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.
35 @dircategory Individual utilities
37 * arch: (coreutils)arch invocation. Print machine hardware name.
38 * base64: (coreutils)base64 invocation. Base64 encode/decode data.
39 * basename: (coreutils)basename invocation. Strip directory and suffix.
40 * cat: (coreutils)cat invocation. Concatenate and write files.
41 * chcon: (coreutils)chcon invocation. Change SELinux CTX of files.
42 * chgrp: (coreutils)chgrp invocation. Change file groups.
43 * chmod: (coreutils)chmod invocation. Change file permissions.
44 * chown: (coreutils)chown invocation. Change file owners/groups.
45 * chroot: (coreutils)chroot invocation. Specify the root directory.
46 * cksum: (coreutils)cksum invocation. Print POSIX CRC checksum.
47 * comm: (coreutils)comm invocation. Compare sorted files by line.
48 * cp: (coreutils)cp invocation. Copy files.
49 * csplit: (coreutils)csplit invocation. Split by context.
50 * cut: (coreutils)cut invocation. Print selected parts of lines.
51 * date: (coreutils)date invocation. Print/set system date and time.
52 * dd: (coreutils)dd invocation. Copy and convert a file.
53 * df: (coreutils)df invocation. Report file system disk usage.
54 * dir: (coreutils)dir invocation. List directories briefly.
55 * dircolors: (coreutils)dircolors invocation. Color setup for ls.
56 * dirname: (coreutils)dirname invocation. Strip last file name component.
57 * du: (coreutils)du invocation. Report on disk usage.
58 * echo: (coreutils)echo invocation. Print a line of text.
59 * env: (coreutils)env invocation. Modify the environment.
60 * expand: (coreutils)expand invocation. Convert tabs to spaces.
61 * expr: (coreutils)expr invocation. Evaluate expressions.
62 * factor: (coreutils)factor invocation. Print prime factors
63 * false: (coreutils)false invocation. Do nothing, unsuccessfully.
64 * fmt: (coreutils)fmt invocation. Reformat paragraph text.
65 * fold: (coreutils)fold invocation. Wrap long input lines.
66 * groups: (coreutils)groups invocation. Print group names a user is in.
67 * head: (coreutils)head invocation. Output the first part of files.
68 * hostid: (coreutils)hostid invocation. Print numeric host identifier.
69 * hostname: (coreutils)hostname invocation. Print or set system name.
70 * id: (coreutils)id invocation. Print user identity.
71 * install: (coreutils)install invocation. Copy and change attributes.
72 * join: (coreutils)join invocation. Join lines on a common field.
73 * kill: (coreutils)kill invocation. Send a signal to processes.
74 * link: (coreutils)link invocation. Make hard links between files.
75 * ln: (coreutils)ln invocation. Make links between files.
76 * logname: (coreutils)logname invocation. Print current login name.
77 * ls: (coreutils)ls invocation. List directory contents.
78 * md5sum: (coreutils)md5sum invocation. Print or check MD5 digests.
79 * mkdir: (coreutils)mkdir invocation. Create directories.
80 * mkfifo: (coreutils)mkfifo invocation. Create FIFOs (named pipes).
81 * mknod: (coreutils)mknod invocation. Create special files.
82 * mktemp: (coreutils)mktemp invocation. Create temporary 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 * nproc: (coreutils)nproc invocation. Print the number of processors.
88 * od: (coreutils)od invocation. Dump files in octal, etc.
89 * paste: (coreutils)paste invocation. Merge lines of files.
90 * pathchk: (coreutils)pathchk invocation. Check file name portability.
91 * pr: (coreutils)pr invocation. Paginate or columnate files.
92 * printenv: (coreutils)printenv invocation. Print environment variables.
93 * printf: (coreutils)printf invocation. Format and print data.
94 * ptx: (coreutils)ptx invocation. Produce permuted indexes.
95 * pwd: (coreutils)pwd invocation. Print working directory.
96 * readlink: (coreutils)readlink invocation. Print referent of a symlink.
97 * rm: (coreutils)rm invocation. Remove files.
98 * rmdir: (coreutils)rmdir invocation. Remove empty directories.
99 * runcon: (coreutils)runcon invocation. Run in specified SELinux CTX.
100 * seq: (coreutils)seq invocation. Print numeric sequences
101 * sha1sum: (coreutils)sha1sum invocation. Print or check SHA-1 digests.
102 * sha2: (coreutils)sha2 utilities. Print or check SHA-2 digests.
103 * shred: (coreutils)shred invocation. Remove files more securely.
104 * shuf: (coreutils)shuf invocation. Shuffling text files.
105 * sleep: (coreutils)sleep invocation. Delay for a specified time.
106 * sort: (coreutils)sort invocation. Sort text files.
107 * split: (coreutils)split invocation. Split into fixed-size pieces.
108 * stat: (coreutils)stat invocation. Report file(system) status.
109 * stdbuf: (coreutils)stdbuf invocation. Modify stdio buffering.
110 * stty: (coreutils)stty invocation. Print/change terminal settings.
111 * su: (coreutils)su invocation. Modify user and group ID.
112 * sum: (coreutils)sum invocation. Print traditional checksum.
113 * sync: (coreutils)sync invocation. Synchronize memory and disk.
114 * tac: (coreutils)tac invocation. Reverse files.
115 * tail: (coreutils)tail invocation. Output the last part of files.
116 * tee: (coreutils)tee invocation. Redirect to multiple files.
117 * test: (coreutils)test invocation. File/string tests.
118 * timeout: (coreutils)timeout invocation. Run with time limit.
119 * touch: (coreutils)touch invocation. Change file timestamps.
120 * tr: (coreutils)tr invocation. Translate characters.
121 * true: (coreutils)true invocation. Do nothing, successfully.
122 * truncate: (coreutils)truncate invocation. Shrink/extend size of a file.
123 * tsort: (coreutils)tsort invocation. Topological sort.
124 * tty: (coreutils)tty invocation. Print terminal name.
125 * uname: (coreutils)uname invocation. Print system information.
126 * unexpand: (coreutils)unexpand invocation. Convert spaces to tabs.
127 * uniq: (coreutils)uniq invocation. Uniquify files.
128 * unlink: (coreutils)unlink invocation. Removal via unlink(2).
129 * uptime: (coreutils)uptime invocation. Print uptime and load.
130 * users: (coreutils)users invocation. Print current user names.
131 * vdir: (coreutils)vdir invocation. List directories verbosely.
132 * wc: (coreutils)wc invocation. Line, word, and byte counts.
133 * who: (coreutils)who invocation. Print who is logged in.
134 * whoami: (coreutils)whoami invocation. Print effective user ID.
135 * yes: (coreutils)yes invocation. Print a string indefinitely.
139 This manual documents version @value{VERSION} of the @sc{gnu} core
140 utilities, including the standard programs for text and file manipulation.
142 Copyright @copyright{} 1994-1996, 2000-2010 Free Software Foundation, Inc.
145 Permission is granted to copy, distribute and/or modify this document
146 under the terms of the GNU Free Documentation License, Version 1.3 or
147 any later version published by the Free Software Foundation; with no
148 Invariant Sections, with no Front-Cover Texts, and with no Back-Cover
149 Texts. A copy of the license is included in the section entitled ``GNU
150 Free Documentation License''.
155 @title @sc{gnu} @code{Coreutils}
156 @subtitle Core GNU utilities
157 @subtitle for version @value{VERSION}, @value{UPDATED}
158 @author David MacKenzie et al.
161 @vskip 0pt plus 1filll
174 @cindex core utilities
175 @cindex text utilities
176 @cindex shell utilities
177 @cindex file utilities
180 * Introduction:: Caveats, overview, and authors
181 * Common options:: Common options
182 * Output of entire files:: cat tac nl od base64
183 * Formatting file contents:: fmt pr fold
184 * Output of parts of files:: head tail split csplit
185 * Summarizing files:: wc sum cksum md5sum sha1sum sha2
186 * Operating on sorted files:: sort shuf uniq comm ptx tsort
187 * Operating on fields:: cut paste join
188 * Operating on characters:: tr expand unexpand
189 * Directory listing:: ls dir vdir dircolors
190 * Basic operations:: cp dd install mv rm shred
191 * Special file types:: mkdir rmdir unlink mkfifo mknod ln link readlink
192 * Changing file attributes:: chgrp chmod chown touch
193 * Disk usage:: df du stat sync truncate
194 * Printing text:: echo printf yes
195 * Conditions:: false true test expr
197 * File name manipulation:: dirname basename pathchk mktemp
198 * Working context:: pwd stty printenv tty
199 * User information:: id logname whoami groups users who
200 * System context:: date arch nproc uname hostname hostid uptime
201 * SELinux context:: chcon runcon
202 * Modified command invocation:: chroot env nice nohup stdbuf su timeout
203 * Process control:: kill
205 * Numeric operations:: factor seq
206 * File permissions:: Access modes
207 * Date input formats:: Specifying date strings
208 * Opening the software toolbox:: The software tools philosophy
209 * GNU Free Documentation License:: Copying and sharing this manual
210 * Concept index:: General index
213 --- The Detailed Node Listing ---
217 * Exit status:: Indicating program success or failure
218 * Backup options:: Backup options
219 * Block size:: Block size
220 * Signal specifications:: Specifying signals
221 * Disambiguating names and IDs:: chgrp and chown owner and group syntax
222 * Random sources:: Sources of random data
223 * Target directory:: Target directory
224 * Trailing slashes:: Trailing slashes
225 * Traversing symlinks:: Traversing symlinks to directories
226 * Treating / specially:: Treating / specially
227 * Standards conformance:: Standards conformance
229 Output of entire files
231 * cat invocation:: Concatenate and write files
232 * tac invocation:: Concatenate and write files in reverse
233 * nl invocation:: Number lines and write files
234 * od invocation:: Write files in octal or other formats
235 * base64 invocation:: Transform data into printable data
237 Formatting file contents
239 * fmt invocation:: Reformat paragraph text
240 * pr invocation:: Paginate or columnate files for printing
241 * fold invocation:: Wrap input lines to fit in specified width
243 Output of parts of files
245 * head invocation:: Output the first part of files
246 * tail invocation:: Output the last part of files
247 * split invocation:: Split a file into fixed-size pieces
248 * csplit invocation:: Split a file into context-determined pieces
252 * wc invocation:: Print newline, word, and byte counts
253 * sum invocation:: Print checksum and block counts
254 * cksum invocation:: Print CRC checksum and byte counts
255 * md5sum invocation:: Print or check MD5 digests
256 * sha1sum invocation:: Print or check SHA-1 digests
257 * sha2 utilities:: Print or check SHA-2 digests
259 Operating on sorted files
261 * sort invocation:: Sort text files
262 * shuf invocation:: Shuffle text files
263 * uniq invocation:: Uniquify files
264 * comm invocation:: Compare two sorted files line by line
265 * ptx invocation:: Produce a permuted index of file contents
266 * tsort invocation:: Topological sort
268 @command{ptx}: Produce permuted indexes
270 * General options in ptx:: Options which affect general program behavior
271 * Charset selection in ptx:: Underlying character set considerations
272 * Input processing in ptx:: Input fields, contexts, and keyword selection
273 * Output formatting in ptx:: Types of output format, and sizing the fields
274 * Compatibility in ptx:: The @acronym{GNU} extensions to @command{ptx}
278 * cut invocation:: Print selected parts of lines
279 * paste invocation:: Merge lines of files
280 * join invocation:: Join lines on a common field
282 Operating on characters
284 * tr invocation:: Translate, squeeze, and/or delete characters
285 * expand invocation:: Convert tabs to spaces
286 * unexpand invocation:: Convert spaces to tabs
288 @command{tr}: Translate, squeeze, and/or delete characters
290 * Character sets:: Specifying sets of characters
291 * Translating:: Changing one set of characters to another
292 * Squeezing:: Squeezing repeats and deleting
296 * ls invocation:: List directory contents
297 * dir invocation:: Briefly list directory contents
298 * vdir invocation:: Verbosely list directory contents
299 * dircolors invocation:: Color setup for @command{ls}
301 @command{ls}: List directory contents
303 * Which files are listed:: Which files are listed
304 * What information is listed:: What information is listed
305 * Sorting the output:: Sorting the output
306 * Details about version sort:: More details about version sort
307 * General output formatting:: General output formatting
308 * Formatting the file names:: Formatting the file names
312 * cp invocation:: Copy files and directories
313 * dd invocation:: Convert and copy a file
314 * install invocation:: Copy files and set attributes
315 * mv invocation:: Move (rename) files
316 * rm invocation:: Remove files or directories
317 * shred invocation:: Remove files more securely
321 * link invocation:: Make a hard link via the link syscall
322 * ln invocation:: Make links between files
323 * mkdir invocation:: Make directories
324 * mkfifo invocation:: Make FIFOs (named pipes)
325 * mknod invocation:: Make block or character special files
326 * readlink invocation:: Print value of a symlink or canonical file name
327 * rmdir invocation:: Remove empty directories
328 * unlink invocation:: Remove files via unlink syscall
330 Changing file attributes
332 * chown invocation:: Change file owner and group
333 * chgrp invocation:: Change group ownership
334 * chmod invocation:: Change access permissions
335 * touch invocation:: Change file timestamps
339 * df invocation:: Report file system disk space usage
340 * du invocation:: Estimate file space usage
341 * stat invocation:: Report file or file system status
342 * sync invocation:: Synchronize data on disk with memory
343 * truncate invocation:: Shrink or extend the size of a file
347 * echo invocation:: Print a line of text
348 * printf invocation:: Format and print data
349 * yes invocation:: Print a string until interrupted
353 * false invocation:: Do nothing, unsuccessfully
354 * true invocation:: Do nothing, successfully
355 * test invocation:: Check file types and compare values
356 * expr invocation:: Evaluate expressions
358 @command{test}: Check file types and compare values
360 * File type tests:: File type tests
361 * Access permission tests:: Access permission tests
362 * File characteristic tests:: File characteristic tests
363 * String tests:: String tests
364 * Numeric tests:: Numeric tests
366 @command{expr}: Evaluate expression
368 * String expressions:: + : match substr index length
369 * Numeric expressions:: + - * / %
370 * Relations for expr:: | & < <= = == != >= >
371 * Examples of expr:: Examples of using @command{expr}
375 * tee invocation:: Redirect output to multiple files or processes
377 File name manipulation
379 * basename invocation:: Strip directory and suffix from a file name
380 * dirname invocation:: Strip last file name component
381 * pathchk invocation:: Check file name validity and portability
382 * mktemp invocation:: Create temporary file or directory
386 * pwd invocation:: Print working directory
387 * stty invocation:: Print or change terminal characteristics
388 * printenv invocation:: Print all or some environment variables
389 * tty invocation:: Print file name of terminal on standard input
391 @command{stty}: Print or change terminal characteristics
393 * Control:: Control settings
394 * Input:: Input settings
395 * Output:: Output settings
396 * Local:: Local settings
397 * Combination:: Combination settings
398 * Characters:: Special characters
399 * Special:: Special settings
403 * id invocation:: Print user identity
404 * logname invocation:: Print current login name
405 * whoami invocation:: Print effective user ID
406 * groups invocation:: Print group names a user is in
407 * users invocation:: Print login names of users currently logged in
408 * who invocation:: Print who is currently logged in
412 * arch invocation:: Print machine hardware name
413 * date invocation:: Print or set system date and time
414 * nproc invocation:: Print the number of processors
415 * uname invocation:: Print system information
416 * hostname invocation:: Print or set system name
417 * hostid invocation:: Print numeric host identifier
418 * uptime invocation:: Print system uptime and load
420 @command{date}: Print or set system date and time
422 * Time conversion specifiers:: %[HIklMNpPrRsSTXzZ]
423 * Date conversion specifiers:: %[aAbBcCdDeFgGhjmuUVwWxyY]
424 * Literal conversion specifiers:: %[%nt]
425 * Padding and other flags:: Pad with zeros, spaces, etc.
426 * Setting the time:: Changing the system clock
427 * Options for date:: Instead of the current time
428 * Date input formats:: Specifying date strings
429 * Examples of date:: Examples
433 * chcon invocation:: Change SELinux context of file
434 * runcon invocation:: Run a command in specified SELinux context
436 Modified command invocation
438 * chroot invocation:: Run a command with a different root directory
439 * env invocation:: Run a command in a modified environment
440 * nice invocation:: Run a command with modified niceness
441 * nohup invocation:: Run a command immune to hangups
442 * stdbuf invocation:: Run a command with modified I/O buffering
443 * su invocation:: Run a command with substitute user and group ID
444 * timeout invocation:: Run a command with a time limit
448 * kill invocation:: Sending a signal to processes.
452 * sleep invocation:: Delay for a specified time
456 * factor invocation:: Print prime factors
457 * seq invocation:: Print numeric sequences
461 * Mode Structure:: Structure of file mode bits
462 * Symbolic Modes:: Mnemonic representation of file mode bits
463 * Numeric Modes:: File mode bits as octal numbers
464 * Directory Setuid and Setgid:: Set-user-ID and set-group-ID on directories
468 * General date syntax:: Common rules
469 * Calendar date items:: 19 Dec 1994
470 * Time of day items:: 9:20pm
471 * Time zone items:: @sc{est}, @sc{pdt}, @sc{gmt}
472 * Day of week items:: Monday and others
473 * Relative items in date strings:: next tuesday, 2 years ago
474 * Pure numbers in date strings:: 19931219, 1440
475 * Seconds since the Epoch:: @@1078100502
476 * Specifying time zone rules:: TZ="America/New_York", TZ="UTC0"
477 * Authors of get_date:: Bellovin, Eggert, Salz, Berets, et al
479 Opening the software toolbox
481 * Toolbox introduction:: Toolbox introduction
482 * I/O redirection:: I/O redirection
483 * The who command:: The @command{who} command
484 * The cut command:: The @command{cut} command
485 * The sort command:: The @command{sort} command
486 * The uniq command:: The @command{uniq} command
487 * Putting the tools together:: Putting the tools together
491 * GNU Free Documentation License:: Copying and sharing this manual
498 @chapter Introduction
500 This manual is a work in progress: many sections make no attempt to explain
501 basic concepts in a way suitable for novices. Thus, if you are interested,
502 please get involved in improving this manual. The entire @sc{gnu} community
505 @cindex @acronym{POSIX}
506 The @sc{gnu} utilities documented here are mostly compatible with the
507 @acronym{POSIX} standard.
508 @cindex bugs, reporting
509 Please report bugs to @email{bug-coreutils@@gnu.org}. Remember
510 to include the version number, machine architecture, input files, and
511 any other information needed to reproduce the bug: your input, what you
512 expected, what you got, and why it is wrong. Diffs are welcome, but
513 please include a description of the problem as well, since this is
514 sometimes difficult to infer. @xref{Bugs, , , gcc, Using and Porting GNU CC}.
520 @cindex MacKenzie, D.
523 This manual was originally derived from the Unix man pages in the
524 distributions, which were written by David MacKenzie and updated by Jim
525 Meyering. What you are reading now is the authoritative documentation
526 for these utilities; the man pages are no longer being maintained. The
527 original @command{fmt} man page was written by Ross Paterson. Fran@,{c}ois
528 Pinard did the initial conversion to Texinfo format. Karl Berry did the
529 indexing, some reorganization, and editing of the results. Brian
530 Youmans of the Free Software Foundation office staff combined the
531 manuals for textutils, fileutils, and sh-utils to produce the present
532 omnibus manual. Richard Stallman contributed his usual invaluable
533 insights to the overall process.
536 @chapter Common options
540 @itemx @w{@kbd{--backup}[=@var{method}]}
543 @vindex VERSION_CONTROL
544 @cindex backups, making
545 @xref{Backup options}.
546 Make a backup of each file that would otherwise be overwritten or removed.
549 @macro optBackupSuffix
550 @item -S @var{suffix}
551 @itemx --suffix=@var{suffix}
554 Append @var{suffix} to each backup file made with @option{-b}.
555 @xref{Backup options}.
558 @macro optTargetDirectory
559 @item -t @var{directory}
560 @itemx @w{@kbd{--target-directory}=@var{directory}}
562 @opindex --target-directory
563 @cindex target directory
564 @cindex destination directory
565 Specify the destination @var{directory}.
566 @xref{Target directory}.
569 @macro optNoTargetDirectory
571 @itemx --no-target-directory
573 @opindex --no-target-directory
574 @cindex target directory
575 @cindex destination directory
576 Do not treat the last operand specially when it is a directory or a
577 symbolic link to a directory. @xref{Target directory}.
585 @cindex output @sc{nul}-byte-terminated lines
586 Output a zero byte (@acronym{ASCII} @sc{nul}) at the end of each line,
587 rather than a newline. This option enables other programs to parse the
588 output of @command{\cmd\} even when that output would contain data
589 with embedded newlines.
596 Append an SI-style abbreviation to each size, such as @samp{M} for
597 megabytes. Powers of 1000 are used, not 1024; @samp{M} stands for
598 1,000,000 bytes. This option is equivalent to
599 @option{--block-size=si}. Use the @option{-h} or
600 @option{--human-readable} option if
601 you prefer powers of 1024.
604 @macro optHumanReadable
606 @itemx --human-readable
608 @opindex --human-readable
609 @cindex human-readable output
610 Append a size letter to each size, such as @samp{M} for mebibytes.
611 Powers of 1024 are used, not 1000; @samp{M} stands for 1,048,576 bytes.
612 This option is equivalent to @option{--block-size=human-readable}.
613 Use the @option{--si} option if you prefer powers of 1000.
616 @macro optStripTrailingSlashes
617 @itemx @w{@kbd{--strip-trailing-slashes}}
618 @opindex --strip-trailing-slashes
619 @cindex stripping trailing slashes
620 Remove any trailing slashes from each @var{source} argument.
621 @xref{Trailing slashes}.
624 @macro mayConflictWithShellBuiltIn{cmd}
625 @cindex conflicts with shell built-ins
626 @cindex built-in shell commands, conflicts with
627 Due to shell aliases and built-in @command{\cmd\} command, using an
628 unadorned @command{\cmd\} interactively or in a script may get you
629 different functionality than that described here. Invoke it via
630 @command{env} (i.e., @code{env \cmd\ @dots{}}) to avoid interference
635 @macro multiplierSuffixes{varName}
636 @var{\varName\} may be, or may be an integer optionally followed by,
637 one of the following multiplicative suffixes:
639 @samp{b} => 512 ("blocks")
640 @samp{KB} => 1000 (KiloBytes)
641 @samp{K} => 1024 (KibiBytes)
642 @samp{MB} => 1000*1000 (MegaBytes)
643 @samp{M} => 1024*1024 (MebiBytes)
644 @samp{GB} => 1000*1000*1000 (GigaBytes)
645 @samp{G} => 1024*1024*1024 (GibiBytes)
647 and so on for @samp{T}, @samp{P}, @samp{E}, @samp{Z}, and @samp{Y}.
650 @c FIXME: same as above, but no ``blocks'' line.
651 @macro multiplierSuffixesNoBlocks{varName}
652 @var{\varName\} may be, or may be an integer optionally followed by,
653 one of the following multiplicative suffixes:
655 @samp{KB} => 1000 (KiloBytes)
656 @samp{K} => 1024 (KibiBytes)
657 @samp{MB} => 1000*1000 (MegaBytes)
658 @samp{M} => 1024*1024 (MebiBytes)
659 @samp{GB} => 1000*1000*1000 (GigaBytes)
660 @samp{G} => 1024*1024*1024 (GibiBytes)
662 and so on for @samp{T}, @samp{P}, @samp{E}, @samp{Z}, and @samp{Y}.
665 @cindex common options
667 Certain options are available in all of these programs. Rather than
668 writing identical descriptions for each of the programs, they are
669 described here. (In fact, every @sc{gnu} program accepts (or should accept)
672 @vindex POSIXLY_CORRECT
673 Normally options and operands can appear in any order, and programs act
674 as if all the options appear before any operands. For example,
675 @samp{sort -r passwd -t :} acts like @samp{sort -r -t : passwd}, since
676 @samp{:} is an option-argument of @option{-t}. However, if the
677 @env{POSIXLY_CORRECT} environment variable is set, options must appear
678 before operands, unless otherwise specified for a particular command.
680 A few programs can usefully have trailing operands with leading
681 @samp{-}. With such a program, options must precede operands even if
682 @env{POSIXLY_CORRECT} is not set, and this fact is noted in the
683 program description. For example, the @command{env} command's options
684 must appear before its operands, since in some cases the operands
685 specify a command that itself contains options.
687 Most programs that accept long options recognize unambiguous
688 abbreviations of those options. For example, @samp{rmdir
689 --ignore-fail-on-non-empty} can be invoked as @samp{rmdir
690 --ignore-fail} or even @samp{rmdir --i}. Ambiguous options, such as
691 @samp{ls --h}, are identified as such.
693 Some of these programs recognize the @option{--help} and @option{--version}
694 options only when one of them is the sole command line argument. For
695 these programs, abbreviations of the long options are not always recognized.
702 Print a usage message listing all available options, then exit successfully.
706 @cindex version number, finding
707 Print the version number, then exit successfully.
711 @cindex option delimiter
712 Delimit the option list. Later arguments, if any, are treated as
713 operands even if they begin with @samp{-}. For example, @samp{sort --
714 -r} reads from the file named @file{-r}.
718 @cindex standard input
719 @cindex standard output
720 A single @samp{-} operand is not really an option, though it looks like one. It
721 stands for standard input, or for standard output if that is clear from
722 the context. For example, @samp{sort -} reads from standard input,
723 and is equivalent to plain @samp{sort}, and @samp{tee -} writes an
724 extra copy of its input to standard output. Unless otherwise
725 specified, @samp{-} can appear as any operand that requires a file
729 * Exit status:: Indicating program success or failure.
730 * Backup options:: -b -S, in some programs.
731 * Block size:: BLOCK_SIZE and --block-size, in some programs.
732 * Signal specifications:: Specifying signals using the --signal option.
733 * Disambiguating names and IDs:: chgrp and chown owner and group syntax
734 * Random sources:: --random-source, in some programs.
735 * Target directory:: Specifying a target directory, in some programs.
736 * Trailing slashes:: --strip-trailing-slashes, in some programs.
737 * Traversing symlinks:: -H, -L, or -P, in some programs.
738 * Treating / specially:: --preserve-root and --no-preserve-root.
739 * Special built-in utilities:: @command{break}, @command{:}, @command{eval}, @dots{}
740 * Standards conformance:: Conformance to the @acronym{POSIX} standard.
748 An exit status of zero indicates success,
749 and a nonzero value indicates failure.
752 Nearly every command invocation yields an integral @dfn{exit status}
753 that can be used to change how other commands work.
754 For the vast majority of commands, an exit status of zero indicates
755 success. Failure is indicated by a nonzero value---typically
756 @samp{1}, though it may differ on unusual platforms as @acronym{POSIX}
757 requires only that it be nonzero.
759 However, some of the programs documented here do produce
760 other exit status values and a few associate different
761 meanings with the values @samp{0} and @samp{1}.
762 Here are some of the exceptions:
763 @command{chroot}, @command{env}, @command{expr}, @command{nice},
764 @command{nohup}, @command{printenv}, @command{sort}, @command{stdbuf},
765 @command{su}, @command{test}, @command{timeout}, @command{tty}.
769 @section Backup options
771 @cindex backup options
773 Some @sc{gnu} programs (at least @command{cp}, @command{install},
774 @command{ln}, and @command{mv}) optionally make backups of files
775 before writing new versions.
776 These options control the details of these backups. The options are also
777 briefly mentioned in the descriptions of the particular programs.
782 @itemx @w{@kbd{--backup}[=@var{method}]}
785 @vindex VERSION_CONTROL
786 @cindex backups, making
787 Make a backup of each file that would otherwise be overwritten or removed.
788 Without this option, the original versions are destroyed.
789 Use @var{method} to determine the type of backups to make.
790 When this option is used but @var{method} is not specified,
791 then the value of the @env{VERSION_CONTROL}
792 environment variable is used. And if @env{VERSION_CONTROL} is not set,
793 the default backup type is @samp{existing}.
795 Note that the short form of this option, @option{-b} does not accept any
796 argument. Using @option{-b} is equivalent to using @option{--backup=existing}.
798 @vindex version-control @r{Emacs variable}
799 This option corresponds to the Emacs variable @samp{version-control};
800 the values for @var{method} are the same as those used in Emacs.
801 This option also accepts more descriptive names.
802 The valid @var{method}s are (unique abbreviations are accepted):
807 @opindex none @r{backup method}
812 @opindex numbered @r{backup method}
813 Always make numbered backups.
817 @opindex existing @r{backup method}
818 Make numbered backups of files that already have them, simple backups
823 @opindex simple @r{backup method}
824 Always make simple backups. Please note @samp{never} is not to be
825 confused with @samp{none}.
829 @item -S @var{suffix}
830 @itemx --suffix=@var{suffix}
833 @cindex backup suffix
834 @vindex SIMPLE_BACKUP_SUFFIX
835 Append @var{suffix} to each backup file made with @option{-b}. If this
836 option is not specified, the value of the @env{SIMPLE_BACKUP_SUFFIX}
837 environment variable is used. And if @env{SIMPLE_BACKUP_SUFFIX} is not
838 set, the default is @samp{~}, just as in Emacs.
847 Some @sc{gnu} programs (at least @command{df}, @command{du}, and
848 @command{ls}) display sizes in ``blocks''. You can adjust the block size
849 and method of display to make sizes easier to read. The block size
850 used for display is independent of any file system block size.
851 Fractional block counts are rounded up to the nearest integer.
853 @opindex --block-size=@var{size}
856 @vindex DF_BLOCK_SIZE
857 @vindex DU_BLOCK_SIZE
858 @vindex LS_BLOCK_SIZE
859 @vindex POSIXLY_CORRECT@r{, and block size}
861 The default block size is chosen by examining the following environment
862 variables in turn; the first one that is set determines the block size.
867 This specifies the default block size for the @command{df} command.
868 Similarly, @env{DU_BLOCK_SIZE} specifies the default for @command{du} and
869 @env{LS_BLOCK_SIZE} for @command{ls}.
872 This specifies the default block size for all three commands, if the
873 above command-specific environment variables are not set.
876 This specifies the default block size for all values that are normally
877 printed as blocks, if neither @env{BLOCK_SIZE} nor the above
878 command-specific environment variables are set. Unlike the other
879 environment variables, @env{BLOCKSIZE} does not affect values that are
880 normally printed as byte counts, e.g., the file sizes contained in
883 @item POSIXLY_CORRECT
884 If neither @env{@var{command}_BLOCK_SIZE}, nor @env{BLOCK_SIZE}, nor
885 @env{BLOCKSIZE} is set, but this variable is set, the block size
890 If none of the above environment variables are set, the block size
891 currently defaults to 1024 bytes in most contexts, but this number may
892 change in the future. For @command{ls} file sizes, the block size
895 @cindex human-readable output
898 A block size specification can be a positive integer specifying the number
899 of bytes per block, or it can be @code{human-readable} or @code{si} to
900 select a human-readable format. Integers may be followed by suffixes
901 that are upward compatible with the
902 @uref{http://www.bipm.fr/enus/3_SI/si-prefixes.html, SI prefixes}
903 for decimal multiples and with the
904 @uref{http://physics.nist.gov/cuu/Units/binary.html, IEC 60027-2
905 prefixes for binary multiples}.
907 With human-readable formats, output sizes are followed by a size letter
908 such as @samp{M} for megabytes. @code{BLOCK_SIZE=human-readable} uses
909 powers of 1024; @samp{M} stands for 1,048,576 bytes.
910 @code{BLOCK_SIZE=si} is similar, but uses powers of 1000 and appends
911 @samp{B}; @samp{MB} stands for 1,000,000 bytes.
914 A block size specification preceded by @samp{'} causes output sizes to
915 be displayed with thousands separators. The @env{LC_NUMERIC} locale
916 specifies the thousands separator and grouping. For example, in an
917 American English locale, @samp{--block-size="'1kB"} would cause a size
918 of 1234000 bytes to be displayed as @samp{1,234}. In the default C
919 locale, there is no thousands separator so a leading @samp{'} has no
922 An integer block size can be followed by a suffix to specify a
923 multiple of that size. A bare size letter,
924 or one followed by @samp{iB}, specifies
925 a multiple using powers of 1024. A size letter followed by @samp{B}
926 specifies powers of 1000 instead. For example, @samp{1M} and
927 @samp{1MiB} are equivalent to @samp{1048576}, whereas @samp{1MB} is
928 equivalent to @samp{1000000}.
930 A plain suffix without a preceding integer acts as if @samp{1} were
931 prepended, except that it causes a size indication to be appended to
932 the output. For example, @samp{--block-size="kB"} displays 3000 as
935 The following suffixes are defined. Large sizes like @code{1Y}
936 may be rejected by your computer due to limitations of its arithmetic.
940 @cindex kilobyte, definition of
941 kilobyte: @math{10^3 = 1000}.
945 @cindex kibibyte, definition of
946 kibibyte: @math{2^{10} = 1024}. @samp{K} is special: the SI prefix is
947 @samp{k} and the IEC 60027-2 prefix is @samp{Ki}, but tradition and
948 @acronym{POSIX} use @samp{k} to mean @samp{KiB}.
950 @cindex megabyte, definition of
951 megabyte: @math{10^6 = 1,000,000}.
954 @cindex mebibyte, definition of
955 mebibyte: @math{2^{20} = 1,048,576}.
957 @cindex gigabyte, definition of
958 gigabyte: @math{10^9 = 1,000,000,000}.
961 @cindex gibibyte, definition of
962 gibibyte: @math{2^{30} = 1,073,741,824}.
964 @cindex terabyte, definition of
965 terabyte: @math{10^{12} = 1,000,000,000,000}.
968 @cindex tebibyte, definition of
969 tebibyte: @math{2^{40} = 1,099,511,627,776}.
971 @cindex petabyte, definition of
972 petabyte: @math{10^{15} = 1,000,000,000,000,000}.
975 @cindex pebibyte, definition of
976 pebibyte: @math{2^{50} = 1,125,899,906,842,624}.
978 @cindex exabyte, definition of
979 exabyte: @math{10^{18} = 1,000,000,000,000,000,000}.
982 @cindex exbibyte, definition of
983 exbibyte: @math{2^{60} = 1,152,921,504,606,846,976}.
985 @cindex zettabyte, definition of
986 zettabyte: @math{10^{21} = 1,000,000,000,000,000,000,000}
989 @math{2^{70} = 1,180,591,620,717,411,303,424}.
990 (@samp{Zi} is a @acronym{GNU} extension to IEC 60027-2.)
992 @cindex yottabyte, definition of
993 yottabyte: @math{10^{24} = 1,000,000,000,000,000,000,000,000}.
996 @math{2^{80} = 1,208,925,819,614,629,174,706,176}.
997 (@samp{Yi} is a @acronym{GNU} extension to IEC 60027-2.)
1002 @opindex --block-size
1003 @opindex --human-readable
1006 Block size defaults can be overridden by an explicit
1007 @option{--block-size=@var{size}} option. The @option{-k}
1008 option is equivalent to @option{--block-size=1K}, which
1009 is the default unless the @env{POSIXLY_CORRECT} environment variable is
1010 set. The @option{-h} or @option{--human-readable} option is equivalent to
1011 @option{--block-size=human-readable}. The @option{--si} option is
1012 equivalent to @option{--block-size=si}.
1014 @node Signal specifications
1015 @section Signal specifications
1016 @cindex signals, specifying
1018 A @var{signal} may be a signal name like @samp{HUP}, or a signal
1019 number like @samp{1}, or an exit status of a process terminated by the
1020 signal. A signal name can be given in canonical form or prefixed by
1021 @samp{SIG}. The case of the letters is ignored. The following signal names
1022 and numbers are supported on all @acronym{POSIX} compliant systems:
1028 2. Terminal interrupt.
1034 9. Kill (cannot be caught or ignored).
1042 Other supported signal names have system-dependent corresponding
1043 numbers. All systems conforming to @acronym{POSIX} 1003.1-2001 also
1044 support the following signals:
1048 Access to an undefined portion of a memory object.
1050 Child process terminated, stopped, or continued.
1052 Continue executing, if stopped.
1054 Erroneous arithmetic operation.
1056 Illegal Instruction.
1058 Write on a pipe with no one to read it.
1060 Invalid memory reference.
1062 Stop executing (cannot be caught or ignored).
1066 Background process attempting read.
1068 Background process attempting write.
1070 High bandwidth data is available at a socket.
1072 User-defined signal 1.
1074 User-defined signal 2.
1078 @acronym{POSIX} 1003.1-2001 systems that support the @acronym{XSI} extension
1079 also support the following signals:
1085 Profiling timer expired.
1089 Trace/breakpoint trap.
1091 Virtual timer expired.
1093 CPU time limit exceeded.
1095 File size limit exceeded.
1099 @acronym{POSIX} 1003.1-2001 systems that support the @acronym{XRT} extension
1100 also support at least eight real-time signals called @samp{RTMIN},
1101 @samp{RTMIN+1}, @dots{}, @samp{RTMAX-1}, @samp{RTMAX}.
1103 @node Disambiguating names and IDs
1104 @section chown and chgrp: Disambiguating user names and IDs
1105 @cindex user names, disambiguating
1106 @cindex user IDs, disambiguating
1107 @cindex group names, disambiguating
1108 @cindex group IDs, disambiguating
1109 @cindex disambiguating group names and IDs
1111 Since the @var{owner} and @var{group} arguments to @command{chown} and
1112 @command{chgrp} may be specified as names or numeric IDs, there is an
1114 What if a user or group @emph{name} is a string of digits?
1115 @footnote{Using a number as a user name is common in some environments.}
1116 Should the command interpret it as a user name or as an ID?
1117 @acronym{POSIX} requires that @command{chown} and @command{chgrp}
1118 first attempt to resolve the specified string as a name, and
1119 only once that fails, then try to interpret it as an ID.
1120 This is troublesome when you want to specify a numeric ID, say 42,
1121 and it must work even in a pathological situation where
1122 @samp{42} is a user name that maps to some other user ID, say 1000.
1123 Simply invoking @code{chown 42 F}, will set @file{F}s owner ID to
1124 1000---not what you intended.
1126 GNU @command{chown} and @command{chgrp} provide a way to work around this,
1127 that at the same time may result in a significant performance improvement
1128 by eliminating a database look-up.
1129 Simply precede each numeric user ID and/or group ID with a @samp{+},
1130 in order to force its interpretation as an integer:
1134 chgrp +$numeric_group_id another-file
1138 GNU @command{chown} and @command{chgrp}
1139 skip the name look-up process for each @samp{+}-prefixed string,
1140 because a string containing @samp{+} is never a valid user or group name.
1141 This syntax is accepted on most common Unix systems, but not on Solaris 10.
1143 @node Random sources
1144 @section Sources of random data
1146 @cindex random sources
1148 The @command{shuf}, @command{shred}, and @command{sort} commands
1149 sometimes need random data to do their work. For example, @samp{sort
1150 -R} must choose a hash function at random, and it needs random data to
1151 make this selection.
1153 By default these commands use an internal pseudorandom generator
1154 initialized by a small amount of entropy, but can be directed to use
1155 an external source with the @option{--random-source=@var{file}} option.
1156 An error is reported if @var{file} does not contain enough bytes.
1158 For example, the device file @file{/dev/urandom} could be used as the
1159 source of random data. Typically, this device gathers environmental
1160 noise from device drivers and other sources into an entropy pool, and
1161 uses the pool to generate random bits. If the pool is short of data,
1162 the device reuses the internal pool to produce more bits, using a
1163 cryptographically secure pseudorandom number generator. But be aware
1164 that this device is not designed for bulk random data generation
1165 and is relatively slow.
1167 @file{/dev/urandom} suffices for most practical uses, but applications
1168 requiring high-value or long-term protection of private data may
1169 require an alternate data source like @file{/dev/random} or
1170 @file{/dev/arandom}. The set of available sources depends on your
1173 To reproduce the results of an earlier invocation of a command, you
1174 can save some random data into a file and then use that file as the
1175 random source in earlier and later invocations of the command.
1177 @node Target directory
1178 @section Target directory
1180 @cindex target directory
1182 The @command{cp}, @command{install}, @command{ln}, and @command{mv}
1183 commands normally treat the last operand specially when it is a
1184 directory or a symbolic link to a directory. For example, @samp{cp
1185 source dest} is equivalent to @samp{cp source dest/source} if
1186 @file{dest} is a directory. Sometimes this behavior is not exactly
1187 what is wanted, so these commands support the following options to
1188 allow more fine-grained control:
1193 @itemx --no-target-directory
1194 @opindex --no-target-directory
1195 @cindex target directory
1196 @cindex destination directory
1197 Do not treat the last operand specially when it is a directory or a
1198 symbolic link to a directory. This can help avoid race conditions in
1199 programs that operate in a shared area. For example, when the command
1200 @samp{mv /tmp/source /tmp/dest} succeeds, there is no guarantee that
1201 @file{/tmp/source} was renamed to @file{/tmp/dest}: it could have been
1202 renamed to @file{/tmp/dest/source} instead, if some other process
1203 created @file{/tmp/dest} as a directory. However, if @file{mv
1204 -T /tmp/source /tmp/dest} succeeds, there is no
1205 question that @file{/tmp/source} was renamed to @file{/tmp/dest}.
1207 In the opposite situation, where you want the last operand to be
1208 treated as a directory and want a diagnostic otherwise, you can use
1209 the @option{--target-directory} (@option{-t}) option.
1211 @item -t @var{directory}
1212 @itemx @w{@kbd{--target-directory}=@var{directory}}
1213 @opindex --target-directory
1214 @cindex target directory
1215 @cindex destination directory
1216 Use @var{directory} as the directory component of each destination
1219 The interface for most programs is that after processing options and a
1220 finite (possibly zero) number of fixed-position arguments, the remaining
1221 argument list is either expected to be empty, or is a list of items
1222 (usually files) that will all be handled identically. The @command{xargs}
1223 program is designed to work well with this convention.
1225 The commands in the @command{mv}-family are unusual in that they take
1226 a variable number of arguments with a special case at the @emph{end}
1227 (namely, the target directory). This makes it nontrivial to perform some
1228 operations, e.g., ``move all files from here to ../d/'', because
1229 @code{mv * ../d/} might exhaust the argument space, and @code{ls | xargs ...}
1230 doesn't have a clean way to specify an extra final argument for each
1231 invocation of the subject command. (It can be done by going through a
1232 shell command, but that requires more human labor and brain power than
1235 The @w{@kbd{--target-directory}} (@option{-t}) option allows the @command{cp},
1236 @command{install}, @command{ln}, and @command{mv} programs to be used
1237 conveniently with @command{xargs}. For example, you can move the files
1238 from the current directory to a sibling directory, @code{d} like this:
1241 ls | xargs mv -t ../d --
1244 However, this doesn't move files whose names begin with @samp{.}.
1245 If you use the @sc{gnu} @command{find} program, you can move those
1246 files too, with this command:
1249 find . -mindepth 1 -maxdepth 1 \
1253 But both of the above approaches fail if there are no files in the
1254 current directory, or if any file has a name containing a blank or
1255 some other special characters.
1256 The following example removes those limitations and requires both
1257 @sc{gnu} @command{find} and @sc{gnu} @command{xargs}:
1260 find . -mindepth 1 -maxdepth 1 -print0 \
1261 | xargs --null --no-run-if-empty \
1268 The @option{--target-directory} (@option{-t}) and
1269 @option{--no-target-directory} (@option{-T})
1270 options cannot be combined.
1272 @node Trailing slashes
1273 @section Trailing slashes
1275 @cindex trailing slashes
1277 Some @sc{gnu} programs (at least @command{cp} and @command{mv}) allow you to
1278 remove any trailing slashes from each @var{source} argument before
1279 operating on it. The @w{@kbd{--strip-trailing-slashes}} option enables
1282 This is useful when a @var{source} argument may have a trailing slash and
1283 @c FIXME: mv's behavior in this case is system-dependent
1284 specify a symbolic link to a directory. This scenario is in fact rather
1285 common because some shells can automatically append a trailing slash when
1286 performing file name completion on such symbolic links. Without this
1287 option, @command{mv}, for example, (via the system's rename function) must
1288 interpret a trailing slash as a request to dereference the symbolic link
1289 and so must rename the indirectly referenced @emph{directory} and not
1290 the symbolic link. Although it may seem surprising that such behavior
1291 be the default, it is required by @acronym{POSIX} and is consistent with
1292 other parts of that standard.
1294 @node Traversing symlinks
1295 @section Traversing symlinks
1297 @cindex symbolic link to directory, controlling traversal of
1299 The following options modify how @command{chown} and @command{chgrp}
1300 @c FIXME: note that `du' has these options, too, but they have slightly
1301 @c different meaning.
1302 traverse a hierarchy when the @option{--recursive} (@option{-R})
1303 option is also specified.
1304 If more than one of the following options is specified, only the final
1306 These options specify whether processing a symbolic link to a directory
1307 entails operating on just the symbolic link or on all files in the
1308 hierarchy rooted at that directory.
1310 These options are independent of @option{--dereference} and
1311 @option{--no-dereference} (@option{-h}), which control whether to modify
1312 a symlink or its referent.
1319 @cindex symbolic link to directory, traverse each that is specified on the command line
1320 If @option{--recursive} (@option{-R}) is specified and
1321 a command line argument is a symbolic link to a directory, traverse it.
1328 @cindex symbolic link to directory, traverse each that is encountered
1329 In a recursive traversal, traverse every symbolic link to a directory
1330 that is encountered.
1337 @cindex symbolic link to directory, never traverse
1338 Do not traverse any symbolic links.
1339 This is the default if none of @option{-H}, @option{-L},
1340 or @option{-P} is specified.
1347 @node Treating / specially
1348 @section Treating @file{/} specially
1350 Certain commands can operate destructively on entire hierarchies.
1351 For example, if a user with appropriate privileges mistakenly runs
1352 @samp{rm -rf / tmp/junk}, that may remove
1353 all files on the entire system. Since there are so few
1354 legitimate uses for such a command,
1355 @sc{gnu} @command{rm} normally declines to operate on any directory
1356 that resolves to @file{/}. If you really want to try to remove all
1357 the files on your system, you can use the @option{--no-preserve-root}
1358 option, but the default behavior, specified by the
1359 @option{--preserve-option}, is safer for most purposes.
1361 The commands @command{chgrp}, @command{chmod} and @command{chown}
1362 can also operate destructively on entire hierarchies, so they too
1363 support these options. Although, unlike @command{rm}, they don't
1364 actually unlink files, these commands are arguably more dangerous
1365 when operating recursively on @file{/}, since they often work much
1366 more quickly, and hence damage more files before an alert user can
1367 interrupt them. Tradition and @acronym{POSIX} require these commands
1368 to operate recursively on @file{/}, so they default to
1369 @option{--no-preserve-root}, but using the @option{--preserve-root}
1370 option makes them safer for most purposes. For convenience you can
1371 specify @option{--preserve-root} in an alias or in a shell function.
1373 Note that the @option{--preserve-root} option also ensures
1374 that @command{chgrp} and @command{chown} do not modify @file{/}
1375 even when dereferencing a symlink pointing to @file{/}.
1377 @node Special built-in utilities
1378 @section Special built-in utilities
1380 Some programs like @command{nice} can invoke other programs; for
1381 example, the command @samp{nice cat file} invokes the program
1382 @command{cat} by executing the command @samp{cat file}. However,
1383 @dfn{special built-in utilities} like @command{exit} cannot be invoked
1384 this way. For example, the command @samp{nice exit} does not have a
1385 well-defined behavior: it may generate an error message instead of
1388 Here is a list of the special built-in utilities that are standardized
1389 by @acronym{POSIX} 1003.1-2004.
1392 @t{.@: : break continue eval exec exit export readonly
1393 return set shift times trap unset}
1396 For example, because @samp{.}, @samp{:}, and @samp{exec} are special,
1397 the commands @samp{nice . foo.sh}, @samp{nice :}, and @samp{nice exec
1398 pwd} do not work as you might expect.
1400 Many shells extend this list. For example, Bash has several extra
1401 special built-in utilities like @command{history}, and
1402 @command{suspend}, and with Bash the command @samp{nice suspend}
1403 generates an error message instead of suspending.
1405 @node Standards conformance
1406 @section Standards conformance
1408 @vindex POSIXLY_CORRECT
1409 In a few cases, the @sc{gnu} utilities' default behavior is
1410 incompatible with the @acronym{POSIX} standard. To suppress these
1411 incompatibilities, define the @env{POSIXLY_CORRECT} environment
1412 variable. Unless you are checking for @acronym{POSIX} conformance, you
1413 probably do not need to define @env{POSIXLY_CORRECT}.
1415 Newer versions of @acronym{POSIX} are occasionally incompatible with older
1416 versions. For example, older versions of @acronym{POSIX} required the
1417 command @samp{sort +1} to sort based on the second and succeeding
1418 fields in each input line, but starting with @acronym{POSIX} 1003.1-2001
1419 the same command is required to sort the file named @file{+1}, and you
1420 must instead use the command @samp{sort -k 2} to get the field-based
1423 @vindex _POSIX2_VERSION
1424 The @sc{gnu} utilities normally conform to the version of @acronym{POSIX}
1425 that is standard for your system. To cause them to conform to a
1426 different version of @acronym{POSIX}, define the @env{_POSIX2_VERSION}
1427 environment variable to a value of the form @var{yyyymm} specifying
1428 the year and month the standard was adopted. Two values are currently
1429 supported for @env{_POSIX2_VERSION}: @samp{199209} stands for
1430 @acronym{POSIX} 1003.2-1992, and @samp{200112} stands for @acronym{POSIX}
1431 1003.1-2001. For example, if you have a newer system but are running software
1432 that assumes an older version of @acronym{POSIX} and uses @samp{sort +1}
1433 or @samp{tail +10}, you can work around any compatibility problems by setting
1434 @samp{_POSIX2_VERSION=199209} in your environment.
1436 @node Output of entire files
1437 @chapter Output of entire files
1439 @cindex output of entire files
1440 @cindex entire files, output of
1442 These commands read and write entire files, possibly transforming them
1446 * cat invocation:: Concatenate and write files.
1447 * tac invocation:: Concatenate and write files in reverse.
1448 * nl invocation:: Number lines and write files.
1449 * od invocation:: Write files in octal or other formats.
1450 * base64 invocation:: Transform data into printable data.
1453 @node cat invocation
1454 @section @command{cat}: Concatenate and write files
1457 @cindex concatenate and write files
1458 @cindex copying files
1460 @command{cat} copies each @var{file} (@samp{-} means standard input), or
1461 standard input if none are given, to standard output. Synopsis:
1464 cat [@var{option}] [@var{file}]@dots{}
1467 The program accepts the following options. Also see @ref{Common options}.
1475 Equivalent to @option{-vET}.
1478 @itemx --number-nonblank
1480 @opindex --number-nonblank
1481 Number all nonempty output lines, starting with 1.
1485 Equivalent to @option{-vE}.
1490 @opindex --show-ends
1491 Display a @samp{$} after the end of each line.
1497 Number all output lines, starting with 1. This option is ignored
1498 if @option{-b} is in effect.
1501 @itemx --squeeze-blank
1503 @opindex --squeeze-blank
1504 @cindex squeezing empty lines
1505 Suppress repeated adjacent empty lines; output just one empty line
1510 Equivalent to @option{-vT}.
1515 @opindex --show-tabs
1516 Display TAB characters as @samp{^I}.
1520 Ignored; for @acronym{POSIX} compatibility.
1523 @itemx --show-nonprinting
1525 @opindex --show-nonprinting
1526 Display control characters except for LFD and TAB using
1527 @samp{^} notation and precede characters that have the high bit set with
1532 On systems like MS-DOS that distinguish between text and binary files,
1533 @command{cat} normally reads and writes in binary mode. However,
1534 @command{cat} reads in text mode if one of the options
1535 @option{-bensAE} is used or if @command{cat} is reading from standard
1536 input and standard input is a terminal. Similarly, @command{cat}
1537 writes in text mode if one of the options @option{-bensAE} is used or
1538 if standard output is a terminal.
1545 # Output f's contents, then standard input, then g's contents.
1548 # Copy standard input to standard output.
1553 @node tac invocation
1554 @section @command{tac}: Concatenate and write files in reverse
1557 @cindex reversing files
1559 @command{tac} copies each @var{file} (@samp{-} means standard input), or
1560 standard input if none are given, to standard output, reversing the
1561 records (lines by default) in each separately. Synopsis:
1564 tac [@var{option}]@dots{} [@var{file}]@dots{}
1567 @dfn{Records} are separated by instances of a string (newline by
1568 default). By default, this separator string is attached to the end of
1569 the record that it follows in the file.
1571 The program accepts the following options. Also see @ref{Common options}.
1579 The separator is attached to the beginning of the record that it
1580 precedes in the file.
1586 Treat the separator string as a regular expression. Users of @command{tac}
1587 on MS-DOS/MS-Windows should note that, since @command{tac} reads files in
1588 binary mode, each line of a text file might end with a CR/LF pair
1589 instead of the Unix-style LF.
1591 @item -s @var{separator}
1592 @itemx --separator=@var{separator}
1594 @opindex --separator
1595 Use @var{separator} as the record separator, instead of newline.
1603 @section @command{nl}: Number lines and write files
1606 @cindex numbering lines
1607 @cindex line numbering
1609 @command{nl} writes each @var{file} (@samp{-} means standard input), or
1610 standard input if none are given, to standard output, with line numbers
1611 added to some or all of the lines. Synopsis:
1614 nl [@var{option}]@dots{} [@var{file}]@dots{}
1617 @cindex logical pages, numbering on
1618 @command{nl} decomposes its input into (logical) pages; by default, the
1619 line number is reset to 1 at the top of each logical page. @command{nl}
1620 treats all of the input files as a single document; it does not reset
1621 line numbers or logical pages between files.
1623 @cindex headers, numbering
1624 @cindex body, numbering
1625 @cindex footers, numbering
1626 A logical page consists of three sections: header, body, and footer.
1627 Any of the sections can be empty. Each can be numbered in a different
1628 style from the others.
1630 The beginnings of the sections of logical pages are indicated in the
1631 input file by a line containing exactly one of these delimiter strings:
1642 The two characters from which these strings are made can be changed from
1643 @samp{\} and @samp{:} via options (see below), but the pattern and
1644 length of each string cannot be changed.
1646 A section delimiter is replaced by an empty line on output. Any text
1647 that comes before the first section delimiter string in the input file
1648 is considered to be part of a body section, so @command{nl} treats a
1649 file that contains no section delimiters as a single body section.
1651 The program accepts the following options. Also see @ref{Common options}.
1655 @item -b @var{style}
1656 @itemx --body-numbering=@var{style}
1658 @opindex --body-numbering
1659 Select the numbering style for lines in the body section of each
1660 logical page. When a line is not numbered, the current line number
1661 is not incremented, but the line number separator character is still
1662 prepended to the line. The styles are:
1668 number only nonempty lines (default for body),
1670 do not number lines (default for header and footer),
1672 number only lines that contain a match for the basic regular
1673 expression @var{bre}.
1674 @xref{Regular Expressions, , Regular Expressions, grep, The GNU Grep Manual}.
1678 @itemx --section-delimiter=@var{cd}
1680 @opindex --section-delimiter
1681 @cindex section delimiters of pages
1682 Set the section delimiter characters to @var{cd}; default is
1683 @samp{\:}. If only @var{c} is given, the second remains @samp{:}.
1684 (Remember to protect @samp{\} or other metacharacters from shell
1685 expansion with quotes or extra backslashes.)
1687 @item -f @var{style}
1688 @itemx --footer-numbering=@var{style}
1690 @opindex --footer-numbering
1691 Analogous to @option{--body-numbering}.
1693 @item -h @var{style}
1694 @itemx --header-numbering=@var{style}
1696 @opindex --header-numbering
1697 Analogous to @option{--body-numbering}.
1699 @item -i @var{number}
1700 @itemx --line-increment=@var{number}
1702 @opindex --line-increment
1703 Increment line numbers by @var{number} (default 1).
1705 @item -l @var{number}
1706 @itemx --join-blank-lines=@var{number}
1708 @opindex --join-blank-lines
1709 @cindex empty lines, numbering
1710 @cindex blank lines, numbering
1711 Consider @var{number} (default 1) consecutive empty lines to be one
1712 logical line for numbering, and only number the last one. Where fewer
1713 than @var{number} consecutive empty lines occur, do not number them.
1714 An empty line is one that contains no characters, not even spaces
1717 @item -n @var{format}
1718 @itemx --number-format=@var{format}
1720 @opindex --number-format
1721 Select the line numbering format (default is @code{rn}):
1725 @opindex ln @r{format for @command{nl}}
1726 left justified, no leading zeros;
1728 @opindex rn @r{format for @command{nl}}
1729 right justified, no leading zeros;
1731 @opindex rz @r{format for @command{nl}}
1732 right justified, leading zeros.
1736 @itemx --no-renumber
1738 @opindex --no-renumber
1739 Do not reset the line number at the start of a logical page.
1741 @item -s @var{string}
1742 @itemx --number-separator=@var{string}
1744 @opindex --number-separator
1745 Separate the line number from the text line in the output with
1746 @var{string} (default is the TAB character).
1748 @item -v @var{number}
1749 @itemx --starting-line-number=@var{number}
1751 @opindex --starting-line-number
1752 Set the initial line number on each logical page to @var{number} (default 1).
1754 @item -w @var{number}
1755 @itemx --number-width=@var{number}
1757 @opindex --number-width
1758 Use @var{number} characters for line numbers (default 6).
1766 @section @command{od}: Write files in octal or other formats
1769 @cindex octal dump of files
1770 @cindex hex dump of files
1771 @cindex ASCII dump of files
1772 @cindex file contents, dumping unambiguously
1774 @command{od} writes an unambiguous representation of each @var{file}
1775 (@samp{-} means standard input), or standard input if none are given.
1779 od [@var{option}]@dots{} [@var{file}]@dots{}
1780 od [-abcdfilosx]@dots{} [@var{file}] [[+]@var{offset}[.][b]]
1781 od [@var{option}]@dots{} --traditional [@var{file}] [[+]@var{offset}[.][b] [[+]@var{label}[.][b]]]
1784 Each line of output consists of the offset in the input, followed by
1785 groups of data from the file. By default, @command{od} prints the offset in
1786 octal, and each group of file data is a C @code{short int}'s worth of input
1787 printed as a single octal number.
1789 If @var{offset} is given, it specifies how many input bytes to skip
1790 before formatting and writing. By default, it is interpreted as an
1791 octal number, but the optional trailing decimal point causes it to be
1792 interpreted as decimal. If no decimal is specified and the offset
1793 begins with @samp{0x} or @samp{0X} it is interpreted as a hexadecimal
1794 number. If there is a trailing @samp{b}, the number of bytes skipped
1795 will be @var{offset} multiplied by 512.
1797 If a command is of both the first and second forms, the second form is
1798 assumed if the last operand begins with @samp{+} or (if there are two
1799 operands) a digit. For example, in @samp{od foo 10} and @samp{od +10}
1800 the @samp{10} is an offset, whereas in @samp{od 10} the @samp{10} is a
1803 The program accepts the following options. Also see @ref{Common options}.
1807 @item -A @var{radix}
1808 @itemx --address-radix=@var{radix}
1810 @opindex --address-radix
1811 @cindex radix for file offsets
1812 @cindex file offset radix
1813 Select the base in which file offsets are printed. @var{radix} can
1814 be one of the following:
1824 none (do not print offsets).
1827 The default is octal.
1829 @item -j @var{bytes}
1830 @itemx --skip-bytes=@var{bytes}
1832 @opindex --skip-bytes
1833 Skip @var{bytes} input bytes before formatting and writing. If
1834 @var{bytes} begins with @samp{0x} or @samp{0X}, it is interpreted in
1835 hexadecimal; otherwise, if it begins with @samp{0}, in octal; otherwise,
1837 @multiplierSuffixes{bytes}
1839 @item -N @var{bytes}
1840 @itemx --read-bytes=@var{bytes}
1842 @opindex --read-bytes
1843 Output at most @var{bytes} bytes of the input. Prefixes and suffixes on
1844 @code{bytes} are interpreted as for the @option{-j} option.
1846 @item -S @var{bytes}
1847 @itemx --strings[=@var{bytes}]
1850 @cindex string constants, outputting
1851 Instead of the normal output, output only @dfn{string constants}: at
1852 least @var{bytes} consecutive @acronym{ASCII} graphic characters,
1853 followed by a zero byte (@acronym{ASCII} @sc{nul}).
1854 Prefixes and suffixes on @code{bytes} are interpreted as for the
1857 If @var{n} is omitted with @option{--strings}, the default is 3.
1860 @itemx --format=@var{type}
1863 Select the format in which to output the file data. @var{type} is a
1864 string of one or more of the below type indicator characters. If you
1865 include more than one type indicator character in a single @var{type}
1866 string, or use this option more than once, @command{od} writes one copy
1867 of each output line using each of the data types that you specified,
1868 in the order that you specified.
1870 Adding a trailing ``z'' to any type specification appends a display
1871 of the @acronym{ASCII} character representation of the printable characters
1872 to the output line generated by the type specification.
1876 named character, ignoring high-order bit
1878 @acronym{ASCII} character or backslash escape,
1891 The type @code{a} outputs things like @samp{sp} for space, @samp{nl} for
1892 newline, and @samp{nul} for a zero byte. Only the least significant
1893 seven bits of each byte is used; the high-order bit is ignored.
1894 Type @code{c} outputs
1895 @samp{ }, @samp{\n}, and @code{\0}, respectively.
1898 Except for types @samp{a} and @samp{c}, you can specify the number
1899 of bytes to use in interpreting each number in the given data type
1900 by following the type indicator character with a decimal integer.
1901 Alternately, you can specify the size of one of the C compiler's
1902 built-in data types by following the type indicator character with
1903 one of the following characters. For integers (@samp{d}, @samp{o},
1904 @samp{u}, @samp{x}):
1917 For floating point (@code{f}):
1929 @itemx --output-duplicates
1931 @opindex --output-duplicates
1932 Output consecutive lines that are identical. By default, when two or
1933 more consecutive output lines would be identical, @command{od} outputs only
1934 the first line, and puts just an asterisk on the following line to
1935 indicate the elision.
1938 @itemx --width[=@var{n}]
1941 Dump @code{n} input bytes per output line. This must be a multiple of
1942 the least common multiple of the sizes associated with the specified
1945 If this option is not given at all, the default is 16. If @var{n} is
1946 omitted, the default is 32.
1950 The next several options are shorthands for format specifications.
1951 @sc{gnu} @command{od} accepts any combination of shorthands and format
1952 specification options. These options accumulate.
1958 Output as named characters. Equivalent to @samp{-t a}.
1962 Output as octal bytes. Equivalent to @samp{-t o1}.
1966 Output as @acronym{ASCII} characters or backslash escapes. Equivalent to
1971 Output as unsigned decimal two-byte units. Equivalent to @samp{-t u2}.
1975 Output as floats. Equivalent to @samp{-t fF}.
1979 Output as decimal ints. Equivalent to @samp{-t dI}.
1983 Output as decimal long ints. Equivalent to @samp{-t dL}.
1987 Output as octal two-byte units. Equivalent to @option{-t o2}.
1991 Output as decimal two-byte units. Equivalent to @option{-t d2}.
1995 Output as hexadecimal two-byte units. Equivalent to @samp{-t x2}.
1998 @opindex --traditional
1999 Recognize the non-option label argument that traditional @command{od}
2000 accepted. The following syntax:
2003 od --traditional [@var{file}] [[+]@var{offset}[.][b] [[+]@var{label}[.][b]]]
2007 can be used to specify at most one file and optional arguments
2008 specifying an offset and a pseudo-start address, @var{label}.
2009 The @var{label} argument is interpreted
2010 just like @var{offset}, but it specifies an initial pseudo-address. The
2011 pseudo-addresses are displayed in parentheses following any normal
2018 @node base64 invocation
2019 @section @command{base64}: Transform data into printable data
2022 @cindex base64 encoding
2024 @command{base64} transforms data read from a file, or standard input,
2025 into (or from) base64 encoded form. The base64 encoded form uses
2026 printable @acronym{ASCII} characters to represent binary data.
2030 base64 [@var{option}]@dots{} [@var{file}]
2031 base64 --decode [@var{option}]@dots{} [@var{file}]
2034 The base64 encoding expands data to roughly 133% of the original.
2035 The format conforms to
2036 @uref{ftp://ftp.rfc-editor.org/in-notes/rfc4648.txt, RFC 4648}.
2038 The program accepts the following options. Also see @ref{Common options}.
2043 @itemx --wrap=@var{cols}
2047 @cindex column to wrap data after
2048 During encoding, wrap lines after @var{cols} characters. This must be
2051 The default is to wrap after 76 characters. Use the value 0 to
2052 disable line wrapping altogether.
2058 @cindex Decode base64 data
2059 @cindex Base64 decoding
2060 Change the mode of operation, from the default of encoding data, to
2061 decoding data. Input is expected to be base64 encoded data, and the
2062 output will be the original data.
2065 @itemx --ignore-garbage
2067 @opindex --ignore-garbage
2068 @cindex Ignore garbage in base64 stream
2069 When decoding, newlines are always accepted.
2070 During decoding, ignore unrecognized bytes,
2071 to permit distorted data to be decoded.
2078 @node Formatting file contents
2079 @chapter Formatting file contents
2081 @cindex formatting file contents
2083 These commands reformat the contents of files.
2086 * fmt invocation:: Reformat paragraph text.
2087 * pr invocation:: Paginate or columnate files for printing.
2088 * fold invocation:: Wrap input lines to fit in specified width.
2092 @node fmt invocation
2093 @section @command{fmt}: Reformat paragraph text
2096 @cindex reformatting paragraph text
2097 @cindex paragraphs, reformatting
2098 @cindex text, reformatting
2100 @command{fmt} fills and joins lines to produce output lines of (at most)
2101 a given number of characters (75 by default). Synopsis:
2104 fmt [@var{option}]@dots{} [@var{file}]@dots{}
2107 @command{fmt} reads from the specified @var{file} arguments (or standard
2108 input if none are given), and writes to standard output.
2110 By default, blank lines, spaces between words, and indentation are
2111 preserved in the output; successive input lines with different
2112 indentation are not joined; tabs are expanded on input and introduced on
2115 @cindex line-breaking
2116 @cindex sentences and line-breaking
2117 @cindex Knuth, Donald E.
2118 @cindex Plass, Michael F.
2119 @command{fmt} prefers breaking lines at the end of a sentence, and tries to
2120 avoid line breaks after the first word of a sentence or before the last
2121 word of a sentence. A @dfn{sentence break} is defined as either the end
2122 of a paragraph or a word ending in any of @samp{.?!}, followed by two
2123 spaces or end of line, ignoring any intervening parentheses or quotes.
2124 Like @TeX{}, @command{fmt} reads entire ``paragraphs'' before choosing line
2125 breaks; the algorithm is a variant of that given by Donald E. Knuth
2126 and Michael F. Plass in ``Breaking Paragraphs Into Lines'',
2127 @cite{Software---Practice & Experience} @b{11}, 11 (November 1981),
2130 The program accepts the following options. Also see @ref{Common options}.
2135 @itemx --crown-margin
2137 @opindex --crown-margin
2138 @cindex crown margin
2139 @dfn{Crown margin} mode: preserve the indentation of the first two
2140 lines within a paragraph, and align the left margin of each subsequent
2141 line with that of the second line.
2144 @itemx --tagged-paragraph
2146 @opindex --tagged-paragraph
2147 @cindex tagged paragraphs
2148 @dfn{Tagged paragraph} mode: like crown margin mode, except that if
2149 indentation of the first line of a paragraph is the same as the
2150 indentation of the second, the first line is treated as a one-line
2156 @opindex --split-only
2157 Split lines only. Do not join short lines to form longer ones. This
2158 prevents sample lines of code, and other such ``formatted'' text from
2159 being unduly combined.
2162 @itemx --uniform-spacing
2164 @opindex --uniform-spacing
2165 Uniform spacing. Reduce spacing between words to one space, and spacing
2166 between sentences to two spaces.
2169 @itemx -w @var{width}
2170 @itemx --width=@var{width}
2171 @opindex -@var{width}
2174 Fill output lines up to @var{width} characters (default 75). @command{fmt}
2175 initially tries to make lines about 7% shorter than this, to give it
2176 room to balance line lengths.
2178 @item -p @var{prefix}
2179 @itemx --prefix=@var{prefix}
2180 Only lines beginning with @var{prefix} (possibly preceded by whitespace)
2181 are subject to formatting. The prefix and any preceding whitespace are
2182 stripped for the formatting and then re-attached to each formatted output
2183 line. One use is to format certain kinds of program comments, while
2184 leaving the code unchanged.
2192 @section @command{pr}: Paginate or columnate files for printing
2195 @cindex printing, preparing files for
2196 @cindex multicolumn output, generating
2197 @cindex merging files in parallel
2199 @command{pr} writes each @var{file} (@samp{-} means standard input), or
2200 standard input if none are given, to standard output, paginating and
2201 optionally outputting in multicolumn format; optionally merges all
2202 @var{file}s, printing all in parallel, one per column. Synopsis:
2205 pr [@var{option}]@dots{} [@var{file}]@dots{}
2209 By default, a 5-line header is printed at each page: two blank lines;
2210 a line with the date, the file name, and the page count; and two more
2211 blank lines. A footer of five blank lines is also printed.
2212 The default @var{page_length} is 66
2213 lines. The default number of text lines is therefore 56.
2214 The text line of the header takes the form
2215 @samp{@var{date} @var{string} @var{page}}, with spaces inserted around
2216 @var{string} so that the line takes up the full @var{page_width}. Here,
2217 @var{date} is the date (see the @option{-D} or @option{--date-format}
2218 option for details), @var{string} is the centered header string, and
2219 @var{page} identifies the page number. The @env{LC_MESSAGES} locale
2220 category affects the spelling of @var{page}; in the default C locale, it
2221 is @samp{Page @var{number}} where @var{number} is the decimal page
2224 Form feeds in the input cause page breaks in the output. Multiple form
2225 feeds produce empty pages.
2227 Columns are of equal width, separated by an optional string (default
2228 is @samp{space}). For multicolumn output, lines will always be truncated to
2229 @var{page_width} (default 72), unless you use the @option{-J} option.
2231 column output no line truncation occurs by default. Use @option{-W} option to
2232 truncate lines in that case.
2234 The following changes were made in version 1.22i and apply to later
2235 versions of @command{pr}:
2236 @c FIXME: this whole section here sounds very awkward to me. I
2237 @c made a few small changes, but really it all needs to be redone. - Brian
2238 @c OK, I fixed another sentence or two, but some of it I just don't understand.
2243 Some small @var{letter options} (@option{-s}, @option{-w}) have been
2244 redefined for better @acronym{POSIX} compliance. The output of some further
2245 cases has been adapted to other Unix systems. These changes are not
2246 compatible with earlier versions of the program.
2249 Some @var{new capital letter} options (@option{-J}, @option{-S}, @option{-W})
2250 have been introduced to turn off unexpected interferences of small letter
2251 options. The @option{-N} option and the second argument @var{last_page}
2252 of @samp{+FIRST_PAGE} offer more flexibility. The detailed handling of
2253 form feeds set in the input files requires the @option{-T} option.
2256 Capital letter options override small letter ones.
2259 Some of the option-arguments (compare @option{-s}, @option{-e},
2260 @option{-i}, @option{-n}) cannot be specified as separate arguments from the
2261 preceding option letter (already stated in the @acronym{POSIX} specification).
2264 The program accepts the following options. Also see @ref{Common options}.
2268 @item +@var{first_page}[:@var{last_page}]
2269 @itemx --pages=@var{first_page}[:@var{last_page}]
2270 @c The two following @opindex lines evoke warnings because they contain `:'
2271 @c The `info' spec does not permit that. If we use those lines, we end
2272 @c up with truncated index entries that don't work.
2273 @c @opindex +@var{first_page}[:@var{last_page}]
2274 @c @opindex --pages=@var{first_page}[:@var{last_page}]
2275 @opindex +@var{page_range}
2276 @opindex --pages=@var{page_range}
2277 Begin printing with page @var{first_page} and stop with @var{last_page}.
2278 Missing @samp{:@var{last_page}} implies end of file. While estimating
2279 the number of skipped pages each form feed in the input file results
2280 in a new page. Page counting with and without @samp{+@var{first_page}}
2281 is identical. By default, counting starts with the first page of input
2282 file (not first page printed). Line numbering may be altered by @option{-N}
2286 @itemx --columns=@var{column}
2287 @opindex -@var{column}
2289 @cindex down columns
2290 With each single @var{file}, produce @var{column} columns of output
2291 (default is 1) and print columns down, unless @option{-a} is used. The
2292 column width is automatically decreased as @var{column} increases; unless
2293 you use the @option{-W/-w} option to increase @var{page_width} as well.
2294 This option might well cause some lines to be truncated. The number of
2295 lines in the columns on each page are balanced. The options @option{-e}
2296 and @option{-i} are on for multiple text-column output. Together with
2297 @option{-J} option column alignment and line truncation is turned off.
2298 Lines of full length are joined in a free field format and @option{-S}
2299 option may set field separators. @option{-@var{column}} may not be used
2300 with @option{-m} option.
2306 @cindex across columns
2307 With each single @var{file}, print columns across rather than down. The
2308 @option{-@var{column}} option must be given with @var{column} greater than one.
2309 If a line is too long to fit in a column, it is truncated.
2312 @itemx --show-control-chars
2314 @opindex --show-control-chars
2315 Print control characters using hat notation (e.g., @samp{^G}); print
2316 other nonprinting characters in octal backslash notation. By default,
2317 nonprinting characters are not changed.
2320 @itemx --double-space
2322 @opindex --double-space
2323 @cindex double spacing
2324 Double space the output.
2326 @item -D @var{format}
2327 @itemx --date-format=@var{format}
2328 @cindex time formats
2329 @cindex formatting times
2330 Format header dates using @var{format}, using the same conventions as
2331 for the command @samp{date +@var{format}}; @xref{date invocation}.
2332 Except for directives, which start with
2333 @samp{%}, characters in @var{format} are printed unchanged. You can use
2334 this option to specify an arbitrary string in place of the header date,
2335 e.g., @option{--date-format="Monday morning"}.
2337 @vindex POSIXLY_CORRECT
2339 The default date format is @samp{%Y-%m-%d %H:%M} (for example,
2340 @samp{2001-12-04 23:59});
2341 but if the @env{POSIXLY_CORRECT} environment variable is set
2342 and the @env{LC_TIME} locale category specifies the @acronym{POSIX}
2343 locale, the default is @samp{%b %e %H:%M %Y} (for example,
2344 @samp{Dec@ @ 4 23:59 2001}.
2347 Time stamps are listed according to the time zone rules specified by
2348 the @env{TZ} environment variable, or by the system default rules if
2349 @env{TZ} is not set. @xref{TZ Variable,, Specifying the Time Zone
2350 with @env{TZ}, libc, The GNU C Library Reference Manual}.
2352 @item -e[@var{in-tabchar}[@var{in-tabwidth}]]
2353 @itemx --expand-tabs[=@var{in-tabchar}[@var{in-tabwidth}]]
2355 @opindex --expand-tabs
2357 Expand @var{tab}s to spaces on input. Optional argument @var{in-tabchar} is
2358 the input tab character (default is the TAB character). Second optional
2359 argument @var{in-tabwidth} is the input tab character's width (default
2367 @opindex --form-feed
2368 Use a form feed instead of newlines to separate output pages. This does
2369 not alter the default page length of 66 lines.
2371 @item -h @var{header}
2372 @itemx --header=@var{header}
2375 Replace the file name in the header with the centered string @var{header}.
2376 When using the shell, @var{header} should be quoted and should be
2377 separated from @option{-h} by a space.
2379 @item -i[@var{out-tabchar}[@var{out-tabwidth}]]
2380 @itemx --output-tabs[=@var{out-tabchar}[@var{out-tabwidth}]]
2382 @opindex --output-tabs
2384 Replace spaces with @var{tab}s on output. Optional argument @var{out-tabchar}
2385 is the output tab character (default is the TAB character). Second optional
2386 argument @var{out-tabwidth} is the output tab character's width (default
2392 @opindex --join-lines
2393 Merge lines of full length. Used together with the column options
2394 @option{-@var{column}}, @option{-a -@var{column}} or @option{-m}. Turns off
2395 @option{-W/-w} line truncation;
2396 no column alignment used; may be used with
2397 @option{--sep-string[=@var{string}]}. @option{-J} has been introduced
2398 (together with @option{-W} and @option{--sep-string})
2399 to disentangle the old (@acronym{POSIX}-compliant) options @option{-w} and
2400 @option{-s} along with the three column options.
2403 @item -l @var{page_length}
2404 @itemx --length=@var{page_length}
2407 Set the page length to @var{page_length} (default 66) lines, including
2408 the lines of the header [and the footer]. If @var{page_length} is less
2409 than or equal to 10, the header and footer are omitted, as if the
2410 @option{-t} option had been given.
2416 Merge and print all @var{file}s in parallel, one in each column. If a
2417 line is too long to fit in a column, it is truncated, unless the @option{-J}
2418 option is used. @option{--sep-string[=@var{string}]} may be used.
2420 some @var{file}s (form feeds set) produce empty columns, still marked
2421 by @var{string}. The result is a continuous line numbering and column
2422 marking throughout the whole merged file. Completely empty merged pages
2423 show no separators or line numbers. The default header becomes
2424 @samp{@var{date} @var{page}} with spaces inserted in the middle; this
2425 may be used with the @option{-h} or @option{--header} option to fill up
2426 the middle blank part.
2428 @item -n[@var{number-separator}[@var{digits}]]
2429 @itemx --number-lines[=@var{number-separator}[@var{digits}]]
2431 @opindex --number-lines
2432 Provide @var{digits} digit line numbering (default for @var{digits} is
2433 5). With multicolumn output the number occupies the first @var{digits}
2434 column positions of each text column or only each line of @option{-m}
2435 output. With single column output the number precedes each line just as
2436 @option{-m} does. Default counting of the line numbers starts with the
2437 first line of the input file (not the first line printed, compare the
2438 @option{--page} option and @option{-N} option).
2439 Optional argument @var{number-separator} is the character appended to
2440 the line number to separate it from the text followed. The default
2441 separator is the TAB character. In a strict sense a TAB is always
2442 printed with single column output only. The TAB width varies
2443 with the TAB position, e.g., with the left @var{margin} specified
2444 by @option{-o} option. With multicolumn output priority is given to
2445 @samp{equal width of output columns} (a @acronym{POSIX} specification).
2446 The TAB width is fixed to the value of the first column and does
2447 not change with different values of left @var{margin}. That means a
2448 fixed number of spaces is always printed in the place of the
2449 @var{number-separator} TAB. The tabification depends upon the output
2452 @item -N @var{line_number}
2453 @itemx --first-line-number=@var{line_number}
2455 @opindex --first-line-number
2456 Start line counting with the number @var{line_number} at first line of
2457 first page printed (in most cases not the first line of the input file).
2459 @item -o @var{margin}
2460 @itemx --indent=@var{margin}
2463 @cindex indenting lines
2465 Indent each line with a margin @var{margin} spaces wide (default is zero).
2466 The total page width is the size of the margin plus the @var{page_width}
2467 set with the @option{-W/-w} option. A limited overflow may occur with
2468 numbered single column output (compare @option{-n} option).
2471 @itemx --no-file-warnings
2473 @opindex --no-file-warnings
2474 Do not print a warning message when an argument @var{file} cannot be
2475 opened. (The exit status will still be nonzero, however.)
2477 @item -s[@var{char}]
2478 @itemx --separator[=@var{char}]
2480 @opindex --separator
2481 Separate columns by a single character @var{char}. The default for
2482 @var{char} is the TAB character without @option{-w} and @samp{no
2483 character} with @option{-w}. Without @option{-s} the default separator
2484 @samp{space} is set. @option{-s[char]} turns off line truncation of all
2485 three column options (@option{-COLUMN}|@option{-a -COLUMN}|@option{-m}) unless
2486 @option{-w} is set. This is a @acronym{POSIX}-compliant formulation.
2489 @item -S@var{string}
2490 @itemx --sep-string[=@var{string}]
2492 @opindex --sep-string
2493 Use @var{string} to separate output columns. The @option{-S} option doesn't
2494 affect the @option{-W/-w} option, unlike the @option{-s} option which does. It
2495 does not affect line truncation or column alignment.
2496 Without @option{-S}, and with @option{-J}, @command{pr} uses the default output
2498 Without @option{-S} or @option{-J}, @command{pr} uses a @samp{space}
2499 (same as @option{-S"@w{ }"}). @option{--sep-string} with no
2500 @samp{=@var{string}} is equivalent to @option{--sep-string=""}.
2503 @itemx --omit-header
2505 @opindex --omit-header
2506 Do not print the usual header [and footer] on each page, and do not fill
2507 out the bottom of pages (with blank lines or a form feed). No page
2508 structure is produced, but form feeds set in the input files are retained.
2509 The predefined pagination is not changed. @option{-t} or @option{-T} may be
2510 useful together with other options; e.g.: @option{-t -e4}, expand TAB characters
2511 in the input file to 4 spaces but don't make any other changes. Use of
2512 @option{-t} overrides @option{-h}.
2515 @itemx --omit-pagination
2517 @opindex --omit-pagination
2518 Do not print header [and footer]. In addition eliminate all form feeds
2519 set in the input files.
2522 @itemx --show-nonprinting
2524 @opindex --show-nonprinting
2525 Print nonprinting characters in octal backslash notation.
2527 @item -w @var{page_width}
2528 @itemx --width=@var{page_width}
2531 Set page width to @var{page_width} characters for multiple text-column
2532 output only (default for @var{page_width} is 72). @option{-s[CHAR]} turns
2533 off the default page width and any line truncation and column alignment.
2534 Lines of full length are merged, regardless of the column options
2535 set. No @var{page_width} setting is possible with single column output.
2536 A @acronym{POSIX}-compliant formulation.
2538 @item -W @var{page_width}
2539 @itemx --page_width=@var{page_width}
2541 @opindex --page_width
2542 Set the page width to @var{page_width} characters. That's valid with and
2543 without a column option. Text lines are truncated, unless @option{-J}
2544 is used. Together with one of the three column options
2545 (@option{-@var{column}}, @option{-a -@var{column}} or @option{-m}) column
2546 alignment is always used. The separator options @option{-S} or @option{-s}
2547 don't affect the @option{-W} option. Default is 72 characters. Without
2548 @option{-W @var{page_width}} and without any of the column options NO line
2549 truncation is used (defined to keep downward compatibility and to meet
2550 most frequent tasks). That's equivalent to @option{-W 72 -J}. The header
2551 line is never truncated.
2558 @node fold invocation
2559 @section @command{fold}: Wrap input lines to fit in specified width
2562 @cindex wrapping long input lines
2563 @cindex folding long input lines
2565 @command{fold} writes each @var{file} (@option{-} means standard input), or
2566 standard input if none are given, to standard output, breaking long
2570 fold [@var{option}]@dots{} [@var{file}]@dots{}
2573 By default, @command{fold} breaks lines wider than 80 columns. The output
2574 is split into as many lines as necessary.
2576 @cindex screen columns
2577 @command{fold} counts screen columns by default; thus, a tab may count more
2578 than one column, backspace decreases the column count, and carriage
2579 return sets the column to zero.
2581 The program accepts the following options. Also see @ref{Common options}.
2589 Count bytes rather than columns, so that tabs, backspaces, and carriage
2590 returns are each counted as taking up one column, just like other
2597 Break at word boundaries: the line is broken after the last blank before
2598 the maximum line length. If the line contains no such blanks, the line
2599 is broken at the maximum line length as usual.
2601 @item -w @var{width}
2602 @itemx --width=@var{width}
2605 Use a maximum line length of @var{width} columns instead of 80.
2607 For compatibility @command{fold} supports an obsolete option syntax
2608 @option{-@var{width}}. New scripts should use @option{-w @var{width}}
2616 @node Output of parts of files
2617 @chapter Output of parts of files
2619 @cindex output of parts of files
2620 @cindex parts of files, output of
2622 These commands output pieces of the input.
2625 * head invocation:: Output the first part of files.
2626 * tail invocation:: Output the last part of files.
2627 * split invocation:: Split a file into fixed-size pieces.
2628 * csplit invocation:: Split a file into context-determined pieces.
2631 @node head invocation
2632 @section @command{head}: Output the first part of files
2635 @cindex initial part of files, outputting
2636 @cindex first part of files, outputting
2638 @command{head} prints the first part (10 lines by default) of each
2639 @var{file}; it reads from standard input if no files are given or
2640 when given a @var{file} of @option{-}. Synopsis:
2643 head [@var{option}]@dots{} [@var{file}]@dots{}
2646 If more than one @var{file} is specified, @command{head} prints a
2647 one-line header consisting of:
2650 ==> @var{file name} <==
2654 before the output for each @var{file}.
2656 The program accepts the following options. Also see @ref{Common options}.
2661 @itemx --bytes=@var{k}
2664 Print the first @var{k} bytes, instead of initial lines.
2665 However, if @var{k} starts with a @samp{-},
2666 print all but the last @var{k} bytes of each file.
2667 @multiplierSuffixes{k}
2670 @itemx --lines=@var{k}
2673 Output the first @var{k} lines.
2674 However, if @var{k} starts with a @samp{-},
2675 print all but the last @var{k} lines of each file.
2676 Size multiplier suffixes are the same as with the @option{-c} option.
2684 Never print file name headers.
2690 Always print file name headers.
2694 For compatibility @command{head} also supports an obsolete option syntax
2695 @option{-@var{count}@var{options}}, which is recognized only if it is
2696 specified first. @var{count} is a decimal number optionally followed
2697 by a size letter (@samp{b}, @samp{k}, @samp{m}) as in @option{-c}, or
2698 @samp{l} to mean count by lines, or other option letters (@samp{cqv}).
2699 Scripts intended for standard hosts should use @option{-c @var{count}}
2700 or @option{-n @var{count}} instead. If your script must also run on
2701 hosts that support only the obsolete syntax, it is usually simpler to
2702 avoid @command{head}, e.g., by using @samp{sed 5q} instead of
2708 @node tail invocation
2709 @section @command{tail}: Output the last part of files
2712 @cindex last part of files, outputting
2714 @command{tail} prints the last part (10 lines by default) of each
2715 @var{file}; it reads from standard input if no files are given or
2716 when given a @var{file} of @samp{-}. Synopsis:
2719 tail [@var{option}]@dots{} [@var{file}]@dots{}
2722 If more than one @var{file} is specified, @command{tail} prints a
2723 one-line header consisting of:
2726 ==> @var{file name} <==
2730 before the output for each @var{file}.
2732 @cindex BSD @command{tail}
2733 @sc{gnu} @command{tail} can output any amount of data (some other versions of
2734 @command{tail} cannot). It also has no @option{-r} option (print in
2735 reverse), since reversing a file is really a different job from printing
2736 the end of a file; BSD @command{tail} (which is the one with @option{-r}) can
2737 only reverse files that are at most as large as its buffer, which is
2738 typically 32 KiB@. A more reliable and versatile way to reverse files is
2739 the @sc{gnu} @command{tac} command.
2741 The program accepts the following options. Also see @ref{Common options}.
2746 @itemx --bytes=@var{k}
2749 Output the last @var{k} bytes, instead of final lines.
2750 However, if @var{k} starts with a @samp{+}, start printing with the
2751 @var{k}th byte from the start of each file, instead of from the end.
2752 @multiplierSuffixes{k}
2755 @itemx --follow[=@var{how}]
2758 @cindex growing files
2759 @vindex name @r{follow option}
2760 @vindex descriptor @r{follow option}
2761 Loop forever trying to read more characters at the end of the file,
2762 presumably because the file is growing.
2763 If more than one file is given, @command{tail} prints a header whenever it
2764 gets output from a different file, to indicate which file that output is
2767 There are two ways to specify how you'd like to track files with this option,
2768 but that difference is noticeable only when a followed file is removed or
2770 If you'd like to continue to track the end of a growing file even after
2771 it has been unlinked, use @option{--follow=descriptor}. This is the default
2772 behavior, but it is not useful if you're tracking a log file that may be
2773 rotated (removed or renamed, then reopened). In that case, use
2774 @option{--follow=name} to track the named file, perhaps by reopening it
2775 periodically to see if it has been removed and recreated by some other program.
2776 Note that the inotify-based implementation handles this case without
2777 the need for any periodic reopening.
2779 No matter which method you use, if the tracked file is determined to have
2780 shrunk, @command{tail} prints a message saying the file has been truncated
2781 and resumes tracking the end of the file from the newly-determined endpoint.
2783 When a file is removed, @command{tail}'s behavior depends on whether it is
2784 following the name or the descriptor. When following by name, tail can
2785 detect that a file has been removed and gives a message to that effect,
2786 and if @option{--retry} has been specified it will continue checking
2787 periodically to see if the file reappears.
2788 When following a descriptor, tail does not detect that the file has
2789 been unlinked or renamed and issues no message; even though the file
2790 may no longer be accessible via its original name, it may still be
2793 The option values @samp{descriptor} and @samp{name} may be specified only
2794 with the long form of the option, not with @option{-f}.
2796 The @option{-f} option is ignored if
2797 no @var{file} operand is specified and standard input is a FIFO or a pipe.
2798 Likewise, the @option{-f} option has no effect for any
2799 operand specified as @samp{-}, when standard input is a FIFO or a pipe.
2803 This option is the same as @option{--follow=name --retry}. That is, tail
2804 will attempt to reopen a file when it is removed. Should this fail, tail
2805 will keep trying until it becomes accessible again.
2809 This option is useful mainly when following by name (i.e., with
2810 @option{--follow=name}).
2811 Without this option, when tail encounters a file that doesn't
2812 exist or is otherwise inaccessible, it reports that fact and
2813 never checks it again.
2815 @itemx --sleep-interval=@var{number}
2816 @opindex --sleep-interval
2817 Change the number of seconds to wait between iterations (the default is 1.0).
2818 During one iteration, every specified file is checked to see if it has
2820 Historical implementations of @command{tail} have required that
2821 @var{number} be an integer. However, GNU @command{tail} accepts
2822 an arbitrary floating point number (using a period before any
2825 @itemx --pid=@var{pid}
2827 When following by name or by descriptor, you may specify the process ID,
2828 @var{pid}, of the sole writer of all @var{file} arguments. Then, shortly
2829 after that process terminates, tail will also terminate. This will
2830 work properly only if the writer and the tailing process are running on
2831 the same machine. For example, to save the output of a build in a file
2832 and to watch the file grow, if you invoke @command{make} and @command{tail}
2833 like this then the tail process will stop when your build completes.
2834 Without this option, you would have had to kill the @code{tail -f}
2838 $ make >& makerr & tail --pid=$! -f makerr
2841 If you specify a @var{pid} that is not in use or that does not correspond
2842 to the process that is writing to the tailed files, then @command{tail}
2843 may terminate long before any @var{file}s stop growing or it may not
2844 terminate until long after the real writer has terminated.
2845 Note that @option{--pid} cannot be supported on some systems; @command{tail}
2846 will print a warning if this is the case.
2848 @itemx --max-unchanged-stats=@var{n}
2849 @opindex --max-unchanged-stats
2850 When tailing a file by name, if there have been @var{n} (default
2851 n=@value{DEFAULT_MAX_N_UNCHANGED_STATS_BETWEEN_OPENS}) consecutive
2852 iterations for which the file has not changed, then
2853 @code{open}/@code{fstat} the file to determine if that file name is
2854 still associated with the same device/inode-number pair as before.
2855 When following a log file that is rotated, this is approximately the
2856 number of seconds between when tail prints the last pre-rotation lines
2857 and when it prints the lines that have accumulated in the new log file.
2858 This option is meaningful only when following by name.
2861 @itemx --lines=@var{k}
2864 Output the last @var{k} lines.
2865 However, if @var{k} starts with a @samp{+}, start printing with the
2866 @var{k}th line from the start of each file, instead of from the end.
2867 Size multiplier suffixes are the same as with the @option{-c} option.
2875 Never print file name headers.
2881 Always print file name headers.
2885 For compatibility @command{tail} also supports an obsolete usage
2886 @samp{tail -[@var{count}][bcl][f] [@var{file}]}, which is recognized
2887 only if it does not conflict with the usage described
2888 above. This obsolete form uses exactly one option and at most one
2889 file. In the option, @var{count} is an optional decimal number optionally
2890 followed by a size letter (@samp{b}, @samp{c}, @samp{l}) to mean count
2891 by 512-byte blocks, bytes, or lines, optionally followed by @samp{f}
2892 which has the same meaning as @option{-f}.
2894 @vindex _POSIX2_VERSION
2895 On older systems, the leading @samp{-} can be replaced by @samp{+} in
2896 the obsolete option syntax with the same meaning as in counts, and
2897 obsolete usage overrides normal usage when the two conflict.
2898 This obsolete behavior can be enabled or disabled with the
2899 @env{_POSIX2_VERSION} environment variable (@pxref{Standards
2902 Scripts intended for use on standard hosts should avoid obsolete
2903 syntax and should use @option{-c @var{count}[b]}, @option{-n
2904 @var{count}}, and/or @option{-f} instead. If your script must also
2905 run on hosts that support only the obsolete syntax, you can often
2906 rewrite it to avoid problematic usages, e.g., by using @samp{sed -n
2907 '$p'} rather than @samp{tail -1}. If that's not possible, the script
2908 can use a test like @samp{if tail -c +1 </dev/null >/dev/null 2>&1;
2909 then @dots{}} to decide which syntax to use.
2911 Even if your script assumes the standard behavior, you should still
2912 beware usages whose behaviors differ depending on the @acronym{POSIX}
2913 version. For example, avoid @samp{tail - main.c}, since it might be
2914 interpreted as either @samp{tail main.c} or as @samp{tail -- -
2915 main.c}; avoid @samp{tail -c 4}, since it might mean either @samp{tail
2916 -c4} or @samp{tail -c 10 4}; and avoid @samp{tail +4}, since it might
2917 mean either @samp{tail ./+4} or @samp{tail -n +4}.
2922 @node split invocation
2923 @section @command{split}: Split a file into fixed-size pieces
2926 @cindex splitting a file into pieces
2927 @cindex pieces, splitting a file into
2929 @command{split} creates output files containing consecutive sections of
2930 @var{input} (standard input if none is given or @var{input} is
2931 @samp{-}). Synopsis:
2934 split [@var{option}] [@var{input} [@var{prefix}]]
2937 By default, @command{split} puts 1000 lines of @var{input} (or whatever is
2938 left over for the last section), into each output file.
2940 @cindex output file name prefix
2941 The output files' names consist of @var{prefix} (@samp{x} by default)
2942 followed by a group of characters (@samp{aa}, @samp{ab}, @dots{} by
2943 default), such that concatenating the output files in traditional
2944 sorted order by file name produces
2945 the original input file. If the output file names are exhausted,
2946 @command{split} reports an error without deleting the output files
2949 The program accepts the following options. Also see @ref{Common options}.
2953 @item -l @var{lines}
2954 @itemx --lines=@var{lines}
2957 Put @var{lines} lines of @var{input} into each output file.
2959 For compatibility @command{split} also supports an obsolete
2960 option syntax @option{-@var{lines}}. New scripts should use @option{-l
2961 @var{lines}} instead.
2964 @itemx --bytes=@var{size}
2967 Put @var{size} bytes of @var{input} into each output file.
2968 @multiplierSuffixes{size}
2971 @itemx --line-bytes=@var{size}
2973 @opindex --line-bytes
2974 Put into each output file as many complete lines of @var{input} as
2975 possible without exceeding @var{size} bytes. Individual lines longer than
2976 @var{size} bytes are broken into multiple files.
2977 @var{size} has the same format as for the @option{--bytes} option.
2979 @item -a @var{length}
2980 @itemx --suffix-length=@var{length}
2982 @opindex --suffix-length
2983 Use suffixes of length @var{length}. The default @var{length} is 2.
2986 @itemx --numeric-suffixes
2988 @opindex --numeric-suffixes
2989 Use digits in suffixes rather than lower-case letters.
2993 Write a diagnostic just before each output file is opened.
3000 @node csplit invocation
3001 @section @command{csplit}: Split a file into context-determined pieces
3004 @cindex context splitting
3005 @cindex splitting a file into pieces by context
3007 @command{csplit} creates zero or more output files containing sections of
3008 @var{input} (standard input if @var{input} is @samp{-}). Synopsis:
3011 csplit [@var{option}]@dots{} @var{input} @var{pattern}@dots{}
3014 The contents of the output files are determined by the @var{pattern}
3015 arguments, as detailed below. An error occurs if a @var{pattern}
3016 argument refers to a nonexistent line of the input file (e.g., if no
3017 remaining line matches a given regular expression). After every
3018 @var{pattern} has been matched, any remaining input is copied into one
3021 By default, @command{csplit} prints the number of bytes written to each
3022 output file after it has been created.
3024 The types of pattern arguments are:
3029 Create an output file containing the input up to but not including line
3030 @var{n} (a positive integer). If followed by a repeat count, also
3031 create an output file containing the next @var{n} lines of the input
3032 file once for each repeat.
3034 @item /@var{regexp}/[@var{offset}]
3035 Create an output file containing the current line up to (but not
3036 including) the next line of the input file that contains a match for
3037 @var{regexp}. The optional @var{offset} is an integer.
3038 If it is given, the input up to (but not including) the
3039 matching line plus or minus @var{offset} is put into the output file,
3040 and the line after that begins the next section of input.
3042 @item %@var{regexp}%[@var{offset}]
3043 Like the previous type, except that it does not create an output
3044 file, so that section of the input file is effectively ignored.
3046 @item @{@var{repeat-count}@}
3047 Repeat the previous pattern @var{repeat-count} additional
3048 times. The @var{repeat-count} can either be a positive integer or an
3049 asterisk, meaning repeat as many times as necessary until the input is
3054 The output files' names consist of a prefix (@samp{xx} by default)
3055 followed by a suffix. By default, the suffix is an ascending sequence
3056 of two-digit decimal numbers from @samp{00} to @samp{99}. In any case,
3057 concatenating the output files in sorted order by file name produces the
3058 original input file.
3060 By default, if @command{csplit} encounters an error or receives a hangup,
3061 interrupt, quit, or terminate signal, it removes any output files
3062 that it has created so far before it exits.
3064 The program accepts the following options. Also see @ref{Common options}.
3068 @item -f @var{prefix}
3069 @itemx --prefix=@var{prefix}
3072 @cindex output file name prefix
3073 Use @var{prefix} as the output file name prefix.
3075 @item -b @var{suffix}
3076 @itemx --suffix=@var{suffix}
3079 @cindex output file name suffix
3080 Use @var{suffix} as the output file name suffix. When this option is
3081 specified, the suffix string must include exactly one
3082 @code{printf(3)}-style conversion specification, possibly including
3083 format specification flags, a field width, a precision specifications,
3084 or all of these kinds of modifiers. The format letter must convert a
3085 binary integer argument to readable form; thus, only @samp{d}, @samp{i},
3086 @samp{u}, @samp{o}, @samp{x}, and @samp{X} conversions are allowed. The
3087 entire @var{suffix} is given (with the current output file number) to
3088 @code{sprintf(3)} to form the file name suffixes for each of the
3089 individual output files in turn. If this option is used, the
3090 @option{--digits} option is ignored.
3092 @item -n @var{digits}
3093 @itemx --digits=@var{digits}
3096 Use output file names containing numbers that are @var{digits} digits
3097 long instead of the default 2.
3102 @opindex --keep-files
3103 Do not remove output files when errors are encountered.
3106 @itemx --elide-empty-files
3108 @opindex --elide-empty-files
3109 Suppress the generation of zero-length output files. (In cases where
3110 the section delimiters of the input file are supposed to mark the first
3111 lines of each of the sections, the first output file will generally be a
3112 zero-length file unless you use this option.) The output file sequence
3113 numbers always run consecutively starting from 0, even when this option
3124 Do not print counts of output file sizes.
3130 Here is an example of its usage.
3131 First, create an empty directory for the exercise,
3138 Now, split the sequence of 1..14 on lines that end with 0 or 5:
3141 $ seq 14 | csplit - '/[05]$/' '@{*@}'
3147 Each number printed above is the size of an output
3148 file that csplit has just created.
3149 List the names of those output files:
3156 Use @command{head} to show their contents:
3181 @node Summarizing files
3182 @chapter Summarizing files
3184 @cindex summarizing files
3186 These commands generate just a few numbers representing entire
3190 * wc invocation:: Print newline, word, and byte counts.
3191 * sum invocation:: Print checksum and block counts.
3192 * cksum invocation:: Print CRC checksum and byte counts.
3193 * md5sum invocation:: Print or check MD5 digests.
3194 * sha1sum invocation:: Print or check SHA-1 digests.
3195 * sha2 utilities:: Print or check SHA-2 digests.
3200 @section @command{wc}: Print newline, word, and byte counts
3204 @cindex character count
3208 @command{wc} counts the number of bytes, characters, whitespace-separated
3209 words, and newlines in each given @var{file}, or standard input if none
3210 are given or for a @var{file} of @samp{-}. Synopsis:
3213 wc [@var{option}]@dots{} [@var{file}]@dots{}
3216 @cindex total counts
3217 @command{wc} prints one line of counts for each file, and if the file was
3218 given as an argument, it prints the file name following the counts. If
3219 more than one @var{file} is given, @command{wc} prints a final line
3220 containing the cumulative counts, with the file name @file{total}. The
3221 counts are printed in this order: newlines, words, characters, bytes,
3222 maximum line length.
3223 Each count is printed right-justified in a field with at least one
3224 space between fields so that the numbers and file names normally line
3225 up nicely in columns. The width of the count fields varies depending
3226 on the inputs, so you should not depend on a particular field width.
3227 However, as a @acronym{GNU} extension, if only one count is printed,
3228 it is guaranteed to be printed without leading spaces.
3230 By default, @command{wc} prints three counts: the newline, words, and byte
3231 counts. Options can specify that only certain counts be printed.
3232 Options do not undo others previously given, so
3239 prints both the byte counts and the word counts.
3241 With the @option{--max-line-length} option, @command{wc} prints the length
3242 of the longest line per file, and if there is more than one file it
3243 prints the maximum (not the sum) of those lengths. The line lengths here
3244 are measured in screen columns, according to the current locale and
3245 assuming tab positions in every 8th column.
3247 The program accepts the following options. Also see @ref{Common options}.
3255 Print only the byte counts.
3261 Print only the character counts.
3267 Print only the word counts.
3273 Print only the newline counts.
3276 @itemx --max-line-length
3278 @opindex --max-line-length
3279 Print only the maximum line lengths.
3281 @macro filesZeroFromOption{cmd,withTotalOption,subListOutput}
3282 @itemx --files0-from=@var{file}
3283 @opindex --files0-from=@var{file}
3284 @c This is commented out to avoid a texi2dvi failure.
3285 @c texi2dvi (GNU Texinfo 4.11) 1.104
3286 @c @cindex including files from @command{\cmd\}
3287 Disallow processing files named on the command line, and instead process
3288 those named in file @var{file}; each name being terminated by a zero byte
3289 (@acronym{ASCII} @sc{nul}).
3290 This is useful \withTotalOption\
3291 when the list of file names is so long that it may exceed a command line
3293 In such cases, running @command{\cmd\} via @command{xargs} is undesirable
3294 because it splits the list into pieces and makes @command{\cmd\} print
3295 \subListOutput\ for each sublist rather than for the entire list.
3296 One way to produce a list of @acronym{ASCII} @sc{nul} terminated file names is with @sc{gnu}
3297 @command{find}, using its @option{-print0} predicate.
3298 If @var{file} is @samp{-} then the @acronym{ASCII} @sc{nul} terminated file names
3299 are read from standard input.
3301 @filesZeroFromOption{wc,,a total}
3303 For example, to find the length of the longest line in any @file{.c} or
3304 @file{.h} file in the current hierarchy, do this:
3307 find . -name '*.[ch]' -print0 |
3308 wc -L --files0-from=- | tail -n1
3316 @node sum invocation
3317 @section @command{sum}: Print checksum and block counts
3320 @cindex 16-bit checksum
3321 @cindex checksum, 16-bit
3323 @command{sum} computes a 16-bit checksum for each given @var{file}, or
3324 standard input if none are given or for a @var{file} of @samp{-}. Synopsis:
3327 sum [@var{option}]@dots{} [@var{file}]@dots{}
3330 @command{sum} prints the checksum for each @var{file} followed by the
3331 number of blocks in the file (rounded up). If more than one @var{file}
3332 is given, file names are also printed (by default). (With the
3333 @option{--sysv} option, corresponding file names are printed when there is
3334 at least one file argument.)
3336 By default, @sc{gnu} @command{sum} computes checksums using an algorithm
3337 compatible with BSD @command{sum} and prints file sizes in units of
3340 The program accepts the following options. Also see @ref{Common options}.
3346 @cindex BSD @command{sum}
3347 Use the default (BSD compatible) algorithm. This option is included for
3348 compatibility with the System V @command{sum}. Unless @option{-s} was also
3349 given, it has no effect.
3355 @cindex System V @command{sum}
3356 Compute checksums using an algorithm compatible with System V
3357 @command{sum}'s default, and print file sizes in units of 512-byte blocks.
3361 @command{sum} is provided for compatibility; the @command{cksum} program (see
3362 next section) is preferable in new applications.
3367 @node cksum invocation
3368 @section @command{cksum}: Print CRC checksum and byte counts
3371 @cindex cyclic redundancy check
3372 @cindex CRC checksum
3374 @command{cksum} computes a cyclic redundancy check (CRC) checksum for each
3375 given @var{file}, or standard input if none are given or for a
3376 @var{file} of @samp{-}. Synopsis:
3379 cksum [@var{option}]@dots{} [@var{file}]@dots{}
3382 @command{cksum} prints the CRC checksum for each file along with the number
3383 of bytes in the file, and the file name unless no arguments were given.
3385 @command{cksum} is typically used to ensure that files
3386 transferred by unreliable means (e.g., netnews) have not been corrupted,
3387 by comparing the @command{cksum} output for the received files with the
3388 @command{cksum} output for the original files (typically given in the
3391 The CRC algorithm is specified by the @acronym{POSIX} standard. It is not
3392 compatible with the BSD or System V @command{sum} algorithms (see the
3393 previous section); it is more robust.
3395 The only options are @option{--help} and @option{--version}. @xref{Common
3401 @node md5sum invocation
3402 @section @command{md5sum}: Print or check MD5 digests
3406 @cindex 128-bit checksum
3407 @cindex checksum, 128-bit
3408 @cindex fingerprint, 128-bit
3409 @cindex message-digest, 128-bit
3411 @command{md5sum} computes a 128-bit checksum (or @dfn{fingerprint} or
3412 @dfn{message-digest}) for each specified @var{file}.
3414 Note: The MD5 digest is more reliable than a simple CRC (provided by
3415 the @command{cksum} command) for detecting accidental file corruption,
3416 as the chances of accidentally having two files with identical MD5
3417 are vanishingly small. However, it should not be considered truly
3418 secure against malicious tampering: although finding a file with a
3419 given MD5 fingerprint, or modifying a file so as to retain its MD5 are
3420 considered infeasible at the moment, it is known how to produce
3421 different files with identical MD5 (a ``collision''), something which
3422 can be a security issue in certain contexts. For more secure hashes,
3423 consider using SHA-1 or SHA-2. @xref{sha1sum invocation}, and
3424 @ref{sha2 utilities}.
3426 If a @var{file} is specified as @samp{-} or if no files are given
3427 @command{md5sum} computes the checksum for the standard input.
3428 @command{md5sum} can also determine whether a file and checksum are
3429 consistent. Synopsis:
3432 md5sum [@var{option}]@dots{} [@var{file}]@dots{}
3435 For each @var{file}, @samp{md5sum} outputs the MD5 checksum, a flag
3436 indicating a binary or text input file, and the file name.
3437 If @var{file} contains a backslash or newline, the
3438 line is started with a backslash, and each problematic character in
3439 the file name is escaped with a backslash, making the output
3440 unambiguous even in the presence of arbitrary file names.
3441 If @var{file} is omitted or specified as @samp{-}, standard input is read.
3443 The program accepts the following options. Also see @ref{Common options}.
3451 @cindex binary input files
3452 Treat each input file as binary, by reading it in binary mode and
3453 outputting a @samp{*} flag. This is the inverse of @option{--text}.
3454 On systems like @acronym{GNU} that do not distinguish between binary
3455 and text files, this option merely flags each input file as binary:
3456 the MD5 checksum is unaffected. This option is the default on systems
3457 like MS-DOS that distinguish between binary and text files, except
3458 for reading standard input when standard input is a terminal.
3462 Read file names and checksum information (not data) from each
3463 @var{file} (or from stdin if no @var{file} was specified) and report
3464 whether the checksums match the contents of the named files.
3465 The input to this mode of @command{md5sum} is usually the output of
3466 a prior, checksum-generating run of @samp{md5sum}.
3467 Each valid line of input consists of an MD5 checksum, a binary/text
3468 flag, and then a file name.
3469 Binary files are marked with @samp{*}, text with @samp{ }.
3470 For each such line, @command{md5sum} reads the named file and computes its
3471 MD5 checksum. Then, if the computed message digest does not match the
3472 one on the line with the file name, the file is noted as having
3473 failed the test. Otherwise, the file passes the test.
3474 By default, for each valid line, one line is written to standard
3475 output indicating whether the named file passed the test.
3476 After all checks have been performed, if there were any failures,
3477 a warning is issued to standard error.
3478 Use the @option{--status} option to inhibit that output.
3479 If any listed file cannot be opened or read, if any valid line has
3480 an MD5 checksum inconsistent with the associated file, or if no valid
3481 line is found, @command{md5sum} exits with nonzero status. Otherwise,
3482 it exits successfully.
3486 @cindex verifying MD5 checksums
3487 This option is useful only when verifying checksums.
3488 When verifying checksums, don't generate an 'OK' message per successfully
3489 checked file. Files that fail the verification are reported in the
3490 default one-line-per-file format. If there is any checksum mismatch,
3491 print a warning summarizing the failures to standard error.
3495 @cindex verifying MD5 checksums
3496 This option is useful only when verifying checksums.
3497 When verifying checksums, don't generate the default one-line-per-file
3498 diagnostic and don't output the warning summarizing any failures.
3499 Failures to open or read a file still evoke individual diagnostics to
3501 If all listed files are readable and are consistent with the associated
3502 MD5 checksums, exit successfully. Otherwise exit with a status code
3503 indicating there was a failure.
3509 @cindex text input files
3510 Treat each input file as text, by reading it in text mode and
3511 outputting a @samp{ } flag. This is the inverse of @option{--binary}.
3512 This option is the default on systems like @acronym{GNU} that do not
3513 distinguish between binary and text files. On other systems, it is
3514 the default for reading standard input when standard input is a
3521 @cindex verifying MD5 checksums
3522 When verifying checksums, warn about improperly formatted MD5 checksum lines.
3523 This option is useful only if all but a few lines in the checked input
3531 @node sha1sum invocation
3532 @section @command{sha1sum}: Print or check SHA-1 digests
3536 @cindex 160-bit checksum
3537 @cindex checksum, 160-bit
3538 @cindex fingerprint, 160-bit
3539 @cindex message-digest, 160-bit
3541 @command{sha1sum} computes a 160-bit checksum for each specified
3542 @var{file}. The usage and options of this command are precisely the
3543 same as for @command{md5sum}. @xref{md5sum invocation}.
3545 Note: The SHA-1 digest is more secure than MD5, and no collisions of
3546 it are known (different files having the same fingerprint). However,
3547 it is known that they can be produced with considerable, but not
3548 unreasonable, resources. For this reason, it is generally considered
3549 that SHA-1 should be gradually phased out in favor of the more secure
3550 SHA-2 hash algorithms. @xref{sha2 utilities}.
3553 @node sha2 utilities
3554 @section sha2 utilities: Print or check SHA-2 digests
3561 @cindex 224-bit checksum
3562 @cindex 256-bit checksum
3563 @cindex 384-bit checksum
3564 @cindex 512-bit checksum
3565 @cindex checksum, 224-bit
3566 @cindex checksum, 256-bit
3567 @cindex checksum, 384-bit
3568 @cindex checksum, 512-bit
3569 @cindex fingerprint, 224-bit
3570 @cindex fingerprint, 256-bit
3571 @cindex fingerprint, 384-bit
3572 @cindex fingerprint, 512-bit
3573 @cindex message-digest, 224-bit
3574 @cindex message-digest, 256-bit
3575 @cindex message-digest, 384-bit
3576 @cindex message-digest, 512-bit
3578 The commands @command{sha224sum}, @command{sha256sum},
3579 @command{sha384sum} and @command{sha512sum} compute checksums of
3580 various lengths (respectively 224, 256, 384 and 512 bits),
3581 collectively known as the SHA-2 hashes. The usage and options of
3582 these commands are precisely the same as for @command{md5sum}.
3583 @xref{md5sum invocation}.
3585 Note: The SHA384 and SHA512 digests are considerably slower to
3586 compute, especially on 32-bit computers, than SHA224 or SHA256.
3589 @node Operating on sorted files
3590 @chapter Operating on sorted files
3592 @cindex operating on sorted files
3593 @cindex sorted files, operations on
3595 These commands work with (or produce) sorted files.
3598 * sort invocation:: Sort text files.
3599 * shuf invocation:: Shuffle text files.
3600 * uniq invocation:: Uniquify files.
3601 * comm invocation:: Compare two sorted files line by line.
3602 * ptx invocation:: Produce a permuted index of file contents.
3603 * tsort invocation:: Topological sort.
3607 @node sort invocation
3608 @section @command{sort}: Sort text files
3611 @cindex sorting files
3613 @command{sort} sorts, merges, or compares all the lines from the given
3614 files, or standard input if none are given or for a @var{file} of
3615 @samp{-}. By default, @command{sort} writes the results to standard
3619 sort [@var{option}]@dots{} [@var{file}]@dots{}
3622 @command{sort} has three modes of operation: sort (the default), merge,
3623 and check for sortedness. The following options change the operation
3630 @itemx --check=diagnose-first
3633 @cindex checking for sortedness
3634 Check whether the given file is already sorted: if it is not all
3635 sorted, print a diagnostic containing the first out-of-order line and
3636 exit with a status of 1.
3637 Otherwise, exit successfully.
3638 At most one input file can be given.
3641 @itemx --check=quiet
3642 @itemx --check=silent
3645 @cindex checking for sortedness
3646 Exit successfully if the given file is already sorted, and
3647 exit with status 1 otherwise.
3648 At most one input file can be given.
3649 This is like @option{-c}, except it does not print a diagnostic.
3655 @cindex merging sorted files
3656 Merge the given files by sorting them as a group. Each input file must
3657 always be individually sorted. It always works to sort instead of
3658 merge; merging is provided because it is faster, in the case where it
3663 @cindex sort stability
3664 @cindex sort's last-resort comparison
3665 A pair of lines is compared as follows:
3666 @command{sort} compares each pair of fields, in the
3667 order specified on the command line, according to the associated
3668 ordering options, until a difference is found or no fields are left.
3669 If no key fields are specified, @command{sort} uses a default key of
3670 the entire line. Finally, as a last resort when all keys compare
3671 equal, @command{sort} compares entire lines as if no ordering options
3672 other than @option{--reverse} (@option{-r}) were specified. The
3673 @option{--stable} (@option{-s}) option disables this @dfn{last-resort
3674 comparison} so that lines in which all fields compare equal are left
3675 in their original relative order. The @option{--unique}
3676 (@option{-u}) option also disables the last-resort comparison.
3680 Unless otherwise specified, all comparisons use the character collating
3681 sequence specified by the @env{LC_COLLATE} locale.@footnote{If you
3682 use a non-@acronym{POSIX} locale (e.g., by setting @env{LC_ALL}
3683 to @samp{en_US}), then @command{sort} may produce output that is sorted
3684 differently than you're accustomed to. In that case, set the @env{LC_ALL}
3685 environment variable to @samp{C}. Note that setting only @env{LC_COLLATE}
3686 has two problems. First, it is ineffective if @env{LC_ALL} is also set.
3687 Second, it has undefined behavior if @env{LC_CTYPE} (or @env{LANG}, if
3688 @env{LC_CTYPE} is unset) is set to an incompatible value. For example,
3689 you get undefined behavior if @env{LC_CTYPE} is @code{ja_JP.PCK} but
3690 @env{LC_COLLATE} is @code{en_US.UTF-8}.}
3692 @sc{gnu} @command{sort} (as specified for all @sc{gnu} utilities) has no
3693 limit on input line length or restrictions on bytes allowed within lines.
3694 In addition, if the final byte of an input file is not a newline, @sc{gnu}
3695 @command{sort} silently supplies one. A line's trailing newline is not
3696 part of the line for comparison purposes.
3698 @cindex exit status of @command{sort}
3702 0 if no error occurred
3703 1 if invoked with @option{-c} or @option{-C} and the input is not sorted
3704 2 if an error occurred
3708 If the environment variable @env{TMPDIR} is set, @command{sort} uses its
3709 value as the directory for temporary files instead of @file{/tmp}. The
3710 @option{--temporary-directory} (@option{-T}) option in turn overrides
3711 the environment variable.
3713 The following options affect the ordering of output lines. They may be
3714 specified globally or as part of a specific key field. If no key
3715 fields are specified, global options apply to comparison of entire
3716 lines; otherwise the global options are inherited by key fields that do
3717 not specify any special options of their own. In pre-@acronym{POSIX}
3718 versions of @command{sort}, global options affect only later key fields,
3719 so portable shell scripts should specify global options first.
3724 @itemx --ignore-leading-blanks
3726 @opindex --ignore-leading-blanks
3727 @cindex blanks, ignoring leading
3729 Ignore leading blanks when finding sort keys in each line.
3730 By default a blank is a space or a tab, but the @env{LC_CTYPE} locale
3731 can change this. Note blanks may be ignored by your locale's collating
3732 rules, but without this option they will be significant for character
3733 positions specified in keys with the @option{-k} option.
3736 @itemx --dictionary-order
3738 @opindex --dictionary-order
3739 @cindex dictionary order
3740 @cindex phone directory order
3741 @cindex telephone directory order
3743 Sort in @dfn{phone directory} order: ignore all characters except
3744 letters, digits and blanks when sorting.
3745 By default letters and digits are those of @acronym{ASCII} and a blank
3746 is a space or a tab, but the @env{LC_CTYPE} locale can change this.
3749 @itemx --ignore-case
3751 @opindex --ignore-case
3752 @cindex ignoring case
3753 @cindex case folding
3755 Fold lowercase characters into the equivalent uppercase characters when
3756 comparing so that, for example, @samp{b} and @samp{B} sort as equal.
3757 The @env{LC_CTYPE} locale determines character types.
3758 When used with @option{--unique} those lower case equivalent lines are
3759 thrown away. (There is currently no way to throw away the upper case
3760 equivalent instead. (Any @option{--reverse} given would only affect
3761 the final result, after the throwing away.))
3764 @itemx --general-numeric-sort
3765 @itemx --sort=general-numeric
3767 @opindex --general-numeric-sort
3769 @cindex general numeric sort
3771 Sort numerically, using the standard C function @code{strtold} to convert
3772 a prefix of each line to a long double-precision floating point number.
3773 This allows floating point numbers to be specified in scientific notation,
3774 like @code{1.0e-34} and @code{10e100}.
3775 The @env{LC_NUMERIC} locale determines the decimal-point character.
3776 Do not report overflow, underflow, or conversion errors.
3777 Use the following collating sequence:
3781 Lines that do not start with numbers (all considered to be equal).
3783 NaNs (``Not a Number'' values, in IEEE floating point arithmetic)
3784 in a consistent but machine-dependent order.
3788 Finite numbers in ascending numeric order (with @math{-0} and @math{+0} equal).
3793 Use this option only if there is no alternative; it is much slower than
3794 @option{--numeric-sort} (@option{-n}) and it can lose information when
3795 converting to floating point.
3798 @itemx --human-numeric-sort
3799 @itemx --sort=human-numeric
3801 @opindex --human-numeric-sort
3803 @cindex human numeric sort
3805 Sort numerically, first by numeric sign (negative, zero, or positive);
3806 then by @acronym{SI} suffix (either empty, or @samp{k} or @samp{K}, or
3807 one of @samp{MGTPEZY}, in that order; @xref{Block size}); and finally
3808 by numeric value. For example, @samp{1023M} sorts before @samp{1G}
3809 because @samp{M} (mega) precedes @samp{G} (giga) as an @acronym{SI}
3810 suffix. This option sorts values that are consistently scaled to the
3811 nearest suffix, regardless of whether suffixes denote powers of 1000
3812 or 1024, and it therefore sorts the output of any single invocation of
3813 the @command{df}, @command{du}, or @command{ls} commands that are
3814 invoked with their @option{--human-readable} or @option{--si} options.
3815 The syntax for numbers is the same as for the @option{--numeric-sort}
3816 option; the @acronym{SI} suffix must immediately follow the number.
3819 @itemx --ignore-nonprinting
3821 @opindex --ignore-nonprinting
3822 @cindex nonprinting characters, ignoring
3823 @cindex unprintable characters, ignoring
3825 Ignore nonprinting characters.
3826 The @env{LC_CTYPE} locale determines character types.
3827 This option has no effect if the stronger @option{--dictionary-order}
3828 (@option{-d}) option is also given.
3834 @opindex --month-sort
3836 @cindex months, sorting by
3838 An initial string, consisting of any amount of blanks, followed
3839 by a month name abbreviation, is folded to UPPER case and
3840 compared in the order @samp{JAN} < @samp{FEB} < @dots{} < @samp{DEC}.
3841 Invalid names compare low to valid names. The @env{LC_TIME} locale
3842 category determines the month spellings.
3843 By default a blank is a space or a tab, but the @env{LC_CTYPE} locale
3847 @itemx --numeric-sort
3848 @itemx --sort=numeric
3850 @opindex --numeric-sort
3852 @cindex numeric sort
3854 Sort numerically. The number begins each line and consists
3855 of optional blanks, an optional @samp{-} sign, and zero or more
3856 digits possibly separated by thousands separators, optionally followed
3857 by a decimal-point character and zero or more digits. An empty
3858 number is treated as @samp{0}. The @env{LC_NUMERIC}
3859 locale specifies the decimal-point character and thousands separator.
3860 By default a blank is a space or a tab, but the @env{LC_CTYPE} locale
3863 Comparison is exact; there is no rounding error.
3865 Neither a leading @samp{+} nor exponential notation is recognized.
3866 To compare such strings numerically, use the
3867 @option{--general-numeric-sort} (@option{-g}) option.
3870 @itemx --version-sort
3872 @opindex --version-sort
3873 @cindex version number sort
3874 Sort by version name and number. It behaves like a standard sort,
3875 except that each sequence of decimal digits is treated numerically
3876 as an index/version number. (@xref{Details about version sort}.)
3882 @cindex reverse sorting
3883 Reverse the result of comparison, so that lines with greater key values
3884 appear earlier in the output instead of later.
3887 @itemx --random-sort
3888 @itemx --sort=random
3890 @opindex --random-sort
3893 Sort by hashing the input keys and then sorting the hash values.
3894 Choose the hash function at random, ensuring that it is free of
3895 collisions so that differing keys have differing hash values. This is
3896 like a random permutation of the inputs (@pxref{shuf invocation}),
3897 except that keys with the same value sort together.
3899 If multiple random sort fields are specified, the same random hash
3900 function is used for all fields. To use different random hash
3901 functions for different fields, you can invoke @command{sort} more
3904 The choice of hash function is affected by the
3905 @option{--random-source} option.
3913 @item --compress-program=@var{prog}
3914 Compress any temporary files with the program @var{prog}.
3916 With no arguments, @var{prog} must compress standard input to standard
3917 output, and when given the @option{-d} option it must decompress
3918 standard input to standard output.
3920 Terminate with an error if @var{prog} exits with nonzero status.
3922 White space and the backslash character should not appear in
3923 @var{prog}; they are reserved for future use.
3925 @filesZeroFromOption{sort,,sorted output}
3927 @item -k @var{pos1}[,@var{pos2}]
3928 @itemx --key=@var{pos1}[,@var{pos2}]
3932 Specify a sort field that consists of the part of the line between
3933 @var{pos1} and @var{pos2} (or the end of the line, if @var{pos2} is
3934 omitted), @emph{inclusive}.
3936 Each @var{pos} has the form @samp{@var{f}[.@var{c}][@var{opts}]},
3937 where @var{f} is the number of the field to use, and @var{c} is the number
3938 of the first character from the beginning of the field. Fields and character
3939 positions are numbered starting with 1; a character position of zero in
3940 @var{pos2} indicates the field's last character. If @samp{.@var{c}} is
3941 omitted from @var{pos1}, it defaults to 1 (the beginning of the field);
3942 if omitted from @var{pos2}, it defaults to 0 (the end of the field).
3943 @var{opts} are ordering options, allowing individual keys to be sorted
3944 according to different rules; see below for details. Keys can span
3947 Example: To sort on the second field, use @option{--key=2,2}
3948 (@option{-k 2,2}). See below for more notes on keys and more examples.
3949 See also the @option{--debug} option to help determine the part
3950 of the line being used in the sort.
3953 Highlight the portion of each line used for sorting.
3954 Also issue warnings about questionable usage to stderr.
3956 @item --batch-size=@var{nmerge}
3957 @opindex --batch-size
3958 @cindex number of inputs to merge, nmerge
3959 Merge at most @var{nmerge} inputs at once.
3961 When @command{sort} has to merge more than @var{nmerge} inputs,
3962 it merges them in groups of @var{nmerge}, saving the result in
3963 a temporary file, which is then used as an input in a subsequent merge.
3965 A large value of @var{nmerge} may improve merge performance and decrease
3966 temporary storage utilization at the expense of increased memory usage
3967 and I/0. Conversely a small value of @var{nmerge} may reduce memory
3968 requirements and I/0 at the expense of temporary storage consumption and
3971 The value of @var{nmerge} must be at least 2. The default value is
3972 currently 16, but this is implementation-dependent and may change in
3975 The value of @var{nmerge} may be bounded by a resource limit for open
3976 file descriptors. The commands @samp{ulimit -n} or @samp{getconf
3977 OPEN_MAX} may display limits for your systems; these limits may be
3978 modified further if your program already has some files open, or if
3979 the operating system has other limits on the number of open files. If
3980 the value of @var{nmerge} exceeds the resource limit, @command{sort}
3981 silently uses a smaller value.
3983 @item -o @var{output-file}
3984 @itemx --output=@var{output-file}
3987 @cindex overwriting of input, allowed
3988 Write output to @var{output-file} instead of standard output.
3989 Normally, @command{sort} reads all input before opening
3990 @var{output-file}, so you can safely sort a file in place by using
3991 commands like @code{sort -o F F} and @code{cat F | sort -o F}.
3992 However, @command{sort} with @option{--merge} (@option{-m}) can open
3993 the output file before reading all input, so a command like @code{cat
3994 F | sort -m -o F - G} is not safe as @command{sort} might start
3995 writing @file{F} before @command{cat} is done reading it.
3997 @vindex POSIXLY_CORRECT
3998 On newer systems, @option{-o} cannot appear after an input file if
3999 @env{POSIXLY_CORRECT} is set, e.g., @samp{sort F -o F}. Portable
4000 scripts should specify @option{-o @var{output-file}} before any input
4003 @item --random-source=@var{file}
4004 @opindex --random-source
4005 @cindex random source for sorting
4006 Use @var{file} as a source of random data used to determine which
4007 random hash function to use with the @option{-R} option. @xref{Random
4014 @cindex sort stability
4015 @cindex sort's last-resort comparison
4017 Make @command{sort} stable by disabling its last-resort comparison.
4018 This option has no effect if no fields or global ordering options
4019 other than @option{--reverse} (@option{-r}) are specified.
4022 @itemx --buffer-size=@var{size}
4024 @opindex --buffer-size
4025 @cindex size for main memory sorting
4026 Use a main-memory sort buffer of the given @var{size}. By default,
4027 @var{size} is in units of 1024 bytes. Appending @samp{%} causes
4028 @var{size} to be interpreted as a percentage of physical memory.
4029 Appending @samp{K} multiplies @var{size} by 1024 (the default),
4030 @samp{M} by 1,048,576, @samp{G} by 1,073,741,824, and so on for
4031 @samp{T}, @samp{P}, @samp{E}, @samp{Z}, and @samp{Y}. Appending
4032 @samp{b} causes @var{size} to be interpreted as a byte count, with no
4035 This option can improve the performance of @command{sort} by causing it
4036 to start with a larger or smaller sort buffer than the default.
4037 However, this option affects only the initial buffer size. The buffer
4038 grows beyond @var{size} if @command{sort} encounters input lines larger
4041 @item -t @var{separator}
4042 @itemx --field-separator=@var{separator}
4044 @opindex --field-separator
4045 @cindex field separator character
4046 Use character @var{separator} as the field separator when finding the
4047 sort keys in each line. By default, fields are separated by the empty
4048 string between a non-blank character and a blank character.
4049 By default a blank is a space or a tab, but the @env{LC_CTYPE} locale
4052 That is, given the input line @w{@samp{ foo bar}}, @command{sort} breaks it
4053 into fields @w{@samp{ foo}} and @w{@samp{ bar}}. The field separator is
4054 not considered to be part of either the field preceding or the field
4055 following, so with @samp{sort @w{-t " "}} the same input line has
4056 three fields: an empty field, @samp{foo}, and @samp{bar}.
4057 However, fields that extend to the end of the line,
4058 as @option{-k 2}, or fields consisting of a range, as @option{-k 2,3},
4059 retain the field separators present between the endpoints of the range.
4061 To specify @acronym{ASCII} @sc{nul} as the field separator,
4062 use the two-character string @samp{\0}, e.g., @samp{sort -t '\0'}.
4064 @item -T @var{tempdir}
4065 @itemx --temporary-directory=@var{tempdir}
4067 @opindex --temporary-directory
4068 @cindex temporary directory
4070 Use directory @var{tempdir} to store temporary files, overriding the
4071 @env{TMPDIR} environment variable. If this option is given more than
4072 once, temporary files are stored in all the directories given. If you
4073 have a large sort or merge that is I/O-bound, you can often improve
4074 performance by using this option to specify directories on different
4075 disks and controllers.
4077 @item --parallel=@var{n}
4079 @cindex multithreaded sort
4080 Limit the number of sorts run in parallel to @var{n}. By default,
4081 @var{n} is set to the number of available processors, and values
4082 greater than that are reduced to that limit. Also see
4083 @ref{nproc invocation}.
4089 @cindex uniquifying output
4091 Normally, output only the first of a sequence of lines that compare
4092 equal. For the @option{--check} (@option{-c} or @option{-C}) option,
4093 check that no pair of consecutive lines compares equal.
4095 This option also disables the default last-resort comparison.
4097 The commands @code{sort -u} and @code{sort | uniq} are equivalent, but
4098 this equivalence does not extend to arbitrary @command{sort} options.
4099 For example, @code{sort -n -u} inspects only the value of the initial
4100 numeric string when checking for uniqueness, whereas @code{sort -n |
4101 uniq} inspects the entire line. @xref{uniq invocation}.
4103 @macro zeroTerminatedOption
4105 @itemx --zero-terminated
4107 @opindex --zero-terminated
4108 @cindex process zero-terminated items
4109 Delimit items with a zero byte rather than a newline (@acronym{ASCII} @sc{lf}).
4110 I.E. treat input as items separated by @acronym{ASCII} @sc{nul}
4111 and terminate output items with @acronym{ASCII} @sc{nul}.
4112 This option can be useful in conjunction with @samp{perl -0} or
4113 @samp{find -print0} and @samp{xargs -0} which do the same in order to
4114 reliably handle arbitrary file names (even those containing blanks
4115 or other special characters).
4117 @zeroTerminatedOption
4121 Historical (BSD and System V) implementations of @command{sort} have
4122 differed in their interpretation of some options, particularly
4123 @option{-b}, @option{-f}, and @option{-n}. @sc{gnu} sort follows the @acronym{POSIX}
4124 behavior, which is usually (but not always!) like the System V behavior.
4125 According to @acronym{POSIX}, @option{-n} no longer implies @option{-b}. For
4126 consistency, @option{-M} has been changed in the same way. This may
4127 affect the meaning of character positions in field specifications in
4128 obscure cases. The only fix is to add an explicit @option{-b}.
4130 A position in a sort field specified with @option{-k} may have any
4131 of the option letters @samp{MbdfghinRrV} appended to it, in which case no
4132 global ordering options are inherited by that particular field. The
4133 @option{-b} option may be independently attached to either or both of
4134 the start and end positions of a field specification, and if it is
4135 inherited from the global options it will be attached to both.
4136 If input lines can contain leading or adjacent blanks and @option{-t}
4137 is not used, then @option{-k} is typically combined with @option{-b} or
4138 an option that implicitly ignores leading blanks (@samp{Mghn}) as otherwise
4139 the varying numbers of leading blanks in fields can cause confusing results.
4141 If the start position in a sort field specifier falls after the end of
4142 the line or after the end field, the field is empty. If the @option{-b}
4143 option was specified, the @samp{.@var{c}} part of a field specification
4144 is counted from the first nonblank character of the field.
4146 @vindex _POSIX2_VERSION
4147 @vindex POSIXLY_CORRECT
4148 On older systems, @command{sort} supports an obsolete origin-zero
4149 syntax @samp{+@var{pos1} [-@var{pos2}]} for specifying sort keys.
4150 The obsolete sequence @samp{sort +@var{a}.@var{x} -@var{b}.@var{y}}
4151 is equivalent to @samp{sort -k @var{a+1}.@var{x+1},@var{b}} if @var{y}
4152 is @samp{0} or absent, otherwise it is equivalent to @samp{sort -k
4153 @var{a+1}.@var{x+1},@var{b+1}.@var{y}}.
4155 This obsolete behavior can be enabled or disabled with the
4156 @env{_POSIX2_VERSION} environment variable (@pxref{Standards
4157 conformance}); it can also be enabled when @env{POSIXLY_CORRECT} is
4158 not set by using the obsolete syntax with @samp{-@var{pos2}} present.
4160 Scripts intended for use on standard hosts should avoid obsolete
4161 syntax and should use @option{-k} instead. For example, avoid
4162 @samp{sort +2}, since it might be interpreted as either @samp{sort
4163 ./+2} or @samp{sort -k 3}. If your script must also run on hosts that
4164 support only the obsolete syntax, it can use a test like @samp{if sort
4165 -k 1 </dev/null >/dev/null 2>&1; then @dots{}} to decide which syntax
4168 Here are some examples to illustrate various combinations of options.
4173 Sort in descending (reverse) numeric order.
4180 Run no more that 4 sorts concurrently, using a buffer size of 10M.
4183 sort --parallel=4 -S 10M
4187 Sort alphabetically, omitting the first and second fields
4188 and the blanks at the start of the third field.
4189 This uses a single key composed of the characters beginning
4190 at the start of the first nonblank character in field three
4191 and extending to the end of each line.
4198 Sort numerically on the second field and resolve ties by sorting
4199 alphabetically on the third and fourth characters of field five.
4200 Use @samp{:} as the field delimiter.
4203 sort -t : -k 2,2n -k 5.3,5.4
4206 Note that if you had written @option{-k 2n} instead of @option{-k 2,2n}
4207 @command{sort} would have used all characters beginning in the second field
4208 and extending to the end of the line as the primary @emph{numeric}
4209 key. For the large majority of applications, treating keys spanning
4210 more than one field as numeric will not do what you expect.
4212 Also note that the @samp{n} modifier was applied to the field-end
4213 specifier for the first key. It would have been equivalent to
4214 specify @option{-k 2n,2} or @option{-k 2n,2n}. All modifiers except
4215 @samp{b} apply to the associated @emph{field}, regardless of whether
4216 the modifier character is attached to the field-start and/or the
4217 field-end part of the key specifier.
4220 Sort the password file on the fifth field and ignore any
4221 leading blanks. Sort lines with equal values in field five
4222 on the numeric user ID in field three. Fields are separated
4226 sort -t : -k 5b,5 -k 3,3n /etc/passwd
4227 sort -t : -n -k 5b,5 -k 3,3 /etc/passwd
4228 sort -t : -b -k 5,5 -k 3,3n /etc/passwd
4231 These three commands have equivalent effect. The first specifies that
4232 the first key's start position ignores leading blanks and the second
4233 key is sorted numerically. The other two commands rely on global
4234 options being inherited by sort keys that lack modifiers. The inheritance
4235 works in this case because @option{-k 5b,5b} and @option{-k 5b,5} are
4236 equivalent, as the location of a field-end lacking a @samp{.@var{c}}
4237 character position is not affected by whether initial blanks are
4241 Sort a set of log files, primarily by IPv4 address and secondarily by
4242 time stamp. If two lines' primary and secondary keys are identical,
4243 output the lines in the same order that they were input. The log
4244 files contain lines that look like this:
4247 4.150.156.3 - - [01/Apr/2004:06:31:51 +0000] message 1
4248 211.24.3.231 - - [24/Apr/2004:20:17:39 +0000] message 2
4251 Fields are separated by exactly one space. Sort IPv4 addresses
4252 lexicographically, e.g., 212.61.52.2 sorts before 212.129.233.201
4253 because 61 is less than 129.
4256 sort -s -t ' ' -k 4.9n -k 4.5M -k 4.2n -k 4.14,4.21 file*.log |
4257 sort -s -t '.' -k 1,1n -k 2,2n -k 3,3n -k 4,4n
4260 This example cannot be done with a single @command{sort} invocation,
4261 since IPv4 address components are separated by @samp{.} while dates
4262 come just after a space. So it is broken down into two invocations of
4263 @command{sort}: the first sorts by time stamp and the second by IPv4
4264 address. The time stamp is sorted by year, then month, then day, and
4265 finally by hour-minute-second field, using @option{-k} to isolate each
4266 field. Except for hour-minute-second there's no need to specify the
4267 end of each key field, since the @samp{n} and @samp{M} modifiers sort
4268 based on leading prefixes that cannot cross field boundaries. The
4269 IPv4 addresses are sorted lexicographically. The second sort uses
4270 @samp{-s} so that ties in the primary key are broken by the secondary
4271 key; the first sort uses @samp{-s} so that the combination of the two
4275 Generate a tags file in case-insensitive sorted order.
4278 find src -type f -print0 | sort -z -f | xargs -0 etags --append
4281 The use of @option{-print0}, @option{-z}, and @option{-0} in this case means
4282 that file names that contain blanks or other special characters are
4284 by the sort operation.
4286 @c This example is a bit contrived and needs more explanation.
4288 @c Sort records separated by an arbitrary string by using a pipe to convert
4289 @c each record delimiter string to @samp{\0}, then using sort's -z option,
4290 @c and converting each @samp{\0} back to the original record delimiter.
4293 @c printf 'c\n\nb\n\na\n'|perl -0pe 's/\n\n/\n\0/g'|sort -z|perl -0pe 's/\0/\n/g'
4297 Use the common @acronym{DSU, Decorate Sort Undecorate} idiom to
4298 sort lines according to their length.
4301 awk '@{print length, $0@}' /etc/passwd | sort -n | cut -f2- -d' '
4304 In general this technique can be used to sort data that the @command{sort}
4305 command does not support, or is inefficient at, sorting directly.
4308 Shuffle a list of directories, but preserve the order of files within
4309 each directory. For instance, one could use this to generate a music
4310 playlist in which albums are shuffled but the songs of each album are
4314 ls */* | sort -t / -k 1,1R -k 2,2
4320 @node shuf invocation
4321 @section @command{shuf}: Shuffling text
4324 @cindex shuffling files
4326 @command{shuf} shuffles its input by outputting a random permutation
4327 of its input lines. Each output permutation is equally likely.
4331 shuf [@var{option}]@dots{} [@var{file}]
4332 shuf -e [@var{option}]@dots{} [@var{arg}]@dots{}
4333 shuf -i @var{lo}-@var{hi} [@var{option}]@dots{}
4336 @command{shuf} has three modes of operation that affect where it
4337 obtains its input lines. By default, it reads lines from standard
4338 input. The following options change the operation mode:
4346 @cindex command-line operands to shuffle
4347 Treat each command-line operand as an input line.
4349 @item -i @var{lo}-@var{hi}
4350 @itemx --input-range=@var{lo}-@var{hi}
4352 @opindex --input-range
4353 @cindex input range to shuffle
4354 Act as if input came from a file containing the range of unsigned
4355 decimal integers @var{lo}@dots{}@var{hi}, one per line.
4359 @command{shuf}'s other options can affect its behavior in all
4364 @item -n @var{lines}
4365 @itemx --head-count=@var{count}
4367 @opindex --head-count
4368 @cindex head of output
4369 Output at most @var{count} lines. By default, all input lines are
4372 @item -o @var{output-file}
4373 @itemx --output=@var{output-file}
4376 @cindex overwriting of input, allowed
4377 Write output to @var{output-file} instead of standard output.
4378 @command{shuf} reads all input before opening
4379 @var{output-file}, so you can safely shuffle a file in place by using
4380 commands like @code{shuf -o F <F} and @code{cat F | shuf -o F}.
4382 @item --random-source=@var{file}
4383 @opindex --random-source
4384 @cindex random source for shuffling
4385 Use @var{file} as a source of random data used to determine which
4386 permutation to generate. @xref{Random sources}.
4388 @zeroTerminatedOption
4404 might produce the output
4414 Similarly, the command:
4417 shuf -e clubs hearts diamonds spades
4431 and the command @samp{shuf -i 1-4} might output:
4441 These examples all have four input lines, so @command{shuf} might
4442 produce any of the twenty-four possible permutations of the input. In
4443 general, if there are @var{n} input lines, there are @var{n}! (i.e.,
4444 @var{n} factorial, or @var{n} * (@var{n} - 1) * @dots{} * 1) possible
4445 output permutations.
4450 @node uniq invocation
4451 @section @command{uniq}: Uniquify files
4454 @cindex uniquify files
4456 @command{uniq} writes the unique lines in the given @file{input}, or
4457 standard input if nothing is given or for an @var{input} name of
4461 uniq [@var{option}]@dots{} [@var{input} [@var{output}]]
4464 By default, @command{uniq} prints its input lines, except that
4465 it discards all but the first of adjacent repeated lines, so that
4466 no output lines are repeated. Optionally, it can instead discard
4467 lines that are not repeated, or all repeated lines.
4469 The input need not be sorted, but repeated input lines are detected
4470 only if they are adjacent. If you want to discard non-adjacent
4471 duplicate lines, perhaps you want to use @code{sort -u}.
4472 @xref{sort invocation}.
4475 Comparisons honor the rules specified by the @env{LC_COLLATE}
4478 If no @var{output} file is specified, @command{uniq} writes to standard
4481 The program accepts the following options. Also see @ref{Common options}.
4486 @itemx --skip-fields=@var{n}
4488 @opindex --skip-fields
4489 Skip @var{n} fields on each line before checking for uniqueness. Use
4490 a null string for comparison if a line has fewer than @var{n} fields. Fields
4491 are sequences of non-space non-tab characters that are separated from
4492 each other by at least one space or tab.
4494 For compatibility @command{uniq} supports an obsolete option syntax
4495 @option{-@var{n}}. New scripts should use @option{-f @var{n}} instead.
4498 @itemx --skip-chars=@var{n}
4500 @opindex --skip-chars
4501 Skip @var{n} characters before checking for uniqueness. Use a null string
4502 for comparison if a line has fewer than @var{n} characters. If you use both
4503 the field and character skipping options, fields are skipped over first.
4505 @vindex _POSIX2_VERSION
4506 On older systems, @command{uniq} supports an obsolete option syntax
4508 This obsolete behavior can be enabled or disabled with the
4509 @env{_POSIX2_VERSION} environment variable (@pxref{Standards
4510 conformance}), but portable scripts should avoid commands whose
4511 behavior depends on this variable.
4512 For example, use @samp{uniq ./+10} or @samp{uniq -s 10} rather than
4513 the ambiguous @samp{uniq +10}.
4519 Print the number of times each line occurred along with the line.
4522 @itemx --ignore-case
4524 @opindex --ignore-case
4525 Ignore differences in case when comparing lines.
4531 @cindex repeated lines, outputting
4532 Discard lines that are not repeated. When used by itself, this option
4533 causes @command{uniq} to print the first copy of each repeated line,
4537 @itemx --all-repeated[=@var{delimit-method}]
4539 @opindex --all-repeated
4540 @cindex all repeated lines, outputting
4541 Do not discard the second and subsequent repeated input lines,
4542 but discard lines that are not repeated.
4543 This option is useful mainly in conjunction with other options e.g.,
4544 to ignore case or to compare only selected fields.
4545 The optional @var{delimit-method} tells how to delimit
4546 groups of repeated lines, and must be one of the following:
4551 Do not delimit groups of repeated lines.
4552 This is equivalent to @option{--all-repeated} (@option{-D}).
4555 Output a newline before each group of repeated lines.
4556 With @option{--zero-terminated} (@option{-z}), use a zero
4557 byte (@acronym{ASCII} @sc{nul}) instead of a newline.
4560 Separate groups of repeated lines with a single newline.
4561 With @option{--zero-terminated} (@option{-z}), use a zero
4562 byte (@acronym{ASCII} @sc{nul}) instead of a newline.
4563 This is the same as using @samp{prepend}, except that
4564 no delimiter is inserted before the first group, and hence
4565 may be better suited for output direct to users.
4568 Note that when groups are delimited and the input stream contains
4569 two or more consecutive blank lines, then the output is ambiguous.
4570 To avoid that, filter the input through @samp{tr -s '\n'} to replace
4571 each sequence of consecutive newlines with a single newline.
4573 This is a @sc{gnu} extension.
4574 @c FIXME: give an example showing *how* it's useful
4580 @cindex unique lines, outputting
4581 Discard the first repeated line. When used by itself, this option
4582 causes @command{uniq} to print unique lines, and nothing else.
4585 @itemx --check-chars=@var{n}
4587 @opindex --check-chars
4588 Compare at most @var{n} characters on each line (after skipping any specified
4589 fields and characters). By default the entire rest of the lines are
4592 @zeroTerminatedOption
4599 @node comm invocation
4600 @section @command{comm}: Compare two sorted files line by line
4603 @cindex line-by-line comparison
4604 @cindex comparing sorted files
4606 @command{comm} writes to standard output lines that are common, and lines
4607 that are unique, to two input files; a file name of @samp{-} means
4608 standard input. Synopsis:
4611 comm [@var{option}]@dots{} @var{file1} @var{file2}
4615 Before @command{comm} can be used, the input files must be sorted using the
4616 collating sequence specified by the @env{LC_COLLATE} locale.
4617 If an input file ends in a non-newline
4618 character, a newline is silently appended. The @command{sort} command with
4619 no options always outputs a file that is suitable input to @command{comm}.
4621 @cindex differing lines
4622 @cindex common lines
4623 With no options, @command{comm} produces three-column output. Column one
4624 contains lines unique to @var{file1}, column two contains lines unique
4625 to @var{file2}, and column three contains lines common to both files.
4626 Columns are separated by a single TAB character.
4627 @c FIXME: when there's an option to supply an alternative separator
4628 @c string, append `by default' to the above sentence.
4633 The options @option{-1}, @option{-2}, and @option{-3} suppress printing of
4634 the corresponding columns (and separators). Also see @ref{Common options}.
4636 Unlike some other comparison utilities, @command{comm} has an exit
4637 status that does not depend on the result of the comparison.
4638 Upon normal completion @command{comm} produces an exit code of zero.
4639 If there is an error it exits with nonzero status.
4641 @macro checkOrderOption{cmd}
4642 If the @option{--check-order} option is given, unsorted inputs will
4643 cause a fatal error message. If the option @option{--nocheck-order}
4644 is given, unsorted inputs will never cause an error message. If
4645 neither of these options is given, wrongly sorted inputs are diagnosed
4646 only if an input file is found to contain unpairable lines. If an
4647 input file is diagnosed as being unsorted, the @command{\cmd\} command
4648 will exit with a nonzero status (and the output should not be used).
4650 Forcing @command{\cmd\} to process wrongly sorted input files
4651 containing unpairable lines by specifying @option{--nocheck-order} is
4652 not guaranteed to produce any particular output. The output will
4653 probably not correspond with whatever you hoped it would be.
4655 @checkOrderOption{comm}
4660 Fail with an error message if either input file is wrongly ordered.
4662 @item --nocheck-order
4663 Do not check that both input files are in sorted order.
4667 @item --output-delimiter=@var{str}
4668 Print @var{str} between adjacent output columns,
4669 rather than the default of a single TAB character.
4671 The delimiter @var{str} may not be empty.
4675 @node ptx invocation
4676 @section @command{ptx}: Produce permuted indexes
4680 @command{ptx} reads a text file and essentially produces a permuted index, with
4681 each keyword in its context. The calling sketch is either one of:
4684 ptx [@var{option} @dots{}] [@var{file} @dots{}]
4685 ptx -G [@var{option} @dots{}] [@var{input} [@var{output}]]
4688 The @option{-G} (or its equivalent: @option{--traditional}) option disables
4689 all @sc{gnu} extensions and reverts to traditional mode, thus introducing some
4690 limitations and changing several of the program's default option values.
4691 When @option{-G} is not specified, @sc{gnu} extensions are always enabled.
4692 @sc{gnu} extensions to @command{ptx} are documented wherever appropriate in this
4693 document. For the full list, see @xref{Compatibility in ptx}.
4695 Individual options are explained in the following sections.
4697 When @sc{gnu} extensions are enabled, there may be zero, one or several
4698 @var{file}s after the options. If there is no @var{file}, the program
4699 reads the standard input. If there is one or several @var{file}s, they
4700 give the name of input files which are all read in turn, as if all the
4701 input files were concatenated. However, there is a full contextual
4702 break between each file and, when automatic referencing is requested,
4703 file names and line numbers refer to individual text input files. In
4704 all cases, the program outputs the permuted index to the standard
4707 When @sc{gnu} extensions are @emph{not} enabled, that is, when the program
4708 operates in traditional mode, there may be zero, one or two parameters
4709 besides the options. If there are no parameters, the program reads the
4710 standard input and outputs the permuted index to the standard output.
4711 If there is only one parameter, it names the text @var{input} to be read
4712 instead of the standard input. If two parameters are given, they give
4713 respectively the name of the @var{input} file to read and the name of
4714 the @var{output} file to produce. @emph{Be very careful} to note that,
4715 in this case, the contents of file given by the second parameter is
4716 destroyed. This behavior is dictated by System V @command{ptx}
4717 compatibility; @sc{gnu} Standards normally discourage output parameters not
4718 introduced by an option.
4720 Note that for @emph{any} file named as the value of an option or as an
4721 input text file, a single dash @kbd{-} may be used, in which case
4722 standard input is assumed. However, it would not make sense to use this
4723 convention more than once per program invocation.
4726 * General options in ptx:: Options which affect general program behavior.
4727 * Charset selection in ptx:: Underlying character set considerations.
4728 * Input processing in ptx:: Input fields, contexts, and keyword selection.
4729 * Output formatting in ptx:: Types of output format, and sizing the fields.
4730 * Compatibility in ptx::
4734 @node General options in ptx
4735 @subsection General options
4740 @itemx --traditional
4741 As already explained, this option disables all @sc{gnu} extensions to
4742 @command{ptx} and switches to traditional mode.
4745 Print a short help on standard output, then exit without further
4749 Print the program version on standard output, then exit without further
4757 @node Charset selection in ptx
4758 @subsection Charset selection
4760 @c FIXME: People don't necessarily know what an IBM-PC was these days.
4761 As it is set up now, the program assumes that the input file is coded
4762 using 8-bit @acronym{ISO} 8859-1 code, also known as Latin-1 character set,
4763 @emph{unless} it is compiled for MS-DOS, in which case it uses the
4764 character set of the IBM-PC@. (@sc{gnu} @command{ptx} is not known to work on
4765 smaller MS-DOS machines anymore.) Compared to 7-bit @acronym{ASCII}, the set
4766 of characters which are letters is different; this alters the behavior
4767 of regular expression matching. Thus, the default regular expression
4768 for a keyword allows foreign or diacriticized letters. Keyword sorting,
4769 however, is still crude; it obeys the underlying character set ordering
4775 @itemx --ignore-case
4776 Fold lower case letters to upper case for sorting.
4781 @node Input processing in ptx
4782 @subsection Word selection and input processing
4787 @itemx --break-file=@var{file}
4789 This option provides an alternative (to @option{-W}) method of describing
4790 which characters make up words. It introduces the name of a
4791 file which contains a list of characters which can@emph{not} be part of
4792 one word; this file is called the @dfn{Break file}. Any character which
4793 is not part of the Break file is a word constituent. If both options
4794 @option{-b} and @option{-W} are specified, then @option{-W} has precedence and
4795 @option{-b} is ignored.
4797 When @sc{gnu} extensions are enabled, the only way to avoid newline as a
4798 break character is to write all the break characters in the file with no
4799 newline at all, not even at the end of the file. When @sc{gnu} extensions
4800 are disabled, spaces, tabs and newlines are always considered as break
4801 characters even if not included in the Break file.
4804 @itemx --ignore-file=@var{file}
4806 The file associated with this option contains a list of words which will
4807 never be taken as keywords in concordance output. It is called the
4808 @dfn{Ignore file}. The file contains exactly one word in each line; the
4809 end of line separation of words is not subject to the value of the
4813 @itemx --only-file=@var{file}
4815 The file associated with this option contains a list of words which will
4816 be retained in concordance output; any word not mentioned in this file
4817 is ignored. The file is called the @dfn{Only file}. The file contains
4818 exactly one word in each line; the end of line separation of words is
4819 not subject to the value of the @option{-S} option.
4821 There is no default for the Only file. When both an Only file and an
4822 Ignore file are specified, a word is considered a keyword only
4823 if it is listed in the Only file and not in the Ignore file.
4828 On each input line, the leading sequence of non-white space characters will be
4829 taken to be a reference that has the purpose of identifying this input
4830 line in the resulting permuted index. For more information about reference
4831 production, see @xref{Output formatting in ptx}.
4832 Using this option changes the default value for option @option{-S}.
4834 Using this option, the program does not try very hard to remove
4835 references from contexts in output, but it succeeds in doing so
4836 @emph{when} the context ends exactly at the newline. If option
4837 @option{-r} is used with @option{-S} default value, or when @sc{gnu} extensions
4838 are disabled, this condition is always met and references are completely
4839 excluded from the output contexts.
4841 @item -S @var{regexp}
4842 @itemx --sentence-regexp=@var{regexp}
4844 This option selects which regular expression will describe the end of a
4845 line or the end of a sentence. In fact, this regular expression is not
4846 the only distinction between end of lines or end of sentences, and input
4847 line boundaries have no special significance outside this option. By
4848 default, when @sc{gnu} extensions are enabled and if @option{-r} option is not
4849 used, end of sentences are used. In this case, this @var{regex} is
4850 imported from @sc{gnu} Emacs:
4853 [.?!][]\"')@}]*\\($\\|\t\\| \\)[ \t\n]*
4856 Whenever @sc{gnu} extensions are disabled or if @option{-r} option is used, end
4857 of lines are used; in this case, the default @var{regexp} is just:
4863 Using an empty @var{regexp} is equivalent to completely disabling end of
4864 line or end of sentence recognition. In this case, the whole file is
4865 considered to be a single big line or sentence. The user might want to
4866 disallow all truncation flag generation as well, through option @option{-F
4867 ""}. @xref{Regexps, , Syntax of Regular Expressions, emacs, The GNU Emacs
4870 When the keywords happen to be near the beginning of the input line or
4871 sentence, this often creates an unused area at the beginning of the
4872 output context line; when the keywords happen to be near the end of the
4873 input line or sentence, this often creates an unused area at the end of
4874 the output context line. The program tries to fill those unused areas
4875 by wrapping around context in them; the tail of the input line or
4876 sentence is used to fill the unused area on the left of the output line;
4877 the head of the input line or sentence is used to fill the unused area
4878 on the right of the output line.
4880 As a matter of convenience to the user, many usual backslashed escape
4881 sequences from the C language are recognized and converted to the
4882 corresponding characters by @command{ptx} itself.
4884 @item -W @var{regexp}
4885 @itemx --word-regexp=@var{regexp}
4887 This option selects which regular expression will describe each keyword.
4888 By default, if @sc{gnu} extensions are enabled, a word is a sequence of
4889 letters; the @var{regexp} used is @samp{\w+}. When @sc{gnu} extensions are
4890 disabled, a word is by default anything which ends with a space, a tab
4891 or a newline; the @var{regexp} used is @samp{[^ \t\n]+}.
4893 An empty @var{regexp} is equivalent to not using this option.
4894 @xref{Regexps, , Syntax of Regular Expressions, emacs, The GNU Emacs
4897 As a matter of convenience to the user, many usual backslashed escape
4898 sequences, as found in the C language, are recognized and converted to
4899 the corresponding characters by @command{ptx} itself.
4904 @node Output formatting in ptx
4905 @subsection Output formatting
4907 Output format is mainly controlled by the @option{-O} and @option{-T} options
4908 described in the table below. When neither @option{-O} nor @option{-T} are
4909 selected, and if @sc{gnu} extensions are enabled, the program chooses an
4910 output format suitable for a dumb terminal. Each keyword occurrence is
4911 output to the center of one line, surrounded by its left and right
4912 contexts. Each field is properly justified, so the concordance output
4913 can be readily observed. As a special feature, if automatic
4914 references are selected by option @option{-A} and are output before the
4915 left context, that is, if option @option{-R} is @emph{not} selected, then
4916 a colon is added after the reference; this nicely interfaces with @sc{gnu}
4917 Emacs @code{next-error} processing. In this default output format, each
4918 white space character, like newline and tab, is merely changed to
4919 exactly one space, with no special attempt to compress consecutive
4920 spaces. This might change in the future. Except for those white space
4921 characters, every other character of the underlying set of 256
4922 characters is transmitted verbatim.
4924 Output format is further controlled by the following options.
4928 @item -g @var{number}
4929 @itemx --gap-size=@var{number}
4931 Select the size of the minimum white space gap between the fields on the
4934 @item -w @var{number}
4935 @itemx --width=@var{number}
4937 Select the maximum output width of each final line. If references are
4938 used, they are included or excluded from the maximum output width
4939 depending on the value of option @option{-R}. If this option is not
4940 selected, that is, when references are output before the left context,
4941 the maximum output width takes into account the maximum length of all
4942 references. If this option is selected, that is, when references are
4943 output after the right context, the maximum output width does not take
4944 into account the space taken by references, nor the gap that precedes
4948 @itemx --auto-reference
4950 Select automatic references. Each input line will have an automatic
4951 reference made up of the file name and the line ordinal, with a single
4952 colon between them. However, the file name will be empty when standard
4953 input is being read. If both @option{-A} and @option{-r} are selected, then
4954 the input reference is still read and skipped, but the automatic
4955 reference is used at output time, overriding the input reference.
4958 @itemx --right-side-refs
4960 In the default output format, when option @option{-R} is not used, any
4961 references produced by the effect of options @option{-r} or @option{-A} are
4962 placed to the far right of output lines, after the right context. With
4963 default output format, when the @option{-R} option is specified, references
4964 are rather placed at the beginning of each output line, before the left
4965 context. For any other output format, option @option{-R} is
4966 ignored, with one exception: with @option{-R} the width of references
4967 is @emph{not} taken into account in total output width given by @option{-w}.
4969 This option is automatically selected whenever @sc{gnu} extensions are
4972 @item -F @var{string}
4973 @itemx --flac-truncation=@var{string}
4975 This option will request that any truncation in the output be reported
4976 using the string @var{string}. Most output fields theoretically extend
4977 towards the beginning or the end of the current line, or current
4978 sentence, as selected with option @option{-S}. But there is a maximum
4979 allowed output line width, changeable through option @option{-w}, which is
4980 further divided into space for various output fields. When a field has
4981 to be truncated because it cannot extend beyond the beginning or the end of
4982 the current line to fit in, then a truncation occurs. By default,
4983 the string used is a single slash, as in @option{-F /}.
4985 @var{string} may have more than one character, as in @option{-F ...}.
4986 Also, in the particular case when @var{string} is empty (@option{-F ""}),
4987 truncation flagging is disabled, and no truncation marks are appended in
4990 As a matter of convenience to the user, many usual backslashed escape
4991 sequences, as found in the C language, are recognized and converted to
4992 the corresponding characters by @command{ptx} itself.
4994 @item -M @var{string}
4995 @itemx --macro-name=@var{string}
4997 Select another @var{string} to be used instead of @samp{xx}, while
4998 generating output suitable for @command{nroff}, @command{troff} or @TeX{}.
5001 @itemx --format=roff
5003 Choose an output format suitable for @command{nroff} or @command{troff}
5004 processing. Each output line will look like:
5007 .xx "@var{tail}" "@var{before}" "@var{keyword_and_after}" "@var{head}" "@var{ref}"
5010 so it will be possible to write a @samp{.xx} roff macro to take care of
5011 the output typesetting. This is the default output format when @sc{gnu}
5012 extensions are disabled. Option @option{-M} can be used to change
5013 @samp{xx} to another macro name.
5015 In this output format, each non-graphical character, like newline and
5016 tab, is merely changed to exactly one space, with no special attempt to
5017 compress consecutive spaces. Each quote character: @kbd{"} is doubled
5018 so it will be correctly processed by @command{nroff} or @command{troff}.
5023 Choose an output format suitable for @TeX{} processing. Each output
5024 line will look like:
5027 \xx @{@var{tail}@}@{@var{before}@}@{@var{keyword}@}@{@var{after}@}@{@var{head}@}@{@var{ref}@}
5031 so it will be possible to write a @code{\xx} definition to take care of
5032 the output typesetting. Note that when references are not being
5033 produced, that is, neither option @option{-A} nor option @option{-r} is
5034 selected, the last parameter of each @code{\xx} call is inhibited.
5035 Option @option{-M} can be used to change @samp{xx} to another macro
5038 In this output format, some special characters, like @kbd{$}, @kbd{%},
5039 @kbd{&}, @kbd{#} and @kbd{_} are automatically protected with a
5040 backslash. Curly brackets @kbd{@{}, @kbd{@}} are protected with a
5041 backslash and a pair of dollar signs (to force mathematical mode). The
5042 backslash itself produces the sequence @code{\backslash@{@}}.
5043 Circumflex and tilde diacritical marks produce the sequence @code{^\@{ @}} and
5044 @code{~\@{ @}} respectively. Other diacriticized characters of the
5045 underlying character set produce an appropriate @TeX{} sequence as far
5046 as possible. The other non-graphical characters, like newline and tab,
5047 and all other characters which are not part of @acronym{ASCII}, are merely
5048 changed to exactly one space, with no special attempt to compress
5049 consecutive spaces. Let me know how to improve this special character
5050 processing for @TeX{}.
5055 @node Compatibility in ptx
5056 @subsection The @sc{gnu} extensions to @command{ptx}
5058 This version of @command{ptx} contains a few features which do not exist in
5059 System V @command{ptx}. These extra features are suppressed by using the
5060 @option{-G} command line option, unless overridden by other command line
5061 options. Some @sc{gnu} extensions cannot be recovered by overriding, so the
5062 simple rule is to avoid @option{-G} if you care about @sc{gnu} extensions.
5063 Here are the differences between this program and System V @command{ptx}.
5068 This program can read many input files at once, it always writes the
5069 resulting concordance on standard output. On the other hand, System V
5070 @command{ptx} reads only one file and sends the result to standard output
5071 or, if a second @var{file} parameter is given on the command, to that
5074 Having output parameters not introduced by options is a dangerous
5075 practice which @sc{gnu} avoids as far as possible. So, for using @command{ptx}
5076 portably between @sc{gnu} and System V, you should always use it with a
5077 single input file, and always expect the result on standard output. You
5078 might also want to automatically configure in a @option{-G} option to
5079 @command{ptx} calls in products using @command{ptx}, if the configurator finds
5080 that the installed @command{ptx} accepts @option{-G}.
5083 The only options available in System V @command{ptx} are options @option{-b},
5084 @option{-f}, @option{-g}, @option{-i}, @option{-o}, @option{-r}, @option{-t} and
5085 @option{-w}. All other options are @sc{gnu} extensions and are not repeated in
5086 this enumeration. Moreover, some options have a slightly different
5087 meaning when @sc{gnu} extensions are enabled, as explained below.
5090 By default, concordance output is not formatted for @command{troff} or
5091 @command{nroff}. It is rather formatted for a dumb terminal. @command{troff}
5092 or @command{nroff} output may still be selected through option @option{-O}.
5095 Unless @option{-R} option is used, the maximum reference width is
5096 subtracted from the total output line width. With @sc{gnu} extensions
5097 disabled, width of references is not taken into account in the output
5098 line width computations.
5101 All 256 bytes, even @acronym{ASCII} @sc{nul} bytes, are always read and
5102 processed from input file with no adverse effect, even if @sc{gnu} extensions
5103 are disabled. However, System V @command{ptx} does not accept 8-bit characters,
5104 a few control characters are rejected, and the tilde @kbd{~} is also rejected.
5107 Input line length is only limited by available memory, even if @sc{gnu}
5108 extensions are disabled. However, System V @command{ptx} processes only
5109 the first 200 characters in each line.
5112 The break (non-word) characters default to be every character except all
5113 letters of the underlying character set, diacriticized or not. When @sc{gnu}
5114 extensions are disabled, the break characters default to space, tab and
5118 The program makes better use of output line width. If @sc{gnu} extensions
5119 are disabled, the program rather tries to imitate System V @command{ptx},
5120 but still, there are some slight disposition glitches this program does
5121 not completely reproduce.
5124 The user can specify both an Ignore file and an Only file. This is not
5125 allowed with System V @command{ptx}.
5130 @node tsort invocation
5131 @section @command{tsort}: Topological sort
5134 @cindex topological sort
5136 @command{tsort} performs a topological sort on the given @var{file}, or
5137 standard input if no input file is given or for a @var{file} of
5138 @samp{-}. For more details and some history, see @ref{tsort background}.
5142 tsort [@var{option}] [@var{file}]
5145 @command{tsort} reads its input as pairs of strings, separated by blanks,
5146 indicating a partial ordering. The output is a total ordering that
5147 corresponds to the given partial ordering.
5161 will produce the output
5172 Consider a more realistic example.
5173 You have a large set of functions all in one file, and they may all be
5174 declared static except one. Currently that one (say @code{main}) is the
5175 first function defined in the file, and the ones it calls directly follow
5176 it, followed by those they call, etc. Let's say that you are determined
5177 to take advantage of prototypes, so you have to choose between declaring
5178 all of those functions (which means duplicating a lot of information from
5179 the definitions) and rearranging the functions so that as many as possible
5180 are defined before they are used. One way to automate the latter process
5181 is to get a list for each function of the functions it calls directly.
5182 Many programs can generate such lists. They describe a call graph.
5183 Consider the following list, in which a given line indicates that the
5184 function on the left calls the one on the right directly.
5190 tail_file pretty_name
5191 tail_file write_header
5193 tail_forever recheck
5194 tail_forever pretty_name
5195 tail_forever write_header
5196 tail_forever dump_remainder
5199 tail_lines start_lines
5200 tail_lines dump_remainder
5201 tail_lines file_lines
5202 tail_lines pipe_lines
5204 tail_bytes start_bytes
5205 tail_bytes dump_remainder
5206 tail_bytes pipe_bytes
5207 file_lines dump_remainder
5211 then you can use @command{tsort} to produce an ordering of those
5212 functions that satisfies your requirement.
5215 example$ tsort call-graph | tac
5235 @command{tsort} detects any cycles in the input and writes the first cycle
5236 encountered to standard error.
5238 Note that for a given partial ordering, generally there is no unique
5239 total ordering. In the context of the call graph above, the function
5240 @code{parse_options} may be placed anywhere in the list as long as it
5241 precedes @code{main}.
5243 The only options are @option{--help} and @option{--version}. @xref{Common
5249 * tsort background:: Where tsort came from.
5252 @node tsort background
5253 @subsection @command{tsort}: Background
5255 @command{tsort} exists because very early versions of the Unix linker processed
5256 an archive file exactly once, and in order. As @command{ld} read each object
5257 in the archive, it decided whether it was needed in the program based on
5258 whether it defined any symbols which were undefined at that point in
5261 This meant that dependencies within the archive had to be handled
5262 specially. For example, @code{scanf} probably calls @code{read}. That means
5263 that in a single pass through an archive, it was important for @code{scanf.o}
5264 to appear before read.o, because otherwise a program which calls
5265 @code{scanf} but not @code{read} might end up with an unexpected unresolved
5266 reference to @code{read}.
5268 The way to address this problem was to first generate a set of
5269 dependencies of one object file on another. This was done by a shell
5270 script called @command{lorder}. The GNU tools don't provide a version of
5271 lorder, as far as I know, but you can still find it in BSD
5274 Then you ran @command{tsort} over the @command{lorder} output, and you used the
5275 resulting sort to define the order in which you added objects to the archive.
5277 This whole procedure has been obsolete since about 1980, because
5278 Unix archives now contain a symbol table (traditionally built by
5279 @command{ranlib}, now generally built by @command{ar} itself), and the Unix
5280 linker uses the symbol table to effectively make multiple passes over
5283 Anyhow, that's where tsort came from. To solve an old problem with
5284 the way the linker handled archive files, which has since been solved
5288 @node Operating on fields
5289 @chapter Operating on fields
5292 * cut invocation:: Print selected parts of lines.
5293 * paste invocation:: Merge lines of files.
5294 * join invocation:: Join lines on a common field.
5298 @node cut invocation
5299 @section @command{cut}: Print selected parts of lines
5302 @command{cut} writes to standard output selected parts of each line of each
5303 input file, or standard input if no files are given or for a file name of
5307 cut @var{option}@dots{} [@var{file}]@dots{}
5310 In the table which follows, the @var{byte-list}, @var{character-list},
5311 and @var{field-list} are one or more numbers or ranges (two numbers
5312 separated by a dash) separated by commas. Bytes, characters, and
5313 fields are numbered starting at 1. Incomplete ranges may be
5314 given: @option{-@var{m}} means @samp{1-@var{m}}; @samp{@var{n}-} means
5315 @samp{@var{n}} through end of line or last field. The list elements
5316 can be repeated, can overlap, and can be specified in any order; but
5317 the selected input is written in the same order that it is read, and
5318 is written exactly once.
5320 The program accepts the following options. Also see @ref{Common
5325 @item -b @var{byte-list}
5326 @itemx --bytes=@var{byte-list}
5329 Select for printing only the bytes in positions listed in
5330 @var{byte-list}. Tabs and backspaces are treated like any other
5331 character; they take up 1 byte. If an output delimiter is specified,
5332 (see the description of @option{--output-delimiter}), then output that
5333 string between ranges of selected bytes.
5335 @item -c @var{character-list}
5336 @itemx --characters=@var{character-list}
5338 @opindex --characters
5339 Select for printing only the characters in positions listed in
5340 @var{character-list}. The same as @option{-b} for now, but
5341 internationalization will change that. Tabs and backspaces are
5342 treated like any other character; they take up 1 character. If an
5343 output delimiter is specified, (see the description of
5344 @option{--output-delimiter}), then output that string between ranges
5347 @item -f @var{field-list}
5348 @itemx --fields=@var{field-list}
5351 Select for printing only the fields listed in @var{field-list}.
5352 Fields are separated by a TAB character by default. Also print any
5353 line that contains no delimiter character, unless the
5354 @option{--only-delimited} (@option{-s}) option is specified.
5355 Note @command{cut} does not support specifying runs of whitespace as a
5356 delimiter, so to achieve that common functionality one can pre-process
5357 with @command{tr} like:
5359 tr -s '[:blank:]' '\t' | cut -f@dots{}
5362 @item -d @var{input_delim_byte}
5363 @itemx --delimiter=@var{input_delim_byte}
5365 @opindex --delimiter
5366 With @option{-f}, use the first byte of @var{input_delim_byte} as
5367 the input fields separator (default is TAB).
5371 Do not split multi-byte characters (no-op for now).
5374 @itemx --only-delimited
5376 @opindex --only-delimited
5377 For @option{-f}, do not print lines that do not contain the field separator
5378 character. Normally, any line without a field separator is printed verbatim.
5380 @item --output-delimiter=@var{output_delim_string}
5381 @opindex --output-delimiter
5382 With @option{-f}, output fields are separated by @var{output_delim_string}.
5383 The default with @option{-f} is to use the input delimiter.
5384 When using @option{-b} or @option{-c} to select ranges of byte or
5385 character offsets (as opposed to ranges of fields),
5386 output @var{output_delim_string} between non-overlapping
5387 ranges of selected bytes.
5390 @opindex --complement
5391 This option is a @acronym{GNU} extension.
5392 Select for printing the complement of the bytes, characters or fields
5393 selected with the @option{-b}, @option{-c} or @option{-f} options.
5394 In other words, do @emph{not} print the bytes, characters or fields
5395 specified via those options. This option is useful when you have
5396 many fields and want to print all but a few of them.
5403 @node paste invocation
5404 @section @command{paste}: Merge lines of files
5407 @cindex merging files
5409 @command{paste} writes to standard output lines consisting of sequentially
5410 corresponding lines of each given file, separated by a TAB character.
5411 Standard input is used for a file name of @samp{-} or if no input files
5433 paste [@var{option}]@dots{} [@var{file}]@dots{}
5436 The program accepts the following options. Also see @ref{Common options}.
5444 Paste the lines of one file at a time rather than one line from each
5445 file. Using the above example data:
5448 $ paste -s num2 let3
5453 @item -d @var{delim-list}
5454 @itemx --delimiters=@var{delim-list}
5456 @opindex --delimiters
5457 Consecutively use the characters in @var{delim-list} instead of
5458 TAB to separate merged lines. When @var{delim-list} is
5459 exhausted, start again at its beginning. Using the above example data:
5462 $ paste -d '%_' num2 let3 num2
5473 @node join invocation
5474 @section @command{join}: Join lines on a common field
5477 @cindex common field, joining on
5479 @command{join} writes to standard output a line for each pair of input
5480 lines that have identical join fields. Synopsis:
5483 join [@var{option}]@dots{} @var{file1} @var{file2}
5486 Either @var{file1} or @var{file2} (but not both) can be @samp{-},
5487 meaning standard input. @var{file1} and @var{file2} should be
5488 sorted on the join fields.
5491 Normally, the sort order is that of the
5492 collating sequence specified by the @env{LC_COLLATE} locale. Unless
5493 the @option{-t} option is given, the sort comparison ignores blanks at
5494 the start of the join field, as in @code{sort -b}. If the
5495 @option{--ignore-case} option is given, the sort comparison ignores
5496 the case of characters in the join field, as in @code{sort -f}.
5498 The @command{sort} and @command{join} commands should use consistent
5499 locales and options if the output of @command{sort} is fed to
5500 @command{join}. You can use a command like @samp{sort -k 1b,1} to
5501 sort a file on its default join field, but if you select a non-default
5502 locale, join field, separator, or comparison options, then you should
5503 do so consistently between @command{join} and @command{sort}.
5504 If @samp{join -t ''} is specified then the whole line is considered which
5505 matches the default operation of sort.
5507 If the input has no unpairable lines, a @acronym{GNU} extension is
5508 available; the sort order can be any order that considers two fields
5509 to be equal if and only if the sort comparison described above
5510 considers them to be equal. For example:
5527 @checkOrderOption{join}
5531 @item the join field is the first field in each line;
5532 @item fields in the input are separated by one or more blanks, with leading
5533 blanks on the line ignored;
5534 @item fields in the output are separated by a space;
5535 @item each output line consists of the join field, the remaining
5536 fields from @var{file1}, then the remaining fields from @var{file2}.
5539 The program accepts the following options. Also see @ref{Common options}.
5543 @item -a @var{file-number}
5545 Print a line for each unpairable line in file @var{file-number} (either
5546 @samp{1} or @samp{2}), in addition to the normal output.
5549 Fail with an error message if either input file is wrongly ordered.
5551 @item --nocheck-order
5552 Do not check that both input files are in sorted order. This is the default.
5554 @item -e @var{string}
5556 Replace those output fields that are missing in the input with
5561 Treat the first line of each input file as a header line. The header lines will
5562 be joined and printed as the first output line. If @option{-o} is used to
5563 specify output format, the header line will be printed according to the
5564 specified format. The header lines will not be checked for ordering even if
5565 @option{--check-order} is specified. Also if the header lines from each file
5566 do not match, the heading fields from the first file will be used.
5569 @itemx --ignore-case
5571 @opindex --ignore-case
5572 Ignore differences in case when comparing keys.
5573 With this option, the lines of the input files must be ordered in the same way.
5574 Use @samp{sort -f} to produce this ordering.
5576 @item -1 @var{field}
5578 Join on field @var{field} (a positive integer) of file 1.
5580 @item -2 @var{field}
5582 Join on field @var{field} (a positive integer) of file 2.
5584 @item -j @var{field}
5585 Equivalent to @option{-1 @var{field} -2 @var{field}}.
5587 @item -o @var{field-list}
5588 Construct each output line according to the format in @var{field-list}.
5589 Each element in @var{field-list} is either the single character @samp{0} or
5590 has the form @var{m.n} where the file number, @var{m}, is @samp{1} or
5591 @samp{2} and @var{n} is a positive field number.
5593 A field specification of @samp{0} denotes the join field.
5594 In most cases, the functionality of the @samp{0} field spec
5595 may be reproduced using the explicit @var{m.n} that corresponds
5596 to the join field. However, when printing unpairable lines
5597 (using either of the @option{-a} or @option{-v} options), there is no way
5598 to specify the join field using @var{m.n} in @var{field-list}
5599 if there are unpairable lines in both files.
5600 To give @command{join} that functionality, @acronym{POSIX} invented the @samp{0}
5601 field specification notation.
5603 The elements in @var{field-list}
5604 are separated by commas or blanks.
5605 Blank separators typically need to be quoted for the shell. For
5606 example, the commands @samp{join -o 1.2,2.2} and @samp{join -o '1.2
5607 2.2'} are equivalent.
5609 All output lines---including those printed because of any -a or -v
5610 option---are subject to the specified @var{field-list}.
5613 Use character @var{char} as the input and output field separator.
5614 Treat as significant each occurrence of @var{char} in the input file.
5615 Use @samp{sort -t @var{char}}, without the @option{-b} option of
5616 @samp{sort}, to produce this ordering. If @samp{join -t ''} is specified,
5617 the whole line is considered, matching the default operation of sort.
5618 If @samp{-t '\0'} is specified then the @acronym{ASCII} @sc{nul}
5619 character is used to delimit the fields.
5621 @item -v @var{file-number}
5622 Print a line for each unpairable line in file @var{file-number}
5623 (either @samp{1} or @samp{2}), instead of the normal output.
5630 @node Operating on characters
5631 @chapter Operating on characters
5633 @cindex operating on characters
5635 This commands operate on individual characters.
5638 * tr invocation:: Translate, squeeze, and/or delete characters.
5639 * expand invocation:: Convert tabs to spaces.
5640 * unexpand invocation:: Convert spaces to tabs.
5645 @section @command{tr}: Translate, squeeze, and/or delete characters
5652 tr [@var{option}]@dots{} @var{set1} [@var{set2}]
5655 @command{tr} copies standard input to standard output, performing
5656 one of the following operations:
5660 translate, and optionally squeeze repeated characters in the result,
5662 squeeze repeated characters,
5666 delete characters, then squeeze repeated characters from the result.
5669 The @var{set1} and (if given) @var{set2} arguments define ordered
5670 sets of characters, referred to below as @var{set1} and @var{set2}. These
5671 sets are the characters of the input that @command{tr} operates on.
5672 The @option{--complement} (@option{-c}, @option{-C}) option replaces
5674 complement (all of the characters that are not in @var{set1}).
5676 Currently @command{tr} fully supports only single-byte characters.
5677 Eventually it will support multibyte characters; when it does, the
5678 @option{-C} option will cause it to complement the set of characters,
5679 whereas @option{-c} will cause it to complement the set of values.
5680 This distinction will matter only when some values are not characters,
5681 and this is possible only in locales using multibyte encodings when
5682 the input contains encoding errors.
5684 The program accepts the @option{--help} and @option{--version}
5685 options. @xref{Common options}. Options must precede operands.
5690 * Character sets:: Specifying sets of characters.
5691 * Translating:: Changing one set of characters to another.
5692 * Squeezing:: Squeezing repeats and deleting.
5696 @node Character sets
5697 @subsection Specifying sets of characters
5699 @cindex specifying sets of characters
5701 The format of the @var{set1} and @var{set2} arguments resembles
5702 the format of regular expressions; however, they are not regular
5703 expressions, only lists of characters. Most characters simply
5704 represent themselves in these strings, but the strings can contain
5705 the shorthands listed below, for convenience. Some of them can be
5706 used only in @var{set1} or @var{set2}, as noted below.
5710 @item Backslash escapes
5711 @cindex backslash escapes
5713 The following backslash escape sequences are recognized:
5731 The character with the value given by @var{ooo}, which is 1 to 3
5737 While a backslash followed by a character not listed above is
5738 interpreted as that character, the backslash also effectively
5739 removes any special significance, so it is useful to escape
5740 @samp{[}, @samp{]}, @samp{*}, and @samp{-}.
5745 The notation @samp{@var{m}-@var{n}} expands to all of the characters
5746 from @var{m} through @var{n}, in ascending order. @var{m} should
5747 collate before @var{n}; if it doesn't, an error results. As an example,
5748 @samp{0-9} is the same as @samp{0123456789}.
5750 @sc{gnu} @command{tr} does not support the System V syntax that uses square
5751 brackets to enclose ranges. Translations specified in that format
5752 sometimes work as expected, since the brackets are often transliterated
5753 to themselves. However, they should be avoided because they sometimes
5754 behave unexpectedly. For example, @samp{tr -d '[0-9]'} deletes brackets
5757 Many historically common and even accepted uses of ranges are not
5758 portable. For example, on @acronym{EBCDIC} hosts using the @samp{A-Z}
5759 range will not do what most would expect because @samp{A} through @samp{Z}
5760 are not contiguous as they are in @acronym{ASCII}.
5761 If you can rely on a @acronym{POSIX} compliant version of @command{tr}, then
5762 the best way to work around this is to use character classes (see below).
5763 Otherwise, it is most portable (and most ugly) to enumerate the members
5766 @item Repeated characters
5767 @cindex repeated characters
5769 The notation @samp{[@var{c}*@var{n}]} in @var{set2} expands to @var{n}
5770 copies of character @var{c}. Thus, @samp{[y*6]} is the same as
5771 @samp{yyyyyy}. The notation @samp{[@var{c}*]} in @var{string2} expands
5772 to as many copies of @var{c} as are needed to make @var{set2} as long as
5773 @var{set1}. If @var{n} begins with @samp{0}, it is interpreted in
5774 octal, otherwise in decimal.
5776 @item Character classes
5777 @cindex character classes
5779 The notation @samp{[:@var{class}:]} expands to all of the characters in
5780 the (predefined) class @var{class}. The characters expand in no
5781 particular order, except for the @code{upper} and @code{lower} classes,
5782 which expand in ascending order. When the @option{--delete} (@option{-d})
5783 and @option{--squeeze-repeats} (@option{-s}) options are both given, any
5784 character class can be used in @var{set2}. Otherwise, only the
5785 character classes @code{lower} and @code{upper} are accepted in
5786 @var{set2}, and then only if the corresponding character class
5787 (@code{upper} and @code{lower}, respectively) is specified in the same
5788 relative position in @var{set1}. Doing this specifies case conversion.
5789 The class names are given below; an error results when an invalid class
5801 Horizontal whitespace.
5810 Printable characters, not including space.
5816 Printable characters, including space.
5819 Punctuation characters.
5822 Horizontal or vertical whitespace.
5831 @item Equivalence classes
5832 @cindex equivalence classes
5834 The syntax @samp{[=@var{c}=]} expands to all of the characters that are
5835 equivalent to @var{c}, in no particular order. Equivalence classes are
5836 a relatively recent invention intended to support non-English alphabets.
5837 But there seems to be no standard way to define them or determine their
5838 contents. Therefore, they are not fully implemented in @sc{gnu} @command{tr};
5839 each character's equivalence class consists only of that character,
5840 which is of no particular use.
5846 @subsection Translating
5848 @cindex translating characters
5850 @command{tr} performs translation when @var{set1} and @var{set2} are
5851 both given and the @option{--delete} (@option{-d}) option is not given.
5852 @command{tr} translates each character of its input that is in @var{set1}
5853 to the corresponding character in @var{set2}. Characters not in
5854 @var{set1} are passed through unchanged. When a character appears more
5855 than once in @var{set1} and the corresponding characters in @var{set2}
5856 are not all the same, only the final one is used. For example, these
5857 two commands are equivalent:
5864 A common use of @command{tr} is to convert lowercase characters to
5865 uppercase. This can be done in many ways. Here are three of them:
5868 tr abcdefghijklmnopqrstuvwxyz ABCDEFGHIJKLMNOPQRSTUVWXYZ
5870 tr '[:lower:]' '[:upper:]'
5874 But note that using ranges like @code{a-z} above is not portable.
5876 When @command{tr} is performing translation, @var{set1} and @var{set2}
5877 typically have the same length. If @var{set1} is shorter than
5878 @var{set2}, the extra characters at the end of @var{set2} are ignored.
5880 On the other hand, making @var{set1} longer than @var{set2} is not
5881 portable; @acronym{POSIX} says that the result is undefined. In this situation,
5882 BSD @command{tr} pads @var{set2} to the length of @var{set1} by repeating
5883 the last character of @var{set2} as many times as necessary. System V
5884 @command{tr} truncates @var{set1} to the length of @var{set2}.
5886 By default, @sc{gnu} @command{tr} handles this case like BSD @command{tr}.
5887 When the @option{--truncate-set1} (@option{-t}) option is given,
5888 @sc{gnu} @command{tr} handles this case like the System V @command{tr}
5889 instead. This option is ignored for operations other than translation.
5891 Acting like System V @command{tr} in this case breaks the relatively common
5895 tr -cs A-Za-z0-9 '\012'
5899 because it converts only zero bytes (the first element in the
5900 complement of @var{set1}), rather than all non-alphanumerics, to
5904 By the way, the above idiom is not portable because it uses ranges, and
5905 it assumes that the octal code for newline is 012.
5906 Assuming a @acronym{POSIX} compliant @command{tr}, here is a better way to write it:
5909 tr -cs '[:alnum:]' '[\n*]'
5914 @subsection Squeezing repeats and deleting
5916 @cindex squeezing repeat characters
5917 @cindex deleting characters
5919 When given just the @option{--delete} (@option{-d}) option, @command{tr}
5920 removes any input characters that are in @var{set1}.
5922 When given just the @option{--squeeze-repeats} (@option{-s}) option,
5923 @command{tr} replaces each input sequence of a repeated character that
5924 is in @var{set1} with a single occurrence of that character.
5926 When given both @option{--delete} and @option{--squeeze-repeats}, @command{tr}
5927 first performs any deletions using @var{set1}, then squeezes repeats
5928 from any remaining characters using @var{set2}.
5930 The @option{--squeeze-repeats} option may also be used when translating,
5931 in which case @command{tr} first performs translation, then squeezes
5932 repeats from any remaining characters using @var{set2}.
5934 Here are some examples to illustrate various combinations of options:
5939 Remove all zero bytes:
5946 Put all words on lines by themselves. This converts all
5947 non-alphanumeric characters to newlines, then squeezes each string
5948 of repeated newlines into a single newline:
5951 tr -cs '[:alnum:]' '[\n*]'
5955 Convert each sequence of repeated newlines to a single newline:
5962 Find doubled occurrences of words in a document.
5963 @c Separate the following two "the"s, so typo checkers don't complain.
5964 For example, people often write ``the @w{}the'' with the repeated words
5965 separated by a newline. The Bourne shell script below works first
5966 by converting each sequence of punctuation and blank characters to a
5967 single newline. That puts each ``word'' on a line by itself.
5968 Next it maps all uppercase characters to lower case, and finally it
5969 runs @command{uniq} with the @option{-d} option to print out only the words
5975 | tr -s '[:punct:][:blank:]' '[\n*]' \
5976 | tr '[:upper:]' '[:lower:]' \
5981 Deleting a small set of characters is usually straightforward. For example,
5982 to remove all @samp{a}s, @samp{x}s, and @samp{M}s you would do this:
5988 However, when @samp{-} is one of those characters, it can be tricky because
5989 @samp{-} has special meanings. Performing the same task as above but also
5990 removing all @samp{-} characters, we might try @code{tr -d -axM}, but
5991 that would fail because @command{tr} would try to interpret @option{-a} as
5992 a command-line option. Alternatively, we could try putting the hyphen
5993 inside the string, @code{tr -d a-xM}, but that wouldn't work either because
5994 it would make @command{tr} interpret @code{a-x} as the range of characters
5995 @samp{a}@dots{}@samp{x} rather than the three.
5996 One way to solve the problem is to put the hyphen at the end of the list
6003 Or you can use @samp{--} to terminate option processing:
6009 More generally, use the character class notation @code{[=c=]}
6010 with @samp{-} (or any other character) in place of the @samp{c}:
6016 Note how single quotes are used in the above example to protect the
6017 square brackets from interpretation by a shell.
6022 @node expand invocation
6023 @section @command{expand}: Convert tabs to spaces
6026 @cindex tabs to spaces, converting
6027 @cindex converting tabs to spaces
6029 @command{expand} writes the contents of each given @var{file}, or standard
6030 input if none are given or for a @var{file} of @samp{-}, to standard
6031 output, with tab characters converted to the appropriate number of
6035 expand [@var{option}]@dots{} [@var{file}]@dots{}
6038 By default, @command{expand} converts all tabs to spaces. It preserves
6039 backspace characters in the output; they decrement the column count for
6040 tab calculations. The default action is equivalent to @option{-t 8} (set
6041 tabs every 8 columns).
6043 The program accepts the following options. Also see @ref{Common options}.
6047 @item -t @var{tab1}[,@var{tab2}]@dots{}
6048 @itemx --tabs=@var{tab1}[,@var{tab2}]@dots{}
6051 @cindex tab stops, setting
6052 If only one tab stop is given, set the tabs @var{tab1} spaces apart
6053 (default is 8). Otherwise, set the tabs at columns @var{tab1},
6054 @var{tab2}, @dots{} (numbered from 0), and replace any tabs beyond the
6055 last tab stop given with single spaces. Tab stops can be separated by
6056 blanks as well as by commas.
6058 For compatibility, GNU @command{expand} also accepts the obsolete
6059 option syntax, @option{-@var{t1}[,@var{t2}]@dots{}}. New scripts
6060 should use @option{-t @var{t1}[,@var{t2}]@dots{}} instead.
6066 @cindex initial tabs, converting
6067 Only convert initial tabs (those that precede all non-space or non-tab
6068 characters) on each line to spaces.
6075 @node unexpand invocation
6076 @section @command{unexpand}: Convert spaces to tabs
6080 @command{unexpand} writes the contents of each given @var{file}, or
6081 standard input if none are given or for a @var{file} of @samp{-}, to
6082 standard output, converting blanks at the beginning of each line into
6083 as many tab characters as needed. In the default @acronym{POSIX}
6084 locale, a @dfn{blank} is a space or a tab; other locales may specify
6085 additional blank characters. Synopsis:
6088 unexpand [@var{option}]@dots{} [@var{file}]@dots{}
6091 By default, @command{unexpand} converts only initial blanks (those
6092 that precede all non-blank characters) on each line. It
6093 preserves backspace characters in the output; they decrement the column
6094 count for tab calculations. By default, tabs are set at every 8th
6097 The program accepts the following options. Also see @ref{Common options}.
6101 @item -t @var{tab1}[,@var{tab2}]@dots{}
6102 @itemx --tabs=@var{tab1}[,@var{tab2}]@dots{}
6105 If only one tab stop is given, set the tabs @var{tab1} columns apart
6106 instead of the default 8. Otherwise, set the tabs at columns
6107 @var{tab1}, @var{tab2}, @dots{} (numbered from 0), and leave blanks
6108 beyond the tab stops given unchanged. Tab stops can be separated by
6109 blanks as well as by commas. This option implies the @option{-a} option.
6111 For compatibility, GNU @command{unexpand} supports the obsolete option syntax,
6112 @option{-@var{tab1}[,@var{tab2}]@dots{}}, where tab stops must be
6113 separated by commas. (Unlike @option{-t}, this obsolete option does
6114 not imply @option{-a}.) New scripts should use @option{--first-only -t
6115 @var{tab1}[,@var{tab2}]@dots{}} instead.
6121 Also convert all sequences of two or more blanks just before a tab stop,
6122 even if they occur after non-blank characters in a line.
6129 @node Directory listing
6130 @chapter Directory listing
6132 This chapter describes the @command{ls} command and its variants @command{dir}
6133 and @command{vdir}, which list information about files.
6136 * ls invocation:: List directory contents.
6137 * dir invocation:: Briefly ls.
6138 * vdir invocation:: Verbosely ls.
6139 * dircolors invocation:: Color setup for ls, etc.
6144 @section @command{ls}: List directory contents
6147 @cindex directory listing
6149 The @command{ls} program lists information about files (of any type,
6150 including directories). Options and file arguments can be intermixed
6151 arbitrarily, as usual.
6153 For non-option command-line arguments that are directories, by default
6154 @command{ls} lists the contents of directories, not recursively, and
6155 omitting files with names beginning with @samp{.}. For other non-option
6156 arguments, by default @command{ls} lists just the file name. If no
6157 non-option argument is specified, @command{ls} operates on the current
6158 directory, acting as if it had been invoked with a single argument of @samp{.}.
6161 By default, the output is sorted alphabetically, according to the locale
6162 settings in effect.@footnote{If you use a non-@acronym{POSIX}
6163 locale (e.g., by setting @env{LC_ALL} to @samp{en_US}), then @command{ls} may
6164 produce output that is sorted differently than you're accustomed to.
6165 In that case, set the @env{LC_ALL} environment variable to @samp{C}.}
6166 If standard output is
6167 a terminal, the output is in columns (sorted vertically) and control
6168 characters are output as question marks; otherwise, the output is listed
6169 one per line and control characters are output as-is.
6171 Because @command{ls} is such a fundamental program, it has accumulated many
6172 options over the years. They are described in the subsections below;
6173 within each section, options are listed alphabetically (ignoring case).
6174 The division of options into the subsections is not absolute, since some
6175 options affect more than one aspect of @command{ls}'s operation.
6177 @cindex exit status of @command{ls}
6182 1 minor problems (e.g., failure to access a file or directory not
6183 specified as a command line argument. This happens when listing a
6184 directory in which entries are actively being removed or renamed.)
6185 2 serious trouble (e.g., memory exhausted, invalid option, failure
6186 to access a file or directory specified as a command line argument
6187 or a directory loop)
6190 Also see @ref{Common options}.
6193 * Which files are listed::
6194 * What information is listed::
6195 * Sorting the output::
6196 * Details about version sort::
6197 * General output formatting::
6198 * Formatting file timestamps::
6199 * Formatting the file names::
6203 @node Which files are listed
6204 @subsection Which files are listed
6206 These options determine which files @command{ls} lists information for.
6207 By default, @command{ls} lists files and the contents of any
6208 directories on the command line, except that in directories it ignores
6209 files whose names start with @samp{.}.
6217 In directories, do not ignore file names that start with @samp{.}.
6222 @opindex --almost-all
6223 In directories, do not ignore all file names that start with @samp{.};
6224 ignore only @file{.} and @file{..}. The @option{--all} (@option{-a})
6225 option overrides this option.
6228 @itemx --ignore-backups
6230 @opindex --ignore-backups
6231 @cindex backup files, ignoring
6232 In directories, ignore files that end with @samp{~}. This option is
6233 equivalent to @samp{--ignore='*~' --ignore='.*~'}.
6238 @opindex --directory
6239 List just the names of directories, as with other types of files, rather
6240 than listing their contents.
6241 @c The following sentence is the same as the one for -F.
6242 Do not follow symbolic links listed on the
6243 command line unless the @option{--dereference-command-line} (@option{-H}),
6244 @option{--dereference} (@option{-L}), or
6245 @option{--dereference-command-line-symlink-to-dir} options are specified.
6248 @itemx --dereference-command-line
6250 @opindex --dereference-command-line
6251 @cindex symbolic links, dereferencing
6252 If a command line argument specifies a symbolic link, show information
6253 for the file the link references rather than for the link itself.
6255 @itemx --dereference-command-line-symlink-to-dir
6256 @opindex --dereference-command-line-symlink-to-dir
6257 @cindex symbolic links, dereferencing
6258 Do not dereference symbolic links, with one exception:
6259 if a command line argument specifies a symbolic link that refers to
6260 a directory, show information for that directory rather than for the
6262 This is the default behavior when no other dereferencing-related
6263 option has been specified (@option{--classify} (@option{-F}),
6264 @option{--directory} (@option{-d}),
6266 @option{--dereference} (@option{-L}), or
6267 @option{--dereference-command-line} (@option{-H})).
6269 @item --group-directories-first
6270 @opindex --group-directories-first
6271 Group all the directories before the files and then sort the
6272 directories and the files separately using the selected sort key
6273 (see --sort option).
6274 That is, this option specifies a primary sort key,
6275 and the --sort option specifies a secondary key.
6276 However, any use of @option{--sort=none}
6277 (@option{-U}) disables this option altogether.
6279 @item --hide=PATTERN
6280 @opindex --hide=@var{pattern}
6281 In directories, ignore files whose names match the shell pattern
6282 @var{pattern}, unless the @option{--all} (@option{-a}) or
6283 @option{--almost-all} (@option{-A}) is also given. This
6284 option acts like @option{--ignore=@var{pattern}} except that it has no
6285 effect if @option{--all} (@option{-a}) or @option{--almost-all}
6286 (@option{-A}) is also given.
6288 This option can be useful in shell aliases. For example, if
6289 @command{lx} is an alias for @samp{ls --hide='*~'} and @command{ly} is
6290 an alias for @samp{ls --ignore='*~'}, then the command @samp{lx -A}
6291 lists the file @file{README~} even though @samp{ly -A} would not.
6293 @item -I @var{pattern}
6294 @itemx --ignore=@var{pattern}
6296 @opindex --ignore=@var{pattern}
6297 In directories, ignore files whose names match the shell pattern
6298 (not regular expression) @var{pattern}. As
6299 in the shell, an initial @samp{.} in a file name does not match a
6300 wildcard at the start of @var{pattern}. Sometimes it is useful
6301 to give this option several times. For example,
6304 $ ls --ignore='.??*' --ignore='.[^.]' --ignore='#*'
6307 The first option ignores names of length 3 or more that start with @samp{.},
6308 the second ignores all two-character names that start with @samp{.}
6309 except @samp{..}, and the third ignores names that start with @samp{#}.
6312 @itemx --dereference
6314 @opindex --dereference
6315 @cindex symbolic links, dereferencing
6316 When showing file information for a symbolic link, show information
6317 for the file the link references rather than the link itself.
6318 However, even with this option, @command{ls} still prints the name
6319 of the link itself, not the name of the file that the link points to.
6324 @opindex --recursive
6325 @cindex recursive directory listing
6326 @cindex directory listing, recursive
6327 List the contents of all directories recursively.
6332 @node What information is listed
6333 @subsection What information is listed
6335 These options affect the information that @command{ls} displays. By
6336 default, only file names are shown.
6342 @cindex hurd, author, printing
6343 List each file's author when producing long format directory listings.
6344 In GNU/Hurd, file authors can differ from their owners, but in other
6345 operating systems the two are the same.
6351 @cindex dired Emacs mode support
6352 With the long listing (@option{-l}) format, print an additional line after
6356 //DIRED// @var{beg1} @var{end1} @var{beg2} @var{end2} @dots{}
6360 The @var{begn} and @var{endn} are unsigned integers that record the
6361 byte position of the beginning and end of each file name in the output.
6362 This makes it easy for Emacs to find the names, even when they contain
6363 unusual characters such as space or newline, without fancy searching.
6365 If directories are being listed recursively (@option{-R}), output a similar
6366 line with offsets for each subdirectory name:
6369 //SUBDIRED// @var{beg1} @var{end1} @dots{}
6372 Finally, output a line of the form:
6375 //DIRED-OPTIONS// --quoting-style=@var{word}
6379 where @var{word} is the quoting style (@pxref{Formatting the file names}).
6381 Here is an actual example:
6384 $ mkdir -p a/sub/deeper a/sub2
6386 $ touch a/sub/deeper/file
6387 $ ls -gloRF --dired a
6390 -rw-r--r-- 1 0 Jun 10 12:27 f1
6391 -rw-r--r-- 1 0 Jun 10 12:27 f2
6392 drwxr-xr-x 3 4096 Jun 10 12:27 sub/
6393 drwxr-xr-x 2 4096 Jun 10 12:27 sub2/
6397 drwxr-xr-x 2 4096 Jun 10 12:27 deeper/
6401 -rw-r--r-- 1 0 Jun 10 12:27 file
6405 //DIRED// 48 50 84 86 120 123 158 162 217 223 282 286
6406 //SUBDIRED// 2 3 167 172 228 240 290 296
6407 //DIRED-OPTIONS// --quoting-style=literal
6410 Note that the pairs of offsets on the @samp{//DIRED//} line above delimit
6411 these names: @file{f1}, @file{f2}, @file{sub}, @file{sub2}, @file{deeper},
6413 The offsets on the @samp{//SUBDIRED//} line delimit the following
6414 directory names: @file{a}, @file{a/sub}, @file{a/sub/deeper}, @file{a/sub2}.
6416 Here is an example of how to extract the fifth entry name, @samp{deeper},
6417 corresponding to the pair of offsets, 222 and 228:
6420 $ ls -gloRF --dired a > out
6421 $ dd bs=1 skip=222 count=6 < out 2>/dev/null; echo
6425 Note that although the listing above includes a trailing slash
6426 for the @samp{deeper} entry, the offsets select the name without
6427 the trailing slash. However, if you invoke @command{ls} with @option{--dired}
6428 along with an option like @option{--escape} (aka @option{-b}) and operate
6429 on a file whose name contains special characters, notice that the backslash
6434 $ ls -blog --dired 'a b'
6435 -rw-r--r-- 1 0 Jun 10 12:28 a\ b
6437 //DIRED-OPTIONS// --quoting-style=escape
6440 If you use a quoting style that adds quote marks
6441 (e.g., @option{--quoting-style=c}), then the offsets include the quote marks.
6442 So beware that the user may select the quoting style via the environment
6443 variable @env{QUOTING_STYLE}. Hence, applications using @option{--dired}
6444 should either specify an explicit @option{--quoting-style=literal} option
6445 (aka @option{-N} or @option{--literal}) on the command line, or else be
6446 prepared to parse the escaped names.
6449 @opindex --full-time
6450 Produce long format directory listings, and list times in full. It is
6451 equivalent to using @option{--format=long} with
6452 @option{--time-style=full-iso} (@pxref{Formatting file timestamps}).
6456 Produce long format directory listings, but don't display owner information.
6462 Inhibit display of group information in a long format directory listing.
6463 (This is the default in some non-@sc{gnu} versions of @command{ls}, so we
6464 provide this option for compatibility.)
6472 @cindex inode number, printing
6473 Print the inode number (also called the file serial number and index
6474 number) of each file to the left of the file name. (This number
6475 uniquely identifies each file within a particular file system.)
6478 @itemx --format=long
6479 @itemx --format=verbose
6482 @opindex long ls @r{format}
6483 @opindex verbose ls @r{format}
6484 In addition to the name of each file, print the file type, file mode bits,
6485 number of hard links, owner name, group name, size, and
6486 timestamp (@pxref{Formatting file timestamps}), normally
6487 the modification time. Print question marks for information that
6488 cannot be determined.
6490 Normally the size is printed as a byte count without punctuation, but
6491 this can be overridden (@pxref{Block size}). For example, @option{-h}
6492 prints an abbreviated, human-readable count, and
6493 @samp{--block-size="'1"} prints a byte count with the thousands
6494 separator of the current locale.
6496 For each directory that is listed, preface the files with a line
6497 @samp{total @var{blocks}}, where @var{blocks} is the total disk allocation
6498 for all files in that directory. The block size currently defaults to 1024
6499 bytes, but this can be overridden (@pxref{Block size}).
6500 The @var{blocks} computed counts each hard link separately;
6501 this is arguably a deficiency.
6503 The file type is one of the following characters:
6505 @c The commented-out entries are ones we're not sure about.
6513 character special file
6515 high performance (``contiguous data'') file
6519 door (Solaris 2.5 and up)
6521 @c semaphore, if this is a distinct file type
6525 @c multiplexed file (7th edition Unix; obsolete)
6527 off-line (``migrated'') file (Cray DMF)
6529 network special file (HP-UX)
6533 port (Solaris 10 and up)
6535 @c message queue, if this is a distinct file type
6539 @c shared memory object, if this is a distinct file type
6541 @c typed memory object, if this is a distinct file type
6543 @c whiteout (4.4BSD; not implemented)
6545 some other file type
6548 @cindex permissions, output by @command{ls}
6549 The file mode bits listed are similar to symbolic mode specifications
6550 (@pxref{Symbolic Modes}). But @command{ls} combines multiple bits into the
6551 third character of each set of permissions as follows:
6555 If the set-user-ID or set-group-ID bit and the corresponding executable bit
6559 If the set-user-ID or set-group-ID bit is set but the corresponding
6560 executable bit is not set.
6563 If the restricted deletion flag or sticky bit, and the
6564 other-executable bit, are both set. The restricted deletion flag is
6565 another name for the sticky bit. @xref{Mode Structure}.
6568 If the restricted deletion flag or sticky bit is set but the
6569 other-executable bit is not set.
6572 If the executable bit is set and none of the above apply.
6578 Following the file mode bits is a single character that specifies
6579 whether an alternate access method such as an access control list
6580 applies to the file. When the character following the file mode bits is a
6581 space, there is no alternate access method. When it is a printing
6582 character, then there is such a method.
6584 GNU @command{ls} uses a @samp{.} character to indicate a file
6585 with an SELinux security context, but no other alternate access method.
6587 A file with any other combination of alternate access methods
6588 is marked with a @samp{+} character.
6591 @itemx --numeric-uid-gid
6593 @opindex --numeric-uid-gid
6594 @cindex numeric uid and gid
6595 @cindex numeric user and group IDs
6596 Produce long format directory listings, but
6597 display numeric user and group IDs instead of the owner and group names.
6601 Produce long format directory listings, but don't display group information.
6602 It is equivalent to using @option{--format=long} with @option{--no-group} .
6608 @cindex disk allocation
6609 @cindex size of files, reporting
6610 Print the disk allocation of each file to the left of the file name.
6611 This is the amount of disk space used by the file, which is usually a
6612 bit more than the file's size, but it can be less if the file has holes.
6614 Normally the disk allocation is printed in units of
6615 1024 bytes, but this can be overridden (@pxref{Block size}).
6617 @cindex NFS mounts from BSD to HP-UX
6618 For files that are NFS-mounted from an HP-UX system to a BSD system,
6619 this option reports sizes that are half the correct values. On HP-UX
6620 systems, it reports sizes that are twice the correct values for files
6621 that are NFS-mounted from BSD systems. This is due to a flaw in HP-UX;
6622 it also affects the HP-UX @command{ls} program.
6631 @cindex security context
6632 Display the SELinux security context or @samp{?} if none is found.
6633 When used with the @option{-l} option, print the security context
6634 to the left of the size column.
6639 @node Sorting the output
6640 @subsection Sorting the output
6642 @cindex sorting @command{ls} output
6643 These options change the order in which @command{ls} sorts the information
6644 it outputs. By default, sorting is done by character code
6645 (e.g., @acronym{ASCII} order).
6651 @itemx --time=status
6654 @opindex ctime@r{, printing or sorting by}
6655 @opindex status time@r{, printing or sorting by}
6656 @opindex use time@r{, printing or sorting files by}
6657 If the long listing format (e.g., @option{-l}, @option{-o}) is being used,
6658 print the status change time (the @samp{ctime} in the inode) instead of
6659 the modification time.
6660 When explicitly sorting by time (@option{--sort=time} or @option{-t})
6661 or when not using a long listing format,
6662 sort according to the status change time.
6666 @cindex unsorted directory listing
6667 @cindex directory order, listing by
6668 Primarily, like @option{-U}---do not sort; list the files in whatever
6669 order they are stored in the directory. But also enable @option{-a} (list
6670 all files) and disable @option{-l}, @option{--color}, and @option{-s} (if they
6671 were specified before the @option{-f}).
6677 @cindex reverse sorting
6678 Reverse whatever the sorting method is---e.g., list files in reverse
6679 alphabetical order, youngest first, smallest first, or whatever.
6685 @opindex size of files@r{, sorting files by}
6686 Sort by file size, largest first.
6692 @opindex modification time@r{, sorting files by}
6693 Sort by modification time (the @samp{mtime} in the inode), newest first.
6697 @itemx --time=access
6701 @opindex use time@r{, printing or sorting files by}
6702 @opindex atime@r{, printing or sorting files by}
6703 @opindex access time@r{, printing or sorting files by}
6704 If the long listing format (e.g., @option{--format=long}) is being used,
6705 print the last access time (the @samp{atime} in the inode).
6706 When explicitly sorting by time (@option{--sort=time} or @option{-t})
6707 or when not using a long listing format, sort according to the access time.
6713 @opindex none@r{, sorting option for @command{ls}}
6714 Do not sort; list the files in whatever order they are
6715 stored in the directory. (Do not do any of the other unrelated things
6716 that @option{-f} does.) This is especially useful when listing very large
6717 directories, since not doing any sorting can be noticeably faster.
6720 @itemx --sort=version
6723 @opindex version@r{, sorting option for @command{ls}}
6724 Sort by version name and number, lowest first. It behaves like a default
6725 sort, except that each sequence of decimal digits is treated numerically
6726 as an index/version number. (@xref{Details about version sort}.)
6729 @itemx --sort=extension
6732 @opindex extension@r{, sorting files by}
6733 Sort directory contents alphabetically by file extension (characters
6734 after the last @samp{.}); files with no extension are sorted first.
6739 @node Details about version sort
6740 @subsection Details about version sort
6742 Version sorting handles the fact that file names frequently include indices or
6743 version numbers. Standard sorting usually does not produce the order that one
6744 expects because comparisons are made on a character-by-character basis.
6745 Version sorting is especially useful when browsing directories that contain
6746 many files with indices/version numbers in their names:
6750 abc.zml-1.gz abc.zml-1.gz
6751 abc.zml-12.gz abc.zml-2.gz
6752 abc.zml-2.gz abc.zml-12.gz
6755 Version-sorted strings are compared such that if @var{ver1} and @var{ver2}
6756 are version numbers and @var{prefix} and @var{suffix} (@var{suffix} matching
6757 the regular expression @samp{(\.[A-Za-z~][A-Za-z0-9~]*)*}) are strings then
6758 @var{ver1} < @var{ver2} implies that the name composed of
6759 ``@var{prefix} @var{ver1} @var{suffix}'' sorts before
6760 ``@var{prefix} @var{ver2} @var{suffix}''.
6762 Note also that leading zeros of numeric parts are ignored:
6766 abc-1.007.tgz abc-1.01a.tgz
6767 abc-1.012b.tgz abc-1.007.tgz
6768 abc-1.01a.tgz abc-1.012b.tgz
6771 This functionality is implemented using gnulib's @code{filevercmp} function,
6772 which has some caveats worth noting.
6775 @item @env{LC_COLLATE} is ignored, which means @samp{ls -v} and @samp{sort -V}
6776 will sort non-numeric prefixes as if the @env{LC_COLLATE} locale category
6777 was set to @samp{C}.
6778 @item Some suffixes will not be matched by the regular
6779 expression mentioned above. Consequently these examples may
6780 not sort as you expect:
6788 abc-1.2.3.4.x86_64.rpm
6789 abc-1.2.3.x86_64.rpm
6793 @node General output formatting
6794 @subsection General output formatting
6796 These options affect the appearance of the overall output.
6801 @itemx --format=single-column
6804 @opindex single-column @r{output of files}
6805 List one file per line. This is the default for @command{ls} when standard
6806 output is not a terminal.
6809 @itemx --format=vertical
6812 @opindex vertical @r{sorted files in columns}
6813 List files in columns, sorted vertically. This is the default for
6814 @command{ls} if standard output is a terminal. It is always the default
6815 for the @command{dir} program.
6816 @sc{gnu} @command{ls} uses variable width columns to display as many files as
6817 possible in the fewest lines.
6819 @item --color [=@var{when}]
6821 @cindex color, distinguishing file types with
6822 Specify whether to use color for distinguishing file types. @var{when}
6823 may be omitted, or one of:
6826 @vindex none @r{color option}
6827 - Do not use color at all. This is the default.
6829 @vindex auto @r{color option}
6830 @cindex terminal, using color iff
6831 - Only use color if standard output is a terminal.
6833 @vindex always @r{color option}
6836 Specifying @option{--color} and no @var{when} is equivalent to
6837 @option{--color=always}.
6838 Piping a colorized listing through a pager like @command{more} or
6839 @command{less} usually produces unreadable results. However, using
6840 @code{more -f} does seem to work.
6844 @itemx --indicator-style=classify
6847 @opindex --indicator-style
6848 @cindex file type and executables, marking
6849 @cindex executables and file type, marking
6850 Append a character to each file name indicating the file type. Also,
6851 for regular files that are executable, append @samp{*}. The file type
6852 indicators are @samp{/} for directories, @samp{@@} for symbolic links,
6853 @samp{|} for FIFOs, @samp{=} for sockets, @samp{>} for doors,
6854 and nothing for regular files.
6855 @c The following sentence is the same as the one for -d.
6856 Do not follow symbolic links listed on the
6857 command line unless the @option{--dereference-command-line} (@option{-H}),
6858 @option{--dereference} (@option{-L}), or
6859 @option{--dereference-command-line-symlink-to-dir} options are specified.
6862 @itemx --indicator-style=file-type
6863 @opindex --file-type
6864 @opindex --indicator-style
6865 @cindex file type, marking
6866 Append a character to each file name indicating the file type. This is
6867 like @option{-F}, except that executables are not marked.
6869 @item --indicator-style=@var{word}
6870 @opindex --indicator-style
6871 Append a character indicator with style @var{word} to entry names,
6876 Do not append any character indicator; this is the default.
6878 Append @samp{/} for directories. This is the same as the @option{-p}
6881 Append @samp{/} for directories, @samp{@@} for symbolic links, @samp{|}
6882 for FIFOs, @samp{=} for sockets, and nothing for regular files. This is
6883 the same as the @option{--file-type} option.
6885 Append @samp{*} for executable regular files, otherwise behave as for
6886 @samp{file-type}. This is the same as the @option{-F} or
6887 @option{--classify} option.
6892 Print file sizes in 1024-byte blocks, overriding the default block
6893 size (@pxref{Block size}).
6894 This option is equivalent to @option{--block-size=1K}.
6897 @itemx --format=commas
6900 @opindex commas@r{, outputting between files}
6901 List files horizontally, with as many as will fit on each line,
6902 separated by @samp{, } (a comma and a space).
6905 @itemx --indicator-style=slash
6907 @opindex --indicator-style
6908 @cindex file type, marking
6909 Append a @samp{/} to directory names.
6912 @itemx --format=across
6913 @itemx --format=horizontal
6916 @opindex across@r{, listing files}
6917 @opindex horizontal@r{, listing files}
6918 List the files in columns, sorted horizontally.
6921 @itemx --tabsize=@var{cols}
6924 Assume that each tab stop is @var{cols} columns wide. The default is 8.
6925 @command{ls} uses tabs where possible in the output, for efficiency. If
6926 @var{cols} is zero, do not use tabs at all.
6928 @c FIXME: remove in 2009, if Apple Terminal has been fixed for long enough.
6929 Some terminal emulators (at least Apple Terminal 1.5 (133) from Mac OS X 10.4.8)
6930 do not properly align columns to the right of a TAB following a
6931 non-@acronym{ASCII} byte. If you use such a terminal emulator, use the
6932 @option{-T0} option or put @code{TABSIZE=0} in your environment to tell
6933 @command{ls} to align using spaces, not tabs.
6936 @itemx --width=@var{cols}
6940 Assume the screen is @var{cols} columns wide. The default is taken
6941 from the terminal settings if possible; otherwise the environment
6942 variable @env{COLUMNS} is used if it is set; otherwise the default
6948 @node Formatting file timestamps
6949 @subsection Formatting file timestamps
6951 By default, file timestamps are listed in abbreviated form, using
6952 a date like @samp{Mar 30@ @ 2002} for non-recent timestamps, and a
6953 date-without-year and time like @samp{Mar 30 23:45} for recent timestamps.
6954 This format can change depending on the current locale as detailed below.
6956 A timestamp is considered to be @dfn{recent} if it is less than six
6957 months old, and is not dated in the future. If a timestamp dated
6958 today is not listed in recent form, the timestamp is in the future,
6959 which means you probably have clock skew problems which may break
6960 programs like @command{make} that rely on file timestamps.
6963 Time stamps are listed according to the time zone rules specified by
6964 the @env{TZ} environment variable, or by the system default rules if
6965 @env{TZ} is not set. @xref{TZ Variable,, Specifying the Time Zone
6966 with @env{TZ}, libc, The GNU C Library Reference Manual}.
6968 The following option changes how file timestamps are printed.
6971 @item --time-style=@var{style}
6972 @opindex --time-style
6974 List timestamps in style @var{style}. The @var{style} should
6975 be one of the following:
6980 List timestamps using @var{format}, where @var{format} is interpreted
6981 like the format argument of @command{date} (@pxref{date invocation}).
6982 For example, @option{--time-style="+%Y-%m-%d %H:%M:%S"} causes
6983 @command{ls} to list timestamps like @samp{2002-03-30 23:45:56}. As
6984 with @command{date}, @var{format}'s interpretation is affected by the
6985 @env{LC_TIME} locale category.
6987 If @var{format} contains two format strings separated by a newline,
6988 the former is used for non-recent files and the latter for recent
6989 files; if you want output columns to line up, you may need to insert
6990 spaces in one of the two formats.
6993 List timestamps in full using @acronym{ISO} 8601 date, time, and time zone
6994 format with nanosecond precision, e.g., @samp{2002-03-30
6995 23:45:56.477817180 -0700}. This style is equivalent to
6996 @samp{+%Y-%m-%d %H:%M:%S.%N %z}.
6998 This is useful because the time output includes all the information that
6999 is available from the operating system. For example, this can help
7000 explain @command{make}'s behavior, since @acronym{GNU} @command{make}
7001 uses the full timestamp to determine whether a file is out of date.
7004 List @acronym{ISO} 8601 date and time in minutes, e.g.,
7005 @samp{2002-03-30 23:45}. These timestamps are shorter than
7006 @samp{full-iso} timestamps, and are usually good enough for everyday
7007 work. This style is equivalent to @samp{+%Y-%m-%d %H:%M}.
7010 List @acronym{ISO} 8601 dates for non-recent timestamps (e.g.,
7011 @samp{2002-03-30@ }), and @acronym{ISO} 8601 month, day, hour, and
7012 minute for recent timestamps (e.g., @samp{03-30 23:45}). These
7013 timestamps are uglier than @samp{long-iso} timestamps, but they carry
7014 nearly the same information in a smaller space and their brevity helps
7015 @command{ls} output fit within traditional 80-column output lines.
7016 The following two @command{ls} invocations are equivalent:
7021 ls -l --time-style="+%Y-%m-%d $newline%m-%d %H:%M"
7022 ls -l --time-style="iso"
7027 List timestamps in a locale-dependent form. For example, a Finnish
7028 locale might list non-recent timestamps like @samp{maalis 30@ @ 2002}
7029 and recent timestamps like @samp{maalis 30 23:45}. Locale-dependent
7030 timestamps typically consume more space than @samp{iso} timestamps and
7031 are harder for programs to parse because locale conventions vary so
7032 widely, but they are easier for many people to read.
7034 The @env{LC_TIME} locale category specifies the timestamp format. The
7035 default @acronym{POSIX} locale uses timestamps like @samp{Mar 30@
7036 @ 2002} and @samp{Mar 30 23:45}; in this locale, the following two
7037 @command{ls} invocations are equivalent:
7042 ls -l --time-style="+%b %e %Y$newline%b %e %H:%M"
7043 ls -l --time-style="locale"
7046 Other locales behave differently. For example, in a German locale,
7047 @option{--time-style="locale"} might be equivalent to
7048 @option{--time-style="+%e. %b %Y $newline%e. %b %H:%M"}
7049 and might generate timestamps like @samp{30. M@"ar 2002@ } and
7050 @samp{30. M@"ar 23:45}.
7052 @item posix-@var{style}
7054 List @acronym{POSIX}-locale timestamps if the @env{LC_TIME} locale
7055 category is @acronym{POSIX}, @var{style} timestamps otherwise. For
7056 example, the @samp{posix-long-iso} style lists
7057 timestamps like @samp{Mar 30@ @ 2002} and @samp{Mar 30 23:45} when in
7058 the @acronym{POSIX} locale, and like @samp{2002-03-30 23:45} otherwise.
7063 You can specify the default value of the @option{--time-style} option
7064 with the environment variable @env{TIME_STYLE}; if @env{TIME_STYLE} is not set
7065 the default style is @samp{locale}. @acronym{GNU} Emacs 21.3 and
7066 later use the @option{--dired} option and therefore can parse any date
7067 format, but if you are using Emacs 21.1 or 21.2 and specify a
7068 non-@acronym{POSIX} locale you may need to set
7069 @samp{TIME_STYLE="posix-long-iso"}.
7071 To avoid certain denial-of-service attacks, timestamps that would be
7072 longer than 1000 bytes may be treated as errors.
7075 @node Formatting the file names
7076 @subsection Formatting the file names
7078 These options change how file names themselves are printed.
7084 @itemx --quoting-style=escape
7087 @opindex --quoting-style
7088 @cindex backslash sequences for file names
7089 Quote nongraphic characters in file names using alphabetic and octal
7090 backslash sequences like those used in C.
7094 @itemx --quoting-style=literal
7097 @opindex --quoting-style
7098 Do not quote file names. However, with @command{ls} nongraphic
7099 characters are still printed as question marks if the output is a
7100 terminal and you do not specify the @option{--show-control-chars}
7104 @itemx --hide-control-chars
7106 @opindex --hide-control-chars
7107 Print question marks instead of nongraphic characters in file names.
7108 This is the default if the output is a terminal and the program is
7113 @itemx --quoting-style=c
7115 @opindex --quote-name
7116 @opindex --quoting-style
7117 Enclose file names in double quotes and quote nongraphic characters as
7120 @item --quoting-style=@var{word}
7121 @opindex --quoting-style
7122 @cindex quoting style
7123 Use style @var{word} to quote file names and other strings that may
7124 contain arbitrary characters. The @var{word} should
7125 be one of the following:
7129 Output strings as-is; this is the same as the @option{-N} or
7130 @option{--literal} option.
7132 Quote strings for the shell if they contain shell metacharacters or would
7133 cause ambiguous output.
7134 The quoting is suitable for @acronym{POSIX}-compatible shells like
7135 @command{bash}, but it does not always work for incompatible shells
7138 Quote strings for the shell, even if they would normally not require quoting.
7140 Quote strings as for C character string literals, including the
7141 surrounding double-quote characters; this is the same as the
7142 @option{-Q} or @option{--quote-name} option.
7144 Quote strings as for C character string literals, except omit the
7145 surrounding double-quote
7146 characters; this is the same as the @option{-b} or @option{--escape} option.
7148 Quote strings as for C character string literals, except use
7149 surrounding quotation marks appropriate for the
7152 @c Use @t instead of @samp to avoid duplicate quoting in some output styles.
7153 Quote strings as for C character string literals, except use
7154 surrounding quotation marks appropriate for the locale, and quote
7155 @t{`like this'} instead of @t{"like
7156 this"} in the default C locale. This looks nicer on many displays.
7159 You can specify the default value of the @option{--quoting-style} option
7160 with the environment variable @env{QUOTING_STYLE}. If that environment
7161 variable is not set, the default value is @samp{literal}, but this
7162 default may change to @samp{shell} in a future version of this package.
7164 @item --show-control-chars
7165 @opindex --show-control-chars
7166 Print nongraphic characters as-is in file names.
7167 This is the default unless the output is a terminal and the program is
7173 @node dir invocation
7174 @section @command{dir}: Briefly list directory contents
7177 @cindex directory listing, brief
7179 @command{dir} is equivalent to @code{ls -C
7180 -b}; that is, by default files are listed in columns, sorted vertically,
7181 and special characters are represented by backslash escape sequences.
7183 @xref{ls invocation, @command{ls}}.
7186 @node vdir invocation
7187 @section @command{vdir}: Verbosely list directory contents
7190 @cindex directory listing, verbose
7192 @command{vdir} is equivalent to @code{ls -l
7193 -b}; that is, by default files are listed in long format and special
7194 characters are represented by backslash escape sequences.
7196 @node dircolors invocation
7197 @section @command{dircolors}: Color setup for @command{ls}
7201 @cindex setup for color
7203 @command{dircolors} outputs a sequence of shell commands to set up the
7204 terminal for color output from @command{ls} (and @command{dir}, etc.).
7208 eval "`dircolors [@var{option}]@dots{} [@var{file}]`"
7211 If @var{file} is specified, @command{dircolors} reads it to determine which
7212 colors to use for which file types and extensions. Otherwise, a
7213 precompiled database is used. For details on the format of these files,
7214 run @samp{dircolors --print-database}.
7216 To make @command{dircolors} read a @file{~/.dircolors} file if it
7217 exists, you can put the following lines in your @file{~/.bashrc} (or
7218 adapt them to your favorite shell):
7222 test -r $d && eval "$(dircolors $d)"
7226 @vindex SHELL @r{environment variable, and color}
7227 The output is a shell command to set the @env{LS_COLORS} environment
7228 variable. You can specify the shell syntax to use on the command line,
7229 or @command{dircolors} will guess it from the value of the @env{SHELL}
7230 environment variable.
7232 The program accepts the following options. Also see @ref{Common options}.
7237 @itemx --bourne-shell
7240 @opindex --bourne-shell
7241 @cindex Bourne shell syntax for color setup
7242 @cindex @command{sh} syntax for color setup
7243 Output Bourne shell commands. This is the default if the @env{SHELL}
7244 environment variable is set and does not end with @samp{csh} or
7253 @cindex C shell syntax for color setup
7254 @cindex @command{csh} syntax for color setup
7255 Output C shell commands. This is the default if @code{SHELL} ends with
7256 @command{csh} or @command{tcsh}.
7259 @itemx --print-database
7261 @opindex --print-database
7262 @cindex color database, printing
7263 @cindex database for color setup, printing
7264 @cindex printing color database
7265 Print the (compiled-in) default color configuration database. This
7266 output is itself a valid configuration file, and is fairly descriptive
7267 of the possibilities.
7274 @node Basic operations
7275 @chapter Basic operations
7277 @cindex manipulating files
7279 This chapter describes the commands for basic file manipulation:
7280 copying, moving (renaming), and deleting (removing).
7283 * cp invocation:: Copy files.
7284 * dd invocation:: Convert and copy a file.
7285 * install invocation:: Copy files and set attributes.
7286 * mv invocation:: Move (rename) files.
7287 * rm invocation:: Remove files or directories.
7288 * shred invocation:: Remove files more securely.
7293 @section @command{cp}: Copy files and directories
7296 @cindex copying files and directories
7297 @cindex files, copying
7298 @cindex directories, copying
7300 @command{cp} copies files (or, optionally, directories). The copy is
7301 completely independent of the original. You can either copy one file to
7302 another, or copy arbitrarily many files to a destination directory.
7306 cp [@var{option}]@dots{} [-T] @var{source} @var{dest}
7307 cp [@var{option}]@dots{} @var{source}@dots{} @var{directory}
7308 cp [@var{option}]@dots{} -t @var{directory} @var{source}@dots{}
7313 If two file names are given, @command{cp} copies the first file to the
7317 If the @option{--target-directory} (@option{-t}) option is given, or
7318 failing that if the last file is a directory and the
7319 @option{--no-target-directory} (@option{-T}) option is not given,
7320 @command{cp} copies each @var{source} file to the specified directory,
7321 using the @var{source}s' names.
7324 Generally, files are written just as they are read. For exceptions,
7325 see the @option{--sparse} option below.
7327 By default, @command{cp} does not copy directories. However, the
7328 @option{-R}, @option{-a}, and @option{-r} options cause @command{cp} to
7329 copy recursively by descending into source directories and copying files
7330 to corresponding destination directories.
7332 When copying from a symbolic link, @command{cp} normally follows the
7333 link only when not copying
7334 recursively. This default can be overridden with the
7335 @option{--archive} (@option{-a}), @option{-d}, @option{--dereference}
7336 (@option{-L}), @option{--no-dereference} (@option{-P}), and
7337 @option{-H} options. If more than one of these options is specified,
7338 the last one silently overrides the others.
7340 When copying to a symbolic link, @command{cp} follows the
7341 link only when it refers to an existing regular file.
7342 However, when copying to a dangling symbolic link, @command{cp}
7343 refuses by default, and fails with a diagnostic, since the operation
7344 is inherently dangerous. This behavior is contrary to historical
7345 practice and to @acronym{POSIX}.
7346 Set @env{POSIXLY_CORRECT} to make @command{cp} attempt to create
7347 the target of a dangling destination symlink, in spite of the possible risk.
7348 Also, when an option like
7349 @option{--backup} or @option{--link} acts to rename or remove the
7350 destination before copying, @command{cp} renames or removes the
7351 symbolic link rather than the file it points to.
7353 By default, @command{cp} copies the contents of special files only
7354 when not copying recursively. This default can be overridden with the
7355 @option{--copy-contents} option.
7357 @cindex self-backups
7358 @cindex backups, making only
7359 @command{cp} generally refuses to copy a file onto itself, with the
7360 following exception: if @option{--force --backup} is specified with
7361 @var{source} and @var{dest} identical, and referring to a regular file,
7362 @command{cp} will make a backup file, either regular or numbered, as
7363 specified in the usual ways (@pxref{Backup options}). This is useful when
7364 you simply want to make a backup of an existing file before changing it.
7366 The program accepts the following options. Also see @ref{Common options}.
7373 Preserve as much as possible of the structure and attributes of the
7374 original files in the copy (but do not attempt to preserve internal
7375 directory structure; i.e., @samp{ls -U} may list the entries in a copied
7376 directory in a different order).
7377 Try to preserve SELinux security context and extended attributes (xattr),
7378 but ignore any failure to do that and print no corresponding diagnostic.
7379 Equivalent to @option{-dR --preserve=all} with the reduced diagnostics.
7381 @itemx --attributes-only
7382 @opindex --attributes-only
7383 Preserve the specified attributes of the original files in the copy,
7384 but do not copy any data. See the @option{--preserve} option for
7385 controlling which attributes to copy.
7388 @itemx @w{@kbd{--backup}[=@var{method}]}
7391 @vindex VERSION_CONTROL
7392 @cindex backups, making
7393 @xref{Backup options}.
7394 Make a backup of each file that would otherwise be overwritten or removed.
7395 As a special case, @command{cp} makes a backup of @var{source} when the force
7396 and backup options are given and @var{source} and @var{dest} are the same
7397 name for an existing, regular file. One useful application of this
7398 combination of options is this tiny Bourne shell script:
7402 # Usage: backup FILE...
7403 # Create a @sc{gnu}-style backup of each listed FILE.
7405 cp --backup --force -- "$i" "$i"
7409 @item --copy-contents
7410 @cindex directories, copying recursively
7411 @cindex copying directories recursively
7412 @cindex recursively copying directories
7413 @cindex non-directories, copying as special files
7414 If copying recursively, copy the contents of any special files (e.g.,
7415 FIFOs and device files) as if they were regular files. This means
7416 trying to read the data in each source file and writing it to the
7417 destination. It is usually a mistake to use this option, as it
7418 normally has undesirable effects on special files like FIFOs and the
7419 ones typically found in the @file{/dev} directory. In most cases,
7420 @code{cp -R --copy-contents} will hang indefinitely trying to read
7421 from FIFOs and special files like @file{/dev/console}, and it will
7422 fill up your destination disk if you use it to copy @file{/dev/zero}.
7423 This option has no effect unless copying recursively, and it does not
7424 affect the copying of symbolic links.
7428 @cindex symbolic links, copying
7429 @cindex hard links, preserving
7430 Copy symbolic links as symbolic links rather than copying the files that
7431 they point to, and preserve hard links between source files in the copies.
7432 Equivalent to @option{--no-dereference --preserve=links}.
7438 When copying without this option and an existing destination file cannot
7439 be opened for writing, the copy fails. However, with @option{--force}),
7440 when a destination file cannot be opened, @command{cp} then removes it and
7441 tries to open it again. Contrast this behavior with that enabled by
7442 @option{--link} and @option{--symbolic-link}, whereby the destination file
7443 is never opened but rather is removed unconditionally. Also see the
7444 description of @option{--remove-destination}.
7446 This option is independent of the @option{--interactive} or
7447 @option{-i} option: neither cancels the effect of the other.
7449 This option is redundant if the @option{--no-clobber} or @option{-n} option is
7454 If a command line argument specifies a symbolic link, then copy the
7455 file it points to rather than the symbolic link itself. However,
7456 copy (preserving its nature) any symbolic link that is encountered
7457 via recursive traversal.
7460 @itemx --interactive
7462 @opindex --interactive
7463 When copying a file other than a directory, prompt whether to
7464 overwrite an existing destination file. The @option{-i} option overrides
7465 a previous @option{-n} option.
7471 Make hard links instead of copies of non-directories.
7474 @itemx --dereference
7476 @opindex --dereference
7477 Follow symbolic links when copying from them.
7478 With this option, @command{cp} cannot create a symbolic link.
7479 For example, a symlink (to regular file) in the source tree will be copied to
7480 a regular file in the destination tree.
7485 @opindex --no-clobber
7486 Do not overwrite an existing file. The @option{-n} option overrides a previous
7487 @option{-i} option. This option is mutually exclusive with @option{-b} or
7488 @option{--backup} option.
7491 @itemx --no-dereference
7493 @opindex --no-dereference
7494 @cindex symbolic links, copying
7495 Copy symbolic links as symbolic links rather than copying the files that
7496 they point to. This option affects only symbolic links in the source;
7497 symbolic links in the destination are always followed if possible.
7500 @itemx @w{@kbd{--preserve}[=@var{attribute_list}]}
7503 @cindex file information, preserving, extended attributes, xattr
7504 Preserve the specified attributes of the original files.
7505 If specified, the @var{attribute_list} must be a comma-separated list
7506 of one or more of the following strings:
7510 Preserve the file mode bits and access control lists.
7512 Preserve the owner and group. On most modern systems,
7513 only users with appropriate privileges may change the owner of a file,
7515 may preserve the group ownership of a file only if they happen to be
7516 a member of the desired group.
7518 Preserve the times of last access and last modification, when possible.
7519 On older systems, it is not possible to preserve these attributes
7520 when the affected file is a symbolic link.
7521 However, many systems now provide the @code{utimensat} function,
7522 which makes it possible even for symbolic links.
7524 Preserve in the destination files
7525 any links between corresponding source files.
7526 Note that with @option{-L} or @option{-H}, this option can convert
7527 symbolic links to hard links. For example,
7529 $ mkdir c; : > a; ln -s a b; cp -aH a b c; ls -i1 c
7534 Note the inputs: @file{b} is a symlink to regular file @file{a},
7535 yet the files in destination directory, @file{c/}, are hard-linked.
7536 Since @option{-a} implies @option{--preserve=links}, and since @option{-H}
7537 tells @command{cp} to dereference command line arguments, it sees two files
7538 with the same inode number, and preserves the perceived hard link.
7540 Here is a similar example that exercises @command{cp}'s @option{-L} option:
7542 $ mkdir b c; (cd b; : > a; ln -s a b); cp -aL b c; ls -i1 c/b
7548 Preserve SELinux security context of the file, or fail with full diagnostics.
7550 Preserve extended attributes of the file, or fail with full diagnostics.
7551 If @command{cp} is built without xattr support, ignore this option.
7552 If SELinux context, ACLs or Capabilities are implemented using xattrs,
7553 they are preserved by this option as well.
7555 Preserve all file attributes.
7556 Equivalent to specifying all of the above, but with the difference
7557 that failure to preserve SELinux security context or extended attributes
7558 does not change @command{cp}'s exit status. In contrast to @option{-a},
7559 all but @samp{Operation not supported} warnings are output.
7562 Using @option{--preserve} with no @var{attribute_list} is equivalent
7563 to @option{--preserve=mode,ownership,timestamps}.
7565 In the absence of this option, each destination file is created with the
7566 mode bits of the corresponding source file, minus the bits set in the
7567 umask and minus the set-user-ID and set-group-ID bits.
7568 @xref{File permissions}.
7570 @itemx @w{@kbd{--no-preserve}=@var{attribute_list}}
7571 @cindex file information, preserving
7572 Do not preserve the specified attributes. The @var{attribute_list}
7573 has the same form as for @option{--preserve}.
7577 @cindex parent directories and @command{cp}
7578 Form the name of each destination file by appending to the target
7579 directory a slash and the specified name of the source file. The last
7580 argument given to @command{cp} must be the name of an existing directory.
7581 For example, the command:
7584 cp --parents a/b/c existing_dir
7588 copies the file @file{a/b/c} to @file{existing_dir/a/b/c}, creating
7589 any missing intermediate directories.
7596 @opindex --recursive
7597 @cindex directories, copying recursively
7598 @cindex copying directories recursively
7599 @cindex recursively copying directories
7600 @cindex non-directories, copying as special files
7601 Copy directories recursively. By default, do not follow symbolic
7602 links in the source; see the @option{--archive} (@option{-a}), @option{-d},
7603 @option{--dereference} (@option{-L}), @option{--no-dereference}
7604 (@option{-P}), and @option{-H} options. Special files are copied by
7605 creating a destination file of the same type as the source; see the
7606 @option{--copy-contents} option. It is not portable to use
7607 @option{-r} to copy symbolic links or special files. On some
7608 non-@sc{gnu} systems, @option{-r} implies the equivalent of
7609 @option{-L} and @option{--copy-contents} for historical reasons.
7610 Also, it is not portable to use @option{-R} to copy symbolic links
7611 unless you also specify @option{-P}, as @acronym{POSIX} allows
7612 implementations that dereference symbolic links by default.
7614 @item --reflink[=@var{when}]
7615 @opindex --reflink[=@var{when}]
7618 @cindex copy on write
7619 Perform a lightweight, copy-on-write (COW) copy.
7620 Copying with this option can succeed only on some file systems.
7621 Once it has succeeded, beware that the source and destination files
7622 share the same disk data blocks as long as they remain unmodified.
7623 Thus, if a disk I/O error affects data blocks of one of the files,
7624 the other suffers the exact same fate.
7626 The @var{when} value can be one of the following:
7630 The default behavior: if the copy-on-write operation is not supported
7631 then report the failure for each file and exit with a failure status.
7634 If the copy-on-write operation is not supported then fall back
7635 to the standard copy behaviour.
7639 @item --remove-destination
7640 @opindex --remove-destination
7641 Remove each existing destination file before attempting to open it
7642 (contrast with @option{-f} above).
7644 @item --sparse=@var{when}
7645 @opindex --sparse=@var{when}
7646 @cindex sparse files, copying
7647 @cindex holes, copying files with
7648 @findex read @r{system call, and holes}
7649 A @dfn{sparse file} contains @dfn{holes}---a sequence of zero bytes that
7650 does not occupy any physical disk blocks; the @samp{read} system call
7651 reads these as zeros. This can both save considerable disk space and
7652 increase speed, since many binary files contain lots of consecutive zero
7653 bytes. By default, @command{cp} detects holes in input source files via a crude
7654 heuristic and makes the corresponding output file sparse as well.
7655 Only regular files may be sparse.
7657 The @var{when} value can be one of the following:
7661 The default behavior: if the input file is sparse, attempt to make
7662 the output file sparse, too. However, if an output file exists but
7663 refers to a non-regular file, then do not attempt to make it sparse.
7666 For each sufficiently long sequence of zero bytes in the input file,
7667 attempt to create a corresponding hole in the output file, even if the
7668 input file does not appear to be sparse.
7669 This is useful when the input file resides on a file system
7670 that does not support sparse files
7671 (for example, @samp{efs} file systems in SGI IRIX 5.3 and earlier),
7672 but the output file is on a type of file system that does support them.
7673 Holes may be created only in regular files, so if the destination file
7674 is of some other type, @command{cp} does not even try to make it sparse.
7677 Never make the output file sparse.
7678 This is useful in creating a file for use with the @command{mkswap} command,
7679 since such a file must not have any holes.
7682 @optStripTrailingSlashes
7685 @itemx --symbolic-link
7687 @opindex --symbolic-link
7688 @cindex symbolic links, copying with
7689 Make symbolic links instead of copies of non-directories. All source
7690 file names must be absolute (starting with @samp{/}) unless the
7691 destination files are in the current directory. This option merely
7692 results in an error message on systems that do not support symbolic links.
7698 @optNoTargetDirectory
7704 @cindex newer files, copying only
7705 Do not copy a non-directory that has an existing destination with the
7706 same or newer modification time. If time stamps are being preserved,
7707 the comparison is to the source time stamp truncated to the
7708 resolutions of the destination file system and of the system calls
7709 used to update time stamps; this avoids duplicate work if several
7710 @samp{cp -pu} commands are executed with the same source and
7717 Print the name of each file before copying it.
7720 @itemx --one-file-system
7722 @opindex --one-file-system
7723 @cindex file systems, omitting copying to different
7724 Skip subdirectories that are on different file systems from the one that
7725 the copy started on.
7726 However, mount point directories @emph{are} copied.
7734 @section @command{dd}: Convert and copy a file
7737 @cindex converting while copying a file
7739 @command{dd} copies a file (from standard input to standard output, by
7740 default) with a changeable I/O block size, while optionally performing
7741 conversions on it. Synopses:
7744 dd [@var{operand}]@dots{}
7748 The only options are @option{--help} and @option{--version}.
7749 @xref{Common options}. @command{dd} accepts the following operands.
7755 Read from @var{file} instead of standard input.
7759 Write to @var{file} instead of standard output. Unless
7760 @samp{conv=notrunc} is given, @command{dd} truncates @var{file} to zero
7761 bytes (or the size specified with @samp{seek=}).
7763 @item ibs=@var{bytes}
7765 @cindex block size of input
7766 @cindex input block size
7767 Set the input block size to @var{bytes}.
7768 This makes @command{dd} read @var{bytes} per block.
7769 The default is 512 bytes.
7771 @item obs=@var{bytes}
7773 @cindex block size of output
7774 @cindex output block size
7775 Set the output block size to @var{bytes}.
7776 This makes @command{dd} write @var{bytes} per block.
7777 The default is 512 bytes.
7779 @item bs=@var{bytes}
7782 Set both input and output block sizes to @var{bytes}.
7783 This makes @command{dd} read and write @var{bytes} per block,
7784 overriding any @samp{ibs} and @samp{obs} settings.
7785 In addition, if no data-transforming @option{conv} option is specified,
7786 each input block is copied to the output as a single block,
7787 without aggregating short reads.
7789 @item cbs=@var{bytes}
7791 @cindex block size of conversion
7792 @cindex conversion block size
7793 @cindex fixed-length records, converting to variable-length
7794 @cindex variable-length records, converting to fixed-length
7795 Set the conversion block size to @var{bytes}.
7796 When converting variable-length records to fixed-length ones
7797 (@option{conv=block}) or the reverse (@option{conv=unblock}),
7798 use @var{bytes} as the fixed record length.
7800 @item skip=@var{blocks}
7802 Skip @var{blocks} @samp{ibs}-byte blocks in the input file before copying.
7804 @item seek=@var{blocks}
7806 Skip @var{blocks} @samp{obs}-byte blocks in the output file before copying.
7808 @item count=@var{blocks}
7810 Copy @var{blocks} @samp{ibs}-byte blocks from the input file, instead
7811 of everything until the end of the file.
7815 Do not print the overall transfer rate and volume statistics
7816 that normally make up the third status line when @command{dd} exits.
7818 @item conv=@var{conversion}[,@var{conversion}]@dots{}
7820 Convert the file as specified by the @var{conversion} argument(s).
7821 (No spaces around any comma(s).)
7828 @opindex ascii@r{, converting to}
7829 Convert @acronym{EBCDIC} to @acronym{ASCII},
7830 using the conversion table specified by @acronym{POSIX}.
7831 This provides a 1:1 translation for all 256 bytes.
7834 @opindex ebcdic@r{, converting to}
7835 Convert @acronym{ASCII} to @acronym{EBCDIC}.
7836 This is the inverse of the @samp{ascii} conversion.
7839 @opindex alternate ebcdic@r{, converting to}
7840 Convert @acronym{ASCII} to alternate @acronym{EBCDIC},
7841 using the alternate conversion table specified by @acronym{POSIX}.
7842 This is not a 1:1 translation, but reflects common historical practice
7843 for @samp{~}, @samp{[}, and @samp{]}.
7845 The @samp{ascii}, @samp{ebcdic}, and @samp{ibm} conversions are
7849 @opindex block @r{(space-padding)}
7850 For each line in the input, output @samp{cbs} bytes, replacing the
7851 input newline with a space and padding with spaces as necessary.
7855 Remove any trailing spaces in each @samp{cbs}-sized input block,
7856 and append a newline.
7858 The @samp{block} and @samp{unblock} conversions are mutually exclusive.
7861 @opindex lcase@r{, converting to}
7862 Change uppercase letters to lowercase.
7865 @opindex ucase@r{, converting to}
7866 Change lowercase letters to uppercase.
7868 The @samp{lcase} and @samp{ucase} conversions are mutually exclusive.
7871 @opindex swab @r{(byte-swapping)}
7872 @cindex byte-swapping
7873 Swap every pair of input bytes. @sc{gnu} @command{dd}, unlike others, works
7874 when an odd number of bytes are read---the last byte is simply copied
7875 (since there is nothing to swap it with).
7879 @cindex read errors, ignoring
7880 Continue after read errors.
7884 @cindex creating output file, avoiding
7885 Do not create the output file; the output file must already exist.
7889 @cindex creating output file, requiring
7890 Fail if the output file already exists; @command{dd} must create the
7893 The @samp{excl} and @samp{nocreat} conversions are mutually exclusive.
7897 @cindex truncating output file, avoiding
7898 Do not truncate the output file.
7901 @opindex sync @r{(padding with @acronym{ASCII} @sc{nul}s)}
7902 Pad every input block to size of @samp{ibs} with trailing zero bytes.
7903 When used with @samp{block} or @samp{unblock}, pad with spaces instead of
7908 @cindex synchronized data writes, before finishing
7909 Synchronize output data just before finishing. This forces a physical
7910 write of output data.
7914 @cindex synchronized data and metadata writes, before finishing
7915 Synchronize output data and metadata just before finishing. This
7916 forces a physical write of output data and metadata.
7920 @item iflag=@var{flag}[,@var{flag}]@dots{}
7922 Access the input file using the flags specified by the @var{flag}
7923 argument(s). (No spaces around any comma(s).)
7925 @item oflag=@var{flag}[,@var{flag}]@dots{}
7927 Access the output file using the flags specified by the @var{flag}
7928 argument(s). (No spaces around any comma(s).)
7930 Here are the flags. Not every flag is supported on every operating
7937 @cindex appending to the output file
7938 Write in append mode, so that even if some other process is writing to
7939 this file, every @command{dd} write will append to the current
7940 contents of the file. This flag makes sense only for output.
7941 If you combine this flag with the @samp{of=@var{file}} operand,
7942 you should also specify @samp{conv=notrunc} unless you want the
7943 output file to be truncated before being appended to.
7947 @cindex concurrent I/O
7948 Use concurrent I/O mode for data. This mode performs direct I/O
7949 and drops the @acronym{POSIX} requirement to serialize all I/O to the same file.
7950 A file cannot be opened in CIO mode and with a standard open at the
7956 Use direct I/O for data, avoiding the buffer cache.
7957 Note that the kernel may impose restrictions on read or write buffer sizes.
7958 For example, with an ext4 destination file system and a linux-based kernel,
7959 using @samp{oflag=direct} will cause writes to fail with @code{EINVAL} if the
7960 output buffer size is not a multiple of 512.
7964 @cindex directory I/O
7966 Fail unless the file is a directory. Most operating systems do not
7967 allow I/O to a directory, so this flag has limited utility.
7971 @cindex synchronized data reads
7972 Use synchronized I/O for data. For the output file, this forces a
7973 physical write of output data on each write. For the input file,
7974 this flag can matter when reading from a remote file that has been
7975 written to synchronously by some other process. Metadata (e.g.,
7976 last-access and last-modified time) is not necessarily synchronized.
7980 @cindex synchronized data and metadata I/O
7981 Use synchronized I/O for both data and metadata.
7985 @cindex nonblocking I/O
7986 Use non-blocking I/O.
7991 Do not update the file's access time.
7992 Some older file systems silently ignore this flag, so it is a good
7993 idea to test it on your files before relying on it.
7997 @cindex controlling terminal
7998 Do not assign the file to be a controlling terminal for @command{dd}.
7999 This has no effect when the file is not a terminal.
8000 On many hosts (e.g., @acronym{GNU}/Linux hosts), this option has no effect
8005 @cindex symbolic links, following
8006 Do not follow symbolic links.
8011 Fail if the file has multiple hard links.
8016 Use binary I/O. This option has an effect only on nonstandard
8017 platforms that distinguish binary from text I/O.
8022 Use text I/O. Like @samp{binary}, this option has no effect on
8027 Accumulate full blocks from input. The @code{read} system call
8028 may return early if a full block is not available.
8029 When that happens, continue calling @code{read} to fill the remainder
8031 This flag can be used only with @code{iflag}.
8035 These flags are not supported on all systems, and @samp{dd} rejects
8036 attempts to use them when they are not supported. When reading from
8037 standard input or writing to standard output, the @samp{nofollow} and
8038 @samp{noctty} flags should not be specified, and the other flags
8039 (e.g., @samp{nonblock}) can affect how other processes behave with the
8040 affected file descriptors, even after @command{dd} exits.
8044 @cindex multipliers after numbers
8045 The numeric-valued strings above (@var{bytes} and @var{blocks}) can be
8046 followed by a multiplier: @samp{b}=512, @samp{c}=1,
8047 @samp{w}=2, @samp{x@var{m}}=@var{m}, or any of the
8048 standard block size suffixes like @samp{k}=1024 (@pxref{Block size}).
8050 Any block size you specify via @samp{bs=}, @samp{ibs=}, @samp{obs=}, @samp{cbs=}
8051 should not be too large---values larger than a few megabytes
8052 are generally wasteful or (as in the gigabyte..exabyte case) downright
8053 counterproductive or error-inducing.
8055 Use different @command{dd} invocations to use different block sizes for
8056 skipping and I/O@. For example, the following shell commands copy data
8057 in 512 KiB blocks between a disk and a tape, but do not save or restore a
8058 4 KiB label at the start of the disk:
8061 disk=/dev/rdsk/c0t1d0s2
8064 # Copy all but the label from disk to tape.
8065 (dd bs=4k skip=1 count=0 && dd bs=512k) <$disk >$tape
8067 # Copy from tape back to disk, but leave the disk label alone.
8068 (dd bs=4k seek=1 count=0 && dd bs=512k) <$tape >$disk
8071 Sending an @samp{INFO} signal to a running @command{dd}
8072 process makes it print I/O statistics to standard error
8073 and then resume copying. In the example below,
8074 @command{dd} is run in the background to copy 10 million blocks.
8075 The @command{kill} command makes it output intermediate I/O statistics,
8076 and when @command{dd} completes normally or is killed by the
8077 @code{SIGINT} signal, it outputs the final statistics.
8080 $ dd if=/dev/zero of=/dev/null count=10MB & pid=$!
8081 $ kill -s INFO $pid; wait $pid
8082 3385223+0 records in
8083 3385223+0 records out
8084 1733234176 bytes (1.7 GB) copied, 6.42173 seconds, 270 MB/s
8085 10000000+0 records in
8086 10000000+0 records out
8087 5120000000 bytes (5.1 GB) copied, 18.913 seconds, 271 MB/s
8090 @vindex POSIXLY_CORRECT
8091 On systems lacking the @samp{INFO} signal @command{dd} responds to the
8092 @samp{USR1} signal instead, unless the @env{POSIXLY_CORRECT}
8093 environment variable is set.
8098 @node install invocation
8099 @section @command{install}: Copy files and set attributes
8102 @cindex copying files and setting attributes
8104 @command{install} copies files while setting their file mode bits and, if
8105 possible, their owner and group. Synopses:
8108 install [@var{option}]@dots{} [-T] @var{source} @var{dest}
8109 install [@var{option}]@dots{} @var{source}@dots{} @var{directory}
8110 install [@var{option}]@dots{} -t @var{directory} @var{source}@dots{}
8111 install [@var{option}]@dots{} -d @var{directory}@dots{}
8116 If two file names are given, @command{install} copies the first file to the
8120 If the @option{--target-directory} (@option{-t}) option is given, or
8121 failing that if the last file is a directory and the
8122 @option{--no-target-directory} (@option{-T}) option is not given,
8123 @command{install} copies each @var{source} file to the specified
8124 directory, using the @var{source}s' names.
8127 If the @option{--directory} (@option{-d}) option is given,
8128 @command{install} creates each @var{directory} and any missing parent
8129 directories. Parent directories are created with mode
8130 @samp{u=rwx,go=rx} (755), regardless of the @option{-m} option or the
8131 current umask. @xref{Directory Setuid and Setgid}, for how the
8132 set-user-ID and set-group-ID bits of parent directories are inherited.
8135 @cindex Makefiles, installing programs in
8136 @command{install} is similar to @command{cp}, but allows you to control the
8137 attributes of destination files. It is typically used in Makefiles to
8138 copy programs into their destination directories. It refuses to copy
8139 files onto themselves.
8141 @cindex extended attributes, xattr
8142 @command{install} never preserves extended attributes (xattr).
8144 The program accepts the following options. Also see @ref{Common options}.
8154 Compare each pair of source and destination files, and if the destination has
8155 identical content and any specified owner, group, permissions, and possibly
8156 SELinux context, then do not modify the destination at all.
8160 Ignored; for compatibility with old Unix versions of @command{install}.
8164 Create any missing parent directories of @var{dest},
8165 then copy @var{source} to @var{dest}.
8166 This option is ignored if a destination directory is specified
8167 via @option{--target-directory=DIR}.
8172 @opindex --directory
8173 @cindex directories, creating with given attributes
8174 @cindex parent directories, creating missing
8175 @cindex leading directories, creating missing
8176 Create any missing parent directories, giving them the default
8177 attributes. Then create each given directory, setting their owner,
8178 group and mode as given on the command line or to the defaults.
8180 @item -g @var{group}
8181 @itemx --group=@var{group}
8184 @cindex group ownership of installed files, setting
8185 Set the group ownership of installed files or directories to
8186 @var{group}. The default is the process's current group. @var{group}
8187 may be either a group name or a numeric group ID.
8190 @itemx --mode=@var{mode}
8193 @cindex permissions of installed files, setting
8194 Set the file mode bits for the installed file or directory to @var{mode},
8195 which can be either an octal number, or a symbolic mode as in
8196 @command{chmod}, with @samp{a=} (no access allowed to anyone) as the
8197 point of departure (@pxref{File permissions}).
8198 The default mode is @samp{u=rwx,go=rx,a-s}---read, write, and
8199 execute for the owner, read and execute for group and other, and with
8200 set-user-ID and set-group-ID disabled.
8201 This default is not quite the same as @samp{755}, since it disables
8202 instead of preserving set-user-ID and set-group-ID on directories.
8203 @xref{Directory Setuid and Setgid}.
8205 @item -o @var{owner}
8206 @itemx --owner=@var{owner}
8209 @cindex ownership of installed files, setting
8210 @cindex appropriate privileges
8211 @vindex root @r{as default owner}
8212 If @command{install} has appropriate privileges (is run as root), set the
8213 ownership of installed files or directories to @var{owner}. The default
8214 is @code{root}. @var{owner} may be either a user name or a numeric user
8217 @item --preserve-context
8218 @opindex --preserve-context
8220 @cindex security context
8221 Preserve the SELinux security context of files and directories.
8222 Failure to preserve the context in all of the files or directories
8223 will result in an exit status of 1. If SELinux is disabled then
8224 print a warning and ignore the option.
8227 @itemx --preserve-timestamps
8229 @opindex --preserve-timestamps
8230 @cindex timestamps of installed files, preserving
8231 Set the time of last access and the time of last modification of each
8232 installed file to match those of each corresponding original file.
8233 When a file is installed without this option, its last access and
8234 last modification times are both set to the time of installation.
8235 This option is useful if you want to use the last modification times
8236 of installed files to keep track of when they were last built as opposed
8237 to when they were last installed.
8243 @cindex symbol table information, stripping
8244 @cindex stripping symbol table information
8245 Strip the symbol tables from installed binary executables.
8247 @itemx --strip-program=@var{program}
8248 @opindex --strip-program
8249 @cindex symbol table information, stripping, program
8250 Program used to strip binaries.
8256 @optNoTargetDirectory
8262 Print the name of each file before copying it.
8264 @item -Z @var{context}
8265 @itemx --context=@var{context}
8269 @cindex security context
8270 Set the default SELinux security context to be used for any
8271 created files and directories. If SELinux is disabled then
8272 print a warning and ignore the option.
8280 @section @command{mv}: Move (rename) files
8284 @command{mv} moves or renames files (or directories). Synopses:
8287 mv [@var{option}]@dots{} [-T] @var{source} @var{dest}
8288 mv [@var{option}]@dots{} @var{source}@dots{} @var{directory}
8289 mv [@var{option}]@dots{} -t @var{directory} @var{source}@dots{}
8294 If two file names are given, @command{mv} moves the first file to the
8298 If the @option{--target-directory} (@option{-t}) option is given, or
8299 failing that if the last file is a directory and the
8300 @option{--no-target-directory} (@option{-T}) option is not given,
8301 @command{mv} moves each @var{source} file to the specified
8302 directory, using the @var{source}s' names.
8305 @command{mv} can move any type of file from one file system to another.
8306 Prior to version @code{4.0} of the fileutils,
8307 @command{mv} could move only regular files between file systems.
8308 For example, now @command{mv} can move an entire directory hierarchy
8309 including special device files from one partition to another. It first
8310 uses some of the same code that's used by @code{cp -a} to copy the
8311 requested directories and files, then (assuming the copy succeeded)
8312 it removes the originals. If the copy fails, then the part that was
8313 copied to the destination partition is removed. If you were to copy
8314 three directories from one partition to another and the copy of the first
8315 directory succeeded, but the second didn't, the first would be left on
8316 the destination partition and the second and third would be left on the
8319 @cindex extended attributes, xattr
8320 @command{mv} always tries to copy extended attributes (xattr), which may
8321 include SELinux context, ACLs or Capabilities.
8322 Upon failure all but @samp{Operation not supported} warnings are output.
8324 @cindex prompting, and @command{mv}
8325 If a destination file exists but is normally unwritable, standard input
8326 is a terminal, and the @option{-f} or @option{--force} option is not given,
8327 @command{mv} prompts the user for whether to replace the file. (You might
8328 own the file, or have write permission on its directory.) If the
8329 response is not affirmative, the file is skipped.
8331 @emph{Warning}: Avoid specifying a source name with a trailing slash,
8332 when it might be a symlink to a directory.
8333 Otherwise, @command{mv} may do something very surprising, since
8334 its behavior depends on the underlying rename system call.
8335 On a system with a modern Linux-based kernel, it fails with @code{errno=ENOTDIR}.
8336 However, on other systems (at least FreeBSD 6.1 and Solaris 10) it silently
8337 renames not the symlink but rather the directory referenced by the symlink.
8338 @xref{Trailing slashes}.
8340 The program accepts the following options. Also see @ref{Common options}.
8350 @cindex prompts, omitting
8351 Do not prompt the user before removing a destination file.
8353 If you specify more than one of the @option{-i}, @option{-f}, @option{-n}
8354 options, only the final one takes effect.
8359 @itemx --interactive
8361 @opindex --interactive
8362 @cindex prompts, forcing
8363 Prompt whether to overwrite each existing destination file, regardless
8365 If the response is not affirmative, the file is skipped.
8371 @opindex --no-clobber
8372 @cindex prompts, omitting
8373 Do not overwrite an existing file.
8375 This option is mutually exclusive with @option{-b} or @option{--backup} option.
8381 @cindex newer files, moving only
8382 Do not move a non-directory that has an existing destination with the
8383 same or newer modification time.
8384 If the move is across file system boundaries, the comparison is to the
8385 source time stamp truncated to the resolutions of the destination file
8386 system and of the system calls used to update time stamps; this avoids
8387 duplicate work if several @samp{mv -u} commands are executed with the
8388 same source and destination.
8394 Print the name of each file before moving it.
8396 @optStripTrailingSlashes
8402 @optNoTargetDirectory
8410 @section @command{rm}: Remove files or directories
8413 @cindex removing files or directories
8415 @command{rm} removes each given @var{file}. By default, it does not remove
8416 directories. Synopsis:
8419 rm [@var{option}]@dots{} [@var{file}]@dots{}
8422 @cindex prompting, and @command{rm}
8423 If the @option{-I} or @option{--interactive=once} option is given,
8424 and there are more than three files or the @option{-r}, @option{-R},
8425 or @option{--recursive} are given, then @command{rm} prompts the user
8426 for whether to proceed with the entire operation. If the response is
8427 not affirmative, the entire command is aborted.
8429 Otherwise, if a file is unwritable, standard input is a terminal, and
8430 the @option{-f} or @option{--force} option is not given, or the
8431 @option{-i} or @option{--interactive=always} option @emph{is} given,
8432 @command{rm} prompts the user for whether to remove the file.
8433 If the response is not affirmative, the file is skipped.
8435 Any attempt to remove a file whose last file name component is
8436 @file{.} or @file{..} is rejected without any prompting.
8438 @emph{Warning}: If you use @command{rm} to remove a file, it is usually
8439 possible to recover the contents of that file. If you want more assurance
8440 that the contents are truly unrecoverable, consider using @command{shred}.
8442 The program accepts the following options. Also see @ref{Common options}.
8450 Ignore nonexistent files and never prompt the user.
8451 Ignore any previous @option{--interactive} (@option{-i}) option.
8455 Prompt whether to remove each file.
8456 If the response is not affirmative, the file is skipped.
8457 Ignore any previous @option{--force} (@option{-f}) option.
8458 Equivalent to @option{--interactive=always}.
8462 Prompt once whether to proceed with the command, if more than three
8463 files are named or if a recursive removal is requested. Ignore any
8464 previous @option{--force} (@option{-f}) option. Equivalent to
8465 @option{--interactive=once}.
8467 @itemx --interactive [=@var{when}]
8468 @opindex --interactive
8469 Specify when to issue an interactive prompt. @var{when} may be
8473 @vindex never @r{interactive option}
8474 - Do not prompt at all.
8476 @vindex once @r{interactive option}
8477 - Prompt once if more than three files are named or if a recursive
8478 removal is requested. Equivalent to @option{-I}.
8480 @vindex always @r{interactive option}
8481 - Prompt for every file being removed. Equivalent to @option{-i}.
8483 @option{--interactive} with no @var{when} is equivalent to
8484 @option{--interactive=always}.
8486 @itemx --one-file-system
8487 @opindex --one-file-system
8488 @cindex one file system, restricting @command{rm} to
8489 When removing a hierarchy recursively, skip any directory that is on a
8490 file system different from that of the corresponding command line argument.
8492 This option is useful when removing a build ``chroot'' hierarchy,
8493 which normally contains no valuable data. However, it is not uncommon
8494 to bind-mount @file{/home} into such a hierarchy, to make it easier to
8495 use one's start-up file. The catch is that it's easy to forget to
8496 unmount @file{/home}. Then, when you use @command{rm -rf} to remove
8497 your normally throw-away chroot, that command will remove everything
8498 under @file{/home}, too.
8499 Use the @option{--one-file-system} option, and it will
8500 warn about and skip directories on other file systems.
8501 Of course, this will not save your @file{/home} if it and your
8502 chroot happen to be on the same file system.
8504 @itemx --preserve-root
8505 @opindex --preserve-root
8506 @cindex root directory, disallow recursive destruction
8507 Fail upon any attempt to remove the root directory, @file{/},
8508 when used with the @option{--recursive} option.
8509 This is the default behavior.
8510 @xref{Treating / specially}.
8512 @itemx --no-preserve-root
8513 @opindex --no-preserve-root
8514 @cindex root directory, allow recursive destruction
8515 Do not treat @file{/} specially when removing recursively.
8516 This option is not recommended unless you really want to
8517 remove all the files on your computer.
8518 @xref{Treating / specially}.
8525 @opindex --recursive
8526 @cindex directories, removing (recursively)
8527 Remove the listed directories and their contents recursively.
8533 Print the name of each file before removing it.
8537 @cindex files beginning with @samp{-}, removing
8538 @cindex @samp{-}, removing files beginning with
8539 One common question is how to remove files whose names begin with a
8540 @samp{-}. @sc{gnu} @command{rm}, like every program that uses the @code{getopt}
8541 function to parse its arguments, lets you use the @samp{--} option to
8542 indicate that all following arguments are non-options. To remove a file
8543 called @file{-f} in the current directory, you could type either:
8556 @opindex - @r{and Unix @command{rm}}
8557 The Unix @command{rm} program's use of a single @samp{-} for this purpose
8558 predates the development of the getopt standard syntax.
8563 @node shred invocation
8564 @section @command{shred}: Remove files more securely
8567 @cindex data, erasing
8568 @cindex erasing data
8570 @command{shred} overwrites devices or files, to help prevent even
8571 very expensive hardware from recovering the data.
8573 Ordinarily when you remove a file (@pxref{rm invocation}), the data is
8574 not actually destroyed. Only the index listing where the file is
8575 stored is destroyed, and the storage is made available for reuse.
8576 There are undelete utilities that will attempt to reconstruct the index
8577 and can bring the file back if the parts were not reused.
8579 On a busy system with a nearly-full drive, space can get reused in a few
8580 seconds. But there is no way to know for sure. If you have sensitive
8581 data, you may want to be sure that recovery is not possible by actually
8582 overwriting the file with non-sensitive data.
8584 However, even after doing that, it is possible to take the disk back
8585 to a laboratory and use a lot of sensitive (and expensive) equipment
8586 to look for the faint ``echoes'' of the original data underneath the
8587 overwritten data. If the data has only been overwritten once, it's not
8590 The best way to remove something irretrievably is to destroy the media
8591 it's on with acid, melt it down, or the like. For cheap removable media
8592 like floppy disks, this is the preferred method. However, hard drives
8593 are expensive and hard to melt, so the @command{shred} utility tries
8594 to achieve a similar effect non-destructively.
8596 This uses many overwrite passes, with the data patterns chosen to
8597 maximize the damage they do to the old data. While this will work on
8598 floppies, the patterns are designed for best effect on hard drives.
8599 For more details, see the source code and Peter Gutmann's paper
8600 @uref{http://www.cs.auckland.ac.nz/~pgut001/pubs/secure_del.html,
8601 @cite{Secure Deletion of Data from Magnetic and Solid-State Memory}},
8602 from the proceedings of the Sixth @acronym{USENIX} Security Symposium (San Jose,
8603 California, July 22--25, 1996).
8605 @strong{Please note} that @command{shred} relies on a very important assumption:
8606 that the file system overwrites data in place. This is the traditional
8607 way to do things, but many modern file system designs do not satisfy this
8608 assumption. Exceptions include:
8613 Log-structured or journaled file systems, such as those supplied with
8614 AIX and Solaris, and JFS, ReiserFS, XFS, Ext3 (in @code{data=journal} mode),
8615 BFS, NTFS, etc.@: when they are configured to journal @emph{data}.
8618 File systems that write redundant data and carry on even if some writes
8619 fail, such as RAID-based file systems.
8622 File systems that make snapshots, such as Network Appliance's NFS server.
8625 File systems that cache in temporary locations, such as NFS version 3
8629 Compressed file systems.
8632 In the particular case of ext3 file systems, the above disclaimer applies (and
8633 @command{shred} is thus of limited effectiveness) only in @code{data=journal}
8634 mode, which journals file data in addition to just metadata. In both
8635 the @code{data=ordered} (default) and @code{data=writeback} modes,
8636 @command{shred} works as usual. Ext3 journaling modes can be changed
8637 by adding the @code{data=something} option to the mount options for a
8638 particular file system in the @file{/etc/fstab} file, as documented in
8639 the mount man page (man mount).
8641 If you are not sure how your file system operates, then you should assume
8642 that it does not overwrite data in place, which means that shred cannot
8643 reliably operate on regular files in your file system.
8645 Generally speaking, it is more reliable to shred a device than a file,
8646 since this bypasses the problem of file system design mentioned above.
8647 However, even shredding devices is not always completely reliable. For
8648 example, most disks map out bad sectors invisibly to the application; if
8649 the bad sectors contain sensitive data, @command{shred} won't be able to
8652 @command{shred} makes no attempt to detect or report this problem, just as
8653 it makes no attempt to do anything about backups. However, since it is
8654 more reliable to shred devices than files, @command{shred} by default does
8655 not truncate or remove the output file. This default is more suitable
8656 for devices, which typically cannot be truncated and should not be
8659 Finally, consider the risk of backups and mirrors.
8660 File system backups and remote mirrors may contain copies of the
8661 file that cannot be removed, and that will allow a shredded file
8662 to be recovered later. So if you keep any data you may later want
8663 to destroy using @command{shred}, be sure that it is not backed up or mirrored.
8666 shred [@var{option}]@dots{} @var{file}[@dots{}]
8669 The program accepts the following options. Also see @ref{Common options}.
8677 @cindex force deletion
8678 Override file permissions if necessary to allow overwriting.
8681 @itemx -n @var{number}
8682 @itemx --iterations=@var{number}
8683 @opindex -n @var{number}
8684 @opindex --iterations=@var{number}
8685 @cindex iterations, selecting the number of
8686 By default, @command{shred} uses @value{SHRED_DEFAULT_PASSES} passes of
8687 overwrite. You can reduce this to save time, or increase it if you think it's
8688 appropriate. After 25 passes all of the internal overwrite patterns will have
8689 been used at least once.
8691 @item --random-source=@var{file}
8692 @opindex --random-source
8693 @cindex random source for shredding
8694 Use @var{file} as a source of random data used to overwrite and to
8695 choose pass ordering. @xref{Random sources}.
8697 @item -s @var{bytes}
8698 @itemx --size=@var{bytes}
8699 @opindex -s @var{bytes}
8700 @opindex --size=@var{bytes}
8701 @cindex size of file to shred
8702 Shred the first @var{bytes} bytes of the file. The default is to shred
8703 the whole file. @var{bytes} can be followed by a size specification like
8704 @samp{K}, @samp{M}, or @samp{G} to specify a multiple. @xref{Block size}.
8710 @cindex removing files after shredding
8711 After shredding a file, truncate it (if possible) and then remove it.
8712 If a file has multiple links, only the named links will be removed.
8718 Display to standard error all status updates as sterilization proceeds.
8724 By default, @command{shred} rounds the size of a regular file up to the next
8725 multiple of the file system block size to fully erase the last block of the file.
8726 Use @option{--exact} to suppress that behavior.
8727 Thus, by default if you shred a 10-byte regular file on a system with 512-byte
8728 blocks, the resulting file will be 512 bytes long. With this option,
8729 shred does not increase the apparent size of the file.
8735 Normally, the last pass that @command{shred} writes is made up of
8736 random data. If this would be conspicuous on your hard drive (for
8737 example, because it looks like encrypted data), or you just think
8738 it's tidier, the @option{--zero} option adds an additional overwrite pass with
8739 all zero bits. This is in addition to the number of passes specified
8740 by the @option{--iterations} option.
8744 You might use the following command to erase all trace of the
8745 file system you'd created on the floppy disk in your first drive.
8746 That command takes about 20 minutes to erase a ``1.44MB'' (actually
8750 shred --verbose /dev/fd0
8753 Similarly, to erase all data on a selected partition of
8754 your hard disk, you could give a command like this:
8757 shred --verbose /dev/sda5
8760 A @var{file} of @samp{-} denotes standard output.
8761 The intended use of this is to shred a removed temporary file.
8768 echo "Hello, world" >&3
8773 However, the command @samp{shred - >file} does not shred the contents
8774 of @var{file}, since the shell truncates @var{file} before invoking
8775 @command{shred}. Use the command @samp{shred file} or (if using a
8776 Bourne-compatible shell) the command @samp{shred - 1<>file} instead.
8781 @node Special file types
8782 @chapter Special file types
8784 @cindex special file types
8785 @cindex file types, special
8787 This chapter describes commands which create special types of files (and
8788 @command{rmdir}, which removes directories, one special file type).
8790 @cindex special file types
8792 Although Unix-like operating systems have markedly fewer special file
8793 types than others, not @emph{everything} can be treated only as the
8794 undifferentiated byte stream of @dfn{normal files}. For example, when a
8795 file is created or removed, the system must record this information,
8796 which it does in a @dfn{directory}---a special type of file. Although
8797 you can read directories as normal files, if you're curious, in order
8798 for the system to do its job it must impose a structure, a certain
8799 order, on the bytes of the file. Thus it is a ``special'' type of file.
8801 Besides directories, other special file types include named pipes
8802 (FIFOs), symbolic links, sockets, and so-called @dfn{special files}.
8805 * link invocation:: Make a hard link via the link syscall
8806 * ln invocation:: Make links between files.
8807 * mkdir invocation:: Make directories.
8808 * mkfifo invocation:: Make FIFOs (named pipes).
8809 * mknod invocation:: Make block or character special files.
8810 * readlink invocation:: Print value of a symlink or canonical file name.
8811 * rmdir invocation:: Remove empty directories.
8812 * unlink invocation:: Remove files via the unlink syscall
8816 @node link invocation
8817 @section @command{link}: Make a hard link via the link syscall
8820 @cindex links, creating
8821 @cindex hard links, creating
8822 @cindex creating links (hard only)
8824 @command{link} creates a single hard link at a time.
8825 It is a minimalist interface to the system-provided
8826 @code{link} function. @xref{Hard Links, , , libc,
8827 The GNU C Library Reference Manual}.
8828 It avoids the bells and whistles of the more commonly-used
8829 @command{ln} command (@pxref{ln invocation}).
8833 link @var{filename} @var{linkname}
8836 @var{filename} must specify an existing file, and @var{linkname}
8837 must specify a nonexistent entry in an existing directory.
8838 @command{link} simply calls @code{link (@var{filename}, @var{linkname})}
8841 On a @acronym{GNU} system, this command acts like @samp{ln --directory
8842 --no-target-directory @var{filename} @var{linkname}}. However, the
8843 @option{--directory} and @option{--no-target-directory} options are
8844 not specified by @acronym{POSIX}, and the @command{link} command is
8845 more portable in practice.
8847 If @var{filename} is a symbolic link, it is unspecified whether
8848 @var{linkname} will be a hard link to the symbolic link or to the
8849 target of the symbolic link. Use @command{ln -P} or @command{ln -L}
8850 to specify which behavior is desired.
8856 @section @command{ln}: Make links between files
8859 @cindex links, creating
8860 @cindex hard links, creating
8861 @cindex symbolic (soft) links, creating
8862 @cindex creating links (hard or soft)
8864 @cindex file systems and hard links
8865 @command{ln} makes links between files. By default, it makes hard links;
8866 with the @option{-s} option, it makes symbolic (or @dfn{soft}) links.
8870 ln [@var{option}]@dots{} [-T] @var{target} @var{linkname}
8871 ln [@var{option}]@dots{} @var{target}
8872 ln [@var{option}]@dots{} @var{target}@dots{} @var{directory}
8873 ln [@var{option}]@dots{} -t @var{directory} @var{target}@dots{}
8879 If two file names are given, @command{ln} creates a link to the first
8880 file from the second.
8883 If one @var{target} is given, @command{ln} creates a link to that file
8884 in the current directory.
8887 If the @option{--target-directory} (@option{-t}) option is given, or
8888 failing that if the last file is a directory and the
8889 @option{--no-target-directory} (@option{-T}) option is not given,
8890 @command{ln} creates a link to each @var{target} file in the specified
8891 directory, using the @var{target}s' names.
8895 Normally @command{ln} does not remove existing files. Use the
8896 @option{--force} (@option{-f}) option to remove them unconditionally,
8897 the @option{--interactive} (@option{-i}) option to remove them
8898 conditionally, and the @option{--backup} (@option{-b}) option to
8901 @cindex hard link, defined
8902 @cindex inode, and hard links
8903 A @dfn{hard link} is another name for an existing file; the link and the
8904 original are indistinguishable. Technically speaking, they share the
8905 same inode, and the inode contains all the information about a
8906 file---indeed, it is not incorrect to say that the inode @emph{is} the
8907 file. Most systems prohibit making a hard link to
8908 a directory; on those where it is allowed, only the super-user can do
8909 so (and with caution, since creating a cycle will cause problems to many
8910 other utilities). Hard links cannot cross file system boundaries. (These
8911 restrictions are not mandated by @acronym{POSIX}, however.)
8913 @cindex dereferencing symbolic links
8914 @cindex symbolic link, defined
8915 @dfn{Symbolic links} (@dfn{symlinks} for short), on the other hand, are
8916 a special file type (which not all kernels support: System V release 3
8917 (and older) systems lack symlinks) in which the link file actually
8918 refers to a different file, by name. When most operations (opening,
8919 reading, writing, and so on) are passed the symbolic link file, the
8920 kernel automatically @dfn{dereferences} the link and operates on the
8921 target of the link. But some operations (e.g., removing) work on the
8922 link file itself, rather than on its target. The owner and group of a
8923 symlink are not significant to file access performed through
8924 the link, but do have implications on deleting a symbolic link from a
8925 directory with the restricted deletion bit set. On the GNU system,
8926 the mode of a symlink has no significance and cannot be changed, but
8927 on some BSD systems, the mode can be changed and will affect whether
8928 the symlink will be traversed in file name resolution. @xref{Symbolic Links,,,
8929 libc, The GNU C Library Reference Manual}.
8931 Symbolic links can contain arbitrary strings; a @dfn{dangling symlink}
8932 occurs when the string in the symlink does not resolve to a file.
8933 There are no restrictions against creating dangling symbolic links.
8934 There are trade-offs to using absolute or relative symlinks. An
8935 absolute symlink always points to the same file, even if the directory
8936 containing the link is moved. However, if the symlink is visible from
8937 more than one machine (such as on a networked file system), the file
8938 pointed to might not always be the same. A relative symbolic link is
8939 resolved in relation to the directory that contains the link, and is
8940 often useful in referring to files on the same device without regards
8941 to what name that device is mounted on when accessed via networked
8944 When creating a relative symlink in a different location than the
8945 current directory, the resolution of the symlink will be different
8946 than the resolution of the same string from the current directory.
8947 Therefore, many users prefer to first change directories to the
8948 location where the relative symlink will be created, so that
8949 tab-completion or other file resolution will find the same target as
8950 what will be placed in the symlink.
8952 The program accepts the following options. Also see @ref{Common options}.
8963 @opindex --directory
8964 @cindex hard links to directories
8965 Allow users with appropriate privileges to attempt to make hard links
8967 However, note that this will probably fail due to
8968 system restrictions, even for the super-user.
8974 Remove existing destination files.
8977 @itemx --interactive
8979 @opindex --interactive
8980 @cindex prompting, and @command{ln}
8981 Prompt whether to remove existing destination files.
8987 If @option{-s} is not in effect, and the source file is a symbolic
8988 link, create the hard link to the file referred to by the symbolic
8989 link, rather than the symbolic link itself.
8992 @itemx --no-dereference
8994 @opindex --no-dereference
8995 Do not treat the last operand specially when it is a symbolic link to
8996 a directory. Instead, treat it as if it were a normal file.
8998 When the destination is an actual directory (not a symlink to one),
8999 there is no ambiguity. The link is created in that directory.
9000 But when the specified destination is a symlink to a directory,
9001 there are two ways to treat the user's request. @command{ln} can
9002 treat the destination just as it would a normal directory and create
9003 the link in it. On the other hand, the destination can be viewed as a
9004 non-directory---as the symlink itself. In that case, @command{ln}
9005 must delete or backup that symlink before creating the new link.
9006 The default is to treat a destination that is a symlink to a directory
9007 just like a directory.
9009 This option is weaker than the @option{--no-target-directory}
9010 (@option{-T}) option, so it has no effect if both options are given.
9016 If @option{-s} is not in effect, and the source file is a symbolic
9017 link, create the hard link to the symbolic link itself. On platforms
9018 where this is not supported by the kernel, this option creates a
9019 symbolic link with identical contents; since symbolic link contents
9020 cannot be edited, any file name resolution performed through either
9021 link will be the same as if a hard link had been created.
9027 Make symbolic links instead of hard links. This option merely produces
9028 an error message on systems that do not support symbolic links.
9034 @optNoTargetDirectory
9040 Print the name of each file after linking it successfully.
9044 @cindex hard links to symbolic links
9045 @cindex symbolic links and @command{ln}
9046 If @option{-L} and @option{-P} are both given, the last one takes
9047 precedence. If @option{-s} is also given, @option{-L} and @option{-P}
9048 are silently ignored. If neither option is given, then this
9049 implementation defaults to @option{-P} if the system @code{link} supports
9050 hard links to symbolic links (such as the GNU system), and @option{-L}
9051 if @code{link} follows symbolic links (such as on BSD).
9060 # Create link ../a pointing to a in that directory.
9061 # Not really useful because it points to itself.
9066 # Change to the target before creating symlinks to avoid being confused.
9072 # Hard coded file names don't move well.
9073 ln -s $(pwd)/a /some/dir/
9077 # Relative file names survive directory moves and also
9078 # work across networked file systems.
9079 ln -s afile anotherfile
9080 ln -s ../adir/afile yetanotherfile
9084 @node mkdir invocation
9085 @section @command{mkdir}: Make directories
9088 @cindex directories, creating
9089 @cindex creating directories
9091 @command{mkdir} creates directories with the specified names. Synopsis:
9094 mkdir [@var{option}]@dots{} @var{name}@dots{}
9097 @command{mkdir} creates each directory @var{name} in the order given.
9098 It reports an error if @var{name} already exists, unless the
9099 @option{-p} option is given and @var{name} is a directory.
9101 The program accepts the following options. Also see @ref{Common options}.
9106 @itemx --mode=@var{mode}
9109 @cindex modes of created directories, setting
9110 Set the file permission bits of created directories to @var{mode},
9111 which uses the same syntax as
9112 in @command{chmod} and uses @samp{a=rwx} (read, write and execute allowed for
9113 everyone) for the point of the departure. @xref{File permissions}.
9115 Normally the directory has the desired file mode bits at the moment it
9116 is created. As a @acronym{GNU} extension, @var{mode} may also mention
9117 special mode bits, but in this case there may be a temporary window
9118 during which the directory exists but its special mode bits are
9119 incorrect. @xref{Directory Setuid and Setgid}, for how the
9120 set-user-ID and set-group-ID bits of directories are inherited unless
9121 overridden in this way.
9127 @cindex parent directories, creating
9128 Make any missing parent directories for each argument, setting their
9129 file permission bits to the umask modified by @samp{u+wx}. Ignore
9130 existing parent directories, and do not change their file permission
9133 To set the file permission bits of any newly-created parent
9134 directories to a value that includes @samp{u+wx}, you can set the
9135 umask before invoking @command{mkdir}. For example, if the shell
9136 command @samp{(umask u=rwx,go=rx; mkdir -p P/Q)} creates the parent
9137 @file{P} it sets the parent's permission bits to @samp{u=rwx,go=rx}.
9138 To set a parent's special mode bits as well, you can invoke
9139 @command{chmod} after @command{mkdir}. @xref{Directory Setuid and
9140 Setgid}, for how the set-user-ID and set-group-ID bits of
9141 newly-created parent directories are inherited.
9147 Print a message for each created directory. This is most useful with
9150 @item -Z @var{context}
9151 @itemx --context=@var{context}
9155 @cindex security context
9156 Set the default SELinux security context to be used for created directories.
9163 @node mkfifo invocation
9164 @section @command{mkfifo}: Make FIFOs (named pipes)
9167 @cindex FIFOs, creating
9168 @cindex named pipes, creating
9169 @cindex creating FIFOs (named pipes)
9171 @command{mkfifo} creates FIFOs (also called @dfn{named pipes}) with the
9172 specified names. Synopsis:
9175 mkfifo [@var{option}] @var{name}@dots{}
9178 A @dfn{FIFO} is a special file type that permits independent processes
9179 to communicate. One process opens the FIFO file for writing, and
9180 another for reading, after which data can flow as with the usual
9181 anonymous pipe in shells or elsewhere.
9183 The program accepts the following option. Also see @ref{Common options}.
9188 @itemx --mode=@var{mode}
9191 @cindex modes of created FIFOs, setting
9192 Set the mode of created FIFOs to @var{mode}, which is symbolic as in
9193 @command{chmod} and uses @samp{a=rw} (read and write allowed for everyone)
9194 for the point of departure. @var{mode} should specify only file
9195 permission bits. @xref{File permissions}.
9197 @item -Z @var{context}
9198 @itemx --context=@var{context}
9202 @cindex security context
9203 Set the default SELinux security context to be used for created FIFOs.
9210 @node mknod invocation
9211 @section @command{mknod}: Make block or character special files
9214 @cindex block special files, creating
9215 @cindex character special files, creating
9217 @command{mknod} creates a FIFO, character special file, or block special
9218 file with the specified name. Synopsis:
9221 mknod [@var{option}]@dots{} @var{name} @var{type} [@var{major} @var{minor}]
9224 @cindex special files
9225 @cindex block special files
9226 @cindex character special files
9227 Unlike the phrase ``special file type'' above, the term @dfn{special
9228 file} has a technical meaning on Unix: something that can generate or
9229 receive data. Usually this corresponds to a physical piece of hardware,
9230 e.g., a printer or a disk. (These files are typically created at
9231 system-configuration time.) The @command{mknod} command is what creates
9232 files of this type. Such devices can be read either a character at a
9233 time or a ``block'' (many characters) at a time, hence we say there are
9234 @dfn{block special} files and @dfn{character special} files.
9236 @c mknod is a shell built-in at least with OpenBSD's /bin/sh
9237 @mayConflictWithShellBuiltIn{mknod}
9239 The arguments after @var{name} specify the type of file to make:
9244 @opindex p @r{for FIFO file}
9248 @opindex b @r{for block special file}
9249 for a block special file
9252 @c Don't document the `u' option -- it's just a synonym for `c'.
9253 @c Do *any* versions of mknod still use it?
9255 @opindex c @r{for character special file}
9256 @c @opindex u @r{for character special file}
9257 for a character special file
9261 When making a block or character special file, the major and minor
9262 device numbers must be given after the file type.
9263 If a major or minor device number begins with @samp{0x} or @samp{0X},
9264 it is interpreted as hexadecimal; otherwise, if it begins with @samp{0},
9265 as octal; otherwise, as decimal.
9267 The program accepts the following option. Also see @ref{Common options}.
9272 @itemx --mode=@var{mode}
9275 Set the mode of created files to @var{mode}, which is symbolic as in
9276 @command{chmod} and uses @samp{a=rw} as the point of departure.
9277 @var{mode} should specify only file permission bits.
9278 @xref{File permissions}.
9280 @item -Z @var{context}
9281 @itemx --context=@var{context}
9285 @cindex security context
9286 Set the default SELinux security context to be used for created files.
9293 @node readlink invocation
9294 @section @command{readlink}: Print value of a symlink or canonical file name
9297 @cindex displaying value of a symbolic link
9298 @cindex canonical file name
9299 @cindex canonicalize a file name
9303 @command{readlink} may work in one of two supported modes:
9309 @command{readlink} outputs the value of the given symbolic link.
9310 If @command{readlink} is invoked with an argument other than the name
9311 of a symbolic link, it produces no output and exits with a nonzero exit code.
9313 @item Canonicalize mode
9315 @command{readlink} outputs the absolute name of the given file which contains
9316 no @file{.}, @file{..} components nor any repeated separators
9317 (@file{/}) or symbolic links.
9322 readlink [@var{option}] @var{file}
9325 By default, @command{readlink} operates in readlink mode.
9327 The program accepts the following options. Also see @ref{Common options}.
9332 @itemx --canonicalize
9334 @opindex --canonicalize
9335 Activate canonicalize mode.
9336 If any component of the file name except the last one is missing or unavailable,
9337 @command{readlink} produces no output and exits with a nonzero exit
9338 code. A trailing slash is ignored.
9341 @itemx --canonicalize-existing
9343 @opindex --canonicalize-existing
9344 Activate canonicalize mode.
9345 If any component is missing or unavailable, @command{readlink} produces
9346 no output and exits with a nonzero exit code. A trailing slash
9347 requires that the name resolve to a directory.
9350 @itemx --canonicalize-missing
9352 @opindex --canonicalize-missing
9353 Activate canonicalize mode.
9354 If any component is missing or unavailable, @command{readlink} treats it
9360 @opindex --no-newline
9361 Do not output the trailing newline.
9371 Suppress most error messages.
9377 Report error messages.
9381 The @command{readlink} utility first appeared in OpenBSD 2.1.
9383 There is a @command{realpath} command on some systems
9384 which operates like @command{readlink} in canonicalize mode.
9389 @node rmdir invocation
9390 @section @command{rmdir}: Remove empty directories
9393 @cindex removing empty directories
9394 @cindex directories, removing empty
9396 @command{rmdir} removes empty directories. Synopsis:
9399 rmdir [@var{option}]@dots{} @var{directory}@dots{}
9402 If any @var{directory} argument does not refer to an existing empty
9403 directory, it is an error.
9405 The program accepts the following options. Also see @ref{Common options}.
9409 @item --ignore-fail-on-non-empty
9410 @opindex --ignore-fail-on-non-empty
9411 @cindex directory deletion, ignoring failures
9412 Ignore each failure to remove a directory that is solely because
9413 the directory is non-empty.
9419 @cindex parent directories, removing
9420 Remove @var{directory}, then try to remove each component of @var{directory}.
9421 So, for example, @samp{rmdir -p a/b/c} is similar to @samp{rmdir a/b/c a/b a}.
9422 As such, it fails if any of those directories turns out not to be empty.
9423 Use the @option{--ignore-fail-on-non-empty} option to make it so such
9424 a failure does not evoke a diagnostic and does not cause @command{rmdir} to
9425 exit unsuccessfully.
9431 @cindex directory deletion, reporting
9432 Give a diagnostic for each successful removal.
9433 @var{directory} is removed.
9437 @xref{rm invocation}, for how to remove non-empty directories (recursively).
9442 @node unlink invocation
9443 @section @command{unlink}: Remove files via the unlink syscall
9446 @cindex removing files or directories (via the unlink syscall)
9448 @command{unlink} deletes a single specified file name.
9449 It is a minimalist interface to the system-provided
9450 @code{unlink} function. @xref{Deleting Files, , , libc,
9451 The GNU C Library Reference Manual}. Synopsis:
9452 It avoids the bells and whistles of the more commonly-used
9453 @command{rm} command (@pxref{rm invocation}).
9456 unlink @var{filename}
9459 On some systems @code{unlink} can be used to delete the name of a
9460 directory. On others, it can be used that way only by a privileged user.
9461 In the GNU system @code{unlink} can never delete the name of a directory.
9463 The @command{unlink} command honors the @option{--help} and
9464 @option{--version} options. To remove a file whose name begins with
9465 @samp{-}, prefix the name with @samp{./}, e.g., @samp{unlink ./--help}.
9470 @node Changing file attributes
9471 @chapter Changing file attributes
9473 @cindex changing file attributes
9474 @cindex file attributes, changing
9475 @cindex attributes, file
9477 A file is not merely its contents, a name, and a file type
9478 (@pxref{Special file types}). A file also has an owner (a user ID), a
9479 group (a group ID), permissions (what the owner can do with the file,
9480 what people in the group can do, and what everyone else can do), various
9481 timestamps, and other information. Collectively, we call these a file's
9484 These commands change file attributes.
9487 * chgrp invocation:: Change file groups.
9488 * chmod invocation:: Change access permissions.
9489 * chown invocation:: Change file owners and groups.
9490 * touch invocation:: Change file timestamps.
9494 @node chown invocation
9495 @section @command{chown}: Change file owner and group
9498 @cindex file ownership, changing
9499 @cindex group ownership, changing
9500 @cindex changing file ownership
9501 @cindex changing group ownership
9503 @command{chown} changes the user and/or group ownership of each given @var{file}
9504 to @var{new-owner} or to the user and group of an existing reference file.
9508 chown [@var{option}]@dots{} @{@var{new-owner} | --reference=@var{ref_file}@} @var{file}@dots{}
9511 If used, @var{new-owner} specifies the new owner and/or group as follows
9512 (with no embedded white space):
9515 [@var{owner}] [ : [@var{group}] ]
9522 If only an @var{owner} (a user name or numeric user ID) is given, that
9523 user is made the owner of each given file, and the files' group is not
9526 @item owner@samp{:}group
9527 If the @var{owner} is followed by a colon and a @var{group} (a
9528 group name or numeric group ID), with no spaces between them, the group
9529 ownership of the files is changed as well (to @var{group}).
9532 If a colon but no group name follows @var{owner}, that user is
9533 made the owner of the files and the group of the files is changed to
9534 @var{owner}'s login group.
9537 If the colon and following @var{group} are given, but the owner
9538 is omitted, only the group of the files is changed; in this case,
9539 @command{chown} performs the same function as @command{chgrp}.
9542 If only a colon is given, or if @var{new-owner} is empty, neither the
9543 owner nor the group is changed.
9547 If @var{owner} or @var{group} is intended to represent a numeric user
9548 or group ID, then you may specify it with a leading @samp{+}.
9549 @xref{Disambiguating names and IDs}.
9551 Some older scripts may still use @samp{.} in place of the @samp{:} separator.
9552 @acronym{POSIX} 1003.1-2001 (@pxref{Standards conformance}) does not
9553 require support for that, but for backward compatibility @acronym{GNU}
9554 @command{chown} supports @samp{.} so long as no ambiguity results.
9555 New scripts should avoid the use of @samp{.} because it is not
9556 portable, and because it has undesirable results if the entire
9557 @var{owner@samp{.}group} happens to identify a user whose name
9560 The @command{chown} command sometimes clears the set-user-ID or
9561 set-group-ID permission bits. This behavior depends on the policy and
9562 functionality of the underlying @code{chown} system call, which may
9563 make system-dependent file mode modifications outside the control of
9564 the @command{chown} command. For example, the @command{chown} command
9565 might not affect those bits when invoked by a user with appropriate
9566 privileges, or when the
9567 bits signify some function other than executable permission (e.g.,
9569 When in doubt, check the underlying system behavior.
9571 The program accepts the following options. Also see @ref{Common options}.
9579 @cindex changed owners, verbosely describing
9580 Verbosely describe the action for each @var{file} whose ownership
9589 @cindex error messages, omitting
9590 Do not print error messages about files whose ownership cannot be
9593 @itemx @w{@kbd{--from}=@var{old-owner}}
9595 @cindex symbolic links, changing owner
9596 Change a @var{file}'s ownership only if it has current attributes specified
9597 by @var{old-owner}. @var{old-owner} has the same form as @var{new-owner}
9599 This option is useful primarily from a security standpoint in that
9600 it narrows considerably the window of potential abuse.
9601 For example, to reflect a user ID numbering change for one user's files
9602 without an option like this, @code{root} might run
9605 find / -owner OLDUSER -print0 | xargs -0 chown -h NEWUSER
9608 But that is dangerous because the interval between when the @command{find}
9609 tests the existing file's owner and when the @command{chown} is actually run
9611 One way to narrow the gap would be to invoke chown for each file
9615 find / -owner OLDUSER -exec chown -h NEWUSER @{@} \;
9618 But that is very slow if there are many affected files.
9619 With this option, it is safer (the gap is narrower still)
9620 though still not perfect:
9623 chown -h -R --from=OLDUSER NEWUSER /
9627 @opindex --dereference
9628 @cindex symbolic links, changing owner
9630 Do not act on symbolic links themselves but rather on what they point to.
9631 This is the default.
9634 @itemx --no-dereference
9636 @opindex --no-dereference
9637 @cindex symbolic links, changing owner
9639 Act on symbolic links themselves instead of what they point to.
9640 This mode relies on the @code{lchown} system call.
9641 On systems that do not provide the @code{lchown} system call,
9642 @command{chown} fails when a file specified on the command line
9644 By default, no diagnostic is issued for symbolic links encountered
9645 during a recursive traversal, but see @option{--verbose}.
9647 @itemx --preserve-root
9648 @opindex --preserve-root
9649 @cindex root directory, disallow recursive modification
9650 Fail upon any attempt to recursively change the root directory, @file{/}.
9651 Without @option{--recursive}, this option has no effect.
9652 @xref{Treating / specially}.
9654 @itemx --no-preserve-root
9655 @opindex --no-preserve-root
9656 @cindex root directory, allow recursive modification
9657 Cancel the effect of any preceding @option{--preserve-root} option.
9658 @xref{Treating / specially}.
9660 @item --reference=@var{ref_file}
9661 @opindex --reference
9662 Change the user and group of each @var{file} to be the same as those of
9663 @var{ref_file}. If @var{ref_file} is a symbolic link, do not use the
9664 user and group of the symbolic link, but rather those of the file it
9671 Output a diagnostic for every file processed.
9672 If a symbolic link is encountered during a recursive traversal
9673 on a system without the @code{lchown} system call, and @option{--no-dereference}
9674 is in effect, then issue a diagnostic saying neither the symbolic link nor
9675 its referent is being changed.
9680 @opindex --recursive
9681 @cindex recursively changing file ownership
9682 Recursively change ownership of directories and their contents.
9685 @xref{Traversing symlinks}.
9688 @xref{Traversing symlinks}.
9691 @xref{Traversing symlinks}.
9700 # Change the owner of /u to "root".
9703 # Likewise, but also change its group to "staff".
9706 # Change the owner of /u and subfiles to "root".
9711 @node chgrp invocation
9712 @section @command{chgrp}: Change group ownership
9715 @cindex group ownership, changing
9716 @cindex changing group ownership
9718 @command{chgrp} changes the group ownership of each given @var{file}
9719 to @var{group} (which can be either a group name or a numeric group ID)
9720 or to the group of an existing reference file. Synopsis:
9723 chgrp [@var{option}]@dots{} @{@var{group} | --reference=@var{ref_file}@} @var{file}@dots{}
9726 If @var{group} is intended to represent a
9727 numeric group ID, then you may specify it with a leading @samp{+}.
9728 @xref{Disambiguating names and IDs}.
9730 The program accepts the following options. Also see @ref{Common options}.
9738 @cindex changed files, verbosely describing
9739 Verbosely describe the action for each @var{file} whose group actually
9748 @cindex error messages, omitting
9749 Do not print error messages about files whose group cannot be
9753 @opindex --dereference
9754 @cindex symbolic links, changing owner
9756 Do not act on symbolic links themselves but rather on what they point to.
9757 This is the default.
9760 @itemx --no-dereference
9762 @opindex --no-dereference
9763 @cindex symbolic links, changing group
9765 Act on symbolic links themselves instead of what they point to.
9766 This mode relies on the @code{lchown} system call.
9767 On systems that do not provide the @code{lchown} system call,
9768 @command{chgrp} fails when a file specified on the command line
9770 By default, no diagnostic is issued for symbolic links encountered
9771 during a recursive traversal, but see @option{--verbose}.
9773 @itemx --preserve-root
9774 @opindex --preserve-root
9775 @cindex root directory, disallow recursive modification
9776 Fail upon any attempt to recursively change the root directory, @file{/}.
9777 Without @option{--recursive}, this option has no effect.
9778 @xref{Treating / specially}.
9780 @itemx --no-preserve-root
9781 @opindex --no-preserve-root
9782 @cindex root directory, allow recursive modification
9783 Cancel the effect of any preceding @option{--preserve-root} option.
9784 @xref{Treating / specially}.
9786 @item --reference=@var{ref_file}
9787 @opindex --reference
9788 Change the group of each @var{file} to be the same as that of
9789 @var{ref_file}. If @var{ref_file} is a symbolic link, do not use the
9790 group of the symbolic link, but rather that of the file it refers to.
9796 Output a diagnostic for every file processed.
9797 If a symbolic link is encountered during a recursive traversal
9798 on a system without the @code{lchown} system call, and @option{--no-dereference}
9799 is in effect, then issue a diagnostic saying neither the symbolic link nor
9800 its referent is being changed.
9805 @opindex --recursive
9806 @cindex recursively changing group ownership
9807 Recursively change the group ownership of directories and their contents.
9810 @xref{Traversing symlinks}.
9813 @xref{Traversing symlinks}.
9816 @xref{Traversing symlinks}.
9825 # Change the group of /u to "staff".
9828 # Change the group of /u and subfiles to "staff".
9833 @node chmod invocation
9834 @section @command{chmod}: Change access permissions
9837 @cindex changing access permissions
9838 @cindex access permissions, changing
9839 @cindex permissions, changing access
9841 @command{chmod} changes the access permissions of the named files. Synopsis:
9844 chmod [@var{option}]@dots{} @{@var{mode} | --reference=@var{ref_file}@} @var{file}@dots{}
9847 @cindex symbolic links, permissions of
9848 @command{chmod} never changes the permissions of symbolic links, since
9849 the @command{chmod} system call cannot change their permissions.
9850 This is not a problem since the permissions of symbolic links are
9851 never used. However, for each symbolic link listed on the command
9852 line, @command{chmod} changes the permissions of the pointed-to file.
9853 In contrast, @command{chmod} ignores symbolic links encountered during
9854 recursive directory traversals.
9856 A successful use of @command{chmod} clears the set-group-ID bit of a
9857 regular file if the file's group ID does not match the user's
9858 effective group ID or one of the user's supplementary group IDs,
9859 unless the user has appropriate privileges. Additional restrictions
9860 may cause the set-user-ID and set-group-ID bits of @var{mode} or
9861 @var{ref_file} to be ignored. This behavior depends on the policy and
9862 functionality of the underlying @code{chmod} system call. When in
9863 doubt, check the underlying system behavior.
9865 If used, @var{mode} specifies the new file mode bits.
9866 For details, see the section on @ref{File permissions}.
9867 If you really want @var{mode} to have a leading @samp{-}, you should
9868 use @option{--} first, e.g., @samp{chmod -- -w file}. Typically,
9869 though, @samp{chmod a-w file} is preferable, and @command{chmod -w
9870 file} (without the @option{--}) complains if it behaves differently
9871 from what @samp{chmod a-w file} would do.
9873 The program accepts the following options. Also see @ref{Common options}.
9881 Verbosely describe the action for each @var{file} whose permissions
9890 @cindex error messages, omitting
9891 Do not print error messages about files whose permissions cannot be
9894 @itemx --preserve-root
9895 @opindex --preserve-root
9896 @cindex root directory, disallow recursive modification
9897 Fail upon any attempt to recursively change the root directory, @file{/}.
9898 Without @option{--recursive}, this option has no effect.
9899 @xref{Treating / specially}.
9901 @itemx --no-preserve-root
9902 @opindex --no-preserve-root
9903 @cindex root directory, allow recursive modification
9904 Cancel the effect of any preceding @option{--preserve-root} option.
9905 @xref{Treating / specially}.
9911 Verbosely describe the action or non-action taken for every @var{file}.
9913 @item --reference=@var{ref_file}
9914 @opindex --reference
9915 Change the mode of each @var{file} to be the same as that of @var{ref_file}.
9916 @xref{File permissions}.
9917 If @var{ref_file} is a symbolic link, do not use the mode
9918 of the symbolic link, but rather that of the file it refers to.
9923 @opindex --recursive
9924 @cindex recursively changing access permissions
9925 Recursively change permissions of directories and their contents.
9932 @node touch invocation
9933 @section @command{touch}: Change file timestamps
9936 @cindex changing file timestamps
9937 @cindex file timestamps, changing
9938 @cindex timestamps, changing file
9940 @command{touch} changes the access and/or modification times of the
9941 specified files. Synopsis:
9944 touch [@var{option}]@dots{} @var{file}@dots{}
9947 @cindex empty files, creating
9948 Any @var{file} argument that does not exist is created empty, unless
9949 option @option{--no-create} (@option{-c}) or @option{--no-dereference}
9950 (@option{-h}) was in effect.
9952 A @var{file} argument string of @samp{-} is handled specially and
9953 causes @command{touch} to change the times of the file associated with
9956 @cindex permissions, for changing file timestamps
9957 If changing both the access and modification times to the current
9958 time, @command{touch} can change the timestamps for files that the user
9959 running it does not own but has write permission for. Otherwise, the
9960 user must own the files.
9962 Although @command{touch} provides options for changing two of the times---the
9963 times of last access and modification---of a file, there is actually
9964 a standard third one as well: the inode change time. This is often
9965 referred to as a file's @code{ctime}.
9966 The inode change time represents the time when the file's meta-information
9967 last changed. One common example of this is when the permissions of a
9968 file change. Changing the permissions doesn't access the file, so
9969 the atime doesn't change, nor does it modify the file, so the mtime
9970 doesn't change. Yet, something about the file itself has changed,
9971 and this must be noted somewhere. This is the job of the ctime field.
9972 This is necessary, so that, for example, a backup program can make a
9973 fresh copy of the file, including the new permissions value.
9974 Another operation that modifies a file's ctime without affecting
9975 the others is renaming. In any case, it is not possible, in normal
9976 operations, for a user to change the ctime field to a user-specified value.
9977 Some operating systems and file systems support a fourth time: the
9978 birth time, when the file was first created; by definition, this
9979 timestamp never changes.
9982 Time stamps assume the time zone rules specified by the @env{TZ}
9983 environment variable, or by the system default rules if @env{TZ} is
9984 not set. @xref{TZ Variable,, Specifying the Time Zone with @env{TZ},
9985 libc, The GNU C Library Reference Manual}.
9986 You can avoid ambiguities during
9987 daylight saving transitions by using @sc{utc} time stamps.
9989 The program accepts the following options. Also see @ref{Common options}.
9995 @itemx --time=access
9999 @opindex atime@r{, changing}
10000 @opindex access @r{time, changing}
10001 @opindex use @r{time, changing}
10002 Change the access time only.
10007 @opindex --no-create
10008 Do not warn about or create files that do not exist.
10011 @itemx --date=@var{time}
10015 Use @var{time} instead of the current time. It can contain month names,
10016 time zones, @samp{am} and @samp{pm}, @samp{yesterday}, etc. For
10017 example, @option{--date="2004-02-27 14:19:13.489392193 +0530"}
10018 specifies the instant of time that is 489,392,193 nanoseconds after
10019 February 27, 2004 at 2:19:13 PM in a time zone that is 5 hours and 30
10020 minutes east of @acronym{UTC}. @xref{Date input formats}.
10021 File systems that do not support high-resolution time stamps
10022 silently ignore any excess precision here.
10026 @cindex BSD @command{touch} compatibility
10027 Ignored; for compatibility with BSD versions of @command{touch}.
10030 @itemx --no-dereference
10032 @opindex --no-dereference
10033 @cindex symbolic links, changing time
10035 Attempt to change the timestamps of a symbolic link, rather than what
10036 the link refers to. When using this option, empty files are not
10037 created, but option @option{-c} must also be used to avoid warning
10038 about files that do not exist. Not all systems support changing the
10039 timestamps of symlinks, since underlying system support for this
10040 action was not required until @acronym{POSIX} 2008. Also, on some
10041 systems, the mere act of examining a symbolic link changes the access
10042 time, such that only changes to the modification time will persist
10043 long enough to be observable. When coupled with option @option{-r}, a
10044 reference timestamp is taken from a symbolic link rather than the file
10048 @itemx --time=mtime
10049 @itemx --time=modify
10052 @opindex mtime@r{, changing}
10053 @opindex modify @r{time, changing}
10054 Change the modification time only.
10056 @item -r @var{file}
10057 @itemx --reference=@var{file}
10059 @opindex --reference
10060 Use the times of the reference @var{file} instead of the current time.
10061 If this option is combined with the @option{--date=@var{time}}
10062 (@option{-d @var{time}}) option, the reference @var{file}'s time is
10063 the origin for any relative @var{time}s given, but is otherwise ignored.
10064 For example, @samp{-r foo -d '-5 seconds'} specifies a time stamp
10065 equal to five seconds before the corresponding time stamp for @file{foo}.
10066 If @var{file} is a symbolic link, the reference timestamp is taken
10067 from the target of the symlink, unless @option{-h} was also in effect.
10069 @item -t [[@var{cc}]@var{yy}]@var{mmddhhmm}[.@var{ss}]
10070 Use the argument (optional four-digit or two-digit years, months,
10071 days, hours, minutes, optional seconds) instead of the current time.
10072 If the year is specified with only two digits, then @var{cc}
10073 is 20 for years in the range 0 @dots{} 68, and 19 for years in
10074 69 @dots{} 99. If no digits of the year are specified,
10075 the argument is interpreted as a date in the current year.
10076 Note that @var{ss} may be @samp{60}, to accommodate leap seconds.
10080 @vindex _POSIX2_VERSION
10081 On older systems, @command{touch} supports an obsolete syntax, as follows.
10082 If no timestamp is given with any of the @option{-d}, @option{-r}, or
10083 @option{-t} options, and if there are two or more @var{file}s and the
10084 first @var{file} is of the form @samp{@var{mmddhhmm}[@var{yy}]} and this
10085 would be a valid argument to the @option{-t} option (if the @var{yy}, if
10086 any, were moved to the front), and if the represented year
10087 is in the range 1969--1999, that argument is interpreted as the time
10088 for the other files instead of as a file name.
10089 This obsolete behavior can be enabled or disabled with the
10090 @env{_POSIX2_VERSION} environment variable (@pxref{Standards
10091 conformance}), but portable scripts should avoid commands whose
10092 behavior depends on this variable.
10093 For example, use @samp{touch ./12312359 main.c} or @samp{touch -t
10094 12312359 main.c} rather than the ambiguous @samp{touch 12312359 main.c}.
10100 @chapter Disk usage
10104 No disk can hold an infinite amount of data. These commands report
10105 how much disk storage is in use or available, report other file and
10106 file status information, and write buffers to disk.
10109 * df invocation:: Report file system disk space usage.
10110 * du invocation:: Estimate file space usage.
10111 * stat invocation:: Report file or file system status.
10112 * sync invocation:: Synchronize memory and disk.
10113 * truncate invocation:: Shrink or extend the size of a file.
10117 @node df invocation
10118 @section @command{df}: Report file system disk space usage
10121 @cindex file system disk usage
10122 @cindex disk usage by file system
10124 @command{df} reports the amount of disk space used and available on
10125 file systems. Synopsis:
10128 df [@var{option}]@dots{} [@var{file}]@dots{}
10131 With no arguments, @command{df} reports the space used and available on all
10132 currently mounted file systems (of all types). Otherwise, @command{df}
10133 reports on the file system containing each argument @var{file}.
10135 Normally the disk space is printed in units of
10136 1024 bytes, but this can be overridden (@pxref{Block size}).
10137 Non-integer quantities are rounded up to the next higher unit.
10139 @cindex disk device file
10140 @cindex device file, disk
10141 If an argument @var{file} is a disk device file containing a mounted
10142 file system, @command{df} shows the space available on that file system
10143 rather than on the file system containing the device node (i.e., the root
10144 file system). @sc{gnu} @command{df} does not attempt to determine the disk usage
10145 on unmounted file systems, because on most kinds of systems doing so
10146 requires extremely nonportable intimate knowledge of file system
10149 The program accepts the following options. Also see @ref{Common options}.
10157 @cindex automounter file systems
10158 @cindex ignore file systems
10159 Include in the listing dummy file systems, which
10160 are omitted by default. Such file systems are typically special-purpose
10161 pseudo-file-systems, such as automounter entries.
10163 @item -B @var{size}
10164 @itemx --block-size=@var{size}
10166 @opindex --block-size
10167 @cindex file system sizes
10168 Scale sizes by @var{size} before printing them (@pxref{Block size}).
10169 For example, @option{-BG} prints sizes in units of 1,073,741,824 bytes.
10173 @cindex grand total of disk size, usage and available space
10174 Print a grand total of all arguments after all arguments have
10175 been processed. This can be used to find out the total disk size, usage
10176 and available space of all listed devices.
10182 Equivalent to @option{--si}.
10188 @cindex inode usage
10189 List inode usage information instead of block usage. An inode (short
10190 for index node) contains information about a file such as its owner,
10191 permissions, timestamps, and location on the disk.
10195 @cindex kibibytes for file system sizes
10196 Print sizes in 1024-byte blocks, overriding the default block size
10197 (@pxref{Block size}).
10198 This option is equivalent to @option{--block-size=1K}.
10204 @cindex file system types, limiting output to certain
10205 Limit the listing to local file systems. By default, remote file systems
10210 @cindex file system space, retrieving old data more quickly
10211 Do not invoke the @code{sync} system call before getting any usage data.
10212 This may make @command{df} run significantly faster on systems with many
10213 disks, but on some systems (notably SunOS) the results may be slightly
10214 out of date. This is the default.
10217 @itemx --portability
10219 @opindex --portability
10220 @cindex one-line output format
10221 @cindex @acronym{POSIX} output format
10222 @cindex portable output format
10223 @cindex output format, portable
10224 Use the @acronym{POSIX} output format. This is like the default format except
10229 The information about each file system is always printed on exactly
10230 one line; a mount device is never put on a line by itself. This means
10231 that if the mount device name is more than 20 characters long (e.g., for
10232 some network mounts), the columns are misaligned.
10235 The labels in the header output line are changed to conform to @acronym{POSIX}.
10238 The default block size and output format are unaffected by the
10239 @env{DF_BLOCK_SIZE}, @env{BLOCK_SIZE} and @env{BLOCKSIZE} environment
10240 variables. However, the default block size is still affected by
10241 @env{POSIXLY_CORRECT}: it is 512 if @env{POSIXLY_CORRECT} is set, 1024
10242 otherwise. @xref{Block size}.
10249 @cindex file system space, retrieving current data more slowly
10250 Invoke the @code{sync} system call before getting any usage data. On
10251 some systems (notably SunOS), doing this yields more up to date results,
10252 but in general this option makes @command{df} much slower, especially when
10253 there are many or very busy file systems.
10255 @item -t @var{fstype}
10256 @itemx --type=@var{fstype}
10259 @cindex file system types, limiting output to certain
10260 Limit the listing to file systems of type @var{fstype}. Multiple
10261 file system types can be specified by giving multiple @option{-t} options.
10262 By default, nothing is omitted.
10265 @itemx --print-type
10267 @opindex --print-type
10268 @cindex file system types, printing
10269 Print each file system's type. The types printed here are the same ones
10270 you can include or exclude with @option{-t} and @option{-x}. The particular
10271 types printed are whatever is supported by the system. Here are some of
10272 the common names (this list is certainly not exhaustive):
10277 @cindex @acronym{NFS} file system type
10278 An @acronym{NFS} file system, i.e., one mounted over a network from another
10279 machine. This is the one type name which seems to be used uniformly by
10282 @item 4.2@r{, }ufs@r{, }efs@dots{}
10283 @cindex Linux file system types
10284 @cindex local file system types
10285 @opindex 4.2 @r{file system type}
10286 @opindex ufs @r{file system type}
10287 @opindex efs @r{file system type}
10288 A file system on a locally-mounted hard disk. (The system might even
10289 support more than one type here; Linux does.)
10291 @item hsfs@r{, }cdfs
10292 @cindex CD-ROM file system type
10293 @cindex High Sierra file system
10294 @opindex hsfs @r{file system type}
10295 @opindex cdfs @r{file system type}
10296 A file system on a CD-ROM drive. HP-UX uses @samp{cdfs}, most other
10297 systems use @samp{hsfs} (@samp{hs} for ``High Sierra'').
10300 @cindex PC file system
10301 @cindex DOS file system
10302 @cindex MS-DOS file system
10303 @cindex diskette file system
10305 An MS-DOS file system, usually on a diskette.
10309 @item -x @var{fstype}
10310 @itemx --exclude-type=@var{fstype}
10312 @opindex --exclude-type
10313 Limit the listing to file systems not of type @var{fstype}.
10314 Multiple file system types can be eliminated by giving multiple
10315 @option{-x} options. By default, no file system types are omitted.
10318 Ignored; for compatibility with System V versions of @command{df}.
10323 Failure includes the case where no output is generated, so you can
10324 inspect the exit status of a command like @samp{df -t ext3 -t reiserfs
10325 @var{dir}} to test whether @var{dir} is on a file system of type
10326 @samp{ext3} or @samp{reiserfs}.
10329 @node du invocation
10330 @section @command{du}: Estimate file space usage
10333 @cindex file space usage
10334 @cindex disk usage for files
10336 @command{du} reports the amount of disk space used by the specified files
10337 and for each subdirectory (of directory arguments). Synopsis:
10340 du [@var{option}]@dots{} [@var{file}]@dots{}
10343 With no arguments, @command{du} reports the disk space for the current
10344 directory. Normally the disk space is printed in units of
10345 1024 bytes, but this can be overridden (@pxref{Block size}).
10346 Non-integer quantities are rounded up to the next higher unit.
10348 If two or more hard links point to the same file, only one of the hard
10349 links is counted. The @var{file} argument order affects which links
10350 are counted, and changing the argument order may change the numbers
10351 that @command{du} outputs.
10353 The program accepts the following options. Also see @ref{Common options}.
10361 Show counts for all files, not just directories.
10363 @itemx --apparent-size
10364 @opindex --apparent-size
10365 Print apparent sizes, rather than disk usage. The apparent size of a
10366 file is the number of bytes reported by @code{wc -c} on regular files,
10367 or more generally, @code{ls -l --block-size=1} or @code{stat --format=%s}.
10368 For example, a file containing the word @samp{zoo} with no newline would,
10369 of course, have an apparent size of 3. Such a small file may require
10370 anywhere from 0 to 16 KiB or more of disk space, depending on
10371 the type and configuration of the file system on which the file resides.
10372 However, a sparse file created with this command:
10375 dd bs=1 seek=2GiB if=/dev/null of=big
10379 has an apparent size of 2 GiB, yet on most modern
10380 systems, it actually uses almost no disk space.
10386 Equivalent to @code{--apparent-size --block-size=1}.
10388 @item -B @var{size}
10389 @itemx --block-size=@var{size}
10391 @opindex --block-size
10393 Scale sizes by @var{size} before printing them (@pxref{Block size}).
10394 For example, @option{-BG} prints sizes in units of 1,073,741,824 bytes.
10400 @cindex grand total of disk space
10401 Print a grand total of all arguments after all arguments have
10402 been processed. This can be used to find out the total disk usage of
10403 a given set of files or directories.
10406 @itemx --dereference-args
10408 @opindex --dereference-args
10409 Dereference symbolic links that are command line arguments.
10410 Does not affect other symbolic links. This is helpful for finding
10411 out the disk usage of directories, such as @file{/usr/tmp}, which
10412 are often symbolic links.
10414 @c --files0-from=FILE
10415 @filesZeroFromOption{du,, with the @option{--total} (@option{-c}) option}
10421 Equivalent to @option{--dereference-args} (@option{-D}).
10425 @cindex kibibytes for file sizes
10426 Print sizes in 1024-byte blocks, overriding the default block size
10427 (@pxref{Block size}).
10428 This option is equivalent to @option{--block-size=1K}.
10431 @itemx --count-links
10433 @opindex --count-links
10434 @cindex hard links, counting in @command{du}
10435 Count the size of all files, even if they have appeared already (as a
10439 @itemx --dereference
10441 @opindex --dereference
10442 @cindex symbolic links, dereferencing in @command{du}
10443 Dereference symbolic links (show the disk space used by the file
10444 or directory that the link points to instead of the space used by
10449 @cindex mebibytes for file sizes
10450 Print sizes in 1,048,576-byte blocks, overriding the default block size
10451 (@pxref{Block size}).
10452 This option is equivalent to @option{--block-size=1M}.
10455 @itemx --no-dereference
10457 @opindex --no-dereference
10458 @cindex symbolic links, dereferencing in @command{du}
10459 For each symbolic links encountered by @command{du},
10460 consider the disk space used by the symbolic link.
10462 @item -d @var{depth}
10463 @item --max-depth=@var{depth}
10464 @opindex -d @var{depth}
10465 @opindex --max-depth=@var{depth}
10466 @cindex limiting output of @command{du}
10467 Show the total for each directory (and file if --all) that is at
10468 most MAX_DEPTH levels down from the root of the hierarchy. The root
10469 is at level 0, so @code{du --max-depth=0} is equivalent to @code{du -s}.
10478 @opindex --summarize
10479 Display only a total for each argument.
10482 @itemx --separate-dirs
10484 @opindex --separate-dirs
10485 Normally, in the output of @command{du} (when not using @option{--summarize}),
10486 the size listed next to a directory name, @var{d}, represents the sum
10487 of sizes of all entries beneath @var{d} as well as the size of @var{d} itself.
10488 With @option{--separate-dirs}, the size reported for a directory name,
10489 @var{d}, is merely the @code{stat.st_size}-derived size of the directory
10494 @cindex last modified dates, displaying in @command{du}
10495 Show time of the most recent modification of any file in the directory,
10496 or any of its subdirectories.
10498 @itemx --time=ctime
10499 @itemx --time=status
10502 @opindex ctime@r{, show the most recent}
10503 @opindex status time@r{, show the most recent}
10504 @opindex use time@r{, show the most recent}
10505 Show the most recent status change time (the @samp{ctime} in the inode) of
10506 any file in the directory, instead of the modification time.
10508 @itemx --time=atime
10509 @itemx --time=access
10511 @opindex atime@r{, show the most recent}
10512 @opindex access time@r{, show the most recent}
10513 Show the most recent access time (the @samp{atime} in the inode) of
10514 any file in the directory, instead of the modification time.
10516 @item --time-style=@var{style}
10517 @opindex --time-style
10519 List timestamps in style @var{style}. This option has an effect only if
10520 the @option{--time} option is also specified. The @var{style} should
10521 be one of the following:
10524 @item +@var{format}
10526 List timestamps using @var{format}, where @var{format} is interpreted
10527 like the format argument of @command{date} (@pxref{date invocation}).
10528 For example, @option{--time-style="+%Y-%m-%d %H:%M:%S"} causes
10529 @command{du} to list timestamps like @samp{2002-03-30 23:45:56}. As
10530 with @command{date}, @var{format}'s interpretation is affected by the
10531 @env{LC_TIME} locale category.
10534 List timestamps in full using @acronym{ISO} 8601 date, time, and time zone
10535 format with nanosecond precision, e.g., @samp{2002-03-30
10536 23:45:56.477817180 -0700}. This style is equivalent to
10537 @samp{+%Y-%m-%d %H:%M:%S.%N %z}.
10540 List @acronym{ISO} 8601 date and time in minutes, e.g.,
10541 @samp{2002-03-30 23:45}. These timestamps are shorter than
10542 @samp{full-iso} timestamps, and are usually good enough for everyday
10543 work. This style is equivalent to @samp{+%Y-%m-%d %H:%M}.
10546 List @acronym{ISO} 8601 dates for timestamps, e.g., @samp{2002-03-30}.
10547 This style is equivalent to @samp{+%Y-%m-%d}.
10551 You can specify the default value of the @option{--time-style} option
10552 with the environment variable @env{TIME_STYLE}; if @env{TIME_STYLE} is not set
10553 the default style is @samp{long-iso}. For compatibility with @command{ls},
10554 if @env{TIME_STYLE} begins with @samp{+} and contains a newline,
10555 the newline and any later characters are ignored; if @env{TIME_STYLE}
10556 begins with @samp{posix-} the @samp{posix-} is ignored; and if
10557 @env{TIME_STYLE} is @samp{locale} it is ignored.
10560 @itemx --one-file-system
10562 @opindex --one-file-system
10563 @cindex one file system, restricting @command{du} to
10564 Skip directories that are on different file systems from the one that
10565 the argument being processed is on.
10567 @item --exclude=@var{pattern}
10568 @opindex --exclude=@var{pattern}
10569 @cindex excluding files from @command{du}
10570 When recursing, skip subdirectories or files matching @var{pattern}.
10571 For example, @code{du --exclude='*.o'} excludes files whose names
10574 @item -X @var{file}
10575 @itemx --exclude-from=@var{file}
10576 @opindex -X @var{file}
10577 @opindex --exclude-from=@var{file}
10578 @cindex excluding files from @command{du}
10579 Like @option{--exclude}, except take the patterns to exclude from @var{file},
10580 one per line. If @var{file} is @samp{-}, take the patterns from standard
10585 @cindex NFS mounts from BSD to HP-UX
10586 On BSD systems, @command{du} reports sizes that are half the correct
10587 values for files that are NFS-mounted from HP-UX systems. On HP-UX
10588 systems, it reports sizes that are twice the correct values for
10589 files that are NFS-mounted from BSD systems. This is due to a flaw
10590 in HP-UX; it also affects the HP-UX @command{du} program.
10595 @node stat invocation
10596 @section @command{stat}: Report file or file system status
10599 @cindex file status
10600 @cindex file system status
10602 @command{stat} displays information about the specified file(s). Synopsis:
10605 stat [@var{option}]@dots{} [@var{file}]@dots{}
10608 With no option, @command{stat} reports all information about the given files.
10609 But it also can be used to report the information of the file systems the
10610 given files are located on. If the files are links, @command{stat} can
10611 also give information about the files the links point to.
10613 @mayConflictWithShellBuiltIn{stat}
10618 @itemx --dereference
10620 @opindex --dereference
10621 @cindex symbolic links, dereferencing in @command{stat}
10622 Change how @command{stat} treats symbolic links.
10623 With this option, @command{stat} acts on the file referenced
10624 by each symbolic link argument.
10625 Without it, @command{stat} acts on any symbolic link argument directly.
10628 @itemx --file-system
10630 @opindex --file-system
10631 @cindex file systems
10632 Report information about the file systems where the given files are located
10633 instead of information about the files themselves.
10636 @itemx --format=@var{format}
10638 @opindex --format=@var{format}
10639 @cindex output format
10640 Use @var{format} rather than the default format.
10641 @var{format} is automatically newline-terminated, so
10642 running a command like the following with two or more @var{file}
10643 operands produces a line of output for each operand:
10645 $ stat --format=%d:%i / /usr
10650 @itemx --printf=@var{format}
10651 @opindex --printf=@var{format}
10652 @cindex output format
10653 Use @var{format} rather than the default format.
10654 Like @option{--format}, but interpret backslash escapes,
10655 and do not output a mandatory trailing newline.
10656 If you want a newline, include @samp{\n} in the @var{format}.
10657 Here's how you would use @option{--printf} to print the device
10658 and inode numbers of @file{/} and @file{/usr}:
10660 $ stat --printf='%d:%i\n' / /usr
10669 @cindex terse output
10670 Print the information in terse form, suitable for parsing by other programs.
10674 The valid @var{format} directives for files with @option{--format} and
10675 @option{--printf} are:
10678 @item %a - Access rights in octal
10679 @item %A - Access rights in human readable form
10680 @item %b - Number of blocks allocated (see @samp{%B})
10681 @item %B - The size in bytes of each block reported by @samp{%b}
10682 @item %d - Device number in decimal
10683 @item %D - Device number in hex
10684 @item %f - Raw mode in hex
10685 @item %F - File type
10686 @item %g - Group ID of owner
10687 @item %G - Group name of owner
10688 @item %h - Number of hard links
10689 @item %i - Inode number
10690 @item %n - File name
10691 @item %N - Quoted file name with dereference if symbolic link
10692 @item %o - I/O block size
10693 @item %s - Total size, in bytes
10694 @item %t - Major device type in hex
10695 @item %T - Minor device type in hex
10696 @item %u - User ID of owner
10697 @item %U - User name of owner
10698 @item %x - Time of last access
10699 @item %X - Time of last access as seconds since Epoch
10700 @item %y - Time of last modification
10701 @item %Y - Time of last modification as seconds since Epoch
10702 @item %z - Time of last change
10703 @item %Z - Time of last change as seconds since Epoch
10706 When listing file system information (@option{--file-system} (@option{-f})),
10707 you must use a different set of @var{format} directives:
10710 @item %a - Free blocks available to non-super-user
10711 @item %b - Total data blocks in file system
10712 @item %c - Total file nodes in file system
10713 @item %d - Free file nodes in file system
10714 @item %f - Free blocks in file system
10715 @item %i - File System ID in hex
10716 @item %l - Maximum length of file names
10717 @item %n - File name
10718 @item %s - Block size (for faster transfers)
10719 @item %S - Fundamental block size (for block counts)
10720 @item %t - Type in hex
10721 @item %T - Type in human readable form
10725 Time stamps are listed according to the time zone rules specified by
10726 the @env{TZ} environment variable, or by the system default rules if
10727 @env{TZ} is not set. @xref{TZ Variable,, Specifying the Time Zone
10728 with @env{TZ}, libc, The GNU C Library Reference Manual}.
10733 @node sync invocation
10734 @section @command{sync}: Synchronize data on disk with memory
10737 @cindex synchronize disk and memory
10739 @cindex superblock, writing
10740 @cindex inodes, written buffered
10741 @command{sync} writes any data buffered in memory out to disk. This can
10742 include (but is not limited to) modified superblocks, modified inodes,
10743 and delayed reads and writes. This must be implemented by the kernel;
10744 The @command{sync} program does nothing but exercise the @code{sync} system
10747 @cindex crashes and corruption
10748 The kernel keeps data in memory to avoid doing (relatively slow) disk
10749 reads and writes. This improves performance, but if the computer
10750 crashes, data may be lost or the file system corrupted as a
10751 result. The @command{sync} command ensures everything in memory
10752 is written to disk.
10754 Any arguments are ignored, except for a lone @option{--help} or
10755 @option{--version} (@pxref{Common options}).
10760 @node truncate invocation
10761 @section @command{truncate}: Shrink or extend the size of a file
10764 @cindex truncating, file sizes
10766 @command{truncate} shrinks or extends the size of each @var{file} to the
10767 specified size. Synopsis:
10770 truncate @var{option}@dots{} @var{file}@dots{}
10773 @cindex files, creating
10774 Any @var{file} that does not exist is created.
10776 @cindex sparse files, creating
10777 @cindex holes, creating files with
10778 If a @var{file} is larger than the specified size, the extra data is lost.
10779 If a @var{file} is shorter, it is extended and the extended part (or hole)
10780 reads as zero bytes.
10782 The program accepts the following options. Also see @ref{Common options}.
10789 @opindex --no-create
10790 Do not create files that do not exist.
10795 @opindex --io-blocks
10796 Treat @var{size} as number of I/O blocks of the @var{file} rather than bytes.
10798 @item -r @var{rfile}
10799 @itemx --reference=@var{rfile}
10801 @opindex --reference
10802 Base the size of each @var{file} on the size of @var{rfile}.
10804 @item -s @var{size}
10805 @itemx --size=@var{size}
10808 Set or adjust the size of each @var{file} according to @var{size}.
10809 @multiplierSuffixesNoBlocks{size}
10811 @var{size} may also be prefixed by one of the following to adjust
10812 the size of each @var{file} based on their current size:
10814 @samp{+} => extend by
10815 @samp{-} => reduce by
10816 @samp{<} => at most
10817 @samp{>} => at least
10818 @samp{/} => round down to multiple of
10819 @samp{%} => round up to multiple of
10827 @node Printing text
10828 @chapter Printing text
10830 @cindex printing text, commands for
10831 @cindex commands for printing text
10833 This section describes commands that display text strings.
10836 * echo invocation:: Print a line of text.
10837 * printf invocation:: Format and print data.
10838 * yes invocation:: Print a string until interrupted.
10842 @node echo invocation
10843 @section @command{echo}: Print a line of text
10846 @cindex displaying text
10847 @cindex printing text
10848 @cindex text, displaying
10849 @cindex arbitrary text, displaying
10851 @command{echo} writes each given @var{string} to standard output, with a
10852 space between each and a newline after the last one. Synopsis:
10855 echo [@var{option}]@dots{} [@var{string}]@dots{}
10858 @mayConflictWithShellBuiltIn{echo}
10860 The program accepts the following options. Also see @ref{Common options}.
10861 Options must precede operands, and the normally-special argument
10862 @samp{--} has no special meaning and is treated like any other
10868 Do not output the trailing newline.
10872 @cindex backslash escapes
10873 Enable interpretation of the following backslash-escaped characters in
10882 produce no further output
10898 the eight-bit value that is the octal number @var{nnn}
10899 (zero to three octal digits)
10901 the eight-bit value that is the octal number @var{nnn}
10902 (one to three octal digits)
10904 the eight-bit value that is the hexadecimal number @var{hh}
10905 (one or two hexadecimal digits)
10910 @cindex backslash escapes
10911 Disable interpretation of backslash escapes in each @var{string}.
10912 This is the default. If @option{-e} and @option{-E} are both
10913 specified, the last one given takes effect.
10917 @vindex POSIXLY_CORRECT
10918 If the @env{POSIXLY_CORRECT} environment variable is set, then when
10919 @command{echo}'s first argument is not @option{-n} it outputs
10920 option-like arguments instead of treating them as options. For
10921 example, @code{echo -ne hello} outputs @samp{-ne hello} instead of
10922 plain @samp{hello}.
10924 @acronym{POSIX} does not require support for any options, and says
10925 that the behavior of @command{echo} is implementation-defined if any
10926 @var{string} contains a backslash or if the first argument is
10927 @option{-n}. Portable programs can use the @command{printf} command
10928 if they need to omit trailing newlines or output control characters or
10929 backslashes. @xref{printf invocation}.
10934 @node printf invocation
10935 @section @command{printf}: Format and print data
10938 @command{printf} does formatted printing of text. Synopsis:
10941 printf @var{format} [@var{argument}]@dots{}
10944 @command{printf} prints the @var{format} string, interpreting @samp{%}
10945 directives and @samp{\} escapes to format numeric and string arguments
10946 in a way that is mostly similar to the C @samp{printf} function.
10947 @xref{Output Conversion Syntax,, @command{printf} format directives,
10948 libc, The GNU C Library Reference Manual}, for details.
10949 The differences are listed below.
10951 @mayConflictWithShellBuiltIn{printf}
10956 The @var{format} argument is reused as necessary to convert all the
10957 given @var{argument}s. For example, the command @samp{printf %s a b}
10961 Missing @var{argument}s are treated as null strings or as zeros,
10962 depending on whether the context expects a string or a number. For
10963 example, the command @samp{printf %sx%d} prints @samp{x0}.
10967 An additional escape, @samp{\c}, causes @command{printf} to produce no
10968 further output. For example, the command @samp{printf 'A%sC\cD%sF' B
10969 E} prints @samp{ABC}.
10972 The hexadecimal escape sequence @samp{\x@var{hh}} has at most two
10973 digits, as opposed to C where it can have an unlimited number of
10974 digits. For example, the command @samp{printf '\x07e'} prints two
10975 bytes, whereas the C statement @samp{printf ("\x07e")} prints just
10980 @command{printf} has an additional directive, @samp{%b}, which prints its
10981 argument string with @samp{\} escapes interpreted in the same way as in
10982 the @var{format} string, except that octal escapes are of the form
10983 @samp{\0@var{ooo}} where @var{ooo} is 0 to 3 octal digits.
10984 If a precision is also given, it limits the number of bytes printed
10985 from the converted string.
10988 Numeric arguments must be single C constants, possibly with leading
10989 @samp{+} or @samp{-}. For example, @samp{printf %.4d -3} outputs
10993 @vindex POSIXLY_CORRECT
10994 If the leading character of a numeric argument is @samp{"} or @samp{'}
10995 then its value is the numeric value of the immediately following
10996 character. Any remaining characters are silently ignored if the
10997 @env{POSIXLY_CORRECT} environment variable is set; otherwise, a
10998 warning is printed. For example, @samp{printf "%d" "'a"} outputs
10999 @samp{97} on hosts that use the @acronym{ASCII} character set, since
11000 @samp{a} has the numeric value 97 in @acronym{ASCII}.
11005 A floating-point argument must use a period before any fractional
11006 digits, but is printed according to the @env{LC_NUMERIC} category of the
11007 current locale. For example, in a locale whose radix character is a
11008 comma, the command @samp{printf %g 3.14} outputs @samp{3,14} whereas
11009 the command @samp{printf %g 3,14} is an error.
11013 @command{printf} interprets @samp{\@var{ooo}} in @var{format} as an octal number
11014 (if @var{ooo} is 1 to 3 octal digits) specifying a character to print,
11015 and @samp{\x@var{hh}} as a hexadecimal number (if @var{hh} is 1 to 2 hex
11016 digits) specifying a character to print.
11021 @cindex ISO/IEC 10646
11023 @command{printf} interprets two character syntaxes introduced in
11024 @acronym{ISO} C 99:
11025 @samp{\u} for 16-bit Unicode (@acronym{ISO}/@acronym{IEC} 10646)
11026 characters, specified as
11027 four hexadecimal digits @var{hhhh}, and @samp{\U} for 32-bit Unicode
11028 characters, specified as eight hexadecimal digits @var{hhhhhhhh}.
11029 @command{printf} outputs the Unicode characters
11030 according to the @env{LC_CTYPE} locale. Unicode characters in the ranges
11031 U+0000...U+009F, U+D800...U+DFFF cannot be specified by this syntax, except
11032 for U+0024 ($), U+0040 (@@), and U+0060 (@`).
11034 The processing of @samp{\u} and @samp{\U} requires a full-featured
11035 @code{iconv} facility. It is activated on systems with glibc 2.2 (or newer),
11036 or when @code{libiconv} is installed prior to this package. Otherwise
11037 @samp{\u} and @samp{\U} will print as-is.
11039 The only options are a lone @option{--help} or
11040 @option{--version}. @xref{Common options}.
11041 Options must precede operands.
11043 The Unicode character syntaxes are useful for writing strings in a locale
11044 independent way. For example, a string containing the Euro currency symbol
11047 $ env printf '\u20AC 14.95'
11051 will be output correctly in all locales supporting the Euro symbol
11052 (@acronym{ISO}-8859-15, UTF-8, and others). Similarly, a Chinese string
11055 $ env printf '\u4e2d\u6587'
11059 will be output correctly in all Chinese locales (GB2312, BIG5, UTF-8, etc).
11061 Note that in these examples, the @command{printf} command has been
11062 invoked via @command{env} to ensure that we run the program found via
11063 your shell's search path, and not a shell alias or a built-in function.
11065 For larger strings, you don't need to look up the hexadecimal code
11066 values of each character one by one. @acronym{ASCII} characters mixed with \u
11067 escape sequences is also known as the JAVA source file encoding. You can
11068 use GNU recode 3.5c (or newer) to convert strings to this encoding. Here
11069 is how to convert a piece of text into a shell script which will output
11070 this text in a locale-independent way:
11073 $ LC_CTYPE=zh_CN.big5 /usr/local/bin/printf \
11074 '\u4e2d\u6587\n' > sample.txt
11075 $ recode BIG5..JAVA < sample.txt \
11076 | sed -e "s|^|/usr/local/bin/printf '|" -e "s|$|\\\\n'|" \
11083 @node yes invocation
11084 @section @command{yes}: Print a string until interrupted
11087 @cindex repeated output of a string
11089 @command{yes} prints the command line arguments, separated by spaces and
11090 followed by a newline, forever until it is killed. If no arguments are
11091 given, it prints @samp{y} followed by a newline forever until killed.
11093 Upon a write error, @command{yes} exits with status @samp{1}.
11095 The only options are a lone @option{--help} or @option{--version}.
11096 To output an argument that begins with
11097 @samp{-}, precede it with @option{--}, e.g., @samp{yes -- --help}.
11098 @xref{Common options}.
11102 @chapter Conditions
11105 @cindex commands for exit status
11106 @cindex exit status commands
11108 This section describes commands that are primarily useful for their exit
11109 status, rather than their output. Thus, they are often used as the
11110 condition of shell @code{if} statements, or as the last command in a
11114 * false invocation:: Do nothing, unsuccessfully.
11115 * true invocation:: Do nothing, successfully.
11116 * test invocation:: Check file types and compare values.
11117 * expr invocation:: Evaluate expressions.
11121 @node false invocation
11122 @section @command{false}: Do nothing, unsuccessfully
11125 @cindex do nothing, unsuccessfully
11126 @cindex failure exit status
11127 @cindex exit status of @command{false}
11129 @command{false} does nothing except return an exit status of 1, meaning
11130 @dfn{failure}. It can be used as a place holder in shell scripts
11131 where an unsuccessful command is needed.
11132 In most modern shells, @command{false} is a built-in command, so when
11133 you use @samp{false} in a script, you're probably using the built-in
11134 command, not the one documented here.
11136 @command{false} honors the @option{--help} and @option{--version} options.
11138 This version of @command{false} is implemented as a C program, and is thus
11139 more secure and faster than a shell script implementation, and may safely
11140 be used as a dummy shell for the purpose of disabling accounts.
11142 Note that @command{false} (unlike all other programs documented herein)
11143 exits unsuccessfully, even when invoked with
11144 @option{--help} or @option{--version}.
11146 Portable programs should not assume that the exit status of
11147 @command{false} is 1, as it is greater than 1 on some
11148 non-@acronym{GNU} hosts.
11151 @node true invocation
11152 @section @command{true}: Do nothing, successfully
11155 @cindex do nothing, successfully
11157 @cindex successful exit
11158 @cindex exit status of @command{true}
11160 @command{true} does nothing except return an exit status of 0, meaning
11161 @dfn{success}. It can be used as a place holder in shell scripts
11162 where a successful command is needed, although the shell built-in
11163 command @code{:} (colon) may do the same thing faster.
11164 In most modern shells, @command{true} is a built-in command, so when
11165 you use @samp{true} in a script, you're probably using the built-in
11166 command, not the one documented here.
11168 @command{true} honors the @option{--help} and @option{--version} options.
11170 Note, however, that it is possible to cause @command{true}
11171 to exit with nonzero status: with the @option{--help} or @option{--version}
11172 option, and with standard
11173 output already closed or redirected to a file that evokes an I/O error.
11174 For example, using a Bourne-compatible shell:
11177 $ ./true --version >&-
11178 ./true: write error: Bad file number
11179 $ ./true --version > /dev/full
11180 ./true: write error: No space left on device
11183 This version of @command{true} is implemented as a C program, and is thus
11184 more secure and faster than a shell script implementation, and may safely
11185 be used as a dummy shell for the purpose of disabling accounts.
11187 @node test invocation
11188 @section @command{test}: Check file types and compare values
11191 @cindex check file types
11192 @cindex compare values
11193 @cindex expression evaluation
11195 @command{test} returns a status of 0 (true) or 1 (false) depending on the
11196 evaluation of the conditional expression @var{expr}. Each part of the
11197 expression must be a separate argument.
11199 @command{test} has file status checks, string operators, and numeric
11200 comparison operators.
11202 @command{test} has an alternate form that uses opening and closing
11203 square brackets instead a leading @samp{test}. For example, instead
11204 of @samp{test -d /}, you can write @samp{[ -d / ]}. The square
11205 brackets must be separate arguments; for example, @samp{[-d /]} does
11206 not have the desired effect. Since @samp{test @var{expr}} and @samp{[
11207 @var{expr} ]} have the same meaning, only the former form is discussed
11213 test @var{expression}
11215 [ @var{expression} ]
11220 @mayConflictWithShellBuiltIn{test}
11222 If @var{expression} is omitted, @command{test} returns false.
11223 If @var{expression} is a single argument,
11224 @command{test} returns false if the argument is null and true otherwise. The argument
11225 can be any string, including strings like @samp{-d}, @samp{-1},
11226 @samp{--}, @samp{--help}, and @samp{--version} that most other
11227 programs would treat as options. To get help and version information,
11228 invoke the commands @samp{[ --help} and @samp{[ --version}, without
11229 the usual closing brackets. @xref{Common options}.
11231 @cindex exit status of @command{test}
11235 0 if the expression is true,
11236 1 if the expression is false,
11237 2 if an error occurred.
11241 * File type tests:: -[bcdfhLpSt]
11242 * Access permission tests:: -[gkruwxOG]
11243 * File characteristic tests:: -e -s -nt -ot -ef
11244 * String tests:: -z -n = !=
11245 * Numeric tests:: -eq -ne -lt -le -gt -ge
11246 * Connectives for test:: ! -a -o
11250 @node File type tests
11251 @subsection File type tests
11253 @cindex file type tests
11255 These options test for particular types of files. (Everything's a file,
11256 but not all files are the same!)
11260 @item -b @var{file}
11262 @cindex block special check
11263 True if @var{file} exists and is a block special device.
11265 @item -c @var{file}
11267 @cindex character special check
11268 True if @var{file} exists and is a character special device.
11270 @item -d @var{file}
11272 @cindex directory check
11273 True if @var{file} exists and is a directory.
11275 @item -f @var{file}
11277 @cindex regular file check
11278 True if @var{file} exists and is a regular file.
11280 @item -h @var{file}
11281 @itemx -L @var{file}
11284 @cindex symbolic link check
11285 True if @var{file} exists and is a symbolic link.
11286 Unlike all other file-related tests, this test does not dereference
11287 @var{file} if it is a symbolic link.
11289 @item -p @var{file}
11291 @cindex named pipe check
11292 True if @var{file} exists and is a named pipe.
11294 @item -S @var{file}
11296 @cindex socket check
11297 True if @var{file} exists and is a socket.
11301 @cindex terminal check
11302 True if @var{fd} is a file descriptor that is associated with a
11308 @node Access permission tests
11309 @subsection Access permission tests
11311 @cindex access permission tests
11312 @cindex permission tests
11314 These options test for particular access permissions.
11318 @item -g @var{file}
11320 @cindex set-group-ID check
11321 True if @var{file} exists and has its set-group-ID bit set.
11323 @item -k @var{file}
11325 @cindex sticky bit check
11326 True if @var{file} exists and has its @dfn{sticky} bit set.
11328 @item -r @var{file}
11330 @cindex readable file check
11331 True if @var{file} exists and read permission is granted.
11333 @item -u @var{file}
11335 @cindex set-user-ID check
11336 True if @var{file} exists and has its set-user-ID bit set.
11338 @item -w @var{file}
11340 @cindex writable file check
11341 True if @var{file} exists and write permission is granted.
11343 @item -x @var{file}
11345 @cindex executable file check
11346 True if @var{file} exists and execute permission is granted
11347 (or search permission, if it is a directory).
11349 @item -O @var{file}
11351 @cindex owned by effective user ID check
11352 True if @var{file} exists and is owned by the current effective user ID.
11354 @item -G @var{file}
11356 @cindex owned by effective group ID check
11357 True if @var{file} exists and is owned by the current effective group ID.
11361 @node File characteristic tests
11362 @subsection File characteristic tests
11364 @cindex file characteristic tests
11366 These options test other file characteristics.
11370 @item -e @var{file}
11372 @cindex existence-of-file check
11373 True if @var{file} exists.
11375 @item -s @var{file}
11377 @cindex nonempty file check
11378 True if @var{file} exists and has a size greater than zero.
11380 @item @var{file1} -nt @var{file2}
11382 @cindex newer-than file check
11383 True if @var{file1} is newer (according to modification date) than
11384 @var{file2}, or if @var{file1} exists and @var{file2} does not.
11386 @item @var{file1} -ot @var{file2}
11388 @cindex older-than file check
11389 True if @var{file1} is older (according to modification date) than
11390 @var{file2}, or if @var{file2} exists and @var{file1} does not.
11392 @item @var{file1} -ef @var{file2}
11394 @cindex same file check
11395 @cindex hard link check
11396 True if @var{file1} and @var{file2} have the same device and inode
11397 numbers, i.e., if they are hard links to each other.
11403 @subsection String tests
11405 @cindex string tests
11407 These options test string characteristics. You may need to quote
11408 @var{string} arguments for the shell. For example:
11414 The quotes here prevent the wrong arguments from being passed to
11415 @command{test} if @samp{$V} is empty or contains special characters.
11419 @item -z @var{string}
11421 @cindex zero-length string check
11422 True if the length of @var{string} is zero.
11424 @item -n @var{string}
11425 @itemx @var{string}
11427 @cindex nonzero-length string check
11428 True if the length of @var{string} is nonzero.
11430 @item @var{string1} = @var{string2}
11432 @cindex equal string check
11433 True if the strings are equal.
11435 @item @var{string1} != @var{string2}
11437 @cindex not-equal string check
11438 True if the strings are not equal.
11443 @node Numeric tests
11444 @subsection Numeric tests
11446 @cindex numeric tests
11447 @cindex arithmetic tests
11449 Numeric relational operators. The arguments must be entirely numeric
11450 (possibly negative), or the special expression @w{@code{-l @var{string}}},
11451 which evaluates to the length of @var{string}.
11455 @item @var{arg1} -eq @var{arg2}
11456 @itemx @var{arg1} -ne @var{arg2}
11457 @itemx @var{arg1} -lt @var{arg2}
11458 @itemx @var{arg1} -le @var{arg2}
11459 @itemx @var{arg1} -gt @var{arg2}
11460 @itemx @var{arg1} -ge @var{arg2}
11467 These arithmetic binary operators return true if @var{arg1} is equal,
11468 not-equal, less-than, less-than-or-equal, greater-than, or
11469 greater-than-or-equal than @var{arg2}, respectively.
11476 test -1 -gt -2 && echo yes
11478 test -l abc -gt 1 && echo yes
11481 @error{} test: integer expression expected before -eq
11485 @node Connectives for test
11486 @subsection Connectives for @command{test}
11488 @cindex logical connectives
11489 @cindex connectives, logical
11491 The usual logical connectives.
11497 True if @var{expr} is false.
11499 @item @var{expr1} -a @var{expr2}
11501 @cindex logical and operator
11502 @cindex and operator
11503 True if both @var{expr1} and @var{expr2} are true.
11505 @item @var{expr1} -o @var{expr2}
11507 @cindex logical or operator
11508 @cindex or operator
11509 True if either @var{expr1} or @var{expr2} is true.
11514 @node expr invocation
11515 @section @command{expr}: Evaluate expressions
11518 @cindex expression evaluation
11519 @cindex evaluation of expressions
11521 @command{expr} evaluates an expression and writes the result on standard
11522 output. Each token of the expression must be a separate argument.
11524 Operands are either integers or strings. Integers consist of one or
11525 more decimal digits, with an optional leading @samp{-}.
11526 @command{expr} converts
11527 anything appearing in an operand position to an integer or a string
11528 depending on the operation being applied to it.
11530 Strings are not quoted for @command{expr} itself, though you may need to
11531 quote them to protect characters with special meaning to the shell,
11532 e.g., spaces. However, regardless of whether it is quoted, a string
11533 operand should not be a parenthesis or any of @command{expr}'s
11534 operators like @code{+}, so you cannot safely pass an arbitrary string
11535 @code{$str} to expr merely by quoting it to the shell. One way to
11536 work around this is to use the @sc{gnu} extension @code{+},
11537 (e.g., @code{+ "$str" = foo}); a more portable way is to use
11538 @code{@w{" $str"}} and to adjust the rest of the expression to take
11539 the leading space into account (e.g., @code{@w{" $str" = " foo"}}).
11541 You should not pass a negative integer or a string with leading
11542 @samp{-} as @command{expr}'s first argument, as it might be
11543 misinterpreted as an option; this can be avoided by parenthesization.
11544 Also, portable scripts should not use a string operand that happens to
11545 take the form of an integer; this can be worked around by inserting
11546 leading spaces as mentioned above.
11548 @cindex parentheses for grouping
11549 Operators may be given as infix symbols or prefix keywords. Parentheses
11550 may be used for grouping in the usual manner. You must quote
11551 parentheses and many operators to avoid the shell evaluating them,
11554 When built with support for the GNU MP library, @command{expr} uses
11555 arbitrary-precision arithmetic; otherwise, it uses native arithmetic
11556 types and may fail due to arithmetic overflow.
11558 The only options are @option{--help} and @option{--version}. @xref{Common
11559 options}. Options must precede operands.
11561 @cindex exit status of @command{expr}
11565 0 if the expression is neither null nor 0,
11566 1 if the expression is null or 0,
11567 2 if the expression is invalid,
11568 3 if an internal error occurred (e.g., arithmetic overflow).
11572 * String expressions:: + : match substr index length
11573 * Numeric expressions:: + - * / %
11574 * Relations for expr:: | & < <= = == != >= >
11575 * Examples of expr:: Examples.
11579 @node String expressions
11580 @subsection String expressions
11582 @cindex string expressions
11583 @cindex expressions, string
11585 @command{expr} supports pattern matching and other string operators. These
11586 have higher precedence than both the numeric and relational operators (in
11587 the next sections).
11591 @item @var{string} : @var{regex}
11592 @cindex pattern matching
11593 @cindex regular expression matching
11594 @cindex matching patterns
11595 Perform pattern matching. The arguments are converted to strings and the
11596 second is considered to be a (basic, a la GNU @code{grep}) regular
11597 expression, with a @code{^} implicitly prepended. The first argument is
11598 then matched against this regular expression.
11600 If the match succeeds and @var{regex} uses @samp{\(} and @samp{\)}, the
11601 @code{:} expression returns the part of @var{string} that matched the
11602 subexpression; otherwise, it returns the number of characters matched.
11604 If the match fails, the @code{:} operator returns the null string if
11605 @samp{\(} and @samp{\)} are used in @var{regex}, otherwise 0.
11607 @kindex \( @r{regexp operator}
11608 Only the first @samp{\( @dots{} \)} pair is relevant to the return
11609 value; additional pairs are meaningful only for grouping the regular
11610 expression operators.
11612 @kindex \+ @r{regexp operator}
11613 @kindex \? @r{regexp operator}
11614 @kindex \| @r{regexp operator}
11615 In the regular expression, @code{\+}, @code{\?}, and @code{\|} are
11616 operators which respectively match one or more, zero or one, or separate
11617 alternatives. SunOS and other @command{expr}'s treat these as regular
11618 characters. (@acronym{POSIX} allows either behavior.)
11619 @xref{Top, , Regular Expression Library, regex, Regex}, for details of
11620 regular expression syntax. Some examples are in @ref{Examples of expr}.
11622 @item match @var{string} @var{regex}
11624 An alternative way to do pattern matching. This is the same as
11625 @w{@samp{@var{string} : @var{regex}}}.
11627 @item substr @var{string} @var{position} @var{length}
11629 Returns the substring of @var{string} beginning at @var{position}
11630 with length at most @var{length}. If either @var{position} or
11631 @var{length} is negative, zero, or non-numeric, returns the null string.
11633 @item index @var{string} @var{charset}
11635 Returns the first position in @var{string} where the first character in
11636 @var{charset} was found. If no character in @var{charset} is found in
11637 @var{string}, return 0.
11639 @item length @var{string}
11641 Returns the length of @var{string}.
11643 @item + @var{token}
11645 Interpret @var{token} as a string, even if it is a keyword like @var{match}
11646 or an operator like @code{/}.
11647 This makes it possible to test @code{expr length + "$x"} or
11648 @code{expr + "$x" : '.*/\(.\)'} and have it do the right thing even if
11649 the value of @var{$x} happens to be (for example) @code{/} or @code{index}.
11650 This operator is a @acronym{GNU} extension. Portable shell scripts should use
11651 @code{@w{" $token"} : @w{' \(.*\)'}} instead of @code{+ "$token"}.
11655 To make @command{expr} interpret keywords as strings, you must use the
11656 @code{quote} operator.
11659 @node Numeric expressions
11660 @subsection Numeric expressions
11662 @cindex numeric expressions
11663 @cindex expressions, numeric
11665 @command{expr} supports the usual numeric operators, in order of increasing
11666 precedence. These numeric operators have lower precedence than the
11667 string operators described in the previous section, and higher precedence
11668 than the connectives (next section).
11676 @cindex subtraction
11677 Addition and subtraction. Both arguments are converted to integers;
11678 an error occurs if this cannot be done.
11684 @cindex multiplication
11687 Multiplication, division, remainder. Both arguments are converted to
11688 integers; an error occurs if this cannot be done.
11693 @node Relations for expr
11694 @subsection Relations for @command{expr}
11696 @cindex connectives, logical
11697 @cindex logical connectives
11698 @cindex relations, numeric or string
11700 @command{expr} supports the usual logical connectives and relations. These
11701 have lower precedence than the string and numeric operators
11702 (previous sections). Here is the list, lowest-precedence operator first.
11708 @cindex logical or operator
11709 @cindex or operator
11710 Returns its first argument if that is neither null nor zero, otherwise
11711 its second argument if it is neither null nor zero, otherwise 0. It
11712 does not evaluate its second argument if its first argument is neither
11717 @cindex logical and operator
11718 @cindex and operator
11719 Return its first argument if neither argument is null or zero, otherwise
11720 0. It does not evaluate its second argument if its first argument is
11723 @item < <= = == != >= >
11730 @cindex comparison operators
11732 Compare the arguments and return 1 if the relation is true, 0 otherwise.
11733 @code{==} is a synonym for @code{=}. @command{expr} first tries to convert
11734 both arguments to integers and do a numeric comparison; if either
11735 conversion fails, it does a lexicographic comparison using the character
11736 collating sequence specified by the @env{LC_COLLATE} locale.
11741 @node Examples of expr
11742 @subsection Examples of using @command{expr}
11744 @cindex examples of @command{expr}
11745 Here are a few examples, including quoting for shell metacharacters.
11747 To add 1 to the shell variable @code{foo}, in Bourne-compatible shells:
11750 foo=`expr $foo + 1`
11753 To print the non-directory part of the file name stored in
11754 @code{$fname}, which need not contain a @code{/}:
11757 expr $fname : '.*/\(.*\)' '|' $fname
11760 An example showing that @code{\+} is an operator:
11768 expr abc : 'a\(.\)c'
11770 expr index abcdef cz
11773 @error{} expr: syntax error
11774 expr index + index a
11780 @chapter Redirection
11782 @cindex redirection
11783 @cindex commands for redirection
11785 Unix shells commonly provide several forms of @dfn{redirection}---ways
11786 to change the input source or output destination of a command. But one
11787 useful redirection is performed by a separate command, not by the shell;
11788 it's described here.
11791 * tee invocation:: Redirect output to multiple files or processes.
11795 @node tee invocation
11796 @section @command{tee}: Redirect output to multiple files or processes
11799 @cindex pipe fitting
11800 @cindex destinations, multiple output
11801 @cindex read from stdin and write to stdout and files
11803 The @command{tee} command copies standard input to standard output and also
11804 to any files given as arguments. This is useful when you want not only
11805 to send some data down a pipe, but also to save a copy. Synopsis:
11808 tee [@var{option}]@dots{} [@var{file}]@dots{}
11811 If a file being written to does not already exist, it is created. If a
11812 file being written to already exists, the data it previously contained
11813 is overwritten unless the @option{-a} option is used.
11815 A @var{file} of @samp{-} causes @command{tee} to send another copy of
11816 input to standard output, but this is typically not that useful as the
11817 copies are interleaved.
11819 The program accepts the following options. Also see @ref{Common options}.
11826 Append standard input to the given files rather than overwriting
11830 @itemx --ignore-interrupts
11832 @opindex --ignore-interrupts
11833 Ignore interrupt signals.
11837 The @command{tee} command is useful when you happen to be transferring a large
11838 amount of data and also want to summarize that data without reading
11839 it a second time. For example, when you are downloading a DVD image,
11840 you often want to verify its signature or checksum right away.
11841 The inefficient way to do it is simply:
11844 wget http://example.com/some.iso && sha1sum some.iso
11847 One problem with the above is that it makes you wait for the
11848 download to complete before starting the time-consuming SHA1 computation.
11849 Perhaps even more importantly, the above requires reading
11850 the DVD image a second time (the first was from the network).
11852 The efficient way to do it is to interleave the download
11853 and SHA1 computation. Then, you'll get the checksum for
11854 free, because the entire process parallelizes so well:
11857 # slightly contrived, to demonstrate process substitution
11858 wget -O - http://example.com/dvd.iso \
11859 | tee >(sha1sum > dvd.sha1) > dvd.iso
11862 That makes @command{tee} write not just to the expected output file,
11863 but also to a pipe running @command{sha1sum} and saving the final
11864 checksum in a file named @file{dvd.sha1}.
11866 Note, however, that this example relies on a feature of modern shells
11867 called @dfn{process substitution}
11868 (the @samp{>(command)} syntax, above;
11869 @xref{Process Substitution,,Process Substitution, bashref,
11870 The Bash Reference Manual}.),
11871 so it works with @command{zsh}, @command{bash}, and @command{ksh},
11872 but not with @command{/bin/sh}. So if you write code like this
11873 in a shell script, be sure to start the script with @samp{#!/bin/bash}.
11875 Since the above example writes to one file and one process,
11876 a more conventional and portable use of @command{tee} is even better:
11879 wget -O - http://example.com/dvd.iso \
11880 | tee dvd.iso | sha1sum > dvd.sha1
11883 You can extend this example to make @command{tee} write to two processes,
11884 computing MD5 and SHA1 checksums in parallel. In this case,
11885 process substitution is required:
11888 wget -O - http://example.com/dvd.iso \
11889 | tee >(sha1sum > dvd.sha1) \
11890 >(md5sum > dvd.md5) \
11894 This technique is also useful when you want to make a @emph{compressed}
11895 copy of the contents of a pipe.
11896 Consider a tool to graphically summarize disk usage data from @samp{du -ak}.
11897 For a large hierarchy, @samp{du -ak} can run for a long time,
11898 and can easily produce terabytes of data, so you won't want to
11899 rerun the command unnecessarily. Nor will you want to save
11900 the uncompressed output.
11902 Doing it the inefficient way, you can't even start the GUI
11903 until after you've compressed all of the @command{du} output:
11906 du -ak | gzip -9 > /tmp/du.gz
11907 gzip -d /tmp/du.gz | xdiskusage -a
11910 With @command{tee} and process substitution, you start the GUI
11911 right away and eliminate the decompression completely:
11914 du -ak | tee >(gzip -9 > /tmp/du.gz) | xdiskusage -a
11917 Finally, if you regularly create more than one type of
11918 compressed tarball at once, for example when @code{make dist} creates
11919 both @command{gzip}-compressed and @command{bzip2}-compressed tarballs,
11920 there may be a better way.
11921 Typical @command{automake}-generated @file{Makefile} rules create
11922 the two compressed tar archives with commands in sequence, like this
11923 (slightly simplified):
11926 tardir=your-pkg-M.N
11927 tar chof - "$tardir" | gzip -9 -c > your-pkg-M.N.tar.gz
11928 tar chof - "$tardir" | bzip2 -9 -c > your-pkg-M.N.tar.bz2
11931 However, if the hierarchy you are archiving and compressing is larger
11932 than a couple megabytes, and especially if you are using a multi-processor
11933 system with plenty of memory, then you can do much better by reading the
11934 directory contents only once and running the compression programs in parallel:
11937 tardir=your-pkg-M.N
11938 tar chof - "$tardir" \
11939 | tee >(gzip -9 -c > your-pkg-M.N.tar.gz) \
11940 | bzip2 -9 -c > your-pkg-M.N.tar.bz2
11946 @node File name manipulation
11947 @chapter File name manipulation
11949 @cindex file name manipulation
11950 @cindex manipulation of file names
11951 @cindex commands for file name manipulation
11953 This section describes commands that manipulate file names.
11956 * basename invocation:: Strip directory and suffix from a file name.
11957 * dirname invocation:: Strip last file name component.
11958 * pathchk invocation:: Check file name validity and portability.
11959 * mktemp invocation:: Create temporary file or directory.
11963 @node basename invocation
11964 @section @command{basename}: Strip directory and suffix from a file name
11967 @cindex strip directory and suffix from file names
11968 @cindex directory, stripping from file names
11969 @cindex suffix, stripping from file names
11970 @cindex file names, stripping directory and suffix
11971 @cindex leading directory components, stripping
11973 @command{basename} removes any leading directory components from
11974 @var{name}. Synopsis:
11977 basename @var{name} [@var{suffix}]
11980 If @var{suffix} is specified and is identical to the end of @var{name},
11981 it is removed from @var{name} as well. Note that since trailing slashes
11982 are removed prior to suffix matching, @var{suffix} will do nothing if it
11983 contains slashes. @command{basename} prints the result on standard
11986 @c This test is used both here and in the section on dirname.
11987 @macro basenameAndDirname
11988 Together, @command{basename} and @command{dirname} are designed such
11989 that if @samp{ls "$name"} succeeds, then the command sequence @samp{cd
11990 "$(dirname "$name")"; ls "$(basename "$name")"} will, too. This works
11991 for everything except file names containing a trailing newline.
11993 @basenameAndDirname
11995 @acronym{POSIX} allows the implementation to define the results if
11996 @var{name} is empty or @samp{//}. In the former case, @acronym{GNU}
11997 @command{basename} returns the empty string. In the latter case, the
11998 result is @samp{//} on platforms where @var{//} is distinct from
11999 @var{/}, and @samp{/} on platforms where there is no difference.
12001 The only options are @option{--help} and @option{--version}. @xref{Common
12002 options}. Options must precede operands.
12010 basename /usr/bin/sort
12013 basename include/stdio.h .h
12017 @node dirname invocation
12018 @section @command{dirname}: Strip last file name component
12021 @cindex directory components, printing
12022 @cindex stripping non-directory suffix
12023 @cindex non-directory suffix, stripping
12025 @command{dirname} prints all but the final slash-delimited component of
12026 @var{name}. Slashes on either side of the final component are also
12027 removed. If the string contains no slash, @command{dirname} prints
12028 @samp{.} (meaning the current directory). Synopsis:
12034 @var{name} need not be a file name, but if it is, this operation
12035 effectively lists the directory that contains the final component,
12036 including the case when the final component is itself a directory.
12038 @basenameAndDirname
12040 @acronym{POSIX} allows the implementation to define the results if
12041 @var{name} is @samp{//}. With @acronym{GNU} @command{dirname}, the
12042 result is @samp{//} on platforms where @var{//} is distinct from
12043 @var{/}, and @samp{/} on platforms where there is no difference.
12045 The only options are @option{--help} and @option{--version}. @xref{Common
12053 # Output "/usr/bin".
12054 dirname /usr/bin/sort
12055 dirname /usr/bin//.//
12062 @node pathchk invocation
12063 @section @command{pathchk}: Check file name validity and portability
12066 @cindex file names, checking validity and portability
12067 @cindex valid file names, checking for
12068 @cindex portable file names, checking for
12070 @command{pathchk} checks validity and portability of file names. Synopsis:
12073 pathchk [@var{option}]@dots{} @var{name}@dots{}
12076 For each @var{name}, @command{pathchk} prints an error message if any of
12077 these conditions is true:
12081 One of the existing directories in @var{name} does not have search
12082 (execute) permission,
12084 The length of @var{name} is larger than the maximum supported by the
12087 The length of one component of @var{name} is longer than
12088 its file system's maximum.
12091 A nonexistent @var{name} is not an error, so long a file with that
12092 name could be created under the above conditions.
12094 The program accepts the following options. Also see @ref{Common options}.
12095 Options must precede operands.
12101 Instead of performing checks based on the underlying file system,
12102 print an error message if any of these conditions is true:
12106 A file name is empty.
12109 A file name contains a character outside the @acronym{POSIX} portable file
12110 name character set, namely, the ASCII letters and digits, @samp{.},
12111 @samp{_}, @samp{-}, and @samp{/}.
12114 The length of a file name or one of its components exceeds the
12115 @acronym{POSIX} minimum limits for portability.
12120 Print an error message if a file name is empty, or if it contains a component
12121 that begins with @samp{-}.
12123 @item --portability
12124 @opindex --portability
12125 Print an error message if a file name is not portable to all @acronym{POSIX}
12126 hosts. This option is equivalent to @samp{-p -P}.
12130 @cindex exit status of @command{pathchk}
12134 0 if all specified file names passed all checks,
12138 @node mktemp invocation
12139 @section @command{mktemp}: Create temporary file or directory
12142 @cindex file names, creating temporary
12143 @cindex directory, creating temporary
12144 @cindex temporary files and directories
12146 @command{mktemp} manages the creation of temporary files and
12147 directories. Synopsis:
12150 mktemp [@var{option}]@dots{} [@var{template}]
12153 Safely create a temporary file or directory based on @var{template},
12154 and print its name. If given, @var{template} must include at least
12155 three consecutive @samp{X}s in the last component. If omitted, the template
12156 @samp{tmp.XXXXXXXXXX} is used, and option @option{--tmpdir} is
12157 implied. The final run of @samp{X}s in the @var{template} will be replaced
12158 by alpha-numeric characters; thus, on a case-sensitive file system,
12159 and with a @var{template} including a run of @var{n} instances of @samp{X},
12160 there are @samp{62**@var{n}} potential file names.
12162 Older scripts used to create temporary files by simply joining the
12163 name of the program with the process id (@samp{$$}) as a suffix.
12164 However, that naming scheme is easily predictable, and suffers from a
12165 race condition where the attacker can create an appropriately named
12166 symbolic link, such that when the script then opens a handle to what
12167 it thought was an unused file, it is instead modifying an existing
12168 file. Using the same scheme to create a directory is slightly safer,
12169 since the @command{mkdir} will fail if the target already exists, but
12170 it is still inferior because it allows for denial of service attacks.
12171 Therefore, modern scripts should use the @command{mktemp} command to
12172 guarantee that the generated name will be unpredictable, and that
12173 knowledge of the temporary file name implies that the file was created
12174 by the current script and cannot be modified by other users.
12176 When creating a file, the resulting file has read and write
12177 permissions for the current user, but no permissions for the group or
12178 others; these permissions are reduced if the current umask is more
12181 Here are some examples (although note that if you repeat them, you
12182 will most likely get different file names):
12187 Create a temporary file in the current directory.
12194 Create a temporary file with a known suffix.
12196 $ mktemp --suffix=.txt file-XXXX
12198 $ mktemp file-XXXX-XXXX.txt
12203 Create a secure fifo relative to the user's choice of @env{TMPDIR},
12204 but falling back to the current directory rather than @file{/tmp}.
12205 Note that @command{mktemp} does not create fifos, but can create a
12206 secure directory in which the fifo can live. Exit the shell if the
12207 directory or fifo could not be created.
12209 $ dir=$(mktemp -p "$@{TMPDIR:-.@}" -d dir-XXXX) || exit 1
12211 $ mkfifo "$fifo" || @{ rmdir "$dir"; exit 1; @}
12215 Create and use a temporary file if possible, but ignore failure. The
12216 file will reside in the directory named by @env{TMPDIR}, if specified,
12217 or else in @file{/tmp}.
12219 $ file=$(mktemp -q) && @{
12220 > # Safe to use $file only within this block. Use quotes,
12221 > # since $TMPDIR, and thus $file, may contain whitespace.
12222 > echo ... > "$file"
12228 Act as a semi-random character generator (it is not fully random,
12229 since it is impacted by the contents of the current directory). To
12230 avoid security holes, do not use the resulting names to create a file.
12240 The program accepts the following options. Also see @ref{Common options}.
12247 @opindex --directory
12248 Create a directory rather than a file. The directory will have read,
12249 write, and search permissions for the current user, but no permissions
12250 for the group or others; these permissions are reduced if the current
12251 umask is more restrictive.
12257 Suppress diagnostics about failure to create a file or directory. The
12258 exit status will still reflect whether a file was created.
12264 Generate a temporary name that does not name an existing file, without
12265 changing the file system contents. Using the output of this command
12266 to create a new file is inherently unsafe, as there is a window of
12267 time between generating the name and using it where another process
12268 can create an object by the same name.
12271 @itemx --tmpdir[=@var{dir}]
12274 Treat @var{template} relative to the directory @var{dir}. If
12275 @var{dir} is not specified (only possible with the long option
12276 @option{--tmpdir}) or is the empty string, use the value of
12277 @env{TMPDIR} if available, otherwise use @samp{/tmp}. If this is
12278 specified, @var{template} must not be absolute. However,
12279 @var{template} can still contain slashes, although intermediate
12280 directories must already exist.
12282 @item --suffix=@var{suffix}
12284 Append @var{suffix} to the @var{template}. @var{suffix} must not
12285 contain slash. If @option{--suffix} is specified, @var{template} must
12286 end in @samp{X}; if it is not specified, then an appropriate
12287 @option{--suffix} is inferred by finding the last @samp{X} in
12288 @var{template}. This option exists for use with the default
12289 @var{template} and for the creation of a @var{suffix} that starts with
12294 Treat @var{template} as a single file relative to the value of
12295 @env{TMPDIR} if available, or to the directory specified by
12296 @option{-p}, otherwise to @samp{/tmp}. @var{template} must not
12297 contain slashes. This option is deprecated; the use of @option{-p}
12298 without @option{-t} offers better defaults (by favoring the command
12299 line over @env{TMPDIR}) and more flexibility (by allowing intermediate
12304 @cindex exit status of @command{mktemp}
12308 0 if the file was created,
12313 @node Working context
12314 @chapter Working context
12316 @cindex working context
12317 @cindex commands for printing the working context
12319 This section describes commands that display or alter the context in
12320 which you are working: the current directory, the terminal settings, and
12321 so forth. See also the user-related commands in the next section.
12324 * pwd invocation:: Print working directory.
12325 * stty invocation:: Print or change terminal characteristics.
12326 * printenv invocation:: Print environment variables.
12327 * tty invocation:: Print file name of terminal on standard input.
12331 @node pwd invocation
12332 @section @command{pwd}: Print working directory
12335 @cindex print name of current directory
12336 @cindex current working directory, printing
12337 @cindex working directory, printing
12340 @command{pwd} prints the name of the current directory. Synopsis:
12343 pwd [@var{option}]@dots{}
12346 The program accepts the following options. Also see @ref{Common options}.
12353 If the contents of the environment variable @env{PWD} provide an
12354 absolute name of the current directory with no @samp{.} or @samp{..}
12355 components, but possibly with symbolic links, then output those
12356 contents. Otherwise, fall back to default @option{-P} handling.
12361 @opindex --physical
12362 Print a fully resolved name for the current directory. That is, all
12363 components of the printed name will be actual directory names---none
12364 will be symbolic links.
12367 @cindex symbolic links and @command{pwd}
12368 If @option{-L} and @option{-P} are both given, the last one takes
12369 precedence. If neither option is given, then this implementation uses
12370 @option{-P} as the default unless the @env{POSIXLY_CORRECT}
12371 environment variable is set.
12373 @mayConflictWithShellBuiltIn{pwd}
12378 @node stty invocation
12379 @section @command{stty}: Print or change terminal characteristics
12382 @cindex change or print terminal settings
12383 @cindex terminal settings
12384 @cindex line settings of terminal
12386 @command{stty} prints or changes terminal characteristics, such as baud rate.
12390 stty [@var{option}] [@var{setting}]@dots{}
12391 stty [@var{option}]
12394 If given no line settings, @command{stty} prints the baud rate, line
12395 discipline number (on systems that support it), and line settings
12396 that have been changed from the values set by @samp{stty sane}.
12397 By default, mode reading and setting are performed on the tty line
12398 connected to standard input, although this can be modified by the
12399 @option{--file} option.
12401 @command{stty} accepts many non-option arguments that change aspects of
12402 the terminal line operation, as described below.
12404 The program accepts the following options. Also see @ref{Common options}.
12411 Print all current settings in human-readable form. This option may not
12412 be used in combination with any line settings.
12414 @item -F @var{device}
12415 @itemx --file=@var{device}
12418 Set the line opened by the file name specified in @var{device} instead of
12419 the tty line connected to standard input. This option is necessary
12420 because opening a @acronym{POSIX} tty requires use of the @code{O_NONDELAY} flag to
12421 prevent a @acronym{POSIX} tty from blocking until the carrier detect line is high if
12422 the @code{clocal} flag is not set. Hence, it is not always possible
12423 to allow the shell to open the device in the traditional manner.
12429 @cindex machine-readable @command{stty} output
12430 Print all current settings in a form that can be used as an argument to
12431 another @command{stty} command to restore the current settings. This option
12432 may not be used in combination with any line settings.
12436 Many settings can be turned off by preceding them with a @samp{-}.
12437 Such arguments are marked below with ``May be negated'' in their
12438 description. The descriptions themselves refer to the positive
12439 case, that is, when @emph{not} negated (unless stated otherwise,
12442 Some settings are not available on all @acronym{POSIX} systems, since they use
12443 extensions. Such arguments are marked below with ``Non-@acronym{POSIX}'' in their
12444 description. On non-@acronym{POSIX} systems, those or other settings also may not
12445 be available, but it's not feasible to document all the variations: just
12451 * Control:: Control settings
12452 * Input:: Input settings
12453 * Output:: Output settings
12454 * Local:: Local settings
12455 * Combination:: Combination settings
12456 * Characters:: Special characters
12457 * Special:: Special settings
12462 @subsection Control settings
12464 @cindex control settings
12470 @cindex two-way parity
12471 Generate parity bit in output and expect parity bit in input.
12477 @cindex even parity
12478 Set odd parity (even if negated). May be negated.
12485 @cindex character size
12486 @cindex eight-bit characters
12487 Set character size to 5, 6, 7, or 8 bits.
12492 Send a hangup signal when the last process closes the tty. May be
12498 Use two stop bits per character (one if negated). May be negated.
12502 Allow input to be received. May be negated.
12506 @cindex modem control
12507 Disable modem control signals. May be negated.
12511 @cindex hardware flow control
12512 @cindex flow control, hardware
12513 @cindex RTS/CTS flow control
12514 Enable RTS/CTS flow control. Non-@acronym{POSIX}. May be negated.
12519 @subsection Input settings
12521 @cindex input settings
12522 These settings control operations on data received from the terminal.
12527 @cindex breaks, ignoring
12528 Ignore break characters. May be negated.
12532 @cindex breaks, cause interrupts
12533 Make breaks cause an interrupt signal. May be negated.
12537 @cindex parity, ignoring
12538 Ignore characters with parity errors. May be negated.
12542 @cindex parity errors, marking
12543 Mark parity errors (with a 255-0-character sequence). May be negated.
12547 Enable input parity checking. May be negated.
12551 @cindex eight-bit input
12552 Clear high (8th) bit of input characters. May be negated.
12556 @cindex newline, translating to return
12557 Translate newline to carriage return. May be negated.
12561 @cindex return, ignoring
12562 Ignore carriage return. May be negated.
12566 @cindex return, translating to newline
12567 Translate carriage return to newline. May be negated.
12571 @cindex input encoding, UTF-8
12572 Assume input characters are UTF-8 encoded. May be negated.
12576 @kindex C-s/C-q flow control
12577 @cindex XON/XOFF flow control
12578 Enable XON/XOFF flow control (that is, @kbd{CTRL-S}/@kbd{CTRL-Q}). May
12585 @cindex software flow control
12586 @cindex flow control, software
12587 Enable sending of @code{stop} character when the system input buffer
12588 is almost full, and @code{start} character when it becomes almost
12589 empty again. May be negated.
12593 @cindex uppercase, translating to lowercase
12594 Translate uppercase characters to lowercase. Non-@acronym{POSIX}. May be
12595 negated. Note ilcuc is not implemented, as one would not be able to issue
12596 almost any (lowercase) Unix command, after invoking it.
12600 Allow any character to restart output (only the start character
12601 if negated). Non-@acronym{POSIX}. May be negated.
12605 @cindex beeping at input buffer full
12606 Enable beeping and not flushing input buffer if a character arrives
12607 when the input buffer is full. Non-@acronym{POSIX}. May be negated.
12612 @subsection Output settings
12614 @cindex output settings
12615 These settings control operations on data sent to the terminal.
12620 Postprocess output. May be negated.
12624 @cindex lowercase, translating to output
12625 Translate lowercase characters to uppercase. Non-@acronym{POSIX}. May be
12626 negated. (Note ouclc is not currently implemented.)
12630 @cindex return, translating to newline
12631 Translate carriage return to newline. Non-@acronym{POSIX}. May be negated.
12635 @cindex newline, translating to crlf
12636 Translate newline to carriage return-newline. Non-@acronym{POSIX}. May be
12641 Do not print carriage returns in the first column. Non-@acronym{POSIX}.
12646 Newline performs a carriage return. Non-@acronym{POSIX}. May be negated.
12650 @cindex pad instead of timing for delaying
12651 Use fill (padding) characters instead of timing for delays. Non-@acronym{POSIX}.
12656 @cindex pad character
12657 Use @acronym{ASCII} @sc{del} characters for fill instead of
12658 @acronym{ASCII} @sc{nul} characters. Non-@acronym{POSIX}.
12664 Newline delay style. Non-@acronym{POSIX}.
12671 Carriage return delay style. Non-@acronym{POSIX}.
12677 @opindex tab@var{n}
12678 Horizontal tab delay style. Non-@acronym{POSIX}.
12683 Backspace delay style. Non-@acronym{POSIX}.
12688 Vertical tab delay style. Non-@acronym{POSIX}.
12693 Form feed delay style. Non-@acronym{POSIX}.
12698 @subsection Local settings
12700 @cindex local settings
12705 Enable @code{interrupt}, @code{quit}, and @code{suspend} special
12706 characters. May be negated.
12710 Enable @code{erase}, @code{kill}, @code{werase}, and @code{rprnt}
12711 special characters. May be negated.
12715 Enable non-@acronym{POSIX} special characters. May be negated.
12719 Echo input characters. May be negated.
12725 Echo @code{erase} characters as backspace-space-backspace. May be
12730 @cindex newline echoing after @code{kill}
12731 Echo a newline after a @code{kill} character. May be negated.
12735 @cindex newline, echoing
12736 Echo newline even if not echoing other characters. May be negated.
12740 @cindex flushing, disabling
12741 Disable flushing after @code{interrupt} and @code{quit} special
12742 characters. May be negated.
12746 @cindex case translation
12747 Enable input and output of uppercase characters by preceding their
12748 lowercase equivalents with @samp{\}, when @code{icanon} is set.
12749 Non-@acronym{POSIX}. May be negated.
12753 @cindex background jobs, stopping at terminal write
12754 Stop background jobs that try to write to the terminal. Non-@acronym{POSIX}.
12761 Echo erased characters backward, between @samp{\} and @samp{/}.
12762 Non-@acronym{POSIX}. May be negated.
12768 @cindex control characters, using @samp{^@var{c}}
12769 @cindex hat notation for control characters
12770 Echo control characters in hat notation (@samp{^@var{c}}) instead
12771 of literally. Non-@acronym{POSIX}. May be negated.
12777 Echo the @code{kill} special character by erasing each character on
12778 the line as indicated by the @code{echoprt} and @code{echoe} settings,
12779 instead of by the @code{echoctl} and @code{echok} settings. Non-@acronym{POSIX}.
12785 @subsection Combination settings
12787 @cindex combination settings
12788 Combination settings:
12795 Same as @code{parenb -parodd cs7}. May be negated. If negated, same
12796 as @code{-parenb cs8}.
12800 Same as @code{parenb parodd cs7}. May be negated. If negated, same
12801 as @code{-parenb cs8}.
12805 Same as @code{-icrnl -onlcr}. May be negated. If negated, same as
12806 @code{icrnl -inlcr -igncr onlcr -ocrnl -onlret}.
12810 Reset the @code{erase} and @code{kill} special characters to their default
12817 @c This is too long to write inline.
12819 cread -ignbrk brkint -inlcr -igncr icrnl -ixoff
12820 -iuclc -ixany imaxbel opost -olcuc -ocrnl onlcr
12821 -onocr -onlret -ofill -ofdel nl0 cr0 tab0 bs0 vt0
12822 ff0 isig icanon iexten echo echoe echok -echonl
12823 -noflsh -xcase -tostop -echoprt echoctl echoke
12827 and also sets all special characters to their default values.
12831 Same as @code{brkint ignpar istrip icrnl ixon opost isig icanon}, plus
12832 sets the @code{eof} and @code{eol} characters to their default values
12833 if they are the same as the @code{min} and @code{time} characters.
12834 May be negated. If negated, same as @code{raw}.
12841 -ignbrk -brkint -ignpar -parmrk -inpck -istrip
12842 -inlcr -igncr -icrnl -ixon -ixoff -iuclc -ixany
12843 -imaxbel -opost -isig -icanon -xcase min 1 time 0
12847 May be negated. If negated, same as @code{cooked}.
12851 Same as @option{-icanon}. May be negated. If negated, same as
12856 @cindex eight-bit characters
12857 Same as @code{-parenb -istrip cs8}. May be negated. If negated,
12858 same as @code{parenb istrip cs7}.
12862 Same as @option{-parenb -istrip -opost cs8}. May be negated.
12863 If negated, same as @code{parenb istrip opost cs7}.
12867 Same as @option{-ixany}. Non-@acronym{POSIX}. May be negated.
12871 Same as @code{tab0}. Non-@acronym{POSIX}. May be negated. If negated, same
12878 Same as @code{xcase iuclc olcuc}. Non-@acronym{POSIX}. May be negated.
12879 (Used for terminals with uppercase characters only.)
12883 Same as @code{echoe echoctl echoke}.
12887 Same as @code{echoe echoctl echoke -ixany intr ^C erase ^? kill C-u}.
12892 @subsection Special characters
12894 @cindex special characters
12895 @cindex characters, special
12897 The special characters' default values vary from system to system.
12898 They are set with the syntax @samp{name value}, where the names are
12899 listed below and the value can be given either literally, in hat
12900 notation (@samp{^@var{c}}), or as an integer which may start with
12901 @samp{0x} to indicate hexadecimal, @samp{0} to indicate octal, or
12902 any other digit to indicate decimal.
12904 @cindex disabling special characters
12905 @kindex u@r{, and disabling special characters}
12906 For GNU stty, giving a value of @code{^-} or @code{undef} disables that
12907 special character. (This is incompatible with Ultrix @command{stty},
12908 which uses a value of @samp{u} to disable a special character. GNU
12909 @command{stty} treats a value @samp{u} like any other, namely to set that
12910 special character to @key{U}.)
12916 Send an interrupt signal.
12920 Send a quit signal.
12924 Erase the last character typed.
12928 Erase the current line.
12932 Send an end of file (terminate the input).
12940 Alternate character to end the line. Non-@acronym{POSIX}.
12944 Switch to a different shell layer. Non-@acronym{POSIX}.
12948 Restart the output after stopping it.
12956 Send a terminal stop signal.
12960 Send a terminal stop signal after flushing the input. Non-@acronym{POSIX}.
12964 Redraw the current line. Non-@acronym{POSIX}.
12968 Erase the last word typed. Non-@acronym{POSIX}.
12972 Enter the next character typed literally, even if it is a special
12973 character. Non-@acronym{POSIX}.
12978 @subsection Special settings
12980 @cindex special settings
12985 Set the minimum number of characters that will satisfy a read until
12986 the time value has expired, when @option{-icanon} is set.
12990 Set the number of tenths of a second before reads time out if the minimum
12991 number of characters have not been read, when @option{-icanon} is set.
12993 @item ispeed @var{n}
12995 Set the input speed to @var{n}.
12997 @item ospeed @var{n}
12999 Set the output speed to @var{n}.
13003 Tell the tty kernel driver that the terminal has @var{n} rows. Non-@acronym{POSIX}.
13006 @itemx columns @var{n}
13009 Tell the kernel that the terminal has @var{n} columns. Non-@acronym{POSIX}.
13015 Print the number of rows and columns that the kernel thinks the
13016 terminal has. (Systems that don't support rows and columns in the kernel
13017 typically use the environment variables @env{LINES} and @env{COLUMNS}
13018 instead; however, GNU @command{stty} does not know anything about them.)
13019 Non-@acronym{POSIX}.
13023 Use line discipline @var{n}. Non-@acronym{POSIX}.
13027 Print the terminal speed.
13030 @cindex baud rate, setting
13031 Set the input and output speeds to @var{n}. @var{n} can be one of: 0
13032 50 75 110 134 134.5 150 200 300 600 1200 1800 2400 4800 9600 19200
13033 38400 @code{exta} @code{extb}. @code{exta} is the same as 19200;
13034 @code{extb} is the same as 38400. Many systems, including GNU/Linux,
13035 support higher speeds. The @command{stty} command includes support
13052 4000000 where the system supports these.
13053 0 hangs up the line if @option{-clocal} is set.
13057 @node printenv invocation
13058 @section @command{printenv}: Print all or some environment variables
13061 @cindex printing all or some environment variables
13062 @cindex environment variables, printing
13064 @command{printenv} prints environment variable values. Synopsis:
13067 printenv [@var{option}] [@var{variable}]@dots{}
13070 If no @var{variable}s are specified, @command{printenv} prints the value of
13071 every environment variable. Otherwise, it prints the value of each
13072 @var{variable} that is set, and nothing for those that are not set.
13074 The program accepts the following option. Also see @ref{Common options}.
13082 @cindex exit status of @command{printenv}
13086 0 if all variables specified were found
13087 1 if at least one specified variable was not found
13088 2 if a write error occurred
13092 @node tty invocation
13093 @section @command{tty}: Print file name of terminal on standard input
13096 @cindex print terminal file name
13097 @cindex terminal file name, printing
13099 @command{tty} prints the file name of the terminal connected to its standard
13100 input. It prints @samp{not a tty} if standard input is not a terminal.
13104 tty [@var{option}]@dots{}
13107 The program accepts the following option. Also see @ref{Common options}.
13117 Print nothing; only return an exit status.
13121 @cindex exit status of @command{tty}
13125 0 if standard input is a terminal
13126 1 if standard input is not a terminal
13127 2 if given incorrect arguments
13128 3 if a write error occurs
13132 @node User information
13133 @chapter User information
13135 @cindex user information, commands for
13136 @cindex commands for printing user information
13138 This section describes commands that print user-related information:
13139 logins, groups, and so forth.
13142 * id invocation:: Print user identity.
13143 * logname invocation:: Print current login name.
13144 * whoami invocation:: Print effective user ID.
13145 * groups invocation:: Print group names a user is in.
13146 * users invocation:: Print login names of users currently logged in.
13147 * who invocation:: Print who is currently logged in.
13151 @node id invocation
13152 @section @command{id}: Print user identity
13155 @cindex real user and group IDs, printing
13156 @cindex effective user and group IDs, printing
13157 @cindex printing real and effective user and group IDs
13159 @command{id} prints information about the given user, or the process
13160 running it if no user is specified. Synopsis:
13163 id [@var{option}]@dots{} [@var{username}]
13166 @vindex POSIXLY_CORRECT
13167 By default, it prints the real user ID, real group ID, effective user ID
13168 if different from the real user ID, effective group ID if different from
13169 the real group ID, and supplemental group IDs.
13170 In addition, if SELinux
13171 is enabled and the @env{POSIXLY_CORRECT} environment variable is not set,
13172 then print @samp{context=@var{c}}, where @var{c} is the security context.
13174 Each of these numeric values is preceded by an identifying string and
13175 followed by the corresponding user or group name in parentheses.
13177 The options cause @command{id} to print only part of the above information.
13178 Also see @ref{Common options}.
13185 Print only the group ID.
13191 Print only the group ID and the supplementary groups.
13197 Print the user or group name instead of the ID number. Requires
13198 @option{-u}, @option{-g}, or @option{-G}.
13204 Print the real, instead of effective, user or group ID. Requires
13205 @option{-u}, @option{-g}, or @option{-G}.
13211 Print only the user ID.
13218 @cindex security context
13219 Print only the security context of the current user.
13220 If SELinux is disabled then print a warning and
13221 set the exit status to 1.
13227 @macro primaryAndSupplementaryGroups{cmd,arg}
13228 Primary and supplementary groups for a process are normally inherited
13229 from its parent and are usually unchanged since login. This means
13230 that if you change the group database after logging in, @command{\cmd\}
13231 will not reflect your changes within your existing login session.
13232 Running @command{\cmd\} with a \arg\ causes the user and group
13233 database to be consulted afresh, and so will give a different result.
13235 @primaryAndSupplementaryGroups{id,user argument}
13237 @node logname invocation
13238 @section @command{logname}: Print current login name
13241 @cindex printing user's login name
13242 @cindex login name, printing
13243 @cindex user name, printing
13246 @command{logname} prints the calling user's name, as found in a
13247 system-maintained file (often @file{/var/run/utmp} or
13248 @file{/etc/utmp}), and exits with a status of 0. If there is no entry
13249 for the calling process, @command{logname} prints
13250 an error message and exits with a status of 1.
13252 The only options are @option{--help} and @option{--version}. @xref{Common
13258 @node whoami invocation
13259 @section @command{whoami}: Print effective user ID
13262 @cindex effective user ID, printing
13263 @cindex printing the effective user ID
13265 @command{whoami} prints the user name associated with the current
13266 effective user ID. It is equivalent to the command @samp{id -un}.
13268 The only options are @option{--help} and @option{--version}. @xref{Common
13274 @node groups invocation
13275 @section @command{groups}: Print group names a user is in
13278 @cindex printing groups a user is in
13279 @cindex supplementary groups, printing
13281 @command{groups} prints the names of the primary and any supplementary
13282 groups for each given @var{username}, or the current process if no names
13283 are given. If more than one name is given, the name of each user is
13285 the list of that user's groups and the user name is separated from the
13286 group list by a colon. Synopsis:
13289 groups [@var{username}]@dots{}
13292 The group lists are equivalent to the output of the command @samp{id -Gn}.
13294 @primaryAndSupplementaryGroups{groups,list of users}
13296 The only options are @option{--help} and @option{--version}. @xref{Common
13302 @node users invocation
13303 @section @command{users}: Print login names of users currently logged in
13306 @cindex printing current usernames
13307 @cindex usernames, printing current
13309 @cindex login sessions, printing users with
13310 @command{users} prints on a single line a blank-separated list of user
13311 names of users currently logged in to the current host. Each user name
13312 corresponds to a login session, so if a user has more than one login
13313 session, that user's name will appear the same number of times in the
13322 With no @var{file} argument, @command{users} extracts its information from
13323 a system-maintained file (often @file{/var/run/utmp} or
13324 @file{/etc/utmp}). If a file argument is given, @command{users} uses
13325 that file instead. A common choice is @file{/var/log/wtmp}.
13327 The only options are @option{--help} and @option{--version}. @xref{Common
13333 @node who invocation
13334 @section @command{who}: Print who is currently logged in
13337 @cindex printing current user information
13338 @cindex information, about current users
13340 @command{who} prints information about users who are currently logged on.
13344 @command{who} [@var{option}] [@var{file}] [am i]
13347 @cindex terminal lines, currently used
13349 @cindex remote hostname
13350 If given no non-option arguments, @command{who} prints the following
13351 information for each user currently logged on: login name, terminal
13352 line, login time, and remote hostname or X display.
13356 If given one non-option argument, @command{who} uses that instead of
13357 a default system-maintained file (often @file{/var/run/utmp} or
13358 @file{/etc/utmp}) as the name of the file containing the record of
13359 users logged on. @file{/var/log/wtmp} is commonly given as an argument
13360 to @command{who} to look at who has previously logged on.
13364 If given two non-option arguments, @command{who} prints only the entry
13365 for the user running it (determined from its standard input), preceded
13366 by the hostname. Traditionally, the two arguments given are @samp{am
13367 i}, as in @samp{who am i}.
13370 Time stamps are listed according to the time zone rules specified by
13371 the @env{TZ} environment variable, or by the system default rules if
13372 @env{TZ} is not set. @xref{TZ Variable,, Specifying the Time Zone
13373 with @env{TZ}, libc, The GNU C Library Reference Manual}.
13375 The program accepts the following options. Also see @ref{Common options}.
13383 Same as @samp{-b -d --login -p -r -t -T -u}.
13389 Print the date and time of last system boot.
13395 Print information corresponding to dead processes.
13401 Print a line of column headings.
13407 List only the entries that correspond to processes via which the
13408 system is waiting for a user to login. The user name is always @samp{LOGIN}.
13412 Attempt to canonicalize hostnames found in utmp through a DNS lookup. This
13413 is not the default because it can cause significant delays on systems with
13414 automatic dial-up internet access.
13418 Same as @samp{who am i}.
13424 List active processes spawned by init.
13430 Print only the login names and the number of users logged on.
13431 Overrides all other options.
13436 @opindex --runlevel
13437 Print the current (and maybe previous) run-level of the init process.
13441 Ignored; for compatibility with other versions of @command{who}.
13447 Print last system clock change.
13452 After the login time, print the number of hours and minutes that the
13453 user has been idle. @samp{.} means the user was active in the last minute.
13454 @samp{old} means the user has been idle for more than 24 hours.
13465 @opindex --writable
13466 @cindex message status
13467 @pindex write@r{, allowed}
13468 After each login name print a character indicating the user's message status:
13471 @samp{+} allowing @code{write} messages
13472 @samp{-} disallowing @code{write} messages
13473 @samp{?} cannot find terminal device
13481 @node System context
13482 @chapter System context
13484 @cindex system context
13485 @cindex context, system
13486 @cindex commands for system context
13488 This section describes commands that print or change system-wide
13492 * date invocation:: Print or set system date and time.
13493 * arch invocation:: Print machine hardware name.
13494 * nproc invocation:: Print the number of processors.
13495 * uname invocation:: Print system information.
13496 * hostname invocation:: Print or set system name.
13497 * hostid invocation:: Print numeric host identifier.
13498 * uptime invocation:: Print system uptime and load.
13501 @node date invocation
13502 @section @command{date}: Print or set system date and time
13505 @cindex time, printing or setting
13506 @cindex printing the current time
13511 date [@var{option}]@dots{} [+@var{format}]
13512 date [-u|--utc|--universal] @c this avoids a newline in the output
13513 [ MMDDhhmm[[CC]YY][.ss] ]
13517 Invoking @command{date} with no @var{format} argument is equivalent to invoking
13518 it with a default format that depends on the @env{LC_TIME} locale category.
13519 In the default C locale, this format is @samp{'+%a %b %e %H:%M:%S %Z %Y'},
13520 so the output looks like @samp{Thu Mar @ 3 13:47:51 PST 2005}.
13523 Normally, @command{date} uses the time zone rules indicated by the
13524 @env{TZ} environment variable, or the system default rules if @env{TZ}
13525 is not set. @xref{TZ Variable,, Specifying the Time Zone with
13526 @env{TZ}, libc, The GNU C Library Reference Manual}.
13528 @findex strftime @r{and @command{date}}
13529 @cindex time formats
13530 @cindex formatting times
13531 If given an argument that starts with a @samp{+}, @command{date} prints the
13532 current date and time (or the date and time specified by the
13533 @option{--date} option, see below) in the format defined by that argument,
13534 which is similar to that of the @code{strftime} function. Except for
13535 conversion specifiers, which start with @samp{%}, characters in the
13536 format string are printed unchanged. The conversion specifiers are
13542 * Time conversion specifiers:: %[HIklMNpPrRsSTXzZ]
13543 * Date conversion specifiers:: %[aAbBcCdDeFgGhjmuUVwWxyY]
13544 * Literal conversion specifiers:: %[%nt]
13545 * Padding and other flags:: Pad with zeros, spaces, etc.
13546 * Setting the time:: Changing the system clock.
13547 * Options for date:: Instead of the current time.
13549 * Date input formats:: Specifying date strings.
13551 * Examples of date:: Examples.
13554 @node Time conversion specifiers
13555 @subsection Time conversion specifiers
13557 @cindex time conversion specifiers
13558 @cindex conversion specifiers, time
13560 @command{date} conversion specifiers related to times.
13564 hour (@samp{00}@dots{}@samp{23})
13566 hour (@samp{01}@dots{}@samp{12})
13568 hour (@samp{ 0}@dots{}@samp{23}).
13569 This is a @acronym{GNU} extension.
13571 hour (@samp{ 1}@dots{}@samp{12}).
13572 This is a @acronym{GNU} extension.
13574 minute (@samp{00}@dots{}@samp{59})
13576 nanoseconds (@samp{000000000}@dots{}@samp{999999999}).
13577 This is a @acronym{GNU} extension.
13579 locale's equivalent of either @samp{AM} or @samp{PM};
13580 blank in many locales.
13581 Noon is treated as @samp{PM} and midnight as @samp{AM}.
13583 like @samp{%p}, except lower case.
13584 This is a @acronym{GNU} extension.
13586 locale's 12-hour clock time (e.g., @samp{11:11:04 PM})
13588 24-hour hour and minute. Same as @samp{%H:%M}.
13589 This is a @acronym{GNU} extension.
13591 @cindex epoch, seconds since
13592 @cindex seconds since the epoch
13593 @cindex beginning of time
13594 seconds since the epoch, i.e., since 1970-01-01 00:00:00 UTC.
13595 Leap seconds are not counted unless leap second support is available.
13596 @xref{%s-examples}, for examples.
13597 This is a @acronym{GNU} extension.
13599 second (@samp{00}@dots{}@samp{60}).
13600 This may be @samp{60} if leap seconds are supported.
13602 24-hour hour, minute, and second. Same as @samp{%H:%M:%S}.
13604 locale's time representation (e.g., @samp{23:13:48})
13606 @w{@acronym{RFC} 2822/@acronym{ISO} 8601} style numeric time zone
13607 (e.g., @samp{-0600} or @samp{+0530}), or nothing if no
13608 time zone is determinable. This value reflects the numeric time zone
13609 appropriate for the current time, using the time zone rules specified
13610 by the @env{TZ} environment variable.
13611 The time (and optionally, the time zone rules) can be overridden
13612 by the @option{--date} option.
13613 This is a @acronym{GNU} extension.
13615 @w{@acronym{RFC} 3339/@acronym{ISO} 8601} style numeric time zone with
13616 @samp{:} (e.g., @samp{-06:00} or @samp{+05:30}), or nothing if no time
13617 zone is determinable.
13618 This is a @acronym{GNU} extension.
13620 Numeric time zone to the nearest second with @samp{:} (e.g.,
13621 @samp{-06:00:00} or @samp{+05:30:00}), or nothing if no time zone is
13623 This is a @acronym{GNU} extension.
13625 Numeric time zone with @samp{:} using the minimum necessary precision
13626 (e.g., @samp{-06}, @samp{+05:30}, or @samp{-04:56:02}), or nothing if
13627 no time zone is determinable.
13628 This is a @acronym{GNU} extension.
13630 alphabetic time zone abbreviation (e.g., @samp{EDT}), or nothing if no
13631 time zone is determinable. See @samp{%z} for how it is determined.
13635 @node Date conversion specifiers
13636 @subsection Date conversion specifiers
13638 @cindex date conversion specifiers
13639 @cindex conversion specifiers, date
13641 @command{date} conversion specifiers related to dates.
13645 locale's abbreviated weekday name (e.g., @samp{Sun})
13647 locale's full weekday name, variable length (e.g., @samp{Sunday})
13649 locale's abbreviated month name (e.g., @samp{Jan})
13651 locale's full month name, variable length (e.g., @samp{January})
13653 locale's date and time (e.g., @samp{Thu Mar @ 3 23:05:25 2005})
13655 century. This is like @samp{%Y}, except the last two digits are omitted.
13656 For example, it is @samp{20} if @samp{%Y} is @samp{2000},
13657 and is @samp{-0} if @samp{%Y} is @samp{-001}.
13658 It is normally at least two characters, but it may be more.
13660 day of month (e.g., @samp{01})
13662 date; same as @samp{%m/%d/%y}
13664 day of month, space padded; same as @samp{%_d}
13666 full date in @acronym{ISO} 8601 format; same as @samp{%Y-%m-%d}.
13667 This is a good choice for a date format, as it is standard and
13668 is easy to sort in the usual case where years are in the range
13670 This is a @acronym{GNU} extension.
13672 year corresponding to the @acronym{ISO} week number, but without the century
13673 (range @samp{00} through @samp{99}). This has the same format and value
13674 as @samp{%y}, except that if the @acronym{ISO} week number (see
13676 to the previous or next year, that year is used instead.
13677 This is a @acronym{GNU} extension.
13679 year corresponding to the @acronym{ISO} week number. This has the
13680 same format and value as @samp{%Y}, except that if the @acronym{ISO}
13682 @samp{%V}) belongs to the previous or next year, that year is used
13684 It is normally useful only if @samp{%V} is also used;
13685 for example, the format @samp{%G-%m-%d} is probably a mistake,
13686 since it combines the ISO week number year with the conventional month and day.
13687 This is a @acronym{GNU} extension.
13691 day of year (@samp{001}@dots{}@samp{366})
13693 month (@samp{01}@dots{}@samp{12})
13695 day of week (@samp{1}@dots{}@samp{7}) with @samp{1} corresponding to Monday
13697 week number of year, with Sunday as the first day of the week
13698 (@samp{00}@dots{}@samp{53}).
13699 Days in a new year preceding the first Sunday are in week zero.
13701 @acronym{ISO} week number, that is, the
13702 week number of year, with Monday as the first day of the week
13703 (@samp{01}@dots{}@samp{53}).
13704 If the week containing January 1 has four or more days in
13705 the new year, then it is considered week 1; otherwise, it is week 53 of
13706 the previous year, and the next week is week 1. (See the @acronym{ISO} 8601
13709 day of week (@samp{0}@dots{}@samp{6}) with 0 corresponding to Sunday
13711 week number of year, with Monday as first day of week
13712 (@samp{00}@dots{}@samp{53}).
13713 Days in a new year preceding the first Monday are in week zero.
13715 locale's date representation (e.g., @samp{12/31/99})
13717 last two digits of year (@samp{00}@dots{}@samp{99})
13719 year. This is normally at least four characters, but it may be more.
13720 Year @samp{0000} precedes year @samp{0001}, and year @samp{-001}
13721 precedes year @samp{0000}.
13725 @node Literal conversion specifiers
13726 @subsection Literal conversion specifiers
13728 @cindex literal conversion specifiers
13729 @cindex conversion specifiers, literal
13731 @command{date} conversion specifiers that produce literal strings.
13743 @node Padding and other flags
13744 @subsection Padding and other flags
13746 @cindex numeric field padding
13747 @cindex padding of numeric fields
13748 @cindex fields, padding numeric
13750 Unless otherwise specified, @command{date} normally pads numeric fields
13751 with zeros, so that, for
13752 example, numeric months are always output as two digits.
13753 Seconds since the epoch are not padded, though,
13754 since there is no natural width for them.
13756 As a @acronym{GNU} extension, @command{date} recognizes any of the
13757 following optional flags after the @samp{%}:
13761 (hyphen) Do not pad the field; useful if the output is intended for
13764 (underscore) Pad with spaces; useful if you need a fixed
13765 number of characters in the output, but zeros are too distracting.
13767 (zero) Pad with zeros even if the conversion specifier
13768 would normally pad with spaces.
13770 Use upper case characters if possible.
13772 Use opposite case characters if possible.
13773 A field that is normally upper case becomes lower case, and vice versa.
13777 Here are some examples of padding:
13780 date +%d/%m -d "Feb 1"
13782 date +%-d/%-m -d "Feb 1"
13784 date +%_d/%_m -d "Feb 1"
13788 As a @acronym{GNU} extension, you can specify the field width
13789 (after any flag, if present) as a decimal number. If the natural size of the
13790 output of the field has less than the specified number of characters,
13791 the result is written right adjusted and padded to the given
13792 size. For example, @samp{%9B} prints the right adjusted month name in
13793 a field of width 9.
13795 An optional modifier can follow the optional flag and width
13796 specification. The modifiers are:
13800 Use the locale's alternate representation for date and time. This
13801 modifier applies to the @samp{%c}, @samp{%C}, @samp{%x}, @samp{%X},
13802 @samp{%y} and @samp{%Y} conversion specifiers. In a Japanese locale, for
13803 example, @samp{%Ex} might yield a date format based on the Japanese
13807 Use the locale's alternate numeric symbols for numbers. This modifier
13808 applies only to numeric conversion specifiers.
13811 If the format supports the modifier but no alternate representation
13812 is available, it is ignored.
13815 @node Setting the time
13816 @subsection Setting the time
13818 @cindex setting the time
13819 @cindex time setting
13820 @cindex appropriate privileges
13822 If given an argument that does not start with @samp{+}, @command{date} sets
13823 the system clock to the date and time specified by that argument (as
13824 described below). You must have appropriate privileges to set the
13825 system clock. The @option{--date} and @option{--set} options may not be
13826 used with such an argument. The @option{--universal} option may be used
13827 with such an argument to indicate that the specified date and time are
13828 relative to Coordinated Universal Time rather than to the local time
13831 The argument must consist entirely of digits, which have the following
13844 first two digits of year (optional)
13846 last two digits of year (optional)
13851 The @option{--set} option also sets the system clock; see the next section.
13854 @node Options for date
13855 @subsection Options for @command{date}
13857 @cindex @command{date} options
13858 @cindex options for @command{date}
13860 The program accepts the following options. Also see @ref{Common options}.
13864 @item -d @var{datestr}
13865 @itemx --date=@var{datestr}
13868 @cindex parsing date strings
13869 @cindex date strings, parsing
13870 @cindex arbitrary date strings, parsing
13873 @opindex next @var{day}
13874 @opindex last @var{day}
13875 Display the date and time specified in @var{datestr} instead of the
13876 current date and time. @var{datestr} can be in almost any common
13877 format. It can contain month names, time zones, @samp{am} and @samp{pm},
13878 @samp{yesterday}, etc. For example, @option{--date="2004-02-27
13879 14:19:13.489392193 +0530"} specifies the instant of time that is
13880 489,392,193 nanoseconds after February 27, 2004 at 2:19:13 PM in a
13881 time zone that is 5 hours and 30 minutes east of @acronym{UTC}.@*
13882 Note: input currently must be in locale independent format. E.g., the
13883 LC_TIME=C below is needed to print back the correct date in many locales:
13885 date -d "$(LC_TIME=C date)"
13887 @xref{Date input formats}.
13889 @item -f @var{datefile}
13890 @itemx --file=@var{datefile}
13893 Parse each line in @var{datefile} as with @option{-d} and display the
13894 resulting date and time. If @var{datefile} is @samp{-}, use standard
13895 input. This is useful when you have many dates to process, because the
13896 system overhead of starting up the @command{date} executable many times can
13899 @item -r @var{file}
13900 @itemx --reference=@var{file}
13902 @opindex --reference
13903 Display the date and time of the last modification of @var{file},
13904 instead of the current date and time.
13911 @opindex --rfc-2822
13912 Display the date and time using the format @samp{%a, %d %b %Y %H:%M:%S
13913 %z}, evaluated in the C locale so abbreviations are always in English.
13917 Fri, 09 Sep 2005 13:51:39 -0700
13920 This format conforms to
13921 @uref{ftp://ftp.rfc-editor.org/in-notes/rfc2822.txt, Internet
13922 @acronym{RFCs} 2822} and
13923 @uref{ftp://ftp.rfc-editor.org/in-notes/rfc822.txt, 822}, the
13924 current and previous standards for Internet email.
13926 @item --rfc-3339=@var{timespec}
13927 @opindex --rfc-3339=@var{timespec}
13928 Display the date using a format specified by
13929 @uref{ftp://ftp.rfc-editor.org/in-notes/rfc3339.txt, Internet
13930 @acronym{RFC} 3339}. This is a subset of the @acronym{ISO} 8601
13931 format, except that it also permits applications to use a space rather
13932 than a @samp{T} to separate dates from times. Unlike the other
13933 standard formats, @acronym{RFC} 3339 format is always suitable as
13934 input for the @option{--date} (@option{-d}) and @option{--file}
13935 (@option{-f}) options, regardless of the current locale.
13937 The argument @var{timespec} specifies how much of the time to include.
13938 It can be one of the following:
13942 Print just the full-date, e.g., @samp{2005-09-14}.
13943 This is equivalent to the format @samp{%Y-%m-%d}.
13946 Print the full-date and full-time separated by a space, e.g.,
13947 @samp{2005-09-14 00:56:06+05:30}. The output ends with a numeric
13948 time-offset; here the @samp{+05:30} means that local time is five
13949 hours and thirty minutes east of @acronym{UTC}. This is equivalent to
13950 the format @samp{%Y-%m-%d %H:%M:%S%:z}.
13953 Like @samp{seconds}, but also print nanoseconds, e.g.,
13954 @samp{2005-09-14 00:56:06.998458565+05:30}.
13955 This is equivalent to the format @samp{%Y-%m-%d %H:%M:%S.%N%:z}.
13959 @item -s @var{datestr}
13960 @itemx --set=@var{datestr}
13963 Set the date and time to @var{datestr}. See @option{-d} above.
13970 @opindex --universal
13971 @cindex Coordinated Universal Time
13973 @cindex Greenwich Mean Time
13976 Use Coordinated Universal Time (@acronym{UTC}) by operating as if the
13977 @env{TZ} environment variable were set to the string @samp{UTC0}.
13979 Universal Time is often called ``Greenwich Mean Time'' (@sc{gmt}) for
13980 historical reasons.
13984 @node Examples of date
13985 @subsection Examples of @command{date}
13987 @cindex examples of @command{date}
13989 Here are a few examples. Also see the documentation for the @option{-d}
13990 option in the previous section.
13995 To print the date of the day before yesterday:
13998 date --date='2 days ago'
14002 To print the date of the day three months and one day hence:
14005 date --date='3 months 1 day'
14009 To print the day of year of Christmas in the current year:
14012 date --date='25 Dec' +%j
14016 To print the current full month name and the day of the month:
14022 But this may not be what you want because for the first nine days of
14023 the month, the @samp{%d} expands to a zero-padded two-digit field,
14024 for example @samp{date -d 1may '+%B %d'} will print @samp{May 01}.
14027 To print a date without the leading zero for one-digit days
14028 of the month, you can use the (@acronym{GNU} extension)
14029 @samp{-} flag to suppress
14030 the padding altogether:
14033 date -d 1may '+%B %-d
14037 To print the current date and time in the format required by many
14038 non-@acronym{GNU} versions of @command{date} when setting the system clock:
14041 date +%m%d%H%M%Y.%S
14045 To set the system clock forward by two minutes:
14048 date --set='+2 minutes'
14052 To print the date in @acronym{RFC} 2822 format,
14053 use @samp{date --rfc-2822}. Here is some example output:
14056 Fri, 09 Sep 2005 13:51:39 -0700
14059 @anchor{%s-examples}
14061 To convert a date string to the number of seconds since the epoch
14062 (which is 1970-01-01 00:00:00 UTC), use the @option{--date} option with
14063 the @samp{%s} format. That can be useful in sorting and/or graphing
14064 and/or comparing data by date. The following command outputs the
14065 number of the seconds since the epoch for the time two minutes after the
14069 date --date='1970-01-01 00:02:00 +0000' +%s
14073 If you do not specify time zone information in the date string,
14074 @command{date} uses your computer's idea of the time zone when
14075 interpreting the string. For example, if your computer's time zone is
14076 that of Cambridge, Massachusetts, which was then 5 hours (i.e., 18,000
14077 seconds) behind UTC:
14080 # local time zone used
14081 date --date='1970-01-01 00:02:00' +%s
14086 If you're sorting or graphing dated data, your raw date values may be
14087 represented as seconds since the epoch. But few people can look at
14088 the date @samp{946684800} and casually note ``Oh, that's the first second
14089 of the year 2000 in Greenwich, England.''
14092 date --date='2000-01-01 UTC' +%s
14096 An alternative is to use the @option{--utc} (@option{-u}) option.
14097 Then you may omit @samp{UTC} from the date string. Although this
14098 produces the same result for @samp{%s} and many other format sequences,
14099 with a time zone offset different from zero, it would give a different
14100 result for zone-dependent formats like @samp{%z}.
14103 date -u --date=2000-01-01 +%s
14107 To convert such an unwieldy number of seconds back to
14108 a more readable form, use a command like this:
14111 # local time zone used
14112 date -d '1970-01-01 UTC 946684800 seconds' +"%Y-%m-%d %T %z"
14113 1999-12-31 19:00:00 -0500
14116 Or if you do not mind depending on the @samp{@@} feature present since
14117 coreutils 5.3.0, you could shorten this to:
14120 date -d @@946684800 +"%F %T %z"
14121 1999-12-31 19:00:00 -0500
14124 Often it is better to output UTC-relative date and time:
14127 date -u -d '1970-01-01 946684800 seconds' +"%Y-%m-%d %T %z"
14128 2000-01-01 00:00:00 +0000
14134 @node arch invocation
14135 @section @command{arch}: Print machine hardware name
14138 @cindex print machine hardware name
14139 @cindex system information, printing
14141 @command{arch} prints the machine hardware name,
14142 and is equivalent to @samp{uname -m}.
14146 arch [@var{option}]
14149 The program accepts the @ref{Common options} only.
14154 @node nproc invocation
14155 @section @command{nproc}: Print the number of available processors
14158 @cindex Print the number of processors
14159 @cindex system information, printing
14161 Print the number of processing units available to the current process,
14162 which may be less than the number of online processors.
14163 If this information is not accessible, then print the number of
14164 processors installed. If the @env{OMP_NUM_THREADS} environment variable is
14165 set, then it will determine the returned value. The result is guaranteed to be
14166 greater than zero. Synopsis:
14169 nproc [@var{option}]
14172 The program accepts the following options. Also see @ref{Common options}.
14178 Print the number of installed processors on the system, which may
14179 be greater than the number online or available to the current process.
14180 The @env{OMP_NUM_THREADS} environment variable is not honored in this case.
14182 @item --ignore=@var{number}
14184 If possible, exclude this @var{number} of processing units.
14191 @node uname invocation
14192 @section @command{uname}: Print system information
14195 @cindex print system information
14196 @cindex system information, printing
14198 @command{uname} prints information about the machine and operating system
14199 it is run on. If no options are given, @command{uname} acts as if the
14200 @option{-s} option were given. Synopsis:
14203 uname [@var{option}]@dots{}
14206 If multiple options or @option{-a} are given, the selected information is
14207 printed in this order:
14210 @var{kernel-name} @var{nodename} @var{kernel-release} @var{kernel-version}
14211 @var{machine} @var{processor} @var{hardware-platform} @var{operating-system}
14214 The information may contain internal spaces, so such output cannot be
14215 parsed reliably. In the following example, @var{release} is
14216 @samp{2.2.18ss.e820-bda652a #4 SMP Tue Jun 5 11:24:08 PDT 2001}:
14220 @result{} Linux dum 2.2.18 #4 SMP Tue Jun 5 11:24:08 PDT 2001 i686 unknown unknown GNU/Linux
14224 The program accepts the following options. Also see @ref{Common options}.
14232 Print all of the below information, except omit the processor type
14233 and the hardware platform name if they are unknown.
14236 @itemx --hardware-platform
14238 @opindex --hardware-platform
14239 @cindex implementation, hardware
14240 @cindex hardware platform
14241 @cindex platform, hardware
14242 Print the hardware platform name
14243 (sometimes called the hardware implementation).
14244 Print @samp{unknown} if the kernel does not make this information
14245 easily available, as is the case with Linux kernels.
14251 @cindex machine type
14252 @cindex hardware class
14253 @cindex hardware type
14254 Print the machine hardware name (sometimes called the hardware class
14260 @opindex --nodename
14263 @cindex network node name
14264 Print the network node hostname.
14269 @opindex --processor
14270 @cindex host processor type
14271 Print the processor type (sometimes called the instruction set
14272 architecture or ISA).
14273 Print @samp{unknown} if the kernel does not make this information
14274 easily available, as is the case with Linux kernels.
14277 @itemx --operating-system
14279 @opindex --operating-system
14280 @cindex operating system name
14281 Print the name of the operating system.
14284 @itemx --kernel-release
14286 @opindex --kernel-release
14287 @cindex kernel release
14288 @cindex release of kernel
14289 Print the kernel release.
14292 @itemx --kernel-name
14294 @opindex --kernel-name
14295 @cindex kernel name
14296 @cindex name of kernel
14297 Print the kernel name.
14298 @acronym{POSIX} 1003.1-2001 (@pxref{Standards conformance}) calls this
14299 ``the implementation of the operating system'', because the
14300 @acronym{POSIX} specification itself has no notion of ``kernel''.
14301 The kernel name might be the same as the operating system name printed
14302 by the @option{-o} or @option{--operating-system} option, but it might
14303 differ. Some operating systems (e.g., FreeBSD, HP-UX) have the same
14304 name as their underlying kernels; others (e.g., GNU/Linux, Solaris)
14308 @itemx --kernel-version
14310 @opindex --kernel-version
14311 @cindex kernel version
14312 @cindex version of kernel
14313 Print the kernel version.
14320 @node hostname invocation
14321 @section @command{hostname}: Print or set system name
14324 @cindex setting the hostname
14325 @cindex printing the hostname
14326 @cindex system name, printing
14327 @cindex appropriate privileges
14329 With no arguments, @command{hostname} prints the name of the current host
14330 system. With one argument, it sets the current host name to the
14331 specified string. You must have appropriate privileges to set the host
14335 hostname [@var{name}]
14338 The only options are @option{--help} and @option{--version}. @xref{Common
14344 @node hostid invocation
14345 @section @command{hostid}: Print numeric host identifier
14348 @cindex printing the host identifier
14350 @command{hostid} prints the numeric identifier of the current host
14351 in hexadecimal. This command accepts no arguments.
14352 The only options are @option{--help} and @option{--version}.
14353 @xref{Common options}.
14355 For example, here's what it prints on one system I use:
14362 On that system, the 32-bit quantity happens to be closely
14363 related to the system's Internet address, but that isn't always
14368 @node uptime invocation
14369 @section @command{uptime}: Print system uptime and load
14372 @cindex printing the system uptime and load
14374 @command{uptime} prints the current time, the system's uptime, the
14375 number of logged-in users and the current load average.
14377 If an argument is specified, it is used as the file to be read
14378 to discover how many users are logged in. If no argument is
14379 specified, a system default is used (@command{uptime --help} indicates
14380 the default setting).
14382 The only options are @option{--help} and @option{--version}.
14383 @xref{Common options}.
14385 For example, here's what it prints right now on one system I use:
14389 14:07 up 3:35, 3 users, load average: 1.39, 1.15, 1.04
14392 The precise method of calculation of load average varies somewhat
14393 between systems. Some systems calculate it as the average number of
14394 runnable processes over the last 1, 5 and 15 minutes, but some systems
14395 also include processes in the uninterruptible sleep state (that is,
14396 those processes which are waiting for disk I/O). The Linux kernel
14397 includes uninterruptible processes.
14399 @node SELinux context
14400 @chapter SELinux context
14402 @cindex SELinux context
14403 @cindex SELinux, context
14404 @cindex commands for SELinux context
14406 This section describes commands for operations with SELinux
14410 * chcon invocation:: Change SELinux context of file
14411 * runcon invocation:: Run a command in specified SELinux context
14414 @node chcon invocation
14415 @section @command{chcon}: Change SELinux context of file
14418 @cindex changing security context
14419 @cindex change SELinux context
14421 @command{chcon} changes the SELinux security context of the selected files.
14425 chcon [@var{option}]@dots{} @var{context} @var{file}@dots{}
14426 chcon [@var{option}]@dots{} [-u @var{user}] [-r @var{role}] [-l @var{range}] [-t @var{type}] @var{file}@dots{}
14427 chcon [@var{option}]@dots{} --reference=@var{rfile} @var{file}@dots{}
14430 Change the SELinux security context of each @var{file} to @var{context}.
14431 With @option{--reference}, change the security context of each @var{file}
14432 to that of @var{rfile}.
14434 The program accepts the following options. Also see @ref{Common options}.
14439 @itemx --no-dereference
14441 @opindex --no-dereference
14442 @cindex no dereference
14443 Affect symbolic links instead of any referenced file.
14445 @item --reference=@var{rfile}
14446 @opindex --reference
14447 @cindex reference file
14448 Use @var{rfile}'s security context rather than specifying a @var{context} value.
14453 @opindex --recursive
14454 Operate on files and directories recursively.
14457 @xref{Traversing symlinks}.
14460 @xref{Traversing symlinks}.
14463 @xref{Traversing symlinks}.
14470 Output a diagnostic for every file processed.
14472 @item -u @var{user}
14473 @itemx --user=@var{user}
14476 Set user @var{user} in the target security context.
14478 @item -r @var{role}
14479 @itemx --role=@var{role}
14482 Set role @var{role} in the target security context.
14484 @item -t @var{type}
14485 @itemx --type=@var{type}
14488 Set type @var{type} in the target security context.
14490 @item -l @var{range}
14491 @itemx --range=@var{range}
14494 Set range @var{range} in the target security context.
14500 @node runcon invocation
14501 @section @command{runcon}: Run a command in specified SELinux context
14504 @cindex run with security context
14507 @command{runcon} runs file in specified SELinux security context.
14511 runcon @var{context} @var{command} [@var{args}]
14512 runcon [ -c ] [-u @var{user}] [-r @var{role}] [-t @var{type}] [-l @var{range}] @var{command} [@var{args}]
14515 Run @var{command} with completely-specified @var{context}, or with
14516 current or transitioned security context modified by one or more of @var{level},
14517 @var{role}, @var{type} and @var{user}.
14519 If none of @option{-c}, @option{-t}, @option{-u}, @option{-r}, or @option{-l}
14520 is specified, the first argument is used as the complete context.
14521 Any additional arguments after @var{command}
14522 are interpreted as arguments to the command.
14524 With neither @var{context} nor @var{command}, print the current security context.
14526 The program accepts the following options. Also see @ref{Common options}.
14534 Compute process transition context before modifying.
14536 @item -u @var{user}
14537 @itemx --user=@var{user}
14540 Set user @var{user} in the target security context.
14542 @item -r @var{role}
14543 @itemx --role=@var{role}
14546 Set role @var{role} in the target security context.
14548 @item -t @var{type}
14549 @itemx --type=@var{type}
14552 Set type @var{type} in the target security context.
14554 @item -l @var{range}
14555 @itemx --range=@var{range}
14558 Set range @var{range} in the target security context.
14562 @cindex exit status of @command{runcon}
14566 126 if @var{command} is found but cannot be invoked
14567 127 if @command{runcon} itself fails or if @var{command} cannot be found
14568 the exit status of @var{command} otherwise
14571 @node Modified command invocation
14572 @chapter Modified command invocation
14574 @cindex modified command invocation
14575 @cindex invocation of commands, modified
14576 @cindex commands for invoking other commands
14578 This section describes commands that run other commands in some context
14579 different than the current one: a modified environment, as a different
14583 * chroot invocation:: Modify the root directory.
14584 * env invocation:: Modify environment variables.
14585 * nice invocation:: Modify niceness.
14586 * nohup invocation:: Immunize to hangups.
14587 * stdbuf invocation:: Modify buffering of standard streams.
14588 * su invocation:: Modify user and group ID.
14589 * timeout invocation:: Run with time limit.
14593 @node chroot invocation
14594 @section @command{chroot}: Run a command with a different root directory
14597 @cindex running a program in a specified root directory
14598 @cindex root directory, running a program in a specified
14600 @command{chroot} runs a command with a specified root directory.
14601 On many systems, only the super-user can do this.@footnote{However,
14602 some systems (e.g., FreeBSD) can be configured to allow certain regular
14603 users to use the @code{chroot} system call, and hence to run this program.
14604 Also, on Cygwin, anyone can run the @command{chroot} command, because the
14605 underlying function is non-privileged due to lack of support in MS-Windows.}
14609 chroot @var{option} @var{newroot} [@var{command} [@var{args}]@dots{}]
14610 chroot @var{option}
14613 Ordinarily, file names are looked up starting at the root of the
14614 directory structure, i.e., @file{/}. @command{chroot} changes the root to
14615 the directory @var{newroot} (which must exist) and then runs
14616 @var{command} with optional @var{args}. If @var{command} is not
14617 specified, the default is the value of the @env{SHELL} environment
14618 variable or @command{/bin/sh} if not set, invoked with the @option{-i} option.
14619 @var{command} must not be a special built-in utility
14620 (@pxref{Special built-in utilities}).
14622 The program accepts the following options. Also see @ref{Common options}.
14623 Options must precede operands.
14627 @itemx --userspec=@var{user}[:@var{group}]
14628 @opindex --userspec
14629 By default, @var{command} is run with the same credentials
14630 as the invoking process.
14631 Use this option to run it as a different @var{user} and/or with a
14632 different primary @var{group}.
14634 @itemx --groups=@var{groups}
14636 Use this option to specify the supplementary @var{groups} to be
14637 used by the new process.
14638 The items in the list (names or numeric IDs) must be separated by commas.
14642 Here are a few tips to help avoid common problems in using chroot.
14643 To start with a simple example, make @var{command} refer to a statically
14644 linked binary. If you were to use a dynamically linked executable, then
14645 you'd have to arrange to have the shared libraries in the right place under
14646 your new root directory.
14648 For example, if you create a statically linked @command{ls} executable,
14649 and put it in @file{/tmp/empty}, you can run this command as root:
14652 $ chroot /tmp/empty /ls -Rl /
14655 Then you'll see output like this:
14660 -rwxr-xr-x 1 0 0 1041745 Aug 16 11:17 ls
14663 If you want to use a dynamically linked executable, say @command{bash},
14664 then first run @samp{ldd bash} to see what shared objects it needs.
14665 Then, in addition to copying the actual binary, also copy the listed
14666 files to the required positions under your intended new root directory.
14667 Finally, if the executable requires any other files (e.g., data, state,
14668 device files), copy them into place, too.
14670 @cindex exit status of @command{chroot}
14674 125 if @command{chroot} itself fails
14675 126 if @var{command} is found but cannot be invoked
14676 127 if @var{command} cannot be found
14677 the exit status of @var{command} otherwise
14681 @node env invocation
14682 @section @command{env}: Run a command in a modified environment
14685 @cindex environment, running a program in a modified
14686 @cindex modified environment, running a program in a
14687 @cindex running a program in a modified environment
14689 @command{env} runs a command with a modified environment. Synopses:
14692 env [@var{option}]@dots{} [@var{name}=@var{value}]@dots{} @c
14693 [@var{command} [@var{args}]@dots{}]
14697 Operands of the form @samp{@var{variable}=@var{value}} set
14698 the environment variable @var{variable} to value @var{value}.
14699 @var{value} may be empty (@samp{@var{variable}=}). Setting a variable
14700 to an empty value is different from unsetting it.
14701 These operands are evaluated left-to-right, so if two operands
14702 mention the same variable the earlier is ignored.
14704 Environment variable names can be empty, and can contain any
14705 characters other than @samp{=} and @acronym{ASCII} @sc{nul}.
14706 However, it is wise to limit yourself to names that
14707 consist solely of underscores, digits, and @acronym{ASCII} letters,
14708 and that begin with a non-digit, as applications like the shell do not
14709 work well with other names.
14712 The first operand that does not contain the character @samp{=}
14713 specifies the program to invoke; it is
14714 searched for according to the @env{PATH} environment variable. Any
14715 remaining arguments are passed as arguments to that program.
14716 The program should not be a special built-in utility
14717 (@pxref{Special built-in utilities}).
14719 Modifications to @env{PATH} take effect prior to searching for
14720 @var{command}. Use caution when reducing @env{PATH}; behavior is
14721 not portable when @env{PATH} is undefined or omits key directories
14722 such as @file{/bin}.
14724 In the rare case that a utility contains a @samp{=} in the name, the
14725 only way to disambiguate it from a variable assignment is to use an
14726 intermediate command for @var{command}, and pass the problematic
14727 program name via @var{args}. For example, if @file{./prog=} is an
14728 executable in the current @env{PATH}:
14731 env prog= true # runs 'true', with prog= in environment
14732 env ./prog= true # runs 'true', with ./prog= in environment
14733 env -- prog= true # runs 'true', with prog= in environment
14734 env sh -c '\prog= true' # runs 'prog=' with argument 'true'
14735 env sh -c 'exec "$@@"' sh prog= true # also runs 'prog='
14738 @cindex environment, printing
14740 If no command name is specified following the environment
14741 specifications, the resulting environment is printed. This is like
14742 specifying the @command{printenv} program.
14744 For some examples, suppose the environment passed to @command{env}
14745 contains @samp{LOGNAME=rms}, @samp{EDITOR=emacs}, and
14746 @samp{PATH=.:/gnubin:/hacks}:
14751 Output the current environment.
14753 $ env | LC_ALL=C sort
14756 PATH=.:/gnubin:/hacks
14760 Run @command{foo} with a reduced environment, preserving only the
14761 original @env{PATH} to avoid problems in locating @command{foo}.
14763 env - PATH="$PATH" foo
14767 Run @command{foo} with the environment containing @samp{LOGNAME=rms},
14768 @samp{EDITOR=emacs}, and @samp{PATH=.:/gnubin:/hacks}, and guarantees
14769 that @command{foo} was found in the file system rather than as a shell
14776 Run @command{nemacs} with the environment containing @samp{LOGNAME=foo},
14777 @samp{EDITOR=emacs}, @samp{PATH=.:/gnubin:/hacks}, and
14778 @samp{DISPLAY=gnu:0}.
14780 env DISPLAY=gnu:0 LOGNAME=foo nemacs
14784 Attempt to run the program @command{/energy/--} (as that is the only
14785 possible path search result); if the command exists, the environment
14786 will contain @samp{LOGNAME=rms} and @samp{PATH=/energy}, and the
14787 arguments will be @samp{e=mc2}, @samp{bar}, and @samp{baz}.
14789 env -u EDITOR PATH=/energy -- e=mc2 bar baz
14795 The program accepts the following options. Also see @ref{Common options}.
14796 Options must precede operands.
14802 @item -u @var{name}
14803 @itemx --unset=@var{name}
14806 Remove variable @var{name} from the environment, if it was in the
14811 @itemx --ignore-environment
14814 @opindex --ignore-environment
14815 Start with an empty environment, ignoring the inherited environment.
14819 @cindex exit status of @command{env}
14823 0 if no @var{command} is specified and the environment is output
14824 125 if @command{env} itself fails
14825 126 if @var{command} is found but cannot be invoked
14826 127 if @var{command} cannot be found
14827 the exit status of @var{command} otherwise
14831 @node nice invocation
14832 @section @command{nice}: Run a command with modified niceness
14836 @cindex scheduling, affecting
14837 @cindex appropriate privileges
14839 @command{nice} prints or modifies a process's @dfn{niceness},
14840 a parameter that affects whether the process is scheduled favorably.
14844 nice [@var{option}]@dots{} [@var{command} [@var{arg}]@dots{}]
14847 If no arguments are given, @command{nice} prints the current niceness.
14848 Otherwise, @command{nice} runs the given @var{command} with its
14849 niceness adjusted. By default, its niceness is incremented by 10.
14851 Niceness values range at least from @minus{}20 (process has high priority
14852 and gets more resources, thus slowing down other processes) through 19
14853 (process has lower priority and runs slowly itself, but has less impact
14854 on the speed of other running processes). Some systems
14855 may have a wider range of nicenesses; conversely, other systems may
14856 enforce more restrictive limits. An attempt to set the niceness
14857 outside the supported range is treated as an attempt to use the
14858 minimum or maximum supported value.
14860 A niceness should not be confused with a scheduling priority, which
14861 lets applications determine the order in which threads are scheduled
14862 to run. Unlike a priority, a niceness is merely advice to the
14863 scheduler, which the scheduler is free to ignore. Also, as a point of
14864 terminology, @acronym{POSIX} defines the behavior of @command{nice} in
14865 terms of a @dfn{nice value}, which is the nonnegative difference
14866 between a niceness and the minimum niceness. Though @command{nice}
14867 conforms to @acronym{POSIX}, its documentation and diagnostics use the
14868 term ``niceness'' for compatibility with historical practice.
14870 @var{command} must not be a special built-in utility (@pxref{Special
14871 built-in utilities}).
14873 @mayConflictWithShellBuiltIn{nice}
14875 The program accepts the following option. Also see @ref{Common options}.
14876 Options must precede operands.
14879 @item -n @var{adjustment}
14880 @itemx --adjustment=@var{adjustment}
14882 @opindex --adjustment
14883 Add @var{adjustment} instead of 10 to the command's niceness. If
14884 @var{adjustment} is negative and you lack appropriate privileges,
14885 @command{nice} issues a warning but otherwise acts as if you specified
14888 For compatibility @command{nice} also supports an obsolete
14889 option syntax @option{-@var{adjustment}}. New scripts should use
14890 @option{-n @var{adjustment}} instead.
14894 @cindex exit status of @command{nice}
14898 0 if no @var{command} is specified and the niceness is output
14899 125 if @command{nice} itself fails
14900 126 if @var{command} is found but cannot be invoked
14901 127 if @var{command} cannot be found
14902 the exit status of @var{command} otherwise
14905 It is sometimes useful to run a non-interactive program with reduced niceness.
14908 $ nice factor 4611686018427387903
14911 Since @command{nice} prints the current niceness,
14912 you can invoke it through itself to demonstrate how it works.
14914 The default behavior is to increase the niceness by @samp{10}:
14925 The @var{adjustment} is relative to the current niceness. In the
14926 next example, the first @command{nice} invocation runs the second one
14927 with niceness 10, and it in turn runs the final one with a niceness
14931 $ nice nice -n 3 nice
14935 Specifying a niceness larger than the supported range
14936 is the same as specifying the maximum supported value:
14939 $ nice -n 10000000000 nice
14943 Only a privileged user may run a process with lower niceness:
14947 nice: cannot set niceness: Permission denied
14949 $ sudo nice -n -1 nice
14954 @node nohup invocation
14955 @section @command{nohup}: Run a command immune to hangups
14958 @cindex hangups, immunity to
14959 @cindex immunity to hangups
14960 @cindex logging out and continuing to run
14963 @command{nohup} runs the given @var{command} with hangup signals ignored,
14964 so that the command can continue running in the background after you log
14968 nohup @var{command} [@var{arg}]@dots{}
14971 If standard input is a terminal, it is redirected from
14972 @file{/dev/null} so that terminal sessions do not mistakenly consider
14973 the terminal to be used by the command. This is a @acronym{GNU}
14974 extension; programs intended to be portable to non-@acronym{GNU} hosts
14975 should use @samp{nohup @var{command} [@var{arg}]@dots{} </dev/null}
14979 If standard output is a terminal, the command's standard output is appended
14980 to the file @file{nohup.out}; if that cannot be written to, it is appended
14981 to the file @file{$HOME/nohup.out}; and if that cannot be written to, the
14982 command is not run.
14983 Any @file{nohup.out} or @file{$HOME/nohup.out} file created by
14984 @command{nohup} is made readable and writable only to the user,
14985 regardless of the current umask settings.
14987 If standard error is a terminal, it is normally redirected to the same file
14988 descriptor as the (possibly-redirected) standard output.
14989 However, if standard output is closed, standard error terminal output
14990 is instead appended to the file @file{nohup.out} or
14991 @file{$HOME/nohup.out} as above.
14993 To capture the command's output to a file other than @file{nohup.out}
14994 you can redirect it. For example, to capture the output of
14998 nohup make > make.log
15001 @command{nohup} does not automatically put the command it runs in the
15002 background; you must do that explicitly, by ending the command line
15003 with an @samp{&}. Also, @command{nohup} does not alter the
15004 niceness of @var{command}; use @command{nice} for that,
15005 e.g., @samp{nohup nice @var{command}}.
15007 @var{command} must not be a special built-in utility (@pxref{Special
15008 built-in utilities}).
15010 The only options are @option{--help} and @option{--version}. @xref{Common
15011 options}. Options must precede operands.
15013 @cindex exit status of @command{nohup}
15017 125 if @command{nohup} itself fails, and @env{POSIXLY_CORRECT} is not set
15018 126 if @var{command} is found but cannot be invoked
15019 127 if @var{command} cannot be found
15020 the exit status of @var{command} otherwise
15023 If @env{POSIXLY_CORRECT} is set, internal failures give status 127
15027 @node stdbuf invocation
15028 @section @command{stdbuf}: Run a command with modified I/O stream buffering
15031 @cindex standard streams, buffering
15032 @cindex line buffered
15034 @command{stdbuf} allows one to modify the buffering operations of the
15035 three standard I/O streams associated with a program. Synopsis:
15038 stdbuf @var{option}@dots{} @var{command}
15041 Any additional @var{arg}s are passed as additional arguments to the
15044 The program accepts the following options. Also see @ref{Common options}.
15048 @item -i @var{mode}
15049 @itemx --input=@var{mode}
15052 Adjust the standard input stream buffering.
15054 @item -o @var{mode}
15055 @itemx --output=@var{mode}
15058 Adjust the standard output stream buffering.
15060 @item -e @var{mode}
15061 @itemx --error=@var{mode}
15064 Adjust the standard error stream buffering.
15068 The @var{mode} can be specified as follows:
15073 Set the stream to line buffered mode.
15074 In this mode data is coalesced until a newline is output or
15075 input is read from any stream attached to a terminal device.
15076 This option is invalid with standard input.
15079 Disable buffering of the selected stream.
15080 In this mode data is output immediately and only the
15081 amount of data requested is read from input.
15084 Specify the size of the buffer to use in fully buffered mode.
15085 @multiplierSuffixesNoBlocks{size}
15089 NOTE: If @var{command} adjusts the buffering of its standard streams
15090 (@command{tee} does for e.g.) then that will override corresponding settings
15091 changed by @command{stdbuf}. Also some filters (like @command{dd} and
15092 @command{cat} etc.) don't use streams for I/O, and are thus unaffected
15093 by @command{stdbuf} settings.
15095 @cindex exit status of @command{stdbuf}
15099 125 if @command{stdbuf} itself fails
15100 126 if @var{command} is found but cannot be invoked
15101 127 if @var{command} cannot be found
15102 the exit status of @var{command} otherwise
15106 @node su invocation
15107 @section @command{su}: Run a command with substitute user and group ID
15110 @cindex substitute user and group IDs
15111 @cindex user ID, switching
15112 @cindex super-user, becoming
15113 @cindex root, becoming
15115 @command{su} allows one user to temporarily become another user. It runs a
15116 command (often an interactive shell) with the real and effective user
15117 ID, group ID, and supplemental groups of a given @var{user}. Synopsis:
15120 su [@var{option}]@dots{} [@var{user} [@var{arg}]@dots{}]
15123 @cindex passwd entry, and @command{su} shell
15125 @flindex /etc/passwd
15126 If no @var{user} is given, the default is @code{root}, the super-user.
15127 The shell to use is taken from @var{user}'s @code{passwd} entry, or
15128 @file{/bin/sh} if none is specified there. If @var{user} has a
15129 password, @command{su} prompts for the password unless run by a user with
15130 effective user ID of zero (the super-user).
15136 @cindex login shell
15137 By default, @command{su} does not change the current directory.
15138 It sets the environment variables @env{HOME} and @env{SHELL}
15139 from the password entry for @var{user}, and if @var{user} is not
15140 the super-user, sets @env{USER} and @env{LOGNAME} to @var{user}.
15141 By default, the shell is not a login shell.
15143 Any additional @var{arg}s are passed as additional arguments to the
15146 @cindex @option{-su}
15147 GNU @command{su} does not treat @file{/bin/sh} or any other shells specially
15148 (e.g., by setting @code{argv[0]} to @option{-su}, passing @option{-c} only
15149 to certain shells, etc.).
15152 @command{su} can optionally be compiled to use @code{syslog} to report
15153 failed, and optionally successful, @command{su} attempts. (If the system
15154 supports @code{syslog}.) However, GNU @command{su} does not check if the
15155 user is a member of the @code{wheel} group; see below.
15157 The program accepts the following options. Also see @ref{Common options}.
15160 @item -c @var{command}
15161 @itemx --command=@var{command}
15164 Pass @var{command}, a single command line to run, to the shell with
15165 a @option{-c} option instead of starting an interactive shell.
15172 @cindex file name pattern expansion, disabled
15173 @cindex globbing, disabled
15174 Pass the @option{-f} option to the shell. This probably only makes sense
15175 if the shell run is @command{csh} or @command{tcsh}, for which the @option{-f}
15176 option prevents reading the startup file (@file{.cshrc}). With
15177 Bourne-like shells, the @option{-f} option disables file name pattern
15178 expansion (globbing), which is not likely to be useful.
15186 @c other variables already indexed above
15189 @cindex login shell, creating
15190 Make the shell a login shell. This means the following. Unset all
15191 environment variables except @env{TERM}, @env{HOME}, and @env{SHELL}
15192 (which are set as described above), and @env{USER} and @env{LOGNAME}
15193 (which are set, even for the super-user, as described above), and set
15194 @env{PATH} to a compiled-in default value. Change to @var{user}'s home
15195 directory. Prepend @samp{-} to the shell's name, intended to make it
15196 read its login startup file(s).
15200 @itemx --preserve-environment
15203 @opindex --preserve-environment
15204 @cindex environment, preserving
15205 @flindex /etc/shells
15206 @cindex restricted shell
15207 Do not change the environment variables @env{HOME}, @env{USER},
15208 @env{LOGNAME}, or @env{SHELL}. Run the shell given in the environment
15209 variable @env{SHELL} instead of the shell from @var{user}'s passwd
15210 entry, unless the user running @command{su} is not the super-user and
15211 @var{user}'s shell is restricted. A @dfn{restricted shell} is one that
15212 is not listed in the file @file{/etc/shells}, or in a compiled-in list
15213 if that file does not exist. Parts of what this option does can be
15214 overridden by @option{--login} and @option{--shell}.
15216 @item -s @var{shell}
15217 @itemx --shell=@var{shell}
15220 Run @var{shell} instead of the shell from @var{user}'s passwd entry,
15221 unless the user running @command{su} is not the super-user and @var{user}'s
15222 shell is restricted (see @option{-m} just above).
15226 @cindex exit status of @command{su}
15230 125 if @command{su} itself fails
15231 126 if subshell is found but cannot be invoked
15232 127 if subshell cannot be found
15233 the exit status of the subshell otherwise
15236 @cindex wheel group, not supported
15237 @cindex group wheel, not supported
15239 @subsection Why GNU @command{su} does not support the @samp{wheel} group
15241 (This section is by Richard Stallman.)
15245 Sometimes a few of the users try to hold total power over all the
15246 rest. For example, in 1984, a few users at the MIT AI lab decided to
15247 seize power by changing the operator password on the Twenex system and
15248 keeping it secret from everyone else. (I was able to thwart this coup
15249 and give power back to the users by patching the kernel, but I
15250 wouldn't know how to do that in Unix.)
15252 However, occasionally the rulers do tell someone. Under the usual
15253 @command{su} mechanism, once someone learns the root password who
15254 sympathizes with the ordinary users, he or she can tell the rest. The
15255 ``wheel group'' feature would make this impossible, and thus cement the
15256 power of the rulers.
15258 I'm on the side of the masses, not that of the rulers. If you are
15259 used to supporting the bosses and sysadmins in whatever they do, you
15260 might find this idea strange at first.
15263 @node timeout invocation
15264 @section @command{timeout}: Run a command with a time limit
15268 @cindex run commands with bounded time
15270 @command{timeout} runs the given @var{command} and kills it if it is
15271 still running after the specified time interval. Synopsis:
15274 timeout [@var{option}] @var{duration} @var{command} [@var{arg}]@dots{}
15277 @var{command} must not be a special built-in utility (@pxref{Special
15278 built-in utilities}).
15280 The program accepts the following options. Also see @ref{Common options}.
15281 Options must precede operands.
15284 @item -k @var{duration}
15285 @itemx --kill-after=@var{duration}
15287 @opindex --kill-after
15288 Ensure the monitored @var{command} is killed by also sending a @samp{KILL}
15289 signal, after the specified @var{duration}. Without this option, if the
15290 selected signal proves not to be fatal, @command{timeout} does not kill
15293 @item -s @var{signal}
15294 @itemx --signal=@var{signal}
15297 Send this @var{signal} to @var{command} on timeout, rather than the
15298 default @samp{TERM} signal. @var{signal} may be a name like @samp{HUP}
15299 or a number. Also see @xref{Signal specifications}.
15303 @var{duration} is an integer followed by an optional unit:
15305 @samp{s} for seconds (the default)
15306 @samp{m} for minutes
15310 A duration of 0 disables the associated timeout.
15312 @cindex exit status of @command{timeout}
15316 124 if @var{command} times out
15317 125 if @command{timeout} itself fails
15318 126 if @var{command} is found but cannot be invoked
15319 127 if @var{command} cannot be found
15320 the exit status of @var{command} otherwise
15324 @node Process control
15325 @chapter Process control
15327 @cindex processes, commands for controlling
15328 @cindex commands for controlling processes
15331 * kill invocation:: Sending a signal to processes.
15335 @node kill invocation
15336 @section @command{kill}: Send a signal to processes
15339 @cindex send a signal to processes
15341 The @command{kill} command sends a signal to processes, causing them
15342 to terminate or otherwise act upon receiving the signal in some way.
15343 Alternatively, it lists information about signals. Synopses:
15346 kill [-s @var{signal} | --signal @var{signal} | -@var{signal}] @var{pid}@dots{}
15347 kill [-l | --list | -t | --table] [@var{signal}]@dots{}
15350 @mayConflictWithShellBuiltIn{kill}
15352 The first form of the @command{kill} command sends a signal to all
15353 @var{pid} arguments. The default signal to send if none is specified
15354 is @samp{TERM}. The special signal number @samp{0} does not denote a
15355 valid signal, but can be used to test whether the @var{pid} arguments
15356 specify processes to which a signal could be sent.
15358 If @var{pid} is positive, the signal is sent to the process with the
15359 process ID @var{pid}. If @var{pid} is zero, the signal is sent to all
15360 processes in the process group of the current process. If @var{pid}
15361 is @minus{}1, the signal is sent to all processes for which the user has
15362 permission to send a signal. If @var{pid} is less than @minus{}1, the signal
15363 is sent to all processes in the process group that equals the absolute
15364 value of @var{pid}.
15366 If @var{pid} is not positive, a system-dependent set of system
15367 processes is excluded from the list of processes to which the signal
15370 If a negative @var{pid} argument is desired as the first one, it
15371 should be preceded by @option{--}. However, as a common extension to
15372 @acronym{POSIX}, @option{--} is not required with @samp{kill
15373 -@var{signal} -@var{pid}}. The following commands are equivalent:
15382 The first form of the @command{kill} command succeeds if every @var{pid}
15383 argument specifies at least one process that the signal was sent to.
15385 The second form of the @command{kill} command lists signal information.
15386 Either the @option{-l} or @option{--list} option, or the @option{-t}
15387 or @option{--table} option must be specified. Without any
15388 @var{signal} argument, all supported signals are listed. The output
15389 of @option{-l} or @option{--list} is a list of the signal names, one
15390 per line; if @var{signal} is already a name, the signal number is
15391 printed instead. The output of @option{-t} or @option{--table} is a
15392 table of signal numbers, names, and descriptions. This form of the
15393 @command{kill} command succeeds if all @var{signal} arguments are valid
15394 and if there is no output error.
15396 The @command{kill} command also supports the @option{--help} and
15397 @option{--version} options. @xref{Common options}.
15399 A @var{signal} may be a signal name like @samp{HUP}, or a signal
15400 number like @samp{1}, or an exit status of a process terminated by the
15401 signal. A signal name can be given in canonical form or prefixed by
15402 @samp{SIG}. The case of the letters is ignored, except for the
15403 @option{-@var{signal}} option which must use upper case to avoid
15404 ambiguity with lower case option letters. For a list of supported
15405 signal names and numbers see @xref{Signal specifications}.
15410 @cindex delaying commands
15411 @cindex commands for delaying
15413 @c Perhaps @command{wait} or other commands should be described here also?
15416 * sleep invocation:: Delay for a specified time.
15420 @node sleep invocation
15421 @section @command{sleep}: Delay for a specified time
15424 @cindex delay for a specified time
15426 @command{sleep} pauses for an amount of time specified by the sum of
15427 the values of the command line arguments.
15431 sleep @var{number}[smhd]@dots{}
15435 Each argument is a number followed by an optional unit; the default
15436 is seconds. The units are:
15449 Historical implementations of @command{sleep} have required that
15450 @var{number} be an integer, and only accepted a single argument
15451 without a suffix. However, GNU @command{sleep} accepts
15452 arbitrary floating point numbers (using a period before any fractional
15455 The only options are @option{--help} and @option{--version}. @xref{Common
15458 @c sleep is a shell built-in at least with Solaris 11's /bin/sh
15459 @mayConflictWithShellBuiltIn{sleep}
15464 @node Numeric operations
15465 @chapter Numeric operations
15467 @cindex numeric operations
15468 These programs do numerically-related operations.
15471 * factor invocation:: Show factors of numbers.
15472 * seq invocation:: Print sequences of numbers.
15476 @node factor invocation
15477 @section @command{factor}: Print prime factors
15480 @cindex prime factors
15482 @command{factor} prints prime factors. Synopses:
15485 factor [@var{number}]@dots{}
15486 factor @var{option}
15489 If no @var{number} is specified on the command line, @command{factor} reads
15490 numbers from standard input, delimited by newlines, tabs, or spaces.
15492 The @command{factor} command supports only a small number of options:
15496 Print a short help on standard output, then exit without further
15500 Print the program version on standard output, then exit without further
15504 Factoring the product of the eighth and ninth Mersenne primes
15505 takes about 30 milliseconds of CPU time on a 2.2 GHz Athlon.
15508 M8=`echo 2^31-1|bc` ; M9=`echo 2^61-1|bc`
15509 /usr/bin/time -f '%U' factor $(echo "$M8 * $M9" | bc)
15510 4951760154835678088235319297: 2147483647 2305843009213693951
15514 Similarly, factoring the eighth Fermat number @math{2^{256}+1} takes
15515 about 20 seconds on the same machine.
15517 Factoring large numbers is, in general, hard. The Pollard Rho
15518 algorithm used by @command{factor} is particularly effective for
15519 numbers with relatively small factors. If you wish to factor large
15520 numbers which do not have small factors (for example, numbers which
15521 are the product of two large primes), other methods are far better.
15523 If @command{factor} is built without using GNU MP, only
15524 single-precision arithmetic is available, and so large numbers
15525 (typically @math{2^{64}} and above) will not be supported. The single-precision
15526 code uses an algorithm which is designed for factoring smaller
15532 @node seq invocation
15533 @section @command{seq}: Print numeric sequences
15536 @cindex numeric sequences
15537 @cindex sequence of numbers
15539 @command{seq} prints a sequence of numbers to standard output. Synopses:
15542 seq [@var{option}]@dots{} @var{last}
15543 seq [@var{option}]@dots{} @var{first} @var{last}
15544 seq [@var{option}]@dots{} @var{first} @var{increment} @var{last}
15547 @command{seq} prints the numbers from @var{first} to @var{last} by
15548 @var{increment}. By default, each number is printed on a separate line.
15549 When @var{increment} is not specified, it defaults to @samp{1},
15550 even when @var{first} is larger than @var{last}.
15551 @var{first} also defaults to @samp{1}. So @code{seq 1} prints
15552 @samp{1}, but @code{seq 0} and @code{seq 10 5} produce no output.
15553 Floating-point numbers
15554 may be specified (using a period before any fractional digits).
15556 The program accepts the following options. Also see @ref{Common options}.
15557 Options must precede operands.
15560 @item -f @var{format}
15561 @itemx --format=@var{format}
15562 @opindex -f @var{format}
15563 @opindex --format=@var{format}
15564 @cindex formatting of numbers in @command{seq}
15565 Print all numbers using @var{format}.
15566 @var{format} must contain exactly one of the @samp{printf}-style
15567 floating point conversion specifications @samp{%a}, @samp{%e},
15568 @samp{%f}, @samp{%g}, @samp{%A}, @samp{%E}, @samp{%F}, @samp{%G}.
15569 The @samp{%} may be followed by zero or more flags taken from the set
15570 @samp{-+#0 '}, then an optional width containing one or more digits,
15571 then an optional precision consisting of a @samp{.} followed by zero
15572 or more digits. @var{format} may also contain any number of @samp{%%}
15573 conversion specifications. All conversion specifications have the
15574 same meaning as with @samp{printf}.
15576 The default format is derived from @var{first}, @var{step}, and
15577 @var{last}. If these all use a fixed point decimal representation,
15578 the default format is @samp{%.@var{p}f}, where @var{p} is the minimum
15579 precision that can represent the output numbers exactly. Otherwise,
15580 the default format is @samp{%g}.
15582 @item -s @var{string}
15583 @itemx --separator=@var{string}
15584 @cindex separator for numbers in @command{seq}
15585 Separate numbers with @var{string}; default is a newline.
15586 The output always terminates with a newline.
15589 @itemx --equal-width
15590 Print all numbers with the same width, by padding with leading zeros.
15591 @var{first}, @var{step}, and @var{last} should all use a fixed point
15592 decimal representation.
15593 (To have other kinds of padding, use @option{--format}).
15597 You can get finer-grained control over output with @option{-f}:
15600 $ seq -f '(%9.2E)' -9e5 1.1e6 1.3e6
15606 If you want hexadecimal integer output, you can use @command{printf}
15607 to perform the conversion:
15610 $ printf '%x\n' `seq 1048575 1024 1050623`
15616 For very long lists of numbers, use xargs to avoid
15617 system limitations on the length of an argument list:
15620 $ seq 1000000 | xargs printf '%x\n' | tail -n 3
15626 To generate octal output, use the printf @code{%o} format instead
15629 On most systems, seq can produce whole-number output for values up to
15630 at least @math{2^{53}}. Larger integers are approximated. The details
15631 differ depending on your floating-point implementation, but a common
15632 case is that @command{seq} works with integers through @math{2^{64}},
15633 and larger integers may not be numerically correct:
15636 $ seq 18446744073709551616 1 18446744073709551618
15637 18446744073709551616
15638 18446744073709551616
15639 18446744073709551618
15642 Be careful when using @command{seq} with outlandish values: otherwise
15643 you may see surprising results, as @command{seq} uses floating point
15644 internally. For example, on the x86 platform, where the internal
15645 representation uses a 64-bit fraction, the command:
15648 seq 1 0.0000000000000000001 1.0000000000000000009
15651 outputs 1.0000000000000000007 twice and skips 1.0000000000000000008.
15656 @node File permissions
15657 @chapter File permissions
15660 @include getdate.texi
15664 @node Opening the software toolbox
15665 @chapter Opening the Software Toolbox
15667 An earlier version of this chapter appeared in
15668 @uref{http://www.linuxjournal.com/article.php?sid=2762, the
15669 @cite{What's GNU?} column of @cite{Linux Journal}, 2 (June, 1994)}.
15670 It was written by Arnold Robbins.
15673 * Toolbox introduction:: Toolbox introduction
15674 * I/O redirection:: I/O redirection
15675 * The who command:: The @command{who} command
15676 * The cut command:: The @command{cut} command
15677 * The sort command:: The @command{sort} command
15678 * The uniq command:: The @command{uniq} command
15679 * Putting the tools together:: Putting the tools together
15683 @node Toolbox introduction
15684 @unnumberedsec Toolbox Introduction
15686 This month's column is only peripherally related to the GNU Project, in
15687 that it describes a number of the GNU tools on your GNU/Linux system and how they
15688 might be used. What it's really about is the ``Software Tools'' philosophy
15689 of program development and usage.
15691 The software tools philosophy was an important and integral concept
15692 in the initial design and development of Unix (of which Linux and GNU are
15693 essentially clones). Unfortunately, in the modern day press of
15694 Internetworking and flashy GUIs, it seems to have fallen by the
15695 wayside. This is a shame, since it provides a powerful mental model
15696 for solving many kinds of problems.
15698 Many people carry a Swiss Army knife around in their pants pockets (or
15699 purse). A Swiss Army knife is a handy tool to have: it has several knife
15700 blades, a screwdriver, tweezers, toothpick, nail file, corkscrew, and perhaps
15701 a number of other things on it. For the everyday, small miscellaneous jobs
15702 where you need a simple, general purpose tool, it's just the thing.
15704 On the other hand, an experienced carpenter doesn't build a house using
15705 a Swiss Army knife. Instead, he has a toolbox chock full of specialized
15706 tools---a saw, a hammer, a screwdriver, a plane, and so on. And he knows
15707 exactly when and where to use each tool; you won't catch him hammering nails
15708 with the handle of his screwdriver.
15710 The Unix developers at Bell Labs were all professional programmers and trained
15711 computer scientists. They had found that while a one-size-fits-all program
15712 might appeal to a user because there's only one program to use, in practice
15717 difficult to write,
15720 difficult to maintain and
15724 difficult to extend to meet new situations.
15727 Instead, they felt that programs should be specialized tools. In short, each
15728 program ``should do one thing well.'' No more and no less. Such programs are
15729 simpler to design, write, and get right---they only do one thing.
15731 Furthermore, they found that with the right machinery for hooking programs
15732 together, that the whole was greater than the sum of the parts. By combining
15733 several special purpose programs, you could accomplish a specific task
15734 that none of the programs was designed for, and accomplish it much more
15735 quickly and easily than if you had to write a special purpose program.
15736 We will see some (classic) examples of this further on in the column.
15737 (An important additional point was that, if necessary, take a detour
15738 and build any software tools you may need first, if you don't already
15739 have something appropriate in the toolbox.)
15741 @node I/O redirection
15742 @unnumberedsec I/O Redirection
15744 Hopefully, you are familiar with the basics of I/O redirection in the
15745 shell, in particular the concepts of ``standard input,'' ``standard output,''
15746 and ``standard error''. Briefly, ``standard input'' is a data source, where
15747 data comes from. A program should not need to either know or care if the
15748 data source is a disk file, a keyboard, a magnetic tape, or even a punched
15749 card reader. Similarly, ``standard output'' is a data sink, where data goes
15750 to. The program should neither know nor care where this might be.
15751 Programs that only read their standard input, do something to the data,
15752 and then send it on, are called @dfn{filters}, by analogy to filters in a
15755 With the Unix shell, it's very easy to set up data pipelines:
15758 program_to_create_data | filter1 | ... | filterN > final.pretty.data
15761 We start out by creating the raw data; each filter applies some successive
15762 transformation to the data, until by the time it comes out of the pipeline,
15763 it is in the desired form.
15765 This is fine and good for standard input and standard output. Where does the
15766 standard error come in to play? Well, think about @command{filter1} in
15767 the pipeline above. What happens if it encounters an error in the data it
15768 sees? If it writes an error message to standard output, it will just
15769 disappear down the pipeline into @command{filter2}'s input, and the
15770 user will probably never see it. So programs need a place where they can send
15771 error messages so that the user will notice them. This is standard error,
15772 and it is usually connected to your console or window, even if you have
15773 redirected standard output of your program away from your screen.
15775 For filter programs to work together, the format of the data has to be
15776 agreed upon. The most straightforward and easiest format to use is simply
15777 lines of text. Unix data files are generally just streams of bytes, with
15778 lines delimited by the @acronym{ASCII} @sc{lf} (Line Feed) character,
15779 conventionally called a ``newline'' in the Unix literature. (This is
15780 @code{'\n'} if you're a C programmer.) This is the format used by all
15781 the traditional filtering programs. (Many earlier operating systems
15782 had elaborate facilities and special purpose programs for managing
15783 binary data. Unix has always shied away from such things, under the
15784 philosophy that it's easiest to simply be able to view and edit your
15785 data with a text editor.)
15787 OK, enough introduction. Let's take a look at some of the tools, and then
15788 we'll see how to hook them together in interesting ways. In the following
15789 discussion, we will only present those command line options that interest
15790 us. As you should always do, double check your system documentation
15791 for the full story.
15793 @node The who command
15794 @unnumberedsec The @command{who} Command
15796 The first program is the @command{who} command. By itself, it generates a
15797 list of the users who are currently logged in. Although I'm writing
15798 this on a single-user system, we'll pretend that several people are
15803 @print{} arnold console Jan 22 19:57
15804 @print{} miriam ttyp0 Jan 23 14:19(:0.0)
15805 @print{} bill ttyp1 Jan 21 09:32(:0.0)
15806 @print{} arnold ttyp2 Jan 23 20:48(:0.0)
15809 Here, the @samp{$} is the usual shell prompt, at which I typed @samp{who}.
15810 There are three people logged in, and I am logged in twice. On traditional
15811 Unix systems, user names are never more than eight characters long. This
15812 little bit of trivia will be useful later. The output of @command{who} is nice,
15813 but the data is not all that exciting.
15815 @node The cut command
15816 @unnumberedsec The @command{cut} Command
15818 The next program we'll look at is the @command{cut} command. This program
15819 cuts out columns or fields of input data. For example, we can tell it
15820 to print just the login name and full name from the @file{/etc/passwd}
15821 file. The @file{/etc/passwd} file has seven fields, separated by
15825 arnold:xyzzy:2076:10:Arnold D. Robbins:/home/arnold:/bin/bash
15828 To get the first and fifth fields, we would use @command{cut} like this:
15831 $ cut -d: -f1,5 /etc/passwd
15832 @print{} root:Operator
15834 @print{} arnold:Arnold D. Robbins
15835 @print{} miriam:Miriam A. Robbins
15839 With the @option{-c} option, @command{cut} will cut out specific characters
15840 (i.e., columns) in the input lines. This is useful for input data
15841 that has fixed width fields, and does not have a field separator. For
15842 example, list the Monday dates for the current month:
15844 @c Is using cal ok? Looked at gcal, but I don't like it.
15855 @node The sort command
15856 @unnumberedsec The @command{sort} Command
15858 Next we'll look at the @command{sort} command. This is one of the most
15859 powerful commands on a Unix-style system; one that you will often find
15860 yourself using when setting up fancy data plumbing.
15863 command reads and sorts each file named on the command line. It then
15864 merges the sorted data and writes it to standard output. It will read
15865 standard input if no files are given on the command line (thus
15866 making it into a filter). The sort is based on the character collating
15867 sequence or based on user-supplied ordering criteria.
15870 @node The uniq command
15871 @unnumberedsec The @command{uniq} Command
15873 Finally (at least for now), we'll look at the @command{uniq} program. When
15874 sorting data, you will often end up with duplicate lines, lines that
15875 are identical. Usually, all you need is one instance of each line.
15876 This is where @command{uniq} comes in. The @command{uniq} program reads its
15877 standard input. It prints only one
15878 copy of each repeated line. It does have several options. Later on,
15879 we'll use the @option{-c} option, which prints each unique line, preceded
15880 by a count of the number of times that line occurred in the input.
15883 @node Putting the tools together
15884 @unnumberedsec Putting the Tools Together
15886 Now, let's suppose this is a large ISP server system with dozens of users
15887 logged in. The management wants the system administrator to write a program that will
15888 generate a sorted list of logged in users. Furthermore, even if a user
15889 is logged in multiple times, his or her name should only show up in the
15892 The administrator could sit down with the system documentation and write a C
15893 program that did this. It would take perhaps a couple of hundred lines
15894 of code and about two hours to write it, test it, and debug it.
15895 However, knowing the software toolbox, the administrator can instead start out
15896 by generating just a list of logged on users:
15906 Next, sort the list:
15909 $ who | cut -c1-8 | sort
15916 Finally, run the sorted list through @command{uniq}, to weed out duplicates:
15919 $ who | cut -c1-8 | sort | uniq
15925 The @command{sort} command actually has a @option{-u} option that does what
15926 @command{uniq} does. However, @command{uniq} has other uses for which one
15927 cannot substitute @samp{sort -u}.
15929 The administrator puts this pipeline into a shell script, and makes it available for
15930 all the users on the system (@samp{#} is the system administrator,
15931 or @code{root}, prompt):
15934 # cat > /usr/local/bin/listusers
15935 who | cut -c1-8 | sort | uniq
15937 # chmod +x /usr/local/bin/listusers
15940 There are four major points to note here. First, with just four
15941 programs, on one command line, the administrator was able to save about two
15942 hours worth of work. Furthermore, the shell pipeline is just about as
15943 efficient as the C program would be, and it is much more efficient in
15944 terms of programmer time. People time is much more expensive than
15945 computer time, and in our modern ``there's never enough time to do
15946 everything'' society, saving two hours of programmer time is no mean
15949 Second, it is also important to emphasize that with the
15950 @emph{combination} of the tools, it is possible to do a special
15951 purpose job never imagined by the authors of the individual programs.
15953 Third, it is also valuable to build up your pipeline in stages, as we did here.
15954 This allows you to view the data at each stage in the pipeline, which helps
15955 you acquire the confidence that you are indeed using these tools correctly.
15957 Finally, by bundling the pipeline in a shell script, other users can use
15958 your command, without having to remember the fancy plumbing you set up for
15959 them. In terms of how you run them, shell scripts and compiled programs are
15962 After the previous warm-up exercise, we'll look at two additional, more
15963 complicated pipelines. For them, we need to introduce two more tools.
15965 The first is the @command{tr} command, which stands for ``transliterate.''
15966 The @command{tr} command works on a character-by-character basis, changing
15967 characters. Normally it is used for things like mapping upper case to
15971 $ echo ThIs ExAmPlE HaS MIXED case! | tr '[:upper:]' '[:lower:]'
15972 @print{} this example has mixed case!
15975 There are several options of interest:
15979 work on the complement of the listed characters, i.e.,
15980 operations apply to characters not in the given set
15983 delete characters in the first set from the output
15986 squeeze repeated characters in the output into just one character.
15989 We will be using all three options in a moment.
15991 The other command we'll look at is @command{comm}. The @command{comm}
15992 command takes two sorted input files as input data, and prints out the
15993 files' lines in three columns. The output columns are the data lines
15994 unique to the first file, the data lines unique to the second file, and
15995 the data lines that are common to both. The @option{-1}, @option{-2}, and
15996 @option{-3} command line options @emph{omit} the respective columns. (This is
15997 non-intuitive and takes a little getting used to.) For example:
16019 The file name @file{-} tells @command{comm} to read standard input
16020 instead of a regular file.
16022 Now we're ready to build a fancy pipeline. The first application is a word
16023 frequency counter. This helps an author determine if he or she is over-using
16026 The first step is to change the case of all the letters in our input file
16027 to one case. ``The'' and ``the'' are the same word when doing counting.
16030 $ tr '[:upper:]' '[:lower:]' < whats.gnu | ...
16033 The next step is to get rid of punctuation. Quoted words and unquoted words
16034 should be treated identically; it's easiest to just get the punctuation out of
16038 $ tr '[:upper:]' '[:lower:]' < whats.gnu | tr -cd '[:alnum:]_ \n' | ...
16041 The second @command{tr} command operates on the complement of the listed
16042 characters, which are all the letters, the digits, the underscore, and
16043 the blank. The @samp{\n} represents the newline character; it has to
16044 be left alone. (The @acronym{ASCII} tab character should also be included for
16045 good measure in a production script.)
16047 At this point, we have data consisting of words separated by blank space.
16048 The words only contain alphanumeric characters (and the underscore). The
16049 next step is break the data apart so that we have one word per line. This
16050 makes the counting operation much easier, as we will see shortly.
16053 $ tr '[:upper:]' '[:lower:]' < whats.gnu | tr -cd '[:alnum:]_ \n' |
16054 > tr -s ' ' '\n' | ...
16057 This command turns blanks into newlines. The @option{-s} option squeezes
16058 multiple newline characters in the output into just one. This helps us
16059 avoid blank lines. (The @samp{>} is the shell's ``secondary prompt.''
16060 This is what the shell prints when it notices you haven't finished
16061 typing in all of a command.)
16063 We now have data consisting of one word per line, no punctuation, all one
16064 case. We're ready to count each word:
16067 $ tr '[:upper:]' '[:lower:]' < whats.gnu | tr -cd '[:alnum:]_ \n' |
16068 > tr -s ' ' '\n' | sort | uniq -c | ...
16071 At this point, the data might look something like this:
16084 The output is sorted by word, not by count! What we want is the most
16085 frequently used words first. Fortunately, this is easy to accomplish,
16086 with the help of two more @command{sort} options:
16090 do a numeric sort, not a textual one
16093 reverse the order of the sort
16096 The final pipeline looks like this:
16099 $ tr '[:upper:]' '[:lower:]' < whats.gnu | tr -cd '[:alnum:]_ \n' |
16100 > tr -s ' ' '\n' | sort | uniq -c | sort -n -r
16109 Whew! That's a lot to digest. Yet, the same principles apply. With six
16110 commands, on two lines (really one long one split for convenience), we've
16111 created a program that does something interesting and useful, in much
16112 less time than we could have written a C program to do the same thing.
16114 A minor modification to the above pipeline can give us a simple spelling
16115 checker! To determine if you've spelled a word correctly, all you have to
16116 do is look it up in a dictionary. If it is not there, then chances are
16117 that your spelling is incorrect. So, we need a dictionary.
16118 The conventional location for a dictionary is @file{/usr/dict/words}.
16119 On my GNU/Linux system,@footnote{Redhat Linux 6.1, for the November 2000
16120 revision of this article.}
16121 this is a sorted, 45,402 word dictionary.
16123 Now, how to compare our file with the dictionary? As before, we generate
16124 a sorted list of words, one per line:
16127 $ tr '[:upper:]' '[:lower:]' < whats.gnu | tr -cd '[:alnum:]_ \n' |
16128 > tr -s ' ' '\n' | sort -u | ...
16131 Now, all we need is a list of words that are @emph{not} in the
16132 dictionary. Here is where the @command{comm} command comes in.
16135 $ tr '[:upper:]' '[:lower:]' < whats.gnu | tr -cd '[:alnum:]_ \n' |
16136 > tr -s ' ' '\n' | sort -u |
16137 > comm -23 - /usr/dict/words
16140 The @option{-2} and @option{-3} options eliminate lines that are only in the
16141 dictionary (the second file), and lines that are in both files. Lines
16142 only in the first file (standard input, our stream of words), are
16143 words that are not in the dictionary. These are likely candidates for
16144 spelling errors. This pipeline was the first cut at a production
16145 spelling checker on Unix.
16147 There are some other tools that deserve brief mention.
16151 search files for text that matches a regular expression
16154 count lines, words, characters
16157 a T-fitting for data pipes, copies data to files and to standard output
16160 the stream editor, an advanced tool
16163 a data manipulation language, another advanced tool
16166 The software tools philosophy also espoused the following bit of
16167 advice: ``Let someone else do the hard part.'' This means, take
16168 something that gives you most of what you need, and then massage it the
16169 rest of the way until it's in the form that you want.
16175 Each program should do one thing well. No more, no less.
16178 Combining programs with appropriate plumbing leads to results where
16179 the whole is greater than the sum of the parts. It also leads to novel
16180 uses of programs that the authors might never have imagined.
16183 Programs should never print extraneous header or trailer data, since these
16184 could get sent on down a pipeline. (A point we didn't mention earlier.)
16187 Let someone else do the hard part.
16190 Know your toolbox! Use each program appropriately. If you don't have an
16191 appropriate tool, build one.
16194 As of this writing, all the programs we've discussed are available via
16195 anonymous @command{ftp} from: @*
16196 @uref{ftp://gnudist.gnu.org/textutils/textutils-1.22.tar.gz}. (There may
16197 be more recent versions available now.)
16199 None of what I have presented in this column is new. The Software Tools
16200 philosophy was first introduced in the book @cite{Software Tools}, by
16201 Brian Kernighan and P.J. Plauger (Addison-Wesley, ISBN 0-201-03669-X).
16202 This book showed how to write and use software tools. It was written in
16203 1976, using a preprocessor for FORTRAN named @command{ratfor} (RATional
16204 FORtran). At the time, C was not as ubiquitous as it is now; FORTRAN
16205 was. The last chapter presented a @command{ratfor} to FORTRAN
16206 processor, written in @command{ratfor}. @command{ratfor} looks an awful
16207 lot like C; if you know C, you won't have any problem following the
16210 In 1981, the book was updated and made available as @cite{Software Tools
16211 in Pascal} (Addison-Wesley, ISBN 0-201-10342-7). Both books are
16212 still in print and are well worth
16213 reading if you're a programmer. They certainly made a major change in
16214 how I view programming.
16216 The programs in both books are available from
16217 @uref{http://cm.bell-labs.com/who/bwk, Brian Kernighan's home page}.
16218 For a number of years, there was an active
16219 Software Tools Users Group, whose members had ported the original
16220 @command{ratfor} programs to essentially every computer system with a
16221 FORTRAN compiler. The popularity of the group waned in the middle 1980s
16222 as Unix began to spread beyond universities.
16224 With the current proliferation of GNU code and other clones of Unix programs,
16225 these programs now receive little attention; modern C versions are
16226 much more efficient and do more than these programs do. Nevertheless, as
16227 exposition of good programming style, and evangelism for a still-valuable
16228 philosophy, these books are unparalleled, and I recommend them highly.
16230 Acknowledgment: I would like to express my gratitude to Brian Kernighan
16231 of Bell Labs, the original Software Toolsmith, for reviewing this column.
16233 @node GNU Free Documentation License
16234 @appendix GNU Free Documentation License
16238 @node Concept index
16245 @c Local variables:
16246 @c texinfo-column-for-description: 32