1BASH_BUILTINS(1)            General Commands Manual           BASH_BUILTINS(1)
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NAME

6       bash,  :,  .,  [, alias, bg, bind, break, builtin, caller, cd, command,
7       compgen, complete, compopt,  continue,  declare,  dirs,  disown,  echo,
8       enable,  eval,  exec, exit, export, false, fc, fg, getopts, hash, help,
9       history, jobs, kill, let, local, logout, mapfile, popd, printf,  pushd,
10       pwd,  read, readonly, return, set, shift, shopt, source, suspend, test,
11       times, trap, true, type, typeset, ulimit, umask, unalias, unset, wait -
12       bash built-in commands, see bash(1)
13

BASH BUILTIN COMMANDS

15       Unless otherwise noted, each builtin command documented in this section
16       as accepting options preceded by - accepts -- to signify the end of the
17       options.   The  :, true, false, and test builtins do not accept options
18       and do not treat -- specially.  The exit, logout, return,  break,  con‐
19       tinue,  let,  and shift builtins accept and process arguments beginning
20       with - without requiring --.  Other builtins that accept arguments  but
21       are  not  specified  as accepting options interpret arguments beginning
22       with - as invalid options and require -- to  prevent  this  interpreta‐
23       tion.
24       : [arguments]
25              No  effect;  the command does nothing beyond expanding arguments
26              and performing any specified redirections.  The return status is
27              zero.
28
29        .  filename [arguments]
30       source filename [arguments]
31              Read  and  execute  commands  from filename in the current shell
32              environment and return the exit status of the last command  exe‐
33              cuted  from  filename.   If  filename  does not contain a slash,
34              filenames in PATH are used  to  find  the  directory  containing
35              filename.  The file searched for in PATH need not be executable.
36              When bash is  not  in  posix  mode,  the  current  directory  is
37              searched  if no file is found in PATH.  If the sourcepath option
38              to the shopt builtin command is turned  off,  the  PATH  is  not
39              searched.   If any arguments are supplied, they become the posi‐
40              tional parameters when  filename  is  executed.   Otherwise  the
41              positional  parameters  are  unchanged.   If  the  -T  option is
42              enabled, source inherits any trap on DEBUG; if it  is  not,  any
43              DEBUG  trap  string  is  saved  and  restored around the call to
44              source, and source unsets the DEBUG trap while it executes.   If
45              -T  is not set, and the sourced file changes the DEBUG trap, the
46              new value is retained when source completes.  The return  status
47              is the status of the last command exited within the script (0 if
48              no commands are executed), and false if filename is not found or
49              cannot be read.
50
51       alias [-p] [name[=value] ...]
52              Alias with no arguments or with the -p option prints the list of
53              aliases in the form alias name=value on standard  output.   When
54              arguments  are supplied, an alias is defined for each name whose
55              value is given.  A trailing space in value causes the next  word
56              to be checked for alias substitution when the alias is expanded.
57              For each name in the argument list for which no  value  is  sup‐
58              plied,  the  name  and  value  of  the  alias is printed.  Alias
59              returns true unless a name is given for which no alias has  been
60              defined.
61
62       bg [jobspec ...]
63              Resume  each  suspended  job jobspec in the background, as if it
64              had been started with &.  If jobspec is not present, the shell's
65              notion  of the current job is used.  bg jobspec returns 0 unless
66              run when job control is disabled or, when run with  job  control
67              enabled,  any  specified  jobspec  was  not found or was started
68              without job control.
69
70       bind [-m keymap] [-lpsvPSVX]
71       bind [-m keymap] [-q function] [-u function] [-r keyseq]
72       bind [-m keymap] -f filename
73       bind [-m keymap] -x keyseq:shell-command
74       bind [-m keymap] keyseq:function-name
75       bind [-m keymap] keyseq:readline-command
76              Display current readline key and function bindings, bind  a  key
77              sequence  to  a  readline  function  or macro, or set a readline
78              variable.  Each non-option argument is a  command  as  it  would
79              appear  in  .inputrc, but each binding or command must be passed
80              as a separate argument; e.g.,  '"\C-x\C-r":  re-read-init-file'.
81              Options, if supplied, have the following meanings:
82              -m keymap
83                     Use keymap as the keymap to be affected by the subsequent
84                     bindings.  Acceptable keymap names are emacs, emacs-stan‐
85                     dard,  emacs-meta,  emacs-ctlx,  vi, vi-move, vi-command,
86                     and vi-insert.  vi is equivalent to  vi-command  (vi-move
87                     is  also  a  synonym); emacs is equivalent to emacs-stan‐
88                     dard.
89              -l     List the names of all readline functions.
90              -p     Display readline function names and bindings  in  such  a
91                     way that they can be re-read.
92              -P     List current readline function names and bindings.
93              -s     Display  readline  key  sequences bound to macros and the
94                     strings they output in such a way that they  can  be  re-
95                     read.
96              -S     Display  readline  key  sequences bound to macros and the
97                     strings they output.
98              -v     Display readline variable names and values in such a  way
99                     that they can be re-read.
100              -V     List current readline variable names and values.
101              -f filename
102                     Read key bindings from filename.
103              -q function
104                     Query about which keys invoke the named function.
105              -u function
106                     Unbind all keys bound to the named function.
107              -r keyseq
108                     Remove any current binding for keyseq.
109              -x keyseq:shell-command
110                     Cause  shell-command  to  be  executed whenever keyseq is
111                     entered.  When shell-command is executed, the shell  sets
112                     the  READLINE_LINE  variable to the contents of the read‐
113                     line line buffer and the READLINE_POINT variable  to  the
114                     current location of the insertion point.  If the executed
115                     command changes  the  value  of  READLINE_LINE  or  READ‐
116                     LINE_POINT,  those  new  values  will be reflected in the
117                     editing state.
118              -X     List all key sequences bound to shell  commands  and  the
119                     associated  commands  in  a  format that can be reused as
120                     input.
121
122              The return value is 0 unless an unrecognized option is given  or
123              an error occurred.
124
125       break [n]
126              Exit  from  within a for, while, until, or select loop.  If n is
127              specified, break n levels.  n must be ≥ 1.  If n is greater than
128              the  number  of enclosing loops, all enclosing loops are exited.
129              The return value is 0 unless n is not greater than or  equal  to
130              1.
131
132       builtin shell-builtin [arguments]
133              Execute  the  specified shell builtin, passing it arguments, and
134              return its exit status.  This is useful when defining a function
135              whose  name  is the same as a shell builtin, retaining the func‐
136              tionality of the builtin within the function.  The cd builtin is
137              commonly  redefined  this  way.   The  return status is false if
138              shell-builtin is not a shell builtin command.
139
140       caller [expr]
141              Returns the context of any active subroutine call (a shell func‐
142              tion or a script executed with the . or source builtins).  With‐
143              out expr, caller displays the line number and source filename of
144              the  current subroutine call.  If a non-negative integer is sup‐
145              plied as expr, caller displays the line number, subroutine name,
146              and  source  file  corresponding to that position in the current
147              execution call stack.  This extra information may be  used,  for
148              example,  to print a stack trace.  The current frame is frame 0.
149              The return value is 0 unless the shell is not executing  a  sub‐
150              routine  call or expr does not correspond to a valid position in
151              the call stack.
152
153       cd [-L|[-P [-e]] [-@]] [dir]
154              Change the current directory to dir.  if dir  is  not  supplied,
155              the  value of the HOME shell variable is the default.  Any addi‐
156              tional arguments following dir are ignored.  The variable CDPATH
157              defines  the  search path for the directory containing dir: each
158              directory name in  CDPATH  is  searched  for  dir.   Alternative
159              directory  names in CDPATH are separated by a colon (:).  A null
160              directory name in CDPATH is the same as the  current  directory,
161              i.e., ``.''.  If dir begins with a slash (/), then CDPATH is not
162              used.  The -P option causes cd to  use  the  physical  directory
163              structure  by  resolving symbolic links while traversing dir and
164              before processing instances of .. in dir (see also the -P option
165              to the set builtin command); the -L option forces symbolic links
166              to be followed by resolving the link after processing  instances
167              of .. in dir.  If .. appears in dir, it is processed by removing
168              the immediately previous pathname component from dir, back to  a
169              slash  or  the  beginning  of dir.  If the -e option is supplied
170              with -P, and the current working directory  cannot  be  success‐
171              fully  determined  after  a successful directory change, cd will
172              return an unsuccessful status.  On systems that support it,  the
173              -@  option  presents  the  extended attributes associated with a
174              file as a directory.  An argument of - is converted  to  $OLDPWD
175              before the directory change is attempted.  If a non-empty direc‐
176              tory name from CDPATH is used, or if - is  the  first  argument,
177              and the directory change is successful, the absolute pathname of
178              the new working directory is written  to  the  standard  output.
179              The  return  value  is  true  if  the directory was successfully
180              changed; false otherwise.
181
182       command [-pVv] command [arg ...]
183              Run command with args  suppressing  the  normal  shell  function
184              lookup.  Only builtin commands or commands found in the PATH are
185              executed.  If the -p option is given, the search for command  is
186              performed  using  a default value for PATH that is guaranteed to
187              find all of the standard utilities.  If  either  the  -V  or  -v
188              option is supplied, a description of command is printed.  The -v
189              option causes a single word indicating the command  or  filename
190              used to invoke command to be displayed; the -V option produces a
191              more verbose description.  If the -V or -v option  is  supplied,
192              the  exit  status  is  0 if command was found, and 1 if not.  If
193              neither option is supplied and an error occurred or command can‐
194              not  be found, the exit status is 127.  Otherwise, the exit sta‐
195              tus of the command builtin is the exit status of command.
196
197       compgen [option] [word]
198              Generate possible completion matches for word according  to  the
199              options,  which  may  be  any  option  accepted  by the complete
200              builtin with the exception of -p and -r, and write  the  matches
201              to  the  standard  output.  When using the -F or -C options, the
202              various shell  variables  set  by  the  programmable  completion
203              facilities, while available, will not have useful values.
204
205              The matches will be generated in the same way as if the program‐
206              mable completion code had generated them directly from a comple‐
207              tion  specification  with the same flags.  If word is specified,
208              only those completions matching word will be displayed.
209
210              The return value is true unless an invalid option  is  supplied,
211              or no matches were generated.
212
213       complete  [-abcdefgjksuv]  [-o comp-option] [-DE] [-A action] [-G glob‐
214       pat] [-W wordlist] [-F function] [-C command]
215              [-X filterpat] [-P prefix] [-S suffix] name [name ...]
216       complete -pr [-DE] [name ...]
217              Specify how arguments to each name should be completed.  If  the
218              -p  option  is supplied, or if no options are supplied, existing
219              completion specifications are printed in a way that allows  them
220              to be reused as input.  The -r option removes a completion spec‐
221              ification for each name, or, if no names are supplied, all  com‐
222              pletion  specifications.   The  -D  option  indicates  that  the
223              remaining options and actions should apply  to  the  ``default''
224              command  completion;  that is, completion attempted on a command
225              for which no completion has previously  been  defined.   The  -E
226              option  indicates  that the remaining options and actions should
227              apply to  ``empty''  command  completion;  that  is,  completion
228              attempted on a blank line.
229
230              The  process  of  applying  these completion specifications when
231              word completion is attempted is described above  under  Program‐
232              mable Completion.
233
234              Other  options,  if specified, have the following meanings.  The
235              arguments to the -G, -W, and -X options (and, if necessary,  the
236              -P  and -S options) should be quoted to protect them from expan‐
237              sion before the complete builtin is invoked.
238              -o comp-option
239                      The comp-option controls several aspects  of  the  comp‐
240                      spec's  behavior beyond the simple generation of comple‐
241                      tions.  comp-option may be one of:
242                      bashdefault
243                              Perform the rest of the default bash completions
244                              if the compspec generates no matches.
245                      default Use  readline's  default  filename completion if
246                              the compspec generates no matches.
247                      dirnames
248                              Perform directory name completion if  the  comp‐
249                              spec generates no matches.
250                      filenames
251                              Tell  readline that the compspec generates file‐
252                              names, so it can perform  any  filename-specific
253                              processing  (like  adding  a  slash to directory
254                              names, quoting special characters, or  suppress‐
255                              ing  trailing spaces).  Intended to be used with
256                              shell functions.
257                      noquote Tell readline not to quote the  completed  words
258                              if  they are filenames (quoting filenames is the
259                              default).
260                      nosort  Tell readline not to sort the list  of  possible
261                              completions alphabetically.
262                      nospace Tell   readline  not  to  append  a  space  (the
263                              default) to words completed at the  end  of  the
264                              line.
265                      plusdirs
266                              After  any  matches  defined by the compspec are
267                              generated,   directory   name   completion    is
268                              attempted  and  any  matches  are  added  to the
269                              results of the other actions.
270              -A action
271                      The action may be one of the  following  to  generate  a
272                      list of possible completions:
273                      alias   Alias names.  May also be specified as -a.
274                      arrayvar
275                              Array variable names.
276                      binding Readline key binding names.
277                      builtin Names  of  shell  builtin commands.  May also be
278                              specified as -b.
279                      command Command names.  May also be specified as -c.
280                      directory
281                              Directory names.  May also be specified as -d.
282                      disabled
283                              Names of disabled shell builtins.
284                      enabled Names of enabled shell builtins.
285                      export  Names of exported shell variables.  May also  be
286                              specified as -e.
287                      file    File names.  May also be specified as -f.
288                      function
289                              Names of shell functions.
290                      group   Group names.  May also be specified as -g.
291                      helptopic
292                              Help topics as accepted by the help builtin.
293                      hostname
294                              Hostnames,  as  taken from the file specified by
295                              the HOSTFILE shell variable.
296                      job     Job names, if job control is active.   May  also
297                              be specified as -j.
298                      keyword Shell  reserved words.  May also be specified as
299                              -k.
300                      running Names of running jobs, if job control is active.
301                      service Service names.  May also be specified as -s.
302                      setopt  Valid arguments for the -o  option  to  the  set
303                              builtin.
304                      shopt   Shell  option  names  as  accepted  by the shopt
305                              builtin.
306                      signal  Signal names.
307                      stopped Names of stopped jobs, if job control is active.
308                      user    User names.  May also be specified as -u.
309                      variable
310                              Names of all shell variables.  May also be spec‐
311                              ified as -v.
312              -C command
313                      command  is  executed in a subshell environment, and its
314                      output is used as the possible completions.
315              -F function
316                      The shell function function is executed in  the  current
317                      shell  environment.   When the function is executed, the
318                      first argument ($1) is the name  of  the  command  whose
319                      arguments  are being completed, the second argument ($2)
320                      is the word being completed, and the third argument ($3)
321                      is  the  word  preceding the word being completed on the
322                      current command line.  When it  finishes,  the  possible
323                      completions  are retrieved from the value of the COMPRE‐
324                      PLY array variable.
325              -G globpat
326                      The pathname expansion pattern globpat  is  expanded  to
327                      generate the possible completions.
328              -P prefix
329                      prefix  is  added at the beginning of each possible com‐
330                      pletion after all other options have been applied.
331              -S suffix
332                      suffix is appended to each possible completion after all
333                      other options have been applied.
334              -W wordlist
335                      The  wordlist  is  split using the characters in the IFS
336                      special variable as delimiters, and each resultant  word
337                      is  expanded.   The possible completions are the members
338                      of the resultant list which match the  word  being  com‐
339                      pleted.
340              -X filterpat
341                      filterpat  is  a pattern as used for pathname expansion.
342                      It is applied to the list of possible completions gener‐
343                      ated  by  the  preceding options and arguments, and each
344                      completion matching filterpat is removed from the  list.
345                      A  leading  !  in filterpat negates the pattern; in this
346                      case, any completion not matching filterpat is removed.
347
348              The return value is true unless an invalid option  is  supplied,
349              an  option  other than -p or -r is supplied without a name argu‐
350              ment, an attempt is made to remove  a  completion  specification
351              for a name for which no specification exists, or an error occurs
352              adding a completion specification.
353
354       compopt [-o option] [-DE] [+o option] [name]
355              Modify  completion  options  for  each  name  according  to  the
356              options,  or  for the currently-executing completion if no names
357              are supplied.  If no options are given, display  the  completion
358              options  for  each name or the current completion.  The possible
359              values of option  are  those  valid  for  the  complete  builtin
360              described  above.   The  -D  option indicates that the remaining
361              options should apply to the ``default'' command completion; that
362              is,  completion  attempted  on a command for which no completion
363              has previously been defined.  The -E option indicates  that  the
364              remaining  options should apply to ``empty'' command completion;
365              that is, completion attempted on a blank line.
366
367              The return value is true unless an invalid option  is  supplied,
368              an attempt is made to modify the options for a name for which no
369              completion specification exists, or an output error occurs.
370
371       continue [n]
372              Resume the next iteration of the enclosing for, while, until, or
373              select  loop.   If  n  is specified, resume at the nth enclosing
374              loop.  n must be ≥ 1.  If  n  is  greater  than  the  number  of
375              enclosing  loops,  the  last  enclosing  loop (the ``top-level''
376              loop) is resumed.  The return value is 0 unless n is not greater
377              than or equal to 1.
378
379       declare [-aAfFgilnrtux] [-p] [name[=value] ...]
380       typeset [-aAfFgilnrtux] [-p] [name[=value] ...]
381              Declare  variables and/or give them attributes.  If no names are
382              given then display the values of variables.  The -p option  will
383              display the attributes and values of each name.  When -p is used
384              with name arguments, additional options, other than -f  and  -F,
385              are  ignored.   When  -p  is supplied without name arguments, it
386              will display the attributes and values of all  variables  having
387              the attributes specified by the additional options.  If no other
388              options  are  supplied  with  -p,  declare  will   display   the
389              attributes  and  values  of  all shell variables.  The -f option
390              will restrict the display to shell  functions.   The  -F  option
391              inhibits  the display of function definitions; only the function
392              name and attributes are printed.  If the extdebug  shell  option
393              is  enabled  using  shopt,  the source file name and line number
394              where each name is defined are displayed as well.  The -F option
395              implies  -f.   The  -g  option forces variables to be created or
396              modified at the global scope, even when declare is executed in a
397              shell  function.  It is ignored in all other cases.  The follow‐
398              ing options can be used to restrict output to variables with the
399              specified attribute or to give variables attributes:
400              -a     Each  name  is  an  indexed  array  variable  (see Arrays
401                     above).
402              -A     Each name is an associative array  variable  (see  Arrays
403                     above).
404              -f     Use function names only.
405              -i     The variable is treated as an integer; arithmetic evalua‐
406                     tion (see ARITHMETIC EVALUATION above) is performed  when
407                     the variable is assigned a value.
408              -l     When  the  variable  is  assigned a value, all upper-case
409                     characters are converted to lower-case.   The  upper-case
410                     attribute is disabled.
411              -n     Give  each  name  the nameref attribute, making it a name
412                     reference to another variable.  That  other  variable  is
413                     defined  by  the  value of name.  All references, assign‐
414                     ments, and attribute modifications to name, except  those
415                     using  or changing the -n attribute itself, are performed
416                     on the variable referenced by name's value.  The  nameref
417                     attribute cannot be applied to array variables.
418              -r     Make names readonly.  These names cannot then be assigned
419                     values by subsequent assignment statements or unset.
420              -t     Give each name the  trace  attribute.   Traced  functions
421                     inherit  the  DEBUG  and  RETURN  traps  from the calling
422                     shell.  The trace attribute has no  special  meaning  for
423                     variables.
424              -u     When  the  variable  is  assigned a value, all lower-case
425                     characters are converted to upper-case.   The  lower-case
426                     attribute is disabled.
427              -x     Mark  names  for  export  to  subsequent commands via the
428                     environment.
429
430              Using `+' instead of `-' turns off the attribute  instead,  with
431              the exceptions that +a may not be used to destroy an array vari‐
432              able and +r will not remove the readonly attribute.   When  used
433              in a function, declare and typeset make each name local, as with
434              the local command, unless the -g option is supplied.  If a vari‐
435              able  name  is  followed by =value, the value of the variable is
436              set to value.  When using -a or -A and the  compound  assignment
437              syntax  to  create array variables, additional attributes do not
438              take effect until subsequent assignments.  The return value is 0
439              unless  an  invalid option is encountered, an attempt is made to
440              define a function using ``-f foo=bar'', an attempt  is  made  to
441              assign  a  value  to  a readonly variable, an attempt is made to
442              assign a value to an array variable without using  the  compound
443              assignment  syntax (see Arrays above), one of the names is not a
444              valid shell variable name, an attempt is made to turn off  read‐
445              only  status for a readonly variable, an attempt is made to turn
446              off array status for an array variable, or an attempt is made to
447              display a non-existent function with -f.
448
449       dirs [-clpv] [+n] [-n]
450              Without  options,  displays  the  list  of  currently remembered
451              directories.  The default display  is  on  a  single  line  with
452              directory  names  separated by spaces.  Directories are added to
453              the list with  the  pushd  command;  the  popd  command  removes
454              entries  from  the  list.   The  current directory is always the
455              first directory in the stack.
456              -c     Clears  the  directory  stack  by  deleting  all  of  the
457                     entries.
458              -l     Produces  a  listing  using  full  pathnames; the default
459                     listing format uses a tilde to denote the home directory.
460              -p     Print the directory stack with one entry per line.
461              -v     Print the directory stack with one entry per  line,  pre‐
462                     fixing each entry with its index in the stack.
463              +n     Displays the nth entry counting from the left of the list
464                     shown by dirs when invoked without options, starting with
465                     zero.
466              -n     Displays  the  nth  entry  counting from the right of the
467                     list shown by dirs when invoked without options, starting
468                     with zero.
469
470              The  return value is 0 unless an invalid option is supplied or n
471              indexes beyond the end of the directory stack.
472
473       disown [-ar] [-h] [jobspec ... | pid ... ]
474              Without options, remove each jobspec from the  table  of  active
475              jobs.   If jobspec is not present, and neither the -a nor the -r
476              option is supplied, the current job is used.  If the  -h  option
477              is  given,  each  jobspec  is not removed from the table, but is
478              marked so that SIGHUP is not  sent  to  the  job  if  the  shell
479              receives  a  SIGHUP.   If  no jobspec is supplied, the -a option
480              means to remove or mark all jobs; the -r option without  a  job‐
481              spec  argument  restricts operation to running jobs.  The return
482              value is 0 unless a jobspec does not specify a valid job.
483
484       echo [-neE] [arg ...]
485              Output the args, separated by spaces,  followed  by  a  newline.
486              The  return  status  is 0 unless a write error occurs.  If -n is
487              specified, the trailing newline is suppressed.  If the -e option
488              is  given,  interpretation  of  the  following backslash-escaped
489              characters is enabled.  The -E option disables  the  interpreta‐
490              tion  of these escape characters, even on systems where they are
491              interpreted by default.  The xpg_echo shell option may  be  used
492              to  dynamically  determine  whether  or  not  echo expands these
493              escape characters by default.  echo does  not  interpret  --  to
494              mean  the  end of options.  echo interprets the following escape
495              sequences:
496              \a     alert (bell)
497              \b     backspace
498              \c     suppress further output
499              \e
500              \E     an escape character
501              \f     form feed
502              \n     new line
503              \r     carriage return
504              \t     horizontal tab
505              \v     vertical tab
506              \\     backslash
507              \0nnn  the eight-bit character whose value is  the  octal  value
508                     nnn (zero to three octal digits)
509              \xHH   the  eight-bit  character  whose value is the hexadecimal
510                     value HH (one or two hex digits)
511              \uHHHH the Unicode (ISO/IEC 10646) character whose value is  the
512                     hexadecimal value HHHH (one to four hex digits)
513              \UHHHHHHHH
514                     the  Unicode (ISO/IEC 10646) character whose value is the
515                     hexadecimal value HHHHHHHH (one to eight hex digits)
516
517       enable [-a] [-dnps] [-f filename] [name ...]
518              Enable and disable builtin shell commands.  Disabling a  builtin
519              allows a disk command which has the same name as a shell builtin
520              to be executed without specifying a full pathname,  even  though
521              the  shell  normally searches for builtins before disk commands.
522              If -n is used, each  name  is  disabled;  otherwise,  names  are
523              enabled.  For example, to use the test binary found via the PATH
524              instead of the shell builtin version, run  ``enable  -n  test''.
525              The  -f  option  means to load the new builtin command name from
526              shared object filename, on systems that support dynamic loading.
527              The  -d  option will delete a builtin previously loaded with -f.
528              If no name arguments are given, or if the -p option is supplied,
529              a list of shell builtins is printed.  With no other option argu‐
530              ments, the list consists of all enabled shell builtins.   If  -n
531              is  supplied, only disabled builtins are printed.  If -a is sup‐
532              plied, the list printed includes all builtins, with  an  indica‐
533              tion  of whether or not each is enabled.  If -s is supplied, the
534              output is restricted to the POSIX special builtins.  The  return
535              value  is  0 unless a name is not a shell builtin or there is an
536              error loading a new builtin from a shared object.
537
538       eval [arg ...]
539              The args are read and concatenated together into a  single  com‐
540              mand.   This command is then read and executed by the shell, and
541              its exit status is returned as the value of eval.  If there  are
542              no args, or only null arguments, eval returns 0.
543
544       exec [-cl] [-a name] [command [arguments]]
545              If  command is specified, it replaces the shell.  No new process
546              is created.  The arguments become the arguments to command.   If
547              the -l option is supplied, the shell places a dash at the begin‐
548              ning of the zeroth argument passed to  command.   This  is  what
549              login(1) does.  The -c option causes command to be executed with
550              an empty environment.  If -a is supplied, the shell passes  name
551              as the zeroth argument to the executed command.  If command can‐
552              not be executed for some reason, a non-interactive shell  exits,
553              unless  the  execfail shell option is enabled.  In that case, it
554              returns failure.  An interactive shell returns  failure  if  the
555              file cannot be executed.  If command is not specified, any redi‐
556              rections take effect in the current shell, and the return status
557              is 0.  If there is a redirection error, the return status is 1.
558
559       exit [n]
560              Cause  the  shell  to exit with a status of n.  If n is omitted,
561              the exit status is that of the last command executed.  A trap on
562              EXIT is executed before the shell terminates.
563
564       export [-fn] [name[=word]] ...
565       export -p
566              The  supplied names are marked for automatic export to the envi‐
567              ronment of subsequently executed commands.  If the -f option  is
568              given,  the names refer to functions.  If no names are given, or
569              if the -p option is supplied, a list of names  of  all  exported
570              variables  is printed.  The -n option causes the export property
571              to be removed from each name.  If a variable name is followed by
572              =word, the value of the variable is set to word.  export returns
573              an exit status of 0 unless an invalid option is encountered, one
574              of  the  names is not a valid shell variable name, or -f is sup‐
575              plied with a name that is not a function.
576
577       fc [-e ename] [-lnr] [first] [last]
578       fc -s [pat=rep] [cmd]
579              The first form selects a range of commands from  first  to  last
580              from  the  history  list  and  displays or edits and re-executes
581              them.  First and last may be specified as a  string  (to  locate
582              the  last command beginning with that string) or as a number (an
583              index into the history list, where a negative number is used  as
584              an  offset  from  the  current  command number).  If last is not
585              specified it is set to the current command for listing (so  that
586              ``fc  -l  -10'' prints the last 10 commands) and to first other‐
587              wise.  If first is not specified it is set to the previous  com‐
588              mand for editing and -16 for listing.
589
590              The  -n option suppresses the command numbers when listing.  The
591              -r option reverses the order of the commands.  If the -l  option
592              is  given,  the  commands are listed on standard output.  Other‐
593              wise, the editor given by ename is invoked on a file  containing
594              those  commands.  If ename is not given, the value of the FCEDIT
595              variable is used, and the value of EDITOR if FCEDIT is not  set.
596              If  neither  variable  is set, vi is used.  When editing is com‐
597              plete, the edited commands are echoed and executed.
598
599              In the second form, command is re-executed after  each  instance
600              of  pat  is  replaced by rep.  Command is intepreted the same as
601              first above.  A useful alias to use with this is ``r="fc  -s"'',
602              so  that  typing  ``r  cc'' runs the last command beginning with
603              ``cc'' and typing ``r'' re-executes the last command.
604
605              If the first form is used, the  return  value  is  0  unless  an
606              invalid  option  is encountered or first or last specify history
607              lines out of range.  If the -e option is  supplied,  the  return
608              value is the value of the last command executed or failure if an
609              error occurs with the temporary file of commands.  If the second
610              form  is  used, the return status is that of the command re-exe‐
611              cuted, unless cmd does not specify  a  valid  history  line,  in
612              which case fc returns failure.
613
614       fg [jobspec]
615              Resume  jobspec  in the foreground, and make it the current job.
616              If jobspec is not present, the shell's notion of the current job
617              is  used.   The  return value is that of the command placed into
618              the foreground, or failure if run when job control  is  disabled
619              or, when run with job control enabled, if jobspec does not spec‐
620              ify a valid job or jobspec specifies  a  job  that  was  started
621              without job control.
622
623       getopts optstring name [args]
624              getopts  is used by shell procedures to parse positional parame‐
625              ters.  optstring contains the option  characters  to  be  recog‐
626              nized;  if  a  character  is  followed by a colon, the option is
627              expected to have an argument, which should be separated from  it
628              by  white space.  The colon and question mark characters may not
629              be used as option characters.  Each time it is invoked,  getopts
630              places  the next option in the shell variable name, initializing
631              name if it does not exist, and the index of the next argument to
632              be processed into the variable OPTIND.  OPTIND is initialized to
633              1 each time the shell or a shell script  is  invoked.   When  an
634              option  requires  an argument, getopts places that argument into
635              the variable OPTARG.  The shell does not reset OPTIND  automati‐
636              cally;  it  must  be  manually  reset  between multiple calls to
637              getopts within the same shell invocation if a new set of parame‐
638              ters is to be used.
639
640              When  the  end  of  options is encountered, getopts exits with a
641              return value greater than zero.  OPTIND is set to the  index  of
642              the first non-option argument, and name is set to ?.
643
644              getopts  normally  parses the positional parameters, but if more
645              arguments are given in args, getopts parses those instead.
646
647              getopts can report errors in two ways.  If the  first  character
648              of  optstring  is  a  colon, silent error reporting is used.  In
649              normal operation, diagnostic messages are printed  when  invalid
650              options  or  missing  option  arguments are encountered.  If the
651              variable OPTERR is set to 0, no  error  messages  will  be  dis‐
652              played, even if the first character of optstring is not a colon.
653
654              If an invalid option is seen, getopts places ? into name and, if
655              not silent, prints an  error  message  and  unsets  OPTARG.   If
656              getopts  is  silent,  the  option  character  found is placed in
657              OPTARG and no diagnostic message is printed.
658
659              If a required argument is not found, and getopts is not  silent,
660              a  question  mark  (?) is placed in name, OPTARG is unset, and a
661              diagnostic message is printed.  If getopts  is  silent,  then  a
662              colon  (:)  is  placed  in  name and OPTARG is set to the option
663              character found.
664
665              getopts returns true if an option, specified or unspecified,  is
666              found.  It returns false if the end of options is encountered or
667              an error occurs.
668
669       hash [-lr] [-p filename] [-dt] [name]
670              Each time hash is invoked, the full pathname of the command name
671              is  determined  by searching the directories in $PATH and remem‐
672              bered.  Any previously-remembered pathname is discarded.  If the
673              -p option is supplied, no path search is performed, and filename
674              is used as the full filename of  the  command.   The  -r  option
675              causes  the  shell  to  forget all remembered locations.  The -d
676              option causes the shell to forget  the  remembered  location  of
677              each  name.   If the -t option is supplied, the full pathname to
678              which each name corresponds is printed.  If multiple name  argu‐
679              ments  are  supplied  with  -t,  the  name is printed before the
680              hashed full pathname.  The -l option causes output  to  be  dis‐
681              played in a format that may be reused as input.  If no arguments
682              are given, or if only -l is supplied, information  about  remem‐
683              bered  commands  is printed.  The return status is true unless a
684              name is not found or an invalid option is supplied.
685
686       help [-dms] [pattern]
687              Display helpful information about builtin commands.  If  pattern
688              is  specified, help gives detailed help on all commands matching
689              pattern; otherwise help for all the builtins and  shell  control
690              structures is printed.
691              -d     Display a short description of each pattern
692              -m     Display the description of each pattern in a manpage-like
693                     format
694              -s     Display only a short usage synopsis for each pattern
695
696              The return status is 0 unless no command matches pattern.
697
698       history [n]
699       history -c
700       history -d offset
701       history -anrw [filename]
702       history -p arg [arg ...]
703       history -s arg [arg ...]
704              With no options, display the command history list with line num‐
705              bers.  Lines listed with a * have been modified.  An argument of
706              n lists only the last n lines.  If the shell variable  HISTTIME‐
707              FORMAT  is  set  and not null, it is used as a format string for
708              strftime(3) to display the time stamp associated with each  dis‐
709              played  history  entry.  No intervening blank is printed between
710              the formatted time stamp and the history line.  If  filename  is
711              supplied,  it  is  used as the name of the history file; if not,
712              the value of HISTFILE is used.  Options, if supplied,  have  the
713              following meanings:
714              -c     Clear the history list by deleting all the entries.
715              -d offset
716                     Delete the history entry at position offset.
717              -a     Append  the  ``new''  history  lines to the history file.
718                     These are history lines entered since  the  beginning  of
719                     the current bash session, but not already appended to the
720                     history file.
721              -n     Read the history lines not already read from the  history
722                     file  into  the  current  history  list.  These are lines
723                     appended to the history file since the beginning  of  the
724                     current bash session.
725              -r     Read  the contents of the history file and append them to
726                     the current history list.
727              -w     Write the current history list to the history file, over‐
728                     writing the history file's contents.
729              -p     Perform  history  substitution  on the following args and
730                     display the result on  the  standard  output.   Does  not
731                     store  the results in the history list.  Each arg must be
732                     quoted to disable normal history expansion.
733              -s     Store the args in the history list  as  a  single  entry.
734                     The  last  command  in the history list is removed before
735                     the args are added.
736
737              If the HISTTIMEFORMAT variable is set, the time  stamp  informa‐
738              tion  associated  with each history entry is written to the his‐
739              tory file, marked with the history comment character.  When  the
740              history  file  is read, lines beginning with the history comment
741              character followed immediately by a  digit  are  interpreted  as
742              timestamps for the following history entry.  The return value is
743              0 unless an invalid option is encountered, an error occurs while
744              reading  or  writing the history file, an invalid offset is sup‐
745              plied as an argument to -d, or the history expansion supplied as
746              an argument to -p fails.
747
748       jobs [-lnprs] [ jobspec ... ]
749       jobs -x command [ args ... ]
750              The first form lists the active jobs.  The options have the fol‐
751              lowing meanings:
752              -l     List process IDs in addition to the normal information.
753              -n     Display information only about  jobs  that  have  changed
754                     status since the user was last notified of their status.
755              -p     List  only  the  process  ID  of  the job's process group
756                     leader.
757              -r     Display only running jobs.
758              -s     Display only stopped jobs.
759
760              If jobspec is given, output is restricted to  information  about
761              that  job.   The  return status is 0 unless an invalid option is
762              encountered or an invalid jobspec is supplied.
763
764              If the -x option is supplied, jobs replaces any jobspec found in
765              command  or  args  with  the corresponding process group ID, and
766              executes command passing it args, returning its exit status.
767
768       kill [-s sigspec | -n signum | -sigspec] [pid | jobspec] ...
769       kill -l|-L [sigspec | exit_status]
770              Send the signal named by sigspec  or  signum  to  the  processes
771              named  by  pid or jobspec.  sigspec is either a case-insensitive
772              signal name such as SIGKILL (with or without the SIG prefix)  or
773              a  signal  number; signum is a signal number.  If sigspec is not
774              present, then SIGTERM is assumed.  An argument of -l  lists  the
775              signal  names.   If any arguments are supplied when -l is given,
776              the names of the signals  corresponding  to  the  arguments  are
777              listed, and the return status is 0.  The exit_status argument to
778              -l is a number specifying either a signal  number  or  the  exit
779              status  of  a  process terminated by a signal.  The -L option is
780              equivalent to -l.  kill returns true if at least one signal  was
781              successfully  sent,  or  false  if an error occurs or an invalid
782              option is encountered.
783
784       let arg [arg ...]
785              Each arg is an arithmetic expression to be evaluated (see ARITH‐
786              METIC  EVALUATION  above).   If the last arg evaluates to 0, let
787              returns 1; 0 is returned otherwise.
788
789       local [option] [name[=value] ... | - ]
790              For each argument, a local variable named name is  created,  and
791              assigned  value.   The option can be any of the options accepted
792              by declare.  When local is used within a function, it causes the
793              variable  name  to have a visible scope restricted to that func‐
794              tion and its children.  If name is -, the set of  shell  options
795              is  made  local to the function in which local is invoked: shell
796              options changed using the set builtin inside  the  function  are
797              restored  to  their  original  values when the function returns.
798              With no operands, local writes a list of local variables to  the
799              standard  output.  It is an error to use local when not within a
800              function.  The return status is 0 unless local is used outside a
801              function,  an  invalid  name  is supplied, or name is a readonly
802              variable.
803
804       logout Exit a login shell.
805
806       mapfile [-d delim] [-n count] [-O origin] [-s count] [-t] [-u  fd]  [-C
807       callback] [-c quantum] [array]
808       readarray [-d delim] [-n count] [-O origin] [-s count] [-t] [-u fd] [-C
809       callback] [-c quantum] [array]
810              Read lines from the standard input into the indexed array  vari‐
811              able  array, or from file descriptor fd if the -u option is sup‐
812              plied.  The variable MAPFILE is the default array.  Options,  if
813              supplied, have the following meanings:
814              -d     The  first  character  of delim is used to terminate each
815                     input line, rather than newline.
816              -n     Copy at most count lines.  If count is 0, all  lines  are
817                     copied.
818              -O     Begin  assigning  to  array at index origin.  The default
819                     index is 0.
820              -s     Discard the first count lines read.
821              -t     Remove a trailing delim (default newline) from each  line
822                     read.
823              -u     Read  lines  from file descriptor fd instead of the stan‐
824                     dard input.
825              -C     Evaluate callback each time quantum lines are read.   The
826                     -c option specifies quantum.
827              -c     Specify  the  number  of  lines read between each call to
828                     callback.
829
830              If -C is specified without -c,  the  default  quantum  is  5000.
831              When callback is evaluated, it is supplied the index of the next
832              array element to be assigned and the line to be assigned to that
833              element  as  additional  arguments.  callback is evaluated after
834              the line is read but before the array element is assigned.
835
836              If not supplied with an  explicit  origin,  mapfile  will  clear
837              array before assigning to it.
838
839              mapfile  returns successfully unless an invalid option or option
840              argument is supplied, array is invalid or  unassignable,  or  if
841              array is not an indexed array.
842
843       popd [-n] [+n] [-n]
844              Removes  entries  from  the directory stack.  With no arguments,
845              removes the top directory from the stack, and performs a  cd  to
846              the new top directory.  Arguments, if supplied, have the follow‐
847              ing meanings:
848              -n     Suppresses the normal change of directory  when  removing
849                     directories  from  the  stack,  so that only the stack is
850                     manipulated.
851              +n     Removes the nth entry counting from the left of the  list
852                     shown  by  dirs, starting with zero.  For example: ``popd
853                     +0'' removes the first directory, ``popd +1'' the second.
854              -n     Removes the nth entry counting from the right of the list
855                     shown  by  dirs, starting with zero.  For example: ``popd
856                     -0'' removes the last directory, ``popd -1'' the next  to
857                     last.
858
859              If  the popd command is successful, a dirs is performed as well,
860              and the return status is 0.  popd returns false  if  an  invalid
861              option is encountered, the directory stack is empty, a non-exis‐
862              tent directory stack entry is specified, or the directory change
863              fails.
864
865       printf [-v var] format [arguments]
866              Write  the  formatted arguments to the standard output under the
867              control of the format.  The -v option causes the  output  to  be
868              assigned  to  the  variable var rather than being printed to the
869              standard output.
870
871              The format is a character string which contains three  types  of
872              objects:  plain  characters, which are simply copied to standard
873              output, character escape  sequences,  which  are  converted  and
874              copied  to  the standard output, and format specifications, each
875              of which causes printing of the next  successive  argument.   In
876              addition to the standard printf(1) format specifications, printf
877              interprets the following extensions:
878              %b     causes printf to expand backslash escape sequences in the
879                     corresponding argument in the same way as echo -e.
880              %q     causes  printf  to output the corresponding argument in a
881                     format that can be reused as shell input.
882              %(datefmt)T
883                     causes printf to output the  date-time  string  resulting
884                     from  using  datefmt  as a format string for strftime(3).
885                     The corresponding argument is an integer representing the
886                     number  of seconds since the epoch.  Two special argument
887                     values may be used: -1 represents the current  time,  and
888                     -2  represents  the  time  the  shell was invoked.  If no
889                     argument is specified, conversion behaves as  if  -1  had
890                     been  given.   This  is  an exception to the usual printf
891                     behavior.
892
893              Arguments to non-string format specifiers are treated as C  con‐
894              stants, except that a leading plus or minus sign is allowed, and
895              if the leading character is a single or double quote, the  value
896              is the ASCII value of the following character.
897
898              The  format  is  reused as necessary to consume all of the argu‐
899              ments.  If the format requires more arguments than are supplied,
900              the  extra  format  specifications  behave as if a zero value or
901              null string, as appropriate,  had  been  supplied.   The  return
902              value is zero on success, non-zero on failure.
903
904       pushd [-n] [+n] [-n]
905       pushd [-n] [dir]
906              Adds  a  directory to the top of the directory stack, or rotates
907              the stack, making the new top of the stack the  current  working
908              directory.   With  no  arguments,  pushd  exchanges  the top two
909              directories and returns 0, unless the directory stack is  empty.
910              Arguments, if supplied, have the following meanings:
911              -n     Suppresses  the  normal change of directory when rotating
912                     or adding directories to the  stack,  so  that  only  the
913                     stack is manipulated.
914              +n     Rotates  the  stack  so  that the nth directory (counting
915                     from the left of the list shown by  dirs,  starting  with
916                     zero) is at the top.
917              -n     Rotates  the  stack  so  that the nth directory (counting
918                     from the right of the list shown by dirs,  starting  with
919                     zero) is at the top.
920              dir    Adds dir to the directory stack at the top, making it the
921                     new current working directory as if it had been  supplied
922                     as the argument to the cd builtin.
923
924              If the pushd command is successful, a dirs is performed as well.
925              If the first form is used, pushd returns 0 unless the cd to  dir
926              fails.   With the second form, pushd returns 0 unless the direc‐
927              tory stack is empty, a non-existent directory stack  element  is
928              specified,  or the directory change to the specified new current
929              directory fails.
930
931       pwd [-LP]
932              Print the absolute pathname of the  current  working  directory.
933              The pathname printed contains no symbolic links if the -P option
934              is supplied or the -o physical option to the set builtin command
935              is  enabled.  If the -L option is used, the pathname printed may
936              contain symbolic links.  The return status is 0 unless an  error
937              occurs  while  reading  the  name of the current directory or an
938              invalid option is supplied.
939
940       read [-ers] [-a aname] [-d delim] [-i text] [-n nchars] [-N nchars] [-p
941       prompt] [-t timeout] [-u fd] [name ...]
942              One  line  is  read  from  the  standard input, or from the file
943              descriptor fd supplied as an argument to the  -u  option,  split
944              into  words  as  described  above  under Word Splitting, and the
945              first word is assigned to the first name, the second word to the
946              second name, and so on.  If there are more words than names, the
947              remaining words and their intervening delimiters are assigned to
948              the  last  name.   If  there are fewer words read from the input
949              stream than names, the remaining names are assigned  empty  val‐
950              ues.   The  characters  in  IFS  are used to split the line into
951              words  using  the  same  rules  the  shell  uses  for  expansion
952              (described above under Word Splitting).  The backslash character
953              (\) may be used to remove any special meaning for the next char‐
954              acter  read  and  for  line continuation.  Options, if supplied,
955              have the following meanings:
956              -a aname
957                     The words are assigned to sequential indices of the array
958                     variable aname, starting at 0.  aname is unset before any
959                     new  values  are  assigned.   Other  name  arguments  are
960                     ignored.
961              -d delim
962                     The  first  character  of  delim is used to terminate the
963                     input line, rather than newline.
964              -e     If the standard input is coming from a terminal, readline
965                     (see  READLINE  above) is used to obtain the line.  Read‐
966                     line uses the current (or default, if  line  editing  was
967                     not previously active) editing settings.
968              -i text
969                     If  readline  is  being  used  to  read the line, text is
970                     placed into the editing buffer before editing begins.
971              -n nchars
972                     read returns after reading nchars characters rather  than
973                     waiting for a complete line of input, but honors a delim‐
974                     iter if fewer than nchars characters are read before  the
975                     delimiter.
976              -N nchars
977                     read  returns  after  reading  exactly  nchars characters
978                     rather than waiting for a complete line of input,  unless
979                     EOF  is encountered or read times out.  Delimiter charac‐
980                     ters encountered in the input are not  treated  specially
981                     and  do  not cause read to return until nchars characters
982                     are read.  The result is not split on the  characters  in
983                     IFS;  the intent is that the variable is assigned exactly
984                     the characters read (with the exception of backslash; see
985                     the -r option below).
986              -p prompt
987                     Display prompt on standard error, without a trailing new‐
988                     line, before attempting to read any input.  The prompt is
989                     displayed only if input is coming from a terminal.
990              -r     Backslash does not act as an escape character.  The back‐
991                     slash is considered to be part of the line.  In  particu‐
992                     lar,  a  backslash-newline pair may not be used as a line
993                     continuation.
994              -s     Silent mode.  If input is coming from a terminal, charac‐
995                     ters are not echoed.
996              -t timeout
997                     Cause  read  to time out and return failure if a complete
998                     line of input (or a specified number  of  characters)  is
999                     not  read within timeout seconds.  timeout may be a deci‐
1000                     mal number with a fractional portion following the  deci‐
1001                     mal  point.   This  option  is  only effective if read is
1002                     reading input from a terminal,  pipe,  or  other  special
1003                     file;  it  has no effect when reading from regular files.
1004                     If read times out, read saves any partial input read into
1005                     the  specified  variable  name.   If  timeout  is 0, read
1006                     returns immediately, without trying  to  read  any  data.
1007                     The  exit status is 0 if input is available on the speci‐
1008                     fied file descriptor, non-zero otherwise.  The exit  sta‐
1009                     tus is greater than 128 if the timeout is exceeded.
1010              -u fd  Read input from file descriptor fd.
1011
1012              If no names are supplied, the line read is assigned to the vari‐
1013              able REPLY.  The exit status  is  zero,  unless  end-of-file  is
1014              encountered, read times out (in which case the status is greater
1015              than 128), a variable assignment error (such as assigning  to  a
1016              readonly variable) occurs, or an invalid file descriptor is sup‐
1017              plied as the argument to -u.
1018
1019       readonly [-aAf] [-p] [name[=word] ...]
1020              The given names are marked readonly; the values of  these  names
1021              may  not  be changed by subsequent assignment.  If the -f option
1022              is supplied, the functions corresponding to  the  names  are  so
1023              marked.   The  -a  option  restricts  the  variables  to indexed
1024              arrays; the -A option restricts  the  variables  to  associative
1025              arrays.   If both options are supplied, -A takes precedence.  If
1026              no name arguments are given, or if the -p option is supplied,  a
1027              list of all readonly names is printed.  The other options may be
1028              used to restrict the output to a subset of the set  of  readonly
1029              names.   The -p option causes output to be displayed in a format
1030              that may be reused as input.  If a variable name is followed  by
1031              =word,  the  value  of  the variable is set to word.  The return
1032              status is 0 unless an invalid option is encountered, one of  the
1033              names is not a valid shell variable name, or -f is supplied with
1034              a name that is not a function.
1035
1036       return [n]
1037              Causes a function to stop executing and return the value  speci‐
1038              fied  by n to its caller.  If n is omitted, the return status is
1039              that of the last command executed  in  the  function  body.   If
1040              return  is  executed by a trap handler, the last command used to
1041              determine the status is the last  command  executed  before  the
1042              trap  handler.   if  return is executed during a DEBUG trap, the
1043              last command used to determine the status is  the  last  command
1044              executed  by  the  trap  handler  before return was invoked.  If
1045              return is used outside a function, but  during  execution  of  a
1046              script  by  the .  (source) command, it causes the shell to stop
1047              executing that script and return either n or the exit status  of
1048              the  last  command executed within the script as the exit status
1049              of the script.  If n is supplied, the return value is its  least
1050              significant  8 bits.  The return status is non-zero if return is
1051              supplied a non-numeric argument, or is used outside  a  function
1052              and  not  during execution of a script by . or source.  Any com‐
1053              mand associated with the RETURN trap is executed  before  execu‐
1054              tion resumes after the function or script.
1055
1056       set [--abefhkmnptuvxBCEHPT] [-o option-name] [arg ...]
1057       set [+abefhkmnptuvxBCEHPT] [+o option-name] [arg ...]
1058              Without  options,  the name and value of each shell variable are
1059              displayed in a format that can be reused as input for setting or
1060              resetting the currently-set variables.  Read-only variables can‐
1061              not be reset.  In posix mode, only shell variables  are  listed.
1062              The  output  is  sorted  according  to the current locale.  When
1063              options are specified, they set or unset shell attributes.   Any
1064              arguments  remaining after option processing are treated as val‐
1065              ues for the positional parameters and are assigned, in order, to
1066              $1,  $2,  ...   $n.   Options,  if specified, have the following
1067              meanings:
1068              -a      Each variable or function that is created or modified is
1069                      given  the export attribute and marked for export to the
1070                      environment of subsequent commands.
1071              -b      Report the status of terminated background jobs  immedi‐
1072                      ately, rather than before the next primary prompt.  This
1073                      is effective only when job control is enabled.
1074              -e      Exit immediately if a pipeline (which may consist  of  a
1075                      single  simple  command),  a list, or a compound command
1076                      (see SHELL GRAMMAR above), exits with a non-zero status.
1077                      The  shell  does  not  exit if the command that fails is
1078                      part of the command list immediately following  a  while
1079                      or  until  keyword, part of the test following the if or
1080                      elif reserved words, part of any command executed  in  a
1081                      &&  or || list except the command following the final &&
1082                      or ||, any command in a pipeline but the last, or if the
1083                      command's  return  value is being inverted with !.  If a
1084                      compound command other than a subshell  returns  a  non-
1085                      zero  status because a command failed while -e was being
1086                      ignored, the shell does not exit.  A  trap  on  ERR,  if
1087                      set,  is  executed  before the shell exits.  This option
1088                      applies to the shell environment and each subshell envi‐
1089                      ronment  separately  (see  COMMAND EXECUTION ENVIRONMENT
1090                      above), and may cause subshells to exit before executing
1091                      all the commands in the subshell.
1092
1093                      If  a  compound  command or shell function executes in a
1094                      context where -e is being ignored, none of the  commands
1095                      executed  within  the  compound command or function body
1096                      will be affected by the -e setting, even if  -e  is  set
1097                      and  a  command returns a failure status.  If a compound
1098                      command or shell function sets -e while executing  in  a
1099                      context  where -e is ignored, that setting will not have
1100                      any effect until the compound  command  or  the  command
1101                      containing the function call completes.
1102              -f      Disable pathname expansion.
1103              -h      Remember  the location of commands as they are looked up
1104                      for execution.  This is enabled by default.
1105              -k      All arguments in the form of assignment  statements  are
1106                      placed  in the environment for a command, not just those
1107                      that precede the command name.
1108              -m      Monitor mode.  Job control is enabled.  This  option  is
1109                      on  by  default  for  interactive shells on systems that
1110                      support it (see JOB CONTROL above).  All  processes  run
1111                      in a separate process group.  When a background job com‐
1112                      pletes, the shell prints a line containing its exit sta‐
1113                      tus.
1114              -n      Read commands but do not execute them.  This may be used
1115                      to check a shell script  for  syntax  errors.   This  is
1116                      ignored by interactive shells.
1117              -o option-name
1118                      The option-name can be one of the following:
1119                      allexport
1120                              Same as -a.
1121                      braceexpand
1122                              Same as -B.
1123                      emacs   Use  an  emacs-style command line editing inter‐
1124                              face.  This is enabled by default when the shell
1125                              is interactive, unless the shell is started with
1126                              the --noediting option.  This also  affects  the
1127                              editing interface used for read -e.
1128                      errexit Same as -e.
1129                      errtrace
1130                              Same as -E.
1131                      functrace
1132                              Same as -T.
1133                      hashall Same as -h.
1134                      histexpand
1135                              Same as -H.
1136                      history Enable command history, as described above under
1137                              HISTORY.  This option is on by default in inter‐
1138                              active shells.
1139                      ignoreeof
1140                              The   effect   is   as   if  the  shell  command
1141                              ``IGNOREEOF=10'' had been  executed  (see  Shell
1142                              Variables above).
1143                      keyword Same as -k.
1144                      monitor Same as -m.
1145                      noclobber
1146                              Same as -C.
1147                      noexec  Same as -n.
1148                      noglob  Same as -f.
1149                      nolog   Currently ignored.
1150                      notify  Same as -b.
1151                      nounset Same as -u.
1152                      onecmd  Same as -t.
1153                      physical
1154                              Same as -P.
1155                      pipefail
1156                              If  set,  the  return value of a pipeline is the
1157                              value of the last (rightmost)  command  to  exit
1158                              with  a non-zero status, or zero if all commands
1159                              in the pipeline exit successfully.  This  option
1160                              is disabled by default.
1161                      posix   Change  the  behavior  of bash where the default
1162                              operation differs from  the  POSIX  standard  to
1163                              match  the  standard (posix mode).  See SEE ALSO
1164                              below for a reference to a document that details
1165                              how posix mode affects bash's behavior.
1166                      privileged
1167                              Same as -p.
1168                      verbose Same as -v.
1169                      vi      Use  a  vi-style command line editing interface.
1170                              This also affects the editing interface used for
1171                              read -e.
1172                      xtrace  Same as -x.
1173                      If -o is supplied with no option-name, the values of the
1174                      current options are printed.  If +o is supplied with  no
1175                      option-name,  a  series  of set commands to recreate the
1176                      current option settings is  displayed  on  the  standard
1177                      output.
1178              -p      Turn  on  privileged  mode.   In this mode, the $ENV and
1179                      $BASH_ENV files are not processed, shell  functions  are
1180                      not  inherited  from the environment, and the SHELLOPTS,
1181                      BASHOPTS, CDPATH,  and  GLOBIGNORE  variables,  if  they
1182                      appear in the environment, are ignored.  If the shell is
1183                      started with the effective user (group) id not equal  to
1184                      the  real user (group) id, and the -p option is not sup‐
1185                      plied, these actions are taken and the effective user id
1186                      is  set  to  the real user id.  If the -p option is sup‐
1187                      plied at startup, the effective user id  is  not  reset.
1188                      Turning  this  option  off causes the effective user and
1189                      group ids to be set to the real user and group ids.
1190              -t      Exit after reading and executing one command.
1191              -u      Treat unset variables and parameters other than the spe‐
1192                      cial  parameters "@" and "*" as an error when performing
1193                      parameter expansion.  If expansion is  attempted  on  an
1194                      unset  variable  or parameter, the shell prints an error
1195                      message, and, if not interactive, exits with a  non-zero
1196                      status.
1197              -v      Print shell input lines as they are read.
1198              -x      After  expanding  each simple command, for command, case
1199                      command, select command, or arithmetic for command, dis‐
1200                      play  the expanded value of PS4, followed by the command
1201                      and its expanded arguments or associated word list.
1202              -B      The shell performs brace expansion (see Brace  Expansion
1203                      above).  This is on by default.
1204              -C      If  set,  bash  does not overwrite an existing file with
1205                      the >, >&, and <> redirection operators.   This  may  be
1206                      overridden when creating output files by using the redi‐
1207                      rection operator >| instead of >.
1208              -E      If set, any trap on ERR is inherited by shell functions,
1209                      command  substitutions,  and commands executed in a sub‐
1210                      shell environment.  The ERR trap is normally not  inher‐
1211                      ited in such cases.
1212              -H      Enable !  style history substitution.  This option is on
1213                      by default when the shell is interactive.
1214              -P      If set, the shell does not resolve symbolic  links  when
1215                      executing  commands  such  as cd that change the current
1216                      working  directory.   It  uses  the  physical  directory
1217                      structure instead.  By default, bash follows the logical
1218                      chain of  directories  when  performing  commands  which
1219                      change the current directory.
1220              -T      If  set,  any traps on DEBUG and RETURN are inherited by
1221                      shell functions,  command  substitutions,  and  commands
1222                      executed  in  a  subshell  environment.   The  DEBUG and
1223                      RETURN traps are normally not inherited in such cases.
1224              --      If no arguments follow this option, then the  positional
1225                      parameters are unset.  Otherwise, the positional parame‐
1226                      ters are set to the args, even if  some  of  them  begin
1227                      with a -.
1228              -       Signal  the  end of options, cause all remaining args to
1229                      be assigned to the positional parameters.  The -x and -v
1230                      options are turned off.  If there are no args, the posi‐
1231                      tional parameters remain unchanged.
1232
1233              The options are off by default unless otherwise noted.  Using  +
1234              rather  than  -  causes  these  options  to  be turned off.  The
1235              options can also be specified as arguments to an  invocation  of
1236              the  shell.  The current set of options may be found in $-.  The
1237              return status is always true unless an invalid option is encoun‐
1238              tered.
1239
1240       shift [n]
1241              The  positional  parameters  from n+1 ... are renamed to $1 ....
1242              Parameters represented by the numbers  $#  down  to  $#-n+1  are
1243              unset.   n  must  be a non-negative number less than or equal to
1244              $#.  If n is 0, no parameters are changed.  If n is  not  given,
1245              it  is assumed to be 1.  If n is greater than $#, the positional
1246              parameters are not changed.  The return status is  greater  than
1247              zero if n is greater than $# or less than zero; otherwise 0.
1248
1249       shopt [-pqsu] [-o] [optname ...]
1250              Toggle  the values of settings controlling optional shell behav‐
1251              ior.  The settings can be either those listed below, or, if  the
1252              -o option is used, those available with the -o option to the set
1253              builtin command.  With no options, or with the -p option, a list
1254              of  all  settable  options  is  displayed, with an indication of
1255              whether or not each is set.  The -p option causes output  to  be
1256              displayed  in a form that may be reused as input.  Other options
1257              have the following meanings:
1258              -s     Enable (set) each optname.
1259              -u     Disable (unset) each optname.
1260              -q     Suppresses normal output (quiet mode); the return  status
1261                     indicates whether the optname is set or unset.  If multi‐
1262                     ple optname arguments are given with -q, the return  sta‐
1263                     tus  is zero if all optnames are enabled; non-zero other‐
1264                     wise.
1265              -o     Restricts the values of optname to be those  defined  for
1266                     the -o option to the set builtin.
1267
1268              If  either  -s  or  -u  is used with no optname arguments, shopt
1269              shows only those options which are set or  unset,  respectively.
1270              Unless  otherwise  noted, the shopt options are disabled (unset)
1271              by default.
1272
1273              The return status when listing options is zero if  all  optnames
1274              are  enabled,  non-zero  otherwise.   When  setting or unsetting
1275              options, the return status is zero unless an optname  is  not  a
1276              valid shell option.
1277
1278              The list of shopt options is:
1279
1280              autocd  If  set,  a command name that is the name of a directory
1281                      is executed as if it were the argument to  the  cd  com‐
1282                      mand.  This option is only used by interactive shells.
1283              cdable_vars
1284                      If  set,  an  argument to the cd builtin command that is
1285                      not a directory is assumed to be the name of a  variable
1286                      whose value is the directory to change to.
1287              cdspell If set, minor errors in the spelling of a directory com‐
1288                      ponent in a cd command will be  corrected.   The  errors
1289                      checked for are transposed characters, a missing charac‐
1290                      ter, and one character too many.   If  a  correction  is
1291                      found,  the  corrected filename is printed, and the com‐
1292                      mand proceeds.  This option is only used by  interactive
1293                      shells.
1294              checkhash
1295                      If set, bash checks that a command found in the hash ta‐
1296                      ble exists before trying to execute  it.   If  a  hashed
1297                      command  no  longer exists, a normal path search is per‐
1298                      formed.
1299              checkjobs
1300                      If set, bash lists the status of any stopped and running
1301                      jobs  before  exiting an interactive shell.  If any jobs
1302                      are running, this causes the exit to be deferred until a
1303                      second  exit is attempted without an intervening command
1304                      (see JOB CONTROL above).   The  shell  always  postpones
1305                      exiting if any jobs are stopped.
1306              checkwinsize
1307                      If  set,  bash checks the window size after each command
1308                      and, if necessary, updates the values of LINES and  COL‐
1309                      UMNS.
1310              cmdhist If  set,  bash attempts to save all lines of a multiple-
1311                      line command in the same  history  entry.   This  allows
1312                      easy re-editing of multi-line commands.
1313              compat31
1314                      If set, bash changes its behavior to that of version 3.1
1315                      with respect to quoted arguments to the  [[  conditional
1316                      command's =~ operator and locale-specific string compar‐
1317                      ison when using the [[ conditional  command's  <  and  >
1318                      operators.   Bash  versions  prior to bash-4.1 use ASCII
1319                      collation and strcmp(3); bash-4.1 and later use the cur‐
1320                      rent locale's collation sequence and strcoll(3).
1321              compat32
1322                      If set, bash changes its behavior to that of version 3.2
1323                      with respect to locale-specific string  comparison  when
1324                      using  the  [[  conditional  command's < and > operators
1325                      (see previous item) and the  effect  of  interrupting  a
1326                      command  list.   Bash  versions 3.2 and earlier continue
1327                      with the next command in the list after  one  terminates
1328                      due to an interrupt.
1329              compat40
1330                      If set, bash changes its behavior to that of version 4.0
1331                      with respect to locale-specific string  comparison  when
1332                      using  the  [[  conditional  command's < and > operators
1333                      (see description of compat31) and the effect  of  inter‐
1334                      rupting  a  command  list.   Bash versions 4.0 and later
1335                      interrupt the list as if the shell received  the  inter‐
1336                      rupt;  previous  versions continue with the next command
1337                      in the list.
1338              compat41
1339                      If set, bash, when in posix mode, treats a single  quote
1340                      in  a  double-quoted  parameter  expansion  as a special
1341                      character.  The single quotes must match (an  even  num‐
1342                      ber)  and  the  characters between the single quotes are
1343                      considered quoted.  This is the behavior of  posix  mode
1344                      through  version 4.1.  The default bash behavior remains
1345                      as in previous versions.
1346              compat42
1347                      If set, bash does not process the replacement string  in
1348                      the  pattern  substitution  word  expansion  using quote
1349                      removal.
1350              compat43
1351                      If set, bash does not print  a  warning  message  if  an
1352                      attempt  is  made to use a quoted compound array assign‐
1353                      ment as an argument to  declare,  makes  word  expansion
1354                      errors  non-fatal  errors that cause the current command
1355                      to fail (the default behavior  is  to  make  them  fatal
1356                      errors that cause the shell to exit), and does not reset
1357                      the loop state when a shell function is  executed  (this
1358                      allows  break  or continue in a shell function to affect
1359                      loops in the caller's context).
1360              complete_fullquote
1361                      If set, bash quotes all shell  metacharacters  in  file‐
1362                      names  and  directory  names when performing completion.
1363                      If not set, bash removes metacharacters such as the dol‐
1364                      lar  sign from the set of characters that will be quoted
1365                      in completed filenames when these metacharacters  appear
1366                      in  shell  variable references in words to be completed.
1367                      This means that dollar  signs  in  variable  names  that
1368                      expand  to  directories will not be quoted; however, any
1369                      dollar signs appearing in filenames will not be  quoted,
1370                      either.   This  is  active only when bash is using back‐
1371                      slashes to quote completed filenames.  This variable  is
1372                      set  by  default,  which is the default bash behavior in
1373                      versions through 4.2.
1374              direxpand
1375                      If set, bash replaces directory names with  the  results
1376                      of  word  expansion when performing filename completion.
1377                      This changes the contents of the readline  editing  buf‐
1378                      fer.   If  not  set,  bash attempts to preserve what the
1379                      user typed.
1380              dirspell
1381                      If set, bash attempts spelling correction  on  directory
1382                      names  during word completion if the directory name ini‐
1383                      tially supplied does not exist.
1384              dotglob If set, bash includes filenames beginning with a `.'  in
1385                      the results of pathname expansion.
1386              execfail
1387                      If set, a non-interactive shell will not exit if it can‐
1388                      not execute the file specified as  an  argument  to  the
1389                      exec  builtin  command.   An  interactive shell does not
1390                      exit if exec fails.
1391              expand_aliases
1392                      If set, aliases are expanded as  described  above  under
1393                      ALIASES.  This option is enabled by default for interac‐
1394                      tive shells.
1395              extdebug
1396                      If set at  shell  invocation,  arrange  to  execute  the
1397                      debugger  profile  before the shell starts, identical to
1398                      the --debugger option.  If set after invocation,  behav‐
1399                      ior intended for use by debuggers is enabled:
1400                      1.     The -F option to the declare builtin displays the
1401                             source file name and line number corresponding to
1402                             each function name supplied as an argument.
1403                      2.     If  the  command  run by the DEBUG trap returns a
1404                             non-zero value, the next command is  skipped  and
1405                             not executed.
1406                      3.     If  the  command  run by the DEBUG trap returns a
1407                             value of 2, and the shell is executing in a  sub‐
1408                             routine  (a shell function or a shell script exe‐
1409                             cuted by the . or  source  builtins),  the  shell
1410                             simulates a call to return.
1411                      4.     BASH_ARGC  and BASH_ARGV are updated as described
1412                             in their descriptions above.
1413                      5.     Function tracing is  enabled:  command  substitu‐
1414                             tion, shell functions, and subshells invoked with
1415                             ( command ) inherit the DEBUG and RETURN traps.
1416                      6.     Error tracing is enabled:  command  substitution,
1417                             shell  functions,  and  subshells  invoked with (
1418                             command ) inherit the ERR trap.
1419              extglob If set, the extended pattern matching features described
1420                      above under Pathname Expansion are enabled.
1421              extquote
1422                      If  set,  $'string'  and  $"string" quoting is performed
1423                      within  ${parameter}  expansions  enclosed   in   double
1424                      quotes.  This option is enabled by default.
1425              failglob
1426                      If  set,  patterns  which fail to match filenames during
1427                      pathname expansion result in an expansion error.
1428              force_fignore
1429                      If set, the suffixes  specified  by  the  FIGNORE  shell
1430                      variable  cause words to be ignored when performing word
1431                      completion even if the ignored words are the only possi‐
1432                      ble  completions.   See  SHELL  VARIABLES  above  for  a
1433                      description of  FIGNORE.   This  option  is  enabled  by
1434                      default.
1435              globasciiranges
1436                      If  set,  range  expressions  used  in  pattern matching
1437                      bracket expressions (see Pattern Matching above)  behave
1438                      as  if  in the traditional C locale when performing com‐
1439                      parisons.   That  is,  the  current  locale's  collating
1440                      sequence  is  not taken into account, so b will not col‐
1441                      late between A and  B,  and  upper-case  and  lower-case
1442                      ASCII characters will collate together.
1443              globstar
1444                      If set, the pattern ** used in a pathname expansion con‐
1445                      text will match all files and zero or  more  directories
1446                      and  subdirectories.  If the pattern is followed by a /,
1447                      only directories and subdirectories match.
1448              gnu_errfmt
1449                      If set, shell error messages are written in the standard
1450                      GNU error message format.
1451              histappend
1452                      If  set,  the history list is appended to the file named
1453                      by the value of the HISTFILE  variable  when  the  shell
1454                      exits, rather than overwriting the file.
1455              histreedit
1456                      If  set, and readline is being used, a user is given the
1457                      opportunity to re-edit a failed history substitution.
1458              histverify
1459                      If set, and readline is being used, the results of  his‐
1460                      tory  substitution  are  not  immediately  passed to the
1461                      shell parser.  Instead, the  resulting  line  is  loaded
1462                      into the readline editing buffer, allowing further modi‐
1463                      fication.
1464              hostcomplete
1465                      If set, and readline is being used, bash will attempt to
1466                      perform  hostname  completion when a word containing a @
1467                      is  being  completed  (see  Completing  under   READLINE
1468                      above).  This is enabled by default.
1469              huponexit
1470                      If set, bash will send SIGHUP to all jobs when an inter‐
1471                      active login shell exits.
1472              inherit_errexit
1473                      If set, command substitution inherits the value  of  the
1474                      errexit  option, instead of unsetting it in the subshell
1475                      environment.  This option is enabled when posix mode  is
1476                      enabled.
1477              interactive_comments
1478                      If set, allow a word beginning with # to cause that word
1479                      and all remaining characters on that line to be  ignored
1480                      in  an  interactive  shell  (see  COMMENTS above).  This
1481                      option is enabled by default.
1482              lastpipe
1483                      If set, and job control is not active,  the  shell  runs
1484                      the last command of a pipeline not executed in the back‐
1485                      ground in the current shell environment.
1486              lithist If set, and the cmdhist option  is  enabled,  multi-line
1487                      commands are saved to the history with embedded newlines
1488                      rather than using semicolon separators where possible.
1489              login_shell
1490                      The shell sets this option if it is started as  a  login
1491                      shell  (see  INVOCATION  above).   The  value may not be
1492                      changed.
1493              mailwarn
1494                      If set, and a file that bash is checking  for  mail  has
1495                      been  accessed  since  the last time it was checked, the
1496                      message ``The mail in mailfile has been read''  is  dis‐
1497                      played.
1498              no_empty_cmd_completion
1499                      If  set,  and  readline  is  being  used,  bash will not
1500                      attempt to search the PATH for possible completions when
1501                      completion is attempted on an empty line.
1502              nocaseglob
1503                      If  set,  bash  matches  filenames in a case-insensitive
1504                      fashion when performing pathname expansion (see Pathname
1505                      Expansion above).
1506              nocasematch
1507                      If  set,  bash  matches  patterns  in a case-insensitive
1508                      fashion when performing matching while executing case or
1509                      [[ conditional commands, when performing pattern substi‐
1510                      tution word expansions, or when filtering possible  com‐
1511                      pletions as part of programmable completion.
1512              nullglob
1513                      If  set,  bash allows patterns which match no files (see
1514                      Pathname Expansion above) to expand to  a  null  string,
1515                      rather than themselves.
1516              progcomp
1517                      If set, the programmable completion facilities (see Pro‐
1518                      grammable Completion above) are enabled.  This option is
1519                      enabled by default.
1520              promptvars
1521                      If set, prompt strings undergo parameter expansion, com‐
1522                      mand  substitution,  arithmetic  expansion,  and   quote
1523                      removal  after  being expanded as described in PROMPTING
1524                      above.  This option is enabled by default.
1525              restricted_shell
1526                      The  shell  sets  this  option  if  it  is  started   in
1527                      restricted mode (see RESTRICTED SHELL below).  The value
1528                      may not be changed.  This is not reset when the  startup
1529                      files  are  executed, allowing the startup files to dis‐
1530                      cover whether or not a shell is restricted.
1531              shift_verbose
1532                      If set, the shift builtin prints an error  message  when
1533                      the shift count exceeds the number of positional parame‐
1534                      ters.
1535              sourcepath
1536                      If set, the source (.) builtin uses the value of PATH to
1537                      find  the  directory  containing the file supplied as an
1538                      argument.  This option is enabled by default.
1539              xpg_echo
1540                      If  set,  the  echo  builtin  expands   backslash-escape
1541                      sequences by default.
1542
1543       suspend [-f]
1544              Suspend  the execution of this shell until it receives a SIGCONT
1545              signal.  A login shell cannot be suspended; the -f option can be
1546              used to override this and force the suspension.  The return sta‐
1547              tus is 0 unless the shell is a login shell and -f  is  not  sup‐
1548              plied, or if job control is not enabled.
1549
1550       test expr
1551       [ expr ]
1552              Return a status of 0 (true) or 1 (false) depending on the evalu‐
1553              ation of the conditional expression expr.  Each operator and op‐
1554              erand  must be a separate argument.  Expressions are composed of
1555              the primaries described  above  under  CONDITIONAL  EXPRESSIONS.
1556              test  does not accept any options, nor does it accept and ignore
1557              an argument of -- as signifying the end of options.
1558
1559              Expressions may  be  combined  using  the  following  operators,
1560              listed  in  decreasing  order  of  precedence.   The  evaluation
1561              depends on the number of arguments; see below.  Operator  prece‐
1562              dence is used when there are five or more arguments.
1563              ! expr True if expr is false.
1564              ( expr )
1565                     Returns  the value of expr.  This may be used to override
1566                     the normal precedence of operators.
1567              expr1 -a expr2
1568                     True if both expr1 and expr2 are true.
1569              expr1 -o expr2
1570                     True if either expr1 or expr2 is true.
1571
1572              test and [ evaluate conditional expressions using a set of rules
1573              based on the number of arguments.
1574
1575              0 arguments
1576                     The expression is false.
1577              1 argument
1578                     The expression is true if and only if the argument is not
1579                     null.
1580              2 arguments
1581                     If the first argument is !, the expression is true if and
1582                     only  if the second argument is null.  If the first argu‐
1583                     ment is one of the  unary  conditional  operators  listed
1584                     above  under  CONDITIONAL  EXPRESSIONS, the expression is
1585                     true if the unary test is true.  If the first argument is
1586                     not a valid unary conditional operator, the expression is
1587                     false.
1588              3 arguments
1589                     The following conditions are applied in the order listed.
1590                     If  the  second argument is one of the binary conditional
1591                     operators listed above under CONDITIONAL EXPRESSIONS, the
1592                     result of the expression is the result of the binary test
1593                     using the first and third arguments as operands.  The  -a
1594                     and  -o  operators  are  considered binary operators when
1595                     there are three arguments.  If the first argument  is  !,
1596                     the  value is the negation of the two-argument test using
1597                     the second and third arguments.  If the first argument is
1598                     exactly ( and the third argument is exactly ), the result
1599                     is the one-argument test of the second argument.   Other‐
1600                     wise, the expression is false.
1601              4 arguments
1602                     If the first argument is !, the result is the negation of
1603                     the three-argument expression composed of  the  remaining
1604                     arguments.  Otherwise, the expression is parsed and eval‐
1605                     uated according to  precedence  using  the  rules  listed
1606                     above.
1607              5 or more arguments
1608                     The  expression  is  parsed  and  evaluated  according to
1609                     precedence using the rules listed above.
1610
1611              When used with test or [, the < and  >  operators  sort  lexico‐
1612              graphically using ASCII ordering.
1613
1614       times  Print  the  accumulated  user and system times for the shell and
1615              for processes run from the shell.  The return status is 0.
1616
1617       trap [-lp] [[arg] sigspec ...]
1618              The command arg is to  be  read  and  executed  when  the  shell
1619              receives  signal(s)  sigspec.   If arg is absent (and there is a
1620              single sigspec) or -, each specified  signal  is  reset  to  its
1621              original  disposition  (the  value  it  had upon entrance to the
1622              shell).  If arg is the null string the signal specified by  each
1623              sigspec  is ignored by the shell and by the commands it invokes.
1624              If arg is not present and -p has been supplied,  then  the  trap
1625              commands  associated  with  each  sigspec  are displayed.  If no
1626              arguments are supplied or if only -p is given, trap  prints  the
1627              list  of  commands  associated  with each signal.  The -l option
1628              causes the shell to print a list of signal names and their  cor‐
1629              responding  numbers.   Each  sigspec  is  either  a  signal name
1630              defined in <signal.h>, or a signal  number.   Signal  names  are
1631              case insensitive and the SIG prefix is optional.
1632
1633              If  a  sigspec  is  EXIT (0) the command arg is executed on exit
1634              from the shell.  If a sigspec is DEBUG, the command arg is  exe‐
1635              cuted  before  every  simple command, for command, case command,
1636              select command, every arithmetic for  command,  and  before  the
1637              first  command  executes  in a shell function (see SHELL GRAMMAR
1638              above).  Refer to the description of the extdebug option to  the
1639              shopt builtin for details of its effect on the DEBUG trap.  If a
1640              sigspec is RETURN, the command arg is executed each time a shell
1641              function or a script executed with the . or source builtins fin‐
1642              ishes executing.
1643
1644              If a sigspec is ERR, the command  arg  is  executed  whenever  a
1645              pipeline (which may consist of a single simple command), a list,
1646              or a compound command returns a non-zero exit status, subject to
1647              the  following  conditions.  The ERR trap is not executed if the
1648              failed command is part of the command list immediately following
1649              a  while  or until keyword, part of the test in an if statement,
1650              part of a command executed in a && or || list except the command
1651              following  the final && or ||, any command in a pipeline but the
1652              last, or if the command's return value is being  inverted  using
1653              !.   These  are  the  same conditions obeyed by the errexit (-e)
1654              option.
1655
1656              Signals ignored upon entry to the shell cannot be trapped, reset
1657              or listed.  Trapped signals that are not being ignored are reset
1658              to their original values in a subshell or  subshell  environment
1659              when  one is created.  The return status is false if any sigspec
1660              is invalid; otherwise trap returns true.
1661
1662       type [-aftpP] name [name ...]
1663              With no options, indicate how each name would be interpreted  if
1664              used as a command name.  If the -t option is used, type prints a
1665              string which is one of alias,  keyword,  function,  builtin,  or
1666              file  if  name  is  an  alias,  shell  reserved  word, function,
1667              builtin, or disk file, respectively.  If the name is not  found,
1668              then  nothing  is  printed,  and  an  exit  status  of  false is
1669              returned.  If the -p option is used,  type  either  returns  the
1670              name of the disk file that would be executed if name were speci‐
1671              fied as a command name, or nothing if ``type -t name'' would not
1672              return  file.  The -P option forces a PATH search for each name,
1673              even if ``type -t name'' would not return file.  If a command is
1674              hashed, -p and -P print the hashed value, which is not necessar‐
1675              ily the file that appears first in PATH.  If the  -a  option  is
1676              used,  type  prints all of the places that contain an executable
1677              named name.  This includes aliases and functions, if and only if
1678              the -p option is not also used.  The table of hashed commands is
1679              not consulted when using -a.  The  -f  option  suppresses  shell
1680              function lookup, as with the command builtin.  type returns true
1681              if all of the arguments are found, false if any are not found.
1682
1683       ulimit [-HSabcdefiklmnpqrstuvxPT [limit]]
1684              Provides control over the resources available to the  shell  and
1685              to  processes started by it, on systems that allow such control.
1686              The -H and -S options specify that the hard or soft limit is set
1687              for  the  given resource.  A hard limit cannot be increased by a
1688              non-root user once it is set; a soft limit may be  increased  up
1689              to  the value of the hard limit.  If neither -H nor -S is speci‐
1690              fied, both the soft and hard limits are set.  The value of limit
1691              can be a number in the unit specified for the resource or one of
1692              the special values hard, soft, or unlimited, which stand for the
1693              current  hard  limit,  the  current  soft  limit,  and no limit,
1694              respectively.  If limit is omitted, the  current  value  of  the
1695              soft  limit  of the resource is printed, unless the -H option is
1696              given.  When more than one resource is specified, the limit name
1697              and unit are printed before the value.  Other options are inter‐
1698              preted as follows:
1699              -a     All current limits are reported
1700              -b     The maximum socket buffer size
1701              -c     The maximum size of core files created
1702              -d     The maximum size of a process's data segment
1703              -e     The maximum scheduling priority ("nice")
1704              -f     The maximum size of files written by the  shell  and  its
1705                     children
1706              -i     The maximum number of pending signals
1707              -k     The maximum number of kqueues that may be allocated
1708              -l     The maximum size that may be locked into memory
1709              -m     The  maximum resident set size (many systems do not honor
1710                     this limit)
1711              -n     The maximum number of open file descriptors (most systems
1712                     do not allow this value to be set)
1713              -p     The pipe size in 512-byte blocks (this may not be set)
1714              -q     The maximum number of bytes in POSIX message queues
1715              -r     The maximum real-time scheduling priority
1716              -s     The maximum stack size
1717              -t     The maximum amount of cpu time in seconds
1718              -u     The  maximum  number  of  processes available to a single
1719                     user
1720              -v     The maximum amount of virtual  memory  available  to  the
1721                     shell and, on some systems, to its children
1722              -x     The maximum number of file locks
1723              -P     The maximum number of pseudoterminals
1724              -T     The maximum number of threads
1725
1726              If  limit  is given, and the -a option is not used, limit is the
1727              new value of the specified resource.  If  no  option  is  given,
1728              then  -f is assumed.  Values are in 1024-byte increments, except
1729              for -t, which is in seconds; -p, which is in units  of  512-byte
1730              blocks;  -P,  -T, -b, -k, -n, and -u, which are unscaled values;
1731              and, when in Posix mode, -c and -f, which are in 512-byte incre‐
1732              ments.  The return status is 0 unless an invalid option or argu‐
1733              ment is supplied, or an error occurs while setting a new  limit.
1734              In  POSIX  Mode  512-byte  blocks are used for the `-c' and `-f'
1735              options.
1736
1737       umask [-p] [-S] [mode]
1738              The user file-creation mask is set to mode.  If mode begins with
1739              a  digit,  it is interpreted as an octal number; otherwise it is
1740              interpreted as a symbolic mode mask similar to that accepted  by
1741              chmod(1).   If mode is omitted, the current value of the mask is
1742              printed.  The -S option causes the mask to be  printed  in  sym‐
1743              bolic  form;  the  default output is an octal number.  If the -p
1744              option is supplied, and mode is omitted, the output is in a form
1745              that may be reused as input.  The return status is 0 if the mode
1746              was successfully changed or if no mode  argument  was  supplied,
1747              and false otherwise.
1748
1749       unalias [-a] [name ...]
1750              Remove  each  name  from  the list of defined aliases.  If -a is
1751              supplied, all alias definitions are removed.  The  return  value
1752              is true unless a supplied name is not a defined alias.
1753
1754       unset [-fv] [-n] [name ...]
1755              For  each  name,  remove the corresponding variable or function.
1756              If the -v option is given, each name refers to a shell variable,
1757              and  that  variable  is removed.  Read-only variables may not be
1758              unset.  If -f is specified, each name refers to  a  shell  func‐
1759              tion,  and the function definition is removed.  If the -n option
1760              is supplied, and name is a variable with the nameref  attribute,
1761              name  will  be unset rather than the variable it references.  -n
1762              has no effect if the -f option is supplied.  If no  options  are
1763              supplied,  each  name refers to a variable; if there is no vari‐
1764              able by that name, any function with that name is  unset.   Each
1765              unset  variable  or  function  is  removed  from the environment
1766              passed to subsequent commands.  If any of COMP_WORDBREAKS,  RAN‐
1767              DOM, SECONDS, LINENO, HISTCMD, FUNCNAME, GROUPS, or DIRSTACK are
1768              unset, they lose their special properties, even if they are sub‐
1769              sequently reset.  The exit status is true unless a name is read‐
1770              only.
1771
1772       wait [-n] [n ...]
1773              Wait for each specified child process and return its termination
1774              status.  Each n may be a process ID or a job specification; if a
1775              job spec is given, all processes  in  that  job's  pipeline  are
1776              waited  for.  If n is not given, all currently active child pro‐
1777              cesses are waited for, and the return status is zero.  If the -n
1778              option  is  supplied,  wait  waits  for any job to terminate and
1779              returns its exit status.  If n specifies a non-existent  process
1780              or  job, the return status is 127.  Otherwise, the return status
1781              is the exit status of the last process or job waited for.
1782

SEE ALSO

1784       bash(1), sh(1)
1785
1786
1787
1788GNU Bash-4.2                      2004 Apr 20                 BASH_BUILTINS(1)
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