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BASH(1)								       BASH(1)

NAME
       bash - GNU Bourne-Again SHell

SYNOPSIS
       bash [options] [command_string | file]

COPYRIGHT
       Bash is Copyright (C) 1989-2016 by the Free Software Foundation, Inc.

DESCRIPTION
       Bash  is	 an  sh-compatible  command language interpreter that executes
       commands read from the standard input or from a file.  Bash also incor‐
       porates useful features from the Korn and C shells (ksh and csh).

       Bash  is	 intended  to  be a conformant implementation of the Shell and
       Utilities portion  of  the  IEEE	 POSIX	specification  (IEEE  Standard
       1003.1).	 Bash can be configured to be POSIX-conformant by default.

OPTIONS
       All of the single-character shell options documented in the description
       of the set builtin command can be used as options  when	the  shell  is
       invoked.	 In addition, bash interprets the following options when it is
       invoked:

       -c	 If the -c option is present, then commands are read from  the
		 first non-option argument command_string.  If there are argu‐
		 ments	after  the  command_string,  the  first	 argument   is
		 assigned  to  $0  and any remaining arguments are assigned to
		 the positional parameters.  The assignment  to	 $0  sets  the
		 name  of  the	shell, which is used in warning and error mes‐
		 sages.
       -i	 If the -i option is present, the shell is interactive.
       -l	 Make bash act as if it had been invoked as a login shell (see
		 INVOCATION below).
       -r	 If  the  -r  option  is present, the shell becomes restricted
		 (see RESTRICTED SHELL below).
       -s	 If the -s option is present, or if no arguments remain	 after
		 option	 processing,  then commands are read from the standard
		 input.	 This option allows the positional  parameters	to  be
		 set when invoking an interactive shell.
       -D	 A  list of all double-quoted strings preceded by $ is printed
		 on the standard output.  These are the strings that are  sub‐
		 ject to language translation when the current locale is not C
		 or POSIX.  This implies the -n option; no  commands  will  be
		 executed.
       [-+]O [shopt_option]
		 shopt_option  is  one	of  the	 shell options accepted by the
		 shopt	builtin	 (see  SHELL  BUILTIN  COMMANDS	 below).    If
		 shopt_option is present, -O sets the value of that option; +O
		 unsets it.  If shopt_option is not supplied,  the  names  and
		 values	 of the shell options accepted by shopt are printed on
		 the standard output.  If the invocation  option  is  +O,  the
		 output is displayed in a format that may be reused as input.
       --	 A  --	signals the end of options and disables further option
		 processing.  Any arguments after the -- are treated as	 file‐
		 names and arguments.  An argument of - is equivalent to --.

       Bash  also  interprets  a  number  of  multi-character  options.	 These
       options must appear on the command  line	 before	 the  single-character
       options to be recognized.

       --debugger
	      Arrange for the debugger profile to be executed before the shell
	      starts.  Turns on extended debugging mode (see  the  description
	      of the extdebug option to the shopt builtin below).
       --dump-po-strings
	      Equivalent  to -D, but the output is in the GNU gettext po (por‐
	      table object) file format.
       --dump-strings
	      Equivalent to -D.
       --help Display a usage message on standard  output  and	exit  success‐
	      fully.
       --init-file file
       --rcfile file
	      Execute  commands	 from file instead of the system wide initial‐
	      ization file /etc/bash.bashrc and the standard personal initial‐
	      ization  file ~/.bashrc if the shell is interactive (see INVOCA‐
	      TION below).

       --login
	      Equivalent to -l.

       --noediting
	      Do not use the GNU readline library to read command  lines  when
	      the shell is interactive.

       --noprofile
	      Do  not read either the system-wide startup file /etc/profile or
	      any  of  the  personal  initialization  files   ~/.bash_profile,
	      ~/.bash_login,  or  ~/.profile.	By  default,  bash reads these
	      files when it is	invoked	 as  a	login  shell  (see  INVOCATION
	      below).

       --norc Do  not  read  and  execute  the system wide initialization file
	      /etc/bash.bashrc and the personal initialization file  ~/.bashrc
	      if  the  shell  is interactive.  This option is on by default if
	      the shell is invoked as sh.

       --posix
	      Change the behavior of bash where the default operation  differs
	      from the POSIX standard to match the standard (posix mode).  See
	      SEE ALSO below for a reference to a document  that  details  how
	      posix mode affects bash's behavior.

       --restricted
	      The shell becomes restricted (see RESTRICTED SHELL below).

       --verbose
	      Equivalent to -v.

       --version
	      Show  version information for this instance of bash on the stan‐
	      dard output and exit successfully.

ARGUMENTS
       If arguments remain after option processing, and neither the -c nor the
       -s  option  has	been supplied, the first argument is assumed to be the
       name of a file containing shell commands.  If bash is invoked  in  this
       fashion,	 $0 is set to the name of the file, and the positional parame‐
       ters are set to the remaining arguments.	 Bash reads and executes  com‐
       mands  from this file, then exits.  Bash's exit status is the exit sta‐
       tus of the last command executed in the script.	 If  no	 commands  are
       executed,  the  exit status is 0.  An attempt is first made to open the
       file in the current directory, and, if no file is found, then the shell
       searches the directories in PATH for the script.

INVOCATION
       A  login shell is one whose first character of argument zero is a -, or
       one started with the --login option.

       An interactive  shell  is  one  started	without	 non-option  arguments
       (unless -s is specified) and without the -c option whose standard input
       and error are both connected to terminals (as determined by isatty(3)),
       or  one	started	 with  the -i option.  PS1 is set and $- includes i if
       bash is interactive, allowing a shell script or a startup file to  test
       this state.

       The  following paragraphs describe how bash executes its startup files.
       If any of the files exist but cannot be read, bash  reports  an	error.
       Tildes  are expanded in filenames as described below under Tilde Expan‐
       sion in the EXPANSION section.

       When bash is invoked as an interactive login shell, or as a  non-inter‐
       active  shell with the --login option, it first reads and executes com‐
       mands from the file /etc/profile, if that file exists.	After  reading
       that file, it looks for ~/.bash_profile, ~/.bash_login, and ~/.profile,
       in that order, and reads and executes commands from the first one  that
       exists  and  is	readable.  The --noprofile option may be used when the
       shell is started to inhibit this behavior.

       When an interactive login shell exits, or a non-interactive login shell
       executes	 the  exit  builtin  command, bash reads and executes commands
       from the file ~/.bash_logout, if it exists.

       When an interactive shell that is not a login shell  is	started,  bash
       reads  and  executes  commands  from /etc/bash.bashrc and ~/.bashrc, if
       these files exist.  This may be inhibited by using the  --norc  option.
       The  --rcfile  file option will force bash to read and execute commands
       from file instead of /etc/bash.bashrc and ~/.bashrc.

       When bash is started non-interactively, to  run	a  shell  script,  for
       example, it looks for the variable BASH_ENV in the environment, expands
       its value if it appears there, and uses the expanded value as the  name
       of  a  file to read and execute.	 Bash behaves as if the following com‐
       mand were executed:
	      if [ -n "$BASH_ENV" ]; then . "$BASH_ENV"; fi
       but the value of the PATH variable is not used to search for the	 file‐
       name.

       If  bash	 is  invoked  with  the name sh, it tries to mimic the startup
       behavior of historical versions of sh as	 closely  as  possible,	 while
       conforming  to the POSIX standard as well.  When invoked as an interac‐
       tive login shell, or a non-interactive shell with the  --login  option,
       it  first  attempts  to read and execute commands from /etc/profile and
       ~/.profile, in that order.  The	--noprofile  option  may  be  used  to
       inhibit	this  behavior.	 When invoked as an interactive shell with the
       name sh, bash looks for the variable ENV, expands its value  if	it  is
       defined,	 and uses the expanded value as the name of a file to read and
       execute.	 Since a shell invoked as sh does not attempt to read and exe‐
       cute  commands from any other startup files, the --rcfile option has no
       effect.	A non-interactive shell invoked with  the  name	 sh  does  not
       attempt	to  read  any  other  startup files.  When invoked as sh, bash
       enters posix mode after the startup files are read.

       When bash is started in posix mode, as with the	--posix	 command  line
       option, it follows the POSIX standard for startup files.	 In this mode,
       interactive shells expand the ENV variable and commands	are  read  and
       executed	 from  the  file  whose	 name is the expanded value.  No other
       startup files are read.

       Bash attempts to determine when it is being run with its standard input
       connected to a network connection, as when executed by the remote shell
       daemon, usually rshd, or the secure shell daemon sshd.  If bash	deter‐
       mines  it  is being run in this fashion, it reads and executes commands
       from ~/.bashrc and ~/.bashrc, if these files exist  and	are  readable.
       It will not do this if invoked as sh.  The --norc option may be used to
       inhibit this behavior, and the --rcfile option may  be  used  to	 force
       another file to be read, but neither rshd nor sshd generally invoke the
       shell with those options or allow them to be specified.

       If the shell is started with the effective user (group) id not equal to
       the real user (group) id, and the -p option is not supplied, no startup
       files are read, shell functions are not inherited from the environment,
       the  SHELLOPTS,	BASHOPTS,  CDPATH,  and	 GLOBIGNORE variables, if they
       appear in the environment, are ignored, and the effective  user	id  is
       set  to	the real user id.  If the -p option is supplied at invocation,
       the startup behavior is the same, but the  effective  user  id  is  not
       reset.

DEFINITIONS
       The  following  definitions  are used throughout the rest of this docu‐
       ment.
       blank  A space or tab.
       word   A sequence of characters considered as  a	 single	 unit  by  the
	      shell.  Also known as a token.
       name   A	 word  consisting  only	 of alphanumeric characters and under‐
	      scores, and beginning with an alphabetic character or an	under‐
	      score.  Also referred to as an identifier.
       metacharacter
	      A	 character  that,  when unquoted, separates words.  One of the
	      following:
	      |	 & ; ( ) < > space tab newline
       control operator
	      A token that performs a control function.	 It is one of the fol‐
	      lowing symbols:
	      || & && ; ;; ;& ;;& ( ) | |& <newline>

RESERVED WORDS
       Reserved words are words that have a special meaning to the shell.  The
       following words are recognized as reserved when unquoted and either the
       first  word  of a simple command (see SHELL GRAMMAR below) or the third
       word of a case or for command:

       ! case  coproc  do done elif else esac fi for  function	if  in	select
       then until while { } time [[ ]]

SHELL GRAMMAR
   Simple Commands
       A  simple  command  is a sequence of optional variable assignments fol‐
       lowed by blank-separated words and redirections, and  terminated	 by  a
       control operator.  The first word specifies the command to be executed,
       and is passed as argument zero.	The  remaining	words  are  passed  as
       arguments to the invoked command.

       The  return  value  of a simple command is its exit status, or 128+n if
       the command is terminated by signal n.

   Pipelines
       A pipeline is a sequence of one or more commands separated  by  one  of
       the control operators | or |&.  The format for a pipeline is:

	      [time [-p]] [ ! ] command [ [|⎪|&] command2 ... ]

       The  standard output of command is connected via a pipe to the standard
       input of command2.  This connection is performed	 before	 any  redirec‐
       tions specified by the command (see REDIRECTION below).	If |& is used,
       command's standard error, in addition to its standard output,  is  con‐
       nected  to  command2's standard input through the pipe; it is shorthand
       for 2>&1 |.  This implicit redirection of the  standard	error  to  the
       standard	 output	 is  performed after any redirections specified by the
       command.

       The return status of a pipeline is the exit status of the last command,
       unless  the  pipefail  option  is enabled.  If pipefail is enabled, the
       pipeline's return status is the value of the last  (rightmost)  command
       to  exit	 with a non-zero status, or zero if all commands exit success‐
       fully.  If the reserved word !  precedes a pipeline, the exit status of
       that  pipeline  is the logical negation of the exit status as described
       above.  The shell waits for all commands in the pipeline	 to  terminate
       before returning a value.

       If  the	time reserved word precedes a pipeline, the elapsed as well as
       user and system time consumed by its execution are  reported  when  the
       pipeline	 terminates.   The -p option changes the output format to that
       specified by POSIX.  When the shell is in posix mode, it does not  rec‐
       ognize  time  as	 a  reserved word if the next token begins with a `-'.
       The TIMEFORMAT variable may be set to a format  string  that  specifies
       how  the timing information should be displayed; see the description of
       TIMEFORMAT under Shell Variables below.

       When the shell is in posix mode, time may be followed by a newline.  In
       this  case,  the shell displays the total user and system time consumed
       by the shell and its children.  The TIMEFORMAT variable may be used  to
       specify the format of the time information.

       Each  command in a pipeline is executed as a separate process (i.e., in
       a subshell).

   Lists
       A list is a sequence of one or more pipelines separated by one  of  the
       operators ;, &, &&, or ||, and optionally terminated by one of ;, &, or
       <newline>.

       Of these list operators, && and || have equal precedence, followed by ;
       and &, which have equal precedence.

       A  sequence  of	one or more newlines may appear in a list instead of a
       semicolon to delimit commands.

       If a command is terminated by the control operator &,  the  shell  exe‐
       cutes  the command in the background in a subshell.  The shell does not
       wait for the command to finish, and the return status is	 0.   Commands
       separated  by  a	 ; are executed sequentially; the shell waits for each
       command to terminate in turn.  The return status is the exit status  of
       the last command executed.

       AND  and	 OR  lists are sequences of one or more pipelines separated by
       the && and || control operators, respectively.  AND and	OR  lists  are
       executed with left associativity.  An AND list has the form

	      command1 && command2

       command2	 is  executed if, and only if, command1 returns an exit status
       of zero.

       An OR list has the form

	      command1 || command2

       command2 is executed if and only if command1 returns  a	non-zero  exit
       status.	 The  return  status of AND and OR lists is the exit status of
       the last command executed in the list.

   Compound Commands
       A compound command is one of the following.  In most cases a list in  a
       command's  description may be separated from the rest of the command by
       one or more newlines, and may be followed by a newline in  place	 of  a
       semicolon.

       (list) list  is	executed in a subshell environment (see COMMAND EXECU‐
	      TION ENVIRONMENT below).	Variable assignments and builtin  com‐
	      mands  that  affect  the	shell's	 environment  do not remain in
	      effect after the command completes.  The return  status  is  the
	      exit status of list.

       { list; }
	      list  is simply executed in the current shell environment.  list
	      must be terminated with a newline or semicolon.  This  is	 known
	      as  a  group  command.   The return status is the exit status of
	      list.  Note that unlike the metacharacters ( and ), { and }  are
	      reserved words and must occur where a reserved word is permitted
	      to be recognized.	 Since they do not cause a  word  break,  they
	      must  be	separated  from	 list  by  whitespace or another shell
	      metacharacter.

       ((expression))
	      The expression is evaluated according  to	 the  rules  described
	      below  under ARITHMETIC EVALUATION.  If the value of the expres‐
	      sion is non-zero, the return status is 0; otherwise  the	return
	      status is 1.  This is exactly equivalent to let "expression".

       [[ expression ]]
	      Return  a	 status	 of  0 or 1 depending on the evaluation of the
	      conditional expression expression.  Expressions are composed  of
	      the  primaries  described	 below	under CONDITIONAL EXPRESSIONS.
	      Word splitting and pathname expansion are not performed  on  the
	      words  between  the  [[  and  ]]; tilde expansion, parameter and
	      variable expansion, arithmetic expansion, command	 substitution,
	      process  substitution,  and quote removal are performed.	Condi‐
	      tional operators such as -f must be unquoted to be recognized as
	      primaries.

	      When  used with [[, the < and > operators sort lexicographically
	      using the current locale.

       See the description of the test builtin command (section SHELL  BUILTIN
       COMMANDS	 below)	 for the handling of parameters (i.e.  missing parame‐
       ters).

       When the == and != operators are used, the string to the right  of  the
       operator	 is  considered	 a  pattern and matched according to the rules
       described below under Pattern Matching, as if the extglob shell	option
       were  enabled.  The = operator is equivalent to ==.  If the nocasematch
       shell option is enabled, the match is performed without regard  to  the
       case  of	 alphabetic  characters.   The return value is 0 if the string
       matches (==) or does not match (!=) the pattern, and 1 otherwise.   Any
       part  of	 the  pattern  may be quoted to force the quoted portion to be
       matched as a string.

       An additional binary operator, =~, is available, with the  same	prece‐
       dence  as  ==  and !=.  When it is used, the string to the right of the
       operator is considered  an  extended  regular  expression  and  matched
       accordingly  (as	 in  regex(3)).	  The  return value is 0 if the string
       matches the pattern, and 1 otherwise.  If  the  regular	expression  is
       syntactically  incorrect,  the conditional expression's return value is
       2.  If the nocasematch shell option is enabled, the match is  performed
       without	regard	to the case of alphabetic characters.  Any part of the
       pattern may be quoted to force the quoted portion to be	matched	 as  a
       string.	 Bracket  expressions  in  regular expressions must be treated
       carefully, since normal quoting characters lose their meanings  between
       brackets.   If  the  pattern is stored in a shell variable, quoting the
       variable expansion forces the entire pattern to be matched as a string.
       Substrings  matched  by parenthesized subexpressions within the regular
       expression are saved in the array variable BASH_REMATCH.	  The  element
       of  BASH_REMATCH with index 0 is the portion of the string matching the
       entire regular expression.  The element of BASH_REMATCH with index n is
       the portion of the string matching the nth parenthesized subexpression.

       Expressions  may	 be  combined using the following operators, listed in
       decreasing order of precedence:

	      ( expression )
		     Returns the value of expression.  This  may  be  used  to
		     override the normal precedence of operators.
	      ! expression
		     True if expression is false.
	      expression1 && expression2
		     True if both expression1 and expression2 are true.
	      expression1 || expression2
		     True if either expression1 or expression2 is true.

	      The && and || operators do not evaluate expression2 if the value
	      of expression1 is sufficient to determine the  return  value  of
	      the entire conditional expression.

       for name [ [ in [ word ... ] ] ; ] do list ; done
	      The list of words following in is expanded, generating a list of
	      items.  The variable name is set to each element of this list in
	      turn,  and  list is executed each time.  If the in word is omit‐
	      ted, the for command executes  list  once	 for  each  positional
	      parameter that is set (see PARAMETERS below).  The return status
	      is the exit status of the last command that  executes.   If  the
	      expansion of the items following in results in an empty list, no
	      commands are executed, and the return status is 0.

       for (( expr1 ; expr2 ; expr3 )) ; do list ; done
	      First, the arithmetic expression expr1 is evaluated according to
	      the  rules  described  below  under  ARITHMETIC EVALUATION.  The
	      arithmetic expression expr2 is then evaluated  repeatedly	 until
	      it  evaluates  to zero.  Each time expr2 evaluates to a non-zero
	      value, list is executed and the arithmetic expression  expr3  is
	      evaluated.   If  any  expression is omitted, it behaves as if it
	      evaluates to 1.  The return value is the exit status of the last
	      command in list that is executed, or false if any of the expres‐
	      sions is invalid.

       select name [ in word ] ; do list ; done
	      The list of words following in is expanded, generating a list of
	      items.   The  set	 of  expanded words is printed on the standard
	      error, each preceded by a number.	 If the in  word  is  omitted,
	      the  positional  parameters  are printed (see PARAMETERS below).
	      The PS3 prompt is then displayed and a line read from the	 stan‐
	      dard  input.   If the line consists of a number corresponding to
	      one of the displayed words, then the value of  name  is  set  to
	      that  word.  If the line is empty, the words and prompt are dis‐
	      played again.  If EOF is read, the command completes.  Any other
	      value  read  causes  name	 to  be set to null.  The line read is
	      saved in the variable REPLY.  The list is	 executed  after  each
	      selection until a break command is executed.  The exit status of
	      select is the exit status of the last command executed in	 list,
	      or zero if no commands were executed.

       case word in [ [(] pattern [ | pattern ] ... ) list ;; ] ... esac
	      A case command first expands word, and tries to match it against
	      each pattern in turn, using the same matching rules as for path‐
	      name  expansion  (see  Pathname  Expansion  below).  The word is
	      expanded using tilde expansion, parameter	 and  variable	expan‐
	      sion,  arithmetic	 expansion, command substitution, process sub‐
	      stitution and quote removal.  Each pattern examined is  expanded
	      using  tilde expansion, parameter and variable expansion, arith‐
	      metic expansion, command substitution, and process substitution.
	      If  the  nocasematch  shell option is enabled, the match is per‐
	      formed without regard to	the  case  of  alphabetic  characters.
	      When  a  match is found, the corresponding list is executed.  If
	      the ;; operator is used, no  subsequent  matches	are  attempted
	      after  the  first pattern match.	Using ;& in place of ;; causes
	      execution to continue with the list associated with the next set
	      of  patterns.  Using ;;& in place of ;; causes the shell to test
	      the next pattern list in the statement, if any, and execute  any
	      associated  list on a successful match.  The exit status is zero
	      if no pattern matches.  Otherwise, it is the exit status of  the
	      last command executed in list.

       if list; then list; [ elif list; then list; ] ... [ else list; ] fi
	      The  if  list is executed.  If its exit status is zero, the then
	      list is executed.	 Otherwise, each  elif	list  is  executed  in
	      turn,  and  if  its  exit status is zero, the corresponding then
	      list is executed and the command completes.  Otherwise, the else
	      list  is executed, if present.  The exit status is the exit sta‐
	      tus of the last command executed, or zero if no condition tested
	      true.

       while list-1; do list-2; done
       until list-1; do list-2; done
	      The  while command continuously executes the list list-2 as long
	      as the last command in the list list-1 returns an exit status of
	      zero.   The  until  command  is  identical to the while command,
	      except that the test is negated: list-2 is executed as  long  as
	      the  last command in list-1 returns a non-zero exit status.  The
	      exit status of the while and until commands is the  exit	status
	      of the last command executed in list-2, or zero if none was exe‐
	      cuted.

   Coprocesses
       A coprocess is a shell command preceded by the coproc reserved word.  A
       coprocess  is  executed asynchronously in a subshell, as if the command
       had been terminated with the & control operator, with  a	 two-way  pipe
       established between the executing shell and the coprocess.

       The format for a coprocess is:

	      coproc [NAME] command [redirections]

       This  creates  a	 coprocess  named  NAME.  If NAME is not supplied, the
       default name is COPROC.	NAME must not be supplied if command is a sim‐
       ple command (see above); otherwise, it is interpreted as the first word
       of the simple command.  When the coprocess is executed, the shell  cre‐
       ates  an array variable (see Arrays below) named NAME in the context of
       the executing shell.  The standard output of command is connected via a
       pipe  to	 a  file  descriptor  in  the  executing  shell, and that file
       descriptor is assigned to NAME[0].  The standard input  of  command  is
       connected  via  a pipe to a file descriptor in the executing shell, and
       that file descriptor is assigned to NAME[1].  This pipe is  established
       before  any  redirections  specified  by	 the  command (see REDIRECTION
       below).	The file descriptors can be utilized  as  arguments  to	 shell
       commands	 and  redirections  using  standard word expansions.  The file
       descriptors are not available in subshells.   The  process  ID  of  the
       shell spawned to execute the coprocess is available as the value of the
       variable NAME_PID.  The wait builtin command may be used	 to  wait  for
       the coprocess to terminate.

       Since  the  coprocess is created as an asynchronous command, the coproc
       command always returns success.	The return status of  a	 coprocess  is
       the exit status of command.

   Shell Function Definitions
       A  shell function is an object that is called like a simple command and
       executes a compound command with a new set  of  positional  parameters.
       Shell functions are declared as follows:

       name () compound-command [redirection]
       function name [()] compound-command [redirection]
	      This  defines a function named name.  The reserved word function
	      is optional.  If the function reserved  word  is	supplied,  the
	      parentheses  are optional.  The body of the function is the com‐
	      pound command compound-command (see  Compound  Commands  above).
	      That  command is usually a list of commands between { and }, but
	      may be any command listed under Compound	Commands  above,  with
	      one  exception:  If  the function reserved word is used, but the
	      parentheses are not supplied, the	 braces	 are  required.	  com‐
	      pound-command is executed whenever name is specified as the name
	      of a simple command.  When in posix mode, name may  not  be  the
	      name  of	one  of	 the POSIX special builtins.  Any redirections
	      (see REDIRECTION below) specified when a function is defined are
	      performed	 when  the function is executed.  The exit status of a
	      function definition is zero unless a syntax error	 occurs	 or  a
	      readonly	function with the same name already exists.  When exe‐
	      cuted, the exit status of a function is the exit status  of  the
	      last command executed in the body.  (See FUNCTIONS below.)

COMMENTS
       In a non-interactive shell, or an interactive shell in which the inter‐
       active_comments option to the  shopt  builtin  is  enabled  (see	 SHELL
       BUILTIN	COMMANDS  below), a word beginning with # causes that word and
       all remaining characters on that line to be  ignored.   An  interactive
       shell  without  the  interactive_comments option enabled does not allow
       comments.  The interactive_comments option is on by default in interac‐
       tive shells.

QUOTING
       Quoting	is used to remove the special meaning of certain characters or
       words to the shell.  Quoting can be used to disable  special  treatment
       for special characters, to prevent reserved words from being recognized
       as such, and to prevent parameter expansion.

       Each of the metacharacters listed above under DEFINITIONS  has  special
       meaning to the shell and must be quoted if it is to represent itself.

       When  the command history expansion facilities are being used (see HIS‐
       TORY EXPANSION below), the history expansion character, usually !, must
       be quoted to prevent history expansion.

       There  are  three  quoting  mechanisms:	the  escape  character, single
       quotes, and double quotes.

       A non-quoted backslash (\) is the escape character.  It	preserves  the
       literal value of the next character that follows, with the exception of
       <newline>.  If a \<newline> pair appears,  and  the  backslash  is  not
       itself  quoted,	the \<newline> is treated as a line continuation (that
       is, it is removed from the input stream and effectively ignored).

       Enclosing characters in single quotes preserves the  literal  value  of
       each character within the quotes.  A single quote may not occur between
       single quotes, even when preceded by a backslash.

       Enclosing characters in double quotes preserves the  literal  value  of
       all  characters	within the quotes, with the exception of $, `, \, and,
       when history expansion is enabled, !.  When the shell is in posix mode,
       the  !  has  no special meaning within double quotes, even when history
       expansion is enabled.  The characters $	and  `	retain	their  special
       meaning	within double quotes.  The backslash retains its special mean‐
       ing only when followed by one of the following characters: $, `, ",  \,
       or  <newline>.	A  double  quote may be quoted within double quotes by
       preceding it with a backslash.  If enabled, history expansion  will  be
       performed  unless  an  !	 appearing in double quotes is escaped using a
       backslash.  The backslash preceding the !  is not removed.

       The special parameters * and @ have  special  meaning  when  in	double
       quotes (see PARAMETERS below).

       Words of the form $'string' are treated specially.  The word expands to
       string, with backslash-escaped characters replaced as specified by  the
       ANSI  C	standard.  Backslash escape sequences, if present, are decoded
       as follows:
	      \a     alert (bell)
	      \b     backspace
	      \e
	      \E     an escape character
	      \f     form feed
	      \n     new line
	      \r     carriage return
	      \t     horizontal tab
	      \v     vertical tab
	      \\     backslash
	      \'     single quote
	      \"     double quote
	      \?     question mark
	      \nnn   the eight-bit character whose value is  the  octal	 value
		     nnn (one to three digits)
	      \xHH   the  eight-bit  character	whose value is the hexadecimal
		     value HH (one or two hex digits)
	      \uHHHH the Unicode (ISO/IEC 10646) character whose value is  the
		     hexadecimal value HHHH (one to four hex digits)
	      \UHHHHHHHH
		     the  Unicode (ISO/IEC 10646) character whose value is the
		     hexadecimal value HHHHHHHH (one to eight hex digits)
	      \cx    a control-x character

       The expanded result is single-quoted, as if the	dollar	sign  had  not
       been present.

       A double-quoted string preceded by a dollar sign ($"string") will cause
       the string to be translated according to the current  locale.   If  the
       current	locale	is  C  or  POSIX,  the dollar sign is ignored.	If the
       string is translated and replaced, the replacement is double-quoted.

PARAMETERS
       A parameter is an entity that stores values.  It can be a name, a  num‐
       ber, or one of the special characters listed below under Special Param‐
       eters.  A variable is a parameter denoted by a name.  A variable has  a
       value  and  zero or more attributes.  Attributes are assigned using the
       declare builtin command (see declare below in SHELL BUILTIN COMMANDS).

       A parameter is set if it has been assigned a value.  The null string is
       a  valid	 value.	 Once a variable is set, it may be unset only by using
       the unset builtin command (see SHELL BUILTIN COMMANDS below).

       A variable may be assigned to by a statement of the form

	      name=[value]

       If value is not given, the variable is assigned the null	 string.   All
       values  undergo tilde expansion, parameter and variable expansion, com‐
       mand substitution, arithmetic expansion, and quote removal (see	EXPAN‐
       SION below).  If the variable has its integer attribute set, then value
       is evaluated as an arithmetic expression even if the $((...)) expansion
       is  not	used  (see Arithmetic Expansion below).	 Word splitting is not
       performed, with the exception of "$@" as explained below under  Special
       Parameters.   Pathname  expansion  is not performed.  Assignment state‐
       ments may also appear as arguments  to  the  alias,  declare,  typeset,
       export,	readonly,  and	local builtin commands (declaration commands).
       When in posix mode, these builtins may appear in a command after one or
       more  instances	of  the	 command  builtin  and retain these assignment
       statement properties.

       In the context where an assignment statement is assigning a value to  a
       shell variable or array index, the += operator can be used to append to
       or add to the variable's previous value.	 This  includes	 arguments  to
       builtin	commands  such	as  declare  that accept assignment statements
       (declaration commands).	When += is applied to a variable for which the
       integer	attribute  has	been  set, value is evaluated as an arithmetic
       expression and added to the variable's current  value,  which  is  also
       evaluated.   When  +=  is  applied  to an array variable using compound
       assignment (see Arrays below), the variable's value is not unset (as it
       is when using =), and new values are appended to the array beginning at
       one greater than the array's maximum  index  (for  indexed  arrays)  or
       added  as  additional  key-value	 pairs	in an associative array.  When
       applied to a string-valued variable, value is expanded and appended  to
       the variable's value.

       A variable can be assigned the nameref attribute using the -n option to
       the declare or local builtin commands (see the descriptions of  declare
       and  local  below) to create a nameref, or a reference to another vari‐
       able.  This allows variables to be  manipulated	indirectly.   Whenever
       the  nameref  variable  is  referenced,	assigned to, unset, or has its
       attributes modified (other than using or changing the nameref attribute
       itself),	 the operation is actually performed on the variable specified
       by the nameref variable's value.	 A nameref  is	commonly  used	within
       shell functions to refer to a variable whose name is passed as an argu‐
       ment to the function.  For instance, if a variable name is passed to  a
       shell function as its first argument, running
	      declare -n ref=$1
       inside  the  function creates a nameref variable ref whose value is the
       variable name passed as the first argument.  References and assignments
       to  ref,	 and  changes  to  its	attributes, are treated as references,
       assignments, and attribute modifications to the variable whose name was
       passed  as  $1.	 If the control variable in a for loop has the nameref
       attribute, the list of words can be a list of shell  variables,	and  a
       name  reference will be established for each word in the list, in turn,
       when the loop is executed.  Array variables cannot be given the nameref
       attribute.   However,  nameref  variables can reference array variables
       and subscripted array variables.	 Namerefs can be unset	using  the  -n
       option  to the unset builtin.  Otherwise, if unset is executed with the
       name of a nameref variable as an argument, the variable	referenced  by
       the nameref variable will be unset.

   Positional Parameters
       A  positional  parameter	 is a parameter denoted by one or more digits,
       other than the single digit 0.  Positional parameters are assigned from
       the  shell's  arguments when it is invoked, and may be reassigned using
       the set builtin command.	 Positional parameters may not be assigned  to
       with  assignment statements.  The positional parameters are temporarily
       replaced when a shell function is executed (see FUNCTIONS below).

       When a positional parameter consisting of more than a single  digit  is
       expanded, it must be enclosed in braces (see EXPANSION below).

   Special Parameters
       The  shell  treats  several parameters specially.  These parameters may
       only be referenced; assignment to them is not allowed.
       *      Expands to the positional parameters, starting from  one.	  When
	      the  expansion  is  not  within  double  quotes, each positional
	      parameter expands to a separate word.  In contexts where	it  is
	      performed, those words are subject to further word splitting and
	      pathname expansion.  When the  expansion	occurs	within	double
	      quotes,  it  expands  to	a  single  word with the value of each
	      parameter separated by the first character of  the  IFS  special
	      variable.	  That	is, "$*" is equivalent to "$1c$2c...", where c
	      is the first character of the value of the IFS variable.	If IFS
	      is  unset,  the  parameters  are separated by spaces.  If IFS is
	      null, the parameters are joined without intervening separators.
       @      Expands to the positional parameters, starting from  one.	  When
	      the  expansion  occurs  within  double  quotes,  each  parameter
	      expands to a separate word.  That is, "$@" is equivalent to "$1"
	      "$2"  ...	  If the double-quoted expansion occurs within a word,
	      the expansion of the first parameter is joined with  the	begin‐
	      ning  part  of  the original word, and the expansion of the last
	      parameter is joined with the last part  of  the  original	 word.
	      When  there  are no positional parameters, "$@" and $@ expand to
	      nothing (i.e., they are removed).
       #      Expands to the number of positional parameters in decimal.
       ?      Expands to the exit status of the most recently  executed	 fore‐
	      ground pipeline.
       -      Expands  to  the	current option flags as specified upon invoca‐
	      tion, by the set builtin command, or  those  set	by  the	 shell
	      itself (such as the -i option).
       $      Expands  to  the	process ID of the shell.  In a () subshell, it
	      expands to the process ID of the current	shell,	not  the  sub‐
	      shell.
       !      Expands  to  the process ID of the job most recently placed into
	      the background, whether executed as an asynchronous  command  or
	      using the bg builtin (see JOB CONTROL below).
       0      Expands  to  the name of the shell or shell script.  This is set
	      at shell initialization.	If bash is invoked with a file of com‐
	      mands,  $0  is set to the name of that file.  If bash is started
	      with the -c option, then $0 is set to the first  argument	 after
	      the  string to be executed, if one is present.  Otherwise, it is
	      set to the filename used to invoke bash, as  given  by  argument
	      zero.
       _      At  shell	 startup,  set to the absolute pathname used to invoke
	      the shell or shell script being executed as passed in the	 envi‐
	      ronment  or  argument  list.   Subsequently, expands to the last
	      argument to the previous command, after expansion.  Also set  to
	      the  full	 pathname  used	 to  invoke  each command executed and
	      placed in the environment exported to that command.  When check‐
	      ing  mail,  this	parameter holds the name of the mail file cur‐
	      rently being checked.

   Shell Variables
       The following variables are set by the shell:

       BASH   Expands to the full filename used to  invoke  this  instance  of
	      bash.
       BASHOPTS
	      A	 colon-separated  list of enabled shell options.  Each word in
	      the list is a valid argument for the  -s	option	to  the	 shopt
	      builtin command (see SHELL BUILTIN COMMANDS below).  The options
	      appearing in BASHOPTS are those reported as  on  by  shopt.   If
	      this  variable  is  in the environment when bash starts up, each
	      shell option in the list will  be	 enabled  before  reading  any
	      startup files.  This variable is read-only.
       BASHPID
	      Expands  to  the	process	 ID of the current bash process.  This
	      differs from $$ under certain circumstances, such	 as  subshells
	      that do not require bash to be re-initialized.
       BASH_ALIASES
	      An  associative  array  variable whose members correspond to the
	      internal list of aliases as maintained  by  the  alias  builtin.
	      Elements	added to this array appear in the alias list; however,
	      unsetting array elements currently does not cause aliases to  be
	      removed from the alias list.  If BASH_ALIASES is unset, it loses
	      its special properties, even if it is subsequently reset.
       BASH_ARGC
	      An array variable whose values are the number of	parameters  in
	      each frame of the current bash execution call stack.  The number
	      of parameters to	the  current  subroutine  (shell  function  or
	      script  executed	with  . or source) is at the top of the stack.
	      When a subroutine is executed, the number of  parameters	passed
	      is pushed onto BASH_ARGC.	 The shell sets BASH_ARGC only when in
	      extended debugging mode (see the	description  of	 the  extdebug
	      option to the shopt builtin below)
       BASH_ARGV
	      An  array	 variable containing all of the parameters in the cur‐
	      rent bash execution call stack.  The final parameter of the last
	      subroutine  call is at the top of the stack; the first parameter
	      of the initial call is at the bottom.  When a subroutine is exe‐
	      cuted,  the  parameters supplied are pushed onto BASH_ARGV.  The
	      shell sets BASH_ARGV only when in extended debugging  mode  (see
	      the  description	of  the	 extdebug  option to the shopt builtin
	      below)
       BASH_CMDS
	      An associative array variable whose members  correspond  to  the
	      internal	hash  table  of	 commands  as  maintained  by the hash
	      builtin.	Elements added to this array appear in the hash table;
	      however,	unsetting array elements currently does not cause com‐
	      mand names to be removed from the hash table.  If	 BASH_CMDS  is
	      unset,  it  loses	 its  special properties, even if it is subse‐
	      quently reset.
       BASH_COMMAND
	      The command currently being executed or about  to	 be  executed,
	      unless the shell is executing a command as the result of a trap,
	      in which case it is the command executing at  the	 time  of  the
	      trap.
       BASH_EXECUTION_STRING
	      The command argument to the -c invocation option.
       BASH_LINENO
	      An  array	 variable whose members are the line numbers in source
	      files where each corresponding member of FUNCNAME	 was  invoked.
	      ${BASH_LINENO[$i]}  is  the  line	 number	 in  the  source  file
	      (${BASH_SOURCE[$i+1]})  where  ${FUNCNAME[$i]}  was  called  (or
	      ${BASH_LINENO[$i-1]}  if	referenced  within another shell func‐
	      tion).  Use LINENO to obtain the current line number.
       BASH_LOADABLES_PATH
	      A colon-separated list of directories in which the  shell	 looks
	      for  dynamically	loadable builtins specified by the enable com‐
	      mand.
       BASH_REMATCH
	      An array variable whose members are assigned by  the  =~	binary
	      operator	to the [[ conditional command.	The element with index
	      0 is the portion of  the	string	matching  the  entire  regular
	      expression.   The	 element  with	index  n is the portion of the
	      string matching the nth parenthesized subexpression.  This vari‐
	      able is read-only.
       BASH_SOURCE
	      An  array	 variable whose members are the source filenames where
	      the corresponding shell function names  in  the  FUNCNAME	 array
	      variable	are  defined.	The  shell function ${FUNCNAME[$i]} is
	      defined  in  the	file  ${BASH_SOURCE[$i]}   and	 called	  from
	      ${BASH_SOURCE[$i+1]}.
       BASH_SUBSHELL
	      Incremented  by one within each subshell or subshell environment
	      when the shell begins executing in that environment.   The  ini‐
	      tial value is 0.
       BASH_VERSINFO
	      A readonly array variable whose members hold version information
	      for this instance of bash.  The values  assigned	to  the	 array
	      members are as follows:
	      BASH_VERSINFO[0]	      The major version number (the release).
	      BASH_VERSINFO[1]	      The minor version number (the version).
	      BASH_VERSINFO[2]	      The patch level.
	      BASH_VERSINFO[3]	      The build version.
	      BASH_VERSINFO[4]	      The release status (e.g., beta1).
	      BASH_VERSINFO[5]	      The value of MACHTYPE.
       BASH_VERSION
	      Expands  to  a string describing the version of this instance of
	      bash.
       COMP_CWORD
	      An index into ${COMP_WORDS} of the word containing  the  current
	      cursor position.	This variable is available only in shell func‐
	      tions invoked by the  programmable  completion  facilities  (see
	      Programmable Completion below).
       COMP_KEY
	      The key (or final key of a key sequence) used to invoke the cur‐
	      rent completion function.
       COMP_LINE
	      The current command line.	 This variable is  available  only  in
	      shell  functions	and  external commands invoked by the program‐
	      mable completion facilities (see Programmable Completion below).
       COMP_POINT
	      The index of the current cursor position relative to the	begin‐
	      ning  of the current command.  If the current cursor position is
	      at the end of the current command, the value of this variable is
	      equal  to	 ${#COMP_LINE}.	  This	variable  is available only in
	      shell functions and external commands invoked  by	 the  program‐
	      mable completion facilities (see Programmable Completion below).
       COMP_TYPE
	      Set  to an integer value corresponding to the type of completion
	      attempted that caused a completion function to be	 called:  TAB,
	      for  normal completion, ?, for listing completions after succes‐
	      sive tabs, !, for listing alternatives on partial	 word  comple‐
	      tion,  @,	 to list completions if the word is not unmodified, or
	      %, for menu completion.  This  variable  is  available  only  in
	      shell  functions	and  external commands invoked by the program‐
	      mable completion facilities (see Programmable Completion below).
       COMP_WORDBREAKS
	      The set of characters that the readline library treats  as  word
	      separators  when performing word completion.  If COMP_WORDBREAKS
	      is unset, it loses its special properties, even if it is	subse‐
	      quently reset.
       COMP_WORDS
	      An  array variable (see Arrays below) consisting of the individ‐
	      ual words in the current command line.  The line is  split  into
	      words  as	 readline  would  split	 it,  using COMP_WORDBREAKS as
	      described above.	This variable is available only in shell func‐
	      tions  invoked  by  the  programmable completion facilities (see
	      Programmable Completion below).
       COPROC An array variable (see Arrays below) created to  hold  the  file
	      descriptors  for	output	from and input to an unnamed coprocess
	      (see Coprocesses above).
       DIRSTACK
	      An array variable (see Arrays below) containing the current con‐
	      tents  of	 the directory stack.  Directories appear in the stack
	      in the order they are displayed by the dirs builtin.   Assigning
	      to members of this array variable may be used to modify directo‐
	      ries already in the stack, but the pushd and popd builtins  must
	      be used to add and remove directories.  Assignment to this vari‐
	      able will not change the	current	 directory.   If  DIRSTACK  is
	      unset,  it  loses	 its  special properties, even if it is subse‐
	      quently reset.
       EUID   Expands to the effective user ID of the current  user,  initial‐
	      ized at shell startup.  This variable is readonly.
       FUNCNAME
	      An  array	 variable  containing the names of all shell functions
	      currently in the execution call stack.  The element with index 0
	      is the name of any currently-executing shell function.  The bot‐
	      tom-most element (the one with the  highest  index)  is  "main".
	      This  variable  exists  only when a shell function is executing.
	      Assignments to FUNCNAME have no effect.  If FUNCNAME  is	unset,
	      it  loses	 its  special  properties,  even if it is subsequently
	      reset.

	      This variable can be  used  with	BASH_LINENO  and  BASH_SOURCE.
	      Each   element   of   FUNCNAME  has  corresponding  elements  in
	      BASH_LINENO and BASH_SOURCE to describe  the  call  stack.   For
	      instance,	   ${FUNCNAME[$i]}    was   called   from   the	  file
	      ${BASH_SOURCE[$i+1]} at  line  number  ${BASH_LINENO[$i]}.   The
	      caller builtin displays the current call stack using this infor‐
	      mation.
       GROUPS An array variable containing the list of	groups	of  which  the
	      current user is a member.	 Assignments to GROUPS have no effect.
	      If GROUPS is unset, it loses its special properties, even if  it
	      is subsequently reset.
       HISTCMD
	      The history number, or index in the history list, of the current
	      command.	If HISTCMD is unset, it loses its special  properties,
	      even if it is subsequently reset.
       HOSTNAME
	      Automatically set to the name of the current host.
       HOSTTYPE
	      Automatically  set  to a string that uniquely describes the type
	      of machine on which bash is executing.  The default  is  system-
	      dependent.
       LINENO Each  time this parameter is referenced, the shell substitutes a
	      decimal number representing the current sequential  line	number
	      (starting	 with  1)  within a script or function.	 When not in a
	      script or function, the value substituted is not	guaranteed  to
	      be meaningful.  If LINENO is unset, it loses its special proper‐
	      ties, even if it is subsequently reset.
       MACHTYPE
	      Automatically set to a string that fully	describes  the	system
	      type  on	which  bash is executing, in the standard GNU cpu-com‐
	      pany-system format.  The default is system-dependent.
       MAPFILE
	      An array variable (see Arrays below) created to  hold  the  text
	      read by the mapfile builtin when no variable name is supplied.
       OLDPWD The previous working directory as set by the cd command.
       OPTARG The  value  of the last option argument processed by the getopts
	      builtin command (see SHELL BUILTIN COMMANDS below).
       OPTIND The index of the next argument to be processed  by  the  getopts
	      builtin command (see SHELL BUILTIN COMMANDS below).
       OSTYPE Automatically  set to a string that describes the operating sys‐
	      tem on which bash is executing.  The  default  is	 system-depen‐
	      dent.
       PIPESTATUS
	      An  array	 variable (see Arrays below) containing a list of exit
	      status values from the processes in  the	most-recently-executed
	      foreground pipeline (which may contain only a single command).
       PPID   The  process  ID	of the shell's parent.	This variable is read‐
	      only.
       PWD    The current working directory as set by the cd command.
       RANDOM Each time this parameter is referenced, a random integer between
	      0 and 32767 is generated.	 The sequence of random numbers may be
	      initialized by assigning a value to RANDOM.  If RANDOM is unset,
	      it  loses	 its  special  properties,  even if it is subsequently
	      reset.
       READLINE_LINE
	      The contents of the readline line buffer, for use with "bind -x"
	      (see SHELL BUILTIN COMMANDS below).
       READLINE_POINT
	      The position of the insertion point in the readline line buffer,
	      for use with "bind -x" (see SHELL BUILTIN COMMANDS below).
       REPLY  Set to the line of input read by the read builtin	 command  when
	      no arguments are supplied.
       SECONDS
	      Each  time  this	parameter is referenced, the number of seconds
	      since shell invocation is returned.  If a value is  assigned  to
	      SECONDS,	the  value  returned upon subsequent references is the
	      number of seconds since the assignment plus the value  assigned.
	      If SECONDS is unset, it loses its special properties, even if it
	      is subsequently reset.
       SHELLOPTS
	      A colon-separated list of enabled shell options.	Each  word  in
	      the  list	 is  a	valid  argument	 for  the -o option to the set
	      builtin command (see SHELL BUILTIN COMMANDS below).  The options
	      appearing	 in  SHELLOPTS are those reported as on by set -o.  If
	      this variable is in the environment when bash  starts  up,  each
	      shell  option  in	 the  list  will be enabled before reading any
	      startup files.  This variable is read-only.
       SHLVL  Incremented by one each time an instance of bash is started.
       UID    Expands to the user ID of the current user, initialized at shell
	      startup.	This variable is readonly.

       The  following  variables  are  used by the shell.  In some cases, bash
       assigns a default value to a variable; these cases are noted below.

       BASH_COMPAT
	      The value is used to set the shell's compatibility  level.   See
	      the  description	of the shopt builtin below under SHELL BUILTIN
	      COMMANDS for a description of the various	 compatibility	levels
	      and  their  effects.   The  value may be a decimal number (e.g.,
	      4.2) or an integer (e.g., 42) corresponding to the desired  com‐
	      patibility  level.   If BASH_COMPAT is unset or set to the empty
	      string, the compatibility level is set to the  default  for  the
	      current  version.	  If BASH_COMPAT is set to a value that is not
	      one of the valid compatibility levels, the shell prints an error
	      message  and sets the compatibility level to the default for the
	      current version.	The valid compatibility levels	correspond  to
	      the   compatibility   options  accepted  by  the	shopt  builtin
	      described below (for example, compat42 means that 4.2 and 42 are
	      valid values).  The current version is also a valid value.
       BASH_ENV
	      If  this parameter is set when bash is executing a shell script,
	      its value is interpreted as a filename  containing  commands  to
	      initialize the shell, as in ~/.bashrc.  The value of BASH_ENV is
	      subjected to  parameter  expansion,  command  substitution,  and
	      arithmetic  expansion  before  being  interpreted as a filename.
	      PATH is not used to search for the resultant filename.
       BASH_XTRACEFD
	      If set to an integer corresponding to a valid  file  descriptor,
	      bash  will  write	 the  trace  output  generated	when set -x is
	      enabled to that file descriptor.	The file descriptor is	closed
	      when  BASH_XTRACEFD is unset or assigned a new value.  Unsetting
	      BASH_XTRACEFD or assigning it the empty string causes the	 trace
	      output  to  be  sent  to	the standard error.  Note that setting
	      BASH_XTRACEFD to 2 (the standard error file descriptor) and then
	      unsetting it will result in the standard error being closed.
       CDPATH The  search  path for the cd command.  This is a colon-separated
	      list of directories in which the	shell  looks  for  destination
	      directories  specified  by  the  cd  command.  A sample value is
	      ".:~:/usr".
       CHILD_MAX
	      Set the number of exited child status values for	the  shell  to
	      remember.	  Bash will not allow this value to be decreased below
	      a POSIX-mandated minimum, and there is  a	 maximum  value	 (cur‐
	      rently  8192)  that  this	 may not exceed.  The minimum value is
	      system-dependent.
       COLUMNS
	      Used by the select compound command to  determine	 the  terminal
	      width  when  printing selection lists.  Automatically set if the
	      checkwinsize option is enabled or in an interactive  shell  upon
	      receipt of a SIGWINCH.
       COMPREPLY
	      An array variable from which bash reads the possible completions
	      generated by a shell function invoked by the  programmable  com‐
	      pletion  facility	 (see  Programmable  Completion	 below).  Each
	      array element contains one possible completion.
       EMACS  If bash finds this variable in the environment  when  the	 shell
	      starts  with  value "t", it assumes that the shell is running in
	      an Emacs shell buffer and disables line editing.
       ENV    Similar to BASH_ENV; used when the shell	is  invoked  in	 POSIX
	      mode.
       EXECIGNORE
	      A	 colon-separated list of shell patterns (see Pattern Matching)
	      defining the list of filenames to be ignored by  command	search
	      using  PATH.  Files whose full pathnames match one of these pat‐
	      terns are not considered executable files for  the  purposes  of
	      completion and command execution via PATH lookup.	 This does not
	      affect the behavior of the [, test, and [[ commands.  Full path‐
	      names  in	 the command hash table are not subject to EXECIGNORE.
	      Use this variable to ignore shared library files that  have  the
	      executable  bit  set, but are not executable files.  The pattern
	      matching honors the setting of the extglob shell option.
       FCEDIT The default editor for the fc builtin command.
       FIGNORE
	      A colon-separated list of suffixes  to  ignore  when  performing
	      filename completion (see READLINE below).	 A filename whose suf‐
	      fix matches one of the entries in FIGNORE is excluded  from  the
	      list of matched filenames.  A sample value is ".o:~" (Quoting is
	      needed when assigning a value to this variable,  which  contains
	      tildes).
       FUNCNEST
	      If  set  to  a  numeric  value greater than 0, defines a maximum
	      function nesting level.  Function invocations that  exceed  this
	      nesting level will cause the current command to abort.
       GLOBIGNORE
	      A colon-separated list of patterns defining the set of filenames
	      to be ignored by pathname expansion.  If a filename matched by a
	      pathname	expansion  pattern also matches one of the patterns in
	      GLOBIGNORE, it is removed from the list of matches.
       HISTCONTROL
	      A colon-separated list of values controlling  how	 commands  are
	      saved  on	 the  history  list.   If  the list of values includes
	      ignorespace, lines which begin with a space  character  are  not
	      saved  in	 the history list.  A value of ignoredups causes lines
	      matching the previous history entry to not be saved.  A value of
	      ignoreboth is shorthand for ignorespace and ignoredups.  A value
	      of erasedups causes all previous lines matching the current line
	      to  be  removed from the history list before that line is saved.
	      Any value not in the above list is ignored.  If  HISTCONTROL  is
	      unset,  or does not include a valid value, all lines read by the
	      shell parser are saved on the history list, subject to the value
	      of  HISTIGNORE.  The second and subsequent lines of a multi-line
	      compound command are not tested, and are added  to  the  history
	      regardless of the value of HISTCONTROL.
       HISTFILE
	      The name of the file in which command history is saved (see HIS‐
	      TORY below).  The default value is ~/.bash_history.   If	unset,
	      the command history is not saved when a shell exits.
       HISTFILESIZE
	      The maximum number of lines contained in the history file.  When
	      this variable is assigned a value, the  history  file  is	 trun‐
	      cated,  if  necessary,  to  contain  no more than that number of
	      lines by removing the oldest entries.  The history file is  also
	      truncated	 to this size after writing it when a shell exits.  If
	      the value is 0, the history file	is  truncated  to  zero	 size.
	      Non-numeric  values  and	numeric	 values less than zero inhibit
	      truncation.  The shell sets the default value to	the  value  of
	      HISTSIZE after reading any startup files.
       HISTIGNORE
	      A	 colon-separated list of patterns used to decide which command
	      lines should be saved on the  history  list.   Each  pattern  is
	      anchored	at  the	 beginning of the line and must match the com‐
	      plete line (no implicit  `*'  is	appended).   Each  pattern  is
	      tested  against  the line after the checks specified by HISTCON‐
	      TROL are applied.	 In  addition  to  the	normal	shell  pattern
	      matching characters, `&' matches the previous history line.  `&'
	      may be escaped using  a  backslash;  the	backslash  is  removed
	      before attempting a match.  The second and subsequent lines of a
	      multi-line compound command are not tested, and are added to the
	      history  regardless  of  the  value  of HISTIGNORE.  The pattern
	      matching honors the setting of the extglob shell option.
       HISTSIZE
	      The number of commands to remember in the command	 history  (see
	      HISTORY  below).	 If  the value is 0, commands are not saved in
	      the history list.	 Numeric values less than zero result in every
	      command  being  saved  on	 the history list (there is no limit).
	      The shell sets the  default  value  to  500  after  reading  any
	      startup files.
       HISTTIMEFORMAT
	      If  this	variable  is  set and not null, its value is used as a
	      format string for strftime(3) to print the time stamp associated
	      with  each  history  entry displayed by the history builtin.  If
	      this variable is set, time stamps are  written  to  the  history
	      file  so they may be preserved across shell sessions.  This uses
	      the history comment character  to	 distinguish  timestamps  from
	      other history lines.
       HOME   The home directory of the current user; the default argument for
	      the cd builtin command.  The value of this variable is also used
	      when performing tilde expansion.
       HOSTFILE
	      Contains	the  name  of  a file in the same format as /etc/hosts
	      that should be read when the shell needs to complete a hostname.
	      The  list	 of possible hostname completions may be changed while
	      the shell is running;  the  next	time  hostname	completion  is
	      attempted	 after the value is changed, bash adds the contents of
	      the new file to the existing list.  If HOSTFILE is set, but  has
	      no  value,  or  does  not name a readable file, bash attempts to
	      read /etc/hosts to obtain the list of possible hostname  comple‐
	      tions.  When HOSTFILE is unset, the hostname list is cleared.
       IFS    The  Internal  Field  Separator  that is used for word splitting
	      after expansion and to split lines  into	words  with  the  read
	      builtin  command.	  The  default	value  is  ``<space><tab><new‐
	      line>''.
       IGNOREEOF
	      Controls the action of an interactive shell on receipt of an EOF
	      character as the sole input.  If set, the value is the number of
	      consecutive EOF characters which must  be	 typed	as  the	 first
	      characters  on an input line before bash exits.  If the variable
	      exists but does not have a numeric value, or has no  value,  the
	      default  value  is  10.  If it does not exist, EOF signifies the
	      end of input to the shell.
       INPUTRC
	      The filename for	the  readline  startup	file,  overriding  the
	      default of ~/.inputrc (see READLINE below).
       LANG   Used  to	determine  the	locale	category  for any category not
	      specifically selected with a variable starting with LC_.
       LC_ALL This variable overrides the value of  LANG  and  any  other  LC_
	      variable specifying a locale category.
       LC_COLLATE
	      This  variable  determines the collation order used when sorting
	      the results of pathname expansion, and determines	 the  behavior
	      of   range   expressions,	 equivalence  classes,	and  collating
	      sequences within pathname expansion and pattern matching.
       LC_CTYPE
	      This variable determines the interpretation  of  characters  and
	      the  behavior of character classes within pathname expansion and
	      pattern matching.
       LC_MESSAGES
	      This variable determines the locale used	to  translate  double-
	      quoted strings preceded by a $.
       LC_NUMERIC
	      This  variable  determines  the  locale category used for number
	      formatting.
       LC_TIME
	      This variable determines the locale category used for  data  and
	      time formatting.
       LINES  Used  by	the  select  compound  command to determine the column
	      length for printing selection lists.  Automatically set  if  the
	      checkwinsize  option  is enabled or in an interactive shell upon
	      receipt of a SIGWINCH.
       MAIL   If this parameter is set to a file or  directory	name  and  the
	      MAILPATH	variable  is  not  set,	 bash  informs the user of the
	      arrival of mail in the specified file or	Maildir-format	direc‐
	      tory.
       MAILCHECK
	      Specifies	 how  often  (in  seconds)  bash checks for mail.  The
	      default is 60 seconds.  When it is time to check for  mail,  the
	      shell  does  so  before  displaying the primary prompt.  If this
	      variable is unset, or set to  a  value  that  is	not  a	number
	      greater than or equal to zero, the shell disables mail checking.
       MAILPATH
	      A colon-separated list of filenames to be checked for mail.  The
	      message to be printed when mail arrives in a particular file may
	      be  specified by separating the filename from the message with a
	      `?'.  When used in the text of the message, $_  expands  to  the
	      name of the current mailfile.  Example:
	      MAILPATH='/var/mail/bfox?"You  have  mail":~/shell-mail?"$_  has
	      mail!"'
	      Bash can be configured to supply a default value for this	 vari‐
	      able  (there  is	no  value by default), but the location of the
	      user  mail  files	 that  it  uses	 is  system  dependent	(e.g.,
	      /var/mail/$USER).
       OPTERR If set to the value 1, bash displays error messages generated by
	      the getopts builtin command (see SHELL BUILTIN COMMANDS  below).
	      OPTERR  is  initialized to 1 each time the shell is invoked or a
	      shell script is executed.
       PATH   The search path for commands.  It is a colon-separated  list  of
	      directories  in  which the shell looks for commands (see COMMAND
	      EXECUTION below).	 A zero-length (null) directory	 name  in  the
	      value of PATH indicates the current directory.  A null directory
	      name may appear as two adjacent colons,  or  as  an  initial  or
	      trailing	colon.	 The  default path is system-dependent, and is
	      set by the administrator who installs bash.  A common value is
	      ``/usr/local/bin:/usr/local/sbin:/usr/bin:/usr/sbin:/bin:
	      /sbin''.
       POSIXLY_CORRECT
	      If this variable is in the environment  when  bash  starts,  the
	      shell  enters posix mode before reading the startup files, as if
	      the --posix invocation option had been supplied.	If it  is  set
	      while  the  shell is running, bash enables posix mode, as if the
	      command set -o posix had been executed.
       PROMPT_COMMAND
	      If set, the value is executed as a command prior to issuing each
	      primary prompt.
       PROMPT_DIRTRIM
	      If  set  to a number greater than zero, the value is used as the
	      number of trailing directory components to retain when expanding
	      the  \w  and  \W	prompt	string	escapes (see PROMPTING below).
	      Characters removed are replaced with an ellipsis.
       PS0    The value of this parameter is expanded  (see  PROMPTING	below)
	      and  displayed by interactive shells after reading a command and
	      before the command is executed.
       PS1    The value of this parameter is expanded  (see  PROMPTING	below)
	      and  used	 as  the  primary prompt string.  The default value is
	      ``\s-\v\$ ''.
       PS2    The value of this parameter is expanded as with PS1 and used  as
	      the secondary prompt string.  The default is ``> ''.
       PS3    The value of this parameter is used as the prompt for the select
	      command (see SHELL GRAMMAR above).
       PS4    The value of this parameter is expanded  as  with	 PS1  and  the
	      value  is	 printed  before  each command bash displays during an
	      execution trace.	The first character of PS4 is replicated  mul‐
	      tiple  times, as necessary, to indicate multiple levels of indi‐
	      rection.	The default is ``+ ''.
       SHELL  The full pathname to the shell is kept in this environment vari‐
	      able.   If  it is not set when the shell starts, bash assigns to
	      it the full pathname of the current user's login shell.
       TIMEFORMAT
	      The value of this parameter is used as a format string  specify‐
	      ing  how	the timing information for pipelines prefixed with the
	      time reserved word should be displayed.  The % character	intro‐
	      duces  an	 escape	 sequence  that is expanded to a time value or
	      other information.  The escape sequences and their meanings  are
	      as follows; the braces denote optional portions.
	      %%	A literal %.
	      %[p][l]R	The elapsed time in seconds.
	      %[p][l]U	The number of CPU seconds spent in user mode.
	      %[p][l]S	The number of CPU seconds spent in system mode.
	      %P	The CPU percentage, computed as (%U + %S) / %R.

	      The  optional  p is a digit specifying the precision, the number
	      of fractional digits after a decimal point.  A value of 0 causes
	      no decimal point or fraction to be output.  At most three places
	      after the decimal point may be specified; values	of  p  greater
	      than  3 are changed to 3.	 If p is not specified, the value 3 is
	      used.

	      The optional l specifies a longer format, including minutes,  of
	      the  form	 MMmSS.FFs.   The value of p determines whether or not
	      the fraction is included.

	      If this variable is not set, bash acts as if it  had  the	 value
	      $'\nreal\t%3lR\nuser\t%3lU\nsys\t%3lS'.	If  the value is null,
	      no timing information is displayed.  A trailing newline is added
	      when the format string is displayed.
       TMOUT  If  set  to  a  value greater than zero, TMOUT is treated as the
	      default timeout for the read builtin.  The select command termi‐
	      nates if input does not arrive after TMOUT seconds when input is
	      coming from a terminal.  In an interactive shell, the  value  is
	      interpreted as the number of seconds to wait for a line of input
	      after issuing the primary prompt.	 Bash terminates after waiting
	      for  that number of seconds if a complete line of input does not
	      arrive.
       TMPDIR If set, bash uses its value as the name of a directory in	 which
	      bash creates temporary files for the shell's use.
       auto_resume
	      This variable controls how the shell interacts with the user and
	      job control.  If this variable is set, single word  simple  com‐
	      mands without redirections are treated as candidates for resump‐
	      tion of an existing stopped job.	There is no ambiguity allowed;
	      if  there	 is more than one job beginning with the string typed,
	      the job most recently accessed  is  selected.   The  name	 of  a
	      stopped  job, in this context, is the command line used to start
	      it.  If set to the value exact, the string supplied  must	 match
	      the  name	 of  a	stopped	 job exactly; if set to substring, the
	      string supplied needs to match a substring  of  the  name	 of  a
	      stopped  job.  The substring value provides functionality analo‐
	      gous to the %?  job identifier (see JOB CONTROL below).  If  set
	      to  any  other  value, the supplied string must be a prefix of a
	      stopped job's name; this provides functionality analogous to the
	      %string job identifier.
       histchars
	      The  two or three characters which control history expansion and
	      tokenization (see HISTORY EXPANSION below).  The first character
	      is  the history expansion character, the character which signals
	      the start of a history  expansion,  normally  `!'.   The	second
	      character	 is the quick substitution character, which is used as
	      shorthand for re-running the previous command  entered,  substi‐
	      tuting  one  string  for another in the command.	The default is
	      `^'.  The optional third character is the character which	 indi‐
	      cates  that the remainder of the line is a comment when found as
	      the first character of a word, normally `#'.  The	 history  com‐
	      ment character causes history substitution to be skipped for the
	      remaining words on the line.  It does not necessarily cause  the
	      shell parser to treat the rest of the line as a comment.

   Arrays
       Bash  provides one-dimensional indexed and associative array variables.
       Any variable may be used as an indexed array; the declare builtin  will
       explicitly  declare an array.  There is no maximum limit on the size of
       an array, nor any requirement that members be indexed or assigned  con‐
       tiguously.   Indexed  arrays  are  referenced using integers (including
       arithmetic expressions) and are zero-based; associative arrays are ref‐
       erenced using arbitrary strings.	 Unless otherwise noted, indexed array
       indices must be non-negative integers.

       An indexed array is created automatically if any variable  is  assigned
       to using the syntax name[subscript]=value.  The subscript is treated as
       an arithmetic expression that must evaluate to a number.	 To explicitly
       declare	an  indexed array, use declare -a name (see SHELL BUILTIN COM‐
       MANDS below).  declare -a name[subscript] is also  accepted;  the  sub‐
       script is ignored.

       Associative arrays are created using declare -A name.

       Attributes may be specified for an array variable using the declare and
       readonly builtins.  Each attribute applies to all members of an array.

       Arrays  are  assigned  to  using	 compound  assignments	of  the	  form
       name=(value1  ...  valuen),  where  each	 value	is  of	the form [sub‐
       script]=string.	Indexed array assignments do not require anything  but
       string.	When assigning to indexed arrays, if the optional brackets and
       subscript are supplied, that index is assigned to; otherwise the	 index
       of  the element assigned is the last index assigned to by the statement
       plus one.  Indexing starts at zero.

       When assigning to an associative array, the subscript is required.

       This syntax is also accepted by the declare builtin.  Individual	 array
       elements	 may  be  assigned  to	using the name[subscript]=value syntax
       introduced above.  When assigning to an indexed array, if name is  sub‐
       scripted	 by  a negative number, that number is interpreted as relative
       to one greater than the maximum index  of  name,	 so  negative  indices
       count back from the end of the array, and an index of -1 references the
       last element.

       Any element of an array may  be	referenced  using  ${name[subscript]}.
       The braces are required to avoid conflicts with pathname expansion.  If
       subscript is @ or *, the word expands to all members  of	 name.	 These
       subscripts  differ only when the word appears within double quotes.  If
       the word is double-quoted, ${name[*]} expands to a single word with the
       value  of each array member separated by the first character of the IFS
       special variable, and ${name[@]} expands each element of name to a sep‐
       arate  word.   When  there  are no array members, ${name[@]} expands to
       nothing.	 If the double-quoted expansion	 occurs	 within	 a  word,  the
       expansion  of  the first parameter is joined with the beginning part of
       the original word, and the expansion of the last	 parameter  is	joined
       with  the  last	part  of  the original word.  This is analogous to the
       expansion of the special parameters * and  @  (see  Special  Parameters
       above).	 ${#name[subscript]}  expands  to  the	length	of ${name[sub‐
       script]}.  If subscript is * or @, the expansion is the number of  ele‐
       ments  in  the array.  If the subscript used to reference an element of
       an indexed array evaluates to a number less than	 zero,	it  is	inter‐
       preted  as relative to one greater than the maximum index of the array,
       so negative indices count back from the end of the array, and an	 index
       of -1 references the last element.

       Referencing an array variable without a subscript is equivalent to ref‐
       erencing the array with a subscript of 0.  Any reference to a  variable
       using a valid subscript is legal, and bash will create an array if nec‐
       essary.

       An array variable is considered set if a subscript has been assigned  a
       value.  The null string is a valid value.

       It  is possible to obtain the keys (indices) of an array as well as the
       values.	${!name[@]} and ${!name[*]} expand to the indices assigned  in
       array variable name.  The treatment when in double quotes is similar to
       the expansion of the special parameters @ and * within double quotes.

       The unset builtin is used to  destroy  arrays.	unset  name[subscript]
       destroys	 the array element at index subscript.	Negative subscripts to
       indexed arrays are interpreted as described above.  Care must be	 taken
       to  avoid  unwanted  side  effects caused by pathname expansion.	 unset
       name, where name is an array, or unset name[subscript], where subscript
       is * or @, removes the entire array.

       The  declare,  local,  and readonly builtins each accept a -a option to
       specify an indexed array and a -A  option  to  specify  an  associative
       array.	If  both  options are supplied, -A takes precedence.  The read
       builtin accepts a -a option to assign a list of	words  read  from  the
       standard input to an array.  The set and declare builtins display array
       values in a way that allows them to be reused as assignments.

EXPANSION
       Expansion is performed on the command line after it has been split into
       words.	There are seven kinds of expansion performed: brace expansion,
       tilde expansion, parameter and variable	expansion,  command  substitu‐
       tion, arithmetic expansion, word splitting, and pathname expansion.

       The order of expansions is: brace expansion; tilde expansion, parameter
       and variable expansion, arithmetic expansion, and command  substitution
       (done  in a left-to-right fashion); word splitting; and pathname expan‐
       sion.

       On systems that can support it, there is an additional expansion avail‐
       able:  process  substitution.   This  is	 performed at the same time as
       tilde, parameter, variable, and arithmetic expansion and	 command  sub‐
       stitution.

       After  these  expansions are performed, quote characters present in the
       original word are removed  unless  they	have  been  quoted  themselves
       (quote removal).

       Only brace expansion, word splitting, and pathname expansion can change
       the number of words of the expansion; other expansions expand a	single
       word  to a single word.	The only exceptions to this are the expansions
       of "$@" and "${name[@]}" as explained above (see PARAMETERS).

   Brace Expansion
       Brace expansion is a mechanism by which arbitrary strings may be gener‐
       ated.   This  mechanism is similar to pathname expansion, but the file‐
       names generated need not exist.	Patterns to be brace expanded take the
       form of an optional preamble, followed by either a series of comma-sep‐
       arated strings or a sequence expression between a pair of braces,  fol‐
       lowed  by  an  optional	postscript.   The preamble is prefixed to each
       string contained within the braces, and the postscript is then appended
       to each resulting string, expanding left to right.

       Brace  expansions  may  be nested.  The results of each expanded string
       are not sorted;	left  to  right	 order	is  preserved.	 For  example,
       a{d,c,b}e expands into `ade ace abe'.

       A  sequence expression takes the form {x..y[..incr]}, where x and y are
       either integers or single characters, and incr, an optional  increment,
       is  an  integer.	 When integers are supplied, the expression expands to
       each number between x and y, inclusive.	Supplied integers may be  pre‐
       fixed  with 0 to force each term to have the same width.	 When either x
       or y begins with a zero, the shell  attempts  to	 force	all  generated
       terms  to  contain the same number of digits, zero-padding where neces‐
       sary.  When characters are supplied, the	 expression  expands  to  each
       character  lexicographically  between  x	 and  y,  inclusive, using the
       default C locale.  Note that both x and y must be  of  the  same	 type.
       When  the  increment  is supplied, it is used as the difference between
       each term.  The default increment is 1 or -1 as appropriate.

       Brace expansion is performed before any other expansions, and any char‐
       acters  special to other expansions are preserved in the result.	 It is
       strictly textual.  Bash does not apply any syntactic interpretation  to
       the context of the expansion or the text between the braces.

       A  correctly-formed  brace  expansion must contain unquoted opening and
       closing braces, and at least one unquoted comma	or  a  valid  sequence
       expression.   Any incorrectly formed brace expansion is left unchanged.
       A { or , may be quoted with a backslash to prevent its being considered
       part  of	 a brace expression.  To avoid conflicts with parameter expan‐
       sion, the string ${ is not considered eligible for brace expansion.

       This construct is typically used as shorthand when the common prefix of
       the strings to be generated is longer than in the above example:

	      mkdir /usr/local/src/bash/{old,new,dist,bugs}
       or
	      chown root /usr/{ucb/{ex,edit},lib/{ex?.?*,how_ex}}

       Brace  expansion	 introduces  a	slight incompatibility with historical
       versions of sh.	sh does not treat opening or closing braces  specially
       when  they  appear as part of a word, and preserves them in the output.
       Bash removes braces from words as a  consequence	 of  brace  expansion.
       For  example,  a word entered to sh as file{1,2} appears identically in
       the output.  The same word is output as file1 file2 after expansion  by
       bash.   If strict compatibility with sh is desired, start bash with the
       +B option or disable brace expansion with the +B option to the set com‐
       mand (see SHELL BUILTIN COMMANDS below).

   Tilde Expansion
       If  a  word  begins  with an unquoted tilde character (`~'), all of the
       characters preceding the first unquoted slash (or  all  characters,  if
       there  is no unquoted slash) are considered a tilde-prefix.  If none of
       the characters in the tilde-prefix are quoted, the  characters  in  the
       tilde-prefix  following the tilde are treated as a possible login name.
       If this login name is the null string, the tilde is replaced  with  the
       value  of  the shell parameter HOME.  If HOME is unset, the home direc‐
       tory of the user executing the shell is	substituted  instead.	Other‐
       wise,  the  tilde-prefix is replaced with the home directory associated
       with the specified login name.

       If the tilde-prefix is a `~+', the value	 of  the  shell	 variable  PWD
       replaces the tilde-prefix.  If the tilde-prefix is a `~-', the value of
       the shell variable OLDPWD, if it is set, is substituted.	 If the	 char‐
       acters  following  the tilde in the tilde-prefix consist of a number N,
       optionally prefixed by a `+' or a `-',  the  tilde-prefix  is  replaced
       with the corresponding element from the directory stack, as it would be
       displayed by the dirs builtin invoked with the tilde-prefix as an argu‐
       ment.   If  the characters following the tilde in the tilde-prefix con‐
       sist of a number without a leading `+' or `-', `+' is assumed.

       If the login name is invalid, or the tilde expansion fails, the word is
       unchanged.

       Each variable assignment is checked for unquoted tilde-prefixes immedi‐
       ately following a : or the first =.  In these cases, tilde expansion is
       also  performed.	  Consequently,	 one  may use filenames with tildes in
       assignments to PATH, MAILPATH, and CDPATH, and the  shell  assigns  the
       expanded value.

   Parameter Expansion
       The `$' character introduces parameter expansion, command substitution,
       or arithmetic expansion.	 The parameter name or symbol to  be  expanded
       may  be enclosed in braces, which are optional but serve to protect the
       variable to be expanded from characters immediately following it	 which
       could be interpreted as part of the name.

       When  braces  are  used, the matching ending brace is the first `}' not
       escaped by a backslash or within a quoted string,  and  not  within  an
       embedded	 arithmetic  expansion,	 command  substitution,	 or  parameter
       expansion.

       ${parameter}
	      The value of parameter is substituted.  The braces are  required
	      when  parameter  is  a  positional  parameter with more than one
	      digit, or when parameter is followed by a character which is not
	      to be interpreted as part of its name.  The parameter is a shell
	      parameter as described above PARAMETERS) or an  array  reference
	      (Arrays).

       If  the	first  character of parameter is an exclamation point (!), and
       parameter is not a nameref, it introduces a level of variable  indirec‐
       tion.   Bash  uses  the	value  of the variable formed from the rest of
       parameter as the name of the variable; this variable is	then  expanded
       and that value is used in the rest of the substitution, rather than the
       value of parameter itself.  This is known as  indirect  expansion.   If
       parameter is a nameref, this expands to the name of the variable refer‐
       enced by parameter instead of performing the complete  indirect	expan‐
       sion.   The  exceptions	to  this are the expansions of ${!prefix*} and
       ${!name[@]} described below.  The exclamation  point  must  immediately
       follow the left brace in order to introduce indirection.

       In each of the cases below, word is subject to tilde expansion, parame‐
       ter expansion, command substitution, and arithmetic expansion.

       When not performing substring expansion,	 using	the  forms  documented
       below  (e.g.,  :-),  bash  tests for a parameter that is unset or null.
       Omitting the colon results in a test  only  for	a  parameter  that  is
       unset.

       ${parameter:-word}
	      Use  Default  Values.  If parameter is unset or null, the expan‐
	      sion of word is substituted.  Otherwise, the value of  parameter
	      is substituted.
       ${parameter:=word}
	      Assign  Default  Values.	 If  parameter	is  unset or null, the
	      expansion of word is assigned to parameter.  The value of param‐
	      eter  is	then  substituted.   Positional parameters and special
	      parameters may not be assigned to in this way.
       ${parameter:?word}
	      Display Error if Null or Unset.  If parameter is null or	unset,
	      the  expansion  of  word (or a message to that effect if word is
	      not present) is written to the standard error and the shell,  if
	      it is not interactive, exits.  Otherwise, the value of parameter
	      is substituted.
       ${parameter:+word}
	      Use Alternate Value.  If parameter is null or unset, nothing  is
	      substituted, otherwise the expansion of word is substituted.
       ${parameter:offset}
       ${parameter:offset:length}
	      Substring	 Expansion.  Expands to up to length characters of the
	      value of parameter starting at the character specified  by  off‐
	      set.  If parameter is @, an indexed array subscripted by @ or *,
	      or an associative array name, the results	 differ	 as  described
	      below.   If  length  is omitted, expands to the substring of the
	      value of parameter starting at the character specified by offset
	      and  extending  to  the end of the value.	 length and offset are
	      arithmetic expressions (see ARITHMETIC EVALUATION below).

	      If offset evaluates to a number less than	 zero,	the  value  is
	      used  as	an  offset  in characters from the end of the value of
	      parameter.  If length evaluates to a number less than  zero,  it
	      is  interpreted  as  an offset in characters from the end of the
	      value of parameter rather than a number of characters,  and  the
	      expansion	 is  the  characters  between  offset and that result.
	      Note that a negative offset must be separated from the colon  by
	      at  least	 one  space to avoid being confused with the :- expan‐
	      sion.

	      If parameter is @, the result is	length	positional  parameters
	      beginning at offset.  A negative offset is taken relative to one
	      greater than the greatest positional parameter, so an offset  of
	      -1  evaluates to the last positional parameter.  It is an expan‐
	      sion error if length evaluates to a number less than zero.

	      If parameter is an indexed array name subscripted by @ or *, the
	      result  is  the  length  members	of  the	 array	beginning with
	      ${parameter[offset]}.  A negative offset is  taken  relative  to
	      one  greater  than the maximum index of the specified array.  It
	      is an expansion error if length evaluates to a number less  than
	      zero.

	      Substring	 expansion  applied  to	 an associative array produces
	      undefined results.

	      Substring indexing is zero-based unless the  positional  parame‐
	      ters  are	 used,	in  which  case	 the  indexing	starts at 1 by
	      default.	If offset is 0,	 and  the  positional  parameters  are
	      used, $0 is prefixed to the list.

       ${!prefix*}
       ${!prefix@}
	      Names  matching prefix.  Expands to the names of variables whose
	      names begin with prefix, separated by the first character of the
	      IFS  special variable.  When @ is used and the expansion appears
	      within double quotes, each variable name expands to  a  separate
	      word.

       ${!name[@]}
       ${!name[*]}
	      List  of	array  keys.  If name is an array variable, expands to
	      the list of array indices (keys) assigned in name.  If  name  is
	      not  an  array,  expands to 0 if name is set and null otherwise.
	      When @ is used and the expansion appears within  double  quotes,
	      each key expands to a separate word.

       ${#parameter}
	      Parameter	 length.   The	length	in  characters of the value of
	      parameter is substituted.	 If parameter is *  or	@,  the	 value
	      substituted  is the number of positional parameters.  If parame‐
	      ter is an array name subscripted by * or @,  the	value  substi‐
	      tuted  is	 the number of elements in the array.  If parameter is
	      an indexed array name subscripted by  a  negative	 number,  that
	      number  is interpreted as relative to one greater than the maxi‐
	      mum index of parameter, so negative indices count back from  the
	      end  of  the  array, and an index of -1 references the last ele‐
	      ment.

       ${parameter#word}
       ${parameter##word}
	      Remove matching prefix pattern.  The word is expanded to produce
	      a pattern just as in pathname expansion.	If the pattern matches
	      the beginning of the value of parameter, then the result of  the
	      expansion	 is  the expanded value of parameter with the shortest
	      matching pattern (the ``#'' case) or the longest	matching  pat‐
	      tern  (the  ``##''  case)	 deleted.  If parameter is @ or *, the
	      pattern removal operation is applied to each positional  parame‐
	      ter in turn, and the expansion is the resultant list.  If param‐
	      eter is an array variable subscripted with @ or *,  the  pattern
	      removal  operation  is  applied  to  each member of the array in
	      turn, and the expansion is the resultant list.

       ${parameter%word}
       ${parameter%%word}
	      Remove matching suffix pattern.  The word is expanded to produce
	      a pattern just as in pathname expansion.	If the pattern matches
	      a trailing portion of the expanded value of parameter, then  the
	      result  of the expansion is the expanded value of parameter with
	      the shortest matching pattern (the ``%'' case)  or  the  longest
	      matching	pattern	 (the ``%%'' case) deleted.  If parameter is @
	      or *, the pattern removal operation is  applied  to  each	 posi‐
	      tional  parameter	 in  turn,  and the expansion is the resultant
	      list.  If parameter is an array variable subscripted with	 @  or
	      *,  the  pattern	removal operation is applied to each member of
	      the array in turn, and the expansion is the resultant list.

       ${parameter/pattern/string}
	      Pattern substitution.  The pattern is expanded to produce a pat‐
	      tern  just  as in pathname expansion.  Parameter is expanded and
	      the longest match of pattern against its value is replaced  with
	      string.	If  pattern  begins with /, all matches of pattern are
	      replaced	with  string.	Normally  only	the  first  match   is
	      replaced.	 If pattern begins with #, it must match at the begin‐
	      ning of the expanded value of parameter.	If pattern begins with
	      %,  it must match at the end of the expanded value of parameter.
	      If string is null, matches of pattern are deleted and the / fol‐
	      lowing  pattern may be omitted.  If the nocasematch shell option
	      is enabled, the match is performed without regard to the case of
	      alphabetic characters.  If parameter is @ or *, the substitution
	      operation is applied to each positional parameter in  turn,  and
	      the  expansion  is the resultant list.  If parameter is an array
	      variable subscripted with @ or *, the substitution operation  is
	      applied  to  each member of the array in turn, and the expansion
	      is the resultant list.

       ${parameter^pattern}
       ${parameter^^pattern}
       ${parameter,pattern}
       ${parameter,,pattern}
	      Case modification.  This expansion modifies the case  of	alpha‐
	      betic  characters in parameter.  The pattern is expanded to pro‐
	      duce a pattern just as in pathname expansion.  Each character in
	      the  expanded value of parameter is tested against pattern, and,
	      if it matches the pattern, its case is converted.	  The  pattern
	      should  not  attempt  to	match  more than one character.	 The ^
	      operator converts lowercase letters matching pattern  to	upper‐
	      case; the , operator converts matching uppercase letters to low‐
	      ercase.  The ^^ and ,, expansions convert each matched character
	      in  the expanded value; the ^ and , expansions match and convert
	      only the first character in the expanded value.  If  pattern  is
	      omitted,	it is treated like a ?, which matches every character.
	      If parameter is @ or  *,	the  case  modification	 operation  is
	      applied  to each positional parameter in turn, and the expansion
	      is the resultant list.  If parameter is an array	variable  sub‐
	      scripted with @ or *, the case modification operation is applied
	      to each member of the array in turn, and the  expansion  is  the
	      resultant list.

       ${parameter@operator}
	      Parameter transformation.	 The expansion is either a transforma‐
	      tion of the value of parameter or	 information  about  parameter
	      itself,  depending on the value of operator.  Each operator is a
	      single letter:

	      Q	     The expansion is a string that is the value of  parameter
		     quoted in a format that can be reused as input.
	      E	     The  expansion is a string that is the value of parameter
		     with backslash escape  sequences  expanded	 as  with  the
		     $'...' quoting mechansim.
	      P	     The expansion is a string that is the result of expanding
		     the value of parameter as if it were a prompt string (see
		     PROMPTING below).
	      A	     The  expansion  is	 a string in the form of an assignment
		     statement or declare command  that,  if  evaluated,  will
		     recreate parameter with its attributes and value.
	      a	     The  expansion is a string consisting of flag values rep‐
		     resenting parameter's attributes.

	      If parameter is @ or *, the operation is applied to  each	 posi‐
	      tional  parameter	 in  turn,  and the expansion is the resultant
	      list.  If parameter is an array variable subscripted with	 @  or
	      *,  the case modification operation is applied to each member of
	      the array in turn, and the expansion is the resultant list.

	      The result of the expansion is subject  to  word	splitting  and
	      pathname expansion as described below.

   Command Substitution
       Command substitution allows the output of a command to replace the com‐
       mand name.  There are two forms:

	      $(command)
       or
	      `command`

       Bash performs the expansion by executing command in a subshell environ‐
       ment and replacing the command substitution with the standard output of
       the command, with any trailing newlines deleted.	 Embedded newlines are
       not  deleted,  but they may be removed during word splitting.  The com‐
       mand substitution $(cat file) can be replaced  by  the  equivalent  but
       faster $(< file).

       When  the  old-style  backquote form of substitution is used, backslash
       retains its literal meaning except when followed by $, `,  or  \.   The
       first backquote not preceded by a backslash terminates the command sub‐
       stitution.  When using the $(command) form, all characters between  the
       parentheses make up the command; none are treated specially.

       Command substitutions may be nested.  To nest when using the backquoted
       form, escape the inner backquotes with backslashes.

       If the substitution appears within double quotes,  word	splitting  and
       pathname expansion are not performed on the results.

   Arithmetic Expansion
       Arithmetic  expansion allows the evaluation of an arithmetic expression
       and the substitution of the result.  The format for  arithmetic	expan‐
       sion is:

	      $((expression))

       The  old	 format	 $[expression]	is  deprecated	and will be removed in
       upcoming versions of bash.

       The expression is treated as if it were within  double  quotes,	but  a
       double  quote  inside  the  parentheses	is not treated specially.  All
       tokens in the expression undergo parameter and variable expansion, com‐
       mand  substitution,  and	 quote	removal.  The result is treated as the
       arithmetic expression to be evaluated.  Arithmetic  expansions  may  be
       nested.

       The  evaluation	is performed according to the rules listed below under
       ARITHMETIC EVALUATION.  If expression is invalid, bash prints a message
       indicating failure and no substitution occurs.

   Process Substitution
       Process	substitution allows a process's input or output to be referred
       to using a filename.  It takes the form of  <(list)  or	>(list).   The
       process	list is run asynchronously, and its input or output appears as
       a filename.  This filename is passed as an argument to the current com‐
       mand  as	 the  result  of  the expansion.  If the >(list) form is used,
       writing to the file will provide input for list.	 If the	 <(list)  form
       is  used,  the  file passed as an argument should be read to obtain the
       output of list.	Process substitution is supported on systems that sup‐
       port named pipes (FIFOs) or the /dev/fd method of naming open files.

       When  available,	 process substitution is performed simultaneously with
       parameter and variable expansion, command substitution, and  arithmetic
       expansion.

   Word Splitting
       The  shell  scans the results of parameter expansion, command substitu‐
       tion, and arithmetic expansion that did not occur within double	quotes
       for word splitting.

       The  shell  treats each character of IFS as a delimiter, and splits the
       results of the other expansions into words using	 these	characters  as
       field   terminators.   If  IFS  is  unset,  or  its  value  is  exactly
       <space><tab><newline>, the default, then sequences of  <space>,	<tab>,
       and  <newline>  at the beginning and end of the results of the previous
       expansions are ignored, and any sequence of IFS characters not  at  the
       beginning  or  end  serves  to delimit words.  If IFS has a value other
       than the default, then sequences of the	whitespace  characters	space,
       tab,  and  newline are ignored at the beginning and end of the word, as
       long as the whitespace character is in the value of IFS (an IFS	white‐
       space  character).   Any	 character  in IFS that is not IFS whitespace,
       along with any adjacent IFS whitespace characters, delimits a field.  A
       sequence	 of  IFS whitespace characters is also treated as a delimiter.
       If the value of IFS is null, no word splitting occurs.

       Explicit null arguments ("" or '') are retained and passed to  commands
       as empty strings.  Unquoted implicit null arguments, resulting from the
       expansion of parameters that have no values, are removed.  If a parame‐
       ter  with  no  value  is expanded within double quotes, a null argument
       results and is retained and passed to a command	as  an	empty  string.
       When  a	quoted null argument appears as part of a word whose expansion
       is non-null, the null argument is removed.   That  is,  the  word  -d''
       becomes -d after word splitting and null argument removal.

       Note that if no expansion occurs, no splitting is performed.

   Pathname Expansion
       After  word  splitting,	unless	the -f option has been set, bash scans
       each word for the characters *, ?, and [.  If one of  these  characters
       appears,	 then  the word is regarded as a pattern, and replaced with an
       alphabetically sorted list of filenames matching the pattern (see  Pat‐
       tern  Matching  below).	 If  no	 matching filenames are found, and the
       shell option nullglob is not enabled, the word is left  unchanged.   If
       the  nullglob  option  is  set,	and  no matches are found, the word is
       removed.	 If the failglob shell option  is  set,	 and  no  matches  are
       found, an error message is printed and the command is not executed.  If
       the shell option nocaseglob is enabled, the match is performed  without
       regard  to  the	case  of  alphabetic characters.  Note that when using
       range expressions like [a-z] (see below), letters of the other case may
       be included, depending on the setting of LC_COLLATE.  When a pattern is
       used for pathname expansion, the character ``.''	 at  the  start	 of  a
       name  or	 immediately  following	 a  slash  must be matched explicitly,
       unless the shell option dotglob is set.	When matching a pathname,  the
       slash character must always be matched explicitly.  In other cases, the
       ``.''  character is not treated	specially.   See  the  description  of
       shopt  below  under  SHELL  BUILTIN  COMMANDS  for a description of the
       nocaseglob, nullglob, failglob, and dotglob shell options.

       The GLOBIGNORE shell variable may be used to restrict the set of	 file‐
       names matching a pattern.  If GLOBIGNORE is set, each matching filename
       that also matches one of the patterns in GLOBIGNORE is removed from the
       list of matches.	 If the nocaseglob option is set, the matching against
       the patterns in GLOBIGNORE is performed without regard  to  case.   The
       filenames  ``.''	 and ``..''  are always ignored when GLOBIGNORE is set
       and not null.  However, setting GLOBIGNORE to a non-null value has  the
       effect  of  enabling  the  dotglob shell option, so all other filenames
       beginning with a ``.''  will match.  To get the old behavior of	ignor‐
       ing  filenames beginning with a ``.'', make ``.*''  one of the patterns
       in GLOBIGNORE.  The dotglob  option  is	disabled  when	GLOBIGNORE  is
       unset.	The  pattern  matching honors the setting of the extglob shell
       option.

       Pattern Matching

       Any character that appears in a pattern, other than the special pattern
       characters  described below, matches itself.  The NUL character may not
       occur in a pattern.  A backslash escapes the following  character;  the
       escaping	 backslash  is	discarded  when matching.  The special pattern
       characters must be quoted if they are to be matched literally.

       The special pattern characters have the following meanings:

	      *	     Matches any string, including the null string.  When  the
		     globstar  shell  option  is  enabled,  and * is used in a
		     pathname expansion context, two adjacent  *s  used	 as  a
		     single  pattern  will  match  all	files and zero or more
		     directories and subdirectories.  If followed by a /,  two
		     adjacent  *s  will match only directories and subdirecto‐
		     ries.
	      ?	     Matches any single character.
	      [...]  Matches any one of the enclosed characters.   A  pair  of
		     characters	 separated by a hyphen denotes a range expres‐
		     sion; any character that falls between those two  charac‐
		     ters,  inclusive,	using  the  current locale's collating
		     sequence and character set, is  matched.	If  the	 first
		     character following the [ is a !  or a ^ then any charac‐
		     ter not enclosed is matched.  The sorting order of	 char‐
		     acters  in range expressions is determined by the current
		     locale and the values of the LC_COLLATE or	 LC_ALL	 shell
		     variables, if set.	 To obtain the traditional interpreta‐
		     tion of range expressions, where [a-d] is	equivalent  to
		     [abcd],  set  value of the LC_ALL shell variable to C, or
		     enable the globasciiranges shell  option.	 A  -  may  be
		     matched by including it as the first or last character in
		     the set.  A ] may be matched by including it as the first
		     character in the set.

		     Within  [ and ], character classes can be specified using
		     the syntax [:class:], where class is one of the following
		     classes defined in the POSIX standard:
		     alnum  alpha  ascii  blank	 cntrl digit graph lower print
		     punct space upper word xdigit
		     A character class matches any character belonging to that
		     class.  The word character class matches letters, digits,
		     and the character _.

		     Within [ and ], an equivalence  class  can	 be  specified
		     using the syntax [=c=], which matches all characters with
		     the same collation weight	(as  defined  by  the  current
		     locale) as the character c.

		     Within [ and ], the syntax [.symbol.] matches the collat‐
		     ing symbol symbol.

       If the extglob shell option is enabled using the shopt builtin, several
       extended	 pattern  matching operators are recognized.  In the following
       description, a pattern-list is a list of one or more patterns separated
       by a |.	Composite patterns may be formed using one or more of the fol‐
       lowing sub-patterns:

	      ?(pattern-list)
		     Matches zero or one occurrence of the given patterns
	      *(pattern-list)
		     Matches zero or more occurrences of the given patterns
	      +(pattern-list)
		     Matches one or more occurrences of the given patterns
	      @(pattern-list)
		     Matches one of the given patterns
	      !(pattern-list)
		     Matches anything except one of the given patterns

   Quote Removal
       After the preceding expansions, all unquoted occurrences of the charac‐
       ters  \,	 ', and " that did not result from one of the above expansions
       are removed.

REDIRECTION
       Before a command is executed, its input and output  may	be  redirected
       using  a special notation interpreted by the shell.  Redirection allows
       commands' file handles to be duplicated, opened, closed, made to	 refer
       to different files, and can change the files the command reads from and
       writes to.  Redirection may also be used to modify file handles in  the
       current	shell execution environment.  The following redirection opera‐
       tors may precede or appear anywhere within a simple command or may fol‐
       low  a  command.	  Redirections are processed in the order they appear,
       from left to right.

       Each redirection that may be preceded by a file descriptor  number  may
       instead be preceded by a word of the form {varname}.  In this case, for
       each redirection operator except >&- and <&-, the shell will allocate a
       file  descriptor	 greater than or equal to 10 and assign it to varname.
       If >&- or <&- is preceded by {varname}, the value  of  varname  defines
       the file descriptor to close.

       In  the	following descriptions, if the file descriptor number is omit‐
       ted, and the first character of the redirection operator is <, the  re‐
       direction  refers  to  the  standard input (file descriptor 0).	If the
       first character of the  redirection  operator  is  >,  the  redirection
       refers to the standard output (file descriptor 1).

       The  word  following the redirection operator in the following descrip‐
       tions, unless otherwise noted, is subjected to brace  expansion,	 tilde
       expansion,  parameter  and  variable  expansion,	 command substitution,
       arithmetic expansion,  quote  removal,  pathname	 expansion,  and  word
       splitting.  If it expands to more than one word, bash reports an error.

       Note  that  the order of redirections is significant.  For example, the
       command

	      ls > dirlist 2>&1

       directs both standard output and standard error to  the	file  dirlist,
       while the command

	      ls 2>&1 > dirlist

       directs	only the standard output to file dirlist, because the standard
       error was duplicated from the standard output before the standard  out‐
       put was redirected to dirlist.

       Bash handles several filenames specially when they are used in redirec‐
       tions, as described in the following table.  If the operating system on
       which bash is running provides these special files, bash will use them;
       otherwise it will emulate them internally with the  behavior  described
       below.

	      /dev/fd/fd
		     If	 fd  is	 a valid integer, file descriptor fd is dupli‐
		     cated.
	      /dev/stdin
		     File descriptor 0 is duplicated.
	      /dev/stdout
		     File descriptor 1 is duplicated.
	      /dev/stderr
		     File descriptor 2 is duplicated.
	      /dev/tcp/host/port
		     If host is a valid hostname or Internet address, and port
		     is	 an integer port number or service name, bash attempts
		     to open the corresponding TCP socket.
	      /dev/udp/host/port
		     If host is a valid hostname or Internet address, and port
		     is	 an integer port number or service name, bash attempts
		     to open the corresponding UDP socket.

       A failure to open or create a file causes the redirection to fail.

       Redirections using file descriptors greater than 9 should be used  with
       care,  as they may conflict with file descriptors the shell uses inter‐
       nally.

       Note that the exec builtin command can make redirections take effect in
       the current shell.

   Redirecting Input
       Redirection of input causes the file whose name results from the expan‐
       sion of word to be opened for reading on	 file  descriptor  n,  or  the
       standard input (file descriptor 0) if n is not specified.

       The general format for redirecting input is:

	      [n]<word

   Redirecting Output
       Redirection  of	output	causes	the  file  whose name results from the
       expansion of word to be opened for writing on file descriptor n, or the
       standard output (file descriptor 1) if n is not specified.  If the file
       does not exist it is created; if it does exist it is truncated to  zero
       size.

       The general format for redirecting output is:

	      [n]>word

       If  the	redirection operator is >, and the noclobber option to the set
       builtin has been enabled, the redirection will fail if the  file	 whose
       name  results  from the expansion of word exists and is a regular file.
       If the redirection operator is >|, or the redirection operator is > and
       the noclobber option to the set builtin command is not enabled, the re‐
       direction is attempted even if the file named by word exists.

   Appending Redirected Output
       Redirection of output in	 this  fashion	causes	the  file  whose  name
       results	from  the expansion of word to be opened for appending on file
       descriptor n, or the standard output (file descriptor 1) if  n  is  not
       specified.  If the file does not exist it is created.

       The general format for appending output is:

	      [n]>>word

   Redirecting Standard Output and Standard Error
       This  construct allows both the standard output (file descriptor 1) and
       the standard error output (file descriptor 2) to be redirected  to  the
       file whose name is the expansion of word.

       There  are  two	formats	 for  redirecting standard output and standard
       error:

	      &>word
       and
	      >&word

       Of the two forms, the first is preferred.  This is semantically equiva‐
       lent to

	      >word 2>&1

       When  using  the second form, word may not expand to a number or -.  If
       it does,	 other	redirection  operators	apply  (see  Duplicating  File
       Descriptors below) for compatibility reasons.

   Appending Standard Output and Standard Error
       This  construct allows both the standard output (file descriptor 1) and
       the standard error output (file descriptor 2) to	 be  appended  to  the
       file whose name is the expansion of word.

       The format for appending standard output and standard error is:

	      &>>word

       This is semantically equivalent to

	      >>word 2>&1

       (see Duplicating File Descriptors below).

   Here Documents
       This  type  of  redirection  instructs the shell to read input from the
       current source until a line containing only delimiter (with no trailing
       blanks)	is seen.  All of the lines read up to that point are then used
       as the standard input (or file descriptor n if n is  specified)	for  a
       command.

       The format of here-documents is:

	      [n]<<[-]word
		      here-document
	      delimiter

       No  parameter  and variable expansion, command substitution, arithmetic
       expansion, or pathname expansion is performed on word.  If any part  of
       word  is	 quoted, the delimiter is the result of quote removal on word,
       and the lines in the  here-document  are	 not  expanded.	  If  word  is
       unquoted,  all  lines  of  the here-document are subjected to parameter
       expansion, command substitution, and arithmetic expansion, the  charac‐
       ter  sequence  \<newline>  is  ignored, and \ must be used to quote the
       characters \, $, and `.

       If the redirection operator is <<-, then all leading tab characters are
       stripped	 from  input  lines  and  the line containing delimiter.  This
       allows here-documents within shell scripts to be indented in a  natural
       fashion.

   Here Strings
       A variant of here documents, the format is:

	      [n]<<<word

       The  word  undergoes  brace  expansion,	tilde expansion, parameter and
       variable expansion, command  substitution,  arithmetic  expansion,  and
       quote  removal.	 Pathname  expansion  and  word splitting are not per‐
       formed.	The result is supplied as a  single  string,  with  a  newline
       appended, to the command on its standard input (or file descriptor n if
       n is specified).

   Duplicating File Descriptors
       The redirection operator

	      [n]<&word

       is used to duplicate input file descriptors.  If word expands to one or
       more  digits,  the file descriptor denoted by n is made to be a copy of
       that file descriptor.  If the digits in word  do	 not  specify  a  file
       descriptor  open for input, a redirection error occurs.	If word evalu‐
       ates to -, file descriptor n is closed.	If n  is  not  specified,  the
       standard input (file descriptor 0) is used.

       The operator

	      [n]>&word

       is  used	 similarly  to duplicate output file descriptors.  If n is not
       specified, the standard output (file descriptor 1)  is  used.   If  the
       digits  in word do not specify a file descriptor open for output, a re‐
       direction error occurs.	If word evaluates to -, file descriptor	 n  is
       closed.	 As  a special case, if n is omitted, and word does not expand
       to one or more digits or -, the standard output and standard error  are
       redirected as described previously.

   Moving File Descriptors
       The redirection operator

	      [n]<&digit-

       moves  the  file descriptor digit to file descriptor n, or the standard
       input (file descriptor 0) if n is not specified.	 digit is closed after
       being duplicated to n.

       Similarly, the redirection operator

	      [n]>&digit-

       moves  the  file descriptor digit to file descriptor n, or the standard
       output (file descriptor 1) if n is not specified.

   Opening File Descriptors for Reading and Writing
       The redirection operator

	      [n]<>word

       causes the file whose name is the expansion of word to  be  opened  for
       both  reading and writing on file descriptor n, or on file descriptor 0
       if n is not specified.  If the file does not exist, it is created.

ALIASES
       Aliases allow a string to be substituted for a word when it is used  as
       the  first  word	 of  a	simple command.	 The shell maintains a list of
       aliases that may be set and unset with the alias	 and  unalias  builtin
       commands	 (see  SHELL  BUILTIN COMMANDS below).	The first word of each
       simple command, if unquoted, is checked to see if it has an alias.   If
       so,  that word is replaced by the text of the alias.  The characters /,
       $, `, and = and any of the shell metacharacters or  quoting  characters
       listed above may not appear in an alias name.  The replacement text may
       contain any valid shell input,  including  shell	 metacharacters.   The
       first  word  of	the replacement text is tested for aliases, but a word
       that is identical to an alias being expanded is not expanded  a	second
       time.   This  means  that  one may alias ls to ls -F, for instance, and
       bash does not try to recursively expand the replacement text.   If  the
       last  character	of  the	 alias value is a blank, then the next command
       word following the alias is also checked for alias expansion.

       Aliases are created and listed with the alias command, and removed with
       the unalias command.

       There  is no mechanism for using arguments in the replacement text.  If
       arguments are needed, a shell function should be	 used  (see  FUNCTIONS
       below).

       Aliases	are not expanded when the shell is not interactive, unless the
       expand_aliases shell option is set using shopt (see the description  of
       shopt under SHELL BUILTIN COMMANDS below).

       The  rules  concerning  the  definition and use of aliases are somewhat
       confusing.  Bash always reads at	 least	one  complete  line  of	 input
       before  executing  any  of  the	commands  on  that  line.  Aliases are
       expanded when a command is read, not when it is	executed.   Therefore,
       an  alias definition appearing on the same line as another command does
       not take effect until the next line of input  is	 read.	 The  commands
       following the alias definition on that line are not affected by the new
       alias.  This behavior is also an issue  when  functions	are  executed.
       Aliases	are  expanded when a function definition is read, not when the
       function is executed, because a function definition is  itself  a  com‐
       mand.   As  a consequence, aliases defined in a function are not avail‐
       able until after that function is executed.  To	be  safe,  always  put
       alias  definitions on a separate line, and do not use alias in compound
       commands.

       For almost every purpose, aliases are superseded by shell functions.

FUNCTIONS
       A shell function, defined  as  described	 above	under  SHELL  GRAMMAR,
       stores  a  series  of commands for later execution.  When the name of a
       shell function is used as a simple command name, the list  of  commands
       associated with that function name is executed.	Functions are executed
       in the context of the current shell;  no	 new  process  is  created  to
       interpret  them	(contrast  this with the execution of a shell script).
       When a function is executed, the arguments to the function  become  the
       positional parameters during its execution.  The special parameter # is
       updated to reflect the change.  Special parameter 0 is unchanged.   The
       first  element of the FUNCNAME variable is set to the name of the func‐
       tion while the function is executing.

       All other aspects of the	 shell	execution  environment	are  identical
       between	a function and its caller with these exceptions: the DEBUG and
       RETURN traps (see the description  of  the  trap	 builtin  under	 SHELL
       BUILTIN	COMMANDS below) are not inherited unless the function has been
       given the trace attribute (see the description of the  declare  builtin
       below)  or  the -o functrace shell option has been enabled with the set
       builtin (in which case all  functions  inherit  the  DEBUG  and	RETURN
       traps),	and the ERR trap is not inherited unless the -o errtrace shell
       option has been enabled.

       Variables local to the function may be declared with the local  builtin
       command.	 Ordinarily, variables and their values are shared between the
       function and its caller.

       The FUNCNEST variable, if set  to  a  numeric  value  greater  than  0,
       defines	a  maximum  function nesting level.  Function invocations that
       exceed the limit cause the entire command to abort.

       If the builtin command return is executed in a function,	 the  function
       completes  and  execution resumes with the next command after the func‐
       tion call.  Any command associated with the  RETURN  trap  is  executed
       before execution resumes.  When a function completes, the values of the
       positional parameters and the special parameter # are restored  to  the
       values they had prior to the function's execution.

       Function	 names and definitions may be listed with the -f option to the
       declare or typeset builtin commands.  The -F option to declare or type‐
       set  will  list the function names only (and optionally the source file
       and line number, if the extdebug shell option is	 enabled).   Functions
       may  be exported so that subshells automatically have them defined with
       the -f option to the export builtin.   A	 function  definition  may  be
       deleted	using  the  -f	option	to the unset builtin.  Note that shell
       functions and variables with the same name may result in multiple iden‐
       tically-named  entries  in  the environment passed to the shell's chil‐
       dren.  Care should be taken in cases where this may cause a problem.

       Functions may be recursive.  The FUNCNEST variable may be used to limit
       the  depth  of the function call stack and restrict the number of func‐
       tion invocations.  By default, no limit is imposed  on  the  number  of
       recursive calls.

ARITHMETIC EVALUATION
       The  shell allows arithmetic expressions to be evaluated, under certain
       circumstances (see the let and declare builtin commands,	 the  ((  com‐
       pound command, and Arithmetic Expansion).  Evaluation is done in fixed-
       width integers with no check for overflow,  though  division  by	 0  is
       trapped	and  flagged as an error.  The operators and their precedence,
       associativity, and values are the same as in the C language.  The  fol‐
       lowing  list  of	 operators  is grouped into levels of equal-precedence
       operators.  The levels are listed in order of decreasing precedence.

       id++ id--
	      variable post-increment and post-decrement
       ++id --id
	      variable pre-increment and pre-decrement
       - +    unary minus and plus
       ! ~    logical and bitwise negation
       **     exponentiation
       * / %  multiplication, division, remainder
       + -    addition, subtraction
       << >>  left and right bitwise shifts
       <= >= < >
	      comparison
       == !=  equality and inequality
       &      bitwise AND
       ^      bitwise exclusive OR
       |      bitwise OR
       &&     logical AND
       ||     logical OR
       expr?expr:expr
	      conditional operator
       = *= /= %= += -= <<= >>= &= ^= |=
	      assignment
       expr1 , expr2
	      comma

       Shell variables are allowed as operands; parameter  expansion  is  per‐
       formed before the expression is evaluated.  Within an expression, shell
       variables may also be referenced by name without	 using	the  parameter
       expansion  syntax.  A shell variable that is null or unset evaluates to
       0 when referenced by name without using the parameter expansion syntax.
       The  value  of a variable is evaluated as an arithmetic expression when
       it is referenced, or when a variable which has been given  the  integer
       attribute using declare -i is assigned a value.	A null value evaluates
       to 0.  A shell variable need not have its integer attribute  turned  on
       to be used in an expression.

       Constants with a leading 0 are interpreted as octal numbers.  A leading
       0x or  0X  denotes  hexadecimal.	  Otherwise,  numbers  take  the  form
       [base#]n,  where the optional base is a decimal number between 2 and 64
       representing the arithmetic base, and n is a number in that  base.   If
       base#  is omitted, then base 10 is used.	 When specifying n, the digits
       greater than 9 are represented by the lowercase letters, the  uppercase
       letters, @, and _, in that order.  If base is less than or equal to 36,
       lowercase and uppercase letters may be used interchangeably  to	repre‐
       sent numbers between 10 and 35.

       Operators  are  evaluated  in  order of precedence.  Sub-expressions in
       parentheses are evaluated first and may override the  precedence	 rules
       above.

CONDITIONAL EXPRESSIONS
       Conditional  expressions	 are  used  by the [[ compound command and the
       test and [ builtin commands to test file attributes and perform	string
       and  arithmetic comparisons.  Expressions are formed from the following
       unary or binary primaries.  Bash handles	 several  filenames  specially
       when  they  are	used in expressions.  If the operating system on which
       bash is running provides these special files, bash will use them;  oth‐
       erwise  it will emulate them internally with this behavior: If any file
       argument to one of the primaries is of the form	/dev/fd/n,  then  file
       descriptor  n is checked.  If the file argument to one of the primaries
       is one of /dev/stdin, /dev/stdout, or /dev/stderr, file	descriptor  0,
       1, or 2, respectively, is checked.

       Unless otherwise specified, primaries that operate on files follow sym‐
       bolic links and operate on the target of the link, rather than the link
       itself.

       When  used  with [[, the < and > operators sort lexicographically using
       the current locale.  The test command sorts using ASCII ordering.

       -a file
	      True if file exists.
       -b file
	      True if file exists and is a block special file.
       -c file
	      True if file exists and is a character special file.
       -d file
	      True if file exists and is a directory.
       -e file
	      True if file exists.
       -f file
	      True if file exists and is a regular file.
       -g file
	      True if file exists and is set-group-id.
       -h file
	      True if file exists and is a symbolic link.
       -k file
	      True if file exists and its ``sticky'' bit is set.
       -p file
	      True if file exists and is a named pipe (FIFO).
       -r file
	      True if file exists and is readable.
       -s file
	      True if file exists and has a size greater than zero.
       -t fd  True if file descriptor fd is open and refers to a terminal.
       -u file
	      True if file exists and its set-user-id bit is set.
       -w file
	      True if file exists and is writable.
       -x file
	      True if file exists and is executable.
       -G file
	      True if file exists and is owned by the effective group id.
       -L file
	      True if file exists and is a symbolic link.
       -N file
	      True if file exists and has been	modified  since	 it  was  last
	      read.
       -O file
	      True if file exists and is owned by the effective user id.
       -S file
	      True if file exists and is a socket.
       file1 -ef file2
	      True  if file1 and file2 refer to the same device and inode num‐
	      bers.
       file1 -nt file2
	      True if file1 is newer (according	 to  modification  date)  than
	      file2, or if file1 exists and file2 does not.
       file1 -ot file2
	      True  if file1 is older than file2, or if file2 exists and file1
	      does not.
       -o optname
	      True if the shell option optname is enabled.  See	 the  list  of
	      options  under  the  description	of  the	 -o  option to the set
	      builtin below.
       -v varname
	      True if the shell variable varname is set (has been  assigned  a
	      value).
       -R varname
	      True  if	the shell variable varname is set and is a name refer‐
	      ence.
       -z string
	      True if the length of string is zero.
       string
       -n string
	      True if the length of string is non-zero.

       string1 == string2
       string1 = string2
	      True if the strings are equal.  = should be used with  the  test
	      command  for  POSIX conformance.	When used with the [[ command,
	      this performs pattern matching as described above (Compound Com‐
	      mands).

       string1 != string2
	      True if the strings are not equal.

       string1 < string2
	      True if string1 sorts before string2 lexicographically.

       string1 > string2
	      True if string1 sorts after string2 lexicographically.

       arg1 OP arg2
	      OP  is one of -eq, -ne, -lt, -le, -gt, or -ge.  These arithmetic
	      binary operators return true if arg1 is equal to, not equal  to,
	      less  than, less than or equal to, greater than, or greater than
	      or equal to arg2, respectively.  Arg1 and arg2 may  be  positive
	      or negative integers.

SIMPLE COMMAND EXPANSION
       When  a	simple	command	 is executed, the shell performs the following
       expansions, assignments, and redirections, from left to right.

       1.     The words that the parser has  marked  as	 variable  assignments
	      (those  preceding	 the  command name) and redirections are saved
	      for later processing.

       2.     The words that are not variable assignments or redirections  are
	      expanded.	  If  any words remain after expansion, the first word
	      is taken to be the name of the command and the  remaining	 words
	      are the arguments.

       3.     Redirections are performed as described above under REDIRECTION.

       4.     The text after the = in each variable assignment undergoes tilde
	      expansion, parameter expansion, command substitution, arithmetic
	      expansion,  and quote removal before being assigned to the vari‐
	      able.

       If no command name results, the variable assignments affect the current
       shell  environment.  Otherwise, the variables are added to the environ‐
       ment of the executed command and do not affect the current shell	 envi‐
       ronment.	  If  any  of  the assignments attempts to assign a value to a
       readonly variable, an error occurs, and the command exits with  a  non-
       zero status.

       If  no  command	name  results,	redirections are performed, but do not
       affect the current shell environment.  A redirection error  causes  the
       command to exit with a non-zero status.

       If  there is a command name left after expansion, execution proceeds as
       described below.	 Otherwise, the command exits.	If one of  the	expan‐
       sions  contained a command substitution, the exit status of the command
       is the exit status of the  last	command	 substitution  performed.   If
       there were no command substitutions, the command exits with a status of
       zero.

COMMAND EXECUTION
       After a command has been split into words, if it results	 in  a	simple
       command	and  an	 optional list of arguments, the following actions are
       taken.

       If the command name contains no slashes, the shell attempts  to	locate
       it.   If	 there	exists a shell function by that name, that function is
       invoked as described above in FUNCTIONS.	 If the name does not match  a
       function,  the shell searches for it in the list of shell builtins.  If
       a match is found, that builtin is invoked.

       If the name is neither a shell function nor a builtin, and contains  no
       slashes,	 bash  searches	 each element of the PATH for a directory con‐
       taining an executable file by that name.	 Bash uses  a  hash  table  to
       remember	 the  full pathnames of executable files (see hash under SHELL
       BUILTIN COMMANDS below).	 A full search of the directories in  PATH  is
       performed  only	if the command is not found in the hash table.	If the
       search is unsuccessful, the shell searches for a defined shell function
       named command_not_found_handle.	If that function exists, it is invoked
       with the original command and the original command's arguments  as  its
       arguments,  and	the  function's exit status becomes the exit status of
       the shell.  If that function is not defined, the shell prints an	 error
       message and returns an exit status of 127.

       If  the	search	is  successful, or if the command name contains one or
       more slashes, the shell executes the named program in a separate execu‐
       tion environment.  Argument 0 is set to the name given, and the remain‐
       ing arguments to the command are set to the arguments given, if any.

       If this execution fails because the file is not in  executable  format,
       and  the file is not a directory, it is assumed to be a shell script, a
       file containing shell commands.	A subshell is spawned to  execute  it.
       This  subshell  reinitializes itself, so that the effect is as if a new
       shell had been invoked to handle the script, with  the  exception  that
       the  locations  of  commands  remembered	 by the parent (see hash below
       under SHELL BUILTIN COMMANDS) are retained by the child.

       If the program is a file beginning with #!, the remainder of the	 first
       line  specifies an interpreter for the program.	The shell executes the
       specified interpreter on operating systems that do not handle this exe‐
       cutable format themselves.  The arguments to the interpreter consist of
       a single optional argument following the interpreter name on the	 first
       line  of	 the program, followed by the name of the program, followed by
       the command arguments, if any.

COMMAND EXECUTION ENVIRONMENT
       The shell has an execution environment, which consists of  the  follow‐
       ing:

       ·      open  files inherited by the shell at invocation, as modified by
	      redirections supplied to the exec builtin

       ·      the current working directory as set by cd, pushd, or  popd,  or
	      inherited by the shell at invocation

       ·      the  file	 creation  mode mask as set by umask or inherited from
	      the shell's parent

       ·      current traps set by trap

       ·      shell parameters that are set by variable assignment or with set
	      or inherited from the shell's parent in the environment

       ·      shell  functions	defined during execution or inherited from the
	      shell's parent in the environment

       ·      options enabled at invocation (either by default	or  with  com‐
	      mand-line arguments) or by set

       ·      options enabled by shopt

       ·      shell aliases defined with alias

       ·      various  process	IDs,  including	 those of background jobs, the
	      value of $$, and the value of PPID

       When a simple command other than a builtin or shell function is	to  be
       executed,  it  is invoked in a separate execution environment that con‐
       sists of the following.	Unless otherwise noted, the values are	inher‐
       ited from the shell.

       ·      the  shell's  open  files,  plus any modifications and additions
	      specified by redirections to the command

       ·      the current working directory

       ·      the file creation mode mask

       ·      shell variables and functions  marked  for  export,  along  with
	      variables exported for the command, passed in the environment

       ·      traps caught by the shell are reset to the values inherited from
	      the shell's parent, and traps ignored by the shell are ignored

       A command invoked  in  this  separate  environment  cannot  affect  the
       shell's execution environment.

       Command	substitution, commands grouped with parentheses, and asynchro‐
       nous commands are invoked in a subshell environment that is a duplicate
       of  the	shell  environment,  except that traps caught by the shell are
       reset to the values that the shell inherited from its parent at invoca‐
       tion.  Builtin commands that are invoked as part of a pipeline are also
       executed in a subshell environment.  Changes made to the subshell envi‐
       ronment cannot affect the shell's execution environment.

       Subshells spawned to execute command substitutions inherit the value of
       the -e option from the parent shell.  When  not	in  posix  mode,  bash
       clears the -e option in such subshells.

       If  a  command  is  followed  by a & and job control is not active, the
       default standard input for the command is  the  empty  file  /dev/null.
       Otherwise,  the	invoked	 command  inherits the file descriptors of the
       calling shell as modified by redirections.

ENVIRONMENT
       When a program is invoked it is given an array of  strings  called  the
       environment.   This  is	a  list	 of  name-value	 pairs,	 of  the  form
       name=value.

       The shell provides several ways	to  manipulate	the  environment.   On
       invocation, the shell scans its own environment and creates a parameter
       for each name found, automatically marking it for export to child  pro‐
       cesses.	 Executed  commands  inherit  the environment.	The export and
       declare -x commands allow parameters and functions to be added  to  and
       deleted from the environment.  If the value of a parameter in the envi‐
       ronment is modified, the new value becomes  part	 of  the  environment,
       replacing  the  old.  The environment inherited by any executed command
       consists of the shell's initial environment, whose values may be	 modi‐
       fied  in	 the  shell, less any pairs removed by the unset command, plus
       any additions via the export and declare -x commands.

       The environment for any simple command or  function  may	 be  augmented
       temporarily  by	prefixing  it with parameter assignments, as described
       above in PARAMETERS.  These assignment statements affect only the envi‐
       ronment seen by that command.

       If  the	-k option is set (see the set builtin command below), then all
       parameter assignments are placed in the environment for a command,  not
       just those that precede the command name.

       When  bash  invokes  an	external command, the variable _ is set to the
       full filename of the command and passed to that command in its environ‐
       ment.

EXIT STATUS
       The  exit  status  of  an executed command is the value returned by the
       waitpid system call or equivalent function.  Exit statuses fall between
       0  and  255, though, as explained below, the shell may use values above
       125 specially.  Exit statuses from shell builtins and compound commands
       are also limited to this range.	Under certain circumstances, the shell
       will use special values to indicate specific failure modes.

       For the shell's purposes, a command which exits with a zero exit status
       has  succeeded.	 An exit status of zero indicates success.  A non-zero
       exit status indicates failure.  When a command terminates  on  a	 fatal
       signal N, bash uses the value of 128+N as the exit status.

       If  a  command  is  not	found, the child process created to execute it
       returns a status of 127.	 If a command is found but is not  executable,
       the return status is 126.

       If a command fails because of an error during expansion or redirection,
       the exit status is greater than zero.

       Shell builtin commands return a status of 0 (true) if  successful,  and
       non-zero	 (false)  if an error occurs while they execute.  All builtins
       return an exit status of	 2  to	indicate  incorrect  usage,  generally
       invalid options or missing arguments.

       Bash  itself  returns  the  exit	 status	 of the last command executed,
       unless a syntax error occurs, in which case it exits  with  a  non-zero
       value.  See also the exit builtin command below.

SIGNALS
       When  bash  is  interactive,  in	 the  absence of any traps, it ignores
       SIGTERM (so that kill 0 does not kill an interactive shell), and SIGINT
       is  caught and handled (so that the wait builtin is interruptible).  In
       all cases, bash ignores SIGQUIT.	 If job control	 is  in	 effect,  bash
       ignores SIGTTIN, SIGTTOU, and SIGTSTP.

       Non-builtin commands run by bash have signal handlers set to the values
       inherited by the shell from its parent.	When job  control  is  not  in
       effect,	asynchronous commands ignore SIGINT and SIGQUIT in addition to
       these inherited handlers.  Commands run as a result of command  substi‐
       tution ignore the keyboard-generated job control signals SIGTTIN, SIGT‐
       TOU, and SIGTSTP.

       The shell exits by default upon receipt of a SIGHUP.   Before  exiting,
       an  interactive	shell  resends	the  SIGHUP  to	 all  jobs, running or
       stopped.	 Stopped jobs are sent SIGCONT to ensure that they receive the
       SIGHUP.	 To  prevent the shell from sending the signal to a particular
       job, it should be removed from the jobs table with the  disown  builtin
       (see  SHELL  BUILTIN  COMMANDS  below)  or marked to not receive SIGHUP
       using disown -h.

       If the huponexit shell option has been set with	shopt,	bash  sends  a
       SIGHUP to all jobs when an interactive login shell exits.

       If  bash is waiting for a command to complete and receives a signal for
       which a trap has been set, the trap will not be executed until the com‐
       mand  completes.	  When bash is waiting for an asynchronous command via
       the wait builtin, the reception of a signal for which a trap  has  been
       set will cause the wait builtin to return immediately with an exit sta‐
       tus greater than 128, immediately after which the trap is executed.

JOB CONTROL
       Job control refers to the ability to  selectively  stop	(suspend)  the
       execution of processes and continue (resume) their execution at a later
       point.  A user typically	 employs  this	facility  via  an  interactive
       interface  supplied  jointly  by the operating system kernel's terminal
       driver and bash.

       The shell associates a job with each pipeline.  It  keeps  a  table  of
       currently  executing  jobs,  which may be listed with the jobs command.
       When bash starts a job asynchronously (in the background), it prints  a
       line that looks like:

	      [1] 25647

       indicating that this job is job number 1 and that the process ID of the
       last process in the pipeline associated with this job is 25647.	All of
       the  processes  in a single pipeline are members of the same job.  Bash
       uses the job abstraction as the basis for job control.

       To facilitate the implementation of the user interface to job  control,
       the operating system maintains the notion of a current terminal process
       group ID.  Members of this process group (processes whose process group
       ID is equal to the current terminal process group ID) receive keyboard-
       generated signals such as SIGINT.  These processes are said  to	be  in
       the  foreground.	 Background processes are those whose process group ID
       differs from the terminal's; such processes are immune to keyboard-gen‐
       erated signals.	Only foreground processes are allowed to read from or,
       if the user so specifies with  stty  tostop,  write  to	the  terminal.
       Background  processes  which  attempt  to read from (write to when stty
       tostop is in effect) the terminal are sent a SIGTTIN  (SIGTTOU)	signal
       by  the	kernel's  terminal  driver, which, unless caught, suspends the
       process.

       If the operating system on which bash is running supports job  control,
       bash contains facilities to use it.  Typing the suspend character (typ‐
       ically ^Z, Control-Z) while a process is running causes that process to
       be  stopped  and	 returns  control to bash.  Typing the delayed suspend
       character (typically ^Y, Control-Y) causes the process  to  be  stopped
       when  it	 attempts  to  read input from the terminal, and control to be
       returned to bash.  The user may then manipulate the state of this  job,
       using  the  bg command to continue it in the background, the fg command
       to continue it in the foreground, or the kill command to kill it.  A ^Z
       takes effect immediately, and has the additional side effect of causing
       pending output and typeahead to be discarded.

       There are a number of ways to refer to a job in the shell.  The charac‐
       ter  %  introduces  a job specification (jobspec).  Job number n may be
       referred to as %n.  A job may also be referred to using a prefix of the
       name used to start it, or using a substring that appears in its command
       line.  For example, %ce refers to  a  stopped  ce  job.	 If  a	prefix
       matches	more  than one job, bash reports an error.  Using %?ce, on the
       other hand, refers to any job containing the string ce in  its  command
       line.   If  the	substring  matches  more than one job, bash reports an
       error.  The symbols %% and %+ refer to the shell's notion of  the  cur‐
       rent  job, which is the last job stopped while it was in the foreground
       or started in the background.  The previous job may be referenced using
       %-.  If there is only a single job, %+ and %- can both be used to refer
       to that job.  In output pertaining to jobs (e.g.,  the  output  of  the
       jobs command), the current job is always flagged with a +, and the pre‐
       vious job with a -.  A single % (with no	 accompanying  job  specifica‐
       tion) also refers to the current job.

       Simply  naming a job can be used to bring it into the foreground: %1 is
       a synonym for ``fg %1'', bringing job 1 from the	 background  into  the
       foreground.   Similarly,	 ``%1  &''  resumes  job  1 in the background,
       equivalent to ``bg %1''.

       The shell learns immediately whenever a job changes  state.   Normally,
       bash waits until it is about to print a prompt before reporting changes
       in a job's status so as to not interrupt any other output.  If  the  -b
       option to the set builtin command is enabled, bash reports such changes
       immediately.  Any trap on SIGCHLD  is  executed	for  each  child  that
       exits.

       If  an  attempt to exit bash is made while jobs are stopped (or, if the
       checkjobs shell option has been enabled using the shopt	builtin,  run‐
       ning), the shell prints a warning message, and, if the checkjobs option
       is enabled, lists the jobs and their statuses.  The  jobs  command  may
       then  be	 used to inspect their status.	If a second attempt to exit is
       made without an intervening command, the shell does not	print  another
       warning, and any stopped jobs are terminated.

PROMPTING
       When executing interactively, bash displays the primary prompt PS1 when
       it is ready to read a command, and the secondary	 prompt	 PS2  when  it
       needs  more  input  to  complete a command.  Bash displays PS0 after it
       reads a command but before executing  it.   Bash	 allows	 these	prompt
       strings	to  be	customized  by inserting a number of backslash-escaped
       special characters that are decoded as follows:
	      \a     an ASCII bell character (07)
	      \d     the date in "Weekday Month Date" format (e.g.,  "Tue  May
		     26")
	      \D{format}
		     the  format  is  passed  to strftime(3) and the result is
		     inserted into the prompt string; an empty format  results
		     in a locale-specific time representation.	The braces are
		     required
	      \e     an ASCII escape character (033)
	      \h     the hostname up to the first `.'
	      \H     the hostname
	      \j     the number of jobs currently managed by the shell
	      \l     the basename of the shell's terminal device name
	      \n     newline
	      \r     carriage return
	      \s     the name of the shell, the basename of  $0	 (the  portion
		     following the final slash)
	      \t     the current time in 24-hour HH:MM:SS format
	      \T     the current time in 12-hour HH:MM:SS format
	      \@     the current time in 12-hour am/pm format
	      \A     the current time in 24-hour HH:MM format
	      \u     the username of the current user
	      \v     the version of bash (e.g., 2.00)
	      \V     the release of bash, version + patch level (e.g., 2.00.0)
	      \w     the  current  working  directory,	with $HOME abbreviated
		     with a tilde (uses the value of the PROMPT_DIRTRIM	 vari‐
		     able)
	      \W     the basename of the current working directory, with $HOME
		     abbreviated with a tilde
	      \!     the history number of this command
	      \#     the command number of this command
	      \$     if the effective UID is 0, a #, otherwise a $
	      \nnn   the character corresponding to the octal number nnn
	      \\     a backslash
	      \[     begin a sequence of non-printing characters, which	 could
		     be	 used  to  embed  a terminal control sequence into the
		     prompt
	      \]     end a sequence of non-printing characters

       The command number and the history number are  usually  different:  the
       history	number of a command is its position in the history list, which
       may include commands  restored  from  the  history  file	 (see  HISTORY
       below),	while  the  command  number is the position in the sequence of
       commands executed during the current shell session.  After  the	string
       is  decoded,  it is expanded via parameter expansion, command substitu‐
       tion, arithmetic expansion, and quote removal, subject to the value  of
       the  promptvars	shell option (see the description of the shopt command
       under SHELL BUILTIN COMMANDS below).

READLINE
       This is the library that handles reading input when using  an  interac‐
       tive shell, unless the --noediting option is given at shell invocation.
       Line editing is also used when using the -e option to the read builtin.
       By default, the line editing commands are similar to those of Emacs.  A
       vi-style line editing interface is also available.  Line editing can be
       enabled	at  any	 time  using  the -o emacs or -o vi options to the set
       builtin (see SHELL BUILTIN COMMANDS below).  To turn off	 line  editing
       after  the  shell  is running, use the +o emacs or +o vi options to the
       set builtin.

   Readline Notation
       In this section, the Emacs-style notation is used to denote keystrokes.
       Control	keys  are  denoted by C-key, e.g., C-n means Control-N.	 Simi‐
       larly, meta keys are denoted by M-key, so M-x means Meta-X.   (On  key‐
       boards  without a meta key, M-x means ESC x, i.e., press the Escape key
       then the x key.	This makes ESC the meta prefix.	 The combination M-C-x
       means  ESC-Control-x, or press the Escape key then hold the Control key
       while pressing the x key.)

       Readline commands may be given numeric arguments, which normally act as
       a  repeat  count.   Sometimes,  however, it is the sign of the argument
       that is significant.  Passing a negative argument  to  a	 command  that
       acts  in the forward direction (e.g., kill-line) causes that command to
       act in a backward direction.  Commands whose  behavior  with  arguments
       deviates from this are noted below.

       When  a command is described as killing text, the text deleted is saved
       for possible future retrieval (yanking).	 The killed text is saved in a
       kill ring.  Consecutive kills cause the text to be accumulated into one
       unit, which can be yanked all at once.  Commands which do not kill text
       separate the chunks of text on the kill ring.

   Readline Initialization
       Readline	 is  customized	 by putting commands in an initialization file
       (the inputrc file).  The name of this file is taken from the  value  of
       the  INPUTRC  variable.	 If  that  variable  is	 unset, the default is
       ~/.inputrc.  When a program which uses the readline library starts  up,
       the initialization file is read, and the key bindings and variables are
       set.  There are only a few basic constructs  allowed  in	 the  readline
       initialization  file.  Blank lines are ignored.	Lines beginning with a
       # are comments.	Lines beginning with a	$  indicate  conditional  con‐
       structs.	 Other lines denote key bindings and variable settings.

       The  default  key-bindings  may be changed with an inputrc file.	 Other
       programs that use this library may add their own commands and bindings.

       For example, placing

	      M-Control-u: universal-argument
       or
	      C-Meta-u: universal-argument
       into the inputrc would make M-C-u execute the readline command  univer‐
       sal-argument.

       The  following  symbolic	 character  names are recognized: RUBOUT, DEL,
       ESC, LFD, NEWLINE, RET, RETURN, SPC, SPACE, and TAB.

       In addition to command names, readline allows keys to  be  bound	 to  a
       string that is inserted when the key is pressed (a macro).

   Readline Key Bindings
       The  syntax for controlling key bindings in the inputrc file is simple.
       All that is required is the name of the command or the text of a	 macro
       and a key sequence to which it should be bound.	The name may be speci‐
       fied in one of two ways: as a symbolic key name, possibly with Meta- or
       Control- prefixes, or as a key sequence.

       When using the form keyname:function-name or macro, keyname is the name
       of a key spelled out in English.	 For example:

	      Control-u: universal-argument
	      Meta-Rubout: backward-kill-word
	      Control-o: "> output"

       In the above example, C-u is bound to the function  universal-argument,
       M-DEL  is bound to the function backward-kill-word, and C-o is bound to
       run the macro expressed on the right hand side (that is, to insert  the
       text ``> output'' into the line).

       In  the	second	form,  "keyseq":function-name or macro, keyseq differs
       from keyname above in that strings denoting an entire key sequence  may
       be  specified  by  placing the sequence within double quotes.  Some GNU
       Emacs style key escapes can be used, as in the following	 example,  but
       the symbolic character names are not recognized.

	      "\C-u": universal-argument
	      "\C-x\C-r": re-read-init-file
	      "\e[11~": "Function Key 1"

       In this example, C-u is again bound to the function universal-argument.
       C-x C-r is bound to the function re-read-init-file, and ESC [ 1 1 ~  is
       bound to insert the text ``Function Key 1''.

       The full set of GNU Emacs style escape sequences is
	      \C-    control prefix
	      \M-    meta prefix
	      \e     an escape character
	      \\     backslash
	      \"     literal "
	      \'     literal '

       In  addition  to	 the GNU Emacs style escape sequences, a second set of
       backslash escapes is available:
	      \a     alert (bell)
	      \b     backspace
	      \d     delete
	      \f     form feed
	      \n     newline
	      \r     carriage return
	      \t     horizontal tab
	      \v     vertical tab
	      \nnn   the eight-bit character whose value is  the  octal	 value
		     nnn (one to three digits)
	      \xHH   the  eight-bit  character	whose value is the hexadecimal
		     value HH (one or two hex digits)

       When entering the text of a macro, single or double quotes must be used
       to indicate a macro definition.	Unquoted text is assumed to be a func‐
       tion name.  In the macro body, the backslash  escapes  described	 above
       are  expanded.	Backslash  will quote any other character in the macro
       text, including " and '.

       Bash allows the current readline key bindings to be displayed or	 modi‐
       fied  with  the bind builtin command.  The editing mode may be switched
       during interactive use by using the -o option to the set	 builtin  com‐
       mand (see SHELL BUILTIN COMMANDS below).

   Readline Variables
       Readline has variables that can be used to further customize its behav‐
       ior.  A variable may be set in the inputrc file with a statement of the
       form

	      set variable-name value

       Except  where  noted,  readline variables can take the values On or Off
       (without regard to case).  Unrecognized	variable  names	 are  ignored.
       When  a variable value is read, empty or null values, "on" (case-insen‐
       sitive), and "1" are equivalent to On.  All other values are equivalent
       to Off.	The variables and their default values are:

       bell-style (audible)
	      Controls	what  happens when readline wants to ring the terminal
	      bell.  If set to none, readline never rings the bell.  If set to
	      visible,	readline  uses a visible bell if one is available.  If
	      set to audible, readline attempts to ring the terminal's bell.
       bind-tty-special-chars (On)
	      If set to On, readline attempts to bind the  control  characters
	      treated specially by the kernel's terminal driver to their read‐
	      line equivalents.
       blink-matching-paren (Off)
	      If set to On, readline attempts to briefly move the cursor to an
	      opening parenthesis when a closing parenthesis is inserted.
       colored-completion-prefix (Off)
	      If  set  to  On, when listing completions, readline displays the
	      common prefix of the set of possible completions using a differ‐
	      ent  color.   The	 color definitions are taken from the value of
	      the LS_COLORS environment variable.
       colored-stats (Off)
	      If set to On, readline displays possible completions using  dif‐
	      ferent  colors  to  indicate their file type.  The color defini‐
	      tions are taken from the	value  of  the	LS_COLORS  environment
	      variable.
       comment-begin (``#'')
	      The  string  that	 is  inserted when the readline insert-comment
	      command is executed.  This command is bound to M-# in emacs mode
	      and to # in vi command mode.
       completion-display-width (-1)
	      The  number  of  screen columns used to display possible matches
	      when performing completion.  The value is ignored if it is  less
	      than  0 or greater than the terminal screen width.  A value of 0
	      will cause matches to be displayed one per  line.	  The  default
	      value is -1.
       completion-ignore-case (Off)
	      If set to On, readline performs filename matching and completion
	      in a case-insensitive fashion.
       completion-map-case (Off)
	      If set to On, and completion-ignore-case	is  enabled,  readline
	      treats  hyphens  (-) and underscores (_) as equivalent when per‐
	      forming case-insensitive filename matching and completion.
       completion-prefix-display-length (0)
	      The length in characters of the common prefix of a list of  pos‐
	      sible  completions that is displayed without modification.  When
	      set to a value greater than zero, common	prefixes  longer  than
	      this  value are replaced with an ellipsis when displaying possi‐
	      ble completions.
       completion-query-items (100)
	      This determines when the user is queried about viewing the  num‐
	      ber  of  possible	 completions generated by the possible-comple‐
	      tions command.  It may be set to any integer value greater  than
	      or  equal	 to  zero.   If	 the number of possible completions is
	      greater than or equal to the value of this variable, the user is
	      asked  whether or not he wishes to view them; otherwise they are
	      simply listed on the terminal.
       convert-meta (On)
	      If set to On, readline will convert characters with  the	eighth
	      bit set to an ASCII key sequence by stripping the eighth bit and
	      prefixing an escape character (in effect, using  escape  as  the
	      meta  prefix).   The  default is On, but readline will set it to
	      Off if the locale contains eight-bit characters.
       disable-completion (Off)
	      If set to On, readline will inhibit word completion.  Completion
	      characters  will	be  inserted into the line as if they had been
	      mapped to self-insert.
       echo-control-characters (On)
	      When set to On, on operating systems that indicate they  support
	      it, readline echoes a character corresponding to a signal gener‐
	      ated from the keyboard.
       editing-mode (emacs)
	      Controls whether readline begins with a set of key bindings sim‐
	      ilar to Emacs or vi.  editing-mode can be set to either emacs or
	      vi.
       enable-bracketed-paste (Off)
	      When set to On, readline will configure the terminal  in	a  way
	      that will enable it to insert each paste into the editing buffer
	      as a single string of characters, instead of treating each char‐
	      acter  as	 if it had been read from the keyboard.	 This can pre‐
	      vent pasted characters from being interpreted  as	 editing  com‐
	      mands.
       enable-keypad (Off)
	      When set to On, readline will try to enable the application key‐
	      pad when it is called.  Some systems need	 this  to  enable  the
	      arrow keys.
       enable-meta-key (On)
	      When  set	 to  On, readline will try to enable any meta modifier
	      key the terminal claims to support when it is called.   On  many
	      terminals, the meta key is used to send eight-bit characters.
       expand-tilde (Off)
	      If  set  to  On,	tilde  expansion  is  performed	 when readline
	      attempts word completion.
       history-preserve-point (Off)
	      If set to On, the history code attempts to place	point  at  the
	      same  location on each history line retrieved with previous-his‐
	      tory or next-history.
       history-size (unset)
	      Set the maximum number of history entries saved in  the  history
	      list.   If set to zero, any existing history entries are deleted
	      and no new entries are saved.  If set to a value less than zero,
	      the  number  of history entries is not limited.  By default, the
	      number of history entries is set to the value  of	 the  HISTSIZE
	      shell  variable.	If an attempt is made to set history-size to a
	      non-numeric value, the maximum number of history entries will be
	      set to 500.
       horizontal-scroll-mode (Off)
	      When  set	 to  On, makes readline use a single line for display,
	      scrolling the input horizontally on a single screen line when it
	      becomes  longer  than the screen width rather than wrapping to a
	      new line.
       input-meta (Off)
	      If set to On, readline will enable eight-bit input (that is,  it
	      will  not	 strip	the  eighth bit from the characters it reads),
	      regardless of what the terminal claims it can support.  The name
	      meta-flag	 is  a synonym for this variable.  The default is Off,
	      but readline will set it to On if the locale contains  eight-bit
	      characters.
       isearch-terminators (``C-[C-J'')
	      The  string  of  characters that should terminate an incremental
	      search without subsequently executing the character  as  a  com‐
	      mand.   If this variable has not been given a value, the charac‐
	      ters ESC and C-J will terminate an incremental search.
       keymap (emacs)
	      Set the current readline keymap.	The set of valid keymap	 names
	      is  emacs,  emacs-standard,  emacs-meta, emacs-ctlx, vi, vi-com‐
	      mand, and vi-insert.  vi is equivalent to vi-command;  emacs  is
	      equivalent  to  emacs-standard.  The default value is emacs; the
	      value of editing-mode also affects the default keymap.
       emacs-mode-string (@)
	      This string is displayed immediately before the last line of the
	      primary  prompt when emacs editing mode is active.  The value is
	      expanded like a key binding, so the standard set	of  meta-  and
	      control  prefixes	 and  backslash escape sequences is available.
	      Use the \1 and \2 escapes to begin and  end  sequences  of  non-
	      printing	characters, which can be used to embed a terminal con‐
	      trol sequence into the mode string.
       keyseq-timeout (500)
	      Specifies the duration readline will wait for a  character  when
	      reading  an ambiguous key sequence (one that can form a complete
	      key sequence using the input read so far, or can take additional
	      input  to	 complete  a  longer  key  sequence).	If no input is
	      received within the timeout, readline will use the  shorter  but
	      complete	key sequence.  The value is specified in milliseconds,
	      so a value of 1000 means that readline will wait one second  for
	      additional  input.  If this variable is set to a value less than
	      or equal to zero, or to a non-numeric value, readline will  wait
	      until  another  key  is  pressed to decide which key sequence to
	      complete.
       mark-directories (On)
	      If set to On, completed directory names have a slash appended.
       mark-modified-lines (Off)
	      If set to On, history lines that have  been  modified  are  dis‐
	      played with a preceding asterisk (*).
       mark-symlinked-directories (Off)
	      If set to On, completed names which are symbolic links to direc‐
	      tories  have  a  slash  appended	(subject  to  the   value   of
	      mark-directories).
       match-hidden-files (On)
	      This  variable,  when  set to On, causes readline to match files
	      whose names begin with a	`.'  (hidden  files)  when  performing
	      filename	completion.   If  set  to Off, the leading `.' must be
	      supplied by the user in the filename to be completed.
       menu-complete-display-prefix (Off)
	      If set to On, menu completion displays the common prefix of  the
	      list of possible completions (which may be empty) before cycling
	      through the list.
       output-meta (Off)
	      If set to On, readline will display characters with  the	eighth
	      bit set directly rather than as a meta-prefixed escape sequence.
	      The default is Off, but readline will set it to On if the locale
	      contains eight-bit characters.
       page-completions (On)
	      If  set to On, readline uses an internal more-like pager to dis‐
	      play a screenful of possible completions at a time.
       print-completions-horizontally (Off)
	      If set to On, readline will  display  completions	 with  matches
	      sorted  horizontally in alphabetical order, rather than down the
	      screen.
       revert-all-at-newline (Off)
	      If set to On, readline will undo all changes  to	history	 lines
	      before returning when accept-line is executed.  By default, his‐
	      tory lines may be modified  and  retain  individual  undo	 lists
	      across calls to readline.
       show-all-if-ambiguous (Off)
	      This  alters  the	 default behavior of the completion functions.
	      If set to On, words which have more than one possible completion
	      cause  the  matches  to be listed immediately instead of ringing
	      the bell.
       show-all-if-unmodified (Off)
	      This alters the default behavior of the completion functions  in
	      a fashion similar to show-all-if-ambiguous.  If set to On, words
	      which have more than one possible completion without any	possi‐
	      ble  partial  completion (the possible completions don't share a
	      common prefix)  cause  the  matches  to  be  listed  immediately
	      instead of ringing the bell.
       show-mode-in-prompt (Off)
	      If  set  to  On,	add a character to the beginning of the prompt
	      indicating the editing mode: emacs (@), vi  command  (:)	or  vi
	      insertion (+).
       skip-completed-text (Off)
	      If  set  to On, this alters the default completion behavior when
	      inserting a single match into the line.  It's only  active  when
	      performing  completion  in  the  middle  of a word.  If enabled,
	      readline does not insert characters  from	 the  completion  that
	      match  characters	 after	point  in the word being completed, so
	      portions of the word following the cursor are not duplicated.
       vi-cmd-mode-string ((cmd))
	      This string is displayed immediately before the last line of the
	      primary  prompt  when  vi	 editing mode is active and in command
	      mode.  The value is expanded like a key binding, so the standard
	      set of meta- and control prefixes and backslash escape sequences
	      is available.  Use the \1	 and  \2  escapes  to  begin  and  end
	      sequences of non-printing characters, which can be used to embed
	      a terminal control sequence into the mode string.
       vi-ins-mode-string ((ins))
	      This string is displayed immediately before the last line of the
	      primary  prompt  when vi editing mode is active and in insertion
	      mode.  The value is expanded like a key binding, so the standard
	      set of meta- and control prefixes and backslash escape sequences
	      is available.  Use the \1	 and  \2  escapes  to  begin  and  end
	      sequences of non-printing characters, which can be used to embed
	      a terminal control sequence into the mode string.
       visible-stats (Off)
	      If set to On, a character denoting a file's type as reported  by
	      stat(2)  is  appended to the filename when listing possible com‐
	      pletions.

   Readline Conditional Constructs
       Readline implements a facility similar in  spirit  to  the  conditional
       compilation  features  of  the C preprocessor which allows key bindings
       and variable settings to be performed as the result  of	tests.	 There
       are four parser directives used.

       $if    The  $if construct allows bindings to be made based on the edit‐
	      ing mode, the terminal being  used,  or  the  application	 using
	      readline.	  The text of the test extends to the end of the line;
	      no characters are required to isolate it.

	      mode   The mode= form of the  $if	 directive  is	used  to  test
		     whether  readline	is  in	emacs or vi mode.  This may be
		     used in conjunction with  the  set	 keymap	 command,  for
		     instance,	to  set	 bindings  in  the  emacs-standard and
		     emacs-ctlx keymaps only if readline is  starting  out  in
		     emacs mode.

	      term   The  term=	 form may be used to include terminal-specific
		     key bindings, perhaps to bind the key sequences output by
		     the terminal's function keys.  The word on the right side
		     of the = is tested against both the full name of the ter‐
		     minal  and	 the  portion  of the terminal name before the
		     first -.  This allows sun to match both sun and  sun-cmd,
		     for instance.

	      application
		     The application construct is used to include application-
		     specific  settings.   Each	 program  using	 the  readline
		     library  sets the application name, and an initialization
		     file can test for a particular value.  This could be used
		     to	 bind key sequences to functions useful for a specific
		     program.  For instance, the following command adds a  key
		     sequence  that  quotes  the  current  or previous word in
		     bash:

		     $if Bash
		     # Quote the current or previous word
		     "\C-xq": "\eb\"\ef\""
		     $endif

       $endif This command, as seen in the previous example, terminates an $if
	      command.

       $else  Commands in this branch of the $if directive are executed if the
	      test fails.

       $include
	      This directive takes a single filename as an argument and	 reads
	      commands	and bindings from that file.  For example, the follow‐
	      ing directive would read /etc/inputrc:

	      $include	/etc/inputrc

   Searching
       Readline provides commands for searching through	 the  command  history
       (see HISTORY below) for lines containing a specified string.  There are
       two search modes: incremental and non-incremental.

       Incremental searches begin before the  user  has	 finished  typing  the
       search  string.	As each character of the search string is typed, read‐
       line displays the next entry from the history matching the string typed
       so  far.	  An  incremental  search  requires only as many characters as
       needed to find the desired history entry.  The  characters  present  in
       the  value of the isearch-terminators variable are used to terminate an
       incremental search.  If that variable has not been assigned a value the
       Escape  and  Control-J characters will terminate an incremental search.
       Control-G will abort an incremental search  and	restore	 the  original
       line.   When the search is terminated, the history entry containing the
       search string becomes the current line.

       To find other matching entries in the history list, type	 Control-S  or
       Control-R  as appropriate.  This will search backward or forward in the
       history for the next entry matching the search  string  typed  so  far.
       Any  other  key sequence bound to a readline command will terminate the
       search and execute that command.	 For instance, a newline  will	termi‐
       nate the search and accept the line, thereby executing the command from
       the history list.

       Readline remembers the last incremental search string.  If two Control-
       Rs  are	typed without any intervening characters defining a new search
       string, any remembered search string is used.

       Non-incremental searches read the entire search string before  starting
       to  search  for matching history lines.	The search string may be typed
       by the user or be part of the contents of the current line.

   Readline Command Names
       The following is a list of the names of the commands  and  the  default
       key sequences to which they are bound.  Command names without an accom‐
       panying key sequence are unbound by default.  In the following descrip‐
       tions,  point refers to the current cursor position, and mark refers to
       a cursor position saved by the set-mark command.	 The text between  the
       point and mark is referred to as the region.

   Commands for Moving
       beginning-of-line (C-a)
	      Move to the start of the current line.
       end-of-line (C-e)
	      Move to the end of the line.
       forward-char (C-f)
	      Move forward a character.
       backward-char (C-b)
	      Move back a character.
       forward-word (M-f)
	      Move forward to the end of the next word.	 Words are composed of
	      alphanumeric characters (letters and digits).
       backward-word (M-b)
	      Move back to the start of the current or previous	 word.	 Words
	      are composed of alphanumeric characters (letters and digits).
       shell-forward-word
	      Move  forward  to the end of the next word.  Words are delimited
	      by non-quoted shell metacharacters.
       shell-backward-word
	      Move back to the start of the current or previous	 word.	 Words
	      are delimited by non-quoted shell metacharacters.
       clear-screen (C-l)
	      Clear  the  screen  leaving  the	current line at the top of the
	      screen.  With an argument,  refresh  the	current	 line  without
	      clearing the screen.
       redraw-current-line
	      Refresh the current line.

   Commands for Manipulating the History
       accept-line (Newline, Return)
	      Accept the line regardless of where the cursor is.  If this line
	      is non-empty, add it to the history list according to the	 state
	      of  the HISTCONTROL variable.  If the line is a modified history
	      line, then restore the history line to its original state.
       previous-history (C-p)
	      Fetch the previous command from the history list, moving back in
	      the list.
       next-history (C-n)
	      Fetch  the next command from the history list, moving forward in
	      the list.
       beginning-of-history (M-<)
	      Move to the first line in the history.
       end-of-history (M->)
	      Move to the end of the input history, i.e., the  line  currently
	      being entered.
       reverse-search-history (C-r)
	      Search  backward	starting  at  the current line and moving `up'
	      through the  history  as	necessary.   This  is  an  incremental
	      search.
       forward-search-history (C-s)
	      Search  forward  starting	 at the current line and moving `down'
	      through the  history  as	necessary.   This  is  an  incremental
	      search.
       non-incremental-reverse-search-history (M-p)
	      Search backward through the history starting at the current line
	      using a non-incremental search for  a  string  supplied  by  the
	      user.
       non-incremental-forward-search-history (M-n)
	      Search  forward  through	the  history  using  a non-incremental
	      search for a string supplied by the user.
       history-search-forward
	      Search forward through the history for the string of  characters
	      between  the start of the current line and the point.  This is a
	      non-incremental search.
       history-search-backward
	      Search backward through the history for the string of characters
	      between  the start of the current line and the point.  This is a
	      non-incremental search.
       yank-nth-arg (M-C-y)
	      Insert the first argument to the previous command	 (usually  the
	      second word on the previous line) at point.  With an argument n,
	      insert the nth word from the previous command (the words in  the
	      previous	command	 begin	with  word  0).	  A  negative argument
	      inserts the nth word from the end of the previous command.  Once
	      the  argument n is computed, the argument is extracted as if the
	      "!n" history expansion had been specified.
       yank-last-arg (M-., M-_)
	      Insert the last argument to the previous command (the last  word
	      of the previous history entry).  With a numeric argument, behave
	      exactly like yank-nth-arg.  Successive  calls  to	 yank-last-arg
	      move  back through the history list, inserting the last word (or
	      the word specified by the argument to the first  call)  of  each
	      line in turn.  Any numeric argument supplied to these successive
	      calls determines the direction to move through the  history.   A
	      negative	argument  switches  the	 direction through the history
	      (back or forward).  The history expansion facilities are used to
	      extract the last word, as if the "!$" history expansion had been
	      specified.
       shell-expand-line (M-C-e)
	      Expand the line as the shell does.  This performs alias and his‐
	      tory expansion as well as all of the shell word expansions.  See
	      HISTORY EXPANSION below for a description of history expansion.
       history-expand-line (M-^)
	      Perform history expansion on  the	 current  line.	  See  HISTORY
	      EXPANSION below for a description of history expansion.
       magic-space
	      Perform  history	expansion  on  the  current  line and insert a
	      space.  See HISTORY EXPANSION below for a description of history
	      expansion.
       alias-expand-line
	      Perform  alias expansion on the current line.  See ALIASES above
	      for a description of alias expansion.
       history-and-alias-expand-line
	      Perform history and alias expansion on the current line.
       insert-last-argument (M-., M-_)
	      A synonym for yank-last-arg.
       operate-and-get-next (C-o)
	      Accept the current line for execution and fetch  the  next  line
	      relative	to the current line from the history for editing.  Any
	      argument is ignored.
       edit-and-execute-command (C-xC-e)
	      Invoke an editor on the current command line,  and  execute  the
	      result  as  shell	 commands.   Bash  attempts to invoke $VISUAL,
	      $EDITOR, and emacs as the editor, in that order.

   Commands for Changing Text
       end-of-file (usually C-d)
	      The character indicating end-of-file as  set,  for  example,  by
	      ``stty''.	  If  this character is read when there are no charac‐
	      ters on the line, and point is at the  beginning	of  the	 line,
	      Readline interprets it as the end of input and returns EOF.
       delete-char (C-d)
	      Delete the character at point.  If this function is bound to the
	      same character as the tty EOF character, as C-d commonly is, see
	      above for the effects.
       backward-delete-char (Rubout)
	      Delete  the  character  behind the cursor.  When given a numeric
	      argument, save the deleted text on the kill ring.
       forward-backward-delete-char
	      Delete the character under the cursor, unless the cursor	is  at
	      the end of the line, in which case the character behind the cur‐
	      sor is deleted.
       quoted-insert (C-q, C-v)
	      Add the next character typed to the line verbatim.  This is  how
	      to insert characters like C-q, for example.
       tab-insert (C-v TAB)
	      Insert a tab character.
       self-insert (a, b, A, 1, !, ...)
	      Insert the character typed.
       transpose-chars (C-t)
	      Drag  the	 character  before point forward over the character at
	      point, moving point forward as well.  If point is at the end  of
	      the  line, then this transposes the two characters before point.
	      Negative arguments have no effect.
       transpose-words (M-t)
	      Drag the word before point past the  word	 after	point,	moving
	      point  over  that	 word  as well.	 If point is at the end of the
	      line, this transposes the last two words on the line.
       upcase-word (M-u)
	      Uppercase the current (or	 following)  word.   With  a  negative
	      argument, uppercase the previous word, but do not move point.
       downcase-word (M-l)
	      Lowercase	 the  current  (or  following)	word.  With a negative
	      argument, lowercase the previous word, but do not move point.
       capitalize-word (M-c)
	      Capitalize the current (or following)  word.   With  a  negative
	      argument, capitalize the previous word, but do not move point.
       overwrite-mode
	      Toggle  overwrite mode.  With an explicit positive numeric argu‐
	      ment, switches to overwrite mode.	 With an explicit non-positive
	      numeric argument, switches to insert mode.  This command affects
	      only emacs mode; vi mode does overwrite differently.  Each  call
	      to readline() starts in insert mode.  In overwrite mode, charac‐
	      ters bound to self-insert replace the text at point rather  than
	      pushing  the  text  to  the  right.   Characters	bound to back‐
	      ward-delete-char replace	the  character	before	point  with  a
	      space.  By default, this command is unbound.

   Killing and Yanking
       kill-line (C-k)
	      Kill the text from point to the end of the line.
       backward-kill-line (C-x Rubout)
	      Kill backward to the beginning of the line.
       unix-line-discard (C-u)
	      Kill  backward  from  point  to  the beginning of the line.  The
	      killed text is saved on the kill-ring.
       kill-whole-line
	      Kill all characters on the current line, no matter  where	 point
	      is.
       kill-word (M-d)
	      Kill  from  point	 to the end of the current word, or if between
	      words, to the end of the next word.   Word  boundaries  are  the
	      same as those used by forward-word.
       backward-kill-word (M-Rubout)
	      Kill  the	 word  behind  point.  Word boundaries are the same as
	      those used by backward-word.
       shell-kill-word
	      Kill from point to the end of the current word,  or  if  between
	      words,  to  the  end  of the next word.  Word boundaries are the
	      same as those used by shell-forward-word.
       shell-backward-kill-word
	      Kill the word behind point.  Word boundaries  are	 the  same  as
	      those used by shell-backward-word.
       unix-word-rubout (C-w)
	      Kill  the	 word behind point, using white space as a word bound‐
	      ary.  The killed text is saved on the kill-ring.
       unix-filename-rubout
	      Kill the word behind point, using	 white	space  and  the	 slash
	      character	 as  the word boundaries.  The killed text is saved on
	      the kill-ring.
       delete-horizontal-space (M-\)
	      Delete all spaces and tabs around point.
       kill-region
	      Kill the text in the current region.
       copy-region-as-kill
	      Copy the text in the region to the kill buffer.
       copy-backward-word
	      Copy the word before point to the kill buffer.  The word	bound‐
	      aries are the same as backward-word.
       copy-forward-word
	      Copy  the	 word  following  point	 to the kill buffer.  The word
	      boundaries are the same as forward-word.
       yank (C-y)
	      Yank the top of the kill ring into the buffer at point.
       yank-pop (M-y)
	      Rotate the kill ring, and yank the new top.  Only works  follow‐
	      ing yank or yank-pop.

   Numeric Arguments
       digit-argument (M-0, M-1, ..., M--)
	      Add  this digit to the argument already accumulating, or start a
	      new argument.  M-- starts a negative argument.
       universal-argument
	      This is another way to specify an argument.  If this command  is
	      followed	by one or more digits, optionally with a leading minus
	      sign, those digits define the argument.  If the command is  fol‐
	      lowed  by	 digits,  executing  universal-argument again ends the
	      numeric argument, but is otherwise ignored.  As a special	 case,
	      if  this	command is immediately followed by a character that is
	      neither a digit nor minus sign, the argument count for the  next
	      command  is multiplied by four.  The argument count is initially
	      one, so executing this function the first time makes  the	 argu‐
	      ment count four, a second time makes the argument count sixteen,
	      and so on.

   Completing
       complete (TAB)
	      Attempt to perform completion on the text	 before	 point.	  Bash
	      attempts completion treating the text as a variable (if the text
	      begins with $), username (if the text begins with	 ~),  hostname
	      (if  the	text begins with @), or command (including aliases and
	      functions) in turn.  If none of these produces a match, filename
	      completion is attempted.
       possible-completions (M-?)
	      List the possible completions of the text before point.
       insert-completions (M-*)
	      Insert  all completions of the text before point that would have
	      been generated by possible-completions.
       menu-complete
	      Similar to complete, but replaces the word to be completed  with
	      a	 single match from the list of possible completions.  Repeated
	      execution of menu-complete steps through the  list  of  possible
	      completions,  inserting  each  match in turn.  At the end of the
	      list of completions, the bell is rung (subject to the setting of
	      bell-style) and the original text is restored.  An argument of n
	      moves n positions forward in the list  of	 matches;  a  negative
	      argument	may  be	 used to move backward through the list.  This
	      command is intended to be	 bound	to  TAB,  but  is  unbound  by
	      default.
       menu-complete-backward
	      Identical	 to menu-complete, but moves backward through the list
	      of possible completions, as if menu-complete had	been  given  a
	      negative argument.  This command is unbound by default.
       delete-char-or-list
	      Deletes  the  character under the cursor if not at the beginning
	      or end of the line (like delete-char).  If at  the  end  of  the
	      line, behaves identically to possible-completions.  This command
	      is unbound by default.
       complete-filename (M-/)
	      Attempt filename completion on the text before point.
       possible-filename-completions (C-x /)
	      List the possible completions of the text before point, treating
	      it as a filename.
       complete-username (M-~)
	      Attempt  completion  on  the text before point, treating it as a
	      username.
       possible-username-completions (C-x ~)
	      List the possible completions of the text before point, treating
	      it as a username.
       complete-variable (M-$)
	      Attempt  completion  on  the text before point, treating it as a
	      shell variable.
       possible-variable-completions (C-x $)
	      List the possible completions of the text before point, treating
	      it as a shell variable.
       complete-hostname (M-@)
	      Attempt  completion  on  the text before point, treating it as a
	      hostname.
       possible-hostname-completions (C-x @)
	      List the possible completions of the text before point, treating
	      it as a hostname.
       complete-command (M-!)
	      Attempt  completion  on  the text before point, treating it as a
	      command name.  Command completion attempts  to  match  the  text
	      against	aliases,   reserved   words,  shell  functions,	 shell
	      builtins, and finally executable filenames, in that order.
       possible-command-completions (C-x !)
	      List the possible completions of the text before point, treating
	      it as a command name.
       dynamic-complete-history (M-TAB)
	      Attempt  completion on the text before point, comparing the text
	      against lines from the  history  list  for  possible  completion
	      matches.
       dabbrev-expand
	      Attempt  menu completion on the text before point, comparing the
	      text against lines from the history list for possible completion
	      matches.
       complete-into-braces (M-{)
	      Perform filename completion and insert the list of possible com‐
	      pletions enclosed within braces so the list is available to  the
	      shell (see Brace Expansion above).

   Keyboard Macros
       start-kbd-macro (C-x ()
	      Begin  saving  the  characters  typed  into the current keyboard
	      macro.
       end-kbd-macro (C-x ))
	      Stop saving the characters typed into the current keyboard macro
	      and store the definition.
       call-last-kbd-macro (C-x e)
	      Re-execute  the last keyboard macro defined, by making the char‐
	      acters in the macro appear as if typed at the keyboard.
       print-last-kbd-macro ()
	      Print the last keyboard macro defined in a format	 suitable  for
	      the inputrc file.

   Miscellaneous
       re-read-init-file (C-x C-r)
	      Read  in	the  contents of the inputrc file, and incorporate any
	      bindings or variable assignments found there.
       abort (C-g)
	      Abort the current editing command and ring the  terminal's  bell
	      (subject to the setting of bell-style).
       do-uppercase-version (M-a, M-b, M-x, ...)
	      If  the  metafied character x is lowercase, run the command that
	      is bound to the corresponding uppercase character.
       prefix-meta (ESC)
	      Metafy the next character typed.	ESC f is equivalent to Meta-f.
       undo (C-_, C-x C-u)
	      Incremental undo, separately remembered for each line.
       revert-line (M-r)
	      Undo all changes made to this line.  This is like executing  the
	      undo  command  enough  times  to	return the line to its initial
	      state.
       tilde-expand (M-&)
	      Perform tilde expansion on the current word.
       set-mark (C-@, M-<space>)
	      Set the mark to the point.  If a numeric argument	 is  supplied,
	      the mark is set to that position.
       exchange-point-and-mark (C-x C-x)
	      Swap  the	 point	with the mark.	The current cursor position is
	      set to the saved position, and the old cursor position is	 saved
	      as the mark.
       character-search (C-])
	      A character is read and point is moved to the next occurrence of
	      that character.  A negative count searches for  previous	occur‐
	      rences.
       character-search-backward (M-C-])
	      A	 character  is	read and point is moved to the previous occur‐
	      rence of that character.	A negative count searches  for	subse‐
	      quent occurrences.
       skip-csi-sequence
	      Read  enough  characters to consume a multi-key sequence such as
	      those defined for keys like Home and End.	 Such sequences	 begin
	      with a Control Sequence Indicator (CSI), usually ESC-[.  If this
	      sequence is bound to "\[", keys producing	 such  sequences  will
	      have  no	effect	unless explicitly bound to a readline command,
	      instead of inserting stray characters into the  editing  buffer.
	      This is unbound by default, but usually bound to ESC-[.
       insert-comment (M-#)
	      Without  a  numeric  argument,  the  value  of the readline com‐
	      ment-begin variable is inserted at the beginning of the  current
	      line.  If a numeric argument is supplied, this command acts as a
	      toggle: if the characters at the beginning of the	 line  do  not
	      match  the value of comment-begin, the value is inserted, other‐
	      wise the characters in comment-begin are deleted from the begin‐
	      ning  of the line.  In either case, the line is accepted as if a
	      newline had been typed.	The  default  value  of	 comment-begin
	      causes  this  command  to make the current line a shell comment.
	      If a  numeric  argument  causes  the  comment  character	to  be
	      removed, the line will be executed by the shell.
       glob-complete-word (M-g)
	      The  word	 before	 point	is  treated  as a pattern for pathname
	      expansion, with an asterisk implicitly appended.	 This  pattern
	      is  used	to  generate a list of matching filenames for possible
	      completions.
       glob-expand-word (C-x *)
	      The word before point is	treated	 as  a	pattern	 for  pathname
	      expansion,  and  the  list  of  matching	filenames is inserted,
	      replacing the word.  If  a  numeric  argument  is	 supplied,  an
	      asterisk is appended before pathname expansion.
       glob-list-expansions (C-x g)
	      The  list	 of  expansions	 that  would  have  been  generated by
	      glob-expand-word is displayed, and the line is  redrawn.	 If  a
	      numeric  argument	 is  supplied,	an asterisk is appended before
	      pathname expansion.
       dump-functions
	      Print all of the functions and their key bindings to  the	 read‐
	      line output stream.  If a numeric argument is supplied, the out‐
	      put is formatted in such a way that it can be made  part	of  an
	      inputrc file.
       dump-variables
	      Print all of the settable readline variables and their values to
	      the readline output stream.  If a numeric argument is  supplied,
	      the  output  is formatted in such a way that it can be made part
	      of an inputrc file.
       dump-macros
	      Print all of the readline key sequences bound to macros and  the
	      strings  they  output.   If  a numeric argument is supplied, the
	      output is formatted in such a way that it can be made part of an
	      inputrc file.
       display-shell-version (C-x C-v)
	      Display version information about the current instance of bash.

   Programmable Completion
       When  word  completion  is  attempted  for an argument to a command for
       which a completion specification (a compspec) has  been	defined	 using
       the  complete  builtin (see SHELL BUILTIN COMMANDS below), the program‐
       mable completion facilities are invoked.

       First, the command name is identified.  If  the	command	 word  is  the
       empty  string (completion attempted at the beginning of an empty line),
       any compspec defined with the -E option to  complete  is	 used.	 If  a
       compspec	 has  been  defined  for that command, the compspec is used to
       generate the list of possible completions for the word.	If the command
       word  is	 a full pathname, a compspec for the full pathname is searched
       for first.  If no compspec is found for the full pathname,  an  attempt
       is  made	 to find a compspec for the portion following the final slash.
       If those searches do not result in a  compspec,	any  compspec  defined
       with the -D option to complete is used as the default.

       Once  a	compspec  has  been  found, it is used to generate the list of
       matching words.	If a compspec is not found, the default	 bash  comple‐
       tion as described above under Completing is performed.

       First,  the  actions  specified by the compspec are used.  Only matches
       which are prefixed by the word being completed are returned.  When  the
       -f  or -d option is used for filename or directory name completion, the
       shell variable FIGNORE is used to filter the matches.

       Any completions specified by a pathname expansion  pattern  to  the  -G
       option are generated next.  The words generated by the pattern need not
       match the word being completed.	The GLOBIGNORE shell variable  is  not
       used to filter the matches, but the FIGNORE variable is used.

       Next,  the string specified as the argument to the -W option is consid‐
       ered.  The string is first split using the characters in the  IFS  spe‐
       cial  variable  as delimiters.  Shell quoting is honored.  Each word is
       then expanded using brace expansion,  tilde  expansion,	parameter  and
       variable	 expansion, command substitution, and arithmetic expansion, as
       described above under EXPANSION.	 The results are split using the rules
       described above under Word Splitting.  The results of the expansion are
       prefix-matched against the word being completed, and the matching words
       become the possible completions.

       After  these matches have been generated, any shell function or command
       specified with the -F and -C options is invoked.	 When the  command  or
       function is invoked, the COMP_LINE, COMP_POINT, COMP_KEY, and COMP_TYPE
       variables are assigned values as described above under Shell Variables.
       If  a  shell  function  is being invoked, the COMP_WORDS and COMP_CWORD
       variables are also set.	When the function or command is	 invoked,  the
       first  argument	($1)  is  the  name of the command whose arguments are
       being completed, the second argument ($2) is the word being  completed,
       and  the	 third argument ($3) is the word preceding the word being com‐
       pleted on the current command line.  No filtering of the generated com‐
       pletions against the word being completed is performed; the function or
       command has complete freedom in generating the matches.

       Any function specified with -F is invoked first.	 The function may  use
       any  of	the  shell facilities, including the compgen builtin described
       below, to generate the matches.	It must put the	 possible  completions
       in the COMPREPLY array variable, one per array element.

       Next,  any  command specified with the -C option is invoked in an envi‐
       ronment equivalent to command substitution.  It should print a list  of
       completions,  one  per  line, to the standard output.  Backslash may be
       used to escape a newline, if necessary.

       After all of the possible completions are generated, any filter	speci‐
       fied  with  the -X option is applied to the list.  The filter is a pat‐
       tern as used for pathname expansion; a & in  the	 pattern  is  replaced
       with  the text of the word being completed.  A literal & may be escaped
       with a backslash; the backslash is removed before attempting  a	match.
       Any  completion that matches the pattern will be removed from the list.
       A leading ! negates the pattern; in this case any completion not match‐
       ing  the	 pattern  will be removed.  If the nocasematch shell option is
       enabled, the match is performed without regard to the  case  of	alpha‐
       betic characters.

       Finally, any prefix and suffix specified with the -P and -S options are
       added to each member of the completion list, and the result is returned
       to the readline completion code as the list of possible completions.

       If  the previously-applied actions do not generate any matches, and the
       -o dirnames option was supplied	to  complete  when  the	 compspec  was
       defined, directory name completion is attempted.

       If  the	-o  plusdirs option was supplied to complete when the compspec
       was defined, directory name completion is attempted and any matches are
       added to the results of the other actions.

       By  default,  if a compspec is found, whatever it generates is returned
       to the completion code as the full set of  possible  completions.   The
       default bash completions are not attempted, and the readline default of
       filename completion is disabled.	 If the -o bashdefault option was sup‐
       plied  to complete when the compspec was defined, the bash default com‐
       pletions are attempted if the compspec generates no matches.  If the -o
       default	option was supplied to complete when the compspec was defined,
       readline's default completion will be performed if the  compspec	 (and,
       if attempted, the default bash completions) generate no matches.

       When  a	compspec  indicates that directory name completion is desired,
       the programmable completion functions force readline to append a	 slash
       to  completed names which are symbolic links to directories, subject to
       the value of the mark-directories readline variable, regardless of  the
       setting of the mark-symlinked-directories readline variable.

       There  is  some support for dynamically modifying completions.  This is
       most useful when used in combination with a default  completion	speci‐
       fied  with  complete -D.	 It's possible for shell functions executed as
       completion handlers to indicate that completion should  be  retried  by
       returning  an exit status of 124.  If a shell function returns 124, and
       changes the compspec associated with the command on which completion is
       being  attempted	 (supplied  as the first argument when the function is
       executed), programmable completion restarts from the beginning, with an
       attempt	to find a new compspec for that command.  This allows a set of
       completions to be built dynamically as completion is attempted,	rather
       than being loaded all at once.

       For  instance, assuming that there is a library of compspecs, each kept
       in a file corresponding to the  name  of	 the  command,	the  following
       default completion function would load completions dynamically:

       _completion_loader()
       {
	    . "/etc/bash_completion.d/$1.sh" >/dev/null 2>&1 && return 124
       }
       complete -D -F _completion_loader -o bashdefault -o default

HISTORY
       When  the  -o  history  option to the set builtin is enabled, the shell
       provides access to the command history, the list of commands previously
       typed.	The  value  of	the HISTSIZE variable is used as the number of
       commands to save in a history list.  The text of the last HISTSIZE com‐
       mands  (default	500)  is  saved.  The shell stores each command in the
       history list prior to parameter and variable expansion  (see  EXPANSION
       above)  but after history expansion is performed, subject to the values
       of the shell variables HISTIGNORE and HISTCONTROL.

       On startup, the history is initialized from the file named by the vari‐
       able  HISTFILE  (default ~/.bash_history).  The file named by the value
       of HISTFILE is truncated, if necessary, to contain  no  more  than  the
       number  of  lines specified by the value of HISTFILESIZE.  If HISTFILE‐
       SIZE is unset, or set to null, a non-numeric value, or a numeric	 value
       less  than  zero,  the history file is not truncated.  When the history
       file is read, lines beginning with the history comment  character  fol‐
       lowed immediately by a digit are interpreted as timestamps for the pre‐
       ceding history line.  These timestamps are optionally displayed depend‐
       ing  on	the  value  of the HISTTIMEFORMAT variable.  When a shell with
       history enabled exits, the last $HISTSIZE lines	are  copied  from  the
       history	list  to $HISTFILE.  If the histappend shell option is enabled
       (see the description of shopt under SHELL BUILTIN COMMANDS below),  the
       lines  are  appended to the history file, otherwise the history file is
       overwritten.   If  HISTFILE  is	unset,	or  if	the  history  file  is
       unwritable,  the	 history is not saved.	If the HISTTIMEFORMAT variable
       is set, time stamps are written to the history file,  marked  with  the
       history	comment	 character, so they may be preserved across shell ses‐
       sions.  This uses the history comment character	to  distinguish	 time‐
       stamps from other history lines.	 After saving the history, the history
       file is truncated to contain no more than HISTFILESIZE lines.  If HIST‐
       FILESIZE	 is  unset,  or set to null, a non-numeric value, or a numeric
       value less than zero, the history file is not truncated.

       The builtin command fc (see SHELL BUILTIN COMMANDS below) may  be  used
       to list or edit and re-execute a portion of the history list.  The his‐
       tory builtin may be used to display or  modify  the  history  list  and
       manipulate  the	history file.  When using command-line editing, search
       commands are available in each editing mode that provide access to  the
       history list.

       The  shell  allows control over which commands are saved on the history
       list.  The HISTCONTROL and HISTIGNORE variables may be set to cause the
       shell to save only a subset of the commands entered.  The cmdhist shell
       option, if enabled, causes the shell to attempt to save each line of  a
       multi-line  command  in the same history entry, adding semicolons where
       necessary to preserve syntactic correctness.  The lithist shell	option
       causes  the shell to save the command with embedded newlines instead of
       semicolons.  See the description of the shopt builtin below under SHELL
       BUILTIN	COMMANDS  for  information  on	setting	 and  unsetting	 shell
       options.

HISTORY EXPANSION
       The shell supports a history expansion feature that is similar  to  the
       history	expansion in csh.  This section describes what syntax features
       are available.  This feature is	enabled	 by  default  for  interactive
       shells, and can be disabled using the +H option to the set builtin com‐
       mand (see SHELL BUILTIN COMMANDS below).	 Non-interactive shells do not
       perform history expansion by default.

       History expansions introduce words from the history list into the input
       stream, making it easy to repeat commands, insert the  arguments	 to  a
       previous command into the current input line, or fix errors in previous
       commands quickly.

       History expansion is performed immediately after	 a  complete  line  is
       read,  before  the  shell  breaks it into words.	 It takes place in two
       parts.  The first is to determine which line from the history  list  to
       use during substitution.	 The second is to select portions of that line
       for inclusion into the current one.  The line selected from the history
       is  the	event,	and  the portions of that line that are acted upon are
       words.  Various modifiers are  available	 to  manipulate	 the  selected
       words.  The line is broken into words in the same fashion as when read‐
       ing input, so that several metacharacter-separated words surrounded  by
       quotes  are  considered one word.  History expansions are introduced by
       the appearance of the  history  expansion  character,  which  is	 !  by
       default.	  Only	backslash  (\) and single quotes can quote the history
       expansion character,  but  the  history	expansion  character  is  also
       treated	as  quoted if it immediately precedes the closing double quote
       in a double-quoted string.

       Several characters inhibit history expansion if found immediately  fol‐
       lowing  the history expansion character, even if it is unquoted: space,
       tab, newline, carriage return, and =.  If the extglob shell  option  is
       enabled, ( will also inhibit expansion.

       Several	shell  options	settable with the shopt builtin may be used to
       tailor the behavior of history  expansion.   If	the  histverify	 shell
       option is enabled (see the description of the shopt builtin below), and
       readline is being  used,	 history  substitutions	 are  not  immediately
       passed  to  the	shell  parser.	Instead, the expanded line is reloaded
       into the readline editing buffer for further modification.  If readline
       is  being  used,	 and  the histreedit shell option is enabled, a failed
       history substitution will be reloaded into the readline editing	buffer
       for  correction.	  The  -p option to the history builtin command may be
       used to see what a history expansion will do before using it.   The  -s
       option to the history builtin may be used to add commands to the end of
       the history list without actually executing  them,  so  that  they  are
       available for subsequent recall.

       The  shell allows control of the various characters used by the history
       expansion mechanism (see the description of histchars above under Shell
       Variables).   The shell uses the history comment character to mark his‐
       tory timestamps when writing the history file.

   Event Designators
       An event designator is a reference to a command line entry in the  his‐
       tory  list.   Unless  the reference is absolute, events are relative to
       the current position in the history list.

       !      Start a history substitution, except when followed by  a	blank,
	      newline,	carriage return, = or ( (when the extglob shell option
	      is enabled using the shopt builtin).
       !n     Refer to command line n.
       !-n    Refer to the current command minus n.
       !!     Refer to the previous command.  This is a synonym for `!-1'.
       !string
	      Refer to the most recent command preceding the current  position
	      in the history list starting with string.
       !?string[?]
	      Refer  to the most recent command preceding the current position
	      in the history list containing string.  The trailing  ?  may  be
	      omitted if string is followed immediately by a newline.
       ^string1^string2^
	      Quick  substitution.   Repeat  the  previous  command, replacing
	      string1 with string2.  Equivalent	 to  ``!!:s/string1/string2/''
	      (see Modifiers below).
       !#     The entire command line typed so far.

   Word Designators
       Word  designators are used to select desired words from the event.  A :
       separates the event specification from the word designator.  It may  be
       omitted	if  the word designator begins with a ^, $, *, -, or %.	 Words
       are numbered from the beginning of the line, with the first word	 being
       denoted	by  0  (zero).	Words are inserted into the current line sepa‐
       rated by single spaces.

       0 (zero)
	      The zeroth word.	For the shell, this is the command word.
       n      The nth word.
       ^      The first argument.  That is, word 1.
       $      The last word.  This is usually  the  last  argument,  but  will
	      expand to the zeroth word if there is only one word in the line.
       %      The word matched by the most recent `?string?' search.
       x-y    A range of words; `-y' abbreviates `0-y'.
       *      All  of  the words but the zeroth.  This is a synonym for `1-$'.
	      It is not an error to use * if there is just  one	 word  in  the
	      event; the empty string is returned in that case.
       x*     Abbreviates x-$.
       x-     Abbreviates x-$ like x*, but omits the last word.

       If  a  word  designator is supplied without an event specification, the
       previous command is used as the event.

   Modifiers
       After the optional word designator, there may appear a sequence of  one
       or more of the following modifiers, each preceded by a `:'.

       h      Remove a trailing filename component, leaving only the head.
       t      Remove all leading filename components, leaving the tail.
       r      Remove a trailing suffix of the form .xxx, leaving the basename.
       e      Remove all but the trailing suffix.
       p      Print the new command but do not execute it.
       q      Quote the substituted words, escaping further substitutions.
       x      Quote  the  substituted words as with q, but break into words at
	      blanks and newlines.
       s/old/new/
	      Substitute new for the first occurrence  of  old	in  the	 event
	      line.   Any  delimiter  can  be  used  in place of /.  The final
	      delimiter is optional if it is the last character of  the	 event
	      line.   The delimiter may be quoted in old and new with a single
	      backslash.  If & appears in new, it is replaced by old.  A  sin‐
	      gle  backslash  will  quote the &.  If old is null, it is set to
	      the last old substituted, or, if no previous  history  substitu‐
	      tions took place, the last string in a !?string[?]  search.
       &      Repeat the previous substitution.
       g      Cause changes to be applied over the entire event line.  This is
	      used in conjunction with `:s' (e.g.,  `:gs/old/new/')  or	 `:&'.
	      If  used with `:s', any delimiter can be used in place of /, and
	      the final delimiter is optional if it is the last	 character  of
	      the event line.  An a may be used as a synonym for g.
       G      Apply  the following `s' modifier once to each word in the event
	      line.

SHELL 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
	      environment  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.	 The file searched for in PATH need not be executable.
	      When  bash  is  not  in  posix  mode,  the  current directory is
	      searched if no file is found in PATH.  If the sourcepath	option
	      to  the  shopt  builtin  command	is turned off, the PATH is not
	      searched.	 If any arguments are supplied, they become the	 posi‐
	      tional  parameters  when	filename  is  executed.	 Otherwise the
	      positional parameters  are  unchanged.   If  the	-T  option  is
	      enabled,	source	inherits  any trap on DEBUG; if it is not, any
	      DEBUG trap string is saved  and  restored	 around	 the  call  to
	      source,  and source unsets the DEBUG trap while it executes.  If
	      -T is not set, and the sourced file changes the DEBUG trap,  the
	      new  value is retained when source 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
	      returns  true unless a name is given for which no alias has been
	      defined.

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

       bind [-m keymap] [-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
	      Display  current	readline key and function bindings, bind a key
	      sequence to a readline function or  macro,  or  set  a  readline
	      variable.	  Each	non-option  argument  is a command as it would
	      appear in .inputrc, but each binding or command must  be	passed
	      as  a  separate argument; e.g., '"\C-x\C-r": re-read-init-file'.
	      Options, if supplied, have the following meanings:
	      -m keymap
		     Use keymap as the keymap to be affected by the subsequent
		     bindings.	Acceptable keymap names are emacs, emacs-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
		     entered.	When shell-command is executed, the shell sets
		     the READLINE_LINE variable to the contents of  the	 read‐
		     line  line	 buffer and the READLINE_POINT variable to the
		     current location of the insertion point.  If the executed
		     command  changes  the  value  of  READLINE_LINE  or READ‐
		     LINE_POINT, 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
		     input.

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

       break [n]
	      Exit from within a for, while, until, or select loop.  If	 n  is
	      specified, break n levels.  n must be ≥ 1.  If n is greater than
	      the number of enclosing loops, all enclosing loops  are  exited.
	      The  return  value is 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.  Any	 addi‐
	      tional arguments following dir are ignored.  The variable CDPATH
	      defines the search path for the directory containing  dir:  each
	      directory	 name  in  CDPATH  is  searched	 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.
	      The return value is  true	 if  the  directory  was  successfully
	      changed; false otherwise.

       command [-pVv] command [arg ...]
	      Run  command  with  args	suppressing  the normal shell function
	      lookup.  Only builtin commands or commands found in the PATH are
	      executed.	  If the -p option is given, the search for command is
	      performed using a default value for PATH that is	guaranteed  to
	      find  all	 of  the  standard  utilities.	If either the -V or -v
	      option is supplied, a description of command is printed.	The -v
	      option  causes  a single word indicating the command or 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 [option] [word]
	      Generate	possible  completion matches for word according to the
	      options, which may  be  any  option  accepted  by	 the  complete
	      builtin  with  the exception of -p and -r, and write the matches
	      to the standard output.  When using the -F or  -C	 options,  the
	      various  shell  variables	 set  by  the  programmable completion
	      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] [-DE] [-A action]  [-G	 glob‐
       pat] [-W wordlist] [-F function] [-C command]
	      [-X filterpat] [-P prefix] [-S suffix] name [name ...]
       complete -pr [-DE] [name ...]
	      Specify  how arguments to each name should be completed.	If the
	      -p option is supplied, or if no options are  supplied,  existing
	      completion  specifications are printed in a way that allows them
	      to be reused as input.  The -r option removes a completion spec‐
	      ification	 for each name, or, if no names are supplied, all com‐
	      pletion  specifications.	 The  -D  option  indicates  that  the
	      remaining	 options  and  actions should apply to the ``default''
	      command completion; that is, completion attempted on  a  command
	      for  which  no  completion  has previously been defined.	The -E
	      option indicates that the remaining options and  actions	should
	      apply  to	 ``empty''  command  completion;  that	is, completion
	      attempted on a blank line.

	      The process of applying  these  completion  specifications  when
	      word  completion	is attempted is described above under Program‐
	      mable Completion.

	      Other options, if specified, have the following  meanings.   The
	      arguments	 to the -G, -W, and -X options (and, if necessary, the
	      -P and -S options) should be quoted to protect them from	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.
		      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
			      default)	to  words  completed at the end of the
			      line.
		      plusdirs
			      After any matches defined by  the	 compspec  are
			      generated,    directory	name   completion   is
			      attempted and  any  matches  are	added  to  the
			      results of the other actions.
	      -A action
		      The  action  may	be  one of the following to generate a
		      list of possible completions:
		      alias   Alias names.  May also be specified as -a.
		      arrayvar
			      Array variable names.
		      binding Readline key binding names.
		      builtin Names of shell builtin commands.	 May  also  be
			      specified as -b.
		      command Command names.  May also be specified as -c.
		      directory
			      Directory names.	May also be specified as -d.
		      disabled
			      Names of disabled shell builtins.
		      enabled Names of enabled shell builtins.
		      export  Names  of exported shell variables.  May also be
			      specified as -e.
		      file    File names.  May also be specified as -f.
		      function
			      Names of shell functions.
		      group   Group names.  May also be specified as -g.
		      helptopic
			      Help topics as accepted by the help builtin.
		      hostname
			      Hostnames, as taken from the file	 specified  by
			      the HOSTFILE shell variable.
		      job     Job  names,  if job control is active.  May also
			      be specified as -j.
		      keyword Shell reserved words.  May also be specified  as
			      -k.
		      running Names of running jobs, if job control is active.
		      service Service names.  May also be specified as -s.
		      setopt  Valid  arguments	for  the  -o option to the set
			      builtin.
		      shopt   Shell option names  as  accepted	by  the	 shopt
			      builtin.
		      signal  Signal names.
		      stopped Names of stopped jobs, if job control is active.
		      user    User names.  May also be specified as -u.
		      variable
			      Names of all shell variables.  May also be spec‐
			      ified as -v.
	      -C command
		      command is executed in a subshell environment,  and  its
		      output is used as the possible completions.
	      -F function
		      The  shell  function function is executed in the current
		      shell environment.  When the function is	executed,  the
		      first  argument  ($1)  is	 the name of the command whose
		      arguments are being completed, the second argument  ($2)
		      is the word being completed, and the third argument ($3)
		      is the word preceding the word being  completed  on  the
		      current  command	line.	When it finishes, the possible
		      completions are retrieved from the value of the  COMPRE‐
		      PLY 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.  The possible completions are  the  members
		      of  the  resultant  list which match the word being com‐
		      pleted.
	      -X filterpat
		      filterpat is a pattern as used for  pathname  expansion.
		      It is applied to the list of possible completions gener‐
		      ated by the preceding options and	 arguments,  and  each
		      completion  matching filterpat is removed from the list.
		      A leading ! in filterpat negates the  pattern;  in  this
		      case, any completion not matching filterpat is removed.

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

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

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

       continue [n]
	      Resume the next iteration of the enclosing for, while, until, or
	      select loop.  If n is specified, resume  at  the	nth  enclosing
	      loop.   n	 must  be  ≥  1.   If  n is greater than the number of
	      enclosing loops, the  last  enclosing  loop  (the	 ``top-level''
	      loop) is resumed.	 The return value is 0 unless n is not greater
	      than or equal to 1.

       declare [-aAfFgilnrtux] [-p] [name[=value] ...]
       typeset [-aAfFgilnrtux] [-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
	      attributes and values of all shell  variables.   The  -f	option
	      will  restrict  the  display  to shell functions.	 The -F option
	      inhibits the display of function definitions; only the  function
	      name  and	 attributes are printed.  If the extdebug shell option
	      is enabled using shopt, the source file  name  and  line	number
	      where each name is defined are displayed as well.	 The -F option
	      implies -f.  The -g option forces variables  to  be  created  or
	      modified at the global scope, even when declare is executed in a
	      shell function.  It is ignored in all other cases.  The  follow‐
	      ing options can be used to restrict output to variables with the
	      specified attribute or to give variables attributes:
	      -a     Each name	is  an	indexed	 array	variable  (see	Arrays
		     above).
	      -A     Each  name	 is  an associative array variable (see Arrays
		     above).
	      -f     Use function names only.
	      -i     The variable is treated as an integer; arithmetic evalua‐
		     tion  (see ARITHMETIC EVALUATION above) is performed when
		     the variable is assigned a value.
	      -l     When the variable is assigned  a  value,  all  upper-case
		     characters	 are  converted to lower-case.	The upper-case
		     attribute is disabled.
	      -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
		     inherit the DEBUG	and  RETURN  traps  from  the  calling
		     shell.   The  trace  attribute has no special meaning for
		     variables.
	      -u     When the variable is assigned  a  value,  all  lower-case
		     characters	 are  converted to upper-case.	The lower-case
		     attribute is disabled.
	      -x     Mark names for export  to	subsequent  commands  via  the
		     environment.

	      Using  `+'  instead of `-' turns off the attribute instead, with
	      the exceptions that +a may not be used to destroy an array vari‐
	      able  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 ``-f foo=bar'', an attempt is made to
	      assign a value to a readonly variable, an	 attempt  is  made  to
	      assign  a	 value to an array variable without using the compound
	      assignment syntax (see Arrays above), one of the names is not  a
	      valid  shell variable name, an attempt is made to turn off read‐
	      only 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
	      directories.   The  default  display  is	on  a single line with
	      directory names separated by spaces.  Directories are  added  to
	      the  list	 with  the  pushd  command;  the  popd command removes
	      entries from the list.  The  current  directory  is  always  the
	      first directory in the stack.
	      -c     Clears  the  directory  stack  by	deleting  all  of  the
		     entries.
	      -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
	      receives a SIGHUP.  If no jobspec is  supplied,  the  -a	option
	      means  to	 remove or mark all jobs; the -r option without a job‐
	      spec argument restricts operation to running jobs.   The	return
	      value is 0 unless a jobspec does not specify a valid job.

       echo [-neE] [arg ...]
	      Output  the  args,  separated  by spaces, followed by a newline.
	      The return status is 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	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
	      \0nnn  the  eight-bit  character	whose value is the octal value
		     nnn (zero to three octal digits)
	      \xHH   the eight-bit character whose value  is  the  hexadecimal
		     value HH (one or two hex digits)
	      \uHHHH the  Unicode (ISO/IEC 10646) character whose value is the
		     hexadecimal value HHHH (one to four hex digits)
	      \UHHHHHHHH
		     the Unicode (ISO/IEC 10646) character whose value is  the
		     hexadecimal value HHHHHHHH (one to eight hex digits)

       enable [-a] [-dnps] [-f filename] [name ...]
	      Enable  and disable builtin shell commands.  Disabling a builtin
	      allows a disk command which has the same name as a shell builtin
	      to  be  executed without specifying a full pathname, even though
	      the shell normally searches for builtins before  disk  commands.
	      If  -n  is  used,	 each  name  is disabled; otherwise, names are
	      enabled.	For example, to use the test binary found via the PATH
	      instead  of  the	shell builtin version, run ``enable -n test''.
	      The -f option means to load the new builtin  command  name  from
	      shared object filename, on systems that support dynamic loading.
	      The -d option will delete a builtin 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.  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
	      login(1) does.  The -c option causes command to be executed with
	      an  empty environment.  If -a is supplied, the shell passes name
	      as the zeroth argument to the executed command.  If command 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.	If command is not specified, any redi‐
	      rections 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.

       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).   If	 last  is  not
	      specified	 it is set to the current command for listing (so that
	      ``fc -l -10'' prints the last 10 commands) and to	 first	other‐
	      wise.   If first is not specified it is set to the previous com‐
	      mand 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 intepreted	 the  same  as
	      first  above.  A useful alias to use with this is ``r="fc -s"'',
	      so that typing ``r cc'' runs the	last  command  beginning  with
	      ``cc'' and typing ``r'' re-executes the last command.

	      If  the  first  form  is	used,  the return value is 0 unless an
	      invalid option is encountered or first or last  specify  history
	      lines  out  of  range.  If the -e option is supplied, the return
	      value is the value of the last command executed or failure if an
	      error occurs with the temporary file of commands.	 If the second
	      form is used, the return status is that of the  command  re-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 [args]
	      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
	      expected	to have an argument, which should be separated from it
	      by white space.  The colon and question mark characters may  not
	      be  used as option characters.  Each time it is invoked, getopts
	      places the next option in the shell variable name,  initializing
	      name if it does not exist, and the index of the next argument to
	      be processed into the variable OPTIND.  OPTIND is initialized to
	      1	 each  time  the  shell or a shell script is invoked.  When an
	      option requires an argument, getopts places that	argument  into
	      the  variable OPTARG.  The shell does not reset OPTIND automati‐
	      cally; it must be	 manually  reset  between  multiple  calls  to
	      getopts within the same shell invocation if a new set of parame‐
	      ters is to be used.

	      When the end of options is encountered,  getopts	exits  with  a
	      return  value  greater than zero.	 OPTIND is set to the index of
	      the first non-option argument, and name is set to ?.

	      getopts normally parses the positional parameters, but  if  more
	      arguments are given in args, getopts parses those instead.

	      getopts  can  report errors in two ways.	If the first character
	      of optstring is a colon, silent error  reporting	is  used.   In
	      normal  operation,  diagnostic messages are printed when invalid
	      options or missing option arguments  are	encountered.   If  the
	      variable	OPTERR	is  set	 to  0, no error messages will be dis‐
	      played, even if the first character of optstring is not a colon.

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

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

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

       hash [-lr] [-p filename] [-dt] [name]
	      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, no path search is performed, and filename
	      is  used	as  the	 full  filename of the command.	 The -r option
	      causes the shell to forget all  remembered  locations.   The  -d
	      option  causes  the  shell  to forget the remembered location of
	      each name.  If the -t option is supplied, the full  pathname  to
	      which  each name corresponds is printed.	If multiple name argu‐
	      ments are supplied with -t,  the	name  is  printed  before  the
	      hashed  full  pathname.	The -l option causes output to be dis‐
	      played in a format that may be reused as input.  If no arguments
	      are  given,  or if only -l is supplied, information about remem‐
	      bered commands is printed.  The return status is true  unless  a
	      name is not found or an invalid option is supplied.

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

	      The return status is 0 unless no command matches pattern.

       history [n]
       history -c
       history -d offset
       history -anrw [filename]
       history -p arg [arg ...]
       history -s arg [arg ...]
	      With no options, display the command history list with line 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.	Options, if supplied, have the
	      following meanings:
	      -c     Clear the history list by deleting all the entries.
	      -d offset
		     Delete the history entry at position offset.
	      -a     Append the ``new'' history lines  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
		     appended  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  is  sup‐
	      plied as an argument to -d, or the history expansion supplied as
	      an argument to -p fails.

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

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

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

       kill [-s sigspec | -n signum | -sigspec] [pid | jobspec] ...
       kill -l|-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
	      option is encountered.

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

       local [option] [name[=value] ... | - ]
	      For  each	 argument, a local variable named name is created, and
	      assigned value.  The option can be any of the  options  accepted
	      by declare.  When local is used within a function, it causes the
	      variable name to have a visible scope restricted to  that	 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 are
	      restored to their original values	 when  the  function  returns.
	      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.
	      -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
	      array before assigning to it.

	      mapfile returns successfully unless an invalid option or	option
	      argument	is  supplied,  array is invalid or unassignable, or if
	      array is not an indexed array.

       popd [-n] [+n] [-n]
	      Removes entries from the directory stack.	  With	no  arguments,
	      removes  the  top directory from the stack, and performs a cd to
	      the new top directory.  Arguments, if supplied, have the follow‐
	      ing meanings:
	      -n     Suppresses	 the  normal change of directory when removing
		     directories from the stack, so that  only	the  stack  is
		     manipulated.
	      +n     Removes  the nth entry counting from the left of the list
		     shown by dirs, starting with zero.	 For  example:	``popd
		     +0'' removes the first directory, ``popd +1'' the second.
	      -n     Removes the nth entry counting from the right of the list
		     shown by dirs, starting with zero.	 For  example:	``popd
		     -0''  removes the last directory, ``popd -1'' the next to
		     last.

	      If the popd command is successful, a dirs is performed as	 well,
	      and  the	return	status is 0.  popd returns false if an invalid
	      option is encountered, the directory stack is empty, a non-exis‐
	      tent directory stack entry is specified, or the directory change
	      fails.

       printf [-v var] format [arguments]
	      Write the formatted arguments to the standard output  under  the
	      control  of  the	format.	 The -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(1) format specifications, printf
	      interprets the following extensions:
	      %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.
	      %(datefmt)T
		     causes  printf  to	 output the date-time string resulting
		     from using datefmt as a format  string  for  strftime(3).
		     The corresponding argument is an integer representing the
		     number of seconds since the epoch.	 Two special  argument
		     values  may  be used: -1 represents the current time, and
		     -2 represents the time the	 shell	was  invoked.	If  no
		     argument  is  specified,  conversion behaves as if -1 had
		     been given.  This is an exception	to  the	 usual	printf
		     behavior.

	      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 on failure.

       pushd [-n] [+n] [-n]
       pushd [-n] [dir]
	      Adds a directory to the top of the directory stack,  or  rotates
	      the  stack,  making the new top of the stack the current working
	      directory.  With no  arguments,  pushd  exchanges	 the  top  two
	      directories  and returns 0, unless the directory stack is empty.
	      Arguments, if supplied, have the following meanings:
	      -n     Suppresses the normal change of directory	when  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, making it the
		     new  current working directory as if it had been supplied
		     as the argument to the cd builtin.

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

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

       read [-ers] [-a aname] [-d delim] [-i text] [-n nchars] [-N nchars] [-p
       prompt] [-t timeout] [-u fd] [name ...]
	      One line is read from the	 standard  input,  or  from  the  file
	      descriptor  fd  supplied	as an argument to the -u option, split
	      into words as described above  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
	      (described above under Word Splitting).  The backslash character
	      (\) may be used to remove any special meaning for the next char‐
	      acter read and for line  continuation.   Options,	 if  supplied,
	      have the following meanings:
	      -a aname
		     The words are assigned to sequential indices of the array
		     variable aname, starting at 0.  aname is unset before any
		     new  values  are  assigned.   Other  name	arguments  are
		     ignored.
	      -d delim
		     The first character of delim is  used  to	terminate  the
		     input line, rather than newline.
	      -e     If the standard input is coming from a terminal, readline
		     (see READLINE above) is used to obtain the	 line.	 Read‐
		     line  uses	 the  current (or default, if line editing was
		     not previously active) editing settings.
	      -i text
		     If readline is being used	to  read  the  line,  text  is
		     placed into the editing buffer before editing begins.
	      -n nchars
		     read  returns after reading nchars characters rather than
		     waiting for a complete line of input, but 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 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
		     returns  immediately,  without  trying  to read any data.
		     The exit status is 0 if input is available on the	speci‐
		     fied  file descriptor, non-zero otherwise.	 The exit sta‐
		     tus is greater than 128 if the timeout is exceeded.
	      -u fd  Read input from file descriptor fd.

	      If no names are supplied, the line read is assigned to the vari‐
	      able  REPLY.   The  exit	status	is zero, unless end-of-file is
	      encountered, read times out (in which case the status is greater
	      than  128),  a variable assignment error (such as assigning to a
	      readonly variable) occurs, or an invalid file descriptor is sup‐
	      plied 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
	      arrays;  the  -A	option	restricts the variables to associative
	      arrays.  If both options are supplied, -A takes precedence.   If
	      no  name arguments are given, or if the -p option is supplied, a
	      list of all readonly names is printed.  The other options may be
	      used  to	restrict the output to a subset of the set of readonly
	      names.  The -p option causes output to be 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
	      return is executed by a trap handler, the last command  used  to
	      determine	 the  status  is  the last command executed before the
	      trap handler.  if return is executed during a  DEBUG  trap,  the
	      last  command  used  to determine the status is the last command
	      executed by the trap handler  before  return  was	 invoked.   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
	      significant 8 bits.  The return status is non-zero if return  is
	      supplied	a  non-numeric argument, or is used outside a function
	      and not during execution of a script by . or source.   Any  com‐
	      mand  associated	with the RETURN trap is executed before execu‐
	      tion resumes after the function or script.

       set [--abefhkmnptuvxBCEHPT] [-o option-name] [arg ...]
       set [+abefhkmnptuvxBCEHPT] [+o option-name] [arg ...]
	      Without options, the name and value of each shell	 variable  are
	      displayed in a format that can be reused as input for setting or
	      resetting the currently-set variables.  Read-only variables can‐
	      not  be  reset.  In posix mode, only shell variables are listed.
	      The output is sorted according  to  the  current	locale.	  When
	      options  are specified, they set or unset shell attributes.  Any
	      arguments remaining after option processing are treated as  val‐
	      ues for the positional parameters and are assigned, in order, to
	      $1, $2, ...  $n.	Options,  if  specified,  have	the  following
	      meanings:
	      -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 above), exits with a non-zero status.
		      The shell does not exit if the  command  that  fails  is
		      part  of	the command list immediately following a while
		      or until 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 final  &&
		      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
		      above), and may cause subshells to exit before executing
		      all the commands in the subshell.

		      If a compound command or shell function  executes	 in  a
		      context  where -e is being ignored, none of the commands
		      executed within the compound command  or	function  body
		      will  be	affected  by the -e setting, even if -e is set
		      and a command returns a failure status.  If  a  compound
		      command  or  shell function sets -e while executing in a
		      context where -e is ignored, that setting will not  have
		      any  effect  until  the  compound command or the command
		      containing the function call completes.
	      -f      Disable pathname expansion.
	      -h      Remember the location of commands as they are looked  up
		      for execution.  This is enabled by default.
	      -k      All  arguments  in the form of assignment statements are
		      placed in the environment for a command, not just	 those
		      that precede the command name.
	      -m      Monitor  mode.   Job control is enabled.	This option is
		      on by default for interactive  shells  on	 systems  that
		      support  it  (see JOB CONTROL above).  All processes run
		      in a separate process group.  When a background job com‐
		      pletes, the shell prints a line containing its exit sta‐
		      tus.
	      -n      Read commands but do not execute them.  This may be used
		      to  check	 a  shell  script  for syntax errors.  This is
		      ignored by interactive shells.
	      -o option-name
		      The option-name can be one of the following:
		      allexport
			      Same as -a.
		      braceexpand
			      Same as -B.
		      emacs   Use an emacs-style command line  editing	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 above under
			      HISTORY.	This option is on by default in inter‐
			      active shells.
		      ignoreeof
			      The  effect  is  as   if	 the   shell   command
			      ``IGNOREEOF=10''	had  been  executed (see Shell
			      Variables above).
		      keyword Same as -k.
		      monitor Same as -m.
		      noclobber
			      Same as -C.
		      noexec  Same as -n.
		      noglob  Same as -f.
		      nolog   Currently ignored.
		      notify  Same as -b.
		      nounset Same as -u.
		      onecmd  Same as -t.
		      physical
			      Same as -P.
		      pipefail
			      If set, the return value of a  pipeline  is  the
			      value  of	 the  last (rightmost) command to exit
			      with a non-zero status, or zero if all  commands
			      in  the pipeline exit successfully.  This option
			      is disabled by default.
		      posix   Change the behavior of bash  where  the  default
			      operation	 differs  from	the  POSIX standard to
			      match the standard (posix mode).	See  SEE  ALSO
			      below 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, the values of the
		      current  options are printed.  If +o is supplied with no
		      option-name, a series of set commands  to	 recreate  the
		      current  option  settings	 is  displayed on the standard
		      output.
	      -p      Turn on privileged mode.	In this	 mode,	the  $ENV  and
		      $BASH_ENV	 files	are not processed, shell functions are
		      not inherited from the environment, and  the  SHELLOPTS,
		      BASHOPTS,	 CDPATH,  and  GLOBIGNORE  variables,  if they
		      appear in the environment, are ignored.  If the shell is
		      started  with the effective user (group) id not equal to
		      the real user (group) id, and the -p option is not  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.
	      -t      Exit after reading and executing one command.
	      -u      Treat unset variables and parameters other than the spe‐
		      cial parameters "@" and "*" as an error when  performing
		      parameter	 expansion.   If  expansion is attempted on an
		      unset variable or parameter, the shell prints  an	 error
		      message,	and, if not interactive, exits with a non-zero
		      status.
	      -v      Print shell input lines as they are read.
	      -x      After expanding each simple command, for	command,  case
		      command, select command, or arithmetic for command, dis‐
		      play the expanded value of PS4, followed by the  command
		      and its expanded arguments or associated word list.
	      -B      The  shell performs brace expansion (see Brace Expansion
		      above).  This is on by default.
	      -C      If set, bash does not overwrite an  existing  file  with
		      the  >,  >&,  and <> redirection operators.  This may be
		      overridden when creating output files by using the 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
		      executed in  a  subshell	environment.   The  DEBUG  and
		      RETURN traps are normally not inherited in such cases.
	      --      If  no arguments follow this option, then the positional
		      parameters are unset.  Otherwise, the positional 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
	      options  can  also be specified as arguments to an invocation of
	      the shell.  The current set of options may be found in $-.   The
	      return status is always true unless an invalid option is encoun‐
	      tered.

       shift [n]
	      The positional parameters from n+1 ... are renamed  to  $1  ....
	      Parameters  represented  by  the	numbers	 $# down to $#-n+1 are
	      unset.  n must be a non-negative number less than	 or  equal  to
	      $#.   If	n is 0, no parameters are changed.  If n is not given,
	      it is assumed to be 1.  If n is greater than $#, the  positional
	      parameters  are  not changed.  The return status is greater than
	      zero if n is greater than $# or less than zero; otherwise 0.

       shopt [-pqsu] [-o] [optname ...]
	      Toggle the values of settings controlling optional shell	behav‐
	      ior.   The settings can be either those listed below, or, if the
	      -o option is used, those available with the -o option to the set
	      builtin command.	With no options, or with the -p option, a list
	      of all settable options is  displayed,  with  an	indication  of
	      whether  or  not each is set.  The -p option causes output to be
	      displayed in a form that may be reused as input.	Other  options
	      have the following meanings:
	      -s     Enable (set) each optname.
	      -u     Disable (unset) each optname.
	      -q     Suppresses	 normal output (quiet mode); the return status
		     indicates whether the optname is set or unset.  If 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
	      options,	the  return  status is zero unless an optname is not a
	      valid shell option.

	      The list of shopt options is:

	      autocd  If set, a command name that is the name of  a  directory
		      is  executed  as	if it were the argument to the cd 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  above).   The shell always postpones
		      exiting if any jobs are stopped.
	      checkwinsize
		      If set, bash checks the window size after	 each  command
		      and,  if necessary, updates the values of LINES and COL‐
		      UMNS.
	      cmdhist If set, bash attempts to save all lines of  a  multiple-
		      line  command  in	 the  same history entry.  This allows
		      easy re-editing of multi-line commands.
	      compat31
		      If set, bash changes its behavior to that of version 3.1
		      with  respect  to quoted arguments to the [[ conditional
		      command's =~ operator and locale-specific string compar‐
		      ison  when  using	 the  [[ conditional command's < and >
		      operators.  Bash versions prior to  bash-4.1  use	 ASCII
		      collation and strcmp(3); bash-4.1 and later use the cur‐
		      rent locale's collation sequence and strcoll(3).
	      compat32
		      If set, bash changes its behavior to that of version 3.2
		      with  respect  to locale-specific string comparison when
		      using the [[ conditional command's  <  and  >  operators
		      (see  previous  item)  and  the effect of interrupting a
		      command list.  Bash versions 3.2	and  earlier  continue
		      with  the	 next command in the list after one terminates
		      due to an interrupt.
	      compat40
		      If set, bash changes its behavior to that of version 4.0
		      with  respect  to locale-specific string comparison when
		      using the [[ conditional command's  <  and  >  operators
		      (see  description	 of compat31) and the effect of inter‐
		      rupting a command list.  Bash  versions  4.0  and	 later
		      interrupt	 the  list as if the shell received the inter‐
		      rupt; previous versions continue with the	 next  command
		      in the list.
	      compat41
		      If  set, bash, when in posix mode, treats a single quote
		      in a double-quoted  parameter  expansion	as  a  special
		      character.   The	single quotes must match (an even num‐
		      ber) and the characters between the  single  quotes  are
		      considered  quoted.   This is the behavior of posix mode
		      through version 4.1.  The default bash behavior  remains
		      as in previous versions.
	      compat42
		      If  set, bash does not process the replacement string in
		      the pattern  substitution	 word  expansion  using	 quote
		      removal.
	      compat43
		      If  set,	bash  does  not	 print a warning message if an
		      attempt is made to use a quoted compound	array  assign‐
		      ment  as	an  argument  to declare, makes word expansion
		      errors non-fatal errors that cause the  current  command
		      to  fail	(the  default  behavior	 is to make them fatal
		      errors that cause the shell to exit), and does not reset
		      the  loop	 state when a shell function is executed (this
		      allows break or continue in a shell function  to	affect
		      loops in the caller's context).
	      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
		      expand 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 buf‐
		      fer.  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.
	      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 above under
		      ALIASES.	This option is enabled by default for interac‐
		      tive shells.
	      extdebug
		      If  set  at  shell  invocation,  arrange	to execute the
		      debugger profile before the shell starts,	 identical  to
		      the  --debugger option.  If set after invocation, behav‐
		      ior intended for use by debuggers is enabled:
		      1.     The -F option to the declare builtin displays the
			     source file name and line number corresponding to
			     each function name supplied as an argument.
		      2.     If the command run by the DEBUG  trap  returns  a
			     non-zero  value,  the next command is skipped and
			     not executed.
		      3.     If the command run by the DEBUG  trap  returns  a
			     value  of 2, and the shell is executing in a sub‐
			     routine (a shell function or a shell script  exe‐
			     cuted  by	the  .	or source builtins), the shell
			     simulates a call to return.
		      4.     BASH_ARGC and BASH_ARGV are updated as  described
			     in their descriptions above.
		      5.     Function  tracing	is  enabled: command substitu‐
			     tion, shell functions, and subshells invoked with
			     ( command ) inherit the DEBUG and RETURN traps.
		      6.     Error  tracing  is enabled: command substitution,
			     shell functions, and  subshells  invoked  with  (
			     command ) inherit the ERR trap.
	      extglob If set, the extended pattern matching features described
		      above under Pathname Expansion are enabled.
	      extquote
		      If set, $'string' and  $"string"	quoting	 is  performed
		      within   ${parameter}   expansions  enclosed  in	double
		      quotes.  This option is enabled by default.
	      failglob
		      If set, patterns which fail to  match  filenames	during
		      pathname expansion result in an expansion error.
	      force_fignore
		      If  set,	the  suffixes  specified  by the FIGNORE shell
		      variable cause words to be ignored when performing  word
		      completion even if the ignored words are the only possi‐
		      ble  completions.	  See  SHELL  VARIABLES	 above	for  a
		      description  of  FIGNORE.	  This	option	is  enabled by
		      default.
	      globasciiranges
		      If set,  range  expressions  used	 in  pattern  matching
		      bracket  expressions (see Pattern Matching above) behave
		      as if in the traditional C locale when  performing  com‐
		      parisons.	  That	is,  the  current  locale's  collating
		      sequence is not taken into account, so b will  not  col‐
		      late  between  A	and  B,	 and upper-case and lower-case
		      ASCII characters will collate together.
	      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
		      exits, rather than overwriting the file.
	      histreedit
		      If set, and readline is being used, a user is given  the
		      opportunity to re-edit a failed history substitution.
	      histverify
		      If  set, and readline is being used, the results of 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
		      above).  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	above).	  This
		      option is enabled by default.
	      lastpipe
		      If  set,	and  job control is not active, the shell runs
		      the last command of a pipeline not 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.
	      login_shell
		      The  shell  sets this option if it is started as a login
		      shell (see INVOCATION above).   The  value  may  not  be
		      changed.
	      mailwarn
		      If  set,	and  a file that bash is checking for mail has
		      been accessed since the last time it  was	 checked,  the
		      message  ``The  mail in mailfile has been read'' is dis‐
		      played.
	      no_empty_cmd_completion
		      If set, and  readline  is	 being	used,  bash  will  not
		      attempt 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 above).
	      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.
	      nullglob
		      If set, bash allows patterns which match no  files  (see
		      Pathname	Expansion  above)  to expand to a null string,
		      rather than themselves.
	      progcomp
		      If set, the programmable completion facilities (see Pro‐
		      grammable Completion above) are enabled.	This option is
		      enabled by default.
	      promptvars
		      If set, prompt strings undergo parameter expansion, com‐
		      mand   substitution,  arithmetic	expansion,  and	 quote
		      removal after being expanded as described	 in  PROMPTING
		      above.  This option is enabled by default.
	      restricted_shell
		      The   shell  sets	 this  option  if  it  is  started  in
		      restricted mode (see RESTRICTED SHELL below).  The value
		      may  not be changed.  This is not reset when the startup
		      files are executed, allowing the startup files  to  dis‐
		      cover 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.
	      xpg_echo
		      If   set,	 the  echo  builtin  expands  backslash-escape
		      sequences by default.

       suspend [-f]
	      Suspend the execution of this shell until it receives a  SIGCONT
	      signal.  A login shell cannot be suspended; the -f option can be
	      used to override this and force the suspension.  The return sta‐
	      tus  is  0  unless the shell is a login shell and -f is not sup‐
	      plied, or if job control is not enabled.

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

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

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

	      0 arguments
		     The expression is false.
	      1 argument
		     The expression is true if and only if the argument is not
		     null.
	      2 arguments
		     If the first argument is !, the expression is true if and
		     only if the second argument is null.  If the first	 argu‐
		     ment  is  one  of	the unary conditional operators listed
		     above under CONDITIONAL EXPRESSIONS,  the	expression  is
		     true if the unary test is true.  If the first argument is
		     not a valid unary conditional operator, the expression is
		     false.
	      3 arguments
		     The following conditions are applied in the order listed.
		     If the second argument is one of the  binary  conditional
		     operators listed above under CONDITIONAL EXPRESSIONS, the
		     result of the expression is the result of the binary test
		     using  the first and third arguments as operands.	The -a
		     and -o operators are  considered  binary  operators  when
		     there  are	 three arguments.  If the first argument is !,
		     the value is the negation of the two-argument test	 using
		     the second and third arguments.  If the first argument is
		     exactly ( and the third argument is exactly ), the result
		     is	 the one-argument test of the second argument.	Other‐
		     wise, the expression is false.
	      4 arguments
		     If the first argument is !, the result is the negation of
		     the  three-argument  expression composed of the remaining
		     arguments.	 Otherwise, the expression is parsed and eval‐
		     uated  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  used  with	test  or [, the < and > operators sort lexico‐
	      graphically 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] [[arg] sigspec ...]
	      The  command  arg	 is  to	 be  read  and executed when the shell
	      receives signal(s) sigspec.  If arg is absent (and  there	 is  a
	      single  sigspec)	or  -,	each  specified signal is reset to its
	      original disposition (the value it  had  upon  entrance  to  the
	      shell).	If arg is the null string the signal specified by each
	      sigspec is ignored by the shell and by the commands it  invokes.
	      If  arg  is  not present and -p has been supplied, then the trap
	      commands associated with each  sigspec  are  displayed.	If  no
	      arguments	 are  supplied or if only -p is given, trap prints the
	      list of commands associated with each  signal.   The  -l	option
	      causes  the shell to print a list of signal names and their cor‐
	      responding numbers.   Each  sigspec  is  either  a  signal  name
	      defined  in  <signal.h>,	or  a signal number.  Signal names are
	      case insensitive and the SIG prefix is optional.

	      If a sigspec is EXIT (0) the command arg	is  executed  on  exit
	      from  the shell.	If a sigspec is DEBUG, the command arg is exe‐
	      cuted before every simple command, for  command,	case  command,
	      select  command,	every  arithmetic  for command, and before the
	      first command executes in a shell function  (see	SHELL  GRAMMAR
	      above).	Refer to the description of the extdebug option to the
	      shopt builtin for details of its effect on the DEBUG trap.  If a
	      sigspec is RETURN, the command arg is executed each time a shell
	      function or a script executed with the . or source builtins fin‐
	      ishes executing.

	      If  a  sigspec  is  ERR,	the command arg 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)
	      option.

	      Signals  ignored	upon  entry  to the shell cannot be trapped or
	      reset.  Trapped signals that are not being ignored are reset  to
	      their original values in a subshell or subshell environment when
	      one is created.  The return status is false if  any  sigspec  is
	      invalid; otherwise trap returns true.

       type [-aftpP] name [name ...]
	      With  no options, indicate how each name would be interpreted if
	      used as a command name.  If the -t option is used, type prints a
	      string  which  is	 one  of alias, keyword, function, builtin, or
	      file if  name  is	 an  alias,  shell  reserved  word,  function,
	      builtin,	or disk file, respectively.  If the name is not found,
	      then nothing  is	printed,  and  an  exit	 status	 of  false  is
	      returned.	  If  the  -p  option is used, type either returns the
	      name of the disk file that would be executed if name were speci‐
	      fied as a command name, or nothing if ``type -t name'' would not
	      return file.  The -P option forces a PATH search for each	 name,
	      even if ``type -t name'' would not return file.  If a command is
	      hashed, -p and -P print the hashed value, 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	an  executable
	      named name.  This includes aliases and functions, if and only if
	      the -p option is not also used.  The table of hashed commands is
	      not  consulted  when  using  -a.	The -f option suppresses shell
	      function lookup, as with the command builtin.  type returns true
	      if all of the arguments are found, false if any are not found.

       ulimit [-HSabcdefiklmnpqrstuvxPT [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,
	      respectively.   If  limit	 is  omitted, the current value of the
	      soft limit of the resource is printed, unless the -H  option  is
	      given.  When more than one resource is specified, the limit name
	      and unit are printed before the value.  Other options are inter‐
	      preted as follows:
	      -a     All current limits are reported
	      -b     The maximum socket buffer size
	      -c     The maximum size of core files created
	      -d     The maximum size of a process's data segment
	      -e     The maximum scheduling priority ("nice")
	      -f     The  maximum  size	 of files written by the shell and its
		     children
	      -i     The maximum number of pending signals
	      -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
	      -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; -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 incre‐
	      ments.  The return status is 0 unless an invalid option or argu‐
	      ment 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 [-a] [name ...]
	      Remove each name from the list of defined	 aliases.   If	-a  is
	      supplied,	 all  alias definitions are removed.  The return value
	      is true unless a supplied name is not a defined alias.

       unset [-fv] [-n] [name ...]
	      For each name, remove the corresponding  variable	 or  function.
	      If the -v option is given, each name refers to a shell variable,
	      and that variable is removed.  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, any function with that name is unset.  Each
	      unset variable or	 function  is  removed	from  the  environment
	      passed  to subsequent commands.  If any of COMP_WORDBREAKS, RAN‐
	      DOM, SECONDS, LINENO, HISTCMD, FUNCNAME, GROUPS, or DIRSTACK 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.

       wait [-n] [n ...]
	      Wait for each specified child process and return its termination
	      status.  Each n may be a process ID or a job specification; if a
	      job  spec	 is  given,  all  processes in that job's pipeline are
	      waited for.  If n is not given, all currently active child  pro‐
	      cesses are waited for, and the return status is zero.  If the -n
	      option is supplied, wait waits for  any  job  to	terminate  and
	      returns  its exit status.	 If n specifies a non-existent process
	      or job, the return status is 127.	 Otherwise, the return	status
	      is the exit status of the last process or job waited for.

RESTRICTED SHELL
       If bash is started with the name rbash, or the -r option is supplied at
       invocation, the shell becomes restricted.  A restricted shell  is  used
       to  set	up an environment more controlled than the standard shell.  It
       behaves identically to bash with the exception that the	following  are
       disallowed or not performed:

       ·      changing directories with cd

       ·      setting or unsetting the values of SHELL, PATH, ENV, or BASH_ENV

       ·      specifying command names containing /

       ·      specifying  a  filename  containing  a / as an argument to the .
	      builtin command

       ·      specifying a filename containing a slash as an argument  to  the
	      -p option to the hash builtin command

       ·      importing	 function  definitions	from  the shell environment at
	      startup

       ·      parsing the value of SHELLOPTS from  the	shell  environment  at
	      startup

       ·      redirecting output using the >, >|, <>, >&, &>, and >> redirect‐
	      ion operators

       ·      using the exec builtin command to replace the shell with another
	      command

       ·      adding  or  deleting builtin commands with the -f and -d options
	      to the enable builtin command

       ·      using the	 enable	 builtin  command  to  enable  disabled	 shell
	      builtins

       ·      specifying the -p option to the command builtin command

       ·      turning off restricted mode with set +r or set +o restricted.

       These restrictions are enforced after any startup files are read.

       When a command that is found to be a shell script is executed (see COM‐
       MAND EXECUTION above), rbash turns off any restrictions	in  the	 shell
       spawned to execute the script.

SEE ALSO
       Bash Reference Manual, Brian Fox and Chet Ramey
       The Gnu Readline Library, Brian Fox and Chet Ramey
       The Gnu History Library, Brian Fox and Chet Ramey
       Portable	 Operating  System  Interface (POSIX) Part 2: Shell and Utili‐
       ties, IEEE --
	      http://pubs.opengroup.org/onlinepubs/9699919799/
       http://tiswww.case.edu/~chet/bash/POSIX -- a description of posix mode
       sh(1), ksh(1), csh(1)
       emacs(1), vi(1)
       readline(3)

FILES
       /bin/bash
	      The bash executable
       /etc/profile
	      The systemwide initialization file, executed for login shells
       /etc/bash.bashrc
	      The systemwide per-interactive-shell startup file
       /etc/bash.bash.logout
	      The systemwide login shell cleanup file, executed when  a	 login
	      shell exits
       ~/.bash_profile
	      The personal initialization file, executed for login shells
       ~/.bashrc
	      The individual per-interactive-shell startup file
       ~/.bash_logout
	      The  individual  login shell cleanup file, executed when a login
	      shell exits
       ~/.inputrc
	      Individual readline initialization file

AUTHORS
       Brian Fox, Free Software Foundation
       bfox@gnu.org

       Chet Ramey, Case Western Reserve University
       chet.ramey@case.edu

BUG REPORTS
       If you find a bug in bash, you should report it.	 But first, you should
       make  sure  that	 it really is a bug, and that it appears in the latest
       version	of  bash.   The	 latest	 version  is  always  available	  from
       ftp://ftp.gnu.org/pub/gnu/bash/.

       Once  you  have	determined that a bug actually exists, use the bashbug
       command to submit a bug report.	If you have a fix, you are  encouraged
       to  mail that as well!  Suggestions and `philosophical' bug reports may
       be mailed  to  bug-bash@gnu.org	or  posted  to	the  Usenet  newsgroup
       gnu.bash.bug.

       ALL bug reports should include:

       The version number of bash
       The hardware and operating system
       The compiler used to compile
       A description of the bug behaviour
       A short script or `recipe' which exercises the bug

       bashbug	inserts	 the first three items automatically into the template
       it provides for filing a bug report.

       Comments and bug reports concerning this manual page should be directed
       to chet.ramey@case.edu.

BUGS
       It's too big and too slow.

       There are some subtle differences between bash and traditional versions
       of sh, mostly because of the POSIX specification.

       Aliases are confusing in some uses.

       Shell builtin commands and functions are not stoppable/restartable.

       Compound commands and command sequences of the form `a ; b ; c' are not
       handled	gracefully  when  process  suspension  is  attempted.	When a
       process is stopped, the shell immediately executes the next command  in
       the  sequence.	It  suffices to place the sequence of commands between
       parentheses to force it into a subshell, which  may  be	stopped	 as  a
       unit.

       Array variables may not (yet) be exported.

       There may be only one active coprocess at a time.

GNU Bash 4.4			2016 August 26			       BASH(1)
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