BASH_BUILTINS(1)            General Commands Manual           BASH_BUILTINS(1)



NAME
       :, ., [, alias, bg, bind, break, builtin, caller, cd, command, compgen,
       complete, compopt, continue, declare, dirs, disown, echo, enable, eval,
       exec,  exit, export, false, fc, fg, getopts, hash, help, history, jobs,
       kill, let, local, logout, mapfile,  popd,  printf,  pushd,  pwd,  read,
       readarray,  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, but filename does not need to be executable.  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 argu-
              ments are supplied, they become the positional  parameters  when
              filename  is  executed.  Otherwise the positional parameters are
              unchanged.  If the -T option is enabled, .. inherits any trap  on
              DEBUG; if it is not, any DEBUG trap string is saved and restored
              around the call to .., and .. unsets the DEBUG trap while it  exe-
              cutes.  If -T is not set, and the sourced file changes the DEBUG
              trap, the new value is retained when ..  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
       bind readline-command-line
              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  a  readline  initialization file such as .inputrc, but
              each binding or command must be passed as a  separate  argument;
              e.g.,  '"\C-x\C-r":  re-read-init-file'.   Options, if supplied,
              have the following meanings:
              -m keymap
                     Use keymap as the keymap to be affected by the subsequent
                     bindings.  Acceptable keymap names are emacs, emacs-stan-
                     dard, emacs-meta, emacs-ctlx,  vi,  vi-move,  vi-command,
                     and  vi-insert.   vi is equivalent to vi-command (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.
                     The shell assigns any numeric argument the user  supplied
                     to the READLINE_ARGUMENT variable.  If there was no argu-
                     ment, that variable is not set.  If the executed  command
                     changes   the   value  of  any  of  READLINE_LINE,  READ-
                     LINE_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.  The  vari-
              able CDPATH defines the search path for the directory containing
              dir: each directory name in CDPATH is searched for dir.   Alter-
              native  directory  names in CDPATH are separated by a colon (:).
              A null directory name in CDPATH is the same as the  current  di-
              rectory,  i.e., ``..''.  If dir begins with a slash (/), then CD-
              PATH 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 sym-
              bolic links to be followed by resolving the link after  process-
              ing  instances  of  .. in dir.  If .. appears in dir, it is pro-
              cessed 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  successfully determined after a successful directory
              change, cd will return an unsuccessful status.  On systems  that
              support it, the --@@ option presents the extended attributes asso-
              ciated with a file as a directory.  An argument  of  --  is  con-
              verted  to $OLDPWD before the directory change is attempted.  If
              a non-empty directory name from CDPATH is used, or if --  is  the
              first  argument, and the directory change is successful, the ab-
              solute pathname of the new working directory is written  to  the
              standard output.  If the directory change is successful, cd sets
              the value of the PWD environment variable to the  new  directory
              name,  and  sets the OLDPWD environment variable to the value of
              the current working directory before  the  change.   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 in bash(1).

              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.  Arguments
                      are passed as with the -F option.
              -F function
                      The shell function function is executed in  the  current
                      shell  environment.   When the function is executed, the
                      first argument ($$11) is the name of the command whose ar-
                      guments are being completed, the second argument ($$22) is
                      the word being completed, and the third argument ($$33) 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] [++oo 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 in
                     bash(1)).
              -A     Each name is an associative array variable (see Arrays in
                     bash(1)).
              -f     Use function names only.
              -i     The variable is treated as an integer; arithmetic evalua-
                     tion (see ARITHMETIC EVALUATION in bash(1)) 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 in bash(1)), one of the names is not
              a  valid  shell  variable  name,  an attempt is made to turn off
              readonly 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
              \\00nnn  the  eight-bit  character  whose value is the octal value
                     nnn (zero to three octal digits)
              \\xx_H_H   the eight-bit character whose value  is  the  hexadecimal
                     value HH (one or two hex digits)
              \\uuHHHH the  Unicode (ISO/IEC 10646) character whose value is the
                     hexadecimal value HHHH (one to four hex digits)
              \\UUHHHHHHHH
                     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.
              Bash will use the value of the BASH_LOADABLES_PATH variable as a
              colon-separated list of directories in which to search for file-
              name.  The default is  system-dependent.   The  -d  option  will
              delete  a  builtin  previously loaded with -f.  If no name argu-
              ments are given, or if the -p option  is  supplied,  a  list  of
              shell  builtins is printed.  With no other option arguments, the
              list consists of all enabled shell builtins.  If -n is supplied,
              only disabled builtins are printed.  If -a is supplied, the list
              printed includes all builtins, with an indication of whether  or
              not  each  is  enabled.   If  -s  is supplied, the output is re-
              stricted to the POSIX special builtins.  If no options are  sup-
              plied  and a name is not a shell builtin, enable will attempt to
              load name from a shared object named name,  as  if  the  command
              were  ``enable  -f  name  name .  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 c' runs the  last  command  beginning  with
              `c' 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  range  of  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 or range
              is supplied as an argument to -d, or the history expansion  sup-
              plied 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  in bash(1)).  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.
              The restore is effected as if a series of set commands were exe-
              cuted  to restore the values that were in place before the func-
              tion.  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 [-nn] [+_n] [-_n]
              Removes entries from the directory stack.  The elements are num-
              bered from 0 starting at the first  directory  listed  by  dirs.
              With  no  arguments,  popd  removes  the  top directory from the
              stack, and changes to the new top directory.  Arguments, if sup-
              plied, have the following 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, from the  stack.   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  top element of the directory stack is modified, and the
              -n option was not supplied, popd uses the cd builtin  to  change
              to the directory at the top of the stack.  If the cd fails, popd
              returns a non-zero value.

              Otherwise, popd returns false if an invalid  option  is  encoun-
              tered, the directory stack is empty, or a non-existent directory
              stack entry is specified.

              If the popd command is successful, bash runs dirs  to  show  the
              final  contents of the directory stack, and the return status is
              0.

       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.
              %Q     like  %%qq, but applies any supplied precision to the argu-
                     ment before quoting it.
              %%((datefmt))TT
                     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  ele-
              ments  of the directory stack.  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

              After the stack has been modified, if the -n option was not sup-
              plied,  pushd  uses the cd builtin to change to the directory at
              the top of the stack.  If the cd fails, pushd returns a non-zero
              value.

              Otherwise,  if no arguments are supplied, pushd returns 0 unless
              the directory stack  is  empty.   When  rotating  the  directory
              stack,  pushd returns 0 unless the directory stack is empty or a
              non-existent directory stack element is specified.

              If the pushd command is successful, bash runs dirs to  show  the
              final contents of the directory stack.

       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 in bash(1)  under  Word  Splitting,  and  the
              first word is assigned to the first name, the second word to the
              second name, and so on.  If there are more words than names, the
              remaining words and their intervening delimiters are assigned to
              the last name.  If there are fewer words  read  from  the  input
              stream  than  names, the remaining names are assigned empty 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 in bash(1) under Word Splitting).  The backslash charac-
              ter  (\\)  may be used to remove any special meaning for the next
              character read and for line continuation.  Options, if supplied,
              have the following meanings:
              -a aname
                     The words are assigned to sequential indices of the array
                     variable aname, starting at 0.  aname is unset before any
                     new  values  are  assigned.  Other name arguments are 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 in bash(1)) is used  to  obtain  the  line.
                     Readline  uses  the  current (or default, if line editing
                     was not previously active)  editing  settings,  but  uses
                     Readline'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, or the read will  return  EOF,  non-zero
                     otherwise.   The  exit  status is greater than 128 if the
                     timeout is exceeded.
              -u fd  Read input from file descriptor fd.

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

       readonly [-aAf] [-p] [name[=word] ...]
              The given names are marked readonly; the values of  these  names
              may  not  be changed by subsequent assignment.  If the -f option
              is supplied, the functions 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] [++oo option-name] [----] [--] [arg ...]
              Without  options, display the name and value of each shell vari-
              able in a format that can be reused as input for setting or  re-
              setting the currently-set variables.  Read-only variables cannot
              be reset.  In posix mode, only shell variables are listed.   The
              output  is sorted according to the current locale.  When options
              are specified, they set or unset shell  attributes.   Any  argu-
              ments  remaining  after  option processing are treated as values
              for the positional parameters and are assigned, in order, to $$11,
              $$22,  ......   $$_n.   Options, if specified, have the following mean-
              ings:
              -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 in bash(1)), 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 fi-
                      nal &&&& 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 in
                      bash(1)), and may cause subshells to exit before execut-
                      ing 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 in bash(1)).  All  processes
                      run  in a separate process group.  When a background job
                      completes, the shell prints a line containing  its  exit
                      status.
              -n      Read commands but do not execute them.  This may be used
                      to check a shell script for syntax errors.  This is  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 in bash(1)
                              under HISTORY.  This option is on by default  in
                              interactive shells.
                      ignoreeof
                              The  effect  is  as  if  the shell command ``IG-
                              NOREEOF=10'' had been executed (see Shell  Vari-
                              ables in bash(1)).
                      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
                              in bash(1) 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.
              -r      Enable restricted shell mode.  This option cannot be un-
                      set once it has been set.
              -t      Exit after reading and executing one command.
              -u      Treat unset variables and parameters other than the spe-
                      cial parameters "@" and "*",  or  array  variables  sub-
                      scripted  with  "@"  or "*", 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
                      in bash(1)).  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 $$11 ........
              Parameters represented by the numbers $$## 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  in bash(1)).  The shell always post-
                      pones exiting 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 in bash(1) under HIS-
                      TORY.
              compat31
              compat32
              compat40
              compat41
              compat42
              compat43
              compat44
              compat50
                      These control aspects of the shell's compatibility  mode
                      (see SHELL COMPATIBILITY MODE in bash(1)).

              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 in bash(1) un-
                      der ALIASES.  This option is enabled by default for  in-
                      teractive 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:

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

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

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

                      44..     BASH_ARGC  and BASH_ARGV are updated as described
                             in their descriptions in bash(1)).

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

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

              extglob If set, the extended pattern matching features described
                      in bash(1) 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 in bash(1) for a
                      description of FIGNORE.  This option is enabled  by  de-
                      fault.

              globasciiranges
                      If  set,  range  expressions  used  in  pattern matching
                      bracket expressions (see Pattern  Matching  in  bash(1))
                      behave as if in the traditional C locale when performing
                      comparisons.  That is, the  current  locale's  collating
                      sequence  is  not taken into account, so bb will not col-
                      late between AA and  BB,  and  upper-case  and  lower-case
                      ASCII characters will collate together.

              globskipdots
                      If  set,  pathname  expansion will never match the file-
                      names ````..''''  and ````....'''', even if the pattern begins with
                      a ````..''''.  This option is enabled by default.

              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  in
                      bash(1)).  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 in bash(1)).  This
                      option is enabled by default.

              lastpipe
                      If set, and job control is not active,  the  shell  runs
                      the last command of a pipeline not executed in the 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 in bash(1)).  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 in bash(1)).

              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.

              noexpand_translation
                      If set, bash encloses the translated results  of  $"..."
                      quoting  in  single quotes instead of double quotes.  If
                      the string is not translated, this has no effect.

              nullglob
                      If set, bash allows patterns which match no  files  (see
                      Pathname  Expansion  in  bash(1))  to  expand  to a null
                      string, rather than themselves.

              patsub_replacement
                      If set, bash expands occurrences of && in the replacement
                      string  of  pattern  substitution to the text matched by
                      the pattern, as described under Parameter  Expansion  in
                      bash(1).  This option is enabled by default.

              progcomp
                      If set, the programmable completion facilities (see Pro-
                      grammable Completion in bash(1)) are enabled.  This  op-
                      tion 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 in
                      bash(1).  This option is enabled by default.

              restricted_shell
                      The shell sets this option  if  it  is  started  in  re-
                      stricted  mode  (see  RESTRICTED SHELL in bash(1)).  The
                      value may not be changed.  This is not  reset  when  the
                      startup  files  are executed, allowing the startup files
                      to discover whether or not a shell is restricted.

              shift_verbose
                      If set, the shift builtin prints an error  message  when
                      the shift count 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.

              varredir_close
                      If set, the shell automatically closes file  descriptors
                      assigned using the {varname} redirection syntax (see RE-
                      DIRECTION in bash(1)) instead of leaving them open  when
                      the command completes.

              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, or a shell without job control enabled,
              cannot be suspended; the -f option can be used to override  this
              and  force  the  suspension.   The return status is 0 unless the
              shell is a login shell or job control is not enabled and  -f  is
              not supplied.

       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  bash(1)  under  CONDITIONAL  EXPRES-
              SIONS.  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 -aa expr2
                     True if both expr1 and expr2 are true.
              expr1 -oo expr2
                     True if either expr1 or expr2 is true.

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

              0 arguments
                     The expression is false.
              1 argument
                     The expression is true if and only if the argument is not
                     null.
              2 arguments
                     If the first argument is !!, the expression is true if and
                     only  if the second argument is null.  If the first argu-
                     ment is one of the unary conditional operators listed  in
                     bash(1)  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 in  bash(1)  under  CONDITIONAL  EXPRES-
                     SIONS,  the result of the expression is the result of the
                     binary test using the first and third arguments as  oper-
                     ands.   The -a and -o operators are considered binary op-
                     erators when there are three arguments.  If the first ar-
                     gument  is  !!, the value is the negation of the two-argu-
                     ment test using the second and third arguments.   If  the
                     first argument is exactly (( and the third argument is ex-
                     actly )), the result is the one-argument test of the  sec-
                     ond argument.  Otherwise, the expression is false.
              4 arguments
                     The following conditions are applied in the order listed.
                     If the first argument is !!, the result is the negation of
                     the  three-argument  expression composed of the remaining
                     arguments.  the two-argument test using  the  second  and
                     third  arguments.  If the first argument is exactly (( and
                     the fourth argument is exactly )), the result is the  two-
                     argument  test of the second and third arguments.  Other-
                     wise, the expression is parsed and evaluated according to
                     precedence using the rules listed above.
              5 or more arguments
                     The  expression  is  parsed  and  evaluated  according to
                     precedence using the rules listed above.

              When used with test or [[, the << and  >>  operators  sort  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 in
              bash(1)).  Refer to the description of the  extdebug  option  to
              the  shopt  builtin for details of its effect on the DEBUG trap.
              If a sigspec is RETURN, the command arg is executed each time  a
              shell  function  or  a  script  executed  with  the  .. or source
              builtins finishes 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 [-HS] -a
       ulimit [-HS] [-bcdefiklmnpqrstuvxPRT [limit]]
              Provides control over the resources available to the  shell  and
              to  processes started by it, on systems that allow such control.
              The -H and -S options specify that the hard or soft limit is set
              for  the  given resource.  A hard limit cannot be increased by a
              non-root user once it is set; a soft limit may be  increased  up
              to  the value of the hard limit.  If neither -H nor -S is 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,  if  appropriate, are printed before the value.  Other op-
              tions are interpreted as follows:
              -a     All current limits are reported; no limits are set
              -b     The maximum socket buffer size
              -c     The maximum size of core files created
              -d     The maximum size of a process's data segment
              -e     The maximum scheduling priority ("nice")
              -f     The maximum size of files written by the  shell  and  its
                     children
              -i     The maximum number of pending signals
              -k     The maximum number of kqueues that may be allocated
              -l     The maximum size that may be locked into memory
              -m     The  maximum resident set size (many systems do not honor
                     this limit)
              -n     The maximum number of open file descriptors (most systems
                     do not allow this value to be set)
              -p     The pipe size in 512-byte blocks (this may not be set)
              -q     The maximum number of bytes in POSIX message queues
              -r     The maximum real-time scheduling priority
              -s     The maximum stack size
              -t     The maximum amount of cpu time in seconds
              -u     The  maximum  number  of  processes available to a single
                     user
              -v     The maximum amount of virtual  memory  available  to  the
                     shell and, on some systems, to its children
              -x     The maximum number of file locks
              -P     The maximum number of pseudoterminals
              -R     The  maximum  time  a  real-time  process  can run before
                     blocking, in 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 [-aa] [name ...]
              Remove  each  name  from  the list of defined aliases.  If -a is
              supplied, all alias definitions are removed.  The  return  value
              is true unless a supplied name is not a defined alias.

       unset [-fv] [-nn] [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 or may not be unset.

       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 _i_ds or, if no _i_ds 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.  If wait is interrupted by a signal,
              the return status will be greater than 128, as  described  under
              SIGNALS  in  bash(1).   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,  speci-
       fied  as  a  set  of options to the shopt builtin ( compat31, compat32,
       compat40, compat41, and so on).  There is only one current  compatibil-
       ity  level  --  each  option  is mutually exclusive.  The compatibility
       level is intended to allow users to select behavior from previous  ver-
       sions  that  is  incompatible  with  newer  versions while they migrate
       scripts to use current features and behavior. It's  intended  to  be  a
       temporary solution.

       This  section does not mention behavior that is standard for a 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 subsequent versions).

       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 compat_N_N 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 compat_N_N 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 compat_N_N 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
              +o      If the command hash table is empty, bash  versions  prior
                     to  bash-5.1 printed an informational message to that ef-
                     fect, even when producing output that can  be  reused  as
                     input.  Bash-5.1  suppresses that message when the -l op-
                     tion is supplied.

       compat51
              +o      The unset builtin treats attempts  to  unset  array  sub-
                     scripts  @@ and ** differently depending on whether the ar-
                     ray is indexed or associative, and  differently  than  in
                     previous versions.

SEE ALSO
       bash(1), sh(1)



GNU Bash 5.2                   2021 November 22               BASH_BUILTINS(1)
