that don't support rows and columns in the kernel
13419 typically use the environment variables @env{LINES} and @env{COLUMNS}
13420 instead; however, GNU @command{stty} does not know anything about them.)
13421 Non-@acronym{POSIX}.
13425 Use line discipline @var{n}. Non-@acronym{POSIX}.
13429 Print the terminal speed.
13432 @cindex baud rate, setting
13433 Set the input and output speeds to @var{n}. @var{n} can be one of: 0
13434 50 75 110 134 134.5 150 200 300 600 1200 1800 2400 4800 9600 19200
13435 38400 @code{exta} @code{extb}. @code{exta} is the same as 19200;
13436 @code{extb} is the same as 38400. Many systems, including GNU/Linux,
13437 support higher speeds. The @command{stty} command includes support
13454 4000000 where the system supports these.
13455 0 hangs up the line if @option{-clocal} is set.
13459 @node printenv invocation
13460 @section @command{printenv}: Print all or some environment variables
13463 @cindex printing all or some environment variables
13464 @cindex environment variables, printing
13466 @command{printenv} prints environment variable values. Synopsis:
13469 printenv [@var{option}] [@var{variable}]@dots{}
13472 If no @var{variable}s are specified, @command{printenv} prints the value of
13473 every environment variable. Otherwise, it prints the value of each
13474 @var{variable} that is set, and nothing for those that are not set.
13476 The program accepts the following option. Also see @ref{Common options}.
13484 @cindex exit status of @command{printenv}
13488 0 if all variables specified were found
13489 1 if at least one specified variable was not found
13490 2 if a write error occurred
13494 @node tty invocation
13495 @section @command{tty}: Print file name of terminal on standard input
13498 @cindex print terminal file name
13499 @cindex terminal file name, printing
13501 @command{tty} prints the file name of the terminal connected to its standard
13502 input. It prints @samp{not a tty} if standard input is not a terminal.
13506 tty [@var{option}]@dots{}
13509 The program accepts the following option. Also see @ref{Common options}.
13519 Print nothing; only return an exit status.
13523 @cindex exit status of @command{tty}
13527 0 if standard input is a terminal
13528 1 if standard input is not a terminal
13529 2 if given incorrect arguments
13530 3 if a write error occurs
13534 @node User information
13535 @chapter User information
13537 @cindex user information, commands for
13538 @cindex commands for printing user information
13540 This section describes commands that print user-related information:
13541 logins, groups, and so forth.
13544 * id invocation:: Print user identity.
13545 * logname invocation:: Print current login name.
13546 * whoami invocation:: Print effective user ID.
13547 * groups invocation:: Print group names a user is in.
13548 * users invocation:: Print login names of users currently logged in.
13549 * who invocation:: Print who is currently logged in.
13553 @node id invocation
13554 @section @command{id}: Print user identity
13557 @cindex real user and group IDs, printing
13558 @cindex effective user and group IDs, printing
13559 @cindex printing real and effective user and group IDs
13561 @command{id} prints information about the given user, or the process
13562 running it if no user is specified. Synopsis:
13565 id [@var{option}]@dots{} [@var{username}]
13568 @vindex POSIXLY_CORRECT
13569 By default, it prints the real user ID, real group ID, effective user ID
13570 if different from the real user ID, effective group ID if different from
13571 the real group ID, and supplemental group IDs.
13572 In addition, if SELinux
13573 is enabled and the @env{POSIXLY_CORRECT} environment variable is not set,
13574 then print @samp{context=@var{c}}, where @var{c} is the security context.
13576 Each of these numeric values is preceded by an identifying string and
13577 followed by the corresponding user or group name in parentheses.
13579 The options cause @command{id} to print only part of the above information.
13580 Also see @ref{Common options}.
13587 Print only the group ID.
13593 Print only the group ID and the supplementary groups.
13599 Print the user or group name instead of the ID number. Requires
13600 @option{-u}, @option{-g}, or @option{-G}.
13606 Print the real, instead of effective, user or group ID. Requires
13607 @option{-u}, @option{-g}, or @option{-G}.
13613 Print only the user ID.
13620 @cindex security context
13621 Print only the security context of the current user.
13622 If SELinux is disabled then print a warning and
13623 set the exit status to 1.
13629 @macro primaryAndSupplementaryGroups{cmd,arg}
13630 Primary and supplementary groups for a process are normally inherited
13631 from its parent and are usually unchanged since login. This means
13632 that if you change the group database after logging in, @command{\cmd\}
13633 will not reflect your changes within your existing login session.
13634 Running @command{\cmd\} with a \arg\ causes the user and group
13635 database to be consulted afresh, and so will give a different result.
13637 @primaryAndSupplementaryGroups{id,user argument}
13639 @node logname invocation
13640 @section @command{logname}: Print current login name
13643 @cindex printing user's login name
13644 @cindex login name, printing
13645 @cindex user name, printing
13648 @command{logname} prints the calling user's name, as found in a
13649 system-maintained file (often @file{/var/run/utmp} or
13650 @file{/etc/utmp}), and exits with a status of 0. If there is no entry
13651 for the calling process, @command{logname} prints
13652 an error message and exits with a status of 1.
13654 The only options are @option{--help} and @option{--version}. @xref{Common
13660 @node whoami invocation
13661 @section @command{whoami}: Print effective user ID
13664 @cindex effective user ID, printing
13665 @cindex printing the effective user ID
13667 @command{whoami} prints the user name associated with the current
13668 effective user ID. It is equivalent to the command @samp{id -un}.
13670 The only options are @option{--help} and @option{--version}. @xref{Common
13676 @node groups invocation
13677 @section @command{groups}: Print group names a user is in
13680 @cindex printing groups a user is in
13681 @cindex supplementary groups, printing
13683 @command{groups} prints the names of the primary and any supplementary
13684 groups for each given @var{username}, or the current process if no names
13685 are given. If more than one name is given, the name of each user is
13687 the list of that user's groups and the user name is separated from the
13688 group list by a colon. Synopsis:
13691 groups [@var{username}]@dots{}
13694 The group lists are equivalent to the output of the command @samp{id -Gn}.
13696 @primaryAndSupplementaryGroups{groups,list of users}
13698 The only options are @option{--help} and @option{--version}. @xref{Common
13704 @node users invocation
13705 @section @command{users}: Print login names of users currently logged in
13708 @cindex printing current usernames
13709 @cindex usernames, printing current
13711 @cindex login sessions, printing users with
13712 @command{users} prints on a single line a blank-separated list of user
13713 names of users currently logged in to the current host. Each user name
13714 corresponds to a login session, so if a user has more than one login
13715 session, that user's name will appear the same number of times in the
13724 With no @var{file} argument, @command{users} extracts its information from
13725 a system-maintained file (often @file{/var/run/utmp} or
13726 @file{/etc/utmp}). If a file argument is given, @command{users} uses
13727 that file instead. A common choice is @file{/var/log/wtmp}.
13729 The only options are @option{--help} and @option{--version}. @xref{Common
13735 @node who invocation
13736 @section @command{who}: Print who is currently logged in
13739 @cindex printing current user information
13740 @cindex information, about current users
13742 @command{who} prints information about users who are currently logged on.
13746 @command{who} [@var{option}] [@var{file}] [am i]
13749 @cindex terminal lines, currently used
13751 @cindex remote hostname
13752 If given no non-option arguments, @command{who} prints the following
13753 information for each user currently logged on: login name, terminal
13754 line, login time, and remote hostname or X display.
13758 If given one non-option argument, @command{who} uses that instead of
13759 a default system-maintained file (often @file{/var/run/utmp} or
13760 @file{/etc/utmp}) as the name of the file containing the record of
13761 users logged on. @file{/var/log/wtmp} is commonly given as an argument
13762 to @command{who} to look at who has previously logged on.
13766 If given two non-option arguments, @command{who} prints only the entry
13767 for the user running it (determined from its standard input), preceded
13768 by the hostname. Traditionally, the two arguments given are @samp{am
13769 i}, as in @samp{who am i}.
13772 Time stamps are listed according to the time zone rules specified by
13773 the @env{TZ} environment variable, or by the system default rules if
13774 @env{TZ} is not set. @xref{TZ Variable,, Specifying the Time Zone
13775 with @env{TZ}, libc, The GNU C Library Reference Manual}.
13777 The program accepts the following options. Also see @ref{Common options}.
13785 Same as @samp{-b -d --login -p -r -t -T -u}.
13791 Print the date and time of last system boot.
13797 Print information corresponding to dead processes.
13803 Print a line of column headings.
13809 List only the entries that correspond to processes via which the
13810 system is waiting for a user to login. The user name is always @samp{LOGIN}.
13814 Attempt to canonicalize hostnames found in utmp through a DNS lookup. This
13815 is not the default because it can cause significant delays on systems with
13816 automatic dial-up internet access.
13820 Same as @samp{who am i}.
13826 List active processes spawned by init.
13832 Print only the login names and the number of users logged on.
13833 Overrides all other options.
13838 @opindex --runlevel
13839 Print the current (and maybe previous) run-level of the init process.
13843 Ignored; for compatibility with other versions of @command{who}.
13849 Print last system clock change.
13854 After the login time, print the number of hours and minutes that the
13855 user has been idle. @samp{.} means the user was active in the last minute.
13856 @samp{old} means the user has been idle for more than 24 hours.
13867 @opindex --writable
13868 @cindex message status
13869 @pindex write@r{, allowed}
13870 After each login name print a character indicating the user's message status:
13873 @samp{+} allowing @code{write} messages
13874 @samp{-} disallowing @code{write} messages
13875 @samp{?} cannot find terminal device
13883 @node System context
13884 @chapter System context
13886 @cindex system context
13887 @cindex context, system
13888 @cindex commands for system context
13890 This section describes commands that print or change system-wide
13894 * date invocation:: Print or set system date and time.
13895 * arch invocation:: Print machine hardware name.
13896 * nproc invocation:: Print the number of processors.
13897 * uname invocation:: Print system information.
13898 * hostname invocation:: Print or set system name.
13899 * hostid invocation:: Print numeric host identifier.
13900 * uptime invocation:: Print system uptime and load.
13903 @node date invocation
13904 @section @command{date}: Print or set system date and time
13907 @cindex time, printing or setting
13908 @cindex printing the current time
13913 date [@var{option}]@dots{} [+@var{format}]
13914 date [-u|--utc|--universal] @c this avoids a newline in the output
13915 [ MMDDhhmm[[CC]YY][.ss] ]
13919 Invoking @command{date} with no @var{format} argument is equivalent to invoking
13920 it with a default format that depends on the @env{LC_TIME} locale category.
13921 In the default C locale, this format is @samp{'+%a %b %e %H:%M:%S %Z %Y'},
13922 so the output looks like @samp{Thu Mar @ 3 13:47:51 PST 2005}.
13925 Normally, @command{date} uses the time zone rules indicated by the
13926 @env{TZ} environment variable, or the system default rules if @env{TZ}
13927 is not set. @xref{TZ Variable,, Specifying the Time Zone with
13928 @env{TZ}, libc, The GNU C Library Reference Manual}.
13930 @findex strftime @r{and @command{date}}
13931 @cindex time formats
13932 @cindex formatting times
13933 If given an argument that starts with a @samp{+}, @command{date} prints the
13934 current date and time (or the date and time specified by the
13935 @option{--date} option, see below) in the format defined by that argument,
13936 which is similar to that of the @code{strftime} function. Except for
13937 conversion specifiers, which start with @samp{%}, characters in the
13938 format string are printed unchanged. The conversion specifiers are
13944 * Time conversion specifiers:: %[HIklMNpPrRsSTXzZ]
13945 * Date conversion specifiers:: %[aAbBcCdDeFgGhjmuUVwWxyY]
13946 * Literal conversion specifiers:: %[%nt]
13947 * Padding and other flags:: Pad with zeros, spaces, etc.
13948 * Setting the time:: Changing the system clock.
13949 * Options for date:: Instead of the current time.
13951 * Date input formats:: Specifying date strings.
13953 * Examples of date:: Examples.
13956 @node Time conversion specifiers
13957 @subsection Time conversion specifiers
13959 @cindex time conversion specifiers
13960 @cindex conversion specifiers, time
13962 @command{date} conversion specifiers related to times.
13966 hour (@samp{00}@dots{}@samp{23})
13968 hour (@samp{01}@dots{}@samp{12})
13970 hour, space padded (@samp{ 0}@dots{}@samp{23}); equivalent to @samp{%_H}.
13971 This is a @acronym{GNU} extension.
13973 hour, space padded (@samp{ 1}@dots{}@samp{12}); equivalent to @samp{%_I}.
13974 This is a @acronym{GNU} extension.
13976 minute (@samp{00}@dots{}@samp{59})
13978 nanoseconds (@samp{000000000}@dots{}@samp{999999999}).
13979 This is a @acronym{GNU} extension.
13981 locale's equivalent of either @samp{AM} or @samp{PM};
13982 blank in many locales.
13983 Noon is treated as @samp{PM} and midnight as @samp{AM}.
13985 like @samp{%p}, except lower case.
13986 This is a @acronym{GNU} extension.
13988 locale's 12-hour clock time (e.g., @samp{11:11:04 PM})
13990 24-hour hour and minute. Same as @samp{%H:%M}.
13992 @cindex epoch, seconds since
13993 @cindex seconds since the epoch
13994 @cindex beginning of time
13995 seconds since the epoch, i.e., since 1970-01-01 00:00:00 UTC.
13996 Leap seconds are not counted unless leap second support is available.
13997 @xref{%s-examples}, for examples.
13998 This is a @acronym{GNU} extension.
14000 second (@samp{00}@dots{}@samp{60}).
14001 This may be @samp{60} if leap seconds are supported.
14003 24-hour hour, minute, and second. Same as @samp{%H:%M:%S}.
14005 locale's time representation (e.g., @samp{23:13:48})
14007 @w{@acronym{RFC} 2822/@acronym{ISO} 8601} style numeric time zone
14008 (e.g., @samp{-0600} or @samp{+0530}), or nothing if no
14009 time zone is determinable. This value reflects the numeric time zone
14010 appropriate for the current time, using the time zone rules specified
14011 by the @env{TZ} environment variable.
14012 The time (and optionally, the time zone rules) can be overridden
14013 by the @option{--date} option.
14015 @w{@acronym{RFC} 3339/@acronym{ISO} 8601} style numeric time zone with
14016 @samp{:} (e.g., @samp{-06:00} or @samp{+05:30}), or nothing if no time
14017 zone is determinable.
14018 This is a @acronym{GNU} extension.
14020 Numeric time zone to the nearest second with @samp{:} (e.g.,
14021 @samp{-06:00:00} or @samp{+05:30:00}), or nothing if no time zone is
14023 This is a @acronym{GNU} extension.
14025 Numeric time zone with @samp{:} using the minimum necessary precision
14026 (e.g., @samp{-06}, @samp{+05:30}, or @samp{-04:56:02}), or nothing if
14027 no time zone is determinable.
14028 This is a @acronym{GNU} extension.
14030 alphabetic time zone abbreviation (e.g., @samp{EDT}), or nothing if no
14031 time zone is determinable. See @samp{%z} for how it is determined.
14035 @node Date conversion specifiers
14036 @subsection Date conversion specifiers
14038 @cindex date conversion specifiers
14039 @cindex conversion specifiers, date
14041 @command{date} conversion specifiers related to dates.
14045 locale's abbreviated weekday name (e.g., @samp{Sun})
14047 locale's full weekday name, variable length (e.g., @samp{Sunday})
14049 locale's abbreviated month name (e.g., @samp{Jan})
14051 locale's full month name, variable length (e.g., @samp{January})
14053 locale's date and time (e.g., @samp{Thu Mar @ 3 23:05:25 2005})
14055 century. This is like @samp{%Y}, except the last two digits are omitted.
14056 For example, it is @samp{20} if @samp{%Y} is @samp{2000},
14057 and is @samp{-0} if @samp{%Y} is @samp{-001}.
14058 It is normally at least two characters, but it may be more.
14060 day of month (e.g., @samp{01})
14062 date; same as @samp{%m/%d/%y}
14064 day of month, space padded; same as @samp{%_d}
14066 full date in @acronym{ISO} 8601 format; same as @samp{%Y-%m-%d}.
14067 This is a good choice for a date format, as it is standard and
14068 is easy to sort in the usual case where years are in the range
14071 year corresponding to the @acronym{ISO} week number, but without the century
14072 (range @samp{00} through @samp{99}). This has the same format and value
14073 as @samp{%y}, except that if the @acronym{ISO} week number (see
14075 to the previous or next year, that year is used instead.
14077 year corresponding to the @acronym{ISO} week number. This has the
14078 same format and value as @samp{%Y}, except that if the @acronym{ISO}
14080 @samp{%V}) belongs to the previous or next year, that year is used
14082 It is normally useful only if @samp{%V} is also used;
14083 for example, the format @samp{%G-%m-%d} is probably a mistake,
14084 since it combines the ISO week number year with the conventional month and day.
14088 day of year (@samp{001}@dots{}@samp{366})
14090 month (@samp{01}@dots{}@samp{12})
14092 day of week (@samp{1}@dots{}@samp{7}) with @samp{1} corresponding to Monday
14094 week number of year, with Sunday as the first day of the week
14095 (@samp{00}@dots{}@samp{53}).
14096 Days in a new year preceding the first Sunday are in week zero.
14098 @acronym{ISO} week number, that is, the
14099 week number of year, with Monday as the first day of the week
14100 (@samp{01}@dots{}@samp{53}).
14101 If the week containing January 1 has four or more days in
14102 the new year, then it is considered week 1; otherwise, it is week 53 of
14103 the previous year, and the next week is week 1. (See the @acronym{ISO} 8601
14106 day of week (@samp{0}@dots{}@samp{6}) with 0 corresponding to Sunday
14108 week number of year, with Monday as first day of week
14109 (@samp{00}@dots{}@samp{53}).
14110 Days in a new year preceding the first Monday are in week zero.
14112 locale's date representation (e.g., @samp{12/31/99})
14114 last two digits of year (@samp{00}@dots{}@samp{99})
14116 year. This is normally at least four characters, but it may be more.
14117 Year @samp{0000} precedes year @samp{0001}, and year @samp{-001}
14118 precedes year @samp{0000}.
14122 @node Literal conversion specifiers
14123 @subsection Literal conversion specifiers
14125 @cindex literal conversion specifiers
14126 @cindex conversion specifiers, literal
14128 @command{date} conversion specifiers that produce literal strings.
14140 @node Padding and other flags
14141 @subsection Padding and other flags
14143 @cindex numeric field padding
14144 @cindex padding of numeric fields
14145 @cindex fields, padding numeric
14147 Unless otherwise specified, @command{date} normally pads numeric fields
14148 with zeros, so that, for
14149 example, numeric months are always output as two digits.
14150 Seconds since the epoch are not padded, though,
14151 since there is no natural width for them.
14153 As a @acronym{GNU} extension, @command{date} recognizes any of the
14154 following optional flags after the @samp{%}:
14158 (hyphen) Do not pad the field; useful if the output is intended for
14161 (underscore) Pad with spaces; useful if you need a fixed
14162 number of characters in the output, but zeros are too distracting.
14164 (zero) Pad with zeros even if the conversion specifier
14165 would normally pad with spaces.
14167 Use upper case characters if possible.
14169 Use opposite case characters if possible.
14170 A field that is normally upper case becomes lower case, and vice versa.
14174 Here are some examples of padding:
14177 date +%d/%m -d "Feb 1"
14179 date +%-d/%-m -d "Feb 1"
14181 date +%_d/%_m -d "Feb 1"
14185 As a @acronym{GNU} extension, you can specify the field width
14186 (after any flag, if present) as a decimal number. If the natural size of the
14187 output of the field has less than the specified number of characters,
14188 the result is written right adjusted and padded to the given
14189 size. For example, @samp{%9B} prints the right adjusted month name in
14190 a field of width 9.
14192 An optional modifier can follow the optional flag and width
14193 specification. The modifiers are:
14197 Use the locale's alternate representation for date and time. This
14198 modifier applies to the @samp{%c}, @samp{%C}, @samp{%x}, @samp{%X},
14199 @samp{%y} and @samp{%Y} conversion specifiers. In a Japanese locale, for
14200 example, @samp{%Ex} might yield a date format based on the Japanese
14204 Use the locale's alternate numeric symbols for numbers. This modifier
14205 applies only to numeric conversion specifiers.
14208 If the format supports the modifier but no alternate representation
14209 is available, it is ignored.
14212 @node Setting the time
14213 @subsection Setting the time
14215 @cindex setting the time
14216 @cindex time setting
14217 @cindex appropriate privileges
14219 If given an argument that does not start with @samp{+}, @command{date} sets
14220 the system clock to the date and time specified by that argument (as
14221 described below). You must have appropriate privileges to set the
14222 system clock. Note for changes to persist across a reboot, the
14223 hardware clock may need to be updated from the system clock, which
14224 might not happen automatically on your system.
14226 The argument must consist entirely of digits, which have the following
14239 first two digits of year (optional)
14241 last two digits of year (optional)
14246 Note, the @option{--date} and @option{--set} options may not be used with an
14247 argument in the above format. The @option{--universal} option may be used
14248 with such an argument to indicate that the specified date and time are
14249 relative to Coordinated Universal Time rather than to the local time zone.
14252 @node Options for date
14253 @subsection Options for @command{date}
14255 @cindex @command{date} options
14256 @cindex options for @command{date}
14258 The program accepts the following options. Also see @ref{Common options}.
14262 @item -d @var{datestr}
14263 @itemx --date=@var{datestr}
14266 @cindex parsing date strings
14267 @cindex date strings, parsing
14268 @cindex arbitrary date strings, parsing
14271 @opindex next @var{day}
14272 @opindex last @var{day}
14273 Display the date and time specified in @var{datestr} instead of the
14274 current date and time. @var{datestr} can be in almost any common
14275 format. It can contain month names, time zones, @samp{am} and @samp{pm},
14276 @samp{yesterday}, etc. For example, @option{--date="2004-02-27
14277 14:19:13.489392193 +0530"} specifies the instant of time that is
14278 489,392,193 nanoseconds after February 27, 2004 at 2:19:13 PM in a
14279 time zone that is 5 hours and 30 minutes east of @acronym{UTC}.@*
14280 Note: input currently must be in locale independent format. E.g., the
14281 LC_TIME=C below is needed to print back the correct date in many locales:
14283 date -d "$(LC_TIME=C date)"
14285 @xref{Date input formats}.
14287 @item -f @var{datefile}
14288 @itemx --file=@var{datefile}
14291 Parse each line in @var{datefile} as with @option{-d} and display the
14292 resulting date and time. If @var{datefile} is @samp{-}, use standard
14293 input. This is useful when you have many dates to process, because the
14294 system overhead of starting up the @command{date} executable many times can
14297 @item -I[@var{timespec}]
14298 @itemx --iso-8601[=@var{timespec}]
14299 @opindex -I[@var{timespec}]
14300 @opindex --iso-8601[=@var{timespec}]
14301 Display the date using the @acronym{ISO} 8601 format, @samp{%Y-%m-%d}.
14303 The argument @var{timespec} specifies the number of additional
14304 terms of the time to include. It can be one of the following:
14307 Print just the date. This is the default if @var{timespec} is omitted.
14310 Append the hour of the day to the date.
14313 Append the hours and minutes.
14316 Append the hours, minutes and seconds.
14319 Append the hours, minutes, seconds and nanoseconds.
14322 If showing any time terms, then include the time zone using the format
14325 @item -r @var{file}
14326 @itemx --reference=@var{file}
14328 @opindex --reference
14329 Display the date and time of the last modification of @var{file},
14330 instead of the current date and time.
14337 @opindex --rfc-2822
14338 Display the date and time using the format @samp{%a, %d %b %Y %H:%M:%S
14339 %z}, evaluated in the C locale so abbreviations are always in English.
14343 Fri, 09 Sep 2005 13:51:39 -0700
14346 This format conforms to
14347 @uref{ftp://ftp.rfc-editor.org/in-notes/rfc2822.txt, Internet
14348 @acronym{RFCs} 2822} and
14349 @uref{ftp://ftp.rfc-editor.org/in-notes/rfc822.txt, 822}, the
14350 current and previous standards for Internet email.
14352 @item --rfc-3339=@var{timespec}
14353 @opindex --rfc-3339=@var{timespec}
14354 Display the date using a format specified by
14355 @uref{ftp://ftp.rfc-editor.org/in-notes/rfc3339.txt, Internet
14356 @acronym{RFC} 3339}. This is a subset of the @acronym{ISO} 8601
14357 format, except that it also permits applications to use a space rather
14358 than a @samp{T} to separate dates from times. Unlike the other
14359 standard formats, @acronym{RFC} 3339 format is always suitable as
14360 input for the @option{--date} (@option{-d}) and @option{--file}
14361 (@option{-f}) options, regardless of the current locale.
14363 The argument @var{timespec} specifies how much of the time to include.
14364 It can be one of the following:
14368 Print just the full-date, e.g., @samp{2005-09-14}.
14369 This is equivalent to the format @samp{%Y-%m-%d}.
14372 Print the full-date and full-time separated by a space, e.g.,
14373 @samp{2005-09-14 00:56:06+05:30}. The output ends with a numeric
14374 time-offset; here the @samp{+05:30} means that local time is five
14375 hours and thirty minutes east of @acronym{UTC}. This is equivalent to
14376 the format @samp{%Y-%m-%d %H:%M:%S%:z}.
14379 Like @samp{seconds}, but also print nanoseconds, e.g.,
14380 @samp{2005-09-14 00:56:06.998458565+05:30}.
14381 This is equivalent to the format @samp{%Y-%m-%d %H:%M:%S.%N%:z}.
14385 @item -s @var{datestr}
14386 @itemx --set=@var{datestr}
14389 Set the date and time to @var{datestr}. See @option{-d} above.
14390 See also @ref{Setting the time}.
14397 @opindex --universal
14398 @cindex Coordinated Universal Time
14400 @cindex Greenwich Mean Time
14403 Use Coordinated Universal Time (@acronym{UTC}) by operating as if the
14404 @env{TZ} environment variable were set to the string @samp{UTC0}.
14406 Universal Time is often called ``Greenwich Mean Time'' (@sc{gmt}) for
14407 historical reasons.
14411 @node Examples of date
14412 @subsection Examples of @command{date}
14414 @cindex examples of @command{date}
14416 Here are a few examples. Also see the documentation for the @option{-d}
14417 option in the previous section.
14422 To print the date of the day before yesterday:
14425 date --date='2 days ago'
14429 To print the date of the day three months and one day hence:
14432 date --date='3 months 1 day'
14436 To print the day of year of Christmas in the current year:
14439 date --date='25 Dec' +%j
14443 To print the current full month name and the day of the month:
14449 But this may not be what you want because for the first nine days of
14450 the month, the @samp{%d} expands to a zero-padded two-digit field,
14451 for example @samp{date -d 1may '+%B %d'} will print @samp{May 01}.
14454 To print a date without the leading zero for one-digit days
14455 of the month, you can use the (@acronym{GNU} extension)
14456 @samp{-} flag to suppress
14457 the padding altogether:
14460 date -d 1may '+%B %-d
14464 To print the current date and time in the format required by many
14465 non-@acronym{GNU} versions of @command{date} when setting the system clock:
14468 date +%m%d%H%M%Y.%S
14472 To set the system clock forward by two minutes:
14475 date --set='+2 minutes'
14479 To print the date in @acronym{RFC} 2822 format,
14480 use @samp{date --rfc-2822}. Here is some example output:
14483 Fri, 09 Sep 2005 13:51:39 -0700
14486 @anchor{%s-examples}
14488 To convert a date string to the number of seconds since the epoch
14489 (which is 1970-01-01 00:00:00 UTC), use the @option{--date} option with
14490 the @samp{%s} format. That can be useful in sorting and/or graphing
14491 and/or comparing data by date. The following command outputs the
14492 number of the seconds since the epoch for the time two minutes after the
14496 date --date='1970-01-01 00:02:00 +0000' +%s
14500 If you do not specify time zone information in the date string,
14501 @command{date} uses your computer's idea of the time zone when
14502 interpreting the string. For example, if your computer's time zone is
14503 that of Cambridge, Massachusetts, which was then 5 hours (i.e., 18,000
14504 seconds) behind UTC:
14507 # local time zone used
14508 date --date='1970-01-01 00:02:00' +%s
14513 If you're sorting or graphing dated data, your raw date values may be
14514 represented as seconds since the epoch. But few people can look at
14515 the date @samp{946684800} and casually note ``Oh, that's the first second
14516 of the year 2000 in Greenwich, England.''
14519 date --date='2000-01-01 UTC' +%s
14523 An alternative is to use the @option{--utc} (@option{-u}) option.
14524 Then you may omit @samp{UTC} from the date string. Although this
14525 produces the same result for @samp{%s} and many other format sequences,
14526 with a time zone offset different from zero, it would give a different
14527 result for zone-dependent formats like @samp{%z}.
14530 date -u --date=2000-01-01 +%s
14534 To convert such an unwieldy number of seconds back to
14535 a more readable form, use a command like this:
14538 # local time zone used
14539 date -d '1970-01-01 UTC 946684800 seconds' +"%Y-%m-%d %T %z"
14540 1999-12-31 19:00:00 -0500
14543 Or if you do not mind depending on the @samp{@@} feature present since
14544 coreutils 5.3.0, you could shorten this to:
14547 date -d @@946684800 +"%F %T %z"
14548 1999-12-31 19:00:00 -0500
14551 Often it is better to output UTC-relative date and time:
14554 date -u -d '1970-01-01 946684800 seconds' +"%Y-%m-%d %T %z"
14555 2000-01-01 00:00:00 +0000
14561 @node arch invocation
14562 @section @command{arch}: Print machine hardware name
14565 @cindex print machine hardware name
14566 @cindex system information, printing
14568 @command{arch} prints the machine hardware name,
14569 and is equivalent to @samp{uname -m}.
14573 arch [@var{option}]
14576 The program accepts the @ref{Common options} only.
14581 @node nproc invocation
14582 @section @command{nproc}: Print the number of available processors
14585 @cindex Print the number of processors
14586 @cindex system information, printing
14588 Print the number of processing units available to the current process,
14589 which may be less than the number of online processors.
14590 If this information is not accessible, then print the number of
14591 processors installed. If the @env{OMP_NUM_THREADS} environment variable is
14592 set, then it will determine the returned value. The result is guaranteed to be
14593 greater than zero. Synopsis:
14596 nproc [@var{option}]
14599 The program accepts the following options. Also see @ref{Common options}.
14605 Print the number of installed processors on the system, which may
14606 be greater than the number online or available to the current process.
14607 The @env{OMP_NUM_THREADS} environment variable is not honored in this case.
14609 @item --ignore=@var{number}
14611 If possible, exclude this @var{number} of processing units.
14618 @node uname invocation
14619 @section @command{uname}: Print system information
14622 @cindex print system information
14623 @cindex system information, printing
14625 @command{uname} prints information about the machine and operating system
14626 it is run on. If no options are given, @command{uname} acts as if the
14627 @option{-s} option were given. Synopsis:
14630 uname [@var{option}]@dots{}
14633 If multiple options or @option{-a} are given, the selected information is
14634 printed in this order:
14637 @var{kernel-name} @var{nodename} @var{kernel-release} @var{kernel-version}
14638 @var{machine} @var{processor} @var{hardware-platform} @var{operating-system}
14641 The information may contain internal spaces, so such output cannot be
14642 parsed reliably. In the following example, @var{release} is
14643 @samp{2.2.18ss.e820-bda652a #4 SMP Tue Jun 5 11:24:08 PDT 2001}:
14647 @result{} Linux dum 2.2.18 #4 SMP Tue Jun 5 11:24:08 PDT 2001 i686@c
14648 unknown unknown GNU/Linux
14652 The program accepts the following options. Also see @ref{Common options}.
14660 Print all of the below information, except omit the processor type
14661 and the hardware platform name if they are unknown.
14664 @itemx --hardware-platform
14666 @opindex --hardware-platform
14667 @cindex implementation, hardware
14668 @cindex hardware platform
14669 @cindex platform, hardware
14670 Print the hardware platform name
14671 (sometimes called the hardware implementation).
14672 Print @samp{unknown} if the kernel does not make this information
14673 easily available, as is the case with Linux kernels.
14679 @cindex machine type
14680 @cindex hardware class
14681 @cindex hardware type
14682 Print the machine hardware name (sometimes called the hardware class
14688 @opindex --nodename
14691 @cindex network node name
14692 Print the network node hostname.
14697 @opindex --processor
14698 @cindex host processor type
14699 Print the processor type (sometimes called the instruction set
14700 architecture or ISA).
14701 Print @samp{unknown} if the kernel does not make this information
14702 easily available, as is the case with Linux kernels.
14705 @itemx --operating-system
14707 @opindex --operating-system
14708 @cindex operating system name
14709 Print the name of the operating system.
14712 @itemx --kernel-release
14714 @opindex --kernel-release
14715 @cindex kernel release
14716 @cindex release of kernel
14717 Print the kernel release.
14720 @itemx --kernel-name
14722 @opindex --kernel-name
14723 @cindex kernel name
14724 @cindex name of kernel
14725 Print the kernel name.
14726 @acronym{POSIX} 1003.1-2001 (@pxref{Standards conformance}) calls this
14727 ``the implementation of the operating system'', because the
14728 @acronym{POSIX} specification itself has no notion of ``kernel''.
14729 The kernel name might be the same as the operating system name printed
14730 by the @option{-o} or @option{--operating-system} option, but it might
14731 differ. Some operating systems (e.g., FreeBSD, HP-UX) have the same
14732 name as their underlying kernels; others (e.g., GNU/Linux, Solaris)
14736 @itemx --kernel-version
14738 @opindex --kernel-version
14739 @cindex kernel version
14740 @cindex version of kernel
14741 Print the kernel version.
14748 @node hostname invocation
14749 @section @command{hostname}: Print or set system name
14752 @cindex setting the hostname
14753 @cindex printing the hostname
14754 @cindex system name, printing
14755 @cindex appropriate privileges
14757 With no arguments, @command{hostname} prints the name of the current host
14758 system. With one argument, it sets the current host name to the
14759 specified string. You must have appropriate privileges to set the host
14763 hostname [@var{name}]
14766 The only options are @option{--help} and @option{--version}. @xref{Common
14772 @node hostid invocation
14773 @section @command{hostid}: Print numeric host identifier
14776 @cindex printing the host identifier
14778 @command{hostid} prints the numeric identifier of the current host
14779 in hexadecimal. This command accepts no arguments.
14780 The only options are @option{--help} and @option{--version}.
14781 @xref{Common options}.
14783 For example, here's what it prints on one system I use:
14790 On that system, the 32-bit quantity happens to be closely
14791 related to the system's Internet address, but that isn't always
14796 @node uptime invocation
14797 @section @command{uptime}: Print system uptime and load
14800 @cindex printing the system uptime and load
14802 @command{uptime} prints the current time, the system's uptime, the
14803 number of logged-in users and the current load average.
14805 If an argument is specified, it is used as the file to be read
14806 to discover how many users are logged in. If no argument is
14807 specified, a system default is used (@command{uptime --help} indicates
14808 the default setting).
14810 The only options are @option{--help} and @option{--version}.
14811 @xref{Common options}.
14813 For example, here's what it prints right now on one system I use:
14817 14:07 up 3:35, 3 users, load average: 1.39, 1.15, 1.04
14820 The precise method of calculation of load average varies somewhat
14821 between systems. Some systems calculate it as the average number of
14822 runnable processes over the last 1, 5 and 15 minutes, but some systems
14823 also include processes in the uninterruptible sleep state (that is,
14824 those processes which are waiting for disk I/O). The Linux kernel
14825 includes uninterruptible processes.
14827 @node SELinux context
14828 @chapter SELinux context
14830 @cindex SELinux context
14831 @cindex SELinux, context
14832 @cindex commands for SELinux context
14834 This section describes commands for operations with SELinux
14838 * chcon invocation:: Change SELinux context of file
14839 * runcon invocation:: Run a command in specified SELinux context
14842 @node chcon invocation
14843 @section @command{chcon}: Change SELinux context of file
14846 @cindex changing security context
14847 @cindex change SELinux context
14849 @command{chcon} changes the SELinux security context of the selected files.
14853 chcon [@var{option}]@dots{} @var{context} @var{file}@dots{}
14854 chcon [@var{option}]@dots{} [-u @var{user}] [-r @var{role}] [-l @var{range}]@c
14855 [-t @var{type}] @var{file}@dots{}
14856 chcon [@var{option}]@dots{} --reference=@var{rfile} @var{file}@dots{}
14859 Change the SELinux security context of each @var{file} to @var{context}.
14860 With @option{--reference}, change the security context of each @var{file}
14861 to that of @var{rfile}.
14863 The program accepts the following options. Also see @ref{Common options}.
14868 @itemx --no-dereference
14870 @opindex --no-dereference
14871 @cindex no dereference
14872 Affect symbolic links instead of any referenced file.
14874 @item --reference=@var{rfile}
14875 @opindex --reference
14876 @cindex reference file
14877 Use @var{rfile}'s security context rather than specifying a @var{context} value.
14882 @opindex --recursive
14883 Operate on files and directories recursively.
14886 @xref{Traversing symlinks}.
14889 @xref{Traversing symlinks}.
14892 @xref{Traversing symlinks}.
14899 Output a diagnostic for every file processed.
14901 @item -u @var{user}
14902 @itemx --user=@var{user}
14905 Set user @var{user} in the target security context.
14907 @item -r @var{role}
14908 @itemx --role=@var{role}
14911 Set role @var{role} in the target security context.
14913 @item -t @var{type}
14914 @itemx --type=@var{type}
14917 Set type @var{type} in the target security context.
14919 @item -l @var{range}
14920 @itemx --range=@var{range}
14923 Set range @var{range} in the target security context.
14929 @node runcon invocation
14930 @section @command{runcon}: Run a command in specified SELinux context
14933 @cindex run with security context
14936 @command{runcon} runs file in specified SELinux security context.
14940 runcon @var{context} @var{command} [@var{args}]
14941 runcon [ -c ] [-u @var{user}] [-r @var{role}] [-t @var{type}]@c
14942 [-l @var{range}] @var{command} [@var{args}]
14945 Run @var{command} with completely-specified @var{context}, or with
14946 current or transitioned security context modified by one or more of @var{level},
14947 @var{role}, @var{type} and @var{user}.
14949 If none of @option{-c}, @option{-t}, @option{-u}, @option{-r}, or @option{-l}
14950 is specified, the first argument is used as the complete context.
14951 Any additional arguments after @var{command}
14952 are interpreted as arguments to the command.
14954 With neither @var{context} nor @var{command}, print the current
14957 The program accepts the following options. Also see @ref{Common options}.
14965 Compute process transition context before modifying.
14967 @item -u @var{user}
14968 @itemx --user=@var{user}
14971 Set user @var{user} in the target security context.
14973 @item -r @var{role}
14974 @itemx --role=@var{role}
14977 Set role @var{role} in the target security context.
14979 @item -t @var{type}
14980 @itemx --type=@var{type}
14983 Set type @var{type} in the target security context.
14985 @item -l @var{range}
14986 @itemx --range=@var{range}
14989 Set range @var{range} in the target security context.
14993 @cindex exit status of @command{runcon}
14997 126 if @var{command} is found but cannot be invoked
14998 127 if @command{runcon} itself fails or if @var{command} cannot be found
14999 the exit status of @var{command} otherwise
15002 @node Modified command invocation
15003 @chapter Modified command invocation
15005 @cindex modified command invocation
15006 @cindex invocation of commands, modified
15007 @cindex commands for invoking other commands
15009 This section describes commands that run other commands in some context
15010 different than the current one: a modified environment, as a different
15014 * chroot invocation:: Modify the root directory.
15015 * env invocation:: Modify environment variables.
15016 * nice invocation:: Modify niceness.
15017 * nohup invocation:: Immunize to hangups.
15018 * stdbuf invocation:: Modify buffering of standard streams.
15019 * su invocation:: Modify user and group ID.
15020 * timeout invocation:: Run with time limit.
15024 @node chroot invocation
15025 @section @command{chroot}: Run a command with a different root directory
15028 @cindex running a program in a specified root directory
15029 @cindex root directory, running a program in a specified
15031 @command{chroot} runs a command with a specified root directory.
15032 On many systems, only the super-user can do this.@footnote{However,
15033 some systems (e.g., FreeBSD) can be configured to allow certain regular
15034 users to use the @code{chroot} system call, and hence to run this program.
15035 Also, on Cygwin, anyone can run the @command{chroot} command, because the
15036 underlying function is non-privileged due to lack of support in MS-Windows.}
15040 chroot @var{option} @var{newroot} [@var{command} [@var{args}]@dots{}]
15041 chroot @var{option}
15044 Ordinarily, file names are looked up starting at the root of the
15045 directory structure, i.e., @file{/}. @command{chroot} changes the root to
15046 the directory @var{newroot} (which must exist) and then runs
15047 @var{command} with optional @var{args}. If @var{command} is not
15048 specified, the default is the value of the @env{SHELL} environment
15049 variable or @command{/bin/sh} if not set, invoked with the @option{-i} option.
15050 @var{command} must not be a special built-in utility
15051 (@pxref{Special built-in utilities}).
15053 The program accepts the following options. Also see @ref{Common options}.
15054 Options must precede operands.
15058 @itemx --userspec=@var{user}[:@var{group}]
15059 @opindex --userspec
15060 By default, @var{command} is run with the same credentials
15061 as the invoking process.
15062 Use this option to run it as a different @var{user} and/or with a
15063 different primary @var{group}.
15065 @itemx --groups=@var{groups}
15067 Use this option to specify the supplementary @var{groups} to be
15068 used by the new process.
15069 The items in the list (names or numeric IDs) must be separated by commas.
15073 Here are a few tips to help avoid common problems in using chroot.
15074 To start with a simple example, make @var{command} refer to a statically
15075 linked binary. If you were to use a dynamically linked executable, then
15076 you'd have to arrange to have the shared libraries in the right place under
15077 your new root directory.
15079 For example, if you create a statically linked @command{ls} executable,
15080 and put it in @file{/tmp/empty}, you can run this command as root:
15083 $ chroot /tmp/empty /ls -Rl /
15086 Then you'll see output like this:
15091 -rwxr-xr-x 1 0 0 1041745 Aug 16 11:17 ls
15094 If you want to use a dynamically linked executable, say @command{bash},
15095 then first run @samp{ldd bash} to see what shared objects it needs.
15096 Then, in addition to copying the actual binary, also copy the listed
15097 files to the required positions under your intended new root directory.
15098 Finally, if the executable requires any other files (e.g., data, state,
15099 device files), copy them into place, too.
15101 @cindex exit status of @command{chroot}
15105 125 if @command{chroot} itself fails
15106 126 if @var{command} is found but cannot be invoked
15107 127 if @var{command} cannot be found
15108 the exit status of @var{command} otherwise
15112 @node env invocation
15113 @section @command{env}: Run a command in a modified environment
15116 @cindex environment, running a program in a modified
15117 @cindex modified environment, running a program in a
15118 @cindex running a program in a modified environment
15120 @command{env} runs a command with a modified environment. Synopses:
15123 env [@var{option}]@dots{} [@var{name}=@var{value}]@dots{} @c
15124 [@var{command} [@var{args}]@dots{}]
15128 Operands of the form @samp{@var{variable}=@var{value}} set
15129 the environment variable @var{variable} to value @var{value}.
15130 @var{value} may be empty (@samp{@var{variable}=}). Setting a variable
15131 to an empty value is different from unsetting it.
15132 These operands are evaluated left-to-right, so if two operands
15133 mention the same variable the earlier is ignored.
15135 Environment variable names can be empty, and can contain any
15136 characters other than @samp{=} and @acronym{ASCII} @sc{nul}.
15137 However, it is wise to limit yourself to names that
15138 consist solely of underscores, digits, and @acronym{ASCII} letters,
15139 and that begin with a non-digit, as applications like the shell do not
15140 work well with other names.
15143 The first operand that does not contain the character @samp{=}
15144 specifies the program to invoke; it is
15145 searched for according to the @env{PATH} environment variable. Any
15146 remaining arguments are passed as arguments to that program.
15147 The program should not be a special built-in utility
15148 (@pxref{Special built-in utilities}).
15150 Modifications to @env{PATH} take effect prior to searching for
15151 @var{command}. Use caution when reducing @env{PATH}; behavior is
15152 not portable when @env{PATH} is undefined or omits key directories
15153 such as @file{/bin}.
15155 In the rare case that a utility contains a @samp{=} in the name, the
15156 only way to disambiguate it from a variable assignment is to use an
15157 intermediate command for @var{command}, and pass the problematic
15158 program name via @var{args}. For example, if @file{./prog=} is an
15159 executable in the current @env{PATH}:
15162 env prog= true # runs 'true', with prog= in environment
15163 env ./prog= true # runs 'true', with ./prog= in environment
15164 env -- prog= true # runs 'true', with prog= in environment
15165 env sh -c '\prog= true' # runs 'prog=' with argument 'true'
15166 env sh -c 'exec "$@@"' sh prog= true # also runs 'prog='
15169 @cindex environment, printing
15171 If no command name is specified following the environment
15172 specifications, the resulting environment is printed. This is like
15173 specifying the @command{printenv} program.
15175 For some examples, suppose the environment passed to @command{env}
15176 contains @samp{LOGNAME=rms}, @samp{EDITOR=emacs}, and
15177 @samp{PATH=.:/gnubin:/hacks}:
15182 Output the current environment.
15184 $ env | LC_ALL=C sort
15187 PATH=.:/gnubin:/hacks
15191 Run @command{foo} with a reduced environment, preserving only the
15192 original @env{PATH} to avoid problems in locating @command{foo}.
15194 env - PATH="$PATH" foo
15198 Run @command{foo} with the environment containing @samp{LOGNAME=rms},
15199 @samp{EDITOR=emacs}, and @samp{PATH=.:/gnubin:/hacks}, and guarantees
15200 that @command{foo} was found in the file system rather than as a shell
15207 Run @command{nemacs} with the environment containing @samp{LOGNAME=foo},
15208 @samp{EDITOR=emacs}, @samp{PATH=.:/gnubin:/hacks}, and
15209 @samp{DISPLAY=gnu:0}.
15211 env DISPLAY=gnu:0 LOGNAME=foo nemacs
15215 Attempt to run the program @command{/energy/--} (as that is the only
15216 possible path search result); if the command exists, the environment
15217 will contain @samp{LOGNAME=rms} and @samp{PATH=/energy}, and the
15218 arguments will be @samp{e=mc2}, @samp{bar}, and @samp{baz}.
15220 env -u EDITOR PATH=/energy -- e=mc2 bar baz
15226 The program accepts the following options. Also see @ref{Common options}.
15227 Options must precede operands.
15233 @item -u @var{name}
15234 @itemx --unset=@var{name}
15237 Remove variable @var{name} from the environment, if it was in the
15242 @itemx --ignore-environment
15245 @opindex --ignore-environment
15246 Start with an empty environment, ignoring the inherited environment.
15250 @cindex exit status of @command{env}
15254 0 if no @var{command} is specified and the environment is output
15255 125 if @command{env} itself fails
15256 126 if @var{command} is found but cannot be invoked
15257 127 if @var{command} cannot be found
15258 the exit status of @var{command} otherwise
15262 @node nice invocation
15263 @section @command{nice}: Run a command with modified niceness
15267 @cindex scheduling, affecting
15268 @cindex appropriate privileges
15270 @command{nice} prints or modifies a process's @dfn{niceness},
15271 a parameter that affects whether the process is scheduled favorably.
15275 nice [@var{option}]@dots{} [@var{command} [@var{arg}]@dots{}]
15278 If no arguments are given, @command{nice} prints the current niceness.
15279 Otherwise, @command{nice} runs the given @var{command} with its
15280 niceness adjusted. By default, its niceness is incremented by 10.
15282 Niceness values range at least from @minus{}20 (process has high priority
15283 and gets more resources, thus slowing down other processes) through 19
15284 (process has lower priority and runs slowly itself, but has less impact
15285 on the speed of other running processes). Some systems
15286 may have a wider range of nicenesses; conversely, other systems may
15287 enforce more restrictive limits. An attempt to set the niceness
15288 outside the supported range is treated as an attempt to use the
15289 minimum or maximum supported value.
15291 A niceness should not be confused with a scheduling priority, which
15292 lets applications determine the order in which threads are scheduled
15293 to run. Unlike a priority, a niceness is merely advice to the
15294 scheduler, which the scheduler is free to ignore. Also, as a point of
15295 terminology, @acronym{POSIX} defines the behavior of @command{nice} in
15296 terms of a @dfn{nice value}, which is the nonnegative difference
15297 between a niceness and the minimum niceness. Though @command{nice}
15298 conforms to @acronym{POSIX}, its documentation and diagnostics use the
15299 term ``niceness'' for compatibility with historical practice.
15301 @var{command} must not be a special built-in utility (@pxref{Special
15302 built-in utilities}).
15304 @mayConflictWithShellBuiltIn{nice}
15306 The program accepts the following option. Also see @ref{Common options}.
15307 Options must precede operands.
15310 @item -n @var{adjustment}
15311 @itemx --adjustment=@var{adjustment}
15313 @opindex --adjustment
15314 Add @var{adjustment} instead of 10 to the command's niceness. If
15315 @var{adjustment} is negative and you lack appropriate privileges,
15316 @command{nice} issues a warning but otherwise acts as if you specified
15319 For compatibility @command{nice} also supports an obsolete
15320 option syntax @option{-@var{adjustment}}. New scripts should use
15321 @option{-n @var{adjustment}} instead.
15325 @cindex exit status of @command{nice}
15329 0 if no @var{command} is specified and the niceness is output
15330 125 if @command{nice} itself fails
15331 126 if @var{command} is found but cannot be invoked
15332 127 if @var{command} cannot be found
15333 the exit status of @var{command} otherwise
15336 It is sometimes useful to run a non-interactive program with reduced niceness.
15339 $ nice factor 4611686018427387903
15342 Since @command{nice} prints the current niceness,
15343 you can invoke it through itself to demonstrate how it works.
15345 The default behavior is to increase the niceness by @samp{10}:
15356 The @var{adjustment} is relative to the current niceness. In the
15357 next example, the first @command{nice} invocation runs the second one
15358 with niceness 10, and it in turn runs the final one with a niceness
15362 $ nice nice -n 3 nice
15366 Specifying a niceness larger than the supported range
15367 is the same as specifying the maximum supported value:
15370 $ nice -n 10000000000 nice
15374 Only a privileged user may run a process with lower niceness:
15378 nice: cannot set niceness: Permission denied
15380 $ sudo nice -n -1 nice
15385 @node nohup invocation
15386 @section @command{nohup}: Run a command immune to hangups
15389 @cindex hangups, immunity to
15390 @cindex immunity to hangups
15391 @cindex logging out and continuing to run
15394 @command{nohup} runs the given @var{command} with hangup signals ignored,
15395 so that the command can continue running in the background after you log
15399 nohup @var{command} [@var{arg}]@dots{}
15402 If standard input is a terminal, it is redirected from
15403 @file{/dev/null} so that terminal sessions do not mistakenly consider
15404 the terminal to be used by the command. This is a @acronym{GNU}
15405 extension; programs intended to be portable to non-@acronym{GNU} hosts
15406 should use @samp{nohup @var{command} [@var{arg}]@dots{} </dev/null}
15410 If standard output is a terminal, the command's standard output is appended
15411 to the file @file{nohup.out}; if that cannot be written to, it is appended
15412 to the file @file{$HOME/nohup.out}; and if that cannot be written to, the
15413 command is not run.
15414 Any @file{nohup.out} or @file{$HOME/nohup.out} file created by
15415 @command{nohup} is made readable and writable only to the user,
15416 regardless of the current umask settings.
15418 If standard error is a terminal, it is normally redirected to the same file
15419 descriptor as the (possibly-redirected) standard output.
15420 However, if standard output is closed, standard error terminal output
15421 is instead appended to the file @file{nohup.out} or
15422 @file{$HOME/nohup.out} as above.
15424 To capture the command's output to a file other than @file{nohup.out}
15425 you can redirect it. For example, to capture the output of
15429 nohup make > make.log
15432 @command{nohup} does not automatically put the command it runs in the
15433 background; you must do that explicitly, by ending the command line
15434 with an @samp{&}. Also, @command{nohup} does not alter the
15435 niceness of @var{command}; use @command{nice} for that,
15436 e.g., @samp{nohup nice @var{command}}.
15438 @var{command} must not be a special built-in utility (@pxref{Special
15439 built-in utilities}).
15441 The only options are @option{--help} and @option{--version}. @xref{Common
15442 options}. Options must precede operands.
15444 @cindex exit status of @command{nohup}
15448 125 if @command{nohup} itself fails, and @env{POSIXLY_CORRECT} is not set
15449 126 if @var{command} is found but cannot be invoked
15450 127 if @var{command} cannot be found
15451 the exit status of @var{command} otherwise
15454 If @env{POSIXLY_CORRECT} is set, internal failures give status 127
15458 @node stdbuf invocation
15459 @section @command{stdbuf}: Run a command with modified I/O stream buffering
15462 @cindex standard streams, buffering
15463 @cindex line buffered
15465 @command{stdbuf} allows one to modify the buffering operations of the
15466 three standard I/O streams associated with a program. Synopsis:
15469 stdbuf @var{option}@dots{} @var{command}
15472 @var{command} must start with the name of a program that
15475 uses the ISO C @code{FILE} streams for input/output (note the
15476 programs @command{dd} and @command{cat} don't do that),
15479 does not adjust the buffering of its standard streams (note the
15480 program @command{tee} is not in this category).
15483 Any additional @var{arg}s are passed as additional arguments to the
15486 The program accepts the following options. Also see @ref{Common options}.
15490 @item -i @var{mode}
15491 @itemx --input=@var{mode}
15494 Adjust the standard input stream buffering.
15496 @item -o @var{mode}
15497 @itemx --output=@var{mode}
15500 Adjust the standard output stream buffering.
15502 @item -e @var{mode}
15503 @itemx --error=@var{mode}
15506 Adjust the standard error stream buffering.
15510 The @var{mode} can be specified as follows:
15515 Set the stream to line buffered mode.
15516 In this mode data is coalesced until a newline is output or
15517 input is read from any stream attached to a terminal device.
15518 This option is invalid with standard input.
15521 Disable buffering of the selected stream.
15522 In this mode, data is output immediately and only the
15523 amount of data requested is read from input.
15524 Note the difference in function for input and output.
15525 Disabling buffering for input will not influence the responsiveness
15526 or blocking behavior of the stream input functions.
15527 For example @code{fread} will still block until @code{EOF} or error,
15528 even if the underlying @code{read} returns less data than requested.
15531 Specify the size of the buffer to use in fully buffered mode.
15532 @multiplierSuffixesNoBlocks{size}
15536 @cindex exit status of @command{stdbuf}
15540 125 if @command{stdbuf} itself fails
15541 126 if @var{command} is found but cannot be invoked
15542 127 if @var{command} cannot be found
15543 the exit status of @var{command} otherwise
15547 @node su invocation
15548 @section @command{su}: Run a command with substitute user and group ID
15551 @cindex substitute user and group IDs
15552 @cindex user ID, switching
15553 @cindex super-user, becoming
15554 @cindex root, becoming
15556 @command{su} allows one user to temporarily become another user. It runs a
15557 command (often an interactive shell) with the real and effective user
15558 ID, group ID, and supplemental groups of a given @var{user}. Synopsis:
15561 su [@var{option}]@dots{} [@var{user} [@var{arg}]@dots{}]
15564 @cindex passwd entry, and @command{su} shell
15566 @flindex /etc/passwd
15567 If no @var{user} is given, the default is @code{root}, the super-user.
15568 The shell to use is taken from @var{user}'s @code{passwd} entry, or
15569 @file{/bin/sh} if none is specified there. If @var{user} has a
15570 password, @command{su} prompts for the password unless run by a user with
15571 effective user ID of zero (the super-user).
15577 @cindex login shell
15578 By default, @command{su} does not change the current directory.
15579 It sets the environment variables @env{HOME} and @env{SHELL}
15580 from the password entry for @var{user}, and if @var{user} is not
15581 the super-user, sets @env{USER} and @env{LOGNAME} to @var{user}.
15582 By default, the shell is not a login shell.
15584 Any additional @var{arg}s are passed as additional arguments to the
15587 @cindex @option{-su}
15588 GNU @command{su} does not treat @file{/bin/sh} or any other shells specially
15589 (e.g., by setting @code{argv[0]} to @option{-su}, passing @option{-c} only
15590 to certain shells, etc.).
15593 @command{su} can optionally be compiled to use @code{syslog} to report
15594 failed, and optionally successful, @command{su} attempts. (If the system
15595 supports @code{syslog}.) However, GNU @command{su} does not check if the
15596 user is a member of the @code{wheel} group; see below.
15598 The program accepts the following options. Also see @ref{Common options}.
15601 @item -c @var{command}
15602 @itemx --command=@var{command}
15605 Pass @var{command}, a single command line to run, to the shell with
15606 a @option{-c} option instead of starting an interactive shell.
15613 @cindex file name pattern expansion, disabled
15614 @cindex globbing, disabled
15615 Pass the @option{-f} option to the shell. This probably only makes sense
15616 if the shell run is @command{csh} or @command{tcsh}, for which the @option{-f}
15617 option prevents reading the startup file (@file{.cshrc}). With
15618 Bourne-like shells, the @option{-f} option disables file name pattern
15619 expansion (globbing), which is not likely to be useful.
15627 @c other variables already indexed above
15630 @cindex login shell, creating
15631 Make the shell a login shell. This means the following. Unset all
15632 environment variables except @env{TERM}, @env{HOME}, and @env{SHELL}
15633 (which are set as described above), and @env{USER} and @env{LOGNAME}
15634 (which are set, even for the super-user, as described above), and set
15635 @env{PATH} to a compiled-in default value. Change to @var{user}'s home
15636 directory. Prepend @samp{-} to the shell's name, intended to make it
15637 read its login startup file(s).
15641 @itemx --preserve-environment
15644 @opindex --preserve-environment
15645 @cindex environment, preserving
15646 @flindex /etc/shells
15647 @cindex restricted shell
15648 Do not change the environment variables @env{HOME}, @env{USER},
15649 @env{LOGNAME}, or @env{SHELL}. Run the shell given in the environment
15650 variable @env{SHELL} instead of the shell from @var{user}'s passwd
15651 entry, unless the user running @command{su} is not the super-user and
15652 @var{user}'s shell is restricted. A @dfn{restricted shell} is one that
15653 is not listed in the file @file{/etc/shells}, or in a compiled-in list
15654 if that file does not exist. Parts of what this option does can be
15655 overridden by @option{--login} and @option{--shell}.
15657 @item -s @var{shell}
15658 @itemx --shell=@var{shell}
15661 Run @var{shell} instead of the shell from @var{user}'s passwd entry,
15662 unless the user running @command{su} is not the super-user and @var{user}'s
15663 shell is restricted (see @option{-m} just above).
15667 @cindex exit status of @command{su}
15671 125 if @command{su} itself fails
15672 126 if subshell is found but cannot be invoked
15673 127 if subshell cannot be found
15674 the exit status of the subshell otherwise
15677 @cindex wheel group, not supported
15678 @cindex group wheel, not supported
15680 @subsection Why GNU @command{su} does not support the @samp{wheel} group
15682 (This section is by Richard Stallman.)
15686 Sometimes a few of the users try to hold total power over all the
15687 rest. For example, in 1984, a few users at the MIT AI lab decided to
15688 seize power by changing the operator password on the Twenex system and
15689 keeping it secret from everyone else. (I was able to thwart this coup
15690 and give power back to the users by patching the kernel, but I
15691 wouldn't know how to do that in Unix.)
15693 However, occasionally the rulers do tell someone. Under the usual
15694 @command{su} mechanism, once someone learns the root password who
15695 sympathizes with the ordinary users, he or she can tell the rest. The
15696 ``wheel group'' feature would make this impossible, and thus cement the
15697 power of the rulers.
15699 I'm on the side of the masses, not that of the rulers. If you are
15700 used to supporting the bosses and sysadmins in whatever they do, you
15701 might find this idea strange at first.
15704 @node timeout invocation
15705 @section @command{timeout}: Run a command with a time limit
15709 @cindex run commands with bounded time
15711 @command{timeout} runs the given @var{command} and kills it if it is
15712 still running after the specified time interval. Synopsis:
15715 timeout [@var{option}] @var{duration} @var{command} [@var{arg}]@dots{}
15718 @var{command} must not be a special built-in utility (@pxref{Special
15719 built-in utilities}).
15721 The program accepts the following options. Also see @ref{Common options}.
15722 Options must precede operands.
15725 @itemx --foreground
15726 @opindex --foreground
15727 Don't create a separate background program group, so that
15728 the managed @var{command} can use the foreground TTY normally.
15729 This is needed to support timing out commands not started
15730 directly from an interactive shell, in two situations.
15733 @var{command} is interactive and needs to read from the terminal for example
15735 the user wants to support sending signals directly to @var{command}
15736 from the terminal (like Ctrl-C for example)
15739 Note in this mode of operation, any children of @var{command}
15740 will not be timed out.
15742 @item -k @var{duration}
15743 @itemx --kill-after=@var{duration}
15745 @opindex --kill-after
15746 Ensure the monitored @var{command} is killed by also sending a @samp{KILL}
15747 signal, after the specified @var{duration}. Without this option, if the
15748 selected signal proves not to be fatal, @command{timeout} does not kill
15751 @item -s @var{signal}
15752 @itemx --signal=@var{signal}
15755 Send this @var{signal} to @var{command} on timeout, rather than the
15756 default @samp{TERM} signal. @var{signal} may be a name like @samp{HUP}
15757 or a number. Also see @xref{Signal specifications}.
15761 @var{duration} is a floating point number followed by an optional unit:
15763 @samp{s} for seconds (the default)
15764 @samp{m} for minutes
15768 A duration of 0 disables the associated timeout.
15769 Note that the actual timeout duration is dependent on system conditions,
15770 which should be especially considered when specifying sub-second timeouts.
15772 @cindex exit status of @command{timeout}
15776 124 if @var{command} times out
15777 125 if @command{timeout} itself fails
15778 126 if @var{command} is found but cannot be invoked
15779 127 if @var{command} cannot be found
15780 the exit status of @var{command} otherwise
15784 @node Process control
15785 @chapter Process control
15787 @cindex processes, commands for controlling
15788 @cindex commands for controlling processes
15791 * kill invocation:: Sending a signal to processes.
15795 @node kill invocation
15796 @section @command{kill}: Send a signal to processes
15799 @cindex send a signal to processes
15801 The @command{kill} command sends a signal to processes, causing them
15802 to terminate or otherwise act upon receiving the signal in some way.
15803 Alternatively, it lists information about signals. Synopses:
15806 kill [-s @var{signal} | --signal @var{signal} | -@var{signal}] @var{pid}@dots{}
15807 kill [-l | --list | -t | --table] [@var{signal}]@dots{}
15810 @mayConflictWithShellBuiltIn{kill}
15812 The first form of the @command{kill} command sends a signal to all
15813 @var{pid} arguments. The default signal to send if none is specified
15814 is @samp{TERM}. The special signal number @samp{0} does not denote a
15815 valid signal, but can be used to test whether the @var{pid} arguments
15816 specify processes to which a signal could be sent.
15818 If @var{pid} is positive, the signal is sent to the process with the
15819 process ID @var{pid}. If @var{pid} is zero, the signal is sent to all
15820 processes in the process group of the current process. If @var{pid}
15821 is @minus{}1, the signal is sent to all processes for which the user has
15822 permission to send a signal. If @var{pid} is less than @minus{}1, the signal
15823 is sent to all processes in the process group that equals the absolute
15824 value of @var{pid}.
15826 If @var{pid} is not positive, a system-dependent set of system
15827 processes is excluded from the list of processes to which the signal
15830 If a negative @var{pid} argument is desired as the first one, it
15831 should be preceded by @option{--}. However, as a common extension to
15832 @acronym{POSIX}, @option{--} is not required with @samp{kill
15833 -@var{signal} -@var{pid}}. The following commands are equivalent:
15842 The first form of the @command{kill} command succeeds if every @var{pid}
15843 argument specifies at least one process that the signal was sent to.
15845 The second form of the @command{kill} command lists signal information.
15846 Either the @option{-l} or @option{--list} option, or the @option{-t}
15847 or @option{--table} option must be specified. Without any
15848 @var{signal} argument, all supported signals are listed. The output
15849 of @option{-l} or @option{--list} is a list of the signal names, one
15850 per line; if @var{signal} is already a name, the signal number is
15851 printed instead. The output of @option{-t} or @option{--table} is a
15852 table of signal numbers, names, and descriptions. This form of the
15853 @command{kill} command succeeds if all @var{signal} arguments are valid
15854 and if there is no output error.
15856 The @command{kill} command also supports the @option{--help} and
15857 @option{--version} options. @xref{Common options}.
15859 A @var{signal} may be a signal name like @samp{HUP}, or a signal
15860 number like @samp{1}, or an exit status of a process terminated by the
15861 signal. A signal name can be given in canonical form or prefixed by
15862 @samp{SIG}. The case of the letters is ignored, except for the
15863 @option{-@var{signal}} option which must use upper case to avoid
15864 ambiguity with lower case option letters. For a list of supported
15865 signal names and numbers see @xref{Signal specifications}.
15870 @cindex delaying commands
15871 @cindex commands for delaying
15873 @c Perhaps @command{wait} or other commands should be described here also?
15876 * sleep invocation:: Delay for a specified time.
15880 @node sleep invocation
15881 @section @command{sleep}: Delay for a specified time
15884 @cindex delay for a specified time
15886 @command{sleep} pauses for an amount of time specified by the sum of
15887 the values of the command line arguments.
15891 sleep @var{number}[smhd]@dots{}
15895 Each argument is a number followed by an optional unit; the default
15896 is seconds. The units are:
15909 Historical implementations of @command{sleep} have required that
15910 @var{number} be an integer, and only accepted a single argument
15911 without a suffix. However, GNU @command{sleep} accepts
15912 arbitrary floating point numbers. @xref{Floating point}.
15914 The only options are @option{--help} and @option{--version}. @xref{Common
15917 @c sleep is a shell built-in at least with Solaris 11's /bin/sh
15918 @mayConflictWithShellBuiltIn{sleep}
15923 @node Numeric operations
15924 @chapter Numeric operations
15926 @cindex numeric operations
15927 These programs do numerically-related operations.
15930 * factor invocation:: Show factors of numbers.
15931 * seq invocation:: Print sequences of numbers.
15935 @node factor invocation
15936 @section @command{factor}: Print prime factors
15939 @cindex prime factors
15941 @command{factor} prints prime factors. Synopses:
15944 factor [@var{number}]@dots{}
15945 factor @var{option}
15948 If no @var{number} is specified on the command line, @command{factor} reads
15949 numbers from standard input, delimited by newlines, tabs, or spaces.
15951 The @command{factor} command supports only a small number of options:
15955 Print a short help on standard output, then exit without further
15959 Print the program version on standard output, then exit without further
15963 Factoring the product of the eighth and ninth Mersenne primes
15964 takes about 30 milliseconds of CPU time on a 2.2 GHz Athlon.
15967 M8=$(echo 2^31-1|bc)
15968 M9=$(echo 2^61-1|bc)
15969 n=$(echo "$M8 * $M9" | bc)
15970 /usr/bin/time -f %U factor $n
15971 4951760154835678088235319297: 2147483647 2305843009213693951
15975 Similarly, factoring the eighth Fermat number @math{2^{256}+1} takes
15976 about 20 seconds on the same machine.
15978 Factoring large numbers is, in general, hard. The Pollard Rho
15979 algorithm used by @command{factor} is particularly effective for
15980 numbers with relatively small factors. If you wish to factor large
15981 numbers which do not have small factors (for example, numbers which
15982 are the product of two large primes), other methods are far better.
15984 If @command{factor} is built without using GNU MP, only
15985 single-precision arithmetic is available, and so large numbers
15986 (typically @math{2^{64}} and above) will not be supported. The single-precision
15987 code uses an algorithm which is designed for factoring smaller
15993 @node seq invocation
15994 @section @command{seq}: Print numeric sequences
15997 @cindex numeric sequences
15998 @cindex sequence of numbers
16000 @command{seq} prints a sequence of numbers to standard output. Synopses:
16003 seq [@var{option}]@dots{} @var{last}
16004 seq [@var{option}]@dots{} @var{first} @var{last}
16005 seq [@var{option}]@dots{} @var{first} @var{increment} @var{last}
16008 @command{seq} prints the numbers from @var{first} to @var{last} by
16009 @var{increment}. By default, each number is printed on a separate line.
16010 When @var{increment} is not specified, it defaults to @samp{1},
16011 even when @var{first} is larger than @var{last}.
16012 @var{first} also defaults to @samp{1}. So @code{seq 1} prints
16013 @samp{1}, but @code{seq 0} and @code{seq 10 5} produce no output.
16014 Floating-point numbers may be specified. @xref{Floating point}.
16016 The program accepts the following options. Also see @ref{Common options}.
16017 Options must precede operands.
16020 @item -f @var{format}
16021 @itemx --format=@var{format}
16022 @opindex -f @var{format}
16023 @opindex --format=@var{format}
16024 @cindex formatting of numbers in @command{seq}
16025 Print all numbers using @var{format}.
16026 @var{format} must contain exactly one of the @samp{printf}-style
16027 floating point conversion specifications @samp{%a}, @samp{%e},
16028 @samp{%f}, @samp{%g}, @samp{%A}, @samp{%E}, @samp{%F}, @samp{%G}.
16029 The @samp{%} may be followed by zero or more flags taken from the set
16030 @samp{-+#0 '}, then an optional width containing one or more digits,
16031 then an optional precision consisting of a @samp{.} followed by zero
16032 or more digits. @var{format} may also contain any number of @samp{%%}
16033 conversion specifications. All conversion specifications have the
16034 same meaning as with @samp{printf}.
16036 The default format is derived from @var{first}, @var{step}, and
16037 @var{last}. If these all use a fixed point decimal representation,
16038 the default format is @samp{%.@var{p}f}, where @var{p} is the minimum
16039 precision that can represent the output numbers exactly. Otherwise,
16040 the default format is @samp{%g}.
16042 @item -s @var{string}
16043 @itemx --separator=@var{string}
16044 @cindex separator for numbers in @command{seq}
16045 Separate numbers with @var{string}; default is a newline.
16046 The output always terminates with a newline.
16049 @itemx --equal-width
16050 Print all numbers with the same width, by padding with leading zeros.
16051 @var{first}, @var{step}, and @var{last} should all use a fixed point
16052 decimal representation.
16053 (To have other kinds of padding, use @option{--format}).
16057 You can get finer-grained control over output with @option{-f}:
16060 $ seq -f '(%9.2E)' -9e5 1.1e6 1.3e6
16066 If you want hexadecimal integer output, you can use @command{printf}
16067 to perform the conversion:
16070 $ printf '%x\n' `seq 1048575 1024 1050623`
16076 For very long lists of numbers, use xargs to avoid
16077 system limitations on the length of an argument list:
16080 $ seq 1000000 | xargs printf '%x\n' | tail -n 3
16086 To generate octal output, use the printf @code{%o} format instead
16089 On most systems, seq can produce whole-number output for values up to
16090 at least @math{2^{53}}. Larger integers are approximated. The details
16091 differ depending on your floating-point implementation.
16092 @xref{Floating point}. A common
16093 case is that @command{seq} works with integers through @math{2^{64}},
16094 and larger integers may not be numerically correct:
16097 $ seq 18446744073709551616 1 18446744073709551618
16098 18446744073709551616
16099 18446744073709551616
16100 18446744073709551618
16103 Be careful when using @command{seq} with outlandish values: otherwise
16104 you may see surprising results, as @command{seq} uses floating point
16105 internally. For example, on the x86 platform, where the internal
16106 representation uses a 64-bit fraction, the command:
16109 seq 1 0.0000000000000000001 1.0000000000000000009
16112 outputs 1.0000000000000000007 twice and skips 1.0000000000000000008.
16117 @node File permissions
16118 @chapter File permissions
16121 @include parse-datetime.texi
16125 @node Opening the software toolbox
16126 @chapter Opening the Software Toolbox
16128 An earlier version of this chapter appeared in
16129 @uref{http://www.linuxjournal.com/article.php?sid=2762, the
16130 @cite{What's GNU?} column of @cite{Linux Journal}, 2 (June, 1994)}.
16131 It was written by Arnold Robbins.
16134 * Toolbox introduction:: Toolbox introduction
16135 * I/O redirection:: I/O redirection
16136 * The who command:: The @command{who} command
16137 * The cut command:: The @command{cut} command
16138 * The sort command:: The @command{sort} command
16139 * The uniq command:: The @command{uniq} command
16140 * Putting the tools together:: Putting the tools together
16144 @node Toolbox introduction
16145 @unnumberedsec Toolbox Introduction
16147 This month's column is only peripherally related to the GNU Project, in
16148 that it describes a number of the GNU tools on your GNU/Linux system
16150 might be used. What it's really about is the ``Software Tools'' philosophy
16151 of program development and usage.
16153 The software tools philosophy was an important and integral concept
16154 in the initial design and development of Unix (of which Linux and GNU are
16155 essentially clones). Unfortunately, in the modern day press of
16156 Internetworking and flashy GUIs, it seems to have fallen by the
16157 wayside. This is a shame, since it provides a powerful mental model
16158 for solving many kinds of problems.
16160 Many people carry a Swiss Army knife around in their pants pockets (or
16161 purse). A Swiss Army knife is a handy tool to have: it has several knife
16162 blades, a screwdriver, tweezers, toothpick, nail file, corkscrew, and perhaps
16163 a number of other things on it. For the everyday, small miscellaneous jobs
16164 where you need a simple, general purpose tool, it's just the thing.
16166 On the other hand, an experienced carpenter doesn't build a house using
16167 a Swiss Army knife. Instead, he has a toolbox chock full of specialized
16168 tools---a saw, a hammer, a screwdriver, a plane, and so on. And he knows
16169 exactly when and where to use each tool; you won't catch him hammering nails
16170 with the handle of his screwdriver.
16172 The Unix developers at Bell Labs were all professional programmers and trained
16173 computer scientists. They had found that while a one-size-fits-all program
16174 might appeal to a user because there's only one program to use, in practice
16179 difficult to write,
16182 difficult to maintain and
16186 difficult to extend to meet new situations.
16189 Instead, they felt that programs should be specialized tools. In short, each
16190 program ``should do one thing well.'' No more and no less. Such programs are
16191 simpler to design, write, and get right---they only do one thing.
16193 Furthermore, they found that with the right machinery for hooking programs
16194 together, that the whole was greater than the sum of the parts. By combining
16195 several special purpose programs, you could accomplish a specific task
16196 that none of the programs was designed for, and accomplish it much more
16197 quickly and easily than if you had to write a special purpose program.
16198 We will see some (classic) examples of this further on in the column.
16199 (An important additional point was that, if necessary, take a detour
16200 and build any software tools you may need first, if you don't already
16201 have something appropriate in the toolbox.)
16203 @node I/O redirection
16204 @unnumberedsec I/O Redirection
16206 Hopefully, you are familiar with the basics of I/O redirection in the
16207 shell, in particular the concepts of ``standard input,'' ``standard output,''
16208 and ``standard error''. Briefly, ``standard input'' is a data source, where
16209 data comes from. A program should not need to either know or care if the
16210 data source is a disk file, a keyboard, a magnetic tape, or even a punched
16211 card reader. Similarly, ``standard output'' is a data sink, where data goes
16212 to. The program should neither know nor care where this might be.
16213 Programs that only read their standard input, do something to the data,
16214 and then send it on, are called @dfn{filters}, by analogy to filters in a
16217 With the Unix shell, it's very easy to set up data pipelines:
16220 program_to_create_data | filter1 | ... | filterN > final.pretty.data
16223 We start out by creating the raw data; each filter applies some successive
16224 transformation to the data, until by the time it comes out of the pipeline,
16225 it is in the desired form.
16227 This is fine and good for standard input and standard output. Where does the
16228 standard error come in to play? Well, think about @command{filter1} in
16229 the pipeline above. What happens if it encounters an error in the data it
16230 sees? If it writes an error message to standard output, it will just
16231 disappear down the pipeline into @command{filter2}'s input, and the
16232 user will probably never see it. So programs need a place where they can send
16233 error messages so that the user will notice them. This is standard error,
16234 and it is usually connected to your console or window, even if you have
16235 redirected standard output of your program away from your screen.
16237 For filter programs to work together, the format of the data has to be
16238 agreed upon. The most straightforward and easiest format to use is simply
16239 lines of text. Unix data files are generally just streams of bytes, with
16240 lines delimited by the @acronym{ASCII} @sc{lf} (Line Feed) character,
16241 conventionally called a ``newline'' in the Unix literature. (This is
16242 @code{'\n'} if you're a C programmer.) This is the format used by all
16243 the traditional filtering programs. (Many earlier operating systems
16244 had elaborate facilities and special purpose programs for managing
16245 binary data. Unix has always shied away from such things, under the
16246 philosophy that it's easiest to simply be able to view and edit your
16247 data with a text editor.)
16249 OK, enough introduction. Let's take a look at some of the tools, and then
16250 we'll see how to hook them together in interesting ways. In the following
16251 discussion, we will only present those command line options that interest
16252 us. As you should always do, double check your system documentation
16253 for the full story.
16255 @node The who command
16256 @unnumberedsec The @command{who} Command
16258 The first program is the @command{who} command. By itself, it generates a
16259 list of the users who are currently logged in. Although I'm writing
16260 this on a single-user system, we'll pretend that several people are
16265 @print{} arnold console Jan 22 19:57
16266 @print{} miriam ttyp0 Jan 23 14:19(:0.0)
16267 @print{} bill ttyp1 Jan 21 09:32(:0.0)
16268 @print{} arnold ttyp2 Jan 23 20:48(:0.0)
16271 Here, the @samp{$} is the usual shell prompt, at which I typed @samp{who}.
16272 There are three people logged in, and I am logged in twice. On traditional
16273 Unix systems, user names are never more than eight characters long. This
16274 little bit of trivia will be useful later. The output of @command{who} is nice,
16275 but the data is not all that exciting.
16277 @node The cut command
16278 @unnumberedsec The @command{cut} Command
16280 The next program we'll look at is the @command{cut} command. This program
16281 cuts out columns or fields of input data. For example, we can tell it
16282 to print just the login name and full name from the @file{/etc/passwd}
16283 file. The @file{/etc/passwd} file has seven fields, separated by
16287 arnold:xyzzy:2076:10:Arnold D. Robbins:/home/arnold:/bin/bash
16290 To get the first and fifth fields, we would use @command{cut} like this:
16293 $ cut -d: -f1,5 /etc/passwd
16294 @print{} root:Operator
16296 @print{} arnold:Arnold D. Robbins
16297 @print{} miriam:Miriam A. Robbins
16301 With the @option{-c} option, @command{cut} will cut out specific characters
16302 (i.e., columns) in the input lines. This is useful for input data
16303 that has fixed width fields, and does not have a field separator. For
16304 example, list the Monday dates for the current month:
16306 @c Is using cal ok? Looked at gcal, but I don't like it.
16317 @node The sort command
16318 @unnumberedsec The @command{sort} Command
16320 Next we'll look at the @command{sort} command. This is one of the most
16321 powerful commands on a Unix-style system; one that you will often find
16322 yourself using when setting up fancy data plumbing.
16325 command reads and sorts each file named on the command line. It then
16326 merges the sorted data and writes it to standard output. It will read
16327 standard input if no files are given on the command line (thus
16328 making it into a filter). The sort is based on the character collating
16329 sequence or based on user-supplied ordering criteria.
16332 @node The uniq command
16333 @unnumberedsec The @command{uniq} Command
16335 Finally (at least for now), we'll look at the @command{uniq} program. When
16336 sorting data, you will often end up with duplicate lines, lines that
16337 are identical. Usually, all you need is one instance of each line.
16338 This is where @command{uniq} comes in. The @command{uniq} program reads its
16339 standard input. It prints only one
16340 copy of each repeated line. It does have several options. Later on,
16341 we'll use the @option{-c} option, which prints each unique line, preceded
16342 by a count of the number of times that line occurred in the input.
16345 @node Putting the tools together
16346 @unnumberedsec Putting the Tools Together
16348 Now, let's suppose this is a large ISP server system with dozens of users
16349 logged in. The management wants the system administrator to write a
16351 generate a sorted list of logged in users. Furthermore, even if a user
16352 is logged in multiple times, his or her name should only show up in the
16355 The administrator could sit down with the system documentation and write a C
16356 program that did this. It would take perhaps a couple of hundred lines
16357 of code and about two hours to write it, test it, and debug it.
16358 However, knowing the software toolbox, the administrator can instead start out
16359 by generating just a list of logged on users:
16369 Next, sort the list:
16372 $ who | cut -c1-8 | sort
16379 Finally, run the sorted list through @command{uniq}, to weed out duplicates:
16382 $ who | cut -c1-8 | sort | uniq
16388 The @command{sort} command actually has a @option{-u} option that does what
16389 @command{uniq} does. However, @command{uniq} has other uses for which one
16390 cannot substitute @samp{sort -u}.
16392 The administrator puts this pipeline into a shell script, and makes it
16394 all the users on the system (@samp{#} is the system administrator,
16395 or @code{root}, prompt):
16398 # cat > /usr/local/bin/listusers
16399 who | cut -c1-8 | sort | uniq
16401 # chmod +x /usr/local/bin/listusers
16404 There are four major points to note here. First, with just four
16405 programs, on one command line, the administrator was able to save about two
16406 hours worth of work. Furthermore, the shell pipeline is just about as
16407 efficient as the C program would be, and it is much more efficient in
16408 terms of programmer time. People time is much more expensive than
16409 computer time, and in our modern ``there's never enough time to do
16410 everything'' society, saving two hours of programmer time is no mean
16413 Second, it is also important to emphasize that with the
16414 @emph{combination} of the tools, it is possible to do a special
16415 purpose job never imagined by the authors of the individual programs.
16417 Third, it is also valuable to build up your pipeline in stages, as we did here.
16418 This allows you to view the data at each stage in the pipeline, which helps
16419 you acquire the confidence that you are indeed using these tools correctly.
16421 Finally, by bundling the pipeline in a shell script, other users can use
16422 your command, without having to remember the fancy plumbing you set up for
16423 them. In terms of how you run them, shell scripts and compiled programs are
16426 After the previous warm-up exercise, we'll look at two additional, more
16427 complicated pipelines. For them, we need to introduce two more tools.
16429 The first is the @command{tr} command, which stands for ``transliterate.''
16430 The @command{tr} command works on a character-by-character basis, changing
16431 characters. Normally it is used for things like mapping upper case to
16435 $ echo ThIs ExAmPlE HaS MIXED case! | tr '[:upper:]' '[:lower:]'
16436 @print{} this example has mixed case!
16439 There are several options of interest:
16443 work on the complement of the listed characters, i.e.,
16444 operations apply to characters not in the given set
16447 delete characters in the first set from the output
16450 squeeze repeated characters in the output into just one character.
16453 We will be using all three options in a moment.
16455 The other command we'll look at is @command{comm}. The @command{comm}
16456 command takes two sorted input files as input data, and prints out the
16457 files' lines in three columns. The output columns are the data lines
16458 unique to the first file, the data lines unique to the second file, and
16459 the data lines that are common to both. The @option{-1}, @option{-2}, and
16460 @option{-3} command line options @emph{omit} the respective columns. (This is
16461 non-intuitive and takes a little getting used to.) For example:
16483 The file name @file{-} tells @command{comm} to read standard input
16484 instead of a regular file.
16486 Now we're ready to build a fancy pipeline. The first application is a word
16487 frequency counter. This helps an author determine if he or she is over-using
16490 The first step is to change the case of all the letters in our input file
16491 to one case. ``The'' and ``the'' are the same word when doing counting.
16494 $ tr '[:upper:]' '[:lower:]' < whats.gnu | ...
16497 The next step is to get rid of punctuation. Quoted words and unquoted words
16498 should be treated identically; it's easiest to just get the punctuation out of
16502 $ tr '[:upper:]' '[:lower:]' < whats.gnu | tr -cd '[:alnum:]_ \n' | ...
16505 The second @command{tr} command operates on the complement of the listed
16506 characters, which are all the letters, the digits, the underscore, and
16507 the blank. The @samp{\n} represents the newline character; it has to
16508 be left alone. (The @acronym{ASCII} tab character should also be included for
16509 good measure in a production script.)
16511 At this point, we have data consisting of words separated by blank space.
16512 The words only contain alphanumeric characters (and the underscore). The
16513 next step is break the data apart so that we have one word per line. This
16514 makes the counting operation much easier, as we will see shortly.
16517 $ tr '[:upper:]' '[:lower:]' < whats.gnu | tr -cd '[:alnum:]_ \n' |
16518 > tr -s ' ' '\n' | ...
16521 This command turns blanks into newlines. The @option{-s} option squeezes
16522 multiple newline characters in the output into just one. This helps us
16523 avoid blank lines. (The @samp{>} is the shell's ``secondary prompt.''
16524 This is what the shell prints when it notices you haven't finished
16525 typing in all of a command.)
16527 We now have data consisting of one word per line, no punctuation, all one
16528 case. We're ready to count each word:
16531 $ tr '[:upper:]' '[:lower:]' < whats.gnu | tr -cd '[:alnum:]_ \n' |
16532 > tr -s ' ' '\n' | sort | uniq -c | ...
16535 At this point, the data might look something like this:
16548 The output is sorted by word, not by count! What we want is the most
16549 frequently used words first. Fortunately, this is easy to accomplish,
16550 with the help of two more @command{sort} options:
16554 do a numeric sort, not a textual one
16557 reverse the order of the sort
16560 The final pipeline looks like this:
16563 $ tr '[:upper:]' '[:lower:]' < whats.gnu | tr -cd '[:alnum:]_ \n' |
16564 > tr -s ' ' '\n' | sort | uniq -c | sort -n -r
16573 Whew! That's a lot to digest. Yet, the same principles apply. With six
16574 commands, on two lines (really one long one split for convenience), we've
16575 created a program that does something interesting and useful, in much
16576 less time than we could have written a C program to do the same thing.
16578 A minor modification to the above pipeline can give us a simple spelling
16579 checker! To determine if you've spelled a word correctly, all you have to
16580 do is look it up in a dictionary. If it is not there, then chances are
16581 that your spelling is incorrect. So, we need a dictionary.
16582 The conventional location for a dictionary is @file{/usr/dict/words}.
16583 On my GNU/Linux system,@footnote{Redhat Linux 6.1, for the November 2000
16584 revision of this article.}
16585 this is a sorted, 45,402 word dictionary.
16587 Now, how to compare our file with the dictionary? As before, we generate
16588 a sorted list of words, one per line:
16591 $ tr '[:upper:]' '[:lower:]' < whats.gnu | tr -cd '[:alnum:]_ \n' |
16592 > tr -s ' ' '\n' | sort -u | ...
16595 Now, all we need is a list of words that are @emph{not} in the
16596 dictionary. Here is where the @command{comm} command comes in.
16599 $ tr '[:upper:]' '[:lower:]' < whats.gnu | tr -cd '[:alnum:]_ \n' |
16600 > tr -s ' ' '\n' | sort -u |
16601 > comm -23 - /usr/dict/words
16604 The @option{-2} and @option{-3} options eliminate lines that are only in the
16605 dictionary (the second file), and lines that are in both files. Lines
16606 only in the first file (standard input, our stream of words), are
16607 words that are not in the dictionary. These are likely candidates for
16608 spelling errors. This pipeline was the first cut at a production
16609 spelling checker on Unix.
16611 There are some other tools that deserve brief mention.
16615 search files for text that matches a regular expression
16618 count lines, words, characters
16621 a T-fitting for data pipes, copies data to files and to standard output
16624 the stream editor, an advanced tool
16627 a data manipulation language, another advanced tool
16630 The software tools philosophy also espoused the following bit of
16631 advice: ``Let someone else do the hard part.'' This means, take
16632 something that gives you most of what you need, and then massage it the
16633 rest of the way until it's in the form that you want.
16639 Each program should do one thing well. No more, no less.
16642 Combining programs with appropriate plumbing leads to results where
16643 the whole is greater than the sum of the parts. It also leads to novel
16644 uses of programs that the authors might never have imagined.
16647 Programs should never print extraneous header or trailer data, since these
16648 could get sent on down a pipeline. (A point we didn't mention earlier.)
16651 Let someone else do the hard part.
16654 Know your toolbox! Use each program appropriately. If you don't have an
16655 appropriate tool, build one.
16658 As of this writing, all the programs we've discussed are available via
16659 anonymous @command{ftp} from: @*
16660 @uref{ftp://gnudist.gnu.org/textutils/textutils-1.22.tar.gz}. (There may
16661 be more recent versions available now.)
16663 None of what I have presented in this column is new. The Software Tools
16664 philosophy was first introduced in the book @cite{Software Tools}, by
16665 Brian Kernighan and P.J. Plauger (Addison-Wesley, ISBN 0-201-03669-X).
16666 This book showed how to write and use software tools. It was written in
16667 1976, using a preprocessor for FORTRAN named @command{ratfor} (RATional
16668 FORtran). At the time, C was not as ubiquitous as it is now; FORTRAN
16669 was. The last chapter presented a @command{ratfor} to FORTRAN
16670 processor, written in @command{ratfor}. @command{ratfor} looks an awful
16671 lot like C; if you know C, you won't have any problem following the
16674 In 1981, the book was updated and made available as @cite{Software Tools
16675 in Pascal} (Addison-Wesley, ISBN 0-201-10342-7). Both books are
16676 still in print and are well worth
16677 reading if you're a programmer. They certainly made a major change in
16678 how I view programming.
16680 The programs in both books are available from
16681 @uref{http://cm.bell-labs.com/who/bwk, Brian Kernighan's home page}.
16682 For a number of years, there was an active
16683 Software Tools Users Group, whose members had ported the original
16684 @command{ratfor} programs to essentially every computer system with a
16685 FORTRAN compiler. The popularity of the group waned in the middle 1980s
16686 as Unix began to spread beyond universities.
16688 With the current proliferation of GNU code and other clones of Unix programs,
16689 these programs now receive little attention; modern C versions are
16690 much more efficient and do more than these programs do. Nevertheless, as
16691 exposition of good programming style, and evangelism for a still-valuable
16692 philosophy, these books are unparalleled, and I recommend them highly.
16694 Acknowledgment: I would like to express my gratitude to Brian Kernighan
16695 of Bell Labs, the original Software Toolsmith, for reviewing this column.
16697 @node GNU Free Documentation License
16698 @appendix GNU Free Documentation License
16702 @node Concept index
16709 @c Local variables:
16710 @c texinfo-column-for-description: 32