BASH_BUILTINS(1)            General Commands Manual           BASH_BUILTINS(1)

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

BASH BUILTIN COMMANDS
       Unless otherwise noted, each builtin command documented in this section
       as accepting options preceded by - accepts -- to signify the end of the
       options.  The :, true, false, and test/[ builtins do not accept options
       and do not treat -- specially.  The exit, logout, return,  break,  con-
       tinue,  let,  and shift builtins accept and process arguments beginning
       with - without requiring --.  Other builtins that accept arguments  but
       are  not  specified  as accepting options interpret arguments beginning
       with - as invalid options and require -- to  prevent  this  interpreta-
       tion.

       : [arguments]
              No  effect;  the command does nothing beyond expanding arguments
              and performing any specified redirections.  The return status is
              zero.

       . [-p path] filename [arguments]
       source [-p path] filename [arguments]
              The . command (source) reads and execute commands from  filename
              in  the current shell environment and returns the exit status of
              the last command executed from filename.

              If filename does not contain a slash, . searches for it.  If the
              -p option is supplied, . treats path as a  colon-separated  list
              of  directories in which to find filename; otherwise, . uses the
              entries in PATH  to  find  the  directory  containing  filename.
              filename  does  not  need to be executable.  When bash is not in
              posix mode, it searches the current directory if filename is not
              found in PATH, but does not search the current directory  if  -p
              is supplied.  If the sourcepath option to the shopt builtin com-
              mand is turned off, . does not search PATH.

              If  any arguments are supplied, they become the positional para-
              meters when filename is executed.  Otherwise the positional  pa-
              rameters are unchanged.

              If the -T option is enabled, . inherits any trap on DEBUG; if it
              is  not,  any DEBUG trap string is saved and restored around the
              call to ., and . unsets the DEBUG trap while it executes.  If -T
              is not set, and the sourced file changes the DEBUG trap, the new
              value persists after . completes.  The return status is the sta-
              tus of the last command executed from filename (0 if no commands
              are executed), and non-zero if filename is not found  or  cannot
              be read.

       alias [-p] [name[=value] ...]
              With  no  arguments or with the -p option, alias prints the list
              of aliases in the form  alias  name=value  on  standard  output.
              When arguments are supplied, define an alias 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
              during  command parsing.  For each name in the argument list for
              which no value is supplied, print the  name  and  value  of  the
              alias  name.  alias returns true unless a name is given (without
              a corresponding =value) 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
              uses its notion of the current job.  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] [-lsvSVX]
       bind [-m keymap] [-q function] [-u function] [-r keyseq]
       bind [-m keymap] -f filename
       bind [-m keymap] -x keyseq[:] shell-command
       bind [-m keymap] keyseq:function-name
       bind [-m keymap] -p|-P [readline-command]
       bind [-m keymap] keyseq:readline-command
       bind readline-command-line
              Display current readline key and function bindings, bind  a  key
              sequence  to a readline function or macro or to a shell command,
              or set a readline variable.  Each non-option argument is  a  key
              binding  or command as it would appear in a readline initializa-
              tion file such as .inputrc, but each binding or command must  be
              passed    as    a    separate    argument;    e.g.,    \C-x\C-r:
              re-read-init-file.  In the following descriptions, output avail-
              able to be re-read is formatted as commands that would appear in
              a readline initialization file or that would be supplied as  in-
              dividual  arguments  to  a  bind command.  Options, if supplied,
              have the following meanings:
              -m keymap
                     Use keymap as the keymap to be affected by the subsequent
                     bindings.  Acceptable keymap names are emacs, emacs-stan-
                     dard, emacs-meta, emacs-ctlx,  vi,  vi-move,  vi-command,
                     and  vi-insert.   vi is equivalent to vi-command (vi-move
                     is also a synonym); emacs is  equivalent  to  emacs-stan-
                     dard.
              -l     List the names of all readline functions.
              -p     Display  readline  function  names and bindings in such a
                     way that they can be used as an argument to a  subsequent
                     bind  command  or  in a readline initialization file.  If
                     arguments remain after  option  processing,  bind  treats
                     them  as  readline  command names and restricts output to
                     those names.
              -P     List current readline function names  and  bindings.   If
                     arguments  remain  after  option  processing, bind treats
                     them as readline command names and  restricts  output  to
                     those names.
              -s     Display  readline  key  sequences bound to macros and the
                     strings they output in such a way that they can  be  used
                     as an argument to a subsequent bind command or in a read-
                     line initialization file.
              -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 used as an argument to a subsequent bind
                     command or in a readline initialization file.
              -V     List current readline variable names and values.
              -f filename
                     Read key bindings from filename.
              -q function
                     Display  key  sequences  that  invoke  the named readline
                     function.
              -u function
                     Unbind all key sequences  bound  to  the  named  readline
                     function.
              -r keyseq
                     Remove any current binding for keyseq.
              -x keyseq[: ]shell-command
                     Cause shell-command to be executed whenever keyseq is en-
                     tered.  The separator between keyseq and shell-command is
                     either  whitespace  or  a  colon  optionally  followed by
                     whitespace.  If the separator is  whitespace,  shell-com-
                     mand  must  be enclosed in double quotes and readline ex-
                     pands any of its special backslash-escapes in  shell-com-
                     mand  before saving it.  If the separator is a colon, any
                     enclosing double quotes are optional, and  readline  does
                     not  expand  the  command string before saving it.  Since
                     the entire key binding expression must be a single  argu-
                     ment,  it  should  be  enclosed  in  single quotes.  When
                     shell-command is  executed,  the  shell  sets  the  READ-
                     LINE_LINE  variable  to the contents of the readline line
                     buffer and the READLINE_POINT and READLINE_MARK variables
                     to the current location of the insertion  point  and  the
                     saved  insertion  point  (the  mark),  respectively.  The
                     shell assigns any numeric argument the user  supplied  to
                     the  READLINE_ARGUMENT  variable.   If there was no argu-
                     ment, that variable is not set.  If the executed  command
                     changes   the   value  of  any  of  READLINE_LINE,  READ-
                     LINE_POINT, or READLINE_MARK, those new  values  will  be
                     reflected in the editing state.
              -X     List  all  key  sequences bound to shell commands and the
                     associated commands in a format that can be reused as  an
                     argument to a subsequent bind command.

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

       break [n]
              Exit from within a for, while, until, or select loop.  If  n  is
              specified, break exits n enclosing loops.  n must be >= 1.  If n
              is  greater  than  the  number of enclosing loops, all enclosing
              loops are exited.  The return value is 0 unless n is not greater
              than or equal to 1.

       builtin shell-builtin [arguments]
              Execute the specified shell builtin  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  sta-
              tus is false if shell-builtin is not a shell builtin command.

       caller [expr]
              Returns the context of any active subroutine call (a shell func-
              tion or a script executed with the . or source builtins).

              Without  expr,  caller displays the line number and source file-
              name of the current subroutine call.  If a non-negative  integer
              is supplied as expr, caller displays the line number, subroutine
              name, and source file corresponding to that position in the cur-
              rent  execution call stack.  This extra information may be used,
              for example, to print a stack trace.  The current frame is frame
              0.

              The return value is 0 unless the shell is not executing  a  sub-
              routine  call or expr does not correspond to a valid position in
              the call stack.

       cd [-L] [-@] [dir]
       cd -P [-e] [-@] [dir]
              Change the current directory to dir.  if dir  is  not  supplied,
              the  value of the HOME shell variable is used as dir.  The vari-
              able CDPATH exists, and dir does not begin with a slash (/),  cd
              uses it as a search path: the shell searches each directory name
              in  CDPATH  for  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.,

              The  -P option causes cd to use the physical directory structure
              by resolving symbolic links while traversing dir and before pro-
              cessing instances of .. in dir (see also the -P  option  to  the
              set builtin command).

              The  -L  option  forces cd to follow symbolic links by resolving
              the link after processing instances of .. in dir.  If .. appears
              in dir, cd processes it by  removing  the  immediately  previous
              pathname component from dir, back to a slash or the beginning of
              dir,  and  verifying that the portion of dir it has processed to
              that point is still a valid directory name  after  removing  the
              pathname component.  If it is not a valid directory name, cd re-
              turns  a  non-zero status.  If neither -L nor -P is supplied, cd
              behaves as if -L had been supplied.

              If the -e option is supplied with -P, and cd cannot successfully
              determine the current working directory after a  successful  di-
              rectory change, it returns a non-zero status.

              On  systems that support it, the -@ option presents the extended
              attributes associated with a file as a directory.

              An argument of - is converted to $OLDPWD before  attempting  the
              directory change.

              If  cd  uses  a non-empty directory name from CDPATH, or if - is
              the first argument, and the directory change is  successful,  cd
              writes the absolute pathname of the new working directory to the
              standard output.

              If  the directory change is successful, cd sets the value of the
              PWD environment variable to the new directory name, and sets the
              OLDPWD environment variable to the value of the current  working
              directory before the change.

              The  return  value  is  true  if  the directory was successfully
              changed; false otherwise.

       command [-pVv] command [arg ...]
              The command builtin runs command with args suppressing the  nor-
              mal shell function lookup for command.  Only builtin commands or
              commands  found  in the PATH named command are executed.  If the
              -p option is supplied, 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, command prints a de-
              scription of command.  The -v option displays a single word  in-
              dicating  the command or filename used to invoke command; the -V
              option produces a more verbose description.

              If the -V or -v option is supplied, the exit status is  zero  if
              command  was  found,  and non-zero 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 [-V varname] [option] [word]
              Generate possible completion matches for word according  to  the
              options,  which  may  be  any  option  accepted  by the complete
              builtin with the exceptions of -p, -r, -D, -E, and -I, and write
              the matches to the standard output.

              If the -V option is supplied, compgen stores the generated  com-
              pletions  into  the  indexed  array  variable varname instead of
              writing them to the standard output.

              When using the -F or -C options, the various shell variables set
              by the programmable completion facilities, while available, will
              not have useful values.

              The matches will be generated in the same way as if the program-
              mable completion code had generated them directly from a comple-
              tion specification with the same flags.  If word  is  specified,
              only  those  completions  matching  word  will  be  displayed or
              stored.

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

       complete [-abcdefgjksuv] [-o comp-option] [-DEI] [-A action]
              [-G globpat] [-W wordlist] [-F function] [-C command]
              [-X filterpat] [-P prefix] [-S suffix] name [name ...]
       complete -pr [-DEI] [name ...]
              Specify how arguments to each name should be completed.

              If the -p option is supplied, or if no options or names are sup-
              plied,  print  existing  completion specifications in a way that
              allows them to be reused as input.  The -r option removes a com-
              pletion specification for each name, or, if no  names  are  sup-
              plied, all completion specifications.

              The  -D option indicates that other supplied options and actions
              should apply to the command completion; that is, completion  at-
              tempted on a command for which no completion has previously been
              defined.   The  -E  option indicates that other supplied options
              and actions should apply to command completion; that is, comple-
              tion attempted on a blank line.  The -I  option  indicates  that
              other supplied options and actions should apply to completion on
              the  initial non-assignment word on the line, or after a command
              delimiter such as ; or |, which is usually command name  comple-
              tion.   If  multiple  options  are supplied, the -D option takes
              precedence over -E, and both take precedence over -I.  If any of
              -D, -E, or -I are supplied, any other  name  arguments  are  ig-
              nored; these completions only apply to the case specified by the
              option.

              The process of applying these completion specifications when at-
              tempting word completion  is described in bash(1).

              Other  options,  if specified, have the following meanings.  The
              arguments to the -G, -W, and -X options (and, if necessary,  the
              -P  and -S options) should be quoted to protect them from expan-
              sion before the complete builtin is invoked.

              -o comp-option
                      The comp-option controls several aspects  of  the  comp-
                      spec's  behavior beyond the simple generation of comple-
                      tions.  comp-option may be one of:
                      bashdefault
                              Perform the rest of the default bash completions
                              if the compspec generates no matches.
                      default Use readline's default  filename  completion  if
                              the compspec generates no matches.
                      dirnames
                              Perform  directory  name completion if the comp-
                              spec generates no matches.
                      filenames
                              Tell readline that the compspec generates  file-
                              names,  so  it can perform any filename-specific
                              processing (such as adding a slash to  directory
                              names,  quoting special characters, or suppress-
                              ing trailing spaces).  This is  intended  to  be
                              used with shell functions.
                      fullquote
                              Tell  readline  to quote all the completed words
                              even if they are not filenames.
                      noquote Tell readline not to quote the  completed  words
                              if  they are filenames (quoting filenames is the
                              default).
                      nosort  Tell readline not to sort the list  of  possible
                              completions alphabetically.
                      nospace Tell  readline  not  to  append a space (the de-
                              fault) to words completed  at  the  end  of  the
                              line.
                      plusdirs
                              After  generating  any  matches  defined  by the
                              compspec, attempt directory name completion  and
                              add  any matches to the results of the other ac-
                              tions.
              -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  and directory names, similar to readline's
                              filename completion.  May also be  specified  as
                              -f.
                      function
                              Names of shell functions.
                      group   Group names.  May also be specified as -g.
                      helptopic
                              Help topics as accepted by the help builtin.
                      hostname
                              Hostnames,  as  taken from the file specified by
                              the HOSTFILE shell variable.
                      job     Job names, if job control is active.   May  also
                              be specified as -j.
                      keyword Shell  reserved words.  May also be specified as
                              -k.
                      running Names of running jobs, if job control is active.
                      service Service names.  May also be specified as -s.
                      setopt  Valid arguments for the -o  option  to  the  set
                              builtin.
                      shopt   Shell  option  names  as  accepted  by the shopt
                              builtin.
                      signal  Signal names.
                      stopped Names of stopped jobs, if job control is active.
                      user    User names.  May also be specified as -u.
                      variable
                              Names of all shell variables.  May also be spec-
                              ified as -v.
              -C command
                      command is executed in a subshell environment,  and  its
                      output  is  used as the possible completions.  Arguments
                      are passed as with the -F option.
              -F function
                      The shell function function is executed in  the  current
                      shell  environment.   When the function is executed, the
                      first argument ($1) is the name of the command whose ar-
                      guments are being completed, the second argument ($2) is
                      the word being completed, and the third argument ($3) is
                      the word preceding the word being completed on the  cur-
                      rent command line.  When function finishes, programmable
                      completion  retrieves  the possible completions from the
                      value of the COMPREPLY array variable.
              -G globpat
                      Expand the pathname expansion pattern globpat to  gener-
                      ate the possible completions.
              -P prefix
                      Add  prefix to the beginning of each possible completion
                      after all other options have been applied.
              -S suffix
                      Append suffix to  each  possible  completion  after  all
                      other options have been applied.
              -W wordlist
                      Split  the wordlist using the characters in the IFS spe-
                      cial variable as delimiters, and expand  each  resulting
                      word.   Shell quoting is honored within wordlist, in or-
                      der to provide a mechanism  for  the  words  to  contain
                      shell  metacharacters or characters in the value of IFS.
                      The possible completions are the members of  the  resul-
                      tant  list  which  match a prefix of the word being com-
                      pleted.
              -X filterpat
                      filterpat is a pattern as used for  pathname  expansion.
                      It is applied to the list of possible completions gener-
                      ated  by  the  preceding options and arguments, and each
                      completion matching filterpat is removed from the  list.
                      A  leading  !  in filterpat negates the pattern; in this
                      case, any completion not matching filterpat is removed.

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

       compopt [-o option] [-DEI] [+o option] [name]
              Modify completion options for each name  according  to  the  op-
              tions, or for the currently-executing completion if no names are
              supplied.   If  no  options are supplied, display the completion
              options for each name or the current completion.   The  possible
              values  of  option  are those valid for the complete builtin de-
              scribed above.

              The -D option indicates that other supplied options should apply
              to the command completion; the -E option  indicates  that  other
              supplied  options should apply to command completion; and the -I
              option indicates that other supplied  options  should  apply  to
              completion  on  the  initial word on the line.  These are deter-
              mined in the same way as the complete builtin.

              If multiple options are supplied, the -D option takes precedence
              over -E, and both take precedence over -I.

              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]
              continue resumes the next iteration of the enclosing for, while,
              until,  or select loop.  If n is specified, bash resumes the nth
              enclosing loop.  n must be >= 1.  If n is greater than the  num-
              ber  of  enclosing  loops,  the shell resumes the last enclosing
              loop (the loop).  The return value is 0 unless n is not  greater
              than or equal to 1.

       declare [-aAfFgiIlnrtux] [-p] [name[=value] ...]
       typeset [-aAfFgiIlnrtux] [-p] [name[=value] ...]
              Declare  variables and/or give them attributes.  If no names are
              given then display the values of variables or functions.  The -p
              option will display the attributes  and  values  of  each  name.
              When  -p  is used with name arguments, additional options, other
              than -f and -F, are ignored.

              When -p is supplied without name arguments, declare 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 restricts the display to
              shell functions.

              The -F option inhibits the display of function definitions; only
              the function name and attributes are printed.  If  the  extdebug
              shell  option  is  enabled using shopt, the source file name and
              line number where each name is defined are  displayed  as  well.
              The -F option implies -f.

              The  -g option forces variables to be created or modified at the
              global scope, even when declare is executed in a shell function.
              It is ignored when declare is not executed in a shell function.

              The -I option causes local variables to inherit  the  attributes
              (except  the  nameref attribute) and value of any existing vari-
              able with the same name at a surrounding scope.  If there is  no
              existing variable, the local variable is initially unset.

              The  following  options  can be used to restrict output to vari-
              ables with the specified attribute or to give variables  attrib-
              utes:
              -a     Each  name  is  an  indexed array variable (see Arrays in
                     bash(1)).
              -A     Each name is an associative array variable (see Arrays in
                     bash(1)).
              -f     Each name refers to a shell function.
              -i     The variable is treated as an integer; arithmetic evalua-
                     tion (see ARITHMETIC EVALUATION in bash(1)) is  performed
                     when the variable is assigned a value.
              -l     When  the  variable  is  assigned a value, all upper-case
                     characters are converted to lower-case.   The  upper-case
                     attribute is disabled.
              -n     Give  each  name  the nameref attribute, making it a name
                     reference to another variable.  That  other  variable  is
                     defined  by  the  value of name.  All references, assign-
                     ments, and attribute modifications to name, except  those
                     using  or changing the -n attribute itself, are performed
                     on the variable referenced by name's value.  The  nameref
                     attribute cannot be applied to array variables.
              -r     Make names readonly.  These names cannot then be assigned
                     values by subsequent assignment statements or unset.
              -t     Give each name the trace attribute.  Traced functions in-
                     herit  the DEBUG and RETURN traps from the calling shell.
                     The trace attribute has no special meaning for variables.
              -u     When the variable is assigned  a  value,  all  lower-case
                     characters  are  converted to upper-case.  The lower-case
                     attribute is disabled.
              -x     Mark each name for export to subsequent commands via  the
                     environment.

              Using instead of turns off the specified attribute instead, with
              the  exceptions  that +a and +A may not be used to destroy array
              variables and +r will not remove the readonly attribute.

              When used in a function, declare and typeset make each name  lo-
              cal,  as  with  the  local command, unless the -g option is sup-
              plied.  If a variable name is followed by =value, the  value  of
              the  variable is set to value.  When using -a or -A and the com-
              pound assignment syntax to create  array  variables,  additional
              attributes do not take effect until subsequent assignments.

              The  return  value is 0 unless an invalid option is encountered,
              an attempt is made to define a function using 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 in bash(1)), one of the  names  is
              not  a valid shell variable name, an attempt is made to turn off
              readonly status for a readonly variable, an attempt is  made  to
              turn  off  array  status for an array variable, or an attempt is
              made to display a non-existent function with -f.

       dirs [-clpv] [+n] [-n]
              Without options, display the list of currently remembered direc-
              tories.  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.   The current directory is always the first directory
              in the stack.

              Options, if supplied, have the following meanings:
              -c     Clears the directory stack by deleting  all  of  the  en-
                     tries.
              -l     Produces  a  listing  using  full  pathnames; the default
                     listing format uses a tilde to denote the home directory.
              -p     Print the directory stack with one entry per line.
              -v     Print the directory stack with one entry per  line,  pre-
                     fixing each entry with its index in the stack.
              +n     Displays the nth entry counting from the left of the list
                     shown by dirs when invoked without options, starting with
                     zero.
              -n     Displays  the  nth  entry  counting from the right of the
                     list shown by dirs when invoked without options, starting
                     with zero.

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

       disown [-ar] [-h] [id ...]
              Without  options,  remove each id from the table of active jobs.
              Each id may be a job specification jobspec or a process ID  pid;
              if id is a pid, disown uses the job containing pid as jobspec.

              If  the  -h  option is supplied, disown does not remove the jobs
              corresponding to each id from the jobs table, but  rather  marks
              them  so  the shell does not send SIGHUP to the job if the shell
              receives a SIGHUP.

              If no id is supplied, the -a option means to remove or mark  all
              jobs; the -r option without an id argument removes or marks run-
              ning  jobs.  If no id is supplied, and neither the -a nor the -r
              option is supplied, disown removes or marks the current job.

              The return value is 0 unless an id does not specify a valid job.

       echo [-neE] [arg ...]
              Output the args, separated by spaces,  followed  by  a  newline.
              The  return  status  is 0 unless a write error occurs.  If -n is
              specified, the trailing newline is not printed.

              If the -e option is given, echo interprets the  following  back-
              slash-escaped characters.  The -E option disables interpretation
              of  these  escape characters, even on systems where they are in-
              terpreted by default.   The  xpg_echo  shell  option  determines
              whether or not echo interprets any options and expands these es-
              cape  characters.  echo does not interpret -- to mean the end of
              options.

              echo interprets the following escape sequences:
              \a     alert (bell)
              \b     backspace
              \c     suppress further output
              \e
              \E     an escape character
              \f     form feed
              \n     new line
              \r     carriage return
              \t     horizontal tab
              \v     vertical tab
              \\     backslash
              \0nnn  The eight-bit character whose value is  the  octal  value
                     nnn (zero to three octal digits).
              \xHH   The  eight-bit  character  whose value is the hexadecimal
                     value HH (one or two hex digits).
              \uHHHH The Unicode (ISO/IEC 10646) character whose value is  the
                     hexadecimal value HHHH (one to four hex digits).
              \UHHHHHHHH
                     The  Unicode (ISO/IEC 10646) character whose value is the
                     hexadecimal value HHHHHHHH (one to eight hex digits).

              echo writes any unrecognized  backslash-escaped  characters  un-
              changed.

       enable [-a] [-dnps] [-f filename] [name ...]
              Enable  and disable builtin shell commands.  Disabling a builtin
              allows an executable file 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 files.

              If -n is supplied, each name is disabled; otherwise,  names  are
              enabled.   For  example, to use the test binary found using PATH
              instead of the shell builtin version, run

              If no name arguments are supplied, or if the -p option  is  sup-
              plied, print a list of shell builtins.  With no other option ar-
              guments, the list consists of all enabled shell builtins.  If -n
              is  supplied,  print only disabled builtins.  If -a is supplied,
              the list printed includes all builtins, with  an  indication  of
              whether or not each is enabled.  The -s option means to restrict
              the output to the POSIX special builtins.

              The  -f  option  means to load the new builtin command name from
              shared object filename, on systems that support dynamic loading.
              If filename does not contain a slash, Bash will use the value of
              the BASH_LOADABLES_PATH variable as a  colon-separated  list  of
              directories  in  which  to search for filename.  The default for
              BASH_LOADABLES_PATH is  system-dependent,  and  may  include  to
              force  a  search  of  the current directory.  The -d option will
              delete a builtin previously loaded with -f.  If -s is used  with
              -f, the new builtin becomes a POSIX special builtin.

              If  no  options  are supplied and a name is not a shell builtin,
              enable will attempt to load name  from  a  shared  object  named
              name, as if the command were

              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 ...]
              Concatenate the args together into a single command,  separating
              them with spaces.  Bash then reads and execute this command, and
              returns  its exit status as the return status 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 without  creating
              a  new  process.  command cannot be a shell builtin or function.
              The arguments become the arguments to command.  If the -l option
              is supplied, the shell places a dash at the beginning of the ze-
              roth argument passed to command.  This is  what  login(1)  does.
              The  -c option causes command to be executed with an empty envi-
              ronment.  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 execfail shell option  is  enabled.   In
              that  case,  it returns a non-zero status.  An interactive shell
              returns a non-zero status if the file  cannot  be  executed.   A
              subshell exits unconditionally if exec fails.

              If command is not specified, any redirections take effect in the
              current  shell, and the return status is 0.  If there is a redi-
              rection error, the return status is 1.

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

       export [-fn] [name[=value]] ...
       export -p [-f]
              The supplied names are marked for automatic export to the  envi-
              ronment  of subsequently executed commands.  If the -f option is
              given, the names refer to functions.

              The -n option unexports, or removes the export  attribute,  from
              each  name.   If no names are given, or if only the -p option is
              supplied, export displays a list of names of all exported  vari-
              ables on the standard output.  Using -p and -f together displays
              exported  functions.   The  -p  option displays output in a form
              that may be reused as input.

              export allows the value of a variable to be set when it  is  ex-
              ported or unexported by following the variable name with =value.
              This sets the value of the variable to value while modifying the
              export  attribute.  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.

       false  Does nothing; returns a non-zero status.

       fc [-e ename] [-lnr] [first] [last]
       fc -s [pat=rep] [cmd]
              The  first  form  selects a range of commands from first to last
              from the history list and  displays  or  edits  and  re-executes
              them.   First  and  last may be specified as a string (to locate
              the last command beginning with that string) or as a number  (an
              index  into the history list, where a negative number is used as
              an offset from the current command number).

              When listing, a first or last of 0 is equivalent to -1 and -0 is
              equivalent to the current command (usually the fc command); oth-
              erwise 0 is equivalent to -1 and -0 is invalid.  If last is  not
              specified, it is set to the current command for listing (so that
              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.

              If  the  -l  option  is supplied, the commands are listed on the
              standard output.  The -n option suppresses the  command  numbers
              when listing.  The -r option reverses the order of the commands.

              Otherwise,  fc  invokes the editor named by ename on a file con-
              taining those commands.  If ename is not supplied, fc  uses  the
              value  of the FCEDIT variable, and the value of EDITOR if FCEDIT
              is not set.  If neither variable is set, fc uses vi. When  edit-
              ing  is  complete,  fc reads the file containing the edited com-
              mands and echoes and executes them.

              In the second form, fc re-executes command after replacing  each
              instance  of  pat  with rep.  Command is interpreted the same as
              first above.

              A useful alias to use with fc is so that typing  runs  the  last
              command beginning with and typing re-executes the last command.

              If  the  first  form is used, the return value is zero unless an
              invalid option is encountered or first or last  specify  history
              lines  out  of  range.   When editing and re-executing a file of
              commands, the return value is the value of the last command exe-
              cuted or failure if an error occurs with the temporary file.  If
              the second form is used, the return status is that of the re-ex-
              ecuted command, unless cmd does not specify a valid history  en-
              try, in which case fc returns a non-zero status.

       fg [jobspec]
              Resume  jobspec  in the foreground, and make it the current job.
              If jobspec is not present, fg uses the  shell's  notion  of  the
              current  job.   The  return  value is that of the command placed
              into the foreground, or failure if run when job control is  dis-
              abled 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 [arg ...]
              getopts is used by shell scripts and functions  to  parse  posi-
              tional  parameters and obtain options and their arguments.  opt-
              string 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 processed into the variable
              OPTIND.   OPTIND  is  initialized  to 1 each time the shell or a
              shell script is invoked.  When an option requires  an  argument,
              getopts places that argument into the variable OPTARG.

              The  shell does not reset OPTIND automatically; it must be manu-
              ally reset between multiple calls to  getopts  within  the  same
              shell invocation to use a new set of parameters.

              When  it reaches the end of options, 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 supplied as arg values, getopts parses  those  in-
              stead.

              getopts  can  report errors in two ways.  If the first character
              of optstring is a colon, getopts uses  silent  error  reporting.
              In  normal operation, getopts prints diagnostic messages when it
              encounters invalid options or missing option arguments.  If  the
              variable  OPTERR is set to 0, getopts does not display any error
              messages, even if the first character  of  optstring  is  not  a
              colon.

              If getopts detects an invalid option, it places ? into name and,
              if  not  silent,  prints an error message and unsets OPTARG.  If
              getopts is silent, it assigns the option character found to  OP-
              TARG and does not print a diagnostic message.

              If  a required argument is not found, and getopts is not silent,
              it sets the value of name to a question mark (?), unsets OPTARG,
              and prints a diagnostic message.  If getopts is silent, it  sets
              the  value  of name to a colon (:) and sets OPTARG to the option
              character found.

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

       hash [-lr] [-p filename] [-dt] [name]
              Each time hash is invoked, it remembers the full pathname of the
              command  name  as  determined  by  searching  the directories in
              $PATH.  Any previously-remembered pathname associated with  name
              is  discarded.  If the -p option is supplied, hash uses filename
              as the full pathname of the command.

              The -r option causes the shell to forget  all  remembered  loca-
              tions.   Assigning  to  the PATH variable also clears all hashed
              filenames.  The -d option causes the shell to forget the  remem-
              bered location of each name.

              If the -t option is supplied, hash prints the full pathname cor-
              responding  to  each  name.  If multiple name arguments are sup-
              plied with -t, hash prints the  name  before  the  corresponding
              hashed full pathname.  The -l option displays output in a format
              that may be reused as input.

              If  no  arguments  are  given,  or  if only -l is supplied, hash
              prints information about remembered commands.  The -t,  -d,  and
              -p  options (the options that act on the name arguments) are mu-
              tually exclusive.  Only one will be active.  If more than one is
              supplied, -t has higher priority than -p, and both  have  higher
              priority than -d.

              The  return  status is zero unless a name is not found or an in-
              valid 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 as described below; otherwise it displays a list of  all
              the builtins and shell compound commands.

              Options, if supplied, have the follow meanings:

              -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

              If  pattern  contains  pattern  matching characters (see Pattern
              Matching above) it's treated as a shell pattern and help  prints
              the description of each help topic matching pattern.

              If  not,  and  pattern exactly matches the name of a help topic,
              help prints the description associated with that topic.   Other-
              wise,  help performs prefix matching and prints the descriptions
              of all matching help topics.

              The return status is 0 unless no command matches pattern.

       history [n]
       history -c
       history -d offset
       history -d start-end
       history -anrw [filename]
       history -p arg [arg ...]
       history -s arg [arg ...]
              With no options, display the command history list with  numbers.
              Entries  prefixed with a * have been modified.  An argument of n
              lists only the last n entries.  If the shell variable  HISTTIME-
              FORMAT  is  set  and not null, it is used as a format string for
              strftime(3) to display the time stamp associated with each  dis-
              played  history  entry.  If history uses HISTTIMEFORMAT, it does
              not print an intervening space between the formatted time  stamp
              and the history entry.

              If filename is supplied, history uses it as the name of the his-
              tory  file;  if not, it uses the value of HISTFILE.  If filename
              is not supplied and HISTFILE is unset or null, the -a,  -n,  -r,
              and -w options have no effect.

              Options, if supplied, have the following meanings:
              -c     Clear the history list by deleting all the entries.  This
                     can be used with the other options to replace the history
                     list.
              -d offset
                     Delete  the  history entry at position offset.  If offset
                     is negative, it is interpreted as relative to one greater
                     than the last history position, so negative indices count
                     back from the end of the history,  and  an  index  of  -1
                     refers to the current history -d command.
              -d start-end
                     Delete  the  range  of  history entries between positions
                     start and end, inclusive.  Positive and  negative  values
                     for start and end are interpreted as described above.
              -a     Append  the history lines to the history file.  These are
                     history lines entered since the beginning of the  current
                     bash  session,  but  not  already appended to the history
                     file.
              -n     Read the history lines not already read from the  history
                     file and add them to the current history list.  These are
                     lines appended to the history file since the beginning of
                     the current bash session.
              -r     Read the history file and append its contents to the cur-
                     rent history list.
              -w     Write the current history list to the history file, over-
                     writing the history file.
              -p     Perform  history  substitution  on the following args and
                     display the result on the standard output, without  stor-
                     ing  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
                     adding the args.

              If the HISTTIMEFORMAT variable is set, history writes  the  time
              stamp information associated with each history entry to the his-
              tory  file,  marked  with  the  history comment character as de-
              scribed above.  When the history file is read,  lines  beginning
              with  the  history  comment  character followed immediately by a
              digit are interpreted as timestamps for  the  following  history
              entry.

              The  return  value is 0 unless an invalid option is encountered,
              an error occurs while reading or writing the  history  file,  an
              invalid offset or range is supplied as an argument to -d, or the
              history expansion supplied as an argument to -p fails.

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

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

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

       kill [-s sigspec | -n signum | -sigspec] id [ ... ]
       kill -l|-L [sigspec | exit_status]
              Send the signal specified by sigspec or signum to the  processes
              named by each id.  Each id may be a job specification jobspec or
              a  process  ID pid.  sigspec is either a case-insensitive signal
              name such as SIGKILL (with or without the SIG prefix) or a  sig-
              nal  number;  signum is a signal number.  If sigspec is not sup-
              plied, then kill sends SIGTERM.

              The -l option lists the signal names.  If any arguments are sup-
              plied when -l is given, kill lists the names of the signals cor-
              responding to the arguments, and the return status  is  0.   The
              exit_status  argument to -l is a number specifying either a sig-
              nal number or the exit status of a process terminated by a  sig-
              nal;  if it is supplied, kill prints the name of the signal that
              caused the process to terminate.  kill assumes that process exit
              statuses are greater than 128; anything less than that is a sig-
              nal number.  The -L option is equivalent to -l.

              kill returns true if at least one signal was successfully  sent,
              or false if an error occurs or an invalid option is encountered.

       let arg [arg ...]
              Each  arg  is  evaluated as an arithmetic expression (see ARITH-
              METIC EVALUATION in bash(1)).  If the last arg evaluates  to  0,
              let returns 1; otherwise let returns 0.

       local [option] [name[=value] ... | - ]
              For each argument, create a local variable named name and assign
              it  value.  The option can be any of the options accepted by de-
              clare.  When local is used within  a  function,  it  causes  the
              variable  name  to have a visible scope restricted to that func-
              tion and its children.  It is an error to  use  local  when  not
              within a function.

              If  name  is  -,  it makes the set of shell options local to the
              function in which local is invoked: any  shell  options  changed
              using  the set builtin inside the function after the call to lo-
              cal are restored to their original values when the function  re-
              turns.   The restore is performed as if a series of set commands
              were executed to restore the values that were  in  place  before
              the function.

              With  no operands, local writes a list of local variables to the
              standard output.

              The return status is 0 unless local is used outside a  function,
              an invalid name is supplied, or name is a readonly variable.

       logout [n]
              Exit  a login shell, returning a status of n to the shell's par-
              ent.

       mapfile [-d delim] [-n count] [-O origin] [-s count] [-t] [-u fd] [-C
       callback] [-c quantum] [array]
       readarray [-d delim] [-n count] [-O origin] [-s count] [-t] [-u fd] [-C
       callback] [-c quantum] [array]
              Read lines from the standard input, or from file  descriptor  fd
              if  the  -u  option is supplied, into the indexed array variable
              array.  The variable MAPFILE is the default array.  Options,  if
              supplied, have the following meanings:
              -d     Use  the first character of delim to terminate each input
                     line, rather than newline.  If delim is the empty string,
                     mapfile will terminate a line when it reads a NUL charac-
                     ter.
              -n     Copy at most count lines.  If count is 0, copy all lines.
              -O     Begin assigning to array at index  origin.   The  default
                     index is 0.
              -s     Discard the first count lines read.
              -t     Remove  a trailing delim (default newline) from each line
                     read.
              -u     Read lines from file descriptor fd instead of  the  stan-
                     dard input.
              -C     Evaluate  callback each time quantum lines are read.  The
                     -c option specifies quantum.
              -c     Specify the number of lines read  between  each  call  to
                     callback.

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

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

              mapfile returns zero 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]
              Remove  entries from the directory stack.  The elements are num-
              bered from 0 starting at the first directory listed by dirs,  so
              popd  is  equivalent  to With no arguments, popd removes the top
              directory from the stack, and changes to the new top  directory.
              Arguments, if supplied, have the following meanings:
              -n     Suppress the normal change of directory when removing di-
                     rectories from the stack, only manipulate the stack.
              +n     Remove  the  nth entry counting from the left of the list
                     shown by dirs, starting with zero, from the  stack.   For
                     example: removes the first directory, the second.
              -n     Remove  the nth entry counting from the right of the list
                     shown by dirs, starting with zero.  For example:  removes
                     the last directory, the next to last.

              If  the  top element of the directory stack is modified, and the
              -n option was not supplied, popd uses the cd builtin  to  change
              to the directory at the top of the stack.  If the cd fails, popd
              returns a non-zero value.

              Otherwise,  popd returns false if an invalid option is supplied,
              the directory stack is empty, or n specifies a non-existent  di-
              rectory stack entry.

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

       printf [-v var] format [arguments]
              Write  the  formatted arguments to the standard output under the
              control of the format.  The -v option assigns the output to  the
              variable var rather than printing it to the standard output.

              The  format  is a character string which contains three types of
              objects: plain characters, which are simply copied  to  standard
              output,  character  escape  sequences,  which  are converted and
              copied to the standard output, and format  specifications,  each
              of  which  causes  printing of the next successive argument.  In
              addition to  the  standard  printf(3)  format  characters  cCsS-
              ndiouxXeEfFgGaA, printf interprets the following additional for-
              mat specifiers:
              %b     causes printf to expand backslash escape sequences in the
                     corresponding argument in the same way as echo -e.
              %q     causes  printf  to output the corresponding argument in a
                     format that can be reused as shell input.  %q and %Q  use
                     the  $  quoting  style  if any characters in the argument
                     string require it, and backslash quoting  otherwise.   If
                     the  format  string uses the printf alternate form, these
                     two  formats  quote  the  argument  string  using  single
                     quotes.
              %Q     like  %q, but applies any supplied precision to the argu-
                     ment before quoting it.
              %(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.  This format specifier
                     recognizes two special argument values: -1 represents the
                     current time, and -2 represents the time  the  shell  was
                     invoked.  If no argument is specified, conversion behaves
                     as  if -1 had been supplied.  This is an exception to the
                     usual printf behavior.

              The %b, %q, and %T format specifiers all use the field width and
              precision arguments from the format specification and write that
              many bytes from (or use that wide a field for) the expanded  ar-
              gument,  which  usually contains more characters than the origi-
              nal.

              The %n format specifier accepts a corresponding argument that is
              treated as a shell variable name.

              The %s and %c format specifiers accept  an  l  (long)  modifier,
              which forces them to convert the argument string to a wide-char-
              acter string and apply any supplied field width and precision in
              terms of characters, not bytes.  The %S and %C format specifiers
              are equivalent to %ls and %lc, respectively.

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

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

       pushd [-n] [+n] [-n]
       pushd [-n] [dir]
              Add a directory to the top of the directory stack, or rotate the
              stack, making the new top of the stack the current  working  di-
              rectory.   With  no  arguments, pushd exchanges the top two ele-
              ments of the directory stack.  Arguments, if supplied, have  the
              following meanings:
              -n     Suppress  the normal change of directory when rotating or
                     adding directories to  the  stack,  only  manipulate  the
                     stack.
              +n     Rotate the stack so that the nth directory (counting from
                     the  left  of the list shown by dirs, starting with zero)
                     is at the top.
              -n     Rotates the stack so that  the  nth  directory  (counting
                     from  the  right of the list shown by dirs, starting with
                     zero) is at the top.
              dir    Adds dir to the directory stack at the top.

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

              Otherwise,  if no arguments are supplied, pushd returns zero un-
              less the directory stack is empty.  When rotating the  directory
              stack, pushd returns zero unless the directory stack is empty or
              n specifies a non-existent directory stack element.

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

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

       read [-Eers] [-a aname] [-d delim] [-i text] [-n nchars] [-N nchars]
       [-p prompt] [-t timeout] [-u fd] [name ...]
              Read one line from the standard input, or from the file descrip-
              tor  fd  supplied as an argument to the -u option, split it into
              words as described in bash (1) under Word Splitting, and  assign
              the  first word to the first name, the second word to the second
              name, and so on.  If there are more words than  names,  the  re-
              maining  words  and their intervening delimiters are assigned to
              the last name.  If there are fewer words  read  from  the  input
              stream  than  names, the remaining names are assigned empty val-
              ues.  The characters in the value of the IFS variable  are  used
              to split the line into words using the same rules the shell uses
              for expansion (described in bash (1) under Word Splitting).  The
              backslash character (\) removes any special meaning for the next
              character read and is used for line continuation.

              Options, if supplied, have the following meanings:
              -a aname
                     The words are assigned to sequential indices of the array
                     variable aname, starting at 0.  aname is unset before any
                     new  values  are  assigned.  Other name arguments are ig-
                     nored.
              -d delim
                     The first character of delim terminates the  input  line,
                     rather  than newline.  If delim is the empty string, read
                     will terminate a line when it reads a NUL character.
              -e     If the standard input is coming  from  a  terminal,  read
                     uses  readline  (see  READLINE  in bash(1)) to obtain the
                     line.  Readline uses the current  (or  default,  if  line
                     editing  was not previously active) editing settings, but
                     uses readline's default filename completion.
              -E     If the standard input is coming  from  a  terminal,  read
                     uses  readline  (see  READLINE  in bash(1)) to obtain the
                     line.  Readline uses the current  (or  default,  if  line
                     editing  was not previously active) editing settings, but
                     uses bash's default  completion,  including  programmable
                     completion.
              -i text
                     If  readline  is being used to read the line, read places
                     text into the editing buffer before editing begins.
              -n nchars
                     read returns after reading nchars characters rather  than
                     waiting  for  a complete line of input, unless it encoun-
                     ters EOF or read times out, but honors a delimiter if  it
                     reads fewer than nchars characters before the delimiter.
              -N nchars
                     read  returns  after  reading  exactly  nchars characters
                     rather than waiting for a complete line of input,  unless
                     it encounters EOF or read times out.  Any delimiter char-
                     acters  in the input are not treated specially and do not
                     cause read to return until it has read nchars characters.
                     The result is not split on the characters in IFS; the in-
                     tent is that the variable is assigned exactly the charac-
                     ters read (with the exception of backslash;  see  the  -r
                     option below).
              -p prompt
                     Display prompt on standard error, without a trailing new-
                     line,  before  attempting  to read any input, but only if
                     input is coming from a terminal.
              -r     Backslash does not act as an escape character.  The back-
                     slash is considered to be part of the line.  In  particu-
                     lar,  a  backslash-newline pair may not then be used as a
                     line continuation.
              -s     Silent mode.  If input is coming from a terminal, charac-
                     ters are not echoed.
              -t timeout
                     Cause read to time out and return failure if it does  not
                     read  a  complete line of input (or a specified number of
                     characters) 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  read  times out, it saves any partial input read into
                     the specified variable  name,  and  the  exit  status  is
                     greater  than 128.  If timeout is 0, read returns immedi-
                     ately, without trying to read any data.   In  this  case,
                     the  exit status is 0 if input is available on the speci-
                     fied file descriptor, or the read will return  EOF,  non-
                     zero otherwise.
              -u fd  Read  input  from file descriptor fd instead of the stan-
                     dard input.

              Other than the case where delim is the empty  string,  read  ig-
              nores any NUL characters in the input.

              If  no  names  are supplied, read assigns the line read, without
              the ending delimiter but otherwise unmodified, to  the  variable
              REPLY.

              The exit status is zero, unless end-of-file is encountered, read
              times  out  (in  which  case  the status is greater than 128), a
              variable assignment error (such as assigning to a readonly vari-
              able) occurs, or an invalid file descriptor is supplied  as  the
              argument to -u.

       readonly [-aAf] [-p] [name[=word] ...]
              The  given  names are marked readonly; the values of these names
              may not be changed by subsequent assignment or unset.  If the -f
              option is supplied, each name refers to a shell  function.   The
              -a  option restricts the variables to indexed arrays; the -A op-
              tion restricts the variables to associative arrays.  If both op-
              tions are supplied, -A takes precedence.  If no  name  arguments
              are  supplied,  or if the -p option is supplied, print a list of
              all readonly names.  The other options may be used  to  restrict
              the output to a subset of the set of readonly names.  The -p op-
              tion displays output in a format that may be reused as input.

              readonly  allows  the  value of a variable to be set at the same
              time the readonly attribute is changed by following the variable
              name with =value.  This sets the value of  the  variable  is  to
              value while modifying the readonly attribute.

              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]
              Stop  executing  a shell function or sourced file and return the
              value specified by n to its caller.  If n is omitted, the return
              status is that of the last command executed.  If return is  exe-
              cuted  by a trap handler, the last command used to determine the
              status is the last command executed before the trap handler.  If
              return is executed during a DEBUG trap, the last command used to
              determine the status is the last command executed  by  the  trap
              handler before return was invoked.

              When return is used to terminate execution of a script being ex-
              ecuted  by  the .  (source) command, it causes the shell to stop
              executing that script and return either n or the exit status  of
              the  last  command executed within the script as the exit status
              of the script.  If n is supplied, the return value is its  least
              significant 8 bits.

              Any  command  associated with the RETURN trap is executed before
              execution resumes after the function or script.

              The return status is non-zero if return is  supplied  a  non-nu-
              meric argument, or is used outside a function and not during ex-
              ecution of a script by . or source.

       set [-abefhkmnptuvxBCEHPT] [-o option-name] [--] [-] [arg ...]
       set [+abefhkmnptuvxBCEHPT] [+o option-name] [--] [-] [arg ...]
       set -o
       set +o Without  options, display the name and value of each shell vari-
              able in a format that can be reused as input for setting or  re-
              setting the currently-set variables.  Read-only variables cannot
              be  reset.  In posix mode, only shell variables are listed.  The
              output is sorted according to the current locale.  When  options
              are  specified,  they  set or unset shell attributes.  Any argu-
              ments remaining after option processing are  treated  as  values
              for the positional parameters and are assigned, in order, to $1,
              $2,  ...,  $n.   Options, if specified, have the following mean-
              ings:
              -a      Each variable or function that is created or modified is
                      given the export attribute and marked for export to  the
                      environment of subsequent commands.
              -b      Report  the status of terminated background jobs immedi-
                      ately, rather than before the next primary prompt or af-
                      ter a foreground command terminates.  This is  effective
                      only when job control is enabled.
              -e      Exit  immediately  if a pipeline (which may consist of a
                      single simple command), a list, or  a  compound  command
                      (see  SHELL  GRAMMAR  in bash(1)), exits with a non-zero
                      status.  The shell does not exit  if  the  command  that
                      fails  is part of the command list immediately following
                      a while or until reserved word, part of the test follow-
                      ing 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 (subject to the state of  the  pipefail  shell  op-
                      tion),  or  if  the  command's return value is being in-
                      verted with !.  If a compound command other than a  sub-
                      shell returns a non-zero status because a command failed
                      while  -e was being ignored, the shell does not exit.  A
                      trap on ERR, if set, is executed before the shell exits.
                      This option applies to the shell  environment  and  each
                      subshell  environment  separately (see COMMAND EXECUTION
                      ENVIRONMENT in bash(1)), and may cause subshells to exit
                      before executing all the commands in the subshell.

                      If a compound command or shell function  executes  in  a
                      context  where -e is being ignored, none of the commands
                      executed within the compound command  or  function  body
                      will  be  affected  by the -e setting, even if -e is set
                      and a command returns a failure status.  If  a  compound
                      command  or  shell function sets -e while executing in a
                      context where -e is ignored, that setting will not  have
                      any  effect  until  the  compound command or the command
                      containing the function call completes.
              -f      Disable pathname expansion.
              -h      Remember the location of commands as they are looked  up
                      for execution.  This is enabled by default.
              -k      All  arguments  in the form of assignment statements are
                      placed in the environment for a command, not just  those
                      that precede the command name.
              -m      Monitor  mode.   Job control is enabled.  This option is
                      on by default for interactive  shells  on  systems  that
                      support  it (see JOB CONTROL in bash(1)).  All processes
                      run in a separate process group.  When a background  job
                      completes,  the  shell prints a line containing its exit
                      status.
              -n      Read commands but do not execute them.  This may be used
                      to check a shell script for syntax errors.  This is  ig-
                      nored by interactive shells.
              -o option-name
                      The option-name can be one of the following:
                      allexport
                              Same as -a.
                      braceexpand
                              Same as -B.
                      emacs   Use  an  emacs-style command line editing inter-
                              face.  This is enabled by default when the shell
                              is interactive, unless the shell is started with
                              the --noediting option.  This also  affects  the
                              editing interface used for read -e.
                      errexit Same as -e.
                      errtrace
                              Same as -E.
                      functrace
                              Same as -T.
                      hashall Same as -h.
                      histexpand
                              Same as -H.
                      history Enable  command history, as described in bash(1)
                              under HISTORY.  This option is on by default  in
                              interactive shells.
                      ignoreeof
                              The  effect  is as if the shell command had been
                              executed (see Shell Variables in bash(1)).
                      keyword Same as -k.
                      monitor Same as -m.
                      noclobber
                              Same as -C.
                      noexec  Same as -n.
                      noglob  Same as -f.
                      nolog   Currently ignored.
                      notify  Same as -b.
                      nounset Same as -u.
                      onecmd  Same as -t.
                      physical
                              Same as -P.
                      pipefail
                              If set, the return value of a  pipeline  is  the
                              value  of  the  last (rightmost) command to exit
                              with a non-zero status, or zero if all  commands
                              in  the pipeline exit successfully.  This option
                              is disabled by default.
                      posix   Enable posix mode; change the behavior  of  bash
                              where  the  default  operation  differs from the
                              POSIX standard to match the standard.   See  SEE
                              ALSO  in  bash(1)  for a reference to a document
                              that details how posix mode affects  bash's  be-
                              havior.
                      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,  set  prints  the
                      current  shell  option settings.  If +o is supplied with
                      no option-name, set prints a series of set  commands  to
                      recreate  the  current  option  settings on the standard
                      output.
              -p      Turn on privileged mode.  In this mode, the  shell  does
                      not  read  the $ENV and $BASH_ENV files, shell functions
                      are not inherited from the environment,  and  the  SHEL-
                      LOPTS,  BASHOPTS,  CDPATH,  and GLOBIGNORE 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.
              -r      Enable restricted shell mode.  This option cannot be un-
                      set once it has been set.
              -t      Exit after reading and executing one command.
              -u      Treat unset variables and parameters other than the spe-
                      cial  parameters and or array variables subscripted with
                      or 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  in-
                      teractive, exits with a non-zero status.
              -v      Print shell input lines as they are read.
              -x      After  expanding  each simple command, for command, case
                      command, select command, or arithmetic for command, dis-
                      play the expanded value of PS4, followed by the  command
                      and  its  expanded arguments or associated word list, to
                      the standard error.
              -B      The shell performs brace expansion (see Brace  Expansion
                      in bash(1)).  This is on by default.
              -C      If  set,  bash  does not overwrite an existing file with
                      the >, >&, and  <>  redirection  operators.   Using  the
                      redirection  operator >| instead of > will override this
                      and force the creation of an output file.
              -E      If set, any trap on ERR is inherited by shell functions,
                      command substitutions, and commands executed in  a  sub-
                      shell  environment.  The ERR trap is normally not inher-
                      ited in such cases.
              -H      Enable !  style history substitution.  This option is on
                      by default when the shell is interactive.
              -P      If set, the shell does not resolve symbolic  links  when
                      executing  commands  such  as cd that change the current
                      working  directory.   It  uses  the  physical  directory
                      structure instead.  By default, bash follows the logical
                      chain  of  directories  when  performing  commands which
                      change the current directory.
              -T      If set, any traps on DEBUG and RETURN are  inherited  by
                      shell functions, command substitutions, and commands ex-
                      ecuted  in a subshell environment.  The DEBUG and RETURN
                      traps are normally not inherited in such cases.
              --      If no arguments follow this option, unset the positional
                      parameters.  Otherwise, set the positional parameters to
                      the args, even if some of them begin with a -.
              -       Signal the end of options, and assign all remaining args
                      to the positional parameters.  The -x and -v options are
                      turned off.  If there are no args, the positional  para-
                      meters remain unchanged.

              The  options are off by default unless otherwise noted.  Using +
              rather than - causes these options to be turned  off.   The  op-
              tions can also be specified as arguments to an invocation of the
              shell.   The current set of options may be found in $-.  The re-
              turn status is always zero unless an invalid option  is  encoun-
              tered.

       shift [n]
              Rename positional parameters from n+1 ... 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  positional  parameters  are
              not  changed.   The  return  status is greater than zero if n is
              greater than $# or less than zero; otherwise 0.

       shopt [-pqsu] [-o] [optname ...]
              Toggle the values of settings controlling optional shell  behav-
              ior.   The settings can be either those listed below, or, if the
              -o option is used, those available with the -o option to the set
              builtin command.

              With no options, or with the -p option, display a  list  of  all
              settable  options,  with an indication of whether or not each is
              set; if any optnames are supplied, the output is  restricted  to
              those options.  The -p option displays output 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 multi-
                     ple optname arguments are supplied with  -q,  the  return
                     status is zero if all optnames are enabled; non-zero oth-
                     erwise.
              -o     Restricts  the  values of optname to be those defined for
                     the -o option to the set builtin.

              If either -s or -u is used  with  no  optname  arguments,  shopt
              shows  only  those options which are set or unset, respectively.
              Unless otherwise noted, the shopt options are  disabled  (unset)
              by default.

              The  return  status when listing options is zero if all optnames
              are enabled, non-zero otherwise.  When setting or unsetting  op-
              tions,  the  return  status  is  zero unless an optname is not a
              valid shell option.

              The list of shopt options is:

              array_expand_once
                      If set, the shell suppresses multiple evaluation of  as-
                      sociative and indexed array subscripts during arithmetic
                      expression evaluation, while executing builtins that can
                      perform   variable   assignments,  and  while  executing
                      builtins that perform array dereferencing.
              assoc_expand_once
                      Deprecated; a synonym for array_expand_once.
              autocd  If set, a command name that is the name of  a  directory
                      is  executed  as  if it were the argument to the cd com-
                      mand.  This option is only used by interactive shells.
              bash_source_fullpath
                      If set, filenames added to the BASH_SOURCE  array  vari-
                      able  are  converted  to full pathnames (see Shell Vari-
                      ables above).
              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, the cd command attempts to correct minor  errors
                      in  the spelling of a directory component.  Minor errors
                      include transposed characters, a missing character,  and
                      one extra character.  If cd corrects the directory name,
                      it  prints  the corrected filename, and the command pro-
                      ceeds.  This option is only used by interactive shells.
              checkhash
                      If set, bash checks that a command found in the hash ta-
                      ble exists before trying to execute  it.   If  a  hashed
                      command  no  longer  exists, bash performs a normal path
                      search.
              checkjobs
                      If set, bash lists the status of any stopped and running
                      jobs before exiting an interactive shell.  If  any  jobs
                      are running, bash defers the exit until a second exit is
                      attempted  without  an intervening command (see JOB CON-
                      TROL in bash(1)).  The shell always postpones exiting if
                      any jobs are stopped.
              checkwinsize
                      If set, bash checks the window size after each  external
                      (non-builtin)  command  and,  if  necessary, updates the
                      values of LINES and COLUMNS, using the  file  descriptor
                      associated  with the standard error if it is a terminal.
                      This option is enabled by default.
              cmdhist If set, bash attempts to save all lines of  a  multiple-
                      line  command  in  the  same history entry.  This allows
                      easy re-editing of multi-line commands.  This option  is
                      enabled  by  default,  but only has an effect if command
                      history is enabled, as described in bash(1)  under  HIS-
                      TORY.
              compat31
              compat32
              compat40
              compat41
              compat42
              compat43
              compat44
                      These  control aspects of the shell's compatibility mode
                      (see SHELL COMPATIBILITY MODE in bash(1)).
              complete_fullquote
                      If set, bash quotes all shell  metacharacters  in  file-
                      names  and  directory  names when performing completion.
                      If not set, bash removes metacharacters such as the dol-
                      lar sign from the set of characters that will be  quoted
                      in  completed filenames when these metacharacters appear
                      in shell variable references in words to  be  completed.
                      This  means that dollar signs in variable names that ex-
                      pand to directories will not  be  quoted;  however,  any
                      dollar  signs appearing in filenames will not be quoted,
                      either.  This is active only when bash  is  using  back-
                      slashes  to quote completed filenames.  This variable is
                      set by default, which is the default  bash  behavior  in
                      versions through 4.2.
              direxpand
                      If  set,  bash replaces directory names with the results
                      of word expansion when performing  filename  completion.
                      This  changes  the  contents  of  the  readline  editing
                      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  ini-
                      tially supplied does not exist.
              dotglob If  set, bash includes filenames beginning with a in the
                      results of pathname expansion.  The filenames .  and  ..
                      must  always  be  matched explicitly, even if dotglob is
                      set.
              execfail
                      If set, a non-interactive shell will not exit if it can-
                      not execute the file specified as  an  argument  to  the
                      exec  builtin.   An  interactive  shell does not exit if
                      exec fails.
              expand_aliases
                      If set, aliases are expanded as described in bash(1) un-
                      der ALIASES.  This option is enabled by default for  in-
                      teractive shells.
              extdebug
                      If  set at shell invocation, or in a shell startup file,
                      arrange to execute the debugger profile before the shell
                      starts, identical to the --debugger option.  If set  af-
                      ter  invocation,  behavior intended for use by debuggers
                      is enabled:
                      1.     The -F option to the declare builtin displays the
                             source file name and line number corresponding to
                             each function name supplied as an argument.
                      2.     If the command run by the DEBUG  trap  returns  a
                             non-zero  value,  the next command is skipped and
                             not executed.
                      3.     If the command run by the DEBUG  trap  returns  a
                             value  of 2, and the shell is executing in a sub-
                             routine (a shell function or a shell script  exe-
                             cuted  by  the  .  or source builtins), the shell
                             simulates a call to return.
                      4.     BASH_ARGC and BASH_ARGV are updated as  described
                             in their descriptions in bash(1)).
                      5.     Function  tracing  is  enabled: command substitu-
                             tion, shell functions, and subshells invoked with
                             ( command ) inherit the DEBUG and RETURN traps.
                      6.     Error tracing is enabled:  command  substitution,
                             shell  functions,  and  subshells  invoked with (
                             command ) inherit the ERR trap.
              extglob If set, enable the extended  pattern  matching  features
                      described in bash(1) under Pathname Expansion.
              extquote
                      If  set, $string and $string quoting is performed within
                      ${parameter} expansions enclosed in double quotes.  This
                      option is enabled by default.
              failglob
                      If set, patterns which fail to  match  filenames  during
                      pathname expansion result in an expansion error.
              force_fignore
                      If  set,  the  suffixes  specified  by the FIGNORE shell
                      variable cause words to be ignored when performing  word
                      completion even if the ignored words are the only possi-
                      ble  completions.   See Shell Variables in bash(1) for a
                      description of FIGNORE.  This option is enabled  by  de-
                      fault.
              globasciiranges
                      If  set,  range  expressions  used  in  pattern matching
                      bracket expressions (see Pattern  Matching  in  bash(1))
                      behave as if in the traditional C locale when performing
                      comparisons.   That  is,  pattern matching does not take
                      the current locale's collating sequence into account, so
                      b will not collate between A and B, and  upper-case  and
                      lower-case ASCII characters will collate together.
              globskipdots
                      If  set,  pathname  expansion will never match the file-
                      names . and .. even if the pattern begins  with  a  This
                      option is enabled by default.
              globstar
                      If set, the pattern ** used in a pathname expansion con-
                      text  will  match all files and zero or more directories
                      and subdirectories.  If the pattern is followed by a  /,
                      only directories and subdirectories match.
              gnu_errfmt
                      If set, shell error messages are written in the standard
                      GNU error message format.
              histappend
                      If  set,  the history list is appended to the file named
                      by the value of the HISTFILE variable when the shell ex-
                      its, rather than overwriting the file.
              histreedit
                      If set, and readline is being used, the  user  is  given
                      the  opportunity  to  re-edit a failed history substitu-
                      tion.
              histverify
                      If set, and readline is being used, the results of  his-
                      tory  substitution  are  not  immediately  passed to the
                      shell parser.  Instead, the  resulting  line  is  loaded
                      into the readline editing buffer, allowing further modi-
                      fication.
              hostcomplete
                      If set, and readline is being used, bash will attempt to
                      perform  hostname  completion when a word containing a @
                      is being completed (see  Completing  under  READLINE  in
                      bash(1)).  This is enabled by default.
              huponexit
                      If set, bash will send SIGHUP to all jobs when an inter-
                      active login shell exits.
              inherit_errexit
                      If  set,  command substitution inherits the value of the
                      errexit option, instead of unsetting it in the  subshell
                      environment.   This option is enabled when posix mode is
                      enabled.
              interactive_comments
                      In an interactive shell, a word beginning with #  causes
                      that  word  and all remaining characters on that line to
                      be ignored, as in a non-interactive shell (see  COMMENTS
                      in bash(1)).  This option is enabled by default.
              lastpipe
                      If  set,  and  job control is not active, the shell runs
                      the last command of a pipeline not executed in the back-
                      ground in the current shell environment.
              lithist If set, and the cmdhist option  is  enabled,  multi-line
                      commands are saved to the history with embedded newlines
                      rather than using semicolon separators where possible.
              localvar_inherit
                      If set, local variables inherit the value and attributes
                      of a variable of the same name that exists at a previous
                      scope before any new value is assigned.  The nameref at-
                      tribute is not inherited.
              localvar_unset
                      If  set,  calling  unset  on local variables in previous
                      function scopes marks them so  subsequent  lookups  find
                      them unset until that function returns.  This is identi-
                      cal  to the behavior of unsetting local variables at the
                      current function scope.
              login_shell
                      The shell sets this option if it is started as  a  login
                      shell (see INVOCATION in bash(1)).  The value may not be
                      changed.
              mailwarn
                      If  set,  and  a file that bash is checking for mail has
                      been accessed since the last time it was  checked,  bash
                      displays the message
              no_empty_cmd_completion
                      If set, and readline is being used, bash does not search
                      PATH  for  possible  completions  when completion is at-
                      tempted on an empty line.
              nocaseglob
                      If set, bash matches  filenames  in  a  case-insensitive
                      fashion when performing pathname expansion (see Pathname
                      Expansion in bash(1)).
              nocasematch
                      If  set,  bash  matches  patterns  in a case-insensitive
                      fashion when performing matching while executing case or
                      [[ conditional commands, when performing pattern substi-
                      tution word expansions, or when filtering possible  com-
                      pletions as part of programmable completion.
              noexpand_translation
                      If  set,  bash  encloses  the translated results of $...
                      quoting in single quotes instead of double  quotes.   If
                      the string is not translated, this has no effect.
              nullglob
                      If set, pathname expansion patterns which match no files
                      (see  Pathname  Expansion  in bash(1)) expand to nothing
                      and are removed, rather than expanding to themselves.
              patsub_replacement
                      If set, bash expands occurrences of & in the replacement
                      string of pattern substitution to the  text  matched  by
                      the  pattern,  as described under Parameter Expansion in
                      bash(1).  This option is enabled by default.
              progcomp
                      If set, enable the  programmable  completion  facilities
                      (see  Programmable  Completion in bash(1)).  This option
                      is enabled by default.
              progcomp_alias
                      If set, and programmable  completion  is  enabled,  bash
                      treats  a command name that doesn't have any completions
                      as a possible alias and attempts alias expansion.  If it
                      has an alias, bash attempts programmable completion  us-
                      ing the command word resulting from the expanded alias.
              promptvars
                      If set, prompt strings undergo parameter expansion, com-
                      mand  substitution,  arithmetic expansion, and quote re-
                      moval after being expanded as described in PROMPTING  in
                      bash(1).  This option is enabled by default.
              restricted_shell
                      The  shell  sets  this  option  if  it is started in re-
                      stricted mode (see RESTRICTED SHELL  in  bash(1)).   The
                      value  may  not  be changed.  This is not reset when the
                      startup files are executed, allowing the  startup  files
                      to discover whether or not a shell is restricted.
              shift_verbose
                      If  set,  the shift builtin prints an error message when
                      the shift count exceeds the number of positional parame-
                      ters.
              sourcepath
                      If set, the . (source) builtin uses the value of PATH to
                      find the directory containing the file  supplied  as  an
                      argument  when  the -p option is not supplied.  This op-
                      tion is enabled by default.
              varredir_close
                      If set, the shell automatically closes file  descriptors
                      assigned  using  the  {varname}  redirection syntax (see
                      REDIRECTION in bash(1)) instead  of  leaving  them  open
                      when the command completes.
              xpg_echo
                      If  set,  the  echo builtin expands backslash-escape se-
                      quences by default.  If the posix shell option  is  also
                      enabled, echo does not interpret any options.

       suspend [-f]
              Suspend  the execution of this shell until it receives a SIGCONT
              signal.  A login shell, or a shell without job control  enabled,
              cannot  be suspended; the -f option will override this and force
              the suspension.  The return status is 0 unless the  shell  is  a
              login  shell  or  job  control is not enabled and -f is not sup-
              plied.

       test expr
       [ expr ]
              Return a status of 0 (true) or 1 (false) depending on the evalu-
              ation of the conditional expression  expr.   Each  operator  and
              operand  must  be a separate argument.  Expressions are composed
              of the primaries described in bash(1) under CONDITIONAL  EXPRES-
              SIONS.  test does not accept any options, nor does it accept and
              ignore an argument of -- as signifying the end of options.

              Expressions  may  be  combined  using  the  following operators,
              listed in decreasing order of precedence.   The  evaluation  de-
              pends on the number of arguments; see below.  test uses operator
              precedence 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
                     normal operator precedence.
              expr1 -a expr2
                     True if both expr1 and expr2 are true.
              expr1 -o expr2
                     True if either expr1 or expr2 is true.

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

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

              When the shell is in posix mode, or if the expression is part of
              the [[ command, the < and > operators sort using the current lo-
              cale.  If the shell is not in posix mode, the test  and  [  com-
              mands sort lexicographically using ASCII ordering.

              The  historical operator-precedence parsing with 4 or more argu-
              ments can lead to ambiguities when it  encounters  strings  that
              look  like  primaries.  The POSIX standard has deprecated the -a
              and -o primaries and enclosing expressions  within  parentheses.
              Scripts  should  no longer use them.  It's much more reliable to
              restrict test invocations to a single primary,  and  to  replace
              uses of -a and -o with the shell's && and || list operators.

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

       trap [-lpP] [[action] sigspec ...]
              The action is a command that is read and executed when the shell
              receives any of the signals sigspec.  If action is  absent  (and
              there is a single sigspec) or -, each specified sigspec is reset
              to  the  value  it had when the shell was started.  If action is
              the null string the signal specified by each sigspec is  ignored
              by the shell and by the commands it invokes.

              If  no arguments are supplied, trap displays the actions associ-
              ated with each trapped signal as a set of trap commands that can
              be reused as shell input to restore the current signal  disposi-
              tions.   If  -p  is  given, and action is not present, then trap
              displays the actions associated with each sigspec  or,  if  none
              are supplied, for all trapped signals, as a set of trap commands
              that  can be reused as shell input to restore the current signal
              dispositions.  The -P option  behaves  similarly,  but  displays
              only  the actions associated with each sigspec argument.  -P re-
              quires at least one sigspec argument.  The -P or -p options  may
              be  used  in a subshell environment (e.g., command substitution)
              and, as long as they are used before trap is used  to  change  a
              signal's handling, will display the state of its parent's traps.

              The  -l  option  prints  a list of signal names and their corre-
              sponding numbers.  Each sigspec is either a signal name  defined
              in <signal.h>, or a signal number.  Signal names are case insen-
              sitive  and  the SIG prefix is optional.  If -l is supplied with
              no sigspec arguments, it prints a list of valid signal names.

              If a sigspec is EXIT (0), action is executed on  exit  from  the
              shell.   If  a sigspec is DEBUG, action is executed before every
              simple command, for command, case command,  select  command,  ((
              arithmetic  command, [[ conditional command, arithmetic for com-
              mand, and before the first command executes in a shell  function
              (see SHELL GRAMMAR in bash(1)).  Refer to the description of the
              extdebug  shell option (see shopt in bash(1)) for details of its
              effect on the DEBUG trap.  If a sigspec is RETURN, action is ex-
              ecuted each time a shell function or a script executed with  the
              . or source builtins finishes executing.

              If  a  sigspec  is  ERR,  action is executed whenever a pipeline
              (which may consist of a single simple command),  a  list,  or  a
              compound  command returns a non-zero exit status, subject to the
              following conditions.  The ERR  trap  is  not  executed  if  the
              failed command is part of the command list immediately following
              a while or until reserved word, part of the test in an if state-
              ment,  part  of a command executed in a && or || list except the
              command following the final && or ||, any command in a  pipeline
              but  the  last  (subject  to the state of the pipefail shell op-
              tion), or if the command's return value is being inverted  using
              !.  These are the same conditions obeyed by the errexit (-e) op-
              tion.

              When the shell is not interactive, signals ignored upon entry to
              the shell cannot be trapped or reset.  Interactive shells permit
              trapping signals ignored on entry.  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.

       true   Does nothing, returns a 0 status.

       type [-aftpP] name [name ...]
              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 executable file, re-
              spectively.  If the name is not found, type prints  nothing  and
              returns a non-zero exit status.

              If  the  -p  option is used, type either returns the pathname of
              the executable file that would be found by searching  $PATH  for
              name  or nothing if would not return file.  The -P option forces
              a PATH search for each name, even if would not return file.   If
              name is present in the table of hashed commands, -p and -P print
              the hashed value, which is not necessarily the file that appears
              first in PATH.

              If  the  -a  option  is used, type prints all of the places that
              contain a command named name.  This includes  aliases,  reserved
              words,  functions, and builtins, but the path search options (-p
              and -P) can be supplied to restrict  the  output  to  executable
              files.   type does not consult the table of hashed commands when
              using -a with -p, and only performs a PATH search for name.

              The -f option suppresses shell function lookup, as with the com-
              mand builtin.  type returns true if all  of  the  arguments  are
              found, false if any are not found.

       ulimit [-HS] -a
       ulimit [-HS] [-bcdefiklmnpqrstuvxPRT [limit]]
              Provides  control  over the resources available to the shell and
              to processes it starts, on systems that allow such control.

              The -H and -S options specify whether the hard or soft limit  is
              set for the given resource.  A hard limit cannot be increased by
              a non-root user once it is set; a soft limit may be increased up
              to  the value of the hard limit.  If neither -H nor -S is speci-
              fied, ulimit sets both the soft and hard limits.

              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, ulimit  prints
              the  current value of the soft limit of the resource, unless the
              -H option is given.  When more than one resource  is  specified,
              the  limit name and unit, if appropriate, are printed before the
              value.  Other options are interpreted as follows:
              -a     Report all current limits; no limits are set.
              -b     The maximum socket buffer size.
              -c     The maximum size of core files created.
              -d     The maximum size of a process's data segment.
              -e     The maximum scheduling priority (
              -f     The maximum size of files written by the  shell  and  its
                     children.
              -i     The maximum number of pending signals.
              -k     The maximum number of kqueues that may be allocated.
              -l     The maximum size that may be locked into memory.
              -m     The  maximum resident set size (many systems do not honor
                     this limit).
              -n     The maximum number of open file descriptors (most systems
                     do not allow this value to be set).
              -p     The pipe size in 512-byte blocks (this may not be set).
              -q     The maximum number of bytes in POSIX message queues.
              -r     The maximum real-time scheduling priority.
              -s     The maximum stack size.
              -t     The maximum amount of cpu time in seconds.
              -u     The maximum number of processes  available  to  a  single
                     user.
              -v     The  maximum  amount  of  virtual memory available to the
                     shell and, on some systems, to its children.
              -x     The maximum number of file locks.
              -P     The maximum number of pseudoterminals.
              -R     The maximum time  a  real-time  process  can  run  before
                     blocking, in microseconds.
              -T     The maximum number of threads.

              If  limit  is  supplied, and the -a option is not used, limit is
              the new value of the specified resource.  If no option  is  sup-
              plied, then -f is assumed.

              Values  are  in 1024-byte increments, except for -t, which is in
              seconds; -R, which is in microseconds; -p, which is in units  of
              512-byte  blocks; -P, -T, -b, -k, -n, and -u, which are unscaled
              values; and, when in  posix  mode,  -c  and  -f,  which  are  in
              512-byte  increments.   The return status is 0 unless an invalid
              option or argument is supplied, or an error occurs while setting
              a new limit.

       umask [-p] [-S] [mode]
              Set the user file-creation mask to mode.  If mode begins with  a
              digit, it is interpreted as an octal number; otherwise it is in-
              terpreted  as  a  symbolic mode mask similar to that accepted by
              chmod(1).  If mode is omitted, umask prints the current value of
              the mask.  The -S option without a mode argument prints the mask
              in a symbolic format; 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  zero
              if  the mode was successfully changed or if no mode argument was
              supplied, and non-zero otherwise.

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

       unset [-fv] [-n] [name ...]
              For each name, remove the corresponding  variable  or  function.
              If the -v option is given, each name refers to a shell variable,
              and  that  variable  is  removed.  If -f is specified, each name
              refers to a shell function, and the function definition  is  re-
              moved.   If  the  -n  option is supplied, and name is a variable
              with the nameref attribute, name will be unset rather  than  the
              variable  it  references.   -n has no effect if the -f option is
              supplied.  Read-only variables and functions may not  be  unset.
              When  variables  or functions are removed, they are also removed
              from the environment passed to subsequent commands.  If  no  op-
              tions  are supplied, each name refers to a variable; if there is
              no variable by that name, a function with that name, if any,  is
              unset.   Some  shell  variables  may  not  be  unset.  If any of
              BASH_ALIASES,  BASH_ARGV0,  BASH_CMDS,  BASH_COMMAND,  BASH_SUB-
              SHELL,   BASHPID,   COMP_WORDBREAKS,   DIRSTACK,  EPOCHREALTIME,
              EPOCHSECONDS, FUNCNAME, GROUPS, HISTCMD,  LINENO,  RANDOM,  SEC-
              ONDS,  or SRANDOM are unset, they lose their special properties,
              even if they are subsequently reset.  The exit  status  is  true
              unless a name is readonly or may not be unset.

       wait [-fn] [-p varname] [id ...]
              Wait for each specified child process id and return the termina-
              tion  status of the last id.  Each id may be a process ID pid or
              a job specification jobspec; if  a  jobspec  is  supplied,  wait
              waits for all processes in the job.

              If  no  options  or ids are supplied, wait waits for all running
              background jobs and the last-executed process  substitution,  if
              its process id is the same as $!, and the return status is zero.

              If  the  -n  option  is  supplied, wait waits for any one of the
              given ids or, if no ids are supplied, any job or process substi-
              tution, to complete and returns its exit status.  If none of the
              supplied ids is a child of the shell, or if no ids are  supplied
              and  the  shell has no unwaited-for children, the exit status is
              127.

              If the -p option is supplied, wait assigns the  process  or  job
              identifier  of  the job for which the exit status is returned to
              the variable varname named by the option  argument.   The  vari-
              able,  which cannot be readonly, will be unset initially, before
              any assignment.  This is useful only when used with the  -n  op-
              tion.

              Supplying  the  -f  option,  when job control is enabled, forces
              wait to wait for each id to terminate before returning its  sta-
              tus, instead of returning when it changes status.

              If  none  of  the  ids  specify  one of the shell's active child
              processes, the return status is 127.  If wait is interrupted  by
              a  signal,  any varname will remain unset, and the return status
              will be greater than 128, as described under SIGNALS in bash(1).
              Otherwise, the return status is the exit status of the last id.

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

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

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

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

       Starting with bash-4.4, bash began deprecating older compatibility lev-
       els.  Eventually, the options will be removed in favor of BASH_COMPAT.

       Bash-5.0 was the final version for which there was an individual  shopt
       option  for the previous version.  BASH_COMPAT is the only mechanism to
       control the compatibility level in versions newer than bash-5.0.

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

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

       compat32
              o      The < and > operators to the [[ command do  not  consider
                     the current locale when comparing strings; they use ASCII
                     ordering.

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

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

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

       compat43
              o      Word  expansion  errors  are  considered non-fatal errors
                     that cause the current command to  fail,  even  in  posix
                     mode  (the  default behavior is to make them fatal errors
                     that cause the shell to exit).
              o      When  executing  a  shell  function,   the   loop   state
                     (while/until/etc.)  is not reset, so break or continue in
                     that function will break or continue loops in the calling
                     context.  Bash-4.4 and later reset the loop state to pre-
                     vent this.

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

       compat50
              o      Bash-5.1 changed the way $RANDOM is generated  to  intro-
                     duce  slightly more randomness.  If the shell compatibil-
                     ity level is set to 50 or lower, it reverts to the method
                     from bash-5.0 and previous versions, so seeding the  ran-
                     dom  number generator by assigning a value to RANDOM will
                     produce the same sequence as in bash-5.0.
              o      If the command hash table is empty, bash  versions  prior
                     to  bash-5.1 printed an informational message to that ef-
                     fect, even when producing output that can  be  reused  as
                     input.   Bash-5.1 suppresses that message when the -l op-
                     tion is supplied.

       compat51
              o      The unset builtin treats attempts  to  unset  array  sub-
                     scripts  @ and * differently depending on whether the ar-
                     ray is indexed or associative, and  differently  than  in
                     previous versions.
              o      Arithmetic commands ( ((...)) ) and the expressions in an
                     arithmetic for statement can be expanded more than once.
              o      Expressions  used as arguments to arithmetic operators in
                     the [[ conditional command  can  be  expanded  more  than
                     once.
              o      The  expressions  in  substring parameter brace expansion
                     can be expanded more than once.
              o      The expressions in the $((...)) word expansion can be ex-
                     panded more than once.
              o      Arithmetic expressions used as indexed  array  subscripts
                     can be expanded more than once.
              o      test  -v,  when  given an argument of A[@], where A is an
                     existing associative array, will return true if the array
                     has any set elements.  Bash-5.2 will look for and  report
                     on a key named @.
              o      The  ${parameter[:]=value}  word  expansion  will  return
                     value, before any variable-specific transformations  have
                     been performed (e.g., converting to lowercase).  Bash-5.2
                     will return the final value assigned to the variable.
              o      Parsing  command substitutions will behave as if extended
                     globbing (see the description of the shopt builtin above)
                     is enabled, so that parsing a command  substitution  con-
                     taining an extglob pattern (say, as part of a shell func-
                     tion)  will  not fail.  This assumes the intent is to en-
                     able extglob before the command is executed and word  ex-
                     pansions  are  performed.  It will fail at word expansion
                     time if extglob hasn't been enabled by the time the  com-
                     mand is executed.

       compat52
              o      The  test  builtin uses its historical algorithm to parse
                     parenthesized subexpressions when given five or more  ar-
                     guments.
              o      If  the  -p or -P option is supplied to the bind builtin,
                     bind treats any arguments remaining after option process-
                     ing as bindable command names, and displays any  key  se-
                     quences  bound to those commands, instead of treating the
                     arguments as key sequences to bind.

SEE ALSO
       bash(1), sh(1)

GNU Bash 5.2                    2023 January 27               BASH_BUILTINS(1)
