bash man page on OpenMandriva

Man page or keyword search:  
man Server   8135 pages
apropos Keyword Search (all sections)
Output format
OpenMandriva logo
[printable version]

BASH(1)								       BASH(1)

NAME
       bash - GNU Bourne-Again SHell

SYNOPSIS
       bash [options] [command_string | file]

COPYRIGHT
       Bash is Copyright (C) 1989-2013 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 descrip‐
       tion 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,  they	are  assigned  to  the
		 positional parameters, starting with $0.
       -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 standard personal ini‐
	      tialization  file	 ~/.bashrc  if	the  shell is interactive (see
	      INVOCATION 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	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).

       --rpm-requires
	      Produce the list of files that are required for the shell script
	      to  run.	 This  implies '-n' and is subject to the same limita‐
	      tions as compile time error checking checking; Command substitu‐
	      tions,  Conditional  expressions and eval builtin are not parsed
	      so some dependencies may be missed.

       --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 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 a login shell exits, 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 ~/.bashrc, if that file exists.	  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
       ~/.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,	 if  that file exists and is 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
       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 of 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.

	      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 ext‐
	      glob shell option were enabled.  The = operator is equivalent to
	      ==.   If	the  shell option nocasematch 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  pat‐
	      tern  may be quoted to force the quoted portion to be matched as
	      a string.

	      An additional binary operator, =~, is available, with  the  same
	      precedence  as  ==  and  !=.  When it is used, the string to the
	      right of the operator is considered an extended regular  expres‐
	      sion 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 shell option nocasematch
	      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	 substitution,	command	 substitution, process
	      substitution  and	 quote	removal.   Each	 pattern  examined  is
	      expanded	using  tilde  expansion, parameter and variable expan‐
	      sion, arithmetic substitution, command substitution, and process
	      substitution.   If  the shell option nocasematch is enabled, the
	      match is performed 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.	  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, !.  The characters $	and  `	retain
       their  special meaning within double quotes.  The backslash retains its
       special meaning 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
	      \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.  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.	 When += is applied to a vari‐
       able 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 or assigned  to,  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 argument 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 are treated as references and assignments 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
       -n 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; unsetting
	      array elements cause aliases to be removed from the alias list.
       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;
	      unsetting array elements cause commands to be removed  from  the
	      hash table.
       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_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 and return an error sta‐
	      tus.  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
	      and  return  an  error status.  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.
       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:~".
       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.
       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.
       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 supplies a default value for this variable, but  the	 loca‐
	      tion  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.
       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
       referenced 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.  Referencing an array variable without a  subscript
       is  equivalent  to referencing the array with a subscript of 0.	If the
       subscript used to reference an element of an indexed array evaluates to
       a  number  less than zero, it is interpreted 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 ele‐
       ment.

       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.

       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 (!), it
       introduces a level of variable indirection.  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.  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  indirec‐
       tion.

       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 parameter is @ or *, the sub‐
	      stitution 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.

   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 and replacing the com‐
       mand  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 command 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 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  is supported on systems that support named pipes
       (FIFOs) or the /dev/fd method of naming open files.  It takes the  form
       of  <(list) or >(list).	The process list is run with its input or out‐
       put connected to a FIFO or some file in /dev/fd.	 The name of this file
       is  passed  as  an argument to the current command as the result of the
       expansion.  If the >(list) form is used, writing to the file will  pro‐
       vide  input  for list.  If the <(list) form is used, the file passed as
       an argument should be read to obtain the output of list.

       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 and
       tab are ignored at the beginning and end of the word, as	 long  as  the
       whitespace  character is in the value of IFS (an IFS whitespace charac‐
       ter).  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.  Unquoted implicit
       null arguments, resulting from the expansion of parameters that have no
       values,	are  removed.  If a parameter with no value is expanded within
       double quotes, a null argument results and is retained.

       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.  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 char‐
       acter 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, null‐
       glob, 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.	 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 ignoring filenames beginning with a ``.'', make ``.*''  one
       of  the	patterns  in  GLOBIGNORE.  The dotglob option is disabled when
       GLOBIGNORE is unset.

       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:

	      /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.

   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 for a command.

       The format of here-documents is:

	      <<[-]word
		      here-document
	      delimiter

       No parameter and variable expansion, command  substitution,  arithmetic
       expansion,  or pathname expansion is performed on word.	If any charac‐
       ters in word are 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:

	      <<<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 to the command on
       its standard input.

   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‐
       pound command.  As a consequence, aliases defined in a function are not
       available until after that function is executed.	 To  be	 safe,	always
       put  alias definitions on a separate line, and do not use alias in com‐
       pound 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 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 following 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.  If any file argument to  one	 of  the  pri‐
       maries 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.

       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 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.
       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-ignore-case (Off)
	      If set to On, readline performs filename matching and completion
	      in a case-insensitive fashion.
       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).
       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.
       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.
       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.
       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 (0)
	      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 not limited.
       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  high  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.
       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.
       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.
       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.
       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 the both 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 (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 shell-forward-word.
       shell-backward-kill-word (M-Rubout)
	      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 or 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.

       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.

       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, break, continue, let,
       and shift builtins accept and process arguments beginning with -	 with‐
       out  requiring  --.   Other  builtins that accept arguments but are not
       specified as accepting options interpret arguments beginning with -  as
       invalid options and require -- to prevent this interpretation.
       : [arguments]
	      No  effect;  the command does nothing beyond expanding arguments
	      and performing any specified redirections.  A zero exit code  is
	      returned.

	.  filename [arguments]
       source filename [arguments]
	      Read  and	 execute  commands  from filename in the current shell
	      environment and return the exit status of the last command  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.  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 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; emacs is
		     equivalent to emacs-standard.
	      -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).
		      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  the  function  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
	      following	 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 and assign‐
		     ments  to	name,  except  for  changing  the -n attribute
		     itself, are  performed  on	 the  variable	referenced  by
		     name's  value.   The  -n  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.
	      -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 ...]
	      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 (history lines entered
		     since the beginning of the current bash session)  to  the
		     history file.
	      -n     Read  the history lines not already read from the history
		     file into the current  history  list.   These  are	 lines
		     appended  to  the history file since the beginning of the
		     current bash session.
	      -r     Read the contents of the history file and 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 previous history line.	 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 [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.  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.  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 [-n count] [-O origin] [-s count] [-t] [-u  fd]	[-C  callback]
       [-c quantum] [array]
       readarray  [-n count] [-O origin] [-s count] [-t] [-u fd] [-C callback]
       [-c quantum] [array]
	      Read lines from the standard input into the indexed array	 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:
	      -n     Copy  at  most count lines.  If count is 0, all lines are
		     copied.
	      -O     Begin assigning to array at index	origin.	  The  default
		     index is 0.
	      -s     Discard the first count lines read.
	      -t     Remove a trailing newline from each line read.
	      -u     Read  lines  from file descriptor fd instead of the 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 (except that \c terminates output,
		     backslashes in \', \", and \? are not removed, and	 octal
		     escapes beginning with \0 may contain up to four digits).
	      %q     causes  printf  to output the corresponding argument in a
		     format that can be reused as shell input.
	      %(datefmt)T
		     causes printf to output the  date-time  string  resulting
		     from  using  datefmt  as a format string for strftime(3).
		     The corresponding argument is an integer representing the
		     number  of seconds since the epoch.  Two special argument
		     values may be used: -1 represents the current  time,  and
		     -2	 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, exchanges the top two directories
	      and returns 0, unless the directory stack is empty.   Arguments,
	      if supplied, have the following meanings:
	      -n     Suppresses	 the  normal  change  of directory when adding
		     directories to the stack,	so  that  only	the  stack  is
		     manipulated.
	      +n     Rotates  the  stack  so  that the nth directory (counting
		     from the left of the list shown by	 dirs,	starting  with
		     zero) is at the top.
	      -n     Rotates  the  stack  so  that the nth directory (counting
		     from the right of the list shown by dirs,	starting  with
		     zero) is at the top.
	      dir    Adds dir to the directory stack at the top, making it the
		     new current working directory 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, and  the
	      first word is assigned to the first name, the second word to the
	      second name, and so on, with leftover words and their  interven‐
	      ing  separators  assigned	 to the last name.  If there are fewer
	      words read from the input stream than names, the remaining names
	      are  assigned  empty  values.  The 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 back‐
	      slash character (\) may be used to remove	 any  special  meaning
	      for the next character read and for line continuation.  Options,
	      if supplied, have the following meanings:
	      -a aname
		     The words are assigned to sequential indices of the array
		     variable aname, starting at 0.  aname is unset before any
		     new  values  are  assigned.   Other  name	arguments  are
		     ignored.
	      -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 honor 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.
	      -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  return  code	is zero, unless end-of-file is
	      encountered, read times out (in which case the  return  code  is
	      greater  than 128), a variable assignment error (such as assign‐
	      ing to a readonly variable) occurs, or an invalid file  descrip‐
	      tor is supplied as the argument to -u.

       readonly [-aAf] [-p] [name[=word] ...]
	      The  given  names are marked readonly; the values of these names
	      may not be changed by subsequent assignment.  If the  -f	option
	      is  supplied,  the  functions  corresponding to the names are so
	      marked.  The  -a	option	restricts  the	variables  to  indexed
	      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 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      Automatically mark variables  and	 functions  which  are
		      modified	or  created  for  export to the environment of
		      subsequent commands.
	      -b      Report the status of terminated background jobs  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  sta‐
		      tus.   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).
	      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.
	      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,	behavior  intended  for	 use  by  debuggers is
		      enabled:
		      1.     The -F option to the declare builtin displays the
			     source file name and line number corresponding to
			     each function name supplied as an argument.
		      2.     If the command run by the DEBUG  trap  returns  a
			     non-zero  value,  the next command is skipped and
			     not executed.
		      3.     If the command run by the DEBUG  trap  returns  a
			     value  of 2, and the shell is executing in a sub‐
			     routine (a shell function or a shell script  exe‐
			     cuted  by	the  .	or source builtins), a call to
			     return is simulated.
		      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.
	      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.
	      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  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 [-HSTabcdefilmnpqrstuvx [limit]]
	      Provides control over the resources available to the  shell  and
	      to  processes started by it, on systems that allow such control.
	      The -H and -S options specify that the hard or soft limit is set
	      for  the	given resource.	 A hard limit cannot be increased by a
	      non-root user once it is set; a soft limit may be	 increased  up
	      to  the value of the hard limit.	If neither -H nor -S is 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
	      -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
	      -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;  and -T, -b, -n, and -u, which are unscaled values.  The
	      return status is 0 unless an invalid option or argument is  sup‐
	      plied, 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
       ~/.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 4.3			2014 February 2			       BASH(1)
[top]

List of man pages available for OpenMandriva

Copyright (c) for man pages and the logo by the respective OS vendor.

For those who want to learn more, the polarhome community provides shell access and support.

[legal] [privacy] [GNU] [policy] [cookies] [netiquette] [sponsors] [FAQ]
Tweet
Polarhome, production since 1999.
Member of Polarhome portal.
Based on Fawad Halim's script.
....................................................................
Vote for polarhome
Free Shell Accounts :: the biggest list on the net