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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
       commands, see bash(1)

BASH BUILTIN COMMANDS
       Unless  otherwise  noted,  each  builtin command documented in this section as accepting options preceded by -
       accepts -- to signify the end of the options.  The :, true, false, and test builtins do not accept options and
       do  not  treat  --  specially.   The exit, logout, break, continue, let, and shift builtins accept and process
       arguments beginning with - 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  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 .inpu‐
              trc, 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
                     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
              subroutine  call.  If a non-negative integer is supplied as expr, caller displays the line number, sub‐
              routine 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 [-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.  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 com‐
              mand); the -L option forces symbolic links to be followed.  If the -e option is supplied with  -P,  and
              the current working directory cannot be successfully determined after a successful directory change, cd
              will return an unsuccessful status.  An argument of - is equivalent to $OLDPWD.  If a non-empty  direc‐
              tory  name  from CDPATH is used, or if - is the first argument, and the directory change is successful,
              the absolute pathname of the new working directory is written to the standard output.  The return value
              is true if the directory was successfully changed; false otherwise.

       command [-pVv] command [arg ...]
              Run  command  with args suppressing the normal shell function lookup. Only builtin commands or commands
              found in the PATH are executed.  If the -p option is given, the search for command is performed using a
              default  value  for PATH that is guaranteed to find all of the standard utilities.  If either the -V or
              -v option is supplied, a description of command is printed.  The -v option causes a single  word  indi‐
              cating  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,

              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 genera‐
                      tion 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  file‐
                              name-specific processing (like adding a slash to directory names, quoting special char‐
                              acters, 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
                      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  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.
              -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 fil‐
                      terpat  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  sup‐
              plied  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-executing  com‐
              pletion  if  no  names  are supplied.  If no options are given, display the completion options for each
              name or the current completion.  The possible values of option are those valid for the complete builtin
              described  above.   The  -D option indicates that the remaining options should apply to the ``default''
              command completion; that is, completion attempted on a command for which no completion  has  previously
              been  defined.   The  -E  option indicates that the remaining options should apply to ``empty'' command
              completion; that is, completion attempted on a blank line.

              The return value is true unless an invalid option is supplied, an attempt is made to modify the options
              for a name for which no 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 vari‐
              -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, 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 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] [-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 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 fol‐
              \t     horizontal tab
              \v     vertical tab
              \\     backslash
              \0nnn  the eight-bit character whose value is the octal value nnn (zero to three octal digits)
              \xHH   the eight-bit character whose value is the hexadecimal value HH (one or two hex digits)
              \uHHHH the Unicode (ISO/IEC 10646) character whose value is the hexadecimal value HHHH (one to four hex
                     digits)
              \UHHHHHHHH
                     the Unicode (ISO/IEC 10646) character whose value is the  hexadecimal  value  HHHHHHHH  (one  to
                     eight hex digits)

       enable [-a] [-dnps] [-f filename] [name ...]
              Enable  and  disable  builtin  shell commands.  Disabling a builtin allows a disk command which has the
              same name as a shell builtin to be executed without specifying a full pathname, even though  the  shell
              normally  searches for builtins before disk commands.  If -n is used, each name is disabled; otherwise,
              names are 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
              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-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 com‐
              mands.  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 function.
              tor 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
              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 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 diag‐
              nostic 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]

              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 out‐
                     put.  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
              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 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 evaluated, it is supplied
              the index of the next array element to be assigned and the line to be assigned to that element as addi‐
              tional  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 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.

                     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 rep‐
                     resents 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  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  sym‐
              bolic  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  char‐
              acters 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.
                     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 [-aAf] [-p] [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 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 dis‐
              played 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
              function or script.

       set [--abefhkmnptuvxBCEHPT] [-o option-name] [arg ...]
       set [+abefhkmnptuvxBCEHPT] [+o option-name] [arg ...]
              Without options, the name and value of each shell variable are displayed in a format that can be reused
              as  input  for  setting or resetting the currently-set variables.  Read-only variables 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  pri‐
              -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.

              -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 parame‐
                      ters.  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 cur‐
              rent  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 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.

                      rected.  The errors checked for are transposed characters, a missing character, and one charac‐
                      ter  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.  Bash versions  prior  to
                      bash-4.1  use ASCII collation and strcmp(3); bash-4.1 and later use the current locale's colla‐
                      tion 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 command 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 considered 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 file‐
                      name 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  cor‐
                             responding 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

              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 exe‐
                      cuted 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 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

                      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  opera‐
              tor and operand must be a separate argument.  Expressions are composed of the primaries described above
              under CONDITIONAL EXPRESSIONS.  test does not accept any options, nor does  it  accept  and  ignore  an
              argument of -- as signifying the end of options.

              Expressions  may  be  combined using the following operators, listed in decreasing order of precedence.
              The evaluation depends on the number of arguments; see below.  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 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
                     The following conditions are applied in the order listed.  If the second argument is one of  the
                     binary  conditional  operators  listed  above  under  CONDITIONAL EXPRESSIONS, the result of the
                     expression is the result of the binary test using the first and  third  arguments  as  operands.
                     The  -a and -o operators are considered binary operators when there are three arguments.  If the
                     first argument is !, the value is the negation of the two-argument test  using  the  second  and
                     third  arguments.   If  the first argument is exactly ( and the third argument is exactly ), the
                     result is the one-argument test of the second argument.  Otherwise, the expression is false.

       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  com‐
              mand  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
              -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 chil‐
                     dren
              -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
              specifies a non-existent process or job, the return status is 127.  Otherwise, the return status is the
              exit status of the last process or job waited for.

SEE ALSO
       bash(1), sh(1)



GNU Bash-4.0                                         2004 Apr 20                                     BASH_BUILTINS(1)