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 * uptime: (coreutils)uptime invocation. FIXME.
36 @dircategory Individual utilities
38 * base64: (coreutils)base64 invocation. Base64 encode/decode data.
39 * basename: (coreutils)basename invocation. Strip directory and suffix.
40 * cat: (coreutils)cat invocation. Concatenate and write files.
41 * chgrp: (coreutils)chgrp invocation. Change file groups.
42 * chmod: (coreutils)chmod invocation. Change file permissions.
43 * chown: (coreutils)chown invocation. Change file owners/groups.
44 * chroot: (coreutils)chroot invocation. Specify the root directory.
45 * cksum: (coreutils)cksum invocation. Print POSIX CRC checksum.
46 * comm: (coreutils)comm invocation. Compare sorted files by line.
47 * cp: (coreutils)cp invocation. Copy files.
48 * csplit: (coreutils)csplit invocation. Split by context.
49 * cut: (coreutils)cut invocation. Print selected parts of lines.
50 * date: (coreutils)date invocation. Print/set system date and time.
51 * dd: (coreutils)dd invocation. Copy and convert a file.
52 * df: (coreutils)df invocation. Report file system disk usage.
53 * dir: (coreutils)dir invocation. List directories briefly.
54 * dircolors: (coreutils)dircolors invocation. Color setup for ls.
55 * dirname: (coreutils)dirname invocation. Strip non-directory suffix.
56 * du: (coreutils)du invocation. Report on disk usage.
57 * echo: (coreutils)echo invocation. Print a line of text.
58 * env: (coreutils)env invocation. Modify the environment.
59 * expand: (coreutils)expand invocation. Convert tabs to spaces.
60 * expr: (coreutils)expr invocation. Evaluate expressions.
61 * factor: (coreutils)factor invocation. Print prime factors
62 * false: (coreutils)false invocation. Do nothing, unsuccessfully.
63 * fmt: (coreutils)fmt invocation. Reformat paragraph text.
64 * fold: (coreutils)fold invocation. Wrap long input lines.
65 * groups: (coreutils)groups invocation. Print group names a user is in.
66 * head: (coreutils)head invocation. Output the first part of files.
67 * hostid: (coreutils)hostid invocation. Print numeric host identifier.
68 * hostname: (coreutils)hostname invocation. Print or set system name.
69 * id: (coreutils)id invocation. Print user identity.
70 * install: (coreutils)install invocation. Copy and change attributes.
71 * join: (coreutils)join invocation. Join lines on a common field.
72 * kill: (coreutils)kill invocation. Send a signal to processes.
73 * link: (coreutils)link invocation. Make hard links between files.
74 * ln: (coreutils)ln invocation. Make links between files.
75 * logname: (coreutils)logname invocation. Print current login name.
76 * ls: (coreutils)ls invocation. List directory contents.
77 * md5sum: (coreutils)md5sum invocation. Print or check MD5 digests.
78 * mkdir: (coreutils)mkdir invocation. Create directories.
79 * mkfifo: (coreutils)mkfifo invocation. Create FIFOs (named pipes).
80 * mknod: (coreutils)mknod invocation. Create special files.
81 * mv: (coreutils)mv invocation. Rename files.
82 * nice: (coreutils)nice invocation. Modify niceness.
83 * nl: (coreutils)nl invocation. Number lines and write files.
84 * nohup: (coreutils)nohup invocation. Immunize to hangups.
85 * od: (coreutils)od invocation. Dump files in octal, etc.
86 * paste: (coreutils)paste invocation. Merge lines of files.
87 * pathchk: (coreutils)pathchk invocation. Check file name portability.
88 * pr: (coreutils)pr invocation. Paginate or columnate files.
89 * printenv: (coreutils)printenv invocation. Print environment variables.
90 * printf: (coreutils)printf invocation. Format and print data.
91 * ptx: (coreutils)ptx invocation. Produce permuted indexes.
92 * pwd: (coreutils)pwd invocation. Print working directory.
93 * readlink: (coreutils)readlink invocation. Print referent of a symlink.
94 * rm: (coreutils)rm invocation. Remove files.
95 * rmdir: (coreutils)rmdir invocation. Remove empty directories.
96 * seq: (coreutils)seq invocation. Print numeric sequences
97 * sha1sum: (coreutils)sha1sum invocation. Print or check SHA-1 digests.
98 * sha2: (coreutils)sha2 utilities. Print or check SHA-2 digests.
99 * shred: (coreutils)shred invocation. Remove files more securely.
100 * sleep: (coreutils)sleep invocation. Delay for a specified time.
101 * sort: (coreutils)sort invocation. Sort text files.
102 * split: (coreutils)split invocation. Split into fixed-size pieces.
103 * stat: (coreutils)stat invocation. Report file(system) status.
104 * stty: (coreutils)stty invocation. Print/change terminal settings.
105 * su: (coreutils)su invocation. Modify user and group ID.
106 * sum: (coreutils)sum invocation. Print traditional checksum.
107 * sync: (coreutils)sync invocation. Synchronize memory and disk.
108 * tac: (coreutils)tac invocation. Reverse files.
109 * tail: (coreutils)tail invocation. Output the last part of files.
110 * tee: (coreutils)tee invocation. Redirect to multiple files.
111 * test: (coreutils)test invocation. File/string tests.
112 * touch: (coreutils)touch invocation. Change file timestamps.
113 * tr: (coreutils)tr invocation. Translate characters.
114 * true: (coreutils)true invocation. Do nothing, successfully.
115 * tsort: (coreutils)tsort invocation. Topological sort.
116 * tty: (coreutils)tty invocation. Print terminal name.
117 * uname: (coreutils)uname invocation. Print system information.
118 * unexpand: (coreutils)unexpand invocation. Convert spaces to tabs.
119 * uniq: (coreutils)uniq invocation. Uniquify files.
120 * unlink: (coreutils)unlink invocation. Removal via unlink(2).
121 * users: (coreutils)users invocation. Print current user names.
122 * vdir: (coreutils)vdir invocation. List directories verbosely.
123 * wc: (coreutils)wc invocation. Line, word, and byte counts.
124 * who: (coreutils)who invocation. Print who is logged in.
125 * whoami: (coreutils)whoami invocation. Print effective user ID.
126 * yes: (coreutils)yes invocation. Print a string indefinitely.
130 This manual documents version @value{VERSION} of the @sc{gnu} core
131 utilities, including the standard programs for text and file manipulation.
133 Copyright @copyright{} 1994, 1995, 1996, 2000, 2001, 2002, 2003, 2004,
134 2005, 2006 Free Software Foundation, Inc.
137 Permission is granted to copy, distribute and/or modify this document
138 under the terms of the GNU Free Documentation License, Version 1.1 or
139 any later version published by the Free Software Foundation; with no
140 Invariant Sections, with no Front-Cover Texts, and with no Back-Cover
141 Texts. A copy of the license is included in the section entitled ``GNU
142 Free Documentation License''.
147 @title @sc{gnu} @code{Coreutils}
148 @subtitle Core GNU utilities
149 @subtitle for version @value{VERSION}, @value{UPDATED}
150 @author David MacKenzie et al.
153 @vskip 0pt plus 1filll
165 @cindex core utilities
166 @cindex text utilities
167 @cindex shell utilities
168 @cindex file utilities
171 * Introduction:: Caveats, overview, and authors.
172 * Common options:: Common options.
173 * Output of entire files:: cat tac nl od
174 * Formatting file contents:: fmt pr fold
175 * Output of parts of files:: head tail split csplit
176 * Summarizing files:: wc sum cksum md5sum sha1sum sha2
177 * Operating on sorted files:: sort uniq comm ptx tsort
178 * Operating on fields within a line:: cut paste join
179 * Operating on characters:: tr expand unexpand
180 * Directory listing:: ls dir vdir dircolors
181 * Basic operations:: cp dd install mv rm shred
182 * Special file types:: ln mkdir rmdir mkfifo mknod
183 * Changing file attributes:: chgrp chmod chown touch
184 * Disk usage:: df du stat sync
185 * Printing text:: echo printf yes
186 * Conditions:: false true test expr
188 * File name manipulation:: dirname basename pathchk
189 * Working context:: pwd stty printenv tty
190 * User information:: id logname whoami groups users who
191 * System context:: date uname hostname
192 * Modified command invocation:: chroot env nice nohup su
193 * Process control:: kill
195 * Numeric operations:: factor seq
196 * File permissions:: Access modes.
197 * Date input formats:: Specifying date strings.
198 * Opening the software toolbox:: The software tools philosophy.
199 * GNU Free Documentation License:: The license for this documentation.
200 * Index:: General index.
203 --- The Detailed Node Listing ---
207 * Exit status:: Indicating program success or failure.
208 * Backup options:: Backup options
209 * Block size:: Block size
210 * Target directory:: Target directory
211 * Trailing slashes:: Trailing slashes
212 * Traversing symlinks:: Traversing symlinks to directories
213 * Treating / specially:: Treating / specially
214 * Standards conformance:: Standards conformance
216 Output of entire files
218 * cat invocation:: Concatenate and write files.
219 * tac invocation:: Concatenate and write files in reverse.
220 * nl invocation:: Number lines and write files.
221 * od invocation:: Write files in octal or other formats.
222 * base64 invocation:: Transform data into printable data.
224 Formatting file contents
226 * fmt invocation:: Reformat paragraph text.
227 * pr invocation:: Paginate or columnate files for printing.
228 * fold invocation:: Wrap input lines to fit in specified width.
230 Output of parts of files
232 * head invocation:: Output the first part of files.
233 * tail invocation:: Output the last part of files.
234 * split invocation:: Split a file into fixed-size pieces.
235 * csplit invocation:: Split a file into context-determined pieces.
239 * wc invocation:: Print newline, word, and byte counts.
240 * sum invocation:: Print checksum and block counts.
241 * cksum invocation:: Print CRC checksum and byte counts.
242 * md5sum invocation:: Print or check MD5 digests.
243 * sha1sum invocation:: Print or check SHA-1 digests.
244 * sha2 utilities:: Print or check SHA-2 digests.
246 Operating on sorted files
248 * sort invocation:: Sort text files.
249 * uniq invocation:: Uniquify files.
250 * comm invocation:: Compare two sorted files line by line.
251 * ptx invocation:: Produce a permuted index of file contents.
252 * tsort invocation:: Topological sort.
254 @command{ptx}: Produce permuted indexes
256 * General options in ptx:: Options which affect general program behavior.
257 * Charset selection in ptx:: Underlying character set considerations.
258 * Input processing in ptx:: Input fields, contexts, and keyword selection.
259 * Output formatting in ptx:: Types of output format, and sizing the fields.
260 * Compatibility in ptx:: The GNU extensions to @command{ptx}
262 Operating on fields within a line
264 * cut invocation:: Print selected parts of lines.
265 * paste invocation:: Merge lines of files.
266 * join invocation:: Join lines on a common field.
268 Operating on characters
270 * tr invocation:: Translate, squeeze, and/or delete characters.
271 * expand invocation:: Convert tabs to spaces.
272 * unexpand invocation:: Convert spaces to tabs.
274 @command{tr}: Translate, squeeze, and/or delete characters
276 * Character sets:: Specifying sets of characters.
277 * Translating:: Changing one set of characters to another.
278 * Squeezing:: Squeezing repeats and deleting.
282 * ls invocation:: List directory contents
283 * dir invocation:: Briefly list directory contents
284 * vdir invocation:: Verbosely list directory contents
285 * dircolors invocation:: Color setup for @command{ls}
287 @command{ls}: List directory contents
289 * Which files are listed:: Which files are listed
290 * What information is listed:: What information is listed
291 * Sorting the output:: Sorting the output
292 * More details about version sort:: More details about version sort
293 * General output formatting:: General output formatting
294 * Formatting the file names:: Formatting the file names
298 * cp invocation:: Copy files and directories
299 * dd invocation:: Convert and copy a file
300 * install invocation:: Copy files and set attributes
301 * mv invocation:: Move (rename) files
302 * rm invocation:: Remove files or directories
303 * shred invocation:: Remove files more securely
307 * link invocation:: Make a hard link via the link syscall
308 * ln invocation:: Make links between files
309 * mkdir invocation:: Make directories
310 * mkfifo invocation:: Make FIFOs (named pipes)
311 * mknod invocation:: Make block or character special files
312 * readlink invocation:: Print the referent of a symbolic link
313 * rmdir invocation:: Remove empty directories
314 * unlink invocation:: Remove files via unlink syscall
316 Changing file attributes
318 * chown invocation:: Change file owner and group
319 * chgrp invocation:: Change group ownership
320 * chmod invocation:: Change access permissions
321 * touch invocation:: Change file timestamps
325 * df invocation:: Report file system disk space usage
326 * du invocation:: Estimate file space usage
327 * stat invocation:: Report file or file system status
328 * sync invocation:: Synchronize data on disk with memory
332 * echo invocation:: Print a line of text
333 * printf invocation:: Format and print data
334 * yes invocation:: Print a string until interrupted
338 * false invocation:: Do nothing, unsuccessfully
339 * true invocation:: Do nothing, successfully
340 * test invocation:: Check file types and compare values
341 * expr invocation:: Evaluate expressions
343 @command{test}: Check file types and compare values
345 * File type tests:: File type tests
346 * Access permission tests:: Access permission tests
347 * File characteristic tests:: File characteristic tests
348 * String tests:: String tests
349 * Numeric tests:: Numeric tests
351 @command{expr}: Evaluate expression
353 * String expressions:: + : match substr index length
354 * Numeric expressions:: + - * / %
355 * Relations for expr:: | & < <= = == != >= >
356 * Examples of expr:: Examples of using @command{expr}
360 * tee invocation:: Redirect output to multiple files
362 File name manipulation
364 * basename invocation:: Strip directory and suffix from a file name
365 * dirname invocation:: Strip non-directory suffix from a file name
366 * pathchk invocation:: Check file name portability
370 * pwd invocation:: Print working directory
371 * stty invocation:: Print or change terminal characteristics
372 * printenv invocation:: Print all or some environment variables
373 * tty invocation:: Print file name of terminal on standard input
375 @command{stty}: Print or change terminal characteristics
377 * Control:: Control settings
378 * Input:: Input settings
379 * Output:: Output settings
380 * Local:: Local settings
381 * Combination:: Combination settings
382 * Characters:: Special characters
383 * Special:: Special settings
387 * id invocation:: Print user identity
388 * logname invocation:: Print current login name
389 * whoami invocation:: Print effective user ID
390 * groups invocation:: Print group names a user is in
391 * users invocation:: Print login names of users currently logged in
392 * who invocation:: Print who is currently logged in
396 * date invocation:: Print or set system date and time
397 * uname invocation:: Print system information
398 * hostname invocation:: Print or set system name
399 * hostid invocation:: Print numeric host identifier.
401 @command{date}: Print or set system date and time
403 * Time conversion specifiers:: %[HIklMNpPrRsSTXzZ]
404 * Date conversion specifiers:: %[aAbBcCdDeFgGhjmuUVwWxyY]
405 * Literal conversion specifiers:: %[%nt]
406 * Padding and other flags:: Pad with zeroes, spaces, etc.
407 * Setting the time:: Changing the system clock.
408 * Options for date:: Instead of the current time.
409 * Examples of date:: Examples.
411 Modified command invocation
413 * chroot invocation:: Run a command with a different root directory
414 * env invocation:: Run a command in a modified environment
415 * nice invocation:: Run a command with modified niceness
416 * nohup invocation:: Run a command immune to hangups
417 * su invocation:: Run a command with substitute user and group ID
421 * kill invocation:: Sending a signal to processes.
425 * sleep invocation:: Delay for a specified time
429 * factor invocation:: Print prime factors
430 * seq invocation:: Print numeric sequences
434 * Mode Structure:: Structure of File Permissions
435 * Symbolic Modes:: Mnemonic permissions representation
436 * Numeric Modes:: Permissions as octal numbers
440 * General date syntax:: Common rules.
441 * Calendar date items:: 19 Dec 1994.
442 * Time of day items:: 9:20pm.
443 * Time zone items:: @sc{est}, @sc{pdt}, @sc{gmt}.
444 * Day of week items:: Monday and others.
445 * Relative items in date strings:: next tuesday, 2 years ago.
446 * Pure numbers in date strings:: 19931219, 1440.
447 * Seconds since the Epoch:: @@1078100502.
448 * Specifying time zone rules:: TZ="America/New_York", TZ="UTC0".
449 * Authors of get_date:: Bellovin, Eggert, Salz, Berets, et al.
451 Opening the software toolbox
453 * Toolbox introduction:: Toolbox introduction
454 * I/O redirection:: I/O redirection
455 * The who command:: The @command{who} command
456 * The cut command:: The @command{cut} command
457 * The sort command:: The @command{sort} command
458 * The uniq command:: The @command{uniq} command
459 * Putting the tools together:: Putting the tools together
461 GNU Free Documentation License
463 * How to use this License for your documents::
470 @chapter Introduction
472 This manual is a work in progress: many sections make no attempt to explain
473 basic concepts in a way suitable for novices. Thus, if you are interested,
474 please get involved in improving this manual. The entire @sc{gnu} community
477 @cindex @acronym{POSIX}
478 The @sc{gnu} utilities documented here are mostly compatible with the
479 @acronym{POSIX} standard.
480 @cindex bugs, reporting
481 Please report bugs to @email{bug-coreutils@@gnu.org}. Remember
482 to include the version number, machine architecture, input files, and
483 any other information needed to reproduce the bug: your input, what you
484 expected, what you got, and why it is wrong. Diffs are welcome, but
485 please include a description of the problem as well, since this is
486 sometimes difficult to infer. @xref{Bugs, , , gcc, Using and Porting GNU CC}.
492 @cindex MacKenzie, D.
495 This manual was originally derived from the Unix man pages in the
496 distributions, which were written by David MacKenzie and updated by Jim
497 Meyering. What you are reading now is the authoritative documentation
498 for these utilities; the man pages are no longer being maintained. The
499 original @command{fmt} man page was written by Ross Paterson. Fran@,{c}ois
500 Pinard did the initial conversion to Texinfo format. Karl Berry did the
501 indexing, some reorganization, and editing of the results. Brian
502 Youmans of the Free Software Foundation office staff combined the
503 manuals for textutils, fileutils, and sh-utils to produce the present
504 omnibus manual. Richard Stallman contributed his usual invaluable
505 insights to the overall process.
508 @chapter Common options
512 @itemx @w{@kbd{--backup}[=@var{method}]}
515 @vindex VERSION_CONTROL
516 @cindex backups, making
517 @xref{Backup options}.
518 Make a backup of each file that would otherwise be overwritten or removed.
521 @macro optBackupSuffix
522 @item -S @var{suffix}
523 @itemx --suffix=@var{suffix}
526 Append @var{suffix} to each backup file made with @option{-b}.
527 @xref{Backup options}.
530 @macro optTargetDirectory
531 @item -t @var{directory}
532 @itemx @w{@kbd{--target-directory}=@var{directory}}
534 @opindex --target-directory
535 @cindex target directory
536 @cindex destination directory
537 Specify the destination @var{directory}.
538 @xref{Target directory}.
541 @macro optNoTargetDirectory
543 @itemx --no-target-directory
545 @opindex --no-target-directory
546 @cindex target directory
547 @cindex destination directory
548 Do not treat the last operand specially when it is a directory or a
549 symbolic link to a directory. @xref{Target directory}.
556 Append an SI-style abbreviation to each size, such as @samp{MB} for
557 megabytes. Powers of 1000 are used, not 1024; @samp{MB} stands for
558 1,000,000 bytes. This option is equivalent to
559 @option{--block-size=si}. Use the @option{-h} or
560 @option{--human-readable} option if
561 you prefer powers of 1024.
564 @macro optHumanReadable
566 @itemx --human-readable
568 @opindex --human-readable
569 @cindex human-readable output
570 Append a size letter to each size, such as @samp{M} for mebibytes.
571 Powers of 1024 are used, not 1000; @samp{M} stands for 1,048,576 bytes.
572 Use the @option{--si} option if you prefer powers of 1000.
575 @macro optStripTrailingSlashes
576 @itemx @w{@kbd{--strip-trailing-slashes}}
577 @opindex --strip-trailing-slashes
578 @cindex stripping trailing slashes
579 Remove any trailing slashes from each @var{source} argument.
580 @xref{Trailing slashes}.
583 @cindex common options
585 Certain options are available in all of these programs. Rather than
586 writing identical descriptions for each of the programs, they are
587 described here. (In fact, every @sc{gnu} program accepts (or should accept)
590 @vindex POSIXLY_CORRECT
591 Normally options and operands can appear in any order, and programs act
592 as if all the options appear before any operands. For example,
593 @samp{sort -r passwd -t :} acts like @samp{sort -r -t : passwd}, since
594 @samp{:} is an option-argument of @option{-t}. However, if the
595 @env{POSIXLY_CORRECT} environment variable is set, options must appear
596 before operands, unless otherwise specified for a particular command.
598 A few programs can usefully have trailing operands with leading
599 @samp{-}. With such a program, options must precede operands even if
600 @env{POSIXLY_CORRECT} is not set, and this fact is noted in the
601 program description. For example, the @command{env} command's options
602 must appear before its operands, since in some cases the operands
603 specify a command that itself contains options.
605 Some of these programs recognize the @option{--help} and @option{--version}
606 options only when one of them is the sole command line argument.
613 Print a usage message listing all available options, then exit successfully.
617 @cindex version number, finding
618 Print the version number, then exit successfully.
622 @cindex option delimiter
623 Delimit the option list. Later arguments, if any, are treated as
624 operands even if they begin with @samp{-}. For example, @samp{sort --
625 -r} reads from the file named @file{-r}.
629 @cindex standard input
630 @cindex standard output
631 A single @samp{-} operand is not really an option, though it looks like one. It
632 stands for standard input, or for standard output if that is clear from
633 the context. For example, @samp{sort -} reads from standard input,
634 and is equivalent to plain @samp{sort}, and @samp{tee -} writes an
635 extra copy of its input to standard output. Unless otherwise
636 specified, @samp{-} can appear as any operand that requires a file
640 * Exit status:: Indicating program success or failure.
641 * Backup options:: -b -S, in some programs.
642 * Block size:: BLOCK_SIZE and --block-size, in some programs.
643 * Target directory:: Specifying a target directory, in some programs.
644 * Trailing slashes:: --strip-trailing-slashes, in some programs.
645 * Traversing symlinks:: -H, -L, or -P, in some programs.
646 * Treating / specially:: --preserve-root and --no-preserve-root.
647 * Special built-in utilities:: @command{break}, @command{:}, @command{eval}, @dots{}
648 * Standards conformance:: Conformance to the @acronym{POSIX} standard.
656 An exit status of zero indicates success,
657 and a nonzero value indicates failure.
660 Nearly every command invocation yields an integral @dfn{exit status}
661 that can be used to change how other commands work.
662 For the vast majority of commands, an exit status of zero indicates
663 success. Failure is indicated by a nonzero value---typically
664 @samp{1}, though it may differ on unusual platforms as @acronym{POSIX}
665 requires only that it be nonzero.
667 However, some of the programs documented here do produce
668 other exit status values and a few associate different
669 meanings with the values @samp{0} and @samp{1}.
670 Here are some of the exceptions:
671 @command{chroot}, @command{env}, @command{expr},
672 @command{nice}, @command{nohup}, @command{printenv},
673 @command{sort}, @command{su}, @command{test}, @command{tty}.
677 @section Backup options
679 @cindex backup options
681 Some @sc{gnu} programs (at least @command{cp}, @command{install},
682 @command{ln}, and @command{mv}) optionally make backups of files
683 before writing new versions.
684 These options control the details of these backups. The options are also
685 briefly mentioned in the descriptions of the particular programs.
690 @itemx @w{@kbd{--backup}[=@var{method}]}
693 @vindex VERSION_CONTROL
694 @cindex backups, making
695 Make a backup of each file that would otherwise be overwritten or removed.
696 Without this option, the original versions are destroyed.
697 Use @var{method} to determine the type of backups to make.
698 When this option is used but @var{method} is not specified,
699 then the value of the @env{VERSION_CONTROL}
700 environment variable is used. And if @env{VERSION_CONTROL} is not set,
701 the default backup type is @samp{existing}.
703 Note that the short form of this option, @option{-b} does not accept any
704 argument. Using @option{-b} is equivalent to using @option{--backup=existing}.
706 @vindex version-control @r{Emacs variable}
707 This option corresponds to the Emacs variable @samp{version-control};
708 the values for @var{method} are the same as those used in Emacs.
709 This option also accepts more descriptive names.
710 The valid @var{method}s are (unique abbreviations are accepted):
715 @opindex none @r{backup method}
720 @opindex numbered @r{backup method}
721 Always make numbered backups.
725 @opindex existing @r{backup method}
726 Make numbered backups of files that already have them, simple backups
731 @opindex simple @r{backup method}
732 Always make simple backups. Please note @samp{never} is not to be
733 confused with @samp{none}.
737 @item -S @var{suffix}
738 @itemx --suffix=@var{suffix}
741 @cindex backup suffix
742 @vindex SIMPLE_BACKUP_SUFFIX
743 Append @var{suffix} to each backup file made with @option{-b}. If this
744 option is not specified, the value of the @env{SIMPLE_BACKUP_SUFFIX}
745 environment variable is used. And if @env{SIMPLE_BACKUP_SUFFIX} is not
746 set, the default is @samp{~}, just as in Emacs.
755 Some @sc{gnu} programs (at least @command{df}, @command{du}, and
756 @command{ls}) display sizes in ``blocks''. You can adjust the block size
757 and method of display to make sizes easier to read. The block size
758 used for display is independent of any file system block size.
759 Fractional block counts are rounded up to the nearest integer.
761 @opindex --block-size=@var{size}
764 @vindex DF_BLOCK_SIZE
765 @vindex DU_BLOCK_SIZE
766 @vindex LS_BLOCK_SIZE
767 @vindex POSIXLY_CORRECT@r{, and block size}
769 The default block size is chosen by examining the following environment
770 variables in turn; the first one that is set determines the block size.
775 This specifies the default block size for the @command{df} command.
776 Similarly, @env{DU_BLOCK_SIZE} specifies the default for @command{du} and
777 @env{LS_BLOCK_SIZE} for @command{ls}.
780 This specifies the default block size for all three commands, if the
781 above command-specific environment variables are not set.
784 This specifies the default block size for all values that are normally
785 printed as blocks, if neither @env{BLOCK_SIZE} nor the above
786 command-specific environment variables are set. Unlike the other
787 environment variables, @env{BLOCKSIZE} does not affect values that are
788 normally printed as byte counts, e.g., the file sizes contained in
791 @item POSIXLY_CORRECT
792 If neither @env{@var{command}_BLOCK_SIZE}, nor @env{BLOCK_SIZE}, nor
793 @env{BLOCKSIZE} is set, but this variable is set, the block size
798 If none of the above environment variables are set, the block size
799 currently defaults to 1024 bytes in most contexts, but this number may
800 change in the future. For @command{ls} file sizes, the block size
803 @cindex human-readable output
806 A block size specification can be a positive integer specifying the number
807 of bytes per block, or it can be @code{human-readable} or @code{si} to
808 select a human-readable format. Integers may be followed by suffixes
809 that are upward compatible with the
810 @uref{http://www.bipm.fr/enus/3_SI/si-prefixes.html, SI prefixes}
811 for decimal multiples and with the
812 @uref{http://physics.nist.gov/cuu/Units/binary.html, IEC 60027-2
813 prefixes for binary multiples}.
815 With human-readable formats, output sizes are followed by a size letter
816 such as @samp{M} for megabytes. @code{BLOCK_SIZE=human-readable} uses
817 powers of 1024; @samp{M} stands for 1,048,576 bytes.
818 @code{BLOCK_SIZE=si} is similar, but uses powers of 1000 and appends
819 @samp{B}; @samp{MB} stands for 1,000,000 bytes.
822 A block size specification preceded by @samp{'} causes output sizes to
823 be displayed with thousands separators. The @env{LC_NUMERIC} locale
824 specifies the thousands separator and grouping. For example, in an
825 American English locale, @samp{--block-size="'1kB"} would cause a size
826 of 1234000 bytes to be displayed as @samp{1,234}. In the default C
827 locale, there is no thousands separator so a leading @samp{'} has no
830 An integer block size can be followed by a suffix to specify a
831 multiple of that size. A bare size letter,
832 or one followed by @samp{iB}, specifies
833 a multiple using powers of 1024. A size letter followed by @samp{B}
834 specifies powers of 1000 instead. For example, @samp{1M} and
835 @samp{1MiB} are equivalent to @samp{1048576}, whereas @samp{1MB} is
836 equivalent to @samp{1000000}.
838 A plain suffix without a preceding integer acts as if @samp{1} were
839 prepended, except that it causes a size indication to be appended to
840 the output. For example, @samp{--block-size="kB"} displays 3000 as
843 The following suffixes are defined. Large sizes like @code{1Y}
844 may be rejected by your computer due to limitations of its arithmetic.
848 @cindex kilobyte, definition of
849 kilobyte: @math{10^3 = 1000}.
853 @cindex kibibyte, definition of
854 kibibyte: @math{2^10 = 1024}. @samp{K} is special: the SI prefix is
855 @samp{k} and the IEC 60027-2 prefix is @samp{Ki}, but tradition and
856 @acronym{POSIX} use @samp{k} to mean @samp{KiB}.
858 @cindex megabyte, definition of
859 megabyte: @math{10^6 = 1,000,000}.
862 @cindex mebibyte, definition of
863 mebibyte: @math{2^20 = 1,048,576}.
865 @cindex gigabyte, definition of
866 gigabyte: @math{10^9 = 1,000,000,000}.
869 @cindex gibibyte, definition of
870 gibibyte: @math{2^30 = 1,073,741,824}.
872 @cindex terabyte, definition of
873 terabyte: @math{10^12 = 1,000,000,000,000}.
876 @cindex tebibyte, definition of
877 tebibyte: @math{2^40 = 1,099,511,627,776}.
879 @cindex petabyte, definition of
880 petabyte: @math{10^15 = 1,000,000,000,000,000}.
883 @cindex pebibyte, definition of
884 pebibyte: @math{2^50 = 1,125,899,906,842,624}.
886 @cindex exabyte, definition of
887 exabyte: @math{10^18 = 1,000,000,000,000,000,000}.
890 @cindex exbibyte, definition of
891 exbibyte: @math{2^60 = 1,152,921,504,606,846,976}.
893 @cindex zettabyte, definition of
894 zettabyte: @math{10^21 = 1,000,000,000,000,000,000,000}
897 @math{2^70 = 1,180,591,620,717,411,303,424}.
898 (@samp{Zi} is a GNU extension to IEC 60027-2.)
900 @cindex yottabyte, definition of
901 yottabyte: @math{10^24 = 1,000,000,000,000,000,000,000,000}.
904 @math{2^80 = 1,208,925,819,614,629,174,706,176}.
905 (@samp{Yi} is a GNU extension to IEC 60027-2.)
910 @opindex --block-size
911 @opindex --human-readable
914 Block size defaults can be overridden by an explicit
915 @option{--block-size=@var{size}} option. The @option{-k}
916 option is equivalent to @option{--block-size=1K}, which
917 is the default unless the @env{POSIXLY_CORRECT} environment variable is
918 set. The @option{-h} or @option{--human-readable} option is equivalent to
919 @option{--block-size=human-readable}. The @option{--si} option is
920 equivalent to @option{--block-size=si}.
922 @node Target directory
923 @section Target directory
925 @cindex target directory
927 The @command{cp}, @command{install}, @command{ln}, and @command{mv}
928 commands normally treat the last operand specially when it is a
929 directory or a symbolic link to a directory. For example, @samp{cp
930 source dest} is equivalent to @samp{cp source dest/source} if
931 @file{dest} is a directory. Sometimes this behavior is not exactly
932 what is wanted, so these commands support the following options to
933 allow more fine-grained control:
938 @itemx --no-target-directory
939 @opindex --no-target-directory
940 @cindex target directory
941 @cindex destination directory
942 Do not treat the last operand specially when it is a directory or a
943 symbolic link to a directory. This can help avoid race conditions in
944 programs that operate in a shared area. For example, when the command
945 @samp{mv /tmp/source /tmp/dest} succeeds, there is no guarantee that
946 @file{/tmp/source} was renamed to @file{/tmp/dest}: it could have been
947 renamed to @file{/tmp/dest/source} instead, if some other process
948 created @file{/tmp/dest} as a directory. However, if @file{mv
949 -T /tmp/source /tmp/dest} succeeds, there is no
950 question that @file{/tmp/source} was renamed to @file{/tmp/dest}.
952 In the opposite situation, where you want the last operand to be
953 treated as a directory and want a diagnostic otherwise, you can use
954 the @option{--target-directory} (@option{-t}) option.
956 @item -t @var{directory}
957 @itemx @w{@kbd{--target-directory}=@var{directory}}
958 @opindex --target-directory
959 @cindex target directory
960 @cindex destination directory
961 Use @var{directory} as the directory component of each destination
964 The interface for most programs is that after processing options and a
965 finite (possibly zero) number of fixed-position arguments, the remaining
966 argument list is either expected to be empty, or is a list of items
967 (usually files) that will all be handled identically. The @command{xargs}
968 program is designed to work well with this convention.
970 The commands in the @command{mv}-family are unusual in that they take
971 a variable number of arguments with a special case at the @emph{end}
972 (namely, the target directory). This makes it nontrivial to perform some
973 operations, e.g., ``move all files from here to ../d/'', because
974 @code{mv * ../d/} might exhaust the argument space, and @code{ls | xargs ...}
975 doesn't have a clean way to specify an extra final argument for each
976 invocation of the subject command. (It can be done by going through a
977 shell command, but that requires more human labor and brain power than
980 The @w{@kbd{--target-directory}} (@option{-t}) option allows the @command{cp},
981 @command{install}, @command{ln}, and @command{mv} programs to be used
982 conveniently with @command{xargs}. For example, you can move the files
983 from the current directory to a sibling directory, @code{d} like this:
986 ls | xargs mv -t ../d --
989 However, this doesn't move files whose names begin with @samp{.}.
990 If you use the @sc{gnu} @command{find} program, you can move those
991 files too, with this command:
994 find . -mindepth 1 -maxdepth 1 \
998 But both of the above approaches fail if there are no files in the
999 current directory, or if any file has a name containing a blank or
1000 some other special characters.
1001 The following example removes those limitations and requires both
1002 @sc{gnu} @command{find} and @sc{gnu} @command{xargs}:
1005 find . -mindepth 1 -maxdepth 1 -print0 \
1006 | xargs --null --no-run-if-empty \
1013 The @option{--target-directory} (@option{-t}) and
1014 @option{--no-target-directory} (@option{-T})
1015 options cannot be combined.
1017 @node Trailing slashes
1018 @section Trailing slashes
1020 @cindex trailing slashes
1022 Some @sc{gnu} programs (at least @command{cp} and @command{mv}) allow you to
1023 remove any trailing slashes from each @var{source} argument before
1024 operating on it. The @w{@kbd{--strip-trailing-slashes}} option enables
1027 This is useful when a @var{source} argument may have a trailing slash and
1028 @c FIXME: mv's behavior in this case is system-dependent
1029 specify a symbolic link to a directory. This scenario is in fact rather
1030 common because some shells can automatically append a trailing slash when
1031 performing file name completion on such symbolic links. Without this
1032 option, @command{mv}, for example, (via the system's rename function) must
1033 interpret a trailing slash as a request to dereference the symbolic link
1034 and so must rename the indirectly referenced @emph{directory} and not
1035 the symbolic link. Although it may seem surprising that such behavior
1036 be the default, it is required by @acronym{POSIX} and is consistent with
1037 other parts of that standard.
1039 @node Traversing symlinks
1040 @section Traversing symlinks
1042 @cindex symbolic link to directory, controlling traversal of
1044 The following options modify how @command{chown} and @command{chgrp}
1045 @c FIXME: note that `du' has these options, too, but they have slightly
1046 @c different meaning.
1047 traverse a hierarchy when the @option{--recursive} (@option{-R})
1048 option is also specified.
1049 If more than one of the following options is specified, only the final
1051 These options specify whether processing a symbolic link to a directory
1052 entails operating on just the symbolic link or on all files in the
1053 hierarchy rooted at that directory.
1055 These options are independent of @option{--dereference} and
1056 @option{--no-dereference} (@option{-h}), which control whether to modify
1057 a symlink or its referent.
1064 @cindex symbolic link to directory, traverse each that is specified on the command line
1065 If @option{--recursive} (@option{-R}) is specified and
1066 a command line argument is a symbolic link to a directory, traverse it.
1073 @cindex symbolic link to directory, traverse each that is encountered
1074 In a recursive traversal, traverse every symbolic link to a directory
1075 that is encountered.
1082 @cindex symbolic link to directory, never traverse
1083 Do not traverse any symbolic links.
1084 This is the default if none of @option{-H}, @option{-L},
1085 or @option{-P} is specified.
1092 @node Treating / specially
1093 @section Treating / specially
1095 Certain commands can operate destructively on entire hierarchies.
1096 For example, if a user with appropriate privileges mistakenly runs
1097 @samp{rm -rf / tmp/junk} or @samp{cd /bin; rm -rf ../}, that may remove
1098 all files on the entire system. Since there are so few
1099 @footnote{If you know of one, please write to @email{bug-coreutils@@gnu.org}.}
1100 legitimate uses for such a command,
1101 @sc{gnu} @command{rm} provides the @option{--preserve-root} option
1102 to make it so @command{rm} declines to operate on any directory
1103 that resolves to @file{/}. The default is still to allow
1104 @samp{rm -rf /} to operate unimpeded.
1105 Another new option, @option{--no-preserve-root}, cancels the
1106 effect of any preceding @option{--preserve-root} option.
1107 Note that the @option{--preserve-root} behavior may become the default
1110 The commands @command{chgrp}, @command{chmod} and @command{chown}
1111 can also operate destructively on entire hierarchies, so they too
1112 support these options. Although, unlike @command{rm}, they don't
1113 actually unlink files, these commands are arguably more dangerous
1114 when operating recursively on @file{/}, since they often work much
1115 more quickly, and hence damage more files before an alert user can
1118 @node Special built-in utilities
1119 @section Special built-in utilities
1121 Some programs like @command{nice} can invoke other programs; for
1122 example, the command @samp{nice cat file} invokes the program
1123 @command{cat} by executing the command @samp{cat file}. However,
1124 @dfn{special built-in utilities} like @command{exit} cannot be invoked
1125 this way. For example, the command @samp{nice exit} does not have a
1126 well-defined behavior: it may generate an error message instead of
1129 Here is a list of the special built-in utilities that are standardized
1130 by @acronym{POSIX} 1003.1-2004.
1133 @t{.@: : break continue eval exec exit export readonly
1134 return set shift times trap unset}
1137 For example, because @samp{.}, @samp{:}, and @samp{exec} are special,
1138 the commands @samp{nice . foo.sh}, @samp{nice :}, and @samp{nice exec
1139 pwd} do not work as you might expect.
1141 Many shells extend this list. For example, Bash has several extra
1142 special built-in utilities like @command{history}, and
1143 @command{suspend}, and with Bash the command @samp{nice suspend}
1144 generates an error message instead of suspending.
1146 @node Standards conformance
1147 @section Standards conformance
1149 @vindex POSIXLY_CORRECT
1150 In a few cases, the @sc{gnu} utilities' default behavior is
1151 incompatible with the @acronym{POSIX} standard. To suppress these
1152 incompatibilities, define the @env{POSIXLY_CORRECT} environment
1153 variable. Unless you are checking for @acronym{POSIX} conformance, you
1154 probably do not need to define @env{POSIXLY_CORRECT}.
1156 Newer versions of @acronym{POSIX} are occasionally incompatible with older
1157 versions. For example, older versions of @acronym{POSIX} required the
1158 command @samp{sort +1} to sort based on the second and succeeding
1159 fields in each input line, but starting with @acronym{POSIX} 1003.1-2001
1160 the same command is required to sort the file named @file{+1}, and you
1161 must instead use the command @samp{sort -k 2} to get the field-based
1164 @vindex _POSIX2_VERSION
1165 The @sc{gnu} utilities normally conform to the version of @acronym{POSIX}
1166 that is standard for your system. To cause them to conform to a
1167 different version of @acronym{POSIX}, define the @env{_POSIX2_VERSION}
1168 environment variable to a value of the form @var{yyyymm} specifying
1169 the year and month the standard was adopted. Two values are currently
1170 supported for @env{_POSIX2_VERSION}: @samp{199209} stands for
1171 @acronym{POSIX} 1003.2-1992, and @samp{200112} stands for @acronym{POSIX}
1172 1003.1-2001. For example, if you have a newer system but are running software
1173 that assumes an older version of @acronym{POSIX} and uses @samp{sort +1}
1174 or @samp{tail +10}, you can work around any compatibility problems by setting
1175 @samp{_POSIX2_VERSION=199209} in your environment.
1177 @node Output of entire files
1178 @chapter Output of entire files
1180 @cindex output of entire files
1181 @cindex entire files, output of
1183 These commands read and write entire files, possibly transforming them
1187 * cat invocation:: Concatenate and write files.
1188 * tac invocation:: Concatenate and write files in reverse.
1189 * nl invocation:: Number lines and write files.
1190 * od invocation:: Write files in octal or other formats.
1191 * base64 invocation:: Transform data into printable data.
1194 @node cat invocation
1195 @section @command{cat}: Concatenate and write files
1198 @cindex concatenate and write files
1199 @cindex copying files
1201 @command{cat} copies each @var{file} (@samp{-} means standard input), or
1202 standard input if none are given, to standard output. Synopsis:
1205 cat [@var{option}] [@var{file}]@dots{}
1208 The program accepts the following options. Also see @ref{Common options}.
1216 Equivalent to @option{-vET}.
1219 @itemx --number-nonblank
1221 @opindex --number-nonblank
1222 Number all nonblank output lines, starting with 1.
1226 Equivalent to @option{-vE}.
1231 @opindex --show-ends
1232 Display a @samp{$} after the end of each line.
1238 Number all output lines, starting with 1.
1241 @itemx --squeeze-blank
1243 @opindex --squeeze-blank
1244 @cindex squeezing blank lines
1245 Replace multiple adjacent blank lines with a single blank line.
1249 Equivalent to @option{-vT}.
1254 @opindex --show-tabs
1255 Display TAB characters as @samp{^I}.
1259 Ignored; for @acronym{POSIX} compatibility.
1262 @itemx --show-nonprinting
1264 @opindex --show-nonprinting
1265 Display control characters except for LFD and TAB using
1266 @samp{^} notation and precede characters that have the high bit set with
1271 On systems like MS-DOS that distinguish between text and binary files,
1272 @command{cat} normally reads and writes in binary mode. However,
1273 @command{cat} reads in text mode if one of the options
1274 @option{-bensAE} is used or if @command{cat} is reading from standard
1275 input and standard input is a terminal. Similarly, @command{cat}
1276 writes in text mode if one of the options @option{-bensAE} is used or
1277 if standard output is a terminal.
1284 # Output f's contents, then standard input, then g's contents.
1287 # Copy standard input to standard output.
1292 @node tac invocation
1293 @section @command{tac}: Concatenate and write files in reverse
1296 @cindex reversing files
1298 @command{tac} copies each @var{file} (@samp{-} means standard input), or
1299 standard input if none are given, to standard output, reversing the
1300 records (lines by default) in each separately. Synopsis:
1303 tac [@var{option}]@dots{} [@var{file}]@dots{}
1306 @dfn{Records} are separated by instances of a string (newline by
1307 default). By default, this separator string is attached to the end of
1308 the record that it follows in the file.
1310 The program accepts the following options. Also see @ref{Common options}.
1318 The separator is attached to the beginning of the record that it
1319 precedes in the file.
1325 Treat the separator string as a regular expression. Users of @command{tac}
1326 on MS-DOS/MS-Windows should note that, since @command{tac} reads files in
1327 binary mode, each line of a text file might end with a CR/LF pair
1328 instead of the Unix-style LF.
1330 @item -s @var{separator}
1331 @itemx --separator=@var{separator}
1333 @opindex --separator
1334 Use @var{separator} as the record separator, instead of newline.
1342 @section @command{nl}: Number lines and write files
1345 @cindex numbering lines
1346 @cindex line numbering
1348 @command{nl} writes each @var{file} (@samp{-} means standard input), or
1349 standard input if none are given, to standard output, with line numbers
1350 added to some or all of the lines. Synopsis:
1353 nl [@var{option}]@dots{} [@var{file}]@dots{}
1356 @cindex logical pages, numbering on
1357 @command{nl} decomposes its input into (logical) pages; by default, the
1358 line number is reset to 1 at the top of each logical page. @command{nl}
1359 treats all of the input files as a single document; it does not reset
1360 line numbers or logical pages between files.
1362 @cindex headers, numbering
1363 @cindex body, numbering
1364 @cindex footers, numbering
1365 A logical page consists of three sections: header, body, and footer.
1366 Any of the sections can be empty. Each can be numbered in a different
1367 style from the others.
1369 The beginnings of the sections of logical pages are indicated in the
1370 input file by a line containing exactly one of these delimiter strings:
1381 The two characters from which these strings are made can be changed from
1382 @samp{\} and @samp{:} via options (see below), but the pattern and
1383 length of each string cannot be changed.
1385 A section delimiter is replaced by an empty line on output. Any text
1386 that comes before the first section delimiter string in the input file
1387 is considered to be part of a body section, so @command{nl} treats a
1388 file that contains no section delimiters as a single body section.
1390 The program accepts the following options. Also see @ref{Common options}.
1394 @item -b @var{style}
1395 @itemx --body-numbering=@var{style}
1397 @opindex --body-numbering
1398 Select the numbering style for lines in the body section of each
1399 logical page. When a line is not numbered, the current line number
1400 is not incremented, but the line number separator character is still
1401 prepended to the line. The styles are:
1407 number only nonempty lines (default for body),
1409 do not number lines (default for header and footer),
1411 number only lines that contain a match for the basic regular
1412 expression @var{bre}.
1413 @xref{Regular Expressions, , Regular Expressions, grep, The GNU Grep Manual}.
1417 @itemx --section-delimiter=@var{cd}
1419 @opindex --section-delimiter
1420 @cindex section delimiters of pages
1421 Set the section delimiter characters to @var{cd}; default is
1422 @samp{\:}. If only @var{c} is given, the second remains @samp{:}.
1423 (Remember to protect @samp{\} or other metacharacters from shell
1424 expansion with quotes or extra backslashes.)
1426 @item -f @var{style}
1427 @itemx --footer-numbering=@var{style}
1429 @opindex --footer-numbering
1430 Analogous to @option{--body-numbering}.
1432 @item -h @var{style}
1433 @itemx --header-numbering=@var{style}
1435 @opindex --header-numbering
1436 Analogous to @option{--body-numbering}.
1438 @item -i @var{number}
1439 @itemx --page-increment=@var{number}
1441 @opindex --page-increment
1442 Increment line numbers by @var{number} (default 1).
1444 @item -l @var{number}
1445 @itemx --join-blank-lines=@var{number}
1447 @opindex --join-blank-lines
1448 @cindex empty lines, numbering
1449 @cindex blank lines, numbering
1450 Consider @var{number} (default 1) consecutive empty lines to be one
1451 logical line for numbering, and only number the last one. Where fewer
1452 than @var{number} consecutive empty lines occur, do not number them.
1453 An empty line is one that contains no characters, not even spaces
1456 @item -n @var{format}
1457 @itemx --number-format=@var{format}
1459 @opindex --number-format
1460 Select the line numbering format (default is @code{rn}):
1464 @opindex ln @r{format for @command{nl}}
1465 left justified, no leading zeros;
1467 @opindex rn @r{format for @command{nl}}
1468 right justified, no leading zeros;
1470 @opindex rz @r{format for @command{nl}}
1471 right justified, leading zeros.
1475 @itemx --no-renumber
1477 @opindex --no-renumber
1478 Do not reset the line number at the start of a logical page.
1480 @item -s @var{string}
1481 @itemx --number-separator=@var{string}
1483 @opindex --number-separator
1484 Separate the line number from the text line in the output with
1485 @var{string} (default is the TAB character).
1487 @item -v @var{number}
1488 @itemx --starting-line-number=@var{number}
1490 @opindex --starting-line-number
1491 Set the initial line number on each logical page to @var{number} (default 1).
1493 @item -w @var{number}
1494 @itemx --number-width=@var{number}
1496 @opindex --number-width
1497 Use @var{number} characters for line numbers (default 6).
1505 @section @command{od}: Write files in octal or other formats
1508 @cindex octal dump of files
1509 @cindex hex dump of files
1510 @cindex ASCII dump of files
1511 @cindex file contents, dumping unambiguously
1513 @command{od} writes an unambiguous representation of each @var{file}
1514 (@samp{-} means standard input), or standard input if none are given.
1518 od [@var{option}]@dots{} [@var{file}]@dots{}
1519 od [-abcdfilosx]@dots{} [@var{file}] [[+]@var{offset}[.][b]]
1520 od [@var{option}]@dots{} --traditional [@var{file}] [[+]@var{offset}[.][b] [[+]@var{label}[.][b]]]
1523 Each line of output consists of the offset in the input, followed by
1524 groups of data from the file. By default, @command{od} prints the offset in
1525 octal, and each group of file data is a C @code{short int}'s worth of input
1526 printed as a single octal number.
1528 If @var{offset} is given, it specifies how many input bytes to skip
1529 before formatting and writing. By default, it is interpreted as an
1530 octal number, but the optional trailing decimal point causes it to be
1531 interpretated as decimal. If no decimal is specified and the offset
1532 begins with @samp{0x} or @samp{0X} it is interpreted as a hexadecimal
1533 number. If there is a trailing @samp{b}, the number of bytes skipped
1534 will be @var{offset} multiplied by 512.
1536 If a command is of both the first and second forms, the second form is
1537 assumed if the last operand begins with @samp{+} or (if there are two
1538 operands) a digit. For example, in @samp{od foo 10} and @samp{od +10}
1539 the @samp{10} is an offset, whereas in @samp{od 10} the @samp{10} is a
1542 The program accepts the following options. Also see @ref{Common options}.
1546 @item -A @var{radix}
1547 @itemx --address-radix=@var{radix}
1549 @opindex --address-radix
1550 @cindex radix for file offsets
1551 @cindex file offset radix
1552 Select the base in which file offsets are printed. @var{radix} can
1553 be one of the following:
1563 none (do not print offsets).
1566 The default is octal.
1568 @item -j @var{bytes}
1569 @itemx --skip-bytes=@var{bytes}
1571 @opindex --skip-bytes
1572 Skip @var{bytes} input bytes before formatting and writing. If
1573 @var{bytes} begins with @samp{0x} or @samp{0X}, it is interpreted in
1574 hexadecimal; otherwise, if it begins with @samp{0}, in octal; otherwise,
1575 in decimal. Appending @samp{b} multiplies @var{bytes} by 512, @samp{k}
1576 by 1024, and @samp{m} by 1048576.
1578 @item -N @var{bytes}
1579 @itemx --read-bytes=@var{bytes}
1581 @opindex --read-bytes
1582 Output at most @var{bytes} bytes of the input. Prefixes and suffixes on
1583 @code{bytes} are interpreted as for the @option{-j} option.
1586 @itemx --strings[=@var{n}]
1589 @cindex string constants, outputting
1590 Instead of the normal output, output only @dfn{string constants}: at
1591 least @var{n} consecutive @acronym{ASCII} graphic characters,
1592 followed by a null (zero) byte.
1594 If @var{n} is omitted with @option{--strings}, the default is 3.
1597 @itemx --format=@var{type}
1600 Select the format in which to output the file data. @var{type} is a
1601 string of one or more of the below type indicator characters. If you
1602 include more than one type indicator character in a single @var{type}
1603 string, or use this option more than once, @command{od} writes one copy
1604 of each output line using each of the data types that you specified,
1605 in the order that you specified.
1607 Adding a trailing ``z'' to any type specification appends a display
1608 of the @acronym{ASCII} character representation of the printable characters
1609 to the output line generated by the type specification.
1613 named character, ignoring high-order bit
1615 @acronym{ASCII} character or backslash escape,
1628 The type @code{a} outputs things like @samp{sp} for space, @samp{nl} for
1629 newline, and @samp{nul} for a null (zero) byte. Only the least significant
1630 seven bits of each byte is used; the high-order bit is ignored.
1631 Type @code{c} outputs
1632 @samp{ }, @samp{\n}, and @code{\0}, respectively.
1635 Except for types @samp{a} and @samp{c}, you can specify the number
1636 of bytes to use in interpreting each number in the given data type
1637 by following the type indicator character with a decimal integer.
1638 Alternately, you can specify the size of one of the C compiler's
1639 built-in data types by following the type indicator character with
1640 one of the following characters. For integers (@samp{d}, @samp{o},
1641 @samp{u}, @samp{x}):
1654 For floating point (@code{f}):
1666 @itemx --output-duplicates
1668 @opindex --output-duplicates
1669 Output consecutive lines that are identical. By default, when two or
1670 more consecutive output lines would be identical, @command{od} outputs only
1671 the first line, and puts just an asterisk on the following line to
1672 indicate the elision.
1675 @itemx --width[=@var{n}]
1678 Dump @code{n} input bytes per output line. This must be a multiple of
1679 the least common multiple of the sizes associated with the specified
1682 If this option is not given at all, the default is 16. If @var{n} is
1683 omitted, the default is 32.
1687 The next several options are shorthands for format specifications.
1688 @sc{gnu} @command{od} accepts any combination of shorthands and format
1689 specification options. These options accumulate.
1695 Output as named characters. Equivalent to @samp{-t a}.
1699 Output as octal bytes. Equivalent to @samp{-t o1}.
1703 Output as @acronym{ASCII} characters or backslash escapes. Equivalent to
1708 Output as unsigned decimal two-byte units. Equivalent to @samp{-t u2}.
1712 Output as floats. Equivalent to @samp{-t fF}.
1716 Output as decimal ints. Equivalent to @samp{-t dI}.
1720 Output as decimal long ints. Equivalent to @samp{-t dL}.
1724 Output as octal two-byte units. Equivalent to @option{-t o2}.
1728 Output as decimal two-byte units. Equivalent to @option{-t d2}.
1732 Output as hexadecimal two-byte units. Equivalent to @samp{-t x2}.
1735 @opindex --traditional
1736 Recognize the non-option label argument that traditional @command{od}
1737 accepted. The following syntax:
1740 od --traditional [@var{file}] [[+]@var{offset}[.][b] [[+]@var{label}[.][b]]]
1744 can be used to specify at most one file and optional arguments
1745 specifying an offset and a pseudo-start address, @var{label}.
1746 The @var{label} argument is interpreted
1747 just like @var{offset}, but it specifies an initial pseudo-address. The
1748 pseudo-addresses are displayed in parentheses following any normal
1755 @node base64 invocation
1756 @section @command{base64}: Transform data into printable data.
1759 @cindex base64 encoding
1761 @command{base64} transforms data read from a file, or standard input,
1762 into (or from) base64 encoded form. The base64 encoded form uses
1763 printable @acronym{ASCII} characters to represent binary data, see
1764 @uref{ftp://ftp.rfc-editor.org/in-notes/rfc3548.txt, RFC 3548}.
1768 base64 [@var{option}]@dots{} [@var{file}]
1769 base64 --decode [@var{option}]@dots{} [@var{file}]
1772 The base64 encoding expands data to roughly 133% of the original.
1774 The program accepts the following options. Also see @ref{Common options}.
1779 @itemx --wrap=@var{COLS}
1783 @cindex column to wrap data after
1784 During encoding, wrap lines after @var{COLS} characters. This must be
1787 The default is to wrap after 76 characters. Use the value 0 to
1788 disable line wrapping altogether.
1794 @cindex Decode base64 data
1795 @cindex Base64 decoding
1796 Change the mode of operation, from the default of encoding data, to
1797 decoding data. Input is expected to be base64 encoded data, and the
1798 output will be the original data.
1801 @itemx --ignore-garbage
1803 @opindex --ignore-garbage
1804 @cindex Ignore garbage in base64 stream
1805 During decoding, ignore unrecognized characters (including newline),
1806 to permit distorted data to be decoded.
1813 @node Formatting file contents
1814 @chapter Formatting file contents
1816 @cindex formatting file contents
1818 These commands reformat the contents of files.
1821 * fmt invocation:: Reformat paragraph text.
1822 * pr invocation:: Paginate or columnate files for printing.
1823 * fold invocation:: Wrap input lines to fit in specified width.
1827 @node fmt invocation
1828 @section @command{fmt}: Reformat paragraph text
1831 @cindex reformatting paragraph text
1832 @cindex paragraphs, reformatting
1833 @cindex text, reformatting
1835 @command{fmt} fills and joins lines to produce output lines of (at most)
1836 a given number of characters (75 by default). Synopsis:
1839 fmt [@var{option}]@dots{} [@var{file}]@dots{}
1842 @command{fmt} reads from the specified @var{file} arguments (or standard
1843 input if none are given), and writes to standard output.
1845 By default, blank lines, spaces between words, and indentation are
1846 preserved in the output; successive input lines with different
1847 indentation are not joined; tabs are expanded on input and introduced on
1850 @cindex line-breaking
1851 @cindex sentences and line-breaking
1852 @cindex Knuth, Donald E.
1853 @cindex Plass, Michael F.
1854 @command{fmt} prefers breaking lines at the end of a sentence, and tries to
1855 avoid line breaks after the first word of a sentence or before the last
1856 word of a sentence. A @dfn{sentence break} is defined as either the end
1857 of a paragraph or a word ending in any of @samp{.?!}, followed by two
1858 spaces or end of line, ignoring any intervening parentheses or quotes.
1859 Like @TeX{}, @command{fmt} reads entire ``paragraphs'' before choosing line
1860 breaks; the algorithm is a variant of that given by Donald E. Knuth
1861 and Michael F. Plass in ``Breaking Paragraphs Into Lines'',
1862 @cite{Software---Practice & Experience} @b{11}, 11 (November 1981),
1865 The program accepts the following options. Also see @ref{Common options}.
1870 @itemx --crown-margin
1872 @opindex --crown-margin
1873 @cindex crown margin
1874 @dfn{Crown margin} mode: preserve the indentation of the first two
1875 lines within a paragraph, and align the left margin of each subsequent
1876 line with that of the second line.
1879 @itemx --tagged-paragraph
1881 @opindex --tagged-paragraph
1882 @cindex tagged paragraphs
1883 @dfn{Tagged paragraph} mode: like crown margin mode, except that if
1884 indentation of the first line of a paragraph is the same as the
1885 indentation of the second, the first line is treated as a one-line
1891 @opindex --split-only
1892 Split lines only. Do not join short lines to form longer ones. This
1893 prevents sample lines of code, and other such ``formatted'' text from
1894 being unduly combined.
1897 @itemx --uniform-spacing
1899 @opindex --uniform-spacing
1900 Uniform spacing. Reduce spacing between words to one space, and spacing
1901 between sentences to two spaces.
1904 @itemx -w @var{width}
1905 @itemx --width=@var{width}
1906 @opindex -@var{width}
1909 Fill output lines up to @var{width} characters (default 75). @command{fmt}
1910 initially tries to make lines about 7% shorter than this, to give it
1911 room to balance line lengths.
1913 @item -p @var{prefix}
1914 @itemx --prefix=@var{prefix}
1915 Only lines beginning with @var{prefix} (possibly preceded by whitespace)
1916 are subject to formatting. The prefix and any preceding whitespace are
1917 stripped for the formatting and then re-attached to each formatted output
1918 line. One use is to format certain kinds of program comments, while
1919 leaving the code unchanged.
1927 @section @command{pr}: Paginate or columnate files for printing
1930 @cindex printing, preparing files for
1931 @cindex multicolumn output, generating
1932 @cindex merging files in parallel
1934 @command{pr} writes each @var{file} (@samp{-} means standard input), or
1935 standard input if none are given, to standard output, paginating and
1936 optionally outputting in multicolumn format; optionally merges all
1937 @var{file}s, printing all in parallel, one per column. Synopsis:
1940 pr [@var{option}]@dots{} [@var{file}]@dots{}
1944 By default, a 5-line header is printed at each page: two blank lines;
1945 a line with the date, the file name, and the page count; and two more
1946 blank lines. A footer of five blank lines is also printed.
1947 With the @option{-F}
1948 option, a 3-line header is printed: the leading two blank lines are
1949 omitted; no footer is used. The default @var{page_length} in both cases is 66
1950 lines. The default number of text lines changes from 56 (without @option{-F})
1951 to 63 (with @option{-F}). The text line of the header takes the form
1952 @samp{@var{date} @var{string} @var{page}}, with spaces inserted around
1953 @var{string} so that the line takes up the full @var{page_width}. Here,
1954 @var{date} is the date (see the @option{-D} or @option{--date-format}
1955 option for details), @var{string} is the centered header string, and
1956 @var{page} identifies the page number. The @env{LC_MESSAGES} locale
1957 category affects the spelling of @var{page}; in the default C locale, it
1958 is @samp{Page @var{number}} where @var{number} is the decimal page
1961 Form feeds in the input cause page breaks in the output. Multiple form
1962 feeds produce empty pages.
1964 Columns are of equal width, separated by an optional string (default
1965 is @samp{space}). For multicolumn output, lines will always be truncated to
1966 @var{page_width} (default 72), unless you use the @option{-J} option.
1968 column output no line truncation occurs by default. Use @option{-W} option to
1969 truncate lines in that case.
1971 The following changes were made in version 1.22i and apply to later
1972 versions of @command{pr}:
1973 @c FIXME: this whole section here sounds very awkward to me. I
1974 @c made a few small changes, but really it all needs to be redone. - Brian
1975 @c OK, I fixed another sentence or two, but some of it I just don't understand.
1980 Some small @var{letter options} (@option{-s}, @option{-w}) have been
1981 redefined for better @acronym{POSIX} compliance. The output of some further
1982 cases has been adapted to other Unix systems. These changes are not
1983 compatible with earlier versions of the program.
1986 Some @var{new capital letter} options (@option{-J}, @option{-S}, @option{-W})
1987 have been introduced to turn off unexpected interferences of small letter
1988 options. The @option{-N} option and the second argument @var{last_page}
1989 of @samp{+FIRST_PAGE} offer more flexibility. The detailed handling of
1990 form feeds set in the input files requires the @option{-T} option.
1993 Capital letter options override small letter ones.
1996 Some of the option-arguments (compare @option{-s}, @option{-e},
1997 @option{-i}, @option{-n}) cannot be specified as separate arguments from the
1998 preceding option letter (already stated in the @acronym{POSIX} specification).
2001 The program accepts the following options. Also see @ref{Common options}.
2005 @item +@var{first_page}[:@var{last_page}]
2006 @itemx --pages=@var{first_page}[:@var{last_page}]
2007 @c The two following @opindex lines evoke warnings because they contain `:'
2008 @c The `info' spec does not permit that. If we use those lines, we end
2009 @c up with truncated index entries that don't work.
2010 @c @opindex +@var{first_page}[:@var{last_page}]
2011 @c @opindex --pages=@var{first_page}[:@var{last_page}]
2012 @opindex +@var{page_range}
2013 @opindex --pages=@var{page_range}
2014 Begin printing with page @var{first_page} and stop with @var{last_page}.
2015 Missing @samp{:@var{last_page}} implies end of file. While estimating
2016 the number of skipped pages each form feed in the input file results
2017 in a new page. Page counting with and without @samp{+@var{first_page}}
2018 is identical. By default, counting starts with the first page of input
2019 file (not first page printed). Line numbering may be altered by @option{-N}
2023 @itemx --columns=@var{column}
2024 @opindex -@var{column}
2026 @cindex down columns
2027 With each single @var{file}, produce @var{column} columns of output
2028 (default is 1) and print columns down, unless @option{-a} is used. The
2029 column width is automatically decreased as @var{column} increases; unless
2030 you use the @option{-W/-w} option to increase @var{page_width} as well.
2031 This option might well cause some lines to be truncated. The number of
2032 lines in the columns on each page are balanced. The options @option{-e}
2033 and @option{-i} are on for multiple text-column output. Together with
2034 @option{-J} option column alignment and line truncation is turned off.
2035 Lines of full length are joined in a free field format and @option{-S}
2036 option may set field separators. @option{-@var{column}} may not be used
2037 with @option{-m} option.
2043 @cindex across columns
2044 With each single @var{file}, print columns across rather than down. The
2045 @option{-@var{column}} option must be given with @var{column} greater than one.
2046 If a line is too long to fit in a column, it is truncated.
2049 @itemx --show-control-chars
2051 @opindex --show-control-chars
2052 Print control characters using hat notation (e.g., @samp{^G}); print
2053 other nonprinting characters in octal backslash notation. By default,
2054 nonprinting characters are not changed.
2057 @itemx --double-space
2059 @opindex --double-space
2060 @cindex double spacing
2061 Double space the output.
2063 @item -D @var{format}
2064 @itemx --date-format=@var{format}
2065 @cindex time formats
2066 @cindex formatting times
2067 Format header dates using @var{format}, using the same conventions as
2068 for the the command @samp{date +@var{format}}; @xref{date invocation}.
2069 Except for directives, which start with
2070 @samp{%}, characters in @var{format} are printed unchanged. You can use
2071 this option to specify an arbitrary string in place of the header date,
2072 e.g., @option{--date-format="Monday morning"}.
2074 @vindex POSIXLY_CORRECT
2077 format defaults to @samp{%Y-%m-%d %H:%M} (for example, @samp{2001-12-04
2078 23:59}); but if the @env{POSIXLY_CORRECT} environment variable is set
2079 and the @env{LC_TIME} locale category specifies the @acronym{POSIX}
2080 locale, the default is @samp{%b %e %H:%M %Y} (for example,
2081 @samp{Dec@ @ 4 23:59 2001}.
2084 Time stamps are listed according to the time zone rules specified by
2085 the @env{TZ} environment variable, or by the system default rules if
2086 @env{TZ} is not set. @xref{TZ Variable,, Specifying the Time Zone
2087 with @env{TZ}, libc, The GNU C Library}.
2089 @item -e[@var{in-tabchar}[@var{in-tabwidth}]]
2090 @itemx --expand-tabs[=@var{in-tabchar}[@var{in-tabwidth}]]
2092 @opindex --expand-tabs
2094 Expand @var{tab}s to spaces on input. Optional argument @var{in-tabchar} is
2095 the input tab character (default is the TAB character). Second optional
2096 argument @var{in-tabwidth} is the input tab character's width (default
2104 @opindex --form-feed
2105 Use a form feed instead of newlines to separate output pages. The default
2106 page length of 66 lines is not altered. But the number of lines of text
2107 per page changes from default 56 to 63 lines.
2109 @item -h @var{HEADER}
2110 @itemx --header=@var{HEADER}
2113 Replace the file name in the header with the centered string @var{header}.
2114 When using the shell, @var{header} should be quoted and should be
2115 separated from @option{-h} by a space.
2117 @item -i[@var{out-tabchar}[@var{out-tabwidth}]]
2118 @itemx --output-tabs[=@var{out-tabchar}[@var{out-tabwidth}]]
2120 @opindex --output-tabs
2122 Replace spaces with @var{tab}s on output. Optional argument @var{out-tabchar}
2123 is the output tab character (default is the TAB character). Second optional
2124 argument @var{out-tabwidth} is the output tab character's width (default
2130 @opindex --join-lines
2131 Merge lines of full length. Used together with the column options
2132 @option{-@var{column}}, @option{-a -@var{column}} or @option{-m}. Turns off
2133 @option{-W/-w} line truncation;
2134 no column alignment used; may be used with
2135 @option{--sep-string[=@var{string}]}. @option{-J} has been introduced
2136 (together with @option{-W} and @option{--sep-string})
2137 to disentangle the old (@acronym{POSIX}-compliant) options @option{-w} and
2138 @option{-s} along with the three column options.
2141 @item -l @var{page_length}
2142 @itemx --length=@var{page_length}
2145 Set the page length to @var{page_length} (default 66) lines, including
2146 the lines of the header [and the footer]. If @var{page_length} is less
2147 than or equal to 10 (or <= 3 with @option{-F}), the header and footer are
2148 omitted, and all form feeds set in input files are eliminated, as if
2149 the @option{-T} option had been given.
2155 Merge and print all @var{file}s in parallel, one in each column. If a
2156 line is too long to fit in a column, it is truncated, unless the @option{-J}
2157 option is used. @option{--sep-string[=@var{string}]} may be used.
2159 some @var{file}s (form feeds set) produce empty columns, still marked
2160 by @var{string}. The result is a continuous line numbering and column
2161 marking throughout the whole merged file. Completely empty merged pages
2162 show no separators or line numbers. The default header becomes
2163 @samp{@var{date} @var{page}} with spaces inserted in the middle; this
2164 may be used with the @option{-h} or @option{--header} option to fill up
2165 the middle blank part.
2167 @item -n[@var{number-separator}[@var{digits}]]
2168 @itemx --number-lines[=@var{number-separator}[@var{digits}]]
2170 @opindex --number-lines
2171 Provide @var{digits} digit line numbering (default for @var{digits} is
2172 5). With multicolumn output the number occupies the first @var{digits}
2173 column positions of each text column or only each line of @option{-m}
2174 output. With single column output the number precedes each line just as
2175 @option{-m} does. Default counting of the line numbers starts with the
2176 first line of the input file (not the first line printed, compare the
2177 @option{--page} option and @option{-N} option).
2178 Optional argument @var{number-separator} is the character appended to
2179 the line number to separate it from the text followed. The default
2180 separator is the TAB character. In a strict sense a TAB is always
2181 printed with single column output only. The @var{TAB}-width varies
2182 with the @var{TAB}-position, e.g., with the left @var{margin} specified
2183 by @option{-o} option. With multicolumn output priority is given to
2184 @samp{equal width of output columns} (a @acronym{POSIX} specification).
2185 The @var{TAB}-width is fixed to the value of the first column and does
2186 not change with different values of left @var{margin}. That means a
2187 fixed number of spaces is always printed in the place of the
2188 @var{number-separator tab}. The tabification depends upon the output
2191 @item -N @var{line_number}
2192 @itemx --first-line-number=@var{line_number}
2194 @opindex --first-line-number
2195 Start line counting with the number @var{line_number} at first line of
2196 first page printed (in most cases not the first line of the input file).
2198 @item -o @var{margin}
2199 @itemx --indent=@var{margin}
2202 @cindex indenting lines
2204 Indent each line with a margin @var{margin} spaces wide (default is zero).
2205 The total page width is the size of the margin plus the @var{page_width}
2206 set with the @option{-W/-w} option. A limited overflow may occur with
2207 numbered single column output (compare @option{-n} option).
2210 @itemx --no-file-warnings
2212 @opindex --no-file-warnings
2213 Do not print a warning message when an argument @var{file} cannot be
2214 opened. (The exit status will still be nonzero, however.)
2216 @item -s[@var{char}]
2217 @itemx --separator[=@var{char}]
2219 @opindex --separator
2220 Separate columns by a single character @var{char}. The default for
2221 @var{char} is the TAB character without @option{-w} and @samp{no
2222 character} with @option{-w}. Without @option{-s} the default separator
2223 @samp{space} is set. @option{-s[char]} turns off line truncation of all
2224 three column options (@option{-COLUMN}|@option{-a -COLUMN}|@option{-m}) unless
2225 @option{-w} is set. This is a @acronym{POSIX}-compliant formulation.
2228 @item -S@var{string}
2229 @itemx --sep-string[=@var{string}]
2231 @opindex --sep-string
2232 Use @var{string} to separate output columns. The @option{-S} option doesn't
2233 affect the @option{-W/-w} option, unlike the @option{-s} option which does. It
2234 does not affect line truncation or column alignment.
2235 Without @option{-S}, and with @option{-J}, @command{pr} uses the default output
2237 Without @option{-S} or @option{-J}, @command{pr} uses a @samp{space}
2238 (same as @option{-S"@w{ }"}). @option{--sep-string} with no
2239 @samp{=@var{string}} is equivalent to @option{--sep-string=""}.
2242 @itemx --omit-header
2244 @opindex --omit-header
2245 Do not print the usual header [and footer] on each page, and do not fill
2246 out the bottom of pages (with blank lines or a form feed). No page
2247 structure is produced, but form feeds set in the input files are retained.
2248 The predefined pagination is not changed. @option{-t} or @option{-T} may be
2249 useful together with other options; e.g.: @option{-t -e4}, expand TAB characters
2250 in the input file to 4 spaces but don't make any other changes. Use of
2251 @option{-t} overrides @option{-h}.
2254 @itemx --omit-pagination
2256 @opindex --omit-pagination
2257 Do not print header [and footer]. In addition eliminate all form feeds
2258 set in the input files.
2261 @itemx --show-nonprinting
2263 @opindex --show-nonprinting
2264 Print nonprinting characters in octal backslash notation.
2266 @item -w @var{page_width}
2267 @itemx --width=@var{page_width}
2270 Set page width to @var{page_width} characters for multiple text-column
2271 output only (default for @var{page_width} is 72). @option{-s[CHAR]} turns
2272 off the default page width and any line truncation and column alignment.
2273 Lines of full length are merged, regardless of the column options
2274 set. No @var{page_width} setting is possible with single column output.
2275 A @acronym{POSIX}-compliant formulation.
2277 @item -W @var{page_width}
2278 @itemx --page_width=@var{page_width}
2280 @opindex --page_width
2281 Set the page width to @var{page_width} characters. That's valid with and
2282 without a column option. Text lines are truncated, unless @option{-J}
2283 is used. Together with one of the three column options
2284 (@option{-@var{column}}, @option{-a -@var{column}} or @option{-m}) column
2285 alignment is always used. The separator options @option{-S} or @option{-s}
2286 don't affect the @option{-W} option. Default is 72 characters. Without
2287 @option{-W @var{page_width}} and without any of the column options NO line
2288 truncation is used (defined to keep downward compatibility and to meet
2289 most frequent tasks). That's equivalent to @option{-W 72 -J}. The header
2290 line is never truncated.
2297 @node fold invocation
2298 @section @command{fold}: Wrap input lines to fit in specified width
2301 @cindex wrapping long input lines
2302 @cindex folding long input lines
2304 @command{fold} writes each @var{file} (@option{-} means standard input), or
2305 standard input if none are given, to standard output, breaking long
2309 fold [@var{option}]@dots{} [@var{file}]@dots{}
2312 By default, @command{fold} breaks lines wider than 80 columns. The output
2313 is split into as many lines as necessary.
2315 @cindex screen columns
2316 @command{fold} counts screen columns by default; thus, a tab may count more
2317 than one column, backspace decreases the column count, and carriage
2318 return sets the column to zero.
2320 The program accepts the following options. Also see @ref{Common options}.
2328 Count bytes rather than columns, so that tabs, backspaces, and carriage
2329 returns are each counted as taking up one column, just like other
2336 Break at word boundaries: the line is broken after the last blank before
2337 the maximum line length. If the line contains no such blanks, the line
2338 is broken at the maximum line length as usual.
2340 @item -w @var{width}
2341 @itemx --width=@var{width}
2344 Use a maximum line length of @var{width} columns instead of 80.
2346 For compatibility @command{fold} supports an obsolete option syntax
2347 @option{-@var{width}}. New scripts should use @option{-w @var{width}}
2355 @node Output of parts of files
2356 @chapter Output of parts of files
2358 @cindex output of parts of files
2359 @cindex parts of files, output of
2361 These commands output pieces of the input.
2364 * head invocation:: Output the first part of files.
2365 * tail invocation:: Output the last part of files.
2366 * split invocation:: Split a file into fixed-size pieces.
2367 * csplit invocation:: Split a file into context-determined pieces.
2370 @node head invocation
2371 @section @command{head}: Output the first part of files
2374 @cindex initial part of files, outputting
2375 @cindex first part of files, outputting
2377 @command{head} prints the first part (10 lines by default) of each
2378 @var{file}; it reads from standard input if no files are given or
2379 when given a @var{file} of @option{-}. Synopsis:
2382 head [@var{option}]@dots{} [@var{file}]@dots{}
2385 If more than one @var{file} is specified, @command{head} prints a
2386 one-line header consisting of:
2389 ==> @var{file name} <==
2393 before the output for each @var{file}.
2395 The program accepts the following options. Also see @ref{Common options}.
2400 @itemx --bytes=@var{n}
2403 Print the first @var{n} bytes, instead of initial lines. Appending
2404 @samp{b} multiplies @var{n} by 512, @samp{k} by 1024, and @samp{m}
2406 However, if @var{n} starts with a @samp{-},
2407 print all but the last @var{n} bytes of each file.
2410 @itemx --lines=@var{n}
2413 Output the first @var{n} lines.
2414 However, if @var{n} starts with a @samp{-},
2415 print all but the last @var{n} lines of each file.
2423 Never print file name headers.
2429 Always print file name headers.
2433 For compatibility @command{head} also supports an obsolete option syntax
2434 @option{-@var{count}@var{options}}, which is recognized only if it is
2435 specified first. @var{count} is a decimal number optionally followed
2436 by a size letter (@samp{b}, @samp{k}, @samp{m}) as in @option{-c}, or
2437 @samp{l} to mean count by lines, or other option letters (@samp{cqv}).
2438 New scripts should use @option{-c @var{count}} or @option{-n
2439 @var{count}} instead.
2444 @node tail invocation
2445 @section @command{tail}: Output the last part of files
2448 @cindex last part of files, outputting
2450 @command{tail} prints the last part (10 lines by default) of each
2451 @var{file}; it reads from standard input if no files are given or
2452 when given a @var{file} of @samp{-}. Synopsis:
2455 tail [@var{option}]@dots{} [@var{file}]@dots{}
2458 If more than one @var{file} is specified, @command{tail} prints a
2459 one-line header consisting of:
2462 ==> @var{file name} <==
2466 before the output for each @var{file}.
2468 @cindex BSD @command{tail}
2469 @sc{gnu} @command{tail} can output any amount of data (some other versions of
2470 @command{tail} cannot). It also has no @option{-r} option (print in
2471 reverse), since reversing a file is really a different job from printing
2472 the end of a file; BSD @command{tail} (which is the one with @option{-r}) can
2473 only reverse files that are at most as large as its buffer, which is
2474 typically 32 KiB@. A more reliable and versatile way to reverse files is
2475 the @sc{gnu} @command{tac} command.
2477 If any option-argument is a number @var{n} starting with a @samp{+},
2478 @command{tail} begins printing with the @var{n}th item from the start of
2479 each file, instead of from the end.
2481 The program accepts the following options. Also see @ref{Common options}.
2485 @item -c @var{bytes}
2486 @itemx --bytes=@var{bytes}
2489 Output the last @var{bytes} bytes, instead of final lines. Appending
2490 @samp{b} multiplies @var{bytes} by 512, @samp{k} by 1024, and @samp{m}
2494 @itemx --follow[=@var{how}]
2497 @cindex growing files
2498 @vindex name @r{follow option}
2499 @vindex descriptor @r{follow option}
2500 Loop forever trying to read more characters at the end of the file,
2501 presumably because the file is growing. This option is ignored if
2502 no @var{file} operand is specified and standard input is a pipe.
2503 If more than one file is given, @command{tail} prints a header whenever it
2504 gets output from a different file, to indicate which file that output is
2507 There are two ways to specify how you'd like to track files with this option,
2508 but that difference is noticeable only when a followed file is removed or
2510 If you'd like to continue to track the end of a growing file even after
2511 it has been unlinked, use @option{--follow=descriptor}. This is the default
2512 behavior, but it is not useful if you're tracking a log file that may be
2513 rotated (removed or renamed, then reopened). In that case, use
2514 @option{--follow=name} to track the named file by reopening it periodically
2515 to see if it has been removed and recreated by some other program.
2517 No matter which method you use, if the tracked file is determined to have
2518 shrunk, @command{tail} prints a message saying the file has been truncated
2519 and resumes tracking the end of the file from the newly-determined endpoint.
2521 When a file is removed, @command{tail}'s behavior depends on whether it is
2522 following the name or the descriptor. When following by name, tail can
2523 detect that a file has been removed and gives a message to that effect,
2524 and if @option{--retry} has been specified it will continue checking
2525 periodically to see if the file reappears.
2526 When following a descriptor, tail does not detect that the file has
2527 been unlinked or renamed and issues no message; even though the file
2528 may no longer be accessible via its original name, it may still be
2531 The option values @samp{descriptor} and @samp{name} may be specified only
2532 with the long form of the option, not with @option{-f}.
2536 This option is the same as @option{--follow=name --retry}. That is, tail
2537 will attempt to reopen a file when it is removed. Should this fail, tail
2538 will keep trying until it becomes accessible again.
2542 This option is useful mainly when following by name (i.e., with
2543 @option{--follow=name}).
2544 Without this option, when tail encounters a file that doesn't
2545 exist or is otherwise inaccessible, it reports that fact and
2546 never checks it again.
2548 @itemx --sleep-interval=@var{number}
2549 @opindex --sleep-interval
2550 Change the number of seconds to wait between iterations (the default is 1.0).
2551 During one iteration, every specified file is checked to see if it has
2553 Historical implementations of @command{tail} have required that
2554 @var{number} be an integer. However, GNU @command{tail} accepts
2555 an arbitrary floating point number (using a period before any
2558 @itemx --pid=@var{pid}
2560 When following by name or by descriptor, you may specify the process ID,
2561 @var{pid}, of the sole writer of all @var{file} arguments. Then, shortly
2562 after that process terminates, tail will also terminate. This will
2563 work properly only if the writer and the tailing process are running on
2564 the same machine. For example, to save the output of a build in a file
2565 and to watch the file grow, if you invoke @command{make} and @command{tail}
2566 like this then the tail process will stop when your build completes.
2567 Without this option, you would have had to kill the @code{tail -f}
2571 $ make >& makerr & tail --pid=$! -f makerr
2574 If you specify a @var{pid} that is not in use or that does not correspond
2575 to the process that is writing to the tailed files, then @command{tail}
2576 may terminate long before any @var{file}s stop growing or it may not
2577 terminate until long after the real writer has terminated.
2578 Note that @option{--pid} cannot be supported on some systems; @command{tail}
2579 will print a warning if this is the case.
2581 @itemx --max-unchanged-stats=@var{n}
2582 @opindex --max-unchanged-stats
2583 When tailing a file by name, if there have been @var{n} (default
2584 n=@value{DEFAULT_MAX_N_UNCHANGED_STATS_BETWEEN_OPENS}) consecutive
2585 iterations for which the file has not changed, then
2586 @code{open}/@code{fstat} the file to determine if that file name is
2587 still associated with the same device/inode-number pair as before.
2588 When following a log file that is rotated, this is approximately the
2589 number of seconds between when tail prints the last pre-rotation lines
2590 and when it prints the lines that have accumulated in the new log file.
2591 This option is meaningful only when following by name.
2594 @itemx --lines=@var{n}
2597 Output the last @var{n} lines.
2605 Never print file name headers.
2611 Always print file name headers.
2615 For compatibility @command{tail} also supports an obsolete usage
2616 @samp{tail -[@var{count}][bcl][f] [@var{file}]}, which is recognized
2617 only if it does not conflict with the usage described
2618 above. This obsolete form uses exactly one option and at most one
2619 file. In the option, @var{count} is an optional decimal number optionally
2620 followed by a size letter (@samp{b}, @samp{c}, @samp{l}) to mean count
2621 by 512-byte blocks, bytes, or lines, optionally followed by @samp{f}
2622 which has the same meaning as @option{-f}.
2623 New scripts should use @option{-c @var{count}[b]},
2624 @option{-n @var{count}}, and/or @option{-f} instead.
2626 @vindex _POSIX2_VERSION
2627 On older systems, the leading @samp{-} can be replaced by @samp{+} in
2628 the obsolete option syntax with the same meaning as in counts, and
2629 obsolete usage overrides normal usage when the two conflict.
2630 This obsolete behavior can be enabled or disabled with the
2631 @env{_POSIX2_VERSION} environment variable (@pxref{Standards
2632 conformance}), but portable scripts should avoid commands whose
2633 behavior depends on this variable.
2634 For example, use @samp{tail -- - main.c} or @samp{tail main.c} rather than
2635 the ambiguous @samp{tail - main.c}, @samp{tail -c4} or @samp{tail -c 10
2636 4} rather than the ambiguous @samp{tail -c 4}, and @samp{tail ./+4}
2637 or @samp{tail -n +4} rather than the ambiguous @samp{tail +4}.
2642 @node split invocation
2643 @section @command{split}: Split a file into fixed-size pieces
2646 @cindex splitting a file into pieces
2647 @cindex pieces, splitting a file into
2649 @command{split} creates output files containing consecutive sections of
2650 @var{input} (standard input if none is given or @var{input} is
2651 @samp{-}). Synopsis:
2654 split [@var{option}] [@var{input} [@var{prefix}]]
2657 By default, @command{split} puts 1000 lines of @var{input} (or whatever is
2658 left over for the last section), into each output file.
2660 @cindex output file name prefix
2661 The output files' names consist of @var{prefix} (@samp{x} by default)
2662 followed by a group of characters (@samp{aa}, @samp{ab}, @dots{} by
2663 default), such that concatenating the output files in traditional
2664 sorted order by file name produces
2665 the original input file. If the output file names are exhausted,
2666 @command{split} reports an error without deleting the output files
2669 The program accepts the following options. Also see @ref{Common options}.
2673 @item -a @var{length}
2674 @itemx --suffix-length=@var{length}
2676 @opindex --suffix-length
2677 Use suffixes of length @var{length}. The default @var{length} is 2.
2679 @item -l @var{lines}
2680 @itemx --lines=@var{lines}
2683 Put @var{lines} lines of @var{input} into each output file.
2685 For compatibility @command{split} also supports an obsolete
2686 option syntax @option{-@var{lines}}. New scripts should use @option{-l
2687 @var{lines}} instead.
2689 @item -b @var{bytes}
2690 @itemx --bytes=@var{bytes}
2693 Put the first @var{bytes} bytes of @var{input} into each output file.
2694 Appending @samp{b} multiplies @var{bytes} by 512, @samp{k} by 1024, and
2695 @samp{m} by 1048576.
2697 @item -C @var{bytes}
2698 @itemx --line-bytes=@var{bytes}
2700 @opindex --line-bytes
2701 Put into each output file as many complete lines of @var{input} as
2702 possible without exceeding @var{bytes} bytes. For lines longer than
2703 @var{bytes} bytes, put @var{bytes} bytes into each output file until
2704 less than @var{bytes} bytes of the line are left, then continue
2705 normally. @var{bytes} has the same format as for the @option{--bytes}
2709 @itemx --numeric-suffixes
2711 @opindex --numeric-suffixes
2712 Use digits in suffixes rather than lower-case letters.
2716 Write a diagnostic to standard error just before each output file is opened.
2723 @node csplit invocation
2724 @section @command{csplit}: Split a file into context-determined pieces
2727 @cindex context splitting
2728 @cindex splitting a file into pieces by context
2730 @command{csplit} creates zero or more output files containing sections of
2731 @var{input} (standard input if @var{input} is @samp{-}). Synopsis:
2734 csplit [@var{option}]@dots{} @var{input} @var{pattern}@dots{}
2737 The contents of the output files are determined by the @var{pattern}
2738 arguments, as detailed below. An error occurs if a @var{pattern}
2739 argument refers to a nonexistent line of the input file (e.g., if no
2740 remaining line matches a given regular expression). After every
2741 @var{pattern} has been matched, any remaining input is copied into one
2744 By default, @command{csplit} prints the number of bytes written to each
2745 output file after it has been created.
2747 The types of pattern arguments are:
2752 Create an output file containing the input up to but not including line
2753 @var{n} (a positive integer). If followed by a repeat count, also
2754 create an output file containing the next @var{n} lines of the input
2755 file once for each repeat.
2757 @item /@var{regexp}/[@var{offset}]
2758 Create an output file containing the current line up to (but not
2759 including) the next line of the input file that contains a match for
2760 @var{regexp}. The optional @var{offset} is an integer.
2761 If it is given, the input up to (but not including) the
2762 matching line plus or minus @var{offset} is put into the output file,
2763 and the line after that begins the next section of input.
2765 @item %@var{regexp}%[@var{offset}]
2766 Like the previous type, except that it does not create an output
2767 file, so that section of the input file is effectively ignored.
2769 @item @{@var{repeat-count}@}
2770 Repeat the previous pattern @var{repeat-count} additional
2771 times. The @var{repeat-count} can either be a positive integer or an
2772 asterisk, meaning repeat as many times as necessary until the input is
2777 The output files' names consist of a prefix (@samp{xx} by default)
2778 followed by a suffix. By default, the suffix is an ascending sequence
2779 of two-digit decimal numbers from @samp{00} to @samp{99}. In any case,
2780 concatenating the output files in sorted order by file name produces the
2781 original input file.
2783 By default, if @command{csplit} encounters an error or receives a hangup,
2784 interrupt, quit, or terminate signal, it removes any output files
2785 that it has created so far before it exits.
2787 The program accepts the following options. Also see @ref{Common options}.
2791 @item -f @var{prefix}
2792 @itemx --prefix=@var{prefix}
2795 @cindex output file name prefix
2796 Use @var{prefix} as the output file name prefix.
2798 @item -b @var{suffix}
2799 @itemx --suffix=@var{suffix}
2802 @cindex output file name suffix
2803 Use @var{suffix} as the output file name suffix. When this option is
2804 specified, the suffix string must include exactly one
2805 @code{printf(3)}-style conversion specification, possibly including
2806 format specification flags, a field width, a precision specifications,
2807 or all of these kinds of modifiers. The format letter must convert a
2808 binary integer argument to readable form; thus, only @samp{d}, @samp{i},
2809 @samp{u}, @samp{o}, @samp{x}, and @samp{X} conversions are allowed. The
2810 entire @var{suffix} is given (with the current output file number) to
2811 @code{sprintf(3)} to form the file name suffixes for each of the
2812 individual output files in turn. If this option is used, the
2813 @option{--digits} option is ignored.
2815 @item -n @var{digits}
2816 @itemx --digits=@var{digits}
2819 Use output file names containing numbers that are @var{digits} digits
2820 long instead of the default 2.
2825 @opindex --keep-files
2826 Do not remove output files when errors are encountered.
2829 @itemx --elide-empty-files
2831 @opindex --elide-empty-files
2832 Suppress the generation of zero-length output files. (In cases where
2833 the section delimiters of the input file are supposed to mark the first
2834 lines of each of the sections, the first output file will generally be a
2835 zero-length file unless you use this option.) The output file sequence
2836 numbers always run consecutively starting from 0, even when this option
2847 Do not print counts of output file sizes.
2854 @node Summarizing files
2855 @chapter Summarizing files
2857 @cindex summarizing files
2859 These commands generate just a few numbers representing entire
2863 * wc invocation:: Print newline, word, and byte counts.
2864 * sum invocation:: Print checksum and block counts.
2865 * cksum invocation:: Print CRC checksum and byte counts.
2866 * md5sum invocation:: Print or check MD5 digests.
2867 * sha1sum invocation:: Print or check SHA-1 digests.
2868 * sha2 utilities:: Print or check SHA-2 digests.
2873 @section @command{wc}: Print newline, word, and byte counts
2877 @cindex character count
2881 @command{wc} counts the number of bytes, characters, whitespace-separated
2882 words, and newlines in each given @var{file}, or standard input if none
2883 are given or for a @var{file} of @samp{-}. Synopsis:
2886 wc [@var{option}]@dots{} [@var{file}]@dots{}
2889 @cindex total counts
2890 @command{wc} prints one line of counts for each file, and if the file was
2891 given as an argument, it prints the file name following the counts. If
2892 more than one @var{file} is given, @command{wc} prints a final line
2893 containing the cumulative counts, with the file name @file{total}. The
2894 counts are printed in this order: newlines, words, characters, bytes.
2895 Each count is printed right-justified in a field with at least one
2896 space between fields so that the numbers and file names normally line
2897 up nicely in columns. The width of the count fields varies depending
2898 on the inputs, so you should not depend on a particular field width.
2899 However, as a @acronym{GNU} extension, if only one count is printed,
2900 it is guaranteed to be printed without leading spaces.
2902 By default, @command{wc} prints three counts: the newline, words, and byte
2903 counts. Options can specify that only certain counts be printed.
2904 Options do not undo others previously given, so
2911 prints both the byte counts and the word counts.
2913 With the @option{--max-line-length} option, @command{wc} prints the length
2914 of the longest line per file, and if there is more than one file it
2915 prints the maximum (not the sum) of those lengths.
2917 The program accepts the following options. Also see @ref{Common options}.
2925 Print only the byte counts.
2931 Print only the character counts.
2937 Print only the word counts.
2943 Print only the newline counts.
2946 @itemx --max-line-length
2948 @opindex --max-line-length
2949 Print only the maximum line lengths.
2956 @node sum invocation
2957 @section @command{sum}: Print checksum and block counts
2960 @cindex 16-bit checksum
2961 @cindex checksum, 16-bit
2963 @command{sum} computes a 16-bit checksum for each given @var{file}, or
2964 standard input if none are given or for a @var{file} of @samp{-}. Synopsis:
2967 sum [@var{option}]@dots{} [@var{file}]@dots{}
2970 @command{sum} prints the checksum for each @var{file} followed by the
2971 number of blocks in the file (rounded up). If more than one @var{file}
2972 is given, file names are also printed (by default). (With the
2973 @option{--sysv} option, corresponding file names are printed when there is
2974 at least one file argument.)
2976 By default, @sc{gnu} @command{sum} computes checksums using an algorithm
2977 compatible with BSD @command{sum} and prints file sizes in units of
2980 The program accepts the following options. Also see @ref{Common options}.
2986 @cindex BSD @command{sum}
2987 Use the default (BSD compatible) algorithm. This option is included for
2988 compatibility with the System V @command{sum}. Unless @option{-s} was also
2989 given, it has no effect.
2995 @cindex System V @command{sum}
2996 Compute checksums using an algorithm compatible with System V
2997 @command{sum}'s default, and print file sizes in units of 512-byte blocks.
3001 @command{sum} is provided for compatibility; the @command{cksum} program (see
3002 next section) is preferable in new applications.
3007 @node cksum invocation
3008 @section @command{cksum}: Print CRC checksum and byte counts
3011 @cindex cyclic redundancy check
3012 @cindex CRC checksum
3014 @command{cksum} computes a cyclic redundancy check (CRC) checksum for each
3015 given @var{file}, or standard input if none are given or for a
3016 @var{file} of @samp{-}. Synopsis:
3019 cksum [@var{option}]@dots{} [@var{file}]@dots{}
3022 @command{cksum} prints the CRC checksum for each file along with the number
3023 of bytes in the file, and the file name unless no arguments were given.
3025 @command{cksum} is typically used to ensure that files
3026 transferred by unreliable means (e.g., netnews) have not been corrupted,
3027 by comparing the @command{cksum} output for the received files with the
3028 @command{cksum} output for the original files (typically given in the
3031 The CRC algorithm is specified by the @acronym{POSIX} standard. It is not
3032 compatible with the BSD or System V @command{sum} algorithms (see the
3033 previous section); it is more robust.
3035 The only options are @option{--help} and @option{--version}. @xref{Common
3041 @node md5sum invocation
3042 @section @command{md5sum}: Print or check MD5 digests
3046 @cindex 128-bit checksum
3047 @cindex checksum, 128-bit
3048 @cindex fingerprint, 128-bit
3049 @cindex message-digest, 128-bit
3051 @command{md5sum} computes a 128-bit checksum (or @dfn{fingerprint} or
3052 @dfn{message-digest}) for each specified @var{file}.
3054 Note: The MD5 digest is more reliable than a simple CRC (provided by
3055 the @command{cksum} command) for detecting accidental file corruption,
3056 as the chances of accidentally having two files with indentical MD5
3057 are vanishingly small. However, it should not be considered truly
3058 secure against malicious tampering: although finding a file with a
3059 given MD5 fingerprint, or modifying a file so as to retain its MD5 are
3060 considered infeasible at the moment, it is known how to produce
3061 different files with identical MD5 (a ``collision''), something which
3062 can be a security issue in certain contexts. For more secure hashes,
3063 consider using SHA-1 or SHA-2. @xref{sha1sum invocation}, and
3064 @ref{sha2 utilities}.
3066 If a @var{file} is specified as @samp{-} or if no files are given
3067 @command{md5sum} computes the checksum for the standard input.
3068 @command{md5sum} can also determine whether a file and checksum are
3069 consistent. Synopsis:
3072 md5sum [@var{option}]@dots{} [@var{file}]@dots{}
3075 For each @var{file}, @samp{md5sum} outputs the MD5 checksum, a flag
3076 indicating a binary or text input file, and the file name.
3077 If @var{file} is omitted or specified as @samp{-}, standard input is read.
3079 The program accepts the following options. Also see @ref{Common options}.
3087 @cindex binary input files
3088 Treat each input file as binary, by reading it in binary mode and
3089 outputting a @samp{*} flag. This is the inverse of @option{--text}.
3090 On systems like @acronym{GNU} that do not distinguish between binary
3091 and text files, this option merely flags each input file as binary:
3092 the MD5 checksum is unaffected. This option is the default on systems
3093 like MS-DOS that distinguish between binary and text files, except
3094 for reading standard input when standard input is a terminal.
3098 Read file names and checksum information (not data) from each
3099 @var{file} (or from stdin if no @var{file} was specified) and report
3100 whether the checksums match the contents of the named files.
3101 The input to this mode of @command{md5sum} is usually the output of
3102 a prior, checksum-generating run of @samp{md5sum}.
3103 Each valid line of input consists of an MD5 checksum, a binary/text
3104 flag, and then a file name.
3105 Binary files are marked with @samp{*}, text with @samp{ }.
3106 For each such line, @command{md5sum} reads the named file and computes its
3107 MD5 checksum. Then, if the computed message digest does not match the
3108 one on the line with the file name, the file is noted as having
3109 failed the test. Otherwise, the file passes the test.
3110 By default, for each valid line, one line is written to standard
3111 output indicating whether the named file passed the test.
3112 After all checks have been performed, if there were any failures,
3113 a warning is issued to standard error.
3114 Use the @option{--status} option to inhibit that output.
3115 If any listed file cannot be opened or read, if any valid line has
3116 an MD5 checksum inconsistent with the associated file, or if no valid
3117 line is found, @command{md5sum} exits with nonzero status. Otherwise,
3118 it exits successfully.
3122 @cindex verifying MD5 checksums
3123 This option is useful only when verifying checksums.
3124 When verifying checksums, don't generate the default one-line-per-file
3125 diagnostic and don't output the warning summarizing any failures.
3126 Failures to open or read a file still evoke individual diagnostics to
3128 If all listed files are readable and are consistent with the associated
3129 MD5 checksums, exit successfully. Otherwise exit with a status code
3130 indicating there was a failure.
3136 @cindex text input files
3137 Treat each input file as text, by reading it in text mode and
3138 outputting a @samp{ } flag. This is the inverse of @option{--binary}.
3139 This option is the default on systems like @acronym{GNU} that do not
3140 distinguish between binary and text files. On other systems, it is
3141 the default for reading standard input when standard input is a
3148 @cindex verifying MD5 checksums
3149 When verifying checksums, warn about improperly formatted MD5 checksum lines.
3150 This option is useful only if all but a few lines in the checked input
3158 @node sha1sum invocation
3159 @section @command{sha1sum}: Print or check SHA-1 digests
3163 @cindex 160-bit checksum
3164 @cindex checksum, 160-bit
3165 @cindex fingerprint, 160-bit
3166 @cindex message-digest, 160-bit
3168 @command{sha1sum} computes a 160-bit checksum for each specified
3169 @var{file}. The usage and options of this command are precisely the
3170 same as for @command{md5sum}. @xref{md5sum invocation}.
3172 Note: The SHA-1 digest is more secure than MD5, and no collisions of
3173 it are known (different files having the same fingerprint). However,
3174 it is known that they can be produced with considerable, but not
3175 unreasonable, resources. For this reason, it is generally considered
3176 that SHA-1 should be gradually phased out in favor of the more secure
3177 SHA-2 hash algorithms. @xref{sha2 utilities}.
3180 @node sha2 utilities
3181 @section sha2 utilities: Print or check SHA-2 digests
3188 @cindex 224-bit checksum
3189 @cindex 256-bit checksum
3190 @cindex 384-bit checksum
3191 @cindex 512-bit checksum
3192 @cindex checksum, 224-bit
3193 @cindex checksum, 256-bit
3194 @cindex checksum, 384-bit
3195 @cindex checksum, 512-bit
3196 @cindex fingerprint, 224-bit
3197 @cindex fingerprint, 256-bit
3198 @cindex fingerprint, 384-bit
3199 @cindex fingerprint, 512-bit
3200 @cindex message-digest, 224-bit
3201 @cindex message-digest, 256-bit
3202 @cindex message-digest, 384-bit
3203 @cindex message-digest, 512-bit
3205 The commands @command{sha224sum}, @command{sha256sum},
3206 @command{sha384sum} and @command{sha512sum} compute checksums of
3207 various lengths (respectively 224, 256, 384 and 512 bits),
3208 collectively known as the SHA-2 hashes. The usage and options of
3209 these commands are precisely the same as for @command{md5sum}.
3210 @xref{md5sum invocation}.
3212 Note: The SHA384 and SHA512 digests are considerably slower to
3213 compute, especially on 32-bit computers, than SHA224 or SHA256.
3216 @node Operating on sorted files
3217 @chapter Operating on sorted files
3219 @cindex operating on sorted files
3220 @cindex sorted files, operations on
3222 These commands work with (or produce) sorted files.
3225 * sort invocation:: Sort text files.
3226 * uniq invocation:: Uniquify files.
3227 * comm invocation:: Compare two sorted files line by line.
3228 * ptx invocation:: Produce a permuted index of file contents.
3229 * tsort invocation:: Topological sort.
3230 * tsort background:: Where tsort came from.
3234 @node sort invocation
3235 @section @command{sort}: Sort text files
3238 @cindex sorting files
3240 @command{sort} sorts, merges, or compares all the lines from the given
3241 files, or standard input if none are given or for a @var{file} of
3242 @samp{-}. By default, @command{sort} writes the results to standard
3246 sort [@var{option}]@dots{} [@var{file}]@dots{}
3249 @command{sort} has three modes of operation: sort (the default), merge,
3250 and check for sortedness. The following options change the operation
3259 @cindex checking for sortedness
3260 Check whether the given files are already sorted: if they are not all
3261 sorted, print an error message and exit with a status of 1.
3262 Otherwise, exit successfully.
3268 @cindex merging sorted files
3269 Merge the given files by sorting them as a group. Each input file must
3270 always be individually sorted. It always works to sort instead of
3271 merge; merging is provided because it is faster, in the case where it
3276 @cindex sort stability
3277 @cindex sort's last-resort comparison
3278 A pair of lines is compared as follows:
3279 @command{sort} compares each pair of fields, in the
3280 order specified on the command line, according to the associated
3281 ordering options, until a difference is found or no fields are left.
3282 If no key fields are specified, @command{sort} uses a default key of
3283 the entire line. Finally, as a last resort when all keys compare
3284 equal, @command{sort} compares entire lines as if no ordering options
3285 other than @option{--reverse} (@option{-r}) were specified. The
3286 @option{--stable} (@option{-s}) option disables this @dfn{last-resort
3287 comparison} so that lines in which all fields compare equal are left
3288 in their original relative order. The @option{--unique}
3289 (@option{-u}) option also disables the last-resort comparison.
3293 Unless otherwise specified, all comparisons use the character collating
3294 sequence specified by the @env{LC_COLLATE} locale.@footnote{If you
3295 use a non-@acronym{POSIX} locale (e.g., by setting @env{LC_ALL}
3296 to @samp{en_US}), then @command{sort} may produce output that is sorted
3297 differently than you're accustomed to. In that case, set the @env{LC_ALL}
3298 environment variable to @samp{C}. Note that setting only @env{LC_COLLATE}
3299 has two problems. First, it is ineffective if @env{LC_ALL} is also set.
3300 Second, it has undefined behavior if @env{LC_CTYPE} (or @env{LANG}, if
3301 @env{LC_CTYPE} is unset) is set to an incompatible value. For example,
3302 you get undefined behavior if @env{LC_CTYPE} is @code{ja_JP.PCK} but
3303 @env{LC_COLLATE} is @code{en_US.UTF-8}.}
3305 @sc{gnu} @command{sort} (as specified for all @sc{gnu} utilities) has no
3306 limit on input line length or restrictions on bytes allowed within lines.
3307 In addition, if the final byte of an input file is not a newline, @sc{gnu}
3308 @command{sort} silently supplies one. A line's trailing newline is not
3309 part of the line for comparison purposes.
3311 @cindex exit status of @command{sort}
3315 0 if no error occurred
3316 1 if invoked with @option{-c} and the input is not properly sorted
3317 2 if an error occurred
3321 If the environment variable @env{TMPDIR} is set, @command{sort} uses its
3322 value as the directory for temporary files instead of @file{/tmp}. The
3323 @option{--temporary-directory} (@option{-T}) option in turn overrides
3324 the environment variable.
3327 The following options affect the ordering of output lines. They may be
3328 specified globally or as part of a specific key field. If no key
3329 fields are specified, global options apply to comparison of entire
3330 lines; otherwise the global options are inherited by key fields that do
3331 not specify any special options of their own. In pre-@acronym{POSIX}
3332 versions of @command{sort}, global options affect only later key fields,
3333 so portable shell scripts should specify global options first.
3338 @itemx --ignore-leading-blanks
3340 @opindex --ignore-leading-blanks
3341 @cindex blanks, ignoring leading
3343 Ignore leading blanks when finding sort keys in each line.
3344 By default a blank is a space or a tab, but the @env{LC_CTYPE} locale
3348 @itemx --dictionary-order
3350 @opindex --dictionary-order
3351 @cindex dictionary order
3352 @cindex phone directory order
3353 @cindex telephone directory order
3355 Sort in @dfn{phone directory} order: ignore all characters except
3356 letters, digits and blanks when sorting.
3357 By default letters and digits are those of @acronym{ASCII} and a blank
3358 is a space or a tab, but the @env{LC_CTYPE} locale can change this.
3361 @itemx --ignore-case
3363 @opindex --ignore-case
3364 @cindex ignoring case
3365 @cindex case folding
3367 Fold lowercase characters into the equivalent uppercase characters when
3368 comparing so that, for example, @samp{b} and @samp{B} sort as equal.
3369 The @env{LC_CTYPE} locale determines character types.
3372 @itemx --general-numeric-sort
3374 @opindex --general-numeric-sort
3375 @cindex general numeric sort
3377 Sort numerically, using the standard C function @code{strtod} to convert
3378 a prefix of each line to a double-precision floating point number.
3379 This allows floating point numbers to be specified in scientific notation,
3380 like @code{1.0e-34} and @code{10e100}.
3381 The @env{LC_NUMERIC} locale determines the decimal-point character.
3382 Do not report overflow, underflow, or conversion errors.
3383 Use the following collating sequence:
3387 Lines that do not start with numbers (all considered to be equal).
3389 NaNs (``Not a Number'' values, in IEEE floating point arithmetic)
3390 in a consistent but machine-dependent order.
3394 Finite numbers in ascending numeric order (with @math{-0} and @math{+0} equal).
3399 Use this option only if there is no alternative; it is much slower than
3400 @option{--numeric-sort} (@option{-n}) and it can lose information when
3401 converting to floating point.
3404 @itemx --ignore-nonprinting
3406 @opindex --ignore-nonprinting
3407 @cindex nonprinting characters, ignoring
3408 @cindex unprintable characters, ignoring
3410 Ignore nonprinting characters.
3411 The @env{LC_CTYPE} locale determines character types.
3412 This option has no effect if the stronger @option{--dictionary-order}
3413 (@option{-d}) option is also given.
3418 @opindex --month-sort
3419 @cindex months, sorting by
3421 An initial string, consisting of any amount of blanks, followed
3422 by a month name abbreviation, is folded to UPPER case and
3423 compared in the order @samp{JAN} < @samp{FEB} < @dots{} < @samp{DEC}.
3424 Invalid names compare low to valid names. The @env{LC_TIME} locale
3425 category determines the month spellings.
3426 By default a blank is a space or a tab, but the @env{LC_CTYPE} locale
3430 @itemx --numeric-sort
3432 @opindex --numeric-sort
3433 @cindex numeric sort
3435 Sort numerically: the number begins each line; specifically, it consists
3436 of optional blanks, an optional @samp{-} sign, and zero or more
3437 digits possibly separated by thousands separators, optionally followed
3438 by a decimal-point character and zero or more digits. A string of
3439 no digits is interpreted as @samp{0}. The @env{LC_NUMERIC}
3440 locale specifies the decimal-point character and thousands separator.
3441 By default a blank is a space or a tab, but the @env{LC_CTYPE} locale
3444 Numeric sort uses what might be considered an unconventional method to
3445 compare strings representing floating point numbers. Rather than first
3446 converting each string to the C @code{double} type and then comparing
3447 those values, @command{sort} aligns the decimal-point characters in the
3448 two strings and compares the strings a character at a time. One benefit
3449 of using this approach is its speed. In practice this is much more
3450 efficient than performing the two corresponding string-to-double (or
3451 even string-to-integer) conversions and then comparing doubles. In
3452 addition, there is no corresponding loss of precision. Converting each
3453 string to @code{double} before comparison would limit precision to about
3454 16 digits on most systems.
3456 Neither a leading @samp{+} nor exponential notation is recognized.
3457 To compare such strings numerically, use the
3458 @option{--general-numeric-sort} (@option{-g}) option.
3464 @cindex reverse sorting
3465 Reverse the result of comparison, so that lines with greater key values
3466 appear earlier in the output instead of later.
3469 @itemx --random-sort
3471 @opindex --random-sort
3473 Sort by hashing the input keys and then sorting the hash values. This
3474 is much like a random shuffle of the inputs, except that keys with the
3475 same value sort together. Normally the hash function is chosen at
3476 random, but this can be overridden with the @option{--seed} option.
3484 @item -k @var{pos1}[,@var{pos2}]
3485 @itemx --key=@var{pos1}[,@var{pos2}]
3489 Specify a sort field that consists of the part of the line between
3490 @var{pos1} and @var{pos2} (or the end of the line, if @var{pos2} is
3491 omitted), @emph{inclusive}. Fields and character positions are numbered
3492 starting with 1. So to sort on the second field, you'd use
3493 @option{--key=2,2} (@option{-k 2,2}). See below for more examples.
3495 @item -o @var{output-file}
3496 @itemx --output=@var{output-file}
3499 @cindex overwriting of input, allowed
3500 Write output to @var{output-file} instead of standard output.
3501 Normally, @command{sort} reads all input before opening
3502 @var{output-file}, so you can safely sort a file in place by using
3503 commands like @code{sort -o F F} and @code{cat F | sort -o F}.
3504 However, @command{sort} with @option{--merge} (@option{-m}) can open
3505 the output file before reading all input, so a command like @code{cat
3506 F | sort -m -o F - G} is not safe as @command{sort} might start
3507 writing @file{F} before @command{cat} is done reading it.
3509 @vindex POSIXLY_CORRECT
3510 On newer systems, @option{-o} cannot appear after an input file if
3511 @env{POSIXLY_CORRECT} is set, e.g., @samp{sort F -o F}. Portable
3512 scripts should specify @option{-o @var{output-file}} before any input
3519 @cindex sort stability
3520 @cindex sort's last-resort comparison
3522 Make @command{sort} stable by disabling its last-resort comparison.
3523 This option has no effect if no fields or global ordering options
3524 other than @option{--reverse} (@option{-R}) are specified.
3527 @itemx --buffer-size=@var{size}
3529 @opindex --buffer-size
3530 @cindex size for main memory sorting
3531 Use a main-memory sort buffer of the given @var{size}. By default,
3532 @var{size} is in units of 1024 bytes. Appending @samp{%} causes
3533 @var{size} to be interpreted as a percentage of physical memory.
3534 Appending @samp{K} multiplies @var{size} by 1024 (the default),
3535 @samp{M} by 1,048,576, @samp{G} by 1,073,741,824, and so on for
3536 @samp{T}, @samp{P}, @samp{E}, @samp{Z}, and @samp{Y}. Appending
3537 @samp{b} causes @var{size} to be interpreted as a byte count, with no
3540 This option can improve the performance of @command{sort} by causing it
3541 to start with a larger or smaller sort buffer than the default.
3542 However, this option affects only the initial buffer size. The buffer
3543 grows beyond @var{size} if @command{sort} encounters input lines larger
3546 @item -t @var{separator}
3547 @itemx --field-separator=@var{separator}
3549 @opindex --field-separator
3550 @cindex field separator character
3551 Use character @var{separator} as the field separator when finding the
3552 sort keys in each line. By default, fields are separated by the empty
3553 string between a non-blank character and a blank character.
3554 By default a blank is a space or a tab, but the @env{LC_CTYPE} locale
3557 That is, given the input line @w{@samp{ foo bar}}, @command{sort} breaks it
3558 into fields @w{@samp{ foo}} and @w{@samp{ bar}}. The field separator is
3559 not considered to be part of either the field preceding or the field
3560 following, so with @samp{sort @w{-t " "}} the same input line has
3561 three fields: an empty field, @samp{foo}, and @samp{bar}.
3562 However, fields that extend to the end of the line,
3563 as @option{-k 2}, or fields consisting of a range, as @option{-k 2,3},
3564 retain the field separators present between the endpoints of the range.
3566 To specify a null character (@acronym{ASCII} @sc{nul}) as
3567 the field separator, use the two-character string @samp{\0}, e.g.,
3568 @samp{sort -t '\0'}.
3570 @item -T @var{tempdir}
3571 @itemx --temporary-directory=@var{tempdir}
3573 @opindex --temporary-directory
3574 @cindex temporary directory
3576 Use directory @var{tempdir} to store temporary files, overriding the
3577 @env{TMPDIR} environment variable. If this option is given more than
3578 once, temporary files are stored in all the directories given. If you
3579 have a large sort or merge that is I/O-bound, you can often improve
3580 performance by using this option to specify directories on different
3581 disks and controllers.
3587 @cindex uniquifying output
3589 Normally, output only the first of a sequence of lines that compare
3590 equal. For the @option{--check} (@option{-c}) option,
3591 check that no pair of consecutive lines compares equal.
3593 This option also disables the default last-resort comparison.
3595 The commands @code{sort -u} and @code{sort | uniq} are equivalent, but
3596 this equivalence does not extend to arbitrary @command{sort} options.
3597 For example, @code{sort -n -u} inspects only the value of the initial
3598 numeric string when checking for uniqueness, whereas @code{sort -n |
3599 uniq} inspects the entire line. @xref{uniq invocation}.
3602 @itemx --zero-terminated
3604 @opindex --zero-terminated
3605 @cindex sort zero-terminated lines
3606 Treat the input as a set of lines, each terminated by a null character
3607 (@acronym{ASCII} @sc{nul}) instead of a line feed
3608 (@acronym{ASCII} @sc{lf}).
3609 This option can be useful in conjunction with @samp{perl -0} or
3610 @samp{find -print0} and @samp{xargs -0} which do the same in order to
3611 reliably handle arbitrary file names (even those containing blanks
3612 or other special characters).
3614 @item --seed=@var{string}
3616 @cindex seed for random hash
3617 Use data from @var{string} to choose the hash function used by the
3618 @option{--random-sort} option. This option can be used to reproduce
3619 results of earlier invocations of @command{sort} with
3620 @option{--random-sort}. However, results are not necessarily
3621 reproducible across different @command{sort} implementations (e.g.,
3622 @command{sort} on little-endian versus big-endian architectures, or
3623 from one version of @command{sort} to the next).
3627 Historical (BSD and System V) implementations of @command{sort} have
3628 differed in their interpretation of some options, particularly
3629 @option{-b}, @option{-f}, and @option{-n}. @sc{gnu} sort follows the @acronym{POSIX}
3630 behavior, which is usually (but not always!) like the System V behavior.
3631 According to @acronym{POSIX}, @option{-n} no longer implies @option{-b}. For
3632 consistency, @option{-M} has been changed in the same way. This may
3633 affect the meaning of character positions in field specifications in
3634 obscure cases. The only fix is to add an explicit @option{-b}.
3636 A position in a sort field specified with the @option{-k}
3637 option has the form @samp{@var{f}.@var{c}}, where @var{f} is the number
3638 of the field to use and @var{c} is the number of the first character
3639 from the beginning of the field. In a start position, an omitted
3640 @samp{.@var{c}} stands for the field's first character. In an end
3641 position, an omitted or zero @samp{.@var{c}} stands for the field's
3642 last character. If the start field falls after the end of the line
3643 or after the end field, the field is empty. If the
3644 @option{-b} option was specified, the @samp{.@var{c}} part of a field
3645 specification is counted from the first nonblank character of the field.
3647 A sort key position may also have any of the option letters @samp{Mbdfinr}
3648 appended to it, in which case the global ordering options are not used
3649 for that particular field. The @option{-b} option may be independently
3650 attached to either or both of the start and
3651 end positions of a field specification, and if it is inherited
3652 from the global options it will be attached to both.
3653 If input lines can contain leading or adjacent blanks and @option{-t}
3654 is not used, then @option{-k} is typically combined with @option{-b},
3655 @option{-g}, @option{-M}, or @option{-n}; otherwise the varying
3656 numbers of leading blanks in fields can cause confusing results.
3658 Keys can span multiple fields.
3660 @vindex _POSIX2_VERSION
3661 On older systems, @command{sort} supports an obsolete origin-zero
3662 syntax @samp{+@var{pos1} [-@var{pos2}]} for specifying sort keys.
3663 This obsolete behavior can be enabled or disabled with the
3664 @env{_POSIX2_VERSION} environment variable (@pxref{Standards
3665 conformance}), but portable scripts should avoid commands whose
3666 behavior depends on this variable.
3667 For example, use @samp{sort ./+2} or @samp{sort -k 3} rather than
3668 the ambiguous @samp{sort +2}.
3670 Here are some examples to illustrate various combinations of options.
3675 Sort in descending (reverse) numeric order.
3682 Sort alphabetically, omitting the first and second fields
3683 and the blanks at the start of the third field.
3684 This uses a single key composed of the characters beginning
3685 at the start of the first nonblank character in field three
3686 and extending to the end of each line.
3693 Sort numerically on the second field and resolve ties by sorting
3694 alphabetically on the third and fourth characters of field five.
3695 Use @samp{:} as the field delimiter.
3698 sort -t : -k 2,2n -k 5.3,5.4
3701 Note that if you had written @option{-k 2n} instead of @option{-k 2,2n}
3702 @command{sort} would have used all characters beginning in the second field
3703 and extending to the end of the line as the primary @emph{numeric}
3704 key. For the large majority of applications, treating keys spanning
3705 more than one field as numeric will not do what you expect.
3707 Also note that the @samp{n} modifier was applied to the field-end
3708 specifier for the first key. It would have been equivalent to
3709 specify @option{-k 2n,2} or @option{-k 2n,2n}. All modifiers except
3710 @samp{b} apply to the associated @emph{field}, regardless of whether
3711 the modifier character is attached to the field-start and/or the
3712 field-end part of the key specifier.
3715 Sort the password file on the fifth field and ignore any
3716 leading blanks. Sort lines with equal values in field five
3717 on the numeric user ID in field three. Fields are separated
3721 sort -t : -k 5b,5 -k 3,3n /etc/passwd
3722 sort -t : -n -k 5b,5 -k 3,3 /etc/passwd
3723 sort -t : -b -k 5,5 -k 3,3n /etc/passwd
3726 These three commands have equivalent effect. The first specifies that
3727 the first key's start position ignores leading blanks and the second
3728 key is sorted numerically. The other two commands rely on global
3729 options being inherited by sort keys that lack modifiers. The inheritance
3730 works in this case because @option{-k 5b,5b} and @option{-k 5b,5} are
3731 equivalent, as the location of a field-end lacking a @samp{.@var{c}}
3732 character position is not affected by whether initial blanks are
3736 Sort a set of log files, primarily by IPv4 address and secondarily by
3737 time stamp. If two lines' primary and secondary keys are identical,
3738 output the lines in the same order that they were input. The log
3739 files contain lines that look like this:
3742 4.150.156.3 - - [01/Apr/2004:06:31:51 +0000] message 1
3743 211.24.3.231 - - [24/Apr/2004:20:17:39 +0000] message 2
3746 Fields are separated by exactly one space. Sort IPv4 addresses
3747 lexicographically, e.g., 212.61.52.2 sorts before 212.129.233.201
3748 because 61 is less than 129.
3751 sort -s -t ' ' -k 4.9n -k 4.5M -k 4.2n -k 4.14,4.21 file*.log |
3752 sort -s -t '.' -k 1,1n -k 2,2n -k 3,3n -k 4,4n
3755 This example cannot be done with a single @command{sort} invocation,
3756 since IPv4 address components are separated by @samp{.} while dates
3757 come just after a space. So it is broken down into two invocations of
3758 @command{sort}: the first sorts by time stamp and the second by IPv4
3759 address. The time stamp is sorted by year, then month, then day, and
3760 finally by hour-minute-second field, using @option{-k} to isolate each
3761 field. Except for hour-minute-second there's no need to specify the
3762 end of each key field, since the @samp{n} and @samp{M} modifiers sort
3763 based on leading prefixes that cannot cross field boundaries. The
3764 IPv4 addresses are sorted lexicographically. The second sort uses
3765 @samp{-s} so that ties in the primary key are broken by the secondary
3766 key; the first sort uses @samp{-s} so that the combination of the two
3770 Generate a tags file in case-insensitive sorted order.
3773 find src -type f -print0 | sort -z -f | xargs -0 etags --append
3776 The use of @option{-print0}, @option{-z}, and @option{-0} in this case means
3777 that file names that contain blanks or other special characters are
3779 by the sort operation.
3781 @c This example is a bit contrived and needs more explanation.
3783 @c Sort records separated by an arbitrary string by using a pipe to convert
3784 @c each record delimiter string to @samp{\0}, then using sort's -z option,
3785 @c and converting each @samp{\0} back to the original record delimiter.
3788 @c printf 'c\n\nb\n\na\n'|perl -0pe 's/\n\n/\n\0/g'|sort -z|perl -0pe 's/\0/\n/g'
3792 Shuffle a list of directories, but preserve the order of files within
3793 each directory. For instance, one could use this to generate a music
3794 playlist in which albums are shuffled but the songs of each album are
3798 ls */* | sort -t / -k 1,1R -k 2,2
3804 @node uniq invocation
3805 @section @command{uniq}: Uniquify files
3808 @cindex uniquify files
3810 @command{uniq} writes the unique lines in the given @file{input}, or
3811 standard input if nothing is given or for an @var{input} name of
3815 uniq [@var{option}]@dots{} [@var{input} [@var{output}]]
3818 By default, @command{uniq} prints its input lines, except that
3819 it discards all but the first of adjacent repeated lines, so that
3820 no output lines are repeated. Optionally, it can instead discard
3821 lines that are not repeated, or all repeated lines.
3823 The input need not be sorted, but repeated input lines are detected
3824 only if they are adjacent. If you want to discard non-adjacent
3825 duplicate lines, perhaps you want to use @code{sort -u}.
3826 @xref{sort invocation}.
3829 Comparisons use the character collating sequence specified by the
3830 @env{LC_COLLATE} locale category.
3832 If no @var{output} file is specified, @command{uniq} writes to standard
3835 The program accepts the following options. Also see @ref{Common options}.
3840 @itemx --skip-fields=@var{n}
3842 @opindex --skip-fields
3843 Skip @var{n} fields on each line before checking for uniqueness. Use
3844 a null string for comparison if a line has fewer than @var{n} fields. Fields
3845 are sequences of non-space non-tab characters that are separated from
3846 each other by at least one space or tab.
3848 For compatibility @command{uniq} supports an obsolete option syntax
3849 @option{-@var{n}}. New scripts should use @option{-f @var{n}} instead.
3852 @itemx --skip-chars=@var{n}
3854 @opindex --skip-chars
3855 Skip @var{n} characters before checking for uniqueness. Use a null string
3856 for comparison if a line has fewer than @var{n} characters. If you use both
3857 the field and character skipping options, fields are skipped over first.
3859 @vindex _POSIX2_VERSION
3860 On older systems, @command{uniq} supports an obsolete option syntax
3862 This obsolete behavior can be enabled or disabled with the
3863 @env{_POSIX2_VERSION} environment variable (@pxref{Standards
3864 conformance}), but portable scripts should avoid commands whose
3865 behavior depends on this variable.
3866 For example, use @samp{uniq ./+10} or @samp{uniq -s 10} rather than
3867 the ambiguous @samp{uniq +10}.
3873 Print the number of times each line occurred along with the line.
3876 @itemx --ignore-case
3878 @opindex --ignore-case
3879 Ignore differences in case when comparing lines.
3885 @cindex repeated lines, outputting
3886 Discard lines that are not repeated. When used by itself, this option
3887 causes @command{uniq} to print the first copy of each repeated line,
3891 @itemx --all-repeated[=@var{delimit-method}]
3893 @opindex --all-repeated
3894 @cindex all repeated lines, outputting
3895 Do not discard the second and subsequent repeated input lines,
3896 but discard lines that are not repeated.
3897 This option is useful mainly in conjunction with other options e.g.,
3898 to ignore case or to compare only selected fields.
3899 The optional @var{delimit-method} tells how to delimit
3900 groups of repeated lines, and must be one of the following:
3905 Do not delimit groups of repeated lines.
3906 This is equivalent to @option{--all-repeated} (@option{-D}).
3909 Output a newline before each group of repeated lines.
3912 Separate groups of repeated lines with a single newline.
3913 This is the same as using @samp{prepend}, except that
3914 there is no newline before the first group, and hence
3915 may be better suited for output direct to users.
3918 Note that when groups are delimited and the input stream contains
3919 two or more consecutive blank lines, then the output is ambiguous.
3920 To avoid that, filter the input through @samp{tr -s '\n'} to replace
3921 each sequence of consecutive newlines with a single newline.
3923 This is a @sc{gnu} extension.
3924 @c FIXME: give an example showing *how* it's useful
3930 @cindex unique lines, outputting
3931 Discard the first repeated line. When used by itself, this option
3932 causes @command{uniq} to print unique lines, and nothing else.
3935 @itemx --check-chars=@var{n}
3937 @opindex --check-chars
3938 Compare at most @var{n} characters on each line (after skipping any specified
3939 fields and characters). By default the entire rest of the lines are
3947 @node comm invocation
3948 @section @command{comm}: Compare two sorted files line by line
3951 @cindex line-by-line comparison
3952 @cindex comparing sorted files
3954 @command{comm} writes to standard output lines that are common, and lines
3955 that are unique, to two input files; a file name of @samp{-} means
3956 standard input. Synopsis:
3959 comm [@var{option}]@dots{} @var{file1} @var{file2}
3963 Before @command{comm} can be used, the input files must be sorted using the
3964 collating sequence specified by the @env{LC_COLLATE} locale.
3965 If an input file ends in a non-newline
3966 character, a newline is silently appended. The @command{sort} command with
3967 no options always outputs a file that is suitable input to @command{comm}.
3969 @cindex differing lines
3970 @cindex common lines
3971 With no options, @command{comm} produces three-column output. Column one
3972 contains lines unique to @var{file1}, column two contains lines unique
3973 to @var{file2}, and column three contains lines common to both files.
3974 Columns are separated by a single TAB character.
3975 @c FIXME: when there's an option to supply an alternative separator
3976 @c string, append `by default' to the above sentence.
3981 The options @option{-1}, @option{-2}, and @option{-3} suppress printing of
3982 the corresponding columns. Also see @ref{Common options}.
3984 Unlike some other comparison utilities, @command{comm} has an exit
3985 status that does not depend on the result of the comparison.
3986 Upon normal completion @command{comm} produces an exit code of zero.
3987 If there is an error it exits with nonzero status.
3990 @node tsort invocation
3991 @section @command{tsort}: Topological sort
3994 @cindex topological sort
3996 @command{tsort} performs a topological sort on the given @var{file}, or
3997 standard input if no input file is given or for a @var{file} of
3998 @samp{-}. For more details and some history, see @ref{tsort background}.
4002 tsort [@var{option}] [@var{file}]
4005 @command{tsort} reads its input as pairs of strings, separated by blanks,
4006 indicating a partial ordering. The output is a total ordering that
4007 corresponds to the given partial ordering.
4021 will produce the output
4032 Consider a more realistic example.
4033 You have a large set of functions all in one file, and they may all be
4034 declared static except one. Currently that one (say @code{main}) is the
4035 first function defined in the file, and the ones it calls directly follow
4036 it, followed by those they call, etc. Let's say that you are determined
4037 to take advantage of prototypes, so you have to choose between declaring
4038 all of those functions (which means duplicating a lot of information from
4039 the definitions) and rearranging the functions so that as many as possible
4040 are defined before they are used. One way to automate the latter process
4041 is to get a list for each function of the functions it calls directly.
4042 Many programs can generate such lists. They describe a call graph.
4043 Consider the following list, in which a given line indicates that the
4044 function on the left calls the one on the right directly.
4050 tail_file pretty_name
4051 tail_file write_header
4053 tail_forever recheck
4054 tail_forever pretty_name
4055 tail_forever write_header
4056 tail_forever dump_remainder
4059 tail_lines start_lines
4060 tail_lines dump_remainder
4061 tail_lines file_lines
4062 tail_lines pipe_lines
4064 tail_bytes start_bytes
4065 tail_bytes dump_remainder
4066 tail_bytes pipe_bytes
4067 file_lines dump_remainder
4071 then you can use @command{tsort} to produce an ordering of those
4072 functions that satisfies your requirement.
4075 example$ tsort call-graph | tac
4095 @command{tsort} detects any cycles in the input and writes the first cycle
4096 encountered to standard error.
4098 Note that for a given partial ordering, generally there is no unique
4099 total ordering. In the context of the call graph above, the function
4100 @code{parse_options} may be placed anywhere in the list as long as it
4101 precedes @code{main}.
4103 The only options are @option{--help} and @option{--version}. @xref{Common
4106 @node tsort background
4107 @section @command{tsort}: Background
4109 @command{tsort} exists because very early versions of the Unix linker processed
4110 an archive file exactly once, and in order. As @command{ld} read each object
4111 in the archive, it decided whether it was needed in the program based on
4112 whether it defined any symbols which were undefined at that point in
4115 This meant that dependencies within the archive had to be handled
4116 specially. For example, @code{scanf} probably calls @code{read}. That means
4117 that in a single pass through an archive, it was important for @code{scanf.o}
4118 to appear before read.o, because otherwise a program which calls
4119 @code{scanf} but not @code{read} might end up with an unexpected unresolved
4120 reference to @code{read}.
4122 The way to address this problem was to first generate a set of
4123 dependencies of one object file on another. This was done by a shell
4124 script called @command{lorder}. The GNU tools don't provide a version of
4125 lorder, as far as I know, but you can still find it in BSD
4128 Then you ran @command{tsort} over the @command{lorder} output, and you used the
4129 resulting sort to define the order in which you added objects to the archive.
4131 This whole procedure has been obsolete since about 1980, because
4132 Unix archives now contain a symbol table (traditionally built by
4133 @command{ranlib}, now generally built by @command{ar} itself), and the Unix
4134 linker uses the symbol table to effectively make multiple passes over
4137 Anyhow, that's where tsort came from. To solve an old problem with
4138 the way the linker handled archive files, which has since been solved
4144 @node ptx invocation
4145 @section @command{ptx}: Produce permuted indexes
4149 @command{ptx} reads a text file and essentially produces a permuted index, with
4150 each keyword in its context. The calling sketch is either one of:
4153 ptx [@var{option} @dots{}] [@var{file} @dots{}]
4154 ptx -G [@var{option} @dots{}] [@var{input} [@var{output}]]
4157 The @option{-G} (or its equivalent: @option{--traditional}) option disables
4158 all @sc{gnu} extensions and reverts to traditional mode, thus introducing some
4159 limitations and changing several of the program's default option values.
4160 When @option{-G} is not specified, @sc{gnu} extensions are always enabled.
4161 @sc{gnu} extensions to @command{ptx} are documented wherever appropriate in this
4162 document. For the full list, see @xref{Compatibility in ptx}.
4164 Individual options are explained in the following sections.
4166 When @sc{gnu} extensions are enabled, there may be zero, one or several
4167 @var{file}s after the options. If there is no @var{file}, the program
4168 reads the standard input. If there is one or several @var{file}s, they
4169 give the name of input files which are all read in turn, as if all the
4170 input files were concatenated. However, there is a full contextual
4171 break between each file and, when automatic referencing is requested,
4172 file names and line numbers refer to individual text input files. In
4173 all cases, the program outputs the permuted index to the standard
4176 When @sc{gnu} extensions are @emph{not} enabled, that is, when the program
4177 operates in traditional mode, there may be zero, one or two parameters
4178 besides the options. If there are no parameters, the program reads the
4179 standard input and outputs the permuted index to the standard output.
4180 If there is only one parameter, it names the text @var{input} to be read
4181 instead of the standard input. If two parameters are given, they give
4182 respectively the name of the @var{input} file to read and the name of
4183 the @var{output} file to produce. @emph{Be very careful} to note that,
4184 in this case, the contents of file given by the second parameter is
4185 destroyed. This behavior is dictated by System V @command{ptx}
4186 compatibility; @sc{gnu} Standards normally discourage output parameters not
4187 introduced by an option.
4189 Note that for @emph{any} file named as the value of an option or as an
4190 input text file, a single dash @kbd{-} may be used, in which case
4191 standard input is assumed. However, it would not make sense to use this
4192 convention more than once per program invocation.
4195 * General options in ptx:: Options which affect general program behavior.
4196 * Charset selection in ptx:: Underlying character set considerations.
4197 * Input processing in ptx:: Input fields, contexts, and keyword selection.
4198 * Output formatting in ptx:: Types of output format, and sizing the fields.
4199 * Compatibility in ptx::
4203 @node General options in ptx
4204 @subsection General options
4210 Print a short note about the copyright and copying conditions, then
4211 exit without further processing.
4214 @itemx --traditional
4215 As already explained, this option disables all @sc{gnu} extensions to
4216 @command{ptx} and switches to traditional mode.
4219 Print a short help on standard output, then exit without further
4223 Print the program version on standard output, then exit without further
4231 @node Charset selection in ptx
4232 @subsection Charset selection
4234 @c FIXME: People don't necessarily know what an IBM-PC was these days.
4235 As it is set up now, the program assumes that the input file is coded
4236 using 8-bit @acronym{ISO} 8859-1 code, also known as Latin-1 character set,
4237 @emph{unless} it is compiled for MS-DOS, in which case it uses the
4238 character set of the IBM-PC@. (@sc{gnu} @command{ptx} is not known to work on
4239 smaller MS-DOS machines anymore.) Compared to 7-bit @acronym{ASCII}, the set
4240 of characters which are letters is different; this alters the behavior
4241 of regular expression matching. Thus, the default regular expression
4242 for a keyword allows foreign or diacriticized letters. Keyword sorting,
4243 however, is still crude; it obeys the underlying character set ordering
4249 @itemx --ignore-case
4250 Fold lower case letters to upper case for sorting.
4255 @node Input processing in ptx
4256 @subsection Word selection and input processing
4261 @item --break-file=@var{file}
4263 This option provides an alternative (to @option{-W}) method of describing
4264 which characters make up words. It introduces the name of a
4265 file which contains a list of characters which can@emph{not} be part of
4266 one word; this file is called the @dfn{Break file}. Any character which
4267 is not part of the Break file is a word constituent. If both options
4268 @option{-b} and @option{-W} are specified, then @option{-W} has precedence and
4269 @option{-b} is ignored.
4271 When @sc{gnu} extensions are enabled, the only way to avoid newline as a
4272 break character is to write all the break characters in the file with no
4273 newline at all, not even at the end of the file. When @sc{gnu} extensions
4274 are disabled, spaces, tabs and newlines are always considered as break
4275 characters even if not included in the Break file.
4278 @itemx --ignore-file=@var{file}
4280 The file associated with this option contains a list of words which will
4281 never be taken as keywords in concordance output. It is called the
4282 @dfn{Ignore file}. The file contains exactly one word in each line; the
4283 end of line separation of words is not subject to the value of the
4286 There is a default Ignore file used by @command{ptx} when this option is
4287 not specified, usually found in @file{/usr/local/lib/eign} if this has
4288 not been changed at installation time. If you want to deactivate the
4289 default Ignore file, specify @code{/dev/null} instead.
4292 @itemx --only-file=@var{file}
4294 The file associated with this option contains a list of words which will
4295 be retained in concordance output; any word not mentioned in this file
4296 is ignored. The file is called the @dfn{Only file}. The file contains
4297 exactly one word in each line; the end of line separation of words is
4298 not subject to the value of the @option{-S} option.
4300 There is no default for the Only file. When both an Only file and an
4301 Ignore file are specified, a word is considered a keyword only
4302 if it is listed in the Only file and not in the Ignore file.
4307 On each input line, the leading sequence of non-white space characters will be
4308 taken to be a reference that has the purpose of identifying this input
4309 line in the resulting permuted index. For more information about reference
4310 production, see @xref{Output formatting in ptx}.
4311 Using this option changes the default value for option @option{-S}.
4313 Using this option, the program does not try very hard to remove
4314 references from contexts in output, but it succeeds in doing so
4315 @emph{when} the context ends exactly at the newline. If option
4316 @option{-r} is used with @option{-S} default value, or when @sc{gnu} extensions
4317 are disabled, this condition is always met and references are completely
4318 excluded from the output contexts.
4320 @item -S @var{regexp}
4321 @itemx --sentence-regexp=@var{regexp}
4323 This option selects which regular expression will describe the end of a
4324 line or the end of a sentence. In fact, this regular expression is not
4325 the only distinction between end of lines or end of sentences, and input
4326 line boundaries have no special significance outside this option. By
4327 default, when @sc{gnu} extensions are enabled and if @option{-r} option is not
4328 used, end of sentences are used. In this case, this @var{regex} is
4329 imported from @sc{gnu} Emacs:
4332 [.?!][]\"')@}]*\\($\\|\t\\| \\)[ \t\n]*
4335 Whenever @sc{gnu} extensions are disabled or if @option{-r} option is used, end
4336 of lines are used; in this case, the default @var{regexp} is just:
4342 Using an empty @var{regexp} is equivalent to completely disabling end of
4343 line or end of sentence recognition. In this case, the whole file is
4344 considered to be a single big line or sentence. The user might want to
4345 disallow all truncation flag generation as well, through option @option{-F
4346 ""}. @xref{Regexps, , Syntax of Regular Expressions, emacs, The GNU Emacs
4349 When the keywords happen to be near the beginning of the input line or
4350 sentence, this often creates an unused area at the beginning of the
4351 output context line; when the keywords happen to be near the end of the
4352 input line or sentence, this often creates an unused area at the end of
4353 the output context line. The program tries to fill those unused areas
4354 by wrapping around context in them; the tail of the input line or
4355 sentence is used to fill the unused area on the left of the output line;
4356 the head of the input line or sentence is used to fill the unused area
4357 on the right of the output line.
4359 As a matter of convenience to the user, many usual backslashed escape
4360 sequences from the C language are recognized and converted to the
4361 corresponding characters by @command{ptx} itself.
4363 @item -W @var{regexp}
4364 @itemx --word-regexp=@var{regexp}
4366 This option selects which regular expression will describe each keyword.
4367 By default, if @sc{gnu} extensions are enabled, a word is a sequence of
4368 letters; the @var{regexp} used is @samp{\w+}. When @sc{gnu} extensions are
4369 disabled, a word is by default anything which ends with a space, a tab
4370 or a newline; the @var{regexp} used is @samp{[^ \t\n]+}.
4372 An empty @var{regexp} is equivalent to not using this option.
4373 @xref{Regexps, , Syntax of Regular Expressions, emacs, The GNU Emacs
4376 As a matter of convenience to the user, many usual backslashed escape
4377 sequences, as found in the C language, are recognized and converted to
4378 the corresponding characters by @command{ptx} itself.
4383 @node Output formatting in ptx
4384 @subsection Output formatting
4386 Output format is mainly controlled by the @option{-O} and @option{-T} options
4387 described in the table below. When neither @option{-O} nor @option{-T} are
4388 selected, and if @sc{gnu} extensions are enabled, the program chooses an
4389 output format suitable for a dumb terminal. Each keyword occurrence is
4390 output to the center of one line, surrounded by its left and right
4391 contexts. Each field is properly justified, so the concordance output
4392 can be readily observed. As a special feature, if automatic
4393 references are selected by option @option{-A} and are output before the
4394 left context, that is, if option @option{-R} is @emph{not} selected, then
4395 a colon is added after the reference; this nicely interfaces with @sc{gnu}
4396 Emacs @code{next-error} processing. In this default output format, each
4397 white space character, like newline and tab, is merely changed to
4398 exactly one space, with no special attempt to compress consecutive
4399 spaces. This might change in the future. Except for those white space
4400 characters, every other character of the underlying set of 256
4401 characters is transmitted verbatim.
4403 Output format is further controlled by the following options.
4407 @item -g @var{number}
4408 @itemx --gap-size=@var{number}
4410 Select the size of the minimum white space gap between the fields on the
4413 @item -w @var{number}
4414 @itemx --width=@var{number}
4416 Select the maximum output width of each final line. If references are
4417 used, they are included or excluded from the maximum output width
4418 depending on the value of option @option{-R}. If this option is not
4419 selected, that is, when references are output before the left context,
4420 the maximum output width takes into account the maximum length of all
4421 references. If this option is selected, that is, when references are
4422 output after the right context, the maximum output width does not take
4423 into account the space taken by references, nor the gap that precedes
4427 @itemx --auto-reference
4429 Select automatic references. Each input line will have an automatic
4430 reference made up of the file name and the line ordinal, with a single
4431 colon between them. However, the file name will be empty when standard
4432 input is being read. If both @option{-A} and @option{-r} are selected, then
4433 the input reference is still read and skipped, but the automatic
4434 reference is used at output time, overriding the input reference.
4437 @itemx --right-side-refs
4439 In the default output format, when option @option{-R} is not used, any
4440 references produced by the effect of options @option{-r} or @option{-A} are
4441 placed to the far right of output lines, after the right context. With
4442 default output format, when the @option{-R} option is specified, references
4443 are rather placed at the beginning of each output line, before the left
4444 context. For any other output format, option @option{-R} is
4445 ignored, with one exception: with @option{-R} the width of references
4446 is @emph{not} taken into account in total output width given by @option{-w}.
4448 This option is automatically selected whenever @sc{gnu} extensions are
4451 @item -F @var{string}
4452 @itemx --flac-truncation=@var{string}
4454 This option will request that any truncation in the output be reported
4455 using the string @var{string}. Most output fields theoretically extend
4456 towards the beginning or the end of the current line, or current
4457 sentence, as selected with option @option{-S}. But there is a maximum
4458 allowed output line width, changeable through option @option{-w}, which is
4459 further divided into space for various output fields. When a field has
4460 to be truncated because it cannot extend beyond the beginning or the end of
4461 the current line to fit in, then a truncation occurs. By default,
4462 the string used is a single slash, as in @option{-F /}.
4464 @var{string} may have more than one character, as in @option{-F ...}.
4465 Also, in the particular case when @var{string} is empty (@option{-F ""}),
4466 truncation flagging is disabled, and no truncation marks are appended in
4469 As a matter of convenience to the user, many usual backslashed escape
4470 sequences, as found in the C language, are recognized and converted to
4471 the corresponding characters by @command{ptx} itself.
4473 @item -M @var{string}
4474 @itemx --macro-name=@var{string}
4476 Select another @var{string} to be used instead of @samp{xx}, while
4477 generating output suitable for @command{nroff}, @command{troff} or @TeX{}.
4480 @itemx --format=roff
4482 Choose an output format suitable for @command{nroff} or @command{troff}
4483 processing. Each output line will look like:
4486 .xx "@var{tail}" "@var{before}" "@var{keyword_and_after}" "@var{head}" "@var{ref}"
4489 so it will be possible to write a @samp{.xx} roff macro to take care of
4490 the output typesetting. This is the default output format when @sc{gnu}
4491 extensions are disabled. Option @option{-M} can be used to change
4492 @samp{xx} to another macro name.
4494 In this output format, each non-graphical character, like newline and
4495 tab, is merely changed to exactly one space, with no special attempt to
4496 compress consecutive spaces. Each quote character: @kbd{"} is doubled
4497 so it will be correctly processed by @command{nroff} or @command{troff}.
4502 Choose an output format suitable for @TeX{} processing. Each output
4503 line will look like:
4506 \xx @{@var{tail}@}@{@var{before}@}@{@var{keyword}@}@{@var{after}@}@{@var{head}@}@{@var{ref}@}
4510 so it will be possible to write a @code{\xx} definition to take care of
4511 the output typesetting. Note that when references are not being
4512 produced, that is, neither option @option{-A} nor option @option{-r} is
4513 selected, the last parameter of each @code{\xx} call is inhibited.
4514 Option @option{-M} can be used to change @samp{xx} to another macro
4517 In this output format, some special characters, like @kbd{$}, @kbd{%},
4518 @kbd{&}, @kbd{#} and @kbd{_} are automatically protected with a
4519 backslash. Curly brackets @kbd{@{}, @kbd{@}} are protected with a
4520 backslash and a pair of dollar signs (to force mathematical mode). The
4521 backslash itself produces the sequence @code{\backslash@{@}}.
4522 Circumflex and tilde diacritical marks produce the sequence @code{^\@{ @}} and
4523 @code{~\@{ @}} respectively. Other diacriticized characters of the
4524 underlying character set produce an appropriate @TeX{} sequence as far
4525 as possible. The other non-graphical characters, like newline and tab,
4526 and all other characters which are not part of @acronym{ASCII}, are merely
4527 changed to exactly one space, with no special attempt to compress
4528 consecutive spaces. Let me know how to improve this special character
4529 processing for @TeX{}.
4534 @node Compatibility in ptx
4535 @subsection The @sc{gnu} extensions to @command{ptx}
4537 This version of @command{ptx} contains a few features which do not exist in
4538 System V @command{ptx}. These extra features are suppressed by using the
4539 @option{-G} command line option, unless overridden by other command line
4540 options. Some @sc{gnu} extensions cannot be recovered by overriding, so the
4541 simple rule is to avoid @option{-G} if you care about @sc{gnu} extensions.
4542 Here are the differences between this program and System V @command{ptx}.
4547 This program can read many input files at once, it always writes the
4548 resulting concordance on standard output. On the other hand, System V
4549 @command{ptx} reads only one file and sends the result to standard output
4550 or, if a second @var{file} parameter is given on the command, to that
4553 Having output parameters not introduced by options is a dangerous
4554 practice which @sc{gnu} avoids as far as possible. So, for using @command{ptx}
4555 portably between @sc{gnu} and System V, you should always use it with a
4556 single input file, and always expect the result on standard output. You
4557 might also want to automatically configure in a @option{-G} option to
4558 @command{ptx} calls in products using @command{ptx}, if the configurator finds
4559 that the installed @command{ptx} accepts @option{-G}.
4562 The only options available in System V @command{ptx} are options @option{-b},
4563 @option{-f}, @option{-g}, @option{-i}, @option{-o}, @option{-r}, @option{-t} and
4564 @option{-w}. All other options are @sc{gnu} extensions and are not repeated in
4565 this enumeration. Moreover, some options have a slightly different
4566 meaning when @sc{gnu} extensions are enabled, as explained below.
4569 By default, concordance output is not formatted for @command{troff} or
4570 @command{nroff}. It is rather formatted for a dumb terminal. @command{troff}
4571 or @command{nroff} output may still be selected through option @option{-O}.
4574 Unless @option{-R} option is used, the maximum reference width is
4575 subtracted from the total output line width. With @sc{gnu} extensions
4576 disabled, width of references is not taken into account in the output
4577 line width computations.
4580 All 256 bytes, even null bytes, are always read and processed from
4581 input file with no adverse effect, even if @sc{gnu} extensions are disabled.
4582 However, System V @command{ptx} does not accept 8-bit characters, a few
4583 control characters are rejected, and the tilde @kbd{~} is also rejected.
4586 Input line length is only limited by available memory, even if @sc{gnu}
4587 extensions are disabled. However, System V @command{ptx} processes only
4588 the first 200 characters in each line.
4591 The break (non-word) characters default to be every character except all
4592 letters of the underlying character set, diacriticized or not. When @sc{gnu}
4593 extensions are disabled, the break characters default to space, tab and
4597 The program makes better use of output line width. If @sc{gnu} extensions
4598 are disabled, the program rather tries to imitate System V @command{ptx},
4599 but still, there are some slight disposition glitches this program does
4600 not completely reproduce.
4603 The user can specify both an Ignore file and an Only file. This is not
4604 allowed with System V @command{ptx}.
4609 @node Operating on fields within a line
4610 @chapter Operating on fields within a line
4613 * cut invocation:: Print selected parts of lines.
4614 * paste invocation:: Merge lines of files.
4615 * join invocation:: Join lines on a common field.
4619 @node cut invocation
4620 @section @command{cut}: Print selected parts of lines
4623 @command{cut} writes to standard output selected parts of each line of each
4624 input file, or standard input if no files are given or for a file name of
4628 cut [@var{option}]@dots{} [@var{file}]@dots{}
4631 In the table which follows, the @var{byte-list}, @var{character-list},
4632 and @var{field-list} are one or more numbers or ranges (two numbers
4633 separated by a dash) separated by commas. Bytes, characters, and
4634 fields are numbered starting at 1. Incomplete ranges may be
4635 given: @option{-@var{m}} means @samp{1-@var{m}}; @samp{@var{n}-} means
4636 @samp{@var{n}} through end of line or last field. The list elements
4637 can be repeated, can overlap, and can be specified in any order; but
4638 the selected input is written in the same order that it is read, and
4639 is written exactly once.
4641 The program accepts the following options. Also see @ref{Common
4646 @item -b @var{byte-list}
4647 @itemx --bytes=@var{byte-list}
4650 Select for printing only the bytes in positions listed in
4651 @var{byte-list}. Tabs and backspaces are treated like any other
4652 character; they take up 1 byte. If an output delimiter is specified,
4653 (see the description of @option{--output-delimiter}), then output that
4654 string between ranges of selected bytes.
4656 @item -c @var{character-list}
4657 @itemx --characters=@var{character-list}
4659 @opindex --characters
4660 Select for printing only the characters in positions listed in
4661 @var{character-list}. The same as @option{-b} for now, but
4662 internationalization will change that. Tabs and backspaces are
4663 treated like any other character; they take up 1 character. If an
4664 output delimiter is specified, (see the description of
4665 @option{--output-delimiter}), then output that string between ranges
4668 @item -f @var{field-list}
4669 @itemx --fields=@var{field-list}
4672 Select for printing only the fields listed in @var{field-list}.
4673 Fields are separated by a TAB character by default. Also print any
4674 line that contains no delimiter character, unless the
4675 @option{--only-delimited} (@option{-s}) option is specified
4677 @item -d @var{input_delim_byte}
4678 @itemx --delimiter=@var{input_delim_byte}
4680 @opindex --delimiter
4681 With @option{-f}, use the first byte of @var{input_delim_byte} as
4682 the input fields separator (default is TAB).
4686 Do not split multi-byte characters (no-op for now).
4689 @itemx --only-delimited
4691 @opindex --only-delimited
4692 For @option{-f}, do not print lines that do not contain the field separator
4693 character. Normally, any line without a field separator is printed verbatim.
4695 @item --output-delimiter=@var{output_delim_string}
4696 @opindex --output-delimiter
4697 With @option{-f}, output fields are separated by @var{output_delim_string}.
4698 The default with @option{-f} is to use the input delimiter.
4699 When using @option{-b} or @option{-c} to select ranges of byte or
4700 character offsets (as opposed to ranges of fields),
4701 output @var{output_delim_string} between non-overlapping
4702 ranges of selected bytes.
4705 @opindex --complement
4706 This option is a GNU extension.
4707 Select for printing the complement of the bytes, characters or fields
4708 selected with the @option{-b}, @option{-c} or @option{-f} options.
4709 In other words, do @emph{not} print the bytes, characters or fields
4710 specified via those options. This option is useful when you have
4711 many fields and want to print all but a few of them.
4718 @node paste invocation
4719 @section @command{paste}: Merge lines of files
4722 @cindex merging files
4724 @command{paste} writes to standard output lines consisting of sequentially
4725 corresponding lines of each given file, separated by a TAB character.
4726 Standard input is used for a file name of @samp{-} or if no input files
4748 paste [@var{option}]@dots{} [@var{file}]@dots{}
4751 The program accepts the following options. Also see @ref{Common options}.
4759 Paste the lines of one file at a time rather than one line from each
4760 file. Using the above example data:
4763 $ paste -s num2 let3
4768 @item -d @var{delim-list}
4769 @itemx --delimiters=@var{delim-list}
4771 @opindex --delimiters
4772 Consecutively use the characters in @var{delim-list} instead of
4773 TAB to separate merged lines. When @var{delim-list} is
4774 exhausted, start again at its beginning. Using the above example data:
4777 $ paste -d '%_' num2 let3 num2
4788 @node join invocation
4789 @section @command{join}: Join lines on a common field
4792 @cindex common field, joining on
4794 @command{join} writes to standard output a line for each pair of input
4795 lines that have identical join fields. Synopsis:
4798 join [@var{option}]@dots{} @var{file1} @var{file2}
4801 Either @var{file1} or @var{file2} (but not both) can be @samp{-},
4802 meaning standard input. @var{file1} and @var{file2} should be
4803 sorted on the join fields.
4806 Normally, the sort order is that of the
4807 collating sequence specified by the @env{LC_COLLATE} locale. Unless
4808 the @option{-t} option is given, the sort comparison ignores blanks at
4809 the start of the join field, as in @code{sort -b}. If the
4810 @option{--ignore-case} option is given, the sort comparison ignores
4811 the case of characters in the join field, as in @code{sort -f}.
4813 The @command{sort} and @command{join} commands should use consistent
4814 locales and options if the output of @command{sort} is fed to
4815 @command{join}. You can use a command like @samp{sort -k 1b,1} to
4816 sort a file on its default join field, but if you select a non-default
4817 locale, join field, separator, or comparison options, then you should
4818 do so consistently between @command{join} and @command{sort}.
4820 As a GNU extension, if the input has no unpairable lines the
4821 sort order can be any order that considers two fields to be equal if and
4822 only if the sort comparison described above considers them to be equal.
4842 @item the join field is the first field in each line;
4843 @item fields in the input are separated by one or more blanks, with leading
4844 blanks on the line ignored;
4845 @item fields in the output are separated by a space;
4846 @item each output line consists of the join field, the remaining
4847 fields from @var{file1}, then the remaining fields from @var{file2}.
4850 The program accepts the following options. Also see @ref{Common options}.
4854 @item -a @var{file-number}
4856 Print a line for each unpairable line in file @var{file-number} (either
4857 @samp{1} or @samp{2}), in addition to the normal output.
4859 @item -e @var{string}
4861 Replace those output fields that are missing in the input with
4865 @itemx --ignore-case
4867 @opindex --ignore-case
4868 Ignore differences in case when comparing keys.
4869 With this option, the lines of the input files must be ordered in the same way.
4870 Use @samp{sort -f} to produce this ordering.
4872 @item -1 @var{field}
4874 Join on field @var{field} (a positive integer) of file 1.
4876 @item -2 @var{field}
4878 Join on field @var{field} (a positive integer) of file 2.
4880 @item -j @var{field}
4881 Equivalent to @option{-1 @var{field} -2 @var{field}}.
4883 @item -o @var{field-list}
4884 Construct each output line according to the format in @var{field-list}.
4885 Each element in @var{field-list} is either the single character @samp{0} or
4886 has the form @var{m.n} where the file number, @var{m}, is @samp{1} or
4887 @samp{2} and @var{n} is a positive field number.
4889 A field specification of @samp{0} denotes the join field.
4890 In most cases, the functionality of the @samp{0} field spec
4891 may be reproduced using the explicit @var{m.n} that corresponds
4892 to the join field. However, when printing unpairable lines
4893 (using either of the @option{-a} or @option{-v} options), there is no way
4894 to specify the join field using @var{m.n} in @var{field-list}
4895 if there are unpairable lines in both files.
4896 To give @command{join} that functionality, @acronym{POSIX} invented the @samp{0}
4897 field specification notation.
4899 The elements in @var{field-list}
4900 are separated by commas or blanks.
4901 Blank separators typically need to be quoted for the shell. For
4902 example, the commands @samp{join -o 1.2,2.2} and @samp{join -o '1.2
4903 2.2'} are equivalent.
4905 All output lines---including those printed because of any -a or -v
4906 option---are subject to the specified @var{field-list}.
4909 Use character @var{char} as the input and output field separator.
4910 Treat as significant each occurrence of @var{char} in the input file.
4911 Use @samp{sort -t @var{char}}, without the @option{-b} option of
4912 @samp{sort}, to produce this ordering.
4914 @item -v @var{file-number}
4915 Print a line for each unpairable line in file @var{file-number}
4916 (either @samp{1} or @samp{2}), instead of the normal output.
4923 @node Operating on characters
4924 @chapter Operating on characters
4926 @cindex operating on characters
4928 This commands operate on individual characters.
4931 * tr invocation:: Translate, squeeze, and/or delete characters.
4932 * expand invocation:: Convert tabs to spaces.
4933 * unexpand invocation:: Convert spaces to tabs.
4938 @section @command{tr}: Translate, squeeze, and/or delete characters
4945 tr [@var{option}]@dots{} @var{set1} [@var{set2}]
4948 @command{tr} copies standard input to standard output, performing
4949 one of the following operations:
4953 translate, and optionally squeeze repeated characters in the result,
4955 squeeze repeated characters,
4959 delete characters, then squeeze repeated characters from the result.
4962 The @var{set1} and (if given) @var{set2} arguments define ordered
4963 sets of characters, referred to below as @var{set1} and @var{set2}. These
4964 sets are the characters of the input that @command{tr} operates on.
4965 The @option{--complement} (@option{-c}, @option{-C}) option replaces
4967 complement (all of the characters that are not in @var{set1}).
4969 Currently @command{tr} fully supports only single-byte characters.
4970 Eventually it will support multibyte characters; when it does, the
4971 @option{-C} option will cause it to complement the set of characters,
4972 whereas @option{-c} will cause it to complement the set of values.
4973 This distinction will matter only when some values are not characters,
4974 and this is possible only in locales using multibyte encodings when
4975 the input contains encoding errors.
4977 The program accepts the @option{--help} and @option{--version}
4978 options. @xref{Common options}. Options must precede operands.
4983 * Character sets:: Specifying sets of characters.
4984 * Translating:: Changing one set of characters to another.
4985 * Squeezing:: Squeezing repeats and deleting.
4989 @node Character sets
4990 @subsection Specifying sets of characters
4992 @cindex specifying sets of characters
4994 The format of the @var{set1} and @var{set2} arguments resembles
4995 the format of regular expressions; however, they are not regular
4996 expressions, only lists of characters. Most characters simply
4997 represent themselves in these strings, but the strings can contain
4998 the shorthands listed below, for convenience. Some of them can be
4999 used only in @var{set1} or @var{set2}, as noted below.
5003 @item Backslash escapes
5004 @cindex backslash escapes
5006 The following backslash escape sequences are recognized:
5024 The character with the value given by @var{ooo}, which is 1 to 3
5030 While a backslash followed by a character not listed above is
5031 interpreted as that character, the backslash also effectively
5032 removes any special significance, so it is useful to escape
5033 @samp{[}, @samp{]}, @samp{*}, and @samp{-}.
5038 The notation @samp{@var{m}-@var{n}} expands to all of the characters
5039 from @var{m} through @var{n}, in ascending order. @var{m} should
5040 collate before @var{n}; if it doesn't, an error results. As an example,
5041 @samp{0-9} is the same as @samp{0123456789}.
5043 @sc{gnu} @command{tr} does not support the System V syntax that uses square
5044 brackets to enclose ranges. Translations specified in that format
5045 sometimes work as expected, since the brackets are often transliterated
5046 to themselves. However, they should be avoided because they sometimes
5047 behave unexpectedly. For example, @samp{tr -d '[0-9]'} deletes brackets
5050 Many historically common and even accepted uses of ranges are not
5051 portable. For example, on @acronym{EBCDIC} hosts using the @samp{A-Z}
5052 range will not do what most would expect because @samp{A} through @samp{Z}
5053 are not contiguous as they are in @acronym{ASCII}.
5054 If you can rely on a @acronym{POSIX} compliant version of @command{tr}, then
5055 the best way to work around this is to use character classes (see below).
5056 Otherwise, it is most portable (and most ugly) to enumerate the members
5059 @item Repeated characters
5060 @cindex repeated characters
5062 The notation @samp{[@var{c}*@var{n}]} in @var{set2} expands to @var{n}
5063 copies of character @var{c}. Thus, @samp{[y*6]} is the same as
5064 @samp{yyyyyy}. The notation @samp{[@var{c}*]} in @var{string2} expands
5065 to as many copies of @var{c} as are needed to make @var{set2} as long as
5066 @var{set1}. If @var{n} begins with @samp{0}, it is interpreted in
5067 octal, otherwise in decimal.
5069 @item Character classes
5070 @cindex character classes
5072 The notation @samp{[:@var{class}:]} expands to all of the characters in
5073 the (predefined) class @var{class}. The characters expand in no
5074 particular order, except for the @code{upper} and @code{lower} classes,
5075 which expand in ascending order. When the @option{--delete} (@option{-d})
5076 and @option{--squeeze-repeats} (@option{-s}) options are both given, any
5077 character class can be used in @var{set2}. Otherwise, only the
5078 character classes @code{lower} and @code{upper} are accepted in
5079 @var{set2}, and then only if the corresponding character class
5080 (@code{upper} and @code{lower}, respectively) is specified in the same
5081 relative position in @var{set1}. Doing this specifies case conversion.
5082 The class names are given below; an error results when an invalid class
5094 Horizontal whitespace.
5103 Printable characters, not including space.
5109 Printable characters, including space.
5112 Punctuation characters.
5115 Horizontal or vertical whitespace.
5124 @item Equivalence classes
5125 @cindex equivalence classes
5127 The syntax @samp{[=@var{c}=]} expands to all of the characters that are
5128 equivalent to @var{c}, in no particular order. Equivalence classes are
5129 a relatively recent invention intended to support non-English alphabets.
5130 But there seems to be no standard way to define them or determine their
5131 contents. Therefore, they are not fully implemented in @sc{gnu} @command{tr};
5132 each character's equivalence class consists only of that character,
5133 which is of no particular use.
5139 @subsection Translating
5141 @cindex translating characters
5143 @command{tr} performs translation when @var{set1} and @var{set2} are
5144 both given and the @option{--delete} (@option{-d}) option is not given.
5145 @command{tr} translates each character of its input that is in @var{set1}
5146 to the corresponding character in @var{set2}. Characters not in
5147 @var{set1} are passed through unchanged. When a character appears more
5148 than once in @var{set1} and the corresponding characters in @var{set2}
5149 are not all the same, only the final one is used. For example, these
5150 two commands are equivalent:
5157 A common use of @command{tr} is to convert lowercase characters to
5158 uppercase. This can be done in many ways. Here are three of them:
5161 tr abcdefghijklmnopqrstuvwxyz ABCDEFGHIJKLMNOPQRSTUVWXYZ
5163 tr '[:lower:]' '[:upper:]'
5167 But note that using ranges like @code{a-z} above is not portable.
5169 When @command{tr} is performing translation, @var{set1} and @var{set2}
5170 typically have the same length. If @var{set1} is shorter than
5171 @var{set2}, the extra characters at the end of @var{set2} are ignored.
5173 On the other hand, making @var{set1} longer than @var{set2} is not
5174 portable; @acronym{POSIX} says that the result is undefined. In this situation,
5175 BSD @command{tr} pads @var{set2} to the length of @var{set1} by repeating
5176 the last character of @var{set2} as many times as necessary. System V
5177 @command{tr} truncates @var{set1} to the length of @var{set2}.
5179 By default, @sc{gnu} @command{tr} handles this case like BSD @command{tr}.
5180 When the @option{--truncate-set1} (@option{-t}) option is given,
5181 @sc{gnu} @command{tr} handles this case like the System V @command{tr}
5182 instead. This option is ignored for operations other than translation.
5184 Acting like System V @command{tr} in this case breaks the relatively common
5188 tr -cs A-Za-z0-9 '\012'
5192 because it converts only zero bytes (the first element in the
5193 complement of @var{set1}), rather than all non-alphanumerics, to
5197 By the way, the above idiom is not portable because it uses ranges, and
5198 it assumes that the octal code for newline is 012.
5199 Assuming a @acronym{POSIX} compliant @command{tr}, here is a better way to write it:
5202 tr -cs '[:alnum:]' '[\n*]'
5207 @subsection Squeezing repeats and deleting
5209 @cindex squeezing repeat characters
5210 @cindex deleting characters
5212 When given just the @option{--delete} (@option{-d}) option, @command{tr}
5213 removes any input characters that are in @var{set1}.
5215 When given just the @option{--squeeze-repeats} (@option{-s}) option,
5216 @command{tr} replaces each input sequence of a repeated character that
5217 is in @var{set1} with a single occurrence of that character.
5219 When given both @option{--delete} and @option{--squeeze-repeats}, @command{tr}
5220 first performs any deletions using @var{set1}, then squeezes repeats
5221 from any remaining characters using @var{set2}.
5223 The @option{--squeeze-repeats} option may also be used when translating,
5224 in which case @command{tr} first performs translation, then squeezes
5225 repeats from any remaining characters using @var{set2}.
5227 Here are some examples to illustrate various combinations of options:
5232 Remove all zero bytes:
5239 Put all words on lines by themselves. This converts all
5240 non-alphanumeric characters to newlines, then squeezes each string
5241 of repeated newlines into a single newline:
5244 tr -cs '[:alnum:]' '[\n*]'
5248 Convert each sequence of repeated newlines to a single newline:
5255 Find doubled occurrences of words in a document.
5256 For example, people often write ``the the'' with the repeated words
5257 separated by a newline. The Bourne shell script below works first
5258 by converting each sequence of punctuation and blank characters to a
5259 single newline. That puts each ``word'' on a line by itself.
5260 Next it maps all uppercase characters to lower case, and finally it
5261 runs @command{uniq} with the @option{-d} option to print out only the words
5267 | tr -s '[:punct:][:blank:]' '[\n*]' \
5268 | tr '[:upper:]' '[:lower:]' \
5273 Deleting a small set of characters is usually straightforward. For example,
5274 to remove all @samp{a}s, @samp{x}s, and @samp{M}s you would do this:
5280 However, when @samp{-} is one of those characters, it can be tricky because
5281 @samp{-} has special meanings. Performing the same task as above but also
5282 removing all @samp{-} characters, we might try @code{tr -d -axM}, but
5283 that would fail because @command{tr} would try to interpret @option{-a} as
5284 a command-line option. Alternatively, we could try putting the hyphen
5285 inside the string, @code{tr -d a-xM}, but that wouldn't work either because
5286 it would make @command{tr} interpret @code{a-x} as the range of characters
5287 @samp{a}@dots{}@samp{x} rather than the three.
5288 One way to solve the problem is to put the hyphen at the end of the list
5295 Or you can use @samp{--} to terminate option processing:
5301 More generally, use the character class notation @code{[=c=]}
5302 with @samp{-} (or any other character) in place of the @samp{c}:
5308 Note how single quotes are used in the above example to protect the
5309 square brackets from interpretation by a shell.
5314 @node expand invocation
5315 @section @command{expand}: Convert tabs to spaces
5318 @cindex tabs to spaces, converting
5319 @cindex converting tabs to spaces
5321 @command{expand} writes the contents of each given @var{file}, or standard
5322 input if none are given or for a @var{file} of @samp{-}, to standard
5323 output, with tab characters converted to the appropriate number of
5327 expand [@var{option}]@dots{} [@var{file}]@dots{}
5330 By default, @command{expand} converts all tabs to spaces. It preserves
5331 backspace characters in the output; they decrement the column count for
5332 tab calculations. The default action is equivalent to @option{-t 8} (set
5333 tabs every 8 columns).
5335 The program accepts the following options. Also see @ref{Common options}.
5339 @item -t @var{tab1}[,@var{tab2}]@dots{}
5340 @itemx --tabs=@var{tab1}[,@var{tab2}]@dots{}
5343 @cindex tab stops, setting
5344 If only one tab stop is given, set the tabs @var{tab1} spaces apart
5345 (default is 8). Otherwise, set the tabs at columns @var{tab1},
5346 @var{tab2}, @dots{} (numbered from 0), and replace any tabs beyond the
5347 last tab stop given with single spaces. Tab stops can be separated by
5348 blanks as well as by commas.
5350 For compatibility, GNU @command{expand} also accepts the obsolete
5351 option syntax, @option{-@var{t1}[,@var{t2}]@dots{}}. New scripts
5352 should use @option{-t @var{t1}[,@var{t2}]@dots{}} instead.
5358 @cindex initial tabs, converting
5359 Only convert initial tabs (those that precede all non-space or non-tab
5360 characters) on each line to spaces.
5367 @node unexpand invocation
5368 @section @command{unexpand}: Convert spaces to tabs
5372 @command{unexpand} writes the contents of each given @var{file}, or
5373 standard input if none are given or for a @var{file} of @samp{-}, to
5374 standard output, converting blanks at the beginning of each line into
5375 as many tab characters as needed. In the default @acronym{POSIX}
5376 locale, a @dfn{blank} is a space or a tab; other locales may specify
5377 additional blank characters. Synopsis:
5380 unexpand [@var{option}]@dots{} [@var{file}]@dots{}
5383 By default, @command{unexpand} converts only initial blanks (those
5384 that precede all non-blank characters) on each line. It
5385 preserves backspace characters in the output; they decrement the column
5386 count for tab calculations. By default, tabs are set at every 8th
5389 The program accepts the following options. Also see @ref{Common options}.
5393 @item -t @var{tab1}[,@var{tab2}]@dots{}
5394 @itemx --tabs=@var{tab1}[,@var{tab2}]@dots{}
5397 If only one tab stop is given, set the tabs @var{tab1} columns apart
5398 instead of the default 8. Otherwise, set the tabs at columns
5399 @var{tab1}, @var{tab2}, @dots{} (numbered from 0), and leave blanks
5400 beyond the tab stops given unchanged. Tab stops can be separated by
5401 blanks as well as by commas. This option implies the @option{-a} option.
5403 For compatibility, GNU @command{unexpand} supports the obsolete option syntax,
5404 @option{-@var{tab1}[,@var{tab2}]@dots{}}, where tab stops must be
5405 separated by commas. (Unlike @option{-t}, this obsolete option does
5406 not imply @option{-a}.) New scripts should use @option{--first-only -t
5407 @var{tab1}[,@var{tab2}]@dots{}} instead.
5413 Also convert all sequences of two or more blanks just before a tab stop.
5414 even if they occur after non-blank characters in a line.
5421 @node Directory listing
5422 @chapter Directory listing
5424 This chapter describes the @command{ls} command and its variants @command{dir}
5425 and @command{vdir}, which list information about files.
5428 * ls invocation:: List directory contents.
5429 * dir invocation:: Briefly ls.
5430 * vdir invocation:: Verbosely ls.
5431 * dircolors invocation:: Color setup for ls, etc.
5436 @section @command{ls}: List directory contents
5439 @cindex directory listing
5441 The @command{ls} program lists information about files (of any type,
5442 including directories). Options and file arguments can be intermixed
5443 arbitrarily, as usual.
5445 For non-option command-line arguments that are directories, by default
5446 @command{ls} lists the contents of directories, not recursively, and
5447 omitting files with names beginning with @samp{.}. For other non-option
5448 arguments, by default @command{ls} lists just the file name. If no
5449 non-option argument is specified, @command{ls} operates on the current
5450 directory, acting as if it had been invoked with a single argument of @samp{.}.
5453 By default, the output is sorted alphabetically, according to the locale
5454 settings in effect.@footnote{If you use a non-@acronym{POSIX}
5455 locale (e.g., by setting @env{LC_ALL} to @samp{en_US}), then @command{ls} may
5456 produce output that is sorted differently than you're accustomed to.
5457 In that case, set the @env{LC_ALL} environment variable to @samp{C}.}
5458 If standard output is
5459 a terminal, the output is in columns (sorted vertically) and control
5460 characters are output as question marks; otherwise, the output is listed
5461 one per line and control characters are output as-is.
5463 Because @command{ls} is such a fundamental program, it has accumulated many
5464 options over the years. They are described in the subsections below;
5465 within each section, options are listed alphabetically (ignoring case).
5466 The division of options into the subsections is not absolute, since some
5467 options affect more than one aspect of @command{ls}'s operation.
5469 @cindex exit status of @command{ls}
5474 1 minor problems (e.g., a subdirectory was not found)
5475 2 serious trouble (e.g., memory exhausted)
5478 Also see @ref{Common options}.
5481 * Which files are listed::
5482 * What information is listed::
5483 * Sorting the output::
5484 * More details about version sort::
5485 * General output formatting::
5486 * Formatting file timestamps::
5487 * Formatting the file names::
5491 @node Which files are listed
5492 @subsection Which files are listed
5494 These options determine which files @command{ls} lists information for.
5495 By default, @command{ls} lists files and the contents of any
5496 directories on the command line, except that in directories it ignores
5497 files whose names start with @samp{.}.
5505 In directories, do not ignore file names that start with @samp{.}.
5510 @opindex --almost-all
5511 In directories, do not ignore all file names that start with @samp{.};
5512 ignore only @file{.} and @file{..}. The @option{--all} (@option{-a})
5513 option overrides this option.
5516 @itemx --ignore-backups
5518 @opindex --ignore-backups
5519 @cindex backup files, ignoring
5520 In directories, ignore files that end with @samp{~}. This option is
5521 equivalent to @samp{--ignore='*~' --ignore='.*~'}.
5526 @opindex --directory
5527 List just the names of directories, as with other types of files, rather
5528 than listing their contents.
5529 @c The following sentence is the same as the one for -F.
5530 Do not follow symbolic links listed on the
5531 command line unless the @option{--dereference-command-line} (@option{-H}),
5532 @option{--dereference} (@option{-L}), or
5533 @option{--dereference-command-line-symlink-to-dir} options are specified.
5536 @itemx --dereference-command-line
5538 @opindex --dereference-command-line
5539 @cindex symbolic links, dereferencing
5540 If a command line argument specifies a symbolic link, show information
5541 for the file the link references rather than for the link itself.
5543 @itemx --dereference-command-line-symlink-to-dir
5544 @opindex --dereference-command-line-symlink-to-dir
5545 @cindex symbolic links, dereferencing
5546 Do not dereference symbolic links, with one exception:
5547 if a command line argument specifies a symbolic link that refers to
5548 a directory, show information for that directory rather than for the
5550 This is the default behavior when no other dereferencing-related
5551 option has been specified (@option{--classify} (@option{-F}),
5552 @option{--directory} (@option{-d}),
5554 @option{--dereference} (@option{-L}), or
5555 @option{--dereference-command-line} (@option{-H})).
5557 @item --hide=PATTERN
5558 @opindex --hide=@var{pattern}
5559 In directories, ignore files whose names match the shell pattern
5560 @var{pattern}, unless the @option{--all} (@option{-a}) or
5561 @option{--almost-all} (@option{-A}) is also given. This
5562 option acts like @option{--ignore=@var{pattern}} except that it has no
5563 effect if @option{--all} (@option{-a}) or @option{--almost-all}
5564 (@option{-A}) is also given.
5566 This option can be useful in shell aliases. For example, if
5567 @command{lx} is an alias for @samp{ls --hide='*~'} and @command{ly} is
5568 an alias for @samp{ls --ignore='*~'}, then the command @samp{lx -A}
5569 lists the file @file{README~} even though @samp{ly -A} would not.
5571 @item -I @var{pattern}
5572 @itemx --ignore=@var{pattern}
5574 @opindex --ignore=@var{pattern}
5575 In directories, ignore files whose names match the shell pattern
5576 (not regular expression) @var{pattern}. As
5577 in the shell, an initial @samp{.} in a file name does not match a
5578 wildcard at the start of @var{pattern}. Sometimes it is useful
5579 to give this option several times. For example,
5582 $ ls --ignore='.??*' --ignore='.[^.]' --ignore='#*'
5585 The first option ignores names of length 3 or more that start with @samp{.},
5586 the second ignores all two-character names that start with @samp{.}
5587 except @samp{..}, and the third ignores names that start with @samp{#}.
5590 @itemx --dereference
5592 @opindex --dereference
5593 @cindex symbolic links, dereferencing
5594 When showing file information for a symbolic link, show information
5595 for the file the link references rather than the link itself.
5596 However, even with this option, @command{ls} still prints the name
5597 of the link itself, not the name of the file that the link points to.
5602 @opindex --recursive
5603 @cindex recursive directory listing
5604 @cindex directory listing, recursive
5605 List the contents of all directories recursively.
5610 @node What information is listed
5611 @subsection What information is listed
5613 These options affect the information that @command{ls} displays. By
5614 default, only file names are shown.
5620 @cindex hurd, author, printing
5621 List each file's author when producing long format directory listings.
5622 In GNU/Hurd, file authors can differ from their owners, but in other
5623 operating systems the two are the same.
5629 @cindex dired Emacs mode support
5630 With the long listing (@option{-l}) format, print an additional line after
5634 //DIRED// @var{beg1} @var{end1} @var{beg2} @var{end2} @dots{}
5638 The @var{begN} and @var{endN} are unsigned integers that record the
5639 byte position of the beginning and end of each file name in the output.
5640 This makes it easy for Emacs to find the names, even when they contain
5641 unusual characters such as space or newline, without fancy searching.
5643 If directories are being listed recursively (@option{-R}), output a similar
5644 line with offsets for each subdirectory name:
5647 //SUBDIRED// @var{beg1} @var{end1} @dots{}
5650 Finally, output a line of the form:
5653 //DIRED-OPTIONS// --quoting-style=@var{word}
5657 where @var{word} is the quoting style (@pxref{Formatting the file names}).
5659 Here is an actual example:
5662 $ mkdir -p a/sub/deeper a/sub2
5664 $ touch a/sub/deeper/file
5665 $ ls -gloRF --dired a
5668 -rw-r--r-- 1 0 Jun 10 12:27 f1
5669 -rw-r--r-- 1 0 Jun 10 12:27 f2
5670 drwxr-xr-x 3 4096 Jun 10 12:27 sub/
5671 drwxr-xr-x 2 4096 Jun 10 12:27 sub2/
5675 drwxr-xr-x 2 4096 Jun 10 12:27 deeper/
5679 -rw-r--r-- 1 0 Jun 10 12:27 file
5683 //DIRED// 48 50 84 86 120 123 158 162 217 223 282 286
5684 //SUBDIRED// 2 3 167 172 228 240 290 296
5685 //DIRED-OPTIONS// --quoting-style=literal
5688 Note that the pairs of offsets on the @samp{//DIRED//} line above delimit
5689 these names: @file{f1}, @file{f2}, @file{sub}, @file{sub2}, @file{deeper},
5691 The offsets on the @samp{//SUBDIRED//} line delimit the following
5692 directory names: @file{a}, @file{a/sub}, @file{a/sub/deeper}, @file{a/sub2}.
5694 Here is an example of how to extract the fifth entry name, @samp{deeper},
5695 corresponding to the pair of offsets, 222 and 228:
5698 $ ls -gloRF --dired a > out
5699 $ dd bs=1 skip=222 count=6 < out 2>/dev/null; echo
5703 Note that although the listing above includes a trailing slash
5704 for the @samp{deeper} entry, the offsets select the name without
5705 the trailing slash. However, if you invoke @command{ls} with @option{--dired}
5706 along with an option like @option{--escape} (aka @option{-b}) and operate
5707 on a file whose name contains special characters, notice that the backslash
5712 $ ls -blog --dired 'a b'
5713 -rw-r--r-- 1 0 Jun 10 12:28 a\ b
5715 //DIRED-OPTIONS// --quoting-style=escape
5718 If you use a quoting style that adds quote marks
5719 (e.g., @option{--quoting-style=c}), then the offsets include the quote marks.
5720 So beware that the user may select the quoting style via the environment
5721 variable @env{QUOTING_STYLE}. Hence, applications using @option{--dired}
5722 should either specify an explicit @option{--quoting-style=literal} option
5723 (aka @option{-N} or @option{--literal}) on the command line, or else be
5724 prepared to parse the escaped names.
5727 @opindex --full-time
5728 Produce long format directory listings, and list times in full. It is
5729 equivalent to using @option{--format=long} with
5730 @option{--time-style=full-iso} (@pxref{Formatting file timestamps}).
5734 Produce long format directory listings, but don't display owner information.
5740 Inhibit display of group information in a long format directory listing.
5741 (This is the default in some non-@sc{gnu} versions of @command{ls}, so we
5742 provide this option for compatibility.)
5750 @cindex inode number, printing
5751 Print the inode number (also called the file serial number and index
5752 number) of each file to the left of the file name. (This number
5753 uniquely identifies each file within a particular file system.)
5756 @itemx --format=long
5757 @itemx --format=verbose
5760 @opindex long ls @r{format}
5761 @opindex verbose ls @r{format}
5762 In addition to the name of each file, print the file type, file mode bits,
5763 number of hard links, owner name, group name, size, and
5764 timestamp (@pxref{Formatting file timestamps}), normally
5765 the modification time.
5767 Normally the size is printed as a byte count without punctuation, but
5768 this can be overridden (@pxref{Block size}). For example, @option{-h}
5769 prints an abbreviated, human-readable count, and
5770 @samp{--block-size="'1"} prints a byte count with the thousands
5771 separator of the current locale.
5773 For each directory that is listed, preface the files with a line
5774 @samp{total @var{blocks}}, where @var{blocks} is the total disk allocation
5775 for all files in that directory. The block size currently defaults to 1024
5776 bytes, but this can be overridden (@pxref{Block size}).
5777 The @var{blocks} computed counts each hard link separately;
5778 this is arguably a deficiency.
5780 @cindex permissions, output by @command{ls}
5781 The file mode bits listed are similar to symbolic mode specifications
5782 (@pxref{Symbolic Modes}). But @command{ls} combines multiple bits into the
5783 third character of each set of permissions as follows:
5786 If the setuid or setgid bit and the corresponding executable bit
5790 If the setuid or setgid bit is set but the corresponding executable bit
5794 If the sticky bit and the other-executable bit are both set.
5797 If the sticky bit is set but the other-executable bit is not set.
5800 If the executable bit is set and none of the above apply.
5806 Following the file mode bits is a single character that specifies
5807 whether an alternate access method such as an access control list
5808 applies to the file. When the character following the file mode bits is a
5809 space, there is no alternate access method. When it is a printing
5810 character, then there is such a method.
5812 For a file with an extended access control list, a @samp{+} character is
5813 listed. Basic access control lists are equivalent to the permissions
5814 listed, and are not considered an alternate access method.
5817 @itemx --numeric-uid-gid
5819 @opindex --numeric-uid-gid
5820 @cindex numeric uid and gid
5821 @cindex numeric user and group IDs
5822 Produce long format directory listings, but
5823 display numeric user and group IDs instead of the owner and group names.
5827 Produce long format directory listings, but don't display group information.
5828 It is equivalent to using @option{--format=long} with @option{--no-group} .
5834 @cindex disk allocation
5835 @cindex size of files, reporting
5836 Print the disk allocation of each file to the left of the file name.
5837 This is the amount of disk space used by the file, which is usually a
5838 bit more than the file's size, but it can be less if the file has holes.
5840 Normally the disk allocation is printed in units of
5841 1024 bytes, but this can be overridden (@pxref{Block size}).
5843 @cindex NFS mounts from BSD to HP-UX
5844 For files that are NFS-mounted from an HP-UX system to a BSD system,
5845 this option reports sizes that are half the correct values. On HP-UX
5846 systems, it reports sizes that are twice the correct values for files
5847 that are NFS-mounted from BSD systems. This is due to a flaw in HP-UX;
5848 it also affects the HP-UX @command{ls} program.
5855 @node Sorting the output
5856 @subsection Sorting the output
5858 @cindex sorting @command{ls} output
5859 These options change the order in which @command{ls} sorts the information
5860 it outputs. By default, sorting is done by character code
5861 (e.g., @acronym{ASCII} order).
5867 @itemx --time=status
5870 @opindex ctime@r{, printing or sorting by}
5871 @opindex status time@r{, printing or sorting by}
5872 @opindex use time@r{, printing or sorting files by}
5873 If the long listing format (e.g., @option{-l}, @option{-o}) is being used,
5874 print the status change time (the @samp{ctime} in the inode) instead of
5875 the modification time.
5876 When explicitly sorting by time (@option{--sort=time} or @option{-t})
5877 or when not using a long listing format,
5878 sort according to the status change time.
5882 @cindex unsorted directory listing
5883 @cindex directory order, listing by
5884 Primarily, like @option{-U}---do not sort; list the files in whatever
5885 order they are stored in the directory. But also enable @option{-a} (list
5886 all files) and disable @option{-l}, @option{--color}, and @option{-s} (if they
5887 were specified before the @option{-f}).
5893 @cindex reverse sorting
5894 Reverse whatever the sorting method is---e.g., list files in reverse
5895 alphabetical order, youngest first, smallest first, or whatever.
5901 @opindex size of files@r{, sorting files by}
5902 Sort by file size, largest first.
5908 @opindex modification time@r{, sorting files by}
5909 Sort by modification time (the @samp{mtime} in the inode), newest first.
5913 @itemx --time=access
5917 @opindex use time@r{, printing or sorting files by}
5918 @opindex atime@r{, printing or sorting files by}
5919 @opindex access time@r{, printing or sorting files by}
5920 If the long listing format (e.g., @option{--format=long}) is being used,
5921 print the last access time (the @samp{atime} in the inode).
5922 When explicitly sorting by time (@option{--sort=time} or @option{-t})
5923 or when not using a long listing format, sort according to the access time.
5929 @opindex none@r{, sorting option for @command{ls}}
5930 Do not sort; list the files in whatever order they are
5931 stored in the directory. (Do not do any of the other unrelated things
5932 that @option{-f} does.) This is especially useful when listing very large
5933 directories, since not doing any sorting can be noticeably faster.
5936 @itemx --sort=version
5939 @opindex version@r{, sorting option for @command{ls}}
5940 Sort by version name and number, lowest first. It behaves like a default
5941 sort, except that each sequence of decimal digits is treated numerically
5942 as an index/version number. (@xref{More details about version sort}.)
5945 @itemx --sort=extension
5948 @opindex extension@r{, sorting files by}
5949 Sort directory contents alphabetically by file extension (characters
5950 after the last @samp{.}); files with no extension are sorted first.
5955 @node More details about version sort
5956 @subsection More details about version sort
5958 The version sort takes into account the fact that file names frequently include
5959 indices or version numbers. Standard sorting functions usually do not produce
5960 the ordering that people expect because comparisons are made on a
5961 character-by-character basis. The version
5962 sort addresses this problem, and is especially useful when browsing
5963 directories that contain many files with indices/version numbers in their
5968 foo.zml-1.gz foo.zml-1.gz
5969 foo.zml-100.gz foo.zml-2.gz
5970 foo.zml-12.gz foo.zml-6.gz
5971 foo.zml-13.gz foo.zml-12.gz
5972 foo.zml-2.gz foo.zml-13.gz
5973 foo.zml-25.gz foo.zml-25.gz
5974 foo.zml-6.gz foo.zml-100.gz
5977 Note also that numeric parts with leading zeroes are considered as
5982 abc-1.007.tgz abc-1.007.tgz
5983 abc-1.012b.tgz abc-1.01a.tgz
5984 abc-1.01a.tgz abc-1.012b.tgz
5987 This functionality is implemented using the @code{strverscmp} function.
5988 @xref{String/Array Comparison, , , libc, The GNU C Library Reference Manual}.
5989 One result of that implementation decision is that @code{ls -v} does not
5990 use the locale category, @env{LC_COLLATE}. As a result, non-numeric prefixes
5991 are sorted as if @env{LC_COLLATE} were set to @code{C}.
5993 @node General output formatting
5994 @subsection General output formatting
5996 These options affect the appearance of the overall output.
6001 @itemx --format=single-column
6004 @opindex single-column @r{output of files}
6005 List one file per line. This is the default for @command{ls} when standard
6006 output is not a terminal.
6009 @itemx --format=vertical
6012 @opindex vertical @r{sorted files in columns}
6013 List files in columns, sorted vertically. This is the default for
6014 @command{ls} if standard output is a terminal. It is always the default
6015 for the @command{dir} program.
6016 @sc{gnu} @command{ls} uses variable width columns to display as many files as
6017 possible in the fewest lines.
6019 @item --color [=@var{when}]
6021 @cindex color, distinguishing file types with
6022 Specify whether to use color for distinguishing file types. @var{when}
6023 may be omitted, or one of:
6026 @vindex none @r{color option}
6027 - Do not use color at all. This is the default.
6029 @vindex auto @r{color option}
6030 @cindex terminal, using color iff
6031 - Only use color if standard output is a terminal.
6033 @vindex always @r{color option}
6036 Specifying @option{--color} and no @var{when} is equivalent to
6037 @option{--color=always}.
6038 Piping a colorized listing through a pager like @command{more} or
6039 @command{less} usually produces unreadable results. However, using
6040 @code{more -f} does seem to work.
6044 @itemx --indicator-style=classify
6047 @opindex --indicator-style
6048 @cindex file type and executables, marking
6049 @cindex executables and file type, marking
6050 Append a character to each file name indicating the file type. Also,
6051 for regular files that are executable, append @samp{*}. The file type
6052 indicators are @samp{/} for directories, @samp{@@} for symbolic links,
6053 @samp{|} for FIFOs, @samp{=} for sockets, @samp{>} for doors,
6054 and nothing for regular files.
6055 @c The following sentence is the same as the one for -d.
6056 Do not follow symbolic links listed on the
6057 command line unless the @option{--dereference-command-line} (@option{-H}),
6058 @option{--dereference} (@option{-L}), or
6059 @option{--dereference-command-line-symlink-to-dir} options are specified.
6062 @itemx --indicator-style=file-type
6063 @opindex --file-type
6064 @opindex --indicator-style
6065 @cindex file type, marking
6066 Append a character to each file name indicating the file type. This is
6067 like @option{-F}, except that executables are not marked.
6069 @item --indicator-style=@var{word}
6070 @opindex --indicator-style
6071 Append a character indicator with style @var{word} to entry names,
6075 Do not append any character indicator; this is the default.
6077 Append @samp{/} for directories. This is the same as the @option{-p}
6080 Append @samp{/} for directories, @samp{@@} for symbolic links, @samp{|}
6081 for FIFOs, @samp{=} for sockets, and nothing for regular files. This is
6082 the same as the @option{--file-type} option.
6084 Append @samp{*} for executable regular files, otherwise behave as for
6085 @samp{file-type}. This is the same as the @option{-F} or
6086 @option{--classify} option.
6091 Print file sizes in 1024-byte blocks, overriding the default block
6092 size (@pxref{Block size}).
6093 This option is equivalent to @option{--block-size=1K}.
6096 @itemx --format=commas
6099 @opindex commas@r{, outputting between files}
6100 List files horizontally, with as many as will fit on each line,
6101 separated by @samp{, } (a comma and a space).
6104 @itemx --indicator-style=slash
6106 @opindex --indicator-style
6107 @cindex file type, marking
6108 Append a @samp{/} to directory names.
6111 @itemx --format=across
6112 @itemx --format=horizontal
6115 @opindex across@r{, listing files}
6116 @opindex horizontal@r{, listing files}
6117 List the files in columns, sorted horizontally.
6120 @itemx --tabsize=@var{cols}
6123 Assume that each tab stop is @var{cols} columns wide. The default is 8.
6124 @command{ls} uses tabs where possible in the output, for efficiency. If
6125 @var{cols} is zero, do not use tabs at all.
6128 @itemx --width=@var{cols}
6132 Assume the screen is @var{cols} columns wide. The default is taken
6133 from the terminal settings if possible; otherwise the environment
6134 variable @env{COLUMNS} is used if it is set; otherwise the default
6140 @node Formatting file timestamps
6141 @subsection Formatting file timestamps
6143 By default, file timestamps are listed in abbreviated form. Most
6144 locales use a timestamp like @samp{2002-03-30 23:45}. However, the
6145 default @acronym{POSIX} locale uses a date like @samp{Mar 30@ @ 2002}
6146 for non-recent timestamps, and a date-without-year and time like
6147 @samp{Mar 30 23:45} for recent timestamps.
6149 A timestamp is considered to be @dfn{recent} if it is less than six
6150 months old, and is not dated in the future. If a timestamp dated
6151 today is not listed in recent form, the timestamp is in the future,
6152 which means you probably have clock skew problems which may break
6153 programs like @command{make} that rely on file timestamps.
6156 Time stamps are listed according to the time zone rules specified by
6157 the @env{TZ} environment variable, or by the system default rules if
6158 @env{TZ} is not set. @xref{TZ Variable,, Specifying the Time Zone
6159 with @env{TZ}, libc, The GNU C Library}.
6161 The following option changes how file timestamps are printed.
6164 @item --time-style=@var{style}
6165 @opindex --time-style
6167 List timestamps in style @var{style}. The @var{style} should
6168 be one of the following:
6173 List timestamps using @var{format}, where @var{format} is interpreted
6174 like the format argument of @command{date} (@pxref{date invocation}).
6175 For example, @option{--time-style="+%Y-%m-%d %H:%M:%S"} causes
6176 @command{ls} to list timestamps like @samp{2002-03-30 23:45:56}. As
6177 with @command{date}, @var{format}'s interpretation is affected by the
6178 @env{LC_TIME} locale category.
6180 If @var{format} contains two format strings separated by a newline,
6181 the former is used for non-recent files and the latter for recent
6182 files; if you want output columns to line up, you may need to insert
6183 spaces in one of the two formats.
6186 List timestamps in full using @acronym{ISO} 8601 date, time, and time zone
6187 format with nanosecond precision, e.g., @samp{2002-03-30
6188 23:45:56.477817180 -0700}. This style is equivalent to
6189 @samp{+%Y-%m-%d %H:%M:%S.%N %z}.
6191 This is useful because the time output includes all the information that
6192 is available from the operating system. For example, this can help
6193 explain @command{make}'s behavior, since @acronym{GNU} @command{make}
6194 uses the full timestamp to determine whether a file is out of date.
6197 List @acronym{ISO} 8601 date and time in minutes, e.g.,
6198 @samp{2002-03-30 23:45}. These timestamps are shorter than
6199 @samp{full-iso} timestamps, and are usually good enough for everyday
6200 work. This style is equivalent to @samp{+%Y-%m-%d %H:%M}.
6203 List @acronym{ISO} 8601 dates for non-recent timestamps (e.g.,
6204 @samp{2002-03-30@ }), and @acronym{ISO} 8601 month, day, hour, and
6205 minute for recent timestamps (e.g., @samp{03-30 23:45}). These
6206 timestamps are uglier than @samp{long-iso} timestamps, but they carry
6207 nearly the same information in a smaller space and their brevity helps
6208 @command{ls} output fit within traditional 80-column output lines.
6209 The following two @command{ls} invocations are equivalent:
6214 ls -l --time-style="+%Y-%m-%d $newline%m-%d %H:%M"
6215 ls -l --time-style="iso"
6220 List timestamps in a locale-dependent form. For example, a Finnish
6221 locale might list non-recent timestamps like @samp{maalis 30@ @ 2002}
6222 and recent timestamps like @samp{maalis 30 23:45}. Locale-dependent
6223 timestamps typically consume more space than @samp{iso} timestamps and
6224 are harder for programs to parse because locale conventions vary so
6225 widely, but they are easier for many people to read.
6227 The @env{LC_TIME} locale category specifies the timestamp format. The
6228 default @acronym{POSIX} locale uses timestamps like @samp{Mar 30@
6229 @ 2002} and @samp{Mar 30 23:45}; in this locale, the following two
6230 @command{ls} invocations are equivalent:
6235 ls -l --time-style="+%b %e %Y$newline%b %e %H:%M"
6236 ls -l --time-style="locale"
6239 Other locales behave differently. For example, in a German locale,
6240 @option{--time-style="locale"} might be equivalent to
6241 @option{--time-style="+%e. %b %Y $newline%e. %b %H:%M"}
6242 and might generate timestamps like @samp{30. M@"ar 2002@ } and
6243 @samp{30. M@"ar 23:45}.
6245 @item posix-@var{style}
6247 List @acronym{POSIX}-locale timestamps if the @env{LC_TIME} locale
6248 category is @acronym{POSIX}, @var{style} timestamps otherwise. For
6249 example, the @samp{posix-long-iso} style lists
6250 timestamps like @samp{Mar 30@ @ 2002} and @samp{Mar 30 23:45} when in
6251 the @acronym{POSIX} locale, and like @samp{2002-03-30 23:45} otherwise.
6256 You can specify the default value of the @option{--time-style} option
6257 with the environment variable @env{TIME_STYLE}; if @env{TIME_STYLE} is not set
6258 the default style is @samp{locale}. @acronym{GNU} Emacs 21.3 and
6259 later use the @option{--dired} option and therefore can parse any date
6260 format, but if you are using Emacs 21.1 or 21.2 and specify a
6261 non-@acronym{POSIX} locale you may need to set
6262 @samp{TIME_STYLE="posix-long-iso"}.
6264 To avoid certain denial-of-service attacks, timestamps that would be
6265 longer than 1000 bytes may be treated as errors.
6268 @node Formatting the file names
6269 @subsection Formatting the file names
6271 These options change how file names themselves are printed.
6277 @itemx --quoting-style=escape
6280 @opindex --quoting-style
6281 @cindex backslash sequences for file names
6282 Quote nongraphic characters in file names using alphabetic and octal
6283 backslash sequences like those used in C.
6287 @itemx --quoting-style=literal
6290 @opindex --quoting-style
6291 Do not quote file names. However, with @command{ls} nongraphic
6292 characters are still printed as question marks if the output is a
6293 terminal and you do not specify the @option{--show-control-chars}
6297 @itemx --hide-control-chars
6299 @opindex --hide-control-chars
6300 Print question marks instead of nongraphic characters in file names.
6301 This is the default if the output is a terminal and the program is
6306 @itemx --quoting-style=c
6308 @opindex --quote-name
6309 @opindex --quoting-style
6310 Enclose file names in double quotes and quote nongraphic characters as
6313 @item --quoting-style=@var{word}
6314 @opindex --quoting-style
6315 @cindex quoting style
6316 Use style @var{word} to quote file names and other strings that may
6317 contain arbitrary characters. The @var{word} should
6318 be one of the following:
6321 Output strings as-is; this is the same as the @option{-N} or
6322 @option{--literal} option.
6324 Quote strings for the shell if they contain shell metacharacters or would
6325 cause ambiguous output.
6326 The quoting is suitable for @acronym{POSIX}-compatible shells like
6327 @command{bash}, but it does not always work for incompatible shells
6330 Quote strings for the shell, even if they would normally not require quoting.
6332 Quote strings as for C character string literals, including the
6333 surrounding double-quote characters; this is the same as the
6334 @option{-Q} or @option{--quote-name} option.
6336 Quote strings as for C character string literals, except omit the
6337 surrounding double-quote
6338 characters; this is the same as the @option{-b} or @option{--escape} option.
6340 Quote strings as for C character string literals, except use
6341 surrounding quotation marks appropriate for the
6344 @c Use @t instead of @samp to avoid duplicate quoting in some output styles.
6345 Quote strings as for C character string literals, except use
6346 surrounding quotation marks appropriate for the locale, and quote
6347 @t{`like this'} instead of @t{"like
6348 this"} in the default C locale. This looks nicer on many displays.
6351 You can specify the default value of the @option{--quoting-style} option
6352 with the environment variable @env{QUOTING_STYLE}. If that environment
6353 variable is not set, the default value is @samp{literal}, but this
6354 default may change to @samp{shell} in a future version of this package.
6356 @item --show-control-chars
6357 @opindex --show-control-chars
6358 Print nongraphic characters as-is in file names.
6359 This is the default unless the output is a terminal and the program is
6365 @node dir invocation
6366 @section @command{dir}: Briefly list directory contents
6369 @cindex directory listing, brief
6371 @command{dir} is equivalent to @code{ls -C
6372 -b}; that is, by default files are listed in columns, sorted vertically,
6373 and special characters are represented by backslash escape sequences.
6375 @xref{ls invocation, @command{ls}}.
6378 @node vdir invocation
6379 @section @command{vdir}: Verbosely list directory contents
6382 @cindex directory listing, verbose
6384 @command{vdir} is equivalent to @code{ls -l
6385 -b}; that is, by default files are listed in long format and special
6386 characters are represented by backslash escape sequences.
6388 @node dircolors invocation
6389 @section @command{dircolors}: Color setup for @command{ls}
6393 @cindex setup for color
6395 @command{dircolors} outputs a sequence of shell commands to set up the
6396 terminal for color output from @command{ls} (and @command{dir}, etc.).
6400 eval "`dircolors [@var{option}]@dots{} [@var{file}]`"
6403 If @var{file} is specified, @command{dircolors} reads it to determine which
6404 colors to use for which file types and extensions. Otherwise, a
6405 precompiled database is used. For details on the format of these files,
6406 run @samp{dircolors --print-database}.
6409 @vindex SHELL @r{environment variable, and color}
6410 The output is a shell command to set the @env{LS_COLORS} environment
6411 variable. You can specify the shell syntax to use on the command line,
6412 or @command{dircolors} will guess it from the value of the @env{SHELL}
6413 environment variable.
6415 The program accepts the following options. Also see @ref{Common options}.
6420 @itemx --bourne-shell
6423 @opindex --bourne-shell
6424 @cindex Bourne shell syntax for color setup
6425 @cindex @command{sh} syntax for color setup
6426 Output Bourne shell commands. This is the default if the @env{SHELL}
6427 environment variable is set and does not end with @samp{csh} or
6436 @cindex C shell syntax for color setup
6437 @cindex @command{csh} syntax for color setup
6438 Output C shell commands. This is the default if @code{SHELL} ends with
6439 @command{csh} or @command{tcsh}.
6442 @itemx --print-database
6444 @opindex --print-database
6445 @cindex color database, printing
6446 @cindex database for color setup, printing
6447 @cindex printing color database
6448 Print the (compiled-in) default color configuration database. This
6449 output is itself a valid configuration file, and is fairly descriptive
6450 of the possibilities.
6457 @node Basic operations
6458 @chapter Basic operations
6460 @cindex manipulating files
6462 This chapter describes the commands for basic file manipulation:
6463 copying, moving (renaming), and deleting (removing).
6466 * cp invocation:: Copy files.
6467 * dd invocation:: Convert and copy a file.
6468 * install invocation:: Copy files and set attributes.
6469 * mv invocation:: Move (rename) files.
6470 * rm invocation:: Remove files or directories.
6471 * shred invocation:: Remove files more securely.
6476 @section @command{cp}: Copy files and directories
6479 @cindex copying files and directories
6480 @cindex files, copying
6481 @cindex directories, copying
6483 @command{cp} copies files (or, optionally, directories). The copy is
6484 completely independent of the original. You can either copy one file to
6485 another, or copy arbitrarily many files to a destination directory.
6489 cp [@var{option}]@dots{} [-T] @var{source} @var{dest}
6490 cp [@var{option}]@dots{} @var{source}@dots{} @var{directory}
6491 cp [@var{option}]@dots{} -t @var{directory} @var{source}@dots{}
6496 If two file names are given, @command{cp} copies the first file to the
6500 If the @option{--target-directory} (@option{-t}) option is given, or
6501 failing that if the last file is a directory and the
6502 @option{--no-target-directory} (@option{-T}) option is not given,
6503 @command{cp} copies each @var{source} file to the specified directory,
6504 using the @var{source}s' names.
6507 Generally, files are written just as they are read. For exceptions,
6508 see the @option{--sparse} option below.
6510 By default, @command{cp} does not copy directories. However, the
6511 @option{-R}, @option{-a}, and @option{-r} options cause @command{cp} to
6512 copy recursively by descending into source directories and copying files
6513 to corresponding destination directories.
6515 By default, @command{cp} follows symbolic links only when not copying
6516 recursively. This default can be overridden with the
6517 @option{--archive} (@option{-a}), @option{-d}, @option{--dereference}
6518 (@option{-L}), @option{--no-dereference} (@option{-P}), and
6519 @option{-H} options. If more than one of these options is specified,
6520 the last one silently overrides the others.
6522 By default, @command{cp} copies the contents of special files only
6523 when not copying recursively. This default can be overridden with the
6524 @option{--copy-contents} option.
6526 @cindex self-backups
6527 @cindex backups, making only
6528 @command{cp} generally refuses to copy a file onto itself, with the
6529 following exception: if @option{--force --backup} is specified with
6530 @var{source} and @var{dest} identical, and referring to a regular file,
6531 @command{cp} will make a backup file, either regular or numbered, as
6532 specified in the usual ways (@pxref{Backup options}). This is useful when
6533 you simply want to make a backup of an existing file before changing it.
6535 The program accepts the following options. Also see @ref{Common options}.
6542 Preserve as much as possible of the structure and attributes of the
6543 original files in the copy (but do not attempt to preserve internal
6544 directory structure; i.e., @samp{ls -U} may list the entries in a copied
6545 directory in a different order).
6546 Equivalent to @option{-dpPR}.
6549 @itemx @w{@kbd{--backup}[=@var{method}]}
6552 @vindex VERSION_CONTROL
6553 @cindex backups, making
6554 @xref{Backup options}.
6555 Make a backup of each file that would otherwise be overwritten or removed.
6556 As a special case, @command{cp} makes a backup of @var{source} when the force
6557 and backup options are given and @var{source} and @var{dest} are the same
6558 name for an existing, regular file. One useful application of this
6559 combination of options is this tiny Bourne shell script:
6563 # Usage: backup FILE...
6564 # Create a @sc{gnu}-style backup of each listed FILE.
6566 cp --backup --force -- "$i" "$i"
6570 @item --copy-contents
6571 @cindex directories, copying recursively
6572 @cindex copying directories recursively
6573 @cindex recursively copying directories
6574 @cindex non-directories, copying as special files
6575 If copying recursively, copy the contents of any special files (e.g.,
6576 FIFOs and device files) as if they were regular files. This means
6577 trying to read the data in each source file and writing it to the
6578 destination. It is usually a mistake to use this option, as it
6579 normally has undesirable effects on special files like FIFOs and the
6580 ones typically found in the @file{/dev} directory. In most cases,
6581 @code{cp -R --copy-contents} will hang indefinitely trying to read
6582 from FIFOs and special files like @file{/dev/console}, and it will
6583 fill up your destination disk if you use it to copy @file{/dev/zero}.
6584 This option has no effect unless copying recursively, and it does not
6585 affect the copying of symbolic links.
6589 @cindex symbolic links, copying
6590 @cindex hard links, preserving
6591 Copy symbolic links as symbolic links rather than copying the files that
6592 they point to, and preserve hard links between source files in the copies.
6593 Equivalent to @option{--no-dereference --preserve=links}.
6599 When copying without this option and an existing destination file cannot
6600 be opened for writing, the copy fails. However, with @option{--force}),
6601 when a destination file cannot be opened, @command{cp} then unlinks it and
6602 tries to open it again. Contrast this behavior with that enabled by
6603 @option{--link} and @option{--symbolic-link}, whereby the destination file
6604 is never opened but rather is unlinked unconditionally. Also see the
6605 description of @option{--remove-destination}.
6609 If a command line argument specifies a symbolic link, then copy the
6610 file it points to rather than the symbolic link itself. However,
6611 copy (preserving its nature) any symbolic link that is encountered
6612 via recursive traversal.
6615 @itemx --interactive
6617 @opindex --interactive
6618 Prompt whether to overwrite existing regular destination files.
6624 Make hard links instead of copies of non-directories.
6627 @itemx --dereference
6629 @opindex --dereference
6630 Always follow symbolic links.
6633 @itemx --no-dereference
6635 @opindex --no-dereference
6636 @cindex symbolic links, copying
6637 Copy symbolic links as symbolic links rather than copying the files that
6641 @itemx @w{@kbd{--preserve}[=@var{attribute_list}]}
6644 @cindex file information, preserving
6645 Preserve the specified attributes of the original files.
6646 If specified, the @var{attribute_list} must be a comma-separated list
6647 of one or more of the following strings:
6651 Preserve the file mode bits and access control lists.
6653 Preserve the owner and group. On most modern systems,
6654 only the super-user may change the owner of a file, and regular users
6655 may preserve the group ownership of a file only if they happen to be
6656 a member of the desired group.
6658 Preserve the times of last access and last modification.
6660 Preserve in the destination files
6661 any links between corresponding source files.
6662 @c Give examples illustrating how hard links are preserved.
6663 @c Also, show how soft links map to hard links with -L and -H.
6665 Preserve all file attributes.
6666 Equivalent to specifying all of the above.
6669 Using @option{--preserve} with no @var{attribute_list} is equivalent
6670 to @option{--preserve=mode,ownership,timestamps}.
6672 In the absence of this option, each destination file is created with the
6673 mode bits of the corresponding source file, minus the bits set in the
6674 umask and minus the set-user-ID and set-group-ID bits.
6675 @xref{File permissions}.
6677 @itemx @w{@kbd{--no-preserve}=@var{attribute_list}}
6678 @cindex file information, preserving
6679 Do not preserve the specified attributes. The @var{attribute_list}
6680 has the same form as for @option{--preserve}.
6684 @cindex parent directories and @command{cp}
6685 Form the name of each destination file by appending to the target
6686 directory a slash and the specified name of the source file. The last
6687 argument given to @command{cp} must be the name of an existing directory.
6688 For example, the command:
6691 cp --parents a/b/c existing_dir
6695 copies the file @file{a/b/c} to @file{existing_dir/a/b/c}, creating
6696 any missing intermediate directories.
6698 @itemx @w{@kbd{--reply}=@var{how}}
6700 @cindex interactivity
6701 @c FIXME: remove in 2008
6702 @strong{Deprecated: to be removed in 2008.}@*
6703 Using @option{--reply=yes} makes @command{cp} act as if @samp{yes} were
6704 given as a response to every prompt about a destination file. That effectively
6705 cancels any preceding @option{--interactive} or @option{-i} option.
6706 Specify @option{--reply=no} to make @command{cp} act as if @samp{no} were
6707 given as a response to every prompt about a destination file.
6708 Specify @option{--reply=query} to make @command{cp} prompt the user
6709 about each existing destination file.
6716 @opindex --recursive
6717 @cindex directories, copying recursively
6718 @cindex copying directories recursively
6719 @cindex recursively copying directories
6720 @cindex non-directories, copying as special files
6721 Copy directories recursively. Symbolic links are not followed by
6722 default; see the @option{--archive} (@option{-a}), @option{-d},
6723 @option{--dereference} (@option{-L}), @option{--no-dereference}
6724 (@option{-P}), and @option{-H} options. Special files are copied by
6725 creating a destination file of the same type as the source; see the
6726 @option{--copy-contents} option. It is not portable to use
6727 @option{-r} to copy symbolic links or special files. On some
6728 non-@sc{gnu} systems, @option{-r} implies the equivalent of
6729 @option{-L} and @option{--copy-contents} for historical reasons.
6730 Also, it is not portable to use @option{-R} to copy symbolic links
6731 unless you also specify @option{-P}, as @acronym{POSIX} allows
6732 implementations that dereference symbolic links by default.
6734 @item --remove-destination
6735 @opindex --remove-destination
6736 Remove each existing destination file before attempting to open it
6737 (contrast with @option{-f} above).
6739 @item --sparse=@var{when}
6740 @opindex --sparse=@var{when}
6741 @cindex sparse files, copying
6742 @cindex holes, copying files with
6743 @findex read @r{system call, and holes}
6744 A @dfn{sparse file} contains @dfn{holes}---a sequence of zero bytes that
6745 does not occupy any physical disk blocks; the @samp{read} system call
6746 reads these as zeroes. This can both save considerable disk space and
6747 increase speed, since many binary files contain lots of consecutive zero
6748 bytes. By default, @command{cp} detects holes in input source files via a crude
6749 heuristic and makes the corresponding output file sparse as well.
6750 Only regular files may be sparse.
6752 The @var{when} value can be one of the following:
6755 The default behavior: if the input file is sparse, attempt to make
6756 the output file sparse, too. However, if an output file exists but
6757 refers to a non-regular file, then do not attempt to make it sparse.
6760 For each sufficiently long sequence of zero bytes in the input file,
6761 attempt to create a corresponding hole in the output file, even if the
6762 input file does not appear to be sparse.
6763 This is useful when the input file resides on a file system
6764 that does not support sparse files
6765 (for example, @samp{efs} file systems in SGI IRIX 5.3 and earlier),
6766 but the output file is on a type of file system that does support them.
6767 Holes may be created only in regular files, so if the destination file
6768 is of some other type, @command{cp} does not even try to make it sparse.
6771 Never make the output file sparse.
6772 This is useful in creating a file for use with the @command{mkswap} command,
6773 since such a file must not have any holes.
6776 @optStripTrailingSlashes
6779 @itemx --symbolic-link
6781 @opindex --symbolic-link
6782 @cindex symbolic links, copying with
6783 Make symbolic links instead of copies of non-directories. All source
6784 file names must be absolute (starting with @samp{/}) unless the
6785 destination files are in the current directory. This option merely
6786 results in an error message on systems that do not support symbolic links.
6792 @optNoTargetDirectory
6798 @cindex newer files, copying only
6799 Do not copy a non-directory that has an existing destination with the
6800 same or newer modification time. If time stamps are being preserved,
6801 the comparison is to the source time stamp truncated to the
6802 resolutions of the destination file system and of the system calls
6803 used to update time stamps; this avoids duplicate work if several
6804 @samp{cp -pu} commands are executed with the same source and
6811 Print the name of each file before copying it.
6814 @itemx --one-file-system
6816 @opindex --one-file-system
6817 @cindex file systems, omitting copying to different
6818 Skip subdirectories that are on different file systems from the one that
6819 the copy started on.
6820 However, mount point directories @emph{are} copied.
6828 @section @command{dd}: Convert and copy a file
6831 @cindex converting while copying a file
6833 @command{dd} copies a file (from standard input to standard output, by
6834 default) with a changeable I/O block size, while optionally performing
6835 conversions on it. Synopses:
6838 dd [@var{operand}]@dots{}
6842 The only options are @option{--help} and @option{--version}.
6843 @xref{Common options}. @command{dd} accepts the following operands.
6849 Read from @var{file} instead of standard input.
6853 Write to @var{file} instead of standard output. Unless
6854 @samp{conv=notrunc} is given, @command{dd} truncates @var{file} to zero
6855 bytes (or the size specified with @samp{seek=}).
6857 @item ibs=@var{bytes}
6859 @cindex block size of input
6860 @cindex input block size
6861 Read @var{bytes} bytes at a time.
6863 @item obs=@var{bytes}
6865 @cindex block size of output
6866 @cindex output block size
6867 Write @var{bytes} bytes at a time.
6869 @item bs=@var{bytes}
6872 Both read and write @var{bytes} bytes at a time. This overrides
6873 @samp{ibs} and @samp{obs}.
6875 @item cbs=@var{bytes}
6877 @cindex block size of conversion
6878 @cindex conversion block size
6879 Convert @var{bytes} bytes at a time.
6881 @item skip=@var{blocks}
6883 Skip @var{blocks} @samp{ibs}-byte blocks in the input file before copying.
6885 @item seek=@var{blocks}
6887 Skip @var{blocks} @samp{obs}-byte blocks in the output file before copying.
6889 @item count=@var{blocks}
6891 Copy @var{blocks} @samp{ibs}-byte blocks from the input file, instead
6892 of everything until the end of the file.
6894 @item conv=@var{conversion}[,@var{conversion}]@dots{}
6896 Convert the file as specified by the @var{conversion} argument(s).
6897 (No spaces around any comma(s).)
6904 @opindex ascii@r{, converting to}
6905 Convert @acronym{EBCDIC} to @acronym{ASCII},
6906 using the conversion table specified by @acronym{POSIX}.
6907 This provides a 1:1 translation for all 256 bytes.
6910 @opindex ebcdic@r{, converting to}
6911 Convert @acronym{ASCII} to @acronym{EBCDIC}.
6912 This is the inverse of the @samp{ascii} conversion.
6915 @opindex alternate ebcdic@r{, converting to}
6916 Convert @acronym{ASCII} to alternate @acronym{EBCDIC},
6917 using the alternate conversion table specified by @acronym{POSIX}.
6918 This is not a 1:1 translation, but reflects common historical practice
6919 for @samp{~}, @samp{[}, and @samp{]}.
6921 The @samp{ascii}, @samp{ebcdic}, and @samp{ibm} conversions are
6925 @opindex block @r{(space-padding)}
6926 For each line in the input, output @samp{cbs} bytes, replacing the
6927 input newline with a space and padding with spaces as necessary.
6931 Replace trailing spaces in each @samp{cbs}-sized input block with a
6934 The @samp{block} and @samp{unblock} conversions are mutually exclusive.
6937 @opindex lcase@r{, converting to}
6938 Change uppercase letters to lowercase.
6941 @opindex ucase@r{, converting to}
6942 Change lowercase letters to uppercase.
6944 The @samp{lcase} and @samp{ucase} conversions are mutually exclusive.
6947 @opindex swab @r{(byte-swapping)}
6948 @cindex byte-swapping
6949 Swap every pair of input bytes. @sc{gnu} @command{dd}, unlike others, works
6950 when an odd number of bytes are read---the last byte is simply copied
6951 (since there is nothing to swap it with).
6955 @cindex read errors, ignoring
6956 Continue after read errors.
6960 @cindex creating output file, avoiding
6961 Do not create the output file; the output file must already exist.
6965 @cindex creating output file, requiring
6966 Fail if the output file already exists; @command{dd} must create the
6969 The @samp{excl} and @samp{nocreat} conversions are mutually exclusive.
6973 @cindex truncating output file, avoiding
6974 Do not truncate the output file.
6977 @opindex sync @r{(padding with nulls)}
6978 Pad every input block to size of @samp{ibs} with trailing zero bytes.
6979 When used with @samp{block} or @samp{unblock}, pad with spaces instead of
6984 @cindex synchronized data writes, before finishing
6985 Synchronize output data just before finishing. This forces a physical
6986 write of output data.
6990 @cindex synchronized data and metadata writes, before finishing
6991 Synchronize output data and metadata just before finishing. This
6992 forces a physical write of output data and metadata.
6996 @item iflag=@var{flag}[,@var{flag}]@dots{}
6998 Access the input file using the flags specified by the @var{flag}
6999 argument(s). (No spaces around any comma(s).)
7001 @item oflag=@var{flag}[,@var{flag}]@dots{}
7003 Access the output file using the flags specified by the @var{flag}
7004 argument(s). (No spaces around any comma(s).)
7012 @cindex appending to the output file
7013 Write in append mode, so that even if some other process is writing to
7014 this file, every @command{dd} write will append to the current
7015 contents of the file. This flag makes sense only for output.
7020 Use direct I/O for data, avoiding the buffer cache.
7024 @cindex synchronized data reads
7025 Use synchronized I/O for data. For the output file, this forces a
7026 physical write of output data on each write. For the input file,
7027 this flag can matter when reading from a remote file that has been
7028 written to synchronously by some other process. Metadata (e.g.,
7029 last-access and last-modified time) is not necessarily synchronized.
7033 @cindex synchronized data and metadata I/O
7034 Use synchronized I/O for both data and metadata.
7038 @cindex nonblocking I/O
7039 Use non-blocking I/O.
7044 Do not update the file's access time.
7048 @cindex symbolic links, following
7049 Do not follow symbolic links.
7053 @cindex controlling terminal
7054 Do not assign the file to be a controlling terminal for @command{dd}.
7055 This has no effect when the file is not a terminal.
7056 On many hosts (e.g., @acronym{GNU}/Linux hosts), this option has no effect
7062 Use binary I/O. This option has an effect only on nonstandard
7063 platforms that distinguish binary from text I/O.
7068 Use text I/O. Like @samp{binary}, this option has no effect on
7073 These flags are not supported on all systems, and @samp{dd} rejects
7074 attempts to use them when they are not supported. When reading from
7075 standard input or writing to standard output, the @samp{nofollow} and
7076 @samp{noctty} flags should not be specified, and the other flags
7077 (e.g., @samp{nonblock}) can affect how other processes behave with the
7078 affected file descriptors, even after @command{dd} exits.
7082 @cindex multipliers after numbers
7083 The numeric-valued strings above (@var{bytes} and @var{blocks}) can be
7084 followed by a multiplier: @samp{b}=512, @samp{c}=1,
7085 @samp{w}=2, @samp{x@var{m}}=@var{m}, or any of the
7086 standard block size suffixes like @samp{k}=1024 (@pxref{Block size}).
7088 Use different @command{dd} invocations to use different block sizes for
7089 skipping and I/O@. For example, the following shell commands copy data
7090 in 512 KiB blocks between a disk and a tape, but do not save or restore a
7091 4 KiB label at the start of the disk:
7094 disk=/dev/rdsk/c0t1d0s2
7097 # Copy all but the label from disk to tape.
7098 (dd bs=4k skip=1 count=0 && dd bs=512k) <$disk >$tape
7100 # Copy from tape back to disk, but leave the disk label alone.
7101 (dd bs=4k seek=1 count=0 && dd bs=512k) <$tape >$disk
7104 Sending an @samp{INFO} signal to a running @command{dd}
7105 process makes it print I/O statistics to standard error
7106 and then resume copying. In the example below,
7107 @command{dd} is run in the background to copy 10 million blocks.
7108 The @command{kill} command makes it output intermediate I/O statistics,
7109 and when @command{dd} completes, it outputs the final statistics.
7112 $ dd if=/dev/zero of=/dev/null count=10MB & pid=$!
7113 $ kill -s INFO $pid; wait $pid
7114 3385223+0 records in
7115 3385223+0 records out
7116 1733234176 bytes (1.7 GB) copied, 6.42173 seconds, 270 MB/s
7117 10000000+0 records in
7118 10000000+0 records out
7119 5120000000 bytes (5.1 GB) copied, 18.913 seconds, 271 MB/s
7122 @vindex POSIXLY_CORRECT
7123 On systems lacking the @samp{INFO} signal @command{dd} responds to the
7124 @samp{USR1} signal instead, unless the @env{POSIXLY_CORRECT}
7125 environment variable is set.
7130 @node install invocation
7131 @section @command{install}: Copy files and set attributes
7134 @cindex copying files and setting attributes
7136 @command{install} copies files while setting their file mode bits and, if
7137 possible, their owner and group. Synopses:
7140 install [@var{option}]@dots{} [-T] @var{source} @var{dest}
7141 install [@var{option}]@dots{} @var{source}@dots{} @var{directory}
7142 install [@var{option}]@dots{} -t @var{directory} @var{source}@dots{}
7143 install [@var{option}]@dots{} -d @var{directory}@dots{}
7148 If two file names are given, @command{install} copies the first file to the
7152 If the @option{--target-directory} (@option{-t}) option is given, or
7153 failing that if the last file is a directory and the
7154 @option{--no-target-directory} (@option{-T}) option is not given,
7155 @command{install} copies each @var{source} file to the specified
7156 directory, using the @var{source}s' names.
7159 If the @option{--directory} (@option{-d}) option is given,
7160 @command{install} creates each @var{directory} and any missing parent
7164 @cindex Makefiles, installing programs in
7165 @command{install} is similar to @command{cp}, but allows you to control the
7166 attributes of destination files. It is typically used in Makefiles to
7167 copy programs into their destination directories. It refuses to copy
7168 files onto themselves.
7170 The program accepts the following options. Also see @ref{Common options}.
7178 Ignored; for compatibility with old Unix versions of @command{install}.
7183 @opindex --directory
7184 @cindex directories, creating with given attributes
7185 @cindex parent directories, creating missing
7186 @cindex leading directories, creating missing
7187 Create each given directory and any missing parent directories, setting
7188 the owner, group and mode as given on the command line or to the
7189 defaults. It also gives any parent directories it creates those
7190 attributes. (This is different from the SunOS 4.x @command{install}, which
7191 gives directories that it creates the default attributes.)
7193 @item -g @var{group}
7194 @itemx --group=@var{group}
7197 @cindex group ownership of installed files, setting
7198 Set the group ownership of installed files or directories to
7199 @var{group}. The default is the process's current group. @var{group}
7200 may be either a group name or a numeric group ID.
7203 @itemx --mode=@var{mode}
7206 @cindex permissions of installed files, setting
7207 Set the file mode bits for the installed file or directory to @var{mode},
7208 which can be either an octal number, or a symbolic mode as in
7209 @command{chmod}, with @samp{a=} (no access allowed to anyone) as the
7210 point of departure (@pxref{File permissions}).
7211 The default mode is @samp{u=rwx,go=rx}---read, write,
7212 and execute for the owner, and read and execute for group and other.
7214 @item -o @var{owner}
7215 @itemx --owner=@var{owner}
7218 @cindex ownership of installed files, setting
7219 @cindex appropriate privileges
7220 @vindex root @r{as default owner}
7221 If @command{install} has appropriate privileges (is run as root), set the
7222 ownership of installed files or directories to @var{owner}. The default
7223 is @code{root}. @var{owner} may be either a user name or a numeric user
7227 @itemx --preserve-timestamps
7229 @opindex --preserve-timestamps
7230 @cindex timestamps of installed files, preserving
7231 Set the time of last access and the time of last modification of each
7232 installed file to match those of each corresponding original file.
7233 When a file is installed without this option, its last access and
7234 last modification times are both set to the time of installation.
7235 This option is useful if you want to use the last modification times
7236 of installed files to keep track of when they were last built as opposed
7237 to when they were last installed.
7243 @cindex symbol table information, stripping
7244 @cindex stripping symbol table information
7245 Strip the symbol tables from installed binary executables.
7251 @optNoTargetDirectory
7257 Print the name of each file before copying it.
7265 @section @command{mv}: Move (rename) files
7269 @command{mv} moves or renames files (or directories). Synopses:
7272 mv [@var{option}]@dots{} [-T] @var{source} @var{dest}
7273 mv [@var{option}]@dots{} @var{source}@dots{} @var{directory}
7274 mv [@var{option}]@dots{} -t @var{directory} @var{source}@dots{}
7279 If two file names are given, @command{mv} moves the first file to the
7283 If the @option{--target-directory} (@option{-t}) option is given, or
7284 failing that if the last file is a directory and the
7285 @option{--no-target-directory} (@option{-T}) option is not given,
7286 @command{mv} moves each @var{source} file to the specified
7287 directory, using the @var{source}s' names.
7290 @command{mv} can move any type of file from one file system to another.
7291 Prior to version @code{4.0} of the fileutils,
7292 @command{mv} could move only regular files between file systems.
7293 For example, now @command{mv} can move an entire directory hierarchy
7294 including special device files from one partition to another. It first
7295 uses some of the same code that's used by @code{cp -a} to copy the
7296 requested directories and files, then (assuming the copy succeeded)
7297 it removes the originals. If the copy fails, then the part that was
7298 copied to the destination partition is removed. If you were to copy
7299 three directories from one partition to another and the copy of the first
7300 directory succeeded, but the second didn't, the first would be left on
7301 the destination partition and the second and third would be left on the
7304 @cindex prompting, and @command{mv}
7305 If a destination file exists but is normally unwritable, standard input
7306 is a terminal, and the @option{-f} or @option{--force} option is not given,
7307 @command{mv} prompts the user for whether to replace the file. (You might
7308 own the file, or have write permission on its directory.) If the
7309 response is not affirmative, the file is skipped.
7311 @emph{Warning}: If you try to move a symlink that points to a directory,
7312 and you specify the symlink with a trailing slash, then @command{mv}
7313 doesn't move the symlink but instead moves the directory referenced
7314 by the symlink. @xref{Trailing slashes}.
7316 The program accepts the following options. Also see @ref{Common options}.
7326 @cindex prompts, omitting
7327 Do not prompt the user before removing a destination file.
7330 @itemx --interactive
7332 @opindex --interactive
7333 @cindex prompts, forcing
7334 Prompt whether to overwrite each existing destination file, regardless
7336 If the response is not affirmative, the file is skipped.
7338 @itemx @w{@kbd{--reply}=@var{how}}
7340 @cindex interactivity
7341 @c FIXME: remove in 2008
7342 @strong{Deprecated: to be removed in 2008.}@*
7343 Specifying @option{--reply=yes} is equivalent to using @option{--force}.
7344 Specify @option{--reply=no} to make @command{mv} act as if @samp{no} were
7345 given as a response to every prompt about a destination file.
7346 Specify @option{--reply=query} to make @command{mv} prompt the user
7347 about each existing destination file.
7348 Note that @option{--reply=no} has an effect only when @command{mv} would prompt
7349 without @option{-i} or equivalent, i.e., when a destination file exists and is
7350 not writable, standard input is a terminal, and no @option{-f} (or equivalent)
7351 option is specified.
7357 @cindex newer files, moving only
7358 Do not move a non-directory that has an existing destination with the
7359 same or newer modification time.
7360 If the move is across file system boundaries, the comparison is to the
7361 source time stamp truncated to the resolutions of the destination file
7362 system and of the system calls used to update time stamps; this avoids
7363 duplicate work if several @samp{mv -u} commands are executed with the
7364 same source and destination.
7370 Print the name of each file before moving it.
7372 @optStripTrailingSlashes
7378 @optNoTargetDirectory
7386 @section @command{rm}: Remove files or directories
7389 @cindex removing files or directories
7391 @command{rm} removes each given @var{file}. By default, it does not remove
7392 directories. Synopsis:
7395 rm [@var{option}]@dots{} [@var{file}]@dots{}
7398 @cindex prompting, and @command{rm}
7399 If the @option{-I} or @option{--interactive=once} option is given,
7400 and there are more than three files or the @option{-r}, @option{-R},
7401 or @option{--recursive} are given, then @command{rm} prompts the user
7402 for whether to proceed with the entire operation. If the response is
7403 not affirmative, the entire command is aborted.
7405 Otherwise, if a file is unwritable, standard input is a terminal, and
7406 the @option{-f} or @option{--force} option is not given, or the
7407 @option{-i} or @option{--interactive=always} option @emph{is} given,
7408 @command{rm} prompts the user for whether to remove the file.
7409 If the response is not affirmative, the file is skipped.
7411 @emph{Warning}: If you use @command{rm} to remove a file, it is usually
7412 possible to recover the contents of that file. If you want more assurance
7413 that the contents are truly unrecoverable, consider using @command{shred}.
7415 The program accepts the following options. Also see @ref{Common options}.
7423 Ignore nonexistent files and never prompt the user.
7424 Ignore any previous @option{--interactive} (@option{-i}) option.
7428 Prompt whether to remove each file.
7429 If the response is not affirmative, the file is skipped.
7430 Ignore any previous @option{--force} (@option{-f}) option.
7431 Equivalent to @option{--interactive=always}.
7435 Prompt once whether to proceed with the command, if more than three
7436 files are named or if a recursive removal is requested. Ignore any
7437 previous @option{--force} (@option{-f}) option. Equivalent to
7438 @option{--interactive=once}.
7440 @itemx --interactive [=@var{when}]
7441 @opindex --interactive
7442 Specify when to issue an interactive prompt. @var{when} may be
7446 @vindex never @r{interactive option}
7447 - Do not prompt at all.
7449 @vindex once @r{interactive option}
7450 - Prompt once if more than three files are named or if a recursive
7451 removal is requested. Equivalent to @option{-I}.
7453 @vindex always @r{interactive option}
7454 - Prompt for every file being removed. Equivalent to @option{-i}.
7456 Specifying @option{--interactive} and no @var{when} is equivalent to
7457 @option{--interactive=always}.
7459 @itemx --preserve-root
7460 @opindex --preserve-root
7461 @cindex root directory, disallow recursive destruction
7462 Fail upon any attempt to remove the file system root, @file{/},
7463 when used with the @option{--recursive} option.
7464 Without @option{--recursive}, this option has no effect.
7465 @xref{Treating / specially}.
7467 @itemx --no-preserve-root
7468 @opindex --no-preserve-root
7469 @cindex root directory, allow recursive destruction
7470 Cancel the effect of any preceding @option{--preserve-root} option.
7471 @xref{Treating / specially}.
7478 @opindex --recursive
7479 @cindex directories, removing (recursively)
7480 Remove the listed directories and their contents recursively.
7486 Print the name of each file before removing it.
7490 @cindex files beginning with @samp{-}, removing
7491 @cindex @samp{-}, removing files beginning with
7492 One common question is how to remove files whose names begin with a
7493 @samp{-}. @sc{gnu} @command{rm}, like every program that uses the @code{getopt}
7494 function to parse its arguments, lets you use the @samp{--} option to
7495 indicate that all following arguments are non-options. To remove a file
7496 called @file{-f} in the current directory, you could type either:
7509 @opindex - @r{and Unix @command{rm}}
7510 The Unix @command{rm} program's use of a single @samp{-} for this purpose
7511 predates the development of the getopt standard syntax.
7516 @node shred invocation
7517 @section @command{shred}: Remove files more securely
7520 @cindex data, erasing
7521 @cindex erasing data
7523 @command{shred} overwrites devices or files, to help prevent even
7524 very expensive hardware from recovering the data.
7526 Ordinarily when you remove a file (@pxref{rm invocation}), the data is
7527 not actually destroyed. Only the index listing where the file is
7528 stored is destroyed, and the storage is made available for reuse.
7529 There are undelete utilities that will attempt to reconstruct the index
7530 and can bring the file back if the parts were not reused.
7532 On a busy system with a nearly-full drive, space can get reused in a few
7533 seconds. But there is no way to know for sure. If you have sensitive
7534 data, you may want to be sure that recovery is not possible by actually
7535 overwriting the file with non-sensitive data.
7537 However, even after doing that, it is possible to take the disk back
7538 to a laboratory and use a lot of sensitive (and expensive) equipment
7539 to look for the faint ``echoes'' of the original data underneath the
7540 overwritten data. If the data has only been overwritten once, it's not
7543 The best way to remove something irretrievably is to destroy the media
7544 it's on with acid, melt it down, or the like. For cheap removable media
7545 like floppy disks, this is the preferred method. However, hard drives
7546 are expensive and hard to melt, so the @command{shred} utility tries
7547 to achieve a similar effect non-destructively.
7549 This uses many overwrite passes, with the data patterns chosen to
7550 maximize the damage they do to the old data. While this will work on
7551 floppies, the patterns are designed for best effect on hard drives.
7552 For more details, see the source code and Peter Gutmann's paper
7553 @uref{http://www.cs.auckland.ac.nz/~pgut001/pubs/secure_del.html,
7554 @cite{Secure Deletion of Data from Magnetic and Solid-State Memory}},
7555 from the proceedings of the Sixth @acronym{USENIX} Security Symposium (San Jose,
7556 California, July 22--25, 1996).
7558 @strong{Please note} that @command{shred} relies on a very important assumption:
7559 that the file system overwrites data in place. This is the traditional
7560 way to do things, but many modern file system designs do not satisfy this
7561 assumption. Exceptions include:
7566 Log-structured or journaled file systems, such as those supplied with
7567 AIX and Solaris, and JFS, ReiserFS, XFS, Ext3 (in @code{data=journal} mode),
7568 BFS, NTFS, etc.@: when they are configured to journal @emph{data}.
7571 File systems that write redundant data and carry on even if some writes
7572 fail, such as RAID-based file systems.
7575 File systems that make snapshots, such as Network Appliance's NFS server.
7578 File systems that cache in temporary locations, such as NFS version 3
7582 Compressed file systems.
7585 In the particular case of ext3 file systems, the above disclaimer applies (and
7586 @command{shred} is thus of limited effectiveness) only in @code{data=journal}
7587 mode, which journals file data in addition to just metadata. In both
7588 the @code{data=ordered} (default) and @code{data=writeback} modes,
7589 @command{shred} works as usual. Ext3 journaling modes can be changed
7590 by adding the @code{data=something} option to the mount options for a
7591 particular file system in the @file{/etc/fstab} file, as documented in
7592 the mount man page (man mount).
7594 If you are not sure how your file system operates, then you should assume
7595 that it does not overwrite data in place, which means that shred cannot
7596 reliably operate on regular files in your file system.
7598 Generally speaking, it is more reliable to shred a device than a file,
7599 since this bypasses the problem of file system design mentioned above.
7600 However, even shredding devices is not always completely reliable. For
7601 example, most disks map out bad sectors invisibly to the application; if
7602 the bad sectors contain sensitive data, @command{shred} won't be able to
7605 @command{shred} makes no attempt to detect or report this problem, just as
7606 it makes no attempt to do anything about backups. However, since it is
7607 more reliable to shred devices than files, @command{shred} by default does
7608 not truncate or remove the output file. This default is more suitable
7609 for devices, which typically cannot be truncated and should not be
7612 Finally, consider the risk of backups and mirrors.
7613 File system backups and remote mirrors may contain copies of the
7614 file that cannot be removed, and that will allow a shredded file
7615 to be recovered later. So if you keep any data you may later want
7616 to destroy using @command{shred}, be sure that it is not backed up or mirrored.
7619 shred [@var{option}]@dots{} @var{file}[@dots{}]
7622 The program accepts the following options. Also see @ref{Common options}.
7630 @cindex force deletion
7631 Override file permissions if necessary to allow overwriting.
7634 @itemx -n @var{NUMBER}
7635 @itemx --iterations=@var{NUMBER}
7636 @opindex -n @var{NUMBER}
7637 @opindex --iterations=@var{NUMBER}
7638 @cindex iterations, selecting the number of
7639 By default, @command{shred} uses 25 passes of overwrite. This is enough
7640 for all of the useful overwrite patterns to be used at least once.
7641 You can reduce this to save time, or increase it if you have a lot of
7644 @item -s @var{BYTES}
7645 @itemx --size=@var{BYTES}
7646 @opindex -s @var{BYTES}
7647 @opindex --size=@var{BYTES}
7648 @cindex size of file to shred
7649 Shred the first @var{BYTES} bytes of the file. The default is to shred
7650 the whole file. @var{BYTES} can be followed by a size specification like
7651 @samp{K}, @samp{M}, or @samp{G} to specify a multiple. @xref{Block size}.
7657 @cindex removing files after shredding
7658 After shredding a file, truncate it (if possible) and then remove it.
7659 If a file has multiple links, only the named links will be removed.
7665 Display status updates as sterilization proceeds.
7671 By default, @command{shred} rounds the size of a regular file up to the next
7672 multiple of the file system block size to fully erase the last block of the file.
7673 Use @option{--exact} to suppress that behavior.
7674 Thus, by default if you shred a 10-byte regular file on a system with 512-byte
7675 blocks, the resulting file will be 512 bytes long. With this option,
7676 shred does not increase the apparent size of the file.
7682 Normally, the last pass that @command{shred} writes is made up of
7683 random data. If this would be conspicuous on your hard drive (for
7684 example, because it looks like encrypted data), or you just think
7685 it's tidier, the @option{--zero} option adds an additional overwrite pass with
7686 all zero bits. This is in addition to the number of passes specified
7687 by the @option{--iterations} option.
7691 You might use the following command to erase all trace of the
7692 file system you'd created on the floppy disk in your first drive.
7693 That command takes about 20 minutes to erase a ``1.44MB'' (actually
7697 shred --verbose /dev/fd0
7700 Similarly, to erase all data on a selected partition of
7701 your hard disk, you could give a command like this:
7704 shred --verbose /dev/sda5
7707 A @var{file} of @samp{-} denotes standard output.
7708 The intended use of this is to shred a removed temporary file.
7712 i=`tempfile -m 0600`
7715 echo "Hello, world" >&3
7720 However, the command @samp{shred - >file} does not shred the contents
7721 of @var{file}, since the shell truncates @var{file} before invoking
7722 @command{shred}. Use the command @samp{shred file} or (if using a
7723 Bourne-compatible shell) the command @samp{shred - 1<>file} instead.
7728 @node Special file types
7729 @chapter Special file types
7731 @cindex special file types
7732 @cindex file types, special
7734 This chapter describes commands which create special types of files (and
7735 @command{rmdir}, which removes directories, one special file type).
7737 @cindex special file types
7739 Although Unix-like operating systems have markedly fewer special file
7740 types than others, not @emph{everything} can be treated only as the
7741 undifferentiated byte stream of @dfn{normal files}. For example, when a
7742 file is created or removed, the system must record this information,
7743 which it does in a @dfn{directory}---a special type of file. Although
7744 you can read directories as normal files, if you're curious, in order
7745 for the system to do its job it must impose a structure, a certain
7746 order, on the bytes of the file. Thus it is a ``special'' type of file.
7748 Besides directories, other special file types include named pipes
7749 (FIFOs), symbolic links, sockets, and so-called @dfn{special files}.
7752 * link invocation:: Make a hard link via the link syscall
7753 * ln invocation:: Make links between files.
7754 * mkdir invocation:: Make directories.
7755 * mkfifo invocation:: Make FIFOs (named pipes).
7756 * mknod invocation:: Make block or character special files.
7757 * readlink invocation:: Print the referent of a symbolic link.
7758 * rmdir invocation:: Remove empty directories.
7759 * unlink invocation:: Remove files via the unlink syscall
7763 @node link invocation
7764 @section @command{link}: Make a hard link via the link syscall
7767 @cindex links, creating
7768 @cindex hard links, creating
7769 @cindex creating links (hard only)
7771 @command{link} creates a single hard link at a time.
7772 It is a minimalist interface to the system-provided
7773 @code{link} function. @xref{Hard Links, , , libc,
7774 The GNU C Library Reference Manual}.
7775 It avoids the bells and whistles of the more commonly-used
7776 @command{ln} command (@pxref{ln invocation}).
7780 link @var{filename} @var{linkname}
7783 @var{filename} must specify an existing file, and @var{linkname}
7784 must specify a nonexistent entry in an existing directory.
7785 @command{link} simply calls @code{link (@var{filename}, @var{linkname})}
7788 On a @acronym{GNU} system, this command acts like @samp{ln --directory
7789 --no-target-directory @var{filename} @var{linkname}}. However, the
7790 @option{--directory} and @option{--no-target-directory} options are
7791 not specified by @acronym{POSIX}, and the @command{link} command is
7792 more portable in practice.
7798 @section @command{ln}: Make links between files
7801 @cindex links, creating
7802 @cindex hard links, creating
7803 @cindex symbolic (soft) links, creating
7804 @cindex creating links (hard or soft)
7806 @cindex file systems and hard links
7807 @command{ln} makes links between files. By default, it makes hard links;
7808 with the @option{-s} option, it makes symbolic (or @dfn{soft}) links.
7812 ln [@var{option}]@dots{} [-T] @var{target} @var{linkname}
7813 ln [@var{option}]@dots{} @var{target}
7814 ln [@var{option}]@dots{} @var{target}@dots{} @var{directory}
7815 ln [@var{option}]@dots{} -t @var{directory} @var{target}@dots{}
7821 If two file names are given, @command{ln} creates a link to the first
7822 file from the second.
7825 If one @var{target} is given, @command{ln} creates a link to that file
7826 in the current directory.
7829 If the @option{--target-directory} (@option{-t}) option is given, or
7830 failing that if the last file is a directory and the
7831 @option{--no-target-directory} (@option{-T}) option is not given,
7832 @command{ln} creates a link to each @var{target} file in the specified
7833 directory, using the @var{target}s' names.
7837 Normally @command{ln} does not remove existing files. Use the
7838 @option{--force} (@option{-f}) option to remove them unconditionally,
7839 the @option{--interactive} (@option{-i}) option to remove them
7840 conditionally, and the @option{--backup} (@option{-b}) option to
7843 @cindex hard link, defined
7844 @cindex inode, and hard links
7845 A @dfn{hard link} is another name for an existing file; the link and the
7846 original are indistinguishable. Technically speaking, they share the
7847 same inode, and the inode contains all the information about a
7848 file---indeed, it is not incorrect to say that the inode @emph{is} the
7849 file. On all existing implementations, you cannot make a hard link to
7850 a directory, and hard links cannot cross file system boundaries. (These
7851 restrictions are not mandated by @acronym{POSIX}, however.)
7853 @cindex dereferencing symbolic links
7854 @cindex symbolic link, defined
7855 @dfn{Symbolic links} (@dfn{symlinks} for short), on the other hand, are
7856 a special file type (which not all kernels support: System V release 3
7857 (and older) systems lack symlinks) in which the link file actually
7858 refers to a different file, by name. When most operations (opening,
7859 reading, writing, and so on) are passed the symbolic link file, the
7860 kernel automatically @dfn{dereferences} the link and operates on the
7861 target of the link. But some operations (e.g., removing) work on the
7862 link file itself, rather than on its target. @xref{Symbolic Links,,,
7863 libc, The GNU C Library Reference Manual}.
7865 The program accepts the following options. Also see @ref{Common options}.
7876 @opindex --directory
7877 @cindex hard links to directories
7878 Allow the super-user to attempt to make hard links to directories.
7879 However, note that this will probably fail due to
7880 system restrictions, even for the super-user.
7886 Remove existing destination files.
7889 @itemx --interactive
7891 @opindex --interactive
7892 @cindex prompting, and @command{ln}
7893 Prompt whether to remove existing destination files.
7896 @itemx --no-dereference
7898 @opindex --no-dereference
7899 Do not treat the last operand specially when it is a symbolic link to
7900 a directory. Instead, treat it as if it were a normal file.
7902 When the destination is an actual directory (not a symlink to one),
7903 there is no ambiguity. The link is created in that directory.
7904 But when the specified destination is a symlink to a directory,
7905 there are two ways to treat the user's request. @command{ln} can
7906 treat the destination just as it would a normal directory and create
7907 the link in it. On the other hand, the destination can be viewed as a
7908 non-directory---as the symlink itself. In that case, @command{ln}
7909 must delete or backup that symlink before creating the new link.
7910 The default is to treat a destination that is a symlink to a directory
7911 just like a directory.
7913 This option is weaker than the @option{--no-target-directory}
7914 (@option{-T}) option, so it has no effect if both options are given.
7920 Make symbolic links instead of hard links. This option merely produces
7921 an error message on systems that do not support symbolic links.
7927 @optNoTargetDirectory
7933 Print the name of each file after linking it successfully.
7944 # Create link ../a pointing to a in that directory.
7945 # Not really useful because it points to itself.
7950 # Change to the target before creating symlinks to avoid being confused.
7956 # Hard coded file names don't move well.
7957 ln -s $(pwd)/a /some/dir/
7961 # Relative file names survive directory moves and also
7962 # work across networked file systems.
7963 ln -s afile anotherfile
7964 ln -s ../adir/afile yetanotherfile
7968 @node mkdir invocation
7969 @section @command{mkdir}: Make directories
7972 @cindex directories, creating
7973 @cindex creating directories
7975 @command{mkdir} creates directories with the specified names. Synopsis:
7978 mkdir [@var{option}]@dots{} @var{name}@dots{}
7981 If a @var{name} is an existing file but not a directory, @command{mkdir} prints
7982 a warning message on stderr and will exit with a status of 1 after
7983 processing any remaining @var{name}s. The same is done when a @var{name} is an
7984 existing directory and the -p option is not given. If a @var{name} is an
7985 existing directory and the -p option is given, @command{mkdir} will ignore it.
7986 That is, @command{mkdir} will not print a warning, raise an error, or change
7987 the mode of the directory (even if the -m option is given), and will
7988 move on to processing any remaining @var{name}s.
7990 The program accepts the following options. Also see @ref{Common options}.
7995 @itemx --mode=@var{mode}
7998 @cindex modes of created directories, setting
7999 Set the mode of created directories to @var{mode}, which is symbolic as
8000 in @command{chmod} and uses @samp{a=rwx} (read, write and execute allowed for
8001 everyone) for the point of the departure. @xref{File permissions}.
8007 @cindex parent directories, creating
8008 Make any missing parent directories for each argument. The file permission
8009 bits of parent directories are set to the umask modified by @samp{u+wx}.
8010 Ignore arguments corresponding to existing directories.
8016 Print a message for each created directory. This is most useful with
8023 @node mkfifo invocation
8024 @section @command{mkfifo}: Make FIFOs (named pipes)
8027 @cindex FIFOs, creating
8028 @cindex named pipes, creating
8029 @cindex creating FIFOs (named pipes)
8031 @command{mkfifo} creates FIFOs (also called @dfn{named pipes}) with the
8032 specified names. Synopsis:
8035 mkfifo [@var{option}] @var{name}@dots{}
8038 A @dfn{FIFO} is a special file type that permits independent processes
8039 to communicate. One process opens the FIFO file for writing, and
8040 another for reading, after which data can flow as with the usual
8041 anonymous pipe in shells or elsewhere.
8043 The program accepts the following option. Also see @ref{Common options}.
8048 @itemx --mode=@var{mode}
8051 @cindex modes of created FIFOs, setting
8052 Set the mode of created FIFOs to @var{mode}, which is symbolic as in
8053 @command{chmod} and uses @samp{a=rw} (read and write allowed for everyone)
8054 for the point of departure. @var{mode} should specify only file
8055 permission bits. @xref{File permissions}.
8062 @node mknod invocation
8063 @section @command{mknod}: Make block or character special files
8066 @cindex block special files, creating
8067 @cindex character special files, creating
8069 @command{mknod} creates a FIFO, character special file, or block special
8070 file with the specified name. Synopsis:
8073 mknod [@var{option}]@dots{} @var{name} @var{type} [@var{major} @var{minor}]
8076 @cindex special files
8077 @cindex block special files
8078 @cindex character special files
8079 Unlike the phrase ``special file type'' above, the term @dfn{special
8080 file} has a technical meaning on Unix: something that can generate or
8081 receive data. Usually this corresponds to a physical piece of hardware,
8082 e.g., a printer or a disk. (These files are typically created at
8083 system-configuration time.) The @command{mknod} command is what creates
8084 files of this type. Such devices can be read either a character at a
8085 time or a ``block'' (many characters) at a time, hence we say there are
8086 @dfn{block special} files and @dfn{character special} files.
8088 The arguments after @var{name} specify the type of file to make:
8093 @opindex p @r{for FIFO file}
8097 @opindex b @r{for block special file}
8098 for a block special file
8101 @c Don't document the `u' option -- it's just a synonym for `c'.
8102 @c Do *any* versions of mknod still use it?
8104 @opindex c @r{for character special file}
8105 @c @opindex u @r{for character special file}
8106 for a character special file
8110 When making a block or character special file, the major and minor
8111 device numbers must be given after the file type.
8112 If a major or minor device number begins with @samp{0x} or @samp{0X},
8113 it is interpreted as hexadecimal; otherwise, if it begins with @samp{0},
8114 as octal; otherwise, as decimal.
8116 The program accepts the following option. Also see @ref{Common options}.
8121 @itemx --mode=@var{mode}
8124 Set the mode of created files to @var{mode}, which is symbolic as in
8125 @command{chmod} and uses @samp{a=rw} as the point of departure.
8126 @var{mode} should specify only file permission bits.
8127 @xref{File permissions}.
8134 @node readlink invocation
8135 @section @command{readlink}: Print the referent of a symbolic link
8138 @cindex displaying value of a symbolic link
8140 @command{readlink} may work in one of two supported modes:
8146 @command{readlink} outputs the value of the given symbolic link.
8147 If @command{readlink} is invoked with an argument other than the name
8148 of a symbolic link, it produces no output and exits with a nonzero exit code.
8150 @item Canonicalize mode
8152 @command{readlink} outputs the absolute name of the given file which contains
8153 no @file{.}, @file{..} components nor any repeated separators
8154 (@file{/}) or symbolic links.
8159 readlink [@var{option}] @var{file}
8162 By default, @command{readlink} operates in readlink mode.
8164 The program accepts the following options. Also see @ref{Common options}.
8169 @itemx --canonicalize
8171 @opindex --canonicalize
8172 Activate canonicalize mode.
8173 If any component of the file name except the last one is missing or unavailable,
8174 @command{readlink} produces no output and exits with a nonzero exit code.
8177 @itemx --canonicalize-existing
8179 @opindex --canonicalize-existing
8180 Activate canonicalize mode.
8181 If any component is missing or unavailable, @command{readlink} produces
8182 no output and exits with a nonzero exit code.
8185 @itemx --canonicalize-missing
8187 @opindex --canonicalize-missing
8188 Activate canonicalize mode.
8189 If any component is missing or unavailable, @command{readlink} treats it
8195 @opindex --no-newline
8196 Do not output the trailing newline.
8206 Suppress most error messages.
8212 Report error messages.
8216 The @command{readlink} utility first appeared in OpenBSD 2.1.
8221 @node rmdir invocation
8222 @section @command{rmdir}: Remove empty directories
8225 @cindex removing empty directories
8226 @cindex directories, removing empty
8228 @command{rmdir} removes empty directories. Synopsis:
8231 rmdir [@var{option}]@dots{} @var{directory}@dots{}
8234 If any @var{directory} argument does not refer to an existing empty
8235 directory, it is an error.
8237 The program accepts the following option. Also see @ref{Common options}.
8241 @item --ignore-fail-on-non-empty
8242 @opindex --ignore-fail-on-non-empty
8243 @cindex directory deletion, ignoring failures
8244 Ignore each failure to remove a directory that is solely because
8245 the directory is non-empty.
8251 @cindex parent directories, removing
8252 Remove @var{directory}, then try to remove each component of @var{directory}.
8253 So, for example, @samp{rmdir -p a/b/c} is similar to @samp{rmdir a/b/c a/b a}.
8254 As such, it fails if any of those directories turns out not to be empty.
8255 Use the @option{--ignore-fail-on-non-empty} option to make it so such
8256 a failure does not evoke a diagnostic and does not cause @command{rmdir} to
8257 exit unsuccessfully.
8263 @cindex directory deletion, reporting
8264 Give a diagnostic for each successful removal.
8265 @var{directory} is removed.
8269 @xref{rm invocation}, for how to remove non-empty directories (recursively).
8274 @node unlink invocation
8275 @section @command{unlink}: Remove files via the unlink syscall
8278 @cindex removing files or directories (via the unlink syscall)
8280 @command{unlink} deletes a single specified file name.
8281 It is a minimalist interface to the system-provided
8282 @code{unlink} function. @xref{Deleting Files, , , libc,
8283 The GNU C Library Reference Manual}. Synopsis:
8284 It avoids the bells and whistles of the more commonly-used
8285 @command{rm} command (@pxref{rm invocation}).
8288 unlink @var{filename}
8291 On some systems @code{unlink} can be used to delete the name of a
8292 directory. On others, it can be used that way only by a privileged user.
8293 In the GNU system @code{unlink} can never delete the name of a directory.
8295 The @command{unlink} command honors the @option{--help} and
8296 @option{--version} options. To remove a file whose name begins with
8297 @samp{-}, prefix the name with @samp{./}, e.g., @samp{unlink ./--help}.
8302 @node Changing file attributes
8303 @chapter Changing file attributes
8305 @cindex changing file attributes
8306 @cindex file attributes, changing
8307 @cindex attributes, file
8309 A file is not merely its contents, a name, and a file type
8310 (@pxref{Special file types}). A file also has an owner (a user ID), a
8311 group (a group ID), permissions (what the owner can do with the file,
8312 what people in the group can do, and what everyone else can do), various
8313 timestamps, and other information. Collectively, we call these a file's
8316 These commands change file attributes.
8319 * chgrp invocation:: Change file groups.
8320 * chmod invocation:: Change access permissions.
8321 * chown invocation:: Change file owners and groups.
8322 * touch invocation:: Change file timestamps.
8326 @node chown invocation
8327 @section @command{chown}: Change file owner and group
8330 @cindex file ownership, changing
8331 @cindex group ownership, changing
8332 @cindex changing file ownership
8333 @cindex changing group ownership
8335 @command{chown} changes the user and/or group ownership of each given @var{file}
8336 to @var{new-owner} or to the user and group of an existing reference file.
8340 chown [@var{option}]@dots{} @{@var{new-owner} | --reference=@var{ref_file}@} @var{file}@dots{}
8343 If used, @var{new-owner} specifies the new owner and/or group as follows
8344 (with no embedded white space):
8347 [@var{owner}] [ : [@var{group}] ]
8354 If only an @var{owner} (a user name or numeric user ID) is given, that
8355 user is made the owner of each given file, and the files' group is not
8358 @item owner@samp{:}group
8359 If the @var{owner} is followed by a colon and a @var{group} (a
8360 group name or numeric group ID), with no spaces between them, the group
8361 ownership of the files is changed as well (to @var{group}).
8364 If a colon but no group name follows @var{owner}, that user is
8365 made the owner of the files and the group of the files is changed to
8366 @var{owner}'s login group.
8369 If the colon and following @var{group} are given, but the owner
8370 is omitted, only the group of the files is changed; in this case,
8371 @command{chown} performs the same function as @command{chgrp}.
8374 If only a colon is given, or if @var{new-owner} is empty, neither the
8375 owner nor the group is changed.
8379 Some older scripts may still use @samp{.} in place of the @samp{:} separator.
8380 @acronym{POSIX} 1003.1-2001 (@pxref{Standards conformance}) does not
8381 require support for that, but for backward compatibility @acronym{GNU}
8382 @command{chown} supports @samp{.} so long as no ambiguity results.
8383 New scripts should avoid the use of @samp{.} because it is not
8384 portable, and because it has undesirable results if the entire
8385 @var{owner@samp{.}group} happens to identify a user whose name
8388 The @command{chown} command sometimes clears the set-user-ID or
8389 set-group-ID permission bits. This behavior depends on the policy and
8390 functionality of the underlying @code{chown} system call, which may
8391 make system-dependent file mode modifications outside the control of
8392 the @command{chown} command. For example, the @command{chown} command
8393 might not affect those bits when operated as the superuser, or if the
8394 bits signify some function other than executable permission (e.g.,
8396 When in doubt, check the underlying system behavior.
8398 The program accepts the following options. Also see @ref{Common options}.
8406 @cindex changed owners, verbosely describing
8407 Verbosely describe the action for each @var{file} whose ownership
8416 @cindex error messages, omitting
8417 Do not print error messages about files whose ownership cannot be
8420 @itemx @w{@kbd{--from}=@var{old-owner}}
8422 @cindex symbolic links, changing owner
8423 Change a @var{file}'s ownership only if it has current attributes specified
8424 by @var{old-owner}. @var{old-owner} has the same form as @var{new-owner}
8426 This option is useful primarily from a security standpoint in that
8427 it narrows considerably the window of potential abuse.
8428 For example, to reflect a user ID numbering change for one user's files
8429 without an option like this, @code{root} might run
8432 find / -owner OLDUSER -print0 | xargs -0 chown -h NEWUSER
8435 But that is dangerous because the interval between when the @command{find}
8436 tests the existing file's owner and when the @command{chown} is actually run
8438 One way to narrow the gap would be to invoke chown for each file
8442 find / -owner OLDUSER -exec chown -h NEWUSER @{@} \;
8445 But that is very slow if there are many affected files.
8446 With this option, it is safer (the gap is narrower still)
8447 though still not perfect:
8450 chown -h -R --from=OLDUSER NEWUSER /
8454 @opindex --dereference
8455 @cindex symbolic links, changing owner
8457 Do not act on symbolic links themselves but rather on what they point to.
8458 This is the default.
8461 @itemx --no-dereference
8463 @opindex --no-dereference
8464 @cindex symbolic links, changing owner
8466 Act on symbolic links themselves instead of what they point to.
8467 This mode relies on the @code{lchown} system call.
8468 On systems that do not provide the @code{lchown} system call,
8469 @command{chown} fails when a file specified on the command line
8471 By default, no diagnostic is issued for symbolic links encountered
8472 during a recursive traversal, but see @option{--verbose}.
8474 @itemx --preserve-root
8475 @opindex --preserve-root
8476 @cindex root directory, disallow recursive modification
8477 Fail upon any attempt to recursively change the file system root, @file{/}.
8478 Without @option{--recursive}, this option has no effect.
8479 @xref{Treating / specially}.
8481 @itemx --no-preserve-root
8482 @opindex --no-preserve-root
8483 @cindex root directory, allow recursive modification
8484 Cancel the effect of any preceding @option{--preserve-root} option.
8485 @xref{Treating / specially}.
8487 @item --reference=@var{ref_file}
8488 @opindex --reference
8489 Change the user and group of each @var{file} to be the same as those of
8490 @var{ref_file}. If @var{ref_file} is a symbolic link, do not use the
8491 user and group of the symbolic link, but rather those of the file it
8498 Output a diagnostic for every file processed.
8499 If a symbolic link is encountered during a recursive traversal
8500 on a system without the @code{lchown} system call, and @option{--no-dereference}
8501 is in effect, then issue a diagnostic saying neither the symbolic link nor
8502 its referent is being changed.
8507 @opindex --recursive
8508 @cindex recursively changing file ownership
8509 Recursively change ownership of directories and their contents.
8512 @xref{Traversing symlinks}.
8515 @xref{Traversing symlinks}.
8518 @xref{Traversing symlinks}.
8527 # Change the owner of /u to "root".
8530 # Likewise, but also change its group to "staff".
8533 # Change the owner of /u and subfiles to "root".
8538 @node chgrp invocation
8539 @section @command{chgrp}: Change group ownership
8542 @cindex group ownership, changing
8543 @cindex changing group ownership
8545 @command{chgrp} changes the group ownership of each given @var{file}
8546 to @var{group} (which can be either a group name or a numeric group ID)
8547 or to the group of an existing reference file. Synopsis:
8550 chgrp [@var{option}]@dots{} @{@var{group} | --reference=@var{ref_file}@} @var{file}@dots{}
8553 The program accepts the following options. Also see @ref{Common options}.
8561 @cindex changed files, verbosely describing
8562 Verbosely describe the action for each @var{file} whose group actually
8571 @cindex error messages, omitting
8572 Do not print error messages about files whose group cannot be
8576 @opindex --dereference
8577 @cindex symbolic links, changing owner
8579 Do not act on symbolic links themselves but rather on what they point to.
8580 This is the default.
8583 @itemx --no-dereference
8585 @opindex --no-dereference
8586 @cindex symbolic links, changing group
8588 Act on symbolic links themselves instead of what they point to.
8589 This mode relies on the @code{lchown} system call.
8590 On systems that do not provide the @code{lchown} system call,
8591 @command{chgrp} fails when a file specified on the command line
8593 By default, no diagnostic is issued for symbolic links encountered
8594 during a recursive traversal, but see @option{--verbose}.
8596 @itemx --preserve-root
8597 @opindex --preserve-root
8598 @cindex root directory, disallow recursive modification
8599 Fail upon any attempt to recursively change the file system root, @file{/}.
8600 Without @option{--recursive}, this option has no effect.
8601 @xref{Treating / specially}.
8603 @itemx --no-preserve-root
8604 @opindex --no-preserve-root
8605 @cindex root directory, allow recursive modification
8606 Cancel the effect of any preceding @option{--preserve-root} option.
8607 @xref{Treating / specially}.
8609 @item --reference=@var{ref_file}
8610 @opindex --reference
8611 Change the group of each @var{file} to be the same as that of
8612 @var{ref_file}. If @var{ref_file} is a symbolic link, do not use the
8613 group of the symbolic link, but rather that of the file it refers to.
8619 Output a diagnostic for every file processed.
8620 If a symbolic link is encountered during a recursive traversal
8621 on a system without the @code{lchown} system call, and @option{--no-dereference}
8622 is in effect, then issue a diagnostic saying neither the symbolic link nor
8623 its referent is being changed.
8628 @opindex --recursive
8629 @cindex recursively changing group ownership
8630 Recursively change the group ownership of directories and their contents.
8633 @xref{Traversing symlinks}.
8636 @xref{Traversing symlinks}.
8639 @xref{Traversing symlinks}.
8648 # Change the group of /u to "staff".
8651 # Change the group of /u and subfiles to "staff".
8656 @node chmod invocation
8657 @section @command{chmod}: Change access permissions
8660 @cindex changing access permissions
8661 @cindex access permissions, changing
8662 @cindex permissions, changing access
8664 @command{chmod} changes the access permissions of the named files. Synopsis:
8667 chmod [@var{option}]@dots{} @{@var{mode} | --reference=@var{ref_file}@} @var{file}@dots{}
8670 @cindex symbolic links, permissions of
8671 @command{chmod} never changes the permissions of symbolic links, since
8672 the @command{chmod} system call cannot change their permissions.
8673 This is not a problem since the permissions of symbolic links are
8674 never used. However, for each symbolic link listed on the command
8675 line, @command{chmod} changes the permissions of the pointed-to file.
8676 In contrast, @command{chmod} ignores symbolic links encountered during
8677 recursive directory traversals.
8679 If used, @var{mode} specifies the new file mode bits.
8680 For details, see the section on @ref{File permissions}.
8681 If you really want @var{mode} to have a leading @samp{-}, you should
8682 use @option{--} first, e.g., @samp{chmod -- -w file}. Typically,
8683 though, @samp{chmod a-w file} is preferable, and @command{chmod -w
8684 file} (without the @option{--}) complains if it behaves differently
8685 from what @samp{chmod a-w file} would do.
8687 The program accepts the following options. Also see @ref{Common options}.
8695 Verbosely describe the action for each @var{file} whose permissions
8704 @cindex error messages, omitting
8705 Do not print error messages about files whose permissions cannot be
8708 @itemx --preserve-root
8709 @opindex --preserve-root
8710 @cindex root directory, disallow recursive modification
8711 Fail upon any attempt to recursively change the file system root, @file{/}.
8712 Without @option{--recursive}, this option has no effect.
8713 @xref{Treating / specially}.
8715 @itemx --no-preserve-root
8716 @opindex --no-preserve-root
8717 @cindex root directory, allow recursive modification
8718 Cancel the effect of any preceding @option{--preserve-root} option.
8719 @xref{Treating / specially}.
8725 Verbosely describe the action or non-action taken for every @var{file}.
8727 @item --reference=@var{ref_file}
8728 @opindex --reference
8729 Change the mode of each @var{file} to be the same as that of @var{ref_file}.
8730 @xref{File permissions}.
8731 If @var{ref_file} is a symbolic link, do not use the mode
8732 of the symbolic link, but rather that of the file it refers to.
8737 @opindex --recursive
8738 @cindex recursively changing access permissions
8739 Recursively change permissions of directories and their contents.
8746 @node touch invocation
8747 @section @command{touch}: Change file timestamps
8750 @cindex changing file timestamps
8751 @cindex file timestamps, changing
8752 @cindex timestamps, changing file
8754 @command{touch} changes the access and/or modification times of the
8755 specified files. Synopsis:
8758 touch [@var{option}]@dots{} @var{file}@dots{}
8761 @cindex empty files, creating
8762 Any @var{file} that does not exist is created empty.
8764 A @var{file} of @samp{-} causes @command{touch} to change the
8765 times of the file associated with standard output.
8767 @cindex permissions, for changing file timestamps
8768 If changing both the access and modification times to the current
8769 time, @command{touch} can change the timestamps for files that the user
8770 running it does not own but has write permission for. Otherwise, the
8771 user must own the files.
8773 Although @command{touch} provides options for changing two of the times---the
8774 times of last access and modification---of a file, there is actually
8775 a third one as well: the inode change time. This is often referred to
8776 as a file's @code{ctime}.
8777 The inode change time represents the time when the file's meta-information
8778 last changed. One common example of this is when the permissions of a
8779 file change. Changing the permissions doesn't access the file, so
8780 the atime doesn't change, nor does it modify the file, so the mtime
8781 doesn't change. Yet, something about the file itself has changed,
8782 and this must be noted somewhere. This is the job of the ctime field.
8783 This is necessary, so that, for example, a backup program can make a
8784 fresh copy of the file, including the new permissions value.
8785 Another operation that modifies a file's ctime without affecting
8786 the others is renaming. In any case, it is not possible, in normal
8787 operations, for a user to change the ctime field to a user-specified value.
8790 Time stamps assume the time zone rules specified by the @env{TZ}
8791 environment variable, or by the system default rules if @env{TZ} is
8792 not set. @xref{TZ Variable,, Specifying the Time Zone with @env{TZ},
8793 libc, The GNU C Library}. You can avoid avoid ambiguities during
8794 daylight saving transitions by using @sc{utc} time stamps.
8796 The program accepts the following options. Also see @ref{Common options}.
8802 @itemx --time=access
8806 @opindex atime@r{, changing}
8807 @opindex access @r{time, changing}
8808 @opindex use @r{time, changing}
8809 Change the access time only.
8814 @opindex --no-create
8815 Do not create files that do not exist.
8818 @itemx --date=@var{time}
8822 Use @var{time} instead of the current time. It can contain month names,
8823 time zones, @samp{am} and @samp{pm}, @samp{yesterday}, etc. For
8824 example, @option{--date="2004-02-27 14:19:13.489392193 +0530"}
8825 specifies the instant of time that is 489,392,193 nanoseconds after
8826 February 27, 2004 at 2:19:13 PM in a time zone that is 5 hours and 30
8827 minutes east of @acronym{UTC}. @xref{Date input formats}.
8828 File systems that do not support high-resolution time stamps
8829 silently ignore any excess precision here.
8833 @cindex BSD @command{touch} compatibility
8834 Ignored; for compatibility with BSD versions of @command{touch}.
8838 @itemx --time=modify
8841 @opindex mtime@r{, changing}
8842 @opindex modify @r{time, changing}
8843 Change the modification time only.
8846 @itemx --reference=@var{file}
8848 @opindex --reference
8849 Use the times of the reference @var{file} instead of the current time.
8850 If this option is combined with the @option{--date=@var{time}}
8851 (@option{-d @var{time}}) option, the reference @var{file}'s time is
8852 the origin for any relative @var{time}s given, but is otherwise ignored.
8853 For example, @samp{-r foo -d '-5 seconds'} specifies a time stamp
8854 equal to five seconds before the corresponding time stamp for @file{foo}.
8856 @item -t [[@var{CC}]@var{YY}]@var{MMDDhhmm}[.@var{ss}]
8857 Use the argument (optional four-digit or two-digit years, months,
8858 days, hours, minutes, optional seconds) instead of the current time.
8859 If the year is specified with only two digits, then @var{CC}
8860 is 20 for years in the range 0 @dots{} 68, and 19 for years in
8861 69 @dots{} 99. If no digits of the year are specified,
8862 the argument is interpreted as a date in the current year.
8866 @vindex _POSIX2_VERSION
8867 On older systems, @command{touch} supports an obsolete syntax, as follows.
8868 If no timestamp is given with any of the @option{-d}, @option{-r}, or
8869 @option{-t} options, and if there are two or more @var{file}s and the
8870 first @var{file} is of the form @samp{@var{MMDDhhmm}[@var{YY}]} and this
8871 would be a valid argument to the @option{-t} option (if the @var{YY}, if
8872 any, were moved to the front), and if the represented year
8873 is in the range 1969--1999, that argument is interpreted as the time
8874 for the other files instead of as a file name.
8875 This obsolete behavior can be enabled or disabled with the
8876 @env{_POSIX2_VERSION} environment variable (@pxref{Standards
8877 conformance}), but portable scripts should avoid commands whose
8878 behavior depends on this variable.
8879 For example, use @samp{touch ./12312359 main.c} or @samp{touch -t
8880 12312359 main.c} rather than the ambiguous @samp{touch 12312359 main.c}.
8890 No disk can hold an infinite amount of data. These commands report on
8891 how much disk storage is in use or available. (This has nothing much to
8892 do with how much @emph{main memory}, i.e., RAM, a program is using when
8893 it runs; for that, you want @command{ps} or @command{pstat} or @command{swap}
8894 or some such command.)
8897 * df invocation:: Report file system disk space usage.
8898 * du invocation:: Estimate file space usage.
8899 * stat invocation:: Report file or file system status.
8900 * sync invocation:: Synchronize memory and disk.
8905 @section @command{df}: Report file system disk space usage
8908 @cindex file system disk usage
8909 @cindex disk usage by file system
8911 @command{df} reports the amount of disk space used and available on
8912 file systems. Synopsis:
8915 df [@var{option}]@dots{} [@var{file}]@dots{}
8918 With no arguments, @command{df} reports the space used and available on all
8919 currently mounted file systems (of all types). Otherwise, @command{df}
8920 reports on the file system containing each argument @var{file}.
8922 Normally the disk space is printed in units of
8923 1024 bytes, but this can be overridden (@pxref{Block size}).
8924 Non-integer quantities are rounded up to the next higher unit.
8926 @cindex disk device file
8927 @cindex device file, disk
8928 If an argument @var{file} is a disk device file containing a mounted
8929 file system, @command{df} shows the space available on that file system
8930 rather than on the file system containing the device node (i.e., the root
8931 file system). @sc{gnu} @command{df} does not attempt to determine the disk usage
8932 on unmounted file systems, because on most kinds of systems doing so
8933 requires extremely nonportable intimate knowledge of file system
8936 The program accepts the following options. Also see @ref{Common options}.
8944 @cindex automounter file systems
8945 @cindex ignore file systems
8946 Include in the listing dummy file systems, which
8947 are omitted by default. Such file systems are typically special-purpose
8948 pseudo-file-systems, such as automounter entries.
8951 @itemx --block-size=@var{size}
8953 @opindex --block-size
8954 @cindex file system sizes
8955 Scale sizes by @var{size} before printing them (@pxref{Block size}).
8956 For example, @option{-BG} prints sizes in units of 1,073,741,824 bytes.
8962 Equivalent to @option{--si}.
8969 List inode usage information instead of block usage. An inode (short
8970 for index node) contains information about a file such as its owner,
8971 permissions, timestamps, and location on the disk.
8975 @cindex kibibytes for file system sizes
8976 Print sizes in 1024-byte blocks, overriding the default block size
8977 (@pxref{Block size}).
8978 This option is equivalent to @option{--block-size=1K}.
8984 @cindex file system types, limiting output to certain
8985 Limit the listing to local file systems. By default, remote file systems
8990 @cindex file system space, retrieving old data more quickly
8991 Do not invoke the @code{sync} system call before getting any usage data.
8992 This may make @command{df} run significantly faster on systems with many
8993 disks, but on some systems (notably SunOS) the results may be slightly
8994 out of date. This is the default.
8997 @itemx --portability
8999 @opindex --portability
9000 @cindex one-line output format
9001 @cindex @acronym{POSIX} output format
9002 @cindex portable output format
9003 @cindex output format, portable
9004 Use the @acronym{POSIX} output format. This is like the default format except
9009 The information about each file system is always printed on exactly
9010 one line; a mount device is never put on a line by itself. This means
9011 that if the mount device name is more than 20 characters long (e.g., for
9012 some network mounts), the columns are misaligned.
9015 The labels in the header output line are changed to conform to @acronym{POSIX}.
9022 @cindex file system space, retrieving current data more slowly
9023 Invoke the @code{sync} system call before getting any usage data. On
9024 some systems (notably SunOS), doing this yields more up to date results,
9025 but in general this option makes @command{df} much slower, especially when
9026 there are many or very busy file systems.
9028 @item -t @var{fstype}
9029 @itemx --type=@var{fstype}
9032 @cindex file system types, limiting output to certain
9033 Limit the listing to file systems of type @var{fstype}. Multiple
9034 file system types can be specified by giving multiple @option{-t} options.
9035 By default, nothing is omitted.
9040 @opindex --print-type
9041 @cindex file system types, printing
9042 Print each file system's type. The types printed here are the same ones
9043 you can include or exclude with @option{-t} and @option{-x}. The particular
9044 types printed are whatever is supported by the system. Here are some of
9045 the common names (this list is certainly not exhaustive):
9050 @cindex @acronym{NFS} file system type
9051 An @acronym{NFS} file system, i.e., one mounted over a network from another
9052 machine. This is the one type name which seems to be used uniformly by
9055 @item 4.2@r{, }ufs@r{, }efs@dots{}
9056 @cindex Linux file system types
9057 @cindex local file system types
9058 @opindex 4.2 @r{file system type}
9059 @opindex ufs @r{file system type}
9060 @opindex efs @r{file system type}
9061 A file system on a locally-mounted hard disk. (The system might even
9062 support more than one type here; Linux does.)
9064 @item hsfs@r{, }cdfs
9065 @cindex CD-ROM file system type
9066 @cindex High Sierra file system
9067 @opindex hsfs @r{file system type}
9068 @opindex cdfs @r{file system type}
9069 A file system on a CD-ROM drive. HP-UX uses @samp{cdfs}, most other
9070 systems use @samp{hsfs} (@samp{hs} for ``High Sierra'').
9073 @cindex PC file system
9074 @cindex DOS file system
9075 @cindex MS-DOS file system
9076 @cindex diskette file system
9078 An MS-DOS file system, usually on a diskette.
9082 @item -x @var{fstype}
9083 @itemx --exclude-type=@var{fstype}
9085 @opindex --exclude-type
9086 Limit the listing to file systems not of type @var{fstype}.
9087 Multiple file system types can be eliminated by giving multiple
9088 @option{-x} options. By default, no file system types are omitted.
9091 Ignored; for compatibility with System V versions of @command{df}.
9099 @section @command{du}: Estimate file space usage
9102 @cindex file space usage
9103 @cindex disk usage for files
9105 @command{du} reports the amount of disk space used by the specified files
9106 and for each subdirectory (of directory arguments). Synopsis:
9109 du [@var{option}]@dots{} [@var{file}]@dots{}
9112 With no arguments, @command{du} reports the disk space for the current
9113 directory. Normally the disk space is printed in units of
9114 1024 bytes, but this can be overridden (@pxref{Block size}).
9115 Non-integer quantities are rounded up to the next higher unit.
9117 The program accepts the following options. Also see @ref{Common options}.
9125 Show counts for all files, not just directories.
9127 @itemx --apparent-size
9128 @opindex --apparent-size
9129 Print apparent sizes, rather than disk usage. The apparent size of a
9130 file is the number of bytes reported by @code{wc -c} on regular files,
9131 or more generally, @code{ls -l --block-size=1} or @code{stat --format=%s}.
9132 For example, a file containing the word @samp{zoo} with no newline would,
9133 of course, have an apparent size of 3. Such a small file may require
9134 anywhere from 0 to 16 KiB or more of disk space, depending on
9135 the type and configuration of the file system on which the file resides.
9136 However, a sparse file created with this command:
9139 dd bs=1 seek=2GiB if=/dev/null of=big
9143 has an apparent size of 2 GiB, yet on most modern
9144 systems, it actually uses almost no disk space.
9150 Equivalent to @code{--apparent-size --block-size=1}.
9153 @itemx --block-size=@var{size}
9155 @opindex --block-size
9157 Scale sizes by @var{size} before printing them (@pxref{Block size}).
9158 For example, @option{-BG} prints sizes in units of 1,073,741,824 bytes.
9164 @cindex grand total of disk space
9165 Print a grand total of all arguments after all arguments have
9166 been processed. This can be used to find out the total disk usage of
9167 a given set of files or directories.
9170 @itemx --dereference-args
9172 @opindex --dereference-args
9173 Dereference symbolic links that are command line arguments.
9174 Does not affect other symbolic links. This is helpful for finding
9175 out the disk usage of directories, such as @file{/usr/tmp}, which
9176 are often symbolic links.
9178 @itemx --files0-from=@var{FILE}
9179 @opindex --files0-from=@var{FILE}
9180 @cindex including files from @command{du}
9181 Rather than processing files named on the command line, process those
9182 named in file @var{FILE}; each name is terminated by a null byte.
9183 This is useful with the @option{--total} (@option{-c}) option when
9184 the list of file names is so long that it may exceed a command line
9186 In such cases, running @command{du} via @command{xargs} is undesirable
9187 because it splits the list into pieces and makes @command{du} print a
9188 total for each sublist rather than for the entire list.
9189 One way to produce a list of null-byte-terminated file names is with @sc{gnu}
9190 @command{find}, using its @option{-print0} predicate.
9191 Do not specify any @var{FILE} on the command line when using this option.
9197 Currently, @option{-H} is the same as @option{--si},
9198 except that @option{-H} evokes a warning.
9199 This option will be changed to be equivalent to
9200 @option{--dereference-args} (@option{-D}).
9204 @cindex kibibytes for file sizes
9205 Print sizes in 1024-byte blocks, overriding the default block size
9206 (@pxref{Block size}).
9207 This option is equivalent to @option{--block-size=1K}.
9210 @itemx --count-links
9212 @opindex --count-links
9213 @cindex hard links, counting in @command{du}
9214 Count the size of all files, even if they have appeared already (as a
9218 @itemx --dereference
9220 @opindex --dereference
9221 @cindex symbolic links, dereferencing in @command{du}
9222 Dereference symbolic links (show the disk space used by the file
9223 or directory that the link points to instead of the space used by
9228 @cindex mebibytes for file sizes
9229 Print sizes in 1,048,576-byte blocks, overriding the default block size
9230 (@pxref{Block size}).
9231 This option is equivalent to @option{--block-size=1M}.
9234 @itemx --no-dereference
9236 @opindex --no-dereference
9237 @cindex symbolic links, dereferencing in @command{du}
9238 For each symbolic links encountered by @command{du},
9239 consider the disk space used by the symbolic link.
9241 @item --max-depth=@var{DEPTH}
9242 @opindex --max-depth=@var{DEPTH}
9243 @cindex limiting output of @command{du}
9244 Show the total for each directory (and file if --all) that is at
9245 most MAX_DEPTH levels down from the root of the hierarchy. The root
9246 is at level 0, so @code{du --max-depth=0} is equivalent to @code{du -s}.
9252 @cindex output null-byte-terminated lines
9253 Output a null byte at the end of each line, rather than a newline.
9254 This option enables other programs to parse the output of @command{du}
9255 even when that output would contain file names with embedded newlines.
9260 Append an SI-style abbreviation to each size, such as @samp{MB} for
9261 megabytes. Powers of 1000 are used, not 1024; @samp{MB} stands for
9262 1,000,000 bytes. Use the @option{-h} or @option{--human-readable} option if
9263 you prefer powers of 1024.
9268 @opindex --summarize
9269 Display only a total for each argument.
9272 @itemx --separate-dirs
9274 @opindex --separate-dirs
9275 Report the size of each directory separately, not including the sizes
9280 @cindex last modified dates, displaying in @command{du}
9281 Show time of the most recent modification of any file in the directory,
9282 or any of its subdirectories.
9285 @itemx --time=status
9288 @opindex ctime@r{, show the most recent}
9289 @opindex status time@r{, show the most recent}
9290 @opindex use time@r{, show the most recent}
9291 Show the most recent status change time (the @samp{ctime} in the inode) of
9292 any file in the directory, instead of the modification time.
9295 @itemx --time=access
9297 @opindex atime@r{, show the most recent}
9298 @opindex access time@r{, show the most recent}
9299 Show the most recent access time (the @samp{atime} in the inode) of
9300 any file in the directory, instead of the modification time.
9302 @item --time-style=@var{style}
9303 @opindex --time-style
9305 List timestamps in style @var{style}. This option has an effect only if
9306 the @option{--time} option is also specified. The @var{style} should
9307 be one of the following:
9312 List timestamps using @var{format}, where @var{format} is interpreted
9313 like the format argument of @command{date} (@pxref{date invocation}).
9314 For example, @option{--time-style="+%Y-%m-%d %H:%M:%S"} causes
9315 @command{du} to list timestamps like @samp{2002-03-30 23:45:56}. As
9316 with @command{date}, @var{format}'s interpretation is affected by the
9317 @env{LC_TIME} locale category.
9320 List timestamps in full using @acronym{ISO} 8601 date, time, and time zone
9321 format with nanosecond precision, e.g., @samp{2002-03-30
9322 23:45:56.477817180 -0700}. This style is equivalent to
9323 @samp{+%Y-%m-%d %H:%M:%S.%N %z}.
9326 List @acronym{ISO} 8601 date and time in minutes, e.g.,
9327 @samp{2002-03-30 23:45}. These timestamps are shorter than
9328 @samp{full-iso} timestamps, and are usually good enough for everyday
9329 work. This style is equivalent to @samp{+%Y-%m-%d %H:%M}.
9332 List @acronym{ISO} 8601 dates for timestamps, e.g., @samp{2002-03-30}.
9333 This style is equivalent to @samp{+%Y-%m-%d}.
9337 You can specify the default value of the @option{--time-style} option
9338 with the environment variable @env{TIME_STYLE}; if @env{TIME_STYLE} is not set
9339 the default style is @samp{long-iso}. For compatibility with @command{ls},
9340 if @env{TIME_STYLE} begins with @samp{+} and contains a newline,
9341 the newline and any later characters are ignored; if @env{TIME_STYLE}
9342 begins with @samp{posix-} the @samp{posix-} is ignored; and if
9343 @env{TIME_STYLE} is @samp{locale} it is ignored.
9346 @itemx --one-file-system
9348 @opindex --one-file-system
9349 @cindex one file system, restricting @command{du} to
9350 Skip directories that are on different file systems from the one that
9351 the argument being processed is on.
9353 @item --exclude=@var{PATTERN}
9354 @opindex --exclude=@var{PATTERN}
9355 @cindex excluding files from @command{du}
9356 When recursing, skip subdirectories or files matching @var{PATTERN}.
9357 For example, @code{du --exclude='*.o'} excludes files whose names
9361 @itemx --exclude-from=@var{FILE}
9362 @opindex -X @var{FILE}
9363 @opindex --exclude-from=@var{FILE}
9364 @cindex excluding files from @command{du}
9365 Like @option{--exclude}, except take the patterns to exclude from @var{FILE},
9366 one per line. If @var{FILE} is @samp{-}, take the patterns from standard
9371 @cindex NFS mounts from BSD to HP-UX
9372 On BSD systems, @command{du} reports sizes that are half the correct
9373 values for files that are NFS-mounted from HP-UX systems. On HP-UX
9374 systems, it reports sizes that are twice the correct values for
9375 files that are NFS-mounted from BSD systems. This is due to a flaw
9376 in HP-UX; it also affects the HP-UX @command{du} program.
9381 @node stat invocation
9382 @section @command{stat}: Report file or file system status
9386 @cindex file system status
9388 @command{stat} displays information about the specified file(s). Synopsis:
9391 stat [@var{option}]@dots{} [@var{file}]@dots{}
9394 With no option, @command{stat} reports all information about the given files.
9395 But it also can be used to report the information of the file systems the
9396 given files are located on. If the files are links, @command{stat} can
9397 also give information about the files the links point to.
9403 @itemx --dereference
9405 @opindex --dereference
9406 @cindex symbolic links, dereferencing in @command{stat}
9407 Change how @command{stat} treats symbolic links.
9408 With this option, @command{stat} acts on the file referenced
9409 by each symbolic link argument.
9410 Without it, @command{stat} acts on any symbolic link argument directly.
9413 @itemx --file-system
9415 @opindex --file-system
9416 @cindex file systems
9417 Report information about the file systems where the given files are located
9418 instead of information about the files themselves.
9421 @itemx --format=@var{format}
9423 @opindex --format=@var{format}
9424 @cindex output format
9425 Use @var{format} rather than the default format.
9426 @var{format} is automatically newline-terminated, so
9427 running a command like the following with two or more @var{file}
9428 operands produces a line of output for each operand:
9430 $ stat --format=%d:%i / /usr
9435 @itemx --printf=@var{format}
9436 @opindex --printf=@var{format}
9437 @cindex output format
9438 Use @var{format} rather than the default format.
9439 Like like @option{--format}, but interpret backslash escapes,
9440 and do not output a mandatory trailing newline.
9441 If you want a newline, include @samp{\n} in the @var{format}.
9442 Here's how you would use @option{--printf} to print the device
9443 and inode numbers of @file{/} and @file{/usr}:
9445 $ stat --printf='%d:%i\n' / /usr
9454 @cindex terse output
9455 Print the information in terse form, suitable for parsing by other programs.
9457 The valid format sequences for files are:
9460 @item %a - Access rights in octal
9461 @item %A - Access rights in human readable form
9462 @item %b - Number of blocks allocated (see @samp{%B})
9463 @item %B - The size in bytes of each block reported by @samp{%b}
9464 @item %d - Device number in decimal
9465 @item %D - Device number in hex
9466 @item %f - Raw mode in hex
9467 @item %F - File type
9468 @item %g - Group ID of owner
9469 @item %G - Group name of owner
9470 @item %h - Number of hard links
9471 @item %i - Inode number
9472 @item %n - File name
9473 @item %N - Quoted file name with dereference if symbolic link
9474 @item %o - I/O block size
9475 @item %s - Total size, in bytes
9476 @item %t - Major device type in hex
9477 @item %T - Minor device type in hex
9478 @item %u - User ID of owner
9479 @item %U - User name of owner
9480 @item %x - Time of last access
9481 @item %X - Time of last access as seconds since Epoch
9482 @item %y - Time of last modification
9483 @item %Y - Time of last modification as seconds since Epoch
9484 @item %z - Time of last change
9485 @item %Z - Time of last change as seconds since Epoch
9488 The valid format sequences for file systems are:
9491 @item %a - Free blocks available to non-superuser
9492 @item %b - Total data blocks in file system
9493 @item %c - Total file nodes in file system
9494 @item %d - Free file nodes in file system
9495 @item %f - Free blocks in file system
9496 @item %i - File System ID in hex
9497 @item %l - Maximum length of file names
9498 @item %n - File name
9499 @item %s - Block size (for faster transfers)
9500 @item %S - Fundamental block size (for block counts)
9501 @item %t - Type in hex
9502 @item %T - Type in human readable form
9506 Time stamps are listed according to the time zone rules specified by
9507 the @env{TZ} environment variable, or by the system default rules if
9508 @env{TZ} is not set. @xref{TZ Variable,, Specifying the Time Zone
9509 with @env{TZ}, libc, The GNU C Library}.
9515 @node sync invocation
9516 @section @command{sync}: Synchronize data on disk with memory
9519 @cindex synchronize disk and memory
9521 @cindex superblock, writing
9522 @cindex inodes, written buffered
9523 @command{sync} writes any data buffered in memory out to disk. This can
9524 include (but is not limited to) modified superblocks, modified inodes,
9525 and delayed reads and writes. This must be implemented by the kernel;
9526 The @command{sync} program does nothing but exercise the @code{sync} system
9529 @cindex crashes and corruption
9530 The kernel keeps data in memory to avoid doing (relatively slow) disk
9531 reads and writes. This improves performance, but if the computer
9532 crashes, data may be lost or the file system corrupted as a
9533 result. The @command{sync} command ensures everything in memory
9536 Any arguments are ignored, except for a lone @option{--help} or
9537 @option{--version} (@pxref{Common options}).
9543 @chapter Printing text
9545 @cindex printing text, commands for
9546 @cindex commands for printing text
9548 This section describes commands that display text strings.
9551 * echo invocation:: Print a line of text.
9552 * printf invocation:: Format and print data.
9553 * yes invocation:: Print a string until interrupted.
9557 @node echo invocation
9558 @section @command{echo}: Print a line of text
9561 @cindex displaying text
9562 @cindex printing text
9563 @cindex text, displaying
9564 @cindex arbitrary text, displaying
9566 @command{echo} writes each given @var{string} to standard output, with a
9567 space between each and a newline after the last one. Synopsis:
9570 echo [@var{option}]@dots{} [@var{string}]@dots{}
9573 The program accepts the following options. Also see @ref{Common options}.
9574 Options must precede operands, and the normally-special argument
9575 @samp{--} has no special meaning and is treated like any other
9581 Do not output the trailing newline.
9585 @cindex backslash escapes
9586 Enable interpretation of the following backslash-escaped characters in
9595 suppress trailing newline
9609 the eight-bit value that is the octal number @var{nnn}
9610 (zero to three octal digits)
9612 the eight-bit value that is the octal number @var{nnn}
9613 (one to three octal digits)
9615 the eight-bit value that is the hexadecimal number @var{hh}
9616 (one or two hexadecimal digits)
9621 @cindex backslash escapes
9622 Disable interpretation of backslash escapes in each @var{string}.
9623 This is the default. If @option{-e} and @option{-E} are both
9624 specified, the last one given takes effect.
9628 @vindex POSIXLY_CORRECT
9629 If the @env{POSIXLY_CORRECT} environment variable is set, then when
9630 @command{echo}'s first argument is not @option{-n} it outputs
9631 option-like arguments instead of treating them as options. For
9632 example, @code{echo -ne hello} outputs @samp{-ne hello} instead of
9635 @acronym{POSIX} does not require support for any options, and says
9636 that the behavior of @command{echo} is implementation-defined if any
9637 @var{string} contains a backslash or if the first argument is
9638 @option{-n}. Portable programs can use the @command{printf} command
9639 if they need to omit trailing newlines or output control characters or
9640 backslashes. @xref{printf invocation}.
9645 @node printf invocation
9646 @section @command{printf}: Format and print data
9649 @command{printf} does formatted printing of text. Synopsis:
9652 printf @var{format} [@var{argument}]@dots{}
9655 @command{printf} prints the @var{format} string, interpreting @samp{%}
9656 directives and @samp{\} escapes to format numeric and string arguments
9657 in a way that is mostly similar to the C @samp{printf} function. The
9658 differences are as follows:
9663 The @var{format} argument is reused as necessary to convert all the
9664 given @var{argument}s. For example, the command @samp{printf %s a b}
9668 Missing @var{argument}s are treated as null strings or as zeros,
9669 depending on whether the context expects a string or a number. For
9670 example, the command @samp{printf %sx%d} prints @samp{x0}.
9674 An additional escape, @samp{\c}, causes @command{printf} to produce no
9675 further output. For example, the command @samp{printf 'A%sC\cD%sF' B
9676 E} prints @samp{ABC}.
9679 The hexadecimal escape sequence @samp{\x@var{hh}} has at most two
9680 digits, as opposed to C where it can have an unlimited number of
9681 digits. For example, the command @samp{printf '\x07e'} prints two
9682 bytes, whereas the C statement @samp{printf ("\x07e")} prints just
9687 @command{printf} has an additional directive, @samp{%b}, which prints its
9688 argument string with @samp{\} escapes interpreted in the same way as in
9689 the @var{format} string, except that octal escapes are of the form
9690 @samp{\0@var{ooo}} where @var{ooo} is 0 to 3 octal digits.
9691 If a precision is also given, it limits the number of bytes printed
9692 from the converted string.
9695 Numeric arguments must be single C constants, possibly with leading
9696 @samp{+} or @samp{-}. For example, @samp{printf %.4d -3} outputs
9700 @vindex POSIXLY_CORRECT
9701 If the leading character of a numeric argument is @samp{"} or @samp{'}
9702 then its value is the numeric value of the immediately following
9703 character. Any remaining characters are silently ignored if the
9704 @env{POSIXLY_CORRECT} environment variable is set; otherwise, a
9705 warning is printed. For example, @samp{printf "%d" "'a"} outputs
9706 @samp{97} on hosts that use the @acronym{ASCII} character set, since
9707 @samp{a} has the numeric value 97 in @acronym{ASCII}.
9712 A floating-point argument must use a period before any fractional
9713 digits, but is printed according to the @env{LC_NUMERIC} category of the
9714 current locale. For example, in a locale whose radix character is a
9715 comma, the command @samp{printf %g 3.14} outputs @samp{3,14} whereas
9716 the command @samp{printf %g 3,14} is an error.
9720 @command{printf} interprets @samp{\@var{ooo}} in @var{format} as an octal number
9721 (if @var{ooo} is 1 to 3 octal digits) specifying a character to print,
9722 and @samp{\x@var{hh}} as a hexadecimal number (if @var{hh} is 1 to 2 hex
9723 digits) specifying a character to print.
9728 @cindex ISO/IEC 10646
9730 @command{printf} interprets two character syntaxes introduced in
9732 @samp{\u} for 16-bit Unicode (@acronym{ISO}/@acronym{IEC} 10646)
9733 characters, specified as
9734 four hexadecimal digits @var{hhhh}, and @samp{\U} for 32-bit Unicode
9735 characters, specified as eight hexadecimal digits @var{hhhhhhhh}.
9736 @command{printf} outputs the Unicode characters
9737 according to the @env{LC_CTYPE} locale.
9739 The processing of @samp{\u} and @samp{\U} requires a full-featured
9740 @code{iconv} facility. It is activated on systems with glibc 2.2 (or newer),
9741 or when @code{libiconv} is installed prior to this package. Otherwise
9742 @samp{\u} and @samp{\U} will print as-is.
9744 The only options are a lone @option{--help} or
9745 @option{--version}. @xref{Common options}.
9746 Options must precede operands.
9748 The Unicode character syntaxes are useful for writing strings in a locale
9749 independent way. For example, a string containing the Euro currency symbol
9752 $ /usr/local/bin/printf '\u20AC 14.95'
9756 will be output correctly in all locales supporting the Euro symbol
9757 (@acronym{ISO}-8859-15, UTF-8, and others). Similarly, a Chinese string
9760 $ /usr/local/bin/printf '\u4e2d\u6587'
9764 will be output correctly in all Chinese locales (GB2312, BIG5, UTF-8, etc).
9766 Note that in these examples, the full name of @command{printf} has been
9767 given, to distinguish it from the GNU @code{bash} built-in function
9770 For larger strings, you don't need to look up the hexadecimal code
9771 values of each character one by one. @acronym{ASCII} characters mixed with \u
9772 escape sequences is also known as the JAVA source file encoding. You can
9773 use GNU recode 3.5c (or newer) to convert strings to this encoding. Here
9774 is how to convert a piece of text into a shell script which will output
9775 this text in a locale-independent way:
9778 $ LC_CTYPE=zh_CN.big5 /usr/local/bin/printf \
9779 '\u4e2d\u6587\n' > sample.txt
9780 $ recode BIG5..JAVA < sample.txt \
9781 | sed -e "s|^|/usr/local/bin/printf '|" -e "s|$|\\\\n'|" \
9788 @node yes invocation
9789 @section @command{yes}: Print a string until interrupted
9792 @cindex repeated output of a string
9794 @command{yes} prints the command line arguments, separated by spaces and
9795 followed by a newline, forever until it is killed. If no arguments are
9796 given, it prints @samp{y} followed by a newline forever until killed.
9798 Upon a write error, @command{yes} exits with status @samp{1}.
9800 The only options are a lone @option{--help} or @option{--version}.
9801 To output an argument that begins with
9802 @samp{-}, precede it with @option{--}, e.g., @samp{yes -- --help}.
9803 @xref{Common options}.
9810 @cindex commands for exit status
9811 @cindex exit status commands
9813 This section describes commands that are primarily useful for their exit
9814 status, rather than their output. Thus, they are often used as the
9815 condition of shell @code{if} statements, or as the last command in a
9819 * false invocation:: Do nothing, unsuccessfully.
9820 * true invocation:: Do nothing, successfully.
9821 * test invocation:: Check file types and compare values.
9822 * expr invocation:: Evaluate expressions.
9826 @node false invocation
9827 @section @command{false}: Do nothing, unsuccessfully
9830 @cindex do nothing, unsuccessfully
9831 @cindex failure exit status
9832 @cindex exit status of @command{false}
9834 @command{false} does nothing except return an exit status of 1, meaning
9835 @dfn{failure}. It can be used as a place holder in shell scripts
9836 where an unsuccessful command is needed.
9837 In most modern shells, @command{false} is a built-in command, so when
9838 you use @samp{false} in a script, you're probably using the built-in
9839 command, not the one documented here.
9841 @command{false} honors the @option{--help} and @option{--version} options.
9843 This version of @command{false} is implemented as a C program, and is thus
9844 more secure and faster than a shell script implementation, and may safely
9845 be used as a dummy shell for the purpose of disabling accounts.
9847 Note that @command{false} (unlike all other programs documented herein)
9848 exits unsuccessfully, even when invoked with
9849 @option{--help} or @option{--version}.
9851 Portable programs should not assume that the exit status of
9852 @command{false} is 1, as it is greater than 1 on some
9853 non-@acronym{GNU} hosts.
9856 @node true invocation
9857 @section @command{true}: Do nothing, successfully
9860 @cindex do nothing, successfully
9862 @cindex successful exit
9863 @cindex exit status of @command{true}
9865 @command{true} does nothing except return an exit status of 0, meaning
9866 @dfn{success}. It can be used as a place holder in shell scripts
9867 where a successful command is needed, although the shell built-in
9868 command @code{:} (colon) may do the same thing faster.
9869 In most modern shells, @command{true} is a built-in command, so when
9870 you use @samp{true} in a script, you're probably using the built-in
9871 command, not the one documented here.
9873 @command{true} honors the @option{--help} and @option{--version} options.
9875 Note, however, that it is possible to cause @command{true}
9876 to exit with nonzero status: with the @option{--help} or @option{--version}
9877 option, and with standard
9878 output already closed or redirected to a file that evokes an I/O error.
9879 For example, using a Bourne-compatible shell:
9882 $ ./true --version >&-
9883 ./true: write error: Bad file number
9884 $ ./true --version > /dev/full
9885 ./true: write error: No space left on device
9888 This version of @command{true} is implemented as a C program, and is thus
9889 more secure and faster than a shell script implementation, and may safely
9890 be used as a dummy shell for the purpose of disabling accounts.
9892 @node test invocation
9893 @section @command{test}: Check file types and compare values
9896 @cindex check file types
9897 @cindex compare values
9898 @cindex expression evaluation
9900 @command{test} returns a status of 0 (true) or 1 (false) depending on the
9901 evaluation of the conditional expression @var{expr}. Each part of the
9902 expression must be a separate argument.
9904 @command{test} has file status checks, string operators, and numeric
9905 comparison operators.
9907 @command{test} has an alternate form that uses opening and closing
9908 square brackets instead a leading @samp{test}. For example, instead
9909 of @samp{test -d /}, you can write @samp{[ -d / ]}. The square
9910 brackets must be separate arguments; for example, @samp{[-d /]} does
9911 not have the desired effect. Since @samp{test @var{expr}} and @samp{[
9912 @var{expr} ]} have the same meaning, only the former form is discussed
9918 test @var{expression}
9920 [ @var{expression} ]
9925 @cindex conflicts with shell built-ins
9926 @cindex built-in shell commands, conflicts with
9927 Because most shells have a built-in @command{test} command, using an
9928 unadorned @command{test} in a script or interactively may get you
9929 different functionality than that described here.
9931 If @var{expression} is omitted, @command{test} returns false.
9932 If @var{expression} is a single argument,
9933 @command{test} returns false if the argument is null and true otherwise. The argument
9934 can be any string, including strings like @samp{-d}, @samp{-1},
9935 @samp{--}, @samp{--help}, and @samp{--version} that most other
9936 programs would treat as options. To get help and version information,
9937 invoke the commands @samp{[ --help} and @samp{[ --version}, without
9938 the usual closing brackets. @xref{Common options}.
9940 @cindex exit status of @command{test}
9944 0 if the expression is true,
9945 1 if the expression is false,
9946 2 if an error occurred.
9950 * File type tests:: -[bcdfhLpSt]
9951 * Access permission tests:: -[gkruwxOG]
9952 * File characteristic tests:: -e -s -nt -ot -ef
9953 * String tests:: -z -n = !=
9954 * Numeric tests:: -eq -ne -lt -le -gt -ge
9955 * Connectives for test:: ! -a -o
9959 @node File type tests
9960 @subsection File type tests
9962 @cindex file type tests
9964 These options test for particular types of files. (Everything's a file,
9965 but not all files are the same!)
9971 @cindex block special check
9972 True if @var{file} exists and is a block special device.
9976 @cindex character special check
9977 True if @var{file} exists and is a character special device.
9981 @cindex directory check
9982 True if @var{file} exists and is a directory.
9986 @cindex regular file check
9987 True if @var{file} exists and is a regular file.
9990 @itemx -L @var{file}
9993 @cindex symbolic link check
9994 True if @var{file} exists and is a symbolic link.
9995 Unlike all other file-related tests, this test does not dereference
9996 @var{file} if it is a symbolic link.
10000 @cindex named pipe check
10001 True if @var{file} exists and is a named pipe.
10003 @item -S @var{file}
10005 @cindex socket check
10006 True if @var{file} exists and is a socket.
10010 @cindex terminal check
10011 True if @var{fd} is a file descriptor that is associated with a
10017 @node Access permission tests
10018 @subsection Access permission tests
10020 @cindex access permission tests
10021 @cindex permission tests
10023 These options test for particular access permissions.
10027 @item -g @var{file}
10029 @cindex set-group-ID check
10030 True if @var{file} exists and has its set-group-ID bit set.
10032 @item -k @var{file}
10034 @cindex sticky bit check
10035 True if @var{file} exists and has its @dfn{sticky} bit set.
10037 @item -r @var{file}
10039 @cindex readable file check
10040 True if @var{file} exists and read permission is granted.
10042 @item -u @var{file}
10044 @cindex set-user-ID check
10045 True if @var{file} exists and has its set-user-ID bit set.
10047 @item -w @var{file}
10049 @cindex writable file check
10050 True if @var{file} exists and write permission is granted.
10052 @item -x @var{file}
10054 @cindex executable file check
10055 True if @var{file} exists and execute permission is granted
10056 (or search permission, if it is a directory).
10058 @item -O @var{file}
10060 @cindex owned by effective user ID check
10061 True if @var{file} exists and is owned by the current effective user ID.
10063 @item -G @var{file}
10065 @cindex owned by effective group ID check
10066 True if @var{file} exists and is owned by the current effective group ID.
10070 @node File characteristic tests
10071 @subsection File characteristic tests
10073 @cindex file characteristic tests
10075 These options test other file characteristics.
10079 @item -e @var{file}
10081 @cindex existence-of-file check
10082 True if @var{file} exists.
10084 @item -s @var{file}
10086 @cindex nonempty file check
10087 True if @var{file} exists and has a size greater than zero.
10089 @item @var{file1} -nt @var{file2}
10091 @cindex newer-than file check
10092 True if @var{file1} is newer (according to modification date) than
10093 @var{file2}, or if @var{file1} exists and @var{file2} does not.
10095 @item @var{file1} -ot @var{file2}
10097 @cindex older-than file check
10098 True if @var{file1} is older (according to modification date) than
10099 @var{file2}, or if @var{file2} exists and @var{file1} does not.
10101 @item @var{file1} -ef @var{file2}
10103 @cindex same file check
10104 @cindex hard link check
10105 True if @var{file1} and @var{file2} have the same device and inode
10106 numbers, i.e., if they are hard links to each other.
10112 @subsection String tests
10114 @cindex string tests
10116 These options test string characteristics. You may need to quote
10117 @var{string} arguments for the shell. For example:
10123 The quotes here prevent the wrong arguments from being passed to
10124 @command{test} if @samp{$V} is empty or contains special characters.
10128 @item -z @var{string}
10130 @cindex zero-length string check
10131 True if the length of @var{string} is zero.
10133 @item -n @var{string}
10134 @itemx @var{string}
10136 @cindex nonzero-length string check
10137 True if the length of @var{string} is nonzero.
10139 @item @var{string1} = @var{string2}
10141 @cindex equal string check
10142 True if the strings are equal.
10144 @item @var{string1} != @var{string2}
10146 @cindex not-equal string check
10147 True if the strings are not equal.
10152 @node Numeric tests
10153 @subsection Numeric tests
10155 @cindex numeric tests
10156 @cindex arithmetic tests
10158 Numeric relationals. The arguments must be entirely numeric (possibly
10159 negative), or the special expression @w{@code{-l @var{string}}}, which
10160 evaluates to the length of @var{string}.
10164 @item @var{arg1} -eq @var{arg2}
10165 @itemx @var{arg1} -ne @var{arg2}
10166 @itemx @var{arg1} -lt @var{arg2}
10167 @itemx @var{arg1} -le @var{arg2}
10168 @itemx @var{arg1} -gt @var{arg2}
10169 @itemx @var{arg1} -ge @var{arg2}
10176 These arithmetic binary operators return true if @var{arg1} is equal,
10177 not-equal, less-than, less-than-or-equal, greater-than, or
10178 greater-than-or-equal than @var{arg2}, respectively.
10185 test -1 -gt -2 && echo yes
10187 test -l abc -gt 1 && echo yes
10190 @error{} test: integer expression expected before -eq
10194 @node Connectives for test
10195 @subsection Connectives for @command{test}
10197 @cindex logical connectives
10198 @cindex connectives, logical
10200 The usual logical connectives.
10206 True if @var{expr} is false.
10208 @item @var{expr1} -a @var{expr2}
10210 @cindex logical and operator
10211 @cindex and operator
10212 True if both @var{expr1} and @var{expr2} are true.
10214 @item @var{expr1} -o @var{expr2}
10216 @cindex logical or operator
10217 @cindex or operator
10218 True if either @var{expr1} or @var{expr2} is true.
10223 @node expr invocation
10224 @section @command{expr}: Evaluate expressions
10227 @cindex expression evaluation
10228 @cindex evaluation of expressions
10230 @command{expr} evaluates an expression and writes the result on standard
10231 output. Each token of the expression must be a separate argument.
10233 Operands are either integers or strings. Integers consist of one or
10234 more decimal digits, with an optional leading @samp{-}.
10235 @command{expr} converts
10236 anything appearing in an operand position to an integer or a string
10237 depending on the operation being applied to it.
10239 Strings are not quoted for @command{expr} itself, though you may need to
10240 quote them to protect characters with special meaning to the shell,
10241 e.g., spaces. However, regardless of whether it is quoted, a string
10242 operand should not be a parenthesis or any of @command{expr}'s
10243 operators like @code{+}, so you cannot safely pass an arbitrary string
10244 @code{$str} to expr merely by quoting it to the shell. One way to
10245 work around this is to use the @sc{gnu} extension @code{+},
10246 (e.g., @code{+ "$str" = foo}); a more portable way is to use
10247 @code{@w{" $str"}} and to adjust the rest of the expression to take
10248 the leading space into account (e.g., @code{@w{" $str" = " foo"}}).
10250 You should not pass a negative integer or a string with leading
10251 @samp{-} as @command{expr}'s first argument, as it might be
10252 misinterpreted as an option; this can be avoided by parenthesization.
10253 Also, portable scripts should not use a string operand that happens to
10254 take the form of an integer; this can be worked around by inserting
10255 leading spaces as mentioned above.
10257 @cindex parentheses for grouping
10258 Operators may be given as infix symbols or prefix keywords. Parentheses
10259 may be used for grouping in the usual manner. You must quote
10260 parentheses and many operators to avoid the shell evaluating them,
10263 The only options are @option{--help} and @option{--version}. @xref{Common
10264 options}. Options must precede operands.
10266 @cindex exit status of @command{expr}
10270 0 if the expression is neither null nor 0,
10271 1 if the expression is null or 0,
10272 2 if the expression is syntactically invalid,
10273 3 if an error occurred.
10277 * String expressions:: + : match substr index length
10278 * Numeric expressions:: + - * / %
10279 * Relations for expr:: | & < <= = == != >= >
10280 * Examples of expr:: Examples.
10284 @node String expressions
10285 @subsection String expressions
10287 @cindex string expressions
10288 @cindex expressions, string
10290 @command{expr} supports pattern matching and other string operators. These
10291 have lower precedence than both the numeric and relational operators (in
10292 the next sections).
10296 @item @var{string} : @var{regex}
10297 @cindex pattern matching
10298 @cindex regular expression matching
10299 @cindex matching patterns
10300 Perform pattern matching. The arguments are converted to strings and the
10301 second is considered to be a (basic, a la GNU @code{grep}) regular
10302 expression, with a @code{^} implicitly prepended. The first argument is
10303 then matched against this regular expression.
10305 If the match succeeds and @var{regex} uses @samp{\(} and @samp{\)}, the
10306 @code{:} expression returns the part of @var{string} that matched the
10307 subexpression; otherwise, it returns the number of characters matched.
10309 If the match fails, the @code{:} operator returns the null string if
10310 @samp{\(} and @samp{\)} are used in @var{regex}, otherwise 0.
10312 @kindex \( @r{regexp operator}
10313 Only the first @samp{\( @dots{} \)} pair is relevant to the return
10314 value; additional pairs are meaningful only for grouping the regular
10315 expression operators.
10317 @kindex \+ @r{regexp operator}
10318 @kindex \? @r{regexp operator}
10319 @kindex \| @r{regexp operator}
10320 In the regular expression, @code{\+}, @code{\?}, and @code{\|} are
10321 operators which respectively match one or more, zero or one, or separate
10322 alternatives. SunOS and other @command{expr}'s treat these as regular
10323 characters. (@acronym{POSIX} allows either behavior.)
10324 @xref{Top, , Regular Expression Library, regex, Regex}, for details of
10325 regular expression syntax. Some examples are in @ref{Examples of expr}.
10327 @item match @var{string} @var{regex}
10329 An alternative way to do pattern matching. This is the same as
10330 @w{@samp{@var{string} : @var{regex}}}.
10332 @item substr @var{string} @var{position} @var{length}
10334 Returns the substring of @var{string} beginning at @var{position}
10335 with length at most @var{length}. If either @var{position} or
10336 @var{length} is negative, zero, or non-numeric, returns the null string.
10338 @item index @var{string} @var{charset}
10340 Returns the first position in @var{string} where the first character in
10341 @var{charset} was found. If no character in @var{charset} is found in
10342 @var{string}, return 0.
10344 @item length @var{string}
10346 Returns the length of @var{string}.
10348 @item + @var{token}
10350 Interpret @var{token} as a string, even if it is a keyword like @var{match}
10351 or an operator like @code{/}.
10352 This makes it possible to test @code{expr length + "$x"} or
10353 @code{expr + "$x" : '.*/\(.\)'} and have it do the right thing even if
10354 the value of @var{$x} happens to be (for example) @code{/} or @code{index}.
10355 This operator is a GNU extension. Portable shell scripts should use
10356 @code{@w{" $token"} : @w{' \(.*\)'}} instead of @code{+ "$token"}.
10360 To make @command{expr} interpret keywords as strings, you must use the
10361 @code{quote} operator.
10364 @node Numeric expressions
10365 @subsection Numeric expressions
10367 @cindex numeric expressions
10368 @cindex expressions, numeric
10370 @command{expr} supports the usual numeric operators, in order of increasing
10371 precedence. The string operators (previous section) have lower precedence,
10372 the connectives (next section) have higher.
10380 @cindex subtraction
10381 Addition and subtraction. Both arguments are converted to integers;
10382 an error occurs if this cannot be done.
10388 @cindex multiplication
10391 Multiplication, division, remainder. Both arguments are converted to
10392 integers; an error occurs if this cannot be done.
10397 @node Relations for expr
10398 @subsection Relations for @command{expr}
10400 @cindex connectives, logical
10401 @cindex logical connectives
10402 @cindex relations, numeric or string
10404 @command{expr} supports the usual logical connectives and relations. These
10405 are higher precedence than either the string or numeric operators
10406 (previous sections). Here is the list, lowest-precedence operator first.
10412 @cindex logical or operator
10413 @cindex or operator
10414 Returns its first argument if that is neither null nor zero, otherwise
10415 its second argument if it is neither null nor zero, otherwise 0. It
10416 does not evaluate its second argument if its first argument is neither
10421 @cindex logical and operator
10422 @cindex and operator
10423 Return its first argument if neither argument is null or zero, otherwise
10424 0. It does not evaluate its second argument if its first argument is
10427 @item < <= = == != >= >
10434 @cindex comparison operators
10436 Compare the arguments and return 1 if the relation is true, 0 otherwise.
10437 @code{==} is a synonym for @code{=}. @command{expr} first tries to convert
10438 both arguments to integers and do a numeric comparison; if either
10439 conversion fails, it does a lexicographic comparison using the character
10440 collating sequence specified by the @env{LC_COLLATE} locale.
10445 @node Examples of expr
10446 @subsection Examples of using @command{expr}
10448 @cindex examples of @command{expr}
10449 Here are a few examples, including quoting for shell metacharacters.
10451 To add 1 to the shell variable @code{foo}, in Bourne-compatible shells:
10454 foo=`expr $foo + 1`
10457 To print the non-directory part of the file name stored in
10458 @code{$fname}, which need not contain a @code{/}:
10461 expr $fname : '.*/\(.*\)' '|' $fname
10464 An example showing that @code{\+} is an operator:
10472 expr abc : 'a\(.\)c'
10474 expr index abcdef cz
10477 @error{} expr: syntax error
10478 expr index quote index a
10484 @chapter Redirection
10486 @cindex redirection
10487 @cindex commands for redirection
10489 Unix shells commonly provide several forms of @dfn{redirection}---ways
10490 to change the input source or output destination of a command. But one
10491 useful redirection is performed by a separate command, not by the shell;
10492 it's described here.
10495 * tee invocation:: Redirect output to multiple files.
10499 @node tee invocation
10500 @section @command{tee}: Redirect output to multiple files
10503 @cindex pipe fitting
10504 @cindex destinations, multiple output
10505 @cindex read from stdin and write to stdout and files
10507 The @command{tee} command copies standard input to standard output and also
10508 to any files given as arguments. This is useful when you want not only
10509 to send some data down a pipe, but also to save a copy. Synopsis:
10512 tee [@var{option}]@dots{} [@var{file}]@dots{}
10515 If a file being written to does not already exist, it is created. If a
10516 file being written to already exists, the data it previously contained
10517 is overwritten unless the @option{-a} option is used.
10519 A @var{file} of @samp{-} causes @command{tee} to send another copy of
10520 input to standard output, but this is typically not that useful as the
10521 copies are interleaved.
10523 The program accepts the following options. Also see @ref{Common options}.
10530 Append standard input to the given files rather than overwriting
10534 @itemx --ignore-interrupts
10536 @opindex --ignore-interrupts
10537 Ignore interrupt signals.
10544 @node File name manipulation
10545 @chapter File name manipulation
10547 @cindex file name manipulation
10548 @cindex manipulation of file names
10549 @cindex commands for file name manipulation
10551 This section describes commands that manipulate file names.
10554 * basename invocation:: Strip directory and suffix from a file name.
10555 * dirname invocation:: Strip non-directory suffix from a file name.
10556 * pathchk invocation:: Check file name portability.
10560 @node basename invocation
10561 @section @command{basename}: Strip directory and suffix from a file name
10564 @cindex strip directory and suffix from file names
10565 @cindex directory, stripping from file names
10566 @cindex suffix, stripping from file names
10567 @cindex file names, stripping directory and suffix
10568 @cindex leading directory components, stripping
10570 @command{basename} removes any leading directory components from
10571 @var{name}. Synopsis:
10574 basename @var{name} [@var{suffix}]
10577 If @var{suffix} is specified and is identical to the end of @var{name},
10578 it is removed from @var{name} as well. @command{basename} prints the
10579 result on standard output.
10581 The only options are @option{--help} and @option{--version}. @xref{Common
10582 options}. Options must precede operands.
10590 basename /usr/bin/sort
10593 basename include/stdio.h .h
10597 @node dirname invocation
10598 @section @command{dirname}: Strip non-directory suffix from a file name
10601 @cindex directory components, printing
10602 @cindex stripping non-directory suffix
10603 @cindex non-directory suffix, stripping
10605 @command{dirname} prints all but the final slash-delimited component of
10606 a string (presumably a file name). Synopsis:
10612 If @var{name} is a single component, @command{dirname} prints @samp{.}
10613 (meaning the current directory).
10615 The only options are @option{--help} and @option{--version}. @xref{Common
10623 # Output "/usr/bin".
10624 dirname /usr/bin/sort
10631 @node pathchk invocation
10632 @section @command{pathchk}: Check file name portability
10635 @cindex file names, checking validity and portability
10636 @cindex valid file names, checking for
10637 @cindex portable file names, checking for
10639 @command{pathchk} checks portability of file names. Synopsis:
10642 pathchk [@var{option}]@dots{} @var{name}@dots{}
10645 For each @var{name}, @command{pathchk} prints a message if any of
10646 these conditions is true:
10650 One of the existing directories in @var{name} does not have search
10651 (execute) permission,
10653 The length of @var{name} is larger than the maximum supported by the
10656 The length of one component of @var{name} is longer than
10657 its file system's maximum.
10660 A nonexistent @var{name} is not an error, so long a file with that
10661 name could be created under the above conditions.
10663 The program accepts the following options. Also see @ref{Common options}.
10664 Options must precede operands.
10670 Instead of performing checks based on the underlying file system,
10671 print a message if any of these conditions is true:
10675 A file name is empty.
10678 The length of a file name or one of its components exceeds the
10679 @acronym{POSIX} minimum limits for portability.
10682 A file name contains a character outside the portable file name
10683 character set, namely, the ASCII letters and digits, @samp{-},
10684 @samp{.}, @samp{/}, and @samp{_}.
10689 Print a message if a file name is empty, or if it contains a component
10690 that begins with @samp{-}.
10692 @item --portability
10693 @opindex --portability
10694 Print a message if a file name is not portable to all @acronym{POSIX}
10695 hosts. This option is equivalent to @samp{-p -P}.
10699 @cindex exit status of @command{pathchk}
10703 0 if all specified file names passed all checks,
10708 @node Working context
10709 @chapter Working context
10711 @cindex working context
10712 @cindex commands for printing the working context
10714 This section describes commands that display or alter the context in
10715 which you are working: the current directory, the terminal settings, and
10716 so forth. See also the user-related commands in the next section.
10719 * pwd invocation:: Print working directory.
10720 * stty invocation:: Print or change terminal characteristics.
10721 * printenv invocation:: Print environment variables.
10722 * tty invocation:: Print file name of terminal on standard input.
10726 @node pwd invocation
10727 @section @command{pwd}: Print working directory
10730 @cindex print name of current directory
10731 @cindex current working directory, printing
10732 @cindex working directory, printing
10734 @cindex symbolic links and @command{pwd}
10735 @command{pwd} prints the fully resolved name of the current directory.
10736 That is, all components of the printed name will be actual directory
10737 names---none will be symbolic links.
10739 @cindex conflicts with shell built-ins
10740 @cindex built-in shell commands, conflicts with
10741 Because most shells have a built-in @command{pwd} command, using an
10742 unadorned @command{pwd} in a script or interactively may get you
10743 different functionality than that described here.
10745 The only options are a lone @option{--help} or
10746 @option{--version}. @xref{Common options}.
10751 @node stty invocation
10752 @section @command{stty}: Print or change terminal characteristics
10755 @cindex change or print terminal settings
10756 @cindex terminal settings
10757 @cindex line settings of terminal
10759 @command{stty} prints or changes terminal characteristics, such as baud rate.
10763 stty [@var{option}] [@var{setting}]@dots{}
10764 stty [@var{option}]
10767 If given no line settings, @command{stty} prints the baud rate, line
10768 discipline number (on systems that support it), and line settings
10769 that have been changed from the values set by @samp{stty sane}.
10770 By default, mode reading and setting are performed on the tty line
10771 connected to standard input, although this can be modified by the
10772 @option{--file} option.
10774 @command{stty} accepts many non-option arguments that change aspects of
10775 the terminal line operation, as described below.
10777 The program accepts the following options. Also see @ref{Common options}.
10784 Print all current settings in human-readable form. This option may not
10785 be used in combination with any line settings.
10787 @item -F @var{device}
10788 @itemx --file=@var{device}
10791 Set the line opened by the file name specified in @var{device} instead of
10792 the tty line connected to standard input. This option is necessary
10793 because opening a @acronym{POSIX} tty requires use of the @code{O_NONDELAY} flag to
10794 prevent a @acronym{POSIX} tty from blocking until the carrier detect line is high if
10795 the @code{clocal} flag is not set. Hence, it is not always possible
10796 to allow the shell to open the device in the traditional manner.
10802 @cindex machine-readable @command{stty} output
10803 Print all current settings in a form that can be used as an argument to
10804 another @command{stty} command to restore the current settings. This option
10805 may not be used in combination with any line settings.
10809 Many settings can be turned off by preceding them with a @samp{-}.
10810 Such arguments are marked below with ``May be negated'' in their
10811 description. The descriptions themselves refer to the positive
10812 case, that is, when @emph{not} negated (unless stated otherwise,
10815 Some settings are not available on all @acronym{POSIX} systems, since they use
10816 extensions. Such arguments are marked below with ``Non-@acronym{POSIX}'' in their
10817 description. On non-@acronym{POSIX} systems, those or other settings also may not
10818 be available, but it's not feasible to document all the variations: just
10824 * Control:: Control settings
10825 * Input:: Input settings
10826 * Output:: Output settings
10827 * Local:: Local settings
10828 * Combination:: Combination settings
10829 * Characters:: Special characters
10830 * Special:: Special settings
10835 @subsection Control settings
10837 @cindex control settings
10843 @cindex two-way parity
10844 Generate parity bit in output and expect parity bit in input.
10850 @cindex even parity
10851 Set odd parity (even if negated). May be negated.
10858 @cindex character size
10859 @cindex eight-bit characters
10860 Set character size to 5, 6, 7, or 8 bits.
10865 Send a hangup signal when the last process closes the tty. May be
10871 Use two stop bits per character (one if negated). May be negated.
10875 Allow input to be received. May be negated.
10879 @cindex modem control
10880 Disable modem control signals. May be negated.
10884 @cindex hardware flow control
10885 @cindex flow control, hardware
10886 @cindex RTS/CTS flow control
10887 Enable RTS/CTS flow control. Non-@acronym{POSIX}. May be negated.
10892 @subsection Input settings
10894 @cindex input settings
10899 @cindex breaks, ignoring
10900 Ignore break characters. May be negated.
10904 @cindex breaks, cause interrupts
10905 Make breaks cause an interrupt signal. May be negated.
10909 @cindex parity, ignoring
10910 Ignore characters with parity errors. May be negated.
10914 @cindex parity errors, marking
10915 Mark parity errors (with a 255-0-character sequence). May be negated.
10919 Enable input parity checking. May be negated.
10923 @cindex eight-bit input
10924 Clear high (8th) bit of input characters. May be negated.
10928 @cindex newline, translating to return
10929 Translate newline to carriage return. May be negated.
10933 @cindex return, ignoring
10934 Ignore carriage return. May be negated.
10938 @cindex return, translating to newline
10939 Translate carriage return to newline. May be negated.
10943 @cindex input encoding, UTF-8
10944 Assume input characters are UTF-8 encoded. May be negated.
10948 @kindex C-s/C-q flow control
10949 @cindex XON/XOFF flow control
10950 Enable XON/XOFF flow control (that is, @kbd{CTRL-S}/@kbd{CTRL-Q}). May
10957 @cindex software flow control
10958 @cindex flow control, software
10959 Enable sending of @code{stop} character when the system input buffer
10960 is almost full, and @code{start} character when it becomes almost
10961 empty again. May be negated.
10965 @cindex uppercase, translating to lowercase
10966 Translate uppercase characters to lowercase. Non-@acronym{POSIX}. May be
10971 Allow any character to restart output (only the start character
10972 if negated). Non-@acronym{POSIX}. May be negated.
10976 @cindex beeping at input buffer full
10977 Enable beeping and not flushing input buffer if a character arrives
10978 when the input buffer is full. Non-@acronym{POSIX}. May be negated.
10983 @subsection Output settings
10985 @cindex output settings
10986 These arguments specify output-related operations.
10991 Postprocess output. May be negated.
10995 @cindex lowercase, translating to output
10996 Translate lowercase characters to uppercase. Non-@acronym{POSIX}. May be
11001 @cindex return, translating to newline
11002 Translate carriage return to newline. Non-@acronym{POSIX}. May be negated.
11006 @cindex newline, translating to crlf
11007 Translate newline to carriage return-newline. Non-@acronym{POSIX}. May be
11012 Do not print carriage returns in the first column. Non-@acronym{POSIX}.
11017 Newline performs a carriage return. Non-@acronym{POSIX}. May be negated.
11021 @cindex pad instead of timing for delaying
11022 Use fill (padding) characters instead of timing for delays. Non-@acronym{POSIX}.
11027 @cindex pad character
11028 Use delete characters for fill instead of null characters. Non-@acronym{POSIX}.
11034 Newline delay style. Non-@acronym{POSIX}.
11041 Carriage return delay style. Non-@acronym{POSIX}.
11047 @opindex tab@var{n}
11048 Horizontal tab delay style. Non-@acronym{POSIX}.
11053 Backspace delay style. Non-@acronym{POSIX}.
11058 Vertical tab delay style. Non-@acronym{POSIX}.
11063 Form feed delay style. Non-@acronym{POSIX}.
11068 @subsection Local settings
11070 @cindex local settings
11075 Enable @code{interrupt}, @code{quit}, and @code{suspend} special
11076 characters. May be negated.
11080 Enable @code{erase}, @code{kill}, @code{werase}, and @code{rprnt}
11081 special characters. May be negated.
11085 Enable non-@acronym{POSIX} special characters. May be negated.
11089 Echo input characters. May be negated.
11095 Echo @code{erase} characters as backspace-space-backspace. May be
11100 @cindex newline echoing after @code{kill}
11101 Echo a newline after a @code{kill} character. May be negated.
11105 @cindex newline, echoing
11106 Echo newline even if not echoing other characters. May be negated.
11110 @cindex flushing, disabling
11111 Disable flushing after @code{interrupt} and @code{quit} special
11112 characters. May be negated.
11116 @cindex case translation
11117 Enable input and output of uppercase characters by preceding their
11118 lowercase equivalents with @samp{\}, when @code{icanon} is set.
11119 Non-@acronym{POSIX}. May be negated.
11123 @cindex background jobs, stopping at terminal write
11124 Stop background jobs that try to write to the terminal. Non-@acronym{POSIX}.
11131 Echo erased characters backward, between @samp{\} and @samp{/}.
11132 Non-@acronym{POSIX}. May be negated.
11138 @cindex control characters, using @samp{^@var{c}}
11139 @cindex hat notation for control characters
11140 Echo control characters in hat notation (@samp{^@var{c}}) instead
11141 of literally. Non-@acronym{POSIX}. May be negated.
11147 Echo the @code{kill} special character by erasing each character on
11148 the line as indicated by the @code{echoprt} and @code{echoe} settings,
11149 instead of by the @code{echoctl} and @code{echok} settings. Non-@acronym{POSIX}.
11155 @subsection Combination settings
11157 @cindex combination settings
11158 Combination settings:
11165 Same as @code{parenb -parodd cs7}. May be negated. If negated, same
11166 as @code{-parenb cs8}.
11170 Same as @code{parenb parodd cs7}. May be negated. If negated, same
11171 as @code{-parenb cs8}.
11175 Same as @code{-icrnl -onlcr}. May be negated. If negated, same as
11176 @code{icrnl -inlcr -igncr onlcr -ocrnl -onlret}.
11180 Reset the @code{erase} and @code{kill} special characters to their default
11187 @c This is too long to write inline.
11189 cread -ignbrk brkint -inlcr -igncr icrnl -ixoff
11190 -iuclc -ixany imaxbel opost -olcuc -ocrnl onlcr
11191 -onocr -onlret -ofill -ofdel nl0 cr0 tab0 bs0 vt0
11192 ff0 isig icanon iexten echo echoe echok -echonl
11193 -noflsh -xcase -tostop -echoprt echoctl echoke
11197 and also sets all special characters to their default values.
11201 Same as @code{brkint ignpar istrip icrnl ixon opost isig icanon}, plus
11202 sets the @code{eof} and @code{eol} characters to their default values
11203 if they are the same as the @code{min} and @code{time} characters.
11204 May be negated. If negated, same as @code{raw}.
11211 -ignbrk -brkint -ignpar -parmrk -inpck -istrip
11212 -inlcr -igncr -icrnl -ixon -ixoff -iuclc -ixany
11213 -imaxbel -opost -isig -icanon -xcase min 1 time 0
11217 May be negated. If negated, same as @code{cooked}.
11221 Same as @option{-icanon}. May be negated. If negated, same as
11226 @cindex eight-bit characters
11227 Same as @code{-parenb -istrip cs8}. May be negated. If negated,
11228 same as @code{parenb istrip cs7}.
11232 Same as @option{-parenb -istrip -opost cs8}. May be negated.
11233 If negated, same as @code{parenb istrip opost cs7}.
11237 Same as @option{-ixany}. Non-@acronym{POSIX}. May be negated.
11241 Same as @code{tab0}. Non-@acronym{POSIX}. May be negated. If negated, same
11248 Same as @code{xcase iuclc olcuc}. Non-@acronym{POSIX}. May be negated.
11252 Same as @code{echoe echoctl echoke}.
11256 Same as @code{echoe echoctl echoke -ixany intr ^C erase ^? kill C-u}.
11261 @subsection Special characters
11263 @cindex special characters
11264 @cindex characters, special
11266 The special characters' default values vary from system to system.
11267 They are set with the syntax @samp{name value}, where the names are
11268 listed below and the value can be given either literally, in hat
11269 notation (@samp{^@var{c}}), or as an integer which may start with
11270 @samp{0x} to indicate hexadecimal, @samp{0} to indicate octal, or
11271 any other digit to indicate decimal.
11273 @cindex disabling special characters
11274 @kindex u@r{, and disabling special characters}
11275 For GNU stty, giving a value of @code{^-} or @code{undef} disables that
11276 special character. (This is incompatible with Ultrix @command{stty},
11277 which uses a value of @samp{u} to disable a special character. GNU
11278 @command{stty} treats a value @samp{u} like any other, namely to set that
11279 special character to @key{U}.)
11285 Send an interrupt signal.
11289 Send a quit signal.
11293 Erase the last character typed.
11297 Erase the current line.
11301 Send an end of file (terminate the input).
11309 Alternate character to end the line. Non-@acronym{POSIX}.
11313 Switch to a different shell layer. Non-@acronym{POSIX}.
11317 Restart the output after stopping it.
11325 Send a terminal stop signal.
11329 Send a terminal stop signal after flushing the input. Non-@acronym{POSIX}.
11333 Redraw the current line. Non-@acronym{POSIX}.
11337 Erase the last word typed. Non-@acronym{POSIX}.
11341 Enter the next character typed literally, even if it is a special
11342 character. Non-@acronym{POSIX}.
11347 @subsection Special settings
11349 @cindex special settings
11354 Set the minimum number of characters that will satisfy a read until
11355 the time value has expired, when @option{-icanon} is set.
11359 Set the number of tenths of a second before reads time out if the minimum
11360 number of characters have not been read, when @option{-icanon} is set.
11362 @item ispeed @var{n}
11364 Set the input speed to @var{n}.
11366 @item ospeed @var{n}
11368 Set the output speed to @var{n}.
11372 Tell the tty kernel driver that the terminal has @var{n} rows. Non-@acronym{POSIX}.
11375 @itemx columns @var{n}
11378 Tell the kernel that the terminal has @var{n} columns. Non-@acronym{POSIX}.
11384 Print the number of rows and columns that the kernel thinks the
11385 terminal has. (Systems that don't support rows and columns in the kernel
11386 typically use the environment variables @env{LINES} and @env{COLUMNS}
11387 instead; however, GNU @command{stty} does not know anything about them.)
11388 Non-@acronym{POSIX}.
11392 Use line discipline @var{n}. Non-@acronym{POSIX}.
11396 Print the terminal speed.
11399 @cindex baud rate, setting
11400 @c FIXME: Is this still true that the baud rate can't be set
11401 @c higher than 38400?
11402 Set the input and output speeds to @var{n}. @var{n} can be one
11403 of: 0 50 75 110 134 134.5 150 200 300 600 1200 1800 2400 4800 9600
11404 19200 38400 @code{exta} @code{extb}. @code{exta} is the same as
11405 19200; @code{extb} is the same as 38400. 0 hangs up the line if
11406 @option{-clocal} is set.
11410 @node printenv invocation
11411 @section @command{printenv}: Print all or some environment variables
11414 @cindex printing all or some environment variables
11415 @cindex environment variables, printing
11417 @command{printenv} prints environment variable values. Synopsis:
11420 printenv [@var{option}] [@var{variable}]@dots{}
11423 If no @var{variable}s are specified, @command{printenv} prints the value of
11424 every environment variable. Otherwise, it prints the value of each
11425 @var{variable} that is set, and nothing for those that are not set.
11427 The only options are a lone @option{--help} or @option{--version}.
11428 @xref{Common options}.
11430 @cindex exit status of @command{printenv}
11434 0 if all variables specified were found
11435 1 if at least one specified variable was not found
11436 2 if a write error occurred
11440 @node tty invocation
11441 @section @command{tty}: Print file name of terminal on standard input
11444 @cindex print terminal file name
11445 @cindex terminal file name, printing
11447 @command{tty} prints the file name of the terminal connected to its standard
11448 input. It prints @samp{not a tty} if standard input is not a terminal.
11452 tty [@var{option}]@dots{}
11455 The program accepts the following option. Also see @ref{Common options}.
11465 Print nothing; only return an exit status.
11469 @cindex exit status of @command{tty}
11473 0 if standard input is a terminal
11474 1 if standard input is not a terminal
11475 2 if given incorrect arguments
11476 3 if a write error occurs
11480 @node User information
11481 @chapter User information
11483 @cindex user information, commands for
11484 @cindex commands for printing user information
11486 This section describes commands that print user-related information:
11487 logins, groups, and so forth.
11490 * id invocation:: Print user identity.
11491 * logname invocation:: Print current login name.
11492 * whoami invocation:: Print effective user ID.
11493 * groups invocation:: Print group names a user is in.
11494 * users invocation:: Print login names of users currently logged in.
11495 * who invocation:: Print who is currently logged in.
11499 @node id invocation
11500 @section @command{id}: Print user identity
11503 @cindex real user and group IDs, printing
11504 @cindex effective user and group IDs, printing
11505 @cindex printing real and effective user and group IDs
11507 @command{id} prints information about the given user, or the process
11508 running it if no user is specified. Synopsis:
11511 id [@var{option}]@dots{} [@var{username}]
11514 By default, it prints the real user ID, real group ID, effective user ID
11515 if different from the real user ID, effective group ID if different from
11516 the real group ID, and supplemental group IDs.
11518 Each of these numeric values is preceded by an identifying string and
11519 followed by the corresponding user or group name in parentheses.
11521 The options cause @command{id} to print only part of the above information.
11522 Also see @ref{Common options}.
11529 Print only the group ID.
11535 Print only the group ID and the supplementary groups.
11541 Print the user or group name instead of the ID number. Requires
11542 @option{-u}, @option{-g}, or @option{-G}.
11548 Print the real, instead of effective, user or group ID. Requires
11549 @option{-u}, @option{-g}, or @option{-G}.
11555 Print only the user ID.
11562 @node logname invocation
11563 @section @command{logname}: Print current login name
11566 @cindex printing user's login name
11567 @cindex login name, printing
11568 @cindex user name, printing
11571 @command{logname} prints the calling user's name, as found in a
11572 system-maintained file (often @file{/var/run/utmp} or
11573 @file{/etc/utmp}), and exits with a status of 0. If there is no entry
11574 for the calling process, @command{logname} prints
11575 an error message and exits with a status of 1.
11577 The only options are @option{--help} and @option{--version}. @xref{Common
11583 @node whoami invocation
11584 @section @command{whoami}: Print effective user ID
11587 @cindex effective user ID, printing
11588 @cindex printing the effective user ID
11590 @command{whoami} prints the user name associated with the current
11591 effective user ID. It is equivalent to the command @samp{id -un}.
11593 The only options are @option{--help} and @option{--version}. @xref{Common
11599 @node groups invocation
11600 @section @command{groups}: Print group names a user is in
11603 @cindex printing groups a user is in
11604 @cindex supplementary groups, printing
11606 @command{groups} prints the names of the primary and any supplementary
11607 groups for each given @var{username}, or the current process if no names
11608 are given. If names are given, the name of each user is printed before
11609 the list of that user's groups. Synopsis:
11612 groups [@var{username}]@dots{}
11615 The group lists are equivalent to the output of the command @samp{id -Gn}.
11617 The only options are @option{--help} and @option{--version}. @xref{Common
11623 @node users invocation
11624 @section @command{users}: Print login names of users currently logged in
11627 @cindex printing current usernames
11628 @cindex usernames, printing current
11630 @cindex login sessions, printing users with
11631 @command{users} prints on a single line a blank-separated list of user
11632 names of users currently logged in to the current host. Each user name
11633 corresponds to a login session, so if a user has more than one login
11634 session, that user's name will appear the same number of times in the
11643 With no @var{file} argument, @command{users} extracts its information from
11644 a system-maintained file (often @file{/var/run/utmp} or
11645 @file{/etc/utmp}). If a file argument is given, @command{users} uses
11646 that file instead. A common choice is @file{/var/log/wtmp}.
11648 The only options are @option{--help} and @option{--version}. @xref{Common
11654 @node who invocation
11655 @section @command{who}: Print who is currently logged in
11658 @cindex printing current user information
11659 @cindex information, about current users
11661 @command{who} prints information about users who are currently logged on.
11665 @command{who} [@var{option}] [@var{file}] [am i]
11668 @cindex terminal lines, currently used
11670 @cindex remote hostname
11671 If given no non-option arguments, @command{who} prints the following
11672 information for each user currently logged on: login name, terminal
11673 line, login time, and remote hostname or X display.
11677 If given one non-option argument, @command{who} uses that instead of
11678 a default system-maintained file (often @file{/var/run/utmp} or
11679 @file{/etc/utmp}) as the name of the file containing the record of
11680 users logged on. @file{/var/log/wtmp} is commonly given as an argument
11681 to @command{who} to look at who has previously logged on.
11685 If given two non-option arguments, @command{who} prints only the entry
11686 for the user running it (determined from its standard input), preceded
11687 by the hostname. Traditionally, the two arguments given are @samp{am
11688 i}, as in @samp{who am i}.
11691 Time stamps are listed according to the time zone rules specified by
11692 the @env{TZ} environment variable, or by the system default rules if
11693 @env{TZ} is not set. @xref{TZ Variable,, Specifying the Time Zone
11694 with @env{TZ}, libc, The GNU C Library}.
11696 The program accepts the following options. Also see @ref{Common options}.
11704 Same as @samp{-b -d --login -p -r -t -T -u}.
11710 Print the date and time of last system boot.
11716 Print information corresponding to dead processes.
11722 Print column headings.
11726 Same as @samp{who am i}.
11732 Print only the login names and the number of users logged on.
11733 Overrides all other options.
11737 Ignored; for compatibility with other versions of @command{who}.
11742 After the login time, print the number of hours and minutes that the
11743 user has been idle. @samp{.} means the user was active in the last minute.
11744 @samp{old} means the user has been idle for more than 24 hours.
11750 List only the entries that correspond to processes via which the
11751 system is waiting for a user to login. The user name is always @samp{LOGIN}.
11755 Attempt to canonicalize hostnames found in utmp through a DNS lookup. This
11756 is not the default because it can cause significant delays on systems with
11757 automatic dial-up internet access.
11763 Print a line of column headings.
11774 @opindex --writable
11775 @cindex message status
11776 @pindex write@r{, allowed}
11777 After each login name print a character indicating the user's message status:
11780 @samp{+} allowing @code{write} messages
11781 @samp{-} disallowing @code{write} messages
11782 @samp{?} cannot find terminal device
11790 @node System context
11791 @chapter System context
11793 @cindex system context
11794 @cindex context, system
11795 @cindex commands for system context
11797 This section describes commands that print or change system-wide
11801 * date invocation:: Print or set system date and time.
11802 * uname invocation:: Print system information.
11803 * hostname invocation:: Print or set system name.
11804 * hostid invocation:: Print numeric host identifier.
11808 @node date invocation
11809 @section @command{date}: Print or set system date and time
11812 @cindex time, printing or setting
11813 @cindex printing the current time
11818 date [@var{option}]@dots{} [+@var{format}]
11819 date [-u|--utc|--universal] @c this avoids a newline in the output
11820 [ MMDDhhmm[[CC]YY][.ss] ]
11824 Invoking @command{date} with no @var{format} argument is equivalent to invoking
11825 it with a default format that depends on the @env{LC_TIME} locale category.
11826 In the default C locale, this format is @samp{'+%a %b %e %H:%M:%S %Z %Y'},
11827 so the output looks like @samp{Thu Mar @ 3 13:47:51 PST 2005}.
11830 Normally, @command{date} uses the time zone rules indicated by the
11831 @env{TZ} environment variable, or the system default rules if @env{TZ}
11832 is not set. @xref{TZ Variable,, Specifying the Time Zone with
11833 @env{TZ}, libc, The GNU C Library}.
11835 @findex strftime @r{and @command{date}}
11836 @cindex time formats
11837 @cindex formatting times
11838 If given an argument that starts with a @samp{+}, @command{date} prints the
11839 current date and time (or the date and time specified by the
11840 @option{--date} option, see below) in the format defined by that argument,
11841 which is similar to that of the @code{strftime} function. Except for
11842 conversion specifiers, which start with @samp{%}, characters in the
11843 format string are printed unchanged. The conversion specifiers are
11849 * Time conversion specifiers:: %[HIklMNpPrRsSTXzZ]
11850 * Date conversion specifiers:: %[aAbBcCdDeFgGhjmuUVwWxyY]
11851 * Literal conversion specifiers:: %[%nt]
11852 * Padding and other flags:: Pad with zeroes, spaces, etc.
11853 * Setting the time:: Changing the system clock.
11854 * Options for date:: Instead of the current time.
11855 * Examples of date:: Examples.
11858 @node Time conversion specifiers
11859 @subsection Time conversion specifiers
11861 @cindex time conversion specifiers
11862 @cindex conversion specifiers, time
11864 @command{date} conversion specifiers related to times.
11868 hour (@samp{00}@dots{}@samp{23})
11870 hour (@samp{01}@dots{}@samp{12})
11872 hour (@samp{ 0}@dots{}@samp{23}).
11873 This is a @acronym{GNU} extension.
11875 hour (@samp{ 1}@dots{}@samp{12}).
11876 This is a @acronym{GNU} extension.
11878 minute (@samp{00}@dots{}@samp{59})
11880 nanoseconds (@samp{000000000}@dots{}@samp{999999999}).
11881 This is a @acronym{GNU} extension.
11883 locale's equivalent of either @samp{AM} or @samp{PM};
11884 blank in many locales.
11885 Noon is treated as @samp{PM} and midnight as @samp{AM}.
11887 like @samp{%p}, except lower case.
11888 This is a @acronym{GNU} extension.
11890 locale's 12-hour clock time (e.g., @samp{11:11:04 PM})
11892 24-hour hour and minute. Same as @samp{%H:%M}.
11893 This is a @acronym{GNU} extension.
11895 @cindex epoch, seconds since
11896 @cindex seconds since the epoch
11897 @cindex beginning of time
11898 seconds since the epoch, i.e., since 1970-01-01 00:00:00 UTC.
11899 Leap seconds are not counted unless leap second support is available.
11900 @xref{%s-examples}, for examples.
11901 This is a @acronym{GNU} extension.
11903 second (@samp{00}@dots{}@samp{60}).
11904 This may be @samp{60} if leap seconds are supported.
11906 24-hour hour, minute, and second. Same as @samp{%H:%M:%S}.
11908 locale's time representation (e.g., @samp{23:13:48})
11910 @w{@acronym{RFC} 2822/@acronym{ISO} 8601} style numeric time zone
11911 (e.g., @samp{-0600} or @samp{+0530}), or nothing if no
11912 time zone is determinable. This value reflects the numeric time zone
11913 appropriate for the current time, using the time zone rules specified
11914 by the @env{TZ} environment variable.
11915 The time (and optionally, the time zone rules) can be overridden
11916 by the @option{--date} option.
11917 This is a @acronym{GNU} extension.
11919 @w{@acronym{RFC} 3339/@acronym{ISO} 8601} style numeric time zone with
11920 @samp{:} (e.g., @samp{-06:00} or @samp{+05:30}), or nothing if no time
11921 zone is determinable.
11922 This is a @acronym{GNU} extension.
11924 Numeric time zone to the nearest second with @samp{:} (e.g.,
11925 @samp{-06:00:00} or @samp{+05:30:00}), or nothing if no time zone is
11927 This is a @acronym{GNU} extension.
11929 Numeric time zone with @samp{:} using the minimum necessary precision
11930 (e.g., @samp{-06}, @samp{+05:30}, or @samp{-04:56:02}), or nothing if
11931 no time zone is determinable.
11932 This is a @acronym{GNU} extension.
11934 alphabetic time zone abbreviation (e.g., @samp{EDT}), or nothing if no
11935 time zone is determinable. See @samp{%z} for how it is determined.
11939 @node Date conversion specifiers
11940 @subsection Date conversion specifiers
11942 @cindex date conversion specifiers
11943 @cindex conversion specifiers, date
11945 @command{date} conversion specifiers related to dates.
11949 locale's abbreviated weekday name (e.g., @samp{Sun})
11951 locale's full weekday name, variable length (e.g., @samp{Sunday})
11953 locale's abbreviated month name (e.g., @samp{Jan})
11955 locale's full month name, variable length (e.g., @samp{January})
11957 locale's date and time (e.g., @samp{Thu Mar @ 3 23:05:25 2005})
11959 century. This is like @samp{%Y}, except the last two digits are omitted.
11960 For example, it is @samp{20} if @samp{%Y} is @samp{2000},
11961 and is @samp{-0} if @samp{%Y} is @samp{-001}.
11962 It is normally at least two characters, but it may be more.
11964 day of month (e.g., @samp{01})
11966 date; same as @samp{%m/%d/%y}
11968 day of month, space padded; same as @samp{%_d}
11970 full date in @acronym{ISO} 8601 format; same as @samp{%Y-%m-%d}.
11971 This is a good choice for a date format, as it is standard and
11972 is easy to sort in the usual case where years are in the range
11974 This is a @acronym{GNU} extension.
11976 year corresponding to the @acronym{ISO} week number, but without the century
11977 (range @samp{00} through @samp{99}). This has the same format and value
11978 as @samp{%y}, except that if the @acronym{ISO} week number (see
11980 to the previous or next year, that year is used instead.
11981 This is a @acronym{GNU} extension.
11983 year corresponding to the @acronym{ISO} week number. This has the
11984 same format and value as @samp{%Y}, except that if the @acronym{ISO}
11986 @samp{%V}) belongs to the previous or next year, that year is used
11988 It is normally useful only if @samp{%V} is also used;
11989 for example, the format @samp{%G-%m-%d} is probably a mistake,
11990 since it combines the ISO week number year with the conventional month and day.
11991 This is a @acronym{GNU} extension.
11995 day of year (@samp{001}@dots{}@samp{366})
11997 month (@samp{01}@dots{}@samp{12})
11999 day of week (@samp{1}@dots{}@samp{7}) with @samp{1} corresponding to Monday
12001 week number of year, with Sunday as the first day of the week
12002 (@samp{00}@dots{}@samp{53}).
12003 Days in a new year preceding the first Sunday are in week zero.
12005 @acronym{ISO} week number, that is, the
12006 week number of year, with Monday as the first day of the week
12007 (@samp{01}@dots{}@samp{53}).
12008 If the week containing January 1 has four or more days in
12009 the new year, then it is considered week 1; otherwise, it is week 53 of
12010 the previous year, and the next week is week 1. (See the @acronym{ISO} 8601
12013 day of week (@samp{0}@dots{}@samp{6}) with 0 corresponding to Sunday
12015 week number of year, with Monday as first day of week
12016 (@samp{00}@dots{}@samp{53}).
12017 Days in a new year preceding the first Monday are in week zero.
12019 locale's date representation (e.g., @samp{12/31/99})
12021 last two digits of year (@samp{00}@dots{}@samp{99})
12023 year. This is normally at least four characters, but it may be more.
12024 Year @samp{0000} precedes year @samp{0001}, and year @samp{-001}
12025 precedes year @samp{0000}.
12029 @node Literal conversion specifiers
12030 @subsection Literal conversion specifiers
12032 @cindex literal conversion specifiers
12033 @cindex conversion specifiers, literal
12035 @command{date} conversion specifiers that produce literal strings.
12047 @node Padding and other flags
12048 @subsection Padding and other flags
12050 @cindex numeric field padding
12051 @cindex padding of numeric fields
12052 @cindex fields, padding numeric
12054 Unless otherwise specified, @command{date} normally pads numeric fields
12055 with zeroes, so that, for
12056 example, numeric months are always output as two digits.
12057 Seconds since the epoch are not padded, though,
12058 since there is no natural width for them.
12060 As a @acronym{GNU} extension, @command{date} recognizes any of the
12061 following optional flags after the @samp{%}:
12065 (hyphen) Do not pad the field; useful if the output is intended for
12068 (underscore) Pad with spaces; useful if you need a fixed
12069 number of characters in the output, but zeroes are too distracting.
12071 (zero) Pad with zeros even if the conversion specifier
12072 would normally pad with spaces.
12074 Use upper case characters if possible.
12076 Use opposite case characters if possible.
12077 A field that is normally upper case becomes lower case, and vice versa.
12081 Here are some examples of padding:
12084 date +%d/%m -d "Feb 1"
12086 date +%-d/%-m -d "Feb 1"
12088 date +%_d/%_m -d "Feb 1"
12092 As a @acronym{GNU} extension, you can specify the field width
12093 (after any flag, if present) as a decimal number. If the natural size of the
12094 output is of the field has less than the specified number of characters,
12095 the result is written right adjusted and padded to the given
12096 size. For example, @samp{%9B} prints the right adjusted month name in
12097 a field of width 9.
12099 An optional modifier can follow the optional flag and width
12100 specification. The modifiers are:
12104 Use the locale's alternate representation for date and time. This
12105 modifier applies to the @samp{%c}, @samp{%C}, @samp{%x}, @samp{%X},
12106 @samp{%y} and @samp{%Y} conversion specifiers. In a Japanese locale, for
12107 example, @samp{%Ex} might yield a date format based on the Japanese
12111 Use the locale's alternate numeric symbols for numbers. This modifier
12112 applies only to numeric conversion specifiers.
12115 If the format supports the modifier but no alternate representation
12116 is available, it is ignored.
12119 @node Setting the time
12120 @subsection Setting the time
12122 @cindex setting the time
12123 @cindex time setting
12124 @cindex appropriate privileges
12126 If given an argument that does not start with @samp{+}, @command{date} sets
12127 the system clock to the date and time specified by that argument (as
12128 described below). You must have appropriate privileges to set the
12129 system clock. The @option{--date} and @option{--set} options may not be
12130 used with such an argument. The @option{--universal} option may be used
12131 with such an argument to indicate that the specified date and time are
12132 relative to Coordinated Universal Time rather than to the local time
12135 The argument must consist entirely of digits, which have the following
12148 first two digits of year (optional)
12150 last two digits of year (optional)
12155 The @option{--set} option also sets the system clock; see the next section.
12158 @node Options for date
12159 @subsection Options for @command{date}
12161 @cindex @command{date} options
12162 @cindex options for @command{date}
12164 The program accepts the following options. Also see @ref{Common options}.
12168 @item -d @var{datestr}
12169 @itemx --date=@var{datestr}
12172 @cindex parsing date strings
12173 @cindex date strings, parsing
12174 @cindex arbitrary date strings, parsing
12177 @opindex next @var{day}
12178 @opindex last @var{day}
12179 Display the date and time specified in @var{datestr} instead of the
12180 current date and time. @var{datestr} can be in almost any common
12181 format. It can contain month names, time zones, @samp{am} and @samp{pm},
12182 @samp{yesterday}, etc. For example, @option{--date="2004-02-27
12183 14:19:13.489392193 +0530"} specifies the instant of time that is
12184 489,392,193 nanoseconds after February 27, 2004 at 2:19:13 PM in a
12185 time zone that is 5 hours and 30 minutes east of @acronym{UTC}.
12186 @xref{Date input formats}.
12188 @item -f @var{datefile}
12189 @itemx --file=@var{datefile}
12192 Parse each line in @var{datefile} as with @option{-d} and display the
12193 resulting date and time. If @var{datefile} is @samp{-}, use standard
12194 input. This is useful when you have many dates to process, because the
12195 system overhead of starting up the @command{date} executable many times can
12198 @item -r @var{file}
12199 @itemx --reference=@var{file}
12201 @opindex --reference
12202 Display the date and time of the last modification of @var{file},
12203 instead of the current date and time.
12210 @opindex --rfc-2822
12211 Display the date and time using the format @samp{%a, %d %b %Y %H:%M:%S
12212 %z}, evaluated in the C locale so abbreviations are always in English.
12216 Fri, 09 Sep 2005 13:51:39 -0700
12219 This format conforms to
12220 @uref{ftp://ftp.rfc-editor.org/in-notes/rfc2822.txt, Internet
12221 @acronym{RFCs} 2822} and
12222 @uref{ftp://ftp.rfc-editor.org/in-notes/rfc822.txt, 822}, the
12223 current and previous standards for Internet email.
12225 @item --rfc-3339=@var{timespec}
12226 @opindex --rfc-3339=@var{timespec}
12227 Display the date using a format specified by
12228 @uref{ftp://ftp.rfc-editor.org/in-notes/rfc3339.txt, Internet
12229 @acronym{RFC} 3339}. This is a subset of the @acronym{ISO} 8601
12230 format, except that it also permits applications to use a space rather
12231 than a @samp{T} to separate dates from times. Unlike the other
12232 standard formats, @acronym{RFC} 3339 format is always suitable as
12233 input for the @option{--date} (@option{-d}) and @option{--file}
12234 (@option{-f}) options, regardless of the current locale.
12236 The argument @var{timespec} specifies how much of the time to include.
12237 It can be one of the following:
12241 Print just the full-date, e.g., @samp{2005-09-14}.
12242 This is equivalent to the format @samp{%Y-%m-%d}.
12245 Print the full-date and full-time separated by a space, e.g.,
12246 @samp{2005-09-14 00:56:06+05:30}. The output ends with a numeric
12247 time-offset; here the @samp{+05:30} means that local time is five
12248 hours and thirty minutes east of @acronym{UTC}. This is equivalent to
12249 the format @samp{%Y-%m-%d %H:%M:%S%:z}.
12252 Like @samp{seconds}, but also print nanoseconds, e.g.,
12253 @samp{2005-09-14 00:56:06.998458565+05:30}.
12254 This is equivalent to the format @samp{%Y-%m-%d %H:%M:%S.%N%:z}.
12258 @item -s @var{datestr}
12259 @itemx --set=@var{datestr}
12262 Set the date and time to @var{datestr}. See @option{-d} above.
12269 @opindex --universal
12270 @cindex Coordinated Universal Time
12272 @cindex Greenwich Mean Time
12275 Use Coordinated Universal Time (@acronym{UTC}) by operating as if the
12276 @env{TZ} environment variable were set to the string @samp{UTC0}.
12278 Universal Time is often called ``Greenwich Mean Time'' (@sc{gmt}) for
12279 historical reasons.
12283 @node Examples of date
12284 @subsection Examples of @command{date}
12286 @cindex examples of @command{date}
12288 Here are a few examples. Also see the documentation for the @option{-d}
12289 option in the previous section.
12294 To print the date of the day before yesterday:
12297 date --date='2 days ago'
12301 To print the date of the day three months and one day hence:
12304 date --date='3 months 1 day'
12308 To print the day of year of Christmas in the current year:
12311 date --date='25 Dec' +%j
12315 To print the current full month name and the day of the month:
12321 But this may not be what you want because for the first nine days of
12322 the month, the @samp{%d} expands to a zero-padded two-digit field,
12323 for example @samp{date -d 1may '+%B %d'} will print @samp{May 01}.
12326 To print a date without the leading zero for one-digit days
12327 of the month, you can use the (@acronym{GNU} extension)
12328 @samp{-} flag to suppress
12329 the padding altogether:
12332 date -d 1may '+%B %-d
12336 To print the current date and time in the format required by many
12337 non-@acronym{GNU} versions of @command{date} when setting the system clock:
12340 date +%m%d%H%M%Y.%S
12344 To set the system clock forward by two minutes:
12347 date --set='+2 minutes'
12351 To print the date in @acronym{RFC} 2822 format,
12352 use @samp{date --rfc-2822}. Here is some example output:
12355 Fri, 09 Sep 2005 13:51:39 -0700
12358 @anchor{%s-examples}
12360 To convert a date string to the number of seconds since the epoch
12361 (which is 1970-01-01 00:00:00 UTC), use the @option{--date} option with
12362 the @samp{%s} format. That can be useful in sorting and/or graphing
12363 and/or comparing data by date. The following command outputs the
12364 number of the seconds since the epoch for the time two minutes after the
12368 date --date='1970-01-01 00:02:00 +0000' +%s
12372 If you do not specify time zone information in the date string,
12373 @command{date} uses your computer's idea of the time zone when
12374 interpreting the string. For example, if your computer's time zone is
12375 that of Cambridge, Massachusetts, which was then 5 hours (i.e., 18,000
12376 seconds) behind UTC:
12379 # local time zone used
12380 date --date='1970-01-01 00:02:00' +%s
12385 If you're sorting or graphing dated data, your raw date values may be
12386 represented as seconds since the epoch. But few people can look at
12387 the date @samp{946684800} and casually note ``Oh, that's the first second
12388 of the year 2000 in Greenwich, England.''
12391 date --date='2000-01-01 UTC' +%s
12395 An alternative is to use the @option{--utc} (@option{-u}) option.
12396 Then you may omit @samp{UTC} from the date string. Although this
12397 produces the same result for @samp{%s} and many other format sequences,
12398 with a time zone offset different from zero, it would give a different
12399 result for zone-dependent formats like @samp{%z}.
12402 date -u --date=2000-01-01 +%s
12406 To convert such an unwieldy number of seconds back to
12407 a more readable form, use a command like this:
12410 # local time zone used
12411 date -d '1970-01-01 UTC 946684800 seconds' +"%Y-%m-%d %T %z"
12412 1999-12-31 19:00:00 -0500
12415 Often it is better to output UTC-relative date and time:
12418 date -u -d '1970-01-01 946684800 seconds' +"%Y-%m-%d %T %z"
12419 2000-01-01 00:00:00 +0000
12425 @node uname invocation
12426 @section @command{uname}: Print system information
12429 @cindex print system information
12430 @cindex system information, printing
12432 @command{uname} prints information about the machine and operating system
12433 it is run on. If no options are given, @command{uname} acts as if the
12434 @option{-s} option were given. Synopsis:
12437 uname [@var{option}]@dots{}
12440 If multiple options or @option{-a} are given, the selected information is
12441 printed in this order:
12444 @var{kernel-name} @var{nodename} @var{kernel-release} @var{kernel-version}
12445 @var{machine} @var{processor} @var{hardware-platform} @var{operating-system}
12448 The information may contain internal spaces, so such output cannot be
12449 parsed reliably. In the following example, @var{release} is
12450 @samp{2.2.18ss.e820-bda652a #4 SMP Tue Jun 5 11:24:08 PDT 2001}:
12454 @result{} Linux dum 2.2.18 #4 SMP Tue Jun 5 11:24:08 PDT 2001 i686 unknown unknown GNU/Linux
12458 The program accepts the following options. Also see @ref{Common options}.
12466 Print all of the below information, except omit the processor type
12467 and the hardware platform name if they are unknown.
12470 @itemx --hardware-platform
12472 @opindex --hardware-platform
12473 @cindex implementation, hardware
12474 @cindex hardware platform
12475 @cindex platform, hardware
12476 Print the hardware platform name
12477 (sometimes called the hardware implementation).
12478 Print @samp{unknown} if the kernel does not make this information
12479 easily available, as is the case with Linux kernels.
12485 @cindex machine type
12486 @cindex hardware class
12487 @cindex hardware type
12488 Print the machine hardware name (sometimes called the hardware class
12494 @opindex --nodename
12497 @cindex network node name
12498 Print the network node hostname.
12503 @opindex --processor
12504 @cindex host processor type
12505 Print the processor type (sometimes called the instruction set
12506 architecture or ISA).
12507 Print @samp{unknown} if the kernel does not make this information
12508 easily available, as is the case with Linux kernels.
12511 @itemx --operating-system
12513 @opindex --operating-system
12514 @cindex operating system name
12515 Print the name of the operating system.
12518 @itemx --kernel-release
12520 @opindex --kernel-release
12521 @cindex kernel release
12522 @cindex release of kernel
12523 Print the kernel release.
12526 @itemx --kernel-name
12528 @opindex --kernel-name
12529 @cindex kernel name
12530 @cindex name of kernel
12531 Print the kernel name.
12532 @acronym{POSIX} 1003.1-2001 (@pxref{Standards conformance}) calls this
12533 ``the implementation of the operating system'', because the
12534 @acronym{POSIX} specification itself has no notion of ``kernel''.
12535 The kernel name might be the same as the operating system name printed
12536 by the @option{-o} or @option{--operating-system} option, but it might
12537 differ. Some operating systems (e.g., FreeBSD, HP-UX) have the same
12538 name as their underlying kernels; others (e.g., GNU/Linux, Solaris)
12542 @itemx --kernel-version
12544 @opindex --kernel-version
12545 @cindex kernel version
12546 @cindex version of kernel
12547 Print the kernel version.
12554 @node hostname invocation
12555 @section @command{hostname}: Print or set system name
12558 @cindex setting the hostname
12559 @cindex printing the hostname
12560 @cindex system name, printing
12561 @cindex appropriate privileges
12563 With no arguments, @command{hostname} prints the name of the current host
12564 system. With one argument, it sets the current host name to the
12565 specified string. You must have appropriate privileges to set the host
12569 hostname [@var{name}]
12572 The only options are @option{--help} and @option{--version}. @xref{Common
12578 @node hostid invocation
12579 @section @command{hostid}: Print numeric host identifier.
12582 @cindex printing the host identifier
12584 @command{hostid} prints the numeric identifier of the current host
12585 in hexadecimal. This command accepts no arguments.
12586 The only options are @option{--help} and @option{--version}.
12587 @xref{Common options}.
12589 For example, here's what it prints on one system I use:
12596 On that system, the 32-bit quantity happens to be closely
12597 related to the system's Internet address, but that isn't always
12603 @node Modified command invocation
12604 @chapter Modified command invocation
12606 @cindex modified command invocation
12607 @cindex invocation of commands, modified
12608 @cindex commands for invoking other commands
12610 This section describes commands that run other commands in some context
12611 different than the current one: a modified environment, as a different
12615 * chroot invocation:: Modify the root directory.
12616 * env invocation:: Modify environment variables.
12617 * nice invocation:: Modify niceness.
12618 * nohup invocation:: Immunize to hangups.
12619 * su invocation:: Modify user and group ID.
12623 @node chroot invocation
12624 @section @command{chroot}: Run a command with a different root directory
12627 @cindex running a program in a specified root directory
12628 @cindex root directory, running a program in a specified
12630 @command{chroot} runs a command with a specified root directory.
12631 On many systems, only the super-user can do this.
12635 chroot @var{newroot} [@var{command} [@var{args}]@dots{}]
12636 chroot @var{option}
12639 Ordinarily, file names are looked up starting at the root of the
12640 directory structure, i.e., @file{/}. @command{chroot} changes the root to
12641 the directory @var{newroot} (which must exist) and then runs
12642 @var{command} with optional @var{args}. If @var{command} is not
12643 specified, the default is the value of the @env{SHELL} environment
12644 variable or @command{/bin/sh} if not set, invoked with the @option{-i} option.
12645 @var{command} must not be a special built-in utility
12646 (@pxref{Special built-in utilities}).
12648 The only options are @option{--help} and @option{--version}. @xref{Common
12649 options}. Options must precede operands.
12651 Here are a few tips to help avoid common problems in using chroot.
12652 To start with a simple example, make @var{command} refer to a statically
12653 linked binary. If you were to use a dynamically linked executable, then
12654 you'd have to arrange to have the shared libraries in the right place under
12655 your new root directory.
12657 For example, if you create a statically linked @command{ls} executable,
12658 and put it in @file{/tmp/empty}, you can run this command as root:
12661 $ chroot /tmp/empty /ls -Rl /
12664 Then you'll see output like this:
12669 -rwxr-xr-x 1 0 0 1041745 Aug 16 11:17 ls
12672 If you want to use a dynamically linked executable, say @command{bash},
12673 then first run @samp{ldd bash} to see what shared objects it needs.
12674 Then, in addition to copying the actual binary, also copy the listed
12675 files to the required positions under your intended new root directory.
12676 Finally, if the executable requires any other files (e.g., data, state,
12677 device files), copy them into place, too.
12679 @cindex exit status of @command{chroot}
12683 1 if @command{chroot} itself fails
12684 126 if @var{command} is found but cannot be invoked
12685 127 if @var{command} cannot be found
12686 the exit status of @var{command} otherwise
12690 @node env invocation
12691 @section @command{env}: Run a command in a modified environment
12694 @cindex environment, running a program in a modified
12695 @cindex modified environment, running a program in a
12696 @cindex running a program in a modified environment
12698 @command{env} runs a command with a modified environment. Synopses:
12701 env [@var{option}]@dots{} [@var{name}=@var{value}]@dots{} @c
12702 [@var{command} [@var{args}]@dots{}]
12706 Operands of the form @samp{@var{variable}=@var{value}} set
12707 the environment variable @var{variable} to value @var{value}.
12708 @var{value} may be empty (@samp{@var{variable}=}). Setting a variable
12709 to an empty value is different from unsetting it.
12710 These operands are evaluated left-to-right, so if two operands
12711 mention the same variable the earlier is ignored.
12713 Environment variable names can be empty, and can contain any
12714 characters other than @samp{=} and the null character (@acronym{ASCII}
12715 @sc{nul}). However, it is wise to limit yourself to names that
12716 consist solely of underscores, digits, and @acronym{ASCII} letters,
12717 and that begin with a non-digit, as applications like the shell do not
12718 work well with other names.
12721 The first operand that does not contain the character @samp{=}
12722 specifies the program to invoke; it is
12723 searched for according to the @env{PATH} environment variable. Any
12724 remaining arguments are passed as arguments to that program.
12725 The program should not be a special built-in utility
12726 (@pxref{Special built-in utilities}).
12728 @cindex environment, printing
12730 If no command name is specified following the environment
12731 specifications, the resulting environment is printed. This is like
12732 specifying the @command{printenv} program.
12734 The program accepts the following options. Also see @ref{Common options}.
12735 Options must precede operands.
12739 @item -u @var{name}
12740 @itemx --unset=@var{name}
12743 Remove variable @var{name} from the environment, if it was in the
12748 @itemx --ignore-environment
12751 @opindex --ignore-environment
12752 Start with an empty environment, ignoring the inherited environment.
12756 @cindex exit status of @command{env}
12760 0 if no @var{command} is specified and the environment is output
12761 1 if @command{env} itself fails
12762 126 if @var{command} is found but cannot be invoked
12763 127 if @var{command} cannot be found
12764 the exit status of @var{command} otherwise
12768 @node nice invocation
12769 @section @command{nice}: Run a command with modified niceness
12773 @cindex scheduling, affecting
12774 @cindex appropriate privileges
12776 @command{nice} prints or modifies a process's @dfn{niceness},
12777 a parameter that affects whether the process is scheduled favorably.
12781 nice [@var{option}]@dots{} [@var{command} [@var{arg}]@dots{}]
12784 If no arguments are given, @command{nice} prints the current niceness.
12785 Otherwise, @command{nice} runs the given @var{command} with its
12786 niceness adjusted. By default, its niceness is incremented by 10.
12788 Nicenesses range at least from @minus{}20 (resulting in the most
12789 favorable scheduling) through 19 (the least favorable). Some systems
12790 may have a wider range of nicenesses; conversely, other systems may
12791 enforce more restrictive limits. An attempt to set the niceness
12792 outside the supported range is treated as an attempt to use the
12793 minimum or maximum supported value.
12795 A niceness should not be confused with a scheduling priority, which
12796 lets applications determine the order in which threads are scheduled
12797 to run. Unlike a priority, a niceness is merely advice to the
12798 scheduler, which the scheduler is free to ignore. Also, as a point of
12799 terminology, @acronym{POSIX} defines the behavior of @command{nice} in
12800 terms of a @dfn{nice value}, which is the nonnegative difference
12801 between a niceness and the minimum niceness. Though @command{nice}
12802 conforms to @acronym{POSIX}, its documentation and diagnostics use the
12803 term ``niceness'' for compatibility with historical practice.
12805 @var{command} must not be a special built-in utility (@pxref{Special
12806 built-in utilities}).
12808 @cindex conflicts with shell built-ins
12809 @cindex built-in shell commands, conflicts with
12810 Because many shells have a built-in @command{nice} command, using an
12811 unadorned @command{nice} in a script or interactively may get you
12812 different functionality than that described here.
12814 The program accepts the following option. Also see @ref{Common options}.
12815 Options must precede operands.
12818 @item -n @var{adjustment}
12819 @itemx --adjustment=@var{adjustment}
12821 @opindex --adjustment
12822 Add @var{adjustment} instead of 10 to the command's niceness. If
12823 @var{adjustment} is negative and you lack appropriate privileges,
12824 @command{nice} issues a warning but otherwise acts as if you specified
12827 For compatibility @command{nice} also supports an obsolete
12828 option syntax @option{-@var{adjustment}}. New scripts should use
12829 @option{-n @var{adjustment}} instead.
12833 @cindex exit status of @command{nice}
12837 0 if no @var{command} is specified and the niceness is output
12838 1 if @command{nice} itself fails
12839 126 if @var{command} is found but cannot be invoked
12840 127 if @var{command} cannot be found
12841 the exit status of @var{command} otherwise
12844 It is sometimes useful to run a non-interactive program with reduced niceness.
12847 $ nice factor 4611686018427387903
12850 Since @command{nice} prints the current niceness,
12851 you can invoke it through itself to demonstrate how it works.
12853 The default behavior is to increase the niceness by @samp{10}:
12864 The @var{adjustment} is relative to the current niceness. In the
12865 next example, the first @command{nice} invocation runs the second one
12866 with niceness 10, and it in turn runs the final one with a niceness
12870 $ nice nice -n 3 nice
12874 Specifying a niceness larger than the supported range
12875 is the same as specifying the maximum supported value:
12878 $ nice -n 10000000000 nice
12882 Only a privileged user may run a process with lower niceness:
12886 nice: cannot set niceness: Permission denied
12888 $ sudo nice -n -1 nice
12893 @node nohup invocation
12894 @section @command{nohup}: Run a command immune to hangups
12897 @cindex hangups, immunity to
12898 @cindex immunity to hangups
12899 @cindex logging out and continuing to run
12902 @command{nohup} runs the given @var{command} with hangup signals ignored,
12903 so that the command can continue running in the background after you log
12907 nohup @var{command} [@var{arg}]@dots{}
12910 If standard input is a terminal, it is redirected from
12911 @file{/dev/null} so that terminal sessions do not mistakenly consider
12912 the terminal to be used by the command. This is a @acronym{GNU}
12913 extension; programs intended to be portable to non-@acronym{GNU} hosts
12914 should use @samp{nohup @var{command} [@var{arg}]@dots{} </dev/null}
12918 If standard output is a terminal, the command's standard output is appended
12919 to the file @file{nohup.out}; if that cannot be written to, it is appended
12920 to the file @file{$HOME/nohup.out}; and if that cannot be written to, the
12921 command is not run.
12922 Any @file{nohup.out} or @file{$HOME/nohup.out} file created by
12923 @command{nohup} is made readable and writable only to the user,
12924 regardless of the current umask settings.
12926 If standard error is a terminal, it is redirected to the same file
12927 descriptor as the (possibly-redirected) standard output.
12929 @command{nohup} does not automatically put the command it runs in the
12930 background; you must do that explicitly, by ending the command line
12931 with an @samp{&}. Also, @command{nohup} does not alter the
12932 niceness of @var{command}; use @command{nice} for that,
12933 e.g., @samp{nohup nice @var{command}}.
12935 @var{command} must not be a special built-in utility (@pxref{Special
12936 built-in utilities}).
12938 The only options are @option{--help} and @option{--version}. @xref{Common
12939 options}. Options must precede operands.
12941 @cindex exit status of @command{nohup}
12945 126 if @var{command} is found but cannot be invoked
12946 127 if @command{nohup} itself fails or if @var{command} cannot be found
12947 the exit status of @var{command} otherwise
12951 @node su invocation
12952 @section @command{su}: Run a command with substitute user and group ID
12955 @cindex substitute user and group IDs
12956 @cindex user ID, switching
12957 @cindex super-user, becoming
12958 @cindex root, becoming
12960 @command{su} allows one user to temporarily become another user. It runs a
12961 command (often an interactive shell) with the real and effective user
12962 ID, group ID, and supplemental groups of a given @var{user}. Synopsis:
12965 su [@var{option}]@dots{} [@var{user} [@var{arg}]@dots{}]
12968 @cindex passwd entry, and @command{su} shell
12970 @flindex /etc/passwd
12971 If no @var{user} is given, the default is @code{root}, the super-user.
12972 The shell to use is taken from @var{user}'s @code{passwd} entry, or
12973 @file{/bin/sh} if none is specified there. If @var{user} has a
12974 password, @command{su} prompts for the password unless run by a user with
12975 effective user ID of zero (the super-user).
12981 @cindex login shell
12982 By default, @command{su} does not change the current directory.
12983 It sets the environment variables @env{HOME} and @env{SHELL}
12984 from the password entry for @var{user}, and if @var{user} is not
12985 the super-user, sets @env{USER} and @env{LOGNAME} to @var{user}.
12986 By default, the shell is not a login shell.
12988 Any additional @var{arg}s are passed as additional arguments to the
12991 @cindex @option{-su}
12992 GNU @command{su} does not treat @file{/bin/sh} or any other shells specially
12993 (e.g., by setting @code{argv[0]} to @option{-su}, passing @option{-c} only
12994 to certain shells, etc.).
12997 @command{su} can optionally be compiled to use @code{syslog} to report
12998 failed, and optionally successful, @command{su} attempts. (If the system
12999 supports @code{syslog}.) However, GNU @command{su} does not check if the
13000 user is a member of the @code{wheel} group; see below.
13002 The program accepts the following options. Also see @ref{Common options}.
13005 @item -c @var{command}
13006 @itemx --command=@var{command}
13009 Pass @var{command}, a single command line to run, to the shell with
13010 a @option{-c} option instead of starting an interactive shell.
13017 @cindex file name pattern expansion, disabled
13018 @cindex globbing, disabled
13019 Pass the @option{-f} option to the shell. This probably only makes sense
13020 if the shell run is @command{csh} or @command{tcsh}, for which the @option{-f}
13021 option prevents reading the startup file (@file{.cshrc}). With
13022 Bourne-like shells, the @option{-f} option disables file name pattern
13023 expansion (globbing), which is not likely to be useful.
13031 @c other variables already indexed above
13034 @cindex login shell, creating
13035 Make the shell a login shell. This means the following. Unset all
13036 environment variables except @env{TERM}, @env{HOME}, and @env{SHELL}
13037 (which are set as described above), and @env{USER} and @env{LOGNAME}
13038 (which are set, even for the super-user, as described above), and set
13039 @env{PATH} to a compiled-in default value. Change to @var{user}'s home
13040 directory. Prepend @samp{-} to the shell's name, intended to make it
13041 read its login startup file(s).
13045 @itemx --preserve-environment
13048 @opindex --preserve-environment
13049 @cindex environment, preserving
13050 @flindex /etc/shells
13051 @cindex restricted shell
13052 Do not change the environment variables @env{HOME}, @env{USER},
13053 @env{LOGNAME}, or @env{SHELL}. Run the shell given in the environment
13054 variable @env{SHELL} instead of the shell from @var{user}'s passwd
13055 entry, unless the user running @command{su} is not the superuser and
13056 @var{user}'s shell is restricted. A @dfn{restricted shell} is one that
13057 is not listed in the file @file{/etc/shells}, or in a compiled-in list
13058 if that file does not exist. Parts of what this option does can be
13059 overridden by @option{--login} and @option{--shell}.
13061 @item -s @var{shell}
13062 @itemx --shell=@var{shell}
13065 Run @var{shell} instead of the shell from @var{user}'s passwd entry,
13066 unless the user running @command{su} is not the superuser and @var{user}'s
13067 shell is restricted (see @option{-m} just above).
13071 @cindex exit status of @command{su}
13075 1 if @command{su} itself fails
13076 126 if subshell is found but cannot be invoked
13077 127 if subshell cannot be found
13078 the exit status of the subshell otherwise
13081 @cindex wheel group, not supported
13082 @cindex group wheel, not supported
13084 @subsection Why GNU @command{su} does not support the @samp{wheel} group
13086 (This section is by Richard Stallman.)
13090 Sometimes a few of the users try to hold total power over all the
13091 rest. For example, in 1984, a few users at the MIT AI lab decided to
13092 seize power by changing the operator password on the Twenex system and
13093 keeping it secret from everyone else. (I was able to thwart this coup
13094 and give power back to the users by patching the kernel, but I
13095 wouldn't know how to do that in Unix.)
13097 However, occasionally the rulers do tell someone. Under the usual
13098 @command{su} mechanism, once someone learns the root password who
13099 sympathizes with the ordinary users, he or she can tell the rest. The
13100 ``wheel group'' feature would make this impossible, and thus cement the
13101 power of the rulers.
13103 I'm on the side of the masses, not that of the rulers. If you are
13104 used to supporting the bosses and sysadmins in whatever they do, you
13105 might find this idea strange at first.
13108 @node Process control
13109 @chapter Process control
13111 @cindex processes, commands for controlling
13112 @cindex commands for controlling processes
13115 * kill invocation:: Sending a signal to processes.
13119 @node kill invocation
13120 @section @command{kill}: Send a signal to processes
13123 @cindex send a signal to processes
13125 The @command{kill} command sends a signal to processes, causing them
13126 to terminate or otherwise act upon receiving the signal in some way.
13127 Alternatively, it lists information about signals. Synopses:
13130 kill [-s @var{signal} | --signal @var{signal} | -@var{signal}] @var{pid}@dots{}
13131 kill [-l | --list | -t | --table] [@var{signal}]@dots{}
13134 The first form of the @command{kill} command sends a signal to all
13135 @var{pid} arguments. The default signal to send if none is specified
13136 is @samp{TERM}. The special signal number @samp{0} does not denote a
13137 valid signal, but can be used to test whether the @var{pid} arguments
13138 specify processes to which a signal could be sent.
13140 If @var{pid} is positive, the signal is sent to the process with the
13141 process ID @var{pid}. If @var{pid} is zero, the signal is sent to all
13142 processes in the process group of the current process. If @var{pid}
13143 is @minus{}1, the signal is sent to all processes for which the user has
13144 permission to send a signal. If @var{pid} is less than @minus{}1, the signal
13145 is sent to all processes in the process group that equals the absolute
13146 value of @var{pid}.
13148 If @var{pid} is not positive, a system-dependent set of system
13149 processes is excluded from the list of processes to which the signal
13152 If a negative @var{PID} argument is desired as the first one, it
13153 should be preceded by @option{--}. However, as a common extension to
13154 @acronym{POSIX}, @option{--} is not required with @samp{kill
13155 -@var{signal} -@var{pid}}. The following commands are equivalent:
13164 The first form of the @command{kill} command succeeds if every @var{pid}
13165 argument specifies at least one process that the signal was sent to.
13167 The second form of the @command{kill} command lists signal information.
13168 Either the @option{-l} or @option{--list} option, or the @option{-t}
13169 or @option{--table} option must be specified. Without any
13170 @var{signal} argument, all supported signals are listed. The output
13171 of @option{-l} or @option{--list} is a list of the signal names, one
13172 per line; if @var{signal} is already a name, the signal number is
13173 printed instead. The output of @option{-t} or @option{--table} is a
13174 table of signal numbers, names, and descriptions. This form of the
13175 @command{kill} command succeeds if all @var{signal} arguments are valid
13176 and if there is no output error.
13178 The @command{kill} command also supports the @option{--help} and
13179 @option{--version} options. @xref{Common options}.
13181 A @var{signal} may be a signal name like @samp{HUP}, or a signal
13182 number like @samp{1}, or an exit status of a process terminated by the
13183 signal. A signal name can be given in canonical form or prefixed by
13184 @samp{SIG}. The case of the letters is ignored, except for the
13185 @option{-@var{signal}} option which must use upper case to avoid
13186 ambiguity with lower case option letters. The following signal names
13187 and numbers are supported on all @acronym{POSIX} compliant systems:
13193 2. Terminal interrupt.
13199 9. Kill (cannot be caught or ignored).
13207 Other supported signal names have system-dependent corresponding
13208 numbers. All systems conforming to @acronym{POSIX} 1003.1-2001 also
13209 support the following signals:
13213 Access to an undefined portion of a memory object.
13215 Child process terminated, stopped, or continued.
13217 Continue executing, if stopped.
13219 Erroneous arithmetic operation.
13221 Illegal Instruction.
13223 Write on a pipe with no one to read it.
13225 Invalid memory reference.
13227 Stop executing (cannot be caught or ignored).
13231 Background process attempting read.
13233 Background process attempting write.
13235 High bandwidth data is available at a socket.
13237 User-defined signal 1.
13239 User-defined signal 2.
13243 @acronym{POSIX} 1003.1-2001 systems that support the @acronym{XSI} extension
13244 also support the following signals:
13250 Profiling timer expired.
13254 Trace/breakpoint trap.
13256 Virtual timer expired.
13258 CPU time limit exceeded.
13260 File size limit exceeded.
13264 @acronym{POSIX} 1003.1-2001 systems that support the @acronym{XRT} extension
13265 also support at least eight real-time signals called @samp{RTMIN},
13266 @samp{RTMIN+1}, @dots{}, @samp{RTMAX-1}, @samp{RTMAX}.
13272 @cindex delaying commands
13273 @cindex commands for delaying
13275 @c Perhaps @command{wait} or other commands should be described here also?
13278 * sleep invocation:: Delay for a specified time.
13282 @node sleep invocation
13283 @section @command{sleep}: Delay for a specified time
13286 @cindex delay for a specified time
13288 @command{sleep} pauses for an amount of time specified by the sum of
13289 the values of the command line arguments.
13293 sleep @var{number}[smhd]@dots{}
13297 Each argument is a number followed by an optional unit; the default
13298 is seconds. The units are:
13311 Historical implementations of @command{sleep} have required that
13312 @var{number} be an integer. However, GNU @command{sleep} accepts
13313 arbitrary floating point numbers (using a period before any fractional
13316 The only options are @option{--help} and @option{--version}. @xref{Common
13322 @node Numeric operations
13323 @chapter Numeric operations
13325 @cindex numeric operations
13326 These programs do numerically-related operations.
13329 * factor invocation:: Show factors of numbers.
13330 * seq invocation:: Print sequences of numbers.
13334 @node factor invocation
13335 @section @command{factor}: Print prime factors
13338 @cindex prime factors
13340 @command{factor} prints prime factors. Synopses:
13343 factor [@var{number}]@dots{}
13344 factor @var{option}
13347 If no @var{number} is specified on the command line, @command{factor} reads
13348 numbers from standard input, delimited by newlines, tabs, or spaces.
13350 The only options are @option{--help} and @option{--version}. @xref{Common
13353 The algorithm it uses is not very sophisticated, so for some inputs
13354 @command{factor} runs for a long time. The hardest numbers to factor are
13355 the products of large primes. Factoring the product of the two largest 32-bit
13356 prime numbers takes about 80 seconds of CPU time on a 1.6 GHz Athlon.
13359 $ p=`echo '4294967279 * 4294967291'|bc`
13361 18446743979220271189: 4294967279 4294967291
13364 Similarly, it takes about 80 seconds for GNU factor (from coreutils-5.1.2)
13365 to ``factor'' the largest 64-bit prime:
13368 $ factor 18446744073709551557
13369 18446744073709551557: 18446744073709551557
13372 In contrast, @command{factor} factors the largest 64-bit number in just
13373 over a tenth of a second:
13376 $ factor `echo '2^64-1'|bc`
13377 18446744073709551615: 3 5 17 257 641 65537 6700417
13383 @node seq invocation
13384 @section @command{seq}: Print numeric sequences
13387 @cindex numeric sequences
13388 @cindex sequence of numbers
13390 @command{seq} prints a sequence of numbers to standard output. Synopses:
13393 seq [@var{option}]@dots{} @var{last}
13394 seq [@var{option}]@dots{} @var{first} @var{last}
13395 seq [@var{option}]@dots{} @var{first} @var{increment} @var{last}
13398 @command{seq} prints the numbers from @var{first} to @var{last} by
13399 @var{increment}. By default, each number is printed on a separate line.
13400 When @var{increment} is not specified, it defaults to @samp{1},
13401 even when @var{first} is larger than @var{last}.
13402 @var{first} also defaults to @samp{1}. So @code{seq 1} prints
13403 @samp{1}, but @code{seq 0} and @code{seq 10 5} produce no output.
13404 Floating-point numbers
13405 may be specified (using a period before any fractional digits).
13407 The program accepts the following options. Also see @ref{Common options}.
13408 Options must precede operands.
13411 @item -f @var{format}
13412 @itemx --format=@var{format}
13413 @opindex -f @var{format}
13414 @opindex --format=@var{format}
13415 @cindex formatting of numbers in @command{seq}
13416 Print all numbers using @var{format}; default @samp{%g}.
13417 @var{format} must contain exactly one of the floating point
13418 output formats @samp{%e}, @samp{%f}, or @samp{%g}.
13420 @item -s @var{string}
13421 @itemx --separator=@var{string}
13422 @cindex separator for numbers in @command{seq}
13423 Separate numbers with @var{string}; default is a newline.
13424 The output always terminates with a newline.
13427 @itemx --equal-width
13428 Print all numbers with the same width, by padding with leading zeroes.
13429 (To have other kinds of padding, use @option{--format}).
13433 If you want to use @command{seq} to print sequences of large integer values,
13434 don't use the default @samp{%g} format since it can result in
13438 $ seq 1000000 1000001
13443 Instead, you can use the format, @samp{%1.f},
13444 to print large decimal numbers with no exponent and no decimal point.
13447 $ seq --format=%1.f 1000000 1000001
13452 If you want hexadecimal output, you can use @command{printf}
13453 to perform the conversion:
13456 $ printf %x'\n' `seq -f %1.f 1048575 1024 1050623`
13462 For very long lists of numbers, use xargs to avoid
13463 system limitations on the length of an argument list:
13466 $ seq -f %1.f 1000000 | xargs printf %x'\n' | tail -n 3
13472 To generate octal output, use the printf @code{%o} format instead
13473 of @code{%x}. Note however that using printf might not work for numbers
13474 outside the usual 32-bit range:
13477 $ printf "%x\n" `seq -f %1.f 4294967295 4294967296`
13479 bash: printf: 4294967296: Numerical result out of range
13482 On most systems, seq can produce whole-number output for values up to
13483 @code{2^53}, so here's a more general approach to base conversion that
13484 also happens to be more robust for such large numbers. It works by
13485 using @code{bc} and setting its output radix variable, @var{obase},
13486 to @samp{16} in this case to produce hexadecimal output.
13489 $ (echo obase=16; seq -f %1.f 4294967295 4294967296)|bc
13494 Be careful when using @command{seq} with a fractional @var{increment},
13495 otherwise you may see surprising results. Most people would expect to
13496 see @code{0.3} printed as the last number in this example:
13499 $ seq -s ' ' 0 .1 .3
13503 But that doesn't happen on most systems because @command{seq} is
13504 implemented using binary floating point arithmetic (via the C
13505 @code{double} type)---which means some decimal numbers like @code{.1}
13506 cannot be represented exactly. That in turn means some nonintuitive
13507 conditions like @w{@code{.1 * 3 > .3}} will end up being true.
13509 To work around that in the above example, use a slightly larger number as
13510 the @var{last} value:
13513 $ seq -s ' ' 0 .1 .31
13517 In general, when using an @var{increment} with a fractional part, where
13518 (@var{last} - @var{first}) / @var{increment} is (mathematically) a whole
13519 number, specify a slightly larger (or smaller, if @var{increment} is negative)
13520 value for @var{last} to ensure that @var{last} is the final value printed
13526 @node File permissions
13527 @chapter File permissions
13530 @include getdate.texi
13534 @node Opening the software toolbox
13535 @chapter Opening the Software Toolbox
13537 An earlier version of this chapter appeared in
13538 @uref{http://www.linuxjournal.com/article.php?sid=2762, the
13539 @cite{What's GNU?} column of @cite{Linux Journal}, 2 (June, 1994)}.
13540 It was written by Arnold Robbins.
13543 * Toolbox introduction:: Toolbox introduction
13544 * I/O redirection:: I/O redirection
13545 * The who command:: The @command{who} command
13546 * The cut command:: The @command{cut} command
13547 * The sort command:: The @command{sort} command
13548 * The uniq command:: The @command{uniq} command
13549 * Putting the tools together:: Putting the tools together
13553 @node Toolbox introduction
13554 @unnumberedsec Toolbox Introduction
13556 This month's column is only peripherally related to the GNU Project, in
13557 that it describes a number of the GNU tools on your GNU/Linux system and how they
13558 might be used. What it's really about is the ``Software Tools'' philosophy
13559 of program development and usage.
13561 The software tools philosophy was an important and integral concept
13562 in the initial design and development of Unix (of which Linux and GNU are
13563 essentially clones). Unfortunately, in the modern day press of
13564 Internetworking and flashy GUIs, it seems to have fallen by the
13565 wayside. This is a shame, since it provides a powerful mental model
13566 for solving many kinds of problems.
13568 Many people carry a Swiss Army knife around in their pants pockets (or
13569 purse). A Swiss Army knife is a handy tool to have: it has several knife
13570 blades, a screwdriver, tweezers, toothpick, nail file, corkscrew, and perhaps
13571 a number of other things on it. For the everyday, small miscellaneous jobs
13572 where you need a simple, general purpose tool, it's just the thing.
13574 On the other hand, an experienced carpenter doesn't build a house using
13575 a Swiss Army knife. Instead, he has a toolbox chock full of specialized
13576 tools---a saw, a hammer, a screwdriver, a plane, and so on. And he knows
13577 exactly when and where to use each tool; you won't catch him hammering nails
13578 with the handle of his screwdriver.
13580 The Unix developers at Bell Labs were all professional programmers and trained
13581 computer scientists. They had found that while a one-size-fits-all program
13582 might appeal to a user because there's only one program to use, in practice
13587 difficult to write,
13590 difficult to maintain and
13594 difficult to extend to meet new situations.
13597 Instead, they felt that programs should be specialized tools. In short, each
13598 program ``should do one thing well.'' No more and no less. Such programs are
13599 simpler to design, write, and get right---they only do one thing.
13601 Furthermore, they found that with the right machinery for hooking programs
13602 together, that the whole was greater than the sum of the parts. By combining
13603 several special purpose programs, you could accomplish a specific task
13604 that none of the programs was designed for, and accomplish it much more
13605 quickly and easily than if you had to write a special purpose program.
13606 We will see some (classic) examples of this further on in the column.
13607 (An important additional point was that, if necessary, take a detour
13608 and build any software tools you may need first, if you don't already
13609 have something appropriate in the toolbox.)
13611 @node I/O redirection
13612 @unnumberedsec I/O Redirection
13614 Hopefully, you are familiar with the basics of I/O redirection in the
13615 shell, in particular the concepts of ``standard input,'' ``standard output,''
13616 and ``standard error''. Briefly, ``standard input'' is a data source, where
13617 data comes from. A program should not need to either know or care if the
13618 data source is a disk file, a keyboard, a magnetic tape, or even a punched
13619 card reader. Similarly, ``standard output'' is a data sink, where data goes
13620 to. The program should neither know nor care where this might be.
13621 Programs that only read their standard input, do something to the data,
13622 and then send it on, are called @dfn{filters}, by analogy to filters in a
13625 With the Unix shell, it's very easy to set up data pipelines:
13628 program_to_create_data | filter1 | ... | filterN > final.pretty.data
13631 We start out by creating the raw data; each filter applies some successive
13632 transformation to the data, until by the time it comes out of the pipeline,
13633 it is in the desired form.
13635 This is fine and good for standard input and standard output. Where does the
13636 standard error come in to play? Well, think about @command{filter1} in
13637 the pipeline above. What happens if it encounters an error in the data it
13638 sees? If it writes an error message to standard output, it will just
13639 disappear down the pipeline into @command{filter2}'s input, and the
13640 user will probably never see it. So programs need a place where they can send
13641 error messages so that the user will notice them. This is standard error,
13642 and it is usually connected to your console or window, even if you have
13643 redirected standard output of your program away from your screen.
13645 For filter programs to work together, the format of the data has to be
13646 agreed upon. The most straightforward and easiest format to use is simply
13647 lines of text. Unix data files are generally just streams of bytes, with
13648 lines delimited by the @acronym{ASCII} @sc{lf} (Line Feed) character,
13649 conventionally called a ``newline'' in the Unix literature. (This is
13650 @code{'\n'} if you're a C programmer.) This is the format used by all
13651 the traditional filtering programs. (Many earlier operating systems
13652 had elaborate facilities and special purpose programs for managing
13653 binary data. Unix has always shied away from such things, under the
13654 philosophy that it's easiest to simply be able to view and edit your
13655 data with a text editor.)
13657 OK, enough introduction. Let's take a look at some of the tools, and then
13658 we'll see how to hook them together in interesting ways. In the following
13659 discussion, we will only present those command line options that interest
13660 us. As you should always do, double check your system documentation
13661 for the full story.
13663 @node The who command
13664 @unnumberedsec The @command{who} Command
13666 The first program is the @command{who} command. By itself, it generates a
13667 list of the users who are currently logged in. Although I'm writing
13668 this on a single-user system, we'll pretend that several people are
13673 @print{} arnold console Jan 22 19:57
13674 @print{} miriam ttyp0 Jan 23 14:19(:0.0)
13675 @print{} bill ttyp1 Jan 21 09:32(:0.0)
13676 @print{} arnold ttyp2 Jan 23 20:48(:0.0)
13679 Here, the @samp{$} is the usual shell prompt, at which I typed @samp{who}.
13680 There are three people logged in, and I am logged in twice. On traditional
13681 Unix systems, user names are never more than eight characters long. This
13682 little bit of trivia will be useful later. The output of @command{who} is nice,
13683 but the data is not all that exciting.
13685 @node The cut command
13686 @unnumberedsec The @command{cut} Command
13688 The next program we'll look at is the @command{cut} command. This program
13689 cuts out columns or fields of input data. For example, we can tell it
13690 to print just the login name and full name from the @file{/etc/passwd}
13691 file. The @file{/etc/passwd} file has seven fields, separated by
13695 arnold:xyzzy:2076:10:Arnold D. Robbins:/home/arnold:/bin/bash
13698 To get the first and fifth fields, we would use @command{cut} like this:
13701 $ cut -d: -f1,5 /etc/passwd
13702 @print{} root:Operator
13704 @print{} arnold:Arnold D. Robbins
13705 @print{} miriam:Miriam A. Robbins
13709 With the @option{-c} option, @command{cut} will cut out specific characters
13710 (i.e., columns) in the input lines. This is useful for input data
13711 that has fixed width fields, and does not have a field separator. For
13712 example, list the Monday dates for the current month:
13714 @c Is using cal ok? Looked at gcal, but I don't like it.
13725 @node The sort command
13726 @unnumberedsec The @command{sort} Command
13728 Next we'll look at the @command{sort} command. This is one of the most
13729 powerful commands on a Unix-style system; one that you will often find
13730 yourself using when setting up fancy data plumbing.
13733 command reads and sorts each file named on the command line. It then
13734 merges the sorted data and writes it to standard output. It will read
13735 standard input if no files are given on the command line (thus
13736 making it into a filter). The sort is based on the character collating
13737 sequence or based on user-supplied ordering criteria.
13740 @node The uniq command
13741 @unnumberedsec The @command{uniq} Command
13743 Finally (at least for now), we'll look at the @command{uniq} program. When
13744 sorting data, you will often end up with duplicate lines, lines that
13745 are identical. Usually, all you need is one instance of each line.
13746 This is where @command{uniq} comes in. The @command{uniq} program reads its
13747 standard input. It prints only one
13748 copy of each repeated line. It does have several options. Later on,
13749 we'll use the @option{-c} option, which prints each unique line, preceded
13750 by a count of the number of times that line occurred in the input.
13753 @node Putting the tools together
13754 @unnumberedsec Putting the Tools Together
13756 Now, let's suppose this is a large ISP server system with dozens of users
13757 logged in. The management wants the system administrator to write a program that will
13758 generate a sorted list of logged in users. Furthermore, even if a user
13759 is logged in multiple times, his or her name should only show up in the
13762 The administrator could sit down with the system documentation and write a C
13763 program that did this. It would take perhaps a couple of hundred lines
13764 of code and about two hours to write it, test it, and debug it.
13765 However, knowing the software toolbox, the administrator can instead start out
13766 by generating just a list of logged on users:
13776 Next, sort the list:
13779 $ who | cut -c1-8 | sort
13786 Finally, run the sorted list through @command{uniq}, to weed out duplicates:
13789 $ who | cut -c1-8 | sort | uniq
13795 The @command{sort} command actually has a @option{-u} option that does what
13796 @command{uniq} does. However, @command{uniq} has other uses for which one
13797 cannot substitute @samp{sort -u}.
13799 The administrator puts this pipeline into a shell script, and makes it available for
13800 all the users on the system (@samp{#} is the system administrator,
13801 or @code{root}, prompt):
13804 # cat > /usr/local/bin/listusers
13805 who | cut -c1-8 | sort | uniq
13807 # chmod +x /usr/local/bin/listusers
13810 There are four major points to note here. First, with just four
13811 programs, on one command line, the administrator was able to save about two
13812 hours worth of work. Furthermore, the shell pipeline is just about as
13813 efficient as the C program would be, and it is much more efficient in
13814 terms of programmer time. People time is much more expensive than
13815 computer time, and in our modern ``there's never enough time to do
13816 everything'' society, saving two hours of programmer time is no mean
13819 Second, it is also important to emphasize that with the
13820 @emph{combination} of the tools, it is possible to do a special
13821 purpose job never imagined by the authors of the individual programs.
13823 Third, it is also valuable to build up your pipeline in stages, as we did here.
13824 This allows you to view the data at each stage in the pipeline, which helps
13825 you acquire the confidence that you are indeed using these tools correctly.
13827 Finally, by bundling the pipeline in a shell script, other users can use
13828 your command, without having to remember the fancy plumbing you set up for
13829 them. In terms of how you run them, shell scripts and compiled programs are
13832 After the previous warm-up exercise, we'll look at two additional, more
13833 complicated pipelines. For them, we need to introduce two more tools.
13835 The first is the @command{tr} command, which stands for ``transliterate.''
13836 The @command{tr} command works on a character-by-character basis, changing
13837 characters. Normally it is used for things like mapping upper case to
13841 $ echo ThIs ExAmPlE HaS MIXED case! | tr '[:upper:]' '[:lower:]'
13842 @print{} this example has mixed case!
13845 There are several options of interest:
13849 work on the complement of the listed characters, i.e.,
13850 operations apply to characters not in the given set
13853 delete characters in the first set from the output
13856 squeeze repeated characters in the output into just one character.
13859 We will be using all three options in a moment.
13861 The other command we'll look at is @command{comm}. The @command{comm}
13862 command takes two sorted input files as input data, and prints out the
13863 files' lines in three columns. The output columns are the data lines
13864 unique to the first file, the data lines unique to the second file, and
13865 the data lines that are common to both. The @option{-1}, @option{-2}, and
13866 @option{-3} command line options @emph{omit} the respective columns. (This is
13867 non-intuitive and takes a little getting used to.) For example:
13889 The file name @file{-} tells @command{comm} to read standard input
13890 instead of a regular file.
13892 Now we're ready to build a fancy pipeline. The first application is a word
13893 frequency counter. This helps an author determine if he or she is over-using
13896 The first step is to change the case of all the letters in our input file
13897 to one case. ``The'' and ``the'' are the same word when doing counting.
13900 $ tr '[:upper:]' '[:lower:]' < whats.gnu | ...
13903 The next step is to get rid of punctuation. Quoted words and unquoted words
13904 should be treated identically; it's easiest to just get the punctuation out of
13908 $ tr '[:upper:]' '[:lower:]' < whats.gnu | tr -cd '[:alnum:]_ \n' | ...
13911 The second @command{tr} command operates on the complement of the listed
13912 characters, which are all the letters, the digits, the underscore, and
13913 the blank. The @samp{\n} represents the newline character; it has to
13914 be left alone. (The @acronym{ASCII} tab character should also be included for
13915 good measure in a production script.)
13917 At this point, we have data consisting of words separated by blank space.
13918 The words only contain alphanumeric characters (and the underscore). The
13919 next step is break the data apart so that we have one word per line. This
13920 makes the counting operation much easier, as we will see shortly.
13923 $ tr '[:upper:]' '[:lower:]' < whats.gnu | tr -cd '[:alnum:]_ \n' |
13924 > tr -s ' ' '\n' | ...
13927 This command turns blanks into newlines. The @option{-s} option squeezes
13928 multiple newline characters in the output into just one. This helps us
13929 avoid blank lines. (The @samp{>} is the shell's ``secondary prompt.''
13930 This is what the shell prints when it notices you haven't finished
13931 typing in all of a command.)
13933 We now have data consisting of one word per line, no punctuation, all one
13934 case. We're ready to count each word:
13937 $ tr '[:upper:]' '[:lower:]' < whats.gnu | tr -cd '[:alnum:]_ \n' |
13938 > tr -s ' ' '\n' | sort | uniq -c | ...
13941 At this point, the data might look something like this:
13954 The output is sorted by word, not by count! What we want is the most
13955 frequently used words first. Fortunately, this is easy to accomplish,
13956 with the help of two more @command{sort} options:
13960 do a numeric sort, not a textual one
13963 reverse the order of the sort
13966 The final pipeline looks like this:
13969 $ tr '[:upper:]' '[:lower:]' < whats.gnu | tr -cd '[:alnum:]_ \n' |
13970 > tr -s ' ' '\n' | sort | uniq -c | sort -n -r
13979 Whew! That's a lot to digest. Yet, the same principles apply. With six
13980 commands, on two lines (really one long one split for convenience), we've
13981 created a program that does something interesting and useful, in much
13982 less time than we could have written a C program to do the same thing.
13984 A minor modification to the above pipeline can give us a simple spelling
13985 checker! To determine if you've spelled a word correctly, all you have to
13986 do is look it up in a dictionary. If it is not there, then chances are
13987 that your spelling is incorrect. So, we need a dictionary.
13988 The conventional location for a dictionary is @file{/usr/dict/words}.
13989 On my GNU/Linux system,@footnote{Redhat Linux 6.1, for the November 2000
13990 revision of this article.}
13991 this is a is a sorted, 45,402 word dictionary.
13993 Now, how to compare our file with the dictionary? As before, we generate
13994 a sorted list of words, one per line:
13997 $ tr '[:upper:]' '[:lower:]' < whats.gnu | tr -cd '[:alnum:]_ \n' |
13998 > tr -s ' ' '\n' | sort -u | ...
14001 Now, all we need is a list of words that are @emph{not} in the
14002 dictionary. Here is where the @command{comm} command comes in.
14005 $ tr '[:upper:]' '[:lower:]' < whats.gnu | tr -cd '[:alnum:]_ \n' |
14006 > tr -s ' ' '\n' | sort -u |
14007 > comm -23 - /usr/dict/words
14010 The @option{-2} and @option{-3} options eliminate lines that are only in the
14011 dictionary (the second file), and lines that are in both files. Lines
14012 only in the first file (standard input, our stream of words), are
14013 words that are not in the dictionary. These are likely candidates for
14014 spelling errors. This pipeline was the first cut at a production
14015 spelling checker on Unix.
14017 There are some other tools that deserve brief mention.
14021 search files for text that matches a regular expression
14024 count lines, words, characters
14027 a T-fitting for data pipes, copies data to files and to standard output
14030 the stream editor, an advanced tool
14033 a data manipulation language, another advanced tool
14036 The software tools philosophy also espoused the following bit of
14037 advice: ``Let someone else do the hard part.'' This means, take
14038 something that gives you most of what you need, and then massage it the
14039 rest of the way until it's in the form that you want.
14045 Each program should do one thing well. No more, no less.
14048 Combining programs with appropriate plumbing leads to results where
14049 the whole is greater than the sum of the parts. It also leads to novel
14050 uses of programs that the authors might never have imagined.
14053 Programs should never print extraneous header or trailer data, since these
14054 could get sent on down a pipeline. (A point we didn't mention earlier.)
14057 Let someone else do the hard part.
14060 Know your toolbox! Use each program appropriately. If you don't have an
14061 appropriate tool, build one.
14064 As of this writing, all the programs we've discussed are available via
14065 anonymous @command{ftp} from: @*
14066 @uref{ftp://gnudist.gnu.org/textutils/textutils-1.22.tar.gz}. (There may
14067 be more recent versions available now.)
14069 None of what I have presented in this column is new. The Software Tools
14070 philosophy was first introduced in the book @cite{Software Tools}, by
14071 Brian Kernighan and P.J. Plauger (Addison-Wesley, ISBN 0-201-03669-X).
14072 This book showed how to write and use software tools. It was written in
14073 1976, using a preprocessor for FORTRAN named @command{ratfor} (RATional
14074 FORtran). At the time, C was not as ubiquitous as it is now; FORTRAN
14075 was. The last chapter presented a @command{ratfor} to FORTRAN
14076 processor, written in @command{ratfor}. @command{ratfor} looks an awful
14077 lot like C; if you know C, you won't have any problem following the
14080 In 1981, the book was updated and made available as @cite{Software Tools
14081 in Pascal} (Addison-Wesley, ISBN 0-201-10342-7). Both books are
14082 still in print and are well worth
14083 reading if you're a programmer. They certainly made a major change in
14084 how I view programming.
14086 The programs in both books are available from
14087 @uref{http://cm.bell-labs.com/who/bwk, Brian Kernighan's home page}.
14088 For a number of years, there was an active
14089 Software Tools Users Group, whose members had ported the original
14090 @command{ratfor} programs to essentially every computer system with a
14091 FORTRAN compiler. The popularity of the group waned in the middle 1980s
14092 as Unix began to spread beyond universities.
14094 With the current proliferation of GNU code and other clones of Unix programs,
14095 these programs now receive little attention; modern C versions are
14096 much more efficient and do more than these programs do. Nevertheless, as
14097 exposition of good programming style, and evangelism for a still-valuable
14098 philosophy, these books are unparalleled, and I recommend them highly.
14100 Acknowledgment: I would like to express my gratitude to Brian Kernighan
14101 of Bell Labs, the original Software Toolsmith, for reviewing this column.
14103 @include doclicense.texi
14114 @c Local variables:
14115 @c texinfo-column-for-description: 32