BASH_BUILTINS(1)            General Commands Manual           BASH_BUILTINS(1)



NAME
       bash,  :,  .,  [, alias, bg, bind, break, builtin, caller, cd, command,
       compgen, complete, compopt, continue, declare, dirs, disown, echo,  en-
       able,  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, return,  break,  con-
       tinue,  let,  and shift builtins accept and process arguments beginning
       with - without requiring --.  Other builtins that accept arguments  but
       are  not  specified  as accepting options interpret arguments beginning
       with - as invalid options and require -- to  prevent  this  interpreta-
       tion.
       : [arguments]
              No  effect;  the command does nothing beyond expanding arguments
              and performing any specified redirections.  The return status is
              zero.

        .  filename [arguments]
       source filename [arguments]
              Read and execute commands from filename in the current shell en-
              vironment and return the exit status of the  last  command  exe-
              cuted  from  filename.   If  filename  does not contain a slash,
              filenames in PATH are used  to  find  the  directory  containing
              filename.  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  po-
              sitional parameters are unchanged.  If the -T option is enabled,
              source inherits any trap on DEBUG; if it is not, any DEBUG  trap
              string  is  saved  and  restored  around the call to source, and
              source unsets the DEBUG trap while it executes.  If  -T  is  not
              set,  and the sourced file changes the DEBUG trap, the new value
              is retained when source completes.  The  return  status  is  the
              status  of  the  last  command exited within the script (0 if no
              commands are executed), and false if filename is  not  found  or
              cannot be read.

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

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

       bind [-m keymap] [-lpsvPSVX]
       bind [-m keymap] [-q function] [-u function] [-r keyseq]
       bind [-m keymap] -f filename
       bind [-m keymap] -x keyseq:shell-command
       bind [-m keymap] keyseq:function-name
       bind [-m keymap] keyseq:readline-command
              Display current readline key and function bindings, bind  a  key
              sequence  to  a  readline  function  or macro, or set a readline
              variable.  Each non-option argument is a command as it would ap-
              pear  in .inputrc, but each binding or command must be passed as
              a separate argument; e.g., '"\C-x\C-r": re-read-init-file'.  Op-
              tions, 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  (vi-move
                     is  also  a  synonym); emacs is equivalent to emacs-stan-
                     dard.
              -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 en-
                     tered.  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 and READLINE_MARK
                     variables  to the current location of the insertion point
                     and the saved insertion point (the  mark),  respectively.
                     If the executed command changes the value of any of READ-
                     LINE_LINE, READLINE_POINT, or  READLINE_MARK,  those  new
                     values will be reflected in the editing state.
              -X     List  all  key  sequences bound to shell commands and the
                     associated commands in a format that can be reused as in-
                     put.

              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  ex-
              ited.   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 [-e]] [-@]] [dir]
              Change  the  current  directory to dir.  if dir is not supplied,
              the value of the HOME shell variable is the default.  Any  addi-
              tional arguments following dir are ignored.  The variable CDPATH
              defines the search path for the directory containing  dir:  each
              directory  name  in CDPATH is searched for dir.  Alternative di-
              rectory 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  causes cd to use the physical directory
              structure by resolving symbolic links while traversing  dir  and
              before processing instances of .. in dir (see also the -P option
              to the set builtin command); the -L option forces symbolic links
              to  be followed by resolving the link after processing instances
              of .. in dir.  If .. appears in dir, it is processed by removing
              the  immediately previous pathname component from dir, back to a
              slash or the beginning of dir.  If the  -e  option  is  supplied
              with  -P,  and  the current working directory cannot be success-
              fully determined after a successful directory  change,  cd  will
              return  an unsuccessful status.  On systems that support it, the
              -@ option presents the extended  attributes  associated  with  a
              file  as  a directory.  An argument of - is converted to $OLDPWD
              before the directory change is attempted.  If a non-empty direc-
              tory  name  from  CDPATH is used, or if - is the first argument,
              and the directory change is successful, the absolute pathname of
              the  new  working  directory  is written to the standard output.
              The return value is  true  if  the  directory  was  successfully
              changed; false otherwise.

       command [-pVv] command [arg ...]
              Run  command  with  args  suppressing  the normal shell function
              lookup.  Only builtin commands or commands found in the PATH are
              executed.   If the -p option is given, the search for command is
              performed using a default value for PATH that is  guaranteed  to
              find  all of the standard utilities.  If either the -V or -v op-
              tion is supplied, a description of command is printed.   The  -v
              option  causes  a single word indicating the command or filename
              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 fa-
              cilities, while available, will not have useful values.

              The matches will be generated in the same way as if the program-
              mable completion code had generated them directly from a comple-
              tion specification with the same flags.  If word  is  specified,
              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] [-DEI] [-A action] [-G  glob-
       pat] [-W wordlist]
              [-F  function]  [-C command] [-X filterpat] [-P prefix] [-S suf-
              fix] name [name ...]
       complete -pr [-DEI] [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 other sup-
              plied options and actions should apply to the  ``default''  com-
              mand  completion; that is, completion attempted on a command for
              which no completion has previously been defined.  The -E  option
              indicates  that  other supplied options and actions should apply
              to ``empty'' command completion; that is,  completion  attempted
              on  a  blank  line.  The -I option indicates that other supplied
              options and actions should apply to completion  on  the  initial
              non-assignment  word  on  the line, or after a command delimiter
              such as ; or |, which is usually command  name  completion.   If
              multiple  options  are  supplied, the -D option takes precedence
              over -E, and both take precedence over -I.  If any of -D, -E, or
              -I  are  supplied,  any  other name arguments are ignored; these
              completions only apply to the case specified by the option.

              The process of applying  these  completion  specifications  when
              word  completion  is attempted is described above under Program-
              mable 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.
                      noquote Tell  readline  not to quote the completed words
                              if they are filenames (quoting filenames is  the
                              default).
                      nosort  Tell  readline  not to sort the list of possible
                              completions alphabetically.
                      nospace Tell readline not to append  a  space  (the  de-
                              fault)  to  words  completed  at  the end of the
                              line.
                      plusdirs
                              After any matches defined by  the  compspec  are
                              generated,  directory  name  completion  is  at-
                              tempted 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.
              -C command
                      command is executed in a subshell environment,  and  its
                      output is used as the possible completions.
              -F function
                      The  shell  function function is executed in the current
                      shell environment.  When the function is  executed,  the
                      first argument ($1) is the name of the command whose ar-
                      guments are being completed, the second argument ($2) is
                      the word being completed, and the third argument ($3) is
                      the word preceding the word being completed on the  cur-
                      rent  command line.  When it finishes, the possible com-
                      pletions are retrieved from the value of  the  COMPREPLY
                      array variable.
              -G globpat
                      The  pathname  expansion  pattern globpat is expanded to
                      generate the possible completions.
              -P prefix
                      prefix is added at the beginning of each  possible  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.
              -W wordlist
                      The wordlist is split using the characters  in  the  IFS
                      special  variable as delimiters, and each resultant word
                      is expanded.  Shell quoting is honored within  wordlist,
                      in order to provide a mechanism for the words to contain
                      shell metacharacters or characters in the value of  IFS.
                      The  possible  completions are the members of the resul-
                      tant list which match the word being completed.
              -X filterpat
                      filterpat is a pattern as used for  pathname  expansion.
                      It is applied to the list of possible completions 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.

              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] [-DEI] [+o option] [name]
              Modify  completion  options  for  each name according to the op-
              tions, or for the currently-executing completion if no names are
              supplied.   If  no options are given, display the completion op-
              tions for each name or the  current  completion.   The  possible
              values  of  option  are those valid for the complete builtin de-
              scribed above.  The -D option indicates that other supplied  op-
              tions  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 other
              supplied options should apply to ``empty''  command  completion;
              that  is,  completion  attempted on a blank line.  The -I option
              indicates that other supplied options should apply to completion
              on  the initial non-assignment word on the line, or after a com-
              mand delimiter such as ; or |, which  is  usually  command  name
              completion.

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

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

       declare [-aAfFgiIlnrtux] [-p] [name[=value] ...]
       typeset [-aAfFgiIlnrtux] [-p] [name[=value] ...]
              Declare variables and/or give them attributes.  If no names  are
              given  then display the values of variables.  The -p option will
              display the attributes and values of each name.  When -p is used
              with  name  arguments, additional options, other than -f and -F,
              are ignored.  When -p is supplied  without  name  arguments,  it
              will  display  the attributes and values of all variables having
              the attributes specified by the additional options.  If no other
              options  are  supplied  with  -p,  declare  will display the at-
              tributes and values of all shell variables.  The -f option  will
              restrict the display to shell functions.  The -F option inhibits
              the display of function definitions; only the function name  and
              attributes are printed.  If the extdebug shell option is enabled
              using shopt, the source file name and  line  number  where  each
              name  is  defined  are displayed as well.  The -F option implies
              -f.  The -g option forces variables to be created or modified at
              the global scope, even when declare is executed in a shell func-
              tion.  It is ignored in all other cases.  The -I  option  causes
              local  variables  to  inherit the attributes (except the nameref
              attribute) and value of any existing variable with the same name
              at  a  surrounding scope.  If there is no existing variable, the
              local variable is initially unset.  The following options can be
              used  to  restrict output to variables with the specified attri-
              bute 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.
              -n     Give each name the nameref attribute, making  it  a  name
                     reference  to  another  variable.  That other variable is
                     defined by the value of name.   All  references,  assign-
                     ments,  and attribute modifications to name, except those
                     using or changing the -n attribute itself, are  performed
                     on  the variable referenced by name's value.  The nameref
                     attribute cannot be applied to array variables.
              -r     Make names readonly.  These names cannot then be assigned
                     values by subsequent assignment statements or unset.
              -t     Give each name the trace attribute.  Traced functions in-
                     herit 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 en-
                     vironment.

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

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

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

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

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

       enable [-a] [-dnps] [-f filename] [name ...]
              Enable and disable builtin shell commands.  Disabling a  builtin
              allows a disk 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  en-
              abled.   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 lo-
              gin(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  execfail shell option is enabled.  In that case, it
              returns failure.  An interactive shell returns  failure  if  the
              file  cannot  be  executed.  A subshell exits unconditionally if
              exec fails.  If command is not specified, any redirections  take
              effect  in  the  current  shell, and the return status is 0.  If
              there is a redirection error, the return status is 1.

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

       export [-fn] [name[=word]] ...
       export -p
              The supplied names are marked for automatic export to the  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 names of all exported
              variables is printed.  The -n option causes the export  property
              to be removed from each name.  If a variable name is followed by
              =word, the value of the variable is set to word.  export returns
              an exit status of 0 unless an invalid option is encountered, one
              of the names is not a valid shell variable name, or -f  is  sup-
              plied with a name that is not a function.

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

              The  -n option suppresses the command numbers when listing.  The
              -r option reverses the order of the commands.  If the -l  option
              is  given,  the  commands are listed on standard output.  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, vi is used.  When editing is com-
              plete, the edited commands are echoed and executed.

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

              If the first form is used, the return value is 0 unless  an  in-
              valid  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 [arg ...]
              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 ex-
              pected 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 op-
              tion requires an argument, getopts places that argument into the
              variable OPTARG.  The shell does not reset OPTIND automatically;
              it  must  be  manually  reset  between multiple calls to getopts
              within the same shell invocation if a new set of  parameters  is
              to be used.

              When the end of options is encountered, getopts exits with a re-
              turn 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 supplied as arg values, getopts parses  those  in-
              stead.

              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  OP-
              TARG 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]
              Each time hash is invoked, the full pathname of the command name
              is determined by searching the directories in $PATH  and  remem-
              bered.  Any previously-remembered pathname is discarded.  If the
              -p option is supplied, no path search is performed, and filename
              is  used  as  the  full  filename of the command.  The -r option
              causes the shell to forget all remembered locations.  The -d op-
              tion  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 -d start-end
       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.   If  offset
                     is negative, it is interpreted as relative to one greater
                     than the last history position, so negative indices count
                     back  from  the  end  of  the history, and an index of -1
                     refers to the current history -d command.
              -d start-end
                     Delete the history entries between  positions  start  and
                     end,  inclusive.   Positive and negative values for start
                     and end are interpreted as described above.
              -a     Append the ``new'' history lines  to  the  history  file.
                     These  are  history  lines entered since the beginning of
                     the current bash session, but not already appended to the
                     history file.
              -n     Read  the history lines not already read from the history
                     file into the current history list.  These are lines  ap-
                     pended  to  the  history  file since the beginning of the
                     current bash session.
              -r     Read the contents of the history file and append them  to
                     the current history list.
              -w     Write the current history list to the history file, over-
                     writing 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 following history entry.  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.
              -n     Display  information  only  about  jobs that have changed
                     status since the user was last notified of their status.
              -p     List only the process  ID  of  the  job's  process  group
                     leader.
              -r     Display only running jobs.
              -s     Display only stopped jobs.

              If  jobspec  is given, output is restricted to information about
              that job.  The 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 ex-
              ecutes command passing it args, returning its exit status.

       kill [-s sigspec | -n signum | -sigspec] [pid | jobspec] ...
       kill -l|-L [sigspec | exit_status]
              Send  the  signal  named  by  sigspec or signum to the processes
              named by pid or 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.  The  -L  option  is
              equivalent  to -l.  kill returns true if at least one signal was
              successfully sent, or false if an error occurs or an invalid op-
              tion 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.  If name is -, the set of shell options
              is made local to the function in which local is  invoked:  shell
              options  changed  using  the set builtin inside the function are
              restored to their original values  when  the  function  returns.
              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  [-d  delim] [-n count] [-O origin] [-s count] [-t] [-u fd] [-C
       callback] [-c quantum] [array]
       readarray [-d delim] [-n count] [-O origin] [-s count] [-t] [-u fd] [-C
       callback] [-c quantum] [array]
              Read  lines from the standard input into the indexed array 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:
              -d     The first character of delim is used  to  terminate  each
                     input  line,  rather than newline.  If delim is the empty
                     string, mapfile will terminate a line when it reads a NUL
                     character.
              -n     Copy  at  most count lines.  If count is 0, all lines are
                     copied.
              -O     Begin assigning to array at index  origin.   The  default
                     index is 0.
              -s     Discard the first count lines read.
              -t     Remove  a trailing delim (default newline) from each line
                     read.
              -u     Read lines from file descriptor fd instead of  the  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 and the line to be assigned to that
              element as additional arguments.  callback  is  evaluated  after
              the line is read but before the array element is assigned.

              If  not supplied with an explicit origin, mapfile will clear ar-
              ray 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 [-n] [+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 ma-
                     nipulated.
              +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 -v option causes the output to be
              assigned to the variable var rather than being  printed  to  the
              standard output.

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

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

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

              The  format  is  reused as necessary to consume all of the 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, pushd exchanges the top two di-
              rectories and returns 0, unless the directory  stack  is  empty.
              Arguments, if supplied, have the following meanings:
              -n     Suppresses  the  normal change of directory when rotating
                     or adding 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 as if it had been  supplied
                     as the argument to the cd builtin.

              If the pushd command is successful, a dirs is performed as well.
              If the first form is used, pushd returns 0 unless the cd to  dir
              fails.   With the second form, pushd returns 0 unless the 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 in-
              valid 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 de-
              scriptor fd supplied as an argument to the -u option, split into
              words  as  described  above  under Word Splitting, and the first
              word is assigned to the first name, the second word to the  sec-
              ond  name,  and  so on.  If there are more words than names, the
              remaining words and their intervening delimiters are assigned to
              the  last  name.   If  there are fewer words read from the input
              stream than names, the remaining names are assigned  empty  val-
              ues.   The  characters  in  IFS  are used to split the line into
              words using the same rules the shell  uses  for  expansion  (de-
              scribed  above  under  Word Splitting).  The backslash character
              (\) may be used to remove any special meaning for the next char-
              acter  read  and  for  line continuation.  Options, if supplied,
              have the following meanings:
              -a aname
                     The words are assigned to sequential indices of the array
                     variable aname, starting at 0.  aname is unset before any
                     new values are assigned.  Other name  arguments  are  ig-
                     nored.
              -d delim
                     The first character of delim is used to terminate the in-
                     put line, rather than newline.  If  delim  is  the  empty
                     string,  read  will  terminate a line when it reads a NUL
                     character.
              -e     If the standard input is coming from a terminal, readline
                     (see  READLINE  above) is used to obtain the line.  Read-
                     line uses the current (or default, if  line  editing  was
                     not  previously  active) editing settings, but uses Read-
                     line's default filename completion.
              -i text
                     If readline is being used  to  read  the  line,  text  is
                     placed into the editing buffer before editing begins.
              -n nchars
                     read  returns after reading nchars characters rather than
                     waiting for a complete line of input, but honors 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.   The result is not split on the characters in
                     IFS; the intent is that the variable is assigned  exactly
                     the characters read (with the exception of backslash; see
                     the -r option below).
              -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 then 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  (or a specified number of characters) is
                     not read within timeout seconds.  timeout may be a  deci-
                     mal  number with a fractional portion following the deci-
                     mal point.  This option is  only  effective  if  read  is
                     reading  input  from  a  terminal, pipe, or other special
                     file; it has no effect when reading from  regular  files.
                     If read times out, read saves any partial input read into
                     the specified variable name.  If timeout is 0,  read  re-
                     turns  immediately, without trying to read any data.  The
                     exit status is 0 if input is available on  the  specified
                     file  descriptor, non-zero otherwise.  The exit status is
                     greater than 128 if the timeout is exceeded.
              -u fd  Read input from file descriptor fd.

              If no names are supplied, the line read is assigned to the vari-
              able  REPLY.  The exit status is zero, unless end-of-file is en-
              countered, read times out (in which case the status  is  greater
              than  128),  a variable assignment error (such as assigning to a
              readonly variable) occurs, or an invalid file descriptor is sup-
              plied as the argument to -u.

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

       return [n]
              Causes  a function to stop executing and return the value speci-
              fied by n to its caller.  If n is omitted, the return status  is
              that  of the last command executed in the function body.  If re-
              turn is executed by a trap handler, the last command used to de-
              termine  the status is the last command executed before the trap
              handler.  If return is executed during a DEBUG  trap,  the  last
              command  used  to  determine the status is the last command exe-
              cuted by the trap handler before return was invoked.  If  return
              is  used outside a function, but during execution of a script by
              the .  (source) command, it causes the shell to  stop  executing
              that  script  and return either n or the exit status of the last
              command executed within the script as the  exit  status  of  the
              script.  If n is supplied, the return value is its least signif-
              icant 8 bits.  The return status is non-zero if return  is  sup-
              plied  a non-numeric argument, or is used outside a function and
              not during execution of a script by . or  source.   Any  command
              associated with the RETURN trap is executed before execution re-
              sumes after the function or script.

       set [--abefhkmnptuvxBCEHPT] [-o option-name] [arg ...]
       set [+abefhkmnptuvxBCEHPT] [+o option-name] [arg ...]
              Without options, the name and value of each shell  variable  are
              displayed in a 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  op-
              tions  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
              $1, $2, ...  $n.  Options,  if  specified,  have  the  following
              meanings:
              -a      Each variable or function that is created or modified is
                      given the export attribute and marked for export to  the
                      environment of subsequent commands.
              -b      Report  the status of terminated background jobs 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 list, or  a  compound  command
                      (see SHELL GRAMMAR above), exits with a non-zero status.
                      The shell does not exit if the  command  that  fails  is
                      part  of  the command list immediately following a while
                      or until keyword, part of the test following the  if  or
                      elif  reserved  words, part of any 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 !.   If  a
                      compound  command  other  than a subshell returns a non-
                      zero status because a command failed while -e was  being
                      ignored,  the  shell  does  not exit.  A trap on ERR, if
                      set, is executed 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.

                      If a compound command or shell function  executes  in  a
                      context  where -e is being ignored, none of the commands
                      executed within the compound command  or  function  body
                      will  be  affected  by the -e setting, even if -e is set
                      and a command returns a failure status.  If  a  compound
                      command  or  shell function sets -e while executing in a
                      context where -e is ignored, that setting will not  have
                      any  effect  until  the  compound command or the command
                      containing the function call completes.
              -f      Disable pathname expansion.
              -h      Remember the location of commands as they are looked  up
                      for execution.  This is enabled by default.
              -k      All  arguments  in the form of assignment statements are
                      placed in the 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).  All processes run
                      in a separate process group.  When a background job com-
                      pletes, the shell prints a line containing its exit sta-
                      tus.
              -n      Read commands but do not execute them.  This may be used
                      to  check a shell script for syntax errors.  This is ig-
                      nored 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  ``IG-
                              NOREEOF=10''  had been executed (see Shell Vari-
                              ables 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).  See  SEE  ALSO
                              below for a reference to a document that details
                              how posix mode affects bash's behavior.
                      privileged
                              Same as -p.
                      verbose Same as -v.
                      vi      Use a vi-style command line  editing  interface.
                              This also affects the editing interface used for
                              read -e.
                      xtrace  Same as -x.
                      If -o is supplied with no option-name, the values of the
                      current  options are printed.  If +o is supplied with no
                      option-name, a series of set 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 ap-
                      pear 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 resolve symbolic links when
                      executing commands such as cd that  change  the  current
                      working  directory.   It  uses  the  physical  directory
                      structure instead.  By default, bash follows the logical
                      chain  of  directories  when  performing  commands which
                      change the current directory.
              -T      If set, any traps on DEBUG and RETURN are  inherited  by
                      shell functions, command substitutions, and commands ex-
                      ecuted 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  op-
              tions can also be specified as arguments to an invocation of the
              shell.  The current set of options may be found in $-.  The  re-
              turn  status  is always true unless an invalid option is encoun-
              tered.

       shift [n]
              The positional parameters from n+1 ... are renamed  to  $1  ....
              Parameters  represented by the numbers $# down to $#-n+1 are un-
              set.  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 param-
              eters  are  not changed.  The return status is greater than zero
              if n is greater than $# or less than zero; otherwise 0.

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

              The list of shopt options is:

              assoc_expand_once
                      If  set, the shell suppresses multiple evaluation of as-
                      sociative array subscripts during arithmetic  expression
                      evaluation,  while  executing  builtins that can perform
                      variable assignments, and while executing builtins  that
                      perform array dereferencing.
              autocd  If  set,  a command name that is the name of a directory
                      is executed as if it were the argument to  the  cd  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 filename 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 ex-
                      iting if any jobs are stopped.
              checkwinsize
                      If  set, bash checks the window size after each external
                      (non-builtin) command and,  if  necessary,  updates  the
                      values  of LINES and COLUMNS.  This option is enabled by
                      default.
              cmdhist If set, bash attempts to save all lines of  a  multiple-
                      line  command  in  the  same history entry.  This allows
                      easy re-editing of multi-line commands.  This option  is
                      enabled  by  default,  but only has an effect if command
                      history is enabled, as described above under HISTORY.
              compat31
              compat32
              compat40
              compat41
              compat42
              compat43
              compat44
                      These control aspects of the shell's compatibility  mode
                      (see SHELL COMPATIBILITY MODE below).

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

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

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

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

              execfail
                      If set, a non-interactive shell will not exit if it 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 at shell invocation, or in a shell startup file,
                      arrange to execute the debugger profile before the shell
                      starts,  identical to the --debugger option.  If set af-
                      ter invocation, behavior intended for use  by  debuggers
                      is enabled:

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

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

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

                      4.     BASH_ARGC  and BASH_ARGV are updated as described
                             in their descriptions above.

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

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

              extglob If set, the extended pattern matching features described
                      above under 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 de-
                      scription of FIGNORE.  This option  is  enabled  by  de-
                      fault.

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

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

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

              histappend
                      If  set,  the history list is appended to the file named
                      by the value of the HISTFILE variable when the shell ex-
                      its, 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.

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

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

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

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

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

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

              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  at-
                      tempt  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, when performing pattern substi-
                      tution  word expansions, or when filtering possible com-
                      pletions as part of programmable completion.

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

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

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

              promptvars
                      If set, prompt strings undergo parameter expansion, com-
                      mand  substitution,  arithmetic expansion, and quote re-
                      moval 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 re-
                      stricted 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 se-
                      quences 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 (true) or 1 (false) depending on the evalu-
              ation of the conditional expression expr.  Each operator and op-
              erand must be a separate argument.  Expressions are composed  of
              the  primaries  described  in  the bash manual page under CONDI-
              TIONAL 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 de-
              pends on the number of arguments; see  below.   Operator  prece-
              dence is used when there are five or more arguments.
              ! expr True if expr is false.
              ( expr )
                     Returns  the value of expr.  This may be used to override
                     the normal precedence of operators.
              expr1 -a expr2
                     True if both expr1 and expr2 are true.
              expr1 -o expr2
                     True if either expr1 or expr2 is true.

              test and [ evaluate conditional expressions using a set of rules
              based on the 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
                     The following conditions are applied in the order listed.
                     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.

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

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

       trap [-lp] [[arg] sigspec ...]
              The command arg is to be read and executed when  the  shell  re-
              ceives signal(s) sigspec.  If arg is absent (and there is a sin-
              gle sigspec) or -, each specified signal is reset to its  origi-
              nal  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  com-
              mands  associated  with  each  signal.  The -l option causes the
              shell to print a list of signal names  and  their  corresponding
              numbers.   Each sigspec is either a signal name defined in <sig-
              nal.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
              pipeline (which may consist of a single simple command), a list,
              or a compound command returns a non-zero exit status, subject to
              the  following  conditions.  The ERR trap is not 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 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  using
              !.  These are the same conditions obeyed by the errexit (-e) op-
              tion.

              Signals ignored upon entry to the shell cannot be trapped or re-
              set.   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 re-
              turned.  If the -p option is used, type either returns the  name
              of  the  disk file that would be executed if name were specified
              as a command name, or nothing if ``type -t name'' would not  re-
              turn  file.   The  -P option forces a PATH search for each name,
              even if ``type -t name'' would not return file.  If a command is
              hashed, -p and -P print the hashed value, which is not necessar-
              ily the file that appears first in PATH.  If the  -a  option  is
              used,  type  prints all of the places that contain an executable
              named name.  This includes aliases and functions, if and only if
              the -p option is not also used.  The table of hashed commands is
              not consulted when using -a.  The  -f  option  suppresses  shell
              function lookup, as with the command builtin.  type returns true
              if all of the arguments are found, false if any are not found.

       ulimit [-HSabcdefiklmnpqrstuvxPRT [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, re-
              spectively.  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
              -k     The maximum number of kqueues that may be allocated
              -l     The maximum size that may be locked into memory
              -m     The  maximum resident set size (many systems do not honor
                     this limit)
              -n     The maximum number of open file descriptors (most systems
                     do not allow this value to be set)
              -p     The pipe size in 512-byte blocks (this may not be set)
              -q     The maximum number of bytes in POSIX message queues
              -r     The maximum real-time scheduling priority
              -s     The maximum stack size
              -t     The maximum amount of cpu time in seconds
              -u     The  maximum  number  of  processes available to a single
                     user
              -v     The maximum amount of virtual  memory  available  to  the
                     shell and, on some systems, to its children
              -x     The maximum number of file locks
              -P     The maximum number of pseudoterminals
              -R     The  maximum  time  a  real-time  process  can run before
                     blocking, in microseconds
              -T     The maximum number of threads

              If limit is given, and the -a option is not used, limit  is  the
              new  value  of  the  specified resource.  If no option is given,
              then -f is assumed.  Values are in 1024-byte increments,  except
              for  -t,  which is in seconds; -R, which is in microseconds; -p,
              which is in units of 512-byte blocks; -P, -T, -b,  -k,  -n,  and
              -u,  which  are unscaled values; and, when in posix mode, -c and
              -f, which are in 512-byte increments.  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 [-a] [name ...]
              Remove  each  name  from  the list of defined aliases.  If -a is
              supplied, all alias definitions are removed.  The  return  value
              is true unless a supplied name is not a defined alias.

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

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

SHELL COMPATIBILITY MODE
       Bash-4.0 introduced the concept of a `shell compatibility level', spec-
       ified as a set of options to the shopt builtin compat31, compat32, com-
       pat40, compat41, and so on).  There is only one  current  compatibility
       level -- each option is mutually exclusive.  The compatibility level is
       intended to allow users to select behavior from previous versions  that
       is  incompatible  with newer versions while they migrate scripts to use
       current features and behavior. It's intended to be  a  temporary  solu-
       tion.

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

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

       Bash-4.3 introduced a new shell variable: BASH_COMPAT.  The  value  as-
       signed to this variable (a decimal version number like 4.2, or an inte-
       ger corresponding to the compatNN option, like 42) determines the  com-
       patibility level.

       Starting  with bash-4.4, Bash has begun deprecating older compatibility
       levels.  Eventually, the options will be removed in favor of  BASH_COM-
       PAT.

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

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

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

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

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

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

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

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

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

       compat50
              o      Bash-5.1  changed  the way $RANDOM is generated to intro-
                     duce slightly more randomness. If the shell compatibility
                     level  is  set  to  50 or lower, it reverts to the method
                     from bash-5.0 and previous versions, so seeding the  ran-
                     dom  number generator by assigning a value to RANDOM will
                     produce the same sequence as in bash-5.0

SEE ALSO
       bash(1), sh(1)



GNU Bash 5.0                      2004 Apr 20                 BASH_BUILTINS(1)
