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BASH_BUILTINS(1)                                              BASH_BUILTINS(1)



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

BASH BUILTIN COMMANDS
       Unless  otherwise  noted,  each  builtin  command documented in this section as accepting options preceded by -
       accepts -- to signify the end of the options.  The :, true, false, and test builtins do not accept options  and
       do not treat -- specially.  The exit, logout, break, continue, let, and shift builtins accept and process argu-
       ments 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 inter-
       pretation.
       : [arguments]
              No effect; the command does nothing beyond expanding arguments and  performing  any  specified  redirec-
              tions.  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 filename.  The file searched for in PATH need not be executable.
              When bash is not in posix mode, the current directory is searched if no file is found in PATH.   If  the
              sourcepath  option  to  the shopt builtin command is turned off, the PATH is not searched.  If any argu-
              ments 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 readline function or macro,
              or set a readline variable.  Each non-option argument is a command as it would appear in  .inputrc,  but
              each  binding  or  command must be passed as a separate argument; e.g., '"\C-x\C-r": re-read-init-file'.
              Options, if supplied, have the following meanings:
              -m keymap
                     Use keymap as the keymap to be affected by the subsequent bindings.  Acceptable keymap names  are
                     emacs,  emacs-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; Otherwise, break returns 0 value.

       builtin shell-builtin [arguments]
              Execute  the  specified shell builtin, passing it arguments, and return its exit status.  This is useful
              when defining a function whose name is the same as a shell builtin, retaining the 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 sub-
              routine call.  If a non-negative integer is supplied as expr, caller displays the line  number,  subrou-
              tine  name,  and  source  file corresponding to that position in the current execution call stack.  This
              extra information may be used, for example, to print a stack trace.  The current frame is frame 0.   The
              return  value  is 0 unless the shell is not executing a subroutine call or expr does not correspond to a
              valid position in the call stack.

       cd [-L|-P] [dir]
              Change the current directory to dir.  The variable HOME is the default dir.  The variable CDPATH defines
              the  search  path for the directory containing dir.  Alternative directory names in CDPATH are separated
              by a colon (:).  A null directory name in CDPATH is the same as the current directory, i.e., ''.''.   If
              dir  begins  with a slash (/), then CDPATH is not used. The -P option says to use the physical directory
              structure instead of following symbolic links (see also the -P option to the set builtin  command);  the
              -L  option  forces symbolic links to be followed.  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 guaranteed to find all of the standard utilities.  If either the -V or -v
              option  is supplied, a description of command is printed.  The -v option causes a single word indicating
              the command or file name used to invoke command to be displayed; the -V option produces a  more  verbose
              description.   If  the  -V or -v option is supplied, the exit status is 0 if command was found, and 1 if
              not.  If neither option is supplied and an error occurred or command 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 facili-
              ties, while available, 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 comple-
              tions matching word will be displayed.

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

       complete [-abcdefgjksuv] [-o comp-option] [-DE] [-A action] [-G globpat] [-W wordlist] [-F function]  [-C  com-
       mand]
              [-X filterpat] [-P prefix] [-S suffix] name [name ...]
       complete -pr [-DE] [name ...]
              Specify how arguments to each name should be completed.  If the -p option is supplied, or if no  options
              are  supplied,  existing completion specifications are printed in a way that allows them to be reused as
              input.  The -r option removes a completion specification for each name, or, if no  names  are  supplied,
              all  completion  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 generates no matches.
                      dirnames
                              Perform directory name completion if the compspec generates no matches.
                      filenames
                              Tell readline that the compspec generates filenames, so it can perform any filename-spe-
                              cific processing (like adding a slash to directory names, quoting special characters, or
                              suppressing trailing spaces).  Intended to be used with shell functions.
                      nospace Tell readline not to append a space (the default) to words completed at the end  of  the
                              line.
                      plusdirs
                              After  any  matches  defined by the compspec are generated, directory name completion is
                              attempted and any matches are added to the results of the other actions.
              -A action
                      The action may be one of the following to generate a list of possible completions:
                      alias   Alias names.  May also be specified as -a.
                      arrayvar
                              Array variable names.
                      binding Readline key binding names.
                      builtin Names of shell builtin commands.  May also be specified as -b.
                      command Command names.  May also be specified as -c.
                      directory
                              Directory names.  May also be specified as -d.
                      disabled
                              Names of disabled shell builtins.
                      enabled Names of enabled shell builtins.
                      export  Names of exported shell variables.  May also be specified as -e.
                      file    File names.  May also be specified as -f.
                      function
                              Names of shell functions.
                      group   Group names.  May also be specified as -g.
                      helptopic
                              Help topics as accepted by the help builtin.
                      hostname
                              Hostnames, as taken from the file specified by the HOSTFILE shell variable.
                      job     Job names, if job control is active.  May also be specified as -j.
                      keyword Shell reserved words.  May also be specified as -k.
                      running Names of running jobs, if job control is active.
                      service Service names.  May also be specified as -s.
                      setopt  Valid arguments for the -o option to the set builtin.
                      shopt   Shell option names as accepted by the shopt builtin.
                      signal  Signal names.
                      stopped Names of stopped jobs, if job control is active.
                      user    User names.  May also be specified as -u.
                      variable
                              Names of all shell variables.  May also be specified as -v.
              -G globpat
                      The pathname expansion pattern globpat is expanded to generate the possible completions.
              -W wordlist
                      The wordlist is split using the characters in the IFS special variable as delimiters,  and  each
                      resultant  word  is  expanded.   The  possible completions are the members of the resultant list
                      which match the word being completed.
              -C command
                      command is executed in a subshell environment, and its output is used as  the  possible  comple-
                      tions.
              -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.
              -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 fil-
                      terpat is removed from the list.  A leading ! in filterpat negates the pattern;  in  this  case,
                      any completion not matching filterpat is removed.
              -P prefix
                      prefix  is  added at the beginning of each possible completion after all other options have been
                      applied.
              -S suffix
                      suffix is appended to each possible completion after all other options have been applied.

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

       compopt [-o option] [-DE] [+o option] [name]
              Modify completion options for each name according to the options, or for the currently-execution comple-
              tion if no names are supplied.  If no options are given, display the completion options for each name or
              the current completion.  The possible values  of  option  are  those  valid  for  the  complete  builtin
              described  above.   The  -D  option indicates that the remaining options should apply to the ''default''
              command completion; that is, completion attempted on a command for which no  completion  has  previously
              been defined.  The -E option indicates that the remaining options should apply to ''empty'' command com-
              pletion; 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  executed
              outside of loop, the return value is 0.

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

              Using '+' instead of '-' turns off the attribute instead, with the exceptions that +a may not be used to
              destroy an array variable and +r will not remove the readonly attribute.  When used in a function, makes
              each  name local, as with the local command.  If a variable name is followed by =value, the value of the
              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 vari-
              able, an attempt is made to assign a value to an array variable without using  the  compound  assignment
              syntax  (see  Arrays  above), one of the names is not a valid shell variable name, an attempt is made to
              turn off readonly status for a 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] [-cplv]
              Without  options,  displays  the  list of currently remembered directories.  The default display is on a
              single line with directory names separated by spaces.  Directories are added to the list with the  pushd
              command; the popd command removes entries from the list.
              +n     Displays  the  nth  entry  counting  from the left of the list shown by dirs when invoked without
                     options, starting with zero.
              -n     Displays the nth entry counting from the right of the list shown by  dirs  when  invoked  without
                     options, starting with zero.
              -c     Clears the directory stack by deleting all of the entries.
              -l     Produces  a longer listing; the default listing format uses a tilde to denote the home directory.
              -p     Print the directory stack with one entry per line.
              -v     Print the directory stack with one entry per line, 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 current job is used.  If the -h option is
              given, each jobspec is not removed from the table, but is marked so that SIGHUP is not sent to  the  job
              if  the shell receives a SIGHUP.  If no jobspec is 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 operation to running jobs.  The return value is
              0 unless a jobspec does not specify a valid job.

       echo [-neE] [arg ...]
              Output the args, separated by spaces, followed by a newline.  The return status is always 0.  If  -n  is
              specified, the trailing newline is suppressed.  If the -e option is given, interpretation of the follow-
              ing 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 characters by default.  echo does
              not interpret -- to mean the end of options.  echo interprets the following escape sequences:
              \a     alert (bell)
              \b     backspace
              \c     suppress further output
              \e     an escape character
              \f     form feed
              \n     new line
              \r     carriage return
              \t     horizontal tab
              \v     vertical tab
              \\     backslash
              \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)

       enable [-a] [-dnps] [-f filename] [name ...]
              Enable and disable builtin shell commands.  Disabling a builtin allows a disk command which has the same
              name as a shell builtin to be executed without specifying a full pathname, even though  the  shell  nor-
              mally  searches  for  builtins  before  disk commands.  If -n is used, each name is disabled; otherwise,
              names are enabled.  For example, to use the test binary found via the PATH instead of the shell  builtin
              version,  run  ''enable -n test''.  The -f option means to load the new builtin command name from shared
              object filename, on systems that support dynamic loading.  The -d option will delete  a  builtin  previ-
              ously  loaded with -f.  If no name arguments are given, or if the -p option is supplied, a list of shell
              builtins is printed.  With no other option arguments, the list consists of all enabled  shell  builtins.
              If -n is supplied, only disabled builtins are printed.  If -a is supplied, the list printed includes all
              builtins, with an indication of whether or not each is enabled.   If  -s  is  supplied,  the  output  is
              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  exe-
              cuted 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 exe-
              cuted 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-interactive shell exits,  unless
              the  shell  option  execfail is enabled, in which case it returns failure.  An interactive shell returns
              failure if the file cannot be executed.  If command is not specified, any 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  com-
              mand 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 subsequently executed commands.
              If the -f option is given, the names refer to functions.  If no names are given, or if the -p option  is
              supplied,  a  list  of  all  names that are exported in this shell is printed.  The -n option causes the
              export property to be removed from each name.  If a variable name is followed by =word, the value of the
              variable  is  set  to word.  export returns an exit status of 0 unless an invalid option is encountered,
              one of the names is not a valid shell variable name, or -f is supplied with a name that is not  a  func-
              tion.

       fc [-e ename] [-lnr] [first] [last]
       fc -s [pat=rep] [cmd]
              Fix  Command.   In  the  first form, a range of commands from first to last is selected from the history
              list.  First and last may be specified as a string (to locate  the  last  command  beginning  with  that
              string)  or  as  a  number (an index into the history list, where a negative number is used as an offset
              from the current command number).  If last is not specified it is set to the current command for listing
              (so  that  ''fc -l -10'' prints the last 10 commands) and to first otherwise.  If first is not 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 com-
              mands.   If  the  -l option is given, the commands are listed on standard output.  Otherwise, the editor
              given by ename is invoked on a file containing those commands.  If ename is not given, the value of  the
              FCEDIT  variable  is used, and the value of EDITOR if FCEDIT is not set.  If neither variable is set, is
              used.  When editing is complete, the edited commands are echoed and executed.

              In the second form, command is re-executed after each instance of pat is  replaced  by  rep.   A  useful
              alias  to  use  with this is ''r="fc -s"'', so that typing ''r 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 contains the option char-
              acters to be recognized; if a character is followed by a colon, the option is expected to have an  argu-
              ment,  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 pro-
              cessed into the variable OPTIND.  OPTIND is initialized to 1 each time the shell or a  shell  script  is
              invoked.   When  an  option requires an argument, getopts places that argument into the variable OPTARG.
              The shell does not reset OPTIND 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 dis-
              played, even if the first character of optstring is not a colon.

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

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

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

       hash [-lr] [-p filename] [-dt] [name]
              For each name, the full file name of the command is determined by searching the directories in $PATH and
              remembered.  If the -p option is supplied, no path search is performed, and filename is used as the full
              file  name  of  the command.  The -r option causes the shell to forget all remembered locations.  The -d
              option causes the shell to forget the remembered location of each name.  If the -t option  is  supplied,
              the  full  pathname  to which each name corresponds is printed.  If multiple name arguments are supplied
              with -t, the name is printed before the hashed full pathname.  The -l option causes output  to  be  dis-
              played  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 current history list.
                     These are lines appended to the history file since the beginning of the current bash session.
              -r     Read the contents of the history file and use them as the current history.
              -w     Write the current history to the history file, 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 his-
                     tory 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.
              -p     List only the process ID of the job's process group leader.
              -n     Display information only about jobs that have changed status since the user was last notified  of
                     their status.
              -r     Restrict output to running jobs.
              -s     Restrict output to stopped jobs.

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

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

       kill [-s sigspec | -n signum | -sigspec] [pid | jobspec] ...
       kill -l [sigspec | exit_status]
              Send  the signal named by sigspec or signum to the processes named by pid or jobspec.  sigspec is either
              a case-insensitive signal name such as SIGKILL (with or without the SIG  prefix)  or  a  signal  number;
              signum is a signal number.  If sigspec is not present, then SIGTERM is assumed.  An argument of -l lists
              the signal names.  If any arguments are supplied when -l is given, the names of the signals  correspond-
              ing 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 variables to the standard output.  It is an error to use local when not within a function.
              The  return status is 0 unless local is used outside a function, an invalid name is supplied, or name is
              a readonly variable.

       logout Exit a login shell.

       mapfile [-n count] [-O origin] [-s count] [-t] [-u fd] [-C callback] [-c quantum] [array]
       readarray [-n count] [-O origin] [-s count] [-t] [-u fd] [-C callback] [-c quantum] [array]
              Read lines from the standard input into the indexed array 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 evaluated, it is  supplied
              the  index  of  the  next array element to be assigned as an additional argument.  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 supplied, array  is  invalid
              or unassignable, or if array is not an indexed array.

       popd [-n] [+n] [-n]
              Removes  entries from the directory stack.  With no arguments, removes the top directory from the stack,
              and performs a cd to the new top directory.  Arguments, if supplied, have the 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 status is 0.  popd
              returns false if an invalid option is encountered, the directory stack is empty, a  non-existent  direc-
              tory stack entry is specified, or the directory change fails.

       printf [-v var] format [arguments]
              Write  the  formatted arguments to the standard output under the control of the format.  The format is a
              character string which contains three types of objects: plain characters, which  are  simply  copied  to
              standard  output, character escape sequences, which are converted and copied to the standard output, and
              format specifications, each of which causes printing of the next successive argument.   In  addition  to
              the standard printf(1) formats, %b causes printf to expand backslash escape sequences in the correspond-
              ing argument (except that \c terminates output, backslashes in \', \", and \? are not removed, and octal
              escapes beginning with \0 may contain up to four digits), and %q causes printf to output the correspond-
              ing argument in a format that can be reused as shell input.

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

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

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

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

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

       read [-ers] [-a aname] [-d delim] [-i text] [-n nchars] [-N nchars] [-p prompt] [-t timeout] [-u fd] [name ...]
              One line is read from the standard input, or from the file descriptor fd supplied as an argument to  the
              -u  option, and the first word is assigned to the first name, the second word to the second name, and so
              on, with leftover words and their intervening 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 charac-
              ters 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 complete  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 coming from a terminal.
              -r     Backslash  does  not  act  as an escape character.  The backslash is considered to be part of the
                     line.  In particular, a backslash-newline pair may not 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 fractional 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 supplied as the argument to -u.

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

       return [n]
              Causes a function to exit with the return value specified by n.  If n is omitted, the return  status  is
              that  of  the last command executed in the function body.  If used outside a function, but during execu-
              tion of a script by the .  (source) command, it causes the shell  to  stop  executing  that  script  and
              return  either n or the exit status of the last command executed within the script as the exit status of
              the script.  If used outside a function and not during execution of a script by ., the return status  is
              false.  Any command associated with the RETURN trap is executed before execution resumes after the func-
              tion or script.

       set [--abefhkmnptuvxBCEHPT] [-o option] [arg ...]
       set [+abefhkmnptuvxBCEHPT] [+o option] [arg ...]
              Without options, the name and value of each shell variable are displayed in a format that can be  reused
              as input for setting or resetting the currently-set variables.  Read-only variables 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 envi-
                      ronment 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 command),  a subshell com-
                      mand enclosed in parentheses, or one of the commands executed as part of a command list enclosed
                      by  braces  (see  SHELL GRAMMAR above) exits with a non-zero status.  The shell does not exit if
                      the command that fails is part of the command list immediately following a while or  until  key-
                      word,  part of the test following the if or elif reserved words, part of any command executed in
                      a && or || list except the command following the final && or ||, any command in a  pipeline  but
                      the  last, or if the command's return value is being inverted with !.  A trap on ERR, if set, is
                      executed before the shell exits.  This option applies to the shell environment and each subshell
                      environment  separately  (see  COMMAND  EXECUTION ENVIRONMENT above), and may cause subshells to
                      exit before executing all the commands in the subshell.
              -f      Disable pathname expansion.
              -h      Remember the location of commands as they are looked up  for  execution.   This  is  enabled  by
                      default.
              -k      All  arguments in the form of assignment statements are placed in the environment for a command,
                      not just those that precede the command name.
              -m      Monitor mode.  Job control is enabled.  This option is on by default for interactive  shells  on
                      systems that support it (see JOB CONTROL above).  Background 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 disabled by default.
                      posix   Change  the behavior of bash where the default operation differs from the POSIX standard
                              to match the standard (posix mode).
                      privileged
                              Same as -p.
                      verbose Same as -v.
                      vi      Use a vi-style command line editing interface.  This also affects the editing  interface
                              used for read -e.
                      xtrace  Same as -x.
                      If  -o is supplied with no option-name, the values of the current options are printed.  If +o is
                      supplied with no option-name, a series of set commands to recreate the current  option  settings
                      is displayed on the standard output.
              -p      Turn  on  privileged  mode.  In this mode, the $ENV and $BASH_ENV files are not processed, shell
                      functions are not inherited from the environment, and the SHELLOPTS, BASHOPTS, CDPATH, and  GLO-
                      BIGNORE variables, if they appear in the environment, are ignored.  If the shell is started with
                      the effective user (group) id not equal to the real user (group) id, and the -p  option  is  not
                      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 effective user and group ids to be set to the real user and group ids.
              -t      Exit after reading and executing one command.
              -u      Treat  unset  variables and parameters other than the special parameters "@" and "*" as an error
                      when performing parameter expansion.  If expansion is attempted on an unset variable or  parame-
                      ter, the shell prints an error message, and, if not interactive, exits with a non-zero status.
              -v      Print shell input lines as they are read.
              -x      After  expanding  each  simple command, for command, case command, select command, or arithmetic
                      for command, display the expanded value of PS4, followed by the command and its  expanded  argu-
                      ments or associated word list.
              -B      The shell performs brace expansion (see Brace Expansion above).  This is on by default.
              -C      If  set,  bash does not overwrite an existing file with the >, >&, and <> redirection operators.
                      This may be overridden when creating output files by using the redirection operator  >|  instead
                      of >.
              -E      If  set,  any  trap  on ERR is inherited by shell functions, command substitutions, 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  interac-
                      tive.
              -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 arguments to an invocation of the shell.  The  current
              set of options may be found in $-.  The return status is always true unless an invalid option is encoun-
              tered.

       shift [n]
              The positional parameters from n+1 ... are renamed to $1 ....  Parameters represented by the numbers  $#
              down  to  $#-n+1  are  unset.   n must be a non-negative number less than or equal to $#.  If n is 0, no
              parameters are changed.  If n is not given, it is assumed to be 1.  If n is greater than $#,  the  posi-
              tional  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  opt-
                     names are enabled; non-zero otherwise.
              -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 interactive shells.
              cdable_vars
                      If  set, an argument to the cd builtin command that is not a directory is assumed to be the name
                      of a variable whose value is the directory to change to.
              cdspell If set, minor errors in the spelling of a directory component in a cd command 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  exiting  an  interactive
                      shell.   If  any  jobs  are  running, this causes the exit to be deferred until a second exit is
                      attempted without an intervening command (see JOB CONTROL above).  The  shell  always  postpones
                      exiting if any jobs are stopped.
              checkwinsize
                      If  set, bash checks the window size after each command and, if necessary, updates the values of
                      LINES and 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.
              compat40
                      If  set, bash changes its behavior to that of version 4.0 with respect to locale-specific string
                      comparison when using the conditional command's < and > operators and the effect of interrupting
                      a command list.
              dirspell
                      If  set,  bash  attempts  spelling  correction  on directory names during word completion if the
                      directory name 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 corre-
                             sponding 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 descriptions 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 ERROR trap.
              extglob If set, the extended pattern matching features described  above  under  Pathname  Expansion  are
                      enabled.
              extquote
                      If  set, $'string' and $"string" quoting is performed within ${parameter} expansions enclosed in
                      double quotes.  This option is enabled by default.
              failglob
                      If set, patterns which fail to match filenames during pathname expansion result in an  expansion
                      error.
              force_fignore
                      If set, the suffixes specified by the FIGNORE shell variable cause words to be ignored when per-
                      forming 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 a files and zero or more
                      directories and subdirectories.  If the pattern is followed by a /, only directories and  subdi-
                      rectories 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.
              lithist If  set,  and  the  cmdhist option is enabled, multi-line commands are saved to the history with
                      embedded newlines rather than using semicolon separators where possible.
              login_shell
                      The shell sets this option if it is started as a login shell (see INVOCATION above).  The  value
                      may not be changed.
              mailwarn
                      If  set,  and a file that bash is checking for mail has been accessed since the last time it was
                      checked, the message ''The mail in mailfile has been read'' is displayed.
              no_empty_cmd_completion
                      If set, and readline is being used, bash will not attempt to search the PATH for  possible  com-
                      pletions when completion is attempted on an empty line.
              nocaseglob
                      If  set, bash matches filenames in a case-insensitive fashion when performing pathname expansion
                      (see Pathname Expansion above).
              nocasematch
                      If set, bash matches patterns in a case-insensitive fashion when performing matching while  exe-
                      cuting 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, sus-
              pend 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 composed  of  the  primaries  described  above
              under CONDITIONAL EXPRESSIONS.  test does not accept any options, nor does it accept and ignore an argu-
              ment of -- as signifying the end of options.

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

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

              0 arguments
                     The expression is false.
              1 argument
                     The expression is true if and only if the argument is not null.
              2 arguments
                     If  the  first  argument is !, the expression is true if and only if the second argument is null.
                     If the first 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 conditional operator, the expression is false.
              3 arguments
                     If the second argument is one of the binary conditional operators listed above under  CONDITIONAL
                     EXPRESSIONS,  the  result  of the expression is the result of the binary test using the first and
                     third arguments as operands.  The -a and -o operators are considered binary operators when  there
                     are  three  arguments.  If the first argument is !, the value is the negation of the two-argument
                     test using the second and third arguments.  If the first argument is  exactly  (  and  the  third
                     argument  is  exactly  ), the result is the one-argument test of the second argument.  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.

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

              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  executed  in  a && or || list, or if the command's return value is being inverted via !.
              These are the same conditions obeyed by the errexit option.

              Signals ignored upon entry to the shell cannot be trapped, 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, keyword, function, builtin, or file if name
              is an alias, shell reserved word, function, builtin, or disk file, respectively.  If  the  name  is  not
              found, then nothing is printed, and an exit status of false is returned.  If the -p option is used, type
              either returns the name of the disk file that would be executed if name  were  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 omitted, the current value of the soft limit of the resource is
              printed, unless the -H option is given.  When more than one resource is specified, the  limit  name  and
              unit are printed before the value.  Other options are 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
              -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  set-
              ting 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
              omitted,  the  output  is in a form that may be reused as input.  The return status is 0 if the mode was
              successfully changed or if no mode argument was supplied, and false otherwise.

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

       unset [-fv] [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 processes are waited for, and the return status is zero.  If n speci-
              fies a non-existent process or job, the return status is 127.  Otherwise, the return status is the  exit
              status of the last process or job waited for.

SEE ALSO
       bash(1), sh(1)



GNU Bash-4.0                      2004 Apr 20                 BASH_BUILTINS(1)