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 base64
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:: 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:: mkdir rmdir unlink mkfifo mknod ln link readlink
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 arch 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}
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 * 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}
621 @var{\varName\} may be, or may be an integer optionally followed by,
622 one of the following multiplicative suffixes:
624 @samp{b} => 512 ("blocks")
625 @samp{KB} => 1000 (KiloBytes)
626 @samp{K} => 1024 (KibiBytes)
627 @samp{MB} => 1000*1000 (MegaBytes)
628 @samp{M} => 1024*1024 (MebiBytes)
629 @samp{GB} => 1000*1000*1000 (GigaBytes)
630 @samp{G} => 1024*1024*1024 (GibiBytes)
632 and so on for @samp{T}, @samp{P}, @samp{E}, @samp{Z}, and @samp{Y}.
635 @c FIXME: same as above, but no ``blocks'' line.
636 @macro multiplierSuffixesNoBlocks{varName}
637 @var{\varName\} may be, or may be an integer optionally followed by,
638 one of the following multiplicative suffixes:
640 @samp{KB} => 1000 (KiloBytes)
641 @samp{K} => 1024 (KibiBytes)
642 @samp{MB} => 1000*1000 (MegaBytes)
643 @samp{M} => 1024*1024 (MebiBytes)
644 @samp{GB} => 1000*1000*1000 (GigaBytes)
645 @samp{G} => 1024*1024*1024 (GibiBytes)
647 and so on for @samp{T}, @samp{P}, @samp{E}, @samp{Z}, and @samp{Y}.
650 @cindex common options
652 Certain options are available in all of these programs. Rather than
653 writing identical descriptions for each of the programs, they are
654 described here. (In fact, every @sc{gnu} program accepts (or should accept)
657 @vindex POSIXLY_CORRECT
658 Normally options and operands can appear in any order, and programs act
659 as if all the options appear before any operands. For example,
660 @samp{sort -r passwd -t :} acts like @samp{sort -r -t : passwd}, since
661 @samp{:} is an option-argument of @option{-t}. However, if the
662 @env{POSIXLY_CORRECT} environment variable is set, options must appear
663 before operands, unless otherwise specified for a particular command.
665 A few programs can usefully have trailing operands with leading
666 @samp{-}. With such a program, options must precede operands even if
667 @env{POSIXLY_CORRECT} is not set, and this fact is noted in the
668 program description. For example, the @command{env} command's options
669 must appear before its operands, since in some cases the operands
670 specify a command that itself contains options.
672 Most programs that accept long options recognize unambiguous
673 abbreviations of those options. For example, @samp{rmdir
674 --ignore-fail-on-non-empty} can be invoked as @samp{rmdir
675 --ignore-fail} or even @samp{rmdir --i}. Ambiguous options, such as
676 @samp{ls --h}, are identified as such.
678 Some of these programs recognize the @option{--help} and @option{--version}
679 options only when one of them is the sole command line argument. For
680 these programs, abbreviations of the long options are not always recognized.
687 Print a usage message listing all available options, then exit successfully.
691 @cindex version number, finding
692 Print the version number, then exit successfully.
696 @cindex option delimiter
697 Delimit the option list. Later arguments, if any, are treated as
698 operands even if they begin with @samp{-}. For example, @samp{sort --
699 -r} reads from the file named @file{-r}.
703 @cindex standard input
704 @cindex standard output
705 A single @samp{-} operand is not really an option, though it looks like one. It
706 stands for standard input, or for standard output if that is clear from
707 the context. For example, @samp{sort -} reads from standard input,
708 and is equivalent to plain @samp{sort}, and @samp{tee -} writes an
709 extra copy of its input to standard output. Unless otherwise
710 specified, @samp{-} can appear as any operand that requires a file
714 * Exit status:: Indicating program success or failure.
715 * Backup options:: -b -S, in some programs.
716 * Block size:: BLOCK_SIZE and --block-size, in some programs.
717 * Signal specifications:: Specifying signals using the --signal option.
718 * Disambiguating names and IDs:: chgrp and chown owner and group syntax
719 * Random sources:: --random-source, in some programs.
720 * Target directory:: Specifying a target directory, in some programs.
721 * Trailing slashes:: --strip-trailing-slashes, in some programs.
722 * Traversing symlinks:: -H, -L, or -P, in some programs.
723 * Treating / specially:: --preserve-root and --no-preserve-root.
724 * Special built-in utilities:: @command{break}, @command{:}, @command{eval}, @dots{}
725 * Standards conformance:: Conformance to the @acronym{POSIX} standard.
733 An exit status of zero indicates success,
734 and a nonzero value indicates failure.
737 Nearly every command invocation yields an integral @dfn{exit status}
738 that can be used to change how other commands work.
739 For the vast majority of commands, an exit status of zero indicates
740 success. Failure is indicated by a nonzero value---typically
741 @samp{1}, though it may differ on unusual platforms as @acronym{POSIX}
742 requires only that it be nonzero.
744 However, some of the programs documented here do produce
745 other exit status values and a few associate different
746 meanings with the values @samp{0} and @samp{1}.
747 Here are some of the exceptions:
748 @command{chroot}, @command{env}, @command{expr}, @command{nice},
749 @command{nohup}, @command{printenv}, @command{sort}, @command{stdbuf},
750 @command{su}, @command{test}, @command{timeout}, @command{tty}.
754 @section Backup options
756 @cindex backup options
758 Some @sc{gnu} programs (at least @command{cp}, @command{install},
759 @command{ln}, and @command{mv}) optionally make backups of files
760 before writing new versions.
761 These options control the details of these backups. The options are also
762 briefly mentioned in the descriptions of the particular programs.
767 @itemx @w{@kbd{--backup}[=@var{method}]}
770 @vindex VERSION_CONTROL
771 @cindex backups, making
772 Make a backup of each file that would otherwise be overwritten or removed.
773 Without this option, the original versions are destroyed.
774 Use @var{method} to determine the type of backups to make.
775 When this option is used but @var{method} is not specified,
776 then the value of the @env{VERSION_CONTROL}
777 environment variable is used. And if @env{VERSION_CONTROL} is not set,
778 the default backup type is @samp{existing}.
780 Note that the short form of this option, @option{-b} does not accept any
781 argument. Using @option{-b} is equivalent to using @option{--backup=existing}.
783 @vindex version-control @r{Emacs variable}
784 This option corresponds to the Emacs variable @samp{version-control};
785 the values for @var{method} are the same as those used in Emacs.
786 This option also accepts more descriptive names.
787 The valid @var{method}s are (unique abbreviations are accepted):
792 @opindex none @r{backup method}
797 @opindex numbered @r{backup method}
798 Always make numbered backups.
802 @opindex existing @r{backup method}
803 Make numbered backups of files that already have them, simple backups
808 @opindex simple @r{backup method}
809 Always make simple backups. Please note @samp{never} is not to be
810 confused with @samp{none}.
814 @item -S @var{suffix}
815 @itemx --suffix=@var{suffix}
818 @cindex backup suffix
819 @vindex SIMPLE_BACKUP_SUFFIX
820 Append @var{suffix} to each backup file made with @option{-b}. If this
821 option is not specified, the value of the @env{SIMPLE_BACKUP_SUFFIX}
822 environment variable is used. And if @env{SIMPLE_BACKUP_SUFFIX} is not
823 set, the default is @samp{~}, just as in Emacs.
832 Some @sc{gnu} programs (at least @command{df}, @command{du}, and
833 @command{ls}) display sizes in ``blocks''. You can adjust the block size
834 and method of display to make sizes easier to read. The block size
835 used for display is independent of any file system block size.
836 Fractional block counts are rounded up to the nearest integer.
838 @opindex --block-size=@var{size}
841 @vindex DF_BLOCK_SIZE
842 @vindex DU_BLOCK_SIZE
843 @vindex LS_BLOCK_SIZE
844 @vindex POSIXLY_CORRECT@r{, and block size}
846 The default block size is chosen by examining the following environment
847 variables in turn; the first one that is set determines the block size.
852 This specifies the default block size for the @command{df} command.
853 Similarly, @env{DU_BLOCK_SIZE} specifies the default for @command{du} and
854 @env{LS_BLOCK_SIZE} for @command{ls}.
857 This specifies the default block size for all three commands, if the
858 above command-specific environment variables are not set.
861 This specifies the default block size for all values that are normally
862 printed as blocks, if neither @env{BLOCK_SIZE} nor the above
863 command-specific environment variables are set. Unlike the other
864 environment variables, @env{BLOCKSIZE} does not affect values that are
865 normally printed as byte counts, e.g., the file sizes contained in
868 @item POSIXLY_CORRECT
869 If neither @env{@var{command}_BLOCK_SIZE}, nor @env{BLOCK_SIZE}, nor
870 @env{BLOCKSIZE} is set, but this variable is set, the block size
875 If none of the above environment variables are set, the block size
876 currently defaults to 1024 bytes in most contexts, but this number may
877 change in the future. For @command{ls} file sizes, the block size
880 @cindex human-readable output
883 A block size specification can be a positive integer specifying the number
884 of bytes per block, or it can be @code{human-readable} or @code{si} to
885 select a human-readable format. Integers may be followed by suffixes
886 that are upward compatible with the
887 @uref{http://www.bipm.fr/enus/3_SI/si-prefixes.html, SI prefixes}
888 for decimal multiples and with the
889 @uref{http://physics.nist.gov/cuu/Units/binary.html, IEC 60027-2
890 prefixes for binary multiples}.
892 With human-readable formats, output sizes are followed by a size letter
893 such as @samp{M} for megabytes. @code{BLOCK_SIZE=human-readable} uses
894 powers of 1024; @samp{M} stands for 1,048,576 bytes.
895 @code{BLOCK_SIZE=si} is similar, but uses powers of 1000 and appends
896 @samp{B}; @samp{MB} stands for 1,000,000 bytes.
899 A block size specification preceded by @samp{'} causes output sizes to
900 be displayed with thousands separators. The @env{LC_NUMERIC} locale
901 specifies the thousands separator and grouping. For example, in an
902 American English locale, @samp{--block-size="'1kB"} would cause a size
903 of 1234000 bytes to be displayed as @samp{1,234}. In the default C
904 locale, there is no thousands separator so a leading @samp{'} has no
907 An integer block size can be followed by a suffix to specify a
908 multiple of that size. A bare size letter,
909 or one followed by @samp{iB}, specifies
910 a multiple using powers of 1024. A size letter followed by @samp{B}
911 specifies powers of 1000 instead. For example, @samp{1M} and
912 @samp{1MiB} are equivalent to @samp{1048576}, whereas @samp{1MB} is
913 equivalent to @samp{1000000}.
915 A plain suffix without a preceding integer acts as if @samp{1} were
916 prepended, except that it causes a size indication to be appended to
917 the output. For example, @samp{--block-size="kB"} displays 3000 as
920 The following suffixes are defined. Large sizes like @code{1Y}
921 may be rejected by your computer due to limitations of its arithmetic.
925 @cindex kilobyte, definition of
926 kilobyte: @math{10^3 = 1000}.
930 @cindex kibibyte, definition of
931 kibibyte: @math{2^{10} = 1024}. @samp{K} is special: the SI prefix is
932 @samp{k} and the IEC 60027-2 prefix is @samp{Ki}, but tradition and
933 @acronym{POSIX} use @samp{k} to mean @samp{KiB}.
935 @cindex megabyte, definition of
936 megabyte: @math{10^6 = 1,000,000}.
939 @cindex mebibyte, definition of
940 mebibyte: @math{2^{20} = 1,048,576}.
942 @cindex gigabyte, definition of
943 gigabyte: @math{10^9 = 1,000,000,000}.
946 @cindex gibibyte, definition of
947 gibibyte: @math{2^{30} = 1,073,741,824}.
949 @cindex terabyte, definition of
950 terabyte: @math{10^{12} = 1,000,000,000,000}.
953 @cindex tebibyte, definition of
954 tebibyte: @math{2^{40} = 1,099,511,627,776}.
956 @cindex petabyte, definition of
957 petabyte: @math{10^{15} = 1,000,000,000,000,000}.
960 @cindex pebibyte, definition of
961 pebibyte: @math{2^{50} = 1,125,899,906,842,624}.
963 @cindex exabyte, definition of
964 exabyte: @math{10^{18} = 1,000,000,000,000,000,000}.
967 @cindex exbibyte, definition of
968 exbibyte: @math{2^{60} = 1,152,921,504,606,846,976}.
970 @cindex zettabyte, definition of
971 zettabyte: @math{10^{21} = 1,000,000,000,000,000,000,000}
974 @math{2^{70} = 1,180,591,620,717,411,303,424}.
975 (@samp{Zi} is a @acronym{GNU} extension to IEC 60027-2.)
977 @cindex yottabyte, definition of
978 yottabyte: @math{10^{24} = 1,000,000,000,000,000,000,000,000}.
981 @math{2^{80} = 1,208,925,819,614,629,174,706,176}.
982 (@samp{Yi} is a @acronym{GNU} extension to IEC 60027-2.)
987 @opindex --block-size
988 @opindex --human-readable
991 Block size defaults can be overridden by an explicit
992 @option{--block-size=@var{size}} option. The @option{-k}
993 option is equivalent to @option{--block-size=1K}, which
994 is the default unless the @env{POSIXLY_CORRECT} environment variable is
995 set. The @option{-h} or @option{--human-readable} option is equivalent to
996 @option{--block-size=human-readable}. The @option{--si} option is
997 equivalent to @option{--block-size=si}.
999 @node Signal specifications
1000 @section Signal specifications
1001 @cindex signals, specifying
1003 A @var{signal} may be a signal name like @samp{HUP}, or a signal
1004 number like @samp{1}, or an exit status of a process terminated by the
1005 signal. A signal name can be given in canonical form or prefixed by
1006 @samp{SIG}. The case of the letters is ignored. The following signal names
1007 and numbers are supported on all @acronym{POSIX} compliant systems:
1013 2. Terminal interrupt.
1019 9. Kill (cannot be caught or ignored).
1027 Other supported signal names have system-dependent corresponding
1028 numbers. All systems conforming to @acronym{POSIX} 1003.1-2001 also
1029 support the following signals:
1033 Access to an undefined portion of a memory object.
1035 Child process terminated, stopped, or continued.
1037 Continue executing, if stopped.
1039 Erroneous arithmetic operation.
1041 Illegal Instruction.
1043 Write on a pipe with no one to read it.
1045 Invalid memory reference.
1047 Stop executing (cannot be caught or ignored).
1051 Background process attempting read.
1053 Background process attempting write.
1055 High bandwidth data is available at a socket.
1057 User-defined signal 1.
1059 User-defined signal 2.
1063 @acronym{POSIX} 1003.1-2001 systems that support the @acronym{XSI} extension
1064 also support the following signals:
1070 Profiling timer expired.
1074 Trace/breakpoint trap.
1076 Virtual timer expired.
1078 CPU time limit exceeded.
1080 File size limit exceeded.
1084 @acronym{POSIX} 1003.1-2001 systems that support the @acronym{XRT} extension
1085 also support at least eight real-time signals called @samp{RTMIN},
1086 @samp{RTMIN+1}, @dots{}, @samp{RTMAX-1}, @samp{RTMAX}.
1088 @node Disambiguating names and IDs
1089 @section chown and chgrp: Disambiguating user names and IDs
1090 @cindex user names, disambiguating
1091 @cindex user IDs, disambiguating
1092 @cindex group names, disambiguating
1093 @cindex group IDs, disambiguating
1094 @cindex disambiguating group names and IDs
1096 Since the @var{owner} and @var{group} arguments to @command{chown} and
1097 @command{chgrp} may be specified as names or numeric IDs, there is an
1099 What if a user or group @emph{name} is a string of digits?
1100 @footnote{Using a number as a user name is common in some environments.}
1101 Should the command interpret it as a user name or as an ID?
1102 @acronym{POSIX} requires that @command{chown} and @command{chgrp}
1103 first attempt to resolve the specified string as a name, and
1104 only once that fails, then try to interpret it as an ID.
1105 This is troublesome when you want to specify a numeric ID, say 42,
1106 and it must work even in a pathological situation where
1107 @samp{42} is a user name that maps to some other user ID, say 1000.
1108 Simply invoking @code{chown 42 F}, will set @file{F}s owner ID to
1109 1000---not what you intended.
1111 GNU @command{chown} and @command{chgrp} provide a way to work around this,
1112 that at the same time may result in a significant performance improvement
1113 by eliminating a database look-up.
1114 Simply precede each numeric user ID and/or group ID with a @samp{+},
1115 in order to force its interpretation as an integer:
1119 chgrp +$numeric_group_id another-file
1123 GNU @command{chown} and @command{chgrp}
1124 skip the name look-up process for each @samp{+}-prefixed string,
1125 because a string containing @samp{+} is never a valid user or group name.
1126 This syntax is accepted on most common Unix systems, but not on Solaris 10.
1128 @node Random sources
1129 @section Sources of random data
1131 @cindex random sources
1133 The @command{shuf}, @command{shred}, and @command{sort} commands
1134 sometimes need random data to do their work. For example, @samp{sort
1135 -R} must choose a hash function at random, and it needs random data to
1136 make this selection.
1138 By default these commands use an internal pseudorandom generator
1139 initialized by a small amount of entropy, but can be directed to use
1140 an external source with the @option{--random-source=@var{file}} option.
1141 An error is reported if @var{file} does not contain enough bytes.
1143 For example, the device file @file{/dev/urandom} could be used as the
1144 source of random data. Typically, this device gathers environmental
1145 noise from device drivers and other sources into an entropy pool, and
1146 uses the pool to generate random bits. If the pool is short of data,
1147 the device reuses the internal pool to produce more bits, using a
1148 cryptographically secure pseudorandom number generator. But be aware
1149 that this device is not designed for bulk random data generation
1150 and is relatively slow.
1152 @file{/dev/urandom} suffices for most practical uses, but applications
1153 requiring high-value or long-term protection of private data may
1154 require an alternate data source like @file{/dev/random} or
1155 @file{/dev/arandom}. The set of available sources depends on your
1158 To reproduce the results of an earlier invocation of a command, you
1159 can save some random data into a file and then use that file as the
1160 random source in earlier and later invocations of the command.
1162 @node Target directory
1163 @section Target directory
1165 @cindex target directory
1167 The @command{cp}, @command{install}, @command{ln}, and @command{mv}
1168 commands normally treat the last operand specially when it is a
1169 directory or a symbolic link to a directory. For example, @samp{cp
1170 source dest} is equivalent to @samp{cp source dest/source} if
1171 @file{dest} is a directory. Sometimes this behavior is not exactly
1172 what is wanted, so these commands support the following options to
1173 allow more fine-grained control:
1178 @itemx --no-target-directory
1179 @opindex --no-target-directory
1180 @cindex target directory
1181 @cindex destination directory
1182 Do not treat the last operand specially when it is a directory or a
1183 symbolic link to a directory. This can help avoid race conditions in
1184 programs that operate in a shared area. For example, when the command
1185 @samp{mv /tmp/source /tmp/dest} succeeds, there is no guarantee that
1186 @file{/tmp/source} was renamed to @file{/tmp/dest}: it could have been
1187 renamed to @file{/tmp/dest/source} instead, if some other process
1188 created @file{/tmp/dest} as a directory. However, if @file{mv
1189 -T /tmp/source /tmp/dest} succeeds, there is no
1190 question that @file{/tmp/source} was renamed to @file{/tmp/dest}.
1192 In the opposite situation, where you want the last operand to be
1193 treated as a directory and want a diagnostic otherwise, you can use
1194 the @option{--target-directory} (@option{-t}) option.
1196 @item -t @var{directory}
1197 @itemx @w{@kbd{--target-directory}=@var{directory}}
1198 @opindex --target-directory
1199 @cindex target directory
1200 @cindex destination directory
1201 Use @var{directory} as the directory component of each destination
1204 The interface for most programs is that after processing options and a
1205 finite (possibly zero) number of fixed-position arguments, the remaining
1206 argument list is either expected to be empty, or is a list of items
1207 (usually files) that will all be handled identically. The @command{xargs}
1208 program is designed to work well with this convention.
1210 The commands in the @command{mv}-family are unusual in that they take
1211 a variable number of arguments with a special case at the @emph{end}
1212 (namely, the target directory). This makes it nontrivial to perform some
1213 operations, e.g., ``move all files from here to ../d/'', because
1214 @code{mv * ../d/} might exhaust the argument space, and @code{ls | xargs ...}
1215 doesn't have a clean way to specify an extra final argument for each
1216 invocation of the subject command. (It can be done by going through a
1217 shell command, but that requires more human labor and brain power than
1220 The @w{@kbd{--target-directory}} (@option{-t}) option allows the @command{cp},
1221 @command{install}, @command{ln}, and @command{mv} programs to be used
1222 conveniently with @command{xargs}. For example, you can move the files
1223 from the current directory to a sibling directory, @code{d} like this:
1226 ls | xargs mv -t ../d --
1229 However, this doesn't move files whose names begin with @samp{.}.
1230 If you use the @sc{gnu} @command{find} program, you can move those
1231 files too, with this command:
1234 find . -mindepth 1 -maxdepth 1 \
1238 But both of the above approaches fail if there are no files in the
1239 current directory, or if any file has a name containing a blank or
1240 some other special characters.
1241 The following example removes those limitations and requires both
1242 @sc{gnu} @command{find} and @sc{gnu} @command{xargs}:
1245 find . -mindepth 1 -maxdepth 1 -print0 \
1246 | xargs --null --no-run-if-empty \
1253 The @option{--target-directory} (@option{-t}) and
1254 @option{--no-target-directory} (@option{-T})
1255 options cannot be combined.
1257 @node Trailing slashes
1258 @section Trailing slashes
1260 @cindex trailing slashes
1262 Some @sc{gnu} programs (at least @command{cp} and @command{mv}) allow you to
1263 remove any trailing slashes from each @var{source} argument before
1264 operating on it. The @w{@kbd{--strip-trailing-slashes}} option enables
1267 This is useful when a @var{source} argument may have a trailing slash and
1268 @c FIXME: mv's behavior in this case is system-dependent
1269 specify a symbolic link to a directory. This scenario is in fact rather
1270 common because some shells can automatically append a trailing slash when
1271 performing file name completion on such symbolic links. Without this
1272 option, @command{mv}, for example, (via the system's rename function) must
1273 interpret a trailing slash as a request to dereference the symbolic link
1274 and so must rename the indirectly referenced @emph{directory} and not
1275 the symbolic link. Although it may seem surprising that such behavior
1276 be the default, it is required by @acronym{POSIX} and is consistent with
1277 other parts of that standard.
1279 @node Traversing symlinks
1280 @section Traversing symlinks
1282 @cindex symbolic link to directory, controlling traversal of
1284 The following options modify how @command{chown} and @command{chgrp}
1285 @c FIXME: note that `du' has these options, too, but they have slightly
1286 @c different meaning.
1287 traverse a hierarchy when the @option{--recursive} (@option{-R})
1288 option is also specified.
1289 If more than one of the following options is specified, only the final
1291 These options specify whether processing a symbolic link to a directory
1292 entails operating on just the symbolic link or on all files in the
1293 hierarchy rooted at that directory.
1295 These options are independent of @option{--dereference} and
1296 @option{--no-dereference} (@option{-h}), which control whether to modify
1297 a symlink or its referent.
1304 @cindex symbolic link to directory, traverse each that is specified on the command line
1305 If @option{--recursive} (@option{-R}) is specified and
1306 a command line argument is a symbolic link to a directory, traverse it.
1313 @cindex symbolic link to directory, traverse each that is encountered
1314 In a recursive traversal, traverse every symbolic link to a directory
1315 that is encountered.
1322 @cindex symbolic link to directory, never traverse
1323 Do not traverse any symbolic links.
1324 This is the default if none of @option{-H}, @option{-L},
1325 or @option{-P} is specified.
1332 @node Treating / specially
1333 @section Treating @file{/} specially
1335 Certain commands can operate destructively on entire hierarchies.
1336 For example, if a user with appropriate privileges mistakenly runs
1337 @samp{rm -rf / tmp/junk}, that may remove
1338 all files on the entire system. Since there are so few
1339 legitimate uses for such a command,
1340 @sc{gnu} @command{rm} normally declines to operate on any directory
1341 that resolves to @file{/}. If you really want to try to remove all
1342 the files on your system, you can use the @option{--no-preserve-root}
1343 option, but the default behavior, specified by the
1344 @option{--preserve-option}, is safer for most purposes.
1346 The commands @command{chgrp}, @command{chmod} and @command{chown}
1347 can also operate destructively on entire hierarchies, so they too
1348 support these options. Although, unlike @command{rm}, they don't
1349 actually unlink files, these commands are arguably more dangerous
1350 when operating recursively on @file{/}, since they often work much
1351 more quickly, and hence damage more files before an alert user can
1352 interrupt them. Tradition and @acronym{POSIX} require these commands
1353 to operate recursively on @file{/}, so they default to
1354 @option{--no-preserve-root}, but using the @option{--preserve-root}
1355 option makes them safer for most purposes. For convenience you can
1356 specify @option{--preserve-root} in an alias or in a shell function.
1358 Note that the @option{--preserve-root} option also ensures
1359 that @command{chgrp} and @command{chown} do not modify @file{/}
1360 even when dereferencing a symlink pointing to @file{/}.
1362 @node Special built-in utilities
1363 @section Special built-in utilities
1365 Some programs like @command{nice} can invoke other programs; for
1366 example, the command @samp{nice cat file} invokes the program
1367 @command{cat} by executing the command @samp{cat file}. However,
1368 @dfn{special built-in utilities} like @command{exit} cannot be invoked
1369 this way. For example, the command @samp{nice exit} does not have a
1370 well-defined behavior: it may generate an error message instead of
1373 Here is a list of the special built-in utilities that are standardized
1374 by @acronym{POSIX} 1003.1-2004.
1377 @t{.@: : break continue eval exec exit export readonly
1378 return set shift times trap unset}
1381 For example, because @samp{.}, @samp{:}, and @samp{exec} are special,
1382 the commands @samp{nice . foo.sh}, @samp{nice :}, and @samp{nice exec
1383 pwd} do not work as you might expect.
1385 Many shells extend this list. For example, Bash has several extra
1386 special built-in utilities like @command{history}, and
1387 @command{suspend}, and with Bash the command @samp{nice suspend}
1388 generates an error message instead of suspending.
1390 @node Standards conformance
1391 @section Standards conformance
1393 @vindex POSIXLY_CORRECT
1394 In a few cases, the @sc{gnu} utilities' default behavior is
1395 incompatible with the @acronym{POSIX} standard. To suppress these
1396 incompatibilities, define the @env{POSIXLY_CORRECT} environment
1397 variable. Unless you are checking for @acronym{POSIX} conformance, you
1398 probably do not need to define @env{POSIXLY_CORRECT}.
1400 Newer versions of @acronym{POSIX} are occasionally incompatible with older
1401 versions. For example, older versions of @acronym{POSIX} required the
1402 command @samp{sort +1} to sort based on the second and succeeding
1403 fields in each input line, but starting with @acronym{POSIX} 1003.1-2001
1404 the same command is required to sort the file named @file{+1}, and you
1405 must instead use the command @samp{sort -k 2} to get the field-based
1408 @vindex _POSIX2_VERSION
1409 The @sc{gnu} utilities normally conform to the version of @acronym{POSIX}
1410 that is standard for your system. To cause them to conform to a
1411 different version of @acronym{POSIX}, define the @env{_POSIX2_VERSION}
1412 environment variable to a value of the form @var{yyyymm} specifying
1413 the year and month the standard was adopted. Two values are currently
1414 supported for @env{_POSIX2_VERSION}: @samp{199209} stands for
1415 @acronym{POSIX} 1003.2-1992, and @samp{200112} stands for @acronym{POSIX}
1416 1003.1-2001. For example, if you have a newer system but are running software
1417 that assumes an older version of @acronym{POSIX} and uses @samp{sort +1}
1418 or @samp{tail +10}, you can work around any compatibility problems by setting
1419 @samp{_POSIX2_VERSION=199209} in your environment.
1421 @node Output of entire files
1422 @chapter Output of entire files
1424 @cindex output of entire files
1425 @cindex entire files, output of
1427 These commands read and write entire files, possibly transforming them
1431 * cat invocation:: Concatenate and write files.
1432 * tac invocation:: Concatenate and write files in reverse.
1433 * nl invocation:: Number lines and write files.
1434 * od invocation:: Write files in octal or other formats.
1435 * base64 invocation:: Transform data into printable data.
1438 @node cat invocation
1439 @section @command{cat}: Concatenate and write files
1442 @cindex concatenate and write files
1443 @cindex copying files
1445 @command{cat} copies each @var{file} (@samp{-} means standard input), or
1446 standard input if none are given, to standard output. Synopsis:
1449 cat [@var{option}] [@var{file}]@dots{}
1452 The program accepts the following options. Also see @ref{Common options}.
1460 Equivalent to @option{-vET}.
1463 @itemx --number-nonblank
1465 @opindex --number-nonblank
1466 Number all nonempty output lines, starting with 1.
1470 Equivalent to @option{-vE}.
1475 @opindex --show-ends
1476 Display a @samp{$} after the end of each line.
1482 Number all output lines, starting with 1.
1485 @itemx --squeeze-blank
1487 @opindex --squeeze-blank
1488 @cindex squeezing empty lines
1489 Suppress repeated adjacent empty lines; output just one empty line
1494 Equivalent to @option{-vT}.
1499 @opindex --show-tabs
1500 Display TAB characters as @samp{^I}.
1504 Ignored; for @acronym{POSIX} compatibility.
1507 @itemx --show-nonprinting
1509 @opindex --show-nonprinting
1510 Display control characters except for LFD and TAB using
1511 @samp{^} notation and precede characters that have the high bit set with
1516 On systems like MS-DOS that distinguish between text and binary files,
1517 @command{cat} normally reads and writes in binary mode. However,
1518 @command{cat} reads in text mode if one of the options
1519 @option{-bensAE} is used or if @command{cat} is reading from standard
1520 input and standard input is a terminal. Similarly, @command{cat}
1521 writes in text mode if one of the options @option{-bensAE} is used or
1522 if standard output is a terminal.
1529 # Output f's contents, then standard input, then g's contents.
1532 # Copy standard input to standard output.
1537 @node tac invocation
1538 @section @command{tac}: Concatenate and write files in reverse
1541 @cindex reversing files
1543 @command{tac} copies each @var{file} (@samp{-} means standard input), or
1544 standard input if none are given, to standard output, reversing the
1545 records (lines by default) in each separately. Synopsis:
1548 tac [@var{option}]@dots{} [@var{file}]@dots{}
1551 @dfn{Records} are separated by instances of a string (newline by
1552 default). By default, this separator string is attached to the end of
1553 the record that it follows in the file.
1555 The program accepts the following options. Also see @ref{Common options}.
1563 The separator is attached to the beginning of the record that it
1564 precedes in the file.
1570 Treat the separator string as a regular expression. Users of @command{tac}
1571 on MS-DOS/MS-Windows should note that, since @command{tac} reads files in
1572 binary mode, each line of a text file might end with a CR/LF pair
1573 instead of the Unix-style LF.
1575 @item -s @var{separator}
1576 @itemx --separator=@var{separator}
1578 @opindex --separator
1579 Use @var{separator} as the record separator, instead of newline.
1587 @section @command{nl}: Number lines and write files
1590 @cindex numbering lines
1591 @cindex line numbering
1593 @command{nl} writes each @var{file} (@samp{-} means standard input), or
1594 standard input if none are given, to standard output, with line numbers
1595 added to some or all of the lines. Synopsis:
1598 nl [@var{option}]@dots{} [@var{file}]@dots{}
1601 @cindex logical pages, numbering on
1602 @command{nl} decomposes its input into (logical) pages; by default, the
1603 line number is reset to 1 at the top of each logical page. @command{nl}
1604 treats all of the input files as a single document; it does not reset
1605 line numbers or logical pages between files.
1607 @cindex headers, numbering
1608 @cindex body, numbering
1609 @cindex footers, numbering
1610 A logical page consists of three sections: header, body, and footer.
1611 Any of the sections can be empty. Each can be numbered in a different
1612 style from the others.
1614 The beginnings of the sections of logical pages are indicated in the
1615 input file by a line containing exactly one of these delimiter strings:
1626 The two characters from which these strings are made can be changed from
1627 @samp{\} and @samp{:} via options (see below), but the pattern and
1628 length of each string cannot be changed.
1630 A section delimiter is replaced by an empty line on output. Any text
1631 that comes before the first section delimiter string in the input file
1632 is considered to be part of a body section, so @command{nl} treats a
1633 file that contains no section delimiters as a single body section.
1635 The program accepts the following options. Also see @ref{Common options}.
1639 @item -b @var{style}
1640 @itemx --body-numbering=@var{style}
1642 @opindex --body-numbering
1643 Select the numbering style for lines in the body section of each
1644 logical page. When a line is not numbered, the current line number
1645 is not incremented, but the line number separator character is still
1646 prepended to the line. The styles are:
1652 number only nonempty lines (default for body),
1654 do not number lines (default for header and footer),
1656 number only lines that contain a match for the basic regular
1657 expression @var{bre}.
1658 @xref{Regular Expressions, , Regular Expressions, grep, The GNU Grep Manual}.
1662 @itemx --section-delimiter=@var{cd}
1664 @opindex --section-delimiter
1665 @cindex section delimiters of pages
1666 Set the section delimiter characters to @var{cd}; default is
1667 @samp{\:}. If only @var{c} is given, the second remains @samp{:}.
1668 (Remember to protect @samp{\} or other metacharacters from shell
1669 expansion with quotes or extra backslashes.)
1671 @item -f @var{style}
1672 @itemx --footer-numbering=@var{style}
1674 @opindex --footer-numbering
1675 Analogous to @option{--body-numbering}.
1677 @item -h @var{style}
1678 @itemx --header-numbering=@var{style}
1680 @opindex --header-numbering
1681 Analogous to @option{--body-numbering}.
1683 @item -i @var{number}
1684 @itemx --line-increment=@var{number}
1686 @opindex --line-increment
1687 Increment line numbers by @var{number} (default 1).
1689 @item -l @var{number}
1690 @itemx --join-blank-lines=@var{number}
1692 @opindex --join-blank-lines
1693 @cindex empty lines, numbering
1694 @cindex blank lines, numbering
1695 Consider @var{number} (default 1) consecutive empty lines to be one
1696 logical line for numbering, and only number the last one. Where fewer
1697 than @var{number} consecutive empty lines occur, do not number them.
1698 An empty line is one that contains no characters, not even spaces
1701 @item -n @var{format}
1702 @itemx --number-format=@var{format}
1704 @opindex --number-format
1705 Select the line numbering format (default is @code{rn}):
1709 @opindex ln @r{format for @command{nl}}
1710 left justified, no leading zeros;
1712 @opindex rn @r{format for @command{nl}}
1713 right justified, no leading zeros;
1715 @opindex rz @r{format for @command{nl}}
1716 right justified, leading zeros.
1720 @itemx --no-renumber
1722 @opindex --no-renumber
1723 Do not reset the line number at the start of a logical page.
1725 @item -s @var{string}
1726 @itemx --number-separator=@var{string}
1728 @opindex --number-separator
1729 Separate the line number from the text line in the output with
1730 @var{string} (default is the TAB character).
1732 @item -v @var{number}
1733 @itemx --starting-line-number=@var{number}
1735 @opindex --starting-line-number
1736 Set the initial line number on each logical page to @var{number} (default 1).
1738 @item -w @var{number}
1739 @itemx --number-width=@var{number}
1741 @opindex --number-width
1742 Use @var{number} characters for line numbers (default 6).
1750 @section @command{od}: Write files in octal or other formats
1753 @cindex octal dump of files
1754 @cindex hex dump of files
1755 @cindex ASCII dump of files
1756 @cindex file contents, dumping unambiguously
1758 @command{od} writes an unambiguous representation of each @var{file}
1759 (@samp{-} means standard input), or standard input if none are given.
1763 od [@var{option}]@dots{} [@var{file}]@dots{}
1764 od [-abcdfilosx]@dots{} [@var{file}] [[+]@var{offset}[.][b]]
1765 od [@var{option}]@dots{} --traditional [@var{file}] [[+]@var{offset}[.][b] [[+]@var{label}[.][b]]]
1768 Each line of output consists of the offset in the input, followed by
1769 groups of data from the file. By default, @command{od} prints the offset in
1770 octal, and each group of file data is a C @code{short int}'s worth of input
1771 printed as a single octal number.
1773 If @var{offset} is given, it specifies how many input bytes to skip
1774 before formatting and writing. By default, it is interpreted as an
1775 octal number, but the optional trailing decimal point causes it to be
1776 interpreted as decimal. If no decimal is specified and the offset
1777 begins with @samp{0x} or @samp{0X} it is interpreted as a hexadecimal
1778 number. If there is a trailing @samp{b}, the number of bytes skipped
1779 will be @var{offset} multiplied by 512.
1781 If a command is of both the first and second forms, the second form is
1782 assumed if the last operand begins with @samp{+} or (if there are two
1783 operands) a digit. For example, in @samp{od foo 10} and @samp{od +10}
1784 the @samp{10} is an offset, whereas in @samp{od 10} the @samp{10} is a
1787 The program accepts the following options. Also see @ref{Common options}.
1791 @item -A @var{radix}
1792 @itemx --address-radix=@var{radix}
1794 @opindex --address-radix
1795 @cindex radix for file offsets
1796 @cindex file offset radix
1797 Select the base in which file offsets are printed. @var{radix} can
1798 be one of the following:
1808 none (do not print offsets).
1811 The default is octal.
1813 @item -j @var{bytes}
1814 @itemx --skip-bytes=@var{bytes}
1816 @opindex --skip-bytes
1817 Skip @var{bytes} input bytes before formatting and writing. If
1818 @var{bytes} begins with @samp{0x} or @samp{0X}, it is interpreted in
1819 hexadecimal; otherwise, if it begins with @samp{0}, in octal; otherwise,
1821 @multiplierSuffixes{bytes}
1823 @item -N @var{bytes}
1824 @itemx --read-bytes=@var{bytes}
1826 @opindex --read-bytes
1827 Output at most @var{bytes} bytes of the input. Prefixes and suffixes on
1828 @code{bytes} are interpreted as for the @option{-j} option.
1830 @item -S @var{bytes}
1831 @itemx --strings[=@var{bytes}]
1834 @cindex string constants, outputting
1835 Instead of the normal output, output only @dfn{string constants}: at
1836 least @var{bytes} consecutive @acronym{ASCII} graphic characters,
1837 followed by a zero byte (@acronym{ASCII} @sc{nul}).
1838 Prefixes and suffixes on @code{bytes} are interpreted as for the
1841 If @var{n} is omitted with @option{--strings}, the default is 3.
1844 @itemx --format=@var{type}
1847 Select the format in which to output the file data. @var{type} is a
1848 string of one or more of the below type indicator characters. If you
1849 include more than one type indicator character in a single @var{type}
1850 string, or use this option more than once, @command{od} writes one copy
1851 of each output line using each of the data types that you specified,
1852 in the order that you specified.
1854 Adding a trailing ``z'' to any type specification appends a display
1855 of the @acronym{ASCII} character representation of the printable characters
1856 to the output line generated by the type specification.
1860 named character, ignoring high-order bit
1862 @acronym{ASCII} character or backslash escape,
1875 The type @code{a} outputs things like @samp{sp} for space, @samp{nl} for
1876 newline, and @samp{nul} for a zero byte. Only the least significant
1877 seven bits of each byte is used; the high-order bit is ignored.
1878 Type @code{c} outputs
1879 @samp{ }, @samp{\n}, and @code{\0}, respectively.
1882 Except for types @samp{a} and @samp{c}, you can specify the number
1883 of bytes to use in interpreting each number in the given data type
1884 by following the type indicator character with a decimal integer.
1885 Alternately, you can specify the size of one of the C compiler's
1886 built-in data types by following the type indicator character with
1887 one of the following characters. For integers (@samp{d}, @samp{o},
1888 @samp{u}, @samp{x}):
1901 For floating point (@code{f}):
1913 @itemx --output-duplicates
1915 @opindex --output-duplicates
1916 Output consecutive lines that are identical. By default, when two or
1917 more consecutive output lines would be identical, @command{od} outputs only
1918 the first line, and puts just an asterisk on the following line to
1919 indicate the elision.
1922 @itemx --width[=@var{n}]
1925 Dump @code{n} input bytes per output line. This must be a multiple of
1926 the least common multiple of the sizes associated with the specified
1929 If this option is not given at all, the default is 16. If @var{n} is
1930 omitted, the default is 32.
1934 The next several options are shorthands for format specifications.
1935 @sc{gnu} @command{od} accepts any combination of shorthands and format
1936 specification options. These options accumulate.
1942 Output as named characters. Equivalent to @samp{-t a}.
1946 Output as octal bytes. Equivalent to @samp{-t o1}.
1950 Output as @acronym{ASCII} characters or backslash escapes. Equivalent to
1955 Output as unsigned decimal two-byte units. Equivalent to @samp{-t u2}.
1959 Output as floats. Equivalent to @samp{-t fF}.
1963 Output as decimal ints. Equivalent to @samp{-t dI}.
1967 Output as decimal long ints. Equivalent to @samp{-t dL}.
1971 Output as octal two-byte units. Equivalent to @option{-t o2}.
1975 Output as decimal two-byte units. Equivalent to @option{-t d2}.
1979 Output as hexadecimal two-byte units. Equivalent to @samp{-t x2}.
1982 @opindex --traditional
1983 Recognize the non-option label argument that traditional @command{od}
1984 accepted. The following syntax:
1987 od --traditional [@var{file}] [[+]@var{offset}[.][b] [[+]@var{label}[.][b]]]
1991 can be used to specify at most one file and optional arguments
1992 specifying an offset and a pseudo-start address, @var{label}.
1993 The @var{label} argument is interpreted
1994 just like @var{offset}, but it specifies an initial pseudo-address. The
1995 pseudo-addresses are displayed in parentheses following any normal
2002 @node base64 invocation
2003 @section @command{base64}: Transform data into printable data
2006 @cindex base64 encoding
2008 @command{base64} transforms data read from a file, or standard input,
2009 into (or from) base64 encoded form. The base64 encoded form uses
2010 printable @acronym{ASCII} characters to represent binary data.
2014 base64 [@var{option}]@dots{} [@var{file}]
2015 base64 --decode [@var{option}]@dots{} [@var{file}]
2018 The base64 encoding expands data to roughly 133% of the original.
2019 The format conforms to
2020 @uref{ftp://ftp.rfc-editor.org/in-notes/rfc4648.txt, RFC 4648}.
2022 The program accepts the following options. Also see @ref{Common options}.
2027 @itemx --wrap=@var{cols}
2031 @cindex column to wrap data after
2032 During encoding, wrap lines after @var{cols} characters. This must be
2035 The default is to wrap after 76 characters. Use the value 0 to
2036 disable line wrapping altogether.
2042 @cindex Decode base64 data
2043 @cindex Base64 decoding
2044 Change the mode of operation, from the default of encoding data, to
2045 decoding data. Input is expected to be base64 encoded data, and the
2046 output will be the original data.
2049 @itemx --ignore-garbage
2051 @opindex --ignore-garbage
2052 @cindex Ignore garbage in base64 stream
2053 When decoding, newlines are always accepted.
2054 During decoding, ignore unrecognized bytes,
2055 to permit distorted data to be decoded.
2062 @node Formatting file contents
2063 @chapter Formatting file contents
2065 @cindex formatting file contents
2067 These commands reformat the contents of files.
2070 * fmt invocation:: Reformat paragraph text.
2071 * pr invocation:: Paginate or columnate files for printing.
2072 * fold invocation:: Wrap input lines to fit in specified width.
2076 @node fmt invocation
2077 @section @command{fmt}: Reformat paragraph text
2080 @cindex reformatting paragraph text
2081 @cindex paragraphs, reformatting
2082 @cindex text, reformatting
2084 @command{fmt} fills and joins lines to produce output lines of (at most)
2085 a given number of characters (75 by default). Synopsis:
2088 fmt [@var{option}]@dots{} [@var{file}]@dots{}
2091 @command{fmt} reads from the specified @var{file} arguments (or standard
2092 input if none are given), and writes to standard output.
2094 By default, blank lines, spaces between words, and indentation are
2095 preserved in the output; successive input lines with different
2096 indentation are not joined; tabs are expanded on input and introduced on
2099 @cindex line-breaking
2100 @cindex sentences and line-breaking
2101 @cindex Knuth, Donald E.
2102 @cindex Plass, Michael F.
2103 @command{fmt} prefers breaking lines at the end of a sentence, and tries to
2104 avoid line breaks after the first word of a sentence or before the last
2105 word of a sentence. A @dfn{sentence break} is defined as either the end
2106 of a paragraph or a word ending in any of @samp{.?!}, followed by two
2107 spaces or end of line, ignoring any intervening parentheses or quotes.
2108 Like @TeX{}, @command{fmt} reads entire ``paragraphs'' before choosing line
2109 breaks; the algorithm is a variant of that given by Donald E. Knuth
2110 and Michael F. Plass in ``Breaking Paragraphs Into Lines'',
2111 @cite{Software---Practice & Experience} @b{11}, 11 (November 1981),
2114 The program accepts the following options. Also see @ref{Common options}.
2119 @itemx --crown-margin
2121 @opindex --crown-margin
2122 @cindex crown margin
2123 @dfn{Crown margin} mode: preserve the indentation of the first two
2124 lines within a paragraph, and align the left margin of each subsequent
2125 line with that of the second line.
2128 @itemx --tagged-paragraph
2130 @opindex --tagged-paragraph
2131 @cindex tagged paragraphs
2132 @dfn{Tagged paragraph} mode: like crown margin mode, except that if
2133 indentation of the first line of a paragraph is the same as the
2134 indentation of the second, the first line is treated as a one-line
2140 @opindex --split-only
2141 Split lines only. Do not join short lines to form longer ones. This
2142 prevents sample lines of code, and other such ``formatted'' text from
2143 being unduly combined.
2146 @itemx --uniform-spacing
2148 @opindex --uniform-spacing
2149 Uniform spacing. Reduce spacing between words to one space, and spacing
2150 between sentences to two spaces.
2153 @itemx -w @var{width}
2154 @itemx --width=@var{width}
2155 @opindex -@var{width}
2158 Fill output lines up to @var{width} characters (default 75). @command{fmt}
2159 initially tries to make lines about 7% shorter than this, to give it
2160 room to balance line lengths.
2162 @item -p @var{prefix}
2163 @itemx --prefix=@var{prefix}
2164 Only lines beginning with @var{prefix} (possibly preceded by whitespace)
2165 are subject to formatting. The prefix and any preceding whitespace are
2166 stripped for the formatting and then re-attached to each formatted output
2167 line. One use is to format certain kinds of program comments, while
2168 leaving the code unchanged.
2176 @section @command{pr}: Paginate or columnate files for printing
2179 @cindex printing, preparing files for
2180 @cindex multicolumn output, generating
2181 @cindex merging files in parallel
2183 @command{pr} writes each @var{file} (@samp{-} means standard input), or
2184 standard input if none are given, to standard output, paginating and
2185 optionally outputting in multicolumn format; optionally merges all
2186 @var{file}s, printing all in parallel, one per column. Synopsis:
2189 pr [@var{option}]@dots{} [@var{file}]@dots{}
2193 By default, a 5-line header is printed at each page: two blank lines;
2194 a line with the date, the file name, and the page count; and two more
2195 blank lines. A footer of five blank lines is also printed.
2196 The default @var{page_length} is 66
2197 lines. The default number of text lines is therefore 56.
2198 The text line of the header takes the form
2199 @samp{@var{date} @var{string} @var{page}}, with spaces inserted around
2200 @var{string} so that the line takes up the full @var{page_width}. Here,
2201 @var{date} is the date (see the @option{-D} or @option{--date-format}
2202 option for details), @var{string} is the centered header string, and
2203 @var{page} identifies the page number. The @env{LC_MESSAGES} locale
2204 category affects the spelling of @var{page}; in the default C locale, it
2205 is @samp{Page @var{number}} where @var{number} is the decimal page
2208 Form feeds in the input cause page breaks in the output. Multiple form
2209 feeds produce empty pages.
2211 Columns are of equal width, separated by an optional string (default
2212 is @samp{space}). For multicolumn output, lines will always be truncated to
2213 @var{page_width} (default 72), unless you use the @option{-J} option.
2215 column output no line truncation occurs by default. Use @option{-W} option to
2216 truncate lines in that case.
2218 The following changes were made in version 1.22i and apply to later
2219 versions of @command{pr}:
2220 @c FIXME: this whole section here sounds very awkward to me. I
2221 @c made a few small changes, but really it all needs to be redone. - Brian
2222 @c OK, I fixed another sentence or two, but some of it I just don't understand.
2227 Some small @var{letter options} (@option{-s}, @option{-w}) have been
2228 redefined for better @acronym{POSIX} compliance. The output of some further
2229 cases has been adapted to other Unix systems. These changes are not
2230 compatible with earlier versions of the program.
2233 Some @var{new capital letter} options (@option{-J}, @option{-S}, @option{-W})
2234 have been introduced to turn off unexpected interferences of small letter
2235 options. The @option{-N} option and the second argument @var{last_page}
2236 of @samp{+FIRST_PAGE} offer more flexibility. The detailed handling of
2237 form feeds set in the input files requires the @option{-T} option.
2240 Capital letter options override small letter ones.
2243 Some of the option-arguments (compare @option{-s}, @option{-e},
2244 @option{-i}, @option{-n}) cannot be specified as separate arguments from the
2245 preceding option letter (already stated in the @acronym{POSIX} specification).
2248 The program accepts the following options. Also see @ref{Common options}.
2252 @item +@var{first_page}[:@var{last_page}]
2253 @itemx --pages=@var{first_page}[:@var{last_page}]
2254 @c The two following @opindex lines evoke warnings because they contain `:'
2255 @c The `info' spec does not permit that. If we use those lines, we end
2256 @c up with truncated index entries that don't work.
2257 @c @opindex +@var{first_page}[:@var{last_page}]
2258 @c @opindex --pages=@var{first_page}[:@var{last_page}]
2259 @opindex +@var{page_range}
2260 @opindex --pages=@var{page_range}
2261 Begin printing with page @var{first_page} and stop with @var{last_page}.
2262 Missing @samp{:@var{last_page}} implies end of file. While estimating
2263 the number of skipped pages each form feed in the input file results
2264 in a new page. Page counting with and without @samp{+@var{first_page}}
2265 is identical. By default, counting starts with the first page of input
2266 file (not first page printed). Line numbering may be altered by @option{-N}
2270 @itemx --columns=@var{column}
2271 @opindex -@var{column}
2273 @cindex down columns
2274 With each single @var{file}, produce @var{column} columns of output
2275 (default is 1) and print columns down, unless @option{-a} is used. The
2276 column width is automatically decreased as @var{column} increases; unless
2277 you use the @option{-W/-w} option to increase @var{page_width} as well.
2278 This option might well cause some lines to be truncated. The number of
2279 lines in the columns on each page are balanced. The options @option{-e}
2280 and @option{-i} are on for multiple text-column output. Together with
2281 @option{-J} option column alignment and line truncation is turned off.
2282 Lines of full length are joined in a free field format and @option{-S}
2283 option may set field separators. @option{-@var{column}} may not be used
2284 with @option{-m} option.
2290 @cindex across columns
2291 With each single @var{file}, print columns across rather than down. The
2292 @option{-@var{column}} option must be given with @var{column} greater than one.
2293 If a line is too long to fit in a column, it is truncated.
2296 @itemx --show-control-chars
2298 @opindex --show-control-chars
2299 Print control characters using hat notation (e.g., @samp{^G}); print
2300 other nonprinting characters in octal backslash notation. By default,
2301 nonprinting characters are not changed.
2304 @itemx --double-space
2306 @opindex --double-space
2307 @cindex double spacing
2308 Double space the output.
2310 @item -D @var{format}
2311 @itemx --date-format=@var{format}
2312 @cindex time formats
2313 @cindex formatting times
2314 Format header dates using @var{format}, using the same conventions as
2315 for the command @samp{date +@var{format}}; @xref{date invocation}.
2316 Except for directives, which start with
2317 @samp{%}, characters in @var{format} are printed unchanged. You can use
2318 this option to specify an arbitrary string in place of the header date,
2319 e.g., @option{--date-format="Monday morning"}.
2321 @vindex POSIXLY_CORRECT
2323 The default date format is @samp{%Y-%m-%d %H:%M} (for example,
2324 @samp{2001-12-04 23:59});
2325 but if the @env{POSIXLY_CORRECT} environment variable is set
2326 and the @env{LC_TIME} locale category specifies the @acronym{POSIX}
2327 locale, the default is @samp{%b %e %H:%M %Y} (for example,
2328 @samp{Dec@ @ 4 23:59 2001}.
2331 Time stamps are listed according to the time zone rules specified by
2332 the @env{TZ} environment variable, or by the system default rules if
2333 @env{TZ} is not set. @xref{TZ Variable,, Specifying the Time Zone
2334 with @env{TZ}, libc, The GNU C Library Reference Manual}.
2336 @item -e[@var{in-tabchar}[@var{in-tabwidth}]]
2337 @itemx --expand-tabs[=@var{in-tabchar}[@var{in-tabwidth}]]
2339 @opindex --expand-tabs
2341 Expand @var{tab}s to spaces on input. Optional argument @var{in-tabchar} is
2342 the input tab character (default is the TAB character). Second optional
2343 argument @var{in-tabwidth} is the input tab character's width (default
2351 @opindex --form-feed
2352 Use a form feed instead of newlines to separate output pages. This does
2353 not alter the default page length of 66 lines.
2355 @item -h @var{header}
2356 @itemx --header=@var{header}
2359 Replace the file name in the header with the centered string @var{header}.
2360 When using the shell, @var{header} should be quoted and should be
2361 separated from @option{-h} by a space.
2363 @item -i[@var{out-tabchar}[@var{out-tabwidth}]]
2364 @itemx --output-tabs[=@var{out-tabchar}[@var{out-tabwidth}]]
2366 @opindex --output-tabs
2368 Replace spaces with @var{tab}s on output. Optional argument @var{out-tabchar}
2369 is the output tab character (default is the TAB character). Second optional
2370 argument @var{out-tabwidth} is the output tab character's width (default
2376 @opindex --join-lines
2377 Merge lines of full length. Used together with the column options
2378 @option{-@var{column}}, @option{-a -@var{column}} or @option{-m}. Turns off
2379 @option{-W/-w} line truncation;
2380 no column alignment used; may be used with
2381 @option{--sep-string[=@var{string}]}. @option{-J} has been introduced
2382 (together with @option{-W} and @option{--sep-string})
2383 to disentangle the old (@acronym{POSIX}-compliant) options @option{-w} and
2384 @option{-s} along with the three column options.
2387 @item -l @var{page_length}
2388 @itemx --length=@var{page_length}
2391 Set the page length to @var{page_length} (default 66) lines, including
2392 the lines of the header [and the footer]. If @var{page_length} is less
2393 than or equal to 10, the header and footer are omitted, as if the
2394 @option{-t} option had been given.
2400 Merge and print all @var{file}s in parallel, one in each column. If a
2401 line is too long to fit in a column, it is truncated, unless the @option{-J}
2402 option is used. @option{--sep-string[=@var{string}]} may be used.
2404 some @var{file}s (form feeds set) produce empty columns, still marked
2405 by @var{string}. The result is a continuous line numbering and column
2406 marking throughout the whole merged file. Completely empty merged pages
2407 show no separators or line numbers. The default header becomes
2408 @samp{@var{date} @var{page}} with spaces inserted in the middle; this
2409 may be used with the @option{-h} or @option{--header} option to fill up
2410 the middle blank part.
2412 @item -n[@var{number-separator}[@var{digits}]]
2413 @itemx --number-lines[=@var{number-separator}[@var{digits}]]
2415 @opindex --number-lines
2416 Provide @var{digits} digit line numbering (default for @var{digits} is
2417 5). With multicolumn output the number occupies the first @var{digits}
2418 column positions of each text column or only each line of @option{-m}
2419 output. With single column output the number precedes each line just as
2420 @option{-m} does. Default counting of the line numbers starts with the
2421 first line of the input file (not the first line printed, compare the
2422 @option{--page} option and @option{-N} option).
2423 Optional argument @var{number-separator} is the character appended to
2424 the line number to separate it from the text followed. The default
2425 separator is the TAB character. In a strict sense a TAB is always
2426 printed with single column output only. The TAB width varies
2427 with the TAB position, e.g., with the left @var{margin} specified
2428 by @option{-o} option. With multicolumn output priority is given to
2429 @samp{equal width of output columns} (a @acronym{POSIX} specification).
2430 The TAB width is fixed to the value of the first column and does
2431 not change with different values of left @var{margin}. That means a
2432 fixed number of spaces is always printed in the place of the
2433 @var{number-separator} TAB. The tabification depends upon the output
2436 @item -N @var{line_number}
2437 @itemx --first-line-number=@var{line_number}
2439 @opindex --first-line-number
2440 Start line counting with the number @var{line_number} at first line of
2441 first page printed (in most cases not the first line of the input file).
2443 @item -o @var{margin}
2444 @itemx --indent=@var{margin}
2447 @cindex indenting lines
2449 Indent each line with a margin @var{margin} spaces wide (default is zero).
2450 The total page width is the size of the margin plus the @var{page_width}
2451 set with the @option{-W/-w} option. A limited overflow may occur with
2452 numbered single column output (compare @option{-n} option).
2455 @itemx --no-file-warnings
2457 @opindex --no-file-warnings
2458 Do not print a warning message when an argument @var{file} cannot be
2459 opened. (The exit status will still be nonzero, however.)
2461 @item -s[@var{char}]
2462 @itemx --separator[=@var{char}]
2464 @opindex --separator
2465 Separate columns by a single character @var{char}. The default for
2466 @var{char} is the TAB character without @option{-w} and @samp{no
2467 character} with @option{-w}. Without @option{-s} the default separator
2468 @samp{space} is set. @option{-s[char]} turns off line truncation of all
2469 three column options (@option{-COLUMN}|@option{-a -COLUMN}|@option{-m}) unless
2470 @option{-w} is set. This is a @acronym{POSIX}-compliant formulation.
2473 @item -S@var{string}
2474 @itemx --sep-string[=@var{string}]
2476 @opindex --sep-string
2477 Use @var{string} to separate output columns. The @option{-S} option doesn't
2478 affect the @option{-W/-w} option, unlike the @option{-s} option which does. It
2479 does not affect line truncation or column alignment.
2480 Without @option{-S}, and with @option{-J}, @command{pr} uses the default output
2482 Without @option{-S} or @option{-J}, @command{pr} uses a @samp{space}
2483 (same as @option{-S"@w{ }"}). @option{--sep-string} with no
2484 @samp{=@var{string}} is equivalent to @option{--sep-string=""}.
2487 @itemx --omit-header
2489 @opindex --omit-header
2490 Do not print the usual header [and footer] on each page, and do not fill
2491 out the bottom of pages (with blank lines or a form feed). No page
2492 structure is produced, but form feeds set in the input files are retained.
2493 The predefined pagination is not changed. @option{-t} or @option{-T} may be
2494 useful together with other options; e.g.: @option{-t -e4}, expand TAB characters
2495 in the input file to 4 spaces but don't make any other changes. Use of
2496 @option{-t} overrides @option{-h}.
2499 @itemx --omit-pagination
2501 @opindex --omit-pagination
2502 Do not print header [and footer]. In addition eliminate all form feeds
2503 set in the input files.
2506 @itemx --show-nonprinting
2508 @opindex --show-nonprinting
2509 Print nonprinting characters in octal backslash notation.
2511 @item -w @var{page_width}
2512 @itemx --width=@var{page_width}
2515 Set page width to @var{page_width} characters for multiple text-column
2516 output only (default for @var{page_width} is 72). @option{-s[CHAR]} turns
2517 off the default page width and any line truncation and column alignment.
2518 Lines of full length are merged, regardless of the column options
2519 set. No @var{page_width} setting is possible with single column output.
2520 A @acronym{POSIX}-compliant formulation.
2522 @item -W @var{page_width}
2523 @itemx --page_width=@var{page_width}
2525 @opindex --page_width
2526 Set the page width to @var{page_width} characters. That's valid with and
2527 without a column option. Text lines are truncated, unless @option{-J}
2528 is used. Together with one of the three column options
2529 (@option{-@var{column}}, @option{-a -@var{column}} or @option{-m}) column
2530 alignment is always used. The separator options @option{-S} or @option{-s}
2531 don't affect the @option{-W} option. Default is 72 characters. Without
2532 @option{-W @var{page_width}} and without any of the column options NO line
2533 truncation is used (defined to keep downward compatibility and to meet
2534 most frequent tasks). That's equivalent to @option{-W 72 -J}. The header
2535 line is never truncated.
2542 @node fold invocation
2543 @section @command{fold}: Wrap input lines to fit in specified width
2546 @cindex wrapping long input lines
2547 @cindex folding long input lines
2549 @command{fold} writes each @var{file} (@option{-} means standard input), or
2550 standard input if none are given, to standard output, breaking long
2554 fold [@var{option}]@dots{} [@var{file}]@dots{}
2557 By default, @command{fold} breaks lines wider than 80 columns. The output
2558 is split into as many lines as necessary.
2560 @cindex screen columns
2561 @command{fold} counts screen columns by default; thus, a tab may count more
2562 than one column, backspace decreases the column count, and carriage
2563 return sets the column to zero.
2565 The program accepts the following options. Also see @ref{Common options}.
2573 Count bytes rather than columns, so that tabs, backspaces, and carriage
2574 returns are each counted as taking up one column, just like other
2581 Break at word boundaries: the line is broken after the last blank before
2582 the maximum line length. If the line contains no such blanks, the line
2583 is broken at the maximum line length as usual.
2585 @item -w @var{width}
2586 @itemx --width=@var{width}
2589 Use a maximum line length of @var{width} columns instead of 80.
2591 For compatibility @command{fold} supports an obsolete option syntax
2592 @option{-@var{width}}. New scripts should use @option{-w @var{width}}
2600 @node Output of parts of files
2601 @chapter Output of parts of files
2603 @cindex output of parts of files
2604 @cindex parts of files, output of
2606 These commands output pieces of the input.
2609 * head invocation:: Output the first part of files.
2610 * tail invocation:: Output the last part of files.
2611 * split invocation:: Split a file into fixed-size pieces.
2612 * csplit invocation:: Split a file into context-determined pieces.
2615 @node head invocation
2616 @section @command{head}: Output the first part of files
2619 @cindex initial part of files, outputting
2620 @cindex first part of files, outputting
2622 @command{head} prints the first part (10 lines by default) of each
2623 @var{file}; it reads from standard input if no files are given or
2624 when given a @var{file} of @option{-}. Synopsis:
2627 head [@var{option}]@dots{} [@var{file}]@dots{}
2630 If more than one @var{file} is specified, @command{head} prints a
2631 one-line header consisting of:
2634 ==> @var{file name} <==
2638 before the output for each @var{file}.
2640 The program accepts the following options. Also see @ref{Common options}.
2645 @itemx --bytes=@var{k}
2648 Print the first @var{k} bytes, instead of initial lines.
2649 However, if @var{k} starts with a @samp{-},
2650 print all but the last @var{k} bytes of each file.
2651 @multiplierSuffixes{k}
2654 @itemx --lines=@var{k}
2657 Output the first @var{k} lines.
2658 However, if @var{k} starts with a @samp{-},
2659 print all but the last @var{k} lines of each file.
2660 Size multiplier suffixes are the same as with the @option{-c} option.
2668 Never print file name headers.
2674 Always print file name headers.
2678 For compatibility @command{head} also supports an obsolete option syntax
2679 @option{-@var{count}@var{options}}, which is recognized only if it is
2680 specified first. @var{count} is a decimal number optionally followed
2681 by a size letter (@samp{b}, @samp{k}, @samp{m}) as in @option{-c}, or
2682 @samp{l} to mean count by lines, or other option letters (@samp{cqv}).
2683 Scripts intended for standard hosts should use @option{-c @var{count}}
2684 or @option{-n @var{count}} instead. If your script must also run on
2685 hosts that support only the obsolete syntax, it is usually simpler to
2686 avoid @command{head}, e.g., by using @samp{sed 5q} instead of
2692 @node tail invocation
2693 @section @command{tail}: Output the last part of files
2696 @cindex last part of files, outputting
2698 @command{tail} prints the last part (10 lines by default) of each
2699 @var{file}; it reads from standard input if no files are given or
2700 when given a @var{file} of @samp{-}. Synopsis:
2703 tail [@var{option}]@dots{} [@var{file}]@dots{}
2706 If more than one @var{file} is specified, @command{tail} prints a
2707 one-line header consisting of:
2710 ==> @var{file name} <==
2714 before the output for each @var{file}.
2716 @cindex BSD @command{tail}
2717 @sc{gnu} @command{tail} can output any amount of data (some other versions of
2718 @command{tail} cannot). It also has no @option{-r} option (print in
2719 reverse), since reversing a file is really a different job from printing
2720 the end of a file; BSD @command{tail} (which is the one with @option{-r}) can
2721 only reverse files that are at most as large as its buffer, which is
2722 typically 32 KiB@. A more reliable and versatile way to reverse files is
2723 the @sc{gnu} @command{tac} command.
2725 The program accepts the following options. Also see @ref{Common options}.
2730 @itemx --bytes=@var{k}
2733 Output the last @var{k} bytes, instead of final lines.
2734 However, if @var{k} starts with a @samp{+}, start printing with the
2735 @var{k}th byte from the start of each file, instead of from the end.
2736 @multiplierSuffixes{k}
2739 @itemx --follow[=@var{how}]
2742 @cindex growing files
2743 @vindex name @r{follow option}
2744 @vindex descriptor @r{follow option}
2745 Loop forever trying to read more characters at the end of the file,
2746 presumably because the file is growing.
2747 If more than one file is given, @command{tail} prints a header whenever it
2748 gets output from a different file, to indicate which file that output is
2751 There are two ways to specify how you'd like to track files with this option,
2752 but that difference is noticeable only when a followed file is removed or
2754 If you'd like to continue to track the end of a growing file even after
2755 it has been unlinked, use @option{--follow=descriptor}. This is the default
2756 behavior, but it is not useful if you're tracking a log file that may be
2757 rotated (removed or renamed, then reopened). In that case, use
2758 @option{--follow=name} to track the named file by reopening it periodically
2759 to see if it has been removed and recreated by some other program.
2761 No matter which method you use, if the tracked file is determined to have
2762 shrunk, @command{tail} prints a message saying the file has been truncated
2763 and resumes tracking the end of the file from the newly-determined endpoint.
2765 When a file is removed, @command{tail}'s behavior depends on whether it is
2766 following the name or the descriptor. When following by name, tail can
2767 detect that a file has been removed and gives a message to that effect,
2768 and if @option{--retry} has been specified it will continue checking
2769 periodically to see if the file reappears.
2770 When following a descriptor, tail does not detect that the file has
2771 been unlinked or renamed and issues no message; even though the file
2772 may no longer be accessible via its original name, it may still be
2775 The option values @samp{descriptor} and @samp{name} may be specified only
2776 with the long form of the option, not with @option{-f}.
2778 The @option{-f} option is ignored if
2779 no @var{file} operand is specified and standard input is a FIFO or a pipe.
2780 Likewise, the @option{-f} option has no effect for any
2781 operand specified as @samp{-}, when standard input is a FIFO or a pipe.
2785 This option is the same as @option{--follow=name --retry}. That is, tail
2786 will attempt to reopen a file when it is removed. Should this fail, tail
2787 will keep trying until it becomes accessible again.
2791 This option is useful mainly when following by name (i.e., with
2792 @option{--follow=name}).
2793 Without this option, when tail encounters a file that doesn't
2794 exist or is otherwise inaccessible, it reports that fact and
2795 never checks it again.
2797 @itemx --sleep-interval=@var{number}
2798 @opindex --sleep-interval
2799 Change the number of seconds to wait between iterations (the default is 1.0).
2800 During one iteration, every specified file is checked to see if it has
2802 Historical implementations of @command{tail} have required that
2803 @var{number} be an integer. However, GNU @command{tail} accepts
2804 an arbitrary floating point number (using a period before any
2807 @itemx --pid=@var{pid}
2809 When following by name or by descriptor, you may specify the process ID,
2810 @var{pid}, of the sole writer of all @var{file} arguments. Then, shortly
2811 after that process terminates, tail will also terminate. This will
2812 work properly only if the writer and the tailing process are running on
2813 the same machine. For example, to save the output of a build in a file
2814 and to watch the file grow, if you invoke @command{make} and @command{tail}
2815 like this then the tail process will stop when your build completes.
2816 Without this option, you would have had to kill the @code{tail -f}
2820 $ make >& makerr & tail --pid=$! -f makerr
2823 If you specify a @var{pid} that is not in use or that does not correspond
2824 to the process that is writing to the tailed files, then @command{tail}
2825 may terminate long before any @var{file}s stop growing or it may not
2826 terminate until long after the real writer has terminated.
2827 Note that @option{--pid} cannot be supported on some systems; @command{tail}
2828 will print a warning if this is the case.
2830 @itemx --max-unchanged-stats=@var{n}
2831 @opindex --max-unchanged-stats
2832 When tailing a file by name, if there have been @var{n} (default
2833 n=@value{DEFAULT_MAX_N_UNCHANGED_STATS_BETWEEN_OPENS}) consecutive
2834 iterations for which the file has not changed, then
2835 @code{open}/@code{fstat} the file to determine if that file name is
2836 still associated with the same device/inode-number pair as before.
2837 When following a log file that is rotated, this is approximately the
2838 number of seconds between when tail prints the last pre-rotation lines
2839 and when it prints the lines that have accumulated in the new log file.
2840 This option is meaningful only when following by name.
2843 @itemx --lines=@var{k}
2846 Output the last @var{k} lines.
2847 However, if @var{k} starts with a @samp{+}, start printing with the
2848 @var{k}th line from the start of each file, instead of from the end.
2849 Size multiplier suffixes are the same as with the @option{-c} option.
2857 Never print file name headers.
2863 Always print file name headers.
2867 For compatibility @command{tail} also supports an obsolete usage
2868 @samp{tail -[@var{count}][bcl][f] [@var{file}]}, which is recognized
2869 only if it does not conflict with the usage described
2870 above. This obsolete form uses exactly one option and at most one
2871 file. In the option, @var{count} is an optional decimal number optionally
2872 followed by a size letter (@samp{b}, @samp{c}, @samp{l}) to mean count
2873 by 512-byte blocks, bytes, or lines, optionally followed by @samp{f}
2874 which has the same meaning as @option{-f}.
2876 @vindex _POSIX2_VERSION
2877 On older systems, the leading @samp{-} can be replaced by @samp{+} in
2878 the obsolete option syntax with the same meaning as in counts, and
2879 obsolete usage overrides normal usage when the two conflict.
2880 This obsolete behavior can be enabled or disabled with the
2881 @env{_POSIX2_VERSION} environment variable (@pxref{Standards
2884 Scripts intended for use on standard hosts should avoid obsolete
2885 syntax and should use @option{-c @var{count}[b]}, @option{-n
2886 @var{count}}, and/or @option{-f} instead. If your script must also
2887 run on hosts that support only the obsolete syntax, you can often
2888 rewrite it to avoid problematic usages, e.g., by using @samp{sed -n
2889 '$p'} rather than @samp{tail -1}. If that's not possible, the script
2890 can use a test like @samp{if tail -c +1 </dev/null >/dev/null 2>&1;
2891 then @dots{}} to decide which syntax to use.
2893 Even if your script assumes the standard behavior, you should still
2894 beware usages whose behaviors differ depending on the @acronym{POSIX}
2895 version. For example, avoid @samp{tail - main.c}, since it might be
2896 interpreted as either @samp{tail main.c} or as @samp{tail -- -
2897 main.c}; avoid @samp{tail -c 4}, since it might mean either @samp{tail
2898 -c4} or @samp{tail -c 10 4}; and avoid @samp{tail +4}, since it might
2899 mean either @samp{tail ./+4} or @samp{tail -n +4}.
2904 @node split invocation
2905 @section @command{split}: Split a file into fixed-size pieces
2908 @cindex splitting a file into pieces
2909 @cindex pieces, splitting a file into
2911 @command{split} creates output files containing consecutive sections of
2912 @var{input} (standard input if none is given or @var{input} is
2913 @samp{-}). Synopsis:
2916 split [@var{option}] [@var{input} [@var{prefix}]]
2919 By default, @command{split} puts 1000 lines of @var{input} (or whatever is
2920 left over for the last section), into each output file.
2922 @cindex output file name prefix
2923 The output files' names consist of @var{prefix} (@samp{x} by default)
2924 followed by a group of characters (@samp{aa}, @samp{ab}, @dots{} by
2925 default), such that concatenating the output files in traditional
2926 sorted order by file name produces
2927 the original input file. If the output file names are exhausted,
2928 @command{split} reports an error without deleting the output files
2931 The program accepts the following options. Also see @ref{Common options}.
2935 @item -l @var{lines}
2936 @itemx --lines=@var{lines}
2939 Put @var{lines} lines of @var{input} into each output file.
2941 For compatibility @command{split} also supports an obsolete
2942 option syntax @option{-@var{lines}}. New scripts should use @option{-l
2943 @var{lines}} instead.
2946 @itemx --bytes=@var{size}
2949 Put @var{size} bytes of @var{input} into each output file.
2950 @multiplierSuffixes{size}
2953 @itemx --line-bytes=@var{size}
2955 @opindex --line-bytes
2956 Put into each output file as many complete lines of @var{input} as
2957 possible without exceeding @var{size} bytes. Individual lines longer than
2958 @var{size} bytes are broken into multiple files.
2959 @var{size} has the same format as for the @option{--bytes} option.
2961 @item -a @var{length}
2962 @itemx --suffix-length=@var{length}
2964 @opindex --suffix-length
2965 Use suffixes of length @var{length}. The default @var{length} is 2.
2968 @itemx --numeric-suffixes
2970 @opindex --numeric-suffixes
2971 Use digits in suffixes rather than lower-case letters.
2975 Write a diagnostic just before each output file is opened.
2982 @node csplit invocation
2983 @section @command{csplit}: Split a file into context-determined pieces
2986 @cindex context splitting
2987 @cindex splitting a file into pieces by context
2989 @command{csplit} creates zero or more output files containing sections of
2990 @var{input} (standard input if @var{input} is @samp{-}). Synopsis:
2993 csplit [@var{option}]@dots{} @var{input} @var{pattern}@dots{}
2996 The contents of the output files are determined by the @var{pattern}
2997 arguments, as detailed below. An error occurs if a @var{pattern}
2998 argument refers to a nonexistent line of the input file (e.g., if no
2999 remaining line matches a given regular expression). After every
3000 @var{pattern} has been matched, any remaining input is copied into one
3003 By default, @command{csplit} prints the number of bytes written to each
3004 output file after it has been created.
3006 The types of pattern arguments are:
3011 Create an output file containing the input up to but not including line
3012 @var{n} (a positive integer). If followed by a repeat count, also
3013 create an output file containing the next @var{n} lines of the input
3014 file once for each repeat.
3016 @item /@var{regexp}/[@var{offset}]
3017 Create an output file containing the current line up to (but not
3018 including) the next line of the input file that contains a match for
3019 @var{regexp}. The optional @var{offset} is an integer.
3020 If it is given, the input up to (but not including) the
3021 matching line plus or minus @var{offset} is put into the output file,
3022 and the line after that begins the next section of input.
3024 @item %@var{regexp}%[@var{offset}]
3025 Like the previous type, except that it does not create an output
3026 file, so that section of the input file is effectively ignored.
3028 @item @{@var{repeat-count}@}
3029 Repeat the previous pattern @var{repeat-count} additional
3030 times. The @var{repeat-count} can either be a positive integer or an
3031 asterisk, meaning repeat as many times as necessary until the input is
3036 The output files' names consist of a prefix (@samp{xx} by default)
3037 followed by a suffix. By default, the suffix is an ascending sequence
3038 of two-digit decimal numbers from @samp{00} to @samp{99}. In any case,
3039 concatenating the output files in sorted order by file name produces the
3040 original input file.
3042 By default, if @command{csplit} encounters an error or receives a hangup,
3043 interrupt, quit, or terminate signal, it removes any output files
3044 that it has created so far before it exits.
3046 The program accepts the following options. Also see @ref{Common options}.
3050 @item -f @var{prefix}
3051 @itemx --prefix=@var{prefix}
3054 @cindex output file name prefix
3055 Use @var{prefix} as the output file name prefix.
3057 @item -b @var{suffix}
3058 @itemx --suffix=@var{suffix}
3061 @cindex output file name suffix
3062 Use @var{suffix} as the output file name suffix. When this option is
3063 specified, the suffix string must include exactly one
3064 @code{printf(3)}-style conversion specification, possibly including
3065 format specification flags, a field width, a precision specifications,
3066 or all of these kinds of modifiers. The format letter must convert a
3067 binary integer argument to readable form; thus, only @samp{d}, @samp{i},
3068 @samp{u}, @samp{o}, @samp{x}, and @samp{X} conversions are allowed. The
3069 entire @var{suffix} is given (with the current output file number) to
3070 @code{sprintf(3)} to form the file name suffixes for each of the
3071 individual output files in turn. If this option is used, the
3072 @option{--digits} option is ignored.
3074 @item -n @var{digits}
3075 @itemx --digits=@var{digits}
3078 Use output file names containing numbers that are @var{digits} digits
3079 long instead of the default 2.
3084 @opindex --keep-files
3085 Do not remove output files when errors are encountered.
3088 @itemx --elide-empty-files
3090 @opindex --elide-empty-files
3091 Suppress the generation of zero-length output files. (In cases where
3092 the section delimiters of the input file are supposed to mark the first
3093 lines of each of the sections, the first output file will generally be a
3094 zero-length file unless you use this option.) The output file sequence
3095 numbers always run consecutively starting from 0, even when this option
3106 Do not print counts of output file sizes.
3112 Here is an example of its usage.
3113 First, create an empty directory for the exercise,
3120 Now, split the sequence of 1..14 on lines that end with 0 or 5:
3123 $ seq 14 | csplit - '/[05]$/' '@{*@}'
3129 Each number printed above is the size of an output
3130 file that csplit has just created.
3131 List the names of those output files:
3138 Use @command{head} to show their contents:
3163 @node Summarizing files
3164 @chapter Summarizing files
3166 @cindex summarizing files
3168 These commands generate just a few numbers representing entire
3172 * wc invocation:: Print newline, word, and byte counts.
3173 * sum invocation:: Print checksum and block counts.
3174 * cksum invocation:: Print CRC checksum and byte counts.
3175 * md5sum invocation:: Print or check MD5 digests.
3176 * sha1sum invocation:: Print or check SHA-1 digests.
3177 * sha2 utilities:: Print or check SHA-2 digests.
3182 @section @command{wc}: Print newline, word, and byte counts
3186 @cindex character count
3190 @command{wc} counts the number of bytes, characters, whitespace-separated
3191 words, and newlines in each given @var{file}, or standard input if none
3192 are given or for a @var{file} of @samp{-}. Synopsis:
3195 wc [@var{option}]@dots{} [@var{file}]@dots{}
3198 @cindex total counts
3199 @command{wc} prints one line of counts for each file, and if the file was
3200 given as an argument, it prints the file name following the counts. If
3201 more than one @var{file} is given, @command{wc} prints a final line
3202 containing the cumulative counts, with the file name @file{total}. The
3203 counts are printed in this order: newlines, words, characters, bytes,
3204 maximum line length.
3205 Each count is printed right-justified in a field with at least one
3206 space between fields so that the numbers and file names normally line
3207 up nicely in columns. The width of the count fields varies depending
3208 on the inputs, so you should not depend on a particular field width.
3209 However, as a @acronym{GNU} extension, if only one count is printed,
3210 it is guaranteed to be printed without leading spaces.
3212 By default, @command{wc} prints three counts: the newline, words, and byte
3213 counts. Options can specify that only certain counts be printed.
3214 Options do not undo others previously given, so
3221 prints both the byte counts and the word counts.
3223 With the @option{--max-line-length} option, @command{wc} prints the length
3224 of the longest line per file, and if there is more than one file it
3225 prints the maximum (not the sum) of those lengths. The line lengths here
3226 are measured in screen columns, according to the current locale and
3227 assuming tab positions in every 8th column.
3229 The program accepts the following options. Also see @ref{Common options}.
3237 Print only the byte counts.
3243 Print only the character counts.
3249 Print only the word counts.
3255 Print only the newline counts.
3258 @itemx --max-line-length
3260 @opindex --max-line-length
3261 Print only the maximum line lengths.
3263 @macro filesZeroFromOption{cmd,withTotalOption,subListOutput}
3264 @itemx --files0-from=@var{file}
3265 @opindex --files0-from=@var{file}
3266 @c This is commented out to avoid a texi2dvi failure.
3267 @c texi2dvi (GNU Texinfo 4.11) 1.104
3268 @c @cindex including files from @command{\cmd\}
3269 Disallow processing files named on the command line, and instead process
3270 those named in file @var{file}; each name being terminated by a zero byte
3271 (@acronym{ASCII} @sc{nul}).
3272 This is useful \withTotalOption\
3273 when the list of file names is so long that it may exceed a command line
3275 In such cases, running @command{\cmd\} via @command{xargs} is undesirable
3276 because it splits the list into pieces and makes @command{\cmd\} print
3277 \subListOutput\ for each sublist rather than for the entire list.
3278 One way to produce a list of @acronym{ASCII} @sc{nul} terminated file names is with @sc{gnu}
3279 @command{find}, using its @option{-print0} predicate.
3280 If @var{file} is @samp{-} then the @acronym{ASCII} @sc{nul} terminated file names
3281 are read from standard input.
3283 @filesZeroFromOption{wc,,a total}
3285 For example, to find the length of the longest line in any @file{.c} or
3286 @file{.h} file in the current hierarchy, do this:
3289 find . -name '*.[ch]' -print0 |
3290 wc -L --files0-from=- | tail -n1
3298 @node sum invocation
3299 @section @command{sum}: Print checksum and block counts
3302 @cindex 16-bit checksum
3303 @cindex checksum, 16-bit
3305 @command{sum} computes a 16-bit checksum for each given @var{file}, or
3306 standard input if none are given or for a @var{file} of @samp{-}. Synopsis:
3309 sum [@var{option}]@dots{} [@var{file}]@dots{}
3312 @command{sum} prints the checksum for each @var{file} followed by the
3313 number of blocks in the file (rounded up). If more than one @var{file}
3314 is given, file names are also printed (by default). (With the
3315 @option{--sysv} option, corresponding file names are printed when there is
3316 at least one file argument.)
3318 By default, @sc{gnu} @command{sum} computes checksums using an algorithm
3319 compatible with BSD @command{sum} and prints file sizes in units of
3322 The program accepts the following options. Also see @ref{Common options}.
3328 @cindex BSD @command{sum}
3329 Use the default (BSD compatible) algorithm. This option is included for
3330 compatibility with the System V @command{sum}. Unless @option{-s} was also
3331 given, it has no effect.
3337 @cindex System V @command{sum}
3338 Compute checksums using an algorithm compatible with System V
3339 @command{sum}'s default, and print file sizes in units of 512-byte blocks.
3343 @command{sum} is provided for compatibility; the @command{cksum} program (see
3344 next section) is preferable in new applications.
3349 @node cksum invocation
3350 @section @command{cksum}: Print CRC checksum and byte counts
3353 @cindex cyclic redundancy check
3354 @cindex CRC checksum
3356 @command{cksum} computes a cyclic redundancy check (CRC) checksum for each
3357 given @var{file}, or standard input if none are given or for a
3358 @var{file} of @samp{-}. Synopsis:
3361 cksum [@var{option}]@dots{} [@var{file}]@dots{}
3364 @command{cksum} prints the CRC checksum for each file along with the number
3365 of bytes in the file, and the file name unless no arguments were given.
3367 @command{cksum} is typically used to ensure that files
3368 transferred by unreliable means (e.g., netnews) have not been corrupted,
3369 by comparing the @command{cksum} output for the received files with the
3370 @command{cksum} output for the original files (typically given in the
3373 The CRC algorithm is specified by the @acronym{POSIX} standard. It is not
3374 compatible with the BSD or System V @command{sum} algorithms (see the
3375 previous section); it is more robust.
3377 The only options are @option{--help} and @option{--version}. @xref{Common
3383 @node md5sum invocation
3384 @section @command{md5sum}: Print or check MD5 digests
3388 @cindex 128-bit checksum
3389 @cindex checksum, 128-bit
3390 @cindex fingerprint, 128-bit
3391 @cindex message-digest, 128-bit
3393 @command{md5sum} computes a 128-bit checksum (or @dfn{fingerprint} or
3394 @dfn{message-digest}) for each specified @var{file}.
3396 Note: The MD5 digest is more reliable than a simple CRC (provided by
3397 the @command{cksum} command) for detecting accidental file corruption,
3398 as the chances of accidentally having two files with identical MD5
3399 are vanishingly small. However, it should not be considered truly
3400 secure against malicious tampering: although finding a file with a
3401 given MD5 fingerprint, or modifying a file so as to retain its MD5 are
3402 considered infeasible at the moment, it is known how to produce
3403 different files with identical MD5 (a ``collision''), something which
3404 can be a security issue in certain contexts. For more secure hashes,
3405 consider using SHA-1 or SHA-2. @xref{sha1sum invocation}, and
3406 @ref{sha2 utilities}.
3408 If a @var{file} is specified as @samp{-} or if no files are given
3409 @command{md5sum} computes the checksum for the standard input.
3410 @command{md5sum} can also determine whether a file and checksum are
3411 consistent. Synopsis:
3414 md5sum [@var{option}]@dots{} [@var{file}]@dots{}
3417 For each @var{file}, @samp{md5sum} outputs the MD5 checksum, a flag
3418 indicating a binary or text input file, and the file name.
3419 If @var{file} contains a backslash or newline, the
3420 line is started with a backslash, and each problematic character in
3421 the file name is escaped with a backslash, making the output
3422 unambiguous even in the presence of arbitrary file names.
3423 If @var{file} is omitted or specified as @samp{-}, standard input is read.
3425 The program accepts the following options. Also see @ref{Common options}.
3433 @cindex binary input files
3434 Treat each input file as binary, by reading it in binary mode and
3435 outputting a @samp{*} flag. This is the inverse of @option{--text}.
3436 On systems like @acronym{GNU} that do not distinguish between binary
3437 and text files, this option merely flags each input file as binary:
3438 the MD5 checksum is unaffected. This option is the default on systems
3439 like MS-DOS that distinguish between binary and text files, except
3440 for reading standard input when standard input is a terminal.
3444 Read file names and checksum information (not data) from each
3445 @var{file} (or from stdin if no @var{file} was specified) and report
3446 whether the checksums match the contents of the named files.
3447 The input to this mode of @command{md5sum} is usually the output of
3448 a prior, checksum-generating run of @samp{md5sum}.
3449 Each valid line of input consists of an MD5 checksum, a binary/text
3450 flag, and then a file name.
3451 Binary files are marked with @samp{*}, text with @samp{ }.
3452 For each such line, @command{md5sum} reads the named file and computes its
3453 MD5 checksum. Then, if the computed message digest does not match the
3454 one on the line with the file name, the file is noted as having
3455 failed the test. Otherwise, the file passes the test.
3456 By default, for each valid line, one line is written to standard
3457 output indicating whether the named file passed the test.
3458 After all checks have been performed, if there were any failures,
3459 a warning is issued to standard error.
3460 Use the @option{--status} option to inhibit that output.
3461 If any listed file cannot be opened or read, if any valid line has
3462 an MD5 checksum inconsistent with the associated file, or if no valid
3463 line is found, @command{md5sum} exits with nonzero status. Otherwise,
3464 it exits successfully.
3468 @cindex verifying MD5 checksums
3469 This option is useful only when verifying checksums.
3470 When verifying checksums, don't generate an 'OK' message per successfully
3471 checked file. Files that fail the verification are reported in the
3472 default one-line-per-file format. If there is any checksum mismatch,
3473 print a warning summarizing the failures to standard error.
3477 @cindex verifying MD5 checksums
3478 This option is useful only when verifying checksums.
3479 When verifying checksums, don't generate the default one-line-per-file
3480 diagnostic and don't output the warning summarizing any failures.
3481 Failures to open or read a file still evoke individual diagnostics to
3483 If all listed files are readable and are consistent with the associated
3484 MD5 checksums, exit successfully. Otherwise exit with a status code
3485 indicating there was a failure.
3491 @cindex text input files
3492 Treat each input file as text, by reading it in text mode and
3493 outputting a @samp{ } flag. This is the inverse of @option{--binary}.
3494 This option is the default on systems like @acronym{GNU} that do not
3495 distinguish between binary and text files. On other systems, it is
3496 the default for reading standard input when standard input is a
3503 @cindex verifying MD5 checksums
3504 When verifying checksums, warn about improperly formatted MD5 checksum lines.
3505 This option is useful only if all but a few lines in the checked input
3513 @node sha1sum invocation
3514 @section @command{sha1sum}: Print or check SHA-1 digests
3518 @cindex 160-bit checksum
3519 @cindex checksum, 160-bit
3520 @cindex fingerprint, 160-bit
3521 @cindex message-digest, 160-bit
3523 @command{sha1sum} computes a 160-bit checksum for each specified
3524 @var{file}. The usage and options of this command are precisely the
3525 same as for @command{md5sum}. @xref{md5sum invocation}.
3527 Note: The SHA-1 digest is more secure than MD5, and no collisions of
3528 it are known (different files having the same fingerprint). However,
3529 it is known that they can be produced with considerable, but not
3530 unreasonable, resources. For this reason, it is generally considered
3531 that SHA-1 should be gradually phased out in favor of the more secure
3532 SHA-2 hash algorithms. @xref{sha2 utilities}.
3535 @node sha2 utilities
3536 @section sha2 utilities: Print or check SHA-2 digests
3543 @cindex 224-bit checksum
3544 @cindex 256-bit checksum
3545 @cindex 384-bit checksum
3546 @cindex 512-bit checksum
3547 @cindex checksum, 224-bit
3548 @cindex checksum, 256-bit
3549 @cindex checksum, 384-bit
3550 @cindex checksum, 512-bit
3551 @cindex fingerprint, 224-bit
3552 @cindex fingerprint, 256-bit
3553 @cindex fingerprint, 384-bit
3554 @cindex fingerprint, 512-bit
3555 @cindex message-digest, 224-bit
3556 @cindex message-digest, 256-bit
3557 @cindex message-digest, 384-bit
3558 @cindex message-digest, 512-bit
3560 The commands @command{sha224sum}, @command{sha256sum},
3561 @command{sha384sum} and @command{sha512sum} compute checksums of
3562 various lengths (respectively 224, 256, 384 and 512 bits),
3563 collectively known as the SHA-2 hashes. The usage and options of
3564 these commands are precisely the same as for @command{md5sum}.
3565 @xref{md5sum invocation}.
3567 Note: The SHA384 and SHA512 digests are considerably slower to
3568 compute, especially on 32-bit computers, than SHA224 or SHA256.
3571 @node Operating on sorted files
3572 @chapter Operating on sorted files
3574 @cindex operating on sorted files
3575 @cindex sorted files, operations on
3577 These commands work with (or produce) sorted files.
3580 * sort invocation:: Sort text files.
3581 * shuf invocation:: Shuffle text files.
3582 * uniq invocation:: Uniquify files.
3583 * comm invocation:: Compare two sorted files line by line.
3584 * ptx invocation:: Produce a permuted index of file contents.
3585 * tsort invocation:: Topological sort.
3589 @node sort invocation
3590 @section @command{sort}: Sort text files
3593 @cindex sorting files
3595 @command{sort} sorts, merges, or compares all the lines from the given
3596 files, or standard input if none are given or for a @var{file} of
3597 @samp{-}. By default, @command{sort} writes the results to standard
3601 sort [@var{option}]@dots{} [@var{file}]@dots{}
3604 @command{sort} has three modes of operation: sort (the default), merge,
3605 and check for sortedness. The following options change the operation
3612 @itemx --check=diagnose-first
3615 @cindex checking for sortedness
3616 Check whether the given file is already sorted: if it is not all
3617 sorted, print a diagnostic containing the first out-of-order line and
3618 exit with a status of 1.
3619 Otherwise, exit successfully.
3620 At most one input file can be given.
3623 @itemx --check=quiet
3624 @itemx --check=silent
3627 @cindex checking for sortedness
3628 Exit successfully if the given file is already sorted, and
3629 exit with status 1 otherwise.
3630 At most one input file can be given.
3631 This is like @option{-c}, except it does not print a diagnostic.
3637 @cindex merging sorted files
3638 Merge the given files by sorting them as a group. Each input file must
3639 always be individually sorted. It always works to sort instead of
3640 merge; merging is provided because it is faster, in the case where it
3645 @cindex sort stability
3646 @cindex sort's last-resort comparison
3647 A pair of lines is compared as follows:
3648 @command{sort} compares each pair of fields, in the
3649 order specified on the command line, according to the associated
3650 ordering options, until a difference is found or no fields are left.
3651 If no key fields are specified, @command{sort} uses a default key of
3652 the entire line. Finally, as a last resort when all keys compare
3653 equal, @command{sort} compares entire lines as if no ordering options
3654 other than @option{--reverse} (@option{-r}) were specified. The
3655 @option{--stable} (@option{-s}) option disables this @dfn{last-resort
3656 comparison} so that lines in which all fields compare equal are left
3657 in their original relative order. The @option{--unique}
3658 (@option{-u}) option also disables the last-resort comparison.
3662 Unless otherwise specified, all comparisons use the character collating
3663 sequence specified by the @env{LC_COLLATE} locale.@footnote{If you
3664 use a non-@acronym{POSIX} locale (e.g., by setting @env{LC_ALL}
3665 to @samp{en_US}), then @command{sort} may produce output that is sorted
3666 differently than you're accustomed to. In that case, set the @env{LC_ALL}
3667 environment variable to @samp{C}. Note that setting only @env{LC_COLLATE}
3668 has two problems. First, it is ineffective if @env{LC_ALL} is also set.
3669 Second, it has undefined behavior if @env{LC_CTYPE} (or @env{LANG}, if
3670 @env{LC_CTYPE} is unset) is set to an incompatible value. For example,
3671 you get undefined behavior if @env{LC_CTYPE} is @code{ja_JP.PCK} but
3672 @env{LC_COLLATE} is @code{en_US.UTF-8}.}
3674 @sc{gnu} @command{sort} (as specified for all @sc{gnu} utilities) has no
3675 limit on input line length or restrictions on bytes allowed within lines.
3676 In addition, if the final byte of an input file is not a newline, @sc{gnu}
3677 @command{sort} silently supplies one. A line's trailing newline is not
3678 part of the line for comparison purposes.
3680 @cindex exit status of @command{sort}
3684 0 if no error occurred
3685 1 if invoked with @option{-c} or @option{-C} and the input is not sorted
3686 2 if an error occurred
3690 If the environment variable @env{TMPDIR} is set, @command{sort} uses its
3691 value as the directory for temporary files instead of @file{/tmp}. The
3692 @option{--temporary-directory} (@option{-T}) option in turn overrides
3693 the environment variable.
3695 The following options affect the ordering of output lines. They may be
3696 specified globally or as part of a specific key field. If no key
3697 fields are specified, global options apply to comparison of entire
3698 lines; otherwise the global options are inherited by key fields that do
3699 not specify any special options of their own. In pre-@acronym{POSIX}
3700 versions of @command{sort}, global options affect only later key fields,
3701 so portable shell scripts should specify global options first.
3706 @itemx --ignore-leading-blanks
3708 @opindex --ignore-leading-blanks
3709 @cindex blanks, ignoring leading
3711 Ignore leading blanks when finding sort keys in each line.
3712 By default a blank is a space or a tab, but the @env{LC_CTYPE} locale
3713 can change this. Note blanks may be ignored by your locale's collating
3714 rules, but without this option they will be significant for character
3715 positions specified in keys with the @option{-k} option.
3718 @itemx --dictionary-order
3720 @opindex --dictionary-order
3721 @cindex dictionary order
3722 @cindex phone directory order
3723 @cindex telephone directory order
3725 Sort in @dfn{phone directory} order: ignore all characters except
3726 letters, digits and blanks when sorting.
3727 By default letters and digits are those of @acronym{ASCII} and a blank
3728 is a space or a tab, but the @env{LC_CTYPE} locale can change this.
3731 @itemx --ignore-case
3733 @opindex --ignore-case
3734 @cindex ignoring case
3735 @cindex case folding
3737 Fold lowercase characters into the equivalent uppercase characters when
3738 comparing so that, for example, @samp{b} and @samp{B} sort as equal.
3739 The @env{LC_CTYPE} locale determines character types.
3740 When used with @option{--unique} those lower case equivalent lines are
3741 thrown away. (There is currently no way to throw away the upper case
3742 equivalent instead. (Any @option{--reverse} given would only affect
3743 the final result, after the throwing away.))
3746 @itemx --general-numeric-sort
3747 @itemx --sort=general-numeric
3749 @opindex --general-numeric-sort
3751 @cindex general numeric sort
3753 Sort numerically, using the standard C function @code{strtod} to convert
3754 a prefix of each line to a double-precision floating point number.
3755 This allows floating point numbers to be specified in scientific notation,
3756 like @code{1.0e-34} and @code{10e100}.
3757 The @env{LC_NUMERIC} locale determines the decimal-point character.
3758 Do not report overflow, underflow, or conversion errors.
3759 Use the following collating sequence:
3763 Lines that do not start with numbers (all considered to be equal).
3765 NaNs (``Not a Number'' values, in IEEE floating point arithmetic)
3766 in a consistent but machine-dependent order.
3770 Finite numbers in ascending numeric order (with @math{-0} and @math{+0} equal).
3775 Use this option only if there is no alternative; it is much slower than
3776 @option{--numeric-sort} (@option{-n}) and it can lose information when
3777 converting to floating point.
3780 @itemx --human-numeric-sort
3781 @itemx --sort=human-numeric
3783 @opindex --human-numeric-sort
3785 @cindex human numeric sort
3787 Sort numerically, as per the @option{--numeric-sort} option below, and in
3788 addition handle IEC or SI suffixes like MiB, MB etc (@ref{Block size}).
3789 Note a mixture of IEC and SI suffixes is not supported and will
3790 be flagged as an error. Also the numbers must be abbreviated uniformly.
3791 I.E. values with different precisions like 6000K and 5M will be sorted
3795 @itemx --ignore-nonprinting
3797 @opindex --ignore-nonprinting
3798 @cindex nonprinting characters, ignoring
3799 @cindex unprintable characters, ignoring
3801 Ignore nonprinting characters.
3802 The @env{LC_CTYPE} locale determines character types.
3803 This option has no effect if the stronger @option{--dictionary-order}
3804 (@option{-d}) option is also given.
3810 @opindex --month-sort
3812 @cindex months, sorting by
3814 An initial string, consisting of any amount of blanks, followed
3815 by a month name abbreviation, is folded to UPPER case and
3816 compared in the order @samp{JAN} < @samp{FEB} < @dots{} < @samp{DEC}.
3817 Invalid names compare low to valid names. The @env{LC_TIME} locale
3818 category determines the month spellings.
3819 By default a blank is a space or a tab, but the @env{LC_CTYPE} locale
3823 @itemx --numeric-sort
3824 @itemx --sort=numeric
3826 @opindex --numeric-sort
3828 @cindex numeric sort
3830 Sort numerically. The number begins each line and consists
3831 of optional blanks, an optional @samp{-} sign, and zero or more
3832 digits possibly separated by thousands separators, optionally followed
3833 by a decimal-point character and zero or more digits. An empty
3834 number is treated as @samp{0}. The @env{LC_NUMERIC}
3835 locale specifies the decimal-point character and thousands separator.
3836 By default a blank is a space or a tab, but the @env{LC_CTYPE} locale
3839 Comparison is exact; there is no rounding error.
3841 Neither a leading @samp{+} nor exponential notation is recognized.
3842 To compare such strings numerically, use the
3843 @option{--general-numeric-sort} (@option{-g}) option.
3846 @itemx --version-sort
3848 @opindex --version-sort
3849 @cindex version number sort
3851 Sort per @code{strverscmp(3)}. This is a normal string comparison, except
3852 that embedded decimal numbers are sorted by numeric value
3853 (see @option{--numeric-sort} above).
3859 @cindex reverse sorting
3860 Reverse the result of comparison, so that lines with greater key values
3861 appear earlier in the output instead of later.
3864 @itemx --random-sort
3865 @itemx --sort=random
3867 @opindex --random-sort
3870 Sort by hashing the input keys and then sorting the hash values.
3871 Choose the hash function at random, ensuring that it is free of
3872 collisions so that differing keys have differing hash values. This is
3873 like a random permutation of the inputs (@pxref{shuf invocation}),
3874 except that keys with the same value sort together.
3876 If multiple random sort fields are specified, the same random hash
3877 function is used for all fields. To use different random hash
3878 functions for different fields, you can invoke @command{sort} more
3881 The choice of hash function is affected by the
3882 @option{--random-source} option.
3890 @item --compress-program=@var{prog}
3891 Compress any temporary files with the program @var{prog}.
3893 With no arguments, @var{prog} must compress standard input to standard
3894 output, and when given the @option{-d} option it must decompress
3895 standard input to standard output.
3897 Terminate with an error if @var{prog} exits with nonzero status.
3899 White space and the backslash character should not appear in
3900 @var{prog}; they are reserved for future use.
3902 @filesZeroFromOption{sort,,sorted output}
3904 @item -k @var{pos1}[,@var{pos2}]
3905 @itemx --key=@var{pos1}[,@var{pos2}]
3909 Specify a sort field that consists of the part of the line between
3910 @var{pos1} and @var{pos2} (or the end of the line, if @var{pos2} is
3911 omitted), @emph{inclusive}.
3913 Each @var{pos} has the form @samp{@var{f}[.@var{c}][@var{opts}]},
3914 where @var{f} is the number of the field to use, and @var{c} is the number
3915 of the first character from the beginning of the field. Fields and character
3916 positions are numbered starting with 1; a character position of zero in
3917 @var{pos2} indicates the field's last character. If @samp{.@var{c}} is
3918 omitted from @var{pos1}, it defaults to 1 (the beginning of the field);
3919 if omitted from @var{pos2}, it defaults to 0 (the end of the field).
3920 @var{opts} are ordering options, allowing individual keys to be sorted
3921 according to different rules; see below for details. Keys can span
3924 Example: To sort on the second field, use @option{--key=2,2}
3925 (@option{-k 2,2}). See below for more notes on keys and more examples.
3927 @item --batch-size=@var{nmerge}
3928 @opindex --batch-size
3929 @cindex number of inputs to merge, nmerge
3930 Merge at most @var{nmerge} inputs at once.
3932 When @command{sort} has to merge more than @var{nmerge} inputs,
3933 it merges them in groups of @var{nmerge}, saving the result in
3934 a temporary file, which is then used as an input in a subsequent merge.
3936 A large value of @var{nmerge} may improve merge performance and decrease
3937 temporary storage utilization at the expense of increased memory usage
3938 and I/0. Conversely a small value of @var{nmerge} may reduce memory
3939 requirements and I/0 at the expense of temporary storage consumption and
3942 The value of @var{nmerge} must be at least 2. The default value is
3943 currently 16, but this is implementation-dependent and may change in
3946 The value of @var{nmerge} may be bounded by a resource limit for open
3947 file descriptors. The commands @samp{ulimit -n} or @samp{getconf
3948 OPEN_MAX} may display limits for your systems; these limits may be
3949 modified further if your program already has some files open, or if
3950 the operating system has other limits on the number of open files. If
3951 the value of @var{nmerge} exceeds the resource limit, @command{sort}
3952 silently uses a smaller value.
3954 @item -o @var{output-file}
3955 @itemx --output=@var{output-file}
3958 @cindex overwriting of input, allowed
3959 Write output to @var{output-file} instead of standard output.
3960 Normally, @command{sort} reads all input before opening
3961 @var{output-file}, so you can safely sort a file in place by using
3962 commands like @code{sort -o F F} and @code{cat F | sort -o F}.
3963 However, @command{sort} with @option{--merge} (@option{-m}) can open
3964 the output file before reading all input, so a command like @code{cat
3965 F | sort -m -o F - G} is not safe as @command{sort} might start
3966 writing @file{F} before @command{cat} is done reading it.
3968 @vindex POSIXLY_CORRECT
3969 On newer systems, @option{-o} cannot appear after an input file if
3970 @env{POSIXLY_CORRECT} is set, e.g., @samp{sort F -o F}. Portable
3971 scripts should specify @option{-o @var{output-file}} before any input
3974 @item --random-source=@var{file}
3975 @opindex --random-source
3976 @cindex random source for sorting
3977 Use @var{file} as a source of random data used to determine which
3978 random hash function to use with the @option{-R} option. @xref{Random
3985 @cindex sort stability
3986 @cindex sort's last-resort comparison
3988 Make @command{sort} stable by disabling its last-resort comparison.
3989 This option has no effect if no fields or global ordering options
3990 other than @option{--reverse} (@option{-r}) are specified.
3993 @itemx --buffer-size=@var{size}
3995 @opindex --buffer-size
3996 @cindex size for main memory sorting
3997 Use a main-memory sort buffer of the given @var{size}. By default,
3998 @var{size} is in units of 1024 bytes. Appending @samp{%} causes
3999 @var{size} to be interpreted as a percentage of physical memory.
4000 Appending @samp{K} multiplies @var{size} by 1024 (the default),
4001 @samp{M} by 1,048,576, @samp{G} by 1,073,741,824, and so on for
4002 @samp{T}, @samp{P}, @samp{E}, @samp{Z}, and @samp{Y}. Appending
4003 @samp{b} causes @var{size} to be interpreted as a byte count, with no
4006 This option can improve the performance of @command{sort} by causing it
4007 to start with a larger or smaller sort buffer than the default.
4008 However, this option affects only the initial buffer size. The buffer
4009 grows beyond @var{size} if @command{sort} encounters input lines larger
4012 @item -t @var{separator}
4013 @itemx --field-separator=@var{separator}
4015 @opindex --field-separator
4016 @cindex field separator character
4017 Use character @var{separator} as the field separator when finding the
4018 sort keys in each line. By default, fields are separated by the empty
4019 string between a non-blank character and a blank character.
4020 By default a blank is a space or a tab, but the @env{LC_CTYPE} locale
4023 That is, given the input line @w{@samp{ foo bar}}, @command{sort} breaks it
4024 into fields @w{@samp{ foo}} and @w{@samp{ bar}}. The field separator is
4025 not considered to be part of either the field preceding or the field
4026 following, so with @samp{sort @w{-t " "}} the same input line has
4027 three fields: an empty field, @samp{foo}, and @samp{bar}.
4028 However, fields that extend to the end of the line,
4029 as @option{-k 2}, or fields consisting of a range, as @option{-k 2,3},
4030 retain the field separators present between the endpoints of the range.
4032 To specify @acronym{ASCII} @sc{nul} as the field separator,
4033 use the two-character string @samp{\0}, e.g., @samp{sort -t '\0'}.
4035 @item -T @var{tempdir}
4036 @itemx --temporary-directory=@var{tempdir}
4038 @opindex --temporary-directory
4039 @cindex temporary directory
4041 Use directory @var{tempdir} to store temporary files, overriding the
4042 @env{TMPDIR} environment variable. If this option is given more than
4043 once, temporary files are stored in all the directories given. If you
4044 have a large sort or merge that is I/O-bound, you can often improve
4045 performance by using this option to specify directories on different
4046 disks and controllers.
4052 @cindex uniquifying output
4054 Normally, output only the first of a sequence of lines that compare
4055 equal. For the @option{--check} (@option{-c} or @option{-C}) option,
4056 check that no pair of consecutive lines compares equal.
4058 This option also disables the default last-resort comparison.
4060 The commands @code{sort -u} and @code{sort | uniq} are equivalent, but
4061 this equivalence does not extend to arbitrary @command{sort} options.
4062 For example, @code{sort -n -u} inspects only the value of the initial
4063 numeric string when checking for uniqueness, whereas @code{sort -n |
4064 uniq} inspects the entire line. @xref{uniq invocation}.
4066 @macro zeroTerminatedOption
4068 @itemx --zero-terminated
4070 @opindex --zero-terminated
4071 @cindex process zero-terminated items
4072 Delimit items with a zero byte rather than a newline (@acronym{ASCII} @sc{lf}).
4073 I.E. treat input as items separated by @acronym{ASCII} @sc{nul}
4074 and terminate output items with @acronym{ASCII} @sc{nul}.
4075 This option can be useful in conjunction with @samp{perl -0} or
4076 @samp{find -print0} and @samp{xargs -0} which do the same in order to
4077 reliably handle arbitrary file names (even those containing blanks
4078 or other special characters).
4080 @zeroTerminatedOption
4084 Historical (BSD and System V) implementations of @command{sort} have
4085 differed in their interpretation of some options, particularly
4086 @option{-b}, @option{-f}, and @option{-n}. @sc{gnu} sort follows the @acronym{POSIX}
4087 behavior, which is usually (but not always!) like the System V behavior.
4088 According to @acronym{POSIX}, @option{-n} no longer implies @option{-b}. For
4089 consistency, @option{-M} has been changed in the same way. This may
4090 affect the meaning of character positions in field specifications in
4091 obscure cases. The only fix is to add an explicit @option{-b}.
4093 A position in a sort field specified with @option{-k} may have any
4094 of the option letters @samp{MbdfghinRrV} appended to it, in which case no
4095 global ordering options are inherited by that particular field. The
4096 @option{-b} option may be independently attached to either or both of
4097 the start and end positions of a field specification, and if it is
4098 inherited from the global options it will be attached to both.
4099 If input lines can contain leading or adjacent blanks and @option{-t}
4100 is not used, then @option{-k} is typically combined with @option{-b} or
4101 an option that implicitly ignores leading blanks (@samp{MghnV}) as otherwise
4102 the varying numbers of leading blanks in fields can cause confusing results.
4104 If the start position in a sort field specifier falls after the end of
4105 the line or after the end field, the field is empty. If the @option{-b}
4106 option was specified, the @samp{.@var{c}} part of a field specification
4107 is counted from the first nonblank character of the field.
4109 @vindex _POSIX2_VERSION
4110 @vindex POSIXLY_CORRECT
4111 On older systems, @command{sort} supports an obsolete origin-zero
4112 syntax @samp{+@var{pos1} [-@var{pos2}]} for specifying sort keys.
4113 This obsolete behavior can be enabled or disabled with the
4114 @env{_POSIX2_VERSION} environment variable (@pxref{Standards
4115 conformance}); it can also be enabled when @env{POSIXLY_CORRECT} is
4116 not set by using the obsolete syntax with @samp{-@var{pos2}} present.
4118 Scripts intended for use on standard hosts should avoid obsolete
4119 syntax and should use @option{-k} instead. For example, avoid
4120 @samp{sort +2}, since it might be interpreted as either @samp{sort
4121 ./+2} or @samp{sort -k 3}. If your script must also run on hosts that
4122 support only the obsolete syntax, it can use a test like @samp{if sort
4123 -k 1 </dev/null >/dev/null 2>&1; then @dots{}} to decide which syntax
4126 Here are some examples to illustrate various combinations of options.
4131 Sort in descending (reverse) numeric order.
4138 Sort alphabetically, omitting the first and second fields
4139 and the blanks at the start of the third field.
4140 This uses a single key composed of the characters beginning
4141 at the start of the first nonblank character in field three
4142 and extending to the end of each line.
4149 Sort numerically on the second field and resolve ties by sorting
4150 alphabetically on the third and fourth characters of field five.
4151 Use @samp{:} as the field delimiter.
4154 sort -t : -k 2,2n -k 5.3,5.4
4157 Note that if you had written @option{-k 2n} instead of @option{-k 2,2n}
4158 @command{sort} would have used all characters beginning in the second field
4159 and extending to the end of the line as the primary @emph{numeric}
4160 key. For the large majority of applications, treating keys spanning
4161 more than one field as numeric will not do what you expect.
4163 Also note that the @samp{n} modifier was applied to the field-end
4164 specifier for the first key. It would have been equivalent to
4165 specify @option{-k 2n,2} or @option{-k 2n,2n}. All modifiers except
4166 @samp{b} apply to the associated @emph{field}, regardless of whether
4167 the modifier character is attached to the field-start and/or the
4168 field-end part of the key specifier.
4171 Sort the password file on the fifth field and ignore any
4172 leading blanks. Sort lines with equal values in field five
4173 on the numeric user ID in field three. Fields are separated
4177 sort -t : -k 5b,5 -k 3,3n /etc/passwd
4178 sort -t : -n -k 5b,5 -k 3,3 /etc/passwd
4179 sort -t : -b -k 5,5 -k 3,3n /etc/passwd
4182 These three commands have equivalent effect. The first specifies that
4183 the first key's start position ignores leading blanks and the second
4184 key is sorted numerically. The other two commands rely on global
4185 options being inherited by sort keys that lack modifiers. The inheritance
4186 works in this case because @option{-k 5b,5b} and @option{-k 5b,5} are
4187 equivalent, as the location of a field-end lacking a @samp{.@var{c}}
4188 character position is not affected by whether initial blanks are
4192 Sort a set of log files, primarily by IPv4 address and secondarily by
4193 time stamp. If two lines' primary and secondary keys are identical,
4194 output the lines in the same order that they were input. The log
4195 files contain lines that look like this:
4198 4.150.156.3 - - [01/Apr/2004:06:31:51 +0000] message 1
4199 211.24.3.231 - - [24/Apr/2004:20:17:39 +0000] message 2
4202 Fields are separated by exactly one space. Sort IPv4 addresses
4203 lexicographically, e.g., 212.61.52.2 sorts before 212.129.233.201
4204 because 61 is less than 129.
4207 sort -s -t ' ' -k 4.9n -k 4.5M -k 4.2n -k 4.14,4.21 file*.log |
4208 sort -s -t '.' -k 1,1n -k 2,2n -k 3,3n -k 4,4n
4211 This example cannot be done with a single @command{sort} invocation,
4212 since IPv4 address components are separated by @samp{.} while dates
4213 come just after a space. So it is broken down into two invocations of
4214 @command{sort}: the first sorts by time stamp and the second by IPv4
4215 address. The time stamp is sorted by year, then month, then day, and
4216 finally by hour-minute-second field, using @option{-k} to isolate each
4217 field. Except for hour-minute-second there's no need to specify the
4218 end of each key field, since the @samp{n} and @samp{M} modifiers sort
4219 based on leading prefixes that cannot cross field boundaries. The
4220 IPv4 addresses are sorted lexicographically. The second sort uses
4221 @samp{-s} so that ties in the primary key are broken by the secondary
4222 key; the first sort uses @samp{-s} so that the combination of the two
4226 Generate a tags file in case-insensitive sorted order.
4229 find src -type f -print0 | sort -z -f | xargs -0 etags --append
4232 The use of @option{-print0}, @option{-z}, and @option{-0} in this case means
4233 that file names that contain blanks or other special characters are
4235 by the sort operation.
4237 @c This example is a bit contrived and needs more explanation.
4239 @c Sort records separated by an arbitrary string by using a pipe to convert
4240 @c each record delimiter string to @samp{\0}, then using sort's -z option,
4241 @c and converting each @samp{\0} back to the original record delimiter.
4244 @c printf 'c\n\nb\n\na\n'|perl -0pe 's/\n\n/\n\0/g'|sort -z|perl -0pe 's/\0/\n/g'
4248 Use the common @acronym{DSU, Decorate Sort Undecorate} idiom to
4249 sort lines according to their length.
4252 awk '@{print length, $0@}' /etc/passwd | sort -n | cut -f2- -d' '
4255 In general this technique can be used to sort data that the @command{sort}
4256 command does not support, or is inefficient at, sorting directly.
4259 Shuffle a list of directories, but preserve the order of files within
4260 each directory. For instance, one could use this to generate a music
4261 playlist in which albums are shuffled but the songs of each album are
4265 ls */* | sort -t / -k 1,1R -k 2,2
4271 @node shuf invocation
4272 @section @command{shuf}: Shuffling text
4275 @cindex shuffling files
4277 @command{shuf} shuffles its input by outputting a random permutation
4278 of its input lines. Each output permutation is equally likely.
4282 shuf [@var{option}]@dots{} [@var{file}]
4283 shuf -e [@var{option}]@dots{} [@var{arg}]@dots{}
4284 shuf -i @var{lo}-@var{hi} [@var{option}]@dots{}
4287 @command{shuf} has three modes of operation that affect where it
4288 obtains its input lines. By default, it reads lines from standard
4289 input. The following options change the operation mode:
4297 @cindex command-line operands to shuffle
4298 Treat each command-line operand as an input line.
4300 @item -i @var{lo}-@var{hi}
4301 @itemx --input-range=@var{lo}-@var{hi}
4303 @opindex --input-range
4304 @cindex input range to shuffle
4305 Act as if input came from a file containing the range of unsigned
4306 decimal integers @var{lo}@dots{}@var{hi}, one per line.
4310 @command{shuf}'s other options can affect its behavior in all
4315 @item -n @var{lines}
4316 @itemx --head-count=@var{count}
4318 @opindex --head-count
4319 @cindex head of output
4320 Output at most @var{count} lines. By default, all input lines are
4323 @item -o @var{output-file}
4324 @itemx --output=@var{output-file}
4327 @cindex overwriting of input, allowed
4328 Write output to @var{output-file} instead of standard output.
4329 @command{shuf} reads all input before opening
4330 @var{output-file}, so you can safely shuffle a file in place by using
4331 commands like @code{shuf -o F <F} and @code{cat F | shuf -o F}.
4333 @item --random-source=@var{file}
4334 @opindex --random-source
4335 @cindex random source for shuffling
4336 Use @var{file} as a source of random data used to determine which
4337 permutation to generate. @xref{Random sources}.
4339 @zeroTerminatedOption
4355 might produce the output
4365 Similarly, the command:
4368 shuf -e clubs hearts diamonds spades
4382 and the command @samp{shuf -i 1-4} might output:
4392 These examples all have four input lines, so @command{shuf} might
4393 produce any of the twenty-four possible permutations of the input. In
4394 general, if there are @var{n} input lines, there are @var{n}! (i.e.,
4395 @var{n} factorial, or @var{n} * (@var{n} - 1) * @dots{} * 1) possible
4396 output permutations.
4401 @node uniq invocation
4402 @section @command{uniq}: Uniquify files
4405 @cindex uniquify files
4407 @command{uniq} writes the unique lines in the given @file{input}, or
4408 standard input if nothing is given or for an @var{input} name of
4412 uniq [@var{option}]@dots{} [@var{input} [@var{output}]]
4415 By default, @command{uniq} prints its input lines, except that
4416 it discards all but the first of adjacent repeated lines, so that
4417 no output lines are repeated. Optionally, it can instead discard
4418 lines that are not repeated, or all repeated lines.
4420 The input need not be sorted, but repeated input lines are detected
4421 only if they are adjacent. If you want to discard non-adjacent
4422 duplicate lines, perhaps you want to use @code{sort -u}.
4423 @xref{sort invocation}.
4426 Comparisons honor the rules specified by the @env{LC_COLLATE}
4429 If no @var{output} file is specified, @command{uniq} writes to standard
4432 The program accepts the following options. Also see @ref{Common options}.
4437 @itemx --skip-fields=@var{n}
4439 @opindex --skip-fields
4440 Skip @var{n} fields on each line before checking for uniqueness. Use
4441 a null string for comparison if a line has fewer than @var{n} fields. Fields
4442 are sequences of non-space non-tab characters that are separated from
4443 each other by at least one space or tab.
4445 For compatibility @command{uniq} supports an obsolete option syntax
4446 @option{-@var{n}}. New scripts should use @option{-f @var{n}} instead.
4449 @itemx --skip-chars=@var{n}
4451 @opindex --skip-chars
4452 Skip @var{n} characters before checking for uniqueness. Use a null string
4453 for comparison if a line has fewer than @var{n} characters. If you use both
4454 the field and character skipping options, fields are skipped over first.
4456 @vindex _POSIX2_VERSION
4457 On older systems, @command{uniq} supports an obsolete option syntax
4459 This obsolete behavior can be enabled or disabled with the
4460 @env{_POSIX2_VERSION} environment variable (@pxref{Standards
4461 conformance}), but portable scripts should avoid commands whose
4462 behavior depends on this variable.
4463 For example, use @samp{uniq ./+10} or @samp{uniq -s 10} rather than
4464 the ambiguous @samp{uniq +10}.
4470 Print the number of times each line occurred along with the line.
4473 @itemx --ignore-case
4475 @opindex --ignore-case
4476 Ignore differences in case when comparing lines.
4482 @cindex repeated lines, outputting
4483 Discard lines that are not repeated. When used by itself, this option
4484 causes @command{uniq} to print the first copy of each repeated line,
4488 @itemx --all-repeated[=@var{delimit-method}]
4490 @opindex --all-repeated
4491 @cindex all repeated lines, outputting
4492 Do not discard the second and subsequent repeated input lines,
4493 but discard lines that are not repeated.
4494 This option is useful mainly in conjunction with other options e.g.,
4495 to ignore case or to compare only selected fields.
4496 The optional @var{delimit-method} tells how to delimit
4497 groups of repeated lines, and must be one of the following:
4502 Do not delimit groups of repeated lines.
4503 This is equivalent to @option{--all-repeated} (@option{-D}).
4506 Output a newline before each group of repeated lines.
4507 With @option{--zero-terminated} (@option{-z}), use a zero
4508 byte (@acronym{ASCII} @sc{nul}) instead of a newline.
4511 Separate groups of repeated lines with a single newline.
4512 With @option{--zero-terminated} (@option{-z}), use a zero
4513 byte (@acronym{ASCII} @sc{nul}) instead of a newline.
4514 This is the same as using @samp{prepend}, except that
4515 no delimiter is inserted before the first group, and hence
4516 may be better suited for output direct to users.
4519 Note that when groups are delimited and the input stream contains
4520 two or more consecutive blank lines, then the output is ambiguous.
4521 To avoid that, filter the input through @samp{tr -s '\n'} to replace
4522 each sequence of consecutive newlines with a single newline.
4524 This is a @sc{gnu} extension.
4525 @c FIXME: give an example showing *how* it's useful
4531 @cindex unique lines, outputting
4532 Discard the first repeated line. When used by itself, this option
4533 causes @command{uniq} to print unique lines, and nothing else.
4536 @itemx --check-chars=@var{n}
4538 @opindex --check-chars
4539 Compare at most @var{n} characters on each line (after skipping any specified
4540 fields and characters). By default the entire rest of the lines are
4543 @zeroTerminatedOption
4550 @node comm invocation
4551 @section @command{comm}: Compare two sorted files line by line
4554 @cindex line-by-line comparison
4555 @cindex comparing sorted files
4557 @command{comm} writes to standard output lines that are common, and lines
4558 that are unique, to two input files; a file name of @samp{-} means
4559 standard input. Synopsis:
4562 comm [@var{option}]@dots{} @var{file1} @var{file2}
4566 Before @command{comm} can be used, the input files must be sorted using the
4567 collating sequence specified by the @env{LC_COLLATE} locale.
4568 If an input file ends in a non-newline
4569 character, a newline is silently appended. The @command{sort} command with
4570 no options always outputs a file that is suitable input to @command{comm}.
4572 @cindex differing lines
4573 @cindex common lines
4574 With no options, @command{comm} produces three-column output. Column one
4575 contains lines unique to @var{file1}, column two contains lines unique
4576 to @var{file2}, and column three contains lines common to both files.
4577 Columns are separated by a single TAB character.
4578 @c FIXME: when there's an option to supply an alternative separator
4579 @c string, append `by default' to the above sentence.
4584 The options @option{-1}, @option{-2}, and @option{-3} suppress printing of
4585 the corresponding columns (and separators). Also see @ref{Common options}.
4587 Unlike some other comparison utilities, @command{comm} has an exit
4588 status that does not depend on the result of the comparison.
4589 Upon normal completion @command{comm} produces an exit code of zero.
4590 If there is an error it exits with nonzero status.
4592 @macro checkOrderOption{cmd}
4593 If the @option{--check-order} option is given, unsorted inputs will
4594 cause a fatal error message. If the option @option{--nocheck-order}
4595 is given, unsorted inputs will never cause an error message. If
4596 neither of these options is given, wrongly sorted inputs are diagnosed
4597 only if an input file is found to contain unpairable lines. If an
4598 input file is diagnosed as being unsorted, the @command{\cmd\} command
4599 will exit with a nonzero status (and the output should not be used).
4601 Forcing @command{\cmd\} to process wrongly sorted input files
4602 containing unpairable lines by specifying @option{--nocheck-order} is
4603 not guaranteed to produce any particular output. The output will
4604 probably not correspond with whatever you hoped it would be.
4606 @checkOrderOption{comm}
4611 Fail with an error message if either input file is wrongly ordered.
4613 @item --nocheck-order
4614 Do not check that both input files are in sorted order.
4618 @item --output-delimiter=@var{str}
4619 Print @var{str} between adjacent output columns,
4620 rather than the default of a single TAB character.
4622 The delimiter @var{str} may not be empty.
4626 @node ptx invocation
4627 @section @command{ptx}: Produce permuted indexes
4631 @command{ptx} reads a text file and essentially produces a permuted index, with
4632 each keyword in its context. The calling sketch is either one of:
4635 ptx [@var{option} @dots{}] [@var{file} @dots{}]
4636 ptx -G [@var{option} @dots{}] [@var{input} [@var{output}]]
4639 The @option{-G} (or its equivalent: @option{--traditional}) option disables
4640 all @sc{gnu} extensions and reverts to traditional mode, thus introducing some
4641 limitations and changing several of the program's default option values.
4642 When @option{-G} is not specified, @sc{gnu} extensions are always enabled.
4643 @sc{gnu} extensions to @command{ptx} are documented wherever appropriate in this
4644 document. For the full list, see @xref{Compatibility in ptx}.
4646 Individual options are explained in the following sections.
4648 When @sc{gnu} extensions are enabled, there may be zero, one or several
4649 @var{file}s after the options. If there is no @var{file}, the program
4650 reads the standard input. If there is one or several @var{file}s, they
4651 give the name of input files which are all read in turn, as if all the
4652 input files were concatenated. However, there is a full contextual
4653 break between each file and, when automatic referencing is requested,
4654 file names and line numbers refer to individual text input files. In
4655 all cases, the program outputs the permuted index to the standard
4658 When @sc{gnu} extensions are @emph{not} enabled, that is, when the program
4659 operates in traditional mode, there may be zero, one or two parameters
4660 besides the options. If there are no parameters, the program reads the
4661 standard input and outputs the permuted index to the standard output.
4662 If there is only one parameter, it names the text @var{input} to be read
4663 instead of the standard input. If two parameters are given, they give
4664 respectively the name of the @var{input} file to read and the name of
4665 the @var{output} file to produce. @emph{Be very careful} to note that,
4666 in this case, the contents of file given by the second parameter is
4667 destroyed. This behavior is dictated by System V @command{ptx}
4668 compatibility; @sc{gnu} Standards normally discourage output parameters not
4669 introduced by an option.
4671 Note that for @emph{any} file named as the value of an option or as an
4672 input text file, a single dash @kbd{-} may be used, in which case
4673 standard input is assumed. However, it would not make sense to use this
4674 convention more than once per program invocation.
4677 * General options in ptx:: Options which affect general program behavior.
4678 * Charset selection in ptx:: Underlying character set considerations.
4679 * Input processing in ptx:: Input fields, contexts, and keyword selection.
4680 * Output formatting in ptx:: Types of output format, and sizing the fields.
4681 * Compatibility in ptx::
4685 @node General options in ptx
4686 @subsection General options
4691 @itemx --traditional
4692 As already explained, this option disables all @sc{gnu} extensions to
4693 @command{ptx} and switches to traditional mode.
4696 Print a short help on standard output, then exit without further
4700 Print the program version on standard output, then exit without further
4708 @node Charset selection in ptx
4709 @subsection Charset selection
4711 @c FIXME: People don't necessarily know what an IBM-PC was these days.
4712 As it is set up now, the program assumes that the input file is coded
4713 using 8-bit @acronym{ISO} 8859-1 code, also known as Latin-1 character set,
4714 @emph{unless} it is compiled for MS-DOS, in which case it uses the
4715 character set of the IBM-PC@. (@sc{gnu} @command{ptx} is not known to work on
4716 smaller MS-DOS machines anymore.) Compared to 7-bit @acronym{ASCII}, the set
4717 of characters which are letters is different; this alters the behavior
4718 of regular expression matching. Thus, the default regular expression
4719 for a keyword allows foreign or diacriticized letters. Keyword sorting,
4720 however, is still crude; it obeys the underlying character set ordering
4726 @itemx --ignore-case
4727 Fold lower case letters to upper case for sorting.
4732 @node Input processing in ptx
4733 @subsection Word selection and input processing
4738 @itemx --break-file=@var{file}
4740 This option provides an alternative (to @option{-W}) method of describing
4741 which characters make up words. It introduces the name of a
4742 file which contains a list of characters which can@emph{not} be part of
4743 one word; this file is called the @dfn{Break file}. Any character which
4744 is not part of the Break file is a word constituent. If both options
4745 @option{-b} and @option{-W} are specified, then @option{-W} has precedence and
4746 @option{-b} is ignored.
4748 When @sc{gnu} extensions are enabled, the only way to avoid newline as a
4749 break character is to write all the break characters in the file with no
4750 newline at all, not even at the end of the file. When @sc{gnu} extensions
4751 are disabled, spaces, tabs and newlines are always considered as break
4752 characters even if not included in the Break file.
4755 @itemx --ignore-file=@var{file}
4757 The file associated with this option contains a list of words which will
4758 never be taken as keywords in concordance output. It is called the
4759 @dfn{Ignore file}. The file contains exactly one word in each line; the
4760 end of line separation of words is not subject to the value of the
4764 @itemx --only-file=@var{file}
4766 The file associated with this option contains a list of words which will
4767 be retained in concordance output; any word not mentioned in this file
4768 is ignored. The file is called the @dfn{Only file}. The file contains
4769 exactly one word in each line; the end of line separation of words is
4770 not subject to the value of the @option{-S} option.
4772 There is no default for the Only file. When both an Only file and an
4773 Ignore file are specified, a word is considered a keyword only
4774 if it is listed in the Only file and not in the Ignore file.
4779 On each input line, the leading sequence of non-white space characters will be
4780 taken to be a reference that has the purpose of identifying this input
4781 line in the resulting permuted index. For more information about reference
4782 production, see @xref{Output formatting in ptx}.
4783 Using this option changes the default value for option @option{-S}.
4785 Using this option, the program does not try very hard to remove
4786 references from contexts in output, but it succeeds in doing so
4787 @emph{when} the context ends exactly at the newline. If option
4788 @option{-r} is used with @option{-S} default value, or when @sc{gnu} extensions
4789 are disabled, this condition is always met and references are completely
4790 excluded from the output contexts.
4792 @item -S @var{regexp}
4793 @itemx --sentence-regexp=@var{regexp}
4795 This option selects which regular expression will describe the end of a
4796 line or the end of a sentence. In fact, this regular expression is not
4797 the only distinction between end of lines or end of sentences, and input
4798 line boundaries have no special significance outside this option. By
4799 default, when @sc{gnu} extensions are enabled and if @option{-r} option is not
4800 used, end of sentences are used. In this case, this @var{regex} is
4801 imported from @sc{gnu} Emacs:
4804 [.?!][]\"')@}]*\\($\\|\t\\| \\)[ \t\n]*
4807 Whenever @sc{gnu} extensions are disabled or if @option{-r} option is used, end
4808 of lines are used; in this case, the default @var{regexp} is just:
4814 Using an empty @var{regexp} is equivalent to completely disabling end of
4815 line or end of sentence recognition. In this case, the whole file is
4816 considered to be a single big line or sentence. The user might want to
4817 disallow all truncation flag generation as well, through option @option{-F
4818 ""}. @xref{Regexps, , Syntax of Regular Expressions, emacs, The GNU Emacs
4821 When the keywords happen to be near the beginning of the input line or
4822 sentence, this often creates an unused area at the beginning of the
4823 output context line; when the keywords happen to be near the end of the
4824 input line or sentence, this often creates an unused area at the end of
4825 the output context line. The program tries to fill those unused areas
4826 by wrapping around context in them; the tail of the input line or
4827 sentence is used to fill the unused area on the left of the output line;
4828 the head of the input line or sentence is used to fill the unused area
4829 on the right of the output line.
4831 As a matter of convenience to the user, many usual backslashed escape
4832 sequences from the C language are recognized and converted to the
4833 corresponding characters by @command{ptx} itself.
4835 @item -W @var{regexp}
4836 @itemx --word-regexp=@var{regexp}
4838 This option selects which regular expression will describe each keyword.
4839 By default, if @sc{gnu} extensions are enabled, a word is a sequence of
4840 letters; the @var{regexp} used is @samp{\w+}. When @sc{gnu} extensions are
4841 disabled, a word is by default anything which ends with a space, a tab
4842 or a newline; the @var{regexp} used is @samp{[^ \t\n]+}.
4844 An empty @var{regexp} is equivalent to not using this option.
4845 @xref{Regexps, , Syntax of Regular Expressions, emacs, The GNU Emacs
4848 As a matter of convenience to the user, many usual backslashed escape
4849 sequences, as found in the C language, are recognized and converted to
4850 the corresponding characters by @command{ptx} itself.
4855 @node Output formatting in ptx
4856 @subsection Output formatting
4858 Output format is mainly controlled by the @option{-O} and @option{-T} options
4859 described in the table below. When neither @option{-O} nor @option{-T} are
4860 selected, and if @sc{gnu} extensions are enabled, the program chooses an
4861 output format suitable for a dumb terminal. Each keyword occurrence is
4862 output to the center of one line, surrounded by its left and right
4863 contexts. Each field is properly justified, so the concordance output
4864 can be readily observed. As a special feature, if automatic
4865 references are selected by option @option{-A} and are output before the
4866 left context, that is, if option @option{-R} is @emph{not} selected, then
4867 a colon is added after the reference; this nicely interfaces with @sc{gnu}
4868 Emacs @code{next-error} processing. In this default output format, each
4869 white space character, like newline and tab, is merely changed to
4870 exactly one space, with no special attempt to compress consecutive
4871 spaces. This might change in the future. Except for those white space
4872 characters, every other character of the underlying set of 256
4873 characters is transmitted verbatim.
4875 Output format is further controlled by the following options.
4879 @item -g @var{number}
4880 @itemx --gap-size=@var{number}
4882 Select the size of the minimum white space gap between the fields on the
4885 @item -w @var{number}
4886 @itemx --width=@var{number}
4888 Select the maximum output width of each final line. If references are
4889 used, they are included or excluded from the maximum output width
4890 depending on the value of option @option{-R}. If this option is not
4891 selected, that is, when references are output before the left context,
4892 the maximum output width takes into account the maximum length of all
4893 references. If this option is selected, that is, when references are
4894 output after the right context, the maximum output width does not take
4895 into account the space taken by references, nor the gap that precedes
4899 @itemx --auto-reference
4901 Select automatic references. Each input line will have an automatic
4902 reference made up of the file name and the line ordinal, with a single
4903 colon between them. However, the file name will be empty when standard
4904 input is being read. If both @option{-A} and @option{-r} are selected, then
4905 the input reference is still read and skipped, but the automatic
4906 reference is used at output time, overriding the input reference.
4909 @itemx --right-side-refs
4911 In the default output format, when option @option{-R} is not used, any
4912 references produced by the effect of options @option{-r} or @option{-A} are
4913 placed to the far right of output lines, after the right context. With
4914 default output format, when the @option{-R} option is specified, references
4915 are rather placed at the beginning of each output line, before the left
4916 context. For any other output format, option @option{-R} is
4917 ignored, with one exception: with @option{-R} the width of references
4918 is @emph{not} taken into account in total output width given by @option{-w}.
4920 This option is automatically selected whenever @sc{gnu} extensions are
4923 @item -F @var{string}
4924 @itemx --flac-truncation=@var{string}
4926 This option will request that any truncation in the output be reported
4927 using the string @var{string}. Most output fields theoretically extend
4928 towards the beginning or the end of the current line, or current
4929 sentence, as selected with option @option{-S}. But there is a maximum
4930 allowed output line width, changeable through option @option{-w}, which is
4931 further divided into space for various output fields. When a field has
4932 to be truncated because it cannot extend beyond the beginning or the end of
4933 the current line to fit in, then a truncation occurs. By default,
4934 the string used is a single slash, as in @option{-F /}.
4936 @var{string} may have more than one character, as in @option{-F ...}.
4937 Also, in the particular case when @var{string} is empty (@option{-F ""}),
4938 truncation flagging is disabled, and no truncation marks are appended in
4941 As a matter of convenience to the user, many usual backslashed escape
4942 sequences, as found in the C language, are recognized and converted to
4943 the corresponding characters by @command{ptx} itself.
4945 @item -M @var{string}
4946 @itemx --macro-name=@var{string}
4948 Select another @var{string} to be used instead of @samp{xx}, while
4949 generating output suitable for @command{nroff}, @command{troff} or @TeX{}.
4952 @itemx --format=roff
4954 Choose an output format suitable for @command{nroff} or @command{troff}
4955 processing. Each output line will look like:
4958 .xx "@var{tail}" "@var{before}" "@var{keyword_and_after}" "@var{head}" "@var{ref}"
4961 so it will be possible to write a @samp{.xx} roff macro to take care of
4962 the output typesetting. This is the default output format when @sc{gnu}
4963 extensions are disabled. Option @option{-M} can be used to change
4964 @samp{xx} to another macro name.
4966 In this output format, each non-graphical character, like newline and
4967 tab, is merely changed to exactly one space, with no special attempt to
4968 compress consecutive spaces. Each quote character: @kbd{"} is doubled
4969 so it will be correctly processed by @command{nroff} or @command{troff}.
4974 Choose an output format suitable for @TeX{} processing. Each output
4975 line will look like:
4978 \xx @{@var{tail}@}@{@var{before}@}@{@var{keyword}@}@{@var{after}@}@{@var{head}@}@{@var{ref}@}
4982 so it will be possible to write a @code{\xx} definition to take care of
4983 the output typesetting. Note that when references are not being
4984 produced, that is, neither option @option{-A} nor option @option{-r} is
4985 selected, the last parameter of each @code{\xx} call is inhibited.
4986 Option @option{-M} can be used to change @samp{xx} to another macro
4989 In this output format, some special characters, like @kbd{$}, @kbd{%},
4990 @kbd{&}, @kbd{#} and @kbd{_} are automatically protected with a
4991 backslash. Curly brackets @kbd{@{}, @kbd{@}} are protected with a
4992 backslash and a pair of dollar signs (to force mathematical mode). The
4993 backslash itself produces the sequence @code{\backslash@{@}}.
4994 Circumflex and tilde diacritical marks produce the sequence @code{^\@{ @}} and
4995 @code{~\@{ @}} respectively. Other diacriticized characters of the
4996 underlying character set produce an appropriate @TeX{} sequence as far
4997 as possible. The other non-graphical characters, like newline and tab,
4998 and all other characters which are not part of @acronym{ASCII}, are merely
4999 changed to exactly one space, with no special attempt to compress
5000 consecutive spaces. Let me know how to improve this special character
5001 processing for @TeX{}.
5006 @node Compatibility in ptx
5007 @subsection The @sc{gnu} extensions to @command{ptx}
5009 This version of @command{ptx} contains a few features which do not exist in
5010 System V @command{ptx}. These extra features are suppressed by using the
5011 @option{-G} command line option, unless overridden by other command line
5012 options. Some @sc{gnu} extensions cannot be recovered by overriding, so the
5013 simple rule is to avoid @option{-G} if you care about @sc{gnu} extensions.
5014 Here are the differences between this program and System V @command{ptx}.
5019 This program can read many input files at once, it always writes the
5020 resulting concordance on standard output. On the other hand, System V
5021 @command{ptx} reads only one file and sends the result to standard output
5022 or, if a second @var{file} parameter is given on the command, to that
5025 Having output parameters not introduced by options is a dangerous
5026 practice which @sc{gnu} avoids as far as possible. So, for using @command{ptx}
5027 portably between @sc{gnu} and System V, you should always use it with a
5028 single input file, and always expect the result on standard output. You
5029 might also want to automatically configure in a @option{-G} option to
5030 @command{ptx} calls in products using @command{ptx}, if the configurator finds
5031 that the installed @command{ptx} accepts @option{-G}.
5034 The only options available in System V @command{ptx} are options @option{-b},
5035 @option{-f}, @option{-g}, @option{-i}, @option{-o}, @option{-r}, @option{-t} and
5036 @option{-w}. All other options are @sc{gnu} extensions and are not repeated in
5037 this enumeration. Moreover, some options have a slightly different
5038 meaning when @sc{gnu} extensions are enabled, as explained below.
5041 By default, concordance output is not formatted for @command{troff} or
5042 @command{nroff}. It is rather formatted for a dumb terminal. @command{troff}
5043 or @command{nroff} output may still be selected through option @option{-O}.
5046 Unless @option{-R} option is used, the maximum reference width is
5047 subtracted from the total output line width. With @sc{gnu} extensions
5048 disabled, width of references is not taken into account in the output
5049 line width computations.
5052 All 256 bytes, even @acronym{ASCII} @sc{nul} bytes, are always read and
5053 processed from input file with no adverse effect, even if @sc{gnu} extensions
5054 are disabled. However, System V @command{ptx} does not accept 8-bit characters,
5055 a few control characters are rejected, and the tilde @kbd{~} is also rejected.
5058 Input line length is only limited by available memory, even if @sc{gnu}
5059 extensions are disabled. However, System V @command{ptx} processes only
5060 the first 200 characters in each line.
5063 The break (non-word) characters default to be every character except all
5064 letters of the underlying character set, diacriticized or not. When @sc{gnu}
5065 extensions are disabled, the break characters default to space, tab and
5069 The program makes better use of output line width. If @sc{gnu} extensions
5070 are disabled, the program rather tries to imitate System V @command{ptx},
5071 but still, there are some slight disposition glitches this program does
5072 not completely reproduce.
5075 The user can specify both an Ignore file and an Only file. This is not
5076 allowed with System V @command{ptx}.
5081 @node tsort invocation
5082 @section @command{tsort}: Topological sort
5085 @cindex topological sort
5087 @command{tsort} performs a topological sort on the given @var{file}, or
5088 standard input if no input file is given or for a @var{file} of
5089 @samp{-}. For more details and some history, see @ref{tsort background}.
5093 tsort [@var{option}] [@var{file}]
5096 @command{tsort} reads its input as pairs of strings, separated by blanks,
5097 indicating a partial ordering. The output is a total ordering that
5098 corresponds to the given partial ordering.
5112 will produce the output
5123 Consider a more realistic example.
5124 You have a large set of functions all in one file, and they may all be
5125 declared static except one. Currently that one (say @code{main}) is the
5126 first function defined in the file, and the ones it calls directly follow
5127 it, followed by those they call, etc. Let's say that you are determined
5128 to take advantage of prototypes, so you have to choose between declaring
5129 all of those functions (which means duplicating a lot of information from
5130 the definitions) and rearranging the functions so that as many as possible
5131 are defined before they are used. One way to automate the latter process
5132 is to get a list for each function of the functions it calls directly.
5133 Many programs can generate such lists. They describe a call graph.
5134 Consider the following list, in which a given line indicates that the
5135 function on the left calls the one on the right directly.
5141 tail_file pretty_name
5142 tail_file write_header
5144 tail_forever recheck
5145 tail_forever pretty_name
5146 tail_forever write_header
5147 tail_forever dump_remainder
5150 tail_lines start_lines
5151 tail_lines dump_remainder
5152 tail_lines file_lines
5153 tail_lines pipe_lines
5155 tail_bytes start_bytes
5156 tail_bytes dump_remainder
5157 tail_bytes pipe_bytes
5158 file_lines dump_remainder
5162 then you can use @command{tsort} to produce an ordering of those
5163 functions that satisfies your requirement.
5166 example$ tsort call-graph | tac
5186 @command{tsort} detects any cycles in the input and writes the first cycle
5187 encountered to standard error.
5189 Note that for a given partial ordering, generally there is no unique
5190 total ordering. In the context of the call graph above, the function
5191 @code{parse_options} may be placed anywhere in the list as long as it
5192 precedes @code{main}.
5194 The only options are @option{--help} and @option{--version}. @xref{Common
5200 * tsort background:: Where tsort came from.
5203 @node tsort background
5204 @subsection @command{tsort}: Background
5206 @command{tsort} exists because very early versions of the Unix linker processed
5207 an archive file exactly once, and in order. As @command{ld} read each object
5208 in the archive, it decided whether it was needed in the program based on
5209 whether it defined any symbols which were undefined at that point in
5212 This meant that dependencies within the archive had to be handled
5213 specially. For example, @code{scanf} probably calls @code{read}. That means
5214 that in a single pass through an archive, it was important for @code{scanf.o}
5215 to appear before read.o, because otherwise a program which calls
5216 @code{scanf} but not @code{read} might end up with an unexpected unresolved
5217 reference to @code{read}.
5219 The way to address this problem was to first generate a set of
5220 dependencies of one object file on another. This was done by a shell
5221 script called @command{lorder}. The GNU tools don't provide a version of
5222 lorder, as far as I know, but you can still find it in BSD
5225 Then you ran @command{tsort} over the @command{lorder} output, and you used the
5226 resulting sort to define the order in which you added objects to the archive.
5228 This whole procedure has been obsolete since about 1980, because
5229 Unix archives now contain a symbol table (traditionally built by
5230 @command{ranlib}, now generally built by @command{ar} itself), and the Unix
5231 linker uses the symbol table to effectively make multiple passes over
5234 Anyhow, that's where tsort came from. To solve an old problem with
5235 the way the linker handled archive files, which has since been solved
5239 @node Operating on fields
5240 @chapter Operating on fields
5243 * cut invocation:: Print selected parts of lines.
5244 * paste invocation:: Merge lines of files.
5245 * join invocation:: Join lines on a common field.
5249 @node cut invocation
5250 @section @command{cut}: Print selected parts of lines
5253 @command{cut} writes to standard output selected parts of each line of each
5254 input file, or standard input if no files are given or for a file name of
5258 cut @var{option}@dots{} [@var{file}]@dots{}
5261 In the table which follows, the @var{byte-list}, @var{character-list},
5262 and @var{field-list} are one or more numbers or ranges (two numbers
5263 separated by a dash) separated by commas. Bytes, characters, and
5264 fields are numbered starting at 1. Incomplete ranges may be
5265 given: @option{-@var{m}} means @samp{1-@var{m}}; @samp{@var{n}-} means
5266 @samp{@var{n}} through end of line or last field. The list elements
5267 can be repeated, can overlap, and can be specified in any order; but
5268 the selected input is written in the same order that it is read, and
5269 is written exactly once.
5271 The program accepts the following options. Also see @ref{Common
5276 @item -b @var{byte-list}
5277 @itemx --bytes=@var{byte-list}
5280 Select for printing only the bytes in positions listed in
5281 @var{byte-list}. Tabs and backspaces are treated like any other
5282 character; they take up 1 byte. If an output delimiter is specified,
5283 (see the description of @option{--output-delimiter}), then output that
5284 string between ranges of selected bytes.
5286 @item -c @var{character-list}
5287 @itemx --characters=@var{character-list}
5289 @opindex --characters
5290 Select for printing only the characters in positions listed in
5291 @var{character-list}. The same as @option{-b} for now, but
5292 internationalization will change that. Tabs and backspaces are
5293 treated like any other character; they take up 1 character. If an
5294 output delimiter is specified, (see the description of
5295 @option{--output-delimiter}), then output that string between ranges
5298 @item -f @var{field-list}
5299 @itemx --fields=@var{field-list}
5302 Select for printing only the fields listed in @var{field-list}.
5303 Fields are separated by a TAB character by default. Also print any
5304 line that contains no delimiter character, unless the
5305 @option{--only-delimited} (@option{-s}) option is specified
5307 @item -d @var{input_delim_byte}
5308 @itemx --delimiter=@var{input_delim_byte}
5310 @opindex --delimiter
5311 With @option{-f}, use the first byte of @var{input_delim_byte} as
5312 the input fields separator (default is TAB).
5316 Do not split multi-byte characters (no-op for now).
5319 @itemx --only-delimited
5321 @opindex --only-delimited
5322 For @option{-f}, do not print lines that do not contain the field separator
5323 character. Normally, any line without a field separator is printed verbatim.
5325 @item --output-delimiter=@var{output_delim_string}
5326 @opindex --output-delimiter
5327 With @option{-f}, output fields are separated by @var{output_delim_string}.
5328 The default with @option{-f} is to use the input delimiter.
5329 When using @option{-b} or @option{-c} to select ranges of byte or
5330 character offsets (as opposed to ranges of fields),
5331 output @var{output_delim_string} between non-overlapping
5332 ranges of selected bytes.
5335 @opindex --complement
5336 This option is a @acronym{GNU} extension.
5337 Select for printing the complement of the bytes, characters or fields
5338 selected with the @option{-b}, @option{-c} or @option{-f} options.
5339 In other words, do @emph{not} print the bytes, characters or fields
5340 specified via those options. This option is useful when you have
5341 many fields and want to print all but a few of them.
5348 @node paste invocation
5349 @section @command{paste}: Merge lines of files
5352 @cindex merging files
5354 @command{paste} writes to standard output lines consisting of sequentially
5355 corresponding lines of each given file, separated by a TAB character.
5356 Standard input is used for a file name of @samp{-} or if no input files
5378 paste [@var{option}]@dots{} [@var{file}]@dots{}
5381 The program accepts the following options. Also see @ref{Common options}.
5389 Paste the lines of one file at a time rather than one line from each
5390 file. Using the above example data:
5393 $ paste -s num2 let3
5398 @item -d @var{delim-list}
5399 @itemx --delimiters=@var{delim-list}
5401 @opindex --delimiters
5402 Consecutively use the characters in @var{delim-list} instead of
5403 TAB to separate merged lines. When @var{delim-list} is
5404 exhausted, start again at its beginning. Using the above example data:
5407 $ paste -d '%_' num2 let3 num2
5418 @node join invocation
5419 @section @command{join}: Join lines on a common field
5422 @cindex common field, joining on
5424 @command{join} writes to standard output a line for each pair of input
5425 lines that have identical join fields. Synopsis:
5428 join [@var{option}]@dots{} @var{file1} @var{file2}
5431 Either @var{file1} or @var{file2} (but not both) can be @samp{-},
5432 meaning standard input. @var{file1} and @var{file2} should be
5433 sorted on the join fields.
5436 Normally, the sort order is that of the
5437 collating sequence specified by the @env{LC_COLLATE} locale. Unless
5438 the @option{-t} option is given, the sort comparison ignores blanks at
5439 the start of the join field, as in @code{sort -b}. If the
5440 @option{--ignore-case} option is given, the sort comparison ignores
5441 the case of characters in the join field, as in @code{sort -f}.
5443 The @command{sort} and @command{join} commands should use consistent
5444 locales and options if the output of @command{sort} is fed to
5445 @command{join}. You can use a command like @samp{sort -k 1b,1} to
5446 sort a file on its default join field, but if you select a non-default
5447 locale, join field, separator, or comparison options, then you should
5448 do so consistently between @command{join} and @command{sort}.
5450 If the input has no unpairable lines, a @acronym{GNU} extension is
5451 available; the sort order can be any order that considers two fields
5452 to be equal if and only if the sort comparison described above
5453 considers them to be equal. For example:
5470 @checkOrderOption{join}
5474 @item the join field is the first field in each line;
5475 @item fields in the input are separated by one or more blanks, with leading
5476 blanks on the line ignored;
5477 @item fields in the output are separated by a space;
5478 @item each output line consists of the join field, the remaining
5479 fields from @var{file1}, then the remaining fields from @var{file2}.
5482 The program accepts the following options. Also see @ref{Common options}.
5486 @item -a @var{file-number}
5488 Print a line for each unpairable line in file @var{file-number} (either
5489 @samp{1} or @samp{2}), in addition to the normal output.
5492 Fail with an error message if either input file is wrongly ordered.
5494 @item --nocheck-order
5495 Do not check that both input files are in sorted order. This is the default.
5497 @item -e @var{string}
5499 Replace those output fields that are missing in the input with
5503 @itemx --ignore-case
5505 @opindex --ignore-case
5506 Ignore differences in case when comparing keys.
5507 With this option, the lines of the input files must be ordered in the same way.
5508 Use @samp{sort -f} to produce this ordering.
5510 @item -1 @var{field}
5512 Join on field @var{field} (a positive integer) of file 1.
5514 @item -2 @var{field}
5516 Join on field @var{field} (a positive integer) of file 2.
5518 @item -j @var{field}
5519 Equivalent to @option{-1 @var{field} -2 @var{field}}.
5521 @item -o @var{field-list}
5522 Construct each output line according to the format in @var{field-list}.
5523 Each element in @var{field-list} is either the single character @samp{0} or
5524 has the form @var{m.n} where the file number, @var{m}, is @samp{1} or
5525 @samp{2} and @var{n} is a positive field number.
5527 A field specification of @samp{0} denotes the join field.
5528 In most cases, the functionality of the @samp{0} field spec
5529 may be reproduced using the explicit @var{m.n} that corresponds
5530 to the join field. However, when printing unpairable lines
5531 (using either of the @option{-a} or @option{-v} options), there is no way
5532 to specify the join field using @var{m.n} in @var{field-list}
5533 if there are unpairable lines in both files.
5534 To give @command{join} that functionality, @acronym{POSIX} invented the @samp{0}
5535 field specification notation.
5537 The elements in @var{field-list}
5538 are separated by commas or blanks.
5539 Blank separators typically need to be quoted for the shell. For
5540 example, the commands @samp{join -o 1.2,2.2} and @samp{join -o '1.2
5541 2.2'} are equivalent.
5543 All output lines---including those printed because of any -a or -v
5544 option---are subject to the specified @var{field-list}.
5547 Use character @var{char} as the input and output field separator.
5548 Treat as significant each occurrence of @var{char} in the input file.
5549 Use @samp{sort -t @var{char}}, without the @option{-b} option of
5550 @samp{sort}, to produce this ordering.
5552 @item -v @var{file-number}
5553 Print a line for each unpairable line in file @var{file-number}
5554 (either @samp{1} or @samp{2}), instead of the normal output.
5561 @node Operating on characters
5562 @chapter Operating on characters
5564 @cindex operating on characters
5566 This commands operate on individual characters.
5569 * tr invocation:: Translate, squeeze, and/or delete characters.
5570 * expand invocation:: Convert tabs to spaces.
5571 * unexpand invocation:: Convert spaces to tabs.
5576 @section @command{tr}: Translate, squeeze, and/or delete characters
5583 tr [@var{option}]@dots{} @var{set1} [@var{set2}]
5586 @command{tr} copies standard input to standard output, performing
5587 one of the following operations:
5591 translate, and optionally squeeze repeated characters in the result,
5593 squeeze repeated characters,
5597 delete characters, then squeeze repeated characters from the result.
5600 The @var{set1} and (if given) @var{set2} arguments define ordered
5601 sets of characters, referred to below as @var{set1} and @var{set2}. These
5602 sets are the characters of the input that @command{tr} operates on.
5603 The @option{--complement} (@option{-c}, @option{-C}) option replaces
5605 complement (all of the characters that are not in @var{set1}).
5607 Currently @command{tr} fully supports only single-byte characters.
5608 Eventually it will support multibyte characters; when it does, the
5609 @option{-C} option will cause it to complement the set of characters,
5610 whereas @option{-c} will cause it to complement the set of values.
5611 This distinction will matter only when some values are not characters,
5612 and this is possible only in locales using multibyte encodings when
5613 the input contains encoding errors.
5615 The program accepts the @option{--help} and @option{--version}
5616 options. @xref{Common options}. Options must precede operands.
5621 * Character sets:: Specifying sets of characters.
5622 * Translating:: Changing one set of characters to another.
5623 * Squeezing:: Squeezing repeats and deleting.
5627 @node Character sets
5628 @subsection Specifying sets of characters
5630 @cindex specifying sets of characters
5632 The format of the @var{set1} and @var{set2} arguments resembles
5633 the format of regular expressions; however, they are not regular
5634 expressions, only lists of characters. Most characters simply
5635 represent themselves in these strings, but the strings can contain
5636 the shorthands listed below, for convenience. Some of them can be
5637 used only in @var{set1} or @var{set2}, as noted below.
5641 @item Backslash escapes
5642 @cindex backslash escapes
5644 The following backslash escape sequences are recognized:
5662 The character with the value given by @var{ooo}, which is 1 to 3
5668 While a backslash followed by a character not listed above is
5669 interpreted as that character, the backslash also effectively
5670 removes any special significance, so it is useful to escape
5671 @samp{[}, @samp{]}, @samp{*}, and @samp{-}.
5676 The notation @samp{@var{m}-@var{n}} expands to all of the characters
5677 from @var{m} through @var{n}, in ascending order. @var{m} should
5678 collate before @var{n}; if it doesn't, an error results. As an example,
5679 @samp{0-9} is the same as @samp{0123456789}.
5681 @sc{gnu} @command{tr} does not support the System V syntax that uses square
5682 brackets to enclose ranges. Translations specified in that format
5683 sometimes work as expected, since the brackets are often transliterated
5684 to themselves. However, they should be avoided because they sometimes
5685 behave unexpectedly. For example, @samp{tr -d '[0-9]'} deletes brackets
5688 Many historically common and even accepted uses of ranges are not
5689 portable. For example, on @acronym{EBCDIC} hosts using the @samp{A-Z}
5690 range will not do what most would expect because @samp{A} through @samp{Z}
5691 are not contiguous as they are in @acronym{ASCII}.
5692 If you can rely on a @acronym{POSIX} compliant version of @command{tr}, then
5693 the best way to work around this is to use character classes (see below).
5694 Otherwise, it is most portable (and most ugly) to enumerate the members
5697 @item Repeated characters
5698 @cindex repeated characters
5700 The notation @samp{[@var{c}*@var{n}]} in @var{set2} expands to @var{n}
5701 copies of character @var{c}. Thus, @samp{[y*6]} is the same as
5702 @samp{yyyyyy}. The notation @samp{[@var{c}*]} in @var{string2} expands
5703 to as many copies of @var{c} as are needed to make @var{set2} as long as
5704 @var{set1}. If @var{n} begins with @samp{0}, it is interpreted in
5705 octal, otherwise in decimal.
5707 @item Character classes
5708 @cindex character classes
5710 The notation @samp{[:@var{class}:]} expands to all of the characters in
5711 the (predefined) class @var{class}. The characters expand in no
5712 particular order, except for the @code{upper} and @code{lower} classes,
5713 which expand in ascending order. When the @option{--delete} (@option{-d})
5714 and @option{--squeeze-repeats} (@option{-s}) options are both given, any
5715 character class can be used in @var{set2}. Otherwise, only the
5716 character classes @code{lower} and @code{upper} are accepted in
5717 @var{set2}, and then only if the corresponding character class
5718 (@code{upper} and @code{lower}, respectively) is specified in the same
5719 relative position in @var{set1}. Doing this specifies case conversion.
5720 The class names are given below; an error results when an invalid class
5732 Horizontal whitespace.
5741 Printable characters, not including space.
5747 Printable characters, including space.
5750 Punctuation characters.
5753 Horizontal or vertical whitespace.
5762 @item Equivalence classes
5763 @cindex equivalence classes
5765 The syntax @samp{[=@var{c}=]} expands to all of the characters that are
5766 equivalent to @var{c}, in no particular order. Equivalence classes are
5767 a relatively recent invention intended to support non-English alphabets.
5768 But there seems to be no standard way to define them or determine their
5769 contents. Therefore, they are not fully implemented in @sc{gnu} @command{tr};
5770 each character's equivalence class consists only of that character,
5771 which is of no particular use.
5777 @subsection Translating
5779 @cindex translating characters
5781 @command{tr} performs translation when @var{set1} and @var{set2} are
5782 both given and the @option{--delete} (@option{-d}) option is not given.
5783 @command{tr} translates each character of its input that is in @var{set1}
5784 to the corresponding character in @var{set2}. Characters not in
5785 @var{set1} are passed through unchanged. When a character appears more
5786 than once in @var{set1} and the corresponding characters in @var{set2}
5787 are not all the same, only the final one is used. For example, these
5788 two commands are equivalent:
5795 A common use of @command{tr} is to convert lowercase characters to
5796 uppercase. This can be done in many ways. Here are three of them:
5799 tr abcdefghijklmnopqrstuvwxyz ABCDEFGHIJKLMNOPQRSTUVWXYZ
5801 tr '[:lower:]' '[:upper:]'
5805 But note that using ranges like @code{a-z} above is not portable.
5807 When @command{tr} is performing translation, @var{set1} and @var{set2}
5808 typically have the same length. If @var{set1} is shorter than
5809 @var{set2}, the extra characters at the end of @var{set2} are ignored.
5811 On the other hand, making @var{set1} longer than @var{set2} is not
5812 portable; @acronym{POSIX} says that the result is undefined. In this situation,
5813 BSD @command{tr} pads @var{set2} to the length of @var{set1} by repeating
5814 the last character of @var{set2} as many times as necessary. System V
5815 @command{tr} truncates @var{set1} to the length of @var{set2}.
5817 By default, @sc{gnu} @command{tr} handles this case like BSD @command{tr}.
5818 When the @option{--truncate-set1} (@option{-t}) option is given,
5819 @sc{gnu} @command{tr} handles this case like the System V @command{tr}
5820 instead. This option is ignored for operations other than translation.
5822 Acting like System V @command{tr} in this case breaks the relatively common
5826 tr -cs A-Za-z0-9 '\012'
5830 because it converts only zero bytes (the first element in the
5831 complement of @var{set1}), rather than all non-alphanumerics, to
5835 By the way, the above idiom is not portable because it uses ranges, and
5836 it assumes that the octal code for newline is 012.
5837 Assuming a @acronym{POSIX} compliant @command{tr}, here is a better way to write it:
5840 tr -cs '[:alnum:]' '[\n*]'
5845 @subsection Squeezing repeats and deleting
5847 @cindex squeezing repeat characters
5848 @cindex deleting characters
5850 When given just the @option{--delete} (@option{-d}) option, @command{tr}
5851 removes any input characters that are in @var{set1}.
5853 When given just the @option{--squeeze-repeats} (@option{-s}) option,
5854 @command{tr} replaces each input sequence of a repeated character that
5855 is in @var{set1} with a single occurrence of that character.
5857 When given both @option{--delete} and @option{--squeeze-repeats}, @command{tr}
5858 first performs any deletions using @var{set1}, then squeezes repeats
5859 from any remaining characters using @var{set2}.
5861 The @option{--squeeze-repeats} option may also be used when translating,
5862 in which case @command{tr} first performs translation, then squeezes
5863 repeats from any remaining characters using @var{set2}.
5865 Here are some examples to illustrate various combinations of options:
5870 Remove all zero bytes:
5877 Put all words on lines by themselves. This converts all
5878 non-alphanumeric characters to newlines, then squeezes each string
5879 of repeated newlines into a single newline:
5882 tr -cs '[:alnum:]' '[\n*]'
5886 Convert each sequence of repeated newlines to a single newline:
5893 Find doubled occurrences of words in a document.
5894 @c Separate the following two "the"s, so typo checkers don't complain.
5895 For example, people often write ``the @w{}the'' with the repeated words
5896 separated by a newline. The Bourne shell script below works first
5897 by converting each sequence of punctuation and blank characters to a
5898 single newline. That puts each ``word'' on a line by itself.
5899 Next it maps all uppercase characters to lower case, and finally it
5900 runs @command{uniq} with the @option{-d} option to print out only the words
5906 | tr -s '[:punct:][:blank:]' '[\n*]' \
5907 | tr '[:upper:]' '[:lower:]' \
5912 Deleting a small set of characters is usually straightforward. For example,
5913 to remove all @samp{a}s, @samp{x}s, and @samp{M}s you would do this:
5919 However, when @samp{-} is one of those characters, it can be tricky because
5920 @samp{-} has special meanings. Performing the same task as above but also
5921 removing all @samp{-} characters, we might try @code{tr -d -axM}, but
5922 that would fail because @command{tr} would try to interpret @option{-a} as
5923 a command-line option. Alternatively, we could try putting the hyphen
5924 inside the string, @code{tr -d a-xM}, but that wouldn't work either because
5925 it would make @command{tr} interpret @code{a-x} as the range of characters
5926 @samp{a}@dots{}@samp{x} rather than the three.
5927 One way to solve the problem is to put the hyphen at the end of the list
5934 Or you can use @samp{--} to terminate option processing:
5940 More generally, use the character class notation @code{[=c=]}
5941 with @samp{-} (or any other character) in place of the @samp{c}:
5947 Note how single quotes are used in the above example to protect the
5948 square brackets from interpretation by a shell.
5953 @node expand invocation
5954 @section @command{expand}: Convert tabs to spaces
5957 @cindex tabs to spaces, converting
5958 @cindex converting tabs to spaces
5960 @command{expand} writes the contents of each given @var{file}, or standard
5961 input if none are given or for a @var{file} of @samp{-}, to standard
5962 output, with tab characters converted to the appropriate number of
5966 expand [@var{option}]@dots{} [@var{file}]@dots{}
5969 By default, @command{expand} converts all tabs to spaces. It preserves
5970 backspace characters in the output; they decrement the column count for
5971 tab calculations. The default action is equivalent to @option{-t 8} (set
5972 tabs every 8 columns).
5974 The program accepts the following options. Also see @ref{Common options}.
5978 @item -t @var{tab1}[,@var{tab2}]@dots{}
5979 @itemx --tabs=@var{tab1}[,@var{tab2}]@dots{}
5982 @cindex tab stops, setting
5983 If only one tab stop is given, set the tabs @var{tab1} spaces apart
5984 (default is 8). Otherwise, set the tabs at columns @var{tab1},
5985 @var{tab2}, @dots{} (numbered from 0), and replace any tabs beyond the
5986 last tab stop given with single spaces. Tab stops can be separated by
5987 blanks as well as by commas.
5989 For compatibility, GNU @command{expand} also accepts the obsolete
5990 option syntax, @option{-@var{t1}[,@var{t2}]@dots{}}. New scripts
5991 should use @option{-t @var{t1}[,@var{t2}]@dots{}} instead.
5997 @cindex initial tabs, converting
5998 Only convert initial tabs (those that precede all non-space or non-tab
5999 characters) on each line to spaces.
6006 @node unexpand invocation
6007 @section @command{unexpand}: Convert spaces to tabs
6011 @command{unexpand} writes the contents of each given @var{file}, or
6012 standard input if none are given or for a @var{file} of @samp{-}, to
6013 standard output, converting blanks at the beginning of each line into
6014 as many tab characters as needed. In the default @acronym{POSIX}
6015 locale, a @dfn{blank} is a space or a tab; other locales may specify
6016 additional blank characters. Synopsis:
6019 unexpand [@var{option}]@dots{} [@var{file}]@dots{}
6022 By default, @command{unexpand} converts only initial blanks (those
6023 that precede all non-blank characters) on each line. It
6024 preserves backspace characters in the output; they decrement the column
6025 count for tab calculations. By default, tabs are set at every 8th
6028 The program accepts the following options. Also see @ref{Common options}.
6032 @item -t @var{tab1}[,@var{tab2}]@dots{}
6033 @itemx --tabs=@var{tab1}[,@var{tab2}]@dots{}
6036 If only one tab stop is given, set the tabs @var{tab1} columns apart
6037 instead of the default 8. Otherwise, set the tabs at columns
6038 @var{tab1}, @var{tab2}, @dots{} (numbered from 0), and leave blanks
6039 beyond the tab stops given unchanged. Tab stops can be separated by
6040 blanks as well as by commas. This option implies the @option{-a} option.
6042 For compatibility, GNU @command{unexpand} supports the obsolete option syntax,
6043 @option{-@var{tab1}[,@var{tab2}]@dots{}}, where tab stops must be
6044 separated by commas. (Unlike @option{-t}, this obsolete option does
6045 not imply @option{-a}.) New scripts should use @option{--first-only -t
6046 @var{tab1}[,@var{tab2}]@dots{}} instead.
6052 Also convert all sequences of two or more blanks just before a tab stop,
6053 even if they occur after non-blank characters in a line.
6060 @node Directory listing
6061 @chapter Directory listing
6063 This chapter describes the @command{ls} command and its variants @command{dir}
6064 and @command{vdir}, which list information about files.
6067 * ls invocation:: List directory contents.
6068 * dir invocation:: Briefly ls.
6069 * vdir invocation:: Verbosely ls.
6070 * dircolors invocation:: Color setup for ls, etc.
6075 @section @command{ls}: List directory contents
6078 @cindex directory listing
6080 The @command{ls} program lists information about files (of any type,
6081 including directories). Options and file arguments can be intermixed
6082 arbitrarily, as usual.
6084 For non-option command-line arguments that are directories, by default
6085 @command{ls} lists the contents of directories, not recursively, and
6086 omitting files with names beginning with @samp{.}. For other non-option
6087 arguments, by default @command{ls} lists just the file name. If no
6088 non-option argument is specified, @command{ls} operates on the current
6089 directory, acting as if it had been invoked with a single argument of @samp{.}.
6092 By default, the output is sorted alphabetically, according to the locale
6093 settings in effect.@footnote{If you use a non-@acronym{POSIX}
6094 locale (e.g., by setting @env{LC_ALL} to @samp{en_US}), then @command{ls} may
6095 produce output that is sorted differently than you're accustomed to.
6096 In that case, set the @env{LC_ALL} environment variable to @samp{C}.}
6097 If standard output is
6098 a terminal, the output is in columns (sorted vertically) and control
6099 characters are output as question marks; otherwise, the output is listed
6100 one per line and control characters are output as-is.
6102 Because @command{ls} is such a fundamental program, it has accumulated many
6103 options over the years. They are described in the subsections below;
6104 within each section, options are listed alphabetically (ignoring case).
6105 The division of options into the subsections is not absolute, since some
6106 options affect more than one aspect of @command{ls}'s operation.
6108 @cindex exit status of @command{ls}
6113 1 minor problems (e.g., failure to access a file or directory not
6114 specified as a command line argument. This happens when listing a
6115 directory in which entries are actively being removed or renamed.)
6116 2 serious trouble (e.g., memory exhausted, invalid option, failure
6117 to access a file or directory specified as a command line argument
6118 or a directory loop)
6121 Also see @ref{Common options}.
6124 * Which files are listed::
6125 * What information is listed::
6126 * Sorting the output::
6127 * Details about version sort::
6128 * General output formatting::
6129 * Formatting file timestamps::
6130 * Formatting the file names::
6134 @node Which files are listed
6135 @subsection Which files are listed
6137 These options determine which files @command{ls} lists information for.
6138 By default, @command{ls} lists files and the contents of any
6139 directories on the command line, except that in directories it ignores
6140 files whose names start with @samp{.}.
6148 In directories, do not ignore file names that start with @samp{.}.
6153 @opindex --almost-all
6154 In directories, do not ignore all file names that start with @samp{.};
6155 ignore only @file{.} and @file{..}. The @option{--all} (@option{-a})
6156 option overrides this option.
6159 @itemx --ignore-backups
6161 @opindex --ignore-backups
6162 @cindex backup files, ignoring
6163 In directories, ignore files that end with @samp{~}. This option is
6164 equivalent to @samp{--ignore='*~' --ignore='.*~'}.
6169 @opindex --directory
6170 List just the names of directories, as with other types of files, rather
6171 than listing their contents.
6172 @c The following sentence is the same as the one for -F.
6173 Do not follow symbolic links listed on the
6174 command line unless the @option{--dereference-command-line} (@option{-H}),
6175 @option{--dereference} (@option{-L}), or
6176 @option{--dereference-command-line-symlink-to-dir} options are specified.
6179 @itemx --dereference-command-line
6181 @opindex --dereference-command-line
6182 @cindex symbolic links, dereferencing
6183 If a command line argument specifies a symbolic link, show information
6184 for the file the link references rather than for the link itself.
6186 @itemx --dereference-command-line-symlink-to-dir
6187 @opindex --dereference-command-line-symlink-to-dir
6188 @cindex symbolic links, dereferencing
6189 Do not dereference symbolic links, with one exception:
6190 if a command line argument specifies a symbolic link that refers to
6191 a directory, show information for that directory rather than for the
6193 This is the default behavior when no other dereferencing-related
6194 option has been specified (@option{--classify} (@option{-F}),
6195 @option{--directory} (@option{-d}),
6197 @option{--dereference} (@option{-L}), or
6198 @option{--dereference-command-line} (@option{-H})).
6200 @item --group-directories-first
6201 @opindex --group-directories-first
6202 Group all the directories before the files and then sort the
6203 directories and the files separately using the selected sort key
6204 (see --sort option).
6205 That is, this option specifies a primary sort key,
6206 and the --sort option specifies a secondary key.
6207 However, any use of @option{--sort=none}
6208 (@option{-U}) disables this option altogether.
6210 @item --hide=PATTERN
6211 @opindex --hide=@var{pattern}
6212 In directories, ignore files whose names match the shell pattern
6213 @var{pattern}, unless the @option{--all} (@option{-a}) or
6214 @option{--almost-all} (@option{-A}) is also given. This
6215 option acts like @option{--ignore=@var{pattern}} except that it has no
6216 effect if @option{--all} (@option{-a}) or @option{--almost-all}
6217 (@option{-A}) is also given.
6219 This option can be useful in shell aliases. For example, if
6220 @command{lx} is an alias for @samp{ls --hide='*~'} and @command{ly} is
6221 an alias for @samp{ls --ignore='*~'}, then the command @samp{lx -A}
6222 lists the file @file{README~} even though @samp{ly -A} would not.
6224 @item -I @var{pattern}
6225 @itemx --ignore=@var{pattern}
6227 @opindex --ignore=@var{pattern}
6228 In directories, ignore files whose names match the shell pattern
6229 (not regular expression) @var{pattern}. As
6230 in the shell, an initial @samp{.} in a file name does not match a
6231 wildcard at the start of @var{pattern}. Sometimes it is useful
6232 to give this option several times. For example,
6235 $ ls --ignore='.??*' --ignore='.[^.]' --ignore='#*'
6238 The first option ignores names of length 3 or more that start with @samp{.},
6239 the second ignores all two-character names that start with @samp{.}
6240 except @samp{..}, and the third ignores names that start with @samp{#}.
6243 @itemx --dereference
6245 @opindex --dereference
6246 @cindex symbolic links, dereferencing
6247 When showing file information for a symbolic link, show information
6248 for the file the link references rather than the link itself.
6249 However, even with this option, @command{ls} still prints the name
6250 of the link itself, not the name of the file that the link points to.
6255 @opindex --recursive
6256 @cindex recursive directory listing
6257 @cindex directory listing, recursive
6258 List the contents of all directories recursively.
6263 @node What information is listed
6264 @subsection What information is listed
6266 These options affect the information that @command{ls} displays. By
6267 default, only file names are shown.
6273 @cindex hurd, author, printing
6274 List each file's author when producing long format directory listings.
6275 In GNU/Hurd, file authors can differ from their owners, but in other
6276 operating systems the two are the same.
6282 @cindex dired Emacs mode support
6283 With the long listing (@option{-l}) format, print an additional line after
6287 //DIRED// @var{beg1} @var{end1} @var{beg2} @var{end2} @dots{}
6291 The @var{begn} and @var{endn} are unsigned integers that record the
6292 byte position of the beginning and end of each file name in the output.
6293 This makes it easy for Emacs to find the names, even when they contain
6294 unusual characters such as space or newline, without fancy searching.
6296 If directories are being listed recursively (@option{-R}), output a similar
6297 line with offsets for each subdirectory name:
6300 //SUBDIRED// @var{beg1} @var{end1} @dots{}
6303 Finally, output a line of the form:
6306 //DIRED-OPTIONS// --quoting-style=@var{word}
6310 where @var{word} is the quoting style (@pxref{Formatting the file names}).
6312 Here is an actual example:
6315 $ mkdir -p a/sub/deeper a/sub2
6317 $ touch a/sub/deeper/file
6318 $ ls -gloRF --dired a
6321 -rw-r--r-- 1 0 Jun 10 12:27 f1
6322 -rw-r--r-- 1 0 Jun 10 12:27 f2
6323 drwxr-xr-x 3 4096 Jun 10 12:27 sub/
6324 drwxr-xr-x 2 4096 Jun 10 12:27 sub2/
6328 drwxr-xr-x 2 4096 Jun 10 12:27 deeper/
6332 -rw-r--r-- 1 0 Jun 10 12:27 file
6336 //DIRED// 48 50 84 86 120 123 158 162 217 223 282 286
6337 //SUBDIRED// 2 3 167 172 228 240 290 296
6338 //DIRED-OPTIONS// --quoting-style=literal
6341 Note that the pairs of offsets on the @samp{//DIRED//} line above delimit
6342 these names: @file{f1}, @file{f2}, @file{sub}, @file{sub2}, @file{deeper},
6344 The offsets on the @samp{//SUBDIRED//} line delimit the following
6345 directory names: @file{a}, @file{a/sub}, @file{a/sub/deeper}, @file{a/sub2}.
6347 Here is an example of how to extract the fifth entry name, @samp{deeper},
6348 corresponding to the pair of offsets, 222 and 228:
6351 $ ls -gloRF --dired a > out
6352 $ dd bs=1 skip=222 count=6 < out 2>/dev/null; echo
6356 Note that although the listing above includes a trailing slash
6357 for the @samp{deeper} entry, the offsets select the name without
6358 the trailing slash. However, if you invoke @command{ls} with @option{--dired}
6359 along with an option like @option{--escape} (aka @option{-b}) and operate
6360 on a file whose name contains special characters, notice that the backslash
6365 $ ls -blog --dired 'a b'
6366 -rw-r--r-- 1 0 Jun 10 12:28 a\ b
6368 //DIRED-OPTIONS// --quoting-style=escape
6371 If you use a quoting style that adds quote marks
6372 (e.g., @option{--quoting-style=c}), then the offsets include the quote marks.
6373 So beware that the user may select the quoting style via the environment
6374 variable @env{QUOTING_STYLE}. Hence, applications using @option{--dired}
6375 should either specify an explicit @option{--quoting-style=literal} option
6376 (aka @option{-N} or @option{--literal}) on the command line, or else be
6377 prepared to parse the escaped names.
6380 @opindex --full-time
6381 Produce long format directory listings, and list times in full. It is
6382 equivalent to using @option{--format=long} with
6383 @option{--time-style=full-iso} (@pxref{Formatting file timestamps}).
6387 Produce long format directory listings, but don't display owner information.
6393 Inhibit display of group information in a long format directory listing.
6394 (This is the default in some non-@sc{gnu} versions of @command{ls}, so we
6395 provide this option for compatibility.)
6403 @cindex inode number, printing
6404 Print the inode number (also called the file serial number and index
6405 number) of each file to the left of the file name. (This number
6406 uniquely identifies each file within a particular file system.)
6409 @itemx --format=long
6410 @itemx --format=verbose
6413 @opindex long ls @r{format}
6414 @opindex verbose ls @r{format}
6415 In addition to the name of each file, print the file type, file mode bits,
6416 number of hard links, owner name, group name, size, and
6417 timestamp (@pxref{Formatting file timestamps}), normally
6418 the modification time. Print question marks for information that
6419 cannot be determined.
6421 Normally the size is printed as a byte count without punctuation, but
6422 this can be overridden (@pxref{Block size}). For example, @option{-h}
6423 prints an abbreviated, human-readable count, and
6424 @samp{--block-size="'1"} prints a byte count with the thousands
6425 separator of the current locale.
6427 For each directory that is listed, preface the files with a line
6428 @samp{total @var{blocks}}, where @var{blocks} is the total disk allocation
6429 for all files in that directory. The block size currently defaults to 1024
6430 bytes, but this can be overridden (@pxref{Block size}).
6431 The @var{blocks} computed counts each hard link separately;
6432 this is arguably a deficiency.
6434 The file type is one of the following characters:
6436 @c The commented-out entries are ones we're not sure about.
6444 character special file
6446 high performance (``contiguous data'') file
6450 door (Solaris 2.5 and up)
6452 @c semaphore, if this is a distinct file type
6456 @c multiplexed file (7th edition Unix; obsolete)
6458 off-line (``migrated'') file (Cray DMF)
6460 network special file (HP-UX)
6464 port (Solaris 10 and up)
6466 @c message queue, if this is a distinct file type
6470 @c shared memory object, if this is a distinct file type
6472 @c typed memory object, if this is a distinct file type
6474 @c whiteout (4.4BSD; not implemented)
6476 some other file type
6479 @cindex permissions, output by @command{ls}
6480 The file mode bits listed are similar to symbolic mode specifications
6481 (@pxref{Symbolic Modes}). But @command{ls} combines multiple bits into the
6482 third character of each set of permissions as follows:
6486 If the set-user-ID or set-group-ID bit and the corresponding executable bit
6490 If the set-user-ID or set-group-ID bit is set but the corresponding
6491 executable bit is not set.
6494 If the restricted deletion flag or sticky bit, and the
6495 other-executable bit, are both set. The restricted deletion flag is
6496 another name for the sticky bit. @xref{Mode Structure}.
6499 If the restricted deletion flag or sticky bit is set but the
6500 other-executable bit is not set.
6503 If the executable bit is set and none of the above apply.
6509 Following the file mode bits is a single character that specifies
6510 whether an alternate access method such as an access control list
6511 applies to the file. When the character following the file mode bits is a
6512 space, there is no alternate access method. When it is a printing
6513 character, then there is such a method.
6515 GNU @command{ls} uses a @samp{.} character to indicate a file
6516 with an SELinux security context, but no other alternate access method.
6518 A file with any other combination of alternate access methods
6519 is marked with a @samp{+} character.
6522 @itemx --numeric-uid-gid
6524 @opindex --numeric-uid-gid
6525 @cindex numeric uid and gid
6526 @cindex numeric user and group IDs
6527 Produce long format directory listings, but
6528 display numeric user and group IDs instead of the owner and group names.
6532 Produce long format directory listings, but don't display group information.
6533 It is equivalent to using @option{--format=long} with @option{--no-group} .
6539 @cindex disk allocation
6540 @cindex size of files, reporting
6541 Print the disk allocation of each file to the left of the file name.
6542 This is the amount of disk space used by the file, which is usually a
6543 bit more than the file's size, but it can be less if the file has holes.
6545 Normally the disk allocation is printed in units of
6546 1024 bytes, but this can be overridden (@pxref{Block size}).
6548 @cindex NFS mounts from BSD to HP-UX
6549 For files that are NFS-mounted from an HP-UX system to a BSD system,
6550 this option reports sizes that are half the correct values. On HP-UX
6551 systems, it reports sizes that are twice the correct values for files
6552 that are NFS-mounted from BSD systems. This is due to a flaw in HP-UX;
6553 it also affects the HP-UX @command{ls} program.
6562 @cindex security context
6563 Display the SELinux security context or @samp{?} if none is found.
6564 When used with the @option{-l} option, print the security context
6565 to the left of the size column.
6570 @node Sorting the output
6571 @subsection Sorting the output
6573 @cindex sorting @command{ls} output
6574 These options change the order in which @command{ls} sorts the information
6575 it outputs. By default, sorting is done by character code
6576 (e.g., @acronym{ASCII} order).
6582 @itemx --time=status
6585 @opindex ctime@r{, printing or sorting by}
6586 @opindex status time@r{, printing or sorting by}
6587 @opindex use time@r{, printing or sorting files by}
6588 If the long listing format (e.g., @option{-l}, @option{-o}) is being used,
6589 print the status change time (the @samp{ctime} in the inode) instead of
6590 the modification time.
6591 When explicitly sorting by time (@option{--sort=time} or @option{-t})
6592 or when not using a long listing format,
6593 sort according to the status change time.
6597 @cindex unsorted directory listing
6598 @cindex directory order, listing by
6599 Primarily, like @option{-U}---do not sort; list the files in whatever
6600 order they are stored in the directory. But also enable @option{-a} (list
6601 all files) and disable @option{-l}, @option{--color}, and @option{-s} (if they
6602 were specified before the @option{-f}).
6608 @cindex reverse sorting
6609 Reverse whatever the sorting method is---e.g., list files in reverse
6610 alphabetical order, youngest first, smallest first, or whatever.
6616 @opindex size of files@r{, sorting files by}
6617 Sort by file size, largest first.
6623 @opindex modification time@r{, sorting files by}
6624 Sort by modification time (the @samp{mtime} in the inode), newest first.
6628 @itemx --time=access
6632 @opindex use time@r{, printing or sorting files by}
6633 @opindex atime@r{, printing or sorting files by}
6634 @opindex access time@r{, printing or sorting files by}
6635 If the long listing format (e.g., @option{--format=long}) is being used,
6636 print the last access time (the @samp{atime} in the inode).
6637 When explicitly sorting by time (@option{--sort=time} or @option{-t})
6638 or when not using a long listing format, sort according to the access time.
6644 @opindex none@r{, sorting option for @command{ls}}
6645 Do not sort; list the files in whatever order they are
6646 stored in the directory. (Do not do any of the other unrelated things
6647 that @option{-f} does.) This is especially useful when listing very large
6648 directories, since not doing any sorting can be noticeably faster.
6651 @itemx --sort=version
6654 @opindex version@r{, sorting option for @command{ls}}
6655 Sort by version name and number, lowest first. It behaves like a default
6656 sort, except that each sequence of decimal digits is treated numerically
6657 as an index/version number. (@xref{Details about version sort}.)
6660 @itemx --sort=extension
6663 @opindex extension@r{, sorting files by}
6664 Sort directory contents alphabetically by file extension (characters
6665 after the last @samp{.}); files with no extension are sorted first.
6670 @node Details about version sort
6671 @subsection Details about version sort
6673 The version sort takes into account the fact that file names frequently include
6674 indices or version numbers. Standard sorting functions usually do not produce
6675 the ordering that people expect because comparisons are made on a
6676 character-by-character basis. The version
6677 sort addresses this problem, and is especially useful when browsing
6678 directories that contain many files with indices/version numbers in their
6683 foo.zml-1.gz foo.zml-1.gz
6684 foo.zml-100.gz foo.zml-2.gz
6685 foo.zml-12.gz foo.zml-6.gz
6686 foo.zml-13.gz foo.zml-12.gz
6687 foo.zml-2.gz foo.zml-13.gz
6688 foo.zml-25.gz foo.zml-25.gz
6689 foo.zml-6.gz foo.zml-100.gz
6692 Version-sorted strings are compared such that if @var{ver1} and @var{ver2}
6693 are version numbers and @var{prefix} and @var{suffix} (@var{suffix} matching
6694 the regular expression @samp{(\.[A-Za-z~][A-Za-z0-9~]*)*}) are strings then
6695 @var{ver1} < @var{ver2} implies that the name composed of
6696 ``@var{prefix} @var{ver1} @var{suffix}'' sorts before
6697 ``@var{prefix} @var{ver2} @var{suffix}''.
6699 Note also that leading zeros of numeric parts are ignored:
6703 abc-1.007.tgz abc-1.01a.tgz
6704 abc-1.012b.tgz abc-1.007.tgz
6705 abc-1.01a.tgz abc-1.012b.tgz
6708 This functionality is implemented using gnulib's @code{filevercmp} function.
6709 One result of that implementation decision is that @samp{ls -v}
6710 and @samp{sort -V} do not use the locale category, @env{LC_COLLATE},
6711 which means non-numeric prefixes are sorted as if @env{LC_COLLATE} were set
6714 @node General output formatting
6715 @subsection General output formatting
6717 These options affect the appearance of the overall output.
6722 @itemx --format=single-column
6725 @opindex single-column @r{output of files}
6726 List one file per line. This is the default for @command{ls} when standard
6727 output is not a terminal.
6730 @itemx --format=vertical
6733 @opindex vertical @r{sorted files in columns}
6734 List files in columns, sorted vertically. This is the default for
6735 @command{ls} if standard output is a terminal. It is always the default
6736 for the @command{dir} program.
6737 @sc{gnu} @command{ls} uses variable width columns to display as many files as
6738 possible in the fewest lines.
6740 @item --color [=@var{when}]
6742 @cindex color, distinguishing file types with
6743 Specify whether to use color for distinguishing file types. @var{when}
6744 may be omitted, or one of:
6747 @vindex none @r{color option}
6748 - Do not use color at all. This is the default.
6750 @vindex auto @r{color option}
6751 @cindex terminal, using color iff
6752 - Only use color if standard output is a terminal.
6754 @vindex always @r{color option}
6757 Specifying @option{--color} and no @var{when} is equivalent to
6758 @option{--color=always}.
6759 Piping a colorized listing through a pager like @command{more} or
6760 @command{less} usually produces unreadable results. However, using
6761 @code{more -f} does seem to work.
6765 @itemx --indicator-style=classify
6768 @opindex --indicator-style
6769 @cindex file type and executables, marking
6770 @cindex executables and file type, marking
6771 Append a character to each file name indicating the file type. Also,
6772 for regular files that are executable, append @samp{*}. The file type
6773 indicators are @samp{/} for directories, @samp{@@} for symbolic links,
6774 @samp{|} for FIFOs, @samp{=} for sockets, @samp{>} for doors,
6775 and nothing for regular files.
6776 @c The following sentence is the same as the one for -d.
6777 Do not follow symbolic links listed on the
6778 command line unless the @option{--dereference-command-line} (@option{-H}),
6779 @option{--dereference} (@option{-L}), or
6780 @option{--dereference-command-line-symlink-to-dir} options are specified.
6783 @itemx --indicator-style=file-type
6784 @opindex --file-type
6785 @opindex --indicator-style
6786 @cindex file type, marking
6787 Append a character to each file name indicating the file type. This is
6788 like @option{-F}, except that executables are not marked.
6790 @item --indicator-style=@var{word}
6791 @opindex --indicator-style
6792 Append a character indicator with style @var{word} to entry names,
6797 Do not append any character indicator; this is the default.
6799 Append @samp{/} for directories. This is the same as the @option{-p}
6802 Append @samp{/} for directories, @samp{@@} for symbolic links, @samp{|}
6803 for FIFOs, @samp{=} for sockets, and nothing for regular files. This is
6804 the same as the @option{--file-type} option.
6806 Append @samp{*} for executable regular files, otherwise behave as for
6807 @samp{file-type}. This is the same as the @option{-F} or
6808 @option{--classify} option.
6813 Print file sizes in 1024-byte blocks, overriding the default block
6814 size (@pxref{Block size}).
6815 This option is equivalent to @option{--block-size=1K}.
6818 @itemx --format=commas
6821 @opindex commas@r{, outputting between files}
6822 List files horizontally, with as many as will fit on each line,
6823 separated by @samp{, } (a comma and a space).
6826 @itemx --indicator-style=slash
6828 @opindex --indicator-style
6829 @cindex file type, marking
6830 Append a @samp{/} to directory names.
6833 @itemx --format=across
6834 @itemx --format=horizontal
6837 @opindex across@r{, listing files}
6838 @opindex horizontal@r{, listing files}
6839 List the files in columns, sorted horizontally.
6842 @itemx --tabsize=@var{cols}
6845 Assume that each tab stop is @var{cols} columns wide. The default is 8.
6846 @command{ls} uses tabs where possible in the output, for efficiency. If
6847 @var{cols} is zero, do not use tabs at all.
6849 @c FIXME: remove in 2009, if Apple Terminal has been fixed for long enough.
6850 Some terminal emulators (at least Apple Terminal 1.5 (133) from Mac OS X 10.4.8)
6851 do not properly align columns to the right of a TAB following a
6852 non-@acronym{ASCII} byte. If you use such a terminal emulator, use the
6853 @option{-T0} option or put @code{TABSIZE=0} in your environment to tell
6854 @command{ls} to align using spaces, not tabs.
6857 @itemx --width=@var{cols}
6861 Assume the screen is @var{cols} columns wide. The default is taken
6862 from the terminal settings if possible; otherwise the environment
6863 variable @env{COLUMNS} is used if it is set; otherwise the default
6869 @node Formatting file timestamps
6870 @subsection Formatting file timestamps
6872 By default, file timestamps are listed in abbreviated form. Most
6873 locales use a timestamp like @samp{2002-03-30 23:45}. However, the
6874 default @acronym{POSIX} locale uses a date like @samp{Mar 30@ @ 2002}
6875 for non-recent timestamps, and a date-without-year and time like
6876 @samp{Mar 30 23:45} for recent timestamps.
6878 A timestamp is considered to be @dfn{recent} if it is less than six
6879 months old, and is not dated in the future. If a timestamp dated
6880 today is not listed in recent form, the timestamp is in the future,
6881 which means you probably have clock skew problems which may break
6882 programs like @command{make} that rely on file timestamps.
6885 Time stamps are listed according to the time zone rules specified by
6886 the @env{TZ} environment variable, or by the system default rules if
6887 @env{TZ} is not set. @xref{TZ Variable,, Specifying the Time Zone
6888 with @env{TZ}, libc, The GNU C Library Reference Manual}.
6890 The following option changes how file timestamps are printed.
6893 @item --time-style=@var{style}
6894 @opindex --time-style
6896 List timestamps in style @var{style}. The @var{style} should
6897 be one of the following:
6902 List timestamps using @var{format}, where @var{format} is interpreted
6903 like the format argument of @command{date} (@pxref{date invocation}).
6904 For example, @option{--time-style="+%Y-%m-%d %H:%M:%S"} causes
6905 @command{ls} to list timestamps like @samp{2002-03-30 23:45:56}. As
6906 with @command{date}, @var{format}'s interpretation is affected by the
6907 @env{LC_TIME} locale category.
6909 If @var{format} contains two format strings separated by a newline,
6910 the former is used for non-recent files and the latter for recent
6911 files; if you want output columns to line up, you may need to insert
6912 spaces in one of the two formats.
6915 List timestamps in full using @acronym{ISO} 8601 date, time, and time zone
6916 format with nanosecond precision, e.g., @samp{2002-03-30
6917 23:45:56.477817180 -0700}. This style is equivalent to
6918 @samp{+%Y-%m-%d %H:%M:%S.%N %z}.
6920 This is useful because the time output includes all the information that
6921 is available from the operating system. For example, this can help
6922 explain @command{make}'s behavior, since @acronym{GNU} @command{make}
6923 uses the full timestamp to determine whether a file is out of date.
6926 List @acronym{ISO} 8601 date and time in minutes, e.g.,
6927 @samp{2002-03-30 23:45}. These timestamps are shorter than
6928 @samp{full-iso} timestamps, and are usually good enough for everyday
6929 work. This style is equivalent to @samp{+%Y-%m-%d %H:%M}.
6932 List @acronym{ISO} 8601 dates for non-recent timestamps (e.g.,
6933 @samp{2002-03-30@ }), and @acronym{ISO} 8601 month, day, hour, and
6934 minute for recent timestamps (e.g., @samp{03-30 23:45}). These
6935 timestamps are uglier than @samp{long-iso} timestamps, but they carry
6936 nearly the same information in a smaller space and their brevity helps
6937 @command{ls} output fit within traditional 80-column output lines.
6938 The following two @command{ls} invocations are equivalent:
6943 ls -l --time-style="+%Y-%m-%d $newline%m-%d %H:%M"
6944 ls -l --time-style="iso"
6949 List timestamps in a locale-dependent form. For example, a Finnish
6950 locale might list non-recent timestamps like @samp{maalis 30@ @ 2002}
6951 and recent timestamps like @samp{maalis 30 23:45}. Locale-dependent
6952 timestamps typically consume more space than @samp{iso} timestamps and
6953 are harder for programs to parse because locale conventions vary so
6954 widely, but they are easier for many people to read.
6956 The @env{LC_TIME} locale category specifies the timestamp format. The
6957 default @acronym{POSIX} locale uses timestamps like @samp{Mar 30@
6958 @ 2002} and @samp{Mar 30 23:45}; in this locale, the following two
6959 @command{ls} invocations are equivalent:
6964 ls -l --time-style="+%b %e %Y$newline%b %e %H:%M"
6965 ls -l --time-style="locale"
6968 Other locales behave differently. For example, in a German locale,
6969 @option{--time-style="locale"} might be equivalent to
6970 @option{--time-style="+%e. %b %Y $newline%e. %b %H:%M"}
6971 and might generate timestamps like @samp{30. M@"ar 2002@ } and
6972 @samp{30. M@"ar 23:45}.
6974 @item posix-@var{style}
6976 List @acronym{POSIX}-locale timestamps if the @env{LC_TIME} locale
6977 category is @acronym{POSIX}, @var{style} timestamps otherwise. For
6978 example, the @samp{posix-long-iso} style lists
6979 timestamps like @samp{Mar 30@ @ 2002} and @samp{Mar 30 23:45} when in
6980 the @acronym{POSIX} locale, and like @samp{2002-03-30 23:45} otherwise.
6985 You can specify the default value of the @option{--time-style} option
6986 with the environment variable @env{TIME_STYLE}; if @env{TIME_STYLE} is not set
6987 the default style is @samp{locale}. @acronym{GNU} Emacs 21.3 and
6988 later use the @option{--dired} option and therefore can parse any date
6989 format, but if you are using Emacs 21.1 or 21.2 and specify a
6990 non-@acronym{POSIX} locale you may need to set
6991 @samp{TIME_STYLE="posix-long-iso"}.
6993 To avoid certain denial-of-service attacks, timestamps that would be
6994 longer than 1000 bytes may be treated as errors.
6997 @node Formatting the file names
6998 @subsection Formatting the file names
7000 These options change how file names themselves are printed.
7006 @itemx --quoting-style=escape
7009 @opindex --quoting-style
7010 @cindex backslash sequences for file names
7011 Quote nongraphic characters in file names using alphabetic and octal
7012 backslash sequences like those used in C.
7016 @itemx --quoting-style=literal
7019 @opindex --quoting-style
7020 Do not quote file names. However, with @command{ls} nongraphic
7021 characters are still printed as question marks if the output is a
7022 terminal and you do not specify the @option{--show-control-chars}
7026 @itemx --hide-control-chars
7028 @opindex --hide-control-chars
7029 Print question marks instead of nongraphic characters in file names.
7030 This is the default if the output is a terminal and the program is
7035 @itemx --quoting-style=c
7037 @opindex --quote-name
7038 @opindex --quoting-style
7039 Enclose file names in double quotes and quote nongraphic characters as
7042 @item --quoting-style=@var{word}
7043 @opindex --quoting-style
7044 @cindex quoting style
7045 Use style @var{word} to quote file names and other strings that may
7046 contain arbitrary characters. The @var{word} should
7047 be one of the following:
7051 Output strings as-is; this is the same as the @option{-N} or
7052 @option{--literal} option.
7054 Quote strings for the shell if they contain shell metacharacters or would
7055 cause ambiguous output.
7056 The quoting is suitable for @acronym{POSIX}-compatible shells like
7057 @command{bash}, but it does not always work for incompatible shells
7060 Quote strings for the shell, even if they would normally not require quoting.
7062 Quote strings as for C character string literals, including the
7063 surrounding double-quote characters; this is the same as the
7064 @option{-Q} or @option{--quote-name} option.
7066 Quote strings as for C character string literals, except omit the
7067 surrounding double-quote
7068 characters; this is the same as the @option{-b} or @option{--escape} option.
7070 Quote strings as for C character string literals, except use
7071 surrounding quotation marks appropriate for the
7074 @c Use @t instead of @samp to avoid duplicate quoting in some output styles.
7075 Quote strings as for C character string literals, except use
7076 surrounding quotation marks appropriate for the locale, and quote
7077 @t{`like this'} instead of @t{"like
7078 this"} in the default C locale. This looks nicer on many displays.
7081 You can specify the default value of the @option{--quoting-style} option
7082 with the environment variable @env{QUOTING_STYLE}. If that environment
7083 variable is not set, the default value is @samp{literal}, but this
7084 default may change to @samp{shell} in a future version of this package.
7086 @item --show-control-chars
7087 @opindex --show-control-chars
7088 Print nongraphic characters as-is in file names.
7089 This is the default unless the output is a terminal and the program is
7095 @node dir invocation
7096 @section @command{dir}: Briefly list directory contents
7099 @cindex directory listing, brief
7101 @command{dir} is equivalent to @code{ls -C
7102 -b}; that is, by default files are listed in columns, sorted vertically,
7103 and special characters are represented by backslash escape sequences.
7105 @xref{ls invocation, @command{ls}}.
7108 @node vdir invocation
7109 @section @command{vdir}: Verbosely list directory contents
7112 @cindex directory listing, verbose
7114 @command{vdir} is equivalent to @code{ls -l
7115 -b}; that is, by default files are listed in long format and special
7116 characters are represented by backslash escape sequences.
7118 @node dircolors invocation
7119 @section @command{dircolors}: Color setup for @command{ls}
7123 @cindex setup for color
7125 @command{dircolors} outputs a sequence of shell commands to set up the
7126 terminal for color output from @command{ls} (and @command{dir}, etc.).
7130 eval "`dircolors [@var{option}]@dots{} [@var{file}]`"
7133 If @var{file} is specified, @command{dircolors} reads it to determine which
7134 colors to use for which file types and extensions. Otherwise, a
7135 precompiled database is used. For details on the format of these files,
7136 run @samp{dircolors --print-database}.
7138 To make @command{dircolors} read a @file{~/.dircolors} file if it
7139 exists, you can put the following lines in your @file{~/.bashrc} (or
7140 adapt them to your favorite shell):
7144 test -r $d && eval "$(dircolors $d)"
7148 @vindex SHELL @r{environment variable, and color}
7149 The output is a shell command to set the @env{LS_COLORS} environment
7150 variable. You can specify the shell syntax to use on the command line,
7151 or @command{dircolors} will guess it from the value of the @env{SHELL}
7152 environment variable.
7154 The program accepts the following options. Also see @ref{Common options}.
7159 @itemx --bourne-shell
7162 @opindex --bourne-shell
7163 @cindex Bourne shell syntax for color setup
7164 @cindex @command{sh} syntax for color setup
7165 Output Bourne shell commands. This is the default if the @env{SHELL}
7166 environment variable is set and does not end with @samp{csh} or
7175 @cindex C shell syntax for color setup
7176 @cindex @command{csh} syntax for color setup
7177 Output C shell commands. This is the default if @code{SHELL} ends with
7178 @command{csh} or @command{tcsh}.
7181 @itemx --print-database
7183 @opindex --print-database
7184 @cindex color database, printing
7185 @cindex database for color setup, printing
7186 @cindex printing color database
7187 Print the (compiled-in) default color configuration database. This
7188 output is itself a valid configuration file, and is fairly descriptive
7189 of the possibilities.
7196 @node Basic operations
7197 @chapter Basic operations
7199 @cindex manipulating files
7201 This chapter describes the commands for basic file manipulation:
7202 copying, moving (renaming), and deleting (removing).
7205 * cp invocation:: Copy files.
7206 * dd invocation:: Convert and copy a file.
7207 * install invocation:: Copy files and set attributes.
7208 * mv invocation:: Move (rename) files.
7209 * rm invocation:: Remove files or directories.
7210 * shred invocation:: Remove files more securely.
7215 @section @command{cp}: Copy files and directories
7218 @cindex copying files and directories
7219 @cindex files, copying
7220 @cindex directories, copying
7222 @command{cp} copies files (or, optionally, directories). The copy is
7223 completely independent of the original. You can either copy one file to
7224 another, or copy arbitrarily many files to a destination directory.
7228 cp [@var{option}]@dots{} [-T] @var{source} @var{dest}
7229 cp [@var{option}]@dots{} @var{source}@dots{} @var{directory}
7230 cp [@var{option}]@dots{} -t @var{directory} @var{source}@dots{}
7235 If two file names are given, @command{cp} copies the first file to the
7239 If the @option{--target-directory} (@option{-t}) option is given, or
7240 failing that if the last file is a directory and the
7241 @option{--no-target-directory} (@option{-T}) option is not given,
7242 @command{cp} copies each @var{source} file to the specified directory,
7243 using the @var{source}s' names.
7246 Generally, files are written just as they are read. For exceptions,
7247 see the @option{--sparse} option below.
7249 By default, @command{cp} does not copy directories. However, the
7250 @option{-R}, @option{-a}, and @option{-r} options cause @command{cp} to
7251 copy recursively by descending into source directories and copying files
7252 to corresponding destination directories.
7254 When copying from a symbolic link, @command{cp} normally follows the
7255 link only when not copying
7256 recursively. This default can be overridden with the
7257 @option{--archive} (@option{-a}), @option{-d}, @option{--dereference}
7258 (@option{-L}), @option{--no-dereference} (@option{-P}), and
7259 @option{-H} options. If more than one of these options is specified,
7260 the last one silently overrides the others.
7262 When copying to a symbolic link, @command{cp} follows the
7263 link only when it refers to an existing regular file.
7264 However, when copying to a dangling symbolic link, @command{cp}
7265 refuses by default, and fails with a diagnostic, since the operation
7266 is inherently dangerous. This behavior is contrary to historical
7267 practice and to @acronym{POSIX}.
7268 Set @env{POSIXLY_CORRECT} to make @command{cp} attempt to create
7269 the target of a dangling destination symlink, in spite of the possible risk.
7270 Also, when an option like
7271 @option{--backup} or @option{--link} acts to rename or remove the
7272 destination before copying, @command{cp} renames or removes the
7273 symbolic link rather than the file it points to.
7275 By default, @command{cp} copies the contents of special files only
7276 when not copying recursively. This default can be overridden with the
7277 @option{--copy-contents} option.
7279 @cindex self-backups
7280 @cindex backups, making only
7281 @command{cp} generally refuses to copy a file onto itself, with the
7282 following exception: if @option{--force --backup} is specified with
7283 @var{source} and @var{dest} identical, and referring to a regular file,
7284 @command{cp} will make a backup file, either regular or numbered, as
7285 specified in the usual ways (@pxref{Backup options}). This is useful when
7286 you simply want to make a backup of an existing file before changing it.
7288 The program accepts the following options. Also see @ref{Common options}.
7295 Preserve as much as possible of the structure and attributes of the
7296 original files in the copy (but do not attempt to preserve internal
7297 directory structure; i.e., @samp{ls -U} may list the entries in a copied
7298 directory in a different order).
7299 Try to preserve SELinux security context and extended attributes (xattr),
7300 but ignore any failure to do that and print no corresponding diagnostic.
7301 Equivalent to @option{-dR --preserve=all} with the reduced diagnostics.
7304 @itemx @w{@kbd{--backup}[=@var{method}]}
7307 @vindex VERSION_CONTROL
7308 @cindex backups, making
7309 @xref{Backup options}.
7310 Make a backup of each file that would otherwise be overwritten or removed.
7311 As a special case, @command{cp} makes a backup of @var{source} when the force
7312 and backup options are given and @var{source} and @var{dest} are the same
7313 name for an existing, regular file. One useful application of this
7314 combination of options is this tiny Bourne shell script:
7318 # Usage: backup FILE...
7319 # Create a @sc{gnu}-style backup of each listed FILE.
7321 cp --backup --force -- "$i" "$i"
7325 @item --copy-contents
7326 @cindex directories, copying recursively
7327 @cindex copying directories recursively
7328 @cindex recursively copying directories
7329 @cindex non-directories, copying as special files
7330 If copying recursively, copy the contents of any special files (e.g.,
7331 FIFOs and device files) as if they were regular files. This means
7332 trying to read the data in each source file and writing it to the
7333 destination. It is usually a mistake to use this option, as it
7334 normally has undesirable effects on special files like FIFOs and the
7335 ones typically found in the @file{/dev} directory. In most cases,
7336 @code{cp -R --copy-contents} will hang indefinitely trying to read
7337 from FIFOs and special files like @file{/dev/console}, and it will
7338 fill up your destination disk if you use it to copy @file{/dev/zero}.
7339 This option has no effect unless copying recursively, and it does not
7340 affect the copying of symbolic links.
7344 @cindex symbolic links, copying
7345 @cindex hard links, preserving
7346 Copy symbolic links as symbolic links rather than copying the files that
7347 they point to, and preserve hard links between source files in the copies.
7348 Equivalent to @option{--no-dereference --preserve=links}.
7354 When copying without this option and an existing destination file cannot
7355 be opened for writing, the copy fails. However, with @option{--force}),
7356 when a destination file cannot be opened, @command{cp} then removes it and
7357 tries to open it again. Contrast this behavior with that enabled by
7358 @option{--link} and @option{--symbolic-link}, whereby the destination file
7359 is never opened but rather is removed unconditionally. Also see the
7360 description of @option{--remove-destination}.
7362 This option is independent of the @option{--interactive} or
7363 @option{-i} option: neither cancels the effect of the other.
7365 This option is redundant if the @option{--no-clobber} or @option{-n} option is
7370 If a command line argument specifies a symbolic link, then copy the
7371 file it points to rather than the symbolic link itself. However,
7372 copy (preserving its nature) any symbolic link that is encountered
7373 via recursive traversal.
7376 @itemx --interactive
7378 @opindex --interactive
7379 When copying a file other than a directory, prompt whether to
7380 overwrite an existing destination file. The @option{-i} option overrides
7381 a previous @option{-n} option.
7387 Make hard links instead of copies of non-directories.
7390 @itemx --dereference
7392 @opindex --dereference
7393 Follow symbolic links when copying from them.
7394 With this option, @command{cp} cannot create a symbolic link.
7395 For example, a symlink (to regular file) in the source tree will be copied to
7396 a regular file in the destination tree.
7401 @opindex --no-clobber
7402 Do not overwrite an existing file. The @option{-n} option overrides a previous
7403 @option{-i} option. This option is mutually exclusive with @option{-b} or
7404 @option{--backup} option.
7407 @itemx --no-dereference
7409 @opindex --no-dereference
7410 @cindex symbolic links, copying
7411 Copy symbolic links as symbolic links rather than copying the files that
7412 they point to. This option affects only symbolic links in the source;
7413 symbolic links in the destination are always followed if possible.
7416 @itemx @w{@kbd{--preserve}[=@var{attribute_list}]}
7419 @cindex file information, preserving, extended attributes, xattr
7420 Preserve the specified attributes of the original files.
7421 If specified, the @var{attribute_list} must be a comma-separated list
7422 of one or more of the following strings:
7426 Preserve the file mode bits and access control lists.
7428 Preserve the owner and group. On most modern systems,
7429 only users with appropriate privileges may change the owner of a file,
7431 may preserve the group ownership of a file only if they happen to be
7432 a member of the desired group.
7434 Preserve the times of last access and last modification, when possible.
7435 On older systems, it is not possible to preserve these attributes
7436 when the affected file is a symbolic link.
7437 However, many systems now provide the @code{utimensat} function,
7438 which makes it possible even for symbolic links.
7440 Preserve in the destination files
7441 any links between corresponding source files.
7442 Note that with @option{-L} or @option{-H}, this option can convert
7443 symbolic links to hard links. For example,
7445 $ mkdir c; : > a; ln -s a b; cp -aH a b c; ls -i1 c
7450 Note the inputs: @file{b} is a symlink to regular file @file{a},
7451 yet the files in destination directory, @file{c/}, are hard-linked.
7452 Since @option{-a} implies @option{--preserve=links}, and since @option{-H}
7453 tells @command{cp} to dereference command line arguments, it sees two files
7454 with the same inode number, and preserves the perceived hard link.
7456 Here is a similar example that exercises @command{cp}'s @option{-L} option:
7458 $ mkdir b c; (cd b; : > a; ln -s a b); cp -aL b c; ls -i1 c/b
7464 Preserve SELinux security context of the file. @command{cp} will fail
7465 if the preserving of SELinux security context is not succesful.
7467 Preserve extended attributes if @command{cp} is built with xattr support,
7468 and xattrs are supported and enabled on your file system.
7469 If SELinux context and/or ACLs are implemented using xattrs,
7470 they are preserved by this option as well.
7472 Preserve all file attributes.
7473 Equivalent to specifying all of the above, but with the difference
7474 that failure to preserve SELinux security context or extended attributes
7475 does not change @command{cp}'s exit status.
7476 @command{cp} does diagnose such failures.
7479 Using @option{--preserve} with no @var{attribute_list} is equivalent
7480 to @option{--preserve=mode,ownership,timestamps}.
7482 In the absence of this option, each destination file is created with the
7483 mode bits of the corresponding source file, minus the bits set in the
7484 umask and minus the set-user-ID and set-group-ID bits.
7485 @xref{File permissions}.
7487 @itemx @w{@kbd{--no-preserve}=@var{attribute_list}}
7488 @cindex file information, preserving
7489 Do not preserve the specified attributes. The @var{attribute_list}
7490 has the same form as for @option{--preserve}.
7494 @cindex parent directories and @command{cp}
7495 Form the name of each destination file by appending to the target
7496 directory a slash and the specified name of the source file. The last
7497 argument given to @command{cp} must be the name of an existing directory.
7498 For example, the command:
7501 cp --parents a/b/c existing_dir
7505 copies the file @file{a/b/c} to @file{existing_dir/a/b/c}, creating
7506 any missing intermediate directories.
7513 @opindex --recursive
7514 @cindex directories, copying recursively
7515 @cindex copying directories recursively
7516 @cindex recursively copying directories
7517 @cindex non-directories, copying as special files
7518 Copy directories recursively. By default, do not follow symbolic
7519 links in the source; see the @option{--archive} (@option{-a}), @option{-d},
7520 @option{--dereference} (@option{-L}), @option{--no-dereference}
7521 (@option{-P}), and @option{-H} options. Special files are copied by
7522 creating a destination file of the same type as the source; see the
7523 @option{--copy-contents} option. It is not portable to use
7524 @option{-r} to copy symbolic links or special files. On some
7525 non-@sc{gnu} systems, @option{-r} implies the equivalent of
7526 @option{-L} and @option{--copy-contents} for historical reasons.
7527 Also, it is not portable to use @option{-R} to copy symbolic links
7528 unless you also specify @option{-P}, as @acronym{POSIX} allows
7529 implementations that dereference symbolic links by default.
7531 @item --reflink[=@var{when}]
7532 @opindex --reflink[=@var{when}]
7535 @cindex copy on write
7536 Perform a lightweight, copy-on-write (COW) copy.
7537 Copying with this option can succeed only on some file systems.
7538 Once it has succeeded, beware that the source and destination files
7539 share the same disk data blocks as long as they remain unmodified.
7540 Thus, if a disk I/O error affects data blocks of one of the files,
7541 the other suffers the exact same fate.
7543 The @var{when} value can be one of the following:
7547 The default behavior: if the copy-on-write operation is not supported
7548 then report the failure for each file and exit with a failure status.
7551 If the copy-on-write operation is not supported then fall back
7552 to the standard copy behaviour.
7556 @item --remove-destination
7557 @opindex --remove-destination
7558 Remove each existing destination file before attempting to open it
7559 (contrast with @option{-f} above).
7561 @item --sparse=@var{when}
7562 @opindex --sparse=@var{when}
7563 @cindex sparse files, copying
7564 @cindex holes, copying files with
7565 @findex read @r{system call, and holes}
7566 A @dfn{sparse file} contains @dfn{holes}---a sequence of zero bytes that
7567 does not occupy any physical disk blocks; the @samp{read} system call
7568 reads these as zeros. This can both save considerable disk space and
7569 increase speed, since many binary files contain lots of consecutive zero
7570 bytes. By default, @command{cp} detects holes in input source files via a crude
7571 heuristic and makes the corresponding output file sparse as well.
7572 Only regular files may be sparse.
7574 The @var{when} value can be one of the following:
7578 The default behavior: if the input file is sparse, attempt to make
7579 the output file sparse, too. However, if an output file exists but
7580 refers to a non-regular file, then do not attempt to make it sparse.
7583 For each sufficiently long sequence of zero bytes in the input file,
7584 attempt to create a corresponding hole in the output file, even if the
7585 input file does not appear to be sparse.
7586 This is useful when the input file resides on a file system
7587 that does not support sparse files
7588 (for example, @samp{efs} file systems in SGI IRIX 5.3 and earlier),
7589 but the output file is on a type of file system that does support them.
7590 Holes may be created only in regular files, so if the destination file
7591 is of some other type, @command{cp} does not even try to make it sparse.
7594 Never make the output file sparse.
7595 This is useful in creating a file for use with the @command{mkswap} command,
7596 since such a file must not have any holes.
7599 @optStripTrailingSlashes
7602 @itemx --symbolic-link
7604 @opindex --symbolic-link
7605 @cindex symbolic links, copying with
7606 Make symbolic links instead of copies of non-directories. All source
7607 file names must be absolute (starting with @samp{/}) unless the
7608 destination files are in the current directory. This option merely
7609 results in an error message on systems that do not support symbolic links.
7615 @optNoTargetDirectory
7621 @cindex newer files, copying only
7622 Do not copy a non-directory that has an existing destination with the
7623 same or newer modification time. If time stamps are being preserved,
7624 the comparison is to the source time stamp truncated to the
7625 resolutions of the destination file system and of the system calls
7626 used to update time stamps; this avoids duplicate work if several
7627 @samp{cp -pu} commands are executed with the same source and
7634 Print the name of each file before copying it.
7637 @itemx --one-file-system
7639 @opindex --one-file-system
7640 @cindex file systems, omitting copying to different
7641 Skip subdirectories that are on different file systems from the one that
7642 the copy started on.
7643 However, mount point directories @emph{are} copied.
7651 @section @command{dd}: Convert and copy a file
7654 @cindex converting while copying a file
7656 @command{dd} copies a file (from standard input to standard output, by
7657 default) with a changeable I/O block size, while optionally performing
7658 conversions on it. Synopses:
7661 dd [@var{operand}]@dots{}
7665 The only options are @option{--help} and @option{--version}.
7666 @xref{Common options}. @command{dd} accepts the following operands.
7672 Read from @var{file} instead of standard input.
7676 Write to @var{file} instead of standard output. Unless
7677 @samp{conv=notrunc} is given, @command{dd} truncates @var{file} to zero
7678 bytes (or the size specified with @samp{seek=}).
7680 @item ibs=@var{bytes}
7682 @cindex block size of input
7683 @cindex input block size
7684 Set the input block size to @var{bytes}.
7685 This makes @command{dd} read @var{bytes} per block.
7686 The default is 512 bytes.
7688 @item obs=@var{bytes}
7690 @cindex block size of output
7691 @cindex output block size
7692 Set the output block size to @var{bytes}.
7693 This makes @command{dd} write @var{bytes} per block.
7694 The default is 512 bytes.
7696 @item bs=@var{bytes}
7699 Set both input and output block sizes to @var{bytes}.
7700 This makes @command{dd} read and write @var{bytes} per block,
7701 overriding any @samp{ibs} and @samp{obs} settings.
7702 In addition, if no data-transforming @option{conv} option is specified,
7703 each input block is copied to the output as a single block,
7704 without aggregating short reads.
7706 @item cbs=@var{bytes}
7708 @cindex block size of conversion
7709 @cindex conversion block size
7710 @cindex fixed-length records, converting to variable-length
7711 @cindex variable-length records, converting to fixed-length
7712 Set the conversion block size to @var{bytes}.
7713 When converting variable-length records to fixed-length ones
7714 (@option{conv=block}) or the reverse (@option{conv=unblock}),
7715 use @var{bytes} as the fixed record length.
7717 @item skip=@var{blocks}
7719 Skip @var{blocks} @samp{ibs}-byte blocks in the input file before copying.
7721 @item seek=@var{blocks}
7723 Skip @var{blocks} @samp{obs}-byte blocks in the output file before copying.
7725 @item count=@var{blocks}
7727 Copy @var{blocks} @samp{ibs}-byte blocks from the input file, instead
7728 of everything until the end of the file.
7732 Do not print the overall transfer rate and volume statistics
7733 that normally make up the third status line when @command{dd} exits.
7735 @item conv=@var{conversion}[,@var{conversion}]@dots{}
7737 Convert the file as specified by the @var{conversion} argument(s).
7738 (No spaces around any comma(s).)
7745 @opindex ascii@r{, converting to}
7746 Convert @acronym{EBCDIC} to @acronym{ASCII},
7747 using the conversion table specified by @acronym{POSIX}.
7748 This provides a 1:1 translation for all 256 bytes.
7751 @opindex ebcdic@r{, converting to}
7752 Convert @acronym{ASCII} to @acronym{EBCDIC}.
7753 This is the inverse of the @samp{ascii} conversion.
7756 @opindex alternate ebcdic@r{, converting to}
7757 Convert @acronym{ASCII} to alternate @acronym{EBCDIC},
7758 using the alternate conversion table specified by @acronym{POSIX}.
7759 This is not a 1:1 translation, but reflects common historical practice
7760 for @samp{~}, @samp{[}, and @samp{]}.
7762 The @samp{ascii}, @samp{ebcdic}, and @samp{ibm} conversions are
7766 @opindex block @r{(space-padding)}
7767 For each line in the input, output @samp{cbs} bytes, replacing the
7768 input newline with a space and padding with spaces as necessary.
7772 Remove any trailing spaces in each @samp{cbs}-sized input block,
7773 and append a newline.
7775 The @samp{block} and @samp{unblock} conversions are mutually exclusive.
7778 @opindex lcase@r{, converting to}
7779 Change uppercase letters to lowercase.
7782 @opindex ucase@r{, converting to}
7783 Change lowercase letters to uppercase.
7785 The @samp{lcase} and @samp{ucase} conversions are mutually exclusive.
7788 @opindex swab @r{(byte-swapping)}
7789 @cindex byte-swapping
7790 Swap every pair of input bytes. @sc{gnu} @command{dd}, unlike others, works
7791 when an odd number of bytes are read---the last byte is simply copied
7792 (since there is nothing to swap it with).
7796 @cindex read errors, ignoring
7797 Continue after read errors.
7801 @cindex creating output file, avoiding
7802 Do not create the output file; the output file must already exist.
7806 @cindex creating output file, requiring
7807 Fail if the output file already exists; @command{dd} must create the
7810 The @samp{excl} and @samp{nocreat} conversions are mutually exclusive.
7814 @cindex truncating output file, avoiding
7815 Do not truncate the output file.
7818 @opindex sync @r{(padding with @acronym{ASCII} @sc{nul}s)}
7819 Pad every input block to size of @samp{ibs} with trailing zero bytes.
7820 When used with @samp{block} or @samp{unblock}, pad with spaces instead of
7825 @cindex synchronized data writes, before finishing
7826 Synchronize output data just before finishing. This forces a physical
7827 write of output data.
7831 @cindex synchronized data and metadata writes, before finishing
7832 Synchronize output data and metadata just before finishing. This
7833 forces a physical write of output data and metadata.
7837 @item iflag=@var{flag}[,@var{flag}]@dots{}
7839 Access the input file using the flags specified by the @var{flag}
7840 argument(s). (No spaces around any comma(s).)
7842 @item oflag=@var{flag}[,@var{flag}]@dots{}
7844 Access the output file using the flags specified by the @var{flag}
7845 argument(s). (No spaces around any comma(s).)
7847 Here are the flags. Not every flag is supported on every operating
7854 @cindex appending to the output file
7855 Write in append mode, so that even if some other process is writing to
7856 this file, every @command{dd} write will append to the current
7857 contents of the file. This flag makes sense only for output.
7858 If you combine this flag with the @samp{of=@var{file}} operand,
7859 you should also specify @samp{conv=notrunc} unless you want the
7860 output file to be truncated before being appended to.
7864 @cindex concurrent I/O
7865 Use concurrent I/O mode for data. This mode performs direct I/O
7866 and drops the @acronym{POSIX} requirement to serialize all I/O to the same file.
7867 A file cannot be opened in CIO mode and with a standard open at the
7873 Use direct I/O for data, avoiding the buffer cache.
7874 Note that the kernel may impose restrictions on read or write buffer sizes.
7875 For example, with an ext4 destination file system and a linux-based kernel,
7876 using @samp{oflag=direct} will cause writes to fail with @code{EINVAL} if the
7877 output buffer size is not a multiple of 512.
7881 @cindex directory I/O
7883 Fail unless the file is a directory. Most operating systems do not
7884 allow I/O to a directory, so this flag has limited utility.
7888 @cindex synchronized data reads
7889 Use synchronized I/O for data. For the output file, this forces a
7890 physical write of output data on each write. For the input file,
7891 this flag can matter when reading from a remote file that has been
7892 written to synchronously by some other process. Metadata (e.g.,
7893 last-access and last-modified time) is not necessarily synchronized.
7897 @cindex synchronized data and metadata I/O
7898 Use synchronized I/O for both data and metadata.
7902 @cindex nonblocking I/O
7903 Use non-blocking I/O.
7908 Do not update the file's access time.
7909 Some older file systems silently ignore this flag, so it is a good
7910 idea to test it on your files before relying on it.
7914 @cindex controlling terminal
7915 Do not assign the file to be a controlling terminal for @command{dd}.
7916 This has no effect when the file is not a terminal.
7917 On many hosts (e.g., @acronym{GNU}/Linux hosts), this option has no effect
7922 @cindex symbolic links, following
7923 Do not follow symbolic links.
7928 Fail if the file has multiple hard links.
7933 Use binary I/O. This option has an effect only on nonstandard
7934 platforms that distinguish binary from text I/O.
7939 Use text I/O. Like @samp{binary}, this option has no effect on
7944 Accumulate full blocks from input. The @code{read} system call
7945 may return early if a full block is not available.
7946 When that happens, continue calling @code{read} to fill the remainder
7948 This flag can be used only with @code{iflag}.
7952 These flags are not supported on all systems, and @samp{dd} rejects
7953 attempts to use them when they are not supported. When reading from
7954 standard input or writing to standard output, the @samp{nofollow} and
7955 @samp{noctty} flags should not be specified, and the other flags
7956 (e.g., @samp{nonblock}) can affect how other processes behave with the
7957 affected file descriptors, even after @command{dd} exits.
7961 @cindex multipliers after numbers
7962 The numeric-valued strings above (@var{bytes} and @var{blocks}) can be
7963 followed by a multiplier: @samp{b}=512, @samp{c}=1,
7964 @samp{w}=2, @samp{x@var{m}}=@var{m}, or any of the
7965 standard block size suffixes like @samp{k}=1024 (@pxref{Block size}).
7967 Use different @command{dd} invocations to use different block sizes for
7968 skipping and I/O@. For example, the following shell commands copy data
7969 in 512 KiB blocks between a disk and a tape, but do not save or restore a
7970 4 KiB label at the start of the disk:
7973 disk=/dev/rdsk/c0t1d0s2
7976 # Copy all but the label from disk to tape.
7977 (dd bs=4k skip=1 count=0 && dd bs=512k) <$disk >$tape
7979 # Copy from tape back to disk, but leave the disk label alone.
7980 (dd bs=4k seek=1 count=0 && dd bs=512k) <$tape >$disk
7983 Sending an @samp{INFO} signal to a running @command{dd}
7984 process makes it print I/O statistics to standard error
7985 and then resume copying. In the example below,
7986 @command{dd} is run in the background to copy 10 million blocks.
7987 The @command{kill} command makes it output intermediate I/O statistics,
7988 and when @command{dd} completes normally or is killed by the
7989 @code{SIGINT} signal, it outputs the final statistics.
7992 $ dd if=/dev/zero of=/dev/null count=10MB & pid=$!
7993 $ kill -s INFO $pid; wait $pid
7994 3385223+0 records in
7995 3385223+0 records out
7996 1733234176 bytes (1.7 GB) copied, 6.42173 seconds, 270 MB/s
7997 10000000+0 records in
7998 10000000+0 records out
7999 5120000000 bytes (5.1 GB) copied, 18.913 seconds, 271 MB/s
8002 @vindex POSIXLY_CORRECT
8003 On systems lacking the @samp{INFO} signal @command{dd} responds to the
8004 @samp{USR1} signal instead, unless the @env{POSIXLY_CORRECT}
8005 environment variable is set.
8010 @node install invocation
8011 @section @command{install}: Copy files and set attributes
8014 @cindex copying files and setting attributes
8016 @command{install} copies files while setting their file mode bits and, if
8017 possible, their owner and group. Synopses:
8020 install [@var{option}]@dots{} [-T] @var{source} @var{dest}
8021 install [@var{option}]@dots{} @var{source}@dots{} @var{directory}
8022 install [@var{option}]@dots{} -t @var{directory} @var{source}@dots{}
8023 install [@var{option}]@dots{} -d @var{directory}@dots{}
8028 If two file names are given, @command{install} copies the first file to the
8032 If the @option{--target-directory} (@option{-t}) option is given, or
8033 failing that if the last file is a directory and the
8034 @option{--no-target-directory} (@option{-T}) option is not given,
8035 @command{install} copies each @var{source} file to the specified
8036 directory, using the @var{source}s' names.
8039 If the @option{--directory} (@option{-d}) option is given,
8040 @command{install} creates each @var{directory} and any missing parent
8041 directories. Parent directories are created with mode
8042 @samp{u=rwx,go=rx} (755), regardless of the @option{-m} option or the
8043 current umask. @xref{Directory Setuid and Setgid}, for how the
8044 set-user-ID and set-group-ID bits of parent directories are inherited.
8047 @cindex Makefiles, installing programs in
8048 @command{install} is similar to @command{cp}, but allows you to control the
8049 attributes of destination files. It is typically used in Makefiles to
8050 copy programs into their destination directories. It refuses to copy
8051 files onto themselves.
8053 @cindex extended attributes, xattr
8054 @command{install} never preserves extended attributes (xattr).
8056 The program accepts the following options. Also see @ref{Common options}.
8066 Compare each pair of source and destination files, and if the destination has
8067 identical content and any specified owner, group, permissions, and possibly
8068 SELinux context, then do not modify the destination at all.
8072 Ignored; for compatibility with old Unix versions of @command{install}.
8076 Create any missing parent directories of @var{dest},
8077 then copy @var{source} to @var{dest}.
8078 This option is ignored if a destination directory is specified
8079 via @option{--target-directory=DIR}.
8084 @opindex --directory
8085 @cindex directories, creating with given attributes
8086 @cindex parent directories, creating missing
8087 @cindex leading directories, creating missing
8088 Create any missing parent directories, giving them the default
8089 attributes. Then create each given directory, setting their owner,
8090 group and mode as given on the command line or to the defaults.
8092 @item -g @var{group}
8093 @itemx --group=@var{group}
8096 @cindex group ownership of installed files, setting
8097 Set the group ownership of installed files or directories to
8098 @var{group}. The default is the process's current group. @var{group}
8099 may be either a group name or a numeric group ID.
8102 @itemx --mode=@var{mode}
8105 @cindex permissions of installed files, setting
8106 Set the file mode bits for the installed file or directory to @var{mode},
8107 which can be either an octal number, or a symbolic mode as in
8108 @command{chmod}, with @samp{a=} (no access allowed to anyone) as the
8109 point of departure (@pxref{File permissions}).
8110 The default mode is @samp{u=rwx,go=rx,a-s}---read, write, and
8111 execute for the owner, read and execute for group and other, and with
8112 set-user-ID and set-group-ID disabled.
8113 This default is not quite the same as @samp{755}, since it disables
8114 instead of preserving set-user-ID and set-group-ID on directories.
8115 @xref{Directory Setuid and Setgid}.
8117 @item -o @var{owner}
8118 @itemx --owner=@var{owner}
8121 @cindex ownership of installed files, setting
8122 @cindex appropriate privileges
8123 @vindex root @r{as default owner}
8124 If @command{install} has appropriate privileges (is run as root), set the
8125 ownership of installed files or directories to @var{owner}. The default
8126 is @code{root}. @var{owner} may be either a user name or a numeric user
8129 @item --preserve-context
8130 @opindex --preserve-context
8132 @cindex security context
8133 Preserve the SELinux security context of files and directories.
8134 Failure to preserve the context in all of the files or directories
8135 will result in an exit status of 1. If SELinux is disabled then
8136 print a warning and ignore the option.
8139 @itemx --preserve-timestamps
8141 @opindex --preserve-timestamps
8142 @cindex timestamps of installed files, preserving
8143 Set the time of last access and the time of last modification of each
8144 installed file to match those of each corresponding original file.
8145 When a file is installed without this option, its last access and
8146 last modification times are both set to the time of installation.
8147 This option is useful if you want to use the last modification times
8148 of installed files to keep track of when they were last built as opposed
8149 to when they were last installed.
8155 @cindex symbol table information, stripping
8156 @cindex stripping symbol table information
8157 Strip the symbol tables from installed binary executables.
8159 @itemx --strip-program=@var{program}
8160 @opindex --strip-program
8161 @cindex symbol table information, stripping, program
8162 Program used to strip binaries.
8168 @optNoTargetDirectory
8174 Print the name of each file before copying it.
8176 @item -Z @var{context}
8177 @itemx --context=@var{context}
8181 @cindex security context
8182 Set the default SELinux security context to be used for any
8183 created files and directories. If SELinux is disabled then
8184 print a warning and ignore the option.
8192 @section @command{mv}: Move (rename) files
8196 @command{mv} moves or renames files (or directories). Synopses:
8199 mv [@var{option}]@dots{} [-T] @var{source} @var{dest}
8200 mv [@var{option}]@dots{} @var{source}@dots{} @var{directory}
8201 mv [@var{option}]@dots{} -t @var{directory} @var{source}@dots{}
8206 If two file names are given, @command{mv} moves the first file to the
8210 If the @option{--target-directory} (@option{-t}) option is given, or
8211 failing that if the last file is a directory and the
8212 @option{--no-target-directory} (@option{-T}) option is not given,
8213 @command{mv} moves each @var{source} file to the specified
8214 directory, using the @var{source}s' names.
8217 @command{mv} can move any type of file from one file system to another.
8218 Prior to version @code{4.0} of the fileutils,
8219 @command{mv} could move only regular files between file systems.
8220 For example, now @command{mv} can move an entire directory hierarchy
8221 including special device files from one partition to another. It first
8222 uses some of the same code that's used by @code{cp -a} to copy the
8223 requested directories and files, then (assuming the copy succeeded)
8224 it removes the originals. If the copy fails, then the part that was
8225 copied to the destination partition is removed. If you were to copy
8226 three directories from one partition to another and the copy of the first
8227 directory succeeded, but the second didn't, the first would be left on
8228 the destination partition and the second and third would be left on the
8231 @cindex extended attributes, xattr
8232 @command{mv} always tries to copy extended attributes (xattr).
8234 @cindex prompting, and @command{mv}
8235 If a destination file exists but is normally unwritable, standard input
8236 is a terminal, and the @option{-f} or @option{--force} option is not given,
8237 @command{mv} prompts the user for whether to replace the file. (You might
8238 own the file, or have write permission on its directory.) If the
8239 response is not affirmative, the file is skipped.
8241 @emph{Warning}: Avoid specifying a source name with a trailing slash,
8242 when it might be a symlink to a directory.
8243 Otherwise, @command{mv} may do something very surprising, since
8244 its behavior depends on the underlying rename system call.
8245 On a system with a modern Linux-based kernel, it fails with @code{errno=ENOTDIR}.
8246 However, on other systems (at least FreeBSD 6.1 and Solaris 10) it silently
8247 renames not the symlink but rather the directory referenced by the symlink.
8248 @xref{Trailing slashes}.
8250 The program accepts the following options. Also see @ref{Common options}.
8260 @cindex prompts, omitting
8261 Do not prompt the user before removing a destination file.
8263 If you specify more than one of the @option{-i}, @option{-f}, @option{-n}
8264 options, only the final one takes effect.
8269 @itemx --interactive
8271 @opindex --interactive
8272 @cindex prompts, forcing
8273 Prompt whether to overwrite each existing destination file, regardless
8275 If the response is not affirmative, the file is skipped.
8281 @opindex --no-clobber
8282 @cindex prompts, omitting
8283 Do not overwrite an existing file.
8285 This option is mutually exclusive with @option{-b} or @option{--backup} option.
8291 @cindex newer files, moving only
8292 Do not move a non-directory that has an existing destination with the
8293 same or newer modification time.
8294 If the move is across file system boundaries, the comparison is to the
8295 source time stamp truncated to the resolutions of the destination file
8296 system and of the system calls used to update time stamps; this avoids
8297 duplicate work if several @samp{mv -u} commands are executed with the
8298 same source and destination.
8304 Print the name of each file before moving it.
8306 @optStripTrailingSlashes
8312 @optNoTargetDirectory
8320 @section @command{rm}: Remove files or directories
8323 @cindex removing files or directories
8325 @command{rm} removes each given @var{file}. By default, it does not remove
8326 directories. Synopsis:
8329 rm [@var{option}]@dots{} [@var{file}]@dots{}
8332 @cindex prompting, and @command{rm}
8333 If the @option{-I} or @option{--interactive=once} option is given,
8334 and there are more than three files or the @option{-r}, @option{-R},
8335 or @option{--recursive} are given, then @command{rm} prompts the user
8336 for whether to proceed with the entire operation. If the response is
8337 not affirmative, the entire command is aborted.
8339 Otherwise, if a file is unwritable, standard input is a terminal, and
8340 the @option{-f} or @option{--force} option is not given, or the
8341 @option{-i} or @option{--interactive=always} option @emph{is} given,
8342 @command{rm} prompts the user for whether to remove the file.
8343 If the response is not affirmative, the file is skipped.
8345 Any attempt to remove a file whose last file name component is
8346 @file{.} or @file{..} is rejected without any prompting.
8348 @emph{Warning}: If you use @command{rm} to remove a file, it is usually
8349 possible to recover the contents of that file. If you want more assurance
8350 that the contents are truly unrecoverable, consider using @command{shred}.
8352 The program accepts the following options. Also see @ref{Common options}.
8360 Ignore nonexistent files and never prompt the user.
8361 Ignore any previous @option{--interactive} (@option{-i}) option.
8365 Prompt whether to remove each file.
8366 If the response is not affirmative, the file is skipped.
8367 Ignore any previous @option{--force} (@option{-f}) option.
8368 Equivalent to @option{--interactive=always}.
8372 Prompt once whether to proceed with the command, if more than three
8373 files are named or if a recursive removal is requested. Ignore any
8374 previous @option{--force} (@option{-f}) option. Equivalent to
8375 @option{--interactive=once}.
8377 @itemx --interactive [=@var{when}]
8378 @opindex --interactive
8379 Specify when to issue an interactive prompt. @var{when} may be
8383 @vindex never @r{interactive option}
8384 - Do not prompt at all.
8386 @vindex once @r{interactive option}
8387 - Prompt once if more than three files are named or if a recursive
8388 removal is requested. Equivalent to @option{-I}.
8390 @vindex always @r{interactive option}
8391 - Prompt for every file being removed. Equivalent to @option{-i}.
8393 @option{--interactive} with no @var{when} is equivalent to
8394 @option{--interactive=always}.
8396 @itemx --one-file-system
8397 @opindex --one-file-system
8398 @cindex one file system, restricting @command{rm} to
8399 When removing a hierarchy recursively, skip any directory that is on a
8400 file system different from that of the corresponding command line argument.
8402 This option is useful when removing a build ``chroot'' hierarchy,
8403 which normally contains no valuable data. However, it is not uncommon
8404 to bind-mount @file{/home} into such a hierarchy, to make it easier to
8405 use one's start-up file. The catch is that it's easy to forget to
8406 unmount @file{/home}. Then, when you use @command{rm -rf} to remove
8407 your normally throw-away chroot, that command will remove everything
8408 under @file{/home}, too.
8409 Use the @option{--one-file-system} option, and it will
8410 warn about and skip directories on other file systems.
8411 Of course, this will not save your @file{/home} if it and your
8412 chroot happen to be on the same file system.
8414 @itemx --preserve-root
8415 @opindex --preserve-root
8416 @cindex root directory, disallow recursive destruction
8417 Fail upon any attempt to remove the root directory, @file{/},
8418 when used with the @option{--recursive} option.
8419 This is the default behavior.
8420 @xref{Treating / specially}.
8422 @itemx --no-preserve-root
8423 @opindex --no-preserve-root
8424 @cindex root directory, allow recursive destruction
8425 Do not treat @file{/} specially when removing recursively.
8426 This option is not recommended unless you really want to
8427 remove all the files on your computer.
8428 @xref{Treating / specially}.
8435 @opindex --recursive
8436 @cindex directories, removing (recursively)
8437 Remove the listed directories and their contents recursively.
8443 Print the name of each file before removing it.
8447 @cindex files beginning with @samp{-}, removing
8448 @cindex @samp{-}, removing files beginning with
8449 One common question is how to remove files whose names begin with a
8450 @samp{-}. @sc{gnu} @command{rm}, like every program that uses the @code{getopt}
8451 function to parse its arguments, lets you use the @samp{--} option to
8452 indicate that all following arguments are non-options. To remove a file
8453 called @file{-f} in the current directory, you could type either:
8466 @opindex - @r{and Unix @command{rm}}
8467 The Unix @command{rm} program's use of a single @samp{-} for this purpose
8468 predates the development of the getopt standard syntax.
8473 @node shred invocation
8474 @section @command{shred}: Remove files more securely
8477 @cindex data, erasing
8478 @cindex erasing data
8480 @command{shred} overwrites devices or files, to help prevent even
8481 very expensive hardware from recovering the data.
8483 Ordinarily when you remove a file (@pxref{rm invocation}), the data is
8484 not actually destroyed. Only the index listing where the file is
8485 stored is destroyed, and the storage is made available for reuse.
8486 There are undelete utilities that will attempt to reconstruct the index
8487 and can bring the file back if the parts were not reused.
8489 On a busy system with a nearly-full drive, space can get reused in a few
8490 seconds. But there is no way to know for sure. If you have sensitive
8491 data, you may want to be sure that recovery is not possible by actually
8492 overwriting the file with non-sensitive data.
8494 However, even after doing that, it is possible to take the disk back
8495 to a laboratory and use a lot of sensitive (and expensive) equipment
8496 to look for the faint ``echoes'' of the original data underneath the
8497 overwritten data. If the data has only been overwritten once, it's not
8500 The best way to remove something irretrievably is to destroy the media
8501 it's on with acid, melt it down, or the like. For cheap removable media
8502 like floppy disks, this is the preferred method. However, hard drives
8503 are expensive and hard to melt, so the @command{shred} utility tries
8504 to achieve a similar effect non-destructively.
8506 This uses many overwrite passes, with the data patterns chosen to
8507 maximize the damage they do to the old data. While this will work on
8508 floppies, the patterns are designed for best effect on hard drives.
8509 For more details, see the source code and Peter Gutmann's paper
8510 @uref{http://www.cs.auckland.ac.nz/~pgut001/pubs/secure_del.html,
8511 @cite{Secure Deletion of Data from Magnetic and Solid-State Memory}},
8512 from the proceedings of the Sixth @acronym{USENIX} Security Symposium (San Jose,
8513 California, July 22--25, 1996).
8515 @strong{Please note} that @command{shred} relies on a very important assumption:
8516 that the file system overwrites data in place. This is the traditional
8517 way to do things, but many modern file system designs do not satisfy this
8518 assumption. Exceptions include:
8523 Log-structured or journaled file systems, such as those supplied with
8524 AIX and Solaris, and JFS, ReiserFS, XFS, Ext3 (in @code{data=journal} mode),
8525 BFS, NTFS, etc.@: when they are configured to journal @emph{data}.
8528 File systems that write redundant data and carry on even if some writes
8529 fail, such as RAID-based file systems.
8532 File systems that make snapshots, such as Network Appliance's NFS server.
8535 File systems that cache in temporary locations, such as NFS version 3
8539 Compressed file systems.
8542 In the particular case of ext3 file systems, the above disclaimer applies (and
8543 @command{shred} is thus of limited effectiveness) only in @code{data=journal}
8544 mode, which journals file data in addition to just metadata. In both
8545 the @code{data=ordered} (default) and @code{data=writeback} modes,
8546 @command{shred} works as usual. Ext3 journaling modes can be changed
8547 by adding the @code{data=something} option to the mount options for a
8548 particular file system in the @file{/etc/fstab} file, as documented in
8549 the mount man page (man mount).
8551 If you are not sure how your file system operates, then you should assume
8552 that it does not overwrite data in place, which means that shred cannot
8553 reliably operate on regular files in your file system.
8555 Generally speaking, it is more reliable to shred a device than a file,
8556 since this bypasses the problem of file system design mentioned above.
8557 However, even shredding devices is not always completely reliable. For
8558 example, most disks map out bad sectors invisibly to the application; if
8559 the bad sectors contain sensitive data, @command{shred} won't be able to
8562 @command{shred} makes no attempt to detect or report this problem, just as
8563 it makes no attempt to do anything about backups. However, since it is
8564 more reliable to shred devices than files, @command{shred} by default does
8565 not truncate or remove the output file. This default is more suitable
8566 for devices, which typically cannot be truncated and should not be
8569 Finally, consider the risk of backups and mirrors.
8570 File system backups and remote mirrors may contain copies of the
8571 file that cannot be removed, and that will allow a shredded file
8572 to be recovered later. So if you keep any data you may later want
8573 to destroy using @command{shred}, be sure that it is not backed up or mirrored.
8576 shred [@var{option}]@dots{} @var{file}[@dots{}]
8579 The program accepts the following options. Also see @ref{Common options}.
8587 @cindex force deletion
8588 Override file permissions if necessary to allow overwriting.
8591 @itemx -n @var{number}
8592 @itemx --iterations=@var{number}
8593 @opindex -n @var{number}
8594 @opindex --iterations=@var{number}
8595 @cindex iterations, selecting the number of
8596 By default, @command{shred} uses @value{SHRED_DEFAULT_PASSES} passes of
8597 overwrite. You can reduce this to save time, or increase it if you think it's
8598 appropriate. After 25 passes all of the internal overwrite patterns will have
8599 been used at least once.
8601 @item --random-source=@var{file}
8602 @opindex --random-source
8603 @cindex random source for shredding
8604 Use @var{file} as a source of random data used to overwrite and to
8605 choose pass ordering. @xref{Random sources}.
8607 @item -s @var{bytes}
8608 @itemx --size=@var{bytes}
8609 @opindex -s @var{bytes}
8610 @opindex --size=@var{bytes}
8611 @cindex size of file to shred
8612 Shred the first @var{bytes} bytes of the file. The default is to shred
8613 the whole file. @var{bytes} can be followed by a size specification like
8614 @samp{K}, @samp{M}, or @samp{G} to specify a multiple. @xref{Block size}.
8620 @cindex removing files after shredding
8621 After shredding a file, truncate it (if possible) and then remove it.
8622 If a file has multiple links, only the named links will be removed.
8628 Display to standard error all status updates as sterilization proceeds.
8634 By default, @command{shred} rounds the size of a regular file up to the next
8635 multiple of the file system block size to fully erase the last block of the file.
8636 Use @option{--exact} to suppress that behavior.
8637 Thus, by default if you shred a 10-byte regular file on a system with 512-byte
8638 blocks, the resulting file will be 512 bytes long. With this option,
8639 shred does not increase the apparent size of the file.
8645 Normally, the last pass that @command{shred} writes is made up of
8646 random data. If this would be conspicuous on your hard drive (for
8647 example, because it looks like encrypted data), or you just think
8648 it's tidier, the @option{--zero} option adds an additional overwrite pass with
8649 all zero bits. This is in addition to the number of passes specified
8650 by the @option{--iterations} option.
8654 You might use the following command to erase all trace of the
8655 file system you'd created on the floppy disk in your first drive.
8656 That command takes about 20 minutes to erase a ``1.44MB'' (actually
8660 shred --verbose /dev/fd0
8663 Similarly, to erase all data on a selected partition of
8664 your hard disk, you could give a command like this:
8667 shred --verbose /dev/sda5
8670 A @var{file} of @samp{-} denotes standard output.
8671 The intended use of this is to shred a removed temporary file.
8675 i=`tempfile -m 0600`
8678 echo "Hello, world" >&3
8683 However, the command @samp{shred - >file} does not shred the contents
8684 of @var{file}, since the shell truncates @var{file} before invoking
8685 @command{shred}. Use the command @samp{shred file} or (if using a
8686 Bourne-compatible shell) the command @samp{shred - 1<>file} instead.
8691 @node Special file types
8692 @chapter Special file types
8694 @cindex special file types
8695 @cindex file types, special
8697 This chapter describes commands which create special types of files (and
8698 @command{rmdir}, which removes directories, one special file type).
8700 @cindex special file types
8702 Although Unix-like operating systems have markedly fewer special file
8703 types than others, not @emph{everything} can be treated only as the
8704 undifferentiated byte stream of @dfn{normal files}. For example, when a
8705 file is created or removed, the system must record this information,
8706 which it does in a @dfn{directory}---a special type of file. Although
8707 you can read directories as normal files, if you're curious, in order
8708 for the system to do its job it must impose a structure, a certain
8709 order, on the bytes of the file. Thus it is a ``special'' type of file.
8711 Besides directories, other special file types include named pipes
8712 (FIFOs), symbolic links, sockets, and so-called @dfn{special files}.
8715 * link invocation:: Make a hard link via the link syscall
8716 * ln invocation:: Make links between files.
8717 * mkdir invocation:: Make directories.
8718 * mkfifo invocation:: Make FIFOs (named pipes).
8719 * mknod invocation:: Make block or character special files.
8720 * readlink invocation:: Print value of a symlink or canonical file name.
8721 * rmdir invocation:: Remove empty directories.
8722 * unlink invocation:: Remove files via the unlink syscall
8726 @node link invocation
8727 @section @command{link}: Make a hard link via the link syscall
8730 @cindex links, creating
8731 @cindex hard links, creating
8732 @cindex creating links (hard only)
8734 @command{link} creates a single hard link at a time.
8735 It is a minimalist interface to the system-provided
8736 @code{link} function. @xref{Hard Links, , , libc,
8737 The GNU C Library Reference Manual}.
8738 It avoids the bells and whistles of the more commonly-used
8739 @command{ln} command (@pxref{ln invocation}).
8743 link @var{filename} @var{linkname}
8746 @var{filename} must specify an existing file, and @var{linkname}
8747 must specify a nonexistent entry in an existing directory.
8748 @command{link} simply calls @code{link (@var{filename}, @var{linkname})}
8751 On a @acronym{GNU} system, this command acts like @samp{ln --directory
8752 --no-target-directory @var{filename} @var{linkname}}. However, the
8753 @option{--directory} and @option{--no-target-directory} options are
8754 not specified by @acronym{POSIX}, and the @command{link} command is
8755 more portable in practice.
8757 If @var{filename} is a symbolic link, it is unspecified whether
8758 @var{linkname} will be a hard link to the symbolic link or to the
8759 target of the symbolic link. Use @command{ln -P} or @command{ln -L}
8760 to specify which behavior is desired.
8766 @section @command{ln}: Make links between files
8769 @cindex links, creating
8770 @cindex hard links, creating
8771 @cindex symbolic (soft) links, creating
8772 @cindex creating links (hard or soft)
8774 @cindex file systems and hard links
8775 @command{ln} makes links between files. By default, it makes hard links;
8776 with the @option{-s} option, it makes symbolic (or @dfn{soft}) links.
8780 ln [@var{option}]@dots{} [-T] @var{target} @var{linkname}
8781 ln [@var{option}]@dots{} @var{target}
8782 ln [@var{option}]@dots{} @var{target}@dots{} @var{directory}
8783 ln [@var{option}]@dots{} -t @var{directory} @var{target}@dots{}
8789 If two file names are given, @command{ln} creates a link to the first
8790 file from the second.
8793 If one @var{target} is given, @command{ln} creates a link to that file
8794 in the current directory.
8797 If the @option{--target-directory} (@option{-t}) option is given, or
8798 failing that if the last file is a directory and the
8799 @option{--no-target-directory} (@option{-T}) option is not given,
8800 @command{ln} creates a link to each @var{target} file in the specified
8801 directory, using the @var{target}s' names.
8805 Normally @command{ln} does not remove existing files. Use the
8806 @option{--force} (@option{-f}) option to remove them unconditionally,
8807 the @option{--interactive} (@option{-i}) option to remove them
8808 conditionally, and the @option{--backup} (@option{-b}) option to
8811 @cindex hard link, defined
8812 @cindex inode, and hard links
8813 A @dfn{hard link} is another name for an existing file; the link and the
8814 original are indistinguishable. Technically speaking, they share the
8815 same inode, and the inode contains all the information about a
8816 file---indeed, it is not incorrect to say that the inode @emph{is} the
8817 file. Most systems prohibit making a hard link to
8818 a directory; on those where it is allowed, only the super-user can do
8819 so (and with caution, since creating a cycle will cause problems to many
8820 other utilities). Hard links cannot cross file system boundaries. (These
8821 restrictions are not mandated by @acronym{POSIX}, however.)
8823 @cindex dereferencing symbolic links
8824 @cindex symbolic link, defined
8825 @dfn{Symbolic links} (@dfn{symlinks} for short), on the other hand, are
8826 a special file type (which not all kernels support: System V release 3
8827 (and older) systems lack symlinks) in which the link file actually
8828 refers to a different file, by name. When most operations (opening,
8829 reading, writing, and so on) are passed the symbolic link file, the
8830 kernel automatically @dfn{dereferences} the link and operates on the
8831 target of the link. But some operations (e.g., removing) work on the
8832 link file itself, rather than on its target. The owner and group of a
8833 symlink are not significant to file access performed through
8834 the link, but do have implications on deleting a symbolic link from a
8835 directory with the restricted deletion bit set. On the GNU system,
8836 the mode of a symlink has no significance and cannot be changed, but
8837 on some BSD systems, the mode can be changed and will affect whether
8838 the symlink will be traversed in file name resolution. @xref{Symbolic Links,,,
8839 libc, The GNU C Library Reference Manual}.
8841 Symbolic links can contain arbitrary strings; a @dfn{dangling symlink}
8842 occurs when the string in the symlink does not resolve to a file.
8843 There are no restrictions against creating dangling symbolic links.
8844 There are trade-offs to using absolute or relative symlinks. An
8845 absolute symlink always points to the same file, even if the directory
8846 containing the link is moved. However, if the symlink is visible from
8847 more than one machine (such as on a networked file system), the file
8848 pointed to might not always be the same. A relative symbolic link is
8849 resolved in relation to the directory that contains the link, and is
8850 often useful in referring to files on the same device without regards
8851 to what name that device is mounted on when accessed via networked
8854 When creating a relative symlink in a different location than the
8855 current directory, the resolution of the symlink will be different
8856 than the resolution of the same string from the current directory.
8857 Therefore, many users prefer to first change directories to the
8858 location where the relative symlink will be created, so that
8859 tab-completion or other file resolution will find the same target as
8860 what will be placed in the symlink.
8862 The program accepts the following options. Also see @ref{Common options}.
8873 @opindex --directory
8874 @cindex hard links to directories
8875 Allow users with appropriate privileges to attempt to make hard links
8877 However, note that this will probably fail due to
8878 system restrictions, even for the super-user.
8884 Remove existing destination files.
8887 @itemx --interactive
8889 @opindex --interactive
8890 @cindex prompting, and @command{ln}
8891 Prompt whether to remove existing destination files.
8897 If @option{-s} is not in effect, and the source file is a symbolic
8898 link, create the hard link to the file referred to by the symbolic
8899 link, rather than the symbolic link itself.
8902 @itemx --no-dereference
8904 @opindex --no-dereference
8905 Do not treat the last operand specially when it is a symbolic link to
8906 a directory. Instead, treat it as if it were a normal file.
8908 When the destination is an actual directory (not a symlink to one),
8909 there is no ambiguity. The link is created in that directory.
8910 But when the specified destination is a symlink to a directory,
8911 there are two ways to treat the user's request. @command{ln} can
8912 treat the destination just as it would a normal directory and create
8913 the link in it. On the other hand, the destination can be viewed as a
8914 non-directory---as the symlink itself. In that case, @command{ln}
8915 must delete or backup that symlink before creating the new link.
8916 The default is to treat a destination that is a symlink to a directory
8917 just like a directory.
8919 This option is weaker than the @option{--no-target-directory}
8920 (@option{-T}) option, so it has no effect if both options are given.
8926 If @option{-s} is not in effect, and the source file is a symbolic
8927 link, create the hard link to the symbolic link itself. On platforms
8928 where this is not supported by the kernel, this option creates a
8929 symbolic link with identical contents; since symbolic link contents
8930 cannot be edited, any file name resolution performed through either
8931 link will be the same as if a hard link had been created.
8937 Make symbolic links instead of hard links. This option merely produces
8938 an error message on systems that do not support symbolic links.
8944 @optNoTargetDirectory
8950 Print the name of each file after linking it successfully.
8954 @cindex hard links to symbolic links
8955 @cindex symbolic links and @command{ln}
8956 If @option{-L} and @option{-P} are both given, the last one takes
8957 precedence. If @option{-s} is also given, @option{-L} and @option{-P}
8958 are silently ignored. If neither option is given, then this
8959 implementation defaults to @option{-P} if the system @code{link} supports
8960 hard links to symbolic links (such as the GNU system), and @option{-L}
8961 if @code{link} follows symbolic links (such as on BSD).
8970 # Create link ../a pointing to a in that directory.
8971 # Not really useful because it points to itself.
8976 # Change to the target before creating symlinks to avoid being confused.
8982 # Hard coded file names don't move well.
8983 ln -s $(pwd)/a /some/dir/
8987 # Relative file names survive directory moves and also
8988 # work across networked file systems.
8989 ln -s afile anotherfile
8990 ln -s ../adir/afile yetanotherfile
8994 @node mkdir invocation
8995 @section @command{mkdir}: Make directories
8998 @cindex directories, creating
8999 @cindex creating directories
9001 @command{mkdir} creates directories with the specified names. Synopsis:
9004 mkdir [@var{option}]@dots{} @var{name}@dots{}
9007 @command{mkdir} creates each directory @var{name} in the order given.
9008 It reports an error if @var{name} already exists, unless the
9009 @option{-p} option is given and @var{name} is a directory.
9011 The program accepts the following options. Also see @ref{Common options}.
9016 @itemx --mode=@var{mode}
9019 @cindex modes of created directories, setting
9020 Set the file permission bits of created directories to @var{mode},
9021 which uses the same syntax as
9022 in @command{chmod} and uses @samp{a=rwx} (read, write and execute allowed for
9023 everyone) for the point of the departure. @xref{File permissions}.
9025 Normally the directory has the desired file mode bits at the moment it
9026 is created. As a @acronym{GNU} extension, @var{mode} may also mention
9027 special mode bits, but in this case there may be a temporary window
9028 during which the directory exists but its special mode bits are
9029 incorrect. @xref{Directory Setuid and Setgid}, for how the
9030 set-user-ID and set-group-ID bits of directories are inherited unless
9031 overridden in this way.
9037 @cindex parent directories, creating
9038 Make any missing parent directories for each argument, setting their
9039 file permission bits to the umask modified by @samp{u+wx}. Ignore
9040 existing parent directories, and do not change their file permission
9043 To set the file permission bits of any newly-created parent
9044 directories to a value that includes @samp{u+wx}, you can set the
9045 umask before invoking @command{mkdir}. For example, if the shell
9046 command @samp{(umask u=rwx,go=rx; mkdir -p P/Q)} creates the parent
9047 @file{P} it sets the parent's permission bits to @samp{u=rwx,go=rx}.
9048 To set a parent's special mode bits as well, you can invoke
9049 @command{chmod} after @command{mkdir}. @xref{Directory Setuid and
9050 Setgid}, for how the set-user-ID and set-group-ID bits of
9051 newly-created parent directories are inherited.
9057 Print a message for each created directory. This is most useful with
9060 @item -Z @var{context}
9061 @itemx --context=@var{context}
9065 @cindex security context
9066 Set the default SELinux security context to be used for created directories.
9073 @node mkfifo invocation
9074 @section @command{mkfifo}: Make FIFOs (named pipes)
9077 @cindex FIFOs, creating
9078 @cindex named pipes, creating
9079 @cindex creating FIFOs (named pipes)
9081 @command{mkfifo} creates FIFOs (also called @dfn{named pipes}) with the
9082 specified names. Synopsis:
9085 mkfifo [@var{option}] @var{name}@dots{}
9088 A @dfn{FIFO} is a special file type that permits independent processes
9089 to communicate. One process opens the FIFO file for writing, and
9090 another for reading, after which data can flow as with the usual
9091 anonymous pipe in shells or elsewhere.
9093 The program accepts the following option. Also see @ref{Common options}.
9098 @itemx --mode=@var{mode}
9101 @cindex modes of created FIFOs, setting
9102 Set the mode of created FIFOs to @var{mode}, which is symbolic as in
9103 @command{chmod} and uses @samp{a=rw} (read and write allowed for everyone)
9104 for the point of departure. @var{mode} should specify only file
9105 permission bits. @xref{File permissions}.
9107 @item -Z @var{context}
9108 @itemx --context=@var{context}
9112 @cindex security context
9113 Set the default SELinux security context to be used for created FIFOs.
9120 @node mknod invocation
9121 @section @command{mknod}: Make block or character special files
9124 @cindex block special files, creating
9125 @cindex character special files, creating
9127 @command{mknod} creates a FIFO, character special file, or block special
9128 file with the specified name. Synopsis:
9131 mknod [@var{option}]@dots{} @var{name} @var{type} [@var{major} @var{minor}]
9134 @cindex special files
9135 @cindex block special files
9136 @cindex character special files
9137 Unlike the phrase ``special file type'' above, the term @dfn{special
9138 file} has a technical meaning on Unix: something that can generate or
9139 receive data. Usually this corresponds to a physical piece of hardware,
9140 e.g., a printer or a disk. (These files are typically created at
9141 system-configuration time.) The @command{mknod} command is what creates
9142 files of this type. Such devices can be read either a character at a
9143 time or a ``block'' (many characters) at a time, hence we say there are
9144 @dfn{block special} files and @dfn{character special} files.
9146 @c mknod is a shell built-in at least with OpenBSD's /bin/sh
9147 @mayConflictWithShellBuiltIn{mknod}
9149 The arguments after @var{name} specify the type of file to make:
9154 @opindex p @r{for FIFO file}
9158 @opindex b @r{for block special file}
9159 for a block special file
9162 @c Don't document the `u' option -- it's just a synonym for `c'.
9163 @c Do *any* versions of mknod still use it?
9165 @opindex c @r{for character special file}
9166 @c @opindex u @r{for character special file}
9167 for a character special file
9171 When making a block or character special file, the major and minor
9172 device numbers must be given after the file type.
9173 If a major or minor device number begins with @samp{0x} or @samp{0X},
9174 it is interpreted as hexadecimal; otherwise, if it begins with @samp{0},
9175 as octal; otherwise, as decimal.
9177 The program accepts the following option. Also see @ref{Common options}.
9182 @itemx --mode=@var{mode}
9185 Set the mode of created files to @var{mode}, which is symbolic as in
9186 @command{chmod} and uses @samp{a=rw} as the point of departure.
9187 @var{mode} should specify only file permission bits.
9188 @xref{File permissions}.
9190 @item -Z @var{context}
9191 @itemx --context=@var{context}
9195 @cindex security context
9196 Set the default SELinux security context to be used for created files.
9203 @node readlink invocation
9204 @section @command{readlink}: Print value of a symlink or canonical file name
9207 @cindex displaying value of a symbolic link
9208 @cindex canonical file name
9209 @cindex canonicalize a file name
9213 @command{readlink} may work in one of two supported modes:
9219 @command{readlink} outputs the value of the given symbolic link.
9220 If @command{readlink} is invoked with an argument other than the name
9221 of a symbolic link, it produces no output and exits with a nonzero exit code.
9223 @item Canonicalize mode
9225 @command{readlink} outputs the absolute name of the given file which contains
9226 no @file{.}, @file{..} components nor any repeated separators
9227 (@file{/}) or symbolic links.
9232 readlink [@var{option}] @var{file}
9235 By default, @command{readlink} operates in readlink mode.
9237 The program accepts the following options. Also see @ref{Common options}.
9242 @itemx --canonicalize
9244 @opindex --canonicalize
9245 Activate canonicalize mode.
9246 If any component of the file name except the last one is missing or unavailable,
9247 @command{readlink} produces no output and exits with a nonzero exit
9248 code. A trailing slash is ignored.
9251 @itemx --canonicalize-existing
9253 @opindex --canonicalize-existing
9254 Activate canonicalize mode.
9255 If any component is missing or unavailable, @command{readlink} produces
9256 no output and exits with a nonzero exit code. A trailing slash
9257 requires that the name resolve to a directory.
9260 @itemx --canonicalize-missing
9262 @opindex --canonicalize-missing
9263 Activate canonicalize mode.
9264 If any component is missing or unavailable, @command{readlink} treats it
9270 @opindex --no-newline
9271 Do not output the trailing newline.
9281 Suppress most error messages.
9287 Report error messages.
9291 The @command{readlink} utility first appeared in OpenBSD 2.1.
9293 There is a @command{realpath} command on some systems
9294 which operates like @command{readlink} in canonicalize mode.
9299 @node rmdir invocation
9300 @section @command{rmdir}: Remove empty directories
9303 @cindex removing empty directories
9304 @cindex directories, removing empty
9306 @command{rmdir} removes empty directories. Synopsis:
9309 rmdir [@var{option}]@dots{} @var{directory}@dots{}
9312 If any @var{directory} argument does not refer to an existing empty
9313 directory, it is an error.
9315 The program accepts the following options. Also see @ref{Common options}.
9319 @item --ignore-fail-on-non-empty
9320 @opindex --ignore-fail-on-non-empty
9321 @cindex directory deletion, ignoring failures
9322 Ignore each failure to remove a directory that is solely because
9323 the directory is non-empty.
9329 @cindex parent directories, removing
9330 Remove @var{directory}, then try to remove each component of @var{directory}.
9331 So, for example, @samp{rmdir -p a/b/c} is similar to @samp{rmdir a/b/c a/b a}.
9332 As such, it fails if any of those directories turns out not to be empty.
9333 Use the @option{--ignore-fail-on-non-empty} option to make it so such
9334 a failure does not evoke a diagnostic and does not cause @command{rmdir} to
9335 exit unsuccessfully.
9341 @cindex directory deletion, reporting
9342 Give a diagnostic for each successful removal.
9343 @var{directory} is removed.
9347 @xref{rm invocation}, for how to remove non-empty directories (recursively).
9352 @node unlink invocation
9353 @section @command{unlink}: Remove files via the unlink syscall
9356 @cindex removing files or directories (via the unlink syscall)
9358 @command{unlink} deletes a single specified file name.
9359 It is a minimalist interface to the system-provided
9360 @code{unlink} function. @xref{Deleting Files, , , libc,
9361 The GNU C Library Reference Manual}. Synopsis:
9362 It avoids the bells and whistles of the more commonly-used
9363 @command{rm} command (@pxref{rm invocation}).
9366 unlink @var{filename}
9369 On some systems @code{unlink} can be used to delete the name of a
9370 directory. On others, it can be used that way only by a privileged user.
9371 In the GNU system @code{unlink} can never delete the name of a directory.
9373 The @command{unlink} command honors the @option{--help} and
9374 @option{--version} options. To remove a file whose name begins with
9375 @samp{-}, prefix the name with @samp{./}, e.g., @samp{unlink ./--help}.
9380 @node Changing file attributes
9381 @chapter Changing file attributes
9383 @cindex changing file attributes
9384 @cindex file attributes, changing
9385 @cindex attributes, file
9387 A file is not merely its contents, a name, and a file type
9388 (@pxref{Special file types}). A file also has an owner (a user ID), a
9389 group (a group ID), permissions (what the owner can do with the file,
9390 what people in the group can do, and what everyone else can do), various
9391 timestamps, and other information. Collectively, we call these a file's
9394 These commands change file attributes.
9397 * chgrp invocation:: Change file groups.
9398 * chmod invocation:: Change access permissions.
9399 * chown invocation:: Change file owners and groups.
9400 * touch invocation:: Change file timestamps.
9404 @node chown invocation
9405 @section @command{chown}: Change file owner and group
9408 @cindex file ownership, changing
9409 @cindex group ownership, changing
9410 @cindex changing file ownership
9411 @cindex changing group ownership
9413 @command{chown} changes the user and/or group ownership of each given @var{file}
9414 to @var{new-owner} or to the user and group of an existing reference file.
9418 chown [@var{option}]@dots{} @{@var{new-owner} | --reference=@var{ref_file}@} @var{file}@dots{}
9421 If used, @var{new-owner} specifies the new owner and/or group as follows
9422 (with no embedded white space):
9425 [@var{owner}] [ : [@var{group}] ]
9432 If only an @var{owner} (a user name or numeric user ID) is given, that
9433 user is made the owner of each given file, and the files' group is not
9436 @item owner@samp{:}group
9437 If the @var{owner} is followed by a colon and a @var{group} (a
9438 group name or numeric group ID), with no spaces between them, the group
9439 ownership of the files is changed as well (to @var{group}).
9442 If a colon but no group name follows @var{owner}, that user is
9443 made the owner of the files and the group of the files is changed to
9444 @var{owner}'s login group.
9447 If the colon and following @var{group} are given, but the owner
9448 is omitted, only the group of the files is changed; in this case,
9449 @command{chown} performs the same function as @command{chgrp}.
9452 If only a colon is given, or if @var{new-owner} is empty, neither the
9453 owner nor the group is changed.
9457 If @var{owner} or @var{group} is intended to represent a numeric user
9458 or group ID, then you may specify it with a leading @samp{+}.
9459 @xref{Disambiguating names and IDs}.
9461 Some older scripts may still use @samp{.} in place of the @samp{:} separator.
9462 @acronym{POSIX} 1003.1-2001 (@pxref{Standards conformance}) does not
9463 require support for that, but for backward compatibility @acronym{GNU}
9464 @command{chown} supports @samp{.} so long as no ambiguity results.
9465 New scripts should avoid the use of @samp{.} because it is not
9466 portable, and because it has undesirable results if the entire
9467 @var{owner@samp{.}group} happens to identify a user whose name
9470 The @command{chown} command sometimes clears the set-user-ID or
9471 set-group-ID permission bits. This behavior depends on the policy and
9472 functionality of the underlying @code{chown} system call, which may
9473 make system-dependent file mode modifications outside the control of
9474 the @command{chown} command. For example, the @command{chown} command
9475 might not affect those bits when invoked by a user with appropriate
9476 privileges, or when the
9477 bits signify some function other than executable permission (e.g.,
9479 When in doubt, check the underlying system behavior.
9481 The program accepts the following options. Also see @ref{Common options}.
9489 @cindex changed owners, verbosely describing
9490 Verbosely describe the action for each @var{file} whose ownership
9499 @cindex error messages, omitting
9500 Do not print error messages about files whose ownership cannot be
9503 @itemx @w{@kbd{--from}=@var{old-owner}}
9505 @cindex symbolic links, changing owner
9506 Change a @var{file}'s ownership only if it has current attributes specified
9507 by @var{old-owner}. @var{old-owner} has the same form as @var{new-owner}
9509 This option is useful primarily from a security standpoint in that
9510 it narrows considerably the window of potential abuse.
9511 For example, to reflect a user ID numbering change for one user's files
9512 without an option like this, @code{root} might run
9515 find / -owner OLDUSER -print0 | xargs -0 chown -h NEWUSER
9518 But that is dangerous because the interval between when the @command{find}
9519 tests the existing file's owner and when the @command{chown} is actually run
9521 One way to narrow the gap would be to invoke chown for each file
9525 find / -owner OLDUSER -exec chown -h NEWUSER @{@} \;
9528 But that is very slow if there are many affected files.
9529 With this option, it is safer (the gap is narrower still)
9530 though still not perfect:
9533 chown -h -R --from=OLDUSER NEWUSER /
9537 @opindex --dereference
9538 @cindex symbolic links, changing owner
9540 Do not act on symbolic links themselves but rather on what they point to.
9541 This is the default.
9544 @itemx --no-dereference
9546 @opindex --no-dereference
9547 @cindex symbolic links, changing owner
9549 Act on symbolic links themselves instead of what they point to.
9550 This mode relies on the @code{lchown} system call.
9551 On systems that do not provide the @code{lchown} system call,
9552 @command{chown} fails when a file specified on the command line
9554 By default, no diagnostic is issued for symbolic links encountered
9555 during a recursive traversal, but see @option{--verbose}.
9557 @itemx --preserve-root
9558 @opindex --preserve-root
9559 @cindex root directory, disallow recursive modification
9560 Fail upon any attempt to recursively change the root directory, @file{/}.
9561 Without @option{--recursive}, this option has no effect.
9562 @xref{Treating / specially}.
9564 @itemx --no-preserve-root
9565 @opindex --no-preserve-root
9566 @cindex root directory, allow recursive modification
9567 Cancel the effect of any preceding @option{--preserve-root} option.
9568 @xref{Treating / specially}.
9570 @item --reference=@var{ref_file}
9571 @opindex --reference
9572 Change the user and group of each @var{file} to be the same as those of
9573 @var{ref_file}. If @var{ref_file} is a symbolic link, do not use the
9574 user and group of the symbolic link, but rather those of the file it
9581 Output a diagnostic for every file processed.
9582 If a symbolic link is encountered during a recursive traversal
9583 on a system without the @code{lchown} system call, and @option{--no-dereference}
9584 is in effect, then issue a diagnostic saying neither the symbolic link nor
9585 its referent is being changed.
9590 @opindex --recursive
9591 @cindex recursively changing file ownership
9592 Recursively change ownership of directories and their contents.
9595 @xref{Traversing symlinks}.
9598 @xref{Traversing symlinks}.
9601 @xref{Traversing symlinks}.
9610 # Change the owner of /u to "root".
9613 # Likewise, but also change its group to "staff".
9616 # Change the owner of /u and subfiles to "root".
9621 @node chgrp invocation
9622 @section @command{chgrp}: Change group ownership
9625 @cindex group ownership, changing
9626 @cindex changing group ownership
9628 @command{chgrp} changes the group ownership of each given @var{file}
9629 to @var{group} (which can be either a group name or a numeric group ID)
9630 or to the group of an existing reference file. Synopsis:
9633 chgrp [@var{option}]@dots{} @{@var{group} | --reference=@var{ref_file}@} @var{file}@dots{}
9636 If @var{group} is intended to represent a
9637 numeric group ID, then you may specify it with a leading @samp{+}.
9638 @xref{Disambiguating names and IDs}.
9640 The program accepts the following options. Also see @ref{Common options}.
9648 @cindex changed files, verbosely describing
9649 Verbosely describe the action for each @var{file} whose group actually
9658 @cindex error messages, omitting
9659 Do not print error messages about files whose group cannot be
9663 @opindex --dereference
9664 @cindex symbolic links, changing owner
9666 Do not act on symbolic links themselves but rather on what they point to.
9667 This is the default.
9670 @itemx --no-dereference
9672 @opindex --no-dereference
9673 @cindex symbolic links, changing group
9675 Act on symbolic links themselves instead of what they point to.
9676 This mode relies on the @code{lchown} system call.
9677 On systems that do not provide the @code{lchown} system call,
9678 @command{chgrp} fails when a file specified on the command line
9680 By default, no diagnostic is issued for symbolic links encountered
9681 during a recursive traversal, but see @option{--verbose}.
9683 @itemx --preserve-root
9684 @opindex --preserve-root
9685 @cindex root directory, disallow recursive modification
9686 Fail upon any attempt to recursively change the root directory, @file{/}.
9687 Without @option{--recursive}, this option has no effect.
9688 @xref{Treating / specially}.
9690 @itemx --no-preserve-root
9691 @opindex --no-preserve-root
9692 @cindex root directory, allow recursive modification
9693 Cancel the effect of any preceding @option{--preserve-root} option.
9694 @xref{Treating / specially}.
9696 @item --reference=@var{ref_file}
9697 @opindex --reference
9698 Change the group of each @var{file} to be the same as that of
9699 @var{ref_file}. If @var{ref_file} is a symbolic link, do not use the
9700 group of the symbolic link, but rather that of the file it refers to.
9706 Output a diagnostic for every file processed.
9707 If a symbolic link is encountered during a recursive traversal
9708 on a system without the @code{lchown} system call, and @option{--no-dereference}
9709 is in effect, then issue a diagnostic saying neither the symbolic link nor
9710 its referent is being changed.
9715 @opindex --recursive
9716 @cindex recursively changing group ownership
9717 Recursively change the group ownership of directories and their contents.
9720 @xref{Traversing symlinks}.
9723 @xref{Traversing symlinks}.
9726 @xref{Traversing symlinks}.
9735 # Change the group of /u to "staff".
9738 # Change the group of /u and subfiles to "staff".
9743 @node chmod invocation
9744 @section @command{chmod}: Change access permissions
9747 @cindex changing access permissions
9748 @cindex access permissions, changing
9749 @cindex permissions, changing access
9751 @command{chmod} changes the access permissions of the named files. Synopsis:
9754 chmod [@var{option}]@dots{} @{@var{mode} | --reference=@var{ref_file}@} @var{file}@dots{}
9757 @cindex symbolic links, permissions of
9758 @command{chmod} never changes the permissions of symbolic links, since
9759 the @command{chmod} system call cannot change their permissions.
9760 This is not a problem since the permissions of symbolic links are
9761 never used. However, for each symbolic link listed on the command
9762 line, @command{chmod} changes the permissions of the pointed-to file.
9763 In contrast, @command{chmod} ignores symbolic links encountered during
9764 recursive directory traversals.
9766 A successful use of @command{chmod} clears the set-group-ID bit of a
9767 regular file if the file's group ID does not match the user's
9768 effective group ID or one of the user's supplementary group IDs,
9769 unless the user has appropriate privileges. Additional restrictions
9770 may cause the set-user-ID and set-group-ID bits of @var{mode} or
9771 @var{ref_file} to be ignored. This behavior depends on the policy and
9772 functionality of the underlying @code{chmod} system call. When in
9773 doubt, check the underlying system behavior.
9775 If used, @var{mode} specifies the new file mode bits.
9776 For details, see the section on @ref{File permissions}.
9777 If you really want @var{mode} to have a leading @samp{-}, you should
9778 use @option{--} first, e.g., @samp{chmod -- -w file}. Typically,
9779 though, @samp{chmod a-w file} is preferable, and @command{chmod -w
9780 file} (without the @option{--}) complains if it behaves differently
9781 from what @samp{chmod a-w file} would do.
9783 The program accepts the following options. Also see @ref{Common options}.
9791 Verbosely describe the action for each @var{file} whose permissions
9800 @cindex error messages, omitting
9801 Do not print error messages about files whose permissions cannot be
9804 @itemx --preserve-root
9805 @opindex --preserve-root
9806 @cindex root directory, disallow recursive modification
9807 Fail upon any attempt to recursively change the root directory, @file{/}.
9808 Without @option{--recursive}, this option has no effect.
9809 @xref{Treating / specially}.
9811 @itemx --no-preserve-root
9812 @opindex --no-preserve-root
9813 @cindex root directory, allow recursive modification
9814 Cancel the effect of any preceding @option{--preserve-root} option.
9815 @xref{Treating / specially}.
9821 Verbosely describe the action or non-action taken for every @var{file}.
9823 @item --reference=@var{ref_file}
9824 @opindex --reference
9825 Change the mode of each @var{file} to be the same as that of @var{ref_file}.
9826 @xref{File permissions}.
9827 If @var{ref_file} is a symbolic link, do not use the mode
9828 of the symbolic link, but rather that of the file it refers to.
9833 @opindex --recursive
9834 @cindex recursively changing access permissions
9835 Recursively change permissions of directories and their contents.
9842 @node touch invocation
9843 @section @command{touch}: Change file timestamps
9846 @cindex changing file timestamps
9847 @cindex file timestamps, changing
9848 @cindex timestamps, changing file
9850 @command{touch} changes the access and/or modification times of the
9851 specified files. Synopsis:
9854 touch [@var{option}]@dots{} @var{file}@dots{}
9857 @cindex empty files, creating
9858 Any @var{file} argument that does not exist is created empty, unless
9859 option @option{--no-create} (@option{-c}) or @option{--no-dereference}
9860 (@option{-h}) was in effect.
9862 A @var{file} argument string of @samp{-} is handled specially and
9863 causes @command{touch} to change the times of the file associated with
9866 @cindex permissions, for changing file timestamps
9867 If changing both the access and modification times to the current
9868 time, @command{touch} can change the timestamps for files that the user
9869 running it does not own but has write permission for. Otherwise, the
9870 user must own the files.
9872 Although @command{touch} provides options for changing two of the times---the
9873 times of last access and modification---of a file, there is actually
9874 a standard third one as well: the inode change time. This is often
9875 referred to as a file's @code{ctime}.
9876 The inode change time represents the time when the file's meta-information
9877 last changed. One common example of this is when the permissions of a
9878 file change. Changing the permissions doesn't access the file, so
9879 the atime doesn't change, nor does it modify the file, so the mtime
9880 doesn't change. Yet, something about the file itself has changed,
9881 and this must be noted somewhere. This is the job of the ctime field.
9882 This is necessary, so that, for example, a backup program can make a
9883 fresh copy of the file, including the new permissions value.
9884 Another operation that modifies a file's ctime without affecting
9885 the others is renaming. In any case, it is not possible, in normal
9886 operations, for a user to change the ctime field to a user-specified value.
9887 Some operating systems and file systems support a fourth time: the
9888 birth time, when the file was first created; by definition, this
9889 timestamp never changes.
9892 Time stamps assume the time zone rules specified by the @env{TZ}
9893 environment variable, or by the system default rules if @env{TZ} is
9894 not set. @xref{TZ Variable,, Specifying the Time Zone with @env{TZ},
9895 libc, The GNU C Library Reference Manual}.
9896 You can avoid ambiguities during
9897 daylight saving transitions by using @sc{utc} time stamps.
9899 The program accepts the following options. Also see @ref{Common options}.
9905 @itemx --time=access
9909 @opindex atime@r{, changing}
9910 @opindex access @r{time, changing}
9911 @opindex use @r{time, changing}
9912 Change the access time only.
9917 @opindex --no-create
9918 Do not warn about or create files that do not exist.
9921 @itemx --date=@var{time}
9925 Use @var{time} instead of the current time. It can contain month names,
9926 time zones, @samp{am} and @samp{pm}, @samp{yesterday}, etc. For
9927 example, @option{--date="2004-02-27 14:19:13.489392193 +0530"}
9928 specifies the instant of time that is 489,392,193 nanoseconds after
9929 February 27, 2004 at 2:19:13 PM in a time zone that is 5 hours and 30
9930 minutes east of @acronym{UTC}. @xref{Date input formats}.
9931 File systems that do not support high-resolution time stamps
9932 silently ignore any excess precision here.
9936 @cindex BSD @command{touch} compatibility
9937 Ignored; for compatibility with BSD versions of @command{touch}.
9940 @itemx --no-dereference
9942 @opindex --no-dereference
9943 @cindex symbolic links, changing time
9945 Attempt to change the timestamps of a symbolic link, rather than what
9946 the link refers to. When using this option, empty files are not
9947 created, but option @option{-c} must also be used to avoid warning
9948 about files that do not exist. Not all systems support changing the
9949 timestamps of symlinks, since underlying system support for this
9950 action was not required until @acronym{POSIX} 2008. Also, on some
9951 systems, the mere act of examining a symbolic link changes the access
9952 time, such that only changes to the modification time will persist
9953 long enough to be observable. When coupled with option @option{-r}, a
9954 reference timestamp is taken from a symbolic link rather than the file
9959 @itemx --time=modify
9962 @opindex mtime@r{, changing}
9963 @opindex modify @r{time, changing}
9964 Change the modification time only.
9967 @itemx --reference=@var{file}
9969 @opindex --reference
9970 Use the times of the reference @var{file} instead of the current time.
9971 If this option is combined with the @option{--date=@var{time}}
9972 (@option{-d @var{time}}) option, the reference @var{file}'s time is
9973 the origin for any relative @var{time}s given, but is otherwise ignored.
9974 For example, @samp{-r foo -d '-5 seconds'} specifies a time stamp
9975 equal to five seconds before the corresponding time stamp for @file{foo}.
9976 If @var{file} is a symbolic link, the reference timestamp is taken
9977 from the target of the symlink, unless @option{-h} was also in effect.
9979 @item -t [[@var{cc}]@var{yy}]@var{mmddhhmm}[.@var{ss}]
9980 Use the argument (optional four-digit or two-digit years, months,
9981 days, hours, minutes, optional seconds) instead of the current time.
9982 If the year is specified with only two digits, then @var{cc}
9983 is 20 for years in the range 0 @dots{} 68, and 19 for years in
9984 69 @dots{} 99. If no digits of the year are specified,
9985 the argument is interpreted as a date in the current year.
9986 Note that @var{ss} may be @samp{60}, to accommodate leap seconds.
9990 @vindex _POSIX2_VERSION
9991 On older systems, @command{touch} supports an obsolete syntax, as follows.
9992 If no timestamp is given with any of the @option{-d}, @option{-r}, or
9993 @option{-t} options, and if there are two or more @var{file}s and the
9994 first @var{file} is of the form @samp{@var{mmddhhmm}[@var{yy}]} and this
9995 would be a valid argument to the @option{-t} option (if the @var{yy}, if
9996 any, were moved to the front), and if the represented year
9997 is in the range 1969--1999, that argument is interpreted as the time
9998 for the other files instead of as a file name.
9999 This obsolete behavior can be enabled or disabled with the
10000 @env{_POSIX2_VERSION} environment variable (@pxref{Standards
10001 conformance}), but portable scripts should avoid commands whose
10002 behavior depends on this variable.
10003 For example, use @samp{touch ./12312359 main.c} or @samp{touch -t
10004 12312359 main.c} rather than the ambiguous @samp{touch 12312359 main.c}.
10010 @chapter Disk usage
10014 No disk can hold an infinite amount of data. These commands report
10015 how much disk storage is in use or available, report other file and
10016 file status information, and write buffers to disk.
10019 * df invocation:: Report file system disk space usage.
10020 * du invocation:: Estimate file space usage.
10021 * stat invocation:: Report file or file system status.
10022 * sync invocation:: Synchronize memory and disk.
10023 * truncate invocation:: Shrink or extend the size of a file.
10027 @node df invocation
10028 @section @command{df}: Report file system disk space usage
10031 @cindex file system disk usage
10032 @cindex disk usage by file system
10034 @command{df} reports the amount of disk space used and available on
10035 file systems. Synopsis:
10038 df [@var{option}]@dots{} [@var{file}]@dots{}
10041 With no arguments, @command{df} reports the space used and available on all
10042 currently mounted file systems (of all types). Otherwise, @command{df}
10043 reports on the file system containing each argument @var{file}.
10045 Normally the disk space is printed in units of
10046 1024 bytes, but this can be overridden (@pxref{Block size}).
10047 Non-integer quantities are rounded up to the next higher unit.
10049 @cindex disk device file
10050 @cindex device file, disk
10051 If an argument @var{file} is a disk device file containing a mounted
10052 file system, @command{df} shows the space available on that file system
10053 rather than on the file system containing the device node (i.e., the root
10054 file system). @sc{gnu} @command{df} does not attempt to determine the disk usage
10055 on unmounted file systems, because on most kinds of systems doing so
10056 requires extremely nonportable intimate knowledge of file system
10059 The program accepts the following options. Also see @ref{Common options}.
10067 @cindex automounter file systems
10068 @cindex ignore file systems
10069 Include in the listing dummy file systems, which
10070 are omitted by default. Such file systems are typically special-purpose
10071 pseudo-file-systems, such as automounter entries.
10073 @item -B @var{size}
10074 @itemx --block-size=@var{size}
10076 @opindex --block-size
10077 @cindex file system sizes
10078 Scale sizes by @var{size} before printing them (@pxref{Block size}).
10079 For example, @option{-BG} prints sizes in units of 1,073,741,824 bytes.
10083 @cindex grand total of disk size, usage and available space
10084 Print a grand total of all arguments after all arguments have
10085 been processed. This can be used to find out the total disk size, usage
10086 and available space of all listed devices.
10092 Equivalent to @option{--si}.
10098 @cindex inode usage
10099 List inode usage information instead of block usage. An inode (short
10100 for index node) contains information about a file such as its owner,
10101 permissions, timestamps, and location on the disk.
10105 @cindex kibibytes for file system sizes
10106 Print sizes in 1024-byte blocks, overriding the default block size
10107 (@pxref{Block size}).
10108 This option is equivalent to @option{--block-size=1K}.
10114 @cindex file system types, limiting output to certain
10115 Limit the listing to local file systems. By default, remote file systems
10120 @cindex file system space, retrieving old data more quickly
10121 Do not invoke the @code{sync} system call before getting any usage data.
10122 This may make @command{df} run significantly faster on systems with many
10123 disks, but on some systems (notably SunOS) the results may be slightly
10124 out of date. This is the default.
10127 @itemx --portability
10129 @opindex --portability
10130 @cindex one-line output format
10131 @cindex @acronym{POSIX} output format
10132 @cindex portable output format
10133 @cindex output format, portable
10134 Use the @acronym{POSIX} output format. This is like the default format except
10139 The information about each file system is always printed on exactly
10140 one line; a mount device is never put on a line by itself. This means
10141 that if the mount device name is more than 20 characters long (e.g., for
10142 some network mounts), the columns are misaligned.
10145 The labels in the header output line are changed to conform to @acronym{POSIX}.
10148 The default block size and output format are unaffected by the
10149 @env{DF_BLOCK_SIZE}, @env{BLOCK_SIZE} and @env{BLOCKSIZE} environment
10150 variables. However, the default block size is still affected by
10151 @env{POSIXLY_CORRECT}: it is 512 if @env{POSIXLY_CORRECT} is set, 1024
10152 otherwise. @xref{Block size}.
10159 @cindex file system space, retrieving current data more slowly
10160 Invoke the @code{sync} system call before getting any usage data. On
10161 some systems (notably SunOS), doing this yields more up to date results,
10162 but in general this option makes @command{df} much slower, especially when
10163 there are many or very busy file systems.
10165 @item -t @var{fstype}
10166 @itemx --type=@var{fstype}
10169 @cindex file system types, limiting output to certain
10170 Limit the listing to file systems of type @var{fstype}. Multiple
10171 file system types can be specified by giving multiple @option{-t} options.
10172 By default, nothing is omitted.
10175 @itemx --print-type
10177 @opindex --print-type
10178 @cindex file system types, printing
10179 Print each file system's type. The types printed here are the same ones
10180 you can include or exclude with @option{-t} and @option{-x}. The particular
10181 types printed are whatever is supported by the system. Here are some of
10182 the common names (this list is certainly not exhaustive):
10187 @cindex @acronym{NFS} file system type
10188 An @acronym{NFS} file system, i.e., one mounted over a network from another
10189 machine. This is the one type name which seems to be used uniformly by
10192 @item 4.2@r{, }ufs@r{, }efs@dots{}
10193 @cindex Linux file system types
10194 @cindex local file system types
10195 @opindex 4.2 @r{file system type}
10196 @opindex ufs @r{file system type}
10197 @opindex efs @r{file system type}
10198 A file system on a locally-mounted hard disk. (The system might even
10199 support more than one type here; Linux does.)
10201 @item hsfs@r{, }cdfs
10202 @cindex CD-ROM file system type
10203 @cindex High Sierra file system
10204 @opindex hsfs @r{file system type}
10205 @opindex cdfs @r{file system type}
10206 A file system on a CD-ROM drive. HP-UX uses @samp{cdfs}, most other
10207 systems use @samp{hsfs} (@samp{hs} for ``High Sierra'').
10210 @cindex PC file system
10211 @cindex DOS file system
10212 @cindex MS-DOS file system
10213 @cindex diskette file system
10215 An MS-DOS file system, usually on a diskette.
10219 @item -x @var{fstype}
10220 @itemx --exclude-type=@var{fstype}
10222 @opindex --exclude-type
10223 Limit the listing to file systems not of type @var{fstype}.
10224 Multiple file system types can be eliminated by giving multiple
10225 @option{-x} options. By default, no file system types are omitted.
10228 Ignored; for compatibility with System V versions of @command{df}.
10233 Failure includes the case where no output is generated, so you can
10234 inspect the exit status of a command like @samp{df -t ext3 -t reiserfs
10235 @var{dir}} to test whether @var{dir} is on a file system of type
10236 @samp{ext3} or @samp{reiserfs}.
10239 @node du invocation
10240 @section @command{du}: Estimate file space usage
10243 @cindex file space usage
10244 @cindex disk usage for files
10246 @command{du} reports the amount of disk space used by the specified files
10247 and for each subdirectory (of directory arguments). Synopsis:
10250 du [@var{option}]@dots{} [@var{file}]@dots{}
10253 With no arguments, @command{du} reports the disk space for the current
10254 directory. Normally the disk space is printed in units of
10255 1024 bytes, but this can be overridden (@pxref{Block size}).
10256 Non-integer quantities are rounded up to the next higher unit.
10258 If two or more hard links point to the same file, only one of the hard
10259 links is counted. The @var{file} argument order affects which links
10260 are counted, and changing the argument order may change the numbers
10261 that @command{du} outputs.
10263 The program accepts the following options. Also see @ref{Common options}.
10271 Show counts for all files, not just directories.
10273 @itemx --apparent-size
10274 @opindex --apparent-size
10275 Print apparent sizes, rather than disk usage. The apparent size of a
10276 file is the number of bytes reported by @code{wc -c} on regular files,
10277 or more generally, @code{ls -l --block-size=1} or @code{stat --format=%s}.
10278 For example, a file containing the word @samp{zoo} with no newline would,
10279 of course, have an apparent size of 3. Such a small file may require
10280 anywhere from 0 to 16 KiB or more of disk space, depending on
10281 the type and configuration of the file system on which the file resides.
10282 However, a sparse file created with this command:
10285 dd bs=1 seek=2GiB if=/dev/null of=big
10289 has an apparent size of 2 GiB, yet on most modern
10290 systems, it actually uses almost no disk space.
10296 Equivalent to @code{--apparent-size --block-size=1}.
10298 @item -B @var{size}
10299 @itemx --block-size=@var{size}
10301 @opindex --block-size
10303 Scale sizes by @var{size} before printing them (@pxref{Block size}).
10304 For example, @option{-BG} prints sizes in units of 1,073,741,824 bytes.
10310 @cindex grand total of disk space
10311 Print a grand total of all arguments after all arguments have
10312 been processed. This can be used to find out the total disk usage of
10313 a given set of files or directories.
10316 @itemx --dereference-args
10318 @opindex --dereference-args
10319 Dereference symbolic links that are command line arguments.
10320 Does not affect other symbolic links. This is helpful for finding
10321 out the disk usage of directories, such as @file{/usr/tmp}, which
10322 are often symbolic links.
10324 @c --files0-from=FILE
10325 @filesZeroFromOption{du,, with the @option{--total} (@option{-c}) option}
10331 Equivalent to @option{--dereference-args} (@option{-D}).
10335 @cindex kibibytes for file sizes
10336 Print sizes in 1024-byte blocks, overriding the default block size
10337 (@pxref{Block size}).
10338 This option is equivalent to @option{--block-size=1K}.
10341 @itemx --count-links
10343 @opindex --count-links
10344 @cindex hard links, counting in @command{du}
10345 Count the size of all files, even if they have appeared already (as a
10349 @itemx --dereference
10351 @opindex --dereference
10352 @cindex symbolic links, dereferencing in @command{du}
10353 Dereference symbolic links (show the disk space used by the file
10354 or directory that the link points to instead of the space used by
10359 @cindex mebibytes for file sizes
10360 Print sizes in 1,048,576-byte blocks, overriding the default block size
10361 (@pxref{Block size}).
10362 This option is equivalent to @option{--block-size=1M}.
10365 @itemx --no-dereference
10367 @opindex --no-dereference
10368 @cindex symbolic links, dereferencing in @command{du}
10369 For each symbolic links encountered by @command{du},
10370 consider the disk space used by the symbolic link.
10372 @item --max-depth=@var{depth}
10373 @opindex --max-depth=@var{depth}
10374 @cindex limiting output of @command{du}
10375 Show the total for each directory (and file if --all) that is at
10376 most MAX_DEPTH levels down from the root of the hierarchy. The root
10377 is at level 0, so @code{du --max-depth=0} is equivalent to @code{du -s}.
10383 @cindex output null-byte-terminated lines
10384 Output a zero byte (@acronym{ASCII} @sc{nul}) at the end of each line,
10385 rather than a newline. This option enables other programs to parse the
10386 output of @command{du} even when that output would contain file names
10387 with embedded newlines.
10394 @opindex --summarize
10395 Display only a total for each argument.
10398 @itemx --separate-dirs
10400 @opindex --separate-dirs
10401 Normally, in the output of @command{du} (when not using @option{--summarize}),
10402 the size listed next to a directory name, @var{d}, represents the sum
10403 of sizes of all entries beneath @var{d} as well as the size of @var{d} itself.
10404 With @option{--separate-dirs}, the size reported for a directory name,
10405 @var{d}, is merely the @code{stat.st_size}-derived size of the directory
10410 @cindex last modified dates, displaying in @command{du}
10411 Show time of the most recent modification of any file in the directory,
10412 or any of its subdirectories.
10414 @itemx --time=ctime
10415 @itemx --time=status
10418 @opindex ctime@r{, show the most recent}
10419 @opindex status time@r{, show the most recent}
10420 @opindex use time@r{, show the most recent}
10421 Show the most recent status change time (the @samp{ctime} in the inode) of
10422 any file in the directory, instead of the modification time.
10424 @itemx --time=atime
10425 @itemx --time=access
10427 @opindex atime@r{, show the most recent}
10428 @opindex access time@r{, show the most recent}
10429 Show the most recent access time (the @samp{atime} in the inode) of
10430 any file in the directory, instead of the modification time.
10432 @item --time-style=@var{style}
10433 @opindex --time-style
10435 List timestamps in style @var{style}. This option has an effect only if
10436 the @option{--time} option is also specified. The @var{style} should
10437 be one of the following:
10440 @item +@var{format}
10442 List timestamps using @var{format}, where @var{format} is interpreted
10443 like the format argument of @command{date} (@pxref{date invocation}).
10444 For example, @option{--time-style="+%Y-%m-%d %H:%M:%S"} causes
10445 @command{du} to list timestamps like @samp{2002-03-30 23:45:56}. As
10446 with @command{date}, @var{format}'s interpretation is affected by the
10447 @env{LC_TIME} locale category.
10450 List timestamps in full using @acronym{ISO} 8601 date, time, and time zone
10451 format with nanosecond precision, e.g., @samp{2002-03-30
10452 23:45:56.477817180 -0700}. This style is equivalent to
10453 @samp{+%Y-%m-%d %H:%M:%S.%N %z}.
10456 List @acronym{ISO} 8601 date and time in minutes, e.g.,
10457 @samp{2002-03-30 23:45}. These timestamps are shorter than
10458 @samp{full-iso} timestamps, and are usually good enough for everyday
10459 work. This style is equivalent to @samp{+%Y-%m-%d %H:%M}.
10462 List @acronym{ISO} 8601 dates for timestamps, e.g., @samp{2002-03-30}.
10463 This style is equivalent to @samp{+%Y-%m-%d}.
10467 You can specify the default value of the @option{--time-style} option
10468 with the environment variable @env{TIME_STYLE}; if @env{TIME_STYLE} is not set
10469 the default style is @samp{long-iso}. For compatibility with @command{ls},
10470 if @env{TIME_STYLE} begins with @samp{+} and contains a newline,
10471 the newline and any later characters are ignored; if @env{TIME_STYLE}
10472 begins with @samp{posix-} the @samp{posix-} is ignored; and if
10473 @env{TIME_STYLE} is @samp{locale} it is ignored.
10476 @itemx --one-file-system
10478 @opindex --one-file-system
10479 @cindex one file system, restricting @command{du} to
10480 Skip directories that are on different file systems from the one that
10481 the argument being processed is on.
10483 @item --exclude=@var{pattern}
10484 @opindex --exclude=@var{pattern}
10485 @cindex excluding files from @command{du}
10486 When recursing, skip subdirectories or files matching @var{pattern}.
10487 For example, @code{du --exclude='*.o'} excludes files whose names
10490 @item -X @var{file}
10491 @itemx --exclude-from=@var{file}
10492 @opindex -X @var{file}
10493 @opindex --exclude-from=@var{file}
10494 @cindex excluding files from @command{du}
10495 Like @option{--exclude}, except take the patterns to exclude from @var{file},
10496 one per line. If @var{file} is @samp{-}, take the patterns from standard
10501 @cindex NFS mounts from BSD to HP-UX
10502 On BSD systems, @command{du} reports sizes that are half the correct
10503 values for files that are NFS-mounted from HP-UX systems. On HP-UX
10504 systems, it reports sizes that are twice the correct values for
10505 files that are NFS-mounted from BSD systems. This is due to a flaw
10506 in HP-UX; it also affects the HP-UX @command{du} program.
10511 @node stat invocation
10512 @section @command{stat}: Report file or file system status
10515 @cindex file status
10516 @cindex file system status
10518 @command{stat} displays information about the specified file(s). Synopsis:
10521 stat [@var{option}]@dots{} [@var{file}]@dots{}
10524 With no option, @command{stat} reports all information about the given files.
10525 But it also can be used to report the information of the file systems the
10526 given files are located on. If the files are links, @command{stat} can
10527 also give information about the files the links point to.
10529 @mayConflictWithShellBuiltIn{stat}
10534 @itemx --dereference
10536 @opindex --dereference
10537 @cindex symbolic links, dereferencing in @command{stat}
10538 Change how @command{stat} treats symbolic links.
10539 With this option, @command{stat} acts on the file referenced
10540 by each symbolic link argument.
10541 Without it, @command{stat} acts on any symbolic link argument directly.
10544 @itemx --file-system
10546 @opindex --file-system
10547 @cindex file systems
10548 Report information about the file systems where the given files are located
10549 instead of information about the files themselves.
10552 @itemx --format=@var{format}
10554 @opindex --format=@var{format}
10555 @cindex output format
10556 Use @var{format} rather than the default format.
10557 @var{format} is automatically newline-terminated, so
10558 running a command like the following with two or more @var{file}
10559 operands produces a line of output for each operand:
10561 $ stat --format=%d:%i / /usr
10566 @itemx --printf=@var{format}
10567 @opindex --printf=@var{format}
10568 @cindex output format
10569 Use @var{format} rather than the default format.
10570 Like @option{--format}, but interpret backslash escapes,
10571 and do not output a mandatory trailing newline.
10572 If you want a newline, include @samp{\n} in the @var{format}.
10573 Here's how you would use @option{--printf} to print the device
10574 and inode numbers of @file{/} and @file{/usr}:
10576 $ stat --printf='%d:%i\n' / /usr
10585 @cindex terse output
10586 Print the information in terse form, suitable for parsing by other programs.
10590 The valid @var{format} directives for files with @option{--format} and
10591 @option{--printf} are:
10594 @item %a - Access rights in octal
10595 @item %A - Access rights in human readable form
10596 @item %b - Number of blocks allocated (see @samp{%B})
10597 @item %B - The size in bytes of each block reported by @samp{%b}
10598 @item %d - Device number in decimal
10599 @item %D - Device number in hex
10600 @item %f - Raw mode in hex
10601 @item %F - File type
10602 @item %g - Group ID of owner
10603 @item %G - Group name of owner
10604 @item %h - Number of hard links
10605 @item %i - Inode number
10606 @item %n - File name
10607 @item %N - Quoted file name with dereference if symbolic link
10608 @item %o - I/O block size
10609 @item %s - Total size, in bytes
10610 @item %t - Major device type in hex
10611 @item %T - Minor device type in hex
10612 @item %u - User ID of owner
10613 @item %U - User name of owner
10614 @item %x - Time of last access
10615 @item %X - Time of last access as seconds since Epoch
10616 @item %y - Time of last modification
10617 @item %Y - Time of last modification as seconds since Epoch
10618 @item %z - Time of last change
10619 @item %Z - Time of last change as seconds since Epoch
10622 When listing file system information (@option{--file-system} (@option{-f})),
10623 you must use a different set of @var{format} directives:
10626 @item %a - Free blocks available to non-super-user
10627 @item %b - Total data blocks in file system
10628 @item %c - Total file nodes in file system
10629 @item %d - Free file nodes in file system
10630 @item %f - Free blocks in file system
10631 @item %i - File System ID in hex
10632 @item %l - Maximum length of file names
10633 @item %n - File name
10634 @item %s - Block size (for faster transfers)
10635 @item %S - Fundamental block size (for block counts)
10636 @item %t - Type in hex
10637 @item %T - Type in human readable form
10641 Time stamps are listed according to the time zone rules specified by
10642 the @env{TZ} environment variable, or by the system default rules if
10643 @env{TZ} is not set. @xref{TZ Variable,, Specifying the Time Zone
10644 with @env{TZ}, libc, The GNU C Library Reference Manual}.
10649 @node sync invocation
10650 @section @command{sync}: Synchronize data on disk with memory
10653 @cindex synchronize disk and memory
10655 @cindex superblock, writing
10656 @cindex inodes, written buffered
10657 @command{sync} writes any data buffered in memory out to disk. This can
10658 include (but is not limited to) modified superblocks, modified inodes,
10659 and delayed reads and writes. This must be implemented by the kernel;
10660 The @command{sync} program does nothing but exercise the @code{sync} system
10663 @cindex crashes and corruption
10664 The kernel keeps data in memory to avoid doing (relatively slow) disk
10665 reads and writes. This improves performance, but if the computer
10666 crashes, data may be lost or the file system corrupted as a
10667 result. The @command{sync} command ensures everything in memory
10668 is written to disk.
10670 Any arguments are ignored, except for a lone @option{--help} or
10671 @option{--version} (@pxref{Common options}).
10676 @node truncate invocation
10677 @section @command{truncate}: Shrink or extend the size of a file
10680 @cindex truncating, file sizes
10682 @command{truncate} shrinks or extends the size of each @var{file} to the
10683 specified size. Synopsis:
10686 truncate @var{option}@dots{} @var{file}@dots{}
10689 @cindex files, creating
10690 Any @var{file} that does not exist is created.
10692 @cindex sparse files, creating
10693 @cindex holes, creating files with
10694 If a @var{file} is larger than the specified size, the extra data is lost.
10695 If a @var{file} is shorter, it is extended and the extended part (or hole)
10696 reads as zero bytes.
10698 The program accepts the following options. Also see @ref{Common options}.
10705 @opindex --no-create
10706 Do not create files that do not exist.
10711 @opindex --io-blocks
10712 Treat @var{size} as number of I/O blocks of the @var{file} rather than bytes.
10714 @item -r @var{rfile}
10715 @itemx --reference=@var{rfile}
10717 @opindex --reference
10718 Set the size of each @var{file} to the same size as @var{rfile}.
10720 @item -s @var{size}
10721 @itemx --size=@var{size}
10724 Set the size of each @var{file} to this @var{size}.
10725 @multiplierSuffixesNoBlocks{size}
10727 @var{size} may also be prefixed by one of the following to adjust
10728 the size of each @var{file} based on their current size:
10730 @samp{+} => extend by
10731 @samp{-} => reduce by
10732 @samp{<} => at most
10733 @samp{>} => at least
10734 @samp{/} => round down to multiple of
10735 @samp{%} => round up to multiple of
10743 @node Printing text
10744 @chapter Printing text
10746 @cindex printing text, commands for
10747 @cindex commands for printing text
10749 This section describes commands that display text strings.
10752 * echo invocation:: Print a line of text.
10753 * printf invocation:: Format and print data.
10754 * yes invocation:: Print a string until interrupted.
10758 @node echo invocation
10759 @section @command{echo}: Print a line of text
10762 @cindex displaying text
10763 @cindex printing text
10764 @cindex text, displaying
10765 @cindex arbitrary text, displaying
10767 @command{echo} writes each given @var{string} to standard output, with a
10768 space between each and a newline after the last one. Synopsis:
10771 echo [@var{option}]@dots{} [@var{string}]@dots{}
10774 @mayConflictWithShellBuiltIn{echo}
10776 The program accepts the following options. Also see @ref{Common options}.
10777 Options must precede operands, and the normally-special argument
10778 @samp{--} has no special meaning and is treated like any other
10784 Do not output the trailing newline.
10788 @cindex backslash escapes
10789 Enable interpretation of the following backslash-escaped characters in
10798 produce no further output
10812 the eight-bit value that is the octal number @var{nnn}
10813 (zero to three octal digits)
10815 the eight-bit value that is the octal number @var{nnn}
10816 (one to three octal digits)
10818 the eight-bit value that is the hexadecimal number @var{hh}
10819 (one or two hexadecimal digits)
10824 @cindex backslash escapes
10825 Disable interpretation of backslash escapes in each @var{string}.
10826 This is the default. If @option{-e} and @option{-E} are both
10827 specified, the last one given takes effect.
10831 @vindex POSIXLY_CORRECT
10832 If the @env{POSIXLY_CORRECT} environment variable is set, then when
10833 @command{echo}'s first argument is not @option{-n} it outputs
10834 option-like arguments instead of treating them as options. For
10835 example, @code{echo -ne hello} outputs @samp{-ne hello} instead of
10836 plain @samp{hello}.
10838 @acronym{POSIX} does not require support for any options, and says
10839 that the behavior of @command{echo} is implementation-defined if any
10840 @var{string} contains a backslash or if the first argument is
10841 @option{-n}. Portable programs can use the @command{printf} command
10842 if they need to omit trailing newlines or output control characters or
10843 backslashes. @xref{printf invocation}.
10848 @node printf invocation
10849 @section @command{printf}: Format and print data
10852 @command{printf} does formatted printing of text. Synopsis:
10855 printf @var{format} [@var{argument}]@dots{}
10858 @command{printf} prints the @var{format} string, interpreting @samp{%}
10859 directives and @samp{\} escapes to format numeric and string arguments
10860 in a way that is mostly similar to the C @samp{printf} function.
10861 @xref{Output Conversion Syntax,, @command{printf} format directives,
10862 libc, The GNU C Library Reference Manual}, for details.
10863 The differences are listed below.
10865 @mayConflictWithShellBuiltIn{printf}
10870 The @var{format} argument is reused as necessary to convert all the
10871 given @var{argument}s. For example, the command @samp{printf %s a b}
10875 Missing @var{argument}s are treated as null strings or as zeros,
10876 depending on whether the context expects a string or a number. For
10877 example, the command @samp{printf %sx%d} prints @samp{x0}.
10881 An additional escape, @samp{\c}, causes @command{printf} to produce no
10882 further output. For example, the command @samp{printf 'A%sC\cD%sF' B
10883 E} prints @samp{ABC}.
10886 The hexadecimal escape sequence @samp{\x@var{hh}} has at most two
10887 digits, as opposed to C where it can have an unlimited number of
10888 digits. For example, the command @samp{printf '\x07e'} prints two
10889 bytes, whereas the C statement @samp{printf ("\x07e")} prints just
10894 @command{printf} has an additional directive, @samp{%b}, which prints its
10895 argument string with @samp{\} escapes interpreted in the same way as in
10896 the @var{format} string, except that octal escapes are of the form
10897 @samp{\0@var{ooo}} where @var{ooo} is 0 to 3 octal digits.
10898 If a precision is also given, it limits the number of bytes printed
10899 from the converted string.
10902 Numeric arguments must be single C constants, possibly with leading
10903 @samp{+} or @samp{-}. For example, @samp{printf %.4d -3} outputs
10907 @vindex POSIXLY_CORRECT
10908 If the leading character of a numeric argument is @samp{"} or @samp{'}
10909 then its value is the numeric value of the immediately following
10910 character. Any remaining characters are silently ignored if the
10911 @env{POSIXLY_CORRECT} environment variable is set; otherwise, a
10912 warning is printed. For example, @samp{printf "%d" "'a"} outputs
10913 @samp{97} on hosts that use the @acronym{ASCII} character set, since
10914 @samp{a} has the numeric value 97 in @acronym{ASCII}.
10919 A floating-point argument must use a period before any fractional
10920 digits, but is printed according to the @env{LC_NUMERIC} category of the
10921 current locale. For example, in a locale whose radix character is a
10922 comma, the command @samp{printf %g 3.14} outputs @samp{3,14} whereas
10923 the command @samp{printf %g 3,14} is an error.
10927 @command{printf} interprets @samp{\@var{ooo}} in @var{format} as an octal number
10928 (if @var{ooo} is 1 to 3 octal digits) specifying a character to print,
10929 and @samp{\x@var{hh}} as a hexadecimal number (if @var{hh} is 1 to 2 hex
10930 digits) specifying a character to print.
10935 @cindex ISO/IEC 10646
10937 @command{printf} interprets two character syntaxes introduced in
10938 @acronym{ISO} C 99:
10939 @samp{\u} for 16-bit Unicode (@acronym{ISO}/@acronym{IEC} 10646)
10940 characters, specified as
10941 four hexadecimal digits @var{hhhh}, and @samp{\U} for 32-bit Unicode
10942 characters, specified as eight hexadecimal digits @var{hhhhhhhh}.
10943 @command{printf} outputs the Unicode characters
10944 according to the @env{LC_CTYPE} locale. Unicode characters in the ranges
10945 U+0000...U+009F, U+D800...U+DFFF cannot be specified by this syntax, except
10946 for U+0024 ($), U+0040 (@@), and U+0060 (@`).
10948 The processing of @samp{\u} and @samp{\U} requires a full-featured
10949 @code{iconv} facility. It is activated on systems with glibc 2.2 (or newer),
10950 or when @code{libiconv} is installed prior to this package. Otherwise
10951 @samp{\u} and @samp{\U} will print as-is.
10953 The only options are a lone @option{--help} or
10954 @option{--version}. @xref{Common options}.
10955 Options must precede operands.
10957 The Unicode character syntaxes are useful for writing strings in a locale
10958 independent way. For example, a string containing the Euro currency symbol
10961 $ env printf '\u20AC 14.95'
10965 will be output correctly in all locales supporting the Euro symbol
10966 (@acronym{ISO}-8859-15, UTF-8, and others). Similarly, a Chinese string
10969 $ env printf '\u4e2d\u6587'
10973 will be output correctly in all Chinese locales (GB2312, BIG5, UTF-8, etc).
10975 Note that in these examples, the @command{printf} command has been
10976 invoked via @command{env} to ensure that we run the program found via
10977 your shell's search path, and not a shell alias or a built-in function.
10979 For larger strings, you don't need to look up the hexadecimal code
10980 values of each character one by one. @acronym{ASCII} characters mixed with \u
10981 escape sequences is also known as the JAVA source file encoding. You can
10982 use GNU recode 3.5c (or newer) to convert strings to this encoding. Here
10983 is how to convert a piece of text into a shell script which will output
10984 this text in a locale-independent way:
10987 $ LC_CTYPE=zh_CN.big5 /usr/local/bin/printf \
10988 '\u4e2d\u6587\n' > sample.txt
10989 $ recode BIG5..JAVA < sample.txt \
10990 | sed -e "s|^|/usr/local/bin/printf '|" -e "s|$|\\\\n'|" \
10997 @node yes invocation
10998 @section @command{yes}: Print a string until interrupted
11001 @cindex repeated output of a string
11003 @command{yes} prints the command line arguments, separated by spaces and
11004 followed by a newline, forever until it is killed. If no arguments are
11005 given, it prints @samp{y} followed by a newline forever until killed.
11007 Upon a write error, @command{yes} exits with status @samp{1}.
11009 The only options are a lone @option{--help} or @option{--version}.
11010 To output an argument that begins with
11011 @samp{-}, precede it with @option{--}, e.g., @samp{yes -- --help}.
11012 @xref{Common options}.
11016 @chapter Conditions
11019 @cindex commands for exit status
11020 @cindex exit status commands
11022 This section describes commands that are primarily useful for their exit
11023 status, rather than their output. Thus, they are often used as the
11024 condition of shell @code{if} statements, or as the last command in a
11028 * false invocation:: Do nothing, unsuccessfully.
11029 * true invocation:: Do nothing, successfully.
11030 * test invocation:: Check file types and compare values.
11031 * expr invocation:: Evaluate expressions.
11035 @node false invocation
11036 @section @command{false}: Do nothing, unsuccessfully
11039 @cindex do nothing, unsuccessfully
11040 @cindex failure exit status
11041 @cindex exit status of @command{false}
11043 @command{false} does nothing except return an exit status of 1, meaning
11044 @dfn{failure}. It can be used as a place holder in shell scripts
11045 where an unsuccessful command is needed.
11046 In most modern shells, @command{false} is a built-in command, so when
11047 you use @samp{false} in a script, you're probably using the built-in
11048 command, not the one documented here.
11050 @command{false} honors the @option{--help} and @option{--version} options.
11052 This version of @command{false} is implemented as a C program, and is thus
11053 more secure and faster than a shell script implementation, and may safely
11054 be used as a dummy shell for the purpose of disabling accounts.
11056 Note that @command{false} (unlike all other programs documented herein)
11057 exits unsuccessfully, even when invoked with
11058 @option{--help} or @option{--version}.
11060 Portable programs should not assume that the exit status of
11061 @command{false} is 1, as it is greater than 1 on some
11062 non-@acronym{GNU} hosts.
11065 @node true invocation
11066 @section @command{true}: Do nothing, successfully
11069 @cindex do nothing, successfully
11071 @cindex successful exit
11072 @cindex exit status of @command{true}
11074 @command{true} does nothing except return an exit status of 0, meaning
11075 @dfn{success}. It can be used as a place holder in shell scripts
11076 where a successful command is needed, although the shell built-in
11077 command @code{:} (colon) may do the same thing faster.
11078 In most modern shells, @command{true} is a built-in command, so when
11079 you use @samp{true} in a script, you're probably using the built-in
11080 command, not the one documented here.
11082 @command{true} honors the @option{--help} and @option{--version} options.
11084 Note, however, that it is possible to cause @command{true}
11085 to exit with nonzero status: with the @option{--help} or @option{--version}
11086 option, and with standard
11087 output already closed or redirected to a file that evokes an I/O error.
11088 For example, using a Bourne-compatible shell:
11091 $ ./true --version >&-
11092 ./true: write error: Bad file number
11093 $ ./true --version > /dev/full
11094 ./true: write error: No space left on device
11097 This version of @command{true} is implemented as a C program, and is thus
11098 more secure and faster than a shell script implementation, and may safely
11099 be used as a dummy shell for the purpose of disabling accounts.
11101 @node test invocation
11102 @section @command{test}: Check file types and compare values
11105 @cindex check file types
11106 @cindex compare values
11107 @cindex expression evaluation
11109 @command{test} returns a status of 0 (true) or 1 (false) depending on the
11110 evaluation of the conditional expression @var{expr}. Each part of the
11111 expression must be a separate argument.
11113 @command{test} has file status checks, string operators, and numeric
11114 comparison operators.
11116 @command{test} has an alternate form that uses opening and closing
11117 square brackets instead a leading @samp{test}. For example, instead
11118 of @samp{test -d /}, you can write @samp{[ -d / ]}. The square
11119 brackets must be separate arguments; for example, @samp{[-d /]} does
11120 not have the desired effect. Since @samp{test @var{expr}} and @samp{[
11121 @var{expr} ]} have the same meaning, only the former form is discussed
11127 test @var{expression}
11129 [ @var{expression} ]
11134 @mayConflictWithShellBuiltIn{test}
11136 If @var{expression} is omitted, @command{test} returns false.
11137 If @var{expression} is a single argument,
11138 @command{test} returns false if the argument is null and true otherwise. The argument
11139 can be any string, including strings like @samp{-d}, @samp{-1},
11140 @samp{--}, @samp{--help}, and @samp{--version} that most other
11141 programs would treat as options. To get help and version information,
11142 invoke the commands @samp{[ --help} and @samp{[ --version}, without
11143 the usual closing brackets. @xref{Common options}.
11145 @cindex exit status of @command{test}
11149 0 if the expression is true,
11150 1 if the expression is false,
11151 2 if an error occurred.
11155 * File type tests:: -[bcdfhLpSt]
11156 * Access permission tests:: -[gkruwxOG]
11157 * File characteristic tests:: -e -s -nt -ot -ef
11158 * String tests:: -z -n = !=
11159 * Numeric tests:: -eq -ne -lt -le -gt -ge
11160 * Connectives for test:: ! -a -o
11164 @node File type tests
11165 @subsection File type tests
11167 @cindex file type tests
11169 These options test for particular types of files. (Everything's a file,
11170 but not all files are the same!)
11174 @item -b @var{file}
11176 @cindex block special check
11177 True if @var{file} exists and is a block special device.
11179 @item -c @var{file}
11181 @cindex character special check
11182 True if @var{file} exists and is a character special device.
11184 @item -d @var{file}
11186 @cindex directory check
11187 True if @var{file} exists and is a directory.
11189 @item -f @var{file}
11191 @cindex regular file check
11192 True if @var{file} exists and is a regular file.
11194 @item -h @var{file}
11195 @itemx -L @var{file}
11198 @cindex symbolic link check
11199 True if @var{file} exists and is a symbolic link.
11200 Unlike all other file-related tests, this test does not dereference
11201 @var{file} if it is a symbolic link.
11203 @item -p @var{file}
11205 @cindex named pipe check
11206 True if @var{file} exists and is a named pipe.
11208 @item -S @var{file}
11210 @cindex socket check
11211 True if @var{file} exists and is a socket.
11215 @cindex terminal check
11216 True if @var{fd} is a file descriptor that is associated with a
11222 @node Access permission tests
11223 @subsection Access permission tests
11225 @cindex access permission tests
11226 @cindex permission tests
11228 These options test for particular access permissions.
11232 @item -g @var{file}
11234 @cindex set-group-ID check
11235 True if @var{file} exists and has its set-group-ID bit set.
11237 @item -k @var{file}
11239 @cindex sticky bit check
11240 True if @var{file} exists and has its @dfn{sticky} bit set.
11242 @item -r @var{file}
11244 @cindex readable file check
11245 True if @var{file} exists and read permission is granted.
11247 @item -u @var{file}
11249 @cindex set-user-ID check
11250 True if @var{file} exists and has its set-user-ID bit set.
11252 @item -w @var{file}
11254 @cindex writable file check
11255 True if @var{file} exists and write permission is granted.
11257 @item -x @var{file}
11259 @cindex executable file check
11260 True if @var{file} exists and execute permission is granted
11261 (or search permission, if it is a directory).
11263 @item -O @var{file}
11265 @cindex owned by effective user ID check
11266 True if @var{file} exists and is owned by the current effective user ID.
11268 @item -G @var{file}
11270 @cindex owned by effective group ID check
11271 True if @var{file} exists and is owned by the current effective group ID.
11275 @node File characteristic tests
11276 @subsection File characteristic tests
11278 @cindex file characteristic tests
11280 These options test other file characteristics.
11284 @item -e @var{file}
11286 @cindex existence-of-file check
11287 True if @var{file} exists.
11289 @item -s @var{file}
11291 @cindex nonempty file check
11292 True if @var{file} exists and has a size greater than zero.
11294 @item @var{file1} -nt @var{file2}
11296 @cindex newer-than file check
11297 True if @var{file1} is newer (according to modification date) than
11298 @var{file2}, or if @var{file1} exists and @var{file2} does not.
11300 @item @var{file1} -ot @var{file2}
11302 @cindex older-than file check
11303 True if @var{file1} is older (according to modification date) than
11304 @var{file2}, or if @var{file2} exists and @var{file1} does not.
11306 @item @var{file1} -ef @var{file2}
11308 @cindex same file check
11309 @cindex hard link check
11310 True if @var{file1} and @var{file2} have the same device and inode
11311 numbers, i.e., if they are hard links to each other.
11317 @subsection String tests
11319 @cindex string tests
11321 These options test string characteristics. You may need to quote
11322 @var{string} arguments for the shell. For example:
11328 The quotes here prevent the wrong arguments from being passed to
11329 @command{test} if @samp{$V} is empty or contains special characters.
11333 @item -z @var{string}
11335 @cindex zero-length string check
11336 True if the length of @var{string} is zero.
11338 @item -n @var{string}
11339 @itemx @var{string}
11341 @cindex nonzero-length string check
11342 True if the length of @var{string} is nonzero.
11344 @item @var{string1} = @var{string2}
11346 @cindex equal string check
11347 True if the strings are equal.
11349 @item @var{string1} != @var{string2}
11351 @cindex not-equal string check
11352 True if the strings are not equal.
11357 @node Numeric tests
11358 @subsection Numeric tests
11360 @cindex numeric tests
11361 @cindex arithmetic tests
11363 Numeric relational operators. The arguments must be entirely numeric
11364 (possibly negative), or the special expression @w{@code{-l @var{string}}},
11365 which evaluates to the length of @var{string}.
11369 @item @var{arg1} -eq @var{arg2}
11370 @itemx @var{arg1} -ne @var{arg2}
11371 @itemx @var{arg1} -lt @var{arg2}
11372 @itemx @var{arg1} -le @var{arg2}
11373 @itemx @var{arg1} -gt @var{arg2}
11374 @itemx @var{arg1} -ge @var{arg2}
11381 These arithmetic binary operators return true if @var{arg1} is equal,
11382 not-equal, less-than, less-than-or-equal, greater-than, or
11383 greater-than-or-equal than @var{arg2}, respectively.
11390 test -1 -gt -2 && echo yes
11392 test -l abc -gt 1 && echo yes
11395 @error{} test: integer expression expected before -eq
11399 @node Connectives for test
11400 @subsection Connectives for @command{test}
11402 @cindex logical connectives
11403 @cindex connectives, logical
11405 The usual logical connectives.
11411 True if @var{expr} is false.
11413 @item @var{expr1} -a @var{expr2}
11415 @cindex logical and operator
11416 @cindex and operator
11417 True if both @var{expr1} and @var{expr2} are true.
11419 @item @var{expr1} -o @var{expr2}
11421 @cindex logical or operator
11422 @cindex or operator
11423 True if either @var{expr1} or @var{expr2} is true.
11428 @node expr invocation
11429 @section @command{expr}: Evaluate expressions
11432 @cindex expression evaluation
11433 @cindex evaluation of expressions
11435 @command{expr} evaluates an expression and writes the result on standard
11436 output. Each token of the expression must be a separate argument.
11438 Operands are either integers or strings. Integers consist of one or
11439 more decimal digits, with an optional leading @samp{-}.
11440 @command{expr} converts
11441 anything appearing in an operand position to an integer or a string
11442 depending on the operation being applied to it.
11444 Strings are not quoted for @command{expr} itself, though you may need to
11445 quote them to protect characters with special meaning to the shell,
11446 e.g., spaces. However, regardless of whether it is quoted, a string
11447 operand should not be a parenthesis or any of @command{expr}'s
11448 operators like @code{+}, so you cannot safely pass an arbitrary string
11449 @code{$str} to expr merely by quoting it to the shell. One way to
11450 work around this is to use the @sc{gnu} extension @code{+},
11451 (e.g., @code{+ "$str" = foo}); a more portable way is to use
11452 @code{@w{" $str"}} and to adjust the rest of the expression to take
11453 the leading space into account (e.g., @code{@w{" $str" = " foo"}}).
11455 You should not pass a negative integer or a string with leading
11456 @samp{-} as @command{expr}'s first argument, as it might be
11457 misinterpreted as an option; this can be avoided by parenthesization.
11458 Also, portable scripts should not use a string operand that happens to
11459 take the form of an integer; this can be worked around by inserting
11460 leading spaces as mentioned above.
11462 @cindex parentheses for grouping
11463 Operators may be given as infix symbols or prefix keywords. Parentheses
11464 may be used for grouping in the usual manner. You must quote
11465 parentheses and many operators to avoid the shell evaluating them,
11468 When built with support for the GNU MP library, @command{expr} uses
11469 arbitrary-precision arithmetic; otherwise, it uses native arithmetic
11470 types and may fail due to arithmetic overflow.
11472 The only options are @option{--help} and @option{--version}. @xref{Common
11473 options}. Options must precede operands.
11475 @cindex exit status of @command{expr}
11479 0 if the expression is neither null nor 0,
11480 1 if the expression is null or 0,
11481 2 if the expression is invalid,
11482 3 if an internal error occurred (e.g., arithmetic overflow).
11486 * String expressions:: + : match substr index length
11487 * Numeric expressions:: + - * / %
11488 * Relations for expr:: | & < <= = == != >= >
11489 * Examples of expr:: Examples.
11493 @node String expressions
11494 @subsection String expressions
11496 @cindex string expressions
11497 @cindex expressions, string
11499 @command{expr} supports pattern matching and other string operators. These
11500 have higher precedence than both the numeric and relational operators (in
11501 the next sections).
11505 @item @var{string} : @var{regex}
11506 @cindex pattern matching
11507 @cindex regular expression matching
11508 @cindex matching patterns
11509 Perform pattern matching. The arguments are converted to strings and the
11510 second is considered to be a (basic, a la GNU @code{grep}) regular
11511 expression, with a @code{^} implicitly prepended. The first argument is
11512 then matched against this regular expression.
11514 If the match succeeds and @var{regex} uses @samp{\(} and @samp{\)}, the
11515 @code{:} expression returns the part of @var{string} that matched the
11516 subexpression; otherwise, it returns the number of characters matched.
11518 If the match fails, the @code{:} operator returns the null string if
11519 @samp{\(} and @samp{\)} are used in @var{regex}, otherwise 0.
11521 @kindex \( @r{regexp operator}
11522 Only the first @samp{\( @dots{} \)} pair is relevant to the return
11523 value; additional pairs are meaningful only for grouping the regular
11524 expression operators.
11526 @kindex \+ @r{regexp operator}
11527 @kindex \? @r{regexp operator}
11528 @kindex \| @r{regexp operator}
11529 In the regular expression, @code{\+}, @code{\?}, and @code{\|} are
11530 operators which respectively match one or more, zero or one, or separate
11531 alternatives. SunOS and other @command{expr}'s treat these as regular
11532 characters. (@acronym{POSIX} allows either behavior.)
11533 @xref{Top, , Regular Expression Library, regex, Regex}, for details of
11534 regular expression syntax. Some examples are in @ref{Examples of expr}.
11536 @item match @var{string} @var{regex}
11538 An alternative way to do pattern matching. This is the same as
11539 @w{@samp{@var{string} : @var{regex}}}.
11541 @item substr @var{string} @var{position} @var{length}
11543 Returns the substring of @var{string} beginning at @var{position}
11544 with length at most @var{length}. If either @var{position} or
11545 @var{length} is negative, zero, or non-numeric, returns the null string.
11547 @item index @var{string} @var{charset}
11549 Returns the first position in @var{string} where the first character in
11550 @var{charset} was found. If no character in @var{charset} is found in
11551 @var{string}, return 0.
11553 @item length @var{string}
11555 Returns the length of @var{string}.
11557 @item + @var{token}
11559 Interpret @var{token} as a string, even if it is a keyword like @var{match}
11560 or an operator like @code{/}.
11561 This makes it possible to test @code{expr length + "$x"} or
11562 @code{expr + "$x" : '.*/\(.\)'} and have it do the right thing even if
11563 the value of @var{$x} happens to be (for example) @code{/} or @code{index}.
11564 This operator is a @acronym{GNU} extension. Portable shell scripts should use
11565 @code{@w{" $token"} : @w{' \(.*\)'}} instead of @code{+ "$token"}.
11569 To make @command{expr} interpret keywords as strings, you must use the
11570 @code{quote} operator.
11573 @node Numeric expressions
11574 @subsection Numeric expressions
11576 @cindex numeric expressions
11577 @cindex expressions, numeric
11579 @command{expr} supports the usual numeric operators, in order of increasing
11580 precedence. These numeric operators have lower precedence than the
11581 string operators described in the previous section, and higher precedence
11582 than the connectives (next section).
11590 @cindex subtraction
11591 Addition and subtraction. Both arguments are converted to integers;
11592 an error occurs if this cannot be done.
11598 @cindex multiplication
11601 Multiplication, division, remainder. Both arguments are converted to
11602 integers; an error occurs if this cannot be done.
11607 @node Relations for expr
11608 @subsection Relations for @command{expr}
11610 @cindex connectives, logical
11611 @cindex logical connectives
11612 @cindex relations, numeric or string
11614 @command{expr} supports the usual logical connectives and relations. These
11615 have lower precedence than the string and numeric operators
11616 (previous sections). Here is the list, lowest-precedence operator first.
11622 @cindex logical or operator
11623 @cindex or operator
11624 Returns its first argument if that is neither null nor zero, otherwise
11625 its second argument if it is neither null nor zero, otherwise 0. It
11626 does not evaluate its second argument if its first argument is neither
11631 @cindex logical and operator
11632 @cindex and operator
11633 Return its first argument if neither argument is null or zero, otherwise
11634 0. It does not evaluate its second argument if its first argument is
11637 @item < <= = == != >= >
11644 @cindex comparison operators
11646 Compare the arguments and return 1 if the relation is true, 0 otherwise.
11647 @code{==} is a synonym for @code{=}. @command{expr} first tries to convert
11648 both arguments to integers and do a numeric comparison; if either
11649 conversion fails, it does a lexicographic comparison using the character
11650 collating sequence specified by the @env{LC_COLLATE} locale.
11655 @node Examples of expr
11656 @subsection Examples of using @command{expr}
11658 @cindex examples of @command{expr}
11659 Here are a few examples, including quoting for shell metacharacters.
11661 To add 1 to the shell variable @code{foo}, in Bourne-compatible shells:
11664 foo=`expr $foo + 1`
11667 To print the non-directory part of the file name stored in
11668 @code{$fname}, which need not contain a @code{/}:
11671 expr $fname : '.*/\(.*\)' '|' $fname
11674 An example showing that @code{\+} is an operator:
11682 expr abc : 'a\(.\)c'
11684 expr index abcdef cz
11687 @error{} expr: syntax error
11688 expr index + index a
11694 @chapter Redirection
11696 @cindex redirection
11697 @cindex commands for redirection
11699 Unix shells commonly provide several forms of @dfn{redirection}---ways
11700 to change the input source or output destination of a command. But one
11701 useful redirection is performed by a separate command, not by the shell;
11702 it's described here.
11705 * tee invocation:: Redirect output to multiple files or processes.
11709 @node tee invocation
11710 @section @command{tee}: Redirect output to multiple files or processes
11713 @cindex pipe fitting
11714 @cindex destinations, multiple output
11715 @cindex read from stdin and write to stdout and files
11717 The @command{tee} command copies standard input to standard output and also
11718 to any files given as arguments. This is useful when you want not only
11719 to send some data down a pipe, but also to save a copy. Synopsis:
11722 tee [@var{option}]@dots{} [@var{file}]@dots{}
11725 If a file being written to does not already exist, it is created. If a
11726 file being written to already exists, the data it previously contained
11727 is overwritten unless the @option{-a} option is used.
11729 A @var{file} of @samp{-} causes @command{tee} to send another copy of
11730 input to standard output, but this is typically not that useful as the
11731 copies are interleaved.
11733 The program accepts the following options. Also see @ref{Common options}.
11740 Append standard input to the given files rather than overwriting
11744 @itemx --ignore-interrupts
11746 @opindex --ignore-interrupts
11747 Ignore interrupt signals.
11751 The @command{tee} command is useful when you happen to be transferring a large
11752 amount of data and also want to summarize that data without reading
11753 it a second time. For example, when you are downloading a DVD image,
11754 you often want to verify its signature or checksum right away.
11755 The inefficient way to do it is simply:
11758 wget http://example.com/some.iso && sha1sum some.iso
11761 One problem with the above is that it makes you wait for the
11762 download to complete before starting the time-consuming SHA1 computation.
11763 Perhaps even more importantly, the above requires reading
11764 the DVD image a second time (the first was from the network).
11766 The efficient way to do it is to interleave the download
11767 and SHA1 computation. Then, you'll get the checksum for
11768 free, because the entire process parallelizes so well:
11771 # slightly contrived, to demonstrate process substitution
11772 wget -O - http://example.com/dvd.iso \
11773 | tee >(sha1sum > dvd.sha1) > dvd.iso
11776 That makes @command{tee} write not just to the expected output file,
11777 but also to a pipe running @command{sha1sum} and saving the final
11778 checksum in a file named @file{dvd.sha1}.
11780 Note, however, that this example relies on a feature of modern shells
11781 called @dfn{process substitution}
11782 (the @samp{>(command)} syntax, above;
11783 @xref{Process Substitution,,Process Substitution, bashref,
11784 The Bash Reference Manual}.),
11785 so it works with @command{zsh}, @command{bash}, and @command{ksh},
11786 but not with @command{/bin/sh}. So if you write code like this
11787 in a shell script, be sure to start the script with @samp{#!/bin/bash}.
11789 Since the above example writes to one file and one process,
11790 a more conventional and portable use of @command{tee} is even better:
11793 wget -O - http://example.com/dvd.iso \
11794 | tee dvd.iso | sha1sum > dvd.sha1
11797 You can extend this example to make @command{tee} write to two processes,
11798 computing MD5 and SHA1 checksums in parallel. In this case,
11799 process substitution is required:
11802 wget -O - http://example.com/dvd.iso \
11803 | tee >(sha1sum > dvd.sha1) \
11804 >(md5sum > dvd.md5) \
11808 This technique is also useful when you want to make a @emph{compressed}
11809 copy of the contents of a pipe.
11810 Consider a tool to graphically summarize disk usage data from @samp{du -ak}.
11811 For a large hierarchy, @samp{du -ak} can run for a long time,
11812 and can easily produce terabytes of data, so you won't want to
11813 rerun the command unnecessarily. Nor will you want to save
11814 the uncompressed output.
11816 Doing it the inefficient way, you can't even start the GUI
11817 until after you've compressed all of the @command{du} output:
11820 du -ak | gzip -9 > /tmp/du.gz
11821 gzip -d /tmp/du.gz | xdiskusage -a
11824 With @command{tee} and process substitution, you start the GUI
11825 right away and eliminate the decompression completely:
11828 du -ak | tee >(gzip -9 > /tmp/du.gz) | xdiskusage -a
11831 Finally, if you regularly create more than one type of
11832 compressed tarball at once, for example when @code{make dist} creates
11833 both @command{gzip}-compressed and @command{bzip2}-compressed tarballs,
11834 there may be a better way.
11835 Typical @command{automake}-generated @file{Makefile} rules create
11836 the two compressed tar archives with commands in sequence, like this
11837 (slightly simplified):
11840 tardir=your-pkg-M.N
11841 tar chof - "$tardir" | gzip -9 -c > your-pkg-M.N.tar.gz
11842 tar chof - "$tardir" | bzip2 -9 -c > your-pkg-M.N.tar.bz2
11845 However, if the hierarchy you are archiving and compressing is larger
11846 than a couple megabytes, and especially if you are using a multi-processor
11847 system with plenty of memory, then you can do much better by reading the
11848 directory contents only once and running the compression programs in parallel:
11851 tardir=your-pkg-M.N
11852 tar chof - "$tardir" \
11853 | tee >(gzip -9 -c > your-pkg-M.N.tar.gz) \
11854 | bzip2 -9 -c > your-pkg-M.N.tar.bz2
11860 @node File name manipulation
11861 @chapter File name manipulation
11863 @cindex file name manipulation
11864 @cindex manipulation of file names
11865 @cindex commands for file name manipulation
11867 This section describes commands that manipulate file names.
11870 * basename invocation:: Strip directory and suffix from a file name.
11871 * dirname invocation:: Strip non-directory suffix from a file name.
11872 * pathchk invocation:: Check file name validity and portability.
11876 @node basename invocation
11877 @section @command{basename}: Strip directory and suffix from a file name
11880 @cindex strip directory and suffix from file names
11881 @cindex directory, stripping from file names
11882 @cindex suffix, stripping from file names
11883 @cindex file names, stripping directory and suffix
11884 @cindex leading directory components, stripping
11886 @command{basename} removes any leading directory components from
11887 @var{name}. Synopsis:
11890 basename @var{name} [@var{suffix}]
11893 If @var{suffix} is specified and is identical to the end of @var{name},
11894 it is removed from @var{name} as well. Note that since trailing slashes
11895 are removed prior to suffix matching, @var{suffix} will do nothing if it
11896 contains slashes. @command{basename} prints the result on standard
11899 @c This test is used both here and in the section on dirname.
11900 @macro basenameAndDirname
11901 Together, @command{basename} and @command{dirname} are designed such
11902 that if @samp{ls "$name"} succeeds, then the command sequence @samp{cd
11903 "$(dirname "$name")"; ls "$(basename "$name")"} will, too. This works
11904 for everything except file names containing a trailing newline.
11906 @basenameAndDirname
11908 @acronym{POSIX} allows the implementation to define the results if
11909 @var{name} is empty or @samp{//}. In the former case, @acronym{GNU}
11910 @command{basename} returns the empty string. In the latter case, the
11911 result is @samp{//} on platforms where @var{//} is distinct from
11912 @var{/}, and @samp{/} on platforms where there is no difference.
11914 The only options are @option{--help} and @option{--version}. @xref{Common
11915 options}. Options must precede operands.
11923 basename /usr/bin/sort
11926 basename include/stdio.h .h
11930 @node dirname invocation
11931 @section @command{dirname}: Strip non-directory suffix from a file name
11934 @cindex directory components, printing
11935 @cindex stripping non-directory suffix
11936 @cindex non-directory suffix, stripping
11938 @command{dirname} prints all but the final slash-delimited component of
11939 a string (presumably a file name). Synopsis:
11945 If @var{name} is a single component, @command{dirname} prints @samp{.}
11946 (meaning the current directory).
11948 @basenameAndDirname
11950 @acronym{POSIX} allows the implementation to define the results if
11951 @var{name} is @samp{//}. With @acronym{GNU} @command{dirname}, the
11952 result is @samp{//} on platforms where @var{//} is distinct from
11953 @var{/}, and @samp{/} on platforms where there is no difference.
11955 The only options are @option{--help} and @option{--version}. @xref{Common
11963 # Output "/usr/bin".
11964 dirname /usr/bin/sort
11971 @node pathchk invocation
11972 @section @command{pathchk}: Check file name validity and portability
11975 @cindex file names, checking validity and portability
11976 @cindex valid file names, checking for
11977 @cindex portable file names, checking for
11979 @command{pathchk} checks validity and portability of file names. Synopsis:
11982 pathchk [@var{option}]@dots{} @var{name}@dots{}
11985 For each @var{name}, @command{pathchk} prints an error message if any of
11986 these conditions is true:
11990 One of the existing directories in @var{name} does not have search
11991 (execute) permission,
11993 The length of @var{name} is larger than the maximum supported by the
11996 The length of one component of @var{name} is longer than
11997 its file system's maximum.
12000 A nonexistent @var{name} is not an error, so long a file with that
12001 name could be created under the above conditions.
12003 The program accepts the following options. Also see @ref{Common options}.
12004 Options must precede operands.
12010 Instead of performing checks based on the underlying file system,
12011 print an error message if any of these conditions is true:
12015 A file name is empty.
12018 A file name contains a character outside the @acronym{POSIX} portable file
12019 name character set, namely, the ASCII letters and digits, @samp{.},
12020 @samp{_}, @samp{-}, and @samp{/}.
12023 The length of a file name or one of its components exceeds the
12024 @acronym{POSIX} minimum limits for portability.
12029 Print an error message if a file name is empty, or if it contains a component
12030 that begins with @samp{-}.
12032 @item --portability
12033 @opindex --portability
12034 Print an error message if a file name is not portable to all @acronym{POSIX}
12035 hosts. This option is equivalent to @samp{-p -P}.
12039 @cindex exit status of @command{pathchk}
12043 0 if all specified file names passed all checks,
12048 @node Working context
12049 @chapter Working context
12051 @cindex working context
12052 @cindex commands for printing the working context
12054 This section describes commands that display or alter the context in
12055 which you are working: the current directory, the terminal settings, and
12056 so forth. See also the user-related commands in the next section.
12059 * pwd invocation:: Print working directory.
12060 * stty invocation:: Print or change terminal characteristics.
12061 * printenv invocation:: Print environment variables.
12062 * tty invocation:: Print file name of terminal on standard input.
12066 @node pwd invocation
12067 @section @command{pwd}: Print working directory
12070 @cindex print name of current directory
12071 @cindex current working directory, printing
12072 @cindex working directory, printing
12075 @command{pwd} prints the name of the current directory. Synopsis:
12078 pwd [@var{option}]@dots{}
12081 The program accepts the following options. Also see @ref{Common options}.
12088 If the contents of the environment variable @env{PWD} provide an
12089 absolute name of the current directory with no @samp{.} or @samp{..}
12090 components, but possibly with symbolic links, then output those
12091 contents. Otherwise, fall back to default @option{-P} handling.
12096 @opindex --physical
12097 Print a fully resolved name for the current directory. That is, all
12098 components of the printed name will be actual directory names---none
12099 will be symbolic links.
12102 @cindex symbolic links and @command{pwd}
12103 If @option{-L} and @option{-P} are both given, the last one takes
12104 precedence. If neither option is given, then this implementation uses
12105 @option{-P} as the default unless the @env{POSIXLY_CORRECT}
12106 environment variable is set.
12108 @mayConflictWithShellBuiltIn{pwd}
12113 @node stty invocation
12114 @section @command{stty}: Print or change terminal characteristics
12117 @cindex change or print terminal settings
12118 @cindex terminal settings
12119 @cindex line settings of terminal
12121 @command{stty} prints or changes terminal characteristics, such as baud rate.
12125 stty [@var{option}] [@var{setting}]@dots{}
12126 stty [@var{option}]
12129 If given no line settings, @command{stty} prints the baud rate, line
12130 discipline number (on systems that support it), and line settings
12131 that have been changed from the values set by @samp{stty sane}.
12132 By default, mode reading and setting are performed on the tty line
12133 connected to standard input, although this can be modified by the
12134 @option{--file} option.
12136 @command{stty} accepts many non-option arguments that change aspects of
12137 the terminal line operation, as described below.
12139 The program accepts the following options. Also see @ref{Common options}.
12146 Print all current settings in human-readable form. This option may not
12147 be used in combination with any line settings.
12149 @item -F @var{device}
12150 @itemx --file=@var{device}
12153 Set the line opened by the file name specified in @var{device} instead of
12154 the tty line connected to standard input. This option is necessary
12155 because opening a @acronym{POSIX} tty requires use of the @code{O_NONDELAY} flag to
12156 prevent a @acronym{POSIX} tty from blocking until the carrier detect line is high if
12157 the @code{clocal} flag is not set. Hence, it is not always possible
12158 to allow the shell to open the device in the traditional manner.
12164 @cindex machine-readable @command{stty} output
12165 Print all current settings in a form that can be used as an argument to
12166 another @command{stty} command to restore the current settings. This option
12167 may not be used in combination with any line settings.
12171 Many settings can be turned off by preceding them with a @samp{-}.
12172 Such arguments are marked below with ``May be negated'' in their
12173 description. The descriptions themselves refer to the positive
12174 case, that is, when @emph{not} negated (unless stated otherwise,
12177 Some settings are not available on all @acronym{POSIX} systems, since they use
12178 extensions. Such arguments are marked below with ``Non-@acronym{POSIX}'' in their
12179 description. On non-@acronym{POSIX} systems, those or other settings also may not
12180 be available, but it's not feasible to document all the variations: just
12186 * Control:: Control settings
12187 * Input:: Input settings
12188 * Output:: Output settings
12189 * Local:: Local settings
12190 * Combination:: Combination settings
12191 * Characters:: Special characters
12192 * Special:: Special settings
12197 @subsection Control settings
12199 @cindex control settings
12205 @cindex two-way parity
12206 Generate parity bit in output and expect parity bit in input.
12212 @cindex even parity
12213 Set odd parity (even if negated). May be negated.
12220 @cindex character size
12221 @cindex eight-bit characters
12222 Set character size to 5, 6, 7, or 8 bits.
12227 Send a hangup signal when the last process closes the tty. May be
12233 Use two stop bits per character (one if negated). May be negated.
12237 Allow input to be received. May be negated.
12241 @cindex modem control
12242 Disable modem control signals. May be negated.
12246 @cindex hardware flow control
12247 @cindex flow control, hardware
12248 @cindex RTS/CTS flow control
12249 Enable RTS/CTS flow control. Non-@acronym{POSIX}. May be negated.
12254 @subsection Input settings
12256 @cindex input settings
12257 These settings control operations on data received from the terminal.
12262 @cindex breaks, ignoring
12263 Ignore break characters. May be negated.
12267 @cindex breaks, cause interrupts
12268 Make breaks cause an interrupt signal. May be negated.
12272 @cindex parity, ignoring
12273 Ignore characters with parity errors. May be negated.
12277 @cindex parity errors, marking
12278 Mark parity errors (with a 255-0-character sequence). May be negated.
12282 Enable input parity checking. May be negated.
12286 @cindex eight-bit input
12287 Clear high (8th) bit of input characters. May be negated.
12291 @cindex newline, translating to return
12292 Translate newline to carriage return. May be negated.
12296 @cindex return, ignoring
12297 Ignore carriage return. May be negated.
12301 @cindex return, translating to newline
12302 Translate carriage return to newline. May be negated.
12306 @cindex input encoding, UTF-8
12307 Assume input characters are UTF-8 encoded. May be negated.
12311 @kindex C-s/C-q flow control
12312 @cindex XON/XOFF flow control
12313 Enable XON/XOFF flow control (that is, @kbd{CTRL-S}/@kbd{CTRL-Q}). May
12320 @cindex software flow control
12321 @cindex flow control, software
12322 Enable sending of @code{stop} character when the system input buffer
12323 is almost full, and @code{start} character when it becomes almost
12324 empty again. May be negated.
12328 @cindex uppercase, translating to lowercase
12329 Translate uppercase characters to lowercase. Non-@acronym{POSIX}. May be
12330 negated. Note ilcuc is not implemented, as one would not be able to issue
12331 almost any (lowercase) Unix command, after invoking it.
12335 Allow any character to restart output (only the start character
12336 if negated). Non-@acronym{POSIX}. May be negated.
12340 @cindex beeping at input buffer full
12341 Enable beeping and not flushing input buffer if a character arrives
12342 when the input buffer is full. Non-@acronym{POSIX}. May be negated.
12347 @subsection Output settings
12349 @cindex output settings
12350 These settings control operations on data sent to the terminal.
12355 Postprocess output. May be negated.
12359 @cindex lowercase, translating to output
12360 Translate lowercase characters to uppercase. Non-@acronym{POSIX}. May be
12361 negated. (Note ouclc is not currently implemented.)
12365 @cindex return, translating to newline
12366 Translate carriage return to newline. Non-@acronym{POSIX}. May be negated.
12370 @cindex newline, translating to crlf
12371 Translate newline to carriage return-newline. Non-@acronym{POSIX}. May be
12376 Do not print carriage returns in the first column. Non-@acronym{POSIX}.
12381 Newline performs a carriage return. Non-@acronym{POSIX}. May be negated.
12385 @cindex pad instead of timing for delaying
12386 Use fill (padding) characters instead of timing for delays. Non-@acronym{POSIX}.
12391 @cindex pad character
12392 Use @acronym{ASCII} @sc{del} characters for fill instead of
12393 @acronym{ASCII} @sc{nul} characters. Non-@acronym{POSIX}.
12399 Newline delay style. Non-@acronym{POSIX}.
12406 Carriage return delay style. Non-@acronym{POSIX}.
12412 @opindex tab@var{n}
12413 Horizontal tab delay style. Non-@acronym{POSIX}.
12418 Backspace delay style. Non-@acronym{POSIX}.
12423 Vertical tab delay style. Non-@acronym{POSIX}.
12428 Form feed delay style. Non-@acronym{POSIX}.
12433 @subsection Local settings
12435 @cindex local settings
12440 Enable @code{interrupt}, @code{quit}, and @code{suspend} special
12441 characters. May be negated.
12445 Enable @code{erase}, @code{kill}, @code{werase}, and @code{rprnt}
12446 special characters. May be negated.
12450 Enable non-@acronym{POSIX} special characters. May be negated.
12454 Echo input characters. May be negated.
12460 Echo @code{erase} characters as backspace-space-backspace. May be
12465 @cindex newline echoing after @code{kill}
12466 Echo a newline after a @code{kill} character. May be negated.
12470 @cindex newline, echoing
12471 Echo newline even if not echoing other characters. May be negated.
12475 @cindex flushing, disabling
12476 Disable flushing after @code{interrupt} and @code{quit} special
12477 characters. May be negated.
12481 @cindex case translation
12482 Enable input and output of uppercase characters by preceding their
12483 lowercase equivalents with @samp{\}, when @code{icanon} is set.
12484 Non-@acronym{POSIX}. May be negated.
12488 @cindex background jobs, stopping at terminal write
12489 Stop background jobs that try to write to the terminal. Non-@acronym{POSIX}.
12496 Echo erased characters backward, between @samp{\} and @samp{/}.
12497 Non-@acronym{POSIX}. May be negated.
12503 @cindex control characters, using @samp{^@var{c}}
12504 @cindex hat notation for control characters
12505 Echo control characters in hat notation (@samp{^@var{c}}) instead
12506 of literally. Non-@acronym{POSIX}. May be negated.
12512 Echo the @code{kill} special character by erasing each character on
12513 the line as indicated by the @code{echoprt} and @code{echoe} settings,
12514 instead of by the @code{echoctl} and @code{echok} settings. Non-@acronym{POSIX}.
12520 @subsection Combination settings
12522 @cindex combination settings
12523 Combination settings:
12530 Same as @code{parenb -parodd cs7}. May be negated. If negated, same
12531 as @code{-parenb cs8}.
12535 Same as @code{parenb parodd cs7}. May be negated. If negated, same
12536 as @code{-parenb cs8}.
12540 Same as @code{-icrnl -onlcr}. May be negated. If negated, same as
12541 @code{icrnl -inlcr -igncr onlcr -ocrnl -onlret}.
12545 Reset the @code{erase} and @code{kill} special characters to their default
12552 @c This is too long to write inline.
12554 cread -ignbrk brkint -inlcr -igncr icrnl -ixoff
12555 -iuclc -ixany imaxbel opost -olcuc -ocrnl onlcr
12556 -onocr -onlret -ofill -ofdel nl0 cr0 tab0 bs0 vt0
12557 ff0 isig icanon iexten echo echoe echok -echonl
12558 -noflsh -xcase -tostop -echoprt echoctl echoke
12562 and also sets all special characters to their default values.
12566 Same as @code{brkint ignpar istrip icrnl ixon opost isig icanon}, plus
12567 sets the @code{eof} and @code{eol} characters to their default values
12568 if they are the same as the @code{min} and @code{time} characters.
12569 May be negated. If negated, same as @code{raw}.
12576 -ignbrk -brkint -ignpar -parmrk -inpck -istrip
12577 -inlcr -igncr -icrnl -ixon -ixoff -iuclc -ixany
12578 -imaxbel -opost -isig -icanon -xcase min 1 time 0
12582 May be negated. If negated, same as @code{cooked}.
12586 Same as @option{-icanon}. May be negated. If negated, same as
12591 @cindex eight-bit characters
12592 Same as @code{-parenb -istrip cs8}. May be negated. If negated,
12593 same as @code{parenb istrip cs7}.
12597 Same as @option{-parenb -istrip -opost cs8}. May be negated.
12598 If negated, same as @code{parenb istrip opost cs7}.
12602 Same as @option{-ixany}. Non-@acronym{POSIX}. May be negated.
12606 Same as @code{tab0}. Non-@acronym{POSIX}. May be negated. If negated, same
12613 Same as @code{xcase iuclc olcuc}. Non-@acronym{POSIX}. May be negated.
12614 (Used for terminals with uppercase characters only.)
12618 Same as @code{echoe echoctl echoke}.
12622 Same as @code{echoe echoctl echoke -ixany intr ^C erase ^? kill C-u}.
12627 @subsection Special characters
12629 @cindex special characters
12630 @cindex characters, special
12632 The special characters' default values vary from system to system.
12633 They are set with the syntax @samp{name value}, where the names are
12634 listed below and the value can be given either literally, in hat
12635 notation (@samp{^@var{c}}), or as an integer which may start with
12636 @samp{0x} to indicate hexadecimal, @samp{0} to indicate octal, or
12637 any other digit to indicate decimal.
12639 @cindex disabling special characters
12640 @kindex u@r{, and disabling special characters}
12641 For GNU stty, giving a value of @code{^-} or @code{undef} disables that
12642 special character. (This is incompatible with Ultrix @command{stty},
12643 which uses a value of @samp{u} to disable a special character. GNU
12644 @command{stty} treats a value @samp{u} like any other, namely to set that
12645 special character to @key{U}.)
12651 Send an interrupt signal.
12655 Send a quit signal.
12659 Erase the last character typed.
12663 Erase the current line.
12667 Send an end of file (terminate the input).
12675 Alternate character to end the line. Non-@acronym{POSIX}.
12679 Switch to a different shell layer. Non-@acronym{POSIX}.
12683 Restart the output after stopping it.
12691 Send a terminal stop signal.
12695 Send a terminal stop signal after flushing the input. Non-@acronym{POSIX}.
12699 Redraw the current line. Non-@acronym{POSIX}.
12703 Erase the last word typed. Non-@acronym{POSIX}.
12707 Enter the next character typed literally, even if it is a special
12708 character. Non-@acronym{POSIX}.
12713 @subsection Special settings
12715 @cindex special settings
12720 Set the minimum number of characters that will satisfy a read until
12721 the time value has expired, when @option{-icanon} is set.
12725 Set the number of tenths of a second before reads time out if the minimum
12726 number of characters have not been read, when @option{-icanon} is set.
12728 @item ispeed @var{n}
12730 Set the input speed to @var{n}.
12732 @item ospeed @var{n}
12734 Set the output speed to @var{n}.
12738 Tell the tty kernel driver that the terminal has @var{n} rows. Non-@acronym{POSIX}.
12741 @itemx columns @var{n}
12744 Tell the kernel that the terminal has @var{n} columns. Non-@acronym{POSIX}.
12750 Print the number of rows and columns that the kernel thinks the
12751 terminal has. (Systems that don't support rows and columns in the kernel
12752 typically use the environment variables @env{LINES} and @env{COLUMNS}
12753 instead; however, GNU @command{stty} does not know anything about them.)
12754 Non-@acronym{POSIX}.
12758 Use line discipline @var{n}. Non-@acronym{POSIX}.
12762 Print the terminal speed.
12765 @cindex baud rate, setting
12766 Set the input and output speeds to @var{n}. @var{n} can be one of: 0
12767 50 75 110 134 134.5 150 200 300 600 1200 1800 2400 4800 9600 19200
12768 38400 @code{exta} @code{extb}. @code{exta} is the same as 19200;
12769 @code{extb} is the same as 38400. Many systems, including GNU/Linux,
12770 support higher speeds. The @command{stty} command includes support
12787 4000000 where the system supports these.
12788 0 hangs up the line if @option{-clocal} is set.
12792 @node printenv invocation
12793 @section @command{printenv}: Print all or some environment variables
12796 @cindex printing all or some environment variables
12797 @cindex environment variables, printing
12799 @command{printenv} prints environment variable values. Synopsis:
12802 printenv [@var{option}] [@var{variable}]@dots{}
12805 If no @var{variable}s are specified, @command{printenv} prints the value of
12806 every environment variable. Otherwise, it prints the value of each
12807 @var{variable} that is set, and nothing for those that are not set.
12809 The only options are a lone @option{--help} or @option{--version}.
12810 @xref{Common options}.
12812 @cindex exit status of @command{printenv}
12816 0 if all variables specified were found
12817 1 if at least one specified variable was not found
12818 2 if a write error occurred
12822 @node tty invocation
12823 @section @command{tty}: Print file name of terminal on standard input
12826 @cindex print terminal file name
12827 @cindex terminal file name, printing
12829 @command{tty} prints the file name of the terminal connected to its standard
12830 input. It prints @samp{not a tty} if standard input is not a terminal.
12834 tty [@var{option}]@dots{}
12837 The program accepts the following option. Also see @ref{Common options}.
12847 Print nothing; only return an exit status.
12851 @cindex exit status of @command{tty}
12855 0 if standard input is a terminal
12856 1 if standard input is not a terminal
12857 2 if given incorrect arguments
12858 3 if a write error occurs
12862 @node User information
12863 @chapter User information
12865 @cindex user information, commands for
12866 @cindex commands for printing user information
12868 This section describes commands that print user-related information:
12869 logins, groups, and so forth.
12872 * id invocation:: Print user identity.
12873 * logname invocation:: Print current login name.
12874 * whoami invocation:: Print effective user ID.
12875 * groups invocation:: Print group names a user is in.
12876 * users invocation:: Print login names of users currently logged in.
12877 * who invocation:: Print who is currently logged in.
12881 @node id invocation
12882 @section @command{id}: Print user identity
12885 @cindex real user and group IDs, printing
12886 @cindex effective user and group IDs, printing
12887 @cindex printing real and effective user and group IDs
12889 @command{id} prints information about the given user, or the process
12890 running it if no user is specified. Synopsis:
12893 id [@var{option}]@dots{} [@var{username}]
12896 @vindex POSIXLY_CORRECT
12897 By default, it prints the real user ID, real group ID, effective user ID
12898 if different from the real user ID, effective group ID if different from
12899 the real group ID, and supplemental group IDs.
12900 In addition, if SELinux
12901 is enabled and the @env{POSIXLY_CORRECT} environment variable is not set,
12902 then print @samp{context=@var{c}}, where @var{c} is the security context.
12904 Each of these numeric values is preceded by an identifying string and
12905 followed by the corresponding user or group name in parentheses.
12907 The options cause @command{id} to print only part of the above information.
12908 Also see @ref{Common options}.
12915 Print only the group ID.
12921 Print only the group ID and the supplementary groups.
12927 Print the user or group name instead of the ID number. Requires
12928 @option{-u}, @option{-g}, or @option{-G}.
12934 Print the real, instead of effective, user or group ID. Requires
12935 @option{-u}, @option{-g}, or @option{-G}.
12941 Print only the user ID.
12948 @cindex security context
12949 Print only the security context of the current user.
12950 If SELinux is disabled then print a warning and
12951 set the exit status to 1.
12957 @macro primaryAndSupplementaryGroups{cmd,arg}
12958 Primary and supplementary groups for a process are normally inherited
12959 from its parent and are usually unchanged since login. This means
12960 that if you change the group database after logging in, @command{\cmd\}
12961 will not reflect your changes within your existing login session.
12962 Running @command{\cmd\} with a \arg\ causes the user and group
12963 database to be consulted afresh, and so will give a different result.
12965 @primaryAndSupplementaryGroups{id,user argument}
12967 @node logname invocation
12968 @section @command{logname}: Print current login name
12971 @cindex printing user's login name
12972 @cindex login name, printing
12973 @cindex user name, printing
12976 @command{logname} prints the calling user's name, as found in a
12977 system-maintained file (often @file{/var/run/utmp} or
12978 @file{/etc/utmp}), and exits with a status of 0. If there is no entry
12979 for the calling process, @command{logname} prints
12980 an error message and exits with a status of 1.
12982 The only options are @option{--help} and @option{--version}. @xref{Common
12988 @node whoami invocation
12989 @section @command{whoami}: Print effective user ID
12992 @cindex effective user ID, printing
12993 @cindex printing the effective user ID
12995 @command{whoami} prints the user name associated with the current
12996 effective user ID. It is equivalent to the command @samp{id -un}.
12998 The only options are @option{--help} and @option{--version}. @xref{Common
13004 @node groups invocation
13005 @section @command{groups}: Print group names a user is in
13008 @cindex printing groups a user is in
13009 @cindex supplementary groups, printing
13011 @command{groups} prints the names of the primary and any supplementary
13012 groups for each given @var{username}, or the current process if no names
13013 are given. If more than one name is given, the name of each user is
13015 the list of that user's groups and the user name is separated from the
13016 group list by a colon. Synopsis:
13019 groups [@var{username}]@dots{}
13022 The group lists are equivalent to the output of the command @samp{id -Gn}.
13024 @primaryAndSupplementaryGroups{groups,list of users}
13026 The only options are @option{--help} and @option{--version}. @xref{Common
13032 @node users invocation
13033 @section @command{users}: Print login names of users currently logged in
13036 @cindex printing current usernames
13037 @cindex usernames, printing current
13039 @cindex login sessions, printing users with
13040 @command{users} prints on a single line a blank-separated list of user
13041 names of users currently logged in to the current host. Each user name
13042 corresponds to a login session, so if a user has more than one login
13043 session, that user's name will appear the same number of times in the
13052 With no @var{file} argument, @command{users} extracts its information from
13053 a system-maintained file (often @file{/var/run/utmp} or
13054 @file{/etc/utmp}). If a file argument is given, @command{users} uses
13055 that file instead. A common choice is @file{/var/log/wtmp}.
13057 The only options are @option{--help} and @option{--version}. @xref{Common
13063 @node who invocation
13064 @section @command{who}: Print who is currently logged in
13067 @cindex printing current user information
13068 @cindex information, about current users
13070 @command{who} prints information about users who are currently logged on.
13074 @command{who} [@var{option}] [@var{file}] [am i]
13077 @cindex terminal lines, currently used
13079 @cindex remote hostname
13080 If given no non-option arguments, @command{who} prints the following
13081 information for each user currently logged on: login name, terminal
13082 line, login time, and remote hostname or X display.
13086 If given one non-option argument, @command{who} uses that instead of
13087 a default system-maintained file (often @file{/var/run/utmp} or
13088 @file{/etc/utmp}) as the name of the file containing the record of
13089 users logged on. @file{/var/log/wtmp} is commonly given as an argument
13090 to @command{who} to look at who has previously logged on.
13094 If given two non-option arguments, @command{who} prints only the entry
13095 for the user running it (determined from its standard input), preceded
13096 by the hostname. Traditionally, the two arguments given are @samp{am
13097 i}, as in @samp{who am i}.
13100 Time stamps are listed according to the time zone rules specified by
13101 the @env{TZ} environment variable, or by the system default rules if
13102 @env{TZ} is not set. @xref{TZ Variable,, Specifying the Time Zone
13103 with @env{TZ}, libc, The GNU C Library Reference Manual}.
13105 The program accepts the following options. Also see @ref{Common options}.
13113 Same as @samp{-b -d --login -p -r -t -T -u}.
13119 Print the date and time of last system boot.
13125 Print information corresponding to dead processes.
13131 Print a line of column headings.
13137 List only the entries that correspond to processes via which the
13138 system is waiting for a user to login. The user name is always @samp{LOGIN}.
13142 Attempt to canonicalize hostnames found in utmp through a DNS lookup. This
13143 is not the default because it can cause significant delays on systems with
13144 automatic dial-up internet access.
13148 Same as @samp{who am i}.
13154 List active processes spawned by init.
13160 Print only the login names and the number of users logged on.
13161 Overrides all other options.
13166 @opindex --runlevel
13167 Print the current (and maybe previous) run-level of the init process.
13171 Ignored; for compatibility with other versions of @command{who}.
13177 Print last system clock change.
13182 After the login time, print the number of hours and minutes that the
13183 user has been idle. @samp{.} means the user was active in the last minute.
13184 @samp{old} means the user has been idle for more than 24 hours.
13195 @opindex --writable
13196 @cindex message status
13197 @pindex write@r{, allowed}
13198 After each login name print a character indicating the user's message status:
13201 @samp{+} allowing @code{write} messages
13202 @samp{-} disallowing @code{write} messages
13203 @samp{?} cannot find terminal device
13211 @node System context
13212 @chapter System context
13214 @cindex system context
13215 @cindex context, system
13216 @cindex commands for system context
13218 This section describes commands that print or change system-wide
13222 * date invocation:: Print or set system date and time.
13223 * arch invocation:: Print machine hardware name.
13224 * uname invocation:: Print system information.
13225 * hostname invocation:: Print or set system name.
13226 * hostid invocation:: Print numeric host identifier.
13227 * uptime invocation:: Print system uptime and load.
13230 @node date invocation
13231 @section @command{date}: Print or set system date and time
13234 @cindex time, printing or setting
13235 @cindex printing the current time
13240 date [@var{option}]@dots{} [+@var{format}]
13241 date [-u|--utc|--universal] @c this avoids a newline in the output
13242 [ MMDDhhmm[[CC]YY][.ss] ]
13246 Invoking @command{date} with no @var{format} argument is equivalent to invoking
13247 it with a default format that depends on the @env{LC_TIME} locale category.
13248 In the default C locale, this format is @samp{'+%a %b %e %H:%M:%S %Z %Y'},
13249 so the output looks like @samp{Thu Mar @ 3 13:47:51 PST 2005}.
13252 Normally, @command{date} uses the time zone rules indicated by the
13253 @env{TZ} environment variable, or the system default rules if @env{TZ}
13254 is not set. @xref{TZ Variable,, Specifying the Time Zone with
13255 @env{TZ}, libc, The GNU C Library Reference Manual}.
13257 @findex strftime @r{and @command{date}}
13258 @cindex time formats
13259 @cindex formatting times
13260 If given an argument that starts with a @samp{+}, @command{date} prints the
13261 current date and time (or the date and time specified by the
13262 @option{--date} option, see below) in the format defined by that argument,
13263 which is similar to that of the @code{strftime} function. Except for
13264 conversion specifiers, which start with @samp{%}, characters in the
13265 format string are printed unchanged. The conversion specifiers are
13271 * Time conversion specifiers:: %[HIklMNpPrRsSTXzZ]
13272 * Date conversion specifiers:: %[aAbBcCdDeFgGhjmuUVwWxyY]
13273 * Literal conversion specifiers:: %[%nt]
13274 * Padding and other flags:: Pad with zeros, spaces, etc.
13275 * Setting the time:: Changing the system clock.
13276 * Options for date:: Instead of the current time.
13278 * Date input formats:: Specifying date strings.
13280 * Examples of date:: Examples.
13283 @node Time conversion specifiers
13284 @subsection Time conversion specifiers
13286 @cindex time conversion specifiers
13287 @cindex conversion specifiers, time
13289 @command{date} conversion specifiers related to times.
13293 hour (@samp{00}@dots{}@samp{23})
13295 hour (@samp{01}@dots{}@samp{12})
13297 hour (@samp{ 0}@dots{}@samp{23}).
13298 This is a @acronym{GNU} extension.
13300 hour (@samp{ 1}@dots{}@samp{12}).
13301 This is a @acronym{GNU} extension.
13303 minute (@samp{00}@dots{}@samp{59})
13305 nanoseconds (@samp{000000000}@dots{}@samp{999999999}).
13306 This is a @acronym{GNU} extension.
13308 locale's equivalent of either @samp{AM} or @samp{PM};
13309 blank in many locales.
13310 Noon is treated as @samp{PM} and midnight as @samp{AM}.
13312 like @samp{%p}, except lower case.
13313 This is a @acronym{GNU} extension.
13315 locale's 12-hour clock time (e.g., @samp{11:11:04 PM})
13317 24-hour hour and minute. Same as @samp{%H:%M}.
13318 This is a @acronym{GNU} extension.
13320 @cindex epoch, seconds since
13321 @cindex seconds since the epoch
13322 @cindex beginning of time
13323 seconds since the epoch, i.e., since 1970-01-01 00:00:00 UTC.
13324 Leap seconds are not counted unless leap second support is available.
13325 @xref{%s-examples}, for examples.
13326 This is a @acronym{GNU} extension.
13328 second (@samp{00}@dots{}@samp{60}).
13329 This may be @samp{60} if leap seconds are supported.
13331 24-hour hour, minute, and second. Same as @samp{%H:%M:%S}.
13333 locale's time representation (e.g., @samp{23:13:48})
13335 @w{@acronym{RFC} 2822/@acronym{ISO} 8601} style numeric time zone
13336 (e.g., @samp{-0600} or @samp{+0530}), or nothing if no
13337 time zone is determinable. This value reflects the numeric time zone
13338 appropriate for the current time, using the time zone rules specified
13339 by the @env{TZ} environment variable.
13340 The time (and optionally, the time zone rules) can be overridden
13341 by the @option{--date} option.
13342 This is a @acronym{GNU} extension.
13344 @w{@acronym{RFC} 3339/@acronym{ISO} 8601} style numeric time zone with
13345 @samp{:} (e.g., @samp{-06:00} or @samp{+05:30}), or nothing if no time
13346 zone is determinable.
13347 This is a @acronym{GNU} extension.
13349 Numeric time zone to the nearest second with @samp{:} (e.g.,
13350 @samp{-06:00:00} or @samp{+05:30:00}), or nothing if no time zone is
13352 This is a @acronym{GNU} extension.
13354 Numeric time zone with @samp{:} using the minimum necessary precision
13355 (e.g., @samp{-06}, @samp{+05:30}, or @samp{-04:56:02}), or nothing if
13356 no time zone is determinable.
13357 This is a @acronym{GNU} extension.
13359 alphabetic time zone abbreviation (e.g., @samp{EDT}), or nothing if no
13360 time zone is determinable. See @samp{%z} for how it is determined.
13364 @node Date conversion specifiers
13365 @subsection Date conversion specifiers
13367 @cindex date conversion specifiers
13368 @cindex conversion specifiers, date
13370 @command{date} conversion specifiers related to dates.
13374 locale's abbreviated weekday name (e.g., @samp{Sun})
13376 locale's full weekday name, variable length (e.g., @samp{Sunday})
13378 locale's abbreviated month name (e.g., @samp{Jan})
13380 locale's full month name, variable length (e.g., @samp{January})
13382 locale's date and time (e.g., @samp{Thu Mar @ 3 23:05:25 2005})
13384 century. This is like @samp{%Y}, except the last two digits are omitted.
13385 For example, it is @samp{20} if @samp{%Y} is @samp{2000},
13386 and is @samp{-0} if @samp{%Y} is @samp{-001}.
13387 It is normally at least two characters, but it may be more.
13389 day of month (e.g., @samp{01})
13391 date; same as @samp{%m/%d/%y}
13393 day of month, space padded; same as @samp{%_d}
13395 full date in @acronym{ISO} 8601 format; same as @samp{%Y-%m-%d}.
13396 This is a good choice for a date format, as it is standard and
13397 is easy to sort in the usual case where years are in the range
13399 This is a @acronym{GNU} extension.
13401 year corresponding to the @acronym{ISO} week number, but without the century
13402 (range @samp{00} through @samp{99}). This has the same format and value
13403 as @samp{%y}, except that if the @acronym{ISO} week number (see
13405 to the previous or next year, that year is used instead.
13406 This is a @acronym{GNU} extension.
13408 year corresponding to the @acronym{ISO} week number. This has the
13409 same format and value as @samp{%Y}, except that if the @acronym{ISO}
13411 @samp{%V}) belongs to the previous or next year, that year is used
13413 It is normally useful only if @samp{%V} is also used;
13414 for example, the format @samp{%G-%m-%d} is probably a mistake,
13415 since it combines the ISO week number year with the conventional month and day.
13416 This is a @acronym{GNU} extension.
13420 day of year (@samp{001}@dots{}@samp{366})
13422 month (@samp{01}@dots{}@samp{12})
13424 day of week (@samp{1}@dots{}@samp{7}) with @samp{1} corresponding to Monday
13426 week number of year, with Sunday as the first day of the week
13427 (@samp{00}@dots{}@samp{53}).
13428 Days in a new year preceding the first Sunday are in week zero.
13430 @acronym{ISO} week number, that is, the
13431 week number of year, with Monday as the first day of the week
13432 (@samp{01}@dots{}@samp{53}).
13433 If the week containing January 1 has four or more days in
13434 the new year, then it is considered week 1; otherwise, it is week 53 of
13435 the previous year, and the next week is week 1. (See the @acronym{ISO} 8601
13438 day of week (@samp{0}@dots{}@samp{6}) with 0 corresponding to Sunday
13440 week number of year, with Monday as first day of week
13441 (@samp{00}@dots{}@samp{53}).
13442 Days in a new year preceding the first Monday are in week zero.
13444 locale's date representation (e.g., @samp{12/31/99})
13446 last two digits of year (@samp{00}@dots{}@samp{99})
13448 year. This is normally at least four characters, but it may be more.
13449 Year @samp{0000} precedes year @samp{0001}, and year @samp{-001}
13450 precedes year @samp{0000}.
13454 @node Literal conversion specifiers
13455 @subsection Literal conversion specifiers
13457 @cindex literal conversion specifiers
13458 @cindex conversion specifiers, literal
13460 @command{date} conversion specifiers that produce literal strings.
13472 @node Padding and other flags
13473 @subsection Padding and other flags
13475 @cindex numeric field padding
13476 @cindex padding of numeric fields
13477 @cindex fields, padding numeric
13479 Unless otherwise specified, @command{date} normally pads numeric fields
13480 with zeros, so that, for
13481 example, numeric months are always output as two digits.
13482 Seconds since the epoch are not padded, though,
13483 since there is no natural width for them.
13485 As a @acronym{GNU} extension, @command{date} recognizes any of the
13486 following optional flags after the @samp{%}:
13490 (hyphen) Do not pad the field; useful if the output is intended for
13493 (underscore) Pad with spaces; useful if you need a fixed
13494 number of characters in the output, but zeros are too distracting.
13496 (zero) Pad with zeros even if the conversion specifier
13497 would normally pad with spaces.
13499 Use upper case characters if possible.
13501 Use opposite case characters if possible.
13502 A field that is normally upper case becomes lower case, and vice versa.
13506 Here are some examples of padding:
13509 date +%d/%m -d "Feb 1"
13511 date +%-d/%-m -d "Feb 1"
13513 date +%_d/%_m -d "Feb 1"
13517 As a @acronym{GNU} extension, you can specify the field width
13518 (after any flag, if present) as a decimal number. If the natural size of the
13519 output of the field has less than the specified number of characters,
13520 the result is written right adjusted and padded to the given
13521 size. For example, @samp{%9B} prints the right adjusted month name in
13522 a field of width 9.
13524 An optional modifier can follow the optional flag and width
13525 specification. The modifiers are:
13529 Use the locale's alternate representation for date and time. This
13530 modifier applies to the @samp{%c}, @samp{%C}, @samp{%x}, @samp{%X},
13531 @samp{%y} and @samp{%Y} conversion specifiers. In a Japanese locale, for
13532 example, @samp{%Ex} might yield a date format based on the Japanese
13536 Use the locale's alternate numeric symbols for numbers. This modifier
13537 applies only to numeric conversion specifiers.
13540 If the format supports the modifier but no alternate representation
13541 is available, it is ignored.
13544 @node Setting the time
13545 @subsection Setting the time
13547 @cindex setting the time
13548 @cindex time setting
13549 @cindex appropriate privileges
13551 If given an argument that does not start with @samp{+}, @command{date} sets
13552 the system clock to the date and time specified by that argument (as
13553 described below). You must have appropriate privileges to set the
13554 system clock. The @option{--date} and @option{--set} options may not be
13555 used with such an argument. The @option{--universal} option may be used
13556 with such an argument to indicate that the specified date and time are
13557 relative to Coordinated Universal Time rather than to the local time
13560 The argument must consist entirely of digits, which have the following
13573 first two digits of year (optional)
13575 last two digits of year (optional)
13580 The @option{--set} option also sets the system clock; see the next section.
13583 @node Options for date
13584 @subsection Options for @command{date}
13586 @cindex @command{date} options
13587 @cindex options for @command{date}
13589 The program accepts the following options. Also see @ref{Common options}.
13593 @item -d @var{datestr}
13594 @itemx --date=@var{datestr}
13597 @cindex parsing date strings
13598 @cindex date strings, parsing
13599 @cindex arbitrary date strings, parsing
13602 @opindex next @var{day}
13603 @opindex last @var{day}
13604 Display the date and time specified in @var{datestr} instead of the
13605 current date and time. @var{datestr} can be in almost any common
13606 format. It can contain month names, time zones, @samp{am} and @samp{pm},
13607 @samp{yesterday}, etc. For example, @option{--date="2004-02-27
13608 14:19:13.489392193 +0530"} specifies the instant of time that is
13609 489,392,193 nanoseconds after February 27, 2004 at 2:19:13 PM in a
13610 time zone that is 5 hours and 30 minutes east of @acronym{UTC}.@*
13611 Note: input currently must be in locale independent format. E.g., the
13612 LC_TIME=C below is needed to print back the correct date in many locales:
13614 date -d "$(LC_TIME=C date)"
13616 @xref{Date input formats}.
13618 @item -f @var{datefile}
13619 @itemx --file=@var{datefile}
13622 Parse each line in @var{datefile} as with @option{-d} and display the
13623 resulting date and time. If @var{datefile} is @samp{-}, use standard
13624 input. This is useful when you have many dates to process, because the
13625 system overhead of starting up the @command{date} executable many times can
13628 @item -r @var{file}
13629 @itemx --reference=@var{file}
13631 @opindex --reference
13632 Display the date and time of the last modification of @var{file},
13633 instead of the current date and time.
13640 @opindex --rfc-2822
13641 Display the date and time using the format @samp{%a, %d %b %Y %H:%M:%S
13642 %z}, evaluated in the C locale so abbreviations are always in English.
13646 Fri, 09 Sep 2005 13:51:39 -0700
13649 This format conforms to
13650 @uref{ftp://ftp.rfc-editor.org/in-notes/rfc2822.txt, Internet
13651 @acronym{RFCs} 2822} and
13652 @uref{ftp://ftp.rfc-editor.org/in-notes/rfc822.txt, 822}, the
13653 current and previous standards for Internet email.
13655 @item --rfc-3339=@var{timespec}
13656 @opindex --rfc-3339=@var{timespec}
13657 Display the date using a format specified by
13658 @uref{ftp://ftp.rfc-editor.org/in-notes/rfc3339.txt, Internet
13659 @acronym{RFC} 3339}. This is a subset of the @acronym{ISO} 8601
13660 format, except that it also permits applications to use a space rather
13661 than a @samp{T} to separate dates from times. Unlike the other
13662 standard formats, @acronym{RFC} 3339 format is always suitable as
13663 input for the @option{--date} (@option{-d}) and @option{--file}
13664 (@option{-f}) options, regardless of the current locale.
13666 The argument @var{timespec} specifies how much of the time to include.
13667 It can be one of the following:
13671 Print just the full-date, e.g., @samp{2005-09-14}.
13672 This is equivalent to the format @samp{%Y-%m-%d}.
13675 Print the full-date and full-time separated by a space, e.g.,
13676 @samp{2005-09-14 00:56:06+05:30}. The output ends with a numeric
13677 time-offset; here the @samp{+05:30} means that local time is five
13678 hours and thirty minutes east of @acronym{UTC}. This is equivalent to
13679 the format @samp{%Y-%m-%d %H:%M:%S%:z}.
13682 Like @samp{seconds}, but also print nanoseconds, e.g.,
13683 @samp{2005-09-14 00:56:06.998458565+05:30}.
13684 This is equivalent to the format @samp{%Y-%m-%d %H:%M:%S.%N%:z}.
13688 @item -s @var{datestr}
13689 @itemx --set=@var{datestr}
13692 Set the date and time to @var{datestr}. See @option{-d} above.
13699 @opindex --universal
13700 @cindex Coordinated Universal Time
13702 @cindex Greenwich Mean Time
13705 Use Coordinated Universal Time (@acronym{UTC}) by operating as if the
13706 @env{TZ} environment variable were set to the string @samp{UTC0}.
13708 Universal Time is often called ``Greenwich Mean Time'' (@sc{gmt}) for
13709 historical reasons.
13713 @node Examples of date
13714 @subsection Examples of @command{date}
13716 @cindex examples of @command{date}
13718 Here are a few examples. Also see the documentation for the @option{-d}
13719 option in the previous section.
13724 To print the date of the day before yesterday:
13727 date --date='2 days ago'
13731 To print the date of the day three months and one day hence:
13734 date --date='3 months 1 day'
13738 To print the day of year of Christmas in the current year:
13741 date --date='25 Dec' +%j
13745 To print the current full month name and the day of the month:
13751 But this may not be what you want because for the first nine days of
13752 the month, the @samp{%d} expands to a zero-padded two-digit field,
13753 for example @samp{date -d 1may '+%B %d'} will print @samp{May 01}.
13756 To print a date without the leading zero for one-digit days
13757 of the month, you can use the (@acronym{GNU} extension)
13758 @samp{-} flag to suppress
13759 the padding altogether:
13762 date -d 1may '+%B %-d
13766 To print the current date and time in the format required by many
13767 non-@acronym{GNU} versions of @command{date} when setting the system clock:
13770 date +%m%d%H%M%Y.%S
13774 To set the system clock forward by two minutes:
13777 date --set='+2 minutes'
13781 To print the date in @acronym{RFC} 2822 format,
13782 use @samp{date --rfc-2822}. Here is some example output:
13785 Fri, 09 Sep 2005 13:51:39 -0700
13788 @anchor{%s-examples}
13790 To convert a date string to the number of seconds since the epoch
13791 (which is 1970-01-01 00:00:00 UTC), use the @option{--date} option with
13792 the @samp{%s} format. That can be useful in sorting and/or graphing
13793 and/or comparing data by date. The following command outputs the
13794 number of the seconds since the epoch for the time two minutes after the
13798 date --date='1970-01-01 00:02:00 +0000' +%s
13802 If you do not specify time zone information in the date string,
13803 @command{date} uses your computer's idea of the time zone when
13804 interpreting the string. For example, if your computer's time zone is
13805 that of Cambridge, Massachusetts, which was then 5 hours (i.e., 18,000
13806 seconds) behind UTC:
13809 # local time zone used
13810 date --date='1970-01-01 00:02:00' +%s
13815 If you're sorting or graphing dated data, your raw date values may be
13816 represented as seconds since the epoch. But few people can look at
13817 the date @samp{946684800} and casually note ``Oh, that's the first second
13818 of the year 2000 in Greenwich, England.''
13821 date --date='2000-01-01 UTC' +%s
13825 An alternative is to use the @option{--utc} (@option{-u}) option.
13826 Then you may omit @samp{UTC} from the date string. Although this
13827 produces the same result for @samp{%s} and many other format sequences,
13828 with a time zone offset different from zero, it would give a different
13829 result for zone-dependent formats like @samp{%z}.
13832 date -u --date=2000-01-01 +%s
13836 To convert such an unwieldy number of seconds back to
13837 a more readable form, use a command like this:
13840 # local time zone used
13841 date -d '1970-01-01 UTC 946684800 seconds' +"%Y-%m-%d %T %z"
13842 1999-12-31 19:00:00 -0500
13845 Or if you do not mind depending on the @samp{@@} feature present since
13846 coreutils 5.3.0, you could shorten this to:
13849 date -d @@946684800 +"%F %T %z"
13850 1999-12-31 19:00:00 -0500
13853 Often it is better to output UTC-relative date and time:
13856 date -u -d '1970-01-01 946684800 seconds' +"%Y-%m-%d %T %z"
13857 2000-01-01 00:00:00 +0000
13863 @node arch invocation
13864 @section @command{arch}: Print machine hardware name
13867 @cindex print machine hardware name
13868 @cindex system information, printing
13870 @command{arch} prints the machine hardware name,
13871 and is equivalent to @samp{uname -m}.
13875 arch [@var{option}]
13878 The program accepts the @ref{Common options} only.
13883 @node uname invocation
13884 @section @command{uname}: Print system information
13887 @cindex print system information
13888 @cindex system information, printing
13890 @command{uname} prints information about the machine and operating system
13891 it is run on. If no options are given, @command{uname} acts as if the
13892 @option{-s} option were given. Synopsis:
13895 uname [@var{option}]@dots{}
13898 If multiple options or @option{-a} are given, the selected information is
13899 printed in this order:
13902 @var{kernel-name} @var{nodename} @var{kernel-release} @var{kernel-version}
13903 @var{machine} @var{processor} @var{hardware-platform} @var{operating-system}
13906 The information may contain internal spaces, so such output cannot be
13907 parsed reliably. In the following example, @var{release} is
13908 @samp{2.2.18ss.e820-bda652a #4 SMP Tue Jun 5 11:24:08 PDT 2001}:
13912 @result{} Linux dum 2.2.18 #4 SMP Tue Jun 5 11:24:08 PDT 2001 i686 unknown unknown GNU/Linux
13916 The program accepts the following options. Also see @ref{Common options}.
13924 Print all of the below information, except omit the processor type
13925 and the hardware platform name if they are unknown.
13928 @itemx --hardware-platform
13930 @opindex --hardware-platform
13931 @cindex implementation, hardware
13932 @cindex hardware platform
13933 @cindex platform, hardware
13934 Print the hardware platform name
13935 (sometimes called the hardware implementation).
13936 Print @samp{unknown} if the kernel does not make this information
13937 easily available, as is the case with Linux kernels.
13943 @cindex machine type
13944 @cindex hardware class
13945 @cindex hardware type
13946 Print the machine hardware name (sometimes called the hardware class
13952 @opindex --nodename
13955 @cindex network node name
13956 Print the network node hostname.
13961 @opindex --processor
13962 @cindex host processor type
13963 Print the processor type (sometimes called the instruction set
13964 architecture or ISA).
13965 Print @samp{unknown} if the kernel does not make this information
13966 easily available, as is the case with Linux kernels.
13969 @itemx --operating-system
13971 @opindex --operating-system
13972 @cindex operating system name
13973 Print the name of the operating system.
13976 @itemx --kernel-release
13978 @opindex --kernel-release
13979 @cindex kernel release
13980 @cindex release of kernel
13981 Print the kernel release.
13984 @itemx --kernel-name
13986 @opindex --kernel-name
13987 @cindex kernel name
13988 @cindex name of kernel
13989 Print the kernel name.
13990 @acronym{POSIX} 1003.1-2001 (@pxref{Standards conformance}) calls this
13991 ``the implementation of the operating system'', because the
13992 @acronym{POSIX} specification itself has no notion of ``kernel''.
13993 The kernel name might be the same as the operating system name printed
13994 by the @option{-o} or @option{--operating-system} option, but it might
13995 differ. Some operating systems (e.g., FreeBSD, HP-UX) have the same
13996 name as their underlying kernels; others (e.g., GNU/Linux, Solaris)
14000 @itemx --kernel-version
14002 @opindex --kernel-version
14003 @cindex kernel version
14004 @cindex version of kernel
14005 Print the kernel version.
14012 @node hostname invocation
14013 @section @command{hostname}: Print or set system name
14016 @cindex setting the hostname
14017 @cindex printing the hostname
14018 @cindex system name, printing
14019 @cindex appropriate privileges
14021 With no arguments, @command{hostname} prints the name of the current host
14022 system. With one argument, it sets the current host name to the
14023 specified string. You must have appropriate privileges to set the host
14027 hostname [@var{name}]
14030 The only options are @option{--help} and @option{--version}. @xref{Common
14036 @node hostid invocation
14037 @section @command{hostid}: Print numeric host identifier
14040 @cindex printing the host identifier
14042 @command{hostid} prints the numeric identifier of the current host
14043 in hexadecimal. This command accepts no arguments.
14044 The only options are @option{--help} and @option{--version}.
14045 @xref{Common options}.
14047 For example, here's what it prints on one system I use:
14054 On that system, the 32-bit quantity happens to be closely
14055 related to the system's Internet address, but that isn't always
14060 @node uptime invocation
14061 @section @command{uptime}: Print system uptime and load
14064 @cindex printing the system uptime and load
14066 @command{uptime} prints the current time, the system's uptime, the
14067 number of logged-in users and the current load average.
14069 If an argument is specified, it is used as the file to be read
14070 to discover how many users are logged in. If no argument is
14071 specified, a system default is used (@command{uptime --help} indicates
14072 the default setting).
14074 The only options are @option{--help} and @option{--version}.
14075 @xref{Common options}.
14077 For example, here's what it prints right now on one system I use:
14081 14:07 up 3:35, 3 users, load average: 1.39, 1.15, 1.04
14084 The precise method of calculation of load average varies somewhat
14085 between systems. Some systems calculate it as the average number of
14086 runnable processes over the last 1, 5 and 15 minutes, but some systems
14087 also include processes in the uninterruptible sleep state (that is,
14088 those processes which are waiting for disk I/O). The Linux kernel
14089 includes uninterruptible processes.
14091 @node SELinux context
14092 @chapter SELinux context
14094 @cindex SELinux context
14095 @cindex SELinux, context
14096 @cindex commands for SELinux context
14098 This section describes commands for operations with SELinux
14102 * chcon invocation:: Change SELinux context of file
14103 * runcon invocation:: Run a command in specified SELinux context
14106 @node chcon invocation
14107 @section @command{chcon}: Change SELinux context of file
14110 @cindex changing security context
14111 @cindex change SELinux context
14113 @command{chcon} changes the SELinux security context of the selected files.
14117 chcon [@var{option}]@dots{} @var{context} @var{file}@dots{}
14118 chcon [@var{option}]@dots{} [-u @var{user}] [-r @var{role}] [-l @var{range}] [-t @var{type}] @var{file}@dots{}
14119 chcon [@var{option}]@dots{} --reference=@var{rfile} @var{file}@dots{}
14122 Change the SELinux security context of each @var{file} to @var{context}.
14123 With @option{--reference}, change the security context of each @var{file}
14124 to that of @var{rfile}.
14126 The program accepts the following options. Also see @ref{Common options}.
14131 @itemx --no-dereference
14133 @opindex --no-dereference
14134 @cindex no dereference
14135 Affect symbolic links instead of any referenced file.
14137 @item --reference=@var{rfile}
14138 @opindex --reference
14139 @cindex reference file
14140 Use @var{rfile}'s security context rather than specifying a @var{context} value.
14145 @opindex --recursive
14146 Operate on files and directories recursively.
14149 @xref{Traversing symlinks}.
14152 @xref{Traversing symlinks}.
14155 @xref{Traversing symlinks}.
14162 Output a diagnostic for every file processed.
14164 @item -u @var{user}
14165 @itemx --user=@var{user}
14168 Set user @var{user} in the target security context.
14170 @item -r @var{role}
14171 @itemx --role=@var{role}
14174 Set role @var{role} in the target security context.
14176 @item -t @var{type}
14177 @itemx --type=@var{type}
14180 Set type @var{type} in the target security context.
14182 @item -l @var{range}
14183 @itemx --range=@var{range}
14186 Set range @var{range} in the target security context.
14192 @node runcon invocation
14193 @section @command{runcon}: Run a command in specified SELinux context
14196 @cindex run with security context
14199 @command{runcon} runs file in specified SELinux security context.
14203 runcon @var{context} @var{command} [@var{args}]
14204 runcon [ -c ] [-u @var{user}] [-r @var{role}] [-t @var{type}] [-l @var{range}] @var{command} [@var{args}]
14207 Run @var{command} with completely-specified @var{context}, or with
14208 current or transitioned security context modified by one or more of @var{level},
14209 @var{role}, @var{type} and @var{user}.
14211 If none of @option{-c}, @option{-t}, @option{-u}, @option{-r}, or @option{-l}
14212 is specified, the first argument is used as the complete context.
14213 Any additional arguments after @var{command}
14214 are interpreted as arguments to the command.
14216 With neither @var{context} nor @var{command}, print the current security context.
14218 The program accepts the following options. Also see @ref{Common options}.
14226 Compute process transition context before modifying.
14228 @item -u @var{user}
14229 @itemx --user=@var{user}
14232 Set user @var{user} in the target security context.
14234 @item -r @var{role}
14235 @itemx --role=@var{role}
14238 Set role @var{role} in the target security context.
14240 @item -t @var{type}
14241 @itemx --type=@var{type}
14244 Set type @var{type} in the target security context.
14246 @item -l @var{range}
14247 @itemx --range=@var{range}
14250 Set range @var{range} in the target security context.
14254 @cindex exit status of @command{runcon}
14258 126 if @var{command} is found but cannot be invoked
14259 127 if @command{runcon} itself fails or if @var{command} cannot be found
14260 the exit status of @var{command} otherwise
14263 @node Modified command invocation
14264 @chapter Modified command invocation
14266 @cindex modified command invocation
14267 @cindex invocation of commands, modified
14268 @cindex commands for invoking other commands
14270 This section describes commands that run other commands in some context
14271 different than the current one: a modified environment, as a different
14275 * chroot invocation:: Modify the root directory.
14276 * env invocation:: Modify environment variables.
14277 * nice invocation:: Modify niceness.
14278 * nohup invocation:: Immunize to hangups.
14279 * stdbuf invocation:: Modify buffering of standard streams.
14280 * su invocation:: Modify user and group ID.
14281 * timeout invocation:: Run with time limit.
14285 @node chroot invocation
14286 @section @command{chroot}: Run a command with a different root directory
14289 @cindex running a program in a specified root directory
14290 @cindex root directory, running a program in a specified
14292 @command{chroot} runs a command with a specified root directory.
14293 On many systems, only the super-user can do this.@footnote{However,
14294 some systems (e.g., FreeBSD) can be configured to allow certain regular
14295 users to use the @code{chroot} system call, and hence to run this program.
14296 Also, on Cygwin, anyone can run the @command{chroot} command, because the
14297 underlying function is non-privileged due to lack of support in MS-Windows.}
14301 chroot @var{option} @var{newroot} [@var{command} [@var{args}]@dots{}]
14302 chroot @var{option}
14305 Ordinarily, file names are looked up starting at the root of the
14306 directory structure, i.e., @file{/}. @command{chroot} changes the root to
14307 the directory @var{newroot} (which must exist) and then runs
14308 @var{command} with optional @var{args}. If @var{command} is not
14309 specified, the default is the value of the @env{SHELL} environment
14310 variable or @command{/bin/sh} if not set, invoked with the @option{-i} option.
14311 @var{command} must not be a special built-in utility
14312 (@pxref{Special built-in utilities}).
14314 The program accepts the following options. Also see @ref{Common options}.
14315 Options must precede operands.
14319 @itemx --userspec=@var{user}[:@var{group}]
14320 @opindex --userspec
14321 By default, @var{command} is run with the same credentials
14322 as the invoking process.
14323 Use this option to run it as a different @var{user} and/or with a
14324 different primary @var{group}.
14326 @itemx --groups=@var{groups}
14328 Use this option to specify the supplementary @var{groups} to be
14329 used by the new process.
14330 The items in the list (names or numeric IDs) must be separated by commas.
14334 Here are a few tips to help avoid common problems in using chroot.
14335 To start with a simple example, make @var{command} refer to a statically
14336 linked binary. If you were to use a dynamically linked executable, then
14337 you'd have to arrange to have the shared libraries in the right place under
14338 your new root directory.
14340 For example, if you create a statically linked @command{ls} executable,
14341 and put it in @file{/tmp/empty}, you can run this command as root:
14344 $ chroot /tmp/empty /ls -Rl /
14347 Then you'll see output like this:
14352 -rwxr-xr-x 1 0 0 1041745 Aug 16 11:17 ls
14355 If you want to use a dynamically linked executable, say @command{bash},
14356 then first run @samp{ldd bash} to see what shared objects it needs.
14357 Then, in addition to copying the actual binary, also copy the listed
14358 files to the required positions under your intended new root directory.
14359 Finally, if the executable requires any other files (e.g., data, state,
14360 device files), copy them into place, too.
14362 @cindex exit status of @command{chroot}
14366 125 if @command{chroot} itself fails
14367 126 if @var{command} is found but cannot be invoked
14368 127 if @var{command} cannot be found
14369 the exit status of @var{command} otherwise
14373 @node env invocation
14374 @section @command{env}: Run a command in a modified environment
14377 @cindex environment, running a program in a modified
14378 @cindex modified environment, running a program in a
14379 @cindex running a program in a modified environment
14381 @command{env} runs a command with a modified environment. Synopses:
14384 env [@var{option}]@dots{} [@var{name}=@var{value}]@dots{} @c
14385 [@var{command} [@var{args}]@dots{}]
14389 Operands of the form @samp{@var{variable}=@var{value}} set
14390 the environment variable @var{variable} to value @var{value}.
14391 @var{value} may be empty (@samp{@var{variable}=}). Setting a variable
14392 to an empty value is different from unsetting it.
14393 These operands are evaluated left-to-right, so if two operands
14394 mention the same variable the earlier is ignored.
14396 Environment variable names can be empty, and can contain any
14397 characters other than @samp{=} and @acronym{ASCII} @sc{nul}.
14398 However, it is wise to limit yourself to names that
14399 consist solely of underscores, digits, and @acronym{ASCII} letters,
14400 and that begin with a non-digit, as applications like the shell do not
14401 work well with other names.
14404 The first operand that does not contain the character @samp{=}
14405 specifies the program to invoke; it is
14406 searched for according to the @env{PATH} environment variable. Any
14407 remaining arguments are passed as arguments to that program.
14408 The program should not be a special built-in utility
14409 (@pxref{Special built-in utilities}).
14411 Modifications to @env{PATH} take effect prior to searching for
14412 @var{command}. Use caution when reducing @env{PATH}; behavior is
14413 not portable when @env{PATH} is undefined or omits key directories
14414 such as @file{/bin}.
14416 In the rare case that a utility contains a @samp{=} in the name, the
14417 only way to disambiguate it from a variable assignment is to use an
14418 intermediate command for @var{command}, and pass the problematic
14419 program name via @var{args}. For example, if @file{./prog=} is an
14420 executable in the current @env{PATH}:
14423 env prog= true # runs 'true', with prog= in environment
14424 env ./prog= true # runs 'true', with ./prog= in environment
14425 env -- prog= true # runs 'true', with prog= in environment
14426 env sh -c '\prog= true' # runs 'prog=' with argument 'true'
14427 env sh -c 'exec "$@@"' sh prog= true # also runs 'prog='
14430 @cindex environment, printing
14432 If no command name is specified following the environment
14433 specifications, the resulting environment is printed. This is like
14434 specifying the @command{printenv} program.
14436 The program accepts the following options. Also see @ref{Common options}.
14437 Options must precede operands.
14441 @item -u @var{name}
14442 @itemx --unset=@var{name}
14445 Remove variable @var{name} from the environment, if it was in the
14450 @itemx --ignore-environment
14453 @opindex --ignore-environment
14454 Start with an empty environment, ignoring the inherited environment.
14458 @cindex exit status of @command{env}
14462 0 if no @var{command} is specified and the environment is output
14463 125 if @command{env} itself fails
14464 126 if @var{command} is found but cannot be invoked
14465 127 if @var{command} cannot be found
14466 the exit status of @var{command} otherwise
14470 @node nice invocation
14471 @section @command{nice}: Run a command with modified niceness
14475 @cindex scheduling, affecting
14476 @cindex appropriate privileges
14478 @command{nice} prints or modifies a process's @dfn{niceness},
14479 a parameter that affects whether the process is scheduled favorably.
14483 nice [@var{option}]@dots{} [@var{command} [@var{arg}]@dots{}]
14486 If no arguments are given, @command{nice} prints the current niceness.
14487 Otherwise, @command{nice} runs the given @var{command} with its
14488 niceness adjusted. By default, its niceness is incremented by 10.
14490 Niceness values range at least from @minus{}20 (process has high priority
14491 and gets more resources, thus slowing down other processes) through 19
14492 (process has lower priority and runs slowly itself, but has less impact
14493 on the speed of other running processes). Some systems
14494 may have a wider range of nicenesses; conversely, other systems may
14495 enforce more restrictive limits. An attempt to set the niceness
14496 outside the supported range is treated as an attempt to use the
14497 minimum or maximum supported value.
14499 A niceness should not be confused with a scheduling priority, which
14500 lets applications determine the order in which threads are scheduled
14501 to run. Unlike a priority, a niceness is merely advice to the
14502 scheduler, which the scheduler is free to ignore. Also, as a point of
14503 terminology, @acronym{POSIX} defines the behavior of @command{nice} in
14504 terms of a @dfn{nice value}, which is the nonnegative difference
14505 between a niceness and the minimum niceness. Though @command{nice}
14506 conforms to @acronym{POSIX}, its documentation and diagnostics use the
14507 term ``niceness'' for compatibility with historical practice.
14509 @var{command} must not be a special built-in utility (@pxref{Special
14510 built-in utilities}).
14512 @mayConflictWithShellBuiltIn{nice}
14514 The program accepts the following option. Also see @ref{Common options}.
14515 Options must precede operands.
14518 @item -n @var{adjustment}
14519 @itemx --adjustment=@var{adjustment}
14521 @opindex --adjustment
14522 Add @var{adjustment} instead of 10 to the command's niceness. If
14523 @var{adjustment} is negative and you lack appropriate privileges,
14524 @command{nice} issues a warning but otherwise acts as if you specified
14527 For compatibility @command{nice} also supports an obsolete
14528 option syntax @option{-@var{adjustment}}. New scripts should use
14529 @option{-n @var{adjustment}} instead.
14533 @cindex exit status of @command{nice}
14537 0 if no @var{command} is specified and the niceness is output
14538 125 if @command{nice} itself fails
14539 126 if @var{command} is found but cannot be invoked
14540 127 if @var{command} cannot be found
14541 the exit status of @var{command} otherwise
14544 It is sometimes useful to run a non-interactive program with reduced niceness.
14547 $ nice factor 4611686018427387903
14550 Since @command{nice} prints the current niceness,
14551 you can invoke it through itself to demonstrate how it works.
14553 The default behavior is to increase the niceness by @samp{10}:
14564 The @var{adjustment} is relative to the current niceness. In the
14565 next example, the first @command{nice} invocation runs the second one
14566 with niceness 10, and it in turn runs the final one with a niceness
14570 $ nice nice -n 3 nice
14574 Specifying a niceness larger than the supported range
14575 is the same as specifying the maximum supported value:
14578 $ nice -n 10000000000 nice
14582 Only a privileged user may run a process with lower niceness:
14586 nice: cannot set niceness: Permission denied
14588 $ sudo nice -n -1 nice
14593 @node nohup invocation
14594 @section @command{nohup}: Run a command immune to hangups
14597 @cindex hangups, immunity to
14598 @cindex immunity to hangups
14599 @cindex logging out and continuing to run
14602 @command{nohup} runs the given @var{command} with hangup signals ignored,
14603 so that the command can continue running in the background after you log
14607 nohup @var{command} [@var{arg}]@dots{}
14610 If standard input is a terminal, it is redirected from
14611 @file{/dev/null} so that terminal sessions do not mistakenly consider
14612 the terminal to be used by the command. This is a @acronym{GNU}
14613 extension; programs intended to be portable to non-@acronym{GNU} hosts
14614 should use @samp{nohup @var{command} [@var{arg}]@dots{} </dev/null}
14618 If standard output is a terminal, the command's standard output is appended
14619 to the file @file{nohup.out}; if that cannot be written to, it is appended
14620 to the file @file{$HOME/nohup.out}; and if that cannot be written to, the
14621 command is not run.
14622 Any @file{nohup.out} or @file{$HOME/nohup.out} file created by
14623 @command{nohup} is made readable and writable only to the user,
14624 regardless of the current umask settings.
14626 If standard error is a terminal, it is normally redirected to the same file
14627 descriptor as the (possibly-redirected) standard output.
14628 However, if standard output is closed, standard error terminal output
14629 is instead appended to the file @file{nohup.out} or
14630 @file{$HOME/nohup.out} as above.
14632 To capture the command's output to a file other than @file{nohup.out}
14633 you can redirect it. For example, to capture the output of
14637 nohup make > make.log
14640 @command{nohup} does not automatically put the command it runs in the
14641 background; you must do that explicitly, by ending the command line
14642 with an @samp{&}. Also, @command{nohup} does not alter the
14643 niceness of @var{command}; use @command{nice} for that,
14644 e.g., @samp{nohup nice @var{command}}.
14646 @var{command} must not be a special built-in utility (@pxref{Special
14647 built-in utilities}).
14649 The only options are @option{--help} and @option{--version}. @xref{Common
14650 options}. Options must precede operands.
14652 @cindex exit status of @command{nohup}
14656 125 if @command{nohup} itself fails, and @env{POSIXLY_CORRECT} is not set
14657 126 if @var{command} is found but cannot be invoked
14658 127 if @var{command} cannot be found
14659 the exit status of @var{command} otherwise
14662 If @env{POSIXLY_CORRECT} is set, internal failures give status 127
14666 @node stdbuf invocation
14667 @section @command{stdbuf}: Run a command with modified I/O stream buffering
14670 @cindex standard streams, buffering
14671 @cindex line buffered
14673 @command{stdbuf} allows one to modify the buffering operations of the
14674 three standard I/O streams associated with a program. Synopsis:
14677 stdbuf @var{option}@dots{} @var{command}
14680 Any additional @var{arg}s are passed as additional arguments to the
14683 The program accepts the following options. Also see @ref{Common options}.
14687 @item -i @var{mode}
14688 @itemx --input=@var{mode}
14691 Adjust the standard input stream buffering.
14693 @item -o @var{mode}
14694 @itemx --output=@var{mode}
14697 Adjust the standard output stream buffering.
14699 @item -e @var{mode}
14700 @itemx --error=@var{mode}
14703 Adjust the standard error stream buffering.
14707 The @var{mode} can be specified as follows:
14712 Set the stream to line buffered mode.
14713 In this mode data is coalesced until a newline is output or
14714 input is read from any stream attached to a terminal device.
14715 This option is invalid with standard input.
14718 Disable buffering of the selected stream.
14719 In this mode data is output immediately and only the
14720 amount of data requested is read from input.
14723 Specify the size of the buffer to use in fully buffered mode.
14724 @multiplierSuffixesNoBlocks{size}
14728 NOTE: If @var{command} adjusts the buffering of its standard streams
14729 (@command{tee} does for e.g.) then that will override corresponding settings
14730 changed by @command{stdbuf}. Also some filters (like @command{dd} and
14731 @command{cat} etc.) don't use streams for I/O, and are thus unaffected
14732 by @command{stdbuf} settings.
14734 @cindex exit status of @command{stdbuf}
14738 125 if @command{stdbuf} itself fails
14739 126 if @var{command} is found but cannot be invoked
14740 127 if @var{command} cannot be found
14741 the exit status of @var{command} otherwise
14745 @node su invocation
14746 @section @command{su}: Run a command with substitute user and group ID
14749 @cindex substitute user and group IDs
14750 @cindex user ID, switching
14751 @cindex super-user, becoming
14752 @cindex root, becoming
14754 @command{su} allows one user to temporarily become another user. It runs a
14755 command (often an interactive shell) with the real and effective user
14756 ID, group ID, and supplemental groups of a given @var{user}. Synopsis:
14759 su [@var{option}]@dots{} [@var{user} [@var{arg}]@dots{}]
14762 @cindex passwd entry, and @command{su} shell
14764 @flindex /etc/passwd
14765 If no @var{user} is given, the default is @code{root}, the super-user.
14766 The shell to use is taken from @var{user}'s @code{passwd} entry, or
14767 @file{/bin/sh} if none is specified there. If @var{user} has a
14768 password, @command{su} prompts for the password unless run by a user with
14769 effective user ID of zero (the super-user).
14775 @cindex login shell
14776 By default, @command{su} does not change the current directory.
14777 It sets the environment variables @env{HOME} and @env{SHELL}
14778 from the password entry for @var{user}, and if @var{user} is not
14779 the super-user, sets @env{USER} and @env{LOGNAME} to @var{user}.
14780 By default, the shell is not a login shell.
14782 Any additional @var{arg}s are passed as additional arguments to the
14785 @cindex @option{-su}
14786 GNU @command{su} does not treat @file{/bin/sh} or any other shells specially
14787 (e.g., by setting @code{argv[0]} to @option{-su}, passing @option{-c} only
14788 to certain shells, etc.).
14791 @command{su} can optionally be compiled to use @code{syslog} to report
14792 failed, and optionally successful, @command{su} attempts. (If the system
14793 supports @code{syslog}.) However, GNU @command{su} does not check if the
14794 user is a member of the @code{wheel} group; see below.
14796 The program accepts the following options. Also see @ref{Common options}.
14799 @item -c @var{command}
14800 @itemx --command=@var{command}
14803 Pass @var{command}, a single command line to run, to the shell with
14804 a @option{-c} option instead of starting an interactive shell.
14811 @cindex file name pattern expansion, disabled
14812 @cindex globbing, disabled
14813 Pass the @option{-f} option to the shell. This probably only makes sense
14814 if the shell run is @command{csh} or @command{tcsh}, for which the @option{-f}
14815 option prevents reading the startup file (@file{.cshrc}). With
14816 Bourne-like shells, the @option{-f} option disables file name pattern
14817 expansion (globbing), which is not likely to be useful.
14825 @c other variables already indexed above
14828 @cindex login shell, creating
14829 Make the shell a login shell. This means the following. Unset all
14830 environment variables except @env{TERM}, @env{HOME}, and @env{SHELL}
14831 (which are set as described above), and @env{USER} and @env{LOGNAME}
14832 (which are set, even for the super-user, as described above), and set
14833 @env{PATH} to a compiled-in default value. Change to @var{user}'s home
14834 directory. Prepend @samp{-} to the shell's name, intended to make it
14835 read its login startup file(s).
14839 @itemx --preserve-environment
14842 @opindex --preserve-environment
14843 @cindex environment, preserving
14844 @flindex /etc/shells
14845 @cindex restricted shell
14846 Do not change the environment variables @env{HOME}, @env{USER},
14847 @env{LOGNAME}, or @env{SHELL}. Run the shell given in the environment
14848 variable @env{SHELL} instead of the shell from @var{user}'s passwd
14849 entry, unless the user running @command{su} is not the super-user and
14850 @var{user}'s shell is restricted. A @dfn{restricted shell} is one that
14851 is not listed in the file @file{/etc/shells}, or in a compiled-in list
14852 if that file does not exist. Parts of what this option does can be
14853 overridden by @option{--login} and @option{--shell}.
14855 @item -s @var{shell}
14856 @itemx --shell=@var{shell}
14859 Run @var{shell} instead of the shell from @var{user}'s passwd entry,
14860 unless the user running @command{su} is not the super-user and @var{user}'s
14861 shell is restricted (see @option{-m} just above).
14865 @cindex exit status of @command{su}
14869 125 if @command{su} itself fails
14870 126 if subshell is found but cannot be invoked
14871 127 if subshell cannot be found
14872 the exit status of the subshell otherwise
14875 @cindex wheel group, not supported
14876 @cindex group wheel, not supported
14878 @subsection Why GNU @command{su} does not support the @samp{wheel} group
14880 (This section is by Richard Stallman.)
14884 Sometimes a few of the users try to hold total power over all the
14885 rest. For example, in 1984, a few users at the MIT AI lab decided to
14886 seize power by changing the operator password on the Twenex system and
14887 keeping it secret from everyone else. (I was able to thwart this coup
14888 and give power back to the users by patching the kernel, but I
14889 wouldn't know how to do that in Unix.)
14891 However, occasionally the rulers do tell someone. Under the usual
14892 @command{su} mechanism, once someone learns the root password who
14893 sympathizes with the ordinary users, he or she can tell the rest. The
14894 ``wheel group'' feature would make this impossible, and thus cement the
14895 power of the rulers.
14897 I'm on the side of the masses, not that of the rulers. If you are
14898 used to supporting the bosses and sysadmins in whatever they do, you
14899 might find this idea strange at first.
14902 @node timeout invocation
14903 @section @command{timeout}: Run a command with a time limit
14907 @cindex run commands with bounded time
14909 @command{timeout} runs the given @var{command} and kills it if it is
14910 still running after the specified time interval. Synopsis:
14913 timeout [@var{option}] @var{number}[smhd] @var{command} [@var{arg}]@dots{}
14917 @var{number} is an integer followed by an optional unit; the default
14918 is seconds. The units are:
14931 @var{command} must not be a special built-in utility (@pxref{Special
14932 built-in utilities}).
14934 The program accepts the following option. Also see @ref{Common options}.
14935 Options must precede operands.
14938 @item -s @var{signal}
14939 @itemx --signal=@var{signal}
14942 Send this @var{signal} to @var{command} on timeout, rather than the
14943 default @samp{TERM} signal. @var{signal} may be a name like @samp{HUP}
14944 or a number. Also see @xref{Signal specifications}.
14948 @cindex exit status of @command{timeout}
14952 124 if @var{command} times out
14953 125 if @command{timeout} itself fails
14954 126 if @var{command} is found but cannot be invoked
14955 127 if @var{command} cannot be found
14956 the exit status of @var{command} otherwise
14960 @node Process control
14961 @chapter Process control
14963 @cindex processes, commands for controlling
14964 @cindex commands for controlling processes
14967 * kill invocation:: Sending a signal to processes.
14971 @node kill invocation
14972 @section @command{kill}: Send a signal to processes
14975 @cindex send a signal to processes
14977 The @command{kill} command sends a signal to processes, causing them
14978 to terminate or otherwise act upon receiving the signal in some way.
14979 Alternatively, it lists information about signals. Synopses:
14982 kill [-s @var{signal} | --signal @var{signal} | -@var{signal}] @var{pid}@dots{}
14983 kill [-l | --list | -t | --table] [@var{signal}]@dots{}
14986 @mayConflictWithShellBuiltIn{kill}
14988 The first form of the @command{kill} command sends a signal to all
14989 @var{pid} arguments. The default signal to send if none is specified
14990 is @samp{TERM}. The special signal number @samp{0} does not denote a
14991 valid signal, but can be used to test whether the @var{pid} arguments
14992 specify processes to which a signal could be sent.
14994 If @var{pid} is positive, the signal is sent to the process with the
14995 process ID @var{pid}. If @var{pid} is zero, the signal is sent to all
14996 processes in the process group of the current process. If @var{pid}
14997 is @minus{}1, the signal is sent to all processes for which the user has
14998 permission to send a signal. If @var{pid} is less than @minus{}1, the signal
14999 is sent to all processes in the process group that equals the absolute
15000 value of @var{pid}.
15002 If @var{pid} is not positive, a system-dependent set of system
15003 processes is excluded from the list of processes to which the signal
15006 If a negative @var{pid} argument is desired as the first one, it
15007 should be preceded by @option{--}. However, as a common extension to
15008 @acronym{POSIX}, @option{--} is not required with @samp{kill
15009 -@var{signal} -@var{pid}}. The following commands are equivalent:
15018 The first form of the @command{kill} command succeeds if every @var{pid}
15019 argument specifies at least one process that the signal was sent to.
15021 The second form of the @command{kill} command lists signal information.
15022 Either the @option{-l} or @option{--list} option, or the @option{-t}
15023 or @option{--table} option must be specified. Without any
15024 @var{signal} argument, all supported signals are listed. The output
15025 of @option{-l} or @option{--list} is a list of the signal names, one
15026 per line; if @var{signal} is already a name, the signal number is
15027 printed instead. The output of @option{-t} or @option{--table} is a
15028 table of signal numbers, names, and descriptions. This form of the
15029 @command{kill} command succeeds if all @var{signal} arguments are valid
15030 and if there is no output error.
15032 The @command{kill} command also supports the @option{--help} and
15033 @option{--version} options. @xref{Common options}.
15035 A @var{signal} may be a signal name like @samp{HUP}, or a signal
15036 number like @samp{1}, or an exit status of a process terminated by the
15037 signal. A signal name can be given in canonical form or prefixed by
15038 @samp{SIG}. The case of the letters is ignored, except for the
15039 @option{-@var{signal}} option which must use upper case to avoid
15040 ambiguity with lower case option letters. For a list of supported
15041 signal names and numbers see @xref{Signal specifications}.
15046 @cindex delaying commands
15047 @cindex commands for delaying
15049 @c Perhaps @command{wait} or other commands should be described here also?
15052 * sleep invocation:: Delay for a specified time.
15056 @node sleep invocation
15057 @section @command{sleep}: Delay for a specified time
15060 @cindex delay for a specified time
15062 @command{sleep} pauses for an amount of time specified by the sum of
15063 the values of the command line arguments.
15067 sleep @var{number}[smhd]@dots{}
15071 Each argument is a number followed by an optional unit; the default
15072 is seconds. The units are:
15085 Historical implementations of @command{sleep} have required that
15086 @var{number} be an integer, and only accepted a single argument
15087 without a suffix. However, GNU @command{sleep} accepts
15088 arbitrary floating point numbers (using a period before any fractional
15091 The only options are @option{--help} and @option{--version}. @xref{Common
15094 @c sleep is a shell built-in at least with Solaris 11's /bin/sh
15095 @mayConflictWithShellBuiltIn{sleep}
15100 @node Numeric operations
15101 @chapter Numeric operations
15103 @cindex numeric operations
15104 These programs do numerically-related operations.
15107 * factor invocation:: Show factors of numbers.
15108 * seq invocation:: Print sequences of numbers.
15112 @node factor invocation
15113 @section @command{factor}: Print prime factors
15116 @cindex prime factors
15118 @command{factor} prints prime factors. Synopses:
15121 factor [@var{number}]@dots{}
15122 factor @var{option}
15125 If no @var{number} is specified on the command line, @command{factor} reads
15126 numbers from standard input, delimited by newlines, tabs, or spaces.
15128 The @command{factor} command supports only a small number of options:
15132 Print a short help on standard output, then exit without further
15136 Print the program version on standard output, then exit without further
15140 Factoring the product of the eighth and ninth Mersenne primes
15141 takes about 30 milliseconds of CPU time on a 2.2 GHz Athlon.
15144 M8=`echo 2^31-1|bc` ; M9=`echo 2^61-1|bc`
15145 /usr/bin/time -f '%U' factor $(echo "$M8 * $M9" | bc)
15146 4951760154835678088235319297: 2147483647 2305843009213693951
15150 Similarly, factoring the eighth Fermat number @math{2^{256}+1} takes
15151 about 20 seconds on the same machine.
15153 Factoring large prime numbers is, in general, hard. The Pollard Rho
15154 algorithm used by @command{factor} is particularly effective for
15155 numbers with relatively small factors. If you wish to factor large
15156 numbers which do not have small factors (for example, numbers which
15157 are the product of two large primes), other methods are far better.
15159 If @command{factor} is built without using GNU MP, only
15160 single-precision arithmetic is available, and so large numbers
15161 (typically @math{2^{64}} and above) will not be supported. The single-precision
15162 code uses an algorithm which is designed for factoring smaller
15168 @node seq invocation
15169 @section @command{seq}: Print numeric sequences
15172 @cindex numeric sequences
15173 @cindex sequence of numbers
15175 @command{seq} prints a sequence of numbers to standard output. Synopses:
15178 seq [@var{option}]@dots{} @var{last}
15179 seq [@var{option}]@dots{} @var{first} @var{last}
15180 seq [@var{option}]@dots{} @var{first} @var{increment} @var{last}
15183 @command{seq} prints the numbers from @var{first} to @var{last} by
15184 @var{increment}. By default, each number is printed on a separate line.
15185 When @var{increment} is not specified, it defaults to @samp{1},
15186 even when @var{first} is larger than @var{last}.
15187 @var{first} also defaults to @samp{1}. So @code{seq 1} prints
15188 @samp{1}, but @code{seq 0} and @code{seq 10 5} produce no output.
15189 Floating-point numbers
15190 may be specified (using a period before any fractional digits).
15192 The program accepts the following options. Also see @ref{Common options}.
15193 Options must precede operands.
15196 @item -f @var{format}
15197 @itemx --format=@var{format}
15198 @opindex -f @var{format}
15199 @opindex --format=@var{format}
15200 @cindex formatting of numbers in @command{seq}
15201 Print all numbers using @var{format}.
15202 @var{format} must contain exactly one of the @samp{printf}-style
15203 floating point conversion specifications @samp{%a}, @samp{%e},
15204 @samp{%f}, @samp{%g}, @samp{%A}, @samp{%E}, @samp{%F}, @samp{%G}.
15205 The @samp{%} may be followed by zero or more flags taken from the set
15206 @samp{-+#0 '}, then an optional width containing one or more digits,
15207 then an optional precision consisting of a @samp{.} followed by zero
15208 or more digits. @var{format} may also contain any number of @samp{%%}
15209 conversion specifications. All conversion specifications have the
15210 same meaning as with @samp{printf}.
15212 The default format is derived from @var{first}, @var{step}, and
15213 @var{last}. If these all use a fixed point decimal representation,
15214 the default format is @samp{%.@var{p}f}, where @var{p} is the minimum
15215 precision that can represent the output numbers exactly. Otherwise,
15216 the default format is @samp{%g}.
15218 @item -s @var{string}
15219 @itemx --separator=@var{string}
15220 @cindex separator for numbers in @command{seq}
15221 Separate numbers with @var{string}; default is a newline.
15222 The output always terminates with a newline.
15225 @itemx --equal-width
15226 Print all numbers with the same width, by padding with leading zeros.
15227 @var{first}, @var{step}, and @var{last} should all use a fixed point
15228 decimal representation.
15229 (To have other kinds of padding, use @option{--format}).
15233 You can get finer-grained control over output with @option{-f}:
15236 $ seq -f '(%9.2E)' -9e5 1.1e6 1.3e6
15242 If you want hexadecimal integer output, you can use @command{printf}
15243 to perform the conversion:
15246 $ printf '%x\n' `seq 1048575 1024 1050623`
15252 For very long lists of numbers, use xargs to avoid
15253 system limitations on the length of an argument list:
15256 $ seq 1000000 | xargs printf '%x\n' | tail -n 3
15262 To generate octal output, use the printf @code{%o} format instead
15265 On most systems, seq can produce whole-number output for values up to
15266 at least @math{2^{53}}. Larger integers are approximated. The details
15267 differ depending on your floating-point implementation, but a common
15268 case is that @command{seq} works with integers through @math{2^{64}},
15269 and larger integers may not be numerically correct:
15272 $ seq 18446744073709551616 1 18446744073709551618
15273 18446744073709551616
15274 18446744073709551616
15275 18446744073709551618
15278 Be careful when using @command{seq} with outlandish values: otherwise
15279 you may see surprising results, as @command{seq} uses floating point
15280 internally. For example, on the x86 platform, where the internal
15281 representation uses a 64-bit fraction, the command:
15284 seq 1 0.0000000000000000001 1.0000000000000000009
15287 outputs 1.0000000000000000007 twice and skips 1.0000000000000000008.
15292 @node File permissions
15293 @chapter File permissions
15296 @include getdate.texi
15300 @node Opening the software toolbox
15301 @chapter Opening the Software Toolbox
15303 An earlier version of this chapter appeared in
15304 @uref{http://www.linuxjournal.com/article.php?sid=2762, the
15305 @cite{What's GNU?} column of @cite{Linux Journal}, 2 (June, 1994)}.
15306 It was written by Arnold Robbins.
15309 * Toolbox introduction:: Toolbox introduction
15310 * I/O redirection:: I/O redirection
15311 * The who command:: The @command{who} command
15312 * The cut command:: The @command{cut} command
15313 * The sort command:: The @command{sort} command
15314 * The uniq command:: The @command{uniq} command
15315 * Putting the tools together:: Putting the tools together
15319 @node Toolbox introduction
15320 @unnumberedsec Toolbox Introduction
15322 This month's column is only peripherally related to the GNU Project, in
15323 that it describes a number of the GNU tools on your GNU/Linux system and how they
15324 might be used. What it's really about is the ``Software Tools'' philosophy
15325 of program development and usage.
15327 The software tools philosophy was an important and integral concept
15328 in the initial design and development of Unix (of which Linux and GNU are
15329 essentially clones). Unfortunately, in the modern day press of
15330 Internetworking and flashy GUIs, it seems to have fallen by the
15331 wayside. This is a shame, since it provides a powerful mental model
15332 for solving many kinds of problems.
15334 Many people carry a Swiss Army knife around in their pants pockets (or
15335 purse). A Swiss Army knife is a handy tool to have: it has several knife
15336 blades, a screwdriver, tweezers, toothpick, nail file, corkscrew, and perhaps
15337 a number of other things on it. For the everyday, small miscellaneous jobs
15338 where you need a simple, general purpose tool, it's just the thing.
15340 On the other hand, an experienced carpenter doesn't build a house using
15341 a Swiss Army knife. Instead, he has a toolbox chock full of specialized
15342 tools---a saw, a hammer, a screwdriver, a plane, and so on. And he knows
15343 exactly when and where to use each tool; you won't catch him hammering nails
15344 with the handle of his screwdriver.
15346 The Unix developers at Bell Labs were all professional programmers and trained
15347 computer scientists. They had found that while a one-size-fits-all program
15348 might appeal to a user because there's only one program to use, in practice
15353 difficult to write,
15356 difficult to maintain and
15360 difficult to extend to meet new situations.
15363 Instead, they felt that programs should be specialized tools. In short, each
15364 program ``should do one thing well.'' No more and no less. Such programs are
15365 simpler to design, write, and get right---they only do one thing.
15367 Furthermore, they found that with the right machinery for hooking programs
15368 together, that the whole was greater than the sum of the parts. By combining
15369 several special purpose programs, you could accomplish a specific task
15370 that none of the programs was designed for, and accomplish it much more
15371 quickly and easily than if you had to write a special purpose program.
15372 We will see some (classic) examples of this further on in the column.
15373 (An important additional point was that, if necessary, take a detour
15374 and build any software tools you may need first, if you don't already
15375 have something appropriate in the toolbox.)
15377 @node I/O redirection
15378 @unnumberedsec I/O Redirection
15380 Hopefully, you are familiar with the basics of I/O redirection in the
15381 shell, in particular the concepts of ``standard input,'' ``standard output,''
15382 and ``standard error''. Briefly, ``standard input'' is a data source, where
15383 data comes from. A program should not need to either know or care if the
15384 data source is a disk file, a keyboard, a magnetic tape, or even a punched
15385 card reader. Similarly, ``standard output'' is a data sink, where data goes
15386 to. The program should neither know nor care where this might be.
15387 Programs that only read their standard input, do something to the data,
15388 and then send it on, are called @dfn{filters}, by analogy to filters in a
15391 With the Unix shell, it's very easy to set up data pipelines:
15394 program_to_create_data | filter1 | ... | filterN > final.pretty.data
15397 We start out by creating the raw data; each filter applies some successive
15398 transformation to the data, until by the time it comes out of the pipeline,
15399 it is in the desired form.
15401 This is fine and good for standard input and standard output. Where does the
15402 standard error come in to play? Well, think about @command{filter1} in
15403 the pipeline above. What happens if it encounters an error in the data it
15404 sees? If it writes an error message to standard output, it will just
15405 disappear down the pipeline into @command{filter2}'s input, and the
15406 user will probably never see it. So programs need a place where they can send
15407 error messages so that the user will notice them. This is standard error,
15408 and it is usually connected to your console or window, even if you have
15409 redirected standard output of your program away from your screen.
15411 For filter programs to work together, the format of the data has to be
15412 agreed upon. The most straightforward and easiest format to use is simply
15413 lines of text. Unix data files are generally just streams of bytes, with
15414 lines delimited by the @acronym{ASCII} @sc{lf} (Line Feed) character,
15415 conventionally called a ``newline'' in the Unix literature. (This is
15416 @code{'\n'} if you're a C programmer.) This is the format used by all
15417 the traditional filtering programs. (Many earlier operating systems
15418 had elaborate facilities and special purpose programs for managing
15419 binary data. Unix has always shied away from such things, under the
15420 philosophy that it's easiest to simply be able to view and edit your
15421 data with a text editor.)
15423 OK, enough introduction. Let's take a look at some of the tools, and then
15424 we'll see how to hook them together in interesting ways. In the following
15425 discussion, we will only present those command line options that interest
15426 us. As you should always do, double check your system documentation
15427 for the full story.
15429 @node The who command
15430 @unnumberedsec The @command{who} Command
15432 The first program is the @command{who} command. By itself, it generates a
15433 list of the users who are currently logged in. Although I'm writing
15434 this on a single-user system, we'll pretend that several people are
15439 @print{} arnold console Jan 22 19:57
15440 @print{} miriam ttyp0 Jan 23 14:19(:0.0)
15441 @print{} bill ttyp1 Jan 21 09:32(:0.0)
15442 @print{} arnold ttyp2 Jan 23 20:48(:0.0)
15445 Here, the @samp{$} is the usual shell prompt, at which I typed @samp{who}.
15446 There are three people logged in, and I am logged in twice. On traditional
15447 Unix systems, user names are never more than eight characters long. This
15448 little bit of trivia will be useful later. The output of @command{who} is nice,
15449 but the data is not all that exciting.
15451 @node The cut command
15452 @unnumberedsec The @command{cut} Command
15454 The next program we'll look at is the @command{cut} command. This program
15455 cuts out columns or fields of input data. For example, we can tell it
15456 to print just the login name and full name from the @file{/etc/passwd}
15457 file. The @file{/etc/passwd} file has seven fields, separated by
15461 arnold:xyzzy:2076:10:Arnold D. Robbins:/home/arnold:/bin/bash
15464 To get the first and fifth fields, we would use @command{cut} like this:
15467 $ cut -d: -f1,5 /etc/passwd
15468 @print{} root:Operator
15470 @print{} arnold:Arnold D. Robbins
15471 @print{} miriam:Miriam A. Robbins
15475 With the @option{-c} option, @command{cut} will cut out specific characters
15476 (i.e., columns) in the input lines. This is useful for input data
15477 that has fixed width fields, and does not have a field separator. For
15478 example, list the Monday dates for the current month:
15480 @c Is using cal ok? Looked at gcal, but I don't like it.
15491 @node The sort command
15492 @unnumberedsec The @command{sort} Command
15494 Next we'll look at the @command{sort} command. This is one of the most
15495 powerful commands on a Unix-style system; one that you will often find
15496 yourself using when setting up fancy data plumbing.
15499 command reads and sorts each file named on the command line. It then
15500 merges the sorted data and writes it to standard output. It will read
15501 standard input if no files are given on the command line (thus
15502 making it into a filter). The sort is based on the character collating
15503 sequence or based on user-supplied ordering criteria.
15506 @node The uniq command
15507 @unnumberedsec The @command{uniq} Command
15509 Finally (at least for now), we'll look at the @command{uniq} program. When
15510 sorting data, you will often end up with duplicate lines, lines that
15511 are identical. Usually, all you need is one instance of each line.
15512 This is where @command{uniq} comes in. The @command{uniq} program reads its
15513 standard input. It prints only one
15514 copy of each repeated line. It does have several options. Later on,
15515 we'll use the @option{-c} option, which prints each unique line, preceded
15516 by a count of the number of times that line occurred in the input.
15519 @node Putting the tools together
15520 @unnumberedsec Putting the Tools Together
15522 Now, let's suppose this is a large ISP server system with dozens of users
15523 logged in. The management wants the system administrator to write a program that will
15524 generate a sorted list of logged in users. Furthermore, even if a user
15525 is logged in multiple times, his or her name should only show up in the
15528 The administrator could sit down with the system documentation and write a C
15529 program that did this. It would take perhaps a couple of hundred lines
15530 of code and about two hours to write it, test it, and debug it.
15531 However, knowing the software toolbox, the administrator can instead start out
15532 by generating just a list of logged on users:
15542 Next, sort the list:
15545 $ who | cut -c1-8 | sort
15552 Finally, run the sorted list through @command{uniq}, to weed out duplicates:
15555 $ who | cut -c1-8 | sort | uniq
15561 The @command{sort} command actually has a @option{-u} option that does what
15562 @command{uniq} does. However, @command{uniq} has other uses for which one
15563 cannot substitute @samp{sort -u}.
15565 The administrator puts this pipeline into a shell script, and makes it available for
15566 all the users on the system (@samp{#} is the system administrator,
15567 or @code{root}, prompt):
15570 # cat > /usr/local/bin/listusers
15571 who | cut -c1-8 | sort | uniq
15573 # chmod +x /usr/local/bin/listusers
15576 There are four major points to note here. First, with just four
15577 programs, on one command line, the administrator was able to save about two
15578 hours worth of work. Furthermore, the shell pipeline is just about as
15579 efficient as the C program would be, and it is much more efficient in
15580 terms of programmer time. People time is much more expensive than
15581 computer time, and in our modern ``there's never enough time to do
15582 everything'' society, saving two hours of programmer time is no mean
15585 Second, it is also important to emphasize that with the
15586 @emph{combination} of the tools, it is possible to do a special
15587 purpose job never imagined by the authors of the individual programs.
15589 Third, it is also valuable to build up your pipeline in stages, as we did here.
15590 This allows you to view the data at each stage in the pipeline, which helps
15591 you acquire the confidence that you are indeed using these tools correctly.
15593 Finally, by bundling the pipeline in a shell script, other users can use
15594 your command, without having to remember the fancy plumbing you set up for
15595 them. In terms of how you run them, shell scripts and compiled programs are
15598 After the previous warm-up exercise, we'll look at two additional, more
15599 complicated pipelines. For them, we need to introduce two more tools.
15601 The first is the @command{tr} command, which stands for ``transliterate.''
15602 The @command{tr} command works on a character-by-character basis, changing
15603 characters. Normally it is used for things like mapping upper case to
15607 $ echo ThIs ExAmPlE HaS MIXED case! | tr '[:upper:]' '[:lower:]'
15608 @print{} this example has mixed case!
15611 There are several options of interest:
15615 work on the complement of the listed characters, i.e.,
15616 operations apply to characters not in the given set
15619 delete characters in the first set from the output
15622 squeeze repeated characters in the output into just one character.
15625 We will be using all three options in a moment.
15627 The other command we'll look at is @command{comm}. The @command{comm}
15628 command takes two sorted input files as input data, and prints out the
15629 files' lines in three columns. The output columns are the data lines
15630 unique to the first file, the data lines unique to the second file, and
15631 the data lines that are common to both. The @option{-1}, @option{-2}, and
15632 @option{-3} command line options @emph{omit} the respective columns. (This is
15633 non-intuitive and takes a little getting used to.) For example:
15655 The file name @file{-} tells @command{comm} to read standard input
15656 instead of a regular file.
15658 Now we're ready to build a fancy pipeline. The first application is a word
15659 frequency counter. This helps an author determine if he or she is over-using
15662 The first step is to change the case of all the letters in our input file
15663 to one case. ``The'' and ``the'' are the same word when doing counting.
15666 $ tr '[:upper:]' '[:lower:]' < whats.gnu | ...
15669 The next step is to get rid of punctuation. Quoted words and unquoted words
15670 should be treated identically; it's easiest to just get the punctuation out of
15674 $ tr '[:upper:]' '[:lower:]' < whats.gnu | tr -cd '[:alnum:]_ \n' | ...
15677 The second @command{tr} command operates on the complement of the listed
15678 characters, which are all the letters, the digits, the underscore, and
15679 the blank. The @samp{\n} represents the newline character; it has to
15680 be left alone. (The @acronym{ASCII} tab character should also be included for
15681 good measure in a production script.)
15683 At this point, we have data consisting of words separated by blank space.
15684 The words only contain alphanumeric characters (and the underscore). The
15685 next step is break the data apart so that we have one word per line. This
15686 makes the counting operation much easier, as we will see shortly.
15689 $ tr '[:upper:]' '[:lower:]' < whats.gnu | tr -cd '[:alnum:]_ \n' |
15690 > tr -s ' ' '\n' | ...
15693 This command turns blanks into newlines. The @option{-s} option squeezes
15694 multiple newline characters in the output into just one. This helps us
15695 avoid blank lines. (The @samp{>} is the shell's ``secondary prompt.''
15696 This is what the shell prints when it notices you haven't finished
15697 typing in all of a command.)
15699 We now have data consisting of one word per line, no punctuation, all one
15700 case. We're ready to count each word:
15703 $ tr '[:upper:]' '[:lower:]' < whats.gnu | tr -cd '[:alnum:]_ \n' |
15704 > tr -s ' ' '\n' | sort | uniq -c | ...
15707 At this point, the data might look something like this:
15720 The output is sorted by word, not by count! What we want is the most
15721 frequently used words first. Fortunately, this is easy to accomplish,
15722 with the help of two more @command{sort} options:
15726 do a numeric sort, not a textual one
15729 reverse the order of the sort
15732 The final pipeline looks like this:
15735 $ tr '[:upper:]' '[:lower:]' < whats.gnu | tr -cd '[:alnum:]_ \n' |
15736 > tr -s ' ' '\n' | sort | uniq -c | sort -n -r
15745 Whew! That's a lot to digest. Yet, the same principles apply. With six
15746 commands, on two lines (really one long one split for convenience), we've
15747 created a program that does something interesting and useful, in much
15748 less time than we could have written a C program to do the same thing.
15750 A minor modification to the above pipeline can give us a simple spelling
15751 checker! To determine if you've spelled a word correctly, all you have to
15752 do is look it up in a dictionary. If it is not there, then chances are
15753 that your spelling is incorrect. So, we need a dictionary.
15754 The conventional location for a dictionary is @file{/usr/dict/words}.
15755 On my GNU/Linux system,@footnote{Redhat Linux 6.1, for the November 2000
15756 revision of this article.}
15757 this is a sorted, 45,402 word dictionary.
15759 Now, how to compare our file with the dictionary? As before, we generate
15760 a sorted list of words, one per line:
15763 $ tr '[:upper:]' '[:lower:]' < whats.gnu | tr -cd '[:alnum:]_ \n' |
15764 > tr -s ' ' '\n' | sort -u | ...
15767 Now, all we need is a list of words that are @emph{not} in the
15768 dictionary. Here is where the @command{comm} command comes in.
15771 $ tr '[:upper:]' '[:lower:]' < whats.gnu | tr -cd '[:alnum:]_ \n' |
15772 > tr -s ' ' '\n' | sort -u |
15773 > comm -23 - /usr/dict/words
15776 The @option{-2} and @option{-3} options eliminate lines that are only in the
15777 dictionary (the second file), and lines that are in both files. Lines
15778 only in the first file (standard input, our stream of words), are
15779 words that are not in the dictionary. These are likely candidates for
15780 spelling errors. This pipeline was the first cut at a production
15781 spelling checker on Unix.
15783 There are some other tools that deserve brief mention.
15787 search files for text that matches a regular expression
15790 count lines, words, characters
15793 a T-fitting for data pipes, copies data to files and to standard output
15796 the stream editor, an advanced tool
15799 a data manipulation language, another advanced tool
15802 The software tools philosophy also espoused the following bit of
15803 advice: ``Let someone else do the hard part.'' This means, take
15804 something that gives you most of what you need, and then massage it the
15805 rest of the way until it's in the form that you want.
15811 Each program should do one thing well. No more, no less.
15814 Combining programs with appropriate plumbing leads to results where
15815 the whole is greater than the sum of the parts. It also leads to novel
15816 uses of programs that the authors might never have imagined.
15819 Programs should never print extraneous header or trailer data, since these
15820 could get sent on down a pipeline. (A point we didn't mention earlier.)
15823 Let someone else do the hard part.
15826 Know your toolbox! Use each program appropriately. If you don't have an
15827 appropriate tool, build one.
15830 As of this writing, all the programs we've discussed are available via
15831 anonymous @command{ftp} from: @*
15832 @uref{ftp://gnudist.gnu.org/textutils/textutils-1.22.tar.gz}. (There may
15833 be more recent versions available now.)
15835 None of what I have presented in this column is new. The Software Tools
15836 philosophy was first introduced in the book @cite{Software Tools}, by
15837 Brian Kernighan and P.J. Plauger (Addison-Wesley, ISBN 0-201-03669-X).
15838 This book showed how to write and use software tools. It was written in
15839 1976, using a preprocessor for FORTRAN named @command{ratfor} (RATional
15840 FORtran). At the time, C was not as ubiquitous as it is now; FORTRAN
15841 was. The last chapter presented a @command{ratfor} to FORTRAN
15842 processor, written in @command{ratfor}. @command{ratfor} looks an awful
15843 lot like C; if you know C, you won't have any problem following the
15846 In 1981, the book was updated and made available as @cite{Software Tools
15847 in Pascal} (Addison-Wesley, ISBN 0-201-10342-7). Both books are
15848 still in print and are well worth
15849 reading if you're a programmer. They certainly made a major change in
15850 how I view programming.
15852 The programs in both books are available from
15853 @uref{http://cm.bell-labs.com/who/bwk, Brian Kernighan's home page}.
15854 For a number of years, there was an active
15855 Software Tools Users Group, whose members had ported the original
15856 @command{ratfor} programs to essentially every computer system with a
15857 FORTRAN compiler. The popularity of the group waned in the middle 1980s
15858 as Unix began to spread beyond universities.
15860 With the current proliferation of GNU code and other clones of Unix programs,
15861 these programs now receive little attention; modern C versions are
15862 much more efficient and do more than these programs do. Nevertheless, as
15863 exposition of good programming style, and evangelism for a still-valuable
15864 philosophy, these books are unparalleled, and I recommend them highly.
15866 Acknowledgment: I would like to express my gratitude to Brian Kernighan
15867 of Bell Labs, the original Software Toolsmith, for reviewing this column.
15869 @node GNU Free Documentation License
15870 @appendix GNU Free Documentation License
15874 @node Concept index
15881 @c Local variables:
15882 @c texinfo-column-for-description: 32