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
              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 the -p option is sup-
              plied, export prints a list of names of all  exported  variables
              on the standard output.

              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)
