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1BASH(1) General Commands Manual BASH(1)
2
3NAME
4 bash - GNU Bourne-Again SHell
5
6SYNOPSIS
7 bash [options] [command_string | file]
8
9COPYRIGHT
10 Bash is Copyright (C) 1989-2016 by the Free Software Foundation, Inc.
11
12DESCRIPTION
13 Bash is an sh-compatible command language interpreter that executes commands read from the standard input or from a file. Bash
14 also incorporates useful features from the Korn and C shells (ksh and csh).
15
16 Bash is intended to be a conformant implementation of the Shell and Utilities portion of the IEEE POSIX specification (IEEE Stanâ€
17 dard 1003.1). Bash can be configured to be POSIX-conformant by default.
18
19OPTIONS
20 All of the single-character shell options documented in the description of the set builtin command can be used as options when
21 the shell is invoked. In addition, bash interprets the following options when it is invoked:
22
23 -c If the -c option is present, then commands are read from the first non-option argument command_string. If there are
24 arguments after the command_string, the first argument is assigned to $0 and any remaining arguments are assigned to
25 the positional parameters. The assignment to $0 sets the name of the shell, which is used in warning and error mesâ€
26 sages.
27 -i If the -i option is present, the shell is interactive.
28 -l Make bash act as if it had been invoked as a login shell (see INVOCATION below).
29 -r If the -r option is present, the shell becomes restricted (see RESTRICTED SHELL below).
30 -s If the -s option is present, or if no arguments remain after option processing, then commands are read from the stanâ€
31 dard input. This option allows the positional parameters to be set when invoking an interactive shell.
32 -D A list of all double-quoted strings preceded by $ is printed on the standard output. These are the strings that are
33 subject to language translation when the current locale is not C or POSIX. This implies the -n option; no commands
34 will be executed.
35 [-+]O [shopt_option]
36 shopt_option is one of the shell options accepted by the shopt builtin (see SHELL BUILTIN COMMANDS below). If
37 shopt_option is present, -O sets the value of that option; +O unsets it. If shopt_option is not supplied, the names
38 and values of the shell options accepted by shopt are printed on the standard output. If the invocation option is +O,
39 the output is displayed in a format that may be reused as input.
40 -- A -- signals the end of options and disables further option processing. Any arguments after the -- are treated as
41 filenames and arguments. An argument of - is equivalent to --.
42
43 Bash also interprets a number of multi-character options. These options must appear on the command line before the single-charâ€
44 acter options to be recognized.
45
46 --debugger
47 Arrange for the debugger profile to be executed before the shell starts. Turns on extended debugging mode (see the
48 description of the extdebug option to the shopt builtin below).
49 --dump-po-strings
50 Equivalent to -D, but the output is in the GNU gettext po (portable object) file format.
51 --dump-strings
52 Equivalent to -D.
53 --help Display a usage message on standard output and exit successfully.
54 --init-file file
55 --rcfile file
56 Execute commands from file instead of the system wide initialization file /etc/bash.bashrc and the standard personal iniâ€
57 tialization file ~/.bashrc if the shell is interactive (see INVOCATION below).
58
59 --login
60 Equivalent to -l.
61
62 --noediting
63 Do not use the GNU readline library to read command lines when the shell is interactive.
64
65 --noprofile
66 Do not read either the system-wide startup file /etc/profile or any of the personal initialization files ~/.bash_profile,
67 ~/.bash_login, or ~/.profile. By default, bash reads these files when it is invoked as a login shell (see INVOCATION
68 below).
69
70 --norc Do not read and execute the system wide initialization file /etc/bash.bashrc and the personal initialization file
71 ~/.bashrc if the shell is interactive. This option is on by default if the shell is invoked as sh.
72
73 --posix
74 Change the behavior of bash where the default operation differs from the POSIX standard to match the standard (posix
75 mode). See SEE ALSO below for a reference to a document that details how posix mode affects bash's behavior.
76
77 --restricted
78 The shell becomes restricted (see RESTRICTED SHELL below).
79
80 --verbose
81 Equivalent to -v.
82
83 --version
84 Show version information for this instance of bash on the standard output and exit successfully.
85
86ARGUMENTS
87 If arguments remain after option processing, and neither the -c nor the -s option has been supplied, the first argument is
88 assumed to be the name of a file containing shell commands. If bash is invoked in this fashion, $0 is set to the name of the
89 file, and the positional parameters are set to the remaining arguments. Bash reads and executes commands from this file, then
90 exits. Bash's exit status is the exit status of the last command executed in the script. If no commands are executed, the exit
91 status is 0. An attempt is first made to open the file in the current directory, and, if no file is found, then the shell
92 searches the directories in PATH for the script.
93
94INVOCATION
95 A login shell is one whose first character of argument zero is a -, or one started with the --login option.
96
97 An interactive shell is one started without non-option arguments (unless -s is specified) and without the -c option whose stanâ€
98 dard input and error are both connected to terminals (as determined by isatty(3)), or one started with the -i option. PS1 is set
99 and $- includes i if bash is interactive, allowing a shell script or a startup file to test this state.
100
101 The following paragraphs describe how bash executes its startup files. If any of the files exist but cannot be read, bash
102 reports an error. Tildes are expanded in filenames as described below under Tilde Expansion in the EXPANSION section.
103
104 When bash is invoked as an interactive login shell, or as a non-interactive shell with the --login option, it first reads and
105 executes commands from the file /etc/profile, if that file exists. After reading that file, it looks for ~/.bash_profile,
106 ~/.bash_login, and ~/.profile, in that order, and reads and executes commands from the first one that exists and is readable.
107 The --noprofile option may be used when the shell is started to inhibit this behavior.
108
109 When an interactive login shell exits, or a non-interactive login shell executes the exit builtin command, bash reads and exeâ€
110 cutes commands from the file ~/.bash_logout, if it exists.
111
112 When an interactive shell that is not a login shell is started, bash reads and executes commands from /etc/bash.bashrc and
113 ~/.bashrc, if these files exist. This may be inhibited by using the --norc option. The --rcfile file option will force bash to
114 read and execute commands from file instead of /etc/bash.bashrc and ~/.bashrc.
115
116 When bash is started non-interactively, to run a shell script, for example, it looks for the variable BASH_ENV in the environâ€
117 ment, expands its value if it appears there, and uses the expanded value as the name of a file to read and execute. Bash behaves
118 as if the following command were executed:
119 if [ -n "$BASH_ENV" ]; then . "$BASH_ENV"; fi
120 but the value of the PATH variable is not used to search for the filename.
121
122 If bash is invoked with the name sh, it tries to mimic the startup behavior of historical versions of sh as closely as possible,
123 while conforming to the POSIX standard as well. When invoked as an interactive login shell, or a non-interactive shell with the
124 --login option, it first attempts to read and execute commands from /etc/profile and ~/.profile, in that order. The --noprofile
125 option may be used to inhibit this behavior. When invoked as an interactive shell with the name sh, bash looks for the variable
126 ENV, expands its value if it is defined, and uses the expanded value as the name of a file to read and execute. Since a shell
127 invoked as sh does not attempt to read and execute commands from any other startup files, the --rcfile option has no effect. A
128 non-interactive shell invoked with the name sh does not attempt to read any other startup files. When invoked as sh, bash enters
129 posix mode after the startup files are read.
130
131 When bash is started in posix mode, as with the --posix command line option, it follows the POSIX standard for startup files. In
132 this mode, interactive shells expand the ENV variable and commands are read and executed from the file whose name is the expanded
133 value. No other startup files are read.
134
135 Bash attempts to determine when it is being run with its standard input connected to a network connection, as when executed by
136 the remote shell daemon, usually rshd, or the secure shell daemon sshd. If bash determines it is being run in this fashion, it
137 reads and executes commands from ~/.bashrc and ~/.bashrc, if these files exist and are readable. It will not do this if invoked
138 as sh. The --norc option may be used to inhibit this behavior, and the --rcfile option may be used to force another file to be
139 read, but neither rshd nor sshd generally invoke the shell with those options or allow them to be specified.
140
141 If the shell is started with the effective user (group) id not equal to the real user (group) id, and the -p option is not supâ€
142 plied, no startup files are read, shell functions are not inherited from the environment, the SHELLOPTS, BASHOPTS, CDPATH, and
143 GLOBIGNORE variables, if they appear in the environment, are ignored, and the effective user id is set to the real user id. If
144 the -p option is supplied at invocation, the startup behavior is the same, but the effective user id is not reset.
145
146DEFINITIONS
147 The following definitions are used throughout the rest of this document.
148 blank A space or tab.
149 word A sequence of characters considered as a single unit by the shell. Also known as a token.
150 name A word consisting only of alphanumeric characters and underscores, and beginning with an alphabetic character or an underâ€
151 score. Also referred to as an identifier.
152 metacharacter
153 A character that, when unquoted, separates words. One of the following:
154 | & ; ( ) < > space tab newline
155 control operator
156 A token that performs a control function. It is one of the following symbols:
157 || & && ; ;; ;& ;;& ( ) | |& <newline>
158
159RESERVED WORDS
160 Reserved words are words that have a special meaning to the shell. The following words are recognized as reserved when unquoted
161 and either the first word of a simple command (see SHELL GRAMMAR below) or the third word of a case or for command:
162
163 ! case coproc do done elif else esac fi for function if in select then until while { } time [[ ]]
164
165SHELL GRAMMAR
166 Simple Commands
167 A simple command is a sequence of optional variable assignments followed by blank-separated words and redirections, and termiâ€
168 nated by a control operator. The first word specifies the command to be executed, and is passed as argument zero. The remaining
169 words are passed as arguments to the invoked command.
170
171 The return value of a simple command is its exit status, or 128+n if the command is terminated by signal n.
172
173 Pipelines
174 A pipeline is a sequence of one or more commands separated by one of the control operators | or |&. The format for a pipeline
175 is:
176
177 [time [-p]] [ ! ] command [ [|⎪|&] command2 ... ]
178
179 The standard output of command is connected via a pipe to the standard input of command2. This connection is performed before
180 any redirections specified by the command (see REDIRECTION below). If |& is used, command's standard error, in addition to its
181 standard output, is connected to command2's standard input through the pipe; it is shorthand for 2>&1 |. This implicit redirectâ€
182 ion of the standard error to the standard output is performed after any redirections specified by the command.
183
184 The return status of a pipeline is the exit status of the last command, unless the pipefail option is enabled. If pipefail is
185 enabled, the pipeline's return status is the value of the last (rightmost) command to exit with a non-zero status, or zero if all
186 commands exit successfully. If the reserved word ! precedes a pipeline, the exit status of that pipeline is the logical negaâ€
187 tion of the exit status as described above. The shell waits for all commands in the pipeline to terminate before returning a
188 value.
189
190 If the time reserved word precedes a pipeline, the elapsed as well as user and system time consumed by its execution are reported
191 when the pipeline terminates. The -p option changes the output format to that specified by POSIX. When the shell is in posix
192 mode, it does not recognize time as a reserved word if the next token begins with a `-'. The TIMEFORMAT variable may be set to a
193 format string that specifies how the timing information should be displayed; see the description of TIMEFORMAT under Shell Variâ€
194 ables below.
195
196 When the shell is in posix mode, time may be followed by a newline. In this case, the shell displays the total user and system
197 time consumed by the shell and its children. The TIMEFORMAT variable may be used to specify the format of the time information.
198
199 Each command in a pipeline is executed as a separate process (i.e., in a subshell).
200
201 Lists
202 A list is a sequence of one or more pipelines separated by one of the operators ;, &, &&, or ||, and optionally terminated by one
203 of ;, &, or <newline>.
204
205 Of these list operators, && and || have equal precedence, followed by ; and &, which have equal precedence.
206
207 A sequence of one or more newlines may appear in a list instead of a semicolon to delimit commands.
208
209 If a command is terminated by the control operator &, the shell executes the command in the background in a subshell. The shell
210 does not wait for the command to finish, and the return status is 0. Commands separated by a ; are executed sequentially; the
211 shell waits for each command to terminate in turn. The return status is the exit status of the last command executed.
212
213 AND and OR lists are sequences of one or more pipelines separated by the && and || control operators, respectively. AND and OR
214 lists are executed with left associativity. An AND list has the form
215
216 command1 && command2
217
218 command2 is executed if, and only if, command1 returns an exit status of zero.
219
220 An OR list has the form
221
222 command1 || command2
223
224 command2 is executed if and only if command1 returns a non-zero exit status. The return status of AND and OR lists is the exit
225 status of the last command executed in the list.
226
227 Compound Commands
228 A compound command is one of the following. In most cases a list in a command's description may be separated from the rest of
229 the command by one or more newlines, and may be followed by a newline in place of a semicolon.
230
231 (list) list is executed in a subshell environment (see COMMAND EXECUTION ENVIRONMENT below). Variable assignments and builtin
232 commands that affect the shell's environment do not remain in effect after the command completes. The return status is
233 the exit status of list.
234
235 { list; }
236 list is simply executed in the current shell environment. list must be terminated with a newline or semicolon. This is
237 known as a group command. The return status is the exit status of list. Note that unlike the metacharacters ( and ), {
238 and } are reserved words and must occur where a reserved word is permitted to be recognized. Since they do not cause a
239 word break, they must be separated from list by whitespace or another shell metacharacter.
240
241 ((expression))
242 The expression is evaluated according to the rules described below under ARITHMETIC EVALUATION. If the value of the
243 expression is non-zero, the return status is 0; otherwise the return status is 1. This is exactly equivalent to let
244 "expression".
245
246 [[ expression ]]
247 Return a status of 0 or 1 depending on the evaluation of the conditional expression expression. Expressions are composed
248 of the primaries described below under CONDITIONAL EXPRESSIONS. Word splitting and pathname expansion are not performed
249 on the words between the [[ and ]]; tilde expansion, parameter and variable expansion, arithmetic expansion, command subâ€
250 stitution, process substitution, and quote removal are performed. Conditional operators such as -f must be unquoted to be
251 recognized as primaries.
252
253 When used with [[, the < and > operators sort lexicographically using the current locale.
254
255 See the description of the test builtin command (section SHELL BUILTIN COMMANDS below) for the handling of parameters (i.e.
256 missing parameters).
257
258 When the == and != operators are used, the string to the right of the operator is considered a pattern and matched according to
259 the rules described below under Pattern Matching, as if the extglob shell option were enabled. The = operator is equivalent to
260 ==. If the nocasematch shell option is enabled, the match is performed without regard to the case of alphabetic characters. The
261 return value is 0 if the string matches (==) or does not match (!=) the pattern, and 1 otherwise. Any part of the pattern may be
262 quoted to force the quoted portion to be matched as a string.
263
264 An additional binary operator, =~, is available, with the same precedence as == and !=. When it is used, the string to the right
265 of the operator is considered an extended regular expression and matched accordingly (as in regex(3)). The return value is 0 if
266 the string matches the pattern, and 1 otherwise. If the regular expression is syntactically incorrect, the conditional expresâ€
267 sion's return value is 2. If the nocasematch shell option is enabled, the match is performed without regard to the case of
268 alphabetic characters. Any part of the pattern may be quoted to force the quoted portion to be matched as a string. Bracket
269 expressions in regular expressions must be treated carefully, since normal quoting characters lose their meanings between brackâ€
270 ets. If the pattern is stored in a shell variable, quoting the variable expansion forces the entire pattern to be matched as a
271 string. Substrings matched by parenthesized subexpressions within the regular expression are saved in the array variable
272 BASH_REMATCH. The element of BASH_REMATCH with index 0 is the portion of the string matching the entire regular expression. The
273 element of BASH_REMATCH with index n is the portion of the string matching the nth parenthesized subexpression.
274
275 Expressions may be combined using the following operators, listed in decreasing order of precedence:
276
277 ( expression )
278 Returns the value of expression. This may be used to override the normal precedence of operators.
279 ! expression
280 True if expression is false.
281 expression1 && expression2
282 True if both expression1 and expression2 are true.
283 expression1 || expression2
284 True if either expression1 or expression2 is true.
285
286 The && and || operators do not evaluate expression2 if the value of expression1 is sufficient to determine the return
287 value of the entire conditional expression.
288
289 for name [ [ in [ word ... ] ] ; ] do list ; done
290 The list of words following in is expanded, generating a list of items. The variable name is set to each element of this
291 list in turn, and list is executed each time. If the in word is omitted, the for command executes list once for each
292 positional parameter that is set (see PARAMETERS below). The return status is the exit status of the last command that
293 executes. If the expansion of the items following in results in an empty list, no commands are executed, and the return
294 status is 0.
295
296 for (( expr1 ; expr2 ; expr3 )) ; do list ; done
297 First, the arithmetic expression expr1 is evaluated according to the rules described below under ARITHMETIC EVALUATION.
298 The arithmetic expression expr2 is then evaluated repeatedly until it evaluates to zero. Each time expr2 evaluates to a
299 non-zero value, list is executed and the arithmetic expression expr3 is evaluated. If any expression is omitted, it
300 behaves as if it evaluates to 1. The return value is the exit status of the last command in list that is executed, or
301 false if any of the expressions is invalid.
302
303 select name [ in word ] ; do list ; done
304 The list of words following in is expanded, generating a list of items. The set of expanded words is printed on the stanâ€
305 dard error, each preceded by a number. If the in word is omitted, the positional parameters are printed (see PARAMETERS
306 below). The PS3 prompt is then displayed and a line read from the standard input. If the line consists of a number corâ€
307 responding to one of the displayed words, then the value of name is set to that word. If the line is empty, the words and
308 prompt are displayed again. If EOF is read, the command completes. Any other value read causes name to be set to null.
309 The line read is saved in the variable REPLY. The list is executed after each selection until a break command is exeâ€
310 cuted. The exit status of select is the exit status of the last command executed in list, or zero if no commands were
311 executed.
312
313 case word in [ [(] pattern [ | pattern ] ... ) list ;; ] ... esac
314 A case command first expands word, and tries to match it against each pattern in turn, using the same matching rules as
315 for pathname expansion (see Pathname Expansion below). The word is expanded using tilde expansion, parameter and variable
316 expansion, arithmetic expansion, command substitution, process substitution and quote removal. Each pattern examined is
317 expanded using tilde expansion, parameter and variable expansion, arithmetic expansion, command substitution, and process
318 substitution. If the nocasematch shell option is enabled, the match is performed without regard to the case of alphabetic
319 characters. When a match is found, the corresponding list is executed. If the ;; operator is used, no subsequent matches
320 are attempted after the first pattern match. Using ;& in place of ;; causes execution to continue with the list associâ€
321 ated with the next set of patterns. Using ;;& in place of ;; causes the shell to test the next pattern list in the stateâ€
322 ment, if any, and execute any associated list on a successful match. The exit status is zero if no pattern matches. Othâ€
323 erwise, it is the exit status of the last command executed in list.
324
325 if list; then list; [ elif list; then list; ] ... [ else list; ] fi
326 The if list is executed. If its exit status is zero, the then list is executed. Otherwise, each elif list is executed in
327 turn, and if its exit status is zero, the corresponding then list is executed and the command completes. Otherwise, the
328 else list is executed, if present. The exit status is the exit status of the last command executed, or zero if no condiâ€
329 tion tested true.
330
331 while list-1; do list-2; done
332 until list-1; do list-2; done
333 The while command continuously executes the list list-2 as long as the last command in the list list-1 returns an exit
334 status of zero. The until command is identical to the while command, except that the test is negated: list-2 is executed
335 as long as the last command in list-1 returns a non-zero exit status. The exit status of the while and until commands is
336 the exit status of the last command executed in list-2, or zero if none was executed.
337
338 Coprocesses
339 A coprocess is a shell command preceded by the coproc reserved word. A coprocess is executed asynchronously in a subshell, as if
340 the command had been terminated with the & control operator, with a two-way pipe established between the executing shell and the
341 coprocess.
342
343 The format for a coprocess is:
344
345 coproc [NAME] command [redirections]
346
347 This creates a coprocess named NAME. If NAME is not supplied, the default name is COPROC. NAME must not be supplied if command
348 is a simple command (see above); otherwise, it is interpreted as the first word of the simple command. When the coprocess is
349 executed, the shell creates an array variable (see Arrays below) named NAME in the context of the executing shell. The standard
350 output of command is connected via a pipe to a file descriptor in the executing shell, and that file descriptor is assigned to
351 NAME[0]. The standard input of command is connected via a pipe to a file descriptor in the executing shell, and that file
352 descriptor is assigned to NAME[1]. This pipe is established before any redirections specified by the command (see REDIRECTION
353 below). The file descriptors can be utilized as arguments to shell commands and redirections using standard word expansions.
354 The file descriptors are not available in subshells. The process ID of the shell spawned to execute the coprocess is available
355 as the value of the variable NAME_PID. The wait builtin command may be used to wait for the coprocess to terminate.
356
357 Since the coprocess is created as an asynchronous command, the coproc command always returns success. The return status of a
358 coprocess is the exit status of command.
359
360 Shell Function Definitions
361 A shell function is an object that is called like a simple command and executes a compound command with a new set of positional
362 parameters. Shell functions are declared as follows:
363
364 name () compound-command [redirection]
365 function name [()] compound-command [redirection]
366 This defines a function named name. The reserved word function is optional. If the function reserved word is supplied,
367 the parentheses are optional. The body of the function is the compound command compound-command (see Compound Commands
368 above). That command is usually a list of commands between { and }, but may be any command listed under Compound Commands
369 above, with one exception: If the function reserved word is used, but the parentheses are not supplied, the braces are
370 required. compound-command is executed whenever name is specified as the name of a simple command. When in posix mode,
371 name may not be the name of one of the POSIX special builtins. Any redirections (see REDIRECTION below) specified when a
372 function is defined are performed when the function is executed. The exit status of a function definition is zero unless
373 a syntax error occurs or a readonly function with the same name already exists. When executed, the exit status of a funcâ€
374 tion is the exit status of the last command executed in the body. (See FUNCTIONS below.)
375
376COMMENTS
377 In a non-interactive shell, or an interactive shell in which the interactive_comments option to the shopt builtin is enabled (see
378 SHELL BUILTIN COMMANDS below), a word beginning with # causes that word and all remaining characters on that line to be ignored.
379 An interactive shell without the interactive_comments option enabled does not allow comments. The interactive_comments option is
380 on by default in interactive shells.
381
382QUOTING
383 Quoting is used to remove the special meaning of certain characters or words to the shell. Quoting can be used to disable speâ€
384 cial treatment for special characters, to prevent reserved words from being recognized as such, and to prevent parameter expanâ€
385 sion.
386
387 Each of the metacharacters listed above under DEFINITIONS has special meaning to the shell and must be quoted if it is to repreâ€
388 sent itself.
389
390 When the command history expansion facilities are being used (see HISTORY EXPANSION below), the history expansion character, usuâ€
391 ally !, must be quoted to prevent history expansion.
392
393 There are three quoting mechanisms: the escape character, single quotes, and double quotes.
394
395 A non-quoted backslash (\) is the escape character. It preserves the literal value of the next character that follows, with the
396 exception of <newline>. If a \<newline> pair appears, and the backslash is not itself quoted, the \<newline> is treated as a
397 line continuation (that is, it is removed from the input stream and effectively ignored).
398
399 Enclosing characters in single quotes preserves the literal value of each character within the quotes. A single quote may not
400 occur between single quotes, even when preceded by a backslash.
401
402 Enclosing characters in double quotes preserves the literal value of all characters within the quotes, with the exception of $,
403 `, \, and, when history expansion is enabled, !. When the shell is in posix mode, the ! has no special meaning within double
404 quotes, even when history expansion is enabled. The characters $ and ` retain their special meaning within double quotes. The
405 backslash retains its special meaning only when followed by one of the following characters: $, `, ", \, or <newline>. A double
406 quote may be quoted within double quotes by preceding it with a backslash. If enabled, history expansion will be performed
407 unless an ! appearing in double quotes is escaped using a backslash. The backslash preceding the ! is not removed.
408
409 The special parameters * and @ have special meaning when in double quotes (see PARAMETERS below).
410
411 Words of the form $'string' are treated specially. The word expands to string, with backslash-escaped characters replaced as
412 specified by the ANSI C standard. Backslash escape sequences, if present, are decoded as follows:
413 \a alert (bell)
414 \b backspace
415 \e
416 \E an escape character
417 \f form feed
418 \n new line
419 \r carriage return
420 \t horizontal tab
421 \v vertical tab
422 \\ backslash
423 \' single quote
424 \" double quote
425 \? question mark
426 \nnn the eight-bit character whose value is the octal value nnn (one to three digits)
427 \xHH the eight-bit character whose value is the hexadecimal value HH (one or two hex digits)
428 \uHHHH the Unicode (ISO/IEC 10646) character whose value is the hexadecimal value HHHH (one to four hex digits)
429 \UHHHHHHHH
430 the Unicode (ISO/IEC 10646) character whose value is the hexadecimal value HHHHHHHH (one to eight hex digits)
431 \cx a control-x character
432
433 The expanded result is single-quoted, as if the dollar sign had not been present.
434
435 A double-quoted string preceded by a dollar sign ($"string") will cause the string to be translated according to the current
436 locale. If the current locale is C or POSIX, the dollar sign is ignored. If the string is translated and replaced, the replaceâ€
437 ment is double-quoted.
438
439PARAMETERS
440 A parameter is an entity that stores values. It can be a name, a number, or one of the special characters listed below under
441 Special Parameters. A variable is a parameter denoted by a name. A variable has a value and zero or more attributes.
442 Attributes are assigned using the declare builtin command (see declare below in SHELL BUILTIN COMMANDS).
443
444 A parameter is set if it has been assigned a value. The null string is a valid value. Once a variable is set, it may be unset
445 only by using the unset builtin command (see SHELL BUILTIN COMMANDS below).
446
447 A variable may be assigned to by a statement of the form
448
449 name=[value]
450
451 If value is not given, the variable is assigned the null string. All values undergo tilde expansion, parameter and variable
452 expansion, command substitution, arithmetic expansion, and quote removal (see EXPANSION below). If the variable has its integer
453 attribute set, then value is evaluated as an arithmetic expression even if the $((...)) expansion is not used (see Arithmetic
454 Expansion below). Word splitting is not performed, with the exception of "$@" as explained below under Special Parameters.
455 Pathname expansion is not performed. Assignment statements may also appear as arguments to the alias, declare, typeset, export,
456 readonly, and local builtin commands (declaration commands). When in posix mode, these builtins may appear in a command after
457 one or more instances of the command builtin and retain these assignment statement properties.
458
459 In the context where an assignment statement is assigning a value to a shell variable or array index, the += operator can be used
460 to append to or add to the variable's previous value. This includes arguments to builtin commands such as declare that accept
461 assignment statements (declaration commands). When += is applied to a variable for which the integer attribute has been set,
462 value is evaluated as an arithmetic expression and added to the variable's current value, which is also evaluated. When += is
463 applied to an array variable using compound assignment (see Arrays below), the variable's value is not unset (as it is when using
464 =), and new values are appended to the array beginning at one greater than the array's maximum index (for indexed arrays) or
465 added as additional key-value pairs in an associative array. When applied to a string-valued variable, value is expanded and
466 appended to the variable's value.
467
468 A variable can be assigned the nameref attribute using the -n option to the declare or local builtin commands (see the descripâ€
469 tions of declare and local below) to create a nameref, or a reference to another variable. This allows variables to be manipuâ€
470 lated indirectly. Whenever the nameref variable is referenced, assigned to, unset, or has its attributes modified (other than
471 using or changing the nameref attribute itself), the operation is actually performed on the variable specified by the nameref
472 variable's value. A nameref is commonly used within shell functions to refer to a variable whose name is passed as an argument
473 to the function. For instance, if a variable name is passed to a shell function as its first argument, running
474 declare -n ref=$1
475 inside the function creates a nameref variable ref whose value is the variable name passed as the first argument. References and
476 assignments to ref, and changes to its attributes, are treated as references, assignments, and attribute modifications to the
477 variable whose name was passed as $1. If the control variable in a for loop has the nameref attribute, the list of words can be
478 a list of shell variables, and a name reference will be established for each word in the list, in turn, when the loop is exeâ€
479 cuted. Array variables cannot be given the nameref attribute. However, nameref variables can reference array variables and subâ€
480 scripted array variables. Namerefs can be unset using the -n option to the unset builtin. Otherwise, if unset is executed with
481 the name of a nameref variable as an argument, the variable referenced by the nameref variable will be unset.
482
483 Positional Parameters
484 A positional parameter is a parameter denoted by one or more digits, other than the single digit 0. Positional parameters are
485 assigned from the shell's arguments when it is invoked, and may be reassigned using the set builtin command. Positional parameâ€
486 ters may not be assigned to with assignment statements. The positional parameters are temporarily replaced when a shell function
487 is executed (see FUNCTIONS below).
488
489 When a positional parameter consisting of more than a single digit is expanded, it must be enclosed in braces (see EXPANSION
490 below).
491
492 Special Parameters
493 The shell treats several parameters specially. These parameters may only be referenced; assignment to them is not allowed.
494 * Expands to the positional parameters, starting from one. When the expansion is not within double quotes, each positional
495 parameter expands to a separate word. In contexts where it is performed, those words are subject to further word splitâ€
496 ting and pathname expansion. When the expansion occurs within double quotes, it expands to a single word with the value
497 of each parameter separated by the first character of the IFS special variable. That is, "$*" is equivalent to
498 "$1c$2c...", where c is the first character of the value of the IFS variable. If IFS is unset, the parameters are sepaâ€
499 rated by spaces. If IFS is null, the parameters are joined without intervening separators.
500 @ Expands to the positional parameters, starting from one. When the expansion occurs within double quotes, each parameter
501 expands to a separate word. That is, "$@" is equivalent to "$1" "$2" ... If the double-quoted expansion occurs within a
502 word, the expansion of the first parameter is joined with the beginning part of the original word, and the expansion of
503 the last parameter is joined with the last part of the original word. When there are no positional parameters, "$@" and
504 $@ expand to nothing (i.e., they are removed).
505 # Expands to the number of positional parameters in decimal.
506 ? Expands to the exit status of the most recently executed foreground pipeline.
507 - Expands to the current option flags as specified upon invocation, by the set builtin command, or those set by the shell
508 itself (such as the -i option).
509 $ Expands to the process ID of the shell. In a () subshell, it expands to the process ID of the current shell, not the subâ€
510 shell.
511 ! Expands to the process ID of the job most recently placed into the background, whether executed as an asynchronous command
512 or using the bg builtin (see JOB CONTROL below).
513 0 Expands to the name of the shell or shell script. This is set at shell initialization. If bash is invoked with a file of
514 commands, $0 is set to the name of that file. If bash is started with the -c option, then $0 is set to the first argument
515 after the string to be executed, if one is present. Otherwise, it is set to the filename used to invoke bash, as given by
516 argument zero.
517 _ At shell startup, set to the absolute pathname used to invoke the shell or shell script being executed as passed in the
518 environment or argument list. Subsequently, expands to the last argument to the previous command, after expansion. Also
519 set to the full pathname used to invoke each command executed and placed in the environment exported to that command.
520 When checking mail, this parameter holds the name of the mail file currently being checked.
521
522 Shell Variables
523 The following variables are set by the shell:
524
525 BASH Expands to the full filename used to invoke this instance of bash.
526 BASHOPTS
527 A colon-separated list of enabled shell options. Each word in the list is a valid argument for the -s option to the shopt
528 builtin command (see SHELL BUILTIN COMMANDS below). The options appearing in BASHOPTS are those reported as on by shopt.
529 If this variable is in the environment when bash starts up, each shell option in the list will be enabled before reading
530 any startup files. This variable is read-only.
531 BASHPID
532 Expands to the process ID of the current bash process. This differs from $$ under certain circumstances, such as subâ€
533 shells that do not require bash to be re-initialized.
534 BASH_ALIASES
535 An associative array variable whose members correspond to the internal list of aliases as maintained by the alias builtin.
536 Elements added to this array appear in the alias list; however, unsetting array elements currently does not cause aliases
537 to be removed from the alias list. If BASH_ALIASES is unset, it loses its special properties, even if it is subsequently
538 reset.
539 BASH_ARGC
540 An array variable whose values are the number of parameters in each frame of the current bash execution call stack. The
541 number of parameters to the current subroutine (shell function or script executed with . or source) is at the top of the
542 stack. When a subroutine is executed, the number of parameters passed is pushed onto BASH_ARGC. The shell sets BASH_ARGC
543 only when in extended debugging mode (see the description of the extdebug option to the shopt builtin below)
544 BASH_ARGV
545 An array variable containing all of the parameters in the current bash execution call stack. The final parameter of the
546 last subroutine call is at the top of the stack; the first parameter of the initial call is at the bottom. When a subrouâ€
547 tine is executed, the parameters supplied are pushed onto BASH_ARGV. The shell sets BASH_ARGV only when in extended
548 debugging mode (see the description of the extdebug option to the shopt builtin below)
549 BASH_CMDS
550 An associative array variable whose members correspond to the internal hash table of commands as maintained by the hash
551 builtin. Elements added to this array appear in the hash table; however, unsetting array elements currently does not
552 cause command names to be removed from the hash table. If BASH_CMDS is unset, it loses its special properties, even if it
553 is subsequently reset.
554 BASH_COMMAND
555 The command currently being executed or about to be executed, unless the shell is executing a command as the result of a
556 trap, in which case it is the command executing at the time of the trap.
557 BASH_EXECUTION_STRING
558 The command argument to the -c invocation option.
559 BASH_LINENO
560 An array variable whose members are the line numbers in source files where each corresponding member of FUNCNAME was
561 invoked. ${BASH_LINENO[$i]} is the line number in the source file (${BASH_SOURCE[$i+1]}) where ${FUNCNAME[$i]} was called
562 (or ${BASH_LINENO[$i-1]} if referenced within another shell function). Use LINENO to obtain the current line number.
563 BASH_LOADABLES_PATH
564 A colon-separated list of directories in which the shell looks for dynamically loadable builtins specified by the enable
565 command.
566 BASH_REMATCH
567 An array variable whose members are assigned by the =~ binary operator to the [[ conditional command. The element with
568 index 0 is the portion of the string matching the entire regular expression. The element with index n is the portion of
569 the string matching the nth parenthesized subexpression. This variable is read-only.
570 BASH_SOURCE
571 An array variable whose members are the source filenames where the corresponding shell function names in the FUNCNAME
572 array variable are defined. The shell function ${FUNCNAME[$i]} is defined in the file ${BASH_SOURCE[$i]} and called from
573 ${BASH_SOURCE[$i+1]}.
574 BASH_SUBSHELL
575 Incremented by one within each subshell or subshell environment when the shell begins executing in that environment. The
576 initial value is 0.
577 BASH_VERSINFO
578 A readonly array variable whose members hold version information for this instance of bash. The values assigned to the
579 array members are as follows:
580 BASH_VERSINFO[0] The major version number (the release).
581 BASH_VERSINFO[1] The minor version number (the version).
582 BASH_VERSINFO[2] The patch level.
583 BASH_VERSINFO[3] The build version.
584 BASH_VERSINFO[4] The release status (e.g., beta1).
585 BASH_VERSINFO[5] The value of MACHTYPE.
586 BASH_VERSION
587 Expands to a string describing the version of this instance of bash.
588 COMP_CWORD
589 An index into ${COMP_WORDS} of the word containing the current cursor position. This variable is available only in shell
590 functions invoked by the programmable completion facilities (see Programmable Completion below).
591 COMP_KEY
592 The key (or final key of a key sequence) used to invoke the current completion function.
593 COMP_LINE
594 The current command line. This variable is available only in shell functions and external commands invoked by the proâ€
595 grammable completion facilities (see Programmable Completion below).
596 COMP_POINT
597 The index of the current cursor position relative to the beginning of the current command. If the current cursor position
598 is at the end of the current command, the value of this variable is equal to ${#COMP_LINE}. This variable is available
599 only in shell functions and external commands invoked by the programmable completion facilities (see Programmable Compleâ€
600 tion below).
601 COMP_TYPE
602 Set to an integer value corresponding to the type of completion attempted that caused a completion function to be called:
603 TAB, for normal completion, ?, for listing completions after successive tabs, !, for listing alternatives on partial word
604 completion, @, to list completions if the word is not unmodified, or %, for menu completion. This variable is available
605 only in shell functions and external commands invoked by the programmable completion facilities (see Programmable Compleâ€
606 tion below).
607 COMP_WORDBREAKS
608 The set of characters that the readline library treats as word separators when performing word completion. If COMP_WORDâ€
609 BREAKS is unset, it loses its special properties, even if it is subsequently reset.
610 COMP_WORDS
611 An array variable (see Arrays below) consisting of the individual words in the current command line. The line is split
612 into words as readline would split it, using COMP_WORDBREAKS as described above. This variable is available only in shell
613 functions invoked by the programmable completion facilities (see Programmable Completion below).
614 COPROC An array variable (see Arrays below) created to hold the file descriptors for output from and input to an unnamed coproâ€
615 cess (see Coprocesses above).
616 DIRSTACK
617 An array variable (see Arrays below) containing the current contents of the directory stack. Directories appear in the
618 stack in the order they are displayed by the dirs builtin. Assigning to members of this array variable may be used to
619 modify directories already in the stack, but the pushd and popd builtins must be used to add and remove directories.
620 Assignment to this variable will not change the current directory. If DIRSTACK is unset, it loses its special properties,
621 even if it is subsequently reset.
622 EUID Expands to the effective user ID of the current user, initialized at shell startup. This variable is readonly.
623 FUNCNAME
624 An array variable containing the names of all shell functions currently in the execution call stack. The element with
625 index 0 is the name of any currently-executing shell function. The bottom-most element (the one with the highest index)
626 is "main". This variable exists only when a shell function is executing. Assignments to FUNCNAME have no effect. If
627 FUNCNAME is unset, it loses its special properties, even if it is subsequently reset.
628
629 This variable can be used with BASH_LINENO and BASH_SOURCE. Each element of FUNCNAME has corresponding elements in
630 BASH_LINENO and BASH_SOURCE to describe the call stack. For instance, ${FUNCNAME[$i]} was called from the file
631 ${BASH_SOURCE[$i+1]} at line number ${BASH_LINENO[$i]}. The caller builtin displays the current call stack using this
632 information.
633 GROUPS An array variable containing the list of groups of which the current user is a member. Assignments to GROUPS have no
634 effect. If GROUPS is unset, it loses its special properties, even if it is subsequently reset.
635 HISTCMD
636 The history number, or index in the history list, of the current command. If HISTCMD is unset, it loses its special propâ€
637 erties, even if it is subsequently reset.
638 HOSTNAME
639 Automatically set to the name of the current host.
640 HOSTTYPE
641 Automatically set to a string that uniquely describes the type of machine on which bash is executing. The default is sysâ€
642 tem-dependent.
643 LINENO Each time this parameter is referenced, the shell substitutes a decimal number representing the current sequential line
644 number (starting with 1) within a script or function. When not in a script or function, the value substituted is not
645 guaranteed to be meaningful. If LINENO is unset, it loses its special properties, even if it is subsequently reset.
646 MACHTYPE
647 Automatically set to a string that fully describes the system type on which bash is executing, in the standard GNU cpu-
648 company-system format. The default is system-dependent.
649 MAPFILE
650 An array variable (see Arrays below) created to hold the text read by the mapfile builtin when no variable name is supâ€
651 plied.
652 OLDPWD The previous working directory as set by the cd command.
653 OPTARG The value of the last option argument processed by the getopts builtin command (see SHELL BUILTIN COMMANDS below).
654 OPTIND The index of the next argument to be processed by the getopts builtin command (see SHELL BUILTIN COMMANDS below).
655 OSTYPE Automatically set to a string that describes the operating system on which bash is executing. The default is system-
656 dependent.
657 PIPESTATUS
658 An array variable (see Arrays below) containing a list of exit status values from the processes in the most-recently-exeâ€
659 cuted foreground pipeline (which may contain only a single command).
660 PPID The process ID of the shell's parent. This variable is readonly.
661 PWD The current working directory as set by the cd command.
662 RANDOM Each time this parameter is referenced, a random integer between 0 and 32767 is generated. The sequence of random numbers
663 may be initialized by assigning a value to RANDOM. If RANDOM is unset, it loses its special properties, even if it is
664 subsequently reset.
665 READLINE_LINE
666 The contents of the readline line buffer, for use with "bind -x" (see SHELL BUILTIN COMMANDS below).
667 READLINE_POINT
668 The position of the insertion point in the readline line buffer, for use with "bind -x" (see SHELL BUILTIN COMMANDS
669 below).
670 REPLY Set to the line of input read by the read builtin command when no arguments are supplied.
671 SECONDS
672 Each time this parameter is referenced, the number of seconds since shell invocation is returned. If a value is assigned
673 to SECONDS, the value returned upon subsequent references is the number of seconds since the assignment plus the value
674 assigned. If SECONDS is unset, it loses its special properties, even if it is subsequently reset.
675 SHELLOPTS
676 A colon-separated list of enabled shell options. Each word in the list is a valid argument for the -o option to the set
677 builtin command (see SHELL BUILTIN COMMANDS below). The options appearing in SHELLOPTS are those reported as on by set
678 -o. If this variable is in the environment when bash starts up, each shell option in the list will be enabled before
679 reading any startup files. This variable is read-only.
680 SHLVL Incremented by one each time an instance of bash is started.
681 UID Expands to the user ID of the current user, initialized at shell startup. This variable is readonly.
682
683 The following variables are used by the shell. In some cases, bash assigns a default value to a variable; these cases are noted
684 below.
685
686 BASH_COMPAT
687 The value is used to set the shell's compatibility level. See the description of the shopt builtin below under SHELL
688 BUILTIN COMMANDS for a description of the various compatibility levels and their effects. The value may be a decimal numâ€
689 ber (e.g., 4.2) or an integer (e.g., 42) corresponding to the desired compatibility level. If BASH_COMPAT is unset or set
690 to the empty string, the compatibility level is set to the default for the current version. If BASH_COMPAT is set to a
691 value that is not one of the valid compatibility levels, the shell prints an error message and sets the compatibility
692 level to the default for the current version. The valid compatibility levels correspond to the compatibility options
693 accepted by the shopt builtin described below (for example, compat42 means that 4.2 and 42 are valid values). The current
694 version is also a valid value.
695 BASH_ENV
696 If this parameter is set when bash is executing a shell script, its value is interpreted as a filename containing commands
697 to initialize the shell, as in ~/.bashrc. The value of BASH_ENV is subjected to parameter expansion, command substituâ€
698 tion, and arithmetic expansion before being interpreted as a filename. PATH is not used to search for the resultant fileâ€
699 name.
700 BASH_XTRACEFD
701 If set to an integer corresponding to a valid file descriptor, bash will write the trace output generated when set -x is
702 enabled to that file descriptor. The file descriptor is closed when BASH_XTRACEFD is unset or assigned a new value.
703 Unsetting BASH_XTRACEFD or assigning it the empty string causes the trace output to be sent to the standard error. Note
704 that setting BASH_XTRACEFD to 2 (the standard error file descriptor) and then unsetting it will result in the standard
705 error being closed.
706 CDPATH The search path for the cd command. This is a colon-separated list of directories in which the shell looks for destinaâ€
707 tion directories specified by the cd command. A sample value is ".:~:/usr".
708 CHILD_MAX
709 Set the number of exited child status values for the shell to remember. Bash will not allow this value to be decreased
710 below a POSIX-mandated minimum, and there is a maximum value (currently 8192) that this may not exceed. The minimum value
711 is system-dependent.
712 COLUMNS
713 Used by the select compound command to determine the terminal width when printing selection lists. Automatically set if
714 the checkwinsize option is enabled or in an interactive shell upon receipt of a SIGWINCH.
715 COMPREPLY
716 An array variable from which bash reads the possible completions generated by a shell function invoked by the programmable
717 completion facility (see Programmable Completion below). Each array element contains one possible completion.
718 EMACS If bash finds this variable in the environment when the shell starts with value "t", it assumes that the shell is running
719 in an Emacs shell buffer and disables line editing.
720 ENV Similar to BASH_ENV; used when the shell is invoked in POSIX mode.
721 EXECIGNORE
722 A colon-separated list of shell patterns (see Pattern Matching) defining the list of filenames to be ignored by command
723 search using PATH. Files whose full pathnames match one of these patterns are not considered executable files for the
724 purposes of completion and command execution via PATH lookup. This does not affect the behavior of the [, test, and [[
725 commands. Full pathnames in the command hash table are not subject to EXECIGNORE. Use this variable to ignore shared
726 library files that have the executable bit set, but are not executable files. The pattern matching honors the setting of
727 the extglob shell option.
728 FCEDIT The default editor for the fc builtin command.
729 FIGNORE
730 A colon-separated list of suffixes to ignore when performing filename completion (see READLINE below). A filename whose
731 suffix matches one of the entries in FIGNORE is excluded from the list of matched filenames. A sample value is ".o:~"
732 (Quoting is needed when assigning a value to this variable, which contains tildes).
733 FUNCNEST
734 If set to a numeric value greater than 0, defines a maximum function nesting level. Function invocations that exceed this
735 nesting level will cause the current command to abort.
736 GLOBIGNORE
737 A colon-separated list of patterns defining the set of filenames to be ignored by pathname expansion. If a filename
738 matched by a pathname expansion pattern also matches one of the patterns in GLOBIGNORE, it is removed from the list of
739 matches.
740 HISTCONTROL
741 A colon-separated list of values controlling how commands are saved on the history list. If the list of values includes
742 ignorespace, lines which begin with a space character are not saved in the history list. A value of ignoredups causes
743 lines matching the previous history entry to not be saved. A value of ignoreboth is shorthand for ignorespace and
744 ignoredups. A value of erasedups causes all previous lines matching the current line to be removed from the history list
745 before that line is saved. Any value not in the above list is ignored. If HISTCONTROL is unset, or does not include a
746 valid value, all lines read by the shell parser are saved on the history list, subject to the value of HISTIGNORE. The
747 second and subsequent lines of a multi-line compound command are not tested, and are added to the history regardless of
748 the value of HISTCONTROL.
749 HISTFILE
750 The name of the file in which command history is saved (see HISTORY below). The default value is ~/.bash_history. If
751 unset, the command history is not saved when a shell exits.
752 HISTFILESIZE
753 The maximum number of lines contained in the history file. When this variable is assigned a value, the history file is
754 truncated, if necessary, to contain no more than that number of lines by removing the oldest entries. The history file is
755 also truncated to this size after writing it when a shell exits. If the value is 0, the history file is truncated to zero
756 size. Non-numeric values and numeric values less than zero inhibit truncation. The shell sets the default value to the
757 value of HISTSIZE after reading any startup files.
758 HISTIGNORE
759 A colon-separated list of patterns used to decide which command lines should be saved on the history list. Each pattern
760 is anchored at the beginning of the line and must match the complete line (no implicit `*' is appended). Each pattern is
761 tested against the line after the checks specified by HISTCONTROL are applied. In addition to the normal shell pattern
762 matching characters, `&' matches the previous history line. `&' may be escaped using a backslash; the backslash is
763 removed before attempting a match. The second and subsequent lines of a multi-line compound command are not tested, and
764 are added to the history regardless of the value of HISTIGNORE. The pattern matching honors the setting of the extglob
765 shell option.
766 HISTSIZE
767 The number of commands to remember in the command history (see HISTORY below). If the value is 0, commands are not saved
768 in the history list. Numeric values less than zero result in every command being saved on the history list (there is no
769 limit). The shell sets the default value to 500 after reading any startup files.
770 HISTTIMEFORMAT
771 If this variable is set and not null, its value is used as a format string for strftime(3) to print the time stamp associâ€
772 ated with each history entry displayed by the history builtin. If this variable is set, time stamps are written to the
773 history file so they may be preserved across shell sessions. This uses the history comment character to distinguish timeâ€
774 stamps from other history lines.
775 HOME The home directory of the current user; the default argument for the cd builtin command. The value of this variable is
776 also used when performing tilde expansion.
777 HOSTFILE
778 Contains the name of a file in the same format as /etc/hosts that should be read when the shell needs to complete a hostâ€
779 name. The list of possible hostname completions may be changed while the shell is running; the next time hostname compleâ€
780 tion is attempted after the value is changed, bash adds the contents of the new file to the existing list. If HOSTFILE is
781 set, but has no value, or does not name a readable file, bash attempts to read /etc/hosts to obtain the list of possible
782 hostname completions. When HOSTFILE is unset, the hostname list is cleared.
783 IFS The Internal Field Separator that is used for word splitting after expansion and to split lines into words with the read
784 builtin command. The default value is ``<space><tab><newline>''.
785 IGNOREEOF
786 Controls the action of an interactive shell on receipt of an EOF character as the sole input. If set, the value is the
787 number of consecutive EOF characters which must be typed as the first characters on an input line before bash exits. If
788 the variable exists but does not have a numeric value, or has no value, the default value is 10. If it does not exist,
789 EOF signifies the end of input to the shell.
790 INPUTRC
791 The filename for the readline startup file, overriding the default of ~/.inputrc (see READLINE below).
792 LANG Used to determine the locale category for any category not specifically selected with a variable starting with LC_.
793 LC_ALL This variable overrides the value of LANG and any other LC_ variable specifying a locale category.
794 LC_COLLATE
795 This variable determines the collation order used when sorting the results of pathname expansion, and determines the
796 behavior of range expressions, equivalence classes, and collating sequences within pathname expansion and pattern matchâ€
797 ing.
798 LC_CTYPE
799 This variable determines the interpretation of characters and the behavior of character classes within pathname expansion
800 and pattern matching.
801 LC_MESSAGES
802 This variable determines the locale used to translate double-quoted strings preceded by a $.
803 LC_NUMERIC
804 This variable determines the locale category used for number formatting.
805 LC_TIME
806 This variable determines the locale category used for data and time formatting.
807 LINES Used by the select compound command to determine the column length for printing selection lists. Automatically set if the
808 checkwinsize option is enabled or in an interactive shell upon receipt of a SIGWINCH.
809 MAIL If this parameter is set to a file or directory name and the MAILPATH variable is not set, bash informs the user of the
810 arrival of mail in the specified file or Maildir-format directory.
811 MAILCHECK
812 Specifies how often (in seconds) bash checks for mail. The default is 60 seconds. When it is time to check for mail, the
813 shell does so before displaying the primary prompt. If this variable is unset, or set to a value that is not a number
814 greater than or equal to zero, the shell disables mail checking.
815 MAILPATH
816 A colon-separated list of filenames to be checked for mail. The message to be printed when mail arrives in a particular
817 file may be specified by separating the filename from the message with a `?'. When used in the text of the message, $_
818 expands to the name of the current mailfile. Example:
819 MAILPATH='/var/mail/bfox?"You have mail":~/shell-mail?"$_ has mail!"'
820 Bash can be configured to supply a default value for this variable (there is no value by default), but the location of the
821 user mail files that it uses is system dependent (e.g., /var/mail/$USER).
822 OPTERR If set to the value 1, bash displays error messages generated by the getopts builtin command (see SHELL BUILTIN COMMANDS
823 below). OPTERR is initialized to 1 each time the shell is invoked or a shell script is executed.
824 PATH The search path for commands. It is a colon-separated list of directories in which the shell looks for commands (see COMâ€
825 MAND EXECUTION below). A zero-length (null) directory name in the value of PATH indicates the current directory. A null
826 directory name may appear as two adjacent colons, or as an initial or trailing colon. The default path is system-depenâ€
827 dent, and is set by the administrator who installs bash. A common value is ``/usr/local/bin:/usr/local/sbin:/usr/bin:
828 /usr/sbin:/bin:/sbin''.
829 POSIXLY_CORRECT
830 If this variable is in the environment when bash starts, the shell enters posix mode before reading the startup files, as
831 if the --posix invocation option had been supplied. If it is set while the shell is running, bash enables posix mode, as
832 if the command set -o posix had been executed.
833 PROMPT_COMMAND
834 If set, the value is executed as a command prior to issuing each primary prompt.
835 PROMPT_DIRTRIM
836 If set to a number greater than zero, the value is used as the number of trailing directory components to retain when
837 expanding the \w and \W prompt string escapes (see PROMPTING below). Characters removed are replaced with an ellipsis.
838 PS0 The value of this parameter is expanded (see PROMPTING below) and displayed by interactive shells after reading a command
839 and before the command is executed.
840 PS1 The value of this parameter is expanded (see PROMPTING below) and used as the primary prompt string. The default value is
841 ``\s-\v\$ ''.
842 PS2 The value of this parameter is expanded as with PS1 and used as the secondary prompt string. The default is ``> ''.
843 PS3 The value of this parameter is used as the prompt for the select command (see SHELL GRAMMAR above).
844 PS4 The value of this parameter is expanded as with PS1 and the value is printed before each command bash displays during an
845 execution trace. The first character of PS4 is replicated multiple times, as necessary, to indicate multiple levels of
846 indirection. The default is ``+ ''.
847 SHELL The full pathname to the shell is kept in this environment variable. If it is not set when the shell starts, bash assigns
848 to it the full pathname of the current user's login shell.
849 TIMEFORMAT
850 The value of this parameter is used as a format string specifying how the timing information for pipelines prefixed with
851 the time reserved word should be displayed. The % character introduces an escape sequence that is expanded to a time
852 value or other information. The escape sequences and their meanings are as follows; the braces denote optional portions.
853 %% A literal %.
854 %[p][l]R The elapsed time in seconds.
855 %[p][l]U The number of CPU seconds spent in user mode.
856 %[p][l]S The number of CPU seconds spent in system mode.
857 %P The CPU percentage, computed as (%U + %S) / %R.
858
859 The optional p is a digit specifying the precision, the number of fractional digits after a decimal point. A value of 0
860 causes no decimal point or fraction to be output. At most three places after the decimal point may be specified; values
861 of p greater than 3 are changed to 3. If p is not specified, the value 3 is used.
862
863 The optional l specifies a longer format, including minutes, of the form MMmSS.FFs. The value of p determines whether or
864 not the fraction is included.
865
866 If this variable is not set, bash acts as if it had the value $'\nreal\t%3lR\nuser\t%3lU\nsys\t%3lS'. If the value is
867 null, no timing information is displayed. A trailing newline is added when the format string is displayed.
868 TMOUT If set to a value greater than zero, TMOUT is treated as the default timeout for the read builtin. The select command
869 terminates if input does not arrive after TMOUT seconds when input is coming from a terminal. In an interactive shell,
870 the value is interpreted as the number of seconds to wait for a line of input after issuing the primary prompt. Bash terâ€
871 minates after waiting for that number of seconds if a complete line of input does not arrive.
872 TMPDIR If set, bash uses its value as the name of a directory in which bash creates temporary files for the shell's use.
873 auto_resume
874 This variable controls how the shell interacts with the user and job control. If this variable is set, single word simple
875 commands without redirections are treated as candidates for resumption of an existing stopped job. There is no ambiguity
876 allowed; if there is more than one job beginning with the string typed, the job most recently accessed is selected. The
877 name of a stopped job, in this context, is the command line used to start it. If set to the value exact, the string supâ€
878 plied must match the name of a stopped job exactly; if set to substring, the string supplied needs to match a substring of
879 the name of a stopped job. The substring value provides functionality analogous to the %? job identifier (see JOB CONâ€
880 TROL below). If set to any other value, the supplied string must be a prefix of a stopped job's name; this provides funcâ€
881 tionality analogous to the %string job identifier.
882 histchars
883 The two or three characters which control history expansion and tokenization (see HISTORY EXPANSION below). The first
884 character is the history expansion character, the character which signals the start of a history expansion, normally `!'.
885 The second character is the quick substitution character, which is used as shorthand for re-running the previous command
886 entered, substituting one string for another in the command. The default is `^'. The optional third character is the
887 character which indicates that the remainder of the line is a comment when found as the first character of a word, norâ€
888 mally `#'. The history comment character causes history substitution to be skipped for the remaining words on the line.
889 It does not necessarily cause the shell parser to treat the rest of the line as a comment.
890
891 Arrays
892 Bash provides one-dimensional indexed and associative array variables. Any variable may be used as an indexed array; the declare
893 builtin will explicitly declare an array. There is no maximum limit on the size of an array, nor any requirement that members be
894 indexed or assigned contiguously. Indexed arrays are referenced using integers (including arithmetic expressions) and are zero-
895 based; associative arrays are referenced using arbitrary strings. Unless otherwise noted, indexed array indices must be non-negâ€
896 ative integers.
897
898 An indexed array is created automatically if any variable is assigned to using the syntax name[subscript]=value. The subscript
899 is treated as an arithmetic expression that must evaluate to a number. To explicitly declare an indexed array, use declare -a
900 name (see SHELL BUILTIN COMMANDS below). declare -a name[subscript] is also accepted; the subscript is ignored.
901
902 Associative arrays are created using declare -A name.
903
904 Attributes may be specified for an array variable using the declare and readonly builtins. Each attribute applies to all members
905 of an array.
906
907 Arrays are assigned to using compound assignments of the form name=(value1 ... valuen), where each value is of the form [subâ€
908 script]=string. Indexed array assignments do not require anything but string. When assigning to indexed arrays, if the optional
909 brackets and subscript are supplied, that index is assigned to; otherwise the index of the element assigned is the last index
910 assigned to by the statement plus one. Indexing starts at zero.
911
912 When assigning to an associative array, the subscript is required.
913
914 This syntax is also accepted by the declare builtin. Individual array elements may be assigned to using the name[subâ€
915 script]=value syntax introduced above. When assigning to an indexed array, if name is subscripted by a negative number, that
916 number is interpreted as relative to one greater than the maximum index of name, so negative indices count back from the end of
917 the array, and an index of -1 references the last element.
918
919 Any element of an array may be referenced using ${name[subscript]}. The braces are required to avoid conflicts with pathname
920 expansion. If subscript is @ or *, the word expands to all members of name. These subscripts differ only when the word appears
921 within double quotes. If the word is double-quoted, ${name[*]} expands to a single word with the value of each array member sepâ€
922 arated by the first character of the IFS special variable, and ${name[@]} expands each element of name to a separate word. When
923 there are no array members, ${name[@]} expands to nothing. If the double-quoted expansion occurs within a word, the expansion of
924 the first parameter is joined with the beginning part of the original word, and the expansion of the last parameter is joined
925 with the last part of the original word. This is analogous to the expansion of the special parameters * and @ (see Special
926 Parameters above). ${#name[subscript]} expands to the length of ${name[subscript]}. If subscript is * or @, the expansion is
927 the number of elements in the array. If the subscript used to reference an element of an indexed array evaluates to a number
928 less than zero, it is interpreted as relative to one greater than the maximum index of the array, so negative indices count back
929 from the end of the array, and an index of -1 references the last element.
930
931 Referencing an array variable without a subscript is equivalent to referencing the array with a subscript of 0. Any reference to
932 a variable using a valid subscript is legal, and bash will create an array if necessary.
933
934 An array variable is considered set if a subscript has been assigned a value. The null string is a valid value.
935
936 It is possible to obtain the keys (indices) of an array as well as the values. ${!name[@]} and ${!name[*]} expand to the indices
937 assigned in array variable name. The treatment when in double quotes is similar to the expansion of the special parameters @ and
938 * within double quotes.
939
940 The unset builtin is used to destroy arrays. unset name[subscript] destroys the array element at index subscript. Negative subâ€
941 scripts to indexed arrays are interpreted as described above. Care must be taken to avoid unwanted side effects caused by pathâ€
942 name expansion. unset name, where name is an array, or unset name[subscript], where subscript is * or @, removes the entire
943 array.
944
945 The declare, local, and readonly builtins each accept a -a option to specify an indexed array and a -A option to specify an assoâ€
946 ciative array. If both options are supplied, -A takes precedence. The read builtin accepts a -a option to assign a list of
947 words read from the standard input to an array. The set and declare builtins display array values in a way that allows them to
948 be reused as assignments.
949
950EXPANSION
951 Expansion is performed on the command line after it has been split into words. There are seven kinds of expansion performed:
952 brace expansion, tilde expansion, parameter and variable expansion, command substitution, arithmetic expansion, word splitting,
953 and pathname expansion.
954
955 The order of expansions is: brace expansion; tilde expansion, parameter and variable expansion, arithmetic expansion, and command
956 substitution (done in a left-to-right fashion); word splitting; and pathname expansion.
957
958 On systems that can support it, there is an additional expansion available: process substitution. This is performed at the same
959 time as tilde, parameter, variable, and arithmetic expansion and command substitution.
960
961 After these expansions are performed, quote characters present in the original word are removed unless they have been quoted
962 themselves (quote removal).
963
964 Only brace expansion, word splitting, and pathname expansion can change the number of words of the expansion; other expansions
965 expand a single word to a single word. The only exceptions to this are the expansions of "$@" and "${name[@]}" as explained
966 above (see PARAMETERS).
967
968 Brace Expansion
969 Brace expansion is a mechanism by which arbitrary strings may be generated. This mechanism is similar to pathname expansion, but
970 the filenames generated need not exist. Patterns to be brace expanded take the form of an optional preamble, followed by either
971 a series of comma-separated strings or a sequence expression between a pair of braces, followed by an optional postscript. The
972 preamble is prefixed to each string contained within the braces, and the postscript is then appended to each resulting string,
973 expanding left to right.
974
975 Brace expansions may be nested. The results of each expanded string are not sorted; left to right order is preserved. For examâ€
976 ple, a{d,c,b}e expands into `ade ace abe'.
977
978 A sequence expression takes the form {x..y[..incr]}, where x and y are either integers or single characters, and incr, an
979 optional increment, is an integer. When integers are supplied, the expression expands to each number between x and y, inclusive.
980 Supplied integers may be prefixed with 0 to force each term to have the same width. When either x or y begins with a zero, the
981 shell attempts to force all generated terms to contain the same number of digits, zero-padding where necessary. When characters
982 are supplied, the expression expands to each character lexicographically between x and y, inclusive, using the default C locale.
983 Note that both x and y must be of the same type. When the increment is supplied, it is used as the difference between each term.
984 The default increment is 1 or -1 as appropriate.
985
986 Brace expansion is performed before any other expansions, and any characters special to other expansions are preserved in the
987 result. It is strictly textual. Bash does not apply any syntactic interpretation to the context of the expansion or the text
988 between the braces.
989
990 A correctly-formed brace expansion must contain unquoted opening and closing braces, and at least one unquoted comma or a valid
991 sequence expression. Any incorrectly formed brace expansion is left unchanged. A { or , may be quoted with a backslash to preâ€
992 vent its being considered part of a brace expression. To avoid conflicts with parameter expansion, the string ${ is not considâ€
993 ered eligible for brace expansion.
994
995 This construct is typically used as shorthand when the common prefix of the strings to be generated is longer than in the above
996 example:
997
998 mkdir /usr/local/src/bash/{old,new,dist,bugs}
999 or
1000 chown root /usr/{ucb/{ex,edit},lib/{ex?.?*,how_ex}}
1001
1002 Brace expansion introduces a slight incompatibility with historical versions of sh. sh does not treat opening or closing braces
1003 specially when they appear as part of a word, and preserves them in the output. Bash removes braces from words as a consequence
1004 of brace expansion. For example, a word entered to sh as file{1,2} appears identically in the output. The same word is output
1005 as file1 file2 after expansion by bash. If strict compatibility with sh is desired, start bash with the +B option or disable
1006 brace expansion with the +B option to the set command (see SHELL BUILTIN COMMANDS below).
1007
1008 Tilde Expansion
1009 If a word begins with an unquoted tilde character (`~'), all of the characters preceding the first unquoted slash (or all characâ€
1010 ters, if there is no unquoted slash) are considered a tilde-prefix. If none of the characters in the tilde-prefix are quoted,
1011 the characters in the tilde-prefix following the tilde are treated as a possible login name. If this login name is the null
1012 string, the tilde is replaced with the value of the shell parameter HOME. If HOME is unset, the home directory of the user exeâ€
1013 cuting the shell is substituted instead. Otherwise, the tilde-prefix is replaced with the home directory associated with the
1014 specified login name.
1015
1016 If the tilde-prefix is a `~+', the value of the shell variable PWD replaces the tilde-prefix. If the tilde-prefix is a `~-', the
1017 value of the shell variable OLDPWD, if it is set, is substituted. If the characters following the tilde in the tilde-prefix conâ€
1018 sist of a number N, optionally prefixed by a `+' or a `-', the tilde-prefix is replaced with the corresponding element from the
1019 directory stack, as it would be displayed by the dirs builtin invoked with the tilde-prefix as an argument. If the characters
1020 following the tilde in the tilde-prefix consist of a number without a leading `+' or `-', `+' is assumed.
1021
1022 If the login name is invalid, or the tilde expansion fails, the word is unchanged.
1023
1024 Each variable assignment is checked for unquoted tilde-prefixes immediately following a : or the first =. In these cases, tilde
1025 expansion is also performed. Consequently, one may use filenames with tildes in assignments to PATH, MAILPATH, and CDPATH, and
1026 the shell assigns the expanded value.
1027
1028 Parameter Expansion
1029 The `$' character introduces parameter expansion, command substitution, or arithmetic expansion. The parameter name or symbol to
1030 be expanded may be enclosed in braces, which are optional but serve to protect the variable to be expanded from characters immeâ€
1031 diately following it which could be interpreted as part of the name.
1032
1033 When braces are used, the matching ending brace is the first `}' not escaped by a backslash or within a quoted string, and not
1034 within an embedded arithmetic expansion, command substitution, or parameter expansion.
1035
1036 ${parameter}
1037 The value of parameter is substituted. The braces are required when parameter is a positional parameter with more than
1038 one digit, or when parameter is followed by a character which is not to be interpreted as part of its name. The parameter
1039 is a shell parameter as described above PARAMETERS) or an array reference (Arrays).
1040
1041 If the first character of parameter is an exclamation point (!), and parameter is not a nameref, it introduces a level of variâ€
1042 able indirection. Bash uses the value of the variable formed from the rest of parameter as the name of the variable; this variâ€
1043 able is then expanded and that value is used in the rest of the substitution, rather than the value of parameter itself. This is
1044 known as indirect expansion. If parameter is a nameref, this expands to the name of the variable referenced by parameter instead
1045 of performing the complete indirect expansion. The exceptions to this are the expansions of ${!prefix*} and ${!name[@]}
1046 described below. The exclamation point must immediately follow the left brace in order to introduce indirection.
1047
1048 In each of the cases below, word is subject to tilde expansion, parameter expansion, command substitution, and arithmetic expanâ€
1049 sion.
1050
1051 When not performing substring expansion, using the forms documented below (e.g., :-), bash tests for a parameter that is unset or
1052 null. Omitting the colon results in a test only for a parameter that is unset.
1053
1054 ${parameter:-word}
1055 Use Default Values. If parameter is unset or null, the expansion of word is substituted. Otherwise, the value of parameâ€
1056 ter is substituted.
1057 ${parameter:=word}
1058 Assign Default Values. If parameter is unset or null, the expansion of word is assigned to parameter. The value of
1059 parameter is then substituted. Positional parameters and special parameters may not be assigned to in this way.
1060 ${parameter:?word}
1061 Display Error if Null or Unset. If parameter is null or unset, the expansion of word (or a message to that effect if word
1062 is not present) is written to the standard error and the shell, if it is not interactive, exits. Otherwise, the value of
1063 parameter is substituted.
1064 ${parameter:+word}
1065 Use Alternate Value. If parameter is null or unset, nothing is substituted, otherwise the expansion of word is substiâ€
1066 tuted.
1067 ${parameter:offset}
1068 ${parameter:offset:length}
1069 Substring Expansion. Expands to up to length characters of the value of parameter starting at the character specified by
1070 offset. If parameter is @, an indexed array subscripted by @ or *, or an associative array name, the results differ as
1071 described below. If length is omitted, expands to the substring of the value of parameter starting at the character specâ€
1072 ified by offset and extending to the end of the value. length and offset are arithmetic expressions (see ARITHMETIC EVALâ€
1073 UATION below).
1074
1075 If offset evaluates to a number less than zero, the value is used as an offset in characters from the end of the value of
1076 parameter. If length evaluates to a number less than zero, it is interpreted as an offset in characters from the end of
1077 the value of parameter rather than a number of characters, and the expansion is the characters between offset and that
1078 result. Note that a negative offset must be separated from the colon by at least one space to avoid being confused with
1079 the :- expansion.
1080
1081 If parameter is @, the result is length positional parameters beginning at offset. A negative offset is taken relative to
1082 one greater than the greatest positional parameter, so an offset of -1 evaluates to the last positional parameter. It is
1083 an expansion error if length evaluates to a number less than zero.
1084
1085 If parameter is an indexed array name subscripted by @ or *, the result is the length members of the array beginning with
1086 ${parameter[offset]}. A negative offset is taken relative to one greater than the maximum index of the specified array.
1087 It is an expansion error if length evaluates to a number less than zero.
1088
1089 Substring expansion applied to an associative array produces undefined results.
1090
1091 Substring indexing is zero-based unless the positional parameters are used, in which case the indexing starts at 1 by
1092 default. If offset is 0, and the positional parameters are used, $0 is prefixed to the list.
1093
1094 ${!prefix*}
1095 ${!prefix@}
1096 Names matching prefix. Expands to the names of variables whose names begin with prefix, separated by the first character
1097 of the IFS special variable. When @ is used and the expansion appears within double quotes, each variable name expands to
1098 a separate word.
1099
1100 ${!name[@]}
1101 ${!name[*]}
1102 List of array keys. If name is an array variable, expands to the list of array indices (keys) assigned in name. If name
1103 is not an array, expands to 0 if name is set and null otherwise. When @ is used and the expansion appears within double
1104 quotes, each key expands to a separate word.
1105
1106 ${#parameter}
1107 Parameter length. The length in characters of the value of parameter is substituted. If parameter is * or @, the value
1108 substituted is the number of positional parameters. If parameter is an array name subscripted by * or @, the value subâ€
1109 stituted is the number of elements in the array. If parameter is an indexed array name subscripted by a negative number,
1110 that number is interpreted as relative to one greater than the maximum index of parameter, so negative indices count back
1111 from the end of the array, and an index of -1 references the last element.
1112
1113 ${parameter#word}
1114 ${parameter##word}
1115 Remove matching prefix pattern. The word is expanded to produce a pattern just as in pathname expansion. If the pattern
1116 matches the beginning of the value of parameter, then the result of the expansion is the expanded value of parameter with
1117 the shortest matching pattern (the ``#'' case) or the longest matching pattern (the ``##'' case) deleted. If parameter is
1118 @ or *, the pattern removal operation is applied to each positional parameter in turn, and the expansion is the resultant
1119 list. If parameter is an array variable subscripted with @ or *, the pattern removal operation is applied to each member
1120 of the array in turn, and the expansion is the resultant list.
1121
1122 ${parameter%word}
1123 ${parameter%%word}
1124 Remove matching suffix pattern. The word is expanded to produce a pattern just as in pathname expansion. If the pattern
1125 matches a trailing portion of the expanded value of parameter, then the result of the expansion is the expanded value of
1126 parameter with the shortest matching pattern (the ``%'' case) or the longest matching pattern (the ``%%'' case) deleted.
1127 If parameter is @ or *, the pattern removal operation is applied to each positional parameter in turn, and the expansion
1128 is the resultant list. If parameter is an array variable subscripted with @ or *, the pattern removal operation is
1129 applied to each member of the array in turn, and the expansion is the resultant list.
1130
1131 ${parameter/pattern/string}
1132 Pattern substitution. The pattern is expanded to produce a pattern just as in pathname expansion. Parameter is expanded
1133 and the longest match of pattern against its value is replaced with string. If pattern begins with /, all matches of patâ€
1134 tern are replaced with string. Normally only the first match is replaced. If pattern begins with #, it must match at the
1135 beginning of the expanded value of parameter. If pattern begins with %, it must match at the end of the expanded value of
1136 parameter. If string is null, matches of pattern are deleted and the / following pattern may be omitted. If the nocaseâ€
1137 match shell option is enabled, the match is performed without regard to the case of alphabetic characters. If parameter
1138 is @ or *, the substitution operation is applied to each positional parameter in turn, and the expansion is the resultant
1139 list. If parameter is an array variable subscripted with @ or *, the substitution operation is applied to each member of
1140 the array in turn, and the expansion is the resultant list.
1141
1142 ${parameter^pattern}
1143 ${parameter^^pattern}
1144 ${parameter,pattern}
1145 ${parameter,,pattern}
1146 Case modification. This expansion modifies the case of alphabetic characters in parameter. The pattern is expanded to
1147 produce a pattern just as in pathname expansion. Each character in the expanded value of parameter is tested against patâ€
1148 tern, and, if it matches the pattern, its case is converted. The pattern should not attempt to match more than one charâ€
1149 acter. The ^ operator converts lowercase letters matching pattern to uppercase; the , operator converts matching upperâ€
1150 case letters to lowercase. The ^^ and ,, expansions convert each matched character in the expanded value; the ^ and ,
1151 expansions match and convert only the first character in the expanded value. If pattern is omitted, it is treated like a
1152 ?, which matches every character. If parameter is @ or *, the case modification operation is applied to each positional
1153 parameter in turn, and the expansion is the resultant list. If parameter is an array variable subscripted with @ or *,
1154 the case modification operation is applied to each member of the array in turn, and the expansion is the resultant list.
1155
1156 ${parameter@operator}
1157 Parameter transformation. The expansion is either a transformation of the value of parameter or information about parameâ€
1158 ter itself, depending on the value of operator. Each operator is a single letter:
1159
1160 Q The expansion is a string that is the value of parameter quoted in a format that can be reused as input.
1161 E The expansion is a string that is the value of parameter with backslash escape sequences expanded as with the
1162 $'...' quoting mechansim.
1163 P The expansion is a string that is the result of expanding the value of parameter as if it were a prompt string (see
1164 PROMPTING below).
1165 A The expansion is a string in the form of an assignment statement or declare command that, if evaluated, will recreâ€
1166 ate parameter with its attributes and value.
1167 a The expansion is a string consisting of flag values representing parameter's attributes.
1168
1169 If parameter is @ or *, the operation is applied to each positional parameter in turn, and the expansion is the resultant
1170 list. If parameter is an array variable subscripted with @ or *, the case modification operation is applied to each memâ€
1171 ber of the array in turn, and the expansion is the resultant list.
1172
1173 The result of the expansion is subject to word splitting and pathname expansion as described below.
1174
1175 Command Substitution
1176 Command substitution allows the output of a command to replace the command name. There are two forms:
1177
1178 $(command)
1179 or
1180 `command`
1181
1182 Bash performs the expansion by executing command in a subshell environment and replacing the command substitution with the stanâ€
1183 dard output of the command, with any trailing newlines deleted. Embedded newlines are not deleted, but they may be removed durâ€
1184 ing word splitting. The command substitution $(cat file) can be replaced by the equivalent but faster $(< file).
1185
1186 When the old-style backquote form of substitution is used, backslash retains its literal meaning except when followed by $, `, or
1187 \. The first backquote not preceded by a backslash terminates the command substitution. When using the $(command) form, all
1188 characters between the parentheses make up the command; none are treated specially.
1189
1190 Command substitutions may be nested. To nest when using the backquoted form, escape the inner backquotes with backslashes.
1191
1192 If the substitution appears within double quotes, word splitting and pathname expansion are not performed on the results.
1193
1194 Arithmetic Expansion
1195 Arithmetic expansion allows the evaluation of an arithmetic expression and the substitution of the result. The format for arithâ€
1196 metic expansion is:
1197
1198 $((expression))
1199
1200 The old format $[expression] is deprecated and will be removed in upcoming versions of bash.
1201
1202 The expression is treated as if it were within double quotes, but a double quote inside the parentheses is not treated specially.
1203 All tokens in the expression undergo parameter and variable expansion, command substitution, and quote removal. The result is
1204 treated as the arithmetic expression to be evaluated. Arithmetic expansions may be nested.
1205
1206 The evaluation is performed according to the rules listed below under ARITHMETIC EVALUATION. If expression is invalid, bash
1207 prints a message indicating failure and no substitution occurs.
1208
1209 Process Substitution
1210 Process substitution allows a process's input or output to be referred to using a filename. It takes the form of <(list) or
1211 >(list). The process list is run asynchronously, and its input or output appears as a filename. This filename is passed as an
1212 argument to the current command as the result of the expansion. If the >(list) form is used, writing to the file will provide
1213 input for list. If the <(list) form is used, the file passed as an argument should be read to obtain the output of list.
1214 Process substitution is supported on systems that support named pipes (FIFOs) or the /dev/fd method of naming open files.
1215
1216 When available, process substitution is performed simultaneously with parameter and variable expansion, command substitution, and
1217 arithmetic expansion.
1218
1219 Word Splitting
1220 The shell scans the results of parameter expansion, command substitution, and arithmetic expansion that did not occur within douâ€
1221 ble quotes for word splitting.
1222
1223 The shell treats each character of IFS as a delimiter, and splits the results of the other expansions into words using these
1224 characters as field terminators. If IFS is unset, or its value is exactly <space><tab><newline>, the default, then sequences of
1225 <space>, <tab>, and <newline> at the beginning and end of the results of the previous expansions are ignored, and any sequence of
1226 IFS characters not at the beginning or end serves to delimit words. If IFS has a value other than the default, then sequences of
1227 the whitespace characters space, tab, and newline are ignored at the beginning and end of the word, as long as the whitespace
1228 character is in the value of IFS (an IFS whitespace character). Any character in IFS that is not IFS whitespace, along with any
1229 adjacent IFS whitespace characters, delimits a field. A sequence of IFS whitespace characters is also treated as a delimiter.
1230 If the value of IFS is null, no word splitting occurs.
1231
1232 Explicit null arguments ("" or '') are retained and passed to commands as empty strings. Unquoted implicit null arguments,
1233 resulting from the expansion of parameters that have no values, are removed. If a parameter with no value is expanded within
1234 double quotes, a null argument results and is retained and passed to a command as an empty string. When a quoted null argument
1235 appears as part of a word whose expansion is non-null, the null argument is removed. That is, the word -d'' becomes -d after
1236 word splitting and null argument removal.
1237
1238 Note that if no expansion occurs, no splitting is performed.
1239
1240 Pathname Expansion
1241 After word splitting, unless the -f option has been set, bash scans each word for the characters *, ?, and [. If one of these
1242 characters appears, then the word is regarded as a pattern, and replaced with an alphabetically sorted list of filenames matching
1243 the pattern (see Pattern Matching below). If no matching filenames are found, and the shell option nullglob is not enabled, the
1244 word is left unchanged. If the nullglob option is set, and no matches are found, the word is removed. If the failglob shell
1245 option is set, and no matches are found, an error message is printed and the command is not executed. If the shell option
1246 nocaseglob is enabled, the match is performed without regard to the case of alphabetic characters. Note that when using range
1247 expressions like [a-z] (see below), letters of the other case may be included, depending on the setting of LC_COLLATE. When a
1248 pattern is used for pathname expansion, the character ``.'' at the start of a name or immediately following a slash must be
1249 matched explicitly, unless the shell option dotglob is set. When matching a pathname, the slash character must always be matched
1250 explicitly. In other cases, the ``.'' character is not treated specially. See the description of shopt below under SHELL
1251 BUILTIN COMMANDS for a description of the nocaseglob, nullglob, failglob, and dotglob shell options.
1252
1253 The GLOBIGNORE shell variable may be used to restrict the set of filenames matching a pattern. If GLOBIGNORE is set, each matchâ€
1254 ing filename that also matches one of the patterns in GLOBIGNORE is removed from the list of matches. If the nocaseglob option
1255 is set, the matching against the patterns in GLOBIGNORE is performed without regard to case. The filenames ``.'' and ``..''
1256 are always ignored when GLOBIGNORE is set and not null. However, setting GLOBIGNORE to a non-null value has the effect of
1257 enabling the dotglob shell option, so all other filenames beginning with a ``.'' will match. To get the old behavior of ignorâ€
1258 ing filenames beginning with a ``.'', make ``.*'' one of the patterns in GLOBIGNORE. The dotglob option is disabled when GLOâ€
1259 BIGNORE is unset. The pattern matching honors the setting of the extglob shell option.
1260
1261 Pattern Matching
1262
1263 Any character that appears in a pattern, other than the special pattern characters described below, matches itself. The NUL
1264 character may not occur in a pattern. A backslash escapes the following character; the escaping backslash is discarded when
1265 matching. The special pattern characters must be quoted if they are to be matched literally.
1266
1267 The special pattern characters have the following meanings:
1268
1269 * Matches any string, including the null string. When the globstar shell option is enabled, and * is used in a pathâ€
1270 name expansion context, two adjacent *s used as a single pattern will match all files and zero or more directories
1271 and subdirectories. If followed by a /, two adjacent *s will match only directories and subdirectories.
1272 ? Matches any single character.
1273 [...] Matches any one of the enclosed characters. A pair of characters separated by a hyphen denotes a range expression;
1274 any character that falls between those two characters, inclusive, using the current locale's collating sequence and
1275 character set, is matched. If the first character following the [ is a ! or a ^ then any character not enclosed
1276 is matched. The sorting order of characters in range expressions is determined by the current locale and the valâ€
1277 ues of the LC_COLLATE or LC_ALL shell variables, if set. To obtain the traditional interpretation of range expresâ€
1278 sions, where [a-d] is equivalent to [abcd], set value of the LC_ALL shell variable to C, or enable the globasciâ€
1279 iranges shell option. A - may be matched by including it as the first or last character in the set. A ] may be
1280 matched by including it as the first character in the set.
1281
1282 Within [ and ], character classes can be specified using the syntax [:class:], where class is one of the following
1283 classes defined in the POSIX standard:
1284 alnum alpha ascii blank cntrl digit graph lower print punct space upper word xdigit
1285 A character class matches any character belonging to that class. The word character class matches letters, digits,
1286 and the character _.
1287
1288 Within [ and ], an equivalence class can be specified using the syntax [=c=], which matches all characters with the
1289 same collation weight (as defined by the current locale) as the character c.
1290
1291 Within [ and ], the syntax [.symbol.] matches the collating symbol symbol.
1292
1293 If the extglob shell option is enabled using the shopt builtin, several extended pattern matching operators are recognized. In
1294 the following description, a pattern-list is a list of one or more patterns separated by a |. Composite patterns may be formed
1295 using one or more of the following sub-patterns:
1296
1297 ?(pattern-list)
1298 Matches zero or one occurrence of the given patterns
1299 *(pattern-list)
1300 Matches zero or more occurrences of the given patterns
1301 +(pattern-list)
1302 Matches one or more occurrences of the given patterns
1303 @(pattern-list)
1304 Matches one of the given patterns
1305 !(pattern-list)
1306 Matches anything except one of the given patterns
1307
1308 Quote Removal
1309 After the preceding expansions, all unquoted occurrences of the characters \, ', and " that did not result from one of the above
1310 expansions are removed.
1311
1312REDIRECTION
1313 Before a command is executed, its input and output may be redirected using a special notation interpreted by the shell. Rediâ€
1314 rection allows commands' file handles to be duplicated, opened, closed, made to refer to different files, and can change the
1315 files the command reads from and writes to. Redirection may also be used to modify file handles in the current shell execution
1316 environment. The following redirection operators may precede or appear anywhere within a simple command or may follow a command.
1317 Redirections are processed in the order they appear, from left to right.
1318
1319 Each redirection that may be preceded by a file descriptor number may instead be preceded by a word of the form {varname}. In
1320 this case, for each redirection operator except >&- and <&-, the shell will allocate a file descriptor greater than or equal to
1321 10 and assign it to varname. If >&- or <&- is preceded by {varname}, the value of varname defines the file descriptor to close.
1322
1323 In the following descriptions, if the file descriptor number is omitted, and the first character of the redirection operator is
1324 <, the redirection refers to the standard input (file descriptor 0). If the first character of the redirection operator is >,
1325 the redirection refers to the standard output (file descriptor 1).
1326
1327 The word following the redirection operator in the following descriptions, unless otherwise noted, is subjected to brace expanâ€
1328 sion, tilde expansion, parameter and variable expansion, command substitution, arithmetic expansion, quote removal, pathname
1329 expansion, and word splitting. If it expands to more than one word, bash reports an error.
1330
1331 Note that the order of redirections is significant. For example, the command
1332
1333 ls > dirlist 2>&1
1334
1335 directs both standard output and standard error to the file dirlist, while the command
1336
1337 ls 2>&1 > dirlist
1338
1339 directs only the standard output to file dirlist, because the standard error was duplicated from the standard output before the
1340 standard output was redirected to dirlist.
1341
1342 Bash handles several filenames specially when they are used in redirections, as described in the following table. If the operatâ€
1343 ing system on which bash is running provides these special files, bash will use them; otherwise it will emulate them internally
1344 with the behavior described below.
1345
1346 /dev/fd/fd
1347 If fd is a valid integer, file descriptor fd is duplicated.
1348 /dev/stdin
1349 File descriptor 0 is duplicated.
1350 /dev/stdout
1351 File descriptor 1 is duplicated.
1352 /dev/stderr
1353 File descriptor 2 is duplicated.
1354 /dev/tcp/host/port
1355 If host is a valid hostname or Internet address, and port is an integer port number or service name, bash attempts
1356 to open the corresponding TCP socket.
1357 /dev/udp/host/port
1358 If host is a valid hostname or Internet address, and port is an integer port number or service name, bash attempts
1359 to open the corresponding UDP socket.
1360
1361 A failure to open or create a file causes the redirection to fail.
1362
1363 Redirections using file descriptors greater than 9 should be used with care, as they may conflict with file descriptors the shell
1364 uses internally.
1365
1366 Note that the exec builtin command can make redirections take effect in the current shell.
1367
1368 Redirecting Input
1369 Redirection of input causes the file whose name results from the expansion of word to be opened for reading on file descriptor n,
1370 or the standard input (file descriptor 0) if n is not specified.
1371
1372 The general format for redirecting input is:
1373
1374 [n]<word
1375
1376 Redirecting Output
1377 Redirection of output causes the file whose name results from the expansion of word to be opened for writing on file descriptor
1378 n, or the standard output (file descriptor 1) if n is not specified. If the file does not exist it is created; if it does exist
1379 it is truncated to zero size.
1380
1381 The general format for redirecting output is:
1382
1383 [n]>word
1384
1385 If the redirection operator is >, and the noclobber option to the set builtin has been enabled, the redirection will fail if the
1386 file whose name results from the expansion of word exists and is a regular file. If the redirection operator is >|, or the rediâ€
1387 rection operator is > and the noclobber option to the set builtin command is not enabled, the redirection is attempted even if
1388 the file named by word exists.
1389
1390 Appending Redirected Output
1391 Redirection of output in this fashion causes the file whose name results from the expansion of word to be opened for appending on
1392 file descriptor n, or the standard output (file descriptor 1) if n is not specified. If the file does not exist it is created.
1393
1394 The general format for appending output is:
1395
1396 [n]>>word
1397
1398 Redirecting Standard Output and Standard Error
1399 This construct allows both the standard output (file descriptor 1) and the standard error output (file descriptor 2) to be rediâ€
1400 rected to the file whose name is the expansion of word.
1401
1402 There are two formats for redirecting standard output and standard error:
1403
1404 &>word
1405 and
1406 >&word
1407
1408 Of the two forms, the first is preferred. This is semantically equivalent to
1409
1410 >word 2>&1
1411
1412 When using the second form, word may not expand to a number or -. If it does, other redirection operators apply (see Duplicating
1413 File Descriptors below) for compatibility reasons.
1414
1415 Appending Standard Output and Standard Error
1416 This construct allows both the standard output (file descriptor 1) and the standard error output (file descriptor 2) to be
1417 appended to the file whose name is the expansion of word.
1418
1419 The format for appending standard output and standard error is:
1420
1421 &>>word
1422
1423 This is semantically equivalent to
1424
1425 >>word 2>&1
1426
1427 (see Duplicating File Descriptors below).
1428
1429 Here Documents
1430 This type of redirection instructs the shell to read input from the current source until a line containing only delimiter (with
1431 no trailing blanks) is seen. All of the lines read up to that point are then used as the standard input (or file descriptor n if
1432 n is specified) for a command.
1433
1434 The format of here-documents is:
1435
1436 [n]<<[-]word
1437 here-document
1438 delimiter
1439
1440 No parameter and variable expansion, command substitution, arithmetic expansion, or pathname expansion is performed on word. If
1441 any part of word is quoted, the delimiter is the result of quote removal on word, and the lines in the here-document are not
1442 expanded. If word is unquoted, all lines of the here-document are subjected to parameter expansion, command substitution, and
1443 arithmetic expansion, the character sequence \<newline> is ignored, and \ must be used to quote the characters \, $, and `.
1444
1445 If the redirection operator is <<-, then all leading tab characters are stripped from input lines and the line containing delimâ€
1446 iter. This allows here-documents within shell scripts to be indented in a natural fashion.
1447
1448 Here Strings
1449 A variant of here documents, the format is:
1450
1451 [n]<<<word
1452
1453 The word undergoes brace expansion, tilde expansion, parameter and variable expansion, command substitution, arithmetic expanâ€
1454 sion, and quote removal. Pathname expansion and word splitting are not performed. The result is supplied as a single string,
1455 with a newline appended, to the command on its standard input (or file descriptor n if n is specified).
1456
1457 Duplicating File Descriptors
1458 The redirection operator
1459
1460 [n]<&word
1461
1462 is used to duplicate input file descriptors. If word expands to one or more digits, the file descriptor denoted by n is made to
1463 be a copy of that file descriptor. If the digits in word do not specify a file descriptor open for input, a redirection error
1464 occurs. If word evaluates to -, file descriptor n is closed. If n is not specified, the standard input (file descriptor 0) is
1465 used.
1466
1467 The operator
1468
1469 [n]>&word
1470
1471 is used similarly to duplicate output file descriptors. If n is not specified, the standard output (file descriptor 1) is used.
1472 If the digits in word do not specify a file descriptor open for output, a redirection error occurs. If word evaluates to -, file
1473 descriptor n is closed. As a special case, if n is omitted, and word does not expand to one or more digits or -, the standard
1474 output and standard error are redirected as described previously.
1475
1476 Moving File Descriptors
1477 The redirection operator
1478
1479 [n]<&digit-
1480
1481 moves the file descriptor digit to file descriptor n, or the standard input (file descriptor 0) if n is not specified. digit is
1482 closed after being duplicated to n.
1483
1484 Similarly, the redirection operator
1485
1486 [n]>&digit-
1487
1488 moves the file descriptor digit to file descriptor n, or the standard output (file descriptor 1) if n is not specified.
1489
1490 Opening File Descriptors for Reading and Writing
1491 The redirection operator
1492
1493 [n]<>word
1494
1495 causes the file whose name is the expansion of word to be opened for both reading and writing on file descriptor n, or on file
1496 descriptor 0 if n is not specified. If the file does not exist, it is created.
1497
1498ALIASES
1499 Aliases allow a string to be substituted for a word when it is used as the first word of a simple command. The shell maintains a
1500 list of aliases that may be set and unset with the alias and unalias builtin commands (see SHELL BUILTIN COMMANDS below). The
1501 first word of each simple command, if unquoted, is checked to see if it has an alias. If so, that word is replaced by the text
1502 of the alias. The characters /, $, `, and = and any of the shell metacharacters or quoting characters listed above may not
1503 appear in an alias name. The replacement text may contain any valid shell input, including shell metacharacters. The first word
1504 of the replacement text is tested for aliases, but a word that is identical to an alias being expanded is not expanded a second
1505 time. This means that one may alias ls to ls -F, for instance, and bash does not try to recursively expand the replacement text.
1506 If the last character of the alias value is a blank, then the next command word following the alias is also checked for alias
1507 expansion.
1508
1509 Aliases are created and listed with the alias command, and removed with the unalias command.
1510
1511 There is no mechanism for using arguments in the replacement text. If arguments are needed, a shell function should be used (see
1512 FUNCTIONS below).
1513
1514 Aliases are not expanded when the shell is not interactive, unless the expand_aliases shell option is set using shopt (see the
1515 description of shopt under SHELL BUILTIN COMMANDS below).
1516
1517 The rules concerning the definition and use of aliases are somewhat confusing. Bash always reads at least one complete line of
1518 input before executing any of the commands on that line. Aliases are expanded when a command is read, not when it is executed.
1519 Therefore, an alias definition appearing on the same line as another command does not take effect until the next line of input is
1520 read. The commands following the alias definition on that line are not affected by the new alias. This behavior is also an
1521 issue when functions are executed. Aliases are expanded when a function definition is read, not when the function is executed,
1522 because a function definition is itself a command. As a consequence, aliases defined in a function are not available until after
1523 that function is executed. To be safe, always put alias definitions on a separate line, and do not use alias in compound comâ€
1524 mands.
1525
1526 For almost every purpose, aliases are superseded by shell functions.
1527
1528FUNCTIONS
1529 A shell function, defined as described above under SHELL GRAMMAR, stores a series of commands for later execution. When the name
1530 of a shell function is used as a simple command name, the list of commands associated with that function name is executed. Funcâ€
1531 tions are executed in the context of the current shell; no new process is created to interpret them (contrast this with the exeâ€
1532 cution of a shell script). When a function is executed, the arguments to the function become the positional parameters during
1533 its execution. The special parameter # is updated to reflect the change. Special parameter 0 is unchanged. The first element
1534 of the FUNCNAME variable is set to the name of the function while the function is executing.
1535
1536 All other aspects of the shell execution environment are identical between a function and its caller with these exceptions: the
1537 DEBUG and RETURN traps (see the description of the trap builtin under SHELL BUILTIN COMMANDS below) are not inherited unless the
1538 function has been given the trace attribute (see the description of the declare builtin below) or the -o functrace shell option
1539 has been enabled with the set builtin (in which case all functions inherit the DEBUG and RETURN traps), and the ERR trap is not
1540 inherited unless the -o errtrace shell option has been enabled.
1541
1542 Variables local to the function may be declared with the local builtin command. Ordinarily, variables and their values are
1543 shared between the function and its caller.
1544
1545 The FUNCNEST variable, if set to a numeric value greater than 0, defines a maximum function nesting level. Function invocations
1546 that exceed the limit cause the entire command to abort.
1547
1548 If the builtin command return is executed in a function, the function completes and execution resumes with the next command after
1549 the function call. Any command associated with the RETURN trap is executed before execution resumes. When a function completes,
1550 the values of the positional parameters and the special parameter # are restored to the values they had prior to the function's
1551 execution.
1552
1553 Function names and definitions may be listed with the -f option to the declare or typeset builtin commands. The -F option to
1554 declare or typeset will list the function names only (and optionally the source file and line number, if the extdebug shell
1555 option is enabled). Functions may be exported so that subshells automatically have them defined with the -f option to the export
1556 builtin. A function definition may be deleted using the -f option to the unset builtin. Note that shell functions and variables
1557 with the same name may result in multiple identically-named entries in the environment passed to the shell's children. Care
1558 should be taken in cases where this may cause a problem.
1559
1560 Functions may be recursive. The FUNCNEST variable may be used to limit the depth of the function call stack and restrict the
1561 number of function invocations. By default, no limit is imposed on the number of recursive calls.
1562
1563ARITHMETIC EVALUATION
1564 The shell allows arithmetic expressions to be evaluated, under certain circumstances (see the let and declare builtin commands,
1565 the (( compound command, and Arithmetic Expansion). Evaluation is done in fixed-width integers with no check for overflow,
1566 though division by 0 is trapped and flagged as an error. The operators and their precedence, associativity, and values are the
1567 same as in the C language. The following list of operators is grouped into levels of equal-precedence operators. The levels are
1568 listed in order of decreasing precedence.
1569
1570 id++ id--
1571 variable post-increment and post-decrement
1572 ++id --id
1573 variable pre-increment and pre-decrement
1574 - + unary minus and plus
1575 ! ~ logical and bitwise negation
1576 ** exponentiation
1577 * / % multiplication, division, remainder
1578 + - addition, subtraction
1579 << >> left and right bitwise shifts
1580 <= >= < >
1581 comparison
1582 == != equality and inequality
1583 & bitwise AND
1584 ^ bitwise exclusive OR
1585 | bitwise OR
1586 && logical AND
1587 || logical OR
1588 expr?expr:expr
1589 conditional operator
1590 = *= /= %= += -= <<= >>= &= ^= |=
1591 assignment
1592 expr1 , expr2
1593 comma
1594
1595 Shell variables are allowed as operands; parameter expansion is performed before the expression is evaluated. Within an expresâ€
1596 sion, shell variables may also be referenced by name without using the parameter expansion syntax. A shell variable that is null
1597 or unset evaluates to 0 when referenced by name without using the parameter expansion syntax. The value of a variable is evaluâ€
1598 ated as an arithmetic expression when it is referenced, or when a variable which has been given the integer attribute using
1599 declare -i is assigned a value. A null value evaluates to 0. A shell variable need not have its integer attribute turned on to
1600 be used in an expression.
1601
1602 Constants with a leading 0 are interpreted as octal numbers. A leading 0x or 0X denotes hexadecimal. Otherwise, numbers take
1603 the form [base#]n, where the optional base is a decimal number between 2 and 64 representing the arithmetic base, and n is a numâ€
1604 ber in that base. If base# is omitted, then base 10 is used. When specifying n, the digits greater than 9 are represented by
1605 the lowercase letters, the uppercase letters, @, and _, in that order. If base is less than or equal to 36, lowercase and upperâ€
1606 case letters may be used interchangeably to represent numbers between 10 and 35.
1607
1608 Operators are evaluated in order of precedence. Sub-expressions in parentheses are evaluated first and may override the preceâ€
1609 dence rules above.
1610
1611CONDITIONAL EXPRESSIONS
1612 Conditional expressions are used by the [[ compound command and the test and [ builtin commands to test file attributes and perâ€
1613 form string and arithmetic comparisons. Expressions are formed from the following unary or binary primaries. Bash handles sevâ€
1614 eral filenames specially when they are used in expressions. If the operating system on which bash is running provides these speâ€
1615 cial files, bash will use them; otherwise it will emulate them internally with this behavior: If any file argument to one of the
1616 primaries is of the form /dev/fd/n, then file descriptor n is checked. If the file argument to one of the primaries is one of
1617 /dev/stdin, /dev/stdout, or /dev/stderr, file descriptor 0, 1, or 2, respectively, is checked.
1618
1619 Unless otherwise specified, primaries that operate on files follow symbolic links and operate on the target of the link, rather
1620 than the link itself.
1621
1622 When used with [[, the < and > operators sort lexicographically using the current locale. The test command sorts using ASCII
1623 ordering.
1624
1625 -a file
1626 True if file exists.
1627 -b file
1628 True if file exists and is a block special file.
1629 -c file
1630 True if file exists and is a character special file.
1631 -d file
1632 True if file exists and is a directory.
1633 -e file
1634 True if file exists.
1635 -f file
1636 True if file exists and is a regular file.
1637 -g file
1638 True if file exists and is set-group-id.
1639 -h file
1640 True if file exists and is a symbolic link.
1641 -k file
1642 True if file exists and its ``sticky'' bit is set.
1643 -p file
1644 True if file exists and is a named pipe (FIFO).
1645 -r file
1646 True if file exists and is readable.
1647 -s file
1648 True if file exists and has a size greater than zero.
1649 -t fd True if file descriptor fd is open and refers to a terminal.
1650 -u file
1651 True if file exists and its set-user-id bit is set.
1652 -w file
1653 True if file exists and is writable.
1654 -x file
1655 True if file exists and is executable.
1656 -G file
1657 True if file exists and is owned by the effective group id.
1658 -L file
1659 True if file exists and is a symbolic link.
1660 -N file
1661 True if file exists and has been modified since it was last read.
1662 -O file
1663 True if file exists and is owned by the effective user id.
1664 -S file
1665 True if file exists and is a socket.
1666 file1 -ef file2
1667 True if file1 and file2 refer to the same device and inode numbers.
1668 file1 -nt file2
1669 True if file1 is newer (according to modification date) than file2, or if file1 exists and file2 does not.
1670 file1 -ot file2
1671 True if file1 is older than file2, or if file2 exists and file1 does not.
1672 -o optname
1673 True if the shell option optname is enabled. See the list of options under the description of the -o option to the set
1674 builtin below.
1675 -v varname
1676 True if the shell variable varname is set (has been assigned a value).
1677 -R varname
1678 True if the shell variable varname is set and is a name reference.
1679 -z string
1680 True if the length of string is zero.
1681 string
1682 -n string
1683 True if the length of string is non-zero.
1684
1685 string1 == string2
1686 string1 = string2
1687 True if the strings are equal. = should be used with the test command for POSIX conformance. When used with the [[ comâ€
1688 mand, this performs pattern matching as described above (Compound Commands).
1689
1690 string1 != string2
1691 True if the strings are not equal.
1692
1693 string1 < string2
1694 True if string1 sorts before string2 lexicographically.
1695
1696 string1 > string2
1697 True if string1 sorts after string2 lexicographically.
1698
1699 arg1 OP arg2
1700 OP is one of -eq, -ne, -lt, -le, -gt, or -ge. These arithmetic binary operators return true if arg1 is equal to, not
1701 equal to, less than, less than or equal to, greater than, or greater than or equal to arg2, respectively. Arg1 and arg2
1702 may be positive or negative integers.
1703
1704SIMPLE COMMAND EXPANSION
1705 When a simple command is executed, the shell performs the following expansions, assignments, and redirections, from left to
1706 right.
1707
1708 1. The words that the parser has marked as variable assignments (those preceding the command name) and redirections are saved
1709 for later processing.
1710
1711 2. The words that are not variable assignments or redirections are expanded. If any words remain after expansion, the first
1712 word is taken to be the name of the command and the remaining words are the arguments.
1713
1714 3. Redirections are performed as described above under REDIRECTION.
1715
1716 4. The text after the = in each variable assignment undergoes tilde expansion, parameter expansion, command substitution,
1717 arithmetic expansion, and quote removal before being assigned to the variable.
1718
1719 If no command name results, the variable assignments affect the current shell environment. Otherwise, the variables are added to
1720 the environment of the executed command and do not affect the current shell environment. If any of the assignments attempts to
1721 assign a value to a readonly variable, an error occurs, and the command exits with a non-zero status.
1722
1723 If no command name results, redirections are performed, but do not affect the current shell environment. A redirection error
1724 causes the command to exit with a non-zero status.
1725
1726 If there is a command name left after expansion, execution proceeds as described below. Otherwise, the command exits. If one of
1727 the expansions contained a command substitution, the exit status of the command is the exit status of the last command substituâ€
1728 tion performed. If there were no command substitutions, the command exits with a status of zero.
1729
1730COMMAND EXECUTION
1731 After a command has been split into words, if it results in a simple command and an optional list of arguments, the following
1732 actions are taken.
1733
1734 If the command name contains no slashes, the shell attempts to locate it. If there exists a shell function by that name, that
1735 function is invoked as described above in FUNCTIONS. If the name does not match a function, the shell searches for it in the
1736 list of shell builtins. If a match is found, that builtin is invoked.
1737
1738 If the name is neither a shell function nor a builtin, and contains no slashes, bash searches each element of the PATH for a
1739 directory containing an executable file by that name. Bash uses a hash table to remember the full pathnames of executable files
1740 (see hash under SHELL BUILTIN COMMANDS below). A full search of the directories in PATH is performed only if the command is not
1741 found in the hash table. If the search is unsuccessful, the shell searches for a defined shell function named comâ€
1742 mand_not_found_handle. If that function exists, it is invoked with the original command and the original command's arguments as
1743 its arguments, and the function's exit status becomes the exit status of the shell. If that function is not defined, the shell
1744 prints an error message and returns an exit status of 127.
1745
1746 If the search is successful, or if the command name contains one or more slashes, the shell executes the named program in a sepaâ€
1747 rate execution environment. Argument 0 is set to the name given, and the remaining arguments to the command are set to the arguâ€
1748 ments given, if any.
1749
1750 If this execution fails because the file is not in executable format, and the file is not a directory, it is assumed to be a
1751 shell script, a file containing shell commands. A subshell is spawned to execute it. This subshell reinitializes itself, so
1752 that the effect is as if a new shell had been invoked to handle the script, with the exception that the locations of commands
1753 remembered by the parent (see hash below under SHELL BUILTIN COMMANDS) are retained by the child.
1754
1755 If the program is a file beginning with #!, the remainder of the first line specifies an interpreter for the program. The shell
1756 executes the specified interpreter on operating systems that do not handle this executable format themselves. The arguments to
1757 the interpreter consist of a single optional argument following the interpreter name on the first line of the program, followed
1758 by the name of the program, followed by the command arguments, if any.
1759
1760COMMAND EXECUTION ENVIRONMENT
1761 The shell has an execution environment, which consists of the following:
1762
1763 · open files inherited by the shell at invocation, as modified by redirections supplied to the exec builtin
1764
1765 · the current working directory as set by cd, pushd, or popd, or inherited by the shell at invocation
1766
1767 · the file creation mode mask as set by umask or inherited from the shell's parent
1768
1769 · current traps set by trap
1770
1771 · shell parameters that are set by variable assignment or with set or inherited from the shell's parent in the environment
1772
1773 · shell functions defined during execution or inherited from the shell's parent in the environment
1774
1775 · options enabled at invocation (either by default or with command-line arguments) or by set
1776
1777 · options enabled by shopt
1778
1779 · shell aliases defined with alias
1780
1781 · various process IDs, including those of background jobs, the value of $$, and the value of PPID
1782
1783 When a simple command other than a builtin or shell function is to be executed, it is invoked in a separate execution environment
1784 that consists of the following. Unless otherwise noted, the values are inherited from the shell.
1785
1786 · the shell's open files, plus any modifications and additions specified by redirections to the command
1787
1788 · the current working directory
1789
1790 · the file creation mode mask
1791
1792 · shell variables and functions marked for export, along with variables exported for the command, passed in the environment
1793
1794 · traps caught by the shell are reset to the values inherited from the shell's parent, and traps ignored by the shell are
1795 ignored
1796
1797 A command invoked in this separate environment cannot affect the shell's execution environment.
1798
1799 Command substitution, commands grouped with parentheses, and asynchronous commands are invoked in a subshell environment that is
1800 a duplicate of the shell environment, except that traps caught by the shell are reset to the values that the shell inherited from
1801 its parent at invocation. Builtin commands that are invoked as part of a pipeline are also executed in a subshell environment.
1802 Changes made to the subshell environment cannot affect the shell's execution environment.
1803
1804 Subshells spawned to execute command substitutions inherit the value of the -e option from the parent shell. When not in posix
1805 mode, bash clears the -e option in such subshells.
1806
1807 If a command is followed by a & and job control is not active, the default standard input for the command is the empty file
1808 /dev/null. Otherwise, the invoked command inherits the file descriptors of the calling shell as modified by redirections.
1809
1810ENVIRONMENT
1811 When a program is invoked it is given an array of strings called the environment. This is a list of name-value pairs, of the
1812 form name=value.
1813
1814 The shell provides several ways to manipulate the environment. On invocation, the shell scans its own environment and creates a
1815 parameter for each name found, automatically marking it for export to child processes. Executed commands inherit the environâ€
1816 ment. The export and declare -x commands allow parameters and functions to be added to and deleted from the environment. If the
1817 value of a parameter in the environment is modified, the new value becomes part of the environment, replacing the old. The enviâ€
1818 ronment inherited by any executed command consists of the shell's initial environment, whose values may be modified in the shell,
1819 less any pairs removed by the unset command, plus any additions via the export and declare -x commands.
1820
1821 The environment for any simple command or function may be augmented temporarily by prefixing it with parameter assignments, as
1822 described above in PARAMETERS. These assignment statements affect only the environment seen by that command.
1823
1824 If the -k option is set (see the set builtin command below), then all parameter assignments are placed in the environment for a
1825 command, not just those that precede the command name.
1826
1827 When bash invokes an external command, the variable _ is set to the full filename of the command and passed to that command in
1828 its environment.
1829
1830EXIT STATUS
1831 The exit status of an executed command is the value returned by the waitpid system call or equivalent function. Exit statuses
1832 fall between 0 and 255, though, as explained below, the shell may use values above 125 specially. Exit statuses from shell
1833 builtins and compound commands are also limited to this range. Under certain circumstances, the shell will use special values to
1834 indicate specific failure modes.
1835
1836 For the shell's purposes, a command which exits with a zero exit status has succeeded. An exit status of zero indicates success.
1837 A non-zero exit status indicates failure. When a command terminates on a fatal signal N, bash uses the value of 128+N as the
1838 exit status.
1839
1840 If a command is not found, the child process created to execute it returns a status of 127. If a command is found but is not
1841 executable, the return status is 126.
1842
1843 If a command fails because of an error during expansion or redirection, the exit status is greater than zero.
1844
1845 Shell builtin commands return a status of 0 (true) if successful, and non-zero (false) if an error occurs while they execute.
1846 All builtins return an exit status of 2 to indicate incorrect usage, generally invalid options or missing arguments.
1847
1848 Bash itself returns the exit status of the last command executed, unless a syntax error occurs, in which case it exits with a
1849 non-zero value. See also the exit builtin command below.
1850
1851SIGNALS
1852 When bash is interactive, in the absence of any traps, it ignores SIGTERM (so that kill 0 does not kill an interactive shell),
1853 and SIGINT is caught and handled (so that the wait builtin is interruptible). In all cases, bash ignores SIGQUIT. If job conâ€
1854 trol is in effect, bash ignores SIGTTIN, SIGTTOU, and SIGTSTP.
1855
1856 Non-builtin commands run by bash have signal handlers set to the values inherited by the shell from its parent. When job control
1857 is not in effect, asynchronous commands ignore SIGINT and SIGQUIT in addition to these inherited handlers. Commands run as a
1858 result of command substitution ignore the keyboard-generated job control signals SIGTTIN, SIGTTOU, and SIGTSTP.
1859
1860 The shell exits by default upon receipt of a SIGHUP. Before exiting, an interactive shell resends the SIGHUP to all jobs, runâ€
1861 ning or stopped. Stopped jobs are sent SIGCONT to ensure that they receive the SIGHUP. To prevent the shell from sending the
1862 signal to a particular job, it should be removed from the jobs table with the disown builtin (see SHELL BUILTIN COMMANDS below)
1863 or marked to not receive SIGHUP using disown -h.
1864
1865 If the huponexit shell option has been set with shopt, bash sends a SIGHUP to all jobs when an interactive login shell exits.
1866
1867 If bash is waiting for a command to complete and receives a signal for which a trap has been set, the trap will not be executed
1868 until the command completes. When bash is waiting for an asynchronous command via the wait builtin, the reception of a signal
1869 for which a trap has been set will cause the wait builtin to return immediately with an exit status greater than 128, immediately
1870 after which the trap is executed.
1871
1872JOB CONTROL
1873 Job control refers to the ability to selectively stop (suspend) the execution of processes and continue (resume) their execution
1874 at a later point. A user typically employs this facility via an interactive interface supplied jointly by the operating system
1875 kernel's terminal driver and bash.
1876
1877 The shell associates a job with each pipeline. It keeps a table of currently executing jobs, which may be listed with the jobs
1878 command. When bash starts a job asynchronously (in the background), it prints a line that looks like:
1879
1880 [1] 25647
1881
1882 indicating that this job is job number 1 and that the process ID of the last process in the pipeline associated with this job is
1883 25647. All of the processes in a single pipeline are members of the same job. Bash uses the job abstraction as the basis for
1884 job control.
1885
1886 To facilitate the implementation of the user interface to job control, the operating system maintains the notion of a current
1887 terminal process group ID. Members of this process group (processes whose process group ID is equal to the current terminal
1888 process group ID) receive keyboard-generated signals such as SIGINT. These processes are said to be in the foreground. Backâ€
1889 ground processes are those whose process group ID differs from the terminal's; such processes are immune to keyboard-generated
1890 signals. Only foreground processes are allowed to read from or, if the user so specifies with stty tostop, write to the termiâ€
1891 nal. Background processes which attempt to read from (write to when stty tostop is in effect) the terminal are sent a SIGTTIN
1892 (SIGTTOU) signal by the kernel's terminal driver, which, unless caught, suspends the process.
1893
1894 If the operating system on which bash is running supports job control, bash contains facilities to use it. Typing the suspend
1895 character (typically ^Z, Control-Z) while a process is running causes that process to be stopped and returns control to bash.
1896 Typing the delayed suspend character (typically ^Y, Control-Y) causes the process to be stopped when it attempts to read input
1897 from the terminal, and control to be returned to bash. The user may then manipulate the state of this job, using the bg command
1898 to continue it in the background, the fg command to continue it in the foreground, or the kill command to kill it. A ^Z takes
1899 effect immediately, and has the additional side effect of causing pending output and typeahead to be discarded.
1900
1901 There are a number of ways to refer to a job in the shell. The character % introduces a job specification (jobspec). Job number
1902 n may be referred to as %n. A job may also be referred to using a prefix of the name used to start it, or using a substring that
1903 appears in its command line. For example, %ce refers to a stopped ce job. If a prefix matches more than one job, bash reports
1904 an error. Using %?ce, on the other hand, refers to any job containing the string ce in its command line. If the substring
1905 matches more than one job, bash reports an error. The symbols %% and %+ refer to the shell's notion of the current job, which is
1906 the last job stopped while it was in the foreground or started in the background. The previous job may be referenced using %-.
1907 If there is only a single job, %+ and %- can both be used to refer to that job. In output pertaining to jobs (e.g., the output
1908 of the jobs command), the current job is always flagged with a +, and the previous job with a -. A single % (with no accompanyâ€
1909 ing job specification) also refers to the current job.
1910
1911 Simply naming a job can be used to bring it into the foreground: %1 is a synonym for ``fg %1'', bringing job 1 from the backâ€
1912 ground into the foreground. Similarly, ``%1 &'' resumes job 1 in the background, equivalent to ``bg %1''.
1913
1914 The shell learns immediately whenever a job changes state. Normally, bash waits until it is about to print a prompt before
1915 reporting changes in a job's status so as to not interrupt any other output. If the -b option to the set builtin command is
1916 enabled, bash reports such changes immediately. Any trap on SIGCHLD is executed for each child that exits.
1917
1918 If an attempt to exit bash is made while jobs are stopped (or, if the checkjobs shell option has been enabled using the shopt
1919 builtin, running), the shell prints a warning message, and, if the checkjobs option is enabled, lists the jobs and their staâ€
1920 tuses. The jobs command may then be used to inspect their status. If a second attempt to exit is made without an intervening
1921 command, the shell does not print another warning, and any stopped jobs are terminated.
1922
1923PROMPTING
1924 When executing interactively, bash displays the primary prompt PS1 when it is ready to read a command, and the secondary prompt
1925 PS2 when it needs more input to complete a command. Bash displays PS0 after it reads a command but before executing it. Bash
1926 allows these prompt strings to be customized by inserting a number of backslash-escaped special characters that are decoded as
1927 follows:
1928 \a an ASCII bell character (07)
1929 \d the date in "Weekday Month Date" format (e.g., "Tue May 26")
1930 \D{format}
1931 the format is passed to strftime(3) and the result is inserted into the prompt string; an empty format results in a
1932 locale-specific time representation. The braces are required
1933 \e an ASCII escape character (033)
1934 \h the hostname up to the first `.'
1935 \H the hostname
1936 \j the number of jobs currently managed by the shell
1937 \l the basename of the shell's terminal device name
1938 \n newline
1939 \r carriage return
1940 \s the name of the shell, the basename of $0 (the portion following the final slash)
1941 \t the current time in 24-hour HH:MM:SS format
1942 \T the current time in 12-hour HH:MM:SS format
1943 \@ the current time in 12-hour am/pm format
1944 \A the current time in 24-hour HH:MM format
1945 \u the username of the current user
1946 \v the version of bash (e.g., 2.00)
1947 \V the release of bash, version + patch level (e.g., 2.00.0)
1948 \w the current working directory, with $HOME abbreviated with a tilde (uses the value of the PROMPT_DIRTRIM variable)
1949 \W the basename of the current working directory, with $HOME abbreviated with a tilde
1950 \! the history number of this command
1951 \# the command number of this command
1952 \$ if the effective UID is 0, a #, otherwise a $
1953 \nnn the character corresponding to the octal number nnn
1954 \\ a backslash
1955 \[ begin a sequence of non-printing characters, which could be used to embed a terminal control sequence into the
1956 prompt
1957 \] end a sequence of non-printing characters
1958
1959 The command number and the history number are usually different: the history number of a command is its position in the history
1960 list, which may include commands restored from the history file (see HISTORY below), while the command number is the position in
1961 the sequence of commands executed during the current shell session. After the string is decoded, it is expanded via parameter
1962 expansion, command substitution, arithmetic expansion, and quote removal, subject to the value of the promptvars shell option
1963 (see the description of the shopt command under SHELL BUILTIN COMMANDS below).
1964
1965READLINE
1966 This is the library that handles reading input when using an interactive shell, unless the --noediting option is given at shell
1967 invocation. Line editing is also used when using the -e option to the read builtin. By default, the line editing commands are
1968 similar to those of Emacs. A vi-style line editing interface is also available. Line editing can be enabled at any time using
1969 the -o emacs or -o vi options to the set builtin (see SHELL BUILTIN COMMANDS below). To turn off line editing after the shell is
1970 running, use the +o emacs or +o vi options to the set builtin.
1971
1972 Readline Notation
1973 In this section, the Emacs-style notation is used to denote keystrokes. Control keys are denoted by C-key, e.g., C-n means Conâ€
1974 trol-N. Similarly, meta keys are denoted by M-key, so M-x means Meta-X. (On keyboards without a meta key, M-x means ESC x,
1975 i.e., press the Escape key then the x key. This makes ESC the meta prefix. The combination M-C-x means ESC-Control-x, or press
1976 the Escape key then hold the Control key while pressing the x key.)
1977
1978 Readline commands may be given numeric arguments, which normally act as a repeat count. Sometimes, however, it is the sign of
1979 the argument that is significant. Passing a negative argument to a command that acts in the forward direction (e.g., kill-line)
1980 causes that command to act in a backward direction. Commands whose behavior with arguments deviates from this are noted below.
1981
1982 When a command is described as killing text, the text deleted is saved for possible future retrieval (yanking). The killed text
1983 is saved in a kill ring. Consecutive kills cause the text to be accumulated into one unit, which can be yanked all at once.
1984 Commands which do not kill text separate the chunks of text on the kill ring.
1985
1986 Readline Initialization
1987 Readline is customized by putting commands in an initialization file (the inputrc file). The name of this file is taken from the
1988 value of the INPUTRC variable. If that variable is unset, the default is ~/.inputrc. When a program which uses the readline
1989 library starts up, the initialization file is read, and the key bindings and variables are set. There are only a few basic conâ€
1990 structs allowed in the readline initialization file. Blank lines are ignored. Lines beginning with a # are comments. Lines
1991 beginning with a $ indicate conditional constructs. Other lines denote key bindings and variable settings.
1992
1993 The default key-bindings may be changed with an inputrc file. Other programs that use this library may add their own commands
1994 and bindings.
1995
1996 For example, placing
1997
1998 M-Control-u: universal-argument
1999 or
2000 C-Meta-u: universal-argument
2001 into the inputrc would make M-C-u execute the readline command universal-argument.
2002
2003 The following symbolic character names are recognized: RUBOUT, DEL, ESC, LFD, NEWLINE, RET, RETURN, SPC, SPACE, and TAB.
2004
2005 In addition to command names, readline allows keys to be bound to a string that is inserted when the key is pressed (a macro).
2006
2007 Readline Key Bindings
2008 The syntax for controlling key bindings in the inputrc file is simple. All that is required is the name of the command or the
2009 text of a macro and a key sequence to which it should be bound. The name may be specified in one of two ways: as a symbolic key
2010 name, possibly with Meta- or Control- prefixes, or as a key sequence.
2011
2012 When using the form keyname:function-name or macro, keyname is the name of a key spelled out in English. For example:
2013
2014 Control-u: universal-argument
2015 Meta-Rubout: backward-kill-word
2016 Control-o: "> output"
2017
2018 In the above example, C-u is bound to the function universal-argument, M-DEL is bound to the function backward-kill-word, and C-o
2019 is bound to run the macro expressed on the right hand side (that is, to insert the text ``> output'' into the line).
2020
2021 In the second form, "keyseq":function-name or macro, keyseq differs from keyname above in that strings denoting an entire key
2022 sequence may be specified by placing the sequence within double quotes. Some GNU Emacs style key escapes can be used, as in the
2023 following example, but the symbolic character names are not recognized.
2024
2025 "\C-u": universal-argument
2026 "\C-x\C-r": re-read-init-file
2027 "\e[11~": "Function Key 1"
2028
2029 In this example, C-u is again bound to the function universal-argument. C-x C-r is bound to the function re-read-init-file, and
2030 ESC [ 1 1 ~ is bound to insert the text ``Function Key 1''.
2031
2032 The full set of GNU Emacs style escape sequences is
2033 \C- control prefix
2034 \M- meta prefix
2035 \e an escape character
2036 \\ backslash
2037 \" literal "
2038 \' literal '
2039
2040 In addition to the GNU Emacs style escape sequences, a second set of backslash escapes is available:
2041 \a alert (bell)
2042 \b backspace
2043 \d delete
2044 \f form feed
2045 \n newline
2046 \r carriage return
2047 \t horizontal tab
2048 \v vertical tab
2049 \nnn the eight-bit character whose value is the octal value nnn (one to three digits)
2050 \xHH the eight-bit character whose value is the hexadecimal value HH (one or two hex digits)
2051
2052 When entering the text of a macro, single or double quotes must be used to indicate a macro definition. Unquoted text is assumed
2053 to be a function name. In the macro body, the backslash escapes described above are expanded. Backslash will quote any other
2054 character in the macro text, including " and '.
2055
2056 Bash allows the current readline key bindings to be displayed or modified with the bind builtin command. The editing mode may be
2057 switched during interactive use by using the -o option to the set builtin command (see SHELL BUILTIN COMMANDS below).
2058
2059 Readline Variables
2060 Readline has variables that can be used to further customize its behavior. A variable may be set in the inputrc file with a
2061 statement of the form
2062
2063 set variable-name value
2064
2065 Except where noted, readline variables can take the values On or Off (without regard to case). Unrecognized variable names are
2066 ignored. When a variable value is read, empty or null values, "on" (case-insensitive), and "1" are equivalent to On. All other
2067 values are equivalent to Off. The variables and their default values are:
2068
2069 bell-style (audible)
2070 Controls what happens when readline wants to ring the terminal bell. If set to none, readline never rings the bell. If
2071 set to visible, readline uses a visible bell if one is available. If set to audible, readline attempts to ring the termiâ€
2072 nal's bell.
2073 bind-tty-special-chars (On)
2074 If set to On, readline attempts to bind the control characters treated specially by the kernel's terminal driver to their
2075 readline equivalents.
2076 blink-matching-paren (Off)
2077 If set to On, readline attempts to briefly move the cursor to an opening parenthesis when a closing parenthesis is
2078 inserted.
2079 colored-completion-prefix (Off)
2080 If set to On, when listing completions, readline displays the common prefix of the set of possible completions using a
2081 different color. The color definitions are taken from the value of the LS_COLORS environment variable.
2082 colored-stats (Off)
2083 If set to On, readline displays possible completions using different colors to indicate their file type. The color defiâ€
2084 nitions are taken from the value of the LS_COLORS environment variable.
2085 comment-begin (``#'')
2086 The string that is inserted when the readline insert-comment command is executed. This command is bound to M-# in emacs
2087 mode and to # in vi command mode.
2088 completion-display-width (-1)
2089 The number of screen columns used to display possible matches when performing completion. The value is ignored if it is
2090 less than 0 or greater than the terminal screen width. A value of 0 will cause matches to be displayed one per line. The
2091 default value is -1.
2092 completion-ignore-case (Off)
2093 If set to On, readline performs filename matching and completion in a case-insensitive fashion.
2094 completion-map-case (Off)
2095 If set to On, and completion-ignore-case is enabled, readline treats hyphens (-) and underscores (_) as equivalent when
2096 performing case-insensitive filename matching and completion.
2097 completion-prefix-display-length (0)
2098 The length in characters of the common prefix of a list of possible completions that is displayed without modification.
2099 When set to a value greater than zero, common prefixes longer than this value are replaced with an ellipsis when displayâ€
2100 ing possible completions.
2101 completion-query-items (100)
2102 This determines when the user is queried about viewing the number of possible completions generated by the possible-comâ€
2103 pletions command. It may be set to any integer value greater than or equal to zero. If the number of possible compleâ€
2104 tions is greater than or equal to the value of this variable, the user is asked whether or not he wishes to view them;
2105 otherwise they are simply listed on the terminal.
2106 convert-meta (On)
2107 If set to On, readline will convert characters with the eighth bit set to an ASCII key sequence by stripping the eighth
2108 bit and prefixing an escape character (in effect, using escape as the meta prefix). The default is On, but readline will
2109 set it to Off if the locale contains eight-bit characters.
2110 disable-completion (Off)
2111 If set to On, readline will inhibit word completion. Completion characters will be inserted into the line as if they had
2112 been mapped to self-insert.
2113 echo-control-characters (On)
2114 When set to On, on operating systems that indicate they support it, readline echoes a character corresponding to a signal
2115 generated from the keyboard.
2116 editing-mode (emacs)
2117 Controls whether readline begins with a set of key bindings similar to Emacs or vi. editing-mode can be set to either
2118 emacs or vi.
2119 enable-bracketed-paste (Off)
2120 When set to On, readline will configure the terminal in a way that will enable it to insert each paste into the editing
2121 buffer as a single string of characters, instead of treating each character as if it had been read from the keyboard.
2122 This can prevent pasted characters from being interpreted as editing commands.
2123 enable-keypad (Off)
2124 When set to On, readline will try to enable the application keypad when it is called. Some systems need this to enable
2125 the arrow keys.
2126 enable-meta-key (On)
2127 When set to On, readline will try to enable any meta modifier key the terminal claims to support when it is called. On
2128 many terminals, the meta key is used to send eight-bit characters.
2129 expand-tilde (Off)
2130 If set to On, tilde expansion is performed when readline attempts word completion.
2131 history-preserve-point (Off)
2132 If set to On, the history code attempts to place point at the same location on each history line retrieved with previous-
2133 history or next-history.
2134 history-size (unset)
2135 Set the maximum number of history entries saved in the history list. If set to zero, any existing history entries are
2136 deleted and no new entries are saved. If set to a value less than zero, the number of history entries is not limited. By
2137 default, the number of history entries is set to the value of the HISTSIZE shell variable. If an attempt is made to set
2138 history-size to a non-numeric value, the maximum number of history entries will be set to 500.
2139 horizontal-scroll-mode (Off)
2140 When set to On, makes readline use a single line for display, scrolling the input horizontally on a single screen line
2141 when it becomes longer than the screen width rather than wrapping to a new line.
2142 input-meta (Off)
2143 If set to On, readline will enable eight-bit input (that is, it will not strip the eighth bit from the characters it
2144 reads), regardless of what the terminal claims it can support. The name meta-flag is a synonym for this variable. The
2145 default is Off, but readline will set it to On if the locale contains eight-bit characters.
2146 isearch-terminators (``C-[C-J'')
2147 The string of characters that should terminate an incremental search without subsequently executing the character as a
2148 command. If this variable has not been given a value, the characters ESC and C-J will terminate an incremental search.
2149 keymap (emacs)
2150 Set the current readline keymap. The set of valid keymap names is emacs, emacs-standard, emacs-meta, emacs-ctlx, vi,
2151 vi-command, and vi-insert. vi is equivalent to vi-command; emacs is equivalent to emacs-standard. The default value is
2152 emacs; the value of editing-mode also affects the default keymap.
2153 emacs-mode-string (@)
2154 This string is displayed immediately before the last line of the primary prompt when emacs editing mode is active. The
2155 value is expanded like a key binding, so the standard set of meta- and control prefixes and backslash escape sequences is
2156 available. Use the \1 and \2 escapes to begin and end sequences of non-printing characters, which can be used to embed a
2157 terminal control sequence into the mode string.
2158 keyseq-timeout (500)
2159 Specifies the duration readline will wait for a character when reading an ambiguous key sequence (one that can form a comâ€
2160 plete key sequence using the input read so far, or can take additional input to complete a longer key sequence). If no
2161 input is received within the timeout, readline will use the shorter but complete key sequence. The value is specified in
2162 milliseconds, so a value of 1000 means that readline will wait one second for additional input. If this variable is set
2163 to a value less than or equal to zero, or to a non-numeric value, readline will wait until another key is pressed to
2164 decide which key sequence to complete.
2165 mark-directories (On)
2166 If set to On, completed directory names have a slash appended.
2167 mark-modified-lines (Off)
2168 If set to On, history lines that have been modified are displayed with a preceding asterisk (*).
2169 mark-symlinked-directories (Off)
2170 If set to On, completed names which are symbolic links to directories have a slash appended (subject to the value of
2171 mark-directories).
2172 match-hidden-files (On)
2173 This variable, when set to On, causes readline to match files whose names begin with a `.' (hidden files) when performing
2174 filename completion. If set to Off, the leading `.' must be supplied by the user in the filename to be completed.
2175 menu-complete-display-prefix (Off)
2176 If set to On, menu completion displays the common prefix of the list of possible completions (which may be empty) before
2177 cycling through the list.
2178 output-meta (Off)
2179 If set to On, readline will display characters with the eighth bit set directly rather than as a meta-prefixed escape
2180 sequence. The default is Off, but readline will set it to On if the locale contains eight-bit characters.
2181 page-completions (On)
2182 If set to On, readline uses an internal more-like pager to display a screenful of possible completions at a time.
2183 print-completions-horizontally (Off)
2184 If set to On, readline will display completions with matches sorted horizontally in alphabetical order, rather than down
2185 the screen.
2186 revert-all-at-newline (Off)
2187 If set to On, readline will undo all changes to history lines before returning when accept-line is executed. By default,
2188 history lines may be modified and retain individual undo lists across calls to readline.
2189 show-all-if-ambiguous (Off)
2190 This alters the default behavior of the completion functions. If set to On, words which have more than one possible comâ€
2191 pletion cause the matches to be listed immediately instead of ringing the bell.
2192 show-all-if-unmodified (Off)
2193 This alters the default behavior of the completion functions in a fashion similar to show-all-if-ambiguous. If set to On,
2194 words which have more than one possible completion without any possible partial completion (the possible completions don't
2195 share a common prefix) cause the matches to be listed immediately instead of ringing the bell.
2196 show-mode-in-prompt (Off)
2197 If set to On, add a character to the beginning of the prompt indicating the editing mode: emacs (@), vi command (:) or vi
2198 insertion (+).
2199 skip-completed-text (Off)
2200 If set to On, this alters the default completion behavior when inserting a single match into the line. It's only active
2201 when performing completion in the middle of a word. If enabled, readline does not insert characters from the completion
2202 that match characters after point in the word being completed, so portions of the word following the cursor are not dupliâ€
2203 cated.
2204 vi-cmd-mode-string ((cmd))
2205 This string is displayed immediately before the last line of the primary prompt when vi editing mode is active and in comâ€
2206 mand mode. The value is expanded like a key binding, so the standard set of meta- and control prefixes and backslash
2207 escape sequences is available. Use the \1 and \2 escapes to begin and end sequences of non-printing characters, which can
2208 be used to embed a terminal control sequence into the mode string.
2209 vi-ins-mode-string ((ins))
2210 This string is displayed immediately before the last line of the primary prompt when vi editing mode is active and in
2211 insertion mode. The value is expanded like a key binding, so the standard set of meta- and control prefixes and backslash
2212 escape sequences is available. Use the \1 and \2 escapes to begin and end sequences of non-printing characters, which can
2213 be used to embed a terminal control sequence into the mode string.
2214 visible-stats (Off)
2215 If set to On, a character denoting a file's type as reported by stat(2) is appended to the filename when listing possible
2216 completions.
2217
2218 Readline Conditional Constructs
2219 Readline implements a facility similar in spirit to the conditional compilation features of the C preprocessor which allows key
2220 bindings and variable settings to be performed as the result of tests. There are four parser directives used.
2221
2222 $if The $if construct allows bindings to be made based on the editing mode, the terminal being used, or the application using
2223 readline. The text of the test extends to the end of the line; no characters are required to isolate it.
2224
2225 mode The mode= form of the $if directive is used to test whether readline is in emacs or vi mode. This may be used in
2226 conjunction with the set keymap command, for instance, to set bindings in the emacs-standard and emacs-ctlx keymaps
2227 only if readline is starting out in emacs mode.
2228
2229 term The term= form may be used to include terminal-specific key bindings, perhaps to bind the key sequences output by
2230 the terminal's function keys. The word on the right side of the = is tested against both the full name of the terâ€
2231 minal and the portion of the terminal name before the first -. This allows sun to match both sun and sun-cmd, for
2232 instance.
2233
2234 application
2235 The application construct is used to include application-specific settings. Each program using the readline
2236 library sets the application name, and an initialization file can test for a particular value. This could be used
2237 to bind key sequences to functions useful for a specific program. For instance, the following command adds a key
2238 sequence that quotes the current or previous word in bash:
2239
2240 $if Bash
2241 # Quote the current or previous word
2242 "\C-xq": "\eb\"\ef\""
2243 $endif
2244
2245 $endif This command, as seen in the previous example, terminates an $if command.
2246
2247 $else Commands in this branch of the $if directive are executed if the test fails.
2248
2249 $include
2250 This directive takes a single filename as an argument and reads commands and bindings from that file. For example, the
2251 following directive would read /etc/inputrc:
2252
2253 $include /etc/inputrc
2254
2255 Searching
2256 Readline provides commands for searching through the command history (see HISTORY below) for lines containing a specified string.
2257 There are two search modes: incremental and non-incremental.
2258
2259 Incremental searches begin before the user has finished typing the search string. As each character of the search string is
2260 typed, readline displays the next entry from the history matching the string typed so far. An incremental search requires only
2261 as many characters as needed to find the desired history entry. The characters present in the value of the isearch-terminators
2262 variable are used to terminate an incremental search. If that variable has not been assigned a value the Escape and Control-J
2263 characters will terminate an incremental search. Control-G will abort an incremental search and restore the original line. When
2264 the search is terminated, the history entry containing the search string becomes the current line.
2265
2266 To find other matching entries in the history list, type Control-S or Control-R as appropriate. This will search backward or
2267 forward in the history for the next entry matching the search string typed so far. Any other key sequence bound to a readline
2268 command will terminate the search and execute that command. For instance, a newline will terminate the search and accept the
2269 line, thereby executing the command from the history list.
2270
2271 Readline remembers the last incremental search string. If two Control-Rs are typed without any intervening characters defining a
2272 new search string, any remembered search string is used.
2273
2274 Non-incremental searches read the entire search string before starting to search for matching history lines. The search string
2275 may be typed by the user or be part of the contents of the current line.
2276
2277 Readline Command Names
2278 The following is a list of the names of the commands and the default key sequences to which they are bound. Command names withâ€
2279 out an accompanying key sequence are unbound by default. In the following descriptions, point refers to the current cursor posiâ€
2280 tion, and mark refers to a cursor position saved by the set-mark command. The text between the point and mark is referred to as
2281 the region.
2282
2283 Commands for Moving
2284 beginning-of-line (C-a)
2285 Move to the start of the current line.
2286 end-of-line (C-e)
2287 Move to the end of the line.
2288 forward-char (C-f)
2289 Move forward a character.
2290 backward-char (C-b)
2291 Move back a character.
2292 forward-word (M-f)
2293 Move forward to the end of the next word. Words are composed of alphanumeric characters (letters and digits).
2294 backward-word (M-b)
2295 Move back to the start of the current or previous word. Words are composed of alphanumeric characters (letters and digâ€
2296 its).
2297 shell-forward-word
2298 Move forward to the end of the next word. Words are delimited by non-quoted shell metacharacters.
2299 shell-backward-word
2300 Move back to the start of the current or previous word. Words are delimited by non-quoted shell metacharacters.
2301 clear-screen (C-l)
2302 Clear the screen leaving the current line at the top of the screen. With an argument, refresh the current line without
2303 clearing the screen.
2304 redraw-current-line
2305 Refresh the current line.
2306
2307 Commands for Manipulating the History
2308 accept-line (Newline, Return)
2309 Accept the line regardless of where the cursor is. If this line is non-empty, add it to the history list according to the
2310 state of the HISTCONTROL variable. If the line is a modified history line, then restore the history line to its original
2311 state.
2312 previous-history (C-p)
2313 Fetch the previous command from the history list, moving back in the list.
2314 next-history (C-n)
2315 Fetch the next command from the history list, moving forward in the list.
2316 beginning-of-history (M-<)
2317 Move to the first line in the history.
2318 end-of-history (M->)
2319 Move to the end of the input history, i.e., the line currently being entered.
2320 reverse-search-history (C-r)
2321 Search backward starting at the current line and moving `up' through the history as necessary. This is an incremental
2322 search.
2323 forward-search-history (C-s)
2324 Search forward starting at the current line and moving `down' through the history as necessary. This is an incremental
2325 search.
2326 non-incremental-reverse-search-history (M-p)
2327 Search backward through the history starting at the current line using a non-incremental search for a string supplied by
2328 the user.
2329 non-incremental-forward-search-history (M-n)
2330 Search forward through the history using a non-incremental search for a string supplied by the user.
2331 history-search-forward
2332 Search forward through the history for the string of characters between the start of the current line and the point. This
2333 is a non-incremental search.
2334 history-search-backward
2335 Search backward through the history for the string of characters between the start of the current line and the point.
2336 This is a non-incremental search.
2337 yank-nth-arg (M-C-y)
2338 Insert the first argument to the previous command (usually the second word on the previous line) at point. With an arguâ€
2339 ment n, insert the nth word from the previous command (the words in the previous command begin with word 0). A negative
2340 argument inserts the nth word from the end of the previous command. Once the argument n is computed, the argument is
2341 extracted as if the "!n" history expansion had been specified.
2342 yank-last-arg (M-., M-_)
2343 Insert the last argument to the previous command (the last word of the previous history entry). With a numeric argument,
2344 behave exactly like yank-nth-arg. Successive calls to yank-last-arg move back through the history list, inserting the
2345 last word (or the word specified by the argument to the first call) of each line in turn. Any numeric argument supplied
2346 to these successive calls determines the direction to move through the history. A negative argument switches the direcâ€
2347 tion through the history (back or forward). The history expansion facilities are used to extract the last word, as if the
2348 "!$" history expansion had been specified.
2349 shell-expand-line (M-C-e)
2350 Expand the line as the shell does. This performs alias and history expansion as well as all of the shell word expansions.
2351 See HISTORY EXPANSION below for a description of history expansion.
2352 history-expand-line (M-^)
2353 Perform history expansion on the current line. See HISTORY EXPANSION below for a description of history expansion.
2354 magic-space
2355 Perform history expansion on the current line and insert a space. See HISTORY EXPANSION below for a description of hisâ€
2356 tory expansion.
2357 alias-expand-line
2358 Perform alias expansion on the current line. See ALIASES above for a description of alias expansion.
2359 history-and-alias-expand-line
2360 Perform history and alias expansion on the current line.
2361 insert-last-argument (M-., M-_)
2362 A synonym for yank-last-arg.
2363 operate-and-get-next (C-o)
2364 Accept the current line for execution and fetch the next line relative to the current line from the history for editing.
2365 Any argument is ignored.
2366 edit-and-execute-command (C-xC-e)
2367 Invoke an editor on the current command line, and execute the result as shell commands. Bash attempts to invoke $VISUAL,
2368 $EDITOR, and emacs as the editor, in that order.
2369
2370 Commands for Changing Text
2371 end-of-file (usually C-d)
2372 The character indicating end-of-file as set, for example, by ``stty''. If this character is read when there are no charâ€
2373 acters on the line, and point is at the beginning of the line, Readline interprets it as the end of input and returns EOF.
2374 delete-char (C-d)
2375 Delete the character at point. If this function is bound to the same character as the tty EOF character, as C-d commonly
2376 is, see above for the effects.
2377 backward-delete-char (Rubout)
2378 Delete the character behind the cursor. When given a numeric argument, save the deleted text on the kill ring.
2379 forward-backward-delete-char
2380 Delete the character under the cursor, unless the cursor is at the end of the line, in which case the character behind the
2381 cursor is deleted.
2382 quoted-insert (C-q, C-v)
2383 Add the next character typed to the line verbatim. This is how to insert characters like C-q, for example.
2384 tab-insert (C-v TAB)
2385 Insert a tab character.
2386 self-insert (a, b, A, 1, !, ...)
2387 Insert the character typed.
2388 transpose-chars (C-t)
2389 Drag the character before point forward over the character at point, moving point forward as well. If point is at the end
2390 of the line, then this transposes the two characters before point. Negative arguments have no effect.
2391 transpose-words (M-t)
2392 Drag the word before point past the word after point, moving point over that word as well. If point is at the end of the
2393 line, this transposes the last two words on the line.
2394 upcase-word (M-u)
2395 Uppercase the current (or following) word. With a negative argument, uppercase the previous word, but do not move point.
2396 downcase-word (M-l)
2397 Lowercase the current (or following) word. With a negative argument, lowercase the previous word, but do not move point.
2398 capitalize-word (M-c)
2399 Capitalize the current (or following) word. With a negative argument, capitalize the previous word, but do not move
2400 point.
2401 overwrite-mode
2402 Toggle overwrite mode. With an explicit positive numeric argument, switches to overwrite mode. With an explicit non-posâ€
2403 itive numeric argument, switches to insert mode. This command affects only emacs mode; vi mode does overwrite differâ€
2404 ently. Each call to readline() starts in insert mode. In overwrite mode, characters bound to self-insert replace the
2405 text at point rather than pushing the text to the right. Characters bound to backward-delete-char replace the character
2406 before point with a space. By default, this command is unbound.
2407
2408 Killing and Yanking
2409 kill-line (C-k)
2410 Kill the text from point to the end of the line.
2411 backward-kill-line (C-x Rubout)
2412 Kill backward to the beginning of the line.
2413 unix-line-discard (C-u)
2414 Kill backward from point to the beginning of the line. The killed text is saved on the kill-ring.
2415 kill-whole-line
2416 Kill all characters on the current line, no matter where point is.
2417 kill-word (M-d)
2418 Kill from point to the end of the current word, or if between words, to the end of the next word. Word boundaries are the
2419 same as those used by forward-word.
2420 backward-kill-word (M-Rubout)
2421 Kill the word behind point. Word boundaries are the same as those used by backward-word.
2422 shell-kill-word
2423 Kill from point to the end of the current word, or if between words, to the end of the next word. Word boundaries are the
2424 same as those used by shell-forward-word.
2425 shell-backward-kill-word
2426 Kill the word behind point. Word boundaries are the same as those used by shell-backward-word.
2427 unix-word-rubout (C-w)
2428 Kill the word behind point, using white space as a word boundary. The killed text is saved on the kill-ring.
2429 unix-filename-rubout
2430 Kill the word behind point, using white space and the slash character as the word boundaries. The killed text is saved on
2431 the kill-ring.
2432 delete-horizontal-space (M-\)
2433 Delete all spaces and tabs around point.
2434 kill-region
2435 Kill the text in the current region.
2436 copy-region-as-kill
2437 Copy the text in the region to the kill buffer.
2438 copy-backward-word
2439 Copy the word before point to the kill buffer. The word boundaries are the same as backward-word.
2440 copy-forward-word
2441 Copy the word following point to the kill buffer. The word boundaries are the same as forward-word.
2442 yank (C-y)
2443 Yank the top of the kill ring into the buffer at point.
2444 yank-pop (M-y)
2445 Rotate the kill ring, and yank the new top. Only works following yank or yank-pop.
2446
2447 Numeric Arguments
2448 digit-argument (M-0, M-1, ..., M--)
2449 Add this digit to the argument already accumulating, or start a new argument. M-- starts a negative argument.
2450 universal-argument
2451 This is another way to specify an argument. If this command is followed by one or more digits, optionally with a leading
2452 minus sign, those digits define the argument. If the command is followed by digits, executing universal-argument again
2453 ends the numeric argument, but is otherwise ignored. As a special case, if this command is immediately followed by a
2454 character that is neither a digit nor minus sign, the argument count for the next command is multiplied by four. The
2455 argument count is initially one, so executing this function the first time makes the argument count four, a second time
2456 makes the argument count sixteen, and so on.
2457
2458 Completing
2459 complete (TAB)
2460 Attempt to perform completion on the text before point. Bash attempts completion treating the text as a variable (if the
2461 text begins with $), username (if the text begins with ~), hostname (if the text begins with @), or command (including
2462 aliases and functions) in turn. If none of these produces a match, filename completion is attempted.
2463 possible-completions (M-?)
2464 List the possible completions of the text before point.
2465 insert-completions (M-*)
2466 Insert all completions of the text before point that would have been generated by possible-completions.
2467 menu-complete
2468 Similar to complete, but replaces the word to be completed with a single match from the list of possible completions.
2469 Repeated execution of menu-complete steps through the list of possible completions, inserting each match in turn. At the
2470 end of the list of completions, the bell is rung (subject to the setting of bell-style) and the original text is restored.
2471 An argument of n moves n positions forward in the list of matches; a negative argument may be used to move backward
2472 through the list. This command is intended to be bound to TAB, but is unbound by default.
2473 menu-complete-backward
2474 Identical to menu-complete, but moves backward through the list of possible completions, as if menu-complete had been
2475 given a negative argument. This command is unbound by default.
2476 delete-char-or-list
2477 Deletes the character under the cursor if not at the beginning or end of the line (like delete-char). If at the end of
2478 the line, behaves identically to possible-completions. This command is unbound by default.
2479 complete-filename (M-/)
2480 Attempt filename completion on the text before point.
2481 possible-filename-completions (C-x /)
2482 List the possible completions of the text before point, treating it as a filename.
2483 complete-username (M-~)
2484 Attempt completion on the text before point, treating it as a username.
2485 possible-username-completions (C-x ~)
2486 List the possible completions of the text before point, treating it as a username.
2487 complete-variable (M-$)
2488 Attempt completion on the text before point, treating it as a shell variable.
2489 possible-variable-completions (C-x $)
2490 List the possible completions of the text before point, treating it as a shell variable.
2491 complete-hostname (M-@)
2492 Attempt completion on the text before point, treating it as a hostname.
2493 possible-hostname-completions (C-x @)
2494 List the possible completions of the text before point, treating it as a hostname.
2495 complete-command (M-!)
2496 Attempt completion on the text before point, treating it as a command name. Command completion attempts to match the text
2497 against aliases, reserved words, shell functions, shell builtins, and finally executable filenames, in that order.
2498 possible-command-completions (C-x !)
2499 List the possible completions of the text before point, treating it as a command name.
2500 dynamic-complete-history (M-TAB)
2501 Attempt completion on the text before point, comparing the text against lines from the history list for possible compleâ€
2502 tion matches.
2503 dabbrev-expand
2504 Attempt menu completion on the text before point, comparing the text against lines from the history list for possible comâ€
2505 pletion matches.
2506 complete-into-braces (M-{)
2507 Perform filename completion and insert the list of possible completions enclosed within braces so the list is available to
2508 the shell (see Brace Expansion above).
2509
2510 Keyboard Macros
2511 start-kbd-macro (C-x ()
2512 Begin saving the characters typed into the current keyboard macro.
2513 end-kbd-macro (C-x ))
2514 Stop saving the characters typed into the current keyboard macro and store the definition.
2515 call-last-kbd-macro (C-x e)
2516 Re-execute the last keyboard macro defined, by making the characters in the macro appear as if typed at the keyboard.
2517 print-last-kbd-macro ()
2518 Print the last keyboard macro defined in a format suitable for the inputrc file.
2519
2520 Miscellaneous
2521 re-read-init-file (C-x C-r)
2522 Read in the contents of the inputrc file, and incorporate any bindings or variable assignments found there.
2523 abort (C-g)
2524 Abort the current editing command and ring the terminal's bell (subject to the setting of bell-style).
2525 do-uppercase-version (M-a, M-b, M-x, ...)
2526 If the metafied character x is lowercase, run the command that is bound to the corresponding uppercase character.
2527 prefix-meta (ESC)
2528 Metafy the next character typed. ESC f is equivalent to Meta-f.
2529 undo (C-_, C-x C-u)
2530 Incremental undo, separately remembered for each line.
2531 revert-line (M-r)
2532 Undo all changes made to this line. This is like executing the undo command enough times to return the line to its iniâ€
2533 tial state.
2534 tilde-expand (M-&)
2535 Perform tilde expansion on the current word.
2536 set-mark (C-@, M-<space>)
2537 Set the mark to the point. If a numeric argument is supplied, the mark is set to that position.
2538 exchange-point-and-mark (C-x C-x)
2539 Swap the point with the mark. The current cursor position is set to the saved position, and the old cursor position is
2540 saved as the mark.
2541 character-search (C-])
2542 A character is read and point is moved to the next occurrence of that character. A negative count searches for previous
2543 occurrences.
2544 character-search-backward (M-C-])
2545 A character is read and point is moved to the previous occurrence of that character. A negative count searches for subseâ€
2546 quent occurrences.
2547 skip-csi-sequence
2548 Read enough characters to consume a multi-key sequence such as those defined for keys like Home and End. Such sequences
2549 begin with a Control Sequence Indicator (CSI), usually ESC-[. If this sequence is bound to "\[", keys producing such
2550 sequences will have no effect unless explicitly bound to a readline command, instead of inserting stray characters into
2551 the editing buffer. This is unbound by default, but usually bound to ESC-[.
2552 insert-comment (M-#)
2553 Without a numeric argument, the value of the readline comment-begin variable is inserted at the beginning of the current
2554 line. If a numeric argument is supplied, this command acts as a toggle: if the characters at the beginning of the line do
2555 not match the value of comment-begin, the value is inserted, otherwise the characters in comment-begin are deleted from
2556 the beginning of the line. In either case, the line is accepted as if a newline had been typed. The default value of
2557 comment-begin causes this command to make the current line a shell comment. If a numeric argument causes the comment
2558 character to be removed, the line will be executed by the shell.
2559 glob-complete-word (M-g)
2560 The word before point is treated as a pattern for pathname expansion, with an asterisk implicitly appended. This pattern
2561 is used to generate a list of matching filenames for possible completions.
2562 glob-expand-word (C-x *)
2563 The word before point is treated as a pattern for pathname expansion, and the list of matching filenames is inserted,
2564 replacing the word. If a numeric argument is supplied, an asterisk is appended before pathname expansion.
2565 glob-list-expansions (C-x g)
2566 The list of expansions that would have been generated by glob-expand-word is displayed, and the line is redrawn. If a
2567 numeric argument is supplied, an asterisk is appended before pathname expansion.
2568 dump-functions
2569 Print all of the functions and their key bindings to the readline output stream. If a numeric argument is supplied, the
2570 output is formatted in such a way that it can be made part of an inputrc file.
2571 dump-variables
2572 Print all of the settable readline variables and their values to the readline output stream. If a numeric argument is
2573 supplied, the output is formatted in such a way that it can be made part of an inputrc file.
2574 dump-macros
2575 Print all of the readline key sequences bound to macros and the strings they output. If a numeric argument is supplied,
2576 the output is formatted in such a way that it can be made part of an inputrc file.
2577 display-shell-version (C-x C-v)
2578 Display version information about the current instance of bash.
2579
2580 Programmable Completion
2581 When word completion is attempted for an argument to a command for which a completion specification (a compspec) has been defined
2582 using the complete builtin (see SHELL BUILTIN COMMANDS below), the programmable completion facilities are invoked.
2583
2584 First, the command name is identified. If the command word is the empty string (completion attempted at the beginning of an
2585 empty line), any compspec defined with the -E option to complete is used. If a compspec has been defined for that command, the
2586 compspec is used to generate the list of possible completions for the word. If the command word is a full pathname, a compspec
2587 for the full pathname is searched for first. If no compspec is found for the full pathname, an attempt is made to find a compâ€
2588 spec for the portion following the final slash. If those searches do not result in a compspec, any compspec defined with the -D
2589 option to complete is used as the default.
2590
2591 Once a compspec has been found, it is used to generate the list of matching words. If a compspec is not found, the default bash
2592 completion as described above under Completing is performed.
2593
2594 First, the actions specified by the compspec are used. Only matches which are prefixed by the word being completed are returned.
2595 When the -f or -d option is used for filename or directory name completion, the shell variable FIGNORE is used to filter the
2596 matches.
2597
2598 Any completions specified by a pathname expansion pattern to the -G option are generated next. The words generated by the patâ€
2599 tern need not match the word being completed. The GLOBIGNORE shell variable is not used to filter the matches, but the FIGNORE
2600 variable is used.
2601
2602 Next, the string specified as the argument to the -W option is considered. The string is first split using the characters in the
2603 IFS special variable as delimiters. Shell quoting is honored. Each word is then expanded using brace expansion, tilde expanâ€
2604 sion, parameter and variable expansion, command substitution, and arithmetic expansion, as described above under EXPANSION. The
2605 results are split using the rules described above under Word Splitting. The results of the expansion are prefix-matched against
2606 the word being completed, and the matching words become the possible completions.
2607
2608 After these matches have been generated, any shell function or command specified with the -F and -C options is invoked. When the
2609 command or function is invoked, the COMP_LINE, COMP_POINT, COMP_KEY, and COMP_TYPE variables are assigned values as described
2610 above under Shell Variables. If a shell function is being invoked, the COMP_WORDS and COMP_CWORD variables are also set. When
2611 the function or command is invoked, the first argument ($1) is the name of the command whose arguments are being completed, the
2612 second argument ($2) is the word being completed, and the third argument ($3) is the word preceding the word being completed on
2613 the current command line. No filtering of the generated completions against the word being completed is performed; the function
2614 or command has complete freedom in generating the matches.
2615
2616 Any function specified with -F is invoked first. The function may use any of the shell facilities, including the compgen builtin
2617 described below, to generate the matches. It must put the possible completions in the COMPREPLY array variable, one per array
2618 element.
2619
2620 Next, any command specified with the -C option is invoked in an environment equivalent to command substitution. It should print
2621 a list of completions, one per line, to the standard output. Backslash may be used to escape a newline, if necessary.
2622
2623 After all of the possible completions are generated, any filter specified with the -X option is applied to the list. The filter
2624 is a pattern as used for pathname expansion; a & in the pattern is replaced with the text of the word being completed. A literal
2625 & may be escaped with a backslash; the backslash is removed before attempting a match. Any completion that matches the pattern
2626 will be removed from the list. A leading ! negates the pattern; in this case any completion not matching the pattern will be
2627 removed. If the nocasematch shell option is enabled, the match is performed without regard to the case of alphabetic characters.
2628
2629 Finally, any prefix and suffix specified with the -P and -S options are added to each member of the completion list, and the
2630 result is returned to the readline completion code as the list of possible completions.
2631
2632 If the previously-applied actions do not generate any matches, and the -o dirnames option was supplied to complete when the compâ€
2633 spec was defined, directory name completion is attempted.
2634
2635 If the -o plusdirs option was supplied to complete when the compspec was defined, directory name completion is attempted and any
2636 matches are added to the results of the other actions.
2637
2638 By default, if a compspec is found, whatever it generates is returned to the completion code as the full set of possible compleâ€
2639 tions. The default bash completions are not attempted, and the readline default of filename completion is disabled. If the -o
2640 bashdefault option was supplied to complete when the compspec was defined, the bash default completions are attempted if the
2641 compspec generates no matches. If the -o default option was supplied to complete when the compspec was defined, readline's
2642 default completion will be performed if the compspec (and, if attempted, the default bash completions) generate no matches.
2643
2644 When a compspec indicates that directory name completion is desired, the programmable completion functions force readline to
2645 append a slash to completed names which are symbolic links to directories, subject to the value of the mark-directories readline
2646 variable, regardless of the setting of the mark-symlinked-directories readline variable.
2647
2648 There is some support for dynamically modifying completions. This is most useful when used in combination with a default compleâ€
2649 tion specified with complete -D. It's possible for shell functions executed as completion handlers to indicate that completion
2650 should be retried by returning an exit status of 124. If a shell function returns 124, and changes the compspec associated with
2651 the command on which completion is being attempted (supplied as the first argument when the function is executed), programmable
2652 completion restarts from the beginning, with an attempt to find a new compspec for that command. This allows a set of compleâ€
2653 tions to be built dynamically as completion is attempted, rather than being loaded all at once.
2654
2655 For instance, assuming that there is a library of compspecs, each kept in a file corresponding to the name of the command, the
2656 following default completion function would load completions dynamically:
2657
2658 _completion_loader()
2659 {
2660 . "/etc/bash_completion.d/$1.sh" >/dev/null 2>&1 && return 124
2661 }
2662 complete -D -F _completion_loader -o bashdefault -o default
2663
2664HISTORY
2665 When the -o history option to the set builtin is enabled, the shell provides access to the command history, the list of commands
2666 previously typed. The value of the HISTSIZE variable is used as the number of commands to save in a history list. The text of
2667 the last HISTSIZE commands (default 500) is saved. The shell stores each command in the history list prior to parameter and
2668 variable expansion (see EXPANSION above) but after history expansion is performed, subject to the values of the shell variables
2669 HISTIGNORE and HISTCONTROL.
2670
2671 On startup, the history is initialized from the file named by the variable HISTFILE (default ~/.bash_history). The file named by
2672 the value of HISTFILE is truncated, if necessary, to contain no more than the number of lines specified by the value of HISTFILEâ€
2673 SIZE. If HISTFILESIZE is unset, or set to null, a non-numeric value, or a numeric value less than zero, the history file is not
2674 truncated. When the history file is read, lines beginning with the history comment character followed immediately by a digit are
2675 interpreted as timestamps for the preceding history line. These timestamps are optionally displayed depending on the value of
2676 the HISTTIMEFORMAT variable. When a shell with history enabled exits, the last $HISTSIZE lines are copied from the history list
2677 to $HISTFILE. If the histappend shell option is enabled (see the description of shopt under SHELL BUILTIN COMMANDS below), the
2678 lines are appended to the history file, otherwise the history file is overwritten. If HISTFILE is unset, or if the history file
2679 is unwritable, the history is not saved. If the HISTTIMEFORMAT variable is set, time stamps are written to the history file,
2680 marked with the history comment character, so they may be preserved across shell sessions. This uses the history comment characâ€
2681 ter to distinguish timestamps from other history lines. After saving the history, the history file is truncated to contain no
2682 more than HISTFILESIZE lines. If HISTFILESIZE is unset, or set to null, a non-numeric value, or a numeric value less than zero,
2683 the history file is not truncated.
2684
2685 The builtin command fc (see SHELL BUILTIN COMMANDS below) may be used to list or edit and re-execute a portion of the history
2686 list. The history builtin may be used to display or modify the history list and manipulate the history file. When using comâ€
2687 mand-line editing, search commands are available in each editing mode that provide access to the history list.
2688
2689 The shell allows control over which commands are saved on the history list. The HISTCONTROL and HISTIGNORE variables may be set
2690 to cause the shell to save only a subset of the commands entered. The cmdhist shell option, if enabled, causes the shell to
2691 attempt to save each line of a multi-line command in the same history entry, adding semicolons where necessary to preserve synâ€
2692 tactic correctness. The lithist shell option causes the shell to save the command with embedded newlines instead of semicolons.
2693 See the description of the shopt builtin below under SHELL BUILTIN COMMANDS for information on setting and unsetting shell
2694 options.
2695
2696HISTORY EXPANSION
2697 The shell supports a history expansion feature that is similar to the history expansion in csh. This section describes what synâ€
2698 tax features are available. This feature is enabled by default for interactive shells, and can be disabled using the +H option
2699 to the set builtin command (see SHELL BUILTIN COMMANDS below). Non-interactive shells do not perform history expansion by
2700 default.
2701
2702 History expansions introduce words from the history list into the input stream, making it easy to repeat commands, insert the
2703 arguments to a previous command into the current input line, or fix errors in previous commands quickly.
2704
2705 History expansion is performed immediately after a complete line is read, before the shell breaks it into words. It takes place
2706 in two parts. The first is to determine which line from the history list to use during substitution. The second is to select
2707 portions of that line for inclusion into the current one. The line selected from the history is the event, and the portions of
2708 that line that are acted upon are words. Various modifiers are available to manipulate the selected words. The line is broken
2709 into words in the same fashion as when reading input, so that several metacharacter-separated words surrounded by quotes are conâ€
2710 sidered one word. History expansions are introduced by the appearance of the history expansion character, which is ! by default.
2711 Only backslash (\) and single quotes can quote the history expansion character, but the history expansion character is also
2712 treated as quoted if it immediately precedes the closing double quote in a double-quoted string.
2713
2714 Several characters inhibit history expansion if found immediately following the history expansion character, even if it is
2715 unquoted: space, tab, newline, carriage return, and =. If the extglob shell option is enabled, ( will also inhibit expansion.
2716
2717 Several shell options settable with the shopt builtin may be used to tailor the behavior of history expansion. If the histverify
2718 shell option is enabled (see the description of the shopt builtin below), and readline is being used, history substitutions are
2719 not immediately passed to the shell parser. Instead, the expanded line is reloaded into the readline editing buffer for further
2720 modification. If readline is being used, and the histreedit shell option is enabled, a failed history substitution will be
2721 reloaded into the readline editing buffer for correction. The -p option to the history builtin command may be used to see what a
2722 history expansion will do before using it. The -s option to the history builtin may be used to add commands to the end of the
2723 history list without actually executing them, so that they are available for subsequent recall.
2724
2725 The shell allows control of the various characters used by the history expansion mechanism (see the description of histchars
2726 above under Shell Variables). The shell uses the history comment character to mark history timestamps when writing the history
2727 file.
2728
2729 Event Designators
2730 An event designator is a reference to a command line entry in the history list. Unless the reference is absolute, events are
2731 relative to the current position in the history list.
2732
2733 ! Start a history substitution, except when followed by a blank, newline, carriage return, = or ( (when the extglob shell
2734 option is enabled using the shopt builtin).
2735 !n Refer to command line n.
2736 !-n Refer to the current command minus n.
2737 !! Refer to the previous command. This is a synonym for `!-1'.
2738 !string
2739 Refer to the most recent command preceding the current position in the history list starting with string.
2740 !?string[?]
2741 Refer to the most recent command preceding the current position in the history list containing string. The trailing ? may
2742 be omitted if string is followed immediately by a newline.
2743 ^string1^string2^
2744 Quick substitution. Repeat the previous command, replacing string1 with string2. Equivalent to ``!!:s/string1/string2/''
2745 (see Modifiers below).
2746 !# The entire command line typed so far.
2747
2748 Word Designators
2749 Word designators are used to select desired words from the event. A : separates the event specification from the word designaâ€
2750 tor. It may be omitted if the word designator begins with a ^, $, *, -, or %. Words are numbered from the beginning of the
2751 line, with the first word being denoted by 0 (zero). Words are inserted into the current line separated by single spaces.
2752
2753 0 (zero)
2754 The zeroth word. For the shell, this is the command word.
2755 n The nth word.
2756 ^ The first argument. That is, word 1.
2757 $ The last word. This is usually the last argument, but will expand to the zeroth word if there is only one word in the
2758 line.
2759 % The word matched by the most recent `?string?' search.
2760 x-y A range of words; `-y' abbreviates `0-y'.
2761 * All of the words but the zeroth. This is a synonym for `1-$'. It is not an error to use * if there is just one word in
2762 the event; the empty string is returned in that case.
2763 x* Abbreviates x-$.
2764 x- Abbreviates x-$ like x*, but omits the last word.
2765
2766 If a word designator is supplied without an event specification, the previous command is used as the event.
2767
2768 Modifiers
2769 After the optional word designator, there may appear a sequence of one or more of the following modifiers, each preceded by a
2770 `:'.
2771
2772 h Remove a trailing filename component, leaving only the head.
2773 t Remove all leading filename components, leaving the tail.
2774 r Remove a trailing suffix of the form .xxx, leaving the basename.
2775 e Remove all but the trailing suffix.
2776 p Print the new command but do not execute it.
2777 q Quote the substituted words, escaping further substitutions.
2778 x Quote the substituted words as with q, but break into words at blanks and newlines.
2779 s/old/new/
2780 Substitute new for the first occurrence of old in the event line. Any delimiter can be used in place of /. The final
2781 delimiter is optional if it is the last character of the event line. The delimiter may be quoted in old and new with a
2782 single backslash. If & appears in new, it is replaced by old. A single backslash will quote the &. If old is null, it
2783 is set to the last old substituted, or, if no previous history substitutions took place, the last string in a !?string[?]
2784 search.
2785 & Repeat the previous substitution.
2786 g Cause changes to be applied over the entire event line. This is used in conjunction with `:s' (e.g., `:gs/old/new/') or
2787 `:&'. If used with `:s', any delimiter can be used in place of /, and the final delimiter is optional if it is the last
2788 character of the event line. An a may be used as a synonym for g.
2789 G Apply the following `s' modifier once to each word in the event line.
2790
2791SHELL BUILTIN COMMANDS
2792 Unless otherwise noted, each builtin command documented in this section as accepting options preceded by - accepts -- to signify
2793 the end of the options. The :, true, false, and test builtins do not accept options and do not treat -- specially. The exit,
2794 logout, return, break, continue, let, and shift builtins accept and process arguments beginning with - without requiring --.
2795 Other builtins that accept arguments but are not specified as accepting options interpret arguments beginning with - as invalid
2796 options and require -- to prevent this interpretation.
2797 : [arguments]
2798 No effect; the command does nothing beyond expanding arguments and performing any specified redirections. The return staâ€
2799 tus is zero.
2800
2801 . filename [arguments]
2802 source filename [arguments]
2803 Read and execute commands from filename in the current shell environment and return the exit status of the last command
2804 executed from filename. If filename does not contain a slash, filenames in PATH are used to find the directory containing
2805 filename. The file searched for in PATH need not be executable. When bash is not in posix mode, the current directory is
2806 searched if no file is found in PATH. If the sourcepath option to the shopt builtin command is turned off, the PATH is
2807 not searched. If any arguments are supplied, they become the positional parameters when filename is executed. Otherwise
2808 the positional parameters are unchanged. If the -T option is enabled, source inherits any trap on DEBUG; if it is not,
2809 any DEBUG trap string is saved and restored around the call to source, and source unsets the DEBUG trap while it executes.
2810 If -T is not set, and the sourced file changes the DEBUG trap, the new value is retained when source completes. The
2811 return status is the status of the last command exited within the script (0 if no commands are executed), and false if
2812 filename is not found or cannot be read.
2813
2814 alias [-p] [name[=value] ...]
2815 Alias with no arguments or with the -p option prints the list of aliases in the form alias name=value on standard output.
2816 When arguments are supplied, an alias is defined for each name whose value is given. A trailing space in value causes the
2817 next word to be checked for alias substitution when the alias is expanded. For each name in the argument list for which
2818 no value is supplied, the name and value of the alias is printed. Alias returns true unless a name is given for which no
2819 alias has been defined.
2820
2821 bg [jobspec ...]
2822 Resume each suspended job jobspec in the background, as if it had been started with &. If jobspec is not present, the
2823 shell's notion of the current job is used. bg jobspec returns 0 unless run when job control is disabled or, when run with
2824 job control enabled, any specified jobspec was not found or was started without job control.
2825
2826 bind [-m keymap] [-lpsvPSVX]
2827 bind [-m keymap] [-q function] [-u function] [-r keyseq]
2828 bind [-m keymap] -f filename
2829 bind [-m keymap] -x keyseq:shell-command
2830 bind [-m keymap] keyseq:function-name
2831 bind [-m keymap] keyseq:readline-command
2832 Display current readline key and function bindings, bind a key sequence to a readline function or macro, or set a readline
2833 variable. Each non-option argument is a command as it would appear in .inputrc, but each binding or command must be
2834 passed as a separate argument; e.g., '"\C-x\C-r": re-read-init-file'. Options, if supplied, have the following meanings:
2835 -m keymap
2836 Use keymap as the keymap to be affected by the subsequent bindings. Acceptable keymap names are emacs, emacs-stanâ€
2837 dard, emacs-meta, emacs-ctlx, vi, vi-move, vi-command, and vi-insert. vi is equivalent to vi-command (vi-move is
2838 also a synonym); emacs is equivalent to emacs-standard.
2839 -l List the names of all readline functions.
2840 -p Display readline function names and bindings in such a way that they can be re-read.
2841 -P List current readline function names and bindings.
2842 -s Display readline key sequences bound to macros and the strings they output in such a way that they can be re-read.
2843 -S Display readline key sequences bound to macros and the strings they output.
2844 -v Display readline variable names and values in such a way that they can be re-read.
2845 -V List current readline variable names and values.
2846 -f filename
2847 Read key bindings from filename.
2848 -q function
2849 Query about which keys invoke the named function.
2850 -u function
2851 Unbind all keys bound to the named function.
2852 -r keyseq
2853 Remove any current binding for keyseq.
2854 -x keyseq:shell-command
2855 Cause shell-command to be executed whenever keyseq is entered. When shell-command is executed, the shell sets the
2856 READLINE_LINE variable to the contents of the readline line buffer and the READLINE_POINT variable to the current
2857 location of the insertion point. If the executed command changes the value of READLINE_LINE or READLINE_POINT,
2858 those new values will be reflected in the editing state.
2859 -X List all key sequences bound to shell commands and the associated commands in a format that can be reused as input.
2860
2861 The return value is 0 unless an unrecognized option is given or an error occurred.
2862
2863 break [n]
2864 Exit from within a for, while, until, or select loop. If n is specified, break n levels. n must be ≥ 1. If n is greater
2865 than the number of enclosing loops, all enclosing loops are exited. The return value is 0 unless n is not greater than or
2866 equal to 1.
2867
2868 builtin shell-builtin [arguments]
2869 Execute the specified shell builtin, passing it arguments, and return its exit status. This is useful when defining a
2870 function whose name is the same as a shell builtin, retaining the functionality of the builtin within the function. The
2871 cd builtin is commonly redefined this way. The return status is false if shell-builtin is not a shell builtin command.
2872
2873 caller [expr]
2874 Returns the context of any active subroutine call (a shell function or a script executed with the . or source builtins).
2875 Without expr, caller displays the line number and source filename of the current subroutine call. If a non-negative inteâ€
2876 ger is supplied as expr, caller displays the line number, subroutine name, and source file corresponding to that position
2877 in the current execution call stack. This extra information may be used, for example, to print a stack trace. The curâ€
2878 rent frame is frame 0. The return value is 0 unless the shell is not executing a subroutine call or expr does not correâ€
2879 spond to a valid position in the call stack.
2880
2881 cd [-L|[-P [-e]] [-@]] [dir]
2882 Change the current directory to dir. if dir is not supplied, the value of the HOME shell variable is the default. Any
2883 additional arguments following dir are ignored. The variable CDPATH defines the search path for the directory containing
2884 dir: each directory name in CDPATH is searched for dir. Alternative directory names in CDPATH are separated by a colon
2885 (:). A null directory name in CDPATH is the same as the current directory, i.e., ``.''. If dir begins with a slash (/),
2886 then CDPATH is not used. The -P option causes cd to use the physical directory structure by resolving symbolic links
2887 while traversing dir and before processing instances of .. in dir (see also the -P option to the set builtin command); the
2888 -L option forces symbolic links to be followed by resolving the link after processing instances of .. in dir. If ..
2889 appears in dir, it is processed by removing the immediately previous pathname component from dir, back to a slash or the
2890 beginning of dir. If the -e option is supplied with -P, and the current working directory cannot be successfully deterâ€
2891 mined after a successful directory change, cd will return an unsuccessful status. On systems that support it, the -@
2892 option presents the extended attributes associated with a file as a directory. An argument of - is converted to $OLDPWD
2893 before the directory change is attempted. If a non-empty directory name from CDPATH is used, or if - is the first arguâ€
2894 ment, and the directory change is successful, the absolute pathname of the new working directory is written to the stanâ€
2895 dard output. The return value is true if the directory was successfully changed; false otherwise.
2896
2897 command [-pVv] command [arg ...]
2898 Run command with args suppressing the normal shell function lookup. Only builtin commands or commands found in the PATH
2899 are executed. If the -p option is given, the search for command is performed using a default value for PATH that is guarâ€
2900 anteed to find all of the standard utilities. If either the -V or -v option is supplied, a description of command is
2901 printed. The -v option causes a single word indicating the command or filename used to invoke command to be displayed;
2902 the -V option produces a more verbose description. If the -V or -v option is supplied, the exit status is 0 if command
2903 was found, and 1 if not. If neither option is supplied and an error occurred or command cannot be found, the exit status
2904 is 127. Otherwise, the exit status of the command builtin is the exit status of command.
2905
2906 compgen [option] [word]
2907 Generate possible completion matches for word according to the options, which may be any option accepted by the complete
2908 builtin with the exception of -p and -r, and write the matches to the standard output. When using the -F or -C options,
2909 the various shell variables set by the programmable completion facilities, while available, will not have useful values.
2910
2911 The matches will be generated in the same way as if the programmable completion code had generated them directly from a
2912 completion specification with the same flags. If word is specified, only those completions matching word will be disâ€
2913 played.
2914
2915 The return value is true unless an invalid option is supplied, or no matches were generated.
2916
2917 complete [-abcdefgjksuv] [-o comp-option] [-DE] [-A action] [-G globpat] [-W wordlist] [-F function] [-C command]
2918 [-X filterpat] [-P prefix] [-S suffix] name [name ...]
2919 complete -pr [-DE] [name ...]
2920 Specify how arguments to each name should be completed. If the -p option is supplied, or if no options are supplied,
2921 existing completion specifications are printed in a way that allows them to be reused as input. The -r option removes a
2922 completion specification for each name, or, if no names are supplied, all completion specifications. The -D option indiâ€
2923 cates that the remaining options and actions should apply to the ``default'' command completion; that is, completion
2924 attempted on a command for which no completion has previously been defined. The -E option indicates that the remaining
2925 options and actions should apply to ``empty'' command completion; that is, completion attempted on a blank line.
2926
2927 The process of applying these completion specifications when word completion is attempted is described above under Proâ€
2928 grammable Completion.
2929
2930 Other options, if specified, have the following meanings. The arguments to the -G, -W, and -X options (and, if necessary,
2931 the -P and -S options) should be quoted to protect them from expansion before the complete builtin is invoked.
2932 -o comp-option
2933 The comp-option controls several aspects of the compspec's behavior beyond the simple generation of completions.
2934 comp-option may be one of:
2935 bashdefault
2936 Perform the rest of the default bash completions if the compspec generates no matches.
2937 default Use readline's default filename completion if the compspec generates no matches.
2938 dirnames
2939 Perform directory name completion if the compspec generates no matches.
2940 filenames
2941 Tell readline that the compspec generates filenames, so it can perform any filename-specific processing
2942 (like adding a slash to directory names, quoting special characters, or suppressing trailing spaces).
2943 Intended to be used with shell functions.
2944 noquote Tell readline not to quote the completed words if they are filenames (quoting filenames is the default).
2945 nosort Tell readline not to sort the list of possible completions alphabetically.
2946 nospace Tell readline not to append a space (the default) to words completed at the end of the line.
2947 plusdirs
2948 After any matches defined by the compspec are generated, directory name completion is attempted and any
2949 matches are added to the results of the other actions.
2950 -A action
2951 The action may be one of the following to generate a list of possible completions:
2952 alias Alias names. May also be specified as -a.
2953 arrayvar
2954 Array variable names.
2955 binding Readline key binding names.
2956 builtin Names of shell builtin commands. May also be specified as -b.
2957 command Command names. May also be specified as -c.
2958 directory
2959 Directory names. May also be specified as -d.
2960 disabled
2961 Names of disabled shell builtins.
2962 enabled Names of enabled shell builtins.
2963 export Names of exported shell variables. May also be specified as -e.
2964 file File names. May also be specified as -f.
2965 function
2966 Names of shell functions.
2967 group Group names. May also be specified as -g.
2968 helptopic
2969 Help topics as accepted by the help builtin.
2970 hostname
2971 Hostnames, as taken from the file specified by the HOSTFILE shell variable.
2972 job Job names, if job control is active. May also be specified as -j.
2973 keyword Shell reserved words. May also be specified as -k.
2974 running Names of running jobs, if job control is active.
2975 service Service names. May also be specified as -s.
2976 setopt Valid arguments for the -o option to the set builtin.
2977 shopt Shell option names as accepted by the shopt builtin.
2978 signal Signal names.
2979 stopped Names of stopped jobs, if job control is active.
2980 user User names. May also be specified as -u.
2981 variable
2982 Names of all shell variables. May also be specified as -v.
2983 -C command
2984 command is executed in a subshell environment, and its output is used as the possible completions.
2985 -F function
2986 The shell function function is executed in the current shell environment. When the function is executed, the
2987 first argument ($1) is the name of the command whose arguments are being completed, the second argument ($2) is
2988 the word being completed, and the third argument ($3) is the word preceding the word being completed on the curâ€
2989 rent command line. When it finishes, the possible completions are retrieved from the value of the COMPREPLY array
2990 variable.
2991 -G globpat
2992 The pathname expansion pattern globpat is expanded to generate the possible completions.
2993 -P prefix
2994 prefix is added at the beginning of each possible completion after all other options have been applied.
2995 -S suffix
2996 suffix is appended to each possible completion after all other options have been applied.
2997 -W wordlist
2998 The wordlist is split using the characters in the IFS special variable as delimiters, and each resultant word is
2999 expanded. The possible completions are the members of the resultant list which match the word being completed.
3000 -X filterpat
3001 filterpat is a pattern as used for pathname expansion. It is applied to the list of possible completions generâ€
3002 ated by the preceding options and arguments, and each completion matching filterpat is removed from the list. A
3003 leading ! in filterpat negates the pattern; in this case, any completion not matching filterpat is removed.
3004
3005 The return value is true unless an invalid option is supplied, an option other than -p or -r is supplied without a name
3006 argument, an attempt is made to remove a completion specification for a name for which no specification exists, or an
3007 error occurs adding a completion specification.
3008
3009 compopt [-o option] [-DE] [+o option] [name]
3010 Modify completion options for each name according to the options, or for the currently-executing completion if no names
3011 are supplied. If no options are given, display the completion options for each name or the current completion. The posâ€
3012 sible values of option are those valid for the complete builtin described above. The -D option indicates that the remainâ€
3013 ing options should apply to the ``default'' command completion; that is, completion attempted on a command for which no
3014 completion has previously been defined. The -E option indicates that the remaining options should apply to ``empty'' comâ€
3015 mand completion; that is, completion attempted on a blank line.
3016
3017 The return value is true unless an invalid option is supplied, an attempt is made to modify the options for a name for
3018 which no completion specification exists, or an output error occurs.
3019
3020 continue [n]
3021 Resume the next iteration of the enclosing for, while, until, or select loop. If n is specified, resume at the nth
3022 enclosing loop. n must be ≥ 1. If n is greater than the number of enclosing loops, the last enclosing loop (the ``top-
3023 level'' loop) is resumed. The return value is 0 unless n is not greater than or equal to 1.
3024
3025 declare [-aAfFgilnrtux] [-p] [name[=value] ...]
3026 typeset [-aAfFgilnrtux] [-p] [name[=value] ...]
3027 Declare variables and/or give them attributes. If no names are given then display the values of variables. The -p option
3028 will display the attributes and values of each name. When -p is used with name arguments, additional options, other than
3029 -f and -F, are ignored. When -p is supplied without name arguments, it will display the attributes and values of all
3030 variables having the attributes specified by the additional options. If no other options are supplied with -p, declare
3031 will display the attributes and values of all shell variables. The -f option will restrict the display to shell funcâ€
3032 tions. The -F option inhibits the display of function definitions; only the function name and attributes are printed. If
3033 the extdebug shell option is enabled using shopt, the source file name and line number where each name is defined are disâ€
3034 played as well. The -F option implies -f. The -g option forces variables to be created or modified at the global scope,
3035 even when declare is executed in a shell function. It is ignored in all other cases. The following options can be used
3036 to restrict output to variables with the specified attribute or to give variables attributes:
3037 -a Each name is an indexed array variable (see Arrays above).
3038 -A Each name is an associative array variable (see Arrays above).
3039 -f Use function names only.
3040 -i The variable is treated as an integer; arithmetic evaluation (see ARITHMETIC EVALUATION above) is performed when
3041 the variable is assigned a value.
3042 -l When the variable is assigned a value, all upper-case characters are converted to lower-case. The upper-case
3043 attribute is disabled.
3044 -n Give each name the nameref attribute, making it a name reference to another variable. That other variable is
3045 defined by the value of name. All references, assignments, and attribute modifications to name, except those using
3046 or changing the -n attribute itself, are performed on the variable referenced by name's value. The nameref
3047 attribute cannot be applied to array variables.
3048 -r Make names readonly. These names cannot then be assigned values by subsequent assignment statements or unset.
3049 -t Give each name the trace attribute. Traced functions inherit the DEBUG and RETURN traps from the calling shell.
3050 The trace attribute has no special meaning for variables.
3051 -u When the variable is assigned a value, all lower-case characters are converted to upper-case. The lower-case
3052 attribute is disabled.
3053 -x Mark names for export to subsequent commands via the environment.
3054
3055 Using `+' instead of `-' turns off the attribute instead, with the exceptions that +a may not be used to destroy an array
3056 variable and +r will not remove the readonly attribute. When used in a function, declare and typeset make each name
3057 local, as with the local command, unless the -g option is supplied. If a variable name is followed by =value, the value
3058 of the variable is set to value. When using -a or -A and the compound assignment syntax to create array variables, addiâ€
3059 tional attributes do not take effect until subsequent assignments. The return value is 0 unless an invalid option is
3060 encountered, an attempt is made to define a function using ``-f foo=bar'', an attempt is made to assign a value to a readâ€
3061 only variable, an attempt is made to assign a value to an array variable without using the compound assignment syntax (see
3062 Arrays above), one of the names is not a valid shell variable name, an attempt is made to turn off readonly status for a
3063 readonly variable, an attempt is made to turn off array status for an array variable, or an attempt is made to display a
3064 non-existent function with -f.
3065
3066 dirs [-clpv] [+n] [-n]
3067 Without options, displays the list of currently remembered directories. The default display is on a single line with
3068 directory names separated by spaces. Directories are added to the list with the pushd command; the popd command removes
3069 entries from the list. The current directory is always the first directory in the stack.
3070 -c Clears the directory stack by deleting all of the entries.
3071 -l Produces a listing using full pathnames; the default listing format uses a tilde to denote the home directory.
3072 -p Print the directory stack with one entry per line.
3073 -v Print the directory stack with one entry per line, prefixing each entry with its index in the stack.
3074 +n Displays the nth entry counting from the left of the list shown by dirs when invoked without options, starting with
3075 zero.
3076 -n Displays the nth entry counting from the right of the list shown by dirs when invoked without options, starting
3077 with zero.
3078
3079 The return value is 0 unless an invalid option is supplied or n indexes beyond the end of the directory stack.
3080
3081 disown [-ar] [-h] [jobspec ... | pid ... ]
3082 Without options, remove each jobspec from the table of active jobs. If jobspec is not present, and neither the -a nor the
3083 -r option is supplied, the current job is used. If the -h option is given, each jobspec is not removed from the table,
3084 but is marked so that SIGHUP is not sent to the job if the shell receives a SIGHUP. If no jobspec is supplied, the -a
3085 option means to remove or mark all jobs; the -r option without a jobspec argument restricts operation to running jobs.
3086 The return value is 0 unless a jobspec does not specify a valid job.
3087
3088 echo [-neE] [arg ...]
3089 Output the args, separated by spaces, followed by a newline. The return status is 0 unless a write error occurs. If -n
3090 is specified, the trailing newline is suppressed. If the -e option is given, interpretation of the following backslash-
3091 escaped characters is enabled. The -E option disables the interpretation of these escape characters, even on systems
3092 where they are interpreted by default. The xpg_echo shell option may be used to dynamically determine whether or not echo
3093 expands these escape characters by default. echo does not interpret -- to mean the end of options. echo interprets the
3094 following escape sequences:
3095 \a alert (bell)
3096 \b backspace
3097 \c suppress further output
3098 \e
3099 \E an escape character
3100 \f form feed
3101 \n new line
3102 \r carriage return
3103 \t horizontal tab
3104 \v vertical tab
3105 \\ backslash
3106 \0nnn the eight-bit character whose value is the octal value nnn (zero to three octal digits)
3107 \xHH the eight-bit character whose value is the hexadecimal value HH (one or two hex digits)
3108 \uHHHH the Unicode (ISO/IEC 10646) character whose value is the hexadecimal value HHHH (one to four hex digits)
3109 \UHHHHHHHH
3110 the Unicode (ISO/IEC 10646) character whose value is the hexadecimal value HHHHHHHH (one to eight hex digits)
3111
3112 enable [-a] [-dnps] [-f filename] [name ...]
3113 Enable and disable builtin shell commands. Disabling a builtin allows a disk command which has the same name as a shell
3114 builtin to be executed without specifying a full pathname, even though the shell normally searches for builtins before
3115 disk commands. If -n is used, each name is disabled; otherwise, names are enabled. For example, to use the test binary
3116 found via the PATH instead of the shell builtin version, run ``enable -n test''. The -f option means to load the new
3117 builtin command name from shared object filename, on systems that support dynamic loading. The -d option will delete a
3118 builtin previously loaded with -f. If no name arguments are given, or if the -p option is supplied, a list of shell
3119 builtins is printed. With no other option arguments, the list consists of all enabled shell builtins. If -n is supplied,
3120 only disabled builtins are printed. If -a is supplied, the list printed includes all builtins, with an indication of
3121 whether or not each is enabled. If -s is supplied, the output is restricted to the POSIX special builtins. The return
3122 value is 0 unless a name is not a shell builtin or there is an error loading a new builtin from a shared object.
3123
3124 eval [arg ...]
3125 The args are read and concatenated together into a single command. This command is then read and executed by the shell,
3126 and its exit status is returned as the value of eval. If there are no args, or only null arguments, eval returns 0.
3127
3128 exec [-cl] [-a name] [command [arguments]]
3129 If command is specified, it replaces the shell. No new process is created. The arguments become the arguments to comâ€
3130 mand. If the -l option is supplied, the shell places a dash at the beginning of the zeroth argument passed to command.
3131 This is what login(1) does. The -c option causes command to be executed with an empty environment. If -a is supplied,
3132 the shell passes name as the zeroth argument to the executed command. If command cannot be executed for some reason, a
3133 non-interactive shell exits, unless the execfail shell option is enabled. In that case, it returns failure. An interacâ€
3134 tive shell returns failure if the file cannot be executed. If command is not specified, any redirections take effect in
3135 the current shell, and the return status is 0. If there is a redirection error, the return status is 1.
3136
3137 exit [n]
3138 Cause the shell to exit with a status of n. If n is omitted, the exit status is that of the last command executed. A
3139 trap on EXIT is executed before the shell terminates.
3140
3141 export [-fn] [name[=word]] ...
3142 export -p
3143 The supplied names are marked for automatic export to the environment of subsequently executed commands. If the -f option
3144 is given, the names refer to functions. If no names are given, or if the -p option is supplied, a list of names of all
3145 exported variables is printed. The -n option causes the export property to be removed from each name. If a variable name
3146 is followed by =word, the value of the variable is set to word. export returns an exit status of 0 unless an invalid
3147 option is encountered, one of the names is not a valid shell variable name, or -f is supplied with a name that is not a
3148 function.
3149
3150 fc [-e ename] [-lnr] [first] [last]
3151 fc -s [pat=rep] [cmd]
3152 The first form selects a range of commands from first to last from the history list and displays or edits and re-executes
3153 them. First and last may be specified as a string (to locate the last command beginning with that string) or as a number
3154 (an index into the history list, where a negative number is used as an offset from the current command number). If last
3155 is not specified it is set to the current command for listing (so that ``fc -l -10'' prints the last 10 commands) and to
3156 first otherwise. If first is not specified it is set to the previous command for editing and -16 for listing.
3157
3158 The -n option suppresses the command numbers when listing. The -r option reverses the order of the commands. If the -l
3159 option is given, the commands are listed on standard output. Otherwise, the editor given by ename is invoked on a file
3160 containing those commands. If ename is not given, the value of the FCEDIT variable is used, and the value of EDITOR if
3161 FCEDIT is not set. If neither variable is set, vi is used. When editing is complete, the edited commands are echoed and
3162 executed.
3163
3164 In the second form, command is re-executed after each instance of pat is replaced by rep. Command is intepreted the same
3165 as first above. A useful alias to use with this is ``r="fc -s"'', so that typing ``r cc'' runs the last command beginning
3166 with ``cc'' and typing ``r'' re-executes the last command.
3167
3168 If the first form is used, the return value is 0 unless an invalid option is encountered or first or last specify history
3169 lines out of range. If the -e option is supplied, the return value is the value of the last command executed or failure
3170 if an error occurs with the temporary file of commands. If the second form is used, the return status is that of the comâ€
3171 mand re-executed, unless cmd does not specify a valid history line, in which case fc returns failure.
3172
3173 fg [jobspec]
3174 Resume jobspec in the foreground, and make it the current job. If jobspec is not present, the shell's notion of the curâ€
3175 rent job is used. The return value is that of the command placed into the foreground, or failure if run when job control
3176 is disabled or, when run with job control enabled, if jobspec does not specify a valid job or jobspec specifies a job that
3177 was started without job control.
3178
3179 getopts optstring name [args]
3180 getopts is used by shell procedures to parse positional parameters. optstring contains the option characters to be recogâ€
3181 nized; if a character is followed by a colon, the option is expected to have an argument, which should be separated from
3182 it by white space. The colon and question mark characters may not be used as option characters. Each time it is invoked,
3183 getopts places the next option in the shell variable name, initializing name if it does not exist, and the index of the
3184 next argument to be processed into the variable OPTIND. OPTIND is initialized to 1 each time the shell or a shell script
3185 is invoked. When an option requires an argument, getopts places that argument into the variable OPTARG. The shell does
3186 not reset OPTIND automatically; it must be manually reset between multiple calls to getopts within the same shell invocaâ€
3187 tion if a new set of parameters is to be used.
3188
3189 When the end of options is encountered, getopts exits with a return value greater than zero. OPTIND is set to the index
3190 of the first non-option argument, and name is set to ?.
3191
3192 getopts normally parses the positional parameters, but if more arguments are given in args, getopts parses those instead.
3193
3194 getopts can report errors in two ways. If the first character of optstring is a colon, silent error reporting is used.
3195 In normal operation, diagnostic messages are printed when invalid options or missing option arguments are encountered. If
3196 the variable OPTERR is set to 0, no error messages will be displayed, even if the first character of optstring is not a
3197 colon.
3198
3199 If an invalid option is seen, getopts places ? into name and, if not silent, prints an error message and unsets OPTARG.
3200 If getopts is silent, the option character found is placed in OPTARG and no diagnostic message is printed.
3201
3202 If a required argument is not found, and getopts is not silent, a question mark (?) is placed in name, OPTARG is unset,
3203 and a diagnostic message is printed. If getopts is silent, then a colon (:) is placed in name and OPTARG is set to the
3204 option character found.
3205
3206 getopts returns true if an option, specified or unspecified, is found. It returns false if the end of options is encounâ€
3207 tered or an error occurs.
3208
3209 hash [-lr] [-p filename] [-dt] [name]
3210 Each time hash is invoked, the full pathname of the command name is determined by searching the directories in $PATH and
3211 remembered. Any previously-remembered pathname is discarded. If the -p option is supplied, no path search is performed,
3212 and filename is used as the full filename of the command. The -r option causes the shell to forget all remembered locaâ€
3213 tions. The -d option causes the shell to forget the remembered location of each name. If the -t option is supplied, the
3214 full pathname to which each name corresponds is printed. If multiple name arguments are supplied with -t, the name is
3215 printed before the hashed full pathname. The -l option causes output to be displayed in a format that may be reused as
3216 input. If no arguments are given, or if only -l is supplied, information about remembered commands is printed. The
3217 return status is true unless a name is not found or an invalid option is supplied.
3218
3219 help [-dms] [pattern]
3220 Display helpful information about builtin commands. If pattern is specified, help gives detailed help on all commands
3221 matching pattern; otherwise help for all the builtins and shell control structures is printed.
3222 -d Display a short description of each pattern
3223 -m Display the description of each pattern in a manpage-like format
3224 -s Display only a short usage synopsis for each pattern
3225
3226 The return status is 0 unless no command matches pattern.
3227
3228 history [n]
3229 history -c
3230 history -d offset
3231 history -anrw [filename]
3232 history -p arg [arg ...]
3233 history -s arg [arg ...]
3234 With no options, display the command history list with line numbers. Lines listed with a * have been modified. An arguâ€
3235 ment of n lists only the last n lines. If the shell variable HISTTIMEFORMAT is set and not null, it is used as a format
3236 string for strftime(3) to display the time stamp associated with each displayed history entry. No intervening blank is
3237 printed between the formatted time stamp and the history line. If filename is supplied, it is used as the name of the
3238 history file; if not, the value of HISTFILE is used. Options, if supplied, have the following meanings:
3239 -c Clear the history list by deleting all the entries.
3240 -d offset
3241 Delete the history entry at position offset.
3242 -a Append the ``new'' history lines to the history file. These are history lines entered since the beginning of the
3243 current bash session, but not already appended to the history file.
3244 -n Read the history lines not already read from the history file into the current history list. These are lines
3245 appended to the history file since the beginning of the current bash session.
3246 -r Read the contents of the history file and append them to the current history list.
3247 -w Write the current history list to the history file, overwriting the history file's contents.
3248 -p Perform history substitution on the following args and display the result on the standard output. Does not store
3249 the results in the history list. Each arg must be quoted to disable normal history expansion.
3250 -s Store the args in the history list as a single entry. The last command in the history list is removed before the
3251 args are added.
3252
3253 If the HISTTIMEFORMAT variable is set, the time stamp information associated with each history entry is written to the
3254 history file, marked with the history comment character. When the history file is read, lines beginning with the history
3255 comment character followed immediately by a digit are interpreted as timestamps for the following history entry. The
3256 return value is 0 unless an invalid option is encountered, an error occurs while reading or writing the history file, an
3257 invalid offset is supplied as an argument to -d, or the history expansion supplied as an argument to -p fails.
3258
3259 jobs [-lnprs] [ jobspec ... ]
3260 jobs -x command [ args ... ]
3261 The first form lists the active jobs. The options have the following meanings:
3262 -l List process IDs in addition to the normal information.
3263 -n Display information only about jobs that have changed status since the user was last notified of their status.
3264 -p List only the process ID of the job's process group leader.
3265 -r Display only running jobs.
3266 -s Display only stopped jobs.
3267
3268 If jobspec is given, output is restricted to information about that job. The return status is 0 unless an invalid option
3269 is encountered or an invalid jobspec is supplied.
3270
3271 If the -x option is supplied, jobs replaces any jobspec found in command or args with the corresponding process group ID,
3272 and executes command passing it args, returning its exit status.
3273
3274 kill [-s sigspec | -n signum | -sigspec] [pid | jobspec] ...
3275 kill -l|-L [sigspec | exit_status]
3276 Send the signal named by sigspec or signum to the processes named by pid or jobspec. sigspec is either a case-insensitive
3277 signal name such as SIGKILL (with or without the SIG prefix) or a signal number; signum is a signal number. If sigspec is
3278 not present, then SIGTERM is assumed. An argument of -l lists the signal names. If any arguments are supplied when -l is
3279 given, the names of the signals corresponding to the arguments are listed, and the return status is 0. The exit_status
3280 argument to -l is a number specifying either a signal number or the exit status of a process terminated by a signal. The
3281 -L option is equivalent to -l. kill returns true if at least one signal was successfully sent, or false if an error
3282 occurs or an invalid option is encountered.
3283
3284 let arg [arg ...]
3285 Each arg is an arithmetic expression to be evaluated (see ARITHMETIC EVALUATION above). If the last arg evaluates to 0,
3286 let returns 1; 0 is returned otherwise.
3287
3288 local [option] [name[=value] ... | - ]
3289 For each argument, a local variable named name is created, and assigned value. The option can be any of the options
3290 accepted by declare. When local is used within a function, it causes the variable name to have a visible scope restricted
3291 to that function and its children. If name is -, the set of shell options is made local to the function in which local is
3292 invoked: shell options changed using the set builtin inside the function are restored to their original values when the
3293 function returns. With no operands, local writes a list of local variables to the standard output. It is an error to use
3294 local when not within a function. The return status is 0 unless local is used outside a function, an invalid name is supâ€
3295 plied, or name is a readonly variable.
3296
3297 logout Exit a login shell.
3298
3299 mapfile [-d delim] [-n count] [-O origin] [-s count] [-t] [-u fd] [-C callback] [-c quantum] [array]
3300 readarray [-d delim] [-n count] [-O origin] [-s count] [-t] [-u fd] [-C callback] [-c quantum] [array]
3301 Read lines from the standard input into the indexed array variable array, or from file descriptor fd if the -u option is
3302 supplied. The variable MAPFILE is the default array. Options, if supplied, have the following meanings:
3303 -d The first character of delim is used to terminate each input line, rather than newline.
3304 -n Copy at most count lines. If count is 0, all lines are copied.
3305 -O Begin assigning to array at index origin. The default index is 0.
3306 -s Discard the first count lines read.
3307 -t Remove a trailing delim (default newline) from each line read.
3308 -u Read lines from file descriptor fd instead of the standard input.
3309 -C Evaluate callback each time quantum lines are read. The -c option specifies quantum.
3310 -c Specify the number of lines read between each call to callback.
3311
3312 If -C is specified without -c, the default quantum is 5000. When callback is evaluated, it is supplied the index of the
3313 next array element to be assigned and the line to be assigned to that element as additional arguments. callback is evaluâ€
3314 ated after the line is read but before the array element is assigned.
3315
3316 If not supplied with an explicit origin, mapfile will clear array before assigning to it.
3317
3318 mapfile returns successfully unless an invalid option or option argument is supplied, array is invalid or unassignable, or
3319 if array is not an indexed array.
3320
3321 popd [-n] [+n] [-n]
3322 Removes entries from the directory stack. With no arguments, removes the top directory from the stack, and performs a cd
3323 to the new top directory. Arguments, if supplied, have the following meanings:
3324 -n Suppresses the normal change of directory when removing directories from the stack, so that only the stack is
3325 manipulated.
3326 +n Removes the nth entry counting from the left of the list shown by dirs, starting with zero. For example: ``popd
3327 +0'' removes the first directory, ``popd +1'' the second.
3328 -n Removes the nth entry counting from the right of the list shown by dirs, starting with zero. For example: ``popd
3329 -0'' removes the last directory, ``popd -1'' the next to last.
3330
3331 If the popd command is successful, a dirs is performed as well, and the return status is 0. popd returns false if an
3332 invalid option is encountered, the directory stack is empty, a non-existent directory stack entry is specified, or the
3333 directory change fails.
3334
3335 printf [-v var] format [arguments]
3336 Write the formatted arguments to the standard output under the control of the format. The -v option causes the output to
3337 be assigned to the variable var rather than being printed to the standard output.
3338
3339 The format is a character string which contains three types of objects: plain characters, which are simply copied to stanâ€
3340 dard output, character escape sequences, which are converted and copied to the standard output, and format specifications,
3341 each of which causes printing of the next successive argument. In addition to the standard printf(1) format specificaâ€
3342 tions, printf interprets the following extensions:
3343 %b causes printf to expand backslash escape sequences in the corresponding argument in the same way as echo -e.
3344 %q causes printf to output the corresponding argument in a format that can be reused as shell input.
3345 %(datefmt)T
3346 causes printf to output the date-time string resulting from using datefmt as a format string for strftime(3). The
3347 corresponding argument is an integer representing the number of seconds since the epoch. Two special argument valâ€
3348 ues may be used: -1 represents the current time, and -2 represents the time the shell was invoked. If no argument
3349 is specified, conversion behaves as if -1 had been given. This is an exception to the usual printf behavior.
3350
3351 Arguments to non-string format specifiers are treated as C constants, except that a leading plus or minus sign is allowed,
3352 and if the leading character is a single or double quote, the value is the ASCII value of the following character.
3353
3354 The format is reused as necessary to consume all of the arguments. If the format requires more arguments than are supâ€
3355 plied, the extra format specifications behave as if a zero value or null string, as appropriate, had been supplied. The
3356 return value is zero on success, non-zero on failure.
3357
3358 pushd [-n] [+n] [-n]
3359 pushd [-n] [dir]
3360 Adds a directory to the top of the directory stack, or rotates the stack, making the new top of the stack the current
3361 working directory. With no arguments, pushd exchanges the top two directories and returns 0, unless the directory stack
3362 is empty. Arguments, if supplied, have the following meanings:
3363 -n Suppresses the normal change of directory when rotating or adding directories to the stack, so that only the stack
3364 is manipulated.
3365 +n Rotates the stack so that the nth directory (counting from the left of the list shown by dirs, starting with zero)
3366 is at the top.
3367 -n Rotates the stack so that the nth directory (counting from the right of the list shown by dirs, starting with zero)
3368 is at the top.
3369 dir Adds dir to the directory stack at the top, making it the new current working directory as if it had been supplied
3370 as the argument to the cd builtin.
3371
3372 If the pushd command is successful, a dirs is performed as well. If the first form is used, pushd returns 0 unless the cd
3373 to dir fails. With the second form, pushd returns 0 unless the directory stack is empty, a non-existent directory stack
3374 element is specified, or the directory change to the specified new current directory fails.
3375
3376 pwd [-LP]
3377 Print the absolute pathname of the current working directory. The pathname printed contains no symbolic links if the -P
3378 option is supplied or the -o physical option to the set builtin command is enabled. If the -L option is used, the pathâ€
3379 name printed may contain symbolic links. The return status is 0 unless an error occurs while reading the name of the curâ€
3380 rent directory or an invalid option is supplied.
3381
3382 read [-ers] [-a aname] [-d delim] [-i text] [-n nchars] [-N nchars] [-p prompt] [-t timeout] [-u fd] [name ...]
3383 One line is read from the standard input, or from the file descriptor fd supplied as an argument to the -u option, split
3384 into words as described above under Word Splitting, and the first word is assigned to the first name, the second word to
3385 the second name, and so on. If there are more words than names, the remaining words and their intervening delimiters are
3386 assigned to the last name. If there are fewer words read from the input stream than names, the remaining names are
3387 assigned empty values. The characters in IFS are used to split the line into words using the same rules the shell uses
3388 for expansion (described above under Word Splitting). The backslash character (\) may be used to remove any special meanâ€
3389 ing for the next character read and for line continuation. Options, if supplied, have the following meanings:
3390 -a aname
3391 The words are assigned to sequential indices of the array variable aname, starting at 0. aname is unset before any
3392 new values are assigned. Other name arguments are ignored.
3393 -d delim
3394 The first character of delim is used to terminate the input line, rather than newline.
3395 -e If the standard input is coming from a terminal, readline (see READLINE above) is used to obtain the line. Readâ€
3396 line uses the current (or default, if line editing was not previously active) editing settings.
3397 -i text
3398 If readline is being used to read the line, text is placed into the editing buffer before editing begins.
3399 -n nchars
3400 read returns after reading nchars characters rather than waiting for a complete line of input, but honors a delimâ€
3401 iter if fewer than nchars characters are read before the delimiter.
3402 -N nchars
3403 read returns after reading exactly nchars characters rather than waiting for a complete line of input, unless EOF
3404 is encountered or read times out. Delimiter characters encountered in the input are not treated specially and do
3405 not cause read to return until nchars characters are read. The result is not split on the characters in IFS; the
3406 intent is that the variable is assigned exactly the characters read (with the exception of backslash; see the -r
3407 option below).
3408 -p prompt
3409 Display prompt on standard error, without a trailing newline, before attempting to read any input. The prompt is
3410 displayed only if input is coming from a terminal.
3411 -r Backslash does not act as an escape character. The backslash is considered to be part of the line. In particular,
3412 a backslash-newline pair may not be used as a line continuation.
3413 -s Silent mode. If input is coming from a terminal, characters are not echoed.
3414 -t timeout
3415 Cause read to time out and return failure if a complete line of input (or a specified number of characters) is not
3416 read within timeout seconds. timeout may be a decimal number with a fractional portion following the decimal
3417 point. This option is only effective if read is reading input from a terminal, pipe, or other special file; it has
3418 no effect when reading from regular files. If read times out, read saves any partial input read into the specified
3419 variable name. If timeout is 0, read returns immediately, without trying to read any data. The exit status is 0
3420 if input is available on the specified file descriptor, non-zero otherwise. The exit status is greater than 128 if
3421 the timeout is exceeded.
3422 -u fd Read input from file descriptor fd.
3423
3424 If no names are supplied, the line read is assigned to the variable REPLY. The exit status is zero, unless end-of-file is
3425 encountered, read times out (in which case the status is greater than 128), a variable assignment error (such as assigning
3426 to a readonly variable) occurs, or an invalid file descriptor is supplied as the argument to -u.
3427
3428 readonly [-aAf] [-p] [name[=word] ...]
3429 The given names are marked readonly; the values of these names may not be changed by subsequent assignment. If the -f
3430 option is supplied, the functions corresponding to the names are so marked. The -a option restricts the variables to
3431 indexed arrays; the -A option restricts the variables to associative arrays. If both options are supplied, -A takes
3432 precedence. If no name arguments are given, or if the -p option is supplied, a list of all readonly names is printed.
3433 The other options may be used to restrict the output to a subset of the set of readonly names. The -p option causes outâ€
3434 put to be displayed in a format that may be reused as input. If a variable name is followed by =word, the value of the
3435 variable is set to word. The return status is 0 unless an invalid option is encountered, one of the names is not a valid
3436 shell variable name, or -f is supplied with a name that is not a function.
3437
3438 return [n]
3439 Causes a function to stop executing and return the value specified by n to its caller. If n is omitted, the return status
3440 is that of the last command executed in the function body. If return is executed by a trap handler, the last command used
3441 to determine the status is the last command executed before the trap handler. if return is executed during a DEBUG trap,
3442 the last command used to determine the status is the last command executed by the trap handler before return was invoked.
3443 If return is used outside a function, but during execution of a script by the . (source) command, it causes the shell to
3444 stop executing that script and return either n or the exit status of the last command executed within the script as the
3445 exit status of the script. If n is supplied, the return value is its least significant 8 bits. The return status is non-
3446 zero if return is supplied a non-numeric argument, or is used outside a function and not during execution of a script by .
3447 or source. Any command associated with the RETURN trap is executed before execution resumes after the function or script.
3448
3449 set [--abefhkmnptuvxBCEHPT] [-o option-name] [arg ...]
3450 set [+abefhkmnptuvxBCEHPT] [+o option-name] [arg ...]
3451 Without options, the name and value of each shell variable are displayed in a format that can be reused as input for setâ€
3452 ting or resetting the currently-set variables. Read-only variables cannot be reset. In posix mode, only shell variables
3453 are listed. The output is sorted according to the current locale. When options are specified, they set or unset shell
3454 attributes. Any arguments remaining after option processing are treated as values for the positional parameters and are
3455 assigned, in order, to $1, $2, ... $n. Options, if specified, have the following meanings:
3456 -a Each variable or function that is created or modified is given the export attribute and marked for export to the
3457 environment of subsequent commands.
3458 -b Report the status of terminated background jobs immediately, rather than before the next primary prompt. This is
3459 effective only when job control is enabled.
3460 -e Exit immediately if a pipeline (which may consist of a single simple command), a list, or a compound command (see
3461 SHELL GRAMMAR above), exits with a non-zero status. The shell does not exit if the command that fails is part of
3462 the command list immediately following a while or until keyword, part of the test following the if or elif
3463 reserved words, part of any command executed in a && or || list except the command following the final && or ||,
3464 any command in a pipeline but the last, or if the command's return value is being inverted with !. If a compound
3465 command other than a subshell returns a non-zero status because a command failed while -e was being ignored, the
3466 shell does not exit. A trap on ERR, if set, is executed before the shell exits. This option applies to the shell
3467 environment and each subshell environment separately (see COMMAND EXECUTION ENVIRONMENT above), and may cause subâ€
3468 shells to exit before executing all the commands in the subshell.
3469
3470 If a compound command or shell function executes in a context where -e is being ignored, none of the commands exeâ€
3471 cuted within the compound command or function body will be affected by the -e setting, even if -e is set and a
3472 command returns a failure status. If a compound command or shell function sets -e while executing in a context
3473 where -e is ignored, that setting will not have any effect until the compound command or the command containing
3474 the function call completes.
3475 -f Disable pathname expansion.
3476 -h Remember the location of commands as they are looked up for execution. This is enabled by default.
3477 -k All arguments in the form of assignment statements are placed in the environment for a command, not just those
3478 that precede the command name.
3479 -m Monitor mode. Job control is enabled. This option is on by default for interactive shells on systems that supâ€
3480 port it (see JOB CONTROL above). All processes run in a separate process group. When a background job completes,
3481 the shell prints a line containing its exit status.
3482 -n Read commands but do not execute them. This may be used to check a shell script for syntax errors. This is
3483 ignored by interactive shells.
3484 -o option-name
3485 The option-name can be one of the following:
3486 allexport
3487 Same as -a.
3488 braceexpand
3489 Same as -B.
3490 emacs Use an emacs-style command line editing interface. This is enabled by default when the shell is interacâ€
3491 tive, unless the shell is started with the --noediting option. This also affects the editing interface
3492 used for read -e.
3493 errexit Same as -e.
3494 errtrace
3495 Same as -E.
3496 functrace
3497 Same as -T.
3498 hashall Same as -h.
3499 histexpand
3500 Same as -H.
3501 history Enable command history, as described above under HISTORY. This option is on by default in interactive
3502 shells.
3503 ignoreeof
3504 The effect is as if the shell command ``IGNOREEOF=10'' had been executed (see Shell Variables above).
3505 keyword Same as -k.
3506 monitor Same as -m.
3507 noclobber
3508 Same as -C.
3509 noexec Same as -n.
3510 noglob Same as -f.
3511 nolog Currently ignored.
3512 notify Same as -b.
3513 nounset Same as -u.
3514 onecmd Same as -t.
3515 physical
3516 Same as -P.
3517 pipefail
3518 If set, the return value of a pipeline is the value of the last (rightmost) command to exit with a non-
3519 zero status, or zero if all commands in the pipeline exit successfully. This option is disabled by
3520 default.
3521 posix Change the behavior of bash where the default operation differs from the POSIX standard to match the stanâ€
3522 dard (posix mode). See SEE ALSO below for a reference to a document that details how posix mode affects
3523 bash's behavior.
3524 privileged
3525 Same as -p.
3526 verbose Same as -v.
3527 vi Use a vi-style command line editing interface. This also affects the editing interface used for read -e.
3528 xtrace Same as -x.
3529 If -o is supplied with no option-name, the values of the current options are printed. If +o is supplied with no
3530 option-name, a series of set commands to recreate the current option settings is displayed on the standard output.
3531 -p Turn on privileged mode. In this mode, the $ENV and $BASH_ENV files are not processed, shell functions are not
3532 inherited from the environment, and the SHELLOPTS, BASHOPTS, CDPATH, and GLOBIGNORE variables, if they appear in
3533 the environment, are ignored. If the shell is started with the effective user (group) id not equal to the real
3534 user (group) id, and the -p option is not supplied, these actions are taken and the effective user id is set to
3535 the real user id. If the -p option is supplied at startup, the effective user id is not reset. Turning this
3536 option off causes the effective user and group ids to be set to the real user and group ids.
3537 -t Exit after reading and executing one command.
3538 -u Treat unset variables and parameters other than the special parameters "@" and "*" as an error when performing
3539 parameter expansion. If expansion is attempted on an unset variable or parameter, the shell prints an error mesâ€
3540 sage, and, if not interactive, exits with a non-zero status.
3541 -v Print shell input lines as they are read.
3542 -x After expanding each simple command, for command, case command, select command, or arithmetic for command, display
3543 the expanded value of PS4, followed by the command and its expanded arguments or associated word list.
3544 -B The shell performs brace expansion (see Brace Expansion above). This is on by default.
3545 -C If set, bash does not overwrite an existing file with the >, >&, and <> redirection operators. This may be overâ€
3546 ridden when creating output files by using the redirection operator >| instead of >.
3547 -E If set, any trap on ERR is inherited by shell functions, command substitutions, and commands executed in a subâ€
3548 shell environment. The ERR trap is normally not inherited in such cases.
3549 -H Enable ! style history substitution. This option is on by default when the shell is interactive.
3550 -P If set, the shell does not resolve symbolic links when executing commands such as cd that change the current workâ€
3551 ing directory. It uses the physical directory structure instead. By default, bash follows the logical chain of
3552 directories when performing commands which change the current directory.
3553 -T If set, any traps on DEBUG and RETURN are inherited by shell functions, command substitutions, and commands exeâ€
3554 cuted in a subshell environment. The DEBUG and RETURN traps are normally not inherited in such cases.
3555 -- If no arguments follow this option, then the positional parameters are unset. Otherwise, the positional parameâ€
3556 ters are set to the args, even if some of them begin with a -.
3557 - Signal the end of options, cause all remaining args to be assigned to the positional parameters. The -x and -v
3558 options are turned off. If there are no args, the positional parameters remain unchanged.
3559
3560 The options are off by default unless otherwise noted. Using + rather than - causes these options to be turned off. The
3561 options can also be specified as arguments to an invocation of the shell. The current set of options may be found in $-.
3562 The return status is always true unless an invalid option is encountered.
3563
3564 shift [n]
3565 The positional parameters from n+1 ... are renamed to $1 .... Parameters represented by the numbers $# down to $#-n+1 are
3566 unset. n must be a non-negative number less than or equal to $#. If n is 0, no parameters are changed. If n is not
3567 given, it is assumed to be 1. If n is greater than $#, the positional parameters are not changed. The return status is
3568 greater than zero if n is greater than $# or less than zero; otherwise 0.
3569
3570 shopt [-pqsu] [-o] [optname ...]
3571 Toggle the values of settings controlling optional shell behavior. The settings can be either those listed below, or, if
3572 the -o option is used, those available with the -o option to the set builtin command. With no options, or with the -p
3573 option, a list of all settable options is displayed, with an indication of whether or not each is set. The -p option
3574 causes output to be displayed in a form that may be reused as input. Other options have the following meanings:
3575 -s Enable (set) each optname.
3576 -u Disable (unset) each optname.
3577 -q Suppresses normal output (quiet mode); the return status indicates whether the optname is set or unset. If multiâ€
3578 ple optname arguments are given with -q, the return status is zero if all optnames are enabled; non-zero otherwise.
3579 -o Restricts the values of optname to be those defined for the -o option to the set builtin.
3580
3581 If either -s or -u is used with no optname arguments, shopt shows only those options which are set or unset, respectively.
3582 Unless otherwise noted, the shopt options are disabled (unset) by default.
3583
3584 The return status when listing options is zero if all optnames are enabled, non-zero otherwise. When setting or unsetting
3585 options, the return status is zero unless an optname is not a valid shell option.
3586
3587 The list of shopt options is:
3588
3589 autocd If set, a command name that is the name of a directory is executed as if it were the argument to the cd command.
3590 This option is only used by interactive shells.
3591 cdable_vars
3592 If set, an argument to the cd builtin command that is not a directory is assumed to be the name of a variable
3593 whose value is the directory to change to.
3594 cdspell If set, minor errors in the spelling of a directory component in a cd command will be corrected. The errors
3595 checked for are transposed characters, a missing character, and one character too many. If a correction is found,
3596 the corrected filename is printed, and the command proceeds. This option is only used by interactive shells.
3597 checkhash
3598 If set, bash checks that a command found in the hash table exists before trying to execute it. If a hashed comâ€
3599 mand no longer exists, a normal path search is performed.
3600 checkjobs
3601 If set, bash lists the status of any stopped and running jobs before exiting an interactive shell. If any jobs
3602 are running, this causes the exit to be deferred until a second exit is attempted without an intervening command
3603 (see JOB CONTROL above). The shell always postpones exiting if any jobs are stopped.
3604 checkwinsize
3605 If set, bash checks the window size after each command and, if necessary, updates the values of LINES and COLUMNS.
3606 cmdhist If set, bash attempts to save all lines of a multiple-line command in the same history entry. This allows easy
3607 re-editing of multi-line commands.
3608 compat31
3609 If set, bash changes its behavior to that of version 3.1 with respect to quoted arguments to the [[ conditional
3610 command's =~ operator and locale-specific string comparison when using the [[ conditional command's < and > operaâ€
3611 tors. Bash versions prior to bash-4.1 use ASCII collation and strcmp(3); bash-4.1 and later use the current
3612 locale's collation sequence and strcoll(3).
3613 compat32
3614 If set, bash changes its behavior to that of version 3.2 with respect to locale-specific string comparison when
3615 using the [[ conditional command's < and > operators (see previous item) and the effect of interrupting a command
3616 list. Bash versions 3.2 and earlier continue with the next command in the list after one terminates due to an
3617 interrupt.
3618 compat40
3619 If set, bash changes its behavior to that of version 4.0 with respect to locale-specific string comparison when
3620 using the [[ conditional command's < and > operators (see description of compat31) and the effect of interrupting
3621 a command list. Bash versions 4.0 and later interrupt the list as if the shell received the interrupt; previous
3622 versions continue with the next command in the list.
3623 compat41
3624 If set, bash, when in posix mode, treats a single quote in a double-quoted parameter expansion as a special charâ€
3625 acter. The single quotes must match (an even number) and the characters between the single quotes are considered
3626 quoted. This is the behavior of posix mode through version 4.1. The default bash behavior remains as in previous
3627 versions.
3628 compat42
3629 If set, bash does not process the replacement string in the pattern substitution word expansion using quote
3630 removal.
3631 compat43
3632 If set, bash does not print a warning message if an attempt is made to use a quoted compound array assignment as
3633 an argument to declare, makes word expansion errors non-fatal errors that cause the current command to fail (the
3634 default behavior is to make them fatal errors that cause the shell to exit), and does not reset the loop state
3635 when a shell function is executed (this allows break or continue in a shell function to affect loops in the callâ€
3636 er's context).
3637 complete_fullquote
3638 If set, bash quotes all shell metacharacters in filenames and directory names when performing completion. If not
3639 set, bash removes metacharacters such as the dollar sign from the set of characters that will be quoted in comâ€
3640 pleted filenames when these metacharacters appear in shell variable references in words to be completed. This
3641 means that dollar signs in variable names that expand to directories will not be quoted; however, any dollar signs
3642 appearing in filenames will not be quoted, either. This is active only when bash is using backslashes to quote
3643 completed filenames. This variable is set by default, which is the default bash behavior in versions through 4.2.
3644 direxpand
3645 If set, bash replaces directory names with the results of word expansion when performing filename completion.
3646 This changes the contents of the readline editing buffer. If not set, bash attempts to preserve what the user
3647 typed.
3648 dirspell
3649 If set, bash attempts spelling correction on directory names during word completion if the directory name iniâ€
3650 tially supplied does not exist.
3651 dotglob If set, bash includes filenames beginning with a `.' in the results of pathname expansion.
3652 execfail
3653 If set, a non-interactive shell will not exit if it cannot execute the file specified as an argument to the exec
3654 builtin command. An interactive shell does not exit if exec fails.
3655 expand_aliases
3656 If set, aliases are expanded as described above under ALIASES. This option is enabled by default for interactive
3657 shells.
3658 extdebug
3659 If set at shell invocation, arrange to execute the debugger profile before the shell starts, identical to the
3660 --debugger option. If set after invocation, behavior intended for use by debuggers is enabled:
3661 1. The -F option to the declare builtin displays the source file name and line number corresponding to each
3662 function name supplied as an argument.
3663 2. If the command run by the DEBUG trap returns a non-zero value, the next command is skipped and not exeâ€
3664 cuted.
3665 3. If the command run by the DEBUG trap returns a value of 2, and the shell is executing in a subroutine (a
3666 shell function or a shell script executed by the . or source builtins), the shell simulates a call to
3667 return.
3668 4. BASH_ARGC and BASH_ARGV are updated as described in their descriptions above.
3669 5. Function tracing is enabled: command substitution, shell functions, and subshells invoked with ( command )
3670 inherit the DEBUG and RETURN traps.
3671 6. Error tracing is enabled: command substitution, shell functions, and subshells invoked with ( command )
3672 inherit the ERR trap.
3673 extglob If set, the extended pattern matching features described above under Pathname Expansion are enabled.
3674 extquote
3675 If set, $'string' and $"string" quoting is performed within ${parameter} expansions enclosed in double quotes.
3676 This option is enabled by default.
3677 failglob
3678 If set, patterns which fail to match filenames during pathname expansion result in an expansion error.
3679 force_fignore
3680 If set, the suffixes specified by the FIGNORE shell variable cause words to be ignored when performing word comâ€
3681 pletion even if the ignored words are the only possible completions. See SHELL VARIABLES above for a description
3682 of FIGNORE. This option is enabled by default.
3683 globasciiranges
3684 If set, range expressions used in pattern matching bracket expressions (see Pattern Matching above) behave as if
3685 in the traditional C locale when performing comparisons. That is, the current locale's collating sequence is not
3686 taken into account, so b will not collate between A and B, and upper-case and lower-case ASCII characters will
3687 collate together.
3688 globstar
3689 If set, the pattern ** used in a pathname expansion context will match all files and zero or more directories and
3690 subdirectories. If the pattern is followed by a /, only directories and subdirectories match.
3691 gnu_errfmt
3692 If set, shell error messages are written in the standard GNU error message format.
3693 histappend
3694 If set, the history list is appended to the file named by the value of the HISTFILE variable when the shell exits,
3695 rather than overwriting the file.
3696 histreedit
3697 If set, and readline is being used, a user is given the opportunity to re-edit a failed history substitution.
3698 histverify
3699 If set, and readline is being used, the results of history substitution are not immediately passed to the shell
3700 parser. Instead, the resulting line is loaded into the readline editing buffer, allowing further modification.
3701 hostcomplete
3702 If set, and readline is being used, bash will attempt to perform hostname completion when a word containing a @ is
3703 being completed (see Completing under READLINE above). This is enabled by default.
3704 huponexit
3705 If set, bash will send SIGHUP to all jobs when an interactive login shell exits.
3706 inherit_errexit
3707 If set, command substitution inherits the value of the errexit option, instead of unsetting it in the subshell
3708 environment. This option is enabled when posix mode is enabled.
3709 interactive_comments
3710 If set, allow a word beginning with # to cause that word and all remaining characters on that line to be ignored
3711 in an interactive shell (see COMMENTS above). This option is enabled by default.
3712 lastpipe
3713 If set, and job control is not active, the shell runs the last command of a pipeline not executed in the backâ€
3714 ground in the current shell environment.
3715 lithist If set, and the cmdhist option is enabled, multi-line commands are saved to the history with embedded newlines
3716 rather than using semicolon separators where possible.
3717 login_shell
3718 The shell sets this option if it is started as a login shell (see INVOCATION above). The value may not be
3719 changed.
3720 mailwarn
3721 If set, and a file that bash is checking for mail has been accessed since the last time it was checked, the mesâ€
3722 sage ``The mail in mailfile has been read'' is displayed.
3723 no_empty_cmd_completion
3724 If set, and readline is being used, bash will not attempt to search the PATH for possible completions when compleâ€
3725 tion is attempted on an empty line.
3726 nocaseglob
3727 If set, bash matches filenames in a case-insensitive fashion when performing pathname expansion (see Pathname
3728 Expansion above).
3729 nocasematch
3730 If set, bash matches patterns in a case-insensitive fashion when performing matching while executing case or [[
3731 conditional commands, when performing pattern substitution word expansions, or when filtering possible completions
3732 as part of programmable completion.
3733 nullglob
3734 If set, bash allows patterns which match no files (see Pathname Expansion above) to expand to a null string,
3735 rather than themselves.
3736 progcomp
3737 If set, the programmable completion facilities (see Programmable Completion above) are enabled. This option is
3738 enabled by default.
3739 promptvars
3740 If set, prompt strings undergo parameter expansion, command substitution, arithmetic expansion, and quote removal
3741 after being expanded as described in PROMPTING above. This option is enabled by default.
3742 restricted_shell
3743 The shell sets this option if it is started in restricted mode (see RESTRICTED SHELL below). The value may not be
3744 changed. This is not reset when the startup files are executed, allowing the startup files to discover whether or
3745 not a shell is restricted.
3746 shift_verbose
3747 If set, the shift builtin prints an error message when the shift count exceeds the number of positional parameâ€
3748 ters.
3749 sourcepath
3750 If set, the source (.) builtin uses the value of PATH to find the directory containing the file supplied as an
3751 argument. This option is enabled by default.
3752 xpg_echo
3753 If set, the echo builtin expands backslash-escape sequences by default.
3754
3755 suspend [-f]
3756 Suspend the execution of this shell until it receives a SIGCONT signal. A login shell cannot be suspended; the -f option
3757 can be used to override this and force the suspension. The return status is 0 unless the shell is a login shell and -f is
3758 not supplied, or if job control is not enabled.
3759
3760 test expr
3761 [ expr ]
3762 Return a status of 0 (true) or 1 (false) depending on the evaluation of the conditional expression expr. Each operator
3763 and operand must be a separate argument. Expressions are composed of the primaries described above under CONDITIONAL
3764 EXPRESSIONS. test does not accept any options, nor does it accept and ignore an argument of -- as signifying the end of
3765 options.
3766
3767 Expressions may be combined using the following operators, listed in decreasing order of precedence. The evaluation
3768 depends on the number of arguments; see below. Operator precedence is used when there are five or more arguments.
3769 ! expr True if expr is false.
3770 ( expr )
3771 Returns the value of expr. This may be used to override the normal precedence of operators.
3772 expr1 -a expr2
3773 True if both expr1 and expr2 are true.
3774 expr1 -o expr2
3775 True if either expr1 or expr2 is true.
3776
3777 test and [ evaluate conditional expressions using a set of rules based on the number of arguments.
3778
3779 0 arguments
3780 The expression is false.
3781 1 argument
3782 The expression is true if and only if the argument is not null.
3783 2 arguments
3784 If the first argument is !, the expression is true if and only if the second argument is null. If the first arguâ€
3785 ment is one of the unary conditional operators listed above under CONDITIONAL EXPRESSIONS, the expression is true
3786 if the unary test is true. If the first argument is not a valid unary conditional operator, the expression is
3787 false.
3788 3 arguments
3789 The following conditions are applied in the order listed. If the second argument is one of the binary conditional
3790 operators listed above under CONDITIONAL EXPRESSIONS, the result of the expression is the result of the binary test
3791 using the first and third arguments as operands. The -a and -o operators are considered binary operators when
3792 there are three arguments. If the first argument is !, the value is the negation of the two-argument test using
3793 the second and third arguments. If the first argument is exactly ( and the third argument is exactly ), the result
3794 is the one-argument test of the second argument. Otherwise, the expression is false.
3795 4 arguments
3796 If the first argument is !, the result is the negation of the three-argument expression composed of the remaining
3797 arguments. Otherwise, the expression is parsed and evaluated according to precedence using the rules listed above.
3798 5 or more arguments
3799 The expression is parsed and evaluated according to precedence using the rules listed above.
3800
3801 When used with test or [, the < and > operators sort lexicographically using ASCII ordering.
3802
3803 times Print the accumulated user and system times for the shell and for processes run from the shell. The return status is 0.
3804
3805 trap [-lp] [[arg] sigspec ...]
3806 The command arg is to be read and executed when the shell receives signal(s) sigspec. If arg is absent (and there is a
3807 single sigspec) or -, each specified signal is reset to its original disposition (the value it had upon entrance to the
3808 shell). If arg is the null string the signal specified by each sigspec is ignored by the shell and by the commands it
3809 invokes. If arg is not present and -p has been supplied, then the trap commands associated with each sigspec are disâ€
3810 played. If no arguments are supplied or if only -p is given, trap prints the list of commands associated with each sigâ€
3811 nal. The -l option causes the shell to print a list of signal names and their corresponding numbers. Each sigspec is
3812 either a signal name defined in <signal.h>, or a signal number. Signal names are case insensitive and the SIG prefix is
3813 optional.
3814
3815 If a sigspec is EXIT (0) the command arg is executed on exit from the shell. If a sigspec is DEBUG, the command arg is
3816 executed before every simple command, for command, case command, select command, every arithmetic for command, and before
3817 the first command executes in a shell function (see SHELL GRAMMAR above). Refer to the description of the extdebug option
3818 to the shopt builtin for details of its effect on the DEBUG trap. If a sigspec is RETURN, the command arg is executed
3819 each time a shell function or a script executed with the . or source builtins finishes executing.
3820
3821 If a sigspec is ERR, the command arg is executed whenever a pipeline (which may consist of a single simple command), a
3822 list, or a compound command returns a non-zero exit status, subject to the following conditions. The ERR trap is not exeâ€
3823 cuted if the failed command is part of the command list immediately following a while or until keyword, part of the test
3824 in an if statement, part of a command executed in a && or || list except the command following the final && or ||, any
3825 command in a pipeline but the last, or if the command's return value is being inverted using !. These are the same condiâ€
3826 tions obeyed by the errexit (-e) option.
3827
3828 Signals ignored upon entry to the shell cannot be trapped or reset. Trapped signals that are not being ignored are reset
3829 to their original values in a subshell or subshell environment when one is created. The return status is false if any
3830 sigspec is invalid; otherwise trap returns true.
3831
3832 type [-aftpP] name [name ...]
3833 With no options, indicate how each name would be interpreted if used as a command name. If the -t option is used, type
3834 prints a string which is one of alias, keyword, function, builtin, or file if name is an alias, shell reserved word, funcâ€
3835 tion, builtin, or disk file, respectively. If the name is not found, then nothing is printed, and an exit status of false
3836 is returned. If the -p option is used, type either returns the name of the disk file that would be executed if name were
3837 specified as a command name, or nothing if ``type -t name'' would not return file. The -P option forces a PATH search for
3838 each name, even if ``type -t name'' would not return file. If a command is hashed, -p and -P print the hashed value,
3839 which is not necessarily the file that appears first in PATH. If the -a option is used, type prints all of the places
3840 that contain an executable named name. This includes aliases and functions, if and only if the -p option is not also
3841 used. The table of hashed commands is not consulted when using -a. The -f option suppresses shell function lookup, as
3842 with the command builtin. type returns true if all of the arguments are found, false if any are not found.
3843
3844 ulimit [-HSabcdefiklmnpqrstuvxPT [limit]]
3845 Provides control over the resources available to the shell and to processes started by it, on systems that allow such conâ€
3846 trol. The -H and -S options specify that the hard or soft limit is set for the given resource. A hard limit cannot be
3847 increased by a non-root user once it is set; a soft limit may be increased up to the value of the hard limit. If neither
3848 -H nor -S is specified, both the soft and hard limits are set. The value of limit can be a number in the unit specified
3849 for the resource or one of the special values hard, soft, or unlimited, which stand for the current hard limit, the curâ€
3850 rent soft limit, and no limit, respectively. If limit is omitted, the current value of the soft limit of the resource is
3851 printed, unless the -H option is given. When more than one resource is specified, the limit name and unit are printed
3852 before the value. Other options are interpreted as follows:
3853 -a All current limits are reported
3854 -b The maximum socket buffer size
3855 -c The maximum size of core files created
3856 -d The maximum size of a process's data segment
3857 -e The maximum scheduling priority ("nice")
3858 -f The maximum size of files written by the shell and its children
3859 -i The maximum number of pending signals
3860 -k The maximum number of kqueues that may be allocated
3861 -l The maximum size that may be locked into memory
3862 -m The maximum resident set size (many systems do not honor this limit)
3863 -n The maximum number of open file descriptors (most systems do not allow this value to be set)
3864 -p The pipe size in 512-byte blocks (this may not be set)
3865 -q The maximum number of bytes in POSIX message queues
3866 -r The maximum real-time scheduling priority
3867 -s The maximum stack size
3868 -t The maximum amount of cpu time in seconds
3869 -u The maximum number of processes available to a single user
3870 -v The maximum amount of virtual memory available to the shell and, on some systems, to its children
3871 -x The maximum number of file locks
3872 -P The maximum number of pseudoterminals
3873 -T The maximum number of threads
3874
3875 If limit is given, and the -a option is not used, limit is the new value of the specified resource. If no option is
3876 given, then -f is assumed. Values are in 1024-byte increments, except for -t, which is in seconds; -p, which is in units
3877 of 512-byte blocks; -P, -T, -b, -k, -n, and -u, which are unscaled values; and, when in Posix mode, -c and -f, which are
3878 in 512-byte increments. The return status is 0 unless an invalid option or argument is supplied, or an error occurs while
3879 setting a new limit.
3880
3881 umask [-p] [-S] [mode]
3882 The user file-creation mask is set to mode. If mode begins with a digit, it is interpreted as an octal number; otherwise
3883 it is interpreted as a symbolic mode mask similar to that accepted by chmod(1). If mode is omitted, the current value of
3884 the mask is printed. The -S option causes the mask to be printed in symbolic form; the default output is an octal number.
3885 If the -p option is supplied, and mode is omitted, the output is in a form that may be reused as input. The return status
3886 is 0 if the mode was successfully changed or if no mode argument was supplied, and false otherwise.
3887
3888 unalias [-a] [name ...]
3889 Remove each name from the list of defined aliases. If -a is supplied, all alias definitions are removed. The return
3890 value is true unless a supplied name is not a defined alias.
3891
3892 unset [-fv] [-n] [name ...]
3893 For each name, remove the corresponding variable or function. If the -v option is given, each name refers to a shell
3894 variable, and that variable is removed. Read-only variables may not be unset. If -f is specified, each name refers to a
3895 shell function, and the function definition is removed. If the -n option is supplied, and name is a variable with the
3896 nameref attribute, name will be unset rather than the variable it references. -n has no effect if the -f option is supâ€
3897 plied. If no options are supplied, each name refers to a variable; if there is no variable by that name, any function
3898 with that name is unset. Each unset variable or function is removed from the environment passed to subsequent commands.
3899 If any of COMP_WORDBREAKS, RANDOM, SECONDS, LINENO, HISTCMD, FUNCNAME, GROUPS, or DIRSTACK are unset, they lose their speâ€
3900 cial properties, even if they are subsequently reset. The exit status is true unless a name is readonly.
3901
3902 wait [-n] [n ...]
3903 Wait for each specified child process and return its termination status. Each n may be a process ID or a job specificaâ€
3904 tion; if a job spec is given, all processes in that job's pipeline are waited for. If n is not given, all currently
3905 active child processes are waited for, and the return status is zero. If the -n option is supplied, wait waits for any
3906 job to terminate and returns its exit status. If n specifies a non-existent process or job, the return status is 127.
3907 Otherwise, the return status is the exit status of the last process or job waited for.
3908
3909RESTRICTED SHELL
3910 If bash is started with the name rbash, or the -r option is supplied at invocation, the shell becomes restricted. A restricted
3911 shell is used to set up an environment more controlled than the standard shell. It behaves identically to bash with the excepâ€
3912 tion that the following are disallowed or not performed:
3913
3914 · changing directories with cd
3915
3916 · setting or unsetting the values of SHELL, PATH, ENV, or BASH_ENV
3917
3918 · specifying command names containing /
3919
3920 · specifying a filename containing a / as an argument to the . builtin command
3921
3922 · specifying a filename containing a slash as an argument to the -p option to the hash builtin command
3923
3924 · importing function definitions from the shell environment at startup
3925
3926 · parsing the value of SHELLOPTS from the shell environment at startup
3927
3928 · redirecting output using the >, >|, <>, >&, &>, and >> redirection operators
3929
3930 · using the exec builtin command to replace the shell with another command
3931
3932 · adding or deleting builtin commands with the -f and -d options to the enable builtin command
3933
3934 · using the enable builtin command to enable disabled shell builtins
3935
3936 · specifying the -p option to the command builtin command
3937
3938 · turning off restricted mode with set +r or set +o restricted.
3939
3940 These restrictions are enforced after any startup files are read.
3941
3942 When a command that is found to be a shell script is executed (see COMMAND EXECUTION above), rbash turns off any restrictions in
3943 the shell spawned to execute the script.
3944
3945SEE ALSO
3946 Bash Reference Manual, Brian Fox and Chet Ramey
3947 The Gnu Readline Library, Brian Fox and Chet Ramey
3948 The Gnu History Library, Brian Fox and Chet Ramey
3949 Portable Operating System Interface (POSIX) Part 2: Shell and Utilities, IEEE --
3950 http://pubs.opengroup.org/onlinepubs/9699919799/
3951 http://tiswww.case.edu/~chet/bash/POSIX -- a description of posix mode
3952 sh(1), ksh(1), csh(1)
3953 emacs(1), vi(1)
3954 readline(3)
3955
3956FILES
3957 /bin/bash
3958 The bash executable
3959 /etc/profile
3960 The systemwide initialization file, executed for login shells
3961 /etc/bash.bashrc
3962 The systemwide per-interactive-shell startup file
3963 /etc/bash.bash.logout
3964 The systemwide login shell cleanup file, executed when a login shell exits
3965 ~/.bash_profile
3966 The personal initialization file, executed for login shells
3967 ~/.bashrc
3968 The individual per-interactive-shell startup file
3969 ~/.bash_logout
3970 The individual login shell cleanup file, executed when a login shell exits
3971 ~/.inputrc
3972 Individual readline initialization file
3973
3974AUTHORS
3975 Brian Fox, Free Software Foundation
3976 bfox@gnu.org
3977
3978 Chet Ramey, Case Western Reserve University
3979 chet.ramey@case.edu
3980
3981BUG REPORTS
3982 If you find a bug in bash, you should report it. But first, you should make sure that it really is a bug, and that it appears in
3983 the latest version of bash. The latest version is always available from ftp://ftp.gnu.org/pub/gnu/bash/.
3984
3985 Once you have determined that a bug actually exists, use the bashbug command to submit a bug report. If you have a fix, you are
3986 encouraged to mail that as well! Suggestions and `philosophical' bug reports may be mailed to bug-bash@gnu.org or posted to the
3987 Usenet newsgroup gnu.bash.bug.
3988
3989 ALL bug reports should include:
3990
3991 The version number of bash
3992 The hardware and operating system
3993 The compiler used to compile
3994 A description of the bug behaviour
3995 A short script or `recipe' which exercises the bug
3996
3997 bashbug inserts the first three items automatically into the template it provides for filing a bug report.
3998
3999 Comments and bug reports concerning this manual page should be directed to chet.ramey@case.edu.
4000
4001BUGS
4002 It's too big and too slow.
4003
4004 There are some subtle differences between bash and traditional versions of sh, mostly because of the POSIX specification.
4005
4006 Aliases are confusing in some uses.
4007
4008 Shell builtin commands and functions are not stoppable/restartable.
4009
4010 Compound commands and command sequences of the form `a ; b ; c' are not handled gracefully when process suspension is attempted.
4011 When a process is stopped, the shell immediately executes the next command in the sequence. It suffices to place the sequence of
4012 commands between parentheses to force it into a subshell, which may be stopped as a unit.
4013
4014 Array variables may not (yet) be exported.
4015
4016 There may be only one active coprocess at a time.
4017
4018GNU Bash 4.4 2016 August 26 BASH(1)