1BASH(1) General Commands Manual BASH(1)
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6 bash - GNU Bourne-Again SHell
7
9 bash [options] [file]
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12 Bash is Copyright (C) 1989-2011 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 descrip‐
25 tion of the set builtin command can be used as options when the shell
26 is invoked. In addition, bash interprets the following options when it
27 is invoked:
28 -c string If the -c option is present, then commands are read from
30 string. If there are arguments after the string, they are
31 assigned to the positional parameters, starting with $0.
32 -i If the -i option is present, the shell is interactive.
33 -l Make bash act as if it had been invoked as a login shell (see
34 INVOCATION below).
35 -r If the -r option is present, the shell becomes restricted
36 (see RESTRICTED SHELL below).
37 -s If the -s option is present, or if no arguments remain after
38 option processing, then commands are read from the standard
39 input. This option allows the positional parameters to be
40 set when invoking an interactive shell.
41 -D A list of all double-quoted strings preceded by $ is printed
42 on the standard output. These are the strings that are sub‐
43 ject to language translation when the current locale is not C
44 or POSIX. This implies the -n option; no commands will be
45 executed.
46 [-+]O [shopt_option]
47 shopt_option is one of the shell options accepted by the
48 shopt builtin (see SHELL BUILTIN COMMANDS below). If
49 shopt_option is present, -O sets the value of that option; +O
50 unsets it. If shopt_option is not supplied, the names and
51 values of the shell options accepted by shopt are printed on
52 the standard output. If the invocation option is +O, the
53 output is displayed in a format that may be reused as input.
54 -- A -- signals the end of options and disables further option
55 processing. Any arguments after the -- are treated as file‐
56 names and arguments. An argument of - is equivalent to --.
57 Bash also interprets a number of multi-character options. These
59 options must appear on the command line before the single-character
60 options to be recognized.
61 --debugger
63 Arrange for the debugger profile to be executed before the shell
64 starts. Turns on extended debugging mode (see the description
65 of the extdebug option to the shopt builtin below).
66 --dump-po-strings
67 Equivalent to -D, but the output is in the GNU gettext po (por‐
68 table object) file format.
69 --dump-strings
70 Equivalent to -D.
71 --help Display a usage message on standard output and exit success‐
72 fully.
73 --init-file file
74 --rcfile file
75 Execute commands from file instead of the standard personal ini‐
76 tialization file ~/.bashrc if the shell is interactive (see
77 INVOCATION below).
78 --login
80 Equivalent to -l.
81 --noediting
83 Do not use the GNU readline library to read command lines when
84 the shell is interactive.
85 --noprofile
87 Do not read either the system-wide startup file /etc/profile or
88 any of the personal initialization files ~/.bash_profile,
89 ~/.bash_login, or ~/.profile. By default, bash reads these
90 files when it is invoked as a login shell (see INVOCATION
91 below).
92 --norc Do not read and execute the personal initialization file
94 ~/.bashrc if the shell is interactive. This option is on by
95 default if the shell is invoked as sh.
96 --posix
98 Change the behavior of bash where the default operation differs
99 from the POSIX standard to match the standard (posix mode).
100 --restricted
102 The shell becomes restricted (see RESTRICTED SHELL below).
103 --rpm-requires
105 Produce the list of files that are required for the shell script
106 to run. This implies '-n' and is subject to the same limita‐
107 tions as compile time error checking checking; Command substitu‐
108 tions, Conditional expressions and eval builtin are not parsed
109 so some dependencies may be missed.
110 --verbose
112 Equivalent to -v.
113 --version
115 Show version information for this instance of bash on the stan‐
116 dard output and exit successfully.
117
119 If arguments remain after option processing, and neither the -c nor the
120 -s option has been supplied, the first argument is assumed to be the
121 name of a file containing shell commands. If bash is invoked in this
122 fashion, $0 is set to the name of the file, and the positional parame‐
123 ters are set to the remaining arguments. Bash reads and executes com‐
124 mands from this file, then exits. Bash's exit status is the exit sta‐
125 tus of the last command executed in the script. If no commands are
126 executed, the exit status is 0. An attempt is first made to open the
127 file in the current directory, and, if no file is found, then the shell
128 searches the directories in PATH for the script.
129
131 A login shell is one whose first character of argument zero is a -, or
132 one started with the --login option.
133 An interactive shell is one started without non-option arguments and
135 without the -c option whose standard input and error are both connected
136 to terminals (as determined by isatty(3)), or one started with the -i
137 option. PS1 is set and $- includes i if bash is interactive, allowing
138 a shell script or a startup file to test this state.
139 The following paragraphs describe how bash executes its startup files.
141 If any of the files exist but cannot be read, bash reports an error.
142 Tildes are expanded in file names as described below under Tilde Expan‐
143 sion in the EXPANSION section.
144 When bash is invoked as an interactive login shell, or as a non-inter‐
146 active shell with the --login option, it first reads and executes com‐
147 mands from the file /etc/profile, if that file exists. After reading
148 that file, it looks for ~/.bash_profile, ~/.bash_login, and ~/.profile,
149 in that order, and reads and executes commands from the first one that
150 exists and is readable. The --noprofile option may be used when the
151 shell is started to inhibit this behavior.
152 When a login shell exits, bash reads and executes commands from the
154 files ~/.bash_logout and /etc/bash.bash_logout, if the files exists.
155 When an interactive shell that is not a login shell is started, bash
157 reads and executes commands from ~/.bashrc, if that file exists. This
158 may be inhibited by using the --norc option. The --rcfile file option
159 will force bash to read and execute commands from file instead of
160 ~/.bashrc.
161 When bash is started non-interactively, to run a shell script, for
163 example, it looks for the variable BASH_ENV in the environment, expands
164 its value if it appears there, and uses the expanded value as the name
165 of a file to read and execute. Bash behaves as if the following com‐
166 mand were executed:
167 if [ -n "$BASH_ENV" ]; then . "$BASH_ENV"; fi
168 but the value of the PATH variable is not used to search for the file
169 name.
170 If bash is invoked with the name sh, it tries to mimic the startup
172 behavior of historical versions of sh as closely as possible, while
173 conforming to the POSIX standard as well. When invoked as an interac‐
174 tive login shell, or a non-interactive shell with the --login option,
175 it first attempts to read and execute commands from /etc/profile and
176 ~/.profile, in that order. The --noprofile option may be used to
177 inhibit this behavior. When invoked as an interactive shell with the
178 name sh, bash looks for the variable ENV, expands its value if it is
179 defined, and uses the expanded value as the name of a file to read and
180 execute. Since a shell invoked as sh does not attempt to read and exe‐
181 cute commands from any other startup files, the --rcfile option has no
182 effect. A non-interactive shell invoked with the name sh does not
183 attempt to read any other startup files. When invoked as sh, bash
184 enters posix mode after the startup files are read.
185 When bash is started in posix mode, as with the --posix command line
187 option, it follows the POSIX standard for startup files. In this mode,
188 interactive shells expand the ENV variable and commands are read and
189 executed from the file whose name is the expanded value. No other
190 startup files are read.
191 Bash attempts to determine when it is being run with its standard input
193 connected to a network connection, as when executed by the remote shell
194 daemon, usually rshd, or the secure shell daemon sshd. If bash deter‐
195 mines it is being run in this fashion, it reads and executes commands
196 from ~/.bashrc, if that file exists and is readable. It will not do
197 this if invoked as sh. The --norc option may be used to inhibit this
198 behavior, and the --rcfile option may be used to force another file to
199 be read, but rshd does not generally invoke the shell with those
200 options or allow them to be specified.
201 If the shell is started with the effective user (group) id not equal to
203 the real user (group) id, and the -p option is not supplied, no startup
204 files are read, shell functions are not inherited from the environment,
205 the SHELLOPTS, BASHOPTS, CDPATH, and GLOBIGNORE variables, if they
206 appear in the environment, are ignored, and the effective user id is
207 set to the real user id. If the -p option is supplied at invocation,
208 the startup behavior is the same, but the effective user id is not
209 reset.
210
212 The following definitions are used throughout the rest of this docu‐
213 ment.
214 blank A space or tab.
215 word A sequence of characters considered as a single unit by the
216 shell. Also known as a token.
217 name A word consisting only of alphanumeric characters and under‐
218 scores, and beginning with an alphabetic character or an under‐
219 score. Also referred to as an identifier.
220 metacharacter
221 A character that, when unquoted, separates words. One of the
222 following:
223 | & ; ( ) < > space tab
224 control operator
225 A token that performs a control function. It is one of the fol‐
226 lowing symbols:
227 || & && ; ;; ( ) | |& <newline>
228
230 Reserved words are words that have a special meaning to the shell. The
231 following words are recognized as reserved when unquoted and either the
232 first word of a simple command (see SHELL GRAMMAR below) or the third
233 word of a case or for command:
234 ! case do done elif else esac fi for function if in select then until
236 while { } time [[ ]]
237
239 Simple Commands
240 A simple command is a sequence of optional variable assignments fol‐
241 lowed by blank-separated words and redirections, and terminated by a
242 control operator. The first word specifies the command to be executed,
243 and is passed as argument zero. The remaining words are passed as
244 arguments to the invoked command.
245 The return value of a simple command is its exit status, or 128+n if
247 the command is terminated by signal n.
248 Pipelines
250 A pipeline is a sequence of one or more commands separated by one of
251 the control operators | or |&. The format for a pipeline is:
252 [time [-p]] [ ! ] command [ [|⎪|&] command2 ... ]
254 The standard output of command is connected via a pipe to the standard
256 input of command2. This connection is performed before any redirec‐
257 tions specified by the command (see REDIRECTION below). If |& is used,
258 the standard error of command is connected to command2's standard input
259 through the pipe; it is shorthand for 2>&1 |. This implicit redirect‐
260 ion of the standard error is performed after any redirections specified
261 by the command.
262 The return status of a pipeline is the exit status of the last command,
264 unless the pipefail option is enabled. If pipefail is enabled, the
265 pipeline's return status is the value of the last (rightmost) command
266 to exit with a non-zero status, or zero if all commands exit success‐
267 fully. If the reserved word ! precedes a pipeline, the exit status of
268 that pipeline is the logical negation of the exit status as described
269 above. The shell waits for all commands in the pipeline to terminate
270 before returning a value.
271 If the time reserved word precedes a pipeline, the elapsed as well as
273 user and system time consumed by its execution are reported when the
274 pipeline terminates. The -p option changes the output format to that
275 specified by POSIX. When the shell is in posix mode, it does not rec‐
276 ognize time as a reserved word if the next token begins with a `-'.
277 The TIMEFORMAT variable may be set to a format string that specifies
278 how the timing information should be displayed; see the description of
279 TIMEFORMAT under Shell Variables below.
280 When the shell is in posix mode, time may be followed by a newline. In
282 this case, the shell displays the total user and system time consumed
283 by the shell and its children. The TIMEFORMAT variable may be used to
284 specify the format of the time information.
285 Each command in a pipeline is executed as a separate process (i.e., in
287 a subshell).
288 Lists
290 A list is a sequence of one or more pipelines separated by one of the
291 operators ;, &, &&, or ||, and optionally terminated by one of ;, &, or
292 <newline>.
293 Of these list operators, && and || have equal precedence, followed by ;
295 and &, which have equal precedence.
296 A sequence of one or more newlines may appear in a list instead of a
298 semicolon to delimit commands.
299 If a command is terminated by the control operator &, the shell exe‐
301 cutes the command in the background in a subshell. The shell does not
302 wait for the command to finish, and the return status is 0. Commands
303 separated by a ; are executed sequentially; the shell waits for each
304 command to terminate in turn. The return status is the exit status of
305 the last command executed.
306 AND and OR lists are sequences of one of more pipelines separated by
308 the && and || control operators, respectively. AND and OR lists are
309 executed with left associativity. An AND list has the form
310 command1 && command2
312 command2 is executed if, and only if, command1 returns an exit status
314 of zero.
315 An OR list has the form
317 command1 || command2
319 command2 is executed if and only if command1 returns a non-zero exit
321 status. The return status of AND and OR lists is the exit status of
322 the last command executed in the list.
323 Compound Commands
325 A compound command is one of the following:
326 (list) list is executed in a subshell environment (see COMMAND EXECU‐
328 TION ENVIRONMENT below). Variable assignments and builtin com‐
329 mands that affect the shell's environment do not remain in
330 effect after the command completes. The return status is the
331 exit status of list.
332 { list; }
334 list is simply executed in the current shell environment. list
335 must be terminated with a newline or semicolon. This is known
336 as a group command. The return status is the exit status of
337 list. Note that unlike the metacharacters ( and ), { and } are
338 reserved words and must occur where a reserved word is permitted
339 to be recognized. Since they do not cause a word break, they
340 must be separated from list by whitespace or another shell
341 metacharacter.
342 ((expression))
344 The expression is evaluated according to the rules described
345 below under ARITHMETIC EVALUATION. If the value of the expres‐
346 sion is non-zero, the return status is 0; otherwise the return
347 status is 1. This is exactly equivalent to let "expression".
348 [[ expression ]]
350 Return a status of 0 or 1 depending on the evaluation of the
351 conditional expression expression. Expressions are composed of
352 the primaries described below under CONDITIONAL EXPRESSIONS.
353 Word splitting and pathname expansion are not performed on the
354 words between the [[ and ]]; tilde expansion, parameter and
355 variable expansion, arithmetic expansion, command substitution,
356 process substitution, and quote removal are performed. Condi‐
357 tional operators such as -f must be unquoted to be recognized as
358 primaries.
359 When used with [[, the < and > operators sort lexicographically
361 using the current locale.
362 When the == and != operators are used, the string to the right
364 of the operator is considered a pattern and matched according to
365 the rules described below under Pattern Matching. If the shell
366 option nocasematch is enabled, the match is performed without
367 regard to the case of alphabetic characters. The return value
368 is 0 if the string matches (==) or does not match (!=) the pat‐
369 tern, and 1 otherwise. Any part of the pattern may be quoted to
370 force it to be matched as a string.
371 An additional binary operator, =~, is available, with the same
373 precedence as == and !=. When it is used, the string to the
374 right of the operator is considered an extended regular expres‐
375 sion and matched accordingly (as in regex(3)). The return value
376 is 0 if the string matches the pattern, and 1 otherwise. If the
377 regular expression is syntactically incorrect, the conditional
378 expression's return value is 2. If the shell option nocasematch
379 is enabled, the match is performed without regard to the case of
380 alphabetic characters. Any part of the pattern may be quoted to
381 force it to be matched as a string. Substrings matched by
382 parenthesized subexpressions within the regular expression are
383 saved in the array variable BASH_REMATCH. The element of
384 BASH_REMATCH with index 0 is the portion of the string matching
385 the entire regular expression. The element of BASH_REMATCH with
386 index n is the portion of the string matching the nth parenthe‐
387 sized subexpression.
388 Expressions may be combined using the following operators,
390 listed in decreasing order of precedence:
391 ( expression )
393 Returns the value of expression. This may be used to
394 override the normal precedence of operators.
395 ! expression
396 True if expression is false.
397 expression1 && expression2
398 True if both expression1 and expression2 are true.
399 expression1 || expression2
400 True if either expression1 or expression2 is true.
401 The && and || operators do not evaluate expression2 if the value
403 of expression1 is sufficient to determine the return value of
404 the entire conditional expression.
405 for name [ [ in [ word ... ] ] ; ] do list ; done
407 The list of words following in is expanded, generating a list of
408 items. The variable name is set to each element of this list in
409 turn, and list is executed each time. If the in word is omit‐
410 ted, the for command executes list once for each positional
411 parameter that is set (see PARAMETERS below). The return status
412 is the exit status of the last command that executes. If the
413 expansion of the items following in results in an empty list, no
414 commands are executed, and the return status is 0.
415 for (( expr1 ; expr2 ; expr3 )) ; do list ; done
417 First, the arithmetic expression expr1 is evaluated according to
418 the rules described below under ARITHMETIC EVALUATION. The
419 arithmetic expression expr2 is then evaluated repeatedly until
420 it evaluates to zero. Each time expr2 evaluates to a non-zero
421 value, list is executed and the arithmetic expression expr3 is
422 evaluated. If any expression is omitted, it behaves as if it
423 evaluates to 1. The return value is the exit status of the last
424 command in list that is executed, or false if any of the expres‐
425 sions is invalid.
426 select name [ in word ] ; do list ; done
428 The list of words following in is expanded, generating a list of
429 items. The set of expanded words is printed on the standard
430 error, each preceded by a number. If the in word is omitted,
431 the positional parameters are printed (see PARAMETERS below).
432 The PS3 prompt is then displayed and a line read from the stan‐
433 dard input. If the line consists of a number corresponding to
434 one of the displayed words, then the value of name is set to
435 that word. If the line is empty, the words and prompt are dis‐
436 played again. If EOF is read, the command completes. Any other
437 value read causes name to be set to null. The line read is
438 saved in the variable REPLY. The list is executed after each
439 selection until a break command is executed. The exit status of
440 select is the exit status of the last command executed in list,
441 or zero if no commands were executed.
442 case word in [ [(] pattern [ | pattern ] ... ) list ;; ] ... esac
444 A case command first expands word, and tries to match it against
445 each pattern in turn, using the same matching rules as for path‐
446 name expansion (see Pathname Expansion below). The word is
447 expanded using tilde expansion, parameter and variable expan‐
448 sion, arithmetic substitution, command substitution, process
449 substitution and quote removal. Each pattern examined is
450 expanded using tilde expansion, parameter and variable expan‐
451 sion, arithmetic substitution, command substitution, and process
452 substitution. If the shell option nocasematch is enabled, the
453 match is performed without regard to the case of alphabetic
454 characters. When a match is found, the corresponding list is
455 executed. If the ;; operator is used, no subsequent matches are
456 attempted after the first pattern match. Using ;& in place of
457 ;; causes execution to continue with the list associated with
458 the next set of patterns. Using ;;& in place of ;; causes the
459 shell to test the next pattern list in the statement, if any,
460 and execute any associated list on a successful match. The exit
461 status is zero if no pattern matches. Otherwise, it is the exit
462 status of the last command executed in list.
463 if list; then list; [ elif list; then list; ] ... [ else list; ] fi
465 The if list is executed. If its exit status is zero, the then
466 list is executed. Otherwise, each elif list is executed in
467 turn, and if its exit status is zero, the corresponding then
468 list is executed and the command completes. Otherwise, the else
469 list is executed, if present. The exit status is the exit sta‐
470 tus of the last command executed, or zero if no condition tested
471 true.
472 while list-1; do list-2; done
474 until list-1; do list-2; done
475 The while command continuously executes the list list-2 as long
476 as the last command in the list list-1 returns an exit status of
477 zero. The until command is identical to the while command,
478 except that the test is negated; list-2 is executed as long as
479 the last command in list-1 returns a non-zero exit status. The
480 exit status of the while and until commands is the exit status
481 of the last command executed in list-2, or zero if none was exe‐
482 cuted.
483 Coprocesses
485 A coprocess is a shell command preceded by the coproc reserved word. A
486 coprocess is executed asynchronously in a subshell, as if the command
487 had been terminated with the & control operator, with a two-way pipe
488 established between the executing shell and the coprocess.
489 The format for a coprocess is:
491 coproc [NAME] command [redirections]
493 This creates a coprocess named NAME. If NAME is not supplied, the
495 default name is COPROC. NAME must not be supplied if command is a sim‐
496 ple command (see above); otherwise, it is interpreted as the first word
497 of the simple command. When the coproc is executed, the shell creates
498 an array variable (see Arrays below) named NAME in the context of the
499 executing shell. The standard output of command is connected via a
500 pipe to a file descriptor in the executing shell, and that file
501 descriptor is assigned to NAME[0]. The standard input of command is
502 connected via a pipe to a file descriptor in the executing shell, and
503 that file descriptor is assigned to NAME[1]. This pipe is established
504 before any redirections specified by the command (see REDIRECTION
505 below). The file descriptors can be utilized as arguments to shell
506 commands and redirections using standard word expansions. The process
507 ID of the shell spawned to execute the coprocess is available as the
508 value of the variable NAME_PID. The wait builtin command may be used
509 to wait for the coprocess to terminate.
510 The return status of a coprocess is the exit status of command.
512 Shell Function Definitions
514 A shell function is an object that is called like a simple command and
515 executes a compound command with a new set of positional parameters.
516 Shell functions are declared as follows:
517 name () compound-command [redirection]
519 function name [()] compound-command [redirection]
520 This defines a function named name. The reserved word function
521 is optional. If the function reserved word is supplied, the
522 parentheses are optional. The body of the function is the com‐
523 pound command compound-command (see Compound Commands above).
524 That command is usually a list of commands between { and }, but
525 may be any command listed under Compound Commands above. com‐
526 pound-command is executed whenever name is specified as the name
527 of a simple command. Any redirections (see REDIRECTION below)
528 specified when a function is defined are performed when the
529 function is executed. The exit status of a function definition
530 is zero unless a syntax error occurs or a readonly function with
531 the same name already exists. When executed, the exit status of
532 a function is the exit status of the last command executed in
533 the body. (See FUNCTIONS below.)
534
536 In a non-interactive shell, or an interactive shell in which the inter‐
537 active_comments option to the shopt builtin is enabled (see SHELL
538 BUILTIN COMMANDS below), a word beginning with # causes that word and
539 all remaining characters on that line to be ignored. An interactive
540 shell without the interactive_comments option enabled does not allow
541 comments. The interactive_comments option is on by default in interac‐
542 tive shells.
543
545 Quoting is used to remove the special meaning of certain characters or
546 words to the shell. Quoting can be used to disable special treatment
547 for special characters, to prevent reserved words from being recognized
548 as such, and to prevent parameter expansion.
549 Each of the metacharacters listed above under DEFINITIONS has special
551 meaning to the shell and must be quoted if it is to represent itself.
552 When the command history expansion facilities are being used (see HIS‐
554 TORY EXPANSION below), the history expansion character, usually !, must
555 be quoted to prevent history expansion.
556 There are three quoting mechanisms: the escape character, single
558 quotes, and double quotes.
559 A non-quoted backslash (\) is the escape character. It preserves the
561 literal value of the next character that follows, with the exception of
562 <newline>. If a \<newline> pair appears, and the backslash is not
563 itself quoted, the \<newline> is treated as a line continuation (that
564 is, it is removed from the input stream and effectively ignored).
565 Enclosing characters in single quotes preserves the literal value of
567 each character within the quotes. A single quote may not occur between
568 single quotes, even when preceded by a backslash.
569 Enclosing characters in double quotes preserves the literal value of
571 all characters within the quotes, with the exception of $, `, \, and,
572 when history expansion is enabled, !. The characters $ and ` retain
573 their special meaning within double quotes. The backslash retains its
574 special meaning only when followed by one of the following characters:
575 $, `, ", \, or <newline>. A double quote may be quoted within double
576 quotes by preceding it with a backslash. If enabled, history expansion
577 will be performed unless an ! appearing in double quotes is escaped
578 using a backslash. The backslash preceding the ! is not removed.
579 The special parameters * and @ have special meaning when in double
581 quotes (see PARAMETERS below).
582 Words of the form $'string' are treated specially. The word expands to
584 string, with backslash-escaped characters replaced as specified by the
585 ANSI C standard. Backslash escape sequences, if present, are decoded
586 as follows:
587 \a alert (bell)
588 \b backspace
589 \e
590 \E an escape character
591 \f form feed
592 \n new line
593 \r carriage return
594 \t horizontal tab
595 \v vertical tab
596 \\ backslash
597 \' single quote
598 \" double quote
599 \nnn the eight-bit character whose value is the octal value
600 nnn (one to three digits)
601 \xHH the eight-bit character whose value is the hexadecimal
602 value HH (one or two hex digits)
603 \uHHHH the Unicode (ISO/IEC 10646) character whose value is the
604 hexadecimal value HHHH (one to four hex digits)
605 \UHHHHHHHH
606 the Unicode (ISO/IEC 10646) character whose value is the
607 hexadecimal value HHHHHHHH (one to eight hex digits)
608 \cx a control-x character
609 The expanded result is single-quoted, as if the dollar sign had not
611 been present.
612 A double-quoted string preceded by a dollar sign ($"string") will cause
614 the string to be translated according to the current locale. If the
615 current locale is C or POSIX, the dollar sign is ignored. If the
616 string is translated and replaced, the replacement is double-quoted.
617
619 A parameter is an entity that stores values. It can be a name, a num‐
620 ber, or one of the special characters listed below under Special Param‐
621 eters. A variable is a parameter denoted by a name. A variable has a
622 value and zero or more attributes. Attributes are assigned using the
623 declare builtin command (see declare below in SHELL BUILTIN COMMANDS).
624 A parameter is set if it has been assigned a value. The null string is
626 a valid value. Once a variable is set, it may be unset only by using
627 the unset builtin command (see SHELL BUILTIN COMMANDS below).
628 A variable may be assigned to by a statement of the form
630 name=[value]
632 If value is not given, the variable is assigned the null string. All
634 values undergo tilde expansion, parameter and variable expansion, com‐
635 mand substitution, arithmetic expansion, and quote removal (see EXPAN‐
636 SION below). If the variable has its integer attribute set, then value
637 is evaluated as an arithmetic expression even if the $((...)) expansion
638 is not used (see Arithmetic Expansion below). Word splitting is not
639 performed, with the exception of "$@" as explained below under Special
640 Parameters. Pathname expansion is not performed. Assignment state‐
641 ments may also appear as arguments to the alias, declare, typeset,
642 export, readonly, and local builtin commands.
643 In the context where an assignment statement is assigning a value to a
645 shell variable or array index, the += operator can be used to append to
646 or add to the variable's previous value. When += is applied to a vari‐
647 able for which the integer attribute has been set, value is evaluated
648 as an arithmetic expression and added to the variable's current value,
649 which is also evaluated. When += is applied to an array variable using
650 compound assignment (see Arrays below), the variable's value is not
651 unset (as it is when using =), and new values are appended to the array
652 beginning at one greater than the array's maximum index (for indexed
653 arrays) or added as additional key-value pairs in an associative array.
654 When applied to a string-valued variable, value is expanded and
655 appended to the variable's value.
656 Positional Parameters
658 A positional parameter is a parameter denoted by one or more digits,
659 other than the single digit 0. Positional parameters are assigned from
660 the shell's arguments when it is invoked, and may be reassigned using
661 the set builtin command. Positional parameters may not be assigned to
662 with assignment statements. The positional parameters are temporarily
663 replaced when a shell function is executed (see FUNCTIONS below).
664 When a positional parameter consisting of more than a single digit is
666 expanded, it must be enclosed in braces (see EXPANSION below).
667 Special Parameters
669 The shell treats several parameters specially. These parameters may
670 only be referenced; assignment to them is not allowed.
671 * Expands to the positional parameters, starting from one. When
672 the expansion occurs within double quotes, it expands to a sin‐
673 gle word with the value of each parameter separated by the first
674 character of the IFS special variable. That is, "$*" is equiva‐
675 lent to "$1c$2c...", where c is the first character of the value
676 of the IFS variable. If IFS is unset, the parameters are sepa‐
677 rated by spaces. If IFS is null, the parameters are joined
678 without intervening separators.
679 @ Expands to the positional parameters, starting from one. When
680 the expansion occurs within double quotes, each parameter
681 expands to a separate word. That is, "$@" is equivalent to "$1"
682 "$2" ... If the double-quoted expansion occurs within a word,
683 the expansion of the first parameter is joined with the begin‐
684 ning part of the original word, and the expansion of the last
685 parameter is joined with the last part of the original word.
686 When there are no positional parameters, "$@" and $@ expand to
687 nothing (i.e., they are removed).
688 # Expands to the number of positional parameters in decimal.
689 ? Expands to the exit status of the most recently executed fore‐
690 ground pipeline.
691 - Expands to the current option flags as specified upon invoca‐
692 tion, by the set builtin command, or those set by the shell
693 itself (such as the -i option).
694 $ Expands to the process ID of the shell. In a () subshell, it
695 expands to the process ID of the current shell, not the sub‐
696 shell.
697 ! Expands to the process ID of the most recently executed back‐
698 ground (asynchronous) command.
699 0 Expands to the name of the shell or shell script. This is set
700 at shell initialization. If bash is invoked with a file of com‐
701 mands, $0 is set to the name of that file. If bash is started
702 with the -c option, then $0 is set to the first argument after
703 the string to be executed, if one is present. Otherwise, it is
704 set to the file name used to invoke bash, as given by argument
705 zero.
706 _ At shell startup, set to the absolute pathname used to invoke
707 the shell or shell script being executed as passed in the envi‐
708 ronment or argument list. Subsequently, expands to the last
709 argument to the previous command, after expansion. Also set to
710 the full pathname used to invoke each command executed and
711 placed in the environment exported to that command. When check‐
712 ing mail, this parameter holds the name of the mail file cur‐
713 rently being checked.
714 Shell Variables
716 The following variables are set by the shell:
717 BASH Expands to the full file name used to invoke this instance of
719 bash.
720 BASHOPTS
721 A colon-separated list of enabled shell options. Each word in
722 the list is a valid argument for the -s option to the shopt
723 builtin command (see SHELL BUILTIN COMMANDS below). The options
724 appearing in BASHOPTS are those reported as on by shopt. If
725 this variable is in the environment when bash starts up, each
726 shell option in the list will be enabled before reading any
727 startup files. This variable is read-only.
728 BASHPID
729 Expands to the process ID of the current bash process. This
730 differs from $$ under certain circumstances, such as subshells
731 that do not require bash to be re-initialized.
732 BASH_ALIASES
733 An associative array variable whose members correspond to the
734 internal list of aliases as maintained by the alias builtin.
735 Elements added to this array appear in the alias list; unsetting
736 array elements cause aliases to be removed from the alias list.
737 BASH_ARGC
738 An array variable whose values are the number of parameters in
739 each frame of the current bash execution call stack. The number
740 of parameters to the current subroutine (shell function or
741 script executed with . or source) is at the top of the stack.
742 When a subroutine is executed, the number of parameters passed
743 is pushed onto BASH_ARGC. The shell sets BASH_ARGC only when in
744 extended debugging mode (see the description of the extdebug
745 option to the shopt builtin below)
746 BASH_ARGV
747 An array variable containing all of the parameters in the cur‐
748 rent bash execution call stack. The final parameter of the last
749 subroutine call is at the top of the stack; the first parameter
750 of the initial call is at the bottom. When a subroutine is exe‐
751 cuted, the parameters supplied are pushed onto BASH_ARGV. The
752 shell sets BASH_ARGV only when in extended debugging mode (see
753 the description of the extdebug option to the shopt builtin
754 below)
755 BASH_CMDS
756 An associative array variable whose members correspond to the
757 internal hash table of commands as maintained by the hash
758 builtin. Elements added to this array appear in the hash table;
759 unsetting array elements cause commands to be removed from the
760 hash table.
761 BASH_COMMAND
762 The command currently being executed or about to be executed,
763 unless the shell is executing a command as the result of a trap,
764 in which case it is the command executing at the time of the
765 trap.
766 BASH_EXECUTION_STRING
767 The command argument to the -c invocation option.
768 BASH_LINENO
769 An array variable whose members are the line numbers in source
770 files where each corresponding member of FUNCNAME was invoked.
771 ${BASH_LINENO[$i]} is the line number in the source file
772 (${BASH_SOURCE[$i+1]}) where ${FUNCNAME[$i]} was called (or
773 ${BASH_LINENO[$i-1]} if referenced within another shell func‐
774 tion). Use LINENO to obtain the current line number.
775 BASH_REMATCH
776 An array variable whose members are assigned by the =~ binary
777 operator to the [[ conditional command. The element with index
778 0 is the portion of the string matching the entire regular
779 expression. The element with index n is the portion of the
780 string matching the nth parenthesized subexpression. This vari‐
781 able is read-only.
782 BASH_SOURCE
783 An array variable whose members are the source filenames where
784 the corresponding shell function names in the FUNCNAME array
785 variable are defined. The shell function ${FUNCNAME[$i]} is
786 defined in the file ${BASH_SOURCE[$i]} and called from
787 ${BASH_SOURCE[$i+1]}.
788 BASH_SUBSHELL
789 Incremented by one each time a subshell or subshell environment
790 is spawned. The initial value is 0.
791 BASH_VERSINFO
792 A readonly array variable whose members hold version information
793 for this instance of bash. The values assigned to the array
794 members are as follows:
795 BASH_VERSINFO[0] The major version number (the release).
796 BASH_VERSINFO[1] The minor version number (the version).
797 BASH_VERSINFO[2] The patch level.
798 BASH_VERSINFO[3] The build version.
799 BASH_VERSINFO[4] The release status (e.g., beta1).
800 BASH_VERSINFO[5] The value of MACHTYPE.
801 BASH_VERSION
802 Expands to a string describing the version of this instance of
803 bash.
804 COMP_CWORD
805 An index into ${COMP_WORDS} of the word containing the current
806 cursor position. This variable is available only in shell func‐
807 tions invoked by the programmable completion facilities (see
808 Programmable Completion below).
809 COMP_KEY
810 The key (or final key of a key sequence) used to invoke the cur‐
811 rent completion function.
812 COMP_LINE
813 The current command line. This variable is available only in
814 shell functions and external commands invoked by the program‐
815 mable completion facilities (see Programmable Completion below).
816 COMP_POINT
817 The index of the current cursor position relative to the begin‐
818 ning of the current command. If the current cursor position is
819 at the end of the current command, the value of this variable is
820 equal to ${#COMP_LINE}. This variable is available only in
821 shell functions and external commands invoked by the program‐
822 mable completion facilities (see Programmable Completion below).
823 COMP_TYPE
824 Set to an integer value corresponding to the type of completion
825 attempted that caused a completion function to be called: TAB,
826 for normal completion, ?, for listing completions after succes‐
827 sive tabs, !, for listing alternatives on partial word comple‐
828 tion, @, to list completions if the word is not unmodified, or
829 %, for menu completion. This variable is available only in
830 shell functions and external commands invoked by the program‐
831 mable completion facilities (see Programmable Completion below).
832 COMP_WORDBREAKS
833 The set of characters that the readline library treats as word
834 separators when performing word completion. If COMP_WORDBREAKS
835 is unset, it loses its special properties, even if it is subse‐
836 quently reset.
837 COMP_WORDS
838 An array variable (see Arrays below) consisting of the individ‐
839 ual words in the current command line. The line is split into
840 words as readline would split it, using COMP_WORDBREAKS as
841 described above. This variable is available only in shell func‐
842 tions invoked by the programmable completion facilities (see
843 Programmable Completion below).
844 COPROC An array variable (see Arrays below) created to hold the file
845 descriptors for output from and input to an unnamed coprocess
846 (see Coprocesses above).
847 DIRSTACK
848 An array variable (see Arrays below) containing the current con‐
849 tents of the directory stack. Directories appear in the stack
850 in the order they are displayed by the dirs builtin. Assigning
851 to members of this array variable may be used to modify directo‐
852 ries already in the stack, but the pushd and popd builtins must
853 be used to add and remove directories. Assignment to this vari‐
854 able will not change the current directory. If DIRSTACK is
855 unset, it loses its special properties, even if it is subse‐
856 quently reset.
857 EUID Expands to the effective user ID of the current user, initial‐
858 ized at shell startup. This variable is readonly.
859 FUNCNAME
860 An array variable containing the names of all shell functions
861 currently in the execution call stack. The element with index 0
862 is the name of any currently-executing shell function. The bot‐
863 tom-most element (the one with the highest index) is "main".
864 This variable exists only when a shell function is executing.
865 Assignments to FUNCNAME have no effect and return an error sta‐
866 tus. If FUNCNAME is unset, it loses its special properties,
867 even if it is subsequently reset.
868 This variable can be used with BASH_LINENO and BASH_SOURCE.
870 Each element of FUNCNAME has corresponding elements in
871 BASH_LINENO and BASH_SOURCE to describe the call stack. For
872 instance, ${FUNCNAME[$i]} was called from the file
873 ${BASH_SOURCE[$i+1]} at line number ${BASH_LINENO[$i]}. The
874 caller builtin displays the current call stack using this infor‐
875 mation.
876 GROUPS An array variable containing the list of groups of which the
877 current user is a member. Assignments to GROUPS have no effect
878 and return an error status. If GROUPS is unset, it loses its
879 special properties, even if it is subsequently reset.
880 HISTCMD
881 The history number, or index in the history list, of the current
882 command. If HISTCMD is unset, it loses its special properties,
883 even if it is subsequently reset.
884 HOSTNAME
885 Automatically set to the name of the current host.
886 HOSTTYPE
887 Automatically set to a string that uniquely describes the type
888 of machine on which bash is executing. The default is system-
889 dependent.
890 LINENO Each time this parameter is referenced, the shell substitutes a
891 decimal number representing the current sequential line number
892 (starting with 1) within a script or function. When not in a
893 script or function, the value substituted is not guaranteed to
894 be meaningful. If LINENO is unset, it loses its special proper‐
895 ties, even if it is subsequently reset.
896 MACHTYPE
897 Automatically set to a string that fully describes the system
898 type on which bash is executing, in the standard GNU cpu-com‐
899 pany-system format. The default is system-dependent.
900 MAPFILE
901 An array variable (see Arrays below) created to hold the text
902 read by the mapfile builtin when no variable name is supplied.
903 OLDPWD The previous working directory as set by the cd command.
904 OPTARG The value of the last option argument processed by the getopts
905 builtin command (see SHELL BUILTIN COMMANDS below).
906 OPTIND The index of the next argument to be processed by the getopts
907 builtin command (see SHELL BUILTIN COMMANDS below).
908 OSTYPE Automatically set to a string that describes the operating sys‐
909 tem on which bash is executing. The default is system-depen‐
910 dent.
911 PIPESTATUS
912 An array variable (see Arrays below) containing a list of exit
913 status values from the processes in the most-recently-executed
914 foreground pipeline (which may contain only a single command).
915 PPID The process ID of the shell's parent. This variable is read‐
916 only.
917 PWD The current working directory as set by the cd command.
918 RANDOM Each time this parameter is referenced, a random integer between
919 0 and 32767 is generated. The sequence of random numbers may be
920 initialized by assigning a value to RANDOM. If RANDOM is unset,
921 it loses its special properties, even if it is subsequently
922 reset.
923 READLINE_LINE
924 The contents of the readline line buffer, for use with "bind -x"
925 (see SHELL BUILTIN COMMANDS below).
926 READLINE_POINT
927 The position of the insertion point in the readline line buffer,
928 for use with "bind -x" (see SHELL BUILTIN COMMANDS below).
929 REPLY Set to the line of input read by the read builtin command when
930 no arguments are supplied.
931 SECONDS
932 Each time this parameter is referenced, the number of seconds
933 since shell invocation is returned. If a value is assigned to
934 SECONDS, the value returned upon subsequent references is the
935 number of seconds since the assignment plus the value assigned.
936 If SECONDS is unset, it loses its special properties, even if it
937 is subsequently reset.
938 SHELLOPTS
939 A colon-separated list of enabled shell options. Each word in
940 the list is a valid argument for the -o option to the set
941 builtin command (see SHELL BUILTIN COMMANDS below). The options
942 appearing in SHELLOPTS are those reported as on by set -o. If
943 this variable is in the environment when bash starts up, each
944 shell option in the list will be enabled before reading any
945 startup files. This variable is read-only.
946 SHLVL Incremented by one each time an instance of bash is started.
947 UID Expands to the user ID of the current user, initialized at shell
948 startup. This variable is readonly.
949 The following variables are used by the shell. In some cases, bash
951 assigns a default value to a variable; these cases are noted below.
952 BASH_ENV
954 If this parameter is set when bash is executing a shell script,
955 its value is interpreted as a filename containing commands to
956 initialize the shell, as in ~/.bashrc. The value of BASH_ENV is
957 subjected to parameter expansion, command substitution, and
958 arithmetic expansion before being interpreted as a file name.
959 PATH is not used to search for the resultant file name.
960 BASH_XTRACEFD
961 If set to an integer corresponding to a valid file descriptor,
962 bash will write the trace output generated when set -x is
963 enabled to that file descriptor. The file descriptor is closed
964 when BASH_XTRACEFD is unset or assigned a new value. Unsetting
965 BASH_XTRACEFD or assigning it the empty string causes the trace
966 output to be sent to the standard error. Note that setting
967 BASH_XTRACEFD to 2 (the standard error file descriptor) and then
968 unsetting it will result in the standard error being closed.
969 CDPATH The search path for the cd command. This is a colon-separated
970 list of directories in which the shell looks for destination
971 directories specified by the cd command. A sample value is
972 ".:~:/usr".
973 COLUMNS
974 Used by the select compound command to determine the terminal
975 width when printing selection lists. Automatically set upon
976 receipt of a SIGWINCH.
977 COMPREPLY
978 An array variable from which bash reads the possible completions
979 generated by a shell function invoked by the programmable com‐
980 pletion facility (see Programmable Completion below).
981 EMACS If bash finds this variable in the environment when the shell
982 starts with value "t", it assumes that the shell is running in
983 an Emacs shell buffer and disables line editing.
984 ENV Similar to BASH_ENV; used when the shell is invoked in POSIX
985 mode.
986 FCEDIT The default editor for the fc builtin command.
987 FIGNORE
988 A colon-separated list of suffixes to ignore when performing
989 filename completion (see READLINE below). A filename whose suf‐
990 fix matches one of the entries in FIGNORE is excluded from the
991 list of matched filenames. A sample value is ".o:~".
992 FUNCNEST
993 If set to a numeric value greater than 0, defines a maximum
994 function nesting level. Function invocations that exceed this
995 nesting level will cause the current command to abort.
996 GLOBIGNORE
997 A colon-separated list of patterns defining the set of filenames
998 to be ignored by pathname expansion. If a filename matched by a
999 pathname expansion pattern also matches one of the patterns in
1000 GLOBIGNORE, it is removed from the list of matches.
1001 HISTCONTROL
1002 A colon-separated list of values controlling how commands are
1003 saved on the history list. If the list of values includes
1004 ignorespace, lines which begin with a space character are not
1005 saved in the history list. A value of ignoredups causes lines
1006 matching the previous history entry to not be saved. A value of
1007 ignoreboth is shorthand for ignorespace and ignoredups. A value
1008 of erasedups causes all previous lines matching the current line
1009 to be removed from the history list before that line is saved.
1010 Any value not in the above list is ignored. If HISTCONTROL is
1011 unset, or does not include a valid value, all lines read by the
1012 shell parser are saved on the history list, subject to the value
1013 of HISTIGNORE. The second and subsequent lines of a multi-line
1014 compound command are not tested, and are added to the history
1015 regardless of the value of HISTCONTROL.
1016 HISTFILE
1017 The name of the file in which command history is saved (see HIS‐
1018 TORY below). The default value is ~/.bash_history. If unset,
1019 the command history is not saved when an interactive shell
1020 exits.
1021 HISTFILESIZE
1022 The maximum number of lines contained in the history file. When
1023 this variable is assigned a value, the history file is trun‐
1024 cated, if necessary, by removing the oldest entries, to contain
1025 no more than that number of lines. The default value is 500.
1026 The history file is also truncated to this size after writing it
1027 when an interactive shell exits.
1028 HISTIGNORE
1029 A colon-separated list of patterns used to decide which command
1030 lines should be saved on the history list. Each pattern is
1031 anchored at the beginning of the line and must match the com‐
1032 plete line (no implicit `*' is appended). Each pattern is
1033 tested against the line after the checks specified by HISTCON‐
1034 TROL are applied. In addition to the normal shell pattern
1035 matching characters, `&' matches the previous history line. `&'
1036 may be escaped using a backslash; the backslash is removed
1037 before attempting a match. The second and subsequent lines of a
1038 multi-line compound command are not tested, and are added to the
1039 history regardless of the value of HISTIGNORE.
1040 HISTSIZE
1041 The number of commands to remember in the command history (see
1042 HISTORY below). The default value is 500.
1043 HISTTIMEFORMAT
1044 If this variable is set and not null, its value is used as a
1045 format string for strftime(3) to print the time stamp associated
1046 with each history entry displayed by the history builtin. If
1047 this variable is set, time stamps are written to the history
1048 file so they may be preserved across shell sessions. This uses
1049 the history comment character to distinguish timestamps from
1050 other history lines.
1051 HOME The home directory of the current user; the default argument for
1052 the cd builtin command. The value of this variable is also used
1053 when performing tilde expansion.
1054 HOSTFILE
1055 Contains the name of a file in the same format as /etc/hosts
1056 that should be read when the shell needs to complete a hostname.
1057 The list of possible hostname completions may be changed while
1058 the shell is running; the next time hostname completion is
1059 attempted after the value is changed, bash adds the contents of
1060 the new file to the existing list. If HOSTFILE is set, but has
1061 no value, or does not name a readable file, bash attempts to
1062 read /etc/hosts to obtain the list of possible hostname comple‐
1063 tions. When HOSTFILE is unset, the hostname list is cleared.
1064 IFS The Internal Field Separator that is used for word splitting
1065 after expansion and to split lines into words with the read
1066 builtin command. The default value is ``<space><tab><new‐
1067 line>''.
1068 IGNOREEOF
1069 Controls the action of an interactive shell on receipt of an EOF
1070 character as the sole input. If set, the value is the number of
1071 consecutive EOF characters which must be typed as the first
1072 characters on an input line before bash exits. If the variable
1073 exists but does not have a numeric value, or has no value, the
1074 default value is 10. If it does not exist, EOF signifies the
1075 end of input to the shell.
1076 INPUTRC
1077 The filename for the readline startup file, overriding the
1078 default of ~/.inputrc (see READLINE below).
1079 LANG Used to determine the locale category for any category not
1080 specifically selected with a variable starting with LC_.
1081 LC_ALL This variable overrides the value of LANG and any other LC_
1082 variable specifying a locale category.
1083 LC_COLLATE
1084 This variable determines the collation order used when sorting
1085 the results of pathname expansion, and determines the behavior
1086 of range expressions, equivalence classes, and collating
1087 sequences within pathname expansion and pattern matching.
1088 LC_CTYPE
1089 This variable determines the interpretation of characters and
1090 the behavior of character classes within pathname expansion and
1091 pattern matching.
1092 LC_MESSAGES
1093 This variable determines the locale used to translate double-
1094 quoted strings preceded by a $.
1095 LC_NUMERIC
1096 This variable determines the locale category used for number
1097 formatting.
1098 LINES Used by the select compound command to determine the column
1099 length for printing selection lists. Automatically set upon
1100 receipt of a SIGWINCH.
1101 MAIL If this parameter is set to a file or directory name and the
1102 MAILPATH variable is not set, bash informs the user of the
1103 arrival of mail in the specified file or Maildir-format direc‐
1104 tory.
1105 MAILCHECK
1106 Specifies how often (in seconds) bash checks for mail. The
1107 default is 60 seconds. When it is time to check for mail, the
1108 shell does so before displaying the primary prompt. If this
1109 variable is unset, or set to a value that is not a number
1110 greater than or equal to zero, the shell disables mail checking.
1111 MAILPATH
1112 A colon-separated list of file names to be checked for mail.
1113 The message to be printed when mail arrives in a particular file
1114 may be specified by separating the file name from the message
1115 with a `?'. When used in the text of the message, $_ expands to
1116 the name of the current mailfile. Example:
1117 MAILPATH='/var/mail/bfox?"You have mail":~/shell-mail?"$_ has
1118 mail!"'
1119 Bash supplies a default value for this variable, but the loca‐
1120 tion of the user mail files that it uses is system dependent
1121 (e.g., /var/mail/$USER).
1122 OPTERR If set to the value 1, bash displays error messages generated by
1123 the getopts builtin command (see SHELL BUILTIN COMMANDS below).
1124 OPTERR is initialized to 1 each time the shell is invoked or a
1125 shell script is executed.
1126 PATH The search path for commands. It is a colon-separated list of
1127 directories in which the shell looks for commands (see COMMAND
1128 EXECUTION below). A zero-length (null) directory name in the
1129 value of PATH indicates the current directory. A null directory
1130 name may appear as two adjacent colons, or as an initial or
1131 trailing colon. The default path is system-dependent, and is
1132 set by the administrator who installs bash. A common value is
1133 ``/usr/gnu/bin:/usr/local/bin:/usr/ucb:/bin:/usr/bin''.
1134 POSIXLY_CORRECT
1135 If this variable is in the environment when bash starts, the
1136 shell enters posix mode before reading the startup files, as if
1137 the --posix invocation option had been supplied. If it is set
1138 while the shell is running, bash enables posix mode, as if the
1139 command set -o posix had been executed.
1140 PROMPT_COMMAND
1141 If set, the value is executed as a command prior to issuing each
1142 primary prompt.
1143 PROMPT_DIRTRIM
1144 If set to a number greater than zero, the value is used as the
1145 number of trailing directory components to retain when expanding
1146 the \w and \W prompt string escapes (see PROMPTING below).
1147 Characters removed are replaced with an ellipsis.
1148 PS1 The value of this parameter is expanded (see PROMPTING below)
1149 and used as the primary prompt string. The default value is
1150 ``\s-\v\$ ''.
1151 PS2 The value of this parameter is expanded as with PS1 and used as
1152 the secondary prompt string. The default is ``> ''.
1153 PS3 The value of this parameter is used as the prompt for the select
1154 command (see SHELL GRAMMAR above).
1155 PS4 The value of this parameter is expanded as with PS1 and the
1156 value is printed before each command bash displays during an
1157 execution trace. The first character of PS4 is replicated mul‐
1158 tiple times, as necessary, to indicate multiple levels of indi‐
1159 rection. The default is ``+ ''.
1160 SHELL The full pathname to the shell is kept in this environment vari‐
1161 able. If it is not set when the shell starts, bash assigns to
1162 it the full pathname of the current user's login shell.
1163 TIMEFORMAT
1164 The value of this parameter is used as a format string specify‐
1165 ing how the timing information for pipelines prefixed with the
1166 time reserved word should be displayed. The % character intro‐
1167 duces an escape sequence that is expanded to a time value or
1168 other information. The escape sequences and their meanings are
1169 as follows; the braces denote optional portions.
1170 %% A literal %.
1171 %[p][l]R The elapsed time in seconds.
1172 %[p][l]U The number of CPU seconds spent in user mode.
1173 %[p][l]S The number of CPU seconds spent in system mode.
1174 %P The CPU percentage, computed as (%U + %S) / %R.
1175 The optional p is a digit specifying the precision, the number
1177 of fractional digits after a decimal point. A value of 0 causes
1178 no decimal point or fraction to be output. At most three places
1179 after the decimal point may be specified; values of p greater
1180 than 3 are changed to 3. If p is not specified, the value 3 is
1181 used.
1182 The optional l specifies a longer format, including minutes, of
1184 the form MMmSS.FFs. The value of p determines whether or not
1185 the fraction is included.
1186 If this variable is not set, bash acts as if it had the value
1188 $'\nreal\t%3lR\nuser\t%3lU\nsys%3lS'. If the value is null, no
1189 timing information is displayed. A trailing newline is added
1190 when the format string is displayed.
1191 TMOUT If set to a value greater than zero, TMOUT is treated as the
1192 default timeout for the read builtin. The select command termi‐
1193 nates if input does not arrive after TMOUT seconds when input is
1194 coming from a terminal. In an interactive shell, the value is
1195 interpreted as the number of seconds to wait for input after
1196 issuing the primary prompt. Bash terminates after waiting for
1197 that number of seconds if input does not arrive.
1198 TMPDIR If set, bash uses its value as the name of a directory in which
1199 bash creates temporary files for the shell's use.
1200 auto_resume
1201 This variable controls how the shell interacts with the user and
1202 job control. If this variable is set, single word simple com‐
1203 mands without redirections are treated as candidates for resump‐
1204 tion of an existing stopped job. There is no ambiguity allowed;
1205 if there is more than one job beginning with the string typed,
1206 the job most recently accessed is selected. The name of a
1207 stopped job, in this context, is the command line used to start
1208 it. If set to the value exact, the string supplied must match
1209 the name of a stopped job exactly; if set to substring, the
1210 string supplied needs to match a substring of the name of a
1211 stopped job. The substring value provides functionality analo‐
1212 gous to the %? job identifier (see JOB CONTROL below). If set
1213 to any other value, the supplied string must be a prefix of a
1214 stopped job's name; this provides functionality analogous to the
1215 %string job identifier.
1216 histchars
1217 The two or three characters which control history expansion and
1218 tokenization (see HISTORY EXPANSION below). The first character
1219 is the history expansion character, the character which signals
1220 the start of a history expansion, normally `!'. The second
1221 character is the quick substitution character, which is used as
1222 shorthand for re-running the previous command entered, substi‐
1223 tuting one string for another in the command. The default is
1224 `^'. The optional third character is the character which indi‐
1225 cates that the remainder of the line is a comment when found as
1226 the first character of a word, normally `#'. The history com‐
1227 ment character causes history substitution to be skipped for the
1228 remaining words on the line. It does not necessarily cause the
1229 shell parser to treat the rest of the line as a comment.
1230 Arrays
1232 Bash provides one-dimensional indexed and associative array variables.
1233 Any variable may be used as an indexed array; the declare builtin will
1234 explicitly declare an array. There is no maximum limit on the size of
1235 an array, nor any requirement that members be indexed or assigned con‐
1236 tiguously. Indexed arrays are referenced using integers (including
1237 arithmetic expressions) and are zero-based; associative arrays are
1238 referenced using arbitrary strings.
1239 An indexed array is created automatically if any variable is assigned
1241 to using the syntax name[subscript]=value. The subscript is treated as
1242 an arithmetic expression that must evaluate to a number. If subscript
1243 evaluates to a number less than zero, it is used as an offset from one
1244 greater than the array's maximum index (so a subcript of -1 refers to
1245 the last element of the array). To explicitly declare an indexed
1246 array, use declare -a name (see SHELL BUILTIN COMMANDS below). declare
1247 -a name[subscript] is also accepted; the subscript is ignored.
1248 Associative arrays are created using declare -A name.
1250 Attributes may be specified for an array variable using the declare and
1252 readonly builtins. Each attribute applies to all members of an array.
1253 Arrays are assigned to using compound assignments of the form
1255 name=(value1 ... valuen), where each value is of the form [sub‐
1256 script]=string. Indexed array assignments do not require the bracket
1257 and subscript. When assigning to indexed arrays, if the optional
1258 brackets and subscript are supplied, that index is assigned to; other‐
1259 wise the index of the element assigned is the last index assigned to by
1260 the statement plus one. Indexing starts at zero.
1261 When assigning to an associative array, the subscript is required.
1263 This syntax is also accepted by the declare builtin. Individual array
1265 elements may be assigned to using the name[subscript]=value syntax
1266 introduced above.
1267 Any element of an array may be referenced using ${name[subscript]}.
1269 The braces are required to avoid conflicts with pathname expansion. If
1270 subscript is @ or *, the word expands to all members of name. These
1271 subscripts differ only when the word appears within double quotes. If
1272 the word is double-quoted, ${name[*]} expands to a single word with the
1273 value of each array member separated by the first character of the IFS
1274 special variable, and ${name[@]} expands each element of name to a sep‐
1275 arate word. When there are no array members, ${name[@]} expands to
1276 nothing. If the double-quoted expansion occurs within a word, the
1277 expansion of the first parameter is joined with the beginning part of
1278 the original word, and the expansion of the last parameter is joined
1279 with the last part of the original word. This is analogous to the
1280 expansion of the special parameters * and @ (see Special Parameters
1281 above). ${#name[subscript]} expands to the length of ${name[sub‐
1282 script]}. If subscript is * or @, the expansion is the number of ele‐
1283 ments in the array. Referencing an array variable without a subscript
1284 is equivalent to referencing the array with a subscript of 0.
1285 An array variable is considered set if a subscript has been assigned a
1287 value. The null string is a valid value.
1288 The unset builtin is used to destroy arrays. unset name[subscript]
1290 destroys the array element at index subscript. Care must be taken to
1291 avoid unwanted side effects caused by pathname expansion. unset name,
1292 where name is an array, or unset name[subscript], where subscript is *
1293 or @, removes the entire array.
1294 The declare, local, and readonly builtins each accept a -a option to
1296 specify an indexed array and a -A option to specify an associative
1297 array. If both options are supplied, -A takes precedence. The read
1298 builtin accepts a -a option to assign a list of words read from the
1299 standard input to an array. The set and declare builtins display array
1300 values in a way that allows them to be reused as assignments.
1301
1303 Expansion is performed on the command line after it has been split into
1304 words. There are seven kinds of expansion performed: brace expansion,
1305 tilde expansion, parameter and variable expansion, command substitu‐
1306 tion, arithmetic expansion, word splitting, and pathname expansion.
1307 The order of expansions is: brace expansion, tilde expansion, parame‐
1309 ter, variable and arithmetic expansion and command substitution (done
1310 in a left-to-right fashion), word splitting, and pathname expansion.
1311 On systems that can support it, there is an additional expansion avail‐
1313 able: process substitution.
1314 Only brace expansion, word splitting, and pathname expansion can change
1316 the number of words of the expansion; other expansions expand a single
1317 word to a single word. The only exceptions to this are the expansions
1318 of "$@" and "${name[@]}" as explained above (see PARAMETERS).
1319 Brace Expansion
1321 Brace expansion is a mechanism by which arbitrary strings may be gener‐
1322 ated. This mechanism is similar to pathname expansion, but the file‐
1323 names generated need not exist. Patterns to be brace expanded take the
1324 form of an optional preamble, followed by either a series of comma-sep‐
1325 arated strings or a sequence expression between a pair of braces, fol‐
1326 lowed by an optional postscript. The preamble is prefixed to each
1327 string contained within the braces, and the postscript is then appended
1328 to each resulting string, expanding left to right.
1329 Brace expansions may be nested. The results of each expanded string
1331 are not sorted; left to right order is preserved. For example,
1332 a{d,c,b}e expands into `ade ace abe'.
1333 A sequence expression takes the form {x..y[..incr]}, where x and y are
1335 either integers or single characters, and incr, an optional increment,
1336 is an integer. When integers are supplied, the expression expands to
1337 each number between x and y, inclusive. Supplied integers may be pre‐
1338 fixed with 0 to force each term to have the same width. When either x
1339 or y begins with a zero, the shell attempts to force all generated
1340 terms to contain the same number of digits, zero-padding where neces‐
1341 sary. When characters are supplied, the expression expands to each
1342 character lexicographically between x and y, inclusive. Note that both
1343 x and y must be of the same type. When the increment is supplied, it
1344 is used as the difference between each term. The default increment is
1345 1 or -1 as appropriate.
1346 Brace expansion is performed before any other expansions, and any char‐
1348 acters special to other expansions are preserved in the result. It is
1349 strictly textual. Bash does not apply any syntactic interpretation to
1350 the context of the expansion or the text between the braces.
1351 A correctly-formed brace expansion must contain unquoted opening and
1353 closing braces, and at least one unquoted comma or a valid sequence
1354 expression. Any incorrectly formed brace expansion is left unchanged.
1355 A { or , may be quoted with a backslash to prevent its being considered
1356 part of a brace expression. To avoid conflicts with parameter expan‐
1357 sion, the string ${ is not considered eligible for brace expansion.
1358 This construct is typically used as shorthand when the common prefix of
1360 the strings to be generated is longer than in the above example:
1361 mkdir /usr/local/src/bash/{old,new,dist,bugs}
1363 or
1364 chown root /usr/{ucb/{ex,edit},lib/{ex?.?*,how_ex}}
1365 Brace expansion introduces a slight incompatibility with historical
1367 versions of sh. sh does not treat opening or closing braces specially
1368 when they appear as part of a word, and preserves them in the output.
1369 Bash removes braces from words as a consequence of brace expansion.
1370 For example, a word entered to sh as file{1,2} appears identically in
1371 the output. The same word is output as file1 file2 after expansion by
1372 bash. If strict compatibility with sh is desired, start bash with the
1373 +B option or disable brace expansion with the +B option to the set com‐
1374 mand (see SHELL BUILTIN COMMANDS below).
1375 Tilde Expansion
1377 If a word begins with an unquoted tilde character (`~'), all of the
1378 characters preceding the first unquoted slash (or all characters, if
1379 there is no unquoted slash) are considered a tilde-prefix. If none of
1380 the characters in the tilde-prefix are quoted, the characters in the
1381 tilde-prefix following the tilde are treated as a possible login name.
1382 If this login name is the null string, the tilde is replaced with the
1383 value of the shell parameter HOME. If HOME is unset, the home direc‐
1384 tory of the user executing the shell is substituted instead. Other‐
1385 wise, the tilde-prefix is replaced with the home directory associated
1386 with the specified login name.
1387 If the tilde-prefix is a `~+', the value of the shell variable PWD
1389 replaces the tilde-prefix. If the tilde-prefix is a `~-', the value of
1390 the shell variable OLDPWD, if it is set, is substituted. If the char‐
1391 acters following the tilde in the tilde-prefix consist of a number N,
1392 optionally prefixed by a `+' or a `-', the tilde-prefix is replaced
1393 with the corresponding element from the directory stack, as it would be
1394 displayed by the dirs builtin invoked with the tilde-prefix as an argu‐
1395 ment. If the characters following the tilde in the tilde-prefix con‐
1396 sist of a number without a leading `+' or `-', `+' is assumed.
1397 If the login name is invalid, or the tilde expansion fails, the word is
1399 unchanged.
1400 Each variable assignment is checked for unquoted tilde-prefixes immedi‐
1402 ately following a : or the first =. In these cases, tilde expansion is
1403 also performed. Consequently, one may use file names with tildes in
1404 assignments to PATH, MAILPATH, and CDPATH, and the shell assigns the
1405 expanded value.
1406 Parameter Expansion
1408 The `$' character introduces parameter expansion, command substitution,
1409 or arithmetic expansion. The parameter name or symbol to be expanded
1410 may be enclosed in braces, which are optional but serve to protect the
1411 variable to be expanded from characters immediately following it which
1412 could be interpreted as part of the name.
1413 When braces are used, the matching ending brace is the first `}' not
1415 escaped by a backslash or within a quoted string, and not within an
1416 embedded arithmetic expansion, command substitution, or parameter
1417 expansion.
1418 ${parameter}
1420 The value of parameter is substituted. The braces are required
1421 when parameter is a positional parameter with more than one
1422 digit, or when parameter is followed by a character which is not
1423 to be interpreted as part of its name.
1424 If the first character of parameter is an exclamation point (!), a
1426 level of variable indirection is introduced. Bash uses the value of
1427 the variable formed from the rest of parameter as the name of the vari‐
1428 able; this variable is then expanded and that value is used in the rest
1429 of the substitution, rather than the value of parameter itself. This
1430 is known as indirect expansion. The exceptions to this are the expan‐
1431 sions of ${!prefix*} and ${!name[@]} described below. The exclamation
1432 point must immediately follow the left brace in order to introduce
1433 indirection.
1434 In each of the cases below, word is subject to tilde expansion, parame‐
1436 ter expansion, command substitution, and arithmetic expansion.
1437 When not performing substring expansion, using the forms documented
1439 below, bash tests for a parameter that is unset or null. Omitting the
1440 colon results in a test only for a parameter that is unset.
1441 ${parameter:-word}
1443 Use Default Values. If parameter is unset or null, the expan‐
1444 sion of word is substituted. Otherwise, the value of parameter
1445 is substituted.
1446 ${parameter:=word}
1447 Assign Default Values. If parameter is unset or null, the
1448 expansion of word is assigned to parameter. The value of param‐
1449 eter is then substituted. Positional parameters and special
1450 parameters may not be assigned to in this way.
1451 ${parameter:?word}
1452 Display Error if Null or Unset. If parameter is null or unset,
1453 the expansion of word (or a message to that effect if word is
1454 not present) is written to the standard error and the shell, if
1455 it is not interactive, exits. Otherwise, the value of parameter
1456 is substituted.
1457 ${parameter:+word}
1458 Use Alternate Value. If parameter is null or unset, nothing is
1459 substituted, otherwise the expansion of word is substituted.
1460 ${parameter:offset}
1461 ${parameter:offset:length}
1462 Substring Expansion. Expands to up to length characters of
1463 parameter starting at the character specified by offset. If
1464 length is omitted, expands to the substring of parameter start‐
1465 ing at the character specified by offset. length and offset are
1466 arithmetic expressions (see ARITHMETIC EVALUATION below). If
1467 offset evaluates to a number less than zero, the value is used
1468 as an offset from the end of the value of parameter. If length
1469 evaluates to a number less than zero, and parameter is not @ and
1470 not an indexed or associative array, it is interpreted as an
1471 offset from the end of the value of parameter rather than a num‐
1472 ber of characters, and the expansion is the characters between
1473 the two offsets. If parameter is @, the result is length posi‐
1474 tional parameters beginning at offset. If parameter is an
1475 indexed array name subscripted by @ or *, the result is the
1476 length members of the array beginning with ${parameter[offset]}.
1477 A negative offset is taken relative to one greater than the max‐
1478 imum index of the specified array. Substring expansion applied
1479 to an associative array produces undefined results. Note that a
1480 negative offset must be separated from the colon by at least one
1481 space to avoid being confused with the :- expansion. Substring
1482 indexing is zero-based unless the positional parameters are
1483 used, in which case the indexing starts at 1 by default. If
1484 offset is 0, and the positional parameters are used, $0 is pre‐
1485 fixed to the list.
1486 ${!prefix*}
1488 ${!prefix@}
1489 Names matching prefix. Expands to the names of variables whose
1490 names begin with prefix, separated by the first character of the
1491 IFS special variable. When @ is used and the expansion appears
1492 within double quotes, each variable name expands to a separate
1493 word.
1494 ${!name[@]}
1496 ${!name[*]}
1497 List of array keys. If name is an array variable, expands to
1498 the list of array indices (keys) assigned in name. If name is
1499 not an array, expands to 0 if name is set and null otherwise.
1500 When @ is used and the expansion appears within double quotes,
1501 each key expands to a separate word.
1502 ${#parameter}
1504 Parameter length. The length in characters of the value of
1505 parameter is substituted. If parameter is * or @, the value
1506 substituted is the number of positional parameters. If parame‐
1507 ter is an array name subscripted by * or @, the value substi‐
1508 tuted is the number of elements in the array.
1509 ${parameter#word}
1511 ${parameter##word}
1512 Remove matching prefix pattern. The word is expanded to produce
1513 a pattern just as in pathname expansion. If the pattern matches
1514 the beginning of the value of parameter, then the result of the
1515 expansion is the expanded value of parameter with the shortest
1516 matching pattern (the ``#'' case) or the longest matching pat‐
1517 tern (the ``##'' case) deleted. If parameter is @ or *, the
1518 pattern removal operation is applied to each positional parame‐
1519 ter in turn, and the expansion is the resultant list. If param‐
1520 eter is an array variable subscripted with @ or *, the pattern
1521 removal operation is applied to each member of the array in
1522 turn, and the expansion is the resultant list.
1523 ${parameter%word}
1525 ${parameter%%word}
1526 Remove matching suffix pattern. The word is expanded to produce
1527 a pattern just as in pathname expansion. If the pattern matches
1528 a trailing portion of the expanded value of parameter, then the
1529 result of the expansion is the expanded value of parameter with
1530 the shortest matching pattern (the ``%'' case) or the longest
1531 matching pattern (the ``%%'' case) deleted. If parameter is @
1532 or *, the pattern removal operation is applied to each posi‐
1533 tional parameter in turn, and the expansion is the resultant
1534 list. If parameter is an array variable subscripted with @ or
1535 *, the pattern removal operation is applied to each member of
1536 the array in turn, and the expansion is the resultant list.
1537 ${parameter/pattern/string}
1539 Pattern substitution. The pattern is expanded to produce a pat‐
1540 tern just as in pathname expansion. Parameter is expanded and
1541 the longest match of pattern against its value is replaced with
1542 string. If pattern begins with /, all matches of pattern are
1543 replaced with string. Normally only the first match is
1544 replaced. If pattern begins with #, it must match at the begin‐
1545 ning of the expanded value of parameter. If pattern begins with
1546 %, it must match at the end of the expanded value of parameter.
1547 If string is null, matches of pattern are deleted and the / fol‐
1548 lowing pattern may be omitted. If parameter is @ or *, the sub‐
1549 stitution operation is applied to each positional parameter in
1550 turn, and the expansion is the resultant list. If parameter is
1551 an array variable subscripted with @ or *, the substitution
1552 operation is applied to each member of the array in turn, and
1553 the expansion is the resultant list.
1554 ${parameter^pattern}
1556 ${parameter^^pattern}
1557 ${parameter,pattern}
1558 ${parameter,,pattern}
1559 Case modification. This expansion modifies the case of alpha‐
1560 betic characters in parameter. The pattern is expanded to pro‐
1561 duce a pattern just as in pathname expansion. The ^ operator
1562 converts lowercase letters matching pattern to uppercase; the ,
1563 operator converts matching uppercase letters to lowercase. The
1564 ^^ and ,, expansions convert each matched character in the
1565 expanded value; the ^ and , expansions match and convert only
1566 the first character in the expanded value. If pattern is omit‐
1567 ted, it is treated like a ?, which matches every character. If
1568 parameter is @ or *, the case modification operation is applied
1569 to each positional parameter in turn, and the expansion is the
1570 resultant list. If parameter is an array variable subscripted
1571 with @ or *, the case modification operation is applied to each
1572 member of the array in turn, and the expansion is the resultant
1573 list.
1574 Command Substitution
1576 Command substitution allows the output of a command to replace the com‐
1577 mand name. There are two forms:
1578 $(command)
1580 or
1581 `command`
1582 Bash performs the expansion by executing command and replacing the com‐
1584 mand substitution with the standard output of the command, with any
1585 trailing newlines deleted. Embedded newlines are not deleted, but they
1586 may be removed during word splitting. The command substitution $(cat
1587 file) can be replaced by the equivalent but faster $(< file).
1588 When the old-style backquote form of substitution is used, backslash
1590 retains its literal meaning except when followed by $, `, or \. The
1591 first backquote not preceded by a backslash terminates the command sub‐
1592 stitution. When using the $(command) form, all characters between the
1593 parentheses make up the command; none are treated specially.
1594 Command substitutions may be nested. To nest when using the backquoted
1596 form, escape the inner backquotes with backslashes.
1597 If the substitution appears within double quotes, word splitting and
1599 pathname expansion are not performed on the results.
1600 Arithmetic Expansion
1602 Arithmetic expansion allows the evaluation of an arithmetic expression
1603 and the substitution of the result. The format for arithmetic expan‐
1604 sion is:
1605 $((expression))
1607 The expression is treated as if it were within double quotes, but a
1609 double quote inside the parentheses is not treated specially. All
1610 tokens in the expression undergo parameter expansion, string expansion,
1611 command substitution, and quote removal. Arithmetic expansions may be
1612 nested.
1613 The evaluation is performed according to the rules listed below under
1615 ARITHMETIC EVALUATION. If expression is invalid, bash prints a message
1616 indicating failure and no substitution occurs.
1617 Process Substitution
1619 Process substitution is supported on systems that support named pipes
1620 (FIFOs) or the /dev/fd method of naming open files. It takes the form
1621 of <(list) or >(list). The process list is run with its input or out‐
1622 put connected to a FIFO or some file in /dev/fd. The name of this file
1623 is passed as an argument to the current command as the result of the
1624 expansion. If the >(list) form is used, writing to the file will pro‐
1625 vide input for list. If the <(list) form is used, the file passed as
1626 an argument should be read to obtain the output of list.
1627 When available, process substitution is performed simultaneously with
1629 parameter and variable expansion, command substitution, and arithmetic
1630 expansion.
1631 Word Splitting
1633 The shell scans the results of parameter expansion, command substitu‐
1634 tion, and arithmetic expansion that did not occur within double quotes
1635 for word splitting.
1636 The shell treats each character of IFS as a delimiter, and splits the
1638 results of the other expansions into words on these characters. If IFS
1639 is unset, or its value is exactly <space><tab><newline>, the default,
1640 then sequences of <space>, <tab>, and <newline> at the beginning and
1641 end of the results of the previous expansions are ignored, and any
1642 sequence of IFS characters not at the beginning or end serves to
1643 delimit words. If IFS has a value other than the default, then
1644 sequences of the whitespace characters space and tab are ignored at the
1645 beginning and end of the word, as long as the whitespace character is
1646 in the value of IFS (an IFS whitespace character). Any character in
1647 IFS that is not IFS whitespace, along with any adjacent IFS whitespace
1648 characters, delimits a field. A sequence of IFS whitespace characters
1649 is also treated as a delimiter. If the value of IFS is null, no word
1650 splitting occurs.
1651 Explicit null arguments ("" or '') are retained. Unquoted implicit
1653 null arguments, resulting from the expansion of parameters that have no
1654 values, are removed. If a parameter with no value is expanded within
1655 double quotes, a null argument results and is retained.
1656 Note that if no expansion occurs, no splitting is performed.
1658 Pathname Expansion
1660 After word splitting, unless the -f option has been set, bash scans
1661 each word for the characters *, ?, and [. If one of these characters
1662 appears, then the word is regarded as a pattern, and replaced with an
1663 alphabetically sorted list of file names matching the pattern. If no
1664 matching file names are found, and the shell option nullglob is not
1665 enabled, the word is left unchanged. If the nullglob option is set,
1666 and no matches are found, the word is removed. If the failglob shell
1667 option is set, and no matches are found, an error message is printed
1668 and the command is not executed. If the shell option nocaseglob is
1669 enabled, the match is performed without regard to the case of alpha‐
1670 betic characters. When a pattern is used for pathname expansion, the
1671 character ``.'' at the start of a name or immediately following a
1672 slash must be matched explicitly, unless the shell option dotglob is
1673 set. When matching a pathname, the slash character must always be
1674 matched explicitly. In other cases, the ``.'' character is not
1675 treated specially. See the description of shopt below under SHELL
1676 BUILTIN COMMANDS for a description of the nocaseglob, nullglob, fail‐
1677 glob, and dotglob shell options.
1678 The GLOBIGNORE shell variable may be used to restrict the set of file
1680 names matching a pattern. If GLOBIGNORE is set, each matching file
1681 name that also matches one of the patterns in GLOBIGNORE is removed
1682 from the list of matches. The file names ``.'' and ``..'' are always
1683 ignored when GLOBIGNORE is set and not null. However, setting GLOBIG‐
1684 NORE to a non-null value has the effect of enabling the dotglob shell
1685 option, so all other file names beginning with a ``.'' will match. To
1686 get the old behavior of ignoring file names beginning with a ``.'',
1687 make ``.*'' one of the patterns in GLOBIGNORE. The dotglob option is
1688 disabled when GLOBIGNORE is unset.
1689 Pattern Matching
1691 Any character that appears in a pattern, other than the special pattern
1693 characters described below, matches itself. The NUL character may not
1694 occur in a pattern. A backslash escapes the following character; the
1695 escaping backslash is discarded when matching. The special pattern
1696 characters must be quoted if they are to be matched literally.
1697 The special pattern characters have the following meanings:
1699 * Matches any string, including the null string. When the
1701 globstar shell option is enabled, and * is used in a
1702 pathname expansion context, two adjacent *s used as a
1703 single pattern will match all files and zero or more
1704 directories and subdirectories. If followed by a /, two
1705 adjacent *s will match only directories and subdirecto‐
1706 ries.
1707 ? Matches any single character.
1708 [...] Matches any one of the enclosed characters. A pair of
1709 characters separated by a hyphen denotes a range expres‐
1710 sion; any character that sorts between those two charac‐
1711 ters, inclusive, using the current locale's collating
1712 sequence and character set, is matched. If the first
1713 character following the [ is a ! or a ^ then any charac‐
1714 ter not enclosed is matched. The sorting order of char‐
1715 acters in range expressions is determined by the current
1716 locale and the value of the LC_COLLATE shell variable, if
1717 set. A - may be matched by including it as the first or
1718 last character in the set. A ] may be matched by includ‐
1719 ing it as the first character in the set.
1720 Within [ and ], character classes can be specified using
1722 the syntax [:class:], where class is one of the following
1723 classes defined in the POSIX standard:
1724 alnum alpha ascii blank cntrl digit graph lower print
1725 punct space upper word xdigit
1726 A character class matches any character belonging to that
1727 class. The word character class matches letters, digits,
1728 and the character _.
1729 Within [ and ], an equivalence class can be specified
1731 using the syntax [=c=], which matches all characters with
1732 the same collation weight (as defined by the current
1733 locale) as the character c.
1734 Within [ and ], the syntax [.symbol.] matches the collat‐
1736 ing symbol symbol.
1737 Several extended pattern matching operators are recognized. In the
1739 following description, a pattern-list is a list of one or more patterns
1740 separated by a |. Composite patterns may be formed using one or more
1741 of the following sub-patterns:
1742 ?(pattern-list)
1744 Matches zero or one occurrence of the given patterns
1745 *(pattern-list)
1746 Matches zero or more occurrences of the given patterns
1747 +(pattern-list)
1748 Matches one or more occurrences of the given patterns
1749 @(pattern-list)
1750 Matches one of the given patterns
1751 If the extglob shell option is enabled using the shopt builtin, follow‐
1753 ing pattern matching operator is recognized as well:
1754 !(pattern-list)
1756 Matches anything except one of the given patterns
1757 Quote Removal
1759 After the preceding expansions, all unquoted occurrences of the charac‐
1760 ters \, ', and " that did not result from one of the above expansions
1761 are removed.
1762
1764 Before a command is executed, its input and output may be redirected
1765 using a special notation interpreted by the shell. Redirection may
1766 also be used to open and close files for the current shell execution
1767 environment. The following redirection operators may precede or appear
1768 anywhere within a simple command or may follow a command. Redirections
1769 are processed in the order they appear, from left to right.
1770 Each redirection that may be preceded by a file descriptor number may
1772 instead be preceded by a word of the form {varname}. In this case, for
1773 each redirection operator except >&- and <&-, the shell will allocate a
1774 file descriptor greater than 10 and assign it to varname. If >&- or
1775 <&- is preceded by {varname}, the value of varname defines the file
1776 descriptor to close.
1777 In the following descriptions, if the file descriptor number is omit‐
1779 ted, and the first character of the redirection operator is <, the re‐
1780 direction refers to the standard input (file descriptor 0). If the
1781 first character of the redirection operator is >, the redirection
1782 refers to the standard output (file descriptor 1).
1783 The word following the redirection operator in the following descrip‐
1785 tions, unless otherwise noted, is subjected to brace expansion, tilde
1786 expansion, parameter expansion, command substitution, arithmetic expan‐
1787 sion, quote removal, pathname expansion, and word splitting. If it
1788 expands to more than one word, bash reports an error.
1789 Note that the order of redirections is significant. For example, the
1791 command
1792 ls > dirlist 2>&1
1794 directs both standard output and standard error to the file dirlist,
1796 while the command
1797 ls 2>&1 > dirlist
1799 directs only the standard output to file dirlist, because the standard
1801 error was duplicated from the standard output before the standard out‐
1802 put was redirected to dirlist.
1803 Bash handles several filenames specially when they are used in redirec‐
1805 tions, as described in the following table:
1806 /dev/fd/fd
1808 If fd is a valid integer, file descriptor fd is dupli‐
1809 cated.
1810 /dev/stdin
1811 File descriptor 0 is duplicated.
1812 /dev/stdout
1813 File descriptor 1 is duplicated.
1814 /dev/stderr
1815 File descriptor 2 is duplicated.
1816 /dev/tcp/host/port
1817 If host is a valid hostname or Internet address, and port
1818 is an integer port number or service name, bash attempts
1819 to open a TCP connection to the corresponding socket.
1820 /dev/udp/host/port
1821 If host is a valid hostname or Internet address, and port
1822 is an integer port number or service name, bash attempts
1823 to open a UDP connection to the corresponding socket.
1824 A failure to open or create a file causes the redirection to fail.
1826 Redirections using file descriptors greater than 9 should be used with
1828 care, as they may conflict with file descriptors the shell uses inter‐
1829 nally.
1830 Redirecting Input
1832 Redirection of input causes the file whose name results from the expan‐
1833 sion of word to be opened for reading on file descriptor n, or the
1834 standard input (file descriptor 0) if n is not specified.
1835 The general format for redirecting input is:
1837 [n]<word
1839 Redirecting Output
1841 Redirection of output causes the file whose name results from the
1842 expansion of word to be opened for writing on file descriptor n, or the
1843 standard output (file descriptor 1) if n is not specified. If the file
1844 does not exist it is created; if it does exist it is truncated to zero
1845 size.
1846 The general format for redirecting output is:
1848 [n]>word
1850 If the redirection operator is >, and the noclobber option to the set
1852 builtin has been enabled, the redirection will fail if the file whose
1853 name results from the expansion of word exists and is a regular file.
1854 If the redirection operator is >|, or the redirection operator is > and
1855 the noclobber option to the set builtin command is not enabled, the re‐
1856 direction is attempted even if the file named by word exists.
1857 Appending Redirected Output
1859 Redirection of output in this fashion causes the file whose name
1860 results from the expansion of word to be opened for appending on file
1861 descriptor n, or the standard output (file descriptor 1) if n is not
1862 specified. If the file does not exist it is created.
1863 The general format for appending output is:
1865 [n]>>word
1867 Redirecting Standard Output and Standard Error
1869 This construct allows both the standard output (file descriptor 1) and
1870 the standard error output (file descriptor 2) to be redirected to the
1871 file whose name is the expansion of word.
1872 There are two formats for redirecting standard output and standard
1874 error:
1875 &>word
1877 and
1878 >&word
1879 Of the two forms, the first is preferred. This is semantically equiva‐
1881 lent to
1882 >word 2>&1
1884 Appending Standard Output and Standard Error
1886 This construct allows both the standard output (file descriptor 1) and
1887 the standard error output (file descriptor 2) to be appended to the
1888 file whose name is the expansion of word.
1889 The format for appending standard output and standard error is:
1891 &>>word
1893 This is semantically equivalent to
1895 >>word 2>&1
1897 Here Documents
1899 This type of redirection instructs the shell to read input from the
1900 current source until a line containing only delimiter (with no trailing
1901 blanks) is seen. All of the lines read up to that point are then used
1902 as the standard input for a command.
1903 The format of here-documents is:
1905 <<[-]word
1907 here-document
1908 delimiter
1909 No parameter expansion, command substitution, arithmetic expansion, or
1911 pathname expansion is performed on word. If any characters in word are
1912 quoted, the delimiter is the result of quote removal on word, and the
1913 lines in the here-document are not expanded. If word is unquoted, all
1914 lines of the here-document are subjected to parameter expansion, com‐
1915 mand substitution, and arithmetic expansion. In the latter case, the
1916 character sequence \<newline> is ignored, and \ must be used to quote
1917 the characters \, $, and `.
1918 If the redirection operator is <<-, then all leading tab characters are
1920 stripped from input lines and the line containing delimiter. This
1921 allows here-documents within shell scripts to be indented in a natural
1922 fashion.
1923 Here Strings
1925 A variant of here documents, the format is:
1926 <<<word
1928 The word is expanded and supplied to the command on its standard input.
1930 Duplicating File Descriptors
1932 The redirection operator
1933 [n]<&word
1935 is used to duplicate input file descriptors. If word expands to one or
1937 more digits, the file descriptor denoted by n is made to be a copy of
1938 that file descriptor. If the digits in word do not specify a file
1939 descriptor open for input, a redirection error occurs. If word evalu‐
1940 ates to -, file descriptor n is closed. If n is not specified, the
1941 standard input (file descriptor 0) is used.
1942 The operator
1944 [n]>&word
1946 is used similarly to duplicate output file descriptors. If n is not
1948 specified, the standard output (file descriptor 1) is used. If the
1949 digits in word do not specify a file descriptor open for output, a re‐
1950 direction error occurs. As a special case, if n is omitted, and word
1951 does not expand to one or more digits, the standard output and standard
1952 error are redirected as described previously.
1953 Moving File Descriptors
1955 The redirection operator
1956 [n]<&digit-
1958 moves the file descriptor digit to file descriptor n, or the standard
1960 input (file descriptor 0) if n is not specified. digit is closed after
1961 being duplicated to n.
1962 Similarly, the redirection operator
1964 [n]>&digit-
1966 moves the file descriptor digit to file descriptor n, or the standard
1968 output (file descriptor 1) if n is not specified.
1969 Opening File Descriptors for Reading and Writing
1971 The redirection operator
1972 [n]<>word
1974 causes the file whose name is the expansion of word to be opened for
1976 both reading and writing on file descriptor n, or on file descriptor 0
1977 if n is not specified. If the file does not exist, it is created.
1978
1980 Aliases allow a string to be substituted for a word when it is used as
1981 the first word of a simple command. The shell maintains a list of
1982 aliases that may be set and unset with the alias and unalias builtin
1983 commands (see SHELL BUILTIN COMMANDS below). The first word of each
1984 simple command, if unquoted, is checked to see if it has an alias. If
1985 so, that word is replaced by the text of the alias. The characters /,
1986 $, `, and = and any of the shell metacharacters or quoting characters
1987 listed above may not appear in an alias name. The replacement text may
1988 contain any valid shell input, including shell metacharacters. The
1989 first word of the replacement text is tested for aliases, but a word
1990 that is identical to an alias being expanded is not expanded a second
1991 time. This means that one may alias ls to ls -F, for instance, and
1992 bash does not try to recursively expand the replacement text. If the
1993 last character of the alias value is a blank, then the next command
1994 word following the alias is also checked for alias expansion.
1995 Aliases are created and listed with the alias command, and removed with
1997 the unalias command.
1998 There is no mechanism for using arguments in the replacement text. If
2000 arguments are needed, a shell function should be used (see FUNCTIONS
2001 below).
2002 Aliases are not expanded when the shell is not interactive, unless the
2004 expand_aliases shell option is set using shopt (see the description of
2005 shopt under SHELL BUILTIN COMMANDS below).
2006 The rules concerning the definition and use of aliases are somewhat
2008 confusing. Bash always reads at least one complete line of input
2009 before executing any of the commands on that line. Aliases are
2010 expanded when a command is read, not when it is executed. Therefore,
2011 an alias definition appearing on the same line as another command does
2012 not take effect until the next line of input is read. The commands
2013 following the alias definition on that line are not affected by the new
2014 alias. This behavior is also an issue when functions are executed.
2015 Aliases are expanded when a function definition is read, not when the
2016 function is executed, because a function definition is itself a com‐
2017 pound command. As a consequence, aliases defined in a function are not
2018 available until after that function is executed. To be safe, always
2019 put alias definitions on a separate line, and do not use alias in com‐
2020 pound commands.
2021 For almost every purpose, aliases are superseded by shell functions.
2023
2025 A shell function, defined as described above under SHELL GRAMMAR,
2026 stores a series of commands for later execution. When the name of a
2027 shell function is used as a simple command name, the list of commands
2028 associated with that function name is executed. Functions are executed
2029 in the context of the current shell; no new process is created to
2030 interpret them (contrast this with the execution of a shell script).
2031 When a function is executed, the arguments to the function become the
2032 positional parameters during its execution. The special parameter # is
2033 updated to reflect the change. Special parameter 0 is unchanged. The
2034 first element of the FUNCNAME variable is set to the name of the func‐
2035 tion while the function is executing.
2036 All other aspects of the shell execution environment are identical
2038 between a function and its caller with these exceptions: the DEBUG and
2039 RETURN traps (see the description of the trap builtin under SHELL
2040 BUILTIN COMMANDS below) are not inherited unless the function has been
2041 given the trace attribute (see the description of the declare builtin
2042 below) or the -o functrace shell option has been enabled with the set
2043 builtin (in which case all functions inherit the DEBUG and RETURN
2044 traps), and the ERR trap is not inherited unless the -o errtrace shell
2045 option has been enabled.
2046 Variables local to the function may be declared with the local builtin
2048 command. Ordinarily, variables and their values are shared between the
2049 function and its caller.
2050 The FUNCNEST variable, if set to a numeric value greater than 0,
2052 defines a maximum function nesting level. Function invocations that
2053 exceed the limit cause the entire command to abort.
2054 If the builtin command return is executed in a function, the function
2056 completes and execution resumes with the next command after the func‐
2057 tion call. Any command associated with the RETURN trap is executed
2058 before execution resumes. When a function completes, the values of the
2059 positional parameters and the special parameter # are restored to the
2060 values they had prior to the function's execution.
2061 Function names and definitions may be listed with the -f option to the
2063 declare or typeset builtin commands. The -F option to declare or type‐
2064 set will list the function names only (and optionally the source file
2065 and line number, if the extdebug shell option is enabled). Functions
2066 may be exported so that subshells automatically have them defined with
2067 the -f option to the export builtin. A function definition may be
2068 deleted using the -f option to the unset builtin. Note that shell
2069 functions and variables with the same name may result in multiple iden‐
2070 tically-named entries in the environment passed to the shell's chil‐
2071 dren. Care should be taken in cases where this may cause a problem.
2072 Functions may be recursive. The FUNCNEST variable may be used to limit
2074 the depth of the function call stack and restrict the number of func‐
2075 tion invocations. By default, no limit is imposed on the number of
2076 recursive calls.
2077
2079 The shell allows arithmetic expressions to be evaluated, under certain
2080 circumstances (see the let and declare builtin commands and Arithmetic
2081 Expansion). Evaluation is done in fixed-width integers with no check
2082 for overflow, though division by 0 is trapped and flagged as an error.
2083 The operators and their precedence, associativity, and values are the
2084 same as in the C language. The following list of operators is grouped
2085 into levels of equal-precedence operators. The levels are listed in
2086 order of decreasing precedence.
2087 id++ id--
2089 variable post-increment and post-decrement
2090 ++id --id
2091 variable pre-increment and pre-decrement
2092 - + unary minus and plus
2093 ! ~ logical and bitwise negation
2094 ** exponentiation
2095 * / % multiplication, division, remainder
2096 + - addition, subtraction
2097 << >> left and right bitwise shifts
2098 <= >= < >
2099 comparison
2100 == != equality and inequality
2101 & bitwise AND
2102 ^ bitwise exclusive OR
2103 | bitwise OR
2104 && logical AND
2105 || logical OR
2106 expr?expr:expr
2107 conditional operator
2108 = *= /= %= += -= <<= >>= &= ^= |=
2109 assignment
2110 expr1 , expr2
2111 comma
2112 Shell variables are allowed as operands; parameter expansion is per‐
2114 formed before the expression is evaluated. Within an expression, shell
2115 variables may also be referenced by name without using the parameter
2116 expansion syntax. A shell variable that is null or unset evaluates to
2117 0 when referenced by name without using the parameter expansion syntax.
2118 The value of a variable is evaluated as an arithmetic expression when
2119 it is referenced, or when a variable which has been given the integer
2120 attribute using declare -i is assigned a value. A null value evaluates
2121 to 0. A shell variable need not have its integer attribute turned on
2122 to be used in an expression.
2123 Constants with a leading 0 are interpreted as octal numbers. A leading
2125 0x or 0X denotes hexadecimal. Otherwise, numbers take the form
2126 [base#]n, where the optional base is a decimal number between 2 and 64
2127 representing the arithmetic base, and n is a number in that base. If
2128 base# is omitted, then base 10 is used. The digits greater than 9 are
2129 represented by the lowercase letters, the uppercase letters, @, and _,
2130 in that order. If base is less than or equal to 36, lowercase and
2131 uppercase letters may be used interchangeably to represent numbers
2132 between 10 and 35.
2133 Operators are evaluated in order of precedence. Sub-expressions in
2135 parentheses are evaluated first and may override the precedence rules
2136 above.
2137
2139 Conditional expressions are used by the [[ compound command and the
2140 test and [ builtin commands to test file attributes and perform string
2141 and arithmetic comparisons. Expressions are formed from the following
2142 unary or binary primaries. If any file argument to one of the pri‐
2143 maries is of the form /dev/fd/n, then file descriptor n is checked. If
2144 the file argument to one of the primaries is one of /dev/stdin,
2145 /dev/stdout, or /dev/stderr, file descriptor 0, 1, or 2, respectively,
2146 is checked.
2147 Unless otherwise specified, primaries that operate on files follow sym‐
2149 bolic links and operate on the target of the link, rather than the link
2150 itself.
2151 When used with [[, the < and > operators sort lexicographically using
2153 the current locale. The test command sorts using ASCII ordering.
2154 -a file
2156 True if file exists.
2157 -b file
2158 True if file exists and is a block special file.
2159 -c file
2160 True if file exists and is a character special file.
2161 -d file
2162 True if file exists and is a directory.
2163 -e file
2164 True if file exists.
2165 -f file
2166 True if file exists and is a regular file.
2167 -g file
2168 True if file exists and is set-group-id.
2169 -h file
2170 True if file exists and is a symbolic link.
2171 -k file
2172 True if file exists and its ``sticky'' bit is set.
2173 -p file
2174 True if file exists and is a named pipe (FIFO).
2175 -r file
2176 True if file exists and is readable.
2177 -s file
2178 True if file exists and has a size greater than zero.
2179 -t fd True if file descriptor fd is open and refers to a terminal.
2180 -u file
2181 True if file exists and its set-user-id bit is set.
2182 -w file
2183 True if file exists and is writable.
2184 -x file
2185 True if file exists and is executable.
2186 -G file
2187 True if file exists and is owned by the effective group id.
2188 -L file
2189 True if file exists and is a symbolic link.
2190 -N file
2191 True if file exists and has been modified since it was last
2192 read.
2193 -O file
2194 True if file exists and is owned by the effective user id.
2195 -S file
2196 True if file exists and is a socket.
2197 file1 -ef file2
2198 True if file1 and file2 refer to the same device and inode num‐
2199 bers.
2200 file1 -nt file2
2201 True if file1 is newer (according to modification date) than
2202 file2, or if file1 exists and file2 does not.
2203 file1 -ot file2
2204 True if file1 is older than file2, or if file2 exists and file1
2205 does not.
2206 -o optname
2207 True if the shell option optname is enabled. See the list of
2208 options under the description of the -o option to the set
2209 builtin below.
2210 -v varname
2211 True if the shell variable varname is set (has been assigned a
2212 value).
2213 -z string
2214 True if the length of string is zero.
2215 string
2216 -n string
2217 True if the length of string is non-zero.
2218 string1 == string2
2220 string1 = string2
2221 True if the strings are equal. = should be used with the test
2222 command for POSIX conformance.
2223 string1 != string2
2225 True if the strings are not equal.
2226 string1 < string2
2228 True if string1 sorts before string2 lexicographically.
2229 string1 > string2
2231 True if string1 sorts after string2 lexicographically.
2232 arg1 OP arg2
2234 OP is one of -eq, -ne, -lt, -le, -gt, or -ge. These arithmetic
2235 binary operators return true if arg1 is equal to, not equal to,
2236 less than, less than or equal to, greater than, or greater than
2237 or equal to arg2, respectively. Arg1 and arg2 may be positive
2238 or negative integers.
2239
2241 When a simple command is executed, the shell performs the following
2242 expansions, assignments, and redirections, from left to right.
2243 1. The words that the parser has marked as variable assignments
2245 (those preceding the command name) and redirections are saved
2246 for later processing.
2247 2. The words that are not variable assignments or redirections are
2249 expanded. If any words remain after expansion, the first word
2250 is taken to be the name of the command and the remaining words
2251 are the arguments.
2252 3. Redirections are performed as described above under REDIRECTION.
2254 4. The text after the = in each variable assignment undergoes tilde
2256 expansion, parameter expansion, command substitution, arithmetic
2257 expansion, and quote removal before being assigned to the vari‐
2258 able.
2259 If no command name results, the variable assignments affect the current
2261 shell environment. Otherwise, the variables are added to the environ‐
2262 ment of the executed command and do not affect the current shell envi‐
2263 ronment. If any of the assignments attempts to assign a value to a
2264 readonly variable, an error occurs, and the command exits with a non-
2265 zero status.
2266 If no command name results, redirections are performed, but do not
2268 affect the current shell environment. A redirection error causes the
2269 command to exit with a non-zero status.
2270 If there is a command name left after expansion, execution proceeds as
2272 described below. Otherwise, the command exits. If one of the expan‐
2273 sions contained a command substitution, the exit status of the command
2274 is the exit status of the last command substitution performed. If
2275 there were no command substitutions, the command exits with a status of
2276 zero.
2277
2279 After a command has been split into words, if it results in a simple
2280 command and an optional list of arguments, the following actions are
2281 taken.
2282 If the command name contains no slashes, the shell attempts to locate
2284 it. If there exists a shell function by that name, that function is
2285 invoked as described above in FUNCTIONS. If the name does not match a
2286 function, the shell searches for it in the list of shell builtins. If
2287 a match is found, that builtin is invoked.
2288 If the name is neither a shell function nor a builtin, and contains no
2290 slashes, bash searches each element of the PATH for a directory con‐
2291 taining an executable file by that name. Bash uses a hash table to
2292 remember the full pathnames of executable files (see hash under SHELL
2293 BUILTIN COMMANDS below). A full search of the directories in PATH is
2294 performed only if the command is not found in the hash table. If the
2295 search is unsuccessful, the shell searches for a defined shell function
2296 named command_not_found_handle. If that function exists, it is invoked
2297 with the original command and the original command's arguments as its
2298 arguments, and the function's exit status becomes the exit status of
2299 the shell. If that function is not defined, the shell prints an error
2300 message and returns an exit status of 127.
2301 If the search is successful, or if the command name contains one or
2303 more slashes, the shell executes the named program in a separate execu‐
2304 tion environment. Argument 0 is set to the name given, and the remain‐
2305 ing arguments to the command are set to the arguments given, if any.
2306 If this execution fails because the file is not in executable format,
2308 and the file is not a directory, it is assumed to be a shell script, a
2309 file containing shell commands. A subshell is spawned to execute it.
2310 This subshell reinitializes itself, so that the effect is as if a new
2311 shell had been invoked to handle the script, with the exception that
2312 the locations of commands remembered by the parent (see hash below
2313 under SHELL BUILTIN COMMANDS) are retained by the child.
2314 If the program is a file beginning with #!, the remainder of the first
2316 line specifies an interpreter for the program. The shell executes the
2317 specified interpreter on operating systems that do not handle this exe‐
2318 cutable format themselves. The arguments to the interpreter consist of
2319 a single optional argument following the interpreter name on the first
2320 line of the program, followed by the name of the program, followed by
2321 the command arguments, if any.
2322
2324 The shell has an execution environment, which consists of the follow‐
2325 ing:
2326 · open files inherited by the shell at invocation, as modified by
2328 redirections supplied to the exec builtin
2329 · the current working directory as set by cd, pushd, or popd, or
2331 inherited by the shell at invocation
2332 · the file creation mode mask as set by umask or inherited from
2334 the shell's parent
2335 · current traps set by trap
2337 · shell parameters that are set by variable assignment or with set
2339 or inherited from the shell's parent in the environment
2340 · shell functions defined during execution or inherited from the
2342 shell's parent in the environment
2343 · options enabled at invocation (either by default or with com‐
2345 mand-line arguments) or by set
2346 · options enabled by shopt
2348 · shell aliases defined with alias
2350 · various process IDs, including those of background jobs, the
2352 value of $$, and the value of PPID
2353 When a simple command other than a builtin or shell function is to be
2355 executed, it is invoked in a separate execution environment that con‐
2356 sists of the following. Unless otherwise noted, the values are inher‐
2357 ited from the shell.
2358 · the shell's open files, plus any modifications and additions
2361 specified by redirections to the command
2362 · the current working directory
2364 · the file creation mode mask
2366 · shell variables and functions marked for export, along with
2368 variables exported for the command, passed in the environment
2369 · traps caught by the shell are reset to the values inherited from
2371 the shell's parent, and traps ignored by the shell are ignored
2372 A command invoked in this separate environment cannot affect the
2374 shell's execution environment.
2375 Command substitution, commands grouped with parentheses, and asynchro‐
2377 nous commands are invoked in a subshell environment that is a duplicate
2378 of the shell environment, except that traps caught by the shell are
2379 reset to the values that the shell inherited from its parent at invoca‐
2380 tion. Builtin commands that are invoked as part of a pipeline are also
2381 executed in a subshell environment. Changes made to the subshell envi‐
2382 ronment cannot affect the shell's execution environment.
2383 Subshells spawned to execute command substitutions inherit the value of
2385 the -e option from the parent shell. When not in posix mode, bash
2386 clears the -e option in such subshells.
2387 If a command is followed by a & and job control is not active, the
2389 default standard input for the command is the empty file /dev/null.
2390 Otherwise, the invoked command inherits the file descriptors of the
2391 calling shell as modified by redirections.
2392
2394 When a program is invoked it is given an array of strings called the
2395 environment. This is a list of name-value pairs, of the form
2396 name=value.
2397 The shell provides several ways to manipulate the environment. On
2399 invocation, the shell scans its own environment and creates a parameter
2400 for each name found, automatically marking it for export to child pro‐
2401 cesses. Executed commands inherit the environment. The export and
2402 declare -x commands allow parameters and functions to be added to and
2403 deleted from the environment. If the value of a parameter in the envi‐
2404 ronment is modified, the new value becomes part of the environment,
2405 replacing the old. The environment inherited by any executed command
2406 consists of the shell's initial environment, whose values may be modi‐
2407 fied in the shell, less any pairs removed by the unset command, plus
2408 any additions via the export and declare -x commands.
2409 The environment for any simple command or function may be augmented
2411 temporarily by prefixing it with parameter assignments, as described
2412 above in PARAMETERS. These assignment statements affect only the envi‐
2413 ronment seen by that command.
2414 If the -k option is set (see the set builtin command below), then all
2416 parameter assignments are placed in the environment for a command, not
2417 just those that precede the command name.
2418 When bash invokes an external command, the variable _ is set to the
2420 full file name of the command and passed to that command in its envi‐
2421 ronment.
2422
2424 The exit status of an executed command is the value returned by the
2425 waitpid system call or equivalent function. Exit statuses fall between
2426 0 and 255, though, as explained below, the shell may use values above
2427 125 specially. Exit statuses from shell builtins and compound commands
2428 are also limited to this range. Under certain circumstances, the shell
2429 will use special values to indicate specific failure modes.
2430 For the shell's purposes, a command which exits with a zero exit status
2432 has succeeded. An exit status of zero indicates success. A non-zero
2433 exit status indicates failure. When a command terminates on a fatal
2434 signal N, bash uses the value of 128+N as the exit status.
2435 If a command is not found, the child process created to execute it
2437 returns a status of 127. If a command is found but is not executable,
2438 the return status is 126.
2439 If a command fails because of an error during expansion or redirection,
2441 the exit status is greater than zero.
2442 Shell builtin commands return a status of 0 (true) if successful, and
2444 non-zero (false) if an error occurs while they execute. All builtins
2445 return an exit status of 2 to indicate incorrect usage.
2446 Bash itself returns the exit status of the last command executed,
2448 unless a syntax error occurs, in which case it exits with a non-zero
2449 value. See also the exit builtin command below.
2450
2452 When bash is interactive, in the absence of any traps, it ignores
2453 SIGTERM (so that kill 0 does not kill an interactive shell), and SIGINT
2454 is caught and handled (so that the wait builtin is interruptible). In
2455 all cases, bash ignores SIGQUIT. If job control is in effect, bash
2456 ignores SIGTTIN, SIGTTOU, and SIGTSTP.
2457 Non-builtin commands run by bash have signal handlers set to the values
2459 inherited by the shell from its parent. When job control is not in
2460 effect, asynchronous commands ignore SIGINT and SIGQUIT in addition to
2461 these inherited handlers. Commands run as a result of command substi‐
2462 tution ignore the keyboard-generated job control signals SIGTTIN, SIGT‐
2463 TOU, and SIGTSTP.
2464 The shell exits by default upon receipt of a SIGHUP. Before exiting,
2466 an interactive shell resends the SIGHUP to all jobs, running or
2467 stopped. Stopped jobs are sent SIGCONT to ensure that they receive the
2468 SIGHUP. To prevent the shell from sending the signal to a particular
2469 job, it should be removed from the jobs table with the disown builtin
2470 (see SHELL BUILTIN COMMANDS below) or marked to not receive SIGHUP
2471 using disown -h.
2472 If the huponexit shell option has been set with shopt, bash sends a
2474 SIGHUP to all jobs when an interactive login shell exits.
2475 If bash is waiting for a command to complete and receives a signal for
2477 which a trap has been set, the trap will not be executed until the com‐
2478 mand completes. When bash is waiting for an asynchronous command via
2479 the wait builtin, the reception of a signal for which a trap has been
2480 set will cause the wait builtin to return immediately with an exit sta‐
2481 tus greater than 128, immediately after which the trap is executed.
2482
2484 Job control refers to the ability to selectively stop (suspend) the
2485 execution of processes and continue (resume) their execution at a later
2486 point. A user typically employs this facility via an interactive
2487 interface supplied jointly by the operating system kernel's terminal
2488 driver and bash.
2489 The shell associates a job with each pipeline. It keeps a table of
2491 currently executing jobs, which may be listed with the jobs command.
2492 When bash starts a job asynchronously (in the background), it prints a
2493 line that looks like:
2494 [1] 25647
2496 indicating that this job is job number 1 and that the process ID of the
2498 last process in the pipeline associated with this job is 25647. All of
2499 the processes in a single pipeline are members of the same job. Bash
2500 uses the job abstraction as the basis for job control.
2501 To facilitate the implementation of the user interface to job control,
2503 the operating system maintains the notion of a current terminal process
2504 group ID. Members of this process group (processes whose process group
2505 ID is equal to the current terminal process group ID) receive keyboard-
2506 generated signals such as SIGINT. These processes are said to be in
2507 the foreground. Background processes are those whose process group ID
2508 differs from the terminal's; such processes are immune to keyboard-gen‐
2509 erated signals. Only foreground processes are allowed to read from or,
2510 if the user so specifies with stty tostop, write to the terminal.
2511 Background processes which attempt to read from (write to when stty
2512 tostop is in effect) the terminal are sent a SIGTTIN (SIGTTOU) signal
2513 by the kernel's terminal driver, which, unless caught, suspends the
2514 process.
2515 If the operating system on which bash is running supports job control,
2517 bash contains facilities to use it. Typing the suspend character (typ‐
2518 ically ^Z, Control-Z) while a process is running causes that process to
2519 be stopped and returns control to bash. Typing the delayed suspend
2520 character (typically ^Y, Control-Y) causes the process to be stopped
2521 when it attempts to read input from the terminal, and control to be
2522 returned to bash. The user may then manipulate the state of this job,
2523 using the bg command to continue it in the background, the fg command
2524 to continue it in the foreground, or the kill command to kill it. A ^Z
2525 takes effect immediately, and has the additional side effect of causing
2526 pending output and typeahead to be discarded.
2527 There are a number of ways to refer to a job in the shell. The charac‐
2529 ter % introduces a job specification (jobspec). Job number n may be
2530 referred to as %n. A job may also be referred to using a prefix of the
2531 name used to start it, or using a substring that appears in its command
2532 line. For example, %ce refers to a stopped ce job. If a prefix
2533 matches more than one job, bash reports an error. Using %?ce, on the
2534 other hand, refers to any job containing the string ce in its command
2535 line. If the substring matches more than one job, bash reports an
2536 error. The symbols %% and %+ refer to the shell's notion of the cur‐
2537 rent job, which is the last job stopped while it was in the foreground
2538 or started in the background. The previous job may be referenced using
2539 %-. If there is only a single job, %+ and %- can both be used to refer
2540 to that job. In output pertaining to jobs (e.g., the output of the
2541 jobs command), the current job is always flagged with a +, and the pre‐
2542 vious job with a -. A single % (with no accompanying job specifica‐
2543 tion) also refers to the current job.
2544 Simply naming a job can be used to bring it into the foreground: %1 is
2546 a synonym for ``fg %1'', bringing job 1 from the background into the
2547 foreground. Similarly, ``%1 &'' resumes job 1 in the background,
2548 equivalent to ``bg %1''.
2549 The shell learns immediately whenever a job changes state. Normally,
2551 bash waits until it is about to print a prompt before reporting changes
2552 in a job's status so as to not interrupt any other output. If the -b
2553 option to the set builtin command is enabled, bash reports such changes
2554 immediately. Any trap on SIGCHLD is executed for each child that
2555 exits.
2556 If an attempt to exit bash is made while jobs are stopped (or, if the
2558 checkjobs shell option has been enabled using the shopt builtin, run‐
2559 ning), the shell prints a warning message, and, if the checkjobs option
2560 is enabled, lists the jobs and their statuses. The jobs command may
2561 then be used to inspect their status. If a second attempt to exit is
2562 made without an intervening command, the shell does not print another
2563 warning, and any stopped jobs are terminated.
2564
2566 When executing interactively, bash displays the primary prompt PS1 when
2567 it is ready to read a command, and the secondary prompt PS2 when it
2568 needs more input to complete a command. Bash allows these prompt
2569 strings to be customized by inserting a number of backslash-escaped
2570 special characters that are decoded as follows:
2571 \a an ASCII bell character (07)
2572 \d the date in "Weekday Month Date" format (e.g., "Tue May
2573 26")
2574 \D{format}
2575 the format is passed to strftime(3) and the result is
2576 inserted into the prompt string; an empty format results
2577 in a locale-specific time representation. The braces are
2578 required
2579 \e an ASCII escape character (033)
2580 \h the hostname up to the first `.'
2581 \H the hostname
2582 \j the number of jobs currently managed by the shell
2583 \l the basename of the shell's terminal device name
2584 \n newline
2585 \r carriage return
2586 \s the name of the shell, the basename of $0 (the portion
2587 following the final slash)
2588 \t the current time in 24-hour HH:MM:SS format
2589 \T the current time in 12-hour HH:MM:SS format
2590 \@ the current time in 12-hour am/pm format
2591 \A the current time in 24-hour HH:MM format
2592 \u the username of the current user
2593 \v the version of bash (e.g., 2.00)
2594 \V the release of bash, version + patch level (e.g., 2.00.0)
2595 \w the current working directory, with $HOME abbreviated
2596 with a tilde (uses the value of the PROMPT_DIRTRIM vari‐
2597 able)
2598 \W the basename of the current working directory, with $HOME
2599 abbreviated with a tilde
2600 \! the history number of this command
2601 \# the command number of this command
2602 \$ if the effective UID is 0, a #, otherwise a $
2603 \nnn the character corresponding to the octal number nnn
2604 \\ a backslash
2605 \[ begin a sequence of non-printing characters, which could
2606 be used to embed a terminal control sequence into the
2607 prompt
2608 \] end a sequence of non-printing characters
2609 The command number and the history number are usually different: the
2611 history number of a command is its position in the history list, which
2612 may include commands restored from the history file (see HISTORY
2613 below), while the command number is the position in the sequence of
2614 commands executed during the current shell session. After the string
2615 is decoded, it is expanded via parameter expansion, command substitu‐
2616 tion, arithmetic expansion, and quote removal, subject to the value of
2617 the promptvars shell option (see the description of the shopt command
2618 under SHELL BUILTIN COMMANDS below).
2619
2621 This is the library that handles reading input when using an interac‐
2622 tive shell, unless the --noediting option is given at shell invocation.
2623 Line editing is also used when using the -e option to the read builtin.
2624 By default, the line editing commands are similar to those of Emacs. A
2625 vi-style line editing interface is also available. Line editing can be
2626 enabled at any time using the -o emacs or -o vi options to the set
2627 builtin (see SHELL BUILTIN COMMANDS below). To turn off line editing
2628 after the shell is running, use the +o emacs or +o vi options to the
2629 set builtin.
2630 Readline Notation
2632 In this section, the Emacs-style notation is used to denote keystrokes.
2633 Control keys are denoted by C-key, e.g., C-n means Control-N. Simi‐
2634 larly, meta keys are denoted by M-key, so M-x means Meta-X. (On key‐
2635 boards without a meta key, M-x means ESC x, i.e., press the Escape key
2636 then the x key. This makes ESC the meta prefix. The combination M-C-x
2637 means ESC-Control-x, or press the Escape key then hold the Control key
2638 while pressing the x key.)
2639 Readline commands may be given numeric arguments, which normally act as
2641 a repeat count. Sometimes, however, it is the sign of the argument
2642 that is significant. Passing a negative argument to a command that
2643 acts in the forward direction (e.g., kill-line) causes that command to
2644 act in a backward direction. Commands whose behavior with arguments
2645 deviates from this are noted below.
2646 When a command is described as killing text, the text deleted is saved
2648 for possible future retrieval (yanking). The killed text is saved in a
2649 kill ring. Consecutive kills cause the text to be accumulated into one
2650 unit, which can be yanked all at once. Commands which do not kill text
2651 separate the chunks of text on the kill ring.
2652 Readline Initialization
2654 Readline is customized by putting commands in an initialization file
2655 (the inputrc file). The name of this file is taken from the value of
2656 the INPUTRC variable. If that variable is unset, the default is
2657 ~/.inputrc. When a program which uses the readline library starts up,
2658 the initialization file is read, and the key bindings and variables are
2659 set. There are only a few basic constructs allowed in the readline
2660 initialization file. Blank lines are ignored. Lines beginning with a
2661 # are comments. Lines beginning with a $ indicate conditional con‐
2662 structs. Other lines denote key bindings and variable settings.
2663 The default key-bindings may be changed with an inputrc file. Other
2665 programs that use this library may add their own commands and bindings.
2666 For example, placing
2668 M-Control-u: universal-argument
2670 or
2671 C-Meta-u: universal-argument
2672 into the inputrc would make M-C-u execute the readline command univer‐
2673 sal-argument.
2674 The following symbolic character names are recognized: RUBOUT, DEL,
2676 ESC, LFD, NEWLINE, RET, RETURN, SPC, SPACE, and TAB.
2677 In addition to command names, readline allows keys to be bound to a
2679 string that is inserted when the key is pressed (a macro).
2680 Readline Key Bindings
2682 The syntax for controlling key bindings in the inputrc file is simple.
2683 All that is required is the name of the command or the text of a macro
2684 and a key sequence to which it should be bound. The name may be speci‐
2685 fied in one of two ways: as a symbolic key name, possibly with Meta- or
2686 Control- prefixes, or as a key sequence.
2687 When using the form keyname:function-name or macro, keyname is the name
2689 of a key spelled out in English. For example:
2690 Control-u: universal-argument
2692 Meta-Rubout: backward-kill-word
2693 Control-o: "> output"
2694 In the above example, C-u is bound to the function universal-argument,
2696 M-DEL is bound to the function backward-kill-word, and C-o is bound to
2697 run the macro expressed on the right hand side (that is, to insert the
2698 text ``> output'' into the line).
2699 In the second form, "keyseq":function-name or macro, keyseq differs
2701 from keyname above in that strings denoting an entire key sequence may
2702 be specified by placing the sequence within double quotes. Some GNU
2703 Emacs style key escapes can be used, as in the following example, but
2704 the symbolic character names are not recognized.
2705 "\C-u": universal-argument
2707 "\C-x\C-r": re-read-init-file
2708 "\e[11~": "Function Key 1"
2709 In this example, C-u is again bound to the function universal-argument.
2711 C-x C-r is bound to the function re-read-init-file, and ESC [ 1 1 ~ is
2712 bound to insert the text ``Function Key 1''.
2713 The full set of GNU Emacs style escape sequences is
2715 \C- control prefix
2716 \M- meta prefix
2717 \e an escape character
2718 \\ backslash
2719 \" literal "
2720 \' literal '
2721 In addition to the GNU Emacs style escape sequences, a second set of
2723 backslash escapes is available:
2724 \a alert (bell)
2725 \b backspace
2726 \d delete
2727 \f form feed
2728 \n newline
2729 \r carriage return
2730 \t horizontal tab
2731 \v vertical tab
2732 \nnn the eight-bit character whose value is the octal value
2733 nnn (one to three digits)
2734 \xHH the eight-bit character whose value is the hexadecimal
2735 value HH (one or two hex digits)
2736 When entering the text of a macro, single or double quotes must be used
2738 to indicate a macro definition. Unquoted text is assumed to be a func‐
2739 tion name. In the macro body, the backslash escapes described above
2740 are expanded. Backslash will quote any other character in the macro
2741 text, including " and '.
2742 Bash allows the current readline key bindings to be displayed or modi‐
2744 fied with the bind builtin command. The editing mode may be switched
2745 during interactive use by using the -o option to the set builtin com‐
2746 mand (see SHELL BUILTIN COMMANDS below).
2747 Readline Variables
2749 Readline has variables that can be used to further customize its behav‐
2750 ior. A variable may be set in the inputrc file with a statement of the
2751 form
2752 set variable-name value
2754 Except where noted, readline variables can take the values On or Off
2756 (without regard to case). Unrecognized variable names are ignored.
2757 When a variable value is read, empty or null values, "on" (case-insen‐
2758 sitive), and "1" are equivalent to On. All other values are equivalent
2759 to Off. The variables and their default values are:
2760 bell-style (audible)
2762 Controls what happens when readline wants to ring the terminal
2763 bell. If set to none, readline never rings the bell. If set to
2764 visible, readline uses a visible bell if one is available. If
2765 set to audible, readline attempts to ring the terminal's bell.
2766 bind-tty-special-chars (On)
2767 If set to On, readline attempts to bind the control characters
2768 treated specially by the kernel's terminal driver to their read‐
2769 line equivalents.
2770 comment-begin (``#'')
2771 The string that is inserted when the readline insert-comment
2772 command is executed. This command is bound to M-# in emacs mode
2773 and to # in vi command mode.
2774 completion-ignore-case (Off)
2775 If set to On, readline performs filename matching and completion
2776 in a case-insensitive fashion.
2777 completion-prefix-display-length (0)
2778 The length in characters of the common prefix of a list of pos‐
2779 sible completions that is displayed without modification. When
2780 set to a value greater than zero, common prefixes longer than
2781 this value are replaced with an ellipsis when displaying possi‐
2782 ble completions.
2783 completion-query-items (100)
2784 This determines when the user is queried about viewing the num‐
2785 ber of possible completions generated by the possible-comple‐
2786 tions command. It may be set to any integer value greater than
2787 or equal to zero. If the number of possible completions is
2788 greater than or equal to the value of this variable, the user is
2789 asked whether or not he wishes to view them; otherwise they are
2790 simply listed on the terminal.
2791 convert-meta (On)
2792 If set to On, readline will convert characters with the eighth
2793 bit set to an ASCII key sequence by stripping the eighth bit and
2794 prefixing an escape character (in effect, using escape as the
2795 meta prefix).
2796 disable-completion (Off)
2797 If set to On, readline will inhibit word completion. Completion
2798 characters will be inserted into the line as if they had been
2799 mapped to self-insert.
2800 editing-mode (emacs)
2801 Controls whether readline begins with a set of key bindings sim‐
2802 ilar to Emacs or vi. editing-mode can be set to either emacs or
2803 vi.
2804 echo-control-characters (On)
2805 When set to On, on operating systems that indicate they support
2806 it, readline echoes a character corresponding to a signal gener‐
2807 ated from the keyboard.
2808 enable-keypad (Off)
2809 When set to On, readline will try to enable the application key‐
2810 pad when it is called. Some systems need this to enable the
2811 arrow keys.
2812 enable-meta-key (On)
2813 When set to On, readline will try to enable any meta modifier
2814 key the terminal claims to support when it is called. On many
2815 terminals, the meta key is used to send eight-bit characters.
2816 expand-tilde (Off)
2817 If set to On, tilde expansion is performed when readline
2818 attempts word completion.
2819 history-preserve-point (Off)
2820 If set to On, the history code attempts to place point at the
2821 same location on each history line retrieved with previous-his‐
2822 tory or next-history.
2823 history-size (0)
2824 Set the maximum number of history entries saved in the history
2825 list. If set to zero, the number of entries in the history list
2826 is not limited.
2827 horizontal-scroll-mode (Off)
2828 When set to On, makes readline use a single line for display,
2829 scrolling the input horizontally on a single screen line when it
2830 becomes longer than the screen width rather than wrapping to a
2831 new line.
2832 input-meta (Off)
2833 If set to On, readline will enable eight-bit input (that is, it
2834 will not strip the high bit from the characters it reads),
2835 regardless of what the terminal claims it can support. The name
2836 meta-flag is a synonym for this variable.
2837 isearch-terminators (``C-[C-J'')
2838 The string of characters that should terminate an incremental
2839 search without subsequently executing the character as a com‐
2840 mand. If this variable has not been given a value, the charac‐
2841 ters ESC and C-J will terminate an incremental search.
2842 keymap (emacs)
2843 Set the current readline keymap. The set of valid keymap names
2844 is emacs, emacs-standard, emacs-meta, emacs-ctlx, vi, vi-com‐
2845 mand, and vi-insert. vi is equivalent to vi-command; emacs is
2846 equivalent to emacs-standard. The default value is emacs; the
2847 value of editing-mode also affects the default keymap.
2848 mark-directories (On)
2849 If set to On, completed directory names have a slash appended.
2850 mark-modified-lines (Off)
2851 If set to On, history lines that have been modified are dis‐
2852 played with a preceding asterisk (*).
2853 mark-symlinked-directories (Off)
2854 If set to On, completed names which are symbolic links to direc‐
2855 tories have a slash appended (subject to the value of
2856 mark-directories).
2857 match-hidden-files (On)
2858 This variable, when set to On, causes readline to match files
2859 whose names begin with a `.' (hidden files) when performing
2860 filename completion. If set to Off, the leading `.' must be
2861 supplied by the user in the filename to be completed.
2862 menu-complete-display-prefix (Off)
2863 If set to On, menu completion displays the common prefix of the
2864 list of possible completions (which may be empty) before cycling
2865 through the list.
2866 output-meta (Off)
2867 If set to On, readline will display characters with the eighth
2868 bit set directly rather than as a meta-prefixed escape sequence.
2869 page-completions (On)
2870 If set to On, readline uses an internal more-like pager to dis‐
2871 play a screenful of possible completions at a time.
2872 print-completions-horizontally (Off)
2873 If set to On, readline will display completions with matches
2874 sorted horizontally in alphabetical order, rather than down the
2875 screen.
2876 revert-all-at-newline (Off)
2877 If set to On, readline will undo all changes to history lines
2878 before returning when accept-line is executed. By default, his‐
2879 tory lines may be modified and retain individual undo lists
2880 across calls to readline.
2881 show-all-if-ambiguous (Off)
2882 This alters the default behavior of the completion functions.
2883 If set to On, words which have more than one possible completion
2884 cause the matches to be listed immediately instead of ringing
2885 the bell.
2886 show-all-if-unmodified (Off)
2887 This alters the default behavior of the completion functions in
2888 a fashion similar to show-all-if-ambiguous. If set to On, words
2889 which have more than one possible completion without any possi‐
2890 ble partial completion (the possible completions don't share a
2891 common prefix) cause the matches to be listed immediately
2892 instead of ringing the bell.
2893 skip-completed-text (Off)
2894 If set to On, this alters the default completion behavior when
2895 inserting a single match into the line. It's only active when
2896 performing completion in the middle of a word. If enabled,
2897 readline does not insert characters from the completion that
2898 match characters after point in the word being completed, so
2899 portions of the word following the cursor are not duplicated.
2900 visible-stats (Off)
2901 If set to On, a character denoting a file's type as reported by
2902 stat(2) is appended to the filename when listing possible com‐
2903 pletions.
2904 Readline Conditional Constructs
2906 Readline implements a facility similar in spirit to the conditional
2907 compilation features of the C preprocessor which allows key bindings
2908 and variable settings to be performed as the result of tests. There
2909 are four parser directives used.
2910 $if The $if construct allows bindings to be made based on the edit‐
2912 ing mode, the terminal being used, or the application using
2913 readline. The text of the test extends to the end of the line;
2914 no characters are required to isolate it.
2915 mode The mode= form of the $if directive is used to test
2917 whether readline is in emacs or vi mode. This may be
2918 used in conjunction with the set keymap command, for
2919 instance, to set bindings in the emacs-standard and
2920 emacs-ctlx keymaps only if readline is starting out in
2921 emacs mode.
2922 term The term= form may be used to include terminal-specific
2924 key bindings, perhaps to bind the key sequences output by
2925 the terminal's function keys. The word on the right side
2926 of the = is tested against the both full name of the ter‐
2927 minal and the portion of the terminal name before the
2928 first -. This allows sun to match both sun and sun-cmd,
2929 for instance.
2930 application
2932 The application construct is used to include application-
2933 specific settings. Each program using the readline
2934 library sets the application name, and an initialization
2935 file can test for a particular value. This could be used
2936 to bind key sequences to functions useful for a specific
2937 program. For instance, the following command adds a key
2938 sequence that quotes the current or previous word in
2939 bash:
2940 $if Bash
2942 # Quote the current or previous word
2943 "\C-xq": "\eb\"\ef\""
2944 $endif
2945 $endif This command, as seen in the previous example, terminates an $if
2947 command.
2948 $else Commands in this branch of the $if directive are executed if the
2950 test fails.
2951 $include
2953 This directive takes a single filename as an argument and reads
2954 commands and bindings from that file. For example, the follow‐
2955 ing directive would read /etc/inputrc:
2956 $include /etc/inputrc
2958 Searching
2960 Readline provides commands for searching through the command history
2961 (see HISTORY below) for lines containing a specified string. There are
2962 two search modes: incremental and non-incremental.
2963 Incremental searches begin before the user has finished typing the
2965 search string. As each character of the search string is typed, read‐
2966 line displays the next entry from the history matching the string typed
2967 so far. An incremental search requires only as many characters as
2968 needed to find the desired history entry. The characters present in
2969 the value of the isearch-terminators variable are used to terminate an
2970 incremental search. If that variable has not been assigned a value the
2971 Escape and Control-J characters will terminate an incremental search.
2972 Control-G will abort an incremental search and restore the original
2973 line. When the search is terminated, the history entry containing the
2974 search string becomes the current line.
2975 To find other matching entries in the history list, type Control-S or
2977 Control-R as appropriate. This will search backward or forward in the
2978 history for the next entry matching the search string typed so far.
2979 Any other key sequence bound to a readline command will terminate the
2980 search and execute that command. For instance, a newline will termi‐
2981 nate the search and accept the line, thereby executing the command from
2982 the history list.
2983 Readline remembers the last incremental search string. If two Control-
2985 Rs are typed without any intervening characters defining a new search
2986 string, any remembered search string is used.
2987 Non-incremental searches read the entire search string before starting
2989 to search for matching history lines. The search string may be typed
2990 by the user or be part of the contents of the current line.
2991 Readline Command Names
2993 The following is a list of the names of the commands and the default
2994 key sequences to which they are bound. Command names without an accom‐
2995 panying key sequence are unbound by default. In the following descrip‐
2996 tions, point refers to the current cursor position, and mark refers to
2997 a cursor position saved by the set-mark command. The text between the
2998 point and mark is referred to as the region.
2999 Commands for Moving
3001 beginning-of-line (C-a)
3002 Move to the start of the current line.
3003 end-of-line (C-e)
3004 Move to the end of the line.
3005 forward-char (C-f)
3006 Move forward a character.
3007 backward-char (C-b)
3008 Move back a character.
3009 forward-word (M-f)
3010 Move forward to the end of the next word. Words are composed of
3011 alphanumeric characters (letters and digits).
3012 backward-word (M-b)
3013 Move back to the start of the current or previous word. Words
3014 are composed of alphanumeric characters (letters and digits).
3015 shell-forward-word
3016 Move forward to the end of the next word. Words are delimited
3017 by non-quoted shell metacharacters.
3018 shell-backward-word
3019 Move back to the start of the current or previous word. Words
3020 are delimited by non-quoted shell metacharacters.
3021 clear-screen (C-l)
3022 Clear the screen leaving the current line at the top of the
3023 screen. With an argument, refresh the current line without
3024 clearing the screen.
3025 redraw-current-line
3026 Refresh the current line.
3027 Commands for Manipulating the History
3029 accept-line (Newline, Return)
3030 Accept the line regardless of where the cursor is. If this line
3031 is non-empty, add it to the history list according to the state
3032 of the HISTCONTROL variable. If the line is a modified history
3033 line, then restore the history line to its original state.
3034 previous-history (C-p)
3035 Fetch the previous command from the history list, moving back in
3036 the list.
3037 next-history (C-n)
3038 Fetch the next command from the history list, moving forward in
3039 the list.
3040 beginning-of-history (M-<)
3041 Move to the first line in the history.
3042 end-of-history (M->)
3043 Move to the end of the input history, i.e., the line currently
3044 being entered.
3045 reverse-search-history (C-r)
3046 Search backward starting at the current line and moving `up'
3047 through the history as necessary. This is an incremental
3048 search.
3049 forward-search-history (C-s)
3050 Search forward starting at the current line and moving `down'
3051 through the history as necessary. This is an incremental
3052 search.
3053 non-incremental-reverse-search-history (M-p)
3054 Search backward through the history starting at the current line
3055 using a non-incremental search for a string supplied by the
3056 user.
3057 non-incremental-forward-search-history (M-n)
3058 Search forward through the history using a non-incremental
3059 search for a string supplied by the user.
3060 history-search-forward
3061 Search forward through the history for the string of characters
3062 between the start of the current line and the point. This is a
3063 non-incremental search.
3064 history-search-backward
3065 Search backward through the history for the string of characters
3066 between the start of the current line and the point. This is a
3067 non-incremental search.
3068 yank-nth-arg (M-C-y)
3069 Insert the first argument to the previous command (usually the
3070 second word on the previous line) at point. With an argument n,
3071 insert the nth word from the previous command (the words in the
3072 previous command begin with word 0). A negative argument
3073 inserts the nth word from the end of the previous command. Once
3074 the argument n is computed, the argument is extracted as if the
3075 "!n" history expansion had been specified.
3076 yank-last-arg (M-., M-_)
3077 Insert the last argument to the previous command (the last word
3078 of the previous history entry). With a numeric argument, behave
3079 exactly like yank-nth-arg. Successive calls to yank-last-arg
3080 move back through the history list, inserting the last word (or
3081 the word specified by the argument to the first call) of each
3082 line in turn. Any numeric argument supplied to these successive
3083 calls determines the direction to move through the history. A
3084 negative argument switches the direction through the history
3085 (back or forward). The history expansion facilities are used to
3086 extract the last argument, as if the "!$" history expansion had
3087 been specified.
3088 shell-expand-line (M-C-e)
3089 Expand the line as the shell does. This performs alias and his‐
3090 tory expansion as well as all of the shell word expansions. See
3091 HISTORY EXPANSION below for a description of history expansion.
3092 history-expand-line (M-^)
3093 Perform history expansion on the current line. See HISTORY
3094 EXPANSION below for a description of history expansion.
3095 magic-space
3096 Perform history expansion on the current line and insert a
3097 space. See HISTORY EXPANSION below for a description of history
3098 expansion.
3099 alias-expand-line
3100 Perform alias expansion on the current line. See ALIASES above
3101 for a description of alias expansion.
3102 history-and-alias-expand-line
3103 Perform history and alias expansion on the current line.
3104 insert-last-argument (M-., M-_)
3105 A synonym for yank-last-arg.
3106 operate-and-get-next (C-o)
3107 Accept the current line for execution and fetch the next line
3108 relative to the current line from the history for editing. Any
3109 argument is ignored.
3110 edit-and-execute-command (C-xC-e)
3111 Invoke an editor on the current command line, and execute the
3112 result as shell commands. Bash attempts to invoke $VISUAL,
3113 $EDITOR, and emacs as the editor, in that order.
3114 Commands for Changing Text
3116 delete-char (C-d)
3117 Delete the character at point. If point is at the beginning of
3118 the line, there are no characters in the line, and the last
3119 character typed was not bound to delete-char, then return EOF.
3120 backward-delete-char (Rubout)
3121 Delete the character behind the cursor. When given a numeric
3122 argument, save the deleted text on the kill ring.
3123 forward-backward-delete-char
3124 Delete the character under the cursor, unless the cursor is at
3125 the end of the line, in which case the character behind the cur‐
3126 sor is deleted.
3127 quoted-insert (C-q, C-v)
3128 Add the next character typed to the line verbatim. This is how
3129 to insert characters like C-q, for example.
3130 tab-insert (C-v TAB)
3131 Insert a tab character.
3132 self-insert (a, b, A, 1, !, ...)
3133 Insert the character typed.
3134 transpose-chars (C-t)
3135 Drag the character before point forward over the character at
3136 point, moving point forward as well. If point is at the end of
3137 the line, then this transposes the two characters before point.
3138 Negative arguments have no effect.
3139 transpose-words (M-t)
3140 Drag the word before point past the word after point, moving
3141 point over that word as well. If point is at the end of the
3142 line, this transposes the last two words on the line.
3143 upcase-word (M-u)
3144 Uppercase the current (or following) word. With a negative
3145 argument, uppercase the previous word, but do not move point.
3146 downcase-word (M-l)
3147 Lowercase the current (or following) word. With a negative
3148 argument, lowercase the previous word, but do not move point.
3149 capitalize-word (M-c)
3150 Capitalize the current (or following) word. With a negative
3151 argument, capitalize the previous word, but do not move point.
3152 overwrite-mode
3153 Toggle overwrite mode. With an explicit positive numeric argu‐
3154 ment, switches to overwrite mode. With an explicit non-positive
3155 numeric argument, switches to insert mode. This command affects
3156 only emacs mode; vi mode does overwrite differently. Each call
3157 to readline() starts in insert mode. In overwrite mode, charac‐
3158 ters bound to self-insert replace the text at point rather than
3159 pushing the text to the right. Characters bound to back‐
3160 ward-delete-char replace the character before point with a
3161 space. By default, this command is unbound.
3162 Killing and Yanking
3164 kill-line (C-k)
3165 Kill the text from point to the end of the line.
3166 backward-kill-line (C-x Rubout)
3167 Kill backward to the beginning of the line.
3168 unix-line-discard (C-u)
3169 Kill backward from point to the beginning of the line. The
3170 killed text is saved on the kill-ring.
3171 kill-whole-line
3172 Kill all characters on the current line, no matter where point
3173 is.
3174 kill-word (M-d)
3175 Kill from point to the end of the current word, or if between
3176 words, to the end of the next word. Word boundaries are the
3177 same as those used by forward-word.
3178 backward-kill-word (M-Rubout)
3179 Kill the word behind point. Word boundaries are the same as
3180 those used by backward-word.
3181 shell-kill-word (M-d)
3182 Kill from point to the end of the current word, or if between
3183 words, to the end of the next word. Word boundaries are the
3184 same as those used by shell-forward-word.
3185 shell-backward-kill-word (M-Rubout)
3186 Kill the word behind point. Word boundaries are the same as
3187 those used by shell-backward-word.
3188 unix-word-rubout (C-w)
3189 Kill the word behind point, using white space as a word bound‐
3190 ary. The killed text is saved on the kill-ring.
3191 unix-filename-rubout
3192 Kill the word behind point, using white space and the slash
3193 character as the word boundaries. The killed text is saved on
3194 the kill-ring.
3195 delete-horizontal-space (M-\)
3196 Delete all spaces and tabs around point.
3197 kill-region
3198 Kill the text in the current region.
3199 copy-region-as-kill
3200 Copy the text in the region to the kill buffer.
3201 copy-backward-word
3202 Copy the word before point to the kill buffer. The word bound‐
3203 aries are the same as backward-word.
3204 copy-forward-word
3205 Copy the word following point to the kill buffer. The word
3206 boundaries are the same as forward-word.
3207 yank (C-y)
3208 Yank the top of the kill ring into the buffer at point.
3209 yank-pop (M-y)
3210 Rotate the kill ring, and yank the new top. Only works follow‐
3211 ing yank or yank-pop.
3212 Numeric Arguments
3214 digit-argument (M-0, M-1, ..., M--)
3215 Add this digit to the argument already accumulating, or start a
3216 new argument. M-- starts a negative argument.
3217 universal-argument
3218 This is another way to specify an argument. If this command is
3219 followed by one or more digits, optionally with a leading minus
3220 sign, those digits define the argument. If the command is fol‐
3221 lowed by digits, executing universal-argument again ends the
3222 numeric argument, but is otherwise ignored. As a special case,
3223 if this command is immediately followed by a character that is
3224 neither a digit or minus sign, the argument count for the next
3225 command is multiplied by four. The argument count is initially
3226 one, so executing this function the first time makes the argu‐
3227 ment count four, a second time makes the argument count sixteen,
3228 and so on.
3229 Completing
3231 complete (TAB)
3232 Attempt to perform completion on the text before point. Bash
3233 attempts completion treating the text as a variable (if the text
3234 begins with $), username (if the text begins with ~), hostname
3235 (if the text begins with @), or command (including aliases and
3236 functions) in turn. If none of these produces a match, filename
3237 completion is attempted.
3238 possible-completions (M-?)
3239 List the possible completions of the text before point.
3240 insert-completions (M-*)
3241 Insert all completions of the text before point that would have
3242 been generated by possible-completions.
3243 menu-complete
3244 Similar to complete, but replaces the word to be completed with
3245 a single match from the list of possible completions. Repeated
3246 execution of menu-complete steps through the list of possible
3247 completions, inserting each match in turn. At the end of the
3248 list of completions, the bell is rung (subject to the setting of
3249 bell-style) and the original text is restored. An argument of n
3250 moves n positions forward in the list of matches; a negative
3251 argument may be used to move backward through the list. This
3252 command is intended to be bound to TAB, but is unbound by
3253 default.
3254 menu-complete-backward
3255 Identical to menu-complete, but moves backward through the list
3256 of possible completions, as if menu-complete had been given a
3257 negative argument. This command is unbound by default.
3258 delete-char-or-list
3259 Deletes the character under the cursor if not at the beginning
3260 or end of the line (like delete-char). If at the end of the
3261 line, behaves identically to possible-completions. This command
3262 is unbound by default.
3263 complete-filename (M-/)
3264 Attempt filename completion on the text before point.
3265 possible-filename-completions (C-x /)
3266 List the possible completions of the text before point, treating
3267 it as a filename.
3268 complete-username (M-~)
3269 Attempt completion on the text before point, treating it as a
3270 username.
3271 possible-username-completions (C-x ~)
3272 List the possible completions of the text before point, treating
3273 it as a username.
3274 complete-variable (M-$)
3275 Attempt completion on the text before point, treating it as a
3276 shell variable.
3277 possible-variable-completions (C-x $)
3278 List the possible completions of the text before point, treating
3279 it as a shell variable.
3280 complete-hostname (M-@)
3281 Attempt completion on the text before point, treating it as a
3282 hostname.
3283 possible-hostname-completions (C-x @)
3284 List the possible completions of the text before point, treating
3285 it as a hostname.
3286 complete-command (M-!)
3287 Attempt completion on the text before point, treating it as a
3288 command name. Command completion attempts to match the text
3289 against aliases, reserved words, shell functions, shell
3290 builtins, and finally executable filenames, in that order.
3291 possible-command-completions (C-x !)
3292 List the possible completions of the text before point, treating
3293 it as a command name.
3294 dynamic-complete-history (M-TAB)
3295 Attempt completion on the text before point, comparing the text
3296 against lines from the history list for possible completion
3297 matches.
3298 dabbrev-expand
3299 Attempt menu completion on the text before point, comparing the
3300 text against lines from the history list for possible completion
3301 matches.
3302 complete-into-braces (M-{)
3303 Perform filename completion and insert the list of possible com‐
3304 pletions enclosed within braces so the list is available to the
3305 shell (see Brace Expansion above).
3306 Keyboard Macros
3308 start-kbd-macro (C-x ()
3309 Begin saving the characters typed into the current keyboard
3310 macro.
3311 end-kbd-macro (C-x ))
3312 Stop saving the characters typed into the current keyboard macro
3313 and store the definition.
3314 call-last-kbd-macro (C-x e)
3315 Re-execute the last keyboard macro defined, by making the char‐
3316 acters in the macro appear as if typed at the keyboard.
3317 Miscellaneous
3319 re-read-init-file (C-x C-r)
3320 Read in the contents of the inputrc file, and incorporate any
3321 bindings or variable assignments found there.
3322 abort (C-g)
3323 Abort the current editing command and ring the terminal's bell
3324 (subject to the setting of bell-style).
3325 do-uppercase-version (M-a, M-b, M-x, ...)
3326 If the metafied character x is lowercase, run the command that
3327 is bound to the corresponding uppercase character.
3328 prefix-meta (ESC)
3329 Metafy the next character typed. ESC f is equivalent to Meta-f.
3330 undo (C-_, C-x C-u)
3331 Incremental undo, separately remembered for each line.
3332 revert-line (M-r)
3333 Undo all changes made to this line. This is like executing the
3334 undo command enough times to return the line to its initial
3335 state.
3336 tilde-expand (M-&)
3337 Perform tilde expansion on the current word.
3338 set-mark (C-@, M-<space>)
3339 Set the mark to the point. If a numeric argument is supplied,
3340 the mark is set to that position.
3341 exchange-point-and-mark (C-x C-x)
3342 Swap the point with the mark. The current cursor position is
3343 set to the saved position, and the old cursor position is saved
3344 as the mark.
3345 character-search (C-])
3346 A character is read and point is moved to the next occurrence of
3347 that character. A negative count searches for previous occur‐
3348 rences.
3349 character-search-backward (M-C-])
3350 A character is read and point is moved to the previous occur‐
3351 rence of that character. A negative count searches for subse‐
3352 quent occurrences.
3353 skip-csi-sequence
3354 Read enough characters to consume a multi-key sequence such as
3355 those defined for keys like Home and End. Such sequences begin
3356 with a Control Sequence Indicator (CSI), usually ESC-[. If this
3357 sequence is bound to "\[", keys producing such sequences will
3358 have no effect unless explicitly bound to a readline command,
3359 instead of inserting stray characters into the editing buffer.
3360 This is unbound by default, but usually bound to ESC-[.
3361 insert-comment (M-#)
3362 Without a numeric argument, the value of the readline com‐
3363 ment-begin variable is inserted at the beginning of the current
3364 line. If a numeric argument is supplied, this command acts as a
3365 toggle: if the characters at the beginning of the line do not
3366 match the value of comment-begin, the value is inserted, other‐
3367 wise the characters in comment-begin are deleted from the begin‐
3368 ning of the line. In either case, the line is accepted as if a
3369 newline had been typed. The default value of comment-begin
3370 causes this command to make the current line a shell comment.
3371 If a numeric argument causes the comment character to be
3372 removed, the line will be executed by the shell.
3373 glob-complete-word (M-g)
3374 The word before point is treated as a pattern for pathname
3375 expansion, with an asterisk implicitly appended. This pattern
3376 is used to generate a list of matching file names for possible
3377 completions.
3378 glob-expand-word (C-x *)
3379 The word before point is treated as a pattern for pathname
3380 expansion, and the list of matching file names is inserted,
3381 replacing the word. If a numeric argument is supplied, an
3382 asterisk is appended before pathname expansion.
3383 glob-list-expansions (C-x g)
3384 The list of expansions that would have been generated by
3385 glob-expand-word is displayed, and the line is redrawn. If a
3386 numeric argument is supplied, an asterisk is appended before
3387 pathname expansion.
3388 dump-functions
3389 Print all of the functions and their key bindings to the read‐
3390 line output stream. If a numeric argument is supplied, the out‐
3391 put is formatted in such a way that it can be made part of an
3392 inputrc file.
3393 dump-variables
3394 Print all of the settable readline variables and their values to
3395 the readline output stream. If a numeric argument is supplied,
3396 the output is formatted in such a way that it can be made part
3397 of an inputrc file.
3398 dump-macros
3399 Print all of the readline key sequences bound to macros and the
3400 strings they output. If a numeric argument is supplied, the
3401 output is formatted in such a way that it can be made part of an
3402 inputrc file.
3403 display-shell-version (C-x C-v)
3404 Display version information about the current instance of bash.
3405 Programmable Completion
3407 When word completion is attempted for an argument to a command for
3408 which a completion specification (a compspec) has been defined using
3409 the complete builtin (see SHELL BUILTIN COMMANDS below), the program‐
3410 mable completion facilities are invoked.
3411 First, the command name is identified. If the command word is the
3413 empty string (completion attempted at the beginning of an empty line),
3414 any compspec defined with the -E option to complete is used. If a
3415 compspec has been defined for that command, the compspec is used to
3416 generate the list of possible completions for the word. If the command
3417 word is a full pathname, a compspec for the full pathname is searched
3418 for first. If no compspec is found for the full pathname, an attempt
3419 is made to find a compspec for the portion following the final slash.
3420 If those searches do not result in a compspec, any compspec defined
3421 with the -D option to complete is used as the default.
3422 Once a compspec has been found, it is used to generate the list of
3424 matching words. If a compspec is not found, the default bash comple‐
3425 tion as described above under Completing is performed.
3426 First, the actions specified by the compspec are used. Only matches
3428 which are prefixed by the word being completed are returned. When the
3429 -f or -d option is used for filename or directory name completion, the
3430 shell variable FIGNORE is used to filter the matches.
3431 Any completions specified by a pathname expansion pattern to the -G
3433 option are generated next. The words generated by the pattern need not
3434 match the word being completed. The GLOBIGNORE shell variable is not
3435 used to filter the matches, but the FIGNORE variable is used.
3436 Next, the string specified as the argument to the -W option is consid‐
3438 ered. The string is first split using the characters in the IFS spe‐
3439 cial variable as delimiters. Shell quoting is honored. Each word is
3440 then expanded using brace expansion, tilde expansion, parameter and
3441 variable expansion, command substitution, and arithmetic expansion, as
3442 described above under EXPANSION. The results are split using the rules
3443 described above under Word Splitting. The results of the expansion are
3444 prefix-matched against the word being completed, and the matching words
3445 become the possible completions.
3446 After these matches have been generated, any shell function or command
3448 specified with the -F and -C options is invoked. When the command or
3449 function is invoked, the COMP_LINE, COMP_POINT, COMP_KEY, and COMP_TYPE
3450 variables are assigned values as described above under Shell Variables.
3451 If a shell function is being invoked, the COMP_WORDS and COMP_CWORD
3452 variables are also set. When the function or command is invoked, the
3453 first argument is the name of the command whose arguments are being
3454 completed, the second argument is the word being completed, and the
3455 third argument is the word preceding the word being completed on the
3456 current command line. No filtering of the generated completions
3457 against the word being completed is performed; the function or command
3458 has complete freedom in generating the matches.
3459 Any function specified with -F is invoked first. The function may use
3461 any of the shell facilities, including the compgen builtin described
3462 below, to generate the matches. It must put the possible completions
3463 in the COMPREPLY array variable.
3464 Next, any command specified with the -C option is invoked in an envi‐
3466 ronment equivalent to command substitution. It should print a list of
3467 completions, one per line, to the standard output. Backslash may be
3468 used to escape a newline, if necessary.
3469 After all of the possible completions are generated, any filter speci‐
3471 fied with the -X option is applied to the list. The filter is a pat‐
3472 tern as used for pathname expansion; a & in the pattern is replaced
3473 with the text of the word being completed. A literal & may be escaped
3474 with a backslash; the backslash is removed before attempting a match.
3475 Any completion that matches the pattern will be removed from the list.
3476 A leading ! negates the pattern; in this case any completion not match‐
3477 ing the pattern will be removed.
3478 Finally, any prefix and suffix specified with the -P and -S options are
3480 added to each member of the completion list, and the result is returned
3481 to the readline completion code as the list of possible completions.
3482 If the previously-applied actions do not generate any matches, and the
3484 -o dirnames option was supplied to complete when the compspec was
3485 defined, directory name completion is attempted.
3486 If the -o plusdirs option was supplied to complete when the compspec
3488 was defined, directory name completion is attempted and any matches are
3489 added to the results of the other actions.
3490 By default, if a compspec is found, whatever it generates is returned
3492 to the completion code as the full set of possible completions. The
3493 default bash completions are not attempted, and the readline default of
3494 filename completion is disabled. If the -o bashdefault option was sup‐
3495 plied to complete when the compspec was defined, the bash default com‐
3496 pletions are attempted if the compspec generates no matches. If the -o
3497 default option was supplied to complete when the compspec was defined,
3498 readline's default completion will be performed if the compspec (and,
3499 if attempted, the default bash completions) generate no matches.
3500 When a compspec indicates that directory name completion is desired,
3502 the programmable completion functions force readline to append a slash
3503 to completed names which are symbolic links to directories, subject to
3504 the value of the mark-directories readline variable, regardless of the
3505 setting of the mark-symlinked-directories readline variable.
3506 There is some support for dynamically modifying completions. This is
3508 most useful when used in combination with a default completion speci‐
3509 fied with complete -D. It's possible for shell functions executed as
3510 completion handlers to indicate that completion should be retried by
3511 returning an exit status of 124. If a shell function returns 124, and
3512 changes the compspec associated with the command on which completion is
3513 being attempted (supplied as the first argument when the function is
3514 executed), programmable completion restarts from the beginning, with an
3515 attempt to find a new compspec for that command. This allows a set of
3516 completions to be built dynamically as completion is attempted, rather
3517 than being loaded all at once.
3518 For instance, assuming that there is a library of compspecs, each kept
3520 in a file corresponding to the name of the command, the following
3521 default completion function would load completions dynamically:
3522 _completion_loader()
3524 {
3525 . "/etc/bash_completion.d/$1.sh" >/dev/null 2>&1 && return 124
3526 }
3527 complete -D -F _completion_loader
3528
3531 When the -o history option to the set builtin is enabled, the shell
3532 provides access to the command history, the list of commands previously
3533 typed. The value of the HISTSIZE variable is used as the number of
3534 commands to save in a history list. The text of the last HISTSIZE com‐
3535 mands (default 500) is saved. The shell stores each command in the
3536 history list prior to parameter and variable expansion (see EXPANSION
3537 above) but after history expansion is performed, subject to the values
3538 of the shell variables HISTIGNORE and HISTCONTROL.
3539 On startup, the history is initialized from the file named by the vari‐
3541 able HISTFILE (default ~/.bash_history). The file named by the value
3542 of HISTFILE is truncated, if necessary, to contain no more than the
3543 number of lines specified by the value of HISTFILESIZE. When the his‐
3544 tory file is read, lines beginning with the history comment character
3545 followed immediately by a digit are interpreted as timestamps for the
3546 preceding history line. These timestamps are optionally displayed
3547 depending on the value of the HISTTIMEFORMAT variable. When an inter‐
3548 active shell exits, the last $HISTSIZE lines are copied from the his‐
3549 tory list to $HISTFILE. If the histappend shell option is enabled (see
3550 the description of shopt under SHELL BUILTIN COMMANDS below), the lines
3551 are appended to the history file, otherwise the history file is over‐
3552 written. If HISTFILE is unset, or if the history file is unwritable,
3553 the history is not saved. If the HISTTIMEFORMAT variable is set, time
3554 stamps are written to the history file, marked with the history comment
3555 character, so they may be preserved across shell sessions. This uses
3556 the history comment character to distinguish timestamps from other his‐
3557 tory lines. After saving the history, the history file is truncated to
3558 contain no more than HISTFILESIZE lines. If HISTFILESIZE is not set,
3559 no truncation is performed.
3560 The builtin command fc (see SHELL BUILTIN COMMANDS below) may be used
3562 to list or edit and re-execute a portion of the history list. The his‐
3563 tory builtin may be used to display or modify the history list and
3564 manipulate the history file. When using command-line editing, search
3565 commands are available in each editing mode that provide access to the
3566 history list.
3567 The shell allows control over which commands are saved on the history
3569 list. The HISTCONTROL and HISTIGNORE variables may be set to cause the
3570 shell to save only a subset of the commands entered. The cmdhist shell
3571 option, if enabled, causes the shell to attempt to save each line of a
3572 multi-line command in the same history entry, adding semicolons where
3573 necessary to preserve syntactic correctness. The lithist shell option
3574 causes the shell to save the command with embedded newlines instead of
3575 semicolons. See the description of the shopt builtin below under SHELL
3576 BUILTIN COMMANDS for information on setting and unsetting shell
3577 options.
3578
3580 The shell supports a history expansion feature that is similar to the
3581 history expansion in csh. This section describes what syntax features
3582 are available. This feature is enabled by default for interactive
3583 shells, and can be disabled using the +H option to the set builtin com‐
3584 mand (see SHELL BUILTIN COMMANDS below). Non-interactive shells do not
3585 perform history expansion by default.
3586 History expansions introduce words from the history list into the input
3588 stream, making it easy to repeat commands, insert the arguments to a
3589 previous command into the current input line, or fix errors in previous
3590 commands quickly.
3591 History expansion is performed immediately after a complete line is
3593 read, before the shell breaks it into words. It takes place in two
3594 parts. The first is to determine which line from the history list to
3595 use during substitution. The second is to select portions of that line
3596 for inclusion into the current one. The line selected from the history
3597 is the event, and the portions of that line that are acted upon are
3598 words. Various modifiers are available to manipulate the selected
3599 words. The line is broken into words in the same fashion as when read‐
3600 ing input, so that several metacharacter-separated words surrounded by
3601 quotes are considered one word. History expansions are introduced by
3602 the appearance of the history expansion character, which is ! by
3603 default. Only backslash (\) and single quotes can quote the history
3604 expansion character.
3605 Several characters inhibit history expansion if found immediately fol‐
3607 lowing the history expansion character, even if it is unquoted: space,
3608 tab, newline, carriage return, and =. If the extglob shell option is
3609 enabled, ( will also inhibit expansion.
3610 Several shell options settable with the shopt builtin may be used to
3612 tailor the behavior of history expansion. If the histverify shell
3613 option is enabled (see the description of the shopt builtin below), and
3614 readline is being used, history substitutions are not immediately
3615 passed to the shell parser. Instead, the expanded line is reloaded
3616 into the readline editing buffer for further modification. If readline
3617 is being used, and the histreedit shell option is enabled, a failed
3618 history substitution will be reloaded into the readline editing buffer
3619 for correction. The -p option to the history builtin command may be
3620 used to see what a history expansion will do before using it. The -s
3621 option to the history builtin may be used to add commands to the end of
3622 the history list without actually executing them, so that they are
3623 available for subsequent recall.
3624 The shell allows control of the various characters used by the history
3626 expansion mechanism (see the description of histchars above under Shell
3627 Variables). The shell uses the history comment character to mark his‐
3628 tory timestamps when writing the history file.
3629 Event Designators
3631 An event designator is a reference to a command line entry in the his‐
3632 tory list. Unless the reference is absolute, events are relative to
3633 the current position in the history list.
3634 ! Start a history substitution, except when followed by a blank,
3636 newline, carriage return, = or ( (when the extglob shell option
3637 is enabled using the shopt builtin).
3638 !n Refer to command line n.
3639 !-n Refer to the current command minus n.
3640 !! Refer to the previous command. This is a synonym for `!-1'.
3641 !string
3642 Refer to the most recent command preceding the current position
3643 in the history list starting with string.
3644 !?string[?]
3645 Refer to the most recent command preceding the current postition
3646 in the history list containing string. The trailing ? may be
3647 omitted if string is followed immediately by a newline.
3648 ^string1^string2^
3649 Quick substitution. Repeat the previous command, replacing
3650 string1 with string2. Equivalent to ``!!:s/string1/string2/''
3651 (see Modifiers below).
3652 !# The entire command line typed so far.
3653 Word Designators
3655 Word designators are used to select desired words from the event. A :
3656 separates the event specification from the word designator. It may be
3657 omitted if the word designator begins with a ^, $, *, -, or %. Words
3658 are numbered from the beginning of the line, with the first word being
3659 denoted by 0 (zero). Words are inserted into the current line sepa‐
3660 rated by single spaces.
3661 0 (zero)
3663 The zeroth word. For the shell, this is the command word.
3664 n The nth word.
3665 ^ The first argument. That is, word 1.
3666 $ The last argument.
3667 % The word matched by the most recent `?string?' search.
3668 x-y A range of words; `-y' abbreviates `0-y'.
3669 * All of the words but the zeroth. This is a synonym for `1-$'.
3670 It is not an error to use * if there is just one word in the
3671 event; the empty string is returned in that case.
3672 x* Abbreviates x-$.
3673 x- Abbreviates x-$ like x*, but omits the last word.
3674 If a word designator is supplied without an event specification, the
3676 previous command is used as the event.
3677 Modifiers
3679 After the optional word designator, there may appear a sequence of one
3680 or more of the following modifiers, each preceded by a `:'.
3681 h Remove a trailing file name component, leaving only the head.
3683 t Remove all leading file name components, leaving the tail.
3684 r Remove a trailing suffix of the form .xxx, leaving the basename.
3685 e Remove all but the trailing suffix.
3686 p Print the new command but do not execute it.
3687 q Quote the substituted words, escaping further substitutions.
3688 x Quote the substituted words as with q, but break into words at
3689 blanks and newlines.
3690 s/old/new/
3691 Substitute new for the first occurrence of old in the event
3692 line. Any delimiter can be used in place of /. The final
3693 delimiter is optional if it is the last character of the event
3694 line. The delimiter may be quoted in old and new with a single
3695 backslash. If & appears in new, it is replaced by old. A sin‐
3696 gle backslash will quote the &. If old is null, it is set to
3697 the last old substituted, or, if no previous history substitu‐
3698 tions took place, the last string in a !?string[?] search.
3699 & Repeat the previous substitution.
3700 g Cause changes to be applied over the entire event line. This is
3701 used in conjunction with `:s' (e.g., `:gs/old/new/') or `:&'.
3702 If used with `:s', any delimiter can be used in place of /, and
3703 the final delimiter is optional if it is the last character of
3704 the event line. An a may be used as a synonym for g.
3705 G Apply the following `s' modifier once to each word in the event
3706 line.
3707
3709 Unless otherwise noted, each builtin command documented in this section
3710 as accepting options preceded by - accepts -- to signify the end of the
3711 options. The :, true, false, and test builtins do not accept options
3712 and do not treat -- specially. The exit, logout, break, continue, let,
3713 and shift builtins accept and process arguments beginning with - with‐
3714 out requiring --. Other builtins that accept arguments but are not
3715 specified as accepting options interpret arguments beginning with - as
3716 invalid options and require -- to prevent this interpretation.
3717 : [arguments]
3718 No effect; the command does nothing beyond expanding arguments
3719 and performing any specified redirections. A zero exit code is
3720 returned.
3721 . filename [arguments]
3723 source filename [arguments]
3724 Read and execute commands from filename in the current shell
3725 environment and return the exit status of the last command exe‐
3726 cuted from filename. If filename does not contain a slash, file
3727 names in PATH are used to find the directory containing file‐
3728 name. The file searched for in PATH need not be executable.
3729 When bash is not in posix mode, the current directory is
3730 searched if no file is found in PATH. If the sourcepath option
3731 to the shopt builtin command is turned off, the PATH is not
3732 searched. If any arguments are supplied, they become the posi‐
3733 tional parameters when filename is executed. Otherwise the
3734 positional parameters are unchanged. The return status is the
3735 status of the last command exited within the script (0 if no
3736 commands are executed), and false if filename is not found or
3737 cannot be read.
3738 alias [-p] [name[=value] ...]
3740 Alias with no arguments or with the -p option prints the list of
3741 aliases in the form alias name=value on standard output. When
3742 arguments are supplied, an alias is defined for each name whose
3743 value is given. A trailing space in value causes the next word
3744 to be checked for alias substitution when the alias is expanded.
3745 For each name in the argument list for which no value is sup‐
3746 plied, the name and value of the alias is printed. Alias
3747 returns true unless a name is given for which no alias has been
3748 defined.
3749 bg [jobspec ...]
3751 Resume each suspended job jobspec in the background, as if it
3752 had been started with &. If jobspec is not present, the shell's
3753 notion of the current job is used. bg jobspec returns 0 unless
3754 run when job control is disabled or, when run with job control
3755 enabled, any specified jobspec was not found or was started
3756 without job control.
3757 bind [-m keymap] [-lpsvPSV]
3759 bind [-m keymap] [-q function] [-u function] [-r keyseq]
3760 bind [-m keymap] -f filename
3761 bind [-m keymap] -x keyseq:shell-command
3762 bind [-m keymap] keyseq:function-name
3763 bind readline-command
3764 Display current readline key and function bindings, bind a key
3765 sequence to a readline function or macro, or set a readline
3766 variable. Each non-option argument is a command as it would
3767 appear in .inputrc, but each binding or command must be passed
3768 as a separate argument; e.g., '"\C-x\C-r": re-read-init-file'.
3769 Options, if supplied, have the following meanings:
3770 -m keymap
3771 Use keymap as the keymap to be affected by the subsequent
3772 bindings. Acceptable keymap names are emacs, emacs-stan‐
3773 dard, emacs-meta, emacs-ctlx, vi, vi-move, vi-command,
3774 and vi-insert. vi is equivalent to vi-command; emacs is
3775 equivalent to emacs-standard.
3776 -l List the names of all readline functions.
3777 -p Display readline function names and bindings in such a
3778 way that they can be re-read.
3779 -P List current readline function names and bindings.
3780 -s Display readline key sequences bound to macros and the
3781 strings they output in such a way that they can be re-
3782 read.
3783 -S Display readline key sequences bound to macros and the
3784 strings they output.
3785 -v Display readline variable names and values in such a way
3786 that they can be re-read.
3787 -V List current readline variable names and values.
3788 -f filename
3789 Read key bindings from filename.
3790 -q function
3791 Query about which keys invoke the named function.
3792 -u function
3793 Unbind all keys bound to the named function.
3794 -r keyseq
3795 Remove any current binding for keyseq.
3796 -x keyseq:shell-command
3797 Cause shell-command to be executed whenever keyseq is
3798 entered. When shell-command is executed, the shell sets
3799 the READLINE_LINE variable to the contents of the read‐
3800 line line buffer and the READLINE_POINT variable to the
3801 current location of the insertion point. If the executed
3802 command changes the value of READLINE_LINE or READ‐
3803 LINE_POINT, those new values will be reflected in the
3804 editing state.
3805 The return value is 0 unless an unrecognized option is given or
3807 an error occurred.
3808 break [n]
3810 Exit from within a for, while, until, or select loop. If n is
3811 specified, break n levels. n must be ≥ 1. If n is greater than
3812 the number of enclosing loops, all enclosing loops are exited.
3813 The return value is non-zero when n is ≤ 0; Otherwise, break
3814 returns 0 value.
3815 builtin shell-builtin [arguments]
3817 Execute the specified shell builtin, passing it arguments, and
3818 return its exit status. This is useful when defining a function
3819 whose name is the same as a shell builtin, retaining the func‐
3820 tionality of the builtin within the function. The cd builtin is
3821 commonly redefined this way. The return status is false if
3822 shell-builtin is not a shell builtin command.
3823 caller [expr]
3825 Returns the context of any active subroutine call (a shell func‐
3826 tion or a script executed with the . or source builtins). With‐
3827 out expr, caller displays the line number and source filename of
3828 the current subroutine call. If a non-negative integer is sup‐
3829 plied as expr, caller displays the line number, subroutine name,
3830 and source file corresponding to that position in the current
3831 execution call stack. This extra information may be used, for
3832 example, to print a stack trace. The current frame is frame 0.
3833 The return value is 0 unless the shell is not executing a sub‐
3834 routine call or expr does not correspond to a valid position in
3835 the call stack.
3836 cd [-L|[-P [-e]]] [dir]
3838 Change the current directory to dir. The variable HOME is the
3839 default dir. The variable CDPATH defines the search path for
3840 the directory containing dir. Alternative directory names in
3841 CDPATH are separated by a colon (:). A null directory name in
3842 CDPATH is the same as the current directory, i.e., ``.''. If
3843 dir begins with a slash (/), then CDPATH is not used. The -P
3844 option says to use the physical directory structure instead of
3845 following symbolic links (see also the -P option to the set
3846 builtin command); the -L option forces symbolic links to be fol‐
3847 lowed. If the -e option is supplied with -P, and the current
3848 working directory cannot be successfully determined after a suc‐
3849 cessful directory change, cd will return an unsuccessful status.
3850 An argument of - is equivalent to $OLDPWD. If a non-empty
3851 directory name from CDPATH is used, or if - is the first argu‐
3852 ment, and the directory change is successful, the absolute path‐
3853 name of the new working directory is written to the standard
3854 output. The return value is true if the directory was success‐
3855 fully changed; false otherwise.
3856 command [-pVv] command [arg ...]
3858 Run command with args suppressing the normal shell function
3859 lookup. Only builtin commands or commands found in the PATH are
3860 executed. If the -p option is given, the search for command is
3861 performed using a default value for PATH that is guaranteed to
3862 find all of the standard utilities. If either the -V or -v
3863 option is supplied, a description of command is printed. The -v
3864 option causes a single word indicating the command or file name
3865 used to invoke command to be displayed; the -V option produces a
3866 more verbose description. If the -V or -v option is supplied,
3867 the exit status is 0 if command was found, and 1 if not. If
3868 neither option is supplied and an error occurred or command can‐
3869 not be found, the exit status is 127. Otherwise, the exit sta‐
3870 tus of the command builtin is the exit status of command.
3871 compgen [option] [word]
3873 Generate possible completion matches for word according to the
3874 options, which may be any option accepted by the complete
3875 builtin with the exception of -p and -r, and write the matches
3876 to the standard output. When using the -F or -C options, the
3877 various shell variables set by the programmable completion
3878 facilities, while available, will not have useful values.
3879 The matches will be generated in the same way as if the program‐
3881 mable completion code had generated them directly from a comple‐
3882 tion specification with the same flags. If word is specified,
3883 only those completions matching word will be displayed.
3884 The return value is true unless an invalid option is supplied,
3886 or no matches were generated.
3887 complete [-abcdefgjksuv] [-o comp-option] [-DE] [-A action] [-G glob‐
3889 pat] [-W wordlist] [-F function] [-C command]
3890 [-X filterpat] [-P prefix] [-S suffix] name [name ...]
3891 complete -pr [-DE] [name ...]
3892 Specify how arguments to each name should be completed. If the
3893 -p option is supplied, or if no options are supplied, existing
3894 completion specifications are printed in a way that allows them
3895 to be reused as input. The -r option removes a completion spec‐
3896 ification for each name, or, if no names are supplied, all com‐
3897 pletion specifications. The -D option indicates that the
3898 remaining options and actions should apply to the ``default''
3899 command completion; that is, completion attempted on a command
3900 for which no completion has previously been defined. The -E
3901 option indicates that the remaining options and actions should
3902 apply to ``empty'' command completion; that is, completion
3903 attempted on a blank line.
3904 The process of applying these completion specifications when
3906 word completion is attempted is described above under Program‐
3907 mable Completion.
3908 Other options, if specified, have the following meanings. The
3910 arguments to the -G, -W, and -X options (and, if necessary, the
3911 -P and -S options) should be quoted to protect them from expan‐
3912 sion before the complete builtin is invoked.
3913 -o comp-option
3914 The comp-option controls several aspects of the comp‐
3915 spec's behavior beyond the simple generation of comple‐
3916 tions. comp-option may be one of:
3917 bashdefault
3918 Perform the rest of the default bash completions
3919 if the compspec generates no matches.
3920 default Use readline's default filename completion if
3921 the compspec generates no matches.
3922 dirnames
3923 Perform directory name completion if the comp‐
3924 spec generates no matches.
3925 filenames
3926 Tell readline that the compspec generates file‐
3927 names, so it can perform any filename-specific
3928 processing (like adding a slash to directory
3929 names, quoting special characters, or suppress‐
3930 ing trailing spaces). Intended to be used with
3931 shell functions.
3932 nospace Tell readline not to append a space (the
3933 default) to words completed at the end of the
3934 line.
3935 plusdirs
3936 After any matches defined by the compspec are
3937 generated, directory name completion is
3938 attempted and any matches are added to the
3939 results of the other actions.
3940 -A action
3941 The action may be one of the following to generate a
3942 list of possible completions:
3943 alias Alias names. May also be specified as -a.
3944 arrayvar
3945 Array variable names.
3946 binding Readline key binding names.
3947 builtin Names of shell builtin commands. May also be
3948 specified as -b.
3949 command Command names. May also be specified as -c.
3950 directory
3951 Directory names. May also be specified as -d.
3952 disabled
3953 Names of disabled shell builtins.
3954 enabled Names of enabled shell builtins.
3955 export Names of exported shell variables. May also be
3956 specified as -e.
3957 file File names. May also be specified as -f.
3958 function
3959 Names of shell functions.
3960 group Group names. May also be specified as -g.
3961 helptopic
3962 Help topics as accepted by the help builtin.
3963 hostname
3964 Hostnames, as taken from the file specified by
3965 the HOSTFILE shell variable.
3966 job Job names, if job control is active. May also
3967 be specified as -j.
3968 keyword Shell reserved words. May also be specified as
3969 -k.
3970 running Names of running jobs, if job control is active.
3971 service Service names. May also be specified as -s.
3972 setopt Valid arguments for the -o option to the set
3973 builtin.
3974 shopt Shell option names as accepted by the shopt
3975 builtin.
3976 signal Signal names.
3977 stopped Names of stopped jobs, if job control is active.
3978 user User names. May also be specified as -u.
3979 variable
3980 Names of all shell variables. May also be spec‐
3981 ified as -v.
3982 -C command
3983 command is executed in a subshell environment, and its
3984 output is used as the possible completions.
3985 -F function
3986 The shell function function is executed in the current
3987 shell environment. When it finishes, the possible com‐
3988 pletions are retrieved from the value of the COMPREPLY
3989 array variable.
3990 -G globpat
3991 The pathname expansion pattern globpat is expanded to
3992 generate the possible completions.
3993 -P prefix
3994 prefix is added at the beginning of each possible com‐
3995 pletion after all other options have been applied.
3996 -S suffix
3997 suffix is appended to each possible completion after all
3998 other options have been applied.
3999 -W wordlist
4000 The wordlist is split using the characters in the IFS
4001 special variable as delimiters, and each resultant word
4002 is expanded. The possible completions are the members
4003 of the resultant list which match the word being com‐
4004 pleted.
4005 -X filterpat
4006 filterpat is a pattern as used for pathname expansion.
4007 It is applied to the list of possible completions gener‐
4008 ated by the preceding options and arguments, and each
4009 completion matching filterpat is removed from the list.
4010 A leading ! in filterpat negates the pattern; in this
4011 case, any completion not matching filterpat is removed.
4012 The return value is true unless an invalid option is supplied,
4014 an option other than -p or -r is supplied without a name argu‐
4015 ment, an attempt is made to remove a completion specification
4016 for a name for which no specification exists, or an error occurs
4017 adding a completion specification.
4018 compopt [-o option] [-DE] [+o option] [name]
4020 Modify completion options for each name according to the
4021 options, or for the currently-executing completion if no names
4022 are supplied. If no options are given, display the completion
4023 options for each name or the current completion. The possible
4024 values of option are those valid for the complete builtin
4025 described above. The -D option indicates that the remaining
4026 options should apply to the ``default'' command completion; that
4027 is, completion attempted on a command for which no completion
4028 has previously been defined. The -E option indicates that the
4029 remaining options should apply to ``empty'' command completion;
4030 that is, completion attempted on a blank line.
4031 The return value is true unless an invalid option is supplied,
4033 an attempt is made to modify the options for a name for which no
4034 completion specification exists, or an output error occurs.
4035 continue [n]
4037 Resume the next iteration of the enclosing for, while, until, or
4038 select loop. If n is specified, resume at the nth enclosing
4039 loop. n must be ≥ 1. If n is greater than the number of
4040 enclosing loops, the last enclosing loop (the ``top-level''
4041 loop) is resumed. When continue is executed inside of loop, the
4042 return value is non-zero when n is ≤ 0; Otherwise, continue
4043 returns 0 value. When continue is executed outside of loop, the
4044 return value is 0.
4045 declare [-aAfFgilrtux] [-p] [name[=value] ...]
4047 typeset [-aAfFgilrtux] [-p] [name[=value] ...]
4048 Declare variables and/or give them attributes. If no names are
4049 given then display the values of variables. The -p option will
4050 display the attributes and values of each name. When -p is used
4051 with name arguments, additional options are ignored. When -p is
4052 supplied without name arguments, it will display the attributes
4053 and values of all variables having the attributes specified by
4054 the additional options. If no other options are supplied with
4055 -p, declare will display the attributes and values of all shell
4056 variables. The -f option will restrict the display to shell
4057 functions. The -F option inhibits the display of function defi‐
4058 nitions; only the function name and attributes are printed. If
4059 the extdebug shell option is enabled using shopt, the source
4060 file name and line number where the function is defined are dis‐
4061 played as well. The -F option implies -f. The -g option forces
4062 variables to be created or modified at the global scope, even
4063 when declare is executed in a shell function. It is ignored in
4064 all other cases. The following options can be used to restrict
4065 output to variables with the specified attribute or to give
4066 variables attributes:
4067 -a Each name is an indexed array variable (see Arrays
4068 above).
4069 -A Each name is an associative array variable (see Arrays
4070 above).
4071 -f Use function names only.
4072 -i The variable is treated as an integer; arithmetic evalua‐
4073 tion (see ARITHMETIC EVALUATION above) is performed when
4074 the variable is assigned a value.
4075 -l When the variable is assigned a value, all upper-case
4076 characters are converted to lower-case. The upper-case
4077 attribute is disabled.
4078 -r Make names readonly. These names cannot then be assigned
4079 values by subsequent assignment statements or unset.
4080 -t Give each name the trace attribute. Traced functions
4081 inherit the DEBUG and RETURN traps from the calling
4082 shell. The trace attribute has no special meaning for
4083 variables.
4084 -u When the variable is assigned a value, all lower-case
4085 characters are converted to upper-case. The lower-case
4086 attribute is disabled.
4087 -x Mark names for export to subsequent commands via the
4088 environment.
4089 Using `+' instead of `-' turns off the attribute instead, with
4091 the exceptions that +a may not be used to destroy an array vari‐
4092 able and +r will not remove the readonly attribute. When used
4093 in a function, makes each name local, as with the local command,
4094 unless the -g option is supplied, If a variable name is followed
4095 by =value, the value of the variable is set to value. The
4096 return value is 0 unless an invalid option is encountered, an
4097 attempt is made to define a function using ``-f foo=bar'', an
4098 attempt is made to assign a value to a readonly variable, an
4099 attempt is made to assign a value to an array variable without
4100 using the compound assignment syntax (see Arrays above), one of
4101 the names is not a valid shell variable name, an attempt is made
4102 to turn off readonly status for a readonly variable, an attempt
4103 is made to turn off array status for an array variable, or an
4104 attempt is made to display a non-existent function with -f.
4105 dirs [+n] [-n] [-clpv]
4107 Without options, displays the list of currently remembered
4108 directories. The default display is on a single line with
4109 directory names separated by spaces. Directories are added to
4110 the list with the pushd command; the popd command removes
4111 entries from the list.
4112 +n Displays the nth entry counting from the left of the list
4113 shown by dirs when invoked without options, starting with
4114 zero.
4115 -n Displays the nth entry counting from the right of the
4116 list shown by dirs when invoked without options, starting
4117 with zero.
4118 -c Clears the directory stack by deleting all of the
4119 entries.
4120 -l Produces a longer listing; the default listing format
4121 uses a tilde to denote the home directory.
4122 -p Print the directory stack with one entry per line.
4123 -v Print the directory stack with one entry per line, pre‐
4124 fixing each entry with its index in the stack.
4125 The return value is 0 unless an invalid option is supplied or n
4127 indexes beyond the end of the directory stack.
4128 disown [-ar] [-h] [jobspec ...]
4130 Without options, each jobspec is removed from the table of
4131 active jobs. If jobspec is not present, and neither -a nor -r
4132 is supplied, the shell's notion of the current job is used. If
4133 the -h option is given, each jobspec is not removed from the ta‐
4134 ble, but is marked so that SIGHUP is not sent to the job if the
4135 shell receives a SIGHUP. If no jobspec is present, and neither
4136 the -a nor the -r option is supplied, the current job is used.
4137 If no jobspec is supplied, the -a option means to remove or mark
4138 all jobs; the -r option without a jobspec argument restricts
4139 operation to running jobs. The return value is 0 unless a job‐
4140 spec does not specify a valid job.
4141 echo [-neE] [arg ...]
4143 Output the args, separated by spaces, followed by a newline.
4144 The return status is always 0. If -n is specified, the trailing
4145 newline is suppressed. If the -e option is given, interpreta‐
4146 tion of the following backslash-escaped characters is enabled.
4147 The -E option disables the interpretation of these escape char‐
4148 acters, even on systems where they are interpreted by default.
4149 The xpg_echo shell option may be used to dynamically determine
4150 whether or not echo expands these escape characters by default.
4151 echo does not interpret -- to mean the end of options. echo
4152 interprets the following escape sequences:
4153 \a alert (bell)
4154 \b backspace
4155 \c suppress further output
4156 \e
4157 \E an escape character
4158 \f form feed
4159 \n new line
4160 \r carriage return
4161 \t horizontal tab
4162 \v vertical tab
4163 \\ backslash
4164 \0nnn the eight-bit character whose value is the octal value
4165 nnn (zero to three octal digits)
4166 \xHH the eight-bit character whose value is the hexadecimal
4167 value HH (one or two hex digits)
4168 \uHHHH the Unicode (ISO/IEC 10646) character whose value is the
4169 hexadecimal value HHHH (one to four hex digits)
4170 \UHHHHHHHH
4171 the Unicode (ISO/IEC 10646) character whose value is the
4172 hexadecimal value HHHHHHHH (one to eight hex digits)
4173 enable [-a] [-dnps] [-f filename] [name ...]
4175 Enable and disable builtin shell commands. Disabling a builtin
4176 allows a disk command which has the same name as a shell builtin
4177 to be executed without specifying a full pathname, even though
4178 the shell normally searches for builtins before disk commands.
4179 If -n is used, each name is disabled; otherwise, names are
4180 enabled. For example, to use the test binary found via the PATH
4181 instead of the shell builtin version, run ``enable -n test''.
4182 The -f option means to load the new builtin command name from
4183 shared object filename, on systems that support dynamic loading.
4184 The -d option will delete a builtin previously loaded with -f.
4185 If no name arguments are given, or if the -p option is supplied,
4186 a list of shell builtins is printed. With no other option argu‐
4187 ments, the list consists of all enabled shell builtins. If -n
4188 is supplied, only disabled builtins are printed. If -a is sup‐
4189 plied, the list printed includes all builtins, with an indica‐
4190 tion of whether or not each is enabled. If -s is supplied, the
4191 output is restricted to the POSIX special builtins. The return
4192 value is 0 unless a name is not a shell builtin or there is an
4193 error loading a new builtin from a shared object.
4194 eval [arg ...]
4196 The args are read and concatenated together into a single com‐
4197 mand. This command is then read and executed by the shell, and
4198 its exit status is returned as the value of eval. If there are
4199 no args, or only null arguments, eval returns 0.
4200 exec [-cl] [-a name] [command [arguments]]
4202 If command is specified, it replaces the shell. No new process
4203 is created. The arguments become the arguments to command. If
4204 the -l option is supplied, the shell places a dash at the begin‐
4205 ning of the zeroth argument passed to command. This is what
4206 login(1) does. The -c option causes command to be executed with
4207 an empty environment. If -a is supplied, the shell passes name
4208 as the zeroth argument to the executed command. If command can‐
4209 not be executed for some reason, a non-interactive shell exits,
4210 unless the shell option execfail is enabled, in which case it
4211 returns failure. An interactive shell returns failure if the
4212 file cannot be executed. If command is not specified, any redi‐
4213 rections take effect in the current shell, and the return status
4214 is 0. If there is a redirection error, the return status is 1.
4215 exit [n]
4217 Cause the shell to exit with a status of n. If n is omitted,
4218 the exit status is that of the last command executed. A trap on
4219 EXIT is executed before the shell terminates.
4220 export [-fn] [name[=word]] ...
4222 export -p
4223 The supplied names are marked for automatic export to the envi‐
4224 ronment of subsequently executed commands. If the -f option is
4225 given, the names refer to functions. If no names are given, or
4226 if the -p option is supplied, a list of all names that are
4227 exported in this shell is printed. The -n option causes the
4228 export property to be removed from each name. If a variable
4229 name is followed by =word, the value of the variable is set to
4230 word. export returns an exit status of 0 unless an invalid
4231 option is encountered, one of the names is not a valid shell
4232 variable name, or -f is supplied with a name that is not a func‐
4233 tion.
4234 fc [-e ename] [-lnr] [first] [last]
4236 fc -s [pat=rep] [cmd]
4237 Fix Command. In the first form, a range of commands from first
4238 to last is selected from the history list. First and last may
4239 be specified as a string (to locate the last command beginning
4240 with that string) or as a number (an index into the history
4241 list, where a negative number is used as an offset from the cur‐
4242 rent command number). If last is not specified it is set to the
4243 current command for listing (so that ``fc -l -10'' prints the
4244 last 10 commands) and to first otherwise. If first is not spec‐
4245 ified it is set to the previous command for editing and -16 for
4246 listing.
4247 The -n option suppresses the command numbers when listing. The
4249 -r option reverses the order of the commands. If the -l option
4250 is given, the commands are listed on standard output. Other‐
4251 wise, the editor given by ename is invoked on a file containing
4252 those commands. If ename is not given, the value of the FCEDIT
4253 variable is used, and the value of EDITOR if FCEDIT is not set.
4254 If neither variable is set, vi is used. When editing is com‐
4255 plete, the edited commands are echoed and executed.
4256 In the second form, command is re-executed after each instance
4258 of pat is replaced by rep. A useful alias to use with this is
4259 ``r="fc -s"'', so that typing ``r cc'' runs the last command
4260 beginning with ``cc'' and typing ``r'' re-executes the last com‐
4261 mand.
4262 If the first form is used, the return value is 0 unless an
4264 invalid option is encountered or first or last specify history
4265 lines out of range. If the -e option is supplied, the return
4266 value is the value of the last command executed or failure if an
4267 error occurs with the temporary file of commands. If the second
4268 form is used, the return status is that of the command re-exe‐
4269 cuted, unless cmd does not specify a valid history line, in
4270 which case fc returns failure.
4271 fg [jobspec]
4273 Resume jobspec in the foreground, and make it the current job.
4274 If jobspec is not present, the shell's notion of the current job
4275 is used. The return value is that of the command placed into
4276 the foreground, or failure if run when job control is disabled
4277 or, when run with job control enabled, if jobspec does not spec‐
4278 ify a valid job or jobspec specifies a job that was started
4279 without job control.
4280 getopts optstring name [args]
4282 getopts is used by shell procedures to parse positional parame‐
4283 ters. optstring contains the option characters to be recog‐
4284 nized; if a character is followed by a colon, the option is
4285 expected to have an argument, which should be separated from it
4286 by white space. The colon and question mark characters may not
4287 be used as option characters. Each time it is invoked, getopts
4288 places the next option in the shell variable name, initializing
4289 name if it does not exist, and the index of the next argument to
4290 be processed into the variable OPTIND. OPTIND is initialized to
4291 1 each time the shell or a shell script is invoked. When an
4292 option requires an argument, getopts places that argument into
4293 the variable OPTARG. The shell does not reset OPTIND automati‐
4294 cally; it must be manually reset between multiple calls to
4295 getopts within the same shell invocation if a new set of parame‐
4296 ters is to be used.
4297 When the end of options is encountered, getopts exits with a
4299 return value greater than zero. OPTIND is set to the index of
4300 the first non-option argument, and name is set to ?.
4301 getopts normally parses the positional parameters, but if more
4303 arguments are given in args, getopts parses those instead.
4304 getopts can report errors in two ways. If the first character
4306 of optstring is a colon, silent error reporting is used. In
4307 normal operation diagnostic messages are printed when invalid
4308 options or missing option arguments are encountered. If the
4309 variable OPTERR is set to 0, no error messages will be dis‐
4310 played, even if the first character of optstring is not a colon.
4311 If an invalid option is seen, getopts places ? into name and, if
4313 not silent, prints an error message and unsets OPTARG. If
4314 getopts is silent, the option character found is placed in
4315 OPTARG and no diagnostic message is printed.
4316 If a required argument is not found, and getopts is not silent,
4318 a question mark (?) is placed in name, OPTARG is unset, and a
4319 diagnostic message is printed. If getopts is silent, then a
4320 colon (:) is placed in name and OPTARG is set to the option
4321 character found.
4322 getopts returns true if an option, specified or unspecified, is
4324 found. It returns false if the end of options is encountered or
4325 an error occurs.
4326 hash [-lr] [-p filename] [-dt] [name]
4328 Each time hash is invoked, the full pathname of the command name
4329 is determined by searching the directories in $PATH and remem‐
4330 bered. Any previously-remembered pathname is discarded. If the
4331 -p option is supplied, no path search is performed, and filename
4332 is used as the full file name of the command. The -r option
4333 causes the shell to forget all remembered locations. The -d
4334 option causes the shell to forget the remembered location of
4335 each name. If the -t option is supplied, the full pathname to
4336 which each name corresponds is printed. If multiple name argu‐
4337 ments are supplied with -t, the name is printed before the
4338 hashed full pathname. The -l option causes output to be dis‐
4339 played in a format that may be reused as input. If no arguments
4340 are given, or if only -l is supplied, information about remem‐
4341 bered commands is printed. The return status is true unless a
4342 name is not found or an invalid option is supplied.
4343 help [-dms] [pattern]
4345 Display helpful information about builtin commands. If pattern
4346 is specified, help gives detailed help on all commands matching
4347 pattern; otherwise help for all the builtins and shell control
4348 structures is printed.
4349 -d Display a short description of each pattern
4350 -m Display the description of each pattern in a manpage-like
4351 format
4352 -s Display only a short usage synopsis for each pattern
4353 The return status is 0 unless no command matches pattern.
4355 history [n]
4357 history -c
4358 history -d offset
4359 history -anrw [filename]
4360 history -p arg [arg ...]
4361 history -s arg [arg ...]
4362 With no options, display the command history list with line num‐
4363 bers. Lines listed with a * have been modified. An argument of
4364 n lists only the last n lines. If the shell variable HISTTIME‐
4365 FORMAT is set and not null, it is used as a format string for
4366 strftime(3) to display the time stamp associated with each dis‐
4367 played history entry. No intervening blank is printed between
4368 the formatted time stamp and the history line. If filename is
4369 supplied, it is used as the name of the history file; if not,
4370 the value of HISTFILE is used. Options, if supplied, have the
4371 following meanings:
4372 -c Clear the history list by deleting all the entries.
4373 -d offset
4374 Delete the history entry at position offset.
4375 -a Append the ``new'' history lines (history lines entered
4376 since the beginning of the current bash session) to the
4377 history file.
4378 -n Read the history lines not already read from the history
4379 file into the current history list. These are lines
4380 appended to the history file since the beginning of the
4381 current bash session.
4382 -r Read the contents of the history file and use them as the
4383 current history.
4384 -w Write the current history to the history file, overwrit‐
4385 ing the history file's contents.
4386 -p Perform history substitution on the following args and
4387 display the result on the standard output. Does not
4388 store the results in the history list. Each arg must be
4389 quoted to disable normal history expansion.
4390 -s Store the args in the history list as a single entry.
4391 The last command in the history list is removed before
4392 the args are added.
4393 If the HISTTIMEFORMAT variable is set, the time stamp informa‐
4395 tion associated with each history entry is written to the his‐
4396 tory file, marked with the history comment character. When the
4397 history file is read, lines beginning with the history comment
4398 character followed immediately by a digit are interpreted as
4399 timestamps for the previous history line. The return value is 0
4400 unless an invalid option is encountered, an error occurs while
4401 reading or writing the history file, an invalid offset is sup‐
4402 plied as an argument to -d, or the history expansion supplied as
4403 an argument to -p fails.
4404 jobs [-lnprs] [ jobspec ... ]
4406 jobs -x command [ args ... ]
4407 The first form lists the active jobs. The options have the fol‐
4408 lowing meanings:
4409 -l List process IDs in addition to the normal information.
4410 -n Display information only about jobs that have changed
4411 status since the user was last notified of their status.
4412 -p List only the process ID of the job's process group
4413 leader.
4414 -r Restrict output to running jobs.
4415 -s Restrict output to stopped jobs.
4416 If jobspec is given, output is restricted to information about
4418 that job. The return status is 0 unless an invalid option is
4419 encountered or an invalid jobspec is supplied.
4420 If the -x option is supplied, jobs replaces any jobspec found in
4422 command or args with the corresponding process group ID, and
4423 executes command passing it args, returning its exit status.
4424 kill [-s sigspec | -n signum | -sigspec] [pid | jobspec] ...
4426 kill -l [sigspec | exit_status]
4427 Send the signal named by sigspec or signum to the processes
4428 named by pid or jobspec. sigspec is either a case-insensitive
4429 signal name such as SIGKILL (with or without the SIG prefix) or
4430 a signal number; signum is a signal number. If sigspec is not
4431 present, then SIGTERM is assumed. An argument of -l lists the
4432 signal names. If any arguments are supplied when -l is given,
4433 the names of the signals corresponding to the arguments are
4434 listed, and the return status is 0. The exit_status argument to
4435 -l is a number specifying either a signal number or the exit
4436 status of a process terminated by a signal. kill returns true
4437 if at least one signal was successfully sent, or false if an
4438 error occurs or an invalid option is encountered.
4439 let arg [arg ...]
4441 Each arg is an arithmetic expression to be evaluated (see ARITH‐
4442 METIC EVALUATION above). If the last arg evaluates to 0, let
4443 returns 1; 0 is returned otherwise.
4444 local [option] [name[=value] ...]
4446 For each argument, a local variable named name is created, and
4447 assigned value. The option can be any of the options accepted
4448 by declare. When local is used within a function, it causes the
4449 variable name to have a visible scope restricted to that func‐
4450 tion and its children. With no operands, local writes a list of
4451 local variables to the standard output. It is an error to use
4452 local when not within a function. The return status is 0 unless
4453 local is used outside a function, an invalid name is supplied,
4454 or name is a readonly variable.
4455 logout Exit a login shell.
4457 mapfile [-n count] [-O origin] [-s count] [-t] [-u fd] [-C callback]
4459 [-c quantum] [array]
4460 readarray [-n count] [-O origin] [-s count] [-t] [-u fd] [-C callback]
4461 [-c quantum] [array]
4462 Read lines from the standard input into the indexed array vari‐
4463 able array, or from file descriptor fd if the -u option is sup‐
4464 plied. The variable MAPFILE is the default array. Options, if
4465 supplied, have the following meanings:
4466 -n Copy at most count lines. If count is 0, all lines are
4467 copied.
4468 -O Begin assigning to array at index origin. The default
4469 index is 0.
4470 -s Discard the first count lines read.
4471 -t Remove a trailing newline from each line read.
4472 -u Read lines from file descriptor fd instead of the stan‐
4473 dard input.
4474 -C Evaluate callback each time quantum lines are read. The
4475 -c option specifies quantum.
4476 -c Specify the number of lines read between each call to
4477 callback.
4478 If -C is specified without -c, the default quantum is 5000.
4480 When callback is evaluated, it is supplied the index of the next
4481 array element to be assigned and the line to be assigned to that
4482 element as additional arguments. callback is evaluated after
4483 the line is read but before the array element is assigned.
4484 If not supplied with an explicit origin, mapfile will clear
4486 array before assigning to it.
4487 mapfile returns successfully unless an invalid option or option
4489 argument is supplied, array is invalid or unassignable, or if
4490 array is not an indexed array.
4491 popd [-n] [+n] [-n]
4493 Removes entries from the directory stack. With no arguments,
4494 removes the top directory from the stack, and performs a cd to
4495 the new top directory. Arguments, if supplied, have the follow‐
4496 ing meanings:
4497 -n Suppresses the normal change of directory when removing
4498 directories from the stack, so that only the stack is
4499 manipulated.
4500 +n Removes the nth entry counting from the left of the list
4501 shown by dirs, starting with zero. For example: ``popd
4502 +0'' removes the first directory, ``popd +1'' the second.
4503 -n Removes the nth entry counting from the right of the list
4504 shown by dirs, starting with zero. For example: ``popd
4505 -0'' removes the last directory, ``popd -1'' the next to
4506 last.
4507 If the popd command is successful, a dirs is performed as well,
4509 and the return status is 0. popd returns false if an invalid
4510 option is encountered, the directory stack is empty, a non-exis‐
4511 tent directory stack entry is specified, or the directory change
4512 fails.
4513 printf [-v var] format [arguments]
4515 Write the formatted arguments to the standard output under the
4516 control of the format. The -v option causes the output to be
4517 assigned to the variable var rather than being printed to the
4518 standard output.
4519 The format is a character string which contains three types of
4521 objects: plain characters, which are simply copied to standard
4522 output, character escape sequences, which are converted and
4523 copied to the standard output, and format specifications, each
4524 of which causes printing of the next successive argument. In
4525 addition to the standard printf(1) format specifications, printf
4526 interprets the following extensions:
4527 %b causes printf to expand backslash escape sequences in the
4528 corresponding argument (except that \c terminates output,
4529 backslashes in \', \", and \? are not removed, and octal
4530 escapes beginning with \0 may contain up to four digits).
4531 %q causes printf to output the corresponding argument in a
4532 format that can be reused as shell input.
4533 %(datefmt)T
4534 causes printf to output the date-time string resulting
4535 from using datefmt as a format string for strftime(3).
4536 The corresponding argument is an integer representing the
4537 number of seconds since the epoch. Two special argument
4538 values may be used: -1 represents the current time, and
4539 -2 represents the time the shell was invoked.
4540 Arguments to non-string format specifiers are treated as C con‐
4542 stants, except that a leading plus or minus sign is allowed, and
4543 if the leading character is a single or double quote, the value
4544 is the ASCII value of the following character.
4545 The format is reused as necessary to consume all of the argu‐
4547 ments. If the format requires more arguments than are supplied,
4548 the extra format specifications behave as if a zero value or
4549 null string, as appropriate, had been supplied. The return
4550 value is zero on success, non-zero on failure.
4551 pushd [-n] [+n] [-n]
4553 pushd [-n] [dir]
4554 Adds a directory to the top of the directory stack, or rotates
4555 the stack, making the new top of the stack the current working
4556 directory. With no arguments, exchanges the top two directories
4557 and returns 0, unless the directory stack is empty. Arguments,
4558 if supplied, have the following meanings:
4559 -n Suppresses the normal change of directory when adding
4560 directories to the stack, so that only the stack is
4561 manipulated.
4562 +n Rotates the stack so that the nth directory (counting
4563 from the left of the list shown by dirs, starting with
4564 zero) is at the top.
4565 -n Rotates the stack so that the nth directory (counting
4566 from the right of the list shown by dirs, starting with
4567 zero) is at the top.
4568 dir Adds dir to the directory stack at the top, making it the
4569 new current working directory.
4570 If the pushd command is successful, a dirs is performed as well.
4572 If the first form is used, pushd returns 0 unless the cd to dir
4573 fails. With the second form, pushd returns 0 unless the direc‐
4574 tory stack is empty, a non-existent directory stack element is
4575 specified, or the directory change to the specified new current
4576 directory fails.
4577 pwd [-LP]
4579 Print the absolute pathname of the current working directory.
4580 The pathname printed contains no symbolic links if the -P option
4581 is supplied or the -o physical option to the set builtin command
4582 is enabled. If the -L option is used, the pathname printed may
4583 contain symbolic links. The return status is 0 unless an error
4584 occurs while reading the name of the current directory or an
4585 invalid option is supplied.
4586 read [-ers] [-a aname] [-d delim] [-i text] [-n nchars] [-N nchars] [-p
4588 prompt] [-t timeout] [-u fd] [name ...]
4589 One line is read from the standard input, or from the file
4590 descriptor fd supplied as an argument to the -u option, and the
4591 first word is assigned to the first name, the second word to the
4592 second name, and so on, with leftover words and their interven‐
4593 ing separators assigned to the last name. If there are fewer
4594 words read from the input stream than names, the remaining names
4595 are assigned empty values. The characters in IFS are used to
4596 split the line into words. The backslash character (\) may be
4597 used to remove any special meaning for the next character read
4598 and for line continuation. Options, if supplied, have the fol‐
4599 lowing meanings:
4600 -a aname
4601 The words are assigned to sequential indices of the array
4602 variable aname, starting at 0. aname is unset before any
4603 new values are assigned. Other name arguments are
4604 ignored.
4605 -d delim
4606 The first character of delim is used to terminate the
4607 input line, rather than newline.
4608 -e If the standard input is coming from a terminal, readline
4609 (see READLINE above) is used to obtain the line. Read‐
4610 line uses the current (or default, if line editing was
4611 not previously active) editing settings.
4612 -i text
4613 If readline is being used to read the line, text is
4614 placed into the editing buffer before editing begins.
4615 -n nchars
4616 read returns after reading nchars characters rather than
4617 waiting for a complete line of input, but honor a delim‐
4618 iter if fewer than nchars characters are read before the
4619 delimiter.
4620 -N nchars
4621 read returns after reading exactly nchars characters
4622 rather than waiting for a complete line of input, unless
4623 EOF is encountered or read times out. Delimiter charac‐
4624 ters encountered in the input are not treated specially
4625 and do not cause read to return until nchars characters
4626 are read.
4627 -p prompt
4628 Display prompt on standard error, without a trailing new‐
4629 line, before attempting to read any input. The prompt is
4630 displayed only if input is coming from a terminal.
4631 -r Backslash does not act as an escape character. The back‐
4632 slash is considered to be part of the line. In particu‐
4633 lar, a backslash-newline pair may not be used as a line
4634 continuation.
4635 -s Silent mode. If input is coming from a terminal, charac‐
4636 ters are not echoed.
4637 -t timeout
4638 Cause read to time out and return failure if a complete
4639 line of input is not read within timeout seconds. time‐
4640 out may be a decimal number with a fractional portion
4641 following the decimal point. This option is only effec‐
4642 tive if read is reading input from a terminal, pipe, or
4643 other special file; it has no effect when reading from
4644 regular files. If timeout is 0, read returns success if
4645 input is available on the specified file descriptor,
4646 failure otherwise. The exit status is greater than 128
4647 if the timeout is exceeded.
4648 -u fd Read input from file descriptor fd.
4649 If no names are supplied, the line read is assigned to the vari‐
4651 able REPLY. The return code is zero, unless end-of-file is
4652 encountered, read times out (in which case the return code is
4653 greater than 128), or an invalid file descriptor is supplied as
4654 the argument to -u.
4655 readonly [-aAf] [-p] [name[=word] ...]
4657 The given names are marked readonly; the values of these names
4658 may not be changed by subsequent assignment. If the -f option
4659 is supplied, the functions corresponding to the names are so
4660 marked. The -a option restricts the variables to indexed
4661 arrays; the -A option restricts the variables to associative
4662 arrays. If both options are supplied, -A takes precedence. If
4663 no name arguments are given, or if the -p option is supplied, a
4664 list of all readonly names is printed. The other options may be
4665 used to restrict the output to a subset of the set of readonly
4666 names. The -p option causes output to be displayed in a format
4667 that may be reused as input. If a variable name is followed by
4668 =word, the value of the variable is set to word. The return
4669 status is 0 unless an invalid option is encountered, one of the
4670 names is not a valid shell variable name, or -f is supplied with
4671 a name that is not a function.
4672 return [n]
4674 Causes a function to exit with the return value specified by n.
4675 If n is omitted, the return status is that of the last command
4676 executed in the function body. If used outside a function, but
4677 during execution of a script by the . (source) command, it
4678 causes the shell to stop executing that script and return either
4679 n or the exit status of the last command executed within the
4680 script as the exit status of the script. If used outside a
4681 function and not during execution of a script by ., the return
4682 status is false. Any command associated with the RETURN trap is
4683 executed before execution resumes after the function or script.
4684 set [--abefhkmnptuvxBCEHPT] [-o option-name] [arg ...]
4686 set [+abefhkmnptuvxBCEHPT] [+o option-name] [arg ...]
4687 Without options, the name and value of each shell variable are
4688 displayed in a format that can be reused as input for setting or
4689 resetting the currently-set variables. Read-only variables can‐
4690 not be reset. In posix mode, only shell variables are listed.
4691 The output is sorted according to the current locale. When
4692 options are specified, they set or unset shell attributes. Any
4693 arguments remaining after option processing are treated as val‐
4694 ues for the positional parameters and are assigned, in order, to
4695 $1, $2, ... $n. Options, if specified, have the following
4696 meanings:
4697 -a Automatically mark variables and functions which are
4698 modified or created for export to the environment of
4699 subsequent commands.
4700 -b Report the status of terminated background jobs immedi‐
4701 ately, rather than before the next primary prompt. This
4702 is effective only when job control is enabled.
4703 -e Exit immediately if a pipeline (which may consist of a
4704 single simple command), a subshell command enclosed in
4705 parentheses, or one of the commands executed as part of
4706 a command list enclosed by braces (see SHELL GRAMMAR
4707 above) exits with a non-zero status. The shell does not
4708 exit if the command that fails is part of the command
4709 list immediately following a while or until keyword,
4710 part of the test following the if or elif reserved
4711 words, part of any command executed in a && or || list
4712 except the command following the final && or ||, any
4713 command in a pipeline but the last, or if the command's
4714 return value is being inverted with !. A trap on ERR,
4715 if set, is executed before the shell exits. This option
4716 applies to the shell environment and each subshell envi‐
4717 ronment separately (see COMMAND EXECUTION ENVIRONMENT
4718 above), and may cause subshells to exit before executing
4719 all the commands in the subshell.
4720 -f Disable pathname expansion.
4721 -h Remember the location of commands as they are looked up
4722 for execution. This is enabled by default.
4723 -k All arguments in the form of assignment statements are
4724 placed in the environment for a command, not just those
4725 that precede the command name.
4726 -m Monitor mode. Job control is enabled. This option is
4727 on by default for interactive shells on systems that
4728 support it (see JOB CONTROL above). Background pro‐
4729 cesses run in a separate process group and a line con‐
4730 taining their exit status is printed upon their comple‐
4731 tion.
4732 -n Read commands but do not execute them. This may be used
4733 to check a shell script for syntax errors. This is
4734 ignored by interactive shells.
4735 -o option-name
4736 The option-name can be one of the following:
4737 allexport
4738 Same as -a.
4739 braceexpand
4740 Same as -B.
4741 emacs Use an emacs-style command line editing inter‐
4742 face. This is enabled by default when the shell
4743 is interactive, unless the shell is started with
4744 the --noediting option. This also affects the
4745 editing interface used for read -e.
4746 errexit Same as -e.
4747 errtrace
4748 Same as -E.
4749 functrace
4750 Same as -T.
4751 hashall Same as -h.
4752 histexpand
4753 Same as -H.
4754 history Enable command history, as described above under
4755 HISTORY. This option is on by default in inter‐
4756 active shells.
4757 ignoreeof
4758 The effect is as if the shell command
4759 ``IGNOREEOF=10'' had been executed (see Shell
4760 Variables above).
4761 keyword Same as -k.
4762 monitor Same as -m.
4763 noclobber
4764 Same as -C.
4765 noexec Same as -n.
4766 noglob Same as -f.
4767 nolog Currently ignored.
4768 notify Same as -b.
4769 nounset Same as -u.
4770 onecmd Same as -t.
4771 physical
4772 Same as -P.
4773 pipefail
4774 If set, the return value of a pipeline is the
4775 value of the last (rightmost) command to exit
4776 with a non-zero status, or zero if all commands
4777 in the pipeline exit successfully. This option
4778 is disabled by default.
4779 posix Change the behavior of bash where the default
4780 operation differs from the POSIX standard to
4781 match the standard (posix mode).
4782 privileged
4783 Same as -p.
4784 verbose Same as -v.
4785 vi Use a vi-style command line editing interface.
4786 This also affects the editing interface used for
4787 read -e.
4788 xtrace Same as -x.
4789 If -o is supplied with no option-name, the values of the
4790 current options are printed. If +o is supplied with no
4791 option-name, a series of set commands to recreate the
4792 current option settings is displayed on the standard
4793 output.
4794 -p Turn on privileged mode. In this mode, the $ENV and
4795 $BASH_ENV files are not processed, shell functions are
4796 not inherited from the environment, and the SHELLOPTS,
4797 BASHOPTS, CDPATH, and GLOBIGNORE variables, if they
4798 appear in the environment, are ignored. If the shell is
4799 started with the effective user (group) id not equal to
4800 the real user (group) id, and the -p option is not sup‐
4801 plied, these actions are taken and the effective user id
4802 is set to the real user id. If the -p option is sup‐
4803 plied at startup, the effective user id is not reset.
4804 Turning this option off causes the effective user and
4805 group ids to be set to the real user and group ids.
4806 -t Exit after reading and executing one command.
4807 -u Treat unset variables and parameters other than the spe‐
4808 cial parameters "@" and "*" as an error when performing
4809 parameter expansion. If expansion is attempted on an
4810 unset variable or parameter, the shell prints an error
4811 message, and, if not interactive, exits with a non-zero
4812 status.
4813 -v Print shell input lines as they are read.
4814 -x After expanding each simple command, for command, case
4815 command, select command, or arithmetic for command, dis‐
4816 play the expanded value of PS4, followed by the command
4817 and its expanded arguments or associated word list.
4818 -B The shell performs brace expansion (see Brace Expansion
4819 above). This is on by default.
4820 -C If set, bash does not overwrite an existing file with
4821 the >, >&, and <> redirection operators. This may be
4822 overridden when creating output files by using the redi‐
4823 rection operator >| instead of >.
4824 -E If set, any trap on ERR is inherited by shell functions,
4825 command substitutions, and commands executed in a sub‐
4826 shell environment. The ERR trap is normally not inher‐
4827 ited in such cases.
4828 -H Enable ! style history substitution. This option is on
4829 by default when the shell is interactive.
4830 -P If set, the shell does not follow symbolic links when
4831 executing commands such as cd that change the current
4832 working directory. It uses the physical directory
4833 structure instead. By default, bash follows the logical
4834 chain of directories when performing commands which
4835 change the current directory.
4836 -T If set, any traps on DEBUG and RETURN are inherited by
4837 shell functions, command substitutions, and commands
4838 executed in a subshell environment. The DEBUG and
4839 RETURN traps are normally not inherited in such cases.
4840 -- If no arguments follow this option, then the positional
4841 parameters are unset. Otherwise, the positional parame‐
4842 ters are set to the args, even if some of them begin
4843 with a -.
4844 - Signal the end of options, cause all remaining args to
4845 be assigned to the positional parameters. The -x and -v
4846 options are turned off. If there are no args, the posi‐
4847 tional parameters remain unchanged.
4848 The options are off by default unless otherwise noted. Using +
4850 rather than - causes these options to be turned off. The
4851 options can also be specified as arguments to an invocation of
4852 the shell. The current set of options may be found in $-. The
4853 return status is always true unless an invalid option is encoun‐
4854 tered.
4855 shift [n]
4857 The positional parameters from n+1 ... are renamed to $1 ....
4858 Parameters represented by the numbers $# down to $#-n+1 are
4859 unset. n must be a non-negative number less than or equal to
4860 $#. If n is 0, no parameters are changed. If n is not given,
4861 it is assumed to be 1. If n is greater than $#, the positional
4862 parameters are not changed. The return status is greater than
4863 zero if n is greater than $# or less than zero; otherwise 0.
4864 shopt [-pqsu] [-o] [optname ...]
4866 Toggle the values of variables controlling optional shell behav‐
4867 ior. With no options, or with the -p option, a list of all set‐
4868 table options is displayed, with an indication of whether or not
4869 each is set. The -p option causes output to be displayed in a
4870 form that may be reused as input. Other options have the fol‐
4871 lowing meanings:
4872 -s Enable (set) each optname.
4873 -u Disable (unset) each optname.
4874 -q Suppresses normal output (quiet mode); the return status
4875 indicates whether the optname is set or unset. If multi‐
4876 ple optname arguments are given with -q, the return sta‐
4877 tus is zero if all optnames are enabled; non-zero other‐
4878 wise.
4879 -o Restricts the values of optname to be those defined for
4880 the -o option to the set builtin.
4881 If either -s or -u is used with no optname arguments, the dis‐
4883 play is limited to those options which are set or unset, respec‐
4884 tively. Unless otherwise noted, the shopt options are disabled
4885 (unset) by default.
4886 The return status when listing options is zero if all optnames
4888 are enabled, non-zero otherwise. When setting or unsetting
4889 options, the return status is zero unless an optname is not a
4890 valid shell option.
4891 The list of shopt options is:
4893 autocd If set, a command name that is the name of a directory
4895 is executed as if it were the argument to the cd com‐
4896 mand. This option is only used by interactive shells.
4897 cdable_vars
4898 If set, an argument to the cd builtin command that is
4899 not a directory is assumed to be the name of a variable
4900 whose value is the directory to change to.
4901 cdspell If set, minor errors in the spelling of a directory com‐
4902 ponent in a cd command will be corrected. The errors
4903 checked for are transposed characters, a missing charac‐
4904 ter, and one character too many. If a correction is
4905 found, the corrected file name is printed, and the com‐
4906 mand proceeds. This option is only used by interactive
4907 shells.
4908 checkhash
4909 If set, bash checks that a command found in the hash ta‐
4910 ble exists before trying to execute it. If a hashed
4911 command no longer exists, a normal path search is per‐
4912 formed.
4913 checkjobs
4914 If set, bash lists the status of any stopped and running
4915 jobs before exiting an interactive shell. If any jobs
4916 are running, this causes the exit to be deferred until a
4917 second exit is attempted without an intervening command
4918 (see JOB CONTROL above). The shell always postpones
4919 exiting if any jobs are stopped.
4920 checkwinsize
4921 If set, bash checks the window size after each command
4922 and, if necessary, updates the values of LINES and COL‐
4923 UMNS.
4924 cmdhist If set, bash attempts to save all lines of a multiple-
4925 line command in the same history entry. This allows
4926 easy re-editing of multi-line commands.
4927 compat31
4928 If set, bash changes its behavior to that of version 3.1
4929 with respect to quoted arguments to the [[ conditional
4930 command's =~ operator.
4931 compat32
4932 If set, bash changes its behavior to that of version 3.2
4933 with respect to locale-specific string comparison when
4934 using the [[ conditional command's < and > operators.
4935 Bash versions prior to bash-4.1 use ASCII collation and
4936 strcmp(3); bash-4.1 and later use the current locale's
4937 collation sequence and strcoll(3).
4938 compat40
4939 If set, bash changes its behavior to that of version 4.0
4940 with respect to locale-specific string comparison when
4941 using the [[ conditional command's < and > operators
4942 (see previous item) and the effect of interrupting a
4943 command list.
4944 compat41
4945 If set, bash, when in posix mode, treats a single quote
4946 in a double-quoted parameter expansion as a special
4947 character. The single quotes must match (an even num‐
4948 ber) and the characters between the single quotes are
4949 considered quoted. This is the behavior of posix mode
4950 through version 4.1. The default bash behavior remains
4951 as in previous versions.
4952 direxpand
4953 If set, bash replaces directory names with the results
4954 of word expansion when performing filename completion.
4955 This changes the contents of the readline editing buf‐
4956 fer. If not set, bash attempts to preserve what the
4957 user typed.
4958 dirspell
4959 If set, bash attempts spelling correction on directory
4960 names during word completion if the directory name ini‐
4961 tially supplied does not exist.
4962 dotglob If set, bash includes filenames beginning with a `.' in
4963 the results of pathname expansion.
4964 execfail
4965 If set, a non-interactive shell will not exit if it can‐
4966 not execute the file specified as an argument to the
4967 exec builtin command. An interactive shell does not
4968 exit if exec fails.
4969 expand_aliases
4970 If set, aliases are expanded as described above under
4971 ALIASES. This option is enabled by default for interac‐
4972 tive shells.
4973 extdebug
4974 If set, behavior intended for use by debuggers is
4975 enabled:
4976 1. The -F option to the declare builtin displays the
4977 source file name and line number corresponding to
4978 each function name supplied as an argument.
4979 2. If the command run by the DEBUG trap returns a
4980 non-zero value, the next command is skipped and
4981 not executed.
4982 3. If the command run by the DEBUG trap returns a
4983 value of 2, and the shell is executing in a sub‐
4984 routine (a shell function or a shell script exe‐
4985 cuted by the . or source builtins), a call to
4986 return is simulated.
4987 4. BASH_ARGC and BASH_ARGV are updated as described
4988 in their descriptions above.
4989 5. Function tracing is enabled: command substitu‐
4990 tion, shell functions, and subshells invoked with
4991 ( command ) inherit the DEBUG and RETURN traps.
4992 6. Error tracing is enabled: command substitution,
4993 shell functions, and subshells invoked with (
4994 command ) inherit the ERR trap.
4995 extglob If set, the extended pattern matching features described
4996 above under Pathname Expansion are enabled.
4997 extquote
4998 If set, $'string' and $"string" quoting is performed
4999 within ${parameter} expansions enclosed in double
5000 quotes. This option is enabled by default.
5001 failglob
5002 If set, patterns which fail to match filenames during
5003 pathname expansion result in an expansion error.
5004 force_fignore
5005 If set, the suffixes specified by the FIGNORE shell
5006 variable cause words to be ignored when performing word
5007 completion even if the ignored words are the only possi‐
5008 ble completions. See SHELL VARIABLES above for a
5009 description of FIGNORE. This option is enabled by
5010 default.
5011 globstar
5012 If set, the pattern ** used in a pathname expansion con‐
5013 text will match all files and zero or more directories
5014 and subdirectories. If the pattern is followed by a /,
5015 only directories and subdirectories match.
5016 gnu_errfmt
5017 If set, shell error messages are written in the standard
5018 GNU error message format.
5019 histappend
5020 If set, the history list is appended to the file named
5021 by the value of the HISTFILE variable when the shell
5022 exits, rather than overwriting the file.
5023 histreedit
5024 If set, and readline is being used, a user is given the
5025 opportunity to re-edit a failed history substitution.
5026 histverify
5027 If set, and readline is being used, the results of his‐
5028 tory substitution are not immediately passed to the
5029 shell parser. Instead, the resulting line is loaded
5030 into the readline editing buffer, allowing further modi‐
5031 fication.
5032 hostcomplete
5033 If set, and readline is being used, bash will attempt to
5034 perform hostname completion when a word containing a @
5035 is being completed (see Completing under READLINE
5036 above). This is enabled by default.
5037 huponexit
5038 If set, bash will send SIGHUP to all jobs when an inter‐
5039 active login shell exits.
5040 interactive_comments
5041 If set, allow a word beginning with # to cause that word
5042 and all remaining characters on that line to be ignored
5043 in an interactive shell (see COMMENTS above). This
5044 option is enabled by default.
5045 lastpipe
5046 If set, and job control is not active, the shell runs
5047 the last command of a pipeline not executed in the back‐
5048 ground in the current shell environment.
5049 lithist If set, and the cmdhist option is enabled, multi-line
5050 commands are saved to the history with embedded newlines
5051 rather than using semicolon separators where possible.
5052 login_shell
5053 The shell sets this option if it is started as a login
5054 shell (see INVOCATION above). The value may not be
5055 changed.
5056 mailwarn
5057 If set, and a file that bash is checking for mail has
5058 been accessed since the last time it was checked, the
5059 message ``The mail in mailfile has been read'' is dis‐
5060 played.
5061 no_empty_cmd_completion
5062 If set, and readline is being used, bash will not
5063 attempt to search the PATH for possible completions when
5064 completion is attempted on an empty line.
5065 nocaseglob
5066 If set, bash matches filenames in a case-insensitive
5067 fashion when performing pathname expansion (see Pathname
5068 Expansion above).
5069 nocasematch
5070 If set, bash matches patterns in a case-insensitive
5071 fashion when performing matching while executing case or
5072 [[ conditional commands.
5073 nullglob
5074 If set, bash allows patterns which match no files (see
5075 Pathname Expansion above) to expand to a null string,
5076 rather than themselves.
5077 progcomp
5078 If set, the programmable completion facilities (see Pro‐
5079 grammable Completion above) are enabled. This option is
5080 enabled by default.
5081 promptvars
5082 If set, prompt strings undergo parameter expansion, com‐
5083 mand substitution, arithmetic expansion, and quote
5084 removal after being expanded as described in PROMPTING
5085 above. This option is enabled by default.
5086 restricted_shell
5087 The shell sets this option if it is started in
5088 restricted mode (see RESTRICTED SHELL below). The value
5089 may not be changed. This is not reset when the startup
5090 files are executed, allowing the startup files to dis‐
5091 cover whether or not a shell is restricted.
5092 shift_verbose
5093 If set, the shift builtin prints an error message when
5094 the shift count exceeds the number of positional parame‐
5095 ters.
5096 sourcepath
5097 If set, the source (.) builtin uses the value of PATH to
5098 find the directory containing the file supplied as an
5099 argument. This option is enabled by default.
5100 xpg_echo
5101 If set, the echo builtin expands backslash-escape
5102 sequences by default.
5103 suspend [-f]
5105 Suspend the execution of this shell until it receives a SIGCONT
5106 signal. When the suspended shell is a background process, it can
5107 be restarted by the fg command. For more information, read the
5108 JOB CONTROL section. The suspend command can not suspend the
5109 login shell. However, when -f option is specified, suspend com‐
5110 mand can suspend even login shell. The return status is 0
5111 unless the shell is a login shell and -f is not supplied, or if
5112 job control is not enabled.
5113 test expr
5115 [ expr ]
5116 Return a status of 0 or 1 depending on the evaluation of the
5117 conditional expression expr. Each operator and operand must be
5118 a separate argument. Expressions are composed of the primaries
5119 described above under CONDITIONAL EXPRESSIONS. test does not
5120 accept any options, nor does it accept and ignore an argument of
5121 -- as signifying the end of options.
5122 Expressions may be combined using the following operators,
5124 listed in decreasing order of precedence. The evaluation
5125 depends on the number of arguments; see below. Operator prece‐
5126 dence is used when there are five or more arguments.
5127 ! expr True if expr is false.
5128 ( expr )
5129 Returns the value of expr. This may be used to override
5130 the normal precedence of operators.
5131 expr1 -a expr2
5132 True if both expr1 and expr2 are true.
5133 expr1 -o expr2
5134 True if either expr1 or expr2 is true.
5135 test and [ evaluate conditional expressions using a set of rules
5137 based on the number of arguments.
5138 0 arguments
5140 The expression is false.
5141 1 argument
5142 The expression is true if and only if the argument is not
5143 null.
5144 2 arguments
5145 If the first argument is !, the expression is true if and
5146 only if the second argument is null. If the first argu‐
5147 ment is one of the unary conditional operators listed
5148 above under CONDITIONAL EXPRESSIONS, the expression is
5149 true if the unary test is true. If the first argument is
5150 not a valid unary conditional operator, the expression is
5151 false.
5152 3 arguments
5153 The following conditions are applied in the order listed.
5154 If the second argument is one of the binary conditional
5155 operators listed above under CONDITIONAL EXPRESSIONS, the
5156 result of the expression is the result of the binary test
5157 using the first and third arguments as operands. The -a
5158 and -o operators are considered binary operators when
5159 there are three arguments. If the first argument is !,
5160 the value is the negation of the two-argument test using
5161 the second and third arguments. If the first argument is
5162 exactly ( and the third argument is exactly ), the result
5163 is the one-argument test of the second argument. Other‐
5164 wise, the expression is false.
5165 4 arguments
5166 If the first argument is !, the result is the negation of
5167 the three-argument expression composed of the remaining
5168 arguments. Otherwise, the expression is parsed and eval‐
5169 uated according to precedence using the rules listed
5170 above.
5171 5 or more arguments
5172 The expression is parsed and evaluated according to
5173 precedence using the rules listed above.
5174 When used with test or [, the < and > operators sort lexico‐
5176 graphically using ASCII ordering.
5177 times Print the accumulated user and system times for the shell and
5179 for processes run from the shell. The return status is 0.
5180 trap [-lp] [[arg] sigspec ...]
5182 The command arg is to be read and executed when the shell
5183 receives signal(s) sigspec. If arg is absent (and there is a
5184 single sigspec) or -, each specified signal is reset to its
5185 original disposition (the value it had upon entrance to the
5186 shell). If arg is the null string the signal specified by each
5187 sigspec is ignored by the shell and by the commands it invokes.
5188 If arg is not present and -p has been supplied, then the trap
5189 commands associated with each sigspec are displayed. If no
5190 arguments are supplied or if only -p is given, trap prints the
5191 list of commands associated with each signal. The -l option
5192 causes the shell to print a list of signal names and their cor‐
5193 responding numbers. Each sigspec is either a signal name
5194 defined in <signal.h>, or a signal number. Signal names are
5195 case insensitive and the SIG prefix is optional.
5196 If a sigspec is EXIT (0) the command arg is executed on exit
5198 from the shell. If a sigspec is DEBUG, the command arg is exe‐
5199 cuted before every simple command, for command, case command,
5200 select command, every arithmetic for command, and before the
5201 first command executes in a shell function (see SHELL GRAMMAR
5202 above). Refer to the description of the extdebug option to the
5203 shopt builtin for details of its effect on the DEBUG trap. If a
5204 sigspec is RETURN, the command arg is executed each time a shell
5205 function or a script executed with the . or source builtins fin‐
5206 ishes executing.
5207 If a sigspec is ERR, the command arg is executed whenever a sim‐
5209 ple command has a non-zero exit status, subject to the following
5210 conditions. The ERR trap is not executed if the failed command
5211 is part of the command list immediately following a while or
5212 until keyword, part of the test in an if statement, part of a
5213 command executed in a && or || list, or if the command's return
5214 value is being inverted via !. These are the same conditions
5215 obeyed by the errexit option.
5216 Signals ignored upon entry to the shell cannot be trapped, reset
5218 or listed. Trapped signals that are not being ignored are reset
5219 to their original values in a subshell or subshell environment
5220 when one is created. The return status is false if any sigspec
5221 is invalid; otherwise trap returns true.
5222 type [-aftpP] name [name ...]
5224 With no options, indicate how each name would be interpreted if
5225 used as a command name. If the -t option is used, type prints a
5226 string which is one of alias, keyword, function, builtin, or
5227 file if name is an alias, shell reserved word, function,
5228 builtin, or disk file, respectively. If the name is not found,
5229 then nothing is printed, and an exit status of false is
5230 returned. If the -p option is used, type either returns the
5231 name of the disk file that would be executed if name were speci‐
5232 fied as a command name, or nothing if ``type -t name'' would not
5233 return file. The -P option forces a PATH search for each name,
5234 even if ``type -t name'' would not return file. If a command is
5235 hashed, -p and -P print the hashed value, not necessarily the
5236 file that appears first in PATH. If the -a option is used, type
5237 prints all of the places that contain an executable named name.
5238 This includes aliases and functions, if and only if the -p
5239 option is not also used. The table of hashed commands is not
5240 consulted when using -a. The -f option suppresses shell func‐
5241 tion lookup, as with the command builtin. type returns true if
5242 all of the arguments are found, false if any are not found.
5243 ulimit [-HSTabcdefilmnpqrstuvx [limit]]
5245 Provides control over the resources available to the shell and
5246 to processes started by it, on systems that allow such control.
5247 The -H and -S options specify that the hard or soft limit is set
5248 for the given resource. A hard limit cannot be increased by a
5249 non-root user once it is set; a soft limit may be increased up
5250 to the value of the hard limit. If neither -H nor -S is speci‐
5251 fied, both the soft and hard limits are set. The value of limit
5252 can be a number in the unit specified for the resource or one of
5253 the special values hard, soft, or unlimited, which stand for the
5254 current hard limit, the current soft limit, and no limit,
5255 respectively. If limit is omitted, the current value of the
5256 soft limit of the resource is printed, unless the -H option is
5257 given. When more than one resource is specified, the limit name
5258 and unit are printed before the value. Other options are inter‐
5259 preted as follows:
5260 -a All current limits are reported
5261 -b The maximum socket buffer size
5262 -c The maximum size of core files created
5263 -d The maximum size of a process's data segment
5264 -e The maximum scheduling priority ("nice")
5265 -f The maximum size of files written by the shell and its
5266 children
5267 -i The maximum number of pending signals
5268 -l The maximum size that may be locked into memory
5269 -m The maximum resident set size (many systems do not honor
5270 this limit)
5271 -n The maximum number of open file descriptors (most systems
5272 do not allow this value to be set)
5273 -p The pipe size in 512-byte blocks (this may not be set)
5274 -q The maximum number of bytes in POSIX message queues
5275 -r The maximum real-time scheduling priority
5276 -s The maximum stack size
5277 -t The maximum amount of cpu time in seconds
5278 -u The maximum number of processes available to a single
5279 user
5280 -v The maximum amount of virtual memory available to the
5281 shell and, on some systems, to its children
5282 -x The maximum number of file locks
5283 -T The maximum number of threads
5284 If limit is given, it is the new value of the specified resource
5286 (the -a option is display only). If no option is given, then -f
5287 is assumed. Values are in 1024-byte increments, except for -t,
5288 which is in seconds, -p, which is in units of 512-byte blocks,
5289 and -T, -b, -n, and -u, which are unscaled values. The return
5290 status is 0 unless an invalid option or argument is supplied, or
5291 an error occurs while setting a new limit. In POSIX Mode
5292 512-byte blocks are used for the `-c' and `-f' options.
5293 umask [-p] [-S] [mode]
5295 The user file-creation mask is set to mode. If mode begins with
5296 a digit, it is interpreted as an octal number; otherwise it is
5297 interpreted as a symbolic mode mask similar to that accepted by
5298 chmod(1). If mode is omitted, the current value of the mask is
5299 printed. The -S option causes the mask to be printed in sym‐
5300 bolic form; the default output is an octal number. If the -p
5301 option is supplied, and mode is omitted, the output is in a form
5302 that may be reused as input. The return status is 0 if the mode
5303 was successfully changed or if no mode argument was supplied,
5304 and false otherwise.
5305 unalias [-a] [name ...]
5307 Remove each name from the list of defined aliases. If -a is
5308 supplied, all alias definitions are removed. The return value
5309 is true unless a supplied name is not a defined alias.
5310 unset [-fv] [name ...]
5312 For each name, remove the corresponding variable or function.
5313 If no options are supplied, or the -v option is given, each name
5314 refers to a shell variable. Read-only variables may not be
5315 unset. If -f is specified, each name refers to a shell func‐
5316 tion, and the function definition is removed. Each unset vari‐
5317 able or function is removed from the environment passed to sub‐
5318 sequent commands. If any of COMP_WORDBREAKS, RANDOM, SECONDS,
5319 LINENO, HISTCMD, FUNCNAME, GROUPS, or DIRSTACK are unset, they
5320 lose their special properties, even if they are subsequently
5321 reset. The exit status is true unless a name is readonly.
5322 wait [n ...]
5324 Wait for each specified process and return its termination sta‐
5325 tus. Each n may be a process ID or a job specification; if a
5326 job spec is given, all processes in that job's pipeline are
5327 waited for. If n is not given, all currently active child pro‐
5328 cesses are waited for, and the return status is zero. If n
5329 specifies a non-existent process or job, the return status is
5330 127. Otherwise, the return status is the exit status of the
5331 last process or job waited for.
5332
5334 If bash is started with the name rbash, or the -r option is supplied at
5335 invocation, the shell becomes restricted. A restricted shell is used
5336 to set up an environment more controlled than the standard shell. It
5337 behaves identically to bash with the exception that the following are
5338 disallowed or not performed:
5339 · changing directories with cd
5341 · setting or unsetting the values of SHELL, PATH, ENV, or BASH_ENV
5343 · specifying command names containing /
5345 · specifying a file name containing a / as an argument to the .
5347 builtin command
5348 · specifying a filename containing a slash as an argument to the
5350 -p option to the hash builtin command
5351 · importing function definitions from the shell environment at
5353 startup
5354 · parsing the value of SHELLOPTS from the shell environment at
5356 startup
5357 · redirecting output using the >, >|, <>, >&, &>, and >> redirect‐
5359 ion operators
5360 · using the exec builtin command to replace the shell with another
5362 command
5363 · adding or deleting builtin commands with the -f and -d options
5365 to the enable builtin command
5366 · using the enable builtin command to enable disabled shell
5368 builtins
5369 · specifying the -p option to the command builtin command
5371 · turning off restricted mode with set +r or set +o restricted.
5373 These restrictions are enforced after any startup files are read.
5375 When a command that is found to be a shell script is executed (see COM‐
5377 MAND EXECUTION above), rbash turns off any restrictions in the shell
5378 spawned to execute the script.
5379
5381 Bash Reference Manual, Brian Fox and Chet Ramey
5382 The Gnu Readline Library, Brian Fox and Chet Ramey
5383 The Gnu History Library, Brian Fox and Chet Ramey
5384 Portable Operating System Interface (POSIX) Part 2: Shell and Utili‐
5385 ties, IEEE
5386 sh(1), ksh(1), csh(1)
5387 emacs(1), vi(1)
5388 readline(3)
5389
5391 /bin/bash
5392 The bash executable
5393 /etc/profile
5394 The systemwide initialization file, executed for login shells
5395 /etc/bash.bash_logout
5396 The systemwide login shell cleanup file, executed when a login
5397 shell exits
5398 ~/.bash_profile
5399 The personal initialization file, executed for login shells
5400 ~/.bashrc
5401 The individual per-interactive-shell startup file
5402 ~/.bash_logout
5403 The individual login shell cleanup file, executed when a login
5404 shell exits
5405 ~/.inputrc
5406 Individual readline initialization file
5407
5409 Brian Fox, Free Software Foundation
5410 bfox@gnu.org
5411 Chet Ramey, Case Western Reserve University
5413 chet.ramey@case.edu
5414
5416 If you find a bug in bash, you should report it. But first, you should
5417 make sure that it really is a bug, and that it appears in the latest
5418 version of bash. The latest version is always available from
5419 ftp://ftp.gnu.org/pub/gnu/bash/.
5420 Once you have determined that a bug actually exists, use the bashbug
5422 command (from the source package) to submit a bug report. If you have
5423 a fix, you are encouraged to mail that as well! Suggestions and
5424 `philosophical' bug reports may be mailed to bug-bash@gnu.org or posted
5425 to the Usenet newsgroup gnu.bash.bug.
5426 ALL bug reports should include:
5428 The version number of bash
5430 The hardware and operating system
5431 The compiler used to compile
5432 A description of the bug behaviour
5433 A short script or `recipe' which exercises the bug
5434 Comments and bug reports concerning this manual page should be directed
5436 to chet.ramey@case.edu.
5437
5439 It's too big and too slow.
5440 There are some subtle differences between bash and traditional versions
5442 of sh, mostly because of the POSIX specification.
5443 Aliases are confusing in some uses.
5445 Shell builtin commands and functions are not stoppable/restartable.
5447 Compound commands and command sequences of the form `a ; b ; c' are not
5449 handled gracefully when process suspension is attempted. When a
5450 process is stopped, the shell immediately executes the next command in
5451 the sequence. It suffices to place the sequence of commands between
5452 parentheses to force it into a subshell, which may be stopped as a
5453 unit.
5454 Array variables may not (yet) be exported.
5456 There may be only one active coprocess at a time.
5458GNU Bash-4.2 2010 December 28 BASH(1)