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BASH(1)								       BASH(1)

NAME
       bash - GNU Bourne-Again SHell

SYNOPSIS
       bash [options] [file]

COPYRIGHT
       Bash is Copyright (C) 1989-2009 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
       In  addition  to	 the  single-character shell options documented in the
       description of the set builtin command, bash interprets	the  following
       options when it is invoked:

       -c string If  the  -c  option  is  present, then commands are read from
		 string.  If there are arguments after the  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)  and	 shell
	      function tracing (see the description of the -o functrace option
	      to the set builtin below).
       --dump-po-strings
	      Equivalent to -D, but the output is in the GNU gettext po	 (por‐
	      table object) file format.
       --dump-strings
	      Equivalent to -D.
       --help Display  a  usage	 message  on standard output and exit success‐
	      fully.
       --init-file file
       --rcfile file
	      Execute commands from file instead of the system	wide  initial‐
	      ization file /etc/bash.bashrc and the standard personal initial‐
	      ization file ~/.bashrc if the shell is interactive (see  INVOCA‐
	      TION below).

       --login
	      Equivalent to -l.

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

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

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

       --posix
	      Change  the behavior of bash where the default operation differs
	      from the POSIX standard to match the standard (posix mode).

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

       --verbose
	      Equivalent to  -v.

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

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

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

       An  interactive	shell  is one started without non-option arguments 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 file names 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	 /etc/bash.bashrc  and	~/.bashrc,  if
       these  files  exist.  This may be inhibited by using the --norc option.
       The --rcfile file option will force bash to read and  execute  commands
       from file instead of /etc/bash.bashrc and ~/.bashrc.

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

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

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

       Bash attempts to determine when it is being run with its standard input
       connected to a a network connection, as if by the remote shell  daemon,
       usually	rshd,  or the secure shell daemon sshd.	 If bash determines it
       is being run in this fashion,  it  reads	 and  executes	commands  from
       ~/.bashrc  and  ~/.bashrc,  if  these files exist and are readable.  It
       will not do this if invoked as sh.  The --norc option may  be  used  to
       inhibit	this  behavior,	 and  the --rcfile option may be used to force
       another file to be read, but rshd does not 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	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,
       the standard error of command is connected to command2's standard input
       through the pipe; it is shorthand for 2>&1 |.  This implicit  redirect‐
       ion of the standard error 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.  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.

       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:

       (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.	 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 pat‐
	      tern, and 1 otherwise.  Any part of the pattern may be quoted to
	      force it 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 it 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 parenthe‐
	      sized 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; do list; done
       until list; do list; done
	      The while command continuously executes the do list as  long  as
	      the  last	 command  in list returns an exit status of zero.  The
	      until command is identical to the while command, except that the
	      test  is	negated;  the  do list is executed as long as the last
	      command in list returns a non-zero exit status.  The exit status
	      of  the  while and until commands is the exit status of the last
	      do list command executed, or zero if none was executed.

   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 coproc is executed, the shell  creates
       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 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.

       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:

       [ 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.  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 executed, 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)
	      \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.

       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.

   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 occurs within double quotes, it expands to a  sin‐
	      gle word with the value of each parameter separated by the first
	      character of the IFS special variable.  That is, "$*" is equiva‐
	      lent to "$1c$2c...", where c is the first character of the value
	      of the IFS variable.  If IFS is unset, the parameters are	 sepa‐
	      rated  by	 spaces.   If  IFS  is null, the parameters are joined
	      without intervening separators.
       @      Expands to the positional parameters, starting from  one.	  When
	      the  expansion  occurs  within  double  quotes,  each  parameter
	      expands to a separate word.  That is, "$@" 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 most recently executed back‐
	      ground (asynchronous) command.
       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 file name 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 file name 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 Ele‐
	      ments 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    corresponding	to    each    member	of   FUNCNAME.
	      ${BASH_LINENO[$i]} is the line number in the source  file	 where
	      ${FUNCNAME[$i]}  was  called  (or ${BASH_LINENO[$i-1]} if refer‐
	      enced within another shell function).  The corresponding	source
	      file  name is ${BASH_SOURCE[$i]}.	 Use LINENO to obtain the cur‐
	      rent 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 corre‐
	      sponding to the elements in the FUNCNAME array variable.
       BASH_SUBSHELL
	      Incremented by one each time a subshell or subshell  environment
	      is spawned.  The initial 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).

       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 is "main".  This variable exists	 only  when  a
	      shell  function  is  executing.  Assignments to FUNCNAME have no
	      effect and return an error status.  If  FUNCNAME	is  unset,  it
	      loses its special properties, even if it is subsequently reset.

       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.

       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.

       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_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  file	 name.
	      PATH is not used to search for the resultant file name.
       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".
       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.
       COLUMNS
	      Used  by	the  select  builtin command to determine the terminal
	      width when printing selection  lists.   Automatically  set  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).
       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.
       FCEDIT The default editor for the fc builtin command.
       FIGNORE
	      A	 colon-separated  list	of  suffixes to ignore when performing
	      filename completion (see READLINE below).	 A filename whose suf‐
	      fix  matches  one of the entries in FIGNORE is excluded from the
	      list of matched filenames.  A sample value is ".o:~" (Quoting is
	      needed  when  assigning a value to this variable, which contains
	      tildes).
       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	an  interactive	 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, by removing the oldest entries, to contain
	      no more than that number of lines.  The default  value  is  500.
	      The history file is also truncated to this size after writing it
	      when an interactive shell exits.
       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).  The default value is 500.
       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  builtin  command  to	determine  the	column
	      length  for  printing  selection	lists.	Automatically set upon
	      receipt of a SIGWINCH.
       MAIL   If this parameter is set to a file name and the  MAILPATH	 vari‐
	      able is not set, bash informs the user of the arrival of mail in
	      the specified file.
       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 file names to  be  checked  for	 mail.
	      The message to be printed when mail arrives in a particular file
	      may be specified by separating the file name  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/gnu/bin:/usr/local/bin:/usr/ucb:/bin:/usr/bin''.
       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%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  input	 after
	      issuing  the  primary prompt.  Bash terminates after waiting for
	      that number of seconds if 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.

       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 greater than or
       equal to zero.  To explicitly declare an indexed array, use declare  -a
       name (see SHELL BUILTIN COMMANDS below).	 declare -a name[subscript] is
       also accepted; the subscript 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 the bracket
       and subscript.  When assigning  to  indexed  arrays,  if	 the  optional
       brackets	 and subscript are supplied, that index is assigned to; other‐
       wise 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.

       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.

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

       The unset builtin is used to  destroy  arrays.	unset  name[subscript]
       destroys	 the  array element at index subscript.	 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.  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  assign‐
       ments.

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,  parame‐
       ter,  variable  and arithmetic expansion and command substitution (done
       in a left-to-right fashion), word splitting, and pathname expansion.

       On systems that can support it, there is an additional expansion avail‐
       able: process substitution.

       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.	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 file names 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.

       If  the	first  character  of  parameter is an exclamation point (!), a
       level of variable indirection is introduced.  Bash uses	the  value  of
       the variable formed from the rest of parameter as the name of the vari‐
       able; 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	expan‐
       sions  of ${!prefix*} and ${!name[@]} described below.  The exclamation
       point must immediately follow the left  brace  in  order	 to  introduce
       indirection.

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

       When not performing substring expansion,	 using	the  forms  documented
       below,  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
	      parameter	 starting  at  the  character specified by offset.  If
	      length is omitted, expands to the substring of parameter	start‐
	      ing at the character specified by offset.	 length and offset are
	      arithmetic  expressions  (see  ARITHMETIC	  EVALUATION   below).
	      length  must evaluate to a number greater than or equal to zero.
	      If offset evaluates to a number less than	 zero,	the  value  is
	      used  as	an  offset  from  the  end  of the value of parameter.
	      Arithmetic expressions starting with a - must  be	 separated  by
	      whitespace from the preceding : to be distinguished from the Use
	      Default Values expansion.	 If parameter  is  @,  the  result  is
	      length  positional parameters beginning at offset.  If parameter
	      is an indexed array name subscripted by @ or *,  the  result  is
	      the  length members of the array beginning with ${parameter[off‐
	      set]}.  A negative offset is taken relative to one greater  than
	      the  maximum  index of the specified array.  Substring expansion
	      applied to an  associative  array	 produces  undefined  results.
	      Note  that a negative offset must be separated from the colon by
	      at least one space to avoid being confused with  the  :-	expan‐
	      sion.   Substring	 indexing  is zero-based unless the positional
	      parameters 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.

       ${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.   The  ^  operator
	      converts	lowercase letters matching pattern to uppercase; the ,
	      operator converts matching uppercase letters to lowercase.   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 omit‐
	      ted, 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 subscripted
	      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  old	 format	 $[expression]	is  deprecated	and will be removed in
       upcoming versions of bash.

       The expression is treated as if it were within  double  quotes,	but  a
       double  quote  inside  the  parentheses	is not treated specially.  All
       tokens in the expression undergo parameter expansion, string expansion,
       command	substitution, and quote removal.  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 on these characters.	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 character).   Any	 character  in
       IFS  that is not IFS whitespace, along with any adjacent IFS whitespace
       characters, delimits a field.  A sequence of IFS whitespace  characters
       is  also	 treated as a delimiter.  If the value of IFS is null, no word
       splitting occurs.

       Explicit null arguments ("" or '')  are	retained.   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 file names matching the pattern.	If  no
       matching	 file  names  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	alpha‐
       betic  characters.   Note  that when using range expressions like [a-z]
       (see below), letters of the other case may be  included,	 depending  on
       the  setting of LC_COLLATE.  When a pattern is used for pathname expan‐
       sion, the character ``.''  at the start of a name or  immediately  fol‐
       lowing a slash must be matched explicitly, unless the shell option dot‐
       glob is set.  When matching a pathname, the slash character must always
       be  matched  explicitly.	  In  other cases, the ``.''  character is not
       treated specially.  See the description	of  shopt  below  under	 SHELL
       BUILTIN	COMMANDS  for a description of the nocaseglob, nullglob, fail‐
       glob, 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 file
       name that also matches one of the patterns  in  GLOBIGNORE  is  removed
       from the list of matches.  The file names ``.''	and ``..''  are always
       ignored when GLOBIGNORE is set and not null.  However, setting  GLOBIG‐
       NORE  to	 a non-null value has the effect of enabling the dotglob shell
       option, so all other file names beginning with a ``.''  will match.  To
       get  the	 old  behavior	of ignoring file names 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 glob‐
	      star shell option is enabled, and * is used in a pathname expan‐
	      sion  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 subdirectories.
       ?      Matches any single character.
       [...]  Matches any one of the enclosed characters.  A pair  of  charac‐
	      ters separated by a hyphen denotes a range expression; any char‐
	      acter that sorts between those two characters, 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	 character not enclosed is matched.  The sorting order
	      of characters in range expressions is determined by the  current
	      locale  and  the value of the LC_COLLATE shell variable, if set.
	      A - may be matched by including it as the first or last  charac‐
	      ter 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	 char‐
	      acter _.

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

	      Within [ and ], the syntax [.symbol.] matches the collating sym‐
	      bol 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  may
       also  be	 used  to open and close files for the current shell execution
       environment.  The following redirection operators may precede or appear
       anywhere within a simple command or may follow 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 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 expansion, command substitution, arithmetic expan‐
       sion, 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 a TCP connection to the corresponding 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 a UDP connection to the corresponding socket.

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

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

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

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

       The general format for redirecting input is:

	      [n]<word

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

       The general format for redirecting output is:

	      [n]>word

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

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

       The general format for appending output is:

	      [n]>>word

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

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

	      &>word
       and
	      >&word

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

	      >word 2>&1

   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

   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 expansion, command substitution, arithmetic expansion, or
       pathname expansion is performed on word.	 If any characters 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, com‐
       mand substitution, and arithmetic expansion.  In the latter  case,  the
       character  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 is expanded and supplied 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.  As a special case, if n is omitted, and word
       does not expand to one or more digits, 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.

       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.  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 base is a decimal number between 2 and 64 representing
       the arithmetic base, and n is a number in that base.  If base# is omit‐
       ted,  then  base 10 is used.  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 represent 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.

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

       -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.
       -O file
	      True if file exists and is owned by the effective user id.
       -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.
       -S file
	      True if file exists and is a socket.
       -N file
	      True  if	file  exists  and  has been modified since it was last
	      read.
       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.
       file1 -ef file2
	      True if file1 and file2 refer to the same device and inode  num‐
	      bers.
       -o optname
	      True  if	shell  option  optname	is  enabled.   See the list of
	      options under the description  of	 the  -o  option  to  the  set
	      builtin below.
       -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.

       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  file  name of the command and passed to that command in its envi‐
       ronment.

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.
       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, the number of entries in the history list
	      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.
       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, unless the leading `.' is supplied  by  the
	      user in the filename to be completed.
       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.
       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	 an  argument,	behave
	      exactly  like  yank-nth-arg.   Successive calls to yank-last-arg
	      move back through the history list, inserting the last  argument
	      of each line in turn.  The history expansion facilities are used
	      to extract the last argument, 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
       delete-char (C-d)
	      Delete  the character at point.  If point is at the beginning of
	      the line, there are no characters in  the	 line,	and  the  last
	      character typed was not bound to delete-char, then return EOF.
       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
	      defaultc
       menu-complete-krd
	      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.

   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 file names	 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  file  names	 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  to	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 is the name of the command  whose	 arguments  are	 being
       completed,  the	second	argument  is the word being completed, and the
       third argument is the word preceding the word being  completed  on  the
       current	command	 line.	 No  filtering	of  the	 generated completions
       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.

       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 compspec for that command.  This allows a set of com‐
       pletions	 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

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.	When the  his‐
       tory  file  is read, lines beginning with the history comment character
       followed immediately by a digit are interpreted as timestamps  for  the
       preceding  history  line.   These  timestamps  are optionally displayed
       depending on the value of the HISTTIMEFORMAT variable.  When an	inter‐
       active  shell  exits, the last $HISTSIZE lines are copied from the his‐
       tory 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	 over‐
       written.	  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 sessions.   This  uses
       the history comment character to distinguish timestamps from other his‐
       tory lines.  After saving the history, the history file is truncated to
       contain	no  more than HISTFILESIZE lines.  If HISTFILESIZE is not set,
       no truncation is performed.

       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.

       !      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 line minus n.
       !!     Refer to the previous command.  This is a synonym for `!-1'.
       !string
	      Refer to the most recent command starting with string.
       !?string[?]
	      Refer  to the most recent command containing string.  The trail‐
	      ing ? may be omitted if string is followed immediately by a new‐
	      line.
       ^string1^string2^
	      Quick  substitution.  Repeat the last command, replacing string1
	      with string2.  Equivalent to ``!!:s/string1/string2/'' (see Mod‐
	      ifiers 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 argument.
       %      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 file name component, leaving only the head.
       t      Remove all leading file name 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, file
	      names  in	 PATH  are used to find the directory containing file‐
	      name.  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] [-lpsvPSV]
       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.

	      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] [dir]
	      Change  the  current directory to dir.  The variable HOME is the
	      default dir.  The variable CDPATH defines the  search  path  for
	      the  directory  containing  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  says  to use the physical directory structure instead of
	      following symbolic links (see also the  -P  option  to  the  set
	      builtin command); the -L option forces symbolic links to be fol‐
	      lowed.  An argument of - is equivalent to $OLDPWD.   If  a  non-
	      empty  directory	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  success‐
	      fully 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 file name
	      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.
		      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.
	      -G globpat
		      The  pathname  expansion	pattern globpat is expanded to
		      generate the possible completions.
	      -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.
	      -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 it finishes, the possible  com‐
		      pletions	are  retrieved from the value of the COMPREPLY
		      array variable.
	      -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.
	      -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.

	      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-execution 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  comple‐
       tion 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 [-aAfFilrtux] [-p] [name[=value] ...]
       typeset [-aAfFilrtux] [-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 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 defi‐
	      nitions; 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 dis‐
	      played  as  well.	  The  -F  option  implies  -f.	 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.
	      -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, makes each name local, as with the local command.
	      If a variable name is followed by =value, the value of the vari‐
	      able  is	set to value.  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 readonly status for a read‐
	      only variable, an attempt is made to turn off array  status  for
	      an  array variable, or an attempt is made to display a non-exis‐
	      tent function with -f.

       dirs [+n] [-n] [-cplv]
	      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.
	      +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.
	      -c     Clears  the  directory  stack  by	deleting  all  of  the
		     entries.
	      -l     Produces  a  longer  listing;  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.

	      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, each jobspec  is	 removed  from	the  table  of
	      active  jobs.   If jobspec is not present, and neither -a nor -r
	      is supplied, the shell's notion of the current job is used.   If
	      the -h option is given, each jobspec is not removed from the ta‐
	      ble, but is marked so that SIGHUP is not sent to the job if  the
	      shell  receives a SIGHUP.	 If no jobspec is present, and neither
	      the -a nor the -r option is supplied, the current job  is	 used.
	      If no jobspec is supplied, the -a option means to remove or mark
	      all jobs; the -r option without  a  jobspec  argument  restricts
	      operation	 to running jobs.  The return value is 0 unless a job‐
	      spec does not specify a valid job.

       echo [-neE] [arg ...]
	      Output the args, separated by spaces,  followed  by  a  newline.
	      The return status is always 0.  If -n is specified, the trailing
	      newline is suppressed.  If the -e option is  given,  interpreta‐
	      tion  of	the following backslash-escaped characters is enabled.
	      The -E option disables the interpretation of these escape	 char‐
	      acters,  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     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)

       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 shell option execfail is enabled, in  which  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 all names that are
	      exported in this shell 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 supplied with a name that is not a func‐
	      tion.

       fc [-e ename] [-lnr] [first] [last]
       fc -s [pat=rep] [cmd]
	      Fix Command.  In the first form, a range of commands from	 first
	      to  last	is selected from the history list.  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 cur‐
	      rent 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 otherwise.	 If first is not spec‐
	      ified it is set to the previous command for editing and -16  for
	      listing.

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

	      In the second form, command is re-executed after	each  instance
	      of  pat  is replaced by rep.  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 com‐
	      mand.

	      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]
	      For each name, the full file name of the command	is  determined
	      by searching the directories in $PATH and remembered.  If the -p
	      option is supplied, no path search is performed, and filename is
	      used as the full file name 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 arguments are
	      supplied with -t, the name is printed  before  the  hashed  full
	      pathname.	 The -l option causes output to be displayed in a for‐
	      mat that may be reused as input.	If no arguments are given,  or
	      if only -l is supplied, information about remembered 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 use them as the
		     current history.
	      -w     Write the current history to the history file,  overwrit‐
		     ing 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.
	      -p     List only the process  ID	of  the	 job's	process	 group
		     leader.
	      -n     Display  information  only	 about	jobs that have changed
		     status since the user was last notified of their status.
	      -r     Restrict output to running jobs.
	      -s     Restrict output to 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 as an additional argument.	 call‐
	      back 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 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  for‐
	      mat  specifications,  each  of which causes printing of the next
	      successive argument.  In addition to the standard printf(1) for‐
	      mats,  %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), and %q	causes
	      printf to output the corresponding argument in a format that can
	      be reused as shell input.

	      The -v option causes the output to be assigned to	 the  variable
	      var rather than being printed to the standard output.

	      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.

	      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.  The backslash character (\) may be
	      used to remove any special meaning for the next  character  read
	      and  for line continuation.  Options, if supplied, have the fol‐
	      lowing 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 is not read within timeout seconds.	 time‐
		     out may be a decimal number  with	a  fractional  portion
		     following	the decimal point.  This option is only effec‐
		     tive if read is reading input from a terminal,  pipe,  or
		     other  special  file;  it has no effect when reading from
		     regular files.  If timeout is 0, read returns success  if
		     input  is	available  on  the  specified file descriptor,
		     failure otherwise.	 The exit status 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), or an invalid file descriptor is supplied  as
	      the argument to -u.

       readonly [-aApf] [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 no name arguments are given, or if the -p option  is
	      supplied,	 a  list  of  all  readonly  names is printed.	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 exit with the return value specified by n.
	      If n is omitted, the return status is that of the	 last  command
	      executed	in the function body.  If 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 used outside a
	      function and not during execution of a script by .,  the	return
	      status is false.	Any command associated with the RETURN trap is
	      executed before execution resumes after the function or script.

       set [--abefhkmnptuvxBCEHPT] [-o option] [arg ...]
       set [+abefhkmnptuvxBCEHPT] [+o option] [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 subshell command enclosed  in
		      parentheses,  or one of the commands executed as part of
		      a command list enclosed by  braces  (see	SHELL  GRAMMAR
		      above) exits with a non-zero status.  The shell does not
		      exit if the command that fails is part  of  the  command
		      list  immediately	 following  a  while or until keyword,
		      part of the test	following  the	if  or	elif  reserved
		      words,  part  of any command executed in a && or ⎪⎪ list
		      except the command following the final  &&  or  ⎪⎪,  any
		      command  in a pipeline but the last, or if the command's
		      return value is being inverted with !.  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.
	      -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).   Background  pro‐
		      cesses  run  in a separate process group and a line con‐
		      taining their exit status is printed upon their  comple‐
		      tion.
	      -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).
		      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 follow	 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 variables controlling optional shell behav‐
	      ior.  With no options, or with the -p option, a list of all set‐
	      table 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 fol‐
	      lowing 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, the dis‐
	      play is limited to those options which are set or unset, respec‐
	      tively.	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 file name 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 com‐
		      mand's =~ operator.
	      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.
	      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 and
		      the effect of interrupting a command list.
	      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 ERROR 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.
	      globstar
		      If set, the pattern ** used in a pathname expansion con‐
		      text will match a 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.
	      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 or 1 depending on  the  evaluation  of  the
	      conditional  expression expr.  Each operator and operand 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.
	      ! 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
		     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.

       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 sim‐
	      ple command has 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, or if the command's return
	      value is being inverted via !.  These are	 the  same  conditions
	      obeyed by the errexit 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,	 not  necessarily  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 func‐
	      tion 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
	      -x     The maximum number of file locks
	      -T     The maximum number of threads

	      If limit is given, it is the new value of the specified resource
	      (the -a option is display only).	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 supplied, or
	      an error occurs while setting a new limit.

       umask [-p] [-S] [mode]
	      The user file-creation mask is set to mode.  If mode begins with
	      a	 digit,	 it is interpreted as an octal number; otherwise it is
	      interpreted as a symbolic mode mask similar to that accepted  by
	      chmod(1).	  If mode is omitted, the current value of the mask is
	      printed.	The -S option causes the mask to be  printed  in  sym‐
	      bolic  form;  the	 default output is an octal number.  If the -p
	      option is supplied, and mode is omitted, the output is in a form
	      that may be reused as input.  The return status is 0 if the mode
	      was successfully changed or if no mode  argument	was  supplied,
	      and false otherwise.

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

       unset [-fv] [name ...]
	      For  each	 name,	remove the corresponding variable or function.
	      If no options are supplied, or the -v option is given, each name
	      refers  to  a  shell  variable.	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.  Each unset vari‐
	      able or function is removed from the environment passed to  sub‐
	      sequent  commands.   If any of COMP_WORDBREAKS, RANDOM, SECONDS,
	      LINENO, HISTCMD, FUNCNAME, GROUPS, or DIRSTACK are  unset,  they
	      lose  their  special  properties,	 even if they are subsequently
	      reset.  The exit status is true unless a name is readonly.

       wait [n ...]
	      Wait for each specified process and return its termination  sta‐
	      tus.   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  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  file  name 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
       sh(1), ksh(1), csh(1)
       emacs(1), vi(1)
       readline(3)

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

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

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

BUG REPORTS
       If you find a bug in bash, you should report it.	 But first, you should
       make  sure  that	 it really is a bug, and that it appears in the latest
       version	of  bash.   The	 latest	 version  is  always  available	  from
       ftp://ftp.gnu.org/pub/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@po.cwru.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-4.1		       2009 December 29			       BASH(1)
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