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.
34 @c * mktemp: (coreutils)mktemp invocation. FIXME.
36 @dircategory Individual utilities
38 * arch: (coreutils)arch invocation. Print machine hardware name.
39 * base64: (coreutils)base64 invocation. Base64 encode/decode data.
40 * basename: (coreutils)basename invocation. Strip directory and suffix.
41 * cat: (coreutils)cat invocation. Concatenate and write files.
42 * chcon: (coreutils)chcon invocation. Change SELinux CTX of files.
43 * chgrp: (coreutils)chgrp invocation. Change file groups.
44 * chmod: (coreutils)chmod invocation. Change file permissions.
45 * chown: (coreutils)chown invocation. Change file owners/groups.
46 * chroot: (coreutils)chroot invocation. Specify the root directory.
47 * cksum: (coreutils)cksum invocation. Print POSIX CRC checksum.
48 * comm: (coreutils)comm invocation. Compare sorted files by line.
49 * cp: (coreutils)cp invocation. Copy files.
50 * csplit: (coreutils)csplit invocation. Split by context.
51 * cut: (coreutils)cut invocation. Print selected parts of lines.
52 * date: (coreutils)date invocation. Print/set system date and time.
53 * dd: (coreutils)dd invocation. Copy and convert a file.
54 * df: (coreutils)df invocation. Report file system disk usage.
55 * dir: (coreutils)dir invocation. List directories briefly.
56 * dircolors: (coreutils)dircolors invocation. Color setup for ls.
57 * dirname: (coreutils)dirname invocation. Strip non-directory suffix.
58 * du: (coreutils)du invocation. Report on disk usage.
59 * echo: (coreutils)echo invocation. Print a line of text.
60 * env: (coreutils)env invocation. Modify the environment.
61 * expand: (coreutils)expand invocation. Convert tabs to spaces.
62 * expr: (coreutils)expr invocation. Evaluate expressions.
63 * factor: (coreutils)factor invocation. Print prime factors
64 * false: (coreutils)false invocation. Do nothing, unsuccessfully.
65 * fmt: (coreutils)fmt invocation. Reformat paragraph text.
66 * fold: (coreutils)fold invocation. Wrap long input lines.
67 * groups: (coreutils)groups invocation. Print group names a user is in.
68 * head: (coreutils)head invocation. Output the first part of files.
69 * hostid: (coreutils)hostid invocation. Print numeric host identifier.
70 * hostname: (coreutils)hostname invocation. Print or set system name.
71 * id: (coreutils)id invocation. Print user identity.
72 * install: (coreutils)install invocation. Copy and change attributes.
73 * join: (coreutils)join invocation. Join lines on a common field.
74 * kill: (coreutils)kill invocation. Send a signal to processes.
75 * link: (coreutils)link invocation. Make hard links between files.
76 * ln: (coreutils)ln invocation. Make links between files.
77 * logname: (coreutils)logname invocation. Print current login name.
78 * ls: (coreutils)ls invocation. List directory contents.
79 * md5sum: (coreutils)md5sum invocation. Print or check MD5 digests.
80 * mkdir: (coreutils)mkdir invocation. Create directories.
81 * mkfifo: (coreutils)mkfifo invocation. Create FIFOs (named pipes).
82 * mknod: (coreutils)mknod invocation. Create special 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 * od: (coreutils)od invocation. Dump files in octal, etc.
88 * paste: (coreutils)paste invocation. Merge lines of files.
89 * pathchk: (coreutils)pathchk invocation. Check file name portability.
90 * pr: (coreutils)pr invocation. Paginate or columnate files.
91 * printenv: (coreutils)printenv invocation. Print environment variables.
92 * printf: (coreutils)printf invocation. Format and print data.
93 * ptx: (coreutils)ptx invocation. Produce permuted indexes.
94 * pwd: (coreutils)pwd invocation. Print working directory.
95 * readlink: (coreutils)readlink invocation. Print referent of a symlink.
96 * rm: (coreutils)rm invocation. Remove files.
97 * rmdir: (coreutils)rmdir invocation. Remove empty directories.
98 * runcon: (coreutils)runcon invocation. Run in specified SELinux CTX.
99 * seq: (coreutils)seq invocation. Print numeric sequences
100 * sha1sum: (coreutils)sha1sum invocation. Print or check SHA-1 digests.
101 * sha2: (coreutils)sha2 utilities. Print or check SHA-2 digests.
102 * shred: (coreutils)shred invocation. Remove files more securely.
103 * shuf: (coreutils)shuf invocation. Shuffling text files.
104 * sleep: (coreutils)sleep invocation. Delay for a specified time.
105 * sort: (coreutils)sort invocation. Sort text files.
106 * split: (coreutils)split invocation. Split into fixed-size pieces.
107 * stat: (coreutils)stat invocation. Report file(system) status.
108 * stdbuf: (coreutils)stdbuf invocation. Modify stdio buffering.
109 * stty: (coreutils)stty invocation. Print/change terminal settings.
110 * su: (coreutils)su invocation. Modify user and group ID.
111 * sum: (coreutils)sum invocation. Print traditional checksum.
112 * sync: (coreutils)sync invocation. Synchronize memory and disk.
113 * tac: (coreutils)tac invocation. Reverse files.
114 * tail: (coreutils)tail invocation. Output the last part of files.
115 * tee: (coreutils)tee invocation. Redirect to multiple files.
116 * test: (coreutils)test invocation. File/string tests.
117 * timeout: (coreutils)timeout invocation. Run with time limit.
118 * touch: (coreutils)touch invocation. Change file timestamps.
119 * tr: (coreutils)tr invocation. Translate characters.
120 * true: (coreutils)true invocation. Do nothing, successfully.
121 * truncate: (coreutils)truncate invocation. Shrink/extend size of a file.
122 * tsort: (coreutils)tsort invocation. Topological sort.
123 * tty: (coreutils)tty invocation. Print terminal name.
124 * uname: (coreutils)uname invocation. Print system information.
125 * unexpand: (coreutils)unexpand invocation. Convert spaces to tabs.
126 * uniq: (coreutils)uniq invocation. Uniquify files.
127 * unlink: (coreutils)unlink invocation. Removal via unlink(2).
128 * uptime: (coreutils)uptime invocation. Print uptime and load.
129 * users: (coreutils)users invocation. Print current user names.
130 * vdir: (coreutils)vdir invocation. List directories verbosely.
131 * wc: (coreutils)wc invocation. Line, word, and byte counts.
132 * who: (coreutils)who invocation. Print who is logged in.
133 * whoami: (coreutils)whoami invocation. Print effective user ID.
134 * yes: (coreutils)yes invocation. Print a string indefinitely.
138 This manual documents version @value{VERSION} of the @sc{gnu} core
139 utilities, including the standard programs for text and file manipulation.
141 Copyright @copyright{} 1994-1996, 2000-2009 Free Software Foundation, Inc.
144 Permission is granted to copy, distribute and/or modify this document
145 under the terms of the GNU Free Documentation License, Version 1.3 or
146 any later version published by the Free Software Foundation; with no
147 Invariant Sections, with no Front-Cover Texts, and with no Back-Cover
148 Texts. A copy of the license is included in the section entitled ``GNU
149 Free Documentation License''.
154 @title @sc{gnu} @code{Coreutils}
155 @subtitle Core GNU utilities
156 @subtitle for version @value{VERSION}, @value{UPDATED}
157 @author David MacKenzie et al.
160 @vskip 0pt plus 1filll
173 @cindex core utilities
174 @cindex text utilities
175 @cindex shell utilities
176 @cindex file utilities
179 * Introduction:: Caveats, overview, and authors.
180 * Common options:: Common options.
181 * Output of entire files:: cat tac nl od
182 * Formatting file contents:: fmt pr fold
183 * Output of parts of files:: head tail split csplit
184 * Summarizing files:: wc sum cksum md5sum sha1sum sha2
185 * Operating on sorted files:: sort shuf uniq comm ptx tsort
186 * Operating on fields within a line:: cut paste join
187 * Operating on characters:: tr expand unexpand
188 * Directory listing:: ls dir vdir dircolors
189 * Basic operations:: cp dd install mv rm shred
190 * Special file types:: ln mkdir rmdir mkfifo mknod
191 * Changing file attributes:: chgrp chmod chown touch
192 * Disk usage:: df du stat sync truncate
193 * Printing text:: echo printf yes
194 * Conditions:: false true test expr
196 * File name manipulation:: dirname basename pathchk
197 * Working context:: pwd stty printenv tty
198 * User information:: id logname whoami groups users who
199 * System context:: date uname hostname hostid uptime
200 * SELinux context:: chcon runcon
201 * Modified command invocation:: chroot env nice nohup stdbuf su timeout
202 * Process control:: kill
204 * Numeric operations:: factor seq
205 * File permissions:: Access modes.
206 * Date input formats:: Specifying date strings.
207 * Opening the software toolbox:: The software tools philosophy.
208 * GNU Free Documentation License:: Copying and sharing this manual.
209 * Concept index:: General index.
212 --- The Detailed Node Listing ---
216 * Exit status:: Indicating program success or failure.
217 * Backup options:: Backup options
218 * Block size:: Block size
219 * Signal specifications:: Specifying signals
220 * Disambiguating names and IDs:: chgrp and chown owner and group syntax
221 * Random sources:: Sources of random data
222 * Target directory:: Target directory
223 * Trailing slashes:: Trailing slashes
224 * Traversing symlinks:: Traversing symlinks to directories
225 * Treating / specially:: Treating / specially
226 * Standards conformance:: Standards conformance
228 Output of entire files
230 * cat invocation:: Concatenate and write files.
231 * tac invocation:: Concatenate and write files in reverse.
232 * nl invocation:: Number lines and write files.
233 * od invocation:: Write files in octal or other formats.
234 * base64 invocation:: Transform data into printable data.
236 Formatting file contents
238 * fmt invocation:: Reformat paragraph text.
239 * pr invocation:: Paginate or columnate files for printing.
240 * fold invocation:: Wrap input lines to fit in specified width.
242 Output of parts of files
244 * head invocation:: Output the first part of files.
245 * tail invocation:: Output the last part of files.
246 * split invocation:: Split a file into fixed-size pieces.
247 * csplit invocation:: Split a file into context-determined pieces.
251 * wc invocation:: Print newline, word, and byte counts.
252 * sum invocation:: Print checksum and block counts.
253 * cksum invocation:: Print CRC checksum and byte counts.
254 * md5sum invocation:: Print or check MD5 digests.
255 * sha1sum invocation:: Print or check SHA-1 digests.
256 * sha2 utilities:: Print or check SHA-2 digests.
258 Operating on sorted files
260 * sort invocation:: Sort text files.
261 * shuf invocation:: Shuffle text files.
262 * uniq invocation:: Uniquify files.
263 * comm invocation:: Compare two sorted files line by line.
264 * ptx invocation:: Produce a permuted index of file contents.
265 * tsort invocation:: Topological sort.
267 @command{ptx}: Produce permuted indexes
269 * General options in ptx:: Options which affect general program behavior.
270 * Charset selection in ptx:: Underlying character set considerations.
271 * Input processing in ptx:: Input fields, contexts, and keyword selection.
272 * Output formatting in ptx:: Types of output format, and sizing the fields.
273 * Compatibility in ptx:: The @acronym{GNU} extensions to @command{ptx}
275 Operating on fields within a line
277 * cut invocation:: Print selected parts of lines.
278 * paste invocation:: Merge lines of files.
279 * join invocation:: Join lines on a common field.
281 Operating on characters
283 * tr invocation:: Translate, squeeze, and/or delete characters.
284 * expand invocation:: Convert tabs to spaces.
285 * unexpand invocation:: Convert spaces to tabs.
287 @command{tr}: Translate, squeeze, and/or delete characters
289 * Character sets:: Specifying sets of characters.
290 * Translating:: Changing one set of characters to another.
291 * Squeezing:: Squeezing repeats and deleting.
295 * ls invocation:: List directory contents
296 * dir invocation:: Briefly list directory contents
297 * vdir invocation:: Verbosely list directory contents
298 * dircolors invocation:: Color setup for @command{ls}
300 @command{ls}: List directory contents
302 * Which files are listed:: Which files are listed
303 * What information is listed:: What information is listed
304 * Sorting the output:: Sorting the output
305 * More details about version sort:: More details about version sort
306 * General output formatting:: General output formatting
307 * Formatting the file names:: Formatting the file names
311 * cp invocation:: Copy files and directories
312 * dd invocation:: Convert and copy a file
313 * install invocation:: Copy files and set attributes
314 * mv invocation:: Move (rename) files
315 * rm invocation:: Remove files or directories
316 * shred invocation:: Remove files more securely
320 * link invocation:: Make a hard link via the link syscall
321 * ln invocation:: Make links between files
322 * mkdir invocation:: Make directories
323 * mkfifo invocation:: Make FIFOs (named pipes)
324 * mknod invocation:: Make block or character special files
325 * readlink invocation:: Print value of a symlink or canonical file name
326 * rmdir invocation:: Remove empty directories
327 * unlink invocation:: Remove files via unlink syscall
329 Changing file attributes
331 * chown invocation:: Change file owner and group
332 * chgrp invocation:: Change group ownership
333 * chmod invocation:: Change access permissions
334 * touch invocation:: Change file timestamps
338 * df invocation:: Report file system disk space usage
339 * du invocation:: Estimate file space usage
340 * stat invocation:: Report file or file system status
341 * sync invocation:: Synchronize data on disk with memory
342 * truncate invocation:: Shrink or extend the size of a file
346 * echo invocation:: Print a line of text
347 * printf invocation:: Format and print data
348 * yes invocation:: Print a string until interrupted
352 * false invocation:: Do nothing, unsuccessfully
353 * true invocation:: Do nothing, successfully
354 * test invocation:: Check file types and compare values
355 * expr invocation:: Evaluate expressions
357 @command{test}: Check file types and compare values
359 * File type tests:: File type tests
360 * Access permission tests:: Access permission tests
361 * File characteristic tests:: File characteristic tests
362 * String tests:: String tests
363 * Numeric tests:: Numeric tests
365 @command{expr}: Evaluate expression
367 * String expressions:: + : match substr index length
368 * Numeric expressions:: + - * / %
369 * Relations for expr:: | & < <= = == != >= >
370 * Examples of expr:: Examples of using @command{expr}
374 * tee invocation:: Redirect output to multiple files or processes
376 File name manipulation
378 * basename invocation:: Strip directory and suffix from a file name
379 * dirname invocation:: Strip non-directory suffix from a file name
380 * pathchk invocation:: Check file name validity and portability
384 * pwd invocation:: Print working directory
385 * stty invocation:: Print or change terminal characteristics
386 * printenv invocation:: Print all or some environment variables
387 * tty invocation:: Print file name of terminal on standard input
389 @command{stty}: Print or change terminal characteristics
391 * Control:: Control settings
392 * Input:: Input settings
393 * Output:: Output settings
394 * Local:: Local settings
395 * Combination:: Combination settings
396 * Characters:: Special characters
397 * Special:: Special settings
401 * id invocation:: Print user identity
402 * logname invocation:: Print current login name
403 * whoami invocation:: Print effective user ID
404 * groups invocation:: Print group names a user is in
405 * users invocation:: Print login names of users currently logged in
406 * who invocation:: Print who is currently logged in
410 * arch invocation:: Print machine hardware name
411 * date invocation:: Print or set system date and time
412 * uname invocation:: Print system information
413 * hostname invocation:: Print or set system name
414 * hostid invocation:: Print numeric host identifier
415 * uptime invocation:: Print system uptime and load
417 @command{date}: Print or set system date and time
419 * Time conversion specifiers:: %[HIklMNpPrRsSTXzZ]
420 * Date conversion specifiers:: %[aAbBcCdDeFgGhjmuUVwWxyY]
421 * Literal conversion specifiers:: %[%nt]
422 * Padding and other flags:: Pad with zeros, spaces, etc.
423 * Setting the time:: Changing the system clock.
424 * Options for date:: Instead of the current time.
425 * Date input formats:: Specifying date strings.
426 * Examples of date:: Examples.
430 * chcon invocation:: Change SELinux context of file
431 * runcon invocation:: Run a command in specified SELinux context
433 Modified command invocation
435 * chroot invocation:: Run a command with a different root directory
436 * env invocation:: Run a command in a modified environment
437 * nice invocation:: Run a command with modified niceness
438 * nohup invocation:: Run a command immune to hangups
439 * stdbuf invocation:: Run a command with modified I/O buffering
440 * su invocation:: Run a command with substitute user and group ID
441 * timeout invocation:: Run a command with a time limit
445 * kill invocation:: Sending a signal to processes.
449 * sleep invocation:: Delay for a specified time
453 * factor invocation:: Print prime factors
454 * seq invocation:: Print numeric sequences
458 * Mode Structure:: Structure of file mode bits.
459 * Symbolic Modes:: Mnemonic representation of file mode bits.
460 * Numeric Modes:: File mode bits as octal numbers.
461 * Directory Setuid and Setgid:: Set-user-ID and set-group-ID on directories.
465 * General date syntax:: Common rules.
466 * Calendar date items:: 19 Dec 1994.
467 * Time of day items:: 9:20pm.
468 * Time zone items:: @sc{est}, @sc{pdt}, @sc{gmt}.
469 * Day of week items:: Monday and others.
470 * Relative items in date strings:: next tuesday, 2 years ago.
471 * Pure numbers in date strings:: 19931219, 1440.
472 * Seconds since the Epoch:: @@1078100502.
473 * Specifying time zone rules:: TZ="America/New_York", TZ="UTC0".
474 * Authors of get_date:: Bellovin, Eggert, Salz, Berets, et al.
476 Opening the software toolbox
478 * Toolbox introduction:: Toolbox introduction
479 * I/O redirection:: I/O redirection
480 * The who command:: The @command{who} command
481 * The cut command:: The @command{cut} command
482 * The sort command:: The @command{sort} command
483 * The uniq command:: The @command{uniq} command
484 * Putting the tools together:: Putting the tools together
488 * GNU Free Documentation License:: Copying and sharing this manual.
495 @chapter Introduction
497 This manual is a work in progress: many sections make no attempt to explain
498 basic concepts in a way suitable for novices. Thus, if you are interested,
499 please get involved in improving this manual. The entire @sc{gnu} community
502 @cindex @acronym{POSIX}
503 The @sc{gnu} utilities documented here are mostly compatible with the
504 @acronym{POSIX} standard.
505 @cindex bugs, reporting
506 Please report bugs to @email{bug-coreutils@@gnu.org}. Remember
507 to include the version number, machine architecture, input files, and
508 any other information needed to reproduce the bug: your input, what you
509 expected, what you got, and why it is wrong. Diffs are welcome, but
510 please include a description of the problem as well, since this is
511 sometimes difficult to infer. @xref{Bugs, , , gcc, Using and Porting GNU CC}.
517 @cindex MacKenzie, D.
520 This manual was originally derived from the Unix man pages in the
521 distributions, which were written by David MacKenzie and updated by Jim
522 Meyering. What you are reading now is the authoritative documentation
523 for these utilities; the man pages are no longer being maintained. The
524 original @command{fmt} man page was written by Ross Paterson. Fran@,{c}ois
525 Pinard did the initial conversion to Texinfo format. Karl Berry did the
526 indexing, some reorganization, and editing of the results. Brian
527 Youmans of the Free Software Foundation office staff combined the
528 manuals for textutils, fileutils, and sh-utils to produce the present
529 omnibus manual. Richard Stallman contributed his usual invaluable
530 insights to the overall process.
533 @chapter Common options
537 @itemx @w{@kbd{--backup}[=@var{method}]}
540 @vindex VERSION_CONTROL
541 @cindex backups, making
542 @xref{Backup options}.
543 Make a backup of each file that would otherwise be overwritten or removed.
546 @macro optBackupSuffix
547 @item -S @var{suffix}
548 @itemx --suffix=@var{suffix}
551 Append @var{suffix} to each backup file made with @option{-b}.
552 @xref{Backup options}.
555 @macro optTargetDirectory
556 @item -t @var{directory}
557 @itemx @w{@kbd{--target-directory}=@var{directory}}
559 @opindex --target-directory
560 @cindex target directory
561 @cindex destination directory
562 Specify the destination @var{directory}.
563 @xref{Target directory}.
566 @macro optNoTargetDirectory
568 @itemx --no-target-directory
570 @opindex --no-target-directory
571 @cindex target directory
572 @cindex destination directory
573 Do not treat the last operand specially when it is a directory or a
574 symbolic link to a directory. @xref{Target directory}.
581 Append an SI-style abbreviation to each size, such as @samp{M} for
582 megabytes. Powers of 1000 are used, not 1024; @samp{M} stands for
583 1,000,000 bytes. This option is equivalent to
584 @option{--block-size=si}. Use the @option{-h} or
585 @option{--human-readable} option if
586 you prefer powers of 1024.
589 @macro optHumanReadable
591 @itemx --human-readable
593 @opindex --human-readable
594 @cindex human-readable output
595 Append a size letter to each size, such as @samp{M} for mebibytes.
596 Powers of 1024 are used, not 1000; @samp{M} stands for 1,048,576 bytes.
597 This option is equivalent to @option{--block-size=human-readable}.
598 Use the @option{--si} option if you prefer powers of 1000.
601 @macro optStripTrailingSlashes
602 @itemx @w{@kbd{--strip-trailing-slashes}}
603 @opindex --strip-trailing-slashes
604 @cindex stripping trailing slashes
605 Remove any trailing slashes from each @var{source} argument.
606 @xref{Trailing slashes}.
609 @macro mayConflictWithShellBuiltIn{cmd}
610 @cindex conflicts with shell built-ins
611 @cindex built-in shell commands, conflicts with
612 Due to shell aliases and built-in @command{\cmd\} command, using an
613 unadorned @command{\cmd\} interactively or in a script may get you
614 different functionality than that described here. Invoke it via
615 @command{env} (i.e., @code{env \cmd\ @dots{}}) to avoid interference
620 @macro multiplierSuffixes{varName}
622 Appending @samp{b} multiplies @var{\varName\} by 512,
623 @samp{kB} by 1000, @samp{K} by 1024,
624 @samp{MB} by 1000*1000, @samp{M} by 1024*1024,
625 @samp{GB} by 1000*1000*1000, @samp{G} by 1024*1024*1024,
626 and so on for @samp{T}, @samp{P}, @samp{E}, @samp{Z}, and @samp{Y}.
628 @var{\varName\} is a number which may have one of the following
629 multiplicative suffixes:
631 @samp{b} => 512 ("blocks")
632 @samp{KB} => 1000 (KiloBytes)
633 @samp{K} => 1024 (KibiBytes)
634 @samp{MB} => 1000*1000 (MegaBytes)
635 @samp{M} => 1024*1024 (MebiBytes)
636 @samp{GB} => 1000*1000*1000 (GigaBytes)
637 @samp{G} => 1024*1024*1024 (GibiBytes)
639 and so on for @samp{T}, @samp{P}, @samp{E}, @samp{Z}, and @samp{Y}.
642 @c FIXME: same as above, but no ``blocks'' line.
643 @macro multiplierSuffixesNoBlocks{varName}
644 @var{\varName\} is a number which may have one of the following
645 multiplicative suffixes:
647 @samp{KB} => 1000 (KiloBytes)
648 @samp{K} => 1024 (KibiBytes)
649 @samp{MB} => 1000*1000 (MegaBytes)
650 @samp{M} => 1024*1024 (MebiBytes)
651 @samp{GB} => 1000*1000*1000 (GigaBytes)
652 @samp{G} => 1024*1024*1024 (GibiBytes)
654 and so on for @samp{T}, @samp{P}, @samp{E}, @samp{Z}, and @samp{Y}.
657 @cindex common options
659 Certain options are available in all of these programs. Rather than
660 writing identical descriptions for each of the programs, they are
661 described here. (In fact, every @sc{gnu} program accepts (or should accept)
664 @vindex POSIXLY_CORRECT
665 Normally options and operands can appear in any order, and programs act
666 as if all the options appear before any operands. For example,
667 @samp{sort -r passwd -t :} acts like @samp{sort -r -t : passwd}, since
668 @samp{:} is an option-argument of @option{-t}. However, if the
669 @env{POSIXLY_CORRECT} environment variable is set, options must appear
670 before operands, unless otherwise specified for a particular command.
672 A few programs can usefully have trailing operands with leading
673 @samp{-}. With such a program, options must precede operands even if
674 @env{POSIXLY_CORRECT} is not set, and this fact is noted in the
675 program description. For example, the @command{env} command's options
676 must appear before its operands, since in some cases the operands
677 specify a command that itself contains options.
679 Most programs that accept long options recognize unambiguous
680 abbreviations of those options. For example, @samp{rmdir
681 --ignore-fail-on-non-empty} can be invoked as @samp{rmdir
682 --ignore-fail} or even @samp{rmdir --i}. Ambiguous options, such as
683 @samp{ls --h}, are identified as such.
685 Some of these programs recognize the @option{--help} and @option{--version}
686 options only when one of them is the sole command line argument. For
687 these programs, abbreviations of the long options are not always recognized.
694 Print a usage message listing all available options, then exit successfully.
698 @cindex version number, finding
699 Print the version number, then exit successfully.
703 @cindex option delimiter
704 Delimit the option list. Later arguments, if any, are treated as
705 operands even if they begin with @samp{-}. For example, @samp{sort --
706 -r} reads from the file named @file{-r}.
710 @cindex standard input
711 @cindex standard output
712 A single @samp{-} operand is not really an option, though it looks like one. It
713 stands for standard input, or for standard output if that is clear from
714 the context. For example, @samp{sort -} reads from standard input,
715 and is equivalent to plain @samp{sort}, and @samp{tee -} writes an
716 extra copy of its input to standard output. Unless otherwise
717 specified, @samp{-} can appear as any operand that requires a file
721 * Exit status:: Indicating program success or failure.
722 * Backup options:: -b -S, in some programs.
723 * Block size:: BLOCK_SIZE and --block-size, in some programs.
724 * Signal specifications:: Specifying signals using the --signal option.
725 * Disambiguating names and IDs:: chgrp and chown owner and group syntax
726 * Random sources:: --random-source, in some programs.
727 * Target directory:: Specifying a target directory, in some programs.
728 * Trailing slashes:: --strip-trailing-slashes, in some programs.
729 * Traversing symlinks:: -H, -L, or -P, in some programs.
730 * Treating / specially:: --preserve-root and --no-preserve-root.
731 * Special built-in utilities:: @command{break}, @command{:}, @command{eval}, @dots{}
732 * Standards conformance:: Conformance to the @acronym{POSIX} standard.
740 An exit status of zero indicates success,
741 and a nonzero value indicates failure.
744 Nearly every command invocation yields an integral @dfn{exit status}
745 that can be used to change how other commands work.
746 For the vast majority of commands, an exit status of zero indicates
747 success. Failure is indicated by a nonzero value---typically
748 @samp{1}, though it may differ on unusual platforms as @acronym{POSIX}
749 requires only that it be nonzero.
751 However, some of the programs documented here do produce
752 other exit status values and a few associate different
753 meanings with the values @samp{0} and @samp{1}.
754 Here are some of the exceptions:
755 @command{chroot}, @command{env}, @command{expr},
756 @command{nice}, @command{nohup}, @command{printenv}, @command{sort},
757 @command{su}, @command{test}, @command{timeout}, @command{tty}.
761 @section Backup options
763 @cindex backup options
765 Some @sc{gnu} programs (at least @command{cp}, @command{install},
766 @command{ln}, and @command{mv}) optionally make backups of files
767 before writing new versions.
768 These options control the details of these backups. The options are also
769 briefly mentioned in the descriptions of the particular programs.
774 @itemx @w{@kbd{--backup}[=@var{method}]}
777 @vindex VERSION_CONTROL
778 @cindex backups, making
779 Make a backup of each file that would otherwise be overwritten or removed.
780 Without this option, the original versions are destroyed.
781 Use @var{method} to determine the type of backups to make.
782 When this option is used but @var{method} is not specified,
783 then the value of the @env{VERSION_CONTROL}
784 environment variable is used. And if @env{VERSION_CONTROL} is not set,
785 the default backup type is @samp{existing}.
787 Note that the short form of this option, @option{-b} does not accept any
788 argument. Using @option{-b} is equivalent to using @option{--backup=existing}.
790 @vindex version-control @r{Emacs variable}
791 This option corresponds to the Emacs variable @samp{version-control};
792 the values for @var{method} are the same as those used in Emacs.
793 This option also accepts more descriptive names.
794 The valid @var{method}s are (unique abbreviations are accepted):
799 @opindex none @r{backup method}
804 @opindex numbered @r{backup method}
805 Always make numbered backups.
809 @opindex existing @r{backup method}
810 Make numbered backups of files that already have them, simple backups
815 @opindex simple @r{backup method}
816 Always make simple backups. Please note @samp{never} is not to be
817 confused with @samp{none}.
821 @item -S @var{suffix}
822 @itemx --suffix=@var{suffix}
825 @cindex backup suffix
826 @vindex SIMPLE_BACKUP_SUFFIX
827 Append @var{suffix} to each backup file made with @option{-b}. If this
828 option is not specified, the value of the @env{SIMPLE_BACKUP_SUFFIX}
829 environment variable is used. And if @env{SIMPLE_BACKUP_SUFFIX} is not
830 set, the default is @samp{~}, just as in Emacs.
839 Some @sc{gnu} programs (at least @command{df}, @command{du}, and
840 @command{ls}) display sizes in ``blocks''. You can adjust the block size
841 and method of display to make sizes easier to read. The block size
842 used for display is independent of any file system block size.
843 Fractional block counts are rounded up to the nearest integer.
845 @opindex --block-size=@var{size}
848 @vindex DF_BLOCK_SIZE
849 @vindex DU_BLOCK_SIZE
850 @vindex LS_BLOCK_SIZE
851 @vindex POSIXLY_CORRECT@r{, and block size}
853 The default block size is chosen by examining the following environment
854 variables in turn; the first one that is set determines the block size.
859 This specifies the default block size for the @command{df} command.
860 Similarly, @env{DU_BLOCK_SIZE} specifies the default for @command{du} and
861 @env{LS_BLOCK_SIZE} for @command{ls}.
864 This specifies the default block size for all three commands, if the
865 above command-specific environment variables are not set.
868 This specifies the default block size for all values that are normally
869 printed as blocks, if neither @env{BLOCK_SIZE} nor the above
870 command-specific environment variables are set. Unlike the other
871 environment variables, @env{BLOCKSIZE} does not affect values that are
872 normally printed as byte counts, e.g., the file sizes contained in
875 @item POSIXLY_CORRECT
876 If neither @env{@var{command}_BLOCK_SIZE}, nor @env{BLOCK_SIZE}, nor
877 @env{BLOCKSIZE} is set, but this variable is set, the block size
882 If none of the above environment variables are set, the block size
883 currently defaults to 1024 bytes in most contexts, but this number may
884 change in the future. For @command{ls} file sizes, the block size
887 @cindex human-readable output
890 A block size specification can be a positive integer specifying the number
891 of bytes per block, or it can be @code{human-readable} or @code{si} to
892 select a human-readable format. Integers may be followed by suffixes
893 that are upward compatible with the
894 @uref{http://www.bipm.fr/enus/3_SI/si-prefixes.html, SI prefixes}
895 for decimal multiples and with the
896 @uref{http://physics.nist.gov/cuu/Units/binary.html, IEC 60027-2
897 prefixes for binary multiples}.
899 With human-readable formats, output sizes are followed by a size letter
900 such as @samp{M} for megabytes. @code{BLOCK_SIZE=human-readable} uses
901 powers of 1024; @samp{M} stands for 1,048,576 bytes.
902 @code{BLOCK_SIZE=si} is similar, but uses powers of 1000 and appends
903 @samp{B}; @samp{MB} stands for 1,000,000 bytes.
906 A block size specification preceded by @samp{'} causes output sizes to
907 be displayed with thousands separators. The @env{LC_NUMERIC} locale
908 specifies the thousands separator and grouping. For example, in an
909 American English locale, @samp{--block-size="'1kB"} would cause a size
910 of 1234000 bytes to be displayed as @samp{1,234}. In the default C
911 locale, there is no thousands separator so a leading @samp{'} has no
914 An integer block size can be followed by a suffix to specify a
915 multiple of that size. A bare size letter,
916 or one followed by @samp{iB}, specifies
917 a multiple using powers of 1024. A size letter followed by @samp{B}
918 specifies powers of 1000 instead. For example, @samp{1M} and
919 @samp{1MiB} are equivalent to @samp{1048576}, whereas @samp{1MB} is
920 equivalent to @samp{1000000}.
922 A plain suffix without a preceding integer acts as if @samp{1} were
923 prepended, except that it causes a size indication to be appended to
924 the output. For example, @samp{--block-size="kB"} displays 3000 as
927 The following suffixes are defined. Large sizes like @code{1Y}
928 may be rejected by your computer due to limitations of its arithmetic.
932 @cindex kilobyte, definition of
933 kilobyte: @math{10^3 = 1000}.
937 @cindex kibibyte, definition of
938 kibibyte: @math{2^{10} = 1024}. @samp{K} is special: the SI prefix is
939 @samp{k} and the IEC 60027-2 prefix is @samp{Ki}, but tradition and
940 @acronym{POSIX} use @samp{k} to mean @samp{KiB}.
942 @cindex megabyte, definition of
943 megabyte: @math{10^6 = 1,000,000}.
946 @cindex mebibyte, definition of
947 mebibyte: @math{2^{20} = 1,048,576}.
949 @cindex gigabyte, definition of
950 gigabyte: @math{10^9 = 1,000,000,000}.
953 @cindex gibibyte, definition of
954 gibibyte: @math{2^{30} = 1,073,741,824}.
956 @cindex terabyte, definition of
957 terabyte: @math{10^{12} = 1,000,000,000,000}.
960 @cindex tebibyte, definition of
961 tebibyte: @math{2^{40} = 1,099,511,627,776}.
963 @cindex petabyte, definition of
964 petabyte: @math{10^{15} = 1,000,000,000,000,000}.
967 @cindex pebibyte, definition of
968 pebibyte: @math{2^{50} = 1,125,899,906,842,624}.
970 @cindex exabyte, definition of
971 exabyte: @math{10^{18} = 1,000,000,000,000,000,000}.
974 @cindex exbibyte, definition of
975 exbibyte: @math{2^{60} = 1,152,921,504,606,846,976}.
977 @cindex zettabyte, definition of
978 zettabyte: @math{10^{21} = 1,000,000,000,000,000,000,000}
981 @math{2^{70} = 1,180,591,620,717,411,303,424}.
982 (@samp{Zi} is a @acronym{GNU} extension to IEC 60027-2.)
984 @cindex yottabyte, definition of
985 yottabyte: @math{10^{24} = 1,000,000,000,000,000,000,000,000}.
988 @math{2^{80} = 1,208,925,819,614,629,174,706,176}.
989 (@samp{Yi} is a @acronym{GNU} extension to IEC 60027-2.)
994 @opindex --block-size
995 @opindex --human-readable
998 Block size defaults can be overridden by an explicit
999 @option{--block-size=@var{size}} option. The @option{-k}
1000 option is equivalent to @option{--block-size=1K}, which
1001 is the default unless the @env{POSIXLY_CORRECT} environment variable is
1002 set. The @option{-h} or @option{--human-readable} option is equivalent to
1003 @option{--block-size=human-readable}. The @option{--si} option is
1004 equivalent to @option{--block-size=si}.
1006 @node Signal specifications
1007 @section Signal specifications
1008 @cindex signals, specifying
1010 A @var{signal} may be a signal name like @samp{HUP}, or a signal
1011 number like @samp{1}, or an exit status of a process terminated by the
1012 signal. A signal name can be given in canonical form or prefixed by
1013 @samp{SIG}. The case of the letters is ignored. The following signal names
1014 and numbers are supported on all @acronym{POSIX} compliant systems:
1020 2. Terminal interrupt.
1026 9. Kill (cannot be caught or ignored).
1034 Other supported signal names have system-dependent corresponding
1035 numbers. All systems conforming to @acronym{POSIX} 1003.1-2001 also
1036 support the following signals:
1040 Access to an undefined portion of a memory object.
1042 Child process terminated, stopped, or continued.
1044 Continue executing, if stopped.
1046 Erroneous arithmetic operation.
1048 Illegal Instruction.
1050 Write on a pipe with no one to read it.
1052 Invalid memory reference.
1054 Stop executing (cannot be caught or ignored).
1058 Background process attempting read.
1060 Background process attempting write.
1062 High bandwidth data is available at a socket.
1064 User-defined signal 1.
1066 User-defined signal 2.
1070 @acronym{POSIX} 1003.1-2001 systems that support the @acronym{XSI} extension
1071 also support the following signals:
1077 Profiling timer expired.
1081 Trace/breakpoint trap.
1083 Virtual timer expired.
1085 CPU time limit exceeded.
1087 File size limit exceeded.
1091 @acronym{POSIX} 1003.1-2001 systems that support the @acronym{XRT} extension
1092 also support at least eight real-time signals called @samp{RTMIN},
1093 @samp{RTMIN+1}, @dots{}, @samp{RTMAX-1}, @samp{RTMAX}.
1095 @node Disambiguating names and IDs
1096 @section chown and chgrp: Disambiguating user names and IDs
1097 @cindex user names, disambiguating
1098 @cindex user IDs, disambiguating
1099 @cindex group names, disambiguating
1100 @cindex group IDs, disambiguating
1101 @cindex disambiguating group names and IDs
1103 Since the @var{owner} and @var{group} arguments to @command{chown} and
1104 @command{chgrp} may be specified as names or numeric IDs, there is an
1106 What if a user or group @emph{name} is a string of digits?
1107 @footnote{Using a number as a user name is common in some environments.}
1108 Should the command interpret it as a user name or as an ID?
1109 @acronym{POSIX} requires that @command{chown} and @command{chgrp}
1110 first attempt to resolve the specified string as a name, and
1111 only once that fails, then try to interpret it as an ID.
1112 This is troublesome when you want to specify a numeric ID, say 42,
1113 and it must work even in a pathological situation where
1114 @samp{42} is a user name that maps to some other user ID, say 1000.
1115 Simply invoking @code{chown 42 F}, will set @file{F}s owner ID to
1116 1000---not what you intended.
1118 GNU @command{chown} and @command{chgrp} provide a way to work around this,
1119 that at the same time may result in a significant performance improvement
1120 by eliminating a database look-up.
1121 Simply precede each numeric user ID and/or group ID with a @samp{+},
1122 in order to force its interpretation as an integer:
1126 chgrp +$numeric_group_id another-file
1130 GNU @command{chown} and @command{chgrp}
1131 skip the name look-up process for each @samp{+}-prefixed string,
1132 because a string containing @samp{+} is never a valid user or group name.
1133 This syntax is accepted on most common Unix systems, but not on Solaris 10.
1135 @node Random sources
1136 @section Sources of random data
1138 @cindex random sources
1140 The @command{shuf}, @command{shred}, and @command{sort} commands
1141 sometimes need random data to do their work. For example, @samp{sort
1142 -R} must choose a hash function at random, and it needs random data to
1143 make this selection.
1145 By default these commands use an internal pseudorandom generator
1146 initialized by a small amount of entropy, but can be directed to use
1147 an external source with the @option{--random-source=@var{file}} option.
1148 An error is reported if @var{file} does not contain enough bytes.
1150 For example, the device file @file{/dev/urandom} could be used as the
1151 source of random data. Typically, this device gathers environmental
1152 noise from device drivers and other sources into an entropy pool, and
1153 uses the pool to generate random bits. If the pool is short of data,
1154 the device reuses the internal pool to produce more bits, using a
1155 cryptographically secure pseudorandom number generator. But be aware
1156 that this device is not designed for bulk random data generation
1157 and is relatively slow.
1159 @file{/dev/urandom} suffices for most practical uses, but applications
1160 requiring high-value or long-term protection of private data may
1161 require an alternate data source like @file{/dev/random} or
1162 @file{/dev/arandom}. The set of available sources depends on your
1165 To reproduce the results of an earlier invocation of a command, you
1166 can save some random data into a file and then use that file as the
1167 random source in earlier and later invocations of the command.
1169 @node Target directory
1170 @section Target directory
1172 @cindex target directory
1174 The @command{cp}, @command{install}, @command{ln}, and @command{mv}
1175 commands normally treat the last operand specially when it is a
1176 directory or a symbolic link to a directory. For example, @samp{cp
1177 source dest} is equivalent to @samp{cp source dest/source} if
1178 @file{dest} is a directory. Sometimes this behavior is not exactly
1179 what is wanted, so these commands support the following options to
1180 allow more fine-grained control:
1185 @itemx --no-target-directory
1186 @opindex --no-target-directory
1187 @cindex target directory
1188 @cindex destination directory
1189 Do not treat the last operand specially when it is a directory or a
1190 symbolic link to a directory. This can help avoid race conditions in
1191 programs that operate in a shared area. For example, when the command
1192 @samp{mv /tmp/source /tmp/dest} succeeds, there is no guarantee that
1193 @file{/tmp/source} was renamed to @file{/tmp/dest}: it could have been
1194 renamed to @file{/tmp/dest/source} instead, if some other process
1195 created @file{/tmp/dest} as a directory. However, if @file{mv
1196 -T /tmp/source /tmp/dest} succeeds, there is no
1197 question that @file{/tmp/source} was renamed to @file{/tmp/dest}.
1199 In the opposite situation, where you want the last operand to be
1200 treated as a directory and want a diagnostic otherwise, you can use
1201 the @option{--target-directory} (@option{-t}) option.
1203 @item -t @var{directory}
1204 @itemx @w{@kbd{--target-directory}=@var{directory}}
1205 @opindex --target-directory
1206 @cindex target directory
1207 @cindex destination directory
1208 Use @var{directory} as the directory component of each destination
1211 The interface for most programs is that after processing options and a
1212 finite (possibly zero) number of fixed-position arguments, the remaining
1213 argument list is either expected to be empty, or is a list of items
1214 (usually files) that will all be handled identically. The @command{xargs}
1215 program is designed to work well with this convention.
1217 The commands in the @command{mv}-family are unusual in that they take
1218 a variable number of arguments with a special case at the @emph{end}
1219 (namely, the target directory). This makes it nontrivial to perform some
1220 operations, e.g., ``move all files from here to ../d/'', because
1221 @code{mv * ../d/} might exhaust the argument space, and @code{ls | xargs ...}
1222 doesn't have a clean way to specify an extra final argument for each
1223 invocation of the subject command. (It can be done by going through a
1224 shell command, but that requires more human labor and brain power than
1227 The @w{@kbd{--target-directory}} (@option{-t}) option allows the @command{cp},
1228 @command{install}, @command{ln}, and @command{mv} programs to be used
1229 conveniently with @command{xargs}. For example, you can move the files
1230 from the current directory to a sibling directory, @code{d} like this:
1233 ls | xargs mv -t ../d --
1236 However, this doesn't move files whose names begin with @samp{.}.
1237 If you use the @sc{gnu} @command{find} program, you can move those
1238 files too, with this command:
1241 find . -mindepth 1 -maxdepth 1 \
1245 But both of the above approaches fail if there are no files in the
1246 current directory, or if any file has a name containing a blank or
1247 some other special characters.
1248 The following example removes those limitations and requires both
1249 @sc{gnu} @command{find} and @sc{gnu} @command{xargs}:
1252 find . -mindepth 1 -maxdepth 1 -print0 \
1253 | xargs --null --no-run-if-empty \
1260 The @option{--target-directory} (@option{-t}) and
1261 @option{--no-target-directory} (@option{-T})
1262 options cannot be combined.
1264 @node Trailing slashes
1265 @section Trailing slashes
1267 @cindex trailing slashes
1269 Some @sc{gnu} programs (at least @command{cp} and @command{mv}) allow you to
1270 remove any trailing slashes from each @var{source} argument before
1271 operating on it. The @w{@kbd{--strip-trailing-slashes}} option enables
1274 This is useful when a @var{source} argument may have a trailing slash and
1275 @c FIXME: mv's behavior in this case is system-dependent
1276 specify a symbolic link to a directory. This scenario is in fact rather
1277 common because some shells can automatically append a trailing slash when
1278 performing file name completion on such symbolic links. Without this
1279 option, @command{mv}, for example, (via the system's rename function) must
1280 interpret a trailing slash as a request to dereference the symbolic link
1281 and so must rename the indirectly referenced @emph{directory} and not
1282 the symbolic link. Although it may seem surprising that such behavior
1283 be the default, it is required by @acronym{POSIX} and is consistent with
1284 other parts of that standard.
1286 @node Traversing symlinks
1287 @section Traversing symlinks
1289 @cindex symbolic link to directory, controlling traversal of
1291 The following options modify how @command{chown} and @command{chgrp}
1292 @c FIXME: note that `du' has these options, too, but they have slightly
1293 @c different meaning.
1294 traverse a hierarchy when the @option{--recursive} (@option{-R})
1295 option is also specified.
1296 If more than one of the following options is specified, only the final
1298 These options specify whether processing a symbolic link to a directory
1299 entails operating on just the symbolic link or on all files in the
1300 hierarchy rooted at that directory.
1302 These options are independent of @option{--dereference} and
1303 @option{--no-dereference} (@option{-h}), which control whether to modify
1304 a symlink or its referent.
1311 @cindex symbolic link to directory, traverse each that is specified on the command line
1312 If @option{--recursive} (@option{-R}) is specified and
1313 a command line argument is a symbolic link to a directory, traverse it.
1320 @cindex symbolic link to directory, traverse each that is encountered
1321 In a recursive traversal, traverse every symbolic link to a directory
1322 that is encountered.
1329 @cindex symbolic link to directory, never traverse
1330 Do not traverse any symbolic links.
1331 This is the default if none of @option{-H}, @option{-L},
1332 or @option{-P} is specified.
1339 @node Treating / specially
1340 @section Treating @file{/} specially
1342 Certain commands can operate destructively on entire hierarchies.
1343 For example, if a user with appropriate privileges mistakenly runs
1344 @samp{rm -rf / tmp/junk}, that may remove
1345 all files on the entire system. Since there are so few
1346 legitimate uses for such a command,
1347 @sc{gnu} @command{rm} normally declines to operate on any directory
1348 that resolves to @file{/}. If you really want to try to remove all
1349 the files on your system, you can use the @option{--no-preserve-root}
1350 option, but the default behavior, specified by the
1351 @option{--preserve-option}, is safer for most purposes.
1353 The commands @command{chgrp}, @command{chmod} and @command{chown}
1354 can also operate destructively on entire hierarchies, so they too
1355 support these options. Although, unlike @command{rm}, they don't
1356 actually unlink files, these commands are arguably more dangerous
1357 when operating recursively on @file{/}, since they often work much
1358 more quickly, and hence damage more files before an alert user can
1359 interrupt them. Tradition and @acronym{POSIX} require these commands
1360 to operate recursively on @file{/}, so they default to
1361 @option{--no-preserve-root}, but using the @option{--preserve-root}
1362 option makes them safer for most purposes. For convenience you can
1363 specify @option{--preserve-root} in an alias or in a shell function.
1365 Note that the @option{--preserve-root} option also ensures
1366 that @command{chgrp} and @command{chown} do not modify @file{/}
1367 even when dereferencing a symlink pointing to @file{/}.
1369 @node Special built-in utilities
1370 @section Special built-in utilities
1372 Some programs like @command{nice} can invoke other programs; for
1373 example, the command @samp{nice cat file} invokes the program
1374 @command{cat} by executing the command @samp{cat file}. However,
1375 @dfn{special built-in utilities} like @command{exit} cannot be invoked
1376 this way. For example, the command @samp{nice exit} does not have a
1377 well-defined behavior: it may generate an error message instead of
1380 Here is a list of the special built-in utilities that are standardized
1381 by @acronym{POSIX} 1003.1-2004.
1384 @t{.@: : break continue eval exec exit export readonly
1385 return set shift times trap unset}
1388 For example, because @samp{.}, @samp{:}, and @samp{exec} are special,
1389 the commands @samp{nice . foo.sh}, @samp{nice :}, and @samp{nice exec
1390 pwd} do not work as you might expect.
1392 Many shells extend this list. For example, Bash has several extra
1393 special built-in utilities like @command{history}, and
1394 @command{suspend}, and with Bash the command @samp{nice suspend}
1395 generates an error message instead of suspending.
1397 @node Standards conformance
1398 @section Standards conformance
1400 @vindex POSIXLY_CORRECT
1401 In a few cases, the @sc{gnu} utilities' default behavior is
1402 incompatible with the @acronym{POSIX} standard. To suppress these
1403 incompatibilities, define the @env{POSIXLY_CORRECT} environment
1404 variable. Unless you are checking for @acronym{POSIX} conformance, you
1405 probably do not need to define @env{POSIXLY_CORRECT}.
1407 Newer versions of @acronym{POSIX} are occasionally incompatible with older
1408 versions. For example, older versions of @acronym{POSIX} required the
1409 command @samp{sort +1} to sort based on the second and succeeding
1410 fields in each input line, but starting with @acronym{POSIX} 1003.1-2001
1411 the same command is required to sort the file named @file{+1}, and you
1412 must instead use the command @samp{sort -k 2} to get the field-based
1415 @vindex _POSIX2_VERSION
1416 The @sc{gnu} utilities normally conform to the version of @acronym{POSIX}
1417 that is standard for your system. To cause them to conform to a
1418 different version of @acronym{POSIX}, define the @env{_POSIX2_VERSION}
1419 environment variable to a value of the form @var{yyyymm} specifying
1420 the year and month the standard was adopted. Two values are currently
1421 supported for @env{_POSIX2_VERSION}: @samp{199209} stands for
1422 @acronym{POSIX} 1003.2-1992, and @samp{200112} stands for @acronym{POSIX}
1423 1003.1-2001. For example, if you have a newer system but are running software
1424 that assumes an older version of @acronym{POSIX} and uses @samp{sort +1}
1425 or @samp{tail +10}, you can work around any compatibility problems by setting
1426 @samp{_POSIX2_VERSION=199209} in your environment.
1428 @node Output of entire files
1429 @chapter Output of entire files
1431 @cindex output of entire files
1432 @cindex entire files, output of
1434 These commands read and write entire files, possibly transforming them
1438 * cat invocation:: Concatenate and write files.
1439 * tac invocation:: Concatenate and write files in reverse.
1440 * nl invocation:: Number lines and write files.
1441 * od invocation:: Write files in octal or other formats.
1442 * base64 invocation:: Transform data into printable data.
1445 @node cat invocation
1446 @section @command{cat}: Concatenate and write files
1449 @cindex concatenate and write files
1450 @cindex copying files
1452 @command{cat} copies each @var{file} (@samp{-} means standard input), or
1453 standard input if none are given, to standard output. Synopsis:
1456 cat [@var{option}] [@var{file}]@dots{}
1459 The program accepts the following options. Also see @ref{Common options}.
1467 Equivalent to @option{-vET}.
1470 @itemx --number-nonblank
1472 @opindex --number-nonblank
1473 Number all nonempty output lines, starting with 1.
1477 Equivalent to @option{-vE}.
1482 @opindex --show-ends
1483 Display a @samp{$} after the end of each line.
1489 Number all output lines, starting with 1.
1492 @itemx --squeeze-blank
1494 @opindex --squeeze-blank
1495 @cindex squeezing empty lines
1496 Suppress repeated adjacent empty lines; output just one empty line
1501 Equivalent to @option{-vT}.
1506 @opindex --show-tabs
1507 Display TAB characters as @samp{^I}.
1511 Ignored; for @acronym{POSIX} compatibility.
1514 @itemx --show-nonprinting
1516 @opindex --show-nonprinting
1517 Display control characters except for LFD and TAB using
1518 @samp{^} notation and precede characters that have the high bit set with
1523 On systems like MS-DOS that distinguish between text and binary files,
1524 @command{cat} normally reads and writes in binary mode. However,
1525 @command{cat} reads in text mode if one of the options
1526 @option{-bensAE} is used or if @command{cat} is reading from standard
1527 input and standard input is a terminal. Similarly, @command{cat}
1528 writes in text mode if one of the options @option{-bensAE} is used or
1529 if standard output is a terminal.
1536 # Output f's contents, then standard input, then g's contents.
1539 # Copy standard input to standard output.
1544 @node tac invocation
1545 @section @command{tac}: Concatenate and write files in reverse
1548 @cindex reversing files
1550 @command{tac} copies each @var{file} (@samp{-} means standard input), or
1551 standard input if none are given, to standard output, reversing the
1552 records (lines by default) in each separately. Synopsis:
1555 tac [@var{option}]@dots{} [@var{file}]@dots{}
1558 @dfn{Records} are separated by instances of a string (newline by
1559 default). By default, this separator string is attached to the end of
1560 the record that it follows in the file.
1562 The program accepts the following options. Also see @ref{Common options}.
1570 The separator is attached to the beginning of the record that it
1571 precedes in the file.
1577 Treat the separator string as a regular expression. Users of @command{tac}
1578 on MS-DOS/MS-Windows should note that, since @command{tac} reads files in
1579 binary mode, each line of a text file might end with a CR/LF pair
1580 instead of the Unix-style LF.
1582 @item -s @var{separator}
1583 @itemx --separator=@var{separator}
1585 @opindex --separator
1586 Use @var{separator} as the record separator, instead of newline.
1594 @section @command{nl}: Number lines and write files
1597 @cindex numbering lines
1598 @cindex line numbering
1600 @command{nl} writes each @var{file} (@samp{-} means standard input), or
1601 standard input if none are given, to standard output, with line numbers
1602 added to some or all of the lines. Synopsis:
1605 nl [@var{option}]@dots{} [@var{file}]@dots{}
1608 @cindex logical pages, numbering on
1609 @command{nl} decomposes its input into (logical) pages; by default, the
1610 line number is reset to 1 at the top of each logical page. @command{nl}
1611 treats all of the input files as a single document; it does not reset
1612 line numbers or logical pages between files.
1614 @cindex headers, numbering
1615 @cindex body, numbering
1616 @cindex footers, numbering
1617 A logical page consists of three sections: header, body, and footer.
1618 Any of the sections can be empty. Each can be numbered in a different
1619 style from the others.
1621 The beginnings of the sections of logical pages are indicated in the
1622 input file by a line containing exactly one of these delimiter strings:
1633 The two characters from which these strings are made can be changed from
1634 @samp{\} and @samp{:} via options (see below), but the pattern and
1635 length of each string cannot be changed.
1637 A section delimiter is replaced by an empty line on output. Any text
1638 that comes before the first section delimiter string in the input file
1639 is considered to be part of a body section, so @command{nl} treats a
1640 file that contains no section delimiters as a single body section.
1642 The program accepts the following options. Also see @ref{Common options}.
1646 @item -b @var{style}
1647 @itemx --body-numbering=@var{style}
1649 @opindex --body-numbering
1650 Select the numbering style for lines in the body section of each
1651 logical page. When a line is not numbered, the current line number
1652 is not incremented, but the line number separator character is still
1653 prepended to the line. The styles are:
1659 number only nonempty lines (default for body),
1661 do not number lines (default for header and footer),
1663 number only lines that contain a match for the basic regular
1664 expression @var{bre}.
1665 @xref{Regular Expressions, , Regular Expressions, grep, The GNU Grep Manual}.
1669 @itemx --section-delimiter=@var{cd}
1671 @opindex --section-delimiter
1672 @cindex section delimiters of pages
1673 Set the section delimiter characters to @var{cd}; default is
1674 @samp{\:}. If only @var{c} is given, the second remains @samp{:}.
1675 (Remember to protect @samp{\} or other metacharacters from shell
1676 expansion with quotes or extra backslashes.)
1678 @item -f @var{style}
1679 @itemx --footer-numbering=@var{style}
1681 @opindex --footer-numbering
1682 Analogous to @option{--body-numbering}.
1684 @item -h @var{style}
1685 @itemx --header-numbering=@var{style}
1687 @opindex --header-numbering
1688 Analogous to @option{--body-numbering}.
1690 @item -i @var{number}
1691 @itemx --page-increment=@var{number}
1693 @opindex --page-increment
1694 Increment line numbers by @var{number} (default 1).
1696 @item -l @var{number}
1697 @itemx --join-blank-lines=@var{number}
1699 @opindex --join-blank-lines
1700 @cindex empty lines, numbering
1701 @cindex blank lines, numbering
1702 Consider @var{number} (default 1) consecutive empty lines to be one
1703 logical line for numbering, and only number the last one. Where fewer
1704 than @var{number} consecutive empty lines occur, do not number them.
1705 An empty line is one that contains no characters, not even spaces
1708 @item -n @var{format}
1709 @itemx --number-format=@var{format}
1711 @opindex --number-format
1712 Select the line numbering format (default is @code{rn}):
1716 @opindex ln @r{format for @command{nl}}
1717 left justified, no leading zeros;
1719 @opindex rn @r{format for @command{nl}}
1720 right justified, no leading zeros;
1722 @opindex rz @r{format for @command{nl}}
1723 right justified, leading zeros.
1727 @itemx --no-renumber
1729 @opindex --no-renumber
1730 Do not reset the line number at the start of a logical page.
1732 @item -s @var{string}
1733 @itemx --number-separator=@var{string}
1735 @opindex --number-separator
1736 Separate the line number from the text line in the output with
1737 @var{string} (default is the TAB character).
1739 @item -v @var{number}
1740 @itemx --starting-line-number=@var{number}
1742 @opindex --starting-line-number
1743 Set the initial line number on each logical page to @var{number} (default 1).
1745 @item -w @var{number}
1746 @itemx --number-width=@var{number}
1748 @opindex --number-width
1749 Use @var{number} characters for line numbers (default 6).
1757 @section @command{od}: Write files in octal or other formats
1760 @cindex octal dump of files
1761 @cindex hex dump of files
1762 @cindex ASCII dump of files
1763 @cindex file contents, dumping unambiguously
1765 @command{od} writes an unambiguous representation of each @var{file}
1766 (@samp{-} means standard input), or standard input if none are given.
1770 od [@var{option}]@dots{} [@var{file}]@dots{}
1771 od [-abcdfilosx]@dots{} [@var{file}] [[+]@var{offset}[.][b]]
1772 od [@var{option}]@dots{} --traditional [@var{file}] [[+]@var{offset}[.][b] [[+]@var{label}[.][b]]]
1775 Each line of output consists of the offset in the input, followed by
1776 groups of data from the file. By default, @command{od} prints the offset in
1777 octal, and each group of file data is a C @code{short int}'s worth of input
1778 printed as a single octal number.
1780 If @var{offset} is given, it specifies how many input bytes to skip
1781 before formatting and writing. By default, it is interpreted as an
1782 octal number, but the optional trailing decimal point causes it to be
1783 interpreted as decimal. If no decimal is specified and the offset
1784 begins with @samp{0x} or @samp{0X} it is interpreted as a hexadecimal
1785 number. If there is a trailing @samp{b}, the number of bytes skipped
1786 will be @var{offset} multiplied by 512.
1788 If a command is of both the first and second forms, the second form is
1789 assumed if the last operand begins with @samp{+} or (if there are two
1790 operands) a digit. For example, in @samp{od foo 10} and @samp{od +10}
1791 the @samp{10} is an offset, whereas in @samp{od 10} the @samp{10} is a
1794 The program accepts the following options. Also see @ref{Common options}.
1798 @item -A @var{radix}
1799 @itemx --address-radix=@var{radix}
1801 @opindex --address-radix
1802 @cindex radix for file offsets
1803 @cindex file offset radix
1804 Select the base in which file offsets are printed. @var{radix} can
1805 be one of the following:
1815 none (do not print offsets).
1818 The default is octal.
1820 @item -j @var{bytes}
1821 @itemx --skip-bytes=@var{bytes}
1823 @opindex --skip-bytes
1824 Skip @var{bytes} input bytes before formatting and writing. If
1825 @var{bytes} begins with @samp{0x} or @samp{0X}, it is interpreted in
1826 hexadecimal; otherwise, if it begins with @samp{0}, in octal; otherwise,
1828 @multiplierSuffixes{bytes}
1830 @item -N @var{bytes}
1831 @itemx --read-bytes=@var{bytes}
1833 @opindex --read-bytes
1834 Output at most @var{bytes} bytes of the input. Prefixes and suffixes on
1835 @code{bytes} are interpreted as for the @option{-j} option.
1837 @item -S @var{bytes}
1838 @itemx --strings[=@var{bytes}]
1841 @cindex string constants, outputting
1842 Instead of the normal output, output only @dfn{string constants}: at
1843 least @var{bytes} consecutive @acronym{ASCII} graphic characters,
1844 followed by a zero byte (@acronym{ASCII} @sc{nul}).
1845 Prefixes and suffixes on @code{bytes} are interpreted as for the
1848 If @var{n} is omitted with @option{--strings}, the default is 3.
1851 @itemx --format=@var{type}
1854 Select the format in which to output the file data. @var{type} is a
1855 string of one or more of the below type indicator characters. If you
1856 include more than one type indicator character in a single @var{type}
1857 string, or use this option more than once, @command{od} writes one copy
1858 of each output line using each of the data types that you specified,
1859 in the order that you specified.
1861 Adding a trailing ``z'' to any type specification appends a display
1862 of the @acronym{ASCII} character representation of the printable characters
1863 to the output line generated by the type specification.
1867 named character, ignoring high-order bit
1869 @acronym{ASCII} character or backslash escape,
1882 The type @code{a} outputs things like @samp{sp} for space, @samp{nl} for
1883 newline, and @samp{nul} for a zero byte. Only the least significant
1884 seven bits of each byte is used; the high-order bit is ignored.
1885 Type @code{c} outputs
1886 @samp{ }, @samp{\n}, and @code{\0}, respectively.
1889 Except for types @samp{a} and @samp{c}, you can specify the number
1890 of bytes to use in interpreting each number in the given data type
1891 by following the type indicator character with a decimal integer.
1892 Alternately, you can specify the size of one of the C compiler's
1893 built-in data types by following the type indicator character with
1894 one of the following characters. For integers (@samp{d}, @samp{o},
1895 @samp{u}, @samp{x}):
1908 For floating point (@code{f}):
1920 @itemx --output-duplicates
1922 @opindex --output-duplicates
1923 Output consecutive lines that are identical. By default, when two or
1924 more consecutive output lines would be identical, @command{od} outputs only
1925 the first line, and puts just an asterisk on the following line to
1926 indicate the elision.
1929 @itemx --width[=@var{n}]
1932 Dump @code{n} input bytes per output line. This must be a multiple of
1933 the least common multiple of the sizes associated with the specified
1936 If this option is not given at all, the default is 16. If @var{n} is
1937 omitted, the default is 32.
1941 The next several options are shorthands for format specifications.
1942 @sc{gnu} @command{od} accepts any combination of shorthands and format
1943 specification options. These options accumulate.
1949 Output as named characters. Equivalent to @samp{-t a}.
1953 Output as octal bytes. Equivalent to @samp{-t o1}.
1957 Output as @acronym{ASCII} characters or backslash escapes. Equivalent to
1962 Output as unsigned decimal two-byte units. Equivalent to @samp{-t u2}.
1966 Output as floats. Equivalent to @samp{-t fF}.
1970 Output as decimal ints. Equivalent to @samp{-t dI}.
1974 Output as decimal long ints. Equivalent to @samp{-t dL}.
1978 Output as octal two-byte units. Equivalent to @option{-t o2}.
1982 Output as decimal two-byte units. Equivalent to @option{-t d2}.
1986 Output as hexadecimal two-byte units. Equivalent to @samp{-t x2}.
1989 @opindex --traditional
1990 Recognize the non-option label argument that traditional @command{od}
1991 accepted. The following syntax:
1994 od --traditional [@var{file}] [[+]@var{offset}[.][b] [[+]@var{label}[.][b]]]
1998 can be used to specify at most one file and optional arguments
1999 specifying an offset and a pseudo-start address, @var{label}.
2000 The @var{label} argument is interpreted
2001 just like @var{offset}, but it specifies an initial pseudo-address. The
2002 pseudo-addresses are displayed in parentheses following any normal
2009 @node base64 invocation
2010 @section @command{base64}: Transform data into printable data
2013 @cindex base64 encoding
2015 @command{base64} transforms data read from a file, or standard input,
2016 into (or from) base64 encoded form. The base64 encoded form uses
2017 printable @acronym{ASCII} characters to represent binary data.
2021 base64 [@var{option}]@dots{} [@var{file}]
2022 base64 --decode [@var{option}]@dots{} [@var{file}]
2025 The base64 encoding expands data to roughly 133% of the original.
2026 The format conforms to
2027 @uref{ftp://ftp.rfc-editor.org/in-notes/rfc4648.txt, RFC 4648}.
2029 The program accepts the following options. Also see @ref{Common options}.
2034 @itemx --wrap=@var{cols}
2038 @cindex column to wrap data after
2039 During encoding, wrap lines after @var{cols} characters. This must be
2042 The default is to wrap after 76 characters. Use the value 0 to
2043 disable line wrapping altogether.
2049 @cindex Decode base64 data
2050 @cindex Base64 decoding
2051 Change the mode of operation, from the default of encoding data, to
2052 decoding data. Input is expected to be base64 encoded data, and the
2053 output will be the original data.
2056 @itemx --ignore-garbage
2058 @opindex --ignore-garbage
2059 @cindex Ignore garbage in base64 stream
2060 When decoding, newlines are always accepted.
2061 During decoding, ignore unrecognized bytes,
2062 to permit distorted data to be decoded.
2069 @node Formatting file contents
2070 @chapter Formatting file contents
2072 @cindex formatting file contents
2074 These commands reformat the contents of files.
2077 * fmt invocation:: Reformat paragraph text.
2078 * pr invocation:: Paginate or columnate files for printing.
2079 * fold invocation:: Wrap input lines to fit in specified width.
2083 @node fmt invocation
2084 @section @command{fmt}: Reformat paragraph text
2087 @cindex reformatting paragraph text
2088 @cindex paragraphs, reformatting
2089 @cindex text, reformatting
2091 @command{fmt} fills and joins lines to produce output lines of (at most)
2092 a given number of characters (75 by default). Synopsis:
2095 fmt [@var{option}]@dots{} [@var{file}]@dots{}
2098 @command{fmt} reads from the specified @var{file} arguments (or standard
2099 input if none are given), and writes to standard output.
2101 By default, blank lines, spaces between words, and indentation are
2102 preserved in the output; successive input lines with different
2103 indentation are not joined; tabs are expanded on input and introduced on
2106 @cindex line-breaking
2107 @cindex sentences and line-breaking
2108 @cindex Knuth, Donald E.
2109 @cindex Plass, Michael F.
2110 @command{fmt} prefers breaking lines at the end of a sentence, and tries to
2111 avoid line breaks after the first word of a sentence or before the last
2112 word of a sentence. A @dfn{sentence break} is defined as either the end
2113 of a paragraph or a word ending in any of @samp{.?!}, followed by two
2114 spaces or end of line, ignoring any intervening parentheses or quotes.
2115 Like @TeX{}, @command{fmt} reads entire ``paragraphs'' before choosing line
2116 breaks; the algorithm is a variant of that given by Donald E. Knuth
2117 and Michael F. Plass in ``Breaking Paragraphs Into Lines'',
2118 @cite{Software---Practice & Experience} @b{11}, 11 (November 1981),
2121 The program accepts the following options. Also see @ref{Common options}.
2129 Compare each pair of source and destination files, and if the destination has
2130 identical content and any specified owner, group, permissions, and possibly
2131 SELinux context, then do not modify the destination at all.
2134 @itemx --crown-margin
2136 @opindex --crown-margin
2137 @cindex crown margin
2138 @dfn{Crown margin} mode: preserve the indentation of the first two
2139 lines within a paragraph, and align the left margin of each subsequent
2140 line with that of the second line.
2143 @itemx --tagged-paragraph
2145 @opindex --tagged-paragraph
2146 @cindex tagged paragraphs
2147 @dfn{Tagged paragraph} mode: like crown margin mode, except that if
2148 indentation of the first line of a paragraph is the same as the
2149 indentation of the second, the first line is treated as a one-line
2155 @opindex --split-only
2156 Split lines only. Do not join short lines to form longer ones. This
2157 prevents sample lines of code, and other such ``formatted'' text from
2158 being unduly combined.
2161 @itemx --uniform-spacing
2163 @opindex --uniform-spacing
2164 Uniform spacing. Reduce spacing between words to one space, and spacing
2165 between sentences to two spaces.
2168 @itemx -w @var{width}
2169 @itemx --width=@var{width}
2170 @opindex -@var{width}
2173 Fill output lines up to @var{width} characters (default 75). @command{fmt}
2174 initially tries to make lines about 7% shorter than this, to give it
2175 room to balance line lengths.
2177 @item -p @var{prefix}
2178 @itemx --prefix=@var{prefix}
2179 Only lines beginning with @var{prefix} (possibly preceded by whitespace)
2180 are subject to formatting. The prefix and any preceding whitespace are
2181 stripped for the formatting and then re-attached to each formatted output
2182 line. One use is to format certain kinds of program comments, while
2183 leaving the code unchanged.
2191 @section @command{pr}: Paginate or columnate files for printing
2194 @cindex printing, preparing files for
2195 @cindex multicolumn output, generating
2196 @cindex merging files in parallel
2198 @command{pr} writes each @var{file} (@samp{-} means standard input), or
2199 standard input if none are given, to standard output, paginating and
2200 optionally outputting in multicolumn format; optionally merges all
2201 @var{file}s, printing all in parallel, one per column. Synopsis:
2204 pr [@var{option}]@dots{} [@var{file}]@dots{}
2208 By default, a 5-line header is printed at each page: two blank lines;
2209 a line with the date, the file name, and the page count; and two more
2210 blank lines. A footer of five blank lines is also printed.
2211 The default @var{page_length} is 66
2212 lines. The default number of text lines is therefore 56.
2213 The text line of the header takes the form
2214 @samp{@var{date} @var{string} @var{page}}, with spaces inserted around
2215 @var{string} so that the line takes up the full @var{page_width}. Here,
2216 @var{date} is the date (see the @option{-D} or @option{--date-format}
2217 option for details), @var{string} is the centered header string, and
2218 @var{page} identifies the page number. The @env{LC_MESSAGES} locale
2219 category affects the spelling of @var{page}; in the default C locale, it
2220 is @samp{Page @var{number}} where @var{number} is the decimal page
2223 Form feeds in the input cause page breaks in the output. Multiple form
2224 feeds produce empty pages.
2226 Columns are of equal width, separated by an optional string (default
2227 is @samp{space}). For multicolumn output, lines will always be truncated to
2228 @var{page_width} (default 72), unless you use the @option{-J} option.
2230 column output no line truncation occurs by default. Use @option{-W} option to
2231 truncate lines in that case.
2233 The following changes were made in version 1.22i and apply to later
2234 versions of @command{pr}:
2235 @c FIXME: this whole section here sounds very awkward to me. I
2236 @c made a few small changes, but really it all needs to be redone. - Brian
2237 @c OK, I fixed another sentence or two, but some of it I just don't understand.
2242 Some small @var{letter options} (@option{-s}, @option{-w}) have been
2243 redefined for better @acronym{POSIX} compliance. The output of some further
2244 cases has been adapted to other Unix systems. These changes are not
2245 compatible with earlier versions of the program.
2248 Some @var{new capital letter} options (@option{-J}, @option{-S}, @option{-W})
2249 have been introduced to turn off unexpected interferences of small letter
2250 options. The @option{-N} option and the second argument @var{last_page}
2251 of @samp{+FIRST_PAGE} offer more flexibility. The detailed handling of
2252 form feeds set in the input files requires the @option{-T} option.
2255 Capital letter options override small letter ones.
2258 Some of the option-arguments (compare @option{-s}, @option{-e},
2259 @option{-i}, @option{-n}) cannot be specified as separate arguments from the
2260 preceding option letter (already stated in the @acronym{POSIX} specification).
2263 The program accepts the following options. Also see @ref{Common options}.
2267 @item +@var{first_page}[:@var{last_page}]
2268 @itemx --pages=@var{first_page}[:@var{last_page}]
2269 @c The two following @opindex lines evoke warnings because they contain `:'
2270 @c The `info' spec does not permit that. If we use those lines, we end
2271 @c up with truncated index entries that don't work.
2272 @c @opindex +@var{first_page}[:@var{last_page}]
2273 @c @opindex --pages=@var{first_page}[:@var{last_page}]
2274 @opindex +@var{page_range}
2275 @opindex --pages=@var{page_range}
2276 Begin printing with page @var{first_page} and stop with @var{last_page}.
2277 Missing @samp{:@var{last_page}} implies end of file. While estimating
2278 the number of skipped pages each form feed in the input file results
2279 in a new page. Page counting with and without @samp{+@var{first_page}}
2280 is identical. By default, counting starts with the first page of input
2281 file (not first page printed). Line numbering may be altered by @option{-N}
2285 @itemx --columns=@var{column}
2286 @opindex -@var{column}
2288 @cindex down columns
2289 With each single @var{file}, produce @var{column} columns of output
2290 (default is 1) and print columns down, unless @option{-a} is used. The
2291 column width is automatically decreased as @var{column} increases; unless
2292 you use the @option{-W/-w} option to increase @var{page_width} as well.
2293 This option might well cause some lines to be truncated. The number of
2294 lines in the columns on each page are balanced. The options @option{-e}
2295 and @option{-i} are on for multiple text-column output. Together with
2296 @option{-J} option column alignment and line truncation is turned off.
2297 Lines of full length are joined in a free field format and @option{-S}
2298 option may set field separators. @option{-@var{column}} may not be used
2299 with @option{-m} option.
2305 @cindex across columns
2306 With each single @var{file}, print columns across rather than down. The
2307 @option{-@var{column}} option must be given with @var{column} greater than one.
2308 If a line is too long to fit in a column, it is truncated.
2311 @itemx --show-control-chars
2313 @opindex --show-control-chars
2314 Print control characters using hat notation (e.g., @samp{^G}); print
2315 other nonprinting characters in octal backslash notation. By default,
2316 nonprinting characters are not changed.
2319 @itemx --double-space
2321 @opindex --double-space
2322 @cindex double spacing
2323 Double space the output.
2325 @item -D @var{format}
2326 @itemx --date-format=@var{format}
2327 @cindex time formats
2328 @cindex formatting times
2329 Format header dates using @var{format}, using the same conventions as
2330 for the command @samp{date +@var{format}}; @xref{date invocation}.
2331 Except for directives, which start with
2332 @samp{%}, characters in @var{format} are printed unchanged. You can use
2333 this option to specify an arbitrary string in place of the header date,
2334 e.g., @option{--date-format="Monday morning"}.
2336 @vindex POSIXLY_CORRECT
2338 The default date format is @samp{%Y-%m-%d %H:%M} (for example,
2339 @samp{2001-12-04 23:59});
2340 but if the @env{POSIXLY_CORRECT} environment variable is set
2341 and the @env{LC_TIME} locale category specifies the @acronym{POSIX}
2342 locale, the default is @samp{%b %e %H:%M %Y} (for example,
2343 @samp{Dec@ @ 4 23:59 2001}.
2346 Time stamps are listed according to the time zone rules specified by
2347 the @env{TZ} environment variable, or by the system default rules if
2348 @env{TZ} is not set. @xref{TZ Variable,, Specifying the Time Zone
2349 with @env{TZ}, libc, The GNU C Library Reference Manual}.
2351 @item -e[@var{in-tabchar}[@var{in-tabwidth}]]
2352 @itemx --expand-tabs[=@var{in-tabchar}[@var{in-tabwidth}]]
2354 @opindex --expand-tabs
2356 Expand @var{tab}s to spaces on input. Optional argument @var{in-tabchar} is
2357 the input tab character (default is the TAB character). Second optional
2358 argument @var{in-tabwidth} is the input tab character's width (default
2366 @opindex --form-feed
2367 Use a form feed instead of newlines to separate output pages. This does
2368 not alter the default page length of 66 lines.
2370 @item -h @var{header}
2371 @itemx --header=@var{header}
2374 Replace the file name in the header with the centered string @var{header}.
2375 When using the shell, @var{header} should be quoted and should be
2376 separated from @option{-h} by a space.
2378 @item -i[@var{out-tabchar}[@var{out-tabwidth}]]
2379 @itemx --output-tabs[=@var{out-tabchar}[@var{out-tabwidth}]]
2381 @opindex --output-tabs
2383 Replace spaces with @var{tab}s on output. Optional argument @var{out-tabchar}
2384 is the output tab character (default is the TAB character). Second optional
2385 argument @var{out-tabwidth} is the output tab character's width (default
2391 @opindex --join-lines
2392 Merge lines of full length. Used together with the column options
2393 @option{-@var{column}}, @option{-a -@var{column}} or @option{-m}. Turns off
2394 @option{-W/-w} line truncation;
2395 no column alignment used; may be used with
2396 @option{--sep-string[=@var{string}]}. @option{-J} has been introduced
2397 (together with @option{-W} and @option{--sep-string})
2398 to disentangle the old (@acronym{POSIX}-compliant) options @option{-w} and
2399 @option{-s} along with the three column options.
2402 @item -l @var{page_length}
2403 @itemx --length=@var{page_length}
2406 Set the page length to @var{page_length} (default 66) lines, including
2407 the lines of the header [and the footer]. If @var{page_length} is less
2408 than or equal to 10, the header and footer are omitted, as if the
2409 @option{-t} option had been given.
2415 Merge and print all @var{file}s in parallel, one in each column. If a
2416 line is too long to fit in a column, it is truncated, unless the @option{-J}
2417 option is used. @option{--sep-string[=@var{string}]} may be used.
2419 some @var{file}s (form feeds set) produce empty columns, still marked
2420 by @var{string}. The result is a continuous line numbering and column
2421 marking throughout the whole merged file. Completely empty merged pages
2422 show no separators or line numbers. The default header becomes
2423 @samp{@var{date} @var{page}} with spaces inserted in the middle; this
2424 may be used with the @option{-h} or @option{--header} option to fill up
2425 the middle blank part.
2427 @item -n[@var{number-separator}[@var{digits}]]
2428 @itemx --number-lines[=@var{number-separator}[@var{digits}]]
2430 @opindex --number-lines
2431 Provide @var{digits} digit line numbering (default for @var{digits} is
2432 5). With multicolumn output the number occupies the first @var{digits}
2433 column positions of each text column or only each line of @option{-m}
2434 output. With single column output the number precedes each line just as
2435 @option{-m} does. Default counting of the line numbers starts with the
2436 first line of the input file (not the first line printed, compare the
2437 @option{--page} option and @option{-N} option).
2438 Optional argument @var{number-separator} is the character appended to
2439 the line number to separate it from the text followed. The default
2440 separator is the TAB character. In a strict sense a TAB is always
2441 printed with single column output only. The TAB width varies
2442 with the TAB position, e.g., with the left @var{margin} specified
2443 by @option{-o} option. With multicolumn output priority is given to
2444 @samp{equal width of output columns} (a @acronym{POSIX} specification).
2445 The TAB width is fixed to the value of the first column and does
2446 not change with different values of left @var{margin}. That means a
2447 fixed number of spaces is always printed in the place of the
2448 @var{number-separator} TAB. The tabification depends upon the output
2451 @item -N @var{line_number}
2452 @itemx --first-line-number=@var{line_number}
2454 @opindex --first-line-number
2455 Start line counting with the number @var{line_number} at first line of
2456 first page printed (in most cases not the first line of the input file).
2458 @item -o @var{margin}
2459 @itemx --indent=@var{margin}
2462 @cindex indenting lines
2464 Indent each line with a margin @var{margin} spaces wide (default is zero).
2465 The total page width is the size of the margin plus the @var{page_width}
2466 set with the @option{-W/-w} option. A limited overflow may occur with
2467 numbered single column output (compare @option{-n} option).
2470 @itemx --no-file-warnings
2472 @opindex --no-file-warnings
2473 Do not print a warning message when an argument @var{file} cannot be
2474 opened. (The exit status will still be nonzero, however.)
2476 @item -s[@var{char}]
2477 @itemx --separator[=@var{char}]
2479 @opindex --separator
2480 Separate columns by a single character @var{char}. The default for
2481 @var{char} is the TAB character without @option{-w} and @samp{no
2482 character} with @option{-w}. Without @option{-s} the default separator
2483 @samp{space} is set. @option{-s[char]} turns off line truncation of all
2484 three column options (@option{-COLUMN}|@option{-a -COLUMN}|@option{-m}) unless
2485 @option{-w} is set. This is a @acronym{POSIX}-compliant formulation.
2488 @item -S@var{string}
2489 @itemx --sep-string[=@var{string}]
2491 @opindex --sep-string
2492 Use @var{string} to separate output columns. The @option{-S} option doesn't
2493 affect the @option{-W/-w} option, unlike the @option{-s} option which does. It
2494 does not affect line truncation or column alignment.
2495 Without @option{-S}, and with @option{-J}, @command{pr} uses the default output
2497 Without @option{-S} or @option{-J}, @command{pr} uses a @samp{space}
2498 (same as @option{-S"@w{ }"}). @option{--sep-string} with no
2499 @samp{=@var{string}} is equivalent to @option{--sep-string=""}.
2502 @itemx --omit-header
2504 @opindex --omit-header
2505 Do not print the usual header [and footer] on each page, and do not fill
2506 out the bottom of pages (with blank lines or a form feed). No page
2507 structure is produced, but form feeds set in the input files are retained.
2508 The predefined pagination is not changed. @option{-t} or @option{-T} may be
2509 useful together with other options; e.g.: @option{-t -e4}, expand TAB characters
2510 in the input file to 4 spaces but don't make any other changes. Use of
2511 @option{-t} overrides @option{-h}.
2514 @itemx --omit-pagination
2516 @opindex --omit-pagination
2517 Do not print header [and footer]. In addition eliminate all form feeds
2518 set in the input files.
2521 @itemx --show-nonprinting
2523 @opindex --show-nonprinting
2524 Print nonprinting characters in octal backslash notation.
2526 @item -w @var{page_width}
2527 @itemx --width=@var{page_width}
2530 Set page width to @var{page_width} characters for multiple text-column
2531 output only (default for @var{page_width} is 72). @option{-s[CHAR]} turns
2532 off the default page width and any line truncation and column alignment.
2533 Lines of full length are merged, regardless of the column options
2534 set. No @var{page_width} setting is possible with single column output.
2535 A @acronym{POSIX}-compliant formulation.
2537 @item -W @var{page_width}
2538 @itemx --page_width=@var{page_width}
2540 @opindex --page_width
2541 Set the page width to @var{page_width} characters. That's valid with and
2542 without a column option. Text lines are truncated, unless @option{-J}
2543 is used. Together with one of the three column options
2544 (@option{-@var{column}}, @option{-a -@var{column}} or @option{-m}) column
2545 alignment is always used. The separator options @option{-S} or @option{-s}
2546 don't affect the @option{-W} option. Default is 72 characters. Without
2547 @option{-W @var{page_width}} and without any of the column options NO line
2548 truncation is used (defined to keep downward compatibility and to meet
2549 most frequent tasks). That's equivalent to @option{-W 72 -J}. The header
2550 line is never truncated.
2557 @node fold invocation
2558 @section @command{fold}: Wrap input lines to fit in specified width
2561 @cindex wrapping long input lines
2562 @cindex folding long input lines
2564 @command{fold} writes each @var{file} (@option{-} means standard input), or
2565 standard input if none are given, to standard output, breaking long
2569 fold [@var{option}]@dots{} [@var{file}]@dots{}
2572 By default, @command{fold} breaks lines wider than 80 columns. The output
2573 is split into as many lines as necessary.
2575 @cindex screen columns
2576 @command{fold} counts screen columns by default; thus, a tab may count more
2577 than one column, backspace decreases the column count, and carriage
2578 return sets the column to zero.
2580 The program accepts the following options. Also see @ref{Common options}.
2588 Count bytes rather than columns, so that tabs, backspaces, and carriage
2589 returns are each counted as taking up one column, just like other
2596 Break at word boundaries: the line is broken after the last blank before
2597 the maximum line length. If the line contains no such blanks, the line
2598 is broken at the maximum line length as usual.
2600 @item -w @var{width}
2601 @itemx --width=@var{width}
2604 Use a maximum line length of @var{width} columns instead of 80.
2606 For compatibility @command{fold} supports an obsolete option syntax
2607 @option{-@var{width}}. New scripts should use @option{-w @var{width}}
2615 @node Output of parts of files
2616 @chapter Output of parts of files
2618 @cindex output of parts of files
2619 @cindex parts of files, output of
2621 These commands output pieces of the input.
2624 * head invocation:: Output the first part of files.
2625 * tail invocation:: Output the last part of files.
2626 * split invocation:: Split a file into fixed-size pieces.
2627 * csplit invocation:: Split a file into context-determined pieces.
2630 @node head invocation
2631 @section @command{head}: Output the first part of files
2634 @cindex initial part of files, outputting
2635 @cindex first part of files, outputting
2637 @command{head} prints the first part (10 lines by default) of each
2638 @var{file}; it reads from standard input if no files are given or
2639 when given a @var{file} of @option{-}. Synopsis:
2642 head [@var{option}]@dots{} [@var{file}]@dots{}
2645 If more than one @var{file} is specified, @command{head} prints a
2646 one-line header consisting of:
2649 ==> @var{file name} <==
2653 before the output for each @var{file}.
2655 The program accepts the following options. Also see @ref{Common options}.
2660 @itemx --bytes=@var{k}
2663 Print the first @var{k} bytes, instead of initial lines.
2664 However, if @var{k} starts with a @samp{-},
2665 print all but the last @var{k} bytes of each file.
2666 @multiplierSuffixes{k}
2669 @itemx --lines=@var{k}
2672 Output the first @var{k} lines.
2673 However, if @var{k} starts with a @samp{-},
2674 print all but the last @var{k} lines of each file.
2675 Size multiplier suffixes are the same as with the @option{-c} option.
2683 Never print file name headers.
2689 Always print file name headers.
2693 For compatibility @command{head} also supports an obsolete option syntax
2694 @option{-@var{count}@var{options}}, which is recognized only if it is
2695 specified first. @var{count} is a decimal number optionally followed
2696 by a size letter (@samp{b}, @samp{k}, @samp{m}) as in @option{-c}, or
2697 @samp{l} to mean count by lines, or other option letters (@samp{cqv}).
2698 Scripts intended for standard hosts should use @option{-c @var{count}}
2699 or @option{-n @var{count}} instead. If your script must also run on
2700 hosts that support only the obsolete syntax, it is usually simpler to
2701 avoid @command{head}, e.g., by using @samp{sed 5q} instead of
2707 @node tail invocation
2708 @section @command{tail}: Output the last part of files
2711 @cindex last part of files, outputting
2713 @command{tail} prints the last part (10 lines by default) of each
2714 @var{file}; it reads from standard input if no files are given or
2715 when given a @var{file} of @samp{-}. Synopsis:
2718 tail [@var{option}]@dots{} [@var{file}]@dots{}
2721 If more than one @var{file} is specified, @command{tail} prints a
2722 one-line header consisting of:
2725 ==> @var{file name} <==
2729 before the output for each @var{file}.
2731 @cindex BSD @command{tail}
2732 @sc{gnu} @command{tail} can output any amount of data (some other versions of
2733 @command{tail} cannot). It also has no @option{-r} option (print in
2734 reverse), since reversing a file is really a different job from printing
2735 the end of a file; BSD @command{tail} (which is the one with @option{-r}) can
2736 only reverse files that are at most as large as its buffer, which is
2737 typically 32 KiB@. A more reliable and versatile way to reverse files is
2738 the @sc{gnu} @command{tac} command.
2740 The program accepts the following options. Also see @ref{Common options}.
2745 @itemx --bytes=@var{k}
2748 Output the last @var{k} bytes, instead of final lines.
2749 However, if @var{k} starts with a @samp{+}, start printing with the
2750 @var{k}th byte from the start of each file, instead of from the end.
2751 @multiplierSuffixes{k}
2754 @itemx --follow[=@var{how}]
2757 @cindex growing files
2758 @vindex name @r{follow option}
2759 @vindex descriptor @r{follow option}
2760 Loop forever trying to read more characters at the end of the file,
2761 presumably because the file is growing.
2762 If more than one file is given, @command{tail} prints a header whenever it
2763 gets output from a different file, to indicate which file that output is
2766 There are two ways to specify how you'd like to track files with this option,
2767 but that difference is noticeable only when a followed file is removed or
2769 If you'd like to continue to track the end of a growing file even after
2770 it has been unlinked, use @option{--follow=descriptor}. This is the default
2771 behavior, but it is not useful if you're tracking a log file that may be
2772 rotated (removed or renamed, then reopened). In that case, use
2773 @option{--follow=name} to track the named file by reopening it periodically
2774 to see if it has been removed and recreated by some other program.
2776 No matter which method you use, if the tracked file is determined to have
2777 shrunk, @command{tail} prints a message saying the file has been truncated
2778 and resumes tracking the end of the file from the newly-determined endpoint.
2780 When a file is removed, @command{tail}'s behavior depends on whether it is
2781 following the name or the descriptor. When following by name, tail can
2782 detect that a file has been removed and gives a message to that effect,
2783 and if @option{--retry} has been specified it will continue checking
2784 periodically to see if the file reappears.
2785 When following a descriptor, tail does not detect that the file has
2786 been unlinked or renamed and issues no message; even though the file
2787 may no longer be accessible via its original name, it may still be
2790 The option values @samp{descriptor} and @samp{name} may be specified only
2791 with the long form of the option, not with @option{-f}.
2793 @vindex POSIXLY_CORRECT
2794 If @env{POSIXLY_CORRECT} is set, the @option{-f} option is ignored if
2795 no @var{file} operand is specified and standard input is a FIFO or a pipe.
2799 This option is the same as @option{--follow=name --retry}. That is, tail
2800 will attempt to reopen a file when it is removed. Should this fail, tail
2801 will keep trying until it becomes accessible again.
2805 This option is useful mainly when following by name (i.e., with
2806 @option{--follow=name}).
2807 Without this option, when tail encounters a file that doesn't
2808 exist or is otherwise inaccessible, it reports that fact and
2809 never checks it again.
2811 @itemx --sleep-interval=@var{number}
2812 @opindex --sleep-interval
2813 Change the number of seconds to wait between iterations (the default is 1.0).
2814 During one iteration, every specified file is checked to see if it has
2816 Historical implementations of @command{tail} have required that
2817 @var{number} be an integer. However, GNU @command{tail} accepts
2818 an arbitrary floating point number (using a period before any
2821 @itemx --pid=@var{pid}
2823 When following by name or by descriptor, you may specify the process ID,
2824 @var{pid}, of the sole writer of all @var{file} arguments. Then, shortly
2825 after that process terminates, tail will also terminate. This will
2826 work properly only if the writer and the tailing process are running on
2827 the same machine. For example, to save the output of a build in a file
2828 and to watch the file grow, if you invoke @command{make} and @command{tail}
2829 like this then the tail process will stop when your build completes.
2830 Without this option, you would have had to kill the @code{tail -f}
2834 $ make >& makerr & tail --pid=$! -f makerr
2837 If you specify a @var{pid} that is not in use or that does not correspond
2838 to the process that is writing to the tailed files, then @command{tail}
2839 may terminate long before any @var{file}s stop growing or it may not
2840 terminate until long after the real writer has terminated.
2841 Note that @option{--pid} cannot be supported on some systems; @command{tail}
2842 will print a warning if this is the case.
2844 @itemx --max-unchanged-stats=@var{n}
2845 @opindex --max-unchanged-stats
2846 When tailing a file by name, if there have been @var{n} (default
2847 n=@value{DEFAULT_MAX_N_UNCHANGED_STATS_BETWEEN_OPENS}) consecutive
2848 iterations for which the file has not changed, then
2849 @code{open}/@code{fstat} the file to determine if that file name is
2850 still associated with the same device/inode-number pair as before.
2851 When following a log file that is rotated, this is approximately the
2852 number of seconds between when tail prints the last pre-rotation lines
2853 and when it prints the lines that have accumulated in the new log file.
2854 This option is meaningful only when following by name.
2857 @itemx --lines=@var{k}
2860 Output the last @var{k} lines.
2861 However, if @var{k} starts with a @samp{+}, start printing with the
2862 @var{k}th line from the start of each file, instead of from the end.
2863 Size multiplier suffixes are the same as with the @option{-c} option.
2871 Never print file name headers.
2877 Always print file name headers.
2881 For compatibility @command{tail} also supports an obsolete usage
2882 @samp{tail -[@var{count}][bcl][f] [@var{file}]}, which is recognized
2883 only if it does not conflict with the usage described
2884 above. This obsolete form uses exactly one option and at most one
2885 file. In the option, @var{count} is an optional decimal number optionally
2886 followed by a size letter (@samp{b}, @samp{c}, @samp{l}) to mean count
2887 by 512-byte blocks, bytes, or lines, optionally followed by @samp{f}
2888 which has the same meaning as @option{-f}.
2890 @vindex _POSIX2_VERSION
2891 On older systems, the leading @samp{-} can be replaced by @samp{+} in
2892 the obsolete option syntax with the same meaning as in counts, and
2893 obsolete usage overrides normal usage when the two conflict.
2894 This obsolete behavior can be enabled or disabled with the
2895 @env{_POSIX2_VERSION} environment variable (@pxref{Standards
2898 Scripts intended for use on standard hosts should avoid obsolete
2899 syntax and should use @option{-c @var{count}[b]}, @option{-n
2900 @var{count}}, and/or @option{-f} instead. If your script must also
2901 run on hosts that support only the obsolete syntax, you can often
2902 rewrite it to avoid problematic usages, e.g., by using @samp{sed -n
2903 '$p'} rather than @samp{tail -1}. If that's not possible, the script
2904 can use a test like @samp{if tail -c +1 </dev/null >/dev/null 2>&1;
2905 then @dots{}} to decide which syntax to use.
2907 Even if your script assumes the standard behavior, you should still
2908 beware usages whose behaviors differ depending on the @acronym{POSIX}
2909 version. For example, avoid @samp{tail - main.c}, since it might be
2910 interpreted as either @samp{tail main.c} or as @samp{tail -- -
2911 main.c}; avoid @samp{tail -c 4}, since it might mean either @samp{tail
2912 -c4} or @samp{tail -c 10 4}; and avoid @samp{tail +4}, since it might
2913 mean either @samp{tail ./+4} or @samp{tail -n +4}.
2918 @node split invocation
2919 @section @command{split}: Split a file into fixed-size pieces
2922 @cindex splitting a file into pieces
2923 @cindex pieces, splitting a file into
2925 @command{split} creates output files containing consecutive sections of
2926 @var{input} (standard input if none is given or @var{input} is
2927 @samp{-}). Synopsis:
2930 split [@var{option}] [@var{input} [@var{prefix}]]
2933 By default, @command{split} puts 1000 lines of @var{input} (or whatever is
2934 left over for the last section), into each output file.
2936 @cindex output file name prefix
2937 The output files' names consist of @var{prefix} (@samp{x} by default)
2938 followed by a group of characters (@samp{aa}, @samp{ab}, @dots{} by
2939 default), such that concatenating the output files in traditional
2940 sorted order by file name produces
2941 the original input file. If the output file names are exhausted,
2942 @command{split} reports an error without deleting the output files
2945 The program accepts the following options. Also see @ref{Common options}.
2949 @item -l @var{lines}
2950 @itemx --lines=@var{lines}
2953 Put @var{lines} lines of @var{input} into each output file.
2955 For compatibility @command{split} also supports an obsolete
2956 option syntax @option{-@var{lines}}. New scripts should use @option{-l
2957 @var{lines}} instead.
2960 @itemx --bytes=@var{size}
2963 Put @var{size} bytes of @var{input} into each output file.
2964 @multiplierSuffixes{size}
2967 @itemx --line-bytes=@var{size}
2969 @opindex --line-bytes
2970 Put into each output file as many complete lines of @var{input} as
2971 possible without exceeding @var{size} bytes. Individual lines longer than
2972 @var{size} bytes are broken into multiple files.
2973 @var{size} has the same format as for the @option{--bytes} option.
2975 @item -a @var{length}
2976 @itemx --suffix-length=@var{length}
2978 @opindex --suffix-length
2979 Use suffixes of length @var{length}. The default @var{length} is 2.
2982 @itemx --numeric-suffixes
2984 @opindex --numeric-suffixes
2985 Use digits in suffixes rather than lower-case letters.
2989 Write a diagnostic just before each output file is opened.
2996 @node csplit invocation
2997 @section @command{csplit}: Split a file into context-determined pieces
3000 @cindex context splitting
3001 @cindex splitting a file into pieces by context
3003 @command{csplit} creates zero or more output files containing sections of
3004 @var{input} (standard input if @var{input} is @samp{-}). Synopsis:
3007 csplit [@var{option}]@dots{} @var{input} @var{pattern}@dots{}
3010 The contents of the output files are determined by the @var{pattern}
3011 arguments, as detailed below. An error occurs if a @var{pattern}
3012 argument refers to a nonexistent line of the input file (e.g., if no
3013 remaining line matches a given regular expression). After every
3014 @var{pattern} has been matched, any remaining input is copied into one
3017 By default, @command{csplit} prints the number of bytes written to each
3018 output file after it has been created.
3020 The types of pattern arguments are:
3025 Create an output file containing the input up to but not including line
3026 @var{n} (a positive integer). If followed by a repeat count, also
3027 create an output file containing the next @var{n} lines of the input
3028 file once for each repeat.
3030 @item /@var{regexp}/[@var{offset}]
3031 Create an output file containing the current line up to (but not
3032 including) the next line of the input file that contains a match for
3033 @var{regexp}. The optional @var{offset} is an integer.
3034 If it is given, the input up to (but not including) the
3035 matching line plus or minus @var{offset} is put into the output file,
3036 and the line after that begins the next section of input.
3038 @item %@var{regexp}%[@var{offset}]
3039 Like the previous type, except that it does not create an output
3040 file, so that section of the input file is effectively ignored.
3042 @item @{@var{repeat-count}@}
3043 Repeat the previous pattern @var{repeat-count} additional
3044 times. The @var{repeat-count} can either be a positive integer or an
3045 asterisk, meaning repeat as many times as necessary until the input is
3050 The output files' names consist of a prefix (@samp{xx} by default)
3051 followed by a suffix. By default, the suffix is an ascending sequence
3052 of two-digit decimal numbers from @samp{00} to @samp{99}. In any case,
3053 concatenating the output files in sorted order by file name produces the
3054 original input file.
3056 By default, if @command{csplit} encounters an error or receives a hangup,
3057 interrupt, quit, or terminate signal, it removes any output files
3058 that it has created so far before it exits.
3060 The program accepts the following options. Also see @ref{Common options}.
3064 @item -f @var{prefix}
3065 @itemx --prefix=@var{prefix}
3068 @cindex output file name prefix
3069 Use @var{prefix} as the output file name prefix.
3071 @item -b @var{suffix}
3072 @itemx --suffix=@var{suffix}
3075 @cindex output file name suffix
3076 Use @var{suffix} as the output file name suffix. When this option is
3077 specified, the suffix string must include exactly one
3078 @code{printf(3)}-style conversion specification, possibly including
3079 format specification flags, a field width, a precision specifications,
3080 or all of these kinds of modifiers. The format letter must convert a
3081 binary integer argument to readable form; thus, only @samp{d}, @samp{i},
3082 @samp{u}, @samp{o}, @samp{x}, and @samp{X} conversions are allowed. The
3083 entire @var{suffix} is given (with the current output file number) to
3084 @code{sprintf(3)} to form the file name suffixes for each of the
3085 individual output files in turn. If this option is used, the
3086 @option{--digits} option is ignored.
3088 @item -n @var{digits}
3089 @itemx --digits=@var{digits}
3092 Use output file names containing numbers that are @var{digits} digits
3093 long instead of the default 2.
3098 @opindex --keep-files
3099 Do not remove output files when errors are encountered.
3102 @itemx --elide-empty-files
3104 @opindex --elide-empty-files
3105 Suppress the generation of zero-length output files. (In cases where
3106 the section delimiters of the input file are supposed to mark the first
3107 lines of each of the sections, the first output file will generally be a
3108 zero-length file unless you use this option.) The output file sequence
3109 numbers always run consecutively starting from 0, even when this option
3120 Do not print counts of output file sizes.
3126 Here is an example of its usage.
3127 First, create an empty directory for the exercise,
3134 Now, split the sequence of 1..14 on lines that end with 0 or 5:
3137 $ seq 14 | csplit - '/[05]$/' '@{*@}'
3143 Each number printed above is the size of an output
3144 file that csplit has just created.
3145 List the names of those output files:
3152 Use @command{head} to show their contents:
3177 @node Summarizing files
3178 @chapter Summarizing files
3180 @cindex summarizing files
3182 These commands generate just a few numbers representing entire
3186 * wc invocation:: Print newline, word, and byte counts.
3187 * sum invocation:: Print checksum and block counts.
3188 * cksum invocation:: Print CRC checksum and byte counts.
3189 * md5sum invocation:: Print or check MD5 digests.
3190 * sha1sum invocation:: Print or check SHA-1 digests.
3191 * sha2 utilities:: Print or check SHA-2 digests.
3196 @section @command{wc}: Print newline, word, and byte counts
3200 @cindex character count
3204 @command{wc} counts the number of bytes, characters, whitespace-separated
3205 words, and newlines in each given @var{file}, or standard input if none
3206 are given or for a @var{file} of @samp{-}. Synopsis:
3209 wc [@var{option}]@dots{} [@var{file}]@dots{}
3212 @cindex total counts
3213 @command{wc} prints one line of counts for each file, and if the file was
3214 given as an argument, it prints the file name following the counts. If
3215 more than one @var{file} is given, @command{wc} prints a final line
3216 containing the cumulative counts, with the file name @file{total}. The
3217 counts are printed in this order: newlines, words, characters, bytes,
3218 maximum line length.
3219 Each count is printed right-justified in a field with at least one
3220 space between fields so that the numbers and file names normally line
3221 up nicely in columns. The width of the count fields varies depending
3222 on the inputs, so you should not depend on a particular field width.
3223 However, as a @acronym{GNU} extension, if only one count is printed,
3224 it is guaranteed to be printed without leading spaces.
3226 By default, @command{wc} prints three counts: the newline, words, and byte
3227 counts. Options can specify that only certain counts be printed.
3228 Options do not undo others previously given, so
3235 prints both the byte counts and the word counts.
3237 With the @option{--max-line-length} option, @command{wc} prints the length
3238 of the longest line per file, and if there is more than one file it
3239 prints the maximum (not the sum) of those lengths. The line lengths here
3240 are measured in screen columns, according to the current locale and
3241 assuming tab positions in every 8th column.
3243 The program accepts the following options. Also see @ref{Common options}.
3251 Print only the byte counts.
3257 Print only the character counts.
3263 Print only the word counts.
3269 Print only the newline counts.
3272 @itemx --max-line-length
3274 @opindex --max-line-length
3275 Print only the maximum line lengths.
3277 @macro filesZeroFromOption{cmd,withTotalOption,subListOutput}
3278 @itemx --files0-from=@var{file}
3279 @opindex --files0-from=@var{file}
3280 @c This is commented out to avoid a texi2dvi failure.
3281 @c texi2dvi (GNU Texinfo 4.11) 1.104
3282 @c @cindex including files from @command{\cmd\}
3283 Disallow processing files named on the command line, and instead process
3284 those named in file @var{file}; each name being terminated by a zero byte
3285 (@acronym{ASCII} @sc{nul}).
3286 This is useful \withTotalOption\
3287 when the list of file names is so long that it may exceed a command line
3289 In such cases, running @command{\cmd\} via @command{xargs} is undesirable
3290 because it splits the list into pieces and makes @command{\cmd\} print
3291 \subListOutput\ for each sublist rather than for the entire list.
3292 One way to produce a list of @acronym{ASCII} @sc{nul} terminated file names is with @sc{gnu}
3293 @command{find}, using its @option{-print0} predicate.
3294 If @var{file} is @samp{-} then the @acronym{ASCII} @sc{nul} terminated file names
3295 are read from standard input.
3297 @filesZeroFromOption{wc,,a total}
3299 For example, to find the length of the longest line in any @file{.c} or
3300 @file{.h} file in the current hierarchy, do this:
3303 find . -name '*.[ch]' -print0 |
3304 wc -L --files0-from=- | tail -n1
3312 @node sum invocation
3313 @section @command{sum}: Print checksum and block counts
3316 @cindex 16-bit checksum
3317 @cindex checksum, 16-bit
3319 @command{sum} computes a 16-bit checksum for each given @var{file}, or
3320 standard input if none are given or for a @var{file} of @samp{-}. Synopsis:
3323 sum [@var{option}]@dots{} [@var{file}]@dots{}
3326 @command{sum} prints the checksum for each @var{file} followed by the
3327 number of blocks in the file (rounded up). If more than one @var{file}
3328 is given, file names are also printed (by default). (With the
3329 @option{--sysv} option, corresponding file names are printed when there is
3330 at least one file argument.)
3332 By default, @sc{gnu} @command{sum} computes checksums using an algorithm
3333 compatible with BSD @command{sum} and prints file sizes in units of
3336 The program accepts the following options. Also see @ref{Common options}.
3342 @cindex BSD @command{sum}
3343 Use the default (BSD compatible) algorithm. This option is included for
3344 compatibility with the System V @command{sum}. Unless @option{-s} was also
3345 given, it has no effect.
3351 @cindex System V @command{sum}
3352 Compute checksums using an algorithm compatible with System V
3353 @command{sum}'s default, and print file sizes in units of 512-byte blocks.
3357 @command{sum} is provided for compatibility; the @command{cksum} program (see
3358 next section) is preferable in new applications.
3363 @node cksum invocation
3364 @section @command{cksum}: Print CRC checksum and byte counts
3367 @cindex cyclic redundancy check
3368 @cindex CRC checksum
3370 @command{cksum} computes a cyclic redundancy check (CRC) checksum for each
3371 given @var{file}, or standard input if none are given or for a
3372 @var{file} of @samp{-}. Synopsis:
3375 cksum [@var{option}]@dots{} [@var{file}]@dots{}
3378 @command{cksum} prints the CRC checksum for each file along with the number
3379 of bytes in the file, and the file name unless no arguments were given.
3381 @command{cksum} is typically used to ensure that files
3382 transferred by unreliable means (e.g., netnews) have not been corrupted,
3383 by comparing the @command{cksum} output for the received files with the
3384 @command{cksum} output for the original files (typically given in the
3387 The CRC algorithm is specified by the @acronym{POSIX} standard. It is not
3388 compatible with the BSD or System V @command{sum} algorithms (see the
3389 previous section); it is more robust.
3391 The only options are @option{--help} and @option{--version}. @xref{Common
3397 @node md5sum invocation
3398 @section @command{md5sum}: Print or check MD5 digests
3402 @cindex 128-bit checksum
3403 @cindex checksum, 128-bit
3404 @cindex fingerprint, 128-bit
3405 @cindex message-digest, 128-bit
3407 @command{md5sum} computes a 128-bit checksum (or @dfn{fingerprint} or
3408 @dfn{message-digest}) for each specified @var{file}.
3410 Note: The MD5 digest is more reliable than a simple CRC (provided by
3411 the @command{cksum} command) for detecting accidental file corruption,
3412 as the chances of accidentally having two files with identical MD5
3413 are vanishingly small. However, it should not be considered truly
3414 secure against malicious tampering: although finding a file with a
3415 given MD5 fingerprint, or modifying a file so as to retain its MD5 are
3416 considered infeasible at the moment, it is known how to produce
3417 different files with identical MD5 (a ``collision''), something which
3418 can be a security issue in certain contexts. For more secure hashes,
3419 consider using SHA-1 or SHA-2. @xref{sha1sum invocation}, and
3420 @ref{sha2 utilities}.
3422 If a @var{file} is specified as @samp{-} or if no files are given
3423 @command{md5sum} computes the checksum for the standard input.
3424 @command{md5sum} can also determine whether a file and checksum are
3425 consistent. Synopsis:
3428 md5sum [@var{option}]@dots{} [@var{file}]@dots{}
3431 For each @var{file}, @samp{md5sum} outputs the MD5 checksum, a flag
3432 indicating a binary or text input file, and the file name.
3433 If @var{file} contains a backslash or newline, the
3434 line is started with a backslash, and each problematic character in
3435 the file name is escaped with a backslash, making the output
3436 unambiguous even in the presence of arbitrary file names.
3437 If @var{file} is omitted or specified as @samp{-}, standard input is read.
3439 The program accepts the following options. Also see @ref{Common options}.
3447 @cindex binary input files
3448 Treat each input file as binary, by reading it in binary mode and
3449 outputting a @samp{*} flag. This is the inverse of @option{--text}.
3450 On systems like @acronym{GNU} that do not distinguish between binary
3451 and text files, this option merely flags each input file as binary:
3452 the MD5 checksum is unaffected. This option is the default on systems
3453 like MS-DOS that distinguish between binary and text files, except
3454 for reading standard input when standard input is a terminal.
3458 Read file names and checksum information (not data) from each
3459 @var{file} (or from stdin if no @var{file} was specified) and report
3460 whether the checksums match the contents of the named files.
3461 The input to this mode of @command{md5sum} is usually the output of
3462 a prior, checksum-generating run of @samp{md5sum}.
3463 Each valid line of input consists of an MD5 checksum, a binary/text
3464 flag, and then a file name.
3465 Binary files are marked with @samp{*}, text with @samp{ }.
3466 For each such line, @command{md5sum} reads the named file and computes its
3467 MD5 checksum. Then, if the computed message digest does not match the
3468 one on the line with the file name, the file is noted as having
3469 failed the test. Otherwise, the file passes the test.
3470 By default, for each valid line, one line is written to standard
3471 output indicating whether the named file passed the test.
3472 After all checks have been performed, if there were any failures,
3473 a warning is issued to standard error.
3474 Use the @option{--status} option to inhibit that output.
3475 If any listed file cannot be opened or read, if any valid line has
3476 an MD5 checksum inconsistent with the associated file, or if no valid
3477 line is found, @command{md5sum} exits with nonzero status. Otherwise,
3478 it exits successfully.
3482 @cindex verifying MD5 checksums
3483 This option is useful only when verifying checksums.
3484 When verifying checksums, don't generate an 'OK' message per successfully
3485 checked file. Files that fail the verification are reported in the
3486 default one-line-per-file format. If there is any checksum mismatch,
3487 print a warning summarizing the failures to standard error.
3491 @cindex verifying MD5 checksums
3492 This option is useful only when verifying checksums.
3493 When verifying checksums, don't generate the default one-line-per-file
3494 diagnostic and don't output the warning summarizing any failures.
3495 Failures to open or read a file still evoke individual diagnostics to
3497 If all listed files are readable and are consistent with the associated
3498 MD5 checksums, exit successfully. Otherwise exit with a status code
3499 indicating there was a failure.
3505 @cindex text input files
3506 Treat each input file as text, by reading it in text mode and
3507 outputting a @samp{ } flag. This is the inverse of @option{--binary}.
3508 This option is the default on systems like @acronym{GNU} that do not
3509 distinguish between binary and text files. On other systems, it is
3510 the default for reading standard input when standard input is a
3517 @cindex verifying MD5 checksums
3518 When verifying checksums, warn about improperly formatted MD5 checksum lines.
3519 This option is useful only if all but a few lines in the checked input
3527 @node sha1sum invocation
3528 @section @command{sha1sum}: Print or check SHA-1 digests
3532 @cindex 160-bit checksum
3533 @cindex checksum, 160-bit
3534 @cindex fingerprint, 160-bit
3535 @cindex message-digest, 160-bit
3537 @command{sha1sum} computes a 160-bit checksum for each specified
3538 @var{file}. The usage and options of this command are precisely the
3539 same as for @command{md5sum}. @xref{md5sum invocation}.
3541 Note: The SHA-1 digest is more secure than MD5, and no collisions of
3542 it are known (different files having the same fingerprint). However,
3543 it is known that they can be produced with considerable, but not
3544 unreasonable, resources. For this reason, it is generally considered
3545 that SHA-1 should be gradually phased out in favor of the more secure
3546 SHA-2 hash algorithms. @xref{sha2 utilities}.
3549 @node sha2 utilities
3550 @section sha2 utilities: Print or check SHA-2 digests
3557 @cindex 224-bit checksum
3558 @cindex 256-bit checksum
3559 @cindex 384-bit checksum
3560 @cindex 512-bit checksum
3561 @cindex checksum, 224-bit
3562 @cindex checksum, 256-bit
3563 @cindex checksum, 384-bit
3564 @cindex checksum, 512-bit
3565 @cindex fingerprint, 224-bit
3566 @cindex fingerprint, 256-bit
3567 @cindex fingerprint, 384-bit
3568 @cindex fingerprint, 512-bit
3569 @cindex message-digest, 224-bit
3570 @cindex message-digest, 256-bit
3571 @cindex message-digest, 384-bit
3572 @cindex message-digest, 512-bit
3574 The commands @command{sha224sum}, @command{sha256sum},
3575 @command{sha384sum} and @command{sha512sum} compute checksums of
3576 various lengths (respectively 224, 256, 384 and 512 bits),
3577 collectively known as the SHA-2 hashes. The usage and options of
3578 these commands are precisely the same as for @command{md5sum}.
3579 @xref{md5sum invocation}.
3581 Note: The SHA384 and SHA512 digests are considerably slower to
3582 compute, especially on 32-bit computers, than SHA224 or SHA256.
3585 @node Operating on sorted files
3586 @chapter Operating on sorted files
3588 @cindex operating on sorted files
3589 @cindex sorted files, operations on
3591 These commands work with (or produce) sorted files.
3594 * sort invocation:: Sort text files.
3595 * shuf invocation:: Shuffle text files.
3596 * uniq invocation:: Uniquify files.
3597 * comm invocation:: Compare two sorted files line by line.
3598 * ptx invocation:: Produce a permuted index of file contents.
3599 * tsort invocation:: Topological sort.
3603 @node sort invocation
3604 @section @command{sort}: Sort text files
3607 @cindex sorting files
3609 @command{sort} sorts, merges, or compares all the lines from the given
3610 files, or standard input if none are given or for a @var{file} of
3611 @samp{-}. By default, @command{sort} writes the results to standard
3615 sort [@var{option}]@dots{} [@var{file}]@dots{}
3618 @command{sort} has three modes of operation: sort (the default), merge,
3619 and check for sortedness. The following options change the operation
3626 @itemx --check=diagnose-first
3629 @cindex checking for sortedness
3630 Check whether the given file is already sorted: if it is not all
3631 sorted, print a diagnostic containing the first out-of-order line and
3632 exit with a status of 1.
3633 Otherwise, exit successfully.
3634 At most one input file can be given.
3637 @itemx --check=quiet
3638 @itemx --check=silent
3641 @cindex checking for sortedness
3642 Exit successfully if the given file is already sorted, and
3643 exit with status 1 otherwise.
3644 At most one input file can be given.
3645 This is like @option{-c}, except it does not print a diagnostic.
3651 @cindex merging sorted files
3652 Merge the given files by sorting them as a group. Each input file must
3653 always be individually sorted. It always works to sort instead of
3654 merge; merging is provided because it is faster, in the case where it
3659 @cindex sort stability
3660 @cindex sort's last-resort comparison
3661 A pair of lines is compared as follows:
3662 @command{sort} compares each pair of fields, in the
3663 order specified on the command line, according to the associated
3664 ordering options, until a difference is found or no fields are left.
3665 If no key fields are specified, @command{sort} uses a default key of
3666 the entire line. Finally, as a last resort when all keys compare
3667 equal, @command{sort} compares entire lines as if no ordering options
3668 other than @option{--reverse} (@option{-r}) were specified. The
3669 @option{--stable} (@option{-s}) option disables this @dfn{last-resort
3670 comparison} so that lines in which all fields compare equal are left
3671 in their original relative order. The @option{--unique}
3672 (@option{-u}) option also disables the last-resort comparison.
3676 Unless otherwise specified, all comparisons use the character collating
3677 sequence specified by the @env{LC_COLLATE} locale.@footnote{If you
3678 use a non-@acronym{POSIX} locale (e.g., by setting @env{LC_ALL}
3679 to @samp{en_US}), then @command{sort} may produce output that is sorted
3680 differently than you're accustomed to. In that case, set the @env{LC_ALL}
3681 environment variable to @samp{C}. Note that setting only @env{LC_COLLATE}
3682 has two problems. First, it is ineffective if @env{LC_ALL} is also set.
3683 Second, it has undefined behavior if @env{LC_CTYPE} (or @env{LANG}, if
3684 @env{LC_CTYPE} is unset) is set to an incompatible value. For example,
3685 you get undefined behavior if @env{LC_CTYPE} is @code{ja_JP.PCK} but
3686 @env{LC_COLLATE} is @code{en_US.UTF-8}.}
3688 @sc{gnu} @command{sort} (as specified for all @sc{gnu} utilities) has no
3689 limit on input line length or restrictions on bytes allowed within lines.
3690 In addition, if the final byte of an input file is not a newline, @sc{gnu}
3691 @command{sort} silently supplies one. A line's trailing newline is not
3692 part of the line for comparison purposes.
3694 @cindex exit status of @command{sort}
3698 0 if no error occurred
3699 1 if invoked with @option{-c} or @option{-C} and the input is not sorted
3700 2 if an error occurred
3704 If the environment variable @env{TMPDIR} is set, @command{sort} uses its
3705 value as the directory for temporary files instead of @file{/tmp}. The
3706 @option{--temporary-directory} (@option{-T}) option in turn overrides
3707 the environment variable.
3709 The following options affect the ordering of output lines. They may be
3710 specified globally or as part of a specific key field. If no key
3711 fields are specified, global options apply to comparison of entire
3712 lines; otherwise the global options are inherited by key fields that do
3713 not specify any special options of their own. In pre-@acronym{POSIX}
3714 versions of @command{sort}, global options affect only later key fields,
3715 so portable shell scripts should specify global options first.
3720 @itemx --ignore-leading-blanks
3722 @opindex --ignore-leading-blanks
3723 @cindex blanks, ignoring leading
3725 Ignore leading blanks when finding sort keys in each line.
3726 By default a blank is a space or a tab, but the @env{LC_CTYPE} locale
3727 can change this. Note blanks may be ignored by your locale's collating
3728 rules, but without this option they will be significant for character
3729 positions specified in keys with the @option{-k} option.
3732 @itemx --dictionary-order
3734 @opindex --dictionary-order
3735 @cindex dictionary order
3736 @cindex phone directory order
3737 @cindex telephone directory order
3739 Sort in @dfn{phone directory} order: ignore all characters except
3740 letters, digits and blanks when sorting.
3741 By default letters and digits are those of @acronym{ASCII} and a blank
3742 is a space or a tab, but the @env{LC_CTYPE} locale can change this.
3745 @itemx --ignore-case
3747 @opindex --ignore-case
3748 @cindex ignoring case
3749 @cindex case folding
3751 Fold lowercase characters into the equivalent uppercase characters when
3752 comparing so that, for example, @samp{b} and @samp{B} sort as equal.
3753 The @env{LC_CTYPE} locale determines character types.
3754 When used with @option{--unique} those lower case equivalent lines are
3755 thrown away. (There is currently no way to throw away the upper case
3756 equivalent instead. (Any @option{--reverse} given would only affect
3757 the final result, after the throwing away.))
3760 @itemx --general-numeric-sort
3761 @itemx --sort=general-numeric
3763 @opindex --general-numeric-sort
3765 @cindex general numeric sort
3767 Sort numerically, using the standard C function @code{strtod} to convert
3768 a prefix of each line to a double-precision floating point number.
3769 This allows floating point numbers to be specified in scientific notation,
3770 like @code{1.0e-34} and @code{10e100}.
3771 The @env{LC_NUMERIC} locale determines the decimal-point character.
3772 Do not report overflow, underflow, or conversion errors.
3773 Use the following collating sequence:
3777 Lines that do not start with numbers (all considered to be equal).
3779 NaNs (``Not a Number'' values, in IEEE floating point arithmetic)
3780 in a consistent but machine-dependent order.
3784 Finite numbers in ascending numeric order (with @math{-0} and @math{+0} equal).
3789 Use this option only if there is no alternative; it is much slower than
3790 @option{--numeric-sort} (@option{-n}) and it can lose information when
3791 converting to floating point.
3794 @itemx --human-numeric-sort
3795 @itemx --sort=human-numeric
3797 @opindex --human-numeric-sort
3799 @cindex human numeric sort
3801 Sort numerically, as per the @option{--numeric-sort} option below, and in
3802 addition handle IEC or SI suffixes like MiB, MB etc (@ref{Block size}).
3803 Note a mixture of IEC and SI suffixes is not supported and will
3804 be flagged as an error. Also the numbers must be abbreviated uniformly.
3805 I.E. values with different precisions like 6000K and 5M will be sorted
3809 @itemx --ignore-nonprinting
3811 @opindex --ignore-nonprinting
3812 @cindex nonprinting characters, ignoring
3813 @cindex unprintable characters, ignoring
3815 Ignore nonprinting characters.
3816 The @env{LC_CTYPE} locale determines character types.
3817 This option has no effect if the stronger @option{--dictionary-order}
3818 (@option{-d}) option is also given.
3824 @opindex --month-sort
3826 @cindex months, sorting by
3828 An initial string, consisting of any amount of blanks, followed
3829 by a month name abbreviation, is folded to UPPER case and
3830 compared in the order @samp{JAN} < @samp{FEB} < @dots{} < @samp{DEC}.
3831 Invalid names compare low to valid names. The @env{LC_TIME} locale
3832 category determines the month spellings.
3833 By default a blank is a space or a tab, but the @env{LC_CTYPE} locale
3837 @itemx --numeric-sort
3838 @itemx --sort=numeric
3840 @opindex --numeric-sort
3842 @cindex numeric sort
3844 Sort numerically. The number begins each line and consists
3845 of optional blanks, an optional @samp{-} sign, and zero or more
3846 digits possibly separated by thousands separators, optionally followed
3847 by a decimal-point character and zero or more digits. An empty
3848 number is treated as @samp{0}. The @env{LC_NUMERIC}
3849 locale specifies the decimal-point character and thousands separator.
3850 By default a blank is a space or a tab, but the @env{LC_CTYPE} locale
3853 Comparison is exact; there is no rounding error.
3855 Neither a leading @samp{+} nor exponential notation is recognized.
3856 To compare such strings numerically, use the
3857 @option{--general-numeric-sort} (@option{-g}) option.
3860 @itemx --version-sort
3862 @opindex --version-sort
3863 @cindex version number sort
3865 Sort per @code{strverscmp(3)}. This is a normal string comparison, except
3866 that embedded decimal numbers are sorted by numeric value
3867 (see @option{--numeric-sort} above).
3873 @cindex reverse sorting
3874 Reverse the result of comparison, so that lines with greater key values
3875 appear earlier in the output instead of later.
3878 @itemx --random-sort
3879 @itemx --sort=random
3881 @opindex --random-sort
3884 Sort by hashing the input keys and then sorting the hash values.
3885 Choose the hash function at random, ensuring that it is free of
3886 collisions so that differing keys have differing hash values. This is
3887 like a random permutation of the inputs (@pxref{shuf invocation}),
3888 except that keys with the same value sort together.
3890 If multiple random sort fields are specified, the same random hash
3891 function is used for all fields. To use different random hash
3892 functions for different fields, you can invoke @command{sort} more
3895 The choice of hash function is affected by the
3896 @option{--random-source} option.
3904 @item --compress-program=@var{prog}
3905 Compress any temporary files with the program @var{prog}.
3907 With no arguments, @var{prog} must compress standard input to standard
3908 output, and when given the @option{-d} option it must decompress
3909 standard input to standard output.
3911 Terminate with an error if @var{prog} exits with nonzero status.
3913 White space and the backslash character should not appear in
3914 @var{prog}; they are reserved for future use.
3916 @filesZeroFromOption{sort,,sorted output}
3918 @item -k @var{pos1}[,@var{pos2}]
3919 @itemx --key=@var{pos1}[,@var{pos2}]
3923 Specify a sort field that consists of the part of the line between
3924 @var{pos1} and @var{pos2} (or the end of the line, if @var{pos2} is
3925 omitted), @emph{inclusive}.
3927 Each @var{pos} has the form @samp{@var{f}[.@var{c}][@var{opts}]},
3928 where @var{f} is the number of the field to use, and @var{c} is the number
3929 of the first character from the beginning of the field. Fields and character
3930 positions are numbered starting with 1; a character position of zero in
3931 @var{pos2} indicates the field's last character. If @samp{.@var{c}} is
3932 omitted from @var{pos1}, it defaults to 1 (the beginning of the field);
3933 if omitted from @var{pos2}, it defaults to 0 (the end of the field).
3934 @var{opts} are ordering options, allowing individual keys to be sorted
3935 according to different rules; see below for details. Keys can span
3938 Example: To sort on the second field, use @option{--key=2,2}
3939 (@option{-k 2,2}). See below for more notes on keys and more examples.
3941 @item --batch-size=@var{nmerge}
3942 @opindex --batch-size
3943 @cindex number of inputs to merge, nmerge
3944 Merge at most @var{nmerge} inputs at once.
3946 When @command{sort} has to merge more than @var{nmerge} inputs,
3947 it merges them in groups of @var{nmerge}, saving the result in
3948 a temporary file, which is then used as an input in a subsequent merge.
3950 A large value of @var{nmerge} may improve merge performance and decrease
3951 temporary storage utilization at the expense of increased memory usage
3952 and I/0. Conversely a small value of @var{nmerge} may reduce memory
3953 requirements and I/0 at the expense of temporary storage consumption and
3956 The value of @var{nmerge} must be at least 2. The default value is
3957 currently 16, but this is implementation-dependent and may change in
3960 The value of @var{nmerge} may be bounded by a resource limit for open
3961 file descriptors. The commands @samp{ulimit -n} or @samp{getconf
3962 OPEN_MAX} may display limits for your systems; these limits may be
3963 modified further if your program already has some files open, or if
3964 the operating system has other limits on the number of open files. If
3965 the value of @var{nmerge} exceeds the resource limit, @command{sort}
3966 silently uses a smaller value.
3968 @item -o @var{output-file}
3969 @itemx --output=@var{output-file}
3972 @cindex overwriting of input, allowed
3973 Write output to @var{output-file} instead of standard output.
3974 Normally, @command{sort} reads all input before opening
3975 @var{output-file}, so you can safely sort a file in place by using
3976 commands like @code{sort -o F F} and @code{cat F | sort -o F}.
3977 However, @command{sort} with @option{--merge} (@option{-m}) can open
3978 the output file before reading all input, so a command like @code{cat
3979 F | sort -m -o F - G} is not safe as @command{sort} might start
3980 writing @file{F} before @command{cat} is done reading it.
3982 @vindex POSIXLY_CORRECT
3983 On newer systems, @option{-o} cannot appear after an input file if
3984 @env{POSIXLY_CORRECT} is set, e.g., @samp{sort F -o F}. Portable
3985 scripts should specify @option{-o @var{output-file}} before any input
3988 @item --random-source=@var{file}
3989 @opindex --random-source
3990 @cindex random source for sorting
3991 Use @var{file} as a source of random data used to determine which
3992 random hash function to use with the @option{-R} option. @xref{Random
3999 @cindex sort stability
4000 @cindex sort's last-resort comparison
4002 Make @command{sort} stable by disabling its last-resort comparison.
4003 This option has no effect if no fields or global ordering options
4004 other than @option{--reverse} (@option{-r}) are specified.
4007 @itemx --buffer-size=@var{size}
4009 @opindex --buffer-size
4010 @cindex size for main memory sorting
4011 Use a main-memory sort buffer of the given @var{size}. By default,
4012 @var{size} is in units of 1024 bytes. Appending @samp{%} causes
4013 @var{size} to be interpreted as a percentage of physical memory.
4014 Appending @samp{K} multiplies @var{size} by 1024 (the default),
4015 @samp{M} by 1,048,576, @samp{G} by 1,073,741,824, and so on for
4016 @samp{T}, @samp{P}, @samp{E}, @samp{Z}, and @samp{Y}. Appending
4017 @samp{b} causes @var{size} to be interpreted as a byte count, with no
4020 This option can improve the performance of @command{sort} by causing it
4021 to start with a larger or smaller sort buffer than the default.
4022 However, this option affects only the initial buffer size. The buffer
4023 grows beyond @var{size} if @command{sort} encounters input lines larger
4026 @item -t @var{separator}
4027 @itemx --field-separator=@var{separator}
4029 @opindex --field-separator
4030 @cindex field separator character
4031 Use character @var{separator} as the field separator when finding the
4032 sort keys in each line. By default, fields are separated by the empty
4033 string between a non-blank character and a blank character.
4034 By default a blank is a space or a tab, but the @env{LC_CTYPE} locale
4037 That is, given the input line @w{@samp{ foo bar}}, @command{sort} breaks it
4038 into fields @w{@samp{ foo}} and @w{@samp{ bar}}. The field separator is
4039 not considered to be part of either the field preceding or the field
4040 following, so with @samp{sort @w{-t " "}} the same input line has
4041 three fields: an empty field, @samp{foo}, and @samp{bar}.
4042 However, fields that extend to the end of the line,
4043 as @option{-k 2}, or fields consisting of a range, as @option{-k 2,3},
4044 retain the field separators present between the endpoints of the range.
4046 To specify @acronym{ASCII} @sc{nul} as the field separator,
4047 use the two-character string @samp{\0}, e.g., @samp{sort -t '\0'}.
4049 @item -T @var{tempdir}
4050 @itemx --temporary-directory=@var{tempdir}
4052 @opindex --temporary-directory
4053 @cindex temporary directory
4055 Use directory @var{tempdir} to store temporary files, overriding the
4056 @env{TMPDIR} environment variable. If this option is given more than
4057 once, temporary files are stored in all the directories given. If you
4058 have a large sort or merge that is I/O-bound, you can often improve
4059 performance by using this option to specify directories on different
4060 disks and controllers.
4066 @cindex uniquifying output
4068 Normally, output only the first of a sequence of lines that compare
4069 equal. For the @option{--check} (@option{-c} or @option{-C}) option,
4070 check that no pair of consecutive lines compares equal.
4072 This option also disables the default last-resort comparison.
4074 The commands @code{sort -u} and @code{sort | uniq} are equivalent, but
4075 this equivalence does not extend to arbitrary @command{sort} options.
4076 For example, @code{sort -n -u} inspects only the value of the initial
4077 numeric string when checking for uniqueness, whereas @code{sort -n |
4078 uniq} inspects the entire line. @xref{uniq invocation}.
4080 @macro zeroTerminatedOption
4082 @itemx --zero-terminated
4084 @opindex --zero-terminated
4085 @cindex process zero-terminated items
4086 Delimit items with a zero byte rather than a newline (@acronym{ASCII} @sc{lf}).
4087 I.E. treat input as items separated by @acronym{ASCII} @sc{nul}
4088 and terminate output items with @acronym{ASCII} @sc{nul}.
4089 This option can be useful in conjunction with @samp{perl -0} or
4090 @samp{find -print0} and @samp{xargs -0} which do the same in order to
4091 reliably handle arbitrary file names (even those containing blanks
4092 or other special characters).
4094 @zeroTerminatedOption
4098 Historical (BSD and System V) implementations of @command{sort} have
4099 differed in their interpretation of some options, particularly
4100 @option{-b}, @option{-f}, and @option{-n}. @sc{gnu} sort follows the @acronym{POSIX}
4101 behavior, which is usually (but not always!) like the System V behavior.
4102 According to @acronym{POSIX}, @option{-n} no longer implies @option{-b}. For
4103 consistency, @option{-M} has been changed in the same way. This may
4104 affect the meaning of character positions in field specifications in
4105 obscure cases. The only fix is to add an explicit @option{-b}.
4107 A position in a sort field specified with @option{-k} may have any
4108 of the option letters @samp{MbdfghinRrV} appended to it, in which case no
4109 global ordering options are inherited by that particular field. The
4110 @option{-b} option may be independently attached to either or both of
4111 the start and end positions of a field specification, and if it is
4112 inherited from the global options it will be attached to both.
4113 If input lines can contain leading or adjacent blanks and @option{-t}
4114 is not used, then @option{-k} is typically combined with @option{-b} or
4115 an option that implicitly ignores leading blanks (@samp{MghnV}) as otherwise
4116 the varying numbers of leading blanks in fields can cause confusing results.
4118 If the start position in a sort field specifier falls after the end of
4119 the line or after the end field, the field is empty. If the @option{-b}
4120 option was specified, the @samp{.@var{c}} part of a field specification
4121 is counted from the first nonblank character of the field.
4123 @vindex _POSIX2_VERSION
4124 @vindex POSIXLY_CORRECT
4125 On older systems, @command{sort} supports an obsolete origin-zero
4126 syntax @samp{+@var{pos1} [-@var{pos2}]} for specifying sort keys.
4127 This obsolete behavior can be enabled or disabled with the
4128 @env{_POSIX2_VERSION} environment variable (@pxref{Standards
4129 conformance}); it can also be enabled when @env{POSIXLY_CORRECT} is
4130 not set by using the obsolete syntax with @samp{-@var{pos2}} present.
4132 Scripts intended for use on standard hosts should avoid obsolete
4133 syntax and should use @option{-k} instead. For example, avoid
4134 @samp{sort +2}, since it might be interpreted as either @samp{sort
4135 ./+2} or @samp{sort -k 3}. If your script must also run on hosts that
4136 support only the obsolete syntax, it can use a test like @samp{if sort
4137 -k 1 </dev/null >/dev/null 2>&1; then @dots{}} to decide which syntax
4140 Here are some examples to illustrate various combinations of options.
4145 Sort in descending (reverse) numeric order.
4152 Sort alphabetically, omitting the first and second fields
4153 and the blanks at the start of the third field.
4154 This uses a single key composed of the characters beginning
4155 at the start of the first nonblank character in field three
4156 and extending to the end of each line.
4163 Sort numerically on the second field and resolve ties by sorting
4164 alphabetically on the third and fourth characters of field five.
4165 Use @samp{:} as the field delimiter.
4168 sort -t : -k 2,2n -k 5.3,5.4
4171 Note that if you had written @option{-k 2n} instead of @option{-k 2,2n}
4172 @command{sort} would have used all characters beginning in the second field
4173 and extending to the end of the line as the primary @emph{numeric}
4174 key. For the large majority of applications, treating keys spanning
4175 more than one field as numeric will not do what you expect.
4177 Also note that the @samp{n} modifier was applied to the field-end
4178 specifier for the first key. It would have been equivalent to
4179 specify @option{-k 2n,2} or @option{-k 2n,2n}. All modifiers except
4180 @samp{b} apply to the associated @emph{field}, regardless of whether
4181 the modifier character is attached to the field-start and/or the
4182 field-end part of the key specifier.
4185 Sort the password file on the fifth field and ignore any
4186 leading blanks. Sort lines with equal values in field five
4187 on the numeric user ID in field three. Fields are separated
4191 sort -t : -k 5b,5 -k 3,3n /etc/passwd
4192 sort -t : -n -k 5b,5 -k 3,3 /etc/passwd
4193 sort -t : -b -k 5,5 -k 3,3n /etc/passwd
4196 These three commands have equivalent effect. The first specifies that
4197 the first key's start position ignores leading blanks and the second
4198 key is sorted numerically. The other two commands rely on global
4199 options being inherited by sort keys that lack modifiers. The inheritance
4200 works in this case because @option{-k 5b,5b} and @option{-k 5b,5} are
4201 equivalent, as the location of a field-end lacking a @samp{.@var{c}}
4202 character position is not affected by whether initial blanks are
4206 Sort a set of log files, primarily by IPv4 address and secondarily by
4207 time stamp. If two lines' primary and secondary keys are identical,
4208 output the lines in the same order that they were input. The log
4209 files contain lines that look like this:
4212 4.150.156.3 - - [01/Apr/2004:06:31:51 +0000] message 1
4213 211.24.3.231 - - [24/Apr/2004:20:17:39 +0000] message 2
4216 Fields are separated by exactly one space. Sort IPv4 addresses
4217 lexicographically, e.g., 212.61.52.2 sorts before 212.129.233.201
4218 because 61 is less than 129.
4221 sort -s -t ' ' -k 4.9n -k 4.5M -k 4.2n -k 4.14,4.21 file*.log |
4222 sort -s -t '.' -k 1,1n -k 2,2n -k 3,3n -k 4,4n
4225 This example cannot be done with a single @command{sort} invocation,
4226 since IPv4 address components are separated by @samp{.} while dates
4227 come just after a space. So it is broken down into two invocations of
4228 @command{sort}: the first sorts by time stamp and the second by IPv4
4229 address. The time stamp is sorted by year, then month, then day, and
4230 finally by hour-minute-second field, using @option{-k} to isolate each
4231 field. Except for hour-minute-second there's no need to specify the
4232 end of each key field, since the @samp{n} and @samp{M} modifiers sort
4233 based on leading prefixes that cannot cross field boundaries. The
4234 IPv4 addresses are sorted lexicographically. The second sort uses
4235 @samp{-s} so that ties in the primary key are broken by the secondary
4236 key; the first sort uses @samp{-s} so that the combination of the two
4240 Generate a tags file in case-insensitive sorted order.
4243 find src -type f -print0 | sort -z -f | xargs -0 etags --append
4246 The use of @option{-print0}, @option{-z}, and @option{-0} in this case means
4247 that file names that contain blanks or other special characters are
4249 by the sort operation.
4251 @c This example is a bit contrived and needs more explanation.
4253 @c Sort records separated by an arbitrary string by using a pipe to convert
4254 @c each record delimiter string to @samp{\0}, then using sort's -z option,
4255 @c and converting each @samp{\0} back to the original record delimiter.
4258 @c printf 'c\n\nb\n\na\n'|perl -0pe 's/\n\n/\n\0/g'|sort -z|perl -0pe 's/\0/\n/g'
4262 Use the common @acronym{DSU, Decorate Sort Undecorate} idiom to
4263 sort lines according to their length.
4266 awk '@{print length, $0@}' /etc/passwd | sort -n | cut -f2- -d' '
4269 In general this technique can be used to sort data that the @command{sort}
4270 command does not support, or is inefficient at, sorting directly.
4273 Shuffle a list of directories, but preserve the order of files within
4274 each directory. For instance, one could use this to generate a music
4275 playlist in which albums are shuffled but the songs of each album are
4279 ls */* | sort -t / -k 1,1R -k 2,2
4285 @node shuf invocation
4286 @section @command{shuf}: Shuffling text
4289 @cindex shuffling files
4291 @command{shuf} shuffles its input by outputting a random permutation
4292 of its input lines. Each output permutation is equally likely.
4296 shuf [@var{option}]@dots{} [@var{file}]
4297 shuf -e [@var{option}]@dots{} [@var{arg}]@dots{}
4298 shuf -i @var{lo}-@var{hi} [@var{option}]@dots{}
4301 @command{shuf} has three modes of operation that affect where it
4302 obtains its input lines. By default, it reads lines from standard
4303 input. The following options change the operation mode:
4311 @cindex command-line operands to shuffle
4312 Treat each command-line operand as an input line.
4314 @item -i @var{lo}-@var{hi}
4315 @itemx --input-range=@var{lo}-@var{hi}
4317 @opindex --input-range
4318 @cindex input range to shuffle
4319 Act as if input came from a file containing the range of unsigned
4320 decimal integers @var{lo}@dots{}@var{hi}, one per line.
4324 @command{shuf}'s other options can affect its behavior in all
4329 @item -n @var{lines}
4330 @itemx --head-count=@var{count}
4332 @opindex --head-count
4333 @cindex head of output
4334 Output at most @var{count} lines. By default, all input lines are
4337 @item -o @var{output-file}
4338 @itemx --output=@var{output-file}
4341 @cindex overwriting of input, allowed
4342 Write output to @var{output-file} instead of standard output.
4343 @command{shuf} reads all input before opening
4344 @var{output-file}, so you can safely shuffle a file in place by using
4345 commands like @code{shuf -o F <F} and @code{cat F | shuf -o F}.
4347 @item --random-source=@var{file}
4348 @opindex --random-source
4349 @cindex random source for shuffling
4350 Use @var{file} as a source of random data used to determine which
4351 permutation to generate. @xref{Random sources}.
4353 @zeroTerminatedOption
4369 might produce the output
4379 Similarly, the command:
4382 shuf -e clubs hearts diamonds spades
4396 and the command @samp{shuf -i 1-4} might output:
4406 These examples all have four input lines, so @command{shuf} might
4407 produce any of the twenty-four possible permutations of the input. In
4408 general, if there are @var{n} input lines, there are @var{n}! (i.e.,
4409 @var{n} factorial, or @var{n} * (@var{n} - 1) * @dots{} * 1) possible
4410 output permutations.
4415 @node uniq invocation
4416 @section @command{uniq}: Uniquify files
4419 @cindex uniquify files
4421 @command{uniq} writes the unique lines in the given @file{input}, or
4422 standard input if nothing is given or for an @var{input} name of
4426 uniq [@var{option}]@dots{} [@var{input} [@var{output}]]
4429 By default, @command{uniq} prints its input lines, except that
4430 it discards all but the first of adjacent repeated lines, so that
4431 no output lines are repeated. Optionally, it can instead discard
4432 lines that are not repeated, or all repeated lines.
4434 The input need not be sorted, but repeated input lines are detected
4435 only if they are adjacent. If you want to discard non-adjacent
4436 duplicate lines, perhaps you want to use @code{sort -u}.
4437 @xref{sort invocation}.
4440 Comparisons honor the rules specified by the @env{LC_COLLATE}
4443 If no @var{output} file is specified, @command{uniq} writes to standard
4446 The program accepts the following options. Also see @ref{Common options}.
4451 @itemx --skip-fields=@var{n}
4453 @opindex --skip-fields
4454 Skip @var{n} fields on each line before checking for uniqueness. Use
4455 a null string for comparison if a line has fewer than @var{n} fields. Fields
4456 are sequences of non-space non-tab characters that are separated from
4457 each other by at least one space or tab.
4459 For compatibility @command{uniq} supports an obsolete option syntax
4460 @option{-@var{n}}. New scripts should use @option{-f @var{n}} instead.
4463 @itemx --skip-chars=@var{n}
4465 @opindex --skip-chars
4466 Skip @var{n} characters before checking for uniqueness. Use a null string
4467 for comparison if a line has fewer than @var{n} characters. If you use both
4468 the field and character skipping options, fields are skipped over first.
4470 @vindex _POSIX2_VERSION
4471 On older systems, @command{uniq} supports an obsolete option syntax
4473 This obsolete behavior can be enabled or disabled with the
4474 @env{_POSIX2_VERSION} environment variable (@pxref{Standards
4475 conformance}), but portable scripts should avoid commands whose
4476 behavior depends on this variable.
4477 For example, use @samp{uniq ./+10} or @samp{uniq -s 10} rather than
4478 the ambiguous @samp{uniq +10}.
4484 Print the number of times each line occurred along with the line.
4487 @itemx --ignore-case
4489 @opindex --ignore-case
4490 Ignore differences in case when comparing lines.
4496 @cindex repeated lines, outputting
4497 Discard lines that are not repeated. When used by itself, this option
4498 causes @command{uniq} to print the first copy of each repeated line,
4502 @itemx --all-repeated[=@var{delimit-method}]
4504 @opindex --all-repeated
4505 @cindex all repeated lines, outputting
4506 Do not discard the second and subsequent repeated input lines,
4507 but discard lines that are not repeated.
4508 This option is useful mainly in conjunction with other options e.g.,
4509 to ignore case or to compare only selected fields.
4510 The optional @var{delimit-method} tells how to delimit
4511 groups of repeated lines, and must be one of the following:
4516 Do not delimit groups of repeated lines.
4517 This is equivalent to @option{--all-repeated} (@option{-D}).
4520 Output a newline before each group of repeated lines.
4521 With @option{--zero-terminated} (@option{-z}), use a zero
4522 byte (@acronym{ASCII} @sc{nul}) instead of a newline.
4525 Separate groups of repeated lines with a single newline.
4526 With @option{--zero-terminated} (@option{-z}), use a zero
4527 byte (@acronym{ASCII} @sc{nul}) instead of a newline.
4528 This is the same as using @samp{prepend}, except that
4529 no delimiter is inserted before the first group, and hence
4530 may be better suited for output direct to users.
4533 Note that when groups are delimited and the input stream contains
4534 two or more consecutive blank lines, then the output is ambiguous.
4535 To avoid that, filter the input through @samp{tr -s '\n'} to replace
4536 each sequence of consecutive newlines with a single newline.
4538 This is a @sc{gnu} extension.
4539 @c FIXME: give an example showing *how* it's useful
4545 @cindex unique lines, outputting
4546 Discard the first repeated line. When used by itself, this option
4547 causes @command{uniq} to print unique lines, and nothing else.
4550 @itemx --check-chars=@var{n}
4552 @opindex --check-chars
4553 Compare at most @var{n} characters on each line (after skipping any specified
4554 fields and characters). By default the entire rest of the lines are
4557 @zeroTerminatedOption
4564 @node comm invocation
4565 @section @command{comm}: Compare two sorted files line by line
4568 @cindex line-by-line comparison
4569 @cindex comparing sorted files
4571 @command{comm} writes to standard output lines that are common, and lines
4572 that are unique, to two input files; a file name of @samp{-} means
4573 standard input. Synopsis:
4576 comm [@var{option}]@dots{} @var{file1} @var{file2}
4580 Before @command{comm} can be used, the input files must be sorted using the
4581 collating sequence specified by the @env{LC_COLLATE} locale.
4582 If an input file ends in a non-newline
4583 character, a newline is silently appended. The @command{sort} command with
4584 no options always outputs a file that is suitable input to @command{comm}.
4586 @cindex differing lines
4587 @cindex common lines
4588 With no options, @command{comm} produces three-column output. Column one
4589 contains lines unique to @var{file1}, column two contains lines unique
4590 to @var{file2}, and column three contains lines common to both files.
4591 Columns are separated by a single TAB character.
4592 @c FIXME: when there's an option to supply an alternative separator
4593 @c string, append `by default' to the above sentence.
4598 The options @option{-1}, @option{-2}, and @option{-3} suppress printing of
4599 the corresponding columns (and separators). Also see @ref{Common options}.
4601 Unlike some other comparison utilities, @command{comm} has an exit
4602 status that does not depend on the result of the comparison.
4603 Upon normal completion @command{comm} produces an exit code of zero.
4604 If there is an error it exits with nonzero status.
4606 @macro checkOrderOption{cmd}
4607 If the @option{--check-order} option is given, unsorted inputs will
4608 cause a fatal error message. If the option @option{--nocheck-order}
4609 is given, unsorted inputs will never cause an error message. If
4610 neither of these options is given, wrongly sorted inputs are diagnosed
4611 only if an input file is found to contain unpairable lines. If an
4612 input file is diagnosed as being unsorted, the @command{\cmd\} command
4613 will exit with a nonzero status (and the output should not be used).
4615 Forcing @command{\cmd\} to process wrongly sorted input files
4616 containing unpairable lines by specifying @option{--nocheck-order} is
4617 not guaranteed to produce any particular output. The output will
4618 probably not correspond with whatever you hoped it would be.
4620 @checkOrderOption{comm}
4625 Fail with an error message if either input file is wrongly ordered.
4627 @item --nocheck-order
4628 Do not check that both input files are in sorted order.
4632 @item --output-delimiter=@var{str}
4633 Print @var{str} between adjacent output columns,
4634 rather than the default of a single TAB character.
4636 The delimiter @var{str} may not be empty.
4640 @node ptx invocation
4641 @section @command{ptx}: Produce permuted indexes
4645 @command{ptx} reads a text file and essentially produces a permuted index, with
4646 each keyword in its context. The calling sketch is either one of:
4649 ptx [@var{option} @dots{}] [@var{file} @dots{}]
4650 ptx -G [@var{option} @dots{}] [@var{input} [@var{output}]]
4653 The @option{-G} (or its equivalent: @option{--traditional}) option disables
4654 all @sc{gnu} extensions and reverts to traditional mode, thus introducing some
4655 limitations and changing several of the program's default option values.
4656 When @option{-G} is not specified, @sc{gnu} extensions are always enabled.
4657 @sc{gnu} extensions to @command{ptx} are documented wherever appropriate in this
4658 document. For the full list, see @xref{Compatibility in ptx}.
4660 Individual options are explained in the following sections.
4662 When @sc{gnu} extensions are enabled, there may be zero, one or several
4663 @var{file}s after the options. If there is no @var{file}, the program
4664 reads the standard input. If there is one or several @var{file}s, they
4665 give the name of input files which are all read in turn, as if all the
4666 input files were concatenated. However, there is a full contextual
4667 break between each file and, when automatic referencing is requested,
4668 file names and line numbers refer to individual text input files. In
4669 all cases, the program outputs the permuted index to the standard
4672 When @sc{gnu} extensions are @emph{not} enabled, that is, when the program
4673 operates in traditional mode, there may be zero, one or two parameters
4674 besides the options. If there are no parameters, the program reads the
4675 standard input and outputs the permuted index to the standard output.
4676 If there is only one parameter, it names the text @var{input} to be read
4677 instead of the standard input. If two parameters are given, they give
4678 respectively the name of the @var{input} file to read and the name of
4679 the @var{output} file to produce. @emph{Be very careful} to note that,
4680 in this case, the contents of file given by the second parameter is
4681 destroyed. This behavior is dictated by System V @command{ptx}
4682 compatibility; @sc{gnu} Standards normally discourage output parameters not
4683 introduced by an option.
4685 Note that for @emph{any} file named as the value of an option or as an
4686 input text file, a single dash @kbd{-} may be used, in which case
4687 standard input is assumed. However, it would not make sense to use this
4688 convention more than once per program invocation.
4691 * General options in ptx:: Options which affect general program behavior.
4692 * Charset selection in ptx:: Underlying character set considerations.
4693 * Input processing in ptx:: Input fields, contexts, and keyword selection.
4694 * Output formatting in ptx:: Types of output format, and sizing the fields.
4695 * Compatibility in ptx::
4699 @node General options in ptx
4700 @subsection General options
4705 @itemx --traditional
4706 As already explained, this option disables all @sc{gnu} extensions to
4707 @command{ptx} and switches to traditional mode.
4710 Print a short help on standard output, then exit without further
4714 Print the program version on standard output, then exit without further
4722 @node Charset selection in ptx
4723 @subsection Charset selection
4725 @c FIXME: People don't necessarily know what an IBM-PC was these days.
4726 As it is set up now, the program assumes that the input file is coded
4727 using 8-bit @acronym{ISO} 8859-1 code, also known as Latin-1 character set,
4728 @emph{unless} it is compiled for MS-DOS, in which case it uses the
4729 character set of the IBM-PC@. (@sc{gnu} @command{ptx} is not known to work on
4730 smaller MS-DOS machines anymore.) Compared to 7-bit @acronym{ASCII}, the set
4731 of characters which are letters is different; this alters the behavior
4732 of regular expression matching. Thus, the default regular expression
4733 for a keyword allows foreign or diacriticized letters. Keyword sorting,
4734 however, is still crude; it obeys the underlying character set ordering
4740 @itemx --ignore-case
4741 Fold lower case letters to upper case for sorting.
4746 @node Input processing in ptx
4747 @subsection Word selection and input processing
4752 @itemx --break-file=@var{file}
4754 This option provides an alternative (to @option{-W}) method of describing
4755 which characters make up words. It introduces the name of a
4756 file which contains a list of characters which can@emph{not} be part of
4757 one word; this file is called the @dfn{Break file}. Any character which
4758 is not part of the Break file is a word constituent. If both options
4759 @option{-b} and @option{-W} are specified, then @option{-W} has precedence and
4760 @option{-b} is ignored.
4762 When @sc{gnu} extensions are enabled, the only way to avoid newline as a
4763 break character is to write all the break characters in the file with no
4764 newline at all, not even at the end of the file. When @sc{gnu} extensions
4765 are disabled, spaces, tabs and newlines are always considered as break
4766 characters even if not included in the Break file.
4769 @itemx --ignore-file=@var{file}
4771 The file associated with this option contains a list of words which will
4772 never be taken as keywords in concordance output. It is called the
4773 @dfn{Ignore file}. The file contains exactly one word in each line; the
4774 end of line separation of words is not subject to the value of the
4778 @itemx --only-file=@var{file}
4780 The file associated with this option contains a list of words which will
4781 be retained in concordance output; any word not mentioned in this file
4782 is ignored. The file is called the @dfn{Only file}. The file contains
4783 exactly one word in each line; the end of line separation of words is
4784 not subject to the value of the @option{-S} option.
4786 There is no default for the Only file. When both an Only file and an
4787 Ignore file are specified, a word is considered a keyword only
4788 if it is listed in the Only file and not in the Ignore file.
4793 On each input line, the leading sequence of non-white space characters will be
4794 taken to be a reference that has the purpose of identifying this input
4795 line in the resulting permuted index. For more information about reference
4796 production, see @xref{Output formatting in ptx}.
4797 Using this option changes the default value for option @option{-S}.
4799 Using this option, the program does not try very hard to remove
4800 references from contexts in output, but it succeeds in doing so
4801 @emph{when} the context ends exactly at the newline. If option
4802 @option{-r} is used with @option{-S} default value, or when @sc{gnu} extensions
4803 are disabled, this condition is always met and references are completely
4804 excluded from the output contexts.
4806 @item -S @var{regexp}
4807 @itemx --sentence-regexp=@var{regexp}
4809 This option selects which regular expression will describe the end of a
4810 line or the end of a sentence. In fact, this regular expression is not
4811 the only distinction between end of lines or end of sentences, and input
4812 line boundaries have no special significance outside this option. By
4813 default, when @sc{gnu} extensions are enabled and if @option{-r} option is not
4814 used, end of sentences are used. In this case, this @var{regex} is
4815 imported from @sc{gnu} Emacs:
4818 [.?!][]\"')@}]*\\($\\|\t\\| \\)[ \t\n]*
4821 Whenever @sc{gnu} extensions are disabled or if @option{-r} option is used, end
4822 of lines are used; in this case, the default @var{regexp} is just:
4828 Using an empty @var{regexp} is equivalent to completely disabling end of
4829 line or end of sentence recognition. In this case, the whole file is
4830 considered to be a single big line or sentence. The user might want to
4831 disallow all truncation flag generation as well, through option @option{-F
4832 ""}. @xref{Regexps, , Syntax of Regular Expressions, emacs, The GNU Emacs
4835 When the keywords happen to be near the beginning of the input line or
4836 sentence, this often creates an unused area at the beginning of the
4837 output context line; when the keywords happen to be near the end of the
4838 input line or sentence, this often creates an unused area at the end of
4839 the output context line. The program tries to fill those unused areas
4840 by wrapping around context in them; the tail of the input line or
4841 sentence is used to fill the unused area on the left of the output line;
4842 the head of the input line or sentence is used to fill the unused area
4843 on the right of the output line.
4845 As a matter of convenience to the user, many usual backslashed escape
4846 sequences from the C language are recognized and converted to the
4847 corresponding characters by @command{ptx} itself.
4849 @item -W @var{regexp}
4850 @itemx --word-regexp=@var{regexp}
4852 This option selects which regular expression will describe each keyword.
4853 By default, if @sc{gnu} extensions are enabled, a word is a sequence of
4854 letters; the @var{regexp} used is @samp{\w+}. When @sc{gnu} extensions are
4855 disabled, a word is by default anything which ends with a space, a tab
4856 or a newline; the @var{regexp} used is @samp{[^ \t\n]+}.
4858 An empty @var{regexp} is equivalent to not using this option.
4859 @xref{Regexps, , Syntax of Regular Expressions, emacs, The GNU Emacs
4862 As a matter of convenience to the user, many usual backslashed escape
4863 sequences, as found in the C language, are recognized and converted to
4864 the corresponding characters by @command{ptx} itself.
4869 @node Output formatting in ptx
4870 @subsection Output formatting
4872 Output format is mainly controlled by the @option{-O} and @option{-T} options
4873 described in the table below. When neither @option{-O} nor @option{-T} are
4874 selected, and if @sc{gnu} extensions are enabled, the program chooses an
4875 output format suitable for a dumb terminal. Each keyword occurrence is
4876 output to the center of one line, surrounded by its left and right
4877 contexts. Each field is properly justified, so the concordance output
4878 can be readily observed. As a special feature, if automatic
4879 references are selected by option @option{-A} and are output before the
4880 left context, that is, if option @option{-R} is @emph{not} selected, then
4881 a colon is added after the reference; this nicely interfaces with @sc{gnu}
4882 Emacs @code{next-error} processing. In this default output format, each
4883 white space character, like newline and tab, is merely changed to
4884 exactly one space, with no special attempt to compress consecutive
4885 spaces. This might change in the future. Except for those white space
4886 characters, every other character of the underlying set of 256
4887 characters is transmitted verbatim.
4889 Output format is further controlled by the following options.
4893 @item -g @var{number}
4894 @itemx --gap-size=@var{number}
4896 Select the size of the minimum white space gap between the fields on the
4899 @item -w @var{number}
4900 @itemx --width=@var{number}
4902 Select the maximum output width of each final line. If references are
4903 used, they are included or excluded from the maximum output width
4904 depending on the value of option @option{-R}. If this option is not
4905 selected, that is, when references are output before the left context,
4906 the maximum output width takes into account the maximum length of all
4907 references. If this option is selected, that is, when references are
4908 output after the right context, the maximum output width does not take
4909 into account the space taken by references, nor the gap that precedes
4913 @itemx --auto-reference
4915 Select automatic references. Each input line will have an automatic
4916 reference made up of the file name and the line ordinal, with a single
4917 colon between them. However, the file name will be empty when standard
4918 input is being read. If both @option{-A} and @option{-r} are selected, then
4919 the input reference is still read and skipped, but the automatic
4920 reference is used at output time, overriding the input reference.
4923 @itemx --right-side-refs
4925 In the default output format, when option @option{-R} is not used, any
4926 references produced by the effect of options @option{-r} or @option{-A} are
4927 placed to the far right of output lines, after the right context. With
4928 default output format, when the @option{-R} option is specified, references
4929 are rather placed at the beginning of each output line, before the left
4930 context. For any other output format, option @option{-R} is
4931 ignored, with one exception: with @option{-R} the width of references
4932 is @emph{not} taken into account in total output width given by @option{-w}.
4934 This option is automatically selected whenever @sc{gnu} extensions are
4937 @item -F @var{string}
4938 @itemx --flac-truncation=@var{string}
4940 This option will request that any truncation in the output be reported
4941 using the string @var{string}. Most output fields theoretically extend
4942 towards the beginning or the end of the current line, or current
4943 sentence, as selected with option @option{-S}. But there is a maximum
4944 allowed output line width, changeable through option @option{-w}, which is
4945 further divided into space for various output fields. When a field has
4946 to be truncated because it cannot extend beyond the beginning or the end of
4947 the current line to fit in, then a truncation occurs. By default,
4948 the string used is a single slash, as in @option{-F /}.
4950 @var{string} may have more than one character, as in @option{-F ...}.
4951 Also, in the particular case when @var{string} is empty (@option{-F ""}),
4952 truncation flagging is disabled, and no truncation marks are appended in
4955 As a matter of convenience to the user, many usual backslashed escape
4956 sequences, as found in the C language, are recognized and converted to
4957 the corresponding characters by @command{ptx} itself.
4959 @item -M @var{string}
4960 @itemx --macro-name=@var{string}
4962 Select another @var{string} to be used instead of @samp{xx}, while
4963 generating output suitable for @command{nroff}, @command{troff} or @TeX{}.
4966 @itemx --format=roff
4968 Choose an output format suitable for @command{nroff} or @command{troff}
4969 processing. Each output line will look like:
4972 .xx "@var{tail}" "@var{before}" "@var{keyword_and_after}" "@var{head}" "@var{ref}"
4975 so it will be possible to write a @samp{.xx} roff macro to take care of
4976 the output typesetting. This is the default output format when @sc{gnu}
4977 extensions are disabled. Option @option{-M} can be used to change
4978 @samp{xx} to another macro name.
4980 In this output format, each non-graphical character, like newline and
4981 tab, is merely changed to exactly one space, with no special attempt to
4982 compress consecutive spaces. Each quote character: @kbd{"} is doubled
4983 so it will be correctly processed by @command{nroff} or @command{troff}.
4988 Choose an output format suitable for @TeX{} processing. Each output
4989 line will look like:
4992 \xx @{@var{tail}@}@{@var{before}@}@{@var{keyword}@}@{@var{after}@}@{@var{head}@}@{@var{ref}@}
4996 so it will be possible to write a @code{\xx} definition to take care of
4997 the output typesetting. Note that when references are not being
4998 produced, that is, neither option @option{-A} nor option @option{-r} is
4999 selected, the last parameter of each @code{\xx} call is inhibited.
5000 Option @option{-M} can be used to change @samp{xx} to another macro
5003 In this output format, some special characters, like @kbd{$}, @kbd{%},
5004 @kbd{&}, @kbd{#} and @kbd{_} are automatically protected with a
5005 backslash. Curly brackets @kbd{@{}, @kbd{@}} are protected with a
5006 backslash and a pair of dollar signs (to force mathematical mode). The
5007 backslash itself produces the sequence @code{\backslash@{@}}.
5008 Circumflex and tilde diacritical marks produce the sequence @code{^\@{ @}} and
5009 @code{~\@{ @}} respectively. Other diacriticized characters of the
5010 underlying character set produce an appropriate @TeX{} sequence as far
5011 as possible. The other non-graphical characters, like newline and tab,
5012 and all other characters which are not part of @acronym{ASCII}, are merely
5013 changed to exactly one space, with no special attempt to compress
5014 consecutive spaces. Let me know how to improve this special character
5015 processing for @TeX{}.
5020 @node Compatibility in ptx
5021 @subsection The @sc{gnu} extensions to @command{ptx}
5023 This version of @command{ptx} contains a few features which do not exist in
5024 System V @command{ptx}. These extra features are suppressed by using the
5025 @option{-G} command line option, unless overridden by other command line
5026 options. Some @sc{gnu} extensions cannot be recovered by overriding, so the
5027 simple rule is to avoid @option{-G} if you care about @sc{gnu} extensions.
5028 Here are the differences between this program and System V @command{ptx}.
5033 This program can read many input files at once, it always writes the
5034 resulting concordance on standard output. On the other hand, System V
5035 @command{ptx} reads only one file and sends the result to standard output
5036 or, if a second @var{file} parameter is given on the command, to that
5039 Having output parameters not introduced by options is a dangerous
5040 practice which @sc{gnu} avoids as far as possible. So, for using @command{ptx}
5041 portably between @sc{gnu} and System V, you should always use it with a
5042 single input file, and always expect the result on standard output. You
5043 might also want to automatically configure in a @option{-G} option to
5044 @command{ptx} calls in products using @command{ptx}, if the configurator finds
5045 that the installed @command{ptx} accepts @option{-G}.
5048 The only options available in System V @command{ptx} are options @option{-b},
5049 @option{-f}, @option{-g}, @option{-i}, @option{-o}, @option{-r}, @option{-t} and
5050 @option{-w}. All other options are @sc{gnu} extensions and are not repeated in
5051 this enumeration. Moreover, some options have a slightly different
5052 meaning when @sc{gnu} extensions are enabled, as explained below.
5055 By default, concordance output is not formatted for @command{troff} or
5056 @command{nroff}. It is rather formatted for a dumb terminal. @command{troff}
5057 or @command{nroff} output may still be selected through option @option{-O}.
5060 Unless @option{-R} option is used, the maximum reference width is
5061 subtracted from the total output line width. With @sc{gnu} extensions
5062 disabled, width of references is not taken into account in the output
5063 line width computations.
5066 All 256 bytes, even @acronym{ASCII} @sc{nul} bytes, are always read and
5067 processed from input file with no adverse effect, even if @sc{gnu} extensions
5068 are disabled. However, System V @command{ptx} does not accept 8-bit characters,
5069 a few control characters are rejected, and the tilde @kbd{~} is also rejected.
5072 Input line length is only limited by available memory, even if @sc{gnu}
5073 extensions are disabled. However, System V @command{ptx} processes only
5074 the first 200 characters in each line.
5077 The break (non-word) characters default to be every character except all
5078 letters of the underlying character set, diacriticized or not. When @sc{gnu}
5079 extensions are disabled, the break characters default to space, tab and
5083 The program makes better use of output line width. If @sc{gnu} extensions
5084 are disabled, the program rather tries to imitate System V @command{ptx},
5085 but still, there are some slight disposition glitches this program does
5086 not completely reproduce.
5089 The user can specify both an Ignore file and an Only file. This is not
5090 allowed with System V @command{ptx}.
5095 @node tsort invocation
5096 @section @command{tsort}: Topological sort
5099 @cindex topological sort
5101 @command{tsort} performs a topological sort on the given @var{file}, or
5102 standard input if no input file is given or for a @var{file} of
5103 @samp{-}. For more details and some history, see @ref{tsort background}.
5107 tsort [@var{option}] [@var{file}]
5110 @command{tsort} reads its input as pairs of strings, separated by blanks,
5111 indicating a partial ordering. The output is a total ordering that
5112 corresponds to the given partial ordering.
5126 will produce the output
5137 Consider a more realistic example.
5138 You have a large set of functions all in one file, and they may all be
5139 declared static except one. Currently that one (say @code{main}) is the
5140 first function defined in the file, and the ones it calls directly follow
5141 it, followed by those they call, etc. Let's say that you are determined
5142 to take advantage of prototypes, so you have to choose between declaring
5143 all of those functions (which means duplicating a lot of information from
5144 the definitions) and rearranging the functions so that as many as possible
5145 are defined before they are used. One way to automate the latter process
5146 is to get a list for each function of the functions it calls directly.
5147 Many programs can generate such lists. They describe a call graph.
5148 Consider the following list, in which a given line indicates that the
5149 function on the left calls the one on the right directly.
5155 tail_file pretty_name
5156 tail_file write_header
5158 tail_forever recheck
5159 tail_forever pretty_name
5160 tail_forever write_header
5161 tail_forever dump_remainder
5164 tail_lines start_lines
5165 tail_lines dump_remainder
5166 tail_lines file_lines
5167 tail_lines pipe_lines
5169 tail_bytes start_bytes
5170 tail_bytes dump_remainder
5171 tail_bytes pipe_bytes
5172 file_lines dump_remainder
5176 then you can use @command{tsort} to produce an ordering of those
5177 functions that satisfies your requirement.
5180 example$ tsort call-graph | tac
5200 @command{tsort} detects any cycles in the input and writes the first cycle
5201 encountered to standard error.
5203 Note that for a given partial ordering, generally there is no unique
5204 total ordering. In the context of the call graph above, the function
5205 @code{parse_options} may be placed anywhere in the list as long as it
5206 precedes @code{main}.
5208 The only options are @option{--help} and @option{--version}. @xref{Common
5214 * tsort background:: Where tsort came from.
5217 @node tsort background
5218 @subsection @command{tsort}: Background
5220 @command{tsort} exists because very early versions of the Unix linker processed
5221 an archive file exactly once, and in order. As @command{ld} read each object
5222 in the archive, it decided whether it was needed in the program based on
5223 whether it defined any symbols which were undefined at that point in
5226 This meant that dependencies within the archive had to be handled
5227 specially. For example, @code{scanf} probably calls @code{read}. That means
5228 that in a single pass through an archive, it was important for @code{scanf.o}
5229 to appear before read.o, because otherwise a program which calls
5230 @code{scanf} but not @code{read} might end up with an unexpected unresolved
5231 reference to @code{read}.
5233 The way to address this problem was to first generate a set of
5234 dependencies of one object file on another. This was done by a shell
5235 script called @command{lorder}. The GNU tools don't provide a version of
5236 lorder, as far as I know, but you can still find it in BSD
5239 Then you ran @command{tsort} over the @command{lorder} output, and you used the
5240 resulting sort to define the order in which you added objects to the archive.
5242 This whole procedure has been obsolete since about 1980, because
5243 Unix archives now contain a symbol table (traditionally built by
5244 @command{ranlib}, now generally built by @command{ar} itself), and the Unix
5245 linker uses the symbol table to effectively make multiple passes over
5248 Anyhow, that's where tsort came from. To solve an old problem with
5249 the way the linker handled archive files, which has since been solved
5253 @node Operating on fields within a line
5254 @chapter Operating on fields within a line
5257 * cut invocation:: Print selected parts of lines.
5258 * paste invocation:: Merge lines of files.
5259 * join invocation:: Join lines on a common field.
5263 @node cut invocation
5264 @section @command{cut}: Print selected parts of lines
5267 @command{cut} writes to standard output selected parts of each line of each
5268 input file, or standard input if no files are given or for a file name of
5272 cut @var{option}@dots{} [@var{file}]@dots{}
5275 In the table which follows, the @var{byte-list}, @var{character-list},
5276 and @var{field-list} are one or more numbers or ranges (two numbers
5277 separated by a dash) separated by commas. Bytes, characters, and
5278 fields are numbered starting at 1. Incomplete ranges may be
5279 given: @option{-@var{m}} means @samp{1-@var{m}}; @samp{@var{n}-} means
5280 @samp{@var{n}} through end of line or last field. The list elements
5281 can be repeated, can overlap, and can be specified in any order; but
5282 the selected input is written in the same order that it is read, and
5283 is written exactly once.
5285 The program accepts the following options. Also see @ref{Common
5290 @item -b @var{byte-list}
5291 @itemx --bytes=@var{byte-list}
5294 Select for printing only the bytes in positions listed in
5295 @var{byte-list}. Tabs and backspaces are treated like any other
5296 character; they take up 1 byte. If an output delimiter is specified,
5297 (see the description of @option{--output-delimiter}), then output that
5298 string between ranges of selected bytes.
5300 @item -c @var{character-list}
5301 @itemx --characters=@var{character-list}
5303 @opindex --characters
5304 Select for printing only the characters in positions listed in
5305 @var{character-list}. The same as @option{-b} for now, but
5306 internationalization will change that. Tabs and backspaces are
5307 treated like any other character; they take up 1 character. If an
5308 output delimiter is specified, (see the description of
5309 @option{--output-delimiter}), then output that string between ranges
5312 @item -f @var{field-list}
5313 @itemx --fields=@var{field-list}
5316 Select for printing only the fields listed in @var{field-list}.
5317 Fields are separated by a TAB character by default. Also print any
5318 line that contains no delimiter character, unless the
5319 @option{--only-delimited} (@option{-s}) option is specified
5321 @item -d @var{input_delim_byte}
5322 @itemx --delimiter=@var{input_delim_byte}
5324 @opindex --delimiter
5325 With @option{-f}, use the first byte of @var{input_delim_byte} as
5326 the input fields separator (default is TAB).
5330 Do not split multi-byte characters (no-op for now).
5333 @itemx --only-delimited
5335 @opindex --only-delimited
5336 For @option{-f}, do not print lines that do not contain the field separator
5337 character. Normally, any line without a field separator is printed verbatim.
5339 @item --output-delimiter=@var{output_delim_string}
5340 @opindex --output-delimiter
5341 With @option{-f}, output fields are separated by @var{output_delim_string}.
5342 The default with @option{-f} is to use the input delimiter.
5343 When using @option{-b} or @option{-c} to select ranges of byte or
5344 character offsets (as opposed to ranges of fields),
5345 output @var{output_delim_string} between non-overlapping
5346 ranges of selected bytes.
5349 @opindex --complement
5350 This option is a @acronym{GNU} extension.
5351 Select for printing the complement of the bytes, characters or fields
5352 selected with the @option{-b}, @option{-c} or @option{-f} options.
5353 In other words, do @emph{not} print the bytes, characters or fields
5354 specified via those options. This option is useful when you have
5355 many fields and want to print all but a few of them.
5362 @node paste invocation
5363 @section @command{paste}: Merge lines of files
5366 @cindex merging files
5368 @command{paste} writes to standard output lines consisting of sequentially
5369 corresponding lines of each given file, separated by a TAB character.
5370 Standard input is used for a file name of @samp{-} or if no input files
5392 paste [@var{option}]@dots{} [@var{file}]@dots{}
5395 The program accepts the following options. Also see @ref{Common options}.
5403 Paste the lines of one file at a time rather than one line from each
5404 file. Using the above example data:
5407 $ paste -s num2 let3
5412 @item -d @var{delim-list}
5413 @itemx --delimiters=@var{delim-list}
5415 @opindex --delimiters
5416 Consecutively use the characters in @var{delim-list} instead of
5417 TAB to separate merged lines. When @var{delim-list} is
5418 exhausted, start again at its beginning. Using the above example data:
5421 $ paste -d '%_' num2 let3 num2
5432 @node join invocation
5433 @section @command{join}: Join lines on a common field
5436 @cindex common field, joining on
5438 @command{join} writes to standard output a line for each pair of input
5439 lines that have identical join fields. Synopsis:
5442 join [@var{option}]@dots{} @var{file1} @var{file2}
5445 Either @var{file1} or @var{file2} (but not both) can be @samp{-},
5446 meaning standard input. @var{file1} and @var{file2} should be
5447 sorted on the join fields.
5450 Normally, the sort order is that of the
5451 collating sequence specified by the @env{LC_COLLATE} locale. Unless
5452 the @option{-t} option is given, the sort comparison ignores blanks at
5453 the start of the join field, as in @code{sort -b}. If the
5454 @option{--ignore-case} option is given, the sort comparison ignores
5455 the case of characters in the join field, as in @code{sort -f}.
5457 The @command{sort} and @command{join} commands should use consistent
5458 locales and options if the output of @command{sort} is fed to
5459 @command{join}. You can use a command like @samp{sort -k 1b,1} to
5460 sort a file on its default join field, but if you select a non-default
5461 locale, join field, separator, or comparison options, then you should
5462 do so consistently between @command{join} and @command{sort}.
5464 If the input has no unpairable lines, a @acronym{GNU} extension is
5465 available; the sort order can be any order that considers two fields
5466 to be equal if and only if the sort comparison described above
5467 considers them to be equal. For example:
5484 @checkOrderOption{join}
5488 @item the join field is the first field in each line;
5489 @item fields in the input are separated by one or more blanks, with leading
5490 blanks on the line ignored;
5491 @item fields in the output are separated by a space;
5492 @item each output line consists of the join field, the remaining
5493 fields from @var{file1}, then the remaining fields from @var{file2}.
5496 The program accepts the following options. Also see @ref{Common options}.
5500 @item -a @var{file-number}
5502 Print a line for each unpairable line in file @var{file-number} (either
5503 @samp{1} or @samp{2}), in addition to the normal output.
5506 Fail with an error message if either input file is wrongly ordered.
5508 @item --nocheck-order
5509 Do not check that both input files are in sorted order. This is the default.
5511 @item -e @var{string}
5513 Replace those output fields that are missing in the input with
5517 @itemx --ignore-case
5519 @opindex --ignore-case
5520 Ignore differences in case when comparing keys.
5521 With this option, the lines of the input files must be ordered in the same way.
5522 Use @samp{sort -f} to produce this ordering.
5524 @item -1 @var{field}
5526 Join on field @var{field} (a positive integer) of file 1.
5528 @item -2 @var{field}
5530 Join on field @var{field} (a positive integer) of file 2.
5532 @item -j @var{field}
5533 Equivalent to @option{-1 @var{field} -2 @var{field}}.
5535 @item -o @var{field-list}
5536 Construct each output line according to the format in @var{field-list}.
5537 Each element in @var{field-list} is either the single character @samp{0} or
5538 has the form @var{m.n} where the file number, @var{m}, is @samp{1} or
5539 @samp{2} and @var{n} is a positive field number.
5541 A field specification of @samp{0} denotes the join field.
5542 In most cases, the functionality of the @samp{0} field spec
5543 may be reproduced using the explicit @var{m.n} that corresponds
5544 to the join field. However, when printing unpairable lines
5545 (using either of the @option{-a} or @option{-v} options), there is no way
5546 to specify the join field using @var{m.n} in @var{field-list}
5547 if there are unpairable lines in both files.
5548 To give @command{join} that functionality, @acronym{POSIX} invented the @samp{0}
5549 field specification notation.
5551 The elements in @var{field-list}
5552 are separated by commas or blanks.
5553 Blank separators typically need to be quoted for the shell. For
5554 example, the commands @samp{join -o 1.2,2.2} and @samp{join -o '1.2
5555 2.2'} are equivalent.
5557 All output lines---including those printed because of any -a or -v
5558 option---are subject to the specified @var{field-list}.
5561 Use character @var{char} as the input and output field separator.
5562 Treat as significant each occurrence of @var{char} in the input file.
5563 Use @samp{sort -t @var{char}}, without the @option{-b} option of
5564 @samp{sort}, to produce this ordering.
5566 @item -v @var{file-number}
5567 Print a line for each unpairable line in file @var{file-number}
5568 (either @samp{1} or @samp{2}), instead of the normal output.
5575 @node Operating on characters
5576 @chapter Operating on characters
5578 @cindex operating on characters
5580 This commands operate on individual characters.
5583 * tr invocation:: Translate, squeeze, and/or delete characters.
5584 * expand invocation:: Convert tabs to spaces.
5585 * unexpand invocation:: Convert spaces to tabs.
5590 @section @command{tr}: Translate, squeeze, and/or delete characters
5597 tr [@var{option}]@dots{} @var{set1} [@var{set2}]
5600 @command{tr} copies standard input to standard output, performing
5601 one of the following operations:
5605 translate, and optionally squeeze repeated characters in the result,
5607 squeeze repeated characters,
5611 delete characters, then squeeze repeated characters from the result.
5614 The @var{set1} and (if given) @var{set2} arguments define ordered
5615 sets of characters, referred to below as @var{set1} and @var{set2}. These
5616 sets are the characters of the input that @command{tr} operates on.
5617 The @option{--complement} (@option{-c}, @option{-C}) option replaces
5619 complement (all of the characters that are not in @var{set1}).
5621 Currently @command{tr} fully supports only single-byte characters.
5622 Eventually it will support multibyte characters; when it does, the
5623 @option{-C} option will cause it to complement the set of characters,
5624 whereas @option{-c} will cause it to complement the set of values.
5625 This distinction will matter only when some values are not characters,
5626 and this is possible only in locales using multibyte encodings when
5627 the input contains encoding errors.
5629 The program accepts the @option{--help} and @option{--version}
5630 options. @xref{Common options}. Options must precede operands.
5635 * Character sets:: Specifying sets of characters.
5636 * Translating:: Changing one set of characters to another.
5637 * Squeezing:: Squeezing repeats and deleting.
5641 @node Character sets
5642 @subsection Specifying sets of characters
5644 @cindex specifying sets of characters
5646 The format of the @var{set1} and @var{set2} arguments resembles
5647 the format of regular expressions; however, they are not regular
5648 expressions, only lists of characters. Most characters simply
5649 represent themselves in these strings, but the strings can contain
5650 the shorthands listed below, for convenience. Some of them can be
5651 used only in @var{set1} or @var{set2}, as noted below.
5655 @item Backslash escapes
5656 @cindex backslash escapes
5658 The following backslash escape sequences are recognized:
5676 The character with the value given by @var{ooo}, which is 1 to 3
5682 While a backslash followed by a character not listed above is
5683 interpreted as that character, the backslash also effectively
5684 removes any special significance, so it is useful to escape
5685 @samp{[}, @samp{]}, @samp{*}, and @samp{-}.
5690 The notation @samp{@var{m}-@var{n}} expands to all of the characters
5691 from @var{m} through @var{n}, in ascending order. @var{m} should
5692 collate before @var{n}; if it doesn't, an error results. As an example,
5693 @samp{0-9} is the same as @samp{0123456789}.
5695 @sc{gnu} @command{tr} does not support the System V syntax that uses square
5696 brackets to enclose ranges. Translations specified in that format
5697 sometimes work as expected, since the brackets are often transliterated
5698 to themselves. However, they should be avoided because they sometimes
5699 behave unexpectedly. For example, @samp{tr -d '[0-9]'} deletes brackets
5702 Many historically common and even accepted uses of ranges are not
5703 portable. For example, on @acronym{EBCDIC} hosts using the @samp{A-Z}
5704 range will not do what most would expect because @samp{A} through @samp{Z}
5705 are not contiguous as they are in @acronym{ASCII}.
5706 If you can rely on a @acronym{POSIX} compliant version of @command{tr}, then
5707 the best way to work around this is to use character classes (see below).
5708 Otherwise, it is most portable (and most ugly) to enumerate the members
5711 @item Repeated characters
5712 @cindex repeated characters
5714 The notation @samp{[@var{c}*@var{n}]} in @var{set2} expands to @var{n}
5715 copies of character @var{c}. Thus, @samp{[y*6]} is the same as
5716 @samp{yyyyyy}. The notation @samp{[@var{c}*]} in @var{string2} expands
5717 to as many copies of @var{c} as are needed to make @var{set2} as long as
5718 @var{set1}. If @var{n} begins with @samp{0}, it is interpreted in
5719 octal, otherwise in decimal.
5721 @item Character classes
5722 @cindex character classes
5724 The notation @samp{[:@var{class}:]} expands to all of the characters in
5725 the (predefined) class @var{class}. The characters expand in no
5726 particular order, except for the @code{upper} and @code{lower} classes,
5727 which expand in ascending order. When the @option{--delete} (@option{-d})
5728 and @option{--squeeze-repeats} (@option{-s}) options are both given, any
5729 character class can be used in @var{set2}. Otherwise, only the
5730 character classes @code{lower} and @code{upper} are accepted in
5731 @var{set2}, and then only if the corresponding character class
5732 (@code{upper} and @code{lower}, respectively) is specified in the same
5733 relative position in @var{set1}. Doing this specifies case conversion.
5734 The class names are given below; an error results when an invalid class
5746 Horizontal whitespace.
5755 Printable characters, not including space.
5761 Printable characters, including space.
5764 Punctuation characters.
5767 Horizontal or vertical whitespace.
5776 @item Equivalence classes
5777 @cindex equivalence classes
5779 The syntax @samp{[=@var{c}=]} expands to all of the characters that are
5780 equivalent to @var{c}, in no particular order. Equivalence classes are
5781 a relatively recent invention intended to support non-English alphabets.
5782 But there seems to be no standard way to define them or determine their
5783 contents. Therefore, they are not fully implemented in @sc{gnu} @command{tr};
5784 each character's equivalence class consists only of that character,
5785 which is of no particular use.
5791 @subsection Translating
5793 @cindex translating characters
5795 @command{tr} performs translation when @var{set1} and @var{set2} are
5796 both given and the @option{--delete} (@option{-d}) option is not given.
5797 @command{tr} translates each character of its input that is in @var{set1}
5798 to the corresponding character in @var{set2}. Characters not in
5799 @var{set1} are passed through unchanged. When a character appears more
5800 than once in @var{set1} and the corresponding characters in @var{set2}
5801 are not all the same, only the final one is used. For example, these
5802 two commands are equivalent:
5809 A common use of @command{tr} is to convert lowercase characters to
5810 uppercase. This can be done in many ways. Here are three of them:
5813 tr abcdefghijklmnopqrstuvwxyz ABCDEFGHIJKLMNOPQRSTUVWXYZ
5815 tr '[:lower:]' '[:upper:]'
5819 But note that using ranges like @code{a-z} above is not portable.
5821 When @command{tr} is performing translation, @var{set1} and @var{set2}
5822 typically have the same length. If @var{set1} is shorter than
5823 @var{set2}, the extra characters at the end of @var{set2} are ignored.
5825 On the other hand, making @var{set1} longer than @var{set2} is not
5826 portable; @acronym{POSIX} says that the result is undefined. In this situation,
5827 BSD @command{tr} pads @var{set2} to the length of @var{set1} by repeating
5828 the last character of @var{set2} as many times as necessary. System V
5829 @command{tr} truncates @var{set1} to the length of @var{set2}.
5831 By default, @sc{gnu} @command{tr} handles this case like BSD @command{tr}.
5832 When the @option{--truncate-set1} (@option{-t}) option is given,
5833 @sc{gnu} @command{tr} handles this case like the System V @command{tr}
5834 instead. This option is ignored for operations other than translation.
5836 Acting like System V @command{tr} in this case breaks the relatively common
5840 tr -cs A-Za-z0-9 '\012'
5844 because it converts only zero bytes (the first element in the
5845 complement of @var{set1}), rather than all non-alphanumerics, to
5849 By the way, the above idiom is not portable because it uses ranges, and
5850 it assumes that the octal code for newline is 012.
5851 Assuming a @acronym{POSIX} compliant @command{tr}, here is a better way to write it:
5854 tr -cs '[:alnum:]' '[\n*]'
5859 @subsection Squeezing repeats and deleting
5861 @cindex squeezing repeat characters
5862 @cindex deleting characters
5864 When given just the @option{--delete} (@option{-d}) option, @command{tr}
5865 removes any input characters that are in @var{set1}.
5867 When given just the @option{--squeeze-repeats} (@option{-s}) option,
5868 @command{tr} replaces each input sequence of a repeated character that
5869 is in @var{set1} with a single occurrence of that character.
5871 When given both @option{--delete} and @option{--squeeze-repeats}, @command{tr}
5872 first performs any deletions using @var{set1}, then squeezes repeats
5873 from any remaining characters using @var{set2}.
5875 The @option{--squeeze-repeats} option may also be used when translating,
5876 in which case @command{tr} first performs translation, then squeezes
5877 repeats from any remaining characters using @var{set2}.
5879 Here are some examples to illustrate various combinations of options:
5884 Remove all zero bytes:
5891 Put all words on lines by themselves. This converts all
5892 non-alphanumeric characters to newlines, then squeezes each string
5893 of repeated newlines into a single newline:
5896 tr -cs '[:alnum:]' '[\n*]'
5900 Convert each sequence of repeated newlines to a single newline:
5907 Find doubled occurrences of words in a document.
5908 @c Separate the following two "the"s, so typo checkers don't complain.
5909 For example, people often write ``the @w{}the'' with the repeated words
5910 separated by a newline. The Bourne shell script below works first
5911 by converting each sequence of punctuation and blank characters to a
5912 single newline. That puts each ``word'' on a line by itself.
5913 Next it maps all uppercase characters to lower case, and finally it
5914 runs @command{uniq} with the @option{-d} option to print out only the words
5920 | tr -s '[:punct:][:blank:]' '[\n*]' \
5921 | tr '[:upper:]' '[:lower:]' \
5926 Deleting a small set of characters is usually straightforward. For example,
5927 to remove all @samp{a}s, @samp{x}s, and @samp{M}s you would do this:
5933 However, when @samp{-} is one of those characters, it can be tricky because
5934 @samp{-} has special meanings. Performing the same task as above but also
5935 removing all @samp{-} characters, we might try @code{tr -d -axM}, but
5936 that would fail because @command{tr} would try to interpret @option{-a} as
5937 a command-line option. Alternatively, we could try putting the hyphen
5938 inside the string, @code{tr -d a-xM}, but that wouldn't work either because
5939 it would make @command{tr} interpret @code{a-x} as the range of characters
5940 @samp{a}@dots{}@samp{x} rather than the three.
5941 One way to solve the problem is to put the hyphen at the end of the list
5948 Or you can use @samp{--} to terminate option processing:
5954 More generally, use the character class notation @code{[=c=]}
5955 with @samp{-} (or any other character) in place of the @samp{c}:
5961 Note how single quotes are used in the above example to protect the
5962 square brackets from interpretation by a shell.
5967 @node expand invocation
5968 @section @command{expand}: Convert tabs to spaces
5971 @cindex tabs to spaces, converting
5972 @cindex converting tabs to spaces
5974 @command{expand} writes the contents of each given @var{file}, or standard
5975 input if none are given or for a @var{file} of @samp{-}, to standard
5976 output, with tab characters converted to the appropriate number of
5980 expand [@var{option}]@dots{} [@var{file}]@dots{}
5983 By default, @command{expand} converts all tabs to spaces. It preserves
5984 backspace characters in the output; they decrement the column count for
5985 tab calculations. The default action is equivalent to @option{-t 8} (set
5986 tabs every 8 columns).
5988 The program accepts the following options. Also see @ref{Common options}.
5992 @item -t @var{tab1}[,@var{tab2}]@dots{}
5993 @itemx --tabs=@var{tab1}[,@var{tab2}]@dots{}
5996 @cindex tab stops, setting
5997 If only one tab stop is given, set the tabs @var{tab1} spaces apart
5998 (default is 8). Otherwise, set the tabs at columns @var{tab1},
5999 @var{tab2}, @dots{} (numbered from 0), and replace any tabs beyond the
6000 last tab stop given with single spaces. Tab stops can be separated by
6001 blanks as well as by commas.
6003 For compatibility, GNU @command{expand} also accepts the obsolete
6004 option syntax, @option{-@var{t1}[,@var{t2}]@dots{}}. New scripts
6005 should use @option{-t @var{t1}[,@var{t2}]@dots{}} instead.
6011 @cindex initial tabs, converting
6012 Only convert initial tabs (those that precede all non-space or non-tab
6013 characters) on each line to spaces.
6020 @node unexpand invocation
6021 @section @command{unexpand}: Convert spaces to tabs
6025 @command{unexpand} writes the contents of each given @var{file}, or
6026 standard input if none are given or for a @var{file} of @samp{-}, to
6027 standard output, converting blanks at the beginning of each line into
6028 as many tab characters as needed. In the default @acronym{POSIX}
6029 locale, a @dfn{blank} is a space or a tab; other locales may specify
6030 additional blank characters. Synopsis:
6033 unexpand [@var{option}]@dots{} [@var{file}]@dots{}
6036 By default, @command{unexpand} converts only initial blanks (those
6037 that precede all non-blank characters) on each line. It
6038 preserves backspace characters in the output; they decrement the column
6039 count for tab calculations. By default, tabs are set at every 8th
6042 The program accepts the following options. Also see @ref{Common options}.
6046 @item -t @var{tab1}[,@var{tab2}]@dots{}
6047 @itemx --tabs=@var{tab1}[,@var{tab2}]@dots{}
6050 If only one tab stop is given, set the tabs @var{tab1} columns apart
6051 instead of the default 8. Otherwise, set the tabs at columns
6052 @var{tab1}, @var{tab2}, @dots{} (numbered from 0), and leave blanks
6053 beyond the tab stops given unchanged. Tab stops can be separated by
6054 blanks as well as by commas. This option implies the @option{-a} option.
6056 For compatibility, GNU @command{unexpand} supports the obsolete option syntax,
6057 @option{-@var{tab1}[,@var{tab2}]@dots{}}, where tab stops must be
6058 separated by commas. (Unlike @option{-t}, this obsolete option does
6059 not imply @option{-a}.) New scripts should use @option{--first-only -t
6060 @var{tab1}[,@var{tab2}]@dots{}} instead.
6066 Also convert all sequences of two or more blanks just before a tab stop,
6067 even if they occur after non-blank characters in a line.
6074 @node Directory listing
6075 @chapter Directory listing
6077 This chapter describes the @command{ls} command and its variants @command{dir}
6078 and @command{vdir}, which list information about files.
6081 * ls invocation:: List directory contents.
6082 * dir invocation:: Briefly ls.
6083 * vdir invocation:: Verbosely ls.
6084 * dircolors invocation:: Color setup for ls, etc.
6089 @section @command{ls}: List directory contents
6092 @cindex directory listing
6094 The @command{ls} program lists information about files (of any type,
6095 including directories). Options and file arguments can be intermixed
6096 arbitrarily, as usual.
6098 For non-option command-line arguments that are directories, by default
6099 @command{ls} lists the contents of directories, not recursively, and
6100 omitting files with names beginning with @samp{.}. For other non-option
6101 arguments, by default @command{ls} lists just the file name. If no
6102 non-option argument is specified, @command{ls} operates on the current
6103 directory, acting as if it had been invoked with a single argument of @samp{.}.
6106 By default, the output is sorted alphabetically, according to the locale
6107 settings in effect.@footnote{If you use a non-@acronym{POSIX}
6108 locale (e.g., by setting @env{LC_ALL} to @samp{en_US}), then @command{ls} may
6109 produce output that is sorted differently than you're accustomed to.
6110 In that case, set the @env{LC_ALL} environment variable to @samp{C}.}
6111 If standard output is
6112 a terminal, the output is in columns (sorted vertically) and control
6113 characters are output as question marks; otherwise, the output is listed
6114 one per line and control characters are output as-is.
6116 Because @command{ls} is such a fundamental program, it has accumulated many
6117 options over the years. They are described in the subsections below;
6118 within each section, options are listed alphabetically (ignoring case).
6119 The division of options into the subsections is not absolute, since some
6120 options affect more than one aspect of @command{ls}'s operation.
6122 @cindex exit status of @command{ls}
6127 1 minor problems (e.g., failure to access a file or directory not
6128 specified as a command line argument. This happens when listing a
6129 directory in which entries are actively being removed or renamed.)
6130 2 serious trouble (e.g., memory exhausted, invalid option or failure
6131 to access file or directory specified as a command line argument)
6134 Also see @ref{Common options}.
6137 * Which files are listed::
6138 * What information is listed::
6139 * Sorting the output::
6140 * More details about version sort::
6141 * General output formatting::
6142 * Formatting file timestamps::
6143 * Formatting the file names::
6147 @node Which files are listed
6148 @subsection Which files are listed
6150 These options determine which files @command{ls} lists information for.
6151 By default, @command{ls} lists files and the contents of any
6152 directories on the command line, except that in directories it ignores
6153 files whose names start with @samp{.}.
6161 In directories, do not ignore file names that start with @samp{.}.
6166 @opindex --almost-all
6167 In directories, do not ignore all file names that start with @samp{.};
6168 ignore only @file{.} and @file{..}. The @option{--all} (@option{-a})
6169 option overrides this option.
6172 @itemx --ignore-backups
6174 @opindex --ignore-backups
6175 @cindex backup files, ignoring
6176 In directories, ignore files that end with @samp{~}. This option is
6177 equivalent to @samp{--ignore='*~' --ignore='.*~'}.
6182 @opindex --directory
6183 List just the names of directories, as with other types of files, rather
6184 than listing their contents.
6185 @c The following sentence is the same as the one for -F.
6186 Do not follow symbolic links listed on the
6187 command line unless the @option{--dereference-command-line} (@option{-H}),
6188 @option{--dereference} (@option{-L}), or
6189 @option{--dereference-command-line-symlink-to-dir} options are specified.
6192 @itemx --dereference-command-line
6194 @opindex --dereference-command-line
6195 @cindex symbolic links, dereferencing
6196 If a command line argument specifies a symbolic link, show information
6197 for the file the link references rather than for the link itself.
6199 @itemx --dereference-command-line-symlink-to-dir
6200 @opindex --dereference-command-line-symlink-to-dir
6201 @cindex symbolic links, dereferencing
6202 Do not dereference symbolic links, with one exception:
6203 if a command line argument specifies a symbolic link that refers to
6204 a directory, show information for that directory rather than for the
6206 This is the default behavior when no other dereferencing-related
6207 option has been specified (@option{--classify} (@option{-F}),
6208 @option{--directory} (@option{-d}),
6210 @option{--dereference} (@option{-L}), or
6211 @option{--dereference-command-line} (@option{-H})).
6213 @item --group-directories-first
6214 @opindex --group-directories-first
6215 Group all the directories before the files and then sort the
6216 directories and the files separately using the selected sort key
6217 (see --sort option).
6218 That is, this option specifies a primary sort key,
6219 and the --sort option specifies a secondary key.
6220 However, any use of @option{--sort=none}
6221 (@option{-U}) disables this option altogether.
6223 @item --hide=PATTERN
6224 @opindex --hide=@var{pattern}
6225 In directories, ignore files whose names match the shell pattern
6226 @var{pattern}, unless the @option{--all} (@option{-a}) or
6227 @option{--almost-all} (@option{-A}) is also given. This
6228 option acts like @option{--ignore=@var{pattern}} except that it has no
6229 effect if @option{--all} (@option{-a}) or @option{--almost-all}
6230 (@option{-A}) is also given.
6232 This option can be useful in shell aliases. For example, if
6233 @command{lx} is an alias for @samp{ls --hide='*~'} and @command{ly} is
6234 an alias for @samp{ls --ignore='*~'}, then the command @samp{lx -A}
6235 lists the file @file{README~} even though @samp{ly -A} would not.
6237 @item -I @var{pattern}
6238 @itemx --ignore=@var{pattern}
6240 @opindex --ignore=@var{pattern}
6241 In directories, ignore files whose names match the shell pattern
6242 (not regular expression) @var{pattern}. As
6243 in the shell, an initial @samp{.} in a file name does not match a
6244 wildcard at the start of @var{pattern}. Sometimes it is useful
6245 to give this option several times. For example,
6248 $ ls --ignore='.??*' --ignore='.[^.]' --ignore='#*'
6251 The first option ignores names of length 3 or more that start with @samp{.},
6252 the second ignores all two-character names that start with @samp{.}
6253 except @samp{..}, and the third ignores names that start with @samp{#}.
6256 @itemx --dereference
6258 @opindex --dereference
6259 @cindex symbolic links, dereferencing
6260 When showing file information for a symbolic link, show information
6261 for the file the link references rather than the link itself.
6262 However, even with this option, @command{ls} still prints the name
6263 of the link itself, not the name of the file that the link points to.
6268 @opindex --recursive
6269 @cindex recursive directory listing
6270 @cindex directory listing, recursive
6271 List the contents of all directories recursively.
6276 @node What information is listed
6277 @subsection What information is listed
6279 These options affect the information that @command{ls} displays. By
6280 default, only file names are shown.
6286 @cindex hurd, author, printing
6287 List each file's author when producing long format directory listings.
6288 In GNU/Hurd, file authors can differ from their owners, but in other
6289 operating systems the two are the same.
6295 @cindex dired Emacs mode support
6296 With the long listing (@option{-l}) format, print an additional line after
6300 //DIRED// @var{beg1} @var{end1} @var{beg2} @var{end2} @dots{}
6304 The @var{begn} and @var{endn} are unsigned integers that record the
6305 byte position of the beginning and end of each file name in the output.
6306 This makes it easy for Emacs to find the names, even when they contain
6307 unusual characters such as space or newline, without fancy searching.
6309 If directories are being listed recursively (@option{-R}), output a similar
6310 line with offsets for each subdirectory name:
6313 //SUBDIRED// @var{beg1} @var{end1} @dots{}
6316 Finally, output a line of the form:
6319 //DIRED-OPTIONS// --quoting-style=@var{word}
6323 where @var{word} is the quoting style (@pxref{Formatting the file names}).
6325 Here is an actual example:
6328 $ mkdir -p a/sub/deeper a/sub2
6330 $ touch a/sub/deeper/file
6331 $ ls -gloRF --dired a
6334 -rw-r--r-- 1 0 Jun 10 12:27 f1
6335 -rw-r--r-- 1 0 Jun 10 12:27 f2
6336 drwxr-xr-x 3 4096 Jun 10 12:27 sub/
6337 drwxr-xr-x 2 4096 Jun 10 12:27 sub2/
6341 drwxr-xr-x 2 4096 Jun 10 12:27 deeper/
6345 -rw-r--r-- 1 0 Jun 10 12:27 file
6349 //DIRED// 48 50 84 86 120 123 158 162 217 223 282 286
6350 //SUBDIRED// 2 3 167 172 228 240 290 296
6351 //DIRED-OPTIONS// --quoting-style=literal
6354 Note that the pairs of offsets on the @samp{//DIRED//} line above delimit
6355 these names: @file{f1}, @file{f2}, @file{sub}, @file{sub2}, @file{deeper},
6357 The offsets on the @samp{//SUBDIRED//} line delimit the following
6358 directory names: @file{a}, @file{a/sub}, @file{a/sub/deeper}, @file{a/sub2}.
6360 Here is an example of how to extract the fifth entry name, @samp{deeper},
6361 corresponding to the pair of offsets, 222 and 228:
6364 $ ls -gloRF --dired a > out
6365 $ dd bs=1 skip=222 count=6 < out 2>/dev/null; echo
6369 Note that although the listing above includes a trailing slash
6370 for the @samp{deeper} entry, the offsets select the name without
6371 the trailing slash. However, if you invoke @command{ls} with @option{--dired}
6372 along with an option like @option{--escape} (aka @option{-b}) and operate
6373 on a file whose name contains special characters, notice that the backslash
6378 $ ls -blog --dired 'a b'
6379 -rw-r--r-- 1 0 Jun 10 12:28 a\ b
6381 //DIRED-OPTIONS// --quoting-style=escape
6384 If you use a quoting style that adds quote marks
6385 (e.g., @option{--quoting-style=c}), then the offsets include the quote marks.
6386 So beware that the user may select the quoting style via the environment
6387 variable @env{QUOTING_STYLE}. Hence, applications using @option{--dired}
6388 should either specify an explicit @option{--quoting-style=literal} option
6389 (aka @option{-N} or @option{--literal}) on the command line, or else be
6390 prepared to parse the escaped names.
6393 @opindex --full-time
6394 Produce long format directory listings, and list times in full. It is
6395 equivalent to using @option{--format=long} with
6396 @option{--time-style=full-iso} (@pxref{Formatting file timestamps}).
6400 Produce long format directory listings, but don't display owner information.
6406 Inhibit display of group information in a long format directory listing.
6407 (This is the default in some non-@sc{gnu} versions of @command{ls}, so we
6408 provide this option for compatibility.)
6416 @cindex inode number, printing
6417 Print the inode number (also called the file serial number and index
6418 number) of each file to the left of the file name. (This number
6419 uniquely identifies each file within a particular file system.)
6422 @itemx --format=long
6423 @itemx --format=verbose
6426 @opindex long ls @r{format}
6427 @opindex verbose ls @r{format}
6428 In addition to the name of each file, print the file type, file mode bits,
6429 number of hard links, owner name, group name, size, and
6430 timestamp (@pxref{Formatting file timestamps}), normally
6431 the modification time. Print question marks for information that
6432 cannot be determined.
6434 Normally the size is printed as a byte count without punctuation, but
6435 this can be overridden (@pxref{Block size}). For example, @option{-h}
6436 prints an abbreviated, human-readable count, and
6437 @samp{--block-size="'1"} prints a byte count with the thousands
6438 separator of the current locale.
6440 For each directory that is listed, preface the files with a line
6441 @samp{total @var{blocks}}, where @var{blocks} is the total disk allocation
6442 for all files in that directory. The block size currently defaults to 1024
6443 bytes, but this can be overridden (@pxref{Block size}).
6444 The @var{blocks} computed counts each hard link separately;
6445 this is arguably a deficiency.
6447 The file type is one of the following characters:
6449 @c The commented-out entries are ones we're not sure about.
6457 character special file
6459 high performance (``contiguous data'') file
6463 door (Solaris 2.5 and up)
6465 @c semaphore, if this is a distinct file type
6469 @c multiplexed file (7th edition Unix; obsolete)
6471 off-line (``migrated'') file (Cray DMF)
6473 network special file (HP-UX)
6477 port (Solaris 10 and up)
6479 @c message queue, if this is a distinct file type
6483 @c shared memory object, if this is a distinct file type
6485 @c typed memory object, if this is a distinct file type
6487 @c whiteout (4.4BSD; not implemented)
6489 some other file type
6492 @cindex permissions, output by @command{ls}
6493 The file mode bits listed are similar to symbolic mode specifications
6494 (@pxref{Symbolic Modes}). But @command{ls} combines multiple bits into the
6495 third character of each set of permissions as follows:
6499 If the set-user-ID or set-group-ID bit and the corresponding executable bit
6503 If the set-user-ID or set-group-ID bit is set but the corresponding
6504 executable bit is not set.
6507 If the restricted deletion flag or sticky bit, and the
6508 other-executable bit, are both set. The restricted deletion flag is
6509 another name for the sticky bit. @xref{Mode Structure}.
6512 If the restricted deletion flag or sticky bit is set but the
6513 other-executable bit is not set.
6516 If the executable bit is set and none of the above apply.
6522 Following the file mode bits is a single character that specifies
6523 whether an alternate access method such as an access control list
6524 applies to the file. When the character following the file mode bits is a
6525 space, there is no alternate access method. When it is a printing
6526 character, then there is such a method.
6528 GNU @command{ls} uses a @samp{.} character to indicate a file
6529 with an SELinux security context, but no other alternate access method.
6531 A file with any other combination of alternate access methods
6532 is marked with a @samp{+} character.
6535 @itemx --numeric-uid-gid
6537 @opindex --numeric-uid-gid
6538 @cindex numeric uid and gid
6539 @cindex numeric user and group IDs
6540 Produce long format directory listings, but
6541 display numeric user and group IDs instead of the owner and group names.
6545 Produce long format directory listings, but don't display group information.
6546 It is equivalent to using @option{--format=long} with @option{--no-group} .
6552 @cindex disk allocation
6553 @cindex size of files, reporting
6554 Print the disk allocation of each file to the left of the file name.
6555 This is the amount of disk space used by the file, which is usually a
6556 bit more than the file's size, but it can be less if the file has holes.
6558 Normally the disk allocation is printed in units of
6559 1024 bytes, but this can be overridden (@pxref{Block size}).
6561 @cindex NFS mounts from BSD to HP-UX
6562 For files that are NFS-mounted from an HP-UX system to a BSD system,
6563 this option reports sizes that are half the correct values. On HP-UX
6564 systems, it reports sizes that are twice the correct values for files
6565 that are NFS-mounted from BSD systems. This is due to a flaw in HP-UX;
6566 it also affects the HP-UX @command{ls} program.
6575 @cindex security context
6576 Display the SELinux security context or @samp{?} if none is found.
6577 When used with the @option{-l} option, print the security context
6578 to the left of the size column.
6583 @node Sorting the output
6584 @subsection Sorting the output
6586 @cindex sorting @command{ls} output
6587 These options change the order in which @command{ls} sorts the information
6588 it outputs. By default, sorting is done by character code
6589 (e.g., @acronym{ASCII} order).
6595 @itemx --time=status
6598 @opindex ctime@r{, printing or sorting by}
6599 @opindex status time@r{, printing or sorting by}
6600 @opindex use time@r{, printing or sorting files by}
6601 If the long listing format (e.g., @option{-l}, @option{-o}) is being used,
6602 print the status change time (the @samp{ctime} in the inode) instead of
6603 the modification time.
6604 When explicitly sorting by time (@option{--sort=time} or @option{-t})
6605 or when not using a long listing format,
6606 sort according to the status change time.
6610 @cindex unsorted directory listing
6611 @cindex directory order, listing by
6612 Primarily, like @option{-U}---do not sort; list the files in whatever
6613 order they are stored in the directory. But also enable @option{-a} (list
6614 all files) and disable @option{-l}, @option{--color}, and @option{-s} (if they
6615 were specified before the @option{-f}).
6621 @cindex reverse sorting
6622 Reverse whatever the sorting method is---e.g., list files in reverse
6623 alphabetical order, youngest first, smallest first, or whatever.
6629 @opindex size of files@r{, sorting files by}
6630 Sort by file size, largest first.
6636 @opindex modification time@r{, sorting files by}
6637 Sort by modification time (the @samp{mtime} in the inode), newest first.
6641 @itemx --time=access
6645 @opindex use time@r{, printing or sorting files by}
6646 @opindex atime@r{, printing or sorting files by}
6647 @opindex access time@r{, printing or sorting files by}
6648 If the long listing format (e.g., @option{--format=long}) is being used,
6649 print the last access time (the @samp{atime} in the inode).
6650 When explicitly sorting by time (@option{--sort=time} or @option{-t})
6651 or when not using a long listing format, sort according to the access time.
6657 @opindex none@r{, sorting option for @command{ls}}
6658 Do not sort; list the files in whatever order they are
6659 stored in the directory. (Do not do any of the other unrelated things
6660 that @option{-f} does.) This is especially useful when listing very large
6661 directories, since not doing any sorting can be noticeably faster.
6664 @itemx --sort=version
6667 @opindex version@r{, sorting option for @command{ls}}
6668 Sort by version name and number, lowest first. It behaves like a default
6669 sort, except that each sequence of decimal digits is treated numerically
6670 as an index/version number. (@xref{More details about version sort}.)
6673 @itemx --sort=extension
6676 @opindex extension@r{, sorting files by}
6677 Sort directory contents alphabetically by file extension (characters
6678 after the last @samp{.}); files with no extension are sorted first.
6683 @node More details about version sort
6684 @subsection More details about version sort
6686 The version sort takes into account the fact that file names frequently include
6687 indices or version numbers. Standard sorting functions usually do not produce
6688 the ordering that people expect because comparisons are made on a
6689 character-by-character basis. The version
6690 sort addresses this problem, and is especially useful when browsing
6691 directories that contain many files with indices/version numbers in their
6696 foo.zml-1.gz foo.zml-1.gz
6697 foo.zml-100.gz foo.zml-2.gz
6698 foo.zml-12.gz foo.zml-6.gz
6699 foo.zml-13.gz foo.zml-12.gz
6700 foo.zml-2.gz foo.zml-13.gz
6701 foo.zml-25.gz foo.zml-25.gz
6702 foo.zml-6.gz foo.zml-100.gz
6705 Version-sorted strings are compared such that if @var{ver1} and @var{ver2}
6706 are version numbers and @var{prefix} and @var{suffix} (@var{suffix} matching
6707 the regular expression @samp{(\.[A-Za-z~][A-Za-z0-9~]*)*}) are strings then
6708 @var{ver1} < @var{ver2} implies that the name composed of
6709 ``@var{prefix} @var{ver1} @var{suffix}'' sorts before
6710 ``@var{prefix} @var{ver2} @var{suffix}''.
6712 Note also that leading zeros of numeric parts are ignored:
6716 abc-1.007.tgz abc-1.01a.tgz
6717 abc-1.012b.tgz abc-1.007.tgz
6718 abc-1.01a.tgz abc-1.012b.tgz
6721 This functionality is implemented using gnulib's @code{filevercmp} function.
6722 One result of that implementation decision is that @samp{ls -v}
6723 and @samp{sort -V} do not use the locale category, @env{LC_COLLATE},
6724 which means non-numeric prefixes are sorted as if @env{LC_COLLATE} were set
6727 @node General output formatting
6728 @subsection General output formatting
6730 These options affect the appearance of the overall output.
6735 @itemx --format=single-column
6738 @opindex single-column @r{output of files}
6739 List one file per line. This is the default for @command{ls} when standard
6740 output is not a terminal.
6743 @itemx --format=vertical
6746 @opindex vertical @r{sorted files in columns}
6747 List files in columns, sorted vertically. This is the default for
6748 @command{ls} if standard output is a terminal. It is always the default
6749 for the @command{dir} program.
6750 @sc{gnu} @command{ls} uses variable width columns to display as many files as
6751 possible in the fewest lines.
6753 @item --color [=@var{when}]
6755 @cindex color, distinguishing file types with
6756 Specify whether to use color for distinguishing file types. @var{when}
6757 may be omitted, or one of:
6760 @vindex none @r{color option}
6761 - Do not use color at all. This is the default.
6763 @vindex auto @r{color option}
6764 @cindex terminal, using color iff
6765 - Only use color if standard output is a terminal.
6767 @vindex always @r{color option}
6770 Specifying @option{--color} and no @var{when} is equivalent to
6771 @option{--color=always}.
6772 Piping a colorized listing through a pager like @command{more} or
6773 @command{less} usually produces unreadable results. However, using
6774 @code{more -f} does seem to work.
6778 @itemx --indicator-style=classify
6781 @opindex --indicator-style
6782 @cindex file type and executables, marking
6783 @cindex executables and file type, marking
6784 Append a character to each file name indicating the file type. Also,
6785 for regular files that are executable, append @samp{*}. The file type
6786 indicators are @samp{/} for directories, @samp{@@} for symbolic links,
6787 @samp{|} for FIFOs, @samp{=} for sockets, @samp{>} for doors,
6788 and nothing for regular files.
6789 @c The following sentence is the same as the one for -d.
6790 Do not follow symbolic links listed on the
6791 command line unless the @option{--dereference-command-line} (@option{-H}),
6792 @option{--dereference} (@option{-L}), or
6793 @option{--dereference-command-line-symlink-to-dir} options are specified.
6796 @itemx --indicator-style=file-type
6797 @opindex --file-type
6798 @opindex --indicator-style
6799 @cindex file type, marking
6800 Append a character to each file name indicating the file type. This is
6801 like @option{-F}, except that executables are not marked.
6803 @item --indicator-style=@var{word}
6804 @opindex --indicator-style
6805 Append a character indicator with style @var{word} to entry names,
6810 Do not append any character indicator; this is the default.
6812 Append @samp{/} for directories. This is the same as the @option{-p}
6815 Append @samp{/} for directories, @samp{@@} for symbolic links, @samp{|}
6816 for FIFOs, @samp{=} for sockets, and nothing for regular files. This is
6817 the same as the @option{--file-type} option.
6819 Append @samp{*} for executable regular files, otherwise behave as for
6820 @samp{file-type}. This is the same as the @option{-F} or
6821 @option{--classify} option.
6826 Print file sizes in 1024-byte blocks, overriding the default block
6827 size (@pxref{Block size}).
6828 This option is equivalent to @option{--block-size=1K}.
6831 @itemx --format=commas
6834 @opindex commas@r{, outputting between files}
6835 List files horizontally, with as many as will fit on each line,
6836 separated by @samp{, } (a comma and a space).
6839 @itemx --indicator-style=slash
6841 @opindex --indicator-style
6842 @cindex file type, marking
6843 Append a @samp{/} to directory names.
6846 @itemx --format=across
6847 @itemx --format=horizontal
6850 @opindex across@r{, listing files}
6851 @opindex horizontal@r{, listing files}
6852 List the files in columns, sorted horizontally.
6855 @itemx --tabsize=@var{cols}
6858 Assume that each tab stop is @var{cols} columns wide. The default is 8.
6859 @command{ls} uses tabs where possible in the output, for efficiency. If
6860 @var{cols} is zero, do not use tabs at all.
6862 @c FIXME: remove in 2009, if Apple Terminal has been fixed for long enough.
6863 Some terminal emulators (at least Apple Terminal 1.5 (133) from Mac OS X 10.4.8)
6864 do not properly align columns to the right of a TAB following a
6865 non-@acronym{ASCII} byte. If you use such a terminal emulator, use the
6866 @option{-T0} option or put @code{TABSIZE=0} in your environment to tell
6867 @command{ls} to align using spaces, not tabs.
6870 @itemx --width=@var{cols}
6874 Assume the screen is @var{cols} columns wide. The default is taken
6875 from the terminal settings if possible; otherwise the environment
6876 variable @env{COLUMNS} is used if it is set; otherwise the default
6882 @node Formatting file timestamps
6883 @subsection Formatting file timestamps
6885 By default, file timestamps are listed in abbreviated form. Most
6886 locales use a timestamp like @samp{2002-03-30 23:45}. However, the
6887 default @acronym{POSIX} locale uses a date like @samp{Mar 30@ @ 2002}
6888 for non-recent timestamps, and a date-without-year and time like
6889 @samp{Mar 30 23:45} for recent timestamps.
6891 A timestamp is considered to be @dfn{recent} if it is less than six
6892 months old, and is not dated in the future. If a timestamp dated
6893 today is not listed in recent form, the timestamp is in the future,
6894 which means you probably have clock skew problems which may break
6895 programs like @command{make} that rely on file timestamps.
6898 Time stamps are listed according to the time zone rules specified by
6899 the @env{TZ} environment variable, or by the system default rules if
6900 @env{TZ} is not set. @xref{TZ Variable,, Specifying the Time Zone
6901 with @env{TZ}, libc, The GNU C Library Reference Manual}.
6903 The following option changes how file timestamps are printed.
6906 @item --time-style=@var{style}
6907 @opindex --time-style
6909 List timestamps in style @var{style}. The @var{style} should
6910 be one of the following:
6915 List timestamps using @var{format}, where @var{format} is interpreted
6916 like the format argument of @command{date} (@pxref{date invocation}).
6917 For example, @option{--time-style="+%Y-%m-%d %H:%M:%S"} causes
6918 @command{ls} to list timestamps like @samp{2002-03-30 23:45:56}. As
6919 with @command{date}, @var{format}'s interpretation is affected by the
6920 @env{LC_TIME} locale category.
6922 If @var{format} contains two format strings separated by a newline,
6923 the former is used for non-recent files and the latter for recent
6924 files; if you want output columns to line up, you may need to insert
6925 spaces in one of the two formats.
6928 List timestamps in full using @acronym{ISO} 8601 date, time, and time zone
6929 format with nanosecond precision, e.g., @samp{2002-03-30
6930 23:45:56.477817180 -0700}. This style is equivalent to
6931 @samp{+%Y-%m-%d %H:%M:%S.%N %z}.
6933 This is useful because the time output includes all the information that
6934 is available from the operating system. For example, this can help
6935 explain @command{make}'s behavior, since @acronym{GNU} @command{make}
6936 uses the full timestamp to determine whether a file is out of date.
6939 List @acronym{ISO} 8601 date and time in minutes, e.g.,
6940 @samp{2002-03-30 23:45}. These timestamps are shorter than
6941 @samp{full-iso} timestamps, and are usually good enough for everyday
6942 work. This style is equivalent to @samp{+%Y-%m-%d %H:%M}.
6945 List @acronym{ISO} 8601 dates for non-recent timestamps (e.g.,
6946 @samp{2002-03-30@ }), and @acronym{ISO} 8601 month, day, hour, and
6947 minute for recent timestamps (e.g., @samp{03-30 23:45}). These
6948 timestamps are uglier than @samp{long-iso} timestamps, but they carry
6949 nearly the same information in a smaller space and their brevity helps
6950 @command{ls} output fit within traditional 80-column output lines.
6951 The following two @command{ls} invocations are equivalent:
6956 ls -l --time-style="+%Y-%m-%d $newline%m-%d %H:%M"
6957 ls -l --time-style="iso"
6962 List timestamps in a locale-dependent form. For example, a Finnish
6963 locale might list non-recent timestamps like @samp{maalis 30@ @ 2002}
6964 and recent timestamps like @samp{maalis 30 23:45}. Locale-dependent
6965 timestamps typically consume more space than @samp{iso} timestamps and
6966 are harder for programs to parse because locale conventions vary so
6967 widely, but they are easier for many people to read.
6969 The @env{LC_TIME} locale category specifies the timestamp format. The
6970 default @acronym{POSIX} locale uses timestamps like @samp{Mar 30@
6971 @ 2002} and @samp{Mar 30 23:45}; in this locale, the following two
6972 @command{ls} invocations are equivalent:
6977 ls -l --time-style="+%b %e %Y$newline%b %e %H:%M"
6978 ls -l --time-style="locale"
6981 Other locales behave differently. For example, in a German locale,
6982 @option{--time-style="locale"} might be equivalent to
6983 @option{--time-style="+%e. %b %Y $newline%e. %b %H:%M"}
6984 and might generate timestamps like @samp{30. M@"ar 2002@ } and
6985 @samp{30. M@"ar 23:45}.
6987 @item posix-@var{style}
6989 List @acronym{POSIX}-locale timestamps if the @env{LC_TIME} locale
6990 category is @acronym{POSIX}, @var{style} timestamps otherwise. For
6991 example, the @samp{posix-long-iso} style lists
6992 timestamps like @samp{Mar 30@ @ 2002} and @samp{Mar 30 23:45} when in
6993 the @acronym{POSIX} locale, and like @samp{2002-03-30 23:45} otherwise.
6998 You can specify the default value of the @option{--time-style} option
6999 with the environment variable @env{TIME_STYLE}; if @env{TIME_STYLE} is not set
7000 the default style is @samp{locale}. @acronym{GNU} Emacs 21.3 and
7001 later use the @option{--dired} option and therefore can parse any date
7002 format, but if you are using Emacs 21.1 or 21.2 and specify a
7003 non-@acronym{POSIX} locale you may need to set
7004 @samp{TIME_STYLE="posix-long-iso"}.
7006 To avoid certain denial-of-service attacks, timestamps that would be
7007 longer than 1000 bytes may be treated as errors.
7010 @node Formatting the file names
7011 @subsection Formatting the file names
7013 These options change how file names themselves are printed.
7019 @itemx --quoting-style=escape
7022 @opindex --quoting-style
7023 @cindex backslash sequences for file names
7024 Quote nongraphic characters in file names using alphabetic and octal
7025 backslash sequences like those used in C.
7029 @itemx --quoting-style=literal
7032 @opindex --quoting-style
7033 Do not quote file names. However, with @command{ls} nongraphic
7034 characters are still printed as question marks if the output is a
7035 terminal and you do not specify the @option{--show-control-chars}
7039 @itemx --hide-control-chars
7041 @opindex --hide-control-chars
7042 Print question marks instead of nongraphic characters in file names.
7043 This is the default if the output is a terminal and the program is
7048 @itemx --quoting-style=c
7050 @opindex --quote-name
7051 @opindex --quoting-style
7052 Enclose file names in double quotes and quote nongraphic characters as
7055 @item --quoting-style=@var{word}
7056 @opindex --quoting-style
7057 @cindex quoting style
7058 Use style @var{word} to quote file names and other strings that may
7059 contain arbitrary characters. The @var{word} should
7060 be one of the following:
7064 Output strings as-is; this is the same as the @option{-N} or
7065 @option{--literal} option.
7067 Quote strings for the shell if they contain shell metacharacters or would
7068 cause ambiguous output.
7069 The quoting is suitable for @acronym{POSIX}-compatible shells like
7070 @command{bash}, but it does not always work for incompatible shells
7073 Quote strings for the shell, even if they would normally not require quoting.
7075 Quote strings as for C character string literals, including the
7076 surrounding double-quote characters; this is the same as the
7077 @option{-Q} or @option{--quote-name} option.
7079 Quote strings as for C character string literals, except omit the
7080 surrounding double-quote
7081 characters; this is the same as the @option{-b} or @option{--escape} option.
7083 Quote strings as for C character string literals, except use
7084 surrounding quotation marks appropriate for the
7087 @c Use @t instead of @samp to avoid duplicate quoting in some output styles.
7088 Quote strings as for C character string literals, except use
7089 surrounding quotation marks appropriate for the locale, and quote
7090 @t{`like this'} instead of @t{"like
7091 this"} in the default C locale. This looks nicer on many displays.
7094 You can specify the default value of the @option{--quoting-style} option
7095 with the environment variable @env{QUOTING_STYLE}. If that environment
7096 variable is not set, the default value is @samp{literal}, but this
7097 default may change to @samp{shell} in a future version of this package.
7099 @item --show-control-chars
7100 @opindex --show-control-chars
7101 Print nongraphic characters as-is in file names.
7102 This is the default unless the output is a terminal and the program is
7108 @node dir invocation
7109 @section @command{dir}: Briefly list directory contents
7112 @cindex directory listing, brief
7114 @command{dir} is equivalent to @code{ls -C
7115 -b}; that is, by default files are listed in columns, sorted vertically,
7116 and special characters are represented by backslash escape sequences.
7118 @xref{ls invocation, @command{ls}}.
7121 @node vdir invocation
7122 @section @command{vdir}: Verbosely list directory contents
7125 @cindex directory listing, verbose
7127 @command{vdir} is equivalent to @code{ls -l
7128 -b}; that is, by default files are listed in long format and special
7129 characters are represented by backslash escape sequences.
7131 @node dircolors invocation
7132 @section @command{dircolors}: Color setup for @command{ls}
7136 @cindex setup for color
7138 @command{dircolors} outputs a sequence of shell commands to set up the
7139 terminal for color output from @command{ls} (and @command{dir}, etc.).
7143 eval "`dircolors [@var{option}]@dots{} [@var{file}]`"
7146 If @var{file} is specified, @command{dircolors} reads it to determine which
7147 colors to use for which file types and extensions. Otherwise, a
7148 precompiled database is used. For details on the format of these files,
7149 run @samp{dircolors --print-database}.
7151 To make @command{dircolors} read a @file{~/.dircolors} file if it
7152 exists, you can put the following lines in your @file{~/.bashrc} (or
7153 adapt them to your favorite shell):
7157 test -r $d && eval "$(dircolors $d)"
7161 @vindex SHELL @r{environment variable, and color}
7162 The output is a shell command to set the @env{LS_COLORS} environment
7163 variable. You can specify the shell syntax to use on the command line,
7164 or @command{dircolors} will guess it from the value of the @env{SHELL}
7165 environment variable.
7167 The program accepts the following options. Also see @ref{Common options}.
7172 @itemx --bourne-shell
7175 @opindex --bourne-shell
7176 @cindex Bourne shell syntax for color setup
7177 @cindex @command{sh} syntax for color setup
7178 Output Bourne shell commands. This is the default if the @env{SHELL}
7179 environment variable is set and does not end with @samp{csh} or
7188 @cindex C shell syntax for color setup
7189 @cindex @command{csh} syntax for color setup
7190 Output C shell commands. This is the default if @code{SHELL} ends with
7191 @command{csh} or @command{tcsh}.
7194 @itemx --print-database
7196 @opindex --print-database
7197 @cindex color database, printing
7198 @cindex database for color setup, printing
7199 @cindex printing color database
7200 Print the (compiled-in) default color configuration database. This
7201 output is itself a valid configuration file, and is fairly descriptive
7202 of the possibilities.
7209 @node Basic operations
7210 @chapter Basic operations
7212 @cindex manipulating files
7214 This chapter describes the commands for basic file manipulation:
7215 copying, moving (renaming), and deleting (removing).
7218 * cp invocation:: Copy files.
7219 * dd invocation:: Convert and copy a file.
7220 * install invocation:: Copy files and set attributes.
7221 * mv invocation:: Move (rename) files.
7222 * rm invocation:: Remove files or directories.
7223 * shred invocation:: Remove files more securely.
7228 @section @command{cp}: Copy files and directories
7231 @cindex copying files and directories
7232 @cindex files, copying
7233 @cindex directories, copying
7235 @command{cp} copies files (or, optionally, directories). The copy is
7236 completely independent of the original. You can either copy one file to
7237 another, or copy arbitrarily many files to a destination directory.
7241 cp [@var{option}]@dots{} [-T] @var{source} @var{dest}
7242 cp [@var{option}]@dots{} @var{source}@dots{} @var{directory}
7243 cp [@var{option}]@dots{} -t @var{directory} @var{source}@dots{}
7248 If two file names are given, @command{cp} copies the first file to the
7252 If the @option{--target-directory} (@option{-t}) option is given, or
7253 failing that if the last file is a directory and the
7254 @option{--no-target-directory} (@option{-T}) option is not given,
7255 @command{cp} copies each @var{source} file to the specified directory,
7256 using the @var{source}s' names.
7259 Generally, files are written just as they are read. For exceptions,
7260 see the @option{--sparse} option below.
7262 By default, @command{cp} does not copy directories. However, the
7263 @option{-R}, @option{-a}, and @option{-r} options cause @command{cp} to
7264 copy recursively by descending into source directories and copying files
7265 to corresponding destination directories.
7267 When copying from a symbolic link, @command{cp} normally follows the
7268 link only when not copying
7269 recursively. This default can be overridden with the
7270 @option{--archive} (@option{-a}), @option{-d}, @option{--dereference}
7271 (@option{-L}), @option{--no-dereference} (@option{-P}), and
7272 @option{-H} options. If more than one of these options is specified,
7273 the last one silently overrides the others.
7275 When copying to a symbolic link, @command{cp} follows the
7276 link only when it refers to an existing regular file.
7277 However, when copying to a dangling symbolic link, @command{cp}
7278 refuses by default, and fails with a diagnostic, since the operation
7279 is inherently dangerous. This behavior is contrary to historical
7280 practice and to @acronym{POSIX}.
7281 Set @env{POSIXLY_CORRECT} to make @command{cp} attempt to create
7282 the target of a dangling destination symlink, in spite of the possible risk.
7283 Also, when an option like
7284 @option{--backup} or @option{--link} acts to rename or remove the
7285 destination before copying, @command{cp} renames or removes the
7286 symbolic link rather than the file it points to.
7288 By default, @command{cp} copies the contents of special files only
7289 when not copying recursively. This default can be overridden with the
7290 @option{--copy-contents} option.
7292 @cindex self-backups
7293 @cindex backups, making only
7294 @command{cp} generally refuses to copy a file onto itself, with the
7295 following exception: if @option{--force --backup} is specified with
7296 @var{source} and @var{dest} identical, and referring to a regular file,
7297 @command{cp} will make a backup file, either regular or numbered, as
7298 specified in the usual ways (@pxref{Backup options}). This is useful when
7299 you simply want to make a backup of an existing file before changing it.
7301 The program accepts the following options. Also see @ref{Common options}.
7308 Preserve as much as possible of the structure and attributes of the
7309 original files in the copy (but do not attempt to preserve internal
7310 directory structure; i.e., @samp{ls -U} may list the entries in a copied
7311 directory in a different order).
7312 Try to preserve SELinux security context and extended attributes (xattr),
7313 but ignore any failure to do that and print no corresponding diagnostic.
7314 Equivalent to @option{-dR --preserve=all} with the reduced diagnostics.
7317 @itemx @w{@kbd{--backup}[=@var{method}]}
7320 @vindex VERSION_CONTROL
7321 @cindex backups, making
7322 @xref{Backup options}.
7323 Make a backup of each file that would otherwise be overwritten or removed.
7324 As a special case, @command{cp} makes a backup of @var{source} when the force
7325 and backup options are given and @var{source} and @var{dest} are the same
7326 name for an existing, regular file. One useful application of this
7327 combination of options is this tiny Bourne shell script:
7331 # Usage: backup FILE...
7332 # Create a @sc{gnu}-style backup of each listed FILE.
7334 cp --backup --force -- "$i" "$i"
7338 @item --copy-contents
7339 @cindex directories, copying recursively
7340 @cindex copying directories recursively
7341 @cindex recursively copying directories
7342 @cindex non-directories, copying as special files
7343 If copying recursively, copy the contents of any special files (e.g.,
7344 FIFOs and device files) as if they were regular files. This means
7345 trying to read the data in each source file and writing it to the
7346 destination. It is usually a mistake to use this option, as it
7347 normally has undesirable effects on special files like FIFOs and the
7348 ones typically found in the @file{/dev} directory. In most cases,
7349 @code{cp -R --copy-contents} will hang indefinitely trying to read
7350 from FIFOs and special files like @file{/dev/console}, and it will
7351 fill up your destination disk if you use it to copy @file{/dev/zero}.
7352 This option has no effect unless copying recursively, and it does not
7353 affect the copying of symbolic links.
7357 @cindex symbolic links, copying
7358 @cindex hard links, preserving
7359 Copy symbolic links as symbolic links rather than copying the files that
7360 they point to, and preserve hard links between source files in the copies.
7361 Equivalent to @option{--no-dereference --preserve=links}.
7367 When copying without this option and an existing destination file cannot
7368 be opened for writing, the copy fails. However, with @option{--force}),
7369 when a destination file cannot be opened, @command{cp} then removes it and
7370 tries to open it again. Contrast this behavior with that enabled by
7371 @option{--link} and @option{--symbolic-link}, whereby the destination file
7372 is never opened but rather is removed unconditionally. Also see the
7373 description of @option{--remove-destination}.
7375 This option is independent of the @option{--interactive} or
7376 @option{-i} option: neither cancels the effect of the other.
7378 This option is redundant if the @option{--no-clobber} or @option{-n} option is
7383 If a command line argument specifies a symbolic link, then copy the
7384 file it points to rather than the symbolic link itself. However,
7385 copy (preserving its nature) any symbolic link that is encountered
7386 via recursive traversal.
7389 @itemx --interactive
7391 @opindex --interactive
7392 When copying a file other than a directory, prompt whether to
7393 overwrite an existing destination file. The @option{-i} option overrides
7394 a previous @option{-n} option.
7400 Make hard links instead of copies of non-directories.
7403 @itemx --dereference
7405 @opindex --dereference
7406 Follow symbolic links when copying from them.
7407 With this option, @command{cp} cannot create a symbolic link.
7408 For example, a symlink (to regular file) in the source tree will be copied to
7409 a regular file in the destination tree.
7414 @opindex --no-clobber
7415 Do not overwrite an existing file. The @option{-n} option overrides a previous
7416 @option{-i} option. This option is mutually exclusive with @option{-b} or
7417 @option{--backup} option.
7420 @itemx --no-dereference
7422 @opindex --no-dereference
7423 @cindex symbolic links, copying
7424 Copy symbolic links as symbolic links rather than copying the files that
7425 they point to. This option affects only symbolic links in the source;
7426 symbolic links in the destination are always followed if possible.
7429 @itemx @w{@kbd{--preserve}[=@var{attribute_list}]}
7432 @cindex file information, preserving, extended attributes, xattr
7433 Preserve the specified attributes of the original files.
7434 If specified, the @var{attribute_list} must be a comma-separated list
7435 of one or more of the following strings:
7439 Preserve the file mode bits and access control lists.
7441 Preserve the owner and group. On most modern systems,
7442 only users with appropriate privileges may change the owner of a file,
7444 may preserve the group ownership of a file only if they happen to be
7445 a member of the desired group.
7447 Preserve the times of last access and last modification, when possible.
7448 In general, it is not possible to preserve these attributes
7449 when the affected file is a symbolic link.
7450 However, FreeBSD now provides the @code{lutimes} function, which makes
7451 it possible even for symbolic links. However, this implementation does
7452 not yet take advantage of that.
7453 @c FIXME: once we provide lutimes support, update the above.
7455 Preserve in the destination files
7456 any links between corresponding source files.
7457 Note that with @option{-L} or @option{-H}, this option can convert
7458 symbolic links to hard links. For example,
7460 $ mkdir c; : > a; ln -s a b; cp -aH a b c; ls -i1 c
7465 Note the inputs: @file{b} is a symlink to regular file @file{a},
7466 yet the files in destination directory, @file{c/}, are hard-linked.
7467 Since @option{-a} implies @option{--preserve=links}, and since @option{-H}
7468 tells @command{cp} to dereference command line arguments, it sees two files
7469 with the same inode number, and preserves the perceived hard link.
7471 Here is a similar example that exercises @command{cp}'s @option{-L} option:
7473 $ mkdir b c; (cd b; : > a; ln -s a b); cp -aL b c; ls -i1 c/b
7479 Preserve SELinux security context of the file. @command{cp} will fail
7480 if the preserving of SELinux security context is not succesful.
7482 Preserve extended attributes if @command{cp} is built with xattr support,
7483 and xattrs are supported and enabled on your file system.
7484 If SELinux context and/or ACLs are implemented using xattrs,
7485 they are preserved by this option as well.
7487 Preserve all file attributes.
7488 Equivalent to specifying all of the above, but with the difference
7489 that failure to preserve SELinux security context or extended attributes
7490 does not change @command{cp}'s exit status.
7491 @command{cp} does diagnose such failures.
7494 Using @option{--preserve} with no @var{attribute_list} is equivalent
7495 to @option{--preserve=mode,ownership,timestamps}.
7497 In the absence of this option, each destination file is created with the
7498 mode bits of the corresponding source file, minus the bits set in the
7499 umask and minus the set-user-ID and set-group-ID bits.
7500 @xref{File permissions}.
7502 @itemx @w{@kbd{--no-preserve}=@var{attribute_list}}
7503 @cindex file information, preserving
7504 Do not preserve the specified attributes. The @var{attribute_list}
7505 has the same form as for @option{--preserve}.
7509 @cindex parent directories and @command{cp}
7510 Form the name of each destination file by appending to the target
7511 directory a slash and the specified name of the source file. The last
7512 argument given to @command{cp} must be the name of an existing directory.
7513 For example, the command:
7516 cp --parents a/b/c existing_dir
7520 copies the file @file{a/b/c} to @file{existing_dir/a/b/c}, creating
7521 any missing intermediate directories.
7528 @opindex --recursive
7529 @cindex directories, copying recursively
7530 @cindex copying directories recursively
7531 @cindex recursively copying directories
7532 @cindex non-directories, copying as special files
7533 Copy directories recursively. By default, do not follow symbolic
7534 links in the source; see the @option{--archive} (@option{-a}), @option{-d},
7535 @option{--dereference} (@option{-L}), @option{--no-dereference}
7536 (@option{-P}), and @option{-H} options. Special files are copied by
7537 creating a destination file of the same type as the source; see the
7538 @option{--copy-contents} option. It is not portable to use
7539 @option{-r} to copy symbolic links or special files. On some
7540 non-@sc{gnu} systems, @option{-r} implies the equivalent of
7541 @option{-L} and @option{--copy-contents} for historical reasons.
7542 Also, it is not portable to use @option{-R} to copy symbolic links
7543 unless you also specify @option{-P}, as @acronym{POSIX} allows
7544 implementations that dereference symbolic links by default.
7546 @item --remove-destination
7547 @opindex --remove-destination
7548 Remove each existing destination file before attempting to open it
7549 (contrast with @option{-f} above).
7551 @item --sparse=@var{when}
7552 @opindex --sparse=@var{when}
7553 @cindex sparse files, copying
7554 @cindex holes, copying files with
7555 @findex read @r{system call, and holes}
7556 A @dfn{sparse file} contains @dfn{holes}---a sequence of zero bytes that
7557 does not occupy any physical disk blocks; the @samp{read} system call
7558 reads these as zeros. This can both save considerable disk space and
7559 increase speed, since many binary files contain lots of consecutive zero
7560 bytes. By default, @command{cp} detects holes in input source files via a crude
7561 heuristic and makes the corresponding output file sparse as well.
7562 Only regular files may be sparse.
7564 The @var{when} value can be one of the following:
7568 The default behavior: if the input file is sparse, attempt to make
7569 the output file sparse, too. However, if an output file exists but
7570 refers to a non-regular file, then do not attempt to make it sparse.
7573 For each sufficiently long sequence of zero bytes in the input file,
7574 attempt to create a corresponding hole in the output file, even if the
7575 input file does not appear to be sparse.
7576 This is useful when the input file resides on a file system
7577 that does not support sparse files
7578 (for example, @samp{efs} file systems in SGI IRIX 5.3 and earlier),
7579 but the output file is on a type of file system that does support them.
7580 Holes may be created only in regular files, so if the destination file
7581 is of some other type, @command{cp} does not even try to make it sparse.
7584 Never make the output file sparse.
7585 This is useful in creating a file for use with the @command{mkswap} command,
7586 since such a file must not have any holes.
7589 @optStripTrailingSlashes
7592 @itemx --symbolic-link
7594 @opindex --symbolic-link
7595 @cindex symbolic links, copying with
7596 Make symbolic links instead of copies of non-directories. All source
7597 file names must be absolute (starting with @samp{/}) unless the
7598 destination files are in the current directory. This option merely
7599 results in an error message on systems that do not support symbolic links.
7605 @optNoTargetDirectory
7611 @cindex newer files, copying only
7612 Do not copy a non-directory that has an existing destination with the
7613 same or newer modification time. If time stamps are being preserved,
7614 the comparison is to the source time stamp truncated to the
7615 resolutions of the destination file system and of the system calls
7616 used to update time stamps; this avoids duplicate work if several
7617 @samp{cp -pu} commands are executed with the same source and
7624 Print the name of each file before copying it.
7627 @itemx --one-file-system
7629 @opindex --one-file-system
7630 @cindex file systems, omitting copying to different
7631 Skip subdirectories that are on different file systems from the one that
7632 the copy started on.
7633 However, mount point directories @emph{are} copied.
7641 @section @command{dd}: Convert and copy a file
7644 @cindex converting while copying a file
7646 @command{dd} copies a file (from standard input to standard output, by
7647 default) with a changeable I/O block size, while optionally performing
7648 conversions on it. Synopses:
7651 dd [@var{operand}]@dots{}
7655 The only options are @option{--help} and @option{--version}.
7656 @xref{Common options}. @command{dd} accepts the following operands.
7662 Read from @var{file} instead of standard input.
7666 Write to @var{file} instead of standard output. Unless
7667 @samp{conv=notrunc} is given, @command{dd} truncates @var{file} to zero
7668 bytes (or the size specified with @samp{seek=}).
7670 @item ibs=@var{bytes}
7672 @cindex block size of input
7673 @cindex input block size
7674 Set the input block size to @var{bytes}.
7675 This makes @command{dd} read @var{bytes} per block.
7676 The default is 512 bytes.
7678 @item obs=@var{bytes}
7680 @cindex block size of output
7681 @cindex output block size
7682 Set the output block size to @var{bytes}.
7683 This makes @command{dd} write @var{bytes} per block.
7684 The default is 512 bytes.
7686 @item bs=@var{bytes}
7689 Set both input and output block sizes to @var{bytes}.
7690 This makes @command{dd} read and write @var{bytes} per block,
7691 overriding any @samp{ibs} and @samp{obs} settings.
7692 In addition, if no data-transforming @option{conv} option is specified,
7693 each input block is copied to the output as a single block,
7694 without aggregating short reads.
7696 @item cbs=@var{bytes}
7698 @cindex block size of conversion
7699 @cindex conversion block size
7700 @cindex fixed-length records, converting to variable-length
7701 @cindex variable-length records, converting to fixed-length
7702 Set the conversion block size to @var{bytes}.
7703 When converting variable-length records to fixed-length ones
7704 (@option{conv=block}) or the reverse (@option{conv=unblock}),
7705 use @var{bytes} as the fixed record length.
7707 @item skip=@var{blocks}
7709 Skip @var{blocks} @samp{ibs}-byte blocks in the input file before copying.
7711 @item seek=@var{blocks}
7713 Skip @var{blocks} @samp{obs}-byte blocks in the output file before copying.
7715 @item count=@var{blocks}
7717 Copy @var{blocks} @samp{ibs}-byte blocks from the input file, instead
7718 of everything until the end of the file.
7722 Do not print the overall transfer rate and volume statistics
7723 that normally make up the third status line when @command{dd} exits.
7725 @item conv=@var{conversion}[,@var{conversion}]@dots{}
7727 Convert the file as specified by the @var{conversion} argument(s).
7728 (No spaces around any comma(s).)
7735 @opindex ascii@r{, converting to}
7736 Convert @acronym{EBCDIC} to @acronym{ASCII},
7737 using the conversion table specified by @acronym{POSIX}.
7738 This provides a 1:1 translation for all 256 bytes.
7741 @opindex ebcdic@r{, converting to}
7742 Convert @acronym{ASCII} to @acronym{EBCDIC}.
7743 This is the inverse of the @samp{ascii} conversion.
7746 @opindex alternate ebcdic@r{, converting to}
7747 Convert @acronym{ASCII} to alternate @acronym{EBCDIC},
7748 using the alternate conversion table specified by @acronym{POSIX}.
7749 This is not a 1:1 translation, but reflects common historical practice
7750 for @samp{~}, @samp{[}, and @samp{]}.
7752 The @samp{ascii}, @samp{ebcdic}, and @samp{ibm} conversions are
7756 @opindex block @r{(space-padding)}
7757 For each line in the input, output @samp{cbs} bytes, replacing the
7758 input newline with a space and padding with spaces as necessary.
7762 Replace trailing spaces in each @samp{cbs}-sized input block with a
7765 The @samp{block} and @samp{unblock} conversions are mutually exclusive.
7768 @opindex lcase@r{, converting to}
7769 Change uppercase letters to lowercase.
7772 @opindex ucase@r{, converting to}
7773 Change lowercase letters to uppercase.
7775 The @samp{lcase} and @samp{ucase} conversions are mutually exclusive.
7778 @opindex swab @r{(byte-swapping)}
7779 @cindex byte-swapping
7780 Swap every pair of input bytes. @sc{gnu} @command{dd}, unlike others, works
7781 when an odd number of bytes are read---the last byte is simply copied
7782 (since there is nothing to swap it with).
7786 @cindex read errors, ignoring
7787 Continue after read errors.
7791 @cindex creating output file, avoiding
7792 Do not create the output file; the output file must already exist.
7796 @cindex creating output file, requiring
7797 Fail if the output file already exists; @command{dd} must create the
7800 The @samp{excl} and @samp{nocreat} conversions are mutually exclusive.
7804 @cindex truncating output file, avoiding
7805 Do not truncate the output file.
7808 @opindex sync @r{(padding with @acronym{ASCII} @sc{nul}s)}
7809 Pad every input block to size of @samp{ibs} with trailing zero bytes.
7810 When used with @samp{block} or @samp{unblock}, pad with spaces instead of
7815 @cindex synchronized data writes, before finishing
7816 Synchronize output data just before finishing. This forces a physical
7817 write of output data.
7821 @cindex synchronized data and metadata writes, before finishing
7822 Synchronize output data and metadata just before finishing. This
7823 forces a physical write of output data and metadata.
7827 @item iflag=@var{flag}[,@var{flag}]@dots{}
7829 Access the input file using the flags specified by the @var{flag}
7830 argument(s). (No spaces around any comma(s).)
7832 @item oflag=@var{flag}[,@var{flag}]@dots{}
7834 Access the output file using the flags specified by the @var{flag}
7835 argument(s). (No spaces around any comma(s).)
7837 Here are the flags. Not every flag is supported on every operating
7844 @cindex appending to the output file
7845 Write in append mode, so that even if some other process is writing to
7846 this file, every @command{dd} write will append to the current
7847 contents of the file. This flag makes sense only for output.
7848 If you combine this flag with the @samp{of=@var{file}} operand,
7849 you should also specify @samp{conv=notrunc} unless you want the
7850 output file to be truncated before being appended to.
7854 @cindex concurrent I/O
7855 Use concurrent I/O mode for data. This mode performs direct I/O
7856 and drops the @acronym{POSIX} requirement to serialize all I/O to the same file.
7857 A file cannot be opened in CIO mode and with a standard open at the
7863 Use direct I/O for data, avoiding the buffer cache.
7867 @cindex directory I/O
7869 Fail unless the file is a directory. Most operating systems do not
7870 allow I/O to a directory, so this flag has limited utility.
7874 @cindex synchronized data reads
7875 Use synchronized I/O for data. For the output file, this forces a
7876 physical write of output data on each write. For the input file,
7877 this flag can matter when reading from a remote file that has been
7878 written to synchronously by some other process. Metadata (e.g.,
7879 last-access and last-modified time) is not necessarily synchronized.
7883 @cindex synchronized data and metadata I/O
7884 Use synchronized I/O for both data and metadata.
7888 @cindex nonblocking I/O
7889 Use non-blocking I/O.
7894 Do not update the file's access time.
7895 Some older file systems silently ignore this flag, so it is a good
7896 idea to test it on your files before relying on it.
7900 @cindex controlling terminal
7901 Do not assign the file to be a controlling terminal for @command{dd}.
7902 This has no effect when the file is not a terminal.
7903 On many hosts (e.g., @acronym{GNU}/Linux hosts), this option has no effect
7908 @cindex symbolic links, following
7909 Do not follow symbolic links.
7914 Fail if the file has multiple hard links.
7919 Use binary I/O. This option has an effect only on nonstandard
7920 platforms that distinguish binary from text I/O.
7925 Use text I/O. Like @samp{binary}, this option has no effect on
7930 Accumulate full blocks from input. The @code{read} system call
7931 may return early if a full block is not available.
7932 When that happens, continue calling @code{read} to fill the remainder
7934 This flag can be used only with @code{iflag}.
7938 These flags are not supported on all systems, and @samp{dd} rejects
7939 attempts to use them when they are not supported. When reading from
7940 standard input or writing to standard output, the @samp{nofollow} and
7941 @samp{noctty} flags should not be specified, and the other flags
7942 (e.g., @samp{nonblock}) can affect how other processes behave with the
7943 affected file descriptors, even after @command{dd} exits.
7947 @cindex multipliers after numbers
7948 The numeric-valued strings above (@var{bytes} and @var{blocks}) can be
7949 followed by a multiplier: @samp{b}=512, @samp{c}=1,
7950 @samp{w}=2, @samp{x@var{m}}=@var{m}, or any of the
7951 standard block size suffixes like @samp{k}=1024 (@pxref{Block size}).
7953 Use different @command{dd} invocations to use different block sizes for
7954 skipping and I/O@. For example, the following shell commands copy data
7955 in 512 KiB blocks between a disk and a tape, but do not save or restore a
7956 4 KiB label at the start of the disk:
7959 disk=/dev/rdsk/c0t1d0s2
7962 # Copy all but the label from disk to tape.
7963 (dd bs=4k skip=1 count=0 && dd bs=512k) <$disk >$tape
7965 # Copy from tape back to disk, but leave the disk label alone.
7966 (dd bs=4k seek=1 count=0 && dd bs=512k) <$tape >$disk
7969 Sending an @samp{INFO} signal to a running @command{dd}
7970 process makes it print I/O statistics to standard error
7971 and then resume copying. In the example below,
7972 @command{dd} is run in the background to copy 10 million blocks.
7973 The @command{kill} command makes it output intermediate I/O statistics,
7974 and when @command{dd} completes normally or is killed by the
7975 @code{SIGINT} signal, it outputs the final statistics.
7978 $ dd if=/dev/zero of=/dev/null count=10MB & pid=$!
7979 $ kill -s INFO $pid; wait $pid
7980 3385223+0 records in
7981 3385223+0 records out
7982 1733234176 bytes (1.7 GB) copied, 6.42173 seconds, 270 MB/s
7983 10000000+0 records in
7984 10000000+0 records out
7985 5120000000 bytes (5.1 GB) copied, 18.913 seconds, 271 MB/s
7988 @vindex POSIXLY_CORRECT
7989 On systems lacking the @samp{INFO} signal @command{dd} responds to the
7990 @samp{USR1} signal instead, unless the @env{POSIXLY_CORRECT}
7991 environment variable is set.
7996 @node install invocation
7997 @section @command{install}: Copy files and set attributes
8000 @cindex copying files and setting attributes
8002 @command{install} copies files while setting their file mode bits and, if
8003 possible, their owner and group. Synopses:
8006 install [@var{option}]@dots{} [-T] @var{source} @var{dest}
8007 install [@var{option}]@dots{} @var{source}@dots{} @var{directory}
8008 install [@var{option}]@dots{} -t @var{directory} @var{source}@dots{}
8009 install [@var{option}]@dots{} -d @var{directory}@dots{}
8014 If two file names are given, @command{install} copies the first file to the
8018 If the @option{--target-directory} (@option{-t}) option is given, or
8019 failing that if the last file is a directory and the
8020 @option{--no-target-directory} (@option{-T}) option is not given,
8021 @command{install} copies each @var{source} file to the specified
8022 directory, using the @var{source}s' names.
8025 If the @option{--directory} (@option{-d}) option is given,
8026 @command{install} creates each @var{directory} and any missing parent
8027 directories. Parent directories are created with mode
8028 @samp{u=rwx,go=rx} (755), regardless of the @option{-m} option or the
8029 current umask. @xref{Directory Setuid and Setgid}, for how the
8030 set-user-ID and set-group-ID bits of parent directories are inherited.
8033 @cindex Makefiles, installing programs in
8034 @command{install} is similar to @command{cp}, but allows you to control the
8035 attributes of destination files. It is typically used in Makefiles to
8036 copy programs into their destination directories. It refuses to copy
8037 files onto themselves.
8039 @cindex extended attributes, xattr
8040 @command{install} never preserves extended attributes (xattr).
8042 The program accepts the following options. Also see @ref{Common options}.
8050 Ignored; for compatibility with old Unix versions of @command{install}.
8054 Create any missing parent directories of @var{dest},
8055 then copy @var{source} to @var{dest}.
8056 This option is ignored if a destination directory is specified
8057 via @option{--target-directory=DIR}.
8062 @opindex --directory
8063 @cindex directories, creating with given attributes
8064 @cindex parent directories, creating missing
8065 @cindex leading directories, creating missing
8066 Create any missing parent directories, giving them the default
8067 attributes. Then create each given directory, setting their owner,
8068 group and mode as given on the command line or to the defaults.
8070 @item -g @var{group}
8071 @itemx --group=@var{group}
8074 @cindex group ownership of installed files, setting
8075 Set the group ownership of installed files or directories to
8076 @var{group}. The default is the process's current group. @var{group}
8077 may be either a group name or a numeric group ID.
8080 @itemx --mode=@var{mode}
8083 @cindex permissions of installed files, setting
8084 Set the file mode bits for the installed file or directory to @var{mode},
8085 which can be either an octal number, or a symbolic mode as in
8086 @command{chmod}, with @samp{a=} (no access allowed to anyone) as the
8087 point of departure (@pxref{File permissions}).
8088 The default mode is @samp{u=rwx,go=rx,a-s}---read, write, and
8089 execute for the owner, read and execute for group and other, and with
8090 set-user-ID and set-group-ID disabled.
8091 This default is not quite the same as @samp{755}, since it disables
8092 instead of preserving set-user-ID and set-group-ID on directories.
8093 @xref{Directory Setuid and Setgid}.
8095 @item -o @var{owner}
8096 @itemx --owner=@var{owner}
8099 @cindex ownership of installed files, setting
8100 @cindex appropriate privileges
8101 @vindex root @r{as default owner}
8102 If @command{install} has appropriate privileges (is run as root), set the
8103 ownership of installed files or directories to @var{owner}. The default
8104 is @code{root}. @var{owner} may be either a user name or a numeric user
8107 @item --preserve-context
8108 @opindex --preserve-context
8110 @cindex security context
8111 Preserve the SELinux security context of files and directories.
8112 Failure to preserve the context in all of the files or directories
8113 will result in an exit status of 1. If SELinux is disabled then
8114 print a warning and ignore the option.
8117 @itemx --preserve-timestamps
8119 @opindex --preserve-timestamps
8120 @cindex timestamps of installed files, preserving
8121 Set the time of last access and the time of last modification of each
8122 installed file to match those of each corresponding original file.
8123 When a file is installed without this option, its last access and
8124 last modification times are both set to the time of installation.
8125 This option is useful if you want to use the last modification times
8126 of installed files to keep track of when they were last built as opposed
8127 to when they were last installed.
8133 @cindex symbol table information, stripping
8134 @cindex stripping symbol table information
8135 Strip the symbol tables from installed binary executables.
8137 @itemx --strip-program=@var{program}
8138 @opindex --strip-program
8139 @cindex symbol table information, stripping, program
8140 Program used to strip binaries.
8146 @optNoTargetDirectory
8152 Print the name of each file before copying it.
8154 @item -Z @var{context}
8155 @itemx --context=@var{context}
8159 @cindex security context
8160 Set the default SELinux security context to be used for any
8161 created files and directories. If SELinux is disabled then
8162 print a warning and ignore the option.
8170 @section @command{mv}: Move (rename) files
8174 @command{mv} moves or renames files (or directories). Synopses:
8177 mv [@var{option}]@dots{} [-T] @var{source} @var{dest}
8178 mv [@var{option}]@dots{} @var{source}@dots{} @var{directory}
8179 mv [@var{option}]@dots{} -t @var{directory} @var{source}@dots{}
8184 If two file names are given, @command{mv} moves the first file to the
8188 If the @option{--target-directory} (@option{-t}) option is given, or
8189 failing that if the last file is a directory and the
8190 @option{--no-target-directory} (@option{-T}) option is not given,
8191 @command{mv} moves each @var{source} file to the specified
8192 directory, using the @var{source}s' names.
8195 @command{mv} can move any type of file from one file system to another.
8196 Prior to version @code{4.0} of the fileutils,
8197 @command{mv} could move only regular files between file systems.
8198 For example, now @command{mv} can move an entire directory hierarchy
8199 including special device files from one partition to another. It first
8200 uses some of the same code that's used by @code{cp -a} to copy the
8201 requested directories and files, then (assuming the copy succeeded)
8202 it removes the originals. If the copy fails, then the part that was
8203 copied to the destination partition is removed. If you were to copy
8204 three directories from one partition to another and the copy of the first
8205 directory succeeded, but the second didn't, the first would be left on
8206 the destination partition and the second and third would be left on the
8209 @cindex extended attributes, xattr
8210 @command{mv} always tries to copy extended attributes (xattr).
8212 @cindex prompting, and @command{mv}
8213 If a destination file exists but is normally unwritable, standard input
8214 is a terminal, and the @option{-f} or @option{--force} option is not given,
8215 @command{mv} prompts the user for whether to replace the file. (You might
8216 own the file, or have write permission on its directory.) If the
8217 response is not affirmative, the file is skipped.
8219 @emph{Warning}: Avoid specifying a source name with a trailing slash,
8220 when it might be a symlink to a directory.
8221 Otherwise, @command{mv} may do something very surprising, since
8222 its behavior depends on the underlying rename system call.
8223 On a system with a modern Linux-based kernel, it fails with @code{errno=ENOTDIR}.
8224 However, on other systems (at least FreeBSD 6.1 and Solaris 10) it silently
8225 renames not the symlink but rather the directory referenced by the symlink.
8226 @xref{Trailing slashes}.
8228 The program accepts the following options. Also see @ref{Common options}.
8238 @cindex prompts, omitting
8239 Do not prompt the user before removing a destination file.
8241 If you specify more than one of the @option{-i}, @option{-f}, @option{-n}
8242 options, only the final one takes effect.
8247 @itemx --interactive
8249 @opindex --interactive
8250 @cindex prompts, forcing
8251 Prompt whether to overwrite each existing destination file, regardless
8253 If the response is not affirmative, the file is skipped.
8259 @opindex --no-clobber
8260 @cindex prompts, omitting
8261 Do not overwrite an existing file.
8263 This option is mutually exclusive with @option{-b} or @option{--backup} option.
8269 @cindex newer files, moving only
8270 Do not move a non-directory that has an existing destination with the
8271 same or newer modification time.
8272 If the move is across file system boundaries, the comparison is to the
8273 source time stamp truncated to the resolutions of the destination file
8274 system and of the system calls used to update time stamps; this avoids
8275 duplicate work if several @samp{mv -u} commands are executed with the
8276 same source and destination.
8282 Print the name of each file before moving it.
8284 @optStripTrailingSlashes
8290 @optNoTargetDirectory
8298 @section @command{rm}: Remove files or directories
8301 @cindex removing files or directories
8303 @command{rm} removes each given @var{file}. By default, it does not remove
8304 directories. Synopsis:
8307 rm [@var{option}]@dots{} [@var{file}]@dots{}
8310 @cindex prompting, and @command{rm}
8311 If the @option{-I} or @option{--interactive=once} option is given,
8312 and there are more than three files or the @option{-r}, @option{-R},
8313 or @option{--recursive} are given, then @command{rm} prompts the user
8314 for whether to proceed with the entire operation. If the response is
8315 not affirmative, the entire command is aborted.
8317 Otherwise, if a file is unwritable, standard input is a terminal, and
8318 the @option{-f} or @option{--force} option is not given, or the
8319 @option{-i} or @option{--interactive=always} option @emph{is} given,
8320 @command{rm} prompts the user for whether to remove the file.
8321 If the response is not affirmative, the file is skipped.
8323 Any attempt to remove a file whose last file name component is
8324 @file{.} or @file{..} is rejected without any prompting.
8326 @emph{Warning}: If you use @command{rm} to remove a file, it is usually
8327 possible to recover the contents of that file. If you want more assurance
8328 that the contents are truly unrecoverable, consider using @command{shred}.
8330 The program accepts the following options. Also see @ref{Common options}.
8338 Ignore nonexistent files and never prompt the user.
8339 Ignore any previous @option{--interactive} (@option{-i}) option.
8343 Prompt whether to remove each file.
8344 If the response is not affirmative, the file is skipped.
8345 Ignore any previous @option{--force} (@option{-f}) option.
8346 Equivalent to @option{--interactive=always}.
8350 Prompt once whether to proceed with the command, if more than three
8351 files are named or if a recursive removal is requested. Ignore any
8352 previous @option{--force} (@option{-f}) option. Equivalent to
8353 @option{--interactive=once}.
8355 @itemx --interactive [=@var{when}]
8356 @opindex --interactive
8357 Specify when to issue an interactive prompt. @var{when} may be
8361 @vindex never @r{interactive option}
8362 - Do not prompt at all.
8364 @vindex once @r{interactive option}
8365 - Prompt once if more than three files are named or if a recursive
8366 removal is requested. Equivalent to @option{-I}.
8368 @vindex always @r{interactive option}
8369 - Prompt for every file being removed. Equivalent to @option{-i}.
8371 @option{--interactive} with no @var{when} is equivalent to
8372 @option{--interactive=always}.
8374 @itemx --one-file-system
8375 @opindex --one-file-system
8376 @cindex one file system, restricting @command{rm} to
8377 When removing a hierarchy recursively, skip any directory that is on a
8378 file system different from that of the corresponding command line argument.
8380 This option is useful when removing a build ``chroot'' hierarchy,
8381 which normally contains no valuable data. However, it is not uncommon
8382 to bind-mount @file{/home} into such a hierarchy, to make it easier to
8383 use one's start-up file. The catch is that it's easy to forget to
8384 unmount @file{/home}. Then, when you use @command{rm -rf} to remove
8385 your normally throw-away chroot, that command will remove everything
8386 under @file{/home}, too.
8387 Use the @option{--one-file-system} option, and it will
8388 warn about and skip directories on other file systems.
8389 Of course, this will not save your @file{/home} if it and your
8390 chroot happen to be on the same file system.
8392 @itemx --preserve-root
8393 @opindex --preserve-root
8394 @cindex root directory, disallow recursive destruction
8395 Fail upon any attempt to remove the root directory, @file{/},
8396 when used with the @option{--recursive} option.
8397 This is the default behavior.
8398 @xref{Treating / specially}.
8400 @itemx --no-preserve-root
8401 @opindex --no-preserve-root
8402 @cindex root directory, allow recursive destruction
8403 Do not treat @file{/} specially when removing recursively.
8404 This option is not recommended unless you really want to
8405 remove all the files on your computer.
8406 @xref{Treating / specially}.
8413 @opindex --recursive
8414 @cindex directories, removing (recursively)
8415 Remove the listed directories and their contents recursively.
8421 Print the name of each file before removing it.
8425 @cindex files beginning with @samp{-}, removing
8426 @cindex @samp{-}, removing files beginning with
8427 One common question is how to remove files whose names begin with a
8428 @samp{-}. @sc{gnu} @command{rm}, like every program that uses the @code{getopt}
8429 function to parse its arguments, lets you use the @samp{--} option to
8430 indicate that all following arguments are non-options. To remove a file
8431 called @file{-f} in the current directory, you could type either:
8444 @opindex - @r{and Unix @command{rm}}
8445 The Unix @command{rm} program's use of a single @samp{-} for this purpose
8446 predates the development of the getopt standard syntax.
8451 @node shred invocation
8452 @section @command{shred}: Remove files more securely
8455 @cindex data, erasing
8456 @cindex erasing data
8458 @command{shred} overwrites devices or files, to help prevent even
8459 very expensive hardware from recovering the data.
8461 Ordinarily when you remove a file (@pxref{rm invocation}), the data is
8462 not actually destroyed. Only the index listing where the file is
8463 stored is destroyed, and the storage is made available for reuse.
8464 There are undelete utilities that will attempt to reconstruct the index
8465 and can bring the file back if the parts were not reused.
8467 On a busy system with a nearly-full drive, space can get reused in a few
8468 seconds. But there is no way to know for sure. If you have sensitive
8469 data, you may want to be sure that recovery is not possible by actually
8470 overwriting the file with non-sensitive data.
8472 However, even after doing that, it is possible to take the disk back
8473 to a laboratory and use a lot of sensitive (and expensive) equipment
8474 to look for the faint ``echoes'' of the original data underneath the
8475 overwritten data. If the data has only been overwritten once, it's not
8478 The best way to remove something irretrievably is to destroy the media
8479 it's on with acid, melt it down, or the like. For cheap removable media
8480 like floppy disks, this is the preferred method. However, hard drives
8481 are expensive and hard to melt, so the @command{shred} utility tries
8482 to achieve a similar effect non-destructively.
8484 This uses many overwrite passes, with the data patterns chosen to
8485 maximize the damage they do to the old data. While this will work on
8486 floppies, the patterns are designed for best effect on hard drives.
8487 For more details, see the source code and Peter Gutmann's paper
8488 @uref{http://www.cs.auckland.ac.nz/~pgut001/pubs/secure_del.html,
8489 @cite{Secure Deletion of Data from Magnetic and Solid-State Memory}},
8490 from the proceedings of the Sixth @acronym{USENIX} Security Symposium (San Jose,
8491 California, July 22--25, 1996).
8493 @strong{Please note} that @command{shred} relies on a very important assumption:
8494 that the file system overwrites data in place. This is the traditional
8495 way to do things, but many modern file system designs do not satisfy this
8496 assumption. Exceptions include:
8501 Log-structured or journaled file systems, such as those supplied with
8502 AIX and Solaris, and JFS, ReiserFS, XFS, Ext3 (in @code{data=journal} mode),
8503 BFS, NTFS, etc.@: when they are configured to journal @emph{data}.
8506 File systems that write redundant data and carry on even if some writes
8507 fail, such as RAID-based file systems.
8510 File systems that make snapshots, such as Network Appliance's NFS server.
8513 File systems that cache in temporary locations, such as NFS version 3
8517 Compressed file systems.
8520 In the particular case of ext3 file systems, the above disclaimer applies (and
8521 @command{shred} is thus of limited effectiveness) only in @code{data=journal}
8522 mode, which journals file data in addition to just metadata. In both
8523 the @code{data=ordered} (default) and @code{data=writeback} modes,
8524 @command{shred} works as usual. Ext3 journaling modes can be changed
8525 by adding the @code{data=something} option to the mount options for a
8526 particular file system in the @file{/etc/fstab} file, as documented in
8527 the mount man page (man mount).
8529 If you are not sure how your file system operates, then you should assume
8530 that it does not overwrite data in place, which means that shred cannot
8531 reliably operate on regular files in your file system.
8533 Generally speaking, it is more reliable to shred a device than a file,
8534 since this bypasses the problem of file system design mentioned above.
8535 However, even shredding devices is not always completely reliable. For
8536 example, most disks map out bad sectors invisibly to the application; if
8537 the bad sectors contain sensitive data, @command{shred} won't be able to
8540 @command{shred} makes no attempt to detect or report this problem, just as
8541 it makes no attempt to do anything about backups. However, since it is
8542 more reliable to shred devices than files, @command{shred} by default does
8543 not truncate or remove the output file. This default is more suitable
8544 for devices, which typically cannot be truncated and should not be
8547 Finally, consider the risk of backups and mirrors.
8548 File system backups and remote mirrors may contain copies of the
8549 file that cannot be removed, and that will allow a shredded file
8550 to be recovered later. So if you keep any data you may later want
8551 to destroy using @command{shred}, be sure that it is not backed up or mirrored.
8554 shred [@var{option}]@dots{} @var{file}[@dots{}]
8557 The program accepts the following options. Also see @ref{Common options}.
8565 @cindex force deletion
8566 Override file permissions if necessary to allow overwriting.
8569 @itemx -n @var{number}
8570 @itemx --iterations=@var{number}
8571 @opindex -n @var{number}
8572 @opindex --iterations=@var{number}
8573 @cindex iterations, selecting the number of
8574 By default, @command{shred} uses @value{SHRED_DEFAULT_PASSES} passes of
8575 overwrite. You can reduce this to save time, or increase it if you think it's
8576 appropriate. After 25 passes all of the internal overwrite patterns will have
8577 been used at least once.
8579 @item --random-source=@var{file}
8580 @opindex --random-source
8581 @cindex random source for shredding
8582 Use @var{file} as a source of random data used to overwrite and to
8583 choose pass ordering. @xref{Random sources}.
8585 @item -s @var{bytes}
8586 @itemx --size=@var{bytes}
8587 @opindex -s @var{bytes}
8588 @opindex --size=@var{bytes}
8589 @cindex size of file to shred
8590 Shred the first @var{bytes} bytes of the file. The default is to shred
8591 the whole file. @var{bytes} can be followed by a size specification like
8592 @samp{K}, @samp{M}, or @samp{G} to specify a multiple. @xref{Block size}.
8598 @cindex removing files after shredding
8599 After shredding a file, truncate it (if possible) and then remove it.
8600 If a file has multiple links, only the named links will be removed.
8606 Display to standard error all status updates as sterilization proceeds.
8612 By default, @command{shred} rounds the size of a regular file up to the next
8613 multiple of the file system block size to fully erase the last block of the file.
8614 Use @option{--exact} to suppress that behavior.
8615 Thus, by default if you shred a 10-byte regular file on a system with 512-byte
8616 blocks, the resulting file will be 512 bytes long. With this option,
8617 shred does not increase the apparent size of the file.
8623 Normally, the last pass that @command{shred} writes is made up of
8624 random data. If this would be conspicuous on your hard drive (for
8625 example, because it looks like encrypted data), or you just think
8626 it's tidier, the @option{--zero} option adds an additional overwrite pass with
8627 all zero bits. This is in addition to the number of passes specified
8628 by the @option{--iterations} option.
8632 You might use the following command to erase all trace of the
8633 file system you'd created on the floppy disk in your first drive.
8634 That command takes about 20 minutes to erase a ``1.44MB'' (actually
8638 shred --verbose /dev/fd0
8641 Similarly, to erase all data on a selected partition of
8642 your hard disk, you could give a command like this:
8645 shred --verbose /dev/sda5
8648 A @var{file} of @samp{-} denotes standard output.
8649 The intended use of this is to shred a removed temporary file.
8653 i=`tempfile -m 0600`
8656 echo "Hello, world" >&3
8661 However, the command @samp{shred - >file} does not shred the contents
8662 of @var{file}, since the shell truncates @var{file} before invoking
8663 @command{shred}. Use the command @samp{shred file} or (if using a
8664 Bourne-compatible shell) the command @samp{shred - 1<>file} instead.
8669 @node Special file types
8670 @chapter Special file types
8672 @cindex special file types
8673 @cindex file types, special
8675 This chapter describes commands which create special types of files (and
8676 @command{rmdir}, which removes directories, one special file type).
8678 @cindex special file types
8680 Although Unix-like operating systems have markedly fewer special file
8681 types than others, not @emph{everything} can be treated only as the
8682 undifferentiated byte stream of @dfn{normal files}. For example, when a
8683 file is created or removed, the system must record this information,
8684 which it does in a @dfn{directory}---a special type of file. Although
8685 you can read directories as normal files, if you're curious, in order
8686 for the system to do its job it must impose a structure, a certain
8687 order, on the bytes of the file. Thus it is a ``special'' type of file.
8689 Besides directories, other special file types include named pipes
8690 (FIFOs), symbolic links, sockets, and so-called @dfn{special files}.
8693 * link invocation:: Make a hard link via the link syscall
8694 * ln invocation:: Make links between files.
8695 * mkdir invocation:: Make directories.
8696 * mkfifo invocation:: Make FIFOs (named pipes).
8697 * mknod invocation:: Make block or character special files.
8698 * readlink invocation:: Print value of a symlink or canonical file name.
8699 * rmdir invocation:: Remove empty directories.
8700 * unlink invocation:: Remove files via the unlink syscall
8704 @node link invocation
8705 @section @command{link}: Make a hard link via the link syscall
8708 @cindex links, creating
8709 @cindex hard links, creating
8710 @cindex creating links (hard only)
8712 @command{link} creates a single hard link at a time.
8713 It is a minimalist interface to the system-provided
8714 @code{link} function. @xref{Hard Links, , , libc,
8715 The GNU C Library Reference Manual}.
8716 It avoids the bells and whistles of the more commonly-used
8717 @command{ln} command (@pxref{ln invocation}).
8721 link @var{filename} @var{linkname}
8724 @var{filename} must specify an existing file, and @var{linkname}
8725 must specify a nonexistent entry in an existing directory.
8726 @command{link} simply calls @code{link (@var{filename}, @var{linkname})}
8729 On a @acronym{GNU} system, this command acts like @samp{ln --directory
8730 --no-target-directory @var{filename} @var{linkname}}. However, the
8731 @option{--directory} and @option{--no-target-directory} options are
8732 not specified by @acronym{POSIX}, and the @command{link} command is
8733 more portable in practice.
8739 @section @command{ln}: Make links between files
8742 @cindex links, creating
8743 @cindex hard links, creating
8744 @cindex symbolic (soft) links, creating
8745 @cindex creating links (hard or soft)
8747 @cindex file systems and hard links
8748 @command{ln} makes links between files. By default, it makes hard links;
8749 with the @option{-s} option, it makes symbolic (or @dfn{soft}) links.
8753 ln [@var{option}]@dots{} [-T] @var{target} @var{linkname}
8754 ln [@var{option}]@dots{} @var{target}
8755 ln [@var{option}]@dots{} @var{target}@dots{} @var{directory}
8756 ln [@var{option}]@dots{} -t @var{directory} @var{target}@dots{}
8762 If two file names are given, @command{ln} creates a link to the first
8763 file from the second.
8766 If one @var{target} is given, @command{ln} creates a link to that file
8767 in the current directory.
8770 If the @option{--target-directory} (@option{-t}) option is given, or
8771 failing that if the last file is a directory and the
8772 @option{--no-target-directory} (@option{-T}) option is not given,
8773 @command{ln} creates a link to each @var{target} file in the specified
8774 directory, using the @var{target}s' names.
8778 Normally @command{ln} does not remove existing files. Use the
8779 @option{--force} (@option{-f}) option to remove them unconditionally,
8780 the @option{--interactive} (@option{-i}) option to remove them
8781 conditionally, and the @option{--backup} (@option{-b}) option to
8784 @cindex hard link, defined
8785 @cindex inode, and hard links
8786 A @dfn{hard link} is another name for an existing file; the link and the
8787 original are indistinguishable. Technically speaking, they share the
8788 same inode, and the inode contains all the information about a
8789 file---indeed, it is not incorrect to say that the inode @emph{is} the
8790 file. On all existing implementations, you cannot make a hard link to
8791 a directory, and hard links cannot cross file system boundaries. (These
8792 restrictions are not mandated by @acronym{POSIX}, however.)
8794 @cindex dereferencing symbolic links
8795 @cindex symbolic link, defined
8796 @dfn{Symbolic links} (@dfn{symlinks} for short), on the other hand, are
8797 a special file type (which not all kernels support: System V release 3
8798 (and older) systems lack symlinks) in which the link file actually
8799 refers to a different file, by name. When most operations (opening,
8800 reading, writing, and so on) are passed the symbolic link file, the
8801 kernel automatically @dfn{dereferences} the link and operates on the
8802 target of the link. But some operations (e.g., removing) work on the
8803 link file itself, rather than on its target. The owner, group, and
8804 mode of a symlink are not significant to file access performed through
8805 the link. @xref{Symbolic Links,,,
8806 libc, The GNU C Library Reference Manual}.
8808 Symbolic links can contain arbitrary strings; a @dfn{dangling symlink}
8809 occurs when the string in the symlink does not resolve to a file.
8810 There are no restrictions against creating dangling symbolic links.
8811 There are trade-offs to using absolute or relative symlinks. An
8812 absolute symlink always points to the same file, even if the directory
8813 containing the link is moved. However, if the symlink is visible from
8814 more than one machine (such as on a networked file system), the file
8815 pointed to might not always be the same. A relative symbolic link is
8816 resolved in relation to the directory that contains the link, and is
8817 often useful in referring to files on the same device without regards
8818 to what name that device is mounted on when accessed via networked
8821 When creating a relative symlink in a different location than the
8822 current directory, the resolution of the symlink will be different
8823 than the resolution of the same string from the current directory.
8824 Therefore, many users prefer to first change directories to the
8825 location where the relative symlink will be created, so that
8826 tab-completion or other file resolution will find the same target as
8827 what will be placed in the symlink.
8829 The program accepts the following options. Also see @ref{Common options}.
8840 @opindex --directory
8841 @cindex hard links to directories
8842 Allow users with appropriate privileges to attempt to make hard links
8844 However, note that this will probably fail due to
8845 system restrictions, even for the super-user.
8851 Remove existing destination files.
8854 @itemx --interactive
8856 @opindex --interactive
8857 @cindex prompting, and @command{ln}
8858 Prompt whether to remove existing destination files.
8861 @itemx --no-dereference
8863 @opindex --no-dereference
8864 Do not treat the last operand specially when it is a symbolic link to
8865 a directory. Instead, treat it as if it were a normal file.
8867 When the destination is an actual directory (not a symlink to one),
8868 there is no ambiguity. The link is created in that directory.
8869 But when the specified destination is a symlink to a directory,
8870 there are two ways to treat the user's request. @command{ln} can
8871 treat the destination just as it would a normal directory and create
8872 the link in it. On the other hand, the destination can be viewed as a
8873 non-directory---as the symlink itself. In that case, @command{ln}
8874 must delete or backup that symlink before creating the new link.
8875 The default is to treat a destination that is a symlink to a directory
8876 just like a directory.
8878 This option is weaker than the @option{--no-target-directory}
8879 (@option{-T}) option, so it has no effect if both options are given.
8885 Make symbolic links instead of hard links. This option merely produces
8886 an error message on systems that do not support symbolic links.
8892 @optNoTargetDirectory
8898 Print the name of each file after linking it successfully.
8909 # Create link ../a pointing to a in that directory.
8910 # Not really useful because it points to itself.
8915 # Change to the target before creating symlinks to avoid being confused.
8921 # Hard coded file names don't move well.
8922 ln -s $(pwd)/a /some/dir/
8926 # Relative file names survive directory moves and also
8927 # work across networked file systems.
8928 ln -s afile anotherfile
8929 ln -s ../adir/afile yetanotherfile
8933 @node mkdir invocation
8934 @section @command{mkdir}: Make directories
8937 @cindex directories, creating
8938 @cindex creating directories
8940 @command{mkdir} creates directories with the specified names. Synopsis:
8943 mkdir [@var{option}]@dots{} @var{name}@dots{}
8946 @command{mkdir} creates each directory @var{name} in the order given.
8947 It reports an error if @var{name} already exists, unless the
8948 @option{-p} option is given and @var{name} is a directory.
8950 The program accepts the following options. Also see @ref{Common options}.
8955 @itemx --mode=@var{mode}
8958 @cindex modes of created directories, setting
8959 Set the file permission bits of created directories to @var{mode},
8960 which uses the same syntax as
8961 in @command{chmod} and uses @samp{a=rwx} (read, write and execute allowed for
8962 everyone) for the point of the departure. @xref{File permissions}.
8964 Normally the directory has the desired file mode bits at the moment it
8965 is created. As a @acronym{GNU} extension, @var{mode} may also mention
8966 special mode bits, but in this case there may be a temporary window
8967 during which the directory exists but its special mode bits are
8968 incorrect. @xref{Directory Setuid and Setgid}, for how the
8969 set-user-ID and set-group-ID bits of directories are inherited unless
8970 overridden in this way.
8976 @cindex parent directories, creating
8977 Make any missing parent directories for each argument, setting their
8978 file permission bits to the umask modified by @samp{u+wx}. Ignore
8979 existing parent directories, and do not change their file permission
8982 To set the file permission bits of any newly-created parent
8983 directories to a value that includes @samp{u+wx}, you can set the
8984 umask before invoking @command{mkdir}. For example, if the shell
8985 command @samp{(umask u=rwx,go=rx; mkdir -p P/Q)} creates the parent
8986 @file{P} it sets the parent's permission bits to @samp{u=rwx,go=rx}.
8987 To set a parent's special mode bits as well, you can invoke
8988 @command{chmod} after @command{mkdir}. @xref{Directory Setuid and
8989 Setgid}, for how the set-user-ID and set-group-ID bits of
8990 newly-created parent directories are inherited.
8996 Print a message for each created directory. This is most useful with
8999 @item -Z @var{context}
9000 @itemx --context=@var{context}
9004 @cindex security context
9005 Set the default SELinux security context to be used for created directories.
9012 @node mkfifo invocation
9013 @section @command{mkfifo}: Make FIFOs (named pipes)
9016 @cindex FIFOs, creating
9017 @cindex named pipes, creating
9018 @cindex creating FIFOs (named pipes)
9020 @command{mkfifo} creates FIFOs (also called @dfn{named pipes}) with the
9021 specified names. Synopsis:
9024 mkfifo [@var{option}] @var{name}@dots{}
9027 A @dfn{FIFO} is a special file type that permits independent processes
9028 to communicate. One process opens the FIFO file for writing, and
9029 another for reading, after which data can flow as with the usual
9030 anonymous pipe in shells or elsewhere.
9032 The program accepts the following option. Also see @ref{Common options}.
9037 @itemx --mode=@var{mode}
9040 @cindex modes of created FIFOs, setting
9041 Set the mode of created FIFOs to @var{mode}, which is symbolic as in
9042 @command{chmod} and uses @samp{a=rw} (read and write allowed for everyone)
9043 for the point of departure. @var{mode} should specify only file
9044 permission bits. @xref{File permissions}.
9046 @item -Z @var{context}
9047 @itemx --context=@var{context}
9051 @cindex security context
9052 Set the default SELinux security context to be used for created FIFOs.
9059 @node mknod invocation
9060 @section @command{mknod}: Make block or character special files
9063 @cindex block special files, creating
9064 @cindex character special files, creating
9066 @command{mknod} creates a FIFO, character special file, or block special
9067 file with the specified name. Synopsis:
9070 mknod [@var{option}]@dots{} @var{name} @var{type} [@var{major} @var{minor}]
9073 @cindex special files
9074 @cindex block special files
9075 @cindex character special files
9076 Unlike the phrase ``special file type'' above, the term @dfn{special
9077 file} has a technical meaning on Unix: something that can generate or
9078 receive data. Usually this corresponds to a physical piece of hardware,
9079 e.g., a printer or a disk. (These files are typically created at
9080 system-configuration time.) The @command{mknod} command is what creates
9081 files of this type. Such devices can be read either a character at a
9082 time or a ``block'' (many characters) at a time, hence we say there are
9083 @dfn{block special} files and @dfn{character special} files.
9085 @c mknod is a shell built-in at least with OpenBSD's /bin/sh
9086 @mayConflictWithShellBuiltIn{mknod}
9088 The arguments after @var{name} specify the type of file to make:
9093 @opindex p @r{for FIFO file}
9097 @opindex b @r{for block special file}
9098 for a block special file
9101 @c Don't document the `u' option -- it's just a synonym for `c'.
9102 @c Do *any* versions of mknod still use it?
9104 @opindex c @r{for character special file}
9105 @c @opindex u @r{for character special file}
9106 for a character special file
9110 When making a block or character special file, the major and minor
9111 device numbers must be given after the file type.
9112 If a major or minor device number begins with @samp{0x} or @samp{0X},
9113 it is interpreted as hexadecimal; otherwise, if it begins with @samp{0},
9114 as octal; otherwise, as decimal.
9116 The program accepts the following option. Also see @ref{Common options}.
9121 @itemx --mode=@var{mode}
9124 Set the mode of created files to @var{mode}, which is symbolic as in
9125 @command{chmod} and uses @samp{a=rw} as the point of departure.
9126 @var{mode} should specify only file permission bits.
9127 @xref{File permissions}.
9129 @item -Z @var{context}
9130 @itemx --context=@var{context}
9134 @cindex security context
9135 Set the default SELinux security context to be used for created files.
9142 @node readlink invocation
9143 @section @command{readlink}: Print value of a symlink or canonical file name
9146 @cindex displaying value of a symbolic link
9147 @cindex canonical file name
9148 @cindex canonicalize a file name
9152 @command{readlink} may work in one of two supported modes:
9158 @command{readlink} outputs the value of the given symbolic link.
9159 If @command{readlink} is invoked with an argument other than the name
9160 of a symbolic link, it produces no output and exits with a nonzero exit code.
9162 @item Canonicalize mode
9164 @command{readlink} outputs the absolute name of the given file which contains
9165 no @file{.}, @file{..} components nor any repeated separators
9166 (@file{/}) or symbolic links.
9171 readlink [@var{option}] @var{file}
9174 By default, @command{readlink} operates in readlink mode.
9176 The program accepts the following options. Also see @ref{Common options}.
9181 @itemx --canonicalize
9183 @opindex --canonicalize
9184 Activate canonicalize mode.
9185 If any component of the file name except the last one is missing or unavailable,
9186 @command{readlink} produces no output and exits with a nonzero exit code.
9189 @itemx --canonicalize-existing
9191 @opindex --canonicalize-existing
9192 Activate canonicalize mode.
9193 If any component is missing or unavailable, @command{readlink} produces
9194 no output and exits with a nonzero exit code.
9197 @itemx --canonicalize-missing
9199 @opindex --canonicalize-missing
9200 Activate canonicalize mode.
9201 If any component is missing or unavailable, @command{readlink} treats it
9207 @opindex --no-newline
9208 Do not output the trailing newline.
9218 Suppress most error messages.
9224 Report error messages.
9228 The @command{readlink} utility first appeared in OpenBSD 2.1.
9230 There is a @command{realpath} command on some systems
9231 which operates like @command{readlink} in canonicalize mode.
9236 @node rmdir invocation
9237 @section @command{rmdir}: Remove empty directories
9240 @cindex removing empty directories
9241 @cindex directories, removing empty
9243 @command{rmdir} removes empty directories. Synopsis:
9246 rmdir [@var{option}]@dots{} @var{directory}@dots{}
9249 If any @var{directory} argument does not refer to an existing empty
9250 directory, it is an error.
9252 The program accepts the following options. Also see @ref{Common options}.
9256 @item --ignore-fail-on-non-empty
9257 @opindex --ignore-fail-on-non-empty
9258 @cindex directory deletion, ignoring failures
9259 Ignore each failure to remove a directory that is solely because
9260 the directory is non-empty.
9266 @cindex parent directories, removing
9267 Remove @var{directory}, then try to remove each component of @var{directory}.
9268 So, for example, @samp{rmdir -p a/b/c} is similar to @samp{rmdir a/b/c a/b a}.
9269 As such, it fails if any of those directories turns out not to be empty.
9270 Use the @option{--ignore-fail-on-non-empty} option to make it so such
9271 a failure does not evoke a diagnostic and does not cause @command{rmdir} to
9272 exit unsuccessfully.
9278 @cindex directory deletion, reporting
9279 Give a diagnostic for each successful removal.
9280 @var{directory} is removed.
9284 @xref{rm invocation}, for how to remove non-empty directories (recursively).
9289 @node unlink invocation
9290 @section @command{unlink}: Remove files via the unlink syscall
9293 @cindex removing files or directories (via the unlink syscall)
9295 @command{unlink} deletes a single specified file name.
9296 It is a minimalist interface to the system-provided
9297 @code{unlink} function. @xref{Deleting Files, , , libc,
9298 The GNU C Library Reference Manual}. Synopsis:
9299 It avoids the bells and whistles of the more commonly-used
9300 @command{rm} command (@pxref{rm invocation}).
9303 unlink @var{filename}
9306 On some systems @code{unlink} can be used to delete the name of a
9307 directory. On others, it can be used that way only by a privileged user.
9308 In the GNU system @code{unlink} can never delete the name of a directory.
9310 The @command{unlink} command honors the @option{--help} and
9311 @option{--version} options. To remove a file whose name begins with
9312 @samp{-}, prefix the name with @samp{./}, e.g., @samp{unlink ./--help}.
9317 @node Changing file attributes
9318 @chapter Changing file attributes
9320 @cindex changing file attributes
9321 @cindex file attributes, changing
9322 @cindex attributes, file
9324 A file is not merely its contents, a name, and a file type
9325 (@pxref{Special file types}). A file also has an owner (a user ID), a
9326 group (a group ID), permissions (what the owner can do with the file,
9327 what people in the group can do, and what everyone else can do), various
9328 timestamps, and other information. Collectively, we call these a file's
9331 These commands change file attributes.
9334 * chgrp invocation:: Change file groups.
9335 * chmod invocation:: Change access permissions.
9336 * chown invocation:: Change file owners and groups.
9337 * touch invocation:: Change file timestamps.
9341 @node chown invocation
9342 @section @command{chown}: Change file owner and group
9345 @cindex file ownership, changing
9346 @cindex group ownership, changing
9347 @cindex changing file ownership
9348 @cindex changing group ownership
9350 @command{chown} changes the user and/or group ownership of each given @var{file}
9351 to @var{new-owner} or to the user and group of an existing reference file.
9355 chown [@var{option}]@dots{} @{@var{new-owner} | --reference=@var{ref_file}@} @var{file}@dots{}
9358 If used, @var{new-owner} specifies the new owner and/or group as follows
9359 (with no embedded white space):
9362 [@var{owner}] [ : [@var{group}] ]
9369 If only an @var{owner} (a user name or numeric user ID) is given, that
9370 user is made the owner of each given file, and the files' group is not
9373 @item owner@samp{:}group
9374 If the @var{owner} is followed by a colon and a @var{group} (a
9375 group name or numeric group ID), with no spaces between them, the group
9376 ownership of the files is changed as well (to @var{group}).
9379 If a colon but no group name follows @var{owner}, that user is
9380 made the owner of the files and the group of the files is changed to
9381 @var{owner}'s login group.
9384 If the colon and following @var{group} are given, but the owner
9385 is omitted, only the group of the files is changed; in this case,
9386 @command{chown} performs the same function as @command{chgrp}.
9389 If only a colon is given, or if @var{new-owner} is empty, neither the
9390 owner nor the group is changed.
9394 If @var{owner} or @var{group} is intended to represent a numeric user
9395 or group ID, then you may specify it with a leading @samp{+}.
9396 @xref{Disambiguating names and IDs}.
9398 Some older scripts may still use @samp{.} in place of the @samp{:} separator.
9399 @acronym{POSIX} 1003.1-2001 (@pxref{Standards conformance}) does not
9400 require support for that, but for backward compatibility @acronym{GNU}
9401 @command{chown} supports @samp{.} so long as no ambiguity results.
9402 New scripts should avoid the use of @samp{.} because it is not
9403 portable, and because it has undesirable results if the entire
9404 @var{owner@samp{.}group} happens to identify a user whose name
9407 The @command{chown} command sometimes clears the set-user-ID or
9408 set-group-ID permission bits. This behavior depends on the policy and
9409 functionality of the underlying @code{chown} system call, which may
9410 make system-dependent file mode modifications outside the control of
9411 the @command{chown} command. For example, the @command{chown} command
9412 might not affect those bits when invoked by a user with appropriate
9413 privileges, or when the
9414 bits signify some function other than executable permission (e.g.,
9416 When in doubt, check the underlying system behavior.
9418 The program accepts the following options. Also see @ref{Common options}.
9426 @cindex changed owners, verbosely describing
9427 Verbosely describe the action for each @var{file} whose ownership
9436 @cindex error messages, omitting
9437 Do not print error messages about files whose ownership cannot be
9440 @itemx @w{@kbd{--from}=@var{old-owner}}
9442 @cindex symbolic links, changing owner
9443 Change a @var{file}'s ownership only if it has current attributes specified
9444 by @var{old-owner}. @var{old-owner} has the same form as @var{new-owner}
9446 This option is useful primarily from a security standpoint in that
9447 it narrows considerably the window of potential abuse.
9448 For example, to reflect a user ID numbering change for one user's files
9449 without an option like this, @code{root} might run
9452 find / -owner OLDUSER -print0 | xargs -0 chown -h NEWUSER
9455 But that is dangerous because the interval between when the @command{find}
9456 tests the existing file's owner and when the @command{chown} is actually run
9458 One way to narrow the gap would be to invoke chown for each file
9462 find / -owner OLDUSER -exec chown -h NEWUSER @{@} \;
9465 But that is very slow if there are many affected files.
9466 With this option, it is safer (the gap is narrower still)
9467 though still not perfect:
9470 chown -h -R --from=OLDUSER NEWUSER /
9474 @opindex --dereference
9475 @cindex symbolic links, changing owner
9477 Do not act on symbolic links themselves but rather on what they point to.
9478 This is the default.
9481 @itemx --no-dereference
9483 @opindex --no-dereference
9484 @cindex symbolic links, changing owner
9486 Act on symbolic links themselves instead of what they point to.
9487 This mode relies on the @code{lchown} system call.
9488 On systems that do not provide the @code{lchown} system call,
9489 @command{chown} fails when a file specified on the command line
9491 By default, no diagnostic is issued for symbolic links encountered
9492 during a recursive traversal, but see @option{--verbose}.
9494 @itemx --preserve-root
9495 @opindex --preserve-root
9496 @cindex root directory, disallow recursive modification
9497 Fail upon any attempt to recursively change the root directory, @file{/}.
9498 Without @option{--recursive}, this option has no effect.
9499 @xref{Treating / specially}.
9501 @itemx --no-preserve-root
9502 @opindex --no-preserve-root
9503 @cindex root directory, allow recursive modification
9504 Cancel the effect of any preceding @option{--preserve-root} option.
9505 @xref{Treating / specially}.
9507 @item --reference=@var{ref_file}
9508 @opindex --reference
9509 Change the user and group of each @var{file} to be the same as those of
9510 @var{ref_file}. If @var{ref_file} is a symbolic link, do not use the
9511 user and group of the symbolic link, but rather those of the file it
9518 Output a diagnostic for every file processed.
9519 If a symbolic link is encountered during a recursive traversal
9520 on a system without the @code{lchown} system call, and @option{--no-dereference}
9521 is in effect, then issue a diagnostic saying neither the symbolic link nor
9522 its referent is being changed.
9527 @opindex --recursive
9528 @cindex recursively changing file ownership
9529 Recursively change ownership of directories and their contents.
9532 @xref{Traversing symlinks}.
9535 @xref{Traversing symlinks}.
9538 @xref{Traversing symlinks}.
9547 # Change the owner of /u to "root".
9550 # Likewise, but also change its group to "staff".
9553 # Change the owner of /u and subfiles to "root".
9558 @node chgrp invocation
9559 @section @command{chgrp}: Change group ownership
9562 @cindex group ownership, changing
9563 @cindex changing group ownership
9565 @command{chgrp} changes the group ownership of each given @var{file}
9566 to @var{group} (which can be either a group name or a numeric group ID)
9567 or to the group of an existing reference file. Synopsis:
9570 chgrp [@var{option}]@dots{} @{@var{group} | --reference=@var{ref_file}@} @var{file}@dots{}
9573 If @var{group} is intended to represent a
9574 numeric group ID, then you may specify it with a leading @samp{+}.
9575 @xref{Disambiguating names and IDs}.
9577 The program accepts the following options. Also see @ref{Common options}.
9585 @cindex changed files, verbosely describing
9586 Verbosely describe the action for each @var{file} whose group actually
9595 @cindex error messages, omitting
9596 Do not print error messages about files whose group cannot be
9600 @opindex --dereference
9601 @cindex symbolic links, changing owner
9603 Do not act on symbolic links themselves but rather on what they point to.
9604 This is the default.
9607 @itemx --no-dereference
9609 @opindex --no-dereference
9610 @cindex symbolic links, changing group
9612 Act on symbolic links themselves instead of what they point to.
9613 This mode relies on the @code{lchown} system call.
9614 On systems that do not provide the @code{lchown} system call,
9615 @command{chgrp} fails when a file specified on the command line
9617 By default, no diagnostic is issued for symbolic links encountered
9618 during a recursive traversal, but see @option{--verbose}.
9620 @itemx --preserve-root
9621 @opindex --preserve-root
9622 @cindex root directory, disallow recursive modification
9623 Fail upon any attempt to recursively change the root directory, @file{/}.
9624 Without @option{--recursive}, this option has no effect.
9625 @xref{Treating / specially}.
9627 @itemx --no-preserve-root
9628 @opindex --no-preserve-root
9629 @cindex root directory, allow recursive modification
9630 Cancel the effect of any preceding @option{--preserve-root} option.
9631 @xref{Treating / specially}.
9633 @item --reference=@var{ref_file}
9634 @opindex --reference
9635 Change the group of each @var{file} to be the same as that of
9636 @var{ref_file}. If @var{ref_file} is a symbolic link, do not use the
9637 group of the symbolic link, but rather that of the file it refers to.
9643 Output a diagnostic for every file processed.
9644 If a symbolic link is encountered during a recursive traversal
9645 on a system without the @code{lchown} system call, and @option{--no-dereference}
9646 is in effect, then issue a diagnostic saying neither the symbolic link nor
9647 its referent is being changed.
9652 @opindex --recursive
9653 @cindex recursively changing group ownership
9654 Recursively change the group ownership of directories and their contents.
9657 @xref{Traversing symlinks}.
9660 @xref{Traversing symlinks}.
9663 @xref{Traversing symlinks}.
9672 # Change the group of /u to "staff".
9675 # Change the group of /u and subfiles to "staff".
9680 @node chmod invocation
9681 @section @command{chmod}: Change access permissions
9684 @cindex changing access permissions
9685 @cindex access permissions, changing
9686 @cindex permissions, changing access
9688 @command{chmod} changes the access permissions of the named files. Synopsis:
9691 chmod [@var{option}]@dots{} @{@var{mode} | --reference=@var{ref_file}@} @var{file}@dots{}
9694 @cindex symbolic links, permissions of
9695 @command{chmod} never changes the permissions of symbolic links, since
9696 the @command{chmod} system call cannot change their permissions.
9697 This is not a problem since the permissions of symbolic links are
9698 never used. However, for each symbolic link listed on the command
9699 line, @command{chmod} changes the permissions of the pointed-to file.
9700 In contrast, @command{chmod} ignores symbolic links encountered during
9701 recursive directory traversals.
9703 A successful use of @command{chmod} clears the set-group-ID bit of a
9704 regular file if the file's group ID does not match the user's
9705 effective group ID or one of the user's supplementary group IDs,
9706 unless the user has appropriate privileges. Additional restrictions
9707 may cause the set-user-ID and set-group-ID bits of @var{mode} or
9708 @var{ref_file} to be ignored. This behavior depends on the policy and
9709 functionality of the underlying @code{chmod} system call. When in
9710 doubt, check the underlying system behavior.
9712 If used, @var{mode} specifies the new file mode bits.
9713 For details, see the section on @ref{File permissions}.
9714 If you really want @var{mode} to have a leading @samp{-}, you should
9715 use @option{--} first, e.g., @samp{chmod -- -w file}. Typically,
9716 though, @samp{chmod a-w file} is preferable, and @command{chmod -w
9717 file} (without the @option{--}) complains if it behaves differently
9718 from what @samp{chmod a-w file} would do.
9720 The program accepts the following options. Also see @ref{Common options}.
9728 Verbosely describe the action for each @var{file} whose permissions
9737 @cindex error messages, omitting
9738 Do not print error messages about files whose permissions cannot be
9741 @itemx --preserve-root
9742 @opindex --preserve-root
9743 @cindex root directory, disallow recursive modification
9744 Fail upon any attempt to recursively change the root directory, @file{/}.
9745 Without @option{--recursive}, this option has no effect.
9746 @xref{Treating / specially}.
9748 @itemx --no-preserve-root
9749 @opindex --no-preserve-root
9750 @cindex root directory, allow recursive modification
9751 Cancel the effect of any preceding @option{--preserve-root} option.
9752 @xref{Treating / specially}.
9758 Verbosely describe the action or non-action taken for every @var{file}.
9760 @item --reference=@var{ref_file}
9761 @opindex --reference
9762 Change the mode of each @var{file} to be the same as that of @var{ref_file}.
9763 @xref{File permissions}.
9764 If @var{ref_file} is a symbolic link, do not use the mode
9765 of the symbolic link, but rather that of the file it refers to.
9770 @opindex --recursive
9771 @cindex recursively changing access permissions
9772 Recursively change permissions of directories and their contents.
9779 @node touch invocation
9780 @section @command{touch}: Change file timestamps
9783 @cindex changing file timestamps
9784 @cindex file timestamps, changing
9785 @cindex timestamps, changing file
9787 @command{touch} changes the access and/or modification times of the
9788 specified files. Synopsis:
9791 touch [@var{option}]@dots{} @var{file}@dots{}
9794 @cindex empty files, creating
9795 Any @var{file} argument that does not exist is created empty.
9797 A @var{file} argument string of @samp{-} is handled specially and
9798 causes @command{touch} to change the times of the file associated with
9801 @cindex permissions, for changing file timestamps
9802 If changing both the access and modification times to the current
9803 time, @command{touch} can change the timestamps for files that the user
9804 running it does not own but has write permission for. Otherwise, the
9805 user must own the files.
9807 Although @command{touch} provides options for changing two of the times---the
9808 times of last access and modification---of a file, there is actually
9809 a third one as well: the inode change time. This is often referred to
9810 as a file's @code{ctime}.
9811 The inode change time represents the time when the file's meta-information
9812 last changed. One common example of this is when the permissions of a
9813 file change. Changing the permissions doesn't access the file, so
9814 the atime doesn't change, nor does it modify the file, so the mtime
9815 doesn't change. Yet, something about the file itself has changed,
9816 and this must be noted somewhere. This is the job of the ctime field.
9817 This is necessary, so that, for example, a backup program can make a
9818 fresh copy of the file, including the new permissions value.
9819 Another operation that modifies a file's ctime without affecting
9820 the others is renaming. In any case, it is not possible, in normal
9821 operations, for a user to change the ctime field to a user-specified value.
9824 Time stamps assume the time zone rules specified by the @env{TZ}
9825 environment variable, or by the system default rules if @env{TZ} is
9826 not set. @xref{TZ Variable,, Specifying the Time Zone with @env{TZ},
9827 libc, The GNU C Library Reference Manual}.
9828 You can avoid ambiguities during
9829 daylight saving transitions by using @sc{utc} time stamps.
9831 The program accepts the following options. Also see @ref{Common options}.
9837 @itemx --time=access
9841 @opindex atime@r{, changing}
9842 @opindex access @r{time, changing}
9843 @opindex use @r{time, changing}
9844 Change the access time only.
9849 @opindex --no-create
9850 Do not create files that do not exist.
9853 @itemx --date=@var{time}
9857 Use @var{time} instead of the current time. It can contain month names,
9858 time zones, @samp{am} and @samp{pm}, @samp{yesterday}, etc. For
9859 example, @option{--date="2004-02-27 14:19:13.489392193 +0530"}
9860 specifies the instant of time that is 489,392,193 nanoseconds after
9861 February 27, 2004 at 2:19:13 PM in a time zone that is 5 hours and 30
9862 minutes east of @acronym{UTC}. @xref{Date input formats}.
9863 File systems that do not support high-resolution time stamps
9864 silently ignore any excess precision here.
9868 @cindex BSD @command{touch} compatibility
9869 Ignored; for compatibility with BSD versions of @command{touch}.
9873 @itemx --time=modify
9876 @opindex mtime@r{, changing}
9877 @opindex modify @r{time, changing}
9878 Change the modification time only.
9881 @itemx --reference=@var{file}
9883 @opindex --reference
9884 Use the times of the reference @var{file} instead of the current time.
9885 If this option is combined with the @option{--date=@var{time}}
9886 (@option{-d @var{time}}) option, the reference @var{file}'s time is
9887 the origin for any relative @var{time}s given, but is otherwise ignored.
9888 For example, @samp{-r foo -d '-5 seconds'} specifies a time stamp
9889 equal to five seconds before the corresponding time stamp for @file{foo}.
9891 @item -t [[@var{cc}]@var{yy}]@var{mmddhhmm}[.@var{ss}]
9892 Use the argument (optional four-digit or two-digit years, months,
9893 days, hours, minutes, optional seconds) instead of the current time.
9894 If the year is specified with only two digits, then @var{cc}
9895 is 20 for years in the range 0 @dots{} 68, and 19 for years in
9896 69 @dots{} 99. If no digits of the year are specified,
9897 the argument is interpreted as a date in the current year.
9901 @vindex _POSIX2_VERSION
9902 On older systems, @command{touch} supports an obsolete syntax, as follows.
9903 If no timestamp is given with any of the @option{-d}, @option{-r}, or
9904 @option{-t} options, and if there are two or more @var{file}s and the
9905 first @var{file} is of the form @samp{@var{mmddhhmm}[@var{yy}]} and this
9906 would be a valid argument to the @option{-t} option (if the @var{yy}, if
9907 any, were moved to the front), and if the represented year
9908 is in the range 1969--1999, that argument is interpreted as the time
9909 for the other files instead of as a file name.
9910 This obsolete behavior can be enabled or disabled with the
9911 @env{_POSIX2_VERSION} environment variable (@pxref{Standards
9912 conformance}), but portable scripts should avoid commands whose
9913 behavior depends on this variable.
9914 For example, use @samp{touch ./12312359 main.c} or @samp{touch -t
9915 12312359 main.c} rather than the ambiguous @samp{touch 12312359 main.c}.
9925 No disk can hold an infinite amount of data. These commands report
9926 how much disk storage is in use or available, report other file and
9927 file status information, and write buffers to disk.
9930 * df invocation:: Report file system disk space usage.
9931 * du invocation:: Estimate file space usage.
9932 * stat invocation:: Report file or file system status.
9933 * sync invocation:: Synchronize memory and disk.
9934 * truncate invocation:: Shrink or extend the size of a file.
9939 @section @command{df}: Report file system disk space usage
9942 @cindex file system disk usage
9943 @cindex disk usage by file system
9945 @command{df} reports the amount of disk space used and available on
9946 file systems. Synopsis:
9949 df [@var{option}]@dots{} [@var{file}]@dots{}
9952 With no arguments, @command{df} reports the space used and available on all
9953 currently mounted file systems (of all types). Otherwise, @command{df}
9954 reports on the file system containing each argument @var{file}.
9956 Normally the disk space is printed in units of
9957 1024 bytes, but this can be overridden (@pxref{Block size}).
9958 Non-integer quantities are rounded up to the next higher unit.
9960 @cindex disk device file
9961 @cindex device file, disk
9962 If an argument @var{file} is a disk device file containing a mounted
9963 file system, @command{df} shows the space available on that file system
9964 rather than on the file system containing the device node (i.e., the root
9965 file system). @sc{gnu} @command{df} does not attempt to determine the disk usage
9966 on unmounted file systems, because on most kinds of systems doing so
9967 requires extremely nonportable intimate knowledge of file system
9970 The program accepts the following options. Also see @ref{Common options}.
9978 @cindex automounter file systems
9979 @cindex ignore file systems
9980 Include in the listing dummy file systems, which
9981 are omitted by default. Such file systems are typically special-purpose
9982 pseudo-file-systems, such as automounter entries.
9985 @itemx --block-size=@var{size}
9987 @opindex --block-size
9988 @cindex file system sizes
9989 Scale sizes by @var{size} before printing them (@pxref{Block size}).
9990 For example, @option{-BG} prints sizes in units of 1,073,741,824 bytes.
9994 @cindex grand total of disk size, usage and available space
9995 Print a grand total of all arguments after all arguments have
9996 been processed. This can be used to find out the total disk size, usage
9997 and available space of all listed devices.
10003 Equivalent to @option{--si}.
10009 @cindex inode usage
10010 List inode usage information instead of block usage. An inode (short
10011 for index node) contains information about a file such as its owner,
10012 permissions, timestamps, and location on the disk.
10016 @cindex kibibytes for file system sizes
10017 Print sizes in 1024-byte blocks, overriding the default block size
10018 (@pxref{Block size}).
10019 This option is equivalent to @option{--block-size=1K}.
10025 @cindex file system types, limiting output to certain
10026 Limit the listing to local file systems. By default, remote file systems
10031 @cindex file system space, retrieving old data more quickly
10032 Do not invoke the @code{sync} system call before getting any usage data.
10033 This may make @command{df} run significantly faster on systems with many
10034 disks, but on some systems (notably SunOS) the results may be slightly
10035 out of date. This is the default.
10038 @itemx --portability
10040 @opindex --portability
10041 @cindex one-line output format
10042 @cindex @acronym{POSIX} output format
10043 @cindex portable output format
10044 @cindex output format, portable
10045 Use the @acronym{POSIX} output format. This is like the default format except
10050 The information about each file system is always printed on exactly
10051 one line; a mount device is never put on a line by itself. This means
10052 that if the mount device name is more than 20 characters long (e.g., for
10053 some network mounts), the columns are misaligned.
10056 The labels in the header output line are changed to conform to @acronym{POSIX}.
10059 The default block size and output format are unaffected by the
10060 @env{DF_BLOCK_SIZE}, @env{BLOCK_SIZE} and @env{BLOCKSIZE} environment
10061 variables. However, the default block size is still affected by
10062 @env{POSIXLY_CORRECT}: it is 512 if @env{POSIXLY_CORRECT} is set, 1024
10063 otherwise. @xref{Block size}.
10070 @cindex file system space, retrieving current data more slowly
10071 Invoke the @code{sync} system call before getting any usage data. On
10072 some systems (notably SunOS), doing this yields more up to date results,
10073 but in general this option makes @command{df} much slower, especially when
10074 there are many or very busy file systems.
10076 @item -t @var{fstype}
10077 @itemx --type=@var{fstype}
10080 @cindex file system types, limiting output to certain
10081 Limit the listing to file systems of type @var{fstype}. Multiple
10082 file system types can be specified by giving multiple @option{-t} options.
10083 By default, nothing is omitted.
10086 @itemx --print-type
10088 @opindex --print-type
10089 @cindex file system types, printing
10090 Print each file system's type. The types printed here are the same ones
10091 you can include or exclude with @option{-t} and @option{-x}. The particular
10092 types printed are whatever is supported by the system. Here are some of
10093 the common names (this list is certainly not exhaustive):
10098 @cindex @acronym{NFS} file system type
10099 An @acronym{NFS} file system, i.e., one mounted over a network from another
10100 machine. This is the one type name which seems to be used uniformly by
10103 @item 4.2@r{, }ufs@r{, }efs@dots{}
10104 @cindex Linux file system types
10105 @cindex local file system types
10106 @opindex 4.2 @r{file system type}
10107 @opindex ufs @r{file system type}
10108 @opindex efs @r{file system type}
10109 A file system on a locally-mounted hard disk. (The system might even
10110 support more than one type here; Linux does.)
10112 @item hsfs@r{, }cdfs
10113 @cindex CD-ROM file system type
10114 @cindex High Sierra file system
10115 @opindex hsfs @r{file system type}
10116 @opindex cdfs @r{file system type}
10117 A file system on a CD-ROM drive. HP-UX uses @samp{cdfs}, most other
10118 systems use @samp{hsfs} (@samp{hs} for ``High Sierra'').
10121 @cindex PC file system
10122 @cindex DOS file system
10123 @cindex MS-DOS file system
10124 @cindex diskette file system
10126 An MS-DOS file system, usually on a diskette.
10130 @item -x @var{fstype}
10131 @itemx --exclude-type=@var{fstype}
10133 @opindex --exclude-type
10134 Limit the listing to file systems not of type @var{fstype}.
10135 Multiple file system types can be eliminated by giving multiple
10136 @option{-x} options. By default, no file system types are omitted.
10139 Ignored; for compatibility with System V versions of @command{df}.
10144 Failure includes the case where no output is generated, so you can
10145 inspect the exit status of a command like @samp{df -t ext3 -t reiserfs
10146 @var{dir}} to test whether @var{dir} is on a file system of type
10147 @samp{ext3} or @samp{reiserfs}.
10150 @node du invocation
10151 @section @command{du}: Estimate file space usage
10154 @cindex file space usage
10155 @cindex disk usage for files
10157 @command{du} reports the amount of disk space used by the specified files
10158 and for each subdirectory (of directory arguments). Synopsis:
10161 du [@var{option}]@dots{} [@var{file}]@dots{}
10164 With no arguments, @command{du} reports the disk space for the current
10165 directory. Normally the disk space is printed in units of
10166 1024 bytes, but this can be overridden (@pxref{Block size}).
10167 Non-integer quantities are rounded up to the next higher unit.
10169 If two or more hard links point to the same file, only one of the hard
10170 links is counted. The @var{file} argument order affects which links
10171 are counted, and changing the argument order may change the numbers
10172 that @command{du} outputs.
10174 The program accepts the following options. Also see @ref{Common options}.
10182 Show counts for all files, not just directories.
10184 @itemx --apparent-size
10185 @opindex --apparent-size
10186 Print apparent sizes, rather than disk usage. The apparent size of a
10187 file is the number of bytes reported by @code{wc -c} on regular files,
10188 or more generally, @code{ls -l --block-size=1} or @code{stat --format=%s}.
10189 For example, a file containing the word @samp{zoo} with no newline would,
10190 of course, have an apparent size of 3. Such a small file may require
10191 anywhere from 0 to 16 KiB or more of disk space, depending on
10192 the type and configuration of the file system on which the file resides.
10193 However, a sparse file created with this command:
10196 dd bs=1 seek=2GiB if=/dev/null of=big
10200 has an apparent size of 2 GiB, yet on most modern
10201 systems, it actually uses almost no disk space.
10207 Equivalent to @code{--apparent-size --block-size=1}.
10209 @item -B @var{size}
10210 @itemx --block-size=@var{size}
10212 @opindex --block-size
10214 Scale sizes by @var{size} before printing them (@pxref{Block size}).
10215 For example, @option{-BG} prints sizes in units of 1,073,741,824 bytes.
10221 @cindex grand total of disk space
10222 Print a grand total of all arguments after all arguments have
10223 been processed. This can be used to find out the total disk usage of
10224 a given set of files or directories.
10227 @itemx --dereference-args
10229 @opindex --dereference-args
10230 Dereference symbolic links that are command line arguments.
10231 Does not affect other symbolic links. This is helpful for finding
10232 out the disk usage of directories, such as @file{/usr/tmp}, which
10233 are often symbolic links.
10235 @c --files0-from=FILE
10236 @filesZeroFromOption{du,, with the @option{--total} (@option{-c}) option}
10242 Equivalent to @option{--dereference-args} (@option{-D}).
10246 @cindex kibibytes for file sizes
10247 Print sizes in 1024-byte blocks, overriding the default block size
10248 (@pxref{Block size}).
10249 This option is equivalent to @option{--block-size=1K}.
10252 @itemx --count-links
10254 @opindex --count-links
10255 @cindex hard links, counting in @command{du}
10256 Count the size of all files, even if they have appeared already (as a
10260 @itemx --dereference
10262 @opindex --dereference
10263 @cindex symbolic links, dereferencing in @command{du}
10264 Dereference symbolic links (show the disk space used by the file
10265 or directory that the link points to instead of the space used by
10270 @cindex mebibytes for file sizes
10271 Print sizes in 1,048,576-byte blocks, overriding the default block size
10272 (@pxref{Block size}).
10273 This option is equivalent to @option{--block-size=1M}.
10276 @itemx --no-dereference
10278 @opindex --no-dereference
10279 @cindex symbolic links, dereferencing in @command{du}
10280 For each symbolic links encountered by @command{du},
10281 consider the disk space used by the symbolic link.
10283 @item --max-depth=@var{depth}
10284 @opindex --max-depth=@var{depth}
10285 @cindex limiting output of @command{du}
10286 Show the total for each directory (and file if --all) that is at
10287 most MAX_DEPTH levels down from the root of the hierarchy. The root
10288 is at level 0, so @code{du --max-depth=0} is equivalent to @code{du -s}.
10294 @cindex output null-byte-terminated lines
10295 Output a zero byte (@acronym{ASCII} @sc{nul}) at the end of each line,
10296 rather than a newline. This option enables other programs to parse the
10297 output of @command{du} even when that output would contain file names
10298 with embedded newlines.
10305 @opindex --summarize
10306 Display only a total for each argument.
10309 @itemx --separate-dirs
10311 @opindex --separate-dirs
10312 Normally, in the output of @command{du} (when not using @option{--summarize}),
10313 the size listed next to a directory name, @var{d}, represents the sum
10314 of sizes of all entries beneath @var{d} as well as the size of @var{d} itself.
10315 With @option{--separate-dirs}, the size reported for a directory name,
10316 @var{d}, is merely the @code{stat.st_size}-derived size of the directory
10321 @cindex last modified dates, displaying in @command{du}
10322 Show time of the most recent modification of any file in the directory,
10323 or any of its subdirectories.
10325 @itemx --time=ctime
10326 @itemx --time=status
10329 @opindex ctime@r{, show the most recent}
10330 @opindex status time@r{, show the most recent}
10331 @opindex use time@r{, show the most recent}
10332 Show the most recent status change time (the @samp{ctime} in the inode) of
10333 any file in the directory, instead of the modification time.
10335 @itemx --time=atime
10336 @itemx --time=access
10338 @opindex atime@r{, show the most recent}
10339 @opindex access time@r{, show the most recent}
10340 Show the most recent access time (the @samp{atime} in the inode) of
10341 any file in the directory, instead of the modification time.
10343 @item --time-style=@var{style}
10344 @opindex --time-style
10346 List timestamps in style @var{style}. This option has an effect only if
10347 the @option{--time} option is also specified. The @var{style} should
10348 be one of the following:
10351 @item +@var{format}
10353 List timestamps using @var{format}, where @var{format} is interpreted
10354 like the format argument of @command{date} (@pxref{date invocation}).
10355 For example, @option{--time-style="+%Y-%m-%d %H:%M:%S"} causes
10356 @command{du} to list timestamps like @samp{2002-03-30 23:45:56}. As
10357 with @command{date}, @var{format}'s interpretation is affected by the
10358 @env{LC_TIME} locale category.
10361 List timestamps in full using @acronym{ISO} 8601 date, time, and time zone
10362 format with nanosecond precision, e.g., @samp{2002-03-30
10363 23:45:56.477817180 -0700}. This style is equivalent to
10364 @samp{+%Y-%m-%d %H:%M:%S.%N %z}.
10367 List @acronym{ISO} 8601 date and time in minutes, e.g.,
10368 @samp{2002-03-30 23:45}. These timestamps are shorter than
10369 @samp{full-iso} timestamps, and are usually good enough for everyday
10370 work. This style is equivalent to @samp{+%Y-%m-%d %H:%M}.
10373 List @acronym{ISO} 8601 dates for timestamps, e.g., @samp{2002-03-30}.
10374 This style is equivalent to @samp{+%Y-%m-%d}.
10378 You can specify the default value of the @option{--time-style} option
10379 with the environment variable @env{TIME_STYLE}; if @env{TIME_STYLE} is not set
10380 the default style is @samp{long-iso}. For compatibility with @command{ls},
10381 if @env{TIME_STYLE} begins with @samp{+} and contains a newline,
10382 the newline and any later characters are ignored; if @env{TIME_STYLE}
10383 begins with @samp{posix-} the @samp{posix-} is ignored; and if
10384 @env{TIME_STYLE} is @samp{locale} it is ignored.
10387 @itemx --one-file-system
10389 @opindex --one-file-system
10390 @cindex one file system, restricting @command{du} to
10391 Skip directories that are on different file systems from the one that
10392 the argument being processed is on.
10394 @item --exclude=@var{pattern}
10395 @opindex --exclude=@var{pattern}
10396 @cindex excluding files from @command{du}
10397 When recursing, skip subdirectories or files matching @var{pattern}.
10398 For example, @code{du --exclude='*.o'} excludes files whose names
10401 @item -X @var{file}
10402 @itemx --exclude-from=@var{file}
10403 @opindex -X @var{file}
10404 @opindex --exclude-from=@var{file}
10405 @cindex excluding files from @command{du}
10406 Like @option{--exclude}, except take the patterns to exclude from @var{file},
10407 one per line. If @var{file} is @samp{-}, take the patterns from standard
10412 @cindex NFS mounts from BSD to HP-UX
10413 On BSD systems, @command{du} reports sizes that are half the correct
10414 values for files that are NFS-mounted from HP-UX systems. On HP-UX
10415 systems, it reports sizes that are twice the correct values for
10416 files that are NFS-mounted from BSD systems. This is due to a flaw
10417 in HP-UX; it also affects the HP-UX @command{du} program.
10422 @node stat invocation
10423 @section @command{stat}: Report file or file system status
10426 @cindex file status
10427 @cindex file system status
10429 @command{stat} displays information about the specified file(s). Synopsis:
10432 stat [@var{option}]@dots{} [@var{file}]@dots{}
10435 With no option, @command{stat} reports all information about the given files.
10436 But it also can be used to report the information of the file systems the
10437 given files are located on. If the files are links, @command{stat} can
10438 also give information about the files the links point to.
10440 @mayConflictWithShellBuiltIn{stat}
10445 @itemx --dereference
10447 @opindex --dereference
10448 @cindex symbolic links, dereferencing in @command{stat}
10449 Change how @command{stat} treats symbolic links.
10450 With this option, @command{stat} acts on the file referenced
10451 by each symbolic link argument.
10452 Without it, @command{stat} acts on any symbolic link argument directly.
10455 @itemx --file-system
10457 @opindex --file-system
10458 @cindex file systems
10459 Report information about the file systems where the given files are located
10460 instead of information about the files themselves.
10463 @itemx --format=@var{format}
10465 @opindex --format=@var{format}
10466 @cindex output format
10467 Use @var{format} rather than the default format.
10468 @var{format} is automatically newline-terminated, so
10469 running a command like the following with two or more @var{file}
10470 operands produces a line of output for each operand:
10472 $ stat --format=%d:%i / /usr
10477 @itemx --printf=@var{format}
10478 @opindex --printf=@var{format}
10479 @cindex output format
10480 Use @var{format} rather than the default format.
10481 Like @option{--format}, but interpret backslash escapes,
10482 and do not output a mandatory trailing newline.
10483 If you want a newline, include @samp{\n} in the @var{format}.
10484 Here's how you would use @option{--printf} to print the device
10485 and inode numbers of @file{/} and @file{/usr}:
10487 $ stat --printf='%d:%i\n' / /usr
10496 @cindex terse output
10497 Print the information in terse form, suitable for parsing by other programs.
10501 The valid @var{format} directives for files with @option{--format} and
10502 @option{--printf} are:
10505 @item %a - Access rights in octal
10506 @item %A - Access rights in human readable form
10507 @item %b - Number of blocks allocated (see @samp{%B})
10508 @item %B - The size in bytes of each block reported by @samp{%b}
10509 @item %d - Device number in decimal
10510 @item %D - Device number in hex
10511 @item %f - Raw mode in hex
10512 @item %F - File type
10513 @item %g - Group ID of owner
10514 @item %G - Group name of owner
10515 @item %h - Number of hard links
10516 @item %i - Inode number
10517 @item %n - File name
10518 @item %N - Quoted file name with dereference if symbolic link
10519 @item %o - I/O block size
10520 @item %s - Total size, in bytes
10521 @item %t - Major device type in hex
10522 @item %T - Minor device type in hex
10523 @item %u - User ID of owner
10524 @item %U - User name of owner
10525 @item %x - Time of last access
10526 @item %X - Time of last access as seconds since Epoch
10527 @item %y - Time of last modification
10528 @item %Y - Time of last modification as seconds since Epoch
10529 @item %z - Time of last change
10530 @item %Z - Time of last change as seconds since Epoch
10533 When listing file system information (@option{--file-system} (@option{-f})),
10534 you must use a different set of @var{format} directives:
10537 @item %a - Free blocks available to non-super-user
10538 @item %b - Total data blocks in file system
10539 @item %c - Total file nodes in file system
10540 @item %d - Free file nodes in file system
10541 @item %f - Free blocks in file system
10542 @item %i - File System ID in hex
10543 @item %l - Maximum length of file names
10544 @item %n - File name
10545 @item %s - Block size (for faster transfers)
10546 @item %S - Fundamental block size (for block counts)
10547 @item %t - Type in hex
10548 @item %T - Type in human readable form
10552 Time stamps are listed according to the time zone rules specified by
10553 the @env{TZ} environment variable, or by the system default rules if
10554 @env{TZ} is not set. @xref{TZ Variable,, Specifying the Time Zone
10555 with @env{TZ}, libc, The GNU C Library Reference Manual}.
10560 @node sync invocation
10561 @section @command{sync}: Synchronize data on disk with memory
10564 @cindex synchronize disk and memory
10566 @cindex superblock, writing
10567 @cindex inodes, written buffered
10568 @command{sync} writes any data buffered in memory out to disk. This can
10569 include (but is not limited to) modified superblocks, modified inodes,
10570 and delayed reads and writes. This must be implemented by the kernel;
10571 The @command{sync} program does nothing but exercise the @code{sync} system
10574 @cindex crashes and corruption
10575 The kernel keeps data in memory to avoid doing (relatively slow) disk
10576 reads and writes. This improves performance, but if the computer
10577 crashes, data may be lost or the file system corrupted as a
10578 result. The @command{sync} command ensures everything in memory
10579 is written to disk.
10581 Any arguments are ignored, except for a lone @option{--help} or
10582 @option{--version} (@pxref{Common options}).
10587 @node truncate invocation
10588 @section @command{truncate}: Shrink or extend the size of a file
10591 @cindex truncating, file sizes
10593 @command{truncate} shrinks or extends the size of each @var{file} to the
10594 specified size. Synopsis:
10597 truncate @var{option}@dots{} @var{file}@dots{}
10600 @cindex files, creating
10601 Any @var{file} that does not exist is created.
10603 @cindex sparse files, creating
10604 @cindex holes, creating files with
10605 If a @var{file} is larger than the specified size, the extra data is lost.
10606 If a @var{file} is shorter, it is extended and the extended part (or hole)
10607 reads as zero bytes.
10609 The program accepts the following options. Also see @ref{Common options}.
10616 @opindex --no-create
10617 Do not create files that do not exist.
10622 @opindex --io-blocks
10623 Treat @var{size} as number of I/O blocks of the @var{file} rather than bytes.
10625 @item -r @var{rfile}
10626 @itemx --reference=@var{rfile}
10628 @opindex --reference
10629 Set the size of each @var{file} to the same size as @var{rfile}.
10631 @item -s @var{size}
10632 @itemx --size=@var{size}
10635 Set the size of each @var{file} to this @var{size}.
10636 @multiplierSuffixesNoBlocks{size}
10638 @var{size} may also be prefixed by one of the following to adjust
10639 the size of each @var{file} based on their current size:
10641 @samp{+} => extend by
10642 @samp{-} => reduce by
10643 @samp{<} => at most
10644 @samp{>} => at least
10645 @samp{/} => round down to multiple of
10646 @samp{%} => round up to multiple of
10654 @node Printing text
10655 @chapter Printing text
10657 @cindex printing text, commands for
10658 @cindex commands for printing text
10660 This section describes commands that display text strings.
10663 * echo invocation:: Print a line of text.
10664 * printf invocation:: Format and print data.
10665 * yes invocation:: Print a string until interrupted.
10669 @node echo invocation
10670 @section @command{echo}: Print a line of text
10673 @cindex displaying text
10674 @cindex printing text
10675 @cindex text, displaying
10676 @cindex arbitrary text, displaying
10678 @command{echo} writes each given @var{string} to standard output, with a
10679 space between each and a newline after the last one. Synopsis:
10682 echo [@var{option}]@dots{} [@var{string}]@dots{}
10685 @mayConflictWithShellBuiltIn{echo}
10687 The program accepts the following options. Also see @ref{Common options}.
10688 Options must precede operands, and the normally-special argument
10689 @samp{--} has no special meaning and is treated like any other
10695 Do not output the trailing newline.
10699 @cindex backslash escapes
10700 Enable interpretation of the following backslash-escaped characters in
10709 produce no further output
10723 the eight-bit value that is the octal number @var{nnn}
10724 (zero to three octal digits)
10726 the eight-bit value that is the octal number @var{nnn}
10727 (one to three octal digits)
10729 the eight-bit value that is the hexadecimal number @var{hh}
10730 (one or two hexadecimal digits)
10735 @cindex backslash escapes
10736 Disable interpretation of backslash escapes in each @var{string}.
10737 This is the default. If @option{-e} and @option{-E} are both
10738 specified, the last one given takes effect.
10742 @vindex POSIXLY_CORRECT
10743 If the @env{POSIXLY_CORRECT} environment variable is set, then when
10744 @command{echo}'s first argument is not @option{-n} it outputs
10745 option-like arguments instead of treating them as options. For
10746 example, @code{echo -ne hello} outputs @samp{-ne hello} instead of
10747 plain @samp{hello}.
10749 @acronym{POSIX} does not require support for any options, and says
10750 that the behavior of @command{echo} is implementation-defined if any
10751 @var{string} contains a backslash or if the first argument is
10752 @option{-n}. Portable programs can use the @command{printf} command
10753 if they need to omit trailing newlines or output control characters or
10754 backslashes. @xref{printf invocation}.
10759 @node printf invocation
10760 @section @command{printf}: Format and print data
10763 @command{printf} does formatted printing of text. Synopsis:
10766 printf @var{format} [@var{argument}]@dots{}
10769 @command{printf} prints the @var{format} string, interpreting @samp{%}
10770 directives and @samp{\} escapes to format numeric and string arguments
10771 in a way that is mostly similar to the C @samp{printf} function.
10772 @xref{Output Conversion Syntax,, @command{printf} format directives,
10773 libc, The GNU C Library Reference Manual}, for details.
10774 The differences are listed below.
10776 @mayConflictWithShellBuiltIn{printf}
10781 The @var{format} argument is reused as necessary to convert all the
10782 given @var{argument}s. For example, the command @samp{printf %s a b}
10786 Missing @var{argument}s are treated as null strings or as zeros,
10787 depending on whether the context expects a string or a number. For
10788 example, the command @samp{printf %sx%d} prints @samp{x0}.
10792 An additional escape, @samp{\c}, causes @command{printf} to produce no
10793 further output. For example, the command @samp{printf 'A%sC\cD%sF' B
10794 E} prints @samp{ABC}.
10797 The hexadecimal escape sequence @samp{\x@var{hh}} has at most two
10798 digits, as opposed to C where it can have an unlimited number of
10799 digits. For example, the command @samp{printf '\x07e'} prints two
10800 bytes, whereas the C statement @samp{printf ("\x07e")} prints just
10805 @command{printf} has an additional directive, @samp{%b}, which prints its
10806 argument string with @samp{\} escapes interpreted in the same way as in
10807 the @var{format} string, except that octal escapes are of the form
10808 @samp{\0@var{ooo}} where @var{ooo} is 0 to 3 octal digits.
10809 If a precision is also given, it limits the number of bytes printed
10810 from the converted string.
10813 Numeric arguments must be single C constants, possibly with leading
10814 @samp{+} or @samp{-}. For example, @samp{printf %.4d -3} outputs
10818 @vindex POSIXLY_CORRECT
10819 If the leading character of a numeric argument is @samp{"} or @samp{'}
10820 then its value is the numeric value of the immediately following
10821 character. Any remaining characters are silently ignored if the
10822 @env{POSIXLY_CORRECT} environment variable is set; otherwise, a
10823 warning is printed. For example, @samp{printf "%d" "'a"} outputs
10824 @samp{97} on hosts that use the @acronym{ASCII} character set, since
10825 @samp{a} has the numeric value 97 in @acronym{ASCII}.
10830 A floating-point argument must use a period before any fractional
10831 digits, but is printed according to the @env{LC_NUMERIC} category of the
10832 current locale. For example, in a locale whose radix character is a
10833 comma, the command @samp{printf %g 3.14} outputs @samp{3,14} whereas
10834 the command @samp{printf %g 3,14} is an error.
10838 @command{printf} interprets @samp{\@var{ooo}} in @var{format} as an octal number
10839 (if @var{ooo} is 1 to 3 octal digits) specifying a character to print,
10840 and @samp{\x@var{hh}} as a hexadecimal number (if @var{hh} is 1 to 2 hex
10841 digits) specifying a character to print.
10846 @cindex ISO/IEC 10646
10848 @command{printf} interprets two character syntaxes introduced in
10849 @acronym{ISO} C 99:
10850 @samp{\u} for 16-bit Unicode (@acronym{ISO}/@acronym{IEC} 10646)
10851 characters, specified as
10852 four hexadecimal digits @var{hhhh}, and @samp{\U} for 32-bit Unicode
10853 characters, specified as eight hexadecimal digits @var{hhhhhhhh}.
10854 @command{printf} outputs the Unicode characters
10855 according to the @env{LC_CTYPE} locale. Unicode characters in the ranges
10856 U+0000...U+009F, U+D800...U+DFFF cannot be specified by this syntax, except
10857 for U+0024 ($), U+0040 (@@), and U+0060 (@`).
10859 The processing of @samp{\u} and @samp{\U} requires a full-featured
10860 @code{iconv} facility. It is activated on systems with glibc 2.2 (or newer),
10861 or when @code{libiconv} is installed prior to this package. Otherwise
10862 @samp{\u} and @samp{\U} will print as-is.
10864 The only options are a lone @option{--help} or
10865 @option{--version}. @xref{Common options}.
10866 Options must precede operands.
10868 The Unicode character syntaxes are useful for writing strings in a locale
10869 independent way. For example, a string containing the Euro currency symbol
10872 $ env printf '\u20AC 14.95'
10876 will be output correctly in all locales supporting the Euro symbol
10877 (@acronym{ISO}-8859-15, UTF-8, and others). Similarly, a Chinese string
10880 $ env printf '\u4e2d\u6587'
10884 will be output correctly in all Chinese locales (GB2312, BIG5, UTF-8, etc).
10886 Note that in these examples, the @command{printf} command has been
10887 invoked via @command{env} to ensure that we run the program found via
10888 your shell's search path, and not a shell alias or a built-in function.
10890 For larger strings, you don't need to look up the hexadecimal code
10891 values of each character one by one. @acronym{ASCII} characters mixed with \u
10892 escape sequences is also known as the JAVA source file encoding. You can
10893 use GNU recode 3.5c (or newer) to convert strings to this encoding. Here
10894 is how to convert a piece of text into a shell script which will output
10895 this text in a locale-independent way:
10898 $ LC_CTYPE=zh_CN.big5 /usr/local/bin/printf \
10899 '\u4e2d\u6587\n' > sample.txt
10900 $ recode BIG5..JAVA < sample.txt \
10901 | sed -e "s|^|/usr/local/bin/printf '|" -e "s|$|\\\\n'|" \
10908 @node yes invocation
10909 @section @command{yes}: Print a string until interrupted
10912 @cindex repeated output of a string
10914 @command{yes} prints the command line arguments, separated by spaces and
10915 followed by a newline, forever until it is killed. If no arguments are
10916 given, it prints @samp{y} followed by a newline forever until killed.
10918 Upon a write error, @command{yes} exits with status @samp{1}.
10920 The only options are a lone @option{--help} or @option{--version}.
10921 To output an argument that begins with
10922 @samp{-}, precede it with @option{--}, e.g., @samp{yes -- --help}.
10923 @xref{Common options}.
10927 @chapter Conditions
10930 @cindex commands for exit status
10931 @cindex exit status commands
10933 This section describes commands that are primarily useful for their exit
10934 status, rather than their output. Thus, they are often used as the
10935 condition of shell @code{if} statements, or as the last command in a
10939 * false invocation:: Do nothing, unsuccessfully.
10940 * true invocation:: Do nothing, successfully.
10941 * test invocation:: Check file types and compare values.
10942 * expr invocation:: Evaluate expressions.
10946 @node false invocation
10947 @section @command{false}: Do nothing, unsuccessfully
10950 @cindex do nothing, unsuccessfully
10951 @cindex failure exit status
10952 @cindex exit status of @command{false}
10954 @command{false} does nothing except return an exit status of 1, meaning
10955 @dfn{failure}. It can be used as a place holder in shell scripts
10956 where an unsuccessful command is needed.
10957 In most modern shells, @command{false} is a built-in command, so when
10958 you use @samp{false} in a script, you're probably using the built-in
10959 command, not the one documented here.
10961 @command{false} honors the @option{--help} and @option{--version} options.
10963 This version of @command{false} is implemented as a C program, and is thus
10964 more secure and faster than a shell script implementation, and may safely
10965 be used as a dummy shell for the purpose of disabling accounts.
10967 Note that @command{false} (unlike all other programs documented herein)
10968 exits unsuccessfully, even when invoked with
10969 @option{--help} or @option{--version}.
10971 Portable programs should not assume that the exit status of
10972 @command{false} is 1, as it is greater than 1 on some
10973 non-@acronym{GNU} hosts.
10976 @node true invocation
10977 @section @command{true}: Do nothing, successfully
10980 @cindex do nothing, successfully
10982 @cindex successful exit
10983 @cindex exit status of @command{true}
10985 @command{true} does nothing except return an exit status of 0, meaning
10986 @dfn{success}. It can be used as a place holder in shell scripts
10987 where a successful command is needed, although the shell built-in
10988 command @code{:} (colon) may do the same thing faster.
10989 In most modern shells, @command{true} is a built-in command, so when
10990 you use @samp{true} in a script, you're probably using the built-in
10991 command, not the one documented here.
10993 @command{true} honors the @option{--help} and @option{--version} options.
10995 Note, however, that it is possible to cause @command{true}
10996 to exit with nonzero status: with the @option{--help} or @option{--version}
10997 option, and with standard
10998 output already closed or redirected to a file that evokes an I/O error.
10999 For example, using a Bourne-compatible shell:
11002 $ ./true --version >&-
11003 ./true: write error: Bad file number
11004 $ ./true --version > /dev/full
11005 ./true: write error: No space left on device
11008 This version of @command{true} is implemented as a C program, and is thus
11009 more secure and faster than a shell script implementation, and may safely
11010 be used as a dummy shell for the purpose of disabling accounts.
11012 @node test invocation
11013 @section @command{test}: Check file types and compare values
11016 @cindex check file types
11017 @cindex compare values
11018 @cindex expression evaluation
11020 @command{test} returns a status of 0 (true) or 1 (false) depending on the
11021 evaluation of the conditional expression @var{expr}. Each part of the
11022 expression must be a separate argument.
11024 @command{test} has file status checks, string operators, and numeric
11025 comparison operators.
11027 @command{test} has an alternate form that uses opening and closing
11028 square brackets instead a leading @samp{test}. For example, instead
11029 of @samp{test -d /}, you can write @samp{[ -d / ]}. The square
11030 brackets must be separate arguments; for example, @samp{[-d /]} does
11031 not have the desired effect. Since @samp{test @var{expr}} and @samp{[
11032 @var{expr} ]} have the same meaning, only the former form is discussed
11038 test @var{expression}
11040 [ @var{expression} ]
11045 @mayConflictWithShellBuiltIn{test}
11047 If @var{expression} is omitted, @command{test} returns false.
11048 If @var{expression} is a single argument,
11049 @command{test} returns false if the argument is null and true otherwise. The argument
11050 can be any string, including strings like @samp{-d}, @samp{-1},
11051 @samp{--}, @samp{--help}, and @samp{--version} that most other
11052 programs would treat as options. To get help and version information,
11053 invoke the commands @samp{[ --help} and @samp{[ --version}, without
11054 the usual closing brackets. @xref{Common options}.
11056 @cindex exit status of @command{test}
11060 0 if the expression is true,
11061 1 if the expression is false,
11062 2 if an error occurred.
11066 * File type tests:: -[bcdfhLpSt]
11067 * Access permission tests:: -[gkruwxOG]
11068 * File characteristic tests:: -e -s -nt -ot -ef
11069 * String tests:: -z -n = !=
11070 * Numeric tests:: -eq -ne -lt -le -gt -ge
11071 * Connectives for test:: ! -a -o
11075 @node File type tests
11076 @subsection File type tests
11078 @cindex file type tests
11080 These options test for particular types of files. (Everything's a file,
11081 but not all files are the same!)
11085 @item -b @var{file}
11087 @cindex block special check
11088 True if @var{file} exists and is a block special device.
11090 @item -c @var{file}
11092 @cindex character special check
11093 True if @var{file} exists and is a character special device.
11095 @item -d @var{file}
11097 @cindex directory check
11098 True if @var{file} exists and is a directory.
11100 @item -f @var{file}
11102 @cindex regular file check
11103 True if @var{file} exists and is a regular file.
11105 @item -h @var{file}
11106 @itemx -L @var{file}
11109 @cindex symbolic link check
11110 True if @var{file} exists and is a symbolic link.
11111 Unlike all other file-related tests, this test does not dereference
11112 @var{file} if it is a symbolic link.
11114 @item -p @var{file}
11116 @cindex named pipe check
11117 True if @var{file} exists and is a named pipe.
11119 @item -S @var{file}
11121 @cindex socket check
11122 True if @var{file} exists and is a socket.
11126 @cindex terminal check
11127 True if @var{fd} is a file descriptor that is associated with a
11133 @node Access permission tests
11134 @subsection Access permission tests
11136 @cindex access permission tests
11137 @cindex permission tests
11139 These options test for particular access permissions.
11143 @item -g @var{file}
11145 @cindex set-group-ID check
11146 True if @var{file} exists and has its set-group-ID bit set.
11148 @item -k @var{file}
11150 @cindex sticky bit check
11151 True if @var{file} exists and has its @dfn{sticky} bit set.
11153 @item -r @var{file}
11155 @cindex readable file check
11156 True if @var{file} exists and read permission is granted.
11158 @item -u @var{file}
11160 @cindex set-user-ID check
11161 True if @var{file} exists and has its set-user-ID bit set.
11163 @item -w @var{file}
11165 @cindex writable file check
11166 True if @var{file} exists and write permission is granted.
11168 @item -x @var{file}
11170 @cindex executable file check
11171 True if @var{file} exists and execute permission is granted
11172 (or search permission, if it is a directory).
11174 @item -O @var{file}
11176 @cindex owned by effective user ID check
11177 True if @var{file} exists and is owned by the current effective user ID.
11179 @item -G @var{file}
11181 @cindex owned by effective group ID check
11182 True if @var{file} exists and is owned by the current effective group ID.
11186 @node File characteristic tests
11187 @subsection File characteristic tests
11189 @cindex file characteristic tests
11191 These options test other file characteristics.
11195 @item -e @var{file}
11197 @cindex existence-of-file check
11198 True if @var{file} exists.
11200 @item -s @var{file}
11202 @cindex nonempty file check
11203 True if @var{file} exists and has a size greater than zero.
11205 @item @var{file1} -nt @var{file2}
11207 @cindex newer-than file check
11208 True if @var{file1} is newer (according to modification date) than
11209 @var{file2}, or if @var{file1} exists and @var{file2} does not.
11211 @item @var{file1} -ot @var{file2}
11213 @cindex older-than file check
11214 True if @var{file1} is older (according to modification date) than
11215 @var{file2}, or if @var{file2} exists and @var{file1} does not.
11217 @item @var{file1} -ef @var{file2}
11219 @cindex same file check
11220 @cindex hard link check
11221 True if @var{file1} and @var{file2} have the same device and inode
11222 numbers, i.e., if they are hard links to each other.
11228 @subsection String tests
11230 @cindex string tests
11232 These options test string characteristics. You may need to quote
11233 @var{string} arguments for the shell. For example:
11239 The quotes here prevent the wrong arguments from being passed to
11240 @command{test} if @samp{$V} is empty or contains special characters.
11244 @item -z @var{string}
11246 @cindex zero-length string check
11247 True if the length of @var{string} is zero.
11249 @item -n @var{string}
11250 @itemx @var{string}
11252 @cindex nonzero-length string check
11253 True if the length of @var{string} is nonzero.
11255 @item @var{string1} = @var{string2}
11257 @cindex equal string check
11258 True if the strings are equal.
11260 @item @var{string1} != @var{string2}
11262 @cindex not-equal string check
11263 True if the strings are not equal.
11268 @node Numeric tests
11269 @subsection Numeric tests
11271 @cindex numeric tests
11272 @cindex arithmetic tests
11274 Numeric relational operators. The arguments must be entirely numeric
11275 (possibly negative), or the special expression @w{@code{-l @var{string}}},
11276 which evaluates to the length of @var{string}.
11280 @item @var{arg1} -eq @var{arg2}
11281 @itemx @var{arg1} -ne @var{arg2}
11282 @itemx @var{arg1} -lt @var{arg2}
11283 @itemx @var{arg1} -le @var{arg2}
11284 @itemx @var{arg1} -gt @var{arg2}
11285 @itemx @var{arg1} -ge @var{arg2}
11292 These arithmetic binary operators return true if @var{arg1} is equal,
11293 not-equal, less-than, less-than-or-equal, greater-than, or
11294 greater-than-or-equal than @var{arg2}, respectively.
11301 test -1 -gt -2 && echo yes
11303 test -l abc -gt 1 && echo yes
11306 @error{} test: integer expression expected before -eq
11310 @node Connectives for test
11311 @subsection Connectives for @command{test}
11313 @cindex logical connectives
11314 @cindex connectives, logical
11316 The usual logical connectives.
11322 True if @var{expr} is false.
11324 @item @var{expr1} -a @var{expr2}
11326 @cindex logical and operator
11327 @cindex and operator
11328 True if both @var{expr1} and @var{expr2} are true.
11330 @item @var{expr1} -o @var{expr2}
11332 @cindex logical or operator
11333 @cindex or operator
11334 True if either @var{expr1} or @var{expr2} is true.
11339 @node expr invocation
11340 @section @command{expr}: Evaluate expressions
11343 @cindex expression evaluation
11344 @cindex evaluation of expressions
11346 @command{expr} evaluates an expression and writes the result on standard
11347 output. Each token of the expression must be a separate argument.
11349 Operands are either integers or strings. Integers consist of one or
11350 more decimal digits, with an optional leading @samp{-}.
11351 @command{expr} converts
11352 anything appearing in an operand position to an integer or a string
11353 depending on the operation being applied to it.
11355 Strings are not quoted for @command{expr} itself, though you may need to
11356 quote them to protect characters with special meaning to the shell,
11357 e.g., spaces. However, regardless of whether it is quoted, a string
11358 operand should not be a parenthesis or any of @command{expr}'s
11359 operators like @code{+}, so you cannot safely pass an arbitrary string
11360 @code{$str} to expr merely by quoting it to the shell. One way to
11361 work around this is to use the @sc{gnu} extension @code{+},
11362 (e.g., @code{+ "$str" = foo}); a more portable way is to use
11363 @code{@w{" $str"}} and to adjust the rest of the expression to take
11364 the leading space into account (e.g., @code{@w{" $str" = " foo"}}).
11366 You should not pass a negative integer or a string with leading
11367 @samp{-} as @command{expr}'s first argument, as it might be
11368 misinterpreted as an option; this can be avoided by parenthesization.
11369 Also, portable scripts should not use a string operand that happens to
11370 take the form of an integer; this can be worked around by inserting
11371 leading spaces as mentioned above.
11373 @cindex parentheses for grouping
11374 Operators may be given as infix symbols or prefix keywords. Parentheses
11375 may be used for grouping in the usual manner. You must quote
11376 parentheses and many operators to avoid the shell evaluating them,
11379 When built with support for the GNU MP library, @command{expr} uses
11380 arbitrary-precision arithmetic; otherwise, it uses native arithmetic
11381 types and may fail due to arithmetic overflow.
11383 The only options are @option{--help} and @option{--version}. @xref{Common
11384 options}. Options must precede operands.
11386 @cindex exit status of @command{expr}
11390 0 if the expression is neither null nor 0,
11391 1 if the expression is null or 0,
11392 2 if the expression is invalid,
11393 3 if an internal error occurred (e.g., arithmetic overflow).
11397 * String expressions:: + : match substr index length
11398 * Numeric expressions:: + - * / %
11399 * Relations for expr:: | & < <= = == != >= >
11400 * Examples of expr:: Examples.
11404 @node String expressions
11405 @subsection String expressions
11407 @cindex string expressions
11408 @cindex expressions, string
11410 @command{expr} supports pattern matching and other string operators. These
11411 have higher precedence than both the numeric and relational operators (in
11412 the next sections).
11416 @item @var{string} : @var{regex}
11417 @cindex pattern matching
11418 @cindex regular expression matching
11419 @cindex matching patterns
11420 Perform pattern matching. The arguments are converted to strings and the
11421 second is considered to be a (basic, a la GNU @code{grep}) regular
11422 expression, with a @code{^} implicitly prepended. The first argument is
11423 then matched against this regular expression.
11425 If the match succeeds and @var{regex} uses @samp{\(} and @samp{\)}, the
11426 @code{:} expression returns the part of @var{string} that matched the
11427 subexpression; otherwise, it returns the number of characters matched.
11429 If the match fails, the @code{:} operator returns the null string if
11430 @samp{\(} and @samp{\)} are used in @var{regex}, otherwise 0.
11432 @kindex \( @r{regexp operator}
11433 Only the first @samp{\( @dots{} \)} pair is relevant to the return
11434 value; additional pairs are meaningful only for grouping the regular
11435 expression operators.
11437 @kindex \+ @r{regexp operator}
11438 @kindex \? @r{regexp operator}
11439 @kindex \| @r{regexp operator}
11440 In the regular expression, @code{\+}, @code{\?}, and @code{\|} are
11441 operators which respectively match one or more, zero or one, or separate
11442 alternatives. SunOS and other @command{expr}'s treat these as regular
11443 characters. (@acronym{POSIX} allows either behavior.)
11444 @xref{Top, , Regular Expression Library, regex, Regex}, for details of
11445 regular expression syntax. Some examples are in @ref{Examples of expr}.
11447 @item match @var{string} @var{regex}
11449 An alternative way to do pattern matching. This is the same as
11450 @w{@samp{@var{string} : @var{regex}}}.
11452 @item substr @var{string} @var{position} @var{length}
11454 Returns the substring of @var{string} beginning at @var{position}
11455 with length at most @var{length}. If either @var{position} or
11456 @var{length} is negative, zero, or non-numeric, returns the null string.
11458 @item index @var{string} @var{charset}
11460 Returns the first position in @var{string} where the first character in
11461 @var{charset} was found. If no character in @var{charset} is found in
11462 @var{string}, return 0.
11464 @item length @var{string}
11466 Returns the length of @var{string}.
11468 @item + @var{token}
11470 Interpret @var{token} as a string, even if it is a keyword like @var{match}
11471 or an operator like @code{/}.
11472 This makes it possible to test @code{expr length + "$x"} or
11473 @code{expr + "$x" : '.*/\(.\)'} and have it do the right thing even if
11474 the value of @var{$x} happens to be (for example) @code{/} or @code{index}.
11475 This operator is a @acronym{GNU} extension. Portable shell scripts should use
11476 @code{@w{" $token"} : @w{' \(.*\)'}} instead of @code{+ "$token"}.
11480 To make @command{expr} interpret keywords as strings, you must use the
11481 @code{quote} operator.
11484 @node Numeric expressions
11485 @subsection Numeric expressions
11487 @cindex numeric expressions
11488 @cindex expressions, numeric
11490 @command{expr} supports the usual numeric operators, in order of increasing
11491 precedence. These numeric operators have lower precedence than the
11492 string operators described in the previous section, and higher precedence
11493 than the connectives (next section).
11501 @cindex subtraction
11502 Addition and subtraction. Both arguments are converted to integers;
11503 an error occurs if this cannot be done.
11509 @cindex multiplication
11512 Multiplication, division, remainder. Both arguments are converted to
11513 integers; an error occurs if this cannot be done.
11518 @node Relations for expr
11519 @subsection Relations for @command{expr}
11521 @cindex connectives, logical
11522 @cindex logical connectives
11523 @cindex relations, numeric or string
11525 @command{expr} supports the usual logical connectives and relations. These
11526 have lower precedence than the string and numeric operators
11527 (previous sections). Here is the list, lowest-precedence operator first.
11533 @cindex logical or operator
11534 @cindex or operator
11535 Returns its first argument if that is neither null nor zero, otherwise
11536 its second argument if it is neither null nor zero, otherwise 0. It
11537 does not evaluate its second argument if its first argument is neither
11542 @cindex logical and operator
11543 @cindex and operator
11544 Return its first argument if neither argument is null or zero, otherwise
11545 0. It does not evaluate its second argument if its first argument is
11548 @item < <= = == != >= >
11555 @cindex comparison operators
11557 Compare the arguments and return 1 if the relation is true, 0 otherwise.
11558 @code{==} is a synonym for @code{=}. @command{expr} first tries to convert
11559 both arguments to integers and do a numeric comparison; if either
11560 conversion fails, it does a lexicographic comparison using the character
11561 collating sequence specified by the @env{LC_COLLATE} locale.
11566 @node Examples of expr
11567 @subsection Examples of using @command{expr}
11569 @cindex examples of @command{expr}
11570 Here are a few examples, including quoting for shell metacharacters.
11572 To add 1 to the shell variable @code{foo}, in Bourne-compatible shells:
11575 foo=`expr $foo + 1`
11578 To print the non-directory part of the file name stored in
11579 @code{$fname}, which need not contain a @code{/}:
11582 expr $fname : '.*/\(.*\)' '|' $fname
11585 An example showing that @code{\+} is an operator:
11593 expr abc : 'a\(.\)c'
11595 expr index abcdef cz
11598 @error{} expr: syntax error
11599 expr index + index a
11605 @chapter Redirection
11607 @cindex redirection
11608 @cindex commands for redirection
11610 Unix shells commonly provide several forms of @dfn{redirection}---ways
11611 to change the input source or output destination of a command. But one
11612 useful redirection is performed by a separate command, not by the shell;
11613 it's described here.
11616 * tee invocation:: Redirect output to multiple files or processes.
11620 @node tee invocation
11621 @section @command{tee}: Redirect output to multiple files or processes
11624 @cindex pipe fitting
11625 @cindex destinations, multiple output
11626 @cindex read from stdin and write to stdout and files
11628 The @command{tee} command copies standard input to standard output and also
11629 to any files given as arguments. This is useful when you want not only
11630 to send some data down a pipe, but also to save a copy. Synopsis:
11633 tee [@var{option}]@dots{} [@var{file}]@dots{}
11636 If a file being written to does not already exist, it is created. If a
11637 file being written to already exists, the data it previously contained
11638 is overwritten unless the @option{-a} option is used.
11640 A @var{file} of @samp{-} causes @command{tee} to send another copy of
11641 input to standard output, but this is typically not that useful as the
11642 copies are interleaved.
11644 The program accepts the following options. Also see @ref{Common options}.
11651 Append standard input to the given files rather than overwriting
11655 @itemx --ignore-interrupts
11657 @opindex --ignore-interrupts
11658 Ignore interrupt signals.
11662 The @command{tee} command is useful when you happen to be transferring a large
11663 amount of data and also want to summarize that data without reading
11664 it a second time. For example, when you are downloading a DVD image,
11665 you often want to verify its signature or checksum right away.
11666 The inefficient way to do it is simply:
11669 wget http://example.com/some.iso && sha1sum some.iso
11672 One problem with the above is that it makes you wait for the
11673 download to complete before starting the time-consuming SHA1 computation.
11674 Perhaps even more importantly, the above requires reading
11675 the DVD image a second time (the first was from the network).
11677 The efficient way to do it is to interleave the download
11678 and SHA1 computation. Then, you'll get the checksum for
11679 free, because the entire process parallelizes so well:
11682 # slightly contrived, to demonstrate process substitution
11683 wget -O - http://example.com/dvd.iso \
11684 | tee >(sha1sum > dvd.sha1) > dvd.iso
11687 That makes @command{tee} write not just to the expected output file,
11688 but also to a pipe running @command{sha1sum} and saving the final
11689 checksum in a file named @file{dvd.sha1}.
11691 Note, however, that this example relies on a feature of modern shells
11692 called @dfn{process substitution}
11693 (the @samp{>(command)} syntax, above;
11694 @xref{Process Substitution,,Process Substitution, bashref,
11695 The Bash Reference Manual}.),
11696 so it works with @command{zsh}, @command{bash}, and @command{ksh},
11697 but not with @command{/bin/sh}. So if you write code like this
11698 in a shell script, be sure to start the script with @samp{#!/bin/bash}.
11700 Since the above example writes to one file and one process,
11701 a more conventional and portable use of @command{tee} is even better:
11704 wget -O - http://example.com/dvd.iso \
11705 | tee dvd.iso | sha1sum > dvd.sha1
11708 You can extend this example to make @command{tee} write to two processes,
11709 computing MD5 and SHA1 checksums in parallel. In this case,
11710 process substitution is required:
11713 wget -O - http://example.com/dvd.iso \
11714 | tee >(sha1sum > dvd.sha1) \
11715 >(md5sum > dvd.md5) \
11719 This technique is also useful when you want to make a @emph{compressed}
11720 copy of the contents of a pipe.
11721 Consider a tool to graphically summarize disk usage data from @samp{du -ak}.
11722 For a large hierarchy, @samp{du -ak} can run for a long time,
11723 and can easily produce terabytes of data, so you won't want to
11724 rerun the command unnecessarily. Nor will you want to save
11725 the uncompressed output.
11727 Doing it the inefficient way, you can't even start the GUI
11728 until after you've compressed all of the @command{du} output:
11731 du -ak | gzip -9 > /tmp/du.gz
11732 gzip -d /tmp/du.gz | xdiskusage -a
11735 With @command{tee} and process substitution, you start the GUI
11736 right away and eliminate the decompression completely:
11739 du -ak | tee >(gzip -9 > /tmp/du.gz) | xdiskusage -a
11742 Finally, if you regularly create more than one type of
11743 compressed tarball at once, for example when @code{make dist} creates
11744 both @command{gzip}-compressed and @command{bzip2}-compressed tarballs,
11745 there may be a better way.
11746 Typical @command{automake}-generated @file{Makefile} rules create
11747 the two compressed tar archives with commands in sequence, like this
11748 (slightly simplified):
11751 tardir=your-pkg-M.N
11752 tar chof - "$tardir" | gzip -9 -c > your-pkg-M.N.tar.gz
11753 tar chof - "$tardir" | bzip2 -9 -c > your-pkg-M.N.tar.bz2
11756 However, if the hierarchy you are archiving and compressing is larger
11757 than a couple megabytes, and especially if you are using a multi-processor
11758 system with plenty of memory, then you can do much better by reading the
11759 directory contents only once and running the compression programs in parallel:
11762 tardir=your-pkg-M.N
11763 tar chof - "$tardir" \
11764 | tee >(gzip -9 -c > your-pkg-M.N.tar.gz) \
11765 | bzip2 -9 -c > your-pkg-M.N.tar.bz2
11771 @node File name manipulation
11772 @chapter File name manipulation
11774 @cindex file name manipulation
11775 @cindex manipulation of file names
11776 @cindex commands for file name manipulation
11778 This section describes commands that manipulate file names.
11781 * basename invocation:: Strip directory and suffix from a file name.
11782 * dirname invocation:: Strip non-directory suffix from a file name.
11783 * pathchk invocation:: Check file name validity and portability.
11787 @node basename invocation
11788 @section @command{basename}: Strip directory and suffix from a file name
11791 @cindex strip directory and suffix from file names
11792 @cindex directory, stripping from file names
11793 @cindex suffix, stripping from file names
11794 @cindex file names, stripping directory and suffix
11795 @cindex leading directory components, stripping
11797 @command{basename} removes any leading directory components from
11798 @var{name}. Synopsis:
11801 basename @var{name} [@var{suffix}]
11804 If @var{suffix} is specified and is identical to the end of @var{name},
11805 it is removed from @var{name} as well. Note that since trailing slashes
11806 are removed prior to suffix matching, @var{suffix} will do nothing if it
11807 contains slashes. @command{basename} prints the result on standard
11810 @c This test is used both here and in the section on dirname.
11811 @macro basenameAndDirname
11812 Together, @command{basename} and @command{dirname} are designed such
11813 that if @samp{ls "$name"} succeeds, then the command sequence @samp{cd
11814 "$(dirname "$name")"; ls "$(basename "$name")"} will, too. This works
11815 for everything except file names containing a trailing newline.
11817 @basenameAndDirname
11819 @acronym{POSIX} allows the implementation to define the results if
11820 @var{name} is empty or @samp{//}. In the former case, @acronym{GNU}
11821 @command{basename} returns the empty string. In the latter case, the
11822 result is @samp{//} on platforms where @var{//} is distinct from
11823 @var{/}, and @samp{/} on platforms where there is no difference.
11825 The only options are @option{--help} and @option{--version}. @xref{Common
11826 options}. Options must precede operands.
11834 basename /usr/bin/sort
11837 basename include/stdio.h .h
11841 @node dirname invocation
11842 @section @command{dirname}: Strip non-directory suffix from a file name
11845 @cindex directory components, printing
11846 @cindex stripping non-directory suffix
11847 @cindex non-directory suffix, stripping
11849 @command{dirname} prints all but the final slash-delimited component of
11850 a string (presumably a file name). Synopsis:
11856 If @var{name} is a single component, @command{dirname} prints @samp{.}
11857 (meaning the current directory).
11859 @basenameAndDirname
11861 @acronym{POSIX} allows the implementation to define the results if
11862 @var{name} is @samp{//}. With @acronym{GNU} @command{dirname}, the
11863 result is @samp{//} on platforms where @var{//} is distinct from
11864 @var{/}, and @samp{/} on platforms where there is no difference.
11866 The only options are @option{--help} and @option{--version}. @xref{Common
11874 # Output "/usr/bin".
11875 dirname /usr/bin/sort
11882 @node pathchk invocation
11883 @section @command{pathchk}: Check file name validity and portability
11886 @cindex file names, checking validity and portability
11887 @cindex valid file names, checking for
11888 @cindex portable file names, checking for
11890 @command{pathchk} checks validity and portability of file names. Synopsis:
11893 pathchk [@var{option}]@dots{} @var{name}@dots{}
11896 For each @var{name}, @command{pathchk} prints an error message if any of
11897 these conditions is true:
11901 One of the existing directories in @var{name} does not have search
11902 (execute) permission,
11904 The length of @var{name} is larger than the maximum supported by the
11907 The length of one component of @var{name} is longer than
11908 its file system's maximum.
11911 A nonexistent @var{name} is not an error, so long a file with that
11912 name could be created under the above conditions.
11914 The program accepts the following options. Also see @ref{Common options}.
11915 Options must precede operands.
11921 Instead of performing checks based on the underlying file system,
11922 print an error message if any of these conditions is true:
11926 A file name is empty.
11929 A file name contains a character outside the @acronym{POSIX} portable file
11930 name character set, namely, the ASCII letters and digits, @samp{.},
11931 @samp{_}, @samp{-}, and @samp{/}.
11934 The length of a file name or one of its components exceeds the
11935 @acronym{POSIX} minimum limits for portability.
11940 Print an error message if a file name is empty, or if it contains a component
11941 that begins with @samp{-}.
11943 @item --portability
11944 @opindex --portability
11945 Print an error message if a file name is not portable to all @acronym{POSIX}
11946 hosts. This option is equivalent to @samp{-p -P}.
11950 @cindex exit status of @command{pathchk}
11954 0 if all specified file names passed all checks,
11959 @node Working context
11960 @chapter Working context
11962 @cindex working context
11963 @cindex commands for printing the working context
11965 This section describes commands that display or alter the context in
11966 which you are working: the current directory, the terminal settings, and
11967 so forth. See also the user-related commands in the next section.
11970 * pwd invocation:: Print working directory.
11971 * stty invocation:: Print or change terminal characteristics.
11972 * printenv invocation:: Print environment variables.
11973 * tty invocation:: Print file name of terminal on standard input.
11977 @node pwd invocation
11978 @section @command{pwd}: Print working directory
11981 @cindex print name of current directory
11982 @cindex current working directory, printing
11983 @cindex working directory, printing
11986 @command{pwd} prints the name of the current directory. Synopsis:
11989 pwd [@var{option}]@dots{}
11992 The program accepts the following options. Also see @ref{Common options}.
11999 If the contents of the environment variable @env{PWD} provide an
12000 absolute name of the current directory with no @samp{.} or @samp{..}
12001 components, but possibly with symbolic links, then output those
12002 contents. Otherwise, fall back to default @option{-P} handling.
12007 @opindex --physical
12008 Print a fully resolved name for the current directory. That is, all
12009 components of the printed name will be actual directory names---none
12010 will be symbolic links.
12013 @cindex symbolic links and @command{pwd}
12014 If @option{-L} and @option{-P} are both given, the last one takes
12015 precedence. If neither option is given, then this implementation uses
12016 @option{-P} as the default unless the @env{POSIXLY_CORRECT}
12017 environment variable is set.
12019 @mayConflictWithShellBuiltIn{pwd}
12024 @node stty invocation
12025 @section @command{stty}: Print or change terminal characteristics
12028 @cindex change or print terminal settings
12029 @cindex terminal settings
12030 @cindex line settings of terminal
12032 @command{stty} prints or changes terminal characteristics, such as baud rate.
12036 stty [@var{option}] [@var{setting}]@dots{}
12037 stty [@var{option}]
12040 If given no line settings, @command{stty} prints the baud rate, line
12041 discipline number (on systems that support it), and line settings
12042 that have been changed from the values set by @samp{stty sane}.
12043 By default, mode reading and setting are performed on the tty line
12044 connected to standard input, although this can be modified by the
12045 @option{--file} option.
12047 @command{stty} accepts many non-option arguments that change aspects of
12048 the terminal line operation, as described below.
12050 The program accepts the following options. Also see @ref{Common options}.
12057 Print all current settings in human-readable form. This option may not
12058 be used in combination with any line settings.
12060 @item -F @var{device}
12061 @itemx --file=@var{device}
12064 Set the line opened by the file name specified in @var{device} instead of
12065 the tty line connected to standard input. This option is necessary
12066 because opening a @acronym{POSIX} tty requires use of the @code{O_NONDELAY} flag to
12067 prevent a @acronym{POSIX} tty from blocking until the carrier detect line is high if
12068 the @code{clocal} flag is not set. Hence, it is not always possible
12069 to allow the shell to open the device in the traditional manner.
12075 @cindex machine-readable @command{stty} output
12076 Print all current settings in a form that can be used as an argument to
12077 another @command{stty} command to restore the current settings. This option
12078 may not be used in combination with any line settings.
12082 Many settings can be turned off by preceding them with a @samp{-}.
12083 Such arguments are marked below with ``May be negated'' in their
12084 description. The descriptions themselves refer to the positive
12085 case, that is, when @emph{not} negated (unless stated otherwise,
12088 Some settings are not available on all @acronym{POSIX} systems, since they use
12089 extensions. Such arguments are marked below with ``Non-@acronym{POSIX}'' in their
12090 description. On non-@acronym{POSIX} systems, those or other settings also may not
12091 be available, but it's not feasible to document all the variations: just
12097 * Control:: Control settings
12098 * Input:: Input settings
12099 * Output:: Output settings
12100 * Local:: Local settings
12101 * Combination:: Combination settings
12102 * Characters:: Special characters
12103 * Special:: Special settings
12108 @subsection Control settings
12110 @cindex control settings
12116 @cindex two-way parity
12117 Generate parity bit in output and expect parity bit in input.
12123 @cindex even parity
12124 Set odd parity (even if negated). May be negated.
12131 @cindex character size
12132 @cindex eight-bit characters
12133 Set character size to 5, 6, 7, or 8 bits.
12138 Send a hangup signal when the last process closes the tty. May be
12144 Use two stop bits per character (one if negated). May be negated.
12148 Allow input to be received. May be negated.
12152 @cindex modem control
12153 Disable modem control signals. May be negated.
12157 @cindex hardware flow control
12158 @cindex flow control, hardware
12159 @cindex RTS/CTS flow control
12160 Enable RTS/CTS flow control. Non-@acronym{POSIX}. May be negated.
12165 @subsection Input settings
12167 @cindex input settings
12168 These settings control operations on data received from the terminal.
12173 @cindex breaks, ignoring
12174 Ignore break characters. May be negated.
12178 @cindex breaks, cause interrupts
12179 Make breaks cause an interrupt signal. May be negated.
12183 @cindex parity, ignoring
12184 Ignore characters with parity errors. May be negated.
12188 @cindex parity errors, marking
12189 Mark parity errors (with a 255-0-character sequence). May be negated.
12193 Enable input parity checking. May be negated.
12197 @cindex eight-bit input
12198 Clear high (8th) bit of input characters. May be negated.
12202 @cindex newline, translating to return
12203 Translate newline to carriage return. May be negated.
12207 @cindex return, ignoring
12208 Ignore carriage return. May be negated.
12212 @cindex return, translating to newline
12213 Translate carriage return to newline. May be negated.
12217 @cindex input encoding, UTF-8
12218 Assume input characters are UTF-8 encoded. May be negated.
12222 @kindex C-s/C-q flow control
12223 @cindex XON/XOFF flow control
12224 Enable XON/XOFF flow control (that is, @kbd{CTRL-S}/@kbd{CTRL-Q}). May
12231 @cindex software flow control
12232 @cindex flow control, software
12233 Enable sending of @code{stop} character when the system input buffer
12234 is almost full, and @code{start} character when it becomes almost
12235 empty again. May be negated.
12239 @cindex uppercase, translating to lowercase
12240 Translate uppercase characters to lowercase. Non-@acronym{POSIX}. May be
12241 negated. Note ilcuc is not implemented, as one would not be able to issue
12242 almost any (lowercase) Unix command, after invoking it.
12246 Allow any character to restart output (only the start character
12247 if negated). Non-@acronym{POSIX}. May be negated.
12251 @cindex beeping at input buffer full
12252 Enable beeping and not flushing input buffer if a character arrives
12253 when the input buffer is full. Non-@acronym{POSIX}. May be negated.
12258 @subsection Output settings
12260 @cindex output settings
12261 These settings control operations on data sent to the terminal.
12266 Postprocess output. May be negated.
12270 @cindex lowercase, translating to output
12271 Translate lowercase characters to uppercase. Non-@acronym{POSIX}. May be
12272 negated. (Note ouclc is not currently implemented.)
12276 @cindex return, translating to newline
12277 Translate carriage return to newline. Non-@acronym{POSIX}. May be negated.
12281 @cindex newline, translating to crlf
12282 Translate newline to carriage return-newline. Non-@acronym{POSIX}. May be
12287 Do not print carriage returns in the first column. Non-@acronym{POSIX}.
12292 Newline performs a carriage return. Non-@acronym{POSIX}. May be negated.
12296 @cindex pad instead of timing for delaying
12297 Use fill (padding) characters instead of timing for delays. Non-@acronym{POSIX}.
12302 @cindex pad character
12303 Use @acronym{ASCII} @sc{del} characters for fill instead of
12304 @acronym{ASCII} @sc{nul} characters. Non-@acronym{POSIX}.
12310 Newline delay style. Non-@acronym{POSIX}.
12317 Carriage return delay style. Non-@acronym{POSIX}.
12323 @opindex tab@var{n}
12324 Horizontal tab delay style. Non-@acronym{POSIX}.
12329 Backspace delay style. Non-@acronym{POSIX}.
12334 Vertical tab delay style. Non-@acronym{POSIX}.
12339 Form feed delay style. Non-@acronym{POSIX}.
12344 @subsection Local settings
12346 @cindex local settings
12351 Enable @code{interrupt}, @code{quit}, and @code{suspend} special
12352 characters. May be negated.
12356 Enable @code{erase}, @code{kill}, @code{werase}, and @code{rprnt}
12357 special characters. May be negated.
12361 Enable non-@acronym{POSIX} special characters. May be negated.
12365 Echo input characters. May be negated.
12371 Echo @code{erase} characters as backspace-space-backspace. May be
12376 @cindex newline echoing after @code{kill}
12377 Echo a newline after a @code{kill} character. May be negated.
12381 @cindex newline, echoing
12382 Echo newline even if not echoing other characters. May be negated.
12386 @cindex flushing, disabling
12387 Disable flushing after @code{interrupt} and @code{quit} special
12388 characters. May be negated.
12392 @cindex case translation
12393 Enable input and output of uppercase characters by preceding their
12394 lowercase equivalents with @samp{\}, when @code{icanon} is set.
12395 Non-@acronym{POSIX}. May be negated.
12399 @cindex background jobs, stopping at terminal write
12400 Stop background jobs that try to write to the terminal. Non-@acronym{POSIX}.
12407 Echo erased characters backward, between @samp{\} and @samp{/}.
12408 Non-@acronym{POSIX}. May be negated.
12414 @cindex control characters, using @samp{^@var{c}}
12415 @cindex hat notation for control characters
12416 Echo control characters in hat notation (@samp{^@var{c}}) instead
12417 of literally. Non-@acronym{POSIX}. May be negated.
12423 Echo the @code{kill} special character by erasing each character on
12424 the line as indicated by the @code{echoprt} and @code{echoe} settings,
12425 instead of by the @code{echoctl} and @code{echok} settings. Non-@acronym{POSIX}.
12431 @subsection Combination settings
12433 @cindex combination settings
12434 Combination settings:
12441 Same as @code{parenb -parodd cs7}. May be negated. If negated, same
12442 as @code{-parenb cs8}.
12446 Same as @code{parenb parodd cs7}. May be negated. If negated, same
12447 as @code{-parenb cs8}.
12451 Same as @code{-icrnl -onlcr}. May be negated. If negated, same as
12452 @code{icrnl -inlcr -igncr onlcr -ocrnl -onlret}.
12456 Reset the @code{erase} and @code{kill} special characters to their default
12463 @c This is too long to write inline.
12465 cread -ignbrk brkint -inlcr -igncr icrnl -ixoff
12466 -iuclc -ixany imaxbel opost -olcuc -ocrnl onlcr
12467 -onocr -onlret -ofill -ofdel nl0 cr0 tab0 bs0 vt0
12468 ff0 isig icanon iexten echo echoe echok -echonl
12469 -noflsh -xcase -tostop -echoprt echoctl echoke
12473 and also sets all special characters to their default values.
12477 Same as @code{brkint ignpar istrip icrnl ixon opost isig icanon}, plus
12478 sets the @code{eof} and @code{eol} characters to their default values
12479 if they are the same as the @code{min} and @code{time} characters.
12480 May be negated. If negated, same as @code{raw}.
12487 -ignbrk -brkint -ignpar -parmrk -inpck -istrip
12488 -inlcr -igncr -icrnl -ixon -ixoff -iuclc -ixany
12489 -imaxbel -opost -isig -icanon -xcase min 1 time 0
12493 May be negated. If negated, same as @code{cooked}.
12497 Same as @option{-icanon}. May be negated. If negated, same as
12502 @cindex eight-bit characters
12503 Same as @code{-parenb -istrip cs8}. May be negated. If negated,
12504 same as @code{parenb istrip cs7}.
12508 Same as @option{-parenb -istrip -opost cs8}. May be negated.
12509 If negated, same as @code{parenb istrip opost cs7}.
12513 Same as @option{-ixany}. Non-@acronym{POSIX}. May be negated.
12517 Same as @code{tab0}. Non-@acronym{POSIX}. May be negated. If negated, same
12524 Same as @code{xcase iuclc olcuc}. Non-@acronym{POSIX}. May be negated.
12525 (Used for terminals with uppercase characters only.)
12529 Same as @code{echoe echoctl echoke}.
12533 Same as @code{echoe echoctl echoke -ixany intr ^C erase ^? kill C-u}.
12538 @subsection Special characters
12540 @cindex special characters
12541 @cindex characters, special
12543 The special characters' default values vary from system to system.
12544 They are set with the syntax @samp{name value}, where the names are
12545 listed below and the value can be given either literally, in hat
12546 notation (@samp{^@var{c}}), or as an integer which may start with
12547 @samp{0x} to indicate hexadecimal, @samp{0} to indicate octal, or
12548 any other digit to indicate decimal.
12550 @cindex disabling special characters
12551 @kindex u@r{, and disabling special characters}
12552 For GNU stty, giving a value of @code{^-} or @code{undef} disables that
12553 special character. (This is incompatible with Ultrix @command{stty},
12554 which uses a value of @samp{u} to disable a special character. GNU
12555 @command{stty} treats a value @samp{u} like any other, namely to set that
12556 special character to @key{U}.)
12562 Send an interrupt signal.
12566 Send a quit signal.
12570 Erase the last character typed.
12574 Erase the current line.
12578 Send an end of file (terminate the input).
12586 Alternate character to end the line. Non-@acronym{POSIX}.
12590 Switch to a different shell layer. Non-@acronym{POSIX}.
12594 Restart the output after stopping it.
12602 Send a terminal stop signal.
12606 Send a terminal stop signal after flushing the input. Non-@acronym{POSIX}.
12610 Redraw the current line. Non-@acronym{POSIX}.
12614 Erase the last word typed. Non-@acronym{POSIX}.
12618 Enter the next character typed literally, even if it is a special
12619 character. Non-@acronym{POSIX}.
12624 @subsection Special settings
12626 @cindex special settings
12631 Set the minimum number of characters that will satisfy a read until
12632 the time value has expired, when @option{-icanon} is set.
12636 Set the number of tenths of a second before reads time out if the minimum
12637 number of characters have not been read, when @option{-icanon} is set.
12639 @item ispeed @var{n}
12641 Set the input speed to @var{n}.
12643 @item ospeed @var{n}
12645 Set the output speed to @var{n}.
12649 Tell the tty kernel driver that the terminal has @var{n} rows. Non-@acronym{POSIX}.
12652 @itemx columns @var{n}
12655 Tell the kernel that the terminal has @var{n} columns. Non-@acronym{POSIX}.
12661 Print the number of rows and columns that the kernel thinks the
12662 terminal has. (Systems that don't support rows and columns in the kernel
12663 typically use the environment variables @env{LINES} and @env{COLUMNS}
12664 instead; however, GNU @command{stty} does not know anything about them.)
12665 Non-@acronym{POSIX}.
12669 Use line discipline @var{n}. Non-@acronym{POSIX}.
12673 Print the terminal speed.
12676 @cindex baud rate, setting
12677 Set the input and output speeds to @var{n}. @var{n} can be one of: 0
12678 50 75 110 134 134.5 150 200 300 600 1200 1800 2400 4800 9600 19200
12679 38400 @code{exta} @code{extb}. @code{exta} is the same as 19200;
12680 @code{extb} is the same as 38400. Many systems, including GNU/Linux,
12681 support higher speeds. The @command{stty} command includes support
12698 4000000 where the system supports these.
12699 0 hangs up the line if @option{-clocal} is set.
12703 @node printenv invocation
12704 @section @command{printenv}: Print all or some environment variables
12707 @cindex printing all or some environment variables
12708 @cindex environment variables, printing
12710 @command{printenv} prints environment variable values. Synopsis:
12713 printenv [@var{option}] [@var{variable}]@dots{}
12716 If no @var{variable}s are specified, @command{printenv} prints the value of
12717 every environment variable. Otherwise, it prints the value of each
12718 @var{variable} that is set, and nothing for those that are not set.
12720 The only options are a lone @option{--help} or @option{--version}.
12721 @xref{Common options}.
12723 @cindex exit status of @command{printenv}
12727 0 if all variables specified were found
12728 1 if at least one specified variable was not found
12729 2 if a write error occurred
12733 @node tty invocation
12734 @section @command{tty}: Print file name of terminal on standard input
12737 @cindex print terminal file name
12738 @cindex terminal file name, printing
12740 @command{tty} prints the file name of the terminal connected to its standard
12741 input. It prints @samp{not a tty} if standard input is not a terminal.
12745 tty [@var{option}]@dots{}
12748 The program accepts the following option. Also see @ref{Common options}.
12758 Print nothing; only return an exit status.
12762 @cindex exit status of @command{tty}
12766 0 if standard input is a terminal
12767 1 if standard input is not a terminal
12768 2 if given incorrect arguments
12769 3 if a write error occurs
12773 @node User information
12774 @chapter User information
12776 @cindex user information, commands for
12777 @cindex commands for printing user information
12779 This section describes commands that print user-related information:
12780 logins, groups, and so forth.
12783 * id invocation:: Print user identity.
12784 * logname invocation:: Print current login name.
12785 * whoami invocation:: Print effective user ID.
12786 * groups invocation:: Print group names a user is in.
12787 * users invocation:: Print login names of users currently logged in.
12788 * who invocation:: Print who is currently logged in.
12792 @node id invocation
12793 @section @command{id}: Print user identity
12796 @cindex real user and group IDs, printing
12797 @cindex effective user and group IDs, printing
12798 @cindex printing real and effective user and group IDs
12800 @command{id} prints information about the given user, or the process
12801 running it if no user is specified. Synopsis:
12804 id [@var{option}]@dots{} [@var{username}]
12807 By default, it prints the real user ID, real group ID, effective user ID
12808 if different from the real user ID, effective group ID if different from
12809 the real group ID, and supplemental group IDs.
12811 Each of these numeric values is preceded by an identifying string and
12812 followed by the corresponding user or group name in parentheses.
12814 The options cause @command{id} to print only part of the above information.
12815 Also see @ref{Common options}.
12822 Print only the group ID.
12828 Print only the group ID and the supplementary groups.
12834 Print the user or group name instead of the ID number. Requires
12835 @option{-u}, @option{-g}, or @option{-G}.
12841 Print the real, instead of effective, user or group ID. Requires
12842 @option{-u}, @option{-g}, or @option{-G}.
12848 Print only the user ID.
12855 @cindex security context
12856 Print only the security context of the current user.
12857 If SELinux is disabled then print a warning and
12858 set the exit status to 1.
12864 @macro primaryAndSupplementaryGroups{cmd,arg}
12865 Primary and supplementary groups for a process are normally inherited
12866 from its parent and are usually unchanged since login. This means
12867 that if you change the group database after logging in, @command{\cmd\}
12868 will not reflect your changes within your existing login session.
12869 Running @command{\cmd\} with a \arg\ causes the user and group
12870 database to be consulted afresh, and so will give a different result.
12872 @primaryAndSupplementaryGroups{id,user argument}
12874 @node logname invocation
12875 @section @command{logname}: Print current login name
12878 @cindex printing user's login name
12879 @cindex login name, printing
12880 @cindex user name, printing
12883 @command{logname} prints the calling user's name, as found in a
12884 system-maintained file (often @file{/var/run/utmp} or
12885 @file{/etc/utmp}), and exits with a status of 0. If there is no entry
12886 for the calling process, @command{logname} prints
12887 an error message and exits with a status of 1.
12889 The only options are @option{--help} and @option{--version}. @xref{Common
12895 @node whoami invocation
12896 @section @command{whoami}: Print effective user ID
12899 @cindex effective user ID, printing
12900 @cindex printing the effective user ID
12902 @command{whoami} prints the user name associated with the current
12903 effective user ID. It is equivalent to the command @samp{id -un}.
12905 The only options are @option{--help} and @option{--version}. @xref{Common
12911 @node groups invocation
12912 @section @command{groups}: Print group names a user is in
12915 @cindex printing groups a user is in
12916 @cindex supplementary groups, printing
12918 @command{groups} prints the names of the primary and any supplementary
12919 groups for each given @var{username}, or the current process if no names
12920 are given. If more than one name is given, the name of each user is
12922 the list of that user's groups and the user name is separated from the
12923 group list by a colon. Synopsis:
12926 groups [@var{username}]@dots{}
12929 The group lists are equivalent to the output of the command @samp{id -Gn}.
12931 @primaryAndSupplementaryGroups{groups,list of users}
12933 The only options are @option{--help} and @option{--version}. @xref{Common
12939 @node users invocation
12940 @section @command{users}: Print login names of users currently logged in
12943 @cindex printing current usernames
12944 @cindex usernames, printing current
12946 @cindex login sessions, printing users with
12947 @command{users} prints on a single line a blank-separated list of user
12948 names of users currently logged in to the current host. Each user name
12949 corresponds to a login session, so if a user has more than one login
12950 session, that user's name will appear the same number of times in the
12959 With no @var{file} argument, @command{users} extracts its information from
12960 a system-maintained file (often @file{/var/run/utmp} or
12961 @file{/etc/utmp}). If a file argument is given, @command{users} uses
12962 that file instead. A common choice is @file{/var/log/wtmp}.
12964 The only options are @option{--help} and @option{--version}. @xref{Common
12970 @node who invocation
12971 @section @command{who}: Print who is currently logged in
12974 @cindex printing current user information
12975 @cindex information, about current users
12977 @command{who} prints information about users who are currently logged on.
12981 @command{who} [@var{option}] [@var{file}] [am i]
12984 @cindex terminal lines, currently used
12986 @cindex remote hostname
12987 If given no non-option arguments, @command{who} prints the following
12988 information for each user currently logged on: login name, terminal
12989 line, login time, and remote hostname or X display.
12993 If given one non-option argument, @command{who} uses that instead of
12994 a default system-maintained file (often @file{/var/run/utmp} or
12995 @file{/etc/utmp}) as the name of the file containing the record of
12996 users logged on. @file{/var/log/wtmp} is commonly given as an argument
12997 to @command{who} to look at who has previously logged on.
13001 If given two non-option arguments, @command{who} prints only the entry
13002 for the user running it (determined from its standard input), preceded
13003 by the hostname. Traditionally, the two arguments given are @samp{am
13004 i}, as in @samp{who am i}.
13007 Time stamps are listed according to the time zone rules specified by
13008 the @env{TZ} environment variable, or by the system default rules if
13009 @env{TZ} is not set. @xref{TZ Variable,, Specifying the Time Zone
13010 with @env{TZ}, libc, The GNU C Library Reference Manual}.
13012 The program accepts the following options. Also see @ref{Common options}.
13020 Same as @samp{-b -d --login -p -r -t -T -u}.
13026 Print the date and time of last system boot.
13032 Print information corresponding to dead processes.
13038 Print a line of column headings.
13044 List only the entries that correspond to processes via which the
13045 system is waiting for a user to login. The user name is always @samp{LOGIN}.
13049 Attempt to canonicalize hostnames found in utmp through a DNS lookup. This
13050 is not the default because it can cause significant delays on systems with
13051 automatic dial-up internet access.
13055 Same as @samp{who am i}.
13061 List active processes spawned by init.
13067 Print only the login names and the number of users logged on.
13068 Overrides all other options.
13073 @opindex --runlevel
13074 Print the current (and maybe previous) run-level of the init process.
13078 Ignored; for compatibility with other versions of @command{who}.
13084 Print last system clock change.
13089 After the login time, print the number of hours and minutes that the
13090 user has been idle. @samp{.} means the user was active in the last minute.
13091 @samp{old} means the user has been idle for more than 24 hours.
13102 @opindex --writable
13103 @cindex message status
13104 @pindex write@r{, allowed}
13105 After each login name print a character indicating the user's message status:
13108 @samp{+} allowing @code{write} messages
13109 @samp{-} disallowing @code{write} messages
13110 @samp{?} cannot find terminal device
13118 @node System context
13119 @chapter System context
13121 @cindex system context
13122 @cindex context, system
13123 @cindex commands for system context
13125 This section describes commands that print or change system-wide
13129 * date invocation:: Print or set system date and time.
13130 * arch invocation:: Print machine hardware name.
13131 * uname invocation:: Print system information.
13132 * hostname invocation:: Print or set system name.
13133 * hostid invocation:: Print numeric host identifier.
13134 * uptime invocation:: Print system uptime and load.
13137 @node date invocation
13138 @section @command{date}: Print or set system date and time
13141 @cindex time, printing or setting
13142 @cindex printing the current time
13147 date [@var{option}]@dots{} [+@var{format}]
13148 date [-u|--utc|--universal] @c this avoids a newline in the output
13149 [ MMDDhhmm[[CC]YY][.ss] ]
13153 Invoking @command{date} with no @var{format} argument is equivalent to invoking
13154 it with a default format that depends on the @env{LC_TIME} locale category.
13155 In the default C locale, this format is @samp{'+%a %b %e %H:%M:%S %Z %Y'},
13156 so the output looks like @samp{Thu Mar @ 3 13:47:51 PST 2005}.
13159 Normally, @command{date} uses the time zone rules indicated by the
13160 @env{TZ} environment variable, or the system default rules if @env{TZ}
13161 is not set. @xref{TZ Variable,, Specifying the Time Zone with
13162 @env{TZ}, libc, The GNU C Library Reference Manual}.
13164 @findex strftime @r{and @command{date}}
13165 @cindex time formats
13166 @cindex formatting times
13167 If given an argument that starts with a @samp{+}, @command{date} prints the
13168 current date and time (or the date and time specified by the
13169 @option{--date} option, see below) in the format defined by that argument,
13170 which is similar to that of the @code{strftime} function. Except for
13171 conversion specifiers, which start with @samp{%}, characters in the
13172 format string are printed unchanged. The conversion specifiers are
13178 * Time conversion specifiers:: %[HIklMNpPrRsSTXzZ]
13179 * Date conversion specifiers:: %[aAbBcCdDeFgGhjmuUVwWxyY]
13180 * Literal conversion specifiers:: %[%nt]
13181 * Padding and other flags:: Pad with zeros, spaces, etc.
13182 * Setting the time:: Changing the system clock.
13183 * Options for date:: Instead of the current time.
13185 * Date input formats:: Specifying date strings.
13187 * Examples of date:: Examples.
13190 @node Time conversion specifiers
13191 @subsection Time conversion specifiers
13193 @cindex time conversion specifiers
13194 @cindex conversion specifiers, time
13196 @command{date} conversion specifiers related to times.
13200 hour (@samp{00}@dots{}@samp{23})
13202 hour (@samp{01}@dots{}@samp{12})
13204 hour (@samp{ 0}@dots{}@samp{23}).
13205 This is a @acronym{GNU} extension.
13207 hour (@samp{ 1}@dots{}@samp{12}).
13208 This is a @acronym{GNU} extension.
13210 minute (@samp{00}@dots{}@samp{59})
13212 nanoseconds (@samp{000000000}@dots{}@samp{999999999}).
13213 This is a @acronym{GNU} extension.
13215 locale's equivalent of either @samp{AM} or @samp{PM};
13216 blank in many locales.
13217 Noon is treated as @samp{PM} and midnight as @samp{AM}.
13219 like @samp{%p}, except lower case.
13220 This is a @acronym{GNU} extension.
13222 locale's 12-hour clock time (e.g., @samp{11:11:04 PM})
13224 24-hour hour and minute. Same as @samp{%H:%M}.
13225 This is a @acronym{GNU} extension.
13227 @cindex epoch, seconds since
13228 @cindex seconds since the epoch
13229 @cindex beginning of time
13230 seconds since the epoch, i.e., since 1970-01-01 00:00:00 UTC.
13231 Leap seconds are not counted unless leap second support is available.
13232 @xref{%s-examples}, for examples.
13233 This is a @acronym{GNU} extension.
13235 second (@samp{00}@dots{}@samp{60}).
13236 This may be @samp{60} if leap seconds are supported.
13238 24-hour hour, minute, and second. Same as @samp{%H:%M:%S}.
13240 locale's time representation (e.g., @samp{23:13:48})
13242 @w{@acronym{RFC} 2822/@acronym{ISO} 8601} style numeric time zone
13243 (e.g., @samp{-0600} or @samp{+0530}), or nothing if no
13244 time zone is determinable. This value reflects the numeric time zone
13245 appropriate for the current time, using the time zone rules specified
13246 by the @env{TZ} environment variable.
13247 The time (and optionally, the time zone rules) can be overridden
13248 by the @option{--date} option.
13249 This is a @acronym{GNU} extension.
13251 @w{@acronym{RFC} 3339/@acronym{ISO} 8601} style numeric time zone with
13252 @samp{:} (e.g., @samp{-06:00} or @samp{+05:30}), or nothing if no time
13253 zone is determinable.
13254 This is a @acronym{GNU} extension.
13256 Numeric time zone to the nearest second with @samp{:} (e.g.,
13257 @samp{-06:00:00} or @samp{+05:30:00}), or nothing if no time zone is
13259 This is a @acronym{GNU} extension.
13261 Numeric time zone with @samp{:} using the minimum necessary precision
13262 (e.g., @samp{-06}, @samp{+05:30}, or @samp{-04:56:02}), or nothing if
13263 no time zone is determinable.
13264 This is a @acronym{GNU} extension.
13266 alphabetic time zone abbreviation (e.g., @samp{EDT}), or nothing if no
13267 time zone is determinable. See @samp{%z} for how it is determined.
13271 @node Date conversion specifiers
13272 @subsection Date conversion specifiers
13274 @cindex date conversion specifiers
13275 @cindex conversion specifiers, date
13277 @command{date} conversion specifiers related to dates.
13281 locale's abbreviated weekday name (e.g., @samp{Sun})
13283 locale's full weekday name, variable length (e.g., @samp{Sunday})
13285 locale's abbreviated month name (e.g., @samp{Jan})
13287 locale's full month name, variable length (e.g., @samp{January})
13289 locale's date and time (e.g., @samp{Thu Mar @ 3 23:05:25 2005})
13291 century. This is like @samp{%Y}, except the last two digits are omitted.
13292 For example, it is @samp{20} if @samp{%Y} is @samp{2000},
13293 and is @samp{-0} if @samp{%Y} is @samp{-001}.
13294 It is normally at least two characters, but it may be more.
13296 day of month (e.g., @samp{01})
13298 date; same as @samp{%m/%d/%y}
13300 day of month, space padded; same as @samp{%_d}
13302 full date in @acronym{ISO} 8601 format; same as @samp{%Y-%m-%d}.
13303 This is a good choice for a date format, as it is standard and
13304 is easy to sort in the usual case where years are in the range
13306 This is a @acronym{GNU} extension.
13308 year corresponding to the @acronym{ISO} week number, but without the century
13309 (range @samp{00} through @samp{99}). This has the same format and value
13310 as @samp{%y}, except that if the @acronym{ISO} week number (see
13312 to the previous or next year, that year is used instead.
13313 This is a @acronym{GNU} extension.
13315 year corresponding to the @acronym{ISO} week number. This has the
13316 same format and value as @samp{%Y}, except that if the @acronym{ISO}
13318 @samp{%V}) belongs to the previous or next year, that year is used
13320 It is normally useful only if @samp{%V} is also used;
13321 for example, the format @samp{%G-%m-%d} is probably a mistake,
13322 since it combines the ISO week number year with the conventional month and day.
13323 This is a @acronym{GNU} extension.
13327 day of year (@samp{001}@dots{}@samp{366})
13329 month (@samp{01}@dots{}@samp{12})
13331 day of week (@samp{1}@dots{}@samp{7}) with @samp{1} corresponding to Monday
13333 week number of year, with Sunday as the first day of the week
13334 (@samp{00}@dots{}@samp{53}).
13335 Days in a new year preceding the first Sunday are in week zero.
13337 @acronym{ISO} week number, that is, the
13338 week number of year, with Monday as the first day of the week
13339 (@samp{01}@dots{}@samp{53}).
13340 If the week containing January 1 has four or more days in
13341 the new year, then it is considered week 1; otherwise, it is week 53 of
13342 the previous year, and the next week is week 1. (See the @acronym{ISO} 8601
13345 day of week (@samp{0}@dots{}@samp{6}) with 0 corresponding to Sunday
13347 week number of year, with Monday as first day of week
13348 (@samp{00}@dots{}@samp{53}).
13349 Days in a new year preceding the first Monday are in week zero.
13351 locale's date representation (e.g., @samp{12/31/99})
13353 last two digits of year (@samp{00}@dots{}@samp{99})
13355 year. This is normally at least four characters, but it may be more.
13356 Year @samp{0000} precedes year @samp{0001}, and year @samp{-001}
13357 precedes year @samp{0000}.
13361 @node Literal conversion specifiers
13362 @subsection Literal conversion specifiers
13364 @cindex literal conversion specifiers
13365 @cindex conversion specifiers, literal
13367 @command{date} conversion specifiers that produce literal strings.
13379 @node Padding and other flags
13380 @subsection Padding and other flags
13382 @cindex numeric field padding
13383 @cindex padding of numeric fields
13384 @cindex fields, padding numeric
13386 Unless otherwise specified, @command{date} normally pads numeric fields
13387 with zeros, so that, for
13388 example, numeric months are always output as two digits.
13389 Seconds since the epoch are not padded, though,
13390 since there is no natural width for them.
13392 As a @acronym{GNU} extension, @command{date} recognizes any of the
13393 following optional flags after the @samp{%}:
13397 (hyphen) Do not pad the field; useful if the output is intended for
13400 (underscore) Pad with spaces; useful if you need a fixed
13401 number of characters in the output, but zeros are too distracting.
13403 (zero) Pad with zeros even if the conversion specifier
13404 would normally pad with spaces.
13406 Use upper case characters if possible.
13408 Use opposite case characters if possible.
13409 A field that is normally upper case becomes lower case, and vice versa.
13413 Here are some examples of padding:
13416 date +%d/%m -d "Feb 1"
13418 date +%-d/%-m -d "Feb 1"
13420 date +%_d/%_m -d "Feb 1"
13424 As a @acronym{GNU} extension, you can specify the field width
13425 (after any flag, if present) as a decimal number. If the natural size of the
13426 output of the field has less than the specified number of characters,
13427 the result is written right adjusted and padded to the given
13428 size. For example, @samp{%9B} prints the right adjusted month name in
13429 a field of width 9.
13431 An optional modifier can follow the optional flag and width
13432 specification. The modifiers are:
13436 Use the locale's alternate representation for date and time. This
13437 modifier applies to the @samp{%c}, @samp{%C}, @samp{%x}, @samp{%X},
13438 @samp{%y} and @samp{%Y} conversion specifiers. In a Japanese locale, for
13439 example, @samp{%Ex} might yield a date format based on the Japanese
13443 Use the locale's alternate numeric symbols for numbers. This modifier
13444 applies only to numeric conversion specifiers.
13447 If the format supports the modifier but no alternate representation
13448 is available, it is ignored.
13451 @node Setting the time
13452 @subsection Setting the time
13454 @cindex setting the time
13455 @cindex time setting
13456 @cindex appropriate privileges
13458 If given an argument that does not start with @samp{+}, @command{date} sets
13459 the system clock to the date and time specified by that argument (as
13460 described below). You must have appropriate privileges to set the
13461 system clock. The @option{--date} and @option{--set} options may not be
13462 used with such an argument. The @option{--universal} option may be used
13463 with such an argument to indicate that the specified date and time are
13464 relative to Coordinated Universal Time rather than to the local time
13467 The argument must consist entirely of digits, which have the following
13480 first two digits of year (optional)
13482 last two digits of year (optional)
13487 The @option{--set} option also sets the system clock; see the next section.
13490 @node Options for date
13491 @subsection Options for @command{date}
13493 @cindex @command{date} options
13494 @cindex options for @command{date}
13496 The program accepts the following options. Also see @ref{Common options}.
13500 @item -d @var{datestr}
13501 @itemx --date=@var{datestr}
13504 @cindex parsing date strings
13505 @cindex date strings, parsing
13506 @cindex arbitrary date strings, parsing
13509 @opindex next @var{day}
13510 @opindex last @var{day}
13511 Display the date and time specified in @var{datestr} instead of the
13512 current date and time. @var{datestr} can be in almost any common
13513 format. It can contain month names, time zones, @samp{am} and @samp{pm},
13514 @samp{yesterday}, etc. For example, @option{--date="2004-02-27
13515 14:19:13.489392193 +0530"} specifies the instant of time that is
13516 489,392,193 nanoseconds after February 27, 2004 at 2:19:13 PM in a
13517 time zone that is 5 hours and 30 minutes east of @acronym{UTC}.@*
13518 Note: input currently must be in locale independent format. E.g., the
13519 LC_TIME=C below is needed to print back the correct date in many locales:
13521 date -d "$(LC_TIME=C date)"
13523 @xref{Date input formats}.
13525 @item -f @var{datefile}
13526 @itemx --file=@var{datefile}
13529 Parse each line in @var{datefile} as with @option{-d} and display the
13530 resulting date and time. If @var{datefile} is @samp{-}, use standard
13531 input. This is useful when you have many dates to process, because the
13532 system overhead of starting up the @command{date} executable many times can
13535 @item -r @var{file}
13536 @itemx --reference=@var{file}
13538 @opindex --reference
13539 Display the date and time of the last modification of @var{file},
13540 instead of the current date and time.
13547 @opindex --rfc-2822
13548 Display the date and time using the format @samp{%a, %d %b %Y %H:%M:%S
13549 %z}, evaluated in the C locale so abbreviations are always in English.
13553 Fri, 09 Sep 2005 13:51:39 -0700
13556 This format conforms to
13557 @uref{ftp://ftp.rfc-editor.org/in-notes/rfc2822.txt, Internet
13558 @acronym{RFCs} 2822} and
13559 @uref{ftp://ftp.rfc-editor.org/in-notes/rfc822.txt, 822}, the
13560 current and previous standards for Internet email.
13562 @item --rfc-3339=@var{timespec}
13563 @opindex --rfc-3339=@var{timespec}
13564 Display the date using a format specified by
13565 @uref{ftp://ftp.rfc-editor.org/in-notes/rfc3339.txt, Internet
13566 @acronym{RFC} 3339}. This is a subset of the @acronym{ISO} 8601
13567 format, except that it also permits applications to use a space rather
13568 than a @samp{T} to separate dates from times. Unlike the other
13569 standard formats, @acronym{RFC} 3339 format is always suitable as
13570 input for the @option{--date} (@option{-d}) and @option{--file}
13571 (@option{-f}) options, regardless of the current locale.
13573 The argument @var{timespec} specifies how much of the time to include.
13574 It can be one of the following:
13578 Print just the full-date, e.g., @samp{2005-09-14}.
13579 This is equivalent to the format @samp{%Y-%m-%d}.
13582 Print the full-date and full-time separated by a space, e.g.,
13583 @samp{2005-09-14 00:56:06+05:30}. The output ends with a numeric
13584 time-offset; here the @samp{+05:30} means that local time is five
13585 hours and thirty minutes east of @acronym{UTC}. This is equivalent to
13586 the format @samp{%Y-%m-%d %H:%M:%S%:z}.
13589 Like @samp{seconds}, but also print nanoseconds, e.g.,
13590 @samp{2005-09-14 00:56:06.998458565+05:30}.
13591 This is equivalent to the format @samp{%Y-%m-%d %H:%M:%S.%N%:z}.
13595 @item -s @var{datestr}
13596 @itemx --set=@var{datestr}
13599 Set the date and time to @var{datestr}. See @option{-d} above.
13606 @opindex --universal
13607 @cindex Coordinated Universal Time
13609 @cindex Greenwich Mean Time
13612 Use Coordinated Universal Time (@acronym{UTC}) by operating as if the
13613 @env{TZ} environment variable were set to the string @samp{UTC0}.
13615 Universal Time is often called ``Greenwich Mean Time'' (@sc{gmt}) for
13616 historical reasons.
13620 @node Examples of date
13621 @subsection Examples of @command{date}
13623 @cindex examples of @command{date}
13625 Here are a few examples. Also see the documentation for the @option{-d}
13626 option in the previous section.
13631 To print the date of the day before yesterday:
13634 date --date='2 days ago'
13638 To print the date of the day three months and one day hence:
13641 date --date='3 months 1 day'
13645 To print the day of year of Christmas in the current year:
13648 date --date='25 Dec' +%j
13652 To print the current full month name and the day of the month:
13658 But this may not be what you want because for the first nine days of
13659 the month, the @samp{%d} expands to a zero-padded two-digit field,
13660 for example @samp{date -d 1may '+%B %d'} will print @samp{May 01}.
13663 To print a date without the leading zero for one-digit days
13664 of the month, you can use the (@acronym{GNU} extension)
13665 @samp{-} flag to suppress
13666 the padding altogether:
13669 date -d 1may '+%B %-d
13673 To print the current date and time in the format required by many
13674 non-@acronym{GNU} versions of @command{date} when setting the system clock:
13677 date +%m%d%H%M%Y.%S
13681 To set the system clock forward by two minutes:
13684 date --set='+2 minutes'
13688 To print the date in @acronym{RFC} 2822 format,
13689 use @samp{date --rfc-2822}. Here is some example output:
13692 Fri, 09 Sep 2005 13:51:39 -0700
13695 @anchor{%s-examples}
13697 To convert a date string to the number of seconds since the epoch
13698 (which is 1970-01-01 00:00:00 UTC), use the @option{--date} option with
13699 the @samp{%s} format. That can be useful in sorting and/or graphing
13700 and/or comparing data by date. The following command outputs the
13701 number of the seconds since the epoch for the time two minutes after the
13705 date --date='1970-01-01 00:02:00 +0000' +%s
13709 If you do not specify time zone information in the date string,
13710 @command{date} uses your computer's idea of the time zone when
13711 interpreting the string. For example, if your computer's time zone is
13712 that of Cambridge, Massachusetts, which was then 5 hours (i.e., 18,000
13713 seconds) behind UTC:
13716 # local time zone used
13717 date --date='1970-01-01 00:02:00' +%s
13722 If you're sorting or graphing dated data, your raw date values may be
13723 represented as seconds since the epoch. But few people can look at
13724 the date @samp{946684800} and casually note ``Oh, that's the first second
13725 of the year 2000 in Greenwich, England.''
13728 date --date='2000-01-01 UTC' +%s
13732 An alternative is to use the @option{--utc} (@option{-u}) option.
13733 Then you may omit @samp{UTC} from the date string. Although this
13734 produces the same result for @samp{%s} and many other format sequences,
13735 with a time zone offset different from zero, it would give a different
13736 result for zone-dependent formats like @samp{%z}.
13739 date -u --date=2000-01-01 +%s
13743 To convert such an unwieldy number of seconds back to
13744 a more readable form, use a command like this:
13747 # local time zone used
13748 date -d '1970-01-01 UTC 946684800 seconds' +"%Y-%m-%d %T %z"
13749 1999-12-31 19:00:00 -0500
13752 Or if you do not mind depending on the @samp{@@} feature present since
13753 coreutils 5.3.0, you could shorten this to:
13756 date -d @@946684800 +"%F %T %z"
13757 1999-12-31 19:00:00 -0500
13760 Often it is better to output UTC-relative date and time:
13763 date -u -d '1970-01-01 946684800 seconds' +"%Y-%m-%d %T %z"
13764 2000-01-01 00:00:00 +0000
13770 @node arch invocation
13771 @section @command{arch}: Print machine hardware name
13774 @cindex print machine hardware name
13775 @cindex system information, printing
13777 @command{arch} prints the machine hardware name,
13778 and is equivalent to @samp{uname -m}.
13782 arch [@var{option}]
13785 The program accepts the @ref{Common options} only.
13790 @node uname invocation
13791 @section @command{uname}: Print system information
13794 @cindex print system information
13795 @cindex system information, printing
13797 @command{uname} prints information about the machine and operating system
13798 it is run on. If no options are given, @command{uname} acts as if the
13799 @option{-s} option were given. Synopsis:
13802 uname [@var{option}]@dots{}
13805 If multiple options or @option{-a} are given, the selected information is
13806 printed in this order:
13809 @var{kernel-name} @var{nodename} @var{kernel-release} @var{kernel-version}
13810 @var{machine} @var{processor} @var{hardware-platform} @var{operating-system}
13813 The information may contain internal spaces, so such output cannot be
13814 parsed reliably. In the following example, @var{release} is
13815 @samp{2.2.18ss.e820-bda652a #4 SMP Tue Jun 5 11:24:08 PDT 2001}:
13819 @result{} Linux dum 2.2.18 #4 SMP Tue Jun 5 11:24:08 PDT 2001 i686 unknown unknown GNU/Linux
13823 The program accepts the following options. Also see @ref{Common options}.
13831 Print all of the below information, except omit the processor type
13832 and the hardware platform name if they are unknown.
13835 @itemx --hardware-platform
13837 @opindex --hardware-platform
13838 @cindex implementation, hardware
13839 @cindex hardware platform
13840 @cindex platform, hardware
13841 Print the hardware platform name
13842 (sometimes called the hardware implementation).
13843 Print @samp{unknown} if the kernel does not make this information
13844 easily available, as is the case with Linux kernels.
13850 @cindex machine type
13851 @cindex hardware class
13852 @cindex hardware type
13853 Print the machine hardware name (sometimes called the hardware class
13859 @opindex --nodename
13862 @cindex network node name
13863 Print the network node hostname.
13868 @opindex --processor
13869 @cindex host processor type
13870 Print the processor type (sometimes called the instruction set
13871 architecture or ISA).
13872 Print @samp{unknown} if the kernel does not make this information
13873 easily available, as is the case with Linux kernels.
13876 @itemx --operating-system
13878 @opindex --operating-system
13879 @cindex operating system name
13880 Print the name of the operating system.
13883 @itemx --kernel-release
13885 @opindex --kernel-release
13886 @cindex kernel release
13887 @cindex release of kernel
13888 Print the kernel release.
13891 @itemx --kernel-name
13893 @opindex --kernel-name
13894 @cindex kernel name
13895 @cindex name of kernel
13896 Print the kernel name.
13897 @acronym{POSIX} 1003.1-2001 (@pxref{Standards conformance}) calls this
13898 ``the implementation of the operating system'', because the
13899 @acronym{POSIX} specification itself has no notion of ``kernel''.
13900 The kernel name might be the same as the operating system name printed
13901 by the @option{-o} or @option{--operating-system} option, but it might
13902 differ. Some operating systems (e.g., FreeBSD, HP-UX) have the same
13903 name as their underlying kernels; others (e.g., GNU/Linux, Solaris)
13907 @itemx --kernel-version
13909 @opindex --kernel-version
13910 @cindex kernel version
13911 @cindex version of kernel
13912 Print the kernel version.
13919 @node hostname invocation
13920 @section @command{hostname}: Print or set system name
13923 @cindex setting the hostname
13924 @cindex printing the hostname
13925 @cindex system name, printing
13926 @cindex appropriate privileges
13928 With no arguments, @command{hostname} prints the name of the current host
13929 system. With one argument, it sets the current host name to the
13930 specified string. You must have appropriate privileges to set the host
13934 hostname [@var{name}]
13937 The only options are @option{--help} and @option{--version}. @xref{Common
13943 @node hostid invocation
13944 @section @command{hostid}: Print numeric host identifier
13947 @cindex printing the host identifier
13949 @command{hostid} prints the numeric identifier of the current host
13950 in hexadecimal. This command accepts no arguments.
13951 The only options are @option{--help} and @option{--version}.
13952 @xref{Common options}.
13954 For example, here's what it prints on one system I use:
13961 On that system, the 32-bit quantity happens to be closely
13962 related to the system's Internet address, but that isn't always
13967 @node uptime invocation
13968 @section @command{uptime}: Print system uptime and load
13971 @cindex printing the system uptime and load
13973 @command{uptime} prints the current time, the system's uptime, the
13974 number of logged-in users and the current load average.
13976 If an argument is specified, it is used as the file to be read
13977 to discover how many users are logged in. If no argument is
13978 specified, a system default is used (@command{uptime --help} indicates
13979 the default setting).
13981 The only options are @option{--help} and @option{--version}.
13982 @xref{Common options}.
13984 For example, here's what it prints right now on one system I use:
13988 14:07 up 3:35, 3 users, load average: 1.39, 1.15, 1.04
13991 The precise method of calculation of load average varies somewhat
13992 between systems. Some systems calculate it as the average number of
13993 runnable processes over the last 1, 5 and 15 minutes, but some systems
13994 also include processes in the uninterruptible sleep state (that is,
13995 those processes which are waiting for disk I/O). The Linux kernel
13996 includes uninterruptible processes.
13998 @node SELinux context
13999 @chapter SELinux context
14001 @cindex SELinux context
14002 @cindex SELinux, context
14003 @cindex commands for SELinux context
14005 This section describes commands for operations with SELinux
14009 * chcon invocation:: Change SELinux context of file
14010 * runcon invocation:: Run a command in specified SELinux context
14013 @node chcon invocation
14014 @section @command{chcon}: Change SELinux context of file
14017 @cindex changing security context
14018 @cindex change SELinux context
14020 @command{chcon} changes the SELinux security context of the selected files.
14024 chcon [@var{option}]@dots{} @var{context} @var{file}@dots{}
14025 chcon [@var{option}]@dots{} [-u @var{user}] [-r @var{role}] [-l @var{range}] [-t @var{type}] @var{file}@dots{}
14026 chcon [@var{option}]@dots{} --reference=@var{rfile} @var{file}@dots{}
14029 Change the SELinux security context of each @var{file} to @var{context}.
14030 With @option{--reference}, change the security context of each @var{file}
14031 to that of @var{rfile}.
14033 The program accepts the following options. Also see @ref{Common options}.
14038 @itemx --no-dereference
14040 @opindex --no-dereference
14041 @cindex no dereference
14042 Affect symbolic links instead of any referenced file.
14044 @item --reference=@var{rfile}
14045 @opindex --reference
14046 @cindex reference file
14047 Use @var{rfile}'s security context rather than specifying a @var{context} value.
14052 @opindex --recursive
14053 Operate on files and directories recursively.
14056 @xref{Traversing symlinks}.
14059 @xref{Traversing symlinks}.
14062 @xref{Traversing symlinks}.
14069 Output a diagnostic for every file processed.
14071 @item -u @var{user}
14072 @itemx --user=@var{user}
14075 Set user @var{user} in the target security context.
14077 @item -r @var{role}
14078 @itemx --role=@var{role}
14081 Set role @var{role} in the target security context.
14083 @item -t @var{type}
14084 @itemx --type=@var{type}
14087 Set type @var{type} in the target security context.
14089 @item -l @var{range}
14090 @itemx --range=@var{range}
14093 Set range @var{range} in the target security context.
14099 @node runcon invocation
14100 @section @command{runcon}: Run a command in specified SELinux context
14103 @cindex run with security context
14106 @command{runcon} runs file in specified SELinux security context.
14110 runcon @var{context} @var{command} [@var{args}]
14111 runcon [ -c ] [-u @var{user}] [-r @var{role}] [-t @var{type}] [-l @var{range}] @var{command} [@var{args}]
14114 Run @var{command} with completely-specified @var{context}, or with
14115 current or transitioned security context modified by one or more of @var{level},
14116 @var{role}, @var{type} and @var{user}.
14118 If none of @option{-c}, @option{-t}, @option{-u}, @option{-r}, or @option{-l}
14119 is specified, the first argument is used as the complete context.
14120 Any additional arguments after @var{command}
14121 are interpreted as arguments to the command.
14123 With neither @var{context} nor @var{command}, print the current security context.
14125 The program accepts the following options. Also see @ref{Common options}.
14133 Compute process transition context before modifying.
14135 @item -u @var{user}
14136 @itemx --user=@var{user}
14139 Set user @var{user} in the target security context.
14141 @item -r @var{role}
14142 @itemx --role=@var{role}
14145 Set role @var{role} in the target security context.
14147 @item -t @var{type}
14148 @itemx --type=@var{type}
14151 Set type @var{type} in the target security context.
14153 @item -l @var{range}
14154 @itemx --range=@var{range}
14157 Set range @var{range} in the target security context.
14161 @cindex exit status of @command{runcon}
14165 126 if @var{command} is found but cannot be invoked
14166 127 if @command{runcon} itself fails or if @var{command} cannot be found
14167 the exit status of @var{command} otherwise
14170 @node Modified command invocation
14171 @chapter Modified command invocation
14173 @cindex modified command invocation
14174 @cindex invocation of commands, modified
14175 @cindex commands for invoking other commands
14177 This section describes commands that run other commands in some context
14178 different than the current one: a modified environment, as a different
14182 * chroot invocation:: Modify the root directory.
14183 * env invocation:: Modify environment variables.
14184 * nice invocation:: Modify niceness.
14185 * nohup invocation:: Immunize to hangups.
14186 * stdbuf invocation:: Modify buffering of standard streams.
14187 * su invocation:: Modify user and group ID.
14188 * timeout invocation:: Run with time limit.
14192 @node chroot invocation
14193 @section @command{chroot}: Run a command with a different root directory
14196 @cindex running a program in a specified root directory
14197 @cindex root directory, running a program in a specified
14199 @command{chroot} runs a command with a specified root directory.
14200 On many systems, only the super-user can do this.@footnote{However,
14201 some systems (e.g., FreeBSD) can be configured to allow certain regular
14202 users to use the @code{chroot} system call, and hence to run this program.
14203 Also, on Cygwin, anyone can run the @command{chroot} command, because the
14204 underlying function is non-privileged due to lack of support in MS-Windows.}
14208 chroot @var{option} @var{newroot} [@var{command} [@var{args}]@dots{}]
14209 chroot @var{option}
14212 Ordinarily, file names are looked up starting at the root of the
14213 directory structure, i.e., @file{/}. @command{chroot} changes the root to
14214 the directory @var{newroot} (which must exist) and then runs
14215 @var{command} with optional @var{args}. If @var{command} is not
14216 specified, the default is the value of the @env{SHELL} environment
14217 variable or @command{/bin/sh} if not set, invoked with the @option{-i} option.
14218 @var{command} must not be a special built-in utility
14219 (@pxref{Special built-in utilities}).
14221 The program accepts the following options. Also see @ref{Common options}.
14222 Options must precede operands.
14226 @itemx --userspec=@var{user}[:@var{group}]
14227 @opindex --userspec
14228 By default, @var{command} is run with the same credentials
14229 as the invoking process.
14230 Use this option to run it as a different @var{user} and/or with a
14231 different primary @var{group}.
14233 @itemx --groups=@var{groups}
14235 Use this option to specify the supplementary @var{groups} to be
14236 used by the new process.
14237 The items in the list (names or numeric IDs) must be separated by commas.
14241 Here are a few tips to help avoid common problems in using chroot.
14242 To start with a simple example, make @var{command} refer to a statically
14243 linked binary. If you were to use a dynamically linked executable, then
14244 you'd have to arrange to have the shared libraries in the right place under
14245 your new root directory.
14247 For example, if you create a statically linked @command{ls} executable,
14248 and put it in @file{/tmp/empty}, you can run this command as root:
14251 $ chroot /tmp/empty /ls -Rl /
14254 Then you'll see output like this:
14259 -rwxr-xr-x 1 0 0 1041745 Aug 16 11:17 ls
14262 If you want to use a dynamically linked executable, say @command{bash},
14263 then first run @samp{ldd bash} to see what shared objects it needs.
14264 Then, in addition to copying the actual binary, also copy the listed
14265 files to the required positions under your intended new root directory.
14266 Finally, if the executable requires any other files (e.g., data, state,
14267 device files), copy them into place, too.
14269 @cindex exit status of @command{chroot}
14273 1 if @command{chroot} itself fails
14274 126 if @var{command} is found but cannot be invoked
14275 127 if @var{command} cannot be found
14276 the exit status of @var{command} otherwise
14280 @node env invocation
14281 @section @command{env}: Run a command in a modified environment
14284 @cindex environment, running a program in a modified
14285 @cindex modified environment, running a program in a
14286 @cindex running a program in a modified environment
14288 @command{env} runs a command with a modified environment. Synopses:
14291 env [@var{option}]@dots{} [@var{name}=@var{value}]@dots{} @c
14292 [@var{command} [@var{args}]@dots{}]
14296 Operands of the form @samp{@var{variable}=@var{value}} set
14297 the environment variable @var{variable} to value @var{value}.
14298 @var{value} may be empty (@samp{@var{variable}=}). Setting a variable
14299 to an empty value is different from unsetting it.
14300 These operands are evaluated left-to-right, so if two operands
14301 mention the same variable the earlier is ignored.
14303 Environment variable names can be empty, and can contain any
14304 characters other than @samp{=} and @acronym{ASCII} @sc{nul}.
14305 However, it is wise to limit yourself to names that
14306 consist solely of underscores, digits, and @acronym{ASCII} letters,
14307 and that begin with a non-digit, as applications like the shell do not
14308 work well with other names.
14311 The first operand that does not contain the character @samp{=}
14312 specifies the program to invoke; it is
14313 searched for according to the @env{PATH} environment variable. Any
14314 remaining arguments are passed as arguments to that program.
14315 The program should not be a special built-in utility
14316 (@pxref{Special built-in utilities}).
14318 @cindex environment, printing
14320 If no command name is specified following the environment
14321 specifications, the resulting environment is printed. This is like
14322 specifying the @command{printenv} program.
14324 The program accepts the following options. Also see @ref{Common options}.
14325 Options must precede operands.
14329 @item -u @var{name}
14330 @itemx --unset=@var{name}
14333 Remove variable @var{name} from the environment, if it was in the
14338 @itemx --ignore-environment
14341 @opindex --ignore-environment
14342 Start with an empty environment, ignoring the inherited environment.
14346 @cindex exit status of @command{env}
14350 0 if no @var{command} is specified and the environment is output
14351 1 if @command{env} itself fails
14352 126 if @var{command} is found but cannot be invoked
14353 127 if @var{command} cannot be found
14354 the exit status of @var{command} otherwise
14358 @node nice invocation
14359 @section @command{nice}: Run a command with modified niceness
14363 @cindex scheduling, affecting
14364 @cindex appropriate privileges
14366 @command{nice} prints or modifies a process's @dfn{niceness},
14367 a parameter that affects whether the process is scheduled favorably.
14371 nice [@var{option}]@dots{} [@var{command} [@var{arg}]@dots{}]
14374 If no arguments are given, @command{nice} prints the current niceness.
14375 Otherwise, @command{nice} runs the given @var{command} with its
14376 niceness adjusted. By default, its niceness is incremented by 10.
14378 Niceness values range at least from @minus{}20 (process has high priority
14379 and gets more resources, thus slowing down other processes) through 19
14380 (process has lower priority and runs slowly itself, but has less impact
14381 on the speed of other running processes). Some systems
14382 may have a wider range of nicenesses; conversely, other systems may
14383 enforce more restrictive limits. An attempt to set the niceness
14384 outside the supported range is treated as an attempt to use the
14385 minimum or maximum supported value.
14387 A niceness should not be confused with a scheduling priority, which
14388 lets applications determine the order in which threads are scheduled
14389 to run. Unlike a priority, a niceness is merely advice to the
14390 scheduler, which the scheduler is free to ignore. Also, as a point of
14391 terminology, @acronym{POSIX} defines the behavior of @command{nice} in
14392 terms of a @dfn{nice value}, which is the nonnegative difference
14393 between a niceness and the minimum niceness. Though @command{nice}
14394 conforms to @acronym{POSIX}, its documentation and diagnostics use the
14395 term ``niceness'' for compatibility with historical practice.
14397 @var{command} must not be a special built-in utility (@pxref{Special
14398 built-in utilities}).
14400 @mayConflictWithShellBuiltIn{nice}
14402 The program accepts the following option. Also see @ref{Common options}.
14403 Options must precede operands.
14406 @item -n @var{adjustment}
14407 @itemx --adjustment=@var{adjustment}
14409 @opindex --adjustment
14410 Add @var{adjustment} instead of 10 to the command's niceness. If
14411 @var{adjustment} is negative and you lack appropriate privileges,
14412 @command{nice} issues a warning but otherwise acts as if you specified
14415 For compatibility @command{nice} also supports an obsolete
14416 option syntax @option{-@var{adjustment}}. New scripts should use
14417 @option{-n @var{adjustment}} instead.
14421 @cindex exit status of @command{nice}
14425 0 if no @var{command} is specified and the niceness is output
14426 1 if @command{nice} itself fails
14427 126 if @var{command} is found but cannot be invoked
14428 127 if @var{command} cannot be found
14429 the exit status of @var{command} otherwise
14432 It is sometimes useful to run a non-interactive program with reduced niceness.
14435 $ nice factor 4611686018427387903
14438 Since @command{nice} prints the current niceness,
14439 you can invoke it through itself to demonstrate how it works.
14441 The default behavior is to increase the niceness by @samp{10}:
14452 The @var{adjustment} is relative to the current niceness. In the
14453 next example, the first @command{nice} invocation runs the second one
14454 with niceness 10, and it in turn runs the final one with a niceness
14458 $ nice nice -n 3 nice
14462 Specifying a niceness larger than the supported range
14463 is the same as specifying the maximum supported value:
14466 $ nice -n 10000000000 nice
14470 Only a privileged user may run a process with lower niceness:
14474 nice: cannot set niceness: Permission denied
14476 $ sudo nice -n -1 nice
14481 @node nohup invocation
14482 @section @command{nohup}: Run a command immune to hangups
14485 @cindex hangups, immunity to
14486 @cindex immunity to hangups
14487 @cindex logging out and continuing to run
14490 @command{nohup} runs the given @var{command} with hangup signals ignored,
14491 so that the command can continue running in the background after you log
14495 nohup @var{command} [@var{arg}]@dots{}
14498 If standard input is a terminal, it is redirected from
14499 @file{/dev/null} so that terminal sessions do not mistakenly consider
14500 the terminal to be used by the command. This is a @acronym{GNU}
14501 extension; programs intended to be portable to non-@acronym{GNU} hosts
14502 should use @samp{nohup @var{command} [@var{arg}]@dots{} </dev/null}
14506 If standard output is a terminal, the command's standard output is appended
14507 to the file @file{nohup.out}; if that cannot be written to, it is appended
14508 to the file @file{$HOME/nohup.out}; and if that cannot be written to, the
14509 command is not run.
14510 Any @file{nohup.out} or @file{$HOME/nohup.out} file created by
14511 @command{nohup} is made readable and writable only to the user,
14512 regardless of the current umask settings.
14514 If standard error is a terminal, it is normally redirected to the same file
14515 descriptor as the (possibly-redirected) standard output.
14516 However, if standard output is closed, standard error terminal output
14517 is instead appended to the file @file{nohup.out} or
14518 @file{$HOME/nohup.out} as above.
14520 To capture the command's output to a file other than @file{nohup.out}
14521 you can redirect it. For example, to capture the output of
14525 nohup make > make.log
14528 @command{nohup} does not automatically put the command it runs in the
14529 background; you must do that explicitly, by ending the command line
14530 with an @samp{&}. Also, @command{nohup} does not alter the
14531 niceness of @var{command}; use @command{nice} for that,
14532 e.g., @samp{nohup nice @var{command}}.
14534 @var{command} must not be a special built-in utility (@pxref{Special
14535 built-in utilities}).
14537 The only options are @option{--help} and @option{--version}. @xref{Common
14538 options}. Options must precede operands.
14540 @cindex exit status of @command{nohup}
14544 126 if @var{command} is found but cannot be invoked
14545 127 if @command{nohup} itself fails or if @var{command} cannot be found
14546 the exit status of @var{command} otherwise
14550 @node stdbuf invocation
14551 @section @command{stdbuf}: Run a command with modified I/O stream buffering
14554 @cindex standard streams, buffering
14555 @cindex line buffered
14557 @command{stdbuf} allows one to modify the buffering operations of the
14558 three standard I/O streams associated with a program. Synopsis:
14561 stdbuf @var{option}@dots{} @var{command}
14564 Any additional @var{arg}s are passed as additional arguments to the
14567 The program accepts the following options. Also see @ref{Common options}.
14571 @item -i @var{mode}
14572 @itemx --input=@var{mode}
14575 Adjust the standard input stream buffering.
14577 @item -o @var{mode}
14578 @itemx --output=@var{mode}
14581 Adjust the standard output stream buffering.
14583 @item -e @var{mode}
14584 @itemx --error=@var{mode}
14587 Adjust the standard error stream buffering.
14591 The @var{mode} can be specified as follows:
14596 Set the stream to line buffered mode.
14597 In this mode data is coalesced until a newline is output or
14598 input is read from any stream attached to a terminal device.
14599 This option is invalid with standard input.
14602 Disable buffering of the selected stream.
14603 In this mode data is output immediately and only the
14604 amount of data requested is read from input.
14607 Specify the size of the buffer to use in fully buffered mode.
14608 @multiplierSuffixesNoBlocks{size}
14612 NOTE: If @var{command} adjusts the buffering of its standard streams
14613 (@command{tee} does for e.g.) then that will override corresponding settings
14614 changed by @command{stdbuf}. Also some filters (like @command{dd} and
14615 @command{cat} etc.) don't use streams for I/O, and are thus unaffected
14616 by @command{stdbuf} settings.
14618 @cindex exit status of @command{stdbuf}
14622 125 if @command{stdbuf} itself fails
14623 126 if @var{command} is found but cannot be invoked
14624 127 if @var{command} cannot be found
14625 the exit status of @var{command} otherwise
14629 @node su invocation
14630 @section @command{su}: Run a command with substitute user and group ID
14633 @cindex substitute user and group IDs
14634 @cindex user ID, switching
14635 @cindex super-user, becoming
14636 @cindex root, becoming
14638 @command{su} allows one user to temporarily become another user. It runs a
14639 command (often an interactive shell) with the real and effective user
14640 ID, group ID, and supplemental groups of a given @var{user}. Synopsis:
14643 su [@var{option}]@dots{} [@var{user} [@var{arg}]@dots{}]
14646 @cindex passwd entry, and @command{su} shell
14648 @flindex /etc/passwd
14649 If no @var{user} is given, the default is @code{root}, the super-user.
14650 The shell to use is taken from @var{user}'s @code{passwd} entry, or
14651 @file{/bin/sh} if none is specified there. If @var{user} has a
14652 password, @command{su} prompts for the password unless run by a user with
14653 effective user ID of zero (the super-user).
14659 @cindex login shell
14660 By default, @command{su} does not change the current directory.
14661 It sets the environment variables @env{HOME} and @env{SHELL}
14662 from the password entry for @var{user}, and if @var{user} is not
14663 the super-user, sets @env{USER} and @env{LOGNAME} to @var{user}.
14664 By default, the shell is not a login shell.
14666 Any additional @var{arg}s are passed as additional arguments to the
14669 @cindex @option{-su}
14670 GNU @command{su} does not treat @file{/bin/sh} or any other shells specially
14671 (e.g., by setting @code{argv[0]} to @option{-su}, passing @option{-c} only
14672 to certain shells, etc.).
14675 @command{su} can optionally be compiled to use @code{syslog} to report
14676 failed, and optionally successful, @command{su} attempts. (If the system
14677 supports @code{syslog}.) However, GNU @command{su} does not check if the
14678 user is a member of the @code{wheel} group; see below.
14680 The program accepts the following options. Also see @ref{Common options}.
14683 @item -c @var{command}
14684 @itemx --command=@var{command}
14687 Pass @var{command}, a single command line to run, to the shell with
14688 a @option{-c} option instead of starting an interactive shell.
14695 @cindex file name pattern expansion, disabled
14696 @cindex globbing, disabled
14697 Pass the @option{-f} option to the shell. This probably only makes sense
14698 if the shell run is @command{csh} or @command{tcsh}, for which the @option{-f}
14699 option prevents reading the startup file (@file{.cshrc}). With
14700 Bourne-like shells, the @option{-f} option disables file name pattern
14701 expansion (globbing), which is not likely to be useful.
14709 @c other variables already indexed above
14712 @cindex login shell, creating
14713 Make the shell a login shell. This means the following. Unset all
14714 environment variables except @env{TERM}, @env{HOME}, and @env{SHELL}
14715 (which are set as described above), and @env{USER} and @env{LOGNAME}
14716 (which are set, even for the super-user, as described above), and set
14717 @env{PATH} to a compiled-in default value. Change to @var{user}'s home
14718 directory. Prepend @samp{-} to the shell's name, intended to make it
14719 read its login startup file(s).
14723 @itemx --preserve-environment
14726 @opindex --preserve-environment
14727 @cindex environment, preserving
14728 @flindex /etc/shells
14729 @cindex restricted shell
14730 Do not change the environment variables @env{HOME}, @env{USER},
14731 @env{LOGNAME}, or @env{SHELL}. Run the shell given in the environment
14732 variable @env{SHELL} instead of the shell from @var{user}'s passwd
14733 entry, unless the user running @command{su} is not the super-user and
14734 @var{user}'s shell is restricted. A @dfn{restricted shell} is one that
14735 is not listed in the file @file{/etc/shells}, or in a compiled-in list
14736 if that file does not exist. Parts of what this option does can be
14737 overridden by @option{--login} and @option{--shell}.
14739 @item -s @var{shell}
14740 @itemx --shell=@var{shell}
14743 Run @var{shell} instead of the shell from @var{user}'s passwd entry,
14744 unless the user running @command{su} is not the super-user and @var{user}'s
14745 shell is restricted (see @option{-m} just above).
14749 @cindex exit status of @command{su}
14753 1 if @command{su} itself fails
14754 126 if subshell is found but cannot be invoked
14755 127 if subshell cannot be found
14756 the exit status of the subshell otherwise
14759 @cindex wheel group, not supported
14760 @cindex group wheel, not supported
14762 @subsection Why GNU @command{su} does not support the @samp{wheel} group
14764 (This section is by Richard Stallman.)
14768 Sometimes a few of the users try to hold total power over all the
14769 rest. For example, in 1984, a few users at the MIT AI lab decided to
14770 seize power by changing the operator password on the Twenex system and
14771 keeping it secret from everyone else. (I was able to thwart this coup
14772 and give power back to the users by patching the kernel, but I
14773 wouldn't know how to do that in Unix.)
14775 However, occasionally the rulers do tell someone. Under the usual
14776 @command{su} mechanism, once someone learns the root password who
14777 sympathizes with the ordinary users, he or she can tell the rest. The
14778 ``wheel group'' feature would make this impossible, and thus cement the
14779 power of the rulers.
14781 I'm on the side of the masses, not that of the rulers. If you are
14782 used to supporting the bosses and sysadmins in whatever they do, you
14783 might find this idea strange at first.
14786 @node timeout invocation
14787 @section @command{timeout}: Run a command with a time limit
14791 @cindex run commands with bounded time
14793 @command{timeout} runs the given @var{command} and kills it if it is
14794 still running after the specified time interval. Synopsis:
14797 timeout [@var{option}] @var{number}[smhd] @var{command} [@var{arg}]@dots{}
14801 @var{number} is an integer followed by an optional unit; the default
14802 is seconds. The units are:
14815 @var{command} must not be a special built-in utility (@pxref{Special
14816 built-in utilities}).
14818 The program accepts the following option. Also see @ref{Common options}.
14819 Options must precede operands.
14822 @item -s @var{signal}
14823 @itemx --signal=@var{signal}
14826 Send this @var{signal} to @var{command} on timeout, rather than the
14827 default @samp{TERM} signal. @var{signal} may be a name like @samp{HUP}
14828 or a number. Also see @xref{Signal specifications}.
14832 @cindex exit status of @command{timeout}
14836 124 if @var{command} times out
14837 125 if @command{timeout} itself fails
14838 126 if @var{command} is found but cannot be invoked
14839 127 if @var{command} cannot be found
14840 the exit status of @var{command} otherwise
14844 @node Process control
14845 @chapter Process control
14847 @cindex processes, commands for controlling
14848 @cindex commands for controlling processes
14851 * kill invocation:: Sending a signal to processes.
14855 @node kill invocation
14856 @section @command{kill}: Send a signal to processes
14859 @cindex send a signal to processes
14861 The @command{kill} command sends a signal to processes, causing them
14862 to terminate or otherwise act upon receiving the signal in some way.
14863 Alternatively, it lists information about signals. Synopses:
14866 kill [-s @var{signal} | --signal @var{signal} | -@var{signal}] @var{pid}@dots{}
14867 kill [-l | --list | -t | --table] [@var{signal}]@dots{}
14870 @mayConflictWithShellBuiltIn{kill}
14872 The first form of the @command{kill} command sends a signal to all
14873 @var{pid} arguments. The default signal to send if none is specified
14874 is @samp{TERM}. The special signal number @samp{0} does not denote a
14875 valid signal, but can be used to test whether the @var{pid} arguments
14876 specify processes to which a signal could be sent.
14878 If @var{pid} is positive, the signal is sent to the process with the
14879 process ID @var{pid}. If @var{pid} is zero, the signal is sent to all
14880 processes in the process group of the current process. If @var{pid}
14881 is @minus{}1, the signal is sent to all processes for which the user has
14882 permission to send a signal. If @var{pid} is less than @minus{}1, the signal
14883 is sent to all processes in the process group that equals the absolute
14884 value of @var{pid}.
14886 If @var{pid} is not positive, a system-dependent set of system
14887 processes is excluded from the list of processes to which the signal
14890 If a negative @var{pid} argument is desired as the first one, it
14891 should be preceded by @option{--}. However, as a common extension to
14892 @acronym{POSIX}, @option{--} is not required with @samp{kill
14893 -@var{signal} -@var{pid}}. The following commands are equivalent:
14902 The first form of the @command{kill} command succeeds if every @var{pid}
14903 argument specifies at least one process that the signal was sent to.
14905 The second form of the @command{kill} command lists signal information.
14906 Either the @option{-l} or @option{--list} option, or the @option{-t}
14907 or @option{--table} option must be specified. Without any
14908 @var{signal} argument, all supported signals are listed. The output
14909 of @option{-l} or @option{--list} is a list of the signal names, one
14910 per line; if @var{signal} is already a name, the signal number is
14911 printed instead. The output of @option{-t} or @option{--table} is a
14912 table of signal numbers, names, and descriptions. This form of the
14913 @command{kill} command succeeds if all @var{signal} arguments are valid
14914 and if there is no output error.
14916 The @command{kill} command also supports the @option{--help} and
14917 @option{--version} options. @xref{Common options}.
14919 A @var{signal} may be a signal name like @samp{HUP}, or a signal
14920 number like @samp{1}, or an exit status of a process terminated by the
14921 signal. A signal name can be given in canonical form or prefixed by
14922 @samp{SIG}. The case of the letters is ignored, except for the
14923 @option{-@var{signal}} option which must use upper case to avoid
14924 ambiguity with lower case option letters. For a list of supported
14925 signal names and numbers see @xref{Signal specifications}.
14930 @cindex delaying commands
14931 @cindex commands for delaying
14933 @c Perhaps @command{wait} or other commands should be described here also?
14936 * sleep invocation:: Delay for a specified time.
14940 @node sleep invocation
14941 @section @command{sleep}: Delay for a specified time
14944 @cindex delay for a specified time
14946 @command{sleep} pauses for an amount of time specified by the sum of
14947 the values of the command line arguments.
14951 sleep @var{number}[smhd]@dots{}
14955 Each argument is a number followed by an optional unit; the default
14956 is seconds. The units are:
14969 Historical implementations of @command{sleep} have required that
14970 @var{number} be an integer, and only accepted a single argument
14971 without a suffix. However, GNU @command{sleep} accepts
14972 arbitrary floating point numbers (using a period before any fractional
14975 The only options are @option{--help} and @option{--version}. @xref{Common
14978 @c sleep is a shell built-in at least with Solaris 11's /bin/sh
14979 @mayConflictWithShellBuiltIn{sleep}
14984 @node Numeric operations
14985 @chapter Numeric operations
14987 @cindex numeric operations
14988 These programs do numerically-related operations.
14991 * factor invocation:: Show factors of numbers.
14992 * seq invocation:: Print sequences of numbers.
14996 @node factor invocation
14997 @section @command{factor}: Print prime factors
15000 @cindex prime factors
15002 @command{factor} prints prime factors. Synopses:
15005 factor [@var{number}]@dots{}
15006 factor @var{option}
15009 If no @var{number} is specified on the command line, @command{factor} reads
15010 numbers from standard input, delimited by newlines, tabs, or spaces.
15012 The @command{factor} command supports only a small number of options:
15016 Print a short help on standard output, then exit without further
15020 Print the program version on standard output, then exit without further
15024 Factoring the product of the eighth and ninth Mersenne primes
15025 takes about 30 milliseconds of CPU time on a 2.2 GHz Athlon.
15028 M8=`echo 2^31-1|bc` ; M9=`echo 2^61-1|bc`
15029 /usr/bin/time -f '%U' factor $(echo "$M8 * $M9" | bc)
15030 4951760154835678088235319297: 2147483647 2305843009213693951
15034 Similarly, factoring the eighth Fermat number @math{2^{256}+1} takes
15035 about 20 seconds on the same machine.
15037 Factoring large prime numbers is, in general, hard. The Pollard Rho
15038 algorithm used by @command{factor} is particularly effective for
15039 numbers with relatively small factors. If you wish to factor large
15040 numbers which do not have small factors (for example, numbers which
15041 are the product of two large primes), other methods are far better.
15043 If @command{factor} is built without using GNU MP, only
15044 single-precision arithmetic is available, and so large numbers
15045 (typically @math{2^{64}} and above) will not be supported. The single-precision
15046 code uses an algorithm which is designed for factoring smaller
15052 @node seq invocation
15053 @section @command{seq}: Print numeric sequences
15056 @cindex numeric sequences
15057 @cindex sequence of numbers
15059 @command{seq} prints a sequence of numbers to standard output. Synopses:
15062 seq [@var{option}]@dots{} @var{last}
15063 seq [@var{option}]@dots{} @var{first} @var{last}
15064 seq [@var{option}]@dots{} @var{first} @var{increment} @var{last}
15067 @command{seq} prints the numbers from @var{first} to @var{last} by
15068 @var{increment}. By default, each number is printed on a separate line.
15069 When @var{increment} is not specified, it defaults to @samp{1},
15070 even when @var{first} is larger than @var{last}.
15071 @var{first} also defaults to @samp{1}. So @code{seq 1} prints
15072 @samp{1}, but @code{seq 0} and @code{seq 10 5} produce no output.
15073 Floating-point numbers
15074 may be specified (using a period before any fractional digits).
15076 The program accepts the following options. Also see @ref{Common options}.
15077 Options must precede operands.
15080 @item -f @var{format}
15081 @itemx --format=@var{format}
15082 @opindex -f @var{format}
15083 @opindex --format=@var{format}
15084 @cindex formatting of numbers in @command{seq}
15085 Print all numbers using @var{format}.
15086 @var{format} must contain exactly one of the @samp{printf}-style
15087 floating point conversion specifications @samp{%a}, @samp{%e},
15088 @samp{%f}, @samp{%g}, @samp{%A}, @samp{%E}, @samp{%F}, @samp{%G}.
15089 The @samp{%} may be followed by zero or more flags taken from the set
15090 @samp{-+#0 '}, then an optional width containing one or more digits,
15091 then an optional precision consisting of a @samp{.} followed by zero
15092 or more digits. @var{format} may also contain any number of @samp{%%}
15093 conversion specifications. All conversion specifications have the
15094 same meaning as with @samp{printf}.
15096 The default format is derived from @var{first}, @var{step}, and
15097 @var{last}. If these all use a fixed point decimal representation,
15098 the default format is @samp{%.@var{p}f}, where @var{p} is the minimum
15099 precision that can represent the output numbers exactly. Otherwise,
15100 the default format is @samp{%g}.
15102 @item -s @var{string}
15103 @itemx --separator=@var{string}
15104 @cindex separator for numbers in @command{seq}
15105 Separate numbers with @var{string}; default is a newline.
15106 The output always terminates with a newline.
15109 @itemx --equal-width
15110 Print all numbers with the same width, by padding with leading zeros.
15111 @var{first}, @var{step}, and @var{last} should all use a fixed point
15112 decimal representation.
15113 (To have other kinds of padding, use @option{--format}).
15117 You can get finer-grained control over output with @option{-f}:
15120 $ seq -f '(%9.2E)' -9e5 1.1e6 1.3e6
15126 If you want hexadecimal integer output, you can use @command{printf}
15127 to perform the conversion:
15130 $ printf '%x\n' `seq 1048575 1024 1050623`
15136 For very long lists of numbers, use xargs to avoid
15137 system limitations on the length of an argument list:
15140 $ seq 1000000 | xargs printf '%x\n' | tail -n 3
15146 To generate octal output, use the printf @code{%o} format instead
15149 On most systems, seq can produce whole-number output for values up to
15150 at least @math{2^{53}}. Larger integers are approximated. The details
15151 differ depending on your floating-point implementation, but a common
15152 case is that @command{seq} works with integers through @math{2^{64}},
15153 and larger integers may not be numerically correct:
15156 $ seq 18446744073709551616 1 18446744073709551618
15157 18446744073709551616
15158 18446744073709551616
15159 18446744073709551618
15162 Be careful when using @command{seq} with outlandish values: otherwise
15163 you may see surprising results, as @command{seq} uses floating point
15164 internally. For example, on the x86 platform, where the internal
15165 representation uses a 64-bit fraction, the command:
15168 seq 1 0.0000000000000000001 1.0000000000000000009
15171 outputs 1.0000000000000000007 twice and skips 1.0000000000000000008.
15176 @node File permissions
15177 @chapter File permissions
15180 @include getdate.texi
15184 @node Opening the software toolbox
15185 @chapter Opening the Software Toolbox
15187 An earlier version of this chapter appeared in
15188 @uref{http://www.linuxjournal.com/article.php?sid=2762, the
15189 @cite{What's GNU?} column of @cite{Linux Journal}, 2 (June, 1994)}.
15190 It was written by Arnold Robbins.
15193 * Toolbox introduction:: Toolbox introduction
15194 * I/O redirection:: I/O redirection
15195 * The who command:: The @command{who} command
15196 * The cut command:: The @command{cut} command
15197 * The sort command:: The @command{sort} command
15198 * The uniq command:: The @command{uniq} command
15199 * Putting the tools together:: Putting the tools together
15203 @node Toolbox introduction
15204 @unnumberedsec Toolbox Introduction
15206 This month's column is only peripherally related to the GNU Project, in
15207 that it describes a number of the GNU tools on your GNU/Linux system and how they
15208 might be used. What it's really about is the ``Software Tools'' philosophy
15209 of program development and usage.
15211 The software tools philosophy was an important and integral concept
15212 in the initial design and development of Unix (of which Linux and GNU are
15213 essentially clones). Unfortunately, in the modern day press of
15214 Internetworking and flashy GUIs, it seems to have fallen by the
15215 wayside. This is a shame, since it provides a powerful mental model
15216 for solving many kinds of problems.
15218 Many people carry a Swiss Army knife around in their pants pockets (or
15219 purse). A Swiss Army knife is a handy tool to have: it has several knife
15220 blades, a screwdriver, tweezers, toothpick, nail file, corkscrew, and perhaps
15221 a number of other things on it. For the everyday, small miscellaneous jobs
15222 where you need a simple, general purpose tool, it's just the thing.
15224 On the other hand, an experienced carpenter doesn't build a house using
15225 a Swiss Army knife. Instead, he has a toolbox chock full of specialized
15226 tools---a saw, a hammer, a screwdriver, a plane, and so on. And he knows
15227 exactly when and where to use each tool; you won't catch him hammering nails
15228 with the handle of his screwdriver.
15230 The Unix developers at Bell Labs were all professional programmers and trained
15231 computer scientists. They had found that while a one-size-fits-all program
15232 might appeal to a user because there's only one program to use, in practice
15237 difficult to write,
15240 difficult to maintain and
15244 difficult to extend to meet new situations.
15247 Instead, they felt that programs should be specialized tools. In short, each
15248 program ``should do one thing well.'' No more and no less. Such programs are
15249 simpler to design, write, and get right---they only do one thing.
15251 Furthermore, they found that with the right machinery for hooking programs
15252 together, that the whole was greater than the sum of the parts. By combining
15253 several special purpose programs, you could accomplish a specific task
15254 that none of the programs was designed for, and accomplish it much more
15255 quickly and easily than if you had to write a special purpose program.
15256 We will see some (classic) examples of this further on in the column.
15257 (An important additional point was that, if necessary, take a detour
15258 and build any software tools you may need first, if you don't already
15259 have something appropriate in the toolbox.)
15261 @node I/O redirection
15262 @unnumberedsec I/O Redirection
15264 Hopefully, you are familiar with the basics of I/O redirection in the
15265 shell, in particular the concepts of ``standard input,'' ``standard output,''
15266 and ``standard error''. Briefly, ``standard input'' is a data source, where
15267 data comes from. A program should not need to either know or care if the
15268 data source is a disk file, a keyboard, a magnetic tape, or even a punched
15269 card reader. Similarly, ``standard output'' is a data sink, where data goes
15270 to. The program should neither know nor care where this might be.
15271 Programs that only read their standard input, do something to the data,
15272 and then send it on, are called @dfn{filters}, by analogy to filters in a
15275 With the Unix shell, it's very easy to set up data pipelines:
15278 program_to_create_data | filter1 | ... | filterN > final.pretty.data
15281 We start out by creating the raw data; each filter applies some successive
15282 transformation to the data, until by the time it comes out of the pipeline,
15283 it is in the desired form.
15285 This is fine and good for standard input and standard output. Where does the
15286 standard error come in to play? Well, think about @command{filter1} in
15287 the pipeline above. What happens if it encounters an error in the data it
15288 sees? If it writes an error message to standard output, it will just
15289 disappear down the pipeline into @command{filter2}'s input, and the
15290 user will probably never see it. So programs need a place where they can send
15291 error messages so that the user will notice them. This is standard error,
15292 and it is usually connected to your console or window, even if you have
15293 redirected standard output of your program away from your screen.
15295 For filter programs to work together, the format of the data has to be
15296 agreed upon. The most straightforward and easiest format to use is simply
15297 lines of text. Unix data files are generally just streams of bytes, with
15298 lines delimited by the @acronym{ASCII} @sc{lf} (Line Feed) character,
15299 conventionally called a ``newline'' in the Unix literature. (This is
15300 @code{'\n'} if you're a C programmer.) This is the format used by all
15301 the traditional filtering programs. (Many earlier operating systems
15302 had elaborate facilities and special purpose programs for managing
15303 binary data. Unix has always shied away from such things, under the
15304 philosophy that it's easiest to simply be able to view and edit your
15305 data with a text editor.)
15307 OK, enough introduction. Let's take a look at some of the tools, and then
15308 we'll see how to hook them together in interesting ways. In the following
15309 discussion, we will only present those command line options that interest
15310 us. As you should always do, double check your system documentation
15311 for the full story.
15313 @node The who command
15314 @unnumberedsec The @command{who} Command
15316 The first program is the @command{who} command. By itself, it generates a
15317 list of the users who are currently logged in. Although I'm writing
15318 this on a single-user system, we'll pretend that several people are
15323 @print{} arnold console Jan 22 19:57
15324 @print{} miriam ttyp0 Jan 23 14:19(:0.0)
15325 @print{} bill ttyp1 Jan 21 09:32(:0.0)
15326 @print{} arnold ttyp2 Jan 23 20:48(:0.0)
15329 Here, the @samp{$} is the usual shell prompt, at which I typed @samp{who}.
15330 There are three people logged in, and I am logged in twice. On traditional
15331 Unix systems, user names are never more than eight characters long. This
15332 little bit of trivia will be useful later. The output of @command{who} is nice,
15333 but the data is not all that exciting.
15335 @node The cut command
15336 @unnumberedsec The @command{cut} Command
15338 The next program we'll look at is the @command{cut} command. This program
15339 cuts out columns or fields of input data. For example, we can tell it
15340 to print just the login name and full name from the @file{/etc/passwd}
15341 file. The @file{/etc/passwd} file has seven fields, separated by
15345 arnold:xyzzy:2076:10:Arnold D. Robbins:/home/arnold:/bin/bash
15348 To get the first and fifth fields, we would use @command{cut} like this:
15351 $ cut -d: -f1,5 /etc/passwd
15352 @print{} root:Operator
15354 @print{} arnold:Arnold D. Robbins
15355 @print{} miriam:Miriam A. Robbins
15359 With the @option{-c} option, @command{cut} will cut out specific characters
15360 (i.e., columns) in the input lines. This is useful for input data
15361 that has fixed width fields, and does not have a field separator. For
15362 example, list the Monday dates for the current month:
15364 @c Is using cal ok? Looked at gcal, but I don't like it.
15375 @node The sort command
15376 @unnumberedsec The @command{sort} Command
15378 Next we'll look at the @command{sort} command. This is one of the most
15379 powerful commands on a Unix-style system; one that you will often find
15380 yourself using when setting up fancy data plumbing.
15383 command reads and sorts each file named on the command line. It then
15384 merges the sorted data and writes it to standard output. It will read
15385 standard input if no files are given on the command line (thus
15386 making it into a filter). The sort is based on the character collating
15387 sequence or based on user-supplied ordering criteria.
15390 @node The uniq command
15391 @unnumberedsec The @command{uniq} Command
15393 Finally (at least for now), we'll look at the @command{uniq} program. When
15394 sorting data, you will often end up with duplicate lines, lines that
15395 are identical. Usually, all you need is one instance of each line.
15396 This is where @command{uniq} comes in. The @command{uniq} program reads its
15397 standard input. It prints only one
15398 copy of each repeated line. It does have several options. Later on,
15399 we'll use the @option{-c} option, which prints each unique line, preceded
15400 by a count of the number of times that line occurred in the input.
15403 @node Putting the tools together
15404 @unnumberedsec Putting the Tools Together
15406 Now, let's suppose this is a large ISP server system with dozens of users
15407 logged in. The management wants the system administrator to write a program that will
15408 generate a sorted list of logged in users. Furthermore, even if a user
15409 is logged in multiple times, his or her name should only show up in the
15412 The administrator could sit down with the system documentation and write a C
15413 program that did this. It would take perhaps a couple of hundred lines
15414 of code and about two hours to write it, test it, and debug it.
15415 However, knowing the software toolbox, the administrator can instead start out
15416 by generating just a list of logged on users:
15426 Next, sort the list:
15429 $ who | cut -c1-8 | sort
15436 Finally, run the sorted list through @command{uniq}, to weed out duplicates:
15439 $ who | cut -c1-8 | sort | uniq
15445 The @command{sort} command actually has a @option{-u} option that does what
15446 @command{uniq} does. However, @command{uniq} has other uses for which one
15447 cannot substitute @samp{sort -u}.
15449 The administrator puts this pipeline into a shell script, and makes it available for
15450 all the users on the system (@samp{#} is the system administrator,
15451 or @code{root}, prompt):
15454 # cat > /usr/local/bin/listusers
15455 who | cut -c1-8 | sort | uniq
15457 # chmod +x /usr/local/bin/listusers
15460 There are four major points to note here. First, with just four
15461 programs, on one command line, the administrator was able to save about two
15462 hours worth of work. Furthermore, the shell pipeline is just about as
15463 efficient as the C program would be, and it is much more efficient in
15464 terms of programmer time. People time is much more expensive than
15465 computer time, and in our modern ``there's never enough time to do
15466 everything'' society, saving two hours of programmer time is no mean
15469 Second, it is also important to emphasize that with the
15470 @emph{combination} of the tools, it is possible to do a special
15471 purpose job never imagined by the authors of the individual programs.
15473 Third, it is also valuable to build up your pipeline in stages, as we did here.
15474 This allows you to view the data at each stage in the pipeline, which helps
15475 you acquire the confidence that you are indeed using these tools correctly.
15477 Finally, by bundling the pipeline in a shell script, other users can use
15478 your command, without having to remember the fancy plumbing you set up for
15479 them. In terms of how you run them, shell scripts and compiled programs are
15482 After the previous warm-up exercise, we'll look at two additional, more
15483 complicated pipelines. For them, we need to introduce two more tools.
15485 The first is the @command{tr} command, which stands for ``transliterate.''
15486 The @command{tr} command works on a character-by-character basis, changing
15487 characters. Normally it is used for things like mapping upper case to
15491 $ echo ThIs ExAmPlE HaS MIXED case! | tr '[:upper:]' '[:lower:]'
15492 @print{} this example has mixed case!
15495 There are several options of interest:
15499 work on the complement of the listed characters, i.e.,
15500 operations apply to characters not in the given set
15503 delete characters in the first set from the output
15506 squeeze repeated characters in the output into just one character.
15509 We will be using all three options in a moment.
15511 The other command we'll look at is @command{comm}. The @command{comm}
15512 command takes two sorted input files as input data, and prints out the
15513 files' lines in three columns. The output columns are the data lines
15514 unique to the first file, the data lines unique to the second file, and
15515 the data lines that are common to both. The @option{-1}, @option{-2}, and
15516 @option{-3} command line options @emph{omit} the respective columns. (This is
15517 non-intuitive and takes a little getting used to.) For example:
15539 The file name @file{-} tells @command{comm} to read standard input
15540 instead of a regular file.
15542 Now we're ready to build a fancy pipeline. The first application is a word
15543 frequency counter. This helps an author determine if he or she is over-using
15546 The first step is to change the case of all the letters in our input file
15547 to one case. ``The'' and ``the'' are the same word when doing counting.
15550 $ tr '[:upper:]' '[:lower:]' < whats.gnu | ...
15553 The next step is to get rid of punctuation. Quoted words and unquoted words
15554 should be treated identically; it's easiest to just get the punctuation out of
15558 $ tr '[:upper:]' '[:lower:]' < whats.gnu | tr -cd '[:alnum:]_ \n' | ...
15561 The second @command{tr} command operates on the complement of the listed
15562 characters, which are all the letters, the digits, the underscore, and
15563 the blank. The @samp{\n} represents the newline character; it has to
15564 be left alone. (The @acronym{ASCII} tab character should also be included for
15565 good measure in a production script.)
15567 At this point, we have data consisting of words separated by blank space.
15568 The words only contain alphanumeric characters (and the underscore). The
15569 next step is break the data apart so that we have one word per line. This
15570 makes the counting operation much easier, as we will see shortly.
15573 $ tr '[:upper:]' '[:lower:]' < whats.gnu | tr -cd '[:alnum:]_ \n' |
15574 > tr -s ' ' '\n' | ...
15577 This command turns blanks into newlines. The @option{-s} option squeezes
15578 multiple newline characters in the output into just one. This helps us
15579 avoid blank lines. (The @samp{>} is the shell's ``secondary prompt.''
15580 This is what the shell prints when it notices you haven't finished
15581 typing in all of a command.)
15583 We now have data consisting of one word per line, no punctuation, all one
15584 case. We're ready to count each word:
15587 $ tr '[:upper:]' '[:lower:]' < whats.gnu | tr -cd '[:alnum:]_ \n' |
15588 > tr -s ' ' '\n' | sort | uniq -c | ...
15591 At this point, the data might look something like this:
15604 The output is sorted by word, not by count! What we want is the most
15605 frequently used words first. Fortunately, this is easy to accomplish,
15606 with the help of two more @command{sort} options:
15610 do a numeric sort, not a textual one
15613 reverse the order of the sort
15616 The final pipeline looks like this:
15619 $ tr '[:upper:]' '[:lower:]' < whats.gnu | tr -cd '[:alnum:]_ \n' |
15620 > tr -s ' ' '\n' | sort | uniq -c | sort -n -r
15629 Whew! That's a lot to digest. Yet, the same principles apply. With six
15630 commands, on two lines (really one long one split for convenience), we've
15631 created a program that does something interesting and useful, in much
15632 less time than we could have written a C program to do the same thing.
15634 A minor modification to the above pipeline can give us a simple spelling
15635 checker! To determine if you've spelled a word correctly, all you have to
15636 do is look it up in a dictionary. If it is not there, then chances are
15637 that your spelling is incorrect. So, we need a dictionary.
15638 The conventional location for a dictionary is @file{/usr/dict/words}.
15639 On my GNU/Linux system,@footnote{Redhat Linux 6.1, for the November 2000
15640 revision of this article.}
15641 this is a sorted, 45,402 word dictionary.
15643 Now, how to compare our file with the dictionary? As before, we generate
15644 a sorted list of words, one per line:
15647 $ tr '[:upper:]' '[:lower:]' < whats.gnu | tr -cd '[:alnum:]_ \n' |
15648 > tr -s ' ' '\n' | sort -u | ...
15651 Now, all we need is a list of words that are @emph{not} in the
15652 dictionary. Here is where the @command{comm} command comes in.
15655 $ tr '[:upper:]' '[:lower:]' < whats.gnu | tr -cd '[:alnum:]_ \n' |
15656 > tr -s ' ' '\n' | sort -u |
15657 > comm -23 - /usr/dict/words
15660 The @option{-2} and @option{-3} options eliminate lines that are only in the
15661 dictionary (the second file), and lines that are in both files. Lines
15662 only in the first file (standard input, our stream of words), are
15663 words that are not in the dictionary. These are likely candidates for
15664 spelling errors. This pipeline was the first cut at a production
15665 spelling checker on Unix.
15667 There are some other tools that deserve brief mention.
15671 search files for text that matches a regular expression
15674 count lines, words, characters
15677 a T-fitting for data pipes, copies data to files and to standard output
15680 the stream editor, an advanced tool
15683 a data manipulation language, another advanced tool
15686 The software tools philosophy also espoused the following bit of
15687 advice: ``Let someone else do the hard part.'' This means, take
15688 something that gives you most of what you need, and then massage it the
15689 rest of the way until it's in the form that you want.
15695 Each program should do one thing well. No more, no less.
15698 Combining programs with appropriate plumbing leads to results where
15699 the whole is greater than the sum of the parts. It also leads to novel
15700 uses of programs that the authors might never have imagined.
15703 Programs should never print extraneous header or trailer data, since these
15704 could get sent on down a pipeline. (A point we didn't mention earlier.)
15707 Let someone else do the hard part.
15710 Know your toolbox! Use each program appropriately. If you don't have an
15711 appropriate tool, build one.
15714 As of this writing, all the programs we've discussed are available via
15715 anonymous @command{ftp} from: @*
15716 @uref{ftp://gnudist.gnu.org/textutils/textutils-1.22.tar.gz}. (There may
15717 be more recent versions available now.)
15719 None of what I have presented in this column is new. The Software Tools
15720 philosophy was first introduced in the book @cite{Software Tools}, by
15721 Brian Kernighan and P.J. Plauger (Addison-Wesley, ISBN 0-201-03669-X).
15722 This book showed how to write and use software tools. It was written in
15723 1976, using a preprocessor for FORTRAN named @command{ratfor} (RATional
15724 FORtran). At the time, C was not as ubiquitous as it is now; FORTRAN
15725 was. The last chapter presented a @command{ratfor} to FORTRAN
15726 processor, written in @command{ratfor}. @command{ratfor} looks an awful
15727 lot like C; if you know C, you won't have any problem following the
15730 In 1981, the book was updated and made available as @cite{Software Tools
15731 in Pascal} (Addison-Wesley, ISBN 0-201-10342-7). Both books are
15732 still in print and are well worth
15733 reading if you're a programmer. They certainly made a major change in
15734 how I view programming.
15736 The programs in both books are available from
15737 @uref{http://cm.bell-labs.com/who/bwk, Brian Kernighan's home page}.
15738 For a number of years, there was an active
15739 Software Tools Users Group, whose members had ported the original
15740 @command{ratfor} programs to essentially every computer system with a
15741 FORTRAN compiler. The popularity of the group waned in the middle 1980s
15742 as Unix began to spread beyond universities.
15744 With the current proliferation of GNU code and other clones of Unix programs,
15745 these programs now receive little attention; modern C versions are
15746 much more efficient and do more than these programs do. Nevertheless, as
15747 exposition of good programming style, and evangelism for a still-valuable
15748 philosophy, these books are unparalleled, and I recommend them highly.
15750 Acknowledgment: I would like to express my gratitude to Brian Kernighan
15751 of Bell Labs, the original Software Toolsmith, for reviewing this column.
15753 @node GNU Free Documentation License
15754 @appendix GNU Free Documentation License
15758 @node Concept index
15765 @c Local variables:
15766 @c texinfo-column-for-description: 32
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