BASH_BUILTINS(1)                                              BASH_BUILTINS(1)



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

BASH BUILTIN COMMANDS
       Unless otherwise noted, each builtin command documented in this section
       as accepting options 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, break, continue, let,
       and  shift builtins accept and process arguments beginning with -- with-
       out 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.  A zero exit code is
              returned.

        ..  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 exe-
              cuted from filename.  If filename does not contain a slash, file
              names  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  posi-
              tional  parameters  when  filename  is  executed.  Otherwise the
              positional parameters are unchanged.  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  sup-
              plied,  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] [-lpsvPSV]
       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 readline-command
              Display current readline key and function bindings, bind  a  key
              sequence  to  a  readline  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 supplied, have the following meanings:
              -m keymap
                     Use keymap as the keymap to be affected by the subsequent
                     bindings.  Acceptable keymap names are emacs, emacs-stan-
                     dard,  emacs-meta,  emacs-ctlx,  vi, vi-move, vi-command,
                     and vi-insert.  vi is equivalent to vi-command; 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  read-
                     line  line  buffer and the READLINE_POINT variable to the
                     current location of the insertion point.  If the executed
                     command  changes  the  value  of  READLINE_LINE  or READ-
                     LINE_POINT, those new values will  be  reflected  in  the
                     editing state.

              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 status.  This is useful when defining a function
              whose name is the same as a shell builtin, retaining  the  func-
              tionality 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 func-
              tion or a script executed with the .. or source builtins.   With-
              out expr, caller displays the line number and source filename of
              the current subroutine call.  If a non-negative integer is  sup-
              plied as expr, caller displays the line number, subroutine name,
              and source file corresponding to that position  in  the  current
              execution  call  stack.  This extra 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] [dir]
              Change  the  current directory to dir.  The variable HOME is the
              default dir.  The variable CDPATH defines the  search  path  for
              the  directory  containing  dir.  Alternative directory names in
              CDPATH 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  says  to use the physical directory structure instead of
              following symbolic links (see also the  -P  option  to  the  set
              builtin command); the -L option forces symbolic links to be fol-
              lowed.  An argument of -- is equivalent to $OLDPWD.   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  success-
              fully 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  guaranteed  to
              find  all  of  the  standard  utilities.  If either the -V or -v
              option is supplied, a description of command is printed.  The -v
              option  causes a single word indicating the command or file name
              used to invoke command to be displayed; the -V option 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 can-
              not be found, the exit status is 127.  Otherwise, the exit  sta-
              tus 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 available, will not have useful values.

              The matches will be generated in the same way  as  if  the  pro-
              grammable  completion  code  had  generated them directly from a
              completion specification with the same flags.  If word is speci-
              fied, only those completions matching word will be displayed.

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

       complete [-abcdefgjksuv] [-o comp-option] [-DE] [-A action]  [-G  glob-
       pat] [-W wordlist] [-F function] [-C command]
              [-X filterpat] [-P prefix] [-S suffix] name [name _._._.]
       complete -pr [-DE] [name ...]
              Specify how arguments to each name should be completed.  If  the
              -p  option  is supplied, 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 spec-
              ification for each name, or, if no names are supplied, all  com-
              pletion  specifications.   The  -D  option  indicates  that  the
              remaining options and actions should apply  to  the  ``default''
              command  completion;  that is, completion attempted on a command
              for which no completion has previously  been  defined.   The  -E
              option  indicates  that the remaining options and actions should
              apply to  ``empty''  command  completion;  that  is,  completion
              attempted on a blank line.

              The  process  of  applying  these completion specifications when
              word completion is  attempted  is  described  above  under  Pro-
              grammable 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 expan-
              sion before the complete builtin is invoked.
              -o comp-option
                      The comp-option controls several aspects  of  the  comp-
                      spec's  behavior beyond the simple generation of comple-
                      tions.  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 generates no matches.
                      dirnames
                              Perform directory name completion if  the  comp-
                              spec generates no matches.
                      filenames
                              Tell  readline that the compspec generates file-
                              names, so it can perform  any  filename-specific
                              processing  (like  adding  a  slash to directory
                              names, quoting special characters, or  suppress-
                              ing  trailing spaces).  Intended to be used with
                              shell functions.
                      nospace Tell  readline  not  to  append  a  space   (the
                              default)  to  words  completed 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
                              results of the other actions.
              -A action
                      The  action  may  be  one of the following to generate a
                      list of possible completions:
                      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 spec-
                              ified as -v.
              -G globpat
                      The pathname expansion pattern globpat  is  expanded  to
                      generate the possible completions.
              -W wordlist
                      The  wordlist  is  split using the characters in the IFS
                      special variable as delimiters, and each resultant  word
                      is  expanded.   The possible completions are the members
                      of the resultant list which match the  word  being  com-
                      pleted.
              -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 it finishes, the possible com-
                      pletions are retrieved from the value of  the  COMPREPLY
                      array variable.
              -X filterpat
                      filterpat  is  a pattern as used for pathname expansion.
                      It is applied to the list of possible completions gener-
                      ated  by  the  preceding options and arguments, 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.
              -P prefix
                      prefix  is  added at the beginning of each possible com-
                      pletion after all other options have been applied.
              -S suffix
                      suffix is appended to each possible completion after all
                      other options have been applied.

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

       compopt [-o option] [-DE] [++oo option] [name]
              Modify  completion  options  for  each  name  according  to  the
              options, or for the currently-execution completion if  no  names
              are  supplied.   If no options are given, display the completion
              options for each name or the current completion.   The  possible
              values  of  option  are  those  valid  for  the complete builtin
              described above.  The -D option  indicates  that  the  remaining
              options should apply to the ``default'' command completion; that
              is, completion attempted on a command for  which  no  completion
              has  previously  been defined.  The -E option indicates that the
              remaining options should apply to ``empty'' command  completion;
              that is, completion attempted on a blank line.

       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  comple-
       tion 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 [-aAfFilrtux] [-p] [name[=value] ...]
       typeset [-aAfFilrtux] [-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 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 defi-
              nitions; 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 the function is defined are dis-
              played  as  well.   The  -F  option  implies  -f.  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 evalua-
                     tion (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 converted to lower-case.   The  upper-case
                     attribute is disabled.
              -r     Make names readonly.  These names cannot then be assigned
                     values by subsequent 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 converted 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 may not be used to destroy an array vari-
              able and +r will not remove the readonly attribute.   When  used
              in a function, makes each name local, as with the local command.
              If a variable name is followed by =value, the value of the vari-
              able  is  set to value.  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 compound 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 read-
              only variable, an attempt is made to turn off array  status  for
              an  array variable, or an attempt is made to display a non-exis-
              tent function with -f.

       dirs [[++_n]] [[--_n]] [-cplv]
              Without options,  displays  the  list  of  currently  remembered
              directories.   The  default  display  is  on  a single line with
              directory names separated by spaces.  Directories are  added  to
              the  list  with  the  pushd  command;  the  popd command removes
              entries from the list.
              ++_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.
              -c     Clears  the  directory  stack  by  deleting  all  of  the
                     entries.
              -l     Produces  a  longer  listing;  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,  pre-
                     fixing each entry with its index in the stack.

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

       echo [-neE] [arg ...]
              Output the args, separated by spaces,  followed  by  a  newline.
              The return status is always 0.  If -n is specified, the trailing
              newline is suppressed.  If the -e option is  given,  interpreta-
              tion  of  the following backslash-escaped characters is enabled.
              The -E option disables the interpretation of these escape  char-
              acters,  even  on systems where they are interpreted by default.
              The xpg_echo shell option may be used to  dynamically  determine
              whether  or not echo expands 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     an escape character
              \f     form feed
              \n     new line
              \r     carriage return
              \t     horizontal tab
              \v     vertical tab
              \\\\     backslash
              \\00nnn  the  eight-bit  character  whose value is the octal value
                     nnn (zero to three octal digits)
              \\xx_H_H   the eight-bit character whose value  is  the  hexadecimal
                     value HH (one or two hex digits)

       enable [-a] [-dnps] [-f filename] [name ...]
              Enable  and disable builtin shell commands.  Disabling a builtin
              allows a disk command 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  command  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 arguments are given, or if the -p option is supplied,
              a list of shell builtins is printed.  With no other option argu-
              ments,  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 indica-
              tion 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 com-
              mand.  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 begin-
              ning  of  the  zeroth  argument passed to command.  This is what
              login(1) does.  The -c option causes command to be executed with
              an  empty environment.  If -a is supplied, the shell passes name
              as the zeroth argument to the executed command.  If command can-
              not  be executed for some reason, a non-interactive shell exits,
              unless the shell option execfail is enabled, in  which  case  it
              returns  failure.   An  interactive shell returns failure if the
              file cannot be executed.  If command is not specified, any redi-
              rections 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 envi-
              ronment of subsequently executed commands.  If the -f option  is
              given,  the names refer to functions.  If no names are given, or
              if the -p option is supplied, a  list  of  all  names  that  are
              exported  in  this  shell  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
              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.

       fc [-e ename] [-lnr] [first] [last]
       fc -s [pat=rep] [cmd]
              Fix  Command.  In the first form, a range of commands from first
              to last is selected from the history list.  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 cur-
              rent command number).  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 spec-
              ified  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.   Other-
              wise,  the editor given by ename is invoked on a file containing
              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, 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.  A useful alias to use with  this  is
              ``r="fc  -s"'',  so  that  typing ``r c' runs the last command
              beginning with `c' and typing ``r'' re-executes the last com-
              mand.

              If  the  first  form  is  used,  the return value is 0 unless an
              invalid option is encountered 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-exe-
              cuted,  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 spec-
              ify  a  valid  job  or  jobspec specifies a job that was started
              without job control.

       getopts optstring name [args]
              getopts is used by shell procedures to parse positional  parame-
              ters.   optstring  contains  the  option characters to be recog-
              nized; 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 option 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 argument, getopts places that  argument  into
              the  variable OPTARG.  The shell does not reset OPTIND automati-
              cally; it must be  manually  reset  between  multiple  calls  to
              getopts within the same shell invocation if a new set of parame-
              ters 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 given in args, 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 dis-
              played, 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 option
              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]
              For each name, the full file name of the command  is  determined
              by searching the directories in $PATH and remembered.  If the -p
              option is supplied, no path search is performed, and filename is
              used as the full file name 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 pathname  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 option causes output to be displayed in a for-
              mat that may be reused as input.  If no arguments are given,  or
              if only -l is supplied, information about remembered commands is
              printed.  The return status is true unless a name is  not  found
              or an invalid 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 -anrw [filename]
       history -p arg [arg _._._.]
       history -s arg [arg _._._.]
              With no options, display the command history list with line num-
              bers.  Lines listed with a ** have been modified.  An argument of
              _n  lists only the last _n lines.  If the shell variable HISTTIME-
              FORMAT is set and not null, it is used as a  format  string  for
              strftime(3)  to display the time stamp associated with each dis-
              played 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.
              -a     Append the ``new'' history lines (history  lines  entered
                     since  the  beginning of the current bash session) to the
                     history file.
              -n     Read the history lines not already read from the  history
                     file  into  the  current  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 use them as the
                     current history.
              -w     Write the current history to the history file,  overwrit-
                     ing 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  informa-
              tion  associated  with each history entry is written to the his-
              tory 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 previous history line.  The return value is 0
              unless an invalid option is encountered, an error  occurs  while
              reading  or  writing the history file, an invalid offset is sup-
              plied 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 fol-
              lowing meanings:
              -l     List process IDs in addition to the normal information.
              -p     List only the process  ID  of  the  job's  process  group
                     leader.
              -n     Display  information  only  about  jobs that have changed
                     status since the user was last notified of their  status.
              -r     Restrict output to running jobs.
              -s     Restrict output to stopped jobs.

              If  jobspec  is given, output is restricted to information about
              that job.  The return 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, returning its exit status.

       kill [-s sigspec | -n signum | --sigspec] [pid | jobspec] ...
       kill -l [sigspec | exit__status]
              Send  the  signal  named  by  sigspec or signum to the processes
              named by pid or jobspec.  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  corresponding 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.  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 ARITH-
              METIC  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 func-
              tion and its children.  With no operands, local writes a list of
              local  variables  to the standard output.  It is an error to use
              local when not within a function.  The return status is 0 unless
              local  is  used outside a function, an invalid name is supplied,
              or name is a readonly variable.

       logout Exit a login shell.

       mapfile [-n count] [-O origin] [-s count] [-t] [-u  fd]  [-C  callback]
       [-c quantum] [array]
       readarray [-n count] [-O origin] [-s count] [-t] [-u fd] [-C  callback]
       [-c quantum] [array]
              Read lines from the standard input into the indexed array  vari-
              able  array, or from file descriptor fd if the -u option is sup-
              plied.  The variable MAPFILE is the default array.  Options,  if
              supplied, have the following meanings:
              -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 newline from each line read.
              -u     Read  lines  from file descriptor fd instead of the stan-
                     dard 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 evaluated, it is supplied the index of the next
              array element to be assigned as an additional  argument.   call-
              back  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 supplied, array is invalid or  unassignable,  or  if
              array is not an indexed array.

       popd [-nn] [+_n] [-_n]
              Removes  entries  from  the directory stack.  With no arguments,
              removes the top directory from the stack, and performs a  cd  to
              the new top directory.  Arguments, if supplied, have the follow-
              ing 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  status is 0.  popd returns false if an invalid
              option is encountered, the directory stack is empty, a non-exis-
              tent 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 format.  The format is a character string which
              contains three types of objects:  plain  characters,  which  are
              simply  copied  to  standard output, character escape sequences,
              which are converted and copied to the standard output, and  for-
              mat  specifications,  each  of which causes printing of the next
              successive argument.  In addition to the standard printf(1) for-
              mats,  %b  causes printf to expand backslash escape sequences in
              the corresponding argument (except that  \c  terminates  output,
              backslashes in \\'', \\"", and \\?? are not removed, and octal escapes
              beginning with \\00 may contain up to four digits), and %q  causes
              printf to output the corresponding argument in a format that can
              be reused as shell input.

              The -v option causes the output to be assigned to  the  variable
              var rather than being printed to the standard output.

              The  format  is  reused as necessary to consume all of the argu-
              ments.  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, 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 adding
                     directories 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 working directory.

              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  direc-
              tory  stack  is empty, a non-existent directory stack element 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 timeout] [-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, and  the
              first word is assigned to the first name, the second word to the
              second name, and so on, with leftover words and their  interven-
              ing  separators  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.  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  fol-
              lowing 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.
              -e     If the standard input is coming from a terminal, readline
                     (see READLINE above) is used to obtain the  line.   Read-
                     line  uses  the  current (or default, if line editing was
                     not previously active) editing settings.
              -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 complete line of input, but honor a  delim-
                     iter  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.  Delimiter  charac-
                     ters  encountered  in the input are not treated specially
                     and do not cause read to return until  nchars  characters
                     are read.
              -p prompt
                     Display prompt on standard error, without a trailing new-
                     line, before attempting 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 back-
                     slash is considered to be part of the line.  In  particu-
                     lar,  a  backslash-newline pair may not be used as a line
                     continuation.
              -s     Silent mode.  If input is coming from a terminal, charac-
                     ters are not echoed.
              -t timeout
                     Cause  read  to time out and return failure if a complete
                     line of input is not read within timeout seconds.   time-
                     out  may  be  a  decimal number with a fractional portion
                     following the decimal point.  This option is only  effec-
                     tive  if  read is reading input from a terminal, pipe, or
                     other special file; it has no effect  when  reading  from
                     regular  files.  If timeout is 0, read returns success if
                     input is available  on  the  specified  file  descriptor,
                     failure  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 is assigned to the vari-
              able  REPLY.   The  return  code  is zero, unless end-of-file is
              encountered, read times out (in which case the  return  code  is
              greater  than 128), or an invalid file descriptor is supplied as
              the argument to -u.

       readonly [-aApf] [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 corresponding 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 no name arguments are given, or if the -p option is
              supplied, a list of all  readonly  names  is  printed.   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 function.

       return [_n]
              Causes a function to exit with the return value specified by  _n.
              If  _n  is omitted, the return status is that of the last command
              executed in the function body.  If 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 either
              _n  or  the  exit  status of the last command executed within the
              script as the exit status of the  script.   If  used  outside  a
              function  and  not during execution of a script by .., the return
              status is false.  Any command associated with the RETURN trap is
              executed  before execution resumes after the function or script.

       set [--abefhkmnptuvxBCEHPT] [-o option] [arg ...]
       set [+abefhkmnptuvxBCEHPT] [++oo option] [arg ...]
              Without options, the name and value of each shell  variable  are
              displayed in a format that can be reused as input for setting or
              resetting the currently-set variables.  Read-only variables can-
              not  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  val-
              ues for the positional parameters and are assigned, in order, to
              $$11, $$22, ......  $$_n.  Options,  if  specified,  have  the  following
              meanings:
              -a      Automatically  mark  variables  and  functions which are
                      modified or created for export  to  the  environment  of
                      subsequent commands.
              -b      Report  the status of terminated background jobs immedi-
                      ately, 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 command),  a subshell command enclosed  in
                      parentheses,  or one of the commands executed as part of
                      a command list enclosed by  braces  (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 command 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 !!.  A trap  on  ERR,
                      if set, is executed before the shell exits.  This option
                      applies to the shell environment and each subshell envi-
                      ronment  separately  (see  COMMAND EXECUTION ENVIRONMENT
                      above), and may cause subshells to exit before executing
                      all the commands in the subshell.
              -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 environment 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).   Background  pro-
                      cesses  run  in a separate process group and a line con-
                      taining their exit status is printed upon their  comple-
                      tion.
              -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 inter-
                              face.  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 option is on by default in inter-
                              active shells.
                      ignoreeof
                              The   effect   is   as   if  the  shell  command
                              ``IGNOREEOF=10'' had been  executed  (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 disabled by default.
                      posix   Change  the  behavior  of bash where the default
                              operation differs from  the  POSIX  standard  to
                              match the standard (posix mode).
                      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 commands 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 effective user (group) id not equal  to
                      the  real user (group) id, and the -p option is not sup-
                      plied, these actions are taken and the effective user id
                      is  set  to  the real user id.  If the -p option is sup-
                      plied at startup, the effective 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 spe-
                      cial  parameters "@" and "*" as an error when performing
                      parameter expansion.  If expansion is  attempted  on  an
                      unset  variable  or parameter, the shell prints an error
                      message, 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 command, or arithmetic for command, dis-
                      play  the expanded value of PS4, followed 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 <<>> redirection operators.   This  may  be
                      overridden when creating output files by using the redi-
                      rection operator >>|| instead of >>.
              -E      If set, any trap on ERR is inherited by shell functions,
                      command  substitutions,  and commands executed in a sub-
                      shell environment.  The ERR trap is normally not  inher-
                      ited 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 follow  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 unset.  Otherwise, the positional parame-
                      ters 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 posi-
                      tional 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 arguments 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 encoun-
              tered.

       shift [_n]
              The  positional  parameters  from _n+1 ... are renamed to $$11 ........
              Parameters represented by the numbers  $$##  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 variables controlling optional shell behav-
              ior.  With no options, or with the -p option, a list of all set-
              table options is displayed, with an indication of whether or not
              each is set.  The -p option causes output to be displayed  in  a
              form  that  may be reused as input.  Other options have the fol-
              lowing 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 multi-
                     ple optname arguments are given with -q, the return  sta-
                     tus  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, the dis-
              play is limited to those options which are set or unset, respec-
              tively.   Unless otherwise noted, the shopt options 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 unless an optname  is  not  a
              valid shell option.

              The list of shopt options is:

              autocd  If  set,  a command name that is the name of a directory
                      is executed as if it were the argument to  the  cd  com-
                      mand.  This option is only used by interactive 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 com-
                      ponent in a cd command will be  corrected.   The  errors
                      checked for are transposed characters, a missing charac-
                      ter, and one character too many.   If  a  correction  is
                      found,  the corrected file name is printed, and the com-
                      mand proceeds.  This option is only used by  interactive
                      shells.
              checkhash
                      If set, bash checks that a command found in the hash ta-
                      ble exists before trying to execute  it.   If  a  hashed
                      command  no  longer exists, a normal path search is per-
                      formed.
              checkjobs
                      If set, bash lists the status of any stopped and running
                      jobs  before  exiting 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 command
                      and, if necessary, updates the values of LINES and  COL-
                      UMNS.
              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.
              compat31
                      If set, bash changes its behavior to that of version 3.1
                      with respect to quoted arguments to the conditional com-
                      mand's =~ operator.
              compat32
                      If set, bash changes its behavior to that of version 3.2
                      with respect to locale-specific string  comparison  when
                      using the conditional command's < and > operators.
              compat40
                      If set, bash changes its behavior to that of version 4.0
                      with respect to locale-specific string  comparison  when
                      using  the  conditional  command's < and > operators and
                      the effect of interrupting a command list.
              dirspell
                      If set, bash attempts spelling correction  on  directory
                      names  during word completion if the directory name ini-
                      tially supplied does not exist.
              dotglob If set, bash includes filenames beginning with a `.'  in
                      the results of pathname expansion.
              execfail
                      If set, a non-interactive shell will not exit if it can-
                      not 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 interac-
                      tive shells.
              extdebug
                      If set,  behavior  intended  for  use  by  debuggers  is
                      enabled:
                      11..     The -F option to the declare builtin displays the
                             source file name and line number corresponding to
                             each function name supplied as an argument.
                      22..     If  the  command  run by the DEBUG trap returns a
                             non-zero value, the next command is  skipped  and
                             not executed.
                      33..     If  the  command  run by the DEBUG trap returns a
                             value of 2, and the shell is executing in a  sub-
                             routine  (a shell function or a shell script exe-
                             cuted by the .. or source  builtins),  a  call  to
                             return is simulated.
                      44..     BASH_ARGC  and BASH_ARGV are updated as described
                             in their descriptions above.
                      55..     Function tracing is enabled:   command  substitu-
                             tion, shell functions, and subshells invoked with
                             (( command )) inherit the DEBUG and RETURN traps.
                      66..     Error tracing is enabled:  command  substitution,
                             shell  functions,  and  subshells  invoked with ((
                             command )) inherit the ERROR trap.
              extglob If set, the extended pattern matching features described
                      above under Pathname 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 possi-
                      ble  completions.   See  SHELL  VARIABLES  above  for  a
                      description of  FIGNORE.   This  option  is  enabled  by
                      default.
              globstar
                      If set, the pattern **** used in a pathname expansion con-
                      text will match a 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  his-
                      tory  substitution  are  not  immediately  passed to the
                      shell parser.  Instead, the  resulting  line  is  loaded
                      into the readline editing buffer, allowing further modi-
                      fication.
              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 inter-
                      active login shell exits.
              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.
              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.
              login_shell
                      The  shell  sets this option if it is started as a login
                      shell (see INVOCATION 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 dis-
                      played.
              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 performing 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.
              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 Pro-
                      grammable Completion above) are enabled.  This option is
                      enabled by default.
              promptvars
                      If set, prompt strings undergo parameter expansion, com-
                      mand   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 RESTRICTED SHELL below).  The value
                      may  not be changed.  This is not reset when the startup
                      files are executed, allowing the startup files  to  dis-
                      cover whether or not a shell is restricted.
              shift_verbose
                      If  set,  the shift builtin prints an error message when
                      the shift count exceeds the number of positional parame-
                      ters.
              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 default.
              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 sta-
              tus  is  0  unless the shell is a login shell and -f is not sup-
              plied, or if job control is not enabled.
       test expr
       [[ expr ]]
              Return a status of 0 or 1 depending on  the  evaluation  of  the
              conditional  expression expr.  Each operator and operand must be
              a separate argument.  Expressions are composed of the  primaries
              described  above  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  order  of  precedence.   The  evaluation
              depends on the number of arguments; see below.
              !! expr True if expr is false.
              (( expr ))
                     Returns  the value of expr.  This may be used to override
                     the normal precedence of operators.
              expr1 -aa expr2
                     True if both expr1 and expr2 are true.
              expr1 -oo expr2
                     True if either expr1 or expr2 is true.

              test and [[ evaluate conditional expressions using a set of rules
              based on the number 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 argu-
                     ment is one of the  unary  conditional  operators  listed
                     above  under  CONDITIONAL  EXPRESSIONS, the expression is
                     true if the unary test is true.  If the first argument is
                     not a valid unary conditional operator, the expression is
                     false.
              3 arguments
                     If the second argument is one of the  binary  conditional
                     operators listed above under CONDITIONAL 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 operators are  considered  binary  operators  when
                     there  are  three arguments.  If the first argument is !!,
                     the value is the negation of the two-argument test  using
                     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.  Other-
                     wise, 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 eval-
                     uated  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.

       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  associated  with each signal.  The -l option
              causes the shell to print a list of signal names and their  cor-
              responding  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  exe-
              cuted  before  every  simple command, for command, 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 fin-
              ishes executing.

              If a sigspec is ERR, the command arg is executed whenever a sim-
              ple command has a non-zero exit status, subject to the following
              conditions.  The ERR trap is not executed 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  executed in a &&&& or |||| list, or if the command's return
              value is being inverted via !!.  These are  the  same  conditions
              obeyed by the errexit option.

              Signals  ignored  upon  entry  to the shell cannot be trapped or
              reset.  Trapped signals 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, keyword, function, builtin, or
              file if  name  is  an  alias,  shell  reserved  word,  function,
              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 speci-
              fied 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,  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 func-
              tion lookup, as with the command builtin.  type returns true  if
              all of the arguments are found, false if any are not found.

       ulimit [-HSTabcdefilmnpqrstuvx [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  speci-
              fied, 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  omitted, 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 are printed before the value.  Other options are inter-
              preted as follows:
              -a     All current limits are reported
              -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
              -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
              -x     The maximum number of file locks
              -T     The maximum number of threads

              If limit is given, it is the new value of the specified resource
              (the -a option is display only).  If no option is given, then -f
              is assumed.  Values are in 1024-byte increments, except for  -t,
              which  is  in seconds, -p, which is in units of 512-byte blocks,
              and -T, -b, -n, and -u, which are unscaled values.   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 interpreted 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  sym-
              bolic  form;  the  default output is an octal number.  If the -p
              option is supplied, and mode is omitted, the output is in a form
              that may be reused as input.  The return status is 0 if the mode
              was successfully changed or if no mode  argument  was  supplied,
              and false otherwise.

       unalias [-aa] [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] [name ...]
              For  each  name,  remove the corresponding variable or function.
              If no options are supplied, or the -v option is given, each name
              refers  to  a  shell  variable.   Read-only variables may not be
              unset.  If -f is specified, each name refers to  a  shell  func-
              tion,  and the function definition is removed.  Each unset vari-
              able or function is removed from the environment passed to  sub-
              sequent  commands.   If any of COMP_WORDBREAKS, RANDOM, SECONDS,
              LINENO, HISTCMD, FUNCNAME, GROUPS, or DIRSTACK are  unset,  they
              lose  their  special  properties,  even if they are subsequently
              reset.  The exit status is true unless a name is readonly.

       wait [_n _._._.]
              Wait for each specified process and return its termination  sta-
              tus.   Each  _n  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 _n is not given, all currently active child pro-
              cesses are waited for, and the return  status  is  zero.   If  _n
              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.

SEE ALSO
       bash(1), sh(1)



GNU Bash-4.0                      2004 Apr 20                 BASH_BUILTINS(1)
