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.

       ..  filename [arguments]
       source filename [arguments]
              Read and execute commands from filename in the current shell en-
              vironment and return the exit status of the  last  command  exe-
              cuted  from  filename.   If  filename  does not contain a slash,
              filenames in PATH are used  to  find  the  directory  containing
              filename, but filename does not need to be executable.  The file
              searched  for  in PATH need not be executable.  When bash is not
              in posix mode, it searches the current directory if no  file  is
              found  in  PATH.   If the sourcepath option to the shopt builtin
              command is turned off, the PATH is not searched.  If  any  argu-
              ments  are  supplied, they become the positional parameters when
              filename is executed.  Otherwise the positional  parameters  are
              unchanged.   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  exe-
              cutes.  If -T is not set, and the sourced file changes the DEBUG
              trap,  the  new  value is retained when .. completes.  The return
              status is the status of  the  last  command  exited  within  the
              script (0 if no commands are executed), and false if filename is
              not found or cannot be read.

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

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

       bind [-m keymap] [-lpsvPSVX]
       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] 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  set  a  readline
              variable.  Each non-option argument is a command as it would ap-
              pear  in  a  readline  initialization 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 descrip-
              tions, output available to be re-read is formatted  as  commands
              that  would  appear  in  a  readline initialization file or that
              would be supplied as individual 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 re-read.
              -P     List current readline function names and bindings.
              -s     Display  readline  key  sequences bound to macros and the
                     strings they output in such a way that they  can  be  re-
                     read.
              -S     Display  readline  key  sequences bound to macros and the
                     strings they output.
              -v     Display readline variable names and values in such a  way
                     that they can be re-read.
              -V     List current readline variable names and values.
              -f filename
                     Read key bindings from filename.
              -q function
                     Query about which keys invoke the named function.
              -u function
                     Unbind all keys bound to the named function.
              -r keyseq
                     Remove any current binding for keyseq.
              -x keyseq[[:: ]]shell-command
                     Cause shell-command to be executed whenever keyseq is 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 quotes.  When shell-com-
                     mand is executed, the shell sets the READLINE_LINE  vari-
                     able  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_ARGU-
                     MENT  variable.   If there was no argument, that variable
                     is not set.  If the executed command changes the value of
                     any of READLINE_LINE, READLINE_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 in-
                     put.

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

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

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

       caller [expr]
              Returns the context of any active subroutine call (a shell func-
              tion or a script executed with the .. or source builtins).  With-
              out expr, caller displays the line number and source filename of
              the current subroutine call.  If a non-negative integer is  sup-
              plied as expr, caller displays the line number, subroutine name,
              and  source  file  corresponding to that position in the current
              execution call stack.  This extra information may be  used,  for
              example,  to print a stack trace.  The 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|[-P [-e]] [-@] [dir]
              Change the current directory to dir.  if dir  is  not  supplied,
              the  value of the HOME shell variable is the default.  The vari-
              able CDPATH defines the search path for the directory containing
              dir: 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., If dir begins with a slash (/), then CDPATH  is
              not used.  The -P option causes cd to use the physical directory
              structure  by  resolving symbolic links while traversing dir and
              before processing instances of .. in dir (see also the -P option
              to the set builtin command); the -L option forces symbolic links
              to be followed by resolving the link after processing  instances
              of .. in dir.  If .. appears in dir, it is processed by removing
              the  immediately previous pathname component from dir, back to a
              slash or the beginning of dir.  If the  -e  option  is  supplied
              with  -P,  and  the current working directory cannot be success-
              fully determined after a successful directory  change,  cd  will
              return  an unsuccessful 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 the directory change is attempted.  If a non-empty direc-
              tory name from CDPATH is used, or if -- is  the  first  argument,
              and the directory change is successful, the absolute pathname of
              the new working directory is written to the standard output.  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 ...]
              Run command with args  suppressing  the  normal  shell  function
              lookup.  Only builtin commands or commands found in the PATH are
              executed.   If the -p option is given, the search for command is
              performed using a default value for PATH that is  guaranteed  to
              find  all of the standard utilities.  If either the -V or -v op-
              tion is supplied, a description of command is printed.   The  -v
              option  causes  a single word indicating the command or filename
              used to invoke command to be displayed; the -V option produces a
              more verbose description.  If the -V or -v option  is  supplied,
              the  exit  status  is  0 if command was found, and 1 if not.  If
              neither option is supplied and an error occurred or command can-
              not be found, the exit status is 127.  Otherwise, the exit  sta-
              tus 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 sup-
              plied, compgen stores the generated completions 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.

              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  supplied,
              existing completion specifications are printed in a way that al-
              lows  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 com-
              mand completion; that is, completion attempted 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, completion 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 completion.  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 ignored; these completions only ap-
              ply to the case specified by the option.

              The  process  of  applying  these completion specifications when
              word completion is attempted 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  (like  adding  a  slash to directory
                              names, quoting special characters, or  suppress-
                              ing  trailing spaces).  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 any matches defined by  the  compspec  are
                              generated,  directory  name  completion  is  at-
                              tempted and any matches are added to the results
                              of the other actions.
              -A action
                      The action may be one of the  following  to  generate  a
                      list of possible completions:
                      alias   Alias names.  May also be specified as -a.
                      arrayvar
                              Array variable names.
                      binding Readline key binding names.
                      builtin Names  of  shell  builtin commands.  May also be
                              specified as -b.
                      command Command names.  May also be specified as -c.
                      directory
                              Directory names.  May also be specified as -d.
                      disabled
                              Names of disabled shell builtins.
                      enabled Names of enabled shell builtins.
                      export  Names of exported shell variables.  May also  be
                              specified as -e.
                      file    File names.  May also be specified as -f.
                      function
                              Names of shell functions.
                      group   Group names.  May also be specified as -g.
                      helptopic
                              Help topics as accepted by the help builtin.
                      hostname
                              Hostnames,  as  taken from the file specified by
                              the HOSTFILE shell variable.
                      job     Job names, if job control is active.   May  also
                              be specified as -j.
                      keyword Shell  reserved words.  May also be specified as
                              -k.
                      running Names of running jobs, if job control is active.
                      service Service names.  May also be specified as -s.
                      setopt  Valid arguments for the -o  option  to  the  set
                              builtin.
                      shopt   Shell  option  names  as  accepted  by the shopt
                              builtin.
                      signal  Signal names.
                      stopped Names of stopped jobs, if job control is active.
                      user    User names.  May also be specified as -u.
                      variable
                              Names of all shell variables.  May also be 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 ($$11) is the name of the command whose ar-
                      guments are being completed, the second argument ($$22) is
                      the word being completed, and the third argument ($$33) is
                      the word preceding the word being completed on the  cur-
                      rent  command line.  When it finishes, the possible com-
                      pletions are retrieved from the value of  the  COMPREPLY
                      array variable.
              -G globpat
                      The  pathname  expansion  pattern globpat is expanded to
                      generate the possible completions.
              -P prefix
                      prefix is added at the beginning of each  possible  com-
                      pletion after all other options have been applied.
              -S suffix
                      suffix is appended to each possible completion after all
                      other options have been applied.
              -W wordlist
                      The  wordlist  is  split using the characters in the IFS
                      special variable as delimiters, and each resultant  word
                      is  expanded.  Shell quoting is honored within wordlist,
                      in order 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 the word being completed.
              -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] [++oo 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 given, display the completion op-
              tions 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  op-
              tions  should  apply to the command completion; that is, comple-
              tion attempted on a command for which no completion  has  previ-
              ously been defined.  The -E option indicates that other supplied
              options  should apply to command completion; that is, completion
              attempted on a blank line.  The -I option indicates  that  other
              supplied  options 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 completion.

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

       continue [_n]
              Resume the next iteration of the enclosing for, while, until, or
              select loop.  If _n is specified, resume  at  the  _nth  enclosing
              loop.   _n  must be >= 1.  If _n is greater than the number of en-
              closing 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.  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, it
              will display the attributes and values of all  variables  having
              the attributes specified by the additional options.  If no other
              options  are  supplied with -p, declare will display the attrib-
              utes and values of all shell variables.  The -f option will  re-
              strict  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 func-
              tion.   It  is ignored in all other cases.  The -I option causes
              local variables to inherit the attributes  (except  the  nameref
              attribute) and value of any existing variable 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  variables  with  the  specified  at-
              tribute or to give variables attributes:
              -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     Use function names only.
              -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 names for export to subsequent commands via the  en-
                     vironment.

              Using  instead  of turns off the attribute instead, with the ex-
              ceptions that +a and +A may not be used to destroy  array  vari-
              ables  and +r will not remove the readonly attribute.  When used
              in a function, declare and typeset make each name local, as with
              the local command, unless the -g option is supplied.  If a vari-
              able name is followed by =value, the value of  the  variable  is
              set  to  value.  When using -a or -A and the compound 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  vari-
              able  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, displays the list of currently  remembered  di-
              rectories.   The default display is on a single line with direc-
              tory 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 direc-
              tory in the stack.
              -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] [jobspec ... | pid ... ]
              Without  options,  remove  each jobspec from the table of active
              jobs.  If jobspec is not present, and neither the -a nor the  -r
              option  is  supplied, the current job is used.  If the -h option
              is given, each jobspec is not removed from  the  table,  but  is
              marked  so  that  SIGHUP is not sent to the job if the shell re-
              ceives a SIGHUP.  If no jobspec is supplied, the -a option means
              to remove or mark all jobs; the -r option without a jobspec  ar-
              gument restricts operation to running jobs.  The return value is
              0 unless a jobspec does not specify a valid job.

       echo [-neE] [arg ...]
              Output  the  args,  separated  by spaces, followed by a newline.
              The return status is 0 unless a write error occurs.   If  -n  is
              specified, the trailing newline is suppressed.  If the -e option
              is  given,  interpretation  of  the  following backslash-escaped
              characters is enabled.  The -E option disables  the  interpreta-
              tion  of these escape characters, even on systems where they are
              interpreted by default.  The xpg_echo shell option may  be  used
              to  dynamically determine whether or not echo interprets any op-
              tions and expands these escape characters by default.  echo does
              not interpret ---- to mean the end of  options.   echo  interprets
              the following escape sequences:
              \a     alert (bell)
              \b     backspace
              \c     suppress further output
              \e
              \E     an escape character
              \f     form feed
              \n     new line
              \r     carriage return
              \t     horizontal tab
              \v     vertical tab
              \\\\     backslash
              \\00nnn  the  eight-bit  character  whose value is the octal value
                     nnn (zero to three octal digits)
              \\xx_H_H   the eight-bit character whose value  is  the  hexadecimal
                     value HH (one or two hex digits)
              \\uuHHHH the  Unicode (ISO/IEC 10646) character whose value is the
                     hexadecimal value HHHH (one to four hex digits)
              \\UUHHHHHHHH
                     the Unicode (ISO/IEC 10646) character whose value is  the
                     hexadecimal value HHHHHHHH (one to eight hex digits)

       enable [-a] [-dnps] [-f filename] [name ...]
              Enable  and disable builtin shell commands.  Disabling a builtin
              allows a disk command which has the same name as a shell builtin
              to be executed without specifying a full pathname,  even  though
              the  shell  normally searches for builtins before disk commands.
              If -n is used, each name is disabled; otherwise, names  are  en-
              abled.   For  example, to use the test binary found via the PATH
              instead of the shell builtin version, run The -f option means to
              load the new builtin command name from shared  object  filename,
              on  systems  that  support  dynamic  loading.  Bash will use the
              value of the BASH_LOADABLES_PATH variable as  a  colon-separated
              list of directories in which to search for filename, if filename
              does  not contain a slash.  The default 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 no
              name arguments are given, or if the -p  option  is  supplied,  a
              list  of  shell builtins is printed.  With no other option argu-
              ments, the list consists of all enabled shell builtins.   If  -n
              is  supplied, only disabled builtins are printed.  If -a is sup-
              plied, the list printed includes all builtins, with  an  indica-
              tion  of whether or not each is enabled.  If -s is supplied, the
              output is restricted to the POSIX special builtins.  If  no  op-
              tions  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 ...]
              The args are read and concatenated together into a  single  com-
              mand.   This command is then read and executed by the shell, and
              its exit status is returned as the value of eval.  If there  are
              no args, or only null arguments, eval returns 0.

       exec [-cl] [-a name] [command [arguments]]
              If  command is specified, it replaces the shell.  No new process
              is created.  The arguments become the arguments to command.   If
              the -l option is supplied, the shell places a dash at the begin-
              ning of the zeroth argument passed to command.  This is what lo-
              gin(1)  does.   The -c option causes command to be executed with
              an empty environment.  If -a is supplied, the shell passes  name
              as the zeroth argument to the executed command.  If command can-
              not  be executed for some reason, a non-interactive shell exits,
              unless the execfail shell option is enabled.  In that  case,  it
              returns  failure.   An  interactive shell returns failure 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 redirection error, the return status is 1.

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

       export [-fn] [name[=word]] ...
       export -p
              The supplied names are marked for automatic export to the  envi-
              ronment  of subsequently executed commands.  If the -f option is
              given, the names refer to functions.  If no names are given,  or
              if  the  -p  option is supplied, a list of names of all exported
              variables is printed.  The -n option causes the export  property
              to be removed from each name.  If a variable name is followed by
              =word, the value of the variable is set to word.  export returns
              an exit status of 0 unless an invalid option is encountered, one
              of  the  names is not a valid shell variable name, or -f is sup-
              plied 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); otherwise 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 spec-
              ified, it is set to the previous command for editing and -16 for
              listing.

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

              In the second form, command is re-executed after  each  instance
              of  pat  is replaced by rep.  Command is interpreted the same as
              first above.  A useful alias to use with this 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 0 unless  an  in-
              valid  option  is  encountered  or first or last specify history
              lines out of range.  If the -e option is  supplied,  the  return
              value is the value of the last command executed or failure if an
              error occurs with the temporary file of commands.  If the second
              form  is  used, the return status is that of the command re-exe-
              cuted, unless cmd does not specify  a  valid  history  line,  in
              which case fc returns failure.

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

       getopts optstring name [arg ...]
              getopts  is used by shell procedures to parse positional parame-
              ters.  optstring contains the option  characters  to  be  recog-
              nized;  if a character is followed by a colon, the option is ex-
              pected 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 op-
              tion requires an argument, getopts places that argument into the
              variable OPTARG.  The shell does not reset OPTIND automatically;
              it  must  be  manually  reset  between multiple calls to getopts
              within the same shell invocation if a new set of  parameters  is
              to be used.

              When the end of options is encountered, getopts exits with a re-
              turn 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, silent error  reporting  is  used.   In
              normal  operation,  diagnostic messages are printed when invalid
              options or missing option arguments  are  encountered.   If  the
              variable  OPTERR  is  set  to  0, no error messages will be dis-
              played, even if the first character of optstring is not a colon.

              If 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, the full pathname of the command name
              is determined by searching the directories in $PATH  and  remem-
              bered.  Any previously-remembered pathname is discarded.  If the
              -p  option  is supplied, hash uses filename as the full filename
              of the command.  The -r option causes the shell  to  forget  all
              remembered  locations.   Assigning  to  the  PATH  variable also
              clears all hashed filenames.  The -d option causes the shell  to
              forget  the  remembered location of each name.  If the -t option
              is supplied, the full pathname to which each name corresponds is
              printed.  If multiple name arguments are supplied with  -t,  the
              name  is printed before the hashed full pathname.  The -l option
              causes output to be displayed in a format that may be reused  as
              input.   If  no  arguments are given, or if only -l is supplied,
              information about remembered commands is printed.  The  -t,  -d,
              and  -p options (the options that act on the name arguments) are
              mutually exclusive.  Only one will be active.  If more than  one
              is supplied, -t has higher priority than -p, and both are higher
              priority  than  -d.   The return status is true unless a name is
              not found or an invalid option is supplied.

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

              The return status is 0 unless no command matches pattern.

       history [[_n]]
       history -c
       history -d offset
       history -d start-end
       history -anrw [filename]
       history -p arg [arg ...]
       history -s arg [arg ...]
              With no options, display the command history list with line num-
              bers.  Lines listed with a ** have been modified.  An argument of
              _n  lists only the last _n lines.  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.  No intervening blank is  printed  between
              the  formatted  time stamp and the history line.  If filename is
              supplied, it is used as the name of the history  file;  if  not,
              the  value of HISTFILE is used.  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.
              -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  into the current history list.  These are lines ap-
                     pended to the history file since  the  beginning  of  the
                     current bash session.
              -r     Read  the contents of the history file and append them to
                     the current history list.
              -w     Write the current history list to the history file, over-
                     writing the history file's contents.
              -p     Perform history substitution on the  following  args  and
                     display  the  result  on  the  standard output.  Does not
                     store the results in the history list.  Each arg must  be
                     quoted to disable normal history expansion.
              -s     Store  the  args  in  the history list as a single entry.
                     The last command in the history list  is  removed  before
                     the args are added.

              If  the  HISTTIMEFORMAT variable is set, the time stamp informa-
              tion associated with each history entry is written to  the  his-
              tory  file, marked with the history comment character.  When the
              history file is read, lines beginning with the  history  comment
              character  followed  immediately  by  a digit are interpreted as
              timestamps for the 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 sup-
              plied 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 given, output is restricted to  information  about
              that  job.   The  return status is 0 unless an invalid option is
              encountered or an invalid jobspec is supplied.

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

       kill [-s sigspec | -n signum | --sigspec] [pid | jobspec] ...
       kill -l|-L [sigspec | exit__status]
              Send the signal named by sigspec  or  signum  to  the  processes
              named  by  pid or jobspec.  sigspec is either a case-insensitive
              signal name such as SIGKILL (with or without the SIG prefix)  or
              a  signal  number; signum is a signal number.  If sigspec is not
              present, then SIGTERM is assumed.  An argument of -l  lists  the
              signal  names.   If any arguments are supplied when -l is given,
              the names of the signals  corresponding  to  the  arguments  are
              listed, and the return status is 0.  The exit__status argument to
              -l  is  a  number  specifying either a signal number or the exit
              status of a process terminated by a signal.  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 op-
              tion is encountered.

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

       local [option] [name[=value] ... | - ]
              For  each  argument, a local variable named name is created, and
              assigned value.  The option can be any of the  options  accepted
              by declare.  When local is used within a function, it causes the
              variable  name  to have a visible scope restricted to that func-
              tion and its children.  If name is -, the set of  shell  options
              is  made  local to the function in which local is invoked: shell
              options changed using the set builtin inside the function  after
              the call to local are restored to their original values when the
              function returns.  The restore is effected 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.  It is an error to use
              local when not within a function.  The return status is 0 unless
              local is used outside a function, an invalid name  is  supplied,
              or name is a readonly variable.

       logout Exit a login shell.

       mapfile [-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 into the indexed array vari-
              able array, or from file descriptor fd if the -u option is  sup-
              plied.   The variable MAPFILE is the default array.  Options, if
              supplied, have the following meanings:
              -d     The first character of delim is used  to  terminate  each
                     input  line,  rather than newline.  If delim is the empty
                     string, mapfile will terminate a line when it reads a NUL
                     character.
              -n     Copy at most count lines.  If count is 0, all  lines  are
                     copied.
              -O     Begin  assigning  to  array at index origin.  The default
                     index is 0.
              -s     Discard the first count lines read.
              -t     Remove a trailing 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 successfully unless an invalid option or option
              argument is supplied, array is invalid or  unassignable,  or  if
              array is not an indexed array.

       popd [-nn] [+_n] [-_n]
              Removes entries from the directory stack.  The elements are num-
              bered  from  0  starting  at the first directory listed by dirs.
              With no arguments, popd  removes  the  top  directory  from  the
              stack, and changes to the new top directory.  Arguments, if sup-
              plied, have the following meanings:
              -n     Suppresses  the  normal change of directory when removing
                     directories from the stack, so that only the stack is ma-
                     nipulated.
              ++_n     Removes 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     Removes 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 encoun-
              tered, the directory stack is empty, or a non-existent directory
              stack entry is specified.

              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 causes the output to be
              assigned to the variable var rather than being  printed  to  the
              standard output.

              The  format  is a character string which contains three types of
              objects: plain 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 csndiouxXe-
              EfFgGaA, printf interprets the following additional format spec-
              ifiers:
              %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 %%qq, but applies any supplied precision to the  argu-
                     ment before quoting it.
              %%((datefmt))TT
                     causes  printf  to  output the date-time string resulting
                     from using datefmt as a format  string  for  strftime(3).
                     The corresponding argument is an integer representing the
                     number  of seconds since the epoch.  Two special argument
                     values may be used: -1 represents the current  time,  and
                     -2  represents the time the shell was invoked.  If no ar-
                     gument is specified, conversion behaves as if -1 had been
                     given.  This is an exception to the usual  printf  behav-
                     ior.

              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.

              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 ASCII value of the following character.

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

              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 0 unless
              the directory stack  is  empty.   When  rotating  the  directory
              stack,  pushd returns 0 unless the directory stack is empty or a
              non-existent directory stack element is specified.

              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 ...]
              One line is read from the standard input, or from the  file  de-
              scriptor fd supplied as an argument to the -u option, split into
              words  as  described  in  bash (1) under Word Splitting, and the
              first word is assigned to the first name, the second word to the
              second name, and so on.  If there are more words than names, the
              remaining 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 IFS are used  to  split  the  line  into
              words  using  the  same  rules the shell uses for expansion (de-
              scribed in bash (1) under Word Splitting).  The backslash  char-
              acter (\\) may be used to remove any special meaning for the next
              character read and for line continuation.  Options, if supplied,
              have the following meanings:
              -a aname
                     The words are assigned to sequential indices of the array
                     variable aname, starting at 0.  aname is unset before any
                     new  values  are  assigned.  Other name arguments are ig-
                     nored.
              -d delim
                     The first character of delim is used to terminate the in-
                     put 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, text is
                     placed into the editing buffer before editing begins.
              -n nchars
                     read returns after reading nchars characters rather  than
                     waiting for a complete line of input, but honors a delim-
                     iter  if fewer than nchars characters are read before the
                     delimiter.
              -N nchars
                     read returns  after  reading  exactly  nchars  characters
                     rather  than waiting for a complete line of input, unless
                     EOF is encountered or read times out.  Delimiter  charac-
                     ters  encountered  in the input are not treated specially
                     and do not cause read to return until  nchars  characters
                     are  read.   The result is not split on the characters in
                     IFS; the intent is that the variable is assigned  exactly
                     the characters 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.  The prompt is
                     displayed 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 a complete
                     line of input (or a specified number  of  characters)  is
                     not  read within timeout seconds.  timeout may be a deci-
                     mal number with a fractional portion following the  deci-
                     mal  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, read saves any partial input read into
                     the specified variable name.  If timeout is 0,  read  re-
                     turns  immediately, without trying to read any data.  The
                     exit status is 0 if input is available on  the  specified
                     file  descriptor,  or  the read will return EOF, non-zero
                     otherwise.  The exit status is greater than  128  if  the
                     timeout is exceeded.
              -u fd  Read input from file descriptor fd.

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

              If no names are supplied, the line read, without the ending  de-
              limiter  but  otherwise  unmodified, is assigned to the variable
              REPLY.  The exit status is zero, unless end-of-file  is  encoun-
              tered,  read times out (in which case the status is greater than
              128), a variable assignment error (such as assigning to a  read-
              only variable) 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.  If the  -f  option
              is  supplied,  the  functions  corresponding to the names are so
              marked.  The -a option restricts the variables  to  indexed  ar-
              rays;  the  -A option restricts the variables to associative ar-
              rays.  If both options are supplied, -A takes precedence.  If no
              name arguments are given, or if the -p  option  is  supplied,  a
              list of all readonly names is printed.  The other options may be
              used  to  restrict the output to a subset of the set of readonly
              names.  The -p option causes output to be displayed in a  format
              that  may be reused as input.  If a variable name is followed by
              =word, the value of the variable is set  to  word.   The  return
              status  is 0 unless an invalid option is encountered, one of the
              names is not a valid shell variable name, or -f is supplied with
              a name that is not a function.

       return [_n]
              Causes a function to stop executing and return the value  speci-
              fied  by _n to its caller.  If _n is omitted, the return status is
              that of the last command executed in the function body.  If  re-
              turn is executed by a trap handler, the last command used to de-
              termine  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 exe-
              cuted by the trap handler before return was invoked.  If  return
              is  used outside a function, but during execution of a script by
              the ..  (source) command, it causes the shell to  stop  executing
              that  script  and return either _n or the exit status of the last
              command executed within the script as the  exit  status  of  the
              script.  If _n is supplied, the return value is its least signif-
              icant  8  bits.  The return status is non-zero if return is sup-
              plied a non-numeric argument, or is used outside a function  and
              not  during  execution  of a script by .. or source.  Any command
              associated with the RETURN trap is executed before execution re-
              sumes after the function or script.

       set [-abefhkmnptuvxBCEHPT] [-o option-name] [----] [--] [arg ...]
       set [+abefhkmnptuvxBCEHPT] [++oo 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 $$11,
              $$22, ..., $$_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.  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 keyword, part of the test following the
                      if or elif reserved words, part of any command  executed
                      in  a &&&& or |||| list except the command following the fi-
                      nal &&&& or ||||, any command in a pipeline but the last, or
                      if the command's return value is being inverted with  !!.
                      If  a  compound  command other than a subshell 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 envi-
                      ronment separately (see COMMAND EXECUTION ENVIRONMENT in
                      bash(1)), and may cause subshells to exit before execut-
                      ing 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   Change the behavior of bash  where  the  default
                              operation  differs  from  the  POSIX standard to
                              match the standard (posix mode).  See  SEE  ALSO
                              in  bash(1)  for  a reference to a document that
                              details how posix mode affects bash's behavior.
                      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 $ENV and
                      $BASH_ENV files are not processed, shell  functions  are
                      not  inherited  from the environment, and the SHELLOPTS,
                      BASHOPTS, CDPATH, and GLOBIGNORE variables, if they  ap-
                      pear  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 sup-
                      plied, these actions are taken and the effective user id
                      is set to the real user id.  If the -p  option  is  sup-
                      plied  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
                      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.   This  may  be
                      overridden when creating output files by using the redi-
                      rection operator >>|| instead of >>.
              -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, then the positional
                      parameters are unset.  Otherwise, the positional parame-
                      ters are set to the args, even if  some  of  them  begin
                      with a --.
              --       Signal  the  end of options, cause all remaining args to
                      be assigned to the positional parameters.  The -x and -v
                      options are turned off.  If there are no args, the posi-
                      tional parameters 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 true unless an invalid option is encoun-
              tered.

       shift [_n]
              The positional parameters from _n+1 ... are renamed  to  $$11  ........
              Parameters  represented by the numbers $$## down to $$##-_n+1 are un-
              set.  _n must be a non-negative number less than or equal to  $$##.
              If  _n is 0, no parameters are changed.  If _n is not given, it is
              assumed to be 1.  If _n is greater than $$##, the positional  para-
              meters  are not changed.  The return status is greater than zero
              if _n is greater than $$## 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, a list
              of all settable options is  displayed,  with  an  indication  of
              whether or not each is set; if optnames are supplied, the output
              is  restricted to those options.  The -p option causes output to
              be displayed in a form that may be reused as input.   Other  op-
              tions 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 given with -q, the return  sta-
                     tus  is zero if all optnames are enabled; non-zero other-
                     wise.
              -o     Restricts the values of optname to be those  defined  for
                     the -o option to the set builtin.

              If  either  -s  or  -u  is used with no optname arguments, 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.
              cdable_vars
                      If  set,  an  argument to the cd builtin command that is
                      not a directory is assumed to be the name of a  variable
                      whose value is the directory to change to.
              cdspell If set, minor errors in the spelling of a directory com-
                      ponent  in  a  cd command will be corrected.  The errors
                      checked for are transposed characters, a missing charac-
                      ter, and one character too many.   If  a  correction  is
                      found,  the  corrected filename is printed, and the com-
                      mand proceeds.  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, a normal path search  is  per-
                      formed.
              checkjobs
                      If set, bash lists the status of any stopped and running
                      jobs  before  exiting an interactive shell.  If any jobs
                      are running, this causes the exit to be deferred until a
                      second exit is attempted without an intervening  command
                      (see  JOB  CONTROL  in bash(1)).  The shell always post-
                      pones 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.  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
              compat50
                      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  command.   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:

                      11..     The -F option to the declare builtin displays the
                             source file name and line number corresponding to
                             each function name supplied as an argument.

                      22..     If the command run by the DEBUG  trap  returns  a
                             non-zero  value,  the next command is skipped and
                             not executed.

                      33..     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.

                      44..     BASH_ARGC and BASH_ARGV are updated as  described
                             in their descriptions in bash(1)).

                      55..     Function  tracing  is  enabled: command substitu-
                             tion, shell functions, and subshells invoked with
                             (( command )) inherit the DEBUG and RETURN traps.

                      66..     Error tracing is enabled:  command  substitution,
                             shell  functions,  and  subshells  invoked with ((
                             command )) inherit the ERR trap.

              extglob If set, the extended pattern matching features described
                      in bash(1) under Pathname Expansion are enabled.

              extquote
                      If set, $$string and $$string quoting is performed  within
                      $${{parameter}} expansions enclosed in double quotes.  This
                      option is enabled by default.

              failglob
                      If  set,  patterns  which fail to match filenames during
                      pathname expansion result in an expansion error.

              force_fignore
                      If set, the suffixes  specified  by  the  FIGNORE  shell
                      variable  cause words to be ignored when 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, the  current  locale's  collating
                      sequence  is  not taken into account, so bb will not col-
                      late between AA and  BB,  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, a user is given  the
                      opportunity to re-edit a failed history substitution.

              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
                      If set, allow a word beginning with ## to cause that word
                      and  all remaining characters on that line to be ignored
                      in an interactive shell (see COMMENTS 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 will not at-
                      tempt to search the PATH for possible  completions  when
                      completion is attempted on an empty line.

              nocaseglob
                      If  set,  bash  matches  filenames in a case-insensitive
                      fashion when 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, the programmable completion facilities (see Pro-
                      grammable  Completion in bash(1)) are enabled.  This op-
                      tion 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.  This option 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 can be used to 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 supplied.

       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.  Operator prece-
              dence is used when there are five or more arguments.
              !! expr True if expr is false.
              (( expr ))
                     Returns the value of expr.  This may be used to  override
                     the normal precedence of operators.
              expr1 -aa expr2
                     True if both expr1 and expr2 are true.
              expr1 -oo 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.   the  two-argument  test using the second and
                     third arguments.  If the first argument is exactly ((  and
                     the  fourth argument is exactly )), the result is the two-
                     argument test of the second and third arguments.   Other-
                     wise, 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.

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

       trap [-lp] [[action] sigspec ...]
              The action is a command that is read and executed when the shell
              receives signal(s) sigspec.  If action is absent (and there is a
              single sigspec) or --, each specified  signal  is  reset  to  its
              original  disposition  (the  value  it  had upon entrance to the
              shell).  If action is the null string the  signal  specified  by
              each  sigspec is ignored by the shell and by the commands it in-
              vokes.

              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 to
              trap may be used in a subshell environment (e.g.,  command  sub-
              stitution)  and, as long as they are used before trap is used to
              change a signal's handling, will display the state of  its  par-
              ent's traps.

              The  -l  option  causes trap to print a list of signal names and
              their corresponding numbers.  Each sigspec is  either  a  signal
              name  defined  in  <signal.h>, or a signal number.  Signal names
              are case insensitive and the SIG prefix is optional.

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

              If a sigspec is ERR, the command 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 keyword, part of the test in an  if  statement,
              part of a command executed in a &&&& or |||| list except the command
              following  the final &&&& or ||||, any command in a pipeline but the
              last, or if the command's return value is being  inverted  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 ...]
              With  no options, indicate how each name would be interpreted if
              used as a command name.  If the -t option is used, type prints a
              string which is one of alias,  keyword,  function,  builtin,  or
              file  if  name  is  an  alias,  shell  reserved  word, function,
              builtin, or executable disk file, respectively.  If the name  is
              not  found, then nothing is printed, and type returns a non-zero
              exit status.  If the -p option is used, type either returns  the
              name  of  the  executable  file that would be found by searching
              $PATH if name were specified as a command 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  a  command  is
              hashed, -p and -P print the hashed value, which is not necessar-
              ily  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 sup-
              plied 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 command  builtin.   type  re-
              turns  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 started by it, on systems that allow such control.
              The -H and -S options specify that the hard or soft limit is set
              for the given resource.  A hard limit cannot be increased  by  a
              non-root  user  once it is set; a soft limit may be increased up
              to the value of the hard limit.  If neither -H nor -S is  speci-
              fied, both the soft and hard limits are set.  The value of limit
              can be a number in the unit specified for the resource or one of
              the special values hard, soft, or unlimited, which stand for the
              current  hard  limit,  the current soft limit, and no limit, re-
              spectively.  If limit is omitted, the current value of the  soft
              limit of the resource is printed, unless the -H option is given.
              When  more  than  one  resource is specified, the limit name and
              unit, if appropriate, are printed before the value.   Other  op-
              tions are interpreted as follows:
              -a     All current limits are reported; 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 given, and the -a option is not used, limit  is  the
              new  value  of  the  specified resource.  If no option is given,
              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]
              The user file-creation mask is set to mode.  If mode begins with
              a digit, it is interpreted as an octal number; otherwise  it  is
              interpreted  as a symbolic mode mask similar to that accepted by
              chmod(1).  If mode is omitted, the current value of the mask  is
              printed.   The  -S  option causes the mask to be printed in sym-
              bolic form; the default output is an octal number.   If  the  -p
              option is supplied, and mode is omitted, the output is in a form
              that may be reused as input.  The return status is 0 if the mode
              was  successfully  changed  or if no mode argument was supplied,
              and false otherwise.

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

       unset [-fv] [-nn] [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.  Read-only variables may not be
              unset.  If -f is specified, each name refers to  a  shell  func-
              tion,  and the function definition is removed.  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.  If no  options  are
              supplied,  each  name refers to a variable; if there is no vari-
              able by that name, a function with that name, if any, is  unset.
              Each  unset variable or function is removed from the environment
              passed  to  subsequent  commands.   If  any   of   BASH_ALIASES,
              BASH_ARGV0,  BASH_CMDS,  BASH_COMMAND,  BASH_SUBSHELL,  BASHPID,
              COMP_WORDBREAKS, DIRSTACK,  EPOCHREALTIME,  EPOCHSECONDS,  FUNC-
              NAME,  GROUPS,  HISTCMD, LINENO, RANDOM, SECONDS, or SRANDOM are
              unset, they lose their special properties, even if they are sub-
              sequently reset.  The exit status is true unless a name is read-
              only or may not be unset.

       wait [-fn] [-p varname] [id ...]
              Wait for each specified child process and return its termination
              status.  Each id may be a process ID or a job specification;  if
              a  job  spec  is given, all processes in that job's pipeline are
              waited for.  If id is not given,  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 a single  job  from
              the list of _i_ds or, if no _i_ds are supplied, any job, to complete
              and  returns its exit status.  If none of the supplied arguments
              is a child of the shell, or if no arguments are supplied and the
              shell has no unwaited-for children, the exit status is 127.   If
              the  -p option is supplied, the process or job identifier of the
              job for which the exit status is returned  is  assigned  to  the
              variable  varname  named  by  the option argument.  The variable
              will be unset initially, before any assignment.  This is  useful
              only  when  the -n option is supplied.  Supplying the -f option,
              when job control is enabled, forces wait to wait for id to  ter-
              minate before returning its status, instead of returning when it
              changes  status.  If id specifies a non-existent process or job,
              the return status is 127.  If wait is interrupted by  a  signal,
              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 process or job waited for.

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 rhs of the
       regexp matching operator quotes special regexp characters in the  word,
       which is default behavior in bash-3.2 and subsequent versions).

       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 compat_N_N option, like 42) determines the com-
       patibility level.

       Starting with bash-4.4, bash has begun deprecating older  compatibility
       levels.   Eventually, the options will be removed in favor of BASH_COM-
       PAT.

       Bash-5.0 was the final version for which there will  be  an  individual
       shopt option for the previous version. Users should control the compat-
       ibility level with BASH_COMPAT.

       The  following  table describes the behavior changes controlled by each
       compatibility level setting.  The compat_N_N 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 compat_N_N 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      the shell does not print a warning message if an  attempt
                     is  made  to use a quoted compound assignment as an argu-
                     ment to declare (e.g., declare -a foo=(1 2)). Later  ver-
                     sions warn that this usage is deprecated
              +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 enabled
              +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 compatibility
                     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  AA  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.

SEE ALSO
       bash(1), sh(1)

GNU Bash 5.2                    2023 January 27               BASH__BUILTINS(1)
