{
    "mode": "man",
    "parameter": "bash-builtins",
    "section": "7",
    "url": "https://www.chedong.com/phpMan.php/man/bash-builtins/7/json",
    "generated": "2026-10-04T15:28:23Z",
    "synopsis": "bash defines the following built-in commands: :, ., [, alias, bg, bind, break, builtin, case,\ncd,  command,  compgen,  complete, continue, declare, dirs, disown, echo, enable, eval, exec,\nexit, export, fc, fg, getopts, hash, help, history, if, jobs, kill, let, local, logout, popd,\nprintf, pushd, pwd, read, readonly, return, set, shift, shopt, source, suspend, test,  times,\ntrap, type, typeset, ulimit, umask, unalias, unset, until, wait, while.",
    "sections": {
        "NAME": {
            "content": "bash-builtins - bash built-in commands, see bash(1)\n",
            "subsections": []
        },
        "SYNOPSIS": {
            "content": "bash defines the following built-in commands: :, ., [, alias, bg, bind, break, builtin, case,\ncd,  command,  compgen,  complete, continue, declare, dirs, disown, echo, enable, eval, exec,\nexit, export, fc, fg, getopts, hash, help, history, if, jobs, kill, let, local, logout, popd,\nprintf, pushd, pwd, read, readonly, return, set, shift, shopt, source, suspend, test,  times,\ntrap, type, typeset, ulimit, umask, unalias, unset, until, wait, while.\n",
            "subsections": []
        },
        "BASH BUILTIN COMMANDS": {
            "content": "Unless  otherwise noted, each builtin command documented in this section as accepting options\npreceded by - accepts -- to signify the end of the options.  The :, true, false,  and  test/[\nbuiltins  do  not  accept  options  and do not treat -- specially.  The exit, logout, return,\nbreak, continue, let, and shift builtins accept and process arguments beginning with -  with‐\nout  requiring  --.   Other builtins that accept arguments but are not specified as accepting\noptions interpret arguments beginning with - as invalid options and  require  --  to  prevent\nthis interpretation.\n: [arguments]\nNo  effect;  the  command  does  nothing beyond expanding arguments and performing any\nspecified redirections.  The return status is zero.\n\n.  filename [arguments]\nsource filename [arguments]\nRead and execute commands from filename in the current shell  environment  and  return\nthe exit status of the last command executed from filename.  If filename does not con‐\ntain  a  slash,  filenames in PATH are used to find the directory containing filename,\nbut filename does not need to be executable.  The file searched for in PATH  need  not\nbe  executable.   When bash is not in posix mode, it searches the current directory if\nno file is found in PATH.  If the sourcepath option to the shopt  builtin  command  is\nturned  off, the PATH is not searched.  If any arguments are supplied, they become the\npositional parameters when filename is executed.  Otherwise the positional  parameters\nare  unchanged.   If  the -T option is enabled, . inherits any trap on DEBUG; if it is\nnot, any DEBUG trap string is saved and restored around the call to .,  and  .  unsets\nthe  DEBUG trap while it executes.  If -T is not set, and the sourced file changes the\nDEBUG trap, the new value is retained when . completes.  The return status is the sta‐\ntus of the last command exited within the script (0 if no commands are executed),  and\nfalse if filename is not found or cannot be read.\n\nalias [-p] [name[=value] ...]\nAlias  with  no arguments or with the -p option prints the list of aliases in the form\nalias name=value on standard output.  When arguments are supplied, an alias is defined\nfor each name whose value is given.  A trailing space in value causes the next word to\nbe checked for alias substitution when the alias is expanded.  For each  name  in  the\nargument  list  for  which  no  value  is supplied, the name and value of the alias is\nprinted.  Alias returns true unless a name is given for which no alias  has  been  de‐\nfined.\n\nbg [jobspec ...]\nResume each suspended job jobspec in the background, as if it had been started with &.\nIf  jobspec is not present, the shell's notion of the current job is used.  bg jobspec\nreturns 0 unless run when job control is disabled or, when run with  job  control  en‐\nabled, any specified jobspec was not found or was started without job control.\n\nbind [-m keymap] [-lpsvPSVX]\nbind [-m keymap] [-q function] [-u function] [-r keyseq]\nbind [-m keymap] -f filename\nbind [-m keymap] -x keyseq:shell-command\nbind [-m keymap] keyseq:function-name\nbind [-m keymap] keyseq:readline-command\nbind readline-command-line\nDisplay  current readline key and function bindings, bind a key sequence to a readline\nfunction or macro, or set a readline variable.  Each non-option argument is a  command\nas  it would appear in a readline initialization file such as .inputrc, but each bind‐\ning  or  command  must  be  passed  as  a  separate   argument;   e.g.,   '\"\\C-x\\C-r\":\nre-read-init-file'.  Options, if supplied, have the following meanings:\n-m keymap\nUse keymap as the keymap to be affected by the subsequent bindings.  Acceptable\nkeymap  names  are  emacs, emacs-standard, emacs-meta, emacs-ctlx, vi, vi-move,\nvi-command, and vi-insert.  vi is equivalent to vi-command (vi-move is  also  a\nsynonym); emacs is equivalent to emacs-standard.\n-l     List the names of all readline functions.\n-p     Display readline function names and bindings in such a way that they can be re-\nread.\n-P     List current readline function names and bindings.\n-s     Display  readline  key sequences bound to macros and the strings they output in\nsuch a way that they can be re-read.\n-S     Display readline key sequences bound to macros and the strings they output.\n-v     Display readline variable names and values in such a way that they can  be  re-\nread.\n-V     List current readline variable names and values.\n-f filename\nRead key bindings from filename.\n-q function\nQuery about which keys invoke the named function.\n-u function\nUnbind all keys bound to the named function.\n-r keyseq\nRemove any current binding for keyseq.\n-x keyseq:shell-command\nCause shell-command to be executed whenever keyseq is entered.  When shell-com‐\nmand  is executed, the shell sets the READLINELINE variable to the contents of\nthe readline line buffer and the READLINEPOINT and READLINEMARK variables  to\nthe  current location of the insertion point and the saved insertion point (the\nmark), respectively.  The shell assigns any numeric argument the user  supplied\nto  the READLINEARGUMENT variable.  If there was no argument, that variable is\nnot set.  If the executed command changes the value of  any  of  READLINELINE,\nREADLINEPOINT,  or  READLINEMARK,  those  new values will be reflected in the\nediting state.\n-X     List all key sequences bound to shell commands and the associated commands in a\nformat that can be reused as input.\n\nThe return value is 0 unless an unrecognized option is given or an error occurred.\n\nbreak [n]\nExit from within a for, while, until, or select loop.  If n is specified, break n lev‐\nels.  n must be ≥ 1.  If n is greater than the number of enclosing loops, all  enclos‐\ning  loops are exited.  The return value is 0 unless n is not greater than or equal to\n1.\n\nbuiltin shell-builtin [arguments]\nExecute the specified shell builtin, passing it arguments, and return its exit status.\nThis is useful when defining a function whose name is the same as a shell builtin, re‐\ntaining the functionality of the builtin within the function.  The cd builtin is  com‐\nmonly  redefined this way.  The return status is false if shell-builtin is not a shell\nbuiltin command.\n\ncaller [expr]\nReturns the context of any active subroutine call (a shell function or a  script  exe‐\ncuted  with  the . or source builtins).  Without expr, caller displays the line number\nand source filename of the current subroutine call.  If a non-negative integer is sup‐\nplied as expr, caller displays the line number, subroutine name, and source file  cor‐\nresponding  to that position in the current execution call stack.  This extra informa‐\ntion may be used, for example, to print a stack trace.  The current frame is frame  0.\nThe return value is 0 unless the shell is not executing a subroutine call or expr does\nnot correspond to a valid position in the call stack.\n\ncd [-L|[-P [-e]] [-@]] [dir]\nChange  the  current  directory to dir.  if dir is not supplied, the value of the HOME\nshell variable is the default.  The variable CDPATH defines the search  path  for  the\ndirectory containing dir: each directory name in CDPATH is searched for dir.  Alterna‐\ntive directory names in CDPATH are separated by a colon (:).  A null directory name in\nCDPATH  is the same as the current directory, i.e., ``.''.  If dir begins with a slash\n(/), then CDPATH is not used.  The -P option causes cd to use the  physical  directory\nstructure  by  resolving symbolic links while traversing dir and before processing in‐\nstances of .. in dir (see also the -P option to the set builtin command); the  -L  op‐\ntion  forces  symbolic links to be followed by resolving the link after processing in‐\nstances of .. in dir.  If .. appears in dir, it is processed by removing  the  immedi‐\nately  previous  pathname component from dir, back to a slash or the beginning of dir.\nIf the -e option is supplied with -P, and the current working directory cannot be suc‐\ncessfully determined after a successful directory change, cd will return an unsuccess‐\nful status.  On systems that support it, the -@ option presents the  extended  attrib‐\nutes  associated with a file as a directory.  An argument of - is converted to $OLDPWD\nbefore the directory change is attempted.  If a non-empty directory name  from  CDPATH\nis  used,  or  if - is the first argument, and the directory change is successful, the\nabsolute pathname of the new working directory is written to the standard output.   If\nthe  directory change is successful, cd sets the value of the PWD environment variable\nto the new directory name, and sets the OLDPWD environment variable to  the  value  of\nthe  current working directory before the change.  The return value is true if the di‐\nrectory was successfully changed; false otherwise.\n\ncommand [-pVv] command [arg ...]\nRun command with args suppressing the normal shell function lookup.  Only builtin com‐\nmands or commands found in the PATH are executed.  If the  -p  option  is  given,  the\nsearch  for  command is performed using a default value for PATH that is guaranteed to\nfind all of the standard utilities.  If either the -V or -v option is supplied, a  de‐\nscription  of  command  is printed.  The -v option causes a single word indicating the\ncommand or filename used to invoke command to be displayed; the -V option  produces  a\nmore verbose description.  If the -V or -v option is supplied, the exit status is 0 if\ncommand  was found, and 1 if not.  If neither option is supplied and an error occurred\nor command cannot be found, the exit status is 127.  Otherwise, the exit status of the\ncommand builtin is the exit status of command.\n\ncompgen [option] [word]\nGenerate possible completion matches for word according to the options, which  may  be\nany option accepted by the complete builtin with the exception of -p and -r, and write\nthe  matches  to  the  standard  output.  When using the -F or -C options, the various\nshell variables set by the programmable completion facilities, while  available,  will\nnot have useful values.\n\nThe  matches  will be generated in the same way as if the programmable completion code\nhad generated them directly from a completion specification with the same  flags.   If\nword is specified, only those completions matching word will be displayed.\n\nThe return value is true unless an invalid option is supplied, or no matches were gen‐\nerated.\n\ncomplete [-abcdefgjksuv] [-o comp-option] [-DEI] [-A action] [-G globpat] [-W wordlist]\n[-F function] [-C command] [-X filterpat] [-P prefix] [-S suffix] name [name ...]\ncomplete -pr [-DEI] [name ...]\nSpecify how arguments to each name should be completed.  If the -p option is supplied,\nor if no options are supplied, existing completion specifications are printed in a way\nthat allows them to be reused as input.  The -r option removes a completion specifica‐\ntion  for each name, or, if no names are supplied, all completion specifications.  The\n-D option indicates that other supplied options and actions should apply to the  ``de‐\nfault''  command  completion;  that is, completion attempted on a command for which no\ncompletion has previously been defined.  The -E option indicates that  other  supplied\noptions  and actions should apply to ``empty'' command completion; that is, completion\nattempted on a blank line.  The -I option indicates that other  supplied  options  and\nactions  should apply to completion on the initial non-assignment word on the line, or\nafter a command delimiter such as ; or |, which is usually  command  name  completion.\nIf  multiple  options  are  supplied, the -D option takes precedence over -E, and both\ntake precedence over -I.  If any of -D, -E, or -I are supplied, any other  name  argu‐\nments are ignored; these completions only apply to the case specified by the option.\n\nThe  process  of  applying these completion specifications when word completion is at‐\ntempted is described in bash(1).\n\nOther options, if specified, have the following meanings.  The arguments  to  the  -G,\n-W, and -X options (and, if necessary, the -P and -S options) should be quoted to pro‐\ntect them from expansion before the complete builtin is invoked.\n-o comp-option\nThe comp-option controls several aspects of the compspec's behavior beyond the\nsimple generation of completions.  comp-option may be one of:\nbashdefault\nPerform  the rest of the default bash completions if the compspec gen‐\nerates no matches.\ndefault Use readline's default filename completion if the  compspec  generates\nno matches.\ndirnames\nPerform  directory  name  completion  if  the  compspec  generates  no\nmatches.\nfilenames\nTell readline that the compspec generates filenames, so it can perform\nany filename-specific processing (like adding  a  slash  to  directory\nnames,  quoting  special  characters, or suppressing trailing spaces).\nIntended to be used with shell functions.\nnoquote Tell readline not to quote the completed words if they  are  filenames\n(quoting filenames is the default).\nnosort  Tell  readline not to sort the list of possible completions alphabeti‐\ncally.\nnospace Tell readline not to append a space (the default) to  words  completed\nat the end of the line.\nplusdirs\nAfter  any  matches  defined  by the compspec are generated, directory\nname completion is attempted and any matches are added to the  results\nof the other actions.\n-A action\nThe  action may be one of the following to generate a list of possible comple‐\ntions:\nalias   Alias names.  May also be specified as -a.\narrayvar\nArray variable names.\nbinding Readline key binding names.\nbuiltin Names of shell builtin commands.  May also be specified as -b.\ncommand Command names.  May also be specified as -c.\ndirectory\nDirectory names.  May also be specified as -d.\ndisabled\nNames of disabled shell builtins.\nenabled Names of enabled shell builtins.\nexport  Names of exported shell variables.  May also be specified as -e.\nfile    File names.  May also be specified as -f.\nfunction\nNames of shell functions.\ngroup   Group names.  May also be specified as -g.\nhelptopic\nHelp topics as accepted by the help builtin.\nhostname\nHostnames, as taken from the file  specified  by  the  HOSTFILE  shell\nvariable.\njob     Job names, if job control is active.  May also be specified as -j.\nkeyword Shell reserved words.  May also be specified as -k.\nrunning Names of running jobs, if job control is active.\nservice Service names.  May also be specified as -s.\nsetopt  Valid arguments for the -o option to the set builtin.\nshopt   Shell option names as accepted by the shopt builtin.\nsignal  Signal names.\nstopped Names of stopped jobs, if job control is active.\nuser    User names.  May also be specified as -u.\nvariable\nNames of all shell variables.  May also be specified as -v.\n-C command\ncommand  is  executed in a subshell environment, and its output is used as the\npossible completions.  Arguments are passed as with the -F option.\n-F function\nThe shell function function is executed  in  the  current  shell  environment.\nWhen the function is executed, the first argument ($1) is the name of the com‐\nmand whose arguments are being completed, the second argument ($2) is the word\nbeing  completed,  and  the third argument ($3) is the word preceding the word\nbeing completed on the current command line.  When it finishes,  the  possible\ncompletions are retrieved from the value of the COMPREPLY array variable.\n-G globpat\nThe  pathname  expansion  pattern globpat is expanded to generate the possible\ncompletions.\n-P prefix\nprefix is added at the beginning of each possible completion after  all  other\noptions have been applied.\n-S suffix\nsuffix  is  appended  to each possible completion after all other options have\nbeen applied.\n-W wordlist\nThe wordlist is split using the characters in the IFS special variable as  de‐\nlimiters,  and  each  resultant  word  is  expanded.  Shell quoting is honored\nwithin wordlist, in order to provide a mechanism  for  the  words  to  contain\nshell  metacharacters or characters in the value of IFS.  The possible comple‐\ntions are the members of the resultant list which match the  word  being  com‐\npleted.\n-X filterpat\nfilterpat  is  a pattern as used for pathname expansion.  It is applied to the\nlist of possible completions generated by the preceding options and arguments,\nand each completion matching filterpat is removed from the list.  A leading  !\nin  filterpat  negates  the pattern; in this case, any completion not matching\nfilterpat is removed.\n\nThe return value is true unless an invalid option is supplied, an option other than -p\nor -r is supplied without a name argument, an attempt is made to remove  a  completion\nspecification  for a name for which no specification exists, or an error occurs adding\na completion specification.\n\ncompopt [-o option] [-DEI] [+o option] [name]\nModify completion options for each name according to the  options,  or  for  the  cur‐\nrently-executing  completion  if no names are supplied.  If no options are given, dis‐\nplay the completion options for each name or the  current  completion.   The  possible\nvalues of option are those valid for the complete builtin described above.  The -D op‐\ntion  indicates  that  other  supplied options should apply to the ``default'' command\ncompletion; that is, completion attempted on a command for  which  no  completion  has\npreviously  been  defined.  The -E option indicates that other supplied options should\napply to ``empty'' command completion; that is, completion attempted on a blank  line.\nThe  -I option indicates that other supplied options should apply to completion on the\ninitial non-assignment word on the line, or after a command delimiter such as ; or  |,\nwhich is usually command name completion.\n\nThe  return  value is true unless an invalid option is supplied, an attempt is made to\nmodify the options for a name for which no completion specification exists, or an out‐\nput error occurs.\n\ncontinue [n]\nResume the next iteration of the enclosing for, while, until, or select loop.  If n is\nspecified, resume at the nth enclosing loop.  n must be ≥ 1.  If n is greater than the\nnumber of enclosing loops, the last enclosing loop (the  ``top-level''  loop)  is  re‐\nsumed.  The return value is 0 unless n is not greater than or equal to 1.\n\ndeclare [-aAfFgiIlnrtux] [-p] [name[=value] ...]\ntypeset [-aAfFgiIlnrtux] [-p] [name[=value] ...]\nDeclare variables and/or give them attributes.  If no names are given then display the\nvalues  of  variables.   The  -p option will display the attributes and values of each\nname.  When -p is used with name arguments, additional options, other than -f and  -F,\nare  ignored.  When -p is supplied without name arguments, it will display the attrib‐\nutes and values of all variables having the attributes specified by the additional op‐\ntions.  If no other options are supplied with -p, declare will display the  attributes\nand  values  of all shell variables.  The -f option will restrict the display to shell\nfunctions.  The -F option inhibits the display of function definitions; only the func‐\ntion name and attributes are printed.  If the extdebug shell option is  enabled  using\nshopt,  the  source file name and line number where each name is defined are displayed\nas well.  The -F option implies -f.  The -g option forces variables to be  created  or\nmodified  at  the global scope, even when declare is executed in a shell function.  It\nis ignored in all other cases.  The -I option causes local variables  to  inherit  the\nattributes  (except the nameref attribute) and value of any existing variable with the\nsame name at a surrounding scope.  If there is no existing variable, the  local  vari‐\nable  is  initially  unset.   The  following options can be used to restrict output to\nvariables with the specified attribute or to give variables attributes:\n-a     Each name is an indexed array variable (see Arrays in bash(1)).\n-A     Each name is an associative array variable (see Arrays in bash(1)).\n-f     Use function names only.\n-i     The variable is treated as an integer; arithmetic  evaluation  (see  ARITHMETIC\nEVALUATION in bash(1)) is performed when the variable is assigned a value.\n-l     When  the variable is assigned a value, all upper-case characters are converted\nto lower-case.  The upper-case attribute is disabled.\n-n     Give each name the nameref attribute, making it a  name  reference  to  another\nvariable.   That  other  variable  is defined by the value of name.  All refer‐\nences, assignments, and attribute modifications to name, except those using  or\nchanging  the  -n attribute itself, are performed on the variable referenced by\nname's value.  The nameref attribute cannot be applied to array variables.\n-r     Make names readonly.  These names cannot then be assigned values by  subsequent\nassignment statements or unset.\n-t     Give each name the trace attribute.  Traced functions inherit the DEBUG and RE‐\nTURN  traps from the calling shell.  The trace attribute has no special meaning\nfor variables.\n-u     When the variable is assigned a value, all lower-case characters are  converted\nto upper-case.  The lower-case attribute is disabled.\n-x     Mark names for export to subsequent commands via the environment.\n\nUsing  `+' instead of `-' turns off the attribute instead, with the exceptions that +a\nand +A may not be used to destroy array variables and +r will not remove the  readonly\nattribute.  When used in a function, declare and typeset make each name local, as with\nthe  local  command, unless the -g option is supplied.  If a variable name is followed\nby =value, the value of the variable is set to value.  When using -a  or  -A  and  the\ncompound  assignment  syntax  to  create array variables, additional attributes do not\ntake effect until subsequent assignments.  The return value is 0 unless an invalid op‐\ntion is encountered, an attempt is made to define a function using ``-f foo=bar'',  an\nattempt is made to assign a value to a readonly variable, an attempt is made to assign\na  value to an array variable without using the compound assignment syntax (see Arrays\nin bash(1)), one of the names is not a valid shell variable name, an attempt  is  made\nto  turn  off  readonly status for a readonly variable, an attempt is made to turn off\narray status for an array variable, or an attempt is made to  display  a  non-existent\nfunction with -f.\n\ndirs [-clpv] [+n] [-n]\nWithout  options,  displays the list of currently remembered directories.  The default\ndisplay is on a single line with directory names separated by spaces.  Directories are\nadded to the list with the pushd command; the popd command removes  entries  from  the\nlist.  The current directory is always the first directory in the stack.\n-c     Clears the directory stack by deleting all of the entries.\n-l     Produces  a  listing  using  full  pathnames; the default listing format uses a\ntilde to denote the home directory.\n-p     Print the directory stack with one entry per line.\n-v     Print the directory stack with one entry per line, prefixing  each  entry  with\nits index in the stack.\n+n     Displays  the  nth  entry counting from the left of the list shown by dirs when\ninvoked without options, starting with zero.\n-n     Displays the nth entry counting from the right of the list shown by  dirs  when\ninvoked without options, starting with zero.\n\nThe return value is 0 unless an invalid option is supplied or n indexes beyond the end\nof the directory stack.\n\ndisown [-ar] [-h] [jobspec ... | pid ... ]\nWithout options, remove each jobspec from the table of active jobs.  If jobspec is not\npresent,  and  neither  the -a nor the -r option is supplied, the current job is used.\nIf the -h option is given, each jobspec is not removed from the table, but  is  marked\nso  that  SIGHUP is not sent to the job if the shell receives a SIGHUP.  If no jobspec\nis supplied, the -a option means to remove or mark all jobs; the -r option  without  a\njobspec  argument restricts operation to running jobs.  The return value is 0 unless a\njobspec does not specify a valid job.\n\necho [-neE] [arg ...]\nOutput the args, separated by spaces, followed by a newline.  The return status  is  0\nunless  a write error occurs.  If -n is specified, the trailing newline is suppressed.\nIf the -e option is given, interpretation of the following  backslash-escaped  charac‐\nters  is  enabled.   The -E option disables the interpretation of these escape charac‐\nters, even on systems where they are interpreted by default.  The xpgecho  shell  op‐\ntion  may  be  used  to dynamically determine whether or not echo expands these escape\ncharacters by default.  echo does not interpret -- to mean the end of  options.   echo\ninterprets the following escape sequences:\n\\a     alert (bell)\n\\b     backspace\n\\c     suppress further output\n\\e\n\\E     an escape character\n\\f     form feed\n\\n     new line\n\\r     carriage return\n\\t     horizontal tab\n\\v     vertical tab\n\\\\     backslash\n\\0nnn  the eight-bit character whose value is the octal value nnn (zero to three octal\ndigits)\n\\xHH   the eight-bit character whose value is the hexadecimal value HH (one or two hex\ndigits)\n\\uHHHH the Unicode (ISO/IEC 10646) character whose value is the hexadecimal value HHHH\n(one to four hex digits)\n\\UHHHHHHHH\nthe Unicode (ISO/IEC 10646) character whose value is the hexadecimal value HHH‐\nHHHHH (one to eight hex digits)\n\nenable [-a] [-dnps] [-f filename] [name ...]\nEnable  and disable builtin shell commands.  Disabling a builtin allows a disk command\nwhich has the same name as a shell builtin to be executed without  specifying  a  full\npathname,  even  though the shell normally searches for builtins before disk commands.\nIf -n is used, each name is disabled; otherwise, names are enabled.  For  example,  to\nuse the test binary found via the PATH instead of the shell builtin version, run ``en‐\nable  -n test''.  The -f option means to load the new builtin command name from shared\nobject filename, on systems that support dynamic loading.  Bash will use the value  of\nthe  BASHLOADABLESPATH variable as a colon-separated list of directories in which to\nsearch for filename.  The default is system-dependent.  The -d option  will  delete  a\nbuiltin  previously  loaded with -f.  If no name arguments are given, or if the -p op‐\ntion is supplied, a list of shell builtins is printed.  With  no  other  option  argu‐\nments,  the list consists of all enabled shell builtins.  If -n is supplied, only dis‐\nabled builtins are printed.   If  -a  is  supplied,  the  list  printed  includes  all\nbuiltins,  with  an  indication of whether or not each is enabled.  If -s is supplied,\nthe output is restricted to the POSIX special builtins.  If no  options  are  supplied\nand  a name is not a shell builtin, enable will attempt to load name from a shared ob‐\nject named name, as if the command were ``enable -f name name .  The return value is 0\nunless a name is not a shell builtin or there is an error loading a new builtin from a\nshared object.\n\neval [arg ...]\nThe args are read and concatenated together into a single command.   This  command  is\nthen  read  and executed by the shell, and its exit status is returned as the value of\neval.  If there are no args, or only null arguments, eval returns 0.\n\nexec [-cl] [-a name] [command [arguments]]\nIf command is specified, it replaces the shell.  No new process is created.  The argu‐\nments become the arguments to command.  If the -l option is supplied, the shell places\na dash at the beginning of the zeroth argument passed to command.  This  is  what  lo‐\ngin(1)  does.   The -c option causes command to be executed with an empty environment.\nIf -a is supplied, the shell passes name as the zeroth argument to the  executed  com‐\nmand.   If  command cannot be executed for some reason, a non-interactive shell exits,\nunless the execfail shell option is enabled.  In that case, it  returns  failure.   An\ninteractive  shell  returns  failure if the file cannot be executed.  A subshell exits\nunconditionally if exec fails.  If command is not specified, any redirections take ef‐\nfect in the current shell, and the return status is 0.  If there is a redirection  er‐\nror, the return status is 1.\n\nexit [n]\nCause  the shell to exit with a status of n.  If n is omitted, the exit status is that\nof the last command executed.  A trap on EXIT is executed before the shell terminates.\n\nexport [-fn] [name[=word]] ...",
            "subsections": [
                {
                    "name": "export -p",
                    "content": "The supplied names are marked for automatic export to the environment of  subsequently\nexecuted  commands.   If  the -f option is given, the names refer to functions.  If no\nnames are given, or if the -p option is supplied, a list  of  names  of  all  exported\nvariables  is  printed.   The  -n option causes the export property to be removed from\neach name.  If a variable name is followed by =word, the value of the variable is  set\nto  word.  export returns an exit status of 0 unless an invalid option is encountered,\none of the names is not a valid shell variable name, or -f is  supplied  with  a  name\nthat is not a function.\n\nfc [-e ename] [-lnr] [first] [last]\nfc -s [pat=rep] [cmd]\nThe  first  form  selects a range of commands from first to last from the history list\nand displays or edits and re-executes them.  First and last  may  be  specified  as  a\nstring  (to locate the last command beginning with that string) or as a number (an in‐\ndex into the history list, where a negative number is used as an offset from the  cur‐\nrent  command  number).  When listing, a first or last of 0 is equivalent to -1 and -0\nis equivalent to the current command (usually the fc command); otherwise 0 is  equiva‐\nlent to -1 and -0 is invalid.  If last is not specified, it is set to the current com‐\nmand for listing (so that ``fc -l -10'' prints the last 10 commands) and to first oth‐\nerwise.   If first is not specified, it is set to the previous command for editing and\n-16 for listing.\n\nThe -n option suppresses the command numbers when listing.  The -r option reverses the\norder of the commands.  If the -l option is given, the commands are listed on standard\noutput.  Otherwise, the editor given by ename is invoked on a  file  containing  those\ncommands.   If  ename  is not given, the value of the FCEDIT variable is used, and the\nvalue of EDITOR if FCEDIT is not set.  If neither variable is set, vi is  used.   When\nediting is complete, the edited commands are echoed and executed.\n\nIn  the  second form, command is re-executed after each instance of pat is replaced by\nrep.  Command is interpreted the same as first above.  A useful alias to use with this\nis ``r=\"fc -s\"'', so that typing ``r cc'' runs the last command beginning with  ``cc''\nand typing ``r'' re-executes the last command.\n\nIf  the  first form is used, the return value is 0 unless an invalid option is encoun‐\ntered or first or last specify history lines out of range.  If the -e option  is  sup‐\nplied, the return value is the value of the last command executed or failure if an er‐\nror  occurs  with the temporary file of commands.  If the second form is used, the re‐\nturn status is that of the command re-executed, unless cmd does not  specify  a  valid\nhistory line, in which case fc returns failure.\n\nfg [jobspec]\nResume  jobspec  in  the  foreground,  and make it the current job.  If jobspec is not\npresent, the shell's notion of the current job is used.  The return value is  that  of\nthe command placed into the foreground, or failure if run when job control is disabled\nor, when run with job control enabled, if jobspec does not specify a valid job or job‐\nspec specifies a job that was started without job control.\n\ngetopts optstring name [arg ...]\ngetopts  is  used  by shell procedures to parse positional parameters.  optstring con‐\ntains the option characters to be recognized; if a character is followed by  a  colon,\nthe option is expected to have an argument, which should be separated from it by white\nspace.   The  colon and question mark characters may not be used as option characters.\nEach time it is invoked, getopts places the next option in the  shell  variable  name,\ninitializing  name  if  it  does  not  exist, and the index of the next argument to be\nprocessed into the variable OPTIND.  OPTIND is initialized to 1 each time the shell or\na shell script is invoked.  When an option requires an argument, getopts  places  that\nargument  into the variable OPTARG.  The shell does not reset OPTIND automatically; it\nmust be manually reset between multiple calls to getopts within the same shell invoca‐\ntion if a new set of parameters is to be used.\n\nWhen the end of options is encountered, getopts exits with a return value greater than\nzero.  OPTIND is set to the index of the first non-option argument, and name is set to\n?.\n\ngetopts normally parses the positional parameters, but if more arguments are  supplied\nas arg values, getopts parses those instead.\n\ngetopts  can  report  errors  in  two  ways.  If the first character of optstring is a\ncolon, silent error reporting is used.  In normal operation, diagnostic  messages  are\nprinted  when  invalid  options  or  missing option arguments are encountered.  If the\nvariable OPTERR is set to 0, no error messages will be displayed, even  if  the  first\ncharacter of optstring is not a colon.\n\nIf an invalid option is seen, getopts places ? into name and, if not silent, prints an\nerror  message and unsets OPTARG.  If getopts is silent, the option character found is\nplaced in OPTARG and no diagnostic message is printed.\n\nIf a required argument is not found, and getopts is not silent, a question mark (?) is\nplaced in name, OPTARG is unset, and a diagnostic message is printed.  If  getopts  is\nsilent,  then  a colon (:) is placed in name and OPTARG is set to the option character\nfound.\n\ngetopts returns true if an option, specified or unspecified,  is  found.   It  returns\nfalse if the end of options is encountered or an error occurs.\n\nhash [-lr] [-p filename] [-dt] [name]\nEach  time  hash  is  invoked,  the full pathname of the command name is determined by\nsearching the directories in $PATH and remembered.  Any previously-remembered pathname\nis discarded.  If the -p option is supplied, no path search is performed, and filename\nis used as the full filename of the command.  The -r option causes the shell to forget\nall remembered locations.  The -d option causes the shell to forget the remembered lo‐\ncation of each name.  If the -t option is supplied, the full pathname  to  which  each\nname  corresponds  is  printed.   If multiple name arguments are supplied with -t, the\nname is printed before the hashed full pathname.  The -l option causes  output  to  be\ndisplayed  in  a format that may be reused as input.  If no arguments are given, or if\nonly -l is supplied, information about remembered commands  is  printed.   The  return\nstatus is true unless a name is not found or an invalid option is supplied.\n\nhelp [-dms] [pattern]\nDisplay  helpful  information  about  builtin commands.  If pattern is specified, help\ngives detailed help on all commands matching  pattern;  otherwise  help  for  all  the\nbuiltins and shell control structures is printed.\n-d     Display a short description of each pattern\n-m     Display the description of each pattern in a manpage-like format\n-s     Display only a short usage synopsis for each pattern\n\nThe return status is 0 unless no command matches pattern.\n\nhistory [n]"
                },
                {
                    "name": "history -c",
                    "content": "history -d offset\nhistory -d start-end\nhistory -anrw [filename]\nhistory -p arg [arg ...]\nhistory -s arg [arg ...]\nWith  no  options,  display  the command history list with line numbers.  Lines listed\nwith a * have been modified.  An argument of n lists only the last n  lines.   If  the\nshell  variable  HISTTIMEFORMAT is set and not null, it is used as a format string for\nstrftime(3) to display the time stamp associated with each  displayed  history  entry.\nNo intervening blank is printed between the formatted time stamp and the history line.\nIf filename is supplied, it is used as the name of the history file; if not, the value\nof HISTFILE is used.  Options, if supplied, have the following meanings:\n-c     Clear the history list by deleting all the entries.\n-d offset\nDelete  the history entry at position offset.  If offset is negative, it is in‐\nterpreted as relative to one greater than the last history position,  so  nega‐\ntive  indices count back from the end of the history, and an index of -1 refers\nto the current history -d command.\n-d start-end\nDelete the range of history entries between positions start and end, inclusive.\nPositive and negative values for start and end  are  interpreted  as  described\nabove.\n-a     Append  the ``new'' history lines to the history file.  These are history lines\nentered since the beginning of the current bash session, but  not  already  ap‐\npended to the history file.\n-n     Read  the history lines not already read from the history file into the current\nhistory list.  These are lines appended to the history file since the beginning\nof the current bash session.\n-r     Read the contents of the history file and append them to  the  current  history\nlist.\n-w     Write  the  current  history  list to the history file, overwriting the history\nfile's contents.\n-p     Perform history substitution on the following args and display  the  result  on\nthe standard output.  Does not store the results in the history list.  Each arg\nmust be quoted to disable normal history expansion.\n-s     Store  the args in the history list as a single entry.  The last command in the\nhistory list is removed before the args are added.\n\nIf the HISTTIMEFORMAT variable is set, the time stamp information associated with each\nhistory entry is written to the history file, marked with the history comment  charac‐\nter.   When the history file is read, lines beginning with the history comment charac‐\nter followed immediately by a digit are interpreted as timestamps  for  the  following\nhistory  entry.  The return value is 0 unless an invalid option is encountered, an er‐\nror occurs while reading or writing the history file, an invalid offset  or  range  is\nsupplied  as an argument to -d, or the history expansion supplied as an argument to -p\nfails.\n\njobs [-lnprs] [ jobspec ... ]\njobs -x command [ args ... ]\nThe first form lists the active jobs.  The options have the following meanings:\n-l     List process IDs in addition to the normal information.\n-n     Display information only about jobs that have changed status since the user was\nlast notified of their status.\n-p     List only the process ID of the job's process group leader.\n-r     Display only running jobs.\n-s     Display only stopped jobs.\n\nIf jobspec is given, output is restricted to information about that job.   The  return\nstatus is 0 unless an invalid option is encountered or an invalid jobspec is supplied.\n\nIf  the -x option is supplied, jobs replaces any jobspec found in command or args with\nthe corresponding process group ID, and executes command passing  it  args,  returning\nits exit status.\n\nkill [-s sigspec | -n signum | -sigspec] [pid | jobspec] ...\nkill -l|-L [sigspec | exitstatus]\nSend  the  signal named by sigspec or signum to the processes named by pid or jobspec.\nsigspec is either a case-insensitive signal name such as SIGKILL (with or without  the\nSIG prefix) or a signal number; signum is a signal number.  If sigspec is not present,\nthen  SIGTERM is assumed.  An argument of -l lists the signal names.  If any arguments\nare supplied when -l is given, the names of the signals corresponding to the arguments\nare listed, and the return status is 0.  The exitstatus argument to -l  is  a  number\nspecifying either a signal number or the exit status of a process terminated by a sig‐\nnal.  The -L option is equivalent to -l.  kill returns true if at least one signal was\nsuccessfully sent, or false if an error occurs or an invalid option is encountered.\n\nlet arg [arg ...]\nEach  arg  is  an  arithmetic expression to be evaluated (see ARITHMETIC EVALUATION in\nbash(1)).  If the last arg evaluates to 0, let returns 1; 0 is returned otherwise.\n\nlocal [option] [name[=value] ... | - ]\nFor each argument, a local variable named name is created, and  assigned  value.   The\noption  can  be  any  of the options accepted by declare.  When local is used within a\nfunction, it causes the variable name to have a visible scope restricted to that func‐\ntion and its children.  If name is -, the set of shell options is made  local  to  the\nfunction in which local is invoked: shell options changed using the set builtin inside\nthe function are restored to their original values when the function returns.  The re‐\nstore  is  effected as if a series of set commands were executed to restore the values\nthat were in place before the function.  With no operands, local writes a list of  lo‐\ncal  variables  to the standard output.  It is an error to use local when not within a\nfunction.  The return status is 0 unless local is used outside a function, an  invalid\nname is supplied, or name is a readonly variable.\n\nlogout Exit a login shell.\n\nmapfile [-d delim] [-n count] [-O origin] [-s count] [-t] [-u fd] [-C callback] [-c quantum]\n[array]\nreadarray [-d delim] [-n count] [-O origin] [-s count] [-t] [-u fd] [-C callback] [-c quan‐\ntum] [array]\nRead lines from the standard input into the indexed array variable array, or from file\ndescriptor  fd  if the -u option is supplied.  The variable MAPFILE is the default ar‐\nray.  Options, if supplied, have the following meanings:\n-d     The first character of delim is used to terminate each input line, rather  than\nnewline.   If  delim is the empty string, mapfile will terminate a line when it\nreads a NUL character.\n-n     Copy at most count lines.  If count is 0, all lines are copied.\n-O     Begin assigning to array at index origin.  The default index is 0.\n-s     Discard the first count lines read.\n-t     Remove a trailing delim (default newline) from each line read.\n-u     Read lines from file descriptor fd instead of the standard input.\n-C     Evaluate callback each time quantum lines are read.  The  -c  option  specifies\nquantum.\n-c     Specify the number of lines read between each call to callback.\n\nIf  -C  is specified without -c, the default quantum is 5000.  When callback is evalu‐\nated, it is supplied the index of the next array element to be assigned and  the  line\nto  be  assigned to that element as additional arguments.  callback is evaluated after\nthe line is read but before the array element is assigned.\n\nIf not supplied with an explicit origin, mapfile will clear array before assigning  to\nit.\n\nmapfile  returns successfully unless an invalid option or option argument is supplied,\narray is invalid or unassignable, or if array is not an indexed array.\n\npopd [-n] [+n] [-n]\nRemoves entries from the directory stack.  The elements are numbered from  0  starting\nat the first directory listed by dirs.  With no arguments, popd removes the top direc‐\ntory  from  the  stack, and changes to the new top directory.  Arguments, if supplied,\nhave the following meanings:\n-n     Suppresses the normal change of directory when removing  directories  from  the\nstack, so that only the stack is manipulated.\n+n     Removes  the nth entry counting from the left of the list shown by dirs, start‐\ning with zero, from the stack.  For example: ``popd +0'' removes the first  di‐\nrectory, ``popd +1'' the second.\n-n     Removes the nth entry counting from the right of the list shown by dirs, start‐\ning  with  zero.   For  example: ``popd -0'' removes the last directory, ``popd\n-1'' the next to last.\n\nIf the top element of the directory stack is modified, and the -n option was not  sup‐\nplied,  popd  uses  the cd builtin to change to the directory at the top of the stack.\nIf the cd fails, popd returns a non-zero value.\n\nOtherwise, popd returns false if an invalid option is encountered, the directory stack\nis empty, or a non-existent directory stack entry is specified.\n\nIf the popd command is successful, bash runs dirs to show the final  contents  of  the\ndirectory stack, and the return status is 0.\n\nprintf [-v var] format [arguments]\nWrite  the formatted arguments to the standard output under the control of the format.\nThe -v option causes the output to be assigned to the variable var rather  than  being\nprinted to the standard output.\n\nThe  format is a character string which contains three types of objects: plain charac‐\nters, which are simply copied to standard output, character  escape  sequences,  which\nare  converted  and  copied to the standard output, and format specifications, each of\nwhich causes printing of the next successive argument.  In addition  to  the  standard\nprintf(1) format specifications, printf interprets the following extensions:\n%b     causes  printf  to expand backslash escape sequences in the corresponding argu‐\nment in the same way as echo -e.\n%q     causes printf to output the corresponding argument in  a  format  that  can  be\nreused as shell input.\n%Q     like %q, but applies any supplied precision to the argument before quoting it.\n%(datefmt)T\ncauses  printf to output the date-time string resulting from using datefmt as a\nformat string for strftime(3).  The corresponding argument is an integer repre‐\nsenting the number of seconds since the epoch.  Two special argument values may\nbe used: -1 represents the current time, and -2 represents the time  the  shell\nwas invoked.  If no argument is specified, conversion behaves as if -1 had been\ngiven.  This is an exception to the usual printf behavior.\n\nThe %b, %q, and %T directives all use the field width and precision arguments from the\nformat specification and write that many bytes from (or use that wide a field for) the\nexpanded argument, which usually contains more characters than the original.\n\nArguments  to  non-string  format specifiers are treated as C constants, except that a\nleading plus or minus sign is allowed, and if the leading character  is  a  single  or\ndouble quote, the value is the ASCII value of the following character.\n\nThe  format is reused as necessary to consume all of the arguments.  If the format re‐\nquires more arguments than are supplied, the extra format specifications behave as  if\na  zero  value or null string, as appropriate, had been supplied.  The return value is\nzero on success, non-zero on failure.\n\npushd [-n] [+n] [-n]\npushd [-n] [dir]\nAdds a directory to the top of the directory stack, or rotates the stack,  making  the\nnew  top  of  the  stack  the current working directory.  With no arguments, pushd ex‐\nchanges the top two elements of the directory stack.  Arguments, if supplied, have the\nfollowing meanings:\n-n     Suppresses the normal change of directory when rotating or  adding  directories\nto the stack, so that only the stack is manipulated.\n+n     Rotates the stack so that the nth directory (counting from the left of the list\nshown by dirs, starting with zero) is at the top.\n-n     Rotates  the  stack  so  that the nth directory (counting from the right of the\nlist shown by dirs, starting with zero) is at the top.\ndir    Adds dir to the directory stack at the top\n\nAfter the stack has been modified, if the -n option was not supplied, pushd  uses  the\ncd builtin to change to the directory at the top of the stack.  If the cd fails, pushd\nreturns a non-zero value.\n\nOtherwise, if no arguments are supplied, pushd returns 0 unless the directory stack is\nempty.   When rotating the directory stack, pushd returns 0 unless the directory stack\nis empty or a non-existent directory stack element is specified.\n\nIf the pushd command is successful, bash runs dirs to show the final contents  of  the\ndirectory stack.\n\npwd [-LP]\nPrint  the  absolute  pathname of the current working directory.  The pathname printed\ncontains no symbolic links if the -P option is supplied or the -o physical  option  to\nthe  set  builtin  command is enabled.  If the -L option is used, the pathname printed\nmay contain symbolic links.  The return status is 0 unless an error occurs while read‐\ning the name of the current directory or an invalid option is supplied.\n\nread [-ers] [-a aname] [-d delim] [-i text] [-n nchars] [-N nchars] [-p prompt] [-t timeout]\n[-u fd] [name ...]\nOne line is read from the standard input, or from the file descriptor fd  supplied  as\nan  argument  to  the  -u  option, split into words as described in bash(1) under Word\nSplitting, and the first word is assigned to the first name, the second  word  to  the\nsecond  name,  and so on.  If there are more words than names, the remaining words and\ntheir intervening delimiters are assigned to the last name.  If there are fewer  words\nread  from the input stream than names, the remaining names are assigned empty values.\nThe characters in IFS are used to split the line into words using the same  rules  the\nshell  uses  for expansion (described in bash(1) under Word Splitting).  The backslash\ncharacter (\\) may be used to remove any special meaning for the  next  character  read\nand for line continuation.  Options, if supplied, have the following meanings:\n-a aname\nThe  words  are  assigned  to  sequential  indices of the array variable aname,\nstarting at 0.  aname is unset before any new values are assigned.  Other  name\narguments are ignored.\n-d delim\nThe  first  character of delim is used to terminate the input line, rather than\nnewline.  If delim is the empty string, read will  terminate  a  line  when  it\nreads a NUL character.\n-e     If  the  standard  input  is  coming from a terminal, readline (see READLINE in\nbash(1)) is used to obtain the line.  Readline uses the current (or default, if\nline editing was not previously active) editing settings, but  uses  readline's\ndefault filename completion.\n-i text\nIf  readline  is  being  used to read the line, text is placed into the editing\nbuffer before editing begins.\n-n nchars\nread returns after reading nchars characters rather than waiting for a complete\nline of input, but honors a delimiter if fewer than nchars characters are  read\nbefore the delimiter.\n-N nchars\nread  returns after reading exactly nchars characters rather than waiting for a\ncomplete line of input, unless EOF is encountered or read times out.  Delimiter\ncharacters encountered in the input are not treated specially and do not  cause\nread  to  return  until nchars characters are read.  The result is not split on\nthe characters in IFS; the intent is that the variable is assigned exactly  the\ncharacters read (with the exception of backslash; see the -r option below).\n-p prompt\nDisplay prompt on standard error, without a trailing newline, before attempting\nto read any input.  The prompt is displayed only if input is coming from a ter‐\nminal.\n-r     Backslash  does not act as an escape character.  The backslash is considered to\nbe part of the line.  In particular, a backslash-newline pair may not  then  be\nused as a line continuation.\n-s     Silent mode.  If input is coming from a terminal, characters are not echoed.\n-t timeout\nCause  read  to  time  out and return failure if a complete line of input (or a\nspecified number of characters) is not read within  timeout  seconds.   timeout\nmay  be a decimal number with a fractional portion following the decimal point.\nThis option is only effective if read is reading input from a  terminal,  pipe,\nor  other  special  file; it has no effect when reading from regular files.  If\nread times out, read saves any partial input read into the  specified  variable\nname.   If  timeout  is 0, read returns immediately, without trying to read any\ndata.  The exit status is 0 if input is available on  the  specified  file  de‐\nscriptor,  or the read will return EOF, non-zero otherwise.  The exit status is\ngreater than 128 if the timeout is exceeded.\n-u fd  Read input from file descriptor fd.\n\nIf no names are supplied, the line read, without the ending  delimiter  but  otherwise\nunmodified,  is  assigned to the variable REPLY.  The exit status is zero, unless end-\nof-file is encountered, read times out (in which case the status is greater than 128),\na variable assignment error (such as assigning to a readonly variable) occurs,  or  an\ninvalid file descriptor is supplied as the argument to -u.\n\nreadonly [-aAf] [-p] [name[=word] ...]\nThe  given  names are marked readonly; the values of these names may not be changed by\nsubsequent assignment.  If the -f option is supplied, the functions  corresponding  to\nthe names are so marked.  The -a option restricts the variables to indexed arrays; the\n-A  option  restricts  the  variables to associative arrays.  If both options are sup‐\nplied, -A takes precedence.  If no name arguments are given, or if the  -p  option  is\nsupplied,  a  list of all readonly names is printed.  The other options may be used to\nrestrict the output to a subset of the set of readonly names.  The  -p  option  causes\noutput to be displayed in a format that may be reused as input.  If a variable name is\nfollowed  by  =word, the value of the variable is set to word.  The return status is 0\nunless an invalid option is encountered, one of the names is not a valid  shell  vari‐\nable name, or -f is supplied with a name that is not a function.\n\nreturn [n]\nCauses a function to stop executing and return the value specified by n to its caller.\nIf  n  is omitted, the return status is that of the last command executed in the func‐\ntion body.  If return is executed by a trap handler, the last command used  to  deter‐\nmine  the  status  is the last command executed before the trap handler.  If return is\nexecuted during a DEBUG trap, the last command used to determine  the  status  is  the\nlast  command  executed  by  the trap handler before return was invoked.  If return is\nused outside a function, but during execution of a script by the .  (source)  command,\nit causes the shell to stop executing that script and return either n or the exit sta‐\ntus  of  the last command executed within the script as the exit status of the script.\nIf n is supplied, the return value is its least significant 8 bits.  The return status\nis non-zero if return is supplied a non-numeric argument, or is used outside  a  func‐\ntion and not during execution of a script by . or source.  Any command associated with\nthe RETURN trap is executed before execution resumes after the function or script.\n\nset [-abefhkmnptuvxBCEHPT] [-o option-name] [--] [-] [arg ...]\nset [+abefhkmnptuvxBCEHPT] [+o option-name] [--] [-] [arg ...]\nWithout  options,  display  the name and value of each shell variable in a format that\ncan be reused as input for setting or resetting the  currently-set  variables.   Read-\nonly  variables cannot be reset.  In posix mode, only shell variables are listed.  The\noutput is sorted according to the current locale.  When options  are  specified,  they\nset  or  unset  shell attributes.  Any arguments remaining after option processing are\ntreated as values for the positional parameters and are assigned, in order, to $1, $2,\n...  $n.  Options, if specified, have the following meanings:\n-a      Each variable or function that is created or modified is given the export  at‐\ntribute and marked for export to the environment of subsequent commands.\n-b      Report  the  status of terminated background jobs immediately, rather than be‐\nfore the next primary prompt.  This is effective only when job control is  en‐\nabled.\n-e      Exit immediately if a pipeline (which may consist of a single simple command),\na  list,  or  a  compound command (see SHELL GRAMMAR in bash(1)), exits with a\nnon-zero status.  The shell does not exit if the command that fails is part of\nthe command list immediately following a while or until keyword, part  of  the\ntest  following the if or elif reserved words, part of any command executed in\na && or || list except the command following the final && or ||,  any  command\nin a pipeline but the last, or if the command's return value is being inverted\nwith !.  If a compound command other than a subshell returns a non-zero status\nbecause  a command failed while -e was being ignored, the shell does not exit.\nA trap on ERR, if set, is executed before the shell exits.   This  option  ap‐\nplies  to  the shell environment and each subshell environment separately (see\nCOMMAND EXECUTION ENVIRONMENT in bash(1)), and may cause subshells to exit be‐\nfore executing all the commands in the subshell.\n\nIf a compound command or shell function executes in a context where -e is  be‐\ning  ignored,  none  of  the  commands executed within the compound command or\nfunction body will be affected by the -e setting, even if -e is set and a com‐\nmand returns a failure status.  If a compound command or shell  function  sets\n-e  while  executing  in  a context where -e is ignored, that setting will not\nhave any effect until the compound command or the command containing the func‐\ntion call completes.\n-f      Disable pathname expansion.\n-h      Remember the location of commands as they are looked up for  execution.   This\nis enabled by default.\n-k      All  arguments in the form of assignment statements are placed in the environ‐\nment for a command, not just those that precede the command name.\n-m      Monitor mode.  Job control is enabled.  This option is on by default  for  in‐\nteractive shells on systems that support it (see JOB CONTROL in bash(1)).  All\nprocesses  run  in a separate process group.  When a background job completes,\nthe shell prints a line containing its exit status.\n-n      Read commands but do not execute them.  This may be  used  to  check  a  shell\nscript for syntax errors.  This is ignored by interactive shells.\n-o option-name\nThe option-name can be one of the following:\nallexport\nSame as -a.\nbraceexpand\nSame as -B.\nemacs   Use an emacs-style command line editing interface.  This is enabled by\ndefault  when  the  shell  is interactive, unless the shell is started\nwith the --noediting option.  This also affects the editing  interface\nused for read -e.\nerrexit Same as -e.\nerrtrace\nSame as -E.\nfunctrace\nSame as -T.\nhashall Same as -h.\nhistexpand\nSame as -H.\nhistory Enable  command  history, as described in bash(1) under HISTORY.  This\noption is on by default in interactive shells.\nignoreeof\nThe effect is as if the shell command ``IGNOREEOF=10'' had  been  exe‐\ncuted (see Shell Variables in bash(1)).\nkeyword Same as -k.\nmonitor Same as -m.\nnoclobber\nSame as -C.\nnoexec  Same as -n.\nnoglob  Same as -f.\nnolog   Currently ignored.\nnotify  Same as -b.\nnounset Same as -u.\nonecmd  Same as -t.\nphysical\nSame as -P.\npipefail\nIf  set,  the  return  value  of  a  pipeline is the value of the last\n(rightmost) command to exit with a non-zero status,  or  zero  if  all\ncommands  in  the pipeline exit successfully.  This option is disabled\nby default.\nposix   Change the behavior of bash where the default operation  differs  from\nthe  POSIX  standard to match the standard (posix mode).  See SEE ALSO\nin bash(1) for a reference to a document that details how  posix  mode\naffects bash's behavior.\nprivileged\nSame as -p.\nverbose Same as -v.\nvi      Use  a vi-style command line editing interface.  This also affects the\nediting interface used for read -e.\nxtrace  Same as -x.\nIf -o is supplied with no option-name, the values of the current  options  are\nprinted.   If  +o is supplied with no option-name, a series of set commands to\nrecreate the current option settings is displayed on the standard output.\n-p      Turn on privileged mode.  In this mode, the $ENV and $BASHENV files  are  not\nprocessed,  shell  functions  are  not inherited from the environment, and the\nSHELLOPTS, BASHOPTS, CDPATH, and GLOBIGNORE variables, if they appear  in  the\nenvironment,  are  ignored.   If  the shell is started with the effective user\n(group) id not equal to the real user (group) id, and the  -p  option  is  not\nsupplied, these actions are taken and the effective user id is set to the real\nuser  id.   If  the -p option is supplied at startup, the effective user id is\nnot reset.  Turning this option off causes the effective user and group ids to\nbe set to the real user and group ids.\n-r      Enable restricted shell mode.  This option cannot be unset once  it  has  been\nset.\n-t      Exit after reading and executing one command.\n-u      Treat unset variables and parameters other than the special parameters \"@\" and\n\"*\", or array variables subscripted with \"@\" or \"*\", as an error when perform‐\ning  parameter  expansion.   If expansion is attempted on an unset variable or\nparameter, the shell prints an error message, and, if not  interactive,  exits\nwith a non-zero status.\n-v      Print shell input lines as they are read.\n-x      After  expanding  each  simple command, for command, case command, select com‐\nmand, or arithmetic for command, display the expanded value of  PS4,  followed\nby the command and its expanded arguments or associated word list.\n-B      The  shell performs brace expansion (see Brace Expansion in bash(1)).  This is\non by default.\n-C      If set, bash does not overwrite an existing file with the >, >&, and <>  redi‐\nrection operators.  This may be overridden when creating output files by using\nthe redirection operator >| instead of >.\n-E      If  set,  any  trap  on ERR is inherited by shell functions, command substitu‐\ntions, and commands executed in a subshell environment.  The ERR trap is  nor‐\nmally not inherited in such cases.\n-H      Enable  !   style history substitution.  This option is on by default when the\nshell is interactive.\n-P      If set, the shell does not resolve symbolic links when executing commands such\nas cd that change the current working directory.  It uses the physical  direc‐\ntory  structure instead.  By default, bash follows the logical chain of direc‐\ntories when performing commands which change the current directory.\n-T      If set, any traps on DEBUG and RETURN are inherited by shell  functions,  com‐\nmand  substitutions, and commands executed in a subshell environment.  The DE‐\nBUG and RETURN traps are normally not inherited in such cases.\n--      If no arguments follow this option, then the positional parameters are  unset.\nOtherwise, the positional parameters are set to the args, even if some of them\nbegin with a -.\n-       Signal  the end of options, cause all remaining args to be assigned to the po‐\nsitional parameters.  The -x and -v options are turned off.  If there  are  no\nargs, the positional parameters remain unchanged.\n\nThe  options  are off by default unless otherwise noted.  Using + rather than - causes\nthese options to be turned off.  The options can also be specified as arguments to  an\ninvocation  of  the shell.  The current set of options may be found in $-.  The return\nstatus is always true unless an invalid option is encountered.\n\nshift [n]\nThe positional parameters from n+1 ... are renamed to $1 ....  Parameters  represented\nby the numbers $# down to $#-n+1 are unset.  n must be a non-negative number less than\nor  equal  to $#.  If n is 0, no parameters are changed.  If n is not given, it is as‐\nsumed to be 1.  If n is greater than $#, the positional parameters  are  not  changed.\nThe return status is greater than zero if n is greater than $# or less than zero; oth‐\nerwise 0.\n\nshopt [-pqsu] [-o] [optname ...]\nToggle  the  values of settings controlling optional shell behavior.  The settings can\nbe either those listed below, or, if the -o option is used, those available  with  the\n-o  option to the set builtin command.  With no options, or with the -p option, a list\nof all settable options is displayed, with an indication of whether  or  not  each  is\nset;  if optnames are supplied, the output is restricted to those options.  The -p op‐\ntion causes output to be displayed in a form that may be reused as input.   Other  op‐\ntions have the following meanings:\n-s     Enable (set) each optname.\n-u     Disable (unset) each optname.\n-q     Suppresses  normal output (quiet mode); the return status indicates whether the\noptname is set or unset.  If multiple optname arguments are given with -q,  the\nreturn status is zero if all optnames are enabled; non-zero otherwise.\n-o     Restricts  the  values  of optname to be those defined for the -o option to the\nset builtin.\n\nIf either -s or -u is used with no optname arguments, shopt shows only  those  options\nwhich  are  set or unset, respectively.  Unless otherwise noted, the shopt options are\ndisabled (unset) by default.\n\nThe return status when listing options is zero if all optnames are  enabled,  non-zero\notherwise.   When  setting  or  unsetting options, the return status is zero unless an\noptname is not a valid shell option.\n\nThe list of shopt options is:\n\nassocexpandonce\nIf set, the shell suppresses multiple evaluation  of  associative  array  sub‐\nscripts during arithmetic expression evaluation, while executing builtins that\ncan  perform  variable  assignments, and while executing builtins that perform\narray dereferencing.\nautocd  If set, a command name that is the name of a directory is executed  as  if  it\nwere  the argument to the cd command.  This option is only used by interactive\nshells.\ncdablevars\nIf set, an argument to the cd builtin command that is not a directory  is  as‐\nsumed to be the name of a variable whose value is the directory to change to.\ncdspell If  set, minor errors in the spelling of a directory component in a cd command\nwill be corrected.  The errors checked for are transposed characters, a  miss‐\ning character, and one character too many.  If a correction is found, the cor‐\nrected  filename  is  printed,  and the command proceeds.  This option is only\nused by interactive shells.\ncheckhash\nIf set, bash checks that a command found in the hash table exists before  try‐\ning to execute it.  If a hashed command no longer exists, a normal path search\nis performed.\ncheckjobs\nIf  set,  bash lists the status of any stopped and running jobs before exiting\nan interactive shell.  If any jobs are running, this causes the exit to be de‐\nferred until a second exit is attempted without an  intervening  command  (see\nJOB  CONTROL  in bash(1)).  The shell always postpones exiting if any jobs are\nstopped.\ncheckwinsize\nIf set, bash checks the window size after each external (non-builtin)  command\nand,  if  necessary,  updates the values of LINES and COLUMNS.  This option is\nenabled by default.\ncmdhist If set, bash attempts to save all lines of a multiple-line command in the same\nhistory entry.  This allows easy re-editing of multi-line commands.  This  op‐\ntion  is  enabled by default, but only has an effect if command history is en‐\nabled, as described in bash(1) under HISTORY.\ncompat31\ncompat32\ncompat40\ncompat41\ncompat42\ncompat43\ncompat44\ncompat50\nThese control aspects of the shell's compatibility mode (see SHELL COMPATIBIL‐\nITY MODE in bash(1)).\n\ncompletefullquote\nIf set, bash quotes all shell metacharacters in filenames and directory  names\nwhen  performing  completion.  If not set, bash removes metacharacters such as\nthe dollar sign from the set of characters that will be  quoted  in  completed\nfilenames  when  these  metacharacters  appear in shell variable references in\nwords to be completed.  This means that dollar signs in  variable  names  that\nexpand  to directories will not be quoted; however, any dollar signs appearing\nin filenames will not be quoted, either.  This is active only when bash is us‐\ning backslashes to quote completed filenames.  This variable  is  set  by  de‐\nfault, which is the default bash behavior in versions through 4.2.\n\ndirexpand\nIf  set, bash replaces directory names with the results of word expansion when\nperforming filename completion.  This changes the  contents  of  the  readline\nediting buffer.  If not set, bash attempts to preserve what the user typed.\n\ndirspell\nIf  set, bash attempts spelling correction on directory names during word com‐\npletion if the directory name initially supplied does not exist.\n\ndotglob If set, bash includes filenames beginning with a `.' in the results  of  path‐\nname  expansion.   The filenames ``.''  and ``..''  must always be matched ex‐\nplicitly, even if dotglob is set.\n\nexecfail\nIf set, a non-interactive shell will not exit if it cannot  execute  the  file\nspecified  as  an  argument to the exec builtin command.  An interactive shell\ndoes not exit if exec fails.\n\nexpandaliases\nIf set, aliases are expanded as described in bash(1) under ALIASES.  This  op‐\ntion is enabled by default for interactive shells.\n\nextdebug\nIf set at shell invocation, or in a shell startup file, arrange to execute the\ndebugger  profile before the shell starts, identical to the --debugger option.\nIf set after invocation, behavior intended for use by debuggers is enabled:\n\n1.     The -F option to the declare builtin displays the source file name  and\nline  number  corresponding  to each function name supplied as an argu‐\nment.\n\n2.     If the command run by the DEBUG trap returns a non-zero value, the next\ncommand is skipped and not executed.\n\n3.     If the command run by the DEBUG trap returns a  value  of  2,  and  the\nshell  is executing in a subroutine (a shell function or a shell script\nexecuted by the . or source builtins), the shell simulates  a  call  to\nreturn.\n\n4.     BASHARGC  and BASHARGV are updated as described in their descriptions\nin bash(1)).\n\n5.     Function tracing is enabled: command substitution, shell functions, and\nsubshells invoked with ( command ) inherit the DEBUG and RETURN traps.\n\n6.     Error tracing is enabled: command substitution,  shell  functions,  and\nsubshells invoked with ( command ) inherit the ERR trap.\n\nextglob If  set,  the  extended  pattern  matching features described in bash(1) under\nPathname Expansion are enabled.\n\nextquote\nIf set, $'string' and $\"string\" quoting is performed within  ${parameter}  ex‐\npansions enclosed in double quotes.  This option is enabled by default.\n\nfailglob\nIf  set,  patterns which fail to match filenames during pathname expansion re‐\nsult in an expansion error.\n\nforcefignore\nIf set, the suffixes specified by the FIGNORE shell variable cause words to be\nignored when performing word completion even if the ignored words are the only\npossible completions.  See SHELL VARIABLES in bash(1)  for  a  description  of\nFIGNORE.  This option is enabled by default.\n\nglobasciiranges\nIf  set,  range  expressions used in pattern matching bracket expressions (see\nPattern Matching in bash(1)) behave as if in the  traditional  C  locale  when\nperforming  comparisons.   That is, the current locale's collating sequence is\nnot taken into account, so b will not collate between A and B, and  upper-case\nand lower-case ASCII characters will collate together.\n\nglobskipdots\nIf  set,  pathname expansion will never match the filenames ``.''  and ``..'',\neven if the pattern begins with a ``.''.  This option is enabled by default.\n\nglobstar\nIf set, the pattern  used in a pathname expansion  context  will  match  all\nfiles and zero or more directories and subdirectories.  If the pattern is fol‐\nlowed by a /, only directories and subdirectories match.\n\ngnuerrfmt\nIf  set,  shell  error  messages are written in the standard GNU error message\nformat.\n\nhistappend\nIf set, the history list is appended to the file named by  the  value  of  the\nHISTFILE variable when the shell exits, rather than overwriting the file.\n\nhistreedit\nIf set, and readline is being used, a user is given the opportunity to re-edit\na failed history substitution.\n\nhistverify\nIf  set,  and  readline is being used, the results of history substitution are\nnot immediately passed to the shell parser.  Instead, the  resulting  line  is\nloaded into the readline editing buffer, allowing further modification.\n\nhostcomplete\nIf set, and readline is being used, bash will attempt to perform hostname com‐\npletion  when  a  word containing a @ is being completed (see Completing under\nREADLINE in bash(1)).  This is enabled by default.\n\nhuponexit\nIf set, bash will send SIGHUP to all jobs when an interactive login shell  ex‐\nits.\n\ninheriterrexit\nIf set, command substitution inherits the value of the errexit option, instead\nof  unsetting  it  in  the  subshell environment.  This option is enabled when\nposix mode is enabled.\n\ninteractivecomments\nIf set, allow a word beginning with # to cause that  word  and  all  remaining\ncharacters on that line to be ignored in an interactive shell (see COMMENTS in\nbash(1)).  This option is enabled by default.\n\nlastpipe\nIf  set,  and  job control is not active, the shell runs the last command of a\npipeline not executed in the background in the current shell environment.\n\nlithist If set, and the cmdhist option is enabled, multi-line commands  are  saved  to\nthe  history  with  embedded  newlines  rather than using semicolon separators\nwhere possible.\n\nlocalvarinherit\nIf set, local variables inherit the value and attributes of a variable of  the\nsame  name  that  exists at a previous scope before any new value is assigned.\nThe nameref attribute is not inherited.\n\nlocalvarunset\nIf set, calling unset on local variables in  previous  function  scopes  marks\nthem  so  subsequent lookups find them unset until that function returns. This\nis identical to the behavior of unsetting local variables at the current func‐\ntion scope.\n\nloginshell\nThe shell sets this option if it is started as a login shell  (see  INVOCATION\nin bash(1)).  The value may not be changed.\n\nmailwarn\nIf  set, and a file that bash is checking for mail has been accessed since the\nlast time it was checked, the message ``The mail in mailfile has  been  read''\nis displayed.\n\nnoemptycmdcompletion\nIf  set,  and readline is being used, bash will not attempt to search the PATH\nfor possible completions when completion is attempted on an empty line.\n\nnocaseglob\nIf set, bash matches filenames in a case-insensitive fashion  when  performing\npathname expansion (see Pathname Expansion in bash(1)).\n\nnocasematch\nIf  set,  bash  matches patterns in a case-insensitive fashion when performing\nmatching while executing case or [[ conditional commands, when performing pat‐\ntern substitution word expansions, or when filtering possible  completions  as\npart of programmable completion.\n\nnoexpandtranslation\nIf  set,  bash  encloses  the  translated  results of $\"...\" quoting in single\nquotes instead of double quotes.  If the string is not translated, this has no\neffect.\n\nnullglob\nIf set, bash allows patterns which match no files (see Pathname  Expansion  in\nbash(1)) to expand to a null string, rather than themselves.\n\npatsubreplacement\nIf  set,  bash  expands  occurrences of & in the replacement string of pattern\nsubstitution to the text matched by the pattern, as described under  Parameter\nExpansion in bash(1).  This option is enabled by default.\n\nprogcomp\nIf set, the programmable completion facilities (see Programmable Completion in\nbash(1)) are enabled.  This option is enabled by default.\n\nprogcompalias\nIf  set,  and  programmable  completion is enabled, bash treats a command name\nthat doesn't have any completions as a possible alias and attempts  alias  ex‐\npansion.  If  it has an alias, bash attempts programmable completion using the\ncommand word resulting from the expanded alias.\n\npromptvars\nIf set, prompt strings  undergo  parameter  expansion,  command  substitution,\narithmetic  expansion,  and quote removal after being expanded as described in\nPROMPTING in bash(1).  This option is enabled by default.\n\nrestrictedshell\nThe shell sets this option if it is started in restricted mode (see RESTRICTED\nSHELL in bash(1)).  The value may not be changed.  This is not reset when  the\nstartup  files are executed, allowing the startup files to discover whether or\nnot a shell is restricted.\n\nshiftverbose\nIf set, the shift builtin prints an error message when the shift count exceeds\nthe number of positional parameters.\n\nsourcepath\nIf set, the . (source) builtin uses the value of PATH to  find  the  directory\ncontaining  the  file  supplied as an argument.  This option is enabled by de‐\nfault.\n\nvarredirclose\nIf set, the shell automatically closes file  descriptors  assigned  using  the\n{varname}  redirection  syntax (see REDIRECTION in bash(1)) instead of leaving\nthem open when the command completes.\n\nxpgecho\nIf set, the echo builtin expands backslash-escape sequences by default.\n\nsuspend [-f]\nSuspend the execution of this shell until it  receives  a  SIGCONT  signal.   A  login\nshell,  or a shell without job control enabled, cannot be suspended; the -f option can\nbe used to override this and force the suspension.  The return status is 0 unless  the\nshell is a login shell or job control is not enabled and -f is not supplied.\n\ntest expr\n[ expr ]\nReturn  a  status  of  0 (true) or 1 (false) depending on the evaluation of the condi‐\ntional expression expr.  Each operator and operand must be a separate  argument.   Ex‐\npressions are composed of the primaries described in bash(1) under CONDITIONAL EXPRES‐\nSIONS.  test does not accept any options, nor does it accept and ignore an argument of\n-- as signifying the end of options.\n\nExpressions  may be combined using the following operators, listed in decreasing order\nof precedence.  The evaluation depends on the number of arguments; see below.   Opera‐\ntor precedence is used when there are five or more arguments.\n! expr True if expr is false.\n( expr )\nReturns  the value of expr.  This may be used to override the normal precedence\nof operators.\nexpr1 -a expr2\nTrue if both expr1 and expr2 are true.\nexpr1 -o expr2\nTrue if either expr1 or expr2 is true.\n\ntest and [ evaluate conditional expressions using a set of rules based on  the  number\nof arguments.\n\n0 arguments\nThe expression is false.\n1 argument\nThe expression is true if and only if the argument is not null.\n2 arguments\nIf  the  first  argument is !, the expression is true if and only if the second\nargument is null.  If the first argument is one of the unary conditional opera‐\ntors listed in bash(1) under CONDITIONAL EXPRESSIONS, the expression is true if\nthe unary test is true.  If the first argument is not a valid unary conditional\noperator, the expression is false.\n3 arguments\nThe following conditions are applied in the order listed.  If the second  argu‐\nment  is one of the binary conditional operators listed in bash(1) under CONDI‐\nTIONAL EXPRESSIONS, the result of the expression is the result  of  the  binary\ntest  using the first and third arguments as operands.  The -a and -o operators\nare considered binary operators when there are three arguments.  If  the  first\nargument  is  !,  the  value is the negation of the two-argument test using the\nsecond and third arguments.  If the first argument is exactly ( and  the  third\nargument  is exactly ), the result is the one-argument test of the second argu‐\nment.  Otherwise, the expression is false.\n4 arguments\nThe following conditions are applied in the order listed.  If the  first  argu‐\nment is !, the result is the negation of the three-argument expression composed\nof  the  remaining arguments.  the two-argument test using the second and third\narguments.  If the first argument is exactly ( and the fourth argument  is  ex‐\nactly ), the result is the two-argument test of the second and third arguments.\nOtherwise, the expression is parsed and evaluated according to precedence using\nthe rules listed above.\n5 or more arguments\nThe  expression is parsed and evaluated according to precedence using the rules\nlisted above.\n\nWhen used with test or [, the < and > operators sort lexicographically using ASCII or‐\ndering.\n\ntimes  Print the accumulated user and system times for the shell and for processes  run  from\nthe shell.  The return status is 0.\n\ntrap [-lp] [[arg] sigspec ...]\nThe  command arg is to be read and executed when the shell receives signal(s) sigspec.\nIf arg is absent (and there is a single sigspec) or -, each specified signal is  reset\nto  its original disposition (the value it had upon entrance to the shell).  If arg is\nthe null string the signal specified by each sigspec is ignored by the  shell  and  by\nthe  commands  it  invokes.   If arg is not present and -p has been supplied, then the\ntrap commands associated with each sigspec are displayed.  If no  arguments  are  sup‐\nplied  or  if  only -p is given, trap prints the list of commands associated with each\nsignal.  The -l option causes the shell to print a list of signal names and their cor‐\nresponding numbers.  Each sigspec is either a signal name defined in <signal.h>, or  a\nsignal number.  Signal names are case insensitive and the SIG prefix is optional.\n\nIf  a  sigspec  is  EXIT (0) the command arg is executed on exit from the shell.  If a\nsigspec is DEBUG, the command arg is executed before every simple  command,  for  com‐\nmand, case command, select command, every arithmetic for command, and before the first\ncommand executes in a shell function (see SHELL GRAMMAR in bash(1)).  Refer to the de‐\nscription of the extdebug option to the shopt builtin for details of its effect on the\nDEBUG  trap.   If  a  sigspec is RETURN, the command arg is executed each time a shell\nfunction or a script executed with the . or source builtins finishes executing.\n\nIf a sigspec is ERR, the command arg is executed whenever a pipeline (which  may  con‐\nsist  of  a  single  simple command), a list, or a compound command returns a non-zero\nexit status, subject to the following conditions.  The ERR trap is not executed if the\nfailed command is part of the command list immediately following a while or until key‐\nword, part of the test in an if statement, part of a command executed in a  &&  or  ||\nlist  except  the  command following the final && or ||, any command in a pipeline but\nthe last, or if the command's return value is being inverted using !.  These  are  the\nsame conditions obeyed by the errexit (-e) option.\n\nSignals  ignored  upon entry to the shell cannot be trapped or reset.  Trapped signals\nthat are not being ignored are reset to their original values in a  subshell  or  sub‐\nshell  environment  when one is created.  The return status is false if any sigspec is\ninvalid; otherwise trap returns true.\n\ntype [-aftpP] name [name ...]\nWith no options, indicate how each name would be interpreted  if  used  as  a  command\nname.   If the -t option is used, type prints a string which is one of alias, keyword,\nfunction, builtin, or file if  name  is  an  alias,  shell  reserved  word,  function,\nbuiltin,  or  disk  file,  respectively.   If  the  name is not found, then nothing is\nprinted, and an exit status of false is returned.  If the -p option is used, type  ei‐\nther  returns  the name of the disk file that would be executed if name were specified\nas a command name, or nothing if ``type -t name'' would not return file.  The  -P  op‐\ntion  forces  a  PATH  search for each name, even if ``type -t name'' would not return\nfile.  If a command is hashed, -p and -P print the hashed value, which is  not  neces‐\nsarily the file that appears first in PATH.  If the -a option is used, type prints all\nof  the places that contain an executable named name.  This includes aliases and func‐\ntions, if and only if the -p option is not also used.  The table of hashed commands is\nnot consulted when using -a.  The -f option suppresses shell function lookup, as  with\nthe  command  builtin.   type returns true if all of the arguments are found, false if\nany are not found.\n\nulimit [-HS] -a\nulimit [-HS] [-bcdefiklmnpqrstuvxPRT [limit]]\nProvides control over the resources available to the shell and to processes started by\nit, on systems that allow such control.  The -H and -S options specify that  the  hard\nor  soft  limit  is set for the given resource.  A hard limit cannot be increased by a\nnon-root user once it is set; a soft limit may be increased up to  the  value  of  the\nhard limit.  If neither -H nor -S is specified, both the soft and hard limits are set.\nThe  value  of  limit can be a number in the unit specified for the resource or one of\nthe special values hard, soft, or unlimited, which stand for the current  hard  limit,\nthe  current soft limit, and no limit, respectively.  If limit is omitted, the current\nvalue of the soft limit of the resource is printed, unless the  -H  option  is  given.\nWhen more than one resource is specified, the limit name and unit, if appropriate, are\nprinted before the value.  Other options are interpreted as follows:\n-a     All current limits are reported; no limits are set\n-b     The maximum socket buffer size\n-c     The maximum size of core files created\n-d     The maximum size of a process's data segment\n-e     The maximum scheduling priority (\"nice\")\n-f     The maximum size of files written by the shell and its children\n-i     The maximum number of pending signals\n-k     The maximum number of kqueues that may be allocated\n-l     The maximum size that may be locked into memory\n-m     The maximum resident set size (many systems do not honor this limit)\n-n     The  maximum  number  of  open file descriptors (most systems do not allow this\nvalue to be set)\n-p     The pipe size in 512-byte blocks (this may not be set)\n-q     The maximum number of bytes in POSIX message queues\n-r     The maximum real-time scheduling priority\n-s     The maximum stack size\n-t     The maximum amount of cpu time in seconds\n-u     The maximum number of processes available to a single user\n-v     The maximum amount of virtual memory available to the shell and, on  some  sys‐\ntems, to its children\n-x     The maximum number of file locks\n-P     The maximum number of pseudoterminals\n-R     The maximum time a real-time process can run before blocking, in microseconds\n-T     The maximum number of threads\n\nIf limit is given, and the -a option is not used, limit is the new value of the speci‐\nfied  resource.   If  no option is given, then -f is assumed.  Values are in 1024-byte\nincrements, except for -t, which is in seconds; -R,  which  is  in  microseconds;  -p,\nwhich  is  in units of 512-byte blocks; -P, -T, -b, -k, -n, and -u, which are unscaled\nvalues; and, when in posix mode, -c and -f, which are in 512-byte increments.  The re‐\nturn status is 0 unless an invalid option or argument is supplied, or an error  occurs\nwhile setting a new limit.\n\numask [-p] [-S] [mode]\nThe user file-creation mask is set to mode.  If mode begins with a digit, it is inter‐\npreted as an octal number; otherwise it is interpreted as a symbolic mode mask similar\nto  that  accepted  by chmod(1).  If mode is omitted, the current value of the mask is\nprinted.  The -S option causes the mask to be printed in symbolic  form;  the  default\noutput  is  an  octal  number.  If the -p option is supplied, and mode is omitted, the\noutput is in a form that may be reused as input.  The return status is 0 if  the  mode\nwas successfully changed or if no mode argument was supplied, and false otherwise.\n\nunalias [-a] [name ...]\nRemove each name from the list of defined aliases.  If -a is supplied, all alias defi‐\nnitions are removed.  The return value is true unless a supplied name is not a defined\nalias.\n\nunset [-fv] [-n] [name ...]\nFor  each  name,  remove  the corresponding variable or function.  If the -v option is\ngiven, each name refers to a shell variable, and that variable is removed.   Read-only\nvariables may not be unset.  If -f is specified, each name refers to a shell function,\nand  the  function definition is removed.  If the -n option is supplied, and name is a\nvariable with the nameref attribute, name will be unset rather than  the  variable  it\nreferences.   -n  has  no effect if the -f option is supplied.  If no options are sup‐\nplied, each name refers to a variable; if there is no variable by that name,  a  func‐\ntion  with  that  name,  if any, is unset.  Each unset variable or function is removed\nfrom  the  environment  passed  to  subsequent  commands.   If  any  of  BASHALIASES,\nBASHARGV0,   BASHCMDS,   BASHCOMMAND,   BASHSUBSHELL,   BASHPID,  COMPWORDBREAKS,\nDIRSTACK, EPOCHREALTIME, EPOCHSECONDS, FUNCNAME, GROUPS, HISTCMD, LINENO, RANDOM, SEC‐\nONDS, or SRANDOM are unset, they lose their special properties, even if they are  sub‐\nsequently  reset.  The exit status is true unless a name is readonly or may not be un‐\nset.\n\nwait [-fn] [-p varname] [id ...]\nWait for each specified child process and return its termination status.  Each id  may\nbe  a process ID or a job specification; if a job spec is given, all processes in that\njob's pipeline are waited for.  If id is not given, wait waits for all  running  back‐\nground  jobs and the last-executed process substitution, if its process id is the same\nas $!, and the return status is zero.  If the -n option is supplied, wait waits for  a\nsingle  job  from the list of ids or, if no ids are supplied, any job, to complete and\nreturns its exit status.  If none of the supplied arguments is a child of  the  shell,\nor  if  no arguments are supplied and the shell has no unwaited-for children, the exit\nstatus is 127.  If the -p option is supplied, the process or job identifier of the job\nfor which the exit status is returned is assigned to the variable varname named by the\noption argument.  The variable will be unset initially, before any  assignment.   This\nis useful only when the -n option is supplied.  Supplying the -f option, when job con‐\ntrol  is enabled, forces wait to wait for id to terminate before returning its status,\ninstead of returning when it changes status.  If id specifies a  non-existent  process\nor job, the return status is 127.  If wait is interrupted by a signal, the return sta‐\ntus  will  be greater than 128, as described under SIGNALS in bash(1).  Otherwise, the\nreturn status is the exit status of the last process or job waited for.\n"
                }
            ]
        },
        "SHELL COMPATIBILITY MODE": {
            "content": "Bash-4.0 introduced the concept of a shell compatibility level, specified as a set of options\nto the shopt builtin ( compat31, compat32, compat40, compat41, and so on).  There is only one\ncurrent compatibility level -- each option is mutually exclusive.  The compatibility level is\nintended to allow users to select behavior from previous versions that is  incompatible  with\nnewer versions while they migrate scripts to use current features and behavior. It's intended\nto be a temporary solution.\n\nThis  section does not mention behavior that is standard for a particular version (e.g., set‐\nting compat32 means that quoting the rhs of the regexp matching operator quotes special  reg‐\nexp characters in the word, which is default behavior in bash-3.2 and subsequent versions).\n\nIf a user enables, say, compat32, it may affect the behavior of other compatibility levels up\nto  and including the current compatibility level.  The idea is that each compatibility level\ncontrols behavior that changed in that version of bash,  but  that  behavior  may  have  been\npresent  in  earlier versions.  For instance, the change to use locale-based comparisons with\nthe [[ command came in bash-4.1, and earlier versions used ASCII-based  comparisons,  so  en‐\nabling  compat32  will  enable  ASCII-based comparisons as well.  That granularity may not be\nsufficient for all uses, and as a result users should employ compatibility levels  carefully.\nRead the documentation for a particular feature to find out the current behavior.\n\nBash-4.3  introduced  a new shell variable: BASHCOMPAT.  The value assigned to this variable\n(a decimal version number like 4.2, or an integer corresponding to the compatNN option,  like\n42) determines the compatibility level.\n\nStarting  with  bash-4.4, Bash has begun deprecating older compatibility levels.  Eventually,\nthe options will be removed in favor of BASHCOMPAT.\n\nBash-5.0 is the final version for which there will be an individual shopt option for the pre‐\nvious version. Users should use BASHCOMPAT on bash-5.0 and later versions.\n\nThe following table describes the behavior changes controlled  by  each  compatibility  level\nsetting.  The compatNN tag is used as shorthand for setting the compatibility level to NN us‐\ning one of the following mechanisms.  For versions prior to bash-5.0, the compatibility level\nmay  be  set using the corresponding compatNN shopt option.  For bash-4.3 and later versions,\nthe BASHCOMPAT variable is preferred, and it is required for bash-5.1 and later versions.\n",
            "subsections": [
                {
                    "name": "compat31",
                    "content": "•      quoting the rhs of the [[ command's regexp matching operator (=~) has  no  spe‐\ncial effect\n"
                },
                {
                    "name": "compat32",
                    "content": "•      interrupting  a  command  list  such as \"a ; b ; c\" causes the execution of the\nnext command in the list (in bash-4.0 and later versions, the shell acts as  if\nit received the interrupt, so interrupting one command in a list aborts the ex‐\necution of the entire list)\n"
                },
                {
                    "name": "compat40",
                    "content": "•      the < and > operators to the [[ command do not consider the current locale when\ncomparing  strings;  they  use ASCII ordering.  Bash versions prior to bash-4.1\nuse ASCII collation and strcmp(3); bash-4.1 and later use the current  locale's\ncollation sequence and strcoll(3).\n"
                },
                {
                    "name": "compat41",
                    "content": "•      in posix mode, time may be followed by options and still be recognized as a re‐\nserved word (this is POSIX interpretation 267)\n•      in  posix  mode, the parser requires that an even number of single quotes occur\nin the word portion of a double-quoted parameter expansion and treats them spe‐\ncially, so that characters within the single quotes are considered quoted (this\nis POSIX interpretation 221)\n"
                },
                {
                    "name": "compat42",
                    "content": "•      the replacement string in double-quoted pattern substitution does  not  undergo\nquote removal, as it does in versions after bash-4.2\n•      in  posix  mode,  single  quotes are considered special when expanding the word\nportion of a double-quoted parameter expansion and can be used to quote a clos‐\ning brace or other special character (this  is  part  of  POSIX  interpretation\n221);  in  later  versions,  single quotes are not special within double-quoted\nword expansions\n"
                },
                {
                    "name": "compat43",
                    "content": "•      the shell does not print a warning message if an  attempt  is  made  to  use  a\nquoted  compound assignment as an argument to declare (e.g., declare -a foo='(1\n2)'). Later versions warn that this usage is deprecated\n•      word expansion errors are considered non-fatal errors that  cause  the  current\ncommand to fail, even in posix mode (the default behavior is to make them fatal\nerrors that cause the shell to exit)\n•      when  executing a shell function, the loop state (while/until/etc.)  is not re‐\nset, so break or continue in that function will break or continue loops in  the\ncalling context. Bash-4.4 and later reset the loop state to prevent this\n"
                },
                {
                    "name": "compat44",
                    "content": "•      the shell sets up the values used by BASHARGV and BASHARGC so they can expand\nto the shell's positional parameters even if extended debugging mode is not en‐\nabled\n•      a  subshell  inherits  loops from its parent context, so break or continue will\ncause the subshell to exit.  Bash-5.0 and later reset the loop state to prevent\nthe exit\n•      variable assignments preceding builtins like export and readonly that  set  at‐\ntributes  continue  to affect variables with the same name in the calling envi‐\nronment even if the shell is not in posix mode\n"
                },
                {
                    "name": "compat50",
                    "content": "•      Bash-5.1 changed the way $RANDOM is generated to introduce slightly  more  ran‐\ndomness.  If the shell compatibility level is set to 50 or lower, it reverts to\nthe method from bash-5.0 and previous versions, so seeding  the  random  number\ngenerator  by  assigning a value to RANDOM will produce the same sequence as in\nbash-5.0\n•      If the command hash table is empty, bash versions prior to bash-5.1 printed  an\ninformational  message  to  that effect, even when producing output that can be\nreused as input. Bash-5.1 suppresses that message when the -l  option  is  sup‐\nplied.\n"
                },
                {
                    "name": "compat51",
                    "content": "•      The unset builtin treats attempts to unset array subscripts @ and * differently\ndepending  on whether the array is indexed or associative, and differently than\nin previous versions.\n"
                }
            ]
        },
        "SEE ALSO": {
            "content": "bash(1), sh(1)\n\nGNU Bash-2.05a                             2001 October 29                          BASH-BUILTINS(7)",
            "subsections": []
        }
    },
    "summary": "bash-builtins - bash built-in commands, see bash(1)",
    "flags": [],
    "examples": [],
    "see_also": [
        {
            "name": "bash",
            "section": "1",
            "url": "https://www.chedong.com/phpMan.php/man/bash/1/json"
        },
        {
            "name": "sh",
            "section": "1",
            "url": "https://www.chedong.com/phpMan.php/man/sh/1/json"
        },
        {
            "name": "BASH-BUILTINS",
            "section": "7",
            "url": "https://www.chedong.com/phpMan.php/man/BASH-BUILTINS/7/json"
        }
    ]
}