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 non-directory suffix.
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, 2000-2009 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 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 non-directory suffix from a file name
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.
1500 @itemx --squeeze-blank
1502 @opindex --squeeze-blank
1503 @cindex squeezing empty lines
1504 Suppress repeated adjacent empty lines; output just one empty line
1509 Equivalent to @option{-vT}.
1514 @opindex --show-tabs
1515 Display TAB characters as @samp{^I}.
1519 Ignored; for @acronym{POSIX} compatibility.
1522 @itemx --show-nonprinting
1524 @opindex --show-nonprinting
1525 Display control characters except for LFD and TAB using
1526 @samp{^} notation and precede characters that have the high bit set with
1531 On systems like MS-DOS that distinguish between text and binary files,
1532 @command{cat} normally reads and writes in binary mode. However,
1533 @command{cat} reads in text mode if one of the options
1534 @option{-bensAE} is used or if @command{cat} is reading from standard
1535 input and standard input is a terminal. Similarly, @command{cat}
1536 writes in text mode if one of the options @option{-bensAE} is used or
1537 if standard output is a terminal.
1544 # Output f's contents, then standard input, then g's contents.
1547 # Copy standard input to standard output.
1552 @node tac invocation
1553 @section @command{tac}: Concatenate and write files in reverse
1556 @cindex reversing files
1558 @command{tac} copies each @var{file} (@samp{-} means standard input), or
1559 standard input if none are given, to standard output, reversing the
1560 records (lines by default) in each separately. Synopsis:
1563 tac [@var{option}]@dots{} [@var{file}]@dots{}
1566 @dfn{Records} are separated by instances of a string (newline by
1567 default). By default, this separator string is attached to the end of
1568 the record that it follows in the file.
1570 The program accepts the following options. Also see @ref{Common options}.
1578 The separator is attached to the beginning of the record that it
1579 precedes in the file.
1585 Treat the separator string as a regular expression. Users of @command{tac}
1586 on MS-DOS/MS-Windows should note that, since @command{tac} reads files in
1587 binary mode, each line of a text file might end with a CR/LF pair
1588 instead of the Unix-style LF.
1590 @item -s @var{separator}
1591 @itemx --separator=@var{separator}
1593 @opindex --separator
1594 Use @var{separator} as the record separator, instead of newline.
1602 @section @command{nl}: Number lines and write files
1605 @cindex numbering lines
1606 @cindex line numbering
1608 @command{nl} writes each @var{file} (@samp{-} means standard input), or
1609 standard input if none are given, to standard output, with line numbers
1610 added to some or all of the lines. Synopsis:
1613 nl [@var{option}]@dots{} [@var{file}]@dots{}
1616 @cindex logical pages, numbering on
1617 @command{nl} decomposes its input into (logical) pages; by default, the
1618 line number is reset to 1 at the top of each logical page. @command{nl}
1619 treats all of the input files as a single document; it does not reset
1620 line numbers or logical pages between files.
1622 @cindex headers, numbering
1623 @cindex body, numbering
1624 @cindex footers, numbering
1625 A logical page consists of three sections: header, body, and footer.
1626 Any of the sections can be empty. Each can be numbered in a different
1627 style from the others.
1629 The beginnings of the sections of logical pages are indicated in the
1630 input file by a line containing exactly one of these delimiter strings:
1641 The two characters from which these strings are made can be changed from
1642 @samp{\} and @samp{:} via options (see below), but the pattern and
1643 length of each string cannot be changed.
1645 A section delimiter is replaced by an empty line on output. Any text
1646 that comes before the first section delimiter string in the input file
1647 is considered to be part of a body section, so @command{nl} treats a
1648 file that contains no section delimiters as a single body section.
1650 The program accepts the following options. Also see @ref{Common options}.
1654 @item -b @var{style}
1655 @itemx --body-numbering=@var{style}
1657 @opindex --body-numbering
1658 Select the numbering style for lines in the body section of each
1659 logical page. When a line is not numbered, the current line number
1660 is not incremented, but the line number separator character is still
1661 prepended to the line. The styles are:
1667 number only nonempty lines (default for body),
1669 do not number lines (default for header and footer),
1671 number only lines that contain a match for the basic regular
1672 expression @var{bre}.
1673 @xref{Regular Expressions, , Regular Expressions, grep, The GNU Grep Manual}.
1677 @itemx --section-delimiter=@var{cd}
1679 @opindex --section-delimiter
1680 @cindex section delimiters of pages
1681 Set the section delimiter characters to @var{cd}; default is
1682 @samp{\:}. If only @var{c} is given, the second remains @samp{:}.
1683 (Remember to protect @samp{\} or other metacharacters from shell
1684 expansion with quotes or extra backslashes.)
1686 @item -f @var{style}
1687 @itemx --footer-numbering=@var{style}
1689 @opindex --footer-numbering
1690 Analogous to @option{--body-numbering}.
1692 @item -h @var{style}
1693 @itemx --header-numbering=@var{style}
1695 @opindex --header-numbering
1696 Analogous to @option{--body-numbering}.
1698 @item -i @var{number}
1699 @itemx --line-increment=@var{number}
1701 @opindex --line-increment
1702 Increment line numbers by @var{number} (default 1).
1704 @item -l @var{number}
1705 @itemx --join-blank-lines=@var{number}
1707 @opindex --join-blank-lines
1708 @cindex empty lines, numbering
1709 @cindex blank lines, numbering
1710 Consider @var{number} (default 1) consecutive empty lines to be one
1711 logical line for numbering, and only number the last one. Where fewer
1712 than @var{number} consecutive empty lines occur, do not number them.
1713 An empty line is one that contains no characters, not even spaces
1716 @item -n @var{format}
1717 @itemx --number-format=@var{format}
1719 @opindex --number-format
1720 Select the line numbering format (default is @code{rn}):
1724 @opindex ln @r{format for @command{nl}}
1725 left justified, no leading zeros;
1727 @opindex rn @r{format for @command{nl}}
1728 right justified, no leading zeros;
1730 @opindex rz @r{format for @command{nl}}
1731 right justified, leading zeros.
1735 @itemx --no-renumber
1737 @opindex --no-renumber
1738 Do not reset the line number at the start of a logical page.
1740 @item -s @var{string}
1741 @itemx --number-separator=@var{string}
1743 @opindex --number-separator
1744 Separate the line number from the text line in the output with
1745 @var{string} (default is the TAB character).
1747 @item -v @var{number}
1748 @itemx --starting-line-number=@var{number}
1750 @opindex --starting-line-number
1751 Set the initial line number on each logical page to @var{number} (default 1).
1753 @item -w @var{number}
1754 @itemx --number-width=@var{number}
1756 @opindex --number-width
1757 Use @var{number} characters for line numbers (default 6).
1765 @section @command{od}: Write files in octal or other formats
1768 @cindex octal dump of files
1769 @cindex hex dump of files
1770 @cindex ASCII dump of files
1771 @cindex file contents, dumping unambiguously
1773 @command{od} writes an unambiguous representation of each @var{file}
1774 (@samp{-} means standard input), or standard input if none are given.
1778 od [@var{option}]@dots{} [@var{file}]@dots{}
1779 od [-abcdfilosx]@dots{} [@var{file}] [[+]@var{offset}[.][b]]
1780 od [@var{option}]@dots{} --traditional [@var{file}] [[+]@var{offset}[.][b] [[+]@var{label}[.][b]]]
1783 Each line of output consists of the offset in the input, followed by
1784 groups of data from the file. By default, @command{od} prints the offset in
1785 octal, and each group of file data is a C @code{short int}'s worth of input
1786 printed as a single octal number.
1788 If @var{offset} is given, it specifies how many input bytes to skip
1789 before formatting and writing. By default, it is interpreted as an
1790 octal number, but the optional trailing decimal point causes it to be
1791 interpreted as decimal. If no decimal is specified and the offset
1792 begins with @samp{0x} or @samp{0X} it is interpreted as a hexadecimal
1793 number. If there is a trailing @samp{b}, the number of bytes skipped
1794 will be @var{offset} multiplied by 512.
1796 If a command is of both the first and second forms, the second form is
1797 assumed if the last operand begins with @samp{+} or (if there are two
1798 operands) a digit. For example, in @samp{od foo 10} and @samp{od +10}
1799 the @samp{10} is an offset, whereas in @samp{od 10} the @samp{10} is a
1802 The program accepts the following options. Also see @ref{Common options}.
1806 @item -A @var{radix}
1807 @itemx --address-radix=@var{radix}
1809 @opindex --address-radix
1810 @cindex radix for file offsets
1811 @cindex file offset radix
1812 Select the base in which file offsets are printed. @var{radix} can
1813 be one of the following:
1823 none (do not print offsets).
1826 The default is octal.
1828 @item -j @var{bytes}
1829 @itemx --skip-bytes=@var{bytes}
1831 @opindex --skip-bytes
1832 Skip @var{bytes} input bytes before formatting and writing. If
1833 @var{bytes} begins with @samp{0x} or @samp{0X}, it is interpreted in
1834 hexadecimal; otherwise, if it begins with @samp{0}, in octal; otherwise,
1836 @multiplierSuffixes{bytes}
1838 @item -N @var{bytes}
1839 @itemx --read-bytes=@var{bytes}
1841 @opindex --read-bytes
1842 Output at most @var{bytes} bytes of the input. Prefixes and suffixes on
1843 @code{bytes} are interpreted as for the @option{-j} option.
1845 @item -S @var{bytes}
1846 @itemx --strings[=@var{bytes}]
1849 @cindex string constants, outputting
1850 Instead of the normal output, output only @dfn{string constants}: at
1851 least @var{bytes} consecutive @acronym{ASCII} graphic characters,
1852 followed by a zero byte (@acronym{ASCII} @sc{nul}).
1853 Prefixes and suffixes on @code{bytes} are interpreted as for the
1856 If @var{n} is omitted with @option{--strings}, the default is 3.
1859 @itemx --format=@var{type}
1862 Select the format in which to output the file data. @var{type} is a
1863 string of one or more of the below type indicator characters. If you
1864 include more than one type indicator character in a single @var{type}
1865 string, or use this option more than once, @command{od} writes one copy
1866 of each output line using each of the data types that you specified,
1867 in the order that you specified.
1869 Adding a trailing ``z'' to any type specification appends a display
1870 of the @acronym{ASCII} character representation of the printable characters
1871 to the output line generated by the type specification.
1875 named character, ignoring high-order bit
1877 @acronym{ASCII} character or backslash escape,
1890 The type @code{a} outputs things like @samp{sp} for space, @samp{nl} for
1891 newline, and @samp{nul} for a zero byte. Only the least significant
1892 seven bits of each byte is used; the high-order bit is ignored.
1893 Type @code{c} outputs
1894 @samp{ }, @samp{\n}, and @code{\0}, respectively.
1897 Except for types @samp{a} and @samp{c}, you can specify the number
1898 of bytes to use in interpreting each number in the given data type
1899 by following the type indicator character with a decimal integer.
1900 Alternately, you can specify the size of one of the C compiler's
1901 built-in data types by following the type indicator character with
1902 one of the following characters. For integers (@samp{d}, @samp{o},
1903 @samp{u}, @samp{x}):
1916 For floating point (@code{f}):
1928 @itemx --output-duplicates
1930 @opindex --output-duplicates
1931 Output consecutive lines that are identical. By default, when two or
1932 more consecutive output lines would be identical, @command{od} outputs only
1933 the first line, and puts just an asterisk on the following line to
1934 indicate the elision.
1937 @itemx --width[=@var{n}]
1940 Dump @code{n} input bytes per output line. This must be a multiple of
1941 the least common multiple of the sizes associated with the specified
1944 If this option is not given at all, the default is 16. If @var{n} is
1945 omitted, the default is 32.
1949 The next several options are shorthands for format specifications.
1950 @sc{gnu} @command{od} accepts any combination of shorthands and format
1951 specification options. These options accumulate.
1957 Output as named characters. Equivalent to @samp{-t a}.
1961 Output as octal bytes. Equivalent to @samp{-t o1}.
1965 Output as @acronym{ASCII} characters or backslash escapes. Equivalent to
1970 Output as unsigned decimal two-byte units. Equivalent to @samp{-t u2}.
1974 Output as floats. Equivalent to @samp{-t fF}.
1978 Output as decimal ints. Equivalent to @samp{-t dI}.
1982 Output as decimal long ints. Equivalent to @samp{-t dL}.
1986 Output as octal two-byte units. Equivalent to @option{-t o2}.
1990 Output as decimal two-byte units. Equivalent to @option{-t d2}.
1994 Output as hexadecimal two-byte units. Equivalent to @samp{-t x2}.
1997 @opindex --traditional
1998 Recognize the non-option label argument that traditional @command{od}
1999 accepted. The following syntax:
2002 od --traditional [@var{file}] [[+]@var{offset}[.][b] [[+]@var{label}[.][b]]]
2006 can be used to specify at most one file and optional arguments
2007 specifying an offset and a pseudo-start address, @var{label}.
2008 The @var{label} argument is interpreted
2009 just like @var{offset}, but it specifies an initial pseudo-address. The
2010 pseudo-addresses are displayed in parentheses following any normal
2017 @node base64 invocation
2018 @section @command{base64}: Transform data into printable data
2021 @cindex base64 encoding
2023 @command{base64} transforms data read from a file, or standard input,
2024 into (or from) base64 encoded form. The base64 encoded form uses
2025 printable @acronym{ASCII} characters to represent binary data.
2029 base64 [@var{option}]@dots{} [@var{file}]
2030 base64 --decode [@var{option}]@dots{} [@var{file}]
2033 The base64 encoding expands data to roughly 133% of the original.
2034 The format conforms to
2035 @uref{ftp://ftp.rfc-editor.org/in-notes/rfc4648.txt, RFC 4648}.
2037 The program accepts the following options. Also see @ref{Common options}.
2042 @itemx --wrap=@var{cols}
2046 @cindex column to wrap data after
2047 During encoding, wrap lines after @var{cols} characters. This must be
2050 The default is to wrap after 76 characters. Use the value 0 to
2051 disable line wrapping altogether.
2057 @cindex Decode base64 data
2058 @cindex Base64 decoding
2059 Change the mode of operation, from the default of encoding data, to
2060 decoding data. Input is expected to be base64 encoded data, and the
2061 output will be the original data.
2064 @itemx --ignore-garbage
2066 @opindex --ignore-garbage
2067 @cindex Ignore garbage in base64 stream
2068 When decoding, newlines are always accepted.
2069 During decoding, ignore unrecognized bytes,
2070 to permit distorted data to be decoded.
2077 @node Formatting file contents
2078 @chapter Formatting file contents
2080 @cindex formatting file contents
2082 These commands reformat the contents of files.
2085 * fmt invocation:: Reformat paragraph text.
2086 * pr invocation:: Paginate or columnate files for printing.
2087 * fold invocation:: Wrap input lines to fit in specified width.
2091 @node fmt invocation
2092 @section @command{fmt}: Reformat paragraph text
2095 @cindex reformatting paragraph text
2096 @cindex paragraphs, reformatting
2097 @cindex text, reformatting
2099 @command{fmt} fills and joins lines to produce output lines of (at most)
2100 a given number of characters (75 by default). Synopsis:
2103 fmt [@var{option}]@dots{} [@var{file}]@dots{}
2106 @command{fmt} reads from the specified @var{file} arguments (or standard
2107 input if none are given), and writes to standard output.
2109 By default, blank lines, spaces between words, and indentation are
2110 preserved in the output; successive input lines with different
2111 indentation are not joined; tabs are expanded on input and introduced on
2114 @cindex line-breaking
2115 @cindex sentences and line-breaking
2116 @cindex Knuth, Donald E.
2117 @cindex Plass, Michael F.
2118 @command{fmt} prefers breaking lines at the end of a sentence, and tries to
2119 avoid line breaks after the first word of a sentence or before the last
2120 word of a sentence. A @dfn{sentence break} is defined as either the end
2121 of a paragraph or a word ending in any of @samp{.?!}, followed by two
2122 spaces or end of line, ignoring any intervening parentheses or quotes.
2123 Like @TeX{}, @command{fmt} reads entire ``paragraphs'' before choosing line
2124 breaks; the algorithm is a variant of that given by Donald E. Knuth
2125 and Michael F. Plass in ``Breaking Paragraphs Into Lines'',
2126 @cite{Software---Practice & Experience} @b{11}, 11 (November 1981),
2129 The program accepts the following options. Also see @ref{Common options}.
2134 @itemx --crown-margin
2136 @opindex --crown-margin
2137 @cindex crown margin
2138 @dfn{Crown margin} mode: preserve the indentation of the first two
2139 lines within a paragraph, and align the left margin of each subsequent
2140 line with that of the second line.
2143 @itemx --tagged-paragraph
2145 @opindex --tagged-paragraph
2146 @cindex tagged paragraphs
2147 @dfn{Tagged paragraph} mode: like crown margin mode, except that if
2148 indentation of the first line of a paragraph is the same as the
2149 indentation of the second, the first line is treated as a one-line
2155 @opindex --split-only
2156 Split lines only. Do not join short lines to form longer ones. This
2157 prevents sample lines of code, and other such ``formatted'' text from
2158 being unduly combined.
2161 @itemx --uniform-spacing
2163 @opindex --uniform-spacing
2164 Uniform spacing. Reduce spacing between words to one space, and spacing
2165 between sentences to two spaces.
2168 @itemx -w @var{width}
2169 @itemx --width=@var{width}
2170 @opindex -@var{width}
2173 Fill output lines up to @var{width} characters (default 75). @command{fmt}
2174 initially tries to make lines about 7% shorter than this, to give it
2175 room to balance line lengths.
2177 @item -p @var{prefix}
2178 @itemx --prefix=@var{prefix}
2179 Only lines beginning with @var{prefix} (possibly preceded by whitespace)
2180 are subject to formatting. The prefix and any preceding whitespace are
2181 stripped for the formatting and then re-attached to each formatted output
2182 line. One use is to format certain kinds of program comments, while
2183 leaving the code unchanged.
2191 @section @command{pr}: Paginate or columnate files for printing
2194 @cindex printing, preparing files for
2195 @cindex multicolumn output, generating
2196 @cindex merging files in parallel
2198 @command{pr} writes each @var{file} (@samp{-} means standard input), or
2199 standard input if none are given, to standard output, paginating and
2200 optionally outputting in multicolumn format; optionally merges all
2201 @var{file}s, printing all in parallel, one per column. Synopsis:
2204 pr [@var{option}]@dots{} [@var{file}]@dots{}
2208 By default, a 5-line header is printed at each page: two blank lines;
2209 a line with the date, the file name, and the page count; and two more
2210 blank lines. A footer of five blank lines is also printed.
2211 The default @var{page_length} is 66
2212 lines. The default number of text lines is therefore 56.
2213 The text line of the header takes the form
2214 @samp{@var{date} @var{string} @var{page}}, with spaces inserted around
2215 @var{string} so that the line takes up the full @var{page_width}. Here,
2216 @var{date} is the date (see the @option{-D} or @option{--date-format}
2217 option for details), @var{string} is the centered header string, and
2218 @var{page} identifies the page number. The @env{LC_MESSAGES} locale
2219 category affects the spelling of @var{page}; in the default C locale, it
2220 is @samp{Page @var{number}} where @var{number} is the decimal page
2223 Form feeds in the input cause page breaks in the output. Multiple form
2224 feeds produce empty pages.
2226 Columns are of equal width, separated by an optional string (default
2227 is @samp{space}). For multicolumn output, lines will always be truncated to
2228 @var{page_width} (default 72), unless you use the @option{-J} option.
2230 column output no line truncation occurs by default. Use @option{-W} option to
2231 truncate lines in that case.
2233 The following changes were made in version 1.22i and apply to later
2234 versions of @command{pr}:
2235 @c FIXME: this whole section here sounds very awkward to me. I
2236 @c made a few small changes, but really it all needs to be redone. - Brian
2237 @c OK, I fixed another sentence or two, but some of it I just don't understand.
2242 Some small @var{letter options} (@option{-s}, @option{-w}) have been
2243 redefined for better @acronym{POSIX} compliance. The output of some further
2244 cases has been adapted to other Unix systems. These changes are not
2245 compatible with earlier versions of the program.
2248 Some @var{new capital letter} options (@option{-J}, @option{-S}, @option{-W})
2249 have been introduced to turn off unexpected interferences of small letter
2250 options. The @option{-N} option and the second argument @var{last_page}
2251 of @samp{+FIRST_PAGE} offer more flexibility. The detailed handling of
2252 form feeds set in the input files requires the @option{-T} option.
2255 Capital letter options override small letter ones.
2258 Some of the option-arguments (compare @option{-s}, @option{-e},
2259 @option{-i}, @option{-n}) cannot be specified as separate arguments from the
2260 preceding option letter (already stated in the @acronym{POSIX} specification).
2263 The program accepts the following options. Also see @ref{Common options}.
2267 @item +@var{first_page}[:@var{last_page}]
2268 @itemx --pages=@var{first_page}[:@var{last_page}]
2269 @c The two following @opindex lines evoke warnings because they contain `:'
2270 @c The `info' spec does not permit that. If we use those lines, we end
2271 @c up with truncated index entries that don't work.
2272 @c @opindex +@var{first_page}[:@var{last_page}]
2273 @c @opindex --pages=@var{first_page}[:@var{last_page}]
2274 @opindex +@var{page_range}
2275 @opindex --pages=@var{page_range}
2276 Begin printing with page @var{first_page} and stop with @var{last_page}.
2277 Missing @samp{:@var{last_page}} implies end of file. While estimating
2278 the number of skipped pages each form feed in the input file results
2279 in a new page. Page counting with and without @samp{+@var{first_page}}
2280 is identical. By default, counting starts with the first page of input
2281 file (not first page printed). Line numbering may be altered by @option{-N}
2285 @itemx --columns=@var{column}
2286 @opindex -@var{column}
2288 @cindex down columns
2289 With each single @var{file}, produce @var{column} columns of output
2290 (default is 1) and print columns down, unless @option{-a} is used. The
2291 column width is automatically decreased as @var{column} increases; unless
2292 you use the @option{-W/-w} option to increase @var{page_width} as well.
2293 This option might well cause some lines to be truncated. The number of
2294 lines in the columns on each page are balanced. The options @option{-e}
2295 and @option{-i} are on for multiple text-column output. Together with
2296 @option{-J} option column alignment and line truncation is turned off.
2297 Lines of full length are joined in a free field format and @option{-S}
2298 option may set field separators. @option{-@var{column}} may not be used
2299 with @option{-m} option.
2305 @cindex across columns
2306 With each single @var{file}, print columns across rather than down. The
2307 @option{-@var{column}} option must be given with @var{column} greater than one.
2308 If a line is too long to fit in a column, it is truncated.
2311 @itemx --show-control-chars
2313 @opindex --show-control-chars
2314 Print control characters using hat notation (e.g., @samp{^G}); print
2315 other nonprinting characters in octal backslash notation. By default,
2316 nonprinting characters are not changed.
2319 @itemx --double-space
2321 @opindex --double-space
2322 @cindex double spacing
2323 Double space the output.
2325 @item -D @var{format}
2326 @itemx --date-format=@var{format}
2327 @cindex time formats
2328 @cindex formatting times
2329 Format header dates using @var{format}, using the same conventions as
2330 for the command @samp{date +@var{format}}; @xref{date invocation}.
2331 Except for directives, which start with
2332 @samp{%}, characters in @var{format} are printed unchanged. You can use
2333 this option to specify an arbitrary string in place of the header date,
2334 e.g., @option{--date-format="Monday morning"}.
2336 @vindex POSIXLY_CORRECT
2338 The default date format is @samp{%Y-%m-%d %H:%M} (for example,
2339 @samp{2001-12-04 23:59});
2340 but if the @env{POSIXLY_CORRECT} environment variable is set
2341 and the @env{LC_TIME} locale category specifies the @acronym{POSIX}
2342 locale, the default is @samp{%b %e %H:%M %Y} (for example,
2343 @samp{Dec@ @ 4 23:59 2001}.
2346 Time stamps are listed according to the time zone rules specified by
2347 the @env{TZ} environment variable, or by the system default rules if
2348 @env{TZ} is not set. @xref{TZ Variable,, Specifying the Time Zone
2349 with @env{TZ}, libc, The GNU C Library Reference Manual}.
2351 @item -e[@var{in-tabchar}[@var{in-tabwidth}]]
2352 @itemx --expand-tabs[=@var{in-tabchar}[@var{in-tabwidth}]]
2354 @opindex --expand-tabs
2356 Expand @var{tab}s to spaces on input. Optional argument @var{in-tabchar} is
2357 the input tab character (default is the TAB character). Second optional
2358 argument @var{in-tabwidth} is the input tab character's width (default
2366 @opindex --form-feed
2367 Use a form feed instead of newlines to separate output pages. This does
2368 not alter the default page length of 66 lines.
2370 @item -h @var{header}
2371 @itemx --header=@var{header}
2374 Replace the file name in the header with the centered string @var{header}.
2375 When using the shell, @var{header} should be quoted and should be
2376 separated from @option{-h} by a space.
2378 @item -i[@var{out-tabchar}[@var{out-tabwidth}]]
2379 @itemx --output-tabs[=@var{out-tabchar}[@var{out-tabwidth}]]
2381 @opindex --output-tabs
2383 Replace spaces with @var{tab}s on output. Optional argument @var{out-tabchar}
2384 is the output tab character (default is the TAB character). Second optional
2385 argument @var{out-tabwidth} is the output tab character's width (default
2391 @opindex --join-lines
2392 Merge lines of full length. Used together with the column options
2393 @option{-@var{column}}, @option{-a -@var{column}} or @option{-m}. Turns off
2394 @option{-W/-w} line truncation;
2395 no column alignment used; may be used with
2396 @option{--sep-string[=@var{string}]}. @option{-J} has been introduced
2397 (together with @option{-W} and @option{--sep-string})
2398 to disentangle the old (@acronym{POSIX}-compliant) options @option{-w} and
2399 @option{-s} along with the three column options.
2402 @item -l @var{page_length}
2403 @itemx --length=@var{page_length}
2406 Set the page length to @var{page_length} (default 66) lines, including
2407 the lines of the header [and the footer]. If @var{page_length} is less
2408 than or equal to 10, the header and footer are omitted, as if the
2409 @option{-t} option had been given.
2415 Merge and print all @var{file}s in parallel, one in each column. If a
2416 line is too long to fit in a column, it is truncated, unless the @option{-J}
2417 option is used. @option{--sep-string[=@var{string}]} may be used.
2419 some @var{file}s (form feeds set) produce empty columns, still marked
2420 by @var{string}. The result is a continuous line numbering and column
2421 marking throughout the whole merged file. Completely empty merged pages
2422 show no separators or line numbers. The default header becomes
2423 @samp{@var{date} @var{page}} with spaces inserted in the middle; this
2424 may be used with the @option{-h} or @option{--header} option to fill up
2425 the middle blank part.
2427 @item -n[@var{number-separator}[@var{digits}]]
2428 @itemx --number-lines[=@var{number-separator}[@var{digits}]]
2430 @opindex --number-lines
2431 Provide @var{digits} digit line numbering (default for @var{digits} is
2432 5). With multicolumn output the number occupies the first @var{digits}
2433 column positions of each text column or only each line of @option{-m}
2434 output. With single column output the number precedes each line just as
2435 @option{-m} does. Default counting of the line numbers starts with the
2436 first line of the input file (not the first line printed, compare the
2437 @option{--page} option and @option{-N} option).
2438 Optional argument @var{number-separator} is the character appended to
2439 the line number to separate it from the text followed. The default
2440 separator is the TAB character. In a strict sense a TAB is always
2441 printed with single column output only. The TAB width varies
2442 with the TAB position, e.g., with the left @var{margin} specified
2443 by @option{-o} option. With multicolumn output priority is given to
2444 @samp{equal width of output columns} (a @acronym{POSIX} specification).
2445 The TAB width is fixed to the value of the first column and does
2446 not change with different values of left @var{margin}. That means a
2447 fixed number of spaces is always printed in the place of the
2448 @var{number-separator} TAB. The tabification depends upon the output
2451 @item -N @var{line_number}
2452 @itemx --first-line-number=@var{line_number}
2454 @opindex --first-line-number
2455 Start line counting with the number @var{line_number} at first line of
2456 first page printed (in most cases not the first line of the input file).
2458 @item -o @var{margin}
2459 @itemx --indent=@var{margin}
2462 @cindex indenting lines
2464 Indent each line with a margin @var{margin} spaces wide (default is zero).
2465 The total page width is the size of the margin plus the @var{page_width}
2466 set with the @option{-W/-w} option. A limited overflow may occur with
2467 numbered single column output (compare @option{-n} option).
2470 @itemx --no-file-warnings
2472 @opindex --no-file-warnings
2473 Do not print a warning message when an argument @var{file} cannot be
2474 opened. (The exit status will still be nonzero, however.)
2476 @item -s[@var{char}]
2477 @itemx --separator[=@var{char}]
2479 @opindex --separator
2480 Separate columns by a single character @var{char}. The default for
2481 @var{char} is the TAB character without @option{-w} and @samp{no
2482 character} with @option{-w}. Without @option{-s} the default separator
2483 @samp{space} is set. @option{-s[char]} turns off line truncation of all
2484 three column options (@option{-COLUMN}|@option{-a -COLUMN}|@option{-m}) unless
2485 @option{-w} is set. This is a @acronym{POSIX}-compliant formulation.
2488 @item -S@var{string}
2489 @itemx --sep-string[=@var{string}]
2491 @opindex --sep-string
2492 Use @var{string} to separate output columns. The @option{-S} option doesn't
2493 affect the @option{-W/-w} option, unlike the @option{-s} option which does. It
2494 does not affect line truncation or column alignment.
2495 Without @option{-S}, and with @option{-J}, @command{pr} uses the default output
2497 Without @option{-S} or @option{-J}, @command{pr} uses a @samp{space}
2498 (same as @option{-S"@w{ }"}). @option{--sep-string} with no
2499 @samp{=@var{string}} is equivalent to @option{--sep-string=""}.
2502 @itemx --omit-header
2504 @opindex --omit-header
2505 Do not print the usual header [and footer] on each page, and do not fill
2506 out the bottom of pages (with blank lines or a form feed). No page
2507 structure is produced, but form feeds set in the input files are retained.
2508 The predefined pagination is not changed. @option{-t} or @option{-T} may be
2509 useful together with other options; e.g.: @option{-t -e4}, expand TAB characters
2510 in the input file to 4 spaces but don't make any other changes. Use of
2511 @option{-t} overrides @option{-h}.
2514 @itemx --omit-pagination
2516 @opindex --omit-pagination
2517 Do not print header [and footer]. In addition eliminate all form feeds
2518 set in the input files.
2521 @itemx --show-nonprinting
2523 @opindex --show-nonprinting
2524 Print nonprinting characters in octal backslash notation.
2526 @item -w @var{page_width}
2527 @itemx --width=@var{page_width}
2530 Set page width to @var{page_width} characters for multiple text-column
2531 output only (default for @var{page_width} is 72). @option{-s[CHAR]} turns
2532 off the default page width and any line truncation and column alignment.
2533 Lines of full length are merged, regardless of the column options
2534 set. No @var{page_width} setting is possible with single column output.
2535 A @acronym{POSIX}-compliant formulation.
2537 @item -W @var{page_width}
2538 @itemx --page_width=@var{page_width}
2540 @opindex --page_width
2541 Set the page width to @var{page_width} characters. That's valid with and
2542 without a column option. Text lines are truncated, unless @option{-J}
2543 is used. Together with one of the three column options
2544 (@option{-@var{column}}, @option{-a -@var{column}} or @option{-m}) column
2545 alignment is always used. The separator options @option{-S} or @option{-s}
2546 don't affect the @option{-W} option. Default is 72 characters. Without
2547 @option{-W @var{page_width}} and without any of the column options NO line
2548 truncation is used (defined to keep downward compatibility and to meet
2549 most frequent tasks). That's equivalent to @option{-W 72 -J}. The header
2550 line is never truncated.
2557 @node fold invocation
2558 @section @command{fold}: Wrap input lines to fit in specified width
2561 @cindex wrapping long input lines
2562 @cindex folding long input lines
2564 @command{fold} writes each @var{file} (@option{-} means standard input), or
2565 standard input if none are given, to standard output, breaking long
2569 fold [@var{option}]@dots{} [@var{file}]@dots{}
2572 By default, @command{fold} breaks lines wider than 80 columns. The output
2573 is split into as many lines as necessary.
2575 @cindex screen columns
2576 @command{fold} counts screen columns by default; thus, a tab may count more
2577 than one column, backspace decreases the column count, and carriage
2578 return sets the column to zero.
2580 The program accepts the following options. Also see @ref{Common options}.
2588 Count bytes rather than columns, so that tabs, backspaces, and carriage
2589 returns are each counted as taking up one column, just like other
2596 Break at word boundaries: the line is broken after the last blank before
2597 the maximum line length. If the line contains no such blanks, the line
2598 is broken at the maximum line length as usual.
2600 @item -w @var{width}
2601 @itemx --width=@var{width}
2604 Use a maximum line length of @var{width} columns instead of 80.
2606 For compatibility @command{fold} supports an obsolete option syntax
2607 @option{-@var{width}}. New scripts should use @option{-w @var{width}}
2615 @node Output of parts of files
2616 @chapter Output of parts of files
2618 @cindex output of parts of files
2619 @cindex parts of files, output of
2621 These commands output pieces of the input.
2624 * head invocation:: Output the first part of files.
2625 * tail invocation:: Output the last part of files.
2626 * split invocation:: Split a file into fixed-size pieces.
2627 * csplit invocation:: Split a file into context-determined pieces.
2630 @node head invocation
2631 @section @command{head}: Output the first part of files
2634 @cindex initial part of files, outputting
2635 @cindex first part of files, outputting
2637 @command{head} prints the first part (10 lines by default) of each
2638 @var{file}; it reads from standard input if no files are given or
2639 when given a @var{file} of @option{-}. Synopsis:
2642 head [@var{option}]@dots{} [@var{file}]@dots{}
2645 If more than one @var{file} is specified, @command{head} prints a
2646 one-line header consisting of:
2649 ==> @var{file name} <==
2653 before the output for each @var{file}.
2655 The program accepts the following options. Also see @ref{Common options}.
2660 @itemx --bytes=@var{k}
2663 Print the first @var{k} bytes, instead of initial lines.
2664 However, if @var{k} starts with a @samp{-},
2665 print all but the last @var{k} bytes of each file.
2666 @multiplierSuffixes{k}
2669 @itemx --lines=@var{k}
2672 Output the first @var{k} lines.
2673 However, if @var{k} starts with a @samp{-},
2674 print all but the last @var{k} lines of each file.
2675 Size multiplier suffixes are the same as with the @option{-c} option.
2683 Never print file name headers.
2689 Always print file name headers.
2693 For compatibility @command{head} also supports an obsolete option syntax
2694 @option{-@var{count}@var{options}}, which is recognized only if it is
2695 specified first. @var{count} is a decimal number optionally followed
2696 by a size letter (@samp{b}, @samp{k}, @samp{m}) as in @option{-c}, or
2697 @samp{l} to mean count by lines, or other option letters (@samp{cqv}).
2698 Scripts intended for standard hosts should use @option{-c @var{count}}
2699 or @option{-n @var{count}} instead. If your script must also run on
2700 hosts that support only the obsolete syntax, it is usually simpler to
2701 avoid @command{head}, e.g., by using @samp{sed 5q} instead of
2707 @node tail invocation
2708 @section @command{tail}: Output the last part of files
2711 @cindex last part of files, outputting
2713 @command{tail} prints the last part (10 lines by default) of each
2714 @var{file}; it reads from standard input if no files are given or
2715 when given a @var{file} of @samp{-}. Synopsis:
2718 tail [@var{option}]@dots{} [@var{file}]@dots{}
2721 If more than one @var{file} is specified, @command{tail} prints a
2722 one-line header consisting of:
2725 ==> @var{file name} <==
2729 before the output for each @var{file}.
2731 @cindex BSD @command{tail}
2732 @sc{gnu} @command{tail} can output any amount of data (some other versions of
2733 @command{tail} cannot). It also has no @option{-r} option (print in
2734 reverse), since reversing a file is really a different job from printing
2735 the end of a file; BSD @command{tail} (which is the one with @option{-r}) can
2736 only reverse files that are at most as large as its buffer, which is
2737 typically 32 KiB@. A more reliable and versatile way to reverse files is
2738 the @sc{gnu} @command{tac} command.
2740 The program accepts the following options. Also see @ref{Common options}.
2745 @itemx --bytes=@var{k}
2748 Output the last @var{k} bytes, instead of final lines.
2749 However, if @var{k} starts with a @samp{+}, start printing with the
2750 @var{k}th byte from the start of each file, instead of from the end.
2751 @multiplierSuffixes{k}
2754 @itemx --follow[=@var{how}]
2757 @cindex growing files
2758 @vindex name @r{follow option}
2759 @vindex descriptor @r{follow option}
2760 Loop forever trying to read more characters at the end of the file,
2761 presumably because the file is growing.
2762 If more than one file is given, @command{tail} prints a header whenever it
2763 gets output from a different file, to indicate which file that output is
2766 There are two ways to specify how you'd like to track files with this option,
2767 but that difference is noticeable only when a followed file is removed or
2769 If you'd like to continue to track the end of a growing file even after
2770 it has been unlinked, use @option{--follow=descriptor}. This is the default
2771 behavior, but it is not useful if you're tracking a log file that may be
2772 rotated (removed or renamed, then reopened). In that case, use
2773 @option{--follow=name} to track the named file by reopening it periodically
2774 to see if it has been removed and recreated by some other program.
2776 No matter which method you use, if the tracked file is determined to have
2777 shrunk, @command{tail} prints a message saying the file has been truncated
2778 and resumes tracking the end of the file from the newly-determined endpoint.
2780 When a file is removed, @command{tail}'s behavior depends on whether it is
2781 following the name or the descriptor. When following by name, tail can
2782 detect that a file has been removed and gives a message to that effect,
2783 and if @option{--retry} has been specified it will continue checking
2784 periodically to see if the file reappears.
2785 When following a descriptor, tail does not detect that the file has
2786 been unlinked or renamed and issues no message; even though the file
2787 may no longer be accessible via its original name, it may still be
2790 The option values @samp{descriptor} and @samp{name} may be specified only
2791 with the long form of the option, not with @option{-f}.
2793 The @option{-f} option is ignored if
2794 no @var{file} operand is specified and standard input is a FIFO or a pipe.
2795 Likewise, the @option{-f} option has no effect for any
2796 operand specified as @samp{-}, when standard input is a FIFO or a pipe.
2800 This option is the same as @option{--follow=name --retry}. That is, tail
2801 will attempt to reopen a file when it is removed. Should this fail, tail
2802 will keep trying until it becomes accessible again.
2806 This option is useful mainly when following by name (i.e., with
2807 @option{--follow=name}).
2808 Without this option, when tail encounters a file that doesn't
2809 exist or is otherwise inaccessible, it reports that fact and
2810 never checks it again.
2812 @itemx --sleep-interval=@var{number}
2813 @opindex --sleep-interval
2814 Change the number of seconds to wait between iterations (the default is 1.0).
2815 During one iteration, every specified file is checked to see if it has
2817 Historical implementations of @command{tail} have required that
2818 @var{number} be an integer. However, GNU @command{tail} accepts
2819 an arbitrary floating point number (using a period before any
2822 @itemx --pid=@var{pid}
2824 When following by name or by descriptor, you may specify the process ID,
2825 @var{pid}, of the sole writer of all @var{file} arguments. Then, shortly
2826 after that process terminates, tail will also terminate. This will
2827 work properly only if the writer and the tailing process are running on
2828 the same machine. For example, to save the output of a build in a file
2829 and to watch the file grow, if you invoke @command{make} and @command{tail}
2830 like this then the tail process will stop when your build completes.
2831 Without this option, you would have had to kill the @code{tail -f}
2835 $ make >& makerr & tail --pid=$! -f makerr
2838 If you specify a @var{pid} that is not in use or that does not correspond
2839 to the process that is writing to the tailed files, then @command{tail}
2840 may terminate long before any @var{file}s stop growing or it may not
2841 terminate until long after the real writer has terminated.
2842 Note that @option{--pid} cannot be supported on some systems; @command{tail}
2843 will print a warning if this is the case.
2845 @itemx --max-unchanged-stats=@var{n}
2846 @opindex --max-unchanged-stats
2847 When tailing a file by name, if there have been @var{n} (default
2848 n=@value{DEFAULT_MAX_N_UNCHANGED_STATS_BETWEEN_OPENS}) consecutive
2849 iterations for which the file has not changed, then
2850 @code{open}/@code{fstat} the file to determine if that file name is
2851 still associated with the same device/inode-number pair as before.
2852 When following a log file that is rotated, this is approximately the
2853 number of seconds between when tail prints the last pre-rotation lines
2854 and when it prints the lines that have accumulated in the new log file.
2855 This option is meaningful only when following by name.
2858 @itemx --lines=@var{k}
2861 Output the last @var{k} lines.
2862 However, if @var{k} starts with a @samp{+}, start printing with the
2863 @var{k}th line from the start of each file, instead of from the end.
2864 Size multiplier suffixes are the same as with the @option{-c} option.
2872 Never print file name headers.
2878 Always print file name headers.
2882 For compatibility @command{tail} also supports an obsolete usage
2883 @samp{tail -[@var{count}][bcl][f] [@var{file}]}, which is recognized
2884 only if it does not conflict with the usage described
2885 above. This obsolete form uses exactly one option and at most one
2886 file. In the option, @var{count} is an optional decimal number optionally
2887 followed by a size letter (@samp{b}, @samp{c}, @samp{l}) to mean count
2888 by 512-byte blocks, bytes, or lines, optionally followed by @samp{f}
2889 which has the same meaning as @option{-f}.
2891 @vindex _POSIX2_VERSION
2892 On older systems, the leading @samp{-} can be replaced by @samp{+} in
2893 the obsolete option syntax with the same meaning as in counts, and
2894 obsolete usage overrides normal usage when the two conflict.
2895 This obsolete behavior can be enabled or disabled with the
2896 @env{_POSIX2_VERSION} environment variable (@pxref{Standards
2899 Scripts intended for use on standard hosts should avoid obsolete
2900 syntax and should use @option{-c @var{count}[b]}, @option{-n
2901 @var{count}}, and/or @option{-f} instead. If your script must also
2902 run on hosts that support only the obsolete syntax, you can often
2903 rewrite it to avoid problematic usages, e.g., by using @samp{sed -n
2904 '$p'} rather than @samp{tail -1}. If that's not possible, the script
2905 can use a test like @samp{if tail -c +1 </dev/null >/dev/null 2>&1;
2906 then @dots{}} to decide which syntax to use.
2908 Even if your script assumes the standard behavior, you should still
2909 beware usages whose behaviors differ depending on the @acronym{POSIX}
2910 version. For example, avoid @samp{tail - main.c}, since it might be
2911 interpreted as either @samp{tail main.c} or as @samp{tail -- -
2912 main.c}; avoid @samp{tail -c 4}, since it might mean either @samp{tail
2913 -c4} or @samp{tail -c 10 4}; and avoid @samp{tail +4}, since it might
2914 mean either @samp{tail ./+4} or @samp{tail -n +4}.
2919 @node split invocation
2920 @section @command{split}: Split a file into fixed-size pieces
2923 @cindex splitting a file into pieces
2924 @cindex pieces, splitting a file into
2926 @command{split} creates output files containing consecutive sections of
2927 @var{input} (standard input if none is given or @var{input} is
2928 @samp{-}). Synopsis:
2931 split [@var{option}] [@var{input} [@var{prefix}]]
2934 By default, @command{split} puts 1000 lines of @var{input} (or whatever is
2935 left over for the last section), into each output file.
2937 @cindex output file name prefix
2938 The output files' names consist of @var{prefix} (@samp{x} by default)
2939 followed by a group of characters (@samp{aa}, @samp{ab}, @dots{} by
2940 default), such that concatenating the output files in traditional
2941 sorted order by file name produces
2942 the original input file. If the output file names are exhausted,
2943 @command{split} reports an error without deleting the output files
2946 The program accepts the following options. Also see @ref{Common options}.
2950 @item -l @var{lines}
2951 @itemx --lines=@var{lines}
2954 Put @var{lines} lines of @var{input} into each output file.
2956 For compatibility @command{split} also supports an obsolete
2957 option syntax @option{-@var{lines}}. New scripts should use @option{-l
2958 @var{lines}} instead.
2961 @itemx --bytes=@var{size}
2964 Put @var{size} bytes of @var{input} into each output file.
2965 @multiplierSuffixes{size}
2968 @itemx --line-bytes=@var{size}
2970 @opindex --line-bytes
2971 Put into each output file as many complete lines of @var{input} as
2972 possible without exceeding @var{size} bytes. Individual lines longer than
2973 @var{size} bytes are broken into multiple files.
2974 @var{size} has the same format as for the @option{--bytes} option.
2976 @item -a @var{length}
2977 @itemx --suffix-length=@var{length}
2979 @opindex --suffix-length
2980 Use suffixes of length @var{length}. The default @var{length} is 2.
2983 @itemx --numeric-suffixes
2985 @opindex --numeric-suffixes
2986 Use digits in suffixes rather than lower-case letters.
2990 Write a diagnostic just before each output file is opened.
2997 @node csplit invocation
2998 @section @command{csplit}: Split a file into context-determined pieces
3001 @cindex context splitting
3002 @cindex splitting a file into pieces by context
3004 @command{csplit} creates zero or more output files containing sections of
3005 @var{input} (standard input if @var{input} is @samp{-}). Synopsis:
3008 csplit [@var{option}]@dots{} @var{input} @var{pattern}@dots{}
3011 The contents of the output files are determined by the @var{pattern}
3012 arguments, as detailed below. An error occurs if a @var{pattern}
3013 argument refers to a nonexistent line of the input file (e.g., if no
3014 remaining line matches a given regular expression). After every
3015 @var{pattern} has been matched, any remaining input is copied into one
3018 By default, @command{csplit} prints the number of bytes written to each
3019 output file after it has been created.
3021 The types of pattern arguments are:
3026 Create an output file containing the input up to but not including line
3027 @var{n} (a positive integer). If followed by a repeat count, also
3028 create an output file containing the next @var{n} lines of the input
3029 file once for each repeat.
3031 @item /@var{regexp}/[@var{offset}]
3032 Create an output file containing the current line up to (but not
3033 including) the next line of the input file that contains a match for
3034 @var{regexp}. The optional @var{offset} is an integer.
3035 If it is given, the input up to (but not including) the
3036 matching line plus or minus @var{offset} is put into the output file,
3037 and the line after that begins the next section of input.
3039 @item %@var{regexp}%[@var{offset}]
3040 Like the previous type, except that it does not create an output
3041 file, so that section of the input file is effectively ignored.
3043 @item @{@var{repeat-count}@}
3044 Repeat the previous pattern @var{repeat-count} additional
3045 times. The @var{repeat-count} can either be a positive integer or an
3046 asterisk, meaning repeat as many times as necessary until the input is
3051 The output files' names consist of a prefix (@samp{xx} by default)
3052 followed by a suffix. By default, the suffix is an ascending sequence
3053 of two-digit decimal numbers from @samp{00} to @samp{99}. In any case,
3054 concatenating the output files in sorted order by file name produces the
3055 original input file.
3057 By default, if @command{csplit} encounters an error or receives a hangup,
3058 interrupt, quit, or terminate signal, it removes any output files
3059 that it has created so far before it exits.
3061 The program accepts the following options. Also see @ref{Common options}.
3065 @item -f @var{prefix}
3066 @itemx --prefix=@var{prefix}
3069 @cindex output file name prefix
3070 Use @var{prefix} as the output file name prefix.
3072 @item -b @var{suffix}
3073 @itemx --suffix=@var{suffix}
3076 @cindex output file name suffix
3077 Use @var{suffix} as the output file name suffix. When this option is
3078 specified, the suffix string must include exactly one
3079 @code{printf(3)}-style conversion specification, possibly including
3080 format specification flags, a field width, a precision specifications,
3081 or all of these kinds of modifiers. The format letter must convert a
3082 binary integer argument to readable form; thus, only @samp{d}, @samp{i},
3083 @samp{u}, @samp{o}, @samp{x}, and @samp{X} conversions are allowed. The
3084 entire @var{suffix} is given (with the current output file number) to
3085 @code{sprintf(3)} to form the file name suffixes for each of the
3086 individual output files in turn. If this option is used, the
3087 @option{--digits} option is ignored.
3089 @item -n @var{digits}
3090 @itemx --digits=@var{digits}
3093 Use output file names containing numbers that are @var{digits} digits
3094 long instead of the default 2.
3099 @opindex --keep-files
3100 Do not remove output files when errors are encountered.
3103 @itemx --elide-empty-files
3105 @opindex --elide-empty-files
3106 Suppress the generation of zero-length output files. (In cases where
3107 the section delimiters of the input file are supposed to mark the first
3108 lines of each of the sections, the first output file will generally be a
3109 zero-length file unless you use this option.) The output file sequence
3110 numbers always run consecutively starting from 0, even when this option
3121 Do not print counts of output file sizes.
3127 Here is an example of its usage.
3128 First, create an empty directory for the exercise,
3135 Now, split the sequence of 1..14 on lines that end with 0 or 5:
3138 $ seq 14 | csplit - '/[05]$/' '@{*@}'
3144 Each number printed above is the size of an output
3145 file that csplit has just created.
3146 List the names of those output files:
3153 Use @command{head} to show their contents:
3178 @node Summarizing files
3179 @chapter Summarizing files
3181 @cindex summarizing files
3183 These commands generate just a few numbers representing entire
3187 * wc invocation:: Print newline, word, and byte counts.
3188 * sum invocation:: Print checksum and block counts.
3189 * cksum invocation:: Print CRC checksum and byte counts.
3190 * md5sum invocation:: Print or check MD5 digests.
3191 * sha1sum invocation:: Print or check SHA-1 digests.
3192 * sha2 utilities:: Print or check SHA-2 digests.
3197 @section @command{wc}: Print newline, word, and byte counts
3201 @cindex character count
3205 @command{wc} counts the number of bytes, characters, whitespace-separated
3206 words, and newlines in each given @var{file}, or standard input if none
3207 are given or for a @var{file} of @samp{-}. Synopsis:
3210 wc [@var{option}]@dots{} [@var{file}]@dots{}
3213 @cindex total counts
3214 @command{wc} prints one line of counts for each file, and if the file was
3215 given as an argument, it prints the file name following the counts. If
3216 more than one @var{file} is given, @command{wc} prints a final line
3217 containing the cumulative counts, with the file name @file{total}. The
3218 counts are printed in this order: newlines, words, characters, bytes,
3219 maximum line length.
3220 Each count is printed right-justified in a field with at least one
3221 space between fields so that the numbers and file names normally line
3222 up nicely in columns. The width of the count fields varies depending
3223 on the inputs, so you should not depend on a particular field width.
3224 However, as a @acronym{GNU} extension, if only one count is printed,
3225 it is guaranteed to be printed without leading spaces.
3227 By default, @command{wc} prints three counts: the newline, words, and byte
3228 counts. Options can specify that only certain counts be printed.
3229 Options do not undo others previously given, so
3236 prints both the byte counts and the word counts.
3238 With the @option{--max-line-length} option, @command{wc} prints the length
3239 of the longest line per file, and if there is more than one file it
3240 prints the maximum (not the sum) of those lengths. The line lengths here
3241 are measured in screen columns, according to the current locale and
3242 assuming tab positions in every 8th column.
3244 The program accepts the following options. Also see @ref{Common options}.
3252 Print only the byte counts.
3258 Print only the character counts.
3264 Print only the word counts.
3270 Print only the newline counts.
3273 @itemx --max-line-length
3275 @opindex --max-line-length
3276 Print only the maximum line lengths.
3278 @macro filesZeroFromOption{cmd,withTotalOption,subListOutput}
3279 @itemx --files0-from=@var{file}
3280 @opindex --files0-from=@var{file}
3281 @c This is commented out to avoid a texi2dvi failure.
3282 @c texi2dvi (GNU Texinfo 4.11) 1.104
3283 @c @cindex including files from @command{\cmd\}
3284 Disallow processing files named on the command line, and instead process
3285 those named in file @var{file}; each name being terminated by a zero byte
3286 (@acronym{ASCII} @sc{nul}).
3287 This is useful \withTotalOption\
3288 when the list of file names is so long that it may exceed a command line
3290 In such cases, running @command{\cmd\} via @command{xargs} is undesirable
3291 because it splits the list into pieces and makes @command{\cmd\} print
3292 \subListOutput\ for each sublist rather than for the entire list.
3293 One way to produce a list of @acronym{ASCII} @sc{nul} terminated file names is with @sc{gnu}
3294 @command{find}, using its @option{-print0} predicate.
3295 If @var{file} is @samp{-} then the @acronym{ASCII} @sc{nul} terminated file names
3296 are read from standard input.
3298 @filesZeroFromOption{wc,,a total}
3300 For example, to find the length of the longest line in any @file{.c} or
3301 @file{.h} file in the current hierarchy, do this:
3304 find . -name '*.[ch]' -print0 |
3305 wc -L --files0-from=- | tail -n1
3313 @node sum invocation
3314 @section @command{sum}: Print checksum and block counts
3317 @cindex 16-bit checksum
3318 @cindex checksum, 16-bit
3320 @command{sum} computes a 16-bit checksum for each given @var{file}, or
3321 standard input if none are given or for a @var{file} of @samp{-}. Synopsis:
3324 sum [@var{option}]@dots{} [@var{file}]@dots{}
3327 @command{sum} prints the checksum for each @var{file} followed by the
3328 number of blocks in the file (rounded up). If more than one @var{file}
3329 is given, file names are also printed (by default). (With the
3330 @option{--sysv} option, corresponding file names are printed when there is
3331 at least one file argument.)
3333 By default, @sc{gnu} @command{sum} computes checksums using an algorithm
3334 compatible with BSD @command{sum} and prints file sizes in units of
3337 The program accepts the following options. Also see @ref{Common options}.
3343 @cindex BSD @command{sum}
3344 Use the default (BSD compatible) algorithm. This option is included for
3345 compatibility with the System V @command{sum}. Unless @option{-s} was also
3346 given, it has no effect.
3352 @cindex System V @command{sum}
3353 Compute checksums using an algorithm compatible with System V
3354 @command{sum}'s default, and print file sizes in units of 512-byte blocks.
3358 @command{sum} is provided for compatibility; the @command{cksum} program (see
3359 next section) is preferable in new applications.
3364 @node cksum invocation
3365 @section @command{cksum}: Print CRC checksum and byte counts
3368 @cindex cyclic redundancy check
3369 @cindex CRC checksum
3371 @command{cksum} computes a cyclic redundancy check (CRC) checksum for each
3372 given @var{file}, or standard input if none are given or for a
3373 @var{file} of @samp{-}. Synopsis:
3376 cksum [@var{option}]@dots{} [@var{file}]@dots{}
3379 @command{cksum} prints the CRC checksum for each file along with the number
3380 of bytes in the file, and the file name unless no arguments were given.
3382 @command{cksum} is typically used to ensure that files
3383 transferred by unreliable means (e.g., netnews) have not been corrupted,
3384 by comparing the @command{cksum} output for the received files with the
3385 @command{cksum} output for the original files (typically given in the
3388 The CRC algorithm is specified by the @acronym{POSIX} standard. It is not
3389 compatible with the BSD or System V @command{sum} algorithms (see the
3390 previous section); it is more robust.
3392 The only options are @option{--help} and @option{--version}. @xref{Common
3398 @node md5sum invocation
3399 @section @command{md5sum}: Print or check MD5 digests
3403 @cindex 128-bit checksum
3404 @cindex checksum, 128-bit
3405 @cindex fingerprint, 128-bit
3406 @cindex message-digest, 128-bit
3408 @command{md5sum} computes a 128-bit checksum (or @dfn{fingerprint} or
3409 @dfn{message-digest}) for each specified @var{file}.
3411 Note: The MD5 digest is more reliable than a simple CRC (provided by
3412 the @command{cksum} command) for detecting accidental file corruption,
3413 as the chances of accidentally having two files with identical MD5
3414 are vanishingly small. However, it should not be considered truly
3415 secure against malicious tampering: although finding a file with a
3416 given MD5 fingerprint, or modifying a file so as to retain its MD5 are
3417 considered infeasible at the moment, it is known how to produce
3418 different files with identical MD5 (a ``collision''), something which
3419 can be a security issue in certain contexts. For more secure hashes,
3420 consider using SHA-1 or SHA-2. @xref{sha1sum invocation}, and
3421 @ref{sha2 utilities}.
3423 If a @var{file} is specified as @samp{-} or if no files are given
3424 @command{md5sum} computes the checksum for the standard input.
3425 @command{md5sum} can also determine whether a file and checksum are
3426 consistent. Synopsis:
3429 md5sum [@var{option}]@dots{} [@var{file}]@dots{}
3432 For each @var{file}, @samp{md5sum} outputs the MD5 checksum, a flag
3433 indicating a binary or text input file, and the file name.
3434 If @var{file} contains a backslash or newline, the
3435 line is started with a backslash, and each problematic character in
3436 the file name is escaped with a backslash, making the output
3437 unambiguous even in the presence of arbitrary file names.
3438 If @var{file} is omitted or specified as @samp{-}, standard input is read.
3440 The program accepts the following options. Also see @ref{Common options}.
3448 @cindex binary input files
3449 Treat each input file as binary, by reading it in binary mode and
3450 outputting a @samp{*} flag. This is the inverse of @option{--text}.
3451 On systems like @acronym{GNU} that do not distinguish between binary
3452 and text files, this option merely flags each input file as binary:
3453 the MD5 checksum is unaffected. This option is the default on systems
3454 like MS-DOS that distinguish between binary and text files, except
3455 for reading standard input when standard input is a terminal.
3459 Read file names and checksum information (not data) from each
3460 @var{file} (or from stdin if no @var{file} was specified) and report
3461 whether the checksums match the contents of the named files.
3462 The input to this mode of @command{md5sum} is usually the output of
3463 a prior, checksum-generating run of @samp{md5sum}.
3464 Each valid line of input consists of an MD5 checksum, a binary/text
3465 flag, and then a file name.
3466 Binary files are marked with @samp{*}, text with @samp{ }.
3467 For each such line, @command{md5sum} reads the named file and computes its
3468 MD5 checksum. Then, if the computed message digest does not match the
3469 one on the line with the file name, the file is noted as having
3470 failed the test. Otherwise, the file passes the test.
3471 By default, for each valid line, one line is written to standard
3472 output indicating whether the named file passed the test.
3473 After all checks have been performed, if there were any failures,
3474 a warning is issued to standard error.
3475 Use the @option{--status} option to inhibit that output.
3476 If any listed file cannot be opened or read, if any valid line has
3477 an MD5 checksum inconsistent with the associated file, or if no valid
3478 line is found, @command{md5sum} exits with nonzero status. Otherwise,
3479 it exits successfully.
3483 @cindex verifying MD5 checksums
3484 This option is useful only when verifying checksums.
3485 When verifying checksums, don't generate an 'OK' message per successfully
3486 checked file. Files that fail the verification are reported in the
3487 default one-line-per-file format. If there is any checksum mismatch,
3488 print a warning summarizing the failures to standard error.
3492 @cindex verifying MD5 checksums
3493 This option is useful only when verifying checksums.
3494 When verifying checksums, don't generate the default one-line-per-file
3495 diagnostic and don't output the warning summarizing any failures.
3496 Failures to open or read a file still evoke individual diagnostics to
3498 If all listed files are readable and are consistent with the associated
3499 MD5 checksums, exit successfully. Otherwise exit with a status code
3500 indicating there was a failure.
3506 @cindex text input files
3507 Treat each input file as text, by reading it in text mode and
3508 outputting a @samp{ } flag. This is the inverse of @option{--binary}.
3509 This option is the default on systems like @acronym{GNU} that do not
3510 distinguish between binary and text files. On other systems, it is
3511 the default for reading standard input when standard input is a
3518 @cindex verifying MD5 checksums
3519 When verifying checksums, warn about improperly formatted MD5 checksum lines.
3520 This option is useful only if all but a few lines in the checked input
3528 @node sha1sum invocation
3529 @section @command{sha1sum}: Print or check SHA-1 digests
3533 @cindex 160-bit checksum
3534 @cindex checksum, 160-bit
3535 @cindex fingerprint, 160-bit
3536 @cindex message-digest, 160-bit
3538 @command{sha1sum} computes a 160-bit checksum for each specified
3539 @var{file}. The usage and options of this command are precisely the
3540 same as for @command{md5sum}. @xref{md5sum invocation}.
3542 Note: The SHA-1 digest is more secure than MD5, and no collisions of
3543 it are known (different files having the same fingerprint). However,
3544 it is known that they can be produced with considerable, but not
3545 unreasonable, resources. For this reason, it is generally considered
3546 that SHA-1 should be gradually phased out in favor of the more secure
3547 SHA-2 hash algorithms. @xref{sha2 utilities}.
3550 @node sha2 utilities
3551 @section sha2 utilities: Print or check SHA-2 digests
3558 @cindex 224-bit checksum
3559 @cindex 256-bit checksum
3560 @cindex 384-bit checksum
3561 @cindex 512-bit checksum
3562 @cindex checksum, 224-bit
3563 @cindex checksum, 256-bit
3564 @cindex checksum, 384-bit
3565 @cindex checksum, 512-bit
3566 @cindex fingerprint, 224-bit
3567 @cindex fingerprint, 256-bit
3568 @cindex fingerprint, 384-bit
3569 @cindex fingerprint, 512-bit
3570 @cindex message-digest, 224-bit
3571 @cindex message-digest, 256-bit
3572 @cindex message-digest, 384-bit
3573 @cindex message-digest, 512-bit
3575 The commands @command{sha224sum}, @command{sha256sum},
3576 @command{sha384sum} and @command{sha512sum} compute checksums of
3577 various lengths (respectively 224, 256, 384 and 512 bits),
3578 collectively known as the SHA-2 hashes. The usage and options of
3579 these commands are precisely the same as for @command{md5sum}.
3580 @xref{md5sum invocation}.
3582 Note: The SHA384 and SHA512 digests are considerably slower to
3583 compute, especially on 32-bit computers, than SHA224 or SHA256.
3586 @node Operating on sorted files
3587 @chapter Operating on sorted files
3589 @cindex operating on sorted files
3590 @cindex sorted files, operations on
3592 These commands work with (or produce) sorted files.
3595 * sort invocation:: Sort text files.
3596 * shuf invocation:: Shuffle text files.
3597 * uniq invocation:: Uniquify files.
3598 * comm invocation:: Compare two sorted files line by line.
3599 * ptx invocation:: Produce a permuted index of file contents.
3600 * tsort invocation:: Topological sort.
3604 @node sort invocation
3605 @section @command{sort}: Sort text files
3608 @cindex sorting files
3610 @command{sort} sorts, merges, or compares all the lines from the given
3611 files, or standard input if none are given or for a @var{file} of
3612 @samp{-}. By default, @command{sort} writes the results to standard
3616 sort [@var{option}]@dots{} [@var{file}]@dots{}
3619 @command{sort} has three modes of operation: sort (the default), merge,
3620 and check for sortedness. The following options change the operation
3627 @itemx --check=diagnose-first
3630 @cindex checking for sortedness
3631 Check whether the given file is already sorted: if it is not all
3632 sorted, print a diagnostic containing the first out-of-order line and
3633 exit with a status of 1.
3634 Otherwise, exit successfully.
3635 At most one input file can be given.
3638 @itemx --check=quiet
3639 @itemx --check=silent
3642 @cindex checking for sortedness
3643 Exit successfully if the given file is already sorted, and
3644 exit with status 1 otherwise.
3645 At most one input file can be given.
3646 This is like @option{-c}, except it does not print a diagnostic.
3652 @cindex merging sorted files
3653 Merge the given files by sorting them as a group. Each input file must
3654 always be individually sorted. It always works to sort instead of
3655 merge; merging is provided because it is faster, in the case where it
3660 @cindex sort stability
3661 @cindex sort's last-resort comparison
3662 A pair of lines is compared as follows:
3663 @command{sort} compares each pair of fields, in the
3664 order specified on the command line, according to the associated
3665 ordering options, until a difference is found or no fields are left.
3666 If no key fields are specified, @command{sort} uses a default key of
3667 the entire line. Finally, as a last resort when all keys compare
3668 equal, @command{sort} compares entire lines as if no ordering options
3669 other than @option{--reverse} (@option{-r}) were specified. The
3670 @option{--stable} (@option{-s}) option disables this @dfn{last-resort
3671 comparison} so that lines in which all fields compare equal are left
3672 in their original relative order. The @option{--unique}
3673 (@option{-u}) option also disables the last-resort comparison.
3677 Unless otherwise specified, all comparisons use the character collating
3678 sequence specified by the @env{LC_COLLATE} locale.@footnote{If you
3679 use a non-@acronym{POSIX} locale (e.g., by setting @env{LC_ALL}
3680 to @samp{en_US}), then @command{sort} may produce output that is sorted
3681 differently than you're accustomed to. In that case, set the @env{LC_ALL}
3682 environment variable to @samp{C}. Note that setting only @env{LC_COLLATE}
3683 has two problems. First, it is ineffective if @env{LC_ALL} is also set.
3684 Second, it has undefined behavior if @env{LC_CTYPE} (or @env{LANG}, if
3685 @env{LC_CTYPE} is unset) is set to an incompatible value. For example,
3686 you get undefined behavior if @env{LC_CTYPE} is @code{ja_JP.PCK} but
3687 @env{LC_COLLATE} is @code{en_US.UTF-8}.}
3689 @sc{gnu} @command{sort} (as specified for all @sc{gnu} utilities) has no
3690 limit on input line length or restrictions on bytes allowed within lines.
3691 In addition, if the final byte of an input file is not a newline, @sc{gnu}
3692 @command{sort} silently supplies one. A line's trailing newline is not
3693 part of the line for comparison purposes.
3695 @cindex exit status of @command{sort}
3699 0 if no error occurred
3700 1 if invoked with @option{-c} or @option{-C} and the input is not sorted
3701 2 if an error occurred
3705 If the environment variable @env{TMPDIR} is set, @command{sort} uses its
3706 value as the directory for temporary files instead of @file{/tmp}. The
3707 @option{--temporary-directory} (@option{-T}) option in turn overrides
3708 the environment variable.
3710 The following options affect the ordering of output lines. They may be
3711 specified globally or as part of a specific key field. If no key
3712 fields are specified, global options apply to comparison of entire
3713 lines; otherwise the global options are inherited by key fields that do
3714 not specify any special options of their own. In pre-@acronym{POSIX}
3715 versions of @command{sort}, global options affect only later key fields,
3716 so portable shell scripts should specify global options first.
3721 @itemx --ignore-leading-blanks
3723 @opindex --ignore-leading-blanks
3724 @cindex blanks, ignoring leading
3726 Ignore leading blanks when finding sort keys in each line.
3727 By default a blank is a space or a tab, but the @env{LC_CTYPE} locale
3728 can change this. Note blanks may be ignored by your locale's collating
3729 rules, but without this option they will be significant for character
3730 positions specified in keys with the @option{-k} option.
3733 @itemx --dictionary-order
3735 @opindex --dictionary-order
3736 @cindex dictionary order
3737 @cindex phone directory order
3738 @cindex telephone directory order
3740 Sort in @dfn{phone directory} order: ignore all characters except
3741 letters, digits and blanks when sorting.
3742 By default letters and digits are those of @acronym{ASCII} and a blank
3743 is a space or a tab, but the @env{LC_CTYPE} locale can change this.
3746 @itemx --ignore-case
3748 @opindex --ignore-case
3749 @cindex ignoring case
3750 @cindex case folding
3752 Fold lowercase characters into the equivalent uppercase characters when
3753 comparing so that, for example, @samp{b} and @samp{B} sort as equal.
3754 The @env{LC_CTYPE} locale determines character types.
3755 When used with @option{--unique} those lower case equivalent lines are
3756 thrown away. (There is currently no way to throw away the upper case
3757 equivalent instead. (Any @option{--reverse} given would only affect
3758 the final result, after the throwing away.))
3761 @itemx --general-numeric-sort
3762 @itemx --sort=general-numeric
3764 @opindex --general-numeric-sort
3766 @cindex general numeric sort
3768 Sort numerically, using the standard C function @code{strtod} to convert
3769 a prefix of each line to a double-precision floating point number.
3770 This allows floating point numbers to be specified in scientific notation,
3771 like @code{1.0e-34} and @code{10e100}.
3772 The @env{LC_NUMERIC} locale determines the decimal-point character.
3773 Do not report overflow, underflow, or conversion errors.
3774 Use the following collating sequence:
3778 Lines that do not start with numbers (all considered to be equal).
3780 NaNs (``Not a Number'' values, in IEEE floating point arithmetic)
3781 in a consistent but machine-dependent order.
3785 Finite numbers in ascending numeric order (with @math{-0} and @math{+0} equal).
3790 Use this option only if there is no alternative; it is much slower than
3791 @option{--numeric-sort} (@option{-n}) and it can lose information when
3792 converting to floating point.
3795 @itemx --human-numeric-sort
3796 @itemx --sort=human-numeric
3798 @opindex --human-numeric-sort
3800 @cindex human numeric sort
3802 Sort numerically, as per the @option{--numeric-sort} option below, and in
3803 addition handle IEC or SI suffixes like MiB, MB etc (@ref{Block size}).
3804 Note a mixture of IEC and SI suffixes is not supported and will
3805 be flagged as an error. Also the numbers must be abbreviated uniformly.
3806 I.E. values with different precisions like 6000K and 5M will be sorted
3810 @itemx --ignore-nonprinting
3812 @opindex --ignore-nonprinting
3813 @cindex nonprinting characters, ignoring
3814 @cindex unprintable characters, ignoring
3816 Ignore nonprinting characters.
3817 The @env{LC_CTYPE} locale determines character types.
3818 This option has no effect if the stronger @option{--dictionary-order}
3819 (@option{-d}) option is also given.
3825 @opindex --month-sort
3827 @cindex months, sorting by
3829 An initial string, consisting of any amount of blanks, followed
3830 by a month name abbreviation, is folded to UPPER case and
3831 compared in the order @samp{JAN} < @samp{FEB} < @dots{} < @samp{DEC}.
3832 Invalid names compare low to valid names. The @env{LC_TIME} locale
3833 category determines the month spellings.
3834 By default a blank is a space or a tab, but the @env{LC_CTYPE} locale
3838 @itemx --numeric-sort
3839 @itemx --sort=numeric
3841 @opindex --numeric-sort
3843 @cindex numeric sort
3845 Sort numerically. The number begins each line and consists
3846 of optional blanks, an optional @samp{-} sign, and zero or more
3847 digits possibly separated by thousands separators, optionally followed
3848 by a decimal-point character and zero or more digits. An empty
3849 number is treated as @samp{0}. The @env{LC_NUMERIC}
3850 locale specifies the decimal-point character and thousands separator.
3851 By default a blank is a space or a tab, but the @env{LC_CTYPE} locale
3854 Comparison is exact; there is no rounding error.
3856 Neither a leading @samp{+} nor exponential notation is recognized.
3857 To compare such strings numerically, use the
3858 @option{--general-numeric-sort} (@option{-g}) option.
3861 @itemx --version-sort
3863 @opindex --version-sort
3864 @cindex version number sort
3865 Sort by version name and number. It behaves like a standard sort,
3866 except that each sequence of decimal digits is treated numerically
3867 as an index/version number. (@xref{Details about version sort}.)
3873 @cindex reverse sorting
3874 Reverse the result of comparison, so that lines with greater key values
3875 appear earlier in the output instead of later.
3878 @itemx --random-sort
3879 @itemx --sort=random
3881 @opindex --random-sort
3884 Sort by hashing the input keys and then sorting the hash values.
3885 Choose the hash function at random, ensuring that it is free of
3886 collisions so that differing keys have differing hash values. This is
3887 like a random permutation of the inputs (@pxref{shuf invocation}),
3888 except that keys with the same value sort together.
3890 If multiple random sort fields are specified, the same random hash
3891 function is used for all fields. To use different random hash
3892 functions for different fields, you can invoke @command{sort} more
3895 The choice of hash function is affected by the
3896 @option{--random-source} option.
3904 @item --compress-program=@var{prog}
3905 Compress any temporary files with the program @var{prog}.
3907 With no arguments, @var{prog} must compress standard input to standard
3908 output, and when given the @option{-d} option it must decompress
3909 standard input to standard output.
3911 Terminate with an error if @var{prog} exits with nonzero status.
3913 White space and the backslash character should not appear in
3914 @var{prog}; they are reserved for future use.
3916 @filesZeroFromOption{sort,,sorted output}
3918 @item -k @var{pos1}[,@var{pos2}]
3919 @itemx --key=@var{pos1}[,@var{pos2}]
3923 Specify a sort field that consists of the part of the line between
3924 @var{pos1} and @var{pos2} (or the end of the line, if @var{pos2} is
3925 omitted), @emph{inclusive}.
3927 Each @var{pos} has the form @samp{@var{f}[.@var{c}][@var{opts}]},
3928 where @var{f} is the number of the field to use, and @var{c} is the number
3929 of the first character from the beginning of the field. Fields and character
3930 positions are numbered starting with 1; a character position of zero in
3931 @var{pos2} indicates the field's last character. If @samp{.@var{c}} is
3932 omitted from @var{pos1}, it defaults to 1 (the beginning of the field);
3933 if omitted from @var{pos2}, it defaults to 0 (the end of the field).
3934 @var{opts} are ordering options, allowing individual keys to be sorted
3935 according to different rules; see below for details. Keys can span
3938 Example: To sort on the second field, use @option{--key=2,2}
3939 (@option{-k 2,2}). See below for more notes on keys and more examples.
3941 @item --batch-size=@var{nmerge}
3942 @opindex --batch-size
3943 @cindex number of inputs to merge, nmerge
3944 Merge at most @var{nmerge} inputs at once.
3946 When @command{sort} has to merge more than @var{nmerge} inputs,
3947 it merges them in groups of @var{nmerge}, saving the result in
3948 a temporary file, which is then used as an input in a subsequent merge.
3950 A large value of @var{nmerge} may improve merge performance and decrease
3951 temporary storage utilization at the expense of increased memory usage
3952 and I/0. Conversely a small value of @var{nmerge} may reduce memory
3953 requirements and I/0 at the expense of temporary storage consumption and
3956 The value of @var{nmerge} must be at least 2. The default value is
3957 currently 16, but this is implementation-dependent and may change in
3960 The value of @var{nmerge} may be bounded by a resource limit for open
3961 file descriptors. The commands @samp{ulimit -n} or @samp{getconf
3962 OPEN_MAX} may display limits for your systems; these limits may be
3963 modified further if your program already has some files open, or if
3964 the operating system has other limits on the number of open files. If
3965 the value of @var{nmerge} exceeds the resource limit, @command{sort}
3966 silently uses a smaller value.
3968 @item -o @var{output-file}
3969 @itemx --output=@var{output-file}
3972 @cindex overwriting of input, allowed
3973 Write output to @var{output-file} instead of standard output.
3974 Normally, @command{sort} reads all input before opening
3975 @var{output-file}, so you can safely sort a file in place by using
3976 commands like @code{sort -o F F} and @code{cat F | sort -o F}.
3977 However, @command{sort} with @option{--merge} (@option{-m}) can open
3978 the output file before reading all input, so a command like @code{cat
3979 F | sort -m -o F - G} is not safe as @command{sort} might start
3980 writing @file{F} before @command{cat} is done reading it.
3982 @vindex POSIXLY_CORRECT
3983 On newer systems, @option{-o} cannot appear after an input file if
3984 @env{POSIXLY_CORRECT} is set, e.g., @samp{sort F -o F}. Portable
3985 scripts should specify @option{-o @var{output-file}} before any input
3988 @item --random-source=@var{file}
3989 @opindex --random-source
3990 @cindex random source for sorting
3991 Use @var{file} as a source of random data used to determine which
3992 random hash function to use with the @option{-R} option. @xref{Random
3999 @cindex sort stability
4000 @cindex sort's last-resort comparison
4002 Make @command{sort} stable by disabling its last-resort comparison.
4003 This option has no effect if no fields or global ordering options
4004 other than @option{--reverse} (@option{-r}) are specified.
4007 @itemx --buffer-size=@var{size}
4009 @opindex --buffer-size
4010 @cindex size for main memory sorting
4011 Use a main-memory sort buffer of the given @var{size}. By default,
4012 @var{size} is in units of 1024 bytes. Appending @samp{%} causes
4013 @var{size} to be interpreted as a percentage of physical memory.
4014 Appending @samp{K} multiplies @var{size} by 1024 (the default),
4015 @samp{M} by 1,048,576, @samp{G} by 1,073,741,824, and so on for
4016 @samp{T}, @samp{P}, @samp{E}, @samp{Z}, and @samp{Y}. Appending
4017 @samp{b} causes @var{size} to be interpreted as a byte count, with no
4020 This option can improve the performance of @command{sort} by causing it
4021 to start with a larger or smaller sort buffer than the default.
4022 However, this option affects only the initial buffer size. The buffer
4023 grows beyond @var{size} if @command{sort} encounters input lines larger
4026 @item -t @var{separator}
4027 @itemx --field-separator=@var{separator}
4029 @opindex --field-separator
4030 @cindex field separator character
4031 Use character @var{separator} as the field separator when finding the
4032 sort keys in each line. By default, fields are separated by the empty
4033 string between a non-blank character and a blank character.
4034 By default a blank is a space or a tab, but the @env{LC_CTYPE} locale
4037 That is, given the input line @w{@samp{ foo bar}}, @command{sort} breaks it
4038 into fields @w{@samp{ foo}} and @w{@samp{ bar}}. The field separator is
4039 not considered to be part of either the field preceding or the field
4040 following, so with @samp{sort @w{-t " "}} the same input line has
4041 three fields: an empty field, @samp{foo}, and @samp{bar}.
4042 However, fields that extend to the end of the line,
4043 as @option{-k 2}, or fields consisting of a range, as @option{-k 2,3},
4044 retain the field separators present between the endpoints of the range.
4046 To specify @acronym{ASCII} @sc{nul} as the field separator,
4047 use the two-character string @samp{\0}, e.g., @samp{sort -t '\0'}.
4049 @item -T @var{tempdir}
4050 @itemx --temporary-directory=@var{tempdir}
4052 @opindex --temporary-directory
4053 @cindex temporary directory
4055 Use directory @var{tempdir} to store temporary files, overriding the
4056 @env{TMPDIR} environment variable. If this option is given more than
4057 once, temporary files are stored in all the directories given. If you
4058 have a large sort or merge that is I/O-bound, you can often improve
4059 performance by using this option to specify directories on different
4060 disks and controllers.
4066 @cindex uniquifying output
4068 Normally, output only the first of a sequence of lines that compare
4069 equal. For the @option{--check} (@option{-c} or @option{-C}) option,
4070 check that no pair of consecutive lines compares equal.
4072 This option also disables the default last-resort comparison.
4074 The commands @code{sort -u} and @code{sort | uniq} are equivalent, but
4075 this equivalence does not extend to arbitrary @command{sort} options.
4076 For example, @code{sort -n -u} inspects only the value of the initial
4077 numeric string when checking for uniqueness, whereas @code{sort -n |
4078 uniq} inspects the entire line. @xref{uniq invocation}.
4080 @macro zeroTerminatedOption
4082 @itemx --zero-terminated
4084 @opindex --zero-terminated
4085 @cindex process zero-terminated items
4086 Delimit items with a zero byte rather than a newline (@acronym{ASCII} @sc{lf}).
4087 I.E. treat input as items separated by @acronym{ASCII} @sc{nul}
4088 and terminate output items with @acronym{ASCII} @sc{nul}.
4089 This option can be useful in conjunction with @samp{perl -0} or
4090 @samp{find -print0} and @samp{xargs -0} which do the same in order to
4091 reliably handle arbitrary file names (even those containing blanks
4092 or other special characters).
4094 @zeroTerminatedOption
4098 Historical (BSD and System V) implementations of @command{sort} have
4099 differed in their interpretation of some options, particularly
4100 @option{-b}, @option{-f}, and @option{-n}. @sc{gnu} sort follows the @acronym{POSIX}
4101 behavior, which is usually (but not always!) like the System V behavior.
4102 According to @acronym{POSIX}, @option{-n} no longer implies @option{-b}. For
4103 consistency, @option{-M} has been changed in the same way. This may
4104 affect the meaning of character positions in field specifications in
4105 obscure cases. The only fix is to add an explicit @option{-b}.
4107 A position in a sort field specified with @option{-k} may have any
4108 of the option letters @samp{MbdfghinRrV} appended to it, in which case no
4109 global ordering options are inherited by that particular field. The
4110 @option{-b} option may be independently attached to either or both of
4111 the start and end positions of a field specification, and if it is
4112 inherited from the global options it will be attached to both.
4113 If input lines can contain leading or adjacent blanks and @option{-t}
4114 is not used, then @option{-k} is typically combined with @option{-b} or
4115 an option that implicitly ignores leading blanks (@samp{MghnV}) as otherwise
4116 the varying numbers of leading blanks in fields can cause confusing results.
4118 If the start position in a sort field specifier falls after the end of
4119 the line or after the end field, the field is empty. If the @option{-b}
4120 option was specified, the @samp{.@var{c}} part of a field specification
4121 is counted from the first nonblank character of the field.
4123 @vindex _POSIX2_VERSION
4124 @vindex POSIXLY_CORRECT
4125 On older systems, @command{sort} supports an obsolete origin-zero
4126 syntax @samp{+@var{pos1} [-@var{pos2}]} for specifying sort keys.
4127 This obsolete behavior can be enabled or disabled with the
4128 @env{_POSIX2_VERSION} environment variable (@pxref{Standards
4129 conformance}); it can also be enabled when @env{POSIXLY_CORRECT} is
4130 not set by using the obsolete syntax with @samp{-@var{pos2}} present.
4132 Scripts intended for use on standard hosts should avoid obsolete
4133 syntax and should use @option{-k} instead. For example, avoid
4134 @samp{sort +2}, since it might be interpreted as either @samp{sort
4135 ./+2} or @samp{sort -k 3}. If your script must also run on hosts that
4136 support only the obsolete syntax, it can use a test like @samp{if sort
4137 -k 1 </dev/null >/dev/null 2>&1; then @dots{}} to decide which syntax
4140 Here are some examples to illustrate various combinations of options.
4145 Sort in descending (reverse) numeric order.
4152 Sort alphabetically, omitting the first and second fields
4153 and the blanks at the start of the third field.
4154 This uses a single key composed of the characters beginning
4155 at the start of the first nonblank character in field three
4156 and extending to the end of each line.
4163 Sort numerically on the second field and resolve ties by sorting
4164 alphabetically on the third and fourth characters of field five.
4165 Use @samp{:} as the field delimiter.
4168 sort -t : -k 2,2n -k 5.3,5.4
4171 Note that if you had written @option{-k 2n} instead of @option{-k 2,2n}
4172 @command{sort} would have used all characters beginning in the second field
4173 and extending to the end of the line as the primary @emph{numeric}
4174 key. For the large majority of applications, treating keys spanning
4175 more than one field as numeric will not do what you expect.
4177 Also note that the @samp{n} modifier was applied to the field-end
4178 specifier for the first key. It would have been equivalent to
4179 specify @option{-k 2n,2} or @option{-k 2n,2n}. All modifiers except
4180 @samp{b} apply to the associated @emph{field}, regardless of whether
4181 the modifier character is attached to the field-start and/or the
4182 field-end part of the key specifier.
4185 Sort the password file on the fifth field and ignore any
4186 leading blanks. Sort lines with equal values in field five
4187 on the numeric user ID in field three. Fields are separated
4191 sort -t : -k 5b,5 -k 3,3n /etc/passwd
4192 sort -t : -n -k 5b,5 -k 3,3 /etc/passwd
4193 sort -t : -b -k 5,5 -k 3,3n /etc/passwd
4196 These three commands have equivalent effect. The first specifies that
4197 the first key's start position ignores leading blanks and the second
4198 key is sorted numerically. The other two commands rely on global
4199 options being inherited by sort keys that lack modifiers. The inheritance
4200 works in this case because @option{-k 5b,5b} and @option{-k 5b,5} are
4201 equivalent, as the location of a field-end lacking a @samp{.@var{c}}
4202 character position is not affected by whether initial blanks are
4206 Sort a set of log files, primarily by IPv4 address and secondarily by
4207 time stamp. If two lines' primary and secondary keys are identical,
4208 output the lines in the same order that they were input. The log
4209 files contain lines that look like this:
4212 4.150.156.3 - - [01/Apr/2004:06:31:51 +0000] message 1
4213 211.24.3.231 - - [24/Apr/2004:20:17:39 +0000] message 2
4216 Fields are separated by exactly one space. Sort IPv4 addresses
4217 lexicographically, e.g., 212.61.52.2 sorts before 212.129.233.201
4218 because 61 is less than 129.
4221 sort -s -t ' ' -k 4.9n -k 4.5M -k 4.2n -k 4.14,4.21 file*.log |
4222 sort -s -t '.' -k 1,1n -k 2,2n -k 3,3n -k 4,4n
4225 This example cannot be done with a single @command{sort} invocation,
4226 since IPv4 address components are separated by @samp{.} while dates
4227 come just after a space. So it is broken down into two invocations of
4228 @command{sort}: the first sorts by time stamp and the second by IPv4
4229 address. The time stamp is sorted by year, then month, then day, and
4230 finally by hour-minute-second field, using @option{-k} to isolate each
4231 field. Except for hour-minute-second there's no need to specify the
4232 end of each key field, since the @samp{n} and @samp{M} modifiers sort
4233 based on leading prefixes that cannot cross field boundaries. The
4234 IPv4 addresses are sorted lexicographically. The second sort uses
4235 @samp{-s} so that ties in the primary key are broken by the secondary
4236 key; the first sort uses @samp{-s} so that the combination of the two
4240 Generate a tags file in case-insensitive sorted order.
4243 find src -type f -print0 | sort -z -f | xargs -0 etags --append
4246 The use of @option{-print0}, @option{-z}, and @option{-0} in this case means
4247 that file names that contain blanks or other special characters are
4249 by the sort operation.
4251 @c This example is a bit contrived and needs more explanation.
4253 @c Sort records separated by an arbitrary string by using a pipe to convert
4254 @c each record delimiter string to @samp{\0}, then using sort's -z option,
4255 @c and converting each @samp{\0} back to the original record delimiter.
4258 @c printf 'c\n\nb\n\na\n'|perl -0pe 's/\n\n/\n\0/g'|sort -z|perl -0pe 's/\0/\n/g'
4262 Use the common @acronym{DSU, Decorate Sort Undecorate} idiom to
4263 sort lines according to their length.
4266 awk '@{print length, $0@}' /etc/passwd | sort -n | cut -f2- -d' '
4269 In general this technique can be used to sort data that the @command{sort}
4270 command does not support, or is inefficient at, sorting directly.
4273 Shuffle a list of directories, but preserve the order of files within
4274 each directory. For instance, one could use this to generate a music
4275 playlist in which albums are shuffled but the songs of each album are
4279 ls */* | sort -t / -k 1,1R -k 2,2
4285 @node shuf invocation
4286 @section @command{shuf}: Shuffling text
4289 @cindex shuffling files
4291 @command{shuf} shuffles its input by outputting a random permutation
4292 of its input lines. Each output permutation is equally likely.
4296 shuf [@var{option}]@dots{} [@var{file}]
4297 shuf -e [@var{option}]@dots{} [@var{arg}]@dots{}
4298 shuf -i @var{lo}-@var{hi} [@var{option}]@dots{}
4301 @command{shuf} has three modes of operation that affect where it
4302 obtains its input lines. By default, it reads lines from standard
4303 input. The following options change the operation mode:
4311 @cindex command-line operands to shuffle
4312 Treat each command-line operand as an input line.
4314 @item -i @var{lo}-@var{hi}
4315 @itemx --input-range=@var{lo}-@var{hi}
4317 @opindex --input-range
4318 @cindex input range to shuffle
4319 Act as if input came from a file containing the range of unsigned
4320 decimal integers @var{lo}@dots{}@var{hi}, one per line.
4324 @command{shuf}'s other options can affect its behavior in all
4329 @item -n @var{lines}
4330 @itemx --head-count=@var{count}
4332 @opindex --head-count
4333 @cindex head of output
4334 Output at most @var{count} lines. By default, all input lines are
4337 @item -o @var{output-file}
4338 @itemx --output=@var{output-file}
4341 @cindex overwriting of input, allowed
4342 Write output to @var{output-file} instead of standard output.
4343 @command{shuf} reads all input before opening
4344 @var{output-file}, so you can safely shuffle a file in place by using
4345 commands like @code{shuf -o F <F} and @code{cat F | shuf -o F}.
4347 @item --random-source=@var{file}
4348 @opindex --random-source
4349 @cindex random source for shuffling
4350 Use @var{file} as a source of random data used to determine which
4351 permutation to generate. @xref{Random sources}.
4353 @zeroTerminatedOption
4369 might produce the output
4379 Similarly, the command:
4382 shuf -e clubs hearts diamonds spades
4396 and the command @samp{shuf -i 1-4} might output:
4406 These examples all have four input lines, so @command{shuf} might
4407 produce any of the twenty-four possible permutations of the input. In
4408 general, if there are @var{n} input lines, there are @var{n}! (i.e.,
4409 @var{n} factorial, or @var{n} * (@var{n} - 1) * @dots{} * 1) possible
4410 output permutations.
4415 @node uniq invocation
4416 @section @command{uniq}: Uniquify files
4419 @cindex uniquify files
4421 @command{uniq} writes the unique lines in the given @file{input}, or
4422 standard input if nothing is given or for an @var{input} name of
4426 uniq [@var{option}]@dots{} [@var{input} [@var{output}]]
4429 By default, @command{uniq} prints its input lines, except that
4430 it discards all but the first of adjacent repeated lines, so that
4431 no output lines are repeated. Optionally, it can instead discard
4432 lines that are not repeated, or all repeated lines.
4434 The input need not be sorted, but repeated input lines are detected
4435 only if they are adjacent. If you want to discard non-adjacent
4436 duplicate lines, perhaps you want to use @code{sort -u}.
4437 @xref{sort invocation}.
4440 Comparisons honor the rules specified by the @env{LC_COLLATE}
4443 If no @var{output} file is specified, @command{uniq} writes to standard
4446 The program accepts the following options. Also see @ref{Common options}.
4451 @itemx --skip-fields=@var{n}
4453 @opindex --skip-fields
4454 Skip @var{n} fields on each line before checking for uniqueness. Use
4455 a null string for comparison if a line has fewer than @var{n} fields. Fields
4456 are sequences of non-space non-tab characters that are separated from
4457 each other by at least one space or tab.
4459 For compatibility @command{uniq} supports an obsolete option syntax
4460 @option{-@var{n}}. New scripts should use @option{-f @var{n}} instead.
4463 @itemx --skip-chars=@var{n}
4465 @opindex --skip-chars
4466 Skip @var{n} characters before checking for uniqueness. Use a null string
4467 for comparison if a line has fewer than @var{n} characters. If you use both
4468 the field and character skipping options, fields are skipped over first.
4470 @vindex _POSIX2_VERSION
4471 On older systems, @command{uniq} supports an obsolete option syntax
4473 This obsolete behavior can be enabled or disabled with the
4474 @env{_POSIX2_VERSION} environment variable (@pxref{Standards
4475 conformance}), but portable scripts should avoid commands whose
4476 behavior depends on this variable.
4477 For example, use @samp{uniq ./+10} or @samp{uniq -s 10} rather than
4478 the ambiguous @samp{uniq +10}.
4484 Print the number of times each line occurred along with the line.
4487 @itemx --ignore-case
4489 @opindex --ignore-case
4490 Ignore differences in case when comparing lines.
4496 @cindex repeated lines, outputting
4497 Discard lines that are not repeated. When used by itself, this option
4498 causes @command{uniq} to print the first copy of each repeated line,
4502 @itemx --all-repeated[=@var{delimit-method}]
4504 @opindex --all-repeated
4505 @cindex all repeated lines, outputting
4506 Do not discard the second and subsequent repeated input lines,
4507 but discard lines that are not repeated.
4508 This option is useful mainly in conjunction with other options e.g.,
4509 to ignore case or to compare only selected fields.
4510 The optional @var{delimit-method} tells how to delimit
4511 groups of repeated lines, and must be one of the following:
4516 Do not delimit groups of repeated lines.
4517 This is equivalent to @option{--all-repeated} (@option{-D}).
4520 Output a newline before each group of repeated lines.
4521 With @option{--zero-terminated} (@option{-z}), use a zero
4522 byte (@acronym{ASCII} @sc{nul}) instead of a newline.
4525 Separate groups of repeated lines with a single newline.
4526 With @option{--zero-terminated} (@option{-z}), use a zero
4527 byte (@acronym{ASCII} @sc{nul}) instead of a newline.
4528 This is the same as using @samp{prepend}, except that
4529 no delimiter is inserted before the first group, and hence
4530 may be better suited for output direct to users.
4533 Note that when groups are delimited and the input stream contains
4534 two or more consecutive blank lines, then the output is ambiguous.
4535 To avoid that, filter the input through @samp{tr -s '\n'} to replace
4536 each sequence of consecutive newlines with a single newline.
4538 This is a @sc{gnu} extension.
4539 @c FIXME: give an example showing *how* it's useful
4545 @cindex unique lines, outputting
4546 Discard the first repeated line. When used by itself, this option
4547 causes @command{uniq} to print unique lines, and nothing else.
4550 @itemx --check-chars=@var{n}
4552 @opindex --check-chars
4553 Compare at most @var{n} characters on each line (after skipping any specified
4554 fields and characters). By default the entire rest of the lines are
4557 @zeroTerminatedOption
4564 @node comm invocation
4565 @section @command{comm}: Compare two sorted files line by line
4568 @cindex line-by-line comparison
4569 @cindex comparing sorted files
4571 @command{comm} writes to standard output lines that are common, and lines
4572 that are unique, to two input files; a file name of @samp{-} means
4573 standard input. Synopsis:
4576 comm [@var{option}]@dots{} @var{file1} @var{file2}
4580 Before @command{comm} can be used, the input files must be sorted using the
4581 collating sequence specified by the @env{LC_COLLATE} locale.
4582 If an input file ends in a non-newline
4583 character, a newline is silently appended. The @command{sort} command with
4584 no options always outputs a file that is suitable input to @command{comm}.
4586 @cindex differing lines
4587 @cindex common lines
4588 With no options, @command{comm} produces three-column output. Column one
4589 contains lines unique to @var{file1}, column two contains lines unique
4590 to @var{file2}, and column three contains lines common to both files.
4591 Columns are separated by a single TAB character.
4592 @c FIXME: when there's an option to supply an alternative separator
4593 @c string, append `by default' to the above sentence.
4598 The options @option{-1}, @option{-2}, and @option{-3} suppress printing of
4599 the corresponding columns (and separators). Also see @ref{Common options}.
4601 Unlike some other comparison utilities, @command{comm} has an exit
4602 status that does not depend on the result of the comparison.
4603 Upon normal completion @command{comm} produces an exit code of zero.
4604 If there is an error it exits with nonzero status.
4606 @macro checkOrderOption{cmd}
4607 If the @option{--check-order} option is given, unsorted inputs will
4608 cause a fatal error message. If the option @option{--nocheck-order}
4609 is given, unsorted inputs will never cause an error message. If
4610 neither of these options is given, wrongly sorted inputs are diagnosed
4611 only if an input file is found to contain unpairable lines. If an
4612 input file is diagnosed as being unsorted, the @command{\cmd\} command
4613 will exit with a nonzero status (and the output should not be used).
4615 Forcing @command{\cmd\} to process wrongly sorted input files
4616 containing unpairable lines by specifying @option{--nocheck-order} is
4617 not guaranteed to produce any particular output. The output will
4618 probably not correspond with whatever you hoped it would be.
4620 @checkOrderOption{comm}
4625 Fail with an error message if either input file is wrongly ordered.
4627 @item --nocheck-order
4628 Do not check that both input files are in sorted order.
4632 @item --output-delimiter=@var{str}
4633 Print @var{str} between adjacent output columns,
4634 rather than the default of a single TAB character.
4636 The delimiter @var{str} may not be empty.
4640 @node ptx invocation
4641 @section @command{ptx}: Produce permuted indexes
4645 @command{ptx} reads a text file and essentially produces a permuted index, with
4646 each keyword in its context. The calling sketch is either one of:
4649 ptx [@var{option} @dots{}] [@var{file} @dots{}]
4650 ptx -G [@var{option} @dots{}] [@var{input} [@var{output}]]
4653 The @option{-G} (or its equivalent: @option{--traditional}) option disables
4654 all @sc{gnu} extensions and reverts to traditional mode, thus introducing some
4655 limitations and changing several of the program's default option values.
4656 When @option{-G} is not specified, @sc{gnu} extensions are always enabled.
4657 @sc{gnu} extensions to @command{ptx} are documented wherever appropriate in this
4658 document. For the full list, see @xref{Compatibility in ptx}.
4660 Individual options are explained in the following sections.
4662 When @sc{gnu} extensions are enabled, there may be zero, one or several
4663 @var{file}s after the options. If there is no @var{file}, the program
4664 reads the standard input. If there is one or several @var{file}s, they
4665 give the name of input files which are all read in turn, as if all the
4666 input files were concatenated. However, there is a full contextual
4667 break between each file and, when automatic referencing is requested,
4668 file names and line numbers refer to individual text input files. In
4669 all cases, the program outputs the permuted index to the standard
4672 When @sc{gnu} extensions are @emph{not} enabled, that is, when the program
4673 operates in traditional mode, there may be zero, one or two parameters
4674 besides the options. If there are no parameters, the program reads the
4675 standard input and outputs the permuted index to the standard output.
4676 If there is only one parameter, it names the text @var{input} to be read
4677 instead of the standard input. If two parameters are given, they give
4678 respectively the name of the @var{input} file to read and the name of
4679 the @var{output} file to produce. @emph{Be very careful} to note that,
4680 in this case, the contents of file given by the second parameter is
4681 destroyed. This behavior is dictated by System V @command{ptx}
4682 compatibility; @sc{gnu} Standards normally discourage output parameters not
4683 introduced by an option.
4685 Note that for @emph{any} file named as the value of an option or as an
4686 input text file, a single dash @kbd{-} may be used, in which case
4687 standard input is assumed. However, it would not make sense to use this
4688 convention more than once per program invocation.
4691 * General options in ptx:: Options which affect general program behavior.
4692 * Charset selection in ptx:: Underlying character set considerations.
4693 * Input processing in ptx:: Input fields, contexts, and keyword selection.
4694 * Output formatting in ptx:: Types of output format, and sizing the fields.
4695 * Compatibility in ptx::
4699 @node General options in ptx
4700 @subsection General options
4705 @itemx --traditional
4706 As already explained, this option disables all @sc{gnu} extensions to
4707 @command{ptx} and switches to traditional mode.
4710 Print a short help on standard output, then exit without further
4714 Print the program version on standard output, then exit without further
4722 @node Charset selection in ptx
4723 @subsection Charset selection
4725 @c FIXME: People don't necessarily know what an IBM-PC was these days.
4726 As it is set up now, the program assumes that the input file is coded
4727 using 8-bit @acronym{ISO} 8859-1 code, also known as Latin-1 character set,
4728 @emph{unless} it is compiled for MS-DOS, in which case it uses the
4729 character set of the IBM-PC@. (@sc{gnu} @command{ptx} is not known to work on
4730 smaller MS-DOS machines anymore.) Compared to 7-bit @acronym{ASCII}, the set
4731 of characters which are letters is different; this alters the behavior
4732 of regular expression matching. Thus, the default regular expression
4733 for a keyword allows foreign or diacriticized letters. Keyword sorting,
4734 however, is still crude; it obeys the underlying character set ordering
4740 @itemx --ignore-case
4741 Fold lower case letters to upper case for sorting.
4746 @node Input processing in ptx
4747 @subsection Word selection and input processing
4752 @itemx --break-file=@var{file}
4754 This option provides an alternative (to @option{-W}) method of describing
4755 which characters make up words. It introduces the name of a
4756 file which contains a list of characters which can@emph{not} be part of
4757 one word; this file is called the @dfn{Break file}. Any character which
4758 is not part of the Break file is a word constituent. If both options
4759 @option{-b} and @option{-W} are specified, then @option{-W} has precedence and
4760 @option{-b} is ignored.
4762 When @sc{gnu} extensions are enabled, the only way to avoid newline as a
4763 break character is to write all the break characters in the file with no
4764 newline at all, not even at the end of the file. When @sc{gnu} extensions
4765 are disabled, spaces, tabs and newlines are always considered as break
4766 characters even if not included in the Break file.
4769 @itemx --ignore-file=@var{file}
4771 The file associated with this option contains a list of words which will
4772 never be taken as keywords in concordance output. It is called the
4773 @dfn{Ignore file}. The file contains exactly one word in each line; the
4774 end of line separation of words is not subject to the value of the
4778 @itemx --only-file=@var{file}
4780 The file associated with this option contains a list of words which will
4781 be retained in concordance output; any word not mentioned in this file
4782 is ignored. The file is called the @dfn{Only file}. The file contains
4783 exactly one word in each line; the end of line separation of words is
4784 not subject to the value of the @option{-S} option.
4786 There is no default for the Only file. When both an Only file and an
4787 Ignore file are specified, a word is considered a keyword only
4788 if it is listed in the Only file and not in the Ignore file.
4793 On each input line, the leading sequence of non-white space characters will be
4794 taken to be a reference that has the purpose of identifying this input
4795 line in the resulting permuted index. For more information about reference
4796 production, see @xref{Output formatting in ptx}.
4797 Using this option changes the default value for option @option{-S}.
4799 Using this option, the program does not try very hard to remove
4800 references from contexts in output, but it succeeds in doing so
4801 @emph{when} the context ends exactly at the newline. If option
4802 @option{-r} is used with @option{-S} default value, or when @sc{gnu} extensions
4803 are disabled, this condition is always met and references are completely
4804 excluded from the output contexts.
4806 @item -S @var{regexp}
4807 @itemx --sentence-regexp=@var{regexp}
4809 This option selects which regular expression will describe the end of a
4810 line or the end of a sentence. In fact, this regular expression is not
4811 the only distinction between end of lines or end of sentences, and input
4812 line boundaries have no special significance outside this option. By
4813 default, when @sc{gnu} extensions are enabled and if @option{-r} option is not
4814 used, end of sentences are used. In this case, this @var{regex} is
4815 imported from @sc{gnu} Emacs:
4818 [.?!][]\"')@}]*\\($\\|\t\\| \\)[ \t\n]*
4821 Whenever @sc{gnu} extensions are disabled or if @option{-r} option is used, end
4822 of lines are used; in this case, the default @var{regexp} is just:
4828 Using an empty @var{regexp} is equivalent to completely disabling end of
4829 line or end of sentence recognition. In this case, the whole file is
4830 considered to be a single big line or sentence. The user might want to
4831 disallow all truncation flag generation as well, through option @option{-F
4832 ""}. @xref{Regexps, , Syntax of Regular Expressions, emacs, The GNU Emacs
4835 When the keywords happen to be near the beginning of the input line or
4836 sentence, this often creates an unused area at the beginning of the
4837 output context line; when the keywords happen to be near the end of the
4838 input line or sentence, this often creates an unused area at the end of
4839 the output context line. The program tries to fill those unused areas
4840 by wrapping around context in them; the tail of the input line or
4841 sentence is used to fill the unused area on the left of the output line;
4842 the head of the input line or sentence is used to fill the unused area
4843 on the right of the output line.
4845 As a matter of convenience to the user, many usual backslashed escape
4846 sequences from the C language are recognized and converted to the
4847 corresponding characters by @command{ptx} itself.
4849 @item -W @var{regexp}
4850 @itemx --word-regexp=@var{regexp}
4852 This option selects which regular expression will describe each keyword.
4853 By default, if @sc{gnu} extensions are enabled, a word is a sequence of
4854 letters; the @var{regexp} used is @samp{\w+}. When @sc{gnu} extensions are
4855 disabled, a word is by default anything which ends with a space, a tab
4856 or a newline; the @var{regexp} used is @samp{[^ \t\n]+}.
4858 An empty @var{regexp} is equivalent to not using this option.
4859 @xref{Regexps, , Syntax of Regular Expressions, emacs, The GNU Emacs
4862 As a matter of convenience to the user, many usual backslashed escape
4863 sequences, as found in the C language, are recognized and converted to
4864 the corresponding characters by @command{ptx} itself.
4869 @node Output formatting in ptx
4870 @subsection Output formatting
4872 Output format is mainly controlled by the @option{-O} and @option{-T} options
4873 described in the table below. When neither @option{-O} nor @option{-T} are
4874 selected, and if @sc{gnu} extensions are enabled, the program chooses an
4875 output format suitable for a dumb terminal. Each keyword occurrence is
4876 output to the center of one line, surrounded by its left and right
4877 contexts. Each field is properly justified, so the concordance output
4878 can be readily observed. As a special feature, if automatic
4879 references are selected by option @option{-A} and are output before the
4880 left context, that is, if option @option{-R} is @emph{not} selected, then
4881 a colon is added after the reference; this nicely interfaces with @sc{gnu}
4882 Emacs @code{next-error} processing. In this default output format, each
4883 white space character, like newline and tab, is merely changed to
4884 exactly one space, with no special attempt to compress consecutive
4885 spaces. This might change in the future. Except for those white space
4886 characters, every other character of the underlying set of 256
4887 characters is transmitted verbatim.
4889 Output format is further controlled by the following options.
4893 @item -g @var{number}
4894 @itemx --gap-size=@var{number}
4896 Select the size of the minimum white space gap between the fields on the
4899 @item -w @var{number}
4900 @itemx --width=@var{number}
4902 Select the maximum output width of each final line. If references are
4903 used, they are included or excluded from the maximum output width
4904 depending on the value of option @option{-R}. If this option is not
4905 selected, that is, when references are output before the left context,
4906 the maximum output width takes into account the maximum length of all
4907 references. If this option is selected, that is, when references are
4908 output after the right context, the maximum output width does not take
4909 into account the space taken by references, nor the gap that precedes
4913 @itemx --auto-reference
4915 Select automatic references. Each input line will have an automatic
4916 reference made up of the file name and the line ordinal, with a single
4917 colon between them. However, the file name will be empty when standard
4918 input is being read. If both @option{-A} and @option{-r} are selected, then
4919 the input reference is still read and skipped, but the automatic
4920 reference is used at output time, overriding the input reference.
4923 @itemx --right-side-refs
4925 In the default output format, when option @option{-R} is not used, any
4926 references produced by the effect of options @option{-r} or @option{-A} are
4927 placed to the far right of output lines, after the right context. With
4928 default output format, when the @option{-R} option is specified, references
4929 are rather placed at the beginning of each output line, before the left
4930 context. For any other output format, option @option{-R} is
4931 ignored, with one exception: with @option{-R} the width of references
4932 is @emph{not} taken into account in total output width given by @option{-w}.
4934 This option is automatically selected whenever @sc{gnu} extensions are
4937 @item -F @var{string}
4938 @itemx --flac-truncation=@var{string}
4940 This option will request that any truncation in the output be reported
4941 using the string @var{string}. Most output fields theoretically extend
4942 towards the beginning or the end of the current line, or current
4943 sentence, as selected with option @option{-S}. But there is a maximum
4944 allowed output line width, changeable through option @option{-w}, which is
4945 further divided into space for various output fields. When a field has
4946 to be truncated because it cannot extend beyond the beginning or the end of
4947 the current line to fit in, then a truncation occurs. By default,
4948 the string used is a single slash, as in @option{-F /}.
4950 @var{string} may have more than one character, as in @option{-F ...}.
4951 Also, in the particular case when @var{string} is empty (@option{-F ""}),
4952 truncation flagging is disabled, and no truncation marks are appended in
4955 As a matter of convenience to the user, many usual backslashed escape
4956 sequences, as found in the C language, are recognized and converted to
4957 the corresponding characters by @command{ptx} itself.
4959 @item -M @var{string}
4960 @itemx --macro-name=@var{string}
4962 Select another @var{string} to be used instead of @samp{xx}, while
4963 generating output suitable for @command{nroff}, @command{troff} or @TeX{}.
4966 @itemx --format=roff
4968 Choose an output format suitable for @command{nroff} or @command{troff}
4969 processing. Each output line will look like:
4972 .xx "@var{tail}" "@var{before}" "@var{keyword_and_after}" "@var{head}" "@var{ref}"
4975 so it will be possible to write a @samp{.xx} roff macro to take care of
4976 the output typesetting. This is the default output format when @sc{gnu}
4977 extensions are disabled. Option @option{-M} can be used to change
4978 @samp{xx} to another macro name.
4980 In this output format, each non-graphical character, like newline and
4981 tab, is merely changed to exactly one space, with no special attempt to
4982 compress consecutive spaces. Each quote character: @kbd{"} is doubled
4983 so it will be correctly processed by @command{nroff} or @command{troff}.
4988 Choose an output format suitable for @TeX{} processing. Each output
4989 line will look like:
4992 \xx @{@var{tail}@}@{@var{before}@}@{@var{keyword}@}@{@var{after}@}@{@var{head}@}@{@var{ref}@}
4996 so it will be possible to write a @code{\xx} definition to take care of
4997 the output typesetting. Note that when references are not being
4998 produced, that is, neither option @option{-A} nor option @option{-r} is
4999 selected, the last parameter of each @code{\xx} call is inhibited.
5000 Option @option{-M} can be used to change @samp{xx} to another macro
5003 In this output format, some special characters, like @kbd{$}, @kbd{%},
5004 @kbd{&}, @kbd{#} and @kbd{_} are automatically protected with a
5005 backslash. Curly brackets @kbd{@{}, @kbd{@}} are protected with a
5006 backslash and a pair of dollar signs (to force mathematical mode). The
5007 backslash itself produces the sequence @code{\backslash@{@}}.
5008 Circumflex and tilde diacritical marks produce the sequence @code{^\@{ @}} and
5009 @code{~\@{ @}} respectively. Other diacriticized characters of the
5010 underlying character set produce an appropriate @TeX{} sequence as far
5011 as possible. The other non-graphical characters, like newline and tab,
5012 and all other characters which are not part of @acronym{ASCII}, are merely
5013 changed to exactly one space, with no special attempt to compress
5014 consecutive spaces. Let me know how to improve this special character
5015 processing for @TeX{}.
5020 @node Compatibility in ptx
5021 @subsection The @sc{gnu} extensions to @command{ptx}
5023 This version of @command{ptx} contains a few features which do not exist in
5024 System V @command{ptx}. These extra features are suppressed by using the
5025 @option{-G} command line option, unless overridden by other command line
5026 options. Some @sc{gnu} extensions cannot be recovered by overriding, so the
5027 simple rule is to avoid @option{-G} if you care about @sc{gnu} extensions.
5028 Here are the differences between this program and System V @command{ptx}.
5033 This program can read many input files at once, it always writes the
5034 resulting concordance on standard output. On the other hand, System V
5035 @command{ptx} reads only one file and sends the result to standard output
5036 or, if a second @var{file} parameter is given on the command, to that
5039 Having output parameters not introduced by options is a dangerous
5040 practice which @sc{gnu} avoids as far as possible. So, for using @command{ptx}
5041 portably between @sc{gnu} and System V, you should always use it with a
5042 single input file, and always expect the result on standard output. You
5043 might also want to automatically configure in a @option{-G} option to
5044 @command{ptx} calls in products using @command{ptx}, if the configurator finds
5045 that the installed @command{ptx} accepts @option{-G}.
5048 The only options available in System V @command{ptx} are options @option{-b},
5049 @option{-f}, @option{-g}, @option{-i}, @option{-o}, @option{-r}, @option{-t} and
5050 @option{-w}. All other options are @sc{gnu} extensions and are not repeated in
5051 this enumeration. Moreover, some options have a slightly different
5052 meaning when @sc{gnu} extensions are enabled, as explained below.
5055 By default, concordance output is not formatted for @command{troff} or
5056 @command{nroff}. It is rather formatted for a dumb terminal. @command{troff}
5057 or @command{nroff} output may still be selected through option @option{-O}.
5060 Unless @option{-R} option is used, the maximum reference width is
5061 subtracted from the total output line width. With @sc{gnu} extensions
5062 disabled, width of references is not taken into account in the output
5063 line width computations.
5066 All 256 bytes, even @acronym{ASCII} @sc{nul} bytes, are always read and
5067 processed from input file with no adverse effect, even if @sc{gnu} extensions
5068 are disabled. However, System V @command{ptx} does not accept 8-bit characters,
5069 a few control characters are rejected, and the tilde @kbd{~} is also rejected.
5072 Input line length is only limited by available memory, even if @sc{gnu}
5073 extensions are disabled. However, System V @command{ptx} processes only
5074 the first 200 characters in each line.
5077 The break (non-word) characters default to be every character except all
5078 letters of the underlying character set, diacriticized or not. When @sc{gnu}
5079 extensions are disabled, the break characters default to space, tab and
5083 The program makes better use of output line width. If @sc{gnu} extensions
5084 are disabled, the program rather tries to imitate System V @command{ptx},
5085 but still, there are some slight disposition glitches this program does
5086 not completely reproduce.
5089 The user can specify both an Ignore file and an Only file. This is not
5090 allowed with System V @command{ptx}.
5095 @node tsort invocation
5096 @section @command{tsort}: Topological sort
5099 @cindex topological sort
5101 @command{tsort} performs a topological sort on the given @var{file}, or
5102 standard input if no input file is given or for a @var{file} of
5103 @samp{-}. For more details and some history, see @ref{tsort background}.
5107 tsort [@var{option}] [@var{file}]
5110 @command{tsort} reads its input as pairs of strings, separated by blanks,
5111 indicating a partial ordering. The output is a total ordering that
5112 corresponds to the given partial ordering.
5126 will produce the output
5137 Consider a more realistic example.
5138 You have a large set of functions all in one file, and they may all be
5139 declared static except one. Currently that one (say @code{main}) is the
5140 first function defined in the file, and the ones it calls directly follow
5141 it, followed by those they call, etc. Let's say that you are determined
5142 to take advantage of prototypes, so you have to choose between declaring
5143 all of those functions (which means duplicating a lot of information from
5144 the definitions) and rearranging the functions so that as many as possible
5145 are defined before they are used. One way to automate the latter process
5146 is to get a list for each function of the functions it calls directly.
5147 Many programs can generate such lists. They describe a call graph.
5148 Consider the following list, in which a given line indicates that the
5149 function on the left calls the one on the right directly.
5155 tail_file pretty_name
5156 tail_file write_header
5158 tail_forever recheck
5159 tail_forever pretty_name
5160 tail_forever write_header
5161 tail_forever dump_remainder
5164 tail_lines start_lines
5165 tail_lines dump_remainder
5166 tail_lines file_lines
5167 tail_lines pipe_lines
5169 tail_bytes start_bytes
5170 tail_bytes dump_remainder
5171 tail_bytes pipe_bytes
5172 file_lines dump_remainder
5176 then you can use @command{tsort} to produce an ordering of those
5177 functions that satisfies your requirement.
5180 example$ tsort call-graph | tac
5200 @command{tsort} detects any cycles in the input and writes the first cycle
5201 encountered to standard error.
5203 Note that for a given partial ordering, generally there is no unique
5204 total ordering. In the context of the call graph above, the function
5205 @code{parse_options} may be placed anywhere in the list as long as it
5206 precedes @code{main}.
5208 The only options are @option{--help} and @option{--version}. @xref{Common
5214 * tsort background:: Where tsort came from.
5217 @node tsort background
5218 @subsection @command{tsort}: Background
5220 @command{tsort} exists because very early versions of the Unix linker processed
5221 an archive file exactly once, and in order. As @command{ld} read each object
5222 in the archive, it decided whether it was needed in the program based on
5223 whether it defined any symbols which were undefined at that point in
5226 This meant that dependencies within the archive had to be handled
5227 specially. For example, @code{scanf} probably calls @code{read}. That means
5228 that in a single pass through an archive, it was important for @code{scanf.o}
5229 to appear before read.o, because otherwise a program which calls
5230 @code{scanf} but not @code{read} might end up with an unexpected unresolved
5231 reference to @code{read}.
5233 The way to address this problem was to first generate a set of
5234 dependencies of one object file on another. This was done by a shell
5235 script called @command{lorder}. The GNU tools don't provide a version of
5236 lorder, as far as I know, but you can still find it in BSD
5239 Then you ran @command{tsort} over the @command{lorder} output, and you used the
5240 resulting sort to define the order in which you added objects to the archive.
5242 This whole procedure has been obsolete since about 1980, because
5243 Unix archives now contain a symbol table (traditionally built by
5244 @command{ranlib}, now generally built by @command{ar} itself), and the Unix
5245 linker uses the symbol table to effectively make multiple passes over
5248 Anyhow, that's where tsort came from. To solve an old problem with
5249 the way the linker handled archive files, which has since been solved
5253 @node Operating on fields
5254 @chapter Operating on fields
5257 * cut invocation:: Print selected parts of lines.
5258 * paste invocation:: Merge lines of files.
5259 * join invocation:: Join lines on a common field.
5263 @node cut invocation
5264 @section @command{cut}: Print selected parts of lines
5267 @command{cut} writes to standard output selected parts of each line of each
5268 input file, or standard input if no files are given or for a file name of
5272 cut @var{option}@dots{} [@var{file}]@dots{}
5275 In the table which follows, the @var{byte-list}, @var{character-list},
5276 and @var{field-list} are one or more numbers or ranges (two numbers
5277 separated by a dash) separated by commas. Bytes, characters, and
5278 fields are numbered starting at 1. Incomplete ranges may be
5279 given: @option{-@var{m}} means @samp{1-@var{m}}; @samp{@var{n}-} means
5280 @samp{@var{n}} through end of line or last field. The list elements
5281 can be repeated, can overlap, and can be specified in any order; but
5282 the selected input is written in the same order that it is read, and
5283 is written exactly once.
5285 The program accepts the following options. Also see @ref{Common
5290 @item -b @var{byte-list}
5291 @itemx --bytes=@var{byte-list}
5294 Select for printing only the bytes in positions listed in
5295 @var{byte-list}. Tabs and backspaces are treated like any other
5296 character; they take up 1 byte. If an output delimiter is specified,
5297 (see the description of @option{--output-delimiter}), then output that
5298 string between ranges of selected bytes.
5300 @item -c @var{character-list}
5301 @itemx --characters=@var{character-list}
5303 @opindex --characters
5304 Select for printing only the characters in positions listed in
5305 @var{character-list}. The same as @option{-b} for now, but
5306 internationalization will change that. Tabs and backspaces are
5307 treated like any other character; they take up 1 character. If an
5308 output delimiter is specified, (see the description of
5309 @option{--output-delimiter}), then output that string between ranges
5312 @item -f @var{field-list}
5313 @itemx --fields=@var{field-list}
5316 Select for printing only the fields listed in @var{field-list}.
5317 Fields are separated by a TAB character by default. Also print any
5318 line that contains no delimiter character, unless the
5319 @option{--only-delimited} (@option{-s}) option is specified
5321 @item -d @var{input_delim_byte}
5322 @itemx --delimiter=@var{input_delim_byte}
5324 @opindex --delimiter
5325 With @option{-f}, use the first byte of @var{input_delim_byte} as
5326 the input fields separator (default is TAB).
5330 Do not split multi-byte characters (no-op for now).
5333 @itemx --only-delimited
5335 @opindex --only-delimited
5336 For @option{-f}, do not print lines that do not contain the field separator
5337 character. Normally, any line without a field separator is printed verbatim.
5339 @item --output-delimiter=@var{output_delim_string}
5340 @opindex --output-delimiter
5341 With @option{-f}, output fields are separated by @var{output_delim_string}.
5342 The default with @option{-f} is to use the input delimiter.
5343 When using @option{-b} or @option{-c} to select ranges of byte or
5344 character offsets (as opposed to ranges of fields),
5345 output @var{output_delim_string} between non-overlapping
5346 ranges of selected bytes.
5349 @opindex --complement
5350 This option is a @acronym{GNU} extension.
5351 Select for printing the complement of the bytes, characters or fields
5352 selected with the @option{-b}, @option{-c} or @option{-f} options.
5353 In other words, do @emph{not} print the bytes, characters or fields
5354 specified via those options. This option is useful when you have
5355 many fields and want to print all but a few of them.
5362 @node paste invocation
5363 @section @command{paste}: Merge lines of files
5366 @cindex merging files
5368 @command{paste} writes to standard output lines consisting of sequentially
5369 corresponding lines of each given file, separated by a TAB character.
5370 Standard input is used for a file name of @samp{-} or if no input files
5392 paste [@var{option}]@dots{} [@var{file}]@dots{}
5395 The program accepts the following options. Also see @ref{Common options}.
5403 Paste the lines of one file at a time rather than one line from each
5404 file. Using the above example data:
5407 $ paste -s num2 let3
5412 @item -d @var{delim-list}
5413 @itemx --delimiters=@var{delim-list}
5415 @opindex --delimiters
5416 Consecutively use the characters in @var{delim-list} instead of
5417 TAB to separate merged lines. When @var{delim-list} is
5418 exhausted, start again at its beginning. Using the above example data:
5421 $ paste -d '%_' num2 let3 num2
5432 @node join invocation
5433 @section @command{join}: Join lines on a common field
5436 @cindex common field, joining on
5438 @command{join} writes to standard output a line for each pair of input
5439 lines that have identical join fields. Synopsis:
5442 join [@var{option}]@dots{} @var{file1} @var{file2}
5445 Either @var{file1} or @var{file2} (but not both) can be @samp{-},
5446 meaning standard input. @var{file1} and @var{file2} should be
5447 sorted on the join fields.
5450 Normally, the sort order is that of the
5451 collating sequence specified by the @env{LC_COLLATE} locale. Unless
5452 the @option{-t} option is given, the sort comparison ignores blanks at
5453 the start of the join field, as in @code{sort -b}. If the
5454 @option{--ignore-case} option is given, the sort comparison ignores
5455 the case of characters in the join field, as in @code{sort -f}.
5457 The @command{sort} and @command{join} commands should use consistent
5458 locales and options if the output of @command{sort} is fed to
5459 @command{join}. You can use a command like @samp{sort -k 1b,1} to
5460 sort a file on its default join field, but if you select a non-default
5461 locale, join field, separator, or comparison options, then you should
5462 do so consistently between @command{join} and @command{sort}.
5464 If the input has no unpairable lines, a @acronym{GNU} extension is
5465 available; the sort order can be any order that considers two fields
5466 to be equal if and only if the sort comparison described above
5467 considers them to be equal. For example:
5484 @checkOrderOption{join}
5488 @item the join field is the first field in each line;
5489 @item fields in the input are separated by one or more blanks, with leading
5490 blanks on the line ignored;
5491 @item fields in the output are separated by a space;
5492 @item each output line consists of the join field, the remaining
5493 fields from @var{file1}, then the remaining fields from @var{file2}.
5496 The program accepts the following options. Also see @ref{Common options}.
5500 @item -a @var{file-number}
5502 Print a line for each unpairable line in file @var{file-number} (either
5503 @samp{1} or @samp{2}), in addition to the normal output.
5506 Fail with an error message if either input file is wrongly ordered.
5508 @item --nocheck-order
5509 Do not check that both input files are in sorted order. This is the default.
5511 @item -e @var{string}
5513 Replace those output fields that are missing in the input with
5517 @itemx --ignore-case
5519 @opindex --ignore-case
5520 Ignore differences in case when comparing keys.
5521 With this option, the lines of the input files must be ordered in the same way.
5522 Use @samp{sort -f} to produce this ordering.
5524 @item -1 @var{field}
5526 Join on field @var{field} (a positive integer) of file 1.
5528 @item -2 @var{field}
5530 Join on field @var{field} (a positive integer) of file 2.
5532 @item -j @var{field}
5533 Equivalent to @option{-1 @var{field} -2 @var{field}}.
5535 @item -o @var{field-list}
5536 Construct each output line according to the format in @var{field-list}.
5537 Each element in @var{field-list} is either the single character @samp{0} or
5538 has the form @var{m.n} where the file number, @var{m}, is @samp{1} or
5539 @samp{2} and @var{n} is a positive field number.
5541 A field specification of @samp{0} denotes the join field.
5542 In most cases, the functionality of the @samp{0} field spec
5543 may be reproduced using the explicit @var{m.n} that corresponds
5544 to the join field. However, when printing unpairable lines
5545 (using either of the @option{-a} or @option{-v} options), there is no way
5546 to specify the join field using @var{m.n} in @var{field-list}
5547 if there are unpairable lines in both files.
5548 To give @command{join} that functionality, @acronym{POSIX} invented the @samp{0}
5549 field specification notation.
5551 The elements in @var{field-list}
5552 are separated by commas or blanks.
5553 Blank separators typically need to be quoted for the shell. For
5554 example, the commands @samp{join -o 1.2,2.2} and @samp{join -o '1.2
5555 2.2'} are equivalent.
5557 All output lines---including those printed because of any -a or -v
5558 option---are subject to the specified @var{field-list}.
5561 Use character @var{char} as the input and output field separator.
5562 Treat as significant each occurrence of @var{char} in the input file.
5563 Use @samp{sort -t @var{char}}, without the @option{-b} option of
5564 @samp{sort}, to produce this ordering.
5566 @item -v @var{file-number}
5567 Print a line for each unpairable line in file @var{file-number}
5568 (either @samp{1} or @samp{2}), instead of the normal output.
5575 @node Operating on characters
5576 @chapter Operating on characters
5578 @cindex operating on characters
5580 This commands operate on individual characters.
5583 * tr invocation:: Translate, squeeze, and/or delete characters.
5584 * expand invocation:: Convert tabs to spaces.
5585 * unexpand invocation:: Convert spaces to tabs.
5590 @section @command{tr}: Translate, squeeze, and/or delete characters
5597 tr [@var{option}]@dots{} @var{set1} [@var{set2}]
5600 @command{tr} copies standard input to standard output, performing
5601 one of the following operations:
5605 translate, and optionally squeeze repeated characters in the result,
5607 squeeze repeated characters,
5611 delete characters, then squeeze repeated characters from the result.
5614 The @var{set1} and (if given) @var{set2} arguments define ordered
5615 sets of characters, referred to below as @var{set1} and @var{set2}. These
5616 sets are the characters of the input that @command{tr} operates on.
5617 The @option{--complement} (@option{-c}, @option{-C}) option replaces
5619 complement (all of the characters that are not in @var{set1}).
5621 Currently @command{tr} fully supports only single-byte characters.
5622 Eventually it will support multibyte characters; when it does, the
5623 @option{-C} option will cause it to complement the set of characters,
5624 whereas @option{-c} will cause it to complement the set of values.
5625 This distinction will matter only when some values are not characters,
5626 and this is possible only in locales using multibyte encodings when
5627 the input contains encoding errors.
5629 The program accepts the @option{--help} and @option{--version}
5630 options. @xref{Common options}. Options must precede operands.
5635 * Character sets:: Specifying sets of characters.
5636 * Translating:: Changing one set of characters to another.
5637 * Squeezing:: Squeezing repeats and deleting.
5641 @node Character sets
5642 @subsection Specifying sets of characters
5644 @cindex specifying sets of characters
5646 The format of the @var{set1} and @var{set2} arguments resembles
5647 the format of regular expressions; however, they are not regular
5648 expressions, only lists of characters. Most characters simply
5649 represent themselves in these strings, but the strings can contain
5650 the shorthands listed below, for convenience. Some of them can be
5651 used only in @var{set1} or @var{set2}, as noted below.
5655 @item Backslash escapes
5656 @cindex backslash escapes
5658 The following backslash escape sequences are recognized:
5676 The character with the value given by @var{ooo}, which is 1 to 3
5682 While a backslash followed by a character not listed above is
5683 interpreted as that character, the backslash also effectively
5684 removes any special significance, so it is useful to escape
5685 @samp{[}, @samp{]}, @samp{*}, and @samp{-}.
5690 The notation @samp{@var{m}-@var{n}} expands to all of the characters
5691 from @var{m} through @var{n}, in ascending order. @var{m} should
5692 collate before @var{n}; if it doesn't, an error results. As an example,
5693 @samp{0-9} is the same as @samp{0123456789}.
5695 @sc{gnu} @command{tr} does not support the System V syntax that uses square
5696 brackets to enclose ranges. Translations specified in that format
5697 sometimes work as expected, since the brackets are often transliterated
5698 to themselves. However, they should be avoided because they sometimes
5699 behave unexpectedly. For example, @samp{tr -d '[0-9]'} deletes brackets
5702 Many historically common and even accepted uses of ranges are not
5703 portable. For example, on @acronym{EBCDIC} hosts using the @samp{A-Z}
5704 range will not do what most would expect because @samp{A} through @samp{Z}
5705 are not contiguous as they are in @acronym{ASCII}.
5706 If you can rely on a @acronym{POSIX} compliant version of @command{tr}, then
5707 the best way to work around this is to use character classes (see below).
5708 Otherwise, it is most portable (and most ugly) to enumerate the members
5711 @item Repeated characters
5712 @cindex repeated characters
5714 The notation @samp{[@var{c}*@var{n}]} in @var{set2} expands to @var{n}
5715 copies of character @var{c}. Thus, @samp{[y*6]} is the same as
5716 @samp{yyyyyy}. The notation @samp{[@var{c}*]} in @var{string2} expands
5717 to as many copies of @var{c} as are needed to make @var{set2} as long as
5718 @var{set1}. If @var{n} begins with @samp{0}, it is interpreted in
5719 octal, otherwise in decimal.
5721 @item Character classes
5722 @cindex character classes
5724 The notation @samp{[:@var{class}:]} expands to all of the characters in
5725 the (predefined) class @var{class}. The characters expand in no
5726 particular order, except for the @code{upper} and @code{lower} classes,
5727 which expand in ascending order. When the @option{--delete} (@option{-d})
5728 and @option{--squeeze-repeats} (@option{-s}) options are both given, any
5729 character class can be used in @var{set2}. Otherwise, only the
5730 character classes @code{lower} and @code{upper} are accepted in
5731 @var{set2}, and then only if the corresponding character class
5732 (@code{upper} and @code{lower}, respectively) is specified in the same
5733 relative position in @var{set1}. Doing this specifies case conversion.
5734 The class names are given below; an error results when an invalid class
5746 Horizontal whitespace.
5755 Printable characters, not including space.
5761 Printable characters, including space.
5764 Punctuation characters.
5767 Horizontal or vertical whitespace.
5776 @item Equivalence classes
5777 @cindex equivalence classes
5779 The syntax @samp{[=@var{c}=]} expands to all of the characters that are
5780 equivalent to @var{c}, in no particular order. Equivalence classes are
5781 a relatively recent invention intended to support non-English alphabets.
5782 But there seems to be no standard way to define them or determine their
5783 contents. Therefore, they are not fully implemented in @sc{gnu} @command{tr};
5784 each character's equivalence class consists only of that character,
5785 which is of no particular use.
5791 @subsection Translating
5793 @cindex translating characters
5795 @command{tr} performs translation when @var{set1} and @var{set2} are
5796 both given and the @option{--delete} (@option{-d}) option is not given.
5797 @command{tr} translates each character of its input that is in @var{set1}
5798 to the corresponding character in @var{set2}. Characters not in
5799 @var{set1} are passed through unchanged. When a character appears more
5800 than once in @var{set1} and the corresponding characters in @var{set2}
5801 are not all the same, only the final one is used. For example, these
5802 two commands are equivalent:
5809 A common use of @command{tr} is to convert lowercase characters to
5810 uppercase. This can be done in many ways. Here are three of them:
5813 tr abcdefghijklmnopqrstuvwxyz ABCDEFGHIJKLMNOPQRSTUVWXYZ
5815 tr '[:lower:]' '[:upper:]'
5819 But note that using ranges like @code{a-z} above is not portable.
5821 When @command{tr} is performing translation, @var{set1} and @var{set2}
5822 typically have the same length. If @var{set1} is shorter than
5823 @var{set2}, the extra characters at the end of @var{set2} are ignored.
5825 On the other hand, making @var{set1} longer than @var{set2} is not
5826 portable; @acronym{POSIX} says that the result is undefined. In this situation,
5827 BSD @command{tr} pads @var{set2} to the length of @var{set1} by repeating
5828 the last character of @var{set2} as many times as necessary. System V
5829 @command{tr} truncates @var{set1} to the length of @var{set2}.
5831 By default, @sc{gnu} @command{tr} handles this case like BSD @command{tr}.
5832 When the @option{--truncate-set1} (@option{-t}) option is given,
5833 @sc{gnu} @command{tr} handles this case like the System V @command{tr}
5834 instead. This option is ignored for operations other than translation.
5836 Acting like System V @command{tr} in this case breaks the relatively common
5840 tr -cs A-Za-z0-9 '\012'
5844 because it converts only zero bytes (the first element in the
5845 complement of @var{set1}), rather than all non-alphanumerics, to
5849 By the way, the above idiom is not portable because it uses ranges, and
5850 it assumes that the octal code for newline is 012.
5851 Assuming a @acronym{POSIX} compliant @command{tr}, here is a better way to write it:
5854 tr -cs '[:alnum:]' '[\n*]'
5859 @subsection Squeezing repeats and deleting
5861 @cindex squeezing repeat characters
5862 @cindex deleting characters
5864 When given just the @option{--delete} (@option{-d}) option, @command{tr}
5865 removes any input characters that are in @var{set1}.
5867 When given just the @option{--squeeze-repeats} (@option{-s}) option,
5868 @command{tr} replaces each input sequence of a repeated character that
5869 is in @var{set1} with a single occurrence of that character.
5871 When given both @option{--delete} and @option{--squeeze-repeats}, @command{tr}
5872 first performs any deletions using @var{set1}, then squeezes repeats
5873 from any remaining characters using @var{set2}.
5875 The @option{--squeeze-repeats} option may also be used when translating,
5876 in which case @command{tr} first performs translation, then squeezes
5877 repeats from any remaining characters using @var{set2}.
5879 Here are some examples to illustrate various combinations of options:
5884 Remove all zero bytes:
5891 Put all words on lines by themselves. This converts all
5892 non-alphanumeric characters to newlines, then squeezes each string
5893 of repeated newlines into a single newline:
5896 tr -cs '[:alnum:]' '[\n*]'
5900 Convert each sequence of repeated newlines to a single newline:
5907 Find doubled occurrences of words in a document.
5908 @c Separate the following two "the"s, so typo checkers don't complain.
5909 For example, people often write ``the @w{}the'' with the repeated words
5910 separated by a newline. The Bourne shell script below works first
5911 by converting each sequence of punctuation and blank characters to a
5912 single newline. That puts each ``word'' on a line by itself.
5913 Next it maps all uppercase characters to lower case, and finally it
5914 runs @command{uniq} with the @option{-d} option to print out only the words
5920 | tr -s '[:punct:][:blank:]' '[\n*]' \
5921 | tr '[:upper:]' '[:lower:]' \
5926 Deleting a small set of characters is usually straightforward. For example,
5927 to remove all @samp{a}s, @samp{x}s, and @samp{M}s you would do this:
5933 However, when @samp{-} is one of those characters, it can be tricky because
5934 @samp{-} has special meanings. Performing the same task as above but also
5935 removing all @samp{-} characters, we might try @code{tr -d -axM}, but
5936 that would fail because @command{tr} would try to interpret @option{-a} as
5937 a command-line option. Alternatively, we could try putting the hyphen
5938 inside the string, @code{tr -d a-xM}, but that wouldn't work either because
5939 it would make @command{tr} interpret @code{a-x} as the range of characters
5940 @samp{a}@dots{}@samp{x} rather than the three.
5941 One way to solve the problem is to put the hyphen at the end of the list
5948 Or you can use @samp{--} to terminate option processing:
5954 More generally, use the character class notation @code{[=c=]}
5955 with @samp{-} (or any other character) in place of the @samp{c}:
5961 Note how single quotes are used in the above example to protect the
5962 square brackets from interpretation by a shell.
5967 @node expand invocation
5968 @section @command{expand}: Convert tabs to spaces
5971 @cindex tabs to spaces, converting
5972 @cindex converting tabs to spaces
5974 @command{expand} writes the contents of each given @var{file}, or standard
5975 input if none are given or for a @var{file} of @samp{-}, to standard
5976 output, with tab characters converted to the appropriate number of
5980 expand [@var{option}]@dots{} [@var{file}]@dots{}
5983 By default, @command{expand} converts all tabs to spaces. It preserves
5984 backspace characters in the output; they decrement the column count for
5985 tab calculations. The default action is equivalent to @option{-t 8} (set
5986 tabs every 8 columns).
5988 The program accepts the following options. Also see @ref{Common options}.
5992 @item -t @var{tab1}[,@var{tab2}]@dots{}
5993 @itemx --tabs=@var{tab1}[,@var{tab2}]@dots{}
5996 @cindex tab stops, setting
5997 If only one tab stop is given, set the tabs @var{tab1} spaces apart
5998 (default is 8). Otherwise, set the tabs at columns @var{tab1},
5999 @var{tab2}, @dots{} (numbered from 0), and replace any tabs beyond the
6000 last tab stop given with single spaces. Tab stops can be separated by
6001 blanks as well as by commas.
6003 For compatibility, GNU @command{expand} also accepts the obsolete
6004 option syntax, @option{-@var{t1}[,@var{t2}]@dots{}}. New scripts
6005 should use @option{-t @var{t1}[,@var{t2}]@dots{}} instead.
6011 @cindex initial tabs, converting
6012 Only convert initial tabs (those that precede all non-space or non-tab
6013 characters) on each line to spaces.
6020 @node unexpand invocation
6021 @section @command{unexpand}: Convert spaces to tabs
6025 @command{unexpand} writes the contents of each given @var{file}, or
6026 standard input if none are given or for a @var{file} of @samp{-}, to
6027 standard output, converting blanks at the beginning of each line into
6028 as many tab characters as needed. In the default @acronym{POSIX}
6029 locale, a @dfn{blank} is a space or a tab; other locales may specify
6030 additional blank characters. Synopsis:
6033 unexpand [@var{option}]@dots{} [@var{file}]@dots{}
6036 By default, @command{unexpand} converts only initial blanks (those
6037 that precede all non-blank characters) on each line. It
6038 preserves backspace characters in the output; they decrement the column
6039 count for tab calculations. By default, tabs are set at every 8th
6042 The program accepts the following options. Also see @ref{Common options}.
6046 @item -t @var{tab1}[,@var{tab2}]@dots{}
6047 @itemx --tabs=@var{tab1}[,@var{tab2}]@dots{}
6050 If only one tab stop is given, set the tabs @var{tab1} columns apart
6051 instead of the default 8. Otherwise, set the tabs at columns
6052 @var{tab1}, @var{tab2}, @dots{} (numbered from 0), and leave blanks
6053 beyond the tab stops given unchanged. Tab stops can be separated by
6054 blanks as well as by commas. This option implies the @option{-a} option.
6056 For compatibility, GNU @command{unexpand} supports the obsolete option syntax,
6057 @option{-@var{tab1}[,@var{tab2}]@dots{}}, where tab stops must be
6058 separated by commas. (Unlike @option{-t}, this obsolete option does
6059 not imply @option{-a}.) New scripts should use @option{--first-only -t
6060 @var{tab1}[,@var{tab2}]@dots{}} instead.
6066 Also convert all sequences of two or more blanks just before a tab stop,
6067 even if they occur after non-blank characters in a line.
6074 @node Directory listing
6075 @chapter Directory listing
6077 This chapter describes the @command{ls} command and its variants @command{dir}
6078 and @command{vdir}, which list information about files.
6081 * ls invocation:: List directory contents.
6082 * dir invocation:: Briefly ls.
6083 * vdir invocation:: Verbosely ls.
6084 * dircolors invocation:: Color setup for ls, etc.
6089 @section @command{ls}: List directory contents
6092 @cindex directory listing
6094 The @command{ls} program lists information about files (of any type,
6095 including directories). Options and file arguments can be intermixed
6096 arbitrarily, as usual.
6098 For non-option command-line arguments that are directories, by default
6099 @command{ls} lists the contents of directories, not recursively, and
6100 omitting files with names beginning with @samp{.}. For other non-option
6101 arguments, by default @command{ls} lists just the file name. If no
6102 non-option argument is specified, @command{ls} operates on the current
6103 directory, acting as if it had been invoked with a single argument of @samp{.}.
6106 By default, the output is sorted alphabetically, according to the locale
6107 settings in effect.@footnote{If you use a non-@acronym{POSIX}
6108 locale (e.g., by setting @env{LC_ALL} to @samp{en_US}), then @command{ls} may
6109 produce output that is sorted differently than you're accustomed to.
6110 In that case, set the @env{LC_ALL} environment variable to @samp{C}.}
6111 If standard output is
6112 a terminal, the output is in columns (sorted vertically) and control
6113 characters are output as question marks; otherwise, the output is listed
6114 one per line and control characters are output as-is.
6116 Because @command{ls} is such a fundamental program, it has accumulated many
6117 options over the years. They are described in the subsections below;
6118 within each section, options are listed alphabetically (ignoring case).
6119 The division of options into the subsections is not absolute, since some
6120 options affect more than one aspect of @command{ls}'s operation.
6122 @cindex exit status of @command{ls}
6127 1 minor problems (e.g., failure to access a file or directory not
6128 specified as a command line argument. This happens when listing a
6129 directory in which entries are actively being removed or renamed.)
6130 2 serious trouble (e.g., memory exhausted, invalid option, failure
6131 to access a file or directory specified as a command line argument
6132 or a directory loop)
6135 Also see @ref{Common options}.
6138 * Which files are listed::
6139 * What information is listed::
6140 * Sorting the output::
6141 * Details about version sort::
6142 * General output formatting::
6143 * Formatting file timestamps::
6144 * Formatting the file names::
6148 @node Which files are listed
6149 @subsection Which files are listed
6151 These options determine which files @command{ls} lists information for.
6152 By default, @command{ls} lists files and the contents of any
6153 directories on the command line, except that in directories it ignores
6154 files whose names start with @samp{.}.
6162 In directories, do not ignore file names that start with @samp{.}.
6167 @opindex --almost-all
6168 In directories, do not ignore all file names that start with @samp{.};
6169 ignore only @file{.} and @file{..}. The @option{--all} (@option{-a})
6170 option overrides this option.
6173 @itemx --ignore-backups
6175 @opindex --ignore-backups
6176 @cindex backup files, ignoring
6177 In directories, ignore files that end with @samp{~}. This option is
6178 equivalent to @samp{--ignore='*~' --ignore='.*~'}.
6183 @opindex --directory
6184 List just the names of directories, as with other types of files, rather
6185 than listing their contents.
6186 @c The following sentence is the same as the one for -F.
6187 Do not follow symbolic links listed on the
6188 command line unless the @option{--dereference-command-line} (@option{-H}),
6189 @option{--dereference} (@option{-L}), or
6190 @option{--dereference-command-line-symlink-to-dir} options are specified.
6193 @itemx --dereference-command-line
6195 @opindex --dereference-command-line
6196 @cindex symbolic links, dereferencing
6197 If a command line argument specifies a symbolic link, show information
6198 for the file the link references rather than for the link itself.
6200 @itemx --dereference-command-line-symlink-to-dir
6201 @opindex --dereference-command-line-symlink-to-dir
6202 @cindex symbolic links, dereferencing
6203 Do not dereference symbolic links, with one exception:
6204 if a command line argument specifies a symbolic link that refers to
6205 a directory, show information for that directory rather than for the
6207 This is the default behavior when no other dereferencing-related
6208 option has been specified (@option{--classify} (@option{-F}),
6209 @option{--directory} (@option{-d}),
6211 @option{--dereference} (@option{-L}), or
6212 @option{--dereference-command-line} (@option{-H})).
6214 @item --group-directories-first
6215 @opindex --group-directories-first
6216 Group all the directories before the files and then sort the
6217 directories and the files separately using the selected sort key
6218 (see --sort option).
6219 That is, this option specifies a primary sort key,
6220 and the --sort option specifies a secondary key.
6221 However, any use of @option{--sort=none}
6222 (@option{-U}) disables this option altogether.
6224 @item --hide=PATTERN
6225 @opindex --hide=@var{pattern}
6226 In directories, ignore files whose names match the shell pattern
6227 @var{pattern}, unless the @option{--all} (@option{-a}) or
6228 @option{--almost-all} (@option{-A}) is also given. This
6229 option acts like @option{--ignore=@var{pattern}} except that it has no
6230 effect if @option{--all} (@option{-a}) or @option{--almost-all}
6231 (@option{-A}) is also given.
6233 This option can be useful in shell aliases. For example, if
6234 @command{lx} is an alias for @samp{ls --hide='*~'} and @command{ly} is
6235 an alias for @samp{ls --ignore='*~'}, then the command @samp{lx -A}
6236 lists the file @file{README~} even though @samp{ly -A} would not.
6238 @item -I @var{pattern}
6239 @itemx --ignore=@var{pattern}
6241 @opindex --ignore=@var{pattern}
6242 In directories, ignore files whose names match the shell pattern
6243 (not regular expression) @var{pattern}. As
6244 in the shell, an initial @samp{.} in a file name does not match a
6245 wildcard at the start of @var{pattern}. Sometimes it is useful
6246 to give this option several times. For example,
6249 $ ls --ignore='.??*' --ignore='.[^.]' --ignore='#*'
6252 The first option ignores names of length 3 or more that start with @samp{.},
6253 the second ignores all two-character names that start with @samp{.}
6254 except @samp{..}, and the third ignores names that start with @samp{#}.
6257 @itemx --dereference
6259 @opindex --dereference
6260 @cindex symbolic links, dereferencing
6261 When showing file information for a symbolic link, show information
6262 for the file the link references rather than the link itself.
6263 However, even with this option, @command{ls} still prints the name
6264 of the link itself, not the name of the file that the link points to.
6269 @opindex --recursive
6270 @cindex recursive directory listing
6271 @cindex directory listing, recursive
6272 List the contents of all directories recursively.
6277 @node What information is listed
6278 @subsection What information is listed
6280 These options affect the information that @command{ls} displays. By
6281 default, only file names are shown.
6287 @cindex hurd, author, printing
6288 List each file's author when producing long format directory listings.
6289 In GNU/Hurd, file authors can differ from their owners, but in other
6290 operating systems the two are the same.
6296 @cindex dired Emacs mode support
6297 With the long listing (@option{-l}) format, print an additional line after
6301 //DIRED// @var{beg1} @var{end1} @var{beg2} @var{end2} @dots{}
6305 The @var{begn} and @var{endn} are unsigned integers that record the
6306 byte position of the beginning and end of each file name in the output.
6307 This makes it easy for Emacs to find the names, even when they contain
6308 unusual characters such as space or newline, without fancy searching.
6310 If directories are being listed recursively (@option{-R}), output a similar
6311 line with offsets for each subdirectory name:
6314 //SUBDIRED// @var{beg1} @var{end1} @dots{}
6317 Finally, output a line of the form:
6320 //DIRED-OPTIONS// --quoting-style=@var{word}
6324 where @var{word} is the quoting style (@pxref{Formatting the file names}).
6326 Here is an actual example:
6329 $ mkdir -p a/sub/deeper a/sub2
6331 $ touch a/sub/deeper/file
6332 $ ls -gloRF --dired a
6335 -rw-r--r-- 1 0 Jun 10 12:27 f1
6336 -rw-r--r-- 1 0 Jun 10 12:27 f2
6337 drwxr-xr-x 3 4096 Jun 10 12:27 sub/
6338 drwxr-xr-x 2 4096 Jun 10 12:27 sub2/
6342 drwxr-xr-x 2 4096 Jun 10 12:27 deeper/
6346 -rw-r--r-- 1 0 Jun 10 12:27 file
6350 //DIRED// 48 50 84 86 120 123 158 162 217 223 282 286
6351 //SUBDIRED// 2 3 167 172 228 240 290 296
6352 //DIRED-OPTIONS// --quoting-style=literal
6355 Note that the pairs of offsets on the @samp{//DIRED//} line above delimit
6356 these names: @file{f1}, @file{f2}, @file{sub}, @file{sub2}, @file{deeper},
6358 The offsets on the @samp{//SUBDIRED//} line delimit the following
6359 directory names: @file{a}, @file{a/sub}, @file{a/sub/deeper}, @file{a/sub2}.
6361 Here is an example of how to extract the fifth entry name, @samp{deeper},
6362 corresponding to the pair of offsets, 222 and 228:
6365 $ ls -gloRF --dired a > out
6366 $ dd bs=1 skip=222 count=6 < out 2>/dev/null; echo
6370 Note that although the listing above includes a trailing slash
6371 for the @samp{deeper} entry, the offsets select the name without
6372 the trailing slash. However, if you invoke @command{ls} with @option{--dired}
6373 along with an option like @option{--escape} (aka @option{-b}) and operate
6374 on a file whose name contains special characters, notice that the backslash
6379 $ ls -blog --dired 'a b'
6380 -rw-r--r-- 1 0 Jun 10 12:28 a\ b
6382 //DIRED-OPTIONS// --quoting-style=escape
6385 If you use a quoting style that adds quote marks
6386 (e.g., @option{--quoting-style=c}), then the offsets include the quote marks.
6387 So beware that the user may select the quoting style via the environment
6388 variable @env{QUOTING_STYLE}. Hence, applications using @option{--dired}
6389 should either specify an explicit @option{--quoting-style=literal} option
6390 (aka @option{-N} or @option{--literal}) on the command line, or else be
6391 prepared to parse the escaped names.
6394 @opindex --full-time
6395 Produce long format directory listings, and list times in full. It is
6396 equivalent to using @option{--format=long} with
6397 @option{--time-style=full-iso} (@pxref{Formatting file timestamps}).
6401 Produce long format directory listings, but don't display owner information.
6407 Inhibit display of group information in a long format directory listing.
6408 (This is the default in some non-@sc{gnu} versions of @command{ls}, so we
6409 provide this option for compatibility.)
6417 @cindex inode number, printing
6418 Print the inode number (also called the file serial number and index
6419 number) of each file to the left of the file name. (This number
6420 uniquely identifies each file within a particular file system.)
6423 @itemx --format=long
6424 @itemx --format=verbose
6427 @opindex long ls @r{format}
6428 @opindex verbose ls @r{format}
6429 In addition to the name of each file, print the file type, file mode bits,
6430 number of hard links, owner name, group name, size, and
6431 timestamp (@pxref{Formatting file timestamps}), normally
6432 the modification time. Print question marks for information that
6433 cannot be determined.
6435 Normally the size is printed as a byte count without punctuation, but
6436 this can be overridden (@pxref{Block size}). For example, @option{-h}
6437 prints an abbreviated, human-readable count, and
6438 @samp{--block-size="'1"} prints a byte count with the thousands
6439 separator of the current locale.
6441 For each directory that is listed, preface the files with a line
6442 @samp{total @var{blocks}}, where @var{blocks} is the total disk allocation
6443 for all files in that directory. The block size currently defaults to 1024
6444 bytes, but this can be overridden (@pxref{Block size}).
6445 The @var{blocks} computed counts each hard link separately;
6446 this is arguably a deficiency.
6448 The file type is one of the following characters:
6450 @c The commented-out entries are ones we're not sure about.
6458 character special file
6460 high performance (``contiguous data'') file
6464 door (Solaris 2.5 and up)
6466 @c semaphore, if this is a distinct file type
6470 @c multiplexed file (7th edition Unix; obsolete)
6472 off-line (``migrated'') file (Cray DMF)
6474 network special file (HP-UX)
6478 port (Solaris 10 and up)
6480 @c message queue, if this is a distinct file type
6484 @c shared memory object, if this is a distinct file type
6486 @c typed memory object, if this is a distinct file type
6488 @c whiteout (4.4BSD; not implemented)
6490 some other file type
6493 @cindex permissions, output by @command{ls}
6494 The file mode bits listed are similar to symbolic mode specifications
6495 (@pxref{Symbolic Modes}). But @command{ls} combines multiple bits into the
6496 third character of each set of permissions as follows:
6500 If the set-user-ID or set-group-ID bit and the corresponding executable bit
6504 If the set-user-ID or set-group-ID bit is set but the corresponding
6505 executable bit is not set.
6508 If the restricted deletion flag or sticky bit, and the
6509 other-executable bit, are both set. The restricted deletion flag is
6510 another name for the sticky bit. @xref{Mode Structure}.
6513 If the restricted deletion flag or sticky bit is set but the
6514 other-executable bit is not set.
6517 If the executable bit is set and none of the above apply.
6523 Following the file mode bits is a single character that specifies
6524 whether an alternate access method such as an access control list
6525 applies to the file. When the character following the file mode bits is a
6526 space, there is no alternate access method. When it is a printing
6527 character, then there is such a method.
6529 GNU @command{ls} uses a @samp{.} character to indicate a file
6530 with an SELinux security context, but no other alternate access method.
6532 A file with any other combination of alternate access methods
6533 is marked with a @samp{+} character.
6536 @itemx --numeric-uid-gid
6538 @opindex --numeric-uid-gid
6539 @cindex numeric uid and gid
6540 @cindex numeric user and group IDs
6541 Produce long format directory listings, but
6542 display numeric user and group IDs instead of the owner and group names.
6546 Produce long format directory listings, but don't display group information.
6547 It is equivalent to using @option{--format=long} with @option{--no-group} .
6553 @cindex disk allocation
6554 @cindex size of files, reporting
6555 Print the disk allocation of each file to the left of the file name.
6556 This is the amount of disk space used by the file, which is usually a
6557 bit more than the file's size, but it can be less if the file has holes.
6559 Normally the disk allocation is printed in units of
6560 1024 bytes, but this can be overridden (@pxref{Block size}).
6562 @cindex NFS mounts from BSD to HP-UX
6563 For files that are NFS-mounted from an HP-UX system to a BSD system,
6564 this option reports sizes that are half the correct values. On HP-UX
6565 systems, it reports sizes that are twice the correct values for files
6566 that are NFS-mounted from BSD systems. This is due to a flaw in HP-UX;
6567 it also affects the HP-UX @command{ls} program.
6576 @cindex security context
6577 Display the SELinux security context or @samp{?} if none is found.
6578 When used with the @option{-l} option, print the security context
6579 to the left of the size column.
6584 @node Sorting the output
6585 @subsection Sorting the output
6587 @cindex sorting @command{ls} output
6588 These options change the order in which @command{ls} sorts the information
6589 it outputs. By default, sorting is done by character code
6590 (e.g., @acronym{ASCII} order).
6596 @itemx --time=status
6599 @opindex ctime@r{, printing or sorting by}
6600 @opindex status time@r{, printing or sorting by}
6601 @opindex use time@r{, printing or sorting files by}
6602 If the long listing format (e.g., @option{-l}, @option{-o}) is being used,
6603 print the status change time (the @samp{ctime} in the inode) instead of
6604 the modification time.
6605 When explicitly sorting by time (@option{--sort=time} or @option{-t})
6606 or when not using a long listing format,
6607 sort according to the status change time.
6611 @cindex unsorted directory listing
6612 @cindex directory order, listing by
6613 Primarily, like @option{-U}---do not sort; list the files in whatever
6614 order they are stored in the directory. But also enable @option{-a} (list
6615 all files) and disable @option{-l}, @option{--color}, and @option{-s} (if they
6616 were specified before the @option{-f}).
6622 @cindex reverse sorting
6623 Reverse whatever the sorting method is---e.g., list files in reverse
6624 alphabetical order, youngest first, smallest first, or whatever.
6630 @opindex size of files@r{, sorting files by}
6631 Sort by file size, largest first.
6637 @opindex modification time@r{, sorting files by}
6638 Sort by modification time (the @samp{mtime} in the inode), newest first.
6642 @itemx --time=access
6646 @opindex use time@r{, printing or sorting files by}
6647 @opindex atime@r{, printing or sorting files by}
6648 @opindex access time@r{, printing or sorting files by}
6649 If the long listing format (e.g., @option{--format=long}) is being used,
6650 print the last access time (the @samp{atime} in the inode).
6651 When explicitly sorting by time (@option{--sort=time} or @option{-t})
6652 or when not using a long listing format, sort according to the access time.
6658 @opindex none@r{, sorting option for @command{ls}}
6659 Do not sort; list the files in whatever order they are
6660 stored in the directory. (Do not do any of the other unrelated things
6661 that @option{-f} does.) This is especially useful when listing very large
6662 directories, since not doing any sorting can be noticeably faster.
6665 @itemx --sort=version
6668 @opindex version@r{, sorting option for @command{ls}}
6669 Sort by version name and number, lowest first. It behaves like a default
6670 sort, except that each sequence of decimal digits is treated numerically
6671 as an index/version number. (@xref{Details about version sort}.)
6674 @itemx --sort=extension
6677 @opindex extension@r{, sorting files by}
6678 Sort directory contents alphabetically by file extension (characters
6679 after the last @samp{.}); files with no extension are sorted first.
6684 @node Details about version sort
6685 @subsection Details about version sort
6687 Version sorting handles the fact that file names frequently include indices or
6688 version numbers. Standard sorting usually does not produce the order that one
6689 expects because comparisons are made on a character-by-character basis.
6690 Version sorting is especially useful when browsing directories that contain
6691 many files with indices/version numbers in their names:
6695 abc.zml-1.gz abc.zml-1.gz
6696 abc.zml-12.gz abc.zml-2.gz
6697 abc.zml-2.gz abc.zml-12.gz
6700 Version-sorted strings are compared such that if @var{ver1} and @var{ver2}
6701 are version numbers and @var{prefix} and @var{suffix} (@var{suffix} matching
6702 the regular expression @samp{(\.[A-Za-z~][A-Za-z0-9~]*)*}) are strings then
6703 @var{ver1} < @var{ver2} implies that the name composed of
6704 ``@var{prefix} @var{ver1} @var{suffix}'' sorts before
6705 ``@var{prefix} @var{ver2} @var{suffix}''.
6707 Note also that leading zeros of numeric parts are ignored:
6711 abc-1.007.tgz abc-1.01a.tgz
6712 abc-1.012b.tgz abc-1.007.tgz
6713 abc-1.01a.tgz abc-1.012b.tgz
6716 This functionality is implemented using gnulib's @code{filevercmp} function,
6717 which has some caveats worth noting.
6720 @item @env{LC_COLLATE} is ignored, which means @samp{ls -v} and @samp{sort -V}
6721 will sort non-numeric prefixes as if the @env{LC_COLLATE} locale category
6722 was set to @samp{C}.
6723 @item Some suffixes will not be matched by the regular
6724 expression mentioned above. Consequently these examples may
6725 not sort as you expect:
6733 abc-1.2.3.4.x86_64.rpm
6734 abc-1.2.3.x86_64.rpm
6738 @node General output formatting
6739 @subsection General output formatting
6741 These options affect the appearance of the overall output.
6746 @itemx --format=single-column
6749 @opindex single-column @r{output of files}
6750 List one file per line. This is the default for @command{ls} when standard
6751 output is not a terminal.
6754 @itemx --format=vertical
6757 @opindex vertical @r{sorted files in columns}
6758 List files in columns, sorted vertically. This is the default for
6759 @command{ls} if standard output is a terminal. It is always the default
6760 for the @command{dir} program.
6761 @sc{gnu} @command{ls} uses variable width columns to display as many files as
6762 possible in the fewest lines.
6764 @item --color [=@var{when}]
6766 @cindex color, distinguishing file types with
6767 Specify whether to use color for distinguishing file types. @var{when}
6768 may be omitted, or one of:
6771 @vindex none @r{color option}
6772 - Do not use color at all. This is the default.
6774 @vindex auto @r{color option}
6775 @cindex terminal, using color iff
6776 - Only use color if standard output is a terminal.
6778 @vindex always @r{color option}
6781 Specifying @option{--color} and no @var{when} is equivalent to
6782 @option{--color=always}.
6783 Piping a colorized listing through a pager like @command{more} or
6784 @command{less} usually produces unreadable results. However, using
6785 @code{more -f} does seem to work.
6789 @itemx --indicator-style=classify
6792 @opindex --indicator-style
6793 @cindex file type and executables, marking
6794 @cindex executables and file type, marking
6795 Append a character to each file name indicating the file type. Also,
6796 for regular files that are executable, append @samp{*}. The file type
6797 indicators are @samp{/} for directories, @samp{@@} for symbolic links,
6798 @samp{|} for FIFOs, @samp{=} for sockets, @samp{>} for doors,
6799 and nothing for regular files.
6800 @c The following sentence is the same as the one for -d.
6801 Do not follow symbolic links listed on the
6802 command line unless the @option{--dereference-command-line} (@option{-H}),
6803 @option{--dereference} (@option{-L}), or
6804 @option{--dereference-command-line-symlink-to-dir} options are specified.
6807 @itemx --indicator-style=file-type
6808 @opindex --file-type
6809 @opindex --indicator-style
6810 @cindex file type, marking
6811 Append a character to each file name indicating the file type. This is
6812 like @option{-F}, except that executables are not marked.
6814 @item --indicator-style=@var{word}
6815 @opindex --indicator-style
6816 Append a character indicator with style @var{word} to entry names,
6821 Do not append any character indicator; this is the default.
6823 Append @samp{/} for directories. This is the same as the @option{-p}
6826 Append @samp{/} for directories, @samp{@@} for symbolic links, @samp{|}
6827 for FIFOs, @samp{=} for sockets, and nothing for regular files. This is
6828 the same as the @option{--file-type} option.
6830 Append @samp{*} for executable regular files, otherwise behave as for
6831 @samp{file-type}. This is the same as the @option{-F} or
6832 @option{--classify} option.
6837 Print file sizes in 1024-byte blocks, overriding the default block
6838 size (@pxref{Block size}).
6839 This option is equivalent to @option{--block-size=1K}.
6842 @itemx --format=commas
6845 @opindex commas@r{, outputting between files}
6846 List files horizontally, with as many as will fit on each line,
6847 separated by @samp{, } (a comma and a space).
6850 @itemx --indicator-style=slash
6852 @opindex --indicator-style
6853 @cindex file type, marking
6854 Append a @samp{/} to directory names.
6857 @itemx --format=across
6858 @itemx --format=horizontal
6861 @opindex across@r{, listing files}
6862 @opindex horizontal@r{, listing files}
6863 List the files in columns, sorted horizontally.
6866 @itemx --tabsize=@var{cols}
6869 Assume that each tab stop is @var{cols} columns wide. The default is 8.
6870 @command{ls} uses tabs where possible in the output, for efficiency. If
6871 @var{cols} is zero, do not use tabs at all.
6873 @c FIXME: remove in 2009, if Apple Terminal has been fixed for long enough.
6874 Some terminal emulators (at least Apple Terminal 1.5 (133) from Mac OS X 10.4.8)
6875 do not properly align columns to the right of a TAB following a
6876 non-@acronym{ASCII} byte. If you use such a terminal emulator, use the
6877 @option{-T0} option or put @code{TABSIZE=0} in your environment to tell
6878 @command{ls} to align using spaces, not tabs.
6881 @itemx --width=@var{cols}
6885 Assume the screen is @var{cols} columns wide. The default is taken
6886 from the terminal settings if possible; otherwise the environment
6887 variable @env{COLUMNS} is used if it is set; otherwise the default
6893 @node Formatting file timestamps
6894 @subsection Formatting file timestamps
6896 By default, file timestamps are listed in abbreviated form. Most
6897 locales use a timestamp like @samp{2002-03-30 23:45}. However, the
6898 default @acronym{POSIX} locale uses a date like @samp{Mar 30@ @ 2002}
6899 for non-recent timestamps, and a date-without-year and time like
6900 @samp{Mar 30 23:45} for recent timestamps.
6902 A timestamp is considered to be @dfn{recent} if it is less than six
6903 months old, and is not dated in the future. If a timestamp dated
6904 today is not listed in recent form, the timestamp is in the future,
6905 which means you probably have clock skew problems which may break
6906 programs like @command{make} that rely on file timestamps.
6909 Time stamps are listed according to the time zone rules specified by
6910 the @env{TZ} environment variable, or by the system default rules if
6911 @env{TZ} is not set. @xref{TZ Variable,, Specifying the Time Zone
6912 with @env{TZ}, libc, The GNU C Library Reference Manual}.
6914 The following option changes how file timestamps are printed.
6917 @item --time-style=@var{style}
6918 @opindex --time-style
6920 List timestamps in style @var{style}. The @var{style} should
6921 be one of the following:
6926 List timestamps using @var{format}, where @var{format} is interpreted
6927 like the format argument of @command{date} (@pxref{date invocation}).
6928 For example, @option{--time-style="+%Y-%m-%d %H:%M:%S"} causes
6929 @command{ls} to list timestamps like @samp{2002-03-30 23:45:56}. As
6930 with @command{date}, @var{format}'s interpretation is affected by the
6931 @env{LC_TIME} locale category.
6933 If @var{format} contains two format strings separated by a newline,
6934 the former is used for non-recent files and the latter for recent
6935 files; if you want output columns to line up, you may need to insert
6936 spaces in one of the two formats.
6939 List timestamps in full using @acronym{ISO} 8601 date, time, and time zone
6940 format with nanosecond precision, e.g., @samp{2002-03-30
6941 23:45:56.477817180 -0700}. This style is equivalent to
6942 @samp{+%Y-%m-%d %H:%M:%S.%N %z}.
6944 This is useful because the time output includes all the information that
6945 is available from the operating system. For example, this can help
6946 explain @command{make}'s behavior, since @acronym{GNU} @command{make}
6947 uses the full timestamp to determine whether a file is out of date.
6950 List @acronym{ISO} 8601 date and time in minutes, e.g.,
6951 @samp{2002-03-30 23:45}. These timestamps are shorter than
6952 @samp{full-iso} timestamps, and are usually good enough for everyday
6953 work. This style is equivalent to @samp{+%Y-%m-%d %H:%M}.
6956 List @acronym{ISO} 8601 dates for non-recent timestamps (e.g.,
6957 @samp{2002-03-30@ }), and @acronym{ISO} 8601 month, day, hour, and
6958 minute for recent timestamps (e.g., @samp{03-30 23:45}). These
6959 timestamps are uglier than @samp{long-iso} timestamps, but they carry
6960 nearly the same information in a smaller space and their brevity helps
6961 @command{ls} output fit within traditional 80-column output lines.
6962 The following two @command{ls} invocations are equivalent:
6967 ls -l --time-style="+%Y-%m-%d $newline%m-%d %H:%M"
6968 ls -l --time-style="iso"
6973 List timestamps in a locale-dependent form. For example, a Finnish
6974 locale might list non-recent timestamps like @samp{maalis 30@ @ 2002}
6975 and recent timestamps like @samp{maalis 30 23:45}. Locale-dependent
6976 timestamps typically consume more space than @samp{iso} timestamps and
6977 are harder for programs to parse because locale conventions vary so
6978 widely, but they are easier for many people to read.
6980 The @env{LC_TIME} locale category specifies the timestamp format. The
6981 default @acronym{POSIX} locale uses timestamps like @samp{Mar 30@
6982 @ 2002} and @samp{Mar 30 23:45}; in this locale, the following two
6983 @command{ls} invocations are equivalent:
6988 ls -l --time-style="+%b %e %Y$newline%b %e %H:%M"
6989 ls -l --time-style="locale"
6992 Other locales behave differently. For example, in a German locale,
6993 @option{--time-style="locale"} might be equivalent to
6994 @option{--time-style="+%e. %b %Y $newline%e. %b %H:%M"}
6995 and might generate timestamps like @samp{30. M@"ar 2002@ } and
6996 @samp{30. M@"ar 23:45}.
6998 @item posix-@var{style}
7000 List @acronym{POSIX}-locale timestamps if the @env{LC_TIME} locale
7001 category is @acronym{POSIX}, @var{style} timestamps otherwise. For
7002 example, the @samp{posix-long-iso} style lists
7003 timestamps like @samp{Mar 30@ @ 2002} and @samp{Mar 30 23:45} when in
7004 the @acronym{POSIX} locale, and like @samp{2002-03-30 23:45} otherwise.
7009 You can specify the default value of the @option{--time-style} option
7010 with the environment variable @env{TIME_STYLE}; if @env{TIME_STYLE} is not set
7011 the default style is @samp{locale}. @acronym{GNU} Emacs 21.3 and
7012 later use the @option{--dired} option and therefore can parse any date
7013 format, but if you are using Emacs 21.1 or 21.2 and specify a
7014 non-@acronym{POSIX} locale you may need to set
7015 @samp{TIME_STYLE="posix-long-iso"}.
7017 To avoid certain denial-of-service attacks, timestamps that would be
7018 longer than 1000 bytes may be treated as errors.
7021 @node Formatting the file names
7022 @subsection Formatting the file names
7024 These options change how file names themselves are printed.
7030 @itemx --quoting-style=escape
7033 @opindex --quoting-style
7034 @cindex backslash sequences for file names
7035 Quote nongraphic characters in file names using alphabetic and octal
7036 backslash sequences like those used in C.
7040 @itemx --quoting-style=literal
7043 @opindex --quoting-style
7044 Do not quote file names. However, with @command{ls} nongraphic
7045 characters are still printed as question marks if the output is a
7046 terminal and you do not specify the @option{--show-control-chars}
7050 @itemx --hide-control-chars
7052 @opindex --hide-control-chars
7053 Print question marks instead of nongraphic characters in file names.
7054 This is the default if the output is a terminal and the program is
7059 @itemx --quoting-style=c
7061 @opindex --quote-name
7062 @opindex --quoting-style
7063 Enclose file names in double quotes and quote nongraphic characters as
7066 @item --quoting-style=@var{word}
7067 @opindex --quoting-style
7068 @cindex quoting style
7069 Use style @var{word} to quote file names and other strings that may
7070 contain arbitrary characters. The @var{word} should
7071 be one of the following:
7075 Output strings as-is; this is the same as the @option{-N} or
7076 @option{--literal} option.
7078 Quote strings for the shell if they contain shell metacharacters or would
7079 cause ambiguous output.
7080 The quoting is suitable for @acronym{POSIX}-compatible shells like
7081 @command{bash}, but it does not always work for incompatible shells
7084 Quote strings for the shell, even if they would normally not require quoting.
7086 Quote strings as for C character string literals, including the
7087 surrounding double-quote characters; this is the same as the
7088 @option{-Q} or @option{--quote-name} option.
7090 Quote strings as for C character string literals, except omit the
7091 surrounding double-quote
7092 characters; this is the same as the @option{-b} or @option{--escape} option.
7094 Quote strings as for C character string literals, except use
7095 surrounding quotation marks appropriate for the
7098 @c Use @t instead of @samp to avoid duplicate quoting in some output styles.
7099 Quote strings as for C character string literals, except use
7100 surrounding quotation marks appropriate for the locale, and quote
7101 @t{`like this'} instead of @t{"like
7102 this"} in the default C locale. This looks nicer on many displays.
7105 You can specify the default value of the @option{--quoting-style} option
7106 with the environment variable @env{QUOTING_STYLE}. If that environment
7107 variable is not set, the default value is @samp{literal}, but this
7108 default may change to @samp{shell} in a future version of this package.
7110 @item --show-control-chars
7111 @opindex --show-control-chars
7112 Print nongraphic characters as-is in file names.
7113 This is the default unless the output is a terminal and the program is
7119 @node dir invocation
7120 @section @command{dir}: Briefly list directory contents
7123 @cindex directory listing, brief
7125 @command{dir} is equivalent to @code{ls -C
7126 -b}; that is, by default files are listed in columns, sorted vertically,
7127 and special characters are represented by backslash escape sequences.
7129 @xref{ls invocation, @command{ls}}.
7132 @node vdir invocation
7133 @section @command{vdir}: Verbosely list directory contents
7136 @cindex directory listing, verbose
7138 @command{vdir} is equivalent to @code{ls -l
7139 -b}; that is, by default files are listed in long format and special
7140 characters are represented by backslash escape sequences.
7142 @node dircolors invocation
7143 @section @command{dircolors}: Color setup for @command{ls}
7147 @cindex setup for color
7149 @command{dircolors} outputs a sequence of shell commands to set up the
7150 terminal for color output from @command{ls} (and @command{dir}, etc.).
7154 eval "`dircolors [@var{option}]@dots{} [@var{file}]`"
7157 If @var{file} is specified, @command{dircolors} reads it to determine which
7158 colors to use for which file types and extensions. Otherwise, a
7159 precompiled database is used. For details on the format of these files,
7160 run @samp{dircolors --print-database}.
7162 To make @command{dircolors} read a @file{~/.dircolors} file if it
7163 exists, you can put the following lines in your @file{~/.bashrc} (or
7164 adapt them to your favorite shell):
7168 test -r $d && eval "$(dircolors $d)"
7172 @vindex SHELL @r{environment variable, and color}
7173 The output is a shell command to set the @env{LS_COLORS} environment
7174 variable. You can specify the shell syntax to use on the command line,
7175 or @command{dircolors} will guess it from the value of the @env{SHELL}
7176 environment variable.
7178 The program accepts the following options. Also see @ref{Common options}.
7183 @itemx --bourne-shell
7186 @opindex --bourne-shell
7187 @cindex Bourne shell syntax for color setup
7188 @cindex @command{sh} syntax for color setup
7189 Output Bourne shell commands. This is the default if the @env{SHELL}
7190 environment variable is set and does not end with @samp{csh} or
7199 @cindex C shell syntax for color setup
7200 @cindex @command{csh} syntax for color setup
7201 Output C shell commands. This is the default if @code{SHELL} ends with
7202 @command{csh} or @command{tcsh}.
7205 @itemx --print-database
7207 @opindex --print-database
7208 @cindex color database, printing
7209 @cindex database for color setup, printing
7210 @cindex printing color database
7211 Print the (compiled-in) default color configuration database. This
7212 output is itself a valid configuration file, and is fairly descriptive
7213 of the possibilities.
7220 @node Basic operations
7221 @chapter Basic operations
7223 @cindex manipulating files
7225 This chapter describes the commands for basic file manipulation:
7226 copying, moving (renaming), and deleting (removing).
7229 * cp invocation:: Copy files.
7230 * dd invocation:: Convert and copy a file.
7231 * install invocation:: Copy files and set attributes.
7232 * mv invocation:: Move (rename) files.
7233 * rm invocation:: Remove files or directories.
7234 * shred invocation:: Remove files more securely.
7239 @section @command{cp}: Copy files and directories
7242 @cindex copying files and directories
7243 @cindex files, copying
7244 @cindex directories, copying
7246 @command{cp} copies files (or, optionally, directories). The copy is
7247 completely independent of the original. You can either copy one file to
7248 another, or copy arbitrarily many files to a destination directory.
7252 cp [@var{option}]@dots{} [-T] @var{source} @var{dest}
7253 cp [@var{option}]@dots{} @var{source}@dots{} @var{directory}
7254 cp [@var{option}]@dots{} -t @var{directory} @var{source}@dots{}
7259 If two file names are given, @command{cp} copies the first file to the
7263 If the @option{--target-directory} (@option{-t}) option is given, or
7264 failing that if the last file is a directory and the
7265 @option{--no-target-directory} (@option{-T}) option is not given,
7266 @command{cp} copies each @var{source} file to the specified directory,
7267 using the @var{source}s' names.
7270 Generally, files are written just as they are read. For exceptions,
7271 see the @option{--sparse} option below.
7273 By default, @command{cp} does not copy directories. However, the
7274 @option{-R}, @option{-a}, and @option{-r} options cause @command{cp} to
7275 copy recursively by descending into source directories and copying files
7276 to corresponding destination directories.
7278 When copying from a symbolic link, @command{cp} normally follows the
7279 link only when not copying
7280 recursively. This default can be overridden with the
7281 @option{--archive} (@option{-a}), @option{-d}, @option{--dereference}
7282 (@option{-L}), @option{--no-dereference} (@option{-P}), and
7283 @option{-H} options. If more than one of these options is specified,
7284 the last one silently overrides the others.
7286 When copying to a symbolic link, @command{cp} follows the
7287 link only when it refers to an existing regular file.
7288 However, when copying to a dangling symbolic link, @command{cp}
7289 refuses by default, and fails with a diagnostic, since the operation
7290 is inherently dangerous. This behavior is contrary to historical
7291 practice and to @acronym{POSIX}.
7292 Set @env{POSIXLY_CORRECT} to make @command{cp} attempt to create
7293 the target of a dangling destination symlink, in spite of the possible risk.
7294 Also, when an option like
7295 @option{--backup} or @option{--link} acts to rename or remove the
7296 destination before copying, @command{cp} renames or removes the
7297 symbolic link rather than the file it points to.
7299 By default, @command{cp} copies the contents of special files only
7300 when not copying recursively. This default can be overridden with the
7301 @option{--copy-contents} option.
7303 @cindex self-backups
7304 @cindex backups, making only
7305 @command{cp} generally refuses to copy a file onto itself, with the
7306 following exception: if @option{--force --backup} is specified with
7307 @var{source} and @var{dest} identical, and referring to a regular file,
7308 @command{cp} will make a backup file, either regular or numbered, as
7309 specified in the usual ways (@pxref{Backup options}). This is useful when
7310 you simply want to make a backup of an existing file before changing it.
7312 The program accepts the following options. Also see @ref{Common options}.
7319 Preserve as much as possible of the structure and attributes of the
7320 original files in the copy (but do not attempt to preserve internal
7321 directory structure; i.e., @samp{ls -U} may list the entries in a copied
7322 directory in a different order).
7323 Try to preserve SELinux security context and extended attributes (xattr),
7324 but ignore any failure to do that and print no corresponding diagnostic.
7325 Equivalent to @option{-dR --preserve=all} with the reduced diagnostics.
7328 @itemx @w{@kbd{--backup}[=@var{method}]}
7331 @vindex VERSION_CONTROL
7332 @cindex backups, making
7333 @xref{Backup options}.
7334 Make a backup of each file that would otherwise be overwritten or removed.
7335 As a special case, @command{cp} makes a backup of @var{source} when the force
7336 and backup options are given and @var{source} and @var{dest} are the same
7337 name for an existing, regular file. One useful application of this
7338 combination of options is this tiny Bourne shell script:
7342 # Usage: backup FILE...
7343 # Create a @sc{gnu}-style backup of each listed FILE.
7345 cp --backup --force -- "$i" "$i"
7349 @item --copy-contents
7350 @cindex directories, copying recursively
7351 @cindex copying directories recursively
7352 @cindex recursively copying directories
7353 @cindex non-directories, copying as special files
7354 If copying recursively, copy the contents of any special files (e.g.,
7355 FIFOs and device files) as if they were regular files. This means
7356 trying to read the data in each source file and writing it to the
7357 destination. It is usually a mistake to use this option, as it
7358 normally has undesirable effects on special files like FIFOs and the
7359 ones typically found in the @file{/dev} directory. In most cases,
7360 @code{cp -R --copy-contents} will hang indefinitely trying to read
7361 from FIFOs and special files like @file{/dev/console}, and it will
7362 fill up your destination disk if you use it to copy @file{/dev/zero}.
7363 This option has no effect unless copying recursively, and it does not
7364 affect the copying of symbolic links.
7368 @cindex symbolic links, copying
7369 @cindex hard links, preserving
7370 Copy symbolic links as symbolic links rather than copying the files that
7371 they point to, and preserve hard links between source files in the copies.
7372 Equivalent to @option{--no-dereference --preserve=links}.
7378 When copying without this option and an existing destination file cannot
7379 be opened for writing, the copy fails. However, with @option{--force}),
7380 when a destination file cannot be opened, @command{cp} then removes it and
7381 tries to open it again. Contrast this behavior with that enabled by
7382 @option{--link} and @option{--symbolic-link}, whereby the destination file
7383 is never opened but rather is removed unconditionally. Also see the
7384 description of @option{--remove-destination}.
7386 This option is independent of the @option{--interactive} or
7387 @option{-i} option: neither cancels the effect of the other.
7389 This option is redundant if the @option{--no-clobber} or @option{-n} option is
7394 If a command line argument specifies a symbolic link, then copy the
7395 file it points to rather than the symbolic link itself. However,
7396 copy (preserving its nature) any symbolic link that is encountered
7397 via recursive traversal.
7400 @itemx --interactive
7402 @opindex --interactive
7403 When copying a file other than a directory, prompt whether to
7404 overwrite an existing destination file. The @option{-i} option overrides
7405 a previous @option{-n} option.
7411 Make hard links instead of copies of non-directories.
7414 @itemx --dereference
7416 @opindex --dereference
7417 Follow symbolic links when copying from them.
7418 With this option, @command{cp} cannot create a symbolic link.
7419 For example, a symlink (to regular file) in the source tree will be copied to
7420 a regular file in the destination tree.
7425 @opindex --no-clobber
7426 Do not overwrite an existing file. The @option{-n} option overrides a previous
7427 @option{-i} option. This option is mutually exclusive with @option{-b} or
7428 @option{--backup} option.
7431 @itemx --no-dereference
7433 @opindex --no-dereference
7434 @cindex symbolic links, copying
7435 Copy symbolic links as symbolic links rather than copying the files that
7436 they point to. This option affects only symbolic links in the source;
7437 symbolic links in the destination are always followed if possible.
7440 @itemx @w{@kbd{--preserve}[=@var{attribute_list}]}
7443 @cindex file information, preserving, extended attributes, xattr
7444 Preserve the specified attributes of the original files.
7445 If specified, the @var{attribute_list} must be a comma-separated list
7446 of one or more of the following strings:
7450 Preserve the file mode bits and access control lists.
7452 Preserve the owner and group. On most modern systems,
7453 only users with appropriate privileges may change the owner of a file,
7455 may preserve the group ownership of a file only if they happen to be
7456 a member of the desired group.
7458 Preserve the times of last access and last modification, when possible.
7459 On older systems, it is not possible to preserve these attributes
7460 when the affected file is a symbolic link.
7461 However, many systems now provide the @code{utimensat} function,
7462 which makes it possible even for symbolic links.
7464 Preserve in the destination files
7465 any links between corresponding source files.
7466 Note that with @option{-L} or @option{-H}, this option can convert
7467 symbolic links to hard links. For example,
7469 $ mkdir c; : > a; ln -s a b; cp -aH a b c; ls -i1 c
7474 Note the inputs: @file{b} is a symlink to regular file @file{a},
7475 yet the files in destination directory, @file{c/}, are hard-linked.
7476 Since @option{-a} implies @option{--preserve=links}, and since @option{-H}
7477 tells @command{cp} to dereference command line arguments, it sees two files
7478 with the same inode number, and preserves the perceived hard link.
7480 Here is a similar example that exercises @command{cp}'s @option{-L} option:
7482 $ mkdir b c; (cd b; : > a; ln -s a b); cp -aL b c; ls -i1 c/b
7488 Preserve SELinux security context of the file. @command{cp} will fail
7489 if the preserving of SELinux security context is not succesful.
7491 Preserve extended attributes if @command{cp} is built with xattr support,
7492 and xattrs are supported and enabled on your file system.
7493 If SELinux context and/or ACLs are implemented using xattrs,
7494 they are preserved by this option as well.
7496 Preserve all file attributes.
7497 Equivalent to specifying all of the above, but with the difference
7498 that failure to preserve SELinux security context or extended attributes
7499 does not change @command{cp}'s exit status.
7500 @command{cp} does diagnose such failures.
7503 Using @option{--preserve} with no @var{attribute_list} is equivalent
7504 to @option{--preserve=mode,ownership,timestamps}.
7506 In the absence of this option, each destination file is created with the
7507 mode bits of the corresponding source file, minus the bits set in the
7508 umask and minus the set-user-ID and set-group-ID bits.
7509 @xref{File permissions}.
7511 @itemx @w{@kbd{--no-preserve}=@var{attribute_list}}
7512 @cindex file information, preserving
7513 Do not preserve the specified attributes. The @var{attribute_list}
7514 has the same form as for @option{--preserve}.
7518 @cindex parent directories and @command{cp}
7519 Form the name of each destination file by appending to the target
7520 directory a slash and the specified name of the source file. The last
7521 argument given to @command{cp} must be the name of an existing directory.
7522 For example, the command:
7525 cp --parents a/b/c existing_dir
7529 copies the file @file{a/b/c} to @file{existing_dir/a/b/c}, creating
7530 any missing intermediate directories.
7537 @opindex --recursive
7538 @cindex directories, copying recursively
7539 @cindex copying directories recursively
7540 @cindex recursively copying directories
7541 @cindex non-directories, copying as special files
7542 Copy directories recursively. By default, do not follow symbolic
7543 links in the source; see the @option{--archive} (@option{-a}), @option{-d},
7544 @option{--dereference} (@option{-L}), @option{--no-dereference}
7545 (@option{-P}), and @option{-H} options. Special files are copied by
7546 creating a destination file of the same type as the source; see the
7547 @option{--copy-contents} option. It is not portable to use
7548 @option{-r} to copy symbolic links or special files. On some
7549 non-@sc{gnu} systems, @option{-r} implies the equivalent of
7550 @option{-L} and @option{--copy-contents} for historical reasons.
7551 Also, it is not portable to use @option{-R} to copy symbolic links
7552 unless you also specify @option{-P}, as @acronym{POSIX} allows
7553 implementations that dereference symbolic links by default.
7555 @item --reflink[=@var{when}]
7556 @opindex --reflink[=@var{when}]
7559 @cindex copy on write
7560 Perform a lightweight, copy-on-write (COW) copy.
7561 Copying with this option can succeed only on some file systems.
7562 Once it has succeeded, beware that the source and destination files
7563 share the same disk data blocks as long as they remain unmodified.
7564 Thus, if a disk I/O error affects data blocks of one of the files,
7565 the other suffers the exact same fate.
7567 The @var{when} value can be one of the following:
7571 The default behavior: if the copy-on-write operation is not supported
7572 then report the failure for each file and exit with a failure status.
7575 If the copy-on-write operation is not supported then fall back
7576 to the standard copy behaviour.
7580 @item --remove-destination
7581 @opindex --remove-destination
7582 Remove each existing destination file before attempting to open it
7583 (contrast with @option{-f} above).
7585 @item --sparse=@var{when}
7586 @opindex --sparse=@var{when}
7587 @cindex sparse files, copying
7588 @cindex holes, copying files with
7589 @findex read @r{system call, and holes}
7590 A @dfn{sparse file} contains @dfn{holes}---a sequence of zero bytes that
7591 does not occupy any physical disk blocks; the @samp{read} system call
7592 reads these as zeros. This can both save considerable disk space and
7593 increase speed, since many binary files contain lots of consecutive zero
7594 bytes. By default, @command{cp} detects holes in input source files via a crude
7595 heuristic and makes the corresponding output file sparse as well.
7596 Only regular files may be sparse.
7598 The @var{when} value can be one of the following:
7602 The default behavior: if the input file is sparse, attempt to make
7603 the output file sparse, too. However, if an output file exists but
7604 refers to a non-regular file, then do not attempt to make it sparse.
7607 For each sufficiently long sequence of zero bytes in the input file,
7608 attempt to create a corresponding hole in the output file, even if the
7609 input file does not appear to be sparse.
7610 This is useful when the input file resides on a file system
7611 that does not support sparse files
7612 (for example, @samp{efs} file systems in SGI IRIX 5.3 and earlier),
7613 but the output file is on a type of file system that does support them.
7614 Holes may be created only in regular files, so if the destination file
7615 is of some other type, @command{cp} does not even try to make it sparse.
7618 Never make the output file sparse.
7619 This is useful in creating a file for use with the @command{mkswap} command,
7620 since such a file must not have any holes.
7623 @optStripTrailingSlashes
7626 @itemx --symbolic-link
7628 @opindex --symbolic-link
7629 @cindex symbolic links, copying with
7630 Make symbolic links instead of copies of non-directories. All source
7631 file names must be absolute (starting with @samp{/}) unless the
7632 destination files are in the current directory. This option merely
7633 results in an error message on systems that do not support symbolic links.
7639 @optNoTargetDirectory
7645 @cindex newer files, copying only
7646 Do not copy a non-directory that has an existing destination with the
7647 same or newer modification time. If time stamps are being preserved,
7648 the comparison is to the source time stamp truncated to the
7649 resolutions of the destination file system and of the system calls
7650 used to update time stamps; this avoids duplicate work if several
7651 @samp{cp -pu} commands are executed with the same source and
7658 Print the name of each file before copying it.
7661 @itemx --one-file-system
7663 @opindex --one-file-system
7664 @cindex file systems, omitting copying to different
7665 Skip subdirectories that are on different file systems from the one that
7666 the copy started on.
7667 However, mount point directories @emph{are} copied.
7675 @section @command{dd}: Convert and copy a file
7678 @cindex converting while copying a file
7680 @command{dd} copies a file (from standard input to standard output, by
7681 default) with a changeable I/O block size, while optionally performing
7682 conversions on it. Synopses:
7685 dd [@var{operand}]@dots{}
7689 The only options are @option{--help} and @option{--version}.
7690 @xref{Common options}. @command{dd} accepts the following operands.
7696 Read from @var{file} instead of standard input.
7700 Write to @var{file} instead of standard output. Unless
7701 @samp{conv=notrunc} is given, @command{dd} truncates @var{file} to zero
7702 bytes (or the size specified with @samp{seek=}).
7704 @item ibs=@var{bytes}
7706 @cindex block size of input
7707 @cindex input block size
7708 Set the input block size to @var{bytes}.
7709 This makes @command{dd} read @var{bytes} per block.
7710 The default is 512 bytes.
7712 @item obs=@var{bytes}
7714 @cindex block size of output
7715 @cindex output block size
7716 Set the output block size to @var{bytes}.
7717 This makes @command{dd} write @var{bytes} per block.
7718 The default is 512 bytes.
7720 @item bs=@var{bytes}
7723 Set both input and output block sizes to @var{bytes}.
7724 This makes @command{dd} read and write @var{bytes} per block,
7725 overriding any @samp{ibs} and @samp{obs} settings.
7726 In addition, if no data-transforming @option{conv} option is specified,
7727 each input block is copied to the output as a single block,
7728 without aggregating short reads.
7730 @item cbs=@var{bytes}
7732 @cindex block size of conversion
7733 @cindex conversion block size
7734 @cindex fixed-length records, converting to variable-length
7735 @cindex variable-length records, converting to fixed-length
7736 Set the conversion block size to @var{bytes}.
7737 When converting variable-length records to fixed-length ones
7738 (@option{conv=block}) or the reverse (@option{conv=unblock}),
7739 use @var{bytes} as the fixed record length.
7741 @item skip=@var{blocks}
7743 Skip @var{blocks} @samp{ibs}-byte blocks in the input file before copying.
7745 @item seek=@var{blocks}
7747 Skip @var{blocks} @samp{obs}-byte blocks in the output file before copying.
7749 @item count=@var{blocks}
7751 Copy @var{blocks} @samp{ibs}-byte blocks from the input file, instead
7752 of everything until the end of the file.
7756 Do not print the overall transfer rate and volume statistics
7757 that normally make up the third status line when @command{dd} exits.
7759 @item conv=@var{conversion}[,@var{conversion}]@dots{}
7761 Convert the file as specified by the @var{conversion} argument(s).
7762 (No spaces around any comma(s).)
7769 @opindex ascii@r{, converting to}
7770 Convert @acronym{EBCDIC} to @acronym{ASCII},
7771 using the conversion table specified by @acronym{POSIX}.
7772 This provides a 1:1 translation for all 256 bytes.
7775 @opindex ebcdic@r{, converting to}
7776 Convert @acronym{ASCII} to @acronym{EBCDIC}.
7777 This is the inverse of the @samp{ascii} conversion.
7780 @opindex alternate ebcdic@r{, converting to}
7781 Convert @acronym{ASCII} to alternate @acronym{EBCDIC},
7782 using the alternate conversion table specified by @acronym{POSIX}.
7783 This is not a 1:1 translation, but reflects common historical practice
7784 for @samp{~}, @samp{[}, and @samp{]}.
7786 The @samp{ascii}, @samp{ebcdic}, and @samp{ibm} conversions are
7790 @opindex block @r{(space-padding)}
7791 For each line in the input, output @samp{cbs} bytes, replacing the
7792 input newline with a space and padding with spaces as necessary.
7796 Remove any trailing spaces in each @samp{cbs}-sized input block,
7797 and append a newline.
7799 The @samp{block} and @samp{unblock} conversions are mutually exclusive.
7802 @opindex lcase@r{, converting to}
7803 Change uppercase letters to lowercase.
7806 @opindex ucase@r{, converting to}
7807 Change lowercase letters to uppercase.
7809 The @samp{lcase} and @samp{ucase} conversions are mutually exclusive.
7812 @opindex swab @r{(byte-swapping)}
7813 @cindex byte-swapping
7814 Swap every pair of input bytes. @sc{gnu} @command{dd}, unlike others, works
7815 when an odd number of bytes are read---the last byte is simply copied
7816 (since there is nothing to swap it with).
7820 @cindex read errors, ignoring
7821 Continue after read errors.
7825 @cindex creating output file, avoiding
7826 Do not create the output file; the output file must already exist.
7830 @cindex creating output file, requiring
7831 Fail if the output file already exists; @command{dd} must create the
7834 The @samp{excl} and @samp{nocreat} conversions are mutually exclusive.
7838 @cindex truncating output file, avoiding
7839 Do not truncate the output file.
7842 @opindex sync @r{(padding with @acronym{ASCII} @sc{nul}s)}
7843 Pad every input block to size of @samp{ibs} with trailing zero bytes.
7844 When used with @samp{block} or @samp{unblock}, pad with spaces instead of
7849 @cindex synchronized data writes, before finishing
7850 Synchronize output data just before finishing. This forces a physical
7851 write of output data.
7855 @cindex synchronized data and metadata writes, before finishing
7856 Synchronize output data and metadata just before finishing. This
7857 forces a physical write of output data and metadata.
7861 @item iflag=@var{flag}[,@var{flag}]@dots{}
7863 Access the input file using the flags specified by the @var{flag}
7864 argument(s). (No spaces around any comma(s).)
7866 @item oflag=@var{flag}[,@var{flag}]@dots{}
7868 Access the output file using the flags specified by the @var{flag}
7869 argument(s). (No spaces around any comma(s).)
7871 Here are the flags. Not every flag is supported on every operating
7878 @cindex appending to the output file
7879 Write in append mode, so that even if some other process is writing to
7880 this file, every @command{dd} write will append to the current
7881 contents of the file. This flag makes sense only for output.
7882 If you combine this flag with the @samp{of=@var{file}} operand,
7883 you should also specify @samp{conv=notrunc} unless you want the
7884 output file to be truncated before being appended to.
7888 @cindex concurrent I/O
7889 Use concurrent I/O mode for data. This mode performs direct I/O
7890 and drops the @acronym{POSIX} requirement to serialize all I/O to the same file.
7891 A file cannot be opened in CIO mode and with a standard open at the
7897 Use direct I/O for data, avoiding the buffer cache.
7898 Note that the kernel may impose restrictions on read or write buffer sizes.
7899 For example, with an ext4 destination file system and a linux-based kernel,
7900 using @samp{oflag=direct} will cause writes to fail with @code{EINVAL} if the
7901 output buffer size is not a multiple of 512.
7905 @cindex directory I/O
7907 Fail unless the file is a directory. Most operating systems do not
7908 allow I/O to a directory, so this flag has limited utility.
7912 @cindex synchronized data reads
7913 Use synchronized I/O for data. For the output file, this forces a
7914 physical write of output data on each write. For the input file,
7915 this flag can matter when reading from a remote file that has been
7916 written to synchronously by some other process. Metadata (e.g.,
7917 last-access and last-modified time) is not necessarily synchronized.
7921 @cindex synchronized data and metadata I/O
7922 Use synchronized I/O for both data and metadata.
7926 @cindex nonblocking I/O
7927 Use non-blocking I/O.
7932 Do not update the file's access time.
7933 Some older file systems silently ignore this flag, so it is a good
7934 idea to test it on your files before relying on it.
7938 @cindex controlling terminal
7939 Do not assign the file to be a controlling terminal for @command{dd}.
7940 This has no effect when the file is not a terminal.
7941 On many hosts (e.g., @acronym{GNU}/Linux hosts), this option has no effect
7946 @cindex symbolic links, following
7947 Do not follow symbolic links.
7952 Fail if the file has multiple hard links.
7957 Use binary I/O. This option has an effect only on nonstandard
7958 platforms that distinguish binary from text I/O.
7963 Use text I/O. Like @samp{binary}, this option has no effect on
7968 Accumulate full blocks from input. The @code{read} system call
7969 may return early if a full block is not available.
7970 When that happens, continue calling @code{read} to fill the remainder
7972 This flag can be used only with @code{iflag}.
7976 These flags are not supported on all systems, and @samp{dd} rejects
7977 attempts to use them when they are not supported. When reading from
7978 standard input or writing to standard output, the @samp{nofollow} and
7979 @samp{noctty} flags should not be specified, and the other flags
7980 (e.g., @samp{nonblock}) can affect how other processes behave with the
7981 affected file descriptors, even after @command{dd} exits.
7985 @cindex multipliers after numbers
7986 The numeric-valued strings above (@var{bytes} and @var{blocks}) can be
7987 followed by a multiplier: @samp{b}=512, @samp{c}=1,
7988 @samp{w}=2, @samp{x@var{m}}=@var{m}, or any of the
7989 standard block size suffixes like @samp{k}=1024 (@pxref{Block size}).
7991 Use different @command{dd} invocations to use different block sizes for
7992 skipping and I/O@. For example, the following shell commands copy data
7993 in 512 KiB blocks between a disk and a tape, but do not save or restore a
7994 4 KiB label at the start of the disk:
7997 disk=/dev/rdsk/c0t1d0s2
8000 # Copy all but the label from disk to tape.
8001 (dd bs=4k skip=1 count=0 && dd bs=512k) <$disk >$tape
8003 # Copy from tape back to disk, but leave the disk label alone.
8004 (dd bs=4k seek=1 count=0 && dd bs=512k) <$tape >$disk
8007 Sending an @samp{INFO} signal to a running @command{dd}
8008 process makes it print I/O statistics to standard error
8009 and then resume copying. In the example below,
8010 @command{dd} is run in the background to copy 10 million blocks.
8011 The @command{kill} command makes it output intermediate I/O statistics,
8012 and when @command{dd} completes normally or is killed by the
8013 @code{SIGINT} signal, it outputs the final statistics.
8016 $ dd if=/dev/zero of=/dev/null count=10MB & pid=$!
8017 $ kill -s INFO $pid; wait $pid
8018 3385223+0 records in
8019 3385223+0 records out
8020 1733234176 bytes (1.7 GB) copied, 6.42173 seconds, 270 MB/s
8021 10000000+0 records in
8022 10000000+0 records out
8023 5120000000 bytes (5.1 GB) copied, 18.913 seconds, 271 MB/s
8026 @vindex POSIXLY_CORRECT
8027 On systems lacking the @samp{INFO} signal @command{dd} responds to the
8028 @samp{USR1} signal instead, unless the @env{POSIXLY_CORRECT}
8029 environment variable is set.
8034 @node install invocation
8035 @section @command{install}: Copy files and set attributes
8038 @cindex copying files and setting attributes
8040 @command{install} copies files while setting their file mode bits and, if
8041 possible, their owner and group. Synopses:
8044 install [@var{option}]@dots{} [-T] @var{source} @var{dest}
8045 install [@var{option}]@dots{} @var{source}@dots{} @var{directory}
8046 install [@var{option}]@dots{} -t @var{directory} @var{source}@dots{}
8047 install [@var{option}]@dots{} -d @var{directory}@dots{}
8052 If two file names are given, @command{install} copies the first file to the
8056 If the @option{--target-directory} (@option{-t}) option is given, or
8057 failing that if the last file is a directory and the
8058 @option{--no-target-directory} (@option{-T}) option is not given,
8059 @command{install} copies each @var{source} file to the specified
8060 directory, using the @var{source}s' names.
8063 If the @option{--directory} (@option{-d}) option is given,
8064 @command{install} creates each @var{directory} and any missing parent
8065 directories. Parent directories are created with mode
8066 @samp{u=rwx,go=rx} (755), regardless of the @option{-m} option or the
8067 current umask. @xref{Directory Setuid and Setgid}, for how the
8068 set-user-ID and set-group-ID bits of parent directories are inherited.
8071 @cindex Makefiles, installing programs in
8072 @command{install} is similar to @command{cp}, but allows you to control the
8073 attributes of destination files. It is typically used in Makefiles to
8074 copy programs into their destination directories. It refuses to copy
8075 files onto themselves.
8077 @cindex extended attributes, xattr
8078 @command{install} never preserves extended attributes (xattr).
8080 The program accepts the following options. Also see @ref{Common options}.
8090 Compare each pair of source and destination files, and if the destination has
8091 identical content and any specified owner, group, permissions, and possibly
8092 SELinux context, then do not modify the destination at all.
8096 Ignored; for compatibility with old Unix versions of @command{install}.
8100 Create any missing parent directories of @var{dest},
8101 then copy @var{source} to @var{dest}.
8102 This option is ignored if a destination directory is specified
8103 via @option{--target-directory=DIR}.
8108 @opindex --directory
8109 @cindex directories, creating with given attributes
8110 @cindex parent directories, creating missing
8111 @cindex leading directories, creating missing
8112 Create any missing parent directories, giving them the default
8113 attributes. Then create each given directory, setting their owner,
8114 group and mode as given on the command line or to the defaults.
8116 @item -g @var{group}
8117 @itemx --group=@var{group}
8120 @cindex group ownership of installed files, setting
8121 Set the group ownership of installed files or directories to
8122 @var{group}. The default is the process's current group. @var{group}
8123 may be either a group name or a numeric group ID.
8126 @itemx --mode=@var{mode}
8129 @cindex permissions of installed files, setting
8130 Set the file mode bits for the installed file or directory to @var{mode},
8131 which can be either an octal number, or a symbolic mode as in
8132 @command{chmod}, with @samp{a=} (no access allowed to anyone) as the
8133 point of departure (@pxref{File permissions}).
8134 The default mode is @samp{u=rwx,go=rx,a-s}---read, write, and
8135 execute for the owner, read and execute for group and other, and with
8136 set-user-ID and set-group-ID disabled.
8137 This default is not quite the same as @samp{755}, since it disables
8138 instead of preserving set-user-ID and set-group-ID on directories.
8139 @xref{Directory Setuid and Setgid}.
8141 @item -o @var{owner}
8142 @itemx --owner=@var{owner}
8145 @cindex ownership of installed files, setting
8146 @cindex appropriate privileges
8147 @vindex root @r{as default owner}
8148 If @command{install} has appropriate privileges (is run as root), set the
8149 ownership of installed files or directories to @var{owner}. The default
8150 is @code{root}. @var{owner} may be either a user name or a numeric user
8153 @item --preserve-context
8154 @opindex --preserve-context
8156 @cindex security context
8157 Preserve the SELinux security context of files and directories.
8158 Failure to preserve the context in all of the files or directories
8159 will result in an exit status of 1. If SELinux is disabled then
8160 print a warning and ignore the option.
8163 @itemx --preserve-timestamps
8165 @opindex --preserve-timestamps
8166 @cindex timestamps of installed files, preserving
8167 Set the time of last access and the time of last modification of each
8168 installed file to match those of each corresponding original file.
8169 When a file is installed without this option, its last access and
8170 last modification times are both set to the time of installation.
8171 This option is useful if you want to use the last modification times
8172 of installed files to keep track of when they were last built as opposed
8173 to when they were last installed.
8179 @cindex symbol table information, stripping
8180 @cindex stripping symbol table information
8181 Strip the symbol tables from installed binary executables.
8183 @itemx --strip-program=@var{program}
8184 @opindex --strip-program
8185 @cindex symbol table information, stripping, program
8186 Program used to strip binaries.
8192 @optNoTargetDirectory
8198 Print the name of each file before copying it.
8200 @item -Z @var{context}
8201 @itemx --context=@var{context}
8205 @cindex security context
8206 Set the default SELinux security context to be used for any
8207 created files and directories. If SELinux is disabled then
8208 print a warning and ignore the option.
8216 @section @command{mv}: Move (rename) files
8220 @command{mv} moves or renames files (or directories). Synopses:
8223 mv [@var{option}]@dots{} [-T] @var{source} @var{dest}
8224 mv [@var{option}]@dots{} @var{source}@dots{} @var{directory}
8225 mv [@var{option}]@dots{} -t @var{directory} @var{source}@dots{}
8230 If two file names are given, @command{mv} moves the first file to the
8234 If the @option{--target-directory} (@option{-t}) option is given, or
8235 failing that if the last file is a directory and the
8236 @option{--no-target-directory} (@option{-T}) option is not given,
8237 @command{mv} moves each @var{source} file to the specified
8238 directory, using the @var{source}s' names.
8241 @command{mv} can move any type of file from one file system to another.
8242 Prior to version @code{4.0} of the fileutils,
8243 @command{mv} could move only regular files between file systems.
8244 For example, now @command{mv} can move an entire directory hierarchy
8245 including special device files from one partition to another. It first
8246 uses some of the same code that's used by @code{cp -a} to copy the
8247 requested directories and files, then (assuming the copy succeeded)
8248 it removes the originals. If the copy fails, then the part that was
8249 copied to the destination partition is removed. If you were to copy
8250 three directories from one partition to another and the copy of the first
8251 directory succeeded, but the second didn't, the first would be left on
8252 the destination partition and the second and third would be left on the
8255 @cindex extended attributes, xattr
8256 @command{mv} always tries to copy extended attributes (xattr).
8258 @cindex prompting, and @command{mv}
8259 If a destination file exists but is normally unwritable, standard input
8260 is a terminal, and the @option{-f} or @option{--force} option is not given,
8261 @command{mv} prompts the user for whether to replace the file. (You might
8262 own the file, or have write permission on its directory.) If the
8263 response is not affirmative, the file is skipped.
8265 @emph{Warning}: Avoid specifying a source name with a trailing slash,
8266 when it might be a symlink to a directory.
8267 Otherwise, @command{mv} may do something very surprising, since
8268 its behavior depends on the underlying rename system call.
8269 On a system with a modern Linux-based kernel, it fails with @code{errno=ENOTDIR}.
8270 However, on other systems (at least FreeBSD 6.1 and Solaris 10) it silently
8271 renames not the symlink but rather the directory referenced by the symlink.
8272 @xref{Trailing slashes}.
8274 The program accepts the following options. Also see @ref{Common options}.
8284 @cindex prompts, omitting
8285 Do not prompt the user before removing a destination file.
8287 If you specify more than one of the @option{-i}, @option{-f}, @option{-n}
8288 options, only the final one takes effect.
8293 @itemx --interactive
8295 @opindex --interactive
8296 @cindex prompts, forcing
8297 Prompt whether to overwrite each existing destination file, regardless
8299 If the response is not affirmative, the file is skipped.
8305 @opindex --no-clobber
8306 @cindex prompts, omitting
8307 Do not overwrite an existing file.
8309 This option is mutually exclusive with @option{-b} or @option{--backup} option.
8315 @cindex newer files, moving only
8316 Do not move a non-directory that has an existing destination with the
8317 same or newer modification time.
8318 If the move is across file system boundaries, the comparison is to the
8319 source time stamp truncated to the resolutions of the destination file
8320 system and of the system calls used to update time stamps; this avoids
8321 duplicate work if several @samp{mv -u} commands are executed with the
8322 same source and destination.
8328 Print the name of each file before moving it.
8330 @optStripTrailingSlashes
8336 @optNoTargetDirectory
8344 @section @command{rm}: Remove files or directories
8347 @cindex removing files or directories
8349 @command{rm} removes each given @var{file}. By default, it does not remove
8350 directories. Synopsis:
8353 rm [@var{option}]@dots{} [@var{file}]@dots{}
8356 @cindex prompting, and @command{rm}
8357 If the @option{-I} or @option{--interactive=once} option is given,
8358 and there are more than three files or the @option{-r}, @option{-R},
8359 or @option{--recursive} are given, then @command{rm} prompts the user
8360 for whether to proceed with the entire operation. If the response is
8361 not affirmative, the entire command is aborted.
8363 Otherwise, if a file is unwritable, standard input is a terminal, and
8364 the @option{-f} or @option{--force} option is not given, or the
8365 @option{-i} or @option{--interactive=always} option @emph{is} given,
8366 @command{rm} prompts the user for whether to remove the file.
8367 If the response is not affirmative, the file is skipped.
8369 Any attempt to remove a file whose last file name component is
8370 @file{.} or @file{..} is rejected without any prompting.
8372 @emph{Warning}: If you use @command{rm} to remove a file, it is usually
8373 possible to recover the contents of that file. If you want more assurance
8374 that the contents are truly unrecoverable, consider using @command{shred}.
8376 The program accepts the following options. Also see @ref{Common options}.
8384 Ignore nonexistent files and never prompt the user.
8385 Ignore any previous @option{--interactive} (@option{-i}) option.
8389 Prompt whether to remove each file.
8390 If the response is not affirmative, the file is skipped.
8391 Ignore any previous @option{--force} (@option{-f}) option.
8392 Equivalent to @option{--interactive=always}.
8396 Prompt once whether to proceed with the command, if more than three
8397 files are named or if a recursive removal is requested. Ignore any
8398 previous @option{--force} (@option{-f}) option. Equivalent to
8399 @option{--interactive=once}.
8401 @itemx --interactive [=@var{when}]
8402 @opindex --interactive
8403 Specify when to issue an interactive prompt. @var{when} may be
8407 @vindex never @r{interactive option}
8408 - Do not prompt at all.
8410 @vindex once @r{interactive option}
8411 - Prompt once if more than three files are named or if a recursive
8412 removal is requested. Equivalent to @option{-I}.
8414 @vindex always @r{interactive option}
8415 - Prompt for every file being removed. Equivalent to @option{-i}.
8417 @option{--interactive} with no @var{when} is equivalent to
8418 @option{--interactive=always}.
8420 @itemx --one-file-system
8421 @opindex --one-file-system
8422 @cindex one file system, restricting @command{rm} to
8423 When removing a hierarchy recursively, skip any directory that is on a
8424 file system different from that of the corresponding command line argument.
8426 This option is useful when removing a build ``chroot'' hierarchy,
8427 which normally contains no valuable data. However, it is not uncommon
8428 to bind-mount @file{/home} into such a hierarchy, to make it easier to
8429 use one's start-up file. The catch is that it's easy to forget to
8430 unmount @file{/home}. Then, when you use @command{rm -rf} to remove
8431 your normally throw-away chroot, that command will remove everything
8432 under @file{/home}, too.
8433 Use the @option{--one-file-system} option, and it will
8434 warn about and skip directories on other file systems.
8435 Of course, this will not save your @file{/home} if it and your
8436 chroot happen to be on the same file system.
8438 @itemx --preserve-root
8439 @opindex --preserve-root
8440 @cindex root directory, disallow recursive destruction
8441 Fail upon any attempt to remove the root directory, @file{/},
8442 when used with the @option{--recursive} option.
8443 This is the default behavior.
8444 @xref{Treating / specially}.
8446 @itemx --no-preserve-root
8447 @opindex --no-preserve-root
8448 @cindex root directory, allow recursive destruction
8449 Do not treat @file{/} specially when removing recursively.
8450 This option is not recommended unless you really want to
8451 remove all the files on your computer.
8452 @xref{Treating / specially}.
8459 @opindex --recursive
8460 @cindex directories, removing (recursively)
8461 Remove the listed directories and their contents recursively.
8467 Print the name of each file before removing it.
8471 @cindex files beginning with @samp{-}, removing
8472 @cindex @samp{-}, removing files beginning with
8473 One common question is how to remove files whose names begin with a
8474 @samp{-}. @sc{gnu} @command{rm}, like every program that uses the @code{getopt}
8475 function to parse its arguments, lets you use the @samp{--} option to
8476 indicate that all following arguments are non-options. To remove a file
8477 called @file{-f} in the current directory, you could type either:
8490 @opindex - @r{and Unix @command{rm}}
8491 The Unix @command{rm} program's use of a single @samp{-} for this purpose
8492 predates the development of the getopt standard syntax.
8497 @node shred invocation
8498 @section @command{shred}: Remove files more securely
8501 @cindex data, erasing
8502 @cindex erasing data
8504 @command{shred} overwrites devices or files, to help prevent even
8505 very expensive hardware from recovering the data.
8507 Ordinarily when you remove a file (@pxref{rm invocation}), the data is
8508 not actually destroyed. Only the index listing where the file is
8509 stored is destroyed, and the storage is made available for reuse.
8510 There are undelete utilities that will attempt to reconstruct the index
8511 and can bring the file back if the parts were not reused.
8513 On a busy system with a nearly-full drive, space can get reused in a few
8514 seconds. But there is no way to know for sure. If you have sensitive
8515 data, you may want to be sure that recovery is not possible by actually
8516 overwriting the file with non-sensitive data.
8518 However, even after doing that, it is possible to take the disk back
8519 to a laboratory and use a lot of sensitive (and expensive) equipment
8520 to look for the faint ``echoes'' of the original data underneath the
8521 overwritten data. If the data has only been overwritten once, it's not
8524 The best way to remove something irretrievably is to destroy the media
8525 it's on with acid, melt it down, or the like. For cheap removable media
8526 like floppy disks, this is the preferred method. However, hard drives
8527 are expensive and hard to melt, so the @command{shred} utility tries
8528 to achieve a similar effect non-destructively.
8530 This uses many overwrite passes, with the data patterns chosen to
8531 maximize the damage they do to the old data. While this will work on
8532 floppies, the patterns are designed for best effect on hard drives.
8533 For more details, see the source code and Peter Gutmann's paper
8534 @uref{http://www.cs.auckland.ac.nz/~pgut001/pubs/secure_del.html,
8535 @cite{Secure Deletion of Data from Magnetic and Solid-State Memory}},
8536 from the proceedings of the Sixth @acronym{USENIX} Security Symposium (San Jose,
8537 California, July 22--25, 1996).
8539 @strong{Please note} that @command{shred} relies on a very important assumption:
8540 that the file system overwrites data in place. This is the traditional
8541 way to do things, but many modern file system designs do not satisfy this
8542 assumption. Exceptions include:
8547 Log-structured or journaled file systems, such as those supplied with
8548 AIX and Solaris, and JFS, ReiserFS, XFS, Ext3 (in @code{data=journal} mode),
8549 BFS, NTFS, etc.@: when they are configured to journal @emph{data}.
8552 File systems that write redundant data and carry on even if some writes
8553 fail, such as RAID-based file systems.
8556 File systems that make snapshots, such as Network Appliance's NFS server.
8559 File systems that cache in temporary locations, such as NFS version 3
8563 Compressed file systems.
8566 In the particular case of ext3 file systems, the above disclaimer applies (and
8567 @command{shred} is thus of limited effectiveness) only in @code{data=journal}
8568 mode, which journals file data in addition to just metadata. In both
8569 the @code{data=ordered} (default) and @code{data=writeback} modes,
8570 @command{shred} works as usual. Ext3 journaling modes can be changed
8571 by adding the @code{data=something} option to the mount options for a
8572 particular file system in the @file{/etc/fstab} file, as documented in
8573 the mount man page (man mount).
8575 If you are not sure how your file system operates, then you should assume
8576 that it does not overwrite data in place, which means that shred cannot
8577 reliably operate on regular files in your file system.
8579 Generally speaking, it is more reliable to shred a device than a file,
8580 since this bypasses the problem of file system design mentioned above.
8581 However, even shredding devices is not always completely reliable. For
8582 example, most disks map out bad sectors invisibly to the application; if
8583 the bad sectors contain sensitive data, @command{shred} won't be able to
8586 @command{shred} makes no attempt to detect or report this problem, just as
8587 it makes no attempt to do anything about backups. However, since it is
8588 more reliable to shred devices than files, @command{shred} by default does
8589 not truncate or remove the output file. This default is more suitable
8590 for devices, which typically cannot be truncated and should not be
8593 Finally, consider the risk of backups and mirrors.
8594 File system backups and remote mirrors may contain copies of the
8595 file that cannot be removed, and that will allow a shredded file
8596 to be recovered later. So if you keep any data you may later want
8597 to destroy using @command{shred}, be sure that it is not backed up or mirrored.
8600 shred [@var{option}]@dots{} @var{file}[@dots{}]
8603 The program accepts the following options. Also see @ref{Common options}.
8611 @cindex force deletion
8612 Override file permissions if necessary to allow overwriting.
8615 @itemx -n @var{number}
8616 @itemx --iterations=@var{number}
8617 @opindex -n @var{number}
8618 @opindex --iterations=@var{number}
8619 @cindex iterations, selecting the number of
8620 By default, @command{shred} uses @value{SHRED_DEFAULT_PASSES} passes of
8621 overwrite. You can reduce this to save time, or increase it if you think it's
8622 appropriate. After 25 passes all of the internal overwrite patterns will have
8623 been used at least once.
8625 @item --random-source=@var{file}
8626 @opindex --random-source
8627 @cindex random source for shredding
8628 Use @var{file} as a source of random data used to overwrite and to
8629 choose pass ordering. @xref{Random sources}.
8631 @item -s @var{bytes}
8632 @itemx --size=@var{bytes}
8633 @opindex -s @var{bytes}
8634 @opindex --size=@var{bytes}
8635 @cindex size of file to shred
8636 Shred the first @var{bytes} bytes of the file. The default is to shred
8637 the whole file. @var{bytes} can be followed by a size specification like
8638 @samp{K}, @samp{M}, or @samp{G} to specify a multiple. @xref{Block size}.
8644 @cindex removing files after shredding
8645 After shredding a file, truncate it (if possible) and then remove it.
8646 If a file has multiple links, only the named links will be removed.
8652 Display to standard error all status updates as sterilization proceeds.
8658 By default, @command{shred} rounds the size of a regular file up to the next
8659 multiple of the file system block size to fully erase the last block of the file.
8660 Use @option{--exact} to suppress that behavior.
8661 Thus, by default if you shred a 10-byte regular file on a system with 512-byte
8662 blocks, the resulting file will be 512 bytes long. With this option,
8663 shred does not increase the apparent size of the file.
8669 Normally, the last pass that @command{shred} writes is made up of
8670 random data. If this would be conspicuous on your hard drive (for
8671 example, because it looks like encrypted data), or you just think
8672 it's tidier, the @option{--zero} option adds an additional overwrite pass with
8673 all zero bits. This is in addition to the number of passes specified
8674 by the @option{--iterations} option.
8678 You might use the following command to erase all trace of the
8679 file system you'd created on the floppy disk in your first drive.
8680 That command takes about 20 minutes to erase a ``1.44MB'' (actually
8684 shred --verbose /dev/fd0
8687 Similarly, to erase all data on a selected partition of
8688 your hard disk, you could give a command like this:
8691 shred --verbose /dev/sda5
8694 A @var{file} of @samp{-} denotes standard output.
8695 The intended use of this is to shred a removed temporary file.
8699 i=`tempfile -m 0600`
8702 echo "Hello, world" >&3
8707 However, the command @samp{shred - >file} does not shred the contents
8708 of @var{file}, since the shell truncates @var{file} before invoking
8709 @command{shred}. Use the command @samp{shred file} or (if using a
8710 Bourne-compatible shell) the command @samp{shred - 1<>file} instead.
8715 @node Special file types
8716 @chapter Special file types
8718 @cindex special file types
8719 @cindex file types, special
8721 This chapter describes commands which create special types of files (and
8722 @command{rmdir}, which removes directories, one special file type).
8724 @cindex special file types
8726 Although Unix-like operating systems have markedly fewer special file
8727 types than others, not @emph{everything} can be treated only as the
8728 undifferentiated byte stream of @dfn{normal files}. For example, when a
8729 file is created or removed, the system must record this information,
8730 which it does in a @dfn{directory}---a special type of file. Although
8731 you can read directories as normal files, if you're curious, in order
8732 for the system to do its job it must impose a structure, a certain
8733 order, on the bytes of the file. Thus it is a ``special'' type of file.
8735 Besides directories, other special file types include named pipes
8736 (FIFOs), symbolic links, sockets, and so-called @dfn{special files}.
8739 * link invocation:: Make a hard link via the link syscall
8740 * ln invocation:: Make links between files.
8741 * mkdir invocation:: Make directories.
8742 * mkfifo invocation:: Make FIFOs (named pipes).
8743 * mknod invocation:: Make block or character special files.
8744 * readlink invocation:: Print value of a symlink or canonical file name.
8745 * rmdir invocation:: Remove empty directories.
8746 * unlink invocation:: Remove files via the unlink syscall
8750 @node link invocation
8751 @section @command{link}: Make a hard link via the link syscall
8754 @cindex links, creating
8755 @cindex hard links, creating
8756 @cindex creating links (hard only)
8758 @command{link} creates a single hard link at a time.
8759 It is a minimalist interface to the system-provided
8760 @code{link} function. @xref{Hard Links, , , libc,
8761 The GNU C Library Reference Manual}.
8762 It avoids the bells and whistles of the more commonly-used
8763 @command{ln} command (@pxref{ln invocation}).
8767 link @var{filename} @var{linkname}
8770 @var{filename} must specify an existing file, and @var{linkname}
8771 must specify a nonexistent entry in an existing directory.
8772 @command{link} simply calls @code{link (@var{filename}, @var{linkname})}
8775 On a @acronym{GNU} system, this command acts like @samp{ln --directory
8776 --no-target-directory @var{filename} @var{linkname}}. However, the
8777 @option{--directory} and @option{--no-target-directory} options are
8778 not specified by @acronym{POSIX}, and the @command{link} command is
8779 more portable in practice.
8781 If @var{filename} is a symbolic link, it is unspecified whether
8782 @var{linkname} will be a hard link to the symbolic link or to the
8783 target of the symbolic link. Use @command{ln -P} or @command{ln -L}
8784 to specify which behavior is desired.
8790 @section @command{ln}: Make links between files
8793 @cindex links, creating
8794 @cindex hard links, creating
8795 @cindex symbolic (soft) links, creating
8796 @cindex creating links (hard or soft)
8798 @cindex file systems and hard links
8799 @command{ln} makes links between files. By default, it makes hard links;
8800 with the @option{-s} option, it makes symbolic (or @dfn{soft}) links.
8804 ln [@var{option}]@dots{} [-T] @var{target} @var{linkname}
8805 ln [@var{option}]@dots{} @var{target}
8806 ln [@var{option}]@dots{} @var{target}@dots{} @var{directory}
8807 ln [@var{option}]@dots{} -t @var{directory} @var{target}@dots{}
8813 If two file names are given, @command{ln} creates a link to the first
8814 file from the second.
8817 If one @var{target} is given, @command{ln} creates a link to that file
8818 in the current directory.
8821 If the @option{--target-directory} (@option{-t}) option is given, or
8822 failing that if the last file is a directory and the
8823 @option{--no-target-directory} (@option{-T}) option is not given,
8824 @command{ln} creates a link to each @var{target} file in the specified
8825 directory, using the @var{target}s' names.
8829 Normally @command{ln} does not remove existing files. Use the
8830 @option{--force} (@option{-f}) option to remove them unconditionally,
8831 the @option{--interactive} (@option{-i}) option to remove them
8832 conditionally, and the @option{--backup} (@option{-b}) option to
8835 @cindex hard link, defined
8836 @cindex inode, and hard links
8837 A @dfn{hard link} is another name for an existing file; the link and the
8838 original are indistinguishable. Technically speaking, they share the
8839 same inode, and the inode contains all the information about a
8840 file---indeed, it is not incorrect to say that the inode @emph{is} the
8841 file. Most systems prohibit making a hard link to
8842 a directory; on those where it is allowed, only the super-user can do
8843 so (and with caution, since creating a cycle will cause problems to many
8844 other utilities). Hard links cannot cross file system boundaries. (These
8845 restrictions are not mandated by @acronym{POSIX}, however.)
8847 @cindex dereferencing symbolic links
8848 @cindex symbolic link, defined
8849 @dfn{Symbolic links} (@dfn{symlinks} for short), on the other hand, are
8850 a special file type (which not all kernels support: System V release 3
8851 (and older) systems lack symlinks) in which the link file actually
8852 refers to a different file, by name. When most operations (opening,
8853 reading, writing, and so on) are passed the symbolic link file, the
8854 kernel automatically @dfn{dereferences} the link and operates on the
8855 target of the link. But some operations (e.g., removing) work on the
8856 link file itself, rather than on its target. The owner and group of a
8857 symlink are not significant to file access performed through
8858 the link, but do have implications on deleting a symbolic link from a
8859 directory with the restricted deletion bit set. On the GNU system,
8860 the mode of a symlink has no significance and cannot be changed, but
8861 on some BSD systems, the mode can be changed and will affect whether
8862 the symlink will be traversed in file name resolution. @xref{Symbolic Links,,,
8863 libc, The GNU C Library Reference Manual}.
8865 Symbolic links can contain arbitrary strings; a @dfn{dangling symlink}
8866 occurs when the string in the symlink does not resolve to a file.
8867 There are no restrictions against creating dangling symbolic links.
8868 There are trade-offs to using absolute or relative symlinks. An
8869 absolute symlink always points to the same file, even if the directory
8870 containing the link is moved. However, if the symlink is visible from
8871 more than one machine (such as on a networked file system), the file
8872 pointed to might not always be the same. A relative symbolic link is
8873 resolved in relation to the directory that contains the link, and is
8874 often useful in referring to files on the same device without regards
8875 to what name that device is mounted on when accessed via networked
8878 When creating a relative symlink in a different location than the
8879 current directory, the resolution of the symlink will be different
8880 than the resolution of the same string from the current directory.
8881 Therefore, many users prefer to first change directories to the
8882 location where the relative symlink will be created, so that
8883 tab-completion or other file resolution will find the same target as
8884 what will be placed in the symlink.
8886 The program accepts the following options. Also see @ref{Common options}.
8897 @opindex --directory
8898 @cindex hard links to directories
8899 Allow users with appropriate privileges to attempt to make hard links
8901 However, note that this will probably fail due to
8902 system restrictions, even for the super-user.
8908 Remove existing destination files.
8911 @itemx --interactive
8913 @opindex --interactive
8914 @cindex prompting, and @command{ln}
8915 Prompt whether to remove existing destination files.
8921 If @option{-s} is not in effect, and the source file is a symbolic
8922 link, create the hard link to the file referred to by the symbolic
8923 link, rather than the symbolic link itself.
8926 @itemx --no-dereference
8928 @opindex --no-dereference
8929 Do not treat the last operand specially when it is a symbolic link to
8930 a directory. Instead, treat it as if it were a normal file.
8932 When the destination is an actual directory (not a symlink to one),
8933 there is no ambiguity. The link is created in that directory.
8934 But when the specified destination is a symlink to a directory,
8935 there are two ways to treat the user's request. @command{ln} can
8936 treat the destination just as it would a normal directory and create
8937 the link in it. On the other hand, the destination can be viewed as a
8938 non-directory---as the symlink itself. In that case, @command{ln}
8939 must delete or backup that symlink before creating the new link.
8940 The default is to treat a destination that is a symlink to a directory
8941 just like a directory.
8943 This option is weaker than the @option{--no-target-directory}
8944 (@option{-T}) option, so it has no effect if both options are given.
8950 If @option{-s} is not in effect, and the source file is a symbolic
8951 link, create the hard link to the symbolic link itself. On platforms
8952 where this is not supported by the kernel, this option creates a
8953 symbolic link with identical contents; since symbolic link contents
8954 cannot be edited, any file name resolution performed through either
8955 link will be the same as if a hard link had been created.
8961 Make symbolic links instead of hard links. This option merely produces
8962 an error message on systems that do not support symbolic links.
8968 @optNoTargetDirectory
8974 Print the name of each file after linking it successfully.
8978 @cindex hard links to symbolic links
8979 @cindex symbolic links and @command{ln}
8980 If @option{-L} and @option{-P} are both given, the last one takes
8981 precedence. If @option{-s} is also given, @option{-L} and @option{-P}
8982 are silently ignored. If neither option is given, then this
8983 implementation defaults to @option{-P} if the system @code{link} supports
8984 hard links to symbolic links (such as the GNU system), and @option{-L}
8985 if @code{link} follows symbolic links (such as on BSD).
8994 # Create link ../a pointing to a in that directory.
8995 # Not really useful because it points to itself.
9000 # Change to the target before creating symlinks to avoid being confused.
9006 # Hard coded file names don't move well.
9007 ln -s $(pwd)/a /some/dir/
9011 # Relative file names survive directory moves and also
9012 # work across networked file systems.
9013 ln -s afile anotherfile
9014 ln -s ../adir/afile yetanotherfile
9018 @node mkdir invocation
9019 @section @command{mkdir}: Make directories
9022 @cindex directories, creating
9023 @cindex creating directories
9025 @command{mkdir} creates directories with the specified names. Synopsis:
9028 mkdir [@var{option}]@dots{} @var{name}@dots{}
9031 @command{mkdir} creates each directory @var{name} in the order given.
9032 It reports an error if @var{name} already exists, unless the
9033 @option{-p} option is given and @var{name} is a directory.
9035 The program accepts the following options. Also see @ref{Common options}.
9040 @itemx --mode=@var{mode}
9043 @cindex modes of created directories, setting
9044 Set the file permission bits of created directories to @var{mode},
9045 which uses the same syntax as
9046 in @command{chmod} and uses @samp{a=rwx} (read, write and execute allowed for
9047 everyone) for the point of the departure. @xref{File permissions}.
9049 Normally the directory has the desired file mode bits at the moment it
9050 is created. As a @acronym{GNU} extension, @var{mode} may also mention
9051 special mode bits, but in this case there may be a temporary window
9052 during which the directory exists but its special mode bits are
9053 incorrect. @xref{Directory Setuid and Setgid}, for how the
9054 set-user-ID and set-group-ID bits of directories are inherited unless
9055 overridden in this way.
9061 @cindex parent directories, creating
9062 Make any missing parent directories for each argument, setting their
9063 file permission bits to the umask modified by @samp{u+wx}. Ignore
9064 existing parent directories, and do not change their file permission
9067 To set the file permission bits of any newly-created parent
9068 directories to a value that includes @samp{u+wx}, you can set the
9069 umask before invoking @command{mkdir}. For example, if the shell
9070 command @samp{(umask u=rwx,go=rx; mkdir -p P/Q)} creates the parent
9071 @file{P} it sets the parent's permission bits to @samp{u=rwx,go=rx}.
9072 To set a parent's special mode bits as well, you can invoke
9073 @command{chmod} after @command{mkdir}. @xref{Directory Setuid and
9074 Setgid}, for how the set-user-ID and set-group-ID bits of
9075 newly-created parent directories are inherited.
9081 Print a message for each created directory. This is most useful with
9084 @item -Z @var{context}
9085 @itemx --context=@var{context}
9089 @cindex security context
9090 Set the default SELinux security context to be used for created directories.
9097 @node mkfifo invocation
9098 @section @command{mkfifo}: Make FIFOs (named pipes)
9101 @cindex FIFOs, creating
9102 @cindex named pipes, creating
9103 @cindex creating FIFOs (named pipes)
9105 @command{mkfifo} creates FIFOs (also called @dfn{named pipes}) with the
9106 specified names. Synopsis:
9109 mkfifo [@var{option}] @var{name}@dots{}
9112 A @dfn{FIFO} is a special file type that permits independent processes
9113 to communicate. One process opens the FIFO file for writing, and
9114 another for reading, after which data can flow as with the usual
9115 anonymous pipe in shells or elsewhere.
9117 The program accepts the following option. Also see @ref{Common options}.
9122 @itemx --mode=@var{mode}
9125 @cindex modes of created FIFOs, setting
9126 Set the mode of created FIFOs to @var{mode}, which is symbolic as in
9127 @command{chmod} and uses @samp{a=rw} (read and write allowed for everyone)
9128 for the point of departure. @var{mode} should specify only file
9129 permission bits. @xref{File permissions}.
9131 @item -Z @var{context}
9132 @itemx --context=@var{context}
9136 @cindex security context
9137 Set the default SELinux security context to be used for created FIFOs.
9144 @node mknod invocation
9145 @section @command{mknod}: Make block or character special files
9148 @cindex block special files, creating
9149 @cindex character special files, creating
9151 @command{mknod} creates a FIFO, character special file, or block special
9152 file with the specified name. Synopsis:
9155 mknod [@var{option}]@dots{} @var{name} @var{type} [@var{major} @var{minor}]
9158 @cindex special files
9159 @cindex block special files
9160 @cindex character special files
9161 Unlike the phrase ``special file type'' above, the term @dfn{special
9162 file} has a technical meaning on Unix: something that can generate or
9163 receive data. Usually this corresponds to a physical piece of hardware,
9164 e.g., a printer or a disk. (These files are typically created at
9165 system-configuration time.) The @command{mknod} command is what creates
9166 files of this type. Such devices can be read either a character at a
9167 time or a ``block'' (many characters) at a time, hence we say there are
9168 @dfn{block special} files and @dfn{character special} files.
9170 @c mknod is a shell built-in at least with OpenBSD's /bin/sh
9171 @mayConflictWithShellBuiltIn{mknod}
9173 The arguments after @var{name} specify the type of file to make:
9178 @opindex p @r{for FIFO file}
9182 @opindex b @r{for block special file}
9183 for a block special file
9186 @c Don't document the `u' option -- it's just a synonym for `c'.
9187 @c Do *any* versions of mknod still use it?
9189 @opindex c @r{for character special file}
9190 @c @opindex u @r{for character special file}
9191 for a character special file
9195 When making a block or character special file, the major and minor
9196 device numbers must be given after the file type.
9197 If a major or minor device number begins with @samp{0x} or @samp{0X},
9198 it is interpreted as hexadecimal; otherwise, if it begins with @samp{0},
9199 as octal; otherwise, as decimal.
9201 The program accepts the following option. Also see @ref{Common options}.
9206 @itemx --mode=@var{mode}
9209 Set the mode of created files to @var{mode}, which is symbolic as in
9210 @command{chmod} and uses @samp{a=rw} as the point of departure.
9211 @var{mode} should specify only file permission bits.
9212 @xref{File permissions}.
9214 @item -Z @var{context}
9215 @itemx --context=@var{context}
9219 @cindex security context
9220 Set the default SELinux security context to be used for created files.
9227 @node readlink invocation
9228 @section @command{readlink}: Print value of a symlink or canonical file name
9231 @cindex displaying value of a symbolic link
9232 @cindex canonical file name
9233 @cindex canonicalize a file name
9237 @command{readlink} may work in one of two supported modes:
9243 @command{readlink} outputs the value of the given symbolic link.
9244 If @command{readlink} is invoked with an argument other than the name
9245 of a symbolic link, it produces no output and exits with a nonzero exit code.
9247 @item Canonicalize mode
9249 @command{readlink} outputs the absolute name of the given file which contains
9250 no @file{.}, @file{..} components nor any repeated separators
9251 (@file{/}) or symbolic links.
9256 readlink [@var{option}] @var{file}
9259 By default, @command{readlink} operates in readlink mode.
9261 The program accepts the following options. Also see @ref{Common options}.
9266 @itemx --canonicalize
9268 @opindex --canonicalize
9269 Activate canonicalize mode.
9270 If any component of the file name except the last one is missing or unavailable,
9271 @command{readlink} produces no output and exits with a nonzero exit
9272 code. A trailing slash is ignored.
9275 @itemx --canonicalize-existing
9277 @opindex --canonicalize-existing
9278 Activate canonicalize mode.
9279 If any component is missing or unavailable, @command{readlink} produces
9280 no output and exits with a nonzero exit code. A trailing slash
9281 requires that the name resolve to a directory.
9284 @itemx --canonicalize-missing
9286 @opindex --canonicalize-missing
9287 Activate canonicalize mode.
9288 If any component is missing or unavailable, @command{readlink} treats it
9294 @opindex --no-newline
9295 Do not output the trailing newline.
9305 Suppress most error messages.
9311 Report error messages.
9315 The @command{readlink} utility first appeared in OpenBSD 2.1.
9317 There is a @command{realpath} command on some systems
9318 which operates like @command{readlink} in canonicalize mode.
9323 @node rmdir invocation
9324 @section @command{rmdir}: Remove empty directories
9327 @cindex removing empty directories
9328 @cindex directories, removing empty
9330 @command{rmdir} removes empty directories. Synopsis:
9333 rmdir [@var{option}]@dots{} @var{directory}@dots{}
9336 If any @var{directory} argument does not refer to an existing empty
9337 directory, it is an error.
9339 The program accepts the following options. Also see @ref{Common options}.
9343 @item --ignore-fail-on-non-empty
9344 @opindex --ignore-fail-on-non-empty
9345 @cindex directory deletion, ignoring failures
9346 Ignore each failure to remove a directory that is solely because
9347 the directory is non-empty.
9353 @cindex parent directories, removing
9354 Remove @var{directory}, then try to remove each component of @var{directory}.
9355 So, for example, @samp{rmdir -p a/b/c} is similar to @samp{rmdir a/b/c a/b a}.
9356 As such, it fails if any of those directories turns out not to be empty.
9357 Use the @option{--ignore-fail-on-non-empty} option to make it so such
9358 a failure does not evoke a diagnostic and does not cause @command{rmdir} to
9359 exit unsuccessfully.
9365 @cindex directory deletion, reporting
9366 Give a diagnostic for each successful removal.
9367 @var{directory} is removed.
9371 @xref{rm invocation}, for how to remove non-empty directories (recursively).
9376 @node unlink invocation
9377 @section @command{unlink}: Remove files via the unlink syscall
9380 @cindex removing files or directories (via the unlink syscall)
9382 @command{unlink} deletes a single specified file name.
9383 It is a minimalist interface to the system-provided
9384 @code{unlink} function. @xref{Deleting Files, , , libc,
9385 The GNU C Library Reference Manual}. Synopsis:
9386 It avoids the bells and whistles of the more commonly-used
9387 @command{rm} command (@pxref{rm invocation}).
9390 unlink @var{filename}
9393 On some systems @code{unlink} can be used to delete the name of a
9394 directory. On others, it can be used that way only by a privileged user.
9395 In the GNU system @code{unlink} can never delete the name of a directory.
9397 The @command{unlink} command honors the @option{--help} and
9398 @option{--version} options. To remove a file whose name begins with
9399 @samp{-}, prefix the name with @samp{./}, e.g., @samp{unlink ./--help}.
9404 @node Changing file attributes
9405 @chapter Changing file attributes
9407 @cindex changing file attributes
9408 @cindex file attributes, changing
9409 @cindex attributes, file
9411 A file is not merely its contents, a name, and a file type
9412 (@pxref{Special file types}). A file also has an owner (a user ID), a
9413 group (a group ID), permissions (what the owner can do with the file,
9414 what people in the group can do, and what everyone else can do), various
9415 timestamps, and other information. Collectively, we call these a file's
9418 These commands change file attributes.
9421 * chgrp invocation:: Change file groups.
9422 * chmod invocation:: Change access permissions.
9423 * chown invocation:: Change file owners and groups.
9424 * touch invocation:: Change file timestamps.
9428 @node chown invocation
9429 @section @command{chown}: Change file owner and group
9432 @cindex file ownership, changing
9433 @cindex group ownership, changing
9434 @cindex changing file ownership
9435 @cindex changing group ownership
9437 @command{chown} changes the user and/or group ownership of each given @var{file}
9438 to @var{new-owner} or to the user and group of an existing reference file.
9442 chown [@var{option}]@dots{} @{@var{new-owner} | --reference=@var{ref_file}@} @var{file}@dots{}
9445 If used, @var{new-owner} specifies the new owner and/or group as follows
9446 (with no embedded white space):
9449 [@var{owner}] [ : [@var{group}] ]
9456 If only an @var{owner} (a user name or numeric user ID) is given, that
9457 user is made the owner of each given file, and the files' group is not
9460 @item owner@samp{:}group
9461 If the @var{owner} is followed by a colon and a @var{group} (a
9462 group name or numeric group ID), with no spaces between them, the group
9463 ownership of the files is changed as well (to @var{group}).
9466 If a colon but no group name follows @var{owner}, that user is
9467 made the owner of the files and the group of the files is changed to
9468 @var{owner}'s login group.
9471 If the colon and following @var{group} are given, but the owner
9472 is omitted, only the group of the files is changed; in this case,
9473 @command{chown} performs the same function as @command{chgrp}.
9476 If only a colon is given, or if @var{new-owner} is empty, neither the
9477 owner nor the group is changed.
9481 If @var{owner} or @var{group} is intended to represent a numeric user
9482 or group ID, then you may specify it with a leading @samp{+}.
9483 @xref{Disambiguating names and IDs}.
9485 Some older scripts may still use @samp{.} in place of the @samp{:} separator.
9486 @acronym{POSIX} 1003.1-2001 (@pxref{Standards conformance}) does not
9487 require support for that, but for backward compatibility @acronym{GNU}
9488 @command{chown} supports @samp{.} so long as no ambiguity results.
9489 New scripts should avoid the use of @samp{.} because it is not
9490 portable, and because it has undesirable results if the entire
9491 @var{owner@samp{.}group} happens to identify a user whose name
9494 The @command{chown} command sometimes clears the set-user-ID or
9495 set-group-ID permission bits. This behavior depends on the policy and
9496 functionality of the underlying @code{chown} system call, which may
9497 make system-dependent file mode modifications outside the control of
9498 the @command{chown} command. For example, the @command{chown} command
9499 might not affect those bits when invoked by a user with appropriate
9500 privileges, or when the
9501 bits signify some function other than executable permission (e.g.,
9503 When in doubt, check the underlying system behavior.
9505 The program accepts the following options. Also see @ref{Common options}.
9513 @cindex changed owners, verbosely describing
9514 Verbosely describe the action for each @var{file} whose ownership
9523 @cindex error messages, omitting
9524 Do not print error messages about files whose ownership cannot be
9527 @itemx @w{@kbd{--from}=@var{old-owner}}
9529 @cindex symbolic links, changing owner
9530 Change a @var{file}'s ownership only if it has current attributes specified
9531 by @var{old-owner}. @var{old-owner} has the same form as @var{new-owner}
9533 This option is useful primarily from a security standpoint in that
9534 it narrows considerably the window of potential abuse.
9535 For example, to reflect a user ID numbering change for one user's files
9536 without an option like this, @code{root} might run
9539 find / -owner OLDUSER -print0 | xargs -0 chown -h NEWUSER
9542 But that is dangerous because the interval between when the @command{find}
9543 tests the existing file's owner and when the @command{chown} is actually run
9545 One way to narrow the gap would be to invoke chown for each file
9549 find / -owner OLDUSER -exec chown -h NEWUSER @{@} \;
9552 But that is very slow if there are many affected files.
9553 With this option, it is safer (the gap is narrower still)
9554 though still not perfect:
9557 chown -h -R --from=OLDUSER NEWUSER /
9561 @opindex --dereference
9562 @cindex symbolic links, changing owner
9564 Do not act on symbolic links themselves but rather on what they point to.
9565 This is the default.
9568 @itemx --no-dereference
9570 @opindex --no-dereference
9571 @cindex symbolic links, changing owner
9573 Act on symbolic links themselves instead of what they point to.
9574 This mode relies on the @code{lchown} system call.
9575 On systems that do not provide the @code{lchown} system call,
9576 @command{chown} fails when a file specified on the command line
9578 By default, no diagnostic is issued for symbolic links encountered
9579 during a recursive traversal, but see @option{--verbose}.
9581 @itemx --preserve-root
9582 @opindex --preserve-root
9583 @cindex root directory, disallow recursive modification
9584 Fail upon any attempt to recursively change the root directory, @file{/}.
9585 Without @option{--recursive}, this option has no effect.
9586 @xref{Treating / specially}.
9588 @itemx --no-preserve-root
9589 @opindex --no-preserve-root
9590 @cindex root directory, allow recursive modification
9591 Cancel the effect of any preceding @option{--preserve-root} option.
9592 @xref{Treating / specially}.
9594 @item --reference=@var{ref_file}
9595 @opindex --reference
9596 Change the user and group of each @var{file} to be the same as those of
9597 @var{ref_file}. If @var{ref_file} is a symbolic link, do not use the
9598 user and group of the symbolic link, but rather those of the file it
9605 Output a diagnostic for every file processed.
9606 If a symbolic link is encountered during a recursive traversal
9607 on a system without the @code{lchown} system call, and @option{--no-dereference}
9608 is in effect, then issue a diagnostic saying neither the symbolic link nor
9609 its referent is being changed.
9614 @opindex --recursive
9615 @cindex recursively changing file ownership
9616 Recursively change ownership of directories and their contents.
9619 @xref{Traversing symlinks}.
9622 @xref{Traversing symlinks}.
9625 @xref{Traversing symlinks}.
9634 # Change the owner of /u to "root".
9637 # Likewise, but also change its group to "staff".
9640 # Change the owner of /u and subfiles to "root".
9645 @node chgrp invocation
9646 @section @command{chgrp}: Change group ownership
9649 @cindex group ownership, changing
9650 @cindex changing group ownership
9652 @command{chgrp} changes the group ownership of each given @var{file}
9653 to @var{group} (which can be either a group name or a numeric group ID)
9654 or to the group of an existing reference file. Synopsis:
9657 chgrp [@var{option}]@dots{} @{@var{group} | --reference=@var{ref_file}@} @var{file}@dots{}
9660 If @var{group} is intended to represent a
9661 numeric group ID, then you may specify it with a leading @samp{+}.
9662 @xref{Disambiguating names and IDs}.
9664 The program accepts the following options. Also see @ref{Common options}.
9672 @cindex changed files, verbosely describing
9673 Verbosely describe the action for each @var{file} whose group actually
9682 @cindex error messages, omitting
9683 Do not print error messages about files whose group cannot be
9687 @opindex --dereference
9688 @cindex symbolic links, changing owner
9690 Do not act on symbolic links themselves but rather on what they point to.
9691 This is the default.
9694 @itemx --no-dereference
9696 @opindex --no-dereference
9697 @cindex symbolic links, changing group
9699 Act on symbolic links themselves instead of what they point to.
9700 This mode relies on the @code{lchown} system call.
9701 On systems that do not provide the @code{lchown} system call,
9702 @command{chgrp} fails when a file specified on the command line
9704 By default, no diagnostic is issued for symbolic links encountered
9705 during a recursive traversal, but see @option{--verbose}.
9707 @itemx --preserve-root
9708 @opindex --preserve-root
9709 @cindex root directory, disallow recursive modification
9710 Fail upon any attempt to recursively change the root directory, @file{/}.
9711 Without @option{--recursive}, this option has no effect.
9712 @xref{Treating / specially}.
9714 @itemx --no-preserve-root
9715 @opindex --no-preserve-root
9716 @cindex root directory, allow recursive modification
9717 Cancel the effect of any preceding @option{--preserve-root} option.
9718 @xref{Treating / specially}.
9720 @item --reference=@var{ref_file}
9721 @opindex --reference
9722 Change the group of each @var{file} to be the same as that of
9723 @var{ref_file}. If @var{ref_file} is a symbolic link, do not use the
9724 group of the symbolic link, but rather that of the file it refers to.
9730 Output a diagnostic for every file processed.
9731 If a symbolic link is encountered during a recursive traversal
9732 on a system without the @code{lchown} system call, and @option{--no-dereference}
9733 is in effect, then issue a diagnostic saying neither the symbolic link nor
9734 its referent is being changed.
9739 @opindex --recursive
9740 @cindex recursively changing group ownership
9741 Recursively change the group ownership of directories and their contents.
9744 @xref{Traversing symlinks}.
9747 @xref{Traversing symlinks}.
9750 @xref{Traversing symlinks}.
9759 # Change the group of /u to "staff".
9762 # Change the group of /u and subfiles to "staff".
9767 @node chmod invocation
9768 @section @command{chmod}: Change access permissions
9771 @cindex changing access permissions
9772 @cindex access permissions, changing
9773 @cindex permissions, changing access
9775 @command{chmod} changes the access permissions of the named files. Synopsis:
9778 chmod [@var{option}]@dots{} @{@var{mode} | --reference=@var{ref_file}@} @var{file}@dots{}
9781 @cindex symbolic links, permissions of
9782 @command{chmod} never changes the permissions of symbolic links, since
9783 the @command{chmod} system call cannot change their permissions.
9784 This is not a problem since the permissions of symbolic links are
9785 never used. However, for each symbolic link listed on the command
9786 line, @command{chmod} changes the permissions of the pointed-to file.
9787 In contrast, @command{chmod} ignores symbolic links encountered during
9788 recursive directory traversals.
9790 A successful use of @command{chmod} clears the set-group-ID bit of a
9791 regular file if the file's group ID does not match the user's
9792 effective group ID or one of the user's supplementary group IDs,
9793 unless the user has appropriate privileges. Additional restrictions
9794 may cause the set-user-ID and set-group-ID bits of @var{mode} or
9795 @var{ref_file} to be ignored. This behavior depends on the policy and
9796 functionality of the underlying @code{chmod} system call. When in
9797 doubt, check the underlying system behavior.
9799 If used, @var{mode} specifies the new file mode bits.
9800 For details, see the section on @ref{File permissions}.
9801 If you really want @var{mode} to have a leading @samp{-}, you should
9802 use @option{--} first, e.g., @samp{chmod -- -w file}. Typically,
9803 though, @samp{chmod a-w file} is preferable, and @command{chmod -w
9804 file} (without the @option{--}) complains if it behaves differently
9805 from what @samp{chmod a-w file} would do.
9807 The program accepts the following options. Also see @ref{Common options}.
9815 Verbosely describe the action for each @var{file} whose permissions
9824 @cindex error messages, omitting
9825 Do not print error messages about files whose permissions cannot be
9828 @itemx --preserve-root
9829 @opindex --preserve-root
9830 @cindex root directory, disallow recursive modification
9831 Fail upon any attempt to recursively change the root directory, @file{/}.
9832 Without @option{--recursive}, this option has no effect.
9833 @xref{Treating / specially}.
9835 @itemx --no-preserve-root
9836 @opindex --no-preserve-root
9837 @cindex root directory, allow recursive modification
9838 Cancel the effect of any preceding @option{--preserve-root} option.
9839 @xref{Treating / specially}.
9845 Verbosely describe the action or non-action taken for every @var{file}.
9847 @item --reference=@var{ref_file}
9848 @opindex --reference
9849 Change the mode of each @var{file} to be the same as that of @var{ref_file}.
9850 @xref{File permissions}.
9851 If @var{ref_file} is a symbolic link, do not use the mode
9852 of the symbolic link, but rather that of the file it refers to.
9857 @opindex --recursive
9858 @cindex recursively changing access permissions
9859 Recursively change permissions of directories and their contents.
9866 @node touch invocation
9867 @section @command{touch}: Change file timestamps
9870 @cindex changing file timestamps
9871 @cindex file timestamps, changing
9872 @cindex timestamps, changing file
9874 @command{touch} changes the access and/or modification times of the
9875 specified files. Synopsis:
9878 touch [@var{option}]@dots{} @var{file}@dots{}
9881 @cindex empty files, creating
9882 Any @var{file} argument that does not exist is created empty, unless
9883 option @option{--no-create} (@option{-c}) or @option{--no-dereference}
9884 (@option{-h}) was in effect.
9886 A @var{file} argument string of @samp{-} is handled specially and
9887 causes @command{touch} to change the times of the file associated with
9890 @cindex permissions, for changing file timestamps
9891 If changing both the access and modification times to the current
9892 time, @command{touch} can change the timestamps for files that the user
9893 running it does not own but has write permission for. Otherwise, the
9894 user must own the files.
9896 Although @command{touch} provides options for changing two of the times---the
9897 times of last access and modification---of a file, there is actually
9898 a standard third one as well: the inode change time. This is often
9899 referred to as a file's @code{ctime}.
9900 The inode change time represents the time when the file's meta-information
9901 last changed. One common example of this is when the permissions of a
9902 file change. Changing the permissions doesn't access the file, so
9903 the atime doesn't change, nor does it modify the file, so the mtime
9904 doesn't change. Yet, something about the file itself has changed,
9905 and this must be noted somewhere. This is the job of the ctime field.
9906 This is necessary, so that, for example, a backup program can make a
9907 fresh copy of the file, including the new permissions value.
9908 Another operation that modifies a file's ctime without affecting
9909 the others is renaming. In any case, it is not possible, in normal
9910 operations, for a user to change the ctime field to a user-specified value.
9911 Some operating systems and file systems support a fourth time: the
9912 birth time, when the file was first created; by definition, this
9913 timestamp never changes.
9916 Time stamps assume the time zone rules specified by the @env{TZ}
9917 environment variable, or by the system default rules if @env{TZ} is
9918 not set. @xref{TZ Variable,, Specifying the Time Zone with @env{TZ},
9919 libc, The GNU C Library Reference Manual}.
9920 You can avoid ambiguities during
9921 daylight saving transitions by using @sc{utc} time stamps.
9923 The program accepts the following options. Also see @ref{Common options}.
9929 @itemx --time=access
9933 @opindex atime@r{, changing}
9934 @opindex access @r{time, changing}
9935 @opindex use @r{time, changing}
9936 Change the access time only.
9941 @opindex --no-create
9942 Do not warn about or create files that do not exist.
9945 @itemx --date=@var{time}
9949 Use @var{time} instead of the current time. It can contain month names,
9950 time zones, @samp{am} and @samp{pm}, @samp{yesterday}, etc. For
9951 example, @option{--date="2004-02-27 14:19:13.489392193 +0530"}
9952 specifies the instant of time that is 489,392,193 nanoseconds after
9953 February 27, 2004 at 2:19:13 PM in a time zone that is 5 hours and 30
9954 minutes east of @acronym{UTC}. @xref{Date input formats}.
9955 File systems that do not support high-resolution time stamps
9956 silently ignore any excess precision here.
9960 @cindex BSD @command{touch} compatibility
9961 Ignored; for compatibility with BSD versions of @command{touch}.
9964 @itemx --no-dereference
9966 @opindex --no-dereference
9967 @cindex symbolic links, changing time
9969 Attempt to change the timestamps of a symbolic link, rather than what
9970 the link refers to. When using this option, empty files are not
9971 created, but option @option{-c} must also be used to avoid warning
9972 about files that do not exist. Not all systems support changing the
9973 timestamps of symlinks, since underlying system support for this
9974 action was not required until @acronym{POSIX} 2008. Also, on some
9975 systems, the mere act of examining a symbolic link changes the access
9976 time, such that only changes to the modification time will persist
9977 long enough to be observable. When coupled with option @option{-r}, a
9978 reference timestamp is taken from a symbolic link rather than the file
9983 @itemx --time=modify
9986 @opindex mtime@r{, changing}
9987 @opindex modify @r{time, changing}
9988 Change the modification time only.
9991 @itemx --reference=@var{file}
9993 @opindex --reference
9994 Use the times of the reference @var{file} instead of the current time.
9995 If this option is combined with the @option{--date=@var{time}}
9996 (@option{-d @var{time}}) option, the reference @var{file}'s time is
9997 the origin for any relative @var{time}s given, but is otherwise ignored.
9998 For example, @samp{-r foo -d '-5 seconds'} specifies a time stamp
9999 equal to five seconds before the corresponding time stamp for @file{foo}.
10000 If @var{file} is a symbolic link, the reference timestamp is taken
10001 from the target of the symlink, unless @option{-h} was also in effect.
10003 @item -t [[@var{cc}]@var{yy}]@var{mmddhhmm}[.@var{ss}]
10004 Use the argument (optional four-digit or two-digit years, months,
10005 days, hours, minutes, optional seconds) instead of the current time.
10006 If the year is specified with only two digits, then @var{cc}
10007 is 20 for years in the range 0 @dots{} 68, and 19 for years in
10008 69 @dots{} 99. If no digits of the year are specified,
10009 the argument is interpreted as a date in the current year.
10010 Note that @var{ss} may be @samp{60}, to accommodate leap seconds.
10014 @vindex _POSIX2_VERSION
10015 On older systems, @command{touch} supports an obsolete syntax, as follows.
10016 If no timestamp is given with any of the @option{-d}, @option{-r}, or
10017 @option{-t} options, and if there are two or more @var{file}s and the
10018 first @var{file} is of the form @samp{@var{mmddhhmm}[@var{yy}]} and this
10019 would be a valid argument to the @option{-t} option (if the @var{yy}, if
10020 any, were moved to the front), and if the represented year
10021 is in the range 1969--1999, that argument is interpreted as the time
10022 for the other files instead of as a file name.
10023 This obsolete behavior can be enabled or disabled with the
10024 @env{_POSIX2_VERSION} environment variable (@pxref{Standards
10025 conformance}), but portable scripts should avoid commands whose
10026 behavior depends on this variable.
10027 For example, use @samp{touch ./12312359 main.c} or @samp{touch -t
10028 12312359 main.c} rather than the ambiguous @samp{touch 12312359 main.c}.
10034 @chapter Disk usage
10038 No disk can hold an infinite amount of data. These commands report
10039 how much disk storage is in use or available, report other file and
10040 file status information, and write buffers to disk.
10043 * df invocation:: Report file system disk space usage.
10044 * du invocation:: Estimate file space usage.
10045 * stat invocation:: Report file or file system status.
10046 * sync invocation:: Synchronize memory and disk.
10047 * truncate invocation:: Shrink or extend the size of a file.
10051 @node df invocation
10052 @section @command{df}: Report file system disk space usage
10055 @cindex file system disk usage
10056 @cindex disk usage by file system
10058 @command{df} reports the amount of disk space used and available on
10059 file systems. Synopsis:
10062 df [@var{option}]@dots{} [@var{file}]@dots{}
10065 With no arguments, @command{df} reports the space used and available on all
10066 currently mounted file systems (of all types). Otherwise, @command{df}
10067 reports on the file system containing each argument @var{file}.
10069 Normally the disk space is printed in units of
10070 1024 bytes, but this can be overridden (@pxref{Block size}).
10071 Non-integer quantities are rounded up to the next higher unit.
10073 @cindex disk device file
10074 @cindex device file, disk
10075 If an argument @var{file} is a disk device file containing a mounted
10076 file system, @command{df} shows the space available on that file system
10077 rather than on the file system containing the device node (i.e., the root
10078 file system). @sc{gnu} @command{df} does not attempt to determine the disk usage
10079 on unmounted file systems, because on most kinds of systems doing so
10080 requires extremely nonportable intimate knowledge of file system
10083 The program accepts the following options. Also see @ref{Common options}.
10091 @cindex automounter file systems
10092 @cindex ignore file systems
10093 Include in the listing dummy file systems, which
10094 are omitted by default. Such file systems are typically special-purpose
10095 pseudo-file-systems, such as automounter entries.
10097 @item -B @var{size}
10098 @itemx --block-size=@var{size}
10100 @opindex --block-size
10101 @cindex file system sizes
10102 Scale sizes by @var{size} before printing them (@pxref{Block size}).
10103 For example, @option{-BG} prints sizes in units of 1,073,741,824 bytes.
10107 @cindex grand total of disk size, usage and available space
10108 Print a grand total of all arguments after all arguments have
10109 been processed. This can be used to find out the total disk size, usage
10110 and available space of all listed devices.
10116 Equivalent to @option{--si}.
10122 @cindex inode usage
10123 List inode usage information instead of block usage. An inode (short
10124 for index node) contains information about a file such as its owner,
10125 permissions, timestamps, and location on the disk.
10129 @cindex kibibytes for file system sizes
10130 Print sizes in 1024-byte blocks, overriding the default block size
10131 (@pxref{Block size}).
10132 This option is equivalent to @option{--block-size=1K}.
10138 @cindex file system types, limiting output to certain
10139 Limit the listing to local file systems. By default, remote file systems
10144 @cindex file system space, retrieving old data more quickly
10145 Do not invoke the @code{sync} system call before getting any usage data.
10146 This may make @command{df} run significantly faster on systems with many
10147 disks, but on some systems (notably SunOS) the results may be slightly
10148 out of date. This is the default.
10151 @itemx --portability
10153 @opindex --portability
10154 @cindex one-line output format
10155 @cindex @acronym{POSIX} output format
10156 @cindex portable output format
10157 @cindex output format, portable
10158 Use the @acronym{POSIX} output format. This is like the default format except
10163 The information about each file system is always printed on exactly
10164 one line; a mount device is never put on a line by itself. This means
10165 that if the mount device name is more than 20 characters long (e.g., for
10166 some network mounts), the columns are misaligned.
10169 The labels in the header output line are changed to conform to @acronym{POSIX}.
10172 The default block size and output format are unaffected by the
10173 @env{DF_BLOCK_SIZE}, @env{BLOCK_SIZE} and @env{BLOCKSIZE} environment
10174 variables. However, the default block size is still affected by
10175 @env{POSIXLY_CORRECT}: it is 512 if @env{POSIXLY_CORRECT} is set, 1024
10176 otherwise. @xref{Block size}.
10183 @cindex file system space, retrieving current data more slowly
10184 Invoke the @code{sync} system call before getting any usage data. On
10185 some systems (notably SunOS), doing this yields more up to date results,
10186 but in general this option makes @command{df} much slower, especially when
10187 there are many or very busy file systems.
10189 @item -t @var{fstype}
10190 @itemx --type=@var{fstype}
10193 @cindex file system types, limiting output to certain
10194 Limit the listing to file systems of type @var{fstype}. Multiple
10195 file system types can be specified by giving multiple @option{-t} options.
10196 By default, nothing is omitted.
10199 @itemx --print-type
10201 @opindex --print-type
10202 @cindex file system types, printing
10203 Print each file system's type. The types printed here are the same ones
10204 you can include or exclude with @option{-t} and @option{-x}. The particular
10205 types printed are whatever is supported by the system. Here are some of
10206 the common names (this list is certainly not exhaustive):
10211 @cindex @acronym{NFS} file system type
10212 An @acronym{NFS} file system, i.e., one mounted over a network from another
10213 machine. This is the one type name which seems to be used uniformly by
10216 @item 4.2@r{, }ufs@r{, }efs@dots{}
10217 @cindex Linux file system types
10218 @cindex local file system types
10219 @opindex 4.2 @r{file system type}
10220 @opindex ufs @r{file system type}
10221 @opindex efs @r{file system type}
10222 A file system on a locally-mounted hard disk. (The system might even
10223 support more than one type here; Linux does.)
10225 @item hsfs@r{, }cdfs
10226 @cindex CD-ROM file system type
10227 @cindex High Sierra file system
10228 @opindex hsfs @r{file system type}
10229 @opindex cdfs @r{file system type}
10230 A file system on a CD-ROM drive. HP-UX uses @samp{cdfs}, most other
10231 systems use @samp{hsfs} (@samp{hs} for ``High Sierra'').
10234 @cindex PC file system
10235 @cindex DOS file system
10236 @cindex MS-DOS file system
10237 @cindex diskette file system
10239 An MS-DOS file system, usually on a diskette.
10243 @item -x @var{fstype}
10244 @itemx --exclude-type=@var{fstype}
10246 @opindex --exclude-type
10247 Limit the listing to file systems not of type @var{fstype}.
10248 Multiple file system types can be eliminated by giving multiple
10249 @option{-x} options. By default, no file system types are omitted.
10252 Ignored; for compatibility with System V versions of @command{df}.
10257 Failure includes the case where no output is generated, so you can
10258 inspect the exit status of a command like @samp{df -t ext3 -t reiserfs
10259 @var{dir}} to test whether @var{dir} is on a file system of type
10260 @samp{ext3} or @samp{reiserfs}.
10263 @node du invocation
10264 @section @command{du}: Estimate file space usage
10267 @cindex file space usage
10268 @cindex disk usage for files
10270 @command{du} reports the amount of disk space used by the specified files
10271 and for each subdirectory (of directory arguments). Synopsis:
10274 du [@var{option}]@dots{} [@var{file}]@dots{}
10277 With no arguments, @command{du} reports the disk space for the current
10278 directory. Normally the disk space is printed in units of
10279 1024 bytes, but this can be overridden (@pxref{Block size}).
10280 Non-integer quantities are rounded up to the next higher unit.
10282 If two or more hard links point to the same file, only one of the hard
10283 links is counted. The @var{file} argument order affects which links
10284 are counted, and changing the argument order may change the numbers
10285 that @command{du} outputs.
10287 The program accepts the following options. Also see @ref{Common options}.
10295 Show counts for all files, not just directories.
10297 @itemx --apparent-size
10298 @opindex --apparent-size
10299 Print apparent sizes, rather than disk usage. The apparent size of a
10300 file is the number of bytes reported by @code{wc -c} on regular files,
10301 or more generally, @code{ls -l --block-size=1} or @code{stat --format=%s}.
10302 For example, a file containing the word @samp{zoo} with no newline would,
10303 of course, have an apparent size of 3. Such a small file may require
10304 anywhere from 0 to 16 KiB or more of disk space, depending on
10305 the type and configuration of the file system on which the file resides.
10306 However, a sparse file created with this command:
10309 dd bs=1 seek=2GiB if=/dev/null of=big
10313 has an apparent size of 2 GiB, yet on most modern
10314 systems, it actually uses almost no disk space.
10320 Equivalent to @code{--apparent-size --block-size=1}.
10322 @item -B @var{size}
10323 @itemx --block-size=@var{size}
10325 @opindex --block-size
10327 Scale sizes by @var{size} before printing them (@pxref{Block size}).
10328 For example, @option{-BG} prints sizes in units of 1,073,741,824 bytes.
10334 @cindex grand total of disk space
10335 Print a grand total of all arguments after all arguments have
10336 been processed. This can be used to find out the total disk usage of
10337 a given set of files or directories.
10340 @itemx --dereference-args
10342 @opindex --dereference-args
10343 Dereference symbolic links that are command line arguments.
10344 Does not affect other symbolic links. This is helpful for finding
10345 out the disk usage of directories, such as @file{/usr/tmp}, which
10346 are often symbolic links.
10348 @c --files0-from=FILE
10349 @filesZeroFromOption{du,, with the @option{--total} (@option{-c}) option}
10355 Equivalent to @option{--dereference-args} (@option{-D}).
10359 @cindex kibibytes for file sizes
10360 Print sizes in 1024-byte blocks, overriding the default block size
10361 (@pxref{Block size}).
10362 This option is equivalent to @option{--block-size=1K}.
10365 @itemx --count-links
10367 @opindex --count-links
10368 @cindex hard links, counting in @command{du}
10369 Count the size of all files, even if they have appeared already (as a
10373 @itemx --dereference
10375 @opindex --dereference
10376 @cindex symbolic links, dereferencing in @command{du}
10377 Dereference symbolic links (show the disk space used by the file
10378 or directory that the link points to instead of the space used by
10383 @cindex mebibytes for file sizes
10384 Print sizes in 1,048,576-byte blocks, overriding the default block size
10385 (@pxref{Block size}).
10386 This option is equivalent to @option{--block-size=1M}.
10389 @itemx --no-dereference
10391 @opindex --no-dereference
10392 @cindex symbolic links, dereferencing in @command{du}
10393 For each symbolic links encountered by @command{du},
10394 consider the disk space used by the symbolic link.
10396 @item --max-depth=@var{depth}
10397 @opindex --max-depth=@var{depth}
10398 @cindex limiting output of @command{du}
10399 Show the total for each directory (and file if --all) that is at
10400 most MAX_DEPTH levels down from the root of the hierarchy. The root
10401 is at level 0, so @code{du --max-depth=0} is equivalent to @code{du -s}.
10410 @opindex --summarize
10411 Display only a total for each argument.
10414 @itemx --separate-dirs
10416 @opindex --separate-dirs
10417 Normally, in the output of @command{du} (when not using @option{--summarize}),
10418 the size listed next to a directory name, @var{d}, represents the sum
10419 of sizes of all entries beneath @var{d} as well as the size of @var{d} itself.
10420 With @option{--separate-dirs}, the size reported for a directory name,
10421 @var{d}, is merely the @code{stat.st_size}-derived size of the directory
10426 @cindex last modified dates, displaying in @command{du}
10427 Show time of the most recent modification of any file in the directory,
10428 or any of its subdirectories.
10430 @itemx --time=ctime
10431 @itemx --time=status
10434 @opindex ctime@r{, show the most recent}
10435 @opindex status time@r{, show the most recent}
10436 @opindex use time@r{, show the most recent}
10437 Show the most recent status change time (the @samp{ctime} in the inode) of
10438 any file in the directory, instead of the modification time.
10440 @itemx --time=atime
10441 @itemx --time=access
10443 @opindex atime@r{, show the most recent}
10444 @opindex access time@r{, show the most recent}
10445 Show the most recent access time (the @samp{atime} in the inode) of
10446 any file in the directory, instead of the modification time.
10448 @item --time-style=@var{style}
10449 @opindex --time-style
10451 List timestamps in style @var{style}. This option has an effect only if
10452 the @option{--time} option is also specified. The @var{style} should
10453 be one of the following:
10456 @item +@var{format}
10458 List timestamps using @var{format}, where @var{format} is interpreted
10459 like the format argument of @command{date} (@pxref{date invocation}).
10460 For example, @option{--time-style="+%Y-%m-%d %H:%M:%S"} causes
10461 @command{du} to list timestamps like @samp{2002-03-30 23:45:56}. As
10462 with @command{date}, @var{format}'s interpretation is affected by the
10463 @env{LC_TIME} locale category.
10466 List timestamps in full using @acronym{ISO} 8601 date, time, and time zone
10467 format with nanosecond precision, e.g., @samp{2002-03-30
10468 23:45:56.477817180 -0700}. This style is equivalent to
10469 @samp{+%Y-%m-%d %H:%M:%S.%N %z}.
10472 List @acronym{ISO} 8601 date and time in minutes, e.g.,
10473 @samp{2002-03-30 23:45}. These timestamps are shorter than
10474 @samp{full-iso} timestamps, and are usually good enough for everyday
10475 work. This style is equivalent to @samp{+%Y-%m-%d %H:%M}.
10478 List @acronym{ISO} 8601 dates for timestamps, e.g., @samp{2002-03-30}.
10479 This style is equivalent to @samp{+%Y-%m-%d}.
10483 You can specify the default value of the @option{--time-style} option
10484 with the environment variable @env{TIME_STYLE}; if @env{TIME_STYLE} is not set
10485 the default style is @samp{long-iso}. For compatibility with @command{ls},
10486 if @env{TIME_STYLE} begins with @samp{+} and contains a newline,
10487 the newline and any later characters are ignored; if @env{TIME_STYLE}
10488 begins with @samp{posix-} the @samp{posix-} is ignored; and if
10489 @env{TIME_STYLE} is @samp{locale} it is ignored.
10492 @itemx --one-file-system
10494 @opindex --one-file-system
10495 @cindex one file system, restricting @command{du} to
10496 Skip directories that are on different file systems from the one that
10497 the argument being processed is on.
10499 @item --exclude=@var{pattern}
10500 @opindex --exclude=@var{pattern}
10501 @cindex excluding files from @command{du}
10502 When recursing, skip subdirectories or files matching @var{pattern}.
10503 For example, @code{du --exclude='*.o'} excludes files whose names
10506 @item -X @var{file}
10507 @itemx --exclude-from=@var{file}
10508 @opindex -X @var{file}
10509 @opindex --exclude-from=@var{file}
10510 @cindex excluding files from @command{du}
10511 Like @option{--exclude}, except take the patterns to exclude from @var{file},
10512 one per line. If @var{file} is @samp{-}, take the patterns from standard
10517 @cindex NFS mounts from BSD to HP-UX
10518 On BSD systems, @command{du} reports sizes that are half the correct
10519 values for files that are NFS-mounted from HP-UX systems. On HP-UX
10520 systems, it reports sizes that are twice the correct values for
10521 files that are NFS-mounted from BSD systems. This is due to a flaw
10522 in HP-UX; it also affects the HP-UX @command{du} program.
10527 @node stat invocation
10528 @section @command{stat}: Report file or file system status
10531 @cindex file status
10532 @cindex file system status
10534 @command{stat} displays information about the specified file(s). Synopsis:
10537 stat [@var{option}]@dots{} [@var{file}]@dots{}
10540 With no option, @command{stat} reports all information about the given files.
10541 But it also can be used to report the information of the file systems the
10542 given files are located on. If the files are links, @command{stat} can
10543 also give information about the files the links point to.
10545 @mayConflictWithShellBuiltIn{stat}
10550 @itemx --dereference
10552 @opindex --dereference
10553 @cindex symbolic links, dereferencing in @command{stat}
10554 Change how @command{stat} treats symbolic links.
10555 With this option, @command{stat} acts on the file referenced
10556 by each symbolic link argument.
10557 Without it, @command{stat} acts on any symbolic link argument directly.
10560 @itemx --file-system
10562 @opindex --file-system
10563 @cindex file systems
10564 Report information about the file systems where the given files are located
10565 instead of information about the files themselves.
10568 @itemx --format=@var{format}
10570 @opindex --format=@var{format}
10571 @cindex output format
10572 Use @var{format} rather than the default format.
10573 @var{format} is automatically newline-terminated, so
10574 running a command like the following with two or more @var{file}
10575 operands produces a line of output for each operand:
10577 $ stat --format=%d:%i / /usr
10582 @itemx --printf=@var{format}
10583 @opindex --printf=@var{format}
10584 @cindex output format
10585 Use @var{format} rather than the default format.
10586 Like @option{--format}, but interpret backslash escapes,
10587 and do not output a mandatory trailing newline.
10588 If you want a newline, include @samp{\n} in the @var{format}.
10589 Here's how you would use @option{--printf} to print the device
10590 and inode numbers of @file{/} and @file{/usr}:
10592 $ stat --printf='%d:%i\n' / /usr
10601 @cindex terse output
10602 Print the information in terse form, suitable for parsing by other programs.
10606 The valid @var{format} directives for files with @option{--format} and
10607 @option{--printf} are:
10610 @item %a - Access rights in octal
10611 @item %A - Access rights in human readable form
10612 @item %b - Number of blocks allocated (see @samp{%B})
10613 @item %B - The size in bytes of each block reported by @samp{%b}
10614 @item %d - Device number in decimal
10615 @item %D - Device number in hex
10616 @item %f - Raw mode in hex
10617 @item %F - File type
10618 @item %g - Group ID of owner
10619 @item %G - Group name of owner
10620 @item %h - Number of hard links
10621 @item %i - Inode number
10622 @item %n - File name
10623 @item %N - Quoted file name with dereference if symbolic link
10624 @item %o - I/O block size
10625 @item %s - Total size, in bytes
10626 @item %t - Major device type in hex
10627 @item %T - Minor device type in hex
10628 @item %u - User ID of owner
10629 @item %U - User name of owner
10630 @item %x - Time of last access
10631 @item %X - Time of last access as seconds since Epoch
10632 @item %y - Time of last modification
10633 @item %Y - Time of last modification as seconds since Epoch
10634 @item %z - Time of last change
10635 @item %Z - Time of last change as seconds since Epoch
10638 When listing file system information (@option{--file-system} (@option{-f})),
10639 you must use a different set of @var{format} directives:
10642 @item %a - Free blocks available to non-super-user
10643 @item %b - Total data blocks in file system
10644 @item %c - Total file nodes in file system
10645 @item %d - Free file nodes in file system
10646 @item %f - Free blocks in file system
10647 @item %i - File System ID in hex
10648 @item %l - Maximum length of file names
10649 @item %n - File name
10650 @item %s - Block size (for faster transfers)
10651 @item %S - Fundamental block size (for block counts)
10652 @item %t - Type in hex
10653 @item %T - Type in human readable form
10657 Time stamps are listed according to the time zone rules specified by
10658 the @env{TZ} environment variable, or by the system default rules if
10659 @env{TZ} is not set. @xref{TZ Variable,, Specifying the Time Zone
10660 with @env{TZ}, libc, The GNU C Library Reference Manual}.
10665 @node sync invocation
10666 @section @command{sync}: Synchronize data on disk with memory
10669 @cindex synchronize disk and memory
10671 @cindex superblock, writing
10672 @cindex inodes, written buffered
10673 @command{sync} writes any data buffered in memory out to disk. This can
10674 include (but is not limited to) modified superblocks, modified inodes,
10675 and delayed reads and writes. This must be implemented by the kernel;
10676 The @command{sync} program does nothing but exercise the @code{sync} system
10679 @cindex crashes and corruption
10680 The kernel keeps data in memory to avoid doing (relatively slow) disk
10681 reads and writes. This improves performance, but if the computer
10682 crashes, data may be lost or the file system corrupted as a
10683 result. The @command{sync} command ensures everything in memory
10684 is written to disk.
10686 Any arguments are ignored, except for a lone @option{--help} or
10687 @option{--version} (@pxref{Common options}).
10692 @node truncate invocation
10693 @section @command{truncate}: Shrink or extend the size of a file
10696 @cindex truncating, file sizes
10698 @command{truncate} shrinks or extends the size of each @var{file} to the
10699 specified size. Synopsis:
10702 truncate @var{option}@dots{} @var{file}@dots{}
10705 @cindex files, creating
10706 Any @var{file} that does not exist is created.
10708 @cindex sparse files, creating
10709 @cindex holes, creating files with
10710 If a @var{file} is larger than the specified size, the extra data is lost.
10711 If a @var{file} is shorter, it is extended and the extended part (or hole)
10712 reads as zero bytes.
10714 The program accepts the following options. Also see @ref{Common options}.
10721 @opindex --no-create
10722 Do not create files that do not exist.
10727 @opindex --io-blocks
10728 Treat @var{size} as number of I/O blocks of the @var{file} rather than bytes.
10730 @item -r @var{rfile}
10731 @itemx --reference=@var{rfile}
10733 @opindex --reference
10734 Set the size of each @var{file} to the same size as @var{rfile}.
10736 @item -s @var{size}
10737 @itemx --size=@var{size}
10740 Set the size of each @var{file} to this @var{size}.
10741 @multiplierSuffixesNoBlocks{size}
10743 @var{size} may also be prefixed by one of the following to adjust
10744 the size of each @var{file} based on their current size:
10746 @samp{+} => extend by
10747 @samp{-} => reduce by
10748 @samp{<} => at most
10749 @samp{>} => at least
10750 @samp{/} => round down to multiple of
10751 @samp{%} => round up to multiple of
10759 @node Printing text
10760 @chapter Printing text
10762 @cindex printing text, commands for
10763 @cindex commands for printing text
10765 This section describes commands that display text strings.
10768 * echo invocation:: Print a line of text.
10769 * printf invocation:: Format and print data.
10770 * yes invocation:: Print a string until interrupted.
10774 @node echo invocation
10775 @section @command{echo}: Print a line of text
10778 @cindex displaying text
10779 @cindex printing text
10780 @cindex text, displaying
10781 @cindex arbitrary text, displaying
10783 @command{echo} writes each given @var{string} to standard output, with a
10784 space between each and a newline after the last one. Synopsis:
10787 echo [@var{option}]@dots{} [@var{string}]@dots{}
10790 @mayConflictWithShellBuiltIn{echo}
10792 The program accepts the following options. Also see @ref{Common options}.
10793 Options must precede operands, and the normally-special argument
10794 @samp{--} has no special meaning and is treated like any other
10800 Do not output the trailing newline.
10804 @cindex backslash escapes
10805 Enable interpretation of the following backslash-escaped characters in
10814 produce no further output
10830 the eight-bit value that is the octal number @var{nnn}
10831 (zero to three octal digits)
10833 the eight-bit value that is the octal number @var{nnn}
10834 (one to three octal digits)
10836 the eight-bit value that is the hexadecimal number @var{hh}
10837 (one or two hexadecimal digits)
10842 @cindex backslash escapes
10843 Disable interpretation of backslash escapes in each @var{string}.
10844 This is the default. If @option{-e} and @option{-E} are both
10845 specified, the last one given takes effect.
10849 @vindex POSIXLY_CORRECT
10850 If the @env{POSIXLY_CORRECT} environment variable is set, then when
10851 @command{echo}'s first argument is not @option{-n} it outputs
10852 option-like arguments instead of treating them as options. For
10853 example, @code{echo -ne hello} outputs @samp{-ne hello} instead of
10854 plain @samp{hello}.
10856 @acronym{POSIX} does not require support for any options, and says
10857 that the behavior of @command{echo} is implementation-defined if any
10858 @var{string} contains a backslash or if the first argument is
10859 @option{-n}. Portable programs can use the @command{printf} command
10860 if they need to omit trailing newlines or output control characters or
10861 backslashes. @xref{printf invocation}.
10866 @node printf invocation
10867 @section @command{printf}: Format and print data
10870 @command{printf} does formatted printing of text. Synopsis:
10873 printf @var{format} [@var{argument}]@dots{}
10876 @command{printf} prints the @var{format} string, interpreting @samp{%}
10877 directives and @samp{\} escapes to format numeric and string arguments
10878 in a way that is mostly similar to the C @samp{printf} function.
10879 @xref{Output Conversion Syntax,, @command{printf} format directives,
10880 libc, The GNU C Library Reference Manual}, for details.
10881 The differences are listed below.
10883 @mayConflictWithShellBuiltIn{printf}
10888 The @var{format} argument is reused as necessary to convert all the
10889 given @var{argument}s. For example, the command @samp{printf %s a b}
10893 Missing @var{argument}s are treated as null strings or as zeros,
10894 depending on whether the context expects a string or a number. For
10895 example, the command @samp{printf %sx%d} prints @samp{x0}.
10899 An additional escape, @samp{\c}, causes @command{printf} to produce no
10900 further output. For example, the command @samp{printf 'A%sC\cD%sF' B
10901 E} prints @samp{ABC}.
10904 The hexadecimal escape sequence @samp{\x@var{hh}} has at most two
10905 digits, as opposed to C where it can have an unlimited number of
10906 digits. For example, the command @samp{printf '\x07e'} prints two
10907 bytes, whereas the C statement @samp{printf ("\x07e")} prints just
10912 @command{printf} has an additional directive, @samp{%b}, which prints its
10913 argument string with @samp{\} escapes interpreted in the same way as in
10914 the @var{format} string, except that octal escapes are of the form
10915 @samp{\0@var{ooo}} where @var{ooo} is 0 to 3 octal digits.
10916 If a precision is also given, it limits the number of bytes printed
10917 from the converted string.
10920 Numeric arguments must be single C constants, possibly with leading
10921 @samp{+} or @samp{-}. For example, @samp{printf %.4d -3} outputs
10925 @vindex POSIXLY_CORRECT
10926 If the leading character of a numeric argument is @samp{"} or @samp{'}
10927 then its value is the numeric value of the immediately following
10928 character. Any remaining characters are silently ignored if the
10929 @env{POSIXLY_CORRECT} environment variable is set; otherwise, a
10930 warning is printed. For example, @samp{printf "%d" "'a"} outputs
10931 @samp{97} on hosts that use the @acronym{ASCII} character set, since
10932 @samp{a} has the numeric value 97 in @acronym{ASCII}.
10937 A floating-point argument must use a period before any fractional
10938 digits, but is printed according to the @env{LC_NUMERIC} category of the
10939 current locale. For example, in a locale whose radix character is a
10940 comma, the command @samp{printf %g 3.14} outputs @samp{3,14} whereas
10941 the command @samp{printf %g 3,14} is an error.
10945 @command{printf} interprets @samp{\@var{ooo}} in @var{format} as an octal number
10946 (if @var{ooo} is 1 to 3 octal digits) specifying a character to print,
10947 and @samp{\x@var{hh}} as a hexadecimal number (if @var{hh} is 1 to 2 hex
10948 digits) specifying a character to print.
10953 @cindex ISO/IEC 10646
10955 @command{printf} interprets two character syntaxes introduced in
10956 @acronym{ISO} C 99:
10957 @samp{\u} for 16-bit Unicode (@acronym{ISO}/@acronym{IEC} 10646)
10958 characters, specified as
10959 four hexadecimal digits @var{hhhh}, and @samp{\U} for 32-bit Unicode
10960 characters, specified as eight hexadecimal digits @var{hhhhhhhh}.
10961 @command{printf} outputs the Unicode characters
10962 according to the @env{LC_CTYPE} locale. Unicode characters in the ranges
10963 U+0000...U+009F, U+D800...U+DFFF cannot be specified by this syntax, except
10964 for U+0024 ($), U+0040 (@@), and U+0060 (@`).
10966 The processing of @samp{\u} and @samp{\U} requires a full-featured
10967 @code{iconv} facility. It is activated on systems with glibc 2.2 (or newer),
10968 or when @code{libiconv} is installed prior to this package. Otherwise
10969 @samp{\u} and @samp{\U} will print as-is.
10971 The only options are a lone @option{--help} or
10972 @option{--version}. @xref{Common options}.
10973 Options must precede operands.
10975 The Unicode character syntaxes are useful for writing strings in a locale
10976 independent way. For example, a string containing the Euro currency symbol
10979 $ env printf '\u20AC 14.95'
10983 will be output correctly in all locales supporting the Euro symbol
10984 (@acronym{ISO}-8859-15, UTF-8, and others). Similarly, a Chinese string
10987 $ env printf '\u4e2d\u6587'
10991 will be output correctly in all Chinese locales (GB2312, BIG5, UTF-8, etc).
10993 Note that in these examples, the @command{printf} command has been
10994 invoked via @command{env} to ensure that we run the program found via
10995 your shell's search path, and not a shell alias or a built-in function.
10997 For larger strings, you don't need to look up the hexadecimal code
10998 values of each character one by one. @acronym{ASCII} characters mixed with \u
10999 escape sequences is also known as the JAVA source file encoding. You can
11000 use GNU recode 3.5c (or newer) to convert strings to this encoding. Here
11001 is how to convert a piece of text into a shell script which will output
11002 this text in a locale-independent way:
11005 $ LC_CTYPE=zh_CN.big5 /usr/local/bin/printf \
11006 '\u4e2d\u6587\n' > sample.txt
11007 $ recode BIG5..JAVA < sample.txt \
11008 | sed -e "s|^|/usr/local/bin/printf '|" -e "s|$|\\\\n'|" \
11015 @node yes invocation
11016 @section @command{yes}: Print a string until interrupted
11019 @cindex repeated output of a string
11021 @command{yes} prints the command line arguments, separated by spaces and
11022 followed by a newline, forever until it is killed. If no arguments are
11023 given, it prints @samp{y} followed by a newline forever until killed.
11025 Upon a write error, @command{yes} exits with status @samp{1}.
11027 The only options are a lone @option{--help} or @option{--version}.
11028 To output an argument that begins with
11029 @samp{-}, precede it with @option{--}, e.g., @samp{yes -- --help}.
11030 @xref{Common options}.
11034 @chapter Conditions
11037 @cindex commands for exit status
11038 @cindex exit status commands
11040 This section describes commands that are primarily useful for their exit
11041 status, rather than their output. Thus, they are often used as the
11042 condition of shell @code{if} statements, or as the last command in a
11046 * false invocation:: Do nothing, unsuccessfully.
11047 * true invocation:: Do nothing, successfully.
11048 * test invocation:: Check file types and compare values.
11049 * expr invocation:: Evaluate expressions.
11053 @node false invocation
11054 @section @command{false}: Do nothing, unsuccessfully
11057 @cindex do nothing, unsuccessfully
11058 @cindex failure exit status
11059 @cindex exit status of @command{false}
11061 @command{false} does nothing except return an exit status of 1, meaning
11062 @dfn{failure}. It can be used as a place holder in shell scripts
11063 where an unsuccessful command is needed.
11064 In most modern shells, @command{false} is a built-in command, so when
11065 you use @samp{false} in a script, you're probably using the built-in
11066 command, not the one documented here.
11068 @command{false} honors the @option{--help} and @option{--version} options.
11070 This version of @command{false} is implemented as a C program, and is thus
11071 more secure and faster than a shell script implementation, and may safely
11072 be used as a dummy shell for the purpose of disabling accounts.
11074 Note that @command{false} (unlike all other programs documented herein)
11075 exits unsuccessfully, even when invoked with
11076 @option{--help} or @option{--version}.
11078 Portable programs should not assume that the exit status of
11079 @command{false} is 1, as it is greater than 1 on some
11080 non-@acronym{GNU} hosts.
11083 @node true invocation
11084 @section @command{true}: Do nothing, successfully
11087 @cindex do nothing, successfully
11089 @cindex successful exit
11090 @cindex exit status of @command{true}
11092 @command{true} does nothing except return an exit status of 0, meaning
11093 @dfn{success}. It can be used as a place holder in shell scripts
11094 where a successful command is needed, although the shell built-in
11095 command @code{:} (colon) may do the same thing faster.
11096 In most modern shells, @command{true} is a built-in command, so when
11097 you use @samp{true} in a script, you're probably using the built-in
11098 command, not the one documented here.
11100 @command{true} honors the @option{--help} and @option{--version} options.
11102 Note, however, that it is possible to cause @command{true}
11103 to exit with nonzero status: with the @option{--help} or @option{--version}
11104 option, and with standard
11105 output already closed or redirected to a file that evokes an I/O error.
11106 For example, using a Bourne-compatible shell:
11109 $ ./true --version >&-
11110 ./true: write error: Bad file number
11111 $ ./true --version > /dev/full
11112 ./true: write error: No space left on device
11115 This version of @command{true} is implemented as a C program, and is thus
11116 more secure and faster than a shell script implementation, and may safely
11117 be used as a dummy shell for the purpose of disabling accounts.
11119 @node test invocation
11120 @section @command{test}: Check file types and compare values
11123 @cindex check file types
11124 @cindex compare values
11125 @cindex expression evaluation
11127 @command{test} returns a status of 0 (true) or 1 (false) depending on the
11128 evaluation of the conditional expression @var{expr}. Each part of the
11129 expression must be a separate argument.
11131 @command{test} has file status checks, string operators, and numeric
11132 comparison operators.
11134 @command{test} has an alternate form that uses opening and closing
11135 square brackets instead a leading @samp{test}. For example, instead
11136 of @samp{test -d /}, you can write @samp{[ -d / ]}. The square
11137 brackets must be separate arguments; for example, @samp{[-d /]} does
11138 not have the desired effect. Since @samp{test @var{expr}} and @samp{[
11139 @var{expr} ]} have the same meaning, only the former form is discussed
11145 test @var{expression}
11147 [ @var{expression} ]
11152 @mayConflictWithShellBuiltIn{test}
11154 If @var{expression} is omitted, @command{test} returns false.
11155 If @var{expression} is a single argument,
11156 @command{test} returns false if the argument is null and true otherwise. The argument
11157 can be any string, including strings like @samp{-d}, @samp{-1},
11158 @samp{--}, @samp{--help}, and @samp{--version} that most other
11159 programs would treat as options. To get help and version information,
11160 invoke the commands @samp{[ --help} and @samp{[ --version}, without
11161 the usual closing brackets. @xref{Common options}.
11163 @cindex exit status of @command{test}
11167 0 if the expression is true,
11168 1 if the expression is false,
11169 2 if an error occurred.
11173 * File type tests:: -[bcdfhLpSt]
11174 * Access permission tests:: -[gkruwxOG]
11175 * File characteristic tests:: -e -s -nt -ot -ef
11176 * String tests:: -z -n = !=
11177 * Numeric tests:: -eq -ne -lt -le -gt -ge
11178 * Connectives for test:: ! -a -o
11182 @node File type tests
11183 @subsection File type tests
11185 @cindex file type tests
11187 These options test for particular types of files. (Everything's a file,
11188 but not all files are the same!)
11192 @item -b @var{file}
11194 @cindex block special check
11195 True if @var{file} exists and is a block special device.
11197 @item -c @var{file}
11199 @cindex character special check
11200 True if @var{file} exists and is a character special device.
11202 @item -d @var{file}
11204 @cindex directory check
11205 True if @var{file} exists and is a directory.
11207 @item -f @var{file}
11209 @cindex regular file check
11210 True if @var{file} exists and is a regular file.
11212 @item -h @var{file}
11213 @itemx -L @var{file}
11216 @cindex symbolic link check
11217 True if @var{file} exists and is a symbolic link.
11218 Unlike all other file-related tests, this test does not dereference
11219 @var{file} if it is a symbolic link.
11221 @item -p @var{file}
11223 @cindex named pipe check
11224 True if @var{file} exists and is a named pipe.
11226 @item -S @var{file}
11228 @cindex socket check
11229 True if @var{file} exists and is a socket.
11233 @cindex terminal check
11234 True if @var{fd} is a file descriptor that is associated with a
11240 @node Access permission tests
11241 @subsection Access permission tests
11243 @cindex access permission tests
11244 @cindex permission tests
11246 These options test for particular access permissions.
11250 @item -g @var{file}
11252 @cindex set-group-ID check
11253 True if @var{file} exists and has its set-group-ID bit set.
11255 @item -k @var{file}
11257 @cindex sticky bit check
11258 True if @var{file} exists and has its @dfn{sticky} bit set.
11260 @item -r @var{file}
11262 @cindex readable file check
11263 True if @var{file} exists and read permission is granted.
11265 @item -u @var{file}
11267 @cindex set-user-ID check
11268 True if @var{file} exists and has its set-user-ID bit set.
11270 @item -w @var{file}
11272 @cindex writable file check
11273 True if @var{file} exists and write permission is granted.
11275 @item -x @var{file}
11277 @cindex executable file check
11278 True if @var{file} exists and execute permission is granted
11279 (or search permission, if it is a directory).
11281 @item -O @var{file}
11283 @cindex owned by effective user ID check
11284 True if @var{file} exists and is owned by the current effective user ID.
11286 @item -G @var{file}
11288 @cindex owned by effective group ID check
11289 True if @var{file} exists and is owned by the current effective group ID.
11293 @node File characteristic tests
11294 @subsection File characteristic tests
11296 @cindex file characteristic tests
11298 These options test other file characteristics.
11302 @item -e @var{file}
11304 @cindex existence-of-file check
11305 True if @var{file} exists.
11307 @item -s @var{file}
11309 @cindex nonempty file check
11310 True if @var{file} exists and has a size greater than zero.
11312 @item @var{file1} -nt @var{file2}
11314 @cindex newer-than file check
11315 True if @var{file1} is newer (according to modification date) than
11316 @var{file2}, or if @var{file1} exists and @var{file2} does not.
11318 @item @var{file1} -ot @var{file2}
11320 @cindex older-than file check
11321 True if @var{file1} is older (according to modification date) than
11322 @var{file2}, or if @var{file2} exists and @var{file1} does not.
11324 @item @var{file1} -ef @var{file2}
11326 @cindex same file check
11327 @cindex hard link check
11328 True if @var{file1} and @var{file2} have the same device and inode
11329 numbers, i.e., if they are hard links to each other.
11335 @subsection String tests
11337 @cindex string tests
11339 These options test string characteristics. You may need to quote
11340 @var{string} arguments for the shell. For example:
11346 The quotes here prevent the wrong arguments from being passed to
11347 @command{test} if @samp{$V} is empty or contains special characters.
11351 @item -z @var{string}
11353 @cindex zero-length string check
11354 True if the length of @var{string} is zero.
11356 @item -n @var{string}
11357 @itemx @var{string}
11359 @cindex nonzero-length string check
11360 True if the length of @var{string} is nonzero.
11362 @item @var{string1} = @var{string2}
11364 @cindex equal string check
11365 True if the strings are equal.
11367 @item @var{string1} != @var{string2}
11369 @cindex not-equal string check
11370 True if the strings are not equal.
11375 @node Numeric tests
11376 @subsection Numeric tests
11378 @cindex numeric tests
11379 @cindex arithmetic tests
11381 Numeric relational operators. The arguments must be entirely numeric
11382 (possibly negative), or the special expression @w{@code{-l @var{string}}},
11383 which evaluates to the length of @var{string}.
11387 @item @var{arg1} -eq @var{arg2}
11388 @itemx @var{arg1} -ne @var{arg2}
11389 @itemx @var{arg1} -lt @var{arg2}
11390 @itemx @var{arg1} -le @var{arg2}
11391 @itemx @var{arg1} -gt @var{arg2}
11392 @itemx @var{arg1} -ge @var{arg2}
11399 These arithmetic binary operators return true if @var{arg1} is equal,
11400 not-equal, less-than, less-than-or-equal, greater-than, or
11401 greater-than-or-equal than @var{arg2}, respectively.
11408 test -1 -gt -2 && echo yes
11410 test -l abc -gt 1 && echo yes
11413 @error{} test: integer expression expected before -eq
11417 @node Connectives for test
11418 @subsection Connectives for @command{test}
11420 @cindex logical connectives
11421 @cindex connectives, logical
11423 The usual logical connectives.
11429 True if @var{expr} is false.
11431 @item @var{expr1} -a @var{expr2}
11433 @cindex logical and operator
11434 @cindex and operator
11435 True if both @var{expr1} and @var{expr2} are true.
11437 @item @var{expr1} -o @var{expr2}
11439 @cindex logical or operator
11440 @cindex or operator
11441 True if either @var{expr1} or @var{expr2} is true.
11446 @node expr invocation
11447 @section @command{expr}: Evaluate expressions
11450 @cindex expression evaluation
11451 @cindex evaluation of expressions
11453 @command{expr} evaluates an expression and writes the result on standard
11454 output. Each token of the expression must be a separate argument.
11456 Operands are either integers or strings. Integers consist of one or
11457 more decimal digits, with an optional leading @samp{-}.
11458 @command{expr} converts
11459 anything appearing in an operand position to an integer or a string
11460 depending on the operation being applied to it.
11462 Strings are not quoted for @command{expr} itself, though you may need to
11463 quote them to protect characters with special meaning to the shell,
11464 e.g., spaces. However, regardless of whether it is quoted, a string
11465 operand should not be a parenthesis or any of @command{expr}'s
11466 operators like @code{+}, so you cannot safely pass an arbitrary string
11467 @code{$str} to expr merely by quoting it to the shell. One way to
11468 work around this is to use the @sc{gnu} extension @code{+},
11469 (e.g., @code{+ "$str" = foo}); a more portable way is to use
11470 @code{@w{" $str"}} and to adjust the rest of the expression to take
11471 the leading space into account (e.g., @code{@w{" $str" = " foo"}}).
11473 You should not pass a negative integer or a string with leading
11474 @samp{-} as @command{expr}'s first argument, as it might be
11475 misinterpreted as an option; this can be avoided by parenthesization.
11476 Also, portable scripts should not use a string operand that happens to
11477 take the form of an integer; this can be worked around by inserting
11478 leading spaces as mentioned above.
11480 @cindex parentheses for grouping
11481 Operators may be given as infix symbols or prefix keywords. Parentheses
11482 may be used for grouping in the usual manner. You must quote
11483 parentheses and many operators to avoid the shell evaluating them,
11486 When built with support for the GNU MP library, @command{expr} uses
11487 arbitrary-precision arithmetic; otherwise, it uses native arithmetic
11488 types and may fail due to arithmetic overflow.
11490 The only options are @option{--help} and @option{--version}. @xref{Common
11491 options}. Options must precede operands.
11493 @cindex exit status of @command{expr}
11497 0 if the expression is neither null nor 0,
11498 1 if the expression is null or 0,
11499 2 if the expression is invalid,
11500 3 if an internal error occurred (e.g., arithmetic overflow).
11504 * String expressions:: + : match substr index length
11505 * Numeric expressions:: + - * / %
11506 * Relations for expr:: | & < <= = == != >= >
11507 * Examples of expr:: Examples.
11511 @node String expressions
11512 @subsection String expressions
11514 @cindex string expressions
11515 @cindex expressions, string
11517 @command{expr} supports pattern matching and other string operators. These
11518 have higher precedence than both the numeric and relational operators (in
11519 the next sections).
11523 @item @var{string} : @var{regex}
11524 @cindex pattern matching
11525 @cindex regular expression matching
11526 @cindex matching patterns
11527 Perform pattern matching. The arguments are converted to strings and the
11528 second is considered to be a (basic, a la GNU @code{grep}) regular
11529 expression, with a @code{^} implicitly prepended. The first argument is
11530 then matched against this regular expression.
11532 If the match succeeds and @var{regex} uses @samp{\(} and @samp{\)}, the
11533 @code{:} expression returns the part of @var{string} that matched the
11534 subexpression; otherwise, it returns the number of characters matched.
11536 If the match fails, the @code{:} operator returns the null string if
11537 @samp{\(} and @samp{\)} are used in @var{regex}, otherwise 0.
11539 @kindex \( @r{regexp operator}
11540 Only the first @samp{\( @dots{} \)} pair is relevant to the return
11541 value; additional pairs are meaningful only for grouping the regular
11542 expression operators.
11544 @kindex \+ @r{regexp operator}
11545 @kindex \? @r{regexp operator}
11546 @kindex \| @r{regexp operator}
11547 In the regular expression, @code{\+}, @code{\?}, and @code{\|} are
11548 operators which respectively match one or more, zero or one, or separate
11549 alternatives. SunOS and other @command{expr}'s treat these as regular
11550 characters. (@acronym{POSIX} allows either behavior.)
11551 @xref{Top, , Regular Expression Library, regex, Regex}, for details of
11552 regular expression syntax. Some examples are in @ref{Examples of expr}.
11554 @item match @var{string} @var{regex}
11556 An alternative way to do pattern matching. This is the same as
11557 @w{@samp{@var{string} : @var{regex}}}.
11559 @item substr @var{string} @var{position} @var{length}
11561 Returns the substring of @var{string} beginning at @var{position}
11562 with length at most @var{length}. If either @var{position} or
11563 @var{length} is negative, zero, or non-numeric, returns the null string.
11565 @item index @var{string} @var{charset}
11567 Returns the first position in @var{string} where the first character in
11568 @var{charset} was found. If no character in @var{charset} is found in
11569 @var{string}, return 0.
11571 @item length @var{string}
11573 Returns the length of @var{string}.
11575 @item + @var{token}
11577 Interpret @var{token} as a string, even if it is a keyword like @var{match}
11578 or an operator like @code{/}.
11579 This makes it possible to test @code{expr length + "$x"} or
11580 @code{expr + "$x" : '.*/\(.\)'} and have it do the right thing even if
11581 the value of @var{$x} happens to be (for example) @code{/} or @code{index}.
11582 This operator is a @acronym{GNU} extension. Portable shell scripts should use
11583 @code{@w{" $token"} : @w{' \(.*\)'}} instead of @code{+ "$token"}.
11587 To make @command{expr} interpret keywords as strings, you must use the
11588 @code{quote} operator.
11591 @node Numeric expressions
11592 @subsection Numeric expressions
11594 @cindex numeric expressions
11595 @cindex expressions, numeric
11597 @command{expr} supports the usual numeric operators, in order of increasing
11598 precedence. These numeric operators have lower precedence than the
11599 string operators described in the previous section, and higher precedence
11600 than the connectives (next section).
11608 @cindex subtraction
11609 Addition and subtraction. Both arguments are converted to integers;
11610 an error occurs if this cannot be done.
11616 @cindex multiplication
11619 Multiplication, division, remainder. Both arguments are converted to
11620 integers; an error occurs if this cannot be done.
11625 @node Relations for expr
11626 @subsection Relations for @command{expr}
11628 @cindex connectives, logical
11629 @cindex logical connectives
11630 @cindex relations, numeric or string
11632 @command{expr} supports the usual logical connectives and relations. These
11633 have lower precedence than the string and numeric operators
11634 (previous sections). Here is the list, lowest-precedence operator first.
11640 @cindex logical or operator
11641 @cindex or operator
11642 Returns its first argument if that is neither null nor zero, otherwise
11643 its second argument if it is neither null nor zero, otherwise 0. It
11644 does not evaluate its second argument if its first argument is neither
11649 @cindex logical and operator
11650 @cindex and operator
11651 Return its first argument if neither argument is null or zero, otherwise
11652 0. It does not evaluate its second argument if its first argument is
11655 @item < <= = == != >= >
11662 @cindex comparison operators
11664 Compare the arguments and return 1 if the relation is true, 0 otherwise.
11665 @code{==} is a synonym for @code{=}. @command{expr} first tries to convert
11666 both arguments to integers and do a numeric comparison; if either
11667 conversion fails, it does a lexicographic comparison using the character
11668 collating sequence specified by the @env{LC_COLLATE} locale.
11673 @node Examples of expr
11674 @subsection Examples of using @command{expr}
11676 @cindex examples of @command{expr}
11677 Here are a few examples, including quoting for shell metacharacters.
11679 To add 1 to the shell variable @code{foo}, in Bourne-compatible shells:
11682 foo=`expr $foo + 1`
11685 To print the non-directory part of the file name stored in
11686 @code{$fname}, which need not contain a @code{/}:
11689 expr $fname : '.*/\(.*\)' '|' $fname
11692 An example showing that @code{\+} is an operator:
11700 expr abc : 'a\(.\)c'
11702 expr index abcdef cz
11705 @error{} expr: syntax error
11706 expr index + index a
11712 @chapter Redirection
11714 @cindex redirection
11715 @cindex commands for redirection
11717 Unix shells commonly provide several forms of @dfn{redirection}---ways
11718 to change the input source or output destination of a command. But one
11719 useful redirection is performed by a separate command, not by the shell;
11720 it's described here.
11723 * tee invocation:: Redirect output to multiple files or processes.
11727 @node tee invocation
11728 @section @command{tee}: Redirect output to multiple files or processes
11731 @cindex pipe fitting
11732 @cindex destinations, multiple output
11733 @cindex read from stdin and write to stdout and files
11735 The @command{tee} command copies standard input to standard output and also
11736 to any files given as arguments. This is useful when you want not only
11737 to send some data down a pipe, but also to save a copy. Synopsis:
11740 tee [@var{option}]@dots{} [@var{file}]@dots{}
11743 If a file being written to does not already exist, it is created. If a
11744 file being written to already exists, the data it previously contained
11745 is overwritten unless the @option{-a} option is used.
11747 A @var{file} of @samp{-} causes @command{tee} to send another copy of
11748 input to standard output, but this is typically not that useful as the
11749 copies are interleaved.
11751 The program accepts the following options. Also see @ref{Common options}.
11758 Append standard input to the given files rather than overwriting
11762 @itemx --ignore-interrupts
11764 @opindex --ignore-interrupts
11765 Ignore interrupt signals.
11769 The @command{tee} command is useful when you happen to be transferring a large
11770 amount of data and also want to summarize that data without reading
11771 it a second time. For example, when you are downloading a DVD image,
11772 you often want to verify its signature or checksum right away.
11773 The inefficient way to do it is simply:
11776 wget http://example.com/some.iso && sha1sum some.iso
11779 One problem with the above is that it makes you wait for the
11780 download to complete before starting the time-consuming SHA1 computation.
11781 Perhaps even more importantly, the above requires reading
11782 the DVD image a second time (the first was from the network).
11784 The efficient way to do it is to interleave the download
11785 and SHA1 computation. Then, you'll get the checksum for
11786 free, because the entire process parallelizes so well:
11789 # slightly contrived, to demonstrate process substitution
11790 wget -O - http://example.com/dvd.iso \
11791 | tee >(sha1sum > dvd.sha1) > dvd.iso
11794 That makes @command{tee} write not just to the expected output file,
11795 but also to a pipe running @command{sha1sum} and saving the final
11796 checksum in a file named @file{dvd.sha1}.
11798 Note, however, that this example relies on a feature of modern shells
11799 called @dfn{process substitution}
11800 (the @samp{>(command)} syntax, above;
11801 @xref{Process Substitution,,Process Substitution, bashref,
11802 The Bash Reference Manual}.),
11803 so it works with @command{zsh}, @command{bash}, and @command{ksh},
11804 but not with @command{/bin/sh}. So if you write code like this
11805 in a shell script, be sure to start the script with @samp{#!/bin/bash}.
11807 Since the above example writes to one file and one process,
11808 a more conventional and portable use of @command{tee} is even better:
11811 wget -O - http://example.com/dvd.iso \
11812 | tee dvd.iso | sha1sum > dvd.sha1
11815 You can extend this example to make @command{tee} write to two processes,
11816 computing MD5 and SHA1 checksums in parallel. In this case,
11817 process substitution is required:
11820 wget -O - http://example.com/dvd.iso \
11821 | tee >(sha1sum > dvd.sha1) \
11822 >(md5sum > dvd.md5) \
11826 This technique is also useful when you want to make a @emph{compressed}
11827 copy of the contents of a pipe.
11828 Consider a tool to graphically summarize disk usage data from @samp{du -ak}.
11829 For a large hierarchy, @samp{du -ak} can run for a long time,
11830 and can easily produce terabytes of data, so you won't want to
11831 rerun the command unnecessarily. Nor will you want to save
11832 the uncompressed output.
11834 Doing it the inefficient way, you can't even start the GUI
11835 until after you've compressed all of the @command{du} output:
11838 du -ak | gzip -9 > /tmp/du.gz
11839 gzip -d /tmp/du.gz | xdiskusage -a
11842 With @command{tee} and process substitution, you start the GUI
11843 right away and eliminate the decompression completely:
11846 du -ak | tee >(gzip -9 > /tmp/du.gz) | xdiskusage -a
11849 Finally, if you regularly create more than one type of
11850 compressed tarball at once, for example when @code{make dist} creates
11851 both @command{gzip}-compressed and @command{bzip2}-compressed tarballs,
11852 there may be a better way.
11853 Typical @command{automake}-generated @file{Makefile} rules create
11854 the two compressed tar archives with commands in sequence, like this
11855 (slightly simplified):
11858 tardir=your-pkg-M.N
11859 tar chof - "$tardir" | gzip -9 -c > your-pkg-M.N.tar.gz
11860 tar chof - "$tardir" | bzip2 -9 -c > your-pkg-M.N.tar.bz2
11863 However, if the hierarchy you are archiving and compressing is larger
11864 than a couple megabytes, and especially if you are using a multi-processor
11865 system with plenty of memory, then you can do much better by reading the
11866 directory contents only once and running the compression programs in parallel:
11869 tardir=your-pkg-M.N
11870 tar chof - "$tardir" \
11871 | tee >(gzip -9 -c > your-pkg-M.N.tar.gz) \
11872 | bzip2 -9 -c > your-pkg-M.N.tar.bz2
11878 @node File name manipulation
11879 @chapter File name manipulation
11881 @cindex file name manipulation
11882 @cindex manipulation of file names
11883 @cindex commands for file name manipulation
11885 This section describes commands that manipulate file names.
11888 * basename invocation:: Strip directory and suffix from a file name.
11889 * dirname invocation:: Strip non-directory suffix from a file name.
11890 * pathchk invocation:: Check file name validity and portability.
11891 * mktemp invocation:: Create temporary file or directory.
11895 @node basename invocation
11896 @section @command{basename}: Strip directory and suffix from a file name
11899 @cindex strip directory and suffix from file names
11900 @cindex directory, stripping from file names
11901 @cindex suffix, stripping from file names
11902 @cindex file names, stripping directory and suffix
11903 @cindex leading directory components, stripping
11905 @command{basename} removes any leading directory components from
11906 @var{name}. Synopsis:
11909 basename @var{name} [@var{suffix}]
11912 If @var{suffix} is specified and is identical to the end of @var{name},
11913 it is removed from @var{name} as well. Note that since trailing slashes
11914 are removed prior to suffix matching, @var{suffix} will do nothing if it
11915 contains slashes. @command{basename} prints the result on standard
11918 @c This test is used both here and in the section on dirname.
11919 @macro basenameAndDirname
11920 Together, @command{basename} and @command{dirname} are designed such
11921 that if @samp{ls "$name"} succeeds, then the command sequence @samp{cd
11922 "$(dirname "$name")"; ls "$(basename "$name")"} will, too. This works
11923 for everything except file names containing a trailing newline.
11925 @basenameAndDirname
11927 @acronym{POSIX} allows the implementation to define the results if
11928 @var{name} is empty or @samp{//}. In the former case, @acronym{GNU}
11929 @command{basename} returns the empty string. In the latter case, the
11930 result is @samp{//} on platforms where @var{//} is distinct from
11931 @var{/}, and @samp{/} on platforms where there is no difference.
11933 The only options are @option{--help} and @option{--version}. @xref{Common
11934 options}. Options must precede operands.
11942 basename /usr/bin/sort
11945 basename include/stdio.h .h
11949 @node dirname invocation
11950 @section @command{dirname}: Strip non-directory suffix from a file name
11953 @cindex directory components, printing
11954 @cindex stripping non-directory suffix
11955 @cindex non-directory suffix, stripping
11957 @command{dirname} prints all but the final slash-delimited component of
11958 a string (presumably a file name). Synopsis:
11964 If @var{name} is a single component, @command{dirname} prints @samp{.}
11965 (meaning the current directory).
11967 @basenameAndDirname
11969 @acronym{POSIX} allows the implementation to define the results if
11970 @var{name} is @samp{//}. With @acronym{GNU} @command{dirname}, the
11971 result is @samp{//} on platforms where @var{//} is distinct from
11972 @var{/}, and @samp{/} on platforms where there is no difference.
11974 The only options are @option{--help} and @option{--version}. @xref{Common
11982 # Output "/usr/bin".
11983 dirname /usr/bin/sort
11990 @node pathchk invocation
11991 @section @command{pathchk}: Check file name validity and portability
11994 @cindex file names, checking validity and portability
11995 @cindex valid file names, checking for
11996 @cindex portable file names, checking for
11998 @command{pathchk} checks validity and portability of file names. Synopsis:
12001 pathchk [@var{option}]@dots{} @var{name}@dots{}
12004 For each @var{name}, @command{pathchk} prints an error message if any of
12005 these conditions is true:
12009 One of the existing directories in @var{name} does not have search
12010 (execute) permission,
12012 The length of @var{name} is larger than the maximum supported by the
12015 The length of one component of @var{name} is longer than
12016 its file system's maximum.
12019 A nonexistent @var{name} is not an error, so long a file with that
12020 name could be created under the above conditions.
12022 The program accepts the following options. Also see @ref{Common options}.
12023 Options must precede operands.
12029 Instead of performing checks based on the underlying file system,
12030 print an error message if any of these conditions is true:
12034 A file name is empty.
12037 A file name contains a character outside the @acronym{POSIX} portable file
12038 name character set, namely, the ASCII letters and digits, @samp{.},
12039 @samp{_}, @samp{-}, and @samp{/}.
12042 The length of a file name or one of its components exceeds the
12043 @acronym{POSIX} minimum limits for portability.
12048 Print an error message if a file name is empty, or if it contains a component
12049 that begins with @samp{-}.
12051 @item --portability
12052 @opindex --portability
12053 Print an error message if a file name is not portable to all @acronym{POSIX}
12054 hosts. This option is equivalent to @samp{-p -P}.
12058 @cindex exit status of @command{pathchk}
12062 0 if all specified file names passed all checks,
12066 @node mktemp invocation
12067 @section @command{mktemp}: Create temporary file or directory
12070 @cindex file names, creating temporary
12071 @cindex directory, creating temporary
12072 @cindex temporary files and directories
12074 @command{mktemp} manages the creation of temporary files and
12075 directories. Synopsis:
12078 mktemp [@var{option}]@dots{} [@var{template}]
12081 Safely create a temporary file or directory based on @var{template},
12082 and print its name. If given, @var{template} must include at least
12083 three consecutive @samp{X}s in the last component. If omitted, the template
12084 @samp{tmp.XXXXXXXXXX} is used, and option @option{--tmpdir} is
12085 implied. The final run of @samp{X}s in the @var{template} will be replaced
12086 by alpha-numeric characters; thus, on a case-sensitive file system,
12087 and with a @var{template} including a run of @var{n} instances of @samp{X},
12088 there are @samp{62**@var{n}} potential file names.
12090 Older scripts used to create temporary files by simply joining the
12091 name of the program with the process id (@samp{$$}) as a suffix.
12092 However, that naming scheme is easily predictable, and suffers from a
12093 race condition where the attacker can create an appropriately named
12094 symbolic link, such that when the script then opens a handle to what
12095 it thought was an unused file, it is instead modifying an existing
12096 file. Using the same scheme to create a directory is slightly safer,
12097 since the @command{mkdir} will fail if the target already exists, but
12098 it is still inferior because it allows for denial of service attacks.
12099 Therefore, modern scripts should use the @command{mktemp} command to
12100 guarantee that the generated name will be unpredictable, and that
12101 knowledge of the temporary file name implies that the file was created
12102 by the current script and cannot be modified by other users.
12104 When creating a file, the resulting file has read and write
12105 permissions for the current user, but no permissions for the group or
12106 others; these permissions are reduced if the current umask is more
12109 Here are some examples (although note that if you repeat them, you
12110 will most likely get different file names):
12115 Create a temporary file in the current directory.
12122 Create a temporary file with a known suffix.
12124 $ mktemp --suffix=.txt file-XXXX
12126 $ mktemp file-XXXX-XXXX.txt
12131 Create a secure fifo relative to the user's choice of @env{TMPDIR},
12132 but falling back to the current directory rather than @file{/tmp}.
12133 Note that @command{mktemp} does not create fifos, but can create a
12134 secure directory in which the fifo can live. Exit the shell if the
12135 directory or fifo could not be created.
12137 $ dir=$(mktemp -p "$@{TMPDIR:-.@}" -d dir-XXXX) || exit 1
12139 $ mkfifo "$fifo" || @{ rmdir "$dir"; exit 1; @}
12143 Create and use a temporary file if possible, but ignore failure. The
12144 file will reside in the directory named by @env{TMPDIR}, if specified,
12145 or else in @file{/tmp}.
12147 $ file=$(mktemp -q) && @{
12148 > # Safe to use $file only within this block. Use quotes,
12149 > # since $TMPDIR, and thus $file, may contain whitespace.
12150 > echo ... > "$file"
12156 Act as a semi-random character generator (it is not fully random,
12157 since it is impacted by the contents of the current directory). To
12158 avoid security holes, do not use the resulting names to create a file.
12168 The program accepts the following options. Also see @ref{Common options}.
12175 @opindex --directory
12176 Create a directory rather than a file. The directory will have read,
12177 write, and search permissions for the current user, but no permissions
12178 for the group or others; these permissions are reduced if the current
12179 umask is more restrictive.
12185 Suppress diagnostics about failure to create a file or directory. The
12186 exit status will still reflect whether a file was created.
12192 Generate a temporary name that does not name an existing file, without
12193 changing the file system contents. Using the output of this command
12194 to create a new file is inherently unsafe, as there is a window of
12195 time between generating the name and using it where another process
12196 can create an object by the same name.
12199 @itemx --tmpdir[=@var{dir}]
12202 Treat @var{template} relative to the directory @var{dir}. If
12203 @var{dir} is not specified (only possible with the long option
12204 @option{--tmpdir}) or is the empty string, use the value of
12205 @env{TMPDIR} if available, otherwise use @samp{/tmp}. If this is
12206 specified, @var{template} must not be absolute. However,
12207 @var{template} can still contain slashes, although intermediate
12208 directories must already exist.
12210 @item --suffix=@var{suffix}
12212 Append @var{suffix} to the @var{template}. @var{suffix} must not
12213 contain slash. If @option{--suffix} is specified, @var{template} must
12214 end in @samp{X}; if it is not specified, then an appropriate
12215 @option{--suffix} is inferred by finding the last @samp{X} in
12216 @var{template}. This option exists for use with the default
12217 @var{template} and for the creation of a @var{suffix} that starts with
12222 Treat @var{template} as a single file relative to the value of
12223 @env{TMPDIR} if available, or to the directory specified by
12224 @option{-p}, otherwise to @samp{/tmp}. @var{template} must not
12225 contain slashes. This option is deprecated; the use of @option{-p}
12226 without @option{-t} offers better defaults (by favoring the command
12227 line over @env{TMPDIR}) and more flexibility (by allowing intermediate
12232 @cindex exit status of @command{mktemp}
12236 0 if the file was created,
12241 @node Working context
12242 @chapter Working context
12244 @cindex working context
12245 @cindex commands for printing the working context
12247 This section describes commands that display or alter the context in
12248 which you are working: the current directory, the terminal settings, and
12249 so forth. See also the user-related commands in the next section.
12252 * pwd invocation:: Print working directory.
12253 * stty invocation:: Print or change terminal characteristics.
12254 * printenv invocation:: Print environment variables.
12255 * tty invocation:: Print file name of terminal on standard input.
12259 @node pwd invocation
12260 @section @command{pwd}: Print working directory
12263 @cindex print name of current directory
12264 @cindex current working directory, printing
12265 @cindex working directory, printing
12268 @command{pwd} prints the name of the current directory. Synopsis:
12271 pwd [@var{option}]@dots{}
12274 The program accepts the following options. Also see @ref{Common options}.
12281 If the contents of the environment variable @env{PWD} provide an
12282 absolute name of the current directory with no @samp{.} or @samp{..}
12283 components, but possibly with symbolic links, then output those
12284 contents. Otherwise, fall back to default @option{-P} handling.
12289 @opindex --physical
12290 Print a fully resolved name for the current directory. That is, all
12291 components of the printed name will be actual directory names---none
12292 will be symbolic links.
12295 @cindex symbolic links and @command{pwd}
12296 If @option{-L} and @option{-P} are both given, the last one takes
12297 precedence. If neither option is given, then this implementation uses
12298 @option{-P} as the default unless the @env{POSIXLY_CORRECT}
12299 environment variable is set.
12301 @mayConflictWithShellBuiltIn{pwd}
12306 @node stty invocation
12307 @section @command{stty}: Print or change terminal characteristics
12310 @cindex change or print terminal settings
12311 @cindex terminal settings
12312 @cindex line settings of terminal
12314 @command{stty} prints or changes terminal characteristics, such as baud rate.
12318 stty [@var{option}] [@var{setting}]@dots{}
12319 stty [@var{option}]
12322 If given no line settings, @command{stty} prints the baud rate, line
12323 discipline number (on systems that support it), and line settings
12324 that have been changed from the values set by @samp{stty sane}.
12325 By default, mode reading and setting are performed on the tty line
12326 connected to standard input, although this can be modified by the
12327 @option{--file} option.
12329 @command{stty} accepts many non-option arguments that change aspects of
12330 the terminal line operation, as described below.
12332 The program accepts the following options. Also see @ref{Common options}.
12339 Print all current settings in human-readable form. This option may not
12340 be used in combination with any line settings.
12342 @item -F @var{device}
12343 @itemx --file=@var{device}
12346 Set the line opened by the file name specified in @var{device} instead of
12347 the tty line connected to standard input. This option is necessary
12348 because opening a @acronym{POSIX} tty requires use of the @code{O_NONDELAY} flag to
12349 prevent a @acronym{POSIX} tty from blocking until the carrier detect line is high if
12350 the @code{clocal} flag is not set. Hence, it is not always possible
12351 to allow the shell to open the device in the traditional manner.
12357 @cindex machine-readable @command{stty} output
12358 Print all current settings in a form that can be used as an argument to
12359 another @command{stty} command to restore the current settings. This option
12360 may not be used in combination with any line settings.
12364 Many settings can be turned off by preceding them with a @samp{-}.
12365 Such arguments are marked below with ``May be negated'' in their
12366 description. The descriptions themselves refer to the positive
12367 case, that is, when @emph{not} negated (unless stated otherwise,
12370 Some settings are not available on all @acronym{POSIX} systems, since they use
12371 extensions. Such arguments are marked below with ``Non-@acronym{POSIX}'' in their
12372 description. On non-@acronym{POSIX} systems, those or other settings also may not
12373 be available, but it's not feasible to document all the variations: just
12379 * Control:: Control settings
12380 * Input:: Input settings
12381 * Output:: Output settings
12382 * Local:: Local settings
12383 * Combination:: Combination settings
12384 * Characters:: Special characters
12385 * Special:: Special settings
12390 @subsection Control settings
12392 @cindex control settings
12398 @cindex two-way parity
12399 Generate parity bit in output and expect parity bit in input.
12405 @cindex even parity
12406 Set odd parity (even if negated). May be negated.
12413 @cindex character size
12414 @cindex eight-bit characters
12415 Set character size to 5, 6, 7, or 8 bits.
12420 Send a hangup signal when the last process closes the tty. May be
12426 Use two stop bits per character (one if negated). May be negated.
12430 Allow input to be received. May be negated.
12434 @cindex modem control
12435 Disable modem control signals. May be negated.
12439 @cindex hardware flow control
12440 @cindex flow control, hardware
12441 @cindex RTS/CTS flow control
12442 Enable RTS/CTS flow control. Non-@acronym{POSIX}. May be negated.
12447 @subsection Input settings
12449 @cindex input settings
12450 These settings control operations on data received from the terminal.
12455 @cindex breaks, ignoring
12456 Ignore break characters. May be negated.
12460 @cindex breaks, cause interrupts
12461 Make breaks cause an interrupt signal. May be negated.
12465 @cindex parity, ignoring
12466 Ignore characters with parity errors. May be negated.
12470 @cindex parity errors, marking
12471 Mark parity errors (with a 255-0-character sequence). May be negated.
12475 Enable input parity checking. May be negated.
12479 @cindex eight-bit input
12480 Clear high (8th) bit of input characters. May be negated.
12484 @cindex newline, translating to return
12485 Translate newline to carriage return. May be negated.
12489 @cindex return, ignoring
12490 Ignore carriage return. May be negated.
12494 @cindex return, translating to newline
12495 Translate carriage return to newline. May be negated.
12499 @cindex input encoding, UTF-8
12500 Assume input characters are UTF-8 encoded. May be negated.
12504 @kindex C-s/C-q flow control
12505 @cindex XON/XOFF flow control
12506 Enable XON/XOFF flow control (that is, @kbd{CTRL-S}/@kbd{CTRL-Q}). May
12513 @cindex software flow control
12514 @cindex flow control, software
12515 Enable sending of @code{stop} character when the system input buffer
12516 is almost full, and @code{start} character when it becomes almost
12517 empty again. May be negated.
12521 @cindex uppercase, translating to lowercase
12522 Translate uppercase characters to lowercase. Non-@acronym{POSIX}. May be
12523 negated. Note ilcuc is not implemented, as one would not be able to issue
12524 almost any (lowercase) Unix command, after invoking it.
12528 Allow any character to restart output (only the start character
12529 if negated). Non-@acronym{POSIX}. May be negated.
12533 @cindex beeping at input buffer full
12534 Enable beeping and not flushing input buffer if a character arrives
12535 when the input buffer is full. Non-@acronym{POSIX}. May be negated.
12540 @subsection Output settings
12542 @cindex output settings
12543 These settings control operations on data sent to the terminal.
12548 Postprocess output. May be negated.
12552 @cindex lowercase, translating to output
12553 Translate lowercase characters to uppercase. Non-@acronym{POSIX}. May be
12554 negated. (Note ouclc is not currently implemented.)
12558 @cindex return, translating to newline
12559 Translate carriage return to newline. Non-@acronym{POSIX}. May be negated.
12563 @cindex newline, translating to crlf
12564 Translate newline to carriage return-newline. Non-@acronym{POSIX}. May be
12569 Do not print carriage returns in the first column. Non-@acronym{POSIX}.
12574 Newline performs a carriage return. Non-@acronym{POSIX}. May be negated.
12578 @cindex pad instead of timing for delaying
12579 Use fill (padding) characters instead of timing for delays. Non-@acronym{POSIX}.
12584 @cindex pad character
12585 Use @acronym{ASCII} @sc{del} characters for fill instead of
12586 @acronym{ASCII} @sc{nul} characters. Non-@acronym{POSIX}.
12592 Newline delay style. Non-@acronym{POSIX}.
12599 Carriage return delay style. Non-@acronym{POSIX}.
12605 @opindex tab@var{n}
12606 Horizontal tab delay style. Non-@acronym{POSIX}.
12611 Backspace delay style. Non-@acronym{POSIX}.
12616 Vertical tab delay style. Non-@acronym{POSIX}.
12621 Form feed delay style. Non-@acronym{POSIX}.
12626 @subsection Local settings
12628 @cindex local settings
12633 Enable @code{interrupt}, @code{quit}, and @code{suspend} special
12634 characters. May be negated.
12638 Enable @code{erase}, @code{kill}, @code{werase}, and @code{rprnt}
12639 special characters. May be negated.
12643 Enable non-@acronym{POSIX} special characters. May be negated.
12647 Echo input characters. May be negated.
12653 Echo @code{erase} characters as backspace-space-backspace. May be
12658 @cindex newline echoing after @code{kill}
12659 Echo a newline after a @code{kill} character. May be negated.
12663 @cindex newline, echoing
12664 Echo newline even if not echoing other characters. May be negated.
12668 @cindex flushing, disabling
12669 Disable flushing after @code{interrupt} and @code{quit} special
12670 characters. May be negated.
12674 @cindex case translation
12675 Enable input and output of uppercase characters by preceding their
12676 lowercase equivalents with @samp{\}, when @code{icanon} is set.
12677 Non-@acronym{POSIX}. May be negated.
12681 @cindex background jobs, stopping at terminal write
12682 Stop background jobs that try to write to the terminal. Non-@acronym{POSIX}.
12689 Echo erased characters backward, between @samp{\} and @samp{/}.
12690 Non-@acronym{POSIX}. May be negated.
12696 @cindex control characters, using @samp{^@var{c}}
12697 @cindex hat notation for control characters
12698 Echo control characters in hat notation (@samp{^@var{c}}) instead
12699 of literally. Non-@acronym{POSIX}. May be negated.
12705 Echo the @code{kill} special character by erasing each character on
12706 the line as indicated by the @code{echoprt} and @code{echoe} settings,
12707 instead of by the @code{echoctl} and @code{echok} settings. Non-@acronym{POSIX}.
12713 @subsection Combination settings
12715 @cindex combination settings
12716 Combination settings:
12723 Same as @code{parenb -parodd cs7}. May be negated. If negated, same
12724 as @code{-parenb cs8}.
12728 Same as @code{parenb parodd cs7}. May be negated. If negated, same
12729 as @code{-parenb cs8}.
12733 Same as @code{-icrnl -onlcr}. May be negated. If negated, same as
12734 @code{icrnl -inlcr -igncr onlcr -ocrnl -onlret}.
12738 Reset the @code{erase} and @code{kill} special characters to their default
12745 @c This is too long to write inline.
12747 cread -ignbrk brkint -inlcr -igncr icrnl -ixoff
12748 -iuclc -ixany imaxbel opost -olcuc -ocrnl onlcr
12749 -onocr -onlret -ofill -ofdel nl0 cr0 tab0 bs0 vt0
12750 ff0 isig icanon iexten echo echoe echok -echonl
12751 -noflsh -xcase -tostop -echoprt echoctl echoke
12755 and also sets all special characters to their default values.
12759 Same as @code{brkint ignpar istrip icrnl ixon opost isig icanon}, plus
12760 sets the @code{eof} and @code{eol} characters to their default values
12761 if they are the same as the @code{min} and @code{time} characters.
12762 May be negated. If negated, same as @code{raw}.
12769 -ignbrk -brkint -ignpar -parmrk -inpck -istrip
12770 -inlcr -igncr -icrnl -ixon -ixoff -iuclc -ixany
12771 -imaxbel -opost -isig -icanon -xcase min 1 time 0
12775 May be negated. If negated, same as @code{cooked}.
12779 Same as @option{-icanon}. May be negated. If negated, same as
12784 @cindex eight-bit characters
12785 Same as @code{-parenb -istrip cs8}. May be negated. If negated,
12786 same as @code{parenb istrip cs7}.
12790 Same as @option{-parenb -istrip -opost cs8}. May be negated.
12791 If negated, same as @code{parenb istrip opost cs7}.
12795 Same as @option{-ixany}. Non-@acronym{POSIX}. May be negated.
12799 Same as @code{tab0}. Non-@acronym{POSIX}. May be negated. If negated, same
12806 Same as @code{xcase iuclc olcuc}. Non-@acronym{POSIX}. May be negated.
12807 (Used for terminals with uppercase characters only.)
12811 Same as @code{echoe echoctl echoke}.
12815 Same as @code{echoe echoctl echoke -ixany intr ^C erase ^? kill C-u}.
12820 @subsection Special characters
12822 @cindex special characters
12823 @cindex characters, special
12825 The special characters' default values vary from system to system.
12826 They are set with the syntax @samp{name value}, where the names are
12827 listed below and the value can be given either literally, in hat
12828 notation (@samp{^@var{c}}), or as an integer which may start with
12829 @samp{0x} to indicate hexadecimal, @samp{0} to indicate octal, or
12830 any other digit to indicate decimal.
12832 @cindex disabling special characters
12833 @kindex u@r{, and disabling special characters}
12834 For GNU stty, giving a value of @code{^-} or @code{undef} disables that
12835 special character. (This is incompatible with Ultrix @command{stty},
12836 which uses a value of @samp{u} to disable a special character. GNU
12837 @command{stty} treats a value @samp{u} like any other, namely to set that
12838 special character to @key{U}.)
12844 Send an interrupt signal.
12848 Send a quit signal.
12852 Erase the last character typed.
12856 Erase the current line.
12860 Send an end of file (terminate the input).
12868 Alternate character to end the line. Non-@acronym{POSIX}.
12872 Switch to a different shell layer. Non-@acronym{POSIX}.
12876 Restart the output after stopping it.
12884 Send a terminal stop signal.
12888 Send a terminal stop signal after flushing the input. Non-@acronym{POSIX}.
12892 Redraw the current line. Non-@acronym{POSIX}.
12896 Erase the last word typed. Non-@acronym{POSIX}.
12900 Enter the next character typed literally, even if it is a special
12901 character. Non-@acronym{POSIX}.
12906 @subsection Special settings
12908 @cindex special settings
12913 Set the minimum number of characters that will satisfy a read until
12914 the time value has expired, when @option{-icanon} is set.
12918 Set the number of tenths of a second before reads time out if the minimum
12919 number of characters have not been read, when @option{-icanon} is set.
12921 @item ispeed @var{n}
12923 Set the input speed to @var{n}.
12925 @item ospeed @var{n}
12927 Set the output speed to @var{n}.
12931 Tell the tty kernel driver that the terminal has @var{n} rows. Non-@acronym{POSIX}.
12934 @itemx columns @var{n}
12937 Tell the kernel that the terminal has @var{n} columns. Non-@acronym{POSIX}.
12943 Print the number of rows and columns that the kernel thinks the
12944 terminal has. (Systems that don't support rows and columns in the kernel
12945 typically use the environment variables @env{LINES} and @env{COLUMNS}
12946 instead; however, GNU @command{stty} does not know anything about them.)
12947 Non-@acronym{POSIX}.
12951 Use line discipline @var{n}. Non-@acronym{POSIX}.
12955 Print the terminal speed.
12958 @cindex baud rate, setting
12959 Set the input and output speeds to @var{n}. @var{n} can be one of: 0
12960 50 75 110 134 134.5 150 200 300 600 1200 1800 2400 4800 9600 19200
12961 38400 @code{exta} @code{extb}. @code{exta} is the same as 19200;
12962 @code{extb} is the same as 38400. Many systems, including GNU/Linux,
12963 support higher speeds. The @command{stty} command includes support
12980 4000000 where the system supports these.
12981 0 hangs up the line if @option{-clocal} is set.
12985 @node printenv invocation
12986 @section @command{printenv}: Print all or some environment variables
12989 @cindex printing all or some environment variables
12990 @cindex environment variables, printing
12992 @command{printenv} prints environment variable values. Synopsis:
12995 printenv [@var{option}] [@var{variable}]@dots{}
12998 If no @var{variable}s are specified, @command{printenv} prints the value of
12999 every environment variable. Otherwise, it prints the value of each
13000 @var{variable} that is set, and nothing for those that are not set.
13002 The program accepts the following option. Also see @ref{Common options}.
13010 @cindex exit status of @command{printenv}
13014 0 if all variables specified were found
13015 1 if at least one specified variable was not found
13016 2 if a write error occurred
13020 @node tty invocation
13021 @section @command{tty}: Print file name of terminal on standard input
13024 @cindex print terminal file name
13025 @cindex terminal file name, printing
13027 @command{tty} prints the file name of the terminal connected to its standard
13028 input. It prints @samp{not a tty} if standard input is not a terminal.
13032 tty [@var{option}]@dots{}
13035 The program accepts the following option. Also see @ref{Common options}.
13045 Print nothing; only return an exit status.
13049 @cindex exit status of @command{tty}
13053 0 if standard input is a terminal
13054 1 if standard input is not a terminal
13055 2 if given incorrect arguments
13056 3 if a write error occurs
13060 @node User information
13061 @chapter User information
13063 @cindex user information, commands for
13064 @cindex commands for printing user information
13066 This section describes commands that print user-related information:
13067 logins, groups, and so forth.
13070 * id invocation:: Print user identity.
13071 * logname invocation:: Print current login name.
13072 * whoami invocation:: Print effective user ID.
13073 * groups invocation:: Print group names a user is in.
13074 * users invocation:: Print login names of users currently logged in.
13075 * who invocation:: Print who is currently logged in.
13079 @node id invocation
13080 @section @command{id}: Print user identity
13083 @cindex real user and group IDs, printing
13084 @cindex effective user and group IDs, printing
13085 @cindex printing real and effective user and group IDs
13087 @command{id} prints information about the given user, or the process
13088 running it if no user is specified. Synopsis:
13091 id [@var{option}]@dots{} [@var{username}]
13094 @vindex POSIXLY_CORRECT
13095 By default, it prints the real user ID, real group ID, effective user ID
13096 if different from the real user ID, effective group ID if different from
13097 the real group ID, and supplemental group IDs.
13098 In addition, if SELinux
13099 is enabled and the @env{POSIXLY_CORRECT} environment variable is not set,
13100 then print @samp{context=@var{c}}, where @var{c} is the security context.
13102 Each of these numeric values is preceded by an identifying string and
13103 followed by the corresponding user or group name in parentheses.
13105 The options cause @command{id} to print only part of the above information.
13106 Also see @ref{Common options}.
13113 Print only the group ID.
13119 Print only the group ID and the supplementary groups.
13125 Print the user or group name instead of the ID number. Requires
13126 @option{-u}, @option{-g}, or @option{-G}.
13132 Print the real, instead of effective, user or group ID. Requires
13133 @option{-u}, @option{-g}, or @option{-G}.
13139 Print only the user ID.
13146 @cindex security context
13147 Print only the security context of the current user.
13148 If SELinux is disabled then print a warning and
13149 set the exit status to 1.
13155 @macro primaryAndSupplementaryGroups{cmd,arg}
13156 Primary and supplementary groups for a process are normally inherited
13157 from its parent and are usually unchanged since login. This means
13158 that if you change the group database after logging in, @command{\cmd\}
13159 will not reflect your changes within your existing login session.
13160 Running @command{\cmd\} with a \arg\ causes the user and group
13161 database to be consulted afresh, and so will give a different result.
13163 @primaryAndSupplementaryGroups{id,user argument}
13165 @node logname invocation
13166 @section @command{logname}: Print current login name
13169 @cindex printing user's login name
13170 @cindex login name, printing
13171 @cindex user name, printing
13174 @command{logname} prints the calling user's name, as found in a
13175 system-maintained file (often @file{/var/run/utmp} or
13176 @file{/etc/utmp}), and exits with a status of 0. If there is no entry
13177 for the calling process, @command{logname} prints
13178 an error message and exits with a status of 1.
13180 The only options are @option{--help} and @option{--version}. @xref{Common
13186 @node whoami invocation
13187 @section @command{whoami}: Print effective user ID
13190 @cindex effective user ID, printing
13191 @cindex printing the effective user ID
13193 @command{whoami} prints the user name associated with the current
13194 effective user ID. It is equivalent to the command @samp{id -un}.
13196 The only options are @option{--help} and @option{--version}. @xref{Common
13202 @node groups invocation
13203 @section @command{groups}: Print group names a user is in
13206 @cindex printing groups a user is in
13207 @cindex supplementary groups, printing
13209 @command{groups} prints the names of the primary and any supplementary
13210 groups for each given @var{username}, or the current process if no names
13211 are given. If more than one name is given, the name of each user is
13213 the list of that user's groups and the user name is separated from the
13214 group list by a colon. Synopsis:
13217 groups [@var{username}]@dots{}
13220 The group lists are equivalent to the output of the command @samp{id -Gn}.
13222 @primaryAndSupplementaryGroups{groups,list of users}
13224 The only options are @option{--help} and @option{--version}. @xref{Common
13230 @node users invocation
13231 @section @command{users}: Print login names of users currently logged in
13234 @cindex printing current usernames
13235 @cindex usernames, printing current
13237 @cindex login sessions, printing users with
13238 @command{users} prints on a single line a blank-separated list of user
13239 names of users currently logged in to the current host. Each user name
13240 corresponds to a login session, so if a user has more than one login
13241 session, that user's name will appear the same number of times in the
13250 With no @var{file} argument, @command{users} extracts its information from
13251 a system-maintained file (often @file{/var/run/utmp} or
13252 @file{/etc/utmp}). If a file argument is given, @command{users} uses
13253 that file instead. A common choice is @file{/var/log/wtmp}.
13255 The only options are @option{--help} and @option{--version}. @xref{Common
13261 @node who invocation
13262 @section @command{who}: Print who is currently logged in
13265 @cindex printing current user information
13266 @cindex information, about current users
13268 @command{who} prints information about users who are currently logged on.
13272 @command{who} [@var{option}] [@var{file}] [am i]
13275 @cindex terminal lines, currently used
13277 @cindex remote hostname
13278 If given no non-option arguments, @command{who} prints the following
13279 information for each user currently logged on: login name, terminal
13280 line, login time, and remote hostname or X display.
13284 If given one non-option argument, @command{who} uses that instead of
13285 a default system-maintained file (often @file{/var/run/utmp} or
13286 @file{/etc/utmp}) as the name of the file containing the record of
13287 users logged on. @file{/var/log/wtmp} is commonly given as an argument
13288 to @command{who} to look at who has previously logged on.
13292 If given two non-option arguments, @command{who} prints only the entry
13293 for the user running it (determined from its standard input), preceded
13294 by the hostname. Traditionally, the two arguments given are @samp{am
13295 i}, as in @samp{who am i}.
13298 Time stamps are listed according to the time zone rules specified by
13299 the @env{TZ} environment variable, or by the system default rules if
13300 @env{TZ} is not set. @xref{TZ Variable,, Specifying the Time Zone
13301 with @env{TZ}, libc, The GNU C Library Reference Manual}.
13303 The program accepts the following options. Also see @ref{Common options}.
13311 Same as @samp{-b -d --login -p -r -t -T -u}.
13317 Print the date and time of last system boot.
13323 Print information corresponding to dead processes.
13329 Print a line of column headings.
13335 List only the entries that correspond to processes via which the
13336 system is waiting for a user to login. The user name is always @samp{LOGIN}.
13340 Attempt to canonicalize hostnames found in utmp through a DNS lookup. This
13341 is not the default because it can cause significant delays on systems with
13342 automatic dial-up internet access.
13346 Same as @samp{who am i}.
13352 List active processes spawned by init.
13358 Print only the login names and the number of users logged on.
13359 Overrides all other options.
13364 @opindex --runlevel
13365 Print the current (and maybe previous) run-level of the init process.
13369 Ignored; for compatibility with other versions of @command{who}.
13375 Print last system clock change.
13380 After the login time, print the number of hours and minutes that the
13381 user has been idle. @samp{.} means the user was active in the last minute.
13382 @samp{old} means the user has been idle for more than 24 hours.
13393 @opindex --writable
13394 @cindex message status
13395 @pindex write@r{, allowed}
13396 After each login name print a character indicating the user's message status:
13399 @samp{+} allowing @code{write} messages
13400 @samp{-} disallowing @code{write} messages
13401 @samp{?} cannot find terminal device
13409 @node System context
13410 @chapter System context
13412 @cindex system context
13413 @cindex context, system
13414 @cindex commands for system context
13416 This section describes commands that print or change system-wide
13420 * date invocation:: Print or set system date and time.
13421 * arch invocation:: Print machine hardware name.
13422 * nproc invocation:: Print the number of processors.
13423 * uname invocation:: Print system information.
13424 * hostname invocation:: Print or set system name.
13425 * hostid invocation:: Print numeric host identifier.
13426 * uptime invocation:: Print system uptime and load.
13429 @node date invocation
13430 @section @command{date}: Print or set system date and time
13433 @cindex time, printing or setting
13434 @cindex printing the current time
13439 date [@var{option}]@dots{} [+@var{format}]
13440 date [-u|--utc|--universal] @c this avoids a newline in the output
13441 [ MMDDhhmm[[CC]YY][.ss] ]
13445 Invoking @command{date} with no @var{format} argument is equivalent to invoking
13446 it with a default format that depends on the @env{LC_TIME} locale category.
13447 In the default C locale, this format is @samp{'+%a %b %e %H:%M:%S %Z %Y'},
13448 so the output looks like @samp{Thu Mar @ 3 13:47:51 PST 2005}.
13451 Normally, @command{date} uses the time zone rules indicated by the
13452 @env{TZ} environment variable, or the system default rules if @env{TZ}
13453 is not set. @xref{TZ Variable,, Specifying the Time Zone with
13454 @env{TZ}, libc, The GNU C Library Reference Manual}.
13456 @findex strftime @r{and @command{date}}
13457 @cindex time formats
13458 @cindex formatting times
13459 If given an argument that starts with a @samp{+}, @command{date} prints the
13460 current date and time (or the date and time specified by the
13461 @option{--date} option, see below) in the format defined by that argument,
13462 which is similar to that of the @code{strftime} function. Except for
13463 conversion specifiers, which start with @samp{%}, characters in the
13464 format string are printed unchanged. The conversion specifiers are
13470 * Time conversion specifiers:: %[HIklMNpPrRsSTXzZ]
13471 * Date conversion specifiers:: %[aAbBcCdDeFgGhjmuUVwWxyY]
13472 * Literal conversion specifiers:: %[%nt]
13473 * Padding and other flags:: Pad with zeros, spaces, etc.
13474 * Setting the time:: Changing the system clock.
13475 * Options for date:: Instead of the current time.
13477 * Date input formats:: Specifying date strings.
13479 * Examples of date:: Examples.
13482 @node Time conversion specifiers
13483 @subsection Time conversion specifiers
13485 @cindex time conversion specifiers
13486 @cindex conversion specifiers, time
13488 @command{date} conversion specifiers related to times.
13492 hour (@samp{00}@dots{}@samp{23})
13494 hour (@samp{01}@dots{}@samp{12})
13496 hour (@samp{ 0}@dots{}@samp{23}).
13497 This is a @acronym{GNU} extension.
13499 hour (@samp{ 1}@dots{}@samp{12}).
13500 This is a @acronym{GNU} extension.
13502 minute (@samp{00}@dots{}@samp{59})
13504 nanoseconds (@samp{000000000}@dots{}@samp{999999999}).
13505 This is a @acronym{GNU} extension.
13507 locale's equivalent of either @samp{AM} or @samp{PM};
13508 blank in many locales.
13509 Noon is treated as @samp{PM} and midnight as @samp{AM}.
13511 like @samp{%p}, except lower case.
13512 This is a @acronym{GNU} extension.
13514 locale's 12-hour clock time (e.g., @samp{11:11:04 PM})
13516 24-hour hour and minute. Same as @samp{%H:%M}.
13517 This is a @acronym{GNU} extension.
13519 @cindex epoch, seconds since
13520 @cindex seconds since the epoch
13521 @cindex beginning of time
13522 seconds since the epoch, i.e., since 1970-01-01 00:00:00 UTC.
13523 Leap seconds are not counted unless leap second support is available.
13524 @xref{%s-examples}, for examples.
13525 This is a @acronym{GNU} extension.
13527 second (@samp{00}@dots{}@samp{60}).
13528 This may be @samp{60} if leap seconds are supported.
13530 24-hour hour, minute, and second. Same as @samp{%H:%M:%S}.
13532 locale's time representation (e.g., @samp{23:13:48})
13534 @w{@acronym{RFC} 2822/@acronym{ISO} 8601} style numeric time zone
13535 (e.g., @samp{-0600} or @samp{+0530}), or nothing if no
13536 time zone is determinable. This value reflects the numeric time zone
13537 appropriate for the current time, using the time zone rules specified
13538 by the @env{TZ} environment variable.
13539 The time (and optionally, the time zone rules) can be overridden
13540 by the @option{--date} option.
13541 This is a @acronym{GNU} extension.
13543 @w{@acronym{RFC} 3339/@acronym{ISO} 8601} style numeric time zone with
13544 @samp{:} (e.g., @samp{-06:00} or @samp{+05:30}), or nothing if no time
13545 zone is determinable.
13546 This is a @acronym{GNU} extension.
13548 Numeric time zone to the nearest second with @samp{:} (e.g.,
13549 @samp{-06:00:00} or @samp{+05:30:00}), or nothing if no time zone is
13551 This is a @acronym{GNU} extension.
13553 Numeric time zone with @samp{:} using the minimum necessary precision
13554 (e.g., @samp{-06}, @samp{+05:30}, or @samp{-04:56:02}), or nothing if
13555 no time zone is determinable.
13556 This is a @acronym{GNU} extension.
13558 alphabetic time zone abbreviation (e.g., @samp{EDT}), or nothing if no
13559 time zone is determinable. See @samp{%z} for how it is determined.
13563 @node Date conversion specifiers
13564 @subsection Date conversion specifiers
13566 @cindex date conversion specifiers
13567 @cindex conversion specifiers, date
13569 @command{date} conversion specifiers related to dates.
13573 locale's abbreviated weekday name (e.g., @samp{Sun})
13575 locale's full weekday name, variable length (e.g., @samp{Sunday})
13577 locale's abbreviated month name (e.g., @samp{Jan})
13579 locale's full month name, variable length (e.g., @samp{January})
13581 locale's date and time (e.g., @samp{Thu Mar @ 3 23:05:25 2005})
13583 century. This is like @samp{%Y}, except the last two digits are omitted.
13584 For example, it is @samp{20} if @samp{%Y} is @samp{2000},
13585 and is @samp{-0} if @samp{%Y} is @samp{-001}.
13586 It is normally at least two characters, but it may be more.
13588 day of month (e.g., @samp{01})
13590 date; same as @samp{%m/%d/%y}
13592 day of month, space padded; same as @samp{%_d}
13594 full date in @acronym{ISO} 8601 format; same as @samp{%Y-%m-%d}.
13595 This is a good choice for a date format, as it is standard and
13596 is easy to sort in the usual case where years are in the range
13598 This is a @acronym{GNU} extension.
13600 year corresponding to the @acronym{ISO} week number, but without the century
13601 (range @samp{00} through @samp{99}). This has the same format and value
13602 as @samp{%y}, except that if the @acronym{ISO} week number (see
13604 to the previous or next year, that year is used instead.
13605 This is a @acronym{GNU} extension.
13607 year corresponding to the @acronym{ISO} week number. This has the
13608 same format and value as @samp{%Y}, except that if the @acronym{ISO}
13610 @samp{%V}) belongs to the previous or next year, that year is used
13612 It is normally useful only if @samp{%V} is also used;
13613 for example, the format @samp{%G-%m-%d} is probably a mistake,
13614 since it combines the ISO week number year with the conventional month and day.
13615 This is a @acronym{GNU} extension.
13619 day of year (@samp{001}@dots{}@samp{366})
13621 month (@samp{01}@dots{}@samp{12})
13623 day of week (@samp{1}@dots{}@samp{7}) with @samp{1} corresponding to Monday
13625 week number of year, with Sunday as the first day of the week
13626 (@samp{00}@dots{}@samp{53}).
13627 Days in a new year preceding the first Sunday are in week zero.
13629 @acronym{ISO} week number, that is, the
13630 week number of year, with Monday as the first day of the week
13631 (@samp{01}@dots{}@samp{53}).
13632 If the week containing January 1 has four or more days in
13633 the new year, then it is considered week 1; otherwise, it is week 53 of
13634 the previous year, and the next week is week 1. (See the @acronym{ISO} 8601
13637 day of week (@samp{0}@dots{}@samp{6}) with 0 corresponding to Sunday
13639 week number of year, with Monday as first day of week
13640 (@samp{00}@dots{}@samp{53}).
13641 Days in a new year preceding the first Monday are in week zero.
13643 locale's date representation (e.g., @samp{12/31/99})
13645 last two digits of year (@samp{00}@dots{}@samp{99})
13647 year. This is normally at least four characters, but it may be more.
13648 Year @samp{0000} precedes year @samp{0001}, and year @samp{-001}
13649 precedes year @samp{0000}.
13653 @node Literal conversion specifiers
13654 @subsection Literal conversion specifiers
13656 @cindex literal conversion specifiers
13657 @cindex conversion specifiers, literal
13659 @command{date} conversion specifiers that produce literal strings.
13671 @node Padding and other flags
13672 @subsection Padding and other flags
13674 @cindex numeric field padding
13675 @cindex padding of numeric fields
13676 @cindex fields, padding numeric
13678 Unless otherwise specified, @command{date} normally pads numeric fields
13679 with zeros, so that, for
13680 example, numeric months are always output as two digits.
13681 Seconds since the epoch are not padded, though,
13682 since there is no natural width for them.
13684 As a @acronym{GNU} extension, @command{date} recognizes any of the
13685 following optional flags after the @samp{%}:
13689 (hyphen) Do not pad the field; useful if the output is intended for
13692 (underscore) Pad with spaces; useful if you need a fixed
13693 number of characters in the output, but zeros are too distracting.
13695 (zero) Pad with zeros even if the conversion specifier
13696 would normally pad with spaces.
13698 Use upper case characters if possible.
13700 Use opposite case characters if possible.
13701 A field that is normally upper case becomes lower case, and vice versa.
13705 Here are some examples of padding:
13708 date +%d/%m -d "Feb 1"
13710 date +%-d/%-m -d "Feb 1"
13712 date +%_d/%_m -d "Feb 1"
13716 As a @acronym{GNU} extension, you can specify the field width
13717 (after any flag, if present) as a decimal number. If the natural size of the
13718 output of the field has less than the specified number of characters,
13719 the result is written right adjusted and padded to the given
13720 size. For example, @samp{%9B} prints the right adjusted month name in
13721 a field of width 9.
13723 An optional modifier can follow the optional flag and width
13724 specification. The modifiers are:
13728 Use the locale's alternate representation for date and time. This
13729 modifier applies to the @samp{%c}, @samp{%C}, @samp{%x}, @samp{%X},
13730 @samp{%y} and @samp{%Y} conversion specifiers. In a Japanese locale, for
13731 example, @samp{%Ex} might yield a date format based on the Japanese
13735 Use the locale's alternate numeric symbols for numbers. This modifier
13736 applies only to numeric conversion specifiers.
13739 If the format supports the modifier but no alternate representation
13740 is available, it is ignored.
13743 @node Setting the time
13744 @subsection Setting the time
13746 @cindex setting the time
13747 @cindex time setting
13748 @cindex appropriate privileges
13750 If given an argument that does not start with @samp{+}, @command{date} sets
13751 the system clock to the date and time specified by that argument (as
13752 described below). You must have appropriate privileges to set the
13753 system clock. The @option{--date} and @option{--set} options may not be
13754 used with such an argument. The @option{--universal} option may be used
13755 with such an argument to indicate that the specified date and time are
13756 relative to Coordinated Universal Time rather than to the local time
13759 The argument must consist entirely of digits, which have the following
13772 first two digits of year (optional)
13774 last two digits of year (optional)
13779 The @option{--set} option also sets the system clock; see the next section.
13782 @node Options for date
13783 @subsection Options for @command{date}
13785 @cindex @command{date} options
13786 @cindex options for @command{date}
13788 The program accepts the following options. Also see @ref{Common options}.
13792 @item -d @var{datestr}
13793 @itemx --date=@var{datestr}
13796 @cindex parsing date strings
13797 @cindex date strings, parsing
13798 @cindex arbitrary date strings, parsing
13801 @opindex next @var{day}
13802 @opindex last @var{day}
13803 Display the date and time specified in @var{datestr} instead of the
13804 current date and time. @var{datestr} can be in almost any common
13805 format. It can contain month names, time zones, @samp{am} and @samp{pm},
13806 @samp{yesterday}, etc. For example, @option{--date="2004-02-27
13807 14:19:13.489392193 +0530"} specifies the instant of time that is
13808 489,392,193 nanoseconds after February 27, 2004 at 2:19:13 PM in a
13809 time zone that is 5 hours and 30 minutes east of @acronym{UTC}.@*
13810 Note: input currently must be in locale independent format. E.g., the
13811 LC_TIME=C below is needed to print back the correct date in many locales:
13813 date -d "$(LC_TIME=C date)"
13815 @xref{Date input formats}.
13817 @item -f @var{datefile}
13818 @itemx --file=@var{datefile}
13821 Parse each line in @var{datefile} as with @option{-d} and display the
13822 resulting date and time. If @var{datefile} is @samp{-}, use standard
13823 input. This is useful when you have many dates to process, because the
13824 system overhead of starting up the @command{date} executable many times can
13827 @item -r @var{file}
13828 @itemx --reference=@var{file}
13830 @opindex --reference
13831 Display the date and time of the last modification of @var{file},
13832 instead of the current date and time.
13839 @opindex --rfc-2822
13840 Display the date and time using the format @samp{%a, %d %b %Y %H:%M:%S
13841 %z}, evaluated in the C locale so abbreviations are always in English.
13845 Fri, 09 Sep 2005 13:51:39 -0700
13848 This format conforms to
13849 @uref{ftp://ftp.rfc-editor.org/in-notes/rfc2822.txt, Internet
13850 @acronym{RFCs} 2822} and
13851 @uref{ftp://ftp.rfc-editor.org/in-notes/rfc822.txt, 822}, the
13852 current and previous standards for Internet email.
13854 @item --rfc-3339=@var{timespec}
13855 @opindex --rfc-3339=@var{timespec}
13856 Display the date using a format specified by
13857 @uref{ftp://ftp.rfc-editor.org/in-notes/rfc3339.txt, Internet
13858 @acronym{RFC} 3339}. This is a subset of the @acronym{ISO} 8601
13859 format, except that it also permits applications to use a space rather
13860 than a @samp{T} to separate dates from times. Unlike the other
13861 standard formats, @acronym{RFC} 3339 format is always suitable as
13862 input for the @option{--date} (@option{-d}) and @option{--file}
13863 (@option{-f}) options, regardless of the current locale.
13865 The argument @var{timespec} specifies how much of the time to include.
13866 It can be one of the following:
13870 Print just the full-date, e.g., @samp{2005-09-14}.
13871 This is equivalent to the format @samp{%Y-%m-%d}.
13874 Print the full-date and full-time separated by a space, e.g.,
13875 @samp{2005-09-14 00:56:06+05:30}. The output ends with a numeric
13876 time-offset; here the @samp{+05:30} means that local time is five
13877 hours and thirty minutes east of @acronym{UTC}. This is equivalent to
13878 the format @samp{%Y-%m-%d %H:%M:%S%:z}.
13881 Like @samp{seconds}, but also print nanoseconds, e.g.,
13882 @samp{2005-09-14 00:56:06.998458565+05:30}.
13883 This is equivalent to the format @samp{%Y-%m-%d %H:%M:%S.%N%:z}.
13887 @item -s @var{datestr}
13888 @itemx --set=@var{datestr}
13891 Set the date and time to @var{datestr}. See @option{-d} above.
13898 @opindex --universal
13899 @cindex Coordinated Universal Time
13901 @cindex Greenwich Mean Time
13904 Use Coordinated Universal Time (@acronym{UTC}) by operating as if the
13905 @env{TZ} environment variable were set to the string @samp{UTC0}.
13907 Universal Time is often called ``Greenwich Mean Time'' (@sc{gmt}) for
13908 historical reasons.
13912 @node Examples of date
13913 @subsection Examples of @command{date}
13915 @cindex examples of @command{date}
13917 Here are a few examples. Also see the documentation for the @option{-d}
13918 option in the previous section.
13923 To print the date of the day before yesterday:
13926 date --date='2 days ago'
13930 To print the date of the day three months and one day hence:
13933 date --date='3 months 1 day'
13937 To print the day of year of Christmas in the current year:
13940 date --date='25 Dec' +%j
13944 To print the current full month name and the day of the month:
13950 But this may not be what you want because for the first nine days of
13951 the month, the @samp{%d} expands to a zero-padded two-digit field,
13952 for example @samp{date -d 1may '+%B %d'} will print @samp{May 01}.
13955 To print a date without the leading zero for one-digit days
13956 of the month, you can use the (@acronym{GNU} extension)
13957 @samp{-} flag to suppress
13958 the padding altogether:
13961 date -d 1may '+%B %-d
13965 To print the current date and time in the format required by many
13966 non-@acronym{GNU} versions of @command{date} when setting the system clock:
13969 date +%m%d%H%M%Y.%S
13973 To set the system clock forward by two minutes:
13976 date --set='+2 minutes'
13980 To print the date in @acronym{RFC} 2822 format,
13981 use @samp{date --rfc-2822}. Here is some example output:
13984 Fri, 09 Sep 2005 13:51:39 -0700
13987 @anchor{%s-examples}
13989 To convert a date string to the number of seconds since the epoch
13990 (which is 1970-01-01 00:00:00 UTC), use the @option{--date} option with
13991 the @samp{%s} format. That can be useful in sorting and/or graphing
13992 and/or comparing data by date. The following command outputs the
13993 number of the seconds since the epoch for the time two minutes after the
13997 date --date='1970-01-01 00:02:00 +0000' +%s
14001 If you do not specify time zone information in the date string,
14002 @command{date} uses your computer's idea of the time zone when
14003 interpreting the string. For example, if your computer's time zone is
14004 that of Cambridge, Massachusetts, which was then 5 hours (i.e., 18,000
14005 seconds) behind UTC:
14008 # local time zone used
14009 date --date='1970-01-01 00:02:00' +%s
14014 If you're sorting or graphing dated data, your raw date values may be
14015 represented as seconds since the epoch. But few people can look at
14016 the date @samp{946684800} and casually note ``Oh, that's the first second
14017 of the year 2000 in Greenwich, England.''
14020 date --date='2000-01-01 UTC' +%s
14024 An alternative is to use the @option{--utc} (@option{-u}) option.
14025 Then you may omit @samp{UTC} from the date string. Although this
14026 produces the same result for @samp{%s} and many other format sequences,
14027 with a time zone offset different from zero, it would give a different
14028 result for zone-dependent formats like @samp{%z}.
14031 date -u --date=2000-01-01 +%s
14035 To convert such an unwieldy number of seconds back to
14036 a more readable form, use a command like this:
14039 # local time zone used
14040 date -d '1970-01-01 UTC 946684800 seconds' +"%Y-%m-%d %T %z"
14041 1999-12-31 19:00:00 -0500
14044 Or if you do not mind depending on the @samp{@@} feature present since
14045 coreutils 5.3.0, you could shorten this to:
14048 date -d @@946684800 +"%F %T %z"
14049 1999-12-31 19:00:00 -0500
14052 Often it is better to output UTC-relative date and time:
14055 date -u -d '1970-01-01 946684800 seconds' +"%Y-%m-%d %T %z"
14056 2000-01-01 00:00:00 +0000
14062 @node arch invocation
14063 @section @command{arch}: Print machine hardware name
14066 @cindex print machine hardware name
14067 @cindex system information, printing
14069 @command{arch} prints the machine hardware name,
14070 and is equivalent to @samp{uname -m}.
14074 arch [@var{option}]
14077 The program accepts the @ref{Common options} only.
14082 @node nproc invocation
14083 @section @command{nproc}: Print the number of available processors
14086 @cindex Print the number of processors
14087 @cindex system information, printing
14089 Print the number of processing units available to the current process,
14090 which may be less than the number of online processors.
14091 If this information is not accessible, then print the number of
14092 processors installed. If the @env{OMP_NUM_THREADS} environment variable is
14093 set, then it will determine the returned value. The result is guaranteed to be
14094 greater than zero. Synopsis:
14097 nproc [@var{option}]
14100 The program accepts the following options. Also see @ref{Common options}.
14106 Print the number of installed processors on the system, which may
14107 be greater than the number online or available to the current process.
14108 The @env{OMP_NUM_THREADS} environment variable is not honored in this case.
14110 @item --ignore=@var{number}
14112 If possible, exclude this @var{number} of processing units.
14119 @node uname invocation
14120 @section @command{uname}: Print system information
14123 @cindex print system information
14124 @cindex system information, printing
14126 @command{uname} prints information about the machine and operating system
14127 it is run on. If no options are given, @command{uname} acts as if the
14128 @option{-s} option were given. Synopsis:
14131 uname [@var{option}]@dots{}
14134 If multiple options or @option{-a} are given, the selected information is
14135 printed in this order:
14138 @var{kernel-name} @var{nodename} @var{kernel-release} @var{kernel-version}
14139 @var{machine} @var{processor} @var{hardware-platform} @var{operating-system}
14142 The information may contain internal spaces, so such output cannot be
14143 parsed reliably. In the following example, @var{release} is
14144 @samp{2.2.18ss.e820-bda652a #4 SMP Tue Jun 5 11:24:08 PDT 2001}:
14148 @result{} Linux dum 2.2.18 #4 SMP Tue Jun 5 11:24:08 PDT 2001 i686 unknown unknown GNU/Linux
14152 The program accepts the following options. Also see @ref{Common options}.
14160 Print all of the below information, except omit the processor type
14161 and the hardware platform name if they are unknown.
14164 @itemx --hardware-platform
14166 @opindex --hardware-platform
14167 @cindex implementation, hardware
14168 @cindex hardware platform
14169 @cindex platform, hardware
14170 Print the hardware platform name
14171 (sometimes called the hardware implementation).
14172 Print @samp{unknown} if the kernel does not make this information
14173 easily available, as is the case with Linux kernels.
14179 @cindex machine type
14180 @cindex hardware class
14181 @cindex hardware type
14182 Print the machine hardware name (sometimes called the hardware class
14188 @opindex --nodename
14191 @cindex network node name
14192 Print the network node hostname.
14197 @opindex --processor
14198 @cindex host processor type
14199 Print the processor type (sometimes called the instruction set
14200 architecture or ISA).
14201 Print @samp{unknown} if the kernel does not make this information
14202 easily available, as is the case with Linux kernels.
14205 @itemx --operating-system
14207 @opindex --operating-system
14208 @cindex operating system name
14209 Print the name of the operating system.
14212 @itemx --kernel-release
14214 @opindex --kernel-release
14215 @cindex kernel release
14216 @cindex release of kernel
14217 Print the kernel release.
14220 @itemx --kernel-name
14222 @opindex --kernel-name
14223 @cindex kernel name
14224 @cindex name of kernel
14225 Print the kernel name.
14226 @acronym{POSIX} 1003.1-2001 (@pxref{Standards conformance}) calls this
14227 ``the implementation of the operating system'', because the
14228 @acronym{POSIX} specification itself has no notion of ``kernel''.
14229 The kernel name might be the same as the operating system name printed
14230 by the @option{-o} or @option{--operating-system} option, but it might
14231 differ. Some operating systems (e.g., FreeBSD, HP-UX) have the same
14232 name as their underlying kernels; others (e.g., GNU/Linux, Solaris)
14236 @itemx --kernel-version
14238 @opindex --kernel-version
14239 @cindex kernel version
14240 @cindex version of kernel
14241 Print the kernel version.
14248 @node hostname invocation
14249 @section @command{hostname}: Print or set system name
14252 @cindex setting the hostname
14253 @cindex printing the hostname
14254 @cindex system name, printing
14255 @cindex appropriate privileges
14257 With no arguments, @command{hostname} prints the name of the current host
14258 system. With one argument, it sets the current host name to the
14259 specified string. You must have appropriate privileges to set the host
14263 hostname [@var{name}]
14266 The only options are @option{--help} and @option{--version}. @xref{Common
14272 @node hostid invocation
14273 @section @command{hostid}: Print numeric host identifier
14276 @cindex printing the host identifier
14278 @command{hostid} prints the numeric identifier of the current host
14279 in hexadecimal. This command accepts no arguments.
14280 The only options are @option{--help} and @option{--version}.
14281 @xref{Common options}.
14283 For example, here's what it prints on one system I use:
14290 On that system, the 32-bit quantity happens to be closely
14291 related to the system's Internet address, but that isn't always
14296 @node uptime invocation
14297 @section @command{uptime}: Print system uptime and load
14300 @cindex printing the system uptime and load
14302 @command{uptime} prints the current time, the system's uptime, the
14303 number of logged-in users and the current load average.
14305 If an argument is specified, it is used as the file to be read
14306 to discover how many users are logged in. If no argument is
14307 specified, a system default is used (@command{uptime --help} indicates
14308 the default setting).
14310 The only options are @option{--help} and @option{--version}.
14311 @xref{Common options}.
14313 For example, here's what it prints right now on one system I use:
14317 14:07 up 3:35, 3 users, load average: 1.39, 1.15, 1.04
14320 The precise method of calculation of load average varies somewhat
14321 between systems. Some systems calculate it as the average number of
14322 runnable processes over the last 1, 5 and 15 minutes, but some systems
14323 also include processes in the uninterruptible sleep state (that is,
14324 those processes which are waiting for disk I/O). The Linux kernel
14325 includes uninterruptible processes.
14327 @node SELinux context
14328 @chapter SELinux context
14330 @cindex SELinux context
14331 @cindex SELinux, context
14332 @cindex commands for SELinux context
14334 This section describes commands for operations with SELinux
14338 * chcon invocation:: Change SELinux context of file
14339 * runcon invocation:: Run a command in specified SELinux context
14342 @node chcon invocation
14343 @section @command{chcon}: Change SELinux context of file
14346 @cindex changing security context
14347 @cindex change SELinux context
14349 @command{chcon} changes the SELinux security context of the selected files.
14353 chcon [@var{option}]@dots{} @var{context} @var{file}@dots{}
14354 chcon [@var{option}]@dots{} [-u @var{user}] [-r @var{role}] [-l @var{range}] [-t @var{type}] @var{file}@dots{}
14355 chcon [@var{option}]@dots{} --reference=@var{rfile} @var{file}@dots{}
14358 Change the SELinux security context of each @var{file} to @var{context}.
14359 With @option{--reference}, change the security context of each @var{file}
14360 to that of @var{rfile}.
14362 The program accepts the following options. Also see @ref{Common options}.
14367 @itemx --no-dereference
14369 @opindex --no-dereference
14370 @cindex no dereference
14371 Affect symbolic links instead of any referenced file.
14373 @item --reference=@var{rfile}
14374 @opindex --reference
14375 @cindex reference file
14376 Use @var{rfile}'s security context rather than specifying a @var{context} value.
14381 @opindex --recursive
14382 Operate on files and directories recursively.
14385 @xref{Traversing symlinks}.
14388 @xref{Traversing symlinks}.
14391 @xref{Traversing symlinks}.
14398 Output a diagnostic for every file processed.
14400 @item -u @var{user}
14401 @itemx --user=@var{user}
14404 Set user @var{user} in the target security context.
14406 @item -r @var{role}
14407 @itemx --role=@var{role}
14410 Set role @var{role} in the target security context.
14412 @item -t @var{type}
14413 @itemx --type=@var{type}
14416 Set type @var{type} in the target security context.
14418 @item -l @var{range}
14419 @itemx --range=@var{range}
14422 Set range @var{range} in the target security context.
14428 @node runcon invocation
14429 @section @command{runcon}: Run a command in specified SELinux context
14432 @cindex run with security context
14435 @command{runcon} runs file in specified SELinux security context.
14439 runcon @var{context} @var{command} [@var{args}]
14440 runcon [ -c ] [-u @var{user}] [-r @var{role}] [-t @var{type}] [-l @var{range}] @var{command} [@var{args}]
14443 Run @var{command} with completely-specified @var{context}, or with
14444 current or transitioned security context modified by one or more of @var{level},
14445 @var{role}, @var{type} and @var{user}.
14447 If none of @option{-c}, @option{-t}, @option{-u}, @option{-r}, or @option{-l}
14448 is specified, the first argument is used as the complete context.
14449 Any additional arguments after @var{command}
14450 are interpreted as arguments to the command.
14452 With neither @var{context} nor @var{command}, print the current security context.
14454 The program accepts the following options. Also see @ref{Common options}.
14462 Compute process transition context before modifying.
14464 @item -u @var{user}
14465 @itemx --user=@var{user}
14468 Set user @var{user} in the target security context.
14470 @item -r @var{role}
14471 @itemx --role=@var{role}
14474 Set role @var{role} in the target security context.
14476 @item -t @var{type}
14477 @itemx --type=@var{type}
14480 Set type @var{type} in the target security context.
14482 @item -l @var{range}
14483 @itemx --range=@var{range}
14486 Set range @var{range} in the target security context.
14490 @cindex exit status of @command{runcon}
14494 126 if @var{command} is found but cannot be invoked
14495 127 if @command{runcon} itself fails or if @var{command} cannot be found
14496 the exit status of @var{command} otherwise
14499 @node Modified command invocation
14500 @chapter Modified command invocation
14502 @cindex modified command invocation
14503 @cindex invocation of commands, modified
14504 @cindex commands for invoking other commands
14506 This section describes commands that run other commands in some context
14507 different than the current one: a modified environment, as a different
14511 * chroot invocation:: Modify the root directory.
14512 * env invocation:: Modify environment variables.
14513 * nice invocation:: Modify niceness.
14514 * nohup invocation:: Immunize to hangups.
14515 * stdbuf invocation:: Modify buffering of standard streams.
14516 * su invocation:: Modify user and group ID.
14517 * timeout invocation:: Run with time limit.
14521 @node chroot invocation
14522 @section @command{chroot}: Run a command with a different root directory
14525 @cindex running a program in a specified root directory
14526 @cindex root directory, running a program in a specified
14528 @command{chroot} runs a command with a specified root directory.
14529 On many systems, only the super-user can do this.@footnote{However,
14530 some systems (e.g., FreeBSD) can be configured to allow certain regular
14531 users to use the @code{chroot} system call, and hence to run this program.
14532 Also, on Cygwin, anyone can run the @command{chroot} command, because the
14533 underlying function is non-privileged due to lack of support in MS-Windows.}
14537 chroot @var{option} @var{newroot} [@var{command} [@var{args}]@dots{}]
14538 chroot @var{option}
14541 Ordinarily, file names are looked up starting at the root of the
14542 directory structure, i.e., @file{/}. @command{chroot} changes the root to
14543 the directory @var{newroot} (which must exist) and then runs
14544 @var{command} with optional @var{args}. If @var{command} is not
14545 specified, the default is the value of the @env{SHELL} environment
14546 variable or @command{/bin/sh} if not set, invoked with the @option{-i} option.
14547 @var{command} must not be a special built-in utility
14548 (@pxref{Special built-in utilities}).
14550 The program accepts the following options. Also see @ref{Common options}.
14551 Options must precede operands.
14555 @itemx --userspec=@var{user}[:@var{group}]
14556 @opindex --userspec
14557 By default, @var{command} is run with the same credentials
14558 as the invoking process.
14559 Use this option to run it as a different @var{user} and/or with a
14560 different primary @var{group}.
14562 @itemx --groups=@var{groups}
14564 Use this option to specify the supplementary @var{groups} to be
14565 used by the new process.
14566 The items in the list (names or numeric IDs) must be separated by commas.
14570 Here are a few tips to help avoid common problems in using chroot.
14571 To start with a simple example, make @var{command} refer to a statically
14572 linked binary. If you were to use a dynamically linked executable, then
14573 you'd have to arrange to have the shared libraries in the right place under
14574 your new root directory.
14576 For example, if you create a statically linked @command{ls} executable,
14577 and put it in @file{/tmp/empty}, you can run this command as root:
14580 $ chroot /tmp/empty /ls -Rl /
14583 Then you'll see output like this:
14588 -rwxr-xr-x 1 0 0 1041745 Aug 16 11:17 ls
14591 If you want to use a dynamically linked executable, say @command{bash},
14592 then first run @samp{ldd bash} to see what shared objects it needs.
14593 Then, in addition to copying the actual binary, also copy the listed
14594 files to the required positions under your intended new root directory.
14595 Finally, if the executable requires any other files (e.g., data, state,
14596 device files), copy them into place, too.
14598 @cindex exit status of @command{chroot}
14602 125 if @command{chroot} itself fails
14603 126 if @var{command} is found but cannot be invoked
14604 127 if @var{command} cannot be found
14605 the exit status of @var{command} otherwise
14609 @node env invocation
14610 @section @command{env}: Run a command in a modified environment
14613 @cindex environment, running a program in a modified
14614 @cindex modified environment, running a program in a
14615 @cindex running a program in a modified environment
14617 @command{env} runs a command with a modified environment. Synopses:
14620 env [@var{option}]@dots{} [@var{name}=@var{value}]@dots{} @c
14621 [@var{command} [@var{args}]@dots{}]
14625 Operands of the form @samp{@var{variable}=@var{value}} set
14626 the environment variable @var{variable} to value @var{value}.
14627 @var{value} may be empty (@samp{@var{variable}=}). Setting a variable
14628 to an empty value is different from unsetting it.
14629 These operands are evaluated left-to-right, so if two operands
14630 mention the same variable the earlier is ignored.
14632 Environment variable names can be empty, and can contain any
14633 characters other than @samp{=} and @acronym{ASCII} @sc{nul}.
14634 However, it is wise to limit yourself to names that
14635 consist solely of underscores, digits, and @acronym{ASCII} letters,
14636 and that begin with a non-digit, as applications like the shell do not
14637 work well with other names.
14640 The first operand that does not contain the character @samp{=}
14641 specifies the program to invoke; it is
14642 searched for according to the @env{PATH} environment variable. Any
14643 remaining arguments are passed as arguments to that program.
14644 The program should not be a special built-in utility
14645 (@pxref{Special built-in utilities}).
14647 Modifications to @env{PATH} take effect prior to searching for
14648 @var{command}. Use caution when reducing @env{PATH}; behavior is
14649 not portable when @env{PATH} is undefined or omits key directories
14650 such as @file{/bin}.
14652 In the rare case that a utility contains a @samp{=} in the name, the
14653 only way to disambiguate it from a variable assignment is to use an
14654 intermediate command for @var{command}, and pass the problematic
14655 program name via @var{args}. For example, if @file{./prog=} is an
14656 executable in the current @env{PATH}:
14659 env prog= true # runs 'true', with prog= in environment
14660 env ./prog= true # runs 'true', with ./prog= in environment
14661 env -- prog= true # runs 'true', with prog= in environment
14662 env sh -c '\prog= true' # runs 'prog=' with argument 'true'
14663 env sh -c 'exec "$@@"' sh prog= true # also runs 'prog='
14666 @cindex environment, printing
14668 If no command name is specified following the environment
14669 specifications, the resulting environment is printed. This is like
14670 specifying the @command{printenv} program.
14672 For some examples, suppose the environment passed to @command{env}
14673 contains @samp{LOGNAME=rms}, @samp{EDITOR=emacs}, and
14674 @samp{PATH=.:/gnubin:/hacks}:
14679 Output the current environment.
14681 $ env | LC_ALL=C sort
14684 PATH=.:/gnubin:/hacks
14688 Run @command{foo} with a reduced environment, preserving only the
14689 original @env{PATH} to avoid problems in locating @command{foo}.
14691 env - PATH="$PATH" foo
14695 Run @command{foo} with the environment containing @samp{LOGNAME=rms},
14696 @samp{EDITOR=emacs}, and @samp{PATH=.:/gnubin:/hacks}, and guarantees
14697 that @command{foo} was found in the file system rather than as a shell
14704 Run @command{nemacs} with the environment containing @samp{LOGNAME=foo},
14705 @samp{EDITOR=emacs}, @samp{PATH=.:/gnubin:/hacks}, and
14706 @samp{DISPLAY=gnu:0}.
14708 env DISPLAY=gnu:0 LOGNAME=foo nemacs
14712 Attempt to run the program @command{/energy/--} (as that is the only
14713 possible path search result); if the command exists, the environment
14714 will contain @samp{LOGNAME=rms} and @samp{PATH=/energy}, and the
14715 arguments will be @samp{e=mc2}, @samp{bar}, and @samp{baz}.
14717 env -u EDITOR PATH=/energy -- e=mc2 bar baz
14723 The program accepts the following options. Also see @ref{Common options}.
14724 Options must precede operands.
14730 @item -u @var{name}
14731 @itemx --unset=@var{name}
14734 Remove variable @var{name} from the environment, if it was in the
14739 @itemx --ignore-environment
14742 @opindex --ignore-environment
14743 Start with an empty environment, ignoring the inherited environment.
14747 @cindex exit status of @command{env}
14751 0 if no @var{command} is specified and the environment is output
14752 125 if @command{env} itself fails
14753 126 if @var{command} is found but cannot be invoked
14754 127 if @var{command} cannot be found
14755 the exit status of @var{command} otherwise
14759 @node nice invocation
14760 @section @command{nice}: Run a command with modified niceness
14764 @cindex scheduling, affecting
14765 @cindex appropriate privileges
14767 @command{nice} prints or modifies a process's @dfn{niceness},
14768 a parameter that affects whether the process is scheduled favorably.
14772 nice [@var{option}]@dots{} [@var{command} [@var{arg}]@dots{}]
14775 If no arguments are given, @command{nice} prints the current niceness.
14776 Otherwise, @command{nice} runs the given @var{command} with its
14777 niceness adjusted. By default, its niceness is incremented by 10.
14779 Niceness values range at least from @minus{}20 (process has high priority
14780 and gets more resources, thus slowing down other processes) through 19
14781 (process has lower priority and runs slowly itself, but has less impact
14782 on the speed of other running processes). Some systems
14783 may have a wider range of nicenesses; conversely, other systems may
14784 enforce more restrictive limits. An attempt to set the niceness
14785 outside the supported range is treated as an attempt to use the
14786 minimum or maximum supported value.
14788 A niceness should not be confused with a scheduling priority, which
14789 lets applications determine the order in which threads are scheduled
14790 to run. Unlike a priority, a niceness is merely advice to the
14791 scheduler, which the scheduler is free to ignore. Also, as a point of
14792 terminology, @acronym{POSIX} defines the behavior of @command{nice} in
14793 terms of a @dfn{nice value}, which is the nonnegative difference
14794 between a niceness and the minimum niceness. Though @command{nice}
14795 conforms to @acronym{POSIX}, its documentation and diagnostics use the
14796 term ``niceness'' for compatibility with historical practice.
14798 @var{command} must not be a special built-in utility (@pxref{Special
14799 built-in utilities}).
14801 @mayConflictWithShellBuiltIn{nice}
14803 The program accepts the following option. Also see @ref{Common options}.
14804 Options must precede operands.
14807 @item -n @var{adjustment}
14808 @itemx --adjustment=@var{adjustment}
14810 @opindex --adjustment
14811 Add @var{adjustment} instead of 10 to the command's niceness. If
14812 @var{adjustment} is negative and you lack appropriate privileges,
14813 @command{nice} issues a warning but otherwise acts as if you specified
14816 For compatibility @command{nice} also supports an obsolete
14817 option syntax @option{-@var{adjustment}}. New scripts should use
14818 @option{-n @var{adjustment}} instead.
14822 @cindex exit status of @command{nice}
14826 0 if no @var{command} is specified and the niceness is output
14827 125 if @command{nice} itself fails
14828 126 if @var{command} is found but cannot be invoked
14829 127 if @var{command} cannot be found
14830 the exit status of @var{command} otherwise
14833 It is sometimes useful to run a non-interactive program with reduced niceness.
14836 $ nice factor 4611686018427387903
14839 Since @command{nice} prints the current niceness,
14840 you can invoke it through itself to demonstrate how it works.
14842 The default behavior is to increase the niceness by @samp{10}:
14853 The @var{adjustment} is relative to the current niceness. In the
14854 next example, the first @command{nice} invocation runs the second one
14855 with niceness 10, and it in turn runs the final one with a niceness
14859 $ nice nice -n 3 nice
14863 Specifying a niceness larger than the supported range
14864 is the same as specifying the maximum supported value:
14867 $ nice -n 10000000000 nice
14871 Only a privileged user may run a process with lower niceness:
14875 nice: cannot set niceness: Permission denied
14877 $ sudo nice -n -1 nice
14882 @node nohup invocation
14883 @section @command{nohup}: Run a command immune to hangups
14886 @cindex hangups, immunity to
14887 @cindex immunity to hangups
14888 @cindex logging out and continuing to run
14891 @command{nohup} runs the given @var{command} with hangup signals ignored,
14892 so that the command can continue running in the background after you log
14896 nohup @var{command} [@var{arg}]@dots{}
14899 If standard input is a terminal, it is redirected from
14900 @file{/dev/null} so that terminal sessions do not mistakenly consider
14901 the terminal to be used by the command. This is a @acronym{GNU}
14902 extension; programs intended to be portable to non-@acronym{GNU} hosts
14903 should use @samp{nohup @var{command} [@var{arg}]@dots{} </dev/null}
14907 If standard output is a terminal, the command's standard output is appended
14908 to the file @file{nohup.out}; if that cannot be written to, it is appended
14909 to the file @file{$HOME/nohup.out}; and if that cannot be written to, the
14910 command is not run.
14911 Any @file{nohup.out} or @file{$HOME/nohup.out} file created by
14912 @command{nohup} is made readable and writable only to the user,
14913 regardless of the current umask settings.
14915 If standard error is a terminal, it is normally redirected to the same file
14916 descriptor as the (possibly-redirected) standard output.
14917 However, if standard output is closed, standard error terminal output
14918 is instead appended to the file @file{nohup.out} or
14919 @file{$HOME/nohup.out} as above.
14921 To capture the command's output to a file other than @file{nohup.out}
14922 you can redirect it. For example, to capture the output of
14926 nohup make > make.log
14929 @command{nohup} does not automatically put the command it runs in the
14930 background; you must do that explicitly, by ending the command line
14931 with an @samp{&}. Also, @command{nohup} does not alter the
14932 niceness of @var{command}; use @command{nice} for that,
14933 e.g., @samp{nohup nice @var{command}}.
14935 @var{command} must not be a special built-in utility (@pxref{Special
14936 built-in utilities}).
14938 The only options are @option{--help} and @option{--version}. @xref{Common
14939 options}. Options must precede operands.
14941 @cindex exit status of @command{nohup}
14945 125 if @command{nohup} itself fails, and @env{POSIXLY_CORRECT} is not set
14946 126 if @var{command} is found but cannot be invoked
14947 127 if @var{command} cannot be found
14948 the exit status of @var{command} otherwise
14951 If @env{POSIXLY_CORRECT} is set, internal failures give status 127
14955 @node stdbuf invocation
14956 @section @command{stdbuf}: Run a command with modified I/O stream buffering
14959 @cindex standard streams, buffering
14960 @cindex line buffered
14962 @command{stdbuf} allows one to modify the buffering operations of the
14963 three standard I/O streams associated with a program. Synopsis:
14966 stdbuf @var{option}@dots{} @var{command}
14969 Any additional @var{arg}s are passed as additional arguments to the
14972 The program accepts the following options. Also see @ref{Common options}.
14976 @item -i @var{mode}
14977 @itemx --input=@var{mode}
14980 Adjust the standard input stream buffering.
14982 @item -o @var{mode}
14983 @itemx --output=@var{mode}
14986 Adjust the standard output stream buffering.
14988 @item -e @var{mode}
14989 @itemx --error=@var{mode}
14992 Adjust the standard error stream buffering.
14996 The @var{mode} can be specified as follows:
15001 Set the stream to line buffered mode.
15002 In this mode data is coalesced until a newline is output or
15003 input is read from any stream attached to a terminal device.
15004 This option is invalid with standard input.
15007 Disable buffering of the selected stream.
15008 In this mode data is output immediately and only the
15009 amount of data requested is read from input.
15012 Specify the size of the buffer to use in fully buffered mode.
15013 @multiplierSuffixesNoBlocks{size}
15017 NOTE: If @var{command} adjusts the buffering of its standard streams
15018 (@command{tee} does for e.g.) then that will override corresponding settings
15019 changed by @command{stdbuf}. Also some filters (like @command{dd} and
15020 @command{cat} etc.) don't use streams for I/O, and are thus unaffected
15021 by @command{stdbuf} settings.
15023 @cindex exit status of @command{stdbuf}
15027 125 if @command{stdbuf} itself fails
15028 126 if @var{command} is found but cannot be invoked
15029 127 if @var{command} cannot be found
15030 the exit status of @var{command} otherwise
15034 @node su invocation
15035 @section @command{su}: Run a command with substitute user and group ID
15038 @cindex substitute user and group IDs
15039 @cindex user ID, switching
15040 @cindex super-user, becoming
15041 @cindex root, becoming
15043 @command{su} allows one user to temporarily become another user. It runs a
15044 command (often an interactive shell) with the real and effective user
15045 ID, group ID, and supplemental groups of a given @var{user}. Synopsis:
15048 su [@var{option}]@dots{} [@var{user} [@var{arg}]@dots{}]
15051 @cindex passwd entry, and @command{su} shell
15053 @flindex /etc/passwd
15054 If no @var{user} is given, the default is @code{root}, the super-user.
15055 The shell to use is taken from @var{user}'s @code{passwd} entry, or
15056 @file{/bin/sh} if none is specified there. If @var{user} has a
15057 password, @command{su} prompts for the password unless run by a user with
15058 effective user ID of zero (the super-user).
15064 @cindex login shell
15065 By default, @command{su} does not change the current directory.
15066 It sets the environment variables @env{HOME} and @env{SHELL}
15067 from the password entry for @var{user}, and if @var{user} is not
15068 the super-user, sets @env{USER} and @env{LOGNAME} to @var{user}.
15069 By default, the shell is not a login shell.
15071 Any additional @var{arg}s are passed as additional arguments to the
15074 @cindex @option{-su}
15075 GNU @command{su} does not treat @file{/bin/sh} or any other shells specially
15076 (e.g., by setting @code{argv[0]} to @option{-su}, passing @option{-c} only
15077 to certain shells, etc.).
15080 @command{su} can optionally be compiled to use @code{syslog} to report
15081 failed, and optionally successful, @command{su} attempts. (If the system
15082 supports @code{syslog}.) However, GNU @command{su} does not check if the
15083 user is a member of the @code{wheel} group; see below.
15085 The program accepts the following options. Also see @ref{Common options}.
15088 @item -c @var{command}
15089 @itemx --command=@var{command}
15092 Pass @var{command}, a single command line to run, to the shell with
15093 a @option{-c} option instead of starting an interactive shell.
15100 @cindex file name pattern expansion, disabled
15101 @cindex globbing, disabled
15102 Pass the @option{-f} option to the shell. This probably only makes sense
15103 if the shell run is @command{csh} or @command{tcsh}, for which the @option{-f}
15104 option prevents reading the startup file (@file{.cshrc}). With
15105 Bourne-like shells, the @option{-f} option disables file name pattern
15106 expansion (globbing), which is not likely to be useful.
15114 @c other variables already indexed above
15117 @cindex login shell, creating
15118 Make the shell a login shell. This means the following. Unset all
15119 environment variables except @env{TERM}, @env{HOME}, and @env{SHELL}
15120 (which are set as described above), and @env{USER} and @env{LOGNAME}
15121 (which are set, even for the super-user, as described above), and set
15122 @env{PATH} to a compiled-in default value. Change to @var{user}'s home
15123 directory. Prepend @samp{-} to the shell's name, intended to make it
15124 read its login startup file(s).
15128 @itemx --preserve-environment
15131 @opindex --preserve-environment
15132 @cindex environment, preserving
15133 @flindex /etc/shells
15134 @cindex restricted shell
15135 Do not change the environment variables @env{HOME}, @env{USER},
15136 @env{LOGNAME}, or @env{SHELL}. Run the shell given in the environment
15137 variable @env{SHELL} instead of the shell from @var{user}'s passwd
15138 entry, unless the user running @command{su} is not the super-user and
15139 @var{user}'s shell is restricted. A @dfn{restricted shell} is one that
15140 is not listed in the file @file{/etc/shells}, or in a compiled-in list
15141 if that file does not exist. Parts of what this option does can be
15142 overridden by @option{--login} and @option{--shell}.
15144 @item -s @var{shell}
15145 @itemx --shell=@var{shell}
15148 Run @var{shell} instead of the shell from @var{user}'s passwd entry,
15149 unless the user running @command{su} is not the super-user and @var{user}'s
15150 shell is restricted (see @option{-m} just above).
15154 @cindex exit status of @command{su}
15158 125 if @command{su} itself fails
15159 126 if subshell is found but cannot be invoked
15160 127 if subshell cannot be found
15161 the exit status of the subshell otherwise
15164 @cindex wheel group, not supported
15165 @cindex group wheel, not supported
15167 @subsection Why GNU @command{su} does not support the @samp{wheel} group
15169 (This section is by Richard Stallman.)
15173 Sometimes a few of the users try to hold total power over all the
15174 rest. For example, in 1984, a few users at the MIT AI lab decided to
15175 seize power by changing the operator password on the Twenex system and
15176 keeping it secret from everyone else. (I was able to thwart this coup
15177 and give power back to the users by patching the kernel, but I
15178 wouldn't know how to do that in Unix.)
15180 However, occasionally the rulers do tell someone. Under the usual
15181 @command{su} mechanism, once someone learns the root password who
15182 sympathizes with the ordinary users, he or she can tell the rest. The
15183 ``wheel group'' feature would make this impossible, and thus cement the
15184 power of the rulers.
15186 I'm on the side of the masses, not that of the rulers. If you are
15187 used to supporting the bosses and sysadmins in whatever they do, you
15188 might find this idea strange at first.
15191 @node timeout invocation
15192 @section @command{timeout}: Run a command with a time limit
15196 @cindex run commands with bounded time
15198 @command{timeout} runs the given @var{command} and kills it if it is
15199 still running after the specified time interval. Synopsis:
15202 timeout [@var{option}] @var{number}[smhd] @var{command} [@var{arg}]@dots{}
15206 @var{number} is an integer followed by an optional unit; the default
15207 is seconds. The units are:
15220 @var{command} must not be a special built-in utility (@pxref{Special
15221 built-in utilities}).
15223 The program accepts the following option. Also see @ref{Common options}.
15224 Options must precede operands.
15227 @item -s @var{signal}
15228 @itemx --signal=@var{signal}
15231 Send this @var{signal} to @var{command} on timeout, rather than the
15232 default @samp{TERM} signal. @var{signal} may be a name like @samp{HUP}
15233 or a number. Also see @xref{Signal specifications}.
15237 @cindex exit status of @command{timeout}
15241 124 if @var{command} times out
15242 125 if @command{timeout} itself fails
15243 126 if @var{command} is found but cannot be invoked
15244 127 if @var{command} cannot be found
15245 the exit status of @var{command} otherwise
15249 @node Process control
15250 @chapter Process control
15252 @cindex processes, commands for controlling
15253 @cindex commands for controlling processes
15256 * kill invocation:: Sending a signal to processes.
15260 @node kill invocation
15261 @section @command{kill}: Send a signal to processes
15264 @cindex send a signal to processes
15266 The @command{kill} command sends a signal to processes, causing them
15267 to terminate or otherwise act upon receiving the signal in some way.
15268 Alternatively, it lists information about signals. Synopses:
15271 kill [-s @var{signal} | --signal @var{signal} | -@var{signal}] @var{pid}@dots{}
15272 kill [-l | --list | -t | --table] [@var{signal}]@dots{}
15275 @mayConflictWithShellBuiltIn{kill}
15277 The first form of the @command{kill} command sends a signal to all
15278 @var{pid} arguments. The default signal to send if none is specified
15279 is @samp{TERM}. The special signal number @samp{0} does not denote a
15280 valid signal, but can be used to test whether the @var{pid} arguments
15281 specify processes to which a signal could be sent.
15283 If @var{pid} is positive, the signal is sent to the process with the
15284 process ID @var{pid}. If @var{pid} is zero, the signal is sent to all
15285 processes in the process group of the current process. If @var{pid}
15286 is @minus{}1, the signal is sent to all processes for which the user has
15287 permission to send a signal. If @var{pid} is less than @minus{}1, the signal
15288 is sent to all processes in the process group that equals the absolute
15289 value of @var{pid}.
15291 If @var{pid} is not positive, a system-dependent set of system
15292 processes is excluded from the list of processes to which the signal
15295 If a negative @var{pid} argument is desired as the first one, it
15296 should be preceded by @option{--}. However, as a common extension to
15297 @acronym{POSIX}, @option{--} is not required with @samp{kill
15298 -@var{signal} -@var{pid}}. The following commands are equivalent:
15307 The first form of the @command{kill} command succeeds if every @var{pid}
15308 argument specifies at least one process that the signal was sent to.
15310 The second form of the @command{kill} command lists signal information.
15311 Either the @option{-l} or @option{--list} option, or the @option{-t}
15312 or @option{--table} option must be specified. Without any
15313 @var{signal} argument, all supported signals are listed. The output
15314 of @option{-l} or @option{--list} is a list of the signal names, one
15315 per line; if @var{signal} is already a name, the signal number is
15316 printed instead. The output of @option{-t} or @option{--table} is a
15317 table of signal numbers, names, and descriptions. This form of the
15318 @command{kill} command succeeds if all @var{signal} arguments are valid
15319 and if there is no output error.
15321 The @command{kill} command also supports the @option{--help} and
15322 @option{--version} options. @xref{Common options}.
15324 A @var{signal} may be a signal name like @samp{HUP}, or a signal
15325 number like @samp{1}, or an exit status of a process terminated by the
15326 signal. A signal name can be given in canonical form or prefixed by
15327 @samp{SIG}. The case of the letters is ignored, except for the
15328 @option{-@var{signal}} option which must use upper case to avoid
15329 ambiguity with lower case option letters. For a list of supported
15330 signal names and numbers see @xref{Signal specifications}.
15335 @cindex delaying commands
15336 @cindex commands for delaying
15338 @c Perhaps @command{wait} or other commands should be described here also?
15341 * sleep invocation:: Delay for a specified time.
15345 @node sleep invocation
15346 @section @command{sleep}: Delay for a specified time
15349 @cindex delay for a specified time
15351 @command{sleep} pauses for an amount of time specified by the sum of
15352 the values of the command line arguments.
15356 sleep @var{number}[smhd]@dots{}
15360 Each argument is a number followed by an optional unit; the default
15361 is seconds. The units are:
15374 Historical implementations of @command{sleep} have required that
15375 @var{number} be an integer, and only accepted a single argument
15376 without a suffix. However, GNU @command{sleep} accepts
15377 arbitrary floating point numbers (using a period before any fractional
15380 The only options are @option{--help} and @option{--version}. @xref{Common
15383 @c sleep is a shell built-in at least with Solaris 11's /bin/sh
15384 @mayConflictWithShellBuiltIn{sleep}
15389 @node Numeric operations
15390 @chapter Numeric operations
15392 @cindex numeric operations
15393 These programs do numerically-related operations.
15396 * factor invocation:: Show factors of numbers.
15397 * seq invocation:: Print sequences of numbers.
15401 @node factor invocation
15402 @section @command{factor}: Print prime factors
15405 @cindex prime factors
15407 @command{factor} prints prime factors. Synopses:
15410 factor [@var{number}]@dots{}
15411 factor @var{option}
15414 If no @var{number} is specified on the command line, @command{factor} reads
15415 numbers from standard input, delimited by newlines, tabs, or spaces.
15417 The @command{factor} command supports only a small number of options:
15421 Print a short help on standard output, then exit without further
15425 Print the program version on standard output, then exit without further
15429 Factoring the product of the eighth and ninth Mersenne primes
15430 takes about 30 milliseconds of CPU time on a 2.2 GHz Athlon.
15433 M8=`echo 2^31-1|bc` ; M9=`echo 2^61-1|bc`
15434 /usr/bin/time -f '%U' factor $(echo "$M8 * $M9" | bc)
15435 4951760154835678088235319297: 2147483647 2305843009213693951
15439 Similarly, factoring the eighth Fermat number @math{2^{256}+1} takes
15440 about 20 seconds on the same machine.
15442 Factoring large prime numbers is, in general, hard. The Pollard Rho
15443 algorithm used by @command{factor} is particularly effective for
15444 numbers with relatively small factors. If you wish to factor large
15445 numbers which do not have small factors (for example, numbers which
15446 are the product of two large primes), other methods are far better.
15448 If @command{factor} is built without using GNU MP, only
15449 single-precision arithmetic is available, and so large numbers
15450 (typically @math{2^{64}} and above) will not be supported. The single-precision
15451 code uses an algorithm which is designed for factoring smaller
15457 @node seq invocation
15458 @section @command{seq}: Print numeric sequences
15461 @cindex numeric sequences
15462 @cindex sequence of numbers
15464 @command{seq} prints a sequence of numbers to standard output. Synopses:
15467 seq [@var{option}]@dots{} @var{last}
15468 seq [@var{option}]@dots{} @var{first} @var{last}
15469 seq [@var{option}]@dots{} @var{first} @var{increment} @var{last}
15472 @command{seq} prints the numbers from @var{first} to @var{last} by
15473 @var{increment}. By default, each number is printed on a separate line.
15474 When @var{increment} is not specified, it defaults to @samp{1},
15475 even when @var{first} is larger than @var{last}.
15476 @var{first} also defaults to @samp{1}. So @code{seq 1} prints
15477 @samp{1}, but @code{seq 0} and @code{seq 10 5} produce no output.
15478 Floating-point numbers
15479 may be specified (using a period before any fractional digits).
15481 The program accepts the following options. Also see @ref{Common options}.
15482 Options must precede operands.
15485 @item -f @var{format}
15486 @itemx --format=@var{format}
15487 @opindex -f @var{format}
15488 @opindex --format=@var{format}
15489 @cindex formatting of numbers in @command{seq}
15490 Print all numbers using @var{format}.
15491 @var{format} must contain exactly one of the @samp{printf}-style
15492 floating point conversion specifications @samp{%a}, @samp{%e},
15493 @samp{%f}, @samp{%g}, @samp{%A}, @samp{%E}, @samp{%F}, @samp{%G}.
15494 The @samp{%} may be followed by zero or more flags taken from the set
15495 @samp{-+#0 '}, then an optional width containing one or more digits,
15496 then an optional precision consisting of a @samp{.} followed by zero
15497 or more digits. @var{format} may also contain any number of @samp{%%}
15498 conversion specifications. All conversion specifications have the
15499 same meaning as with @samp{printf}.
15501 The default format is derived from @var{first}, @var{step}, and
15502 @var{last}. If these all use a fixed point decimal representation,
15503 the default format is @samp{%.@var{p}f}, where @var{p} is the minimum
15504 precision that can represent the output numbers exactly. Otherwise,
15505 the default format is @samp{%g}.
15507 @item -s @var{string}
15508 @itemx --separator=@var{string}
15509 @cindex separator for numbers in @command{seq}
15510 Separate numbers with @var{string}; default is a newline.
15511 The output always terminates with a newline.
15514 @itemx --equal-width
15515 Print all numbers with the same width, by padding with leading zeros.
15516 @var{first}, @var{step}, and @var{last} should all use a fixed point
15517 decimal representation.
15518 (To have other kinds of padding, use @option{--format}).
15522 You can get finer-grained control over output with @option{-f}:
15525 $ seq -f '(%9.2E)' -9e5 1.1e6 1.3e6
15531 If you want hexadecimal integer output, you can use @command{printf}
15532 to perform the conversion:
15535 $ printf '%x\n' `seq 1048575 1024 1050623`
15541 For very long lists of numbers, use xargs to avoid
15542 system limitations on the length of an argument list:
15545 $ seq 1000000 | xargs printf '%x\n' | tail -n 3
15551 To generate octal output, use the printf @code{%o} format instead
15554 On most systems, seq can produce whole-number output for values up to
15555 at least @math{2^{53}}. Larger integers are approximated. The details
15556 differ depending on your floating-point implementation, but a common
15557 case is that @command{seq} works with integers through @math{2^{64}},
15558 and larger integers may not be numerically correct:
15561 $ seq 18446744073709551616 1 18446744073709551618
15562 18446744073709551616
15563 18446744073709551616
15564 18446744073709551618
15567 Be careful when using @command{seq} with outlandish values: otherwise
15568 you may see surprising results, as @command{seq} uses floating point
15569 internally. For example, on the x86 platform, where the internal
15570 representation uses a 64-bit fraction, the command:
15573 seq 1 0.0000000000000000001 1.0000000000000000009
15576 outputs 1.0000000000000000007 twice and skips 1.0000000000000000008.
15581 @node File permissions
15582 @chapter File permissions
15585 @include getdate.texi
15589 @node Opening the software toolbox
15590 @chapter Opening the Software Toolbox
15592 An earlier version of this chapter appeared in
15593 @uref{http://www.linuxjournal.com/article.php?sid=2762, the
15594 @cite{What's GNU?} column of @cite{Linux Journal}, 2 (June, 1994)}.
15595 It was written by Arnold Robbins.
15598 * Toolbox introduction:: Toolbox introduction
15599 * I/O redirection:: I/O redirection
15600 * The who command:: The @command{who} command
15601 * The cut command:: The @command{cut} command
15602 * The sort command:: The @command{sort} command
15603 * The uniq command:: The @command{uniq} command
15604 * Putting the tools together:: Putting the tools together
15608 @node Toolbox introduction
15609 @unnumberedsec Toolbox Introduction
15611 This month's column is only peripherally related to the GNU Project, in
15612 that it describes a number of the GNU tools on your GNU/Linux system and how they
15613 might be used. What it's really about is the ``Software Tools'' philosophy
15614 of program development and usage.
15616 The software tools philosophy was an important and integral concept
15617 in the initial design and development of Unix (of which Linux and GNU are
15618 essentially clones). Unfortunately, in the modern day press of
15619 Internetworking and flashy GUIs, it seems to have fallen by the
15620 wayside. This is a shame, since it provides a powerful mental model
15621 for solving many kinds of problems.
15623 Many people carry a Swiss Army knife around in their pants pockets (or
15624 purse). A Swiss Army knife is a handy tool to have: it has several knife
15625 blades, a screwdriver, tweezers, toothpick, nail file, corkscrew, and perhaps
15626 a number of other things on it. For the everyday, small miscellaneous jobs
15627 where you need a simple, general purpose tool, it's just the thing.
15629 On the other hand, an experienced carpenter doesn't build a house using
15630 a Swiss Army knife. Instead, he has a toolbox chock full of specialized
15631 tools---a saw, a hammer, a screwdriver, a plane, and so on. And he knows
15632 exactly when and where to use each tool; you won't catch him hammering nails
15633 with the handle of his screwdriver.
15635 The Unix developers at Bell Labs were all professional programmers and trained
15636 computer scientists. They had found that while a one-size-fits-all program
15637 might appeal to a user because there's only one program to use, in practice
15642 difficult to write,
15645 difficult to maintain and
15649 difficult to extend to meet new situations.
15652 Instead, they felt that programs should be specialized tools. In short, each
15653 program ``should do one thing well.'' No more and no less. Such programs are
15654 simpler to design, write, and get right---they only do one thing.
15656 Furthermore, they found that with the right machinery for hooking programs
15657 together, that the whole was greater than the sum of the parts. By combining
15658 several special purpose programs, you could accomplish a specific task
15659 that none of the programs was designed for, and accomplish it much more
15660 quickly and easily than if you had to write a special purpose program.
15661 We will see some (classic) examples of this further on in the column.
15662 (An important additional point was that, if necessary, take a detour
15663 and build any software tools you may need first, if you don't already
15664 have something appropriate in the toolbox.)
15666 @node I/O redirection
15667 @unnumberedsec I/O Redirection
15669 Hopefully, you are familiar with the basics of I/O redirection in the
15670 shell, in particular the concepts of ``standard input,'' ``standard output,''
15671 and ``standard error''. Briefly, ``standard input'' is a data source, where
15672 data comes from. A program should not need to either know or care if the
15673 data source is a disk file, a keyboard, a magnetic tape, or even a punched
15674 card reader. Similarly, ``standard output'' is a data sink, where data goes
15675 to. The program should neither know nor care where this might be.
15676 Programs that only read their standard input, do something to the data,
15677 and then send it on, are called @dfn{filters}, by analogy to filters in a
15680 With the Unix shell, it's very easy to set up data pipelines:
15683 program_to_create_data | filter1 | ... | filterN > final.pretty.data
15686 We start out by creating the raw data; each filter applies some successive
15687 transformation to the data, until by the time it comes out of the pipeline,
15688 it is in the desired form.
15690 This is fine and good for standard input and standard output. Where does the
15691 standard error come in to play? Well, think about @command{filter1} in
15692 the pipeline above. What happens if it encounters an error in the data it
15693 sees? If it writes an error message to standard output, it will just
15694 disappear down the pipeline into @command{filter2}'s input, and the
15695 user will probably never see it. So programs need a place where they can send
15696 error messages so that the user will notice them. This is standard error,
15697 and it is usually connected to your console or window, even if you have
15698 redirected standard output of your program away from your screen.
15700 For filter programs to work together, the format of the data has to be
15701 agreed upon. The most straightforward and easiest format to use is simply
15702 lines of text. Unix data files are generally just streams of bytes, with
15703 lines delimited by the @acronym{ASCII} @sc{lf} (Line Feed) character,
15704 conventionally called a ``newline'' in the Unix literature. (This is
15705 @code{'\n'} if you're a C programmer.) This is the format used by all
15706 the traditional filtering programs. (Many earlier operating systems
15707 had elaborate facilities and special purpose programs for managing
15708 binary data. Unix has always shied away from such things, under the
15709 philosophy that it's easiest to simply be able to view and edit your
15710 data with a text editor.)
15712 OK, enough introduction. Let's take a look at some of the tools, and then
15713 we'll see how to hook them together in interesting ways. In the following
15714 discussion, we will only present those command line options that interest
15715 us. As you should always do, double check your system documentation
15716 for the full story.
15718 @node The who command
15719 @unnumberedsec The @command{who} Command
15721 The first program is the @command{who} command. By itself, it generates a
15722 list of the users who are currently logged in. Although I'm writing
15723 this on a single-user system, we'll pretend that several people are
15728 @print{} arnold console Jan 22 19:57
15729 @print{} miriam ttyp0 Jan 23 14:19(:0.0)
15730 @print{} bill ttyp1 Jan 21 09:32(:0.0)
15731 @print{} arnold ttyp2 Jan 23 20:48(:0.0)
15734 Here, the @samp{$} is the usual shell prompt, at which I typed @samp{who}.
15735 There are three people logged in, and I am logged in twice. On traditional
15736 Unix systems, user names are never more than eight characters long. This
15737 little bit of trivia will be useful later. The output of @command{who} is nice,
15738 but the data is not all that exciting.
15740 @node The cut command
15741 @unnumberedsec The @command{cut} Command
15743 The next program we'll look at is the @command{cut} command. This program
15744 cuts out columns or fields of input data. For example, we can tell it
15745 to print just the login name and full name from the @file{/etc/passwd}
15746 file. The @file{/etc/passwd} file has seven fields, separated by
15750 arnold:xyzzy:2076:10:Arnold D. Robbins:/home/arnold:/bin/bash
15753 To get the first and fifth fields, we would use @command{cut} like this:
15756 $ cut -d: -f1,5 /etc/passwd
15757 @print{} root:Operator
15759 @print{} arnold:Arnold D. Robbins
15760 @print{} miriam:Miriam A. Robbins
15764 With the @option{-c} option, @command{cut} will cut out specific characters
15765 (i.e., columns) in the input lines. This is useful for input data
15766 that has fixed width fields, and does not have a field separator. For
15767 example, list the Monday dates for the current month:
15769 @c Is using cal ok? Looked at gcal, but I don't like it.
15780 @node The sort command
15781 @unnumberedsec The @command{sort} Command
15783 Next we'll look at the @command{sort} command. This is one of the most
15784 powerful commands on a Unix-style system; one that you will often find
15785 yourself using when setting up fancy data plumbing.
15788 command reads and sorts each file named on the command line. It then
15789 merges the sorted data and writes it to standard output. It will read
15790 standard input if no files are given on the command line (thus
15791 making it into a filter). The sort is based on the character collating
15792 sequence or based on user-supplied ordering criteria.
15795 @node The uniq command
15796 @unnumberedsec The @command{uniq} Command
15798 Finally (at least for now), we'll look at the @command{uniq} program. When
15799 sorting data, you will often end up with duplicate lines, lines that
15800 are identical. Usually, all you need is one instance of each line.
15801 This is where @command{uniq} comes in. The @command{uniq} program reads its
15802 standard input. It prints only one
15803 copy of each repeated line. It does have several options. Later on,
15804 we'll use the @option{-c} option, which prints each unique line, preceded
15805 by a count of the number of times that line occurred in the input.
15808 @node Putting the tools together
15809 @unnumberedsec Putting the Tools Together
15811 Now, let's suppose this is a large ISP server system with dozens of users
15812 logged in. The management wants the system administrator to write a program that will
15813 generate a sorted list of logged in users. Furthermore, even if a user
15814 is logged in multiple times, his or her name should only show up in the
15817 The administrator could sit down with the system documentation and write a C
15818 program that did this. It would take perhaps a couple of hundred lines
15819 of code and about two hours to write it, test it, and debug it.
15820 However, knowing the software toolbox, the administrator can instead start out
15821 by generating just a list of logged on users:
15831 Next, sort the list:
15834 $ who | cut -c1-8 | sort
15841 Finally, run the sorted list through @command{uniq}, to weed out duplicates:
15844 $ who | cut -c1-8 | sort | uniq
15850 The @command{sort} command actually has a @option{-u} option that does what
15851 @command{uniq} does. However, @command{uniq} has other uses for which one
15852 cannot substitute @samp{sort -u}.
15854 The administrator puts this pipeline into a shell script, and makes it available for
15855 all the users on the system (@samp{#} is the system administrator,
15856 or @code{root}, prompt):
15859 # cat > /usr/local/bin/listusers
15860 who | cut -c1-8 | sort | uniq
15862 # chmod +x /usr/local/bin/listusers
15865 There are four major points to note here. First, with just four
15866 programs, on one command line, the administrator was able to save about two
15867 hours worth of work. Furthermore, the shell pipeline is just about as
15868 efficient as the C program would be, and it is much more efficient in
15869 terms of programmer time. People time is much more expensive than
15870 computer time, and in our modern ``there's never enough time to do
15871 everything'' society, saving two hours of programmer time is no mean
15874 Second, it is also important to emphasize that with the
15875 @emph{combination} of the tools, it is possible to do a special
15876 purpose job never imagined by the authors of the individual programs.
15878 Third, it is also valuable to build up your pipeline in stages, as we did here.
15879 This allows you to view the data at each stage in the pipeline, which helps
15880 you acquire the confidence that you are indeed using these tools correctly.
15882 Finally, by bundling the pipeline in a shell script, other users can use
15883 your command, without having to remember the fancy plumbing you set up for
15884 them. In terms of how you run them, shell scripts and compiled programs are
15887 After the previous warm-up exercise, we'll look at two additional, more
15888 complicated pipelines. For them, we need to introduce two more tools.
15890 The first is the @command{tr} command, which stands for ``transliterate.''
15891 The @command{tr} command works on a character-by-character basis, changing
15892 characters. Normally it is used for things like mapping upper case to
15896 $ echo ThIs ExAmPlE HaS MIXED case! | tr '[:upper:]' '[:lower:]'
15897 @print{} this example has mixed case!
15900 There are several options of interest:
15904 work on the complement of the listed characters, i.e.,
15905 operations apply to characters not in the given set
15908 delete characters in the first set from the output
15911 squeeze repeated characters in the output into just one character.
15914 We will be using all three options in a moment.
15916 The other command we'll look at is @command{comm}. The @command{comm}
15917 command takes two sorted input files as input data, and prints out the
15918 files' lines in three columns. The output columns are the data lines
15919 unique to the first file, the data lines unique to the second file, and
15920 the data lines that are common to both. The @option{-1}, @option{-2}, and
15921 @option{-3} command line options @emph{omit} the respective columns. (This is
15922 non-intuitive and takes a little getting used to.) For example:
15944 The file name @file{-} tells @command{comm} to read standard input
15945 instead of a regular file.
15947 Now we're ready to build a fancy pipeline. The first application is a word
15948 frequency counter. This helps an author determine if he or she is over-using
15951 The first step is to change the case of all the letters in our input file
15952 to one case. ``The'' and ``the'' are the same word when doing counting.
15955 $ tr '[:upper:]' '[:lower:]' < whats.gnu | ...
15958 The next step is to get rid of punctuation. Quoted words and unquoted words
15959 should be treated identically; it's easiest to just get the punctuation out of
15963 $ tr '[:upper:]' '[:lower:]' < whats.gnu | tr -cd '[:alnum:]_ \n' | ...
15966 The second @command{tr} command operates on the complement of the listed
15967 characters, which are all the letters, the digits, the underscore, and
15968 the blank. The @samp{\n} represents the newline character; it has to
15969 be left alone. (The @acronym{ASCII} tab character should also be included for
15970 good measure in a production script.)
15972 At this point, we have data consisting of words separated by blank space.
15973 The words only contain alphanumeric characters (and the underscore). The
15974 next step is break the data apart so that we have one word per line. This
15975 makes the counting operation much easier, as we will see shortly.
15978 $ tr '[:upper:]' '[:lower:]' < whats.gnu | tr -cd '[:alnum:]_ \n' |
15979 > tr -s ' ' '\n' | ...
15982 This command turns blanks into newlines. The @option{-s} option squeezes
15983 multiple newline characters in the output into just one. This helps us
15984 avoid blank lines. (The @samp{>} is the shell's ``secondary prompt.''
15985 This is what the shell prints when it notices you haven't finished
15986 typing in all of a command.)
15988 We now have data consisting of one word per line, no punctuation, all one
15989 case. We're ready to count each word:
15992 $ tr '[:upper:]' '[:lower:]' < whats.gnu | tr -cd '[:alnum:]_ \n' |
15993 > tr -s ' ' '\n' | sort | uniq -c | ...
15996 At this point, the data might look something like this:
16009 The output is sorted by word, not by count! What we want is the most
16010 frequently used words first. Fortunately, this is easy to accomplish,
16011 with the help of two more @command{sort} options:
16015 do a numeric sort, not a textual one
16018 reverse the order of the sort
16021 The final pipeline looks like this:
16024 $ tr '[:upper:]' '[:lower:]' < whats.gnu | tr -cd '[:alnum:]_ \n' |
16025 > tr -s ' ' '\n' | sort | uniq -c | sort -n -r
16034 Whew! That's a lot to digest. Yet, the same principles apply. With six
16035 commands, on two lines (really one long one split for convenience), we've
16036 created a program that does something interesting and useful, in much
16037 less time than we could have written a C program to do the same thing.
16039 A minor modification to the above pipeline can give us a simple spelling
16040 checker! To determine if you've spelled a word correctly, all you have to
16041 do is look it up in a dictionary. If it is not there, then chances are
16042 that your spelling is incorrect. So, we need a dictionary.
16043 The conventional location for a dictionary is @file{/usr/dict/words}.
16044 On my GNU/Linux system,@footnote{Redhat Linux 6.1, for the November 2000
16045 revision of this article.}
16046 this is a sorted, 45,402 word dictionary.
16048 Now, how to compare our file with the dictionary? As before, we generate
16049 a sorted list of words, one per line:
16052 $ tr '[:upper:]' '[:lower:]' < whats.gnu | tr -cd '[:alnum:]_ \n' |
16053 > tr -s ' ' '\n' | sort -u | ...
16056 Now, all we need is a list of words that are @emph{not} in the
16057 dictionary. Here is where the @command{comm} command comes in.
16060 $ tr '[:upper:]' '[:lower:]' < whats.gnu | tr -cd '[:alnum:]_ \n' |
16061 > tr -s ' ' '\n' | sort -u |
16062 > comm -23 - /usr/dict/words
16065 The @option{-2} and @option{-3} options eliminate lines that are only in the
16066 dictionary (the second file), and lines that are in both files. Lines
16067 only in the first file (standard input, our stream of words), are
16068 words that are not in the dictionary. These are likely candidates for
16069 spelling errors. This pipeline was the first cut at a production
16070 spelling checker on Unix.
16072 There are some other tools that deserve brief mention.
16076 search files for text that matches a regular expression
16079 count lines, words, characters
16082 a T-fitting for data pipes, copies data to files and to standard output
16085 the stream editor, an advanced tool
16088 a data manipulation language, another advanced tool
16091 The software tools philosophy also espoused the following bit of
16092 advice: ``Let someone else do the hard part.'' This means, take
16093 something that gives you most of what you need, and then massage it the
16094 rest of the way until it's in the form that you want.
16100 Each program should do one thing well. No more, no less.
16103 Combining programs with appropriate plumbing leads to results where
16104 the whole is greater than the sum of the parts. It also leads to novel
16105 uses of programs that the authors might never have imagined.
16108 Programs should never print extraneous header or trailer data, since these
16109 could get sent on down a pipeline. (A point we didn't mention earlier.)
16112 Let someone else do the hard part.
16115 Know your toolbox! Use each program appropriately. If you don't have an
16116 appropriate tool, build one.
16119 As of this writing, all the programs we've discussed are available via
16120 anonymous @command{ftp} from: @*
16121 @uref{ftp://gnudist.gnu.org/textutils/textutils-1.22.tar.gz}. (There may
16122 be more recent versions available now.)
16124 None of what I have presented in this column is new. The Software Tools
16125 philosophy was first introduced in the book @cite{Software Tools}, by
16126 Brian Kernighan and P.J. Plauger (Addison-Wesley, ISBN 0-201-03669-X).
16127 This book showed how to write and use software tools. It was written in
16128 1976, using a preprocessor for FORTRAN named @command{ratfor} (RATional
16129 FORtran). At the time, C was not as ubiquitous as it is now; FORTRAN
16130 was. The last chapter presented a @command{ratfor} to FORTRAN
16131 processor, written in @command{ratfor}. @command{ratfor} looks an awful
16132 lot like C; if you know C, you won't have any problem following the
16135 In 1981, the book was updated and made available as @cite{Software Tools
16136 in Pascal} (Addison-Wesley, ISBN 0-201-10342-7). Both books are
16137 still in print and are well worth
16138 reading if you're a programmer. They certainly made a major change in
16139 how I view programming.
16141 The programs in both books are available from
16142 @uref{http://cm.bell-labs.com/who/bwk, Brian Kernighan's home page}.
16143 For a number of years, there was an active
16144 Software Tools Users Group, whose members had ported the original
16145 @command{ratfor} programs to essentially every computer system with a
16146 FORTRAN compiler. The popularity of the group waned in the middle 1980s
16147 as Unix began to spread beyond universities.
16149 With the current proliferation of GNU code and other clones of Unix programs,
16150 these programs now receive little attention; modern C versions are
16151 much more efficient and do more than these programs do. Nevertheless, as
16152 exposition of good programming style, and evangelism for a still-valuable
16153 philosophy, these books are unparalleled, and I recommend them highly.
16155 Acknowledgment: I would like to express my gratitude to Brian Kernighan
16156 of Bell Labs, the original Software Toolsmith, for reviewing this column.
16158 @node GNU Free Documentation License
16159 @appendix GNU Free Documentation License
16163 @node Concept index
16170 @c Local variables:
16171 @c texinfo-column-for-description: 32