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BASH(1)								       BASH(1)

NAME
       bash - GNU Bourne-Again SHell

SYNOPSIS
       bash [options] [file]

COPYRIGHT
       Bash is Copyright (C) 1989-2005 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 standard personal ini‐
	      tialization  file	 ~/.bashrc  if	the  shell is interactive (see
	      INVOCATION below).

       --login
	      Equivalent to -l.

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

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

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

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

       --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 ~/.bashrc, if that file exists.	  This
       may  be inhibited by using the --norc option.  The --rcfile file option
       will force bash to read and  execute  commands  from  file  instead  of
       ~/.bashrc.

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

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

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

       Bash  attempts  to  determine  when it is being run by the remote shell
       daemon, usually rshd.  If bash determines it is being run by  rshd,  it
       reads  and executes commands from ~/.bashrc, if that file exists and is
       readable.  It will not do this if invoked as sh.	 The --norc option may
       be  used	 to inhibit this behavior, and the --rcfile option may be used
       to force another file to be read, but 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 variable, if it appears in the environment,  is  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 the char‐
       acter |.	 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).

       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.

       The  control operators && and ⎪⎪ denote AND lists and OR lists, respec‐
       tively.	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.

       ((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 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.  Substrings matched by parenthesized sub‐
	      expressions 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 expres‐
	      sion.   The  element of BASH_REMATCH with index n is the portion
	      of the string matching the nth parenthesized subexpression.

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

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

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

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

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

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

       case word in [ [(] pattern [ | pattern ] ... ) list ;; ] ... esac
	      A case command first expands word, and tries to match it against
	      each pattern in turn, using the same matching rules as for path‐
	      name expansion (see Pathname  Expansion  below).	 The  word  is
	      expanded	using  tilde  expansion, parameter and variable expan‐
	      sion, arithmetic	substitution,  command	substitution,  process
	      substitution  and	 quote	removal.   Each	 pattern  examined  is
	      expanded using tilde expansion, parameter	 and  variable	expan‐
	      sion, arithmetic substitution, command substitution, and process
	      substitution.  If the shell option nocasematch is	 enabled,  the
	      match  is	 performed  without  regard  to the case of alphabetic
	      characters.  When a match is found, the  corresponding  list  is
	      executed.	  After	 the  first  match,  no subsequent matches are
	      attempted.  The exit status is zero if no pattern matches.  Oth‐
	      erwise,  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.

   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     an escape character
	      \f     form feed
	      \n     new line
	      \r     carriage return
	      \t     horizontal tab
	      \v     vertical tab
	      \\     backslash
	      \'     single 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 ($) will cause the
       string to be translated according to the current locale.	 If  the  cur‐
       rent  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.  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 status of the most recently executed foreground
	      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.
       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_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
	      ${FUNCNAME[$ifP]}	 was  called.	The  corresponding source file
	      name is ${BASH_SOURCE[$i]}.  Use LINENO to  obtain  the  current
	      line number.
       BASH_REMATCH
	      An  array	 variable  whose members are assigned by the =~ binary
	      operator to the [[ conditional command.  The element with	 index
	      0	 is  the  portion  of  the  string matching the entire regular
	      expression.  The element with index n  is	 the  portion  of  the
	      string matching the nth parenthesized subexpression.  This vari‐
	      able is read-only.
       BASH_SOURCE
	      An array variable whose members are the source filenames	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_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_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 words are split on
	      shell metacharacters as the shell parser	would  separate	 them.
	      This  variable  is  available only in shell functions invoked by
	      the programmable completion facilities (see Programmable Comple‐
	      tion 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".
       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:~".
       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.
       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, bash attempts to read /etc/hosts to obtain the list of
	      possible hostname completions.   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.
       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 array variables.	Any  variable  may  be
       used as an 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 contiguously.  Arrays are indexed
       using integers and are zero-based.

       An 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 array, use declare -a name
       (see SHELL BUILTIN COMMANDS below).  declare -a name[subscript] is also
       accepted; the subscript is ignored.  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.	Only string is required.  If the optional brackets and
       subscript are supplied, that index is assigned to; otherwise the	 index
       of  the element assigned is the last index assigned to by the statement
       plus one.  Indexing starts at zero.  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 element zero.

       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 filename generation.  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  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 assignments.

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

       The  order  of expansions is: brace expansion, tilde expansion, 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}, where x and y  are	either
       integers or single characters.  When integers are supplied, the expres‐
       sion expands to each number between x and y, inclusive.	 When  charac‐
       ters  are  supplied,  the  expression expands to each character lexico‐
       graphically between x and y, inclusive.	Note that both x and y must be
       of the same type.

       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 vari‐
       able formed from the rest of parameter as the  name  of	the  variable;
       this  variable  is  then expanded and that value is used in the rest of
       the substitution, rather than the value of parameter itself.   This  is
       known as indirect expansion.  The exceptions to this are the expansions
       of ${!prefix*} and ${!name[@]} described below.	The exclamation	 point
       must  immediately  follow the left brace in order to introduce indirec‐
       tion.

       In each of the cases below, word is subject to tilde expansion, parame‐
       ter  expansion,	command	 substitution, and arithmetic expansion.  When
       not performing substring expansion, bash tests for a parameter that  is
       unset  or null; omitting the colon results in a test only for a parame‐
       ter 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.  If
	      parameter is @,  the  result  is	length	positional  parameters
	      beginning at offset.  If parameter is an array name indexed by @
	      or *, the result is the length members of	 the  array  beginning
	      with  ${parameter[offset]}.  A negative offset is taken relative
	      to one greater than the maximum index of	the  specified	array.
	      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.

       ${!prefix*}
       ${!prefix@}
	      Expands to the names of variables whose names begin with prefix,
	      separated by the first character of the IFS special variable.

       ${!name[@]}
       ${!name[*]}
	      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}
	      The  length  in  characters of the value of parameter is substi‐
	      tuted.  If parameter is * or @, the  value  substituted  is  the
	      number  of positional parameters.	 If parameter is an array name
	      subscripted by * or @, the value substituted is  the  number  of
	      elements in the array.

       ${parameter#word}
       ${parameter##word}
	      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 pattern (the ``##'' case) deleted.
	      If parameter is @ or *, the pattern removal 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 pattern removal operation is applied to each
	      member of the array in turn, and the expansion is the  resultant
	      list.

       ${parameter%word}
       ${parameter%%word}
	      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  pat‐
	      tern  (the  ``%''	 case)	or  the	 longest matching pattern (the
	      ``%%'' case) deleted.  If parameter  is  @  or  *,  the  pattern
	      removal  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 pattern removal
	      operation is applied to each member of the array	in  turn,  and
	      the expansion is the resultant list.

       ${parameter/pattern/string}
	      The pattern is expanded to produce a pattern just as in pathname
	      expansion.  Parameter is expanded and the longest match of  pat‐
	      tern  against  its  value	 is replaced with string.  If Ipattern
	      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 beginning 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 / following pattern may be omit‐
	      ted.  If parameter is @ or  *,  the  substitution	 operation  is
	      applied  to each positional parameter in turn, and the expansion
	      is the resultant list.  If parameter is an array	variable  sub‐
	      scripted	with  @ or *, the substitution operation is applied to
	      each member of the array in  turn,  and  the  expansion  is  the
	      resultant list.

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

	      $(command)
       or
	      `command`

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

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

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

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

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

	      $((expression))

       The expression is treated as if it were within  double  quotes,	but  a
       double  quote  inside  the  parentheses	is not treated specially.  All
       tokens in the expression undergo parameter 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 any sequence of IFS characters 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 white‐
       space,  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  dis‐
       abled,  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.  When a pattern is used for pathname  expansion,  the
       character  ``.''	  at  the  start  of a name or immediately following a
       slash must be matched explicitly, unless the shell  option  dotglob  is
       set.   When  matching  a	 pathname,  the slash character must always be
       matched explicitly.  In	other  cases,  the  ``.''   character  is  not
       treated	specially.   See  the  description  of shopt below under SHELL
       BUILTIN COMMANDS for a description of the nocaseglob,  nullglob,	 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.
       ?      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.

       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 as standard output before the standard output 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.

   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
       Bash allows both the standard output (file descriptor 1) and the	 stan‐
       dard  error  output  (file  descriptor  2) to be redirected to the file
       whose name is the expansion of word with this construct.

       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

   Here Documents
       This type of redirection instructs the shell to	read  input  from  the
       current	source	until  a  line	containing only word (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 the exception that the DEBUG and RETURN traps (see the description
       of  the trap builtin under SHELL BUILTIN COMMANDS below) are not inher‐
       ited 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	 func‐
       tions inherit the DEBUG and RETURN traps).

       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.

       -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
	      True if the strings are equal.  = may be used in place of == for
	      strict POSIX compliance.

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

       string1 < string2
	      True if string1 sorts before string2  lexicographically  in  the
	      current locale.

       string1 > string2
	      True  if	string1	 sorts	after string2 lexicographically in the
	      current locale.

       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 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.

       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
       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 system'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
       write to the terminal.  Background processes which attempt to read from
       (write to) the terminal are sent a SIGTTIN (SIGTTOU) signal by the ter‐
       minal 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 name.  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 exam‐
       ple, %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 current job, which	 is  the  last
       job  stopped  while  it	was  in the foreground or started in the back‐
       ground.	The previous job may be referenced using %-.  In  output  per‐
       taining to jobs (e.g., the output of the jobs command), the current job
       is always flagged with a +, and the previous job with a -.  A single  %
       (with  no  accompanying	job  specification) 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,  the	 shell
       prints a warning message.  The jobs command may then be used to inspect
       their status.  If a second attempt to exit is made without an interven‐
       ing  command, the shell does not print another warning, and the 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
	      \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.
       By default, the line editing commands are similar to those of emacs.  A
       vi-style line editing interface is also available.  To  turn  off  line
       editing	after  the shell is running, use the +o emacs or +o vi options
       to the set builtin (see SHELL BUILTIN COMMANDS below).

   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-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.
       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.
       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.
       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.
       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.
       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).
       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 $FCEDIT,
	      $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.
       unix-word-rubout (C-w)
	      Kill  the	 word behind point, using white space as a word bound‐
	      ary.  The killed text is saved on the kill-ring.
       unix-filename-rubout
	      Kill the word behind point, using	 white	space  and  the	 slash
	      character	 as  the word boundaries.  The killed text is saved on
	      the kill-ring.
       delete-horizontal-space (M-\)
	      Delete all spaces and tabs around point.
       kill-region
	      Kill the text in the current region.
       copy-region-as-kill
	      Copy the text in the region to the kill buffer.
       copy-backward-word
	      Copy the word before point to the kill buffer.  The word	bound‐
	      aries are the same as backward-word.
       copy-forward-word
	      Copy  the	 word  following  point	 to the kill buffer.  The word
	      boundaries are the same as forward-word.
       yank (C-y)
	      Yank the top of the kill ring into the buffer at point.
       yank-pop (M-y)
	      Rotate the kill ring, and yank the new top.  Only works  follow‐
	      ing yank or yank-pop.

   Numeric Arguments
       digit-argument (M-0, M-1, ..., M--)
	      Add  this digit to the argument already accumulating, or start a
	      new argument.  M-- starts a negative argument.
       universal-argument
	      This is another way to specify an argument.  If this command  is
	      followed	by one or more digits, optionally with a leading minus
	      sign, those digits define the argument.  If the command is  fol‐
	      lowed  by	 digits,  executing  universal-argument again ends the
	      numeric argument, but is otherwise ignored.  As a special	 case,
	      if  this	command is immediately followed by a character that is
	      neither a digit or minus sign, the argument count for  the  next
	      command  is multiplied by four.  The argument count is initially
	      one, so executing this function the first time makes  the	 argu‐
	      ment count four, a second time makes the argument count sixteen,
	      and so on.

   Completing
       complete (TAB)
	      Attempt to perform completion on the text	 before	 point.	  Bash
	      attempts completion treating the text as a variable (if the text
	      begins with $), username (if the text begins with	 ~),  hostname
	      (if  the	text begins with @), or command (including aliases and
	      functions) in turn.  If none of these produces a match, filename
	      completion is attempted.
       possible-completions (M-?)
	      List the possible completions of the text before point.
       insert-completions (M-*)
	      Insert  all completions of the text before point that would have
	      been generated by possible-completions.
       menu-complete
	      Similar to complete, but replaces the word to be completed  with
	      a	 single match from the list of possible completions.  Repeated
	      execution of menu-complete steps through the  list  of  possible
	      completions,  inserting  each  match in turn.  At the end of the
	      list of completions, the bell is rung (subject to the setting of
	      bell-style) and the original text is restored.  An argument of n
	      moves n positions forward in the list  of	 matches;  a  negative
	      argument	may  be	 used to move backward through the list.  This
	      command is intended to be	 bound	to  TAB,  but  is  unbound  by
	      default.
       delete-char-or-list
	      Deletes  the  character under the cursor if not at the beginning
	      or end of the line (like delete-char).  If at  the  end  of  the
	      line, behaves identically to possible-completions.  This command
	      is unbound by default.
       complete-filename (M-/)
	      Attempt filename completion on the text before point.
       possible-filename-completions (C-x /)
	      List the possible completions of the text before point, treating
	      it as a filename.
       complete-username (M-~)
	      Attempt  completion  on  the text before point, treating it as a
	      username.
       possible-username-completions (C-x ~)
	      List the possible completions of the text before point, treating
	      it as a username.
       complete-variable (M-$)
	      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.
       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.
       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 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.

       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 filename 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  and  COMP_POINT	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.

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 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.  After saving the history, the	 history  file
       is  truncated to contain no more than HISTFILESIZE lines.  If HISTFILE‐
       SIZE 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), and read‐
       line 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 sub‐
       stitution will be reloaded into the readline editing buffer for correc‐
       tion.   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).

   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.	 For example, the :, true, false, and  test  builtins  do  not
       accept options.
       : [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.
	      -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.
	      -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.
	      -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.

	      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 the shell is not executing  a  loop
	      when break is executed.

       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.

       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.

       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.

       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] [-A action] [-G globpat] [-W
       wordlist] [-P prefix] [-S suffix]
	      [-X filterpat] [-F function] [-C command] name [name ...]
       complete -pr [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  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 or suppressing 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  filename  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  filename  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.

       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 the shell is not
	      executing a loop when continue is executed.

       declare [-afFirtx] [-p] [name[=value] ...]
       typeset [-afFirtx] [-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,  additional	 options  are ignored.	The -F option inhibits
	      the display of function definitions; only the function name  and
	      attributes are printed.  If the extdebug shell option is enabled
	      using shopt, the source file name	 and  line  number  where  the
	      function	is  defined  are  displayed  as	 well.	 The -F option
	      implies -f.  The following options can be used to restrict  out‐
	      put  to  variables with the specified attribute or to give vari‐
	      ables attributes:
	      -a     Each name is an array variable (see Arrays above).
	      -f     Use function names only.
	      -i     The variable is treated as an integer; arithmetic evalua‐
		     tion  (see	 ARITHMETIC EVALUATION ) is performed when the
		     variable is assigned a value.
	      -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.
	      -x     Mark names for export  to	subsequent  commands  via  the
		     environment.

	      Using  `+'  instead of `-' turns off the attribute instead, with
	      the exception that +a may not be used to destroy an array	 vari‐
	      able.   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 variable 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 read‐
	      only status for a readonly variable, an attempt is made to  turn
	      off array status for an array variable, or an attempt is made to
	      display a non-existent function with -f.

       dirs [-clpv] [+n] [-n]
	      Without options,	displays  the  list  of	 currently  remembered
	      directories.   The  default  display  is	on  a single line with
	      directory names separated by spaces.  Directories are  added  to
	      the  list	 with  the  pushd  command;  the  popd command removes
	      entries from the list.
	      +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  the  -h option is given, each jobspec is not
	      removed from the table, but is marked so that SIGHUP is not sent
	      to  the  job  if	the shell receives a SIGHUP.  If no jobspec is
	      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  job‐
	      spec  argument  restricts operation to running jobs.  The return
	      value is 0 unless a jobspec does not specify a valid job.

       echo [-neE] [arg ...]
	      Output the args, separated by spaces,  followed  by  a  newline.
	      The return status is 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 trailing newline
	      \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 [-adnps] [-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 arg 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  cannot  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 can‐
	      not be executed.	If command is not specified, any  redirections
	      take  effect  in	the current shell, and the return status is 0.
	      If there is a redirection error, the return status is 1.

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

       export [-fn] [name[=word]] ...
       export -p
	      The supplied names are marked for automatic export to the	 envi‐
	      ronment  of subsequently executed commands.  If the -f option is
	      given, the names refer to functions.  If no names are given,  or
	      if  the  -p  option  is  supplied,  a list of 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] [-nlr] [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 [-s] [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.  The -s option restricts the  information
	      displayed	 to  a	short  usage synopsis.	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 is set, the time stamp information associ‐
	      ated with each history entry is written  to  the	history	 file.
	      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 supplied as an argument to -d, or the history
	      expansion supplied as an argument to -p fails.

       jobs [-lnprs] [ jobspec ... ]
       jobs -x command [ args ... ]
	      The first form lists the active jobs.  The options have the fol‐
	      lowing meanings:
	      -l     List process IDs in addition to the normal information.
	      -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).  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.

       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     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.
	      -n     Suppresses the normal change of directory	when  removing
		     directories  from	the  stack,  so that only the stack is
		     manipulated.

	      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] [dir]
       pushd [-n] [+n] [-n]
	      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     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.
	      -n     Suppresses	 the  normal  change  of directory when adding
		     directories to the stack,	so  that  only	the  stack  is
		     manipulated.
	      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] [-u fd] [-t timeout] [-a aname] [-p prompt] [-n nchars] [-d
       delim] [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.
	      -n nchars
		     read  returns after reading nchars characters rather than
		     waiting for a complete line of input.
	      -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.  This
		     option has no effect if read is not  reading  input  from
		     the terminal or a pipe.
	      -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, or an invalid file descriptor is
	      supplied as the argument to -u.

       readonly [-apf] [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 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 vari‐
	      able 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 func‐
	      tion.

       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 [--abefhkmnptuvxBCHP] [-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 the options are processed are  treated
	      as  values  for  the  positional parameters and are assigned, in
	      order, to $1, $2, ...  $n.  Options, if specified, have the fol‐
	      lowing 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 simple command (see SHELL GRAMMAR
		      above) exits with a non-zero status.  The shell does not
		      exit  if	the  command that fails is part of the command
		      list immediately following a  while  or  until  keyword,
		      part  of the test in an if statement, part of a && or ⎪⎪
		      list, or if the command's return value is being inverted
		      via  !.	A  trap on ERR, if set, is executed before the
		      shell exits.
	      -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.
		      errtrace
			      Same as -E.
		      functrace
			      Same as -T.
		      errexit Same as -e.
		      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.
		      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
		      variable, if it appears in the environment, is  ignored.
		      If  the shell is started with the effective user (group)
		      id not equal to the real user (group)  id,  and  the  -p
		      option  is not supplied, these actions are taken and the
		      effective user id is set to the real user id.  If the -p
		      option  is supplied at startup, the effective user id is
		      not reset.  Turning this option off causes the effective
		      user  and group ids to be set to the real user and group
		      ids.
	      -t      Exit after reading and executing one command.
	      -u      Treat unset variables as an error when performing param‐
		      eter  expansion.	 If expansion is attempted on an unset
		      variable, 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:

	      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.
	      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.
	      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.
	      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.  The -f option says not to complain if this is  a	 login
	      shell;  just  suspend anyway.  The return status is 0 unless the
	      shell is a login shell and -f is not supplied, 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.
	      ! 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.	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.  Otherwise,  the	expression  is	false.
		     The  -a  and -o operators are considered binary operators
		     in this case.
	      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 executed 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  ERR,
	      the  command  arg	 is  executed  whenever a simple 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 && or ⎪⎪ list, or
	      if the command's return value is being inverted  via  !.	 These
	      are  the	same  conditions  obeyed  by the errexit option.  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.	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 child process when it 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
	      any of the arguments are found, false if none are found.

       ulimit [-SHacdefilmnpqrstuvx [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 once
	      it is set; a soft limit may be increased up to the value of  the
	      hard  limit.   If	 neither -H nor -S is specified, 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 interpreted as fol‐
	      lows:
	      -a     All current limits are reported
	      -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
	      -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

	      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 -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 RANDOM, SECONDS, LINENO, HISTCMD,
	      FUNCNAME, GROUPS, or DIRSTACK are unset, they lose their special
	      properties,  even if they are subsequently reset.	 The exit sta‐
	      tus 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
       ~/.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@po.cwru.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.

       Commands inside of $(...) command substitution  are  not	 parsed	 until
       substitution  is attempted.  This will delay error reporting until some
       time after the command is entered.  For example, unmatched parentheses,
       even  inside  shell  comments,  will result in error messages while the
       construct is being read.

       Array variables may not (yet) be exported.

GNU Bash-3.2		       2006 September 28		       BASH(1)
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