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BASH-BUILTINS(7)                 Miscellaneous Information Manual                BASH-BUILTINS(7)

NAME
       bash-builtins - bash built-in commands, see bash(1)

SYNOPSIS
       bash  defines  the  following built-in commands: :, ., [, alias, bg, bind, break, builtin,
       case, cd, command, compgen, complete, continue, declare, dirs, disown, echo, enable, eval,
       exec,  exit, export, fc, fg, getopts, hash, help, history, if, jobs, kill, let, local, lo-
       gout, popd, printf, pushd, pwd, read, readonly, return, set, shift,  shopt,  source,  sus-
       pend, test, times, trap, type, typeset, ulimit, umask, unalias, unset, until, wait, while.

BASH BUILTIN COMMANDS
       Unless  otherwise  noted, each builtin command documented in this section as accepting op-
       tions preceded by - accepts -- to signify the end of the options.  The :, true, false, and
       test/[  builtins  do  not accept options and do not treat -- specially.  The exit, logout,
       return, break, continue, let, and shift builtins accept and  process  arguments  beginning
       with  -  without requiring --.  Other builtins that accept arguments but are not specified
       as accepting options interpret arguments beginning with - as invalid options  and  require
       -- to prevent this interpretation.
       : [arguments]
              No  effect;  the command does nothing beyond expanding arguments and performing any
              specified redirections.  The return status is zero.

        .  filename [arguments]
       source filename [arguments]
              Read and execute commands from filename in the current shell environment and return
              the  exit  status of the last command executed from filename.  If filename does not
              contain a slash, filenames in PATH are used to find the directory containing  file-
              name.   The  file searched for in PATH need not be executable.  When bash is not in
              posix mode, the current directory is searched if no file is found in PATH.  If  the
              sourcepath  option  to  the  shopt  builtin  command is turned off, the PATH is not
              searched.  If any arguments are supplied, they  become  the  positional  parameters
              when  filename is executed.  Otherwise the positional parameters are unchanged.  If
              the -T option is enabled, source inherits any trap on DEBUG; if it is not, any  DE-
              BUG  trap string is saved and restored around the call to source, and source unsets
              the DEBUG trap while it executes.  If -T is not set, and the sourced  file  changes
              the DEBUG trap, the new value is retained when source completes.  The return status
              is the status of the last command exited within the script (0 if  no  commands  are
              executed), and false if filename is not found or cannot be read.

       alias [-p] [name[=value] ...]
              Alias  with  no  arguments  or with the -p option prints the list of aliases in the
              form alias name=value on standard output.  When arguments are supplied, an alias is
              defined  for  each name whose value is given.  A trailing space in value causes the
              next word to be checked for alias substitution when the  alias  is  expanded.   For
              each  name  in the argument list for which no value is supplied, the name and value
              of the alias is printed.  Alias returns true unless a name is given  for  which  no
              alias has been defined.

       bg [jobspec ...]
              Resume each suspended job jobspec in the background, as if it had been started with
              &.  If jobspec is not present, the shell's notion of the current job is  used.   bg
              jobspec  returns  0  unless  run when job control is disabled or, when run with job
              control enabled, any specified jobspec was not found or  was  started  without  job
              control.

       bind [-m keymap] [-lpsvPSVX]
       bind [-m keymap] [-q function] [-u function] [-r keyseq]
       bind [-m keymap] -f filename
       bind [-m keymap] -x keyseq:shell-command
       bind [-m keymap] keyseq:function-name
       bind [-m keymap] keyseq:readline-command
              Display  current readline key and function bindings, bind a key sequence to a read-
              line function or macro, or set a readline variable.  Each non-option argument is  a
              command  as it would appear in .inputrc, but each binding or command must be passed
              as a separate argument; e.g., '"\C-x\C-r": re-read-init-file'.   Options,  if  sup-
              plied, have the following meanings:
              -m keymap
                     Use keymap as the keymap to be affected by the subsequent bindings.  Accept-
                     able keymap names are emacs,  emacs-standard,  emacs-meta,  emacs-ctlx,  vi,
                     vi-move, vi-command, and vi-insert.  vi is equivalent to vi-command (vi-move
                     is also a synonym); emacs is equivalent to emacs-standard.
              -l     List the names of all readline functions.
              -p     Display readline function names and bindings in such a way that they can  be
                     re-read.
              -P     List current readline function names and bindings.
              -s     Display  readline  key sequences bound to macros and the strings they output
                     in such a way that they can be re-read.
              -S     Display readline key sequences bound to macros and the strings they output.
              -v     Display readline variable names and values in such a way that  they  can  be
                     re-read.
              -V     List current readline variable names and values.
              -f filename
                     Read key bindings from filename.
              -q function
                     Query about which keys invoke the named function.
              -u function
                     Unbind all keys bound to the named function.
              -r keyseq
                     Remove any current binding for keyseq.
              -x keyseq:shell-command
                     Cause  shell-command  to  be  executed  whenever  keyseq  is  entered.  When
                     shell-command is executed, the shell sets the READLINE_LINE variable to  the
                     contents  of  the  readline  line  buffer  and  the READLINE_POINT and READ-
                     LINE_MARK variables to the current location of the insertion point  and  the
                     saved  insertion  point  (the  mark), respectively.  If the executed command
                     changes the value of any of READLINE_LINE, READLINE_POINT, or READLINE_MARK,
                     those new values will be reflected in the editing state.
              -X     List  all  key sequences bound to shell commands and the associated commands
                     in a format that can be reused as input.

              The return value is 0 unless an unrecognized option is given or an error occurred.

       break [n]
              Exit from within a for, while, until, or select loop.  If n is specified,  break  n
              levels.   n  must be >= 1.  If n is greater than the number of enclosing loops, all
              enclosing loops are exited.  The return value is 0 unless n is not greater than  or
              equal to 1.

       builtin shell-builtin [arguments]
              Execute the specified shell builtin, passing it arguments, and return its exit sta-
              tus.  This is useful when defining a function whose name is the  same  as  a  shell
              builtin,  retaining  the  functionality of the builtin within the function.  The cd
              builtin  is  commonly  redefined  this  way.   The  return  status  is   false   if
              shell-builtin is not a shell builtin command.

       caller [expr]
              Returns the context of any active subroutine call (a shell function or a script ex-
              ecuted with the . or source builtins).  Without expr, caller displays the line num-
              ber  and source filename of the current subroutine call.  If a non-negative integer
              is supplied as expr, caller displays the line number, subroutine name,  and  source
              file  corresponding to that position in the current execution call stack.  This ex-
              tra information may be used, for example, to print  a  stack  trace.   The  current
              frame  is  frame 0.  The return value is 0 unless the shell is not executing a sub-
              routine call or expr does not correspond to a valid position in the call stack.

       cd [-L|[-P [-e]] [-@]] [dir]
              Change the current directory to dir.  if dir is not supplied, the value of the HOME
              shell variable is the default.  Any additional arguments following dir are ignored.
              The variable CDPATH defines the search path for the directory containing dir:  each
              directory  name  in CDPATH is searched for dir.  Alternative directory names in CD-
              PATH are separated by a colon (:).  A null directory name in CDPATH is the same  as
              the current directory, i.e., ``.''.  If dir begins with a slash (/), then CDPATH is
              not used.  The -P option causes cd to use the physical directory structure  by  re-
              solving  symbolic  links while traversing dir and before processing instances of ..
              in dir (see also the -P option to the set builtin command); the  -L  option  forces
              symbolic  links  to be followed by resolving the link after processing instances of
              .. in dir.  If .. appears in dir, it is processed by removing the immediately  pre-
              vious pathname component from dir, back to a slash or the beginning of dir.  If the
              -e option is supplied with -P, and the current working directory cannot be success-
              fully  determined after a successful directory change, cd will return an unsuccess-
              ful status.  On systems that support it, the -@ option presents  the  extended  at-
              tributes  associated  with a file as a directory.  An argument of - is converted to
              $OLDPWD before the directory change is attempted.  If a  non-empty  directory  name
              from  CDPATH  is  used,  or if - is the first argument, and the directory change is
              successful, the absolute pathname of the new working directory is  written  to  the
              standard  output.   The  return  value  is  true  if the directory was successfully
              changed; false otherwise.

       command [-pVv] command [arg ...]
              Run command with args suppressing the normal shell function lookup.   Only  builtin
              commands  or  commands  found in the PATH are executed.  If the -p option is given,
              the search for command is performed using a default value for PATH that is  guaran-
              teed  to find all of the standard utilities.  If either the -V or -v option is sup-
              plied, a description of command is printed.  The -v option causes a single word in-
              dicating the command or filename used to invoke command to be displayed; the -V op-
              tion produces a more verbose description.  If the -V or -v option is supplied,  the
              exit status is 0 if command was found, and 1 if not.  If neither option is supplied
              and an error occurred or command cannot be found, the exit status is  127.   Other-
              wise, the exit status of the command builtin is the exit status of command.

       compgen [option] [word]
              Generate  possible  completion matches for word according to the options, which may
              be any option accepted by the complete builtin with the exception of -p and -r, and
              write  the  matches  to  the standard output.  When using the -F or -C options, the
              various shell variables set by the programmable completion facilities, while avail-
              able, will not have useful values.

              The  matches  will  be  generated in the same way as if the programmable completion
              code had generated them directly from a  completion  specification  with  the  same
              flags.   If  word  is  specified, only those completions matching word will be dis-
              played.

              The return value is true unless an invalid option is supplied, or no  matches  were
              generated.

       complete [-abcdefgjksuv] [-o comp-option] [-DEI] [-A action] [-G globpat] [-W wordlist]
              [-F function] [-C command] [-X filterpat] [-P prefix] [-S suffix] name [name ...]
       complete -pr [-DEI] [name ...]
              Specify  how  arguments to each name should be completed.  If the -p option is sup-
              plied, or if no  options  are  supplied,  existing  completion  specifications  are
              printed  in  a way that allows them to be reused as input.  The -r option removes a
              completion specification for each name, or, if no names are supplied,  all  comple-
              tion  specifications.   The -D option indicates that other supplied options and ac-
              tions should apply to the ``default'' command completion; that is,  completion  at-
              tempted  on  a command for which no completion has previously been defined.  The -E
              option indicates that other supplied options and actions should apply to  ``empty''
              command  completion;  that is, completion attempted on a blank line.  The -I option
              indicates that other supplied options and actions should apply to completion on the
              initial  non-assignment word on the line, or after a command delimiter such as ; or
              |, which is usually command name completion.  If multiple options are supplied, the
              -D  option  takes  precedence over -E, and both take precedence over -I.  If any of
              -D, -E, or -I are supplied, any other name arguments are ignored; these completions
              only apply to the case specified by the option.

              The process of applying these completion specifications when word completion is at-
              tempted is described above under Programmable Completion.

              Other options, if specified, have the following meanings.  The arguments to the -G,
              -W,  and  -X options (and, if necessary, the -P and -S options) should be quoted to
              protect them from expansion before the complete builtin is invoked.
              -o comp-option
                      The comp-option controls several aspects of the compspec's behavior  beyond
                      the simple generation of completions.  comp-option may be one of:
                      bashdefault
                              Perform  the  rest  of the default bash completions if the compspec
                              generates no matches.
                      default Use readline's default filename completion if the  compspec  gener-
                              ates no matches.
                      dirnames
                              Perform  directory  name  completion  if  the compspec generates no
                              matches.
                      filenames
                              Tell readline that the compspec generates filenames, so it can per-
                              form  any  filename-specific processing (like adding a slash to di-
                              rectory names, quoting special characters, or suppressing  trailing
                              spaces).  Intended to be used with shell functions.
                      noquote Tell  readline  not  to quote the completed words if they are file-
                              names (quoting filenames is the default).
                      nosort  Tell readline not to sort the list of possible  completions  alpha-
                              betically.
                      nospace Tell  readline  not  to  append a space (the default) to words com-
                              pleted at the end of the line.
                      plusdirs
                              After any matches defined by the compspec are generated,  directory
                              name  completion  is attempted and any matches are added to the re-
                              sults of the other actions.
              -A action
                      The action may be one of the following to generate a list of possible  com-
                      pletions:
                      alias   Alias names.  May also be specified as -a.
                      arrayvar
                              Array variable names.
                      binding Readline key binding names.
                      builtin Names of shell builtin commands.  May also be specified as -b.
                      command Command names.  May also be specified as -c.
                      directory
                              Directory names.  May also be specified as -d.
                      disabled
                              Names of disabled shell builtins.
                      enabled Names of enabled shell builtins.
                      export  Names of exported shell variables.  May also be specified as -e.
                      file    File names.  May also be specified as -f.
                      function
                              Names of shell functions.
                      group   Group names.  May also be specified as -g.
                      helptopic
                              Help topics as accepted by the help builtin.
                      hostname
                              Hostnames,  as  taken from the file specified by the HOSTFILE shell
                              variable.
                      job     Job names, if job control is active.  May also be specified as -j.
                      keyword Shell reserved words.  May also be specified as -k.
                      running Names of running jobs, if job control is active.
                      service Service names.  May also be specified as -s.
                      setopt  Valid arguments for the -o option to the set builtin.
                      shopt   Shell option names as accepted by the shopt builtin.
                      signal  Signal names.
                      stopped Names of stopped jobs, if job control is active.
                      user    User names.  May also be specified as -u.
                      variable
                              Names of all shell variables.  May also be specified as -v.
              -C command
                      command is executed in a subshell environment, and its output  is  used  as
                      the possible completions.
              -F function
                      The  shell  function function is executed in the current shell environment.
                      When the function is executed, the first argument ($1) is the name  of  the
                      command  whose  arguments  are being completed, the second argument ($2) is
                      the word being completed, and the third argument ($3) is the word preceding
                      the  word  being  completed on the current command line.  When it finishes,
                      the possible completions are retrieved from the value of the COMPREPLY  ar-
                      ray variable.
              -G globpat
                      The pathname expansion pattern globpat is expanded to generate the possible
                      completions.
              -P prefix
                      prefix is added at the beginning of  each  possible  completion  after  all
                      other options have been applied.
              -S suffix
                      suffix is appended to each possible completion after all other options have
                      been applied.
              -W wordlist
                      The wordlist is split using the characters in the IFS special  variable  as
                      delimiters,  and each resultant word is expanded.  Shell quoting is honored
                      within wordlist, in order to provide a mechanism for the words  to  contain
                      shell  metacharacters or characters in the value of IFS.  The possible com-
                      pletions are the members of the resultant list which match the  word  being
                      completed.
              -X filterpat
                      filterpat  is  a  pattern as used for pathname expansion.  It is applied to
                      the list of possible completions generated by the preceding options and ar-
                      guments,  and  each completion matching filterpat is removed from the list.
                      A leading ! in filterpat negates the pattern; in this case, any  completion
                      not matching filterpat is removed.

              The return value is true unless an invalid option is supplied, an option other than
              -p or -r is supplied without a name argument, an attempt is made to remove  a  com-
              pletion specification for a name for which no specification exists, or an error oc-
              curs adding a completion specification.

       compopt [-o option] [-DEI] [+o option] [name]
              Modify completion options for each name according to the options, or for  the  cur-
              rently-executing  completion  if  no  names are supplied.  If no options are given,
              display the completion options for each name or the current completion.  The possi-
              ble values of option are those valid for the complete builtin described above.  The
              -D option indicates that other supplied options should  apply  to  the  ``default''
              command completion; that is, completion attempted on a command for which no comple-
              tion has previously been defined.  The -E option indicates that other supplied  op-
              tions  should  apply to ``empty'' command completion; that is, completion attempted
              on a blank line.  The -I option indicates that other supplied options should  apply
              to  completion  on  the initial non-assignment word on the line, or after a command
              delimiter such as ; or |, which is usually command name completion.

              The return value is true unless an invalid option is supplied, an attempt  is  made
              to  modify  the options for a name for which no completion specification exists, or
              an output error occurs.

       continue [n]
              Resume the next iteration of the enclosing for, while, until, or select loop.  If n
              is  specified,  resume at the nth enclosing loop.  n must be >= 1.  If n is greater
              than the number of enclosing loops, the  last  enclosing  loop  (the  ``top-level''
              loop)  is  resumed.  The return value is 0 unless n is not greater than or equal to
              1.

       declare [-aAfFgiIlnrtux] [-p] [name[=value] ...]
       typeset [-aAfFgiIlnrtux] [-p] [name[=value] ...]
              Declare variables and/or give them attributes.  If no names are given then  display
              the  values  of variables.  The -p option will display the attributes and values of
              each name.  When -p is used with name arguments, additional options, other than  -f
              and  -F,  are ignored.  When -p is supplied without name arguments, it will display
              the attributes and values of all variables having the attributes specified  by  the
              additional options.  If no other options are supplied with -p, declare will display
              the attributes and values of all shell variables.  The -f option will restrict  the
              display to shell functions.  The -F option inhibits the display of function defini-
              tions; only the function name and attributes are printed.  If  the  extdebug  shell
              option is enabled using shopt, the source file name and line number where each name
              is defined are displayed as well.  The -F option implies -f.  The -g option  forces
              variables  to be created or modified at the global scope, even when declare is exe-
              cuted in a shell function.  It is ignored in all other cases.  The -I option causes
              local  variables to inherit the attributes (except the nameref attribute) and value
              of any existing variable with the same name at a surrounding scope.  If there is no
              existing  variable,  the  local variable is initially unset.  The following options
              can be used to restrict output to variables with the specified attribute or to give
              variables attributes:
              -a     Each name is an indexed array variable (see Arrays above).
              -A     Each name is an associative array variable (see Arrays above).
              -f     Use function names only.
              -i     The variable is treated as an integer; arithmetic evaluation (see ARITHMETIC
                     EVALUATION above) is performed when the variable is assigned a value.
              -l     When the variable is assigned a value, all upper-case  characters  are  con-
                     verted to lower-case.  The upper-case attribute is disabled.
              -n     Give  each name the nameref attribute, making it a name reference to another
                     variable.  That other variable is defined by the value of name.  All  refer-
                     ences,  assignments, and attribute modifications to name, except those using
                     or changing the -n attribute itself, are performed on  the  variable  refer-
                     enced  by  name's  value.   The nameref attribute cannot be applied to array
                     variables.
              -r     Make names readonly.  These names cannot then be assigned values  by  subse-
                     quent assignment statements or unset.
              -t     Give  each name the trace attribute.  Traced functions inherit the DEBUG and
                     RETURN traps from the calling shell.  The trace  attribute  has  no  special
                     meaning for variables.
              -u     When  the  variable  is assigned a value, all lower-case characters are con-
                     verted to upper-case.  The lower-case attribute is disabled.
              -x     Mark names for export to subsequent commands via the environment.

              Using `+' instead of `-' turns off the attribute instead, with the exceptions  that
              +a  and  +A  may  not be used to destroy array variables and +r will not remove the
              readonly attribute.  When used in a function, declare and typeset  make  each  name
              local,  as with the local command, unless the -g option is supplied.  If a variable
              name is followed by =value, the value of the variable is set to value.  When  using
              -a  or  -A and the compound assignment syntax to create array variables, additional
              attributes do not take effect until subsequent assignments.  The return value is  0
              unless  an  invalid  option is encountered, an attempt is made to define a function
              using ``-f foo=bar'', an attempt is made to assign a value to a readonly  variable,
              an  attempt  is  made to assign a value to an array variable without using the com-
              pound assignment syntax (see Arrays above), one of the names is not a  valid  shell
              variable  name, an attempt is made to turn off readonly status for a readonly vari-
              able, an attempt is made to turn off array status for an array variable, or an  at-
              tempt is made to display a non-existent function with -f.

       dirs [-clpv] [+n] [-n]
              Without  options,  displays  the list of currently remembered directories.  The de-
              fault display is on a single line with directory names separated by spaces.  Direc-
              tories  are  added to the list with the pushd command; the popd command removes en-
              tries from the list.  The current directory is always the first  directory  in  the
              stack.
              -c     Clears the directory stack by deleting all of the entries.
              -l     Produces  a  listing using full pathnames; the default listing format uses a
                     tilde to denote the home directory.
              -p     Print the directory stack with one entry per line.
              -v     Print the directory stack with one entry per line, prefixing each entry with
                     its index in the stack.
              +n     Displays the nth entry counting from the left of the list shown by dirs when
                     invoked without options, starting with zero.
              -n     Displays the nth entry counting from the right of the  list  shown  by  dirs
                     when invoked without options, starting with zero.

              The  return value is 0 unless an invalid option is supplied or n indexes beyond the
              end of the directory stack.

       disown [-ar] [-h] [jobspec ... | pid ... ]
              Without options, remove each jobspec from the table of active jobs.  If jobspec  is
              not  present,  and neither the -a nor the -r option is supplied, the current job is
              used.  If the -h option is given, each jobspec is not removed from the  table,  but
              is marked so that SIGHUP is not sent to the job if the shell receives a SIGHUP.  If
              no jobspec is supplied, the -a option means to remove or mark all jobs; the -r  op-
              tion  without  a  jobspec argument restricts operation to running jobs.  The return
              value is 0 unless a jobspec does not specify a valid job.

       echo [-neE] [arg ...]
              Output the args, separated by spaces, followed by a newline.  The return status  is
              0  unless  a  write error occurs.  If -n is specified, the trailing newline is sup-
              pressed.  If the -e option is given, interpretation of the following  backslash-es-
              caped  characters  is  enabled.  The -E option disables the interpretation of these
              escape characters, even on systems where they  are  interpreted  by  default.   The
              xpg_echo  shell option may be used to dynamically determine whether or not echo ex-
              pands these escape characters by default.  echo does not interpret -- to  mean  the
              end of options.  echo interprets the following escape sequences:
              \a     alert (bell)
              \b     backspace
              \c     suppress further output
              \e
              \E     an escape character
              \f     form feed
              \n     new line
              \r     carriage return
              \t     horizontal tab
              \v     vertical tab
              \\     backslash
              \0nnn  the  eight-bit  character  whose value is the octal value nnn (zero to three
                     octal digits)
              \xHH   the eight-bit character whose value is the hexadecimal value HH (one or  two
                     hex digits)
              \uHHHH the  Unicode  (ISO/IEC 10646) character whose value is the hexadecimal value
                     HHHH (one to four hex digits)
              \UHHHHHHHH
                     the Unicode (ISO/IEC 10646) character whose value is the  hexadecimal  value
                     HHHHHHHH (one to eight hex digits)

       enable [-a] [-dnps] [-f filename] [name ...]
              Enable  and disable builtin shell commands.  Disabling a builtin allows a disk com-
              mand which has the same name as a shell builtin to be executed without specifying a
              full  pathname,  even  though  the shell normally searches for builtins before disk
              commands.  If -n is used, each name is disabled; otherwise, names are enabled.  For
              example,  to  use  the  test binary found via the PATH instead of the shell builtin
              version, run ``enable -n test''.  The -f option means to load the new builtin  com-
              mand  name  from  shared  object filename, on systems that support dynamic loading.
              The -d option will delete a builtin previously loaded with -f.  If  no  name  argu-
              ments  are  given,  or  if  the  -p option is supplied, a list of shell builtins is
              printed.  With no other option arguments, the list consists of  all  enabled  shell
              builtins.   If  -n  is supplied, only disabled builtins are printed.  If -a is sup-
              plied, the list printed includes all builtins, with an indication of whether or not
              each  is enabled.  If -s is supplied, the output is restricted to the POSIX special
              builtins.  The return value is 0 unless a name is not a shell builtin or  there  is
              an error loading a new builtin from a shared object.

       eval [arg ...]
              The args are read and concatenated together into a single command.  This command is
              then read and executed by the shell, and its exit status is returned as  the  value
              of eval.  If there are no args, or only null arguments, eval returns 0.

       exec [-cl] [-a name] [command [arguments]]
              If  command  is  specified, it replaces the shell.  No new process is created.  The
              arguments become the arguments to command.  If the -l option is supplied, the shell
              places  a  dash at the beginning of the zeroth argument passed to command.  This is
              what login(1) does.  The -c option causes command to be executed with an empty  en-
              vironment.   If -a is supplied, the shell passes name as the zeroth argument to the
              executed command.  If command cannot be executed for some reason, a non-interactive
              shell exits, unless the execfail shell option is enabled.  In that case, it returns
              failure.  An interactive shell returns failure if the file cannot be  executed.   A
              subshell  exits  unconditionally  if  exec fails.  If command is not specified, any
              redirections take effect in the current shell, and the  return  status  is  0.   If
              there is a redirection error, the return status is 1.

       exit [n]
              Cause  the  shell  to exit with a status of n.  If n is omitted, the exit status is
              that of the last command executed.  A trap on EXIT is  executed  before  the  shell
              terminates.

       export [-fn] [name[=word]] ...
       export -p
              The  supplied  names  are  marked for automatic export to the environment of subse-
              quently executed commands.  If the -f option is given, the  names  refer  to  func-
              tions.   If no names are given, or if the -p option is supplied, a list of names of
              all exported variables is printed.  The -n option causes the export property to  be
              removed  from each name.  If a variable name is followed by =word, the value of the
              variable is set to word.  export returns an exit status of 0 unless an invalid  op-
              tion  is encountered, one of the names is not a valid shell variable name, or -f is
              supplied with a name that is not a function.

       fc [-e ename] [-lnr] [first] [last]
       fc -s [pat=rep] [cmd]
              The first form selects a range of commands from first to last from the history list
              and  displays  or edits and re-executes them.  First and last may be specified as a
              string (to locate the last command beginning with that string) or as a  number  (an
              index  into the history list, where a negative number is used as an offset from the
              current command number).  When listing, a first or last of 0 is  equivalent  to  -1
              and  -0  is equivalent to the current command (usually the fc command); otherwise 0
              is equivalent to -1 and -0 is invalid.  If last is not specified, it is set to  the
              current command for listing (so that ``fc -l -10'' prints the last 10 commands) and
              to first otherwise.  If first is not specified, it is set to the  previous  command
              for editing and -16 for listing.

              The  -n option suppresses the command numbers when listing.  The -r option reverses
              the order of the commands.  If the -l option is given, the commands are  listed  on
              standard  output.   Otherwise,  the editor given by ename is invoked on a file con-
              taining those commands.  If ename is not given, the value of the FCEDIT variable is
              used, and the value of EDITOR if FCEDIT is not set.  If neither variable is set, vi
              is used.  When editing is complete, the edited commands are echoed and executed.

              In the second form, command is re-executed after each instance of pat  is  replaced
              by  rep.   Command  is  interpreted the same as first above.  A useful alias to use
              with this is ``r="fc -s"'', so that typing ``r cc'' runs the last command beginning
              with ``cc'' and typing ``r'' re-executes the last command.

              If  the  first  form is used, the return value is 0 unless an invalid option is en-
              countered or first or last specify history lines out of range.  If the -e option is
              supplied,  the return value is the value of the last command executed or failure if
              an error occurs with the temporary file of commands.  If the second form  is  used,
              the return status is that of the command re-executed, unless cmd does not specify a
              valid history line, in which case fc returns failure.

       fg [jobspec]
              Resume jobspec in the foreground, and make it the current job.  If jobspec  is  not
              present,  the  shell's notion of the current job is used.  The return value is that
              of the command placed into the foreground, or failure if run when  job  control  is
              disabled or, when run with job control enabled, if jobspec does not specify a valid
              job or jobspec specifies a job that was started without job control.

       getopts optstring name [arg ...]
              getopts is used by shell procedures to parse positional parameters.  optstring con-
              tains  the  option  characters  to  be  recognized; if a character is followed by a
              colon, the option is expected to have an argument, which should be  separated  from
              it  by  white space.  The colon and question mark characters may not be used as op-
              tion characters.  Each time it is invoked, getopts places the next  option  in  the
              shell  variable  name, initializing name if it does not exist, and the index of the
              next argument to be processed into the variable OPTIND.  OPTIND is initialized to 1
              each time the shell or a shell script is invoked.  When an option requires an argu-
              ment, getopts places that argument into the variable OPTARG.  The  shell  does  not
              reset  OPTIND  automatically;  it  must be manually reset between multiple calls to
              getopts within the same shell invocation if a new set of parameters is to be used.

              When the end of options is encountered, getopts exits with a return  value  greater
              than  zero.   OPTIND is set to the index of the first non-option argument, and name
              is set to ?.

              getopts normally parses the positional parameters, but if more arguments  are  sup-
              plied as arg values, getopts parses those instead.

              getopts  can  report  errors in two ways.  If the first character of optstring is a
              colon, silent error reporting is used.  In normal  operation,  diagnostic  messages
              are  printed  when invalid options or missing option arguments are encountered.  If
              the variable OPTERR is set to 0, no error messages will be displayed, even  if  the
              first character of optstring is not a colon.

              If an invalid option is seen, getopts places ? into name and, if not silent, prints
              an error message and unsets OPTARG.  If getopts is  silent,  the  option  character
              found is placed in OPTARG and no diagnostic message is printed.

              If a required argument is not found, and getopts is not silent, a question mark (?)
              is placed in name, OPTARG is unset,  and  a  diagnostic  message  is  printed.   If
              getopts  is silent, then a colon (:) is placed in name and OPTARG is set to the op-
              tion character found.

              getopts returns true if an option, specified or unspecified, is found.  It  returns
              false if the end of options is encountered or an error occurs.

       hash [-lr] [-p filename] [-dt] [name]
              Each  time  hash is invoked, the full pathname of the command name is determined by
              searching the directories in $PATH and remembered.  Any previously-remembered path-
              name  is discarded.  If the -p option is supplied, no path search is performed, and
              filename is used as the full filename of the command.  The  -r  option  causes  the
              shell to forget all remembered locations.  The -d option causes the shell to forget
              the remembered location of each name.  If the -t option is supplied, the full path-
              name  to  which  each  name corresponds is printed.  If multiple name arguments are
              supplied with -t, the name is printed before the hashed full pathname.  The -l  op-
              tion  causes output to be displayed in a format that may be reused as input.  If no
              arguments are given, or if only -l is supplied, information about  remembered  com-
              mands  is  printed.  The return status is true unless a name is not found or an in-
              valid option is supplied.

       help [-dms] [pattern]
              Display helpful information about builtin commands.  If pattern is specified,  help
              gives  detailed  help  on all commands matching pattern; otherwise help for all the
              builtins and shell control structures is printed.
              -d     Display a short description of each pattern
              -m     Display the description of each pattern in a manpage-like format
              -s     Display only a short usage synopsis for each pattern

              The return status is 0 unless no command matches pattern.

       history [n]
       history -c
       history -d offset
       history -d start-end
       history -anrw [filename]
       history -p arg [arg ...]
       history -s arg [arg ...]
              With no options, display the command history list with line numbers.  Lines  listed
              with a * have been modified.  An argument of n lists only the last n lines.  If the
              shell variable HISTTIMEFORMAT is set and not null, it is used as  a  format  string
              for  strftime(3)  to  display the time stamp associated with each displayed history
              entry.  No intervening blank is printed between the formatted time  stamp  and  the
              history line.  If filename is supplied, it is used as the name of the history file;
              if not, the value of HISTFILE is used.  Options, if supplied,  have  the  following
              meanings:
              -c     Clear the history list by deleting all the entries.
              -d offset
                     Delete  the  history entry at position offset.  If offset is negative, it is
                     interpreted as relative to one greater than the last  history  position,  so
                     negative  indices count back from the end of the history, and an index of -1
                     refers to the current history -d command.
              -d start-end
                     Delete the history entries between positions start and end, inclusive.  Pos-
                     itive  and  negative  values  for start and end are interpreted as described
                     above.
              -a     Append the ``new'' history lines to the history  file.   These  are  history
                     lines  entered  since the beginning of the current bash session, but not al-
                     ready appended to the history file.
              -n     Read the history lines not already read from the history file into the  cur-
                     rent  history  list.  These are lines appended to the history file since the
                     beginning of the current bash session.
              -r     Read the contents of the history file and append them to the current history
                     list.
              -w     Write  the current history list to the history file, overwriting the history
                     file's contents.
              -p     Perform history substitution on the following args and display the result on
                     the  standard output.  Does not store the results in the history list.  Each
                     arg must be quoted to disable normal history expansion.
              -s     Store the args in the history list as a single entry.  The last  command  in
                     the history list is removed before the args are added.

              If  the  HISTTIMEFORMAT variable is set, the time stamp information associated with
              each history entry is written to the history file, marked with the history  comment
              character.  When the history file is read, lines beginning with the history comment
              character followed immediately by a digit are interpreted  as  timestamps  for  the
              following history entry.  The return value is 0 unless an invalid option is encoun-
              tered, an error occurs while reading or writing the history file, an invalid offset
              is  supplied as an argument to -d, or the history expansion supplied as an argument
              to -p fails.

       jobs [-lnprs] [ jobspec ... ]
       jobs -x command [ args ... ]
              The first form lists the active jobs.  The options have the following meanings:
              -l     List process IDs in addition to the normal information.
              -n     Display information only about jobs that have changed status since the  user
                     was last notified of their status.
              -p     List only the process ID of the job's process group leader.
              -r     Display only running jobs.
              -s     Display only stopped jobs.

              If  jobspec  is given, output is restricted to information about that job.  The re-
              turn status is 0 unless an invalid option is encountered or an invalid  jobspec  is
              supplied.

              If  the  -x  option is supplied, jobs replaces any jobspec found in command or args
              with the corresponding process group ID, and executes command passing it args,  re-
              turning its exit status.

       kill [-s sigspec | -n signum | -sigspec] [pid | jobspec] ...
       kill -l|-L [sigspec | exit_status]
              Send  the  signal  named by sigspec or signum to the processes named by pid or job-
              spec.  sigspec is either a case-insensitive signal name such as  SIGKILL  (with  or
              without  the SIG prefix) or a signal number; signum is a signal number.  If sigspec
              is not present, then SIGTERM is assumed.  An argument of -l lists the signal names.
              If  any  arguments  are  supplied when -l is given, the names of the signals corre-
              sponding to the arguments are listed, and the return status is 0.  The  exit_status
              argument  to -l is a number specifying either a signal number or the exit status of
              a process terminated by a signal.  The -L option is equivalent to -l.  kill returns
              true  if  at least one signal was successfully sent, or false if an error occurs or
              an invalid option is encountered.

       let arg [arg ...]
              Each arg is an arithmetic expression to be  evaluated  (see  ARITHMETIC  EVALUATION
              above).  If the last arg evaluates to 0, let returns 1; 0 is returned otherwise.

       local [option] [name[=value] ... | - ]
              For each argument, a local variable named name is created, and assigned value.  The
              option can be any of the options accepted by declare.  When local is used within  a
              function,  it  causes  the variable name to have a visible scope restricted to that
              function and its children.  If name is -, the set of shell options is made local to
              the function in which local is invoked: shell options changed using the set builtin
              inside the function are restored to their original values  when  the  function  re-
              turns.  The restore is effected as if a series of set commands were executed to re-
              store the values that were in place before the function.  With no  operands,  local
              writes a list of local variables to the standard output.  It is an error to use lo-
              cal when not within a function.  The return status is 0 unless local is  used  out-
              side a function, an invalid name is supplied, or name is a readonly variable.

       logout Exit a login shell.

       mapfile  [-d delim] [-n count] [-O origin] [-s count] [-t] [-u fd] [-C callback] [-c quan-
       tum] [array]
       readarray [-d delim] [-n count] [-O origin] [-s count] [-t]  [-u  fd]  [-C  callback]  [-c
       quantum] [array]
              Read  lines  from the standard input into the indexed array variable array, or from
              file descriptor fd if the -u option is supplied.  The variable MAPFILE is  the  de-
              fault array.  Options, if supplied, have the following meanings:
              -d     The  first  character  of delim is used to terminate each input line, rather
                     than newline.  If delim is the empty string, mapfile will terminate  a  line
                     when it reads a NUL character.
              -n     Copy at most count lines.  If count is 0, all lines are copied.
              -O     Begin assigning to array at index origin.  The default index is 0.
              -s     Discard the first count lines read.
              -t     Remove a trailing delim (default newline) from each line read.
              -u     Read lines from file descriptor fd instead of the standard input.
              -C     Evaluate callback each time quantum lines are read.  The -c option specifies
                     quantum.
              -c     Specify the number of lines read between each call to callback.

              If -C is specified without -c, the default quantum is 5000.  When callback is eval-
              uated,  it  is  supplied the index of the next array element to be assigned and the
              line to be assigned to that element as additional arguments.  callback is evaluated
              after the line is read but before the array element is assigned.

              If  not supplied with an explicit origin, mapfile will clear array before assigning
              to it.

              mapfile returns successfully unless an invalid option or option  argument  is  sup-
              plied, array is invalid or unassignable, or if array is not an indexed array.

       popd [-n] [+n] [-n]
              Removes  entries  from the directory stack.  With no arguments, removes the top di-
              rectory from the stack, and performs a cd to the new top directory.  Arguments,  if
              supplied, have the following meanings:
              -n     Suppresses the normal change of directory when removing directories from the
                     stack, so that only the stack is manipulated.
              +n     Removes the nth entry counting from the left of  the  list  shown  by  dirs,
                     starting  with  zero.  For example: ``popd +0'' removes the first directory,
                     ``popd +1'' the second.
              -n     Removes the nth entry counting from the right of the  list  shown  by  dirs,
                     starting  with  zero.   For example: ``popd -0'' removes the last directory,
                     ``popd -1'' the next to last.

              If the popd command is successful, a dirs is performed as well, and the return sta-
              tus  is  0.   popd returns false if an invalid option is encountered, the directory
              stack is empty, a non-existent directory stack entry is specified, or the directory
              change fails.

       printf [-v var] format [arguments]
              Write  the formatted arguments to the standard output under the control of the for-
              mat.  The -v option causes the output to be assigned to  the  variable  var  rather
              than being printed to the standard output.

              The format is a character string which contains three types of objects: plain char-
              acters, which are simply copied to standard  output,  character  escape  sequences,
              which  are  converted and copied to the standard output, and format specifications,
              each of which causes printing of the next successive argument.  In addition to  the
              standard  printf(1)  format  specifications, printf interprets the following exten-
              sions:
              %b     causes printf to expand backslash escape sequences in the corresponding  ar-
                     gument in the same way as echo -e.
              %q     causes  printf  to output the corresponding argument in a format that can be
                     reused as shell input.
              %(datefmt)T
                     causes printf to output the date-time string resulting from using datefmt as
                     a  format  string for strftime(3).  The corresponding argument is an integer
                     representing the number of seconds since the epoch.   Two  special  argument
                     values  may  be  used: -1 represents the current time, and -2 represents the
                     time the shell was invoked.  If no argument is specified, conversion behaves
                     as if -1 had been given.  This is an exception to the usual printf behavior.

              The  %b, %q, and %T directives all use the field width and precision arguments from
              the format specification and write that many bytes from (or use that wide  a  field
              for)  the expanded argument, which usually contains more characters than the origi-
              nal.

              Arguments to non-string format specifiers are treated as C constants, except that a
              leading  plus or minus sign is allowed, and if the leading character is a single or
              double quote, the value is the ASCII value of the following character.

              The format is reused as necessary to consume all of the arguments.  If  the  format
              requires  more  arguments than are supplied, the extra format specifications behave
              as if a zero value or null string, as appropriate, had been supplied.   The  return
              value is zero on success, non-zero on failure.

       pushd [-n] [+n] [-n]
       pushd [-n] [dir]
              Adds  a  directory  to the top of the directory stack, or rotates the stack, making
              the new top of the stack the current working directory.  With no  arguments,  pushd
              exchanges  the  top  two  directories  and returns 0, unless the directory stack is
              empty.  Arguments, if supplied, have the following meanings:
              -n     Suppresses the normal change of directory when rotating or  adding  directo-
                     ries to the stack, so that only the stack is manipulated.
              +n     Rotates  the  stack so that the nth directory (counting from the left of the
                     list shown by dirs, starting with zero) is at the top.
              -n     Rotates the stack so that the nth directory (counting from the right of  the
                     list shown by dirs, starting with zero) is at the top.
              dir    Adds  dir to the directory stack at the top, making it the new current work-
                     ing directory as if it had been supplied as the argument to the cd builtin.

              If the pushd command is successful, a dirs is performed as well.  If the first form
              is  used,  pushd returns 0 unless the cd to dir fails.  With the second form, pushd
              returns 0 unless the directory stack is empty, a non-existent directory stack  ele-
              ment  is  specified, or the directory change to the specified new current directory
              fails.

       pwd [-LP]
              Print the absolute pathname of the current working directory.  The pathname printed
              contains  no  symbolic links if the -P option is supplied or the -o physical option
              to the set builtin command is enabled.  If the -L  option  is  used,  the  pathname
              printed  may contain symbolic links.  The return status is 0 unless an error occurs
              while reading the name of the current directory or an invalid option is supplied.

       read [-ers] [-a aname] [-d delim] [-i text] [-n nchars] [-N nchars] [-p prompt] [-t  time-
       out] [-u fd] [name ...]
              One  line  is read from the standard input, or from the file descriptor fd supplied
              as an argument to the -u option, split into words as  described  above  under  Word
              Splitting, and the first word is assigned to the first name, the second word to the
              second name, and so on.  If there are more words than names,  the  remaining  words
              and their intervening delimiters are assigned to the last name.  If there are fewer
              words read from the input stream than names, the remaining names are assigned empty
              values.  The characters in IFS are used to split the line into words using the same
              rules the shell uses for expansion (described above  under  Word  Splitting).   The
              backslash  character  (\)  may  be  used to remove any special meaning for the next
              character read and for line continuation.  Options, if supplied, have the following
              meanings:
              -a aname
                     The  words  are  assigned to sequential indices of the array variable aname,
                     starting at 0.  aname is unset before any new values  are  assigned.   Other
                     name arguments are ignored.
              -d delim
                     The  first  character  of  delim is used to terminate the input line, rather
                     than newline.  If delim is the empty string, read will terminate a line when
                     it reads a NUL character.
              -e     If  the  standard  input  is  coming from a terminal, readline (see READLINE
                     above) is used to obtain the line.  Readline uses the current  (or  default,
                     if  line editing was not previously active) editing settings, but uses Read-
                     line's default filename completion.
              -i text
                     If readline is being used to read the line, text is placed into the  editing
                     buffer before editing begins.
              -n nchars
                     read  returns after reading nchars characters rather than waiting for a com-
                     plete line of input, but honors a delimiter if fewer than nchars  characters
                     are read before the delimiter.
              -N nchars
                     read returns after reading exactly nchars characters rather than waiting for
                     a complete line of input, unless EOF is encountered or read times out.   De-
                     limiter characters encountered in the input are not treated specially and do
                     not cause read to return until nchars characters are read.   The  result  is
                     not  split  on the characters in IFS; the intent is that the variable is as-
                     signed exactly the characters read (with the exception of backslash; see the
                     -r option below).
              -p prompt
                     Display  prompt  on  standard  error, without a trailing newline, before at-
                     tempting to read any input.  The prompt is displayed only if input is coming
                     from a terminal.
              -r     Backslash  does not act as an escape character.  The backslash is considered
                     to be part of the line.  In particular, a  backslash-newline  pair  may  not
                     then be used as a line continuation.
              -s     Silent mode.  If input is coming from a terminal, characters are not echoed.
              -t timeout
                     Cause  read to time out and return failure if a complete line of input (or a
                     specified number of characters) is not read within timeout seconds.  timeout
                     may  be  a  decimal  number  with a fractional portion following the decimal
                     point.  This option is only effective if read is reading input from a termi-
                     nal, pipe, or other special file; it has no effect when reading from regular
                     files.  If read times out, read saves any partial input read into the speci-
                     fied variable name.  If timeout is 0, read returns immediately, without try-
                     ing to read any data.  The exit status is 0 if input  is  available  on  the
                     specified  file  descriptor, non-zero otherwise.  The exit status is greater
                     than 128 if the timeout is exceeded.
              -u fd  Read input from file descriptor fd.

              If no names are supplied, the line read, without the ending delimiter but otherwise
              unmodified,  is  assigned  to  the variable REPLY.  The exit status is zero, unless
              end-of-file is encountered, read times out (in which case  the  status  is  greater
              than  128),  a variable assignment error (such as assigning to a readonly variable)
              occurs, or an invalid file descriptor is supplied as the argument to -u.

       readonly [-aAf] [-p] [name[=word] ...]
              The given names are marked readonly; the values of these names may not  be  changed
              by  subsequent assignment.  If the -f option is supplied, the functions correspond-
              ing to the names are so marked.  The -a option restricts the variables  to  indexed
              arrays;  the  -A option restricts the variables to associative arrays.  If both op-
              tions are supplied, -A takes precedence.  If no name arguments are given, or if the
              -p  option is supplied, a list of all readonly names is printed.  The other options
              may be used to restrict the output to a subset of the set of readonly  names.   The
              -p  option  causes  output to be displayed in a format that may be reused as input.
              If a variable name is followed by =word, the value of the variable is set to  word.
              The return status is 0 unless an invalid option is encountered, one of the names is
              not a valid shell variable name, or -f is supplied with a name that is not a  func-
              tion.

       return [n]
              Causes  a  function  to  stop  executing and return the value specified by n to its
              caller.  If n is omitted, the return status is that of the last command executed in
              the  function body.  If return is executed by a trap handler, the last command used
              to determine the status is the last command executed before the trap  handler.   If
              return is executed during a DEBUG trap, the last command used to determine the sta-
              tus is the last command executed by the trap handler before return was invoked.  If
              return  is  used  outside  a  function,  but  during execution of a script by the .
              (source) command, it causes the shell to stop executing that script and return  ei-
              ther  n  or  the  exit status of the last command executed within the script as the
              exit status of the script.  If n is supplied, the return value is its least signif-
              icant  8  bits.   The return status is non-zero if return is supplied a non-numeric
              argument, or is used outside a function and not during execution of a script  by  .
              or  source.   Any command associated with the RETURN trap is executed before execu-
              tion resumes after the function or script.

       set [--abefhkmnptuvxBCEHPT] [-o option-name] [arg ...]
       set [+abefhkmnptuvxBCEHPT] [+o option-name] [arg ...]
              Without options, the name and value of each shell variable are displayed in a  for-
              mat  that  can  be reused as input for setting or resetting the currently-set vari-
              ables.  Read-only variables cannot be reset.  In posix mode, only  shell  variables
              are  listed.   The  output is sorted according to the current locale.  When options
              are specified, they set or unset shell attributes.  Any arguments  remaining  after
              option  processing  are treated as values for the positional parameters and are as-
              signed, in order, to $1, $2, ...  $n.  Options, if specified,  have  the  following
              meanings:
              -a      Each  variable  or function that is created or modified is given the export
                      attribute and marked for export to the environment of subsequent commands.
              -b      Report the status of terminated background jobs  immediately,  rather  than
                      before the next primary prompt.  This is effective only when job control is
                      enabled.
              -e      Exit immediately if a pipeline (which may consist of a single  simple  com-
                      mand),  a list, or a compound command (see SHELL GRAMMAR above), exits with
                      a non-zero status.  The shell does not exit if the command  that  fails  is
                      part  of  the  command list immediately following a while or until keyword,
                      part of the test following the if or elif reserved words, part of any  com-
                      mand  executed in a && or || list except the command following the final &&
                      or ||, any command in a pipeline but the last, or if the  command's  return
                      value  is  being  inverted with !.  If a compound command other than a sub-
                      shell returns a non-zero status because a command failed while -e was being
                      ignored,  the  shell does not exit.  A trap on ERR, if set, is executed be-
                      fore the shell exits.  This option applies to  the  shell  environment  and
                      each  subshell  environment  separately  (see COMMAND EXECUTION ENVIRONMENT
                      above), and may cause subshells to exit before executing all  the  commands
                      in the subshell.

                      If  a  compound command or shell function executes in a context where -e is
                      being ignored, none of the commands executed within the compound command or
                      function  body  will be affected by the -e setting, even if -e is set and a
                      command returns a failure status.  If a compound command or shell  function
                      sets -e while executing in a context where -e is ignored, that setting will
                      not have any effect until the compound command or  the  command  containing
                      the function call completes.
              -f      Disable pathname expansion.
              -h      Remember  the  location  of  commands  as they are looked up for execution.
                      This is enabled by default.
              -k      All arguments in the form of assignment statements are placed in the  envi-
                      ronment for a command, not just those that precede the command name.
              -m      Monitor  mode.   Job  control is enabled.  This option is on by default for
                      interactive shells on systems that support it (see JOB CONTROL above).  All
                      processes  run  in  a  separate  process group.  When a background job com-
                      pletes, the shell prints a line containing its exit status.
              -n      Read commands but do not execute them.  This may be used to check  a  shell
                      script for syntax errors.  This is ignored by interactive shells.
              -o option-name
                      The option-name can be one of the following:
                      allexport
                              Same as -a.
                      braceexpand
                              Same as -B.
                      emacs   Use an emacs-style command line editing interface.  This is enabled
                              by default when the shell  is  interactive,  unless  the  shell  is
                              started with the --noediting option.  This also affects the editing
                              interface used for read -e.
                      errexit Same as -e.
                      errtrace
                              Same as -E.
                      functrace
                              Same as -T.
                      hashall Same as -h.
                      histexpand
                              Same as -H.
                      history Enable command history, as described above under HISTORY.  This op-
                              tion is on by default in interactive shells.
                      ignoreeof
                              The effect is as if the shell command ``IGNOREEOF=10'' had been ex-
                              ecuted (see Shell Variables above).
                      keyword Same as -k.
                      monitor Same as -m.
                      noclobber
                              Same as -C.
                      noexec  Same as -n.
                      noglob  Same as -f.
                      nolog   Currently ignored.
                      notify  Same as -b.
                      nounset Same as -u.
                      onecmd  Same as -t.
                      physical
                              Same as -P.
                      pipefail
                              If set, the return value of a pipeline is the  value  of  the  last
                              (rightmost)  command to exit with a non-zero status, or zero if all
                              commands in the pipeline exit successfully.  This  option  is  dis-
                              abled by default.
                      posix   Change  the  behavior  of  bash where the default operation differs
                              from the POSIX standard to match the standard  (posix  mode).   See
                              SEE ALSO below for a reference to a document that details how posix
                              mode affects bash's behavior.
                      privileged
                              Same as -p.
                      verbose Same as -v.
                      vi      Use a vi-style command line editing interface.  This  also  affects
                              the editing interface used for read -e.
                      xtrace  Same as -x.
                      If  -o  is  supplied with no option-name, the values of the current options
                      are printed.  If +o is supplied with no option-name, a series of  set  com-
                      mands  to recreate the current option settings is displayed on the standard
                      output.
              -p      Turn on privileged mode.  In this mode, the $ENV and  $BASH_ENV  files  are
                      not  processed, shell functions are not inherited from the environment, and
                      the SHELLOPTS, BASHOPTS, CDPATH, and GLOBIGNORE variables, if  they  appear
                      in  the  environment, are ignored.  If the shell is started with the effec-
                      tive user (group) id not equal to the real user (group) id, and the -p  op-
                      tion  is not supplied, these actions are taken and the effective user id is
                      set to the real user id.  If the -p option is supplied at startup, the  ef-
                      fective user id is not reset.  Turning this option off causes the effective
                      user and group ids to be set to the real user and group ids.
              -t      Exit after reading and executing one command.
              -u      Treat unset variables and parameters other than the special parameters  "@"
                      and  "*"  as an error when performing parameter expansion.  If expansion is
                      attempted on an unset variable or parameter, the shell prints an error mes-
                      sage, and, if not interactive, exits with a non-zero status.
              -v      Print shell input lines as they are read.
              -x      After expanding each simple command, for command, case command, select com-
                      mand, or arithmetic for command, display the expanded value  of  PS4,  fol-
                      lowed by the command and its expanded arguments or associated word list.
              -B      The shell performs brace expansion (see Brace Expansion above).  This is on
                      by default.
              -C      If set, bash does not overwrite an existing file with the >, >&, and <> re-
                      direction  operators.  This may be overridden when creating output files by
                      using the redirection operator >| instead of >.
              -E      If set, any trap on ERR is inherited by shell functions, command  substitu-
                      tions,  and  commands  executed in a subshell environment.  The ERR trap is
                      normally not inherited in such cases.
              -H      Enable !  style history substitution.  This option is on  by  default  when
                      the shell is interactive.
              -P      If  set,  the shell does not resolve symbolic links when executing commands
                      such as cd that change the current working directory.  It uses the physical
                      directory structure instead.  By default, bash follows the logical chain of
                      directories when performing commands which change the current directory.
              -T      If set, any traps on DEBUG and RETURN are  inherited  by  shell  functions,
                      command  substitutions,  and  commands  executed in a subshell environment.
                      The DEBUG and RETURN traps are normally not inherited in such cases.
              --      If no arguments follow this option, then the positional parameters are  un-
                      set.   Otherwise,  the  positional  parameters are set to the args, even if
                      some of them begin with a -.
              -       Signal the end of options, cause all remaining args to be assigned  to  the
                      positional parameters.  The -x and -v options are turned off.  If there are
                      no args, the positional parameters remain unchanged.

              The options are off by default unless otherwise  noted.   Using  +  rather  than  -
              causes  these options to be turned off.  The options can also be specified as argu-
              ments to an invocation of the shell.  The current set of options may  be  found  in
              $-.  The return status is always true unless an invalid option is encountered.

       shift [n]
              The  positional  parameters  from n+1 ... are renamed to $1 ....  Parameters repre-
              sented by the numbers $# down to $#-n+1 are unset.  n must be a non-negative number
              less  than  or  equal  to  $#.   If n is 0, no parameters are changed.  If n is not
              given, it is assumed to be 1.  If n is greater than $#, the  positional  parameters
              are not changed.  The return status is greater than zero if n is greater than $# or
              less than zero; otherwise 0.

       shopt [-pqsu] [-o] [optname ...]
              Toggle the values of settings controlling optional shell  behavior.   The  settings
              can  be  either  those  listed below, or, if the -o option is used, those available
              with the -o option to the set builtin command.  With no options, or with the -p op-
              tion, a list of all settable options is displayed, with an indication of whether or
              not each is set; if optnames are supplied, the output is restricted  to  those  op-
              tions.  The -p option causes output to be displayed in a form that may be reused as
              input.  Other options have the following meanings:
              -s     Enable (set) each optname.
              -u     Disable (unset) each optname.
              -q     Suppresses normal output (quiet mode); the return status  indicates  whether
                     the  optname  is set or unset.  If multiple optname arguments are given with
                     -q, the return status is zero if all optnames are enabled;  non-zero  other-
                     wise.
              -o     Restricts the values of optname to be those defined for the -o option to the
                     set builtin.

              If either -s or -u is used with no optname arguments, shopt shows  only  those  op-
              tions  which are set or unset, respectively.  Unless otherwise noted, the shopt op-
              tions are disabled (unset) by default.

              The return status when listing options is zero if all optnames  are  enabled,  non-
              zero  otherwise.   When setting or unsetting options, the return status is zero un-
              less an optname is not a valid shell option.

              The list of shopt options is:

              assoc_expand_once
                      If set, the shell suppresses multiple evaluation of associative array  sub-
                      scripts  during  arithmetic expression evaluation, while executing builtins
                      that can perform variable assignments, and while  executing  builtins  that
                      perform array dereferencing.
              autocd  If set, a command name that is the name of a directory is executed as if it
                      were the argument to the cd command.  This option is only used by  interac-
                      tive shells.
              cdable_vars
                      If  set,  an  argument to the cd builtin command that is not a directory is
                      assumed to be the name of a variable whose value is the directory to change
                      to.
              cdspell If  set, minor errors in the spelling of a directory component in a cd com-
                      mand will be corrected.  The errors checked for are transposed  characters,
                      a missing character, and one character too many.  If a correction is found,
                      the corrected filename is printed, and the command proceeds.   This  option
                      is only used by interactive shells.
              checkhash
                      If  set,  bash  checks that a command found in the hash table exists before
                      trying to execute it.  If a hashed command no longer exists, a normal  path
                      search is performed.
              checkjobs
                      If  set, bash lists the status of any stopped and running jobs before exit-
                      ing an interactive shell.  If any jobs are running, this causes the exit to
                      be deferred until a second exit is attempted without an intervening command
                      (see JOB CONTROL above).  The shell always postpones exiting  if  any  jobs
                      are stopped.
              checkwinsize
                      If  set, bash checks the window size after each external (non-builtin) com-
                      mand and, if necessary, updates the values of LINES and COLUMNS.  This  op-
                      tion is enabled by default.
              cmdhist If  set,  bash attempts to save all lines of a multiple-line command in the
                      same history entry.  This allows easy re-editing  of  multi-line  commands.
                      This  option  is enabled by default, but only has an effect if command his-
                      tory is enabled, as described above under HISTORY.
              compat31
              compat32
              compat40
              compat41
              compat42
              compat43
              compat44
                      These control aspects of the shell's compatibility mode (see SHELL COMPATI-
                      BILITY MODE below).

              complete_fullquote
                      If  set,  bash  quotes  all shell metacharacters in filenames and directory
                      names when performing completion.  If not set, bash removes  metacharacters
                      such  as  the dollar sign from the set of characters that will be quoted in
                      completed filenames when these metacharacters appear in shell variable ref-
                      erences in words to be completed.  This means that dollar signs in variable
                      names that expand to directories will not be quoted;  however,  any  dollar
                      signs  appearing  in  filenames will not be quoted, either.  This is active
                      only when bash is using backslashes to  quote  completed  filenames.   This
                      variable  is set by default, which is the default bash behavior in versions
                      through 4.2.

              direxpand
                      If set, bash replaces directory names with the results  of  word  expansion
                      when  performing  filename  completion.   This  changes the contents of the
                      readline editing buffer.  If not set, bash attempts to  preserve  what  the
                      user typed.

              dirspell
                      If  set,  bash  attempts spelling correction on directory names during word
                      completion if the directory name initially supplied does not exist.

              dotglob If set, bash includes filenames beginning with a  `.'  in  the  results  of
                      pathname  expansion.   The  filenames  ``.''   and  ``..''   must always be
                      matched explicitly, even if dotglob is set.

              execfail
                      If set, a non-interactive shell will not exit if it cannot execute the file
                      specified as an argument to the exec builtin command.  An interactive shell
                      does not exit if exec fails.

              expand_aliases
                      If set, aliases are expanded as described above under ALIASES.  This option
                      is enabled by default for interactive shells.

              extdebug
                      If  set at shell invocation, or in a shell startup file, arrange to execute
                      the debugger profile before the shell starts, identical to  the  --debugger
                      option.  If set after invocation, behavior intended for use by debuggers is
                      enabled:

                      1.     The -F option to the declare builtin displays the source  file  name
                             and  line  number corresponding to each function name supplied as an
                             argument.

                      2.     If the command run by the DEBUG trap returns a non-zero  value,  the
                             next command is skipped and not executed.

                      3.     If  the  command run by the DEBUG trap returns a value of 2, and the
                             shell is executing in a subroutine (a  shell  function  or  a  shell
                             script  executed by the . or source builtins), the shell simulates a
                             call to return.

                      4.     BASH_ARGC and BASH_ARGV are updated as described in  their  descrip-
                             tions above.

                      5.     Function  tracing is enabled: command substitution, shell functions,
                             and subshells invoked with ( command ) inherit the DEBUG and  RETURN
                             traps.

                      6.     Error tracing is enabled: command substitution, shell functions, and
                             subshells invoked with ( command ) inherit the ERR trap.

              extglob If set, the extended pattern matching features described above under  Path-
                      name Expansion are enabled.

              extquote
                      If  set,  $'string'  and $"string" quoting is performed within ${parameter}
                      expansions enclosed in double quotes.  This option is enabled by default.

              failglob
                      If set, patterns which fail to match filenames  during  pathname  expansion
                      result in an expansion error.

              force_fignore
                      If set, the suffixes specified by the FIGNORE shell variable cause words to
                      be ignored when performing word completion even if the  ignored  words  are
                      the only possible completions.  See SHELL VARIABLES above for a description
                      of FIGNORE.  This option is enabled by default.

              globasciiranges
                      If set, range expressions used in pattern matching bracket expressions (see
                      Pattern  Matching above) behave as if in the traditional C locale when per-
                      forming comparisons.  That is, the current locale's collating  sequence  is
                      not  taken  into account, so b will not collate between A and B, and upper-
                      case and lower-case ASCII characters will collate together.

              globstar
                      If set, the pattern ** used in a pathname expansion context will match  all
                      files  and  zero or more directories and subdirectories.  If the pattern is
                      followed by a /, only directories and subdirectories match.

              gnu_errfmt
                      If set, shell error messages are written in the standard GNU error  message
                      format.

              histappend
                      If  set, the history list is appended to the file named by the value of the
                      HISTFILE variable when the shell exits, rather than overwriting the file.

              histreedit
                      If set, and readline is being used, a user is given the opportunity to  re-
                      edit a failed history substitution.

              histverify
                      If set, and readline is being used, the results of history substitution are
                      not immediately passed to the shell parser.  Instead, the resulting line is
                      loaded into the readline editing buffer, allowing further modification.

              hostcomplete
                      If  set,  and readline is being used, bash will attempt to perform hostname
                      completion when a word containing a @ is being  completed  (see  Completing
                      under READLINE above).  This is enabled by default.

              huponexit
                      If  set,  bash will send SIGHUP to all jobs when an interactive login shell
                      exits.

              inherit_errexit
                      If set, command substitution inherits the value of the errexit option,  in-
                      stead  of unsetting it in the subshell environment.  This option is enabled
                      when posix mode is enabled.

              interactive_comments
                      If set, allow a word beginning with # to cause that word and all  remaining
                      characters on that line to be ignored in an interactive shell (see COMMENTS
                      above).  This option is enabled by default.

              lastpipe
                      If set, and job control is not active, the shell runs the last command of a
                      pipeline not executed in the background in the current shell environment.

              lithist If set, and the cmdhist option is enabled, multi-line commands are saved to
                      the history with embedded newlines rather than using  semicolon  separators
                      where possible.

              localvar_inherit
                      If  set,  local variables inherit the value and attributes of a variable of
                      the same name that exists at a previous scope before any new value  is  as-
                      signed.  The nameref attribute is not inherited.

              localvar_unset
                      If  set, calling unset on local variables in previous function scopes marks
                      them so subsequent lookups find them unset  until  that  function  returns.
                      This  is identical to the behavior of unsetting local variables at the cur-
                      rent function scope.

              login_shell
                      The shell sets this option if it is started as a login shell  (see  INVOCA-
                      TION above).  The value may not be changed.

              mailwarn
                      If  set,  and a file that bash is checking for mail has been accessed since
                      the last time it was checked, the message ``The mail in mailfile  has  been
                      read'' is displayed.

              no_empty_cmd_completion
                      If  set,  and  readline  is being used, bash will not attempt to search the
                      PATH for possible completions when completion  is  attempted  on  an  empty
                      line.

              nocaseglob
                      If  set, bash matches filenames in a case-insensitive fashion when perform-
                      ing pathname expansion (see Pathname Expansion above).

              nocasematch
                      If set, bash matches patterns in a case-insensitive fashion when performing
                      matching  while  executing case or [[ conditional commands, when performing
                      pattern substitution word expansions, or when  filtering  possible  comple-
                      tions as part of programmable completion.

              nullglob
                      If  set,  bash allows patterns which match no files (see Pathname Expansion
                      above) to expand to a null string, rather than themselves.

              progcomp
                      If set, the programmable completion facilities (see Programmable Completion
                      above) are enabled.  This option is enabled by default.

              progcomp_alias
                      If  set, and programmable completion is enabled, bash treats a command name
                      that doesn't have any completions as a possible alias  and  attempts  alias
                      expansion.  If it has an alias, bash attempts programmable completion using
                      the command word resulting from the expanded alias.

              promptvars
                      If set, prompt strings undergo parameter expansion,  command  substitution,
                      arithmetic  expansion,  and quote removal after being expanded as described
                      in PROMPTING above.  This option is enabled by default.

              restricted_shell
                      The shell sets this option if it is started in  restricted  mode  (see  RE-
                      STRICTED  SHELL  below).   The value may not be changed.  This is not reset
                      when the startup files are executed, allowing the startup files to discover
                      whether or not a shell is restricted.

              shift_verbose
                      If  set, the shift builtin prints an error message when the shift count ex-
                      ceeds the number of positional parameters.

              sourcepath
                      If set, the source (.) builtin uses the value of PATH to find the directory
                      containing the file supplied as an argument.  This option is enabled by de-
                      fault.

              xpg_echo
                      If set, the echo builtin expands backslash-escape sequences by default.

       suspend [-f]
              Suspend the execution of this shell until it receives a SIGCONT  signal.   A  login
              shell cannot be suspended; the -f option can be used to override this and force the
              suspension.  The return status is 0 unless the shell is a login shell and -f is not
              supplied, or if job control is not enabled.

       test expr
       [ expr ]
              Return  a status of 0 (true) or 1 (false) depending on the evaluation of the condi-
              tional expression expr.  Each operator and operand must  be  a  separate  argument.
              Expressions  are  composed of the primaries described in the bash manual page under
              CONDITIONAL EXPRESSIONS.  test does not accept any options, nor does it accept  and
              ignore an argument of -- as signifying the end of options.

              Expressions may be combined using the following operators, listed in decreasing or-
              der of precedence.  The evaluation depends on the number of arguments;  see  below.
              Operator precedence is used when there are five or more arguments.
              ! expr True if expr is false.
              ( expr )
                     Returns  the  value of expr.  This may be used to override the normal prece-
                     dence of operators.
              expr1 -a expr2
                     True if both expr1 and expr2 are true.
              expr1 -o expr2
                     True if either expr1 or expr2 is true.

              test and [ evaluate conditional expressions using a set of rules based on the  num-
              ber of arguments.

              0 arguments
                     The expression is false.
              1 argument
                     The expression is true if and only if the argument is not null.
              2 arguments
                     If the first argument is !, the expression is true if and only if the second
                     argument is null.  If the first argument is one of the unary conditional op-
                     erators  listed  above under CONDITIONAL EXPRESSIONS, the expression is true
                     if the unary test is true.  If the first argument is not a valid unary  con-
                     ditional operator, the expression is false.
              3 arguments
                     The following conditions are applied in the order listed.  If the second ar-
                     gument is one of the binary conditional operators listed above under  CONDI-
                     TIONAL EXPRESSIONS, the result of the expression is the result of the binary
                     test using the first and third arguments as operands.  The -a and -o  opera-
                     tors are considered binary operators when there are three arguments.  If the
                     first argument is !, the value is the negation of the two-argument test  us-
                     ing  the second and third arguments.  If the first argument is exactly ( and
                     the third argument is exactly ), the result is the one-argument test of  the
                     second argument.  Otherwise, the expression is false.
              4 arguments
                     If the first argument is !, the result is the negation of the three-argument
                     expression composed of the remaining arguments.  Otherwise,  the  expression
                     is  parsed  and  evaluated  according  to  precedence using the rules listed
                     above.
              5 or more arguments
                     The expression is parsed and evaluated according  to  precedence  using  the
                     rules listed above.

              When  used with test or [, the < and > operators sort lexicographically using ASCII
              ordering.

       times  Print the accumulated user and system times for the shell  and  for  processes  run
              from the shell.  The return status is 0.

       trap [-lp] [[arg] sigspec ...]
              The  command  arg  is  to  be  read  and executed when the shell receives signal(s)
              sigspec.  If arg is absent (and there is a single sigspec)  or  -,  each  specified
              signal  is reset to its original disposition (the value it had upon entrance to the
              shell).  If arg is the null string the signal specified by each sigspec is  ignored
              by the shell and by the commands it invokes.  If arg is not present and -p has been
              supplied, then the trap commands associated with each sigspec are displayed.  If no
              arguments are supplied or if only -p is given, trap prints the list of commands as-
              sociated with each signal.  The -l option causes the shell to print a list of  sig-
              nal  names  and  their corresponding numbers.  Each sigspec is either a signal name
              defined in <signal.h>, or a signal number.  Signal names are case  insensitive  and
              the SIG prefix is optional.

              If  a sigspec is EXIT (0) the command arg is executed on exit from the shell.  If a
              sigspec is DEBUG, the command arg is executed before every simple command, for com-
              mand,  case  command,  select command, every arithmetic for command, and before the
              first command executes in a shell function (see SHELL GRAMMAR above).  Refer to the
              description  of  the extdebug option to the shopt builtin for details of its effect
              on the DEBUG trap.  If a sigspec is RETURN, the command arg is executed each time a
              shell  function or a script executed with the . or source builtins finishes execut-
              ing.

              If a sigspec is ERR, the command arg is executed whenever  a  pipeline  (which  may
              consist  of  a  single  simple  command),  a  list, or a compound command returns a
              non-zero exit status, subject to the following conditions.  The ERR trap is not ex-
              ecuted  if  the  failed command is part of the command list immediately following a
              while or until keyword, part of the test in an if statement, part of a command exe-
              cuted  in a && or || list except the command following the final && or ||, any com-
              mand in a pipeline but the last, or if the command's return value is being inverted
              using !.  These are the same conditions obeyed by the errexit (-e) option.

              Signals  ignored  upon entry to the shell cannot be trapped or reset.  Trapped sig-
              nals that are not being ignored are reset to their original values in a subshell or
              subshell  environment  when  one  is  created.   The  return status is false if any
              sigspec is invalid; otherwise trap returns true.

       type [-aftpP] name [name ...]
              With no options, indicate how each name would be interpreted if used as  a  command
              name.   If  the -t option is used, type prints a string which is one of alias, key-
              word, function, builtin, or file if name is an alias, shell  reserved  word,  func-
              tion,  builtin, or disk file, respectively.  If the name is not found, then nothing
              is printed, and an exit status of false is returned.  If the  -p  option  is  used,
              type  either  returns the name of the disk file that would be executed if name were
              specified as a command name, or nothing if ``type -t name'' would not return  file.
              The  -P  option  forces a PATH search for each name, even if ``type -t name'' would
              not return file.  If a command is hashed, -p and -P print the hashed  value,  which
              is  not necessarily the file that appears first in PATH.  If the -a option is used,
              type prints all of the places that contain an executable named name.  This includes
              aliases and functions, if and only if the -p option is not also used.  The table of
              hashed commands is not consulted when using -a.  The  -f  option  suppresses  shell
              function  lookup, as with the command builtin.  type returns true if all of the ar-
              guments are found, false if any are not found.

       ulimit [-HS] -a
       ulimit [-HS] [-bcdefiklmnpqrstuvxPRT [limit]]
              Provides control over the resources available to the shell and to processes started
              by  it, on systems that allow such control.  The -H and -S options specify that the
              hard or soft limit is set for the given resource.  A hard limit cannot be increased
              by a non-root user once it is set; a soft limit may be increased up to the value of
              the hard limit.  If neither -H nor -S is specified, both the soft and  hard  limits
              are set.  The value of limit can be a number in the unit specified for the resource
              or one of the special values hard, soft, or unlimited, which stand for the  current
              hard  limit, the current soft limit, and no limit, respectively.  If limit is omit-
              ted, the current value of the soft limit of the resource is printed, unless the  -H
              option  is  given.   When  more  than one resource is specified, the limit name and
              unit, if appropriate, are printed before the value.  Other options are  interpreted
              as follows:
              -a     All current limits are reported; no limits are set
              -b     The maximum socket buffer size
              -c     The maximum size of core files created
              -d     The maximum size of a process's data segment
              -e     The maximum scheduling priority ("nice")
              -f     The maximum size of files written by the shell and its children
              -i     The maximum number of pending signals
              -k     The maximum number of kqueues that may be allocated
              -l     The maximum size that may be locked into memory
              -m     The maximum resident set size (many systems do not honor this limit)
              -n     The  maximum number of open file descriptors (most systems do not allow this
                     value to be set)
              -p     The pipe size in 512-byte blocks (this may not be set)
              -q     The maximum number of bytes in POSIX message queues
              -r     The maximum real-time scheduling priority
              -s     The maximum stack size
              -t     The maximum amount of cpu time in seconds
              -u     The maximum number of processes available to a single user
              -v     The maximum amount of virtual memory available to the  shell  and,  on  some
                     systems, to its children
              -x     The maximum number of file locks
              -P     The maximum number of pseudoterminals
              -R     The  maximum  time a real-time process can run before blocking, in microsec-
                     onds
              -T     The maximum number of threads

              If limit is given, and the -a option is not used, limit is the  new  value  of  the
              specified  resource.   If  no  option  is given, then -f is assumed.  Values are in
              1024-byte increments, except for -t, which is in seconds; -R, which is in microsec-
              onds;  -p,  which is in units of 512-byte blocks; -P, -T, -b, -k, -n, and -u, which
              are unscaled values; and, when in posix mode, -c and -f, which are in 512-byte  in-
              crements.  The return status is 0 unless an invalid option or argument is supplied,
              or an error occurs while setting a new limit.

       umask [-p] [-S] [mode]
              The user file-creation mask is set to mode.  If mode begins with a digit, it is in-
              terpreted  as  an octal number; otherwise it is interpreted as a symbolic mode mask
              similar to that accepted by chmod(1).  If mode is omitted, the current value of the
              mask is printed.  The -S option causes the mask to be printed in symbolic form; the
              default output is an octal number.  If the -p option is supplied, and mode is omit-
              ted,  the  output is in a form that may be reused as input.  The return status is 0
              if the mode was successfully changed or if no mode argument was supplied, and false
              otherwise.

       unalias [-a] [name ...]
              Remove  each  name  from the list of defined aliases.  If -a is supplied, all alias
              definitions are removed.  The return value is true unless a supplied name is not  a
              defined alias.

       unset [-fv] [-n] [name ...]
              For  each name, remove the corresponding variable or function.  If the -v option is
              given, each name refers to a shell variable, and that variable is  removed.   Read-
              only  variables  may not be unset.  If -f is specified, each name refers to a shell
              function, and the function definition is removed.  If the -n  option  is  supplied,
              and  name  is a variable with the nameref attribute, name will be unset rather than
              the variable it references.  -n has no effect if the -f option is supplied.  If  no
              options  are  supplied,  each name refers to a variable; if there is no variable by
              that name, a function with that name, if any, is unset.   Each  unset  variable  or
              function  is removed from the environment passed to subsequent commands.  If any of
              BASH_ALIASES,  BASH_ARGV0,   BASH_CMDS,   BASH_COMMAND,   BASH_SUBSHELL,   BASHPID,
              COMP_WORDBREAKS,  DIRSTACK, EPOCHREALTIME, EPOCHSECONDS, FUNCNAME, GROUPS, HISTCMD,
              LINENO, RANDOM, SECONDS, or SRANDOM are unset, they lose their special  properties,
              even  if  they  are  subsequently  reset.  The exit status is true unless a name is
              readonly.

       wait [-fn] [-p varname] [id ...]
              Wait for each specified child process and return its termination status.   Each  id
              may  be  a process ID or a job specification; if a job spec is given, all processes
              in that job's pipeline are waited for.  If id is not given, wait waits for all run-
              ning  background jobs and the last-executed process substitution, if its process id
              is the same as $!, and the return status is zero.  If the -n  option  is  supplied,
              wait  waits  for  a single job from the list of ids or, if no ids are supplied, any
              job, to complete and returns its exit status.  If none of the supplied arguments is
              a  child  of  the  shell,  or if no arguments are supplied and the shell has no un-
              waited-for children, the exit status is 127.  If the -p  option  is  supplied,  the
              process  or  job identifier of the job for which the exit status is returned is as-
              signed to the variable varname named by the option argument.  The variable will  be
              unset  initially, before any assignment.  This is useful only when the -n option is
              supplied.  Supplying the -f option, when job control is  enabled,  forces  wait  to
              wait  for id to terminate before returning its status, instead of returning when it
              changes status.  If id specifies a non-existent process or job, the  return  status
              is 127.  Otherwise, the return status is the exit status of the last process or job
              waited for.

SHELL COMPATIBILITY MODE
       Bash-4.0 introduced the concept of a `shell compatibility level', specified as  a  set  of
       options to the shopt builtin compat31, compat32, compat40, compat41, and so on).  There is
       only one current compatibility level -- each option is mutually exclusive.   The  compati-
       bility  level is intended to allow users to select behavior from previous versions that is
       incompatible with newer versions while they migrate scripts to use  current  features  and
       behavior. It's intended to be a temporary solution.

       This  section  does  not mention behavior that is standard for a particular version (e.g.,
       setting compat32 means that quoting the rhs of the regexp matching operator quotes special
       regexp characters in the word, which is default behavior in bash-3.2 and above).

       If a user enables, say, compat32, it may affect the behavior of other compatibility levels
       up to and including the current compatibility level.  The idea is that each  compatibility
       level  controls  behavior that changed in that version of bash, but that behavior may have
       been present in earlier versions.  For instance, the change to  use  locale-based  compar-
       isons  with the [[ command came in bash-4.1, and earlier versions used ASCII-based compar-
       isons, so enabling compat32 will enable ASCII-based comparisons as well.  That granularity
       may not be sufficient for all uses, and as a result users should employ compatibility lev-
       els carefully.  Read the documentation for a particular feature to find  out  the  current
       behavior.

       Bash-4.3  introduced  a new shell variable: BASH_COMPAT.  The value assigned to this vari-
       able (a decimal version number like 4.2, or an integer corresponding to the  compatNN  op-
       tion, like 42) determines the compatibility level.

       Starting  with  bash-4.4,  Bash has begun deprecating older compatibility levels.  Eventu-
       ally, the options will be removed in favor of BASH_COMPAT.

       Bash-5.0 is the final version for which there will be an individual shopt option  for  the
       previous version. Users should use BASH_COMPAT on bash-5.0 and later versions.

       The  following table describes the behavior changes controlled by each compatibility level
       setting.  The compatNN tag is used as shorthand for setting the compatibility level to  NN
       using  one of the following mechanisms.  For versions prior to bash-5.0, the compatibility
       level may be set using the corresponding compatNN shopt option.  For  bash-4.3  and  later
       versions, the BASH_COMPAT variable is preferred, and it is required for bash-5.1 and later
       versions.

       compat31
              o      quoting the rhs of the [[ command's regexp matching  operator  (=~)  has  no
                     special effect

       compat32
              o      interrupting  a command list such as "a ; b ; c" causes the execution of the
                     next command in the list (in bash-4.0 and later versions, the shell acts  as
                     if  it  received the interrupt, so interrupting one command in a list aborts
                     the execution of the entire list)

       compat40
              o      the < and > operators to the [[ command do not consider the  current  locale
                     when  comparing  strings;  they  use ASCII ordering.  Bash versions prior to
                     bash-4.1 use ASCII collation and strcmp(3); bash-4.1 and later use the  cur-
                     rent locale's collation sequence and strcoll(3).

       compat41
              o      in  posix mode, time may be followed by options and still be recognized as a
                     reserved word (this is POSIX interpretation 267)
              o      in posix mode, the parser requires that an even number of single quotes  oc-
                     cur  in  the  word portion of a double-quoted parameter expansion and treats
                     them specially, so that characters within the single quotes  are  considered
                     quoted (this is POSIX interpretation 221)

       compat42
              o      the  replacement  string  in double-quoted pattern substitution does not un-
                     dergo quote removal, as it does in versions after bash-4.2
              o      in posix mode, single quotes are considered special when expanding the  word
                     portion  of  a  double-quoted parameter expansion and can be used to quote a
                     closing brace or other special character (this is part of POSIX  interpreta-
                     tion  221);  in later versions, single quotes are not special within double-
                     quoted word expansions

       compat43
              o      the shell does not print a warning message if an attempt is made  to  use  a
                     quoted  compound  assignment  as  an argument to declare (declare -a foo='(1
                     2)'). Later versions warn that this usage is deprecated
              o      word expansion errors are considered non-fatal errors that cause the current
                     command  to  fail,  even in posix mode (the default behavior is to make them
                     fatal errors that cause the shell to exit)
              o      when executing a shell function, the loop state (while/until/etc.)   is  not
                     reset, so break or continue in that function will break or continue loops in
                     the calling context. Bash-4.4 and later reset the loop state to prevent this

       compat44
              o      the shell sets up the values used by BASH_ARGV and BASH_ARGC so they can ex-
                     pand to the shell's positional parameters even if extended debugging mode is
                     not enabled
              o      a subshell inherits loops from its parent context, so break or continue will
                     cause the subshell to exit.  Bash-5.0 and later reset the loop state to pre-
                     vent the exit
              o      variable assignments preceding builtins like export and  readonly  that  set
                     attributes  continue  to  affect variables with the same name in the calling
                     environment even if the shell is not in posix mode

       compat50
              o      Bash-5.1 changed the way $RANDOM is generated  to  introduce  slightly  more
                     randomness.  If  the shell compatibility level is set to 50 or lower, it re-
                     verts to the method from bash-5.0 and previous versions, so seeding the ran-
                     dom  number  generator  by assigning a value to RANDOM will produce the same
                     sequence as in bash-5.0
              o      If the command hash table is empty, bash versions prior to bash-5.1  printed
                     an informational message to that effect, even when producing output that can
                     be reused as input. Bash-5.1 suppresses that message when the -l  option  is
                     supplied.

SEE ALSO
       bash(1), sh(1)

GNU Bash-2.05a                           2001 October 29                         BASH-BUILTINS(7)

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