3 @setfilename coreutils.info
4 @settitle @sc{gnu} Coreutils
9 @include constants.texi
11 @c Define new indices.
15 @c Put everything in one index (arbitrarily chosen to be the concept index).
25 * Coreutils: (coreutils). Core GNU (file, text, shell) utilities.
26 * Common options: (coreutils)Common options. Common options.
27 * File permissions: (coreutils)File permissions. Access modes.
28 * Date input formats: (coreutils)Date input formats.
31 @c FIXME: the following need documentation
32 @c * [: (coreutils)[ invocation. File/string tests.
33 @c * pinky: (coreutils)pinky invocation. FIXME.
34 @c * mktemp: (coreutils)mktemp invocation. FIXME.
35 @c * chcon: (coreutils)chcon invocation. FIXME.
37 @dircategory Individual utilities
39 * arch: (coreutils)arch invocation. Print machine hardware name.
40 * base64: (coreutils)base64 invocation. Base64 encode/decode data.
41 * basename: (coreutils)basename invocation. Strip directory and suffix.
42 * cat: (coreutils)cat invocation. Concatenate and write files.
43 * chgrp: (coreutils)chgrp invocation. Change file groups.
44 * chmod: (coreutils)chmod invocation. Change file permissions.
45 * chown: (coreutils)chown invocation. Change file owners/groups.
46 * chroot: (coreutils)chroot invocation. Specify the root directory.
47 * cksum: (coreutils)cksum invocation. Print POSIX CRC checksum.
48 * comm: (coreutils)comm invocation. Compare sorted files by line.
49 * cp: (coreutils)cp invocation. Copy files.
50 * csplit: (coreutils)csplit invocation. Split by context.
51 * cut: (coreutils)cut invocation. Print selected parts of lines.
52 * date: (coreutils)date invocation. Print/set system date and time.
53 * dd: (coreutils)dd invocation. Copy and convert a file.
54 * df: (coreutils)df invocation. Report file system disk usage.
55 * dir: (coreutils)dir invocation. List directories briefly.
56 * dircolors: (coreutils)dircolors invocation. Color setup for ls.
57 * dirname: (coreutils)dirname invocation. Strip non-directory suffix.
58 * du: (coreutils)du invocation. Report on disk usage.
59 * echo: (coreutils)echo invocation. Print a line of text.
60 * env: (coreutils)env invocation. Modify the environment.
61 * expand: (coreutils)expand invocation. Convert tabs to spaces.
62 * expr: (coreutils)expr invocation. Evaluate expressions.
63 * factor: (coreutils)factor invocation. Print prime factors
64 * false: (coreutils)false invocation. Do nothing, unsuccessfully.
65 * fmt: (coreutils)fmt invocation. Reformat paragraph text.
66 * fold: (coreutils)fold invocation. Wrap long input lines.
67 * groups: (coreutils)groups invocation. Print group names a user is in.
68 * head: (coreutils)head invocation. Output the first part of files.
69 * hostid: (coreutils)hostid invocation. Print numeric host identifier.
70 * hostname: (coreutils)hostname invocation. Print or set system name.
71 * id: (coreutils)id invocation. Print user identity.
72 * install: (coreutils)install invocation. Copy and change attributes.
73 * join: (coreutils)join invocation. Join lines on a common field.
74 * kill: (coreutils)kill invocation. Send a signal to processes.
75 * link: (coreutils)link invocation. Make hard links between files.
76 * ln: (coreutils)ln invocation. Make links between files.
77 * logname: (coreutils)logname invocation. Print current login name.
78 * ls: (coreutils)ls invocation. List directory contents.
79 * md5sum: (coreutils)md5sum invocation. Print or check MD5 digests.
80 * mkdir: (coreutils)mkdir invocation. Create directories.
81 * mkfifo: (coreutils)mkfifo invocation. Create FIFOs (named pipes).
82 * mknod: (coreutils)mknod invocation. Create special files.
83 * mv: (coreutils)mv invocation. Rename files.
84 * nice: (coreutils)nice invocation. Modify niceness.
85 * nl: (coreutils)nl invocation. Number lines and write files.
86 * nohup: (coreutils)nohup invocation. Immunize to hangups.
87 * od: (coreutils)od invocation. Dump files in octal, etc.
88 * paste: (coreutils)paste invocation. Merge lines of files.
89 * pathchk: (coreutils)pathchk invocation. Check file name portability.
90 * pr: (coreutils)pr invocation. Paginate or columnate files.
91 * printenv: (coreutils)printenv invocation. Print environment variables.
92 * printf: (coreutils)printf invocation. Format and print data.
93 * ptx: (coreutils)ptx invocation. Produce permuted indexes.
94 * pwd: (coreutils)pwd invocation. Print working directory.
95 * readlink: (coreutils)readlink invocation. Print referent of a symlink.
96 * rm: (coreutils)rm invocation. Remove files.
97 * rmdir: (coreutils)rmdir invocation. Remove empty directories.
98 * seq: (coreutils)seq invocation. Print numeric sequences
99 * sha1sum: (coreutils)sha1sum invocation. Print or check SHA-1 digests.
100 * sha2: (coreutils)sha2 utilities. Print or check SHA-2 digests.
101 * shred: (coreutils)shred invocation. Remove files more securely.
102 * shuf: (coreutils)shuf invocation. Shuffling text files.
103 * sleep: (coreutils)sleep invocation. Delay for a specified time.
104 * sort: (coreutils)sort invocation. Sort text files.
105 * split: (coreutils)split invocation. Split into fixed-size pieces.
106 * stat: (coreutils)stat invocation. Report file(system) status.
107 * stty: (coreutils)stty invocation. Print/change terminal settings.
108 * su: (coreutils)su invocation. Modify user and group ID.
109 * sum: (coreutils)sum invocation. Print traditional checksum.
110 * sync: (coreutils)sync invocation. Synchronize memory and disk.
111 * tac: (coreutils)tac invocation. Reverse files.
112 * tail: (coreutils)tail invocation. Output the last part of files.
113 * tee: (coreutils)tee invocation. Redirect to multiple files.
114 * test: (coreutils)test invocation. File/string tests.
115 * timeout: (coreutils)timeout invocation. Run with time limit.
116 * touch: (coreutils)touch invocation. Change file timestamps.
117 * tr: (coreutils)tr invocation. Translate characters.
118 * true: (coreutils)true invocation. Do nothing, successfully.
119 * truncate: (coreutils)truncate invocation. Shrink/extend size of a file.
120 * tsort: (coreutils)tsort invocation. Topological sort.
121 * tty: (coreutils)tty invocation. Print terminal name.
122 * uname: (coreutils)uname invocation. Print system information.
123 * unexpand: (coreutils)unexpand invocation. Convert spaces to tabs.
124 * uniq: (coreutils)uniq invocation. Uniquify files.
125 * unlink: (coreutils)unlink invocation. Removal via unlink(2).
126 * uptime: (coreutils)uptime invocation. Print uptime and load.
127 * users: (coreutils)users invocation. Print current user names.
128 * vdir: (coreutils)vdir invocation. List directories verbosely.
129 * wc: (coreutils)wc invocation. Line, word, and byte counts.
130 * who: (coreutils)who invocation. Print who is logged in.
131 * whoami: (coreutils)whoami invocation. Print effective user ID.
132 * yes: (coreutils)yes invocation. Print a string indefinitely.
136 This manual documents version @value{VERSION} of the @sc{gnu} core
137 utilities, including the standard programs for text and file manipulation.
139 Copyright @copyright{} 1994-1996, 2000-2008 Free Software Foundation, Inc.
142 Permission is granted to copy, distribute and/or modify this document
143 under the terms of the GNU Free Documentation License, Version 1.2 or
144 any later version published by the Free Software Foundation; with no
145 Invariant Sections, with no Front-Cover Texts, and with no Back-Cover
146 Texts. A copy of the license is included in the section entitled ``GNU
147 Free Documentation License''.
152 @title @sc{gnu} @code{Coreutils}
153 @subtitle Core GNU utilities
154 @subtitle for version @value{VERSION}, @value{UPDATED}
155 @author David MacKenzie et al.
158 @vskip 0pt plus 1filll
170 @cindex core utilities
171 @cindex text utilities
172 @cindex shell utilities
173 @cindex file utilities
176 * Introduction:: Caveats, overview, and authors.
177 * Common options:: Common options.
178 * Output of entire files:: cat tac nl od
179 * Formatting file contents:: fmt pr fold
180 * Output of parts of files:: head tail split csplit
181 * Summarizing files:: wc sum cksum md5sum sha1sum sha2
182 * Operating on sorted files:: sort shuf uniq comm ptx tsort
183 * Operating on fields within a line:: cut paste join
184 * Operating on characters:: tr expand unexpand
185 * Directory listing:: ls dir vdir dircolors
186 * Basic operations:: cp dd install mv rm shred
187 * Special file types:: ln mkdir rmdir mkfifo mknod
188 * Changing file attributes:: chgrp chmod chown touch
189 * Disk usage:: df du stat sync truncate
190 * Printing text:: echo printf yes
191 * Conditions:: false true test expr
193 * File name manipulation:: dirname basename pathchk
194 * Working context:: pwd stty printenv tty
195 * User information:: id logname whoami groups users who
196 * System context:: date uname hostname hostid uptime
197 * Modified command invocation:: chroot env nice nohup su timeout
198 * Process control:: kill
200 * Numeric operations:: factor seq
201 * File permissions:: Access modes.
202 * Date input formats:: Specifying date strings.
203 * Opening the software toolbox:: The software tools philosophy.
204 * GNU Free Documentation License:: Copying and sharing this manual.
205 * Concept index:: General index.
208 --- The Detailed Node Listing ---
212 * Exit status:: Indicating program success or failure.
213 * Backup options:: Backup options
214 * Block size:: Block size
215 * Signal specifications:: Specifying signals
216 * Disambiguating names and IDs:: chgrp and chown owner and group syntax
217 * Random sources:: Sources of random data
218 * Target directory:: Target directory
219 * Trailing slashes:: Trailing slashes
220 * Traversing symlinks:: Traversing symlinks to directories
221 * Treating / specially:: Treating / specially
222 * Standards conformance:: Standards conformance
224 Output of entire files
226 * cat invocation:: Concatenate and write files.
227 * tac invocation:: Concatenate and write files in reverse.
228 * nl invocation:: Number lines and write files.
229 * od invocation:: Write files in octal or other formats.
230 * base64 invocation:: Transform data into printable data.
232 Formatting file contents
234 * fmt invocation:: Reformat paragraph text.
235 * pr invocation:: Paginate or columnate files for printing.
236 * fold invocation:: Wrap input lines to fit in specified width.
238 Output of parts of files
240 * head invocation:: Output the first part of files.
241 * tail invocation:: Output the last part of files.
242 * split invocation:: Split a file into fixed-size pieces.
243 * csplit invocation:: Split a file into context-determined pieces.
247 * wc invocation:: Print newline, word, and byte counts.
248 * sum invocation:: Print checksum and block counts.
249 * cksum invocation:: Print CRC checksum and byte counts.
250 * md5sum invocation:: Print or check MD5 digests.
251 * sha1sum invocation:: Print or check SHA-1 digests.
252 * sha2 utilities:: Print or check SHA-2 digests.
254 Operating on sorted files
256 * sort invocation:: Sort text files.
257 * shuf invocation:: Shuffle text files.
258 * uniq invocation:: Uniquify files.
259 * comm invocation:: Compare two sorted files line by line.
260 * ptx invocation:: Produce a permuted index of file contents.
261 * tsort invocation:: Topological sort.
263 @command{ptx}: Produce permuted indexes
265 * General options in ptx:: Options which affect general program behavior.
266 * Charset selection in ptx:: Underlying character set considerations.
267 * Input processing in ptx:: Input fields, contexts, and keyword selection.
268 * Output formatting in ptx:: Types of output format, and sizing the fields.
269 * Compatibility in ptx:: The @acronym{GNU} extensions to @command{ptx}
271 Operating on fields within a line
273 * cut invocation:: Print selected parts of lines.
274 * paste invocation:: Merge lines of files.
275 * join invocation:: Join lines on a common field.
277 Operating on characters
279 * tr invocation:: Translate, squeeze, and/or delete characters.
280 * expand invocation:: Convert tabs to spaces.
281 * unexpand invocation:: Convert spaces to tabs.
283 @command{tr}: Translate, squeeze, and/or delete characters
285 * Character sets:: Specifying sets of characters.
286 * Translating:: Changing one set of characters to another.
287 * Squeezing:: Squeezing repeats and deleting.
291 * ls invocation:: List directory contents
292 * dir invocation:: Briefly list directory contents
293 * vdir invocation:: Verbosely list directory contents
294 * dircolors invocation:: Color setup for @command{ls}
296 @command{ls}: List directory contents
298 * Which files are listed:: Which files are listed
299 * What information is listed:: What information is listed
300 * Sorting the output:: Sorting the output
301 * More details about version sort:: More details about version sort
302 * General output formatting:: General output formatting
303 * Formatting the file names:: Formatting the file names
307 * cp invocation:: Copy files and directories
308 * dd invocation:: Convert and copy a file
309 * install invocation:: Copy files and set attributes
310 * mv invocation:: Move (rename) files
311 * rm invocation:: Remove files or directories
312 * shred invocation:: Remove files more securely
316 * link invocation:: Make a hard link via the link syscall
317 * ln invocation:: Make links between files
318 * mkdir invocation:: Make directories
319 * mkfifo invocation:: Make FIFOs (named pipes)
320 * mknod invocation:: Make block or character special files
321 * readlink invocation:: Print the referent of a symbolic link
322 * rmdir invocation:: Remove empty directories
323 * unlink invocation:: Remove files via unlink syscall
325 Changing file attributes
327 * chown invocation:: Change file owner and group
328 * chgrp invocation:: Change group ownership
329 * chmod invocation:: Change access permissions
330 * touch invocation:: Change file timestamps
334 * df invocation:: Report file system disk space usage
335 * du invocation:: Estimate file space usage
336 * stat invocation:: Report file or file system status
337 * sync invocation:: Synchronize data on disk with memory
338 * truncate invocation:: Shrink or extend the size of a file
342 * echo invocation:: Print a line of text
343 * printf invocation:: Format and print data
344 * yes invocation:: Print a string until interrupted
348 * false invocation:: Do nothing, unsuccessfully
349 * true invocation:: Do nothing, successfully
350 * test invocation:: Check file types and compare values
351 * expr invocation:: Evaluate expressions
353 @command{test}: Check file types and compare values
355 * File type tests:: File type tests
356 * Access permission tests:: Access permission tests
357 * File characteristic tests:: File characteristic tests
358 * String tests:: String tests
359 * Numeric tests:: Numeric tests
361 @command{expr}: Evaluate expression
363 * String expressions:: + : match substr index length
364 * Numeric expressions:: + - * / %
365 * Relations for expr:: | & < <= = == != >= >
366 * Examples of expr:: Examples of using @command{expr}
370 * tee invocation:: Redirect output to multiple files or processes
372 File name manipulation
374 * basename invocation:: Strip directory and suffix from a file name
375 * dirname invocation:: Strip non-directory suffix from a file name
376 * pathchk invocation:: Check file name portability
380 * pwd invocation:: Print working directory
381 * stty invocation:: Print or change terminal characteristics
382 * printenv invocation:: Print all or some environment variables
383 * tty invocation:: Print file name of terminal on standard input
385 @command{stty}: Print or change terminal characteristics
387 * Control:: Control settings
388 * Input:: Input settings
389 * Output:: Output settings
390 * Local:: Local settings
391 * Combination:: Combination settings
392 * Characters:: Special characters
393 * Special:: Special settings
397 * id invocation:: Print user identity
398 * logname invocation:: Print current login name
399 * whoami invocation:: Print effective user ID
400 * groups invocation:: Print group names a user is in
401 * users invocation:: Print login names of users currently logged in
402 * who invocation:: Print who is currently logged in
406 * arch invocation:: Print machine hardware name
407 * date invocation:: Print or set system date and time
408 * uname invocation:: Print system information
409 * hostname invocation:: Print or set system name
410 * hostid invocation:: Print numeric host identifier
411 * uptime invocation:: Print system uptime and load
413 @command{date}: Print or set system date and time
415 * Time conversion specifiers:: %[HIklMNpPrRsSTXzZ]
416 * Date conversion specifiers:: %[aAbBcCdDeFgGhjmuUVwWxyY]
417 * Literal conversion specifiers:: %[%nt]
418 * Padding and other flags:: Pad with zeros, spaces, etc.
419 * Setting the time:: Changing the system clock.
420 * Options for date:: Instead of the current time.
421 * Date input formats:: Specifying date strings.
422 * Examples of date:: Examples.
424 Modified command invocation
426 * chroot invocation:: Run a command with a different root directory
427 * env invocation:: Run a command in a modified environment
428 * nice invocation:: Run a command with modified niceness
429 * nohup invocation:: Run a command immune to hangups
430 * su invocation:: Run a command with substitute user and group ID
431 * timeout invocation:: Run a command with a time limit
435 * kill invocation:: Sending a signal to processes.
439 * sleep invocation:: Delay for a specified time
443 * factor invocation:: Print prime factors
444 * seq invocation:: Print numeric sequences
448 * Mode Structure:: Structure of file mode bits.
449 * Symbolic Modes:: Mnemonic representation of file mode bits.
450 * Numeric Modes:: File mode bits as octal numbers.
451 * Directory Setuid and Setgid:: Set-user-ID and set-group-ID on directories.
455 * General date syntax:: Common rules.
456 * Calendar date items:: 19 Dec 1994.
457 * Time of day items:: 9:20pm.
458 * Time zone items:: @sc{est}, @sc{pdt}, @sc{gmt}.
459 * Day of week items:: Monday and others.
460 * Relative items in date strings:: next tuesday, 2 years ago.
461 * Pure numbers in date strings:: 19931219, 1440.
462 * Seconds since the Epoch:: @@1078100502.
463 * Specifying time zone rules:: TZ="America/New_York", TZ="UTC0".
464 * Authors of get_date:: Bellovin, Eggert, Salz, Berets, et al.
466 Opening the software toolbox
468 * Toolbox introduction:: Toolbox introduction
469 * I/O redirection:: I/O redirection
470 * The who command:: The @command{who} command
471 * The cut command:: The @command{cut} command
472 * The sort command:: The @command{sort} command
473 * The uniq command:: The @command{uniq} command
474 * Putting the tools together:: Putting the tools together
478 * GNU Free Documentation License:: Copying and sharing this manual.
485 @chapter Introduction
487 This manual is a work in progress: many sections make no attempt to explain
488 basic concepts in a way suitable for novices. Thus, if you are interested,
489 please get involved in improving this manual. The entire @sc{gnu} community
492 @cindex @acronym{POSIX}
493 The @sc{gnu} utilities documented here are mostly compatible with the
494 @acronym{POSIX} standard.
495 @cindex bugs, reporting
496 Please report bugs to @email{bug-coreutils@@gnu.org}. Remember
497 to include the version number, machine architecture, input files, and
498 any other information needed to reproduce the bug: your input, what you
499 expected, what you got, and why it is wrong. Diffs are welcome, but
500 please include a description of the problem as well, since this is
501 sometimes difficult to infer. @xref{Bugs, , , gcc, Using and Porting GNU CC}.
507 @cindex MacKenzie, D.
510 This manual was originally derived from the Unix man pages in the
511 distributions, which were written by David MacKenzie and updated by Jim
512 Meyering. What you are reading now is the authoritative documentation
513 for these utilities; the man pages are no longer being maintained. The
514 original @command{fmt} man page was written by Ross Paterson. Fran@,{c}ois
515 Pinard did the initial conversion to Texinfo format. Karl Berry did the
516 indexing, some reorganization, and editing of the results. Brian
517 Youmans of the Free Software Foundation office staff combined the
518 manuals for textutils, fileutils, and sh-utils to produce the present
519 omnibus manual. Richard Stallman contributed his usual invaluable
520 insights to the overall process.
523 @chapter Common options
527 @itemx @w{@kbd{--backup}[=@var{method}]}
530 @vindex VERSION_CONTROL
531 @cindex backups, making
532 @xref{Backup options}.
533 Make a backup of each file that would otherwise be overwritten or removed.
536 @macro optBackupSuffix
537 @item -S @var{suffix}
538 @itemx --suffix=@var{suffix}
541 Append @var{suffix} to each backup file made with @option{-b}.
542 @xref{Backup options}.
545 @macro optTargetDirectory
546 @item -t @var{directory}
547 @itemx @w{@kbd{--target-directory}=@var{directory}}
549 @opindex --target-directory
550 @cindex target directory
551 @cindex destination directory
552 Specify the destination @var{directory}.
553 @xref{Target directory}.
556 @macro optNoTargetDirectory
558 @itemx --no-target-directory
560 @opindex --no-target-directory
561 @cindex target directory
562 @cindex destination directory
563 Do not treat the last operand specially when it is a directory or a
564 symbolic link to a directory. @xref{Target directory}.
571 Append an SI-style abbreviation to each size, such as @samp{M} for
572 megabytes. Powers of 1000 are used, not 1024; @samp{M} stands for
573 1,000,000 bytes. This option is equivalent to
574 @option{--block-size=si}. Use the @option{-h} or
575 @option{--human-readable} option if
576 you prefer powers of 1024.
579 @macro optHumanReadable
581 @itemx --human-readable
583 @opindex --human-readable
584 @cindex human-readable output
585 Append a size letter to each size, such as @samp{M} for mebibytes.
586 Powers of 1024 are used, not 1000; @samp{M} stands for 1,048,576 bytes.
587 This option is equivalent to @option{--block-size=human-readable}.
588 Use the @option{--si} option if you prefer powers of 1000.
591 @macro optStripTrailingSlashes
592 @itemx @w{@kbd{--strip-trailing-slashes}}
593 @opindex --strip-trailing-slashes
594 @cindex stripping trailing slashes
595 Remove any trailing slashes from each @var{source} argument.
596 @xref{Trailing slashes}.
599 @cindex common options
601 Certain options are available in all of these programs. Rather than
602 writing identical descriptions for each of the programs, they are
603 described here. (In fact, every @sc{gnu} program accepts (or should accept)
606 @vindex POSIXLY_CORRECT
607 Normally options and operands can appear in any order, and programs act
608 as if all the options appear before any operands. For example,
609 @samp{sort -r passwd -t :} acts like @samp{sort -r -t : passwd}, since
610 @samp{:} is an option-argument of @option{-t}. However, if the
611 @env{POSIXLY_CORRECT} environment variable is set, options must appear
612 before operands, unless otherwise specified for a particular command.
614 A few programs can usefully have trailing operands with leading
615 @samp{-}. With such a program, options must precede operands even if
616 @env{POSIXLY_CORRECT} is not set, and this fact is noted in the
617 program description. For example, the @command{env} command's options
618 must appear before its operands, since in some cases the operands
619 specify a command that itself contains options.
621 Some of these programs recognize the @option{--help} and @option{--version}
622 options only when one of them is the sole command line argument.
629 Print a usage message listing all available options, then exit successfully.
633 @cindex version number, finding
634 Print the version number, then exit successfully.
638 @cindex option delimiter
639 Delimit the option list. Later arguments, if any, are treated as
640 operands even if they begin with @samp{-}. For example, @samp{sort --
641 -r} reads from the file named @file{-r}.
645 @cindex standard input
646 @cindex standard output
647 A single @samp{-} operand is not really an option, though it looks like one. It
648 stands for standard input, or for standard output if that is clear from
649 the context. For example, @samp{sort -} reads from standard input,
650 and is equivalent to plain @samp{sort}, and @samp{tee -} writes an
651 extra copy of its input to standard output. Unless otherwise
652 specified, @samp{-} can appear as any operand that requires a file
656 * Exit status:: Indicating program success or failure.
657 * Backup options:: -b -S, in some programs.
658 * Block size:: BLOCK_SIZE and --block-size, in some programs.
659 * Signal specifications:: Specifying signals using the --signal option.
660 * Disambiguating names and IDs:: chgrp and chown owner and group syntax
661 * Random sources:: --random-source, in some programs.
662 * Target directory:: Specifying a target directory, in some programs.
663 * Trailing slashes:: --strip-trailing-slashes, in some programs.
664 * Traversing symlinks:: -H, -L, or -P, in some programs.
665 * Treating / specially:: --preserve-root and --no-preserve-root.
666 * Special built-in utilities:: @command{break}, @command{:}, @command{eval}, @dots{}
667 * Standards conformance:: Conformance to the @acronym{POSIX} standard.
675 An exit status of zero indicates success,
676 and a nonzero value indicates failure.
679 Nearly every command invocation yields an integral @dfn{exit status}
680 that can be used to change how other commands work.
681 For the vast majority of commands, an exit status of zero indicates
682 success. Failure is indicated by a nonzero value---typically
683 @samp{1}, though it may differ on unusual platforms as @acronym{POSIX}
684 requires only that it be nonzero.
686 However, some of the programs documented here do produce
687 other exit status values and a few associate different
688 meanings with the values @samp{0} and @samp{1}.
689 Here are some of the exceptions:
690 @command{chroot}, @command{env}, @command{expr},
691 @command{nice}, @command{nohup}, @command{printenv}, @command{sort},
692 @command{su}, @command{test}, @command{timeout}, @command{tty}.
696 @section Backup options
698 @cindex backup options
700 Some @sc{gnu} programs (at least @command{cp}, @command{install},
701 @command{ln}, and @command{mv}) optionally make backups of files
702 before writing new versions.
703 These options control the details of these backups. The options are also
704 briefly mentioned in the descriptions of the particular programs.
709 @itemx @w{@kbd{--backup}[=@var{method}]}
712 @vindex VERSION_CONTROL
713 @cindex backups, making
714 Make a backup of each file that would otherwise be overwritten or removed.
715 Without this option, the original versions are destroyed.
716 Use @var{method} to determine the type of backups to make.
717 When this option is used but @var{method} is not specified,
718 then the value of the @env{VERSION_CONTROL}
719 environment variable is used. And if @env{VERSION_CONTROL} is not set,
720 the default backup type is @samp{existing}.
722 Note that the short form of this option, @option{-b} does not accept any
723 argument. Using @option{-b} is equivalent to using @option{--backup=existing}.
725 @vindex version-control @r{Emacs variable}
726 This option corresponds to the Emacs variable @samp{version-control};
727 the values for @var{method} are the same as those used in Emacs.
728 This option also accepts more descriptive names.
729 The valid @var{method}s are (unique abbreviations are accepted):
734 @opindex none @r{backup method}
739 @opindex numbered @r{backup method}
740 Always make numbered backups.
744 @opindex existing @r{backup method}
745 Make numbered backups of files that already have them, simple backups
750 @opindex simple @r{backup method}
751 Always make simple backups. Please note @samp{never} is not to be
752 confused with @samp{none}.
756 @item -S @var{suffix}
757 @itemx --suffix=@var{suffix}
760 @cindex backup suffix
761 @vindex SIMPLE_BACKUP_SUFFIX
762 Append @var{suffix} to each backup file made with @option{-b}. If this
763 option is not specified, the value of the @env{SIMPLE_BACKUP_SUFFIX}
764 environment variable is used. And if @env{SIMPLE_BACKUP_SUFFIX} is not
765 set, the default is @samp{~}, just as in Emacs.
774 Some @sc{gnu} programs (at least @command{df}, @command{du}, and
775 @command{ls}) display sizes in ``blocks''. You can adjust the block size
776 and method of display to make sizes easier to read. The block size
777 used for display is independent of any file system block size.
778 Fractional block counts are rounded up to the nearest integer.
780 @opindex --block-size=@var{size}
783 @vindex DF_BLOCK_SIZE
784 @vindex DU_BLOCK_SIZE
785 @vindex LS_BLOCK_SIZE
786 @vindex POSIXLY_CORRECT@r{, and block size}
788 The default block size is chosen by examining the following environment
789 variables in turn; the first one that is set determines the block size.
794 This specifies the default block size for the @command{df} command.
795 Similarly, @env{DU_BLOCK_SIZE} specifies the default for @command{du} and
796 @env{LS_BLOCK_SIZE} for @command{ls}.
799 This specifies the default block size for all three commands, if the
800 above command-specific environment variables are not set.
803 This specifies the default block size for all values that are normally
804 printed as blocks, if neither @env{BLOCK_SIZE} nor the above
805 command-specific environment variables are set. Unlike the other
806 environment variables, @env{BLOCKSIZE} does not affect values that are
807 normally printed as byte counts, e.g., the file sizes contained in
810 @item POSIXLY_CORRECT
811 If neither @env{@var{command}_BLOCK_SIZE}, nor @env{BLOCK_SIZE}, nor
812 @env{BLOCKSIZE} is set, but this variable is set, the block size
817 If none of the above environment variables are set, the block size
818 currently defaults to 1024 bytes in most contexts, but this number may
819 change in the future. For @command{ls} file sizes, the block size
822 @cindex human-readable output
825 A block size specification can be a positive integer specifying the number
826 of bytes per block, or it can be @code{human-readable} or @code{si} to
827 select a human-readable format. Integers may be followed by suffixes
828 that are upward compatible with the
829 @uref{http://www.bipm.fr/enus/3_SI/si-prefixes.html, SI prefixes}
830 for decimal multiples and with the
831 @uref{http://physics.nist.gov/cuu/Units/binary.html, IEC 60027-2
832 prefixes for binary multiples}.
834 With human-readable formats, output sizes are followed by a size letter
835 such as @samp{M} for megabytes. @code{BLOCK_SIZE=human-readable} uses
836 powers of 1024; @samp{M} stands for 1,048,576 bytes.
837 @code{BLOCK_SIZE=si} is similar, but uses powers of 1000 and appends
838 @samp{B}; @samp{MB} stands for 1,000,000 bytes.
841 A block size specification preceded by @samp{'} causes output sizes to
842 be displayed with thousands separators. The @env{LC_NUMERIC} locale
843 specifies the thousands separator and grouping. For example, in an
844 American English locale, @samp{--block-size="'1kB"} would cause a size
845 of 1234000 bytes to be displayed as @samp{1,234}. In the default C
846 locale, there is no thousands separator so a leading @samp{'} has no
849 An integer block size can be followed by a suffix to specify a
850 multiple of that size. A bare size letter,
851 or one followed by @samp{iB}, specifies
852 a multiple using powers of 1024. A size letter followed by @samp{B}
853 specifies powers of 1000 instead. For example, @samp{1M} and
854 @samp{1MiB} are equivalent to @samp{1048576}, whereas @samp{1MB} is
855 equivalent to @samp{1000000}.
857 A plain suffix without a preceding integer acts as if @samp{1} were
858 prepended, except that it causes a size indication to be appended to
859 the output. For example, @samp{--block-size="kB"} displays 3000 as
862 The following suffixes are defined. Large sizes like @code{1Y}
863 may be rejected by your computer due to limitations of its arithmetic.
867 @cindex kilobyte, definition of
868 kilobyte: @math{10^3 = 1000}.
872 @cindex kibibyte, definition of
873 kibibyte: @math{2^{10} = 1024}. @samp{K} is special: the SI prefix is
874 @samp{k} and the IEC 60027-2 prefix is @samp{Ki}, but tradition and
875 @acronym{POSIX} use @samp{k} to mean @samp{KiB}.
877 @cindex megabyte, definition of
878 megabyte: @math{10^6 = 1,000,000}.
881 @cindex mebibyte, definition of
882 mebibyte: @math{2^{20} = 1,048,576}.
884 @cindex gigabyte, definition of
885 gigabyte: @math{10^9 = 1,000,000,000}.
888 @cindex gibibyte, definition of
889 gibibyte: @math{2^{30} = 1,073,741,824}.
891 @cindex terabyte, definition of
892 terabyte: @math{10^{12} = 1,000,000,000,000}.
895 @cindex tebibyte, definition of
896 tebibyte: @math{2^{40} = 1,099,511,627,776}.
898 @cindex petabyte, definition of
899 petabyte: @math{10^{15} = 1,000,000,000,000,000}.
902 @cindex pebibyte, definition of
903 pebibyte: @math{2^{50} = 1,125,899,906,842,624}.
905 @cindex exabyte, definition of
906 exabyte: @math{10^{18} = 1,000,000,000,000,000,000}.
909 @cindex exbibyte, definition of
910 exbibyte: @math{2^{60} = 1,152,921,504,606,846,976}.
912 @cindex zettabyte, definition of
913 zettabyte: @math{10^{21} = 1,000,000,000,000,000,000,000}
916 @math{2^{70} = 1,180,591,620,717,411,303,424}.
917 (@samp{Zi} is a @acronym{GNU} extension to IEC 60027-2.)
919 @cindex yottabyte, definition of
920 yottabyte: @math{10^{24} = 1,000,000,000,000,000,000,000,000}.
923 @math{2^{80} = 1,208,925,819,614,629,174,706,176}.
924 (@samp{Yi} is a @acronym{GNU} extension to IEC 60027-2.)
929 @opindex --block-size
930 @opindex --human-readable
933 Block size defaults can be overridden by an explicit
934 @option{--block-size=@var{size}} option. The @option{-k}
935 option is equivalent to @option{--block-size=1K}, which
936 is the default unless the @env{POSIXLY_CORRECT} environment variable is
937 set. The @option{-h} or @option{--human-readable} option is equivalent to
938 @option{--block-size=human-readable}. The @option{--si} option is
939 equivalent to @option{--block-size=si}.
941 @node Signal specifications
942 @section Signal specifications
943 @cindex signals, specifying
945 A @var{signal} may be a signal name like @samp{HUP}, or a signal
946 number like @samp{1}, or an exit status of a process terminated by the
947 signal. A signal name can be given in canonical form or prefixed by
948 @samp{SIG}. The case of the letters is ignored. The following signal names
949 and numbers are supported on all @acronym{POSIX} compliant systems:
955 2. Terminal interrupt.
961 9. Kill (cannot be caught or ignored).
969 Other supported signal names have system-dependent corresponding
970 numbers. All systems conforming to @acronym{POSIX} 1003.1-2001 also
971 support the following signals:
975 Access to an undefined portion of a memory object.
977 Child process terminated, stopped, or continued.
979 Continue executing, if stopped.
981 Erroneous arithmetic operation.
985 Write on a pipe with no one to read it.
987 Invalid memory reference.
989 Stop executing (cannot be caught or ignored).
993 Background process attempting read.
995 Background process attempting write.
997 High bandwidth data is available at a socket.
999 User-defined signal 1.
1001 User-defined signal 2.
1005 @acronym{POSIX} 1003.1-2001 systems that support the @acronym{XSI} extension
1006 also support the following signals:
1012 Profiling timer expired.
1016 Trace/breakpoint trap.
1018 Virtual timer expired.
1020 CPU time limit exceeded.
1022 File size limit exceeded.
1026 @acronym{POSIX} 1003.1-2001 systems that support the @acronym{XRT} extension
1027 also support at least eight real-time signals called @samp{RTMIN},
1028 @samp{RTMIN+1}, @dots{}, @samp{RTMAX-1}, @samp{RTMAX}.
1030 @node Disambiguating names and IDs
1031 @section chown and chgrp: Disambiguating user names and IDs
1032 @cindex user names, disambiguating
1033 @cindex user IDs, disambiguating
1034 @cindex group names, disambiguating
1035 @cindex group IDs, disambiguating
1036 @cindex disambiguating group names and IDs
1038 Since the @var{owner} and @var{group} arguments to @command{chown} and
1039 @command{chgrp} may be specified as names or numeric IDs, there is an
1041 What if a user or group @emph{name} is a string of digits?
1042 @footnote{Using a number as a user name is common in some environments.}
1043 Should the command interpret it as a user name or as an ID?
1044 @acronym{POSIX} requires that @command{chown} and @command{chgrp}
1045 first attempt to resolve the specified string as a name, and
1046 only once that fails, then try to interpret it as an ID.
1047 This is troublesome when you want to specify a numeric ID, say 42,
1048 and it must work even in a pathological situation where
1049 @samp{42} is a user name that maps to some other user ID, say 1000.
1050 Simply invoking @code{chown 42 F}, will set @file{F}s owner ID to
1051 1000---not what you intended.
1053 GNU @command{chown} and @command{chgrp} provide a way to work around this,
1054 that at the same time may result in a significant performance improvement
1055 by eliminating a database look-up.
1056 Simply precede each numeric user ID and/or group ID with a @samp{+},
1057 in order to force its interpretation as an integer:
1061 chgrp +$numeric_group_id another-file
1065 GNU @command{chown} and @command{chgrp}
1066 skip the name look-up process for each @samp{+}-prefixed string,
1067 because a string containing @samp{+} is never a valid user or group name.
1068 This syntax is accepted on most common Unix systems, but not on Solaris 10.
1070 @node Random sources
1071 @section Sources of random data
1073 @cindex random sources
1075 The @command{shuf}, @command{shred}, and @command{sort} commands
1076 sometimes need random data to do their work. For example, @samp{sort
1077 -R} must choose a hash function at random, and it needs random data to
1078 make this selection.
1080 Normally these commands use the device file @file{/dev/urandom} as the
1081 source of random data. Typically, this device gathers environmental
1082 noise from device drivers and other sources into an entropy pool, and
1083 uses the pool to generate random bits. If the pool is short of data,
1084 the device reuses the internal pool to produce more bits, using a
1085 cryptographically secure pseudorandom number generator.
1087 @file{/dev/urandom} suffices for most practical uses, but applications
1088 requiring high-value or long-term protection of private data may
1089 require an alternate data source like @file{/dev/random} or
1090 @file{/dev/arandom}. The set of available sources depends on your
1093 To use such a source, specify the @option{--random-source=@var{file}}
1094 option, e.g., @samp{shuf --random-source=/dev/random}. The contents
1095 of @var{file} should be as random as possible. An error is reported
1096 if @var{file} does not contain enough bytes to randomize the input
1099 To reproduce the results of an earlier invocation of a command, you
1100 can save some random data into a file and then use that file as the
1101 random source in earlier and later invocations of the command.
1103 Some old-fashioned or stripped-down operating systems lack support for
1104 @command{/dev/urandom}. On these systems commands like @command{shuf}
1105 by default fall back on an internal pseudorandom generator initialized
1106 by a small amount of entropy.
1108 @node Target directory
1109 @section Target directory
1111 @cindex target directory
1113 The @command{cp}, @command{install}, @command{ln}, and @command{mv}
1114 commands normally treat the last operand specially when it is a
1115 directory or a symbolic link to a directory. For example, @samp{cp
1116 source dest} is equivalent to @samp{cp source dest/source} if
1117 @file{dest} is a directory. Sometimes this behavior is not exactly
1118 what is wanted, so these commands support the following options to
1119 allow more fine-grained control:
1124 @itemx --no-target-directory
1125 @opindex --no-target-directory
1126 @cindex target directory
1127 @cindex destination directory
1128 Do not treat the last operand specially when it is a directory or a
1129 symbolic link to a directory. This can help avoid race conditions in
1130 programs that operate in a shared area. For example, when the command
1131 @samp{mv /tmp/source /tmp/dest} succeeds, there is no guarantee that
1132 @file{/tmp/source} was renamed to @file{/tmp/dest}: it could have been
1133 renamed to @file{/tmp/dest/source} instead, if some other process
1134 created @file{/tmp/dest} as a directory. However, if @file{mv
1135 -T /tmp/source /tmp/dest} succeeds, there is no
1136 question that @file{/tmp/source} was renamed to @file{/tmp/dest}.
1138 In the opposite situation, where you want the last operand to be
1139 treated as a directory and want a diagnostic otherwise, you can use
1140 the @option{--target-directory} (@option{-t}) option.
1142 @item -t @var{directory}
1143 @itemx @w{@kbd{--target-directory}=@var{directory}}
1144 @opindex --target-directory
1145 @cindex target directory
1146 @cindex destination directory
1147 Use @var{directory} as the directory component of each destination
1150 The interface for most programs is that after processing options and a
1151 finite (possibly zero) number of fixed-position arguments, the remaining
1152 argument list is either expected to be empty, or is a list of items
1153 (usually files) that will all be handled identically. The @command{xargs}
1154 program is designed to work well with this convention.
1156 The commands in the @command{mv}-family are unusual in that they take
1157 a variable number of arguments with a special case at the @emph{end}
1158 (namely, the target directory). This makes it nontrivial to perform some
1159 operations, e.g., ``move all files from here to ../d/'', because
1160 @code{mv * ../d/} might exhaust the argument space, and @code{ls | xargs ...}
1161 doesn't have a clean way to specify an extra final argument for each
1162 invocation of the subject command. (It can be done by going through a
1163 shell command, but that requires more human labor and brain power than
1166 The @w{@kbd{--target-directory}} (@option{-t}) option allows the @command{cp},
1167 @command{install}, @command{ln}, and @command{mv} programs to be used
1168 conveniently with @command{xargs}. For example, you can move the files
1169 from the current directory to a sibling directory, @code{d} like this:
1172 ls | xargs mv -t ../d --
1175 However, this doesn't move files whose names begin with @samp{.}.
1176 If you use the @sc{gnu} @command{find} program, you can move those
1177 files too, with this command:
1180 find . -mindepth 1 -maxdepth 1 \
1184 But both of the above approaches fail if there are no files in the
1185 current directory, or if any file has a name containing a blank or
1186 some other special characters.
1187 The following example removes those limitations and requires both
1188 @sc{gnu} @command{find} and @sc{gnu} @command{xargs}:
1191 find . -mindepth 1 -maxdepth 1 -print0 \
1192 | xargs --null --no-run-if-empty \
1199 The @option{--target-directory} (@option{-t}) and
1200 @option{--no-target-directory} (@option{-T})
1201 options cannot be combined.
1203 @node Trailing slashes
1204 @section Trailing slashes
1206 @cindex trailing slashes
1208 Some @sc{gnu} programs (at least @command{cp} and @command{mv}) allow you to
1209 remove any trailing slashes from each @var{source} argument before
1210 operating on it. The @w{@kbd{--strip-trailing-slashes}} option enables
1213 This is useful when a @var{source} argument may have a trailing slash and
1214 @c FIXME: mv's behavior in this case is system-dependent
1215 specify a symbolic link to a directory. This scenario is in fact rather
1216 common because some shells can automatically append a trailing slash when
1217 performing file name completion on such symbolic links. Without this
1218 option, @command{mv}, for example, (via the system's rename function) must
1219 interpret a trailing slash as a request to dereference the symbolic link
1220 and so must rename the indirectly referenced @emph{directory} and not
1221 the symbolic link. Although it may seem surprising that such behavior
1222 be the default, it is required by @acronym{POSIX} and is consistent with
1223 other parts of that standard.
1225 @node Traversing symlinks
1226 @section Traversing symlinks
1228 @cindex symbolic link to directory, controlling traversal of
1230 The following options modify how @command{chown} and @command{chgrp}
1231 @c FIXME: note that `du' has these options, too, but they have slightly
1232 @c different meaning.
1233 traverse a hierarchy when the @option{--recursive} (@option{-R})
1234 option is also specified.
1235 If more than one of the following options is specified, only the final
1237 These options specify whether processing a symbolic link to a directory
1238 entails operating on just the symbolic link or on all files in the
1239 hierarchy rooted at that directory.
1241 These options are independent of @option{--dereference} and
1242 @option{--no-dereference} (@option{-h}), which control whether to modify
1243 a symlink or its referent.
1250 @cindex symbolic link to directory, traverse each that is specified on the command line
1251 If @option{--recursive} (@option{-R}) is specified and
1252 a command line argument is a symbolic link to a directory, traverse it.
1259 @cindex symbolic link to directory, traverse each that is encountered
1260 In a recursive traversal, traverse every symbolic link to a directory
1261 that is encountered.
1268 @cindex symbolic link to directory, never traverse
1269 Do not traverse any symbolic links.
1270 This is the default if none of @option{-H}, @option{-L},
1271 or @option{-P} is specified.
1278 @node Treating / specially
1279 @section Treating @file{/} specially
1281 Certain commands can operate destructively on entire hierarchies.
1282 For example, if a user with appropriate privileges mistakenly runs
1283 @samp{rm -rf / tmp/junk}, that may remove
1284 all files on the entire system. Since there are so few
1285 legitimate uses for such a command,
1286 @sc{gnu} @command{rm} normally declines to operate on any directory
1287 that resolves to @file{/}. If you really want to try to remove all
1288 the files on your system, you can use the @option{--no-preserve-root}
1289 option, but the default behavior, specified by the
1290 @option{--preserve-option}, is safer for most purposes.
1292 The commands @command{chgrp}, @command{chmod} and @command{chown}
1293 can also operate destructively on entire hierarchies, so they too
1294 support these options. Although, unlike @command{rm}, they don't
1295 actually unlink files, these commands are arguably more dangerous
1296 when operating recursively on @file{/}, since they often work much
1297 more quickly, and hence damage more files before an alert user can
1298 interrupt them. Tradition and @acronym{POSIX} require these commands
1299 to operate recursively on @file{/}, so they default to
1300 @option{--no-preserve-root}, but using the @option{--preserve-root}
1301 option makes them safer for most purposes. For convenience you can
1302 specify @option{--preserve-root} in an alias or in a shell function.
1304 Note that the @option{--preserve-root} option also ensures
1305 that @command{chgrp} and @command{chown} do not modify @file{/}
1306 even when dereferencing a symlink pointing to @file{/}.
1308 @node Special built-in utilities
1309 @section Special built-in utilities
1311 Some programs like @command{nice} can invoke other programs; for
1312 example, the command @samp{nice cat file} invokes the program
1313 @command{cat} by executing the command @samp{cat file}. However,
1314 @dfn{special built-in utilities} like @command{exit} cannot be invoked
1315 this way. For example, the command @samp{nice exit} does not have a
1316 well-defined behavior: it may generate an error message instead of
1319 Here is a list of the special built-in utilities that are standardized
1320 by @acronym{POSIX} 1003.1-2004.
1323 @t{.@: : break continue eval exec exit export readonly
1324 return set shift times trap unset}
1327 For example, because @samp{.}, @samp{:}, and @samp{exec} are special,
1328 the commands @samp{nice . foo.sh}, @samp{nice :}, and @samp{nice exec
1329 pwd} do not work as you might expect.
1331 Many shells extend this list. For example, Bash has several extra
1332 special built-in utilities like @command{history}, and
1333 @command{suspend}, and with Bash the command @samp{nice suspend}
1334 generates an error message instead of suspending.
1336 @node Standards conformance
1337 @section Standards conformance
1339 @vindex POSIXLY_CORRECT
1340 In a few cases, the @sc{gnu} utilities' default behavior is
1341 incompatible with the @acronym{POSIX} standard. To suppress these
1342 incompatibilities, define the @env{POSIXLY_CORRECT} environment
1343 variable. Unless you are checking for @acronym{POSIX} conformance, you
1344 probably do not need to define @env{POSIXLY_CORRECT}.
1346 Newer versions of @acronym{POSIX} are occasionally incompatible with older
1347 versions. For example, older versions of @acronym{POSIX} required the
1348 command @samp{sort +1} to sort based on the second and succeeding
1349 fields in each input line, but starting with @acronym{POSIX} 1003.1-2001
1350 the same command is required to sort the file named @file{+1}, and you
1351 must instead use the command @samp{sort -k 2} to get the field-based
1354 @vindex _POSIX2_VERSION
1355 The @sc{gnu} utilities normally conform to the version of @acronym{POSIX}
1356 that is standard for your system. To cause them to conform to a
1357 different version of @acronym{POSIX}, define the @env{_POSIX2_VERSION}
1358 environment variable to a value of the form @var{yyyymm} specifying
1359 the year and month the standard was adopted. Two values are currently
1360 supported for @env{_POSIX2_VERSION}: @samp{199209} stands for
1361 @acronym{POSIX} 1003.2-1992, and @samp{200112} stands for @acronym{POSIX}
1362 1003.1-2001. For example, if you have a newer system but are running software
1363 that assumes an older version of @acronym{POSIX} and uses @samp{sort +1}
1364 or @samp{tail +10}, you can work around any compatibility problems by setting
1365 @samp{_POSIX2_VERSION=199209} in your environment.
1367 @node Output of entire files
1368 @chapter Output of entire files
1370 @cindex output of entire files
1371 @cindex entire files, output of
1373 These commands read and write entire files, possibly transforming them
1377 * cat invocation:: Concatenate and write files.
1378 * tac invocation:: Concatenate and write files in reverse.
1379 * nl invocation:: Number lines and write files.
1380 * od invocation:: Write files in octal or other formats.
1381 * base64 invocation:: Transform data into printable data.
1384 @node cat invocation
1385 @section @command{cat}: Concatenate and write files
1388 @cindex concatenate and write files
1389 @cindex copying files
1391 @command{cat} copies each @var{file} (@samp{-} means standard input), or
1392 standard input if none are given, to standard output. Synopsis:
1395 cat [@var{option}] [@var{file}]@dots{}
1398 The program accepts the following options. Also see @ref{Common options}.
1406 Equivalent to @option{-vET}.
1409 @itemx --number-nonblank
1411 @opindex --number-nonblank
1412 Number all nonempty output lines, starting with 1.
1416 Equivalent to @option{-vE}.
1421 @opindex --show-ends
1422 Display a @samp{$} after the end of each line.
1428 Number all output lines, starting with 1.
1431 @itemx --squeeze-blank
1433 @opindex --squeeze-blank
1434 @cindex squeezing empty lines
1435 Suppress repeated adjacent empty lines; output just one empty line
1440 Equivalent to @option{-vT}.
1445 @opindex --show-tabs
1446 Display TAB characters as @samp{^I}.
1450 Ignored; for @acronym{POSIX} compatibility.
1453 @itemx --show-nonprinting
1455 @opindex --show-nonprinting
1456 Display control characters except for LFD and TAB using
1457 @samp{^} notation and precede characters that have the high bit set with
1462 On systems like MS-DOS that distinguish between text and binary files,
1463 @command{cat} normally reads and writes in binary mode. However,
1464 @command{cat} reads in text mode if one of the options
1465 @option{-bensAE} is used or if @command{cat} is reading from standard
1466 input and standard input is a terminal. Similarly, @command{cat}
1467 writes in text mode if one of the options @option{-bensAE} is used or
1468 if standard output is a terminal.
1475 # Output f's contents, then standard input, then g's contents.
1478 # Copy standard input to standard output.
1483 @node tac invocation
1484 @section @command{tac}: Concatenate and write files in reverse
1487 @cindex reversing files
1489 @command{tac} copies each @var{file} (@samp{-} means standard input), or
1490 standard input if none are given, to standard output, reversing the
1491 records (lines by default) in each separately. Synopsis:
1494 tac [@var{option}]@dots{} [@var{file}]@dots{}
1497 @dfn{Records} are separated by instances of a string (newline by
1498 default). By default, this separator string is attached to the end of
1499 the record that it follows in the file.
1501 The program accepts the following options. Also see @ref{Common options}.
1509 The separator is attached to the beginning of the record that it
1510 precedes in the file.
1516 Treat the separator string as a regular expression. Users of @command{tac}
1517 on MS-DOS/MS-Windows should note that, since @command{tac} reads files in
1518 binary mode, each line of a text file might end with a CR/LF pair
1519 instead of the Unix-style LF.
1521 @item -s @var{separator}
1522 @itemx --separator=@var{separator}
1524 @opindex --separator
1525 Use @var{separator} as the record separator, instead of newline.
1533 @section @command{nl}: Number lines and write files
1536 @cindex numbering lines
1537 @cindex line numbering
1539 @command{nl} writes each @var{file} (@samp{-} means standard input), or
1540 standard input if none are given, to standard output, with line numbers
1541 added to some or all of the lines. Synopsis:
1544 nl [@var{option}]@dots{} [@var{file}]@dots{}
1547 @cindex logical pages, numbering on
1548 @command{nl} decomposes its input into (logical) pages; by default, the
1549 line number is reset to 1 at the top of each logical page. @command{nl}
1550 treats all of the input files as a single document; it does not reset
1551 line numbers or logical pages between files.
1553 @cindex headers, numbering
1554 @cindex body, numbering
1555 @cindex footers, numbering
1556 A logical page consists of three sections: header, body, and footer.
1557 Any of the sections can be empty. Each can be numbered in a different
1558 style from the others.
1560 The beginnings of the sections of logical pages are indicated in the
1561 input file by a line containing exactly one of these delimiter strings:
1572 The two characters from which these strings are made can be changed from
1573 @samp{\} and @samp{:} via options (see below), but the pattern and
1574 length of each string cannot be changed.
1576 A section delimiter is replaced by an empty line on output. Any text
1577 that comes before the first section delimiter string in the input file
1578 is considered to be part of a body section, so @command{nl} treats a
1579 file that contains no section delimiters as a single body section.
1581 The program accepts the following options. Also see @ref{Common options}.
1585 @item -b @var{style}
1586 @itemx --body-numbering=@var{style}
1588 @opindex --body-numbering
1589 Select the numbering style for lines in the body section of each
1590 logical page. When a line is not numbered, the current line number
1591 is not incremented, but the line number separator character is still
1592 prepended to the line. The styles are:
1598 number only nonempty lines (default for body),
1600 do not number lines (default for header and footer),
1602 number only lines that contain a match for the basic regular
1603 expression @var{bre}.
1604 @xref{Regular Expressions, , Regular Expressions, grep, The GNU Grep Manual}.
1608 @itemx --section-delimiter=@var{cd}
1610 @opindex --section-delimiter
1611 @cindex section delimiters of pages
1612 Set the section delimiter characters to @var{cd}; default is
1613 @samp{\:}. If only @var{c} is given, the second remains @samp{:}.
1614 (Remember to protect @samp{\} or other metacharacters from shell
1615 expansion with quotes or extra backslashes.)
1617 @item -f @var{style}
1618 @itemx --footer-numbering=@var{style}
1620 @opindex --footer-numbering
1621 Analogous to @option{--body-numbering}.
1623 @item -h @var{style}
1624 @itemx --header-numbering=@var{style}
1626 @opindex --header-numbering
1627 Analogous to @option{--body-numbering}.
1629 @item -i @var{number}
1630 @itemx --page-increment=@var{number}
1632 @opindex --page-increment
1633 Increment line numbers by @var{number} (default 1).
1635 @item -l @var{number}
1636 @itemx --join-blank-lines=@var{number}
1638 @opindex --join-blank-lines
1639 @cindex empty lines, numbering
1640 @cindex blank lines, numbering
1641 Consider @var{number} (default 1) consecutive empty lines to be one
1642 logical line for numbering, and only number the last one. Where fewer
1643 than @var{number} consecutive empty lines occur, do not number them.
1644 An empty line is one that contains no characters, not even spaces
1647 @item -n @var{format}
1648 @itemx --number-format=@var{format}
1650 @opindex --number-format
1651 Select the line numbering format (default is @code{rn}):
1655 @opindex ln @r{format for @command{nl}}
1656 left justified, no leading zeros;
1658 @opindex rn @r{format for @command{nl}}
1659 right justified, no leading zeros;
1661 @opindex rz @r{format for @command{nl}}
1662 right justified, leading zeros.
1666 @itemx --no-renumber
1668 @opindex --no-renumber
1669 Do not reset the line number at the start of a logical page.
1671 @item -s @var{string}
1672 @itemx --number-separator=@var{string}
1674 @opindex --number-separator
1675 Separate the line number from the text line in the output with
1676 @var{string} (default is the TAB character).
1678 @item -v @var{number}
1679 @itemx --starting-line-number=@var{number}
1681 @opindex --starting-line-number
1682 Set the initial line number on each logical page to @var{number} (default 1).
1684 @item -w @var{number}
1685 @itemx --number-width=@var{number}
1687 @opindex --number-width
1688 Use @var{number} characters for line numbers (default 6).
1696 @section @command{od}: Write files in octal or other formats
1699 @cindex octal dump of files
1700 @cindex hex dump of files
1701 @cindex ASCII dump of files
1702 @cindex file contents, dumping unambiguously
1704 @command{od} writes an unambiguous representation of each @var{file}
1705 (@samp{-} means standard input), or standard input if none are given.
1709 od [@var{option}]@dots{} [@var{file}]@dots{}
1710 od [-abcdfilosx]@dots{} [@var{file}] [[+]@var{offset}[.][b]]
1711 od [@var{option}]@dots{} --traditional [@var{file}] [[+]@var{offset}[.][b] [[+]@var{label}[.][b]]]
1714 Each line of output consists of the offset in the input, followed by
1715 groups of data from the file. By default, @command{od} prints the offset in
1716 octal, and each group of file data is a C @code{short int}'s worth of input
1717 printed as a single octal number.
1719 If @var{offset} is given, it specifies how many input bytes to skip
1720 before formatting and writing. By default, it is interpreted as an
1721 octal number, but the optional trailing decimal point causes it to be
1722 interpreted as decimal. If no decimal is specified and the offset
1723 begins with @samp{0x} or @samp{0X} it is interpreted as a hexadecimal
1724 number. If there is a trailing @samp{b}, the number of bytes skipped
1725 will be @var{offset} multiplied by 512.
1727 If a command is of both the first and second forms, the second form is
1728 assumed if the last operand begins with @samp{+} or (if there are two
1729 operands) a digit. For example, in @samp{od foo 10} and @samp{od +10}
1730 the @samp{10} is an offset, whereas in @samp{od 10} the @samp{10} is a
1733 The program accepts the following options. Also see @ref{Common options}.
1737 @item -A @var{radix}
1738 @itemx --address-radix=@var{radix}
1740 @opindex --address-radix
1741 @cindex radix for file offsets
1742 @cindex file offset radix
1743 Select the base in which file offsets are printed. @var{radix} can
1744 be one of the following:
1754 none (do not print offsets).
1757 The default is octal.
1759 @item -j @var{bytes}
1760 @itemx --skip-bytes=@var{bytes}
1762 @opindex --skip-bytes
1763 Skip @var{bytes} input bytes before formatting and writing. If
1764 @var{bytes} begins with @samp{0x} or @samp{0X}, it is interpreted in
1765 hexadecimal; otherwise, if it begins with @samp{0}, in octal; otherwise,
1766 in decimal. Appending @samp{b} multiplies @var{bytes} by 512,
1767 @samp{kB} by 1000, @samp{K} by 1024,
1768 @samp{MB} by 1000*1000, @samp{M} by 1024*1024,
1769 @samp{GB} by 1000*1000*1000, @samp{G} by 1024*1024*1024,
1770 and so on for @samp{T}, @samp{P}, @samp{E}, @samp{Z}, and @samp{Y}.
1772 @item -N @var{bytes}
1773 @itemx --read-bytes=@var{bytes}
1775 @opindex --read-bytes
1776 Output at most @var{bytes} bytes of the input. Prefixes and suffixes on
1777 @code{bytes} are interpreted as for the @option{-j} option.
1779 @item -S @var{bytes}
1780 @itemx --strings[=@var{bytes}]
1783 @cindex string constants, outputting
1784 Instead of the normal output, output only @dfn{string constants}: at
1785 least @var{bytes} consecutive @acronym{ASCII} graphic characters,
1786 followed by a null (zero) byte.
1787 Prefixes and suffixes on @code{bytes} are interpreted as for the
1790 If @var{n} is omitted with @option{--strings}, the default is 3.
1793 @itemx --format=@var{type}
1796 Select the format in which to output the file data. @var{type} is a
1797 string of one or more of the below type indicator characters. If you
1798 include more than one type indicator character in a single @var{type}
1799 string, or use this option more than once, @command{od} writes one copy
1800 of each output line using each of the data types that you specified,
1801 in the order that you specified.
1803 Adding a trailing ``z'' to any type specification appends a display
1804 of the @acronym{ASCII} character representation of the printable characters
1805 to the output line generated by the type specification.
1809 named character, ignoring high-order bit
1811 @acronym{ASCII} character or backslash escape,
1824 The type @code{a} outputs things like @samp{sp} for space, @samp{nl} for
1825 newline, and @samp{nul} for a null (zero) byte. Only the least significant
1826 seven bits of each byte is used; the high-order bit is ignored.
1827 Type @code{c} outputs
1828 @samp{ }, @samp{\n}, and @code{\0}, respectively.
1831 Except for types @samp{a} and @samp{c}, you can specify the number
1832 of bytes to use in interpreting each number in the given data type
1833 by following the type indicator character with a decimal integer.
1834 Alternately, you can specify the size of one of the C compiler's
1835 built-in data types by following the type indicator character with
1836 one of the following characters. For integers (@samp{d}, @samp{o},
1837 @samp{u}, @samp{x}):
1850 For floating point (@code{f}):
1862 @itemx --output-duplicates
1864 @opindex --output-duplicates
1865 Output consecutive lines that are identical. By default, when two or
1866 more consecutive output lines would be identical, @command{od} outputs only
1867 the first line, and puts just an asterisk on the following line to
1868 indicate the elision.
1871 @itemx --width[=@var{n}]
1874 Dump @code{n} input bytes per output line. This must be a multiple of
1875 the least common multiple of the sizes associated with the specified
1878 If this option is not given at all, the default is 16. If @var{n} is
1879 omitted, the default is 32.
1883 The next several options are shorthands for format specifications.
1884 @sc{gnu} @command{od} accepts any combination of shorthands and format
1885 specification options. These options accumulate.
1891 Output as named characters. Equivalent to @samp{-t a}.
1895 Output as octal bytes. Equivalent to @samp{-t o1}.
1899 Output as @acronym{ASCII} characters or backslash escapes. Equivalent to
1904 Output as unsigned decimal two-byte units. Equivalent to @samp{-t u2}.
1908 Output as floats. Equivalent to @samp{-t fF}.
1912 Output as decimal ints. Equivalent to @samp{-t dI}.
1916 Output as decimal long ints. Equivalent to @samp{-t dL}.
1920 Output as octal two-byte units. Equivalent to @option{-t o2}.
1924 Output as decimal two-byte units. Equivalent to @option{-t d2}.
1928 Output as hexadecimal two-byte units. Equivalent to @samp{-t x2}.
1931 @opindex --traditional
1932 Recognize the non-option label argument that traditional @command{od}
1933 accepted. The following syntax:
1936 od --traditional [@var{file}] [[+]@var{offset}[.][b] [[+]@var{label}[.][b]]]
1940 can be used to specify at most one file and optional arguments
1941 specifying an offset and a pseudo-start address, @var{label}.
1942 The @var{label} argument is interpreted
1943 just like @var{offset}, but it specifies an initial pseudo-address. The
1944 pseudo-addresses are displayed in parentheses following any normal
1951 @node base64 invocation
1952 @section @command{base64}: Transform data into printable data.
1955 @cindex base64 encoding
1957 @command{base64} transforms data read from a file, or standard input,
1958 into (or from) base64 encoded form. The base64 encoded form uses
1959 printable @acronym{ASCII} characters to represent binary data.
1963 base64 [@var{option}]@dots{} [@var{file}]
1964 base64 --decode [@var{option}]@dots{} [@var{file}]
1967 The base64 encoding expands data to roughly 133% of the original.
1968 The format conforms to
1969 @uref{ftp://ftp.rfc-editor.org/in-notes/rfc4648.txt, RFC 4648}.
1971 The program accepts the following options. Also see @ref{Common options}.
1976 @itemx --wrap=@var{COLS}
1980 @cindex column to wrap data after
1981 During encoding, wrap lines after @var{COLS} characters. This must be
1984 The default is to wrap after 76 characters. Use the value 0 to
1985 disable line wrapping altogether.
1991 @cindex Decode base64 data
1992 @cindex Base64 decoding
1993 Change the mode of operation, from the default of encoding data, to
1994 decoding data. Input is expected to be base64 encoded data, and the
1995 output will be the original data.
1998 @itemx --ignore-garbage
2000 @opindex --ignore-garbage
2001 @cindex Ignore garbage in base64 stream
2002 When decoding, newlines are always accepted.
2003 During decoding, ignore unrecognized bytes,
2004 to permit distorted data to be decoded.
2011 @node Formatting file contents
2012 @chapter Formatting file contents
2014 @cindex formatting file contents
2016 These commands reformat the contents of files.
2019 * fmt invocation:: Reformat paragraph text.
2020 * pr invocation:: Paginate or columnate files for printing.
2021 * fold invocation:: Wrap input lines to fit in specified width.
2025 @node fmt invocation
2026 @section @command{fmt}: Reformat paragraph text
2029 @cindex reformatting paragraph text
2030 @cindex paragraphs, reformatting
2031 @cindex text, reformatting
2033 @command{fmt} fills and joins lines to produce output lines of (at most)
2034 a given number of characters (75 by default). Synopsis:
2037 fmt [@var{option}]@dots{} [@var{file}]@dots{}
2040 @command{fmt} reads from the specified @var{file} arguments (or standard
2041 input if none are given), and writes to standard output.
2043 By default, blank lines, spaces between words, and indentation are
2044 preserved in the output; successive input lines with different
2045 indentation are not joined; tabs are expanded on input and introduced on
2048 @cindex line-breaking
2049 @cindex sentences and line-breaking
2050 @cindex Knuth, Donald E.
2051 @cindex Plass, Michael F.
2052 @command{fmt} prefers breaking lines at the end of a sentence, and tries to
2053 avoid line breaks after the first word of a sentence or before the last
2054 word of a sentence. A @dfn{sentence break} is defined as either the end
2055 of a paragraph or a word ending in any of @samp{.?!}, followed by two
2056 spaces or end of line, ignoring any intervening parentheses or quotes.
2057 Like @TeX{}, @command{fmt} reads entire ``paragraphs'' before choosing line
2058 breaks; the algorithm is a variant of that given by Donald E. Knuth
2059 and Michael F. Plass in ``Breaking Paragraphs Into Lines'',
2060 @cite{Software---Practice & Experience} @b{11}, 11 (November 1981),
2063 The program accepts the following options. Also see @ref{Common options}.
2068 @itemx --crown-margin
2070 @opindex --crown-margin
2071 @cindex crown margin
2072 @dfn{Crown margin} mode: preserve the indentation of the first two
2073 lines within a paragraph, and align the left margin of each subsequent
2074 line with that of the second line.
2077 @itemx --tagged-paragraph
2079 @opindex --tagged-paragraph
2080 @cindex tagged paragraphs
2081 @dfn{Tagged paragraph} mode: like crown margin mode, except that if
2082 indentation of the first line of a paragraph is the same as the
2083 indentation of the second, the first line is treated as a one-line
2089 @opindex --split-only
2090 Split lines only. Do not join short lines to form longer ones. This
2091 prevents sample lines of code, and other such ``formatted'' text from
2092 being unduly combined.
2095 @itemx --uniform-spacing
2097 @opindex --uniform-spacing
2098 Uniform spacing. Reduce spacing between words to one space, and spacing
2099 between sentences to two spaces.
2102 @itemx -w @var{width}
2103 @itemx --width=@var{width}
2104 @opindex -@var{width}
2107 Fill output lines up to @var{width} characters (default 75). @command{fmt}
2108 initially tries to make lines about 7% shorter than this, to give it
2109 room to balance line lengths.
2111 @item -p @var{prefix}
2112 @itemx --prefix=@var{prefix}
2113 Only lines beginning with @var{prefix} (possibly preceded by whitespace)
2114 are subject to formatting. The prefix and any preceding whitespace are
2115 stripped for the formatting and then re-attached to each formatted output
2116 line. One use is to format certain kinds of program comments, while
2117 leaving the code unchanged.
2125 @section @command{pr}: Paginate or columnate files for printing
2128 @cindex printing, preparing files for
2129 @cindex multicolumn output, generating
2130 @cindex merging files in parallel
2132 @command{pr} writes each @var{file} (@samp{-} means standard input), or
2133 standard input if none are given, to standard output, paginating and
2134 optionally outputting in multicolumn format; optionally merges all
2135 @var{file}s, printing all in parallel, one per column. Synopsis:
2138 pr [@var{option}]@dots{} [@var{file}]@dots{}
2142 By default, a 5-line header is printed at each page: two blank lines;
2143 a line with the date, the file name, and the page count; and two more
2144 blank lines. A footer of five blank lines is also printed.
2145 The default @var{page_length} is 66
2146 lines. The default number of text lines is therefore 56.
2147 The text line of the header takes the form
2148 @samp{@var{date} @var{string} @var{page}}, with spaces inserted around
2149 @var{string} so that the line takes up the full @var{page_width}. Here,
2150 @var{date} is the date (see the @option{-D} or @option{--date-format}
2151 option for details), @var{string} is the centered header string, and
2152 @var{page} identifies the page number. The @env{LC_MESSAGES} locale
2153 category affects the spelling of @var{page}; in the default C locale, it
2154 is @samp{Page @var{number}} where @var{number} is the decimal page
2157 Form feeds in the input cause page breaks in the output. Multiple form
2158 feeds produce empty pages.
2160 Columns are of equal width, separated by an optional string (default
2161 is @samp{space}). For multicolumn output, lines will always be truncated to
2162 @var{page_width} (default 72), unless you use the @option{-J} option.
2164 column output no line truncation occurs by default. Use @option{-W} option to
2165 truncate lines in that case.
2167 The following changes were made in version 1.22i and apply to later
2168 versions of @command{pr}:
2169 @c FIXME: this whole section here sounds very awkward to me. I
2170 @c made a few small changes, but really it all needs to be redone. - Brian
2171 @c OK, I fixed another sentence or two, but some of it I just don't understand.
2176 Some small @var{letter options} (@option{-s}, @option{-w}) have been
2177 redefined for better @acronym{POSIX} compliance. The output of some further
2178 cases has been adapted to other Unix systems. These changes are not
2179 compatible with earlier versions of the program.
2182 Some @var{new capital letter} options (@option{-J}, @option{-S}, @option{-W})
2183 have been introduced to turn off unexpected interferences of small letter
2184 options. The @option{-N} option and the second argument @var{last_page}
2185 of @samp{+FIRST_PAGE} offer more flexibility. The detailed handling of
2186 form feeds set in the input files requires the @option{-T} option.
2189 Capital letter options override small letter ones.
2192 Some of the option-arguments (compare @option{-s}, @option{-e},
2193 @option{-i}, @option{-n}) cannot be specified as separate arguments from the
2194 preceding option letter (already stated in the @acronym{POSIX} specification).
2197 The program accepts the following options. Also see @ref{Common options}.
2201 @item +@var{first_page}[:@var{last_page}]
2202 @itemx --pages=@var{first_page}[:@var{last_page}]
2203 @c The two following @opindex lines evoke warnings because they contain `:'
2204 @c The `info' spec does not permit that. If we use those lines, we end
2205 @c up with truncated index entries that don't work.
2206 @c @opindex +@var{first_page}[:@var{last_page}]
2207 @c @opindex --pages=@var{first_page}[:@var{last_page}]
2208 @opindex +@var{page_range}
2209 @opindex --pages=@var{page_range}
2210 Begin printing with page @var{first_page} and stop with @var{last_page}.
2211 Missing @samp{:@var{last_page}} implies end of file. While estimating
2212 the number of skipped pages each form feed in the input file results
2213 in a new page. Page counting with and without @samp{+@var{first_page}}
2214 is identical. By default, counting starts with the first page of input
2215 file (not first page printed). Line numbering may be altered by @option{-N}
2219 @itemx --columns=@var{column}
2220 @opindex -@var{column}
2222 @cindex down columns
2223 With each single @var{file}, produce @var{column} columns of output
2224 (default is 1) and print columns down, unless @option{-a} is used. The
2225 column width is automatically decreased as @var{column} increases; unless
2226 you use the @option{-W/-w} option to increase @var{page_width} as well.
2227 This option might well cause some lines to be truncated. The number of
2228 lines in the columns on each page are balanced. The options @option{-e}
2229 and @option{-i} are on for multiple text-column output. Together with
2230 @option{-J} option column alignment and line truncation is turned off.
2231 Lines of full length are joined in a free field format and @option{-S}
2232 option may set field separators. @option{-@var{column}} may not be used
2233 with @option{-m} option.
2239 @cindex across columns
2240 With each single @var{file}, print columns across rather than down. The
2241 @option{-@var{column}} option must be given with @var{column} greater than one.
2242 If a line is too long to fit in a column, it is truncated.
2245 @itemx --show-control-chars
2247 @opindex --show-control-chars
2248 Print control characters using hat notation (e.g., @samp{^G}); print
2249 other nonprinting characters in octal backslash notation. By default,
2250 nonprinting characters are not changed.
2253 @itemx --double-space
2255 @opindex --double-space
2256 @cindex double spacing
2257 Double space the output.
2259 @item -D @var{format}
2260 @itemx --date-format=@var{format}
2261 @cindex time formats
2262 @cindex formatting times
2263 Format header dates using @var{format}, using the same conventions as
2264 for the command @samp{date +@var{format}}; @xref{date invocation}.
2265 Except for directives, which start with
2266 @samp{%}, characters in @var{format} are printed unchanged. You can use
2267 this option to specify an arbitrary string in place of the header date,
2268 e.g., @option{--date-format="Monday morning"}.
2270 @vindex POSIXLY_CORRECT
2272 The default date format is @samp{%Y-%m-%d %H:%M} (for example,
2273 @samp{2001-12-04 23:59});
2274 but if the @env{POSIXLY_CORRECT} environment variable is set
2275 and the @env{LC_TIME} locale category specifies the @acronym{POSIX}
2276 locale, the default is @samp{%b %e %H:%M %Y} (for example,
2277 @samp{Dec@ @ 4 23:59 2001}.
2280 Time stamps are listed according to the time zone rules specified by
2281 the @env{TZ} environment variable, or by the system default rules if
2282 @env{TZ} is not set. @xref{TZ Variable,, Specifying the Time Zone
2283 with @env{TZ}, libc, The GNU C Library Reference Manual}.
2285 @item -e[@var{in-tabchar}[@var{in-tabwidth}]]
2286 @itemx --expand-tabs[=@var{in-tabchar}[@var{in-tabwidth}]]
2288 @opindex --expand-tabs
2290 Expand @var{tab}s to spaces on input. Optional argument @var{in-tabchar} is
2291 the input tab character (default is the TAB character). Second optional
2292 argument @var{in-tabwidth} is the input tab character's width (default
2300 @opindex --form-feed
2301 Use a form feed instead of newlines to separate output pages. This does
2302 not alter the default page length of 66 lines.
2304 @item -h @var{HEADER}
2305 @itemx --header=@var{HEADER}
2308 Replace the file name in the header with the centered string @var{header}.
2309 When using the shell, @var{header} should be quoted and should be
2310 separated from @option{-h} by a space.
2312 @item -i[@var{out-tabchar}[@var{out-tabwidth}]]
2313 @itemx --output-tabs[=@var{out-tabchar}[@var{out-tabwidth}]]
2315 @opindex --output-tabs
2317 Replace spaces with @var{tab}s on output. Optional argument @var{out-tabchar}
2318 is the output tab character (default is the TAB character). Second optional
2319 argument @var{out-tabwidth} is the output tab character's width (default
2325 @opindex --join-lines
2326 Merge lines of full length. Used together with the column options
2327 @option{-@var{column}}, @option{-a -@var{column}} or @option{-m}. Turns off
2328 @option{-W/-w} line truncation;
2329 no column alignment used; may be used with
2330 @option{--sep-string[=@var{string}]}. @option{-J} has been introduced
2331 (together with @option{-W} and @option{--sep-string})
2332 to disentangle the old (@acronym{POSIX}-compliant) options @option{-w} and
2333 @option{-s} along with the three column options.
2336 @item -l @var{page_length}
2337 @itemx --length=@var{page_length}
2340 Set the page length to @var{page_length} (default 66) lines, including
2341 the lines of the header [and the footer]. If @var{page_length} is less
2342 than or equal to 10, the header and footer are omitted, as if the
2343 @option{-t} option had been given.
2349 Merge and print all @var{file}s in parallel, one in each column. If a
2350 line is too long to fit in a column, it is truncated, unless the @option{-J}
2351 option is used. @option{--sep-string[=@var{string}]} may be used.
2353 some @var{file}s (form feeds set) produce empty columns, still marked
2354 by @var{string}. The result is a continuous line numbering and column
2355 marking throughout the whole merged file. Completely empty merged pages
2356 show no separators or line numbers. The default header becomes
2357 @samp{@var{date} @var{page}} with spaces inserted in the middle; this
2358 may be used with the @option{-h} or @option{--header} option to fill up
2359 the middle blank part.
2361 @item -n[@var{number-separator}[@var{digits}]]
2362 @itemx --number-lines[=@var{number-separator}[@var{digits}]]
2364 @opindex --number-lines
2365 Provide @var{digits} digit line numbering (default for @var{digits} is
2366 5). With multicolumn output the number occupies the first @var{digits}
2367 column positions of each text column or only each line of @option{-m}
2368 output. With single column output the number precedes each line just as
2369 @option{-m} does. Default counting of the line numbers starts with the
2370 first line of the input file (not the first line printed, compare the
2371 @option{--page} option and @option{-N} option).
2372 Optional argument @var{number-separator} is the character appended to
2373 the line number to separate it from the text followed. The default
2374 separator is the TAB character. In a strict sense a TAB is always
2375 printed with single column output only. The @var{TAB}-width varies
2376 with the @var{TAB}-position, e.g., with the left @var{margin} specified
2377 by @option{-o} option. With multicolumn output priority is given to
2378 @samp{equal width of output columns} (a @acronym{POSIX} specification).
2379 The @var{TAB}-width is fixed to the value of the first column and does
2380 not change with different values of left @var{margin}. That means a
2381 fixed number of spaces is always printed in the place of the
2382 @var{number-separator tab}. The tabification depends upon the output
2385 @item -N @var{line_number}
2386 @itemx --first-line-number=@var{line_number}
2388 @opindex --first-line-number
2389 Start line counting with the number @var{line_number} at first line of
2390 first page printed (in most cases not the first line of the input file).
2392 @item -o @var{margin}
2393 @itemx --indent=@var{margin}
2396 @cindex indenting lines
2398 Indent each line with a margin @var{margin} spaces wide (default is zero).
2399 The total page width is the size of the margin plus the @var{page_width}
2400 set with the @option{-W/-w} option. A limited overflow may occur with
2401 numbered single column output (compare @option{-n} option).
2404 @itemx --no-file-warnings
2406 @opindex --no-file-warnings
2407 Do not print a warning message when an argument @var{file} cannot be
2408 opened. (The exit status will still be nonzero, however.)
2410 @item -s[@var{char}]
2411 @itemx --separator[=@var{char}]
2413 @opindex --separator
2414 Separate columns by a single character @var{char}. The default for
2415 @var{char} is the TAB character without @option{-w} and @samp{no
2416 character} with @option{-w}. Without @option{-s} the default separator
2417 @samp{space} is set. @option{-s[char]} turns off line truncation of all
2418 three column options (@option{-COLUMN}|@option{-a -COLUMN}|@option{-m}) unless
2419 @option{-w} is set. This is a @acronym{POSIX}-compliant formulation.
2422 @item -S@var{string}
2423 @itemx --sep-string[=@var{string}]
2425 @opindex --sep-string
2426 Use @var{string} to separate output columns. The @option{-S} option doesn't
2427 affect the @option{-W/-w} option, unlike the @option{-s} option which does. It
2428 does not affect line truncation or column alignment.
2429 Without @option{-S}, and with @option{-J}, @command{pr} uses the default output
2431 Without @option{-S} or @option{-J}, @command{pr} uses a @samp{space}
2432 (same as @option{-S"@w{ }"}). @option{--sep-string} with no
2433 @samp{=@var{string}} is equivalent to @option{--sep-string=""}.
2436 @itemx --omit-header
2438 @opindex --omit-header
2439 Do not print the usual header [and footer] on each page, and do not fill
2440 out the bottom of pages (with blank lines or a form feed). No page
2441 structure is produced, but form feeds set in the input files are retained.
2442 The predefined pagination is not changed. @option{-t} or @option{-T} may be
2443 useful together with other options; e.g.: @option{-t -e4}, expand TAB characters
2444 in the input file to 4 spaces but don't make any other changes. Use of
2445 @option{-t} overrides @option{-h}.
2448 @itemx --omit-pagination
2450 @opindex --omit-pagination
2451 Do not print header [and footer]. In addition eliminate all form feeds
2452 set in the input files.
2455 @itemx --show-nonprinting
2457 @opindex --show-nonprinting
2458 Print nonprinting characters in octal backslash notation.
2460 @item -w @var{page_width}
2461 @itemx --width=@var{page_width}
2464 Set page width to @var{page_width} characters for multiple text-column
2465 output only (default for @var{page_width} is 72). @option{-s[CHAR]} turns
2466 off the default page width and any line truncation and column alignment.
2467 Lines of full length are merged, regardless of the column options
2468 set. No @var{page_width} setting is possible with single column output.
2469 A @acronym{POSIX}-compliant formulation.
2471 @item -W @var{page_width}
2472 @itemx --page_width=@var{page_width}
2474 @opindex --page_width
2475 Set the page width to @var{page_width} characters. That's valid with and
2476 without a column option. Text lines are truncated, unless @option{-J}
2477 is used. Together with one of the three column options
2478 (@option{-@var{column}}, @option{-a -@var{column}} or @option{-m}) column
2479 alignment is always used. The separator options @option{-S} or @option{-s}
2480 don't affect the @option{-W} option. Default is 72 characters. Without
2481 @option{-W @var{page_width}} and without any of the column options NO line
2482 truncation is used (defined to keep downward compatibility and to meet
2483 most frequent tasks). That's equivalent to @option{-W 72 -J}. The header
2484 line is never truncated.
2491 @node fold invocation
2492 @section @command{fold}: Wrap input lines to fit in specified width
2495 @cindex wrapping long input lines
2496 @cindex folding long input lines
2498 @command{fold} writes each @var{file} (@option{-} means standard input), or
2499 standard input if none are given, to standard output, breaking long
2503 fold [@var{option}]@dots{} [@var{file}]@dots{}
2506 By default, @command{fold} breaks lines wider than 80 columns. The output
2507 is split into as many lines as necessary.
2509 @cindex screen columns
2510 @command{fold} counts screen columns by default; thus, a tab may count more
2511 than one column, backspace decreases the column count, and carriage
2512 return sets the column to zero.
2514 The program accepts the following options. Also see @ref{Common options}.
2522 Count bytes rather than columns, so that tabs, backspaces, and carriage
2523 returns are each counted as taking up one column, just like other
2530 Break at word boundaries: the line is broken after the last blank before
2531 the maximum line length. If the line contains no such blanks, the line
2532 is broken at the maximum line length as usual.
2534 @item -w @var{width}
2535 @itemx --width=@var{width}
2538 Use a maximum line length of @var{width} columns instead of 80.
2540 For compatibility @command{fold} supports an obsolete option syntax
2541 @option{-@var{width}}. New scripts should use @option{-w @var{width}}
2549 @node Output of parts of files
2550 @chapter Output of parts of files
2552 @cindex output of parts of files
2553 @cindex parts of files, output of
2555 These commands output pieces of the input.
2558 * head invocation:: Output the first part of files.
2559 * tail invocation:: Output the last part of files.
2560 * split invocation:: Split a file into fixed-size pieces.
2561 * csplit invocation:: Split a file into context-determined pieces.
2564 @node head invocation
2565 @section @command{head}: Output the first part of files
2568 @cindex initial part of files, outputting
2569 @cindex first part of files, outputting
2571 @command{head} prints the first part (10 lines by default) of each
2572 @var{file}; it reads from standard input if no files are given or
2573 when given a @var{file} of @option{-}. Synopsis:
2576 head [@var{option}]@dots{} [@var{file}]@dots{}
2579 If more than one @var{file} is specified, @command{head} prints a
2580 one-line header consisting of:
2583 ==> @var{file name} <==
2587 before the output for each @var{file}.
2589 The program accepts the following options. Also see @ref{Common options}.
2594 @itemx --bytes=@var{n}
2597 Print the first @var{n} bytes, instead of initial lines.
2598 However, if @var{n} starts with a @samp{-},
2599 print all but the last @var{n} bytes of each file.
2600 Appending @samp{b} multiplies @var{n} by 512,
2601 @samp{kB} by 1000, @samp{K} by 1024,
2602 @samp{MB} by 1000*1000, @samp{M} by 1024*1024,
2603 @samp{GB} by 1000*1000*1000, @samp{G} by 1024*1024*1024,
2604 and so on for @samp{T}, @samp{P}, @samp{E}, @samp{Z}, and @samp{Y}.
2607 @itemx --lines=@var{n}
2610 Output the first @var{n} lines.
2611 However, if @var{n} starts with a @samp{-},
2612 print all but the last @var{n} lines of each file.
2613 Size multiplier suffixes are the same as with the @option{-c} option.
2621 Never print file name headers.
2627 Always print file name headers.
2631 For compatibility @command{head} also supports an obsolete option syntax
2632 @option{-@var{count}@var{options}}, which is recognized only if it is
2633 specified first. @var{count} is a decimal number optionally followed
2634 by a size letter (@samp{b}, @samp{k}, @samp{m}) as in @option{-c}, or
2635 @samp{l} to mean count by lines, or other option letters (@samp{cqv}).
2636 Scripts intended for standard hosts should use @option{-c @var{count}}
2637 or @option{-n @var{count}} instead. If your script must also run on
2638 hosts that support only the obsolete syntax, it is usually simpler to
2639 avoid @command{head}, e.g., by using @samp{sed 5q} instead of
2645 @node tail invocation
2646 @section @command{tail}: Output the last part of files
2649 @cindex last part of files, outputting
2651 @command{tail} prints the last part (10 lines by default) of each
2652 @var{file}; it reads from standard input if no files are given or
2653 when given a @var{file} of @samp{-}. Synopsis:
2656 tail [@var{option}]@dots{} [@var{file}]@dots{}
2659 If more than one @var{file} is specified, @command{tail} prints a
2660 one-line header consisting of:
2663 ==> @var{file name} <==
2667 before the output for each @var{file}.
2669 @cindex BSD @command{tail}
2670 @sc{gnu} @command{tail} can output any amount of data (some other versions of
2671 @command{tail} cannot). It also has no @option{-r} option (print in
2672 reverse), since reversing a file is really a different job from printing
2673 the end of a file; BSD @command{tail} (which is the one with @option{-r}) can
2674 only reverse files that are at most as large as its buffer, which is
2675 typically 32 KiB@. A more reliable and versatile way to reverse files is
2676 the @sc{gnu} @command{tac} command.
2678 The program accepts the following options. Also see @ref{Common options}.
2682 @item -c @var{bytes}
2683 @itemx --bytes=@var{bytes}
2686 Output the last @var{bytes} bytes, instead of final lines.
2687 However, if @var{n} starts with a @samp{+}, start printing with the
2688 @var{n}th byte from the start of each file, instead of from the end.
2689 Appending @samp{b} multiplies @var{bytes} by 512,
2690 @samp{kB} by 1000, @samp{K} by 1024,
2691 @samp{MB} by 1000*1000, @samp{M} by 1024*1024,
2692 @samp{GB} by 1000*1000*1000, @samp{G} by 1024*1024*1024,
2693 and so on for @samp{T}, @samp{P}, @samp{E}, @samp{Z}, and @samp{Y}.
2696 @itemx --follow[=@var{how}]
2699 @cindex growing files
2700 @vindex name @r{follow option}
2701 @vindex descriptor @r{follow option}
2702 Loop forever trying to read more characters at the end of the file,
2703 presumably because the file is growing.
2704 If more than one file is given, @command{tail} prints a header whenever it
2705 gets output from a different file, to indicate which file that output is
2708 There are two ways to specify how you'd like to track files with this option,
2709 but that difference is noticeable only when a followed file is removed or
2711 If you'd like to continue to track the end of a growing file even after
2712 it has been unlinked, use @option{--follow=descriptor}. This is the default
2713 behavior, but it is not useful if you're tracking a log file that may be
2714 rotated (removed or renamed, then reopened). In that case, use
2715 @option{--follow=name} to track the named file by reopening it periodically
2716 to see if it has been removed and recreated by some other program.
2718 No matter which method you use, if the tracked file is determined to have
2719 shrunk, @command{tail} prints a message saying the file has been truncated
2720 and resumes tracking the end of the file from the newly-determined endpoint.
2722 When a file is removed, @command{tail}'s behavior depends on whether it is
2723 following the name or the descriptor. When following by name, tail can
2724 detect that a file has been removed and gives a message to that effect,
2725 and if @option{--retry} has been specified it will continue checking
2726 periodically to see if the file reappears.
2727 When following a descriptor, tail does not detect that the file has
2728 been unlinked or renamed and issues no message; even though the file
2729 may no longer be accessible via its original name, it may still be
2732 The option values @samp{descriptor} and @samp{name} may be specified only
2733 with the long form of the option, not with @option{-f}.
2735 @vindex POSIXLY_CORRECT
2736 If @env{POSIXLY_CORRECT} is set, the @option{-f} option is ignored if
2737 no @var{file} operand is specified and standard input is a FIFO or a pipe.
2741 This option is the same as @option{--follow=name --retry}. That is, tail
2742 will attempt to reopen a file when it is removed. Should this fail, tail
2743 will keep trying until it becomes accessible again.
2747 This option is useful mainly when following by name (i.e., with
2748 @option{--follow=name}).
2749 Without this option, when tail encounters a file that doesn't
2750 exist or is otherwise inaccessible, it reports that fact and
2751 never checks it again.
2753 @itemx --sleep-interval=@var{number}
2754 @opindex --sleep-interval
2755 Change the number of seconds to wait between iterations (the default is 1.0).
2756 During one iteration, every specified file is checked to see if it has
2758 Historical implementations of @command{tail} have required that
2759 @var{number} be an integer. However, GNU @command{tail} accepts
2760 an arbitrary floating point number (using a period before any
2763 @itemx --pid=@var{pid}
2765 When following by name or by descriptor, you may specify the process ID,
2766 @var{pid}, of the sole writer of all @var{file} arguments. Then, shortly
2767 after that process terminates, tail will also terminate. This will
2768 work properly only if the writer and the tailing process are running on
2769 the same machine. For example, to save the output of a build in a file
2770 and to watch the file grow, if you invoke @command{make} and @command{tail}
2771 like this then the tail process will stop when your build completes.
2772 Without this option, you would have had to kill the @code{tail -f}
2776 $ make >& makerr & tail --pid=$! -f makerr
2779 If you specify a @var{pid} that is not in use or that does not correspond
2780 to the process that is writing to the tailed files, then @command{tail}
2781 may terminate long before any @var{file}s stop growing or it may not
2782 terminate until long after the real writer has terminated.
2783 Note that @option{--pid} cannot be supported on some systems; @command{tail}
2784 will print a warning if this is the case.
2786 @itemx --max-unchanged-stats=@var{n}
2787 @opindex --max-unchanged-stats
2788 When tailing a file by name, if there have been @var{n} (default
2789 n=@value{DEFAULT_MAX_N_UNCHANGED_STATS_BETWEEN_OPENS}) consecutive
2790 iterations for which the file has not changed, then
2791 @code{open}/@code{fstat} the file to determine if that file name is
2792 still associated with the same device/inode-number pair as before.
2793 When following a log file that is rotated, this is approximately the
2794 number of seconds between when tail prints the last pre-rotation lines
2795 and when it prints the lines that have accumulated in the new log file.
2796 This option is meaningful only when following by name.
2799 @itemx --lines=@var{n}
2802 Output the last @var{n} lines.
2803 However, if @var{n} starts with a @samp{+}, start printing with the
2804 @var{n}th line from the start of each file, instead of from the end.
2805 Size multiplier suffixes are the same as with the @option{-c} option.
2813 Never print file name headers.
2819 Always print file name headers.
2823 For compatibility @command{tail} also supports an obsolete usage
2824 @samp{tail -[@var{count}][bcl][f] [@var{file}]}, which is recognized
2825 only if it does not conflict with the usage described
2826 above. This obsolete form uses exactly one option and at most one
2827 file. In the option, @var{count} is an optional decimal number optionally
2828 followed by a size letter (@samp{b}, @samp{c}, @samp{l}) to mean count
2829 by 512-byte blocks, bytes, or lines, optionally followed by @samp{f}
2830 which has the same meaning as @option{-f}.
2832 @vindex _POSIX2_VERSION
2833 On older systems, the leading @samp{-} can be replaced by @samp{+} in
2834 the obsolete option syntax with the same meaning as in counts, and
2835 obsolete usage overrides normal usage when the two conflict.
2836 This obsolete behavior can be enabled or disabled with the
2837 @env{_POSIX2_VERSION} environment variable (@pxref{Standards
2840 Scripts intended for use on standard hosts should avoid obsolete
2841 syntax and should use @option{-c @var{count}[b]}, @option{-n
2842 @var{count}}, and/or @option{-f} instead. If your script must also
2843 run on hosts that support only the obsolete syntax, you can often
2844 rewrite it to avoid problematic usages, e.g., by using @samp{sed -n
2845 '$p'} rather than @samp{tail -1}. If that's not possible, the script
2846 can use a test like @samp{if tail -c +1 </dev/null >/dev/null 2>&1;
2847 then @dots{}} to decide which syntax to use.
2849 Even if your script assumes the standard behavior, you should still
2850 beware usages whose behaviors differ depending on the @acronym{POSIX}
2851 version. For example, avoid @samp{tail - main.c}, since it might be
2852 interpreted as either @samp{tail main.c} or as @samp{tail -- -
2853 main.c}; avoid @samp{tail -c 4}, since it might mean either @samp{tail
2854 -c4} or @samp{tail -c 10 4}; and avoid @samp{tail +4}, since it might
2855 mean either @samp{tail ./+4} or @samp{tail -n +4}.
2860 @node split invocation
2861 @section @command{split}: Split a file into fixed-size pieces
2864 @cindex splitting a file into pieces
2865 @cindex pieces, splitting a file into
2867 @command{split} creates output files containing consecutive sections of
2868 @var{input} (standard input if none is given or @var{input} is
2869 @samp{-}). Synopsis:
2872 split [@var{option}] [@var{input} [@var{prefix}]]
2875 By default, @command{split} puts 1000 lines of @var{input} (or whatever is
2876 left over for the last section), into each output file.
2878 @cindex output file name prefix
2879 The output files' names consist of @var{prefix} (@samp{x} by default)
2880 followed by a group of characters (@samp{aa}, @samp{ab}, @dots{} by
2881 default), such that concatenating the output files in traditional
2882 sorted order by file name produces
2883 the original input file. If the output file names are exhausted,
2884 @command{split} reports an error without deleting the output files
2887 The program accepts the following options. Also see @ref{Common options}.
2891 @item -l @var{lines}
2892 @itemx --lines=@var{lines}
2895 Put @var{lines} lines of @var{input} into each output file.
2897 For compatibility @command{split} also supports an obsolete
2898 option syntax @option{-@var{lines}}. New scripts should use @option{-l
2899 @var{lines}} instead.
2902 @itemx --bytes=@var{size}
2905 Put @var{size} bytes of @var{input} into each output file.
2906 @var{size} is a number which may be followed by one of these
2907 multiplicative suffixes:
2909 @samp{b} => 512 ("blocks")
2910 @samp{KB} => 1000 (KiloBytes)
2911 @samp{K} => 1024 (KibiBytes)
2912 @samp{MB} => 1000*1000 (MegaBytes)
2913 @samp{M} => 1024*1024 (MebiBytes)
2915 and so on for @samp{G}, @samp{T}, @samp{P}, @samp{E}, @samp{Z}, and @samp{Y}.
2918 @itemx --line-bytes=@var{size}
2920 @opindex --line-bytes
2921 Put into each output file as many complete lines of @var{input} as
2922 possible without exceeding @var{size} bytes. Individual lines longer than
2923 @var{size} bytes are broken into multiple files.
2924 @var{size} has the same format as for the @option{--bytes} option.
2926 @item -a @var{length}
2927 @itemx --suffix-length=@var{length}
2929 @opindex --suffix-length
2930 Use suffixes of length @var{length}. The default @var{length} is 2.
2933 @itemx --numeric-suffixes
2935 @opindex --numeric-suffixes
2936 Use digits in suffixes rather than lower-case letters.
2940 Write a diagnostic just before each output file is opened.
2947 @node csplit invocation
2948 @section @command{csplit}: Split a file into context-determined pieces
2951 @cindex context splitting
2952 @cindex splitting a file into pieces by context
2954 @command{csplit} creates zero or more output files containing sections of
2955 @var{input} (standard input if @var{input} is @samp{-}). Synopsis:
2958 csplit [@var{option}]@dots{} @var{input} @var{pattern}@dots{}
2961 The contents of the output files are determined by the @var{pattern}
2962 arguments, as detailed below. An error occurs if a @var{pattern}
2963 argument refers to a nonexistent line of the input file (e.g., if no
2964 remaining line matches a given regular expression). After every
2965 @var{pattern} has been matched, any remaining input is copied into one
2968 By default, @command{csplit} prints the number of bytes written to each
2969 output file after it has been created.
2971 The types of pattern arguments are:
2976 Create an output file containing the input up to but not including line
2977 @var{n} (a positive integer). If followed by a repeat count, also
2978 create an output file containing the next @var{n} lines of the input
2979 file once for each repeat.
2981 @item /@var{regexp}/[@var{offset}]
2982 Create an output file containing the current line up to (but not
2983 including) the next line of the input file that contains a match for
2984 @var{regexp}. The optional @var{offset} is an integer.
2985 If it is given, the input up to (but not including) the
2986 matching line plus or minus @var{offset} is put into the output file,
2987 and the line after that begins the next section of input.
2989 @item %@var{regexp}%[@var{offset}]
2990 Like the previous type, except that it does not create an output
2991 file, so that section of the input file is effectively ignored.
2993 @item @{@var{repeat-count}@}
2994 Repeat the previous pattern @var{repeat-count} additional
2995 times. The @var{repeat-count} can either be a positive integer or an
2996 asterisk, meaning repeat as many times as necessary until the input is
3001 The output files' names consist of a prefix (@samp{xx} by default)
3002 followed by a suffix. By default, the suffix is an ascending sequence
3003 of two-digit decimal numbers from @samp{00} to @samp{99}. In any case,
3004 concatenating the output files in sorted order by file name produces the
3005 original input file.
3007 By default, if @command{csplit} encounters an error or receives a hangup,
3008 interrupt, quit, or terminate signal, it removes any output files
3009 that it has created so far before it exits.
3011 The program accepts the following options. Also see @ref{Common options}.
3015 @item -f @var{prefix}
3016 @itemx --prefix=@var{prefix}
3019 @cindex output file name prefix
3020 Use @var{prefix} as the output file name prefix.
3022 @item -b @var{suffix}
3023 @itemx --suffix=@var{suffix}
3026 @cindex output file name suffix
3027 Use @var{suffix} as the output file name suffix. When this option is
3028 specified, the suffix string must include exactly one
3029 @code{printf(3)}-style conversion specification, possibly including
3030 format specification flags, a field width, a precision specifications,
3031 or all of these kinds of modifiers. The format letter must convert a
3032 binary integer argument to readable form; thus, only @samp{d}, @samp{i},
3033 @samp{u}, @samp{o}, @samp{x}, and @samp{X} conversions are allowed. The
3034 entire @var{suffix} is given (with the current output file number) to
3035 @code{sprintf(3)} to form the file name suffixes for each of the
3036 individual output files in turn. If this option is used, the
3037 @option{--digits} option is ignored.
3039 @item -n @var{digits}
3040 @itemx --digits=@var{digits}
3043 Use output file names containing numbers that are @var{digits} digits
3044 long instead of the default 2.
3049 @opindex --keep-files
3050 Do not remove output files when errors are encountered.
3053 @itemx --elide-empty-files
3055 @opindex --elide-empty-files
3056 Suppress the generation of zero-length output files. (In cases where
3057 the section delimiters of the input file are supposed to mark the first
3058 lines of each of the sections, the first output file will generally be a
3059 zero-length file unless you use this option.) The output file sequence
3060 numbers always run consecutively starting from 0, even when this option
3071 Do not print counts of output file sizes.
3078 @node Summarizing files
3079 @chapter Summarizing files
3081 @cindex summarizing files
3083 These commands generate just a few numbers representing entire
3087 * wc invocation:: Print newline, word, and byte counts.
3088 * sum invocation:: Print checksum and block counts.
3089 * cksum invocation:: Print CRC checksum and byte counts.
3090 * md5sum invocation:: Print or check MD5 digests.
3091 * sha1sum invocation:: Print or check SHA-1 digests.
3092 * sha2 utilities:: Print or check SHA-2 digests.
3097 @section @command{wc}: Print newline, word, and byte counts
3101 @cindex character count
3105 @command{wc} counts the number of bytes, characters, whitespace-separated
3106 words, and newlines in each given @var{file}, or standard input if none
3107 are given or for a @var{file} of @samp{-}. Synopsis:
3110 wc [@var{option}]@dots{} [@var{file}]@dots{}
3113 @cindex total counts
3114 @command{wc} prints one line of counts for each file, and if the file was
3115 given as an argument, it prints the file name following the counts. If
3116 more than one @var{file} is given, @command{wc} prints a final line
3117 containing the cumulative counts, with the file name @file{total}. The
3118 counts are printed in this order: newlines, words, characters, bytes,
3119 maximum line length.
3120 Each count is printed right-justified in a field with at least one
3121 space between fields so that the numbers and file names normally line
3122 up nicely in columns. The width of the count fields varies depending
3123 on the inputs, so you should not depend on a particular field width.
3124 However, as a @acronym{GNU} extension, if only one count is printed,
3125 it is guaranteed to be printed without leading spaces.
3127 By default, @command{wc} prints three counts: the newline, words, and byte
3128 counts. Options can specify that only certain counts be printed.
3129 Options do not undo others previously given, so
3136 prints both the byte counts and the word counts.
3138 With the @option{--max-line-length} option, @command{wc} prints the length
3139 of the longest line per file, and if there is more than one file it
3140 prints the maximum (not the sum) of those lengths. The line lengths here
3141 are measured in screen columns, according to the current locale and
3142 assuming tab positions in every 8th column.
3144 The program accepts the following options. Also see @ref{Common options}.
3152 Print only the byte counts.
3158 Print only the character counts.
3164 Print only the word counts.
3170 Print only the newline counts.
3173 @itemx --max-line-length
3175 @opindex --max-line-length
3176 Print only the maximum line lengths.
3178 @macro filesZeroFromOption{cmd,withTotalOption,subListOutput}
3179 @itemx --files0-from=@var{FILE}
3180 @opindex --files0-from=@var{FILE}
3181 @c This is commented out to avoid a texi2dvi failure.
3182 @c texi2dvi (GNU Texinfo 4.11) 1.104
3183 @c @cindex including files from @command{\cmd\}
3184 Rather than processing files named on the command line, process those
3185 named in file @var{FILE}; each name is terminated by a null byte.
3186 This is useful \withTotalOption\
3187 when the list of file names is so long that it may exceed a command line
3189 In such cases, running @command{\cmd\} via @command{xargs} is undesirable
3190 because it splits the list into pieces and makes @command{\cmd\} print
3191 \subListOutput\ for each sublist rather than for the entire list.
3192 One way to produce a list of null-byte-terminated file names is with @sc{gnu}
3193 @command{find}, using its @option{-print0} predicate.
3194 Do not specify any @var{FILE} on the command line when using this option.
3196 @filesZeroFromOption{wc,,a total}
3198 For example, to find the length of the longest line in any @file{.c} or
3199 @file{.h} file in the current hierarchy, do this:
3202 find . -name '*.[ch]' -print0 |
3203 wc -L --files0-from=- | tail -n1
3211 @node sum invocation
3212 @section @command{sum}: Print checksum and block counts
3215 @cindex 16-bit checksum
3216 @cindex checksum, 16-bit
3218 @command{sum} computes a 16-bit checksum for each given @var{file}, or
3219 standard input if none are given or for a @var{file} of @samp{-}. Synopsis:
3222 sum [@var{option}]@dots{} [@var{file}]@dots{}
3225 @command{sum} prints the checksum for each @var{file} followed by the
3226 number of blocks in the file (rounded up). If more than one @var{file}
3227 is given, file names are also printed (by default). (With the
3228 @option{--sysv} option, corresponding file names are printed when there is
3229 at least one file argument.)
3231 By default, @sc{gnu} @command{sum} computes checksums using an algorithm
3232 compatible with BSD @command{sum} and prints file sizes in units of
3235 The program accepts the following options. Also see @ref{Common options}.
3241 @cindex BSD @command{sum}
3242 Use the default (BSD compatible) algorithm. This option is included for
3243 compatibility with the System V @command{sum}. Unless @option{-s} was also
3244 given, it has no effect.
3250 @cindex System V @command{sum}
3251 Compute checksums using an algorithm compatible with System V
3252 @command{sum}'s default, and print file sizes in units of 512-byte blocks.
3256 @command{sum} is provided for compatibility; the @command{cksum} program (see
3257 next section) is preferable in new applications.
3262 @node cksum invocation
3263 @section @command{cksum}: Print CRC checksum and byte counts
3266 @cindex cyclic redundancy check
3267 @cindex CRC checksum
3269 @command{cksum} computes a cyclic redundancy check (CRC) checksum for each
3270 given @var{file}, or standard input if none are given or for a
3271 @var{file} of @samp{-}. Synopsis:
3274 cksum [@var{option}]@dots{} [@var{file}]@dots{}
3277 @command{cksum} prints the CRC checksum for each file along with the number
3278 of bytes in the file, and the file name unless no arguments were given.
3280 @command{cksum} is typically used to ensure that files
3281 transferred by unreliable means (e.g., netnews) have not been corrupted,
3282 by comparing the @command{cksum} output for the received files with the
3283 @command{cksum} output for the original files (typically given in the
3286 The CRC algorithm is specified by the @acronym{POSIX} standard. It is not
3287 compatible with the BSD or System V @command{sum} algorithms (see the
3288 previous section); it is more robust.
3290 The only options are @option{--help} and @option{--version}. @xref{Common
3296 @node md5sum invocation
3297 @section @command{md5sum}: Print or check MD5 digests
3301 @cindex 128-bit checksum
3302 @cindex checksum, 128-bit
3303 @cindex fingerprint, 128-bit
3304 @cindex message-digest, 128-bit
3306 @command{md5sum} computes a 128-bit checksum (or @dfn{fingerprint} or
3307 @dfn{message-digest}) for each specified @var{file}.
3309 Note: The MD5 digest is more reliable than a simple CRC (provided by
3310 the @command{cksum} command) for detecting accidental file corruption,
3311 as the chances of accidentally having two files with identical MD5
3312 are vanishingly small. However, it should not be considered truly
3313 secure against malicious tampering: although finding a file with a
3314 given MD5 fingerprint, or modifying a file so as to retain its MD5 are
3315 considered infeasible at the moment, it is known how to produce
3316 different files with identical MD5 (a ``collision''), something which
3317 can be a security issue in certain contexts. For more secure hashes,
3318 consider using SHA-1 or SHA-2. @xref{sha1sum invocation}, and
3319 @ref{sha2 utilities}.
3321 If a @var{file} is specified as @samp{-} or if no files are given
3322 @command{md5sum} computes the checksum for the standard input.
3323 @command{md5sum} can also determine whether a file and checksum are
3324 consistent. Synopsis:
3327 md5sum [@var{option}]@dots{} [@var{file}]@dots{}
3330 For each @var{file}, @samp{md5sum} outputs the MD5 checksum, a flag
3331 indicating a binary or text input file, and the file name.
3332 If @var{file} contains a backslash or newline, the
3333 line is started with a backslash, and each problematic character in
3334 the file name is escaped with a backslash, making the output
3335 unambiguous even in the presence of arbitrary file names.
3336 If @var{file} is omitted or specified as @samp{-}, standard input is read.
3338 The program accepts the following options. Also see @ref{Common options}.
3346 @cindex binary input files
3347 Treat each input file as binary, by reading it in binary mode and
3348 outputting a @samp{*} flag. This is the inverse of @option{--text}.
3349 On systems like @acronym{GNU} that do not distinguish between binary
3350 and text files, this option merely flags each input file as binary:
3351 the MD5 checksum is unaffected. This option is the default on systems
3352 like MS-DOS that distinguish between binary and text files, except
3353 for reading standard input when standard input is a terminal.
3357 Read file names and checksum information (not data) from each
3358 @var{file} (or from stdin if no @var{file} was specified) and report
3359 whether the checksums match the contents of the named files.
3360 The input to this mode of @command{md5sum} is usually the output of
3361 a prior, checksum-generating run of @samp{md5sum}.
3362 Each valid line of input consists of an MD5 checksum, a binary/text
3363 flag, and then a file name.
3364 Binary files are marked with @samp{*}, text with @samp{ }.
3365 For each such line, @command{md5sum} reads the named file and computes its
3366 MD5 checksum. Then, if the computed message digest does not match the
3367 one on the line with the file name, the file is noted as having
3368 failed the test. Otherwise, the file passes the test.
3369 By default, for each valid line, one line is written to standard
3370 output indicating whether the named file passed the test.
3371 After all checks have been performed, if there were any failures,
3372 a warning is issued to standard error.
3373 Use the @option{--status} option to inhibit that output.
3374 If any listed file cannot be opened or read, if any valid line has
3375 an MD5 checksum inconsistent with the associated file, or if no valid
3376 line is found, @command{md5sum} exits with nonzero status. Otherwise,
3377 it exits successfully.
3381 @cindex verifying MD5 checksums
3382 This option is useful only when verifying checksums.
3383 When verifying checksums, don't generate an 'OK' message per successfully
3384 checked file. Files that fail the verification are reported in the
3385 default one-line-per-file format. If there is any checksum mismatch,
3386 print a warning summarizing the failures to standard error.
3390 @cindex verifying MD5 checksums
3391 This option is useful only when verifying checksums.
3392 When verifying checksums, don't generate the default one-line-per-file
3393 diagnostic and don't output the warning summarizing any failures.
3394 Failures to open or read a file still evoke individual diagnostics to
3396 If all listed files are readable and are consistent with the associated
3397 MD5 checksums, exit successfully. Otherwise exit with a status code
3398 indicating there was a failure.
3404 @cindex text input files
3405 Treat each input file as text, by reading it in text mode and
3406 outputting a @samp{ } flag. This is the inverse of @option{--binary}.
3407 This option is the default on systems like @acronym{GNU} that do not
3408 distinguish between binary and text files. On other systems, it is
3409 the default for reading standard input when standard input is a
3416 @cindex verifying MD5 checksums
3417 When verifying checksums, warn about improperly formatted MD5 checksum lines.
3418 This option is useful only if all but a few lines in the checked input
3426 @node sha1sum invocation
3427 @section @command{sha1sum}: Print or check SHA-1 digests
3431 @cindex 160-bit checksum
3432 @cindex checksum, 160-bit
3433 @cindex fingerprint, 160-bit
3434 @cindex message-digest, 160-bit
3436 @command{sha1sum} computes a 160-bit checksum for each specified
3437 @var{file}. The usage and options of this command are precisely the
3438 same as for @command{md5sum}. @xref{md5sum invocation}.
3440 Note: The SHA-1 digest is more secure than MD5, and no collisions of
3441 it are known (different files having the same fingerprint). However,
3442 it is known that they can be produced with considerable, but not
3443 unreasonable, resources. For this reason, it is generally considered
3444 that SHA-1 should be gradually phased out in favor of the more secure
3445 SHA-2 hash algorithms. @xref{sha2 utilities}.
3448 @node sha2 utilities
3449 @section sha2 utilities: Print or check SHA-2 digests
3456 @cindex 224-bit checksum
3457 @cindex 256-bit checksum
3458 @cindex 384-bit checksum
3459 @cindex 512-bit checksum
3460 @cindex checksum, 224-bit
3461 @cindex checksum, 256-bit
3462 @cindex checksum, 384-bit
3463 @cindex checksum, 512-bit
3464 @cindex fingerprint, 224-bit
3465 @cindex fingerprint, 256-bit
3466 @cindex fingerprint, 384-bit
3467 @cindex fingerprint, 512-bit
3468 @cindex message-digest, 224-bit
3469 @cindex message-digest, 256-bit
3470 @cindex message-digest, 384-bit
3471 @cindex message-digest, 512-bit
3473 The commands @command{sha224sum}, @command{sha256sum},
3474 @command{sha384sum} and @command{sha512sum} compute checksums of
3475 various lengths (respectively 224, 256, 384 and 512 bits),
3476 collectively known as the SHA-2 hashes. The usage and options of
3477 these commands are precisely the same as for @command{md5sum}.
3478 @xref{md5sum invocation}.
3480 Note: The SHA384 and SHA512 digests are considerably slower to
3481 compute, especially on 32-bit computers, than SHA224 or SHA256.
3484 @node Operating on sorted files
3485 @chapter Operating on sorted files
3487 @cindex operating on sorted files
3488 @cindex sorted files, operations on
3490 These commands work with (or produce) sorted files.
3493 * sort invocation:: Sort text files.
3494 * shuf invocation:: Shuffle text files.
3495 * uniq invocation:: Uniquify files.
3496 * comm invocation:: Compare two sorted files line by line.
3497 * ptx invocation:: Produce a permuted index of file contents.
3498 * tsort invocation:: Topological sort.
3499 * tsort background:: Where tsort came from.
3503 @node sort invocation
3504 @section @command{sort}: Sort text files
3507 @cindex sorting files
3509 @command{sort} sorts, merges, or compares all the lines from the given
3510 files, or standard input if none are given or for a @var{file} of
3511 @samp{-}. By default, @command{sort} writes the results to standard
3515 sort [@var{option}]@dots{} [@var{file}]@dots{}
3518 @command{sort} has three modes of operation: sort (the default), merge,
3519 and check for sortedness. The following options change the operation
3526 @itemx --check=diagnose-first
3529 @cindex checking for sortedness
3530 Check whether the given file is already sorted: if it is not all
3531 sorted, print a diagnostic containing the first out-of-order line and
3532 exit with a status of 1.
3533 Otherwise, exit successfully.
3534 At most one input file can be given.
3537 @itemx --check=quiet
3538 @itemx --check=silent
3541 @cindex checking for sortedness
3542 Exit successfully if the given file is already sorted, and
3543 exit with status 1 otherwise.
3544 At most one input file can be given.
3545 This is like @option{-c}, except it does not print a diagnostic.
3551 @cindex merging sorted files
3552 Merge the given files by sorting them as a group. Each input file must
3553 always be individually sorted. It always works to sort instead of
3554 merge; merging is provided because it is faster, in the case where it
3559 @cindex sort stability
3560 @cindex sort's last-resort comparison
3561 A pair of lines is compared as follows:
3562 @command{sort} compares each pair of fields, in the
3563 order specified on the command line, according to the associated
3564 ordering options, until a difference is found or no fields are left.
3565 If no key fields are specified, @command{sort} uses a default key of
3566 the entire line. Finally, as a last resort when all keys compare
3567 equal, @command{sort} compares entire lines as if no ordering options
3568 other than @option{--reverse} (@option{-r}) were specified. The
3569 @option{--stable} (@option{-s}) option disables this @dfn{last-resort
3570 comparison} so that lines in which all fields compare equal are left
3571 in their original relative order. The @option{--unique}
3572 (@option{-u}) option also disables the last-resort comparison.
3576 Unless otherwise specified, all comparisons use the character collating
3577 sequence specified by the @env{LC_COLLATE} locale.@footnote{If you
3578 use a non-@acronym{POSIX} locale (e.g., by setting @env{LC_ALL}
3579 to @samp{en_US}), then @command{sort} may produce output that is sorted
3580 differently than you're accustomed to. In that case, set the @env{LC_ALL}
3581 environment variable to @samp{C}. Note that setting only @env{LC_COLLATE}
3582 has two problems. First, it is ineffective if @env{LC_ALL} is also set.
3583 Second, it has undefined behavior if @env{LC_CTYPE} (or @env{LANG}, if
3584 @env{LC_CTYPE} is unset) is set to an incompatible value. For example,
3585 you get undefined behavior if @env{LC_CTYPE} is @code{ja_JP.PCK} but
3586 @env{LC_COLLATE} is @code{en_US.UTF-8}.}
3588 @sc{gnu} @command{sort} (as specified for all @sc{gnu} utilities) has no
3589 limit on input line length or restrictions on bytes allowed within lines.
3590 In addition, if the final byte of an input file is not a newline, @sc{gnu}
3591 @command{sort} silently supplies one. A line's trailing newline is not
3592 part of the line for comparison purposes.
3594 @cindex exit status of @command{sort}
3598 0 if no error occurred
3599 1 if invoked with @option{-c} or @option{-C} and the input is not sorted
3600 2 if an error occurred
3604 If the environment variable @env{TMPDIR} is set, @command{sort} uses its
3605 value as the directory for temporary files instead of @file{/tmp}. The
3606 @option{--temporary-directory} (@option{-T}) option in turn overrides
3607 the environment variable.
3609 The following options affect the ordering of output lines. They may be
3610 specified globally or as part of a specific key field. If no key
3611 fields are specified, global options apply to comparison of entire
3612 lines; otherwise the global options are inherited by key fields that do
3613 not specify any special options of their own. In pre-@acronym{POSIX}
3614 versions of @command{sort}, global options affect only later key fields,
3615 so portable shell scripts should specify global options first.
3620 @itemx --ignore-leading-blanks
3622 @opindex --ignore-leading-blanks
3623 @cindex blanks, ignoring leading
3625 Ignore leading blanks when finding sort keys in each line.
3626 By default a blank is a space or a tab, but the @env{LC_CTYPE} locale
3630 @itemx --dictionary-order
3632 @opindex --dictionary-order
3633 @cindex dictionary order
3634 @cindex phone directory order
3635 @cindex telephone directory order
3637 Sort in @dfn{phone directory} order: ignore all characters except
3638 letters, digits and blanks when sorting.
3639 By default letters and digits are those of @acronym{ASCII} and a blank
3640 is a space or a tab, but the @env{LC_CTYPE} locale can change this.
3643 @itemx --ignore-case
3645 @opindex --ignore-case
3646 @cindex ignoring case
3647 @cindex case folding
3649 Fold lowercase characters into the equivalent uppercase characters when
3650 comparing so that, for example, @samp{b} and @samp{B} sort as equal.
3651 The @env{LC_CTYPE} locale determines character types.
3654 @itemx --general-numeric-sort
3655 @itemx --sort=general-numeric
3657 @opindex --general-numeric-sort
3659 @cindex general numeric sort
3661 Sort numerically, using the standard C function @code{strtod} to convert
3662 a prefix of each line to a double-precision floating point number.
3663 This allows floating point numbers to be specified in scientific notation,
3664 like @code{1.0e-34} and @code{10e100}.
3665 The @env{LC_NUMERIC} locale determines the decimal-point character.
3666 Do not report overflow, underflow, or conversion errors.
3667 Use the following collating sequence:
3671 Lines that do not start with numbers (all considered to be equal).
3673 NaNs (``Not a Number'' values, in IEEE floating point arithmetic)
3674 in a consistent but machine-dependent order.
3678 Finite numbers in ascending numeric order (with @math{-0} and @math{+0} equal).
3683 Use this option only if there is no alternative; it is much slower than
3684 @option{--numeric-sort} (@option{-n}) and it can lose information when
3685 converting to floating point.
3688 @itemx --ignore-nonprinting
3690 @opindex --ignore-nonprinting
3691 @cindex nonprinting characters, ignoring
3692 @cindex unprintable characters, ignoring
3694 Ignore nonprinting characters.
3695 The @env{LC_CTYPE} locale determines character types.
3696 This option has no effect if the stronger @option{--dictionary-order}
3697 (@option{-d}) option is also given.
3703 @opindex --month-sort
3705 @cindex months, sorting by
3707 An initial string, consisting of any amount of blanks, followed
3708 by a month name abbreviation, is folded to UPPER case and
3709 compared in the order @samp{JAN} < @samp{FEB} < @dots{} < @samp{DEC}.
3710 Invalid names compare low to valid names. The @env{LC_TIME} locale
3711 category determines the month spellings.
3712 By default a blank is a space or a tab, but the @env{LC_CTYPE} locale
3716 @itemx --numeric-sort
3717 @itemx --sort=numeric
3719 @opindex --numeric-sort
3721 @cindex numeric sort
3723 Sort numerically. The number begins each line and consists
3724 of optional blanks, an optional @samp{-} sign, and zero or more
3725 digits possibly separated by thousands separators, optionally followed
3726 by a decimal-point character and zero or more digits. An empty
3727 number is treated as @samp{0}. The @env{LC_NUMERIC}
3728 locale specifies the decimal-point character and thousands separator.
3729 By default a blank is a space or a tab, but the @env{LC_CTYPE} locale
3732 Comparison is exact; there is no rounding error.
3734 Neither a leading @samp{+} nor exponential notation is recognized.
3735 To compare such strings numerically, use the
3736 @option{--general-numeric-sort} (@option{-g}) option.
3739 @itemx --version-sort
3741 @opindex --version-sort
3742 @cindex version number sort
3744 Sort per @code{strverscmp(3)}. This is a normal string comparison, except
3745 that embedded decimal numbers are sorted by numeric value
3746 (see @option{--numeric-sort} above).
3752 @cindex reverse sorting
3753 Reverse the result of comparison, so that lines with greater key values
3754 appear earlier in the output instead of later.
3757 @itemx --random-sort
3758 @itemx --sort=random
3760 @opindex --random-sort
3763 Sort by hashing the input keys and then sorting the hash values.
3764 Choose the hash function at random, ensuring that it is free of
3765 collisions so that differing keys have differing hash values. This is
3766 like a random permutation of the inputs (@pxref{shuf invocation}),
3767 except that keys with the same value sort together.
3769 If multiple random sort fields are specified, the same random hash
3770 function is used for all fields. To use different random hash
3771 functions for different fields, you can invoke @command{sort} more
3774 The choice of hash function is affected by the
3775 @option{--random-source} option.
3783 @item --compress-program=@var{prog}
3784 Compress any temporary files with the program @var{prog}.
3786 With no arguments, @var{prog} must compress standard input to standard
3787 output, and when given the @option{-d} option it must decompress
3788 standard input to standard output.
3790 Terminate with an error if @var{prog} exits with nonzero status.
3792 White space and the backslash character should not appear in
3793 @var{prog}; they are reserved for future use.
3795 @filesZeroFromOption{sort,,sorted output}
3797 @item -k @var{pos1}[,@var{pos2}]
3798 @itemx --key=@var{pos1}[,@var{pos2}]
3802 Specify a sort field that consists of the part of the line between
3803 @var{pos1} and @var{pos2} (or the end of the line, if @var{pos2} is
3804 omitted), @emph{inclusive}.
3806 Each @var{pos} has the form @samp{@var{f}[.@var{c}][@var{opts}]},
3807 where @var{f} is the number of the field to use, and @var{c} is the number
3808 of the first character from the beginning of the field. Fields and character
3809 positions are numbered starting with 1; a character position of zero in
3810 @var{pos2} indicates the field's last character. If @samp{.@var{c}} is
3811 omitted from @var{pos1}, it defaults to 1 (the beginning of the field);
3812 if omitted from @var{pos2}, it defaults to 0 (the end of the field).
3813 @var{opts} are ordering options, allowing individual keys to be sorted
3814 according to different rules; see below for details. Keys can span
3817 Example: To sort on the second field, use @option{--key=2,2}
3818 (@option{-k 2,2}). See below for more examples.
3820 @item --batch-size=@var{nmerge}
3821 @opindex --batch-size
3822 @cindex number of inputs to merge, nmerge
3823 Merge at most @var{nmerge} inputs at once.
3825 When @command{sort} has to merge more than @var{nmerge} inputs,
3826 it merges them in groups of @var{nmerge}, saving the result in
3827 a temporary file, which is then used as an input in a subsequent merge.
3829 A large value of @var{nmerge} may improve merge performance and decrease
3830 temporary storage utilization at the expense of increased memory usage
3831 and I/0. Conversely a small value of @var{nmerge} may reduce memory
3832 requirements and I/0 at the expense of temporary storage consumption and
3835 The value of @var{nmerge} must be at least 2.
3837 The value of @var{nmerge} may be bounded by a resource limit for open
3838 file descriptors. Try @samp{ulimit -n} or @samp{getconf OPEN_MAX} to
3839 to display the limit for a particular system.
3840 If the value of @var{nmerge} exceeds this limit, then @command{sort} will
3841 issue a warning to standard error and exit with a nonzero status.
3843 @item -o @var{output-file}
3844 @itemx --output=@var{output-file}
3847 @cindex overwriting of input, allowed
3848 Write output to @var{output-file} instead of standard output.
3849 Normally, @command{sort} reads all input before opening
3850 @var{output-file}, so you can safely sort a file in place by using
3851 commands like @code{sort -o F F} and @code{cat F | sort -o F}.
3852 However, @command{sort} with @option{--merge} (@option{-m}) can open
3853 the output file before reading all input, so a command like @code{cat
3854 F | sort -m -o F - G} is not safe as @command{sort} might start
3855 writing @file{F} before @command{cat} is done reading it.
3857 @vindex POSIXLY_CORRECT
3858 On newer systems, @option{-o} cannot appear after an input file if
3859 @env{POSIXLY_CORRECT} is set, e.g., @samp{sort F -o F}. Portable
3860 scripts should specify @option{-o @var{output-file}} before any input
3863 @item --random-source=@var{file}
3864 @opindex --random-source
3865 @cindex random source for sorting
3866 Use @var{file} as a source of random data used to determine which
3867 random hash function to use with the @option{-R} option. @xref{Random
3874 @cindex sort stability
3875 @cindex sort's last-resort comparison
3877 Make @command{sort} stable by disabling its last-resort comparison.
3878 This option has no effect if no fields or global ordering options
3879 other than @option{--reverse} (@option{-r}) are specified.
3882 @itemx --buffer-size=@var{size}
3884 @opindex --buffer-size
3885 @cindex size for main memory sorting
3886 Use a main-memory sort buffer of the given @var{size}. By default,
3887 @var{size} is in units of 1024 bytes. Appending @samp{%} causes
3888 @var{size} to be interpreted as a percentage of physical memory.
3889 Appending @samp{K} multiplies @var{size} by 1024 (the default),
3890 @samp{M} by 1,048,576, @samp{G} by 1,073,741,824, and so on for
3891 @samp{T}, @samp{P}, @samp{E}, @samp{Z}, and @samp{Y}. Appending
3892 @samp{b} causes @var{size} to be interpreted as a byte count, with no
3895 This option can improve the performance of @command{sort} by causing it
3896 to start with a larger or smaller sort buffer than the default.
3897 However, this option affects only the initial buffer size. The buffer
3898 grows beyond @var{size} if @command{sort} encounters input lines larger
3901 @item -t @var{separator}
3902 @itemx --field-separator=@var{separator}
3904 @opindex --field-separator
3905 @cindex field separator character
3906 Use character @var{separator} as the field separator when finding the
3907 sort keys in each line. By default, fields are separated by the empty
3908 string between a non-blank character and a blank character.
3909 By default a blank is a space or a tab, but the @env{LC_CTYPE} locale
3912 That is, given the input line @w{@samp{ foo bar}}, @command{sort} breaks it
3913 into fields @w{@samp{ foo}} and @w{@samp{ bar}}. The field separator is
3914 not considered to be part of either the field preceding or the field
3915 following, so with @samp{sort @w{-t " "}} the same input line has
3916 three fields: an empty field, @samp{foo}, and @samp{bar}.
3917 However, fields that extend to the end of the line,
3918 as @option{-k 2}, or fields consisting of a range, as @option{-k 2,3},
3919 retain the field separators present between the endpoints of the range.
3921 To specify a null character (@acronym{ASCII} @sc{nul}) as
3922 the field separator, use the two-character string @samp{\0}, e.g.,
3923 @samp{sort -t '\0'}.
3925 @item -T @var{tempdir}
3926 @itemx --temporary-directory=@var{tempdir}
3928 @opindex --temporary-directory
3929 @cindex temporary directory
3931 Use directory @var{tempdir} to store temporary files, overriding the
3932 @env{TMPDIR} environment variable. If this option is given more than
3933 once, temporary files are stored in all the directories given. If you
3934 have a large sort or merge that is I/O-bound, you can often improve
3935 performance by using this option to specify directories on different
3936 disks and controllers.
3942 @cindex uniquifying output
3944 Normally, output only the first of a sequence of lines that compare
3945 equal. For the @option{--check} (@option{-c} or @option{-C}) option,
3946 check that no pair of consecutive lines compares equal.
3948 This option also disables the default last-resort comparison.
3950 The commands @code{sort -u} and @code{sort | uniq} are equivalent, but
3951 this equivalence does not extend to arbitrary @command{sort} options.
3952 For example, @code{sort -n -u} inspects only the value of the initial
3953 numeric string when checking for uniqueness, whereas @code{sort -n |
3954 uniq} inspects the entire line. @xref{uniq invocation}.
3957 @itemx --zero-terminated
3959 @opindex --zero-terminated
3960 @cindex sort zero-terminated lines
3961 Treat the input as a set of lines, each terminated by a null character
3962 (@acronym{ASCII} @sc{nul}) instead of a line feed
3963 (@acronym{ASCII} @sc{lf}).
3964 This option can be useful in conjunction with @samp{perl -0} or
3965 @samp{find -print0} and @samp{xargs -0} which do the same in order to
3966 reliably handle arbitrary file names (even those containing blanks
3967 or other special characters).
3971 Historical (BSD and System V) implementations of @command{sort} have
3972 differed in their interpretation of some options, particularly
3973 @option{-b}, @option{-f}, and @option{-n}. @sc{gnu} sort follows the @acronym{POSIX}
3974 behavior, which is usually (but not always!) like the System V behavior.
3975 According to @acronym{POSIX}, @option{-n} no longer implies @option{-b}. For
3976 consistency, @option{-M} has been changed in the same way. This may
3977 affect the meaning of character positions in field specifications in
3978 obscure cases. The only fix is to add an explicit @option{-b}.
3980 A position in a sort field specified with @option{-k} may have any
3981 of the option letters @samp{Mbdfinr} appended to it, in which case the
3982 global ordering options are not used for that particular field. The
3983 @option{-b} option may be independently attached to either or both of
3984 the start and end positions of a field specification, and if it is
3985 inherited from the global options it will be attached to both.
3986 If input lines can contain leading or adjacent blanks and @option{-t}
3987 is not used, then @option{-k} is typically combined with @option{-b},
3988 @option{-g}, @option{-M}, or @option{-n}; otherwise the varying
3989 numbers of leading blanks in fields can cause confusing results.
3991 If the start position in a sort field specifier falls after the end of
3992 the line or after the end field, the field is empty. If the @option{-b}
3993 option was specified, the @samp{.@var{c}} part of a field specification
3994 is counted from the first nonblank character of the field.
3996 @vindex _POSIX2_VERSION
3997 @vindex POSIXLY_CORRECT
3998 On older systems, @command{sort} supports an obsolete origin-zero
3999 syntax @samp{+@var{pos1} [-@var{pos2}]} for specifying sort keys.
4000 This obsolete behavior can be enabled or disabled with the
4001 @env{_POSIX2_VERSION} environment variable (@pxref{Standards
4002 conformance}); it can also be enabled when @env{POSIXLY_CORRECT} is
4003 not set by using the obsolete syntax with @samp{-@var{pos2}} present.
4005 Scripts intended for use on standard hosts should avoid obsolete
4006 syntax and should use @option{-k} instead. For example, avoid
4007 @samp{sort +2}, since it might be interpreted as either @samp{sort
4008 ./+2} or @samp{sort -k 3}. If your script must also run on hosts that
4009 support only the obsolete syntax, it can use a test like @samp{if sort
4010 -k 1 </dev/null >/dev/null 2>&1; then @dots{}} to decide which syntax
4013 Here are some examples to illustrate various combinations of options.
4018 Sort in descending (reverse) numeric order.
4025 Sort alphabetically, omitting the first and second fields
4026 and the blanks at the start of the third field.
4027 This uses a single key composed of the characters beginning
4028 at the start of the first nonblank character in field three
4029 and extending to the end of each line.
4036 Sort numerically on the second field and resolve ties by sorting
4037 alphabetically on the third and fourth characters of field five.
4038 Use @samp{:} as the field delimiter.
4041 sort -t : -k 2,2n -k 5.3,5.4
4044 Note that if you had written @option{-k 2n} instead of @option{-k 2,2n}
4045 @command{sort} would have used all characters beginning in the second field
4046 and extending to the end of the line as the primary @emph{numeric}
4047 key. For the large majority of applications, treating keys spanning
4048 more than one field as numeric will not do what you expect.
4050 Also note that the @samp{n} modifier was applied to the field-end
4051 specifier for the first key. It would have been equivalent to
4052 specify @option{-k 2n,2} or @option{-k 2n,2n}. All modifiers except
4053 @samp{b} apply to the associated @emph{field}, regardless of whether
4054 the modifier character is attached to the field-start and/or the
4055 field-end part of the key specifier.
4058 Sort the password file on the fifth field and ignore any
4059 leading blanks. Sort lines with equal values in field five
4060 on the numeric user ID in field three. Fields are separated
4064 sort -t : -k 5b,5 -k 3,3n /etc/passwd
4065 sort -t : -n -k 5b,5 -k 3,3 /etc/passwd
4066 sort -t : -b -k 5,5 -k 3,3n /etc/passwd
4069 These three commands have equivalent effect. The first specifies that
4070 the first key's start position ignores leading blanks and the second
4071 key is sorted numerically. The other two commands rely on global
4072 options being inherited by sort keys that lack modifiers. The inheritance
4073 works in this case because @option{-k 5b,5b} and @option{-k 5b,5} are
4074 equivalent, as the location of a field-end lacking a @samp{.@var{c}}
4075 character position is not affected by whether initial blanks are
4079 Sort a set of log files, primarily by IPv4 address and secondarily by
4080 time stamp. If two lines' primary and secondary keys are identical,
4081 output the lines in the same order that they were input. The log
4082 files contain lines that look like this:
4085 4.150.156.3 - - [01/Apr/2004:06:31:51 +0000] message 1
4086 211.24.3.231 - - [24/Apr/2004:20:17:39 +0000] message 2
4089 Fields are separated by exactly one space. Sort IPv4 addresses
4090 lexicographically, e.g., 212.61.52.2 sorts before 212.129.233.201
4091 because 61 is less than 129.
4094 sort -s -t ' ' -k 4.9n -k 4.5M -k 4.2n -k 4.14,4.21 file*.log |
4095 sort -s -t '.' -k 1,1n -k 2,2n -k 3,3n -k 4,4n
4098 This example cannot be done with a single @command{sort} invocation,
4099 since IPv4 address components are separated by @samp{.} while dates
4100 come just after a space. So it is broken down into two invocations of
4101 @command{sort}: the first sorts by time stamp and the second by IPv4
4102 address. The time stamp is sorted by year, then month, then day, and
4103 finally by hour-minute-second field, using @option{-k} to isolate each
4104 field. Except for hour-minute-second there's no need to specify the
4105 end of each key field, since the @samp{n} and @samp{M} modifiers sort
4106 based on leading prefixes that cannot cross field boundaries. The
4107 IPv4 addresses are sorted lexicographically. The second sort uses
4108 @samp{-s} so that ties in the primary key are broken by the secondary
4109 key; the first sort uses @samp{-s} so that the combination of the two
4113 Generate a tags file in case-insensitive sorted order.
4116 find src -type f -print0 | sort -z -f | xargs -0 etags --append
4119 The use of @option{-print0}, @option{-z}, and @option{-0} in this case means
4120 that file names that contain blanks or other special characters are
4122 by the sort operation.
4124 @c This example is a bit contrived and needs more explanation.
4126 @c Sort records separated by an arbitrary string by using a pipe to convert
4127 @c each record delimiter string to @samp{\0}, then using sort's -z option,
4128 @c and converting each @samp{\0} back to the original record delimiter.
4131 @c printf 'c\n\nb\n\na\n'|perl -0pe 's/\n\n/\n\0/g'|sort -z|perl -0pe 's/\0/\n/g'
4135 Shuffle a list of directories, but preserve the order of files within
4136 each directory. For instance, one could use this to generate a music
4137 playlist in which albums are shuffled but the songs of each album are
4141 ls */* | sort -t / -k 1,1R -k 2,2
4147 @node shuf invocation
4148 @section @command{shuf}: Shuffling text
4151 @cindex shuffling files
4153 @command{shuf} shuffles its input by outputting a random permutation
4154 of its input lines. Each output permutation is equally likely.
4158 shuf [@var{option}]@dots{} [@var{file}]
4159 shuf -e [@var{option}]@dots{} [@var{arg}]@dots{}
4160 shuf -i @var{lo}-@var{hi} [@var{option}]@dots{}
4163 @command{shuf} has three modes of operation that affect where it
4164 obtains its input lines. By default, it reads lines from standard
4165 input. The following options change the operation mode:
4173 @cindex command-line operands to shuffle
4174 Treat each command-line operand as an input line.
4176 @item -i @var{lo}-@var{hi}
4177 @itemx --input-range=@var{lo}-@var{hi}
4179 @opindex --input-range
4180 @cindex input range to shuffle
4181 Act as if input came from a file containing the range of unsigned
4182 decimal integers @var{lo}@dots{}@var{hi}, one per line.
4186 @command{shuf}'s other options can affect its behavior in all
4191 @item -n @var{lines}
4192 @itemx --head-count=@var{count}
4194 @opindex --head-count
4195 @cindex head of output
4196 Output at most @var{count} lines. By default, all input lines are
4199 @item -o @var{output-file}
4200 @itemx --output=@var{output-file}
4203 @cindex overwriting of input, allowed
4204 Write output to @var{output-file} instead of standard output.
4205 @command{shuf} reads all input before opening
4206 @var{output-file}, so you can safely shuffle a file in place by using
4207 commands like @code{shuf -o F <F} and @code{cat F | shuf -o F}.
4209 @item --random-source=@var{file}
4210 @opindex --random-source
4211 @cindex random source for shuffling
4212 Use @var{file} as a source of random data used to determine which
4213 permutation to generate. @xref{Random sources}.
4216 @itemx --zero-terminated
4218 @opindex --zero-terminated
4219 @cindex sort zero-terminated lines
4220 Treat the input and output as a set of lines, each terminated by a zero byte
4221 (@acronym{ASCII} @sc{nul} (Null) character) instead of an
4222 @acronym{ASCII} @sc{lf} (Line Feed).
4223 This option can be useful in conjunction with @samp{perl -0} or
4224 @samp{find -print0} and @samp{xargs -0} which do the same in order to
4225 reliably handle arbitrary file names (even those containing blanks
4226 or other special characters).
4242 might produce the output
4252 Similarly, the command:
4255 shuf -e clubs hearts diamonds spades
4269 and the command @samp{shuf -i 1-4} might output:
4279 These examples all have four input lines, so @command{shuf} might
4280 produce any of the twenty-four possible permutations of the input. In
4281 general, if there are @var{N} input lines, there are @var{N}! (i.e.,
4282 @var{N} factorial, or @var{N} * (@var{N} - 1) * @dots{} * 1) possible
4283 output permutations.
4288 @node uniq invocation
4289 @section @command{uniq}: Uniquify files
4292 @cindex uniquify files
4294 @command{uniq} writes the unique lines in the given @file{input}, or
4295 standard input if nothing is given or for an @var{input} name of
4299 uniq [@var{option}]@dots{} [@var{input} [@var{output}]]
4302 By default, @command{uniq} prints its input lines, except that
4303 it discards all but the first of adjacent repeated lines, so that
4304 no output lines are repeated. Optionally, it can instead discard
4305 lines that are not repeated, or all repeated lines.
4307 The input need not be sorted, but repeated input lines are detected
4308 only if they are adjacent. If you want to discard non-adjacent
4309 duplicate lines, perhaps you want to use @code{sort -u}.
4310 @xref{sort invocation}.
4313 Comparisons use the character collating sequence specified by the
4314 @env{LC_COLLATE} locale category.
4316 If no @var{output} file is specified, @command{uniq} writes to standard
4319 The program accepts the following options. Also see @ref{Common options}.
4324 @itemx --skip-fields=@var{n}
4326 @opindex --skip-fields
4327 Skip @var{n} fields on each line before checking for uniqueness. Use
4328 a null string for comparison if a line has fewer than @var{n} fields. Fields
4329 are sequences of non-space non-tab characters that are separated from
4330 each other by at least one space or tab.
4332 For compatibility @command{uniq} supports an obsolete option syntax
4333 @option{-@var{n}}. New scripts should use @option{-f @var{n}} instead.
4336 @itemx --skip-chars=@var{n}
4338 @opindex --skip-chars
4339 Skip @var{n} characters before checking for uniqueness. Use a null string
4340 for comparison if a line has fewer than @var{n} characters. If you use both
4341 the field and character skipping options, fields are skipped over first.
4343 @vindex _POSIX2_VERSION
4344 On older systems, @command{uniq} supports an obsolete option syntax
4346 This obsolete behavior can be enabled or disabled with the
4347 @env{_POSIX2_VERSION} environment variable (@pxref{Standards
4348 conformance}), but portable scripts should avoid commands whose
4349 behavior depends on this variable.
4350 For example, use @samp{uniq ./+10} or @samp{uniq -s 10} rather than
4351 the ambiguous @samp{uniq +10}.
4357 Print the number of times each line occurred along with the line.
4360 @itemx --ignore-case
4362 @opindex --ignore-case
4363 Ignore differences in case when comparing lines.
4369 @cindex repeated lines, outputting
4370 Discard lines that are not repeated. When used by itself, this option
4371 causes @command{uniq} to print the first copy of each repeated line,
4375 @itemx --all-repeated[=@var{delimit-method}]
4377 @opindex --all-repeated
4378 @cindex all repeated lines, outputting
4379 Do not discard the second and subsequent repeated input lines,
4380 but discard lines that are not repeated.
4381 This option is useful mainly in conjunction with other options e.g.,
4382 to ignore case or to compare only selected fields.
4383 The optional @var{delimit-method} tells how to delimit
4384 groups of repeated lines, and must be one of the following:
4389 Do not delimit groups of repeated lines.
4390 This is equivalent to @option{--all-repeated} (@option{-D}).
4393 Output a newline before each group of repeated lines.
4394 With @option{--zero-terminated} (@option{-z}), use
4395 an @acronym{ASCII} @sc{nul} (zero) byte instead of a newline.
4398 Separate groups of repeated lines with a single newline.
4399 With @option{--zero-terminated} (@option{-z}), use
4400 an @acronym{ASCII} @sc{nul} (zero) byte instead of a newline.
4401 This is the same as using @samp{prepend}, except that
4402 no delimiter is inserted before the first group, and hence
4403 may be better suited for output direct to users.
4406 Note that when groups are delimited and the input stream contains
4407 two or more consecutive blank lines, then the output is ambiguous.
4408 To avoid that, filter the input through @samp{tr -s '\n'} to replace
4409 each sequence of consecutive newlines with a single newline.
4411 This is a @sc{gnu} extension.
4412 @c FIXME: give an example showing *how* it's useful
4418 @cindex unique lines, outputting
4419 Discard the first repeated line. When used by itself, this option
4420 causes @command{uniq} to print unique lines, and nothing else.
4423 @itemx --check-chars=@var{n}
4425 @opindex --check-chars
4426 Compare at most @var{n} characters on each line (after skipping any specified
4427 fields and characters). By default the entire rest of the lines are
4431 @itemx --zero-terminated
4433 @opindex --zero-terminated
4434 @cindex sort zero-terminated lines
4435 Treat the input as a set of lines, each terminated by a null character
4436 (@acronym{ASCII} @sc{nul}) instead of a line feed
4437 (@acronym{ASCII} @sc{lf}).
4438 This option can be useful in conjunction with @samp{sort -z}, @samp{perl -0} or
4439 @samp{find -print0} and @samp{xargs -0} which do the same in order to
4440 reliably handle arbitrary file names (even those containing blanks
4441 or other special characters).
4448 @node comm invocation
4449 @section @command{comm}: Compare two sorted files line by line
4452 @cindex line-by-line comparison
4453 @cindex comparing sorted files
4455 @command{comm} writes to standard output lines that are common, and lines
4456 that are unique, to two input files; a file name of @samp{-} means
4457 standard input. Synopsis:
4460 comm [@var{option}]@dots{} @var{file1} @var{file2}
4464 Before @command{comm} can be used, the input files must be sorted using the
4465 collating sequence specified by the @env{LC_COLLATE} locale.
4466 If an input file ends in a non-newline
4467 character, a newline is silently appended. The @command{sort} command with
4468 no options always outputs a file that is suitable input to @command{comm}.
4470 @cindex differing lines
4471 @cindex common lines
4472 With no options, @command{comm} produces three-column output. Column one
4473 contains lines unique to @var{file1}, column two contains lines unique
4474 to @var{file2}, and column three contains lines common to both files.
4475 Columns are separated by a single TAB character.
4476 @c FIXME: when there's an option to supply an alternative separator
4477 @c string, append `by default' to the above sentence.
4482 The options @option{-1}, @option{-2}, and @option{-3} suppress printing of
4483 the corresponding columns. Also see @ref{Common options}.
4485 Unlike some other comparison utilities, @command{comm} has an exit
4486 status that does not depend on the result of the comparison.
4487 Upon normal completion @command{comm} produces an exit code of zero.
4488 If there is an error it exits with nonzero status.
4490 @macro checkOrderOption{cmd}
4491 If the @option{--check-order} option is given, unsorted inputs will
4492 cause a fatal error message. If the option @option{--nocheck-order}
4493 is given, unsorted inputs will never cause an error message. If
4494 neither of these options is given, wrongly sorted inputs are diagnosed
4495 only if an input file is found to contain unpairable lines. If an
4496 input file is diagnosed as being unsorted, the @command{\cmd\} command
4497 will exit with a nonzero status (and the output should not be used).
4499 Forcing @command{\cmd\} to process wrongly sorted input files
4500 containing unpairable lines by specifying @option{--nocheck-order} is
4501 not guaranteed to produce any particular output. The output will
4502 probably not correspond with whatever you hoped it would be.
4504 @checkOrderOption{comm}
4509 Fail with an error message if either input file is wrongly ordered.
4511 @item --nocheck-order
4512 Do not check that both input files are in sorted order.
4516 @item --output-delimiter=@var{str}
4517 Print @var{str} between adjacent output columns,
4518 rather than the default of a single TAB character.
4520 The delimiter @var{str} may not be empty.
4524 @node tsort invocation
4525 @section @command{tsort}: Topological sort
4528 @cindex topological sort
4530 @command{tsort} performs a topological sort on the given @var{file}, or
4531 standard input if no input file is given or for a @var{file} of
4532 @samp{-}. For more details and some history, see @ref{tsort background}.
4536 tsort [@var{option}] [@var{file}]
4539 @command{tsort} reads its input as pairs of strings, separated by blanks,
4540 indicating a partial ordering. The output is a total ordering that
4541 corresponds to the given partial ordering.
4555 will produce the output
4566 Consider a more realistic example.
4567 You have a large set of functions all in one file, and they may all be
4568 declared static except one. Currently that one (say @code{main}) is the
4569 first function defined in the file, and the ones it calls directly follow
4570 it, followed by those they call, etc. Let's say that you are determined
4571 to take advantage of prototypes, so you have to choose between declaring
4572 all of those functions (which means duplicating a lot of information from
4573 the definitions) and rearranging the functions so that as many as possible
4574 are defined before they are used. One way to automate the latter process
4575 is to get a list for each function of the functions it calls directly.
4576 Many programs can generate such lists. They describe a call graph.
4577 Consider the following list, in which a given line indicates that the
4578 function on the left calls the one on the right directly.
4584 tail_file pretty_name
4585 tail_file write_header
4587 tail_forever recheck
4588 tail_forever pretty_name
4589 tail_forever write_header
4590 tail_forever dump_remainder
4593 tail_lines start_lines
4594 tail_lines dump_remainder
4595 tail_lines file_lines
4596 tail_lines pipe_lines
4598 tail_bytes start_bytes
4599 tail_bytes dump_remainder
4600 tail_bytes pipe_bytes
4601 file_lines dump_remainder
4605 then you can use @command{tsort} to produce an ordering of those
4606 functions that satisfies your requirement.
4609 example$ tsort call-graph | tac
4629 @command{tsort} detects any cycles in the input and writes the first cycle
4630 encountered to standard error.
4632 Note that for a given partial ordering, generally there is no unique
4633 total ordering. In the context of the call graph above, the function
4634 @code{parse_options} may be placed anywhere in the list as long as it
4635 precedes @code{main}.
4637 The only options are @option{--help} and @option{--version}. @xref{Common
4642 @node tsort background
4643 @section @command{tsort}: Background
4645 @command{tsort} exists because very early versions of the Unix linker processed
4646 an archive file exactly once, and in order. As @command{ld} read each object
4647 in the archive, it decided whether it was needed in the program based on
4648 whether it defined any symbols which were undefined at that point in
4651 This meant that dependencies within the archive had to be handled
4652 specially. For example, @code{scanf} probably calls @code{read}. That means
4653 that in a single pass through an archive, it was important for @code{scanf.o}
4654 to appear before read.o, because otherwise a program which calls
4655 @code{scanf} but not @code{read} might end up with an unexpected unresolved
4656 reference to @code{read}.
4658 The way to address this problem was to first generate a set of
4659 dependencies of one object file on another. This was done by a shell
4660 script called @command{lorder}. The GNU tools don't provide a version of
4661 lorder, as far as I know, but you can still find it in BSD
4664 Then you ran @command{tsort} over the @command{lorder} output, and you used the
4665 resulting sort to define the order in which you added objects to the archive.
4667 This whole procedure has been obsolete since about 1980, because
4668 Unix archives now contain a symbol table (traditionally built by
4669 @command{ranlib}, now generally built by @command{ar} itself), and the Unix
4670 linker uses the symbol table to effectively make multiple passes over
4673 Anyhow, that's where tsort came from. To solve an old problem with
4674 the way the linker handled archive files, which has since been solved
4678 @node ptx invocation
4679 @section @command{ptx}: Produce permuted indexes
4683 @command{ptx} reads a text file and essentially produces a permuted index, with
4684 each keyword in its context. The calling sketch is either one of:
4687 ptx [@var{option} @dots{}] [@var{file} @dots{}]
4688 ptx -G [@var{option} @dots{}] [@var{input} [@var{output}]]
4691 The @option{-G} (or its equivalent: @option{--traditional}) option disables
4692 all @sc{gnu} extensions and reverts to traditional mode, thus introducing some
4693 limitations and changing several of the program's default option values.
4694 When @option{-G} is not specified, @sc{gnu} extensions are always enabled.
4695 @sc{gnu} extensions to @command{ptx} are documented wherever appropriate in this
4696 document. For the full list, see @xref{Compatibility in ptx}.
4698 Individual options are explained in the following sections.
4700 When @sc{gnu} extensions are enabled, there may be zero, one or several
4701 @var{file}s after the options. If there is no @var{file}, the program
4702 reads the standard input. If there is one or several @var{file}s, they
4703 give the name of input files which are all read in turn, as if all the
4704 input files were concatenated. However, there is a full contextual
4705 break between each file and, when automatic referencing is requested,
4706 file names and line numbers refer to individual text input files. In
4707 all cases, the program outputs the permuted index to the standard
4710 When @sc{gnu} extensions are @emph{not} enabled, that is, when the program
4711 operates in traditional mode, there may be zero, one or two parameters
4712 besides the options. If there are no parameters, the program reads the
4713 standard input and outputs the permuted index to the standard output.
4714 If there is only one parameter, it names the text @var{input} to be read
4715 instead of the standard input. If two parameters are given, they give
4716 respectively the name of the @var{input} file to read and the name of
4717 the @var{output} file to produce. @emph{Be very careful} to note that,
4718 in this case, the contents of file given by the second parameter is
4719 destroyed. This behavior is dictated by System V @command{ptx}
4720 compatibility; @sc{gnu} Standards normally discourage output parameters not
4721 introduced by an option.
4723 Note that for @emph{any} file named as the value of an option or as an
4724 input text file, a single dash @kbd{-} may be used, in which case
4725 standard input is assumed. However, it would not make sense to use this
4726 convention more than once per program invocation.
4729 * General options in ptx:: Options which affect general program behavior.
4730 * Charset selection in ptx:: Underlying character set considerations.
4731 * Input processing in ptx:: Input fields, contexts, and keyword selection.
4732 * Output formatting in ptx:: Types of output format, and sizing the fields.
4733 * Compatibility in ptx::
4737 @node General options in ptx
4738 @subsection General options
4743 @itemx --traditional
4744 As already explained, this option disables all @sc{gnu} extensions to
4745 @command{ptx} and switches to traditional mode.
4748 Print a short help on standard output, then exit without further
4752 Print the program version on standard output, then exit without further
4760 @node Charset selection in ptx
4761 @subsection Charset selection
4763 @c FIXME: People don't necessarily know what an IBM-PC was these days.
4764 As it is set up now, the program assumes that the input file is coded
4765 using 8-bit @acronym{ISO} 8859-1 code, also known as Latin-1 character set,
4766 @emph{unless} it is compiled for MS-DOS, in which case it uses the
4767 character set of the IBM-PC@. (@sc{gnu} @command{ptx} is not known to work on
4768 smaller MS-DOS machines anymore.) Compared to 7-bit @acronym{ASCII}, the set
4769 of characters which are letters is different; this alters the behavior
4770 of regular expression matching. Thus, the default regular expression
4771 for a keyword allows foreign or diacriticized letters. Keyword sorting,
4772 however, is still crude; it obeys the underlying character set ordering
4778 @itemx --ignore-case
4779 Fold lower case letters to upper case for sorting.
4784 @node Input processing in ptx
4785 @subsection Word selection and input processing
4790 @itemx --break-file=@var{file}
4792 This option provides an alternative (to @option{-W}) method of describing
4793 which characters make up words. It introduces the name of a
4794 file which contains a list of characters which can@emph{not} be part of
4795 one word; this file is called the @dfn{Break file}. Any character which
4796 is not part of the Break file is a word constituent. If both options
4797 @option{-b} and @option{-W} are specified, then @option{-W} has precedence and
4798 @option{-b} is ignored.
4800 When @sc{gnu} extensions are enabled, the only way to avoid newline as a
4801 break character is to write all the break characters in the file with no
4802 newline at all, not even at the end of the file. When @sc{gnu} extensions
4803 are disabled, spaces, tabs and newlines are always considered as break
4804 characters even if not included in the Break file.
4807 @itemx --ignore-file=@var{file}
4809 The file associated with this option contains a list of words which will
4810 never be taken as keywords in concordance output. It is called the
4811 @dfn{Ignore file}. The file contains exactly one word in each line; the
4812 end of line separation of words is not subject to the value of the
4816 @itemx --only-file=@var{file}
4818 The file associated with this option contains a list of words which will
4819 be retained in concordance output; any word not mentioned in this file
4820 is ignored. The file is called the @dfn{Only file}. The file contains
4821 exactly one word in each line; the end of line separation of words is
4822 not subject to the value of the @option{-S} option.
4824 There is no default for the Only file. When both an Only file and an
4825 Ignore file are specified, a word is considered a keyword only
4826 if it is listed in the Only file and not in the Ignore file.
4831 On each input line, the leading sequence of non-white space characters will be
4832 taken to be a reference that has the purpose of identifying this input
4833 line in the resulting permuted index. For more information about reference
4834 production, see @xref{Output formatting in ptx}.
4835 Using this option changes the default value for option @option{-S}.
4837 Using this option, the program does not try very hard to remove
4838 references from contexts in output, but it succeeds in doing so
4839 @emph{when} the context ends exactly at the newline. If option
4840 @option{-r} is used with @option{-S} default value, or when @sc{gnu} extensions
4841 are disabled, this condition is always met and references are completely
4842 excluded from the output contexts.
4844 @item -S @var{regexp}
4845 @itemx --sentence-regexp=@var{regexp}
4847 This option selects which regular expression will describe the end of a
4848 line or the end of a sentence. In fact, this regular expression is not
4849 the only distinction between end of lines or end of sentences, and input
4850 line boundaries have no special significance outside this option. By
4851 default, when @sc{gnu} extensions are enabled and if @option{-r} option is not
4852 used, end of sentences are used. In this case, this @var{regex} is
4853 imported from @sc{gnu} Emacs:
4856 [.?!][]\"')@}]*\\($\\|\t\\| \\)[ \t\n]*
4859 Whenever @sc{gnu} extensions are disabled or if @option{-r} option is used, end
4860 of lines are used; in this case, the default @var{regexp} is just:
4866 Using an empty @var{regexp} is equivalent to completely disabling end of
4867 line or end of sentence recognition. In this case, the whole file is
4868 considered to be a single big line or sentence. The user might want to
4869 disallow all truncation flag generation as well, through option @option{-F
4870 ""}. @xref{Regexps, , Syntax of Regular Expressions, emacs, The GNU Emacs
4873 When the keywords happen to be near the beginning of the input line or
4874 sentence, this often creates an unused area at the beginning of the
4875 output context line; when the keywords happen to be near the end of the
4876 input line or sentence, this often creates an unused area at the end of
4877 the output context line. The program tries to fill those unused areas
4878 by wrapping around context in them; the tail of the input line or
4879 sentence is used to fill the unused area on the left of the output line;
4880 the head of the input line or sentence is used to fill the unused area
4881 on the right of the output line.
4883 As a matter of convenience to the user, many usual backslashed escape
4884 sequences from the C language are recognized and converted to the
4885 corresponding characters by @command{ptx} itself.
4887 @item -W @var{regexp}
4888 @itemx --word-regexp=@var{regexp}
4890 This option selects which regular expression will describe each keyword.
4891 By default, if @sc{gnu} extensions are enabled, a word is a sequence of
4892 letters; the @var{regexp} used is @samp{\w+}. When @sc{gnu} extensions are
4893 disabled, a word is by default anything which ends with a space, a tab
4894 or a newline; the @var{regexp} used is @samp{[^ \t\n]+}.
4896 An empty @var{regexp} is equivalent to not using this option.
4897 @xref{Regexps, , Syntax of Regular Expressions, emacs, The GNU Emacs
4900 As a matter of convenience to the user, many usual backslashed escape
4901 sequences, as found in the C language, are recognized and converted to
4902 the corresponding characters by @command{ptx} itself.
4907 @node Output formatting in ptx
4908 @subsection Output formatting
4910 Output format is mainly controlled by the @option{-O} and @option{-T} options
4911 described in the table below. When neither @option{-O} nor @option{-T} are
4912 selected, and if @sc{gnu} extensions are enabled, the program chooses an
4913 output format suitable for a dumb terminal. Each keyword occurrence is
4914 output to the center of one line, surrounded by its left and right
4915 contexts. Each field is properly justified, so the concordance output
4916 can be readily observed. As a special feature, if automatic
4917 references are selected by option @option{-A} and are output before the
4918 left context, that is, if option @option{-R} is @emph{not} selected, then
4919 a colon is added after the reference; this nicely interfaces with @sc{gnu}
4920 Emacs @code{next-error} processing. In this default output format, each
4921 white space character, like newline and tab, is merely changed to
4922 exactly one space, with no special attempt to compress consecutive
4923 spaces. This might change in the future. Except for those white space
4924 characters, every other character of the underlying set of 256
4925 characters is transmitted verbatim.
4927 Output format is further controlled by the following options.
4931 @item -g @var{number}
4932 @itemx --gap-size=@var{number}
4934 Select the size of the minimum white space gap between the fields on the
4937 @item -w @var{number}
4938 @itemx --width=@var{number}
4940 Select the maximum output width of each final line. If references are
4941 used, they are included or excluded from the maximum output width
4942 depending on the value of option @option{-R}. If this option is not
4943 selected, that is, when references are output before the left context,
4944 the maximum output width takes into account the maximum length of all
4945 references. If this option is selected, that is, when references are
4946 output after the right context, the maximum output width does not take
4947 into account the space taken by references, nor the gap that precedes
4951 @itemx --auto-reference
4953 Select automatic references. Each input line will have an automatic
4954 reference made up of the file name and the line ordinal, with a single
4955 colon between them. However, the file name will be empty when standard
4956 input is being read. If both @option{-A} and @option{-r} are selected, then
4957 the input reference is still read and skipped, but the automatic
4958 reference is used at output time, overriding the input reference.
4961 @itemx --right-side-refs
4963 In the default output format, when option @option{-R} is not used, any
4964 references produced by the effect of options @option{-r} or @option{-A} are
4965 placed to the far right of output lines, after the right context. With
4966 default output format, when the @option{-R} option is specified, references
4967 are rather placed at the beginning of each output line, before the left
4968 context. For any other output format, option @option{-R} is
4969 ignored, with one exception: with @option{-R} the width of references
4970 is @emph{not} taken into account in total output width given by @option{-w}.
4972 This option is automatically selected whenever @sc{gnu} extensions are
4975 @item -F @var{string}
4976 @itemx --flac-truncation=@var{string}
4978 This option will request that any truncation in the output be reported
4979 using the string @var{string}. Most output fields theoretically extend
4980 towards the beginning or the end of the current line, or current
4981 sentence, as selected with option @option{-S}. But there is a maximum
4982 allowed output line width, changeable through option @option{-w}, which is
4983 further divided into space for various output fields. When a field has
4984 to be truncated because it cannot extend beyond the beginning or the end of
4985 the current line to fit in, then a truncation occurs. By default,
4986 the string used is a single slash, as in @option{-F /}.
4988 @var{string} may have more than one character, as in @option{-F ...}.
4989 Also, in the particular case when @var{string} is empty (@option{-F ""}),
4990 truncation flagging is disabled, and no truncation marks are appended in
4993 As a matter of convenience to the user, many usual backslashed escape
4994 sequences, as found in the C language, are recognized and converted to
4995 the corresponding characters by @command{ptx} itself.
4997 @item -M @var{string}
4998 @itemx --macro-name=@var{string}
5000 Select another @var{string} to be used instead of @samp{xx}, while
5001 generating output suitable for @command{nroff}, @command{troff} or @TeX{}.
5004 @itemx --format=roff
5006 Choose an output format suitable for @command{nroff} or @command{troff}
5007 processing. Each output line will look like:
5010 .xx "@var{tail}" "@var{before}" "@var{keyword_and_after}" "@var{head}" "@var{ref}"
5013 so it will be possible to write a @samp{.xx} roff macro to take care of
5014 the output typesetting. This is the default output format when @sc{gnu}
5015 extensions are disabled. Option @option{-M} can be used to change
5016 @samp{xx} to another macro name.
5018 In this output format, each non-graphical character, like newline and
5019 tab, is merely changed to exactly one space, with no special attempt to
5020 compress consecutive spaces. Each quote character: @kbd{"} is doubled
5021 so it will be correctly processed by @command{nroff} or @command{troff}.
5026 Choose an output format suitable for @TeX{} processing. Each output
5027 line will look like:
5030 \xx @{@var{tail}@}@{@var{before}@}@{@var{keyword}@}@{@var{after}@}@{@var{head}@}@{@var{ref}@}
5034 so it will be possible to write a @code{\xx} definition to take care of
5035 the output typesetting. Note that when references are not being
5036 produced, that is, neither option @option{-A} nor option @option{-r} is
5037 selected, the last parameter of each @code{\xx} call is inhibited.
5038 Option @option{-M} can be used to change @samp{xx} to another macro
5041 In this output format, some special characters, like @kbd{$}, @kbd{%},
5042 @kbd{&}, @kbd{#} and @kbd{_} are automatically protected with a
5043 backslash. Curly brackets @kbd{@{}, @kbd{@}} are protected with a
5044 backslash and a pair of dollar signs (to force mathematical mode). The
5045 backslash itself produces the sequence @code{\backslash@{@}}.
5046 Circumflex and tilde diacritical marks produce the sequence @code{^\@{ @}} and
5047 @code{~\@{ @}} respectively. Other diacriticized characters of the
5048 underlying character set produce an appropriate @TeX{} sequence as far
5049 as possible. The other non-graphical characters, like newline and tab,
5050 and all other characters which are not part of @acronym{ASCII}, are merely
5051 changed to exactly one space, with no special attempt to compress
5052 consecutive spaces. Let me know how to improve this special character
5053 processing for @TeX{}.
5058 @node Compatibility in ptx
5059 @subsection The @sc{gnu} extensions to @command{ptx}
5061 This version of @command{ptx} contains a few features which do not exist in
5062 System V @command{ptx}. These extra features are suppressed by using the
5063 @option{-G} command line option, unless overridden by other command line
5064 options. Some @sc{gnu} extensions cannot be recovered by overriding, so the
5065 simple rule is to avoid @option{-G} if you care about @sc{gnu} extensions.
5066 Here are the differences between this program and System V @command{ptx}.
5071 This program can read many input files at once, it always writes the
5072 resulting concordance on standard output. On the other hand, System V
5073 @command{ptx} reads only one file and sends the result to standard output
5074 or, if a second @var{file} parameter is given on the command, to that
5077 Having output parameters not introduced by options is a dangerous
5078 practice which @sc{gnu} avoids as far as possible. So, for using @command{ptx}
5079 portably between @sc{gnu} and System V, you should always use it with a
5080 single input file, and always expect the result on standard output. You
5081 might also want to automatically configure in a @option{-G} option to
5082 @command{ptx} calls in products using @command{ptx}, if the configurator finds
5083 that the installed @command{ptx} accepts @option{-G}.
5086 The only options available in System V @command{ptx} are options @option{-b},
5087 @option{-f}, @option{-g}, @option{-i}, @option{-o}, @option{-r}, @option{-t} and
5088 @option{-w}. All other options are @sc{gnu} extensions and are not repeated in
5089 this enumeration. Moreover, some options have a slightly different
5090 meaning when @sc{gnu} extensions are enabled, as explained below.
5093 By default, concordance output is not formatted for @command{troff} or
5094 @command{nroff}. It is rather formatted for a dumb terminal. @command{troff}
5095 or @command{nroff} output may still be selected through option @option{-O}.
5098 Unless @option{-R} option is used, the maximum reference width is
5099 subtracted from the total output line width. With @sc{gnu} extensions
5100 disabled, width of references is not taken into account in the output
5101 line width computations.
5104 All 256 bytes, even null bytes, are always read and processed from
5105 input file with no adverse effect, even if @sc{gnu} extensions are disabled.
5106 However, System V @command{ptx} does not accept 8-bit characters, a few
5107 control characters are rejected, and the tilde @kbd{~} is also rejected.
5110 Input line length is only limited by available memory, even if @sc{gnu}
5111 extensions are disabled. However, System V @command{ptx} processes only
5112 the first 200 characters in each line.
5115 The break (non-word) characters default to be every character except all
5116 letters of the underlying character set, diacriticized or not. When @sc{gnu}
5117 extensions are disabled, the break characters default to space, tab and
5121 The program makes better use of output line width. If @sc{gnu} extensions
5122 are disabled, the program rather tries to imitate System V @command{ptx},
5123 but still, there are some slight disposition glitches this program does
5124 not completely reproduce.
5127 The user can specify both an Ignore file and an Only file. This is not
5128 allowed with System V @command{ptx}.
5133 @node Operating on fields within a line
5134 @chapter Operating on fields within a line
5137 * cut invocation:: Print selected parts of lines.
5138 * paste invocation:: Merge lines of files.
5139 * join invocation:: Join lines on a common field.
5143 @node cut invocation
5144 @section @command{cut}: Print selected parts of lines
5147 @command{cut} writes to standard output selected parts of each line of each
5148 input file, or standard input if no files are given or for a file name of
5152 cut @var{option}@dots{} [@var{file}]@dots{}
5155 In the table which follows, the @var{byte-list}, @var{character-list},
5156 and @var{field-list} are one or more numbers or ranges (two numbers
5157 separated by a dash) separated by commas. Bytes, characters, and
5158 fields are numbered starting at 1. Incomplete ranges may be
5159 given: @option{-@var{m}} means @samp{1-@var{m}}; @samp{@var{n}-} means
5160 @samp{@var{n}} through end of line or last field. The list elements
5161 can be repeated, can overlap, and can be specified in any order; but
5162 the selected input is written in the same order that it is read, and
5163 is written exactly once.
5165 The program accepts the following options. Also see @ref{Common
5170 @item -b @var{byte-list}
5171 @itemx --bytes=@var{byte-list}
5174 Select for printing only the bytes in positions listed in
5175 @var{byte-list}. Tabs and backspaces are treated like any other
5176 character; they take up 1 byte. If an output delimiter is specified,
5177 (see the description of @option{--output-delimiter}), then output that
5178 string between ranges of selected bytes.
5180 @item -c @var{character-list}
5181 @itemx --characters=@var{character-list}
5183 @opindex --characters
5184 Select for printing only the characters in positions listed in
5185 @var{character-list}. The same as @option{-b} for now, but
5186 internationalization will change that. Tabs and backspaces are
5187 treated like any other character; they take up 1 character. If an
5188 output delimiter is specified, (see the description of
5189 @option{--output-delimiter}), then output that string between ranges
5192 @item -f @var{field-list}
5193 @itemx --fields=@var{field-list}
5196 Select for printing only the fields listed in @var{field-list}.
5197 Fields are separated by a TAB character by default. Also print any
5198 line that contains no delimiter character, unless the
5199 @option{--only-delimited} (@option{-s}) option is specified
5201 @item -d @var{input_delim_byte}
5202 @itemx --delimiter=@var{input_delim_byte}
5204 @opindex --delimiter
5205 With @option{-f}, use the first byte of @var{input_delim_byte} as
5206 the input fields separator (default is TAB).
5210 Do not split multi-byte characters (no-op for now).
5213 @itemx --only-delimited
5215 @opindex --only-delimited
5216 For @option{-f}, do not print lines that do not contain the field separator
5217 character. Normally, any line without a field separator is printed verbatim.
5219 @item --output-delimiter=@var{output_delim_string}
5220 @opindex --output-delimiter
5221 With @option{-f}, output fields are separated by @var{output_delim_string}.
5222 The default with @option{-f} is to use the input delimiter.
5223 When using @option{-b} or @option{-c} to select ranges of byte or
5224 character offsets (as opposed to ranges of fields),
5225 output @var{output_delim_string} between non-overlapping
5226 ranges of selected bytes.
5229 @opindex --complement
5230 This option is a @acronym{GNU} extension.
5231 Select for printing the complement of the bytes, characters or fields
5232 selected with the @option{-b}, @option{-c} or @option{-f} options.
5233 In other words, do @emph{not} print the bytes, characters or fields
5234 specified via those options. This option is useful when you have
5235 many fields and want to print all but a few of them.
5242 @node paste invocation
5243 @section @command{paste}: Merge lines of files
5246 @cindex merging files
5248 @command{paste} writes to standard output lines consisting of sequentially
5249 corresponding lines of each given file, separated by a TAB character.
5250 Standard input is used for a file name of @samp{-} or if no input files
5272 paste [@var{option}]@dots{} [@var{file}]@dots{}
5275 The program accepts the following options. Also see @ref{Common options}.
5283 Paste the lines of one file at a time rather than one line from each
5284 file. Using the above example data:
5287 $ paste -s num2 let3
5292 @item -d @var{delim-list}
5293 @itemx --delimiters=@var{delim-list}
5295 @opindex --delimiters
5296 Consecutively use the characters in @var{delim-list} instead of
5297 TAB to separate merged lines. When @var{delim-list} is
5298 exhausted, start again at its beginning. Using the above example data:
5301 $ paste -d '%_' num2 let3 num2
5312 @node join invocation
5313 @section @command{join}: Join lines on a common field
5316 @cindex common field, joining on
5318 @command{join} writes to standard output a line for each pair of input
5319 lines that have identical join fields. Synopsis:
5322 join [@var{option}]@dots{} @var{file1} @var{file2}
5325 Either @var{file1} or @var{file2} (but not both) can be @samp{-},
5326 meaning standard input. @var{file1} and @var{file2} should be
5327 sorted on the join fields.
5330 Normally, the sort order is that of the
5331 collating sequence specified by the @env{LC_COLLATE} locale. Unless
5332 the @option{-t} option is given, the sort comparison ignores blanks at
5333 the start of the join field, as in @code{sort -b}. If the
5334 @option{--ignore-case} option is given, the sort comparison ignores
5335 the case of characters in the join field, as in @code{sort -f}.
5337 The @command{sort} and @command{join} commands should use consistent
5338 locales and options if the output of @command{sort} is fed to
5339 @command{join}. You can use a command like @samp{sort -k 1b,1} to
5340 sort a file on its default join field, but if you select a non-default
5341 locale, join field, separator, or comparison options, then you should
5342 do so consistently between @command{join} and @command{sort}.
5344 If the input has no unpairable lines, a @acronym{GNU} extension is
5345 available; the sort order can be any order that considers two fields
5346 to be equal if and only if the sort comparison described above
5347 considers them to be equal. For example:
5364 @checkOrderOption{join}
5368 @item the join field is the first field in each line;
5369 @item fields in the input are separated by one or more blanks, with leading
5370 blanks on the line ignored;
5371 @item fields in the output are separated by a space;
5372 @item each output line consists of the join field, the remaining
5373 fields from @var{file1}, then the remaining fields from @var{file2}.
5376 The program accepts the following options. Also see @ref{Common options}.
5380 @item -a @var{file-number}
5382 Print a line for each unpairable line in file @var{file-number} (either
5383 @samp{1} or @samp{2}), in addition to the normal output.
5386 Fail with an error message if either input file is wrongly ordered.
5388 @item --nocheck-order
5389 Do not check that both input files are in sorted order. This is the default.
5391 @item -e @var{string}
5393 Replace those output fields that are missing in the input with
5397 @itemx --ignore-case
5399 @opindex --ignore-case
5400 Ignore differences in case when comparing keys.
5401 With this option, the lines of the input files must be ordered in the same way.
5402 Use @samp{sort -f} to produce this ordering.
5404 @item -1 @var{field}
5406 Join on field @var{field} (a positive integer) of file 1.
5408 @item -2 @var{field}
5410 Join on field @var{field} (a positive integer) of file 2.
5412 @item -j @var{field}
5413 Equivalent to @option{-1 @var{field} -2 @var{field}}.
5415 @item -o @var{field-list}
5416 Construct each output line according to the format in @var{field-list}.
5417 Each element in @var{field-list} is either the single character @samp{0} or
5418 has the form @var{m.n} where the file number, @var{m}, is @samp{1} or
5419 @samp{2} and @var{n} is a positive field number.
5421 A field specification of @samp{0} denotes the join field.
5422 In most cases, the functionality of the @samp{0} field spec
5423 may be reproduced using the explicit @var{m.n} that corresponds
5424 to the join field. However, when printing unpairable lines
5425 (using either of the @option{-a} or @option{-v} options), there is no way
5426 to specify the join field using @var{m.n} in @var{field-list}
5427 if there are unpairable lines in both files.
5428 To give @command{join} that functionality, @acronym{POSIX} invented the @samp{0}
5429 field specification notation.
5431 The elements in @var{field-list}
5432 are separated by commas or blanks.
5433 Blank separators typically need to be quoted for the shell. For
5434 example, the commands @samp{join -o 1.2,2.2} and @samp{join -o '1.2
5435 2.2'} are equivalent.
5437 All output lines---including those printed because of any -a or -v
5438 option---are subject to the specified @var{field-list}.
5441 Use character @var{char} as the input and output field separator.
5442 Treat as significant each occurrence of @var{char} in the input file.
5443 Use @samp{sort -t @var{char}}, without the @option{-b} option of
5444 @samp{sort}, to produce this ordering.
5446 @item -v @var{file-number}
5447 Print a line for each unpairable line in file @var{file-number}
5448 (either @samp{1} or @samp{2}), instead of the normal output.
5455 @node Operating on characters
5456 @chapter Operating on characters
5458 @cindex operating on characters
5460 This commands operate on individual characters.
5463 * tr invocation:: Translate, squeeze, and/or delete characters.
5464 * expand invocation:: Convert tabs to spaces.
5465 * unexpand invocation:: Convert spaces to tabs.
5470 @section @command{tr}: Translate, squeeze, and/or delete characters
5477 tr [@var{option}]@dots{} @var{set1} [@var{set2}]
5480 @command{tr} copies standard input to standard output, performing
5481 one of the following operations:
5485 translate, and optionally squeeze repeated characters in the result,
5487 squeeze repeated characters,
5491 delete characters, then squeeze repeated characters from the result.
5494 The @var{set1} and (if given) @var{set2} arguments define ordered
5495 sets of characters, referred to below as @var{set1} and @var{set2}. These
5496 sets are the characters of the input that @command{tr} operates on.
5497 The @option{--complement} (@option{-c}, @option{-C}) option replaces
5499 complement (all of the characters that are not in @var{set1}).
5501 Currently @command{tr} fully supports only single-byte characters.
5502 Eventually it will support multibyte characters; when it does, the
5503 @option{-C} option will cause it to complement the set of characters,
5504 whereas @option{-c} will cause it to complement the set of values.
5505 This distinction will matter only when some values are not characters,
5506 and this is possible only in locales using multibyte encodings when
5507 the input contains encoding errors.
5509 The program accepts the @option{--help} and @option{--version}
5510 options. @xref{Common options}. Options must precede operands.
5515 * Character sets:: Specifying sets of characters.
5516 * Translating:: Changing one set of characters to another.
5517 * Squeezing:: Squeezing repeats and deleting.
5521 @node Character sets
5522 @subsection Specifying sets of characters
5524 @cindex specifying sets of characters
5526 The format of the @var{set1} and @var{set2} arguments resembles
5527 the format of regular expressions; however, they are not regular
5528 expressions, only lists of characters. Most characters simply
5529 represent themselves in these strings, but the strings can contain
5530 the shorthands listed below, for convenience. Some of them can be
5531 used only in @var{set1} or @var{set2}, as noted below.
5535 @item Backslash escapes
5536 @cindex backslash escapes
5538 The following backslash escape sequences are recognized:
5556 The character with the value given by @var{ooo}, which is 1 to 3
5562 While a backslash followed by a character not listed above is
5563 interpreted as that character, the backslash also effectively
5564 removes any special significance, so it is useful to escape
5565 @samp{[}, @samp{]}, @samp{*}, and @samp{-}.
5570 The notation @samp{@var{m}-@var{n}} expands to all of the characters
5571 from @var{m} through @var{n}, in ascending order. @var{m} should
5572 collate before @var{n}; if it doesn't, an error results. As an example,
5573 @samp{0-9} is the same as @samp{0123456789}.
5575 @sc{gnu} @command{tr} does not support the System V syntax that uses square
5576 brackets to enclose ranges. Translations specified in that format
5577 sometimes work as expected, since the brackets are often transliterated
5578 to themselves. However, they should be avoided because they sometimes
5579 behave unexpectedly. For example, @samp{tr -d '[0-9]'} deletes brackets
5582 Many historically common and even accepted uses of ranges are not
5583 portable. For example, on @acronym{EBCDIC} hosts using the @samp{A-Z}
5584 range will not do what most would expect because @samp{A} through @samp{Z}
5585 are not contiguous as they are in @acronym{ASCII}.
5586 If you can rely on a @acronym{POSIX} compliant version of @command{tr}, then
5587 the best way to work around this is to use character classes (see below).
5588 Otherwise, it is most portable (and most ugly) to enumerate the members
5591 @item Repeated characters
5592 @cindex repeated characters
5594 The notation @samp{[@var{c}*@var{n}]} in @var{set2} expands to @var{n}
5595 copies of character @var{c}. Thus, @samp{[y*6]} is the same as
5596 @samp{yyyyyy}. The notation @samp{[@var{c}*]} in @var{string2} expands
5597 to as many copies of @var{c} as are needed to make @var{set2} as long as
5598 @var{set1}. If @var{n} begins with @samp{0}, it is interpreted in
5599 octal, otherwise in decimal.
5601 @item Character classes
5602 @cindex character classes
5604 The notation @samp{[:@var{class}:]} expands to all of the characters in
5605 the (predefined) class @var{class}. The characters expand in no
5606 particular order, except for the @code{upper} and @code{lower} classes,
5607 which expand in ascending order. When the @option{--delete} (@option{-d})
5608 and @option{--squeeze-repeats} (@option{-s}) options are both given, any
5609 character class can be used in @var{set2}. Otherwise, only the
5610 character classes @code{lower} and @code{upper} are accepted in
5611 @var{set2}, and then only if the corresponding character class
5612 (@code{upper} and @code{lower}, respectively) is specified in the same
5613 relative position in @var{set1}. Doing this specifies case conversion.
5614 The class names are given below; an error results when an invalid class
5626 Horizontal whitespace.
5635 Printable characters, not including space.
5641 Printable characters, including space.
5644 Punctuation characters.
5647 Horizontal or vertical whitespace.
5656 @item Equivalence classes
5657 @cindex equivalence classes
5659 The syntax @samp{[=@var{c}=]} expands to all of the characters that are
5660 equivalent to @var{c}, in no particular order. Equivalence classes are
5661 a relatively recent invention intended to support non-English alphabets.
5662 But there seems to be no standard way to define them or determine their
5663 contents. Therefore, they are not fully implemented in @sc{gnu} @command{tr};
5664 each character's equivalence class consists only of that character,
5665 which is of no particular use.
5671 @subsection Translating
5673 @cindex translating characters
5675 @command{tr} performs translation when @var{set1} and @var{set2} are
5676 both given and the @option{--delete} (@option{-d}) option is not given.
5677 @command{tr} translates each character of its input that is in @var{set1}
5678 to the corresponding character in @var{set2}. Characters not in
5679 @var{set1} are passed through unchanged. When a character appears more
5680 than once in @var{set1} and the corresponding characters in @var{set2}
5681 are not all the same, only the final one is used. For example, these
5682 two commands are equivalent:
5689 A common use of @command{tr} is to convert lowercase characters to
5690 uppercase. This can be done in many ways. Here are three of them:
5693 tr abcdefghijklmnopqrstuvwxyz ABCDEFGHIJKLMNOPQRSTUVWXYZ
5695 tr '[:lower:]' '[:upper:]'
5699 But note that using ranges like @code{a-z} above is not portable.
5701 When @command{tr} is performing translation, @var{set1} and @var{set2}
5702 typically have the same length. If @var{set1} is shorter than
5703 @var{set2}, the extra characters at the end of @var{set2} are ignored.
5705 On the other hand, making @var{set1} longer than @var{set2} is not
5706 portable; @acronym{POSIX} says that the result is undefined. In this situation,
5707 BSD @command{tr} pads @var{set2} to the length of @var{set1} by repeating
5708 the last character of @var{set2} as many times as necessary. System V
5709 @command{tr} truncates @var{set1} to the length of @var{set2}.
5711 By default, @sc{gnu} @command{tr} handles this case like BSD @command{tr}.
5712 When the @option{--truncate-set1} (@option{-t}) option is given,
5713 @sc{gnu} @command{tr} handles this case like the System V @command{tr}
5714 instead. This option is ignored for operations other than translation.
5716 Acting like System V @command{tr} in this case breaks the relatively common
5720 tr -cs A-Za-z0-9 '\012'
5724 because it converts only zero bytes (the first element in the
5725 complement of @var{set1}), rather than all non-alphanumerics, to
5729 By the way, the above idiom is not portable because it uses ranges, and
5730 it assumes that the octal code for newline is 012.
5731 Assuming a @acronym{POSIX} compliant @command{tr}, here is a better way to write it:
5734 tr -cs '[:alnum:]' '[\n*]'
5739 @subsection Squeezing repeats and deleting
5741 @cindex squeezing repeat characters
5742 @cindex deleting characters
5744 When given just the @option{--delete} (@option{-d}) option, @command{tr}
5745 removes any input characters that are in @var{set1}.
5747 When given just the @option{--squeeze-repeats} (@option{-s}) option,
5748 @command{tr} replaces each input sequence of a repeated character that
5749 is in @var{set1} with a single occurrence of that character.
5751 When given both @option{--delete} and @option{--squeeze-repeats}, @command{tr}
5752 first performs any deletions using @var{set1}, then squeezes repeats
5753 from any remaining characters using @var{set2}.
5755 The @option{--squeeze-repeats} option may also be used when translating,
5756 in which case @command{tr} first performs translation, then squeezes
5757 repeats from any remaining characters using @var{set2}.
5759 Here are some examples to illustrate various combinations of options:
5764 Remove all zero bytes:
5771 Put all words on lines by themselves. This converts all
5772 non-alphanumeric characters to newlines, then squeezes each string
5773 of repeated newlines into a single newline:
5776 tr -cs '[:alnum:]' '[\n*]'
5780 Convert each sequence of repeated newlines to a single newline:
5787 Find doubled occurrences of words in a document.
5788 @c Separate the following two "the"s, so typo checkers don't complain.
5789 For example, people often write ``the @w{}the'' with the repeated words
5790 separated by a newline. The Bourne shell script below works first
5791 by converting each sequence of punctuation and blank characters to a
5792 single newline. That puts each ``word'' on a line by itself.
5793 Next it maps all uppercase characters to lower case, and finally it
5794 runs @command{uniq} with the @option{-d} option to print out only the words
5800 | tr -s '[:punct:][:blank:]' '[\n*]' \
5801 | tr '[:upper:]' '[:lower:]' \
5806 Deleting a small set of characters is usually straightforward. For example,
5807 to remove all @samp{a}s, @samp{x}s, and @samp{M}s you would do this:
5813 However, when @samp{-} is one of those characters, it can be tricky because
5814 @samp{-} has special meanings. Performing the same task as above but also
5815 removing all @samp{-} characters, we might try @code{tr -d -axM}, but
5816 that would fail because @command{tr} would try to interpret @option{-a} as
5817 a command-line option. Alternatively, we could try putting the hyphen
5818 inside the string, @code{tr -d a-xM}, but that wouldn't work either because
5819 it would make @command{tr} interpret @code{a-x} as the range of characters
5820 @samp{a}@dots{}@samp{x} rather than the three.
5821 One way to solve the problem is to put the hyphen at the end of the list
5828 Or you can use @samp{--} to terminate option processing:
5834 More generally, use the character class notation @code{[=c=]}
5835 with @samp{-} (or any other character) in place of the @samp{c}:
5841 Note how single quotes are used in the above example to protect the
5842 square brackets from interpretation by a shell.
5847 @node expand invocation
5848 @section @command{expand}: Convert tabs to spaces
5851 @cindex tabs to spaces, converting
5852 @cindex converting tabs to spaces
5854 @command{expand} writes the contents of each given @var{file}, or standard
5855 input if none are given or for a @var{file} of @samp{-}, to standard
5856 output, with tab characters converted to the appropriate number of
5860 expand [@var{option}]@dots{} [@var{file}]@dots{}
5863 By default, @command{expand} converts all tabs to spaces. It preserves
5864 backspace characters in the output; they decrement the column count for
5865 tab calculations. The default action is equivalent to @option{-t 8} (set
5866 tabs every 8 columns).
5868 The program accepts the following options. Also see @ref{Common options}.
5872 @item -t @var{tab1}[,@var{tab2}]@dots{}
5873 @itemx --tabs=@var{tab1}[,@var{tab2}]@dots{}
5876 @cindex tab stops, setting
5877 If only one tab stop is given, set the tabs @var{tab1} spaces apart
5878 (default is 8). Otherwise, set the tabs at columns @var{tab1},
5879 @var{tab2}, @dots{} (numbered from 0), and replace any tabs beyond the
5880 last tab stop given with single spaces. Tab stops can be separated by
5881 blanks as well as by commas.
5883 For compatibility, GNU @command{expand} also accepts the obsolete
5884 option syntax, @option{-@var{t1}[,@var{t2}]@dots{}}. New scripts
5885 should use @option{-t @var{t1}[,@var{t2}]@dots{}} instead.
5891 @cindex initial tabs, converting
5892 Only convert initial tabs (those that precede all non-space or non-tab
5893 characters) on each line to spaces.
5900 @node unexpand invocation
5901 @section @command{unexpand}: Convert spaces to tabs
5905 @command{unexpand} writes the contents of each given @var{file}, or
5906 standard input if none are given or for a @var{file} of @samp{-}, to
5907 standard output, converting blanks at the beginning of each line into
5908 as many tab characters as needed. In the default @acronym{POSIX}
5909 locale, a @dfn{blank} is a space or a tab; other locales may specify
5910 additional blank characters. Synopsis:
5913 unexpand [@var{option}]@dots{} [@var{file}]@dots{}
5916 By default, @command{unexpand} converts only initial blanks (those
5917 that precede all non-blank characters) on each line. It
5918 preserves backspace characters in the output; they decrement the column
5919 count for tab calculations. By default, tabs are set at every 8th
5922 The program accepts the following options. Also see @ref{Common options}.
5926 @item -t @var{tab1}[,@var{tab2}]@dots{}
5927 @itemx --tabs=@var{tab1}[,@var{tab2}]@dots{}
5930 If only one tab stop is given, set the tabs @var{tab1} columns apart
5931 instead of the default 8. Otherwise, set the tabs at columns
5932 @var{tab1}, @var{tab2}, @dots{} (numbered from 0), and leave blanks
5933 beyond the tab stops given unchanged. Tab stops can be separated by
5934 blanks as well as by commas. This option implies the @option{-a} option.
5936 For compatibility, GNU @command{unexpand} supports the obsolete option syntax,
5937 @option{-@var{tab1}[,@var{tab2}]@dots{}}, where tab stops must be
5938 separated by commas. (Unlike @option{-t}, this obsolete option does
5939 not imply @option{-a}.) New scripts should use @option{--first-only -t
5940 @var{tab1}[,@var{tab2}]@dots{}} instead.
5946 Also convert all sequences of two or more blanks just before a tab stop,
5947 even if they occur after non-blank characters in a line.
5954 @node Directory listing
5955 @chapter Directory listing
5957 This chapter describes the @command{ls} command and its variants @command{dir}
5958 and @command{vdir}, which list information about files.
5961 * ls invocation:: List directory contents.
5962 * dir invocation:: Briefly ls.
5963 * vdir invocation:: Verbosely ls.
5964 * dircolors invocation:: Color setup for ls, etc.
5969 @section @command{ls}: List directory contents
5972 @cindex directory listing
5974 The @command{ls} program lists information about files (of any type,
5975 including directories). Options and file arguments can be intermixed
5976 arbitrarily, as usual.
5978 For non-option command-line arguments that are directories, by default
5979 @command{ls} lists the contents of directories, not recursively, and
5980 omitting files with names beginning with @samp{.}. For other non-option
5981 arguments, by default @command{ls} lists just the file name. If no
5982 non-option argument is specified, @command{ls} operates on the current
5983 directory, acting as if it had been invoked with a single argument of @samp{.}.
5986 By default, the output is sorted alphabetically, according to the locale
5987 settings in effect.@footnote{If you use a non-@acronym{POSIX}
5988 locale (e.g., by setting @env{LC_ALL} to @samp{en_US}), then @command{ls} may
5989 produce output that is sorted differently than you're accustomed to.
5990 In that case, set the @env{LC_ALL} environment variable to @samp{C}.}
5991 If standard output is
5992 a terminal, the output is in columns (sorted vertically) and control
5993 characters are output as question marks; otherwise, the output is listed
5994 one per line and control characters are output as-is.
5996 Because @command{ls} is such a fundamental program, it has accumulated many
5997 options over the years. They are described in the subsections below;
5998 within each section, options are listed alphabetically (ignoring case).
5999 The division of options into the subsections is not absolute, since some
6000 options affect more than one aspect of @command{ls}'s operation.
6002 @cindex exit status of @command{ls}
6007 1 minor problems (e.g., a subdirectory was not found)
6008 2 serious trouble (e.g., memory exhausted)
6011 Also see @ref{Common options}.
6014 * Which files are listed::
6015 * What information is listed::
6016 * Sorting the output::
6017 * More details about version sort::
6018 * General output formatting::
6019 * Formatting file timestamps::
6020 * Formatting the file names::
6024 @node Which files are listed
6025 @subsection Which files are listed
6027 These options determine which files @command{ls} lists information for.
6028 By default, @command{ls} lists files and the contents of any
6029 directories on the command line, except that in directories it ignores
6030 files whose names start with @samp{.}.
6038 In directories, do not ignore file names that start with @samp{.}.
6043 @opindex --almost-all
6044 In directories, do not ignore all file names that start with @samp{.};
6045 ignore only @file{.} and @file{..}. The @option{--all} (@option{-a})
6046 option overrides this option.
6049 @itemx --ignore-backups
6051 @opindex --ignore-backups
6052 @cindex backup files, ignoring
6053 In directories, ignore files that end with @samp{~}. This option is
6054 equivalent to @samp{--ignore='*~' --ignore='.*~'}.
6059 @opindex --directory
6060 List just the names of directories, as with other types of files, rather
6061 than listing their contents.
6062 @c The following sentence is the same as the one for -F.
6063 Do not follow symbolic links listed on the
6064 command line unless the @option{--dereference-command-line} (@option{-H}),
6065 @option{--dereference} (@option{-L}), or
6066 @option{--dereference-command-line-symlink-to-dir} options are specified.
6069 @itemx --dereference-command-line
6071 @opindex --dereference-command-line
6072 @cindex symbolic links, dereferencing
6073 If a command line argument specifies a symbolic link, show information
6074 for the file the link references rather than for the link itself.
6076 @itemx --dereference-command-line-symlink-to-dir
6077 @opindex --dereference-command-line-symlink-to-dir
6078 @cindex symbolic links, dereferencing
6079 Do not dereference symbolic links, with one exception:
6080 if a command line argument specifies a symbolic link that refers to
6081 a directory, show information for that directory rather than for the
6083 This is the default behavior when no other dereferencing-related
6084 option has been specified (@option{--classify} (@option{-F}),
6085 @option{--directory} (@option{-d}),
6087 @option{--dereference} (@option{-L}), or
6088 @option{--dereference-command-line} (@option{-H})).
6090 @item --group-directories-first
6091 @opindex --group-directories-first
6092 Group all the directories before the files and then sort the
6093 directories and the files separately using the selected sort key
6094 (see --sort option).
6095 That is, this option specifies a primary sort key,
6096 and the --sort option specifies a secondary key.
6097 However, any use of @option{--sort=none}
6098 (@option{-U}) disables this option altogether.
6100 @item --hide=PATTERN
6101 @opindex --hide=@var{pattern}
6102 In directories, ignore files whose names match the shell pattern
6103 @var{pattern}, unless the @option{--all} (@option{-a}) or
6104 @option{--almost-all} (@option{-A}) is also given. This
6105 option acts like @option{--ignore=@var{pattern}} except that it has no
6106 effect if @option{--all} (@option{-a}) or @option{--almost-all}
6107 (@option{-A}) is also given.
6109 This option can be useful in shell aliases. For example, if
6110 @command{lx} is an alias for @samp{ls --hide='*~'} and @command{ly} is
6111 an alias for @samp{ls --ignore='*~'}, then the command @samp{lx -A}
6112 lists the file @file{README~} even though @samp{ly -A} would not.
6114 @item -I @var{pattern}
6115 @itemx --ignore=@var{pattern}
6117 @opindex --ignore=@var{pattern}
6118 In directories, ignore files whose names match the shell pattern
6119 (not regular expression) @var{pattern}. As
6120 in the shell, an initial @samp{.} in a file name does not match a
6121 wildcard at the start of @var{pattern}. Sometimes it is useful
6122 to give this option several times. For example,
6125 $ ls --ignore='.??*' --ignore='.[^.]' --ignore='#*'
6128 The first option ignores names of length 3 or more that start with @samp{.},
6129 the second ignores all two-character names that start with @samp{.}
6130 except @samp{..}, and the third ignores names that start with @samp{#}.
6133 @itemx --dereference
6135 @opindex --dereference
6136 @cindex symbolic links, dereferencing
6137 When showing file information for a symbolic link, show information
6138 for the file the link references rather than the link itself.
6139 However, even with this option, @command{ls} still prints the name
6140 of the link itself, not the name of the file that the link points to.
6145 @opindex --recursive
6146 @cindex recursive directory listing
6147 @cindex directory listing, recursive
6148 List the contents of all directories recursively.
6153 @node What information is listed
6154 @subsection What information is listed
6156 These options affect the information that @command{ls} displays. By
6157 default, only file names are shown.
6163 @cindex hurd, author, printing
6164 List each file's author when producing long format directory listings.
6165 In GNU/Hurd, file authors can differ from their owners, but in other
6166 operating systems the two are the same.
6172 @cindex dired Emacs mode support
6173 With the long listing (@option{-l}) format, print an additional line after
6177 //DIRED// @var{beg1} @var{end1} @var{beg2} @var{end2} @dots{}
6181 The @var{begN} and @var{endN} are unsigned integers that record the
6182 byte position of the beginning and end of each file name in the output.
6183 This makes it easy for Emacs to find the names, even when they contain
6184 unusual characters such as space or newline, without fancy searching.
6186 If directories are being listed recursively (@option{-R}), output a similar
6187 line with offsets for each subdirectory name:
6190 //SUBDIRED// @var{beg1} @var{end1} @dots{}
6193 Finally, output a line of the form:
6196 //DIRED-OPTIONS// --quoting-style=@var{word}
6200 where @var{word} is the quoting style (@pxref{Formatting the file names}).
6202 Here is an actual example:
6205 $ mkdir -p a/sub/deeper a/sub2
6207 $ touch a/sub/deeper/file
6208 $ ls -gloRF --dired a
6211 -rw-r--r-- 1 0 Jun 10 12:27 f1
6212 -rw-r--r-- 1 0 Jun 10 12:27 f2
6213 drwxr-xr-x 3 4096 Jun 10 12:27 sub/
6214 drwxr-xr-x 2 4096 Jun 10 12:27 sub2/
6218 drwxr-xr-x 2 4096 Jun 10 12:27 deeper/
6222 -rw-r--r-- 1 0 Jun 10 12:27 file
6226 //DIRED// 48 50 84 86 120 123 158 162 217 223 282 286
6227 //SUBDIRED// 2 3 167 172 228 240 290 296
6228 //DIRED-OPTIONS// --quoting-style=literal
6231 Note that the pairs of offsets on the @samp{//DIRED//} line above delimit
6232 these names: @file{f1}, @file{f2}, @file{sub}, @file{sub2}, @file{deeper},
6234 The offsets on the @samp{//SUBDIRED//} line delimit the following
6235 directory names: @file{a}, @file{a/sub}, @file{a/sub/deeper}, @file{a/sub2}.
6237 Here is an example of how to extract the fifth entry name, @samp{deeper},
6238 corresponding to the pair of offsets, 222 and 228:
6241 $ ls -gloRF --dired a > out
6242 $ dd bs=1 skip=222 count=6 < out 2>/dev/null; echo
6246 Note that although the listing above includes a trailing slash
6247 for the @samp{deeper} entry, the offsets select the name without
6248 the trailing slash. However, if you invoke @command{ls} with @option{--dired}
6249 along with an option like @option{--escape} (aka @option{-b}) and operate
6250 on a file whose name contains special characters, notice that the backslash
6255 $ ls -blog --dired 'a b'
6256 -rw-r--r-- 1 0 Jun 10 12:28 a\ b
6258 //DIRED-OPTIONS// --quoting-style=escape
6261 If you use a quoting style that adds quote marks
6262 (e.g., @option{--quoting-style=c}), then the offsets include the quote marks.
6263 So beware that the user may select the quoting style via the environment
6264 variable @env{QUOTING_STYLE}. Hence, applications using @option{--dired}
6265 should either specify an explicit @option{--quoting-style=literal} option
6266 (aka @option{-N} or @option{--literal}) on the command line, or else be
6267 prepared to parse the escaped names.
6270 @opindex --full-time
6271 Produce long format directory listings, and list times in full. It is
6272 equivalent to using @option{--format=long} with
6273 @option{--time-style=full-iso} (@pxref{Formatting file timestamps}).
6277 Produce long format directory listings, but don't display owner information.
6283 Inhibit display of group information in a long format directory listing.
6284 (This is the default in some non-@sc{gnu} versions of @command{ls}, so we
6285 provide this option for compatibility.)
6293 @cindex inode number, printing
6294 Print the inode number (also called the file serial number and index
6295 number) of each file to the left of the file name. (This number
6296 uniquely identifies each file within a particular file system.)
6299 @itemx --format=long
6300 @itemx --format=verbose
6303 @opindex long ls @r{format}
6304 @opindex verbose ls @r{format}
6305 In addition to the name of each file, print the file type, file mode bits,
6306 number of hard links, owner name, group name, size, and
6307 timestamp (@pxref{Formatting file timestamps}), normally
6308 the modification time. Print question marks for information that
6309 cannot be determined.
6311 Normally the size is printed as a byte count without punctuation, but
6312 this can be overridden (@pxref{Block size}). For example, @option{-h}
6313 prints an abbreviated, human-readable count, and
6314 @samp{--block-size="'1"} prints a byte count with the thousands
6315 separator of the current locale.
6317 For each directory that is listed, preface the files with a line
6318 @samp{total @var{blocks}}, where @var{blocks} is the total disk allocation
6319 for all files in that directory. The block size currently defaults to 1024
6320 bytes, but this can be overridden (@pxref{Block size}).
6321 The @var{blocks} computed counts each hard link separately;
6322 this is arguably a deficiency.
6324 The file type is one of the following characters:
6326 @c The commented-out entries are ones we're not sure about.
6334 character special file
6336 high performance (``contiguous data'') file
6340 door (Solaris 2.5 and up)
6342 @c semaphore, if this is a distinct file type
6346 @c multiplexed file (7th edition Unix; obsolete)
6348 off-line (``migrated'') file (Cray DMF)
6350 network special file (HP-UX)
6354 port (Solaris 10 and up)
6356 @c message queue, if this is a distinct file type
6360 @c shared memory object, if this is a distinct file type
6362 @c typed memory object, if this is a distinct file type
6364 @c whiteout (4.4BSD; not implemented)
6366 some other file type
6369 @cindex permissions, output by @command{ls}
6370 The file mode bits listed are similar to symbolic mode specifications
6371 (@pxref{Symbolic Modes}). But @command{ls} combines multiple bits into the
6372 third character of each set of permissions as follows:
6376 If the set-user-ID or set-group-ID bit and the corresponding executable bit
6380 If the set-user-ID or set-group-ID bit is set but the corresponding
6381 executable bit is not set.
6384 If the restricted deletion flag or sticky bit, and the
6385 other-executable bit, are both set. The restricted deletion flag is
6386 another name for the sticky bit. @xref{Mode Structure}.
6389 If the restricted deletion flag or sticky bit is set but the
6390 other-executable bit is not set.
6393 If the executable bit is set and none of the above apply.
6399 Following the file mode bits is a single character that specifies
6400 whether an alternate access method such as an access control list
6401 applies to the file. When the character following the file mode bits is a
6402 space, there is no alternate access method. When it is a printing
6403 character, then there is such a method.
6405 For a file with an extended access control list, a @samp{+} character is
6406 listed. Basic access control lists are equivalent to the permissions
6407 listed, and are not considered an alternate access method.
6410 @itemx --numeric-uid-gid
6412 @opindex --numeric-uid-gid
6413 @cindex numeric uid and gid
6414 @cindex numeric user and group IDs
6415 Produce long format directory listings, but
6416 display numeric user and group IDs instead of the owner and group names.
6420 Produce long format directory listings, but don't display group information.
6421 It is equivalent to using @option{--format=long} with @option{--no-group} .
6427 @cindex disk allocation
6428 @cindex size of files, reporting
6429 Print the disk allocation of each file to the left of the file name.
6430 This is the amount of disk space used by the file, which is usually a
6431 bit more than the file's size, but it can be less if the file has holes.
6433 Normally the disk allocation is printed in units of
6434 1024 bytes, but this can be overridden (@pxref{Block size}).
6436 @cindex NFS mounts from BSD to HP-UX
6437 For files that are NFS-mounted from an HP-UX system to a BSD system,
6438 this option reports sizes that are half the correct values. On HP-UX
6439 systems, it reports sizes that are twice the correct values for files
6440 that are NFS-mounted from BSD systems. This is due to a flaw in HP-UX;
6441 it also affects the HP-UX @command{ls} program.
6448 @node Sorting the output
6449 @subsection Sorting the output
6451 @cindex sorting @command{ls} output
6452 These options change the order in which @command{ls} sorts the information
6453 it outputs. By default, sorting is done by character code
6454 (e.g., @acronym{ASCII} order).
6460 @itemx --time=status
6463 @opindex ctime@r{, printing or sorting by}
6464 @opindex status time@r{, printing or sorting by}
6465 @opindex use time@r{, printing or sorting files by}
6466 If the long listing format (e.g., @option{-l}, @option{-o}) is being used,
6467 print the status change time (the @samp{ctime} in the inode) instead of
6468 the modification time.
6469 When explicitly sorting by time (@option{--sort=time} or @option{-t})
6470 or when not using a long listing format,
6471 sort according to the status change time.
6475 @cindex unsorted directory listing
6476 @cindex directory order, listing by
6477 Primarily, like @option{-U}---do not sort; list the files in whatever
6478 order they are stored in the directory. But also enable @option{-a} (list
6479 all files) and disable @option{-l}, @option{--color}, and @option{-s} (if they
6480 were specified before the @option{-f}).
6486 @cindex reverse sorting
6487 Reverse whatever the sorting method is---e.g., list files in reverse
6488 alphabetical order, youngest first, smallest first, or whatever.
6494 @opindex size of files@r{, sorting files by}
6495 Sort by file size, largest first.
6501 @opindex modification time@r{, sorting files by}
6502 Sort by modification time (the @samp{mtime} in the inode), newest first.
6506 @itemx --time=access
6510 @opindex use time@r{, printing or sorting files by}
6511 @opindex atime@r{, printing or sorting files by}
6512 @opindex access time@r{, printing or sorting files by}
6513 If the long listing format (e.g., @option{--format=long}) is being used,
6514 print the last access time (the @samp{atime} in the inode).
6515 When explicitly sorting by time (@option{--sort=time} or @option{-t})
6516 or when not using a long listing format, sort according to the access time.
6522 @opindex none@r{, sorting option for @command{ls}}
6523 Do not sort; list the files in whatever order they are
6524 stored in the directory. (Do not do any of the other unrelated things
6525 that @option{-f} does.) This is especially useful when listing very large
6526 directories, since not doing any sorting can be noticeably faster.
6529 @itemx --sort=version
6532 @opindex version@r{, sorting option for @command{ls}}
6533 Sort by version name and number, lowest first. It behaves like a default
6534 sort, except that each sequence of decimal digits is treated numerically
6535 as an index/version number. (@xref{More details about version sort}.)
6538 @itemx --sort=extension
6541 @opindex extension@r{, sorting files by}
6542 Sort directory contents alphabetically by file extension (characters
6543 after the last @samp{.}); files with no extension are sorted first.
6548 @node More details about version sort
6549 @subsection More details about version sort
6551 The version sort takes into account the fact that file names frequently include
6552 indices or version numbers. Standard sorting functions usually do not produce
6553 the ordering that people expect because comparisons are made on a
6554 character-by-character basis. The version
6555 sort addresses this problem, and is especially useful when browsing
6556 directories that contain many files with indices/version numbers in their
6561 foo.zml-1.gz foo.zml-1.gz
6562 foo.zml-100.gz foo.zml-2.gz
6563 foo.zml-12.gz foo.zml-6.gz
6564 foo.zml-13.gz foo.zml-12.gz
6565 foo.zml-2.gz foo.zml-13.gz
6566 foo.zml-25.gz foo.zml-25.gz
6567 foo.zml-6.gz foo.zml-100.gz
6570 Note also that numeric parts with leading zeros are considered as
6575 abc-1.007.tgz abc-1.007.tgz
6576 abc-1.012b.tgz abc-1.01a.tgz
6577 abc-1.01a.tgz abc-1.012b.tgz
6580 This functionality is implemented using the @code{strverscmp} function.
6581 @xref{String/Array Comparison, , , libc, The GNU C Library Reference Manual}.
6582 One result of that implementation decision is that @code{ls -v} does not
6583 use the locale category, @env{LC_COLLATE}. As a result, non-numeric prefixes
6584 are sorted as if @env{LC_COLLATE} were set to @code{C}.
6586 @node General output formatting
6587 @subsection General output formatting
6589 These options affect the appearance of the overall output.
6594 @itemx --format=single-column
6597 @opindex single-column @r{output of files}
6598 List one file per line. This is the default for @command{ls} when standard
6599 output is not a terminal.
6602 @itemx --format=vertical
6605 @opindex vertical @r{sorted files in columns}
6606 List files in columns, sorted vertically. This is the default for
6607 @command{ls} if standard output is a terminal. It is always the default
6608 for the @command{dir} program.
6609 @sc{gnu} @command{ls} uses variable width columns to display as many files as
6610 possible in the fewest lines.
6612 @item --color [=@var{when}]
6614 @cindex color, distinguishing file types with
6615 Specify whether to use color for distinguishing file types. @var{when}
6616 may be omitted, or one of:
6619 @vindex none @r{color option}
6620 - Do not use color at all. This is the default.
6622 @vindex auto @r{color option}
6623 @cindex terminal, using color iff
6624 - Only use color if standard output is a terminal.
6626 @vindex always @r{color option}
6629 Specifying @option{--color} and no @var{when} is equivalent to
6630 @option{--color=always}.
6631 Piping a colorized listing through a pager like @command{more} or
6632 @command{less} usually produces unreadable results. However, using
6633 @code{more -f} does seem to work.
6637 @itemx --indicator-style=classify
6640 @opindex --indicator-style
6641 @cindex file type and executables, marking
6642 @cindex executables and file type, marking
6643 Append a character to each file name indicating the file type. Also,
6644 for regular files that are executable, append @samp{*}. The file type
6645 indicators are @samp{/} for directories, @samp{@@} for symbolic links,
6646 @samp{|} for FIFOs, @samp{=} for sockets, @samp{>} for doors,
6647 and nothing for regular files.
6648 @c The following sentence is the same as the one for -d.
6649 Do not follow symbolic links listed on the
6650 command line unless the @option{--dereference-command-line} (@option{-H}),
6651 @option{--dereference} (@option{-L}), or
6652 @option{--dereference-command-line-symlink-to-dir} options are specified.
6655 @itemx --indicator-style=file-type
6656 @opindex --file-type
6657 @opindex --indicator-style
6658 @cindex file type, marking
6659 Append a character to each file name indicating the file type. This is
6660 like @option{-F}, except that executables are not marked.
6662 @item --indicator-style=@var{word}
6663 @opindex --indicator-style
6664 Append a character indicator with style @var{word} to entry names,
6669 Do not append any character indicator; this is the default.
6671 Append @samp{/} for directories. This is the same as the @option{-p}
6674 Append @samp{/} for directories, @samp{@@} for symbolic links, @samp{|}
6675 for FIFOs, @samp{=} for sockets, and nothing for regular files. This is
6676 the same as the @option{--file-type} option.
6678 Append @samp{*} for executable regular files, otherwise behave as for
6679 @samp{file-type}. This is the same as the @option{-F} or
6680 @option{--classify} option.
6685 Print file sizes in 1024-byte blocks, overriding the default block
6686 size (@pxref{Block size}).
6687 This option is equivalent to @option{--block-size=1K}.
6690 @itemx --format=commas
6693 @opindex commas@r{, outputting between files}
6694 List files horizontally, with as many as will fit on each line,
6695 separated by @samp{, } (a comma and a space).
6698 @itemx --indicator-style=slash
6700 @opindex --indicator-style
6701 @cindex file type, marking
6702 Append a @samp{/} to directory names.
6705 @itemx --format=across
6706 @itemx --format=horizontal
6709 @opindex across@r{, listing files}
6710 @opindex horizontal@r{, listing files}
6711 List the files in columns, sorted horizontally.
6714 @itemx --tabsize=@var{cols}
6717 Assume that each tab stop is @var{cols} columns wide. The default is 8.
6718 @command{ls} uses tabs where possible in the output, for efficiency. If
6719 @var{cols} is zero, do not use tabs at all.
6721 @c FIXME: remove in 2009, if Apple Terminal has been fixed for long enough.
6722 Some terminal emulators (at least Apple Terminal 1.5 (133) from Mac OS X 10.4.8)
6723 do not properly align columns to the right of a TAB following a
6724 non-@acronym{ASCII} byte. If you use such a terminal emulator, use the
6725 @option{-T0} option or put @code{TABSIZE=0} in your environment to tell
6726 @command{ls} to align using spaces, not tabs.
6729 @itemx --width=@var{cols}
6733 Assume the screen is @var{cols} columns wide. The default is taken
6734 from the terminal settings if possible; otherwise the environment
6735 variable @env{COLUMNS} is used if it is set; otherwise the default
6741 @node Formatting file timestamps
6742 @subsection Formatting file timestamps
6744 By default, file timestamps are listed in abbreviated form. Most
6745 locales use a timestamp like @samp{2002-03-30 23:45}. However, the
6746 default @acronym{POSIX} locale uses a date like @samp{Mar 30@ @ 2002}
6747 for non-recent timestamps, and a date-without-year and time like
6748 @samp{Mar 30 23:45} for recent timestamps.
6750 A timestamp is considered to be @dfn{recent} if it is less than six
6751 months old, and is not dated in the future. If a timestamp dated
6752 today is not listed in recent form, the timestamp is in the future,
6753 which means you probably have clock skew problems which may break
6754 programs like @command{make} that rely on file timestamps.
6757 Time stamps are listed according to the time zone rules specified by
6758 the @env{TZ} environment variable, or by the system default rules if
6759 @env{TZ} is not set. @xref{TZ Variable,, Specifying the Time Zone
6760 with @env{TZ}, libc, The GNU C Library Reference Manual}.
6762 The following option changes how file timestamps are printed.
6765 @item --time-style=@var{style}
6766 @opindex --time-style
6768 List timestamps in style @var{style}. The @var{style} should
6769 be one of the following:
6774 List timestamps using @var{format}, where @var{format} is interpreted
6775 like the format argument of @command{date} (@pxref{date invocation}).
6776 For example, @option{--time-style="+%Y-%m-%d %H:%M:%S"} causes
6777 @command{ls} to list timestamps like @samp{2002-03-30 23:45:56}. As
6778 with @command{date}, @var{format}'s interpretation is affected by the
6779 @env{LC_TIME} locale category.
6781 If @var{format} contains two format strings separated by a newline,
6782 the former is used for non-recent files and the latter for recent
6783 files; if you want output columns to line up, you may need to insert
6784 spaces in one of the two formats.
6787 List timestamps in full using @acronym{ISO} 8601 date, time, and time zone
6788 format with nanosecond precision, e.g., @samp{2002-03-30
6789 23:45:56.477817180 -0700}. This style is equivalent to
6790 @samp{+%Y-%m-%d %H:%M:%S.%N %z}.
6792 This is useful because the time output includes all the information that
6793 is available from the operating system. For example, this can help
6794 explain @command{make}'s behavior, since @acronym{GNU} @command{make}
6795 uses the full timestamp to determine whether a file is out of date.
6798 List @acronym{ISO} 8601 date and time in minutes, e.g.,
6799 @samp{2002-03-30 23:45}. These timestamps are shorter than
6800 @samp{full-iso} timestamps, and are usually good enough for everyday
6801 work. This style is equivalent to @samp{+%Y-%m-%d %H:%M}.
6804 List @acronym{ISO} 8601 dates for non-recent timestamps (e.g.,
6805 @samp{2002-03-30@ }), and @acronym{ISO} 8601 month, day, hour, and
6806 minute for recent timestamps (e.g., @samp{03-30 23:45}). These
6807 timestamps are uglier than @samp{long-iso} timestamps, but they carry
6808 nearly the same information in a smaller space and their brevity helps
6809 @command{ls} output fit within traditional 80-column output lines.
6810 The following two @command{ls} invocations are equivalent:
6815 ls -l --time-style="+%Y-%m-%d $newline%m-%d %H:%M"
6816 ls -l --time-style="iso"
6821 List timestamps in a locale-dependent form. For example, a Finnish
6822 locale might list non-recent timestamps like @samp{maalis 30@ @ 2002}
6823 and recent timestamps like @samp{maalis 30 23:45}. Locale-dependent
6824 timestamps typically consume more space than @samp{iso} timestamps and
6825 are harder for programs to parse because locale conventions vary so
6826 widely, but they are easier for many people to read.
6828 The @env{LC_TIME} locale category specifies the timestamp format. The
6829 default @acronym{POSIX} locale uses timestamps like @samp{Mar 30@
6830 @ 2002} and @samp{Mar 30 23:45}; in this locale, the following two
6831 @command{ls} invocations are equivalent:
6836 ls -l --time-style="+%b %e %Y$newline%b %e %H:%M"
6837 ls -l --time-style="locale"
6840 Other locales behave differently. For example, in a German locale,
6841 @option{--time-style="locale"} might be equivalent to
6842 @option{--time-style="+%e. %b %Y $newline%e. %b %H:%M"}
6843 and might generate timestamps like @samp{30. M@"ar 2002@ } and
6844 @samp{30. M@"ar 23:45}.
6846 @item posix-@var{style}
6848 List @acronym{POSIX}-locale timestamps if the @env{LC_TIME} locale
6849 category is @acronym{POSIX}, @var{style} timestamps otherwise. For
6850 example, the @samp{posix-long-iso} style lists
6851 timestamps like @samp{Mar 30@ @ 2002} and @samp{Mar 30 23:45} when in
6852 the @acronym{POSIX} locale, and like @samp{2002-03-30 23:45} otherwise.
6857 You can specify the default value of the @option{--time-style} option
6858 with the environment variable @env{TIME_STYLE}; if @env{TIME_STYLE} is not set
6859 the default style is @samp{locale}. @acronym{GNU} Emacs 21.3 and
6860 later use the @option{--dired} option and therefore can parse any date
6861 format, but if you are using Emacs 21.1 or 21.2 and specify a
6862 non-@acronym{POSIX} locale you may need to set
6863 @samp{TIME_STYLE="posix-long-iso"}.
6865 To avoid certain denial-of-service attacks, timestamps that would be
6866 longer than 1000 bytes may be treated as errors.
6869 @node Formatting the file names
6870 @subsection Formatting the file names
6872 These options change how file names themselves are printed.
6878 @itemx --quoting-style=escape
6881 @opindex --quoting-style
6882 @cindex backslash sequences for file names
6883 Quote nongraphic characters in file names using alphabetic and octal
6884 backslash sequences like those used in C.
6888 @itemx --quoting-style=literal
6891 @opindex --quoting-style
6892 Do not quote file names. However, with @command{ls} nongraphic
6893 characters are still printed as question marks if the output is a
6894 terminal and you do not specify the @option{--show-control-chars}
6898 @itemx --hide-control-chars
6900 @opindex --hide-control-chars
6901 Print question marks instead of nongraphic characters in file names.
6902 This is the default if the output is a terminal and the program is
6907 @itemx --quoting-style=c
6909 @opindex --quote-name
6910 @opindex --quoting-style
6911 Enclose file names in double quotes and quote nongraphic characters as
6914 @item --quoting-style=@var{word}
6915 @opindex --quoting-style
6916 @cindex quoting style
6917 Use style @var{word} to quote file names and other strings that may
6918 contain arbitrary characters. The @var{word} should
6919 be one of the following:
6923 Output strings as-is; this is the same as the @option{-N} or
6924 @option{--literal} option.
6926 Quote strings for the shell if they contain shell metacharacters or would
6927 cause ambiguous output.
6928 The quoting is suitable for @acronym{POSIX}-compatible shells like
6929 @command{bash}, but it does not always work for incompatible shells
6932 Quote strings for the shell, even if they would normally not require quoting.
6934 Quote strings as for C character string literals, including the
6935 surrounding double-quote characters; this is the same as the
6936 @option{-Q} or @option{--quote-name} option.
6938 Quote strings as for C character string literals, except omit the
6939 surrounding double-quote
6940 characters; this is the same as the @option{-b} or @option{--escape} option.
6942 Quote strings as for C character string literals, except use
6943 surrounding quotation marks appropriate for the
6946 @c Use @t instead of @samp to avoid duplicate quoting in some output styles.
6947 Quote strings as for C character string literals, except use
6948 surrounding quotation marks appropriate for the locale, and quote
6949 @t{`like this'} instead of @t{"like
6950 this"} in the default C locale. This looks nicer on many displays.
6953 You can specify the default value of the @option{--quoting-style} option
6954 with the environment variable @env{QUOTING_STYLE}. If that environment
6955 variable is not set, the default value is @samp{literal}, but this
6956 default may change to @samp{shell} in a future version of this package.
6958 @item --show-control-chars
6959 @opindex --show-control-chars
6960 Print nongraphic characters as-is in file names.
6961 This is the default unless the output is a terminal and the program is
6967 @node dir invocation
6968 @section @command{dir}: Briefly list directory contents
6971 @cindex directory listing, brief
6973 @command{dir} is equivalent to @code{ls -C
6974 -b}; that is, by default files are listed in columns, sorted vertically,
6975 and special characters are represented by backslash escape sequences.
6977 @xref{ls invocation, @command{ls}}.
6980 @node vdir invocation
6981 @section @command{vdir}: Verbosely list directory contents
6984 @cindex directory listing, verbose
6986 @command{vdir} is equivalent to @code{ls -l
6987 -b}; that is, by default files are listed in long format and special
6988 characters are represented by backslash escape sequences.
6990 @node dircolors invocation
6991 @section @command{dircolors}: Color setup for @command{ls}
6995 @cindex setup for color
6997 @command{dircolors} outputs a sequence of shell commands to set up the
6998 terminal for color output from @command{ls} (and @command{dir}, etc.).
7002 eval "`dircolors [@var{option}]@dots{} [@var{file}]`"
7005 If @var{file} is specified, @command{dircolors} reads it to determine which
7006 colors to use for which file types and extensions. Otherwise, a
7007 precompiled database is used. For details on the format of these files,
7008 run @samp{dircolors --print-database}.
7010 To make @command{dircolors} read a @file{~/.dircolors} file if it
7011 exists, you can put the following lines in your @file{~/.bashrc} (or
7012 adapt them to your favorite shell):
7016 test -r $d && eval "$(dircolors $d)"
7020 @vindex SHELL @r{environment variable, and color}
7021 The output is a shell command to set the @env{LS_COLORS} environment
7022 variable. You can specify the shell syntax to use on the command line,
7023 or @command{dircolors} will guess it from the value of the @env{SHELL}
7024 environment variable.
7026 The program accepts the following options. Also see @ref{Common options}.
7031 @itemx --bourne-shell
7034 @opindex --bourne-shell
7035 @cindex Bourne shell syntax for color setup
7036 @cindex @command{sh} syntax for color setup
7037 Output Bourne shell commands. This is the default if the @env{SHELL}
7038 environment variable is set and does not end with @samp{csh} or
7047 @cindex C shell syntax for color setup
7048 @cindex @command{csh} syntax for color setup
7049 Output C shell commands. This is the default if @code{SHELL} ends with
7050 @command{csh} or @command{tcsh}.
7053 @itemx --print-database
7055 @opindex --print-database
7056 @cindex color database, printing
7057 @cindex database for color setup, printing
7058 @cindex printing color database
7059 Print the (compiled-in) default color configuration database. This
7060 output is itself a valid configuration file, and is fairly descriptive
7061 of the possibilities.
7068 @node Basic operations
7069 @chapter Basic operations
7071 @cindex manipulating files
7073 This chapter describes the commands for basic file manipulation:
7074 copying, moving (renaming), and deleting (removing).
7077 * cp invocation:: Copy files.
7078 * dd invocation:: Convert and copy a file.
7079 * install invocation:: Copy files and set attributes.
7080 * mv invocation:: Move (rename) files.
7081 * rm invocation:: Remove files or directories.
7082 * shred invocation:: Remove files more securely.
7087 @section @command{cp}: Copy files and directories
7090 @cindex copying files and directories
7091 @cindex files, copying
7092 @cindex directories, copying
7094 @command{cp} copies files (or, optionally, directories). The copy is
7095 completely independent of the original. You can either copy one file to
7096 another, or copy arbitrarily many files to a destination directory.
7100 cp [@var{option}]@dots{} [-T] @var{source} @var{dest}
7101 cp [@var{option}]@dots{} @var{source}@dots{} @var{directory}
7102 cp [@var{option}]@dots{} -t @var{directory} @var{source}@dots{}
7107 If two file names are given, @command{cp} copies the first file to the
7111 If the @option{--target-directory} (@option{-t}) option is given, or
7112 failing that if the last file is a directory and the
7113 @option{--no-target-directory} (@option{-T}) option is not given,
7114 @command{cp} copies each @var{source} file to the specified directory,
7115 using the @var{source}s' names.
7118 Generally, files are written just as they are read. For exceptions,
7119 see the @option{--sparse} option below.
7121 By default, @command{cp} does not copy directories. However, the
7122 @option{-R}, @option{-a}, and @option{-r} options cause @command{cp} to
7123 copy recursively by descending into source directories and copying files
7124 to corresponding destination directories.
7126 When copying from a symbolic link, @command{cp} normally follows the
7127 link only when not copying
7128 recursively. This default can be overridden with the
7129 @option{--archive} (@option{-a}), @option{-d}, @option{--dereference}
7130 (@option{-L}), @option{--no-dereference} (@option{-P}), and
7131 @option{-H} options. If more than one of these options is specified,
7132 the last one silently overrides the others.
7134 When copying to a symbolic link, @command{cp} follows the
7135 link only when it refers to an existing regular file.
7136 However, when copying to a dangling symbolic link, @command{cp}
7137 refuses by default, and fails with a diagnostic, since the operation
7138 is inherently dangerous. This behavior is contrary to historical
7139 practice and to @acronym{POSIX}.
7140 Set @env{POSIXLY_CORRECT} to make @command{cp} attempt to create
7141 the target of a dangling destination symlink, in spite of the possible risk.
7142 Also, when an option like
7143 @option{--backup} or @option{--link} acts to rename or remove the
7144 destination before copying, @command{cp} renames or removes the
7145 symbolic link rather than the file it points to.
7147 By default, @command{cp} copies the contents of special files only
7148 when not copying recursively. This default can be overridden with the
7149 @option{--copy-contents} option.
7151 @cindex self-backups
7152 @cindex backups, making only
7153 @command{cp} generally refuses to copy a file onto itself, with the
7154 following exception: if @option{--force --backup} is specified with
7155 @var{source} and @var{dest} identical, and referring to a regular file,
7156 @command{cp} will make a backup file, either regular or numbered, as
7157 specified in the usual ways (@pxref{Backup options}). This is useful when
7158 you simply want to make a backup of an existing file before changing it.
7160 The program accepts the following options. Also see @ref{Common options}.
7167 Preserve as much as possible of the structure and attributes of the
7168 original files in the copy (but do not attempt to preserve internal
7169 directory structure; i.e., @samp{ls -U} may list the entries in a copied
7170 directory in a different order).
7171 Equivalent to @option{-dpR}.
7174 @itemx @w{@kbd{--backup}[=@var{method}]}
7177 @vindex VERSION_CONTROL
7178 @cindex backups, making
7179 @xref{Backup options}.
7180 Make a backup of each file that would otherwise be overwritten or removed.
7181 As a special case, @command{cp} makes a backup of @var{source} when the force
7182 and backup options are given and @var{source} and @var{dest} are the same
7183 name for an existing, regular file. One useful application of this
7184 combination of options is this tiny Bourne shell script:
7188 # Usage: backup FILE...
7189 # Create a @sc{gnu}-style backup of each listed FILE.
7191 cp --backup --force -- "$i" "$i"
7195 @item --copy-contents
7196 @cindex directories, copying recursively
7197 @cindex copying directories recursively
7198 @cindex recursively copying directories
7199 @cindex non-directories, copying as special files
7200 If copying recursively, copy the contents of any special files (e.g.,
7201 FIFOs and device files) as if they were regular files. This means
7202 trying to read the data in each source file and writing it to the
7203 destination. It is usually a mistake to use this option, as it
7204 normally has undesirable effects on special files like FIFOs and the
7205 ones typically found in the @file{/dev} directory. In most cases,
7206 @code{cp -R --copy-contents} will hang indefinitely trying to read
7207 from FIFOs and special files like @file{/dev/console}, and it will
7208 fill up your destination disk if you use it to copy @file{/dev/zero}.
7209 This option has no effect unless copying recursively, and it does not
7210 affect the copying of symbolic links.
7214 @cindex symbolic links, copying
7215 @cindex hard links, preserving
7216 Copy symbolic links as symbolic links rather than copying the files that
7217 they point to, and preserve hard links between source files in the copies.
7218 Equivalent to @option{--no-dereference --preserve=links}.
7224 When copying without this option and an existing destination file cannot
7225 be opened for writing, the copy fails. However, with @option{--force}),
7226 when a destination file cannot be opened, @command{cp} then removes it and
7227 tries to open it again. Contrast this behavior with that enabled by
7228 @option{--link} and @option{--symbolic-link}, whereby the destination file
7229 is never opened but rather is removed unconditionally. Also see the
7230 description of @option{--remove-destination}.
7232 This option is independent of the @option{--interactive} or
7233 @option{-i} option: neither cancels the effect of the other.
7237 If a command line argument specifies a symbolic link, then copy the
7238 file it points to rather than the symbolic link itself. However,
7239 copy (preserving its nature) any symbolic link that is encountered
7240 via recursive traversal.
7243 @itemx --interactive
7245 @opindex --interactive
7246 When copying a file other than a directory, prompt whether to
7247 overwrite an existing destination file.
7253 Make hard links instead of copies of non-directories.
7256 @itemx --dereference
7258 @opindex --dereference
7259 Follow symbolic links when copying from them.
7262 @itemx --no-dereference
7264 @opindex --no-dereference
7265 @cindex symbolic links, copying
7266 Copy symbolic links as symbolic links rather than copying the files that
7267 they point to. This option affects only symbolic links in the source;
7268 symbolic links in the destination are always followed if possible.
7271 @itemx @w{@kbd{--preserve}[=@var{attribute_list}]}
7274 @cindex file information, preserving
7275 Preserve the specified attributes of the original files.
7276 If specified, the @var{attribute_list} must be a comma-separated list
7277 of one or more of the following strings:
7281 Preserve the file mode bits and access control lists.
7283 Preserve the owner and group. On most modern systems,
7284 only users with appropriate privileges may change the owner of a file,
7286 may preserve the group ownership of a file only if they happen to be
7287 a member of the desired group.
7289 Preserve the times of last access and last modification, when possible.
7290 In general, it is not possible to preserve these attributes
7291 when the affected file is a symbolic link.
7292 However, FreeBSD now provides the @code{lutimes} function, which makes
7293 it possible even for symbolic links. However, this implementation does
7294 not yet take advantage of that.
7295 @c FIXME: once we provide lutimes support, update the above.
7297 Preserve in the destination files
7298 any links between corresponding source files.
7299 @c Give examples illustrating how hard links are preserved.
7300 @c Also, show how soft links map to hard links with -L and -H.
7302 Preserve all file attributes.
7303 Equivalent to specifying all of the above.
7306 Using @option{--preserve} with no @var{attribute_list} is equivalent
7307 to @option{--preserve=mode,ownership,timestamps}.
7309 In the absence of this option, each destination file is created with the
7310 mode bits of the corresponding source file, minus the bits set in the
7311 umask and minus the set-user-ID and set-group-ID bits.
7312 @xref{File permissions}.
7314 @itemx @w{@kbd{--no-preserve}=@var{attribute_list}}
7315 @cindex file information, preserving
7316 Do not preserve the specified attributes. The @var{attribute_list}
7317 has the same form as for @option{--preserve}.
7321 @cindex parent directories and @command{cp}
7322 Form the name of each destination file by appending to the target
7323 directory a slash and the specified name of the source file. The last
7324 argument given to @command{cp} must be the name of an existing directory.
7325 For example, the command:
7328 cp --parents a/b/c existing_dir
7332 copies the file @file{a/b/c} to @file{existing_dir/a/b/c}, creating
7333 any missing intermediate directories.
7335 @c The --reply option was deprecated in 2005, and is scheduled to
7336 @c be removed in 2008. It is already missing from the --help output.
7337 @itemx @w{@kbd{--reply}=@var{how}}
7339 @cindex interactivity
7340 This option is deprecated.
7347 @opindex --recursive
7348 @cindex directories, copying recursively
7349 @cindex copying directories recursively
7350 @cindex recursively copying directories
7351 @cindex non-directories, copying as special files
7352 Copy directories recursively. By default, do not follow symbolic
7353 links in the source; see the @option{--archive} (@option{-a}), @option{-d},
7354 @option{--dereference} (@option{-L}), @option{--no-dereference}
7355 (@option{-P}), and @option{-H} options. Special files are copied by
7356 creating a destination file of the same type as the source; see the
7357 @option{--copy-contents} option. It is not portable to use
7358 @option{-r} to copy symbolic links or special files. On some
7359 non-@sc{gnu} systems, @option{-r} implies the equivalent of
7360 @option{-L} and @option{--copy-contents} for historical reasons.
7361 Also, it is not portable to use @option{-R} to copy symbolic links
7362 unless you also specify @option{-P}, as @acronym{POSIX} allows
7363 implementations that dereference symbolic links by default.
7365 @item --remove-destination
7366 @opindex --remove-destination
7367 Remove each existing destination file before attempting to open it
7368 (contrast with @option{-f} above).
7370 @item --sparse=@var{when}
7371 @opindex --sparse=@var{when}
7372 @cindex sparse files, copying
7373 @cindex holes, copying files with
7374 @findex read @r{system call, and holes}
7375 A @dfn{sparse file} contains @dfn{holes}---a sequence of zero bytes that
7376 does not occupy any physical disk blocks; the @samp{read} system call
7377 reads these as zeros. This can both save considerable disk space and
7378 increase speed, since many binary files contain lots of consecutive zero
7379 bytes. By default, @command{cp} detects holes in input source files via a crude
7380 heuristic and makes the corresponding output file sparse as well.
7381 Only regular files may be sparse.
7383 The @var{when} value can be one of the following:
7387 The default behavior: if the input file is sparse, attempt to make
7388 the output file sparse, too. However, if an output file exists but
7389 refers to a non-regular file, then do not attempt to make it sparse.
7392 For each sufficiently long sequence of zero bytes in the input file,
7393 attempt to create a corresponding hole in the output file, even if the
7394 input file does not appear to be sparse.
7395 This is useful when the input file resides on a file system
7396 that does not support sparse files
7397 (for example, @samp{efs} file systems in SGI IRIX 5.3 and earlier),
7398 but the output file is on a type of file system that does support them.
7399 Holes may be created only in regular files, so if the destination file
7400 is of some other type, @command{cp} does not even try to make it sparse.
7403 Never make the output file sparse.
7404 This is useful in creating a file for use with the @command{mkswap} command,
7405 since such a file must not have any holes.
7408 @optStripTrailingSlashes
7411 @itemx --symbolic-link
7413 @opindex --symbolic-link
7414 @cindex symbolic links, copying with
7415 Make symbolic links instead of copies of non-directories. All source
7416 file names must be absolute (starting with @samp{/}) unless the
7417 destination files are in the current directory. This option merely
7418 results in an error message on systems that do not support symbolic links.
7424 @optNoTargetDirectory
7430 @cindex newer files, copying only
7431 Do not copy a non-directory that has an existing destination with the
7432 same or newer modification time. If time stamps are being preserved,
7433 the comparison is to the source time stamp truncated to the
7434 resolutions of the destination file system and of the system calls
7435 used to update time stamps; this avoids duplicate work if several
7436 @samp{cp -pu} commands are executed with the same source and
7443 Print the name of each file before copying it.
7446 @itemx --one-file-system
7448 @opindex --one-file-system
7449 @cindex file systems, omitting copying to different
7450 Skip subdirectories that are on different file systems from the one that
7451 the copy started on.
7452 However, mount point directories @emph{are} copied.
7460 @section @command{dd}: Convert and copy a file
7463 @cindex converting while copying a file
7465 @command{dd} copies a file (from standard input to standard output, by
7466 default) with a changeable I/O block size, while optionally performing
7467 conversions on it. Synopses:
7470 dd [@var{operand}]@dots{}
7474 The only options are @option{--help} and @option{--version}.
7475 @xref{Common options}. @command{dd} accepts the following operands.
7481 Read from @var{file} instead of standard input.
7485 Write to @var{file} instead of standard output. Unless
7486 @samp{conv=notrunc} is given, @command{dd} truncates @var{file} to zero
7487 bytes (or the size specified with @samp{seek=}).
7489 @item ibs=@var{bytes}
7491 @cindex block size of input
7492 @cindex input block size
7493 Set the input block size to @var{bytes}.
7494 This makes @command{dd} read @var{bytes} per block.
7496 @item obs=@var{bytes}
7498 @cindex block size of output
7499 @cindex output block size
7500 Set the output block size to @var{bytes}.
7501 This makes @command{dd} write @var{bytes} per block.
7503 @item bs=@var{bytes}
7506 Set both input and output block sizes to @var{bytes}.
7507 This makes @command{dd} read and write @var{bytes} per block,
7508 overriding any @samp{ibs} and @samp{obs} settings.
7510 @item cbs=@var{bytes}
7512 @cindex block size of conversion
7513 @cindex conversion block size
7514 @cindex fixed-length records, converting to variable-length
7515 @cindex variable-length records, converting to fixed-length
7516 Set the conversion block size to @var{bytes}.
7517 When converting variable-length records to fixed-length ones
7518 (@option{conv=block}) or the reverse (@option{conv=unblock}),
7519 use @var{bytes} as the fixed record length.
7521 @item skip=@var{blocks}
7523 Skip @var{blocks} @samp{ibs}-byte blocks in the input file before copying.
7525 @item seek=@var{blocks}
7527 Skip @var{blocks} @samp{obs}-byte blocks in the output file before copying.
7529 @item count=@var{blocks}
7531 Copy @var{blocks} @samp{ibs}-byte blocks from the input file, instead
7532 of everything until the end of the file.
7534 @item conv=@var{conversion}[,@var{conversion}]@dots{}
7536 Convert the file as specified by the @var{conversion} argument(s).
7537 (No spaces around any comma(s).)
7544 @opindex ascii@r{, converting to}
7545 Convert @acronym{EBCDIC} to @acronym{ASCII},
7546 using the conversion table specified by @acronym{POSIX}.
7547 This provides a 1:1 translation for all 256 bytes.
7550 @opindex ebcdic@r{, converting to}
7551 Convert @acronym{ASCII} to @acronym{EBCDIC}.
7552 This is the inverse of the @samp{ascii} conversion.
7555 @opindex alternate ebcdic@r{, converting to}
7556 Convert @acronym{ASCII} to alternate @acronym{EBCDIC},
7557 using the alternate conversion table specified by @acronym{POSIX}.
7558 This is not a 1:1 translation, but reflects common historical practice
7559 for @samp{~}, @samp{[}, and @samp{]}.
7561 The @samp{ascii}, @samp{ebcdic}, and @samp{ibm} conversions are
7565 @opindex block @r{(space-padding)}
7566 For each line in the input, output @samp{cbs} bytes, replacing the
7567 input newline with a space and padding with spaces as necessary.
7571 Replace trailing spaces in each @samp{cbs}-sized input block with a
7574 The @samp{block} and @samp{unblock} conversions are mutually exclusive.
7577 @opindex lcase@r{, converting to}
7578 Change uppercase letters to lowercase.
7581 @opindex ucase@r{, converting to}
7582 Change lowercase letters to uppercase.
7584 The @samp{lcase} and @samp{ucase} conversions are mutually exclusive.
7587 @opindex swab @r{(byte-swapping)}
7588 @cindex byte-swapping
7589 Swap every pair of input bytes. @sc{gnu} @command{dd}, unlike others, works
7590 when an odd number of bytes are read---the last byte is simply copied
7591 (since there is nothing to swap it with).
7595 @cindex read errors, ignoring
7596 Continue after read errors.
7600 @cindex creating output file, avoiding
7601 Do not create the output file; the output file must already exist.
7605 @cindex creating output file, requiring
7606 Fail if the output file already exists; @command{dd} must create the
7609 The @samp{excl} and @samp{nocreat} conversions are mutually exclusive.
7613 @cindex truncating output file, avoiding
7614 Do not truncate the output file.
7617 @opindex sync @r{(padding with nulls)}
7618 Pad every input block to size of @samp{ibs} with trailing zero bytes.
7619 When used with @samp{block} or @samp{unblock}, pad with spaces instead of
7624 @cindex synchronized data writes, before finishing
7625 Synchronize output data just before finishing. This forces a physical
7626 write of output data.
7630 @cindex synchronized data and metadata writes, before finishing
7631 Synchronize output data and metadata just before finishing. This
7632 forces a physical write of output data and metadata.
7636 @item iflag=@var{flag}[,@var{flag}]@dots{}
7638 Access the input file using the flags specified by the @var{flag}
7639 argument(s). (No spaces around any comma(s).)
7641 @item oflag=@var{flag}[,@var{flag}]@dots{}
7643 Access the output file using the flags specified by the @var{flag}
7644 argument(s). (No spaces around any comma(s).)
7646 Here are the flags. Not every flag is supported on every operating
7653 @cindex appending to the output file
7654 Write in append mode, so that even if some other process is writing to
7655 this file, every @command{dd} write will append to the current
7656 contents of the file. This flag makes sense only for output.
7657 If you combine this flag with the @samp{of=@var{file}} operand,
7658 you should also specify @samp{conv=notrunc} unless you want the
7659 output file to be truncated before being appended to.
7664 Use direct I/O for data, avoiding the buffer cache.
7668 @cindex directory I/O
7670 Fail unless the file is a directory. Most operating systems do not
7671 allow I/O to a directory, so this flag has limited utility.
7675 @cindex synchronized data reads
7676 Use synchronized I/O for data. For the output file, this forces a
7677 physical write of output data on each write. For the input file,
7678 this flag can matter when reading from a remote file that has been
7679 written to synchronously by some other process. Metadata (e.g.,
7680 last-access and last-modified time) is not necessarily synchronized.
7684 @cindex synchronized data and metadata I/O
7685 Use synchronized I/O for both data and metadata.
7689 @cindex nonblocking I/O
7690 Use non-blocking I/O.
7695 Do not update the file's access time.
7696 Some older file systems silently ignore this flag, so it is a good
7697 idea to test it on your files before relying on it.
7701 @cindex controlling terminal
7702 Do not assign the file to be a controlling terminal for @command{dd}.
7703 This has no effect when the file is not a terminal.
7704 On many hosts (e.g., @acronym{GNU}/Linux hosts), this option has no effect
7709 @cindex symbolic links, following
7710 Do not follow symbolic links.
7715 Fail if the file has multiple hard links.
7720 Use binary I/O. This option has an effect only on nonstandard
7721 platforms that distinguish binary from text I/O.
7726 Use text I/O. Like @samp{binary}, this option has no effect on
7731 Accumulate full blocks from input. The @code{read} system call
7732 may return early if a full block is not available.
7733 When that happens, continue calling @code{read} to fill the remainder
7735 This flag can be used only with @code{iflag}.
7739 These flags are not supported on all systems, and @samp{dd} rejects
7740 attempts to use them when they are not supported. When reading from
7741 standard input or writing to standard output, the @samp{nofollow} and
7742 @samp{noctty} flags should not be specified, and the other flags
7743 (e.g., @samp{nonblock}) can affect how other processes behave with the
7744 affected file descriptors, even after @command{dd} exits.
7748 @cindex multipliers after numbers
7749 The numeric-valued strings above (@var{bytes} and @var{blocks}) can be
7750 followed by a multiplier: @samp{b}=512, @samp{c}=1,
7751 @samp{w}=2, @samp{x@var{m}}=@var{m}, or any of the
7752 standard block size suffixes like @samp{k}=1024 (@pxref{Block size}).
7754 Use different @command{dd} invocations to use different block sizes for
7755 skipping and I/O@. For example, the following shell commands copy data
7756 in 512 KiB blocks between a disk and a tape, but do not save or restore a
7757 4 KiB label at the start of the disk:
7760 disk=/dev/rdsk/c0t1d0s2
7763 # Copy all but the label from disk to tape.
7764 (dd bs=4k skip=1 count=0 && dd bs=512k) <$disk >$tape
7766 # Copy from tape back to disk, but leave the disk label alone.
7767 (dd bs=4k seek=1 count=0 && dd bs=512k) <$tape >$disk
7770 Sending an @samp{INFO} signal to a running @command{dd}
7771 process makes it print I/O statistics to standard error
7772 and then resume copying. In the example below,
7773 @command{dd} is run in the background to copy 10 million blocks.
7774 The @command{kill} command makes it output intermediate I/O statistics,
7775 and when @command{dd} completes normally or is killed by the
7776 @code{SIGINT} signal, it outputs the final statistics.
7779 $ dd if=/dev/zero of=/dev/null count=10MB & pid=$!
7780 $ kill -s INFO $pid; wait $pid
7781 3385223+0 records in
7782 3385223+0 records out
7783 1733234176 bytes (1.7 GB) copied, 6.42173 seconds, 270 MB/s
7784 10000000+0 records in
7785 10000000+0 records out
7786 5120000000 bytes (5.1 GB) copied, 18.913 seconds, 271 MB/s
7789 @vindex POSIXLY_CORRECT
7790 On systems lacking the @samp{INFO} signal @command{dd} responds to the
7791 @samp{USR1} signal instead, unless the @env{POSIXLY_CORRECT}
7792 environment variable is set.
7797 @node install invocation
7798 @section @command{install}: Copy files and set attributes
7801 @cindex copying files and setting attributes
7803 @command{install} copies files while setting their file mode bits and, if
7804 possible, their owner and group. Synopses:
7807 install [@var{option}]@dots{} [-T] @var{source} @var{dest}
7808 install [@var{option}]@dots{} @var{source}@dots{} @var{directory}
7809 install [@var{option}]@dots{} -t @var{directory} @var{source}@dots{}
7810 install [@var{option}]@dots{} -d @var{directory}@dots{}
7815 If two file names are given, @command{install} copies the first file to the
7819 If the @option{--target-directory} (@option{-t}) option is given, or
7820 failing that if the last file is a directory and the
7821 @option{--no-target-directory} (@option{-T}) option is not given,
7822 @command{install} copies each @var{source} file to the specified
7823 directory, using the @var{source}s' names.
7826 If the @option{--directory} (@option{-d}) option is given,
7827 @command{install} creates each @var{directory} and any missing parent
7828 directories. Parent directories are created with mode
7829 @samp{u=rwx,go=rx} (755), regardless of the @option{-m} option or the
7830 current umask. @xref{Directory Setuid and Setgid}, for how the
7831 set-user-ID and set-group-ID bits of parent directories are inherited.
7834 @cindex Makefiles, installing programs in
7835 @command{install} is similar to @command{cp}, but allows you to control the
7836 attributes of destination files. It is typically used in Makefiles to
7837 copy programs into their destination directories. It refuses to copy
7838 files onto themselves.
7840 The program accepts the following options. Also see @ref{Common options}.
7848 Ignored; for compatibility with old Unix versions of @command{install}.
7852 Create any missing parent directories of @var{dest},
7853 then copy @var{source} to @var{dest}.
7854 This option is ignored if a destination directory is specified
7855 via @option{--target-directory=DIR}.
7860 @opindex --directory
7861 @cindex directories, creating with given attributes
7862 @cindex parent directories, creating missing
7863 @cindex leading directories, creating missing
7864 Create any missing parent directories, giving them the default
7865 attributes. Then create each given directory, setting their owner,
7866 group and mode as given on the command line or to the defaults.
7868 @item -g @var{group}
7869 @itemx --group=@var{group}
7872 @cindex group ownership of installed files, setting
7873 Set the group ownership of installed files or directories to
7874 @var{group}. The default is the process's current group. @var{group}
7875 may be either a group name or a numeric group ID.
7878 @itemx --mode=@var{mode}
7881 @cindex permissions of installed files, setting
7882 Set the file mode bits for the installed file or directory to @var{mode},
7883 which can be either an octal number, or a symbolic mode as in
7884 @command{chmod}, with @samp{a=} (no access allowed to anyone) as the
7885 point of departure (@pxref{File permissions}).
7886 The default mode is @samp{u=rwx,go=rx,a-s}---read, write, and
7887 execute for the owner, read and execute for group and other, and with
7888 set-user-ID and set-group-ID disabled.
7889 This default is not quite the same as @samp{755}, since it disables
7890 instead of preserving set-user-ID and set-group-ID on directories.
7891 @xref{Directory Setuid and Setgid}.
7893 @item -o @var{owner}
7894 @itemx --owner=@var{owner}
7897 @cindex ownership of installed files, setting
7898 @cindex appropriate privileges
7899 @vindex root @r{as default owner}
7900 If @command{install} has appropriate privileges (is run as root), set the
7901 ownership of installed files or directories to @var{owner}. The default
7902 is @code{root}. @var{owner} may be either a user name or a numeric user
7906 @itemx --preserve-timestamps
7908 @opindex --preserve-timestamps
7909 @cindex timestamps of installed files, preserving
7910 Set the time of last access and the time of last modification of each
7911 installed file to match those of each corresponding original file.
7912 When a file is installed without this option, its last access and
7913 last modification times are both set to the time of installation.
7914 This option is useful if you want to use the last modification times
7915 of installed files to keep track of when they were last built as opposed
7916 to when they were last installed.
7922 @cindex symbol table information, stripping
7923 @cindex stripping symbol table information
7924 Strip the symbol tables from installed binary executables.
7926 @itemx --strip-program=@var{program}
7927 @opindex --strip-program
7928 @cindex symbol table information, stripping, program
7929 Program used to strip binaries.
7935 @optNoTargetDirectory
7941 Print the name of each file before copying it.
7949 @section @command{mv}: Move (rename) files
7953 @command{mv} moves or renames files (or directories). Synopses:
7956 mv [@var{option}]@dots{} [-T] @var{source} @var{dest}
7957 mv [@var{option}]@dots{} @var{source}@dots{} @var{directory}
7958 mv [@var{option}]@dots{} -t @var{directory} @var{source}@dots{}
7963 If two file names are given, @command{mv} moves the first file to the
7967 If the @option{--target-directory} (@option{-t}) option is given, or
7968 failing that if the last file is a directory and the
7969 @option{--no-target-directory} (@option{-T}) option is not given,
7970 @command{mv} moves each @var{source} file to the specified
7971 directory, using the @var{source}s' names.
7974 @command{mv} can move any type of file from one file system to another.
7975 Prior to version @code{4.0} of the fileutils,
7976 @command{mv} could move only regular files between file systems.
7977 For example, now @command{mv} can move an entire directory hierarchy
7978 including special device files from one partition to another. It first
7979 uses some of the same code that's used by @code{cp -a} to copy the
7980 requested directories and files, then (assuming the copy succeeded)
7981 it removes the originals. If the copy fails, then the part that was
7982 copied to the destination partition is removed. If you were to copy
7983 three directories from one partition to another and the copy of the first
7984 directory succeeded, but the second didn't, the first would be left on
7985 the destination partition and the second and third would be left on the
7988 @cindex prompting, and @command{mv}
7989 If a destination file exists but is normally unwritable, standard input
7990 is a terminal, and the @option{-f} or @option{--force} option is not given,
7991 @command{mv} prompts the user for whether to replace the file. (You might
7992 own the file, or have write permission on its directory.) If the
7993 response is not affirmative, the file is skipped.
7995 @emph{Warning}: Avoid specifying a source name with a trailing slash,
7996 when it might be a symlink to a directory.
7997 Otherwise, @command{mv} may do something very surprising, since
7998 its behavior depends on the underlying rename system call.
7999 On a system with a modern Linux-based kernel, it fails with @code{errno=ENOTDIR}.
8000 However, on other systems (at least FreeBSD 6.1 and Solaris 10) it silently
8001 renames not the symlink but rather the directory referenced by the symlink.
8002 @xref{Trailing slashes}.
8004 The program accepts the following options. Also see @ref{Common options}.
8014 @cindex prompts, omitting
8015 Do not prompt the user before removing a destination file.
8018 @itemx --interactive
8020 @opindex --interactive
8021 @cindex prompts, forcing
8022 Prompt whether to overwrite each existing destination file, regardless
8024 If the response is not affirmative, the file is skipped.
8026 @itemx @w{@kbd{--reply}=@var{how}}
8028 @cindex interactivity
8029 This option is deprecated.
8035 @cindex newer files, moving only
8036 Do not move a non-directory that has an existing destination with the
8037 same or newer modification time.
8038 If the move is across file system boundaries, the comparison is to the
8039 source time stamp truncated to the resolutions of the destination file
8040 system and of the system calls used to update time stamps; this avoids
8041 duplicate work if several @samp{mv -u} commands are executed with the
8042 same source and destination.
8048 Print the name of each file before moving it.
8050 @optStripTrailingSlashes
8056 @optNoTargetDirectory
8064 @section @command{rm}: Remove files or directories
8067 @cindex removing files or directories
8069 @command{rm} removes each given @var{file}. By default, it does not remove
8070 directories. Synopsis:
8073 rm [@var{option}]@dots{} [@var{file}]@dots{}
8076 @cindex prompting, and @command{rm}
8077 If the @option{-I} or @option{--interactive=once} option is given,
8078 and there are more than three files or the @option{-r}, @option{-R},
8079 or @option{--recursive} are given, then @command{rm} prompts the user
8080 for whether to proceed with the entire operation. If the response is
8081 not affirmative, the entire command is aborted.
8083 Otherwise, if a file is unwritable, standard input is a terminal, and
8084 the @option{-f} or @option{--force} option is not given, or the
8085 @option{-i} or @option{--interactive=always} option @emph{is} given,
8086 @command{rm} prompts the user for whether to remove the file.
8087 If the response is not affirmative, the file is skipped.
8089 Any attempt to remove a file whose last file name component is
8090 @file{.} or @file{..} is rejected without any prompting.
8092 @emph{Warning}: If you use @command{rm} to remove a file, it is usually
8093 possible to recover the contents of that file. If you want more assurance
8094 that the contents are truly unrecoverable, consider using @command{shred}.
8096 The program accepts the following options. Also see @ref{Common options}.
8104 Ignore nonexistent files and never prompt the user.
8105 Ignore any previous @option{--interactive} (@option{-i}) option.
8109 Prompt whether to remove each file.
8110 If the response is not affirmative, the file is skipped.
8111 Ignore any previous @option{--force} (@option{-f}) option.
8112 Equivalent to @option{--interactive=always}.
8116 Prompt once whether to proceed with the command, if more than three
8117 files are named or if a recursive removal is requested. Ignore any
8118 previous @option{--force} (@option{-f}) option. Equivalent to
8119 @option{--interactive=once}.
8121 @itemx --interactive [=@var{when}]
8122 @opindex --interactive
8123 Specify when to issue an interactive prompt. @var{when} may be
8127 @vindex never @r{interactive option}
8128 - Do not prompt at all.
8130 @vindex once @r{interactive option}
8131 - Prompt once if more than three files are named or if a recursive
8132 removal is requested. Equivalent to @option{-I}.
8134 @vindex always @r{interactive option}
8135 - Prompt for every file being removed. Equivalent to @option{-i}.
8137 @option{--interactive} with no @var{when} is equivalent to
8138 @option{--interactive=always}.
8140 @itemx --one-file-system
8141 @opindex --one-file-system
8142 @cindex one file system, restricting @command{rm} to
8143 When removing a hierarchy recursively, skip any directory that is on a
8144 file system different from that of the corresponding command line argument.
8146 This option is useful when removing a build ``chroot'' hierarchy,
8147 which normally contains no valuable data. However, it is not uncommon
8148 to bind-mount @file{/home} into such a hierarchy, to make it easier to
8149 use one's start-up file. The catch is that it's easy to forget to
8150 unmount @file{/home}. Then, when you use @command{rm -rf} to remove
8151 your normally throw-away chroot, that command will remove everything
8152 under @file{/home}, too.
8153 Use the @option{--one-file-system} option, and it will
8154 warn about and skip directories on other file systems.
8155 Of course, this will not save your @file{/home} if it and your
8156 chroot happen to be on the same file system.
8158 @itemx --preserve-root
8159 @opindex --preserve-root
8160 @cindex root directory, disallow recursive destruction
8161 Fail upon any attempt to remove the root directory, @file{/},
8162 when used with the @option{--recursive} option.
8163 This is the default behavior.
8164 @xref{Treating / specially}.
8166 @itemx --no-preserve-root
8167 @opindex --no-preserve-root
8168 @cindex root directory, allow recursive destruction
8169 Do not treat @file{/} specially when removing recursively.
8170 This option is not recommended unless you really want to
8171 remove all the files on your computer.
8172 @xref{Treating / specially}.
8179 @opindex --recursive
8180 @cindex directories, removing (recursively)
8181 Remove the listed directories and their contents recursively.
8187 Print the name of each file before removing it.
8191 @cindex files beginning with @samp{-}, removing
8192 @cindex @samp{-}, removing files beginning with
8193 One common question is how to remove files whose names begin with a
8194 @samp{-}. @sc{gnu} @command{rm}, like every program that uses the @code{getopt}
8195 function to parse its arguments, lets you use the @samp{--} option to
8196 indicate that all following arguments are non-options. To remove a file
8197 called @file{-f} in the current directory, you could type either:
8210 @opindex - @r{and Unix @command{rm}}
8211 The Unix @command{rm} program's use of a single @samp{-} for this purpose
8212 predates the development of the getopt standard syntax.
8217 @node shred invocation
8218 @section @command{shred}: Remove files more securely
8221 @cindex data, erasing
8222 @cindex erasing data
8224 @command{shred} overwrites devices or files, to help prevent even
8225 very expensive hardware from recovering the data.
8227 Ordinarily when you remove a file (@pxref{rm invocation}), the data is
8228 not actually destroyed. Only the index listing where the file is
8229 stored is destroyed, and the storage is made available for reuse.
8230 There are undelete utilities that will attempt to reconstruct the index
8231 and can bring the file back if the parts were not reused.
8233 On a busy system with a nearly-full drive, space can get reused in a few
8234 seconds. But there is no way to know for sure. If you have sensitive
8235 data, you may want to be sure that recovery is not possible by actually
8236 overwriting the file with non-sensitive data.
8238 However, even after doing that, it is possible to take the disk back
8239 to a laboratory and use a lot of sensitive (and expensive) equipment
8240 to look for the faint ``echoes'' of the original data underneath the
8241 overwritten data. If the data has only been overwritten once, it's not
8244 The best way to remove something irretrievably is to destroy the media
8245 it's on with acid, melt it down, or the like. For cheap removable media
8246 like floppy disks, this is the preferred method. However, hard drives
8247 are expensive and hard to melt, so the @command{shred} utility tries
8248 to achieve a similar effect non-destructively.
8250 This uses many overwrite passes, with the data patterns chosen to
8251 maximize the damage they do to the old data. While this will work on
8252 floppies, the patterns are designed for best effect on hard drives.
8253 For more details, see the source code and Peter Gutmann's paper
8254 @uref{http://www.cs.auckland.ac.nz/~pgut001/pubs/secure_del.html,
8255 @cite{Secure Deletion of Data from Magnetic and Solid-State Memory}},
8256 from the proceedings of the Sixth @acronym{USENIX} Security Symposium (San Jose,
8257 California, July 22--25, 1996).
8259 @strong{Please note} that @command{shred} relies on a very important assumption:
8260 that the file system overwrites data in place. This is the traditional
8261 way to do things, but many modern file system designs do not satisfy this
8262 assumption. Exceptions include:
8267 Log-structured or journaled file systems, such as those supplied with
8268 AIX and Solaris, and JFS, ReiserFS, XFS, Ext3 (in @code{data=journal} mode),
8269 BFS, NTFS, etc.@: when they are configured to journal @emph{data}.
8272 File systems that write redundant data and carry on even if some writes
8273 fail, such as RAID-based file systems.
8276 File systems that make snapshots, such as Network Appliance's NFS server.
8279 File systems that cache in temporary locations, such as NFS version 3
8283 Compressed file systems.
8286 In the particular case of ext3 file systems, the above disclaimer applies (and
8287 @command{shred} is thus of limited effectiveness) only in @code{data=journal}
8288 mode, which journals file data in addition to just metadata. In both
8289 the @code{data=ordered} (default) and @code{data=writeback} modes,
8290 @command{shred} works as usual. Ext3 journaling modes can be changed
8291 by adding the @code{data=something} option to the mount options for a
8292 particular file system in the @file{/etc/fstab} file, as documented in
8293 the mount man page (man mount).
8295 If you are not sure how your file system operates, then you should assume
8296 that it does not overwrite data in place, which means that shred cannot
8297 reliably operate on regular files in your file system.
8299 Generally speaking, it is more reliable to shred a device than a file,
8300 since this bypasses the problem of file system design mentioned above.
8301 However, even shredding devices is not always completely reliable. For
8302 example, most disks map out bad sectors invisibly to the application; if
8303 the bad sectors contain sensitive data, @command{shred} won't be able to
8306 @command{shred} makes no attempt to detect or report this problem, just as
8307 it makes no attempt to do anything about backups. However, since it is
8308 more reliable to shred devices than files, @command{shred} by default does
8309 not truncate or remove the output file. This default is more suitable
8310 for devices, which typically cannot be truncated and should not be
8313 Finally, consider the risk of backups and mirrors.
8314 File system backups and remote mirrors may contain copies of the
8315 file that cannot be removed, and that will allow a shredded file
8316 to be recovered later. So if you keep any data you may later want
8317 to destroy using @command{shred}, be sure that it is not backed up or mirrored.
8320 shred [@var{option}]@dots{} @var{file}[@dots{}]
8323 The program accepts the following options. Also see @ref{Common options}.
8331 @cindex force deletion
8332 Override file permissions if necessary to allow overwriting.
8335 @itemx -n @var{NUMBER}
8336 @itemx --iterations=@var{NUMBER}
8337 @opindex -n @var{NUMBER}
8338 @opindex --iterations=@var{NUMBER}
8339 @cindex iterations, selecting the number of
8340 By default, @command{shred} uses 25 passes of overwrite. This is enough
8341 for all of the useful overwrite patterns to be used at least once.
8342 You can reduce this to save time, or increase it if you have a lot of
8345 @item --random-source=@var{file}
8346 @opindex --random-source
8347 @cindex random source for shredding
8348 Use @var{file} as a source of random data used to overwrite and to
8349 choose pass ordering. @xref{Random sources}.
8351 @item -s @var{BYTES}
8352 @itemx --size=@var{BYTES}
8353 @opindex -s @var{BYTES}
8354 @opindex --size=@var{BYTES}
8355 @cindex size of file to shred
8356 Shred the first @var{BYTES} bytes of the file. The default is to shred
8357 the whole file. @var{BYTES} can be followed by a size specification like
8358 @samp{K}, @samp{M}, or @samp{G} to specify a multiple. @xref{Block size}.
8364 @cindex removing files after shredding
8365 After shredding a file, truncate it (if possible) and then remove it.
8366 If a file has multiple links, only the named links will be removed.
8372 Display to standard error all status updates as sterilization proceeds.
8378 By default, @command{shred} rounds the size of a regular file up to the next
8379 multiple of the file system block size to fully erase the last block of the file.
8380 Use @option{--exact} to suppress that behavior.
8381 Thus, by default if you shred a 10-byte regular file on a system with 512-byte
8382 blocks, the resulting file will be 512 bytes long. With this option,
8383 shred does not increase the apparent size of the file.
8389 Normally, the last pass that @command{shred} writes is made up of
8390 random data. If this would be conspicuous on your hard drive (for
8391 example, because it looks like encrypted data), or you just think
8392 it's tidier, the @option{--zero} option adds an additional overwrite pass with
8393 all zero bits. This is in addition to the number of passes specified
8394 by the @option{--iterations} option.
8398 You might use the following command to erase all trace of the
8399 file system you'd created on the floppy disk in your first drive.
8400 That command takes about 20 minutes to erase a ``1.44MB'' (actually
8404 shred --verbose /dev/fd0
8407 Similarly, to erase all data on a selected partition of
8408 your hard disk, you could give a command like this:
8411 shred --verbose /dev/sda5
8414 A @var{file} of @samp{-} denotes standard output.
8415 The intended use of this is to shred a removed temporary file.
8419 i=`tempfile -m 0600`
8422 echo "Hello, world" >&3
8427 However, the command @samp{shred - >file} does not shred the contents
8428 of @var{file}, since the shell truncates @var{file} before invoking
8429 @command{shred}. Use the command @samp{shred file} or (if using a
8430 Bourne-compatible shell) the command @samp{shred - 1<>file} instead.
8435 @node Special file types
8436 @chapter Special file types
8438 @cindex special file types
8439 @cindex file types, special
8441 This chapter describes commands which create special types of files (and
8442 @command{rmdir}, which removes directories, one special file type).
8444 @cindex special file types
8446 Although Unix-like operating systems have markedly fewer special file
8447 types than others, not @emph{everything} can be treated only as the
8448 undifferentiated byte stream of @dfn{normal files}. For example, when a
8449 file is created or removed, the system must record this information,
8450 which it does in a @dfn{directory}---a special type of file. Although
8451 you can read directories as normal files, if you're curious, in order
8452 for the system to do its job it must impose a structure, a certain
8453 order, on the bytes of the file. Thus it is a ``special'' type of file.
8455 Besides directories, other special file types include named pipes
8456 (FIFOs), symbolic links, sockets, and so-called @dfn{special files}.
8459 * link invocation:: Make a hard link via the link syscall
8460 * ln invocation:: Make links between files.
8461 * mkdir invocation:: Make directories.
8462 * mkfifo invocation:: Make FIFOs (named pipes).
8463 * mknod invocation:: Make block or character special files.
8464 * readlink invocation:: Print the referent of a symbolic link.
8465 * rmdir invocation:: Remove empty directories.
8466 * unlink invocation:: Remove files via the unlink syscall
8470 @node link invocation
8471 @section @command{link}: Make a hard link via the link syscall
8474 @cindex links, creating
8475 @cindex hard links, creating
8476 @cindex creating links (hard only)
8478 @command{link} creates a single hard link at a time.
8479 It is a minimalist interface to the system-provided
8480 @code{link} function. @xref{Hard Links, , , libc,
8481 The GNU C Library Reference Manual}.
8482 It avoids the bells and whistles of the more commonly-used
8483 @command{ln} command (@pxref{ln invocation}).
8487 link @var{filename} @var{linkname}
8490 @var{filename} must specify an existing file, and @var{linkname}
8491 must specify a nonexistent entry in an existing directory.
8492 @command{link} simply calls @code{link (@var{filename}, @var{linkname})}
8495 On a @acronym{GNU} system, this command acts like @samp{ln --directory
8496 --no-target-directory @var{filename} @var{linkname}}. However, the
8497 @option{--directory} and @option{--no-target-directory} options are
8498 not specified by @acronym{POSIX}, and the @command{link} command is
8499 more portable in practice.
8505 @section @command{ln}: Make links between files
8508 @cindex links, creating
8509 @cindex hard links, creating
8510 @cindex symbolic (soft) links, creating
8511 @cindex creating links (hard or soft)
8513 @cindex file systems and hard links
8514 @command{ln} makes links between files. By default, it makes hard links;
8515 with the @option{-s} option, it makes symbolic (or @dfn{soft}) links.
8519 ln [@var{option}]@dots{} [-T] @var{target} @var{linkname}
8520 ln [@var{option}]@dots{} @var{target}
8521 ln [@var{option}]@dots{} @var{target}@dots{} @var{directory}
8522 ln [@var{option}]@dots{} -t @var{directory} @var{target}@dots{}
8528 If two file names are given, @command{ln} creates a link to the first
8529 file from the second.
8532 If one @var{target} is given, @command{ln} creates a link to that file
8533 in the current directory.
8536 If the @option{--target-directory} (@option{-t}) option is given, or
8537 failing that if the last file is a directory and the
8538 @option{--no-target-directory} (@option{-T}) option is not given,
8539 @command{ln} creates a link to each @var{target} file in the specified
8540 directory, using the @var{target}s' names.
8544 Normally @command{ln} does not remove existing files. Use the
8545 @option{--force} (@option{-f}) option to remove them unconditionally,
8546 the @option{--interactive} (@option{-i}) option to remove them
8547 conditionally, and the @option{--backup} (@option{-b}) option to
8550 @cindex hard link, defined
8551 @cindex inode, and hard links
8552 A @dfn{hard link} is another name for an existing file; the link and the
8553 original are indistinguishable. Technically speaking, they share the
8554 same inode, and the inode contains all the information about a
8555 file---indeed, it is not incorrect to say that the inode @emph{is} the
8556 file. On all existing implementations, you cannot make a hard link to
8557 a directory, and hard links cannot cross file system boundaries. (These
8558 restrictions are not mandated by @acronym{POSIX}, however.)
8560 @cindex dereferencing symbolic links
8561 @cindex symbolic link, defined
8562 @dfn{Symbolic links} (@dfn{symlinks} for short), on the other hand, are
8563 a special file type (which not all kernels support: System V release 3
8564 (and older) systems lack symlinks) in which the link file actually
8565 refers to a different file, by name. When most operations (opening,
8566 reading, writing, and so on) are passed the symbolic link file, the
8567 kernel automatically @dfn{dereferences} the link and operates on the
8568 target of the link. But some operations (e.g., removing) work on the
8569 link file itself, rather than on its target. @xref{Symbolic Links,,,
8570 libc, The GNU C Library Reference Manual}.
8572 The program accepts the following options. Also see @ref{Common options}.
8583 @opindex --directory
8584 @cindex hard links to directories
8585 Allow users with appropriate privileges to attempt to make hard links
8587 However, note that this will probably fail due to
8588 system restrictions, even for the super-user.
8594 Remove existing destination files.
8597 @itemx --interactive
8599 @opindex --interactive
8600 @cindex prompting, and @command{ln}
8601 Prompt whether to remove existing destination files.
8604 @itemx --no-dereference
8606 @opindex --no-dereference
8607 Do not treat the last operand specially when it is a symbolic link to
8608 a directory. Instead, treat it as if it were a normal file.
8610 When the destination is an actual directory (not a symlink to one),
8611 there is no ambiguity. The link is created in that directory.
8612 But when the specified destination is a symlink to a directory,
8613 there are two ways to treat the user's request. @command{ln} can
8614 treat the destination just as it would a normal directory and create
8615 the link in it. On the other hand, the destination can be viewed as a
8616 non-directory---as the symlink itself. In that case, @command{ln}
8617 must delete or backup that symlink before creating the new link.
8618 The default is to treat a destination that is a symlink to a directory
8619 just like a directory.
8621 This option is weaker than the @option{--no-target-directory}
8622 (@option{-T}) option, so it has no effect if both options are given.
8628 Make symbolic links instead of hard links. This option merely produces
8629 an error message on systems that do not support symbolic links.
8635 @optNoTargetDirectory
8641 Print the name of each file after linking it successfully.
8652 # Create link ../a pointing to a in that directory.
8653 # Not really useful because it points to itself.
8658 # Change to the target before creating symlinks to avoid being confused.
8664 # Hard coded file names don't move well.
8665 ln -s $(pwd)/a /some/dir/
8669 # Relative file names survive directory moves and also
8670 # work across networked file systems.
8671 ln -s afile anotherfile
8672 ln -s ../adir/afile yetanotherfile
8676 @node mkdir invocation
8677 @section @command{mkdir}: Make directories
8680 @cindex directories, creating
8681 @cindex creating directories
8683 @command{mkdir} creates directories with the specified names. Synopsis:
8686 mkdir [@var{option}]@dots{} @var{name}@dots{}
8689 @command{mkdir} creates each directory @var{name} in the order given.
8690 It reports an error if @var{name} already exists, unless the
8691 @option{-p} option is given and @var{name} is a directory.
8693 The program accepts the following options. Also see @ref{Common options}.
8698 @itemx --mode=@var{mode}
8701 @cindex modes of created directories, setting
8702 Set the file permission bits of created directories to @var{mode},
8703 which uses the same syntax as
8704 in @command{chmod} and uses @samp{a=rwx} (read, write and execute allowed for
8705 everyone) for the point of the departure. @xref{File permissions}.
8707 Normally the directory has the desired file mode bits at the moment it
8708 is created. As a @acronym{GNU} extension, @var{mode} may also mention
8709 special mode bits, but in this case there may be a temporary window
8710 during which the directory exists but its special mode bits are
8711 incorrect. @xref{Directory Setuid and Setgid}, for how the
8712 set-user-ID and set-group-ID bits of directories are inherited unless
8713 overridden in this way.
8719 @cindex parent directories, creating
8720 Make any missing parent directories for each argument, setting their
8721 file permission bits to the umask modified by @samp{u+wx}. Ignore
8722 existing parent directories, and do not change their file permission
8725 To set the file permission bits of any newly-created parent
8726 directories to a value that includes @samp{u+wx}, you can set the
8727 umask before invoking @command{mkdir}. For example, if the shell
8728 command @samp{(umask u=rwx,go=rx; mkdir -p P/Q)} creates the parent
8729 @file{P} it sets the parent's permission bits to @samp{u=rwx,go=rx}.
8730 To set a parent's special mode bits as well, you can invoke
8731 @command{chmod} after @command{mkdir}. @xref{Directory Setuid and
8732 Setgid}, for how the set-user-ID and set-group-ID bits of
8733 newly-created parent directories are inherited.
8739 Print a message for each created directory. This is most useful with
8746 @node mkfifo invocation
8747 @section @command{mkfifo}: Make FIFOs (named pipes)
8750 @cindex FIFOs, creating
8751 @cindex named pipes, creating
8752 @cindex creating FIFOs (named pipes)
8754 @command{mkfifo} creates FIFOs (also called @dfn{named pipes}) with the
8755 specified names. Synopsis:
8758 mkfifo [@var{option}] @var{name}@dots{}
8761 A @dfn{FIFO} is a special file type that permits independent processes
8762 to communicate. One process opens the FIFO file for writing, and
8763 another for reading, after which data can flow as with the usual
8764 anonymous pipe in shells or elsewhere.
8766 The program accepts the following option. Also see @ref{Common options}.
8771 @itemx --mode=@var{mode}
8774 @cindex modes of created FIFOs, setting
8775 Set the mode of created FIFOs to @var{mode}, which is symbolic as in
8776 @command{chmod} and uses @samp{a=rw} (read and write allowed for everyone)
8777 for the point of departure. @var{mode} should specify only file
8778 permission bits. @xref{File permissions}.
8785 @node mknod invocation
8786 @section @command{mknod}: Make block or character special files
8789 @cindex block special files, creating
8790 @cindex character special files, creating
8792 @command{mknod} creates a FIFO, character special file, or block special
8793 file with the specified name. Synopsis:
8796 mknod [@var{option}]@dots{} @var{name} @var{type} [@var{major} @var{minor}]
8799 @cindex special files
8800 @cindex block special files
8801 @cindex character special files
8802 Unlike the phrase ``special file type'' above, the term @dfn{special
8803 file} has a technical meaning on Unix: something that can generate or
8804 receive data. Usually this corresponds to a physical piece of hardware,
8805 e.g., a printer or a disk. (These files are typically created at
8806 system-configuration time.) The @command{mknod} command is what creates
8807 files of this type. Such devices can be read either a character at a
8808 time or a ``block'' (many characters) at a time, hence we say there are
8809 @dfn{block special} files and @dfn{character special} files.
8811 The arguments after @var{name} specify the type of file to make:
8816 @opindex p @r{for FIFO file}
8820 @opindex b @r{for block special file}
8821 for a block special file
8824 @c Don't document the `u' option -- it's just a synonym for `c'.
8825 @c Do *any* versions of mknod still use it?
8827 @opindex c @r{for character special file}
8828 @c @opindex u @r{for character special file}
8829 for a character special file
8833 When making a block or character special file, the major and minor
8834 device numbers must be given after the file type.
8835 If a major or minor device number begins with @samp{0x} or @samp{0X},
8836 it is interpreted as hexadecimal; otherwise, if it begins with @samp{0},
8837 as octal; otherwise, as decimal.
8839 The program accepts the following option. Also see @ref{Common options}.
8844 @itemx --mode=@var{mode}
8847 Set the mode of created files to @var{mode}, which is symbolic as in
8848 @command{chmod} and uses @samp{a=rw} as the point of departure.
8849 @var{mode} should specify only file permission bits.
8850 @xref{File permissions}.
8857 @node readlink invocation
8858 @section @command{readlink}: Print the referent of a symbolic link
8861 @cindex displaying value of a symbolic link
8863 @command{readlink} may work in one of two supported modes:
8869 @command{readlink} outputs the value of the given symbolic link.
8870 If @command{readlink} is invoked with an argument other than the name
8871 of a symbolic link, it produces no output and exits with a nonzero exit code.
8873 @item Canonicalize mode
8875 @command{readlink} outputs the absolute name of the given file which contains
8876 no @file{.}, @file{..} components nor any repeated separators
8877 (@file{/}) or symbolic links.
8882 readlink [@var{option}] @var{file}
8885 By default, @command{readlink} operates in readlink mode.
8887 The program accepts the following options. Also see @ref{Common options}.
8892 @itemx --canonicalize
8894 @opindex --canonicalize
8895 Activate canonicalize mode.
8896 If any component of the file name except the last one is missing or unavailable,
8897 @command{readlink} produces no output and exits with a nonzero exit code.
8900 @itemx --canonicalize-existing
8902 @opindex --canonicalize-existing
8903 Activate canonicalize mode.
8904 If any component is missing or unavailable, @command{readlink} produces
8905 no output and exits with a nonzero exit code.
8908 @itemx --canonicalize-missing
8910 @opindex --canonicalize-missing
8911 Activate canonicalize mode.
8912 If any component is missing or unavailable, @command{readlink} treats it
8918 @opindex --no-newline
8919 Do not output the trailing newline.
8929 Suppress most error messages.
8935 Report error messages.
8939 The @command{readlink} utility first appeared in OpenBSD 2.1.
8944 @node rmdir invocation
8945 @section @command{rmdir}: Remove empty directories
8948 @cindex removing empty directories
8949 @cindex directories, removing empty
8951 @command{rmdir} removes empty directories. Synopsis:
8954 rmdir [@var{option}]@dots{} @var{directory}@dots{}
8957 If any @var{directory} argument does not refer to an existing empty
8958 directory, it is an error.
8960 The program accepts the following options. Also see @ref{Common options}.
8964 @item --ignore-fail-on-non-empty
8965 @opindex --ignore-fail-on-non-empty
8966 @cindex directory deletion, ignoring failures
8967 Ignore each failure to remove a directory that is solely because
8968 the directory is non-empty.
8974 @cindex parent directories, removing
8975 Remove @var{directory}, then try to remove each component of @var{directory}.
8976 So, for example, @samp{rmdir -p a/b/c} is similar to @samp{rmdir a/b/c a/b a}.
8977 As such, it fails if any of those directories turns out not to be empty.
8978 Use the @option{--ignore-fail-on-non-empty} option to make it so such
8979 a failure does not evoke a diagnostic and does not cause @command{rmdir} to
8980 exit unsuccessfully.
8986 @cindex directory deletion, reporting
8987 Give a diagnostic for each successful removal.
8988 @var{directory} is removed.
8992 @xref{rm invocation}, for how to remove non-empty directories (recursively).
8997 @node unlink invocation
8998 @section @command{unlink}: Remove files via the unlink syscall
9001 @cindex removing files or directories (via the unlink syscall)
9003 @command{unlink} deletes a single specified file name.
9004 It is a minimalist interface to the system-provided
9005 @code{unlink} function. @xref{Deleting Files, , , libc,
9006 The GNU C Library Reference Manual}. Synopsis:
9007 It avoids the bells and whistles of the more commonly-used
9008 @command{rm} command (@pxref{rm invocation}).
9011 unlink @var{filename}
9014 On some systems @code{unlink} can be used to delete the name of a
9015 directory. On others, it can be used that way only by a privileged user.
9016 In the GNU system @code{unlink} can never delete the name of a directory.
9018 The @command{unlink} command honors the @option{--help} and
9019 @option{--version} options. To remove a file whose name begins with
9020 @samp{-}, prefix the name with @samp{./}, e.g., @samp{unlink ./--help}.
9025 @node Changing file attributes
9026 @chapter Changing file attributes
9028 @cindex changing file attributes
9029 @cindex file attributes, changing
9030 @cindex attributes, file
9032 A file is not merely its contents, a name, and a file type
9033 (@pxref{Special file types}). A file also has an owner (a user ID), a
9034 group (a group ID), permissions (what the owner can do with the file,
9035 what people in the group can do, and what everyone else can do), various
9036 timestamps, and other information. Collectively, we call these a file's
9039 These commands change file attributes.
9042 * chgrp invocation:: Change file groups.
9043 * chmod invocation:: Change access permissions.
9044 * chown invocation:: Change file owners and groups.
9045 * touch invocation:: Change file timestamps.
9049 @node chown invocation
9050 @section @command{chown}: Change file owner and group
9053 @cindex file ownership, changing
9054 @cindex group ownership, changing
9055 @cindex changing file ownership
9056 @cindex changing group ownership
9058 @command{chown} changes the user and/or group ownership of each given @var{file}
9059 to @var{new-owner} or to the user and group of an existing reference file.
9063 chown [@var{option}]@dots{} @{@var{new-owner} | --reference=@var{ref_file}@} @var{file}@dots{}
9066 If used, @var{new-owner} specifies the new owner and/or group as follows
9067 (with no embedded white space):
9070 [@var{owner}] [ : [@var{group}] ]
9077 If only an @var{owner} (a user name or numeric user ID) is given, that
9078 user is made the owner of each given file, and the files' group is not
9081 @item owner@samp{:}group
9082 If the @var{owner} is followed by a colon and a @var{group} (a
9083 group name or numeric group ID), with no spaces between them, the group
9084 ownership of the files is changed as well (to @var{group}).
9087 If a colon but no group name follows @var{owner}, that user is
9088 made the owner of the files and the group of the files is changed to
9089 @var{owner}'s login group.
9092 If the colon and following @var{group} are given, but the owner
9093 is omitted, only the group of the files is changed; in this case,
9094 @command{chown} performs the same function as @command{chgrp}.
9097 If only a colon is given, or if @var{new-owner} is empty, neither the
9098 owner nor the group is changed.
9102 If @var{owner} or @var{group} is intended to represent a numeric user
9103 or group ID, then you may specify it with a leading @samp{+}.
9104 @xref{Disambiguating names and IDs}.
9106 Some older scripts may still use @samp{.} in place of the @samp{:} separator.
9107 @acronym{POSIX} 1003.1-2001 (@pxref{Standards conformance}) does not
9108 require support for that, but for backward compatibility @acronym{GNU}
9109 @command{chown} supports @samp{.} so long as no ambiguity results.
9110 New scripts should avoid the use of @samp{.} because it is not
9111 portable, and because it has undesirable results if the entire
9112 @var{owner@samp{.}group} happens to identify a user whose name
9115 The @command{chown} command sometimes clears the set-user-ID or
9116 set-group-ID permission bits. This behavior depends on the policy and
9117 functionality of the underlying @code{chown} system call, which may
9118 make system-dependent file mode modifications outside the control of
9119 the @command{chown} command. For example, the @command{chown} command
9120 might not affect those bits when invoked by a user with appropriate
9121 privileges, or when the
9122 bits signify some function other than executable permission (e.g.,
9124 When in doubt, check the underlying system behavior.
9126 The program accepts the following options. Also see @ref{Common options}.
9134 @cindex changed owners, verbosely describing
9135 Verbosely describe the action for each @var{file} whose ownership
9144 @cindex error messages, omitting
9145 Do not print error messages about files whose ownership cannot be
9148 @itemx @w{@kbd{--from}=@var{old-owner}}
9150 @cindex symbolic links, changing owner
9151 Change a @var{file}'s ownership only if it has current attributes specified
9152 by @var{old-owner}. @var{old-owner} has the same form as @var{new-owner}
9154 This option is useful primarily from a security standpoint in that
9155 it narrows considerably the window of potential abuse.
9156 For example, to reflect a user ID numbering change for one user's files
9157 without an option like this, @code{root} might run
9160 find / -owner OLDUSER -print0 | xargs -0 chown -h NEWUSER
9163 But that is dangerous because the interval between when the @command{find}
9164 tests the existing file's owner and when the @command{chown} is actually run
9166 One way to narrow the gap would be to invoke chown for each file
9170 find / -owner OLDUSER -exec chown -h NEWUSER @{@} \;
9173 But that is very slow if there are many affected files.
9174 With this option, it is safer (the gap is narrower still)
9175 though still not perfect:
9178 chown -h -R --from=OLDUSER NEWUSER /
9182 @opindex --dereference
9183 @cindex symbolic links, changing owner
9185 Do not act on symbolic links themselves but rather on what they point to.
9186 This is the default.
9189 @itemx --no-dereference
9191 @opindex --no-dereference
9192 @cindex symbolic links, changing owner
9194 Act on symbolic links themselves instead of what they point to.
9195 This mode relies on the @code{lchown} system call.
9196 On systems that do not provide the @code{lchown} system call,
9197 @command{chown} fails when a file specified on the command line
9199 By default, no diagnostic is issued for symbolic links encountered
9200 during a recursive traversal, but see @option{--verbose}.
9202 @itemx --preserve-root
9203 @opindex --preserve-root
9204 @cindex root directory, disallow recursive modification
9205 Fail upon any attempt to recursively change the root directory, @file{/}.
9206 Without @option{--recursive}, this option has no effect.
9207 @xref{Treating / specially}.
9209 @itemx --no-preserve-root
9210 @opindex --no-preserve-root
9211 @cindex root directory, allow recursive modification
9212 Cancel the effect of any preceding @option{--preserve-root} option.
9213 @xref{Treating / specially}.
9215 @item --reference=@var{ref_file}
9216 @opindex --reference
9217 Change the user and group of each @var{file} to be the same as those of
9218 @var{ref_file}. If @var{ref_file} is a symbolic link, do not use the
9219 user and group of the symbolic link, but rather those of the file it
9226 Output a diagnostic for every file processed.
9227 If a symbolic link is encountered during a recursive traversal
9228 on a system without the @code{lchown} system call, and @option{--no-dereference}
9229 is in effect, then issue a diagnostic saying neither the symbolic link nor
9230 its referent is being changed.
9235 @opindex --recursive
9236 @cindex recursively changing file ownership
9237 Recursively change ownership of directories and their contents.
9240 @xref{Traversing symlinks}.
9243 @xref{Traversing symlinks}.
9246 @xref{Traversing symlinks}.
9255 # Change the owner of /u to "root".
9258 # Likewise, but also change its group to "staff".
9261 # Change the owner of /u and subfiles to "root".
9266 @node chgrp invocation
9267 @section @command{chgrp}: Change group ownership
9270 @cindex group ownership, changing
9271 @cindex changing group ownership
9273 @command{chgrp} changes the group ownership of each given @var{file}
9274 to @var{group} (which can be either a group name or a numeric group ID)
9275 or to the group of an existing reference file. Synopsis:
9278 chgrp [@var{option}]@dots{} @{@var{group} | --reference=@var{ref_file}@} @var{file}@dots{}
9281 If @var{group} is intended to represent a
9282 numeric group ID, then you may specify it with a leading @samp{+}.
9283 @xref{Disambiguating names and IDs}.
9285 The program accepts the following options. Also see @ref{Common options}.
9293 @cindex changed files, verbosely describing
9294 Verbosely describe the action for each @var{file} whose group actually
9303 @cindex error messages, omitting
9304 Do not print error messages about files whose group cannot be
9308 @opindex --dereference
9309 @cindex symbolic links, changing owner
9311 Do not act on symbolic links themselves but rather on what they point to.
9312 This is the default.
9315 @itemx --no-dereference
9317 @opindex --no-dereference
9318 @cindex symbolic links, changing group
9320 Act on symbolic links themselves instead of what they point to.
9321 This mode relies on the @code{lchown} system call.
9322 On systems that do not provide the @code{lchown} system call,
9323 @command{chgrp} fails when a file specified on the command line
9325 By default, no diagnostic is issued for symbolic links encountered
9326 during a recursive traversal, but see @option{--verbose}.
9328 @itemx --preserve-root
9329 @opindex --preserve-root
9330 @cindex root directory, disallow recursive modification
9331 Fail upon any attempt to recursively change the root directory, @file{/}.
9332 Without @option{--recursive}, this option has no effect.
9333 @xref{Treating / specially}.
9335 @itemx --no-preserve-root
9336 @opindex --no-preserve-root
9337 @cindex root directory, allow recursive modification
9338 Cancel the effect of any preceding @option{--preserve-root} option.
9339 @xref{Treating / specially}.
9341 @item --reference=@var{ref_file}
9342 @opindex --reference
9343 Change the group of each @var{file} to be the same as that of
9344 @var{ref_file}. If @var{ref_file} is a symbolic link, do not use the
9345 group of the symbolic link, but rather that of the file it refers to.
9351 Output a diagnostic for every file processed.
9352 If a symbolic link is encountered during a recursive traversal
9353 on a system without the @code{lchown} system call, and @option{--no-dereference}
9354 is in effect, then issue a diagnostic saying neither the symbolic link nor
9355 its referent is being changed.
9360 @opindex --recursive
9361 @cindex recursively changing group ownership
9362 Recursively change the group ownership of directories and their contents.
9365 @xref{Traversing symlinks}.
9368 @xref{Traversing symlinks}.
9371 @xref{Traversing symlinks}.
9380 # Change the group of /u to "staff".
9383 # Change the group of /u and subfiles to "staff".
9388 @node chmod invocation
9389 @section @command{chmod}: Change access permissions
9392 @cindex changing access permissions
9393 @cindex access permissions, changing
9394 @cindex permissions, changing access
9396 @command{chmod} changes the access permissions of the named files. Synopsis:
9399 chmod [@var{option}]@dots{} @{@var{mode} | --reference=@var{ref_file}@} @var{file}@dots{}
9402 @cindex symbolic links, permissions of
9403 @command{chmod} never changes the permissions of symbolic links, since
9404 the @command{chmod} system call cannot change their permissions.
9405 This is not a problem since the permissions of symbolic links are
9406 never used. However, for each symbolic link listed on the command
9407 line, @command{chmod} changes the permissions of the pointed-to file.
9408 In contrast, @command{chmod} ignores symbolic links encountered during
9409 recursive directory traversals.
9411 A successful use of @command{chmod} clears the set-group-ID bit of a
9412 regular file if the file's group ID does not match the user's
9413 effective group ID or one of the user's supplementary group IDs,
9414 unless the user has appropriate privileges. Additional restrictions
9415 may cause the set-user-ID and set-group-ID bits of @var{mode} or
9416 @var{ref_file} to be ignored. This behavior depends on the policy and
9417 functionality of the underlying @code{chmod} system call. When in
9418 doubt, check the underlying system behavior.
9420 If used, @var{mode} specifies the new file mode bits.
9421 For details, see the section on @ref{File permissions}.
9422 If you really want @var{mode} to have a leading @samp{-}, you should
9423 use @option{--} first, e.g., @samp{chmod -- -w file}. Typically,
9424 though, @samp{chmod a-w file} is preferable, and @command{chmod -w
9425 file} (without the @option{--}) complains if it behaves differently
9426 from what @samp{chmod a-w file} would do.
9428 The program accepts the following options. Also see @ref{Common options}.
9436 Verbosely describe the action for each @var{file} whose permissions
9445 @cindex error messages, omitting
9446 Do not print error messages about files whose permissions cannot be
9449 @itemx --preserve-root
9450 @opindex --preserve-root
9451 @cindex root directory, disallow recursive modification
9452 Fail upon any attempt to recursively change the root directory, @file{/}.
9453 Without @option{--recursive}, this option has no effect.
9454 @xref{Treating / specially}.
9456 @itemx --no-preserve-root
9457 @opindex --no-preserve-root
9458 @cindex root directory, allow recursive modification
9459 Cancel the effect of any preceding @option{--preserve-root} option.
9460 @xref{Treating / specially}.
9466 Verbosely describe the action or non-action taken for every @var{file}.
9468 @item --reference=@var{ref_file}
9469 @opindex --reference
9470 Change the mode of each @var{file} to be the same as that of @var{ref_file}.
9471 @xref{File permissions}.
9472 If @var{ref_file} is a symbolic link, do not use the mode
9473 of the symbolic link, but rather that of the file it refers to.
9478 @opindex --recursive
9479 @cindex recursively changing access permissions
9480 Recursively change permissions of directories and their contents.
9487 @node touch invocation
9488 @section @command{touch}: Change file timestamps
9491 @cindex changing file timestamps
9492 @cindex file timestamps, changing
9493 @cindex timestamps, changing file
9495 @command{touch} changes the access and/or modification times of the
9496 specified files. Synopsis:
9499 touch [@var{option}]@dots{} @var{file}@dots{}
9502 @cindex empty files, creating
9503 Any @var{file} argument that does not exist is created empty.
9505 A @var{file} argument string of @samp{-} is handled specially and
9506 causes @command{touch} to change the times of the file associated with
9509 @cindex permissions, for changing file timestamps
9510 If changing both the access and modification times to the current
9511 time, @command{touch} can change the timestamps for files that the user
9512 running it does not own but has write permission for. Otherwise, the
9513 user must own the files.
9515 Although @command{touch} provides options for changing two of the times---the
9516 times of last access and modification---of a file, there is actually
9517 a third one as well: the inode change time. This is often referred to
9518 as a file's @code{ctime}.
9519 The inode change time represents the time when the file's meta-information
9520 last changed. One common example of this is when the permissions of a
9521 file change. Changing the permissions doesn't access the file, so
9522 the atime doesn't change, nor does it modify the file, so the mtime
9523 doesn't change. Yet, something about the file itself has changed,
9524 and this must be noted somewhere. This is the job of the ctime field.
9525 This is necessary, so that, for example, a backup program can make a
9526 fresh copy of the file, including the new permissions value.
9527 Another operation that modifies a file's ctime without affecting
9528 the others is renaming. In any case, it is not possible, in normal
9529 operations, for a user to change the ctime field to a user-specified value.
9532 Time stamps assume the time zone rules specified by the @env{TZ}
9533 environment variable, or by the system default rules if @env{TZ} is
9534 not set. @xref{TZ Variable,, Specifying the Time Zone with @env{TZ},
9535 libc, The GNU C Library Reference Manual}.
9536 You can avoid ambiguities during
9537 daylight saving transitions by using @sc{utc} time stamps.
9539 The program accepts the following options. Also see @ref{Common options}.
9545 @itemx --time=access
9549 @opindex atime@r{, changing}
9550 @opindex access @r{time, changing}
9551 @opindex use @r{time, changing}
9552 Change the access time only.
9557 @opindex --no-create
9558 Do not create files that do not exist.
9561 @itemx --date=@var{time}
9565 Use @var{time} instead of the current time. It can contain month names,
9566 time zones, @samp{am} and @samp{pm}, @samp{yesterday}, etc. For
9567 example, @option{--date="2004-02-27 14:19:13.489392193 +0530"}
9568 specifies the instant of time that is 489,392,193 nanoseconds after
9569 February 27, 2004 at 2:19:13 PM in a time zone that is 5 hours and 30
9570 minutes east of @acronym{UTC}. @xref{Date input formats}.
9571 File systems that do not support high-resolution time stamps
9572 silently ignore any excess precision here.
9576 @cindex BSD @command{touch} compatibility
9577 Ignored; for compatibility with BSD versions of @command{touch}.
9581 @itemx --time=modify
9584 @opindex mtime@r{, changing}
9585 @opindex modify @r{time, changing}
9586 Change the modification time only.
9589 @itemx --reference=@var{file}
9591 @opindex --reference
9592 Use the times of the reference @var{file} instead of the current time.
9593 If this option is combined with the @option{--date=@var{time}}
9594 (@option{-d @var{time}}) option, the reference @var{file}'s time is
9595 the origin for any relative @var{time}s given, but is otherwise ignored.
9596 For example, @samp{-r foo -d '-5 seconds'} specifies a time stamp
9597 equal to five seconds before the corresponding time stamp for @file{foo}.
9599 @item -t [[@var{CC}]@var{YY}]@var{MMDDhhmm}[.@var{ss}]
9600 Use the argument (optional four-digit or two-digit years, months,
9601 days, hours, minutes, optional seconds) instead of the current time.
9602 If the year is specified with only two digits, then @var{CC}
9603 is 20 for years in the range 0 @dots{} 68, and 19 for years in
9604 69 @dots{} 99. If no digits of the year are specified,
9605 the argument is interpreted as a date in the current year.
9609 @vindex _POSIX2_VERSION
9610 On older systems, @command{touch} supports an obsolete syntax, as follows.
9611 If no timestamp is given with any of the @option{-d}, @option{-r}, or
9612 @option{-t} options, and if there are two or more @var{file}s and the
9613 first @var{file} is of the form @samp{@var{MMDDhhmm}[@var{YY}]} and this
9614 would be a valid argument to the @option{-t} option (if the @var{YY}, if
9615 any, were moved to the front), and if the represented year
9616 is in the range 1969--1999, that argument is interpreted as the time
9617 for the other files instead of as a file name.
9618 This obsolete behavior can be enabled or disabled with the
9619 @env{_POSIX2_VERSION} environment variable (@pxref{Standards
9620 conformance}), but portable scripts should avoid commands whose
9621 behavior depends on this variable.
9622 For example, use @samp{touch ./12312359 main.c} or @samp{touch -t
9623 12312359 main.c} rather than the ambiguous @samp{touch 12312359 main.c}.
9633 No disk can hold an infinite amount of data. These commands report
9634 how much disk storage is in use or available, report other file and
9635 file status information, and write buffers to disk.
9638 * df invocation:: Report file system disk space usage.
9639 * du invocation:: Estimate file space usage.
9640 * stat invocation:: Report file or file system status.
9641 * sync invocation:: Synchronize memory and disk.
9642 * truncate invocation:: Shrink or extend the size of a file.
9647 @section @command{df}: Report file system disk space usage
9650 @cindex file system disk usage
9651 @cindex disk usage by file system
9653 @command{df} reports the amount of disk space used and available on
9654 file systems. Synopsis:
9657 df [@var{option}]@dots{} [@var{file}]@dots{}
9660 With no arguments, @command{df} reports the space used and available on all
9661 currently mounted file systems (of all types). Otherwise, @command{df}
9662 reports on the file system containing each argument @var{file}.
9664 Normally the disk space is printed in units of
9665 1024 bytes, but this can be overridden (@pxref{Block size}).
9666 Non-integer quantities are rounded up to the next higher unit.
9668 @cindex disk device file
9669 @cindex device file, disk
9670 If an argument @var{file} is a disk device file containing a mounted
9671 file system, @command{df} shows the space available on that file system
9672 rather than on the file system containing the device node (i.e., the root
9673 file system). @sc{gnu} @command{df} does not attempt to determine the disk usage
9674 on unmounted file systems, because on most kinds of systems doing so
9675 requires extremely nonportable intimate knowledge of file system
9678 The program accepts the following options. Also see @ref{Common options}.
9686 @cindex automounter file systems
9687 @cindex ignore file systems
9688 Include in the listing dummy file systems, which
9689 are omitted by default. Such file systems are typically special-purpose
9690 pseudo-file-systems, such as automounter entries.
9693 @itemx --block-size=@var{size}
9695 @opindex --block-size
9696 @cindex file system sizes
9697 Scale sizes by @var{size} before printing them (@pxref{Block size}).
9698 For example, @option{-BG} prints sizes in units of 1,073,741,824 bytes.
9702 @cindex grand total of disk size, usage and available space
9703 Print a grand total of all arguments after all arguments have
9704 been processed. This can be used to find out the total disk size, usage
9705 and available space of all listed devices.
9711 Equivalent to @option{--si}.
9718 List inode usage information instead of block usage. An inode (short
9719 for index node) contains information about a file such as its owner,
9720 permissions, timestamps, and location on the disk.
9724 @cindex kibibytes for file system sizes
9725 Print sizes in 1024-byte blocks, overriding the default block size
9726 (@pxref{Block size}).
9727 This option is equivalent to @option{--block-size=1K}.
9733 @cindex file system types, limiting output to certain
9734 Limit the listing to local file systems. By default, remote file systems
9739 @cindex file system space, retrieving old data more quickly
9740 Do not invoke the @code{sync} system call before getting any usage data.
9741 This may make @command{df} run significantly faster on systems with many
9742 disks, but on some systems (notably SunOS) the results may be slightly
9743 out of date. This is the default.
9746 @itemx --portability
9748 @opindex --portability
9749 @cindex one-line output format
9750 @cindex @acronym{POSIX} output format
9751 @cindex portable output format
9752 @cindex output format, portable
9753 Use the @acronym{POSIX} output format. This is like the default format except
9758 The information about each file system is always printed on exactly
9759 one line; a mount device is never put on a line by itself. This means
9760 that if the mount device name is more than 20 characters long (e.g., for
9761 some network mounts), the columns are misaligned.
9764 The labels in the header output line are changed to conform to @acronym{POSIX}.
9767 The default block size and output format are unaffected by the
9768 @env{DF_BLOCK_SIZE}, @env{BLOCK_SIZE} and @env{BLOCKSIZE} environment
9769 variables. However, the default block size is still affected by
9770 @env{POSIXLY_CORRECT}: it is 512 if @env{POSIXLY_CORRECT} is set, 1024
9771 otherwise. @xref{Block size}.
9778 @cindex file system space, retrieving current data more slowly
9779 Invoke the @code{sync} system call before getting any usage data. On
9780 some systems (notably SunOS), doing this yields more up to date results,
9781 but in general this option makes @command{df} much slower, especially when
9782 there are many or very busy file systems.
9784 @item -t @var{fstype}
9785 @itemx --type=@var{fstype}
9788 @cindex file system types, limiting output to certain
9789 Limit the listing to file systems of type @var{fstype}. Multiple
9790 file system types can be specified by giving multiple @option{-t} options.
9791 By default, nothing is omitted.
9796 @opindex --print-type
9797 @cindex file system types, printing
9798 Print each file system's type. The types printed here are the same ones
9799 you can include or exclude with @option{-t} and @option{-x}. The particular
9800 types printed are whatever is supported by the system. Here are some of
9801 the common names (this list is certainly not exhaustive):
9806 @cindex @acronym{NFS} file system type
9807 An @acronym{NFS} file system, i.e., one mounted over a network from another
9808 machine. This is the one type name which seems to be used uniformly by
9811 @item 4.2@r{, }ufs@r{, }efs@dots{}
9812 @cindex Linux file system types
9813 @cindex local file system types
9814 @opindex 4.2 @r{file system type}
9815 @opindex ufs @r{file system type}
9816 @opindex efs @r{file system type}
9817 A file system on a locally-mounted hard disk. (The system might even
9818 support more than one type here; Linux does.)
9820 @item hsfs@r{, }cdfs
9821 @cindex CD-ROM file system type
9822 @cindex High Sierra file system
9823 @opindex hsfs @r{file system type}
9824 @opindex cdfs @r{file system type}
9825 A file system on a CD-ROM drive. HP-UX uses @samp{cdfs}, most other
9826 systems use @samp{hsfs} (@samp{hs} for ``High Sierra'').
9829 @cindex PC file system
9830 @cindex DOS file system
9831 @cindex MS-DOS file system
9832 @cindex diskette file system
9834 An MS-DOS file system, usually on a diskette.
9838 @item -x @var{fstype}
9839 @itemx --exclude-type=@var{fstype}
9841 @opindex --exclude-type
9842 Limit the listing to file systems not of type @var{fstype}.
9843 Multiple file system types can be eliminated by giving multiple
9844 @option{-x} options. By default, no file system types are omitted.
9847 Ignored; for compatibility with System V versions of @command{df}.
9852 Failure includes the case where no output is generated, so you can
9853 inspect the exit status of a command like @samp{df -t ext3 -t reiserfs
9854 @var{dir}} to test whether @var{dir} is on a file system of type
9855 @samp{ext3} or @samp{reiserfs}.
9859 @section @command{du}: Estimate file space usage
9862 @cindex file space usage
9863 @cindex disk usage for files
9865 @command{du} reports the amount of disk space used by the specified files
9866 and for each subdirectory (of directory arguments). Synopsis:
9869 du [@var{option}]@dots{} [@var{file}]@dots{}
9872 With no arguments, @command{du} reports the disk space for the current
9873 directory. Normally the disk space is printed in units of
9874 1024 bytes, but this can be overridden (@pxref{Block size}).
9875 Non-integer quantities are rounded up to the next higher unit.
9877 If two or more hard links point to the same file, only one of the hard
9878 links is counted. The @var{file} argument order affects which links
9879 are counted, and changing the argument order may change the numbers
9880 that @command{du} outputs.
9882 The program accepts the following options. Also see @ref{Common options}.
9890 Show counts for all files, not just directories.
9892 @itemx --apparent-size
9893 @opindex --apparent-size
9894 Print apparent sizes, rather than disk usage. The apparent size of a
9895 file is the number of bytes reported by @code{wc -c} on regular files,
9896 or more generally, @code{ls -l --block-size=1} or @code{stat --format=%s}.
9897 For example, a file containing the word @samp{zoo} with no newline would,
9898 of course, have an apparent size of 3. Such a small file may require
9899 anywhere from 0 to 16 KiB or more of disk space, depending on
9900 the type and configuration of the file system on which the file resides.
9901 However, a sparse file created with this command:
9904 dd bs=1 seek=2GiB if=/dev/null of=big
9908 has an apparent size of 2 GiB, yet on most modern
9909 systems, it actually uses almost no disk space.
9915 Equivalent to @code{--apparent-size --block-size=1}.
9918 @itemx --block-size=@var{size}
9920 @opindex --block-size
9922 Scale sizes by @var{size} before printing them (@pxref{Block size}).
9923 For example, @option{-BG} prints sizes in units of 1,073,741,824 bytes.
9929 @cindex grand total of disk space
9930 Print a grand total of all arguments after all arguments have
9931 been processed. This can be used to find out the total disk usage of
9932 a given set of files or directories.
9935 @itemx --dereference-args
9937 @opindex --dereference-args
9938 Dereference symbolic links that are command line arguments.
9939 Does not affect other symbolic links. This is helpful for finding
9940 out the disk usage of directories, such as @file{/usr/tmp}, which
9941 are often symbolic links.
9943 @c --files0-from=FILE
9944 @filesZeroFromOption{du,, with the @option{--total} (@option{-c}) option}
9950 Currently, @option{-H} is the same as @option{--si},
9951 except that @option{-H} evokes a warning.
9952 This option will be changed to be equivalent to
9953 @option{--dereference-args} (@option{-D}).
9957 @cindex kibibytes for file sizes
9958 Print sizes in 1024-byte blocks, overriding the default block size
9959 (@pxref{Block size}).
9960 This option is equivalent to @option{--block-size=1K}.
9963 @itemx --count-links
9965 @opindex --count-links
9966 @cindex hard links, counting in @command{du}
9967 Count the size of all files, even if they have appeared already (as a
9971 @itemx --dereference
9973 @opindex --dereference
9974 @cindex symbolic links, dereferencing in @command{du}
9975 Dereference symbolic links (show the disk space used by the file
9976 or directory that the link points to instead of the space used by
9981 @cindex mebibytes for file sizes
9982 Print sizes in 1,048,576-byte blocks, overriding the default block size
9983 (@pxref{Block size}).
9984 This option is equivalent to @option{--block-size=1M}.
9987 @itemx --no-dereference
9989 @opindex --no-dereference
9990 @cindex symbolic links, dereferencing in @command{du}
9991 For each symbolic links encountered by @command{du},
9992 consider the disk space used by the symbolic link.
9994 @item --max-depth=@var{DEPTH}
9995 @opindex --max-depth=@var{DEPTH}
9996 @cindex limiting output of @command{du}
9997 Show the total for each directory (and file if --all) that is at
9998 most MAX_DEPTH levels down from the root of the hierarchy. The root
9999 is at level 0, so @code{du --max-depth=0} is equivalent to @code{du -s}.
10005 @cindex output null-byte-terminated lines
10006 Output a null byte at the end of each line, rather than a newline.
10007 This option enables other programs to parse the output of @command{du}
10008 even when that output would contain file names with embedded newlines.
10015 @opindex --summarize
10016 Display only a total for each argument.
10019 @itemx --separate-dirs
10021 @opindex --separate-dirs
10022 Normally, in the output of @command{du} (when not using @option{--summarize}),
10023 the size listed next to a directory name, @var{d}, represents the sum
10024 of sizes of all entries beneath @var{d} as well as the size of @var{d} itself.
10025 With @option{--separate-dirs}, the size reported for a directory name,
10026 @var{d}, is merely the @code{stat.st_size}-derived size of the directory
10031 @cindex last modified dates, displaying in @command{du}
10032 Show time of the most recent modification of any file in the directory,
10033 or any of its subdirectories.
10035 @itemx --time=ctime
10036 @itemx --time=status
10039 @opindex ctime@r{, show the most recent}
10040 @opindex status time@r{, show the most recent}
10041 @opindex use time@r{, show the most recent}
10042 Show the most recent status change time (the @samp{ctime} in the inode) of
10043 any file in the directory, instead of the modification time.
10045 @itemx --time=atime
10046 @itemx --time=access
10048 @opindex atime@r{, show the most recent}
10049 @opindex access time@r{, show the most recent}
10050 Show the most recent access time (the @samp{atime} in the inode) of
10051 any file in the directory, instead of the modification time.
10053 @item --time-style=@var{style}
10054 @opindex --time-style
10056 List timestamps in style @var{style}. This option has an effect only if
10057 the @option{--time} option is also specified. The @var{style} should
10058 be one of the following:
10061 @item +@var{format}
10063 List timestamps using @var{format}, where @var{format} is interpreted
10064 like the format argument of @command{date} (@pxref{date invocation}).
10065 For example, @option{--time-style="+%Y-%m-%d %H:%M:%S"} causes
10066 @command{du} to list timestamps like @samp{2002-03-30 23:45:56}. As
10067 with @command{date}, @var{format}'s interpretation is affected by the
10068 @env{LC_TIME} locale category.
10071 List timestamps in full using @acronym{ISO} 8601 date, time, and time zone
10072 format with nanosecond precision, e.g., @samp{2002-03-30
10073 23:45:56.477817180 -0700}. This style is equivalent to
10074 @samp{+%Y-%m-%d %H:%M:%S.%N %z}.
10077 List @acronym{ISO} 8601 date and time in minutes, e.g.,
10078 @samp{2002-03-30 23:45}. These timestamps are shorter than
10079 @samp{full-iso} timestamps, and are usually good enough for everyday
10080 work. This style is equivalent to @samp{+%Y-%m-%d %H:%M}.
10083 List @acronym{ISO} 8601 dates for timestamps, e.g., @samp{2002-03-30}.
10084 This style is equivalent to @samp{+%Y-%m-%d}.
10088 You can specify the default value of the @option{--time-style} option
10089 with the environment variable @env{TIME_STYLE}; if @env{TIME_STYLE} is not set
10090 the default style is @samp{long-iso}. For compatibility with @command{ls},
10091 if @env{TIME_STYLE} begins with @samp{+} and contains a newline,
10092 the newline and any later characters are ignored; if @env{TIME_STYLE}
10093 begins with @samp{posix-} the @samp{posix-} is ignored; and if
10094 @env{TIME_STYLE} is @samp{locale} it is ignored.
10097 @itemx --one-file-system
10099 @opindex --one-file-system
10100 @cindex one file system, restricting @command{du} to
10101 Skip directories that are on different file systems from the one that
10102 the argument being processed is on.
10104 @item --exclude=@var{PATTERN}
10105 @opindex --exclude=@var{PATTERN}
10106 @cindex excluding files from @command{du}
10107 When recursing, skip subdirectories or files matching @var{PATTERN}.
10108 For example, @code{du --exclude='*.o'} excludes files whose names
10111 @item -X @var{FILE}
10112 @itemx --exclude-from=@var{FILE}
10113 @opindex -X @var{FILE}
10114 @opindex --exclude-from=@var{FILE}
10115 @cindex excluding files from @command{du}
10116 Like @option{--exclude}, except take the patterns to exclude from @var{FILE},
10117 one per line. If @var{FILE} is @samp{-}, take the patterns from standard
10122 @cindex NFS mounts from BSD to HP-UX
10123 On BSD systems, @command{du} reports sizes that are half the correct
10124 values for files that are NFS-mounted from HP-UX systems. On HP-UX
10125 systems, it reports sizes that are twice the correct values for
10126 files that are NFS-mounted from BSD systems. This is due to a flaw
10127 in HP-UX; it also affects the HP-UX @command{du} program.
10132 @node stat invocation
10133 @section @command{stat}: Report file or file system status
10136 @cindex file status
10137 @cindex file system status
10139 @command{stat} displays information about the specified file(s). Synopsis:
10142 stat [@var{option}]@dots{} [@var{file}]@dots{}
10145 With no option, @command{stat} reports all information about the given files.
10146 But it also can be used to report the information of the file systems the
10147 given files are located on. If the files are links, @command{stat} can
10148 also give information about the files the links point to.
10154 @itemx --dereference
10156 @opindex --dereference
10157 @cindex symbolic links, dereferencing in @command{stat}
10158 Change how @command{stat} treats symbolic links.
10159 With this option, @command{stat} acts on the file referenced
10160 by each symbolic link argument.
10161 Without it, @command{stat} acts on any symbolic link argument directly.
10164 @itemx --file-system
10166 @opindex --file-system
10167 @cindex file systems
10168 Report information about the file systems where the given files are located
10169 instead of information about the files themselves.
10172 @itemx --format=@var{format}
10174 @opindex --format=@var{format}
10175 @cindex output format
10176 Use @var{format} rather than the default format.
10177 @var{format} is automatically newline-terminated, so
10178 running a command like the following with two or more @var{file}
10179 operands produces a line of output for each operand:
10181 $ stat --format=%d:%i / /usr
10186 @itemx --printf=@var{format}
10187 @opindex --printf=@var{format}
10188 @cindex output format
10189 Use @var{format} rather than the default format.
10190 Like @option{--format}, but interpret backslash escapes,
10191 and do not output a mandatory trailing newline.
10192 If you want a newline, include @samp{\n} in the @var{format}.
10193 Here's how you would use @option{--printf} to print the device
10194 and inode numbers of @file{/} and @file{/usr}:
10196 $ stat --printf='%d:%i\n' / /usr
10205 @cindex terse output
10206 Print the information in terse form, suitable for parsing by other programs.
10208 The valid format sequences for files are:
10211 @item %a - Access rights in octal
10212 @item %A - Access rights in human readable form
10213 @item %b - Number of blocks allocated (see @samp{%B})
10214 @item %B - The size in bytes of each block reported by @samp{%b}
10215 @item %d - Device number in decimal
10216 @item %D - Device number in hex
10217 @item %f - Raw mode in hex
10218 @item %F - File type
10219 @item %g - Group ID of owner
10220 @item %G - Group name of owner
10221 @item %h - Number of hard links
10222 @item %i - Inode number
10223 @item %n - File name
10224 @item %N - Quoted file name with dereference if symbolic link
10225 @item %o - I/O block size
10226 @item %s - Total size, in bytes
10227 @item %t - Major device type in hex
10228 @item %T - Minor device type in hex
10229 @item %u - User ID of owner
10230 @item %U - User name of owner
10231 @item %x - Time of last access
10232 @item %X - Time of last access as seconds since Epoch
10233 @item %y - Time of last modification
10234 @item %Y - Time of last modification as seconds since Epoch
10235 @item %z - Time of last change
10236 @item %Z - Time of last change as seconds since Epoch
10239 The valid format sequences for file systems are:
10242 @item %a - Free blocks available to non-super-user
10243 @item %b - Total data blocks in file system
10244 @item %c - Total file nodes in file system
10245 @item %d - Free file nodes in file system
10246 @item %f - Free blocks in file system
10247 @item %i - File System ID in hex
10248 @item %l - Maximum length of file names
10249 @item %n - File name
10250 @item %s - Block size (for faster transfers)
10251 @item %S - Fundamental block size (for block counts)
10252 @item %t - Type in hex
10253 @item %T - Type in human readable form
10257 Time stamps are listed according to the time zone rules specified by
10258 the @env{TZ} environment variable, or by the system default rules if
10259 @env{TZ} is not set. @xref{TZ Variable,, Specifying the Time Zone
10260 with @env{TZ}, libc, The GNU C Library Reference Manual}.
10266 @node sync invocation
10267 @section @command{sync}: Synchronize data on disk with memory
10270 @cindex synchronize disk and memory
10272 @cindex superblock, writing
10273 @cindex inodes, written buffered
10274 @command{sync} writes any data buffered in memory out to disk. This can
10275 include (but is not limited to) modified superblocks, modified inodes,
10276 and delayed reads and writes. This must be implemented by the kernel;
10277 The @command{sync} program does nothing but exercise the @code{sync} system
10280 @cindex crashes and corruption
10281 The kernel keeps data in memory to avoid doing (relatively slow) disk
10282 reads and writes. This improves performance, but if the computer
10283 crashes, data may be lost or the file system corrupted as a
10284 result. The @command{sync} command ensures everything in memory
10285 is written to disk.
10287 Any arguments are ignored, except for a lone @option{--help} or
10288 @option{--version} (@pxref{Common options}).
10293 @node truncate invocation
10294 @section @command{truncate}: Shrink or extend the size of a file
10297 @cindex truncating, file sizes
10299 @command{truncate} shrinks or extends the size of each @var{file} to the
10300 specified size. Synopsis:
10303 truncate @var{option}@dots{} @var{file}@dots{}
10306 @cindex files, creating
10307 Any @var{file} that does not exist is created.
10309 @cindex sparse files, creating
10310 @cindex holes, creating files with
10311 If a @var{file} is larger than the specified size, the extra data is lost.
10312 If a @var{file} is shorter, it is extended and the extended part (or hole)
10313 reads as zero bytes.
10315 The program accepts the following options. Also see @ref{Common options}.
10322 @opindex --no-create
10323 Do not create files that do not exist.
10328 @opindex --io-blocks
10329 Treat @var{size} as number of I/O blocks of the @var{FILE} rather than bytes.
10331 @item -r @var{rfile}
10332 @itemx --reference=@var{rfile}
10334 @opindex --reference
10335 Set the size of each @var{file} to the same size as @var{rfile}.
10337 @item -s @var{size}
10338 @itemx --size=@var{size}
10341 Set the size of each @var{file} to this @var{size}.
10342 @var{size} is a number which may be followed by one of these
10343 multiplicative suffixes:
10345 @samp{KB} => 1000 (KiloBytes)
10346 @samp{K} => 1024 (KibiBytes)
10347 @samp{MB} => 1000*1000 (MegaBytes)
10348 @samp{M} => 1024*1024 (MebiBytes)
10350 and so on for @samp{G}, @samp{T}, @samp{P}, @samp{E}, @samp{Z}, and @samp{Y}.
10352 @var{size} may also be prefixed by one of the following to adjust
10353 the size of each @var{file} based on their current size:
10355 @samp{+} => extend by
10356 @samp{-} => reduce by
10357 @samp{<} => at most
10358 @samp{>} => at least
10359 @samp{/} => round down to multiple of
10360 @samp{%} => round up to multiple of
10368 @node Printing text
10369 @chapter Printing text
10371 @cindex printing text, commands for
10372 @cindex commands for printing text
10374 This section describes commands that display text strings.
10377 * echo invocation:: Print a line of text.
10378 * printf invocation:: Format and print data.
10379 * yes invocation:: Print a string until interrupted.
10383 @node echo invocation
10384 @section @command{echo}: Print a line of text
10387 @cindex displaying text
10388 @cindex printing text
10389 @cindex text, displaying
10390 @cindex arbitrary text, displaying
10392 @command{echo} writes each given @var{string} to standard output, with a
10393 space between each and a newline after the last one. Synopsis:
10396 echo [@var{option}]@dots{} [@var{string}]@dots{}
10399 The program accepts the following options. Also see @ref{Common options}.
10400 Options must precede operands, and the normally-special argument
10401 @samp{--} has no special meaning and is treated like any other
10407 Do not output the trailing newline.
10411 @cindex backslash escapes
10412 Enable interpretation of the following backslash-escaped characters in
10421 produce no further output
10435 the eight-bit value that is the octal number @var{nnn}
10436 (zero to three octal digits)
10438 the eight-bit value that is the octal number @var{nnn}
10439 (one to three octal digits)
10441 the eight-bit value that is the hexadecimal number @var{hh}
10442 (one or two hexadecimal digits)
10447 @cindex backslash escapes
10448 Disable interpretation of backslash escapes in each @var{string}.
10449 This is the default. If @option{-e} and @option{-E} are both
10450 specified, the last one given takes effect.
10454 @vindex POSIXLY_CORRECT
10455 If the @env{POSIXLY_CORRECT} environment variable is set, then when
10456 @command{echo}'s first argument is not @option{-n} it outputs
10457 option-like arguments instead of treating them as options. For
10458 example, @code{echo -ne hello} outputs @samp{-ne hello} instead of
10459 plain @samp{hello}.
10461 @acronym{POSIX} does not require support for any options, and says
10462 that the behavior of @command{echo} is implementation-defined if any
10463 @var{string} contains a backslash or if the first argument is
10464 @option{-n}. Portable programs can use the @command{printf} command
10465 if they need to omit trailing newlines or output control characters or
10466 backslashes. @xref{printf invocation}.
10471 @node printf invocation
10472 @section @command{printf}: Format and print data
10475 @command{printf} does formatted printing of text. Synopsis:
10478 printf @var{format} [@var{argument}]@dots{}
10481 @command{printf} prints the @var{format} string, interpreting @samp{%}
10482 directives and @samp{\} escapes to format numeric and string arguments
10483 in a way that is mostly similar to the C @samp{printf} function.
10484 @xref{Output Conversion Syntax,, @command{printf} format directives,
10485 libc, The GNU C Library Reference Manual}, for details.
10486 The differences are as follows:
10491 The @var{format} argument is reused as necessary to convert all the
10492 given @var{argument}s. For example, the command @samp{printf %s a b}
10496 Missing @var{argument}s are treated as null strings or as zeros,
10497 depending on whether the context expects a string or a number. For
10498 example, the command @samp{printf %sx%d} prints @samp{x0}.
10502 An additional escape, @samp{\c}, causes @command{printf} to produce no
10503 further output. For example, the command @samp{printf 'A%sC\cD%sF' B
10504 E} prints @samp{ABC}.
10507 The hexadecimal escape sequence @samp{\x@var{hh}} has at most two
10508 digits, as opposed to C where it can have an unlimited number of
10509 digits. For example, the command @samp{printf '\x07e'} prints two
10510 bytes, whereas the C statement @samp{printf ("\x07e")} prints just
10515 @command{printf} has an additional directive, @samp{%b}, which prints its
10516 argument string with @samp{\} escapes interpreted in the same way as in
10517 the @var{format} string, except that octal escapes are of the form
10518 @samp{\0@var{ooo}} where @var{ooo} is 0 to 3 octal digits.
10519 If a precision is also given, it limits the number of bytes printed
10520 from the converted string.
10523 Numeric arguments must be single C constants, possibly with leading
10524 @samp{+} or @samp{-}. For example, @samp{printf %.4d -3} outputs
10528 @vindex POSIXLY_CORRECT
10529 If the leading character of a numeric argument is @samp{"} or @samp{'}
10530 then its value is the numeric value of the immediately following
10531 character. Any remaining characters are silently ignored if the
10532 @env{POSIXLY_CORRECT} environment variable is set; otherwise, a
10533 warning is printed. For example, @samp{printf "%d" "'a"} outputs
10534 @samp{97} on hosts that use the @acronym{ASCII} character set, since
10535 @samp{a} has the numeric value 97 in @acronym{ASCII}.
10540 A floating-point argument must use a period before any fractional
10541 digits, but is printed according to the @env{LC_NUMERIC} category of the
10542 current locale. For example, in a locale whose radix character is a
10543 comma, the command @samp{printf %g 3.14} outputs @samp{3,14} whereas
10544 the command @samp{printf %g 3,14} is an error.
10548 @command{printf} interprets @samp{\@var{ooo}} in @var{format} as an octal number
10549 (if @var{ooo} is 1 to 3 octal digits) specifying a character to print,
10550 and @samp{\x@var{hh}} as a hexadecimal number (if @var{hh} is 1 to 2 hex
10551 digits) specifying a character to print.
10556 @cindex ISO/IEC 10646
10558 @command{printf} interprets two character syntaxes introduced in
10559 @acronym{ISO} C 99:
10560 @samp{\u} for 16-bit Unicode (@acronym{ISO}/@acronym{IEC} 10646)
10561 characters, specified as
10562 four hexadecimal digits @var{hhhh}, and @samp{\U} for 32-bit Unicode
10563 characters, specified as eight hexadecimal digits @var{hhhhhhhh}.
10564 @command{printf} outputs the Unicode characters
10565 according to the @env{LC_CTYPE} locale. Unicode characters in the ranges
10566 U+0000...U+009F, U+D800...U+DFFF cannot be specified by this syntax, except
10567 for U+0024 ($), U+0040 (@@), and U+0060 (@`).
10569 The processing of @samp{\u} and @samp{\U} requires a full-featured
10570 @code{iconv} facility. It is activated on systems with glibc 2.2 (or newer),
10571 or when @code{libiconv} is installed prior to this package. Otherwise
10572 @samp{\u} and @samp{\U} will print as-is.
10574 The only options are a lone @option{--help} or
10575 @option{--version}. @xref{Common options}.
10576 Options must precede operands.
10578 The Unicode character syntaxes are useful for writing strings in a locale
10579 independent way. For example, a string containing the Euro currency symbol
10582 $ /usr/local/bin/printf '\u20AC 14.95'
10586 will be output correctly in all locales supporting the Euro symbol
10587 (@acronym{ISO}-8859-15, UTF-8, and others). Similarly, a Chinese string
10590 $ /usr/local/bin/printf '\u4e2d\u6587'
10594 will be output correctly in all Chinese locales (GB2312, BIG5, UTF-8, etc).
10596 Note that in these examples, the full name of @command{printf} has been
10597 given, to distinguish it from the GNU @code{bash} built-in function
10600 For larger strings, you don't need to look up the hexadecimal code
10601 values of each character one by one. @acronym{ASCII} characters mixed with \u
10602 escape sequences is also known as the JAVA source file encoding. You can
10603 use GNU recode 3.5c (or newer) to convert strings to this encoding. Here
10604 is how to convert a piece of text into a shell script which will output
10605 this text in a locale-independent way:
10608 $ LC_CTYPE=zh_CN.big5 /usr/local/bin/printf \
10609 '\u4e2d\u6587\n' > sample.txt
10610 $ recode BIG5..JAVA < sample.txt \
10611 | sed -e "s|^|/usr/local/bin/printf '|" -e "s|$|\\\\n'|" \
10618 @node yes invocation
10619 @section @command{yes}: Print a string until interrupted
10622 @cindex repeated output of a string
10624 @command{yes} prints the command line arguments, separated by spaces and
10625 followed by a newline, forever until it is killed. If no arguments are
10626 given, it prints @samp{y} followed by a newline forever until killed.
10628 Upon a write error, @command{yes} exits with status @samp{1}.
10630 The only options are a lone @option{--help} or @option{--version}.
10631 To output an argument that begins with
10632 @samp{-}, precede it with @option{--}, e.g., @samp{yes -- --help}.
10633 @xref{Common options}.
10637 @chapter Conditions
10640 @cindex commands for exit status
10641 @cindex exit status commands
10643 This section describes commands that are primarily useful for their exit
10644 status, rather than their output. Thus, they are often used as the
10645 condition of shell @code{if} statements, or as the last command in a
10649 * false invocation:: Do nothing, unsuccessfully.
10650 * true invocation:: Do nothing, successfully.
10651 * test invocation:: Check file types and compare values.
10652 * expr invocation:: Evaluate expressions.
10656 @node false invocation
10657 @section @command{false}: Do nothing, unsuccessfully
10660 @cindex do nothing, unsuccessfully
10661 @cindex failure exit status
10662 @cindex exit status of @command{false}
10664 @command{false} does nothing except return an exit status of 1, meaning
10665 @dfn{failure}. It can be used as a place holder in shell scripts
10666 where an unsuccessful command is needed.
10667 In most modern shells, @command{false} is a built-in command, so when
10668 you use @samp{false} in a script, you're probably using the built-in
10669 command, not the one documented here.
10671 @command{false} honors the @option{--help} and @option{--version} options.
10673 This version of @command{false} is implemented as a C program, and is thus
10674 more secure and faster than a shell script implementation, and may safely
10675 be used as a dummy shell for the purpose of disabling accounts.
10677 Note that @command{false} (unlike all other programs documented herein)
10678 exits unsuccessfully, even when invoked with
10679 @option{--help} or @option{--version}.
10681 Portable programs should not assume that the exit status of
10682 @command{false} is 1, as it is greater than 1 on some
10683 non-@acronym{GNU} hosts.
10686 @node true invocation
10687 @section @command{true}: Do nothing, successfully
10690 @cindex do nothing, successfully
10692 @cindex successful exit
10693 @cindex exit status of @command{true}
10695 @command{true} does nothing except return an exit status of 0, meaning
10696 @dfn{success}. It can be used as a place holder in shell scripts
10697 where a successful command is needed, although the shell built-in
10698 command @code{:} (colon) may do the same thing faster.
10699 In most modern shells, @command{true} is a built-in command, so when
10700 you use @samp{true} in a script, you're probably using the built-in
10701 command, not the one documented here.
10703 @command{true} honors the @option{--help} and @option{--version} options.
10705 Note, however, that it is possible to cause @command{true}
10706 to exit with nonzero status: with the @option{--help} or @option{--version}
10707 option, and with standard
10708 output already closed or redirected to a file that evokes an I/O error.
10709 For example, using a Bourne-compatible shell:
10712 $ ./true --version >&-
10713 ./true: write error: Bad file number
10714 $ ./true --version > /dev/full
10715 ./true: write error: No space left on device
10718 This version of @command{true} is implemented as a C program, and is thus
10719 more secure and faster than a shell script implementation, and may safely
10720 be used as a dummy shell for the purpose of disabling accounts.
10722 @node test invocation
10723 @section @command{test}: Check file types and compare values
10726 @cindex check file types
10727 @cindex compare values
10728 @cindex expression evaluation
10730 @command{test} returns a status of 0 (true) or 1 (false) depending on the
10731 evaluation of the conditional expression @var{expr}. Each part of the
10732 expression must be a separate argument.
10734 @command{test} has file status checks, string operators, and numeric
10735 comparison operators.
10737 @command{test} has an alternate form that uses opening and closing
10738 square brackets instead a leading @samp{test}. For example, instead
10739 of @samp{test -d /}, you can write @samp{[ -d / ]}. The square
10740 brackets must be separate arguments; for example, @samp{[-d /]} does
10741 not have the desired effect. Since @samp{test @var{expr}} and @samp{[
10742 @var{expr} ]} have the same meaning, only the former form is discussed
10748 test @var{expression}
10750 [ @var{expression} ]
10755 @cindex conflicts with shell built-ins
10756 @cindex built-in shell commands, conflicts with
10757 Because most shells have a built-in @command{test} command, using an
10758 unadorned @command{test} in a script or interactively may get you
10759 different functionality than that described here.
10761 If @var{expression} is omitted, @command{test} returns false.
10762 If @var{expression} is a single argument,
10763 @command{test} returns false if the argument is null and true otherwise. The argument
10764 can be any string, including strings like @samp{-d}, @samp{-1},
10765 @samp{--}, @samp{--help}, and @samp{--version} that most other
10766 programs would treat as options. To get help and version information,
10767 invoke the commands @samp{[ --help} and @samp{[ --version}, without
10768 the usual closing brackets. @xref{Common options}.
10770 @cindex exit status of @command{test}
10774 0 if the expression is true,
10775 1 if the expression is false,
10776 2 if an error occurred.
10780 * File type tests:: -[bcdfhLpSt]
10781 * Access permission tests:: -[gkruwxOG]
10782 * File characteristic tests:: -e -s -nt -ot -ef
10783 * String tests:: -z -n = !=
10784 * Numeric tests:: -eq -ne -lt -le -gt -ge
10785 * Connectives for test:: ! -a -o
10789 @node File type tests
10790 @subsection File type tests
10792 @cindex file type tests
10794 These options test for particular types of files. (Everything's a file,
10795 but not all files are the same!)
10799 @item -b @var{file}
10801 @cindex block special check
10802 True if @var{file} exists and is a block special device.
10804 @item -c @var{file}
10806 @cindex character special check
10807 True if @var{file} exists and is a character special device.
10809 @item -d @var{file}
10811 @cindex directory check
10812 True if @var{file} exists and is a directory.
10814 @item -f @var{file}
10816 @cindex regular file check
10817 True if @var{file} exists and is a regular file.
10819 @item -h @var{file}
10820 @itemx -L @var{file}
10823 @cindex symbolic link check
10824 True if @var{file} exists and is a symbolic link.
10825 Unlike all other file-related tests, this test does not dereference
10826 @var{file} if it is a symbolic link.
10828 @item -p @var{file}
10830 @cindex named pipe check
10831 True if @var{file} exists and is a named pipe.
10833 @item -S @var{file}
10835 @cindex socket check
10836 True if @var{file} exists and is a socket.
10840 @cindex terminal check
10841 True if @var{fd} is a file descriptor that is associated with a
10847 @node Access permission tests
10848 @subsection Access permission tests
10850 @cindex access permission tests
10851 @cindex permission tests
10853 These options test for particular access permissions.
10857 @item -g @var{file}
10859 @cindex set-group-ID check
10860 True if @var{file} exists and has its set-group-ID bit set.
10862 @item -k @var{file}
10864 @cindex sticky bit check
10865 True if @var{file} exists and has its @dfn{sticky} bit set.
10867 @item -r @var{file}
10869 @cindex readable file check
10870 True if @var{file} exists and read permission is granted.
10872 @item -u @var{file}
10874 @cindex set-user-ID check
10875 True if @var{file} exists and has its set-user-ID bit set.
10877 @item -w @var{file}
10879 @cindex writable file check
10880 True if @var{file} exists and write permission is granted.
10882 @item -x @var{file}
10884 @cindex executable file check
10885 True if @var{file} exists and execute permission is granted
10886 (or search permission, if it is a directory).
10888 @item -O @var{file}
10890 @cindex owned by effective user ID check
10891 True if @var{file} exists and is owned by the current effective user ID.
10893 @item -G @var{file}
10895 @cindex owned by effective group ID check
10896 True if @var{file} exists and is owned by the current effective group ID.
10900 @node File characteristic tests
10901 @subsection File characteristic tests
10903 @cindex file characteristic tests
10905 These options test other file characteristics.
10909 @item -e @var{file}
10911 @cindex existence-of-file check
10912 True if @var{file} exists.
10914 @item -s @var{file}
10916 @cindex nonempty file check
10917 True if @var{file} exists and has a size greater than zero.
10919 @item @var{file1} -nt @var{file2}
10921 @cindex newer-than file check
10922 True if @var{file1} is newer (according to modification date) than
10923 @var{file2}, or if @var{file1} exists and @var{file2} does not.
10925 @item @var{file1} -ot @var{file2}
10927 @cindex older-than file check
10928 True if @var{file1} is older (according to modification date) than
10929 @var{file2}, or if @var{file2} exists and @var{file1} does not.
10931 @item @var{file1} -ef @var{file2}
10933 @cindex same file check
10934 @cindex hard link check
10935 True if @var{file1} and @var{file2} have the same device and inode
10936 numbers, i.e., if they are hard links to each other.
10942 @subsection String tests
10944 @cindex string tests
10946 These options test string characteristics. You may need to quote
10947 @var{string} arguments for the shell. For example:
10953 The quotes here prevent the wrong arguments from being passed to
10954 @command{test} if @samp{$V} is empty or contains special characters.
10958 @item -z @var{string}
10960 @cindex zero-length string check
10961 True if the length of @var{string} is zero.
10963 @item -n @var{string}
10964 @itemx @var{string}
10966 @cindex nonzero-length string check
10967 True if the length of @var{string} is nonzero.
10969 @item @var{string1} = @var{string2}
10971 @cindex equal string check
10972 True if the strings are equal.
10974 @item @var{string1} != @var{string2}
10976 @cindex not-equal string check
10977 True if the strings are not equal.
10982 @node Numeric tests
10983 @subsection Numeric tests
10985 @cindex numeric tests
10986 @cindex arithmetic tests
10988 Numeric relational operators. The arguments must be entirely numeric
10989 (possibly negative), or the special expression @w{@code{-l @var{string}}},
10990 which evaluates to the length of @var{string}.
10994 @item @var{arg1} -eq @var{arg2}
10995 @itemx @var{arg1} -ne @var{arg2}
10996 @itemx @var{arg1} -lt @var{arg2}
10997 @itemx @var{arg1} -le @var{arg2}
10998 @itemx @var{arg1} -gt @var{arg2}
10999 @itemx @var{arg1} -ge @var{arg2}
11006 These arithmetic binary operators return true if @var{arg1} is equal,
11007 not-equal, less-than, less-than-or-equal, greater-than, or
11008 greater-than-or-equal than @var{arg2}, respectively.
11015 test -1 -gt -2 && echo yes
11017 test -l abc -gt 1 && echo yes
11020 @error{} test: integer expression expected before -eq
11024 @node Connectives for test
11025 @subsection Connectives for @command{test}
11027 @cindex logical connectives
11028 @cindex connectives, logical
11030 The usual logical connectives.
11036 True if @var{expr} is false.
11038 @item @var{expr1} -a @var{expr2}
11040 @cindex logical and operator
11041 @cindex and operator
11042 True if both @var{expr1} and @var{expr2} are true.
11044 @item @var{expr1} -o @var{expr2}
11046 @cindex logical or operator
11047 @cindex or operator
11048 True if either @var{expr1} or @var{expr2} is true.
11053 @node expr invocation
11054 @section @command{expr}: Evaluate expressions
11057 @cindex expression evaluation
11058 @cindex evaluation of expressions
11060 @command{expr} evaluates an expression and writes the result on standard
11061 output. Each token of the expression must be a separate argument.
11063 Operands are either integers or strings. Integers consist of one or
11064 more decimal digits, with an optional leading @samp{-}.
11065 @command{expr} converts
11066 anything appearing in an operand position to an integer or a string
11067 depending on the operation being applied to it.
11069 Strings are not quoted for @command{expr} itself, though you may need to
11070 quote them to protect characters with special meaning to the shell,
11071 e.g., spaces. However, regardless of whether it is quoted, a string
11072 operand should not be a parenthesis or any of @command{expr}'s
11073 operators like @code{+}, so you cannot safely pass an arbitrary string
11074 @code{$str} to expr merely by quoting it to the shell. One way to
11075 work around this is to use the @sc{gnu} extension @code{+},
11076 (e.g., @code{+ "$str" = foo}); a more portable way is to use
11077 @code{@w{" $str"}} and to adjust the rest of the expression to take
11078 the leading space into account (e.g., @code{@w{" $str" = " foo"}}).
11080 You should not pass a negative integer or a string with leading
11081 @samp{-} as @command{expr}'s first argument, as it might be
11082 misinterpreted as an option; this can be avoided by parenthesization.
11083 Also, portable scripts should not use a string operand that happens to
11084 take the form of an integer; this can be worked around by inserting
11085 leading spaces as mentioned above.
11087 @cindex parentheses for grouping
11088 Operators may be given as infix symbols or prefix keywords. Parentheses
11089 may be used for grouping in the usual manner. You must quote
11090 parentheses and many operators to avoid the shell evaluating them,
11093 By default, @command{expr} performs operations using native arithmetic
11094 types, but if a numeric overflow occurs and @command{expr} was built
11095 with support for the GNU MP library, @command{expr}, it
11096 uses arbitrary-precision arithmetic.
11098 Apart from @option{--help} and @option{--version} (@pxref{Common
11099 options}), the following options are supported:
11103 Perform arithmetic operations using unlimited precision via the GNU MP library.
11105 Use only limited-precision native operations.
11106 In the event of numeric overflow, @command{expr} fails,
11107 even if GNU MP is available.
11110 @cindex exit status of @command{expr}
11114 0 if the expression is neither null nor 0,
11115 1 if the expression is null or 0,
11116 2 if the expression is invalid,
11117 3 if an internal error occurred (e.g., arithmetic overflow).
11121 * String expressions:: + : match substr index length
11122 * Numeric expressions:: + - * / %
11123 * Relations for expr:: | & < <= = == != >= >
11124 * Examples of expr:: Examples.
11128 @node String expressions
11129 @subsection String expressions
11131 @cindex string expressions
11132 @cindex expressions, string
11134 @command{expr} supports pattern matching and other string operators. These
11135 have higher precedence than both the numeric and relational operators (in
11136 the next sections).
11140 @item @var{string} : @var{regex}
11141 @cindex pattern matching
11142 @cindex regular expression matching
11143 @cindex matching patterns
11144 Perform pattern matching. The arguments are converted to strings and the
11145 second is considered to be a (basic, a la GNU @code{grep}) regular
11146 expression, with a @code{^} implicitly prepended. The first argument is
11147 then matched against this regular expression.
11149 If the match succeeds and @var{regex} uses @samp{\(} and @samp{\)}, the
11150 @code{:} expression returns the part of @var{string} that matched the
11151 subexpression; otherwise, it returns the number of characters matched.
11153 If the match fails, the @code{:} operator returns the null string if
11154 @samp{\(} and @samp{\)} are used in @var{regex}, otherwise 0.
11156 @kindex \( @r{regexp operator}
11157 Only the first @samp{\( @dots{} \)} pair is relevant to the return
11158 value; additional pairs are meaningful only for grouping the regular
11159 expression operators.
11161 @kindex \+ @r{regexp operator}
11162 @kindex \? @r{regexp operator}
11163 @kindex \| @r{regexp operator}
11164 In the regular expression, @code{\+}, @code{\?}, and @code{\|} are
11165 operators which respectively match one or more, zero or one, or separate
11166 alternatives. SunOS and other @command{expr}'s treat these as regular
11167 characters. (@acronym{POSIX} allows either behavior.)
11168 @xref{Top, , Regular Expression Library, regex, Regex}, for details of
11169 regular expression syntax. Some examples are in @ref{Examples of expr}.
11171 @item match @var{string} @var{regex}
11173 An alternative way to do pattern matching. This is the same as
11174 @w{@samp{@var{string} : @var{regex}}}.
11176 @item substr @var{string} @var{position} @var{length}
11178 Returns the substring of @var{string} beginning at @var{position}
11179 with length at most @var{length}. If either @var{position} or
11180 @var{length} is negative, zero, or non-numeric, returns the null string.
11182 @item index @var{string} @var{charset}
11184 Returns the first position in @var{string} where the first character in
11185 @var{charset} was found. If no character in @var{charset} is found in
11186 @var{string}, return 0.
11188 @item length @var{string}
11190 Returns the length of @var{string}.
11192 @item + @var{token}
11194 Interpret @var{token} as a string, even if it is a keyword like @var{match}
11195 or an operator like @code{/}.
11196 This makes it possible to test @code{expr length + "$x"} or
11197 @code{expr + "$x" : '.*/\(.\)'} and have it do the right thing even if
11198 the value of @var{$x} happens to be (for example) @code{/} or @code{index}.
11199 This operator is a @acronym{GNU} extension. Portable shell scripts should use
11200 @code{@w{" $token"} : @w{' \(.*\)'}} instead of @code{+ "$token"}.
11204 To make @command{expr} interpret keywords as strings, you must use the
11205 @code{quote} operator.
11208 @node Numeric expressions
11209 @subsection Numeric expressions
11211 @cindex numeric expressions
11212 @cindex expressions, numeric
11214 @command{expr} supports the usual numeric operators, in order of increasing
11215 precedence. These numeric operators have lower precedence than the
11216 string operators described in the previous section, and higher precedence
11217 than the connectives (next section).
11225 @cindex subtraction
11226 Addition and subtraction. Both arguments are converted to integers;
11227 an error occurs if this cannot be done.
11233 @cindex multiplication
11236 Multiplication, division, remainder. Both arguments are converted to
11237 integers; an error occurs if this cannot be done.
11242 @node Relations for expr
11243 @subsection Relations for @command{expr}
11245 @cindex connectives, logical
11246 @cindex logical connectives
11247 @cindex relations, numeric or string
11249 @command{expr} supports the usual logical connectives and relations. These
11250 have lower precedence than the string and numeric operators
11251 (previous sections). Here is the list, lowest-precedence operator first.
11257 @cindex logical or operator
11258 @cindex or operator
11259 Returns its first argument if that is neither null nor zero, otherwise
11260 its second argument if it is neither null nor zero, otherwise 0. It
11261 does not evaluate its second argument if its first argument is neither
11266 @cindex logical and operator
11267 @cindex and operator
11268 Return its first argument if neither argument is null or zero, otherwise
11269 0. It does not evaluate its second argument if its first argument is
11272 @item < <= = == != >= >
11279 @cindex comparison operators
11281 Compare the arguments and return 1 if the relation is true, 0 otherwise.
11282 @code{==} is a synonym for @code{=}. @command{expr} first tries to convert
11283 both arguments to integers and do a numeric comparison; if either
11284 conversion fails, it does a lexicographic comparison using the character
11285 collating sequence specified by the @env{LC_COLLATE} locale.
11290 @node Examples of expr
11291 @subsection Examples of using @command{expr}
11293 @cindex examples of @command{expr}
11294 Here are a few examples, including quoting for shell metacharacters.
11296 To add 1 to the shell variable @code{foo}, in Bourne-compatible shells:
11299 foo=`expr $foo + 1`
11302 To print the non-directory part of the file name stored in
11303 @code{$fname}, which need not contain a @code{/}:
11306 expr $fname : '.*/\(.*\)' '|' $fname
11309 An example showing that @code{\+} is an operator:
11317 expr abc : 'a\(.\)c'
11319 expr index abcdef cz
11322 @error{} expr: syntax error
11323 expr index + index a
11329 @chapter Redirection
11331 @cindex redirection
11332 @cindex commands for redirection
11334 Unix shells commonly provide several forms of @dfn{redirection}---ways
11335 to change the input source or output destination of a command. But one
11336 useful redirection is performed by a separate command, not by the shell;
11337 it's described here.
11340 * tee invocation:: Redirect output to multiple files or processes.
11344 @node tee invocation
11345 @section @command{tee}: Redirect output to multiple files or processes
11348 @cindex pipe fitting
11349 @cindex destinations, multiple output
11350 @cindex read from stdin and write to stdout and files
11352 The @command{tee} command copies standard input to standard output and also
11353 to any files given as arguments. This is useful when you want not only
11354 to send some data down a pipe, but also to save a copy. Synopsis:
11357 tee [@var{option}]@dots{} [@var{file}]@dots{}
11360 If a file being written to does not already exist, it is created. If a
11361 file being written to already exists, the data it previously contained
11362 is overwritten unless the @option{-a} option is used.
11364 A @var{file} of @samp{-} causes @command{tee} to send another copy of
11365 input to standard output, but this is typically not that useful as the
11366 copies are interleaved.
11368 The program accepts the following options. Also see @ref{Common options}.
11375 Append standard input to the given files rather than overwriting
11379 @itemx --ignore-interrupts
11381 @opindex --ignore-interrupts
11382 Ignore interrupt signals.
11386 The @command{tee} command is useful when you happen to be transferring a large
11387 amount of data and also want to summarize that data without reading
11388 it a second time. For example, when you are downloading a DVD image,
11389 you often want to verify its signature or checksum right away.
11390 The inefficient way to do it is simply:
11393 wget http://example.com/some.iso && sha1sum some.iso
11396 One problem with the above is that it makes you wait for the
11397 download to complete before starting the time-consuming SHA1 computation.
11398 Perhaps even more importantly, the above requires reading
11399 the DVD image a second time (the first was from the network).
11401 The efficient way to do it is to interleave the download
11402 and SHA1 computation. Then, you'll get the checksum for
11403 free, because the entire process parallelizes so well:
11406 # slightly contrived, to demonstrate process substitution
11407 wget -O - http://example.com/dvd.iso \
11408 | tee >(sha1sum > dvd.sha1) > dvd.iso
11411 That makes @command{tee} write not just to the expected output file,
11412 but also to a pipe running @command{sha1sum} and saving the final
11413 checksum in a file named @file{dvd.sha1}.
11415 Note, however, that this example relies on a feature of modern shells
11416 called @dfn{process substitution}
11417 (the @samp{>(command)} syntax, above;
11418 @xref{Process Substitution,,Process Substitution, bashref,
11419 The Bash Reference Manual}.),
11420 so it works with @command{zsh}, @command{bash}, and @command{ksh},
11421 but not with @command{/bin/sh}. So if you write code like this
11422 in a shell script, be sure to start the script with @samp{#!/bin/bash}.
11424 Since the above example writes to one file and one process,
11425 a more conventional and portable use of @command{tee} is even better:
11428 wget -O - http://example.com/dvd.iso \
11429 | tee dvd.iso | sha1sum > dvd.sha1
11432 You can extend this example to make @command{tee} write to two processes,
11433 computing MD5 and SHA1 checksums in parallel. In this case,
11434 process substitution is required:
11437 wget -O - http://example.com/dvd.iso \
11438 | tee >(sha1sum > dvd.sha1) \
11439 >(md5sum > dvd.md5) \
11443 This technique is also useful when you want to make a @emph{compressed}
11444 copy of the contents of a pipe.
11445 Consider a tool to graphically summarize disk usage data from @samp{du -ak}.
11446 For a large hierarchy, @samp{du -ak} can run for a long time,
11447 and can easily produce terabytes of data, so you won't want to
11448 rerun the command unnecessarily. Nor will you want to save
11449 the uncompressed output.
11451 Doing it the inefficient way, you can't even start the GUI
11452 until after you've compressed all of the @command{du} output:
11455 du -ak | gzip -9 > /tmp/du.gz
11456 gzip -d /tmp/du.gz | xdiskusage -a
11459 With @command{tee} and process substitution, you start the GUI
11460 right away and eliminate the decompression completely:
11463 du -ak | tee >(gzip -9 > /tmp/du.gz) | xdiskusage -a
11466 Finally, if you regularly create more than one type of
11467 compressed tarball at once, for example when @code{make dist} creates
11468 both @command{gzip}-compressed and @command{bzip2}-compressed tarballs,
11469 there may be a better way.
11470 Typical @command{automake}-generated @file{Makefile} rules create
11471 the two compressed tar archives with commands in sequence, like this
11472 (slightly simplified):
11475 tardir=your-pkg-M.N
11476 tar chof - "$tardir" | gzip -9 -c > your-pkg-M.N.tar.gz
11477 tar chof - "$tardir" | bzip2 -9 -c > your-pkg-M.N.tar.bz2
11480 However, if the hierarchy you are archiving and compressing is larger
11481 than a couple megabytes, and especially if you are using a multi-processor
11482 system with plenty of memory, then you can do much better by reading the
11483 directory contents only once and running the compression programs in parallel:
11486 tardir=your-pkg-M.N
11487 tar chof - "$tardir" \
11488 | tee >(gzip -9 -c > your-pkg-M.N.tar.gz) \
11489 | bzip2 -9 -c > your-pkg-M.N.tar.bz2
11495 @node File name manipulation
11496 @chapter File name manipulation
11498 @cindex file name manipulation
11499 @cindex manipulation of file names
11500 @cindex commands for file name manipulation
11502 This section describes commands that manipulate file names.
11505 * basename invocation:: Strip directory and suffix from a file name.
11506 * dirname invocation:: Strip non-directory suffix from a file name.
11507 * pathchk invocation:: Check file name portability.
11511 @node basename invocation
11512 @section @command{basename}: Strip directory and suffix from a file name
11515 @cindex strip directory and suffix from file names
11516 @cindex directory, stripping from file names
11517 @cindex suffix, stripping from file names
11518 @cindex file names, stripping directory and suffix
11519 @cindex leading directory components, stripping
11521 @command{basename} removes any leading directory components from
11522 @var{name}. Synopsis:
11525 basename @var{name} [@var{suffix}]
11528 If @var{suffix} is specified and is identical to the end of @var{name},
11529 it is removed from @var{name} as well. Note that since trailing slashes
11530 are removed prior to suffix matching, @var{suffix} will do nothing if it
11531 contains slashes. @command{basename} prints the result on standard
11534 @c This test is used both here and in the section on dirname.
11535 @macro basenameAndDirname
11536 Together, @command{basename} and @command{dirname} are designed such
11537 that if @samp{ls "$name"} succeeds, then the command sequence @samp{cd
11538 "$(dirname "$name")"; ls "$(basename "$name")"} will, too. This works
11539 for everything except file names containing a trailing newline.
11541 @basenameAndDirname
11543 @acronym{POSIX} allows the implementation to define the results if
11544 @var{name} is empty or @samp{//}. In the former case, @acronym{GNU}
11545 @command{basename} returns the empty string. In the latter case, the
11546 result is @samp{//} on platforms where @var{//} is distinct from
11547 @var{/}, and @samp{/} on platforms where there is no difference.
11549 The only options are @option{--help} and @option{--version}. @xref{Common
11550 options}. Options must precede operands.
11558 basename /usr/bin/sort
11561 basename include/stdio.h .h
11565 @node dirname invocation
11566 @section @command{dirname}: Strip non-directory suffix from a file name
11569 @cindex directory components, printing
11570 @cindex stripping non-directory suffix
11571 @cindex non-directory suffix, stripping
11573 @command{dirname} prints all but the final slash-delimited component of
11574 a string (presumably a file name). Synopsis:
11580 If @var{name} is a single component, @command{dirname} prints @samp{.}
11581 (meaning the current directory).
11583 @basenameAndDirname
11585 @acronym{POSIX} allows the implementation to define the results if
11586 @var{name} is @samp{//}. With @acronym{GNU} @command{dirname}, the
11587 result is @samp{//} on platforms where @var{//} is distinct from
11588 @var{/}, and @samp{/} on platforms where there is no difference.
11590 The only options are @option{--help} and @option{--version}. @xref{Common
11598 # Output "/usr/bin".
11599 dirname /usr/bin/sort
11606 @node pathchk invocation
11607 @section @command{pathchk}: Check file name portability
11610 @cindex file names, checking validity and portability
11611 @cindex valid file names, checking for
11612 @cindex portable file names, checking for
11614 @command{pathchk} checks portability of file names. Synopsis:
11617 pathchk [@var{option}]@dots{} @var{name}@dots{}
11620 For each @var{name}, @command{pathchk} prints a message if any of
11621 these conditions is true:
11625 One of the existing directories in @var{name} does not have search
11626 (execute) permission,
11628 The length of @var{name} is larger than the maximum supported by the
11631 The length of one component of @var{name} is longer than
11632 its file system's maximum.
11635 A nonexistent @var{name} is not an error, so long a file with that
11636 name could be created under the above conditions.
11638 The program accepts the following options. Also see @ref{Common options}.
11639 Options must precede operands.
11645 Instead of performing checks based on the underlying file system,
11646 print a message if any of these conditions is true:
11650 A file name is empty.
11653 The length of a file name or one of its components exceeds the
11654 @acronym{POSIX} minimum limits for portability.
11657 A file name contains a character outside the portable file name
11658 character set, namely, the ASCII letters and digits, @samp{-},
11659 @samp{.}, @samp{/}, and @samp{_}.
11664 Print a message if a file name is empty, or if it contains a component
11665 that begins with @samp{-}.
11667 @item --portability
11668 @opindex --portability
11669 Print a message if a file name is not portable to all @acronym{POSIX}
11670 hosts. This option is equivalent to @samp{-p -P}.
11674 @cindex exit status of @command{pathchk}
11678 0 if all specified file names passed all checks,
11683 @node Working context
11684 @chapter Working context
11686 @cindex working context
11687 @cindex commands for printing the working context
11689 This section describes commands that display or alter the context in
11690 which you are working: the current directory, the terminal settings, and
11691 so forth. See also the user-related commands in the next section.
11694 * pwd invocation:: Print working directory.
11695 * stty invocation:: Print or change terminal characteristics.
11696 * printenv invocation:: Print environment variables.
11697 * tty invocation:: Print file name of terminal on standard input.
11701 @node pwd invocation
11702 @section @command{pwd}: Print working directory
11705 @cindex print name of current directory
11706 @cindex current working directory, printing
11707 @cindex working directory, printing
11709 @cindex symbolic links and @command{pwd}
11710 @command{pwd} prints the fully resolved name of the current directory.
11711 That is, all components of the printed name will be actual directory
11712 names---none will be symbolic links.
11714 @cindex conflicts with shell built-ins
11715 @cindex built-in shell commands, conflicts with
11716 Because most shells have a built-in @command{pwd} command, using an
11717 unadorned @command{pwd} in a script or interactively may get you
11718 different functionality than that described here.
11720 The only options are a lone @option{--help} or
11721 @option{--version}. @xref{Common options}.
11726 @node stty invocation
11727 @section @command{stty}: Print or change terminal characteristics
11730 @cindex change or print terminal settings
11731 @cindex terminal settings
11732 @cindex line settings of terminal
11734 @command{stty} prints or changes terminal characteristics, such as baud rate.
11738 stty [@var{option}] [@var{setting}]@dots{}
11739 stty [@var{option}]
11742 If given no line settings, @command{stty} prints the baud rate, line
11743 discipline number (on systems that support it), and line settings
11744 that have been changed from the values set by @samp{stty sane}.
11745 By default, mode reading and setting are performed on the tty line
11746 connected to standard input, although this can be modified by the
11747 @option{--file} option.
11749 @command{stty} accepts many non-option arguments that change aspects of
11750 the terminal line operation, as described below.
11752 The program accepts the following options. Also see @ref{Common options}.
11759 Print all current settings in human-readable form. This option may not
11760 be used in combination with any line settings.
11762 @item -F @var{device}
11763 @itemx --file=@var{device}
11766 Set the line opened by the file name specified in @var{device} instead of
11767 the tty line connected to standard input. This option is necessary
11768 because opening a @acronym{POSIX} tty requires use of the @code{O_NONDELAY} flag to
11769 prevent a @acronym{POSIX} tty from blocking until the carrier detect line is high if
11770 the @code{clocal} flag is not set. Hence, it is not always possible
11771 to allow the shell to open the device in the traditional manner.
11777 @cindex machine-readable @command{stty} output
11778 Print all current settings in a form that can be used as an argument to
11779 another @command{stty} command to restore the current settings. This option
11780 may not be used in combination with any line settings.
11784 Many settings can be turned off by preceding them with a @samp{-}.
11785 Such arguments are marked below with ``May be negated'' in their
11786 description. The descriptions themselves refer to the positive
11787 case, that is, when @emph{not} negated (unless stated otherwise,
11790 Some settings are not available on all @acronym{POSIX} systems, since they use
11791 extensions. Such arguments are marked below with ``Non-@acronym{POSIX}'' in their
11792 description. On non-@acronym{POSIX} systems, those or other settings also may not
11793 be available, but it's not feasible to document all the variations: just
11799 * Control:: Control settings
11800 * Input:: Input settings
11801 * Output:: Output settings
11802 * Local:: Local settings
11803 * Combination:: Combination settings
11804 * Characters:: Special characters
11805 * Special:: Special settings
11810 @subsection Control settings
11812 @cindex control settings
11818 @cindex two-way parity
11819 Generate parity bit in output and expect parity bit in input.
11825 @cindex even parity
11826 Set odd parity (even if negated). May be negated.
11833 @cindex character size
11834 @cindex eight-bit characters
11835 Set character size to 5, 6, 7, or 8 bits.
11840 Send a hangup signal when the last process closes the tty. May be
11846 Use two stop bits per character (one if negated). May be negated.
11850 Allow input to be received. May be negated.
11854 @cindex modem control
11855 Disable modem control signals. May be negated.
11859 @cindex hardware flow control
11860 @cindex flow control, hardware
11861 @cindex RTS/CTS flow control
11862 Enable RTS/CTS flow control. Non-@acronym{POSIX}. May be negated.
11867 @subsection Input settings
11869 @cindex input settings
11874 @cindex breaks, ignoring
11875 Ignore break characters. May be negated.
11879 @cindex breaks, cause interrupts
11880 Make breaks cause an interrupt signal. May be negated.
11884 @cindex parity, ignoring
11885 Ignore characters with parity errors. May be negated.
11889 @cindex parity errors, marking
11890 Mark parity errors (with a 255-0-character sequence). May be negated.
11894 Enable input parity checking. May be negated.
11898 @cindex eight-bit input
11899 Clear high (8th) bit of input characters. May be negated.
11903 @cindex newline, translating to return
11904 Translate newline to carriage return. May be negated.
11908 @cindex return, ignoring
11909 Ignore carriage return. May be negated.
11913 @cindex return, translating to newline
11914 Translate carriage return to newline. May be negated.
11918 @cindex input encoding, UTF-8
11919 Assume input characters are UTF-8 encoded. May be negated.
11923 @kindex C-s/C-q flow control
11924 @cindex XON/XOFF flow control
11925 Enable XON/XOFF flow control (that is, @kbd{CTRL-S}/@kbd{CTRL-Q}). May
11932 @cindex software flow control
11933 @cindex flow control, software
11934 Enable sending of @code{stop} character when the system input buffer
11935 is almost full, and @code{start} character when it becomes almost
11936 empty again. May be negated.
11940 @cindex uppercase, translating to lowercase
11941 Translate uppercase characters to lowercase. Non-@acronym{POSIX}. May be
11946 Allow any character to restart output (only the start character
11947 if negated). Non-@acronym{POSIX}. May be negated.
11951 @cindex beeping at input buffer full
11952 Enable beeping and not flushing input buffer if a character arrives
11953 when the input buffer is full. Non-@acronym{POSIX}. May be negated.
11958 @subsection Output settings
11960 @cindex output settings
11961 These arguments specify output-related operations.
11966 Postprocess output. May be negated.
11970 @cindex lowercase, translating to output
11971 Translate lowercase characters to uppercase. Non-@acronym{POSIX}. May be
11976 @cindex return, translating to newline
11977 Translate carriage return to newline. Non-@acronym{POSIX}. May be negated.
11981 @cindex newline, translating to crlf
11982 Translate newline to carriage return-newline. Non-@acronym{POSIX}. May be
11987 Do not print carriage returns in the first column. Non-@acronym{POSIX}.
11992 Newline performs a carriage return. Non-@acronym{POSIX}. May be negated.
11996 @cindex pad instead of timing for delaying
11997 Use fill (padding) characters instead of timing for delays. Non-@acronym{POSIX}.
12002 @cindex pad character
12003 Use delete characters for fill instead of null characters. Non-@acronym{POSIX}.
12009 Newline delay style. Non-@acronym{POSIX}.
12016 Carriage return delay style. Non-@acronym{POSIX}.
12022 @opindex tab@var{n}
12023 Horizontal tab delay style. Non-@acronym{POSIX}.
12028 Backspace delay style. Non-@acronym{POSIX}.
12033 Vertical tab delay style. Non-@acronym{POSIX}.
12038 Form feed delay style. Non-@acronym{POSIX}.
12043 @subsection Local settings
12045 @cindex local settings
12050 Enable @code{interrupt}, @code{quit}, and @code{suspend} special
12051 characters. May be negated.
12055 Enable @code{erase}, @code{kill}, @code{werase}, and @code{rprnt}
12056 special characters. May be negated.
12060 Enable non-@acronym{POSIX} special characters. May be negated.
12064 Echo input characters. May be negated.
12070 Echo @code{erase} characters as backspace-space-backspace. May be
12075 @cindex newline echoing after @code{kill}
12076 Echo a newline after a @code{kill} character. May be negated.
12080 @cindex newline, echoing
12081 Echo newline even if not echoing other characters. May be negated.
12085 @cindex flushing, disabling
12086 Disable flushing after @code{interrupt} and @code{quit} special
12087 characters. May be negated.
12091 @cindex case translation
12092 Enable input and output of uppercase characters by preceding their
12093 lowercase equivalents with @samp{\}, when @code{icanon} is set.
12094 Non-@acronym{POSIX}. May be negated.
12098 @cindex background jobs, stopping at terminal write
12099 Stop background jobs that try to write to the terminal. Non-@acronym{POSIX}.
12106 Echo erased characters backward, between @samp{\} and @samp{/}.
12107 Non-@acronym{POSIX}. May be negated.
12113 @cindex control characters, using @samp{^@var{c}}
12114 @cindex hat notation for control characters
12115 Echo control characters in hat notation (@samp{^@var{c}}) instead
12116 of literally. Non-@acronym{POSIX}. May be negated.
12122 Echo the @code{kill} special character by erasing each character on
12123 the line as indicated by the @code{echoprt} and @code{echoe} settings,
12124 instead of by the @code{echoctl} and @code{echok} settings. Non-@acronym{POSIX}.
12130 @subsection Combination settings
12132 @cindex combination settings
12133 Combination settings:
12140 Same as @code{parenb -parodd cs7}. May be negated. If negated, same
12141 as @code{-parenb cs8}.
12145 Same as @code{parenb parodd cs7}. May be negated. If negated, same
12146 as @code{-parenb cs8}.
12150 Same as @code{-icrnl -onlcr}. May be negated. If negated, same as
12151 @code{icrnl -inlcr -igncr onlcr -ocrnl -onlret}.
12155 Reset the @code{erase} and @code{kill} special characters to their default
12162 @c This is too long to write inline.
12164 cread -ignbrk brkint -inlcr -igncr icrnl -ixoff
12165 -iuclc -ixany imaxbel opost -olcuc -ocrnl onlcr
12166 -onocr -onlret -ofill -ofdel nl0 cr0 tab0 bs0 vt0
12167 ff0 isig icanon iexten echo echoe echok -echonl
12168 -noflsh -xcase -tostop -echoprt echoctl echoke
12172 and also sets all special characters to their default values.
12176 Same as @code{brkint ignpar istrip icrnl ixon opost isig icanon}, plus
12177 sets the @code{eof} and @code{eol} characters to their default values
12178 if they are the same as the @code{min} and @code{time} characters.
12179 May be negated. If negated, same as @code{raw}.
12186 -ignbrk -brkint -ignpar -parmrk -inpck -istrip
12187 -inlcr -igncr -icrnl -ixon -ixoff -iuclc -ixany
12188 -imaxbel -opost -isig -icanon -xcase min 1 time 0
12192 May be negated. If negated, same as @code{cooked}.
12196 Same as @option{-icanon}. May be negated. If negated, same as
12201 @cindex eight-bit characters
12202 Same as @code{-parenb -istrip cs8}. May be negated. If negated,
12203 same as @code{parenb istrip cs7}.
12207 Same as @option{-parenb -istrip -opost cs8}. May be negated.
12208 If negated, same as @code{parenb istrip opost cs7}.
12212 Same as @option{-ixany}. Non-@acronym{POSIX}. May be negated.
12216 Same as @code{tab0}. Non-@acronym{POSIX}. May be negated. If negated, same
12223 Same as @code{xcase iuclc olcuc}. Non-@acronym{POSIX}. May be negated.
12227 Same as @code{echoe echoctl echoke}.
12231 Same as @code{echoe echoctl echoke -ixany intr ^C erase ^? kill C-u}.
12236 @subsection Special characters
12238 @cindex special characters
12239 @cindex characters, special
12241 The special characters' default values vary from system to system.
12242 They are set with the syntax @samp{name value}, where the names are
12243 listed below and the value can be given either literally, in hat
12244 notation (@samp{^@var{c}}), or as an integer which may start with
12245 @samp{0x} to indicate hexadecimal, @samp{0} to indicate octal, or
12246 any other digit to indicate decimal.
12248 @cindex disabling special characters
12249 @kindex u@r{, and disabling special characters}
12250 For GNU stty, giving a value of @code{^-} or @code{undef} disables that
12251 special character. (This is incompatible with Ultrix @command{stty},
12252 which uses a value of @samp{u} to disable a special character. GNU
12253 @command{stty} treats a value @samp{u} like any other, namely to set that
12254 special character to @key{U}.)
12260 Send an interrupt signal.
12264 Send a quit signal.
12268 Erase the last character typed.
12272 Erase the current line.
12276 Send an end of file (terminate the input).
12284 Alternate character to end the line. Non-@acronym{POSIX}.
12288 Switch to a different shell layer. Non-@acronym{POSIX}.
12292 Restart the output after stopping it.
12300 Send a terminal stop signal.
12304 Send a terminal stop signal after flushing the input. Non-@acronym{POSIX}.
12308 Redraw the current line. Non-@acronym{POSIX}.
12312 Erase the last word typed. Non-@acronym{POSIX}.
12316 Enter the next character typed literally, even if it is a special
12317 character. Non-@acronym{POSIX}.
12322 @subsection Special settings
12324 @cindex special settings
12329 Set the minimum number of characters that will satisfy a read until
12330 the time value has expired, when @option{-icanon} is set.
12334 Set the number of tenths of a second before reads time out if the minimum
12335 number of characters have not been read, when @option{-icanon} is set.
12337 @item ispeed @var{n}
12339 Set the input speed to @var{n}.
12341 @item ospeed @var{n}
12343 Set the output speed to @var{n}.
12347 Tell the tty kernel driver that the terminal has @var{n} rows. Non-@acronym{POSIX}.
12350 @itemx columns @var{n}
12353 Tell the kernel that the terminal has @var{n} columns. Non-@acronym{POSIX}.
12359 Print the number of rows and columns that the kernel thinks the
12360 terminal has. (Systems that don't support rows and columns in the kernel
12361 typically use the environment variables @env{LINES} and @env{COLUMNS}
12362 instead; however, GNU @command{stty} does not know anything about them.)
12363 Non-@acronym{POSIX}.
12367 Use line discipline @var{n}. Non-@acronym{POSIX}.
12371 Print the terminal speed.
12374 @cindex baud rate, setting
12375 Set the input and output speeds to @var{n}. @var{n} can be one of: 0
12376 50 75 110 134 134.5 150 200 300 600 1200 1800 2400 4800 9600 19200
12377 38400 @code{exta} @code{extb}. @code{exta} is the same as 19200;
12378 @code{extb} is the same as 38400. Many systems, including GNU/Linux,
12379 support higher speeds. The @command{stty} command includes support
12396 4000000 where the system supports these.
12397 0 hangs up the line if @option{-clocal} is set.
12401 @node printenv invocation
12402 @section @command{printenv}: Print all or some environment variables
12405 @cindex printing all or some environment variables
12406 @cindex environment variables, printing
12408 @command{printenv} prints environment variable values. Synopsis:
12411 printenv [@var{option}] [@var{variable}]@dots{}
12414 If no @var{variable}s are specified, @command{printenv} prints the value of
12415 every environment variable. Otherwise, it prints the value of each
12416 @var{variable} that is set, and nothing for those that are not set.
12418 The only options are a lone @option{--help} or @option{--version}.
12419 @xref{Common options}.
12421 @cindex exit status of @command{printenv}
12425 0 if all variables specified were found
12426 1 if at least one specified variable was not found
12427 2 if a write error occurred
12431 @node tty invocation
12432 @section @command{tty}: Print file name of terminal on standard input
12435 @cindex print terminal file name
12436 @cindex terminal file name, printing
12438 @command{tty} prints the file name of the terminal connected to its standard
12439 input. It prints @samp{not a tty} if standard input is not a terminal.
12443 tty [@var{option}]@dots{}
12446 The program accepts the following option. Also see @ref{Common options}.
12456 Print nothing; only return an exit status.
12460 @cindex exit status of @command{tty}
12464 0 if standard input is a terminal
12465 1 if standard input is not a terminal
12466 2 if given incorrect arguments
12467 3 if a write error occurs
12471 @node User information
12472 @chapter User information
12474 @cindex user information, commands for
12475 @cindex commands for printing user information
12477 This section describes commands that print user-related information:
12478 logins, groups, and so forth.
12481 * id invocation:: Print user identity.
12482 * logname invocation:: Print current login name.
12483 * whoami invocation:: Print effective user ID.
12484 * groups invocation:: Print group names a user is in.
12485 * users invocation:: Print login names of users currently logged in.
12486 * who invocation:: Print who is currently logged in.
12490 @node id invocation
12491 @section @command{id}: Print user identity
12494 @cindex real user and group IDs, printing
12495 @cindex effective user and group IDs, printing
12496 @cindex printing real and effective user and group IDs
12498 @command{id} prints information about the given user, or the process
12499 running it if no user is specified. Synopsis:
12502 id [@var{option}]@dots{} [@var{username}]
12505 By default, it prints the real user ID, real group ID, effective user ID
12506 if different from the real user ID, effective group ID if different from
12507 the real group ID, and supplemental group IDs.
12509 Each of these numeric values is preceded by an identifying string and
12510 followed by the corresponding user or group name in parentheses.
12512 The options cause @command{id} to print only part of the above information.
12513 Also see @ref{Common options}.
12520 Print only the group ID.
12526 Print only the group ID and the supplementary groups.
12532 Print the user or group name instead of the ID number. Requires
12533 @option{-u}, @option{-g}, or @option{-G}.
12539 Print the real, instead of effective, user or group ID. Requires
12540 @option{-u}, @option{-g}, or @option{-G}.
12546 Print only the user ID.
12552 @macro primaryAndSupplementaryGroups{cmd,arg}
12553 Primary and supplementary groups for a process are normally inherited
12554 from its parent and are usually unchanged since login. This means
12555 that if you change the group database after logging in, @command{\cmd\}
12556 will not reflect your changes within your existing login session.
12557 Running @command{\cmd\} with a \arg\ causes the user and group
12558 database to be consulted afresh, and so will give a different result.
12560 @primaryAndSupplementaryGroups{id,user argument}
12562 @node logname invocation
12563 @section @command{logname}: Print current login name
12566 @cindex printing user's login name
12567 @cindex login name, printing
12568 @cindex user name, printing
12571 @command{logname} prints the calling user's name, as found in a
12572 system-maintained file (often @file{/var/run/utmp} or
12573 @file{/etc/utmp}), and exits with a status of 0. If there is no entry
12574 for the calling process, @command{logname} prints
12575 an error message and exits with a status of 1.
12577 The only options are @option{--help} and @option{--version}. @xref{Common
12583 @node whoami invocation
12584 @section @command{whoami}: Print effective user ID
12587 @cindex effective user ID, printing
12588 @cindex printing the effective user ID
12590 @command{whoami} prints the user name associated with the current
12591 effective user ID. It is equivalent to the command @samp{id -un}.
12593 The only options are @option{--help} and @option{--version}. @xref{Common
12599 @node groups invocation
12600 @section @command{groups}: Print group names a user is in
12603 @cindex printing groups a user is in
12604 @cindex supplementary groups, printing
12606 @command{groups} prints the names of the primary and any supplementary
12607 groups for each given @var{username}, or the current process if no names
12608 are given. If more than one name is given, the name of each user is
12610 the list of that user's groups and the user name is separated from the
12611 group list by a colon. Synopsis:
12614 groups [@var{username}]@dots{}
12617 The group lists are equivalent to the output of the command @samp{id -Gn}.
12619 @primaryAndSupplementaryGroups{groups,list of users}
12621 The only options are @option{--help} and @option{--version}. @xref{Common
12627 @node users invocation
12628 @section @command{users}: Print login names of users currently logged in
12631 @cindex printing current usernames
12632 @cindex usernames, printing current
12634 @cindex login sessions, printing users with
12635 @command{users} prints on a single line a blank-separated list of user
12636 names of users currently logged in to the current host. Each user name
12637 corresponds to a login session, so if a user has more than one login
12638 session, that user's name will appear the same number of times in the
12647 With no @var{file} argument, @command{users} extracts its information from
12648 a system-maintained file (often @file{/var/run/utmp} or
12649 @file{/etc/utmp}). If a file argument is given, @command{users} uses
12650 that file instead. A common choice is @file{/var/log/wtmp}.
12652 The only options are @option{--help} and @option{--version}. @xref{Common
12658 @node who invocation
12659 @section @command{who}: Print who is currently logged in
12662 @cindex printing current user information
12663 @cindex information, about current users
12665 @command{who} prints information about users who are currently logged on.
12669 @command{who} [@var{option}] [@var{file}] [am i]
12672 @cindex terminal lines, currently used
12674 @cindex remote hostname
12675 If given no non-option arguments, @command{who} prints the following
12676 information for each user currently logged on: login name, terminal
12677 line, login time, and remote hostname or X display.
12681 If given one non-option argument, @command{who} uses that instead of
12682 a default system-maintained file (often @file{/var/run/utmp} or
12683 @file{/etc/utmp}) as the name of the file containing the record of
12684 users logged on. @file{/var/log/wtmp} is commonly given as an argument
12685 to @command{who} to look at who has previously logged on.
12689 If given two non-option arguments, @command{who} prints only the entry
12690 for the user running it (determined from its standard input), preceded
12691 by the hostname. Traditionally, the two arguments given are @samp{am
12692 i}, as in @samp{who am i}.
12695 Time stamps are listed according to the time zone rules specified by
12696 the @env{TZ} environment variable, or by the system default rules if
12697 @env{TZ} is not set. @xref{TZ Variable,, Specifying the Time Zone
12698 with @env{TZ}, libc, The GNU C Library Reference Manual}.
12700 The program accepts the following options. Also see @ref{Common options}.
12708 Same as @samp{-b -d --login -p -r -t -T -u}.
12714 Print the date and time of last system boot.
12720 Print information corresponding to dead processes.
12726 Print column headings.
12730 Same as @samp{who am i}.
12736 Print only the login names and the number of users logged on.
12737 Overrides all other options.
12741 Ignored; for compatibility with other versions of @command{who}.
12746 After the login time, print the number of hours and minutes that the
12747 user has been idle. @samp{.} means the user was active in the last minute.
12748 @samp{old} means the user has been idle for more than 24 hours.
12754 List only the entries that correspond to processes via which the
12755 system is waiting for a user to login. The user name is always @samp{LOGIN}.
12759 Attempt to canonicalize hostnames found in utmp through a DNS lookup. This
12760 is not the default because it can cause significant delays on systems with
12761 automatic dial-up internet access.
12767 Print a line of column headings.
12773 List active processes spawned by init.
12778 @opindex --runlevel
12779 Print the current (and maybe previous) run-level of the init process.
12785 Print last system clock change.
12796 @opindex --writable
12797 @cindex message status
12798 @pindex write@r{, allowed}
12799 After each login name print a character indicating the user's message status:
12802 @samp{+} allowing @code{write} messages
12803 @samp{-} disallowing @code{write} messages
12804 @samp{?} cannot find terminal device
12812 @node System context
12813 @chapter System context
12815 @cindex system context
12816 @cindex context, system
12817 @cindex commands for system context
12819 This section describes commands that print or change system-wide
12823 * arch invocation:: Print machine hardware name.
12824 * date invocation:: Print or set system date and time.
12825 * uname invocation:: Print system information.
12826 * hostname invocation:: Print or set system name.
12827 * hostid invocation:: Print numeric host identifier.
12828 * uptime invocation:: Print system uptime and load
12832 @node date invocation
12833 @section @command{date}: Print or set system date and time
12836 @cindex time, printing or setting
12837 @cindex printing the current time
12842 date [@var{option}]@dots{} [+@var{format}]
12843 date [-u|--utc|--universal] @c this avoids a newline in the output
12844 [ MMDDhhmm[[CC]YY][.ss] ]
12848 Invoking @command{date} with no @var{format} argument is equivalent to invoking
12849 it with a default format that depends on the @env{LC_TIME} locale category.
12850 In the default C locale, this format is @samp{'+%a %b %e %H:%M:%S %Z %Y'},
12851 so the output looks like @samp{Thu Mar @ 3 13:47:51 PST 2005}.
12854 Normally, @command{date} uses the time zone rules indicated by the
12855 @env{TZ} environment variable, or the system default rules if @env{TZ}
12856 is not set. @xref{TZ Variable,, Specifying the Time Zone with
12857 @env{TZ}, libc, The GNU C Library Reference Manual}.
12859 @findex strftime @r{and @command{date}}
12860 @cindex time formats
12861 @cindex formatting times
12862 If given an argument that starts with a @samp{+}, @command{date} prints the
12863 current date and time (or the date and time specified by the
12864 @option{--date} option, see below) in the format defined by that argument,
12865 which is similar to that of the @code{strftime} function. Except for
12866 conversion specifiers, which start with @samp{%}, characters in the
12867 format string are printed unchanged. The conversion specifiers are
12873 * Time conversion specifiers:: %[HIklMNpPrRsSTXzZ]
12874 * Date conversion specifiers:: %[aAbBcCdDeFgGhjmuUVwWxyY]
12875 * Literal conversion specifiers:: %[%nt]
12876 * Padding and other flags:: Pad with zeros, spaces, etc.
12877 * Setting the time:: Changing the system clock.
12878 * Options for date:: Instead of the current time.
12880 * Date input formats:: Specifying date strings.
12882 * Examples of date:: Examples.
12885 @node Time conversion specifiers
12886 @subsection Time conversion specifiers
12888 @cindex time conversion specifiers
12889 @cindex conversion specifiers, time
12891 @command{date} conversion specifiers related to times.
12895 hour (@samp{00}@dots{}@samp{23})
12897 hour (@samp{01}@dots{}@samp{12})
12899 hour (@samp{ 0}@dots{}@samp{23}).
12900 This is a @acronym{GNU} extension.
12902 hour (@samp{ 1}@dots{}@samp{12}).
12903 This is a @acronym{GNU} extension.
12905 minute (@samp{00}@dots{}@samp{59})
12907 nanoseconds (@samp{000000000}@dots{}@samp{999999999}).
12908 This is a @acronym{GNU} extension.
12910 locale's equivalent of either @samp{AM} or @samp{PM};
12911 blank in many locales.
12912 Noon is treated as @samp{PM} and midnight as @samp{AM}.
12914 like @samp{%p}, except lower case.
12915 This is a @acronym{GNU} extension.
12917 locale's 12-hour clock time (e.g., @samp{11:11:04 PM})
12919 24-hour hour and minute. Same as @samp{%H:%M}.
12920 This is a @acronym{GNU} extension.
12922 @cindex epoch, seconds since
12923 @cindex seconds since the epoch
12924 @cindex beginning of time
12925 seconds since the epoch, i.e., since 1970-01-01 00:00:00 UTC.
12926 Leap seconds are not counted unless leap second support is available.
12927 @xref{%s-examples}, for examples.
12928 This is a @acronym{GNU} extension.
12930 second (@samp{00}@dots{}@samp{60}).
12931 This may be @samp{60} if leap seconds are supported.
12933 24-hour hour, minute, and second. Same as @samp{%H:%M:%S}.
12935 locale's time representation (e.g., @samp{23:13:48})
12937 @w{@acronym{RFC} 2822/@acronym{ISO} 8601} style numeric time zone
12938 (e.g., @samp{-0600} or @samp{+0530}), or nothing if no
12939 time zone is determinable. This value reflects the numeric time zone
12940 appropriate for the current time, using the time zone rules specified
12941 by the @env{TZ} environment variable.
12942 The time (and optionally, the time zone rules) can be overridden
12943 by the @option{--date} option.
12944 This is a @acronym{GNU} extension.
12946 @w{@acronym{RFC} 3339/@acronym{ISO} 8601} style numeric time zone with
12947 @samp{:} (e.g., @samp{-06:00} or @samp{+05:30}), or nothing if no time
12948 zone is determinable.
12949 This is a @acronym{GNU} extension.
12951 Numeric time zone to the nearest second with @samp{:} (e.g.,
12952 @samp{-06:00:00} or @samp{+05:30:00}), or nothing if no time zone is
12954 This is a @acronym{GNU} extension.
12956 Numeric time zone with @samp{:} using the minimum necessary precision
12957 (e.g., @samp{-06}, @samp{+05:30}, or @samp{-04:56:02}), or nothing if
12958 no time zone is determinable.
12959 This is a @acronym{GNU} extension.
12961 alphabetic time zone abbreviation (e.g., @samp{EDT}), or nothing if no
12962 time zone is determinable. See @samp{%z} for how it is determined.
12966 @node Date conversion specifiers
12967 @subsection Date conversion specifiers
12969 @cindex date conversion specifiers
12970 @cindex conversion specifiers, date
12972 @command{date} conversion specifiers related to dates.
12976 locale's abbreviated weekday name (e.g., @samp{Sun})
12978 locale's full weekday name, variable length (e.g., @samp{Sunday})
12980 locale's abbreviated month name (e.g., @samp{Jan})
12982 locale's full month name, variable length (e.g., @samp{January})
12984 locale's date and time (e.g., @samp{Thu Mar @ 3 23:05:25 2005})
12986 century. This is like @samp{%Y}, except the last two digits are omitted.
12987 For example, it is @samp{20} if @samp{%Y} is @samp{2000},
12988 and is @samp{-0} if @samp{%Y} is @samp{-001}.
12989 It is normally at least two characters, but it may be more.
12991 day of month (e.g., @samp{01})
12993 date; same as @samp{%m/%d/%y}
12995 day of month, space padded; same as @samp{%_d}
12997 full date in @acronym{ISO} 8601 format; same as @samp{%Y-%m-%d}.
12998 This is a good choice for a date format, as it is standard and
12999 is easy to sort in the usual case where years are in the range
13001 This is a @acronym{GNU} extension.
13003 year corresponding to the @acronym{ISO} week number, but without the century
13004 (range @samp{00} through @samp{99}). This has the same format and value
13005 as @samp{%y}, except that if the @acronym{ISO} week number (see
13007 to the previous or next year, that year is used instead.
13008 This is a @acronym{GNU} extension.
13010 year corresponding to the @acronym{ISO} week number. This has the
13011 same format and value as @samp{%Y}, except that if the @acronym{ISO}
13013 @samp{%V}) belongs to the previous or next year, that year is used
13015 It is normally useful only if @samp{%V} is also used;
13016 for example, the format @samp{%G-%m-%d} is probably a mistake,
13017 since it combines the ISO week number year with the conventional month and day.
13018 This is a @acronym{GNU} extension.
13022 day of year (@samp{001}@dots{}@samp{366})
13024 month (@samp{01}@dots{}@samp{12})
13026 day of week (@samp{1}@dots{}@samp{7}) with @samp{1} corresponding to Monday
13028 week number of year, with Sunday as the first day of the week
13029 (@samp{00}@dots{}@samp{53}).
13030 Days in a new year preceding the first Sunday are in week zero.
13032 @acronym{ISO} week number, that is, the
13033 week number of year, with Monday as the first day of the week
13034 (@samp{01}@dots{}@samp{53}).
13035 If the week containing January 1 has four or more days in
13036 the new year, then it is considered week 1; otherwise, it is week 53 of
13037 the previous year, and the next week is week 1. (See the @acronym{ISO} 8601
13040 day of week (@samp{0}@dots{}@samp{6}) with 0 corresponding to Sunday
13042 week number of year, with Monday as first day of week
13043 (@samp{00}@dots{}@samp{53}).
13044 Days in a new year preceding the first Monday are in week zero.
13046 locale's date representation (e.g., @samp{12/31/99})
13048 last two digits of year (@samp{00}@dots{}@samp{99})
13050 year. This is normally at least four characters, but it may be more.
13051 Year @samp{0000} precedes year @samp{0001}, and year @samp{-001}
13052 precedes year @samp{0000}.
13056 @node Literal conversion specifiers
13057 @subsection Literal conversion specifiers
13059 @cindex literal conversion specifiers
13060 @cindex conversion specifiers, literal
13062 @command{date} conversion specifiers that produce literal strings.
13074 @node Padding and other flags
13075 @subsection Padding and other flags
13077 @cindex numeric field padding
13078 @cindex padding of numeric fields
13079 @cindex fields, padding numeric
13081 Unless otherwise specified, @command{date} normally pads numeric fields
13082 with zeros, so that, for
13083 example, numeric months are always output as two digits.
13084 Seconds since the epoch are not padded, though,
13085 since there is no natural width for them.
13087 As a @acronym{GNU} extension, @command{date} recognizes any of the
13088 following optional flags after the @samp{%}:
13092 (hyphen) Do not pad the field; useful if the output is intended for
13095 (underscore) Pad with spaces; useful if you need a fixed
13096 number of characters in the output, but zeros are too distracting.
13098 (zero) Pad with zeros even if the conversion specifier
13099 would normally pad with spaces.
13101 Use upper case characters if possible.
13103 Use opposite case characters if possible.
13104 A field that is normally upper case becomes lower case, and vice versa.
13108 Here are some examples of padding:
13111 date +%d/%m -d "Feb 1"
13113 date +%-d/%-m -d "Feb 1"
13115 date +%_d/%_m -d "Feb 1"
13119 As a @acronym{GNU} extension, you can specify the field width
13120 (after any flag, if present) as a decimal number. If the natural size of the
13121 output of the field has less than the specified number of characters,
13122 the result is written right adjusted and padded to the given
13123 size. For example, @samp{%9B} prints the right adjusted month name in
13124 a field of width 9.
13126 An optional modifier can follow the optional flag and width
13127 specification. The modifiers are:
13131 Use the locale's alternate representation for date and time. This
13132 modifier applies to the @samp{%c}, @samp{%C}, @samp{%x}, @samp{%X},
13133 @samp{%y} and @samp{%Y} conversion specifiers. In a Japanese locale, for
13134 example, @samp{%Ex} might yield a date format based on the Japanese
13138 Use the locale's alternate numeric symbols for numbers. This modifier
13139 applies only to numeric conversion specifiers.
13142 If the format supports the modifier but no alternate representation
13143 is available, it is ignored.
13146 @node Setting the time
13147 @subsection Setting the time
13149 @cindex setting the time
13150 @cindex time setting
13151 @cindex appropriate privileges
13153 If given an argument that does not start with @samp{+}, @command{date} sets
13154 the system clock to the date and time specified by that argument (as
13155 described below). You must have appropriate privileges to set the
13156 system clock. The @option{--date} and @option{--set} options may not be
13157 used with such an argument. The @option{--universal} option may be used
13158 with such an argument to indicate that the specified date and time are
13159 relative to Coordinated Universal Time rather than to the local time
13162 The argument must consist entirely of digits, which have the following
13175 first two digits of year (optional)
13177 last two digits of year (optional)
13182 The @option{--set} option also sets the system clock; see the next section.
13185 @node Options for date
13186 @subsection Options for @command{date}
13188 @cindex @command{date} options
13189 @cindex options for @command{date}
13191 The program accepts the following options. Also see @ref{Common options}.
13195 @item -d @var{datestr}
13196 @itemx --date=@var{datestr}
13199 @cindex parsing date strings
13200 @cindex date strings, parsing
13201 @cindex arbitrary date strings, parsing
13204 @opindex next @var{day}
13205 @opindex last @var{day}
13206 Display the date and time specified in @var{datestr} instead of the
13207 current date and time. @var{datestr} can be in almost any common
13208 format. It can contain month names, time zones, @samp{am} and @samp{pm},
13209 @samp{yesterday}, etc. For example, @option{--date="2004-02-27
13210 14:19:13.489392193 +0530"} specifies the instant of time that is
13211 489,392,193 nanoseconds after February 27, 2004 at 2:19:13 PM in a
13212 time zone that is 5 hours and 30 minutes east of @acronym{UTC}.@*
13213 @xref{Date input formats}.
13215 @item -f @var{datefile}
13216 @itemx --file=@var{datefile}
13219 Parse each line in @var{datefile} as with @option{-d} and display the
13220 resulting date and time. If @var{datefile} is @samp{-}, use standard
13221 input. This is useful when you have many dates to process, because the
13222 system overhead of starting up the @command{date} executable many times can
13225 @item -r @var{file}
13226 @itemx --reference=@var{file}
13228 @opindex --reference
13229 Display the date and time of the last modification of @var{file},
13230 instead of the current date and time.
13237 @opindex --rfc-2822
13238 Display the date and time using the format @samp{%a, %d %b %Y %H:%M:%S
13239 %z}, evaluated in the C locale so abbreviations are always in English.
13243 Fri, 09 Sep 2005 13:51:39 -0700
13246 This format conforms to
13247 @uref{ftp://ftp.rfc-editor.org/in-notes/rfc2822.txt, Internet
13248 @acronym{RFCs} 2822} and
13249 @uref{ftp://ftp.rfc-editor.org/in-notes/rfc822.txt, 822}, the
13250 current and previous standards for Internet email.
13252 @item --rfc-3339=@var{timespec}
13253 @opindex --rfc-3339=@var{timespec}
13254 Display the date using a format specified by
13255 @uref{ftp://ftp.rfc-editor.org/in-notes/rfc3339.txt, Internet
13256 @acronym{RFC} 3339}. This is a subset of the @acronym{ISO} 8601
13257 format, except that it also permits applications to use a space rather
13258 than a @samp{T} to separate dates from times. Unlike the other
13259 standard formats, @acronym{RFC} 3339 format is always suitable as
13260 input for the @option{--date} (@option{-d}) and @option{--file}
13261 (@option{-f}) options, regardless of the current locale.
13263 The argument @var{timespec} specifies how much of the time to include.
13264 It can be one of the following:
13268 Print just the full-date, e.g., @samp{2005-09-14}.
13269 This is equivalent to the format @samp{%Y-%m-%d}.
13272 Print the full-date and full-time separated by a space, e.g.,
13273 @samp{2005-09-14 00:56:06+05:30}. The output ends with a numeric
13274 time-offset; here the @samp{+05:30} means that local time is five
13275 hours and thirty minutes east of @acronym{UTC}. This is equivalent to
13276 the format @samp{%Y-%m-%d %H:%M:%S%:z}.
13279 Like @samp{seconds}, but also print nanoseconds, e.g.,
13280 @samp{2005-09-14 00:56:06.998458565+05:30}.
13281 This is equivalent to the format @samp{%Y-%m-%d %H:%M:%S.%N%:z}.
13285 @item -s @var{datestr}
13286 @itemx --set=@var{datestr}
13289 Set the date and time to @var{datestr}. See @option{-d} above.
13296 @opindex --universal
13297 @cindex Coordinated Universal Time
13299 @cindex Greenwich Mean Time
13302 Use Coordinated Universal Time (@acronym{UTC}) by operating as if the
13303 @env{TZ} environment variable were set to the string @samp{UTC0}.
13305 Universal Time is often called ``Greenwich Mean Time'' (@sc{gmt}) for
13306 historical reasons.
13310 @node Examples of date
13311 @subsection Examples of @command{date}
13313 @cindex examples of @command{date}
13315 Here are a few examples. Also see the documentation for the @option{-d}
13316 option in the previous section.
13321 To print the date of the day before yesterday:
13324 date --date='2 days ago'
13328 To print the date of the day three months and one day hence:
13331 date --date='3 months 1 day'
13335 To print the day of year of Christmas in the current year:
13338 date --date='25 Dec' +%j
13342 To print the current full month name and the day of the month:
13348 But this may not be what you want because for the first nine days of
13349 the month, the @samp{%d} expands to a zero-padded two-digit field,
13350 for example @samp{date -d 1may '+%B %d'} will print @samp{May 01}.
13353 To print a date without the leading zero for one-digit days
13354 of the month, you can use the (@acronym{GNU} extension)
13355 @samp{-} flag to suppress
13356 the padding altogether:
13359 date -d 1may '+%B %-d
13363 To print the current date and time in the format required by many
13364 non-@acronym{GNU} versions of @command{date} when setting the system clock:
13367 date +%m%d%H%M%Y.%S
13371 To set the system clock forward by two minutes:
13374 date --set='+2 minutes'
13378 To print the date in @acronym{RFC} 2822 format,
13379 use @samp{date --rfc-2822}. Here is some example output:
13382 Fri, 09 Sep 2005 13:51:39 -0700
13385 @anchor{%s-examples}
13387 To convert a date string to the number of seconds since the epoch
13388 (which is 1970-01-01 00:00:00 UTC), use the @option{--date} option with
13389 the @samp{%s} format. That can be useful in sorting and/or graphing
13390 and/or comparing data by date. The following command outputs the
13391 number of the seconds since the epoch for the time two minutes after the
13395 date --date='1970-01-01 00:02:00 +0000' +%s
13399 If you do not specify time zone information in the date string,
13400 @command{date} uses your computer's idea of the time zone when
13401 interpreting the string. For example, if your computer's time zone is
13402 that of Cambridge, Massachusetts, which was then 5 hours (i.e., 18,000
13403 seconds) behind UTC:
13406 # local time zone used
13407 date --date='1970-01-01 00:02:00' +%s
13412 If you're sorting or graphing dated data, your raw date values may be
13413 represented as seconds since the epoch. But few people can look at
13414 the date @samp{946684800} and casually note ``Oh, that's the first second
13415 of the year 2000 in Greenwich, England.''
13418 date --date='2000-01-01 UTC' +%s
13422 An alternative is to use the @option{--utc} (@option{-u}) option.
13423 Then you may omit @samp{UTC} from the date string. Although this
13424 produces the same result for @samp{%s} and many other format sequences,
13425 with a time zone offset different from zero, it would give a different
13426 result for zone-dependent formats like @samp{%z}.
13429 date -u --date=2000-01-01 +%s
13433 To convert such an unwieldy number of seconds back to
13434 a more readable form, use a command like this:
13437 # local time zone used
13438 date -d '1970-01-01 UTC 946684800 seconds' +"%Y-%m-%d %T %z"
13439 1999-12-31 19:00:00 -0500
13442 Or if you do not mind depending on the @samp{@@} feature present since
13443 coreutils 5.3.0, you could shorten this to:
13446 date -d @@946684800 +"%F %T %z"
13447 1999-12-31 19:00:00 -0500
13450 Often it is better to output UTC-relative date and time:
13453 date -u -d '1970-01-01 946684800 seconds' +"%Y-%m-%d %T %z"
13454 2000-01-01 00:00:00 +0000
13460 @node arch invocation
13461 @section @command{arch}: Print machine hardware name
13464 @cindex print machine hardware name
13465 @cindex system information, printing
13467 @command{arch} prints the machine hardware name,
13468 and is equivalent to @samp{uname -m}.
13472 arch [@var{option}]
13475 The program accepts the @ref{Common options} only.
13480 @node uname invocation
13481 @section @command{uname}: Print system information
13484 @cindex print system information
13485 @cindex system information, printing
13487 @command{uname} prints information about the machine and operating system
13488 it is run on. If no options are given, @command{uname} acts as if the
13489 @option{-s} option were given. Synopsis:
13492 uname [@var{option}]@dots{}
13495 If multiple options or @option{-a} are given, the selected information is
13496 printed in this order:
13499 @var{kernel-name} @var{nodename} @var{kernel-release} @var{kernel-version}
13500 @var{machine} @var{processor} @var{hardware-platform} @var{operating-system}
13503 The information may contain internal spaces, so such output cannot be
13504 parsed reliably. In the following example, @var{release} is
13505 @samp{2.2.18ss.e820-bda652a #4 SMP Tue Jun 5 11:24:08 PDT 2001}:
13509 @result{} Linux dum 2.2.18 #4 SMP Tue Jun 5 11:24:08 PDT 2001 i686 unknown unknown GNU/Linux
13513 The program accepts the following options. Also see @ref{Common options}.
13521 Print all of the below information, except omit the processor type
13522 and the hardware platform name if they are unknown.
13525 @itemx --hardware-platform
13527 @opindex --hardware-platform
13528 @cindex implementation, hardware
13529 @cindex hardware platform
13530 @cindex platform, hardware
13531 Print the hardware platform name
13532 (sometimes called the hardware implementation).
13533 Print @samp{unknown} if the kernel does not make this information
13534 easily available, as is the case with Linux kernels.
13540 @cindex machine type
13541 @cindex hardware class
13542 @cindex hardware type
13543 Print the machine hardware name (sometimes called the hardware class
13549 @opindex --nodename
13552 @cindex network node name
13553 Print the network node hostname.
13558 @opindex --processor
13559 @cindex host processor type
13560 Print the processor type (sometimes called the instruction set
13561 architecture or ISA).
13562 Print @samp{unknown} if the kernel does not make this information
13563 easily available, as is the case with Linux kernels.
13566 @itemx --operating-system
13568 @opindex --operating-system
13569 @cindex operating system name
13570 Print the name of the operating system.
13573 @itemx --kernel-release
13575 @opindex --kernel-release
13576 @cindex kernel release
13577 @cindex release of kernel
13578 Print the kernel release.
13581 @itemx --kernel-name
13583 @opindex --kernel-name
13584 @cindex kernel name
13585 @cindex name of kernel
13586 Print the kernel name.
13587 @acronym{POSIX} 1003.1-2001 (@pxref{Standards conformance}) calls this
13588 ``the implementation of the operating system'', because the
13589 @acronym{POSIX} specification itself has no notion of ``kernel''.
13590 The kernel name might be the same as the operating system name printed
13591 by the @option{-o} or @option{--operating-system} option, but it might
13592 differ. Some operating systems (e.g., FreeBSD, HP-UX) have the same
13593 name as their underlying kernels; others (e.g., GNU/Linux, Solaris)
13597 @itemx --kernel-version
13599 @opindex --kernel-version
13600 @cindex kernel version
13601 @cindex version of kernel
13602 Print the kernel version.
13609 @node hostname invocation
13610 @section @command{hostname}: Print or set system name
13613 @cindex setting the hostname
13614 @cindex printing the hostname
13615 @cindex system name, printing
13616 @cindex appropriate privileges
13618 With no arguments, @command{hostname} prints the name of the current host
13619 system. With one argument, it sets the current host name to the
13620 specified string. You must have appropriate privileges to set the host
13624 hostname [@var{name}]
13627 The only options are @option{--help} and @option{--version}. @xref{Common
13633 @node hostid invocation
13634 @section @command{hostid}: Print numeric host identifier.
13637 @cindex printing the host identifier
13639 @command{hostid} prints the numeric identifier of the current host
13640 in hexadecimal. This command accepts no arguments.
13641 The only options are @option{--help} and @option{--version}.
13642 @xref{Common options}.
13644 For example, here's what it prints on one system I use:
13651 On that system, the 32-bit quantity happens to be closely
13652 related to the system's Internet address, but that isn't always
13657 @node uptime invocation
13658 @section @command{uptime}: Print system uptime and load
13661 @cindex printing the system uptime and load
13663 @command{uptime} prints the current time, the system's uptime, the
13664 number of logged-in users and the current load average.
13666 If an argument is specified, it is used as the file to be read
13667 to discover how many users are logged in. If no argument is
13668 specified, a system default is used (@command{uptime --help} indicates
13669 the default setting).
13671 The only options are @option{--help} and @option{--version}.
13672 @xref{Common options}.
13674 For example, here's what it prints right now on one system I use:
13678 14:07 up 3:35, 3 users, load average: 1.39, 1.15, 1.04
13681 The precise method of calculation of load average varies somewhat
13682 between systems. Some systems calculate it as the average number of
13683 runnable processes over the last 1, 5 and 15 minutes, but some systems
13684 also include processes in the uninterruptible sleep state (that is,
13685 those processes which are waiting for disk I/O). The Linux kernel
13686 includes uninterruptible processes.
13688 @node Modified command invocation
13689 @chapter Modified command invocation
13691 @cindex modified command invocation
13692 @cindex invocation of commands, modified
13693 @cindex commands for invoking other commands
13695 This section describes commands that run other commands in some context
13696 different than the current one: a modified environment, as a different
13700 * chroot invocation:: Modify the root directory.
13701 * env invocation:: Modify environment variables.
13702 * nice invocation:: Modify niceness.
13703 * nohup invocation:: Immunize to hangups.
13704 * su invocation:: Modify user and group ID.
13705 * timeout invocation:: Run with time limit.
13709 @node chroot invocation
13710 @section @command{chroot}: Run a command with a different root directory
13713 @cindex running a program in a specified root directory
13714 @cindex root directory, running a program in a specified
13716 @command{chroot} runs a command with a specified root directory.
13717 On many systems, only the super-user can do this.@footnote{However,
13718 some systems (e.g., FreeBSD) can be configured to allow certain regular
13719 users to use the @code{chroot} system call, and hence to run this program.
13720 Also, on Cygwin, anyone can run the @command{chroot} command, because the
13721 underlying function is non-privileged due to lack of support in MS-Windows.}
13725 chroot @var{newroot} [@var{command} [@var{args}]@dots{}]
13726 chroot @var{option}
13729 Ordinarily, file names are looked up starting at the root of the
13730 directory structure, i.e., @file{/}. @command{chroot} changes the root to
13731 the directory @var{newroot} (which must exist) and then runs
13732 @var{command} with optional @var{args}. If @var{command} is not
13733 specified, the default is the value of the @env{SHELL} environment
13734 variable or @command{/bin/sh} if not set, invoked with the @option{-i} option.
13735 @var{command} must not be a special built-in utility
13736 (@pxref{Special built-in utilities}).
13738 The only options are @option{--help} and @option{--version}. @xref{Common
13739 options}. Options must precede operands.
13741 Here are a few tips to help avoid common problems in using chroot.
13742 To start with a simple example, make @var{command} refer to a statically
13743 linked binary. If you were to use a dynamically linked executable, then
13744 you'd have to arrange to have the shared libraries in the right place under
13745 your new root directory.
13747 For example, if you create a statically linked @command{ls} executable,
13748 and put it in @file{/tmp/empty}, you can run this command as root:
13751 $ chroot /tmp/empty /ls -Rl /
13754 Then you'll see output like this:
13759 -rwxr-xr-x 1 0 0 1041745 Aug 16 11:17 ls
13762 If you want to use a dynamically linked executable, say @command{bash},
13763 then first run @samp{ldd bash} to see what shared objects it needs.
13764 Then, in addition to copying the actual binary, also copy the listed
13765 files to the required positions under your intended new root directory.
13766 Finally, if the executable requires any other files (e.g., data, state,
13767 device files), copy them into place, too.
13769 @cindex exit status of @command{chroot}
13773 1 if @command{chroot} itself fails
13774 126 if @var{command} is found but cannot be invoked
13775 127 if @var{command} cannot be found
13776 the exit status of @var{command} otherwise
13780 @node env invocation
13781 @section @command{env}: Run a command in a modified environment
13784 @cindex environment, running a program in a modified
13785 @cindex modified environment, running a program in a
13786 @cindex running a program in a modified environment
13788 @command{env} runs a command with a modified environment. Synopses:
13791 env [@var{option}]@dots{} [@var{name}=@var{value}]@dots{} @c
13792 [@var{command} [@var{args}]@dots{}]
13796 Operands of the form @samp{@var{variable}=@var{value}} set
13797 the environment variable @var{variable} to value @var{value}.
13798 @var{value} may be empty (@samp{@var{variable}=}). Setting a variable
13799 to an empty value is different from unsetting it.
13800 These operands are evaluated left-to-right, so if two operands
13801 mention the same variable the earlier is ignored.
13803 Environment variable names can be empty, and can contain any
13804 characters other than @samp{=} and the null character (@acronym{ASCII}
13805 @sc{nul}). However, it is wise to limit yourself to names that
13806 consist solely of underscores, digits, and @acronym{ASCII} letters,
13807 and that begin with a non-digit, as applications like the shell do not
13808 work well with other names.
13811 The first operand that does not contain the character @samp{=}
13812 specifies the program to invoke; it is
13813 searched for according to the @env{PATH} environment variable. Any
13814 remaining arguments are passed as arguments to that program.
13815 The program should not be a special built-in utility
13816 (@pxref{Special built-in utilities}).
13818 @cindex environment, printing
13820 If no command name is specified following the environment
13821 specifications, the resulting environment is printed. This is like
13822 specifying the @command{printenv} program.
13824 The program accepts the following options. Also see @ref{Common options}.
13825 Options must precede operands.
13829 @item -u @var{name}
13830 @itemx --unset=@var{name}
13833 Remove variable @var{name} from the environment, if it was in the
13838 @itemx --ignore-environment
13841 @opindex --ignore-environment
13842 Start with an empty environment, ignoring the inherited environment.
13846 @cindex exit status of @command{env}
13850 0 if no @var{command} is specified and the environment is output
13851 1 if @command{env} itself fails
13852 126 if @var{command} is found but cannot be invoked
13853 127 if @var{command} cannot be found
13854 the exit status of @var{command} otherwise
13858 @node nice invocation
13859 @section @command{nice}: Run a command with modified niceness
13863 @cindex scheduling, affecting
13864 @cindex appropriate privileges
13866 @command{nice} prints or modifies a process's @dfn{niceness},
13867 a parameter that affects whether the process is scheduled favorably.
13871 nice [@var{option}]@dots{} [@var{command} [@var{arg}]@dots{}]
13874 If no arguments are given, @command{nice} prints the current niceness.
13875 Otherwise, @command{nice} runs the given @var{command} with its
13876 niceness adjusted. By default, its niceness is incremented by 10.
13878 Niceness values range at least from @minus{}20 (process has high priority
13879 and gets more resources, thus slowing down other processes) through 19
13880 (process has lower priority and runs slowly itself, but has less impact
13881 on the speed of other running processes). Some systems
13882 may have a wider range of nicenesses; conversely, other systems may
13883 enforce more restrictive limits. An attempt to set the niceness
13884 outside the supported range is treated as an attempt to use the
13885 minimum or maximum supported value.
13887 A niceness should not be confused with a scheduling priority, which
13888 lets applications determine the order in which threads are scheduled
13889 to run. Unlike a priority, a niceness is merely advice to the
13890 scheduler, which the scheduler is free to ignore. Also, as a point of
13891 terminology, @acronym{POSIX} defines the behavior of @command{nice} in
13892 terms of a @dfn{nice value}, which is the nonnegative difference
13893 between a niceness and the minimum niceness. Though @command{nice}
13894 conforms to @acronym{POSIX}, its documentation and diagnostics use the
13895 term ``niceness'' for compatibility with historical practice.
13897 @var{command} must not be a special built-in utility (@pxref{Special
13898 built-in utilities}).
13900 @cindex conflicts with shell built-ins
13901 @cindex built-in shell commands, conflicts with
13902 Because many shells have a built-in @command{nice} command, using an
13903 unadorned @command{nice} in a script or interactively may get you
13904 different functionality than that described here.
13906 The program accepts the following option. Also see @ref{Common options}.
13907 Options must precede operands.
13910 @item -n @var{adjustment}
13911 @itemx --adjustment=@var{adjustment}
13913 @opindex --adjustment
13914 Add @var{adjustment} instead of 10 to the command's niceness. If
13915 @var{adjustment} is negative and you lack appropriate privileges,
13916 @command{nice} issues a warning but otherwise acts as if you specified
13919 For compatibility @command{nice} also supports an obsolete
13920 option syntax @option{-@var{adjustment}}. New scripts should use
13921 @option{-n @var{adjustment}} instead.
13925 @cindex exit status of @command{nice}
13929 0 if no @var{command} is specified and the niceness is output
13930 1 if @command{nice} itself fails
13931 126 if @var{command} is found but cannot be invoked
13932 127 if @var{command} cannot be found
13933 the exit status of @var{command} otherwise
13936 It is sometimes useful to run a non-interactive program with reduced niceness.
13939 $ nice factor 4611686018427387903
13942 Since @command{nice} prints the current niceness,
13943 you can invoke it through itself to demonstrate how it works.
13945 The default behavior is to increase the niceness by @samp{10}:
13956 The @var{adjustment} is relative to the current niceness. In the
13957 next example, the first @command{nice} invocation runs the second one
13958 with niceness 10, and it in turn runs the final one with a niceness
13962 $ nice nice -n 3 nice
13966 Specifying a niceness larger than the supported range
13967 is the same as specifying the maximum supported value:
13970 $ nice -n 10000000000 nice
13974 Only a privileged user may run a process with lower niceness:
13978 nice: cannot set niceness: Permission denied
13980 $ sudo nice -n -1 nice
13985 @node nohup invocation
13986 @section @command{nohup}: Run a command immune to hangups
13989 @cindex hangups, immunity to
13990 @cindex immunity to hangups
13991 @cindex logging out and continuing to run
13994 @command{nohup} runs the given @var{command} with hangup signals ignored,
13995 so that the command can continue running in the background after you log
13999 nohup @var{command} [@var{arg}]@dots{}
14002 If standard input is a terminal, it is redirected from
14003 @file{/dev/null} so that terminal sessions do not mistakenly consider
14004 the terminal to be used by the command. This is a @acronym{GNU}
14005 extension; programs intended to be portable to non-@acronym{GNU} hosts
14006 should use @samp{nohup @var{command} [@var{arg}]@dots{} </dev/null}
14010 If standard output is a terminal, the command's standard output is appended
14011 to the file @file{nohup.out}; if that cannot be written to, it is appended
14012 to the file @file{$HOME/nohup.out}; and if that cannot be written to, the
14013 command is not run.
14014 Any @file{nohup.out} or @file{$HOME/nohup.out} file created by
14015 @command{nohup} is made readable and writable only to the user,
14016 regardless of the current umask settings.
14018 If standard error is a terminal, it is normally redirected to the same file
14019 descriptor as the (possibly-redirected) standard output.
14020 However, if standard output is closed, standard error terminal output
14021 is instead appended to the file @file{nohup.out} or
14022 @file{$HOME/nohup.out} as above.
14024 To capture the command's output to a file other than @file{nohup.out}
14025 you can redirect it. For example, to capture the output of
14029 nohup make > make.log
14032 @command{nohup} does not automatically put the command it runs in the
14033 background; you must do that explicitly, by ending the command line
14034 with an @samp{&}. Also, @command{nohup} does not alter the
14035 niceness of @var{command}; use @command{nice} for that,
14036 e.g., @samp{nohup nice @var{command}}.
14038 @var{command} must not be a special built-in utility (@pxref{Special
14039 built-in utilities}).
14041 The only options are @option{--help} and @option{--version}. @xref{Common
14042 options}. Options must precede operands.
14044 @cindex exit status of @command{nohup}
14048 126 if @var{command} is found but cannot be invoked
14049 127 if @command{nohup} itself fails or if @var{command} cannot be found
14050 the exit status of @var{command} otherwise
14054 @node su invocation
14055 @section @command{su}: Run a command with substitute user and group ID
14058 @cindex substitute user and group IDs
14059 @cindex user ID, switching
14060 @cindex super-user, becoming
14061 @cindex root, becoming
14063 @command{su} allows one user to temporarily become another user. It runs a
14064 command (often an interactive shell) with the real and effective user
14065 ID, group ID, and supplemental groups of a given @var{user}. Synopsis:
14068 su [@var{option}]@dots{} [@var{user} [@var{arg}]@dots{}]
14071 @cindex passwd entry, and @command{su} shell
14073 @flindex /etc/passwd
14074 If no @var{user} is given, the default is @code{root}, the super-user.
14075 The shell to use is taken from @var{user}'s @code{passwd} entry, or
14076 @file{/bin/sh} if none is specified there. If @var{user} has a
14077 password, @command{su} prompts for the password unless run by a user with
14078 effective user ID of zero (the super-user).
14084 @cindex login shell
14085 By default, @command{su} does not change the current directory.
14086 It sets the environment variables @env{HOME} and @env{SHELL}
14087 from the password entry for @var{user}, and if @var{user} is not
14088 the super-user, sets @env{USER} and @env{LOGNAME} to @var{user}.
14089 By default, the shell is not a login shell.
14091 Any additional @var{arg}s are passed as additional arguments to the
14094 @cindex @option{-su}
14095 GNU @command{su} does not treat @file{/bin/sh} or any other shells specially
14096 (e.g., by setting @code{argv[0]} to @option{-su}, passing @option{-c} only
14097 to certain shells, etc.).
14100 @command{su} can optionally be compiled to use @code{syslog} to report
14101 failed, and optionally successful, @command{su} attempts. (If the system
14102 supports @code{syslog}.) However, GNU @command{su} does not check if the
14103 user is a member of the @code{wheel} group; see below.
14105 The program accepts the following options. Also see @ref{Common options}.
14108 @item -c @var{command}
14109 @itemx --command=@var{command}
14112 Pass @var{command}, a single command line to run, to the shell with
14113 a @option{-c} option instead of starting an interactive shell.
14120 @cindex file name pattern expansion, disabled
14121 @cindex globbing, disabled
14122 Pass the @option{-f} option to the shell. This probably only makes sense
14123 if the shell run is @command{csh} or @command{tcsh}, for which the @option{-f}
14124 option prevents reading the startup file (@file{.cshrc}). With
14125 Bourne-like shells, the @option{-f} option disables file name pattern
14126 expansion (globbing), which is not likely to be useful.
14134 @c other variables already indexed above
14137 @cindex login shell, creating
14138 Make the shell a login shell. This means the following. Unset all
14139 environment variables except @env{TERM}, @env{HOME}, and @env{SHELL}
14140 (which are set as described above), and @env{USER} and @env{LOGNAME}
14141 (which are set, even for the super-user, as described above), and set
14142 @env{PATH} to a compiled-in default value. Change to @var{user}'s home
14143 directory. Prepend @samp{-} to the shell's name, intended to make it
14144 read its login startup file(s).
14148 @itemx --preserve-environment
14151 @opindex --preserve-environment
14152 @cindex environment, preserving
14153 @flindex /etc/shells
14154 @cindex restricted shell
14155 Do not change the environment variables @env{HOME}, @env{USER},
14156 @env{LOGNAME}, or @env{SHELL}. Run the shell given in the environment
14157 variable @env{SHELL} instead of the shell from @var{user}'s passwd
14158 entry, unless the user running @command{su} is not the super-user and
14159 @var{user}'s shell is restricted. A @dfn{restricted shell} is one that
14160 is not listed in the file @file{/etc/shells}, or in a compiled-in list
14161 if that file does not exist. Parts of what this option does can be
14162 overridden by @option{--login} and @option{--shell}.
14164 @item -s @var{shell}
14165 @itemx --shell=@var{shell}
14168 Run @var{shell} instead of the shell from @var{user}'s passwd entry,
14169 unless the user running @command{su} is not the super-user and @var{user}'s
14170 shell is restricted (see @option{-m} just above).
14174 @cindex exit status of @command{su}
14178 1 if @command{su} itself fails
14179 126 if subshell is found but cannot be invoked
14180 127 if subshell cannot be found
14181 the exit status of the subshell otherwise
14184 @cindex wheel group, not supported
14185 @cindex group wheel, not supported
14187 @subsection Why GNU @command{su} does not support the @samp{wheel} group
14189 (This section is by Richard Stallman.)
14193 Sometimes a few of the users try to hold total power over all the
14194 rest. For example, in 1984, a few users at the MIT AI lab decided to
14195 seize power by changing the operator password on the Twenex system and
14196 keeping it secret from everyone else. (I was able to thwart this coup
14197 and give power back to the users by patching the kernel, but I
14198 wouldn't know how to do that in Unix.)
14200 However, occasionally the rulers do tell someone. Under the usual
14201 @command{su} mechanism, once someone learns the root password who
14202 sympathizes with the ordinary users, he or she can tell the rest. The
14203 ``wheel group'' feature would make this impossible, and thus cement the
14204 power of the rulers.
14206 I'm on the side of the masses, not that of the rulers. If you are
14207 used to supporting the bosses and sysadmins in whatever they do, you
14208 might find this idea strange at first.
14211 @node timeout invocation
14212 @section @command{timeout}: Run a command with a time limit
14216 @cindex run commands with bounded time
14218 @command{timeout} runs the given @var{command} and kills it if it is
14219 still running after the specified time interval. Synopsis:
14222 timeout [@var{option}] @var{number}[smhd] @var{command} [@var{arg}]@dots{}
14226 @var{number} is an integer followed by an optional unit; the default
14227 is seconds. The units are:
14240 @var{command} must not be a special built-in utility (@pxref{Special
14241 built-in utilities}).
14243 The program accepts the following option. Also see @ref{Common options}.
14244 Options must precede operands.
14247 @item -s @var{signal}
14248 @itemx --signal=@var{signal}
14251 Send this @var{signal} to @var{command} on timeout, rather than the
14252 default @samp{TERM} signal. @var{signal} may be a name like @samp{HUP}
14253 or a number. Also see @xref{Signal specifications}.
14257 @cindex exit status of @command{timeout}
14261 124 if @var{command} times out
14262 125 if @command{timeout} itself fails
14263 126 if @var{command} is found but cannot be invoked
14264 127 if @var{command} cannot be found
14265 the exit status of @var{command} otherwise
14269 @node Process control
14270 @chapter Process control
14272 @cindex processes, commands for controlling
14273 @cindex commands for controlling processes
14276 * kill invocation:: Sending a signal to processes.
14280 @node kill invocation
14281 @section @command{kill}: Send a signal to processes
14284 @cindex send a signal to processes
14286 The @command{kill} command sends a signal to processes, causing them
14287 to terminate or otherwise act upon receiving the signal in some way.
14288 Alternatively, it lists information about signals. Synopses:
14291 kill [-s @var{signal} | --signal @var{signal} | -@var{signal}] @var{pid}@dots{}
14292 kill [-l | --list | -t | --table] [@var{signal}]@dots{}
14295 The first form of the @command{kill} command sends a signal to all
14296 @var{pid} arguments. The default signal to send if none is specified
14297 is @samp{TERM}. The special signal number @samp{0} does not denote a
14298 valid signal, but can be used to test whether the @var{pid} arguments
14299 specify processes to which a signal could be sent.
14301 If @var{pid} is positive, the signal is sent to the process with the
14302 process ID @var{pid}. If @var{pid} is zero, the signal is sent to all
14303 processes in the process group of the current process. If @var{pid}
14304 is @minus{}1, the signal is sent to all processes for which the user has
14305 permission to send a signal. If @var{pid} is less than @minus{}1, the signal
14306 is sent to all processes in the process group that equals the absolute
14307 value of @var{pid}.
14309 If @var{pid} is not positive, a system-dependent set of system
14310 processes is excluded from the list of processes to which the signal
14313 If a negative @var{PID} argument is desired as the first one, it
14314 should be preceded by @option{--}. However, as a common extension to
14315 @acronym{POSIX}, @option{--} is not required with @samp{kill
14316 -@var{signal} -@var{pid}}. The following commands are equivalent:
14325 The first form of the @command{kill} command succeeds if every @var{pid}
14326 argument specifies at least one process that the signal was sent to.
14328 The second form of the @command{kill} command lists signal information.
14329 Either the @option{-l} or @option{--list} option, or the @option{-t}
14330 or @option{--table} option must be specified. Without any
14331 @var{signal} argument, all supported signals are listed. The output
14332 of @option{-l} or @option{--list} is a list of the signal names, one
14333 per line; if @var{signal} is already a name, the signal number is
14334 printed instead. The output of @option{-t} or @option{--table} is a
14335 table of signal numbers, names, and descriptions. This form of the
14336 @command{kill} command succeeds if all @var{signal} arguments are valid
14337 and if there is no output error.
14339 The @command{kill} command also supports the @option{--help} and
14340 @option{--version} options. @xref{Common options}.
14342 A @var{signal} may be a signal name like @samp{HUP}, or a signal
14343 number like @samp{1}, or an exit status of a process terminated by the
14344 signal. A signal name can be given in canonical form or prefixed by
14345 @samp{SIG}. The case of the letters is ignored, except for the
14346 @option{-@var{signal}} option which must use upper case to avoid
14347 ambiguity with lower case option letters. For a list of supported
14348 signal names and numbers see @xref{Signal specifications}.
14353 @cindex delaying commands
14354 @cindex commands for delaying
14356 @c Perhaps @command{wait} or other commands should be described here also?
14359 * sleep invocation:: Delay for a specified time.
14363 @node sleep invocation
14364 @section @command{sleep}: Delay for a specified time
14367 @cindex delay for a specified time
14369 @command{sleep} pauses for an amount of time specified by the sum of
14370 the values of the command line arguments.
14374 sleep @var{number}[smhd]@dots{}
14378 Each argument is a number followed by an optional unit; the default
14379 is seconds. The units are:
14392 Historical implementations of @command{sleep} have required that
14393 @var{number} be an integer, and only accepted a single argument
14394 without a suffix. However, GNU @command{sleep} accepts
14395 arbitrary floating point numbers (using a period before any fractional
14398 The only options are @option{--help} and @option{--version}. @xref{Common
14404 @node Numeric operations
14405 @chapter Numeric operations
14407 @cindex numeric operations
14408 These programs do numerically-related operations.
14411 * factor invocation:: Show factors of numbers.
14412 * seq invocation:: Print sequences of numbers.
14416 @node factor invocation
14417 @section @command{factor}: Print prime factors
14420 @cindex prime factors
14422 @command{factor} prints prime factors. Synopses:
14425 factor [@var{number}]@dots{}
14426 factor @var{option}
14429 If no @var{number} is specified on the command line, @command{factor} reads
14430 numbers from standard input, delimited by newlines, tabs, or spaces.
14432 The @command{factor} command supports only a small number of options:
14436 Print a short help on standard output, then exit without further
14440 Always use unlimited precision arithmetic via the GNU MP library.
14441 By default, @command{factor} selects between using GNU MP and using
14442 native operations on the basis of the length of the number to be factored.
14445 Always use limited-precision native operations, not GNU MP.
14446 This causes @command{factor} to fail for larger inputs.
14449 Print the program version on standard output, then exit without further
14453 Factoring the product of the eighth and ninth Mersenne primes
14454 takes about 30 milliseconds of CPU time on a 2.2 GHz Athlon.
14457 M8=`echo 2^31-1|bc` ; M9=`echo 2^61-1|bc`
14458 /usr/bin/time -f '%U' factor $(echo "$M8 * $M9" | bc)
14459 4951760154835678088235319297: 2147483647 2305843009213693951
14463 Similarly, factoring the eighth Fermat number @math{2^{256}+1} takes
14464 about 20 seconds on the same machine.
14466 Factoring large prime numbers is, in general, hard. The Pollard Rho
14467 algorithm used by @command{factor} is particularly effective for
14468 numbers with relatively small factors. If you wish to factor large
14469 numbers which do not have small factors (for example, numbers which
14470 are the product of two large primes), other methods are far better.
14472 If @command{factor} is built without using GNU MP, only
14473 single-precision arithmetic is available, and so large numbers
14474 (typically @math{2^{64}} and above) will not be supported. The single-precision
14475 code uses an algorithm which is designed for factoring smaller
14481 @node seq invocation
14482 @section @command{seq}: Print numeric sequences
14485 @cindex numeric sequences
14486 @cindex sequence of numbers
14488 @command{seq} prints a sequence of numbers to standard output. Synopses:
14491 seq [@var{option}]@dots{} @var{last}
14492 seq [@var{option}]@dots{} @var{first} @var{last}
14493 seq [@var{option}]@dots{} @var{first} @var{increment} @var{last}
14496 @command{seq} prints the numbers from @var{first} to @var{last} by
14497 @var{increment}. By default, each number is printed on a separate line.
14498 When @var{increment} is not specified, it defaults to @samp{1},
14499 even when @var{first} is larger than @var{last}.
14500 @var{first} also defaults to @samp{1}. So @code{seq 1} prints
14501 @samp{1}, but @code{seq 0} and @code{seq 10 5} produce no output.
14502 Floating-point numbers
14503 may be specified (using a period before any fractional digits).
14505 The program accepts the following options. Also see @ref{Common options}.
14506 Options must precede operands.
14509 @item -f @var{format}
14510 @itemx --format=@var{format}
14511 @opindex -f @var{format}
14512 @opindex --format=@var{format}
14513 @cindex formatting of numbers in @command{seq}
14514 Print all numbers using @var{format}.
14515 @var{format} must contain exactly one of the @samp{printf}-style
14516 floating point conversion specifications @samp{%a}, @samp{%e},
14517 @samp{%f}, @samp{%g}, @samp{%A}, @samp{%E}, @samp{%F}, @samp{%G}.
14518 The @samp{%} may be followed by zero or more flags taken from the set
14519 @samp{-+#0 '}, then an optional width containing one or more digits,
14520 then an optional precision consisting of a @samp{.} followed by zero
14521 or more digits. @var{format} may also contain any number of @samp{%%}
14522 conversion specifications. All conversion specifications have the
14523 same meaning as with @samp{printf}.
14525 The default format is derived from @var{first}, @var{step}, and
14526 @var{last}. If these all use a fixed point decimal representation,
14527 the default format is @samp{%.@var{p}f}, where @var{p} is the minimum
14528 precision that can represent the output numbers exactly. Otherwise,
14529 the default format is @samp{%g}.
14531 @item -s @var{string}
14532 @itemx --separator=@var{string}
14533 @cindex separator for numbers in @command{seq}
14534 Separate numbers with @var{string}; default is a newline.
14535 The output always terminates with a newline.
14538 @itemx --equal-width
14539 Print all numbers with the same width, by padding with leading zeros.
14540 @var{first}, @var{step}, and @var{last} should all use a fixed point
14541 decimal representation.
14542 (To have other kinds of padding, use @option{--format}).
14546 You can get finer-grained control over output with @option{-f}:
14549 $ seq -f '(%9.2E)' -9e5 1.1e6 1.3e6
14555 If you want hexadecimal integer output, you can use @command{printf}
14556 to perform the conversion:
14559 $ printf '%x\n' `seq 1048575 1024 1050623`
14565 For very long lists of numbers, use xargs to avoid
14566 system limitations on the length of an argument list:
14569 $ seq 1000000 | xargs printf '%x\n' | tail -n 3
14575 To generate octal output, use the printf @code{%o} format instead
14578 On most systems, seq can produce whole-number output for values up to
14579 at least @math{2^{53}}. Larger integers are approximated. The details
14580 differ depending on your floating-point implementation, but a common
14581 case is that @command{seq} works with integers through @math{2^{64}},
14582 and larger integers may not be numerically correct:
14585 $ seq 18446744073709551616 1 18446744073709551618
14586 18446744073709551616
14587 18446744073709551616
14588 18446744073709551618
14591 Be careful when using @command{seq} with outlandish values: otherwise
14592 you may see surprising results, as @command{seq} uses floating point
14593 internally. For example, on the x86 platform, where the internal
14594 representation uses a 64-bit fraction, the command:
14597 seq 1 0.0000000000000000001 1.0000000000000000009
14600 outputs 1.0000000000000000007 twice and skips 1.0000000000000000008.
14605 @node File permissions
14606 @chapter File permissions
14609 @include getdate.texi
14613 @node Opening the software toolbox
14614 @chapter Opening the Software Toolbox
14616 An earlier version of this chapter appeared in
14617 @uref{http://www.linuxjournal.com/article.php?sid=2762, the
14618 @cite{What's GNU?} column of @cite{Linux Journal}, 2 (June, 1994)}.
14619 It was written by Arnold Robbins.
14622 * Toolbox introduction:: Toolbox introduction
14623 * I/O redirection:: I/O redirection
14624 * The who command:: The @command{who} command
14625 * The cut command:: The @command{cut} command
14626 * The sort command:: The @command{sort} command
14627 * The uniq command:: The @command{uniq} command
14628 * Putting the tools together:: Putting the tools together
14632 @node Toolbox introduction
14633 @unnumberedsec Toolbox Introduction
14635 This month's column is only peripherally related to the GNU Project, in
14636 that it describes a number of the GNU tools on your GNU/Linux system and how they
14637 might be used. What it's really about is the ``Software Tools'' philosophy
14638 of program development and usage.
14640 The software tools philosophy was an important and integral concept
14641 in the initial design and development of Unix (of which Linux and GNU are
14642 essentially clones). Unfortunately, in the modern day press of
14643 Internetworking and flashy GUIs, it seems to have fallen by the
14644 wayside. This is a shame, since it provides a powerful mental model
14645 for solving many kinds of problems.
14647 Many people carry a Swiss Army knife around in their pants pockets (or
14648 purse). A Swiss Army knife is a handy tool to have: it has several knife
14649 blades, a screwdriver, tweezers, toothpick, nail file, corkscrew, and perhaps
14650 a number of other things on it. For the everyday, small miscellaneous jobs
14651 where you need a simple, general purpose tool, it's just the thing.
14653 On the other hand, an experienced carpenter doesn't build a house using
14654 a Swiss Army knife. Instead, he has a toolbox chock full of specialized
14655 tools---a saw, a hammer, a screwdriver, a plane, and so on. And he knows
14656 exactly when and where to use each tool; you won't catch him hammering nails
14657 with the handle of his screwdriver.
14659 The Unix developers at Bell Labs were all professional programmers and trained
14660 computer scientists. They had found that while a one-size-fits-all program
14661 might appeal to a user because there's only one program to use, in practice
14666 difficult to write,
14669 difficult to maintain and
14673 difficult to extend to meet new situations.
14676 Instead, they felt that programs should be specialized tools. In short, each
14677 program ``should do one thing well.'' No more and no less. Such programs are
14678 simpler to design, write, and get right---they only do one thing.
14680 Furthermore, they found that with the right machinery for hooking programs
14681 together, that the whole was greater than the sum of the parts. By combining
14682 several special purpose programs, you could accomplish a specific task
14683 that none of the programs was designed for, and accomplish it much more
14684 quickly and easily than if you had to write a special purpose program.
14685 We will see some (classic) examples of this further on in the column.
14686 (An important additional point was that, if necessary, take a detour
14687 and build any software tools you may need first, if you don't already
14688 have something appropriate in the toolbox.)
14690 @node I/O redirection
14691 @unnumberedsec I/O Redirection
14693 Hopefully, you are familiar with the basics of I/O redirection in the
14694 shell, in particular the concepts of ``standard input,'' ``standard output,''
14695 and ``standard error''. Briefly, ``standard input'' is a data source, where
14696 data comes from. A program should not need to either know or care if the
14697 data source is a disk file, a keyboard, a magnetic tape, or even a punched
14698 card reader. Similarly, ``standard output'' is a data sink, where data goes
14699 to. The program should neither know nor care where this might be.
14700 Programs that only read their standard input, do something to the data,
14701 and then send it on, are called @dfn{filters}, by analogy to filters in a
14704 With the Unix shell, it's very easy to set up data pipelines:
14707 program_to_create_data | filter1 | ... | filterN > final.pretty.data
14710 We start out by creating the raw data; each filter applies some successive
14711 transformation to the data, until by the time it comes out of the pipeline,
14712 it is in the desired form.
14714 This is fine and good for standard input and standard output. Where does the
14715 standard error come in to play? Well, think about @command{filter1} in
14716 the pipeline above. What happens if it encounters an error in the data it
14717 sees? If it writes an error message to standard output, it will just
14718 disappear down the pipeline into @command{filter2}'s input, and the
14719 user will probably never see it. So programs need a place where they can send
14720 error messages so that the user will notice them. This is standard error,
14721 and it is usually connected to your console or window, even if you have
14722 redirected standard output of your program away from your screen.
14724 For filter programs to work together, the format of the data has to be
14725 agreed upon. The most straightforward and easiest format to use is simply
14726 lines of text. Unix data files are generally just streams of bytes, with
14727 lines delimited by the @acronym{ASCII} @sc{lf} (Line Feed) character,
14728 conventionally called a ``newline'' in the Unix literature. (This is
14729 @code{'\n'} if you're a C programmer.) This is the format used by all
14730 the traditional filtering programs. (Many earlier operating systems
14731 had elaborate facilities and special purpose programs for managing
14732 binary data. Unix has always shied away from such things, under the
14733 philosophy that it's easiest to simply be able to view and edit your
14734 data with a text editor.)
14736 OK, enough introduction. Let's take a look at some of the tools, and then
14737 we'll see how to hook them together in interesting ways. In the following
14738 discussion, we will only present those command line options that interest
14739 us. As you should always do, double check your system documentation
14740 for the full story.
14742 @node The who command
14743 @unnumberedsec The @command{who} Command
14745 The first program is the @command{who} command. By itself, it generates a
14746 list of the users who are currently logged in. Although I'm writing
14747 this on a single-user system, we'll pretend that several people are
14752 @print{} arnold console Jan 22 19:57
14753 @print{} miriam ttyp0 Jan 23 14:19(:0.0)
14754 @print{} bill ttyp1 Jan 21 09:32(:0.0)
14755 @print{} arnold ttyp2 Jan 23 20:48(:0.0)
14758 Here, the @samp{$} is the usual shell prompt, at which I typed @samp{who}.
14759 There are three people logged in, and I am logged in twice. On traditional
14760 Unix systems, user names are never more than eight characters long. This
14761 little bit of trivia will be useful later. The output of @command{who} is nice,
14762 but the data is not all that exciting.
14764 @node The cut command
14765 @unnumberedsec The @command{cut} Command
14767 The next program we'll look at is the @command{cut} command. This program
14768 cuts out columns or fields of input data. For example, we can tell it
14769 to print just the login name and full name from the @file{/etc/passwd}
14770 file. The @file{/etc/passwd} file has seven fields, separated by
14774 arnold:xyzzy:2076:10:Arnold D. Robbins:/home/arnold:/bin/bash
14777 To get the first and fifth fields, we would use @command{cut} like this:
14780 $ cut -d: -f1,5 /etc/passwd
14781 @print{} root:Operator
14783 @print{} arnold:Arnold D. Robbins
14784 @print{} miriam:Miriam A. Robbins
14788 With the @option{-c} option, @command{cut} will cut out specific characters
14789 (i.e., columns) in the input lines. This is useful for input data
14790 that has fixed width fields, and does not have a field separator. For
14791 example, list the Monday dates for the current month:
14793 @c Is using cal ok? Looked at gcal, but I don't like it.
14804 @node The sort command
14805 @unnumberedsec The @command{sort} Command
14807 Next we'll look at the @command{sort} command. This is one of the most
14808 powerful commands on a Unix-style system; one that you will often find
14809 yourself using when setting up fancy data plumbing.
14812 command reads and sorts each file named on the command line. It then
14813 merges the sorted data and writes it to standard output. It will read
14814 standard input if no files are given on the command line (thus
14815 making it into a filter). The sort is based on the character collating
14816 sequence or based on user-supplied ordering criteria.
14819 @node The uniq command
14820 @unnumberedsec The @command{uniq} Command
14822 Finally (at least for now), we'll look at the @command{uniq} program. When
14823 sorting data, you will often end up with duplicate lines, lines that
14824 are identical. Usually, all you need is one instance of each line.
14825 This is where @command{uniq} comes in. The @command{uniq} program reads its
14826 standard input. It prints only one
14827 copy of each repeated line. It does have several options. Later on,
14828 we'll use the @option{-c} option, which prints each unique line, preceded
14829 by a count of the number of times that line occurred in the input.
14832 @node Putting the tools together
14833 @unnumberedsec Putting the Tools Together
14835 Now, let's suppose this is a large ISP server system with dozens of users
14836 logged in. The management wants the system administrator to write a program that will
14837 generate a sorted list of logged in users. Furthermore, even if a user
14838 is logged in multiple times, his or her name should only show up in the
14841 The administrator could sit down with the system documentation and write a C
14842 program that did this. It would take perhaps a couple of hundred lines
14843 of code and about two hours to write it, test it, and debug it.
14844 However, knowing the software toolbox, the administrator can instead start out
14845 by generating just a list of logged on users:
14855 Next, sort the list:
14858 $ who | cut -c1-8 | sort
14865 Finally, run the sorted list through @command{uniq}, to weed out duplicates:
14868 $ who | cut -c1-8 | sort | uniq
14874 The @command{sort} command actually has a @option{-u} option that does what
14875 @command{uniq} does. However, @command{uniq} has other uses for which one
14876 cannot substitute @samp{sort -u}.
14878 The administrator puts this pipeline into a shell script, and makes it available for
14879 all the users on the system (@samp{#} is the system administrator,
14880 or @code{root}, prompt):
14883 # cat > /usr/local/bin/listusers
14884 who | cut -c1-8 | sort | uniq
14886 # chmod +x /usr/local/bin/listusers
14889 There are four major points to note here. First, with just four
14890 programs, on one command line, the administrator was able to save about two
14891 hours worth of work. Furthermore, the shell pipeline is just about as
14892 efficient as the C program would be, and it is much more efficient in
14893 terms of programmer time. People time is much more expensive than
14894 computer time, and in our modern ``there's never enough time to do
14895 everything'' society, saving two hours of programmer time is no mean
14898 Second, it is also important to emphasize that with the
14899 @emph{combination} of the tools, it is possible to do a special
14900 purpose job never imagined by the authors of the individual programs.
14902 Third, it is also valuable to build up your pipeline in stages, as we did here.
14903 This allows you to view the data at each stage in the pipeline, which helps
14904 you acquire the confidence that you are indeed using these tools correctly.
14906 Finally, by bundling the pipeline in a shell script, other users can use
14907 your command, without having to remember the fancy plumbing you set up for
14908 them. In terms of how you run them, shell scripts and compiled programs are
14911 After the previous warm-up exercise, we'll look at two additional, more
14912 complicated pipelines. For them, we need to introduce two more tools.
14914 The first is the @command{tr} command, which stands for ``transliterate.''
14915 The @command{tr} command works on a character-by-character basis, changing
14916 characters. Normally it is used for things like mapping upper case to
14920 $ echo ThIs ExAmPlE HaS MIXED case! | tr '[:upper:]' '[:lower:]'
14921 @print{} this example has mixed case!
14924 There are several options of interest:
14928 work on the complement of the listed characters, i.e.,
14929 operations apply to characters not in the given set
14932 delete characters in the first set from the output
14935 squeeze repeated characters in the output into just one character.
14938 We will be using all three options in a moment.
14940 The other command we'll look at is @command{comm}. The @command{comm}
14941 command takes two sorted input files as input data, and prints out the
14942 files' lines in three columns. The output columns are the data lines
14943 unique to the first file, the data lines unique to the second file, and
14944 the data lines that are common to both. The @option{-1}, @option{-2}, and
14945 @option{-3} command line options @emph{omit} the respective columns. (This is
14946 non-intuitive and takes a little getting used to.) For example:
14968 The file name @file{-} tells @command{comm} to read standard input
14969 instead of a regular file.
14971 Now we're ready to build a fancy pipeline. The first application is a word
14972 frequency counter. This helps an author determine if he or she is over-using
14975 The first step is to change the case of all the letters in our input file
14976 to one case. ``The'' and ``the'' are the same word when doing counting.
14979 $ tr '[:upper:]' '[:lower:]' < whats.gnu | ...
14982 The next step is to get rid of punctuation. Quoted words and unquoted words
14983 should be treated identically; it's easiest to just get the punctuation out of
14987 $ tr '[:upper:]' '[:lower:]' < whats.gnu | tr -cd '[:alnum:]_ \n' | ...
14990 The second @command{tr} command operates on the complement of the listed
14991 characters, which are all the letters, the digits, the underscore, and
14992 the blank. The @samp{\n} represents the newline character; it has to
14993 be left alone. (The @acronym{ASCII} tab character should also be included for
14994 good measure in a production script.)
14996 At this point, we have data consisting of words separated by blank space.
14997 The words only contain alphanumeric characters (and the underscore). The
14998 next step is break the data apart so that we have one word per line. This
14999 makes the counting operation much easier, as we will see shortly.
15002 $ tr '[:upper:]' '[:lower:]' < whats.gnu | tr -cd '[:alnum:]_ \n' |
15003 > tr -s ' ' '\n' | ...
15006 This command turns blanks into newlines. The @option{-s} option squeezes
15007 multiple newline characters in the output into just one. This helps us
15008 avoid blank lines. (The @samp{>} is the shell's ``secondary prompt.''
15009 This is what the shell prints when it notices you haven't finished
15010 typing in all of a command.)
15012 We now have data consisting of one word per line, no punctuation, all one
15013 case. We're ready to count each word:
15016 $ tr '[:upper:]' '[:lower:]' < whats.gnu | tr -cd '[:alnum:]_ \n' |
15017 > tr -s ' ' '\n' | sort | uniq -c | ...
15020 At this point, the data might look something like this:
15033 The output is sorted by word, not by count! What we want is the most
15034 frequently used words first. Fortunately, this is easy to accomplish,
15035 with the help of two more @command{sort} options:
15039 do a numeric sort, not a textual one
15042 reverse the order of the sort
15045 The final pipeline looks like this:
15048 $ tr '[:upper:]' '[:lower:]' < whats.gnu | tr -cd '[:alnum:]_ \n' |
15049 > tr -s ' ' '\n' | sort | uniq -c | sort -n -r
15058 Whew! That's a lot to digest. Yet, the same principles apply. With six
15059 commands, on two lines (really one long one split for convenience), we've
15060 created a program that does something interesting and useful, in much
15061 less time than we could have written a C program to do the same thing.
15063 A minor modification to the above pipeline can give us a simple spelling
15064 checker! To determine if you've spelled a word correctly, all you have to
15065 do is look it up in a dictionary. If it is not there, then chances are
15066 that your spelling is incorrect. So, we need a dictionary.
15067 The conventional location for a dictionary is @file{/usr/dict/words}.
15068 On my GNU/Linux system,@footnote{Redhat Linux 6.1, for the November 2000
15069 revision of this article.}
15070 this is a is a sorted, 45,402 word dictionary.
15072 Now, how to compare our file with the dictionary? As before, we generate
15073 a sorted list of words, one per line:
15076 $ tr '[:upper:]' '[:lower:]' < whats.gnu | tr -cd '[:alnum:]_ \n' |
15077 > tr -s ' ' '\n' | sort -u | ...
15080 Now, all we need is a list of words that are @emph{not} in the
15081 dictionary. Here is where the @command{comm} command comes in.
15084 $ tr '[:upper:]' '[:lower:]' < whats.gnu | tr -cd '[:alnum:]_ \n' |
15085 > tr -s ' ' '\n' | sort -u |
15086 > comm -23 - /usr/dict/words
15089 The @option{-2} and @option{-3} options eliminate lines that are only in the
15090 dictionary (the second file), and lines that are in both files. Lines
15091 only in the first file (standard input, our stream of words), are
15092 words that are not in the dictionary. These are likely candidates for
15093 spelling errors. This pipeline was the first cut at a production
15094 spelling checker on Unix.
15096 There are some other tools that deserve brief mention.
15100 search files for text that matches a regular expression
15103 count lines, words, characters
15106 a T-fitting for data pipes, copies data to files and to standard output
15109 the stream editor, an advanced tool
15112 a data manipulation language, another advanced tool
15115 The software tools philosophy also espoused the following bit of
15116 advice: ``Let someone else do the hard part.'' This means, take
15117 something that gives you most of what you need, and then massage it the
15118 rest of the way until it's in the form that you want.
15124 Each program should do one thing well. No more, no less.
15127 Combining programs with appropriate plumbing leads to results where
15128 the whole is greater than the sum of the parts. It also leads to novel
15129 uses of programs that the authors might never have imagined.
15132 Programs should never print extraneous header or trailer data, since these
15133 could get sent on down a pipeline. (A point we didn't mention earlier.)
15136 Let someone else do the hard part.
15139 Know your toolbox! Use each program appropriately. If you don't have an
15140 appropriate tool, build one.
15143 As of this writing, all the programs we've discussed are available via
15144 anonymous @command{ftp} from: @*
15145 @uref{ftp://gnudist.gnu.org/textutils/textutils-1.22.tar.gz}. (There may
15146 be more recent versions available now.)
15148 None of what I have presented in this column is new. The Software Tools
15149 philosophy was first introduced in the book @cite{Software Tools}, by
15150 Brian Kernighan and P.J. Plauger (Addison-Wesley, ISBN 0-201-03669-X).
15151 This book showed how to write and use software tools. It was written in
15152 1976, using a preprocessor for FORTRAN named @command{ratfor} (RATional
15153 FORtran). At the time, C was not as ubiquitous as it is now; FORTRAN
15154 was. The last chapter presented a @command{ratfor} to FORTRAN
15155 processor, written in @command{ratfor}. @command{ratfor} looks an awful
15156 lot like C; if you know C, you won't have any problem following the
15159 In 1981, the book was updated and made available as @cite{Software Tools
15160 in Pascal} (Addison-Wesley, ISBN 0-201-10342-7). Both books are
15161 still in print and are well worth
15162 reading if you're a programmer. They certainly made a major change in
15163 how I view programming.
15165 The programs in both books are available from
15166 @uref{http://cm.bell-labs.com/who/bwk, Brian Kernighan's home page}.
15167 For a number of years, there was an active
15168 Software Tools Users Group, whose members had ported the original
15169 @command{ratfor} programs to essentially every computer system with a
15170 FORTRAN compiler. The popularity of the group waned in the middle 1980s
15171 as Unix began to spread beyond universities.
15173 With the current proliferation of GNU code and other clones of Unix programs,
15174 these programs now receive little attention; modern C versions are
15175 much more efficient and do more than these programs do. Nevertheless, as
15176 exposition of good programming style, and evangelism for a still-valuable
15177 philosophy, these books are unparalleled, and I recommend them highly.
15179 Acknowledgment: I would like to express my gratitude to Brian Kernighan
15180 of Bell Labs, the original Software Toolsmith, for reviewing this column.
15182 @node GNU Free Documentation License
15183 @appendix GNU Free Documentation License
15187 @node Concept index
15196 @c Local variables:
15197 @c texinfo-column-for-description: 32