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 --line-increment=@var{number}
1693 @opindex --line-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}.
2126 @itemx --crown-margin
2128 @opindex --crown-margin
2129 @cindex crown margin
2130 @dfn{Crown margin} mode: preserve the indentation of the first two
2131 lines within a paragraph, and align the left margin of each subsequent
2132 line with that of the second line.
2135 @itemx --tagged-paragraph
2137 @opindex --tagged-paragraph
2138 @cindex tagged paragraphs
2139 @dfn{Tagged paragraph} mode: like crown margin mode, except that if
2140 indentation of the first line of a paragraph is the same as the
2141 indentation of the second, the first line is treated as a one-line
2147 @opindex --split-only
2148 Split lines only. Do not join short lines to form longer ones. This
2149 prevents sample lines of code, and other such ``formatted'' text from
2150 being unduly combined.
2153 @itemx --uniform-spacing
2155 @opindex --uniform-spacing
2156 Uniform spacing. Reduce spacing between words to one space, and spacing
2157 between sentences to two spaces.
2160 @itemx -w @var{width}
2161 @itemx --width=@var{width}
2162 @opindex -@var{width}
2165 Fill output lines up to @var{width} characters (default 75). @command{fmt}
2166 initially tries to make lines about 7% shorter than this, to give it
2167 room to balance line lengths.
2169 @item -p @var{prefix}
2170 @itemx --prefix=@var{prefix}
2171 Only lines beginning with @var{prefix} (possibly preceded by whitespace)
2172 are subject to formatting. The prefix and any preceding whitespace are
2173 stripped for the formatting and then re-attached to each formatted output
2174 line. One use is to format certain kinds of program comments, while
2175 leaving the code unchanged.
2183 @section @command{pr}: Paginate or columnate files for printing
2186 @cindex printing, preparing files for
2187 @cindex multicolumn output, generating
2188 @cindex merging files in parallel
2190 @command{pr} writes each @var{file} (@samp{-} means standard input), or
2191 standard input if none are given, to standard output, paginating and
2192 optionally outputting in multicolumn format; optionally merges all
2193 @var{file}s, printing all in parallel, one per column. Synopsis:
2196 pr [@var{option}]@dots{} [@var{file}]@dots{}
2200 By default, a 5-line header is printed at each page: two blank lines;
2201 a line with the date, the file name, and the page count; and two more
2202 blank lines. A footer of five blank lines is also printed.
2203 The default @var{page_length} is 66
2204 lines. The default number of text lines is therefore 56.
2205 The text line of the header takes the form
2206 @samp{@var{date} @var{string} @var{page}}, with spaces inserted around
2207 @var{string} so that the line takes up the full @var{page_width}. Here,
2208 @var{date} is the date (see the @option{-D} or @option{--date-format}
2209 option for details), @var{string} is the centered header string, and
2210 @var{page} identifies the page number. The @env{LC_MESSAGES} locale
2211 category affects the spelling of @var{page}; in the default C locale, it
2212 is @samp{Page @var{number}} where @var{number} is the decimal page
2215 Form feeds in the input cause page breaks in the output. Multiple form
2216 feeds produce empty pages.
2218 Columns are of equal width, separated by an optional string (default
2219 is @samp{space}). For multicolumn output, lines will always be truncated to
2220 @var{page_width} (default 72), unless you use the @option{-J} option.
2222 column output no line truncation occurs by default. Use @option{-W} option to
2223 truncate lines in that case.
2225 The following changes were made in version 1.22i and apply to later
2226 versions of @command{pr}:
2227 @c FIXME: this whole section here sounds very awkward to me. I
2228 @c made a few small changes, but really it all needs to be redone. - Brian
2229 @c OK, I fixed another sentence or two, but some of it I just don't understand.
2234 Some small @var{letter options} (@option{-s}, @option{-w}) have been
2235 redefined for better @acronym{POSIX} compliance. The output of some further
2236 cases has been adapted to other Unix systems. These changes are not
2237 compatible with earlier versions of the program.
2240 Some @var{new capital letter} options (@option{-J}, @option{-S}, @option{-W})
2241 have been introduced to turn off unexpected interferences of small letter
2242 options. The @option{-N} option and the second argument @var{last_page}
2243 of @samp{+FIRST_PAGE} offer more flexibility. The detailed handling of
2244 form feeds set in the input files requires the @option{-T} option.
2247 Capital letter options override small letter ones.
2250 Some of the option-arguments (compare @option{-s}, @option{-e},
2251 @option{-i}, @option{-n}) cannot be specified as separate arguments from the
2252 preceding option letter (already stated in the @acronym{POSIX} specification).
2255 The program accepts the following options. Also see @ref{Common options}.
2259 @item +@var{first_page}[:@var{last_page}]
2260 @itemx --pages=@var{first_page}[:@var{last_page}]
2261 @c The two following @opindex lines evoke warnings because they contain `:'
2262 @c The `info' spec does not permit that. If we use those lines, we end
2263 @c up with truncated index entries that don't work.
2264 @c @opindex +@var{first_page}[:@var{last_page}]
2265 @c @opindex --pages=@var{first_page}[:@var{last_page}]
2266 @opindex +@var{page_range}
2267 @opindex --pages=@var{page_range}
2268 Begin printing with page @var{first_page} and stop with @var{last_page}.
2269 Missing @samp{:@var{last_page}} implies end of file. While estimating
2270 the number of skipped pages each form feed in the input file results
2271 in a new page. Page counting with and without @samp{+@var{first_page}}
2272 is identical. By default, counting starts with the first page of input
2273 file (not first page printed). Line numbering may be altered by @option{-N}
2277 @itemx --columns=@var{column}
2278 @opindex -@var{column}
2280 @cindex down columns
2281 With each single @var{file}, produce @var{column} columns of output
2282 (default is 1) and print columns down, unless @option{-a} is used. The
2283 column width is automatically decreased as @var{column} increases; unless
2284 you use the @option{-W/-w} option to increase @var{page_width} as well.
2285 This option might well cause some lines to be truncated. The number of
2286 lines in the columns on each page are balanced. The options @option{-e}
2287 and @option{-i} are on for multiple text-column output. Together with
2288 @option{-J} option column alignment and line truncation is turned off.
2289 Lines of full length are joined in a free field format and @option{-S}
2290 option may set field separators. @option{-@var{column}} may not be used
2291 with @option{-m} option.
2297 @cindex across columns
2298 With each single @var{file}, print columns across rather than down. The
2299 @option{-@var{column}} option must be given with @var{column} greater than one.
2300 If a line is too long to fit in a column, it is truncated.
2303 @itemx --show-control-chars
2305 @opindex --show-control-chars
2306 Print control characters using hat notation (e.g., @samp{^G}); print
2307 other nonprinting characters in octal backslash notation. By default,
2308 nonprinting characters are not changed.
2311 @itemx --double-space
2313 @opindex --double-space
2314 @cindex double spacing
2315 Double space the output.
2317 @item -D @var{format}
2318 @itemx --date-format=@var{format}
2319 @cindex time formats
2320 @cindex formatting times
2321 Format header dates using @var{format}, using the same conventions as
2322 for the command @samp{date +@var{format}}; @xref{date invocation}.
2323 Except for directives, which start with
2324 @samp{%}, characters in @var{format} are printed unchanged. You can use
2325 this option to specify an arbitrary string in place of the header date,
2326 e.g., @option{--date-format="Monday morning"}.
2328 @vindex POSIXLY_CORRECT
2330 The default date format is @samp{%Y-%m-%d %H:%M} (for example,
2331 @samp{2001-12-04 23:59});
2332 but if the @env{POSIXLY_CORRECT} environment variable is set
2333 and the @env{LC_TIME} locale category specifies the @acronym{POSIX}
2334 locale, the default is @samp{%b %e %H:%M %Y} (for example,
2335 @samp{Dec@ @ 4 23:59 2001}.
2338 Time stamps are listed according to the time zone rules specified by
2339 the @env{TZ} environment variable, or by the system default rules if
2340 @env{TZ} is not set. @xref{TZ Variable,, Specifying the Time Zone
2341 with @env{TZ}, libc, The GNU C Library Reference Manual}.
2343 @item -e[@var{in-tabchar}[@var{in-tabwidth}]]
2344 @itemx --expand-tabs[=@var{in-tabchar}[@var{in-tabwidth}]]
2346 @opindex --expand-tabs
2348 Expand @var{tab}s to spaces on input. Optional argument @var{in-tabchar} is
2349 the input tab character (default is the TAB character). Second optional
2350 argument @var{in-tabwidth} is the input tab character's width (default
2358 @opindex --form-feed
2359 Use a form feed instead of newlines to separate output pages. This does
2360 not alter the default page length of 66 lines.
2362 @item -h @var{header}
2363 @itemx --header=@var{header}
2366 Replace the file name in the header with the centered string @var{header}.
2367 When using the shell, @var{header} should be quoted and should be
2368 separated from @option{-h} by a space.
2370 @item -i[@var{out-tabchar}[@var{out-tabwidth}]]
2371 @itemx --output-tabs[=@var{out-tabchar}[@var{out-tabwidth}]]
2373 @opindex --output-tabs
2375 Replace spaces with @var{tab}s on output. Optional argument @var{out-tabchar}
2376 is the output tab character (default is the TAB character). Second optional
2377 argument @var{out-tabwidth} is the output tab character's width (default
2383 @opindex --join-lines
2384 Merge lines of full length. Used together with the column options
2385 @option{-@var{column}}, @option{-a -@var{column}} or @option{-m}. Turns off
2386 @option{-W/-w} line truncation;
2387 no column alignment used; may be used with
2388 @option{--sep-string[=@var{string}]}. @option{-J} has been introduced
2389 (together with @option{-W} and @option{--sep-string})
2390 to disentangle the old (@acronym{POSIX}-compliant) options @option{-w} and
2391 @option{-s} along with the three column options.
2394 @item -l @var{page_length}
2395 @itemx --length=@var{page_length}
2398 Set the page length to @var{page_length} (default 66) lines, including
2399 the lines of the header [and the footer]. If @var{page_length} is less
2400 than or equal to 10, the header and footer are omitted, as if the
2401 @option{-t} option had been given.
2407 Merge and print all @var{file}s in parallel, one in each column. If a
2408 line is too long to fit in a column, it is truncated, unless the @option{-J}
2409 option is used. @option{--sep-string[=@var{string}]} may be used.
2411 some @var{file}s (form feeds set) produce empty columns, still marked
2412 by @var{string}. The result is a continuous line numbering and column
2413 marking throughout the whole merged file. Completely empty merged pages
2414 show no separators or line numbers. The default header becomes
2415 @samp{@var{date} @var{page}} with spaces inserted in the middle; this
2416 may be used with the @option{-h} or @option{--header} option to fill up
2417 the middle blank part.
2419 @item -n[@var{number-separator}[@var{digits}]]
2420 @itemx --number-lines[=@var{number-separator}[@var{digits}]]
2422 @opindex --number-lines
2423 Provide @var{digits} digit line numbering (default for @var{digits} is
2424 5). With multicolumn output the number occupies the first @var{digits}
2425 column positions of each text column or only each line of @option{-m}
2426 output. With single column output the number precedes each line just as
2427 @option{-m} does. Default counting of the line numbers starts with the
2428 first line of the input file (not the first line printed, compare the
2429 @option{--page} option and @option{-N} option).
2430 Optional argument @var{number-separator} is the character appended to
2431 the line number to separate it from the text followed. The default
2432 separator is the TAB character. In a strict sense a TAB is always
2433 printed with single column output only. The TAB width varies
2434 with the TAB position, e.g., with the left @var{margin} specified
2435 by @option{-o} option. With multicolumn output priority is given to
2436 @samp{equal width of output columns} (a @acronym{POSIX} specification).
2437 The TAB width is fixed to the value of the first column and does
2438 not change with different values of left @var{margin}. That means a
2439 fixed number of spaces is always printed in the place of the
2440 @var{number-separator} TAB. The tabification depends upon the output
2443 @item -N @var{line_number}
2444 @itemx --first-line-number=@var{line_number}
2446 @opindex --first-line-number
2447 Start line counting with the number @var{line_number} at first line of
2448 first page printed (in most cases not the first line of the input file).
2450 @item -o @var{margin}
2451 @itemx --indent=@var{margin}
2454 @cindex indenting lines
2456 Indent each line with a margin @var{margin} spaces wide (default is zero).
2457 The total page width is the size of the margin plus the @var{page_width}
2458 set with the @option{-W/-w} option. A limited overflow may occur with
2459 numbered single column output (compare @option{-n} option).
2462 @itemx --no-file-warnings
2464 @opindex --no-file-warnings
2465 Do not print a warning message when an argument @var{file} cannot be
2466 opened. (The exit status will still be nonzero, however.)
2468 @item -s[@var{char}]
2469 @itemx --separator[=@var{char}]
2471 @opindex --separator
2472 Separate columns by a single character @var{char}. The default for
2473 @var{char} is the TAB character without @option{-w} and @samp{no
2474 character} with @option{-w}. Without @option{-s} the default separator
2475 @samp{space} is set. @option{-s[char]} turns off line truncation of all
2476 three column options (@option{-COLUMN}|@option{-a -COLUMN}|@option{-m}) unless
2477 @option{-w} is set. This is a @acronym{POSIX}-compliant formulation.
2480 @item -S@var{string}
2481 @itemx --sep-string[=@var{string}]
2483 @opindex --sep-string
2484 Use @var{string} to separate output columns. The @option{-S} option doesn't
2485 affect the @option{-W/-w} option, unlike the @option{-s} option which does. It
2486 does not affect line truncation or column alignment.
2487 Without @option{-S}, and with @option{-J}, @command{pr} uses the default output
2489 Without @option{-S} or @option{-J}, @command{pr} uses a @samp{space}
2490 (same as @option{-S"@w{ }"}). @option{--sep-string} with no
2491 @samp{=@var{string}} is equivalent to @option{--sep-string=""}.
2494 @itemx --omit-header
2496 @opindex --omit-header
2497 Do not print the usual header [and footer] on each page, and do not fill
2498 out the bottom of pages (with blank lines or a form feed). No page
2499 structure is produced, but form feeds set in the input files are retained.
2500 The predefined pagination is not changed. @option{-t} or @option{-T} may be
2501 useful together with other options; e.g.: @option{-t -e4}, expand TAB characters
2502 in the input file to 4 spaces but don't make any other changes. Use of
2503 @option{-t} overrides @option{-h}.
2506 @itemx --omit-pagination
2508 @opindex --omit-pagination
2509 Do not print header [and footer]. In addition eliminate all form feeds
2510 set in the input files.
2513 @itemx --show-nonprinting
2515 @opindex --show-nonprinting
2516 Print nonprinting characters in octal backslash notation.
2518 @item -w @var{page_width}
2519 @itemx --width=@var{page_width}
2522 Set page width to @var{page_width} characters for multiple text-column
2523 output only (default for @var{page_width} is 72). @option{-s[CHAR]} turns
2524 off the default page width and any line truncation and column alignment.
2525 Lines of full length are merged, regardless of the column options
2526 set. No @var{page_width} setting is possible with single column output.
2527 A @acronym{POSIX}-compliant formulation.
2529 @item -W @var{page_width}
2530 @itemx --page_width=@var{page_width}
2532 @opindex --page_width
2533 Set the page width to @var{page_width} characters. That's valid with and
2534 without a column option. Text lines are truncated, unless @option{-J}
2535 is used. Together with one of the three column options
2536 (@option{-@var{column}}, @option{-a -@var{column}} or @option{-m}) column
2537 alignment is always used. The separator options @option{-S} or @option{-s}
2538 don't affect the @option{-W} option. Default is 72 characters. Without
2539 @option{-W @var{page_width}} and without any of the column options NO line
2540 truncation is used (defined to keep downward compatibility and to meet
2541 most frequent tasks). That's equivalent to @option{-W 72 -J}. The header
2542 line is never truncated.
2549 @node fold invocation
2550 @section @command{fold}: Wrap input lines to fit in specified width
2553 @cindex wrapping long input lines
2554 @cindex folding long input lines
2556 @command{fold} writes each @var{file} (@option{-} means standard input), or
2557 standard input if none are given, to standard output, breaking long
2561 fold [@var{option}]@dots{} [@var{file}]@dots{}
2564 By default, @command{fold} breaks lines wider than 80 columns. The output
2565 is split into as many lines as necessary.
2567 @cindex screen columns
2568 @command{fold} counts screen columns by default; thus, a tab may count more
2569 than one column, backspace decreases the column count, and carriage
2570 return sets the column to zero.
2572 The program accepts the following options. Also see @ref{Common options}.
2580 Count bytes rather than columns, so that tabs, backspaces, and carriage
2581 returns are each counted as taking up one column, just like other
2588 Break at word boundaries: the line is broken after the last blank before
2589 the maximum line length. If the line contains no such blanks, the line
2590 is broken at the maximum line length as usual.
2592 @item -w @var{width}
2593 @itemx --width=@var{width}
2596 Use a maximum line length of @var{width} columns instead of 80.
2598 For compatibility @command{fold} supports an obsolete option syntax
2599 @option{-@var{width}}. New scripts should use @option{-w @var{width}}
2607 @node Output of parts of files
2608 @chapter Output of parts of files
2610 @cindex output of parts of files
2611 @cindex parts of files, output of
2613 These commands output pieces of the input.
2616 * head invocation:: Output the first part of files.
2617 * tail invocation:: Output the last part of files.
2618 * split invocation:: Split a file into fixed-size pieces.
2619 * csplit invocation:: Split a file into context-determined pieces.
2622 @node head invocation
2623 @section @command{head}: Output the first part of files
2626 @cindex initial part of files, outputting
2627 @cindex first part of files, outputting
2629 @command{head} prints the first part (10 lines by default) of each
2630 @var{file}; it reads from standard input if no files are given or
2631 when given a @var{file} of @option{-}. Synopsis:
2634 head [@var{option}]@dots{} [@var{file}]@dots{}
2637 If more than one @var{file} is specified, @command{head} prints a
2638 one-line header consisting of:
2641 ==> @var{file name} <==
2645 before the output for each @var{file}.
2647 The program accepts the following options. Also see @ref{Common options}.
2652 @itemx --bytes=@var{k}
2655 Print the first @var{k} bytes, instead of initial lines.
2656 However, if @var{k} starts with a @samp{-},
2657 print all but the last @var{k} bytes of each file.
2658 @multiplierSuffixes{k}
2661 @itemx --lines=@var{k}
2664 Output the first @var{k} lines.
2665 However, if @var{k} starts with a @samp{-},
2666 print all but the last @var{k} lines of each file.
2667 Size multiplier suffixes are the same as with the @option{-c} option.
2675 Never print file name headers.
2681 Always print file name headers.
2685 For compatibility @command{head} also supports an obsolete option syntax
2686 @option{-@var{count}@var{options}}, which is recognized only if it is
2687 specified first. @var{count} is a decimal number optionally followed
2688 by a size letter (@samp{b}, @samp{k}, @samp{m}) as in @option{-c}, or
2689 @samp{l} to mean count by lines, or other option letters (@samp{cqv}).
2690 Scripts intended for standard hosts should use @option{-c @var{count}}
2691 or @option{-n @var{count}} instead. If your script must also run on
2692 hosts that support only the obsolete syntax, it is usually simpler to
2693 avoid @command{head}, e.g., by using @samp{sed 5q} instead of
2699 @node tail invocation
2700 @section @command{tail}: Output the last part of files
2703 @cindex last part of files, outputting
2705 @command{tail} prints the last part (10 lines by default) of each
2706 @var{file}; it reads from standard input if no files are given or
2707 when given a @var{file} of @samp{-}. Synopsis:
2710 tail [@var{option}]@dots{} [@var{file}]@dots{}
2713 If more than one @var{file} is specified, @command{tail} prints a
2714 one-line header consisting of:
2717 ==> @var{file name} <==
2721 before the output for each @var{file}.
2723 @cindex BSD @command{tail}
2724 @sc{gnu} @command{tail} can output any amount of data (some other versions of
2725 @command{tail} cannot). It also has no @option{-r} option (print in
2726 reverse), since reversing a file is really a different job from printing
2727 the end of a file; BSD @command{tail} (which is the one with @option{-r}) can
2728 only reverse files that are at most as large as its buffer, which is
2729 typically 32 KiB@. A more reliable and versatile way to reverse files is
2730 the @sc{gnu} @command{tac} command.
2732 The program accepts the following options. Also see @ref{Common options}.
2737 @itemx --bytes=@var{k}
2740 Output the last @var{k} bytes, instead of final lines.
2741 However, if @var{k} starts with a @samp{+}, start printing with the
2742 @var{k}th byte from the start of each file, instead of from the end.
2743 @multiplierSuffixes{k}
2746 @itemx --follow[=@var{how}]
2749 @cindex growing files
2750 @vindex name @r{follow option}
2751 @vindex descriptor @r{follow option}
2752 Loop forever trying to read more characters at the end of the file,
2753 presumably because the file is growing.
2754 If more than one file is given, @command{tail} prints a header whenever it
2755 gets output from a different file, to indicate which file that output is
2758 There are two ways to specify how you'd like to track files with this option,
2759 but that difference is noticeable only when a followed file is removed or
2761 If you'd like to continue to track the end of a growing file even after
2762 it has been unlinked, use @option{--follow=descriptor}. This is the default
2763 behavior, but it is not useful if you're tracking a log file that may be
2764 rotated (removed or renamed, then reopened). In that case, use
2765 @option{--follow=name} to track the named file by reopening it periodically
2766 to see if it has been removed and recreated by some other program.
2768 No matter which method you use, if the tracked file is determined to have
2769 shrunk, @command{tail} prints a message saying the file has been truncated
2770 and resumes tracking the end of the file from the newly-determined endpoint.
2772 When a file is removed, @command{tail}'s behavior depends on whether it is
2773 following the name or the descriptor. When following by name, tail can
2774 detect that a file has been removed and gives a message to that effect,
2775 and if @option{--retry} has been specified it will continue checking
2776 periodically to see if the file reappears.
2777 When following a descriptor, tail does not detect that the file has
2778 been unlinked or renamed and issues no message; even though the file
2779 may no longer be accessible via its original name, it may still be
2782 The option values @samp{descriptor} and @samp{name} may be specified only
2783 with the long form of the option, not with @option{-f}.
2785 The @option{-f} option is ignored if
2786 no @var{file} operand is specified and standard input is a FIFO or a pipe.
2787 Likewise, the @option{-f} option has no effect for any
2788 operand specified as @samp{-}, when standard input is a FIFO or a pipe.
2792 This option is the same as @option{--follow=name --retry}. That is, tail
2793 will attempt to reopen a file when it is removed. Should this fail, tail
2794 will keep trying until it becomes accessible again.
2798 This option is useful mainly when following by name (i.e., with
2799 @option{--follow=name}).
2800 Without this option, when tail encounters a file that doesn't
2801 exist or is otherwise inaccessible, it reports that fact and
2802 never checks it again.
2804 @itemx --sleep-interval=@var{number}
2805 @opindex --sleep-interval
2806 Change the number of seconds to wait between iterations (the default is 1.0).
2807 During one iteration, every specified file is checked to see if it has
2809 Historical implementations of @command{tail} have required that
2810 @var{number} be an integer. However, GNU @command{tail} accepts
2811 an arbitrary floating point number (using a period before any
2814 @itemx --pid=@var{pid}
2816 When following by name or by descriptor, you may specify the process ID,
2817 @var{pid}, of the sole writer of all @var{file} arguments. Then, shortly
2818 after that process terminates, tail will also terminate. This will
2819 work properly only if the writer and the tailing process are running on
2820 the same machine. For example, to save the output of a build in a file
2821 and to watch the file grow, if you invoke @command{make} and @command{tail}
2822 like this then the tail process will stop when your build completes.
2823 Without this option, you would have had to kill the @code{tail -f}
2827 $ make >& makerr & tail --pid=$! -f makerr
2830 If you specify a @var{pid} that is not in use or that does not correspond
2831 to the process that is writing to the tailed files, then @command{tail}
2832 may terminate long before any @var{file}s stop growing or it may not
2833 terminate until long after the real writer has terminated.
2834 Note that @option{--pid} cannot be supported on some systems; @command{tail}
2835 will print a warning if this is the case.
2837 @itemx --max-unchanged-stats=@var{n}
2838 @opindex --max-unchanged-stats
2839 When tailing a file by name, if there have been @var{n} (default
2840 n=@value{DEFAULT_MAX_N_UNCHANGED_STATS_BETWEEN_OPENS}) consecutive
2841 iterations for which the file has not changed, then
2842 @code{open}/@code{fstat} the file to determine if that file name is
2843 still associated with the same device/inode-number pair as before.
2844 When following a log file that is rotated, this is approximately the
2845 number of seconds between when tail prints the last pre-rotation lines
2846 and when it prints the lines that have accumulated in the new log file.
2847 This option is meaningful only when following by name.
2850 @itemx --lines=@var{k}
2853 Output the last @var{k} lines.
2854 However, if @var{k} starts with a @samp{+}, start printing with the
2855 @var{k}th line from the start of each file, instead of from the end.
2856 Size multiplier suffixes are the same as with the @option{-c} option.
2864 Never print file name headers.
2870 Always print file name headers.
2874 For compatibility @command{tail} also supports an obsolete usage
2875 @samp{tail -[@var{count}][bcl][f] [@var{file}]}, which is recognized
2876 only if it does not conflict with the usage described
2877 above. This obsolete form uses exactly one option and at most one
2878 file. In the option, @var{count} is an optional decimal number optionally
2879 followed by a size letter (@samp{b}, @samp{c}, @samp{l}) to mean count
2880 by 512-byte blocks, bytes, or lines, optionally followed by @samp{f}
2881 which has the same meaning as @option{-f}.
2883 @vindex _POSIX2_VERSION
2884 On older systems, the leading @samp{-} can be replaced by @samp{+} in
2885 the obsolete option syntax with the same meaning as in counts, and
2886 obsolete usage overrides normal usage when the two conflict.
2887 This obsolete behavior can be enabled or disabled with the
2888 @env{_POSIX2_VERSION} environment variable (@pxref{Standards
2891 Scripts intended for use on standard hosts should avoid obsolete
2892 syntax and should use @option{-c @var{count}[b]}, @option{-n
2893 @var{count}}, and/or @option{-f} instead. If your script must also
2894 run on hosts that support only the obsolete syntax, you can often
2895 rewrite it to avoid problematic usages, e.g., by using @samp{sed -n
2896 '$p'} rather than @samp{tail -1}. If that's not possible, the script
2897 can use a test like @samp{if tail -c +1 </dev/null >/dev/null 2>&1;
2898 then @dots{}} to decide which syntax to use.
2900 Even if your script assumes the standard behavior, you should still
2901 beware usages whose behaviors differ depending on the @acronym{POSIX}
2902 version. For example, avoid @samp{tail - main.c}, since it might be
2903 interpreted as either @samp{tail main.c} or as @samp{tail -- -
2904 main.c}; avoid @samp{tail -c 4}, since it might mean either @samp{tail
2905 -c4} or @samp{tail -c 10 4}; and avoid @samp{tail +4}, since it might
2906 mean either @samp{tail ./+4} or @samp{tail -n +4}.
2911 @node split invocation
2912 @section @command{split}: Split a file into fixed-size pieces
2915 @cindex splitting a file into pieces
2916 @cindex pieces, splitting a file into
2918 @command{split} creates output files containing consecutive sections of
2919 @var{input} (standard input if none is given or @var{input} is
2920 @samp{-}). Synopsis:
2923 split [@var{option}] [@var{input} [@var{prefix}]]
2926 By default, @command{split} puts 1000 lines of @var{input} (or whatever is
2927 left over for the last section), into each output file.
2929 @cindex output file name prefix
2930 The output files' names consist of @var{prefix} (@samp{x} by default)
2931 followed by a group of characters (@samp{aa}, @samp{ab}, @dots{} by
2932 default), such that concatenating the output files in traditional
2933 sorted order by file name produces
2934 the original input file. If the output file names are exhausted,
2935 @command{split} reports an error without deleting the output files
2938 The program accepts the following options. Also see @ref{Common options}.
2942 @item -l @var{lines}
2943 @itemx --lines=@var{lines}
2946 Put @var{lines} lines of @var{input} into each output file.
2948 For compatibility @command{split} also supports an obsolete
2949 option syntax @option{-@var{lines}}. New scripts should use @option{-l
2950 @var{lines}} instead.
2953 @itemx --bytes=@var{size}
2956 Put @var{size} bytes of @var{input} into each output file.
2957 @multiplierSuffixes{size}
2960 @itemx --line-bytes=@var{size}
2962 @opindex --line-bytes
2963 Put into each output file as many complete lines of @var{input} as
2964 possible without exceeding @var{size} bytes. Individual lines longer than
2965 @var{size} bytes are broken into multiple files.
2966 @var{size} has the same format as for the @option{--bytes} option.
2968 @item -a @var{length}
2969 @itemx --suffix-length=@var{length}
2971 @opindex --suffix-length
2972 Use suffixes of length @var{length}. The default @var{length} is 2.
2975 @itemx --numeric-suffixes
2977 @opindex --numeric-suffixes
2978 Use digits in suffixes rather than lower-case letters.
2982 Write a diagnostic just before each output file is opened.
2989 @node csplit invocation
2990 @section @command{csplit}: Split a file into context-determined pieces
2993 @cindex context splitting
2994 @cindex splitting a file into pieces by context
2996 @command{csplit} creates zero or more output files containing sections of
2997 @var{input} (standard input if @var{input} is @samp{-}). Synopsis:
3000 csplit [@var{option}]@dots{} @var{input} @var{pattern}@dots{}
3003 The contents of the output files are determined by the @var{pattern}
3004 arguments, as detailed below. An error occurs if a @var{pattern}
3005 argument refers to a nonexistent line of the input file (e.g., if no
3006 remaining line matches a given regular expression). After every
3007 @var{pattern} has been matched, any remaining input is copied into one
3010 By default, @command{csplit} prints the number of bytes written to each
3011 output file after it has been created.
3013 The types of pattern arguments are:
3018 Create an output file containing the input up to but not including line
3019 @var{n} (a positive integer). If followed by a repeat count, also
3020 create an output file containing the next @var{n} lines of the input
3021 file once for each repeat.
3023 @item /@var{regexp}/[@var{offset}]
3024 Create an output file containing the current line up to (but not
3025 including) the next line of the input file that contains a match for
3026 @var{regexp}. The optional @var{offset} is an integer.
3027 If it is given, the input up to (but not including) the
3028 matching line plus or minus @var{offset} is put into the output file,
3029 and the line after that begins the next section of input.
3031 @item %@var{regexp}%[@var{offset}]
3032 Like the previous type, except that it does not create an output
3033 file, so that section of the input file is effectively ignored.
3035 @item @{@var{repeat-count}@}
3036 Repeat the previous pattern @var{repeat-count} additional
3037 times. The @var{repeat-count} can either be a positive integer or an
3038 asterisk, meaning repeat as many times as necessary until the input is
3043 The output files' names consist of a prefix (@samp{xx} by default)
3044 followed by a suffix. By default, the suffix is an ascending sequence
3045 of two-digit decimal numbers from @samp{00} to @samp{99}. In any case,
3046 concatenating the output files in sorted order by file name produces the
3047 original input file.
3049 By default, if @command{csplit} encounters an error or receives a hangup,
3050 interrupt, quit, or terminate signal, it removes any output files
3051 that it has created so far before it exits.
3053 The program accepts the following options. Also see @ref{Common options}.
3057 @item -f @var{prefix}
3058 @itemx --prefix=@var{prefix}
3061 @cindex output file name prefix
3062 Use @var{prefix} as the output file name prefix.
3064 @item -b @var{suffix}
3065 @itemx --suffix=@var{suffix}
3068 @cindex output file name suffix
3069 Use @var{suffix} as the output file name suffix. When this option is
3070 specified, the suffix string must include exactly one
3071 @code{printf(3)}-style conversion specification, possibly including
3072 format specification flags, a field width, a precision specifications,
3073 or all of these kinds of modifiers. The format letter must convert a
3074 binary integer argument to readable form; thus, only @samp{d}, @samp{i},
3075 @samp{u}, @samp{o}, @samp{x}, and @samp{X} conversions are allowed. The
3076 entire @var{suffix} is given (with the current output file number) to
3077 @code{sprintf(3)} to form the file name suffixes for each of the
3078 individual output files in turn. If this option is used, the
3079 @option{--digits} option is ignored.
3081 @item -n @var{digits}
3082 @itemx --digits=@var{digits}
3085 Use output file names containing numbers that are @var{digits} digits
3086 long instead of the default 2.
3091 @opindex --keep-files
3092 Do not remove output files when errors are encountered.
3095 @itemx --elide-empty-files
3097 @opindex --elide-empty-files
3098 Suppress the generation of zero-length output files. (In cases where
3099 the section delimiters of the input file are supposed to mark the first
3100 lines of each of the sections, the first output file will generally be a
3101 zero-length file unless you use this option.) The output file sequence
3102 numbers always run consecutively starting from 0, even when this option
3113 Do not print counts of output file sizes.
3119 Here is an example of its usage.
3120 First, create an empty directory for the exercise,
3127 Now, split the sequence of 1..14 on lines that end with 0 or 5:
3130 $ seq 14 | csplit - '/[05]$/' '@{*@}'
3136 Each number printed above is the size of an output
3137 file that csplit has just created.
3138 List the names of those output files:
3145 Use @command{head} to show their contents:
3170 @node Summarizing files
3171 @chapter Summarizing files
3173 @cindex summarizing files
3175 These commands generate just a few numbers representing entire
3179 * wc invocation:: Print newline, word, and byte counts.
3180 * sum invocation:: Print checksum and block counts.
3181 * cksum invocation:: Print CRC checksum and byte counts.
3182 * md5sum invocation:: Print or check MD5 digests.
3183 * sha1sum invocation:: Print or check SHA-1 digests.
3184 * sha2 utilities:: Print or check SHA-2 digests.
3189 @section @command{wc}: Print newline, word, and byte counts
3193 @cindex character count
3197 @command{wc} counts the number of bytes, characters, whitespace-separated
3198 words, and newlines in each given @var{file}, or standard input if none
3199 are given or for a @var{file} of @samp{-}. Synopsis:
3202 wc [@var{option}]@dots{} [@var{file}]@dots{}
3205 @cindex total counts
3206 @command{wc} prints one line of counts for each file, and if the file was
3207 given as an argument, it prints the file name following the counts. If
3208 more than one @var{file} is given, @command{wc} prints a final line
3209 containing the cumulative counts, with the file name @file{total}. The
3210 counts are printed in this order: newlines, words, characters, bytes,
3211 maximum line length.
3212 Each count is printed right-justified in a field with at least one
3213 space between fields so that the numbers and file names normally line
3214 up nicely in columns. The width of the count fields varies depending
3215 on the inputs, so you should not depend on a particular field width.
3216 However, as a @acronym{GNU} extension, if only one count is printed,
3217 it is guaranteed to be printed without leading spaces.
3219 By default, @command{wc} prints three counts: the newline, words, and byte
3220 counts. Options can specify that only certain counts be printed.
3221 Options do not undo others previously given, so
3228 prints both the byte counts and the word counts.
3230 With the @option{--max-line-length} option, @command{wc} prints the length
3231 of the longest line per file, and if there is more than one file it
3232 prints the maximum (not the sum) of those lengths. The line lengths here
3233 are measured in screen columns, according to the current locale and
3234 assuming tab positions in every 8th column.
3236 The program accepts the following options. Also see @ref{Common options}.
3244 Print only the byte counts.
3250 Print only the character counts.
3256 Print only the word counts.
3262 Print only the newline counts.
3265 @itemx --max-line-length
3267 @opindex --max-line-length
3268 Print only the maximum line lengths.
3270 @macro filesZeroFromOption{cmd,withTotalOption,subListOutput}
3271 @itemx --files0-from=@var{file}
3272 @opindex --files0-from=@var{file}
3273 @c This is commented out to avoid a texi2dvi failure.
3274 @c texi2dvi (GNU Texinfo 4.11) 1.104
3275 @c @cindex including files from @command{\cmd\}
3276 Disallow processing files named on the command line, and instead process
3277 those named in file @var{file}; each name being terminated by a zero byte
3278 (@acronym{ASCII} @sc{nul}).
3279 This is useful \withTotalOption\
3280 when the list of file names is so long that it may exceed a command line
3282 In such cases, running @command{\cmd\} via @command{xargs} is undesirable
3283 because it splits the list into pieces and makes @command{\cmd\} print
3284 \subListOutput\ for each sublist rather than for the entire list.
3285 One way to produce a list of @acronym{ASCII} @sc{nul} terminated file names is with @sc{gnu}
3286 @command{find}, using its @option{-print0} predicate.
3287 If @var{file} is @samp{-} then the @acronym{ASCII} @sc{nul} terminated file names
3288 are read from standard input.
3290 @filesZeroFromOption{wc,,a total}
3292 For example, to find the length of the longest line in any @file{.c} or
3293 @file{.h} file in the current hierarchy, do this:
3296 find . -name '*.[ch]' -print0 |
3297 wc -L --files0-from=- | tail -n1
3305 @node sum invocation
3306 @section @command{sum}: Print checksum and block counts
3309 @cindex 16-bit checksum
3310 @cindex checksum, 16-bit
3312 @command{sum} computes a 16-bit checksum for each given @var{file}, or
3313 standard input if none are given or for a @var{file} of @samp{-}. Synopsis:
3316 sum [@var{option}]@dots{} [@var{file}]@dots{}
3319 @command{sum} prints the checksum for each @var{file} followed by the
3320 number of blocks in the file (rounded up). If more than one @var{file}
3321 is given, file names are also printed (by default). (With the
3322 @option{--sysv} option, corresponding file names are printed when there is
3323 at least one file argument.)
3325 By default, @sc{gnu} @command{sum} computes checksums using an algorithm
3326 compatible with BSD @command{sum} and prints file sizes in units of
3329 The program accepts the following options. Also see @ref{Common options}.
3335 @cindex BSD @command{sum}
3336 Use the default (BSD compatible) algorithm. This option is included for
3337 compatibility with the System V @command{sum}. Unless @option{-s} was also
3338 given, it has no effect.
3344 @cindex System V @command{sum}
3345 Compute checksums using an algorithm compatible with System V
3346 @command{sum}'s default, and print file sizes in units of 512-byte blocks.
3350 @command{sum} is provided for compatibility; the @command{cksum} program (see
3351 next section) is preferable in new applications.
3356 @node cksum invocation
3357 @section @command{cksum}: Print CRC checksum and byte counts
3360 @cindex cyclic redundancy check
3361 @cindex CRC checksum
3363 @command{cksum} computes a cyclic redundancy check (CRC) checksum for each
3364 given @var{file}, or standard input if none are given or for a
3365 @var{file} of @samp{-}. Synopsis:
3368 cksum [@var{option}]@dots{} [@var{file}]@dots{}
3371 @command{cksum} prints the CRC checksum for each file along with the number
3372 of bytes in the file, and the file name unless no arguments were given.
3374 @command{cksum} is typically used to ensure that files
3375 transferred by unreliable means (e.g., netnews) have not been corrupted,
3376 by comparing the @command{cksum} output for the received files with the
3377 @command{cksum} output for the original files (typically given in the
3380 The CRC algorithm is specified by the @acronym{POSIX} standard. It is not
3381 compatible with the BSD or System V @command{sum} algorithms (see the
3382 previous section); it is more robust.
3384 The only options are @option{--help} and @option{--version}. @xref{Common
3390 @node md5sum invocation
3391 @section @command{md5sum}: Print or check MD5 digests
3395 @cindex 128-bit checksum
3396 @cindex checksum, 128-bit
3397 @cindex fingerprint, 128-bit
3398 @cindex message-digest, 128-bit
3400 @command{md5sum} computes a 128-bit checksum (or @dfn{fingerprint} or
3401 @dfn{message-digest}) for each specified @var{file}.
3403 Note: The MD5 digest is more reliable than a simple CRC (provided by
3404 the @command{cksum} command) for detecting accidental file corruption,
3405 as the chances of accidentally having two files with identical MD5
3406 are vanishingly small. However, it should not be considered truly
3407 secure against malicious tampering: although finding a file with a
3408 given MD5 fingerprint, or modifying a file so as to retain its MD5 are
3409 considered infeasible at the moment, it is known how to produce
3410 different files with identical MD5 (a ``collision''), something which
3411 can be a security issue in certain contexts. For more secure hashes,
3412 consider using SHA-1 or SHA-2. @xref{sha1sum invocation}, and
3413 @ref{sha2 utilities}.
3415 If a @var{file} is specified as @samp{-} or if no files are given
3416 @command{md5sum} computes the checksum for the standard input.
3417 @command{md5sum} can also determine whether a file and checksum are
3418 consistent. Synopsis:
3421 md5sum [@var{option}]@dots{} [@var{file}]@dots{}
3424 For each @var{file}, @samp{md5sum} outputs the MD5 checksum, a flag
3425 indicating a binary or text input file, and the file name.
3426 If @var{file} contains a backslash or newline, the
3427 line is started with a backslash, and each problematic character in
3428 the file name is escaped with a backslash, making the output
3429 unambiguous even in the presence of arbitrary file names.
3430 If @var{file} is omitted or specified as @samp{-}, standard input is read.
3432 The program accepts the following options. Also see @ref{Common options}.
3440 @cindex binary input files
3441 Treat each input file as binary, by reading it in binary mode and
3442 outputting a @samp{*} flag. This is the inverse of @option{--text}.
3443 On systems like @acronym{GNU} that do not distinguish between binary
3444 and text files, this option merely flags each input file as binary:
3445 the MD5 checksum is unaffected. This option is the default on systems
3446 like MS-DOS that distinguish between binary and text files, except
3447 for reading standard input when standard input is a terminal.
3451 Read file names and checksum information (not data) from each
3452 @var{file} (or from stdin if no @var{file} was specified) and report
3453 whether the checksums match the contents of the named files.
3454 The input to this mode of @command{md5sum} is usually the output of
3455 a prior, checksum-generating run of @samp{md5sum}.
3456 Each valid line of input consists of an MD5 checksum, a binary/text
3457 flag, and then a file name.
3458 Binary files are marked with @samp{*}, text with @samp{ }.
3459 For each such line, @command{md5sum} reads the named file and computes its
3460 MD5 checksum. Then, if the computed message digest does not match the
3461 one on the line with the file name, the file is noted as having
3462 failed the test. Otherwise, the file passes the test.
3463 By default, for each valid line, one line is written to standard
3464 output indicating whether the named file passed the test.
3465 After all checks have been performed, if there were any failures,
3466 a warning is issued to standard error.
3467 Use the @option{--status} option to inhibit that output.
3468 If any listed file cannot be opened or read, if any valid line has
3469 an MD5 checksum inconsistent with the associated file, or if no valid
3470 line is found, @command{md5sum} exits with nonzero status. Otherwise,
3471 it exits successfully.
3475 @cindex verifying MD5 checksums
3476 This option is useful only when verifying checksums.
3477 When verifying checksums, don't generate an 'OK' message per successfully
3478 checked file. Files that fail the verification are reported in the
3479 default one-line-per-file format. If there is any checksum mismatch,
3480 print a warning summarizing the failures to standard error.
3484 @cindex verifying MD5 checksums
3485 This option is useful only when verifying checksums.
3486 When verifying checksums, don't generate the default one-line-per-file
3487 diagnostic and don't output the warning summarizing any failures.
3488 Failures to open or read a file still evoke individual diagnostics to
3490 If all listed files are readable and are consistent with the associated
3491 MD5 checksums, exit successfully. Otherwise exit with a status code
3492 indicating there was a failure.
3498 @cindex text input files
3499 Treat each input file as text, by reading it in text mode and
3500 outputting a @samp{ } flag. This is the inverse of @option{--binary}.
3501 This option is the default on systems like @acronym{GNU} that do not
3502 distinguish between binary and text files. On other systems, it is
3503 the default for reading standard input when standard input is a
3510 @cindex verifying MD5 checksums
3511 When verifying checksums, warn about improperly formatted MD5 checksum lines.
3512 This option is useful only if all but a few lines in the checked input
3520 @node sha1sum invocation
3521 @section @command{sha1sum}: Print or check SHA-1 digests
3525 @cindex 160-bit checksum
3526 @cindex checksum, 160-bit
3527 @cindex fingerprint, 160-bit
3528 @cindex message-digest, 160-bit
3530 @command{sha1sum} computes a 160-bit checksum for each specified
3531 @var{file}. The usage and options of this command are precisely the
3532 same as for @command{md5sum}. @xref{md5sum invocation}.
3534 Note: The SHA-1 digest is more secure than MD5, and no collisions of
3535 it are known (different files having the same fingerprint). However,
3536 it is known that they can be produced with considerable, but not
3537 unreasonable, resources. For this reason, it is generally considered
3538 that SHA-1 should be gradually phased out in favor of the more secure
3539 SHA-2 hash algorithms. @xref{sha2 utilities}.
3542 @node sha2 utilities
3543 @section sha2 utilities: Print or check SHA-2 digests
3550 @cindex 224-bit checksum
3551 @cindex 256-bit checksum
3552 @cindex 384-bit checksum
3553 @cindex 512-bit checksum
3554 @cindex checksum, 224-bit
3555 @cindex checksum, 256-bit
3556 @cindex checksum, 384-bit
3557 @cindex checksum, 512-bit
3558 @cindex fingerprint, 224-bit
3559 @cindex fingerprint, 256-bit
3560 @cindex fingerprint, 384-bit
3561 @cindex fingerprint, 512-bit
3562 @cindex message-digest, 224-bit
3563 @cindex message-digest, 256-bit
3564 @cindex message-digest, 384-bit
3565 @cindex message-digest, 512-bit
3567 The commands @command{sha224sum}, @command{sha256sum},
3568 @command{sha384sum} and @command{sha512sum} compute checksums of
3569 various lengths (respectively 224, 256, 384 and 512 bits),
3570 collectively known as the SHA-2 hashes. The usage and options of
3571 these commands are precisely the same as for @command{md5sum}.
3572 @xref{md5sum invocation}.
3574 Note: The SHA384 and SHA512 digests are considerably slower to
3575 compute, especially on 32-bit computers, than SHA224 or SHA256.
3578 @node Operating on sorted files
3579 @chapter Operating on sorted files
3581 @cindex operating on sorted files
3582 @cindex sorted files, operations on
3584 These commands work with (or produce) sorted files.
3587 * sort invocation:: Sort text files.
3588 * shuf invocation:: Shuffle text files.
3589 * uniq invocation:: Uniquify files.
3590 * comm invocation:: Compare two sorted files line by line.
3591 * ptx invocation:: Produce a permuted index of file contents.
3592 * tsort invocation:: Topological sort.
3596 @node sort invocation
3597 @section @command{sort}: Sort text files
3600 @cindex sorting files
3602 @command{sort} sorts, merges, or compares all the lines from the given
3603 files, or standard input if none are given or for a @var{file} of
3604 @samp{-}. By default, @command{sort} writes the results to standard
3608 sort [@var{option}]@dots{} [@var{file}]@dots{}
3611 @command{sort} has three modes of operation: sort (the default), merge,
3612 and check for sortedness. The following options change the operation
3619 @itemx --check=diagnose-first
3622 @cindex checking for sortedness
3623 Check whether the given file is already sorted: if it is not all
3624 sorted, print a diagnostic containing the first out-of-order line and
3625 exit with a status of 1.
3626 Otherwise, exit successfully.
3627 At most one input file can be given.
3630 @itemx --check=quiet
3631 @itemx --check=silent
3634 @cindex checking for sortedness
3635 Exit successfully if the given file is already sorted, and
3636 exit with status 1 otherwise.
3637 At most one input file can be given.
3638 This is like @option{-c}, except it does not print a diagnostic.
3644 @cindex merging sorted files
3645 Merge the given files by sorting them as a group. Each input file must
3646 always be individually sorted. It always works to sort instead of
3647 merge; merging is provided because it is faster, in the case where it
3652 @cindex sort stability
3653 @cindex sort's last-resort comparison
3654 A pair of lines is compared as follows:
3655 @command{sort} compares each pair of fields, in the
3656 order specified on the command line, according to the associated
3657 ordering options, until a difference is found or no fields are left.
3658 If no key fields are specified, @command{sort} uses a default key of
3659 the entire line. Finally, as a last resort when all keys compare
3660 equal, @command{sort} compares entire lines as if no ordering options
3661 other than @option{--reverse} (@option{-r}) were specified. The
3662 @option{--stable} (@option{-s}) option disables this @dfn{last-resort
3663 comparison} so that lines in which all fields compare equal are left
3664 in their original relative order. The @option{--unique}
3665 (@option{-u}) option also disables the last-resort comparison.
3669 Unless otherwise specified, all comparisons use the character collating
3670 sequence specified by the @env{LC_COLLATE} locale.@footnote{If you
3671 use a non-@acronym{POSIX} locale (e.g., by setting @env{LC_ALL}
3672 to @samp{en_US}), then @command{sort} may produce output that is sorted
3673 differently than you're accustomed to. In that case, set the @env{LC_ALL}
3674 environment variable to @samp{C}. Note that setting only @env{LC_COLLATE}
3675 has two problems. First, it is ineffective if @env{LC_ALL} is also set.
3676 Second, it has undefined behavior if @env{LC_CTYPE} (or @env{LANG}, if
3677 @env{LC_CTYPE} is unset) is set to an incompatible value. For example,
3678 you get undefined behavior if @env{LC_CTYPE} is @code{ja_JP.PCK} but
3679 @env{LC_COLLATE} is @code{en_US.UTF-8}.}
3681 @sc{gnu} @command{sort} (as specified for all @sc{gnu} utilities) has no
3682 limit on input line length or restrictions on bytes allowed within lines.
3683 In addition, if the final byte of an input file is not a newline, @sc{gnu}
3684 @command{sort} silently supplies one. A line's trailing newline is not
3685 part of the line for comparison purposes.
3687 @cindex exit status of @command{sort}
3691 0 if no error occurred
3692 1 if invoked with @option{-c} or @option{-C} and the input is not sorted
3693 2 if an error occurred
3697 If the environment variable @env{TMPDIR} is set, @command{sort} uses its
3698 value as the directory for temporary files instead of @file{/tmp}. The
3699 @option{--temporary-directory} (@option{-T}) option in turn overrides
3700 the environment variable.
3702 The following options affect the ordering of output lines. They may be
3703 specified globally or as part of a specific key field. If no key
3704 fields are specified, global options apply to comparison of entire
3705 lines; otherwise the global options are inherited by key fields that do
3706 not specify any special options of their own. In pre-@acronym{POSIX}
3707 versions of @command{sort}, global options affect only later key fields,
3708 so portable shell scripts should specify global options first.
3713 @itemx --ignore-leading-blanks
3715 @opindex --ignore-leading-blanks
3716 @cindex blanks, ignoring leading
3718 Ignore leading blanks when finding sort keys in each line.
3719 By default a blank is a space or a tab, but the @env{LC_CTYPE} locale
3720 can change this. Note blanks may be ignored by your locale's collating
3721 rules, but without this option they will be significant for character
3722 positions specified in keys with the @option{-k} option.
3725 @itemx --dictionary-order
3727 @opindex --dictionary-order
3728 @cindex dictionary order
3729 @cindex phone directory order
3730 @cindex telephone directory order
3732 Sort in @dfn{phone directory} order: ignore all characters except
3733 letters, digits and blanks when sorting.
3734 By default letters and digits are those of @acronym{ASCII} and a blank
3735 is a space or a tab, but the @env{LC_CTYPE} locale can change this.
3738 @itemx --ignore-case
3740 @opindex --ignore-case
3741 @cindex ignoring case
3742 @cindex case folding
3744 Fold lowercase characters into the equivalent uppercase characters when
3745 comparing so that, for example, @samp{b} and @samp{B} sort as equal.
3746 The @env{LC_CTYPE} locale determines character types.
3747 When used with @option{--unique} those lower case equivalent lines are
3748 thrown away. (There is currently no way to throw away the upper case
3749 equivalent instead. (Any @option{--reverse} given would only affect
3750 the final result, after the throwing away.))
3753 @itemx --general-numeric-sort
3754 @itemx --sort=general-numeric
3756 @opindex --general-numeric-sort
3758 @cindex general numeric sort
3760 Sort numerically, using the standard C function @code{strtod} to convert
3761 a prefix of each line to a double-precision floating point number.
3762 This allows floating point numbers to be specified in scientific notation,
3763 like @code{1.0e-34} and @code{10e100}.
3764 The @env{LC_NUMERIC} locale determines the decimal-point character.
3765 Do not report overflow, underflow, or conversion errors.
3766 Use the following collating sequence:
3770 Lines that do not start with numbers (all considered to be equal).
3772 NaNs (``Not a Number'' values, in IEEE floating point arithmetic)
3773 in a consistent but machine-dependent order.
3777 Finite numbers in ascending numeric order (with @math{-0} and @math{+0} equal).
3782 Use this option only if there is no alternative; it is much slower than
3783 @option{--numeric-sort} (@option{-n}) and it can lose information when
3784 converting to floating point.
3787 @itemx --human-numeric-sort
3788 @itemx --sort=human-numeric
3790 @opindex --human-numeric-sort
3792 @cindex human numeric sort
3794 Sort numerically, as per the @option{--numeric-sort} option below, and in
3795 addition handle IEC or SI suffixes like MiB, MB etc (@ref{Block size}).
3796 Note a mixture of IEC and SI suffixes is not supported and will
3797 be flagged as an error. Also the numbers must be abbreviated uniformly.
3798 I.E. values with different precisions like 6000K and 5M will be sorted
3802 @itemx --ignore-nonprinting
3804 @opindex --ignore-nonprinting
3805 @cindex nonprinting characters, ignoring
3806 @cindex unprintable characters, ignoring
3808 Ignore nonprinting characters.
3809 The @env{LC_CTYPE} locale determines character types.
3810 This option has no effect if the stronger @option{--dictionary-order}
3811 (@option{-d}) option is also given.
3817 @opindex --month-sort
3819 @cindex months, sorting by
3821 An initial string, consisting of any amount of blanks, followed
3822 by a month name abbreviation, is folded to UPPER case and
3823 compared in the order @samp{JAN} < @samp{FEB} < @dots{} < @samp{DEC}.
3824 Invalid names compare low to valid names. The @env{LC_TIME} locale
3825 category determines the month spellings.
3826 By default a blank is a space or a tab, but the @env{LC_CTYPE} locale
3830 @itemx --numeric-sort
3831 @itemx --sort=numeric
3833 @opindex --numeric-sort
3835 @cindex numeric sort
3837 Sort numerically. The number begins each line and consists
3838 of optional blanks, an optional @samp{-} sign, and zero or more
3839 digits possibly separated by thousands separators, optionally followed
3840 by a decimal-point character and zero or more digits. An empty
3841 number is treated as @samp{0}. The @env{LC_NUMERIC}
3842 locale specifies the decimal-point character and thousands separator.
3843 By default a blank is a space or a tab, but the @env{LC_CTYPE} locale
3846 Comparison is exact; there is no rounding error.
3848 Neither a leading @samp{+} nor exponential notation is recognized.
3849 To compare such strings numerically, use the
3850 @option{--general-numeric-sort} (@option{-g}) option.
3853 @itemx --version-sort
3855 @opindex --version-sort
3856 @cindex version number sort
3858 Sort per @code{strverscmp(3)}. This is a normal string comparison, except
3859 that embedded decimal numbers are sorted by numeric value
3860 (see @option{--numeric-sort} above).
3866 @cindex reverse sorting
3867 Reverse the result of comparison, so that lines with greater key values
3868 appear earlier in the output instead of later.
3871 @itemx --random-sort
3872 @itemx --sort=random
3874 @opindex --random-sort
3877 Sort by hashing the input keys and then sorting the hash values.
3878 Choose the hash function at random, ensuring that it is free of
3879 collisions so that differing keys have differing hash values. This is
3880 like a random permutation of the inputs (@pxref{shuf invocation}),
3881 except that keys with the same value sort together.
3883 If multiple random sort fields are specified, the same random hash
3884 function is used for all fields. To use different random hash
3885 functions for different fields, you can invoke @command{sort} more
3888 The choice of hash function is affected by the
3889 @option{--random-source} option.
3897 @item --compress-program=@var{prog}
3898 Compress any temporary files with the program @var{prog}.
3900 With no arguments, @var{prog} must compress standard input to standard
3901 output, and when given the @option{-d} option it must decompress
3902 standard input to standard output.
3904 Terminate with an error if @var{prog} exits with nonzero status.
3906 White space and the backslash character should not appear in
3907 @var{prog}; they are reserved for future use.
3909 @filesZeroFromOption{sort,,sorted output}
3911 @item -k @var{pos1}[,@var{pos2}]
3912 @itemx --key=@var{pos1}[,@var{pos2}]
3916 Specify a sort field that consists of the part of the line between
3917 @var{pos1} and @var{pos2} (or the end of the line, if @var{pos2} is
3918 omitted), @emph{inclusive}.
3920 Each @var{pos} has the form @samp{@var{f}[.@var{c}][@var{opts}]},
3921 where @var{f} is the number of the field to use, and @var{c} is the number
3922 of the first character from the beginning of the field. Fields and character
3923 positions are numbered starting with 1; a character position of zero in
3924 @var{pos2} indicates the field's last character. If @samp{.@var{c}} is
3925 omitted from @var{pos1}, it defaults to 1 (the beginning of the field);
3926 if omitted from @var{pos2}, it defaults to 0 (the end of the field).
3927 @var{opts} are ordering options, allowing individual keys to be sorted
3928 according to different rules; see below for details. Keys can span
3931 Example: To sort on the second field, use @option{--key=2,2}
3932 (@option{-k 2,2}). See below for more notes on keys and more examples.
3934 @item --batch-size=@var{nmerge}
3935 @opindex --batch-size
3936 @cindex number of inputs to merge, nmerge
3937 Merge at most @var{nmerge} inputs at once.
3939 When @command{sort} has to merge more than @var{nmerge} inputs,
3940 it merges them in groups of @var{nmerge}, saving the result in
3941 a temporary file, which is then used as an input in a subsequent merge.
3943 A large value of @var{nmerge} may improve merge performance and decrease
3944 temporary storage utilization at the expense of increased memory usage
3945 and I/0. Conversely a small value of @var{nmerge} may reduce memory
3946 requirements and I/0 at the expense of temporary storage consumption and
3949 The value of @var{nmerge} must be at least 2. The default value is
3950 currently 16, but this is implementation-dependent and may change in
3953 The value of @var{nmerge} may be bounded by a resource limit for open
3954 file descriptors. The commands @samp{ulimit -n} or @samp{getconf
3955 OPEN_MAX} may display limits for your systems; these limits may be
3956 modified further if your program already has some files open, or if
3957 the operating system has other limits on the number of open files. If
3958 the value of @var{nmerge} exceeds the resource limit, @command{sort}
3959 silently uses a smaller value.
3961 @item -o @var{output-file}
3962 @itemx --output=@var{output-file}
3965 @cindex overwriting of input, allowed
3966 Write output to @var{output-file} instead of standard output.
3967 Normally, @command{sort} reads all input before opening
3968 @var{output-file}, so you can safely sort a file in place by using
3969 commands like @code{sort -o F F} and @code{cat F | sort -o F}.
3970 However, @command{sort} with @option{--merge} (@option{-m}) can open
3971 the output file before reading all input, so a command like @code{cat
3972 F | sort -m -o F - G} is not safe as @command{sort} might start
3973 writing @file{F} before @command{cat} is done reading it.
3975 @vindex POSIXLY_CORRECT
3976 On newer systems, @option{-o} cannot appear after an input file if
3977 @env{POSIXLY_CORRECT} is set, e.g., @samp{sort F -o F}. Portable
3978 scripts should specify @option{-o @var{output-file}} before any input
3981 @item --random-source=@var{file}
3982 @opindex --random-source
3983 @cindex random source for sorting
3984 Use @var{file} as a source of random data used to determine which
3985 random hash function to use with the @option{-R} option. @xref{Random
3992 @cindex sort stability
3993 @cindex sort's last-resort comparison
3995 Make @command{sort} stable by disabling its last-resort comparison.
3996 This option has no effect if no fields or global ordering options
3997 other than @option{--reverse} (@option{-r}) are specified.
4000 @itemx --buffer-size=@var{size}
4002 @opindex --buffer-size
4003 @cindex size for main memory sorting
4004 Use a main-memory sort buffer of the given @var{size}. By default,
4005 @var{size} is in units of 1024 bytes. Appending @samp{%} causes
4006 @var{size} to be interpreted as a percentage of physical memory.
4007 Appending @samp{K} multiplies @var{size} by 1024 (the default),
4008 @samp{M} by 1,048,576, @samp{G} by 1,073,741,824, and so on for
4009 @samp{T}, @samp{P}, @samp{E}, @samp{Z}, and @samp{Y}. Appending
4010 @samp{b} causes @var{size} to be interpreted as a byte count, with no
4013 This option can improve the performance of @command{sort} by causing it
4014 to start with a larger or smaller sort buffer than the default.
4015 However, this option affects only the initial buffer size. The buffer
4016 grows beyond @var{size} if @command{sort} encounters input lines larger
4019 @item -t @var{separator}
4020 @itemx --field-separator=@var{separator}
4022 @opindex --field-separator
4023 @cindex field separator character
4024 Use character @var{separator} as the field separator when finding the
4025 sort keys in each line. By default, fields are separated by the empty
4026 string between a non-blank character and a blank character.
4027 By default a blank is a space or a tab, but the @env{LC_CTYPE} locale
4030 That is, given the input line @w{@samp{ foo bar}}, @command{sort} breaks it
4031 into fields @w{@samp{ foo}} and @w{@samp{ bar}}. The field separator is
4032 not considered to be part of either the field preceding or the field
4033 following, so with @samp{sort @w{-t " "}} the same input line has
4034 three fields: an empty field, @samp{foo}, and @samp{bar}.
4035 However, fields that extend to the end of the line,
4036 as @option{-k 2}, or fields consisting of a range, as @option{-k 2,3},
4037 retain the field separators present between the endpoints of the range.
4039 To specify @acronym{ASCII} @sc{nul} as the field separator,
4040 use the two-character string @samp{\0}, e.g., @samp{sort -t '\0'}.
4042 @item -T @var{tempdir}
4043 @itemx --temporary-directory=@var{tempdir}
4045 @opindex --temporary-directory
4046 @cindex temporary directory
4048 Use directory @var{tempdir} to store temporary files, overriding the
4049 @env{TMPDIR} environment variable. If this option is given more than
4050 once, temporary files are stored in all the directories given. If you
4051 have a large sort or merge that is I/O-bound, you can often improve
4052 performance by using this option to specify directories on different
4053 disks and controllers.
4059 @cindex uniquifying output
4061 Normally, output only the first of a sequence of lines that compare
4062 equal. For the @option{--check} (@option{-c} or @option{-C}) option,
4063 check that no pair of consecutive lines compares equal.
4065 This option also disables the default last-resort comparison.
4067 The commands @code{sort -u} and @code{sort | uniq} are equivalent, but
4068 this equivalence does not extend to arbitrary @command{sort} options.
4069 For example, @code{sort -n -u} inspects only the value of the initial
4070 numeric string when checking for uniqueness, whereas @code{sort -n |
4071 uniq} inspects the entire line. @xref{uniq invocation}.
4073 @macro zeroTerminatedOption
4075 @itemx --zero-terminated
4077 @opindex --zero-terminated
4078 @cindex process zero-terminated items
4079 Delimit items with a zero byte rather than a newline (@acronym{ASCII} @sc{lf}).
4080 I.E. treat input as items separated by @acronym{ASCII} @sc{nul}
4081 and terminate output items with @acronym{ASCII} @sc{nul}.
4082 This option can be useful in conjunction with @samp{perl -0} or
4083 @samp{find -print0} and @samp{xargs -0} which do the same in order to
4084 reliably handle arbitrary file names (even those containing blanks
4085 or other special characters).
4087 @zeroTerminatedOption
4091 Historical (BSD and System V) implementations of @command{sort} have
4092 differed in their interpretation of some options, particularly
4093 @option{-b}, @option{-f}, and @option{-n}. @sc{gnu} sort follows the @acronym{POSIX}
4094 behavior, which is usually (but not always!) like the System V behavior.
4095 According to @acronym{POSIX}, @option{-n} no longer implies @option{-b}. For
4096 consistency, @option{-M} has been changed in the same way. This may
4097 affect the meaning of character positions in field specifications in
4098 obscure cases. The only fix is to add an explicit @option{-b}.
4100 A position in a sort field specified with @option{-k} may have any
4101 of the option letters @samp{MbdfghinRrV} appended to it, in which case no
4102 global ordering options are inherited by that particular field. The
4103 @option{-b} option may be independently attached to either or both of
4104 the start and end positions of a field specification, and if it is
4105 inherited from the global options it will be attached to both.
4106 If input lines can contain leading or adjacent blanks and @option{-t}
4107 is not used, then @option{-k} is typically combined with @option{-b} or
4108 an option that implicitly ignores leading blanks (@samp{MghnV}) as otherwise
4109 the varying numbers of leading blanks in fields can cause confusing results.
4111 If the start position in a sort field specifier falls after the end of
4112 the line or after the end field, the field is empty. If the @option{-b}
4113 option was specified, the @samp{.@var{c}} part of a field specification
4114 is counted from the first nonblank character of the field.
4116 @vindex _POSIX2_VERSION
4117 @vindex POSIXLY_CORRECT
4118 On older systems, @command{sort} supports an obsolete origin-zero
4119 syntax @samp{+@var{pos1} [-@var{pos2}]} for specifying sort keys.
4120 This obsolete behavior can be enabled or disabled with the
4121 @env{_POSIX2_VERSION} environment variable (@pxref{Standards
4122 conformance}); it can also be enabled when @env{POSIXLY_CORRECT} is
4123 not set by using the obsolete syntax with @samp{-@var{pos2}} present.
4125 Scripts intended for use on standard hosts should avoid obsolete
4126 syntax and should use @option{-k} instead. For example, avoid
4127 @samp{sort +2}, since it might be interpreted as either @samp{sort
4128 ./+2} or @samp{sort -k 3}. If your script must also run on hosts that
4129 support only the obsolete syntax, it can use a test like @samp{if sort
4130 -k 1 </dev/null >/dev/null 2>&1; then @dots{}} to decide which syntax
4133 Here are some examples to illustrate various combinations of options.
4138 Sort in descending (reverse) numeric order.
4145 Sort alphabetically, omitting the first and second fields
4146 and the blanks at the start of the third field.
4147 This uses a single key composed of the characters beginning
4148 at the start of the first nonblank character in field three
4149 and extending to the end of each line.
4156 Sort numerically on the second field and resolve ties by sorting
4157 alphabetically on the third and fourth characters of field five.
4158 Use @samp{:} as the field delimiter.
4161 sort -t : -k 2,2n -k 5.3,5.4
4164 Note that if you had written @option{-k 2n} instead of @option{-k 2,2n}
4165 @command{sort} would have used all characters beginning in the second field
4166 and extending to the end of the line as the primary @emph{numeric}
4167 key. For the large majority of applications, treating keys spanning
4168 more than one field as numeric will not do what you expect.
4170 Also note that the @samp{n} modifier was applied to the field-end
4171 specifier for the first key. It would have been equivalent to
4172 specify @option{-k 2n,2} or @option{-k 2n,2n}. All modifiers except
4173 @samp{b} apply to the associated @emph{field}, regardless of whether
4174 the modifier character is attached to the field-start and/or the
4175 field-end part of the key specifier.
4178 Sort the password file on the fifth field and ignore any
4179 leading blanks. Sort lines with equal values in field five
4180 on the numeric user ID in field three. Fields are separated
4184 sort -t : -k 5b,5 -k 3,3n /etc/passwd
4185 sort -t : -n -k 5b,5 -k 3,3 /etc/passwd
4186 sort -t : -b -k 5,5 -k 3,3n /etc/passwd
4189 These three commands have equivalent effect. The first specifies that
4190 the first key's start position ignores leading blanks and the second
4191 key is sorted numerically. The other two commands rely on global
4192 options being inherited by sort keys that lack modifiers. The inheritance
4193 works in this case because @option{-k 5b,5b} and @option{-k 5b,5} are
4194 equivalent, as the location of a field-end lacking a @samp{.@var{c}}
4195 character position is not affected by whether initial blanks are
4199 Sort a set of log files, primarily by IPv4 address and secondarily by
4200 time stamp. If two lines' primary and secondary keys are identical,
4201 output the lines in the same order that they were input. The log
4202 files contain lines that look like this:
4205 4.150.156.3 - - [01/Apr/2004:06:31:51 +0000] message 1
4206 211.24.3.231 - - [24/Apr/2004:20:17:39 +0000] message 2
4209 Fields are separated by exactly one space. Sort IPv4 addresses
4210 lexicographically, e.g., 212.61.52.2 sorts before 212.129.233.201
4211 because 61 is less than 129.
4214 sort -s -t ' ' -k 4.9n -k 4.5M -k 4.2n -k 4.14,4.21 file*.log |
4215 sort -s -t '.' -k 1,1n -k 2,2n -k 3,3n -k 4,4n
4218 This example cannot be done with a single @command{sort} invocation,
4219 since IPv4 address components are separated by @samp{.} while dates
4220 come just after a space. So it is broken down into two invocations of
4221 @command{sort}: the first sorts by time stamp and the second by IPv4
4222 address. The time stamp is sorted by year, then month, then day, and
4223 finally by hour-minute-second field, using @option{-k} to isolate each
4224 field. Except for hour-minute-second there's no need to specify the
4225 end of each key field, since the @samp{n} and @samp{M} modifiers sort
4226 based on leading prefixes that cannot cross field boundaries. The
4227 IPv4 addresses are sorted lexicographically. The second sort uses
4228 @samp{-s} so that ties in the primary key are broken by the secondary
4229 key; the first sort uses @samp{-s} so that the combination of the two
4233 Generate a tags file in case-insensitive sorted order.
4236 find src -type f -print0 | sort -z -f | xargs -0 etags --append
4239 The use of @option{-print0}, @option{-z}, and @option{-0} in this case means
4240 that file names that contain blanks or other special characters are
4242 by the sort operation.
4244 @c This example is a bit contrived and needs more explanation.
4246 @c Sort records separated by an arbitrary string by using a pipe to convert
4247 @c each record delimiter string to @samp{\0}, then using sort's -z option,
4248 @c and converting each @samp{\0} back to the original record delimiter.
4251 @c printf 'c\n\nb\n\na\n'|perl -0pe 's/\n\n/\n\0/g'|sort -z|perl -0pe 's/\0/\n/g'
4255 Use the common @acronym{DSU, Decorate Sort Undecorate} idiom to
4256 sort lines according to their length.
4259 awk '@{print length, $0@}' /etc/passwd | sort -n | cut -f2- -d' '
4262 In general this technique can be used to sort data that the @command{sort}
4263 command does not support, or is inefficient at, sorting directly.
4266 Shuffle a list of directories, but preserve the order of files within
4267 each directory. For instance, one could use this to generate a music
4268 playlist in which albums are shuffled but the songs of each album are
4272 ls */* | sort -t / -k 1,1R -k 2,2
4278 @node shuf invocation
4279 @section @command{shuf}: Shuffling text
4282 @cindex shuffling files
4284 @command{shuf} shuffles its input by outputting a random permutation
4285 of its input lines. Each output permutation is equally likely.
4289 shuf [@var{option}]@dots{} [@var{file}]
4290 shuf -e [@var{option}]@dots{} [@var{arg}]@dots{}
4291 shuf -i @var{lo}-@var{hi} [@var{option}]@dots{}
4294 @command{shuf} has three modes of operation that affect where it
4295 obtains its input lines. By default, it reads lines from standard
4296 input. The following options change the operation mode:
4304 @cindex command-line operands to shuffle
4305 Treat each command-line operand as an input line.
4307 @item -i @var{lo}-@var{hi}
4308 @itemx --input-range=@var{lo}-@var{hi}
4310 @opindex --input-range
4311 @cindex input range to shuffle
4312 Act as if input came from a file containing the range of unsigned
4313 decimal integers @var{lo}@dots{}@var{hi}, one per line.
4317 @command{shuf}'s other options can affect its behavior in all
4322 @item -n @var{lines}
4323 @itemx --head-count=@var{count}
4325 @opindex --head-count
4326 @cindex head of output
4327 Output at most @var{count} lines. By default, all input lines are
4330 @item -o @var{output-file}
4331 @itemx --output=@var{output-file}
4334 @cindex overwriting of input, allowed
4335 Write output to @var{output-file} instead of standard output.
4336 @command{shuf} reads all input before opening
4337 @var{output-file}, so you can safely shuffle a file in place by using
4338 commands like @code{shuf -o F <F} and @code{cat F | shuf -o F}.
4340 @item --random-source=@var{file}
4341 @opindex --random-source
4342 @cindex random source for shuffling
4343 Use @var{file} as a source of random data used to determine which
4344 permutation to generate. @xref{Random sources}.
4346 @zeroTerminatedOption
4362 might produce the output
4372 Similarly, the command:
4375 shuf -e clubs hearts diamonds spades
4389 and the command @samp{shuf -i 1-4} might output:
4399 These examples all have four input lines, so @command{shuf} might
4400 produce any of the twenty-four possible permutations of the input. In
4401 general, if there are @var{n} input lines, there are @var{n}! (i.e.,
4402 @var{n} factorial, or @var{n} * (@var{n} - 1) * @dots{} * 1) possible
4403 output permutations.
4408 @node uniq invocation
4409 @section @command{uniq}: Uniquify files
4412 @cindex uniquify files
4414 @command{uniq} writes the unique lines in the given @file{input}, or
4415 standard input if nothing is given or for an @var{input} name of
4419 uniq [@var{option}]@dots{} [@var{input} [@var{output}]]
4422 By default, @command{uniq} prints its input lines, except that
4423 it discards all but the first of adjacent repeated lines, so that
4424 no output lines are repeated. Optionally, it can instead discard
4425 lines that are not repeated, or all repeated lines.
4427 The input need not be sorted, but repeated input lines are detected
4428 only if they are adjacent. If you want to discard non-adjacent
4429 duplicate lines, perhaps you want to use @code{sort -u}.
4430 @xref{sort invocation}.
4433 Comparisons honor the rules specified by the @env{LC_COLLATE}
4436 If no @var{output} file is specified, @command{uniq} writes to standard
4439 The program accepts the following options. Also see @ref{Common options}.
4444 @itemx --skip-fields=@var{n}
4446 @opindex --skip-fields
4447 Skip @var{n} fields on each line before checking for uniqueness. Use
4448 a null string for comparison if a line has fewer than @var{n} fields. Fields
4449 are sequences of non-space non-tab characters that are separated from
4450 each other by at least one space or tab.
4452 For compatibility @command{uniq} supports an obsolete option syntax
4453 @option{-@var{n}}. New scripts should use @option{-f @var{n}} instead.
4456 @itemx --skip-chars=@var{n}
4458 @opindex --skip-chars
4459 Skip @var{n} characters before checking for uniqueness. Use a null string
4460 for comparison if a line has fewer than @var{n} characters. If you use both
4461 the field and character skipping options, fields are skipped over first.
4463 @vindex _POSIX2_VERSION
4464 On older systems, @command{uniq} supports an obsolete option syntax
4466 This obsolete behavior can be enabled or disabled with the
4467 @env{_POSIX2_VERSION} environment variable (@pxref{Standards
4468 conformance}), but portable scripts should avoid commands whose
4469 behavior depends on this variable.
4470 For example, use @samp{uniq ./+10} or @samp{uniq -s 10} rather than
4471 the ambiguous @samp{uniq +10}.
4477 Print the number of times each line occurred along with the line.
4480 @itemx --ignore-case
4482 @opindex --ignore-case
4483 Ignore differences in case when comparing lines.
4489 @cindex repeated lines, outputting
4490 Discard lines that are not repeated. When used by itself, this option
4491 causes @command{uniq} to print the first copy of each repeated line,
4495 @itemx --all-repeated[=@var{delimit-method}]
4497 @opindex --all-repeated
4498 @cindex all repeated lines, outputting
4499 Do not discard the second and subsequent repeated input lines,
4500 but discard lines that are not repeated.
4501 This option is useful mainly in conjunction with other options e.g.,
4502 to ignore case or to compare only selected fields.
4503 The optional @var{delimit-method} tells how to delimit
4504 groups of repeated lines, and must be one of the following:
4509 Do not delimit groups of repeated lines.
4510 This is equivalent to @option{--all-repeated} (@option{-D}).
4513 Output a newline before each group of repeated lines.
4514 With @option{--zero-terminated} (@option{-z}), use a zero
4515 byte (@acronym{ASCII} @sc{nul}) instead of a newline.
4518 Separate groups of repeated lines with a single newline.
4519 With @option{--zero-terminated} (@option{-z}), use a zero
4520 byte (@acronym{ASCII} @sc{nul}) instead of a newline.
4521 This is the same as using @samp{prepend}, except that
4522 no delimiter is inserted before the first group, and hence
4523 may be better suited for output direct to users.
4526 Note that when groups are delimited and the input stream contains
4527 two or more consecutive blank lines, then the output is ambiguous.
4528 To avoid that, filter the input through @samp{tr -s '\n'} to replace
4529 each sequence of consecutive newlines with a single newline.
4531 This is a @sc{gnu} extension.
4532 @c FIXME: give an example showing *how* it's useful
4538 @cindex unique lines, outputting
4539 Discard the first repeated line. When used by itself, this option
4540 causes @command{uniq} to print unique lines, and nothing else.
4543 @itemx --check-chars=@var{n}
4545 @opindex --check-chars
4546 Compare at most @var{n} characters on each line (after skipping any specified
4547 fields and characters). By default the entire rest of the lines are
4550 @zeroTerminatedOption
4557 @node comm invocation
4558 @section @command{comm}: Compare two sorted files line by line
4561 @cindex line-by-line comparison
4562 @cindex comparing sorted files
4564 @command{comm} writes to standard output lines that are common, and lines
4565 that are unique, to two input files; a file name of @samp{-} means
4566 standard input. Synopsis:
4569 comm [@var{option}]@dots{} @var{file1} @var{file2}
4573 Before @command{comm} can be used, the input files must be sorted using the
4574 collating sequence specified by the @env{LC_COLLATE} locale.
4575 If an input file ends in a non-newline
4576 character, a newline is silently appended. The @command{sort} command with
4577 no options always outputs a file that is suitable input to @command{comm}.
4579 @cindex differing lines
4580 @cindex common lines
4581 With no options, @command{comm} produces three-column output. Column one
4582 contains lines unique to @var{file1}, column two contains lines unique
4583 to @var{file2}, and column three contains lines common to both files.
4584 Columns are separated by a single TAB character.
4585 @c FIXME: when there's an option to supply an alternative separator
4586 @c string, append `by default' to the above sentence.
4591 The options @option{-1}, @option{-2}, and @option{-3} suppress printing of
4592 the corresponding columns (and separators). Also see @ref{Common options}.
4594 Unlike some other comparison utilities, @command{comm} has an exit
4595 status that does not depend on the result of the comparison.
4596 Upon normal completion @command{comm} produces an exit code of zero.
4597 If there is an error it exits with nonzero status.
4599 @macro checkOrderOption{cmd}
4600 If the @option{--check-order} option is given, unsorted inputs will
4601 cause a fatal error message. If the option @option{--nocheck-order}
4602 is given, unsorted inputs will never cause an error message. If
4603 neither of these options is given, wrongly sorted inputs are diagnosed
4604 only if an input file is found to contain unpairable lines. If an
4605 input file is diagnosed as being unsorted, the @command{\cmd\} command
4606 will exit with a nonzero status (and the output should not be used).
4608 Forcing @command{\cmd\} to process wrongly sorted input files
4609 containing unpairable lines by specifying @option{--nocheck-order} is
4610 not guaranteed to produce any particular output. The output will
4611 probably not correspond with whatever you hoped it would be.
4613 @checkOrderOption{comm}
4618 Fail with an error message if either input file is wrongly ordered.
4620 @item --nocheck-order
4621 Do not check that both input files are in sorted order.
4625 @item --output-delimiter=@var{str}
4626 Print @var{str} between adjacent output columns,
4627 rather than the default of a single TAB character.
4629 The delimiter @var{str} may not be empty.
4633 @node ptx invocation
4634 @section @command{ptx}: Produce permuted indexes
4638 @command{ptx} reads a text file and essentially produces a permuted index, with
4639 each keyword in its context. The calling sketch is either one of:
4642 ptx [@var{option} @dots{}] [@var{file} @dots{}]
4643 ptx -G [@var{option} @dots{}] [@var{input} [@var{output}]]
4646 The @option{-G} (or its equivalent: @option{--traditional}) option disables
4647 all @sc{gnu} extensions and reverts to traditional mode, thus introducing some
4648 limitations and changing several of the program's default option values.
4649 When @option{-G} is not specified, @sc{gnu} extensions are always enabled.
4650 @sc{gnu} extensions to @command{ptx} are documented wherever appropriate in this
4651 document. For the full list, see @xref{Compatibility in ptx}.
4653 Individual options are explained in the following sections.
4655 When @sc{gnu} extensions are enabled, there may be zero, one or several
4656 @var{file}s after the options. If there is no @var{file}, the program
4657 reads the standard input. If there is one or several @var{file}s, they
4658 give the name of input files which are all read in turn, as if all the
4659 input files were concatenated. However, there is a full contextual
4660 break between each file and, when automatic referencing is requested,
4661 file names and line numbers refer to individual text input files. In
4662 all cases, the program outputs the permuted index to the standard
4665 When @sc{gnu} extensions are @emph{not} enabled, that is, when the program
4666 operates in traditional mode, there may be zero, one or two parameters
4667 besides the options. If there are no parameters, the program reads the
4668 standard input and outputs the permuted index to the standard output.
4669 If there is only one parameter, it names the text @var{input} to be read
4670 instead of the standard input. If two parameters are given, they give
4671 respectively the name of the @var{input} file to read and the name of
4672 the @var{output} file to produce. @emph{Be very careful} to note that,
4673 in this case, the contents of file given by the second parameter is
4674 destroyed. This behavior is dictated by System V @command{ptx}
4675 compatibility; @sc{gnu} Standards normally discourage output parameters not
4676 introduced by an option.
4678 Note that for @emph{any} file named as the value of an option or as an
4679 input text file, a single dash @kbd{-} may be used, in which case
4680 standard input is assumed. However, it would not make sense to use this
4681 convention more than once per program invocation.
4684 * General options in ptx:: Options which affect general program behavior.
4685 * Charset selection in ptx:: Underlying character set considerations.
4686 * Input processing in ptx:: Input fields, contexts, and keyword selection.
4687 * Output formatting in ptx:: Types of output format, and sizing the fields.
4688 * Compatibility in ptx::
4692 @node General options in ptx
4693 @subsection General options
4698 @itemx --traditional
4699 As already explained, this option disables all @sc{gnu} extensions to
4700 @command{ptx} and switches to traditional mode.
4703 Print a short help on standard output, then exit without further
4707 Print the program version on standard output, then exit without further
4715 @node Charset selection in ptx
4716 @subsection Charset selection
4718 @c FIXME: People don't necessarily know what an IBM-PC was these days.
4719 As it is set up now, the program assumes that the input file is coded
4720 using 8-bit @acronym{ISO} 8859-1 code, also known as Latin-1 character set,
4721 @emph{unless} it is compiled for MS-DOS, in which case it uses the
4722 character set of the IBM-PC@. (@sc{gnu} @command{ptx} is not known to work on
4723 smaller MS-DOS machines anymore.) Compared to 7-bit @acronym{ASCII}, the set
4724 of characters which are letters is different; this alters the behavior
4725 of regular expression matching. Thus, the default regular expression
4726 for a keyword allows foreign or diacriticized letters. Keyword sorting,
4727 however, is still crude; it obeys the underlying character set ordering
4733 @itemx --ignore-case
4734 Fold lower case letters to upper case for sorting.
4739 @node Input processing in ptx
4740 @subsection Word selection and input processing
4745 @itemx --break-file=@var{file}
4747 This option provides an alternative (to @option{-W}) method of describing
4748 which characters make up words. It introduces the name of a
4749 file which contains a list of characters which can@emph{not} be part of
4750 one word; this file is called the @dfn{Break file}. Any character which
4751 is not part of the Break file is a word constituent. If both options
4752 @option{-b} and @option{-W} are specified, then @option{-W} has precedence and
4753 @option{-b} is ignored.
4755 When @sc{gnu} extensions are enabled, the only way to avoid newline as a
4756 break character is to write all the break characters in the file with no
4757 newline at all, not even at the end of the file. When @sc{gnu} extensions
4758 are disabled, spaces, tabs and newlines are always considered as break
4759 characters even if not included in the Break file.
4762 @itemx --ignore-file=@var{file}
4764 The file associated with this option contains a list of words which will
4765 never be taken as keywords in concordance output. It is called the
4766 @dfn{Ignore file}. The file contains exactly one word in each line; the
4767 end of line separation of words is not subject to the value of the
4771 @itemx --only-file=@var{file}
4773 The file associated with this option contains a list of words which will
4774 be retained in concordance output; any word not mentioned in this file
4775 is ignored. The file is called the @dfn{Only file}. The file contains
4776 exactly one word in each line; the end of line separation of words is
4777 not subject to the value of the @option{-S} option.
4779 There is no default for the Only file. When both an Only file and an
4780 Ignore file are specified, a word is considered a keyword only
4781 if it is listed in the Only file and not in the Ignore file.
4786 On each input line, the leading sequence of non-white space characters will be
4787 taken to be a reference that has the purpose of identifying this input
4788 line in the resulting permuted index. For more information about reference
4789 production, see @xref{Output formatting in ptx}.
4790 Using this option changes the default value for option @option{-S}.
4792 Using this option, the program does not try very hard to remove
4793 references from contexts in output, but it succeeds in doing so
4794 @emph{when} the context ends exactly at the newline. If option
4795 @option{-r} is used with @option{-S} default value, or when @sc{gnu} extensions
4796 are disabled, this condition is always met and references are completely
4797 excluded from the output contexts.
4799 @item -S @var{regexp}
4800 @itemx --sentence-regexp=@var{regexp}
4802 This option selects which regular expression will describe the end of a
4803 line or the end of a sentence. In fact, this regular expression is not
4804 the only distinction between end of lines or end of sentences, and input
4805 line boundaries have no special significance outside this option. By
4806 default, when @sc{gnu} extensions are enabled and if @option{-r} option is not
4807 used, end of sentences are used. In this case, this @var{regex} is
4808 imported from @sc{gnu} Emacs:
4811 [.?!][]\"')@}]*\\($\\|\t\\| \\)[ \t\n]*
4814 Whenever @sc{gnu} extensions are disabled or if @option{-r} option is used, end
4815 of lines are used; in this case, the default @var{regexp} is just:
4821 Using an empty @var{regexp} is equivalent to completely disabling end of
4822 line or end of sentence recognition. In this case, the whole file is
4823 considered to be a single big line or sentence. The user might want to
4824 disallow all truncation flag generation as well, through option @option{-F
4825 ""}. @xref{Regexps, , Syntax of Regular Expressions, emacs, The GNU Emacs
4828 When the keywords happen to be near the beginning of the input line or
4829 sentence, this often creates an unused area at the beginning of the
4830 output context line; when the keywords happen to be near the end of the
4831 input line or sentence, this often creates an unused area at the end of
4832 the output context line. The program tries to fill those unused areas
4833 by wrapping around context in them; the tail of the input line or
4834 sentence is used to fill the unused area on the left of the output line;
4835 the head of the input line or sentence is used to fill the unused area
4836 on the right of the output line.
4838 As a matter of convenience to the user, many usual backslashed escape
4839 sequences from the C language are recognized and converted to the
4840 corresponding characters by @command{ptx} itself.
4842 @item -W @var{regexp}
4843 @itemx --word-regexp=@var{regexp}
4845 This option selects which regular expression will describe each keyword.
4846 By default, if @sc{gnu} extensions are enabled, a word is a sequence of
4847 letters; the @var{regexp} used is @samp{\w+}. When @sc{gnu} extensions are
4848 disabled, a word is by default anything which ends with a space, a tab
4849 or a newline; the @var{regexp} used is @samp{[^ \t\n]+}.
4851 An empty @var{regexp} is equivalent to not using this option.
4852 @xref{Regexps, , Syntax of Regular Expressions, emacs, The GNU Emacs
4855 As a matter of convenience to the user, many usual backslashed escape
4856 sequences, as found in the C language, are recognized and converted to
4857 the corresponding characters by @command{ptx} itself.
4862 @node Output formatting in ptx
4863 @subsection Output formatting
4865 Output format is mainly controlled by the @option{-O} and @option{-T} options
4866 described in the table below. When neither @option{-O} nor @option{-T} are
4867 selected, and if @sc{gnu} extensions are enabled, the program chooses an
4868 output format suitable for a dumb terminal. Each keyword occurrence is
4869 output to the center of one line, surrounded by its left and right
4870 contexts. Each field is properly justified, so the concordance output
4871 can be readily observed. As a special feature, if automatic
4872 references are selected by option @option{-A} and are output before the
4873 left context, that is, if option @option{-R} is @emph{not} selected, then
4874 a colon is added after the reference; this nicely interfaces with @sc{gnu}
4875 Emacs @code{next-error} processing. In this default output format, each
4876 white space character, like newline and tab, is merely changed to
4877 exactly one space, with no special attempt to compress consecutive
4878 spaces. This might change in the future. Except for those white space
4879 characters, every other character of the underlying set of 256
4880 characters is transmitted verbatim.
4882 Output format is further controlled by the following options.
4886 @item -g @var{number}
4887 @itemx --gap-size=@var{number}
4889 Select the size of the minimum white space gap between the fields on the
4892 @item -w @var{number}
4893 @itemx --width=@var{number}
4895 Select the maximum output width of each final line. If references are
4896 used, they are included or excluded from the maximum output width
4897 depending on the value of option @option{-R}. If this option is not
4898 selected, that is, when references are output before the left context,
4899 the maximum output width takes into account the maximum length of all
4900 references. If this option is selected, that is, when references are
4901 output after the right context, the maximum output width does not take
4902 into account the space taken by references, nor the gap that precedes
4906 @itemx --auto-reference
4908 Select automatic references. Each input line will have an automatic
4909 reference made up of the file name and the line ordinal, with a single
4910 colon between them. However, the file name will be empty when standard
4911 input is being read. If both @option{-A} and @option{-r} are selected, then
4912 the input reference is still read and skipped, but the automatic
4913 reference is used at output time, overriding the input reference.
4916 @itemx --right-side-refs
4918 In the default output format, when option @option{-R} is not used, any
4919 references produced by the effect of options @option{-r} or @option{-A} are
4920 placed to the far right of output lines, after the right context. With
4921 default output format, when the @option{-R} option is specified, references
4922 are rather placed at the beginning of each output line, before the left
4923 context. For any other output format, option @option{-R} is
4924 ignored, with one exception: with @option{-R} the width of references
4925 is @emph{not} taken into account in total output width given by @option{-w}.
4927 This option is automatically selected whenever @sc{gnu} extensions are
4930 @item -F @var{string}
4931 @itemx --flac-truncation=@var{string}
4933 This option will request that any truncation in the output be reported
4934 using the string @var{string}. Most output fields theoretically extend
4935 towards the beginning or the end of the current line, or current
4936 sentence, as selected with option @option{-S}. But there is a maximum
4937 allowed output line width, changeable through option @option{-w}, which is
4938 further divided into space for various output fields. When a field has
4939 to be truncated because it cannot extend beyond the beginning or the end of
4940 the current line to fit in, then a truncation occurs. By default,
4941 the string used is a single slash, as in @option{-F /}.
4943 @var{string} may have more than one character, as in @option{-F ...}.
4944 Also, in the particular case when @var{string} is empty (@option{-F ""}),
4945 truncation flagging is disabled, and no truncation marks are appended in
4948 As a matter of convenience to the user, many usual backslashed escape
4949 sequences, as found in the C language, are recognized and converted to
4950 the corresponding characters by @command{ptx} itself.
4952 @item -M @var{string}
4953 @itemx --macro-name=@var{string}
4955 Select another @var{string} to be used instead of @samp{xx}, while
4956 generating output suitable for @command{nroff}, @command{troff} or @TeX{}.
4959 @itemx --format=roff
4961 Choose an output format suitable for @command{nroff} or @command{troff}
4962 processing. Each output line will look like:
4965 .xx "@var{tail}" "@var{before}" "@var{keyword_and_after}" "@var{head}" "@var{ref}"
4968 so it will be possible to write a @samp{.xx} roff macro to take care of
4969 the output typesetting. This is the default output format when @sc{gnu}
4970 extensions are disabled. Option @option{-M} can be used to change
4971 @samp{xx} to another macro name.
4973 In this output format, each non-graphical character, like newline and
4974 tab, is merely changed to exactly one space, with no special attempt to
4975 compress consecutive spaces. Each quote character: @kbd{"} is doubled
4976 so it will be correctly processed by @command{nroff} or @command{troff}.
4981 Choose an output format suitable for @TeX{} processing. Each output
4982 line will look like:
4985 \xx @{@var{tail}@}@{@var{before}@}@{@var{keyword}@}@{@var{after}@}@{@var{head}@}@{@var{ref}@}
4989 so it will be possible to write a @code{\xx} definition to take care of
4990 the output typesetting. Note that when references are not being
4991 produced, that is, neither option @option{-A} nor option @option{-r} is
4992 selected, the last parameter of each @code{\xx} call is inhibited.
4993 Option @option{-M} can be used to change @samp{xx} to another macro
4996 In this output format, some special characters, like @kbd{$}, @kbd{%},
4997 @kbd{&}, @kbd{#} and @kbd{_} are automatically protected with a
4998 backslash. Curly brackets @kbd{@{}, @kbd{@}} are protected with a
4999 backslash and a pair of dollar signs (to force mathematical mode). The
5000 backslash itself produces the sequence @code{\backslash@{@}}.
5001 Circumflex and tilde diacritical marks produce the sequence @code{^\@{ @}} and
5002 @code{~\@{ @}} respectively. Other diacriticized characters of the
5003 underlying character set produce an appropriate @TeX{} sequence as far
5004 as possible. The other non-graphical characters, like newline and tab,
5005 and all other characters which are not part of @acronym{ASCII}, are merely
5006 changed to exactly one space, with no special attempt to compress
5007 consecutive spaces. Let me know how to improve this special character
5008 processing for @TeX{}.
5013 @node Compatibility in ptx
5014 @subsection The @sc{gnu} extensions to @command{ptx}
5016 This version of @command{ptx} contains a few features which do not exist in
5017 System V @command{ptx}. These extra features are suppressed by using the
5018 @option{-G} command line option, unless overridden by other command line
5019 options. Some @sc{gnu} extensions cannot be recovered by overriding, so the
5020 simple rule is to avoid @option{-G} if you care about @sc{gnu} extensions.
5021 Here are the differences between this program and System V @command{ptx}.
5026 This program can read many input files at once, it always writes the
5027 resulting concordance on standard output. On the other hand, System V
5028 @command{ptx} reads only one file and sends the result to standard output
5029 or, if a second @var{file} parameter is given on the command, to that
5032 Having output parameters not introduced by options is a dangerous
5033 practice which @sc{gnu} avoids as far as possible. So, for using @command{ptx}
5034 portably between @sc{gnu} and System V, you should always use it with a
5035 single input file, and always expect the result on standard output. You
5036 might also want to automatically configure in a @option{-G} option to
5037 @command{ptx} calls in products using @command{ptx}, if the configurator finds
5038 that the installed @command{ptx} accepts @option{-G}.
5041 The only options available in System V @command{ptx} are options @option{-b},
5042 @option{-f}, @option{-g}, @option{-i}, @option{-o}, @option{-r}, @option{-t} and
5043 @option{-w}. All other options are @sc{gnu} extensions and are not repeated in
5044 this enumeration. Moreover, some options have a slightly different
5045 meaning when @sc{gnu} extensions are enabled, as explained below.
5048 By default, concordance output is not formatted for @command{troff} or
5049 @command{nroff}. It is rather formatted for a dumb terminal. @command{troff}
5050 or @command{nroff} output may still be selected through option @option{-O}.
5053 Unless @option{-R} option is used, the maximum reference width is
5054 subtracted from the total output line width. With @sc{gnu} extensions
5055 disabled, width of references is not taken into account in the output
5056 line width computations.
5059 All 256 bytes, even @acronym{ASCII} @sc{nul} bytes, are always read and
5060 processed from input file with no adverse effect, even if @sc{gnu} extensions
5061 are disabled. However, System V @command{ptx} does not accept 8-bit characters,
5062 a few control characters are rejected, and the tilde @kbd{~} is also rejected.
5065 Input line length is only limited by available memory, even if @sc{gnu}
5066 extensions are disabled. However, System V @command{ptx} processes only
5067 the first 200 characters in each line.
5070 The break (non-word) characters default to be every character except all
5071 letters of the underlying character set, diacriticized or not. When @sc{gnu}
5072 extensions are disabled, the break characters default to space, tab and
5076 The program makes better use of output line width. If @sc{gnu} extensions
5077 are disabled, the program rather tries to imitate System V @command{ptx},
5078 but still, there are some slight disposition glitches this program does
5079 not completely reproduce.
5082 The user can specify both an Ignore file and an Only file. This is not
5083 allowed with System V @command{ptx}.
5088 @node tsort invocation
5089 @section @command{tsort}: Topological sort
5092 @cindex topological sort
5094 @command{tsort} performs a topological sort on the given @var{file}, or
5095 standard input if no input file is given or for a @var{file} of
5096 @samp{-}. For more details and some history, see @ref{tsort background}.
5100 tsort [@var{option}] [@var{file}]
5103 @command{tsort} reads its input as pairs of strings, separated by blanks,
5104 indicating a partial ordering. The output is a total ordering that
5105 corresponds to the given partial ordering.
5119 will produce the output
5130 Consider a more realistic example.
5131 You have a large set of functions all in one file, and they may all be
5132 declared static except one. Currently that one (say @code{main}) is the
5133 first function defined in the file, and the ones it calls directly follow
5134 it, followed by those they call, etc. Let's say that you are determined
5135 to take advantage of prototypes, so you have to choose between declaring
5136 all of those functions (which means duplicating a lot of information from
5137 the definitions) and rearranging the functions so that as many as possible
5138 are defined before they are used. One way to automate the latter process
5139 is to get a list for each function of the functions it calls directly.
5140 Many programs can generate such lists. They describe a call graph.
5141 Consider the following list, in which a given line indicates that the
5142 function on the left calls the one on the right directly.
5148 tail_file pretty_name
5149 tail_file write_header
5151 tail_forever recheck
5152 tail_forever pretty_name
5153 tail_forever write_header
5154 tail_forever dump_remainder
5157 tail_lines start_lines
5158 tail_lines dump_remainder
5159 tail_lines file_lines
5160 tail_lines pipe_lines
5162 tail_bytes start_bytes
5163 tail_bytes dump_remainder
5164 tail_bytes pipe_bytes
5165 file_lines dump_remainder
5169 then you can use @command{tsort} to produce an ordering of those
5170 functions that satisfies your requirement.
5173 example$ tsort call-graph | tac
5193 @command{tsort} detects any cycles in the input and writes the first cycle
5194 encountered to standard error.
5196 Note that for a given partial ordering, generally there is no unique
5197 total ordering. In the context of the call graph above, the function
5198 @code{parse_options} may be placed anywhere in the list as long as it
5199 precedes @code{main}.
5201 The only options are @option{--help} and @option{--version}. @xref{Common
5207 * tsort background:: Where tsort came from.
5210 @node tsort background
5211 @subsection @command{tsort}: Background
5213 @command{tsort} exists because very early versions of the Unix linker processed
5214 an archive file exactly once, and in order. As @command{ld} read each object
5215 in the archive, it decided whether it was needed in the program based on
5216 whether it defined any symbols which were undefined at that point in
5219 This meant that dependencies within the archive had to be handled
5220 specially. For example, @code{scanf} probably calls @code{read}. That means
5221 that in a single pass through an archive, it was important for @code{scanf.o}
5222 to appear before read.o, because otherwise a program which calls
5223 @code{scanf} but not @code{read} might end up with an unexpected unresolved
5224 reference to @code{read}.
5226 The way to address this problem was to first generate a set of
5227 dependencies of one object file on another. This was done by a shell
5228 script called @command{lorder}. The GNU tools don't provide a version of
5229 lorder, as far as I know, but you can still find it in BSD
5232 Then you ran @command{tsort} over the @command{lorder} output, and you used the
5233 resulting sort to define the order in which you added objects to the archive.
5235 This whole procedure has been obsolete since about 1980, because
5236 Unix archives now contain a symbol table (traditionally built by
5237 @command{ranlib}, now generally built by @command{ar} itself), and the Unix
5238 linker uses the symbol table to effectively make multiple passes over
5241 Anyhow, that's where tsort came from. To solve an old problem with
5242 the way the linker handled archive files, which has since been solved
5246 @node Operating on fields within a line
5247 @chapter Operating on fields within a line
5250 * cut invocation:: Print selected parts of lines.
5251 * paste invocation:: Merge lines of files.
5252 * join invocation:: Join lines on a common field.
5256 @node cut invocation
5257 @section @command{cut}: Print selected parts of lines
5260 @command{cut} writes to standard output selected parts of each line of each
5261 input file, or standard input if no files are given or for a file name of
5265 cut @var{option}@dots{} [@var{file}]@dots{}
5268 In the table which follows, the @var{byte-list}, @var{character-list},
5269 and @var{field-list} are one or more numbers or ranges (two numbers
5270 separated by a dash) separated by commas. Bytes, characters, and
5271 fields are numbered starting at 1. Incomplete ranges may be
5272 given: @option{-@var{m}} means @samp{1-@var{m}}; @samp{@var{n}-} means
5273 @samp{@var{n}} through end of line or last field. The list elements
5274 can be repeated, can overlap, and can be specified in any order; but
5275 the selected input is written in the same order that it is read, and
5276 is written exactly once.
5278 The program accepts the following options. Also see @ref{Common
5283 @item -b @var{byte-list}
5284 @itemx --bytes=@var{byte-list}
5287 Select for printing only the bytes in positions listed in
5288 @var{byte-list}. Tabs and backspaces are treated like any other
5289 character; they take up 1 byte. If an output delimiter is specified,
5290 (see the description of @option{--output-delimiter}), then output that
5291 string between ranges of selected bytes.
5293 @item -c @var{character-list}
5294 @itemx --characters=@var{character-list}
5296 @opindex --characters
5297 Select for printing only the characters in positions listed in
5298 @var{character-list}. The same as @option{-b} for now, but
5299 internationalization will change that. Tabs and backspaces are
5300 treated like any other character; they take up 1 character. If an
5301 output delimiter is specified, (see the description of
5302 @option{--output-delimiter}), then output that string between ranges
5305 @item -f @var{field-list}
5306 @itemx --fields=@var{field-list}
5309 Select for printing only the fields listed in @var{field-list}.
5310 Fields are separated by a TAB character by default. Also print any
5311 line that contains no delimiter character, unless the
5312 @option{--only-delimited} (@option{-s}) option is specified
5314 @item -d @var{input_delim_byte}
5315 @itemx --delimiter=@var{input_delim_byte}
5317 @opindex --delimiter
5318 With @option{-f}, use the first byte of @var{input_delim_byte} as
5319 the input fields separator (default is TAB).
5323 Do not split multi-byte characters (no-op for now).
5326 @itemx --only-delimited
5328 @opindex --only-delimited
5329 For @option{-f}, do not print lines that do not contain the field separator
5330 character. Normally, any line without a field separator is printed verbatim.
5332 @item --output-delimiter=@var{output_delim_string}
5333 @opindex --output-delimiter
5334 With @option{-f}, output fields are separated by @var{output_delim_string}.
5335 The default with @option{-f} is to use the input delimiter.
5336 When using @option{-b} or @option{-c} to select ranges of byte or
5337 character offsets (as opposed to ranges of fields),
5338 output @var{output_delim_string} between non-overlapping
5339 ranges of selected bytes.
5342 @opindex --complement
5343 This option is a @acronym{GNU} extension.
5344 Select for printing the complement of the bytes, characters or fields
5345 selected with the @option{-b}, @option{-c} or @option{-f} options.
5346 In other words, do @emph{not} print the bytes, characters or fields
5347 specified via those options. This option is useful when you have
5348 many fields and want to print all but a few of them.
5355 @node paste invocation
5356 @section @command{paste}: Merge lines of files
5359 @cindex merging files
5361 @command{paste} writes to standard output lines consisting of sequentially
5362 corresponding lines of each given file, separated by a TAB character.
5363 Standard input is used for a file name of @samp{-} or if no input files
5385 paste [@var{option}]@dots{} [@var{file}]@dots{}
5388 The program accepts the following options. Also see @ref{Common options}.
5396 Paste the lines of one file at a time rather than one line from each
5397 file. Using the above example data:
5400 $ paste -s num2 let3
5405 @item -d @var{delim-list}
5406 @itemx --delimiters=@var{delim-list}
5408 @opindex --delimiters
5409 Consecutively use the characters in @var{delim-list} instead of
5410 TAB to separate merged lines. When @var{delim-list} is
5411 exhausted, start again at its beginning. Using the above example data:
5414 $ paste -d '%_' num2 let3 num2
5425 @node join invocation
5426 @section @command{join}: Join lines on a common field
5429 @cindex common field, joining on
5431 @command{join} writes to standard output a line for each pair of input
5432 lines that have identical join fields. Synopsis:
5435 join [@var{option}]@dots{} @var{file1} @var{file2}
5438 Either @var{file1} or @var{file2} (but not both) can be @samp{-},
5439 meaning standard input. @var{file1} and @var{file2} should be
5440 sorted on the join fields.
5443 Normally, the sort order is that of the
5444 collating sequence specified by the @env{LC_COLLATE} locale. Unless
5445 the @option{-t} option is given, the sort comparison ignores blanks at
5446 the start of the join field, as in @code{sort -b}. If the
5447 @option{--ignore-case} option is given, the sort comparison ignores
5448 the case of characters in the join field, as in @code{sort -f}.
5450 The @command{sort} and @command{join} commands should use consistent
5451 locales and options if the output of @command{sort} is fed to
5452 @command{join}. You can use a command like @samp{sort -k 1b,1} to
5453 sort a file on its default join field, but if you select a non-default
5454 locale, join field, separator, or comparison options, then you should
5455 do so consistently between @command{join} and @command{sort}.
5457 If the input has no unpairable lines, a @acronym{GNU} extension is
5458 available; the sort order can be any order that considers two fields
5459 to be equal if and only if the sort comparison described above
5460 considers them to be equal. For example:
5477 @checkOrderOption{join}
5481 @item the join field is the first field in each line;
5482 @item fields in the input are separated by one or more blanks, with leading
5483 blanks on the line ignored;
5484 @item fields in the output are separated by a space;
5485 @item each output line consists of the join field, the remaining
5486 fields from @var{file1}, then the remaining fields from @var{file2}.
5489 The program accepts the following options. Also see @ref{Common options}.
5493 @item -a @var{file-number}
5495 Print a line for each unpairable line in file @var{file-number} (either
5496 @samp{1} or @samp{2}), in addition to the normal output.
5499 Fail with an error message if either input file is wrongly ordered.
5501 @item --nocheck-order
5502 Do not check that both input files are in sorted order. This is the default.
5504 @item -e @var{string}
5506 Replace those output fields that are missing in the input with
5510 @itemx --ignore-case
5512 @opindex --ignore-case
5513 Ignore differences in case when comparing keys.
5514 With this option, the lines of the input files must be ordered in the same way.
5515 Use @samp{sort -f} to produce this ordering.
5517 @item -1 @var{field}
5519 Join on field @var{field} (a positive integer) of file 1.
5521 @item -2 @var{field}
5523 Join on field @var{field} (a positive integer) of file 2.
5525 @item -j @var{field}
5526 Equivalent to @option{-1 @var{field} -2 @var{field}}.
5528 @item -o @var{field-list}
5529 Construct each output line according to the format in @var{field-list}.
5530 Each element in @var{field-list} is either the single character @samp{0} or
5531 has the form @var{m.n} where the file number, @var{m}, is @samp{1} or
5532 @samp{2} and @var{n} is a positive field number.
5534 A field specification of @samp{0} denotes the join field.
5535 In most cases, the functionality of the @samp{0} field spec
5536 may be reproduced using the explicit @var{m.n} that corresponds
5537 to the join field. However, when printing unpairable lines
5538 (using either of the @option{-a} or @option{-v} options), there is no way
5539 to specify the join field using @var{m.n} in @var{field-list}
5540 if there are unpairable lines in both files.
5541 To give @command{join} that functionality, @acronym{POSIX} invented the @samp{0}
5542 field specification notation.
5544 The elements in @var{field-list}
5545 are separated by commas or blanks.
5546 Blank separators typically need to be quoted for the shell. For
5547 example, the commands @samp{join -o 1.2,2.2} and @samp{join -o '1.2
5548 2.2'} are equivalent.
5550 All output lines---including those printed because of any -a or -v
5551 option---are subject to the specified @var{field-list}.
5554 Use character @var{char} as the input and output field separator.
5555 Treat as significant each occurrence of @var{char} in the input file.
5556 Use @samp{sort -t @var{char}}, without the @option{-b} option of
5557 @samp{sort}, to produce this ordering.
5559 @item -v @var{file-number}
5560 Print a line for each unpairable line in file @var{file-number}
5561 (either @samp{1} or @samp{2}), instead of the normal output.
5568 @node Operating on characters
5569 @chapter Operating on characters
5571 @cindex operating on characters
5573 This commands operate on individual characters.
5576 * tr invocation:: Translate, squeeze, and/or delete characters.
5577 * expand invocation:: Convert tabs to spaces.
5578 * unexpand invocation:: Convert spaces to tabs.
5583 @section @command{tr}: Translate, squeeze, and/or delete characters
5590 tr [@var{option}]@dots{} @var{set1} [@var{set2}]
5593 @command{tr} copies standard input to standard output, performing
5594 one of the following operations:
5598 translate, and optionally squeeze repeated characters in the result,
5600 squeeze repeated characters,
5604 delete characters, then squeeze repeated characters from the result.
5607 The @var{set1} and (if given) @var{set2} arguments define ordered
5608 sets of characters, referred to below as @var{set1} and @var{set2}. These
5609 sets are the characters of the input that @command{tr} operates on.
5610 The @option{--complement} (@option{-c}, @option{-C}) option replaces
5612 complement (all of the characters that are not in @var{set1}).
5614 Currently @command{tr} fully supports only single-byte characters.
5615 Eventually it will support multibyte characters; when it does, the
5616 @option{-C} option will cause it to complement the set of characters,
5617 whereas @option{-c} will cause it to complement the set of values.
5618 This distinction will matter only when some values are not characters,
5619 and this is possible only in locales using multibyte encodings when
5620 the input contains encoding errors.
5622 The program accepts the @option{--help} and @option{--version}
5623 options. @xref{Common options}. Options must precede operands.
5628 * Character sets:: Specifying sets of characters.
5629 * Translating:: Changing one set of characters to another.
5630 * Squeezing:: Squeezing repeats and deleting.
5634 @node Character sets
5635 @subsection Specifying sets of characters
5637 @cindex specifying sets of characters
5639 The format of the @var{set1} and @var{set2} arguments resembles
5640 the format of regular expressions; however, they are not regular
5641 expressions, only lists of characters. Most characters simply
5642 represent themselves in these strings, but the strings can contain
5643 the shorthands listed below, for convenience. Some of them can be
5644 used only in @var{set1} or @var{set2}, as noted below.
5648 @item Backslash escapes
5649 @cindex backslash escapes
5651 The following backslash escape sequences are recognized:
5669 The character with the value given by @var{ooo}, which is 1 to 3
5675 While a backslash followed by a character not listed above is
5676 interpreted as that character, the backslash also effectively
5677 removes any special significance, so it is useful to escape
5678 @samp{[}, @samp{]}, @samp{*}, and @samp{-}.
5683 The notation @samp{@var{m}-@var{n}} expands to all of the characters
5684 from @var{m} through @var{n}, in ascending order. @var{m} should
5685 collate before @var{n}; if it doesn't, an error results. As an example,
5686 @samp{0-9} is the same as @samp{0123456789}.
5688 @sc{gnu} @command{tr} does not support the System V syntax that uses square
5689 brackets to enclose ranges. Translations specified in that format
5690 sometimes work as expected, since the brackets are often transliterated
5691 to themselves. However, they should be avoided because they sometimes
5692 behave unexpectedly. For example, @samp{tr -d '[0-9]'} deletes brackets
5695 Many historically common and even accepted uses of ranges are not
5696 portable. For example, on @acronym{EBCDIC} hosts using the @samp{A-Z}
5697 range will not do what most would expect because @samp{A} through @samp{Z}
5698 are not contiguous as they are in @acronym{ASCII}.
5699 If you can rely on a @acronym{POSIX} compliant version of @command{tr}, then
5700 the best way to work around this is to use character classes (see below).
5701 Otherwise, it is most portable (and most ugly) to enumerate the members
5704 @item Repeated characters
5705 @cindex repeated characters
5707 The notation @samp{[@var{c}*@var{n}]} in @var{set2} expands to @var{n}
5708 copies of character @var{c}. Thus, @samp{[y*6]} is the same as
5709 @samp{yyyyyy}. The notation @samp{[@var{c}*]} in @var{string2} expands
5710 to as many copies of @var{c} as are needed to make @var{set2} as long as
5711 @var{set1}. If @var{n} begins with @samp{0}, it is interpreted in
5712 octal, otherwise in decimal.
5714 @item Character classes
5715 @cindex character classes
5717 The notation @samp{[:@var{class}:]} expands to all of the characters in
5718 the (predefined) class @var{class}. The characters expand in no
5719 particular order, except for the @code{upper} and @code{lower} classes,
5720 which expand in ascending order. When the @option{--delete} (@option{-d})
5721 and @option{--squeeze-repeats} (@option{-s}) options are both given, any
5722 character class can be used in @var{set2}. Otherwise, only the
5723 character classes @code{lower} and @code{upper} are accepted in
5724 @var{set2}, and then only if the corresponding character class
5725 (@code{upper} and @code{lower}, respectively) is specified in the same
5726 relative position in @var{set1}. Doing this specifies case conversion.
5727 The class names are given below; an error results when an invalid class
5739 Horizontal whitespace.
5748 Printable characters, not including space.
5754 Printable characters, including space.
5757 Punctuation characters.
5760 Horizontal or vertical whitespace.
5769 @item Equivalence classes
5770 @cindex equivalence classes
5772 The syntax @samp{[=@var{c}=]} expands to all of the characters that are
5773 equivalent to @var{c}, in no particular order. Equivalence classes are
5774 a relatively recent invention intended to support non-English alphabets.
5775 But there seems to be no standard way to define them or determine their
5776 contents. Therefore, they are not fully implemented in @sc{gnu} @command{tr};
5777 each character's equivalence class consists only of that character,
5778 which is of no particular use.
5784 @subsection Translating
5786 @cindex translating characters
5788 @command{tr} performs translation when @var{set1} and @var{set2} are
5789 both given and the @option{--delete} (@option{-d}) option is not given.
5790 @command{tr} translates each character of its input that is in @var{set1}
5791 to the corresponding character in @var{set2}. Characters not in
5792 @var{set1} are passed through unchanged. When a character appears more
5793 than once in @var{set1} and the corresponding characters in @var{set2}
5794 are not all the same, only the final one is used. For example, these
5795 two commands are equivalent:
5802 A common use of @command{tr} is to convert lowercase characters to
5803 uppercase. This can be done in many ways. Here are three of them:
5806 tr abcdefghijklmnopqrstuvwxyz ABCDEFGHIJKLMNOPQRSTUVWXYZ
5808 tr '[:lower:]' '[:upper:]'
5812 But note that using ranges like @code{a-z} above is not portable.
5814 When @command{tr} is performing translation, @var{set1} and @var{set2}
5815 typically have the same length. If @var{set1} is shorter than
5816 @var{set2}, the extra characters at the end of @var{set2} are ignored.
5818 On the other hand, making @var{set1} longer than @var{set2} is not
5819 portable; @acronym{POSIX} says that the result is undefined. In this situation,
5820 BSD @command{tr} pads @var{set2} to the length of @var{set1} by repeating
5821 the last character of @var{set2} as many times as necessary. System V
5822 @command{tr} truncates @var{set1} to the length of @var{set2}.
5824 By default, @sc{gnu} @command{tr} handles this case like BSD @command{tr}.
5825 When the @option{--truncate-set1} (@option{-t}) option is given,
5826 @sc{gnu} @command{tr} handles this case like the System V @command{tr}
5827 instead. This option is ignored for operations other than translation.
5829 Acting like System V @command{tr} in this case breaks the relatively common
5833 tr -cs A-Za-z0-9 '\012'
5837 because it converts only zero bytes (the first element in the
5838 complement of @var{set1}), rather than all non-alphanumerics, to
5842 By the way, the above idiom is not portable because it uses ranges, and
5843 it assumes that the octal code for newline is 012.
5844 Assuming a @acronym{POSIX} compliant @command{tr}, here is a better way to write it:
5847 tr -cs '[:alnum:]' '[\n*]'
5852 @subsection Squeezing repeats and deleting
5854 @cindex squeezing repeat characters
5855 @cindex deleting characters
5857 When given just the @option{--delete} (@option{-d}) option, @command{tr}
5858 removes any input characters that are in @var{set1}.
5860 When given just the @option{--squeeze-repeats} (@option{-s}) option,
5861 @command{tr} replaces each input sequence of a repeated character that
5862 is in @var{set1} with a single occurrence of that character.
5864 When given both @option{--delete} and @option{--squeeze-repeats}, @command{tr}
5865 first performs any deletions using @var{set1}, then squeezes repeats
5866 from any remaining characters using @var{set2}.
5868 The @option{--squeeze-repeats} option may also be used when translating,
5869 in which case @command{tr} first performs translation, then squeezes
5870 repeats from any remaining characters using @var{set2}.
5872 Here are some examples to illustrate various combinations of options:
5877 Remove all zero bytes:
5884 Put all words on lines by themselves. This converts all
5885 non-alphanumeric characters to newlines, then squeezes each string
5886 of repeated newlines into a single newline:
5889 tr -cs '[:alnum:]' '[\n*]'
5893 Convert each sequence of repeated newlines to a single newline:
5900 Find doubled occurrences of words in a document.
5901 @c Separate the following two "the"s, so typo checkers don't complain.
5902 For example, people often write ``the @w{}the'' with the repeated words
5903 separated by a newline. The Bourne shell script below works first
5904 by converting each sequence of punctuation and blank characters to a
5905 single newline. That puts each ``word'' on a line by itself.
5906 Next it maps all uppercase characters to lower case, and finally it
5907 runs @command{uniq} with the @option{-d} option to print out only the words
5913 | tr -s '[:punct:][:blank:]' '[\n*]' \
5914 | tr '[:upper:]' '[:lower:]' \
5919 Deleting a small set of characters is usually straightforward. For example,
5920 to remove all @samp{a}s, @samp{x}s, and @samp{M}s you would do this:
5926 However, when @samp{-} is one of those characters, it can be tricky because
5927 @samp{-} has special meanings. Performing the same task as above but also
5928 removing all @samp{-} characters, we might try @code{tr -d -axM}, but
5929 that would fail because @command{tr} would try to interpret @option{-a} as
5930 a command-line option. Alternatively, we could try putting the hyphen
5931 inside the string, @code{tr -d a-xM}, but that wouldn't work either because
5932 it would make @command{tr} interpret @code{a-x} as the range of characters
5933 @samp{a}@dots{}@samp{x} rather than the three.
5934 One way to solve the problem is to put the hyphen at the end of the list
5941 Or you can use @samp{--} to terminate option processing:
5947 More generally, use the character class notation @code{[=c=]}
5948 with @samp{-} (or any other character) in place of the @samp{c}:
5954 Note how single quotes are used in the above example to protect the
5955 square brackets from interpretation by a shell.
5960 @node expand invocation
5961 @section @command{expand}: Convert tabs to spaces
5964 @cindex tabs to spaces, converting
5965 @cindex converting tabs to spaces
5967 @command{expand} writes the contents of each given @var{file}, or standard
5968 input if none are given or for a @var{file} of @samp{-}, to standard
5969 output, with tab characters converted to the appropriate number of
5973 expand [@var{option}]@dots{} [@var{file}]@dots{}
5976 By default, @command{expand} converts all tabs to spaces. It preserves
5977 backspace characters in the output; they decrement the column count for
5978 tab calculations. The default action is equivalent to @option{-t 8} (set
5979 tabs every 8 columns).
5981 The program accepts the following options. Also see @ref{Common options}.
5985 @item -t @var{tab1}[,@var{tab2}]@dots{}
5986 @itemx --tabs=@var{tab1}[,@var{tab2}]@dots{}
5989 @cindex tab stops, setting
5990 If only one tab stop is given, set the tabs @var{tab1} spaces apart
5991 (default is 8). Otherwise, set the tabs at columns @var{tab1},
5992 @var{tab2}, @dots{} (numbered from 0), and replace any tabs beyond the
5993 last tab stop given with single spaces. Tab stops can be separated by
5994 blanks as well as by commas.
5996 For compatibility, GNU @command{expand} also accepts the obsolete
5997 option syntax, @option{-@var{t1}[,@var{t2}]@dots{}}. New scripts
5998 should use @option{-t @var{t1}[,@var{t2}]@dots{}} instead.
6004 @cindex initial tabs, converting
6005 Only convert initial tabs (those that precede all non-space or non-tab
6006 characters) on each line to spaces.
6013 @node unexpand invocation
6014 @section @command{unexpand}: Convert spaces to tabs
6018 @command{unexpand} writes the contents of each given @var{file}, or
6019 standard input if none are given or for a @var{file} of @samp{-}, to
6020 standard output, converting blanks at the beginning of each line into
6021 as many tab characters as needed. In the default @acronym{POSIX}
6022 locale, a @dfn{blank} is a space or a tab; other locales may specify
6023 additional blank characters. Synopsis:
6026 unexpand [@var{option}]@dots{} [@var{file}]@dots{}
6029 By default, @command{unexpand} converts only initial blanks (those
6030 that precede all non-blank characters) on each line. It
6031 preserves backspace characters in the output; they decrement the column
6032 count for tab calculations. By default, tabs are set at every 8th
6035 The program accepts the following options. Also see @ref{Common options}.
6039 @item -t @var{tab1}[,@var{tab2}]@dots{}
6040 @itemx --tabs=@var{tab1}[,@var{tab2}]@dots{}
6043 If only one tab stop is given, set the tabs @var{tab1} columns apart
6044 instead of the default 8. Otherwise, set the tabs at columns
6045 @var{tab1}, @var{tab2}, @dots{} (numbered from 0), and leave blanks
6046 beyond the tab stops given unchanged. Tab stops can be separated by
6047 blanks as well as by commas. This option implies the @option{-a} option.
6049 For compatibility, GNU @command{unexpand} supports the obsolete option syntax,
6050 @option{-@var{tab1}[,@var{tab2}]@dots{}}, where tab stops must be
6051 separated by commas. (Unlike @option{-t}, this obsolete option does
6052 not imply @option{-a}.) New scripts should use @option{--first-only -t
6053 @var{tab1}[,@var{tab2}]@dots{}} instead.
6059 Also convert all sequences of two or more blanks just before a tab stop,
6060 even if they occur after non-blank characters in a line.
6067 @node Directory listing
6068 @chapter Directory listing
6070 This chapter describes the @command{ls} command and its variants @command{dir}
6071 and @command{vdir}, which list information about files.
6074 * ls invocation:: List directory contents.
6075 * dir invocation:: Briefly ls.
6076 * vdir invocation:: Verbosely ls.
6077 * dircolors invocation:: Color setup for ls, etc.
6082 @section @command{ls}: List directory contents
6085 @cindex directory listing
6087 The @command{ls} program lists information about files (of any type,
6088 including directories). Options and file arguments can be intermixed
6089 arbitrarily, as usual.
6091 For non-option command-line arguments that are directories, by default
6092 @command{ls} lists the contents of directories, not recursively, and
6093 omitting files with names beginning with @samp{.}. For other non-option
6094 arguments, by default @command{ls} lists just the file name. If no
6095 non-option argument is specified, @command{ls} operates on the current
6096 directory, acting as if it had been invoked with a single argument of @samp{.}.
6099 By default, the output is sorted alphabetically, according to the locale
6100 settings in effect.@footnote{If you use a non-@acronym{POSIX}
6101 locale (e.g., by setting @env{LC_ALL} to @samp{en_US}), then @command{ls} may
6102 produce output that is sorted differently than you're accustomed to.
6103 In that case, set the @env{LC_ALL} environment variable to @samp{C}.}
6104 If standard output is
6105 a terminal, the output is in columns (sorted vertically) and control
6106 characters are output as question marks; otherwise, the output is listed
6107 one per line and control characters are output as-is.
6109 Because @command{ls} is such a fundamental program, it has accumulated many
6110 options over the years. They are described in the subsections below;
6111 within each section, options are listed alphabetically (ignoring case).
6112 The division of options into the subsections is not absolute, since some
6113 options affect more than one aspect of @command{ls}'s operation.
6115 @cindex exit status of @command{ls}
6120 1 minor problems (e.g., failure to access a file or directory not
6121 specified as a command line argument. This happens when listing a
6122 directory in which entries are actively being removed or renamed.)
6123 2 serious trouble (e.g., memory exhausted, invalid option or failure
6124 to access file or directory specified as a command line argument)
6127 Also see @ref{Common options}.
6130 * Which files are listed::
6131 * What information is listed::
6132 * Sorting the output::
6133 * More details about version sort::
6134 * General output formatting::
6135 * Formatting file timestamps::
6136 * Formatting the file names::
6140 @node Which files are listed
6141 @subsection Which files are listed
6143 These options determine which files @command{ls} lists information for.
6144 By default, @command{ls} lists files and the contents of any
6145 directories on the command line, except that in directories it ignores
6146 files whose names start with @samp{.}.
6154 In directories, do not ignore file names that start with @samp{.}.
6159 @opindex --almost-all
6160 In directories, do not ignore all file names that start with @samp{.};
6161 ignore only @file{.} and @file{..}. The @option{--all} (@option{-a})
6162 option overrides this option.
6165 @itemx --ignore-backups
6167 @opindex --ignore-backups
6168 @cindex backup files, ignoring
6169 In directories, ignore files that end with @samp{~}. This option is
6170 equivalent to @samp{--ignore='*~' --ignore='.*~'}.
6175 @opindex --directory
6176 List just the names of directories, as with other types of files, rather
6177 than listing their contents.
6178 @c The following sentence is the same as the one for -F.
6179 Do not follow symbolic links listed on the
6180 command line unless the @option{--dereference-command-line} (@option{-H}),
6181 @option{--dereference} (@option{-L}), or
6182 @option{--dereference-command-line-symlink-to-dir} options are specified.
6185 @itemx --dereference-command-line
6187 @opindex --dereference-command-line
6188 @cindex symbolic links, dereferencing
6189 If a command line argument specifies a symbolic link, show information
6190 for the file the link references rather than for the link itself.
6192 @itemx --dereference-command-line-symlink-to-dir
6193 @opindex --dereference-command-line-symlink-to-dir
6194 @cindex symbolic links, dereferencing
6195 Do not dereference symbolic links, with one exception:
6196 if a command line argument specifies a symbolic link that refers to
6197 a directory, show information for that directory rather than for the
6199 This is the default behavior when no other dereferencing-related
6200 option has been specified (@option{--classify} (@option{-F}),
6201 @option{--directory} (@option{-d}),
6203 @option{--dereference} (@option{-L}), or
6204 @option{--dereference-command-line} (@option{-H})).
6206 @item --group-directories-first
6207 @opindex --group-directories-first
6208 Group all the directories before the files and then sort the
6209 directories and the files separately using the selected sort key
6210 (see --sort option).
6211 That is, this option specifies a primary sort key,
6212 and the --sort option specifies a secondary key.
6213 However, any use of @option{--sort=none}
6214 (@option{-U}) disables this option altogether.
6216 @item --hide=PATTERN
6217 @opindex --hide=@var{pattern}
6218 In directories, ignore files whose names match the shell pattern
6219 @var{pattern}, unless the @option{--all} (@option{-a}) or
6220 @option{--almost-all} (@option{-A}) is also given. This
6221 option acts like @option{--ignore=@var{pattern}} except that it has no
6222 effect if @option{--all} (@option{-a}) or @option{--almost-all}
6223 (@option{-A}) is also given.
6225 This option can be useful in shell aliases. For example, if
6226 @command{lx} is an alias for @samp{ls --hide='*~'} and @command{ly} is
6227 an alias for @samp{ls --ignore='*~'}, then the command @samp{lx -A}
6228 lists the file @file{README~} even though @samp{ly -A} would not.
6230 @item -I @var{pattern}
6231 @itemx --ignore=@var{pattern}
6233 @opindex --ignore=@var{pattern}
6234 In directories, ignore files whose names match the shell pattern
6235 (not regular expression) @var{pattern}. As
6236 in the shell, an initial @samp{.} in a file name does not match a
6237 wildcard at the start of @var{pattern}. Sometimes it is useful
6238 to give this option several times. For example,
6241 $ ls --ignore='.??*' --ignore='.[^.]' --ignore='#*'
6244 The first option ignores names of length 3 or more that start with @samp{.},
6245 the second ignores all two-character names that start with @samp{.}
6246 except @samp{..}, and the third ignores names that start with @samp{#}.
6249 @itemx --dereference
6251 @opindex --dereference
6252 @cindex symbolic links, dereferencing
6253 When showing file information for a symbolic link, show information
6254 for the file the link references rather than the link itself.
6255 However, even with this option, @command{ls} still prints the name
6256 of the link itself, not the name of the file that the link points to.
6261 @opindex --recursive
6262 @cindex recursive directory listing
6263 @cindex directory listing, recursive
6264 List the contents of all directories recursively.
6269 @node What information is listed
6270 @subsection What information is listed
6272 These options affect the information that @command{ls} displays. By
6273 default, only file names are shown.
6279 @cindex hurd, author, printing
6280 List each file's author when producing long format directory listings.
6281 In GNU/Hurd, file authors can differ from their owners, but in other
6282 operating systems the two are the same.
6288 @cindex dired Emacs mode support
6289 With the long listing (@option{-l}) format, print an additional line after
6293 //DIRED// @var{beg1} @var{end1} @var{beg2} @var{end2} @dots{}
6297 The @var{begn} and @var{endn} are unsigned integers that record the
6298 byte position of the beginning and end of each file name in the output.
6299 This makes it easy for Emacs to find the names, even when they contain
6300 unusual characters such as space or newline, without fancy searching.
6302 If directories are being listed recursively (@option{-R}), output a similar
6303 line with offsets for each subdirectory name:
6306 //SUBDIRED// @var{beg1} @var{end1} @dots{}
6309 Finally, output a line of the form:
6312 //DIRED-OPTIONS// --quoting-style=@var{word}
6316 where @var{word} is the quoting style (@pxref{Formatting the file names}).
6318 Here is an actual example:
6321 $ mkdir -p a/sub/deeper a/sub2
6323 $ touch a/sub/deeper/file
6324 $ ls -gloRF --dired a
6327 -rw-r--r-- 1 0 Jun 10 12:27 f1
6328 -rw-r--r-- 1 0 Jun 10 12:27 f2
6329 drwxr-xr-x 3 4096 Jun 10 12:27 sub/
6330 drwxr-xr-x 2 4096 Jun 10 12:27 sub2/
6334 drwxr-xr-x 2 4096 Jun 10 12:27 deeper/
6338 -rw-r--r-- 1 0 Jun 10 12:27 file
6342 //DIRED// 48 50 84 86 120 123 158 162 217 223 282 286
6343 //SUBDIRED// 2 3 167 172 228 240 290 296
6344 //DIRED-OPTIONS// --quoting-style=literal
6347 Note that the pairs of offsets on the @samp{//DIRED//} line above delimit
6348 these names: @file{f1}, @file{f2}, @file{sub}, @file{sub2}, @file{deeper},
6350 The offsets on the @samp{//SUBDIRED//} line delimit the following
6351 directory names: @file{a}, @file{a/sub}, @file{a/sub/deeper}, @file{a/sub2}.
6353 Here is an example of how to extract the fifth entry name, @samp{deeper},
6354 corresponding to the pair of offsets, 222 and 228:
6357 $ ls -gloRF --dired a > out
6358 $ dd bs=1 skip=222 count=6 < out 2>/dev/null; echo
6362 Note that although the listing above includes a trailing slash
6363 for the @samp{deeper} entry, the offsets select the name without
6364 the trailing slash. However, if you invoke @command{ls} with @option{--dired}
6365 along with an option like @option{--escape} (aka @option{-b}) and operate
6366 on a file whose name contains special characters, notice that the backslash
6371 $ ls -blog --dired 'a b'
6372 -rw-r--r-- 1 0 Jun 10 12:28 a\ b
6374 //DIRED-OPTIONS// --quoting-style=escape
6377 If you use a quoting style that adds quote marks
6378 (e.g., @option{--quoting-style=c}), then the offsets include the quote marks.
6379 So beware that the user may select the quoting style via the environment
6380 variable @env{QUOTING_STYLE}. Hence, applications using @option{--dired}
6381 should either specify an explicit @option{--quoting-style=literal} option
6382 (aka @option{-N} or @option{--literal}) on the command line, or else be
6383 prepared to parse the escaped names.
6386 @opindex --full-time
6387 Produce long format directory listings, and list times in full. It is
6388 equivalent to using @option{--format=long} with
6389 @option{--time-style=full-iso} (@pxref{Formatting file timestamps}).
6393 Produce long format directory listings, but don't display owner information.
6399 Inhibit display of group information in a long format directory listing.
6400 (This is the default in some non-@sc{gnu} versions of @command{ls}, so we
6401 provide this option for compatibility.)
6409 @cindex inode number, printing
6410 Print the inode number (also called the file serial number and index
6411 number) of each file to the left of the file name. (This number
6412 uniquely identifies each file within a particular file system.)
6415 @itemx --format=long
6416 @itemx --format=verbose
6419 @opindex long ls @r{format}
6420 @opindex verbose ls @r{format}
6421 In addition to the name of each file, print the file type, file mode bits,
6422 number of hard links, owner name, group name, size, and
6423 timestamp (@pxref{Formatting file timestamps}), normally
6424 the modification time. Print question marks for information that
6425 cannot be determined.
6427 Normally the size is printed as a byte count without punctuation, but
6428 this can be overridden (@pxref{Block size}). For example, @option{-h}
6429 prints an abbreviated, human-readable count, and
6430 @samp{--block-size="'1"} prints a byte count with the thousands
6431 separator of the current locale.
6433 For each directory that is listed, preface the files with a line
6434 @samp{total @var{blocks}}, where @var{blocks} is the total disk allocation
6435 for all files in that directory. The block size currently defaults to 1024
6436 bytes, but this can be overridden (@pxref{Block size}).
6437 The @var{blocks} computed counts each hard link separately;
6438 this is arguably a deficiency.
6440 The file type is one of the following characters:
6442 @c The commented-out entries are ones we're not sure about.
6450 character special file
6452 high performance (``contiguous data'') file
6456 door (Solaris 2.5 and up)
6458 @c semaphore, if this is a distinct file type
6462 @c multiplexed file (7th edition Unix; obsolete)
6464 off-line (``migrated'') file (Cray DMF)
6466 network special file (HP-UX)
6470 port (Solaris 10 and up)
6472 @c message queue, if this is a distinct file type
6476 @c shared memory object, if this is a distinct file type
6478 @c typed memory object, if this is a distinct file type
6480 @c whiteout (4.4BSD; not implemented)
6482 some other file type
6485 @cindex permissions, output by @command{ls}
6486 The file mode bits listed are similar to symbolic mode specifications
6487 (@pxref{Symbolic Modes}). But @command{ls} combines multiple bits into the
6488 third character of each set of permissions as follows:
6492 If the set-user-ID or set-group-ID bit and the corresponding executable bit
6496 If the set-user-ID or set-group-ID bit is set but the corresponding
6497 executable bit is not set.
6500 If the restricted deletion flag or sticky bit, and the
6501 other-executable bit, are both set. The restricted deletion flag is
6502 another name for the sticky bit. @xref{Mode Structure}.
6505 If the restricted deletion flag or sticky bit is set but the
6506 other-executable bit is not set.
6509 If the executable bit is set and none of the above apply.
6515 Following the file mode bits is a single character that specifies
6516 whether an alternate access method such as an access control list
6517 applies to the file. When the character following the file mode bits is a
6518 space, there is no alternate access method. When it is a printing
6519 character, then there is such a method.
6521 GNU @command{ls} uses a @samp{.} character to indicate a file
6522 with an SELinux security context, but no other alternate access method.
6524 A file with any other combination of alternate access methods
6525 is marked with a @samp{+} character.
6528 @itemx --numeric-uid-gid
6530 @opindex --numeric-uid-gid
6531 @cindex numeric uid and gid
6532 @cindex numeric user and group IDs
6533 Produce long format directory listings, but
6534 display numeric user and group IDs instead of the owner and group names.
6538 Produce long format directory listings, but don't display group information.
6539 It is equivalent to using @option{--format=long} with @option{--no-group} .
6545 @cindex disk allocation
6546 @cindex size of files, reporting
6547 Print the disk allocation of each file to the left of the file name.
6548 This is the amount of disk space used by the file, which is usually a
6549 bit more than the file's size, but it can be less if the file has holes.
6551 Normally the disk allocation is printed in units of
6552 1024 bytes, but this can be overridden (@pxref{Block size}).
6554 @cindex NFS mounts from BSD to HP-UX
6555 For files that are NFS-mounted from an HP-UX system to a BSD system,
6556 this option reports sizes that are half the correct values. On HP-UX
6557 systems, it reports sizes that are twice the correct values for files
6558 that are NFS-mounted from BSD systems. This is due to a flaw in HP-UX;
6559 it also affects the HP-UX @command{ls} program.
6568 @cindex security context
6569 Display the SELinux security context or @samp{?} if none is found.
6570 When used with the @option{-l} option, print the security context
6571 to the left of the size column.
6576 @node Sorting the output
6577 @subsection Sorting the output
6579 @cindex sorting @command{ls} output
6580 These options change the order in which @command{ls} sorts the information
6581 it outputs. By default, sorting is done by character code
6582 (e.g., @acronym{ASCII} order).
6588 @itemx --time=status
6591 @opindex ctime@r{, printing or sorting by}
6592 @opindex status time@r{, printing or sorting by}
6593 @opindex use time@r{, printing or sorting files by}
6594 If the long listing format (e.g., @option{-l}, @option{-o}) is being used,
6595 print the status change time (the @samp{ctime} in the inode) instead of
6596 the modification time.
6597 When explicitly sorting by time (@option{--sort=time} or @option{-t})
6598 or when not using a long listing format,
6599 sort according to the status change time.
6603 @cindex unsorted directory listing
6604 @cindex directory order, listing by
6605 Primarily, like @option{-U}---do not sort; list the files in whatever
6606 order they are stored in the directory. But also enable @option{-a} (list
6607 all files) and disable @option{-l}, @option{--color}, and @option{-s} (if they
6608 were specified before the @option{-f}).
6614 @cindex reverse sorting
6615 Reverse whatever the sorting method is---e.g., list files in reverse
6616 alphabetical order, youngest first, smallest first, or whatever.
6622 @opindex size of files@r{, sorting files by}
6623 Sort by file size, largest first.
6629 @opindex modification time@r{, sorting files by}
6630 Sort by modification time (the @samp{mtime} in the inode), newest first.
6634 @itemx --time=access
6638 @opindex use time@r{, printing or sorting files by}
6639 @opindex atime@r{, printing or sorting files by}
6640 @opindex access time@r{, printing or sorting files by}
6641 If the long listing format (e.g., @option{--format=long}) is being used,
6642 print the last access time (the @samp{atime} in the inode).
6643 When explicitly sorting by time (@option{--sort=time} or @option{-t})
6644 or when not using a long listing format, sort according to the access time.
6650 @opindex none@r{, sorting option for @command{ls}}
6651 Do not sort; list the files in whatever order they are
6652 stored in the directory. (Do not do any of the other unrelated things
6653 that @option{-f} does.) This is especially useful when listing very large
6654 directories, since not doing any sorting can be noticeably faster.
6657 @itemx --sort=version
6660 @opindex version@r{, sorting option for @command{ls}}
6661 Sort by version name and number, lowest first. It behaves like a default
6662 sort, except that each sequence of decimal digits is treated numerically
6663 as an index/version number. (@xref{More details about version sort}.)
6666 @itemx --sort=extension
6669 @opindex extension@r{, sorting files by}
6670 Sort directory contents alphabetically by file extension (characters
6671 after the last @samp{.}); files with no extension are sorted first.
6676 @node More details about version sort
6677 @subsection More details about version sort
6679 The version sort takes into account the fact that file names frequently include
6680 indices or version numbers. Standard sorting functions usually do not produce
6681 the ordering that people expect because comparisons are made on a
6682 character-by-character basis. The version
6683 sort addresses this problem, and is especially useful when browsing
6684 directories that contain many files with indices/version numbers in their
6689 foo.zml-1.gz foo.zml-1.gz
6690 foo.zml-100.gz foo.zml-2.gz
6691 foo.zml-12.gz foo.zml-6.gz
6692 foo.zml-13.gz foo.zml-12.gz
6693 foo.zml-2.gz foo.zml-13.gz
6694 foo.zml-25.gz foo.zml-25.gz
6695 foo.zml-6.gz foo.zml-100.gz
6698 Version-sorted strings are compared such that if @var{ver1} and @var{ver2}
6699 are version numbers and @var{prefix} and @var{suffix} (@var{suffix} matching
6700 the regular expression @samp{(\.[A-Za-z~][A-Za-z0-9~]*)*}) are strings then
6701 @var{ver1} < @var{ver2} implies that the name composed of
6702 ``@var{prefix} @var{ver1} @var{suffix}'' sorts before
6703 ``@var{prefix} @var{ver2} @var{suffix}''.
6705 Note also that leading zeros of numeric parts are ignored:
6709 abc-1.007.tgz abc-1.01a.tgz
6710 abc-1.012b.tgz abc-1.007.tgz
6711 abc-1.01a.tgz abc-1.012b.tgz
6714 This functionality is implemented using gnulib's @code{filevercmp} function.
6715 One result of that implementation decision is that @samp{ls -v}
6716 and @samp{sort -V} do not use the locale category, @env{LC_COLLATE},
6717 which means non-numeric prefixes are sorted as if @env{LC_COLLATE} were set
6720 @node General output formatting
6721 @subsection General output formatting
6723 These options affect the appearance of the overall output.
6728 @itemx --format=single-column
6731 @opindex single-column @r{output of files}
6732 List one file per line. This is the default for @command{ls} when standard
6733 output is not a terminal.
6736 @itemx --format=vertical
6739 @opindex vertical @r{sorted files in columns}
6740 List files in columns, sorted vertically. This is the default for
6741 @command{ls} if standard output is a terminal. It is always the default
6742 for the @command{dir} program.
6743 @sc{gnu} @command{ls} uses variable width columns to display as many files as
6744 possible in the fewest lines.
6746 @item --color [=@var{when}]
6748 @cindex color, distinguishing file types with
6749 Specify whether to use color for distinguishing file types. @var{when}
6750 may be omitted, or one of:
6753 @vindex none @r{color option}
6754 - Do not use color at all. This is the default.
6756 @vindex auto @r{color option}
6757 @cindex terminal, using color iff
6758 - Only use color if standard output is a terminal.
6760 @vindex always @r{color option}
6763 Specifying @option{--color} and no @var{when} is equivalent to
6764 @option{--color=always}.
6765 Piping a colorized listing through a pager like @command{more} or
6766 @command{less} usually produces unreadable results. However, using
6767 @code{more -f} does seem to work.
6771 @itemx --indicator-style=classify
6774 @opindex --indicator-style
6775 @cindex file type and executables, marking
6776 @cindex executables and file type, marking
6777 Append a character to each file name indicating the file type. Also,
6778 for regular files that are executable, append @samp{*}. The file type
6779 indicators are @samp{/} for directories, @samp{@@} for symbolic links,
6780 @samp{|} for FIFOs, @samp{=} for sockets, @samp{>} for doors,
6781 and nothing for regular files.
6782 @c The following sentence is the same as the one for -d.
6783 Do not follow symbolic links listed on the
6784 command line unless the @option{--dereference-command-line} (@option{-H}),
6785 @option{--dereference} (@option{-L}), or
6786 @option{--dereference-command-line-symlink-to-dir} options are specified.
6789 @itemx --indicator-style=file-type
6790 @opindex --file-type
6791 @opindex --indicator-style
6792 @cindex file type, marking
6793 Append a character to each file name indicating the file type. This is
6794 like @option{-F}, except that executables are not marked.
6796 @item --indicator-style=@var{word}
6797 @opindex --indicator-style
6798 Append a character indicator with style @var{word} to entry names,
6803 Do not append any character indicator; this is the default.
6805 Append @samp{/} for directories. This is the same as the @option{-p}
6808 Append @samp{/} for directories, @samp{@@} for symbolic links, @samp{|}
6809 for FIFOs, @samp{=} for sockets, and nothing for regular files. This is
6810 the same as the @option{--file-type} option.
6812 Append @samp{*} for executable regular files, otherwise behave as for
6813 @samp{file-type}. This is the same as the @option{-F} or
6814 @option{--classify} option.
6819 Print file sizes in 1024-byte blocks, overriding the default block
6820 size (@pxref{Block size}).
6821 This option is equivalent to @option{--block-size=1K}.
6824 @itemx --format=commas
6827 @opindex commas@r{, outputting between files}
6828 List files horizontally, with as many as will fit on each line,
6829 separated by @samp{, } (a comma and a space).
6832 @itemx --indicator-style=slash
6834 @opindex --indicator-style
6835 @cindex file type, marking
6836 Append a @samp{/} to directory names.
6839 @itemx --format=across
6840 @itemx --format=horizontal
6843 @opindex across@r{, listing files}
6844 @opindex horizontal@r{, listing files}
6845 List the files in columns, sorted horizontally.
6848 @itemx --tabsize=@var{cols}
6851 Assume that each tab stop is @var{cols} columns wide. The default is 8.
6852 @command{ls} uses tabs where possible in the output, for efficiency. If
6853 @var{cols} is zero, do not use tabs at all.
6855 @c FIXME: remove in 2009, if Apple Terminal has been fixed for long enough.
6856 Some terminal emulators (at least Apple Terminal 1.5 (133) from Mac OS X 10.4.8)
6857 do not properly align columns to the right of a TAB following a
6858 non-@acronym{ASCII} byte. If you use such a terminal emulator, use the
6859 @option{-T0} option or put @code{TABSIZE=0} in your environment to tell
6860 @command{ls} to align using spaces, not tabs.
6863 @itemx --width=@var{cols}
6867 Assume the screen is @var{cols} columns wide. The default is taken
6868 from the terminal settings if possible; otherwise the environment
6869 variable @env{COLUMNS} is used if it is set; otherwise the default
6875 @node Formatting file timestamps
6876 @subsection Formatting file timestamps
6878 By default, file timestamps are listed in abbreviated form. Most
6879 locales use a timestamp like @samp{2002-03-30 23:45}. However, the
6880 default @acronym{POSIX} locale uses a date like @samp{Mar 30@ @ 2002}
6881 for non-recent timestamps, and a date-without-year and time like
6882 @samp{Mar 30 23:45} for recent timestamps.
6884 A timestamp is considered to be @dfn{recent} if it is less than six
6885 months old, and is not dated in the future. If a timestamp dated
6886 today is not listed in recent form, the timestamp is in the future,
6887 which means you probably have clock skew problems which may break
6888 programs like @command{make} that rely on file timestamps.
6891 Time stamps are listed according to the time zone rules specified by
6892 the @env{TZ} environment variable, or by the system default rules if
6893 @env{TZ} is not set. @xref{TZ Variable,, Specifying the Time Zone
6894 with @env{TZ}, libc, The GNU C Library Reference Manual}.
6896 The following option changes how file timestamps are printed.
6899 @item --time-style=@var{style}
6900 @opindex --time-style
6902 List timestamps in style @var{style}. The @var{style} should
6903 be one of the following:
6908 List timestamps using @var{format}, where @var{format} is interpreted
6909 like the format argument of @command{date} (@pxref{date invocation}).
6910 For example, @option{--time-style="+%Y-%m-%d %H:%M:%S"} causes
6911 @command{ls} to list timestamps like @samp{2002-03-30 23:45:56}. As
6912 with @command{date}, @var{format}'s interpretation is affected by the
6913 @env{LC_TIME} locale category.
6915 If @var{format} contains two format strings separated by a newline,
6916 the former is used for non-recent files and the latter for recent
6917 files; if you want output columns to line up, you may need to insert
6918 spaces in one of the two formats.
6921 List timestamps in full using @acronym{ISO} 8601 date, time, and time zone
6922 format with nanosecond precision, e.g., @samp{2002-03-30
6923 23:45:56.477817180 -0700}. This style is equivalent to
6924 @samp{+%Y-%m-%d %H:%M:%S.%N %z}.
6926 This is useful because the time output includes all the information that
6927 is available from the operating system. For example, this can help
6928 explain @command{make}'s behavior, since @acronym{GNU} @command{make}
6929 uses the full timestamp to determine whether a file is out of date.
6932 List @acronym{ISO} 8601 date and time in minutes, e.g.,
6933 @samp{2002-03-30 23:45}. These timestamps are shorter than
6934 @samp{full-iso} timestamps, and are usually good enough for everyday
6935 work. This style is equivalent to @samp{+%Y-%m-%d %H:%M}.
6938 List @acronym{ISO} 8601 dates for non-recent timestamps (e.g.,
6939 @samp{2002-03-30@ }), and @acronym{ISO} 8601 month, day, hour, and
6940 minute for recent timestamps (e.g., @samp{03-30 23:45}). These
6941 timestamps are uglier than @samp{long-iso} timestamps, but they carry
6942 nearly the same information in a smaller space and their brevity helps
6943 @command{ls} output fit within traditional 80-column output lines.
6944 The following two @command{ls} invocations are equivalent:
6949 ls -l --time-style="+%Y-%m-%d $newline%m-%d %H:%M"
6950 ls -l --time-style="iso"
6955 List timestamps in a locale-dependent form. For example, a Finnish
6956 locale might list non-recent timestamps like @samp{maalis 30@ @ 2002}
6957 and recent timestamps like @samp{maalis 30 23:45}. Locale-dependent
6958 timestamps typically consume more space than @samp{iso} timestamps and
6959 are harder for programs to parse because locale conventions vary so
6960 widely, but they are easier for many people to read.
6962 The @env{LC_TIME} locale category specifies the timestamp format. The
6963 default @acronym{POSIX} locale uses timestamps like @samp{Mar 30@
6964 @ 2002} and @samp{Mar 30 23:45}; in this locale, the following two
6965 @command{ls} invocations are equivalent:
6970 ls -l --time-style="+%b %e %Y$newline%b %e %H:%M"
6971 ls -l --time-style="locale"
6974 Other locales behave differently. For example, in a German locale,
6975 @option{--time-style="locale"} might be equivalent to
6976 @option{--time-style="+%e. %b %Y $newline%e. %b %H:%M"}
6977 and might generate timestamps like @samp{30. M@"ar 2002@ } and
6978 @samp{30. M@"ar 23:45}.
6980 @item posix-@var{style}
6982 List @acronym{POSIX}-locale timestamps if the @env{LC_TIME} locale
6983 category is @acronym{POSIX}, @var{style} timestamps otherwise. For
6984 example, the @samp{posix-long-iso} style lists
6985 timestamps like @samp{Mar 30@ @ 2002} and @samp{Mar 30 23:45} when in
6986 the @acronym{POSIX} locale, and like @samp{2002-03-30 23:45} otherwise.
6991 You can specify the default value of the @option{--time-style} option
6992 with the environment variable @env{TIME_STYLE}; if @env{TIME_STYLE} is not set
6993 the default style is @samp{locale}. @acronym{GNU} Emacs 21.3 and
6994 later use the @option{--dired} option and therefore can parse any date
6995 format, but if you are using Emacs 21.1 or 21.2 and specify a
6996 non-@acronym{POSIX} locale you may need to set
6997 @samp{TIME_STYLE="posix-long-iso"}.
6999 To avoid certain denial-of-service attacks, timestamps that would be
7000 longer than 1000 bytes may be treated as errors.
7003 @node Formatting the file names
7004 @subsection Formatting the file names
7006 These options change how file names themselves are printed.
7012 @itemx --quoting-style=escape
7015 @opindex --quoting-style
7016 @cindex backslash sequences for file names
7017 Quote nongraphic characters in file names using alphabetic and octal
7018 backslash sequences like those used in C.
7022 @itemx --quoting-style=literal
7025 @opindex --quoting-style
7026 Do not quote file names. However, with @command{ls} nongraphic
7027 characters are still printed as question marks if the output is a
7028 terminal and you do not specify the @option{--show-control-chars}
7032 @itemx --hide-control-chars
7034 @opindex --hide-control-chars
7035 Print question marks instead of nongraphic characters in file names.
7036 This is the default if the output is a terminal and the program is
7041 @itemx --quoting-style=c
7043 @opindex --quote-name
7044 @opindex --quoting-style
7045 Enclose file names in double quotes and quote nongraphic characters as
7048 @item --quoting-style=@var{word}
7049 @opindex --quoting-style
7050 @cindex quoting style
7051 Use style @var{word} to quote file names and other strings that may
7052 contain arbitrary characters. The @var{word} should
7053 be one of the following:
7057 Output strings as-is; this is the same as the @option{-N} or
7058 @option{--literal} option.
7060 Quote strings for the shell if they contain shell metacharacters or would
7061 cause ambiguous output.
7062 The quoting is suitable for @acronym{POSIX}-compatible shells like
7063 @command{bash}, but it does not always work for incompatible shells
7066 Quote strings for the shell, even if they would normally not require quoting.
7068 Quote strings as for C character string literals, including the
7069 surrounding double-quote characters; this is the same as the
7070 @option{-Q} or @option{--quote-name} option.
7072 Quote strings as for C character string literals, except omit the
7073 surrounding double-quote
7074 characters; this is the same as the @option{-b} or @option{--escape} option.
7076 Quote strings as for C character string literals, except use
7077 surrounding quotation marks appropriate for the
7080 @c Use @t instead of @samp to avoid duplicate quoting in some output styles.
7081 Quote strings as for C character string literals, except use
7082 surrounding quotation marks appropriate for the locale, and quote
7083 @t{`like this'} instead of @t{"like
7084 this"} in the default C locale. This looks nicer on many displays.
7087 You can specify the default value of the @option{--quoting-style} option
7088 with the environment variable @env{QUOTING_STYLE}. If that environment
7089 variable is not set, the default value is @samp{literal}, but this
7090 default may change to @samp{shell} in a future version of this package.
7092 @item --show-control-chars
7093 @opindex --show-control-chars
7094 Print nongraphic characters as-is in file names.
7095 This is the default unless the output is a terminal and the program is
7101 @node dir invocation
7102 @section @command{dir}: Briefly list directory contents
7105 @cindex directory listing, brief
7107 @command{dir} is equivalent to @code{ls -C
7108 -b}; that is, by default files are listed in columns, sorted vertically,
7109 and special characters are represented by backslash escape sequences.
7111 @xref{ls invocation, @command{ls}}.
7114 @node vdir invocation
7115 @section @command{vdir}: Verbosely list directory contents
7118 @cindex directory listing, verbose
7120 @command{vdir} is equivalent to @code{ls -l
7121 -b}; that is, by default files are listed in long format and special
7122 characters are represented by backslash escape sequences.
7124 @node dircolors invocation
7125 @section @command{dircolors}: Color setup for @command{ls}
7129 @cindex setup for color
7131 @command{dircolors} outputs a sequence of shell commands to set up the
7132 terminal for color output from @command{ls} (and @command{dir}, etc.).
7136 eval "`dircolors [@var{option}]@dots{} [@var{file}]`"
7139 If @var{file} is specified, @command{dircolors} reads it to determine which
7140 colors to use for which file types and extensions. Otherwise, a
7141 precompiled database is used. For details on the format of these files,
7142 run @samp{dircolors --print-database}.
7144 To make @command{dircolors} read a @file{~/.dircolors} file if it
7145 exists, you can put the following lines in your @file{~/.bashrc} (or
7146 adapt them to your favorite shell):
7150 test -r $d && eval "$(dircolors $d)"
7154 @vindex SHELL @r{environment variable, and color}
7155 The output is a shell command to set the @env{LS_COLORS} environment
7156 variable. You can specify the shell syntax to use on the command line,
7157 or @command{dircolors} will guess it from the value of the @env{SHELL}
7158 environment variable.
7160 The program accepts the following options. Also see @ref{Common options}.
7165 @itemx --bourne-shell
7168 @opindex --bourne-shell
7169 @cindex Bourne shell syntax for color setup
7170 @cindex @command{sh} syntax for color setup
7171 Output Bourne shell commands. This is the default if the @env{SHELL}
7172 environment variable is set and does not end with @samp{csh} or
7181 @cindex C shell syntax for color setup
7182 @cindex @command{csh} syntax for color setup
7183 Output C shell commands. This is the default if @code{SHELL} ends with
7184 @command{csh} or @command{tcsh}.
7187 @itemx --print-database
7189 @opindex --print-database
7190 @cindex color database, printing
7191 @cindex database for color setup, printing
7192 @cindex printing color database
7193 Print the (compiled-in) default color configuration database. This
7194 output is itself a valid configuration file, and is fairly descriptive
7195 of the possibilities.
7202 @node Basic operations
7203 @chapter Basic operations
7205 @cindex manipulating files
7207 This chapter describes the commands for basic file manipulation:
7208 copying, moving (renaming), and deleting (removing).
7211 * cp invocation:: Copy files.
7212 * dd invocation:: Convert and copy a file.
7213 * install invocation:: Copy files and set attributes.
7214 * mv invocation:: Move (rename) files.
7215 * rm invocation:: Remove files or directories.
7216 * shred invocation:: Remove files more securely.
7221 @section @command{cp}: Copy files and directories
7224 @cindex copying files and directories
7225 @cindex files, copying
7226 @cindex directories, copying
7228 @command{cp} copies files (or, optionally, directories). The copy is
7229 completely independent of the original. You can either copy one file to
7230 another, or copy arbitrarily many files to a destination directory.
7234 cp [@var{option}]@dots{} [-T] @var{source} @var{dest}
7235 cp [@var{option}]@dots{} @var{source}@dots{} @var{directory}
7236 cp [@var{option}]@dots{} -t @var{directory} @var{source}@dots{}
7241 If two file names are given, @command{cp} copies the first file to the
7245 If the @option{--target-directory} (@option{-t}) option is given, or
7246 failing that if the last file is a directory and the
7247 @option{--no-target-directory} (@option{-T}) option is not given,
7248 @command{cp} copies each @var{source} file to the specified directory,
7249 using the @var{source}s' names.
7252 Generally, files are written just as they are read. For exceptions,
7253 see the @option{--sparse} option below.
7255 By default, @command{cp} does not copy directories. However, the
7256 @option{-R}, @option{-a}, and @option{-r} options cause @command{cp} to
7257 copy recursively by descending into source directories and copying files
7258 to corresponding destination directories.
7260 When copying from a symbolic link, @command{cp} normally follows the
7261 link only when not copying
7262 recursively. This default can be overridden with the
7263 @option{--archive} (@option{-a}), @option{-d}, @option{--dereference}
7264 (@option{-L}), @option{--no-dereference} (@option{-P}), and
7265 @option{-H} options. If more than one of these options is specified,
7266 the last one silently overrides the others.
7268 When copying to a symbolic link, @command{cp} follows the
7269 link only when it refers to an existing regular file.
7270 However, when copying to a dangling symbolic link, @command{cp}
7271 refuses by default, and fails with a diagnostic, since the operation
7272 is inherently dangerous. This behavior is contrary to historical
7273 practice and to @acronym{POSIX}.
7274 Set @env{POSIXLY_CORRECT} to make @command{cp} attempt to create
7275 the target of a dangling destination symlink, in spite of the possible risk.
7276 Also, when an option like
7277 @option{--backup} or @option{--link} acts to rename or remove the
7278 destination before copying, @command{cp} renames or removes the
7279 symbolic link rather than the file it points to.
7281 By default, @command{cp} copies the contents of special files only
7282 when not copying recursively. This default can be overridden with the
7283 @option{--copy-contents} option.
7285 @cindex self-backups
7286 @cindex backups, making only
7287 @command{cp} generally refuses to copy a file onto itself, with the
7288 following exception: if @option{--force --backup} is specified with
7289 @var{source} and @var{dest} identical, and referring to a regular file,
7290 @command{cp} will make a backup file, either regular or numbered, as
7291 specified in the usual ways (@pxref{Backup options}). This is useful when
7292 you simply want to make a backup of an existing file before changing it.
7294 The program accepts the following options. Also see @ref{Common options}.
7301 Preserve as much as possible of the structure and attributes of the
7302 original files in the copy (but do not attempt to preserve internal
7303 directory structure; i.e., @samp{ls -U} may list the entries in a copied
7304 directory in a different order).
7305 Try to preserve SELinux security context and extended attributes (xattr),
7306 but ignore any failure to do that and print no corresponding diagnostic.
7307 Equivalent to @option{-dR --preserve=all} with the reduced diagnostics.
7310 @itemx @w{@kbd{--backup}[=@var{method}]}
7313 @vindex VERSION_CONTROL
7314 @cindex backups, making
7315 @xref{Backup options}.
7316 Make a backup of each file that would otherwise be overwritten or removed.
7317 As a special case, @command{cp} makes a backup of @var{source} when the force
7318 and backup options are given and @var{source} and @var{dest} are the same
7319 name for an existing, regular file. One useful application of this
7320 combination of options is this tiny Bourne shell script:
7324 # Usage: backup FILE...
7325 # Create a @sc{gnu}-style backup of each listed FILE.
7327 cp --backup --force -- "$i" "$i"
7331 @item --copy-contents
7332 @cindex directories, copying recursively
7333 @cindex copying directories recursively
7334 @cindex recursively copying directories
7335 @cindex non-directories, copying as special files
7336 If copying recursively, copy the contents of any special files (e.g.,
7337 FIFOs and device files) as if they were regular files. This means
7338 trying to read the data in each source file and writing it to the
7339 destination. It is usually a mistake to use this option, as it
7340 normally has undesirable effects on special files like FIFOs and the
7341 ones typically found in the @file{/dev} directory. In most cases,
7342 @code{cp -R --copy-contents} will hang indefinitely trying to read
7343 from FIFOs and special files like @file{/dev/console}, and it will
7344 fill up your destination disk if you use it to copy @file{/dev/zero}.
7345 This option has no effect unless copying recursively, and it does not
7346 affect the copying of symbolic links.
7350 @cindex symbolic links, copying
7351 @cindex hard links, preserving
7352 Copy symbolic links as symbolic links rather than copying the files that
7353 they point to, and preserve hard links between source files in the copies.
7354 Equivalent to @option{--no-dereference --preserve=links}.
7360 When copying without this option and an existing destination file cannot
7361 be opened for writing, the copy fails. However, with @option{--force}),
7362 when a destination file cannot be opened, @command{cp} then removes it and
7363 tries to open it again. Contrast this behavior with that enabled by
7364 @option{--link} and @option{--symbolic-link}, whereby the destination file
7365 is never opened but rather is removed unconditionally. Also see the
7366 description of @option{--remove-destination}.
7368 This option is independent of the @option{--interactive} or
7369 @option{-i} option: neither cancels the effect of the other.
7371 This option is redundant if the @option{--no-clobber} or @option{-n} option is
7376 If a command line argument specifies a symbolic link, then copy the
7377 file it points to rather than the symbolic link itself. However,
7378 copy (preserving its nature) any symbolic link that is encountered
7379 via recursive traversal.
7382 @itemx --interactive
7384 @opindex --interactive
7385 When copying a file other than a directory, prompt whether to
7386 overwrite an existing destination file. The @option{-i} option overrides
7387 a previous @option{-n} option.
7393 Make hard links instead of copies of non-directories.
7396 @itemx --dereference
7398 @opindex --dereference
7399 Follow symbolic links when copying from them.
7400 With this option, @command{cp} cannot create a symbolic link.
7401 For example, a symlink (to regular file) in the source tree will be copied to
7402 a regular file in the destination tree.
7407 @opindex --no-clobber
7408 Do not overwrite an existing file. The @option{-n} option overrides a previous
7409 @option{-i} option. This option is mutually exclusive with @option{-b} or
7410 @option{--backup} option.
7413 @itemx --no-dereference
7415 @opindex --no-dereference
7416 @cindex symbolic links, copying
7417 Copy symbolic links as symbolic links rather than copying the files that
7418 they point to. This option affects only symbolic links in the source;
7419 symbolic links in the destination are always followed if possible.
7422 @itemx @w{@kbd{--preserve}[=@var{attribute_list}]}
7425 @cindex file information, preserving, extended attributes, xattr
7426 Preserve the specified attributes of the original files.
7427 If specified, the @var{attribute_list} must be a comma-separated list
7428 of one or more of the following strings:
7432 Preserve the file mode bits and access control lists.
7434 Preserve the owner and group. On most modern systems,
7435 only users with appropriate privileges may change the owner of a file,
7437 may preserve the group ownership of a file only if they happen to be
7438 a member of the desired group.
7440 Preserve the times of last access and last modification, when possible.
7441 On older systems, it is not possible to preserve these attributes
7442 when the affected file is a symbolic link.
7443 However, many systems now provide the @code{utimensat} function,
7444 which makes it possible even for symbolic links.
7446 Preserve in the destination files
7447 any links between corresponding source files.
7448 Note that with @option{-L} or @option{-H}, this option can convert
7449 symbolic links to hard links. For example,
7451 $ mkdir c; : > a; ln -s a b; cp -aH a b c; ls -i1 c
7456 Note the inputs: @file{b} is a symlink to regular file @file{a},
7457 yet the files in destination directory, @file{c/}, are hard-linked.
7458 Since @option{-a} implies @option{--preserve=links}, and since @option{-H}
7459 tells @command{cp} to dereference command line arguments, it sees two files
7460 with the same inode number, and preserves the perceived hard link.
7462 Here is a similar example that exercises @command{cp}'s @option{-L} option:
7464 $ mkdir b c; (cd b; : > a; ln -s a b); cp -aL b c; ls -i1 c/b
7470 Preserve SELinux security context of the file. @command{cp} will fail
7471 if the preserving of SELinux security context is not succesful.
7473 Preserve extended attributes if @command{cp} is built with xattr support,
7474 and xattrs are supported and enabled on your file system.
7475 If SELinux context and/or ACLs are implemented using xattrs,
7476 they are preserved by this option as well.
7478 Preserve all file attributes.
7479 Equivalent to specifying all of the above, but with the difference
7480 that failure to preserve SELinux security context or extended attributes
7481 does not change @command{cp}'s exit status.
7482 @command{cp} does diagnose such failures.
7485 Using @option{--preserve} with no @var{attribute_list} is equivalent
7486 to @option{--preserve=mode,ownership,timestamps}.
7488 In the absence of this option, each destination file is created with the
7489 mode bits of the corresponding source file, minus the bits set in the
7490 umask and minus the set-user-ID and set-group-ID bits.
7491 @xref{File permissions}.
7493 @itemx @w{@kbd{--no-preserve}=@var{attribute_list}}
7494 @cindex file information, preserving
7495 Do not preserve the specified attributes. The @var{attribute_list}
7496 has the same form as for @option{--preserve}.
7500 @cindex parent directories and @command{cp}
7501 Form the name of each destination file by appending to the target
7502 directory a slash and the specified name of the source file. The last
7503 argument given to @command{cp} must be the name of an existing directory.
7504 For example, the command:
7507 cp --parents a/b/c existing_dir
7511 copies the file @file{a/b/c} to @file{existing_dir/a/b/c}, creating
7512 any missing intermediate directories.
7519 @opindex --recursive
7520 @cindex directories, copying recursively
7521 @cindex copying directories recursively
7522 @cindex recursively copying directories
7523 @cindex non-directories, copying as special files
7524 Copy directories recursively. By default, do not follow symbolic
7525 links in the source; see the @option{--archive} (@option{-a}), @option{-d},
7526 @option{--dereference} (@option{-L}), @option{--no-dereference}
7527 (@option{-P}), and @option{-H} options. Special files are copied by
7528 creating a destination file of the same type as the source; see the
7529 @option{--copy-contents} option. It is not portable to use
7530 @option{-r} to copy symbolic links or special files. On some
7531 non-@sc{gnu} systems, @option{-r} implies the equivalent of
7532 @option{-L} and @option{--copy-contents} for historical reasons.
7533 Also, it is not portable to use @option{-R} to copy symbolic links
7534 unless you also specify @option{-P}, as @acronym{POSIX} allows
7535 implementations that dereference symbolic links by default.
7537 @item --reflink[=@var{when}]
7538 @opindex --reflink[=@var{when}]
7541 @cindex copy on write
7542 Perform a lightweight, copy-on-write (COW) copy.
7543 Copying with this option can succeed only on some file systems.
7544 Once it has succeeded, beware that the source and destination files
7545 share the same disk data blocks as long as they remain unmodified.
7546 Thus, if a disk I/O error affects data blocks of one of the files,
7547 the other suffers the exact same fate.
7549 The @var{when} value can be one of the following:
7553 The default behavior: if the copy-on-write operation is not supported
7554 then report the failure for each file and exit with a failure status.
7557 If the copy-on-write operation is not supported then fall back
7558 to the standard copy behaviour.
7562 @item --remove-destination
7563 @opindex --remove-destination
7564 Remove each existing destination file before attempting to open it
7565 (contrast with @option{-f} above).
7567 @item --sparse=@var{when}
7568 @opindex --sparse=@var{when}
7569 @cindex sparse files, copying
7570 @cindex holes, copying files with
7571 @findex read @r{system call, and holes}
7572 A @dfn{sparse file} contains @dfn{holes}---a sequence of zero bytes that
7573 does not occupy any physical disk blocks; the @samp{read} system call
7574 reads these as zeros. This can both save considerable disk space and
7575 increase speed, since many binary files contain lots of consecutive zero
7576 bytes. By default, @command{cp} detects holes in input source files via a crude
7577 heuristic and makes the corresponding output file sparse as well.
7578 Only regular files may be sparse.
7580 The @var{when} value can be one of the following:
7584 The default behavior: if the input file is sparse, attempt to make
7585 the output file sparse, too. However, if an output file exists but
7586 refers to a non-regular file, then do not attempt to make it sparse.
7589 For each sufficiently long sequence of zero bytes in the input file,
7590 attempt to create a corresponding hole in the output file, even if the
7591 input file does not appear to be sparse.
7592 This is useful when the input file resides on a file system
7593 that does not support sparse files
7594 (for example, @samp{efs} file systems in SGI IRIX 5.3 and earlier),
7595 but the output file is on a type of file system that does support them.
7596 Holes may be created only in regular files, so if the destination file
7597 is of some other type, @command{cp} does not even try to make it sparse.
7600 Never make the output file sparse.
7601 This is useful in creating a file for use with the @command{mkswap} command,
7602 since such a file must not have any holes.
7605 @optStripTrailingSlashes
7608 @itemx --symbolic-link
7610 @opindex --symbolic-link
7611 @cindex symbolic links, copying with
7612 Make symbolic links instead of copies of non-directories. All source
7613 file names must be absolute (starting with @samp{/}) unless the
7614 destination files are in the current directory. This option merely
7615 results in an error message on systems that do not support symbolic links.
7621 @optNoTargetDirectory
7627 @cindex newer files, copying only
7628 Do not copy a non-directory that has an existing destination with the
7629 same or newer modification time. If time stamps are being preserved,
7630 the comparison is to the source time stamp truncated to the
7631 resolutions of the destination file system and of the system calls
7632 used to update time stamps; this avoids duplicate work if several
7633 @samp{cp -pu} commands are executed with the same source and
7640 Print the name of each file before copying it.
7643 @itemx --one-file-system
7645 @opindex --one-file-system
7646 @cindex file systems, omitting copying to different
7647 Skip subdirectories that are on different file systems from the one that
7648 the copy started on.
7649 However, mount point directories @emph{are} copied.
7657 @section @command{dd}: Convert and copy a file
7660 @cindex converting while copying a file
7662 @command{dd} copies a file (from standard input to standard output, by
7663 default) with a changeable I/O block size, while optionally performing
7664 conversions on it. Synopses:
7667 dd [@var{operand}]@dots{}
7671 The only options are @option{--help} and @option{--version}.
7672 @xref{Common options}. @command{dd} accepts the following operands.
7678 Read from @var{file} instead of standard input.
7682 Write to @var{file} instead of standard output. Unless
7683 @samp{conv=notrunc} is given, @command{dd} truncates @var{file} to zero
7684 bytes (or the size specified with @samp{seek=}).
7686 @item ibs=@var{bytes}
7688 @cindex block size of input
7689 @cindex input block size
7690 Set the input block size to @var{bytes}.
7691 This makes @command{dd} read @var{bytes} per block.
7692 The default is 512 bytes.
7694 @item obs=@var{bytes}
7696 @cindex block size of output
7697 @cindex output block size
7698 Set the output block size to @var{bytes}.
7699 This makes @command{dd} write @var{bytes} per block.
7700 The default is 512 bytes.
7702 @item bs=@var{bytes}
7705 Set both input and output block sizes to @var{bytes}.
7706 This makes @command{dd} read and write @var{bytes} per block,
7707 overriding any @samp{ibs} and @samp{obs} settings.
7708 In addition, if no data-transforming @option{conv} option is specified,
7709 each input block is copied to the output as a single block,
7710 without aggregating short reads.
7712 @item cbs=@var{bytes}
7714 @cindex block size of conversion
7715 @cindex conversion block size
7716 @cindex fixed-length records, converting to variable-length
7717 @cindex variable-length records, converting to fixed-length
7718 Set the conversion block size to @var{bytes}.
7719 When converting variable-length records to fixed-length ones
7720 (@option{conv=block}) or the reverse (@option{conv=unblock}),
7721 use @var{bytes} as the fixed record length.
7723 @item skip=@var{blocks}
7725 Skip @var{blocks} @samp{ibs}-byte blocks in the input file before copying.
7727 @item seek=@var{blocks}
7729 Skip @var{blocks} @samp{obs}-byte blocks in the output file before copying.
7731 @item count=@var{blocks}
7733 Copy @var{blocks} @samp{ibs}-byte blocks from the input file, instead
7734 of everything until the end of the file.
7738 Do not print the overall transfer rate and volume statistics
7739 that normally make up the third status line when @command{dd} exits.
7741 @item conv=@var{conversion}[,@var{conversion}]@dots{}
7743 Convert the file as specified by the @var{conversion} argument(s).
7744 (No spaces around any comma(s).)
7751 @opindex ascii@r{, converting to}
7752 Convert @acronym{EBCDIC} to @acronym{ASCII},
7753 using the conversion table specified by @acronym{POSIX}.
7754 This provides a 1:1 translation for all 256 bytes.
7757 @opindex ebcdic@r{, converting to}
7758 Convert @acronym{ASCII} to @acronym{EBCDIC}.
7759 This is the inverse of the @samp{ascii} conversion.
7762 @opindex alternate ebcdic@r{, converting to}
7763 Convert @acronym{ASCII} to alternate @acronym{EBCDIC},
7764 using the alternate conversion table specified by @acronym{POSIX}.
7765 This is not a 1:1 translation, but reflects common historical practice
7766 for @samp{~}, @samp{[}, and @samp{]}.
7768 The @samp{ascii}, @samp{ebcdic}, and @samp{ibm} conversions are
7772 @opindex block @r{(space-padding)}
7773 For each line in the input, output @samp{cbs} bytes, replacing the
7774 input newline with a space and padding with spaces as necessary.
7778 Remove any trailing spaces in each @samp{cbs}-sized input block,
7779 and append a newline.
7781 The @samp{block} and @samp{unblock} conversions are mutually exclusive.
7784 @opindex lcase@r{, converting to}
7785 Change uppercase letters to lowercase.
7788 @opindex ucase@r{, converting to}
7789 Change lowercase letters to uppercase.
7791 The @samp{lcase} and @samp{ucase} conversions are mutually exclusive.
7794 @opindex swab @r{(byte-swapping)}
7795 @cindex byte-swapping
7796 Swap every pair of input bytes. @sc{gnu} @command{dd}, unlike others, works
7797 when an odd number of bytes are read---the last byte is simply copied
7798 (since there is nothing to swap it with).
7802 @cindex read errors, ignoring
7803 Continue after read errors.
7807 @cindex creating output file, avoiding
7808 Do not create the output file; the output file must already exist.
7812 @cindex creating output file, requiring
7813 Fail if the output file already exists; @command{dd} must create the
7816 The @samp{excl} and @samp{nocreat} conversions are mutually exclusive.
7820 @cindex truncating output file, avoiding
7821 Do not truncate the output file.
7824 @opindex sync @r{(padding with @acronym{ASCII} @sc{nul}s)}
7825 Pad every input block to size of @samp{ibs} with trailing zero bytes.
7826 When used with @samp{block} or @samp{unblock}, pad with spaces instead of
7831 @cindex synchronized data writes, before finishing
7832 Synchronize output data just before finishing. This forces a physical
7833 write of output data.
7837 @cindex synchronized data and metadata writes, before finishing
7838 Synchronize output data and metadata just before finishing. This
7839 forces a physical write of output data and metadata.
7843 @item iflag=@var{flag}[,@var{flag}]@dots{}
7845 Access the input file using the flags specified by the @var{flag}
7846 argument(s). (No spaces around any comma(s).)
7848 @item oflag=@var{flag}[,@var{flag}]@dots{}
7850 Access the output file using the flags specified by the @var{flag}
7851 argument(s). (No spaces around any comma(s).)
7853 Here are the flags. Not every flag is supported on every operating
7860 @cindex appending to the output file
7861 Write in append mode, so that even if some other process is writing to
7862 this file, every @command{dd} write will append to the current
7863 contents of the file. This flag makes sense only for output.
7864 If you combine this flag with the @samp{of=@var{file}} operand,
7865 you should also specify @samp{conv=notrunc} unless you want the
7866 output file to be truncated before being appended to.
7870 @cindex concurrent I/O
7871 Use concurrent I/O mode for data. This mode performs direct I/O
7872 and drops the @acronym{POSIX} requirement to serialize all I/O to the same file.
7873 A file cannot be opened in CIO mode and with a standard open at the
7879 Use direct I/O for data, avoiding the buffer cache.
7880 Note that the kernel may impose restrictions on read or write buffer sizes.
7881 For example, with an ext4 destination file system and a linux-based kernel,
7882 using @samp{oflag=direct} will cause writes to fail with @code{EINVAL} if the
7883 output buffer size is not a multiple of 512.
7887 @cindex directory I/O
7889 Fail unless the file is a directory. Most operating systems do not
7890 allow I/O to a directory, so this flag has limited utility.
7894 @cindex synchronized data reads
7895 Use synchronized I/O for data. For the output file, this forces a
7896 physical write of output data on each write. For the input file,
7897 this flag can matter when reading from a remote file that has been
7898 written to synchronously by some other process. Metadata (e.g.,
7899 last-access and last-modified time) is not necessarily synchronized.
7903 @cindex synchronized data and metadata I/O
7904 Use synchronized I/O for both data and metadata.
7908 @cindex nonblocking I/O
7909 Use non-blocking I/O.
7914 Do not update the file's access time.
7915 Some older file systems silently ignore this flag, so it is a good
7916 idea to test it on your files before relying on it.
7920 @cindex controlling terminal
7921 Do not assign the file to be a controlling terminal for @command{dd}.
7922 This has no effect when the file is not a terminal.
7923 On many hosts (e.g., @acronym{GNU}/Linux hosts), this option has no effect
7928 @cindex symbolic links, following
7929 Do not follow symbolic links.
7934 Fail if the file has multiple hard links.
7939 Use binary I/O. This option has an effect only on nonstandard
7940 platforms that distinguish binary from text I/O.
7945 Use text I/O. Like @samp{binary}, this option has no effect on
7950 Accumulate full blocks from input. The @code{read} system call
7951 may return early if a full block is not available.
7952 When that happens, continue calling @code{read} to fill the remainder
7954 This flag can be used only with @code{iflag}.
7958 These flags are not supported on all systems, and @samp{dd} rejects
7959 attempts to use them when they are not supported. When reading from
7960 standard input or writing to standard output, the @samp{nofollow} and
7961 @samp{noctty} flags should not be specified, and the other flags
7962 (e.g., @samp{nonblock}) can affect how other processes behave with the
7963 affected file descriptors, even after @command{dd} exits.
7967 @cindex multipliers after numbers
7968 The numeric-valued strings above (@var{bytes} and @var{blocks}) can be
7969 followed by a multiplier: @samp{b}=512, @samp{c}=1,
7970 @samp{w}=2, @samp{x@var{m}}=@var{m}, or any of the
7971 standard block size suffixes like @samp{k}=1024 (@pxref{Block size}).
7973 Use different @command{dd} invocations to use different block sizes for
7974 skipping and I/O@. For example, the following shell commands copy data
7975 in 512 KiB blocks between a disk and a tape, but do not save or restore a
7976 4 KiB label at the start of the disk:
7979 disk=/dev/rdsk/c0t1d0s2
7982 # Copy all but the label from disk to tape.
7983 (dd bs=4k skip=1 count=0 && dd bs=512k) <$disk >$tape
7985 # Copy from tape back to disk, but leave the disk label alone.
7986 (dd bs=4k seek=1 count=0 && dd bs=512k) <$tape >$disk
7989 Sending an @samp{INFO} signal to a running @command{dd}
7990 process makes it print I/O statistics to standard error
7991 and then resume copying. In the example below,
7992 @command{dd} is run in the background to copy 10 million blocks.
7993 The @command{kill} command makes it output intermediate I/O statistics,
7994 and when @command{dd} completes normally or is killed by the
7995 @code{SIGINT} signal, it outputs the final statistics.
7998 $ dd if=/dev/zero of=/dev/null count=10MB & pid=$!
7999 $ kill -s INFO $pid; wait $pid
8000 3385223+0 records in
8001 3385223+0 records out
8002 1733234176 bytes (1.7 GB) copied, 6.42173 seconds, 270 MB/s
8003 10000000+0 records in
8004 10000000+0 records out
8005 5120000000 bytes (5.1 GB) copied, 18.913 seconds, 271 MB/s
8008 @vindex POSIXLY_CORRECT
8009 On systems lacking the @samp{INFO} signal @command{dd} responds to the
8010 @samp{USR1} signal instead, unless the @env{POSIXLY_CORRECT}
8011 environment variable is set.
8016 @node install invocation
8017 @section @command{install}: Copy files and set attributes
8020 @cindex copying files and setting attributes
8022 @command{install} copies files while setting their file mode bits and, if
8023 possible, their owner and group. Synopses:
8026 install [@var{option}]@dots{} [-T] @var{source} @var{dest}
8027 install [@var{option}]@dots{} @var{source}@dots{} @var{directory}
8028 install [@var{option}]@dots{} -t @var{directory} @var{source}@dots{}
8029 install [@var{option}]@dots{} -d @var{directory}@dots{}
8034 If two file names are given, @command{install} copies the first file to the
8038 If the @option{--target-directory} (@option{-t}) option is given, or
8039 failing that if the last file is a directory and the
8040 @option{--no-target-directory} (@option{-T}) option is not given,
8041 @command{install} copies each @var{source} file to the specified
8042 directory, using the @var{source}s' names.
8045 If the @option{--directory} (@option{-d}) option is given,
8046 @command{install} creates each @var{directory} and any missing parent
8047 directories. Parent directories are created with mode
8048 @samp{u=rwx,go=rx} (755), regardless of the @option{-m} option or the
8049 current umask. @xref{Directory Setuid and Setgid}, for how the
8050 set-user-ID and set-group-ID bits of parent directories are inherited.
8053 @cindex Makefiles, installing programs in
8054 @command{install} is similar to @command{cp}, but allows you to control the
8055 attributes of destination files. It is typically used in Makefiles to
8056 copy programs into their destination directories. It refuses to copy
8057 files onto themselves.
8059 @cindex extended attributes, xattr
8060 @command{install} never preserves extended attributes (xattr).
8062 The program accepts the following options. Also see @ref{Common options}.
8072 Compare each pair of source and destination files, and if the destination has
8073 identical content and any specified owner, group, permissions, and possibly
8074 SELinux context, then do not modify the destination at all.
8078 Ignored; for compatibility with old Unix versions of @command{install}.
8082 Create any missing parent directories of @var{dest},
8083 then copy @var{source} to @var{dest}.
8084 This option is ignored if a destination directory is specified
8085 via @option{--target-directory=DIR}.
8090 @opindex --directory
8091 @cindex directories, creating with given attributes
8092 @cindex parent directories, creating missing
8093 @cindex leading directories, creating missing
8094 Create any missing parent directories, giving them the default
8095 attributes. Then create each given directory, setting their owner,
8096 group and mode as given on the command line or to the defaults.
8098 @item -g @var{group}
8099 @itemx --group=@var{group}
8102 @cindex group ownership of installed files, setting
8103 Set the group ownership of installed files or directories to
8104 @var{group}. The default is the process's current group. @var{group}
8105 may be either a group name or a numeric group ID.
8108 @itemx --mode=@var{mode}
8111 @cindex permissions of installed files, setting
8112 Set the file mode bits for the installed file or directory to @var{mode},
8113 which can be either an octal number, or a symbolic mode as in
8114 @command{chmod}, with @samp{a=} (no access allowed to anyone) as the
8115 point of departure (@pxref{File permissions}).
8116 The default mode is @samp{u=rwx,go=rx,a-s}---read, write, and
8117 execute for the owner, read and execute for group and other, and with
8118 set-user-ID and set-group-ID disabled.
8119 This default is not quite the same as @samp{755}, since it disables
8120 instead of preserving set-user-ID and set-group-ID on directories.
8121 @xref{Directory Setuid and Setgid}.
8123 @item -o @var{owner}
8124 @itemx --owner=@var{owner}
8127 @cindex ownership of installed files, setting
8128 @cindex appropriate privileges
8129 @vindex root @r{as default owner}
8130 If @command{install} has appropriate privileges (is run as root), set the
8131 ownership of installed files or directories to @var{owner}. The default
8132 is @code{root}. @var{owner} may be either a user name or a numeric user
8135 @item --preserve-context
8136 @opindex --preserve-context
8138 @cindex security context
8139 Preserve the SELinux security context of files and directories.
8140 Failure to preserve the context in all of the files or directories
8141 will result in an exit status of 1. If SELinux is disabled then
8142 print a warning and ignore the option.
8145 @itemx --preserve-timestamps
8147 @opindex --preserve-timestamps
8148 @cindex timestamps of installed files, preserving
8149 Set the time of last access and the time of last modification of each
8150 installed file to match those of each corresponding original file.
8151 When a file is installed without this option, its last access and
8152 last modification times are both set to the time of installation.
8153 This option is useful if you want to use the last modification times
8154 of installed files to keep track of when they were last built as opposed
8155 to when they were last installed.
8161 @cindex symbol table information, stripping
8162 @cindex stripping symbol table information
8163 Strip the symbol tables from installed binary executables.
8165 @itemx --strip-program=@var{program}
8166 @opindex --strip-program
8167 @cindex symbol table information, stripping, program
8168 Program used to strip binaries.
8174 @optNoTargetDirectory
8180 Print the name of each file before copying it.
8182 @item -Z @var{context}
8183 @itemx --context=@var{context}
8187 @cindex security context
8188 Set the default SELinux security context to be used for any
8189 created files and directories. If SELinux is disabled then
8190 print a warning and ignore the option.
8198 @section @command{mv}: Move (rename) files
8202 @command{mv} moves or renames files (or directories). Synopses:
8205 mv [@var{option}]@dots{} [-T] @var{source} @var{dest}
8206 mv [@var{option}]@dots{} @var{source}@dots{} @var{directory}
8207 mv [@var{option}]@dots{} -t @var{directory} @var{source}@dots{}
8212 If two file names are given, @command{mv} moves the first file to the
8216 If the @option{--target-directory} (@option{-t}) option is given, or
8217 failing that if the last file is a directory and the
8218 @option{--no-target-directory} (@option{-T}) option is not given,
8219 @command{mv} moves each @var{source} file to the specified
8220 directory, using the @var{source}s' names.
8223 @command{mv} can move any type of file from one file system to another.
8224 Prior to version @code{4.0} of the fileutils,
8225 @command{mv} could move only regular files between file systems.
8226 For example, now @command{mv} can move an entire directory hierarchy
8227 including special device files from one partition to another. It first
8228 uses some of the same code that's used by @code{cp -a} to copy the
8229 requested directories and files, then (assuming the copy succeeded)
8230 it removes the originals. If the copy fails, then the part that was
8231 copied to the destination partition is removed. If you were to copy
8232 three directories from one partition to another and the copy of the first
8233 directory succeeded, but the second didn't, the first would be left on
8234 the destination partition and the second and third would be left on the
8237 @cindex extended attributes, xattr
8238 @command{mv} always tries to copy extended attributes (xattr).
8240 @cindex prompting, and @command{mv}
8241 If a destination file exists but is normally unwritable, standard input
8242 is a terminal, and the @option{-f} or @option{--force} option is not given,
8243 @command{mv} prompts the user for whether to replace the file. (You might
8244 own the file, or have write permission on its directory.) If the
8245 response is not affirmative, the file is skipped.
8247 @emph{Warning}: Avoid specifying a source name with a trailing slash,
8248 when it might be a symlink to a directory.
8249 Otherwise, @command{mv} may do something very surprising, since
8250 its behavior depends on the underlying rename system call.
8251 On a system with a modern Linux-based kernel, it fails with @code{errno=ENOTDIR}.
8252 However, on other systems (at least FreeBSD 6.1 and Solaris 10) it silently
8253 renames not the symlink but rather the directory referenced by the symlink.
8254 @xref{Trailing slashes}.
8256 The program accepts the following options. Also see @ref{Common options}.
8266 @cindex prompts, omitting
8267 Do not prompt the user before removing a destination file.
8269 If you specify more than one of the @option{-i}, @option{-f}, @option{-n}
8270 options, only the final one takes effect.
8275 @itemx --interactive
8277 @opindex --interactive
8278 @cindex prompts, forcing
8279 Prompt whether to overwrite each existing destination file, regardless
8281 If the response is not affirmative, the file is skipped.
8287 @opindex --no-clobber
8288 @cindex prompts, omitting
8289 Do not overwrite an existing file.
8291 This option is mutually exclusive with @option{-b} or @option{--backup} option.
8297 @cindex newer files, moving only
8298 Do not move a non-directory that has an existing destination with the
8299 same or newer modification time.
8300 If the move is across file system boundaries, the comparison is to the
8301 source time stamp truncated to the resolutions of the destination file
8302 system and of the system calls used to update time stamps; this avoids
8303 duplicate work if several @samp{mv -u} commands are executed with the
8304 same source and destination.
8310 Print the name of each file before moving it.
8312 @optStripTrailingSlashes
8318 @optNoTargetDirectory
8326 @section @command{rm}: Remove files or directories
8329 @cindex removing files or directories
8331 @command{rm} removes each given @var{file}. By default, it does not remove
8332 directories. Synopsis:
8335 rm [@var{option}]@dots{} [@var{file}]@dots{}
8338 @cindex prompting, and @command{rm}
8339 If the @option{-I} or @option{--interactive=once} option is given,
8340 and there are more than three files or the @option{-r}, @option{-R},
8341 or @option{--recursive} are given, then @command{rm} prompts the user
8342 for whether to proceed with the entire operation. If the response is
8343 not affirmative, the entire command is aborted.
8345 Otherwise, if a file is unwritable, standard input is a terminal, and
8346 the @option{-f} or @option{--force} option is not given, or the
8347 @option{-i} or @option{--interactive=always} option @emph{is} given,
8348 @command{rm} prompts the user for whether to remove the file.
8349 If the response is not affirmative, the file is skipped.
8351 Any attempt to remove a file whose last file name component is
8352 @file{.} or @file{..} is rejected without any prompting.
8354 @emph{Warning}: If you use @command{rm} to remove a file, it is usually
8355 possible to recover the contents of that file. If you want more assurance
8356 that the contents are truly unrecoverable, consider using @command{shred}.
8358 The program accepts the following options. Also see @ref{Common options}.
8366 Ignore nonexistent files and never prompt the user.
8367 Ignore any previous @option{--interactive} (@option{-i}) option.
8371 Prompt whether to remove each file.
8372 If the response is not affirmative, the file is skipped.
8373 Ignore any previous @option{--force} (@option{-f}) option.
8374 Equivalent to @option{--interactive=always}.
8378 Prompt once whether to proceed with the command, if more than three
8379 files are named or if a recursive removal is requested. Ignore any
8380 previous @option{--force} (@option{-f}) option. Equivalent to
8381 @option{--interactive=once}.
8383 @itemx --interactive [=@var{when}]
8384 @opindex --interactive
8385 Specify when to issue an interactive prompt. @var{when} may be
8389 @vindex never @r{interactive option}
8390 - Do not prompt at all.
8392 @vindex once @r{interactive option}
8393 - Prompt once if more than three files are named or if a recursive
8394 removal is requested. Equivalent to @option{-I}.
8396 @vindex always @r{interactive option}
8397 - Prompt for every file being removed. Equivalent to @option{-i}.
8399 @option{--interactive} with no @var{when} is equivalent to
8400 @option{--interactive=always}.
8402 @itemx --one-file-system
8403 @opindex --one-file-system
8404 @cindex one file system, restricting @command{rm} to
8405 When removing a hierarchy recursively, skip any directory that is on a
8406 file system different from that of the corresponding command line argument.
8408 This option is useful when removing a build ``chroot'' hierarchy,
8409 which normally contains no valuable data. However, it is not uncommon
8410 to bind-mount @file{/home} into such a hierarchy, to make it easier to
8411 use one's start-up file. The catch is that it's easy to forget to
8412 unmount @file{/home}. Then, when you use @command{rm -rf} to remove
8413 your normally throw-away chroot, that command will remove everything
8414 under @file{/home}, too.
8415 Use the @option{--one-file-system} option, and it will
8416 warn about and skip directories on other file systems.
8417 Of course, this will not save your @file{/home} if it and your
8418 chroot happen to be on the same file system.
8420 @itemx --preserve-root
8421 @opindex --preserve-root
8422 @cindex root directory, disallow recursive destruction
8423 Fail upon any attempt to remove the root directory, @file{/},
8424 when used with the @option{--recursive} option.
8425 This is the default behavior.
8426 @xref{Treating / specially}.
8428 @itemx --no-preserve-root
8429 @opindex --no-preserve-root
8430 @cindex root directory, allow recursive destruction
8431 Do not treat @file{/} specially when removing recursively.
8432 This option is not recommended unless you really want to
8433 remove all the files on your computer.
8434 @xref{Treating / specially}.
8441 @opindex --recursive
8442 @cindex directories, removing (recursively)
8443 Remove the listed directories and their contents recursively.
8449 Print the name of each file before removing it.
8453 @cindex files beginning with @samp{-}, removing
8454 @cindex @samp{-}, removing files beginning with
8455 One common question is how to remove files whose names begin with a
8456 @samp{-}. @sc{gnu} @command{rm}, like every program that uses the @code{getopt}
8457 function to parse its arguments, lets you use the @samp{--} option to
8458 indicate that all following arguments are non-options. To remove a file
8459 called @file{-f} in the current directory, you could type either:
8472 @opindex - @r{and Unix @command{rm}}
8473 The Unix @command{rm} program's use of a single @samp{-} for this purpose
8474 predates the development of the getopt standard syntax.
8479 @node shred invocation
8480 @section @command{shred}: Remove files more securely
8483 @cindex data, erasing
8484 @cindex erasing data
8486 @command{shred} overwrites devices or files, to help prevent even
8487 very expensive hardware from recovering the data.
8489 Ordinarily when you remove a file (@pxref{rm invocation}), the data is
8490 not actually destroyed. Only the index listing where the file is
8491 stored is destroyed, and the storage is made available for reuse.
8492 There are undelete utilities that will attempt to reconstruct the index
8493 and can bring the file back if the parts were not reused.
8495 On a busy system with a nearly-full drive, space can get reused in a few
8496 seconds. But there is no way to know for sure. If you have sensitive
8497 data, you may want to be sure that recovery is not possible by actually
8498 overwriting the file with non-sensitive data.
8500 However, even after doing that, it is possible to take the disk back
8501 to a laboratory and use a lot of sensitive (and expensive) equipment
8502 to look for the faint ``echoes'' of the original data underneath the
8503 overwritten data. If the data has only been overwritten once, it's not
8506 The best way to remove something irretrievably is to destroy the media
8507 it's on with acid, melt it down, or the like. For cheap removable media
8508 like floppy disks, this is the preferred method. However, hard drives
8509 are expensive and hard to melt, so the @command{shred} utility tries
8510 to achieve a similar effect non-destructively.
8512 This uses many overwrite passes, with the data patterns chosen to
8513 maximize the damage they do to the old data. While this will work on
8514 floppies, the patterns are designed for best effect on hard drives.
8515 For more details, see the source code and Peter Gutmann's paper
8516 @uref{http://www.cs.auckland.ac.nz/~pgut001/pubs/secure_del.html,
8517 @cite{Secure Deletion of Data from Magnetic and Solid-State Memory}},
8518 from the proceedings of the Sixth @acronym{USENIX} Security Symposium (San Jose,
8519 California, July 22--25, 1996).
8521 @strong{Please note} that @command{shred} relies on a very important assumption:
8522 that the file system overwrites data in place. This is the traditional
8523 way to do things, but many modern file system designs do not satisfy this
8524 assumption. Exceptions include:
8529 Log-structured or journaled file systems, such as those supplied with
8530 AIX and Solaris, and JFS, ReiserFS, XFS, Ext3 (in @code{data=journal} mode),
8531 BFS, NTFS, etc.@: when they are configured to journal @emph{data}.
8534 File systems that write redundant data and carry on even if some writes
8535 fail, such as RAID-based file systems.
8538 File systems that make snapshots, such as Network Appliance's NFS server.
8541 File systems that cache in temporary locations, such as NFS version 3
8545 Compressed file systems.
8548 In the particular case of ext3 file systems, the above disclaimer applies (and
8549 @command{shred} is thus of limited effectiveness) only in @code{data=journal}
8550 mode, which journals file data in addition to just metadata. In both
8551 the @code{data=ordered} (default) and @code{data=writeback} modes,
8552 @command{shred} works as usual. Ext3 journaling modes can be changed
8553 by adding the @code{data=something} option to the mount options for a
8554 particular file system in the @file{/etc/fstab} file, as documented in
8555 the mount man page (man mount).
8557 If you are not sure how your file system operates, then you should assume
8558 that it does not overwrite data in place, which means that shred cannot
8559 reliably operate on regular files in your file system.
8561 Generally speaking, it is more reliable to shred a device than a file,
8562 since this bypasses the problem of file system design mentioned above.
8563 However, even shredding devices is not always completely reliable. For
8564 example, most disks map out bad sectors invisibly to the application; if
8565 the bad sectors contain sensitive data, @command{shred} won't be able to
8568 @command{shred} makes no attempt to detect or report this problem, just as
8569 it makes no attempt to do anything about backups. However, since it is
8570 more reliable to shred devices than files, @command{shred} by default does
8571 not truncate or remove the output file. This default is more suitable
8572 for devices, which typically cannot be truncated and should not be
8575 Finally, consider the risk of backups and mirrors.
8576 File system backups and remote mirrors may contain copies of the
8577 file that cannot be removed, and that will allow a shredded file
8578 to be recovered later. So if you keep any data you may later want
8579 to destroy using @command{shred}, be sure that it is not backed up or mirrored.
8582 shred [@var{option}]@dots{} @var{file}[@dots{}]
8585 The program accepts the following options. Also see @ref{Common options}.
8593 @cindex force deletion
8594 Override file permissions if necessary to allow overwriting.
8597 @itemx -n @var{number}
8598 @itemx --iterations=@var{number}
8599 @opindex -n @var{number}
8600 @opindex --iterations=@var{number}
8601 @cindex iterations, selecting the number of
8602 By default, @command{shred} uses @value{SHRED_DEFAULT_PASSES} passes of
8603 overwrite. You can reduce this to save time, or increase it if you think it's
8604 appropriate. After 25 passes all of the internal overwrite patterns will have
8605 been used at least once.
8607 @item --random-source=@var{file}
8608 @opindex --random-source
8609 @cindex random source for shredding
8610 Use @var{file} as a source of random data used to overwrite and to
8611 choose pass ordering. @xref{Random sources}.
8613 @item -s @var{bytes}
8614 @itemx --size=@var{bytes}
8615 @opindex -s @var{bytes}
8616 @opindex --size=@var{bytes}
8617 @cindex size of file to shred
8618 Shred the first @var{bytes} bytes of the file. The default is to shred
8619 the whole file. @var{bytes} can be followed by a size specification like
8620 @samp{K}, @samp{M}, or @samp{G} to specify a multiple. @xref{Block size}.
8626 @cindex removing files after shredding
8627 After shredding a file, truncate it (if possible) and then remove it.
8628 If a file has multiple links, only the named links will be removed.
8634 Display to standard error all status updates as sterilization proceeds.
8640 By default, @command{shred} rounds the size of a regular file up to the next
8641 multiple of the file system block size to fully erase the last block of the file.
8642 Use @option{--exact} to suppress that behavior.
8643 Thus, by default if you shred a 10-byte regular file on a system with 512-byte
8644 blocks, the resulting file will be 512 bytes long. With this option,
8645 shred does not increase the apparent size of the file.
8651 Normally, the last pass that @command{shred} writes is made up of
8652 random data. If this would be conspicuous on your hard drive (for
8653 example, because it looks like encrypted data), or you just think
8654 it's tidier, the @option{--zero} option adds an additional overwrite pass with
8655 all zero bits. This is in addition to the number of passes specified
8656 by the @option{--iterations} option.
8660 You might use the following command to erase all trace of the
8661 file system you'd created on the floppy disk in your first drive.
8662 That command takes about 20 minutes to erase a ``1.44MB'' (actually
8666 shred --verbose /dev/fd0
8669 Similarly, to erase all data on a selected partition of
8670 your hard disk, you could give a command like this:
8673 shred --verbose /dev/sda5
8676 A @var{file} of @samp{-} denotes standard output.
8677 The intended use of this is to shred a removed temporary file.
8681 i=`tempfile -m 0600`
8684 echo "Hello, world" >&3
8689 However, the command @samp{shred - >file} does not shred the contents
8690 of @var{file}, since the shell truncates @var{file} before invoking
8691 @command{shred}. Use the command @samp{shred file} or (if using a
8692 Bourne-compatible shell) the command @samp{shred - 1<>file} instead.
8697 @node Special file types
8698 @chapter Special file types
8700 @cindex special file types
8701 @cindex file types, special
8703 This chapter describes commands which create special types of files (and
8704 @command{rmdir}, which removes directories, one special file type).
8706 @cindex special file types
8708 Although Unix-like operating systems have markedly fewer special file
8709 types than others, not @emph{everything} can be treated only as the
8710 undifferentiated byte stream of @dfn{normal files}. For example, when a
8711 file is created or removed, the system must record this information,
8712 which it does in a @dfn{directory}---a special type of file. Although
8713 you can read directories as normal files, if you're curious, in order
8714 for the system to do its job it must impose a structure, a certain
8715 order, on the bytes of the file. Thus it is a ``special'' type of file.
8717 Besides directories, other special file types include named pipes
8718 (FIFOs), symbolic links, sockets, and so-called @dfn{special files}.
8721 * link invocation:: Make a hard link via the link syscall
8722 * ln invocation:: Make links between files.
8723 * mkdir invocation:: Make directories.
8724 * mkfifo invocation:: Make FIFOs (named pipes).
8725 * mknod invocation:: Make block or character special files.
8726 * readlink invocation:: Print value of a symlink or canonical file name.
8727 * rmdir invocation:: Remove empty directories.
8728 * unlink invocation:: Remove files via the unlink syscall
8732 @node link invocation
8733 @section @command{link}: Make a hard link via the link syscall
8736 @cindex links, creating
8737 @cindex hard links, creating
8738 @cindex creating links (hard only)
8740 @command{link} creates a single hard link at a time.
8741 It is a minimalist interface to the system-provided
8742 @code{link} function. @xref{Hard Links, , , libc,
8743 The GNU C Library Reference Manual}.
8744 It avoids the bells and whistles of the more commonly-used
8745 @command{ln} command (@pxref{ln invocation}).
8749 link @var{filename} @var{linkname}
8752 @var{filename} must specify an existing file, and @var{linkname}
8753 must specify a nonexistent entry in an existing directory.
8754 @command{link} simply calls @code{link (@var{filename}, @var{linkname})}
8757 On a @acronym{GNU} system, this command acts like @samp{ln --directory
8758 --no-target-directory @var{filename} @var{linkname}}. However, the
8759 @option{--directory} and @option{--no-target-directory} options are
8760 not specified by @acronym{POSIX}, and the @command{link} command is
8761 more portable in practice.
8767 @section @command{ln}: Make links between files
8770 @cindex links, creating
8771 @cindex hard links, creating
8772 @cindex symbolic (soft) links, creating
8773 @cindex creating links (hard or soft)
8775 @cindex file systems and hard links
8776 @command{ln} makes links between files. By default, it makes hard links;
8777 with the @option{-s} option, it makes symbolic (or @dfn{soft}) links.
8781 ln [@var{option}]@dots{} [-T] @var{target} @var{linkname}
8782 ln [@var{option}]@dots{} @var{target}
8783 ln [@var{option}]@dots{} @var{target}@dots{} @var{directory}
8784 ln [@var{option}]@dots{} -t @var{directory} @var{target}@dots{}
8790 If two file names are given, @command{ln} creates a link to the first
8791 file from the second.
8794 If one @var{target} is given, @command{ln} creates a link to that file
8795 in the current directory.
8798 If the @option{--target-directory} (@option{-t}) option is given, or
8799 failing that if the last file is a directory and the
8800 @option{--no-target-directory} (@option{-T}) option is not given,
8801 @command{ln} creates a link to each @var{target} file in the specified
8802 directory, using the @var{target}s' names.
8806 Normally @command{ln} does not remove existing files. Use the
8807 @option{--force} (@option{-f}) option to remove them unconditionally,
8808 the @option{--interactive} (@option{-i}) option to remove them
8809 conditionally, and the @option{--backup} (@option{-b}) option to
8812 @cindex hard link, defined
8813 @cindex inode, and hard links
8814 A @dfn{hard link} is another name for an existing file; the link and the
8815 original are indistinguishable. Technically speaking, they share the
8816 same inode, and the inode contains all the information about a
8817 file---indeed, it is not incorrect to say that the inode @emph{is} the
8818 file. On all existing implementations, you cannot make a hard link to
8819 a directory, and hard links cannot cross file system boundaries. (These
8820 restrictions are not mandated by @acronym{POSIX}, however.)
8822 @cindex dereferencing symbolic links
8823 @cindex symbolic link, defined
8824 @dfn{Symbolic links} (@dfn{symlinks} for short), on the other hand, are
8825 a special file type (which not all kernels support: System V release 3
8826 (and older) systems lack symlinks) in which the link file actually
8827 refers to a different file, by name. When most operations (opening,
8828 reading, writing, and so on) are passed the symbolic link file, the
8829 kernel automatically @dfn{dereferences} the link and operates on the
8830 target of the link. But some operations (e.g., removing) work on the
8831 link file itself, rather than on its target. The owner, group, and
8832 mode of a symlink are not significant to file access performed through
8833 the link. @xref{Symbolic Links,,,
8834 libc, The GNU C Library Reference Manual}.
8836 Symbolic links can contain arbitrary strings; a @dfn{dangling symlink}
8837 occurs when the string in the symlink does not resolve to a file.
8838 There are no restrictions against creating dangling symbolic links.
8839 There are trade-offs to using absolute or relative symlinks. An
8840 absolute symlink always points to the same file, even if the directory
8841 containing the link is moved. However, if the symlink is visible from
8842 more than one machine (such as on a networked file system), the file
8843 pointed to might not always be the same. A relative symbolic link is
8844 resolved in relation to the directory that contains the link, and is
8845 often useful in referring to files on the same device without regards
8846 to what name that device is mounted on when accessed via networked
8849 When creating a relative symlink in a different location than the
8850 current directory, the resolution of the symlink will be different
8851 than the resolution of the same string from the current directory.
8852 Therefore, many users prefer to first change directories to the
8853 location where the relative symlink will be created, so that
8854 tab-completion or other file resolution will find the same target as
8855 what will be placed in the symlink.
8857 The program accepts the following options. Also see @ref{Common options}.
8868 @opindex --directory
8869 @cindex hard links to directories
8870 Allow users with appropriate privileges to attempt to make hard links
8872 However, note that this will probably fail due to
8873 system restrictions, even for the super-user.
8879 Remove existing destination files.
8882 @itemx --interactive
8884 @opindex --interactive
8885 @cindex prompting, and @command{ln}
8886 Prompt whether to remove existing destination files.
8889 @itemx --no-dereference
8891 @opindex --no-dereference
8892 Do not treat the last operand specially when it is a symbolic link to
8893 a directory. Instead, treat it as if it were a normal file.
8895 When the destination is an actual directory (not a symlink to one),
8896 there is no ambiguity. The link is created in that directory.
8897 But when the specified destination is a symlink to a directory,
8898 there are two ways to treat the user's request. @command{ln} can
8899 treat the destination just as it would a normal directory and create
8900 the link in it. On the other hand, the destination can be viewed as a
8901 non-directory---as the symlink itself. In that case, @command{ln}
8902 must delete or backup that symlink before creating the new link.
8903 The default is to treat a destination that is a symlink to a directory
8904 just like a directory.
8906 This option is weaker than the @option{--no-target-directory}
8907 (@option{-T}) option, so it has no effect if both options are given.
8913 Make symbolic links instead of hard links. This option merely produces
8914 an error message on systems that do not support symbolic links.
8920 @optNoTargetDirectory
8926 Print the name of each file after linking it successfully.
8937 # Create link ../a pointing to a in that directory.
8938 # Not really useful because it points to itself.
8943 # Change to the target before creating symlinks to avoid being confused.
8949 # Hard coded file names don't move well.
8950 ln -s $(pwd)/a /some/dir/
8954 # Relative file names survive directory moves and also
8955 # work across networked file systems.
8956 ln -s afile anotherfile
8957 ln -s ../adir/afile yetanotherfile
8961 @node mkdir invocation
8962 @section @command{mkdir}: Make directories
8965 @cindex directories, creating
8966 @cindex creating directories
8968 @command{mkdir} creates directories with the specified names. Synopsis:
8971 mkdir [@var{option}]@dots{} @var{name}@dots{}
8974 @command{mkdir} creates each directory @var{name} in the order given.
8975 It reports an error if @var{name} already exists, unless the
8976 @option{-p} option is given and @var{name} is a directory.
8978 The program accepts the following options. Also see @ref{Common options}.
8983 @itemx --mode=@var{mode}
8986 @cindex modes of created directories, setting
8987 Set the file permission bits of created directories to @var{mode},
8988 which uses the same syntax as
8989 in @command{chmod} and uses @samp{a=rwx} (read, write and execute allowed for
8990 everyone) for the point of the departure. @xref{File permissions}.
8992 Normally the directory has the desired file mode bits at the moment it
8993 is created. As a @acronym{GNU} extension, @var{mode} may also mention
8994 special mode bits, but in this case there may be a temporary window
8995 during which the directory exists but its special mode bits are
8996 incorrect. @xref{Directory Setuid and Setgid}, for how the
8997 set-user-ID and set-group-ID bits of directories are inherited unless
8998 overridden in this way.
9004 @cindex parent directories, creating
9005 Make any missing parent directories for each argument, setting their
9006 file permission bits to the umask modified by @samp{u+wx}. Ignore
9007 existing parent directories, and do not change their file permission
9010 To set the file permission bits of any newly-created parent
9011 directories to a value that includes @samp{u+wx}, you can set the
9012 umask before invoking @command{mkdir}. For example, if the shell
9013 command @samp{(umask u=rwx,go=rx; mkdir -p P/Q)} creates the parent
9014 @file{P} it sets the parent's permission bits to @samp{u=rwx,go=rx}.
9015 To set a parent's special mode bits as well, you can invoke
9016 @command{chmod} after @command{mkdir}. @xref{Directory Setuid and
9017 Setgid}, for how the set-user-ID and set-group-ID bits of
9018 newly-created parent directories are inherited.
9024 Print a message for each created directory. This is most useful with
9027 @item -Z @var{context}
9028 @itemx --context=@var{context}
9032 @cindex security context
9033 Set the default SELinux security context to be used for created directories.
9040 @node mkfifo invocation
9041 @section @command{mkfifo}: Make FIFOs (named pipes)
9044 @cindex FIFOs, creating
9045 @cindex named pipes, creating
9046 @cindex creating FIFOs (named pipes)
9048 @command{mkfifo} creates FIFOs (also called @dfn{named pipes}) with the
9049 specified names. Synopsis:
9052 mkfifo [@var{option}] @var{name}@dots{}
9055 A @dfn{FIFO} is a special file type that permits independent processes
9056 to communicate. One process opens the FIFO file for writing, and
9057 another for reading, after which data can flow as with the usual
9058 anonymous pipe in shells or elsewhere.
9060 The program accepts the following option. Also see @ref{Common options}.
9065 @itemx --mode=@var{mode}
9068 @cindex modes of created FIFOs, setting
9069 Set the mode of created FIFOs to @var{mode}, which is symbolic as in
9070 @command{chmod} and uses @samp{a=rw} (read and write allowed for everyone)
9071 for the point of departure. @var{mode} should specify only file
9072 permission bits. @xref{File permissions}.
9074 @item -Z @var{context}
9075 @itemx --context=@var{context}
9079 @cindex security context
9080 Set the default SELinux security context to be used for created FIFOs.
9087 @node mknod invocation
9088 @section @command{mknod}: Make block or character special files
9091 @cindex block special files, creating
9092 @cindex character special files, creating
9094 @command{mknod} creates a FIFO, character special file, or block special
9095 file with the specified name. Synopsis:
9098 mknod [@var{option}]@dots{} @var{name} @var{type} [@var{major} @var{minor}]
9101 @cindex special files
9102 @cindex block special files
9103 @cindex character special files
9104 Unlike the phrase ``special file type'' above, the term @dfn{special
9105 file} has a technical meaning on Unix: something that can generate or
9106 receive data. Usually this corresponds to a physical piece of hardware,
9107 e.g., a printer or a disk. (These files are typically created at
9108 system-configuration time.) The @command{mknod} command is what creates
9109 files of this type. Such devices can be read either a character at a
9110 time or a ``block'' (many characters) at a time, hence we say there are
9111 @dfn{block special} files and @dfn{character special} files.
9113 @c mknod is a shell built-in at least with OpenBSD's /bin/sh
9114 @mayConflictWithShellBuiltIn{mknod}
9116 The arguments after @var{name} specify the type of file to make:
9121 @opindex p @r{for FIFO file}
9125 @opindex b @r{for block special file}
9126 for a block special file
9129 @c Don't document the `u' option -- it's just a synonym for `c'.
9130 @c Do *any* versions of mknod still use it?
9132 @opindex c @r{for character special file}
9133 @c @opindex u @r{for character special file}
9134 for a character special file
9138 When making a block or character special file, the major and minor
9139 device numbers must be given after the file type.
9140 If a major or minor device number begins with @samp{0x} or @samp{0X},
9141 it is interpreted as hexadecimal; otherwise, if it begins with @samp{0},
9142 as octal; otherwise, as decimal.
9144 The program accepts the following option. Also see @ref{Common options}.
9149 @itemx --mode=@var{mode}
9152 Set the mode of created files to @var{mode}, which is symbolic as in
9153 @command{chmod} and uses @samp{a=rw} as the point of departure.
9154 @var{mode} should specify only file permission bits.
9155 @xref{File permissions}.
9157 @item -Z @var{context}
9158 @itemx --context=@var{context}
9162 @cindex security context
9163 Set the default SELinux security context to be used for created files.
9170 @node readlink invocation
9171 @section @command{readlink}: Print value of a symlink or canonical file name
9174 @cindex displaying value of a symbolic link
9175 @cindex canonical file name
9176 @cindex canonicalize a file name
9180 @command{readlink} may work in one of two supported modes:
9186 @command{readlink} outputs the value of the given symbolic link.
9187 If @command{readlink} is invoked with an argument other than the name
9188 of a symbolic link, it produces no output and exits with a nonzero exit code.
9190 @item Canonicalize mode
9192 @command{readlink} outputs the absolute name of the given file which contains
9193 no @file{.}, @file{..} components nor any repeated separators
9194 (@file{/}) or symbolic links.
9199 readlink [@var{option}] @var{file}
9202 By default, @command{readlink} operates in readlink mode.
9204 The program accepts the following options. Also see @ref{Common options}.
9209 @itemx --canonicalize
9211 @opindex --canonicalize
9212 Activate canonicalize mode.
9213 If any component of the file name except the last one is missing or unavailable,
9214 @command{readlink} produces no output and exits with a nonzero exit code.
9217 @itemx --canonicalize-existing
9219 @opindex --canonicalize-existing
9220 Activate canonicalize mode.
9221 If any component is missing or unavailable, @command{readlink} produces
9222 no output and exits with a nonzero exit code.
9225 @itemx --canonicalize-missing
9227 @opindex --canonicalize-missing
9228 Activate canonicalize mode.
9229 If any component is missing or unavailable, @command{readlink} treats it
9235 @opindex --no-newline
9236 Do not output the trailing newline.
9246 Suppress most error messages.
9252 Report error messages.
9256 The @command{readlink} utility first appeared in OpenBSD 2.1.
9258 There is a @command{realpath} command on some systems
9259 which operates like @command{readlink} in canonicalize mode.
9264 @node rmdir invocation
9265 @section @command{rmdir}: Remove empty directories
9268 @cindex removing empty directories
9269 @cindex directories, removing empty
9271 @command{rmdir} removes empty directories. Synopsis:
9274 rmdir [@var{option}]@dots{} @var{directory}@dots{}
9277 If any @var{directory} argument does not refer to an existing empty
9278 directory, it is an error.
9280 The program accepts the following options. Also see @ref{Common options}.
9284 @item --ignore-fail-on-non-empty
9285 @opindex --ignore-fail-on-non-empty
9286 @cindex directory deletion, ignoring failures
9287 Ignore each failure to remove a directory that is solely because
9288 the directory is non-empty.
9294 @cindex parent directories, removing
9295 Remove @var{directory}, then try to remove each component of @var{directory}.
9296 So, for example, @samp{rmdir -p a/b/c} is similar to @samp{rmdir a/b/c a/b a}.
9297 As such, it fails if any of those directories turns out not to be empty.
9298 Use the @option{--ignore-fail-on-non-empty} option to make it so such
9299 a failure does not evoke a diagnostic and does not cause @command{rmdir} to
9300 exit unsuccessfully.
9306 @cindex directory deletion, reporting
9307 Give a diagnostic for each successful removal.
9308 @var{directory} is removed.
9312 @xref{rm invocation}, for how to remove non-empty directories (recursively).
9317 @node unlink invocation
9318 @section @command{unlink}: Remove files via the unlink syscall
9321 @cindex removing files or directories (via the unlink syscall)
9323 @command{unlink} deletes a single specified file name.
9324 It is a minimalist interface to the system-provided
9325 @code{unlink} function. @xref{Deleting Files, , , libc,
9326 The GNU C Library Reference Manual}. Synopsis:
9327 It avoids the bells and whistles of the more commonly-used
9328 @command{rm} command (@pxref{rm invocation}).
9331 unlink @var{filename}
9334 On some systems @code{unlink} can be used to delete the name of a
9335 directory. On others, it can be used that way only by a privileged user.
9336 In the GNU system @code{unlink} can never delete the name of a directory.
9338 The @command{unlink} command honors the @option{--help} and
9339 @option{--version} options. To remove a file whose name begins with
9340 @samp{-}, prefix the name with @samp{./}, e.g., @samp{unlink ./--help}.
9345 @node Changing file attributes
9346 @chapter Changing file attributes
9348 @cindex changing file attributes
9349 @cindex file attributes, changing
9350 @cindex attributes, file
9352 A file is not merely its contents, a name, and a file type
9353 (@pxref{Special file types}). A file also has an owner (a user ID), a
9354 group (a group ID), permissions (what the owner can do with the file,
9355 what people in the group can do, and what everyone else can do), various
9356 timestamps, and other information. Collectively, we call these a file's
9359 These commands change file attributes.
9362 * chgrp invocation:: Change file groups.
9363 * chmod invocation:: Change access permissions.
9364 * chown invocation:: Change file owners and groups.
9365 * touch invocation:: Change file timestamps.
9369 @node chown invocation
9370 @section @command{chown}: Change file owner and group
9373 @cindex file ownership, changing
9374 @cindex group ownership, changing
9375 @cindex changing file ownership
9376 @cindex changing group ownership
9378 @command{chown} changes the user and/or group ownership of each given @var{file}
9379 to @var{new-owner} or to the user and group of an existing reference file.
9383 chown [@var{option}]@dots{} @{@var{new-owner} | --reference=@var{ref_file}@} @var{file}@dots{}
9386 If used, @var{new-owner} specifies the new owner and/or group as follows
9387 (with no embedded white space):
9390 [@var{owner}] [ : [@var{group}] ]
9397 If only an @var{owner} (a user name or numeric user ID) is given, that
9398 user is made the owner of each given file, and the files' group is not
9401 @item owner@samp{:}group
9402 If the @var{owner} is followed by a colon and a @var{group} (a
9403 group name or numeric group ID), with no spaces between them, the group
9404 ownership of the files is changed as well (to @var{group}).
9407 If a colon but no group name follows @var{owner}, that user is
9408 made the owner of the files and the group of the files is changed to
9409 @var{owner}'s login group.
9412 If the colon and following @var{group} are given, but the owner
9413 is omitted, only the group of the files is changed; in this case,
9414 @command{chown} performs the same function as @command{chgrp}.
9417 If only a colon is given, or if @var{new-owner} is empty, neither the
9418 owner nor the group is changed.
9422 If @var{owner} or @var{group} is intended to represent a numeric user
9423 or group ID, then you may specify it with a leading @samp{+}.
9424 @xref{Disambiguating names and IDs}.
9426 Some older scripts may still use @samp{.} in place of the @samp{:} separator.
9427 @acronym{POSIX} 1003.1-2001 (@pxref{Standards conformance}) does not
9428 require support for that, but for backward compatibility @acronym{GNU}
9429 @command{chown} supports @samp{.} so long as no ambiguity results.
9430 New scripts should avoid the use of @samp{.} because it is not
9431 portable, and because it has undesirable results if the entire
9432 @var{owner@samp{.}group} happens to identify a user whose name
9435 The @command{chown} command sometimes clears the set-user-ID or
9436 set-group-ID permission bits. This behavior depends on the policy and
9437 functionality of the underlying @code{chown} system call, which may
9438 make system-dependent file mode modifications outside the control of
9439 the @command{chown} command. For example, the @command{chown} command
9440 might not affect those bits when invoked by a user with appropriate
9441 privileges, or when the
9442 bits signify some function other than executable permission (e.g.,
9444 When in doubt, check the underlying system behavior.
9446 The program accepts the following options. Also see @ref{Common options}.
9454 @cindex changed owners, verbosely describing
9455 Verbosely describe the action for each @var{file} whose ownership
9464 @cindex error messages, omitting
9465 Do not print error messages about files whose ownership cannot be
9468 @itemx @w{@kbd{--from}=@var{old-owner}}
9470 @cindex symbolic links, changing owner
9471 Change a @var{file}'s ownership only if it has current attributes specified
9472 by @var{old-owner}. @var{old-owner} has the same form as @var{new-owner}
9474 This option is useful primarily from a security standpoint in that
9475 it narrows considerably the window of potential abuse.
9476 For example, to reflect a user ID numbering change for one user's files
9477 without an option like this, @code{root} might run
9480 find / -owner OLDUSER -print0 | xargs -0 chown -h NEWUSER
9483 But that is dangerous because the interval between when the @command{find}
9484 tests the existing file's owner and when the @command{chown} is actually run
9486 One way to narrow the gap would be to invoke chown for each file
9490 find / -owner OLDUSER -exec chown -h NEWUSER @{@} \;
9493 But that is very slow if there are many affected files.
9494 With this option, it is safer (the gap is narrower still)
9495 though still not perfect:
9498 chown -h -R --from=OLDUSER NEWUSER /
9502 @opindex --dereference
9503 @cindex symbolic links, changing owner
9505 Do not act on symbolic links themselves but rather on what they point to.
9506 This is the default.
9509 @itemx --no-dereference
9511 @opindex --no-dereference
9512 @cindex symbolic links, changing owner
9514 Act on symbolic links themselves instead of what they point to.
9515 This mode relies on the @code{lchown} system call.
9516 On systems that do not provide the @code{lchown} system call,
9517 @command{chown} fails when a file specified on the command line
9519 By default, no diagnostic is issued for symbolic links encountered
9520 during a recursive traversal, but see @option{--verbose}.
9522 @itemx --preserve-root
9523 @opindex --preserve-root
9524 @cindex root directory, disallow recursive modification
9525 Fail upon any attempt to recursively change the root directory, @file{/}.
9526 Without @option{--recursive}, this option has no effect.
9527 @xref{Treating / specially}.
9529 @itemx --no-preserve-root
9530 @opindex --no-preserve-root
9531 @cindex root directory, allow recursive modification
9532 Cancel the effect of any preceding @option{--preserve-root} option.
9533 @xref{Treating / specially}.
9535 @item --reference=@var{ref_file}
9536 @opindex --reference
9537 Change the user and group of each @var{file} to be the same as those of
9538 @var{ref_file}. If @var{ref_file} is a symbolic link, do not use the
9539 user and group of the symbolic link, but rather those of the file it
9546 Output a diagnostic for every file processed.
9547 If a symbolic link is encountered during a recursive traversal
9548 on a system without the @code{lchown} system call, and @option{--no-dereference}
9549 is in effect, then issue a diagnostic saying neither the symbolic link nor
9550 its referent is being changed.
9555 @opindex --recursive
9556 @cindex recursively changing file ownership
9557 Recursively change ownership of directories and their contents.
9560 @xref{Traversing symlinks}.
9563 @xref{Traversing symlinks}.
9566 @xref{Traversing symlinks}.
9575 # Change the owner of /u to "root".
9578 # Likewise, but also change its group to "staff".
9581 # Change the owner of /u and subfiles to "root".
9586 @node chgrp invocation
9587 @section @command{chgrp}: Change group ownership
9590 @cindex group ownership, changing
9591 @cindex changing group ownership
9593 @command{chgrp} changes the group ownership of each given @var{file}
9594 to @var{group} (which can be either a group name or a numeric group ID)
9595 or to the group of an existing reference file. Synopsis:
9598 chgrp [@var{option}]@dots{} @{@var{group} | --reference=@var{ref_file}@} @var{file}@dots{}
9601 If @var{group} is intended to represent a
9602 numeric group ID, then you may specify it with a leading @samp{+}.
9603 @xref{Disambiguating names and IDs}.
9605 The program accepts the following options. Also see @ref{Common options}.
9613 @cindex changed files, verbosely describing
9614 Verbosely describe the action for each @var{file} whose group actually
9623 @cindex error messages, omitting
9624 Do not print error messages about files whose group cannot be
9628 @opindex --dereference
9629 @cindex symbolic links, changing owner
9631 Do not act on symbolic links themselves but rather on what they point to.
9632 This is the default.
9635 @itemx --no-dereference
9637 @opindex --no-dereference
9638 @cindex symbolic links, changing group
9640 Act on symbolic links themselves instead of what they point to.
9641 This mode relies on the @code{lchown} system call.
9642 On systems that do not provide the @code{lchown} system call,
9643 @command{chgrp} fails when a file specified on the command line
9645 By default, no diagnostic is issued for symbolic links encountered
9646 during a recursive traversal, but see @option{--verbose}.
9648 @itemx --preserve-root
9649 @opindex --preserve-root
9650 @cindex root directory, disallow recursive modification
9651 Fail upon any attempt to recursively change the root directory, @file{/}.
9652 Without @option{--recursive}, this option has no effect.
9653 @xref{Treating / specially}.
9655 @itemx --no-preserve-root
9656 @opindex --no-preserve-root
9657 @cindex root directory, allow recursive modification
9658 Cancel the effect of any preceding @option{--preserve-root} option.
9659 @xref{Treating / specially}.
9661 @item --reference=@var{ref_file}
9662 @opindex --reference
9663 Change the group of each @var{file} to be the same as that of
9664 @var{ref_file}. If @var{ref_file} is a symbolic link, do not use the
9665 group of the symbolic link, but rather that of the file it refers to.
9671 Output a diagnostic for every file processed.
9672 If a symbolic link is encountered during a recursive traversal
9673 on a system without the @code{lchown} system call, and @option{--no-dereference}
9674 is in effect, then issue a diagnostic saying neither the symbolic link nor
9675 its referent is being changed.
9680 @opindex --recursive
9681 @cindex recursively changing group ownership
9682 Recursively change the group ownership of directories and their contents.
9685 @xref{Traversing symlinks}.
9688 @xref{Traversing symlinks}.
9691 @xref{Traversing symlinks}.
9700 # Change the group of /u to "staff".
9703 # Change the group of /u and subfiles to "staff".
9708 @node chmod invocation
9709 @section @command{chmod}: Change access permissions
9712 @cindex changing access permissions
9713 @cindex access permissions, changing
9714 @cindex permissions, changing access
9716 @command{chmod} changes the access permissions of the named files. Synopsis:
9719 chmod [@var{option}]@dots{} @{@var{mode} | --reference=@var{ref_file}@} @var{file}@dots{}
9722 @cindex symbolic links, permissions of
9723 @command{chmod} never changes the permissions of symbolic links, since
9724 the @command{chmod} system call cannot change their permissions.
9725 This is not a problem since the permissions of symbolic links are
9726 never used. However, for each symbolic link listed on the command
9727 line, @command{chmod} changes the permissions of the pointed-to file.
9728 In contrast, @command{chmod} ignores symbolic links encountered during
9729 recursive directory traversals.
9731 A successful use of @command{chmod} clears the set-group-ID bit of a
9732 regular file if the file's group ID does not match the user's
9733 effective group ID or one of the user's supplementary group IDs,
9734 unless the user has appropriate privileges. Additional restrictions
9735 may cause the set-user-ID and set-group-ID bits of @var{mode} or
9736 @var{ref_file} to be ignored. This behavior depends on the policy and
9737 functionality of the underlying @code{chmod} system call. When in
9738 doubt, check the underlying system behavior.
9740 If used, @var{mode} specifies the new file mode bits.
9741 For details, see the section on @ref{File permissions}.
9742 If you really want @var{mode} to have a leading @samp{-}, you should
9743 use @option{--} first, e.g., @samp{chmod -- -w file}. Typically,
9744 though, @samp{chmod a-w file} is preferable, and @command{chmod -w
9745 file} (without the @option{--}) complains if it behaves differently
9746 from what @samp{chmod a-w file} would do.
9748 The program accepts the following options. Also see @ref{Common options}.
9756 Verbosely describe the action for each @var{file} whose permissions
9765 @cindex error messages, omitting
9766 Do not print error messages about files whose permissions cannot be
9769 @itemx --preserve-root
9770 @opindex --preserve-root
9771 @cindex root directory, disallow recursive modification
9772 Fail upon any attempt to recursively change the root directory, @file{/}.
9773 Without @option{--recursive}, this option has no effect.
9774 @xref{Treating / specially}.
9776 @itemx --no-preserve-root
9777 @opindex --no-preserve-root
9778 @cindex root directory, allow recursive modification
9779 Cancel the effect of any preceding @option{--preserve-root} option.
9780 @xref{Treating / specially}.
9786 Verbosely describe the action or non-action taken for every @var{file}.
9788 @item --reference=@var{ref_file}
9789 @opindex --reference
9790 Change the mode of each @var{file} to be the same as that of @var{ref_file}.
9791 @xref{File permissions}.
9792 If @var{ref_file} is a symbolic link, do not use the mode
9793 of the symbolic link, but rather that of the file it refers to.
9798 @opindex --recursive
9799 @cindex recursively changing access permissions
9800 Recursively change permissions of directories and their contents.
9807 @node touch invocation
9808 @section @command{touch}: Change file timestamps
9811 @cindex changing file timestamps
9812 @cindex file timestamps, changing
9813 @cindex timestamps, changing file
9815 @command{touch} changes the access and/or modification times of the
9816 specified files. Synopsis:
9819 touch [@var{option}]@dots{} @var{file}@dots{}
9822 @cindex empty files, creating
9823 Any @var{file} argument that does not exist is created empty.
9825 A @var{file} argument string of @samp{-} is handled specially and
9826 causes @command{touch} to change the times of the file associated with
9829 @cindex permissions, for changing file timestamps
9830 If changing both the access and modification times to the current
9831 time, @command{touch} can change the timestamps for files that the user
9832 running it does not own but has write permission for. Otherwise, the
9833 user must own the files.
9835 Although @command{touch} provides options for changing two of the times---the
9836 times of last access and modification---of a file, there is actually
9837 a third one as well: the inode change time. This is often referred to
9838 as a file's @code{ctime}.
9839 The inode change time represents the time when the file's meta-information
9840 last changed. One common example of this is when the permissions of a
9841 file change. Changing the permissions doesn't access the file, so
9842 the atime doesn't change, nor does it modify the file, so the mtime
9843 doesn't change. Yet, something about the file itself has changed,
9844 and this must be noted somewhere. This is the job of the ctime field.
9845 This is necessary, so that, for example, a backup program can make a
9846 fresh copy of the file, including the new permissions value.
9847 Another operation that modifies a file's ctime without affecting
9848 the others is renaming. In any case, it is not possible, in normal
9849 operations, for a user to change the ctime field to a user-specified value.
9852 Time stamps assume the time zone rules specified by the @env{TZ}
9853 environment variable, or by the system default rules if @env{TZ} is
9854 not set. @xref{TZ Variable,, Specifying the Time Zone with @env{TZ},
9855 libc, The GNU C Library Reference Manual}.
9856 You can avoid ambiguities during
9857 daylight saving transitions by using @sc{utc} time stamps.
9859 The program accepts the following options. Also see @ref{Common options}.
9865 @itemx --time=access
9869 @opindex atime@r{, changing}
9870 @opindex access @r{time, changing}
9871 @opindex use @r{time, changing}
9872 Change the access time only.
9877 @opindex --no-create
9878 Do not create files that do not exist.
9881 @itemx --date=@var{time}
9885 Use @var{time} instead of the current time. It can contain month names,
9886 time zones, @samp{am} and @samp{pm}, @samp{yesterday}, etc. For
9887 example, @option{--date="2004-02-27 14:19:13.489392193 +0530"}
9888 specifies the instant of time that is 489,392,193 nanoseconds after
9889 February 27, 2004 at 2:19:13 PM in a time zone that is 5 hours and 30
9890 minutes east of @acronym{UTC}. @xref{Date input formats}.
9891 File systems that do not support high-resolution time stamps
9892 silently ignore any excess precision here.
9896 @cindex BSD @command{touch} compatibility
9897 Ignored; for compatibility with BSD versions of @command{touch}.
9901 @itemx --time=modify
9904 @opindex mtime@r{, changing}
9905 @opindex modify @r{time, changing}
9906 Change the modification time only.
9909 @itemx --reference=@var{file}
9911 @opindex --reference
9912 Use the times of the reference @var{file} instead of the current time.
9913 If this option is combined with the @option{--date=@var{time}}
9914 (@option{-d @var{time}}) option, the reference @var{file}'s time is
9915 the origin for any relative @var{time}s given, but is otherwise ignored.
9916 For example, @samp{-r foo -d '-5 seconds'} specifies a time stamp
9917 equal to five seconds before the corresponding time stamp for @file{foo}.
9919 @item -t [[@var{cc}]@var{yy}]@var{mmddhhmm}[.@var{ss}]
9920 Use the argument (optional four-digit or two-digit years, months,
9921 days, hours, minutes, optional seconds) instead of the current time.
9922 If the year is specified with only two digits, then @var{cc}
9923 is 20 for years in the range 0 @dots{} 68, and 19 for years in
9924 69 @dots{} 99. If no digits of the year are specified,
9925 the argument is interpreted as a date in the current year.
9929 @vindex _POSIX2_VERSION
9930 On older systems, @command{touch} supports an obsolete syntax, as follows.
9931 If no timestamp is given with any of the @option{-d}, @option{-r}, or
9932 @option{-t} options, and if there are two or more @var{file}s and the
9933 first @var{file} is of the form @samp{@var{mmddhhmm}[@var{yy}]} and this
9934 would be a valid argument to the @option{-t} option (if the @var{yy}, if
9935 any, were moved to the front), and if the represented year
9936 is in the range 1969--1999, that argument is interpreted as the time
9937 for the other files instead of as a file name.
9938 This obsolete behavior can be enabled or disabled with the
9939 @env{_POSIX2_VERSION} environment variable (@pxref{Standards
9940 conformance}), but portable scripts should avoid commands whose
9941 behavior depends on this variable.
9942 For example, use @samp{touch ./12312359 main.c} or @samp{touch -t
9943 12312359 main.c} rather than the ambiguous @samp{touch 12312359 main.c}.
9953 No disk can hold an infinite amount of data. These commands report
9954 how much disk storage is in use or available, report other file and
9955 file status information, and write buffers to disk.
9958 * df invocation:: Report file system disk space usage.
9959 * du invocation:: Estimate file space usage.
9960 * stat invocation:: Report file or file system status.
9961 * sync invocation:: Synchronize memory and disk.
9962 * truncate invocation:: Shrink or extend the size of a file.
9967 @section @command{df}: Report file system disk space usage
9970 @cindex file system disk usage
9971 @cindex disk usage by file system
9973 @command{df} reports the amount of disk space used and available on
9974 file systems. Synopsis:
9977 df [@var{option}]@dots{} [@var{file}]@dots{}
9980 With no arguments, @command{df} reports the space used and available on all
9981 currently mounted file systems (of all types). Otherwise, @command{df}
9982 reports on the file system containing each argument @var{file}.
9984 Normally the disk space is printed in units of
9985 1024 bytes, but this can be overridden (@pxref{Block size}).
9986 Non-integer quantities are rounded up to the next higher unit.
9988 @cindex disk device file
9989 @cindex device file, disk
9990 If an argument @var{file} is a disk device file containing a mounted
9991 file system, @command{df} shows the space available on that file system
9992 rather than on the file system containing the device node (i.e., the root
9993 file system). @sc{gnu} @command{df} does not attempt to determine the disk usage
9994 on unmounted file systems, because on most kinds of systems doing so
9995 requires extremely nonportable intimate knowledge of file system
9998 The program accepts the following options. Also see @ref{Common options}.
10006 @cindex automounter file systems
10007 @cindex ignore file systems
10008 Include in the listing dummy file systems, which
10009 are omitted by default. Such file systems are typically special-purpose
10010 pseudo-file-systems, such as automounter entries.
10012 @item -B @var{size}
10013 @itemx --block-size=@var{size}
10015 @opindex --block-size
10016 @cindex file system sizes
10017 Scale sizes by @var{size} before printing them (@pxref{Block size}).
10018 For example, @option{-BG} prints sizes in units of 1,073,741,824 bytes.
10022 @cindex grand total of disk size, usage and available space
10023 Print a grand total of all arguments after all arguments have
10024 been processed. This can be used to find out the total disk size, usage
10025 and available space of all listed devices.
10031 Equivalent to @option{--si}.
10037 @cindex inode usage
10038 List inode usage information instead of block usage. An inode (short
10039 for index node) contains information about a file such as its owner,
10040 permissions, timestamps, and location on the disk.
10044 @cindex kibibytes for file system sizes
10045 Print sizes in 1024-byte blocks, overriding the default block size
10046 (@pxref{Block size}).
10047 This option is equivalent to @option{--block-size=1K}.
10053 @cindex file system types, limiting output to certain
10054 Limit the listing to local file systems. By default, remote file systems
10059 @cindex file system space, retrieving old data more quickly
10060 Do not invoke the @code{sync} system call before getting any usage data.
10061 This may make @command{df} run significantly faster on systems with many
10062 disks, but on some systems (notably SunOS) the results may be slightly
10063 out of date. This is the default.
10066 @itemx --portability
10068 @opindex --portability
10069 @cindex one-line output format
10070 @cindex @acronym{POSIX} output format
10071 @cindex portable output format
10072 @cindex output format, portable
10073 Use the @acronym{POSIX} output format. This is like the default format except
10078 The information about each file system is always printed on exactly
10079 one line; a mount device is never put on a line by itself. This means
10080 that if the mount device name is more than 20 characters long (e.g., for
10081 some network mounts), the columns are misaligned.
10084 The labels in the header output line are changed to conform to @acronym{POSIX}.
10087 The default block size and output format are unaffected by the
10088 @env{DF_BLOCK_SIZE}, @env{BLOCK_SIZE} and @env{BLOCKSIZE} environment
10089 variables. However, the default block size is still affected by
10090 @env{POSIXLY_CORRECT}: it is 512 if @env{POSIXLY_CORRECT} is set, 1024
10091 otherwise. @xref{Block size}.
10098 @cindex file system space, retrieving current data more slowly
10099 Invoke the @code{sync} system call before getting any usage data. On
10100 some systems (notably SunOS), doing this yields more up to date results,
10101 but in general this option makes @command{df} much slower, especially when
10102 there are many or very busy file systems.
10104 @item -t @var{fstype}
10105 @itemx --type=@var{fstype}
10108 @cindex file system types, limiting output to certain
10109 Limit the listing to file systems of type @var{fstype}. Multiple
10110 file system types can be specified by giving multiple @option{-t} options.
10111 By default, nothing is omitted.
10114 @itemx --print-type
10116 @opindex --print-type
10117 @cindex file system types, printing
10118 Print each file system's type. The types printed here are the same ones
10119 you can include or exclude with @option{-t} and @option{-x}. The particular
10120 types printed are whatever is supported by the system. Here are some of
10121 the common names (this list is certainly not exhaustive):
10126 @cindex @acronym{NFS} file system type
10127 An @acronym{NFS} file system, i.e., one mounted over a network from another
10128 machine. This is the one type name which seems to be used uniformly by
10131 @item 4.2@r{, }ufs@r{, }efs@dots{}
10132 @cindex Linux file system types
10133 @cindex local file system types
10134 @opindex 4.2 @r{file system type}
10135 @opindex ufs @r{file system type}
10136 @opindex efs @r{file system type}
10137 A file system on a locally-mounted hard disk. (The system might even
10138 support more than one type here; Linux does.)
10140 @item hsfs@r{, }cdfs
10141 @cindex CD-ROM file system type
10142 @cindex High Sierra file system
10143 @opindex hsfs @r{file system type}
10144 @opindex cdfs @r{file system type}
10145 A file system on a CD-ROM drive. HP-UX uses @samp{cdfs}, most other
10146 systems use @samp{hsfs} (@samp{hs} for ``High Sierra'').
10149 @cindex PC file system
10150 @cindex DOS file system
10151 @cindex MS-DOS file system
10152 @cindex diskette file system
10154 An MS-DOS file system, usually on a diskette.
10158 @item -x @var{fstype}
10159 @itemx --exclude-type=@var{fstype}
10161 @opindex --exclude-type
10162 Limit the listing to file systems not of type @var{fstype}.
10163 Multiple file system types can be eliminated by giving multiple
10164 @option{-x} options. By default, no file system types are omitted.
10167 Ignored; for compatibility with System V versions of @command{df}.
10172 Failure includes the case where no output is generated, so you can
10173 inspect the exit status of a command like @samp{df -t ext3 -t reiserfs
10174 @var{dir}} to test whether @var{dir} is on a file system of type
10175 @samp{ext3} or @samp{reiserfs}.
10178 @node du invocation
10179 @section @command{du}: Estimate file space usage
10182 @cindex file space usage
10183 @cindex disk usage for files
10185 @command{du} reports the amount of disk space used by the specified files
10186 and for each subdirectory (of directory arguments). Synopsis:
10189 du [@var{option}]@dots{} [@var{file}]@dots{}
10192 With no arguments, @command{du} reports the disk space for the current
10193 directory. Normally the disk space is printed in units of
10194 1024 bytes, but this can be overridden (@pxref{Block size}).
10195 Non-integer quantities are rounded up to the next higher unit.
10197 If two or more hard links point to the same file, only one of the hard
10198 links is counted. The @var{file} argument order affects which links
10199 are counted, and changing the argument order may change the numbers
10200 that @command{du} outputs.
10202 The program accepts the following options. Also see @ref{Common options}.
10210 Show counts for all files, not just directories.
10212 @itemx --apparent-size
10213 @opindex --apparent-size
10214 Print apparent sizes, rather than disk usage. The apparent size of a
10215 file is the number of bytes reported by @code{wc -c} on regular files,
10216 or more generally, @code{ls -l --block-size=1} or @code{stat --format=%s}.
10217 For example, a file containing the word @samp{zoo} with no newline would,
10218 of course, have an apparent size of 3. Such a small file may require
10219 anywhere from 0 to 16 KiB or more of disk space, depending on
10220 the type and configuration of the file system on which the file resides.
10221 However, a sparse file created with this command:
10224 dd bs=1 seek=2GiB if=/dev/null of=big
10228 has an apparent size of 2 GiB, yet on most modern
10229 systems, it actually uses almost no disk space.
10235 Equivalent to @code{--apparent-size --block-size=1}.
10237 @item -B @var{size}
10238 @itemx --block-size=@var{size}
10240 @opindex --block-size
10242 Scale sizes by @var{size} before printing them (@pxref{Block size}).
10243 For example, @option{-BG} prints sizes in units of 1,073,741,824 bytes.
10249 @cindex grand total of disk space
10250 Print a grand total of all arguments after all arguments have
10251 been processed. This can be used to find out the total disk usage of
10252 a given set of files or directories.
10255 @itemx --dereference-args
10257 @opindex --dereference-args
10258 Dereference symbolic links that are command line arguments.
10259 Does not affect other symbolic links. This is helpful for finding
10260 out the disk usage of directories, such as @file{/usr/tmp}, which
10261 are often symbolic links.
10263 @c --files0-from=FILE
10264 @filesZeroFromOption{du,, with the @option{--total} (@option{-c}) option}
10270 Equivalent to @option{--dereference-args} (@option{-D}).
10274 @cindex kibibytes for file sizes
10275 Print sizes in 1024-byte blocks, overriding the default block size
10276 (@pxref{Block size}).
10277 This option is equivalent to @option{--block-size=1K}.
10280 @itemx --count-links
10282 @opindex --count-links
10283 @cindex hard links, counting in @command{du}
10284 Count the size of all files, even if they have appeared already (as a
10288 @itemx --dereference
10290 @opindex --dereference
10291 @cindex symbolic links, dereferencing in @command{du}
10292 Dereference symbolic links (show the disk space used by the file
10293 or directory that the link points to instead of the space used by
10298 @cindex mebibytes for file sizes
10299 Print sizes in 1,048,576-byte blocks, overriding the default block size
10300 (@pxref{Block size}).
10301 This option is equivalent to @option{--block-size=1M}.
10304 @itemx --no-dereference
10306 @opindex --no-dereference
10307 @cindex symbolic links, dereferencing in @command{du}
10308 For each symbolic links encountered by @command{du},
10309 consider the disk space used by the symbolic link.
10311 @item --max-depth=@var{depth}
10312 @opindex --max-depth=@var{depth}
10313 @cindex limiting output of @command{du}
10314 Show the total for each directory (and file if --all) that is at
10315 most MAX_DEPTH levels down from the root of the hierarchy. The root
10316 is at level 0, so @code{du --max-depth=0} is equivalent to @code{du -s}.
10322 @cindex output null-byte-terminated lines
10323 Output a zero byte (@acronym{ASCII} @sc{nul}) at the end of each line,
10324 rather than a newline. This option enables other programs to parse the
10325 output of @command{du} even when that output would contain file names
10326 with embedded newlines.
10333 @opindex --summarize
10334 Display only a total for each argument.
10337 @itemx --separate-dirs
10339 @opindex --separate-dirs
10340 Normally, in the output of @command{du} (when not using @option{--summarize}),
10341 the size listed next to a directory name, @var{d}, represents the sum
10342 of sizes of all entries beneath @var{d} as well as the size of @var{d} itself.
10343 With @option{--separate-dirs}, the size reported for a directory name,
10344 @var{d}, is merely the @code{stat.st_size}-derived size of the directory
10349 @cindex last modified dates, displaying in @command{du}
10350 Show time of the most recent modification of any file in the directory,
10351 or any of its subdirectories.
10353 @itemx --time=ctime
10354 @itemx --time=status
10357 @opindex ctime@r{, show the most recent}
10358 @opindex status time@r{, show the most recent}
10359 @opindex use time@r{, show the most recent}
10360 Show the most recent status change time (the @samp{ctime} in the inode) of
10361 any file in the directory, instead of the modification time.
10363 @itemx --time=atime
10364 @itemx --time=access
10366 @opindex atime@r{, show the most recent}
10367 @opindex access time@r{, show the most recent}
10368 Show the most recent access time (the @samp{atime} in the inode) of
10369 any file in the directory, instead of the modification time.
10371 @item --time-style=@var{style}
10372 @opindex --time-style
10374 List timestamps in style @var{style}. This option has an effect only if
10375 the @option{--time} option is also specified. The @var{style} should
10376 be one of the following:
10379 @item +@var{format}
10381 List timestamps using @var{format}, where @var{format} is interpreted
10382 like the format argument of @command{date} (@pxref{date invocation}).
10383 For example, @option{--time-style="+%Y-%m-%d %H:%M:%S"} causes
10384 @command{du} to list timestamps like @samp{2002-03-30 23:45:56}. As
10385 with @command{date}, @var{format}'s interpretation is affected by the
10386 @env{LC_TIME} locale category.
10389 List timestamps in full using @acronym{ISO} 8601 date, time, and time zone
10390 format with nanosecond precision, e.g., @samp{2002-03-30
10391 23:45:56.477817180 -0700}. This style is equivalent to
10392 @samp{+%Y-%m-%d %H:%M:%S.%N %z}.
10395 List @acronym{ISO} 8601 date and time in minutes, e.g.,
10396 @samp{2002-03-30 23:45}. These timestamps are shorter than
10397 @samp{full-iso} timestamps, and are usually good enough for everyday
10398 work. This style is equivalent to @samp{+%Y-%m-%d %H:%M}.
10401 List @acronym{ISO} 8601 dates for timestamps, e.g., @samp{2002-03-30}.
10402 This style is equivalent to @samp{+%Y-%m-%d}.
10406 You can specify the default value of the @option{--time-style} option
10407 with the environment variable @env{TIME_STYLE}; if @env{TIME_STYLE} is not set
10408 the default style is @samp{long-iso}. For compatibility with @command{ls},
10409 if @env{TIME_STYLE} begins with @samp{+} and contains a newline,
10410 the newline and any later characters are ignored; if @env{TIME_STYLE}
10411 begins with @samp{posix-} the @samp{posix-} is ignored; and if
10412 @env{TIME_STYLE} is @samp{locale} it is ignored.
10415 @itemx --one-file-system
10417 @opindex --one-file-system
10418 @cindex one file system, restricting @command{du} to
10419 Skip directories that are on different file systems from the one that
10420 the argument being processed is on.
10422 @item --exclude=@var{pattern}
10423 @opindex --exclude=@var{pattern}
10424 @cindex excluding files from @command{du}
10425 When recursing, skip subdirectories or files matching @var{pattern}.
10426 For example, @code{du --exclude='*.o'} excludes files whose names
10429 @item -X @var{file}
10430 @itemx --exclude-from=@var{file}
10431 @opindex -X @var{file}
10432 @opindex --exclude-from=@var{file}
10433 @cindex excluding files from @command{du}
10434 Like @option{--exclude}, except take the patterns to exclude from @var{file},
10435 one per line. If @var{file} is @samp{-}, take the patterns from standard
10440 @cindex NFS mounts from BSD to HP-UX
10441 On BSD systems, @command{du} reports sizes that are half the correct
10442 values for files that are NFS-mounted from HP-UX systems. On HP-UX
10443 systems, it reports sizes that are twice the correct values for
10444 files that are NFS-mounted from BSD systems. This is due to a flaw
10445 in HP-UX; it also affects the HP-UX @command{du} program.
10450 @node stat invocation
10451 @section @command{stat}: Report file or file system status
10454 @cindex file status
10455 @cindex file system status
10457 @command{stat} displays information about the specified file(s). Synopsis:
10460 stat [@var{option}]@dots{} [@var{file}]@dots{}
10463 With no option, @command{stat} reports all information about the given files.
10464 But it also can be used to report the information of the file systems the
10465 given files are located on. If the files are links, @command{stat} can
10466 also give information about the files the links point to.
10468 @mayConflictWithShellBuiltIn{stat}
10473 @itemx --dereference
10475 @opindex --dereference
10476 @cindex symbolic links, dereferencing in @command{stat}
10477 Change how @command{stat} treats symbolic links.
10478 With this option, @command{stat} acts on the file referenced
10479 by each symbolic link argument.
10480 Without it, @command{stat} acts on any symbolic link argument directly.
10483 @itemx --file-system
10485 @opindex --file-system
10486 @cindex file systems
10487 Report information about the file systems where the given files are located
10488 instead of information about the files themselves.
10491 @itemx --format=@var{format}
10493 @opindex --format=@var{format}
10494 @cindex output format
10495 Use @var{format} rather than the default format.
10496 @var{format} is automatically newline-terminated, so
10497 running a command like the following with two or more @var{file}
10498 operands produces a line of output for each operand:
10500 $ stat --format=%d:%i / /usr
10505 @itemx --printf=@var{format}
10506 @opindex --printf=@var{format}
10507 @cindex output format
10508 Use @var{format} rather than the default format.
10509 Like @option{--format}, but interpret backslash escapes,
10510 and do not output a mandatory trailing newline.
10511 If you want a newline, include @samp{\n} in the @var{format}.
10512 Here's how you would use @option{--printf} to print the device
10513 and inode numbers of @file{/} and @file{/usr}:
10515 $ stat --printf='%d:%i\n' / /usr
10524 @cindex terse output
10525 Print the information in terse form, suitable for parsing by other programs.
10529 The valid @var{format} directives for files with @option{--format} and
10530 @option{--printf} are:
10533 @item %a - Access rights in octal
10534 @item %A - Access rights in human readable form
10535 @item %b - Number of blocks allocated (see @samp{%B})
10536 @item %B - The size in bytes of each block reported by @samp{%b}
10537 @item %d - Device number in decimal
10538 @item %D - Device number in hex
10539 @item %f - Raw mode in hex
10540 @item %F - File type
10541 @item %g - Group ID of owner
10542 @item %G - Group name of owner
10543 @item %h - Number of hard links
10544 @item %i - Inode number
10545 @item %n - File name
10546 @item %N - Quoted file name with dereference if symbolic link
10547 @item %o - I/O block size
10548 @item %s - Total size, in bytes
10549 @item %t - Major device type in hex
10550 @item %T - Minor device type in hex
10551 @item %u - User ID of owner
10552 @item %U - User name of owner
10553 @item %x - Time of last access
10554 @item %X - Time of last access as seconds since Epoch
10555 @item %y - Time of last modification
10556 @item %Y - Time of last modification as seconds since Epoch
10557 @item %z - Time of last change
10558 @item %Z - Time of last change as seconds since Epoch
10561 When listing file system information (@option{--file-system} (@option{-f})),
10562 you must use a different set of @var{format} directives:
10565 @item %a - Free blocks available to non-super-user
10566 @item %b - Total data blocks in file system
10567 @item %c - Total file nodes in file system
10568 @item %d - Free file nodes in file system
10569 @item %f - Free blocks in file system
10570 @item %i - File System ID in hex
10571 @item %l - Maximum length of file names
10572 @item %n - File name
10573 @item %s - Block size (for faster transfers)
10574 @item %S - Fundamental block size (for block counts)
10575 @item %t - Type in hex
10576 @item %T - Type in human readable form
10580 Time stamps are listed according to the time zone rules specified by
10581 the @env{TZ} environment variable, or by the system default rules if
10582 @env{TZ} is not set. @xref{TZ Variable,, Specifying the Time Zone
10583 with @env{TZ}, libc, The GNU C Library Reference Manual}.
10588 @node sync invocation
10589 @section @command{sync}: Synchronize data on disk with memory
10592 @cindex synchronize disk and memory
10594 @cindex superblock, writing
10595 @cindex inodes, written buffered
10596 @command{sync} writes any data buffered in memory out to disk. This can
10597 include (but is not limited to) modified superblocks, modified inodes,
10598 and delayed reads and writes. This must be implemented by the kernel;
10599 The @command{sync} program does nothing but exercise the @code{sync} system
10602 @cindex crashes and corruption
10603 The kernel keeps data in memory to avoid doing (relatively slow) disk
10604 reads and writes. This improves performance, but if the computer
10605 crashes, data may be lost or the file system corrupted as a
10606 result. The @command{sync} command ensures everything in memory
10607 is written to disk.
10609 Any arguments are ignored, except for a lone @option{--help} or
10610 @option{--version} (@pxref{Common options}).
10615 @node truncate invocation
10616 @section @command{truncate}: Shrink or extend the size of a file
10619 @cindex truncating, file sizes
10621 @command{truncate} shrinks or extends the size of each @var{file} to the
10622 specified size. Synopsis:
10625 truncate @var{option}@dots{} @var{file}@dots{}
10628 @cindex files, creating
10629 Any @var{file} that does not exist is created.
10631 @cindex sparse files, creating
10632 @cindex holes, creating files with
10633 If a @var{file} is larger than the specified size, the extra data is lost.
10634 If a @var{file} is shorter, it is extended and the extended part (or hole)
10635 reads as zero bytes.
10637 The program accepts the following options. Also see @ref{Common options}.
10644 @opindex --no-create
10645 Do not create files that do not exist.
10650 @opindex --io-blocks
10651 Treat @var{size} as number of I/O blocks of the @var{file} rather than bytes.
10653 @item -r @var{rfile}
10654 @itemx --reference=@var{rfile}
10656 @opindex --reference
10657 Set the size of each @var{file} to the same size as @var{rfile}.
10659 @item -s @var{size}
10660 @itemx --size=@var{size}
10663 Set the size of each @var{file} to this @var{size}.
10664 @multiplierSuffixesNoBlocks{size}
10666 @var{size} may also be prefixed by one of the following to adjust
10667 the size of each @var{file} based on their current size:
10669 @samp{+} => extend by
10670 @samp{-} => reduce by
10671 @samp{<} => at most
10672 @samp{>} => at least
10673 @samp{/} => round down to multiple of
10674 @samp{%} => round up to multiple of
10682 @node Printing text
10683 @chapter Printing text
10685 @cindex printing text, commands for
10686 @cindex commands for printing text
10688 This section describes commands that display text strings.
10691 * echo invocation:: Print a line of text.
10692 * printf invocation:: Format and print data.
10693 * yes invocation:: Print a string until interrupted.
10697 @node echo invocation
10698 @section @command{echo}: Print a line of text
10701 @cindex displaying text
10702 @cindex printing text
10703 @cindex text, displaying
10704 @cindex arbitrary text, displaying
10706 @command{echo} writes each given @var{string} to standard output, with a
10707 space between each and a newline after the last one. Synopsis:
10710 echo [@var{option}]@dots{} [@var{string}]@dots{}
10713 @mayConflictWithShellBuiltIn{echo}
10715 The program accepts the following options. Also see @ref{Common options}.
10716 Options must precede operands, and the normally-special argument
10717 @samp{--} has no special meaning and is treated like any other
10723 Do not output the trailing newline.
10727 @cindex backslash escapes
10728 Enable interpretation of the following backslash-escaped characters in
10737 produce no further output
10751 the eight-bit value that is the octal number @var{nnn}
10752 (zero to three octal digits)
10754 the eight-bit value that is the octal number @var{nnn}
10755 (one to three octal digits)
10757 the eight-bit value that is the hexadecimal number @var{hh}
10758 (one or two hexadecimal digits)
10763 @cindex backslash escapes
10764 Disable interpretation of backslash escapes in each @var{string}.
10765 This is the default. If @option{-e} and @option{-E} are both
10766 specified, the last one given takes effect.
10770 @vindex POSIXLY_CORRECT
10771 If the @env{POSIXLY_CORRECT} environment variable is set, then when
10772 @command{echo}'s first argument is not @option{-n} it outputs
10773 option-like arguments instead of treating them as options. For
10774 example, @code{echo -ne hello} outputs @samp{-ne hello} instead of
10775 plain @samp{hello}.
10777 @acronym{POSIX} does not require support for any options, and says
10778 that the behavior of @command{echo} is implementation-defined if any
10779 @var{string} contains a backslash or if the first argument is
10780 @option{-n}. Portable programs can use the @command{printf} command
10781 if they need to omit trailing newlines or output control characters or
10782 backslashes. @xref{printf invocation}.
10787 @node printf invocation
10788 @section @command{printf}: Format and print data
10791 @command{printf} does formatted printing of text. Synopsis:
10794 printf @var{format} [@var{argument}]@dots{}
10797 @command{printf} prints the @var{format} string, interpreting @samp{%}
10798 directives and @samp{\} escapes to format numeric and string arguments
10799 in a way that is mostly similar to the C @samp{printf} function.
10800 @xref{Output Conversion Syntax,, @command{printf} format directives,
10801 libc, The GNU C Library Reference Manual}, for details.
10802 The differences are listed below.
10804 @mayConflictWithShellBuiltIn{printf}
10809 The @var{format} argument is reused as necessary to convert all the
10810 given @var{argument}s. For example, the command @samp{printf %s a b}
10814 Missing @var{argument}s are treated as null strings or as zeros,
10815 depending on whether the context expects a string or a number. For
10816 example, the command @samp{printf %sx%d} prints @samp{x0}.
10820 An additional escape, @samp{\c}, causes @command{printf} to produce no
10821 further output. For example, the command @samp{printf 'A%sC\cD%sF' B
10822 E} prints @samp{ABC}.
10825 The hexadecimal escape sequence @samp{\x@var{hh}} has at most two
10826 digits, as opposed to C where it can have an unlimited number of
10827 digits. For example, the command @samp{printf '\x07e'} prints two
10828 bytes, whereas the C statement @samp{printf ("\x07e")} prints just
10833 @command{printf} has an additional directive, @samp{%b}, which prints its
10834 argument string with @samp{\} escapes interpreted in the same way as in
10835 the @var{format} string, except that octal escapes are of the form
10836 @samp{\0@var{ooo}} where @var{ooo} is 0 to 3 octal digits.
10837 If a precision is also given, it limits the number of bytes printed
10838 from the converted string.
10841 Numeric arguments must be single C constants, possibly with leading
10842 @samp{+} or @samp{-}. For example, @samp{printf %.4d -3} outputs
10846 @vindex POSIXLY_CORRECT
10847 If the leading character of a numeric argument is @samp{"} or @samp{'}
10848 then its value is the numeric value of the immediately following
10849 character. Any remaining characters are silently ignored if the
10850 @env{POSIXLY_CORRECT} environment variable is set; otherwise, a
10851 warning is printed. For example, @samp{printf "%d" "'a"} outputs
10852 @samp{97} on hosts that use the @acronym{ASCII} character set, since
10853 @samp{a} has the numeric value 97 in @acronym{ASCII}.
10858 A floating-point argument must use a period before any fractional
10859 digits, but is printed according to the @env{LC_NUMERIC} category of the
10860 current locale. For example, in a locale whose radix character is a
10861 comma, the command @samp{printf %g 3.14} outputs @samp{3,14} whereas
10862 the command @samp{printf %g 3,14} is an error.
10866 @command{printf} interprets @samp{\@var{ooo}} in @var{format} as an octal number
10867 (if @var{ooo} is 1 to 3 octal digits) specifying a character to print,
10868 and @samp{\x@var{hh}} as a hexadecimal number (if @var{hh} is 1 to 2 hex
10869 digits) specifying a character to print.
10874 @cindex ISO/IEC 10646
10876 @command{printf} interprets two character syntaxes introduced in
10877 @acronym{ISO} C 99:
10878 @samp{\u} for 16-bit Unicode (@acronym{ISO}/@acronym{IEC} 10646)
10879 characters, specified as
10880 four hexadecimal digits @var{hhhh}, and @samp{\U} for 32-bit Unicode
10881 characters, specified as eight hexadecimal digits @var{hhhhhhhh}.
10882 @command{printf} outputs the Unicode characters
10883 according to the @env{LC_CTYPE} locale. Unicode characters in the ranges
10884 U+0000...U+009F, U+D800...U+DFFF cannot be specified by this syntax, except
10885 for U+0024 ($), U+0040 (@@), and U+0060 (@`).
10887 The processing of @samp{\u} and @samp{\U} requires a full-featured
10888 @code{iconv} facility. It is activated on systems with glibc 2.2 (or newer),
10889 or when @code{libiconv} is installed prior to this package. Otherwise
10890 @samp{\u} and @samp{\U} will print as-is.
10892 The only options are a lone @option{--help} or
10893 @option{--version}. @xref{Common options}.
10894 Options must precede operands.
10896 The Unicode character syntaxes are useful for writing strings in a locale
10897 independent way. For example, a string containing the Euro currency symbol
10900 $ env printf '\u20AC 14.95'
10904 will be output correctly in all locales supporting the Euro symbol
10905 (@acronym{ISO}-8859-15, UTF-8, and others). Similarly, a Chinese string
10908 $ env printf '\u4e2d\u6587'
10912 will be output correctly in all Chinese locales (GB2312, BIG5, UTF-8, etc).
10914 Note that in these examples, the @command{printf} command has been
10915 invoked via @command{env} to ensure that we run the program found via
10916 your shell's search path, and not a shell alias or a built-in function.
10918 For larger strings, you don't need to look up the hexadecimal code
10919 values of each character one by one. @acronym{ASCII} characters mixed with \u
10920 escape sequences is also known as the JAVA source file encoding. You can
10921 use GNU recode 3.5c (or newer) to convert strings to this encoding. Here
10922 is how to convert a piece of text into a shell script which will output
10923 this text in a locale-independent way:
10926 $ LC_CTYPE=zh_CN.big5 /usr/local/bin/printf \
10927 '\u4e2d\u6587\n' > sample.txt
10928 $ recode BIG5..JAVA < sample.txt \
10929 | sed -e "s|^|/usr/local/bin/printf '|" -e "s|$|\\\\n'|" \
10936 @node yes invocation
10937 @section @command{yes}: Print a string until interrupted
10940 @cindex repeated output of a string
10942 @command{yes} prints the command line arguments, separated by spaces and
10943 followed by a newline, forever until it is killed. If no arguments are
10944 given, it prints @samp{y} followed by a newline forever until killed.
10946 Upon a write error, @command{yes} exits with status @samp{1}.
10948 The only options are a lone @option{--help} or @option{--version}.
10949 To output an argument that begins with
10950 @samp{-}, precede it with @option{--}, e.g., @samp{yes -- --help}.
10951 @xref{Common options}.
10955 @chapter Conditions
10958 @cindex commands for exit status
10959 @cindex exit status commands
10961 This section describes commands that are primarily useful for their exit
10962 status, rather than their output. Thus, they are often used as the
10963 condition of shell @code{if} statements, or as the last command in a
10967 * false invocation:: Do nothing, unsuccessfully.
10968 * true invocation:: Do nothing, successfully.
10969 * test invocation:: Check file types and compare values.
10970 * expr invocation:: Evaluate expressions.
10974 @node false invocation
10975 @section @command{false}: Do nothing, unsuccessfully
10978 @cindex do nothing, unsuccessfully
10979 @cindex failure exit status
10980 @cindex exit status of @command{false}
10982 @command{false} does nothing except return an exit status of 1, meaning
10983 @dfn{failure}. It can be used as a place holder in shell scripts
10984 where an unsuccessful command is needed.
10985 In most modern shells, @command{false} is a built-in command, so when
10986 you use @samp{false} in a script, you're probably using the built-in
10987 command, not the one documented here.
10989 @command{false} honors the @option{--help} and @option{--version} options.
10991 This version of @command{false} is implemented as a C program, and is thus
10992 more secure and faster than a shell script implementation, and may safely
10993 be used as a dummy shell for the purpose of disabling accounts.
10995 Note that @command{false} (unlike all other programs documented herein)
10996 exits unsuccessfully, even when invoked with
10997 @option{--help} or @option{--version}.
10999 Portable programs should not assume that the exit status of
11000 @command{false} is 1, as it is greater than 1 on some
11001 non-@acronym{GNU} hosts.
11004 @node true invocation
11005 @section @command{true}: Do nothing, successfully
11008 @cindex do nothing, successfully
11010 @cindex successful exit
11011 @cindex exit status of @command{true}
11013 @command{true} does nothing except return an exit status of 0, meaning
11014 @dfn{success}. It can be used as a place holder in shell scripts
11015 where a successful command is needed, although the shell built-in
11016 command @code{:} (colon) may do the same thing faster.
11017 In most modern shells, @command{true} is a built-in command, so when
11018 you use @samp{true} in a script, you're probably using the built-in
11019 command, not the one documented here.
11021 @command{true} honors the @option{--help} and @option{--version} options.
11023 Note, however, that it is possible to cause @command{true}
11024 to exit with nonzero status: with the @option{--help} or @option{--version}
11025 option, and with standard
11026 output already closed or redirected to a file that evokes an I/O error.
11027 For example, using a Bourne-compatible shell:
11030 $ ./true --version >&-
11031 ./true: write error: Bad file number
11032 $ ./true --version > /dev/full
11033 ./true: write error: No space left on device
11036 This version of @command{true} is implemented as a C program, and is thus
11037 more secure and faster than a shell script implementation, and may safely
11038 be used as a dummy shell for the purpose of disabling accounts.
11040 @node test invocation
11041 @section @command{test}: Check file types and compare values
11044 @cindex check file types
11045 @cindex compare values
11046 @cindex expression evaluation
11048 @command{test} returns a status of 0 (true) or 1 (false) depending on the
11049 evaluation of the conditional expression @var{expr}. Each part of the
11050 expression must be a separate argument.
11052 @command{test} has file status checks, string operators, and numeric
11053 comparison operators.
11055 @command{test} has an alternate form that uses opening and closing
11056 square brackets instead a leading @samp{test}. For example, instead
11057 of @samp{test -d /}, you can write @samp{[ -d / ]}. The square
11058 brackets must be separate arguments; for example, @samp{[-d /]} does
11059 not have the desired effect. Since @samp{test @var{expr}} and @samp{[
11060 @var{expr} ]} have the same meaning, only the former form is discussed
11066 test @var{expression}
11068 [ @var{expression} ]
11073 @mayConflictWithShellBuiltIn{test}
11075 If @var{expression} is omitted, @command{test} returns false.
11076 If @var{expression} is a single argument,
11077 @command{test} returns false if the argument is null and true otherwise. The argument
11078 can be any string, including strings like @samp{-d}, @samp{-1},
11079 @samp{--}, @samp{--help}, and @samp{--version} that most other
11080 programs would treat as options. To get help and version information,
11081 invoke the commands @samp{[ --help} and @samp{[ --version}, without
11082 the usual closing brackets. @xref{Common options}.
11084 @cindex exit status of @command{test}
11088 0 if the expression is true,
11089 1 if the expression is false,
11090 2 if an error occurred.
11094 * File type tests:: -[bcdfhLpSt]
11095 * Access permission tests:: -[gkruwxOG]
11096 * File characteristic tests:: -e -s -nt -ot -ef
11097 * String tests:: -z -n = !=
11098 * Numeric tests:: -eq -ne -lt -le -gt -ge
11099 * Connectives for test:: ! -a -o
11103 @node File type tests
11104 @subsection File type tests
11106 @cindex file type tests
11108 These options test for particular types of files. (Everything's a file,
11109 but not all files are the same!)
11113 @item -b @var{file}
11115 @cindex block special check
11116 True if @var{file} exists and is a block special device.
11118 @item -c @var{file}
11120 @cindex character special check
11121 True if @var{file} exists and is a character special device.
11123 @item -d @var{file}
11125 @cindex directory check
11126 True if @var{file} exists and is a directory.
11128 @item -f @var{file}
11130 @cindex regular file check
11131 True if @var{file} exists and is a regular file.
11133 @item -h @var{file}
11134 @itemx -L @var{file}
11137 @cindex symbolic link check
11138 True if @var{file} exists and is a symbolic link.
11139 Unlike all other file-related tests, this test does not dereference
11140 @var{file} if it is a symbolic link.
11142 @item -p @var{file}
11144 @cindex named pipe check
11145 True if @var{file} exists and is a named pipe.
11147 @item -S @var{file}
11149 @cindex socket check
11150 True if @var{file} exists and is a socket.
11154 @cindex terminal check
11155 True if @var{fd} is a file descriptor that is associated with a
11161 @node Access permission tests
11162 @subsection Access permission tests
11164 @cindex access permission tests
11165 @cindex permission tests
11167 These options test for particular access permissions.
11171 @item -g @var{file}
11173 @cindex set-group-ID check
11174 True if @var{file} exists and has its set-group-ID bit set.
11176 @item -k @var{file}
11178 @cindex sticky bit check
11179 True if @var{file} exists and has its @dfn{sticky} bit set.
11181 @item -r @var{file}
11183 @cindex readable file check
11184 True if @var{file} exists and read permission is granted.
11186 @item -u @var{file}
11188 @cindex set-user-ID check
11189 True if @var{file} exists and has its set-user-ID bit set.
11191 @item -w @var{file}
11193 @cindex writable file check
11194 True if @var{file} exists and write permission is granted.
11196 @item -x @var{file}
11198 @cindex executable file check
11199 True if @var{file} exists and execute permission is granted
11200 (or search permission, if it is a directory).
11202 @item -O @var{file}
11204 @cindex owned by effective user ID check
11205 True if @var{file} exists and is owned by the current effective user ID.
11207 @item -G @var{file}
11209 @cindex owned by effective group ID check
11210 True if @var{file} exists and is owned by the current effective group ID.
11214 @node File characteristic tests
11215 @subsection File characteristic tests
11217 @cindex file characteristic tests
11219 These options test other file characteristics.
11223 @item -e @var{file}
11225 @cindex existence-of-file check
11226 True if @var{file} exists.
11228 @item -s @var{file}
11230 @cindex nonempty file check
11231 True if @var{file} exists and has a size greater than zero.
11233 @item @var{file1} -nt @var{file2}
11235 @cindex newer-than file check
11236 True if @var{file1} is newer (according to modification date) than
11237 @var{file2}, or if @var{file1} exists and @var{file2} does not.
11239 @item @var{file1} -ot @var{file2}
11241 @cindex older-than file check
11242 True if @var{file1} is older (according to modification date) than
11243 @var{file2}, or if @var{file2} exists and @var{file1} does not.
11245 @item @var{file1} -ef @var{file2}
11247 @cindex same file check
11248 @cindex hard link check
11249 True if @var{file1} and @var{file2} have the same device and inode
11250 numbers, i.e., if they are hard links to each other.
11256 @subsection String tests
11258 @cindex string tests
11260 These options test string characteristics. You may need to quote
11261 @var{string} arguments for the shell. For example:
11267 The quotes here prevent the wrong arguments from being passed to
11268 @command{test} if @samp{$V} is empty or contains special characters.
11272 @item -z @var{string}
11274 @cindex zero-length string check
11275 True if the length of @var{string} is zero.
11277 @item -n @var{string}
11278 @itemx @var{string}
11280 @cindex nonzero-length string check
11281 True if the length of @var{string} is nonzero.
11283 @item @var{string1} = @var{string2}
11285 @cindex equal string check
11286 True if the strings are equal.
11288 @item @var{string1} != @var{string2}
11290 @cindex not-equal string check
11291 True if the strings are not equal.
11296 @node Numeric tests
11297 @subsection Numeric tests
11299 @cindex numeric tests
11300 @cindex arithmetic tests
11302 Numeric relational operators. The arguments must be entirely numeric
11303 (possibly negative), or the special expression @w{@code{-l @var{string}}},
11304 which evaluates to the length of @var{string}.
11308 @item @var{arg1} -eq @var{arg2}
11309 @itemx @var{arg1} -ne @var{arg2}
11310 @itemx @var{arg1} -lt @var{arg2}
11311 @itemx @var{arg1} -le @var{arg2}
11312 @itemx @var{arg1} -gt @var{arg2}
11313 @itemx @var{arg1} -ge @var{arg2}
11320 These arithmetic binary operators return true if @var{arg1} is equal,
11321 not-equal, less-than, less-than-or-equal, greater-than, or
11322 greater-than-or-equal than @var{arg2}, respectively.
11329 test -1 -gt -2 && echo yes
11331 test -l abc -gt 1 && echo yes
11334 @error{} test: integer expression expected before -eq
11338 @node Connectives for test
11339 @subsection Connectives for @command{test}
11341 @cindex logical connectives
11342 @cindex connectives, logical
11344 The usual logical connectives.
11350 True if @var{expr} is false.
11352 @item @var{expr1} -a @var{expr2}
11354 @cindex logical and operator
11355 @cindex and operator
11356 True if both @var{expr1} and @var{expr2} are true.
11358 @item @var{expr1} -o @var{expr2}
11360 @cindex logical or operator
11361 @cindex or operator
11362 True if either @var{expr1} or @var{expr2} is true.
11367 @node expr invocation
11368 @section @command{expr}: Evaluate expressions
11371 @cindex expression evaluation
11372 @cindex evaluation of expressions
11374 @command{expr} evaluates an expression and writes the result on standard
11375 output. Each token of the expression must be a separate argument.
11377 Operands are either integers or strings. Integers consist of one or
11378 more decimal digits, with an optional leading @samp{-}.
11379 @command{expr} converts
11380 anything appearing in an operand position to an integer or a string
11381 depending on the operation being applied to it.
11383 Strings are not quoted for @command{expr} itself, though you may need to
11384 quote them to protect characters with special meaning to the shell,
11385 e.g., spaces. However, regardless of whether it is quoted, a string
11386 operand should not be a parenthesis or any of @command{expr}'s
11387 operators like @code{+}, so you cannot safely pass an arbitrary string
11388 @code{$str} to expr merely by quoting it to the shell. One way to
11389 work around this is to use the @sc{gnu} extension @code{+},
11390 (e.g., @code{+ "$str" = foo}); a more portable way is to use
11391 @code{@w{" $str"}} and to adjust the rest of the expression to take
11392 the leading space into account (e.g., @code{@w{" $str" = " foo"}}).
11394 You should not pass a negative integer or a string with leading
11395 @samp{-} as @command{expr}'s first argument, as it might be
11396 misinterpreted as an option; this can be avoided by parenthesization.
11397 Also, portable scripts should not use a string operand that happens to
11398 take the form of an integer; this can be worked around by inserting
11399 leading spaces as mentioned above.
11401 @cindex parentheses for grouping
11402 Operators may be given as infix symbols or prefix keywords. Parentheses
11403 may be used for grouping in the usual manner. You must quote
11404 parentheses and many operators to avoid the shell evaluating them,
11407 When built with support for the GNU MP library, @command{expr} uses
11408 arbitrary-precision arithmetic; otherwise, it uses native arithmetic
11409 types and may fail due to arithmetic overflow.
11411 The only options are @option{--help} and @option{--version}. @xref{Common
11412 options}. Options must precede operands.
11414 @cindex exit status of @command{expr}
11418 0 if the expression is neither null nor 0,
11419 1 if the expression is null or 0,
11420 2 if the expression is invalid,
11421 3 if an internal error occurred (e.g., arithmetic overflow).
11425 * String expressions:: + : match substr index length
11426 * Numeric expressions:: + - * / %
11427 * Relations for expr:: | & < <= = == != >= >
11428 * Examples of expr:: Examples.
11432 @node String expressions
11433 @subsection String expressions
11435 @cindex string expressions
11436 @cindex expressions, string
11438 @command{expr} supports pattern matching and other string operators. These
11439 have higher precedence than both the numeric and relational operators (in
11440 the next sections).
11444 @item @var{string} : @var{regex}
11445 @cindex pattern matching
11446 @cindex regular expression matching
11447 @cindex matching patterns
11448 Perform pattern matching. The arguments are converted to strings and the
11449 second is considered to be a (basic, a la GNU @code{grep}) regular
11450 expression, with a @code{^} implicitly prepended. The first argument is
11451 then matched against this regular expression.
11453 If the match succeeds and @var{regex} uses @samp{\(} and @samp{\)}, the
11454 @code{:} expression returns the part of @var{string} that matched the
11455 subexpression; otherwise, it returns the number of characters matched.
11457 If the match fails, the @code{:} operator returns the null string if
11458 @samp{\(} and @samp{\)} are used in @var{regex}, otherwise 0.
11460 @kindex \( @r{regexp operator}
11461 Only the first @samp{\( @dots{} \)} pair is relevant to the return
11462 value; additional pairs are meaningful only for grouping the regular
11463 expression operators.
11465 @kindex \+ @r{regexp operator}
11466 @kindex \? @r{regexp operator}
11467 @kindex \| @r{regexp operator}
11468 In the regular expression, @code{\+}, @code{\?}, and @code{\|} are
11469 operators which respectively match one or more, zero or one, or separate
11470 alternatives. SunOS and other @command{expr}'s treat these as regular
11471 characters. (@acronym{POSIX} allows either behavior.)
11472 @xref{Top, , Regular Expression Library, regex, Regex}, for details of
11473 regular expression syntax. Some examples are in @ref{Examples of expr}.
11475 @item match @var{string} @var{regex}
11477 An alternative way to do pattern matching. This is the same as
11478 @w{@samp{@var{string} : @var{regex}}}.
11480 @item substr @var{string} @var{position} @var{length}
11482 Returns the substring of @var{string} beginning at @var{position}
11483 with length at most @var{length}. If either @var{position} or
11484 @var{length} is negative, zero, or non-numeric, returns the null string.
11486 @item index @var{string} @var{charset}
11488 Returns the first position in @var{string} where the first character in
11489 @var{charset} was found. If no character in @var{charset} is found in
11490 @var{string}, return 0.
11492 @item length @var{string}
11494 Returns the length of @var{string}.
11496 @item + @var{token}
11498 Interpret @var{token} as a string, even if it is a keyword like @var{match}
11499 or an operator like @code{/}.
11500 This makes it possible to test @code{expr length + "$x"} or
11501 @code{expr + "$x" : '.*/\(.\)'} and have it do the right thing even if
11502 the value of @var{$x} happens to be (for example) @code{/} or @code{index}.
11503 This operator is a @acronym{GNU} extension. Portable shell scripts should use
11504 @code{@w{" $token"} : @w{' \(.*\)'}} instead of @code{+ "$token"}.
11508 To make @command{expr} interpret keywords as strings, you must use the
11509 @code{quote} operator.
11512 @node Numeric expressions
11513 @subsection Numeric expressions
11515 @cindex numeric expressions
11516 @cindex expressions, numeric
11518 @command{expr} supports the usual numeric operators, in order of increasing
11519 precedence. These numeric operators have lower precedence than the
11520 string operators described in the previous section, and higher precedence
11521 than the connectives (next section).
11529 @cindex subtraction
11530 Addition and subtraction. Both arguments are converted to integers;
11531 an error occurs if this cannot be done.
11537 @cindex multiplication
11540 Multiplication, division, remainder. Both arguments are converted to
11541 integers; an error occurs if this cannot be done.
11546 @node Relations for expr
11547 @subsection Relations for @command{expr}
11549 @cindex connectives, logical
11550 @cindex logical connectives
11551 @cindex relations, numeric or string
11553 @command{expr} supports the usual logical connectives and relations. These
11554 have lower precedence than the string and numeric operators
11555 (previous sections). Here is the list, lowest-precedence operator first.
11561 @cindex logical or operator
11562 @cindex or operator
11563 Returns its first argument if that is neither null nor zero, otherwise
11564 its second argument if it is neither null nor zero, otherwise 0. It
11565 does not evaluate its second argument if its first argument is neither
11570 @cindex logical and operator
11571 @cindex and operator
11572 Return its first argument if neither argument is null or zero, otherwise
11573 0. It does not evaluate its second argument if its first argument is
11576 @item < <= = == != >= >
11583 @cindex comparison operators
11585 Compare the arguments and return 1 if the relation is true, 0 otherwise.
11586 @code{==} is a synonym for @code{=}. @command{expr} first tries to convert
11587 both arguments to integers and do a numeric comparison; if either
11588 conversion fails, it does a lexicographic comparison using the character
11589 collating sequence specified by the @env{LC_COLLATE} locale.
11594 @node Examples of expr
11595 @subsection Examples of using @command{expr}
11597 @cindex examples of @command{expr}
11598 Here are a few examples, including quoting for shell metacharacters.
11600 To add 1 to the shell variable @code{foo}, in Bourne-compatible shells:
11603 foo=`expr $foo + 1`
11606 To print the non-directory part of the file name stored in
11607 @code{$fname}, which need not contain a @code{/}:
11610 expr $fname : '.*/\(.*\)' '|' $fname
11613 An example showing that @code{\+} is an operator:
11621 expr abc : 'a\(.\)c'
11623 expr index abcdef cz
11626 @error{} expr: syntax error
11627 expr index + index a
11633 @chapter Redirection
11635 @cindex redirection
11636 @cindex commands for redirection
11638 Unix shells commonly provide several forms of @dfn{redirection}---ways
11639 to change the input source or output destination of a command. But one
11640 useful redirection is performed by a separate command, not by the shell;
11641 it's described here.
11644 * tee invocation:: Redirect output to multiple files or processes.
11648 @node tee invocation
11649 @section @command{tee}: Redirect output to multiple files or processes
11652 @cindex pipe fitting
11653 @cindex destinations, multiple output
11654 @cindex read from stdin and write to stdout and files
11656 The @command{tee} command copies standard input to standard output and also
11657 to any files given as arguments. This is useful when you want not only
11658 to send some data down a pipe, but also to save a copy. Synopsis:
11661 tee [@var{option}]@dots{} [@var{file}]@dots{}
11664 If a file being written to does not already exist, it is created. If a
11665 file being written to already exists, the data it previously contained
11666 is overwritten unless the @option{-a} option is used.
11668 A @var{file} of @samp{-} causes @command{tee} to send another copy of
11669 input to standard output, but this is typically not that useful as the
11670 copies are interleaved.
11672 The program accepts the following options. Also see @ref{Common options}.
11679 Append standard input to the given files rather than overwriting
11683 @itemx --ignore-interrupts
11685 @opindex --ignore-interrupts
11686 Ignore interrupt signals.
11690 The @command{tee} command is useful when you happen to be transferring a large
11691 amount of data and also want to summarize that data without reading
11692 it a second time. For example, when you are downloading a DVD image,
11693 you often want to verify its signature or checksum right away.
11694 The inefficient way to do it is simply:
11697 wget http://example.com/some.iso && sha1sum some.iso
11700 One problem with the above is that it makes you wait for the
11701 download to complete before starting the time-consuming SHA1 computation.
11702 Perhaps even more importantly, the above requires reading
11703 the DVD image a second time (the first was from the network).
11705 The efficient way to do it is to interleave the download
11706 and SHA1 computation. Then, you'll get the checksum for
11707 free, because the entire process parallelizes so well:
11710 # slightly contrived, to demonstrate process substitution
11711 wget -O - http://example.com/dvd.iso \
11712 | tee >(sha1sum > dvd.sha1) > dvd.iso
11715 That makes @command{tee} write not just to the expected output file,
11716 but also to a pipe running @command{sha1sum} and saving the final
11717 checksum in a file named @file{dvd.sha1}.
11719 Note, however, that this example relies on a feature of modern shells
11720 called @dfn{process substitution}
11721 (the @samp{>(command)} syntax, above;
11722 @xref{Process Substitution,,Process Substitution, bashref,
11723 The Bash Reference Manual}.),
11724 so it works with @command{zsh}, @command{bash}, and @command{ksh},
11725 but not with @command{/bin/sh}. So if you write code like this
11726 in a shell script, be sure to start the script with @samp{#!/bin/bash}.
11728 Since the above example writes to one file and one process,
11729 a more conventional and portable use of @command{tee} is even better:
11732 wget -O - http://example.com/dvd.iso \
11733 | tee dvd.iso | sha1sum > dvd.sha1
11736 You can extend this example to make @command{tee} write to two processes,
11737 computing MD5 and SHA1 checksums in parallel. In this case,
11738 process substitution is required:
11741 wget -O - http://example.com/dvd.iso \
11742 | tee >(sha1sum > dvd.sha1) \
11743 >(md5sum > dvd.md5) \
11747 This technique is also useful when you want to make a @emph{compressed}
11748 copy of the contents of a pipe.
11749 Consider a tool to graphically summarize disk usage data from @samp{du -ak}.
11750 For a large hierarchy, @samp{du -ak} can run for a long time,
11751 and can easily produce terabytes of data, so you won't want to
11752 rerun the command unnecessarily. Nor will you want to save
11753 the uncompressed output.
11755 Doing it the inefficient way, you can't even start the GUI
11756 until after you've compressed all of the @command{du} output:
11759 du -ak | gzip -9 > /tmp/du.gz
11760 gzip -d /tmp/du.gz | xdiskusage -a
11763 With @command{tee} and process substitution, you start the GUI
11764 right away and eliminate the decompression completely:
11767 du -ak | tee >(gzip -9 > /tmp/du.gz) | xdiskusage -a
11770 Finally, if you regularly create more than one type of
11771 compressed tarball at once, for example when @code{make dist} creates
11772 both @command{gzip}-compressed and @command{bzip2}-compressed tarballs,
11773 there may be a better way.
11774 Typical @command{automake}-generated @file{Makefile} rules create
11775 the two compressed tar archives with commands in sequence, like this
11776 (slightly simplified):
11779 tardir=your-pkg-M.N
11780 tar chof - "$tardir" | gzip -9 -c > your-pkg-M.N.tar.gz
11781 tar chof - "$tardir" | bzip2 -9 -c > your-pkg-M.N.tar.bz2
11784 However, if the hierarchy you are archiving and compressing is larger
11785 than a couple megabytes, and especially if you are using a multi-processor
11786 system with plenty of memory, then you can do much better by reading the
11787 directory contents only once and running the compression programs in parallel:
11790 tardir=your-pkg-M.N
11791 tar chof - "$tardir" \
11792 | tee >(gzip -9 -c > your-pkg-M.N.tar.gz) \
11793 | bzip2 -9 -c > your-pkg-M.N.tar.bz2
11799 @node File name manipulation
11800 @chapter File name manipulation
11802 @cindex file name manipulation
11803 @cindex manipulation of file names
11804 @cindex commands for file name manipulation
11806 This section describes commands that manipulate file names.
11809 * basename invocation:: Strip directory and suffix from a file name.
11810 * dirname invocation:: Strip non-directory suffix from a file name.
11811 * pathchk invocation:: Check file name validity and portability.
11815 @node basename invocation
11816 @section @command{basename}: Strip directory and suffix from a file name
11819 @cindex strip directory and suffix from file names
11820 @cindex directory, stripping from file names
11821 @cindex suffix, stripping from file names
11822 @cindex file names, stripping directory and suffix
11823 @cindex leading directory components, stripping
11825 @command{basename} removes any leading directory components from
11826 @var{name}. Synopsis:
11829 basename @var{name} [@var{suffix}]
11832 If @var{suffix} is specified and is identical to the end of @var{name},
11833 it is removed from @var{name} as well. Note that since trailing slashes
11834 are removed prior to suffix matching, @var{suffix} will do nothing if it
11835 contains slashes. @command{basename} prints the result on standard
11838 @c This test is used both here and in the section on dirname.
11839 @macro basenameAndDirname
11840 Together, @command{basename} and @command{dirname} are designed such
11841 that if @samp{ls "$name"} succeeds, then the command sequence @samp{cd
11842 "$(dirname "$name")"; ls "$(basename "$name")"} will, too. This works
11843 for everything except file names containing a trailing newline.
11845 @basenameAndDirname
11847 @acronym{POSIX} allows the implementation to define the results if
11848 @var{name} is empty or @samp{//}. In the former case, @acronym{GNU}
11849 @command{basename} returns the empty string. In the latter case, the
11850 result is @samp{//} on platforms where @var{//} is distinct from
11851 @var{/}, and @samp{/} on platforms where there is no difference.
11853 The only options are @option{--help} and @option{--version}. @xref{Common
11854 options}. Options must precede operands.
11862 basename /usr/bin/sort
11865 basename include/stdio.h .h
11869 @node dirname invocation
11870 @section @command{dirname}: Strip non-directory suffix from a file name
11873 @cindex directory components, printing
11874 @cindex stripping non-directory suffix
11875 @cindex non-directory suffix, stripping
11877 @command{dirname} prints all but the final slash-delimited component of
11878 a string (presumably a file name). Synopsis:
11884 If @var{name} is a single component, @command{dirname} prints @samp{.}
11885 (meaning the current directory).
11887 @basenameAndDirname
11889 @acronym{POSIX} allows the implementation to define the results if
11890 @var{name} is @samp{//}. With @acronym{GNU} @command{dirname}, the
11891 result is @samp{//} on platforms where @var{//} is distinct from
11892 @var{/}, and @samp{/} on platforms where there is no difference.
11894 The only options are @option{--help} and @option{--version}. @xref{Common
11902 # Output "/usr/bin".
11903 dirname /usr/bin/sort
11910 @node pathchk invocation
11911 @section @command{pathchk}: Check file name validity and portability
11914 @cindex file names, checking validity and portability
11915 @cindex valid file names, checking for
11916 @cindex portable file names, checking for
11918 @command{pathchk} checks validity and portability of file names. Synopsis:
11921 pathchk [@var{option}]@dots{} @var{name}@dots{}
11924 For each @var{name}, @command{pathchk} prints an error message if any of
11925 these conditions is true:
11929 One of the existing directories in @var{name} does not have search
11930 (execute) permission,
11932 The length of @var{name} is larger than the maximum supported by the
11935 The length of one component of @var{name} is longer than
11936 its file system's maximum.
11939 A nonexistent @var{name} is not an error, so long a file with that
11940 name could be created under the above conditions.
11942 The program accepts the following options. Also see @ref{Common options}.
11943 Options must precede operands.
11949 Instead of performing checks based on the underlying file system,
11950 print an error message if any of these conditions is true:
11954 A file name is empty.
11957 A file name contains a character outside the @acronym{POSIX} portable file
11958 name character set, namely, the ASCII letters and digits, @samp{.},
11959 @samp{_}, @samp{-}, and @samp{/}.
11962 The length of a file name or one of its components exceeds the
11963 @acronym{POSIX} minimum limits for portability.
11968 Print an error message if a file name is empty, or if it contains a component
11969 that begins with @samp{-}.
11971 @item --portability
11972 @opindex --portability
11973 Print an error message if a file name is not portable to all @acronym{POSIX}
11974 hosts. This option is equivalent to @samp{-p -P}.
11978 @cindex exit status of @command{pathchk}
11982 0 if all specified file names passed all checks,
11987 @node Working context
11988 @chapter Working context
11990 @cindex working context
11991 @cindex commands for printing the working context
11993 This section describes commands that display or alter the context in
11994 which you are working: the current directory, the terminal settings, and
11995 so forth. See also the user-related commands in the next section.
11998 * pwd invocation:: Print working directory.
11999 * stty invocation:: Print or change terminal characteristics.
12000 * printenv invocation:: Print environment variables.
12001 * tty invocation:: Print file name of terminal on standard input.
12005 @node pwd invocation
12006 @section @command{pwd}: Print working directory
12009 @cindex print name of current directory
12010 @cindex current working directory, printing
12011 @cindex working directory, printing
12014 @command{pwd} prints the name of the current directory. Synopsis:
12017 pwd [@var{option}]@dots{}
12020 The program accepts the following options. Also see @ref{Common options}.
12027 If the contents of the environment variable @env{PWD} provide an
12028 absolute name of the current directory with no @samp{.} or @samp{..}
12029 components, but possibly with symbolic links, then output those
12030 contents. Otherwise, fall back to default @option{-P} handling.
12035 @opindex --physical
12036 Print a fully resolved name for the current directory. That is, all
12037 components of the printed name will be actual directory names---none
12038 will be symbolic links.
12041 @cindex symbolic links and @command{pwd}
12042 If @option{-L} and @option{-P} are both given, the last one takes
12043 precedence. If neither option is given, then this implementation uses
12044 @option{-P} as the default unless the @env{POSIXLY_CORRECT}
12045 environment variable is set.
12047 @mayConflictWithShellBuiltIn{pwd}
12052 @node stty invocation
12053 @section @command{stty}: Print or change terminal characteristics
12056 @cindex change or print terminal settings
12057 @cindex terminal settings
12058 @cindex line settings of terminal
12060 @command{stty} prints or changes terminal characteristics, such as baud rate.
12064 stty [@var{option}] [@var{setting}]@dots{}
12065 stty [@var{option}]
12068 If given no line settings, @command{stty} prints the baud rate, line
12069 discipline number (on systems that support it), and line settings
12070 that have been changed from the values set by @samp{stty sane}.
12071 By default, mode reading and setting are performed on the tty line
12072 connected to standard input, although this can be modified by the
12073 @option{--file} option.
12075 @command{stty} accepts many non-option arguments that change aspects of
12076 the terminal line operation, as described below.
12078 The program accepts the following options. Also see @ref{Common options}.
12085 Print all current settings in human-readable form. This option may not
12086 be used in combination with any line settings.
12088 @item -F @var{device}
12089 @itemx --file=@var{device}
12092 Set the line opened by the file name specified in @var{device} instead of
12093 the tty line connected to standard input. This option is necessary
12094 because opening a @acronym{POSIX} tty requires use of the @code{O_NONDELAY} flag to
12095 prevent a @acronym{POSIX} tty from blocking until the carrier detect line is high if
12096 the @code{clocal} flag is not set. Hence, it is not always possible
12097 to allow the shell to open the device in the traditional manner.
12103 @cindex machine-readable @command{stty} output
12104 Print all current settings in a form that can be used as an argument to
12105 another @command{stty} command to restore the current settings. This option
12106 may not be used in combination with any line settings.
12110 Many settings can be turned off by preceding them with a @samp{-}.
12111 Such arguments are marked below with ``May be negated'' in their
12112 description. The descriptions themselves refer to the positive
12113 case, that is, when @emph{not} negated (unless stated otherwise,
12116 Some settings are not available on all @acronym{POSIX} systems, since they use
12117 extensions. Such arguments are marked below with ``Non-@acronym{POSIX}'' in their
12118 description. On non-@acronym{POSIX} systems, those or other settings also may not
12119 be available, but it's not feasible to document all the variations: just
12125 * Control:: Control settings
12126 * Input:: Input settings
12127 * Output:: Output settings
12128 * Local:: Local settings
12129 * Combination:: Combination settings
12130 * Characters:: Special characters
12131 * Special:: Special settings
12136 @subsection Control settings
12138 @cindex control settings
12144 @cindex two-way parity
12145 Generate parity bit in output and expect parity bit in input.
12151 @cindex even parity
12152 Set odd parity (even if negated). May be negated.
12159 @cindex character size
12160 @cindex eight-bit characters
12161 Set character size to 5, 6, 7, or 8 bits.
12166 Send a hangup signal when the last process closes the tty. May be
12172 Use two stop bits per character (one if negated). May be negated.
12176 Allow input to be received. May be negated.
12180 @cindex modem control
12181 Disable modem control signals. May be negated.
12185 @cindex hardware flow control
12186 @cindex flow control, hardware
12187 @cindex RTS/CTS flow control
12188 Enable RTS/CTS flow control. Non-@acronym{POSIX}. May be negated.
12193 @subsection Input settings
12195 @cindex input settings
12196 These settings control operations on data received from the terminal.
12201 @cindex breaks, ignoring
12202 Ignore break characters. May be negated.
12206 @cindex breaks, cause interrupts
12207 Make breaks cause an interrupt signal. May be negated.
12211 @cindex parity, ignoring
12212 Ignore characters with parity errors. May be negated.
12216 @cindex parity errors, marking
12217 Mark parity errors (with a 255-0-character sequence). May be negated.
12221 Enable input parity checking. May be negated.
12225 @cindex eight-bit input
12226 Clear high (8th) bit of input characters. May be negated.
12230 @cindex newline, translating to return
12231 Translate newline to carriage return. May be negated.
12235 @cindex return, ignoring
12236 Ignore carriage return. May be negated.
12240 @cindex return, translating to newline
12241 Translate carriage return to newline. May be negated.
12245 @cindex input encoding, UTF-8
12246 Assume input characters are UTF-8 encoded. May be negated.
12250 @kindex C-s/C-q flow control
12251 @cindex XON/XOFF flow control
12252 Enable XON/XOFF flow control (that is, @kbd{CTRL-S}/@kbd{CTRL-Q}). May
12259 @cindex software flow control
12260 @cindex flow control, software
12261 Enable sending of @code{stop} character when the system input buffer
12262 is almost full, and @code{start} character when it becomes almost
12263 empty again. May be negated.
12267 @cindex uppercase, translating to lowercase
12268 Translate uppercase characters to lowercase. Non-@acronym{POSIX}. May be
12269 negated. Note ilcuc is not implemented, as one would not be able to issue
12270 almost any (lowercase) Unix command, after invoking it.
12274 Allow any character to restart output (only the start character
12275 if negated). Non-@acronym{POSIX}. May be negated.
12279 @cindex beeping at input buffer full
12280 Enable beeping and not flushing input buffer if a character arrives
12281 when the input buffer is full. Non-@acronym{POSIX}. May be negated.
12286 @subsection Output settings
12288 @cindex output settings
12289 These settings control operations on data sent to the terminal.
12294 Postprocess output. May be negated.
12298 @cindex lowercase, translating to output
12299 Translate lowercase characters to uppercase. Non-@acronym{POSIX}. May be
12300 negated. (Note ouclc is not currently implemented.)
12304 @cindex return, translating to newline
12305 Translate carriage return to newline. Non-@acronym{POSIX}. May be negated.
12309 @cindex newline, translating to crlf
12310 Translate newline to carriage return-newline. Non-@acronym{POSIX}. May be
12315 Do not print carriage returns in the first column. Non-@acronym{POSIX}.
12320 Newline performs a carriage return. Non-@acronym{POSIX}. May be negated.
12324 @cindex pad instead of timing for delaying
12325 Use fill (padding) characters instead of timing for delays. Non-@acronym{POSIX}.
12330 @cindex pad character
12331 Use @acronym{ASCII} @sc{del} characters for fill instead of
12332 @acronym{ASCII} @sc{nul} characters. Non-@acronym{POSIX}.
12338 Newline delay style. Non-@acronym{POSIX}.
12345 Carriage return delay style. Non-@acronym{POSIX}.
12351 @opindex tab@var{n}
12352 Horizontal tab delay style. Non-@acronym{POSIX}.
12357 Backspace delay style. Non-@acronym{POSIX}.
12362 Vertical tab delay style. Non-@acronym{POSIX}.
12367 Form feed delay style. Non-@acronym{POSIX}.
12372 @subsection Local settings
12374 @cindex local settings
12379 Enable @code{interrupt}, @code{quit}, and @code{suspend} special
12380 characters. May be negated.
12384 Enable @code{erase}, @code{kill}, @code{werase}, and @code{rprnt}
12385 special characters. May be negated.
12389 Enable non-@acronym{POSIX} special characters. May be negated.
12393 Echo input characters. May be negated.
12399 Echo @code{erase} characters as backspace-space-backspace. May be
12404 @cindex newline echoing after @code{kill}
12405 Echo a newline after a @code{kill} character. May be negated.
12409 @cindex newline, echoing
12410 Echo newline even if not echoing other characters. May be negated.
12414 @cindex flushing, disabling
12415 Disable flushing after @code{interrupt} and @code{quit} special
12416 characters. May be negated.
12420 @cindex case translation
12421 Enable input and output of uppercase characters by preceding their
12422 lowercase equivalents with @samp{\}, when @code{icanon} is set.
12423 Non-@acronym{POSIX}. May be negated.
12427 @cindex background jobs, stopping at terminal write
12428 Stop background jobs that try to write to the terminal. Non-@acronym{POSIX}.
12435 Echo erased characters backward, between @samp{\} and @samp{/}.
12436 Non-@acronym{POSIX}. May be negated.
12442 @cindex control characters, using @samp{^@var{c}}
12443 @cindex hat notation for control characters
12444 Echo control characters in hat notation (@samp{^@var{c}}) instead
12445 of literally. Non-@acronym{POSIX}. May be negated.
12451 Echo the @code{kill} special character by erasing each character on
12452 the line as indicated by the @code{echoprt} and @code{echoe} settings,
12453 instead of by the @code{echoctl} and @code{echok} settings. Non-@acronym{POSIX}.
12459 @subsection Combination settings
12461 @cindex combination settings
12462 Combination settings:
12469 Same as @code{parenb -parodd cs7}. May be negated. If negated, same
12470 as @code{-parenb cs8}.
12474 Same as @code{parenb parodd cs7}. May be negated. If negated, same
12475 as @code{-parenb cs8}.
12479 Same as @code{-icrnl -onlcr}. May be negated. If negated, same as
12480 @code{icrnl -inlcr -igncr onlcr -ocrnl -onlret}.
12484 Reset the @code{erase} and @code{kill} special characters to their default
12491 @c This is too long to write inline.
12493 cread -ignbrk brkint -inlcr -igncr icrnl -ixoff
12494 -iuclc -ixany imaxbel opost -olcuc -ocrnl onlcr
12495 -onocr -onlret -ofill -ofdel nl0 cr0 tab0 bs0 vt0
12496 ff0 isig icanon iexten echo echoe echok -echonl
12497 -noflsh -xcase -tostop -echoprt echoctl echoke
12501 and also sets all special characters to their default values.
12505 Same as @code{brkint ignpar istrip icrnl ixon opost isig icanon}, plus
12506 sets the @code{eof} and @code{eol} characters to their default values
12507 if they are the same as the @code{min} and @code{time} characters.
12508 May be negated. If negated, same as @code{raw}.
12515 -ignbrk -brkint -ignpar -parmrk -inpck -istrip
12516 -inlcr -igncr -icrnl -ixon -ixoff -iuclc -ixany
12517 -imaxbel -opost -isig -icanon -xcase min 1 time 0
12521 May be negated. If negated, same as @code{cooked}.
12525 Same as @option{-icanon}. May be negated. If negated, same as
12530 @cindex eight-bit characters
12531 Same as @code{-parenb -istrip cs8}. May be negated. If negated,
12532 same as @code{parenb istrip cs7}.
12536 Same as @option{-parenb -istrip -opost cs8}. May be negated.
12537 If negated, same as @code{parenb istrip opost cs7}.
12541 Same as @option{-ixany}. Non-@acronym{POSIX}. May be negated.
12545 Same as @code{tab0}. Non-@acronym{POSIX}. May be negated. If negated, same
12552 Same as @code{xcase iuclc olcuc}. Non-@acronym{POSIX}. May be negated.
12553 (Used for terminals with uppercase characters only.)
12557 Same as @code{echoe echoctl echoke}.
12561 Same as @code{echoe echoctl echoke -ixany intr ^C erase ^? kill C-u}.
12566 @subsection Special characters
12568 @cindex special characters
12569 @cindex characters, special
12571 The special characters' default values vary from system to system.
12572 They are set with the syntax @samp{name value}, where the names are
12573 listed below and the value can be given either literally, in hat
12574 notation (@samp{^@var{c}}), or as an integer which may start with
12575 @samp{0x} to indicate hexadecimal, @samp{0} to indicate octal, or
12576 any other digit to indicate decimal.
12578 @cindex disabling special characters
12579 @kindex u@r{, and disabling special characters}
12580 For GNU stty, giving a value of @code{^-} or @code{undef} disables that
12581 special character. (This is incompatible with Ultrix @command{stty},
12582 which uses a value of @samp{u} to disable a special character. GNU
12583 @command{stty} treats a value @samp{u} like any other, namely to set that
12584 special character to @key{U}.)
12590 Send an interrupt signal.
12594 Send a quit signal.
12598 Erase the last character typed.
12602 Erase the current line.
12606 Send an end of file (terminate the input).
12614 Alternate character to end the line. Non-@acronym{POSIX}.
12618 Switch to a different shell layer. Non-@acronym{POSIX}.
12622 Restart the output after stopping it.
12630 Send a terminal stop signal.
12634 Send a terminal stop signal after flushing the input. Non-@acronym{POSIX}.
12638 Redraw the current line. Non-@acronym{POSIX}.
12642 Erase the last word typed. Non-@acronym{POSIX}.
12646 Enter the next character typed literally, even if it is a special
12647 character. Non-@acronym{POSIX}.
12652 @subsection Special settings
12654 @cindex special settings
12659 Set the minimum number of characters that will satisfy a read until
12660 the time value has expired, when @option{-icanon} is set.
12664 Set the number of tenths of a second before reads time out if the minimum
12665 number of characters have not been read, when @option{-icanon} is set.
12667 @item ispeed @var{n}
12669 Set the input speed to @var{n}.
12671 @item ospeed @var{n}
12673 Set the output speed to @var{n}.
12677 Tell the tty kernel driver that the terminal has @var{n} rows. Non-@acronym{POSIX}.
12680 @itemx columns @var{n}
12683 Tell the kernel that the terminal has @var{n} columns. Non-@acronym{POSIX}.
12689 Print the number of rows and columns that the kernel thinks the
12690 terminal has. (Systems that don't support rows and columns in the kernel
12691 typically use the environment variables @env{LINES} and @env{COLUMNS}
12692 instead; however, GNU @command{stty} does not know anything about them.)
12693 Non-@acronym{POSIX}.
12697 Use line discipline @var{n}. Non-@acronym{POSIX}.
12701 Print the terminal speed.
12704 @cindex baud rate, setting
12705 Set the input and output speeds to @var{n}. @var{n} can be one of: 0
12706 50 75 110 134 134.5 150 200 300 600 1200 1800 2400 4800 9600 19200
12707 38400 @code{exta} @code{extb}. @code{exta} is the same as 19200;
12708 @code{extb} is the same as 38400. Many systems, including GNU/Linux,
12709 support higher speeds. The @command{stty} command includes support
12726 4000000 where the system supports these.
12727 0 hangs up the line if @option{-clocal} is set.
12731 @node printenv invocation
12732 @section @command{printenv}: Print all or some environment variables
12735 @cindex printing all or some environment variables
12736 @cindex environment variables, printing
12738 @command{printenv} prints environment variable values. Synopsis:
12741 printenv [@var{option}] [@var{variable}]@dots{}
12744 If no @var{variable}s are specified, @command{printenv} prints the value of
12745 every environment variable. Otherwise, it prints the value of each
12746 @var{variable} that is set, and nothing for those that are not set.
12748 The only options are a lone @option{--help} or @option{--version}.
12749 @xref{Common options}.
12751 @cindex exit status of @command{printenv}
12755 0 if all variables specified were found
12756 1 if at least one specified variable was not found
12757 2 if a write error occurred
12761 @node tty invocation
12762 @section @command{tty}: Print file name of terminal on standard input
12765 @cindex print terminal file name
12766 @cindex terminal file name, printing
12768 @command{tty} prints the file name of the terminal connected to its standard
12769 input. It prints @samp{not a tty} if standard input is not a terminal.
12773 tty [@var{option}]@dots{}
12776 The program accepts the following option. Also see @ref{Common options}.
12786 Print nothing; only return an exit status.
12790 @cindex exit status of @command{tty}
12794 0 if standard input is a terminal
12795 1 if standard input is not a terminal
12796 2 if given incorrect arguments
12797 3 if a write error occurs
12801 @node User information
12802 @chapter User information
12804 @cindex user information, commands for
12805 @cindex commands for printing user information
12807 This section describes commands that print user-related information:
12808 logins, groups, and so forth.
12811 * id invocation:: Print user identity.
12812 * logname invocation:: Print current login name.
12813 * whoami invocation:: Print effective user ID.
12814 * groups invocation:: Print group names a user is in.
12815 * users invocation:: Print login names of users currently logged in.
12816 * who invocation:: Print who is currently logged in.
12820 @node id invocation
12821 @section @command{id}: Print user identity
12824 @cindex real user and group IDs, printing
12825 @cindex effective user and group IDs, printing
12826 @cindex printing real and effective user and group IDs
12828 @command{id} prints information about the given user, or the process
12829 running it if no user is specified. Synopsis:
12832 id [@var{option}]@dots{} [@var{username}]
12835 By default, it prints the real user ID, real group ID, effective user ID
12836 if different from the real user ID, effective group ID if different from
12837 the real group ID, and supplemental group IDs.
12839 Each of these numeric values is preceded by an identifying string and
12840 followed by the corresponding user or group name in parentheses.
12842 The options cause @command{id} to print only part of the above information.
12843 Also see @ref{Common options}.
12850 Print only the group ID.
12856 Print only the group ID and the supplementary groups.
12862 Print the user or group name instead of the ID number. Requires
12863 @option{-u}, @option{-g}, or @option{-G}.
12869 Print the real, instead of effective, user or group ID. Requires
12870 @option{-u}, @option{-g}, or @option{-G}.
12876 Print only the user ID.
12883 @cindex security context
12884 Print only the security context of the current user.
12885 If SELinux is disabled then print a warning and
12886 set the exit status to 1.
12892 @macro primaryAndSupplementaryGroups{cmd,arg}
12893 Primary and supplementary groups for a process are normally inherited
12894 from its parent and are usually unchanged since login. This means
12895 that if you change the group database after logging in, @command{\cmd\}
12896 will not reflect your changes within your existing login session.
12897 Running @command{\cmd\} with a \arg\ causes the user and group
12898 database to be consulted afresh, and so will give a different result.
12900 @primaryAndSupplementaryGroups{id,user argument}
12902 @node logname invocation
12903 @section @command{logname}: Print current login name
12906 @cindex printing user's login name
12907 @cindex login name, printing
12908 @cindex user name, printing
12911 @command{logname} prints the calling user's name, as found in a
12912 system-maintained file (often @file{/var/run/utmp} or
12913 @file{/etc/utmp}), and exits with a status of 0. If there is no entry
12914 for the calling process, @command{logname} prints
12915 an error message and exits with a status of 1.
12917 The only options are @option{--help} and @option{--version}. @xref{Common
12923 @node whoami invocation
12924 @section @command{whoami}: Print effective user ID
12927 @cindex effective user ID, printing
12928 @cindex printing the effective user ID
12930 @command{whoami} prints the user name associated with the current
12931 effective user ID. It is equivalent to the command @samp{id -un}.
12933 The only options are @option{--help} and @option{--version}. @xref{Common
12939 @node groups invocation
12940 @section @command{groups}: Print group names a user is in
12943 @cindex printing groups a user is in
12944 @cindex supplementary groups, printing
12946 @command{groups} prints the names of the primary and any supplementary
12947 groups for each given @var{username}, or the current process if no names
12948 are given. If more than one name is given, the name of each user is
12950 the list of that user's groups and the user name is separated from the
12951 group list by a colon. Synopsis:
12954 groups [@var{username}]@dots{}
12957 The group lists are equivalent to the output of the command @samp{id -Gn}.
12959 @primaryAndSupplementaryGroups{groups,list of users}
12961 The only options are @option{--help} and @option{--version}. @xref{Common
12967 @node users invocation
12968 @section @command{users}: Print login names of users currently logged in
12971 @cindex printing current usernames
12972 @cindex usernames, printing current
12974 @cindex login sessions, printing users with
12975 @command{users} prints on a single line a blank-separated list of user
12976 names of users currently logged in to the current host. Each user name
12977 corresponds to a login session, so if a user has more than one login
12978 session, that user's name will appear the same number of times in the
12987 With no @var{file} argument, @command{users} extracts its information from
12988 a system-maintained file (often @file{/var/run/utmp} or
12989 @file{/etc/utmp}). If a file argument is given, @command{users} uses
12990 that file instead. A common choice is @file{/var/log/wtmp}.
12992 The only options are @option{--help} and @option{--version}. @xref{Common
12998 @node who invocation
12999 @section @command{who}: Print who is currently logged in
13002 @cindex printing current user information
13003 @cindex information, about current users
13005 @command{who} prints information about users who are currently logged on.
13009 @command{who} [@var{option}] [@var{file}] [am i]
13012 @cindex terminal lines, currently used
13014 @cindex remote hostname
13015 If given no non-option arguments, @command{who} prints the following
13016 information for each user currently logged on: login name, terminal
13017 line, login time, and remote hostname or X display.
13021 If given one non-option argument, @command{who} uses that instead of
13022 a default system-maintained file (often @file{/var/run/utmp} or
13023 @file{/etc/utmp}) as the name of the file containing the record of
13024 users logged on. @file{/var/log/wtmp} is commonly given as an argument
13025 to @command{who} to look at who has previously logged on.
13029 If given two non-option arguments, @command{who} prints only the entry
13030 for the user running it (determined from its standard input), preceded
13031 by the hostname. Traditionally, the two arguments given are @samp{am
13032 i}, as in @samp{who am i}.
13035 Time stamps are listed according to the time zone rules specified by
13036 the @env{TZ} environment variable, or by the system default rules if
13037 @env{TZ} is not set. @xref{TZ Variable,, Specifying the Time Zone
13038 with @env{TZ}, libc, The GNU C Library Reference Manual}.
13040 The program accepts the following options. Also see @ref{Common options}.
13048 Same as @samp{-b -d --login -p -r -t -T -u}.
13054 Print the date and time of last system boot.
13060 Print information corresponding to dead processes.
13066 Print a line of column headings.
13072 List only the entries that correspond to processes via which the
13073 system is waiting for a user to login. The user name is always @samp{LOGIN}.
13077 Attempt to canonicalize hostnames found in utmp through a DNS lookup. This
13078 is not the default because it can cause significant delays on systems with
13079 automatic dial-up internet access.
13083 Same as @samp{who am i}.
13089 List active processes spawned by init.
13095 Print only the login names and the number of users logged on.
13096 Overrides all other options.
13101 @opindex --runlevel
13102 Print the current (and maybe previous) run-level of the init process.
13106 Ignored; for compatibility with other versions of @command{who}.
13112 Print last system clock change.
13117 After the login time, print the number of hours and minutes that the
13118 user has been idle. @samp{.} means the user was active in the last minute.
13119 @samp{old} means the user has been idle for more than 24 hours.
13130 @opindex --writable
13131 @cindex message status
13132 @pindex write@r{, allowed}
13133 After each login name print a character indicating the user's message status:
13136 @samp{+} allowing @code{write} messages
13137 @samp{-} disallowing @code{write} messages
13138 @samp{?} cannot find terminal device
13146 @node System context
13147 @chapter System context
13149 @cindex system context
13150 @cindex context, system
13151 @cindex commands for system context
13153 This section describes commands that print or change system-wide
13157 * date invocation:: Print or set system date and time.
13158 * arch invocation:: Print machine hardware name.
13159 * uname invocation:: Print system information.
13160 * hostname invocation:: Print or set system name.
13161 * hostid invocation:: Print numeric host identifier.
13162 * uptime invocation:: Print system uptime and load.
13165 @node date invocation
13166 @section @command{date}: Print or set system date and time
13169 @cindex time, printing or setting
13170 @cindex printing the current time
13175 date [@var{option}]@dots{} [+@var{format}]
13176 date [-u|--utc|--universal] @c this avoids a newline in the output
13177 [ MMDDhhmm[[CC]YY][.ss] ]
13181 Invoking @command{date} with no @var{format} argument is equivalent to invoking
13182 it with a default format that depends on the @env{LC_TIME} locale category.
13183 In the default C locale, this format is @samp{'+%a %b %e %H:%M:%S %Z %Y'},
13184 so the output looks like @samp{Thu Mar @ 3 13:47:51 PST 2005}.
13187 Normally, @command{date} uses the time zone rules indicated by the
13188 @env{TZ} environment variable, or the system default rules if @env{TZ}
13189 is not set. @xref{TZ Variable,, Specifying the Time Zone with
13190 @env{TZ}, libc, The GNU C Library Reference Manual}.
13192 @findex strftime @r{and @command{date}}
13193 @cindex time formats
13194 @cindex formatting times
13195 If given an argument that starts with a @samp{+}, @command{date} prints the
13196 current date and time (or the date and time specified by the
13197 @option{--date} option, see below) in the format defined by that argument,
13198 which is similar to that of the @code{strftime} function. Except for
13199 conversion specifiers, which start with @samp{%}, characters in the
13200 format string are printed unchanged. The conversion specifiers are
13206 * Time conversion specifiers:: %[HIklMNpPrRsSTXzZ]
13207 * Date conversion specifiers:: %[aAbBcCdDeFgGhjmuUVwWxyY]
13208 * Literal conversion specifiers:: %[%nt]
13209 * Padding and other flags:: Pad with zeros, spaces, etc.
13210 * Setting the time:: Changing the system clock.
13211 * Options for date:: Instead of the current time.
13213 * Date input formats:: Specifying date strings.
13215 * Examples of date:: Examples.
13218 @node Time conversion specifiers
13219 @subsection Time conversion specifiers
13221 @cindex time conversion specifiers
13222 @cindex conversion specifiers, time
13224 @command{date} conversion specifiers related to times.
13228 hour (@samp{00}@dots{}@samp{23})
13230 hour (@samp{01}@dots{}@samp{12})
13232 hour (@samp{ 0}@dots{}@samp{23}).
13233 This is a @acronym{GNU} extension.
13235 hour (@samp{ 1}@dots{}@samp{12}).
13236 This is a @acronym{GNU} extension.
13238 minute (@samp{00}@dots{}@samp{59})
13240 nanoseconds (@samp{000000000}@dots{}@samp{999999999}).
13241 This is a @acronym{GNU} extension.
13243 locale's equivalent of either @samp{AM} or @samp{PM};
13244 blank in many locales.
13245 Noon is treated as @samp{PM} and midnight as @samp{AM}.
13247 like @samp{%p}, except lower case.
13248 This is a @acronym{GNU} extension.
13250 locale's 12-hour clock time (e.g., @samp{11:11:04 PM})
13252 24-hour hour and minute. Same as @samp{%H:%M}.
13253 This is a @acronym{GNU} extension.
13255 @cindex epoch, seconds since
13256 @cindex seconds since the epoch
13257 @cindex beginning of time
13258 seconds since the epoch, i.e., since 1970-01-01 00:00:00 UTC.
13259 Leap seconds are not counted unless leap second support is available.
13260 @xref{%s-examples}, for examples.
13261 This is a @acronym{GNU} extension.
13263 second (@samp{00}@dots{}@samp{60}).
13264 This may be @samp{60} if leap seconds are supported.
13266 24-hour hour, minute, and second. Same as @samp{%H:%M:%S}.
13268 locale's time representation (e.g., @samp{23:13:48})
13270 @w{@acronym{RFC} 2822/@acronym{ISO} 8601} style numeric time zone
13271 (e.g., @samp{-0600} or @samp{+0530}), or nothing if no
13272 time zone is determinable. This value reflects the numeric time zone
13273 appropriate for the current time, using the time zone rules specified
13274 by the @env{TZ} environment variable.
13275 The time (and optionally, the time zone rules) can be overridden
13276 by the @option{--date} option.
13277 This is a @acronym{GNU} extension.
13279 @w{@acronym{RFC} 3339/@acronym{ISO} 8601} style numeric time zone with
13280 @samp{:} (e.g., @samp{-06:00} or @samp{+05:30}), or nothing if no time
13281 zone is determinable.
13282 This is a @acronym{GNU} extension.
13284 Numeric time zone to the nearest second with @samp{:} (e.g.,
13285 @samp{-06:00:00} or @samp{+05:30:00}), or nothing if no time zone is
13287 This is a @acronym{GNU} extension.
13289 Numeric time zone with @samp{:} using the minimum necessary precision
13290 (e.g., @samp{-06}, @samp{+05:30}, or @samp{-04:56:02}), or nothing if
13291 no time zone is determinable.
13292 This is a @acronym{GNU} extension.
13294 alphabetic time zone abbreviation (e.g., @samp{EDT}), or nothing if no
13295 time zone is determinable. See @samp{%z} for how it is determined.
13299 @node Date conversion specifiers
13300 @subsection Date conversion specifiers
13302 @cindex date conversion specifiers
13303 @cindex conversion specifiers, date
13305 @command{date} conversion specifiers related to dates.
13309 locale's abbreviated weekday name (e.g., @samp{Sun})
13311 locale's full weekday name, variable length (e.g., @samp{Sunday})
13313 locale's abbreviated month name (e.g., @samp{Jan})
13315 locale's full month name, variable length (e.g., @samp{January})
13317 locale's date and time (e.g., @samp{Thu Mar @ 3 23:05:25 2005})
13319 century. This is like @samp{%Y}, except the last two digits are omitted.
13320 For example, it is @samp{20} if @samp{%Y} is @samp{2000},
13321 and is @samp{-0} if @samp{%Y} is @samp{-001}.
13322 It is normally at least two characters, but it may be more.
13324 day of month (e.g., @samp{01})
13326 date; same as @samp{%m/%d/%y}
13328 day of month, space padded; same as @samp{%_d}
13330 full date in @acronym{ISO} 8601 format; same as @samp{%Y-%m-%d}.
13331 This is a good choice for a date format, as it is standard and
13332 is easy to sort in the usual case where years are in the range
13334 This is a @acronym{GNU} extension.
13336 year corresponding to the @acronym{ISO} week number, but without the century
13337 (range @samp{00} through @samp{99}). This has the same format and value
13338 as @samp{%y}, except that if the @acronym{ISO} week number (see
13340 to the previous or next year, that year is used instead.
13341 This is a @acronym{GNU} extension.
13343 year corresponding to the @acronym{ISO} week number. This has the
13344 same format and value as @samp{%Y}, except that if the @acronym{ISO}
13346 @samp{%V}) belongs to the previous or next year, that year is used
13348 It is normally useful only if @samp{%V} is also used;
13349 for example, the format @samp{%G-%m-%d} is probably a mistake,
13350 since it combines the ISO week number year with the conventional month and day.
13351 This is a @acronym{GNU} extension.
13355 day of year (@samp{001}@dots{}@samp{366})
13357 month (@samp{01}@dots{}@samp{12})
13359 day of week (@samp{1}@dots{}@samp{7}) with @samp{1} corresponding to Monday
13361 week number of year, with Sunday as the first day of the week
13362 (@samp{00}@dots{}@samp{53}).
13363 Days in a new year preceding the first Sunday are in week zero.
13365 @acronym{ISO} week number, that is, the
13366 week number of year, with Monday as the first day of the week
13367 (@samp{01}@dots{}@samp{53}).
13368 If the week containing January 1 has four or more days in
13369 the new year, then it is considered week 1; otherwise, it is week 53 of
13370 the previous year, and the next week is week 1. (See the @acronym{ISO} 8601
13373 day of week (@samp{0}@dots{}@samp{6}) with 0 corresponding to Sunday
13375 week number of year, with Monday as first day of week
13376 (@samp{00}@dots{}@samp{53}).
13377 Days in a new year preceding the first Monday are in week zero.
13379 locale's date representation (e.g., @samp{12/31/99})
13381 last two digits of year (@samp{00}@dots{}@samp{99})
13383 year. This is normally at least four characters, but it may be more.
13384 Year @samp{0000} precedes year @samp{0001}, and year @samp{-001}
13385 precedes year @samp{0000}.
13389 @node Literal conversion specifiers
13390 @subsection Literal conversion specifiers
13392 @cindex literal conversion specifiers
13393 @cindex conversion specifiers, literal
13395 @command{date} conversion specifiers that produce literal strings.
13407 @node Padding and other flags
13408 @subsection Padding and other flags
13410 @cindex numeric field padding
13411 @cindex padding of numeric fields
13412 @cindex fields, padding numeric
13414 Unless otherwise specified, @command{date} normally pads numeric fields
13415 with zeros, so that, for
13416 example, numeric months are always output as two digits.
13417 Seconds since the epoch are not padded, though,
13418 since there is no natural width for them.
13420 As a @acronym{GNU} extension, @command{date} recognizes any of the
13421 following optional flags after the @samp{%}:
13425 (hyphen) Do not pad the field; useful if the output is intended for
13428 (underscore) Pad with spaces; useful if you need a fixed
13429 number of characters in the output, but zeros are too distracting.
13431 (zero) Pad with zeros even if the conversion specifier
13432 would normally pad with spaces.
13434 Use upper case characters if possible.
13436 Use opposite case characters if possible.
13437 A field that is normally upper case becomes lower case, and vice versa.
13441 Here are some examples of padding:
13444 date +%d/%m -d "Feb 1"
13446 date +%-d/%-m -d "Feb 1"
13448 date +%_d/%_m -d "Feb 1"
13452 As a @acronym{GNU} extension, you can specify the field width
13453 (after any flag, if present) as a decimal number. If the natural size of the
13454 output of the field has less than the specified number of characters,
13455 the result is written right adjusted and padded to the given
13456 size. For example, @samp{%9B} prints the right adjusted month name in
13457 a field of width 9.
13459 An optional modifier can follow the optional flag and width
13460 specification. The modifiers are:
13464 Use the locale's alternate representation for date and time. This
13465 modifier applies to the @samp{%c}, @samp{%C}, @samp{%x}, @samp{%X},
13466 @samp{%y} and @samp{%Y} conversion specifiers. In a Japanese locale, for
13467 example, @samp{%Ex} might yield a date format based on the Japanese
13471 Use the locale's alternate numeric symbols for numbers. This modifier
13472 applies only to numeric conversion specifiers.
13475 If the format supports the modifier but no alternate representation
13476 is available, it is ignored.
13479 @node Setting the time
13480 @subsection Setting the time
13482 @cindex setting the time
13483 @cindex time setting
13484 @cindex appropriate privileges
13486 If given an argument that does not start with @samp{+}, @command{date} sets
13487 the system clock to the date and time specified by that argument (as
13488 described below). You must have appropriate privileges to set the
13489 system clock. The @option{--date} and @option{--set} options may not be
13490 used with such an argument. The @option{--universal} option may be used
13491 with such an argument to indicate that the specified date and time are
13492 relative to Coordinated Universal Time rather than to the local time
13495 The argument must consist entirely of digits, which have the following
13508 first two digits of year (optional)
13510 last two digits of year (optional)
13515 The @option{--set} option also sets the system clock; see the next section.
13518 @node Options for date
13519 @subsection Options for @command{date}
13521 @cindex @command{date} options
13522 @cindex options for @command{date}
13524 The program accepts the following options. Also see @ref{Common options}.
13528 @item -d @var{datestr}
13529 @itemx --date=@var{datestr}
13532 @cindex parsing date strings
13533 @cindex date strings, parsing
13534 @cindex arbitrary date strings, parsing
13537 @opindex next @var{day}
13538 @opindex last @var{day}
13539 Display the date and time specified in @var{datestr} instead of the
13540 current date and time. @var{datestr} can be in almost any common
13541 format. It can contain month names, time zones, @samp{am} and @samp{pm},
13542 @samp{yesterday}, etc. For example, @option{--date="2004-02-27
13543 14:19:13.489392193 +0530"} specifies the instant of time that is
13544 489,392,193 nanoseconds after February 27, 2004 at 2:19:13 PM in a
13545 time zone that is 5 hours and 30 minutes east of @acronym{UTC}.@*
13546 Note: input currently must be in locale independent format. E.g., the
13547 LC_TIME=C below is needed to print back the correct date in many locales:
13549 date -d "$(LC_TIME=C date)"
13551 @xref{Date input formats}.
13553 @item -f @var{datefile}
13554 @itemx --file=@var{datefile}
13557 Parse each line in @var{datefile} as with @option{-d} and display the
13558 resulting date and time. If @var{datefile} is @samp{-}, use standard
13559 input. This is useful when you have many dates to process, because the
13560 system overhead of starting up the @command{date} executable many times can
13563 @item -r @var{file}
13564 @itemx --reference=@var{file}
13566 @opindex --reference
13567 Display the date and time of the last modification of @var{file},
13568 instead of the current date and time.
13575 @opindex --rfc-2822
13576 Display the date and time using the format @samp{%a, %d %b %Y %H:%M:%S
13577 %z}, evaluated in the C locale so abbreviations are always in English.
13581 Fri, 09 Sep 2005 13:51:39 -0700
13584 This format conforms to
13585 @uref{ftp://ftp.rfc-editor.org/in-notes/rfc2822.txt, Internet
13586 @acronym{RFCs} 2822} and
13587 @uref{ftp://ftp.rfc-editor.org/in-notes/rfc822.txt, 822}, the
13588 current and previous standards for Internet email.
13590 @item --rfc-3339=@var{timespec}
13591 @opindex --rfc-3339=@var{timespec}
13592 Display the date using a format specified by
13593 @uref{ftp://ftp.rfc-editor.org/in-notes/rfc3339.txt, Internet
13594 @acronym{RFC} 3339}. This is a subset of the @acronym{ISO} 8601
13595 format, except that it also permits applications to use a space rather
13596 than a @samp{T} to separate dates from times. Unlike the other
13597 standard formats, @acronym{RFC} 3339 format is always suitable as
13598 input for the @option{--date} (@option{-d}) and @option{--file}
13599 (@option{-f}) options, regardless of the current locale.
13601 The argument @var{timespec} specifies how much of the time to include.
13602 It can be one of the following:
13606 Print just the full-date, e.g., @samp{2005-09-14}.
13607 This is equivalent to the format @samp{%Y-%m-%d}.
13610 Print the full-date and full-time separated by a space, e.g.,
13611 @samp{2005-09-14 00:56:06+05:30}. The output ends with a numeric
13612 time-offset; here the @samp{+05:30} means that local time is five
13613 hours and thirty minutes east of @acronym{UTC}. This is equivalent to
13614 the format @samp{%Y-%m-%d %H:%M:%S%:z}.
13617 Like @samp{seconds}, but also print nanoseconds, e.g.,
13618 @samp{2005-09-14 00:56:06.998458565+05:30}.
13619 This is equivalent to the format @samp{%Y-%m-%d %H:%M:%S.%N%:z}.
13623 @item -s @var{datestr}
13624 @itemx --set=@var{datestr}
13627 Set the date and time to @var{datestr}. See @option{-d} above.
13634 @opindex --universal
13635 @cindex Coordinated Universal Time
13637 @cindex Greenwich Mean Time
13640 Use Coordinated Universal Time (@acronym{UTC}) by operating as if the
13641 @env{TZ} environment variable were set to the string @samp{UTC0}.
13643 Universal Time is often called ``Greenwich Mean Time'' (@sc{gmt}) for
13644 historical reasons.
13648 @node Examples of date
13649 @subsection Examples of @command{date}
13651 @cindex examples of @command{date}
13653 Here are a few examples. Also see the documentation for the @option{-d}
13654 option in the previous section.
13659 To print the date of the day before yesterday:
13662 date --date='2 days ago'
13666 To print the date of the day three months and one day hence:
13669 date --date='3 months 1 day'
13673 To print the day of year of Christmas in the current year:
13676 date --date='25 Dec' +%j
13680 To print the current full month name and the day of the month:
13686 But this may not be what you want because for the first nine days of
13687 the month, the @samp{%d} expands to a zero-padded two-digit field,
13688 for example @samp{date -d 1may '+%B %d'} will print @samp{May 01}.
13691 To print a date without the leading zero for one-digit days
13692 of the month, you can use the (@acronym{GNU} extension)
13693 @samp{-} flag to suppress
13694 the padding altogether:
13697 date -d 1may '+%B %-d
13701 To print the current date and time in the format required by many
13702 non-@acronym{GNU} versions of @command{date} when setting the system clock:
13705 date +%m%d%H%M%Y.%S
13709 To set the system clock forward by two minutes:
13712 date --set='+2 minutes'
13716 To print the date in @acronym{RFC} 2822 format,
13717 use @samp{date --rfc-2822}. Here is some example output:
13720 Fri, 09 Sep 2005 13:51:39 -0700
13723 @anchor{%s-examples}
13725 To convert a date string to the number of seconds since the epoch
13726 (which is 1970-01-01 00:00:00 UTC), use the @option{--date} option with
13727 the @samp{%s} format. That can be useful in sorting and/or graphing
13728 and/or comparing data by date. The following command outputs the
13729 number of the seconds since the epoch for the time two minutes after the
13733 date --date='1970-01-01 00:02:00 +0000' +%s
13737 If you do not specify time zone information in the date string,
13738 @command{date} uses your computer's idea of the time zone when
13739 interpreting the string. For example, if your computer's time zone is
13740 that of Cambridge, Massachusetts, which was then 5 hours (i.e., 18,000
13741 seconds) behind UTC:
13744 # local time zone used
13745 date --date='1970-01-01 00:02:00' +%s
13750 If you're sorting or graphing dated data, your raw date values may be
13751 represented as seconds since the epoch. But few people can look at
13752 the date @samp{946684800} and casually note ``Oh, that's the first second
13753 of the year 2000 in Greenwich, England.''
13756 date --date='2000-01-01 UTC' +%s
13760 An alternative is to use the @option{--utc} (@option{-u}) option.
13761 Then you may omit @samp{UTC} from the date string. Although this
13762 produces the same result for @samp{%s} and many other format sequences,
13763 with a time zone offset different from zero, it would give a different
13764 result for zone-dependent formats like @samp{%z}.
13767 date -u --date=2000-01-01 +%s
13771 To convert such an unwieldy number of seconds back to
13772 a more readable form, use a command like this:
13775 # local time zone used
13776 date -d '1970-01-01 UTC 946684800 seconds' +"%Y-%m-%d %T %z"
13777 1999-12-31 19:00:00 -0500
13780 Or if you do not mind depending on the @samp{@@} feature present since
13781 coreutils 5.3.0, you could shorten this to:
13784 date -d @@946684800 +"%F %T %z"
13785 1999-12-31 19:00:00 -0500
13788 Often it is better to output UTC-relative date and time:
13791 date -u -d '1970-01-01 946684800 seconds' +"%Y-%m-%d %T %z"
13792 2000-01-01 00:00:00 +0000
13798 @node arch invocation
13799 @section @command{arch}: Print machine hardware name
13802 @cindex print machine hardware name
13803 @cindex system information, printing
13805 @command{arch} prints the machine hardware name,
13806 and is equivalent to @samp{uname -m}.
13810 arch [@var{option}]
13813 The program accepts the @ref{Common options} only.
13818 @node uname invocation
13819 @section @command{uname}: Print system information
13822 @cindex print system information
13823 @cindex system information, printing
13825 @command{uname} prints information about the machine and operating system
13826 it is run on. If no options are given, @command{uname} acts as if the
13827 @option{-s} option were given. Synopsis:
13830 uname [@var{option}]@dots{}
13833 If multiple options or @option{-a} are given, the selected information is
13834 printed in this order:
13837 @var{kernel-name} @var{nodename} @var{kernel-release} @var{kernel-version}
13838 @var{machine} @var{processor} @var{hardware-platform} @var{operating-system}
13841 The information may contain internal spaces, so such output cannot be
13842 parsed reliably. In the following example, @var{release} is
13843 @samp{2.2.18ss.e820-bda652a #4 SMP Tue Jun 5 11:24:08 PDT 2001}:
13847 @result{} Linux dum 2.2.18 #4 SMP Tue Jun 5 11:24:08 PDT 2001 i686 unknown unknown GNU/Linux
13851 The program accepts the following options. Also see @ref{Common options}.
13859 Print all of the below information, except omit the processor type
13860 and the hardware platform name if they are unknown.
13863 @itemx --hardware-platform
13865 @opindex --hardware-platform
13866 @cindex implementation, hardware
13867 @cindex hardware platform
13868 @cindex platform, hardware
13869 Print the hardware platform name
13870 (sometimes called the hardware implementation).
13871 Print @samp{unknown} if the kernel does not make this information
13872 easily available, as is the case with Linux kernels.
13878 @cindex machine type
13879 @cindex hardware class
13880 @cindex hardware type
13881 Print the machine hardware name (sometimes called the hardware class
13887 @opindex --nodename
13890 @cindex network node name
13891 Print the network node hostname.
13896 @opindex --processor
13897 @cindex host processor type
13898 Print the processor type (sometimes called the instruction set
13899 architecture or ISA).
13900 Print @samp{unknown} if the kernel does not make this information
13901 easily available, as is the case with Linux kernels.
13904 @itemx --operating-system
13906 @opindex --operating-system
13907 @cindex operating system name
13908 Print the name of the operating system.
13911 @itemx --kernel-release
13913 @opindex --kernel-release
13914 @cindex kernel release
13915 @cindex release of kernel
13916 Print the kernel release.
13919 @itemx --kernel-name
13921 @opindex --kernel-name
13922 @cindex kernel name
13923 @cindex name of kernel
13924 Print the kernel name.
13925 @acronym{POSIX} 1003.1-2001 (@pxref{Standards conformance}) calls this
13926 ``the implementation of the operating system'', because the
13927 @acronym{POSIX} specification itself has no notion of ``kernel''.
13928 The kernel name might be the same as the operating system name printed
13929 by the @option{-o} or @option{--operating-system} option, but it might
13930 differ. Some operating systems (e.g., FreeBSD, HP-UX) have the same
13931 name as their underlying kernels; others (e.g., GNU/Linux, Solaris)
13935 @itemx --kernel-version
13937 @opindex --kernel-version
13938 @cindex kernel version
13939 @cindex version of kernel
13940 Print the kernel version.
13947 @node hostname invocation
13948 @section @command{hostname}: Print or set system name
13951 @cindex setting the hostname
13952 @cindex printing the hostname
13953 @cindex system name, printing
13954 @cindex appropriate privileges
13956 With no arguments, @command{hostname} prints the name of the current host
13957 system. With one argument, it sets the current host name to the
13958 specified string. You must have appropriate privileges to set the host
13962 hostname [@var{name}]
13965 The only options are @option{--help} and @option{--version}. @xref{Common
13971 @node hostid invocation
13972 @section @command{hostid}: Print numeric host identifier
13975 @cindex printing the host identifier
13977 @command{hostid} prints the numeric identifier of the current host
13978 in hexadecimal. This command accepts no arguments.
13979 The only options are @option{--help} and @option{--version}.
13980 @xref{Common options}.
13982 For example, here's what it prints on one system I use:
13989 On that system, the 32-bit quantity happens to be closely
13990 related to the system's Internet address, but that isn't always
13995 @node uptime invocation
13996 @section @command{uptime}: Print system uptime and load
13999 @cindex printing the system uptime and load
14001 @command{uptime} prints the current time, the system's uptime, the
14002 number of logged-in users and the current load average.
14004 If an argument is specified, it is used as the file to be read
14005 to discover how many users are logged in. If no argument is
14006 specified, a system default is used (@command{uptime --help} indicates
14007 the default setting).
14009 The only options are @option{--help} and @option{--version}.
14010 @xref{Common options}.
14012 For example, here's what it prints right now on one system I use:
14016 14:07 up 3:35, 3 users, load average: 1.39, 1.15, 1.04
14019 The precise method of calculation of load average varies somewhat
14020 between systems. Some systems calculate it as the average number of
14021 runnable processes over the last 1, 5 and 15 minutes, but some systems
14022 also include processes in the uninterruptible sleep state (that is,
14023 those processes which are waiting for disk I/O). The Linux kernel
14024 includes uninterruptible processes.
14026 @node SELinux context
14027 @chapter SELinux context
14029 @cindex SELinux context
14030 @cindex SELinux, context
14031 @cindex commands for SELinux context
14033 This section describes commands for operations with SELinux
14037 * chcon invocation:: Change SELinux context of file
14038 * runcon invocation:: Run a command in specified SELinux context
14041 @node chcon invocation
14042 @section @command{chcon}: Change SELinux context of file
14045 @cindex changing security context
14046 @cindex change SELinux context
14048 @command{chcon} changes the SELinux security context of the selected files.
14052 chcon [@var{option}]@dots{} @var{context} @var{file}@dots{}
14053 chcon [@var{option}]@dots{} [-u @var{user}] [-r @var{role}] [-l @var{range}] [-t @var{type}] @var{file}@dots{}
14054 chcon [@var{option}]@dots{} --reference=@var{rfile} @var{file}@dots{}
14057 Change the SELinux security context of each @var{file} to @var{context}.
14058 With @option{--reference}, change the security context of each @var{file}
14059 to that of @var{rfile}.
14061 The program accepts the following options. Also see @ref{Common options}.
14066 @itemx --no-dereference
14068 @opindex --no-dereference
14069 @cindex no dereference
14070 Affect symbolic links instead of any referenced file.
14072 @item --reference=@var{rfile}
14073 @opindex --reference
14074 @cindex reference file
14075 Use @var{rfile}'s security context rather than specifying a @var{context} value.
14080 @opindex --recursive
14081 Operate on files and directories recursively.
14084 @xref{Traversing symlinks}.
14087 @xref{Traversing symlinks}.
14090 @xref{Traversing symlinks}.
14097 Output a diagnostic for every file processed.
14099 @item -u @var{user}
14100 @itemx --user=@var{user}
14103 Set user @var{user} in the target security context.
14105 @item -r @var{role}
14106 @itemx --role=@var{role}
14109 Set role @var{role} in the target security context.
14111 @item -t @var{type}
14112 @itemx --type=@var{type}
14115 Set type @var{type} in the target security context.
14117 @item -l @var{range}
14118 @itemx --range=@var{range}
14121 Set range @var{range} in the target security context.
14127 @node runcon invocation
14128 @section @command{runcon}: Run a command in specified SELinux context
14131 @cindex run with security context
14134 @command{runcon} runs file in specified SELinux security context.
14138 runcon @var{context} @var{command} [@var{args}]
14139 runcon [ -c ] [-u @var{user}] [-r @var{role}] [-t @var{type}] [-l @var{range}] @var{command} [@var{args}]
14142 Run @var{command} with completely-specified @var{context}, or with
14143 current or transitioned security context modified by one or more of @var{level},
14144 @var{role}, @var{type} and @var{user}.
14146 If none of @option{-c}, @option{-t}, @option{-u}, @option{-r}, or @option{-l}
14147 is specified, the first argument is used as the complete context.
14148 Any additional arguments after @var{command}
14149 are interpreted as arguments to the command.
14151 With neither @var{context} nor @var{command}, print the current security context.
14153 The program accepts the following options. Also see @ref{Common options}.
14161 Compute process transition context before modifying.
14163 @item -u @var{user}
14164 @itemx --user=@var{user}
14167 Set user @var{user} in the target security context.
14169 @item -r @var{role}
14170 @itemx --role=@var{role}
14173 Set role @var{role} in the target security context.
14175 @item -t @var{type}
14176 @itemx --type=@var{type}
14179 Set type @var{type} in the target security context.
14181 @item -l @var{range}
14182 @itemx --range=@var{range}
14185 Set range @var{range} in the target security context.
14189 @cindex exit status of @command{runcon}
14193 126 if @var{command} is found but cannot be invoked
14194 127 if @command{runcon} itself fails or if @var{command} cannot be found
14195 the exit status of @var{command} otherwise
14198 @node Modified command invocation
14199 @chapter Modified command invocation
14201 @cindex modified command invocation
14202 @cindex invocation of commands, modified
14203 @cindex commands for invoking other commands
14205 This section describes commands that run other commands in some context
14206 different than the current one: a modified environment, as a different
14210 * chroot invocation:: Modify the root directory.
14211 * env invocation:: Modify environment variables.
14212 * nice invocation:: Modify niceness.
14213 * nohup invocation:: Immunize to hangups.
14214 * stdbuf invocation:: Modify buffering of standard streams.
14215 * su invocation:: Modify user and group ID.
14216 * timeout invocation:: Run with time limit.
14220 @node chroot invocation
14221 @section @command{chroot}: Run a command with a different root directory
14224 @cindex running a program in a specified root directory
14225 @cindex root directory, running a program in a specified
14227 @command{chroot} runs a command with a specified root directory.
14228 On many systems, only the super-user can do this.@footnote{However,
14229 some systems (e.g., FreeBSD) can be configured to allow certain regular
14230 users to use the @code{chroot} system call, and hence to run this program.
14231 Also, on Cygwin, anyone can run the @command{chroot} command, because the
14232 underlying function is non-privileged due to lack of support in MS-Windows.}
14236 chroot @var{option} @var{newroot} [@var{command} [@var{args}]@dots{}]
14237 chroot @var{option}
14240 Ordinarily, file names are looked up starting at the root of the
14241 directory structure, i.e., @file{/}. @command{chroot} changes the root to
14242 the directory @var{newroot} (which must exist) and then runs
14243 @var{command} with optional @var{args}. If @var{command} is not
14244 specified, the default is the value of the @env{SHELL} environment
14245 variable or @command{/bin/sh} if not set, invoked with the @option{-i} option.
14246 @var{command} must not be a special built-in utility
14247 (@pxref{Special built-in utilities}).
14249 The program accepts the following options. Also see @ref{Common options}.
14250 Options must precede operands.
14254 @itemx --userspec=@var{user}[:@var{group}]
14255 @opindex --userspec
14256 By default, @var{command} is run with the same credentials
14257 as the invoking process.
14258 Use this option to run it as a different @var{user} and/or with a
14259 different primary @var{group}.
14261 @itemx --groups=@var{groups}
14263 Use this option to specify the supplementary @var{groups} to be
14264 used by the new process.
14265 The items in the list (names or numeric IDs) must be separated by commas.
14269 Here are a few tips to help avoid common problems in using chroot.
14270 To start with a simple example, make @var{command} refer to a statically
14271 linked binary. If you were to use a dynamically linked executable, then
14272 you'd have to arrange to have the shared libraries in the right place under
14273 your new root directory.
14275 For example, if you create a statically linked @command{ls} executable,
14276 and put it in @file{/tmp/empty}, you can run this command as root:
14279 $ chroot /tmp/empty /ls -Rl /
14282 Then you'll see output like this:
14287 -rwxr-xr-x 1 0 0 1041745 Aug 16 11:17 ls
14290 If you want to use a dynamically linked executable, say @command{bash},
14291 then first run @samp{ldd bash} to see what shared objects it needs.
14292 Then, in addition to copying the actual binary, also copy the listed
14293 files to the required positions under your intended new root directory.
14294 Finally, if the executable requires any other files (e.g., data, state,
14295 device files), copy them into place, too.
14297 @cindex exit status of @command{chroot}
14301 1 if @command{chroot} itself fails
14302 126 if @var{command} is found but cannot be invoked
14303 127 if @var{command} cannot be found
14304 the exit status of @var{command} otherwise
14308 @node env invocation
14309 @section @command{env}: Run a command in a modified environment
14312 @cindex environment, running a program in a modified
14313 @cindex modified environment, running a program in a
14314 @cindex running a program in a modified environment
14316 @command{env} runs a command with a modified environment. Synopses:
14319 env [@var{option}]@dots{} [@var{name}=@var{value}]@dots{} @c
14320 [@var{command} [@var{args}]@dots{}]
14324 Operands of the form @samp{@var{variable}=@var{value}} set
14325 the environment variable @var{variable} to value @var{value}.
14326 @var{value} may be empty (@samp{@var{variable}=}). Setting a variable
14327 to an empty value is different from unsetting it.
14328 These operands are evaluated left-to-right, so if two operands
14329 mention the same variable the earlier is ignored.
14331 Environment variable names can be empty, and can contain any
14332 characters other than @samp{=} and @acronym{ASCII} @sc{nul}.
14333 However, it is wise to limit yourself to names that
14334 consist solely of underscores, digits, and @acronym{ASCII} letters,
14335 and that begin with a non-digit, as applications like the shell do not
14336 work well with other names.
14339 The first operand that does not contain the character @samp{=}
14340 specifies the program to invoke; it is
14341 searched for according to the @env{PATH} environment variable. Any
14342 remaining arguments are passed as arguments to that program.
14343 The program should not be a special built-in utility
14344 (@pxref{Special built-in utilities}).
14346 @cindex environment, printing
14348 If no command name is specified following the environment
14349 specifications, the resulting environment is printed. This is like
14350 specifying the @command{printenv} program.
14352 The program accepts the following options. Also see @ref{Common options}.
14353 Options must precede operands.
14357 @item -u @var{name}
14358 @itemx --unset=@var{name}
14361 Remove variable @var{name} from the environment, if it was in the
14366 @itemx --ignore-environment
14369 @opindex --ignore-environment
14370 Start with an empty environment, ignoring the inherited environment.
14374 @cindex exit status of @command{env}
14378 0 if no @var{command} is specified and the environment is output
14379 1 if @command{env} itself fails
14380 126 if @var{command} is found but cannot be invoked
14381 127 if @var{command} cannot be found
14382 the exit status of @var{command} otherwise
14386 @node nice invocation
14387 @section @command{nice}: Run a command with modified niceness
14391 @cindex scheduling, affecting
14392 @cindex appropriate privileges
14394 @command{nice} prints or modifies a process's @dfn{niceness},
14395 a parameter that affects whether the process is scheduled favorably.
14399 nice [@var{option}]@dots{} [@var{command} [@var{arg}]@dots{}]
14402 If no arguments are given, @command{nice} prints the current niceness.
14403 Otherwise, @command{nice} runs the given @var{command} with its
14404 niceness adjusted. By default, its niceness is incremented by 10.
14406 Niceness values range at least from @minus{}20 (process has high priority
14407 and gets more resources, thus slowing down other processes) through 19
14408 (process has lower priority and runs slowly itself, but has less impact
14409 on the speed of other running processes). Some systems
14410 may have a wider range of nicenesses; conversely, other systems may
14411 enforce more restrictive limits. An attempt to set the niceness
14412 outside the supported range is treated as an attempt to use the
14413 minimum or maximum supported value.
14415 A niceness should not be confused with a scheduling priority, which
14416 lets applications determine the order in which threads are scheduled
14417 to run. Unlike a priority, a niceness is merely advice to the
14418 scheduler, which the scheduler is free to ignore. Also, as a point of
14419 terminology, @acronym{POSIX} defines the behavior of @command{nice} in
14420 terms of a @dfn{nice value}, which is the nonnegative difference
14421 between a niceness and the minimum niceness. Though @command{nice}
14422 conforms to @acronym{POSIX}, its documentation and diagnostics use the
14423 term ``niceness'' for compatibility with historical practice.
14425 @var{command} must not be a special built-in utility (@pxref{Special
14426 built-in utilities}).
14428 @mayConflictWithShellBuiltIn{nice}
14430 The program accepts the following option. Also see @ref{Common options}.
14431 Options must precede operands.
14434 @item -n @var{adjustment}
14435 @itemx --adjustment=@var{adjustment}
14437 @opindex --adjustment
14438 Add @var{adjustment} instead of 10 to the command's niceness. If
14439 @var{adjustment} is negative and you lack appropriate privileges,
14440 @command{nice} issues a warning but otherwise acts as if you specified
14443 For compatibility @command{nice} also supports an obsolete
14444 option syntax @option{-@var{adjustment}}. New scripts should use
14445 @option{-n @var{adjustment}} instead.
14449 @cindex exit status of @command{nice}
14453 0 if no @var{command} is specified and the niceness is output
14454 1 if @command{nice} itself fails
14455 126 if @var{command} is found but cannot be invoked
14456 127 if @var{command} cannot be found
14457 the exit status of @var{command} otherwise
14460 It is sometimes useful to run a non-interactive program with reduced niceness.
14463 $ nice factor 4611686018427387903
14466 Since @command{nice} prints the current niceness,
14467 you can invoke it through itself to demonstrate how it works.
14469 The default behavior is to increase the niceness by @samp{10}:
14480 The @var{adjustment} is relative to the current niceness. In the
14481 next example, the first @command{nice} invocation runs the second one
14482 with niceness 10, and it in turn runs the final one with a niceness
14486 $ nice nice -n 3 nice
14490 Specifying a niceness larger than the supported range
14491 is the same as specifying the maximum supported value:
14494 $ nice -n 10000000000 nice
14498 Only a privileged user may run a process with lower niceness:
14502 nice: cannot set niceness: Permission denied
14504 $ sudo nice -n -1 nice
14509 @node nohup invocation
14510 @section @command{nohup}: Run a command immune to hangups
14513 @cindex hangups, immunity to
14514 @cindex immunity to hangups
14515 @cindex logging out and continuing to run
14518 @command{nohup} runs the given @var{command} with hangup signals ignored,
14519 so that the command can continue running in the background after you log
14523 nohup @var{command} [@var{arg}]@dots{}
14526 If standard input is a terminal, it is redirected from
14527 @file{/dev/null} so that terminal sessions do not mistakenly consider
14528 the terminal to be used by the command. This is a @acronym{GNU}
14529 extension; programs intended to be portable to non-@acronym{GNU} hosts
14530 should use @samp{nohup @var{command} [@var{arg}]@dots{} </dev/null}
14534 If standard output is a terminal, the command's standard output is appended
14535 to the file @file{nohup.out}; if that cannot be written to, it is appended
14536 to the file @file{$HOME/nohup.out}; and if that cannot be written to, the
14537 command is not run.
14538 Any @file{nohup.out} or @file{$HOME/nohup.out} file created by
14539 @command{nohup} is made readable and writable only to the user,
14540 regardless of the current umask settings.
14542 If standard error is a terminal, it is normally redirected to the same file
14543 descriptor as the (possibly-redirected) standard output.
14544 However, if standard output is closed, standard error terminal output
14545 is instead appended to the file @file{nohup.out} or
14546 @file{$HOME/nohup.out} as above.
14548 To capture the command's output to a file other than @file{nohup.out}
14549 you can redirect it. For example, to capture the output of
14553 nohup make > make.log
14556 @command{nohup} does not automatically put the command it runs in the
14557 background; you must do that explicitly, by ending the command line
14558 with an @samp{&}. Also, @command{nohup} does not alter the
14559 niceness of @var{command}; use @command{nice} for that,
14560 e.g., @samp{nohup nice @var{command}}.
14562 @var{command} must not be a special built-in utility (@pxref{Special
14563 built-in utilities}).
14565 The only options are @option{--help} and @option{--version}. @xref{Common
14566 options}. Options must precede operands.
14568 @cindex exit status of @command{nohup}
14572 126 if @var{command} is found but cannot be invoked
14573 127 if @command{nohup} itself fails or if @var{command} cannot be found
14574 the exit status of @var{command} otherwise
14578 @node stdbuf invocation
14579 @section @command{stdbuf}: Run a command with modified I/O stream buffering
14582 @cindex standard streams, buffering
14583 @cindex line buffered
14585 @command{stdbuf} allows one to modify the buffering operations of the
14586 three standard I/O streams associated with a program. Synopsis:
14589 stdbuf @var{option}@dots{} @var{command}
14592 Any additional @var{arg}s are passed as additional arguments to the
14595 The program accepts the following options. Also see @ref{Common options}.
14599 @item -i @var{mode}
14600 @itemx --input=@var{mode}
14603 Adjust the standard input stream buffering.
14605 @item -o @var{mode}
14606 @itemx --output=@var{mode}
14609 Adjust the standard output stream buffering.
14611 @item -e @var{mode}
14612 @itemx --error=@var{mode}
14615 Adjust the standard error stream buffering.
14619 The @var{mode} can be specified as follows:
14624 Set the stream to line buffered mode.
14625 In this mode data is coalesced until a newline is output or
14626 input is read from any stream attached to a terminal device.
14627 This option is invalid with standard input.
14630 Disable buffering of the selected stream.
14631 In this mode data is output immediately and only the
14632 amount of data requested is read from input.
14635 Specify the size of the buffer to use in fully buffered mode.
14636 @multiplierSuffixesNoBlocks{size}
14640 NOTE: If @var{command} adjusts the buffering of its standard streams
14641 (@command{tee} does for e.g.) then that will override corresponding settings
14642 changed by @command{stdbuf}. Also some filters (like @command{dd} and
14643 @command{cat} etc.) don't use streams for I/O, and are thus unaffected
14644 by @command{stdbuf} settings.
14646 @cindex exit status of @command{stdbuf}
14650 125 if @command{stdbuf} itself fails
14651 126 if @var{command} is found but cannot be invoked
14652 127 if @var{command} cannot be found
14653 the exit status of @var{command} otherwise
14657 @node su invocation
14658 @section @command{su}: Run a command with substitute user and group ID
14661 @cindex substitute user and group IDs
14662 @cindex user ID, switching
14663 @cindex super-user, becoming
14664 @cindex root, becoming
14666 @command{su} allows one user to temporarily become another user. It runs a
14667 command (often an interactive shell) with the real and effective user
14668 ID, group ID, and supplemental groups of a given @var{user}. Synopsis:
14671 su [@var{option}]@dots{} [@var{user} [@var{arg}]@dots{}]
14674 @cindex passwd entry, and @command{su} shell
14676 @flindex /etc/passwd
14677 If no @var{user} is given, the default is @code{root}, the super-user.
14678 The shell to use is taken from @var{user}'s @code{passwd} entry, or
14679 @file{/bin/sh} if none is specified there. If @var{user} has a
14680 password, @command{su} prompts for the password unless run by a user with
14681 effective user ID of zero (the super-user).
14687 @cindex login shell
14688 By default, @command{su} does not change the current directory.
14689 It sets the environment variables @env{HOME} and @env{SHELL}
14690 from the password entry for @var{user}, and if @var{user} is not
14691 the super-user, sets @env{USER} and @env{LOGNAME} to @var{user}.
14692 By default, the shell is not a login shell.
14694 Any additional @var{arg}s are passed as additional arguments to the
14697 @cindex @option{-su}
14698 GNU @command{su} does not treat @file{/bin/sh} or any other shells specially
14699 (e.g., by setting @code{argv[0]} to @option{-su}, passing @option{-c} only
14700 to certain shells, etc.).
14703 @command{su} can optionally be compiled to use @code{syslog} to report
14704 failed, and optionally successful, @command{su} attempts. (If the system
14705 supports @code{syslog}.) However, GNU @command{su} does not check if the
14706 user is a member of the @code{wheel} group; see below.
14708 The program accepts the following options. Also see @ref{Common options}.
14711 @item -c @var{command}
14712 @itemx --command=@var{command}
14715 Pass @var{command}, a single command line to run, to the shell with
14716 a @option{-c} option instead of starting an interactive shell.
14723 @cindex file name pattern expansion, disabled
14724 @cindex globbing, disabled
14725 Pass the @option{-f} option to the shell. This probably only makes sense
14726 if the shell run is @command{csh} or @command{tcsh}, for which the @option{-f}
14727 option prevents reading the startup file (@file{.cshrc}). With
14728 Bourne-like shells, the @option{-f} option disables file name pattern
14729 expansion (globbing), which is not likely to be useful.
14737 @c other variables already indexed above
14740 @cindex login shell, creating
14741 Make the shell a login shell. This means the following. Unset all
14742 environment variables except @env{TERM}, @env{HOME}, and @env{SHELL}
14743 (which are set as described above), and @env{USER} and @env{LOGNAME}
14744 (which are set, even for the super-user, as described above), and set
14745 @env{PATH} to a compiled-in default value. Change to @var{user}'s home
14746 directory. Prepend @samp{-} to the shell's name, intended to make it
14747 read its login startup file(s).
14751 @itemx --preserve-environment
14754 @opindex --preserve-environment
14755 @cindex environment, preserving
14756 @flindex /etc/shells
14757 @cindex restricted shell
14758 Do not change the environment variables @env{HOME}, @env{USER},
14759 @env{LOGNAME}, or @env{SHELL}. Run the shell given in the environment
14760 variable @env{SHELL} instead of the shell from @var{user}'s passwd
14761 entry, unless the user running @command{su} is not the super-user and
14762 @var{user}'s shell is restricted. A @dfn{restricted shell} is one that
14763 is not listed in the file @file{/etc/shells}, or in a compiled-in list
14764 if that file does not exist. Parts of what this option does can be
14765 overridden by @option{--login} and @option{--shell}.
14767 @item -s @var{shell}
14768 @itemx --shell=@var{shell}
14771 Run @var{shell} instead of the shell from @var{user}'s passwd entry,
14772 unless the user running @command{su} is not the super-user and @var{user}'s
14773 shell is restricted (see @option{-m} just above).
14777 @cindex exit status of @command{su}
14781 1 if @command{su} itself fails
14782 126 if subshell is found but cannot be invoked
14783 127 if subshell cannot be found
14784 the exit status of the subshell otherwise
14787 @cindex wheel group, not supported
14788 @cindex group wheel, not supported
14790 @subsection Why GNU @command{su} does not support the @samp{wheel} group
14792 (This section is by Richard Stallman.)
14796 Sometimes a few of the users try to hold total power over all the
14797 rest. For example, in 1984, a few users at the MIT AI lab decided to
14798 seize power by changing the operator password on the Twenex system and
14799 keeping it secret from everyone else. (I was able to thwart this coup
14800 and give power back to the users by patching the kernel, but I
14801 wouldn't know how to do that in Unix.)
14803 However, occasionally the rulers do tell someone. Under the usual
14804 @command{su} mechanism, once someone learns the root password who
14805 sympathizes with the ordinary users, he or she can tell the rest. The
14806 ``wheel group'' feature would make this impossible, and thus cement the
14807 power of the rulers.
14809 I'm on the side of the masses, not that of the rulers. If you are
14810 used to supporting the bosses and sysadmins in whatever they do, you
14811 might find this idea strange at first.
14814 @node timeout invocation
14815 @section @command{timeout}: Run a command with a time limit
14819 @cindex run commands with bounded time
14821 @command{timeout} runs the given @var{command} and kills it if it is
14822 still running after the specified time interval. Synopsis:
14825 timeout [@var{option}] @var{number}[smhd] @var{command} [@var{arg}]@dots{}
14829 @var{number} is an integer followed by an optional unit; the default
14830 is seconds. The units are:
14843 @var{command} must not be a special built-in utility (@pxref{Special
14844 built-in utilities}).
14846 The program accepts the following option. Also see @ref{Common options}.
14847 Options must precede operands.
14850 @item -s @var{signal}
14851 @itemx --signal=@var{signal}
14854 Send this @var{signal} to @var{command} on timeout, rather than the
14855 default @samp{TERM} signal. @var{signal} may be a name like @samp{HUP}
14856 or a number. Also see @xref{Signal specifications}.
14860 @cindex exit status of @command{timeout}
14864 124 if @var{command} times out
14865 125 if @command{timeout} itself fails
14866 126 if @var{command} is found but cannot be invoked
14867 127 if @var{command} cannot be found
14868 the exit status of @var{command} otherwise
14872 @node Process control
14873 @chapter Process control
14875 @cindex processes, commands for controlling
14876 @cindex commands for controlling processes
14879 * kill invocation:: Sending a signal to processes.
14883 @node kill invocation
14884 @section @command{kill}: Send a signal to processes
14887 @cindex send a signal to processes
14889 The @command{kill} command sends a signal to processes, causing them
14890 to terminate or otherwise act upon receiving the signal in some way.
14891 Alternatively, it lists information about signals. Synopses:
14894 kill [-s @var{signal} | --signal @var{signal} | -@var{signal}] @var{pid}@dots{}
14895 kill [-l | --list | -t | --table] [@var{signal}]@dots{}
14898 @mayConflictWithShellBuiltIn{kill}
14900 The first form of the @command{kill} command sends a signal to all
14901 @var{pid} arguments. The default signal to send if none is specified
14902 is @samp{TERM}. The special signal number @samp{0} does not denote a
14903 valid signal, but can be used to test whether the @var{pid} arguments
14904 specify processes to which a signal could be sent.
14906 If @var{pid} is positive, the signal is sent to the process with the
14907 process ID @var{pid}. If @var{pid} is zero, the signal is sent to all
14908 processes in the process group of the current process. If @var{pid}
14909 is @minus{}1, the signal is sent to all processes for which the user has
14910 permission to send a signal. If @var{pid} is less than @minus{}1, the signal
14911 is sent to all processes in the process group that equals the absolute
14912 value of @var{pid}.
14914 If @var{pid} is not positive, a system-dependent set of system
14915 processes is excluded from the list of processes to which the signal
14918 If a negative @var{pid} argument is desired as the first one, it
14919 should be preceded by @option{--}. However, as a common extension to
14920 @acronym{POSIX}, @option{--} is not required with @samp{kill
14921 -@var{signal} -@var{pid}}. The following commands are equivalent:
14930 The first form of the @command{kill} command succeeds if every @var{pid}
14931 argument specifies at least one process that the signal was sent to.
14933 The second form of the @command{kill} command lists signal information.
14934 Either the @option{-l} or @option{--list} option, or the @option{-t}
14935 or @option{--table} option must be specified. Without any
14936 @var{signal} argument, all supported signals are listed. The output
14937 of @option{-l} or @option{--list} is a list of the signal names, one
14938 per line; if @var{signal} is already a name, the signal number is
14939 printed instead. The output of @option{-t} or @option{--table} is a
14940 table of signal numbers, names, and descriptions. This form of the
14941 @command{kill} command succeeds if all @var{signal} arguments are valid
14942 and if there is no output error.
14944 The @command{kill} command also supports the @option{--help} and
14945 @option{--version} options. @xref{Common options}.
14947 A @var{signal} may be a signal name like @samp{HUP}, or a signal
14948 number like @samp{1}, or an exit status of a process terminated by the
14949 signal. A signal name can be given in canonical form or prefixed by
14950 @samp{SIG}. The case of the letters is ignored, except for the
14951 @option{-@var{signal}} option which must use upper case to avoid
14952 ambiguity with lower case option letters. For a list of supported
14953 signal names and numbers see @xref{Signal specifications}.
14958 @cindex delaying commands
14959 @cindex commands for delaying
14961 @c Perhaps @command{wait} or other commands should be described here also?
14964 * sleep invocation:: Delay for a specified time.
14968 @node sleep invocation
14969 @section @command{sleep}: Delay for a specified time
14972 @cindex delay for a specified time
14974 @command{sleep} pauses for an amount of time specified by the sum of
14975 the values of the command line arguments.
14979 sleep @var{number}[smhd]@dots{}
14983 Each argument is a number followed by an optional unit; the default
14984 is seconds. The units are:
14997 Historical implementations of @command{sleep} have required that
14998 @var{number} be an integer, and only accepted a single argument
14999 without a suffix. However, GNU @command{sleep} accepts
15000 arbitrary floating point numbers (using a period before any fractional
15003 The only options are @option{--help} and @option{--version}. @xref{Common
15006 @c sleep is a shell built-in at least with Solaris 11's /bin/sh
15007 @mayConflictWithShellBuiltIn{sleep}
15012 @node Numeric operations
15013 @chapter Numeric operations
15015 @cindex numeric operations
15016 These programs do numerically-related operations.
15019 * factor invocation:: Show factors of numbers.
15020 * seq invocation:: Print sequences of numbers.
15024 @node factor invocation
15025 @section @command{factor}: Print prime factors
15028 @cindex prime factors
15030 @command{factor} prints prime factors. Synopses:
15033 factor [@var{number}]@dots{}
15034 factor @var{option}
15037 If no @var{number} is specified on the command line, @command{factor} reads
15038 numbers from standard input, delimited by newlines, tabs, or spaces.
15040 The @command{factor} command supports only a small number of options:
15044 Print a short help on standard output, then exit without further
15048 Print the program version on standard output, then exit without further
15052 Factoring the product of the eighth and ninth Mersenne primes
15053 takes about 30 milliseconds of CPU time on a 2.2 GHz Athlon.
15056 M8=`echo 2^31-1|bc` ; M9=`echo 2^61-1|bc`
15057 /usr/bin/time -f '%U' factor $(echo "$M8 * $M9" | bc)
15058 4951760154835678088235319297: 2147483647 2305843009213693951
15062 Similarly, factoring the eighth Fermat number @math{2^{256}+1} takes
15063 about 20 seconds on the same machine.
15065 Factoring large prime numbers is, in general, hard. The Pollard Rho
15066 algorithm used by @command{factor} is particularly effective for
15067 numbers with relatively small factors. If you wish to factor large
15068 numbers which do not have small factors (for example, numbers which
15069 are the product of two large primes), other methods are far better.
15071 If @command{factor} is built without using GNU MP, only
15072 single-precision arithmetic is available, and so large numbers
15073 (typically @math{2^{64}} and above) will not be supported. The single-precision
15074 code uses an algorithm which is designed for factoring smaller
15080 @node seq invocation
15081 @section @command{seq}: Print numeric sequences
15084 @cindex numeric sequences
15085 @cindex sequence of numbers
15087 @command{seq} prints a sequence of numbers to standard output. Synopses:
15090 seq [@var{option}]@dots{} @var{last}
15091 seq [@var{option}]@dots{} @var{first} @var{last}
15092 seq [@var{option}]@dots{} @var{first} @var{increment} @var{last}
15095 @command{seq} prints the numbers from @var{first} to @var{last} by
15096 @var{increment}. By default, each number is printed on a separate line.
15097 When @var{increment} is not specified, it defaults to @samp{1},
15098 even when @var{first} is larger than @var{last}.
15099 @var{first} also defaults to @samp{1}. So @code{seq 1} prints
15100 @samp{1}, but @code{seq 0} and @code{seq 10 5} produce no output.
15101 Floating-point numbers
15102 may be specified (using a period before any fractional digits).
15104 The program accepts the following options. Also see @ref{Common options}.
15105 Options must precede operands.
15108 @item -f @var{format}
15109 @itemx --format=@var{format}
15110 @opindex -f @var{format}
15111 @opindex --format=@var{format}
15112 @cindex formatting of numbers in @command{seq}
15113 Print all numbers using @var{format}.
15114 @var{format} must contain exactly one of the @samp{printf}-style
15115 floating point conversion specifications @samp{%a}, @samp{%e},
15116 @samp{%f}, @samp{%g}, @samp{%A}, @samp{%E}, @samp{%F}, @samp{%G}.
15117 The @samp{%} may be followed by zero or more flags taken from the set
15118 @samp{-+#0 '}, then an optional width containing one or more digits,
15119 then an optional precision consisting of a @samp{.} followed by zero
15120 or more digits. @var{format} may also contain any number of @samp{%%}
15121 conversion specifications. All conversion specifications have the
15122 same meaning as with @samp{printf}.
15124 The default format is derived from @var{first}, @var{step}, and
15125 @var{last}. If these all use a fixed point decimal representation,
15126 the default format is @samp{%.@var{p}f}, where @var{p} is the minimum
15127 precision that can represent the output numbers exactly. Otherwise,
15128 the default format is @samp{%g}.
15130 @item -s @var{string}
15131 @itemx --separator=@var{string}
15132 @cindex separator for numbers in @command{seq}
15133 Separate numbers with @var{string}; default is a newline.
15134 The output always terminates with a newline.
15137 @itemx --equal-width
15138 Print all numbers with the same width, by padding with leading zeros.
15139 @var{first}, @var{step}, and @var{last} should all use a fixed point
15140 decimal representation.
15141 (To have other kinds of padding, use @option{--format}).
15145 You can get finer-grained control over output with @option{-f}:
15148 $ seq -f '(%9.2E)' -9e5 1.1e6 1.3e6
15154 If you want hexadecimal integer output, you can use @command{printf}
15155 to perform the conversion:
15158 $ printf '%x\n' `seq 1048575 1024 1050623`
15164 For very long lists of numbers, use xargs to avoid
15165 system limitations on the length of an argument list:
15168 $ seq 1000000 | xargs printf '%x\n' | tail -n 3
15174 To generate octal output, use the printf @code{%o} format instead
15177 On most systems, seq can produce whole-number output for values up to
15178 at least @math{2^{53}}. Larger integers are approximated. The details
15179 differ depending on your floating-point implementation, but a common
15180 case is that @command{seq} works with integers through @math{2^{64}},
15181 and larger integers may not be numerically correct:
15184 $ seq 18446744073709551616 1 18446744073709551618
15185 18446744073709551616
15186 18446744073709551616
15187 18446744073709551618
15190 Be careful when using @command{seq} with outlandish values: otherwise
15191 you may see surprising results, as @command{seq} uses floating point
15192 internally. For example, on the x86 platform, where the internal
15193 representation uses a 64-bit fraction, the command:
15196 seq 1 0.0000000000000000001 1.0000000000000000009
15199 outputs 1.0000000000000000007 twice and skips 1.0000000000000000008.
15204 @node File permissions
15205 @chapter File permissions
15208 @include getdate.texi
15212 @node Opening the software toolbox
15213 @chapter Opening the Software Toolbox
15215 An earlier version of this chapter appeared in
15216 @uref{http://www.linuxjournal.com/article.php?sid=2762, the
15217 @cite{What's GNU?} column of @cite{Linux Journal}, 2 (June, 1994)}.
15218 It was written by Arnold Robbins.
15221 * Toolbox introduction:: Toolbox introduction
15222 * I/O redirection:: I/O redirection
15223 * The who command:: The @command{who} command
15224 * The cut command:: The @command{cut} command
15225 * The sort command:: The @command{sort} command
15226 * The uniq command:: The @command{uniq} command
15227 * Putting the tools together:: Putting the tools together
15231 @node Toolbox introduction
15232 @unnumberedsec Toolbox Introduction
15234 This month's column is only peripherally related to the GNU Project, in
15235 that it describes a number of the GNU tools on your GNU/Linux system and how they
15236 might be used. What it's really about is the ``Software Tools'' philosophy
15237 of program development and usage.
15239 The software tools philosophy was an important and integral concept
15240 in the initial design and development of Unix (of which Linux and GNU are
15241 essentially clones). Unfortunately, in the modern day press of
15242 Internetworking and flashy GUIs, it seems to have fallen by the
15243 wayside. This is a shame, since it provides a powerful mental model
15244 for solving many kinds of problems.
15246 Many people carry a Swiss Army knife around in their pants pockets (or
15247 purse). A Swiss Army knife is a handy tool to have: it has several knife
15248 blades, a screwdriver, tweezers, toothpick, nail file, corkscrew, and perhaps
15249 a number of other things on it. For the everyday, small miscellaneous jobs
15250 where you need a simple, general purpose tool, it's just the thing.
15252 On the other hand, an experienced carpenter doesn't build a house using
15253 a Swiss Army knife. Instead, he has a toolbox chock full of specialized
15254 tools---a saw, a hammer, a screwdriver, a plane, and so on. And he knows
15255 exactly when and where to use each tool; you won't catch him hammering nails
15256 with the handle of his screwdriver.
15258 The Unix developers at Bell Labs were all professional programmers and trained
15259 computer scientists. They had found that while a one-size-fits-all program
15260 might appeal to a user because there's only one program to use, in practice
15265 difficult to write,
15268 difficult to maintain and
15272 difficult to extend to meet new situations.
15275 Instead, they felt that programs should be specialized tools. In short, each
15276 program ``should do one thing well.'' No more and no less. Such programs are
15277 simpler to design, write, and get right---they only do one thing.
15279 Furthermore, they found that with the right machinery for hooking programs
15280 together, that the whole was greater than the sum of the parts. By combining
15281 several special purpose programs, you could accomplish a specific task
15282 that none of the programs was designed for, and accomplish it much more
15283 quickly and easily than if you had to write a special purpose program.
15284 We will see some (classic) examples of this further on in the column.
15285 (An important additional point was that, if necessary, take a detour
15286 and build any software tools you may need first, if you don't already
15287 have something appropriate in the toolbox.)
15289 @node I/O redirection
15290 @unnumberedsec I/O Redirection
15292 Hopefully, you are familiar with the basics of I/O redirection in the
15293 shell, in particular the concepts of ``standard input,'' ``standard output,''
15294 and ``standard error''. Briefly, ``standard input'' is a data source, where
15295 data comes from. A program should not need to either know or care if the
15296 data source is a disk file, a keyboard, a magnetic tape, or even a punched
15297 card reader. Similarly, ``standard output'' is a data sink, where data goes
15298 to. The program should neither know nor care where this might be.
15299 Programs that only read their standard input, do something to the data,
15300 and then send it on, are called @dfn{filters}, by analogy to filters in a
15303 With the Unix shell, it's very easy to set up data pipelines:
15306 program_to_create_data | filter1 | ... | filterN > final.pretty.data
15309 We start out by creating the raw data; each filter applies some successive
15310 transformation to the data, until by the time it comes out of the pipeline,
15311 it is in the desired form.
15313 This is fine and good for standard input and standard output. Where does the
15314 standard error come in to play? Well, think about @command{filter1} in
15315 the pipeline above. What happens if it encounters an error in the data it
15316 sees? If it writes an error message to standard output, it will just
15317 disappear down the pipeline into @command{filter2}'s input, and the
15318 user will probably never see it. So programs need a place where they can send
15319 error messages so that the user will notice them. This is standard error,
15320 and it is usually connected to your console or window, even if you have
15321 redirected standard output of your program away from your screen.
15323 For filter programs to work together, the format of the data has to be
15324 agreed upon. The most straightforward and easiest format to use is simply
15325 lines of text. Unix data files are generally just streams of bytes, with
15326 lines delimited by the @acronym{ASCII} @sc{lf} (Line Feed) character,
15327 conventionally called a ``newline'' in the Unix literature. (This is
15328 @code{'\n'} if you're a C programmer.) This is the format used by all
15329 the traditional filtering programs. (Many earlier operating systems
15330 had elaborate facilities and special purpose programs for managing
15331 binary data. Unix has always shied away from such things, under the
15332 philosophy that it's easiest to simply be able to view and edit your
15333 data with a text editor.)
15335 OK, enough introduction. Let's take a look at some of the tools, and then
15336 we'll see how to hook them together in interesting ways. In the following
15337 discussion, we will only present those command line options that interest
15338 us. As you should always do, double check your system documentation
15339 for the full story.
15341 @node The who command
15342 @unnumberedsec The @command{who} Command
15344 The first program is the @command{who} command. By itself, it generates a
15345 list of the users who are currently logged in. Although I'm writing
15346 this on a single-user system, we'll pretend that several people are
15351 @print{} arnold console Jan 22 19:57
15352 @print{} miriam ttyp0 Jan 23 14:19(:0.0)
15353 @print{} bill ttyp1 Jan 21 09:32(:0.0)
15354 @print{} arnold ttyp2 Jan 23 20:48(:0.0)
15357 Here, the @samp{$} is the usual shell prompt, at which I typed @samp{who}.
15358 There are three people logged in, and I am logged in twice. On traditional
15359 Unix systems, user names are never more than eight characters long. This
15360 little bit of trivia will be useful later. The output of @command{who} is nice,
15361 but the data is not all that exciting.
15363 @node The cut command
15364 @unnumberedsec The @command{cut} Command
15366 The next program we'll look at is the @command{cut} command. This program
15367 cuts out columns or fields of input data. For example, we can tell it
15368 to print just the login name and full name from the @file{/etc/passwd}
15369 file. The @file{/etc/passwd} file has seven fields, separated by
15373 arnold:xyzzy:2076:10:Arnold D. Robbins:/home/arnold:/bin/bash
15376 To get the first and fifth fields, we would use @command{cut} like this:
15379 $ cut -d: -f1,5 /etc/passwd
15380 @print{} root:Operator
15382 @print{} arnold:Arnold D. Robbins
15383 @print{} miriam:Miriam A. Robbins
15387 With the @option{-c} option, @command{cut} will cut out specific characters
15388 (i.e., columns) in the input lines. This is useful for input data
15389 that has fixed width fields, and does not have a field separator. For
15390 example, list the Monday dates for the current month:
15392 @c Is using cal ok? Looked at gcal, but I don't like it.
15403 @node The sort command
15404 @unnumberedsec The @command{sort} Command
15406 Next we'll look at the @command{sort} command. This is one of the most
15407 powerful commands on a Unix-style system; one that you will often find
15408 yourself using when setting up fancy data plumbing.
15411 command reads and sorts each file named on the command line. It then
15412 merges the sorted data and writes it to standard output. It will read
15413 standard input if no files are given on the command line (thus
15414 making it into a filter). The sort is based on the character collating
15415 sequence or based on user-supplied ordering criteria.
15418 @node The uniq command
15419 @unnumberedsec The @command{uniq} Command
15421 Finally (at least for now), we'll look at the @command{uniq} program. When
15422 sorting data, you will often end up with duplicate lines, lines that
15423 are identical. Usually, all you need is one instance of each line.
15424 This is where @command{uniq} comes in. The @command{uniq} program reads its
15425 standard input. It prints only one
15426 copy of each repeated line. It does have several options. Later on,
15427 we'll use the @option{-c} option, which prints each unique line, preceded
15428 by a count of the number of times that line occurred in the input.
15431 @node Putting the tools together
15432 @unnumberedsec Putting the Tools Together
15434 Now, let's suppose this is a large ISP server system with dozens of users
15435 logged in. The management wants the system administrator to write a program that will
15436 generate a sorted list of logged in users. Furthermore, even if a user
15437 is logged in multiple times, his or her name should only show up in the
15440 The administrator could sit down with the system documentation and write a C
15441 program that did this. It would take perhaps a couple of hundred lines
15442 of code and about two hours to write it, test it, and debug it.
15443 However, knowing the software toolbox, the administrator can instead start out
15444 by generating just a list of logged on users:
15454 Next, sort the list:
15457 $ who | cut -c1-8 | sort
15464 Finally, run the sorted list through @command{uniq}, to weed out duplicates:
15467 $ who | cut -c1-8 | sort | uniq
15473 The @command{sort} command actually has a @option{-u} option that does what
15474 @command{uniq} does. However, @command{uniq} has other uses for which one
15475 cannot substitute @samp{sort -u}.
15477 The administrator puts this pipeline into a shell script, and makes it available for
15478 all the users on the system (@samp{#} is the system administrator,
15479 or @code{root}, prompt):
15482 # cat > /usr/local/bin/listusers
15483 who | cut -c1-8 | sort | uniq
15485 # chmod +x /usr/local/bin/listusers
15488 There are four major points to note here. First, with just four
15489 programs, on one command line, the administrator was able to save about two
15490 hours worth of work. Furthermore, the shell pipeline is just about as
15491 efficient as the C program would be, and it is much more efficient in
15492 terms of programmer time. People time is much more expensive than
15493 computer time, and in our modern ``there's never enough time to do
15494 everything'' society, saving two hours of programmer time is no mean
15497 Second, it is also important to emphasize that with the
15498 @emph{combination} of the tools, it is possible to do a special
15499 purpose job never imagined by the authors of the individual programs.
15501 Third, it is also valuable to build up your pipeline in stages, as we did here.
15502 This allows you to view the data at each stage in the pipeline, which helps
15503 you acquire the confidence that you are indeed using these tools correctly.
15505 Finally, by bundling the pipeline in a shell script, other users can use
15506 your command, without having to remember the fancy plumbing you set up for
15507 them. In terms of how you run them, shell scripts and compiled programs are
15510 After the previous warm-up exercise, we'll look at two additional, more
15511 complicated pipelines. For them, we need to introduce two more tools.
15513 The first is the @command{tr} command, which stands for ``transliterate.''
15514 The @command{tr} command works on a character-by-character basis, changing
15515 characters. Normally it is used for things like mapping upper case to
15519 $ echo ThIs ExAmPlE HaS MIXED case! | tr '[:upper:]' '[:lower:]'
15520 @print{} this example has mixed case!
15523 There are several options of interest:
15527 work on the complement of the listed characters, i.e.,
15528 operations apply to characters not in the given set
15531 delete characters in the first set from the output
15534 squeeze repeated characters in the output into just one character.
15537 We will be using all three options in a moment.
15539 The other command we'll look at is @command{comm}. The @command{comm}
15540 command takes two sorted input files as input data, and prints out the
15541 files' lines in three columns. The output columns are the data lines
15542 unique to the first file, the data lines unique to the second file, and
15543 the data lines that are common to both. The @option{-1}, @option{-2}, and
15544 @option{-3} command line options @emph{omit} the respective columns. (This is
15545 non-intuitive and takes a little getting used to.) For example:
15567 The file name @file{-} tells @command{comm} to read standard input
15568 instead of a regular file.
15570 Now we're ready to build a fancy pipeline. The first application is a word
15571 frequency counter. This helps an author determine if he or she is over-using
15574 The first step is to change the case of all the letters in our input file
15575 to one case. ``The'' and ``the'' are the same word when doing counting.
15578 $ tr '[:upper:]' '[:lower:]' < whats.gnu | ...
15581 The next step is to get rid of punctuation. Quoted words and unquoted words
15582 should be treated identically; it's easiest to just get the punctuation out of
15586 $ tr '[:upper:]' '[:lower:]' < whats.gnu | tr -cd '[:alnum:]_ \n' | ...
15589 The second @command{tr} command operates on the complement of the listed
15590 characters, which are all the letters, the digits, the underscore, and
15591 the blank. The @samp{\n} represents the newline character; it has to
15592 be left alone. (The @acronym{ASCII} tab character should also be included for
15593 good measure in a production script.)
15595 At this point, we have data consisting of words separated by blank space.
15596 The words only contain alphanumeric characters (and the underscore). The
15597 next step is break the data apart so that we have one word per line. This
15598 makes the counting operation much easier, as we will see shortly.
15601 $ tr '[:upper:]' '[:lower:]' < whats.gnu | tr -cd '[:alnum:]_ \n' |
15602 > tr -s ' ' '\n' | ...
15605 This command turns blanks into newlines. The @option{-s} option squeezes
15606 multiple newline characters in the output into just one. This helps us
15607 avoid blank lines. (The @samp{>} is the shell's ``secondary prompt.''
15608 This is what the shell prints when it notices you haven't finished
15609 typing in all of a command.)
15611 We now have data consisting of one word per line, no punctuation, all one
15612 case. We're ready to count each word:
15615 $ tr '[:upper:]' '[:lower:]' < whats.gnu | tr -cd '[:alnum:]_ \n' |
15616 > tr -s ' ' '\n' | sort | uniq -c | ...
15619 At this point, the data might look something like this:
15632 The output is sorted by word, not by count! What we want is the most
15633 frequently used words first. Fortunately, this is easy to accomplish,
15634 with the help of two more @command{sort} options:
15638 do a numeric sort, not a textual one
15641 reverse the order of the sort
15644 The final pipeline looks like this:
15647 $ tr '[:upper:]' '[:lower:]' < whats.gnu | tr -cd '[:alnum:]_ \n' |
15648 > tr -s ' ' '\n' | sort | uniq -c | sort -n -r
15657 Whew! That's a lot to digest. Yet, the same principles apply. With six
15658 commands, on two lines (really one long one split for convenience), we've
15659 created a program that does something interesting and useful, in much
15660 less time than we could have written a C program to do the same thing.
15662 A minor modification to the above pipeline can give us a simple spelling
15663 checker! To determine if you've spelled a word correctly, all you have to
15664 do is look it up in a dictionary. If it is not there, then chances are
15665 that your spelling is incorrect. So, we need a dictionary.
15666 The conventional location for a dictionary is @file{/usr/dict/words}.
15667 On my GNU/Linux system,@footnote{Redhat Linux 6.1, for the November 2000
15668 revision of this article.}
15669 this is a sorted, 45,402 word dictionary.
15671 Now, how to compare our file with the dictionary? As before, we generate
15672 a sorted list of words, one per line:
15675 $ tr '[:upper:]' '[:lower:]' < whats.gnu | tr -cd '[:alnum:]_ \n' |
15676 > tr -s ' ' '\n' | sort -u | ...
15679 Now, all we need is a list of words that are @emph{not} in the
15680 dictionary. Here is where the @command{comm} command comes in.
15683 $ tr '[:upper:]' '[:lower:]' < whats.gnu | tr -cd '[:alnum:]_ \n' |
15684 > tr -s ' ' '\n' | sort -u |
15685 > comm -23 - /usr/dict/words
15688 The @option{-2} and @option{-3} options eliminate lines that are only in the
15689 dictionary (the second file), and lines that are in both files. Lines
15690 only in the first file (standard input, our stream of words), are
15691 words that are not in the dictionary. These are likely candidates for
15692 spelling errors. This pipeline was the first cut at a production
15693 spelling checker on Unix.
15695 There are some other tools that deserve brief mention.
15699 search files for text that matches a regular expression
15702 count lines, words, characters
15705 a T-fitting for data pipes, copies data to files and to standard output
15708 the stream editor, an advanced tool
15711 a data manipulation language, another advanced tool
15714 The software tools philosophy also espoused the following bit of
15715 advice: ``Let someone else do the hard part.'' This means, take
15716 something that gives you most of what you need, and then massage it the
15717 rest of the way until it's in the form that you want.
15723 Each program should do one thing well. No more, no less.
15726 Combining programs with appropriate plumbing leads to results where
15727 the whole is greater than the sum of the parts. It also leads to novel
15728 uses of programs that the authors might never have imagined.
15731 Programs should never print extraneous header or trailer data, since these
15732 could get sent on down a pipeline. (A point we didn't mention earlier.)
15735 Let someone else do the hard part.
15738 Know your toolbox! Use each program appropriately. If you don't have an
15739 appropriate tool, build one.
15742 As of this writing, all the programs we've discussed are available via
15743 anonymous @command{ftp} from: @*
15744 @uref{ftp://gnudist.gnu.org/textutils/textutils-1.22.tar.gz}. (There may
15745 be more recent versions available now.)
15747 None of what I have presented in this column is new. The Software Tools
15748 philosophy was first introduced in the book @cite{Software Tools}, by
15749 Brian Kernighan and P.J. Plauger (Addison-Wesley, ISBN 0-201-03669-X).
15750 This book showed how to write and use software tools. It was written in
15751 1976, using a preprocessor for FORTRAN named @command{ratfor} (RATional
15752 FORtran). At the time, C was not as ubiquitous as it is now; FORTRAN
15753 was. The last chapter presented a @command{ratfor} to FORTRAN
15754 processor, written in @command{ratfor}. @command{ratfor} looks an awful
15755 lot like C; if you know C, you won't have any problem following the
15758 In 1981, the book was updated and made available as @cite{Software Tools
15759 in Pascal} (Addison-Wesley, ISBN 0-201-10342-7). Both books are
15760 still in print and are well worth
15761 reading if you're a programmer. They certainly made a major change in
15762 how I view programming.
15764 The programs in both books are available from
15765 @uref{http://cm.bell-labs.com/who/bwk, Brian Kernighan's home page}.
15766 For a number of years, there was an active
15767 Software Tools Users Group, whose members had ported the original
15768 @command{ratfor} programs to essentially every computer system with a
15769 FORTRAN compiler. The popularity of the group waned in the middle 1980s
15770 as Unix began to spread beyond universities.
15772 With the current proliferation of GNU code and other clones of Unix programs,
15773 these programs now receive little attention; modern C versions are
15774 much more efficient and do more than these programs do. Nevertheless, as
15775 exposition of good programming style, and evangelism for a still-valuable
15776 philosophy, these books are unparalleled, and I recommend them highly.
15778 Acknowledgment: I would like to express my gratitude to Brian Kernighan
15779 of Bell Labs, the original Software Toolsmith, for reviewing this column.
15781 @node GNU Free Documentation License
15782 @appendix GNU Free Documentation License
15786 @node Concept index
15793 @c Local variables:
15794 @c texinfo-column-for-description: 32
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