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BASH_BUILTINS(1)                     General Commands Manual                     BASH_BUILTINS(1)



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

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

        .  filename [arguments]
       source filename [arguments]
              Read and execute commands from filename in the current shell environment and return
              the exit status of the last command executed from filename.  If filename  does  not
              contain a slash, file names in PATH are used to find the directory containing file-
              name.  The file searched for in PATH need not be executable.  When bash is  not  in
              posix  mode, the current directory is searched if no file is found in PATH.  If the
              sourcepath option to the shopt builtin command is  turned  off,  the  PATH  is  not
              searched.   If  any  arguments  are supplied, they become the positional parameters
              when filename is executed.  Otherwise the positional parameters are unchanged.  The
              return  status  is the status of the last command exited within the script (0 if no
              commands are executed), and false if filename is not found or cannot be read.

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

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

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

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

       break [n]
              Exit  from  within a for, while, until, or select loop.  If n is specified, break n
              levels.  n must be >= 1.  If n is greater than the number of enclosing  loops,  all
              enclosing  loops  are  exited.  The return value is non-zero when n is <= 0; Other-
              wise, break returns 0 value.

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

       caller [expr]
              Returns the context of any active subroutine call (a shell  function  or  a  script
              executed  with  the  . or source builtins).  Without expr, caller displays the line
              number and source filename of the current subroutine call.  If a non-negative inte-
              ger  is  supplied  as  expr,  caller displays the line number, subroutine name, and
              source file corresponding to that position in the  current  execution  call  stack.
              This  extra information may be used, for example, to print a stack trace.  The cur-
              rent frame is frame 0.  The return value is 0 unless the shell is not  executing  a
              subroutine 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.  The variable HOME is the default dir.  The
              variable CDPATH defines the search path for the directory containing dir.  Alterna-
              tive directory names in CDPATH are separated by a colon (:).  A null directory name
              in CDPATH is the same as the current directory, i.e., ``.''.  If dir begins with  a
              slash  (/),  then CDPATH is not used. The -P option says to use the physical direc-
              tory structure instead of following symbolic links (see also the -P option  to  the
              set  builtin  command); the -L option forces symbolic links to be followed.  If the
              -e option is supplied with -P, and the current working directory cannot be success-
              fully  determined after a successful directory change, cd will return an unsuccess-
              ful status.  An argument of - is equivalent to $OLDPWD.  If a  non-empty  directory
              name  from  CDPATH is used, or if - is the first argument, and the directory change
              is successful, the absolute pathname of the new working directory is written to the
              standard  output.   The  return  value  is  true  if the directory was successfully
              changed; false otherwise.

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

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

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

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

       complete [-abcdefgjksuv] [-o comp-option] [-DE] [-A action] [-G globpat] [-W wordlist] [-F
       function] [-C command]
              [-X filterpat] [-P prefix] [-S suffix] name [name ...]
       complete -pr [-DE] [name ...]
              Specify how arguments to each name should be completed.  If the -p option  is  sup-
              plied,  or  if  no  options  are  supplied,  existing completion specifications are
              printed in a way that allows them to be reused as input.  The -r option  removes  a
              completion  specification  for each name, or, if no names are supplied, all comple-
              tion specifications.  The -D  option  indicates  that  the  remaining  options  and
              actions  should  apply  to  the ``default'' command completion; that is, completion
              attempted on a command for which no completion has previously been defined.  The -E
              option  indicates  that the remaining options and actions should apply to ``empty''
              command completion; that is, completion attempted on a blank line.

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

              Other options, if specified, have the following meanings.  The arguments to the -G,
              -W, and -X options (and, if necessary, the -P and -S options) should be  quoted  to
              protect them from expansion before the complete builtin is invoked.
              -o comp-option
                      The  comp-option controls several aspects of the compspec's behavior beyond
                      the simple generation of completions.  comp-option may be one of:
                      bashdefault
                              Perform the rest of the default bash completions  if  the  compspec
                              generates no matches.
                      default Use  readline's  default filename completion if the compspec gener-
                              ates no matches.
                      dirnames
                              Perform directory name completion  if  the  compspec  generates  no
                              matches.
                      filenames
                              Tell readline that the compspec generates filenames, so it can per-
                              form any filename-specific  processing  (like  adding  a  slash  to
                              directory  names, quoting special characters, or suppressing trail-
                              ing spaces).  Intended to be used with shell functions.
                      nospace Tell readline not to append a space (the  default)  to  words  com-
                              pleted at the end of the line.
                      plusdirs
                              After  any matches defined by the compspec are generated, directory
                              name completion is attempted and  any  matches  are  added  to  the
                              results of the other actions.
              -A action
                      The  action may be one of the following to generate a list of possible com-
                      pletions:
                      alias   Alias names.  May also be specified as -a.
                      arrayvar
                              Array variable names.
                      binding Readline key binding names.
                      builtin Names of shell builtin commands.  May also be specified as -b.
                      command Command names.  May also be specified as -c.
                      directory
                              Directory names.  May also be specified as -d.
                      disabled
                              Names of disabled shell builtins.
                      enabled Names of enabled shell builtins.
                      export  Names of exported shell variables.  May also be specified as -e.
                      file    File names.  May also be specified as -f.
                      function
                              Names of shell functions.
                      group   Group names.  May also be specified as -g.
                      helptopic
                              Help topics as accepted by the help builtin.
                      hostname
                              Hostnames, as taken from the file specified by the  HOSTFILE  shell
                              variable.
                      job     Job names, if job control is active.  May also be specified as -j.
                      keyword Shell reserved words.  May also be specified as -k.
                      running Names of running jobs, if job control is active.
                      service Service names.  May also be specified as -s.
                      setopt  Valid arguments for the -o option to the set builtin.
                      shopt   Shell option names as accepted by the shopt builtin.
                      signal  Signal names.
                      stopped Names of stopped jobs, if job control is active.
                      user    User names.  May also be specified as -u.
                      variable
                              Names of all shell variables.  May also be specified as -v.
              -C command
                      command  is  executed  in a subshell environment, and its output is used as
                      the possible completions.
              -F function
                      The shell function function is executed in the current  shell  environment.
                      When  it finishes, the possible completions 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 completion after all
                      other options have been applied.
              -S suffix
                      suffix is appended to each possible completion after all other options have
                      been applied.
              -W wordlist
                      The  wordlist  is split using the characters in the IFS special variable as
                      delimiters, and each resultant word is expanded.  The possible  completions
                      are the members of the resultant list which match the word being completed.
              -X filterpat
                      filterpat  is  a  pattern as used for pathname expansion.  It is applied to
                      the list of possible completions generated by  the  preceding  options  and
                      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 argument, an attempt is made to remove  a  com-
              pletion  specification  for  a  name for which no specification exists, or an error
              occurs adding a completion specification.

       compopt [-o option] [-DE] [+o option] [name]
              Modify completion options for each name according to the options, or for  the  cur-
              rently-executing  completion  if  no  names are supplied.  If no options are given,
              display the completion options for each name or the current completion.  The possi-
              ble values of option are those valid for the complete builtin described above.  The
              -D option indicates that the remaining options 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  the  remaining  options
              should  apply  to  ``empty'' command completion; that is, completion attempted on a
              blank line.

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

       continue [n]
              Resume the next iteration of the enclosing for, while, until, or select loop.  If n
              is  specified,  resume at the nth enclosing loop.  n must be >= 1.  If n is greater
              than the number of enclosing loops, the  last  enclosing  loop  (the  ``top-level''
              loop)  is  resumed.   When continue is executed inside of loop, the return value is
              non-zero when n is <= 0; Otherwise, continue returns 0 value. When continue is exe-
              cuted outside of loop, the return value is 0.

       declare [-aAfFgilrtux] [-p] [name[=value] ...]
       typeset [-aAfFgilrtux] [-p] [name[=value] ...]
              Declare  variables and/or give them attributes.  If no names are given then display
              the values of variables.  The -p option will display the attributes and  values  of
              each  name.   When  -p is used with name arguments, additional options are ignored.
              When -p is supplied without name arguments, it will display the attributes and val-
              ues of all variables having the attributes specified by the additional options.  If
              no other options are supplied with -p, declare will display the attributes and val-
              ues of all shell variables.  The -f option will restrict the display to shell func-
              tions.  The -F option inhibits the display of function definitions; only the  func-
              tion  name  and  attributes  are  printed.  If the extdebug shell option is enabled
              using shopt, the source file name and line number where the function is defined are
              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
              function.   It is ignored in all other cases.  The following options can be used to
              restrict output to variables with the specified  attribute  or  to  give  variables
              attributes:
              -a     Each name is an indexed array variable (see Arrays above).
              -A     Each name is an associative array variable (see Arrays above).
              -f     Use function names only.
              -i     The variable is treated as an integer; arithmetic evaluation (see ARITHMETIC
                     EVALUATION above) is performed when the variable is assigned a value.
              -l     When the variable is assigned a value, all upper-case  characters  are  con-
                     verted to lower-case.  The upper-case attribute is disabled.
              -r     Make  names  readonly.  These names cannot then be assigned values by subse-
                     quent assignment statements or unset.
              -t     Give each name the trace attribute.  Traced functions inherit the DEBUG  and
                     RETURN  traps  from  the  calling shell.  The trace attribute has no special
                     meaning for variables.
              -u     When the variable is assigned a value, all lower-case  characters  are  con-
                     verted to upper-case.  The lower-case attribute is disabled.
              -x     Mark names for export to subsequent commands via the environment.

              Using  `+' instead of `-' turns off the attribute instead, with the exceptions that
              +a may not be used to destroy an array variable and +r will not remove the readonly
              attribute.   When used in a function, makes each name local, as with the local com-
              mand, unless the -g option is supplied, If a variable name is followed  by  =value,
              the value of the variable is set to value.  The return value is 0 unless an invalid
              option is encountered,  an  attempt  is  made  to  define  a  function  using  ``-f
              foo=bar'',  an attempt is made to assign a value to a readonly variable, an attempt
              is made to assign a value to an array variable without using the  compound  assign-
              ment  syntax  (see  Arrays  above),  one of the names is not a valid shell variable
              name, an attempt is made to turn off readonly status for a  readonly  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 [+n] [-n] [-clpv]
              Without options, displays  the  list  of  currently  remembered  directories.   The
              default  display  is  on  a  single  line with directory names separated by spaces.
              Directories are added to the list with the pushd command; the popd command  removes
              entries from the list.
              +n     Displays the nth entry counting from the left of the list shown by dirs when
                     invoked without options, starting with zero.
              -n     Displays the nth entry counting from the right of the  list  shown  by  dirs
                     when invoked without options, starting with zero.
              -c     Clears the directory stack by deleting all of the entries.
              -l     Produces a longer listing; the default listing format uses a tilde to denote
                     the home directory.
              -p     Print the directory stack with one entry per line.
              -v     Print the directory stack with one entry per line, prefixing each entry with
                     its index in the stack.

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

       disown [-ar] [-h] [jobspec ...]
              Without options, each jobspec is removed from the table of active jobs.  If jobspec
              is  not  present, and neither -a nor -r is supplied, the shell's notion of the cur-
              rent job is used.  If the -h option is given, each jobspec is not removed from  the
              table,  but is marked so that SIGHUP is not sent to the job if the shell receives a
              SIGHUP.  If no jobspec is present, and neither the -a nor the  -r  option  is  sup-
              plied,  the current job is used.  If no jobspec is supplied, the -a option means to
              remove or mark all jobs; the -r option without a jobspec argument restricts  opera-
              tion  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
              always  0.   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 interpretation of these escape characters,
              even on systems where they are interpreted by default.  The xpg_echo  shell  option
              may be used to dynamically determine whether or not echo expands these escape char-
              acters by default.  echo does not interpret -- to mean the end  of  options.   echo
              interprets the following escape sequences:
              \a     alert (bell)
              \b     backspace
              \c     suppress further output
              \e
              \E     an escape character
              \f     form feed
              \n     new line
              \r     carriage return
              \t     horizontal tab
              \v     vertical tab
              \\     backslash
              \0nnn  the  eight-bit  character  whose value is the octal value nnn (zero to three
                     octal digits)
              \xHH   the eight-bit character whose value is the hexadecimal value HH (one or  two
                     hex digits)
              \uHHHH the  Unicode  (ISO/IEC 10646) character whose value is the hexadecimal value
                     HHHH (one to four hex digits)
              \UHHHHHHHH
                     the Unicode (ISO/IEC 10646) character whose value is the  hexadecimal  value
                     HHHHHHHH (one to eight hex digits)

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

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

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

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

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

       fc [-e ename] [-lnr] [first] [last]
       fc -s [pat=rep] [cmd]
              Fix Command.  In the first form, a range of commands from first to last is selected
              from  the history list.  First and last may be specified as a string (to locate the
              last command beginning with that string) or as a number (an index into the  history
              list,  where  a  negative number is used as an offset from the current command num-
              ber).  If last is not specified it is set to the current command  for  listing  (so
              that  ``fc  -l -10'' prints the last 10 commands) and to first otherwise.  If first
              is not specified it is set to the previous command for editing and -16 for listing.

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

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

              If the first form is used, the return value  is  0  unless  an  invalid  option  is
              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-executed,  unless  cmd  does  not
              specify a valid history line, in which case fc returns failure.

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

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

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

              getopts  normally parses the positional parameters, but if more arguments are given
              in args, getopts parses those instead.

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

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

              If a required argument is not found, and getopts is not silent, a question mark (?)
              is  placed  in  name,  OPTARG  is  unset,  and a diagnostic message is printed.  If
              getopts is silent, then a colon (:) is placed in name and  OPTARG  is  set  to  the
              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 remembered.  Any previously-remembered path-
              name is discarded.  If the -p option is supplied, no path search is performed,  and
              filename  is  used  as the full file name of the command.  The -r option causes the
              shell to forget all remembered locations.  The -d option causes the shell to forget
              the remembered location of each name.  If the -t option is supplied, the full path-
              name to which each name corresponds is printed.  If  multiple  name  arguments  are
              supplied  with  -t,  the  name  is printed before the hashed full pathname.  The -l
              option causes output to be displayed in a format that may be reused as  input.   If
              no  arguments  are  given,  or if only -l is supplied, information about remembered
              commands is printed.  The return status is true unless a name is not  found  or  an
              invalid option is supplied.

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

              The return status is 0 unless no command matches pattern.

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

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

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

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

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

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

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

       local [option] [name[=value] ...]
              For each argument, a local variable named name is created, and assigned value.  The
              option  can be any of the options accepted by declare.  When local is used within a
              function, it causes the variable name to have a visible scope  restricted  to  that
              function  and  its  children.  With no operands, local writes a list of local vari-
              ables to the standard output.  It is an error to use local when not within a  func-
              tion.   The  return status is 0 unless local is used outside a function, an invalid
              name is supplied, or name is a readonly variable.

       logout Exit a login shell.

       mapfile [-n count] [-O origin] [-s count] [-t] [-u fd] [-C callback] [-c quantum] [array]
       readarray [-n count] [-O origin] [-s count]  [-t]  [-u  fd]  [-C  callback]  [-c  quantum]
       [array]
              Read  lines  from the standard input into the indexed array variable array, or from
              file descriptor fd if the -u option is  supplied.   The  variable  MAPFILE  is  the
              default array.  Options, if supplied, have the following meanings:
              -n     Copy at most count lines.  If count is 0, all lines are copied.
              -O     Begin assigning to array at index origin.  The default index is 0.
              -s     Discard the first count lines read.
              -t     Remove a trailing newline from each line read.
              -u     Read lines from file descriptor fd instead of the standard input.
              -C     Evaluate callback each time quantum lines are read.  The -c option specifies
                     quantum.
              -c     Specify the number of lines read between each call to callback.

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

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

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

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

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

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

              The format is a character string which contains three types of objects: plain char-
              acters, which are simply copied to standard  output,  character  escape  sequences,
              which  are  converted and copied to the standard output, and format specifications,
              each of which causes printing of the next successive argument.  In addition to  the
              standard  printf(1)  format  specifications, printf interprets the following exten-
              sions:
              %b     causes printf to expand backslash  escape  sequences  in  the  corresponding
                     argument  (except  that  \c terminates output, backslashes in \', \", and \?
                     are not removed, and octal escapes beginning with \0 may contain up to  four
                     digits).
              %q     causes  printf  to output the corresponding argument in a format that can be
                     reused as shell input.
              %(datefmt)T
                     causes printf to output the date-time string resulting from using datefmt as
                     a  format  string for strftime(3).  The corresponding argument is an integer
                     representing the number of seconds since the epoch.   Two  special  argument
                     values  may  be  used: -1 represents the current time, and -2 represents the
                     time the shell was invoked.

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

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

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

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

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

       read [-ers] [-a aname] [-d delim] [-i text] [-n nchars] [-N nchars] [-p prompt] [-t  time-
       out] [-u fd] [name ...]
              One  line  is read from the standard input, or from the file descriptor fd supplied
              as an argument to the -u option, and the first word is assigned to the first  name,
              the second word to the second name, and so on, with leftover words and their inter-
              vening separators assigned to the last name.  If there are fewer  words  read  from
              the  input  stream  than names, the remaining names are assigned empty values.  The
              characters in IFS are used to split the line into words.  The  backslash  character
              (\)  may  be used to remove any special meaning for the next character read and for
              line continuation.  Options, if supplied, have the following meanings:
              -a aname
                     The words are assigned to sequential indices of the  array  variable  aname,
                     starting  at  0.   aname is unset before any new values are assigned.  Other
                     name arguments are ignored.
              -d delim
                     The first character of delim is used to terminate  the  input  line,  rather
                     than newline.
              -e     If  the  standard  input  is  coming from a terminal, readline (see READLINE
                     above) is used to obtain the line.  Readline uses the current  (or  default,
                     if line editing was not previously active) editing settings.
              -i text
                     If  readline is being used to read the line, text is placed into the editing
                     buffer before editing begins.
              -n nchars
                     read returns after reading nchars characters rather than waiting for a  com-
                     plete  line  of input, but honor a delimiter if fewer than nchars characters
                     are read before the delimiter.
              -N nchars
                     read returns after reading exactly nchars characters rather than waiting for
                     a  complete  line  of  input,  unless  EOF is encountered or read times out.
                     Delimiter characters encountered in the input are not treated specially  and
                     do not cause read to return until nchars characters are read.
              -p prompt
                     Display  prompt  on  standard  error,  without  a  trailing  newline, before
                     attempting to read any input.  The prompt is displayed only if input is com-
                     ing from a terminal.
              -r     Backslash  does not act as an escape character.  The backslash is considered
                     to be part of the line.  In particular, a backslash-newline pair may not  be
                     used as a line continuation.
              -s     Silent mode.  If input is coming from a terminal, characters are not echoed.
              -t timeout
                     Cause read to time out and return failure if a complete line of input is not
                     read within timeout seconds.  timeout may be a decimal number with  a  frac-
                     tional  portion  following the decimal 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 timeout is 0, read
                     returns success if input is available  on  the  specified  file  descriptor,
                     failure  otherwise.   The  exit status is greater than 128 if the timeout is
                     exceeded.
              -u fd  Read input from file descriptor fd.

              If no names are supplied, the line read is assigned to  the  variable  REPLY.   The
              return  code  is  zero, unless end-of-file is encountered, read times out (in which
              case the return code is greater than 128), or an invalid file  descriptor  is  sup-
              plied as the argument to -u.

       readonly [-aAf] [-p] [name[=word] ...]
              The  given  names are marked readonly; the values of these names may not be changed
              by subsequent assignment.  If the -f option is supplied, the functions  correspond-
              ing  to  the names are so marked.  The -a option restricts the variables to indexed
              arrays; the -A option restricts the  variables  to  associative  arrays.   If  both
              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 exit with the return value specified by n.  If n  is  omitted,
              the  return  status  is that of the last command executed in the function body.  If
              used outside a function, but during execution of a script by the .   (source)  com-
              mand,  it causes the shell to stop executing that script and return either n or the
              exit status of the last command executed within the script as the  exit  status  of
              the  script.  If used outside a function and not during execution of a script by .,
              the return status is false.  Any command associated with the RETURN  trap  is  exe-
              cuted before execution resumes after the function or script.

       set [--abefhkmnptuvxBCEHPT] [-o option-name] [arg ...]
       set [+abefhkmnptuvxBCEHPT] [+o option-name] [arg ...]
              Without  options, the name and value of each shell variable are displayed in a for-
              mat that can be reused as input for setting or resetting  the  currently-set  vari-
              ables.   Read-only  variables cannot be reset.  In posix mode, only shell variables
              are listed.  The output is sorted according to the current  locale.   When  options
              are  specified,  they set or unset shell attributes.  Any arguments remaining after
              option processing are treated as values  for  the  positional  parameters  and  are
              assigned,  in order, to $1, $2, ...  $n.  Options, if specified, have the following
              meanings:
              -a      Automatically mark variables and functions which are  modified  or  created
                      for export to the environment of subsequent commands.
              -b      Report  the  status  of terminated background jobs immediately, rather than
                      before the next primary prompt.  This is effective only when job control is
                      enabled.
              -e      Exit  immediately  if a pipeline (which may consist of a single simple com-
                      mand),  a subshell command enclosed in parentheses, or one of the  commands
                      executed  as  part  of a command list enclosed by braces (see SHELL GRAMMAR
                      above) exits with a non-zero status.  The shell does not exit if  the  com-
                      mand  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 follow-
                      ing the final && or ||, any command in a pipeline but the last, or  if  the
                      command's return value is being inverted with !.  A trap on ERR, if set, is
                      executed before the shell exits.  This option applies to the shell environ-
                      ment  and each subshell environment separately (see COMMAND EXECUTION ENVI-
                      RONMENT above), and may cause subshells to exit before  executing  all  the
                      commands in the subshell.
              -f      Disable pathname expansion.
              -h      Remember  the  location  of  commands  as they are looked up for execution.
                      This is enabled by default.
              -k      All arguments in the form of assignment statements are placed in the  envi-
                      ronment for a command, not just those that precede the command name.
              -m      Monitor  mode.   Job  control is enabled.  This option is on by default for
                      interactive shells on systems that support  it  (see  JOB  CONTROL  above).
                      Background  processes run in a separate process group and a line containing
                      their exit status is printed upon their completion.
              -n      Read commands but do not execute them.  This may be used to check  a  shell
                      script for syntax errors.  This is ignored by interactive shells.
              -o option-name
                      The option-name can be one of the following:
                      allexport
                              Same as -a.
                      braceexpand
                              Same as -B.
                      emacs   Use an emacs-style command line editing interface.  This is enabled
                              by default when the shell  is  interactive,  unless  the  shell  is
                              started with the --noediting option.  This also affects the editing
                              interface used for read -e.
                      errexit Same as -e.
                      errtrace
                              Same as -E.
                      functrace
                              Same as -T.
                      hashall Same as -h.
                      histexpand
                              Same as -H.
                      history Enable command history, as described  above  under  HISTORY.   This
                              option is on by default in interactive shells.
                      ignoreeof
                              The  effect  is  as  if the shell command ``IGNOREEOF=10'' had been
                              executed (see Shell Variables above).
                      keyword Same as -k.
                      monitor Same as -m.
                      noclobber
                              Same as -C.
                      noexec  Same as -n.
                      noglob  Same as -f.
                      nolog   Currently ignored.
                      notify  Same as -b.
                      nounset Same as -u.
                      onecmd  Same as -t.
                      physical
                              Same as -P.
                      pipefail
                              If set, the return value of a pipeline is the  value  of  the  last
                              (rightmost)  command to exit with a non-zero status, or zero if all
                              commands in the pipeline exit successfully.  This  option  is  dis-
                              abled by default.
                      posix   Change  the  behavior  of  bash where the default operation differs
                              from the POSIX standard to match the standard (posix mode).
                      privileged
                              Same as -p.
                      verbose Same as -v.
                      vi      Use a vi-style command line editing interface.  This  also  affects
                              the editing interface used for read -e.
                      xtrace  Same as -x.
                      If  -o  is  supplied with no option-name, the values of the current options
                      are printed.  If +o is supplied with no option-name, a series of  set  com-
                      mands  to recreate the current option settings is displayed on the standard
                      output.
              -p      Turn on privileged mode.  In this mode, the $ENV and  $BASH_ENV  files  are
                      not  processed, shell functions are not inherited from the environment, and
                      the SHELLOPTS, BASHOPTS, CDPATH, and GLOBIGNORE variables, if  they  appear
                      in  the  environment, are ignored.  If the shell is started with the effec-
                      tive user (group) id not equal to the real user  (group)  id,  and  the  -p
                      option  is  not supplied, these actions are taken and the effective user id
                      is set to the real user id.  If the -p option is supplied at  startup,  the
                      effective  user id is not reset.  Turning this option off causes the effec-
                      tive user and group ids to be set to the real user and group ids.
              -t      Exit after reading and executing one command.
              -u      Treat unset variables and parameters other than the special parameters  "@"
                      and  "*"  as an error when performing parameter expansion.  If expansion is
                      attempted on an unset variable or parameter, the shell prints an error mes-
                      sage, and, if not interactive, exits with a non-zero status.
              -v      Print shell input lines as they are read.
              -x      After expanding each simple command, for command, case command, select com-
                      mand, or arithmetic for command, display the expanded value  of  PS4,  fol-
                      lowed by the command and its expanded arguments or associated word list.
              -B      The shell performs brace expansion (see Brace Expansion above).  This is on
                      by default.
              -C      If set, bash does not overwrite an existing file with the >, >&, and <> re-
                      direction  operators.  This may be overridden when creating output files by
                      using the redirection operator >| instead of >.
              -E      If set, any trap on ERR is inherited by shell functions, command  substitu-
                      tions,  and  commands  executed in a subshell environment.  The ERR trap is
                      normally not inherited in such cases.
              -H      Enable !  style history substitution.  This option is on  by  default  when
                      the shell is interactive.
              -P      If  set,  the  shell does not follow symbolic links when executing commands
                      such as cd that change the current working directory.  It uses the physical
                      directory structure instead.  By default, bash follows the logical chain of
                      directories when performing commands which change the current directory.
              -T      If set, any traps on DEBUG and RETURN are  inherited  by  shell  functions,
                      command  substitutions,  and  commands  executed in a subshell environment.
                      The DEBUG and RETURN traps are normally not inherited in such cases.
              --      If no arguments follow this option,  then  the  positional  parameters  are
                      unset.   Otherwise,  the positional parameters are set to the args, even if
                      some of them begin with a -.
              -       Signal the end of options, cause all remaining args to be assigned  to  the
                      positional parameters.  The -x and -v options are turned off.  If there are
                      no args, the positional parameters remain unchanged.

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

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

       shopt [-pqsu] [-o] [optname ...]
              Toggle the values of  variables  controlling  optional  shell  behavior.   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.  The -p option  causes  output  to  be
              displayed  in a form that may be reused as input.  Other options have the following
              meanings:
              -s     Enable (set) each optname.
              -u     Disable (unset) each optname.
              -q     Suppresses normal output (quiet mode); the return status  indicates  whether
                     the  optname  is set or unset.  If multiple optname arguments are given with
                     -q, the return status is zero if all optnames are enabled;  non-zero  other-
                     wise.
              -o     Restricts the values of optname to be those defined for the -o option to the
                     set builtin.

              If either -s or -u is used with no optname arguments, the  display  is  limited  to
              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  options, the return status is zero
              unless an optname is not a valid shell option.

              The list of shopt options is:

              autocd  If set, a command name that is the name of a directory is executed as if it
                      were  the argument to the cd command.  This option is only used by interac-
                      tive shells.
              cdable_vars
                      If set, an argument to the cd builtin command that is not  a  directory  is
                      assumed to be the name of a variable whose value is the directory to change
                      to.
              cdspell If set, minor errors in the spelling of a directory component in a cd  com-
                      mand  will be corrected.  The errors checked for are transposed characters,
                      a missing character, and one character too many.  If a correction is found,
                      the  corrected file name is printed, and the command proceeds.  This option
                      is only used by interactive shells.
              checkhash
                      If set, bash checks that a command found in the hash  table  exists  before
                      trying  to execute it.  If a hashed command no longer exists, a normal path
                      search is performed.
              checkjobs
                      If set, bash lists the status of any stopped and running jobs before  exit-
                      ing an interactive shell.  If any jobs are running, this causes the exit to
                      be deferred until a second exit is attempted without an intervening command
                      (see  JOB  CONTROL  above).  The shell always postpones exiting if any jobs
                      are stopped.
              checkwinsize
                      If set, bash checks the window size after each command and,  if  necessary,
                      updates the values of LINES and COLUMNS.
              cmdhist If  set,  bash attempts to save all lines of a multiple-line command in the
                      same history entry.  This allows easy re-editing of multi-line commands.
              compat31
                      If set, bash changes its behavior to that of version 3.1  with  respect  to
                      quoted arguments to the [[ conditional command's =~ operator.
              compat32
                      If  set,  bash  changes its behavior to that of version 3.2 with respect to
                      locale-specific string comparison when using the [[ conditional command's <
                      and  >  operators.  Bash versions prior to bash-4.1 use ASCII collation and
                      strcmp(3); bash-4.1 and later use the current locale's  collation  sequence
                      and strcoll(3).
              compat40
                      If  set,  bash  changes its behavior to that of version 4.0 with respect to
                      locale-specific string comparison when using the [[ conditional command's <
                      and  >  operators (see previous item) and the effect of interrupting a com-
                      mand list.
              compat41
                      If set, bash, when in posix mode, treats a single quote in a  double-quoted
                      parameter  expansion  as a special character.  The single quotes must match
                      (an even number) and the characters between the single quotes  are  consid-
                      ered  quoted.  This is the behavior of posix mode through version 4.1.  The
                      default bash behavior remains as in previous versions.
              direxpand
                      If set, bash replaces directory names with the results  of  word  expansion
                      when  performing  filename  completion.   This  changes the contents of the
                      readline editing buffer.  If not set, bash attempts to  preserve  what  the
                      user typed.
              dirspell
                      If  set,  bash  attempts spelling correction on directory names during word
                      completion if the directory name initially supplied does not exist.
              dotglob If set, bash includes filenames beginning with a  `.'  in  the  results  of
                      pathname expansion.
              execfail
                      If set, a non-interactive shell will not exit if it cannot execute the file
                      specified as an argument to the exec builtin command.  An interactive shell
                      does not exit if exec fails.
              expand_aliases
                      If set, aliases are expanded as described above under ALIASES.  This option
                      is enabled by default for interactive shells.
              extdebug
                      If set, behavior intended for use by debuggers is enabled:
                      1.     The -F option to the declare builtin displays the source  file  name
                             and  line  number corresponding to each function name supplied as an
                             argument.
                      2.     If the command run by the DEBUG trap returns a non-zero  value,  the
                             next command is skipped and not executed.
                      3.     If  the  command run by the DEBUG trap returns a value of 2, and the
                             shell is executing in a subroutine (a  shell  function  or  a  shell
                             script  executed  by  the . or source builtins), a call to return is
                             simulated.
                      4.     BASH_ARGC and BASH_ARGV are updated as described in  their  descrip-
                             tions above.
                      5.     Function tracing is enabled:  command substitution, shell functions,
                             and subshells invoked with ( command ) inherit the DEBUG and  RETURN
                             traps.
                      6.     Error  tracing  is  enabled:  command substitution, shell functions,
                             and subshells invoked with ( command ) inherit the ERR trap.
              extglob If set, the extended pattern matching features described above under  Path-
                      name Expansion are enabled.
              extquote
                      If  set,  $'string'  and $"string" quoting is performed within ${parameter}
                      expansions enclosed in double quotes.  This option is enabled by default.
              failglob
                      If set, patterns which fail to match filenames  during  pathname  expansion
                      result in an expansion error.
              force_fignore
                      If set, the suffixes specified by the FIGNORE shell variable cause words to
                      be ignored when performing word completion even if the  ignored  words  are
                      the only possible completions.  See SHELL VARIABLES above for a description
                      of FIGNORE.  This option is enabled by default.
              globstar
                      If set, the pattern ** used in a pathname expansion context will match  all
                      files  and  zero or more directories and subdirectories.  If the pattern is
                      followed by a /, only directories and subdirectories match.
              gnu_errfmt
                      If set, shell error messages are written in the standard GNU error  message
                      format.
              histappend
                      If  set, the history list is appended to the file named by the value of the
                      HISTFILE variable when the shell exits, rather than overwriting the file.
              histreedit
                      If set, and readline is being used, a user is given the opportunity to  re-
                      edit a failed history substitution.
              histverify
                      If set, and readline is being used, the results of history substitution are
                      not immediately passed to the shell parser.  Instead, the resulting line is
                      loaded into the readline editing buffer, allowing further modification.
              hostcomplete
                      If  set,  and readline is being used, bash will attempt to perform hostname
                      completion when a word containing a @ is being  completed  (see  Completing
                      under READLINE above).  This is enabled by default.
              huponexit
                      If  set,  bash will send SIGHUP to all jobs when an interactive login shell
                      exits.
              interactive_comments
                      If set, allow a word beginning with # to cause that word and all  remaining
                      characters on that line to be ignored in an interactive shell (see COMMENTS
                      above).  This option is enabled by default.
              lastpipe
                      If set, and job control is not active, the shell runs the last command of a
                      pipeline not executed in the background in the current shell environment.
              lithist If set, and the cmdhist option is enabled, multi-line commands are saved to
                      the history with embedded newlines rather than using  semicolon  separators
                      where possible.
              login_shell
                      The  shell  sets this option if it is started as a login shell (see INVOCA-
                      TION above).  The value may not be changed.
              mailwarn
                      If set, and a file that bash is checking for mail has been  accessed  since
                      the  last  time it was checked, the message ``The mail in mailfile has been
                      read'' is displayed.
              no_empty_cmd_completion
                      If set, and readline is being used, bash will not  attempt  to  search  the
                      PATH  for  possible  completions  when  completion is attempted on an empty
                      line.
              nocaseglob
                      If set, bash matches filenames in a case-insensitive fashion when  perform-
                      ing pathname expansion (see Pathname Expansion above).
              nocasematch
                      If set, bash matches patterns in a case-insensitive fashion when performing
                      matching while executing case or [[ conditional commands.
              nullglob
                      If set, bash allows patterns which match no files (see  Pathname  Expansion
                      above) to expand to a null string, rather than themselves.
              progcomp
                      If set, the programmable completion facilities (see Programmable Completion
                      above) are enabled.  This option is enabled by default.
              promptvars
                      If set, prompt strings undergo parameter expansion,  command  substitution,
                      arithmetic  expansion,  and quote removal after being expanded as described
                      in PROMPTING above.  This option is enabled by default.
              restricted_shell
                      The shell sets this option  if  it  is  started  in  restricted  mode  (see
                      RESTRICTED  SHELL below).  The value may not be changed.  This is not reset
                      when the startup files are executed, allowing the startup files to discover
                      whether or not a shell is restricted.
              shift_verbose
                      If  set,  the  shift  builtin  prints an error message when the shift count
                      exceeds the number of positional parameters.
              sourcepath
                      If set, the source (.) builtin uses the value of PATH to find the directory
                      containing  the  file  supplied  as an argument.  This option is enabled by
                      default.
              xpg_echo
                      If set, the echo builtin expands backslash-escape sequences by default.

       suspend [-f]
              Suspend the execution of this shell until it receives a SIGCONT  signal.  When  the
              suspended shell is a background process, it can be restarted by the fg command. For
              more information, read the JOB CONTROL section. The suspend command can not suspend
              the  login shell. However, when -f option is specified, suspend command can suspend
              even login shell.  The return status is 0 unless the shell is a login shell and  -f
              is not supplied, or if job control is not enabled.

       test expr
       [ expr ]
              Return a status of 0 or 1 depending on the evaluation of the conditional expression
              expr.  Each operator and operand must be a separate argument.  Expressions are com-
              posed  of  the  primaries described above under CONDITIONAL EXPRESSIONS.  test does
              not accept any options, nor does it accept and ignore an argument of -- as signify-
              ing the end of options.

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

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

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

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

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

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

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

              If a sigspec is ERR, the command arg is executed whenever a simple  command  has  a
              non-zero  exit  status,  subject  to the following conditions.  The ERR trap is not
              executed if the failed command is part of the command list immediately following  a
              while or until keyword, part of the test in an if statement, part of a command exe-
              cuted in a && or || list, or if the command's return value is being inverted via !.
              These are the same conditions obeyed by the errexit option.

              Signals  ignored  upon  entry  to  the  shell  cannot  be trapped, reset or listed.
              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, key-
              word, function, builtin, or file if name is an alias, shell  reserved  word,  func-
              tion,  builtin, or disk file, respectively.  If the name is not found, then nothing
              is printed, and an exit status of false is returned.  If the  -p  option  is  used,
              type  either  returns the name of the disk file that would be executed if name were
              specified as a command name, or nothing if ``type -t name'' would not return  file.
              The  -P  option  forces a PATH search for each name, even if ``type -t name'' would
              not return file.  If a command is hashed, -p and -P print  the  hashed  value,  not
              necessarily  the  file  that appears first in PATH.  If the -a option is used, type
              prints all of the places that contain an  executable  named  name.   This  includes
              aliases and functions, if and only if the -p option is not also used.  The table of
              hashed commands is not consulted when using -a.  The  -f  option  suppresses  shell
              function  lookup,  as  with  the  command builtin.  type returns true if all of the
              arguments are found, false if any are not found.

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

              If limit is given, it is the new value of the specified resource (the -a option  is
              display only).  If no option is given, then -f is assumed.  Values are in 1024-byte
              increments, except for -t, which is in seconds, -p, which is in units  of  512-byte
              blocks,  and -T, -b, -n, and -u, which are unscaled values.  The return status is 0
              unless an invalid option or argument is supplied, or an error occurs while  setting
              a new limit.  In POSIX Mode 512-byte blocks are used for the `-c' and `-f' options.

       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 symbolic form; the
              default output is an octal number.  If the -p option is supplied, and mode is omit-
              ted, the output is in a form that may be reused as input.  The return status  is  0
              if the mode was successfully changed or if no mode argument was supplied, and false
              otherwise.

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

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

       wait [n ...]
              Wait for each specified process and return its termination status.  Each n may be a
              process ID or a job specification; if a job spec is given, all  processes  in  that
              job's  pipeline are waited for.  If n is not given, all currently active child pro-
              cesses are waited for, and the return status is zero.  If n specifies  a  non-exis-
              tent process or job, the return status is 127.  Otherwise, the return status is the
              exit status of the last process or job waited for.

SEE ALSO
       bash(1), sh(1)



GNU Bash-4.0                               2004 Apr 20                           BASH_BUILTINS(1)

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