1BASH(1) General Commands Manual BASH(1)
2
6 bash - GNU Bourne-Again SHell
7
9 bash [options] [command_string | file]
10
12 Bash is Copyright (C) 1989-2022 by the Free Software Foundation, Inc.
13
15 Bash is an sh-compatible command language interpreter that executes
16 commands read from the standard input or from a file. Bash also incor‐
17 porates useful features from the Korn and C shells (ksh and csh).
18 Bash is intended to be a conformant implementation of the Shell and
20 Utilities portion of the IEEE POSIX specification (IEEE Standard
21 1003.1). Bash can be configured to be POSIX-conformant by default.
22
24 All of the single-character shell options documented in the description
25 of the set builtin command, including -o, can be used as options when
26 the shell is invoked. In addition, bash interprets the following op‐
27 tions when it is invoked:
28 -c If the -c option is present, then commands are read from the
30 first non-option argument command_string. If there are argu‐
31 ments after the command_string, the first argument is as‐
32 signed to $0 and any remaining arguments are assigned to the
33 positional parameters. The assignment to $0 sets the name of
34 the shell, which is used in warning and error messages.
35 -i If the -i option is present, the shell is interactive.
36 -l Make bash act as if it had been invoked as a login shell (see
37 INVOCATION below).
38 -r If the -r option is present, the shell becomes restricted
39 (see RESTRICTED SHELL below).
40 -s If the -s option is present, or if no arguments remain after
41 option processing, then commands are read from the standard
42 input. This option allows the positional parameters to be
43 set when invoking an interactive shell or when reading input
44 through a pipe.
45 -D A list of all double-quoted strings preceded by $ is printed
46 on the standard output. These are the strings that are sub‐
47 ject to language translation when the current locale is not C
48 or POSIX. This implies the -n option; no commands will be
49 executed.
50 [-+]O [shopt_option]
51 shopt_option is one of the shell options accepted by the
52 shopt builtin (see SHELL BUILTIN COMMANDS below). If
53 shopt_option is present, -O sets the value of that option; +O
54 unsets it. If shopt_option is not supplied, the names and
55 values of the shell options accepted by shopt are printed on
56 the standard output. If the invocation option is +O, the
57 output is displayed in a format that may be reused as input.
58 -- A -- signals the end of options and disables further option
59 processing. Any arguments after the -- are treated as file‐
60 names and arguments. An argument of - is equivalent to --.
61 Bash also interprets a number of multi-character options. These op‐
63 tions must appear on the command line before the single-character op‐
64 tions to be recognized.
65 --debugger
67 Arrange for the debugger profile to be executed before the shell
68 starts. Turns on extended debugging mode (see the description
69 of the extdebug option to the shopt builtin below).
70 --dump-po-strings
71 Equivalent to -D, but the output is in the GNU gettext po (por‐
72 table object) file format.
73 --dump-strings
74 Equivalent to -D.
75 --help Display a usage message on standard output and exit success‐
76 fully.
77 --init-file file
78 --rcfile file
79 Execute commands from file instead of the standard personal ini‐
80 tialization file ~/.bashrc if the shell is interactive (see IN‐
81 VOCATION below).
82 --login
84 Equivalent to -l.
85 --noediting
87 Do not use the GNU readline library to read command lines when
88 the shell is interactive.
89 --noprofile
91 Do not read either the system-wide startup file /etc/profile or
92 any of the personal initialization files ~/.bash_profile,
93 ~/.bash_login, or ~/.profile. By default, bash reads these
94 files when it is invoked as a login shell (see INVOCATION be‐
95 low).
96 --norc Do not read and execute the personal initialization file
98 ~/.bashrc if the shell is interactive. This option is on by de‐
99 fault if the shell is invoked as sh.
100 --posix
102 Change the behavior of bash where the default operation differs
103 from the POSIX standard to match the standard (posix mode). See
104 SEE ALSO below for a reference to a document that details how
105 posix mode affects bash's behavior.
106 --restricted
108 The shell becomes restricted (see RESTRICTED SHELL below).
109 --rpm-requires
111 Produce the list of files that are required for the shell script
112 to run. This implies '-n' and is subject to the same limita‐
113 tions as compile time error checking checking; Command substitu‐
114 tions, Conditional expressions and eval builtin are not parsed
115 so some dependencies may be missed.
116 --verbose
118 Equivalent to -v.
119 --version
121 Show version information for this instance of bash on the stan‐
122 dard output and exit successfully.
123
125 If arguments remain after option processing, and neither the -c nor the
126 -s option has been supplied, the first argument is assumed to be the
127 name of a file containing shell commands. If bash is invoked in this
128 fashion, $0 is set to the name of the file, and the positional parame‐
129 ters are set to the remaining arguments. Bash reads and executes com‐
130 mands from this file, then exits. Bash's exit status is the exit sta‐
131 tus of the last command executed in the script. If no commands are ex‐
132 ecuted, the exit status is 0. An attempt is first made to open the
133 file in the current directory, and, if no file is found, then the shell
134 searches the directories in PATH for the script.
135
137 A login shell is one whose first character of argument zero is a -, or
138 one started with the --login option.
139 An interactive shell is one started without non-option arguments (un‐
141 less -s is specified) and without the -c option, whose standard input
142 and error are both connected to terminals (as determined by isatty(3)),
143 or one started with the -i option. PS1 is set and $- includes i if
144 bash is interactive, allowing a shell script or a startup file to test
145 this state.
146 The following paragraphs describe how bash executes its startup files.
148 If any of the files exist but cannot be read, bash reports an error.
149 Tildes are expanded in filenames as described below under Tilde Expan‐
150 sion in the EXPANSION section.
151 When bash is invoked as an interactive login shell, or as a non-inter‐
153 active shell with the --login option, it first reads and executes com‐
154 mands from the file /etc/profile, if that file exists. After reading
155 that file, it looks for ~/.bash_profile, ~/.bash_login, and ~/.profile,
156 in that order, and reads and executes commands from the first one that
157 exists and is readable. The --noprofile option may be used when the
158 shell is started to inhibit this behavior.
159 When an interactive login shell exits, or a non-interactive login shell
161 executes the exit builtin command, bash reads and executes commands
162 from the files ~/.bash_logout and /etc/bash.bash_logout, if the files
163 exists.
164 When an interactive shell that is not a login shell is started, bash
166 reads and executes commands from ~/.bashrc, if that file exists. This
167 may be inhibited by using the --norc option. The --rcfile file option
168 will force bash to read and execute commands from file instead of
169 ~/.bashrc.
170 When bash is started non-interactively, to run a shell script, for ex‐
172 ample, it looks for the variable BASH_ENV in the environment, expands
173 its value if it appears there, and uses the expanded value as the name
174 of a file to read and execute. Bash behaves as if the following com‐
175 mand were executed:
176 if [ -n "$BASH_ENV" ]; then . "$BASH_ENV"; fi
177 but the value of the PATH variable is not used to search for the file‐
178 name.
179 If bash is invoked with the name sh, it tries to mimic the startup be‐
181 havior of historical versions of sh as closely as possible, while con‐
182 forming to the POSIX standard as well. When invoked as an interactive
183 login shell, or a non-interactive shell with the --login option, it
184 first attempts to read and execute commands from /etc/profile and
185 ~/.profile, in that order. The --noprofile option may be used to in‐
186 hibit this behavior. When invoked as an interactive shell with the
187 name sh, bash looks for the variable ENV, expands its value if it is
188 defined, and uses the expanded value as the name of a file to read and
189 execute. Since a shell invoked as sh does not attempt to read and exe‐
190 cute commands from any other startup files, the --rcfile option has no
191 effect. A non-interactive shell invoked with the name sh does not at‐
192 tempt to read any other startup files. When invoked as sh, bash enters
193 posix mode after the startup files are read.
194 When bash is started in posix mode, as with the --posix command line
196 option, it follows the POSIX standard for startup files. In this mode,
197 interactive shells expand the ENV variable and commands are read and
198 executed from the file whose name is the expanded value. No other
199 startup files are read.
200 Bash attempts to determine when it is being run with its standard input
202 connected to a network connection, as when executed by the historical
203 remote shell daemon, usually rshd, or the secure shell daemon sshd. If
204 bash determines it is being run non-interactively in this fashion, it
205 reads and executes commands from ~/.bashrc, if that file exists and is
206 readable. It will not do this if invoked as sh. The --norc option may
207 be used to inhibit this behavior, and the --rcfile option may be used
208 to force another file to be read, but neither rshd nor sshd generally
209 invoke the shell with those options or allow them to be specified.
210 If the shell is started with the effective user (group) id not equal to
212 the real user (group) id, and the -p option is not supplied, no startup
213 files are read, shell functions are not inherited from the environment,
214 the SHELLOPTS, BASHOPTS, CDPATH, and GLOBIGNORE variables, if they ap‐
215 pear in the environment, are ignored, and the effective user id is set
216 to the real user id. If the -p option is supplied at invocation, the
217 startup behavior is the same, but the effective user id is not reset.
218
220 The following definitions are used throughout the rest of this docu‐
221 ment.
222 blank A space or tab.
223 word A sequence of characters considered as a single unit by the
224 shell. Also known as a token.
225 name A word consisting only of alphanumeric characters and under‐
226 scores, and beginning with an alphabetic character or an under‐
227 score. Also referred to as an identifier.
228 metacharacter
229 A character that, when unquoted, separates words. One of the
230 following:
231 | & ; ( ) < > space tab newline
232 control operator
233 A token that performs a control function. It is one of the fol‐
234 lowing symbols:
235 || & && ; ;; ;& ;;& ( ) | |& <newline>
236
238 Reserved words are words that have a special meaning to the shell. The
239 following words are recognized as reserved when unquoted and either the
240 first word of a command (see SHELL GRAMMAR below), the third word of a
241 case or select command (only in is valid), or the third word of a for
242 command (only in and do are valid):
243 ! case coproc do done elif else esac fi for function if in select
245 then until while { } time [[ ]]
246
248 This section describes the syntax of the various forms of shell com‐
249 mands.
250 Simple Commands
252 A simple command is a sequence of optional variable assignments fol‐
253 lowed by blank-separated words and redirections, and terminated by a
254 control operator. The first word specifies the command to be executed,
255 and is passed as argument zero. The remaining words are passed as ar‐
256 guments to the invoked command.
257 The return value of a simple command is its exit status, or 128+n if
259 the command is terminated by signal n.
260 Pipelines
262 A pipeline is a sequence of one or more commands separated by one of
263 the control operators | or |&. The format for a pipeline is:
264 [time [-p]] [ ! ] command1 [ [|⎪|&] command2 ... ]
266 The standard output of command1 is connected via a pipe to the standard
268 input of command2. This connection is performed before any redirec‐
269 tions specified by the command1(see REDIRECTION below). If |& is used,
270 command1's standard error, in addition to its standard output, is con‐
271 nected to command2's standard input through the pipe; it is shorthand
272 for 2>&1 |. This implicit redirection of the standard error to the
273 standard output is performed after any redirections specified by com‐
274 mand1.
275 The return status of a pipeline is the exit status of the last command,
277 unless the pipefail option is enabled. If pipefail is enabled, the
278 pipeline's return status is the value of the last (rightmost) command
279 to exit with a non-zero status, or zero if all commands exit success‐
280 fully. If the reserved word ! precedes a pipeline, the exit status of
281 that pipeline is the logical negation of the exit status as described
282 above. The shell waits for all commands in the pipeline to terminate
283 before returning a value.
284 If the time reserved word precedes a pipeline, the elapsed as well as
286 user and system time consumed by its execution are reported when the
287 pipeline terminates. The -p option changes the output format to that
288 specified by POSIX. When the shell is in posix mode, it does not rec‐
289 ognize time as a reserved word if the next token begins with a `-'.
290 The TIMEFORMAT variable may be set to a format string that specifies
291 how the timing information should be displayed; see the description of
292 TIMEFORMAT under Shell Variables below.
293 When the shell is in posix mode, time may be followed by a newline. In
295 this case, the shell displays the total user and system time consumed
296 by the shell and its children. The TIMEFORMAT variable may be used to
297 specify the format of the time information.
298 Each command in a multi-command pipeline, where pipes are created, is
300 executed in a subshell, which is a separate process. See COMMAND EXE‐
301 CUTION ENVIRONMENT for a description of subshells and a subshell envi‐
302 ronment. If the lastpipe option is enabled using the shopt builtin
303 (see the description of shopt below), the last element of a pipeline
304 may be run by the shell process when job control is not active.
305 Lists
307 A list is a sequence of one or more pipelines separated by one of the
308 operators ;, &, &&, or ||, and optionally terminated by one of ;, &, or
309 <newline>.
310 Of these list operators, && and || have equal precedence, followed by ;
312 and &, which have equal precedence.
313 A sequence of one or more newlines may appear in a list instead of a
315 semicolon to delimit commands.
316 If a command is terminated by the control operator &, the shell exe‐
318 cutes the command in the background in a subshell. The shell does not
319 wait for the command to finish, and the return status is 0. These are
320 referred to as asynchronous commands. Commands separated by a ; are
321 executed sequentially; the shell waits for each command to terminate in
322 turn. The return status is the exit status of the last command exe‐
323 cuted.
324 AND and OR lists are sequences of one or more pipelines separated by
326 the && and || control operators, respectively. AND and OR lists are
327 executed with left associativity. An AND list has the form
328 command1 && command2
330 command2 is executed if, and only if, command1 returns an exit status
332 of zero (success).
333 An OR list has the form
335 command1 || command2
337 command2 is executed if, and only if, command1 returns a non-zero exit
339 status. The return status of AND and OR lists is the exit status of
340 the last command executed in the list.
341 Compound Commands
343 A compound command is one of the following. In most cases a list in a
344 command's description may be separated from the rest of the command by
345 one or more newlines, and may be followed by a newline in place of a
346 semicolon.
347 (list) list is executed in a subshell (see COMMAND EXECUTION ENVIRON‐
349 MENT below for a description of a subshell environment). Vari‐
350 able assignments and builtin commands that affect the shell's
351 environment do not remain in effect after the command completes.
352 The return status is the exit status of list.
353 { list; }
355 list is simply executed in the current shell environment. list
356 must be terminated with a newline or semicolon. This is known
357 as a group command. The return status is the exit status of
358 list. Note that unlike the metacharacters ( and ), { and } are
359 reserved words and must occur where a reserved word is permitted
360 to be recognized. Since they do not cause a word break, they
361 must be separated from list by whitespace or another shell
362 metacharacter.
363 ((expression))
365 The expression is evaluated according to the rules described be‐
366 low under ARITHMETIC EVALUATION. If the value of the expression
367 is non-zero, the return status is 0; otherwise the return status
368 is 1. The expression undergoes the same expansions as if it
369 were within double quotes, but double quote characters in ex‐
370 pression are not treated specially and are removed.
371 [[ expression ]]
373 Return a status of 0 or 1 depending on the evaluation of the
374 conditional expression expression. Expressions are composed of
375 the primaries described below under CONDITIONAL EXPRESSIONS.
376 The words between the [[ and ]] do not undergo word splitting
377 and pathname expansion. The shell performs tilde expansion, pa‐
378 rameter and variable expansion, arithmetic expansion, command
379 substitution, process substitution, and quote removal on those
380 words (the expansions that would occur if the words were en‐
381 closed in double quotes). Conditional operators such as -f must
382 be unquoted to be recognized as primaries.
383 When used with [[, the < and > operators sort lexicographically
385 using the current locale.
386 When the == and != operators are used, the string to the right
388 of the operator is considered a pattern and matched according to
389 the rules described below under Pattern Matching, as if the ext‐
390 glob shell option were enabled. The = operator is equivalent to
391 ==. If the nocasematch shell option is enabled, the match is
392 performed without regard to the case of alphabetic characters.
393 The return value is 0 if the string matches (==) or does not
394 match (!=) the pattern, and 1 otherwise. Any part of the pat‐
395 tern may be quoted to force the quoted portion to be matched as
396 a string.
397 An additional binary operator, =~, is available, with the same
399 precedence as == and !=. When it is used, the string to the
400 right of the operator is considered a POSIX extended regular ex‐
401 pression and matched accordingly (using the POSIX regcomp and
402 regexec interfaces usually described in regex(3)). The return
403 value is 0 if the string matches the pattern, and 1 otherwise.
404 If the regular expression is syntactically incorrect, the condi‐
405 tional expression's return value is 2. If the nocasematch shell
406 option is enabled, the match is performed without regard to the
407 case of alphabetic characters. If any part of the pattern is
408 quoted, the quoted portion is matched literally. This means ev‐
409 ery character in the quoted portion matches itself, instead of
410 having any special pattern matching meaning. If the pattern is
411 stored in a shell variable, quoting the variable expansion
412 forces the entire pattern to be matched literally. Treat
413 bracket expressions in regular expressions carefully, since nor‐
414 mal quoting and pattern characters lose their meanings between
415 brackets.
416 The pattern will match if it matches any part of the string.
418 Anchor the pattern using the ^ and $ regular expression opera‐
419 tors to force it to match the entire string. The array variable
420 BASH_REMATCH records which parts of the string matched the pat‐
421 tern. The element of BASH_REMATCH with index 0 contains the
422 portion of the string matching the entire regular expression.
423 Substrings matched by parenthesized subexpressions within the
424 regular expression are saved in the remaining BASH_REMATCH in‐
425 dices. The element of BASH_REMATCH with index n is the portion
426 of the string matching the nth parenthesized subexpression.
427 Bash sets BASH_REMATCH in the global scope; declaring it as a
428 local variable will lead to unexpected results.
429 Expressions may be combined using the following operators,
431 listed in decreasing order of precedence:
432 ( expression )
434 Returns the value of expression. This may be used to
435 override the normal precedence of operators.
436 ! expression
437 True if expression is false.
438 expression1 && expression2
439 True if both expression1 and expression2 are true.
440 expression1 || expression2
441 True if either expression1 or expression2 is true.
442 The && and || operators do not evaluate expression2 if the value
444 of expression1 is sufficient to determine the return value of
445 the entire conditional expression.
446 for name [ [ in [ word ... ] ] ; ] do list ; done
448 The list of words following in is expanded, generating a list of
449 items. The variable name is set to each element of this list in
450 turn, and list is executed each time. If the in word is omit‐
451 ted, the for command executes list once for each positional pa‐
452 rameter that is set (see PARAMETERS below). The return status
453 is the exit status of the last command that executes. If the
454 expansion of the items following in results in an empty list, no
455 commands are executed, and the return status is 0.
456 for (( expr1 ; expr2 ; expr3 )) ; do list ; done
458 First, the arithmetic expression expr1 is evaluated according to
459 the rules described below under ARITHMETIC EVALUATION. The
460 arithmetic expression expr2 is then evaluated repeatedly until
461 it evaluates to zero. Each time expr2 evaluates to a non-zero
462 value, list is executed and the arithmetic expression expr3 is
463 evaluated. If any expression is omitted, it behaves as if it
464 evaluates to 1. The return value is the exit status of the last
465 command in list that is executed, or false if any of the expres‐
466 sions is invalid.
467 select name [ in word ] ; do list ; done
469 The list of words following in is expanded, generating a list of
470 items, and the set of expanded words is printed on the standard
471 error, each preceded by a number. If the in word is omitted,
472 the positional parameters are printed (see PARAMETERS below).
473 select then displays the PS3 prompt and reads a line from the
474 standard input. If the line consists of a number corresponding
475 to one of the displayed words, then the value of name is set to
476 that word. If the line is empty, the words and prompt are dis‐
477 played again. If EOF is read, the select command completes and
478 returns 1. Any other value read causes name to be set to null.
479 The line read is saved in the variable REPLY. The list is exe‐
480 cuted after each selection until a break command is executed.
481 The exit status of select is the exit status of the last command
482 executed in list, or zero if no commands were executed.
483 case word in [ [(] pattern [ | pattern ] ... ) list ;; ] ... esac
485 A case command first expands word, and tries to match it against
486 each pattern in turn, using the matching rules described under
487 Pattern Matching below. The word is expanded using tilde expan‐
488 sion, parameter and variable expansion, arithmetic expansion,
489 command substitution, process substitution and quote removal.
490 Each pattern examined is expanded using tilde expansion, parame‐
491 ter and variable expansion, arithmetic expansion, command sub‐
492 stitution, process substitution, and quote removal. If the no‐
493 casematch shell option is enabled, the match is performed with‐
494 out regard to the case of alphabetic characters. When a match
495 is found, the corresponding list is executed. If the ;; opera‐
496 tor is used, no subsequent matches are attempted after the first
497 pattern match. Using ;& in place of ;; causes execution to con‐
498 tinue with the list associated with the next set of patterns.
499 Using ;;& in place of ;; causes the shell to test the next pat‐
500 tern list in the statement, if any, and execute any associated
501 list on a successful match, continuing the case statement execu‐
502 tion as if the pattern list had not matched. The exit status is
503 zero if no pattern matches. Otherwise, it is the exit status of
504 the last command executed in list.
505 if list; then list; [ elif list; then list; ] ... [ else list; ] fi
507 The if list is executed. If its exit status is zero, the then
508 list is executed. Otherwise, each elif list is executed in
509 turn, and if its exit status is zero, the corresponding then
510 list is executed and the command completes. Otherwise, the else
511 list is executed, if present. The exit status is the exit sta‐
512 tus of the last command executed, or zero if no condition tested
513 true.
514 while list-1; do list-2; done
516 until list-1; do list-2; done
517 The while command continuously executes the list list-2 as long
518 as the last command in the list list-1 returns an exit status of
519 zero. The until command is identical to the while command, ex‐
520 cept that the test is negated: list-2 is executed as long as the
521 last command in list-1 returns a non-zero exit status. The exit
522 status of the while and until commands is the exit status of the
523 last command executed in list-2, or zero if none was executed.
524 Coprocesses
526 A coprocess is a shell command preceded by the coproc reserved word. A
527 coprocess is executed asynchronously in a subshell, as if the command
528 had been terminated with the & control operator, with a two-way pipe
529 established between the executing shell and the coprocess.
530 The syntax for a coprocess is:
532 coproc [NAME] command [redirections]
534 This creates a coprocess named NAME. command may be either a simple
536 command or a compound command (see above). NAME is a shell variable
537 name. If NAME is not supplied, the default name is COPROC.
538 The recommended form to use for a coprocess is
540 coproc NAME { command [redirections]; }
542 This form is recommended because simple commands result in the copro‐
544 cess always being named COPROC, and it is simpler to use and more com‐
545 plete than the other compound commands.
546 If command is a compound command, NAME is optional. The word following
548 coproc determines whether that word is interpreted as a variable name:
549 it is interpreted as NAME if it is not a reserved word that introduces
550 a compound command. If command is a simple command, NAME is not al‐
551 lowed; this is to avoid confusion between NAME and the first word of
552 the simple command.
553 When the coprocess is executed, the shell creates an array variable
555 (see Arrays below) named NAME in the context of the executing shell.
556 The standard output of command is connected via a pipe to a file de‐
557 scriptor in the executing shell, and that file descriptor is assigned
558 to NAME[0]. The standard input of command is connected via a pipe to a
559 file descriptor in the executing shell, and that file descriptor is as‐
560 signed to NAME[1]. This pipe is established before any redirections
561 specified by the command (see REDIRECTION below). The file descriptors
562 can be utilized as arguments to shell commands and redirections using
563 standard word expansions. Other than those created to execute command
564 and process substitutions, the file descriptors are not available in
565 subshells.
566 The process ID of the shell spawned to execute the coprocess is avail‐
568 able as the value of the variable NAME_PID. The wait builtin command
569 may be used to wait for the coprocess to terminate.
570 Since the coprocess is created as an asynchronous command, the coproc
572 command always returns success. The return status of a coprocess is
573 the exit status of command.
574 Shell Function Definitions
576 A shell function is an object that is called like a simple command and
577 executes a compound command with a new set of positional parameters.
578 Shell functions are declared as follows:
579 fname () compound-command [redirection]
581 function fname [()] compound-command [redirection]
582 This defines a function named fname. The reserved word function
583 is optional. If the function reserved word is supplied, the
584 parentheses are optional. The body of the function is the com‐
585 pound command compound-command (see Compound Commands above).
586 That command is usually a list of commands between { and }, but
587 may be any command listed under Compound Commands above. If the
588 function reserved word is used, but the parentheses are not sup‐
589 plied, the braces are recommended. compound-command is executed
590 whenever fname is specified as the name of a simple command.
591 When in posix mode, fname must be a valid shell name and may not
592 be the name of one of the POSIX special builtins. In default
593 mode, a function name can be any unquoted shell word that does
594 not contain $. Any redirections (see REDIRECTION below) speci‐
595 fied when a function is defined are performed when the function
596 is executed. The exit status of a function definition is zero
597 unless a syntax error occurs or a readonly function with the
598 same name already exists. When executed, the exit status of a
599 function is the exit status of the last command executed in the
600 body. (See FUNCTIONS below.)
601
603 In a non-interactive shell, or an interactive shell in which the inter‐
604 active_comments option to the shopt builtin is enabled (see SHELL
605 BUILTIN COMMANDS below), a word beginning with # causes that word and
606 all remaining characters on that line to be ignored. An interactive
607 shell without the interactive_comments option enabled does not allow
608 comments. The interactive_comments option is on by default in interac‐
609 tive shells.
610
612 Quoting is used to remove the special meaning of certain characters or
613 words to the shell. Quoting can be used to disable special treatment
614 for special characters, to prevent reserved words from being recognized
615 as such, and to prevent parameter expansion.
616 Each of the metacharacters listed above under DEFINITIONS has special
618 meaning to the shell and must be quoted if it is to represent itself.
619 When the command history expansion facilities are being used (see HIS‐
621 TORY EXPANSION below), the history expansion character, usually !, must
622 be quoted to prevent history expansion.
623 There are three quoting mechanisms: the escape character, single
625 quotes, and double quotes.
626 A non-quoted backslash (\) is the escape character. It preserves the
628 literal value of the next character that follows, with the exception of
629 <newline>. If a \<newline> pair appears, and the backslash is not it‐
630 self quoted, the \<newline> is treated as a line continuation (that is,
631 it is removed from the input stream and effectively ignored).
632 Enclosing characters in single quotes preserves the literal value of
634 each character within the quotes. A single quote may not occur between
635 single quotes, even when preceded by a backslash.
636 Enclosing characters in double quotes preserves the literal value of
638 all characters within the quotes, with the exception of $, `, \, and,
639 when history expansion is enabled, !. When the shell is in posix mode,
640 the ! has no special meaning within double quotes, even when history
641 expansion is enabled. The characters $ and ` retain their special
642 meaning within double quotes. The backslash retains its special mean‐
643 ing only when followed by one of the following characters: $, `, ", \,
644 or <newline>. A double quote may be quoted within double quotes by
645 preceding it with a backslash. If enabled, history expansion will be
646 performed unless an ! appearing in double quotes is escaped using a
647 backslash. The backslash preceding the ! is not removed.
648 The special parameters * and @ have special meaning when in double
650 quotes (see PARAMETERS below).
651 Character sequences of the form $'string' are treated as a special
653 variant of single quotes. The sequence expands to string, with back‐
654 slash-escaped characters in string replaced as specified by the ANSI C
655 standard. Backslash escape sequences, if present, are decoded as fol‐
656 lows:
657 \a alert (bell)
658 \b backspace
659 \e
660 \E an escape character
661 \f form feed
662 \n new line
663 \r carriage return
664 \t horizontal tab
665 \v vertical tab
666 \\ backslash
667 \' single quote
668 \" double quote
669 \? question mark
670 \nnn the eight-bit character whose value is the octal value
671 nnn (one to three octal digits)
672 \xHH the eight-bit character whose value is the hexadecimal
673 value HH (one or two hex digits)
674 \uHHHH the Unicode (ISO/IEC 10646) character whose value is the
675 hexadecimal value HHHH (one to four hex digits)
676 \UHHHHHHHH
677 the Unicode (ISO/IEC 10646) character whose value is the
678 hexadecimal value HHHHHHHH (one to eight hex digits)
679 \cx a control-x character
680 The expanded result is single-quoted, as if the dollar sign had not
682 been present.
683 A double-quoted string preceded by a dollar sign ($"string") will cause
685 the string to be translated according to the current locale. The get‐
686 text infrastructure performs the lookup and translation, using the
687 LC_MESSAGES, TEXTDOMAINDIR, and TEXTDOMAIN shell variables. If the
688 current locale is C or POSIX, if there are no translations available,
689 or if the string is not translated, the dollar sign is ignored. This
690 is a form of double quoting, so the string remains double-quoted by de‐
691 fault, whether or not it is translated and replaced. If the noex‐
692 pand_translation option is enabled using the shopt builtin, translated
693 strings are single-quoted instead of double-quoted. See the descrip‐
694 tion of shopt below under SHELLBUILTINCOMMANDS.
695
697 A parameter is an entity that stores values. It can be a name, a num‐
698 ber, or one of the special characters listed below under Special Param‐
699 eters. A variable is a parameter denoted by a name. A variable has a
700 value and zero or more attributes. Attributes are assigned using the
701 declare builtin command (see declare below in SHELL BUILTIN COMMANDS).
702 A parameter is set if it has been assigned a value. The null string is
704 a valid value. Once a variable is set, it may be unset only by using
705 the unset builtin command (see SHELL BUILTIN COMMANDS below).
706 A variable may be assigned to by a statement of the form
708 name=[value]
710 If value is not given, the variable is assigned the null string. All
712 values undergo tilde expansion, parameter and variable expansion, com‐
713 mand substitution, arithmetic expansion, and quote removal (see EXPAN‐
714 SION below). If the variable has its integer attribute set, then value
715 is evaluated as an arithmetic expression even if the $((...)) expansion
716 is not used (see Arithmetic Expansion below). Word splitting and path‐
717 name expansion are not performed. Assignment statements may also ap‐
718 pear as arguments to the alias, declare, typeset, export, readonly, and
719 local builtin commands (declaration commands). When in posix mode,
720 these builtins may appear in a command after one or more instances of
721 the command builtin and retain these assignment statement properties.
722 In the context where an assignment statement is assigning a value to a
724 shell variable or array index, the += operator can be used to append to
725 or add to the variable's previous value. This includes arguments to
726 builtin commands such as declare that accept assignment statements
727 (declaration commands). When += is applied to a variable for which the
728 integer attribute has been set, value is evaluated as an arithmetic ex‐
729 pression and added to the variable's current value, which is also eval‐
730 uated. When += is applied to an array variable using compound assign‐
731 ment (see Arrays below), the variable's value is not unset (as it is
732 when using =), and new values are appended to the array beginning at
733 one greater than the array's maximum index (for indexed arrays) or
734 added as additional key-value pairs in an associative array. When ap‐
735 plied to a string-valued variable, value is expanded and appended to
736 the variable's value.
737 A variable can be assigned the nameref attribute using the -n option to
739 the declare or local builtin commands (see the descriptions of declare
740 and local below) to create a nameref, or a reference to another vari‐
741 able. This allows variables to be manipulated indirectly. Whenever
742 the nameref variable is referenced, assigned to, unset, or has its at‐
743 tributes modified (other than using or changing the nameref attribute
744 itself), the operation is actually performed on the variable specified
745 by the nameref variable's value. A nameref is commonly used within
746 shell functions to refer to a variable whose name is passed as an argu‐
747 ment to the function. For instance, if a variable name is passed to a
748 shell function as its first argument, running
749 declare -n ref=$1
750 inside the function creates a nameref variable ref whose value is the
751 variable name passed as the first argument. References and assignments
752 to ref, and changes to its attributes, are treated as references, as‐
753 signments, and attribute modifications to the variable whose name was
754 passed as $1. If the control variable in a for loop has the nameref
755 attribute, the list of words can be a list of shell variables, and a
756 name reference will be established for each word in the list, in turn,
757 when the loop is executed. Array variables cannot be given the nameref
758 attribute. However, nameref variables can reference array variables
759 and subscripted array variables. Namerefs can be unset using the -n
760 option to the unset builtin. Otherwise, if unset is executed with the
761 name of a nameref variable as an argument, the variable referenced by
762 the nameref variable will be unset.
763 Positional Parameters
765 A positional parameter is a parameter denoted by one or more digits,
766 other than the single digit 0. Positional parameters are assigned from
767 the shell's arguments when it is invoked, and may be reassigned using
768 the set builtin command. Positional parameters may not be assigned to
769 with assignment statements. The positional parameters are temporarily
770 replaced when a shell function is executed (see FUNCTIONS below).
771 When a positional parameter consisting of more than a single digit is
773 expanded, it must be enclosed in braces (see EXPANSION below).
774 Special Parameters
776 The shell treats several parameters specially. These parameters may
777 only be referenced; assignment to them is not allowed.
778 * Expands to the positional parameters, starting from one. When
779 the expansion is not within double quotes, each positional pa‐
780 rameter expands to a separate word. In contexts where it is
781 performed, those words are subject to further word splitting and
782 pathname expansion. When the expansion occurs within double
783 quotes, it expands to a single word with the value of each pa‐
784 rameter separated by the first character of the IFS special
785 variable. That is, "$*" is equivalent to "$1c$2c...", where c
786 is the first character of the value of the IFS variable. If IFS
787 is unset, the parameters are separated by spaces. If IFS is
788 null, the parameters are joined without intervening separators.
789 @ Expands to the positional parameters, starting from one. In
790 contexts where word splitting is performed, this expands each
791 positional parameter to a separate word; if not within double
792 quotes, these words are subject to word splitting. In contexts
793 where word splitting is not performed, this expands to a single
794 word with each positional parameter separated by a space. When
795 the expansion occurs within double quotes, each parameter ex‐
796 pands to a separate word. That is, "$@" is equivalent to "$1"
797 "$2" ... If the double-quoted expansion occurs within a word,
798 the expansion of the first parameter is joined with the begin‐
799 ning part of the original word, and the expansion of the last
800 parameter is joined with the last part of the original word.
801 When there are no positional parameters, "$@" and $@ expand to
802 nothing (i.e., they are removed).
803 # Expands to the number of positional parameters in decimal.
804 ? Expands to the exit status of the most recently executed fore‐
805 ground pipeline.
806 - Expands to the current option flags as specified upon invoca‐
807 tion, by the set builtin command, or those set by the shell it‐
808 self (such as the -i option).
809 $ Expands to the process ID of the shell. In a subshell, it ex‐
810 pands to the process ID of the current shell, not the subshell.
811 ! Expands to the process ID of the job most recently placed into
812 the background, whether executed as an asynchronous command or
813 using the bg builtin (see JOB CONTROL below).
814 0 Expands to the name of the shell or shell script. This is set
815 at shell initialization. If bash is invoked with a file of com‐
816 mands, $0 is set to the name of that file. If bash is started
817 with the -c option, then $0 is set to the first argument after
818 the string to be executed, if one is present. Otherwise, it is
819 set to the filename used to invoke bash, as given by argument
820 zero.
821 Shell Variables
823 The following variables are set by the shell:
824 _ At shell startup, set to the pathname used to invoke the shell
826 or shell script being executed as passed in the environment or
827 argument list. Subsequently, expands to the last argument to
828 the previous simple command executed in the foreground, after
829 expansion. Also set to the full pathname used to invoke each
830 command executed and placed in the environment exported to that
831 command. When checking mail, this parameter holds the name of
832 the mail file currently being checked.
833 BASH Expands to the full filename used to invoke this instance of
834 bash.
835 BASHOPTS
836 A colon-separated list of enabled shell options. Each word in
837 the list is a valid argument for the -s option to the shopt
838 builtin command (see SHELL BUILTIN COMMANDS below). The options
839 appearing in BASHOPTS are those reported as on by shopt. If
840 this variable is in the environment when bash starts up, each
841 shell option in the list will be enabled before reading any
842 startup files. This variable is read-only.
843 BASHPID
844 Expands to the process ID of the current bash process. This
845 differs from $$ under certain circumstances, such as subshells
846 that do not require bash to be re-initialized. Assignments to
847 BASHPID have no effect. If BASHPID is unset, it loses its spe‐
848 cial properties, even if it is subsequently reset.
849 BASH_ALIASES
850 An associative array variable whose members correspond to the
851 internal list of aliases as maintained by the alias builtin.
852 Elements added to this array appear in the alias list; however,
853 unsetting array elements currently does not cause aliases to be
854 removed from the alias list. If BASH_ALIASES is unset, it loses
855 its special properties, even if it is subsequently reset.
856 BASH_ARGC
857 An array variable whose values are the number of parameters in
858 each frame of the current bash execution call stack. The number
859 of parameters to the current subroutine (shell function or
860 script executed with . or source) is at the top of the stack.
861 When a subroutine is executed, the number of parameters passed
862 is pushed onto BASH_ARGC. The shell sets BASH_ARGC only when in
863 extended debugging mode (see the description of the extdebug op‐
864 tion to the shopt builtin below). Setting extdebug after the
865 shell has started to execute a script, or referencing this vari‐
866 able when extdebug is not set, may result in inconsistent val‐
867 ues.
868 BASH_ARGV
869 An array variable containing all of the parameters in the cur‐
870 rent bash execution call stack. The final parameter of the last
871 subroutine call is at the top of the stack; the first parameter
872 of the initial call is at the bottom. When a subroutine is exe‐
873 cuted, the parameters supplied are pushed onto BASH_ARGV. The
874 shell sets BASH_ARGV only when in extended debugging mode (see
875 the description of the extdebug option to the shopt builtin be‐
876 low). Setting extdebug after the shell has started to execute a
877 script, or referencing this variable when extdebug is not set,
878 may result in inconsistent values.
879 BASH_ARGV0
880 When referenced, this variable expands to the name of the shell
881 or shell script (identical to $0; see the description of special
882 parameter 0 above). Assignment to BASH_ARGV0 causes the value
883 assigned to also be assigned to $0. If BASH_ARGV0 is unset, it
884 loses its special properties, even if it is subsequently reset.
885 BASH_CMDS
886 An associative array variable whose members correspond to the
887 internal hash table of commands as maintained by the hash
888 builtin. Elements added to this array appear in the hash table;
889 however, unsetting array elements currently does not cause com‐
890 mand names to be removed from the hash table. If BASH_CMDS is
891 unset, it loses its special properties, even if it is subse‐
892 quently reset.
893 BASH_COMMAND
894 The command currently being executed or about to be executed,
895 unless the shell is executing a command as the result of a trap,
896 in which case it is the command executing at the time of the
897 trap. If BASH_COMMAND is unset, it loses its special proper‐
898 ties, even if it is subsequently reset.
899 BASH_EXECUTION_STRING
900 The command argument to the -c invocation option.
901 BASH_LINENO
902 An array variable whose members are the line numbers in source
903 files where each corresponding member of FUNCNAME was invoked.
904 ${BASH_LINENO[$i]} is the line number in the source file
905 (${BASH_SOURCE[$i+1]}) where ${FUNCNAME[$i]} was called (or
906 ${BASH_LINENO[$i-1]} if referenced within another shell func‐
907 tion). Use LINENO to obtain the current line number.
908 BASH_LOADABLES_PATH
909 A colon-separated list of directories in which the shell looks
910 for dynamically loadable builtins specified by the enable com‐
911 mand.
912 BASH_REMATCH
913 An array variable whose members are assigned by the =~ binary
914 operator to the [[ conditional command. The element with index
915 0 is the portion of the string matching the entire regular ex‐
916 pression. The element with index n is the portion of the string
917 matching the nth parenthesized subexpression.
918 BASH_SOURCE
919 An array variable whose members are the source filenames where
920 the corresponding shell function names in the FUNCNAME array
921 variable are defined. The shell function ${FUNCNAME[$i]} is de‐
922 fined in the file ${BASH_SOURCE[$i]} and called from
923 ${BASH_SOURCE[$i+1]}.
924 BASH_SUBSHELL
925 Incremented by one within each subshell or subshell environment
926 when the shell begins executing in that environment. The ini‐
927 tial value is 0. If BASH_SUBSHELL is unset, it loses its spe‐
928 cial properties, even if it is subsequently reset.
929 BASH_VERSINFO
930 A readonly array variable whose members hold version information
931 for this instance of bash. The values assigned to the array
932 members are as follows:
933 BASH_VERSINFO[0] The major version number (the release).
934 BASH_VERSINFO[1] The minor version number (the version).
935 BASH_VERSINFO[2] The patch level.
936 BASH_VERSINFO[3] The build version.
937 BASH_VERSINFO[4] The release status (e.g., beta1).
938 BASH_VERSINFO[5] The value of MACHTYPE.
939 BASH_VERSION
940 Expands to a string describing the version of this instance of
941 bash.
942 COMP_CWORD
943 An index into ${COMP_WORDS} of the word containing the current
944 cursor position. This variable is available only in shell func‐
945 tions invoked by the programmable completion facilities (see
946 Programmable Completion below).
947 COMP_KEY
948 The key (or final key of a key sequence) used to invoke the cur‐
949 rent completion function.
950 COMP_LINE
951 The current command line. This variable is available only in
952 shell functions and external commands invoked by the program‐
953 mable completion facilities (see Programmable Completion below).
954 COMP_POINT
955 The index of the current cursor position relative to the begin‐
956 ning of the current command. If the current cursor position is
957 at the end of the current command, the value of this variable is
958 equal to ${#COMP_LINE}. This variable is available only in
959 shell functions and external commands invoked by the program‐
960 mable completion facilities (see Programmable Completion below).
961 COMP_TYPE
962 Set to an integer value corresponding to the type of completion
963 attempted that caused a completion function to be called: TAB,
964 for normal completion, ?, for listing completions after succes‐
965 sive tabs, !, for listing alternatives on partial word comple‐
966 tion, @, to list completions if the word is not unmodified, or
967 %, for menu completion. This variable is available only in
968 shell functions and external commands invoked by the program‐
969 mable completion facilities (see Programmable Completion below).
970 COMP_WORDBREAKS
971 The set of characters that the readline library treats as word
972 separators when performing word completion. If COMP_WORDBREAKS
973 is unset, it loses its special properties, even if it is subse‐
974 quently reset.
975 COMP_WORDS
976 An array variable (see Arrays below) consisting of the individ‐
977 ual words in the current command line. The line is split into
978 words as readline would split it, using COMP_WORDBREAKS as de‐
979 scribed above. This variable is available only in shell func‐
980 tions invoked by the programmable completion facilities (see
981 Programmable Completion below).
982 COPROC An array variable (see Arrays below) created to hold the file
983 descriptors for output from and input to an unnamed coprocess
984 (see Coprocesses above).
985 DIRSTACK
986 An array variable (see Arrays below) containing the current con‐
987 tents of the directory stack. Directories appear in the stack
988 in the order they are displayed by the dirs builtin. Assigning
989 to members of this array variable may be used to modify directo‐
990 ries already in the stack, but the pushd and popd builtins must
991 be used to add and remove directories. Assignment to this vari‐
992 able will not change the current directory. If DIRSTACK is un‐
993 set, it loses its special properties, even if it is subsequently
994 reset.
995 EPOCHREALTIME
996 Each time this parameter is referenced, it expands to the number
997 of seconds since the Unix Epoch (see time(3)) as a floating
998 point value with micro-second granularity. Assignments to
999 EPOCHREALTIME are ignored. If EPOCHREALTIME is unset, it loses
1000 its special properties, even if it is subsequently reset.
1001 EPOCHSECONDS
1002 Each time this parameter is referenced, it expands to the number
1003 of seconds since the Unix Epoch (see time(3)). Assignments to
1004 EPOCHSECONDS are ignored. If EPOCHSECONDS is unset, it loses
1005 its special properties, even if it is subsequently reset.
1006 EUID Expands to the effective user ID of the current user, initial‐
1007 ized at shell startup. This variable is readonly.
1008 FUNCNAME
1009 An array variable containing the names of all shell functions
1010 currently in the execution call stack. The element with index 0
1011 is the name of any currently-executing shell function. The bot‐
1012 tom-most element (the one with the highest index) is "main".
1013 This variable exists only when a shell function is executing.
1014 Assignments to FUNCNAME have no effect. If FUNCNAME is unset,
1015 it loses its special properties, even if it is subsequently re‐
1016 set.
1017 This variable can be used with BASH_LINENO and BASH_SOURCE.
1019 Each element of FUNCNAME has corresponding elements in
1020 BASH_LINENO and BASH_SOURCE to describe the call stack. For in‐
1021 stance, ${FUNCNAME[$i]} was called from the file
1022 ${BASH_SOURCE[$i+1]} at line number ${BASH_LINENO[$i]}. The
1023 caller builtin displays the current call stack using this infor‐
1024 mation.
1025 GROUPS An array variable containing the list of groups of which the
1026 current user is a member. Assignments to GROUPS have no effect.
1027 If GROUPS is unset, it loses its special properties, even if it
1028 is subsequently reset.
1029 HISTCMD
1030 The history number, or index in the history list, of the current
1031 command. Assignments to HISTCMD are ignored. If HISTCMD is un‐
1032 set, it loses its special properties, even if it is subsequently
1033 reset.
1034 HOSTNAME
1035 Automatically set to the name of the current host.
1036 HOSTTYPE
1037 Automatically set to a string that uniquely describes the type
1038 of machine on which bash is executing. The default is system-
1039 dependent.
1040 LINENO Each time this parameter is referenced, the shell substitutes a
1041 decimal number representing the current sequential line number
1042 (starting with 1) within a script or function. When not in a
1043 script or function, the value substituted is not guaranteed to
1044 be meaningful. If LINENO is unset, it loses its special proper‐
1045 ties, even if it is subsequently reset.
1046 MACHTYPE
1047 Automatically set to a string that fully describes the system
1048 type on which bash is executing, in the standard GNU cpu-com‐
1049 pany-system format. The default is system-dependent.
1050 MAPFILE
1051 An array variable (see Arrays below) created to hold the text
1052 read by the mapfile builtin when no variable name is supplied.
1053 OLDPWD The previous working directory as set by the cd command.
1054 OPTARG The value of the last option argument processed by the getopts
1055 builtin command (see SHELL BUILTIN COMMANDS below).
1056 OPTIND The index of the next argument to be processed by the getopts
1057 builtin command (see SHELL BUILTIN COMMANDS below).
1058 OSTYPE Automatically set to a string that describes the operating sys‐
1059 tem on which bash is executing. The default is system-depen‐
1060 dent.
1061 PIPESTATUS
1062 An array variable (see Arrays below) containing a list of exit
1063 status values from the processes in the most-recently-executed
1064 foreground pipeline (which may contain only a single command).
1065 PPID The process ID of the shell's parent. This variable is read‐
1066 only.
1067 PWD The current working directory as set by the cd command.
1068 RANDOM Each time this parameter is referenced, it expands to a random
1069 integer between 0 and 32767. Assigning a value to RANDOM ini‐
1070 tializes (seeds) the sequence of random numbers. If RANDOM is
1071 unset, it loses its special properties, even if it is subse‐
1072 quently reset.
1073 READLINE_ARGUMENT
1074 Any numeric argument given to a readline command that was de‐
1075 fined using "bind -x" (see SHELL BUILTIN COMMANDS below) when it
1076 was invoked.
1077 READLINE_LINE
1078 The contents of the readline line buffer, for use with "bind -x"
1079 (see SHELL BUILTIN COMMANDS below).
1080 READLINE_MARK
1081 The position of the mark (saved insertion point) in the readline
1082 line buffer, for use with "bind -x" (see SHELL BUILTIN COMMANDS
1083 below). The characters between the insertion point and the mark
1084 are often called the region.
1085 READLINE_POINT
1086 The position of the insertion point in the readline line buffer,
1087 for use with "bind -x" (see SHELL BUILTIN COMMANDS below).
1088 REPLY Set to the line of input read by the read builtin command when
1089 no arguments are supplied.
1090 SECONDS
1091 Each time this parameter is referenced, it expands to the number
1092 of seconds since shell invocation. If a value is assigned to
1093 SECONDS, the value returned upon subsequent references is the
1094 number of seconds since the assignment plus the value assigned.
1095 The number of seconds at shell invocation and the current time
1096 are always determined by querying the system clock. If SECONDS
1097 is unset, it loses its special properties, even if it is subse‐
1098 quently reset.
1099 SHELLOPTS
1100 A colon-separated list of enabled shell options. Each word in
1101 the list is a valid argument for the -o option to the set
1102 builtin command (see SHELL BUILTIN COMMANDS below). The options
1103 appearing in SHELLOPTS are those reported as on by set -o. If
1104 this variable is in the environment when bash starts up, each
1105 shell option in the list will be enabled before reading any
1106 startup files. This variable is read-only.
1107 SHLVL Incremented by one each time an instance of bash is started.
1108 SRANDOM
1109 This variable expands to a 32-bit pseudo-random number each time
1110 it is referenced. The random number generator is not linear on
1111 systems that support /dev/urandom or arc4random, so each re‐
1112 turned number has no relationship to the numbers preceding it.
1113 The random number generator cannot be seeded, so assignments to
1114 this variable have no effect. If SRANDOM is unset, it loses its
1115 special properties, even if it is subsequently reset.
1116 UID Expands to the user ID of the current user, initialized at shell
1117 startup. This variable is readonly.
1118 The following variables are used by the shell. In some cases, bash as‐
1120 signs a default value to a variable; these cases are noted below.
1121 BASH_COMPAT
1123 The value is used to set the shell's compatibility level. See
1124 SHELL COMPATIBILITY MODE below for a description of the various
1125 compatibility levels and their effects. The value may be a dec‐
1126 imal number (e.g., 4.2) or an integer (e.g., 42) corresponding
1127 to the desired compatibility level. If BASH_COMPAT is unset or
1128 set to the empty string, the compatibility level is set to the
1129 default for the current version. If BASH_COMPAT is set to a
1130 value that is not one of the valid compatibility levels, the
1131 shell prints an error message and sets the compatibility level
1132 to the default for the current version. The valid values corre‐
1133 spond to the compatibility levels described below under SHELL
1134 COMPATIBILITY MODE. For example, 4.2 and 42 are valid values
1135 that correspond to the compat42 shopt option and set the compat‐
1136 ibility level to 42. The current version is also a valid value.
1137 BASH_ENV
1138 If this parameter is set when bash is executing a shell script,
1139 its value is interpreted as a filename containing commands to
1140 initialize the shell, as in ~/.bashrc. The value of BASH_ENV is
1141 subjected to parameter expansion, command substitution, and
1142 arithmetic expansion before being interpreted as a filename.
1143 PATH is not used to search for the resultant filename.
1144 BASH_XTRACEFD
1145 If set to an integer corresponding to a valid file descriptor,
1146 bash will write the trace output generated when set -x is en‐
1147 abled to that file descriptor. The file descriptor is closed
1148 when BASH_XTRACEFD is unset or assigned a new value. Unsetting
1149 BASH_XTRACEFD or assigning it the empty string causes the trace
1150 output to be sent to the standard error. Note that setting
1151 BASH_XTRACEFD to 2 (the standard error file descriptor) and then
1152 unsetting it will result in the standard error being closed.
1153 CDPATH The search path for the cd command. This is a colon-separated
1154 list of directories in which the shell looks for destination di‐
1155 rectories specified by the cd command. A sample value is
1156 ".:~:/usr".
1157 CHILD_MAX
1158 Set the number of exited child status values for the shell to
1159 remember. Bash will not allow this value to be decreased below
1160 a POSIX-mandated minimum, and there is a maximum value (cur‐
1161 rently 8192) that this may not exceed. The minimum value is
1162 system-dependent.
1163 COLUMNS
1164 Used by the select compound command to determine the terminal
1165 width when printing selection lists. Automatically set if the
1166 checkwinsize option is enabled or in an interactive shell upon
1167 receipt of a SIGWINCH.
1168 COMPREPLY
1169 An array variable from which bash reads the possible completions
1170 generated by a shell function invoked by the programmable com‐
1171 pletion facility (see Programmable Completion below). Each ar‐
1172 ray element contains one possible completion.
1173 EMACS If bash finds this variable in the environment when the shell
1174 starts with value "t", it assumes that the shell is running in
1175 an Emacs shell buffer and disables line editing.
1176 ENV Expanded and executed similarly to BASH_ENV (see INVOCATION
1177 above) when an interactive shell is invoked in posix mode.
1178 EXECIGNORE
1179 A colon-separated list of shell patterns (see Pattern Matching)
1180 defining the list of filenames to be ignored by command search
1181 using PATH. Files whose full pathnames match one of these pat‐
1182 terns are not considered executable files for the purposes of
1183 completion and command execution via PATH lookup. This does not
1184 affect the behavior of the [, test, and [[ commands. Full path‐
1185 names in the command hash table are not subject to EXECIGNORE.
1186 Use this variable to ignore shared library files that have the
1187 executable bit set, but are not executable files. The pattern
1188 matching honors the setting of the extglob shell option.
1189 FCEDIT The default editor for the fc builtin command.
1190 FIGNORE
1191 A colon-separated list of suffixes to ignore when performing
1192 filename completion (see READLINE below). A filename whose suf‐
1193 fix matches one of the entries in FIGNORE is excluded from the
1194 list of matched filenames. A sample value is ".o:~".
1195 FUNCNEST
1196 If set to a numeric value greater than 0, defines a maximum
1197 function nesting level. Function invocations that exceed this
1198 nesting level will cause the current command to abort.
1199 GLOBIGNORE
1200 A colon-separated list of patterns defining the set of file
1201 names to be ignored by pathname expansion. If a file name
1202 matched by a pathname expansion pattern also matches one of the
1203 patterns in GLOBIGNORE, it is removed from the list of matches.
1204 HISTCONTROL
1205 A colon-separated list of values controlling how commands are
1206 saved on the history list. If the list of values includes ig‐
1207 norespace, lines which begin with a space character are not
1208 saved in the history list. A value of ignoredups causes lines
1209 matching the previous history entry to not be saved. A value of
1210 ignoreboth is shorthand for ignorespace and ignoredups. A value
1211 of erasedups causes all previous lines matching the current line
1212 to be removed from the history list before that line is saved.
1213 Any value not in the above list is ignored. If HISTCONTROL is
1214 unset, or does not include a valid value, all lines read by the
1215 shell parser are saved on the history list, subject to the value
1216 of HISTIGNORE. The second and subsequent lines of a multi-line
1217 compound command are not tested, and are added to the history
1218 regardless of the value of HISTCONTROL.
1219 HISTFILE
1220 The name of the file in which command history is saved (see HIS‐
1221 TORY below). The default value is ~/.bash_history. If unset,
1222 the command history is not saved when a shell exits.
1223 HISTFILESIZE
1224 The maximum number of lines contained in the history file. When
1225 this variable is assigned a value, the history file is trun‐
1226 cated, if necessary, to contain no more than that number of
1227 lines by removing the oldest entries. The history file is also
1228 truncated to this size after writing it when a shell exits. If
1229 the value is 0, the history file is truncated to zero size.
1230 Non-numeric values and numeric values less than zero inhibit
1231 truncation. The shell sets the default value to the value of
1232 HISTSIZE after reading any startup files.
1233 HISTIGNORE
1234 A colon-separated list of patterns used to decide which command
1235 lines should be saved on the history list. Each pattern is an‐
1236 chored at the beginning of the line and must match the complete
1237 line (no implicit `*' is appended). Each pattern is tested
1238 against the line after the checks specified by HISTCONTROL are
1239 applied. In addition to the normal shell pattern matching char‐
1240 acters, `&' matches the previous history line. `&' may be es‐
1241 caped using a backslash; the backslash is removed before at‐
1242 tempting a match. The second and subsequent lines of a multi-
1243 line compound command are not tested, and are added to the his‐
1244 tory regardless of the value of HISTIGNORE. The pattern match‐
1245 ing honors the setting of the extglob shell option.
1246 HISTSIZE
1247 The number of commands to remember in the command history (see
1248 HISTORY below). If the value is 0, commands are not saved in
1249 the history list. Numeric values less than zero result in every
1250 command being saved on the history list (there is no limit).
1251 The shell sets the default value to 500 after reading any
1252 startup files.
1253 HISTTIMEFORMAT
1254 If this variable is set and not null, its value is used as a
1255 format string for strftime(3) to print the time stamp associated
1256 with each history entry displayed by the history builtin. If
1257 this variable is set, time stamps are written to the history
1258 file so they may be preserved across shell sessions. This uses
1259 the history comment character to distinguish timestamps from
1260 other history lines.
1261 HOME The home directory of the current user; the default argument for
1262 the cd builtin command. The value of this variable is also used
1263 when performing tilde expansion.
1264 HOSTFILE
1265 Contains the name of a file in the same format as /etc/hosts
1266 that should be read when the shell needs to complete a hostname.
1267 The list of possible hostname completions may be changed while
1268 the shell is running; the next time hostname completion is at‐
1269 tempted after the value is changed, bash adds the contents of
1270 the new file to the existing list. If HOSTFILE is set, but has
1271 no value, or does not name a readable file, bash attempts to
1272 read /etc/hosts to obtain the list of possible hostname comple‐
1273 tions. When HOSTFILE is unset, the hostname list is cleared.
1274 IFS The Internal Field Separator that is used for word splitting af‐
1275 ter expansion and to split lines into words with the read
1276 builtin command. The default value is ``<space><tab><new‐
1277 line>''.
1278 IGNOREEOF
1279 Controls the action of an interactive shell on receipt of an EOF
1280 character as the sole input. If set, the value is the number of
1281 consecutive EOF characters which must be typed as the first
1282 characters on an input line before bash exits. If the variable
1283 exists but does not have a numeric value, or has no value, the
1284 default value is 10. If it does not exist, EOF signifies the
1285 end of input to the shell.
1286 INPUTRC
1287 The filename for the readline startup file, overriding the de‐
1288 fault of ~/.inputrc (see READLINE below).
1289 INSIDE_EMACS
1290 If this variable appears in the environment when the shell
1291 starts, bash assumes that it is running inside an Emacs shell
1292 buffer and may disable line editing, depending on the value of
1293 TERM.
1294 LANG Used to determine the locale category for any category not
1295 specifically selected with a variable starting with LC_.
1296 LC_ALL This variable overrides the value of LANG and any other LC_
1297 variable specifying a locale category.
1298 LC_COLLATE
1299 This variable determines the collation order used when sorting
1300 the results of pathname expansion, and determines the behavior
1301 of range expressions, equivalence classes, and collating se‐
1302 quences within pathname expansion and pattern matching.
1303 LC_CTYPE
1304 This variable determines the interpretation of characters and
1305 the behavior of character classes within pathname expansion and
1306 pattern matching.
1307 LC_MESSAGES
1308 This variable determines the locale used to translate double-
1309 quoted strings preceded by a $.
1310 LC_NUMERIC
1311 This variable determines the locale category used for number
1312 formatting.
1313 LC_TIME
1314 This variable determines the locale category used for data and
1315 time formatting.
1316 LINES Used by the select compound command to determine the column
1317 length for printing selection lists. Automatically set if the
1318 checkwinsize option is enabled or in an interactive shell upon
1319 receipt of a SIGWINCH.
1320 MAIL If this parameter is set to a file or directory name and the
1321 MAILPATH variable is not set, bash informs the user of the ar‐
1322 rival of mail in the specified file or Maildir-format directory.
1323 MAILCHECK
1324 Specifies how often (in seconds) bash checks for mail. The de‐
1325 fault is 60 seconds. When it is time to check for mail, the
1326 shell does so before displaying the primary prompt. If this
1327 variable is unset, or set to a value that is not a number
1328 greater than or equal to zero, the shell disables mail checking.
1329 MAILPATH
1330 A colon-separated list of filenames to be checked for mail. The
1331 message to be printed when mail arrives in a particular file may
1332 be specified by separating the filename from the message with a
1333 `?'. When used in the text of the message, $_ expands to the
1334 name of the current mailfile. Example:
1335 MAILPATH='/var/mail/bfox?"You have mail":~/shell-mail?"$_ has
1336 mail!"'
1337 Bash can be configured to supply a default value for this vari‐
1338 able (there is no value by default), but the location of the
1339 user mail files that it uses is system dependent (e.g.,
1340 /var/mail/$USER).
1341 OPTERR If set to the value 1, bash displays error messages generated by
1342 the getopts builtin command (see SHELL BUILTIN COMMANDS below).
1343 OPTERR is initialized to 1 each time the shell is invoked or a
1344 shell script is executed.
1345 PATH The search path for commands. It is a colon-separated list of
1346 directories in which the shell looks for commands (see COMMAND
1347 EXECUTION below). A zero-length (null) directory name in the
1348 value of PATH indicates the current directory. A null directory
1349 name may appear as two adjacent colons, or as an initial or
1350 trailing colon. The default path is system-dependent, and is
1351 set by the administrator who installs bash. A common value is
1352 ``/usr/local/bin:/usr/lo‐
1353 cal/sbin:/usr/bin:/usr/sbin:/bin:/sbin''.
1354 POSIXLY_CORRECT
1355 If this variable is in the environment when bash starts, the
1356 shell enters posix mode before reading the startup files, as if
1357 the --posix invocation option had been supplied. If it is set
1358 while the shell is running, bash enables posix mode, as if the
1359 command set -o posix had been executed. When the shell enters
1360 posix mode, it sets this variable if it was not already set.
1361 PROMPT_COMMAND
1362 If this variable is set, and is an array, the value of each set
1363 element is executed as a command prior to issuing each primary
1364 prompt. If this is set but not an array variable, its value is
1365 used as a command to execute instead.
1366 PROMPT_DIRTRIM
1367 If set to a number greater than zero, the value is used as the
1368 number of trailing directory components to retain when expanding
1369 the \w and \W prompt string escapes (see PROMPTING below).
1370 Characters removed are replaced with an ellipsis.
1371 PS0 The value of this parameter is expanded (see PROMPTING below)
1372 and displayed by interactive shells after reading a command and
1373 before the command is executed.
1374 PS1 The value of this parameter is expanded (see PROMPTING below)
1375 and used as the primary prompt string. The default value is
1376 ``\s-\v\$ ''.
1377 PS2 The value of this parameter is expanded as with PS1 and used as
1378 the secondary prompt string. The default is ``> ''.
1379 PS3 The value of this parameter is used as the prompt for the select
1380 command (see SHELL GRAMMAR above).
1381 PS4 The value of this parameter is expanded as with PS1 and the
1382 value is printed before each command bash displays during an ex‐
1383 ecution trace. The first character of the expanded value of PS4
1384 is replicated multiple times, as necessary, to indicate multiple
1385 levels of indirection. The default is ``+ ''.
1386 SHELL This variable expands to the full pathname to the shell. If it
1387 is not set when the shell starts, bash assigns to it the full
1388 pathname of the current user's login shell.
1389 TIMEFORMAT
1390 The value of this parameter is used as a format string specify‐
1391 ing how the timing information for pipelines prefixed with the
1392 time reserved word should be displayed. The % character intro‐
1393 duces an escape sequence that is expanded to a time value or
1394 other information. The escape sequences and their meanings are
1395 as follows; the braces denote optional portions.
1396 %% A literal %.
1397 %[p][l]R The elapsed time in seconds.
1398 %[p][l]U The number of CPU seconds spent in user mode.
1399 %[p][l]S The number of CPU seconds spent in system mode.
1400 %P The CPU percentage, computed as (%U + %S) / %R.
1401 The optional p is a digit specifying the precision, the number
1403 of fractional digits after a decimal point. A value of 0 causes
1404 no decimal point or fraction to be output. At most three places
1405 after the decimal point may be specified; values of p greater
1406 than 3 are changed to 3. If p is not specified, the value 3 is
1407 used.
1408 The optional l specifies a longer format, including minutes, of
1410 the form MMmSS.FFs. The value of p determines whether or not
1411 the fraction is included.
1412 If this variable is not set, bash acts as if it had the value
1414 $'\nreal\t%3lR\nuser\t%3lU\nsys\t%3lS'. If the value is null,
1415 no timing information is displayed. A trailing newline is added
1416 when the format string is displayed.
1417 TMOUT If set to a value greater than zero, TMOUT is treated as the de‐
1418 fault timeout for the read builtin. The select command termi‐
1419 nates if input does not arrive after TMOUT seconds when input is
1420 coming from a terminal. In an interactive shell, the value is
1421 interpreted as the number of seconds to wait for a line of input
1422 after issuing the primary prompt. Bash terminates after waiting
1423 for that number of seconds if a complete line of input does not
1424 arrive.
1425 TMPDIR If set, bash uses its value as the name of a directory in which
1426 bash creates temporary files for the shell's use.
1427 auto_resume
1428 This variable controls how the shell interacts with the user and
1429 job control. If this variable is set, single word simple com‐
1430 mands without redirections are treated as candidates for resump‐
1431 tion of an existing stopped job. There is no ambiguity allowed;
1432 if there is more than one job beginning with the string typed,
1433 the job most recently accessed is selected. The name of a
1434 stopped job, in this context, is the command line used to start
1435 it. If set to the value exact, the string supplied must match
1436 the name of a stopped job exactly; if set to substring, the
1437 string supplied needs to match a substring of the name of a
1438 stopped job. The substring value provides functionality analo‐
1439 gous to the %? job identifier (see JOB CONTROL below). If set
1440 to any other value, the supplied string must be a prefix of a
1441 stopped job's name; this provides functionality analogous to the
1442 %string job identifier.
1443 histchars
1444 The two or three characters which control history expansion and
1445 tokenization (see HISTORY EXPANSION below). The first character
1446 is the history expansion character, the character which signals
1447 the start of a history expansion, normally `!'. The second
1448 character is the quick substitution character, which is used as
1449 shorthand for re-running the previous command entered, substi‐
1450 tuting one string for another in the command. The default is
1451 `^'. The optional third character is the character which indi‐
1452 cates that the remainder of the line is a comment when found as
1453 the first character of a word, normally `#'. The history com‐
1454 ment character causes history substitution to be skipped for the
1455 remaining words on the line. It does not necessarily cause the
1456 shell parser to treat the rest of the line as a comment.
1457 Arrays
1459 Bash provides one-dimensional indexed and associative array variables.
1460 Any variable may be used as an indexed array; the declare builtin will
1461 explicitly declare an array. There is no maximum limit on the size of
1462 an array, nor any requirement that members be indexed or assigned con‐
1463 tiguously. Indexed arrays are referenced using integers (including
1464 arithmetic expressions) and are zero-based; associative arrays are ref‐
1465 erenced using arbitrary strings. Unless otherwise noted, indexed array
1466 indices must be non-negative integers.
1467 An indexed array is created automatically if any variable is assigned
1469 to using the syntax name[subscript]=value. The subscript is treated as
1470 an arithmetic expression that must evaluate to a number. To explicitly
1471 declare an indexed array, use declare -a name (see SHELL BUILTIN COM‐
1472 MANDS below). declare -a name[subscript] is also accepted; the sub‐
1473 script is ignored.
1474 Associative arrays are created using declare -A name.
1476 Attributes may be specified for an array variable using the declare and
1478 readonly builtins. Each attribute applies to all members of an array.
1479 Arrays are assigned to using compound assignments of the form
1481 name=(value1 ... valuen), where each value may be of the form [sub‐
1482 script]=string. Indexed array assignments do not require anything but
1483 string. Each value in the list is expanded using all the shell expan‐
1484 sions described below under EXPANSION. When assigning to indexed ar‐
1485 rays, if the optional brackets and subscript are supplied, that index
1486 is assigned to; otherwise the index of the element assigned is the last
1487 index assigned to by the statement plus one. Indexing starts at zero.
1488 When assigning to an associative array, the words in a compound assign‐
1490 ment may be either assignment statements, for which the subscript is
1491 required, or a list of words that is interpreted as a sequence of al‐
1492 ternating keys and values: name=( key1 value1 key2 value2 ...). These
1493 are treated identically to name=( [key1]=value1 [key2]=value2 ...).
1494 The first word in the list determines how the remaining words are in‐
1495 terpreted; all assignments in a list must be of the same type. When
1496 using key/value pairs, the keys may not be missing or empty; a final
1497 missing value is treated like the empty string.
1498 This syntax is also accepted by the declare builtin. Individual array
1500 elements may be assigned to using the name[subscript]=value syntax in‐
1501 troduced above. When assigning to an indexed array, if name is sub‐
1502 scripted by a negative number, that number is interpreted as relative
1503 to one greater than the maximum index of name, so negative indices
1504 count back from the end of the array, and an index of -1 references the
1505 last element.
1506 The += operator will append to an array variable when assigning using
1508 the compound assignment syntax; see PARAMETERS above.
1509 Any element of an array may be referenced using ${name[subscript]}.
1511 The braces are required to avoid conflicts with pathname expansion. If
1512 subscript is @ or *, the word expands to all members of name. These
1513 subscripts differ only when the word appears within double quotes. If
1514 the word is double-quoted, ${name[*]} expands to a single word with the
1515 value of each array member separated by the first character of the IFS
1516 special variable, and ${name[@]} expands each element of name to a sep‐
1517 arate word. When there are no array members, ${name[@]} expands to
1518 nothing. If the double-quoted expansion occurs within a word, the ex‐
1519 pansion of the first parameter is joined with the beginning part of the
1520 original word, and the expansion of the last parameter is joined with
1521 the last part of the original word. This is analogous to the expansion
1522 of the special parameters * and @ (see Special Parameters above).
1523 ${#name[subscript]} expands to the length of ${name[subscript]}. If
1524 subscript is * or @, the expansion is the number of elements in the ar‐
1525 ray. If the subscript used to reference an element of an indexed array
1526 evaluates to a number less than zero, it is interpreted as relative to
1527 one greater than the maximum index of the array, so negative indices
1528 count back from the end of the array, and an index of -1 references the
1529 last element.
1530 Referencing an array variable without a subscript is equivalent to ref‐
1532 erencing the array with a subscript of 0. Any reference to a variable
1533 using a valid subscript is legal, and bash will create an array if nec‐
1534 essary.
1535 An array variable is considered set if a subscript has been assigned a
1537 value. The null string is a valid value.
1538 It is possible to obtain the keys (indices) of an array as well as the
1540 values. ${!name[@]} and ${!name[*]} expand to the indices assigned in
1541 array variable name. The treatment when in double quotes is similar to
1542 the expansion of the special parameters @ and * within double quotes.
1543 The unset builtin is used to destroy arrays. unset name[subscript] de‐
1545 stroys the array element at index subscript, for both indexed and asso‐
1546 ciative arrays. Negative subscripts to indexed arrays are interpreted
1547 as described above. Unsetting the last element of an array variable
1548 does not unset the variable. unset name, where name is an array, re‐
1549 moves the entire array. unset name[subscript], where subscript is * or
1550 @, behaves differently depending on whether name is an indexed or asso‐
1551 ciative array. If name is an associative array, this unsets the ele‐
1552 ment with subscript * or @. If name is an indexed array, unset removes
1553 all of the elements but does not remove the array itself.
1554 When using a variable name with a subscript as an argument to a com‐
1556 mand, such as with unset, without using the word expansion syntax de‐
1557 scribed above, the argument is subject to pathname expansion. If path‐
1558 name expansion is not desired, the argument should be quoted.
1559 The declare, local, and readonly builtins each accept a -a option to
1561 specify an indexed array and a -A option to specify an associative ar‐
1562 ray. If both options are supplied, -A takes precedence. The read
1563 builtin accepts a -a option to assign a list of words read from the
1564 standard input to an array. The set and declare builtins display array
1565 values in a way that allows them to be reused as assignments.
1566
1568 Expansion is performed on the command line after it has been split into
1569 words. There are seven kinds of expansion performed: brace expansion,
1570 tilde expansion, parameter and variable expansion, command substitu‐
1571 tion, arithmetic expansion, word splitting, and pathname expansion.
1572 The order of expansions is: brace expansion; tilde expansion, parameter
1574 and variable expansion, arithmetic expansion, and command substitution
1575 (done in a left-to-right fashion); word splitting; and pathname expan‐
1576 sion.
1577 On systems that can support it, there is an additional expansion avail‐
1579 able: process substitution. This is performed at the same time as
1580 tilde, parameter, variable, and arithmetic expansion and command sub‐
1581 stitution.
1582 After these expansions are performed, quote characters present in the
1584 original word are removed unless they have been quoted themselves
1585 (quote removal).
1586 Only brace expansion, word splitting, and pathname expansion can in‐
1588 crease the number of words of the expansion; other expansions expand a
1589 single word to a single word. The only exceptions to this are the ex‐
1590 pansions of "$@" and "${name[@]}", and, in most cases, $* and
1591 ${name[*]} as explained above (see PARAMETERS).
1592 Brace Expansion
1594 Brace expansion is a mechanism by which arbitrary strings may be gener‐
1595 ated. This mechanism is similar to pathname expansion, but the file‐
1596 names generated need not exist. Patterns to be brace expanded take the
1597 form of an optional preamble, followed by either a series of comma-sep‐
1598 arated strings or a sequence expression between a pair of braces, fol‐
1599 lowed by an optional postscript. The preamble is prefixed to each
1600 string contained within the braces, and the postscript is then appended
1601 to each resulting string, expanding left to right.
1602 Brace expansions may be nested. The results of each expanded string
1604 are not sorted; left to right order is preserved. For example,
1605 a{d,c,b}e expands into `ade ace abe'.
1606 A sequence expression takes the form {x..y[..incr]}, where x and y are
1608 either integers or single letters, and incr, an optional increment, is
1609 an integer. When integers are supplied, the expression expands to each
1610 number between x and y, inclusive. Supplied integers may be prefixed
1611 with 0 to force each term to have the same width. When either x or y
1612 begins with a zero, the shell attempts to force all generated terms to
1613 contain the same number of digits, zero-padding where necessary. When
1614 letters are supplied, the expression expands to each character lexico‐
1615 graphically between x and y, inclusive, using the default C locale.
1616 Note that both x and y must be of the same type (integer or letter).
1617 When the increment is supplied, it is used as the difference between
1618 each term. The default increment is 1 or -1 as appropriate.
1619 Brace expansion is performed before any other expansions, and any char‐
1621 acters special to other expansions are preserved in the result. It is
1622 strictly textual. Bash does not apply any syntactic interpretation to
1623 the context of the expansion or the text between the braces.
1624 A correctly-formed brace expansion must contain unquoted opening and
1626 closing braces, and at least one unquoted comma or a valid sequence ex‐
1627 pression. Any incorrectly formed brace expansion is left unchanged. A
1628 { or , may be quoted with a backslash to prevent its being considered
1629 part of a brace expression. To avoid conflicts with parameter expan‐
1630 sion, the string ${ is not considered eligible for brace expansion, and
1631 inhibits brace expansion until the closing }.
1632 This construct is typically used as shorthand when the common prefix of
1634 the strings to be generated is longer than in the above example:
1635 mkdir /usr/local/src/bash/{old,new,dist,bugs}
1637 or
1638 chown root /usr/{ucb/{ex,edit},lib/{ex?.?*,how_ex}}
1639 Brace expansion introduces a slight incompatibility with historical
1641 versions of sh. sh does not treat opening or closing braces specially
1642 when they appear as part of a word, and preserves them in the output.
1643 Bash removes braces from words as a consequence of brace expansion.
1644 For example, a word entered to sh as file{1,2} appears identically in
1645 the output. The same word is output as file1 file2 after expansion by
1646 bash. If strict compatibility with sh is desired, start bash with the
1647 +B option or disable brace expansion with the +B option to the set com‐
1648 mand (see SHELL BUILTIN COMMANDS below).
1649 Tilde Expansion
1651 If a word begins with an unquoted tilde character (`~'), all of the
1652 characters preceding the first unquoted slash (or all characters, if
1653 there is no unquoted slash) are considered a tilde-prefix. If none of
1654 the characters in the tilde-prefix are quoted, the characters in the
1655 tilde-prefix following the tilde are treated as a possible login name.
1656 If this login name is the null string, the tilde is replaced with the
1657 value of the shell parameter HOME. If HOME is unset, the home direc‐
1658 tory of the user executing the shell is substituted instead. Other‐
1659 wise, the tilde-prefix is replaced with the home directory associated
1660 with the specified login name.
1661 If the tilde-prefix is a `~+', the value of the shell variable PWD re‐
1663 places the tilde-prefix. If the tilde-prefix is a `~-', the value of
1664 the shell variable OLDPWD, if it is set, is substituted. If the char‐
1665 acters following the tilde in the tilde-prefix consist of a number N,
1666 optionally prefixed by a `+' or a `-', the tilde-prefix is replaced
1667 with the corresponding element from the directory stack, as it would be
1668 displayed by the dirs builtin invoked with the tilde-prefix as an argu‐
1669 ment. If the characters following the tilde in the tilde-prefix con‐
1670 sist of a number without a leading `+' or `-', `+' is assumed.
1671 If the login name is invalid, or the tilde expansion fails, the word is
1673 unchanged.
1674 Each variable assignment is checked for unquoted tilde-prefixes immedi‐
1676 ately following a : or the first =. In these cases, tilde expansion is
1677 also performed. Consequently, one may use filenames with tildes in as‐
1678 signments to PATH, MAILPATH, and CDPATH, and the shell assigns the ex‐
1679 panded value.
1680 Bash also performs tilde expansion on words satisfying the conditions
1682 of variable assignments (as described above under PARAMETERS) when they
1683 appear as arguments to simple commands. Bash does not do this, except
1684 for the declaration commands listed above, when in posix mode.
1685 Parameter Expansion
1687 The `$' character introduces parameter expansion, command substitution,
1688 or arithmetic expansion. The parameter name or symbol to be expanded
1689 may be enclosed in braces, which are optional but serve to protect the
1690 variable to be expanded from characters immediately following it which
1691 could be interpreted as part of the name.
1692 When braces are used, the matching ending brace is the first `}' not
1694 escaped by a backslash or within a quoted string, and not within an em‐
1695 bedded arithmetic expansion, command substitution, or parameter expan‐
1696 sion.
1697 ${parameter}
1699 The value of parameter is substituted. The braces are required
1700 when parameter is a positional parameter with more than one
1701 digit, or when parameter is followed by a character which is not
1702 to be interpreted as part of its name. The parameter is a shell
1703 parameter as described above PARAMETERS) or an array reference
1704 (Arrays).
1705 If the first character of parameter is an exclamation point (!), and
1707 parameter is not a nameref, it introduces a level of indirection. Bash
1708 uses the value formed by expanding the rest of parameter as the new pa‐
1709 rameter; this is then expanded and that value is used in the rest of
1710 the expansion, rather than the expansion of the original parameter.
1711 This is known as indirect expansion. The value is subject to tilde ex‐
1712 pansion, parameter expansion, command substitution, and arithmetic ex‐
1713 pansion. If parameter is a nameref, this expands to the name of the
1714 parameter referenced by parameter instead of performing the complete
1715 indirect expansion. The exceptions to this are the expansions of
1716 ${!prefix*} and ${!name[@]} described below. The exclamation point
1717 must immediately follow the left brace in order to introduce indirec‐
1718 tion.
1719 In each of the cases below, word is subject to tilde expansion, parame‐
1721 ter expansion, command substitution, and arithmetic expansion.
1722 When not performing substring expansion, using the forms documented be‐
1724 low (e.g., :-), bash tests for a parameter that is unset or null.
1725 Omitting the colon results in a test only for a parameter that is un‐
1726 set.
1727 ${parameter:-word}
1729 Use Default Values. If parameter is unset or null, the expan‐
1730 sion of word is substituted. Otherwise, the value of parameter
1731 is substituted.
1732 ${parameter:=word}
1733 Assign Default Values. If parameter is unset or null, the ex‐
1734 pansion of word is assigned to parameter. The value of parame‐
1735 ter is then substituted. Positional parameters and special pa‐
1736 rameters may not be assigned to in this way.
1737 ${parameter:?word}
1738 Display Error if Null or Unset. If parameter is null or unset,
1739 the expansion of word (or a message to that effect if word is
1740 not present) is written to the standard error and the shell, if
1741 it is not interactive, exits. Otherwise, the value of parameter
1742 is substituted.
1743 ${parameter:+word}
1744 Use Alternate Value. If parameter is null or unset, nothing is
1745 substituted, otherwise the expansion of word is substituted.
1746 ${parameter:offset}
1747 ${parameter:offset:length}
1748 Substring Expansion. Expands to up to length characters of the
1749 value of parameter starting at the character specified by off‐
1750 set. If parameter is @ or *, an indexed array subscripted by @
1751 or *, or an associative array name, the results differ as de‐
1752 scribed below. If length is omitted, expands to the substring
1753 of the value of parameter starting at the character specified by
1754 offset and extending to the end of the value. length and offset
1755 are arithmetic expressions (see ARITHMETIC EVALUATION below).
1756 If offset evaluates to a number less than zero, the value is
1758 used as an offset in characters from the end of the value of pa‐
1759 rameter. If length evaluates to a number less than zero, it is
1760 interpreted as an offset in characters from the end of the value
1761 of parameter rather than a number of characters, and the expan‐
1762 sion is the characters between offset and that result. Note
1763 that a negative offset must be separated from the colon by at
1764 least one space to avoid being confused with the :- expansion.
1765 If parameter is @ or *, the result is length positional parame‐
1767 ters beginning at offset. A negative offset is taken relative
1768 to one greater than the greatest positional parameter, so an
1769 offset of -1 evaluates to the last positional parameter. It is
1770 an expansion error if length evaluates to a number less than
1771 zero.
1772 If parameter is an indexed array name subscripted by @ or *, the
1774 result is the length members of the array beginning with ${pa‐
1775 rameter[offset]}. A negative offset is taken relative to one
1776 greater than the maximum index of the specified array. It is an
1777 expansion error if length evaluates to a number less than zero.
1778 Substring expansion applied to an associative array produces un‐
1780 defined results.
1781 Substring indexing is zero-based unless the positional parame‐
1783 ters are used, in which case the indexing starts at 1 by de‐
1784 fault. If offset is 0, and the positional parameters are used,
1785 $0 is prefixed to the list.
1786 ${!prefix*}
1788 ${!prefix@}
1789 Names matching prefix. Expands to the names of variables whose
1790 names begin with prefix, separated by the first character of the
1791 IFS special variable. When @ is used and the expansion appears
1792 within double quotes, each variable name expands to a separate
1793 word.
1794 ${!name[@]}
1796 ${!name[*]}
1797 List of array keys. If name is an array variable, expands to
1798 the list of array indices (keys) assigned in name. If name is
1799 not an array, expands to 0 if name is set and null otherwise.
1800 When @ is used and the expansion appears within double quotes,
1801 each key expands to a separate word.
1802 ${#parameter}
1804 Parameter length. The length in characters of the value of pa‐
1805 rameter is substituted. If parameter is * or @, the value sub‐
1806 stituted is the number of positional parameters. If parameter
1807 is an array name subscripted by * or @, the value substituted is
1808 the number of elements in the array. If parameter is an indexed
1809 array name subscripted by a negative number, that number is in‐
1810 terpreted as relative to one greater than the maximum index of
1811 parameter, so negative indices count back from the end of the
1812 array, and an index of -1 references the last element.
1813 ${parameter#word}
1815 ${parameter##word}
1816 Remove matching prefix pattern. The word is expanded to produce
1817 a pattern just as in pathname expansion, and matched against the
1818 expanded value of parameter using the rules described under Pat‐
1819 tern Matching below. If the pattern matches the beginning of
1820 the value of parameter, then the result of the expansion is the
1821 expanded value of parameter with the shortest matching pattern
1822 (the ``#'' case) or the longest matching pattern (the ``##''
1823 case) deleted. If parameter is @ or *, the pattern removal op‐
1824 eration is applied to each positional parameter in turn, and the
1825 expansion is the resultant list. If parameter is an array vari‐
1826 able subscripted with @ or *, the pattern removal operation is
1827 applied to each member of the array in turn, and the expansion
1828 is the resultant list.
1829 ${parameter%word}
1831 ${parameter%%word}
1832 Remove matching suffix pattern. The word is expanded to produce
1833 a pattern just as in pathname expansion, and matched against the
1834 expanded value of parameter using the rules described under Pat‐
1835 tern Matching below. If the pattern matches a trailing portion
1836 of the expanded value of parameter, then the result of the ex‐
1837 pansion is the expanded value of parameter with the shortest
1838 matching pattern (the ``%'' case) or the longest matching pat‐
1839 tern (the ``%%'' case) deleted. If parameter is @ or *, the
1840 pattern removal operation is applied to each positional parame‐
1841 ter in turn, and the expansion is the resultant list. If param‐
1842 eter is an array variable subscripted with @ or *, the pattern
1843 removal operation is applied to each member of the array in
1844 turn, and the expansion is the resultant list.
1845 ${parameter/pattern/string}
1847 ${parameter//pattern/string}
1848 ${parameter/#pattern/string}
1849 ${parameter/%pattern/string}
1850 Pattern substitution. The pattern is expanded to produce a pat‐
1851 tern just as in pathname expansion. Parameter is expanded and
1852 the longest match of pattern against its value is replaced with
1853 string. string undergoes tilde expansion, parameter and vari‐
1854 able expansion, arithmetic expansion, command and process sub‐
1855 stitution, and quote removal. The match is performed using the
1856 rules described under Pattern Matching below. In the first form
1857 above, only the first match is replaced. If there are two
1858 slashes separating parameter and pattern (the second form
1859 above), all matches of pattern are replaced with string. If
1860 pattern is preceded by # (the third form above), it must match
1861 at the beginning of the expanded value of parameter. If pattern
1862 is preceded by % (the fourth form above), it must match at the
1863 end of the expanded value of parameter. If the expansion of
1864 string is null, matches of pattern are deleted. If string is
1865 null, matches of pattern are deleted and the / following pattern
1866 may be omitted.
1867 If the patsub_replacement shell option is enabled using shopt,
1869 any unquoted instances of & in string are replaced with the
1870 matching portion of pattern.
1871 Quoting any part of string inhibits replacement in the expansion
1873 of the quoted portion, including replacement strings stored in
1874 shell variables. Backslash will escape & in string; the back‐
1875 slash is removed in order to permit a literal & in the replace‐
1876 ment string. Backslash can also be used to escape a backslash;
1877 \\ results in a literal backslash in the replacement. Users
1878 should take care if string is double-quoted to avoid unwanted
1879 interactions between the backslash and double-quoting, since
1880 backslash has special meaning within double quotes. Pattern
1881 substitution performs the check for unquoted & after expanding
1882 string; shell programmers should quote any occurrences of & they
1883 want to be taken literally in the replacement and ensure any in‐
1884 stances of & they want to be replaced are unquoted.
1885 If the nocasematch shell option is enabled, the match is per‐
1887 formed without regard to the case of alphabetic characters. If
1888 parameter is @ or *, the substitution operation is applied to
1889 each positional parameter in turn, and the expansion is the re‐
1890 sultant list. If parameter is an array variable subscripted
1891 with @ or *, the substitution operation is applied to each mem‐
1892 ber of the array in turn, and the expansion is the resultant
1893 list.
1894 ${parameter^pattern}
1896 ${parameter^^pattern}
1897 ${parameter,pattern}
1898 ${parameter,,pattern}
1899 Case modification. This expansion modifies the case of alpha‐
1900 betic characters in parameter. The pattern is expanded to pro‐
1901 duce a pattern just as in pathname expansion. Each character in
1902 the expanded value of parameter is tested against pattern, and,
1903 if it matches the pattern, its case is converted. The pattern
1904 should not attempt to match more than one character. The ^ op‐
1905 erator converts lowercase letters matching pattern to uppercase;
1906 the , operator converts matching uppercase letters to lowercase.
1907 The ^^ and ,, expansions convert each matched character in the
1908 expanded value; the ^ and , expansions match and convert only
1909 the first character in the expanded value. If pattern is omit‐
1910 ted, it is treated like a ?, which matches every character. If
1911 parameter is @ or *, the case modification operation is applied
1912 to each positional parameter in turn, and the expansion is the
1913 resultant list. If parameter is an array variable subscripted
1914 with @ or *, the case modification operation is applied to each
1915 member of the array in turn, and the expansion is the resultant
1916 list.
1917 ${parameter@operator}
1919 Parameter transformation. The expansion is either a transforma‐
1920 tion of the value of parameter or information about parameter
1921 itself, depending on the value of operator. Each operator is a
1922 single letter:
1923 U The expansion is a string that is the value of parameter
1925 with lowercase alphabetic characters converted to upper‐
1926 case.
1927 u The expansion is a string that is the value of parameter
1928 with the first character converted to uppercase, if it is
1929 alphabetic.
1930 L The expansion is a string that is the value of parameter
1931 with uppercase alphabetic characters converted to lower‐
1932 case.
1933 Q The expansion is a string that is the value of parameter
1934 quoted in a format that can be reused as input.
1935 E The expansion is a string that is the value of parameter
1936 with backslash escape sequences expanded as with the
1937 $'...' quoting mechanism.
1938 P The expansion is a string that is the result of expanding
1939 the value of parameter as if it were a prompt string (see
1940 PROMPTING below).
1941 A The expansion is a string in the form of an assignment
1942 statement or declare command that, if evaluated, will
1943 recreate parameter with its attributes and value.
1944 K Produces a possibly-quoted version of the value of param‐
1945 eter, except that it prints the values of indexed and as‐
1946 sociative arrays as a sequence of quoted key-value pairs
1947 (see Arrays above).
1948 a The expansion is a string consisting of flag values rep‐
1949 resenting parameter's attributes.
1950 k Like the K transformation, but expands the keys and val‐
1951 ues of indexed and associative arrays to separate words
1952 after word splitting.
1953 If parameter is @ or *, the operation is applied to each posi‐
1955 tional parameter in turn, and the expansion is the resultant
1956 list. If parameter is an array variable subscripted with @ or
1957 *, the operation is applied to each member of the array in turn,
1958 and the expansion is the resultant list.
1959 The result of the expansion is subject to word splitting and
1961 pathname expansion as described below.
1962 Command Substitution
1964 Command substitution allows the output of a command to replace the com‐
1965 mand name. There are two forms:
1966 $(command)
1968 or
1969 `command`
1970 Bash performs the expansion by executing command in a subshell environ‐
1972 ment and replacing the command substitution with the standard output of
1973 the command, with any trailing newlines deleted. Embedded newlines are
1974 not deleted, but they may be removed during word splitting. The com‐
1975 mand substitution $(cat file) can be replaced by the equivalent but
1976 faster $(< file).
1977 When the old-style backquote form of substitution is used, backslash
1979 retains its literal meaning except when followed by $, `, or \. The
1980 first backquote not preceded by a backslash terminates the command sub‐
1981 stitution. When using the $(command) form, all characters between the
1982 parentheses make up the command; none are treated specially.
1983 Command substitutions may be nested. To nest when using the backquoted
1985 form, escape the inner backquotes with backslashes.
1986 If the substitution appears within double quotes, word splitting and
1988 pathname expansion are not performed on the results.
1989 Arithmetic Expansion
1991 Arithmetic expansion allows the evaluation of an arithmetic expression
1992 and the substitution of the result. The format for arithmetic expan‐
1993 sion is:
1994 $((expression))
1996 The expression undergoes the same expansions as if it were within dou‐
1998 ble quotes, but double quote characters in expression are not treated
1999 specially and are removed. All tokens in the expression undergo param‐
2000 eter and variable expansion, command substitution, and quote removal.
2001 The result is treated as the arithmetic expression to be evaluated.
2002 Arithmetic expansions may be nested.
2003 The evaluation is performed according to the rules listed below under
2005 ARITHMETIC EVALUATION. If expression is invalid, bash prints a message
2006 indicating failure and no substitution occurs.
2007 Process Substitution
2009 Process substitution allows a process's input or output to be referred
2010 to using a filename. It takes the form of <(list) or >(list). The
2011 process list is run asynchronously, and its input or output appears as
2012 a filename. This filename is passed as an argument to the current com‐
2013 mand as the result of the expansion. If the >(list) form is used,
2014 writing to the file will provide input for list. If the <(list) form
2015 is used, the file passed as an argument should be read to obtain the
2016 output of list. Process substitution is supported on systems that sup‐
2017 port named pipes (FIFOs) or the /dev/fd method of naming open files.
2018 When available, process substitution is performed simultaneously with
2020 parameter and variable expansion, command substitution, and arithmetic
2021 expansion.
2022 Word Splitting
2024 The shell scans the results of parameter expansion, command substitu‐
2025 tion, and arithmetic expansion that did not occur within double quotes
2026 for word splitting.
2027 The shell treats each character of IFS as a delimiter, and splits the
2029 results of the other expansions into words using these characters as
2030 field terminators. If IFS is unset, or its value is exactly
2031 <space><tab><newline>, the default, then sequences of <space>, <tab>,
2032 and <newline> at the beginning and end of the results of the previous
2033 expansions are ignored, and any sequence of IFS characters not at the
2034 beginning or end serves to delimit words. If IFS has a value other
2035 than the default, then sequences of the whitespace characters space,
2036 tab, and newline are ignored at the beginning and end of the word, as
2037 long as the whitespace character is in the value of IFS (an IFS white‐
2038 space character). Any character in IFS that is not IFS whitespace,
2039 along with any adjacent IFS whitespace characters, delimits a field. A
2040 sequence of IFS whitespace characters is also treated as a delimiter.
2041 If the value of IFS is null, no word splitting occurs.
2042 Explicit null arguments ("" or '') are retained and passed to commands
2044 as empty strings. Unquoted implicit null arguments, resulting from the
2045 expansion of parameters that have no values, are removed. If a parame‐
2046 ter with no value is expanded within double quotes, a null argument re‐
2047 sults and is retained and passed to a command as an empty string. When
2048 a quoted null argument appears as part of a word whose expansion is
2049 non-null, the null argument is removed. That is, the word -d'' becomes
2050 -d after word splitting and null argument removal.
2051 Note that if no expansion occurs, no splitting is performed.
2053 Pathname Expansion
2055 After word splitting, unless the -f option has been set, bash scans
2056 each word for the characters *, ?, and [. If one of these characters
2057 appears, and is not quoted, then the word is regarded as a pattern, and
2058 replaced with an alphabetically sorted list of filenames matching the
2059 pattern (see Pattern Matching below). If no matching filenames are
2060 found, and the shell option nullglob is not enabled, the word is left
2061 unchanged. If the nullglob option is set, and no matches are found,
2062 the word is removed. If the failglob shell option is set, and no
2063 matches are found, an error message is printed and the command is not
2064 executed. If the shell option nocaseglob is enabled, the match is per‐
2065 formed without regard to the case of alphabetic characters. When a
2066 pattern is used for pathname expansion, the character ``.'' at the
2067 start of a name or immediately following a slash must be matched ex‐
2068 plicitly, unless the shell option dotglob is set. In order to match
2069 the filenames ``.'' and ``..'', the pattern must begin with ``.'' (for
2070 example, ``.?''), even if dotglob is set. If the globskipdots shell
2071 option is enabled, the filenames ``.'' and ``..'' are never matched,
2072 even if the pattern begins with a ``.''. When not matching pathnames,
2073 the ``.'' character is not treated specially. When matching a path‐
2074 name, the slash character must always be matched explicitly by a slash
2075 in the pattern, but in other matching contexts it can be matched by a
2076 special pattern character as described below under Pattern Matching.
2077 See the description of shopt below under SHELL BUILTIN COMMANDS for a
2078 description of the nocaseglob, nullglob, globskipdots, failglob, and
2079 dotglob shell options.
2080 The GLOBIGNORE shell variable may be used to restrict the set of file
2082 names matching a pattern. If GLOBIGNORE is set, each matching file
2083 name that also matches one of the patterns in GLOBIGNORE is removed
2084 from the list of matches. If the nocaseglob option is set, the match‐
2085 ing against the patterns in GLOBIGNORE is performed without regard to
2086 case. The filenames ``.'' and ``..'' are always ignored when GLOBIG‐
2087 NORE is set and not null. However, setting GLOBIGNORE to a non-null
2088 value has the effect of enabling the dotglob shell option, so all other
2089 filenames beginning with a ``.'' will match. To get the old behavior
2090 of ignoring filenames beginning with a ``.'', make ``.*'' one of the
2091 patterns in GLOBIGNORE. The dotglob option is disabled when GLOBIGNORE
2092 is unset. The pattern matching honors the setting of the extglob shell
2093 option.
2094 Pattern Matching
2096 Any character that appears in a pattern, other than the special pattern
2098 characters described below, matches itself. The NUL character may not
2099 occur in a pattern. A backslash escapes the following character; the
2100 escaping backslash is discarded when matching. The special pattern
2101 characters must be quoted if they are to be matched literally.
2102 The special pattern characters have the following meanings:
2104 * Matches any string, including the null string. When the
2106 globstar shell option is enabled, and * is used in a
2107 pathname expansion context, two adjacent *s used as a
2108 single pattern will match all files and zero or more di‐
2109 rectories and subdirectories. If followed by a /, two
2110 adjacent *s will match only directories and subdirecto‐
2111 ries.
2112 ? Matches any single character.
2113 [...] Matches any one of the enclosed characters. A pair of
2114 characters separated by a hyphen denotes a range expres‐
2115 sion; any character that falls between those two charac‐
2116 ters, inclusive, using the current locale's collating se‐
2117 quence and character set, is matched. If the first char‐
2118 acter following the [ is a ! or a ^ then any character
2119 not enclosed is matched. The sorting order of characters
2120 in range expressions, and the characters included in the
2121 range, are determined by the current locale and the val‐
2122 ues of the LC_COLLATE or LC_ALL shell variables, if set.
2123 To obtain the traditional interpretation of range expres‐
2124 sions, where [a-d] is equivalent to [abcd], set value of
2125 the LC_ALL shell variable to C, or enable the globasci‐
2126 iranges shell option. A - may be matched by including it
2127 as the first or last character in the set. A ] may be
2128 matched by including it as the first character in the
2129 set.
2130 Within [ and ], character classes can be specified using
2132 the syntax [:class:], where class is one of the following
2133 classes defined in the POSIX standard:
2134 alnum alpha ascii blank cntrl digit graph lower print
2135 punct space upper word xdigit
2136 A character class matches any character belonging to that
2137 class. The word character class matches letters, digits,
2138 and the character _.
2139 Within [ and ], an equivalence class can be specified us‐
2141 ing the syntax [=c=], which matches all characters with
2142 the same collation weight (as defined by the current lo‐
2143 cale) as the character c.
2144 Within [ and ], the syntax [.symbol.] matches the collat‐
2146 ing symbol symbol.
2147 If the extglob shell option is enabled using the shopt builtin, the
2149 shell recognizes several extended pattern matching operators. In the
2150 following description, a pattern-list is a list of one or more patterns
2151 separated by a |. Composite patterns may be formed using one or more
2152 of the following sub-patterns:
2153 ?(pattern-list)
2155 Matches zero or one occurrence of the given patterns
2156 *(pattern-list)
2157 Matches zero or more occurrences of the given patterns
2158 +(pattern-list)
2159 Matches one or more occurrences of the given patterns
2160 @(pattern-list)
2161 Matches one of the given patterns
2162 !(pattern-list)
2163 Matches anything except one of the given patterns
2164 Theextglob option changes the behavior of the parser, since the paren‐
2166 theses are normally treated as operators with syntactic meaning. To
2167 ensure that extended matching patterns are parsed correctly, make sure
2168 that extglob is enabled before parsing constructs containing the pat‐
2169 terns, including shell functions and command substitutions.
2170 When matching filenames, the dotglob shell option determines the set of
2172 filenames that are tested: when dotglob is enabled, the set of file‐
2173 names includes all files beginning with ``.'', but ``.'' and ``..''
2174 must be matched by a pattern or sub-pattern that begins with a dot;
2175 when it is disabled, the set does not include any filenames beginning
2176 with ``.'' unless the pattern or sub-pattern begins with a ``.''. As
2177 above, ``.'' only has a special meaning when matching filenames.
2178 Complicated extended pattern matching against long strings is slow, es‐
2180 pecially when the patterns contain alternations and the strings contain
2181 multiple matches. Using separate matches against shorter strings, or
2182 using arrays of strings instead of a single long string, may be faster.
2183 Quote Removal
2185 After the preceding expansions, all unquoted occurrences of the charac‐
2186 ters \, ', and " that did not result from one of the above expansions
2187 are removed.
2188
2190 Before a command is executed, its input and output may be redirected
2191 using a special notation interpreted by the shell. Redirection allows
2192 commands' file handles to be duplicated, opened, closed, made to refer
2193 to different files, and can change the files the command reads from and
2194 writes to. Redirection may also be used to modify file handles in the
2195 current shell execution environment. The following redirection opera‐
2196 tors may precede or appear anywhere within a simple command or may fol‐
2197 low a command. Redirections are processed in the order they appear,
2198 from left to right.
2199 Each redirection that may be preceded by a file descriptor number may
2201 instead be preceded by a word of the form {varname}. In this case, for
2202 each redirection operator except >&- and <&-, the shell will allocate a
2203 file descriptor greater than or equal to 10 and assign it to varname.
2204 If >&- or <&- is preceded by {varname}, the value of varname defines
2205 the file descriptor to close. If {varname} is supplied, the redirect‐
2206 ion persists beyond the scope of the command, allowing the shell pro‐
2207 grammer to manage the file descriptor's lifetime manually. The
2208 varredir_close shell option manages this behavior.
2209 In the following descriptions, if the file descriptor number is omit‐
2211 ted, and the first character of the redirection operator is <, the re‐
2212 direction refers to the standard input (file descriptor 0). If the
2213 first character of the redirection operator is >, the redirection
2214 refers to the standard output (file descriptor 1).
2215 The word following the redirection operator in the following descrip‐
2217 tions, unless otherwise noted, is subjected to brace expansion, tilde
2218 expansion, parameter and variable expansion, command substitution,
2219 arithmetic expansion, quote removal, pathname expansion, and word
2220 splitting. If it expands to more than one word, bash reports an error.
2221 Note that the order of redirections is significant. For example, the
2223 command
2224 ls > dirlist 2>&1
2226 directs both standard output and standard error to the file dirlist,
2228 while the command
2229 ls 2>&1 > dirlist
2231 directs only the standard output to file dirlist, because the standard
2233 error was duplicated from the standard output before the standard out‐
2234 put was redirected to dirlist.
2235 Bash handles several filenames specially when they are used in redirec‐
2237 tions, as described in the following table. If the operating system on
2238 which bash is running provides these special files, bash will use them;
2239 otherwise it will emulate them internally with the behavior described
2240 below.
2241 /dev/fd/fd
2243 If fd is a valid integer, file descriptor fd is dupli‐
2244 cated.
2245 /dev/stdin
2246 File descriptor 0 is duplicated.
2247 /dev/stdout
2248 File descriptor 1 is duplicated.
2249 /dev/stderr
2250 File descriptor 2 is duplicated.
2251 /dev/tcp/host/port
2252 If host is a valid hostname or Internet address, and port
2253 is an integer port number or service name, bash attempts
2254 to open the corresponding TCP socket.
2255 /dev/udp/host/port
2256 If host is a valid hostname or Internet address, and port
2257 is an integer port number or service name, bash attempts
2258 to open the corresponding UDP socket.
2259 A failure to open or create a file causes the redirection to fail.
2261 Redirections using file descriptors greater than 9 should be used with
2263 care, as they may conflict with file descriptors the shell uses inter‐
2264 nally.
2265 Redirecting Input
2267 Redirection of input causes the file whose name results from the expan‐
2268 sion of word to be opened for reading on file descriptor n, or the
2269 standard input (file descriptor 0) if n is not specified.
2270 The general format for redirecting input is:
2272 [n]<word
2274 Redirecting Output
2276 Redirection of output causes the file whose name results from the ex‐
2277 pansion of word to be opened for writing on file descriptor n, or the
2278 standard output (file descriptor 1) if n is not specified. If the file
2279 does not exist it is created; if it does exist it is truncated to zero
2280 size.
2281 The general format for redirecting output is:
2283 [n]>word
2285 If the redirection operator is >, and the noclobber option to the set
2287 builtin has been enabled, the redirection will fail if the file whose
2288 name results from the expansion of word exists and is a regular file.
2289 If the redirection operator is >|, or the redirection operator is > and
2290 the noclobber option to the set builtin command is not enabled, the re‐
2291 direction is attempted even if the file named by word exists.
2292 Appending Redirected Output
2294 Redirection of output in this fashion causes the file whose name re‐
2295 sults from the expansion of word to be opened for appending on file de‐
2296 scriptor n, or the standard output (file descriptor 1) if n is not
2297 specified. If the file does not exist it is created.
2298 The general format for appending output is:
2300 [n]>>word
2302 Redirecting Standard Output and Standard Error
2304 This construct allows both the standard output (file descriptor 1) and
2305 the standard error output (file descriptor 2) to be redirected to the
2306 file whose name is the expansion of word.
2307 There are two formats for redirecting standard output and standard er‐
2309 ror:
2310 &>word
2312 and
2313 >&word
2314 Of the two forms, the first is preferred. This is semantically equiva‐
2316 lent to
2317 >word 2>&1
2319 When using the second form, word may not expand to a number or -. If
2321 it does, other redirection operators apply (see Duplicating File De‐
2322 scriptors below) for compatibility reasons.
2323 Appending Standard Output and Standard Error
2325 This construct allows both the standard output (file descriptor 1) and
2326 the standard error output (file descriptor 2) to be appended to the
2327 file whose name is the expansion of word.
2328 The format for appending standard output and standard error is:
2330 &>>word
2332 This is semantically equivalent to
2334 >>word 2>&1
2336 (see Duplicating File Descriptors below).
2338 Here Documents
2340 This type of redirection instructs the shell to read input from the
2341 current source until a line containing only delimiter (with no trailing
2342 blanks) is seen. All of the lines read up to that point are then used
2343 as the standard input (or file descriptor n if n is specified) for a
2344 command.
2345 The format of here-documents is:
2347 [n]<<[-]word
2349 here-document
2350 delimiter
2351 No parameter and variable expansion, command substitution, arithmetic
2353 expansion, or pathname expansion is performed on word. If any part of
2354 word is quoted, the delimiter is the result of quote removal on word,
2355 and the lines in the here-document are not expanded. If word is un‐
2356 quoted, all lines of the here-document are subjected to parameter ex‐
2357 pansion, command substitution, and arithmetic expansion, the character
2358 sequence \<newline> is ignored, and \ must be used to quote the charac‐
2359 ters \, $, and `.
2360 If the redirection operator is <<-, then all leading tab characters are
2362 stripped from input lines and the line containing delimiter. This al‐
2363 lows here-documents within shell scripts to be indented in a natural
2364 fashion.
2365 Here Strings
2367 A variant of here documents, the format is:
2368 [n]<<<word
2370 The word undergoes tilde expansion, parameter and variable expansion,
2372 command substitution, arithmetic expansion, and quote removal. Path‐
2373 name expansion and word splitting are not performed. The result is
2374 supplied as a single string, with a newline appended, to the command on
2375 its standard input (or file descriptor n if n is specified).
2376 Duplicating File Descriptors
2378 The redirection operator
2379 [n]<&word
2381 is used to duplicate input file descriptors. If word expands to one or
2383 more digits, the file descriptor denoted by n is made to be a copy of
2384 that file descriptor. If the digits in word do not specify a file de‐
2385 scriptor open for input, a redirection error occurs. If word evaluates
2386 to -, file descriptor n is closed. If n is not specified, the standard
2387 input (file descriptor 0) is used.
2388 The operator
2390 [n]>&word
2392 is used similarly to duplicate output file descriptors. If n is not
2394 specified, the standard output (file descriptor 1) is used. If the
2395 digits in word do not specify a file descriptor open for output, a re‐
2396 direction error occurs. If word evaluates to -, file descriptor n is
2397 closed. As a special case, if n is omitted, and word does not expand
2398 to one or more digits or -, the standard output and standard error are
2399 redirected as described previously.
2400 Moving File Descriptors
2402 The redirection operator
2403 [n]<&digit-
2405 moves the file descriptor digit to file descriptor n, or the standard
2407 input (file descriptor 0) if n is not specified. digit is closed after
2408 being duplicated to n.
2409 Similarly, the redirection operator
2411 [n]>&digit-
2413 moves the file descriptor digit to file descriptor n, or the standard
2415 output (file descriptor 1) if n is not specified.
2416 Opening File Descriptors for Reading and Writing
2418 The redirection operator
2419 [n]<>word
2421 causes the file whose name is the expansion of word to be opened for
2423 both reading and writing on file descriptor n, or on file descriptor 0
2424 if n is not specified. If the file does not exist, it is created.
2425
2427 Aliases allow a string to be substituted for a word when it is used as
2428 the first word of a simple command. The shell maintains a list of
2429 aliases that may be set and unset with the alias and unalias builtin
2430 commands (see SHELL BUILTIN COMMANDS below). The first word of each
2431 simple command, if unquoted, is checked to see if it has an alias. If
2432 so, that word is replaced by the text of the alias. The characters /,
2433 $, `, and = and any of the shell metacharacters or quoting characters
2434 listed above may not appear in an alias name. The replacement text may
2435 contain any valid shell input, including shell metacharacters. The
2436 first word of the replacement text is tested for aliases, but a word
2437 that is identical to an alias being expanded is not expanded a second
2438 time. This means that one may alias ls to ls -F, for instance, and
2439 bash does not try to recursively expand the replacement text. If the
2440 last character of the alias value is a blank, then the next command
2441 word following the alias is also checked for alias expansion.
2442 Aliases are created and listed with the alias command, and removed with
2444 the unalias command.
2445 There is no mechanism for using arguments in the replacement text. If
2447 arguments are needed, use a shell function (see FUNCTIONS below).
2448 Aliases are not expanded when the shell is not interactive, unless the
2450 expand_aliases shell option is set using shopt (see the description of
2451 shopt under SHELL BUILTIN COMMANDS below).
2452 The rules concerning the definition and use of aliases are somewhat
2454 confusing. Bash always reads at least one complete line of input, and
2455 all lines that make up a compound command, before executing any of the
2456 commands on that line or the compound command. Aliases are expanded
2457 when a command is read, not when it is executed. Therefore, an alias
2458 definition appearing on the same line as another command does not take
2459 effect until the next line of input is read. The commands following
2460 the alias definition on that line are not affected by the new alias.
2461 This behavior is also an issue when functions are executed. Aliases
2462 are expanded when a function definition is read, not when the function
2463 is executed, because a function definition is itself a command. As a
2464 consequence, aliases defined in a function are not available until af‐
2465 ter that function is executed. To be safe, always put alias defini‐
2466 tions on a separate line, and do not use alias in compound commands.
2467 For almost every purpose, aliases are superseded by shell functions.
2469
2471 A shell function, defined as described above under SHELL GRAMMAR,
2472 stores a series of commands for later execution. When the name of a
2473 shell function is used as a simple command name, the list of commands
2474 associated with that function name is executed. Functions are executed
2475 in the context of the current shell; no new process is created to in‐
2476 terpret them (contrast this with the execution of a shell script).
2477 When a function is executed, the arguments to the function become the
2478 positional parameters during its execution. The special parameter # is
2479 updated to reflect the change. Special parameter 0 is unchanged. The
2480 first element of the FUNCNAME variable is set to the name of the func‐
2481 tion while the function is executing.
2482 All other aspects of the shell execution environment are identical be‐
2484 tween a function and its caller with these exceptions: the DEBUG and
2485 RETURN traps (see the description of the trap builtin under SHELL
2486 BUILTIN COMMANDS below) are not inherited unless the function has been
2487 given the trace attribute (see the description of the declare builtin
2488 below) or the -o functrace shell option has been enabled with the set
2489 builtin (in which case all functions inherit the DEBUG and RETURN
2490 traps), and the ERR trap is not inherited unless the -o errtrace shell
2491 option has been enabled.
2492 Variables local to the function may be declared with the local builtin
2494 command (local variables). Ordinarily, variables and their values are
2495 shared between the function and its caller. If a variable is declared
2496 local, the variable's visible scope is restricted to that function and
2497 its children (including the functions it calls).
2498 In the following description, the current scope is a currently- execut‐
2500 ing function. Previous scopes consist of that function's caller and so
2501 on, back to the "global" scope, where the shell is not executing any
2502 shell function. Consequently, a local variable at the current scope is
2503 a variable declared using the local or declare builtins in the function
2504 that is currently executing.
2505 Local variables "shadow" variables with the same name declared at pre‐
2507 vious scopes. For instance, a local variable declared in a function
2508 hides a global variable of the same name: references and assignments
2509 refer to the local variable, leaving the global variable unmodified.
2510 When the function returns, the global variable is once again visible.
2511 The shell uses dynamic scoping to control a variable's visibility
2513 within functions. With dynamic scoping, visible variables and their
2514 values are a result of the sequence of function calls that caused exe‐
2515 cution to reach the current function. The value of a variable that a
2516 function sees depends on its value within its caller, if any, whether
2517 that caller is the "global" scope or another shell function. This is
2518 also the value that a local variable declaration "shadows", and the
2519 value that is restored when the function returns.
2520 For example, if a variable var is declared as local in function func1,
2522 and func1 calls another function func2, references to var made from
2523 within func2 will resolve to the local variable var from func1, shadow‐
2524 ing any global variable named var.
2525 The unset builtin also acts using the same dynamic scope: if a variable
2527 is local to the current scope, unset will unset it; otherwise the unset
2528 will refer to the variable found in any calling scope as described
2529 above. If a variable at the current local scope is unset, it will re‐
2530 main so (appearing as unset) until it is reset in that scope or until
2531 the function returns. Once the function returns, any instance of the
2532 variable at a previous scope will become visible. If the unset acts on
2533 a variable at a previous scope, any instance of a variable with that
2534 name that had been shadowed will become visible (see below how the lo‐
2535 calvar_unset shell option changes this behavior).
2536 The FUNCNEST variable, if set to a numeric value greater than 0, de‐
2538 fines a maximum function nesting level. Function invocations that ex‐
2539 ceed the limit cause the entire command to abort.
2540 If the builtin command return is executed in a function, the function
2542 completes and execution resumes with the next command after the func‐
2543 tion call. Any command associated with the RETURN trap is executed be‐
2544 fore execution resumes. When a function completes, the values of the
2545 positional parameters and the special parameter # are restored to the
2546 values they had prior to the function's execution.
2547 Function names and definitions may be listed with the -f option to the
2549 declare or typeset builtin commands. The -F option to declare or type‐
2550 set will list the function names only (and optionally the source file
2551 and line number, if the extdebug shell option is enabled). Functions
2552 may be exported so that child shell processes (those created when exe‐
2553 cuting a separate shell invocation) automatically have them defined
2554 with the -f option to the export builtin. A function definition may be
2555 deleted using the -f option to the unset builtin.
2556 Functions may be recursive. The FUNCNEST variable may be used to limit
2558 the depth of the function call stack and restrict the number of func‐
2559 tion invocations. By default, no limit is imposed on the number of re‐
2560 cursive calls.
2561
2563 The shell allows arithmetic expressions to be evaluated, under certain
2564 circumstances (see the let and declare builtin commands, the (( com‐
2565 pound command, and Arithmetic Expansion). Evaluation is done in fixed-
2566 width integers with no check for overflow, though division by 0 is
2567 trapped and flagged as an error. The operators and their precedence,
2568 associativity, and values are the same as in the C language. The fol‐
2569 lowing list of operators is grouped into levels of equal-precedence op‐
2570 erators. The levels are listed in order of decreasing precedence.
2571 id++ id--
2573 variable post-increment and post-decrement
2574 - + unary minus and plus
2575 ++id --id
2576 variable pre-increment and pre-decrement
2577 ! ~ logical and bitwise negation
2578 ** exponentiation
2579 * / % multiplication, division, remainder
2580 + - addition, subtraction
2581 << >> left and right bitwise shifts
2582 <= >= < >
2583 comparison
2584 == != equality and inequality
2585 & bitwise AND
2586 ^ bitwise exclusive OR
2587 | bitwise OR
2588 && logical AND
2589 || logical OR
2590 expr?expr:expr
2591 conditional operator
2592 = *= /= %= += -= <<= >>= &= ^= |=
2593 assignment
2594 expr1 , expr2
2595 comma
2596 Shell variables are allowed as operands; parameter expansion is per‐
2598 formed before the expression is evaluated. Within an expression, shell
2599 variables may also be referenced by name without using the parameter
2600 expansion syntax. A shell variable that is null or unset evaluates to
2601 0 when referenced by name without using the parameter expansion syntax.
2602 The value of a variable is evaluated as an arithmetic expression when
2603 it is referenced, or when a variable which has been given the integer
2604 attribute using declare -i is assigned a value. A null value evaluates
2605 to 0. A shell variable need not have its integer attribute turned on
2606 to be used in an expression.
2607 Integer constants follow the C language definition, without suffixes or
2609 character constants. Constants with a leading 0 are interpreted as oc‐
2610 tal numbers. A leading 0x or 0X denotes hexadecimal. Otherwise, num‐
2611 bers take the form [base#]n, where the optional base is a decimal num‐
2612 ber between 2 and 64 representing the arithmetic base, and n is a num‐
2613 ber in that base. If base# is omitted, then base 10 is used. When
2614 specifying n, if a non-digit is required, the digits greater than 9 are
2615 represented by the lowercase letters, the uppercase letters, @, and _,
2616 in that order. If base is less than or equal to 36, lowercase and up‐
2617 percase letters may be used interchangeably to represent numbers be‐
2618 tween 10 and 35.
2619 Operators are evaluated in order of precedence. Sub-expressions in
2621 parentheses are evaluated first and may override the precedence rules
2622 above.
2623
2625 Conditional expressions are used by the [[ compound command and the
2626 test and [ builtin commands to test file attributes and perform string
2627 and arithmetic comparisons. The test and [ commands determine their
2628 behavior based on the number of arguments; see the descriptions of
2629 those commands for any other command-specific actions.
2630 Expressions are formed from the following unary or binary primaries.
2632 Bash handles several filenames specially when they are used in expres‐
2633 sions. If the operating system on which bash is running provides these
2634 special files, bash will use them; otherwise it will emulate them in‐
2635 ternally with this behavior: If any file argument to one of the pri‐
2636 maries is of the form /dev/fd/n, then file descriptor n is checked. If
2637 the file argument to one of the primaries is one of /dev/stdin,
2638 /dev/stdout, or /dev/stderr, file descriptor 0, 1, or 2, respectively,
2639 is checked.
2640 Unless otherwise specified, primaries that operate on files follow sym‐
2642 bolic links and operate on the target of the link, rather than the link
2643 itself.
2644 When used with [[, the < and > operators sort lexicographically using
2646 the current locale. The test command sorts using ASCII ordering.
2647 -a file
2649 True if file exists.
2650 -b file
2651 True if file exists and is a block special file.
2652 -c file
2653 True if file exists and is a character special file.
2654 -d file
2655 True if file exists and is a directory.
2656 -e file
2657 True if file exists.
2658 -f file
2659 True if file exists and is a regular file.
2660 -g file
2661 True if file exists and is set-group-id.
2662 -h file
2663 True if file exists and is a symbolic link.
2664 -k file
2665 True if file exists and its ``sticky'' bit is set.
2666 -p file
2667 True if file exists and is a named pipe (FIFO).
2668 -r file
2669 True if file exists and is readable.
2670 -s file
2671 True if file exists and has a size greater than zero.
2672 -t fd True if file descriptor fd is open and refers to a terminal.
2673 -u file
2674 True if file exists and its set-user-id bit is set.
2675 -w file
2676 True if file exists and is writable.
2677 -x file
2678 True if file exists and is executable.
2679 -G file
2680 True if file exists and is owned by the effective group id.
2681 -L file
2682 True if file exists and is a symbolic link.
2683 -N file
2684 True if file exists and has been modified since it was last
2685 read.
2686 -O file
2687 True if file exists and is owned by the effective user id.
2688 -S file
2689 True if file exists and is a socket.
2690 file1 -ef file2
2691 True if file1 and file2 refer to the same device and inode num‐
2692 bers.
2693 file1 -nt file2
2694 True if file1 is newer (according to modification date) than
2695 file2, or if file1 exists and file2 does not.
2696 file1 -ot file2
2697 True if file1 is older than file2, or if file2 exists and file1
2698 does not.
2699 -o optname
2700 True if the shell option optname is enabled. See the list of
2701 options under the description of the -o option to the set
2702 builtin below.
2703 -v varname
2704 True if the shell variable varname is set (has been assigned a
2705 value).
2706 -R varname
2707 True if the shell variable varname is set and is a name refer‐
2708 ence.
2709 -z string
2710 True if the length of string is zero.
2711 string
2712 -n string
2713 True if the length of string is non-zero.
2714 string1 == string2
2716 string1 = string2
2717 True if the strings are equal. = should be used with the test
2718 command for POSIX conformance. When used with the [[ command,
2719 this performs pattern matching as described above (Compound Com‐
2720 mands).
2721 string1 != string2
2723 True if the strings are not equal.
2724 string1 < string2
2726 True if string1 sorts before string2 lexicographically.
2727 string1 > string2
2729 True if string1 sorts after string2 lexicographically.
2730 arg1 OP arg2
2732 OP is one of -eq, -ne, -lt, -le, -gt, or -ge. These arithmetic
2733 binary operators return true if arg1 is equal to, not equal to,
2734 less than, less than or equal to, greater than, or greater than
2735 or equal to arg2, respectively. Arg1 and arg2 may be positive
2736 or negative integers. When used with the [[ command, Arg1 and
2737 Arg2 are evaluated as arithmetic expressions (see ARITHMETIC
2738 EVALUATION above).
2739
2741 When a simple command is executed, the shell performs the following ex‐
2742 pansions, assignments, and redirections, from left to right, in the
2743 following order.
2744 1. The words that the parser has marked as variable assignments
2746 (those preceding the command name) and redirections are saved
2747 for later processing.
2748 2. The words that are not variable assignments or redirections are
2750 expanded. If any words remain after expansion, the first word
2751 is taken to be the name of the command and the remaining words
2752 are the arguments.
2753 3. Redirections are performed as described above under REDIRECTION.
2755 4. The text after the = in each variable assignment undergoes tilde
2757 expansion, parameter expansion, command substitution, arithmetic
2758 expansion, and quote removal before being assigned to the vari‐
2759 able.
2760 If no command name results, the variable assignments affect the current
2762 shell environment. In the case of such a command (one that consists
2763 only of assignment statements and redirections), assignment statements
2764 are performed before redirections. Otherwise, the variables are added
2765 to the environment of the executed command and do not affect the cur‐
2766 rent shell environment. If any of the assignments attempts to assign a
2767 value to a readonly variable, an error occurs, and the command exits
2768 with a non-zero status.
2769 If no command name results, redirections are performed, but do not af‐
2771 fect the current shell environment. A redirection error causes the
2772 command to exit with a non-zero status.
2773 If there is a command name left after expansion, execution proceeds as
2775 described below. Otherwise, the command exits. If one of the expan‐
2776 sions contained a command substitution, the exit status of the command
2777 is the exit status of the last command substitution performed. If
2778 there were no command substitutions, the command exits with a status of
2779 zero.
2780
2782 After a command has been split into words, if it results in a simple
2783 command and an optional list of arguments, the following actions are
2784 taken.
2785 If the command name contains no slashes, the shell attempts to locate
2787 it. If there exists a shell function by that name, that function is
2788 invoked as described above in FUNCTIONS. If the name does not match a
2789 function, the shell searches for it in the list of shell builtins. If
2790 a match is found, that builtin is invoked.
2791 If the name is neither a shell function nor a builtin, and contains no
2793 slashes, bash searches each element of the PATH for a directory con‐
2794 taining an executable file by that name. Bash uses a hash table to re‐
2795 member the full pathnames of executable files (see hash under SHELL
2796 BUILTIN COMMANDS below). A full search of the directories in PATH is
2797 performed only if the command is not found in the hash table. If the
2798 search is unsuccessful, the shell searches for a defined shell function
2799 named command_not_found_handle. If that function exists, it is invoked
2800 in a separate execution environment with the original command and the
2801 original command's arguments as its arguments, and the function's exit
2802 status becomes the exit status of that subshell. If that function is
2803 not defined, the shell prints an error message and returns an exit sta‐
2804 tus of 127.
2805 If the search is successful, or if the command name contains one or
2807 more slashes, the shell executes the named program in a separate execu‐
2808 tion environment. Argument 0 is set to the name given, and the remain‐
2809 ing arguments to the command are set to the arguments given, if any.
2810 If this execution fails because the file is not in executable format,
2812 and the file is not a directory, it is assumed to be a shell script, a
2813 file containing shell commands, and the shell creates a new instance of
2814 itself to execute it. This subshell reinitializes itself, so that the
2815 effect is as if a new shell had been invoked to handle the script, with
2816 the exception that the locations of commands remembered by the parent
2817 (see hash below under SHELL BUILTIN COMMANDS) are retained by the
2818 child.
2819 If the program is a file beginning with #!, the remainder of the first
2821 line specifies an interpreter for the program. The shell executes the
2822 specified interpreter on operating systems that do not handle this exe‐
2823 cutable format themselves. The arguments to the interpreter consist of
2824 a single optional argument following the interpreter name on the first
2825 line of the program, followed by the name of the program, followed by
2826 the command arguments, if any.
2827
2829 The shell has an execution environment, which consists of the follow‐
2830 ing:
2831 • open files inherited by the shell at invocation, as modified by
2833 redirections supplied to the exec builtin
2834 • the current working directory as set by cd, pushd, or popd, or
2836 inherited by the shell at invocation
2837 • the file creation mode mask as set by umask or inherited from
2839 the shell's parent
2840 • current traps set by trap
2842 • shell parameters that are set by variable assignment or with set
2844 or inherited from the shell's parent in the environment
2845 • shell functions defined during execution or inherited from the
2847 shell's parent in the environment
2848 • options enabled at invocation (either by default or with com‐
2850 mand-line arguments) or by set
2851 • options enabled by shopt
2853 • shell aliases defined with alias
2855 • various process IDs, including those of background jobs, the
2857 value of $$, and the value of PPID
2858 When a simple command other than a builtin or shell function is to be
2860 executed, it is invoked in a separate execution environment that con‐
2861 sists of the following. Unless otherwise noted, the values are inher‐
2862 ited from the shell.
2863 • the shell's open files, plus any modifications and additions
2866 specified by redirections to the command
2867 • the current working directory
2869 • the file creation mode mask
2871 • shell variables and functions marked for export, along with
2873 variables exported for the command, passed in the environment
2874 • traps caught by the shell are reset to the values inherited from
2876 the shell's parent, and traps ignored by the shell are ignored
2877 A command invoked in this separate environment cannot affect the
2879 shell's execution environment.
2880 A subshell is a copy of the shell process.
2882 Command substitution, commands grouped with parentheses, and asynchro‐
2884 nous commands are invoked in a subshell environment that is a duplicate
2885 of the shell environment, except that traps caught by the shell are re‐
2886 set to the values that the shell inherited from its parent at invoca‐
2887 tion. Builtin commands that are invoked as part of a pipeline are also
2888 executed in a subshell environment. Changes made to the subshell envi‐
2889 ronment cannot affect the shell's execution environment.
2890 Subshells spawned to execute command substitutions inherit the value of
2892 the -e option from the parent shell. When not in posix mode, bash
2893 clears the -e option in such subshells.
2894 If a command is followed by a & and job control is not active, the de‐
2896 fault standard input for the command is the empty file /dev/null. Oth‐
2897 erwise, the invoked command inherits the file descriptors of the call‐
2898 ing shell as modified by redirections.
2899
2901 When a program is invoked it is given an array of strings called the
2902 environment. This is a list of name-value pairs, of the form
2903 name=value.
2904 The shell provides several ways to manipulate the environment. On in‐
2906 vocation, the shell scans its own environment and creates a parameter
2907 for each name found, automatically marking it for export to child pro‐
2908 cesses. Executed commands inherit the environment. The export and de‐
2909 clare -x commands allow parameters and functions to be added to and
2910 deleted from the environment. If the value of a parameter in the envi‐
2911 ronment is modified, the new value becomes part of the environment, re‐
2912 placing the old. The environment inherited by any executed command
2913 consists of the shell's initial environment, whose values may be modi‐
2914 fied in the shell, less any pairs removed by the unset command, plus
2915 any additions via the export and declare -x commands.
2916 The environment for any simple command or function may be augmented
2918 temporarily by prefixing it with parameter assignments, as described
2919 above in PARAMETERS. These assignment statements affect only the envi‐
2920 ronment seen by that command.
2921 If the -k option is set (see the set builtin command below), then all
2923 parameter assignments are placed in the environment for a command, not
2924 just those that precede the command name.
2925 When bash invokes an external command, the variable _ is set to the
2927 full filename of the command and passed to that command in its environ‐
2928 ment.
2929
2931 The exit status of an executed command is the value returned by the
2932 waitpid system call or equivalent function. Exit statuses fall between
2933 0 and 255, though, as explained below, the shell may use values above
2934 125 specially. Exit statuses from shell builtins and compound commands
2935 are also limited to this range. Under certain circumstances, the shell
2936 will use special values to indicate specific failure modes.
2937 For the shell's purposes, a command which exits with a zero exit status
2939 has succeeded. An exit status of zero indicates success. A non-zero
2940 exit status indicates failure. When a command terminates on a fatal
2941 signal N, bash uses the value of 128+N as the exit status.
2942 If a command is not found, the child process created to execute it re‐
2944 turns a status of 127. If a command is found but is not executable,
2945 the return status is 126.
2946 If a command fails because of an error during expansion or redirection,
2948 the exit status is greater than zero.
2949 Shell builtin commands return a status of 0 (true) if successful, and
2951 non-zero (false) if an error occurs while they execute. All builtins
2952 return an exit status of 2 to indicate incorrect usage, generally in‐
2953 valid options or missing arguments.
2954 The exit status of the last command is available in the special parame‐
2956 ter $?.
2957 Bash itself returns the exit status of the last command executed, un‐
2959 less a syntax error occurs, in which case it exits with a non-zero
2960 value. See also the exit builtin command below.
2961
2963 When bash is interactive, in the absence of any traps, it ignores
2964 SIGTERM (so that kill 0 does not kill an interactive shell), and SIGINT
2965 is caught and handled (so that the wait builtin is interruptible). In
2966 all cases, bash ignores SIGQUIT. If job control is in effect, bash ig‐
2967 nores SIGTTIN, SIGTTOU, and SIGTSTP.
2968 Non-builtin commands run by bash have signal handlers set to the values
2970 inherited by the shell from its parent. When job control is not in ef‐
2971 fect, asynchronous commands ignore SIGINT and SIGQUIT in addition to
2972 these inherited handlers. Commands run as a result of command substi‐
2973 tution ignore the keyboard-generated job control signals SIGTTIN, SIGT‐
2974 TOU, and SIGTSTP.
2975 The shell exits by default upon receipt of a SIGHUP. Before exiting,
2977 an interactive shell resends the SIGHUP to all jobs, running or
2978 stopped. Stopped jobs are sent SIGCONT to ensure that they receive the
2979 SIGHUP. To prevent the shell from sending the signal to a particular
2980 job, it should be removed from the jobs table with the disown builtin
2981 (see SHELL BUILTIN COMMANDS below) or marked to not receive SIGHUP us‐
2982 ing disown -h.
2983 If the huponexit shell option has been set with shopt, bash sends a
2985 SIGHUP to all jobs when an interactive login shell exits.
2986 If bash is waiting for a command to complete and receives a signal for
2988 which a trap has been set, the trap will not be executed until the com‐
2989 mand completes. When bash is waiting for an asynchronous command via
2990 the wait builtin, the reception of a signal for which a trap has been
2991 set will cause the wait builtin to return immediately with an exit sta‐
2992 tus greater than 128, immediately after which the trap is executed.
2993 When job control is not enabled, and bash is waiting for a foreground
2995 command to complete, the shell receives keyboard-generated signals such
2996 as SIGINT (usually generated by ^C) that users commonly intend to send
2997 to that command. This happens because the shell and the command are in
2998 the same process group as the terminal, and ^C sends SIGINT to all pro‐
2999 cesses in that process group.
3000 When bash is running without job control enabled and receives SIGINT
3002 while waiting for a foreground command, it waits until that foreground
3003 command terminates and then decides what to do about the SIGINT:
3004 1. If the command terminates due to the SIGINT, bash concludes that
3006 the user meant to end the entire script, and acts on the SIGINT
3007 (e.g., by running a SIGINT trap or exiting itself);
3008 2. If the command does not terminate due to SIGINT, the program
3010 handled the SIGINT itself and did not treat it as a fatal sig‐
3011 nal. In that case, bash does not treat SIGINT as a fatal sig‐
3012 nal, either, instead assuming that the SIGINT was used as part
3013 of the program's normal operation (e.g., emacs uses it to abort
3014 editing commands) or deliberately discarded. However, bash will
3015 run any trap set on SIGINT, as it does with any other trapped
3016 signal it receives while it is waiting for the foreground com‐
3017 mand to complete, for compatibility.
3018
3020 Job control refers to the ability to selectively stop (suspend) the ex‐
3021 ecution of processes and continue (resume) their execution at a later
3022 point. A user typically employs this facility via an interactive in‐
3023 terface supplied jointly by the operating system kernel's terminal
3024 driver and bash.
3025 The shell associates a job with each pipeline. It keeps a table of
3027 currently executing jobs, which may be listed with the jobs command.
3028 When bash starts a job asynchronously (in the background), it prints a
3029 line that looks like:
3030 [1] 25647
3032 indicating that this job is job number 1 and that the process ID of the
3034 last process in the pipeline associated with this job is 25647. All of
3035 the processes in a single pipeline are members of the same job. Bash
3036 uses the job abstraction as the basis for job control.
3037 To facilitate the implementation of the user interface to job control,
3039 the operating system maintains the notion of a current terminal process
3040 group ID. Members of this process group (processes whose process group
3041 ID is equal to the current terminal process group ID) receive keyboard-
3042 generated signals such as SIGINT. These processes are said to be in
3043 the foreground. Background processes are those whose process group ID
3044 differs from the terminal's; such processes are immune to keyboard-gen‐
3045 erated signals. Only foreground processes are allowed to read from or,
3046 if the user so specifies with stty tostop, write to the terminal.
3047 Background processes which attempt to read from (write to when stty
3048 tostop is in effect) the terminal are sent a SIGTTIN (SIGTTOU) signal
3049 by the kernel's terminal driver, which, unless caught, suspends the
3050 process.
3051 If the operating system on which bash is running supports job control,
3053 bash contains facilities to use it. Typing the suspend character (typ‐
3054 ically ^Z, Control-Z) while a process is running causes that process to
3055 be stopped and returns control to bash. Typing the delayed suspend
3056 character (typically ^Y, Control-Y) causes the process to be stopped
3057 when it attempts to read input from the terminal, and control to be re‐
3058 turned to bash. The user may then manipulate the state of this job,
3059 using the bg command to continue it in the background, the fg command
3060 to continue it in the foreground, or the kill command to kill it. A ^Z
3061 takes effect immediately, and has the additional side effect of causing
3062 pending output and typeahead to be discarded.
3063 There are a number of ways to refer to a job in the shell. The charac‐
3065 ter % introduces a job specification (jobspec). Job number n may be
3066 referred to as %n. A job may also be referred to using a prefix of the
3067 name used to start it, or using a substring that appears in its command
3068 line. For example, %ce refers to a stopped job whose command name be‐
3069 gins with ce. If a prefix matches more than one job, bash reports an
3070 error. Using %?ce, on the other hand, refers to any job containing the
3071 string ce in its command line. If the substring matches more than one
3072 job, bash reports an error. The symbols %% and %+ refer to the shell's
3073 notion of the current job, which is the last job stopped while it was
3074 in the foreground or started in the background. The previous job may
3075 be referenced using %-. If there is only a single job, %+ and %- can
3076 both be used to refer to that job. In output pertaining to jobs (e.g.,
3077 the output of the jobs command), the current job is always flagged with
3078 a +, and the previous job with a -. A single % (with no accompanying
3079 job specification) also refers to the current job.
3080 Simply naming a job can be used to bring it into the foreground: %1 is
3082 a synonym for ``fg %1'', bringing job 1 from the background into the
3083 foreground. Similarly, ``%1 &'' resumes job 1 in the background,
3084 equivalent to ``bg %1''.
3085 The shell learns immediately whenever a job changes state. Normally,
3087 bash waits until it is about to print a prompt before reporting changes
3088 in a job's status so as to not interrupt any other output. If the -b
3089 option to the set builtin command is enabled, bash reports such changes
3090 immediately. Any trap on SIGCHLD is executed for each child that ex‐
3091 its.
3092 If an attempt to exit bash is made while jobs are stopped (or, if the
3094 checkjobs shell option has been enabled using the shopt builtin, run‐
3095 ning), the shell prints a warning message, and, if the checkjobs option
3096 is enabled, lists the jobs and their statuses. The jobs command may
3097 then be used to inspect their status. If a second attempt to exit is
3098 made without an intervening command, the shell does not print another
3099 warning, and any stopped jobs are terminated.
3100 When the shell is waiting for a job or process using the wait builtin,
3102 and job control is enabled, wait will return when the job changes
3103 state. The -f option causes wait to wait until the job or process ter‐
3104 minates before returning.
3105
3107 When executing interactively, bash displays the primary prompt PS1 when
3108 it is ready to read a command, and the secondary prompt PS2 when it
3109 needs more input to complete a command. Bash displays PS0 after it
3110 reads a command but before executing it. Bash displays PS4 as de‐
3111 scribed above before tracing each command when the -x option is en‐
3112 abled. Bash allows these prompt strings to be customized by inserting
3113 a number of backslash-escaped special characters that are decoded as
3114 follows:
3115 \a an ASCII bell character (07)
3116 \d the date in "Weekday Month Date" format (e.g., "Tue May
3117 26")
3118 \D{format}
3119 the format is passed to strftime(3) and the result is in‐
3120 serted into the prompt string; an empty format results in
3121 a locale-specific time representation. The braces are
3122 required
3123 \e an ASCII escape character (033)
3124 \h the hostname up to the first `.'
3125 \H the hostname
3126 \j the number of jobs currently managed by the shell
3127 \l the basename of the shell's terminal device name
3128 \n newline
3129 \r carriage return
3130 \s the name of the shell, the basename of $0 (the portion
3131 following the final slash)
3132 \t the current time in 24-hour HH:MM:SS format
3133 \T the current time in 12-hour HH:MM:SS format
3134 \@ the current time in 12-hour am/pm format
3135 \A the current time in 24-hour HH:MM format
3136 \u the username of the current user
3137 \v the version of bash (e.g., 2.00)
3138 \V the release of bash, version + patch level (e.g., 2.00.0)
3139 \w the value of the PWD shell variable ($PWD), with $HOME
3140 abbreviated with a tilde (uses the value of the
3141 PROMPT_DIRTRIM variable)
3142 \W the basename of $PWD, with $HOME abbreviated with a tilde
3143 \! the history number of this command
3144 \# the command number of this command
3145 \$ if the effective UID is 0, a #, otherwise a $
3146 \nnn the character corresponding to the octal number nnn
3147 \\ a backslash
3148 \[ begin a sequence of non-printing characters, which could
3149 be used to embed a terminal control sequence into the
3150 prompt
3151 \] end a sequence of non-printing characters
3152 The command number and the history number are usually different: the
3154 history number of a command is its position in the history list, which
3155 may include commands restored from the history file (see HISTORY be‐
3156 low), while the command number is the position in the sequence of com‐
3157 mands executed during the current shell session. After the string is
3158 decoded, it is expanded via parameter expansion, command substitution,
3159 arithmetic expansion, and quote removal, subject to the value of the
3160 promptvars shell option (see the description of the shopt command under
3161 SHELL BUILTIN COMMANDS below). This can have unwanted side effects if
3162 escaped portions of the string appear within command substitution or
3163 contain characters special to word expansion.
3164
3166 This is the library that handles reading input when using an interac‐
3167 tive shell, unless the --noediting option is given at shell invocation.
3168 Line editing is also used when using the -e option to the read builtin.
3169 By default, the line editing commands are similar to those of Emacs. A
3170 vi-style line editing interface is also available. Line editing can be
3171 enabled at any time using the -o emacs or -o vi options to the set
3172 builtin (see SHELL BUILTIN COMMANDS below). To turn off line editing
3173 after the shell is running, use the +o emacs or +o vi options to the
3174 set builtin.
3175 Readline Notation
3177 In this section, the Emacs-style notation is used to denote keystrokes.
3178 Control keys are denoted by C-key, e.g., C-n means Control-N. Simi‐
3179 larly, meta keys are denoted by M-key, so M-x means Meta-X. (On key‐
3180 boards without a meta key, M-x means ESC x, i.e., press the Escape key
3181 then the x key. This makes ESC the meta prefix. The combination M-C-x
3182 means ESC-Control-x, or press the Escape key then hold the Control key
3183 while pressing the x key.)
3184 Readline commands may be given numeric arguments, which normally act as
3186 a repeat count. Sometimes, however, it is the sign of the argument
3187 that is significant. Passing a negative argument to a command that
3188 acts in the forward direction (e.g., kill-line) causes that command to
3189 act in a backward direction. Commands whose behavior with arguments
3190 deviates from this are noted below.
3191 When a command is described as killing text, the text deleted is saved
3193 for possible future retrieval (yanking). The killed text is saved in a
3194 kill ring. Consecutive kills cause the text to be accumulated into one
3195 unit, which can be yanked all at once. Commands which do not kill text
3196 separate the chunks of text on the kill ring.
3197 Readline Initialization
3199 Readline is customized by putting commands in an initialization file
3200 (the inputrc file). The name of this file is taken from the value of
3201 the INPUTRC variable. If that variable is unset, the default is ~/.in‐
3202 putrc. If that file does not exist or cannot be read, the ultimate
3203 default is /etc/inputrc. When a program which uses the readline li‐
3204 brary starts up, the initialization file is read, and the key bindings
3205 and variables are set. There are only a few basic constructs allowed
3206 in the readline initialization file. Blank lines are ignored. Lines
3207 beginning with a # are comments. Lines beginning with a $ indicate
3208 conditional constructs. Other lines denote key bindings and variable
3209 settings.
3210 The default key-bindings may be changed with an inputrc file. Other
3212 programs that use this library may add their own commands and bindings.
3213 For example, placing
3215 M-Control-u: universal-argument
3217 or
3218 C-Meta-u: universal-argument
3219 into the inputrc would make M-C-u execute the readline command univer‐
3220 sal-argument.
3221 The following symbolic character names are recognized: RUBOUT, DEL,
3223 ESC, LFD, NEWLINE, RET, RETURN, SPC, SPACE, and TAB.
3224 In addition to command names, readline allows keys to be bound to a
3226 string that is inserted when the key is pressed (a macro).
3227 Readline Key Bindings
3229 The syntax for controlling key bindings in the inputrc file is simple.
3230 All that is required is the name of the command or the text of a macro
3231 and a key sequence to which it should be bound. The name may be speci‐
3232 fied in one of two ways: as a symbolic key name, possibly with Meta- or
3233 Control- prefixes, or as a key sequence.
3234 When using the form keyname:function-name or macro, keyname is the name
3236 of a key spelled out in English. For example:
3237 Control-u: universal-argument
3239 Meta-Rubout: backward-kill-word
3240 Control-o: "> output"
3241 In the above example, C-u is bound to the function universal-argument,
3243 M-DEL is bound to the function backward-kill-word, and C-o is bound to
3244 run the macro expressed on the right hand side (that is, to insert the
3245 text ``> output'' into the line).
3246 In the second form, "keyseq":function-name or macro, keyseq differs
3248 from keyname above in that strings denoting an entire key sequence may
3249 be specified by placing the sequence within double quotes. Some GNU
3250 Emacs style key escapes can be used, as in the following example, but
3251 the symbolic character names are not recognized.
3252 "\C-u": universal-argument
3254 "\C-x\C-r": re-read-init-file
3255 "\e[11~": "Function Key 1"
3256 In this example, C-u is again bound to the function universal-argument.
3258 C-x C-r is bound to the function re-read-init-file, and ESC [ 1 1 ~ is
3259 bound to insert the text ``Function Key 1''.
3260 The full set of GNU Emacs style escape sequences is
3262 \C- control prefix
3263 \M- meta prefix
3264 \e an escape character
3265 \\ backslash
3266 \" literal "
3267 \' literal '
3268 In addition to the GNU Emacs style escape sequences, a second set of
3270 backslash escapes is available:
3271 \a alert (bell)
3272 \b backspace
3273 \d delete
3274 \f form feed
3275 \n newline
3276 \r carriage return
3277 \t horizontal tab
3278 \v vertical tab
3279 \nnn the eight-bit character whose value is the octal value
3280 nnn (one to three digits)
3281 \xHH the eight-bit character whose value is the hexadecimal
3282 value HH (one or two hex digits)
3283 When entering the text of a macro, single or double quotes must be used
3285 to indicate a macro definition. Unquoted text is assumed to be a func‐
3286 tion name. In the macro body, the backslash escapes described above
3287 are expanded. Backslash will quote any other character in the macro
3288 text, including " and '.
3289 Bash allows the current readline key bindings to be displayed or modi‐
3291 fied with the bind builtin command. The editing mode may be switched
3292 during interactive use by using the -o option to the set builtin com‐
3293 mand (see SHELL BUILTIN COMMANDS below).
3294 Readline Variables
3296 Readline has variables that can be used to further customize its behav‐
3297 ior. A variable may be set in the inputrc file with a statement of the
3298 form
3299 set variable-name value
3301 or using the bind builtin command (see SHELL BUILTIN COMMANDS below).
3302 Except where noted, readline variables can take the values On or Off
3304 (without regard to case). Unrecognized variable names are ignored.
3305 When a variable value is read, empty or null values, "on" (case-insen‐
3306 sitive), and "1" are equivalent to On. All other values are equivalent
3307 to Off. The variables and their default values are:
3308 active-region-start-color
3310 A string variable that controls the text color and background
3311 when displaying the text in the active region (see the descrip‐
3312 tion of enable-active-region below). This string must not take
3313 up any physical character positions on the display, so it should
3314 consist only of terminal escape sequences. It is output to the
3315 terminal before displaying the text in the active region. This
3316 variable is reset to the default value whenever the terminal
3317 type changes. The default value is the string that puts the
3318 terminal in standout mode, as obtained from the terminal's ter‐
3319 minfo description. A sample value might be "\e[01;33m".
3320 active-region-end-color
3321 A string variable that "undoes" the effects of active-re‐
3322 gion-start-color and restores "normal" terminal display appear‐
3323 ance after displaying text in the active region. This string
3324 must not take up any physical character positions on the dis‐
3325 play, so it should consist only of terminal escape sequences.
3326 It is output to the terminal after displaying the text in the
3327 active region. This variable is reset to the default value
3328 whenever the terminal type changes. The default value is the
3329 string that restores the terminal from standout mode, as ob‐
3330 tained from the terminal's terminfo description. A sample value
3331 might be "\e[0m".
3332 bell-style (audible)
3333 Controls what happens when readline wants to ring the terminal
3334 bell. If set to none, readline never rings the bell. If set to
3335 visible, readline uses a visible bell if one is available. If
3336 set to audible, readline attempts to ring the terminal's bell.
3337 bind-tty-special-chars (On)
3338 If set to On, readline attempts to bind the control characters
3339 treated specially by the kernel's terminal driver to their read‐
3340 line equivalents.
3341 blink-matching-paren (Off)
3342 If set to On, readline attempts to briefly move the cursor to an
3343 opening parenthesis when a closing parenthesis is inserted.
3344 colored-completion-prefix (Off)
3345 If set to On, when listing completions, readline displays the
3346 common prefix of the set of possible completions using a differ‐
3347 ent color. The color definitions are taken from the value of
3348 the LS_COLORS environment variable. If there is a color defini‐
3349 tion in $LS_COLORS for the custom suffix "readline-colored-com‐
3350 pletion-prefix", readline uses this color for the common prefix
3351 instead of its default.
3352 colored-stats (Off)
3353 If set to On, readline displays possible completions using dif‐
3354 ferent colors to indicate their file type. The color defini‐
3355 tions are taken from the value of the LS_COLORS environment
3356 variable.
3357 comment-begin (``#'')
3358 The string that is inserted when the readline insert-comment
3359 command is executed. This command is bound to M-# in emacs mode
3360 and to # in vi command mode.
3361 completion-display-width (-1)
3362 The number of screen columns used to display possible matches
3363 when performing completion. The value is ignored if it is less
3364 than 0 or greater than the terminal screen width. A value of 0
3365 will cause matches to be displayed one per line. The default
3366 value is -1.
3367 completion-ignore-case (Off)
3368 If set to On, readline performs filename matching and completion
3369 in a case-insensitive fashion.
3370 completion-map-case (Off)
3371 If set to On, and completion-ignore-case is enabled, readline
3372 treats hyphens (-) and underscores (_) as equivalent when per‐
3373 forming case-insensitive filename matching and completion.
3374 completion-prefix-display-length (0)
3375 The length in characters of the common prefix of a list of pos‐
3376 sible completions that is displayed without modification. When
3377 set to a value greater than zero, common prefixes longer than
3378 this value are replaced with an ellipsis when displaying possi‐
3379 ble completions.
3380 completion-query-items (100)
3381 This determines when the user is queried about viewing the num‐
3382 ber of possible completions generated by the possible-comple‐
3383 tions command. It may be set to any integer value greater than
3384 or equal to zero. If the number of possible completions is
3385 greater than or equal to the value of this variable, readline
3386 will ask whether or not the user wishes to view them; otherwise
3387 they are simply listed on the terminal. A zero value means
3388 readline should never ask; negative values are treated as zero.
3389 convert-meta (On)
3390 If set to On, readline will convert characters with the eighth
3391 bit set to an ASCII key sequence by stripping the eighth bit and
3392 prefixing an escape character (in effect, using escape as the
3393 meta prefix). The default is On, but readline will set it to
3394 Off if the locale contains eight-bit characters. This variable
3395 is dependent on the LC_CTYPE locale category, and may change if
3396 the locale is changed.
3397 disable-completion (Off)
3398 If set to On, readline will inhibit word completion. Completion
3399 characters will be inserted into the line as if they had been
3400 mapped to self-insert.
3401 echo-control-characters (On)
3402 When set to On, on operating systems that indicate they support
3403 it, readline echoes a character corresponding to a signal gener‐
3404 ated from the keyboard.
3405 editing-mode (emacs)
3406 Controls whether readline begins with a set of key bindings sim‐
3407 ilar to Emacs or vi. editing-mode can be set to either emacs or
3408 vi.
3409 emacs-mode-string (@)
3410 If the show-mode-in-prompt variable is enabled, this string is
3411 displayed immediately before the last line of the primary prompt
3412 when emacs editing mode is active. The value is expanded like a
3413 key binding, so the standard set of meta- and control prefixes
3414 and backslash escape sequences is available. Use the \1 and \2
3415 escapes to begin and end sequences of non-printing characters,
3416 which can be used to embed a terminal control sequence into the
3417 mode string.
3418 enable-active-region (On)
3419 The point is the current cursor position, and mark refers to a
3420 saved cursor position. The text between the point and mark is
3421 referred to as the region. When this variable is set to On,
3422 readline allows certain commands to designate the region as ac‐
3423 tive. When the region is active, readline highlights the text
3424 in the region using the value of the active-region-start-color,
3425 which defaults to the string that enables the terminal's stand‐
3426 out mode. The active region shows the text inserted by brack‐
3427 eted-paste and any matching text found by incremental and non-
3428 incremental history searches.
3429 enable-bracketed-paste (On)
3430 When set to On, readline configures the terminal to insert each
3431 paste into the editing buffer as a single string of characters,
3432 instead of treating each character as if it had been read from
3433 the keyboard. This prevents readline from executing any editing
3434 commands bound to key sequences appearing in the pasted text.
3435 enable-keypad (Off)
3436 When set to On, readline will try to enable the application key‐
3437 pad when it is called. Some systems need this to enable the ar‐
3438 row keys.
3439 enable-meta-key (On)
3440 When set to On, readline will try to enable any meta modifier
3441 key the terminal claims to support when it is called. On many
3442 terminals, the meta key is used to send eight-bit characters.
3443 expand-tilde (Off)
3444 If set to On, tilde expansion is performed when readline at‐
3445 tempts word completion.
3446 history-preserve-point (Off)
3447 If set to On, the history code attempts to place point at the
3448 same location on each history line retrieved with previous-his‐
3449 tory or next-history.
3450 history-size (unset)
3451 Set the maximum number of history entries saved in the history
3452 list. If set to zero, any existing history entries are deleted
3453 and no new entries are saved. If set to a value less than zero,
3454 the number of history entries is not limited. By default, the
3455 number of history entries is set to the value of the HISTSIZE
3456 shell variable. If an attempt is made to set history-size to a
3457 non-numeric value, the maximum number of history entries will be
3458 set to 500.
3459 horizontal-scroll-mode (Off)
3460 When set to On, makes readline use a single line for display,
3461 scrolling the input horizontally on a single screen line when it
3462 becomes longer than the screen width rather than wrapping to a
3463 new line. This setting is automatically enabled for terminals
3464 of height 1.
3465 input-meta (Off)
3466 If set to On, readline will enable eight-bit input (that is, it
3467 will not strip the eighth bit from the characters it reads), re‐
3468 gardless of what the terminal claims it can support. The name
3469 meta-flag is a synonym for this variable. The default is Off,
3470 but readline will set it to On if the locale contains eight-bit
3471 characters. This variable is dependent on the LC_CTYPE locale
3472 category, and may change if the locale is changed.
3473 isearch-terminators (``C-[C-J'')
3474 The string of characters that should terminate an incremental
3475 search without subsequently executing the character as a com‐
3476 mand. If this variable has not been given a value, the charac‐
3477 ters ESC and C-J will terminate an incremental search.
3478 keymap (emacs)
3479 Set the current readline keymap. The set of valid keymap names
3480 is emacs, emacs-standard, emacs-meta, emacs-ctlx, vi, vi-com‐
3481 mand, and vi-insert. vi is equivalent to vi-command; emacs is
3482 equivalent to emacs-standard. The default value is emacs; the
3483 value of editing-mode also affects the default keymap.
3484 keyseq-timeout (500)
3485 Specifies the duration readline will wait for a character when
3486 reading an ambiguous key sequence (one that can form a complete
3487 key sequence using the input read so far, or can take additional
3488 input to complete a longer key sequence). If no input is re‐
3489 ceived within the timeout, readline will use the shorter but
3490 complete key sequence. The value is specified in milliseconds,
3491 so a value of 1000 means that readline will wait one second for
3492 additional input. If this variable is set to a value less than
3493 or equal to zero, or to a non-numeric value, readline will wait
3494 until another key is pressed to decide which key sequence to
3495 complete.
3496 mark-directories (On)
3497 If set to On, completed directory names have a slash appended.
3498 mark-modified-lines (Off)
3499 If set to On, history lines that have been modified are dis‐
3500 played with a preceding asterisk (*).
3501 mark-symlinked-directories (Off)
3502 If set to On, completed names which are symbolic links to direc‐
3503 tories have a slash appended (subject to the value of mark-di‐
3504 rectories).
3505 match-hidden-files (On)
3506 This variable, when set to On, causes readline to match files
3507 whose names begin with a `.' (hidden files) when performing
3508 filename completion. If set to Off, the leading `.' must be
3509 supplied by the user in the filename to be completed.
3510 menu-complete-display-prefix (Off)
3511 If set to On, menu completion displays the common prefix of the
3512 list of possible completions (which may be empty) before cycling
3513 through the list.
3514 output-meta (Off)
3515 If set to On, readline will display characters with the eighth
3516 bit set directly rather than as a meta-prefixed escape sequence.
3517 The default is Off, but readline will set it to On if the locale
3518 contains eight-bit characters. This variable is dependent on
3519 the LC_CTYPE locale category, and may change if the locale is
3520 changed.
3521 page-completions (On)
3522 If set to On, readline uses an internal more-like pager to dis‐
3523 play a screenful of possible completions at a time.
3524 print-completions-horizontally (Off)
3525 If set to On, readline will display completions with matches
3526 sorted horizontally in alphabetical order, rather than down the
3527 screen.
3528 revert-all-at-newline (Off)
3529 If set to On, readline will undo all changes to history lines
3530 before returning when accept-line is executed. By default, his‐
3531 tory lines may be modified and retain individual undo lists
3532 across calls to readline.
3533 show-all-if-ambiguous (Off)
3534 This alters the default behavior of the completion functions.
3535 If set to On, words which have more than one possible completion
3536 cause the matches to be listed immediately instead of ringing
3537 the bell.
3538 show-all-if-unmodified (Off)
3539 This alters the default behavior of the completion functions in
3540 a fashion similar to show-all-if-ambiguous. If set to On, words
3541 which have more than one possible completion without any possi‐
3542 ble partial completion (the possible completions don't share a
3543 common prefix) cause the matches to be listed immediately in‐
3544 stead of ringing the bell.
3545 show-mode-in-prompt (Off)
3546 If set to On, add a string to the beginning of the prompt indi‐
3547 cating the editing mode: emacs, vi command, or vi insertion.
3548 The mode strings are user-settable (e.g., emacs-mode-string).
3549 skip-completed-text (Off)
3550 If set to On, this alters the default completion behavior when
3551 inserting a single match into the line. It's only active when
3552 performing completion in the middle of a word. If enabled,
3553 readline does not insert characters from the completion that
3554 match characters after point in the word being completed, so
3555 portions of the word following the cursor are not duplicated.
3556 vi-cmd-mode-string ((cmd))
3557 If the show-mode-in-prompt variable is enabled, this string is
3558 displayed immediately before the last line of the primary prompt
3559 when vi editing mode is active and in command mode. The value
3560 is expanded like a key binding, so the standard set of meta- and
3561 control prefixes and backslash escape sequences is available.
3562 Use the \1 and \2 escapes to begin and end sequences of non-
3563 printing characters, which can be used to embed a terminal con‐
3564 trol sequence into the mode string.
3565 vi-ins-mode-string ((ins))
3566 If the show-mode-in-prompt variable is enabled, this string is
3567 displayed immediately before the last line of the primary prompt
3568 when vi editing mode is active and in insertion mode. The value
3569 is expanded like a key binding, so the standard set of meta- and
3570 control prefixes and backslash escape sequences is available.
3571 Use the \1 and \2 escapes to begin and end sequences of non-
3572 printing characters, which can be used to embed a terminal con‐
3573 trol sequence into the mode string.
3574 visible-stats (Off)
3575 If set to On, a character denoting a file's type as reported by
3576 stat(2) is appended to the filename when listing possible com‐
3577 pletions.
3578 Readline Conditional Constructs
3580 Readline implements a facility similar in spirit to the conditional
3581 compilation features of the C preprocessor which allows key bindings
3582 and variable settings to be performed as the result of tests. There
3583 are four parser directives used.
3584 $if The $if construct allows bindings to be made based on the edit‐
3586 ing mode, the terminal being used, or the application using
3587 readline. The text of the test, after any comparison operator,
3588 extends to the end of the line; unless otherwise noted, no
3589 characters are required to isolate it.
3590 mode The mode= form of the $if directive is used to test
3592 whether readline is in emacs or vi mode. This may be
3593 used in conjunction with the set keymap command, for in‐
3594 stance, to set bindings in the emacs-standard and
3595 emacs-ctlx keymaps only if readline is starting out in
3596 emacs mode.
3597 term The term= form may be used to include terminal-specific
3599 key bindings, perhaps to bind the key sequences output by
3600 the terminal's function keys. The word on the right side
3601 of the = is tested against both the full name of the ter‐
3602 minal and the portion of the terminal name before the
3603 first -. This allows sun to match both sun and sun-cmd,
3604 for instance.
3605 version
3607 The version test may be used to perform comparisons
3608 against specific readline versions. The version expands
3609 to the current readline version. The set of comparison
3610 operators includes =, (and ==), !=, <=, >=, <, and >.
3611 The version number supplied on the right side of the op‐
3612 erator consists of a major version number, an optional
3613 decimal point, and an optional minor version (e.g., 7.1).
3614 If the minor version is omitted, it is assumed to be 0.
3615 The operator may be separated from the string version and
3616 from the version number argument by whitespace.
3617 application
3619 The application construct is used to include application-
3620 specific settings. Each program using the readline li‐
3621 brary sets the application name, and an initialization
3622 file can test for a particular value. This could be used
3623 to bind key sequences to functions useful for a specific
3624 program. For instance, the following command adds a key
3625 sequence that quotes the current or previous word in
3626 bash:
3627 $if Bash
3629 # Quote the current or previous word
3630 "\C-xq": "\eb\"\ef\""
3631 $endif
3632 variable
3634 The variable construct provides simple equality tests for
3635 readline variables and values. The permitted comparison
3636 operators are =, ==, and !=. The variable name must be
3637 separated from the comparison operator by whitespace; the
3638 operator may be separated from the value on the right
3639 hand side by whitespace. Both string and boolean vari‐
3640 ables may be tested. Boolean variables must be tested
3641 against the values on and off.
3642 $endif This command, as seen in the previous example, terminates an $if
3644 command.
3645 $else Commands in this branch of the $if directive are executed if the
3647 test fails.
3648 $include
3650 This directive takes a single filename as an argument and reads
3651 commands and bindings from that file. For example, the follow‐
3652 ing directive would read /etc/inputrc:
3653 $include /etc/inputrc
3655 Searching
3657 Readline provides commands for searching through the command history
3658 (see HISTORY below) for lines containing a specified string. There are
3659 two search modes: incremental and non-incremental.
3660 Incremental searches begin before the user has finished typing the
3662 search string. As each character of the search string is typed, read‐
3663 line displays the next entry from the history matching the string typed
3664 so far. An incremental search requires only as many characters as
3665 needed to find the desired history entry. The characters present in
3666 the value of the isearch-terminators variable are used to terminate an
3667 incremental search. If that variable has not been assigned a value the
3668 Escape and Control-J characters will terminate an incremental search.
3669 Control-G will abort an incremental search and restore the original
3670 line. When the search is terminated, the history entry containing the
3671 search string becomes the current line.
3672 To find other matching entries in the history list, type Control-S or
3674 Control-R as appropriate. This will search backward or forward in the
3675 history for the next entry matching the search string typed so far.
3676 Any other key sequence bound to a readline command will terminate the
3677 search and execute that command. For instance, a newline will termi‐
3678 nate the search and accept the line, thereby executing the command from
3679 the history list.
3680 Readline remembers the last incremental search string. If two Control-
3682 Rs are typed without any intervening characters defining a new search
3683 string, any remembered search string is used.
3684 Non-incremental searches read the entire search string before starting
3686 to search for matching history lines. The search string may be typed
3687 by the user or be part of the contents of the current line.
3688 Readline Command Names
3690 The following is a list of the names of the commands and the default
3691 key sequences to which they are bound. Command names without an accom‐
3692 panying key sequence are unbound by default. In the following descrip‐
3693 tions, point refers to the current cursor position, and mark refers to
3694 a cursor position saved by the set-mark command. The text between the
3695 point and mark is referred to as the region.
3696 Commands for Moving
3698 beginning-of-line (C-a)
3699 Move to the start of the current line.
3700 end-of-line (C-e)
3701 Move to the end of the line.
3702 forward-char (C-f)
3703 Move forward a character.
3704 backward-char (C-b)
3705 Move back a character.
3706 forward-word (M-f)
3707 Move forward to the end of the next word. Words are composed of
3708 alphanumeric characters (letters and digits).
3709 backward-word (M-b)
3710 Move back to the start of the current or previous word. Words
3711 are composed of alphanumeric characters (letters and digits).
3712 shell-forward-word
3713 Move forward to the end of the next word. Words are delimited
3714 by non-quoted shell metacharacters.
3715 shell-backward-word
3716 Move back to the start of the current or previous word. Words
3717 are delimited by non-quoted shell metacharacters.
3718 previous-screen-line
3719 Attempt to move point to the same physical screen column on the
3720 previous physical screen line. This will not have the desired
3721 effect if the current readline line does not take up more than
3722 one physical line or if point is not greater than the length of
3723 the prompt plus the screen width.
3724 next-screen-line
3725 Attempt to move point to the same physical screen column on the
3726 next physical screen line. This will not have the desired effect
3727 if the current readline line does not take up more than one
3728 physical line or if the length of the current readline line is
3729 not greater than the length of the prompt plus the screen width.
3730 clear-display (M-C-l)
3731 Clear the screen and, if possible, the terminal's scrollback
3732 buffer, then redraw the current line, leaving the current line
3733 at the top of the screen.
3734 clear-screen (C-l)
3735 Clear the screen, then redraw the current line, leaving the cur‐
3736 rent line at the top of the screen. With an argument, refresh
3737 the current line without clearing the screen.
3738 redraw-current-line
3739 Refresh the current line.
3740 Commands for Manipulating the History
3742 accept-line (Newline, Return)
3743 Accept the line regardless of where the cursor is. If this line
3744 is non-empty, add it to the history list according to the state
3745 of the HISTCONTROL variable. If the line is a modified history
3746 line, then restore the history line to its original state.
3747 previous-history (C-p)
3748 Fetch the previous command from the history list, moving back in
3749 the list.
3750 next-history (C-n)
3751 Fetch the next command from the history list, moving forward in
3752 the list.
3753 beginning-of-history (M-<)
3754 Move to the first line in the history.
3755 end-of-history (M->)
3756 Move to the end of the input history, i.e., the line currently
3757 being entered.
3758 operate-and-get-next (C-o)
3759 Accept the current line for execution and fetch the next line
3760 relative to the current line from the history for editing. A
3761 numeric argument, if supplied, specifies the history entry to
3762 use instead of the current line.
3763 fetch-history
3764 With a numeric argument, fetch that entry from the history list
3765 and make it the current line. Without an argument, move back to
3766 the first entry in the history list.
3767 reverse-search-history (C-r)
3768 Search backward starting at the current line and moving `up'
3769 through the history as necessary. This is an incremental
3770 search.
3771 forward-search-history (C-s)
3772 Search forward starting at the current line and moving `down'
3773 through the history as necessary. This is an incremental
3774 search.
3775 non-incremental-reverse-search-history (M-p)
3776 Search backward through the history starting at the current line
3777 using a non-incremental search for a string supplied by the
3778 user.
3779 non-incremental-forward-search-history (M-n)
3780 Search forward through the history using a non-incremental
3781 search for a string supplied by the user.
3782 history-search-forward
3783 Search forward through the history for the string of characters
3784 between the start of the current line and the point. This is a
3785 non-incremental search.
3786 history-search-backward
3787 Search backward through the history for the string of characters
3788 between the start of the current line and the point. This is a
3789 non-incremental search.
3790 history-substring-search-backward
3791 Search backward through the history for the string of characters
3792 between the start of the current line and the current cursor po‐
3793 sition (the point). The search string may match anywhere in a
3794 history line. This is a non-incremental search.
3795 history-substring-search-forward
3796 Search forward through the history for the string of characters
3797 between the start of the current line and the point. The search
3798 string may match anywhere in a history line. This is a non-in‐
3799 cremental search.
3800 yank-nth-arg (M-C-y)
3801 Insert the first argument to the previous command (usually the
3802 second word on the previous line) at point. With an argument n,
3803 insert the nth word from the previous command (the words in the
3804 previous command begin with word 0). A negative argument in‐
3805 serts the nth word from the end of the previous command. Once
3806 the argument n is computed, the argument is extracted as if the
3807 "!n" history expansion had been specified.
3808 yank-last-arg (M-., M-_)
3809 Insert the last argument to the previous command (the last word
3810 of the previous history entry). With a numeric argument, behave
3811 exactly like yank-nth-arg. Successive calls to yank-last-arg
3812 move back through the history list, inserting the last word (or
3813 the word specified by the argument to the first call) of each
3814 line in turn. Any numeric argument supplied to these successive
3815 calls determines the direction to move through the history. A
3816 negative argument switches the direction through the history
3817 (back or forward). The history expansion facilities are used to
3818 extract the last word, as if the "!$" history expansion had been
3819 specified.
3820 shell-expand-line (M-C-e)
3821 Expand the line as the shell does. This performs alias and his‐
3822 tory expansion as well as all of the shell word expansions. See
3823 HISTORY EXPANSION below for a description of history expansion.
3824 history-expand-line (M-^)
3825 Perform history expansion on the current line. See HISTORY EX‐
3826 PANSION below for a description of history expansion.
3827 magic-space
3828 Perform history expansion on the current line and insert a
3829 space. See HISTORY EXPANSION below for a description of history
3830 expansion.
3831 alias-expand-line
3832 Perform alias expansion on the current line. See ALIASES above
3833 for a description of alias expansion.
3834 history-and-alias-expand-line
3835 Perform history and alias expansion on the current line.
3836 insert-last-argument (M-., M-_)
3837 A synonym for yank-last-arg.
3838 edit-and-execute-command (C-x C-e)
3839 Invoke an editor on the current command line, and execute the
3840 result as shell commands. Bash attempts to invoke $VISUAL, $ED‐
3841 ITOR, and emacs as the editor, in that order.
3842 Commands for Changing Text
3844 end-of-file (usually C-d)
3845 The character indicating end-of-file as set, for example, by
3846 ``stty''. If this character is read when there are no charac‐
3847 ters on the line, and point is at the beginning of the line,
3848 readline interprets it as the end of input and returns EOF.
3849 delete-char (C-d)
3850 Delete the character at point. If this function is bound to the
3851 same character as the tty EOF character, as C-d commonly is, see
3852 above for the effects.
3853 backward-delete-char (Rubout)
3854 Delete the character behind the cursor. When given a numeric
3855 argument, save the deleted text on the kill ring.
3856 forward-backward-delete-char
3857 Delete the character under the cursor, unless the cursor is at
3858 the end of the line, in which case the character behind the cur‐
3859 sor is deleted.
3860 quoted-insert (C-q, C-v)
3861 Add the next character typed to the line verbatim. This is how
3862 to insert characters like C-q, for example.
3863 tab-insert (C-v TAB)
3864 Insert a tab character.
3865 self-insert (a, b, A, 1, !, ...)
3866 Insert the character typed.
3867 transpose-chars (C-t)
3868 Drag the character before point forward over the character at
3869 point, moving point forward as well. If point is at the end of
3870 the line, then this transposes the two characters before point.
3871 Negative arguments have no effect.
3872 transpose-words (M-t)
3873 Drag the word before point past the word after point, moving
3874 point over that word as well. If point is at the end of the
3875 line, this transposes the last two words on the line.
3876 upcase-word (M-u)
3877 Uppercase the current (or following) word. With a negative ar‐
3878 gument, uppercase the previous word, but do not move point.
3879 downcase-word (M-l)
3880 Lowercase the current (or following) word. With a negative ar‐
3881 gument, lowercase the previous word, but do not move point.
3882 capitalize-word (M-c)
3883 Capitalize the current (or following) word. With a negative ar‐
3884 gument, capitalize the previous word, but do not move point.
3885 overwrite-mode
3886 Toggle overwrite mode. With an explicit positive numeric argu‐
3887 ment, switches to overwrite mode. With an explicit non-positive
3888 numeric argument, switches to insert mode. This command affects
3889 only emacs mode; vi mode does overwrite differently. Each call
3890 to readline() starts in insert mode. In overwrite mode, charac‐
3891 ters bound to self-insert replace the text at point rather than
3892 pushing the text to the right. Characters bound to back‐
3893 ward-delete-char replace the character before point with a
3894 space. By default, this command is unbound.
3895 Killing and Yanking
3897 kill-line (C-k)
3898 Kill the text from point to the end of the line.
3899 backward-kill-line (C-x Rubout)
3900 Kill backward to the beginning of the line.
3901 unix-line-discard (C-u)
3902 Kill backward from point to the beginning of the line. The
3903 killed text is saved on the kill-ring.
3904 kill-whole-line
3905 Kill all characters on the current line, no matter where point
3906 is.
3907 kill-word (M-d)
3908 Kill from point to the end of the current word, or if between
3909 words, to the end of the next word. Word boundaries are the
3910 same as those used by forward-word.
3911 backward-kill-word (M-Rubout)
3912 Kill the word behind point. Word boundaries are the same as
3913 those used by backward-word.
3914 shell-kill-word
3915 Kill from point to the end of the current word, or if between
3916 words, to the end of the next word. Word boundaries are the
3917 same as those used by shell-forward-word.
3918 shell-backward-kill-word
3919 Kill the word behind point. Word boundaries are the same as
3920 those used by shell-backward-word.
3921 unix-word-rubout (C-w)
3922 Kill the word behind point, using white space as a word bound‐
3923 ary. The killed text is saved on the kill-ring.
3924 unix-filename-rubout
3925 Kill the word behind point, using white space and the slash
3926 character as the word boundaries. The killed text is saved on
3927 the kill-ring.
3928 delete-horizontal-space (M-\)
3929 Delete all spaces and tabs around point.
3930 kill-region
3931 Kill the text in the current region.
3932 copy-region-as-kill
3933 Copy the text in the region to the kill buffer.
3934 copy-backward-word
3935 Copy the word before point to the kill buffer. The word bound‐
3936 aries are the same as backward-word.
3937 copy-forward-word
3938 Copy the word following point to the kill buffer. The word
3939 boundaries are the same as forward-word.
3940 yank (C-y)
3941 Yank the top of the kill ring into the buffer at point.
3942 yank-pop (M-y)
3943 Rotate the kill ring, and yank the new top. Only works follow‐
3944 ing yank or yank-pop.
3945 Numeric Arguments
3947 digit-argument (M-0, M-1, ..., M--)
3948 Add this digit to the argument already accumulating, or start a
3949 new argument. M-- starts a negative argument.
3950 universal-argument
3951 This is another way to specify an argument. If this command is
3952 followed by one or more digits, optionally with a leading minus
3953 sign, those digits define the argument. If the command is fol‐
3954 lowed by digits, executing universal-argument again ends the nu‐
3955 meric argument, but is otherwise ignored. As a special case, if
3956 this command is immediately followed by a character that is nei‐
3957 ther a digit nor minus sign, the argument count for the next
3958 command is multiplied by four. The argument count is initially
3959 one, so executing this function the first time makes the argu‐
3960 ment count four, a second time makes the argument count sixteen,
3961 and so on.
3962 Completing
3964 complete (TAB)
3965 Attempt to perform completion on the text before point. Bash
3966 attempts completion treating the text as a variable (if the text
3967 begins with $), username (if the text begins with ~), hostname
3968 (if the text begins with @), or command (including aliases and
3969 functions) in turn. If none of these produces a match, filename
3970 completion is attempted.
3971 possible-completions (M-?)
3972 List the possible completions of the text before point.
3973 insert-completions (M-*)
3974 Insert all completions of the text before point that would have
3975 been generated by possible-completions.
3976 menu-complete
3977 Similar to complete, but replaces the word to be completed with
3978 a single match from the list of possible completions. Repeated
3979 execution of menu-complete steps through the list of possible
3980 completions, inserting each match in turn. At the end of the
3981 list of completions, the bell is rung (subject to the setting of
3982 bell-style) and the original text is restored. An argument of n
3983 moves n positions forward in the list of matches; a negative ar‐
3984 gument may be used to move backward through the list. This com‐
3985 mand is intended to be bound to TAB, but is unbound by default.
3986 menu-complete-backward
3987 Identical to menu-complete, but moves backward through the list
3988 of possible completions, as if menu-complete had been given a
3989 negative argument. This command is unbound by default.
3990 delete-char-or-list
3991 Deletes the character under the cursor if not at the beginning
3992 or end of the line (like delete-char). If at the end of the
3993 line, behaves identically to possible-completions. This command
3994 is unbound by default.
3995 complete-filename (M-/)
3996 Attempt filename completion on the text before point.
3997 possible-filename-completions (C-x /)
3998 List the possible completions of the text before point, treating
3999 it as a filename.
4000 complete-username (M-~)
4001 Attempt completion on the text before point, treating it as a
4002 username.
4003 possible-username-completions (C-x ~)
4004 List the possible completions of the text before point, treating
4005 it as a username.
4006 complete-variable (M-$)
4007 Attempt completion on the text before point, treating it as a
4008 shell variable.
4009 possible-variable-completions (C-x $)
4010 List the possible completions of the text before point, treating
4011 it as a shell variable.
4012 complete-hostname (M-@)
4013 Attempt completion on the text before point, treating it as a
4014 hostname.
4015 possible-hostname-completions (C-x @)
4016 List the possible completions of the text before point, treating
4017 it as a hostname.
4018 complete-command (M-!)
4019 Attempt completion on the text before point, treating it as a
4020 command name. Command completion attempts to match the text
4021 against aliases, reserved words, shell functions, shell
4022 builtins, and finally executable filenames, in that order.
4023 possible-command-completions (C-x !)
4024 List the possible completions of the text before point, treating
4025 it as a command name.
4026 dynamic-complete-history (M-TAB)
4027 Attempt completion on the text before point, comparing the text
4028 against lines from the history list for possible completion
4029 matches.
4030 dabbrev-expand
4031 Attempt menu completion on the text before point, comparing the
4032 text against lines from the history list for possible completion
4033 matches.
4034 complete-into-braces (M-{)
4035 Perform filename completion and insert the list of possible com‐
4036 pletions enclosed within braces so the list is available to the
4037 shell (see Brace Expansion above).
4038 Keyboard Macros
4040 start-kbd-macro (C-x ()
4041 Begin saving the characters typed into the current keyboard
4042 macro.
4043 end-kbd-macro (C-x ))
4044 Stop saving the characters typed into the current keyboard macro
4045 and store the definition.
4046 call-last-kbd-macro (C-x e)
4047 Re-execute the last keyboard macro defined, by making the char‐
4048 acters in the macro appear as if typed at the keyboard.
4049 print-last-kbd-macro ()
4050 Print the last keyboard macro defined in a format suitable for
4051 the inputrc file.
4052 Miscellaneous
4054 re-read-init-file (C-x C-r)
4055 Read in the contents of the inputrc file, and incorporate any
4056 bindings or variable assignments found there.
4057 abort (C-g)
4058 Abort the current editing command and ring the terminal's bell
4059 (subject to the setting of bell-style).
4060 do-lowercase-version (M-A, M-B, M-x, ...)
4061 If the metafied character x is uppercase, run the command that
4062 is bound to the corresponding metafied lowercase character. The
4063 behavior is undefined if x is already lowercase.
4064 prefix-meta (ESC)
4065 Metafy the next character typed. ESC f is equivalent to Meta-f.
4066 undo (C-_, C-x C-u)
4067 Incremental undo, separately remembered for each line.
4068 revert-line (M-r)
4069 Undo all changes made to this line. This is like executing the
4070 undo command enough times to return the line to its initial
4071 state.
4072 tilde-expand (M-&)
4073 Perform tilde expansion on the current word.
4074 set-mark (C-@, M-<space>)
4075 Set the mark to the point. If a numeric argument is supplied,
4076 the mark is set to that position.
4077 exchange-point-and-mark (C-x C-x)
4078 Swap the point with the mark. The current cursor position is
4079 set to the saved position, and the old cursor position is saved
4080 as the mark.
4081 character-search (C-])
4082 A character is read and point is moved to the next occurrence of
4083 that character. A negative argument searches for previous oc‐
4084 currences.
4085 character-search-backward (M-C-])
4086 A character is read and point is moved to the previous occur‐
4087 rence of that character. A negative argument searches for sub‐
4088 sequent occurrences.
4089 skip-csi-sequence
4090 Read enough characters to consume a multi-key sequence such as
4091 those defined for keys like Home and End. Such sequences begin
4092 with a Control Sequence Indicator (CSI), usually ESC-[. If this
4093 sequence is bound to "\[", keys producing such sequences will
4094 have no effect unless explicitly bound to a readline command,
4095 instead of inserting stray characters into the editing buffer.
4096 This is unbound by default, but usually bound to ESC-[.
4097 insert-comment (M-#)
4098 Without a numeric argument, the value of the readline com‐
4099 ment-begin variable is inserted at the beginning of the current
4100 line. If a numeric argument is supplied, this command acts as a
4101 toggle: if the characters at the beginning of the line do not
4102 match the value of comment-begin, the value is inserted, other‐
4103 wise the characters in comment-begin are deleted from the begin‐
4104 ning of the line. In either case, the line is accepted as if a
4105 newline had been typed. The default value of comment-begin
4106 causes this command to make the current line a shell comment.
4107 If a numeric argument causes the comment character to be re‐
4108 moved, the line will be executed by the shell.
4109 spell-correct-word (C-x s)
4110 Perform spelling correction on the current word, treating it as
4111 a directory or filename, in the same way as the cdspell shell
4112 option. Word boundaries are the same as those used by
4113 shell-forward-word.
4114 glob-complete-word (M-g)
4115 The word before point is treated as a pattern for pathname ex‐
4116 pansion, with an asterisk implicitly appended. This pattern is
4117 used to generate a list of matching filenames for possible com‐
4118 pletions.
4119 glob-expand-word (C-x *)
4120 The word before point is treated as a pattern for pathname ex‐
4121 pansion, and the list of matching filenames is inserted, replac‐
4122 ing the word. If a numeric argument is supplied, an asterisk is
4123 appended before pathname expansion.
4124 glob-list-expansions (C-x g)
4125 The list of expansions that would have been generated by
4126 glob-expand-word is displayed, and the line is redrawn. If a
4127 numeric argument is supplied, an asterisk is appended before
4128 pathname expansion.
4129 dump-functions
4130 Print all of the functions and their key bindings to the read‐
4131 line output stream. If a numeric argument is supplied, the out‐
4132 put is formatted in such a way that it can be made part of an
4133 inputrc file.
4134 dump-variables
4135 Print all of the settable readline variables and their values to
4136 the readline output stream. If a numeric argument is supplied,
4137 the output is formatted in such a way that it can be made part
4138 of an inputrc file.
4139 dump-macros
4140 Print all of the readline key sequences bound to macros and the
4141 strings they output. If a numeric argument is supplied, the
4142 output is formatted in such a way that it can be made part of an
4143 inputrc file.
4144 display-shell-version (C-x C-v)
4145 Display version information about the current instance of bash.
4146 Programmable Completion
4148 When word completion is attempted for an argument to a command for
4149 which a completion specification (a compspec) has been defined using
4150 the complete builtin (see SHELL BUILTIN COMMANDS below), the program‐
4151 mable completion facilities are invoked.
4152 First, the command name is identified. If the command word is the
4154 empty string (completion attempted at the beginning of an empty line),
4155 any compspec defined with the -E option to complete is used. If a
4156 compspec has been defined for that command, the compspec is used to
4157 generate the list of possible completions for the word. If the command
4158 word is a full pathname, a compspec for the full pathname is searched
4159 for first. If no compspec is found for the full pathname, an attempt
4160 is made to find a compspec for the portion following the final slash.
4161 If those searches do not result in a compspec, any compspec defined
4162 with the -D option to complete is used as the default. If there is no
4163 default compspec, bash attempts alias expansion on the command word as
4164 a final resort, and attempts to find a compspec for the command word
4165 from any successful expansion.
4166 Once a compspec has been found, it is used to generate the list of
4168 matching words. If a compspec is not found, the default bash comple‐
4169 tion as described above under Completing is performed.
4170 First, the actions specified by the compspec are used. Only matches
4172 which are prefixed by the word being completed are returned. When the
4173 -f or -d option is used for filename or directory name completion, the
4174 shell variable FIGNORE is used to filter the matches.
4175 Any completions specified by a pathname expansion pattern to the -G op‐
4177 tion are generated next. The words generated by the pattern need not
4178 match the word being completed. The GLOBIGNORE shell variable is not
4179 used to filter the matches, but the FIGNORE variable is used.
4180 Next, the string specified as the argument to the -W option is consid‐
4182 ered. The string is first split using the characters in the IFS spe‐
4183 cial variable as delimiters. Shell quoting is honored. Each word is
4184 then expanded using brace expansion, tilde expansion, parameter and
4185 variable expansion, command substitution, and arithmetic expansion, as
4186 described above under EXPANSION. The results are split using the rules
4187 described above under Word Splitting. The results of the expansion are
4188 prefix-matched against the word being completed, and the matching words
4189 become the possible completions.
4190 After these matches have been generated, any shell function or command
4192 specified with the -F and -C options is invoked. When the command or
4193 function is invoked, the COMP_LINE, COMP_POINT, COMP_KEY, and COMP_TYPE
4194 variables are assigned values as described above under Shell Variables.
4195 If a shell function is being invoked, the COMP_WORDS and COMP_CWORD
4196 variables are also set. When the function or command is invoked, the
4197 first argument ($1) is the name of the command whose arguments are be‐
4198 ing completed, the second argument ($2) is the word being completed,
4199 and the third argument ($3) is the word preceding the word being com‐
4200 pleted on the current command line. No filtering of the generated com‐
4201 pletions against the word being completed is performed; the function or
4202 command has complete freedom in generating the matches.
4203 Any function specified with -F is invoked first. The function may use
4205 any of the shell facilities, including the compgen builtin described
4206 below, to generate the matches. It must put the possible completions
4207 in the COMPREPLY array variable, one per array element.
4208 Next, any command specified with the -C option is invoked in an envi‐
4210 ronment equivalent to command substitution. It should print a list of
4211 completions, one per line, to the standard output. Backslash may be
4212 used to escape a newline, if necessary.
4213 After all of the possible completions are generated, any filter speci‐
4215 fied with the -X option is applied to the list. The filter is a pat‐
4216 tern as used for pathname expansion; a & in the pattern is replaced
4217 with the text of the word being completed. A literal & may be escaped
4218 with a backslash; the backslash is removed before attempting a match.
4219 Any completion that matches the pattern will be removed from the list.
4220 A leading ! negates the pattern; in this case any completion not match‐
4221 ing the pattern will be removed. If the nocasematch shell option is
4222 enabled, the match is performed without regard to the case of alpha‐
4223 betic characters.
4224 Finally, any prefix and suffix specified with the -P and -S options are
4226 added to each member of the completion list, and the result is returned
4227 to the readline completion code as the list of possible completions.
4228 If the previously-applied actions do not generate any matches, and the
4230 -o dirnames option was supplied to complete when the compspec was de‐
4231 fined, directory name completion is attempted.
4232 If the -o plusdirs option was supplied to complete when the compspec
4234 was defined, directory name completion is attempted and any matches are
4235 added to the results of the other actions.
4236 By default, if a compspec is found, whatever it generates is returned
4238 to the completion code as the full set of possible completions. The
4239 default bash completions are not attempted, and the readline default of
4240 filename completion is disabled. If the -o bashdefault option was sup‐
4241 plied to complete when the compspec was defined, the bash default com‐
4242 pletions are attempted if the compspec generates no matches. If the -o
4243 default option was supplied to complete when the compspec was defined,
4244 readline's default completion will be performed if the compspec (and,
4245 if attempted, the default bash completions) generate no matches.
4246 When a compspec indicates that directory name completion is desired,
4248 the programmable completion functions force readline to append a slash
4249 to completed names which are symbolic links to directories, subject to
4250 the value of the mark-directories readline variable, regardless of the
4251 setting of the mark-symlinked-directories readline variable.
4252 There is some support for dynamically modifying completions. This is
4254 most useful when used in combination with a default completion speci‐
4255 fied with complete -D. It's possible for shell functions executed as
4256 completion handlers to indicate that completion should be retried by
4257 returning an exit status of 124. If a shell function returns 124, and
4258 changes the compspec associated with the command on which completion is
4259 being attempted (supplied as the first argument when the function is
4260 executed), programmable completion restarts from the beginning, with an
4261 attempt to find a new compspec for that command. This allows a set of
4262 completions to be built dynamically as completion is attempted, rather
4263 than being loaded all at once.
4264 For instance, assuming that there is a library of compspecs, each kept
4266 in a file corresponding to the name of the command, the following de‐
4267 fault completion function would load completions dynamically:
4268 _completion_loader()
4270 {
4271 . "/etc/bash_completion.d/$1.sh" >/dev/null 2>&1 && return 124
4272 }
4273 complete -D -F _completion_loader -o bashdefault -o default
4274
4277 When the -o history option to the set builtin is enabled, the shell
4278 provides access to the command history, the list of commands previously
4279 typed. The value of the HISTSIZE variable is used as the number of
4280 commands to save in a history list. The text of the last HISTSIZE com‐
4281 mands (default 500) is saved. The shell stores each command in the
4282 history list prior to parameter and variable expansion (see EXPANSION
4283 above) but after history expansion is performed, subject to the values
4284 of the shell variables HISTIGNORE and HISTCONTROL.
4285 On startup, the history is initialized from the file named by the vari‐
4287 able HISTFILE (default ~/.bash_history). The file named by the value
4288 of HISTFILE is truncated, if necessary, to contain no more than the
4289 number of lines specified by the value of HISTFILESIZE. If HISTFILE‐
4290 SIZE is unset, or set to null, a non-numeric value, or a numeric value
4291 less than zero, the history file is not truncated. When the history
4292 file is read, lines beginning with the history comment character fol‐
4293 lowed immediately by a digit are interpreted as timestamps for the fol‐
4294 lowing history line. These timestamps are optionally displayed depend‐
4295 ing on the value of the HISTTIMEFORMAT variable. When a shell with
4296 history enabled exits, the last $HISTSIZE lines are copied from the
4297 history list to $HISTFILE. If the histappend shell option is enabled
4298 (see the description of shopt under SHELL BUILTIN COMMANDS below), the
4299 lines are appended to the history file, otherwise the history file is
4300 overwritten. If HISTFILE is unset, or if the history file is un‐
4301 writable, the history is not saved. If the HISTTIMEFORMAT variable is
4302 set, time stamps are written to the history file, marked with the his‐
4303 tory comment character, so they may be preserved across shell sessions.
4304 This uses the history comment character to distinguish timestamps from
4305 other history lines. After saving the history, the history file is
4306 truncated to contain no more than HISTFILESIZE lines. If HISTFILESIZE
4307 is unset, or set to null, a non-numeric value, or a numeric value less
4308 than zero, the history file is not truncated.
4309 The builtin command fc (see SHELL BUILTIN COMMANDS below) may be used
4311 to list or edit and re-execute a portion of the history list. The his‐
4312 tory builtin may be used to display or modify the history list and ma‐
4313 nipulate the history file. When using command-line editing, search
4314 commands are available in each editing mode that provide access to the
4315 history list.
4316 The shell allows control over which commands are saved on the history
4318 list. The HISTCONTROL and HISTIGNORE variables may be set to cause the
4319 shell to save only a subset of the commands entered. The cmdhist shell
4320 option, if enabled, causes the shell to attempt to save each line of a
4321 multi-line command in the same history entry, adding semicolons where
4322 necessary to preserve syntactic correctness. The lithist shell option
4323 causes the shell to save the command with embedded newlines instead of
4324 semicolons. See the description of the shopt builtin below under SHELL
4325 BUILTIN COMMANDS for information on setting and unsetting shell op‐
4326 tions.
4327
4329 The shell supports a history expansion feature that is similar to the
4330 history expansion in csh. This section describes what syntax features
4331 are available. This feature is enabled by default for interactive
4332 shells, and can be disabled using the +H option to the set builtin com‐
4333 mand (see SHELL BUILTIN COMMANDS below). Non-interactive shells do not
4334 perform history expansion by default.
4335 History expansions introduce words from the history list into the input
4337 stream, making it easy to repeat commands, insert the arguments to a
4338 previous command into the current input line, or fix errors in previous
4339 commands quickly.
4340 History expansion is performed immediately after a complete line is
4342 read, before the shell breaks it into words, and is performed on each
4343 line individually without taking quoting on previous lines into ac‐
4344 count. It takes place in two parts. The first is to determine which
4345 line from the history list to use during substitution. The second is
4346 to select portions of that line for inclusion into the current one.
4347 The line selected from the history is the event, and the portions of
4348 that line that are acted upon are words. Various modifiers are avail‐
4349 able to manipulate the selected words. The line is broken into words
4350 in the same fashion as when reading input, so that several metacharac‐
4351 ter-separated words surrounded by quotes are considered one word. His‐
4352 tory expansions are introduced by the appearance of the history expan‐
4353 sion character, which is ! by default. Only backslash (\) and single
4354 quotes can quote the history expansion character, but the history ex‐
4355 pansion character is also treated as quoted if it immediately precedes
4356 the closing double quote in a double-quoted string.
4357 Several characters inhibit history expansion if found immediately fol‐
4359 lowing the history expansion character, even if it is unquoted: space,
4360 tab, newline, carriage return, and =. If the extglob shell option is
4361 enabled, ( will also inhibit expansion.
4362 Several shell options settable with the shopt builtin may be used to
4364 tailor the behavior of history expansion. If the histverify shell op‐
4365 tion is enabled (see the description of the shopt builtin below), and
4366 readline is being used, history substitutions are not immediately
4367 passed to the shell parser. Instead, the expanded line is reloaded
4368 into the readline editing buffer for further modification. If readline
4369 is being used, and the histreedit shell option is enabled, a failed
4370 history substitution will be reloaded into the readline editing buffer
4371 for correction. The -p option to the history builtin command may be
4372 used to see what a history expansion will do before using it. The -s
4373 option to the history builtin may be used to add commands to the end of
4374 the history list without actually executing them, so that they are
4375 available for subsequent recall.
4376 The shell allows control of the various characters used by the history
4378 expansion mechanism (see the description of histchars above under Shell
4379 Variables). The shell uses the history comment character to mark his‐
4380 tory timestamps when writing the history file.
4381 Event Designators
4383 An event designator is a reference to a command line entry in the his‐
4384 tory list. Unless the reference is absolute, events are relative to
4385 the current position in the history list.
4386 ! Start a history substitution, except when followed by a blank,
4388 newline, carriage return, = or ( (when the extglob shell option
4389 is enabled using the shopt builtin).
4390 !n Refer to command line n.
4391 !-n Refer to the current command minus n.
4392 !! Refer to the previous command. This is a synonym for `!-1'.
4393 !string
4394 Refer to the most recent command preceding the current position
4395 in the history list starting with string.
4396 !?string[?]
4397 Refer to the most recent command preceding the current position
4398 in the history list containing string. The trailing ? may be
4399 omitted if string is followed immediately by a newline. If
4400 string is missing, the string from the most recent search is
4401 used; it is an error if there is no previous search string.
4402 ^string1^string2^
4403 Quick substitution. Repeat the previous command, replacing
4404 string1 with string2. Equivalent to ``!!:s^string1^string2^''
4405 (see Modifiers below).
4406 !# The entire command line typed so far.
4407 Word Designators
4409 Word designators are used to select desired words from the event. A :
4410 separates the event specification from the word designator. It may be
4411 omitted if the word designator begins with a ^, $, *, -, or %. Words
4412 are numbered from the beginning of the line, with the first word being
4413 denoted by 0 (zero). Words are inserted into the current line sepa‐
4414 rated by single spaces.
4415 0 (zero)
4417 The zeroth word. For the shell, this is the command word.
4418 n The nth word.
4419 ^ The first argument. That is, word 1.
4420 $ The last word. This is usually the last argument, but will ex‐
4421 pand to the zeroth word if there is only one word in the line.
4422 % The first word matched by the most recent `?string?' search, if
4423 the search string begins with a character that is part of a
4424 word.
4425 x-y A range of words; `-y' abbreviates `0-y'.
4426 * All of the words but the zeroth. This is a synonym for `1-$'.
4427 It is not an error to use * if there is just one word in the
4428 event; the empty string is returned in that case.
4429 x* Abbreviates x-$.
4430 x- Abbreviates x-$ like x*, but omits the last word. If x is miss‐
4431 ing, it defaults to 0.
4432 If a word designator is supplied without an event specification, the
4434 previous command is used as the event.
4435 Modifiers
4437 After the optional word designator, there may appear a sequence of one
4438 or more of the following modifiers, each preceded by a `:'. These mod‐
4439 ify, or edit, the word or words selected from the history event.
4440 h Remove a trailing filename component, leaving only the head.
4442 t Remove all leading filename components, leaving the tail.
4443 r Remove a trailing suffix of the form .xxx, leaving the basename.
4444 e Remove all but the trailing suffix.
4445 p Print the new command but do not execute it.
4446 q Quote the substituted words, escaping further substitutions.
4447 x Quote the substituted words as with q, but break into words at
4448 blanks and newlines. The q and x modifiers are mutually exclu‐
4449 sive; the last one supplied is used.
4450 s/old/new/
4451 Substitute new for the first occurrence of old in the event
4452 line. Any character may be used as the delimiter in place of /.
4453 The final delimiter is optional if it is the last character of
4454 the event line. The delimiter may be quoted in old and new with
4455 a single backslash. If & appears in new, it is replaced by old.
4456 A single backslash will quote the &. If old is null, it is set
4457 to the last old substituted, or, if no previous history substi‐
4458 tutions took place, the last string in a !?string[?] search.
4459 If new is null, each matching old is deleted.
4460 & Repeat the previous substitution.
4461 g Cause changes to be applied over the entire event line. This is
4462 used in conjunction with `:s' (e.g., `:gs/old/new/') or `:&'.
4463 If used with `:s', any delimiter can be used in place of /, and
4464 the final delimiter is optional if it is the last character of
4465 the event line. An a may be used as a synonym for g.
4466 G Apply the following `s' or `&' modifier once to each word in the
4467 event line.
4468
4470 Unless otherwise noted, each builtin command documented in this section
4471 as accepting options preceded by - accepts -- to signify the end of the
4472 options. The :, true, false, and test/[ builtins do not accept options
4473 and do not treat -- specially. The exit, logout, return, break, con‐
4474 tinue, let, and shift builtins accept and process arguments beginning
4475 with - without requiring --. Other builtins that accept arguments but
4476 are not specified as accepting options interpret arguments beginning
4477 with - as invalid options and require -- to prevent this interpreta‐
4478 tion.
4479 : [arguments]
4480 No effect; the command does nothing beyond expanding arguments
4481 and performing any specified redirections. The return status is
4482 zero.
4483 . filename [arguments]
4485 source filename [arguments]
4486 Read and execute commands from filename in the current shell en‐
4487 vironment and return the exit status of the last command exe‐
4488 cuted from filename. If filename does not contain a slash,
4489 filenames in PATH are used to find the directory containing
4490 filename, but filename does not need to be executable. The file
4491 searched for in PATH need not be executable. When bash is not
4492 in posix mode, it searches the current directory if no file is
4493 found in PATH. If the sourcepath option to the shopt builtin
4494 command is turned off, the PATH is not searched. If any argu‐
4495 ments are supplied, they become the positional parameters when
4496 filename is executed. Otherwise the positional parameters are
4497 unchanged. If the -T option is enabled, . inherits any trap on
4498 DEBUG; if it is not, any DEBUG trap string is saved and restored
4499 around the call to ., and . unsets the DEBUG trap while it exe‐
4500 cutes. If -T is not set, and the sourced file changes the DEBUG
4501 trap, the new value is retained when . completes. The return
4502 status is the status of the last command exited within the
4503 script (0 if no commands are executed), and false if filename is
4504 not found or cannot be read.
4505 alias [-p] [name[=value] ...]
4507 Alias with no arguments or with the -p option prints the list of
4508 aliases in the form alias name=value on standard output. When
4509 arguments are supplied, an alias is defined for each name whose
4510 value is given. A trailing space in value causes the next word
4511 to be checked for alias substitution when the alias is expanded.
4512 For each name in the argument list for which no value is sup‐
4513 plied, the name and value of the alias is printed. Alias re‐
4514 turns true unless a name is given for which no alias has been
4515 defined.
4516 bg [jobspec ...]
4518 Resume each suspended job jobspec in the background, as if it
4519 had been started with &. If jobspec is not present, the shell's
4520 notion of the current job is used. bg jobspec returns 0 unless
4521 run when job control is disabled or, when run with job control
4522 enabled, any specified jobspec was not found or was started
4523 without job control.
4524 bind [-m keymap] [-lpsvPSVX]
4526 bind [-m keymap] [-q function] [-u function] [-r keyseq]
4527 bind [-m keymap] -f filename
4528 bind [-m keymap] -x keyseq:shell-command
4529 bind [-m keymap] keyseq:function-name
4530 bind [-m keymap] keyseq:readline-command
4531 bind readline-command-line
4532 Display current readline key and function bindings, bind a key
4533 sequence to a readline function or macro, or set a readline
4534 variable. Each non-option argument is a command as it would ap‐
4535 pear in a readline initialization file such as .inputrc, but
4536 each binding or command must be passed as a separate argument;
4537 e.g., '"\C-x\C-r": re-read-init-file'. Options, if supplied,
4538 have the following meanings:
4539 -m keymap
4540 Use keymap as the keymap to be affected by the subsequent
4541 bindings. Acceptable keymap names are emacs, emacs-stan‐
4542 dard, emacs-meta, emacs-ctlx, vi, vi-move, vi-command,
4543 and vi-insert. vi is equivalent to vi-command (vi-move
4544 is also a synonym); emacs is equivalent to emacs-stan‐
4545 dard.
4546 -l List the names of all readline functions.
4547 -p Display readline function names and bindings in such a
4548 way that they can be re-read.
4549 -P List current readline function names and bindings.
4550 -s Display readline key sequences bound to macros and the
4551 strings they output in such a way that they can be re-
4552 read.
4553 -S Display readline key sequences bound to macros and the
4554 strings they output.
4555 -v Display readline variable names and values in such a way
4556 that they can be re-read.
4557 -V List current readline variable names and values.
4558 -f filename
4559 Read key bindings from filename.
4560 -q function
4561 Query about which keys invoke the named function.
4562 -u function
4563 Unbind all keys bound to the named function.
4564 -r keyseq
4565 Remove any current binding for keyseq.
4566 -x keyseq:shell-command
4567 Cause shell-command to be executed whenever keyseq is en‐
4568 tered. When shell-command is executed, the shell sets
4569 the READLINE_LINE variable to the contents of the read‐
4570 line line buffer and the READLINE_POINT and READLINE_MARK
4571 variables to the current location of the insertion point
4572 and the saved insertion point (the mark), respectively.
4573 The shell assigns any numeric argument the user supplied
4574 to the READLINE_ARGUMENT variable. If there was no argu‐
4575 ment, that variable is not set. If the executed command
4576 changes the value of any of READLINE_LINE, READ‐
4577 LINE_POINT, or READLINE_MARK, those new values will be
4578 reflected in the editing state.
4579 -X List all key sequences bound to shell commands and the
4580 associated commands in a format that can be reused as in‐
4581 put.
4582 The return value is 0 unless an unrecognized option is given or
4584 an error occurred.
4585 break [n]
4587 Exit from within a for, while, until, or select loop. If n is
4588 specified, break n levels. n must be ≥ 1. If n is greater than
4589 the number of enclosing loops, all enclosing loops are exited.
4590 The return value is 0 unless n is not greater than or equal to
4591 1.
4592 builtin shell-builtin [arguments]
4594 Execute the specified shell builtin, passing it arguments, and
4595 return its exit status. This is useful when defining a function
4596 whose name is the same as a shell builtin, retaining the func‐
4597 tionality of the builtin within the function. The cd builtin is
4598 commonly redefined this way. The return status is false if
4599 shell-builtin is not a shell builtin command.
4600 caller [expr]
4602 Returns the context of any active subroutine call (a shell func‐
4603 tion or a script executed with the . or source builtins). With‐
4604 out expr, caller displays the line number and source filename of
4605 the current subroutine call. If a non-negative integer is sup‐
4606 plied as expr, caller displays the line number, subroutine name,
4607 and source file corresponding to that position in the current
4608 execution call stack. This extra information may be used, for
4609 example, to print a stack trace. The current frame is frame 0.
4610 The return value is 0 unless the shell is not executing a sub‐
4611 routine call or expr does not correspond to a valid position in
4612 the call stack.
4613 cd [-L|[-P [-e]] [-@]] [dir]
4615 Change the current directory to dir. if dir is not supplied,
4616 the value of the HOME shell variable is the default. The vari‐
4617 able CDPATH defines the search path for the directory containing
4618 dir: each directory name in CDPATH is searched for dir. Alter‐
4619 native directory names in CDPATH are separated by a colon (:).
4620 A null directory name in CDPATH is the same as the current di‐
4621 rectory, i.e., ``.''. If dir begins with a slash (/), then CD‐
4622 PATH is not used. The -P option causes cd to use the physical
4623 directory structure by resolving symbolic links while traversing
4624 dir and before processing instances of .. in dir (see also the
4625 -P option to the set builtin command); the -L option forces sym‐
4626 bolic links to be followed by resolving the link after process‐
4627 ing instances of .. in dir. If .. appears in dir, it is pro‐
4628 cessed by removing the immediately previous pathname component
4629 from dir, back to a slash or the beginning of dir. If the -e
4630 option is supplied with -P, and the current working directory
4631 cannot be successfully determined after a successful directory
4632 change, cd will return an unsuccessful status. On systems that
4633 support it, the -@ option presents the extended attributes asso‐
4634 ciated with a file as a directory. An argument of - is con‐
4635 verted to $OLDPWD before the directory change is attempted. If
4636 a non-empty directory name from CDPATH is used, or if - is the
4637 first argument, and the directory change is successful, the ab‐
4638 solute pathname of the new working directory is written to the
4639 standard output. If the directory change is successful, cd sets
4640 the value of the PWD environment variable to the new directory
4641 name, and sets the OLDPWD environment variable to the value of
4642 the current working directory before the change. The return
4643 value is true if the directory was successfully changed; false
4644 otherwise.
4645 command [-pVv] command [arg ...]
4647 Run command with args suppressing the normal shell function
4648 lookup. Only builtin commands or commands found in the PATH are
4649 executed. If the -p option is given, the search for command is
4650 performed using a default value for PATH that is guaranteed to
4651 find all of the standard utilities. If either the -V or -v op‐
4652 tion is supplied, a description of command is printed. The -v
4653 option causes a single word indicating the command or filename
4654 used to invoke command to be displayed; the -V option produces a
4655 more verbose description. If the -V or -v option is supplied,
4656 the exit status is 0 if command was found, and 1 if not. If
4657 neither option is supplied and an error occurred or command can‐
4658 not be found, the exit status is 127. Otherwise, the exit sta‐
4659 tus of the command builtin is the exit status of command.
4660 compgen [option] [word]
4662 Generate possible completion matches for word according to the
4663 options, which may be any option accepted by the complete
4664 builtin with the exception of -p and -r, and write the matches
4665 to the standard output. When using the -F or -C options, the
4666 various shell variables set by the programmable completion fa‐
4667 cilities, while available, will not have useful values.
4668 The matches will be generated in the same way as if the program‐
4670 mable completion code had generated them directly from a comple‐
4671 tion specification with the same flags. If word is specified,
4672 only those completions matching word will be displayed.
4673 The return value is true unless an invalid option is supplied,
4675 or no matches were generated.
4676 complete [-abcdefgjksuv] [-o comp-option] [-DEI] [-A action] [-G glob‐
4678 pat] [-W wordlist]
4679 [-F function] [-C command] [-X filterpat] [-P prefix] [-S suf‐
4680 fix] name [name ...]
4681 complete -pr [-DEI] [name ...]
4682 Specify how arguments to each name should be completed. If the
4683 -p option is supplied, or if no options are supplied, existing
4684 completion specifications are printed in a way that allows them
4685 to be reused as input. The -r option removes a completion spec‐
4686 ification for each name, or, if no names are supplied, all com‐
4687 pletion specifications. The -D option indicates that other sup‐
4688 plied options and actions should apply to the ``default'' com‐
4689 mand completion; that is, completion attempted on a command for
4690 which no completion has previously been defined. The -E option
4691 indicates that other supplied options and actions should apply
4692 to ``empty'' command completion; that is, completion attempted
4693 on a blank line. The -I option indicates that other supplied
4694 options and actions should apply to completion on the initial
4695 non-assignment word on the line, or after a command delimiter
4696 such as ; or |, which is usually command name completion. If
4697 multiple options are supplied, the -D option takes precedence
4698 over -E, and both take precedence over -I. If any of -D, -E, or
4699 -I are supplied, any other name arguments are ignored; these
4700 completions only apply to the case specified by the option.
4701 The process of applying these completion specifications when
4703 word completion is attempted is described above under Program‐
4704 mable Completion.
4705 Other options, if specified, have the following meanings. The
4707 arguments to the -G, -W, and -X options (and, if necessary, the
4708 -P and -S options) should be quoted to protect them from expan‐
4709 sion before the complete builtin is invoked.
4710 -o comp-option
4711 The comp-option controls several aspects of the comp‐
4712 spec's behavior beyond the simple generation of comple‐
4713 tions. comp-option may be one of:
4714 bashdefault
4715 Perform the rest of the default bash completions
4716 if the compspec generates no matches.
4717 default Use readline's default filename completion if
4718 the compspec generates no matches.
4719 dirnames
4720 Perform directory name completion if the comp‐
4721 spec generates no matches.
4722 filenames
4723 Tell readline that the compspec generates file‐
4724 names, so it can perform any filename-specific
4725 processing (like adding a slash to directory
4726 names, quoting special characters, or suppress‐
4727 ing trailing spaces). Intended to be used with
4728 shell functions.
4729 noquote Tell readline not to quote the completed words
4730 if they are filenames (quoting filenames is the
4731 default).
4732 nosort Tell readline not to sort the list of possible
4733 completions alphabetically.
4734 nospace Tell readline not to append a space (the de‐
4735 fault) to words completed at the end of the
4736 line.
4737 plusdirs
4738 After any matches defined by the compspec are
4739 generated, directory name completion is at‐
4740 tempted and any matches are added to the results
4741 of the other actions.
4742 -A action
4743 The action may be one of the following to generate a
4744 list of possible completions:
4745 alias Alias names. May also be specified as -a.
4746 arrayvar
4747 Array variable names.
4748 binding Readline key binding names.
4749 builtin Names of shell builtin commands. May also be
4750 specified as -b.
4751 command Command names. May also be specified as -c.
4752 directory
4753 Directory names. May also be specified as -d.
4754 disabled
4755 Names of disabled shell builtins.
4756 enabled Names of enabled shell builtins.
4757 export Names of exported shell variables. May also be
4758 specified as -e.
4759 file File names. May also be specified as -f.
4760 function
4761 Names of shell functions.
4762 group Group names. May also be specified as -g.
4763 helptopic
4764 Help topics as accepted by the help builtin.
4765 hostname
4766 Hostnames, as taken from the file specified by
4767 the HOSTFILE shell variable.
4768 job Job names, if job control is active. May also
4769 be specified as -j.
4770 keyword Shell reserved words. May also be specified as
4771 -k.
4772 running Names of running jobs, if job control is active.
4773 service Service names. May also be specified as -s.
4774 setopt Valid arguments for the -o option to the set
4775 builtin.
4776 shopt Shell option names as accepted by the shopt
4777 builtin.
4778 signal Signal names.
4779 stopped Names of stopped jobs, if job control is active.
4780 user User names. May also be specified as -u.
4781 variable
4782 Names of all shell variables. May also be spec‐
4783 ified as -v.
4784 -C command
4785 command is executed in a subshell environment, and its
4786 output is used as the possible completions. Arguments
4787 are passed as with the -F option.
4788 -F function
4789 The shell function function is executed in the current
4790 shell environment. When the function is executed, the
4791 first argument ($1) is the name of the command whose ar‐
4792 guments are being completed, the second argument ($2) is
4793 the word being completed, and the third argument ($3) is
4794 the word preceding the word being completed on the cur‐
4795 rent command line. When it finishes, the possible com‐
4796 pletions are retrieved from the value of the COMPREPLY
4797 array variable.
4798 -G globpat
4799 The pathname expansion pattern globpat is expanded to
4800 generate the possible completions.
4801 -P prefix
4802 prefix is added at the beginning of each possible com‐
4803 pletion after all other options have been applied.
4804 -S suffix
4805 suffix is appended to each possible completion after all
4806 other options have been applied.
4807 -W wordlist
4808 The wordlist is split using the characters in the IFS
4809 special variable as delimiters, and each resultant word
4810 is expanded. Shell quoting is honored within wordlist,
4811 in order to provide a mechanism for the words to contain
4812 shell metacharacters or characters in the value of IFS.
4813 The possible completions are the members of the resul‐
4814 tant list which match the word being completed.
4815 -X filterpat
4816 filterpat is a pattern as used for pathname expansion.
4817 It is applied to the list of possible completions gener‐
4818 ated by the preceding options and arguments, and each
4819 completion matching filterpat is removed from the list.
4820 A leading ! in filterpat negates the pattern; in this
4821 case, any completion not matching filterpat is removed.
4822 The return value is true unless an invalid option is supplied,
4824 an option other than -p or -r is supplied without a name argu‐
4825 ment, an attempt is made to remove a completion specification
4826 for a name for which no specification exists, or an error occurs
4827 adding a completion specification.
4828 compopt [-o option] [-DEI] [+o option] [name]
4830 Modify completion options for each name according to the op‐
4831 tions, or for the currently-executing completion if no names are
4832 supplied. If no options are given, display the completion op‐
4833 tions for each name or the current completion. The possible
4834 values of option are those valid for the complete builtin de‐
4835 scribed above. The -D option indicates that other supplied op‐
4836 tions should apply to the ``default'' command completion; that
4837 is, completion attempted on a command for which no completion
4838 has previously been defined. The -E option indicates that other
4839 supplied options should apply to ``empty'' command completion;
4840 that is, completion attempted on a blank line. The -I option
4841 indicates that other supplied options should apply to completion
4842 on the initial non-assignment word on the line, or after a com‐
4843 mand delimiter such as ; or |, which is usually command name
4844 completion.
4845 The return value is true unless an invalid option is supplied,
4847 an attempt is made to modify the options for a name for which no
4848 completion specification exists, or an output error occurs.
4849 continue [n]
4851 Resume the next iteration of the enclosing for, while, until, or
4852 select loop. If n is specified, resume at the nth enclosing
4853 loop. n must be ≥ 1. If n is greater than the number of en‐
4854 closing loops, the last enclosing loop (the ``top-level'' loop)
4855 is resumed. The return value is 0 unless n is not greater than
4856 or equal to 1.
4857 declare [-aAfFgiIlnrtux] [-p] [name[=value] ...]
4859 typeset [-aAfFgiIlnrtux] [-p] [name[=value] ...]
4860 Declare variables and/or give them attributes. If no names are
4861 given then display the values of variables. The -p option will
4862 display the attributes and values of each name. When -p is used
4863 with name arguments, additional options, other than -f and -F,
4864 are ignored. When -p is supplied without name arguments, it
4865 will display the attributes and values of all variables having
4866 the attributes specified by the additional options. If no other
4867 options are supplied with -p, declare will display the at‐
4868 tributes and values of all shell variables. The -f option will
4869 restrict the display to shell functions. The -F option inhibits
4870 the display of function definitions; only the function name and
4871 attributes are printed. If the extdebug shell option is enabled
4872 using shopt, the source file name and line number where each
4873 name is defined are displayed as well. The -F option implies
4874 -f. The -g option forces variables to be created or modified at
4875 the global scope, even when declare is executed in a shell func‐
4876 tion. It is ignored in all other cases. The -I option causes
4877 local variables to inherit the attributes (except the nameref
4878 attribute) and value of any existing variable with the same name
4879 at a surrounding scope. If there is no existing variable, the
4880 local variable is initially unset. The following options can be
4881 used to restrict output to variables with the specified attri‐
4882 bute or to give variables attributes:
4883 -a Each name is an indexed array variable (see Arrays
4884 above).
4885 -A Each name is an associative array variable (see Arrays
4886 above).
4887 -f Use function names only.
4888 -i The variable is treated as an integer; arithmetic evalua‐
4889 tion (see ARITHMETIC EVALUATION above) is performed when
4890 the variable is assigned a value.
4891 -l When the variable is assigned a value, all upper-case
4892 characters are converted to lower-case. The upper-case
4893 attribute is disabled.
4894 -n Give each name the nameref attribute, making it a name
4895 reference to another variable. That other variable is
4896 defined by the value of name. All references, assign‐
4897 ments, and attribute modifications to name, except those
4898 using or changing the -n attribute itself, are performed
4899 on the variable referenced by name's value. The nameref
4900 attribute cannot be applied to array variables.
4901 -r Make names readonly. These names cannot then be assigned
4902 values by subsequent assignment statements or unset.
4903 -t Give each name the trace attribute. Traced functions in‐
4904 herit the DEBUG and RETURN traps from the calling shell.
4905 The trace attribute has no special meaning for variables.
4906 -u When the variable is assigned a value, all lower-case
4907 characters are converted to upper-case. The lower-case
4908 attribute is disabled.
4909 -x Mark names for export to subsequent commands via the en‐
4910 vironment.
4911 Using `+' instead of `-' turns off the attribute instead, with
4913 the exceptions that +a and +A may not be used to destroy array
4914 variables and +r will not remove the readonly attribute. When
4915 used in a function, declare and typeset make each name local, as
4916 with the local command, unless the -g option is supplied. If a
4917 variable name is followed by =value, the value of the variable
4918 is set to value. When using -a or -A and the compound assign‐
4919 ment syntax to create array variables, additional attributes do
4920 not take effect until subsequent assignments. The return value
4921 is 0 unless an invalid option is encountered, an attempt is made
4922 to define a function using ``-f foo=bar'', an attempt is made to
4923 assign a value to a readonly variable, an attempt is made to as‐
4924 sign a value to an array variable without using the compound as‐
4925 signment syntax (see Arrays above), one of the names is not a
4926 valid shell variable name, an attempt is made to turn off read‐
4927 only status for a readonly variable, an attempt is made to turn
4928 off array status for an array variable, or an attempt is made to
4929 display a non-existent function with -f.
4930 dirs [-clpv] [+n] [-n]
4932 Without options, displays the list of currently remembered di‐
4933 rectories. The default display is on a single line with direc‐
4934 tory names separated by spaces. Directories are added to the
4935 list with the pushd command; the popd command removes entries
4936 from the list. The current directory is always the first direc‐
4937 tory in the stack.
4938 -c Clears the directory stack by deleting all of the en‐
4939 tries.
4940 -l Produces a listing using full pathnames; the default
4941 listing format uses a tilde to denote the home directory.
4942 -p Print the directory stack with one entry per line.
4943 -v Print the directory stack with one entry per line, pre‐
4944 fixing each entry with its index in the stack.
4945 +n Displays the nth entry counting from the left of the list
4946 shown by dirs when invoked without options, starting with
4947 zero.
4948 -n Displays the nth entry counting from the right of the
4949 list shown by dirs when invoked without options, starting
4950 with zero.
4951 The return value is 0 unless an invalid option is supplied or n
4953 indexes beyond the end of the directory stack.
4954 disown [-ar] [-h] [jobspec ... | pid ... ]
4956 Without options, remove each jobspec from the table of active
4957 jobs. If jobspec is not present, and neither the -a nor the -r
4958 option is supplied, the current job is used. If the -h option
4959 is given, each jobspec is not removed from the table, but is
4960 marked so that SIGHUP is not sent to the job if the shell re‐
4961 ceives a SIGHUP. If no jobspec is supplied, the -a option means
4962 to remove or mark all jobs; the -r option without a jobspec ar‐
4963 gument restricts operation to running jobs. The return value is
4964 0 unless a jobspec does not specify a valid job.
4965 echo [-neE] [arg ...]
4967 Output the args, separated by spaces, followed by a newline.
4968 The return status is 0 unless a write error occurs. If -n is
4969 specified, the trailing newline is suppressed. If the -e option
4970 is given, interpretation of the following backslash-escaped
4971 characters is enabled. The -E option disables the interpreta‐
4972 tion of these escape characters, even on systems where they are
4973 interpreted by default. The xpg_echo shell option may be used
4974 to dynamically determine whether or not echo expands these es‐
4975 cape characters by default. echo does not interpret -- to mean
4976 the end of options. echo interprets the following escape se‐
4977 quences:
4978 \a alert (bell)
4979 \b backspace
4980 \c suppress further output
4981 \e
4982 \E an escape character
4983 \f form feed
4984 \n new line
4985 \r carriage return
4986 \t horizontal tab
4987 \v vertical tab
4988 \\ backslash
4989 \0nnn the eight-bit character whose value is the octal value
4990 nnn (zero to three octal digits)
4991 \xHH the eight-bit character whose value is the hexadecimal
4992 value HH (one or two hex digits)
4993 \uHHHH the Unicode (ISO/IEC 10646) character whose value is the
4994 hexadecimal value HHHH (one to four hex digits)
4995 \UHHHHHHHH
4996 the Unicode (ISO/IEC 10646) character whose value is the
4997 hexadecimal value HHHHHHHH (one to eight hex digits)
4998 enable [-a] [-dnps] [-f filename] [name ...]
5000 Enable and disable builtin shell commands. Disabling a builtin
5001 allows a disk command which has the same name as a shell builtin
5002 to be executed without specifying a full pathname, even though
5003 the shell normally searches for builtins before disk commands.
5004 If -n is used, each name is disabled; otherwise, names are en‐
5005 abled. For example, to use the test binary found via the PATH
5006 instead of the shell builtin version, run ``enable -n test''.
5007 The -f option means to load the new builtin command name from
5008 shared object filename, on systems that support dynamic loading.
5009 Bash will use the value of the BASH_LOADABLES_PATH variable as a
5010 colon-separated list of directories in which to search for file‐
5011 name. The default is system-dependent. The -d option will
5012 delete a builtin previously loaded with -f. If no name argu‐
5013 ments are given, or if the -p option is supplied, a list of
5014 shell builtins is printed. With no other option arguments, the
5015 list consists of all enabled shell builtins. If -n is supplied,
5016 only disabled builtins are printed. If -a is supplied, the list
5017 printed includes all builtins, with an indication of whether or
5018 not each is enabled. If -s is supplied, the output is re‐
5019 stricted to the POSIX special builtins. If no options are sup‐
5020 plied and a name is not a shell builtin, enable will attempt to
5021 load name from a shared object named name, as if the command
5022 were ``enable -f name name . The return value is 0 unless a
5023 name is not a shell builtin or there is an error loading a new
5024 builtin from a shared object.
5025 eval [arg ...]
5027 The args are read and concatenated together into a single com‐
5028 mand. This command is then read and executed by the shell, and
5029 its exit status is returned as the value of eval. If there are
5030 no args, or only null arguments, eval returns 0.
5031 exec [-cl] [-a name] [command [arguments]]
5033 If command is specified, it replaces the shell. No new process
5034 is created. The arguments become the arguments to command. If
5035 the -l option is supplied, the shell places a dash at the begin‐
5036 ning of the zeroth argument passed to command. This is what lo‐
5037 gin(1) does. The -c option causes command to be executed with
5038 an empty environment. If -a is supplied, the shell passes name
5039 as the zeroth argument to the executed command. If command can‐
5040 not be executed for some reason, a non-interactive shell exits,
5041 unless the execfail shell option is enabled. In that case, it
5042 returns failure. An interactive shell returns failure if the
5043 file cannot be executed. A subshell exits unconditionally if
5044 exec fails. If command is not specified, any redirections take
5045 effect in the current shell, and the return status is 0. If
5046 there is a redirection error, the return status is 1.
5047 exit [n]
5049 Cause the shell to exit with a status of n. If n is omitted,
5050 the exit status is that of the last command executed. A trap on
5051 EXIT is executed before the shell terminates.
5052 export [-fn] [name[=word]] ...
5054 export -p
5055 The supplied names are marked for automatic export to the envi‐
5056 ronment of subsequently executed commands. If the -f option is
5057 given, the names refer to functions. If no names are given, or
5058 if the -p option is supplied, a list of names of all exported
5059 variables is printed. The -n option causes the export property
5060 to be removed from each name. If a variable name is followed by
5061 =word, the value of the variable is set to word. export returns
5062 an exit status of 0 unless an invalid option is encountered, one
5063 of the names is not a valid shell variable name, or -f is sup‐
5064 plied with a name that is not a function.
5065 fc [-e ename] [-lnr] [first] [last]
5067 fc -s [pat=rep] [cmd]
5068 The first form selects a range of commands from first to last
5069 from the history list and displays or edits and re-executes
5070 them. First and last may be specified as a string (to locate
5071 the last command beginning with that string) or as a number (an
5072 index into the history list, where a negative number is used as
5073 an offset from the current command number). When listing, a
5074 first or last of 0 is equivalent to -1 and -0 is equivalent to
5075 the current command (usually the fc command); otherwise 0 is
5076 equivalent to -1 and -0 is invalid. If last is not specified,
5077 it is set to the current command for listing (so that ``fc -l
5078 -10'' prints the last 10 commands) and to first otherwise. If
5079 first is not specified, it is set to the previous command for
5080 editing and -16 for listing.
5081 The -n option suppresses the command numbers when listing. The
5083 -r option reverses the order of the commands. If the -l option
5084 is given, the commands are listed on standard output. Other‐
5085 wise, the editor given by ename is invoked on a file containing
5086 those commands. If ename is not given, the value of the FCEDIT
5087 variable is used, and the value of EDITOR if FCEDIT is not set.
5088 If neither variable is set, vi is used. When editing is com‐
5089 plete, the edited commands are echoed and executed.
5090 In the second form, command is re-executed after each instance
5092 of pat is replaced by rep. Command is interpreted the same as
5093 first above. A useful alias to use with this is ``r="fc -s"'',
5094 so that typing ``r cc'' runs the last command beginning with
5095 ``cc'' and typing ``r'' re-executes the last command.
5096 If the first form is used, the return value is 0 unless an in‐
5098 valid option is encountered or first or last specify history
5099 lines out of range. If the -e option is supplied, the return
5100 value is the value of the last command executed or failure if an
5101 error occurs with the temporary file of commands. If the second
5102 form is used, the return status is that of the command re-exe‐
5103 cuted, unless cmd does not specify a valid history line, in
5104 which case fc returns failure.
5105 fg [jobspec]
5107 Resume jobspec in the foreground, and make it the current job.
5108 If jobspec is not present, the shell's notion of the current job
5109 is used. The return value is that of the command placed into
5110 the foreground, or failure if run when job control is disabled
5111 or, when run with job control enabled, if jobspec does not spec‐
5112 ify a valid job or jobspec specifies a job that was started
5113 without job control.
5114 getopts optstring name [arg ...]
5116 getopts is used by shell procedures to parse positional parame‐
5117 ters. optstring contains the option characters to be recog‐
5118 nized; if a character is followed by a colon, the option is ex‐
5119 pected to have an argument, which should be separated from it by
5120 white space. The colon and question mark characters may not be
5121 used as option characters. Each time it is invoked, getopts
5122 places the next option in the shell variable name, initializing
5123 name if it does not exist, and the index of the next argument to
5124 be processed into the variable OPTIND. OPTIND is initialized to
5125 1 each time the shell or a shell script is invoked. When an op‐
5126 tion requires an argument, getopts places that argument into the
5127 variable OPTARG. The shell does not reset OPTIND automatically;
5128 it must be manually reset between multiple calls to getopts
5129 within the same shell invocation if a new set of parameters is
5130 to be used.
5131 When the end of options is encountered, getopts exits with a re‐
5133 turn value greater than zero. OPTIND is set to the index of the
5134 first non-option argument, and name is set to ?.
5135 getopts normally parses the positional parameters, but if more
5137 arguments are supplied as arg values, getopts parses those in‐
5138 stead.
5139 getopts can report errors in two ways. If the first character
5141 of optstring is a colon, silent error reporting is used. In
5142 normal operation, diagnostic messages are printed when invalid
5143 options or missing option arguments are encountered. If the
5144 variable OPTERR is set to 0, no error messages will be dis‐
5145 played, even if the first character of optstring is not a colon.
5146 If an invalid option is seen, getopts places ? into name and, if
5148 not silent, prints an error message and unsets OPTARG. If
5149 getopts is silent, the option character found is placed in OP‐
5150 TARG and no diagnostic message is printed.
5151 If a required argument is not found, and getopts is not silent,
5153 a question mark (?) is placed in name, OPTARG is unset, and a
5154 diagnostic message is printed. If getopts is silent, then a
5155 colon (:) is placed in name and OPTARG is set to the option
5156 character found.
5157 getopts returns true if an option, specified or unspecified, is
5159 found. It returns false if the end of options is encountered or
5160 an error occurs.
5161 hash [-lr] [-p filename] [-dt] [name]
5163 Each time hash is invoked, the full pathname of the command name
5164 is determined by searching the directories in $PATH and remem‐
5165 bered. Any previously-remembered pathname is discarded. If the
5166 -p option is supplied, no path search is performed, and filename
5167 is used as the full filename of the command. The -r option
5168 causes the shell to forget all remembered locations. The -d op‐
5169 tion causes the shell to forget the remembered location of each
5170 name. If the -t option is supplied, the full pathname to which
5171 each name corresponds is printed. If multiple name arguments
5172 are supplied with -t, the name is printed before the hashed full
5173 pathname. The -l option causes output to be displayed in a for‐
5174 mat that may be reused as input. If no arguments are given, or
5175 if only -l is supplied, information about remembered commands is
5176 printed. The return status is true unless a name is not found
5177 or an invalid option is supplied.
5178 help [-dms] [pattern]
5180 Display helpful information about builtin commands. If pattern
5181 is specified, help gives detailed help on all commands matching
5182 pattern; otherwise help for all the builtins and shell control
5183 structures is printed.
5184 -d Display a short description of each pattern
5185 -m Display the description of each pattern in a manpage-like
5186 format
5187 -s Display only a short usage synopsis for each pattern
5188 The return status is 0 unless no command matches pattern.
5190 history [n]
5192 history -c
5193 history -d offset
5194 history -d start-end
5195 history -anrw [filename]
5196 history -p arg [arg ...]
5197 history -s arg [arg ...]
5198 With no options, display the command history list with line num‐
5199 bers. Lines listed with a * have been modified. An argument of
5200 n lists only the last n lines. If the shell variable HISTTIME‐
5201 FORMAT is set and not null, it is used as a format string for
5202 strftime(3) to display the time stamp associated with each dis‐
5203 played history entry. No intervening blank is printed between
5204 the formatted time stamp and the history line. If filename is
5205 supplied, it is used as the name of the history file; if not,
5206 the value of HISTFILE is used. Options, if supplied, have the
5207 following meanings:
5208 -c Clear the history list by deleting all the entries.
5209 -d offset
5210 Delete the history entry at position offset. If offset
5211 is negative, it is interpreted as relative to one greater
5212 than the last history position, so negative indices count
5213 back from the end of the history, and an index of -1
5214 refers to the current history -d command.
5215 -d start-end
5216 Delete the range of history entries between positions
5217 start and end, inclusive. Positive and negative values
5218 for start and end are interpreted as described above.
5219 -a Append the ``new'' history lines to the history file.
5220 These are history lines entered since the beginning of
5221 the current bash session, but not already appended to the
5222 history file.
5223 -n Read the history lines not already read from the history
5224 file into the current history list. These are lines ap‐
5225 pended to the history file since the beginning of the
5226 current bash session.
5227 -r Read the contents of the history file and append them to
5228 the current history list.
5229 -w Write the current history list to the history file, over‐
5230 writing the history file's contents.
5231 -p Perform history substitution on the following args and
5232 display the result on the standard output. Does not
5233 store the results in the history list. Each arg must be
5234 quoted to disable normal history expansion.
5235 -s Store the args in the history list as a single entry.
5236 The last command in the history list is removed before
5237 the args are added.
5238 If the HISTTIMEFORMAT variable is set, the time stamp informa‐
5240 tion associated with each history entry is written to the his‐
5241 tory file, marked with the history comment character. When the
5242 history file is read, lines beginning with the history comment
5243 character followed immediately by a digit are interpreted as
5244 timestamps for the following history entry. The return value is
5245 0 unless an invalid option is encountered, an error occurs while
5246 reading or writing the history file, an invalid offset or range
5247 is supplied as an argument to -d, or the history expansion sup‐
5248 plied as an argument to -p fails.
5249 jobs [-lnprs] [ jobspec ... ]
5251 jobs -x command [ args ... ]
5252 The first form lists the active jobs. The options have the fol‐
5253 lowing meanings:
5254 -l List process IDs in addition to the normal information.
5255 -n Display information only about jobs that have changed
5256 status since the user was last notified of their status.
5257 -p List only the process ID of the job's process group
5258 leader.
5259 -r Display only running jobs.
5260 -s Display only stopped jobs.
5261 If jobspec is given, output is restricted to information about
5263 that job. The return status is 0 unless an invalid option is
5264 encountered or an invalid jobspec is supplied.
5265 If the -x option is supplied, jobs replaces any jobspec found in
5267 command or args with the corresponding process group ID, and ex‐
5268 ecutes command passing it args, returning its exit status.
5269 kill [-s sigspec | -n signum | -sigspec] [pid | jobspec] ...
5271 kill -l|-L [sigspec | exit_status]
5272 Send the signal named by sigspec or signum to the processes
5273 named by pid or jobspec. sigspec is either a case-insensitive
5274 signal name such as SIGKILL (with or without the SIG prefix) or
5275 a signal number; signum is a signal number. If sigspec is not
5276 present, then SIGTERM is assumed. An argument of -l lists the
5277 signal names. If any arguments are supplied when -l is given,
5278 the names of the signals corresponding to the arguments are
5279 listed, and the return status is 0. The exit_status argument to
5280 -l is a number specifying either a signal number or the exit
5281 status of a process terminated by a signal. The -L option is
5282 equivalent to -l. kill returns true if at least one signal was
5283 successfully sent, or false if an error occurs or an invalid op‐
5284 tion is encountered.
5285 let arg [arg ...]
5287 Each arg is an arithmetic expression to be evaluated (see ARITH‐
5288 METIC EVALUATION above). If the last arg evaluates to 0, let
5289 returns 1; 0 is returned otherwise.
5290 local [option] [name[=value] ... | - ]
5292 For each argument, a local variable named name is created, and
5293 assigned value. The option can be any of the options accepted
5294 by declare. When local is used within a function, it causes the
5295 variable name to have a visible scope restricted to that func‐
5296 tion and its children. If name is -, the set of shell options
5297 is made local to the function in which local is invoked: shell
5298 options changed using the set builtin inside the function are
5299 restored to their original values when the function returns.
5300 The restore is effected as if a series of set commands were exe‐
5301 cuted to restore the values that were in place before the func‐
5302 tion. With no operands, local writes a list of local variables
5303 to the standard output. It is an error to use local when not
5304 within a function. The return status is 0 unless local is used
5305 outside a function, an invalid name is supplied, or name is a
5306 readonly variable.
5307 logout Exit a login shell.
5309 mapfile [-d delim] [-n count] [-O origin] [-s count] [-t] [-u fd] [-C
5311 callback] [-c quantum] [array]
5312 readarray [-d delim] [-n count] [-O origin] [-s count] [-t] [-u fd] [-C
5313 callback] [-c quantum] [array]
5314 Read lines from the standard input into the indexed array vari‐
5315 able array, or from file descriptor fd if the -u option is sup‐
5316 plied. The variable MAPFILE is the default array. Options, if
5317 supplied, have the following meanings:
5318 -d The first character of delim is used to terminate each
5319 input line, rather than newline. If delim is the empty
5320 string, mapfile will terminate a line when it reads a NUL
5321 character.
5322 -n Copy at most count lines. If count is 0, all lines are
5323 copied.
5324 -O Begin assigning to array at index origin. The default
5325 index is 0.
5326 -s Discard the first count lines read.
5327 -t Remove a trailing delim (default newline) from each line
5328 read.
5329 -u Read lines from file descriptor fd instead of the stan‐
5330 dard input.
5331 -C Evaluate callback each time quantum lines are read. The
5332 -c option specifies quantum.
5333 -c Specify the number of lines read between each call to
5334 callback.
5335 If -C is specified without -c, the default quantum is 5000.
5337 When callback is evaluated, it is supplied the index of the next
5338 array element to be assigned and the line to be assigned to that
5339 element as additional arguments. callback is evaluated after
5340 the line is read but before the array element is assigned.
5341 If not supplied with an explicit origin, mapfile will clear ar‐
5343 ray before assigning to it.
5344 mapfile returns successfully unless an invalid option or option
5346 argument is supplied, array is invalid or unassignable, or if
5347 array is not an indexed array.
5348 popd [-n] [+n] [-n]
5350 Removes entries from the directory stack. The elements are num‐
5351 bered from 0 starting at the first directory listed by dirs.
5352 With no arguments, popd removes the top directory from the
5353 stack, and changes to the new top directory. Arguments, if sup‐
5354 plied, have the following meanings:
5355 -n Suppresses the normal change of directory when removing
5356 directories from the stack, so that only the stack is ma‐
5357 nipulated.
5358 +n Removes the nth entry counting from the left of the list
5359 shown by dirs, starting with zero, from the stack. For
5360 example: ``popd +0'' removes the first directory, ``popd
5361 +1'' the second.
5362 -n Removes the nth entry counting from the right of the list
5363 shown by dirs, starting with zero. For example: ``popd
5364 -0'' removes the last directory, ``popd -1'' the next to
5365 last.
5366 If the top element of the directory stack is modified, and the
5368 -n option was not supplied, popd uses the cd builtin to change
5369 to the directory at the top of the stack. If the cd fails, popd
5370 returns a non-zero value.
5371 Otherwise, popd returns false if an invalid option is encoun‐
5373 tered, the directory stack is empty, or a non-existent directory
5374 stack entry is specified.
5375 If the popd command is successful, bash runs dirs to show the
5377 final contents of the directory stack, and the return status is
5378 0.
5379 printf [-v var] format [arguments]
5381 Write the formatted arguments to the standard output under the
5382 control of the format. The -v option causes the output to be
5383 assigned to the variable var rather than being printed to the
5384 standard output.
5385 The format is a character string which contains three types of
5387 objects: plain characters, which are simply copied to standard
5388 output, character escape sequences, which are converted and
5389 copied to the standard output, and format specifications, each
5390 of which causes printing of the next successive argument. In
5391 addition to the standard printf(1) format specifications, printf
5392 interprets the following extensions:
5393 %b causes printf to expand backslash escape sequences in the
5394 corresponding argument in the same way as echo -e.
5395 %q causes printf to output the corresponding argument in a
5396 format that can be reused as shell input.
5397 %Q like %q, but applies any supplied precision to the argu‐
5398 ment before quoting it.
5399 %(datefmt)T
5400 causes printf to output the date-time string resulting
5401 from using datefmt as a format string for strftime(3).
5402 The corresponding argument is an integer representing the
5403 number of seconds since the epoch. Two special argument
5404 values may be used: -1 represents the current time, and
5405 -2 represents the time the shell was invoked. If no ar‐
5406 gument is specified, conversion behaves as if -1 had been
5407 given. This is an exception to the usual printf behav‐
5408 ior.
5409 The %b, %q, and %T directives all use the field width and preci‐
5411 sion arguments from the format specification and write that many
5412 bytes from (or use that wide a field for) the expanded argument,
5413 which usually contains more characters than the original.
5414 Arguments to non-string format specifiers are treated as C con‐
5416 stants, except that a leading plus or minus sign is allowed, and
5417 if the leading character is a single or double quote, the value
5418 is the ASCII value of the following character.
5419 The format is reused as necessary to consume all of the argu‐
5421 ments. If the format requires more arguments than are supplied,
5422 the extra format specifications behave as if a zero value or
5423 null string, as appropriate, had been supplied. The return
5424 value is zero on success, non-zero on failure.
5425 pushd [-n] [+n] [-n]
5427 pushd [-n] [dir]
5428 Adds a directory to the top of the directory stack, or rotates
5429 the stack, making the new top of the stack the current working
5430 directory. With no arguments, pushd exchanges the top two ele‐
5431 ments of the directory stack. Arguments, if supplied, have the
5432 following meanings:
5433 -n Suppresses the normal change of directory when rotating
5434 or adding directories to the stack, so that only the
5435 stack is manipulated.
5436 +n Rotates the stack so that the nth directory (counting
5437 from the left of the list shown by dirs, starting with
5438 zero) is at the top.
5439 -n Rotates the stack so that the nth directory (counting
5440 from the right of the list shown by dirs, starting with
5441 zero) is at the top.
5442 dir Adds dir to the directory stack at the top
5443 After the stack has been modified, if the -n option was not sup‐
5445 plied, pushd uses the cd builtin to change to the directory at
5446 the top of the stack. If the cd fails, pushd returns a non-zero
5447 value.
5448 Otherwise, if no arguments are supplied, pushd returns 0 unless
5450 the directory stack is empty. When rotating the directory
5451 stack, pushd returns 0 unless the directory stack is empty or a
5452 non-existent directory stack element is specified.
5453 If the pushd command is successful, bash runs dirs to show the
5455 final contents of the directory stack.
5456 pwd [-LP]
5458 Print the absolute pathname of the current working directory.
5459 The pathname printed contains no symbolic links if the -P option
5460 is supplied or the -o physical option to the set builtin command
5461 is enabled. If the -L option is used, the pathname printed may
5462 contain symbolic links. The return status is 0 unless an error
5463 occurs while reading the name of the current directory or an in‐
5464 valid option is supplied.
5465 read [-ers] [-a aname] [-d delim] [-i text] [-n nchars] [-N nchars] [-p
5467 prompt] [-t timeout] [-u fd] [name ...]
5468 One line is read from the standard input, or from the file de‐
5469 scriptor fd supplied as an argument to the -u option, split into
5470 words as described above under Word Splitting, and the first
5471 word is assigned to the first name, the second word to the sec‐
5472 ond name, and so on. If there are more words than names, the
5473 remaining words and their intervening delimiters are assigned to
5474 the last name. If there are fewer words read from the input
5475 stream than names, the remaining names are assigned empty val‐
5476 ues. The characters in IFS are used to split the line into
5477 words using the same rules the shell uses for expansion (de‐
5478 scribed above under Word Splitting). The backslash character
5479 (\) may be used to remove any special meaning for the next char‐
5480 acter read and for line continuation. Options, if supplied,
5481 have the following meanings:
5482 -a aname
5483 The words are assigned to sequential indices of the array
5484 variable aname, starting at 0. aname is unset before any
5485 new values are assigned. Other name arguments are ig‐
5486 nored.
5487 -d delim
5488 The first character of delim is used to terminate the in‐
5489 put line, rather than newline. If delim is the empty
5490 string, read will terminate a line when it reads a NUL
5491 character.
5492 -e If the standard input is coming from a terminal, readline
5493 (see READLINE above) is used to obtain the line. Read‐
5494 line uses the current (or default, if line editing was
5495 not previously active) editing settings, but uses read‐
5496 line's default filename completion.
5497 -i text
5498 If readline is being used to read the line, text is
5499 placed into the editing buffer before editing begins.
5500 -n nchars
5501 read returns after reading nchars characters rather than
5502 waiting for a complete line of input, but honors a delim‐
5503 iter if fewer than nchars characters are read before the
5504 delimiter.
5505 -N nchars
5506 read returns after reading exactly nchars characters
5507 rather than waiting for a complete line of input, unless
5508 EOF is encountered or read times out. Delimiter charac‐
5509 ters encountered in the input are not treated specially
5510 and do not cause read to return until nchars characters
5511 are read. The result is not split on the characters in
5512 IFS; the intent is that the variable is assigned exactly
5513 the characters read (with the exception of backslash; see
5514 the -r option below).
5515 -p prompt
5516 Display prompt on standard error, without a trailing new‐
5517 line, before attempting to read any input. The prompt is
5518 displayed only if input is coming from a terminal.
5519 -r Backslash does not act as an escape character. The back‐
5520 slash is considered to be part of the line. In particu‐
5521 lar, a backslash-newline pair may not then be used as a
5522 line continuation.
5523 -s Silent mode. If input is coming from a terminal, charac‐
5524 ters are not echoed.
5525 -t timeout
5526 Cause read to time out and return failure if a complete
5527 line of input (or a specified number of characters) is
5528 not read within timeout seconds. timeout may be a deci‐
5529 mal number with a fractional portion following the deci‐
5530 mal point. This option is only effective if read is
5531 reading input from a terminal, pipe, or other special
5532 file; it has no effect when reading from regular files.
5533 If read times out, read saves any partial input read into
5534 the specified variable name. If timeout is 0, read re‐
5535 turns immediately, without trying to read any data. The
5536 exit status is 0 if input is available on the specified
5537 file descriptor, or the read will return EOF, non-zero
5538 otherwise. The exit status is greater than 128 if the
5539 timeout is exceeded.
5540 -u fd Read input from file descriptor fd.
5541 If no names are supplied, the line read, without the ending de‐
5543 limiter but otherwise unmodified, is assigned to the variable
5544 REPLY. The exit status is zero, unless end-of-file is encoun‐
5545 tered, read times out (in which case the status is greater than
5546 128), a variable assignment error (such as assigning to a read‐
5547 only variable) occurs, or an invalid file descriptor is supplied
5548 as the argument to -u.
5549 readonly [-aAf] [-p] [name[=word] ...]
5551 The given names are marked readonly; the values of these names
5552 may not be changed by subsequent assignment. If the -f option
5553 is supplied, the functions corresponding to the names are so
5554 marked. The -a option restricts the variables to indexed ar‐
5555 rays; the -A option restricts the variables to associative ar‐
5556 rays. If both options are supplied, -A takes precedence. If no
5557 name arguments are given, or if the -p option is supplied, a
5558 list of all readonly names is printed. The other options may be
5559 used to restrict the output to a subset of the set of readonly
5560 names. The -p option causes output to be displayed in a format
5561 that may be reused as input. If a variable name is followed by
5562 =word, the value of the variable is set to word. The return
5563 status is 0 unless an invalid option is encountered, one of the
5564 names is not a valid shell variable name, or -f is supplied with
5565 a name that is not a function.
5566 return [n]
5568 Causes a function to stop executing and return the value speci‐
5569 fied by n to its caller. If n is omitted, the return status is
5570 that of the last command executed in the function body. If re‐
5571 turn is executed by a trap handler, the last command used to de‐
5572 termine the status is the last command executed before the trap
5573 handler. If return is executed during a DEBUG trap, the last
5574 command used to determine the status is the last command exe‐
5575 cuted by the trap handler before return was invoked. If return
5576 is used outside a function, but during execution of a script by
5577 the . (source) command, it causes the shell to stop executing
5578 that script and return either n or the exit status of the last
5579 command executed within the script as the exit status of the
5580 script. If n is supplied, the return value is its least signif‐
5581 icant 8 bits. The return status is non-zero if return is sup‐
5582 plied a non-numeric argument, or is used outside a function and
5583 not during execution of a script by . or source. Any command
5584 associated with the RETURN trap is executed before execution re‐
5585 sumes after the function or script.
5586 set [-abefhkmnptuvxBCEHPT] [-o option-name] [--] [-] [arg ...]
5588 set [+abefhkmnptuvxBCEHPT] [+o option-name] [--] [-] [arg ...]
5589 Without options, display the name and value of each shell vari‐
5590 able in a format that can be reused as input for setting or re‐
5591 setting the currently-set variables. Read-only variables cannot
5592 be reset. In posix mode, only shell variables are listed. The
5593 output is sorted according to the current locale. When options
5594 are specified, they set or unset shell attributes. Any argu‐
5595 ments remaining after option processing are treated as values
5596 for the positional parameters and are assigned, in order, to $1,
5597 $2, ... $n. Options, if specified, have the following mean‐
5598 ings:
5599 -a Each variable or function that is created or modified is
5600 given the export attribute and marked for export to the
5601 environment of subsequent commands.
5602 -b Report the status of terminated background jobs immedi‐
5603 ately, rather than before the next primary prompt. This
5604 is effective only when job control is enabled.
5605 -e Exit immediately if a pipeline (which may consist of a
5606 single simple command), a list, or a compound command
5607 (see SHELL GRAMMAR above), exits with a non-zero status.
5608 The shell does not exit if the command that fails is
5609 part of the command list immediately following a while
5610 or until keyword, part of the test following the if or
5611 elif reserved words, part of any command executed in a
5612 && or || list except the command following the final &&
5613 or ||, any command in a pipeline but the last, or if the
5614 command's return value is being inverted with !. If a
5615 compound command other than a subshell returns a non-
5616 zero status because a command failed while -e was being
5617 ignored, the shell does not exit. A trap on ERR, if
5618 set, is executed before the shell exits. This option
5619 applies to the shell environment and each subshell envi‐
5620 ronment separately (see COMMAND EXECUTION ENVIRONMENT
5621 above), and may cause subshells to exit before executing
5622 all the commands in the subshell.
5623 If a compound command or shell function executes in a
5625 context where -e is being ignored, none of the commands
5626 executed within the compound command or function body
5627 will be affected by the -e setting, even if -e is set
5628 and a command returns a failure status. If a compound
5629 command or shell function sets -e while executing in a
5630 context where -e is ignored, that setting will not have
5631 any effect until the compound command or the command
5632 containing the function call completes.
5633 -f Disable pathname expansion.
5634 -h Remember the location of commands as they are looked up
5635 for execution. This is enabled by default.
5636 -k All arguments in the form of assignment statements are
5637 placed in the environment for a command, not just those
5638 that precede the command name.
5639 -m Monitor mode. Job control is enabled. This option is
5640 on by default for interactive shells on systems that
5641 support it (see JOB CONTROL above). All processes run
5642 in a separate process group. When a background job com‐
5643 pletes, the shell prints a line containing its exit sta‐
5644 tus.
5645 -n Read commands but do not execute them. This may be used
5646 to check a shell script for syntax errors. This is ig‐
5647 nored by interactive shells.
5648 -o option-name
5649 The option-name can be one of the following:
5650 allexport
5651 Same as -a.
5652 braceexpand
5653 Same as -B.
5654 emacs Use an emacs-style command line editing inter‐
5655 face. This is enabled by default when the shell
5656 is interactive, unless the shell is started with
5657 the --noediting option. This also affects the
5658 editing interface used for read -e.
5659 errexit Same as -e.
5660 errtrace
5661 Same as -E.
5662 functrace
5663 Same as -T.
5664 hashall Same as -h.
5665 histexpand
5666 Same as -H.
5667 history Enable command history, as described above under
5668 HISTORY. This option is on by default in inter‐
5669 active shells.
5670 ignoreeof
5671 The effect is as if the shell command ``IG‐
5672 NOREEOF=10'' had been executed (see Shell Vari‐
5673 ables above).
5674 keyword Same as -k.
5675 monitor Same as -m.
5676 noclobber
5677 Same as -C.
5678 noexec Same as -n.
5679 noglob Same as -f.
5680 nolog Currently ignored.
5681 notify Same as -b.
5682 nounset Same as -u.
5683 onecmd Same as -t.
5684 physical
5685 Same as -P.
5686 pipefail
5687 If set, the return value of a pipeline is the
5688 value of the last (rightmost) command to exit
5689 with a non-zero status, or zero if all commands
5690 in the pipeline exit successfully. This option
5691 is disabled by default.
5692 posix Change the behavior of bash where the default
5693 operation differs from the POSIX standard to
5694 match the standard (posix mode). See SEE ALSO
5695 below for a reference to a document that details
5696 how posix mode affects bash's behavior.
5697 privileged
5698 Same as -p.
5699 verbose Same as -v.
5700 vi Use a vi-style command line editing interface.
5701 This also affects the editing interface used for
5702 read -e.
5703 xtrace Same as -x.
5704 If -o is supplied with no option-name, the values of the
5705 current options are printed. If +o is supplied with no
5706 option-name, a series of set commands to recreate the
5707 current option settings is displayed on the standard
5708 output.
5709 -p Turn on privileged mode. In this mode, the $ENV and
5710 $BASH_ENV files are not processed, shell functions are
5711 not inherited from the environment, and the SHELLOPTS,
5712 BASHOPTS, CDPATH, and GLOBIGNORE variables, if they ap‐
5713 pear in the environment, are ignored. If the shell is
5714 started with the effective user (group) id not equal to
5715 the real user (group) id, and the -p option is not sup‐
5716 plied, these actions are taken and the effective user id
5717 is set to the real user id. If the -p option is sup‐
5718 plied at startup, the effective user id is not reset.
5719 Turning this option off causes the effective user and
5720 group ids to be set to the real user and group ids.
5721 -r Enable restricted shell mode. This option cannot be un‐
5722 set once it has been set.
5723 -t Exit after reading and executing one command.
5724 -u Treat unset variables and parameters other than the spe‐
5725 cial parameters "@" and "*", or array variables sub‐
5726 scripted with "@" or "*", as an error when performing
5727 parameter expansion. If expansion is attempted on an
5728 unset variable or parameter, the shell prints an error
5729 message, and, if not interactive, exits with a non-zero
5730 status.
5731 -v Print shell input lines as they are read.
5732 -x After expanding each simple command, for command, case
5733 command, select command, or arithmetic for command, dis‐
5734 play the expanded value of PS4, followed by the command
5735 and its expanded arguments or associated word list.
5736 -B The shell performs brace expansion (see Brace Expansion
5737 above). This is on by default.
5738 -C If set, bash does not overwrite an existing file with
5739 the >, >&, and <> redirection operators. This may be
5740 overridden when creating output files by using the redi‐
5741 rection operator >| instead of >.
5742 -E If set, any trap on ERR is inherited by shell functions,
5743 command substitutions, and commands executed in a sub‐
5744 shell environment. The ERR trap is normally not inher‐
5745 ited in such cases.
5746 -H Enable ! style history substitution. This option is on
5747 by default when the shell is interactive.
5748 -P If set, the shell does not resolve symbolic links when
5749 executing commands such as cd that change the current
5750 working directory. It uses the physical directory
5751 structure instead. By default, bash follows the logical
5752 chain of directories when performing commands which
5753 change the current directory.
5754 -T If set, any traps on DEBUG and RETURN are inherited by
5755 shell functions, command substitutions, and commands ex‐
5756 ecuted in a subshell environment. The DEBUG and RETURN
5757 traps are normally not inherited in such cases.
5758 -- If no arguments follow this option, then the positional
5759 parameters are unset. Otherwise, the positional parame‐
5760 ters are set to the args, even if some of them begin
5761 with a -.
5762 - Signal the end of options, cause all remaining args to
5763 be assigned to the positional parameters. The -x and -v
5764 options are turned off. If there are no args, the posi‐
5765 tional parameters remain unchanged.
5766 The options are off by default unless otherwise noted. Using +
5768 rather than - causes these options to be turned off. The op‐
5769 tions can also be specified as arguments to an invocation of the
5770 shell. The current set of options may be found in $-. The re‐
5771 turn status is always true unless an invalid option is encoun‐
5772 tered.
5773 shift [n]
5775 The positional parameters from n+1 ... are renamed to $1 ....
5776 Parameters represented by the numbers $# down to $#-n+1 are un‐
5777 set. n must be a non-negative number less than or equal to $#.
5778 If n is 0, no parameters are changed. If n is not given, it is
5779 assumed to be 1. If n is greater than $#, the positional param‐
5780 eters are not changed. The return status is greater than zero
5781 if n is greater than $# or less than zero; otherwise 0.
5782 shopt [-pqsu] [-o] [optname ...]
5784 Toggle the values of settings controlling optional shell behav‐
5785 ior. The settings can be either those listed below, or, if the
5786 -o option is used, those available with the -o option to the set
5787 builtin command. With no options, or with the -p option, a list
5788 of all settable options is displayed, with an indication of
5789 whether or not each is set; if optnames are supplied, the output
5790 is restricted to those options. The -p option causes output to
5791 be displayed in a form that may be reused as input. Other op‐
5792 tions have the following meanings:
5793 -s Enable (set) each optname.
5794 -u Disable (unset) each optname.
5795 -q Suppresses normal output (quiet mode); the return status
5796 indicates whether the optname is set or unset. If multi‐
5797 ple optname arguments are given with -q, the return sta‐
5798 tus is zero if all optnames are enabled; non-zero other‐
5799 wise.
5800 -o Restricts the values of optname to be those defined for
5801 the -o option to the set builtin.
5802 If either -s or -u is used with no optname arguments, shopt
5804 shows only those options which are set or unset, respectively.
5805 Unless otherwise noted, the shopt options are disabled (unset)
5806 by default.
5807 The return status when listing options is zero if all optnames
5809 are enabled, non-zero otherwise. When setting or unsetting op‐
5810 tions, the return status is zero unless an optname is not a
5811 valid shell option.
5812 The list of shopt options is:
5814 assoc_expand_once
5816 If set, the shell suppresses multiple evaluation of as‐
5817 sociative array subscripts during arithmetic expression
5818 evaluation, while executing builtins that can perform
5819 variable assignments, and while executing builtins that
5820 perform array dereferencing.
5821 autocd If set, a command name that is the name of a directory
5822 is executed as if it were the argument to the cd com‐
5823 mand. This option is only used by interactive shells.
5824 cdable_vars
5825 If set, an argument to the cd builtin command that is
5826 not a directory is assumed to be the name of a variable
5827 whose value is the directory to change to.
5828 cdspell If set, minor errors in the spelling of a directory com‐
5829 ponent in a cd command will be corrected. The errors
5830 checked for are transposed characters, a missing charac‐
5831 ter, and one character too many. If a correction is
5832 found, the corrected filename is printed, and the com‐
5833 mand proceeds. This option is only used by interactive
5834 shells.
5835 checkhash
5836 If set, bash checks that a command found in the hash ta‐
5837 ble exists before trying to execute it. If a hashed
5838 command no longer exists, a normal path search is per‐
5839 formed.
5840 checkjobs
5841 If set, bash lists the status of any stopped and running
5842 jobs before exiting an interactive shell. If any jobs
5843 are running, this causes the exit to be deferred until a
5844 second exit is attempted without an intervening command
5845 (see JOB CONTROL above). The shell always postpones ex‐
5846 iting if any jobs are stopped.
5847 checkwinsize
5848 If set, bash checks the window size after each external
5849 (non-builtin) command and, if necessary, updates the
5850 values of LINES and COLUMNS. This option is enabled by
5851 default.
5852 cmdhist If set, bash attempts to save all lines of a multiple-
5853 line command in the same history entry. This allows
5854 easy re-editing of multi-line commands. This option is
5855 enabled by default, but only has an effect if command
5856 history is enabled, as described above under HISTORY.
5857 compat31
5858 compat32
5859 compat40
5860 compat41
5861 compat42
5862 compat43
5863 compat44
5864 compat50
5865 These control aspects of the shell's compatibility mode
5866 (see SHELL COMPATIBILITY MODE below).
5867 complete_fullquote
5869 If set, bash quotes all shell metacharacters in file‐
5870 names and directory names when performing completion.
5871 If not set, bash removes metacharacters such as the dol‐
5872 lar sign from the set of characters that will be quoted
5873 in completed filenames when these metacharacters appear
5874 in shell variable references in words to be completed.
5875 This means that dollar signs in variable names that ex‐
5876 pand to directories will not be quoted; however, any
5877 dollar signs appearing in filenames will not be quoted,
5878 either. This is active only when bash is using back‐
5879 slashes to quote completed filenames. This variable is
5880 set by default, which is the default bash behavior in
5881 versions through 4.2.
5882 direxpand
5884 If set, bash replaces directory names with the results
5885 of word expansion when performing filename completion.
5886 This changes the contents of the readline editing buf‐
5887 fer. If not set, bash attempts to preserve what the
5888 user typed.
5889 dirspell
5891 If set, bash attempts spelling correction on directory
5892 names during word completion if the directory name ini‐
5893 tially supplied does not exist.
5894 dotglob If set, bash includes filenames beginning with a `.' in
5896 the results of pathname expansion. The filenames ``.''
5897 and ``..'' must always be matched explicitly, even if
5898 dotglob is set.
5899 execfail
5901 If set, a non-interactive shell will not exit if it can‐
5902 not execute the file specified as an argument to the
5903 exec builtin command. An interactive shell does not
5904 exit if exec fails.
5905 expand_aliases
5907 If set, aliases are expanded as described above under
5908 ALIASES. This option is enabled by default for interac‐
5909 tive shells.
5910 extdebug
5912 If set at shell invocation, or in a shell startup file,
5913 arrange to execute the debugger profile before the shell
5914 starts, identical to the --debugger option. If set af‐
5915 ter invocation, behavior intended for use by debuggers
5916 is enabled:
5917 1. The -F option to the declare builtin displays the
5919 source file name and line number corresponding to
5920 each function name supplied as an argument.
5921 2. If the command run by the DEBUG trap returns a
5923 non-zero value, the next command is skipped and
5924 not executed.
5925 3. If the command run by the DEBUG trap returns a
5927 value of 2, and the shell is executing in a sub‐
5928 routine (a shell function or a shell script exe‐
5929 cuted by the . or source builtins), the shell
5930 simulates a call to return.
5931 4. BASH_ARGC and BASH_ARGV are updated as described
5933 in their descriptions above).
5934 5. Function tracing is enabled: command substitu‐
5936 tion, shell functions, and subshells invoked with
5937 ( command ) inherit the DEBUG and RETURN traps.
5938 6. Error tracing is enabled: command substitution,
5940 shell functions, and subshells invoked with (
5941 command ) inherit the ERR trap.
5942 extglob If set, the extended pattern matching features described
5944 above under Pathname Expansion are enabled.
5945 extquote
5947 If set, $'string' and $"string" quoting is performed
5948 within ${parameter} expansions enclosed in double
5949 quotes. This option is enabled by default.
5950 failglob
5952 If set, patterns which fail to match filenames during
5953 pathname expansion result in an expansion error.
5954 force_fignore
5956 If set, the suffixes specified by the FIGNORE shell
5957 variable cause words to be ignored when performing word
5958 completion even if the ignored words are the only possi‐
5959 ble completions. See SHELL VARIABLES above for a de‐
5960 scription of FIGNORE. This option is enabled by de‐
5961 fault.
5962 globasciiranges
5964 If set, range expressions used in pattern matching
5965 bracket expressions (see Pattern Matching above) behave
5966 as if in the traditional C locale when performing com‐
5967 parisons. That is, the current locale's collating se‐
5968 quence is not taken into account, so b will not collate
5969 between A and B, and upper-case and lower-case ASCII
5970 characters will collate together.
5971 globskipdots
5973 If set, pathname expansion will never match the file‐
5974 names ``.'' and ``..'', even if the pattern begins with
5975 a ``.''. This option is enabled by default.
5976 globstar
5978 If set, the pattern ** used in a pathname expansion con‐
5979 text will match all files and zero or more directories
5980 and subdirectories. If the pattern is followed by a /,
5981 only directories and subdirectories match.
5982 gnu_errfmt
5984 If set, shell error messages are written in the standard
5985 GNU error message format.
5986 histappend
5988 If set, the history list is appended to the file named
5989 by the value of the HISTFILE variable when the shell ex‐
5990 its, rather than overwriting the file.
5991 histreedit
5993 If set, and readline is being used, a user is given the
5994 opportunity to re-edit a failed history substitution.
5995 histverify
5997 If set, and readline is being used, the results of his‐
5998 tory substitution are not immediately passed to the
5999 shell parser. Instead, the resulting line is loaded
6000 into the readline editing buffer, allowing further modi‐
6001 fication.
6002 hostcomplete
6004 If set, and readline is being used, bash will attempt to
6005 perform hostname completion when a word containing a @
6006 is being completed (see Completing under READLINE
6007 above). This is enabled by default.
6008 huponexit
6010 If set, bash will send SIGHUP to all jobs when an inter‐
6011 active login shell exits.
6012 inherit_errexit
6014 If set, command substitution inherits the value of the
6015 errexit option, instead of unsetting it in the subshell
6016 environment. This option is enabled when posix mode is
6017 enabled.
6018 interactive_comments
6020 If set, allow a word beginning with # to cause that word
6021 and all remaining characters on that line to be ignored
6022 in an interactive shell (see COMMENTS above). This op‐
6023 tion is enabled by default.
6024 lastpipe
6026 If set, and job control is not active, the shell runs
6027 the last command of a pipeline not executed in the back‐
6028 ground in the current shell environment.
6029 lithist If set, and the cmdhist option is enabled, multi-line
6031 commands are saved to the history with embedded newlines
6032 rather than using semicolon separators where possible.
6033 localvar_inherit
6035 If set, local variables inherit the value and attributes
6036 of a variable of the same name that exists at a previous
6037 scope before any new value is assigned. The nameref at‐
6038 tribute is not inherited.
6039 localvar_unset
6041 If set, calling unset on local variables in previous
6042 function scopes marks them so subsequent lookups find
6043 them unset until that function returns. This is identi‐
6044 cal to the behavior of unsetting local variables at the
6045 current function scope.
6046 login_shell
6048 The shell sets this option if it is started as a login
6049 shell (see INVOCATION above). The value may not be
6050 changed.
6051 mailwarn
6053 If set, and a file that bash is checking for mail has
6054 been accessed since the last time it was checked, the
6055 message ``The mail in mailfile has been read'' is dis‐
6056 played.
6057 no_empty_cmd_completion
6059 If set, and readline is being used, bash will not at‐
6060 tempt to search the PATH for possible completions when
6061 completion is attempted on an empty line.
6062 nocaseglob
6064 If set, bash matches filenames in a case-insensitive
6065 fashion when performing pathname expansion (see Pathname
6066 Expansion above).
6067 nocasematch
6069 If set, bash matches patterns in a case-insensitive
6070 fashion when performing matching while executing case or
6071 [[ conditional commands, when performing pattern substi‐
6072 tution word expansions, or when filtering possible com‐
6073 pletions as part of programmable completion.
6074 noexpand_translation
6076 If set, bash encloses the translated results of $"..."
6077 quoting in single quotes instead of double quotes. If
6078 the string is not translated, this has no effect.
6079 nullglob
6081 If set, bash allows patterns which match no files (see
6082 Pathname Expansion above) to expand to a null string,
6083 rather than themselves.
6084 patsub_replacement
6086 If set, bash expands occurrences of & in the replacement
6087 string of pattern substitution to the text matched by
6088 the pattern, as described under Parameter Expansion
6089 above. This option is enabled by default.
6090 progcomp
6092 If set, the programmable completion facilities (see Pro‐
6093 grammable Completion above) are enabled. This option is
6094 enabled by default.
6095 progcomp_alias
6097 If set, and programmable completion is enabled, bash
6098 treats a command name that doesn't have any completions
6099 as a possible alias and attempts alias expansion. If it
6100 has an alias, bash attempts programmable completion us‐
6101 ing the command word resulting from the expanded alias.
6102 promptvars
6104 If set, prompt strings undergo parameter expansion, com‐
6105 mand substitution, arithmetic expansion, and quote re‐
6106 moval after being expanded as described in PROMPTING
6107 above. This option is enabled by default.
6108 restricted_shell
6110 The shell sets this option if it is started in re‐
6111 stricted mode (see RESTRICTED SHELL below). The value
6112 may not be changed. This is not reset when the startup
6113 files are executed, allowing the startup files to dis‐
6114 cover whether or not a shell is restricted.
6115 shift_verbose
6117 If set, the shift builtin prints an error message when
6118 the shift count exceeds the number of positional parame‐
6119 ters.
6120 sourcepath
6122 If set, the . (source) builtin uses the value of PATH to
6123 find the directory containing the file supplied as an
6124 argument. This option is enabled by default.
6125 varredir_close
6127 If set, the shell automatically closes file descriptors
6128 assigned using the {varname} redirection syntax (see RE‐
6129 DIRECTION above) instead of leaving them open when the
6130 command completes.
6131 syslog_history
6133 If set, command history is logged to syslog.
6134 xpg_echo
6136 If set, the echo builtin expands backslash-escape se‐
6137 quences by default.
6138 suspend [-f]
6140 Suspend the execution of this shell until it receives a SIGCONT
6141 signal. A login shell, or a shell without job control enabled,
6142 cannot be suspended; the -f option can be used to override this
6143 and force the suspension. The return status is 0 unless the
6144 shell is a login shell or job control is not enabled and -f is
6145 not supplied.
6146 test expr
6148 [ expr ]
6149 Return a status of 0 (true) or 1 (false) depending on the evalu‐
6150 ation of the conditional expression expr. Each operator and op‐
6151 erand must be a separate argument. Expressions are composed of
6152 the primaries described above under CONDITIONAL EXPRESSIONS.
6153 test does not accept any options, nor does it accept and ignore
6154 an argument of -- as signifying the end of options.
6155 Expressions may be combined using the following operators,
6157 listed in decreasing order of precedence. The evaluation de‐
6158 pends on the number of arguments; see below. Operator prece‐
6159 dence is used when there are five or more arguments.
6160 ! expr True if expr is false.
6161 ( expr )
6162 Returns the value of expr. This may be used to override
6163 the normal precedence of operators.
6164 expr1 -a expr2
6165 True if both expr1 and expr2 are true.
6166 expr1 -o expr2
6167 True if either expr1 or expr2 is true.
6168 test and [ evaluate conditional expressions using a set of rules
6170 based on the number of arguments.
6171 0 arguments
6173 The expression is false.
6174 1 argument
6175 The expression is true if and only if the argument is not
6176 null.
6177 2 arguments
6178 If the first argument is !, the expression is true if and
6179 only if the second argument is null. If the first argu‐
6180 ment is one of the unary conditional operators listed
6181 above under CONDITIONAL EXPRESSIONS, the expression is
6182 true if the unary test is true. If the first argument is
6183 not a valid unary conditional operator, the expression is
6184 false.
6185 3 arguments
6186 The following conditions are applied in the order listed.
6187 If the second argument is one of the binary conditional
6188 operators listed above under CONDITIONAL EXPRESSIONS, the
6189 result of the expression is the result of the binary test
6190 using the first and third arguments as operands. The -a
6191 and -o operators are considered binary operators when
6192 there are three arguments. If the first argument is !,
6193 the value is the negation of the two-argument test using
6194 the second and third arguments. If the first argument is
6195 exactly ( and the third argument is exactly ), the result
6196 is the one-argument test of the second argument. Other‐
6197 wise, the expression is false.
6198 4 arguments
6199 The following conditions are applied in the order listed.
6200 If the first argument is !, the result is the negation of
6201 the three-argument expression composed of the remaining
6202 arguments. the two-argument test using the second and
6203 third arguments. If the first argument is exactly ( and
6204 the fourth argument is exactly ), the result is the two-
6205 argument test of the second and third arguments. Other‐
6206 wise, the expression is parsed and evaluated according to
6207 precedence using the rules listed above.
6208 5 or more arguments
6209 The expression is parsed and evaluated according to
6210 precedence using the rules listed above.
6211 When used with test or [, the < and > operators sort lexico‐
6213 graphically using ASCII ordering.
6214 times Print the accumulated user and system times for the shell and
6216 for processes run from the shell. The return status is 0.
6217 trap [-lp] [[arg] sigspec ...]
6219 The command arg is to be read and executed when the shell re‐
6220 ceives signal(s) sigspec. If arg is absent (and there is a sin‐
6221 gle sigspec) or -, each specified signal is reset to its origi‐
6222 nal disposition (the value it had upon entrance to the shell).
6223 If arg is the null string the signal specified by each sigspec
6224 is ignored by the shell and by the commands it invokes. If arg
6225 is not present and -p has been supplied, then the trap commands
6226 associated with each sigspec are displayed. If no arguments are
6227 supplied or if only -p is given, trap prints the list of com‐
6228 mands associated with each signal. The -l option causes the
6229 shell to print a list of signal names and their corresponding
6230 numbers. Each sigspec is either a signal name defined in <sig‐
6231 nal.h>, or a signal number. Signal names are case insensitive
6232 and the SIG prefix is optional.
6233 If a sigspec is EXIT (0) the command arg is executed on exit
6235 from the shell. If a sigspec is DEBUG, the command arg is exe‐
6236 cuted before every simple command, for command, case command,
6237 select command, every arithmetic for command, and before the
6238 first command executes in a shell function (see SHELL GRAMMAR
6239 above). Refer to the description of the extdebug option to the
6240 shopt builtin for details of its effect on the DEBUG trap. If a
6241 sigspec is RETURN, the command arg is executed each time a shell
6242 function or a script executed with the . or source builtins fin‐
6243 ishes executing.
6244 If a sigspec is ERR, the command arg is executed whenever a
6246 pipeline (which may consist of a single simple command), a list,
6247 or a compound command returns a non-zero exit status, subject to
6248 the following conditions. The ERR trap is not executed if the
6249 failed command is part of the command list immediately following
6250 a while or until keyword, part of the test in an if statement,
6251 part of a command executed in a && or || list except the command
6252 following the final && or ||, any command in a pipeline but the
6253 last, or if the command's return value is being inverted using
6254 !. These are the same conditions obeyed by the errexit (-e) op‐
6255 tion.
6256 Signals ignored upon entry to the shell cannot be trapped, reset
6258 or listed. Trapped signals that are not being ignored are reset
6259 to their original values in a subshell or subshell environment
6260 when one is created. The return status is false if any sigspec
6261 is invalid; otherwise trap returns true.
6262 type [-aftpP] name [name ...]
6264 With no options, indicate how each name would be interpreted if
6265 used as a command name. If the -t option is used, type prints a
6266 string which is one of alias, keyword, function, builtin, or
6267 file if name is an alias, shell reserved word, function,
6268 builtin, or disk file, respectively. If the name is not found,
6269 then nothing is printed, and an exit status of false is re‐
6270 turned. If the -p option is used, type either returns the name
6271 of the disk file that would be executed if name were specified
6272 as a command name, or nothing if ``type -t name'' would not re‐
6273 turn file. The -P option forces a PATH search for each name,
6274 even if ``type -t name'' would not return file. If a command is
6275 hashed, -p and -P print the hashed value, which is not necessar‐
6276 ily the file that appears first in PATH. If the -a option is
6277 used, type prints all of the places that contain an executable
6278 named name. This includes aliases and functions, if and only if
6279 the -p option is not also used. The table of hashed commands is
6280 not consulted when using -a. The -f option suppresses shell
6281 function lookup, as with the command builtin. type returns true
6282 if all of the arguments are found, false if any are not found.
6283 ulimit [-HS] -a
6285 ulimit [-HS] [-bcdefiklmnpqrstuvxPRT [limit]]
6286 Provides control over the resources available to the shell and
6287 to processes started by it, on systems that allow such control.
6288 The -H and -S options specify that the hard or soft limit is set
6289 for the given resource. A hard limit cannot be increased by a
6290 non-root user once it is set; a soft limit may be increased up
6291 to the value of the hard limit. If neither -H nor -S is speci‐
6292 fied, both the soft and hard limits are set. The value of limit
6293 can be a number in the unit specified for the resource or one of
6294 the special values hard, soft, or unlimited, which stand for the
6295 current hard limit, the current soft limit, and no limit, re‐
6296 spectively. If limit is omitted, the current value of the soft
6297 limit of the resource is printed, unless the -H option is given.
6298 When more than one resource is specified, the limit name and
6299 unit, if appropriate, are printed before the value. Other op‐
6300 tions are interpreted as follows:
6301 -a All current limits are reported; no limits are set
6302 -b The maximum socket buffer size
6303 -c The maximum size of core files created
6304 -d The maximum size of a process's data segment
6305 -e The maximum scheduling priority ("nice")
6306 -f The maximum size of files written by the shell and its
6307 children
6308 -i The maximum number of pending signals
6309 -k The maximum number of kqueues that may be allocated
6310 -l The maximum size that may be locked into memory
6311 -m The maximum resident set size (many systems do not honor
6312 this limit)
6313 -n The maximum number of open file descriptors (most systems
6314 do not allow this value to be set)
6315 -p The pipe size in 512-byte blocks (this may not be set)
6316 -q The maximum number of bytes in POSIX message queues
6317 -r The maximum real-time scheduling priority
6318 -s The maximum stack size
6319 -t The maximum amount of cpu time in seconds
6320 -u The maximum number of processes available to a single
6321 user
6322 -v The maximum amount of virtual memory available to the
6323 shell and, on some systems, to its children
6324 -x The maximum number of file locks
6325 -P The maximum number of pseudoterminals
6326 -R The maximum time a real-time process can run before
6327 blocking, in microseconds
6328 -T The maximum number of threads
6329 If limit is given, and the -a option is not used, limit is the
6331 new value of the specified resource. If no option is given,
6332 then -f is assumed. Values are in 1024-byte increments, except
6333 for -t, which is in seconds; -R, which is in microseconds; -p,
6334 which is in units of 512-byte blocks; -P, -T, -b, -k, -n, and
6335 -u, which are unscaled values; and, when in posix mode, -c and
6336 -f, which are in 512-byte increments. The return status is 0
6337 unless an invalid option or argument is supplied, or an error
6338 occurs while setting a new limit. In POSIX Mode 512-byte blocks
6339 are used for the `-c' and `-f' options.
6340 umask [-p] [-S] [mode]
6342 The user file-creation mask is set to mode. If mode begins with
6343 a digit, it is interpreted as an octal number; otherwise it is
6344 interpreted as a symbolic mode mask similar to that accepted by
6345 chmod(1). If mode is omitted, the current value of the mask is
6346 printed. The -S option causes the mask to be printed in sym‐
6347 bolic form; the default output is an octal number. If the -p
6348 option is supplied, and mode is omitted, the output is in a form
6349 that may be reused as input. The return status is 0 if the mode
6350 was successfully changed or if no mode argument was supplied,
6351 and false otherwise.
6352 unalias [-a] [name ...]
6354 Remove each name from the list of defined aliases. If -a is
6355 supplied, all alias definitions are removed. The return value
6356 is true unless a supplied name is not a defined alias.
6357 unset [-fv] [-n] [name ...]
6359 For each name, remove the corresponding variable or function.
6360 If the -v option is given, each name refers to a shell variable,
6361 and that variable is removed. Read-only variables may not be
6362 unset. If -f is specified, each name refers to a shell func‐
6363 tion, and the function definition is removed. If the -n option
6364 is supplied, and name is a variable with the nameref attribute,
6365 name will be unset rather than the variable it references. -n
6366 has no effect if the -f option is supplied. If no options are
6367 supplied, each name refers to a variable; if there is no vari‐
6368 able by that name, a function with that name, if any, is unset.
6369 Each unset variable or function is removed from the environment
6370 passed to subsequent commands. If any of BASH_ALIASES,
6371 BASH_ARGV0, BASH_CMDS, BASH_COMMAND, BASH_SUBSHELL, BASHPID,
6372 COMP_WORDBREAKS, DIRSTACK, EPOCHREALTIME, EPOCHSECONDS, FUNC‐
6373 NAME, GROUPS, HISTCMD, LINENO, RANDOM, SECONDS, or SRANDOM are
6374 unset, they lose their special properties, even if they are sub‐
6375 sequently reset. The exit status is true unless a name is read‐
6376 only or may not be unset.
6377 wait [-fn] [-p varname] [id ...]
6379 Wait for each specified child process and return its termination
6380 status. Each id may be a process ID or a job specification; if
6381 a job spec is given, all processes in that job's pipeline are
6382 waited for. If id is not given, wait waits for all running
6383 background jobs and the last-executed process substitution, if
6384 its process id is the same as $!, and the return status is zero.
6385 If the -n option is supplied, wait waits for a single job from
6386 the list of ids or, if no ids are supplied, any job, to complete
6387 and returns its exit status. If none of the supplied arguments
6388 is a child of the shell, or if no arguments are supplied and the
6389 shell has no unwaited-for children, the exit status is 127. If
6390 the -p option is supplied, the process or job identifier of the
6391 job for which the exit status is returned is assigned to the
6392 variable varname named by the option argument. The variable
6393 will be unset initially, before any assignment. This is useful
6394 only when the -n option is supplied. Supplying the -f option,
6395 when job control is enabled, forces wait to wait for id to ter‐
6396 minate before returning its status, instead of returning when it
6397 changes status. If id specifies a non-existent process or job,
6398 the return status is 127. If wait is interrupted by a signal,
6399 the return status will be greater than 128, as described under
6400 SIGNALS above. Otherwise, the return status is the exit status
6401 of the last process or job waited for.
6402
6404 Bash-4.0 introduced the concept of a shell compatibility level, speci‐
6405 fied as a set of options to the shopt builtin ( compat31, compat32,
6406 compat40, compat41, and so on). There is only one current compatibil‐
6407 ity level -- each option is mutually exclusive. The compatibility
6408 level is intended to allow users to select behavior from previous ver‐
6409 sions that is incompatible with newer versions while they migrate
6410 scripts to use current features and behavior. It's intended to be a
6411 temporary solution.
6412 This section does not mention behavior that is standard for a particu‐
6414 lar version (e.g., setting compat32 means that quoting the rhs of the
6415 regexp matching operator quotes special regexp characters in the word,
6416 which is default behavior in bash-3.2 and subsequent versions).
6417 If a user enables, say, compat32, it may affect the behavior of other
6419 compatibility levels up to and including the current compatibility
6420 level. The idea is that each compatibility level controls behavior
6421 that changed in that version of bash, but that behavior may have been
6422 present in earlier versions. For instance, the change to use locale-
6423 based comparisons with the [[ command came in bash-4.1, and earlier
6424 versions used ASCII-based comparisons, so enabling compat32 will enable
6425 ASCII-based comparisons as well. That granularity may not be suffi‐
6426 cient for all uses, and as a result users should employ compatibility
6427 levels carefully. Read the documentation for a particular feature to
6428 find out the current behavior.
6429 Bash-4.3 introduced a new shell variable: BASH_COMPAT. The value as‐
6431 signed to this variable (a decimal version number like 4.2, or an inte‐
6432 ger corresponding to the compatNN option, like 42) determines the com‐
6433 patibility level.
6434 Starting with bash-4.4, Bash has begun deprecating older compatibility
6436 levels. Eventually, the options will be removed in favor of BASH_COM‐
6437 PAT.
6438 Bash-5.0 is the final version for which there will be an individual
6440 shopt option for the previous version. Users should use BASH_COMPAT on
6441 bash-5.0 and later versions.
6442 The following table describes the behavior changes controlled by each
6444 compatibility level setting. The compatNN tag is used as shorthand for
6445 setting the compatibility level to NN using one of the following mecha‐
6446 nisms. For versions prior to bash-5.0, the compatibility level may be
6447 set using the corresponding compatNN shopt option. For bash-4.3 and
6448 later versions, the BASH_COMPAT variable is preferred, and it is re‐
6449 quired for bash-5.1 and later versions.
6450 compat31
6452 • quoting the rhs of the [[ command's regexp matching oper‐
6453 ator (=~) has no special effect
6454 compat32
6456 • interrupting a command list such as "a ; b ; c" causes
6457 the execution of the next command in the list (in
6458 bash-4.0 and later versions, the shell acts as if it re‐
6459 ceived the interrupt, so interrupting one command in a
6460 list aborts the execution of the entire list)
6461 compat40
6463 • the < and > operators to the [[ command do not consider
6464 the current locale when comparing strings; they use ASCII
6465 ordering. Bash versions prior to bash-4.1 use ASCII col‐
6466 lation and strcmp(3); bash-4.1 and later use the current
6467 locale's collation sequence and strcoll(3).
6468 compat41
6470 • in posix mode, time may be followed by options and still
6471 be recognized as a reserved word (this is POSIX interpre‐
6472 tation 267)
6473 • in posix mode, the parser requires that an even number of
6474 single quotes occur in the word portion of a double-
6475 quoted parameter expansion and treats them specially, so
6476 that characters within the single quotes are considered
6477 quoted (this is POSIX interpretation 221)
6478 compat42
6480 • the replacement string in double-quoted pattern substitu‐
6481 tion does not undergo quote removal, as it does in ver‐
6482 sions after bash-4.2
6483 • in posix mode, single quotes are considered special when
6484 expanding the word portion of a double-quoted parameter
6485 expansion and can be used to quote a closing brace or
6486 other special character (this is part of POSIX interpre‐
6487 tation 221); in later versions, single quotes are not
6488 special within double-quoted word expansions
6489 compat43
6491 • the shell does not print a warning message if an attempt
6492 is made to use a quoted compound assignment as an argu‐
6493 ment to declare (e.g., declare -a foo='(1 2)'). Later
6494 versions warn that this usage is deprecated
6495 • word expansion errors are considered non-fatal errors
6496 that cause the current command to fail, even in posix
6497 mode (the default behavior is to make them fatal errors
6498 that cause the shell to exit)
6499 • when executing a shell function, the loop state
6500 (while/until/etc.) is not reset, so break or continue in
6501 that function will break or continue loops in the calling
6502 context. Bash-4.4 and later reset the loop state to pre‐
6503 vent this
6504 compat44
6506 • the shell sets up the values used by BASH_ARGV and
6507 BASH_ARGC so they can expand to the shell's positional
6508 parameters even if extended debugging mode is not enabled
6509 • a subshell inherits loops from its parent context, so
6510 break or continue will cause the subshell to exit.
6511 Bash-5.0 and later reset the loop state to prevent the
6512 exit
6513 • variable assignments preceding builtins like export and
6514 readonly that set attributes continue to affect variables
6515 with the same name in the calling environment even if the
6516 shell is not in posix mode
6517 compat50
6519 • Bash-5.1 changed the way $RANDOM is generated to intro‐
6520 duce slightly more randomness. If the shell compatibility
6521 level is set to 50 or lower, it reverts to the method
6522 from bash-5.0 and previous versions, so seeding the ran‐
6523 dom number generator by assigning a value to RANDOM will
6524 produce the same sequence as in bash-5.0
6525 • If the command hash table is empty, bash versions prior
6526 to bash-5.1 printed an informational message to that ef‐
6527 fect, even when producing output that can be reused as
6528 input. Bash-5.1 suppresses that message when the -l op‐
6529 tion is supplied.
6530 compat51
6532 • The unset builtin treats attempts to unset array sub‐
6533 scripts @ and * differently depending on whether the ar‐
6534 ray is indexed or associative, and differently than in
6535 previous versions.
6536
6538 If bash is started with the name rbash, or the -r option is supplied at
6539 invocation, the shell becomes restricted. A restricted shell is used
6540 to set up an environment more controlled than the standard shell. It
6541 behaves identically to bash with the exception that the following are
6542 disallowed or not performed:
6543 • changing directories with cd
6545 • setting or unsetting the values of SHELL, PATH, HISTFILE, ENV,
6547 or BASH_ENV
6548 • specifying command names containing /
6550 • specifying a filename containing a / as an argument to the .
6552 builtin command
6553 • specifying a filename containing a slash as an argument to the
6555 history builtin command
6556 • specifying a filename containing a slash as an argument to the
6558 -p option to the hash builtin command
6559 • importing function definitions from the shell environment at
6561 startup
6562 • parsing the value of SHELLOPTS from the shell environment at
6564 startup
6565 • redirecting output using the >, >|, <>, >&, &>, and >> redirect‐
6567 ion operators
6568 • using the exec builtin command to replace the shell with another
6570 command
6571 • adding or deleting builtin commands with the -f and -d options
6573 to the enable builtin command
6574 • using the enable builtin command to enable disabled shell
6576 builtins
6577 • specifying the -p option to the command builtin command
6579 • turning off restricted mode with set +r or shopt -u re‐
6581 stricted_shell.
6582 These restrictions are enforced after any startup files are read.
6584 When a command that is found to be a shell script is executed (see COM‐
6586 MAND EXECUTION above), rbash turns off any restrictions in the shell
6587 spawned to execute the script.
6588
6590 Bash Reference Manual, Brian Fox and Chet Ramey
6591 The Gnu Readline Library, Brian Fox and Chet Ramey
6592 The Gnu History Library, Brian Fox and Chet Ramey
6593 Portable Operating System Interface (POSIX) Part 2: Shell and Utili‐
6594 ties, IEEE --
6595 http://pubs.opengroup.org/onlinepubs/9699919799/
6596 http://tiswww.case.edu/~chet/bash/POSIX -- a description of posix mode
6597 sh(1), ksh(1), csh(1)
6598 emacs(1), vi(1)
6599 readline(3)
6600
6602 /bin/bash
6603 The bash executable
6604 /etc/profile
6605 The systemwide initialization file, executed for login shells
6606 /etc/bash.bash_logout
6607 The systemwide login shell cleanup file, executed when a login
6608 shell exits
6609 ~/.bash_profile
6610 The personal initialization file, executed for login shells
6611 ~/.bashrc
6612 The individual per-interactive-shell startup file
6613 ~/.bash_logout
6614 The individual login shell cleanup file, executed when a login
6615 shell exits
6616 ~/.bash_history
6617 The default value of HISTFILE, the file in which bash saves the
6618 command history
6619 ~/.inputrc
6620 Individual readline initialization file
6621
6623 Brian Fox, Free Software Foundation
6624 bfox@gnu.org
6625 Chet Ramey, Case Western Reserve University
6627 chet.ramey@case.edu
6628
6630 If you find a bug in bash, you should report it. But first, you should
6631 make sure that it really is a bug, and that it appears in the latest
6632 version of bash. The latest version is always available from
6633 ftp://ftp.gnu.org/pub/gnu/bash/ and http://git.savan‐
6634 nah.gnu.org/cgit/bash.git/snapshot/bash-master.tar.gz.
6635 Once you have determined that a bug actually exists, use the bashbug
6637 command to submit a bug report. If you have a fix, you are encouraged
6638 to mail that as well! Suggestions and `philosophical' bug reports may
6639 be mailed to bug-bash@gnu.org or posted to the Usenet newsgroup
6640 gnu.bash.bug.
6641 ALL bug reports should include:
6643 The version number of bash
6645 The hardware and operating system
6646 The compiler used to compile
6647 A description of the bug behaviour
6648 A short script or `recipe' which exercises the bug
6649 bashbug inserts the first three items automatically into the template
6651 it provides for filing a bug report.
6652 Comments and bug reports concerning this manual page should be directed
6654 to chet.ramey@case.edu.
6655
6657 It's too big and too slow.
6658 There are some subtle differences between bash and traditional versions
6660 of sh, mostly because of the POSIX specification.
6661 Aliases are confusing in some uses.
6663 Shell builtin commands and functions are not stoppable/restartable.
6665 Compound commands and command sequences of the form `a ; b ; c' are not
6667 handled gracefully when process suspension is attempted. When a
6668 process is stopped, the shell immediately executes the next command in
6669 the sequence. It suffices to place the sequence of commands between
6670 parentheses to force it into a subshell, which may be stopped as a
6671 unit.
6672 Array variables may not (yet) be exported.
6674 There may be only one active coprocess at a time.
6676GNU Bash 5.2 2022 September 19 BASH(1)