BASH(1)                     General Commands Manual                    BASH(1)



NAME
       bash - GNU Bourne-Again SHell

SYNOPSIS
       bash [options] [command_string | file]

COPYRIGHT
       Bash is Copyright (C) 1989-2022 by the Free Software Foundation, Inc.

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

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

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

       -c        If the -c option is present, then commands are read from  the
                 first non-option argument command_string.  If there are argu-
                 ments after the command_string, the  first  argument  is  as-
                 signed  to $0 and any remaining arguments are assigned to the
                 positional parameters.  The assignment to $0 sets the name of
                 the shell, which is used in warning and error messages.
       -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 or when reading  input
                 through a pipe.
       -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 op-
       tions must appear on the command line before the  single-character  op-
       tions to be recognized.

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

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

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

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

       --verbose
              Equivalent to -v.

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

ARGUMENTS
       If arguments remain after option processing, and neither the -c nor the
       -s  option  has  been supplied, the first argument is assumed to be the
       name of a file containing shell commands.  If bash is invoked  in  this
       fashion,  $0 is set to the name of the file, and the positional parame-
       ters are set to the remaining arguments.  Bash reads and executes  com-
       mands  from this file, then exits.  Bash's exit status is the exit sta-
       tus of the last command executed in the script.  If no commands are ex-
       ecuted,  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  (un-
       less  -s  is specified) and without the -c option, whose standard input
       and error are both connected to terminals (as determined by isatty(3)),
       or  one  started  with  the -i option.  PS1 is set and $- includes i if
       bash is interactive, allowing a shell script or a startup file to  test
       this state.

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

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

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

       When an interactive shell that is not a login shell  is  started,  bash
       reads  and executes commands from ~/.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  ex-
       ample,  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 be-
       havior of historical versions of sh as closely as possible, while  con-
       forming  to the POSIX standard as well.  When invoked as an interactive
       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  in-
       hibit  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  at-
       tempt to read any other startup files.  When invoked as sh, bash enters
       posix mode after the startup files are read.

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

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

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

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

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

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

SHELL GRAMMAR
       This  section  describes  the syntax of the various forms of shell com-
       mands.

   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 ar-
       guments to the invoked command.

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

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

              [time [-p]] [ ! ] command1 [ [|||&] command2 ... ]

       The standard output of command1 is connected via a pipe to the standard
       input  of  command2.   This connection is performed before any redirec-
       tions specified by the command1(see REDIRECTION below).  If |& is used,
       command1's  standard error, in addition to its standard output, is con-
       nected to command2's standard input through the pipe; it  is  shorthand
       for  2>&1  |.   This  implicit redirection of the standard error to the
       standard output is performed after any redirections specified  by  com-
       mand1.

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

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

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

       Each command in a multi-command pipeline, where pipes are  created,  is
       executed  in a subshell, which is a separate process.  See COMMAND EXE-
       CUTION ENVIRONMENT for a description of subshells and a subshell  envi-
       ronment.   If  the  lastpipe  option is enabled using the shopt builtin
       (see the description of shopt below), the last element  of  a  pipeline
       may be run by the shell process when job control is not active.

   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.  These are
       referred to as asynchronous commands.  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  exe-
       cuted.

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

              command1 && command2

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

       An OR list has the form

              command1 || command2

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

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

       (list) list  is  executed in a subshell (see COMMAND EXECUTION ENVIRON-
              MENT below for a description of a subshell environment).   Vari-
              able  assignments  and  builtin commands that affect the shell's
              environment do not remain in effect after the command completes.
              The return status is the exit status of list.

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

       ((expression))
              The expression is evaluated according to the rules described be-
              low under ARITHMETIC EVALUATION.  If the value of the expression
              is non-zero, the return status is 0; otherwise the return status
              is  1.   The  expression  undergoes the same expansions as if it
              were within double quotes, but double quote  characters  in  ex-
              pression are not treated specially and are removed.

       [[ 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.
              The words between the [[ and ]] do not  undergo  word  splitting
              and pathname expansion.  The shell performs tilde expansion, pa-
              rameter and variable expansion,  arithmetic  expansion,  command
              substitution,  process  substitution, and quote removal on those
              words (the expansions that would occur if  the  words  were  en-
              closed in double quotes).  Conditional operators such as -f must
              be unquoted to be recognized as primaries.

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

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

              An additional binary operator, =~, is available, with  the  same
              precedence  as  ==  and  !=.  When it is used, the string to the
              right of the operator is considered a POSIX extended regular ex-
              pression  and  matched  accordingly (using the POSIX regcomp and
              regexec interfaces usually described 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 condi-
              tional expression's return value is 2.  If the nocasematch shell
              option is enabled, the match is performed without regard to  the
              case  of  alphabetic  characters.  If any part of the pattern is
              quoted, the quoted portion is matched literally.  This means ev-
              ery  character  in the quoted portion matches itself, instead of
              having any special pattern matching meaning.  If the pattern  is
              stored  in  a  shell  variable,  quoting  the variable expansion
              forces the  entire  pattern  to  be  matched  literally.   Treat
              bracket expressions in regular expressions carefully, since nor-
              mal quoting and pattern characters lose their  meanings  between
              brackets.

              The  pattern  will  match  if it matches any part of the string.
              Anchor the pattern using the ^ and $ regular  expression  opera-
              tors to force it to match the entire string.  The array variable
              BASH_REMATCH records which parts of the string matched the  pat-
              tern.   The  element  of  BASH_REMATCH with index 0 contains the
              portion of the string matching the  entire  regular  expression.
              Substrings  matched  by  parenthesized subexpressions within the
              regular expression are saved in the remaining  BASH_REMATCH  in-
              dices.  The  element of BASH_REMATCH with index n is the portion
              of the string  matching  the  nth  parenthesized  subexpression.
              Bash  sets  BASH_REMATCH  in the global scope; declaring it as a
              local variable will lead to unexpected results.

              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 pa-
              rameter 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, and 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).
              select  then  displays  the PS3 prompt and reads a line from the
              standard 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 select command completes and
              returns 1.  Any other value read causes name to be set to  null.
              The  line read is saved in the variable REPLY.  The list is exe-
              cuted 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 matching rules described under
              Pattern Matching below.  The word is expanded using tilde expan-
              sion,  parameter  and  variable expansion, arithmetic expansion,
              command substitution, process substitution  and  quote  removal.
              Each pattern examined is expanded using tilde expansion, parame-
              ter and variable expansion, arithmetic expansion,  command  sub-
              stitution,  process substitution, and quote removal.  If the no-
              casematch shell option is enabled, the match is performed  with-
              out  regard  to the case of alphabetic characters.  When a match
              is found, the corresponding list is executed.  If the ;;  opera-
              tor is used, no subsequent matches are attempted after the first
              pattern match.  Using ;& in place of ;; causes execution to con-
              tinue  with  the  list associated with the next set of patterns.
              Using ;;& in place of ;; causes the shell to test the next  pat-
              tern  list  in the statement, if any, and execute any associated
              list on a successful match, continuing the case statement execu-
              tion as if the pattern list had not matched.  The exit status is
              zero if no pattern matches.  Otherwise, it is the exit status of
              the last command executed in list.

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

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

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

       The syntax for a coprocess is:

              coproc [NAME] command [redirections]

       This creates a coprocess named NAME.  command may be  either  a  simple
       command  or  a  compound command (see above).  NAME is a shell variable
       name.  If NAME is not supplied, the default name is COPROC.

       The recommended form to use for a coprocess is

              coproc NAME { command [redirections]; }

       This form is recommended because simple commands result in  the  copro-
       cess  always being named COPROC, and it is simpler to use and more com-
       plete than the other compound commands.

       If command is a compound command, NAME is optional. The word  following
       coproc  determines whether that word is interpreted as a variable name:
       it is interpreted as NAME if it is not a reserved word that  introduces
       a  compound  command.   If command is a simple command, NAME is not al-
       lowed; this is to avoid confusion between NAME and the  first  word  of
       the simple command.

       When  the  coprocess  is  executed, the shell creates an array variable
       (see Arrays below) named NAME in the context of  the  executing  shell.
       The  standard  output  of command is connected via a pipe to a file de-
       scriptor in the executing shell, and that file descriptor  is  assigned
       to NAME[0].  The standard input of command is connected via a pipe to a
       file descriptor in the executing shell, and that file descriptor is as-
       signed  to  NAME[1].   This pipe is established before any redirections
       specified by the command (see REDIRECTION below).  The file descriptors
       can  be  utilized as arguments to shell commands and redirections using
       standard word expansions.  Other than those created to execute  command
       and  process  substitutions,  the file descriptors are not available in
       subshells.

       The process ID of the shell spawned to execute the coprocess is  avail-
       able  as  the value of the variable NAME_PID.  The wait builtin command
       may be used to wait for the coprocess to terminate.

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

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

       fname () compound-command [redirection]
       function fname [()] compound-command [redirection]
              This defines a function named fname.  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.  If the
              function reserved word is used, but the parentheses are not sup-
              plied, the braces are recommended.  compound-command is executed
              whenever fname is specified as the name  of  a  simple  command.
              When in posix mode, fname must be a valid shell name and may not
              be the name of one of the POSIX special  builtins.   In  default
              mode,  a  function name can be any unquoted shell word that does
              not contain $.  Any redirections (see REDIRECTION below)  speci-
              fied  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 it-
       self quoted, the \<newline> is treated as a line continuation (that is,
       it is removed from the input stream and effectively ignored).

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

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

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

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

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

       A double-quoted string preceded by a dollar sign ($"string") will cause
       the string to be translated according to the current locale.  The  get-
       text  infrastructure  performs  the  lookup  and translation, using the
       LC_MESSAGES, TEXTDOMAINDIR, and TEXTDOMAIN  shell  variables.   If  the
       current  locale  is C or POSIX, if there are no translations available,
       or if the string is not translated, the dollar sign is  ignored.   This
       is a form of double quoting, so the string remains double-quoted by de-
       fault, whether or not it is translated  and  replaced.   If  the  noex-
       pand_translation  option is enabled using the shopt builtin, translated
       strings are single-quoted instead of double-quoted.  See  the  descrip-
       tion of shopt below under SHELLBUILTINCOMMANDS.

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 and path-
       name  expansion  are not performed.  Assignment statements may also ap-
       pear as arguments to the alias, declare, typeset, export, readonly, and
       local  builtin  commands  (declaration  commands).  When in posix mode,
       these builtins may appear in a command after one or more  instances  of
       the command builtin and retain these assignment statement properties.

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

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

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

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

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

   Shell Variables
       The following variables are set by the shell:

       _      At shell startup, set to the pathname used to invoke  the  shell
              or  shell  script being executed as passed in the environment or
              argument list.  Subsequently, expands to the  last  argument  to
              the  previous  simple  command executed in the foreground, after
              expansion.  Also set to the full pathname used  to  invoke  each
              command  executed and placed in the environment exported to that
              command.  When checking mail, this parameter holds the  name  of
              the mail file currently being checked.
       BASH   Expands  to  the  full  filename used to invoke this instance of
              bash.
       BASHOPTS
              A colon-separated list of enabled shell options.  Each  word  in
              the  list  is  a  valid  argument for the -s option to the shopt
              builtin command (see SHELL BUILTIN COMMANDS below).  The options
              appearing  in  BASHOPTS  are  those reported as on by shopt.  If
              this variable is in the environment when bash  starts  up,  each
              shell  option  in  the  list  will be enabled before reading any
              startup files.  This variable is read-only.
       BASHPID
              Expands to the process ID of the  current  bash  process.   This
              differs  from  $$ under certain circumstances, such as subshells
              that do not require bash to be re-initialized.   Assignments  to
              BASHPID  have no effect.  If BASHPID is unset, it loses its spe-
              cial properties, even if it is subsequently reset.
       BASH_ALIASES
              An associative array variable whose members  correspond  to  the
              internal  list  of  aliases  as maintained by the alias builtin.
              Elements added to this array appear in the alias list;  however,
              unsetting  array elements currently does not cause aliases to be
              removed from the alias list.  If BASH_ALIASES is unset, it loses
              its special properties, even if it is subsequently reset.
       BASH_ARGC
              An  array  variable whose values are the number of parameters in
              each frame of the current bash execution call stack.  The number
              of  parameters  to  the  current  subroutine  (shell function or
              script executed with . or source) is at the top  of  the  stack.
              When  a  subroutine is executed, the number of parameters passed
              is pushed onto BASH_ARGC.  The shell sets BASH_ARGC only when in
              extended debugging mode (see the description of the extdebug op-
              tion to the shopt builtin below).  Setting  extdebug  after  the
              shell has started to execute a script, or referencing this vari-
              able when extdebug is not set, may result in  inconsistent  val-
              ues.
       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 be-
              low).  Setting extdebug after the shell has started to execute a
              script,  or  referencing this variable when extdebug is not set,
              may result in inconsistent values.
       BASH_ARGV0
              When referenced, this variable expands to the name of the  shell
              or shell script (identical to $0; see the description of special
              parameter 0 above).  Assignment to BASH_ARGV0 causes  the  value
              assigned  to also be assigned to $0.  If BASH_ARGV0 is unset, it
              loses its special properties, even if it is subsequently reset.
       BASH_CMDS
              An associative array variable whose members  correspond  to  the
              internal  hash  table  of  commands  as  maintained  by the hash
              builtin.  Elements added to this array appear in the hash table;
              however,  unsetting array elements currently does not cause com-
              mand names to be removed from the hash table.  If  BASH_CMDS  is
              unset,  it  loses  its  special properties, even if it is subse-
              quently reset.
       BASH_COMMAND
              The command currently being executed or about  to  be  executed,
              unless the shell is executing a command as the result of a trap,
              in which case it is the command executing at  the  time  of  the
              trap.   If  BASH_COMMAND  is unset, it loses its special proper-
              ties, even if it is subsequently reset.
       BASH_EXECUTION_STRING
              The command argument to the -c invocation option.
       BASH_LINENO
              An array variable whose members are the line numbers  in  source
              files  where  each corresponding member of FUNCNAME was invoked.
              ${BASH_LINENO[$i]}  is  the  line  number  in  the  source  file
              (${BASH_SOURCE[$i+1]})  where  ${FUNCNAME[$i]}  was  called  (or
              ${BASH_LINENO[$i-1]} if referenced within  another  shell  func-
              tion).  Use LINENO to obtain the current line number.
       BASH_LOADABLES_PATH
              A  colon-separated  list of directories in which the shell looks
              for dynamically loadable builtins specified by the  enable  com-
              mand.
       BASH_REMATCH
              An  array  variable  whose members are assigned by the =~ binary
              operator to the [[ conditional command.  The element with  index
              0  is  the portion of the string matching the entire regular ex-
              pression.  The element with index n is the portion of the string
              matching the nth parenthesized subexpression.
       BASH_SOURCE
              An  array  variable whose members are the source filenames where
              the corresponding shell function names  in  the  FUNCNAME  array
              variable are defined.  The shell function ${FUNCNAME[$i]} is de-
              fined  in  the   file   ${BASH_SOURCE[$i]}   and   called   from
              ${BASH_SOURCE[$i+1]}.
       BASH_SUBSHELL
              Incremented  by one within each subshell or subshell environment
              when the shell begins executing in that environment.   The  ini-
              tial  value  is 0.  If BASH_SUBSHELL is unset, it loses its spe-
              cial properties, even if it is subsequently reset.
       BASH_VERSINFO
              A readonly array variable whose members hold version information
              for  this  instance  of  bash.  The values assigned to the array
              members are as follows:
              BASH_VERSINFO[0]        The major version number (the release).
              BASH_VERSINFO[1]        The minor version number (the version).
              BASH_VERSINFO[2]        The patch level.
              BASH_VERSINFO[3]        The build version.
              BASH_VERSINFO[4]        The release status (e.g., beta1).
              BASH_VERSINFO[5]        The value of MACHTYPE.
       BASH_VERSION
              Expands to a string describing the version of this  instance  of
              bash.
       COMP_CWORD
              An  index  into ${COMP_WORDS} of the word containing the current
              cursor position.  This variable is available only in shell func-
              tions  invoked  by  the  programmable completion facilities (see
              Programmable Completion below).
       COMP_KEY
              The key (or final key of a key sequence) used to invoke the cur-
              rent completion function.
       COMP_LINE
              The  current  command  line.  This variable is available only in
              shell functions and external commands invoked  by  the  program-
              mable completion facilities (see Programmable Completion below).
       COMP_POINT
              The  index of the current cursor position relative to the begin-
              ning of the current command.  If the current cursor position  is
              at the end of the current command, the value of this variable is
              equal to ${#COMP_LINE}.  This  variable  is  available  only  in
              shell  functions  and  external commands invoked by the program-
              mable completion facilities (see Programmable Completion below).
       COMP_TYPE
              Set to an integer value corresponding to the type of  completion
              attempted  that  caused a completion function to be called: TAB,
              for normal completion, ?, for listing completions after  succes-
              sive  tabs,  !, for listing alternatives on partial word comple-
              tion, @, to list completions if the word is not  unmodified,  or
              %,  for  menu  completion.   This  variable is available only in
              shell functions and external commands invoked  by  the  program-
              mable completion facilities (see Programmable Completion below).
       COMP_WORDBREAKS
              The  set  of characters that the readline library treats as word
              separators when performing word completion.  If  COMP_WORDBREAKS
              is  unset, it loses its special properties, even if it is subse-
              quently reset.
       COMP_WORDS
              An array variable (see Arrays below) consisting of the  individ-
              ual  words  in the current command line.  The line is split into
              words as readline would split it, using COMP_WORDBREAKS  as  de-
              scribed  above.   This variable is available only in shell func-
              tions invoked by the  programmable  completion  facilities  (see
              Programmable Completion below).
       COPROC An  array  variable  (see Arrays below) created to hold the file
              descriptors for output from and input to  an  unnamed  coprocess
              (see Coprocesses above).
       DIRSTACK
              An array variable (see Arrays below) containing the current con-
              tents of the directory stack.  Directories appear in  the  stack
              in  the order they are displayed by the dirs builtin.  Assigning
              to members of this array variable may be used to modify directo-
              ries  already in the stack, but the pushd and popd builtins must
              be used to add and remove directories.  Assignment to this vari-
              able  will not change the current directory.  If DIRSTACK is un-
              set, it loses its special properties, even if it is subsequently
              reset.
       EPOCHREALTIME
              Each time this parameter is referenced, it expands to the number
              of seconds since the Unix Epoch  (see  time(3))  as  a  floating
              point  value  with  micro-second  granularity.   Assignments  to
              EPOCHREALTIME are ignored.  If EPOCHREALTIME is unset, it  loses
              its special properties, even if it is subsequently reset.
       EPOCHSECONDS
              Each time this parameter is referenced, it expands to the number
              of seconds since the Unix Epoch (see time(3)).   Assignments  to
              EPOCHSECONDS  are  ignored.   If EPOCHSECONDS is unset, it loses
              its special properties, even if it is subsequently reset.
       EUID   Expands to the effective user ID of the current  user,  initial-
              ized at shell startup.  This variable is readonly.
       FUNCNAME
              An  array  variable  containing the names of all shell functions
              currently in the execution call stack.  The element with index 0
              is the name of any currently-executing shell function.  The bot-
              tom-most element (the one with the  highest  index)  is  "main".
              This  variable  exists  only when a shell function is executing.
              Assignments to FUNCNAME have no effect.  If FUNCNAME  is  unset,
              it  loses its special properties, even if it is subsequently re-
              set.

              This variable can be  used  with  BASH_LINENO  and  BASH_SOURCE.
              Each   element   of   FUNCNAME  has  corresponding  elements  in
              BASH_LINENO and BASH_SOURCE to describe the call stack.  For in-
              stance,    ${FUNCNAME[$i]}    was    called    from   the   file
              ${BASH_SOURCE[$i+1]} at  line  number  ${BASH_LINENO[$i]}.   The
              caller builtin displays the current call stack using this infor-
              mation.
       GROUPS An array variable containing the list of  groups  of  which  the
              current user is a member.  Assignments to GROUPS have no effect.
              If GROUPS is unset, it loses its special properties, even if  it
              is subsequently reset.
       HISTCMD
              The history number, or index in the history list, of the current
              command.  Assignments to HISTCMD are ignored.  If HISTCMD is un-
              set, it loses its special properties, even if it is subsequently
              reset.
       HOSTNAME
              Automatically set to the name of the current host.
       HOSTTYPE
              Automatically set to a string that uniquely describes  the  type
              of  machine  on which bash is executing.  The default is system-
              dependent.
       LINENO Each time this parameter is referenced, the shell substitutes  a
              decimal  number  representing the current sequential line number
              (starting with 1) within a script or function.  When  not  in  a
              script  or  function, the value substituted is not guaranteed to
              be meaningful.  If LINENO is unset, it loses its special proper-
              ties, even if it is subsequently reset.
       MACHTYPE
              Automatically  set  to  a string that fully describes the system
              type on which bash is executing, in the  standard  GNU  cpu-com-
              pany-system format.  The default is system-dependent.
       MAPFILE
              An  array  variable  (see Arrays below) created to hold the text
              read by the mapfile builtin when no variable name is supplied.
       OLDPWD The previous working directory as set by the cd command.
       OPTARG The value of the last option argument processed by  the  getopts
              builtin command (see SHELL BUILTIN COMMANDS below).
       OPTIND The  index  of  the next argument to be processed by the getopts
              builtin command (see SHELL BUILTIN COMMANDS below).
       OSTYPE Automatically set to a string that describes the operating  sys-
              tem  on  which  bash is executing.  The default is system-depen-
              dent.
       PIPESTATUS
              An array variable (see Arrays below) containing a list  of  exit
              status  values  from the processes in the most-recently-executed
              foreground pipeline (which may contain only a single command).
       PPID   The process ID of the shell's parent.  This  variable  is  read-
              only.
       PWD    The current working directory as set by the cd command.
       RANDOM Each  time  this parameter is referenced, it expands to a random
              integer between 0 and 32767.  Assigning a value to  RANDOM  ini-
              tializes  (seeds)  the sequence of random numbers.  If RANDOM is
              unset, it loses its special properties, even  if  it  is  subse-
              quently reset.
       READLINE_ARGUMENT
              Any  numeric  argument  given to a readline command that was de-
              fined using "bind -x" (see SHELL BUILTIN COMMANDS below) when it
              was invoked.
       READLINE_LINE
              The contents of the readline line buffer, for use with "bind -x"
              (see SHELL BUILTIN COMMANDS below).
       READLINE_MARK
              The position of the mark (saved insertion point) in the readline
              line  buffer, for use with "bind -x" (see SHELL BUILTIN COMMANDS
              below).  The characters between the insertion point and the mark
              are often called the region.
       READLINE_POINT
              The position of the insertion point in the readline line buffer,
              for use with "bind -x" (see SHELL BUILTIN COMMANDS below).
       REPLY  Set to the line of input read by the read builtin  command  when
              no arguments are supplied.
       SECONDS
              Each time this parameter is referenced, it expands to the number
              of seconds since shell invocation.  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.
              The  number  of seconds at shell invocation and the current time
              are always determined by querying the system clock.  If  SECONDS
              is  unset, it loses its special properties, even if it is subse-
              quently 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.
       SRANDOM
              This variable expands to a 32-bit pseudo-random number each time
              it  is  referenced. The random number generator is not linear on
              systems that support /dev/urandom or  arc4random,  so  each  re-
              turned  number  has no relationship to the numbers preceding it.
              The random number generator cannot be seeded, so assignments  to
              this variable have no effect.  If SRANDOM is unset, it loses its
              special properties, even if it is subsequently reset.
       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 as-
       signs a default value to a variable; these cases are noted below.

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

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

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

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

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

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

       Associative arrays are created using declare -A name.

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

       Arrays   are  assigned  to  using  compound  assignments  of  the  form
       name=(value1 ... valuen), where each value may be  of  the  form  [sub-
       script]=string.   Indexed array assignments do not require anything but
       string.  Each value in the list is expanded using all the shell  expan-
       sions  described  below under EXPANSION.  When assigning to indexed ar-
       rays, if the optional brackets and subscript are supplied,  that  index
       is assigned to; otherwise the index of the element assigned is the last
       index assigned to by the statement plus one.  Indexing starts at zero.

       When assigning to an associative array, the words in a compound assign-
       ment  may  be  either assignment statements, for which the subscript is
       required, or a list of words that is interpreted as a sequence  of  al-
       ternating  keys and values: name=( key1 value1 key2 value2 ...).  These
       are treated identically to  name=(  [key1]=value1  [key2]=value2  ...).
       The  first  word in the list determines how the remaining words are in-
       terpreted; all assignments in a list must be of the  same  type.   When
       using  key/value  pairs,  the keys may not be missing or empty; a final
       missing value is treated like the empty string.

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

       The += operator will append to an array variable when  assigning  using
       the compound assignment syntax; see PARAMETERS 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 ex-
       pansion 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[subscript]}.   If
       subscript is * or @, the expansion is the number of elements in the ar-
       ray.  If the subscript used to reference an element of an indexed array
       evaluates  to a number less than zero, it is interpreted as relative to
       one greater than the maximum index of the array,  so  negative  indices
       count back from the end of the array, and an index of -1 references the
       last element.

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

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

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

       The unset builtin is used to destroy arrays.  unset name[subscript] de-
       stroys the array element at index subscript, for both indexed and asso-
       ciative  arrays.  Negative subscripts to indexed arrays are interpreted
       as described above.  Unsetting the last element of  an  array  variable
       does  not  unset the variable.  unset name, where name is an array, re-
       moves the entire array.  unset name[subscript], where subscript is * or
       @, behaves differently depending on whether name is an indexed or asso-
       ciative array.  If name is an associative array, this unsets  the  ele-
       ment with subscript * or @.  If name is an indexed array, unset removes
       all of the elements but does not remove the array itself.

       When using a variable name with a subscript as an argument  to  a  com-
       mand,  such  as with unset, without using the word expansion syntax de-
       scribed above, the argument is subject to pathname expansion.  If path-
       name expansion is not desired, the argument should be quoted.

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

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

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

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

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

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

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

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

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

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

       A correctly-formed brace expansion must contain  unquoted  opening  and
       closing braces, and at least one unquoted comma or a valid sequence ex-
       pression.  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, and
       inhibits brace expansion until the closing }.

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

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

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

       Bash  also  performs tilde expansion on words satisfying the conditions
       of variable assignments (as described above under PARAMETERS) when they
       appear  as arguments to simple commands.  Bash does not do this, except
       for the declaration commands listed above, when in posix mode.

   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 em-
       bedded arithmetic expansion, command substitution, or parameter  expan-
       sion.

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

       If the first character of parameter is an exclamation  point  (!),  and
       parameter is not a nameref, it introduces a level of indirection.  Bash
       uses the value formed by expanding the rest of parameter as the new pa-
       rameter;  this  is  then expanded and that value is used in the rest of
       the expansion, rather than the expansion  of  the  original  parameter.
       This is known as indirect expansion.  The value is subject to tilde ex-
       pansion, parameter expansion, command substitution, and arithmetic  ex-
       pansion.   If  parameter  is a nameref, this expands to the name of the
       parameter referenced by parameter instead of  performing  the  complete
       indirect  expansion.   The  exceptions  to  this  are the expansions of
       ${!prefix*} and ${!name[@]} described  below.   The  exclamation  point
       must  immediately  follow the left brace in order to introduce indirec-
       tion.

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

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

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

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

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

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

              Substring expansion applied to an associative array produces un-
              defined results.

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

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

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

       ${#parameter}
              Parameter  length.  The length in characters of the value of pa-
              rameter is substituted.  If parameter is * or @, the value  sub-
              stituted  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.  If parameter is an indexed
              array name subscripted by a negative number, that number is  in-
              terpreted  as  relative to one greater than the maximum index of
              parameter, so negative indices count back from the  end  of  the
              array, and an index of -1 references the last element.

       ${parameter#word}
       ${parameter##word}
              Remove matching prefix pattern.  The word is expanded to produce
              a pattern just as in pathname expansion, and matched against the
              expanded value of parameter using the rules described under Pat-
              tern Matching below.  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  op-
              eration is applied to each positional parameter in turn, and the
              expansion is the resultant list.  If parameter is an array vari-
              able  subscripted  with @ or *, the pattern removal operation is
              applied to each member of the array in turn, and  the  expansion
              is the resultant list.

       ${parameter%word}
       ${parameter%%word}
              Remove matching suffix pattern.  The word is expanded to produce
              a pattern just as in pathname expansion, and matched against the
              expanded value of parameter using the rules described under Pat-
              tern Matching below.  If the pattern matches a trailing  portion
              of  the  expanded value of parameter, then the result of the ex-
              pansion is the expanded value of  parameter  with  the  shortest
              matching  pattern  (the ``%'' case) or the longest matching pat-
              tern (the ``%%'' case) deleted.  If parameter is  @  or  *,  the
              pattern  removal operation is applied to each positional parame-
              ter in turn, and the expansion is the resultant list.  If param-
              eter  is  an array variable subscripted with @ or *, the pattern
              removal operation is applied to each  member  of  the  array  in
              turn, and the expansion is the resultant list.

       ${parameter/pattern/string}
       ${parameter//pattern/string}
       ${parameter/#pattern/string}
       ${parameter/%pattern/string}
              Pattern substitution.  The pattern is expanded to produce a pat-
              tern just as in pathname expansion.  Parameter is  expanded  and
              the  longest match of pattern against its value is replaced with
              string.  string undergoes tilde expansion, parameter  and  vari-
              able  expansion,  arithmetic expansion, command and process sub-
              stitution, and quote removal.  The match is performed using  the
              rules described under Pattern Matching below.  In the first form
              above, only the first match  is  replaced.   If  there  are  two
              slashes  separating  parameter  and  pattern  (the  second  form
              above), all matches of pattern are  replaced  with  string.   If
              pattern  is  preceded by # (the third form above), it must match
              at the beginning of the expanded value of parameter.  If pattern
              is  preceded  by % (the fourth form above), it must match at the
              end of the expanded value of parameter.   If  the  expansion  of
              string  is  null,  matches of pattern are deleted.  If string is
              null, matches of pattern are deleted and the / following pattern
              may be omitted.

              If  the  patsub_replacement shell option is enabled using shopt,
              any unquoted instances of & in  string  are  replaced  with  the
              matching portion of pattern.

              Quoting any part of string inhibits replacement in the expansion
              of the quoted portion, including replacement strings  stored  in
              shell  variables.   Backslash will escape & in string; the back-
              slash is removed in order to permit a literal & in the  replace-
              ment  string.  Backslash can also be used to escape a backslash;
              \\ results in a literal backslash  in  the  replacement.   Users
              should  take  care  if string is double-quoted to avoid unwanted
              interactions between the  backslash  and  double-quoting,  since
              backslash  has  special  meaning  within double quotes.  Pattern
              substitution performs the check for unquoted &  after  expanding
              string; shell programmers should quote any occurrences of & they
              want to be taken literally in the replacement and ensure any in-
              stances of & they want to be replaced are unquoted.

              If  the  nocasematch  shell option is enabled, the match is per-
              formed without regard to the case of alphabetic characters.   If
              parameter  is  @  or *, the substitution operation is applied to
              each positional parameter in turn, and the expansion is the  re-
              sultant  list.   If  parameter  is an array variable subscripted
              with @ or *, the substitution operation is applied to each  mem-
              ber  of  the  array  in turn, and the expansion is the resultant
              list.

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

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

              U      The expansion is a string that is the value of  parameter
                     with  lowercase alphabetic characters converted to upper-
                     case.
              u      The expansion is a string that is the value of  parameter
                     with the first character converted to uppercase, if it is
                     alphabetic.
              L      The expansion is a string that is the value of  parameter
                     with  uppercase alphabetic characters converted to lower-
                     case.
              Q      The expansion is a string that is the value of  parameter
                     quoted in a format that can be reused as input.
              E      The  expansion is a string that is the value of parameter
                     with backslash escape  sequences  expanded  as  with  the
                     $'...' quoting mechanism.
              P      The expansion is a string that is the result of expanding
                     the value of parameter as if it were a prompt string (see
                     PROMPTING below).
              A      The  expansion  is  a string in the form of an assignment
                     statement or declare command  that,  if  evaluated,  will
                     recreate parameter with its attributes and value.
              K      Produces a possibly-quoted version of the value of param-
                     eter, except that it prints the values of indexed and as-
                     sociative  arrays as a sequence of quoted key-value pairs
                     (see Arrays above).
              a      The expansion is a string consisting of flag values  rep-
                     resenting parameter's attributes.
              k      Like  the K transformation, but expands the keys and val-
                     ues of indexed and associative arrays to  separate  words
                     after word splitting.

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

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

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

              $(command)
       or
              `command`

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

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

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

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

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

              $((expression))

       The expression undergoes the same expansions as if it were within  dou-
       ble  quotes,  but double quote characters in expression are not treated
       specially and are removed.  All tokens in the expression undergo param-
       eter  and  variable expansion, command substitution, and quote removal.
       The result is treated as the arithmetic  expression  to  be  evaluated.
       Arithmetic expansions may be nested.

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

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

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

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

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

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

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

   Pathname Expansion
       After  word  splitting,  unless  the -f option has been set, bash scans
       each word for the characters *, ?, and [.  If one of  these  characters
       appears, and is not quoted, then the word is regarded as a pattern, and
       replaced with an alphabetically sorted list of filenames  matching  the
       pattern  (see  Pattern  Matching  below).  If no matching filenames are
       found, and the shell option nullglob is not enabled, the word  is  left
       unchanged.   If  the  nullglob option is set, and no matches are found,
       the word is removed.  If the failglob  shell  option  is  set,  and  no
       matches  are  found, an error message is printed and the command is not
       executed.  If the shell option nocaseglob is enabled, the match is per-
       formed  without  regard  to  the case of alphabetic characters.  When a
       pattern is used for pathname expansion, the  character  ``.''   at  the
       start  of  a  name or immediately following a slash must be matched ex-
       plicitly, unless the shell option dotglob is set.  In  order  to  match
       the filenames ``.''  and ``..'', the pattern must begin with ``.'' (for
       example, ``.?''), even if dotglob is set.  If  the  globskipdots  shell
       option  is enabled, the filenames ``.''  and ``..''  are never matched,
       even if the pattern begins with a ``.''.  When not matching  pathnames,
       the  ``.''   character is not treated specially.  When matching a path-
       name, the slash character must always be matched explicitly by a  slash
       in  the  pattern, but in other matching contexts it can be matched by a
       special pattern character as described below  under  Pattern  Matching.
       See  the  description of shopt below under SHELL BUILTIN COMMANDS for a
       description of the nocaseglob, nullglob,  globskipdots,  failglob,  and
       dotglob shell options.

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

       Pattern Matching

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

       The special pattern characters have the following meanings:

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

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

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

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

       If the extglob shell option is enabled using  the  shopt  builtin,  the
       shell  recognizes  several extended pattern matching operators.  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 following 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

       Theextglob option changes the behavior of the parser, since the  paren-
       theses  are  normally  treated as operators with syntactic meaning.  To
       ensure that extended matching patterns are parsed correctly, make  sure
       that  extglob  is enabled before parsing constructs containing the pat-
       terns, including shell functions and command substitutions.

       When matching filenames, the dotglob shell option determines the set of
       filenames  that  are  tested: when dotglob is enabled, the set of file-
       names includes all files beginning with ``.'',  but  ``.''  and  ``..''
       must  be  matched  by  a pattern or sub-pattern that begins with a dot;
       when it is disabled, the set does not include any  filenames  beginning
       with  ``.''  unless the pattern or sub-pattern begins with a ``.''.  As
       above, ``.'' only has a special meaning when matching filenames.

       Complicated extended pattern matching against long strings is slow, es-
       pecially when the patterns contain alternations and the strings contain
       multiple matches.  Using separate matches against shorter  strings,  or
       using arrays of strings instead of a single long string, may be faster.

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

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

       Each  redirection  that may be preceded by a file descriptor number may
       instead be preceded by a word of the form {varname}.  In this case, for
       each redirection operator except >&- and <&-, the shell will allocate a
       file descriptor greater than or equal to 10 and assign it  to  varname.
       If  >&-  or  <&- is preceded by {varname}, the value of varname defines
       the file descriptor to close.  If {varname} is supplied, the  redirect-
       ion  persists  beyond the scope of the command, allowing the shell pro-
       grammer  to  manage  the  file  descriptor's  lifetime  manually.   The
       varredir_close shell option manages this behavior.

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

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

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

              ls > dirlist 2>&1

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

              ls 2>&1 > dirlist

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

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

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

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

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

   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  ex-
       pansion  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 re-
       sults from the expansion of word to be opened for appending on file de-
       scriptor  n,  or  the  standard  output (file descriptor 1) if n is not
       specified.  If the file does not exist it is created.

       The general format for appending output is:

              [n]>>word

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

       There are two formats for redirecting standard output and standard  er-
       ror:

              &>word
       and
              >&word

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

              >word 2>&1

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

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

       The format for appending standard output and standard error is:

              &>>word

       This is semantically equivalent to

              >>word 2>&1

       (see Duplicating File Descriptors below).

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

       The format of here-documents is:

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

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

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

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

              [n]<<<word

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

   Duplicating File Descriptors
       The redirection operator

              [n]<&word

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

       The operator

              [n]>&word

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

   Moving File Descriptors
       The redirection operator

              [n]<&digit-

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

       Similarly, the redirection operator

              [n]>&digit-

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

   Opening File Descriptors for Reading and Writing
       The redirection operator

              [n]<>word

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

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

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

       There  is no mechanism for using arguments in the replacement text.  If
       arguments are needed, use a shell function (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, and
       all lines that make up a compound command, before executing any of  the
       commands  on  that  line or the compound command.  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 command.   As  a
       consequence,  aliases defined in a function are not available until af-
       ter that function is executed.  To be safe, always  put  alias  defini-
       tions on a separate line, and do not use alias in compound commands.

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

FUNCTIONS
       A  shell  function,  defined  as  described  above under SHELL GRAMMAR,
       stores a series of commands for later execution.  When the  name  of  a
       shell  function  is used as a simple command name, the list of commands
       associated with that function name is executed.  Functions are executed
       in  the  context of the current shell; no new process is created to in-
       terpret 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 be-
       tween a function and its caller with these exceptions:  the  DEBUG  and
       RETURN  traps  (see  the  description  of  the trap builtin under SHELL
       BUILTIN COMMANDS below) are not inherited unless the function has  been
       given  the  trace attribute (see the description of the declare builtin
       below) or the -o functrace shell option has been enabled with  the  set
       builtin  (in  which  case  all  functions  inherit the DEBUG and RETURN
       traps), and the ERR trap is not inherited unless the -o errtrace  shell
       option has been enabled.

       Variables  local to the function may be declared with the local builtin
       command (local variables).  Ordinarily, variables and their values  are
       shared  between the function and its caller.  If a variable is declared
       local, the variable's visible scope is restricted to that function  and
       its children (including the functions it calls).

       In the following description, the current scope is a currently- execut-
       ing function.  Previous scopes consist of that function's caller and so
       on,  back  to  the "global" scope, where the shell is not executing any
       shell function.  Consequently, a local variable at the current scope is
       a variable declared using the local or declare builtins in the function
       that is currently executing.

       Local variables "shadow" variables with the same name declared at  pre-
       vious  scopes.   For  instance, a local variable declared in a function
       hides a global variable of the same name:  references  and  assignments
       refer  to  the  local variable, leaving the global variable unmodified.
       When the function returns, the global variable is once again visible.

       The shell uses dynamic  scoping  to  control  a  variable's  visibility
       within  functions.   With  dynamic scoping, visible variables and their
       values are a result of the sequence of function calls that caused  exe-
       cution  to  reach the current function.  The value of a variable that a
       function sees depends on its value within its caller, if  any,  whether
       that  caller  is the "global" scope or another shell function.  This is
       also the value that a local variable  declaration  "shadows",  and  the
       value that is restored when the function returns.

       For  example, if a variable var is declared as local in function func1,
       and func1 calls another function func2, references  to  var  made  from
       within func2 will resolve to the local variable var from func1, shadow-
       ing any global variable named var.

       The unset builtin also acts using the same dynamic scope: if a variable
       is local to the current scope, unset will unset it; otherwise the unset
       will refer to the variable found in  any  calling  scope  as  described
       above.   If a variable at the current local scope is unset, it will re-
       main so (appearing as unset) until it is reset in that scope  or  until
       the  function  returns.  Once the function returns, any instance of the
       variable at a previous scope will become visible.  If the unset acts on
       a  variable  at  a previous scope, any instance of a variable with that
       name that had been shadowed will become visible (see below how the  lo-
       calvar_unset shell option changes this behavior).

       The  FUNCNEST  variable,  if set to a numeric value greater than 0, de-
       fines a maximum function nesting level.  Function invocations that  ex-
       ceed the limit cause the entire command to abort.

       If  the  builtin command return is executed in a function, the function
       completes and execution resumes with the next command after  the  func-
       tion call.  Any command associated with the RETURN trap is executed be-
       fore 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 child shell processes (those created when  exe-
       cuting  a  separate  shell  invocation) 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.

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

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

       id++ id--
              variable post-increment and post-decrement
       - +    unary minus and plus
       ++id --id
              variable pre-increment and pre-decrement
       ! ~    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.

       Integer constants follow the C language definition, without suffixes or
       character constants.  Constants with a leading 0 are interpreted as oc-
       tal numbers.  A leading 0x or 0X denotes hexadecimal.  Otherwise,  num-
       bers  take the form [base#]n, where the optional base is a decimal num-
       ber between 2 and 64 representing the arithmetic base, and n is a  num-
       ber  in  that  base.   If base# is omitted, then base 10 is used.  When
       specifying n, if a non-digit is required, 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  up-
       percase  letters  may  be used interchangeably to represent numbers be-
       tween 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.  The test and [  commands  determine  their
       behavior  based  on  the  number  of arguments; see the descriptions of
       those commands for any other command-specific actions.

       Expressions are formed from the following unary  or  binary  primaries.
       Bash  handles several filenames specially when they are used in expres-
       sions.  If the operating system on which bash is running provides these
       special  files,  bash will use them; otherwise it will emulate them in-
       ternally with this behavior: If any file argument to one  of  the  pri-
       maries is of the form /dev/fd/n, then file descriptor n is checked.  If
       the file argument to  one  of  the  primaries  is  one  of  /dev/stdin,
       /dev/stdout,  or /dev/stderr, file descriptor 0, 1, or 2, respectively,
       is checked.

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

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

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

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

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

       string1 < string2
              True if string1 sorts before string2 lexicographically.

       string1 > string2
              True if string1 sorts after string2 lexicographically.

       arg1 OP arg2
              OP is one of -eq, -ne, -lt, -le, -gt, or -ge.  These  arithmetic
              binary  operators return true if arg1 is equal to, not equal to,
              less than, less than or equal to, greater than, or greater  than
              or  equal  to arg2, respectively.  Arg1 and arg2 may be positive
              or negative integers.  When used with the [[ command,  Arg1  and
              Arg2  are  evaluated  as  arithmetic expressions (see ARITHMETIC
              EVALUATION above).

SIMPLE COMMAND EXPANSION
       When a simple command is executed, the shell performs the following ex-
       pansions,  assignments,  and  redirections,  from left to right, in the
       following order.

       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.   In  the case of such a command (one that consists
       only of assignment statements and redirections), assignment  statements
       are  performed before redirections.  Otherwise, the variables are added
       to the environment of the executed command and do not affect  the  cur-
       rent shell environment.  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 af-
       fect 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 re-
       member  the  full  pathnames  of executable files (see hash under SHELL
       BUILTIN COMMANDS below).  A full search of the directories in  PATH  is
       performed  only  if the command is not found in the hash table.  If the
       search is unsuccessful, the shell searches for a defined shell function
       named command_not_found_handle.  If that function exists, it is invoked
       in a separate execution environment with the original command  and  the
       original  command's arguments as its arguments, and the function's exit
       status becomes the exit status of that subshell.  If that  function  is
       not defined, the shell prints an error message and returns an exit sta-
       tus 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, and the shell creates a new instance of
       itself 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:

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

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

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

       o      current traps set by trap

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

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

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

       o      options enabled by shopt

       o      shell aliases defined with alias

       o      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.


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

       o      the current working directory

       o      the file creation mode mask

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

       o      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.

       A subshell is a copy of the shell process.

       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 re-
       set to the values that the shell inherited from its parent  at  invoca-
       tion.  Builtin commands that are invoked as part of a pipeline are also
       executed in a subshell environment.  Changes made to the subshell envi-
       ronment cannot affect the shell's execution environment.

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

       If  a command is followed by a & and job control is not active, the de-
       fault standard input for the command is the empty file /dev/null.  Oth-
       erwise,  the invoked command inherits the file descriptors of the call-
       ing 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  in-
       vocation,  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 de-
       clare -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, re-
       placing  the  old.   The  environment inherited by any executed command
       consists of the shell's initial environment, whose values may be  modi-
       fied  in  the  shell, less any pairs removed by the unset command, plus
       any additions via the export and declare -x commands.

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

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

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

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

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

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

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

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

       The exit status of the last command is available in the special parame-
       ter $?.

       Bash itself returns the exit status of the last command  executed,  un-
       less  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 ig-
       nores 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 ef-
       fect, 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  us-
       ing 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.

       When  job  control is not enabled, and bash is waiting for a foreground
       command to complete, the shell receives keyboard-generated signals such
       as  SIGINT (usually generated by ^C) that users commonly intend to send
       to that command.  This happens because the shell and the command are in
       the same process group as the terminal, and ^C sends SIGINT to all pro-
       cesses in that process group.

       When bash is running without job control enabled  and  receives  SIGINT
       while  waiting for a foreground command, it waits until that foreground
       command terminates and then decides what to do about the SIGINT:

       1.     If the command terminates due to the SIGINT, bash concludes that
              the  user meant to end the entire script, and acts on the SIGINT
              (e.g., by running a SIGINT trap or exiting itself);

       2.     If the command does not terminate due  to  SIGINT,  the  program
              handled  the  SIGINT itself and did not treat it as a fatal sig-
              nal.  In that case, bash does not treat SIGINT as a  fatal  sig-
              nal,  either,  instead assuming that the SIGINT was used as part
              of the program's normal operation (e.g., emacs uses it to  abort
              editing commands) or deliberately discarded.  However, bash will
              run any trap set on SIGINT, as it does with  any  other  trapped
              signal  it  receives while it is waiting for the foreground com-
              mand to complete, for compatibility.

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

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

              [1] 25647

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

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

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

       There are a number of ways to refer to a job in the shell.  The charac-
       ter  %  introduces  a job specification (jobspec).  Job number n may be
       referred to as %n.  A job may also be referred to using a prefix of the
       name used to start it, or using a substring that appears in its command
       line.  For example, %ce refers to a stopped job whose command name  be-
       gins  with  ce.  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 background.  The previous  job  may
       be  referenced  using %-.  If there is only a single job, %+ and %- can
       both be used to refer to that job.  In output pertaining to jobs (e.g.,
       the output of the jobs command), the current job is always flagged with
       a +, and the 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  ex-
       its.

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

       When  the shell is waiting for a job or process using the wait builtin,
       and job control is enabled, wait  will  return  when  the  job  changes
       state.  The -f option causes wait to wait until the job or process ter-
       minates before returning.

PROMPTING
       When executing interactively, bash displays the primary prompt PS1 when
       it  is  ready  to  read a command, and the secondary prompt PS2 when it
       needs more input to complete a command.  Bash  displays  PS0  after  it
       reads  a  command  but  before  executing it.  Bash displays PS4 as de-
       scribed above before tracing each command when the  -x  option  is  en-
       abled.   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 in-
                     serted 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 $0 (the portion
                     following the final slash)
              \t     the current time in 24-hour HH:MM:SS format
              \T     the current time in 12-hour HH:MM:SS format
              \@     the current time in 12-hour am/pm format
              \A     the current time in 24-hour HH:MM format
              \u     the username of the current user
              \v     the version of bash (e.g., 2.00)
              \V     the release of bash, version + patch level (e.g., 2.00.0)
              \w     the value of the PWD shell variable  ($PWD),  with  $HOME
                     abbreviated   with   a  tilde  (uses  the  value  of  the
                     PROMPT_DIRTRIM variable)
              \W     the basename of $PWD, 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  be-
       low),  while the command number is the position in the sequence of com-
       mands executed during the current shell session.  After the  string  is
       decoded,  it is expanded via parameter expansion, command substitution,
       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).  This can have unwanted side effects  if
       escaped  portions  of  the string appear within command substitution or
       contain characters special to word expansion.

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

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

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

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

   Readline Initialization
       Readline  is  customized  by putting commands in an initialization file
       (the inputrc file).  The name of this file is taken from the  value  of
       the INPUTRC variable.  If that variable is unset, the default is ~/.in-
       putrc.  If that file  does not exist or cannot be  read,  the  ultimate
       default  is  /etc/inputrc.   When a program which uses the readline li-
       brary 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 constructs.  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
       or using the bind builtin command (see SHELL BUILTIN COMMANDS below).

       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:

       active-region-start-color
              A  string  variable  that controls the text color and background
              when displaying the text in the active region (see the  descrip-
              tion  of enable-active-region below).  This string must not take
              up any physical character positions on the display, so it should
              consist  only of terminal escape sequences.  It is output to the
              terminal before displaying the text in the active region.   This
              variable  is  reset  to  the default value whenever the terminal
              type changes.  The default value is the  string  that  puts  the
              terminal  in standout mode, as obtained from the terminal's ter-
              minfo description.  A sample value might be "\e[01;33m".
       active-region-end-color
              A string  variable  that  "undoes"  the  effects  of  active-re-
              gion-start-color  and restores "normal" terminal display appear-
              ance after displaying text in the active  region.   This  string
              must  not  take  up any physical character positions on the dis-
              play, so it should consist only of  terminal  escape  sequences.
              It  is  output  to the terminal after displaying the text in the
              active region.  This variable is  reset  to  the  default  value
              whenever  the  terminal  type changes.  The default value is the
              string that restores the terminal from  standout  mode,  as  ob-
              tained from the terminal's terminfo description.  A sample value
              might be "\e[0m".
       bell-style (audible)
              Controls what happens when readline wants to ring  the  terminal
              bell.  If set to none, readline never rings the bell.  If set to
              visible, readline uses a visible bell if one is  available.   If
              set to audible, readline attempts to ring the terminal's bell.
       bind-tty-special-chars (On)
              If  set  to On, readline attempts to bind the control characters
              treated specially by the kernel's terminal driver to their read-
              line equivalents.
       blink-matching-paren (Off)
              If set to On, readline attempts to briefly move the cursor to an
              opening parenthesis when a closing parenthesis is inserted.
       colored-completion-prefix (Off)
              If set to On, when listing completions,  readline  displays  the
              common prefix of the set of possible completions using a differ-
              ent color.  The color definitions are taken from  the  value  of
              the LS_COLORS environment variable.  If there is a color defini-
              tion in $LS_COLORS for the custom suffix  "readline-colored-com-
              pletion-prefix",  readline uses this color for the common prefix
              instead of its default.
       colored-stats (Off)
              If set to On, readline displays possible completions using  dif-
              ferent  colors  to  indicate their file type.  The color defini-
              tions are taken from the  value  of  the  LS_COLORS  environment
              variable.
       comment-begin (``#'')
              The  string  that  is  inserted when the readline insert-comment
              command is executed.  This command is bound to M-# in emacs mode
              and to # in vi command mode.
       completion-display-width (-1)
              The  number  of  screen columns used to display possible matches
              when performing completion.  The value is ignored if it is  less
              than  0 or greater than the terminal screen width.  A value of 0
              will cause matches to be displayed one per  line.   The  default
              value is -1.
       completion-ignore-case (Off)
              If set to On, readline performs filename matching and completion
              in a case-insensitive fashion.
       completion-map-case (Off)
              If set to On, and completion-ignore-case  is  enabled,  readline
              treats  hyphens  (-) and underscores (_) as equivalent when per-
              forming case-insensitive filename matching and completion.
       completion-prefix-display-length (0)
              The length in characters of the common prefix of a list of  pos-
              sible  completions that is displayed without modification.  When
              set to a value greater than zero, common  prefixes  longer  than
              this  value are replaced with an ellipsis when displaying possi-
              ble completions.
       completion-query-items (100)
              This determines when the user is queried about viewing the  num-
              ber  of  possible  completions generated by the possible-comple-
              tions command.  It may be set to any integer value greater  than
              or  equal  to  zero.   If  the number of possible completions is
              greater than or equal to the value of  this  variable,  readline
              will  ask whether or not the user wishes to view them; otherwise
              they are simply listed on the  terminal.   A  zero  value  means
              readline should never ask; negative values are treated as zero.
       convert-meta (On)
              If  set  to On, readline will convert characters with the eighth
              bit set to an ASCII key sequence by stripping the eighth bit and
              prefixing  an  escape  character (in effect, using escape as the
              meta prefix).  The default is On, but readline will  set  it  to
              Off  if the locale contains eight-bit characters.  This variable
              is dependent on the LC_CTYPE locale category, and may change  if
              the locale is changed.
       disable-completion (Off)
              If set to On, readline will inhibit word completion.  Completion
              characters will be inserted into the line as if  they  had  been
              mapped to self-insert.
       echo-control-characters (On)
              When  set to On, on operating systems that indicate they support
              it, readline echoes a character corresponding to a signal gener-
              ated from the keyboard.
       editing-mode (emacs)
              Controls whether readline begins with a set of key bindings sim-
              ilar to Emacs or vi.  editing-mode can be set to either emacs or
              vi.
       emacs-mode-string (@)
              If  the  show-mode-in-prompt variable is enabled, this string is
              displayed immediately before the last line of the primary prompt
              when emacs editing mode is active.  The value is expanded like a
              key binding, so the standard set of meta- and  control  prefixes
              and  backslash escape sequences is available.  Use the \1 and \2
              escapes to begin and end sequences of  non-printing  characters,
              which  can be used to embed a terminal control sequence into the
              mode string.
       enable-active-region (On)
              The point is the current cursor position, and mark refers  to  a
              saved  cursor  position.  The text between the point and mark is
              referred to as the region.  When this variable  is  set  to  On,
              readline  allows certain commands to designate the region as ac-
              tive.  When the region is active, readline highlights  the  text
              in  the region using the value of the active-region-start-color,
              which defaults to the string that enables the terminal's  stand-
              out  mode.   The active region shows the text inserted by brack-
              eted-paste and any matching text found by incremental  and  non-
              incremental history searches.
       enable-bracketed-paste (On)
              When  set to On, readline configures the terminal to insert each
              paste into the editing buffer as a single string of  characters,
              instead  of  treating each character as if it had been read from
              the keyboard.  This prevents readline from executing any editing
              commands bound to key sequences appearing in the pasted text.
       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 ar-
              row keys.
       enable-meta-key (On)
              When  set  to  On, readline will try to enable any meta modifier
              key the terminal claims to support when it is called.   On  many
              terminals, the meta key is used to send eight-bit characters.
       expand-tilde (Off)
              If  set  to  On,  tilde expansion is performed when readline at-
              tempts word completion.
       history-preserve-point (Off)
              If set to On, the history code attempts to place  point  at  the
              same  location on each history line retrieved with previous-his-
              tory or next-history.
       history-size (unset)
              Set the maximum number of history entries saved in  the  history
              list.   If set to zero, any existing history entries are deleted
              and no new entries are saved.  If set to a value less than zero,
              the  number  of history entries is not limited.  By default, the
              number of history entries is set to the value  of  the  HISTSIZE
              shell  variable.  If an attempt is made to set history-size to a
              non-numeric value, the maximum number of history entries will be
              set to 500.
       horizontal-scroll-mode (Off)
              When  set  to  On, makes readline use a single line for display,
              scrolling the input horizontally on a single screen line when it
              becomes  longer  than the screen width rather than wrapping to a
              new line.  This setting is automatically enabled  for  terminals
              of height 1.
       input-meta (Off)
              If  set to On, readline will enable eight-bit input (that is, it
              will not strip the eighth bit from the characters it reads), re-
              gardless  of  what the terminal claims it can support.  The name
              meta-flag is a synonym for this variable.  The default  is  Off,
              but  readline will set it to On if the locale contains eight-bit
              characters.  This variable is dependent on the  LC_CTYPE  locale
              category, and may change if the locale is changed.
       isearch-terminators (``C-[C-J'')
              The  string  of  characters that should terminate an incremental
              search without subsequently executing the character  as  a  com-
              mand.   If this variable has not been given a value, the charac-
              ters ESC and C-J will terminate an incremental search.
       keymap (emacs)
              Set the current readline keymap.  The set of valid keymap  names
              is  emacs,  emacs-standard,  emacs-meta, emacs-ctlx, vi, vi-com-
              mand, and vi-insert.  vi is equivalent to vi-command;  emacs  is
              equivalent  to  emacs-standard.  The default value is emacs; the
              value of editing-mode also affects the default keymap.
       keyseq-timeout (500)
              Specifies the duration readline will wait for a  character  when
              reading  an ambiguous key sequence (one that can form a complete
              key sequence using the input read so far, or can take additional
              input  to  complete  a longer key sequence).  If no input is re-
              ceived within the timeout, readline will  use  the  shorter  but
              complete  key sequence.  The value is specified in milliseconds,
              so a value of 1000 means that readline will wait one second  for
              additional  input.  If this variable is set to a value less than
              or equal to zero, or to a non-numeric value, readline will  wait
              until  another  key  is  pressed to decide which key sequence to
              complete.
       mark-directories (On)
              If set to On, completed directory names have a slash appended.
       mark-modified-lines (Off)
              If set to On, history lines that have  been  modified  are  dis-
              played with a preceding asterisk (*).
       mark-symlinked-directories (Off)
              If set to On, completed names which are symbolic links to direc-
              tories have a slash appended (subject to the value  of  mark-di-
              rectories).
       match-hidden-files (On)
              This  variable,  when  set to On, causes readline to match files
              whose names begin with a  `.'  (hidden  files)  when  performing
              filename  completion.   If  set  to Off, the leading `.' must be
              supplied by the user in the filename to be completed.
       menu-complete-display-prefix (Off)
              If set to On, menu completion displays the common prefix of  the
              list of possible completions (which may be empty) before cycling
              through the list.
       output-meta (Off)
              If set to On, readline will display characters with  the  eighth
              bit set directly rather than as a meta-prefixed escape sequence.
              The default is Off, but readline will set it to On if the locale
              contains  eight-bit  characters.   This variable is dependent on
              the LC_CTYPE locale category, and may change if  the  locale  is
              changed.
       page-completions (On)
              If  set to On, readline uses an internal more-like pager to dis-
              play a screenful of possible completions at a time.
       print-completions-horizontally (Off)
              If set to On, readline will  display  completions  with  matches
              sorted  horizontally in alphabetical order, rather than down the
              screen.
       revert-all-at-newline (Off)
              If set to On, readline will undo all changes  to  history  lines
              before returning when accept-line is executed.  By default, his-
              tory lines may be modified  and  retain  individual  undo  lists
              across calls to readline.
       show-all-if-ambiguous (Off)
              This  alters  the  default behavior of the completion functions.
              If set to On, words which have more than one possible completion
              cause  the  matches  to be listed immediately instead of ringing
              the bell.
       show-all-if-unmodified (Off)
              This alters the default behavior of the completion functions  in
              a fashion similar to show-all-if-ambiguous.  If set to On, words
              which have more than one possible completion without any  possi-
              ble  partial  completion (the possible completions don't share a
              common prefix) cause the matches to be  listed  immediately  in-
              stead of ringing the bell.
       show-mode-in-prompt (Off)
              If  set to On, add a string to the beginning of the prompt indi-
              cating the editing mode: emacs, vi  command,  or  vi  insertion.
              The mode strings are user-settable (e.g., emacs-mode-string).
       skip-completed-text (Off)
              If  set  to On, this alters the default completion behavior when
              inserting a single match into the line.  It's only  active  when
              performing  completion  in  the  middle  of a word.  If enabled,
              readline does not insert characters  from  the  completion  that
              match  characters  after  point  in the word being completed, so
              portions of the word following the cursor are not duplicated.
       vi-cmd-mode-string ((cmd))
              If the show-mode-in-prompt variable is enabled, this  string  is
              displayed immediately before the last line of the primary prompt
              when vi editing mode is active and in command mode.   The  value
              is expanded like a key binding, so the standard set of meta- and
              control prefixes and backslash escape  sequences  is  available.
              Use  the  \1  and  \2 escapes to begin and end sequences of non-
              printing characters, which can be used to embed a terminal  con-
              trol sequence into the mode string.
       vi-ins-mode-string ((ins))
              If  the  show-mode-in-prompt variable is enabled, this string is
              displayed immediately before the last line of the primary prompt
              when vi editing mode is active and in insertion mode.  The value
              is expanded like a key binding, so the standard set of meta- and
              control  prefixes  and  backslash escape sequences is available.
              Use the \1 and \2 escapes to begin and  end  sequences  of  non-
              printing  characters, which can be used to embed a terminal con-
              trol sequence into the mode string.
       visible-stats (Off)
              If set to On, a character denoting a file's type as reported  by
              stat(2)  is  appended to the filename when listing possible com-
              pletions.

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

       $if    The  $if construct allows bindings to be made based on the edit-
              ing mode, the terminal being  used,  or  the  application  using
              readline.  The text of the test, after any comparison operator,
               extends  to  the  end  of  the line; unless otherwise noted, 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  in-
                     stance,   to  set  bindings  in  the  emacs-standard  and
                     emacs-ctlx keymaps only if readline is  starting  out  in
                     emacs mode.

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

              version
                     The  version  test  may  be  used  to perform comparisons
                     against specific readline versions.  The version  expands
                     to  the  current readline version.  The set of comparison
                     operators includes =, (and ==), !=, <=,  >=,  <,  and  >.
                     The  version number supplied on the right side of the op-
                     erator consists of a major version  number,  an  optional
                     decimal point, and an optional minor version (e.g., 7.1).
                     If the minor version is omitted, it is assumed to  be  0.
                     The operator may be separated from the string version and
                     from the version number argument by whitespace.

              application
                     The application construct is used to include application-
                     specific  settings.   Each program using the readline li-
                     brary 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

              variable
                     The variable construct provides simple equality tests for
                     readline variables and values.  The permitted  comparison
                     operators  are  =, ==, and !=.  The variable name must be
                     separated from the comparison operator by whitespace; the
                     operator  may  be  separated  from the value on the right
                     hand side by whitespace.  Both string and  boolean  vari-
                     ables  may  be  tested.  Boolean variables must be tested
                     against the values on and off.

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

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

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

              $include  /etc/inputrc

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

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

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

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

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

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

   Commands for Moving
       beginning-of-line (C-a)
              Move to the start of the current line.
       end-of-line (C-e)
              Move to the end of the line.
       forward-char (C-f)
              Move forward a character.
       backward-char (C-b)
              Move back a character.
       forward-word (M-f)
              Move forward to the end of the next word.  Words are composed of
              alphanumeric characters (letters and digits).
       backward-word (M-b)
              Move back to the start of the current or previous  word.   Words
              are composed of alphanumeric characters (letters and digits).
       shell-forward-word
              Move  forward  to the end of the next word.  Words are delimited
              by non-quoted shell metacharacters.
       shell-backward-word
              Move back to the start of the current or previous  word.   Words
              are delimited by non-quoted shell metacharacters.
       previous-screen-line
              Attempt  to move point to the same physical screen column on the
              previous physical screen line. This will not  have  the  desired
              effect  if  the current readline line does not take up more than
              one physical line or if point is not greater than the length  of
              the prompt plus the screen width.
       next-screen-line
              Attempt  to move point to the same physical screen column on the
              next physical screen line. This will not have the desired effect
              if  the  current  readline  line  does not take up more than one
              physical line or if the length of the current readline  line  is
              not greater than the length of the prompt plus the screen width.
       clear-display (M-C-l)
              Clear  the  screen  and,  if possible, the terminal's scrollback
              buffer, then redraw the current line, leaving the  current  line
              at the top of the screen.
       clear-screen (C-l)
              Clear the screen, then redraw the current line, leaving the cur-
              rent 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.
       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.   A
              numeric  argument,  if  supplied, specifies the history entry to
              use instead of the current line.
       fetch-history
              With a numeric argument, fetch that entry from the history  list
              and make it the current line.  Without an argument, move back to
              the first entry in the history list.
       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.
       history-substring-search-backward
              Search backward through the history for the string of characters
              between the start of the current line and the current cursor po-
              sition  (the  point).  The search string may match anywhere in a
              history line.  This is a non-incremental search.
       history-substring-search-forward
              Search forward through the history for the string of  characters
              between the start of the current line and the point.  The search
              string may match anywhere in a history line.  This is a  non-in-
              cremental 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  in-
              serts  the  nth word from the end of the previous command.  Once
              the argument n is computed, the argument is extracted as if  the
              "!n" history expansion had been specified.
       yank-last-arg (M-., M-_)
              Insert  the last argument to the previous command (the last word
              of the previous history entry).  With a numeric argument, behave
              exactly  like  yank-nth-arg.   Successive calls to yank-last-arg
              move back through the history list, inserting the last word  (or
              the  word  specified  by the argument to the first call) of each
              line in turn.  Any numeric argument supplied to these successive
              calls  determines  the direction to move through the history.  A
              negative argument switches the  direction  through  the  history
              (back or forward).  The history expansion facilities are used to
              extract the last word, as if the "!$" history expansion had been
              specified.
       shell-expand-line (M-C-e)
              Expand the line as the shell does.  This performs alias and his-
              tory expansion as well as all of the shell word expansions.  See
              HISTORY EXPANSION below for a description of history expansion.
       history-expand-line (M-^)
              Perform  history expansion on the current line.  See HISTORY EX-
              PANSION 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.
       edit-and-execute-command (C-x C-e)
              Invoke  an  editor  on the current command line, and execute the
              result as shell commands.  Bash attempts to invoke $VISUAL, $ED-
              ITOR, and emacs as the editor, in that order.

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

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

   Numeric Arguments
       digit-argument (M-0, M-1, ..., M--)
              Add this digit to the argument already accumulating, or start  a
              new argument.  M-- starts a negative argument.
       universal-argument
              This  is another way to specify an argument.  If this command is
              followed by one or more digits, optionally with a leading  minus
              sign,  those digits define the argument.  If the command is fol-
              lowed by digits, executing universal-argument again ends the nu-
              meric argument, but is otherwise ignored.  As a special case, if
              this command is immediately followed by a character that is nei-
              ther  a  digit  nor  minus sign, the argument count for the next
              command is multiplied by four.  The argument count is  initially
              one,  so  executing this function the first time makes the argu-
              ment count four, a second time makes the argument count sixteen,
              and so on.

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

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

   Miscellaneous
       re-read-init-file (C-x C-r)
              Read  in  the  contents of the inputrc file, and incorporate any
              bindings or variable assignments found there.
       abort (C-g)
              Abort the current editing command and ring the  terminal's  bell
              (subject to the setting of bell-style).
       do-lowercase-version (M-A, M-B, M-x, ...)
              If  the  metafied character x is uppercase, run the command that
              is bound to the corresponding metafied lowercase character.  The
              behavior is undefined if x is already lowercase.
       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 argument searches for previous oc-
              currences.
       character-search-backward (M-C-])
              A character is read and point is moved to  the  previous  occur-
              rence  of that character.  A negative argument searches for sub-
              sequent occurrences.
       skip-csi-sequence
              Read enough characters to consume a multi-key sequence  such  as
              those  defined for keys like Home and End.  Such sequences begin
              with a Control Sequence Indicator (CSI), usually ESC-[.  If this
              sequence  is  bound  to "\[", keys producing such sequences will
              have no effect unless explicitly bound to  a  readline  command,
              instead  of  inserting stray characters into the editing buffer.
              This is unbound by default, but usually bound to ESC-[.
       insert-comment (M-#)
              Without a numeric argument,  the  value  of  the  readline  com-
              ment-begin  variable is inserted at the beginning of the current
              line.  If a numeric argument is supplied, this command acts as a
              toggle:  if  the  characters at the beginning of the line do not
              match the value of comment-begin, the value is inserted,  other-
              wise the characters in comment-begin are deleted from the begin-
              ning of the line.  In either case, the line is accepted as if  a
              newline  had  been  typed.   The  default value of comment-begin
              causes this command to make the current line  a  shell  comment.
              If  a  numeric  argument  causes the comment character to be re-
              moved, the line will be executed by the shell.
       spell-correct-word (C-x s)
              Perform spelling correction on the current word, treating it  as
              a  directory  or  filename, in the same way as the cdspell shell
              option.   Word  boundaries  are  the  same  as  those  used   by
              shell-forward-word.
       glob-complete-word (M-g)
              The  word  before point is treated as a pattern for pathname ex-
              pansion, with an asterisk implicitly appended.  This pattern  is
              used  to generate a list of matching filenames for possible com-
              pletions.
       glob-expand-word (C-x *)
              The word before point is treated as a pattern for  pathname  ex-
              pansion, and the list of matching filenames is inserted, replac-
              ing the word.  If a numeric argument is supplied, an asterisk is
              appended before pathname expansion.
       glob-list-expansions (C-x g)
              The  list  of  expansions  that  would  have  been  generated by
              glob-expand-word is displayed, and the line is  redrawn.   If  a
              numeric  argument  is  supplied,  an asterisk is appended before
              pathname expansion.
       dump-functions
              Print all of the functions and their key bindings to  the  read-
              line output stream.  If a numeric argument is supplied, the out-
              put is formatted in such a way that it can be made  part  of  an
              inputrc file.
       dump-variables
              Print all of the settable readline variables and their values to
              the readline output stream.  If a numeric argument is  supplied,
              the  output  is formatted in such a way that it can be made part
              of an inputrc file.
       dump-macros
              Print all of the readline key sequences bound to macros and  the
              strings  they  output.   If  a numeric argument is supplied, the
              output is formatted in such a way that it can be made part of an
              inputrc file.
       display-shell-version (C-x C-v)
              Display version information about the current instance of bash.

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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


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

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

       The  builtin  command fc (see SHELL BUILTIN COMMANDS below) may be used
       to list or edit and re-execute a portion of the history list.  The his-
       tory  builtin may be used to display or modify the history list and ma-
       nipulate 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  op-
       tions.

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, and is performed  on  each
       line  individually  without  taking  quoting on previous lines into ac-
       count.  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  avail-
       able  to  manipulate the selected words.  The line is broken into words
       in the same fashion as when reading input, so that several  metacharac-
       ter-separated words surrounded by quotes are considered one word.  His-
       tory expansions are introduced by the appearance of the history  expan-
       sion  character,  which is ! by default.  Only backslash (\) and single
       quotes can quote the history expansion character, but the  history  ex-
       pansion  character is also treated as quoted if it immediately precedes
       the closing double quote in a double-quoted string.

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

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

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

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

       !      Start a history substitution, except when followed by  a  blank,
              newline,  carriage return, = or ( (when the extglob shell option
              is enabled using the shopt builtin).
       !n     Refer to command line n.
       !-n    Refer to the current command minus n.
       !!     Refer to the previous command.  This is a synonym for `!-1'.
       !string
              Refer to the most recent command preceding the current  position
              in the history list starting with string.
       !?string[?]
              Refer  to the most recent command preceding the current position
              in the history list containing string.  The trailing  ?  may  be
              omitted  if  string  is  followed  immediately by a newline.  If
              string is missing, the string from the  most  recent  search  is
              used; it is an error if there is no previous search string.
       ^string1^string2^
              Quick  substitution.   Repeat  the  previous  command, replacing
              string1 with string2.  Equivalent  to  ``!!:s^string1^string2^''
              (see Modifiers below).
       !#     The entire command line typed so far.

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

       0 (zero)
              The zeroth word.  For the shell, this is the command word.
       n      The nth word.
       ^      The first argument.  That is, word 1.
       $      The last word.  This is usually the last argument, but will  ex-
              pand to the zeroth word if there is only one word in the line.
       %      The  first word matched by the most recent `?string?' search, if
              the search string begins with a character  that  is  part  of  a
              word.
       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 x is miss-
              ing, it defaults to 0.

       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 `:'.  These mod-
       ify, or edit, the word or words selected from the history event.

       h      Remove a trailing filename component, leaving only the head.
       t      Remove all leading filename components, leaving the tail.
       r      Remove a trailing suffix of the form .xxx, leaving the basename.
       e      Remove all but the trailing suffix.
       p      Print the new command but do not execute it.
       q      Quote the substituted words, escaping further substitutions.
       x      Quote  the  substituted words as with q, but break into words at
              blanks and newlines.  The q and x modifiers are mutually  exclu-
              sive; the last one supplied is used.
       s/old/new/
              Substitute  new  for  the  first  occurrence of old in the event
              line.  Any character may be used as the delimiter 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 single backslash will quote the &.  If old is null, it is  set
              to  the last old substituted, or, if no previous history substi-
              tutions took place, the last string in  a  !?string[?]   search.
              If new is null, each matching old is deleted.
       &      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' or `&' modifier once to each word in the
              event line.

SHELL BUILTIN COMMANDS
       Unless otherwise noted, each builtin command documented in this section
       as accepting options preceded by - accepts -- to signify the end of the
       options.  The :, true, false, and test/[ builtins do not accept options
       and  do  not treat -- specially.  The exit, logout, return, break, con-
       tinue, let, and shift builtins accept and process  arguments  beginning
       with  - without requiring --.  Other builtins that accept arguments but
       are not specified as accepting options  interpret  arguments  beginning
       with  -  as  invalid options and require -- to prevent this interpreta-
       tion.
       : [arguments]
              No effect; the command does nothing beyond  expanding  arguments
              and performing any specified redirections.  The return status is
              zero.

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

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

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

       bind [-m keymap] [-lpsvPSVX]
       bind [-m keymap] [-q function] [-u function] [-r keyseq]
       bind [-m keymap] -f filename
       bind [-m keymap] -x keyseq:shell-command
       bind [-m keymap] keyseq:function-name
       bind [-m keymap] keyseq:readline-command
       bind readline-command-line
              Display  current  readline key and function bindings, bind a key
              sequence to a readline function or  macro,  or  set  a  readline
              variable.  Each non-option argument is a command as it would ap-
              pear in a readline initialization file  such  as  .inputrc,  but
              each  binding  or command must be passed as a separate argument;
              e.g., '"\C-x\C-r": re-read-init-file'.   Options,  if  supplied,
              have the following meanings:
              -m keymap
                     Use keymap as the keymap to be affected by the subsequent
                     bindings.  Acceptable keymap names are emacs, emacs-stan-
                     dard,  emacs-meta,  emacs-ctlx,  vi, vi-move, vi-command,
                     and vi-insert.  vi is equivalent to  vi-command  (vi-move
                     is  also  a  synonym); emacs is equivalent to emacs-stan-
                     dard.
              -l     List the names of all readline functions.
              -p     Display readline function names and bindings  in  such  a
                     way that they can be re-read.
              -P     List current readline function names and bindings.
              -s     Display  readline  key  sequences bound to macros and the
                     strings they output in such a way that they  can  be  re-
                     read.
              -S     Display  readline  key  sequences bound to macros and the
                     strings they output.
              -v     Display readline variable names and values in such a  way
                     that they can be re-read.
              -V     List current readline variable names and values.
              -f filename
                     Read key bindings from filename.
              -q function
                     Query about which keys invoke the named function.
              -u function
                     Unbind all keys bound to the named function.
              -r keyseq
                     Remove any current binding for keyseq.
              -x keyseq:shell-command
                     Cause shell-command to be executed whenever keyseq is en-
                     tered.  When shell-command is executed,  the  shell  sets
                     the  READLINE_LINE  variable to the contents of the read-
                     line line buffer and the READLINE_POINT and READLINE_MARK
                     variables  to the current location of the insertion point
                     and the saved insertion point (the  mark),  respectively.
                     The  shell assigns any numeric argument the user supplied
                     to the READLINE_ARGUMENT variable.  If there was no argu-
                     ment,  that variable is not set.  If the executed command
                     changes  the  value  of  any  of   READLINE_LINE,   READ-
                     LINE_POINT,  or  READLINE_MARK,  those new values will be
                     reflected in the editing state.
              -X     List all key sequences bound to shell  commands  and  the
                     associated commands in a format that can be reused as in-
                     put.

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

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

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

       caller [expr]
              Returns the context of any active subroutine call (a shell func-
              tion or a script executed with the . or source builtins).  With-
              out expr, caller displays the line number and source filename of
              the  current subroutine call.  If a non-negative integer is sup-
              plied as expr, caller displays the line number, subroutine name,
              and  source  file  corresponding to that position in the current
              execution call stack.  This extra information may be  used,  for
              example,  to print a stack trace.  The current frame is frame 0.
              The return value is 0 unless the shell is not executing  a  sub-
              routine  call or expr does not correspond to a valid position in
              the call stack.

       cd [-L|[-P [-e]] [-@]] [dir]
              Change the current directory to dir.  if dir  is  not  supplied,
              the  value of the HOME shell variable is the default.  The vari-
              able CDPATH defines the search path for the directory containing
              dir:  each directory name in CDPATH is searched for dir.  Alter-
              native directory names in CDPATH are separated by a  colon  (:).
              A  null  directory name in CDPATH is the same as the current di-
              rectory, i.e., ``.''.  If dir begins with a slash (/), then  CD-
              PATH  is  not used.  The -P option causes cd to use the physical
              directory structure by resolving symbolic links while traversing
              dir  and  before processing instances of .. in dir (see also the
              -P option to the set builtin command); the -L option forces sym-
              bolic  links to be followed by resolving the link after process-
              ing instances of .. in dir.  If .. appears in dir,  it  is  pro-
              cessed  by  removing the immediately previous pathname component
              from dir, back to a slash or the beginning of dir.   If  the  -e
              option  is  supplied  with -P, and the current working directory
              cannot be successfully determined after a  successful  directory
              change,  cd will return an unsuccessful status.  On systems that
              support it, the -@ option presents the extended attributes asso-
              ciated  with  a  file  as a directory.  An argument of - is con-
              verted to $OLDPWD before the directory change is attempted.   If
              a  non-empty  directory name from CDPATH is used, or if - is the
              first argument, and the directory change is successful, the  ab-
              solute  pathname  of the new working directory is written to the
              standard output.  If the directory change is successful, cd sets
              the  value  of the PWD environment variable to the new directory
              name, and sets the OLDPWD environment variable to the  value  of
              the  current  working  directory  before the change.  The return
              value is true if the directory was successfully  changed;  false
              otherwise.

       command [-pVv] command [arg ...]
              Run  command  with  args  suppressing  the normal shell function
              lookup.  Only builtin commands or commands found in the PATH are
              executed.   If the -p option is given, the search for command is
              performed using a default value for PATH that is  guaranteed  to
              find  all of the standard utilities.  If either the -V or -v op-
              tion is supplied, a description of command is printed.   The  -v
              option  causes  a single word indicating the command or filename
              used to invoke command to be displayed; the -V option produces a
              more  verbose  description.  If the -V or -v option is supplied,
              the exit status is 0 if command was found, and  1  if  not.   If
              neither option is supplied and an error occurred or command can-
              not be found, the exit status is 127.  Otherwise, the exit  sta-
              tus of the command builtin is the exit status of command.

       compgen [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 fa-
              cilities, while available, will not have useful values.

              The matches will be generated in the same way as if the program-
              mable completion code had generated them directly from a comple-
              tion specification with the same flags.  If word  is  specified,
              only those completions matching word will be displayed.

              The  return  value is true unless an invalid option is supplied,
              or no matches were generated.

       complete [-abcdefgjksuv] [-o comp-option] [-DEI] [-A action] [-G  glob-
       pat] [-W wordlist]
              [-F  function]  [-C command] [-X filterpat] [-P prefix] [-S suf-
              fix] name [name ...]
       complete -pr [-DEI] [name ...]
              Specify how arguments to each name should be completed.  If  the
              -p  option  is supplied, or if no options are supplied, existing
              completion specifications are printed in a way that allows  them
              to be reused as input.  The -r option removes a completion spec-
              ification for each name, or, if no names are supplied, all  com-
              pletion specifications.  The -D option indicates that other sup-
              plied options and actions should apply to the  ``default''  com-
              mand  completion; that is, completion attempted on a command for
              which no completion has previously been defined.  The -E  option
              indicates  that  other supplied options and actions should apply
              to ``empty'' command completion; that is,  completion  attempted
              on  a  blank  line.  The -I option indicates that other supplied
              options and actions should apply to completion  on  the  initial
              non-assignment  word  on  the line, or after a command delimiter
              such as ; or |, which is usually command  name  completion.   If
              multiple  options  are  supplied, the -D option takes precedence
              over -E, and both take precedence over -I.  If any of -D, -E, or
              -I  are  supplied,  any  other name arguments are ignored; these
              completions only apply to the case specified by the option.

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

              Other options, if specified, have the following  meanings.   The
              arguments  to the -G, -W, and -X options (and, if necessary, the
              -P and -S options) should be quoted to protect them from  expan-
              sion before the complete builtin is invoked.
              -o comp-option
                      The  comp-option  controls  several aspects of the comp-
                      spec's behavior beyond the simple generation of  comple-
                      tions.  comp-option may be one of:
                      bashdefault
                              Perform the rest of the default bash completions
                              if the compspec generates no matches.
                      default Use readline's default  filename  completion  if
                              the compspec generates no matches.
                      dirnames
                              Perform  directory  name completion if the comp-
                              spec generates no matches.
                      filenames
                              Tell readline that the compspec generates  file-
                              names,  so  it can perform any filename-specific
                              processing (like adding  a  slash  to  directory
                              names,  quoting special characters, or suppress-
                              ing trailing spaces).  Intended to be used  with
                              shell functions.
                      noquote Tell  readline  not to quote the completed words
                              if they are filenames (quoting filenames is  the
                              default).
                      nosort  Tell  readline  not to sort the list of possible
                              completions alphabetically.
                      nospace Tell readline not to append  a  space  (the  de-
                              fault)  to  words  completed  at  the end of the
                              line.
                      plusdirs
                              After any matches defined by  the  compspec  are
                              generated,  directory  name  completion  is  at-
                              tempted and any matches are added to the results
                              of the other actions.
              -A action
                      The  action  may  be  one of the following to generate a
                      list of possible completions:
                      alias   Alias names.  May also be specified as -a.
                      arrayvar
                              Array variable names.
                      binding Readline key binding names.
                      builtin Names of shell builtin commands.   May  also  be
                              specified as -b.
                      command Command names.  May also be specified as -c.
                      directory
                              Directory names.  May also be specified as -d.
                      disabled
                              Names of disabled shell builtins.
                      enabled Names of enabled shell builtins.
                      export  Names  of exported shell variables.  May also be
                              specified as -e.
                      file    File names.  May also be specified as -f.
                      function
                              Names of shell functions.
                      group   Group names.  May also be specified as -g.
                      helptopic
                              Help topics as accepted by the help builtin.
                      hostname
                              Hostnames, as taken from the file  specified  by
                              the HOSTFILE shell variable.
                      job     Job  names,  if job control is active.  May also
                              be specified as -j.
                      keyword Shell reserved words.  May also be specified  as
                              -k.
                      running Names of running jobs, if job control is active.
                      service Service names.  May also be specified as -s.
                      setopt  Valid  arguments  for  the  -o option to the set
                              builtin.
                      shopt   Shell option names  as  accepted  by  the  shopt
                              builtin.
                      signal  Signal names.
                      stopped Names of stopped jobs, if job control is active.
                      user    User names.  May also be specified as -u.
                      variable
                              Names of all shell variables.  May also be spec-
                              ified as -v.
              -C command
                      command is executed in a subshell environment,  and  its
                      output  is  used as the possible completions.  Arguments
                      are passed as with the -F option.
              -F function
                      The shell function function is executed in  the  current
                      shell  environment.   When the function is executed, the
                      first argument ($1) is the name of the command whose ar-
                      guments are being completed, the second argument ($2) is
                      the word being completed, and the third argument ($3) is
                      the  word preceding the word being completed on the cur-
                      rent command line.  When it finishes, the possible  com-
                      pletions  are  retrieved from the value of the COMPREPLY
                      array variable.
              -G globpat
                      The pathname expansion pattern globpat  is  expanded  to
                      generate the possible completions.
              -P prefix
                      prefix  is  added at the beginning of each possible com-
                      pletion after all other options have been applied.
              -S suffix
                      suffix is appended to each possible completion after all
                      other options have been applied.
              -W wordlist
                      The  wordlist  is  split using the characters in the IFS
                      special variable as delimiters, and each resultant  word
                      is  expanded.  Shell quoting is honored within wordlist,
                      in order to provide a mechanism for the words to contain
                      shell  metacharacters or characters in the value of IFS.
                      The possible completions are the members of  the  resul-
                      tant list which match the word being completed.
              -X filterpat
                      filterpat  is  a pattern as used for pathname expansion.
                      It is applied to the list of possible completions gener-
                      ated  by  the  preceding options and arguments, and each
                      completion matching filterpat is removed from the  list.
                      A  leading  !  in filterpat negates the pattern; in this
                      case, any completion not matching filterpat is removed.

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

       compopt [-o option] [-DEI] [+o option] [name]
              Modify completion options for each name  according  to  the  op-
              tions, or for the currently-executing completion if no names are
              supplied.  If no options are given, display the  completion  op-
              tions  for  each  name  or the current completion.  The possible
              values of option are those valid for the  complete  builtin  de-
              scribed  above.  The -D option indicates that other supplied op-
              tions should apply to the ``default'' command  completion;  that
              is,  completion  attempted  on a command for which no completion
              has previously been defined.  The -E option indicates that other
              supplied  options  should apply to ``empty'' command completion;
              that is, completion attempted on a blank line.   The  -I  option
              indicates that other supplied options should apply to completion
              on the initial non-assignment word on the line, or after a  com-
              mand  delimiter  such  as  ; or |, which is usually command name
              completion.

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

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

       declare [-aAfFgiIlnrtux] [-p] [name[=value] ...]
       typeset [-aAfFgiIlnrtux] [-p] [name[=value] ...]
              Declare  variables and/or give them attributes.  If no names are
              given then display the values of variables.  The -p option  will
              display the attributes and values of each name.  When -p is used
              with name arguments, additional options, other than -f  and  -F,
              are  ignored.   When  -p  is supplied without name arguments, it
              will display the attributes and values of all  variables  having
              the attributes specified by the additional options.  If no other
              options are supplied with  -p,  declare  will  display  the  at-
              tributes  and values of all shell variables.  The -f option will
              restrict the display to shell functions.  The -F option inhibits
              the  display of function definitions; only the function name and
              attributes are printed.  If the extdebug shell option is enabled
              using  shopt,  the  source  file name and line number where each
              name is defined are displayed as well.  The  -F  option  implies
              -f.  The -g option forces variables to be created or modified at
              the global scope, even when declare is executed in a shell func-
              tion.   It  is ignored in all other cases.  The -I option causes
              local variables to inherit the attributes  (except  the  nameref
              attribute) and value of any existing variable with the same name
              at a surrounding scope.  If there is no existing  variable,  the
              local variable is initially unset.  The following options can be
              used to restrict output to variables with the  specified  attri-
              bute or to give variables attributes:
              -a     Each  name  is  an  indexed  array  variable  (see Arrays
                     above).
              -A     Each name is an associative array  variable  (see  Arrays
                     above).
              -f     Use function names only.
              -i     The variable is treated as an integer; arithmetic evalua-
                     tion (see ARITHMETIC EVALUATION above) is performed  when
                     the variable is assigned a value.
              -l     When  the  variable  is  assigned a value, all upper-case
                     characters are converted to lower-case.   The  upper-case
                     attribute is disabled.
              -n     Give  each  name  the nameref attribute, making it a name
                     reference to another variable.  That  other  variable  is
                     defined  by  the  value of name.  All references, assign-
                     ments, and attribute modifications to name, except  those
                     using  or changing the -n attribute itself, are performed
                     on the variable referenced by name's value.  The  nameref
                     attribute cannot be applied to array variables.
              -r     Make names readonly.  These names cannot then be assigned
                     values by subsequent assignment statements or unset.
              -t     Give each name the trace attribute.  Traced functions in-
                     herit  the DEBUG and RETURN traps from the calling shell.
                     The trace attribute has no special meaning for variables.
              -u     When the variable is assigned  a  value,  all  lower-case
                     characters  are  converted to upper-case.  The lower-case
                     attribute is disabled.
              -x     Mark names for export to subsequent commands via the  en-
                     vironment.

              Using  `+'  instead of `-' turns off the attribute instead, with
              the exceptions that +a and +A may not be used to  destroy  array
              variables  and  +r will not remove the readonly attribute.  When
              used in a function, declare and typeset make each name local, as
              with  the local command, unless the -g option is supplied.  If a
              variable name is followed by =value, the value of  the  variable
              is  set  to value.  When using -a or -A and the compound assign-
              ment syntax to create array variables, additional attributes  do
              not  take effect until subsequent assignments.  The return value
              is 0 unless an invalid option is encountered, an attempt is made
              to define a function using ``-f foo=bar'', an attempt is made to
              assign a value to a readonly variable, an attempt is made to as-
              sign a value to an array variable without using the compound as-
              signment 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  di-
              rectories.   The default display is on a single line with direc-
              tory names separated by spaces.  Directories are  added  to  the
              list  with  the  pushd command; the popd command removes entries
              from the list.  The current directory is always the first direc-
              tory in the stack.
              -c     Clears  the  directory  stack  by deleting all of the en-
                     tries.
              -l     Produces a listing  using  full  pathnames;  the  default
                     listing format uses a tilde to denote the home directory.
              -p     Print the directory stack with one entry per line.
              -v     Print  the  directory stack with one entry per line, pre-
                     fixing each entry with its index in the stack.
              +n     Displays the nth entry counting from the left of the list
                     shown by dirs when invoked without options, starting with
                     zero.
              -n     Displays the nth entry counting from  the  right  of  the
                     list shown by dirs when invoked without options, starting
                     with zero.

              The return value is 0 unless an invalid option is supplied or  n
              indexes beyond the end of the directory stack.

       disown [-ar] [-h] [jobspec ... | pid ... ]
              Without  options,  remove  each jobspec from the table of active
              jobs.  If jobspec is not present, and neither the -a nor the  -r
              option  is  supplied, the current job is used.  If the -h option
              is given, each jobspec is not removed from  the  table,  but  is
              marked  so  that  SIGHUP is not sent to the job if the shell re-
              ceives a SIGHUP.  If no jobspec is supplied, the -a option means
              to  remove or mark all jobs; the -r option without a jobspec ar-
              gument restricts operation to running jobs.  The return value is
              0 unless a jobspec does not specify a valid job.

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

       enable [-a] [-dnps] [-f filename] [name ...]
              Enable  and disable builtin shell commands.  Disabling a builtin
              allows a disk command which has the same name as a shell builtin
              to  be  executed without specifying a full pathname, even though
              the shell normally searches for builtins before  disk  commands.
              If  -n  is used, each name is disabled; otherwise, names are en-
              abled.  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.
              Bash will use the value of the BASH_LOADABLES_PATH variable as a
              colon-separated list of directories in which to search for file-
              name.  The default is  system-dependent.   The  -d  option  will
              delete  a  builtin  previously loaded with -f.  If no name argu-
              ments are given, or if the -p option  is  supplied,  a  list  of
              shell  builtins is printed.  With no other option arguments, the
              list consists of all enabled shell builtins.  If -n is supplied,
              only disabled builtins are printed.  If -a is supplied, the list
              printed includes all builtins, with an indication of whether  or
              not  each  is  enabled.   If  -s  is supplied, the output is re-
              stricted to the POSIX special builtins.  If no options are  sup-
              plied  and a name is not a shell builtin, enable will attempt to
              load name from a shared object named name,  as  if  the  command
              were  ``enable  -f  name  name .  The return value is 0 unless a
              name is not a shell builtin or there is an error loading  a  new
              builtin from a shared object.

       eval [arg ...]
              The  args  are read and concatenated together into a single com-
              mand.  This command is then read and executed by the shell,  and
              its  exit status is returned as the value of eval.  If there are
              no args, or only null arguments, eval returns 0.

       exec [-cl] [-a name] [command [arguments]]
              If command is specified, it replaces the shell.  No new  process
              is  created.  The arguments become the arguments to command.  If
              the -l option is supplied, the shell places a dash at the begin-
              ning of the zeroth argument passed to command.  This is what lo-
              gin(1) does.  The -c option causes command to be  executed  with
              an  empty environment.  If -a is supplied, the shell passes name
              as the zeroth argument to the executed command.  If command can-
              not  be executed for some reason, a non-interactive shell exits,
              unless the execfail shell option is enabled.  In that  case,  it
              returns  failure.   An  interactive shell returns failure if the
              file cannot be executed.  A subshell  exits  unconditionally  if
              exec  fails.  If command is not specified, any redirections take
              effect in the current shell, and the return  status  is  0.   If
              there is a redirection error, the return status is 1.

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

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

       fc [-e ename] [-lnr] [first] [last]
       fc -s [pat=rep] [cmd]
              The first form selects a range of commands from  first  to  last
              from  the  history  list  and  displays or edits and re-executes
              them.  First and last may be specified as a  string  (to  locate
              the  last command beginning with that string) or as a number (an
              index into the history list, where a negative number is used  as
              an  offset  from  the  current command number).  When listing, a
              first or last of 0 is equivalent to -1 and -0 is  equivalent  to
              the  current  command  (usually  the fc command); otherwise 0 is
              equivalent to -1 and -0 is invalid.  If last is  not  specified,
              it  is  set  to the current command for listing (so that ``fc -l
              -10'' prints the last 10 commands) and to first  otherwise.   If
              first  is  not  specified, it is set to the previous command for
              editing and -16 for listing.

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

              In  the  second form, command is re-executed after each instance
              of pat is replaced by rep.  Command is interpreted the  same  as
              first  above.  A useful alias to use with this is ``r="fc -s"'',
              so that typing ``r cc'' runs the  last  command  beginning  with
              ``cc'' and typing ``r'' re-executes the last command.

              If  the  first form is used, the return value is 0 unless an in-
              valid option is encountered or first  or  last  specify  history
              lines  out  of  range.  If the -e option is supplied, the return
              value is the value of the last command executed or failure if an
              error occurs with the temporary file of commands.  If the second
              form is used, the return status is that of the  command  re-exe-
              cuted,  unless  cmd  does  not  specify a valid history line, in
              which case fc returns failure.

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

       getopts optstring name [arg ...]
              getopts is used by shell procedures to parse positional  parame-
              ters.   optstring  contains  the  option characters to be recog-
              nized; if a character is followed by a colon, the option is  ex-
              pected to have an argument, which should be separated from it by
              white space.  The colon and question mark characters may not  be
              used  as  option  characters.   Each time it is invoked, getopts
              places the next option in the shell variable name,  initializing
              name if it does not exist, and the index of the next argument to
              be processed into the variable OPTIND.  OPTIND is initialized to
              1 each time the shell or a shell script is invoked.  When an op-
              tion requires an argument, getopts places that argument into the
              variable OPTARG.  The shell does not reset OPTIND automatically;
              it must be manually reset  between  multiple  calls  to  getopts
              within  the  same shell invocation if a new set of parameters is
              to be used.

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

              getopts normally parses the positional parameters, but  if  more
              arguments  are  supplied as arg values, getopts parses those in-
              stead.

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

              If 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 OP-
              TARG and no diagnostic message is printed.

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

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

       hash [-lr] [-p filename] [-dt] [name]
              Each time hash is invoked, the full pathname of the command name
              is  determined  by searching the directories in $PATH and remem-
              bered.  Any previously-remembered pathname is discarded.  If the
              -p option is supplied, no path search is performed, and filename
              is used as the full filename of  the  command.   The  -r  option
              causes the shell to forget all remembered locations.  The -d op-
              tion causes the shell to forget the remembered location of  each
              name.   If the -t option is supplied, the full pathname to which
              each name corresponds is printed.  If  multiple  name  arguments
              are supplied with -t, the name is printed before the hashed full
              pathname.  The -l option causes output to be displayed in a for-
              mat  that may be reused as input.  If no arguments are given, or
              if only -l is supplied, information about remembered commands is
              printed.   The  return status is true unless a name is not found
              or an invalid option is supplied.

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

              The return status is 0 unless no command matches pattern.

       history [n]
       history -c
       history -d offset
       history -d start-end
       history -anrw [filename]
       history -p arg [arg ...]
       history -s arg [arg ...]
              With no options, display the command history list with line num-
              bers.  Lines listed with a * have been modified.  An argument of
              n lists only the last n lines.  If the shell variable  HISTTIME-
              FORMAT  is  set  and not null, it is used as a format string for
              strftime(3) to display the time stamp associated with each  dis-
              played  history  entry.  No intervening blank is printed between
              the formatted time stamp and the history line.  If  filename  is
              supplied,  it  is  used as the name of the history file; if not,
              the value of HISTFILE is used.  Options, if supplied,  have  the
              following meanings:
              -c     Clear the history list by deleting all the entries.
              -d offset
                     Delete  the  history entry at position offset.  If offset
                     is negative, it is interpreted as relative to one greater
                     than the last history position, so negative indices count
                     back from the end of the history,  and  an  index  of  -1
                     refers to the current history -d command.
              -d start-end
                     Delete  the  range  of  history entries between positions
                     start and end, inclusive.  Positive and  negative  values
                     for start and end are interpreted as described above.
              -a     Append  the  ``new''  history  lines to the history file.
                     These are history lines entered since  the  beginning  of
                     the current bash session, but not already appended to the
                     history file.
              -n     Read the history lines not already read from the  history
                     file  into the current history list.  These are lines ap-
                     pended to the history file since  the  beginning  of  the
                     current bash session.
              -r     Read  the contents of the history file and append them to
                     the current history list.
              -w     Write the current history list to the history file, over-
                     writing the history file's contents.
              -p     Perform  history  substitution  on the following args and
                     display the result on  the  standard  output.   Does  not
                     store  the results in the history list.  Each arg must be
                     quoted to disable normal history expansion.
              -s     Store the args in the history list  as  a  single  entry.
                     The  last  command  in the history list is removed before
                     the args are added.

              If the HISTTIMEFORMAT variable is set, the time  stamp  informa-
              tion  associated  with each history entry is written to the his-
              tory file, marked with the history comment character.  When  the
              history  file  is read, lines beginning with the history comment
              character followed immediately by a  digit  are  interpreted  as
              timestamps for the following history entry.  The return value is
              0 unless an invalid option is encountered, an error occurs while
              reading  or writing the history file, an invalid offset or range
              is supplied as an argument to -d, or the history expansion  sup-
              plied as an argument to -p fails.

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

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

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

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

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

       local [option] [name[=value] ... | - ]
              For each argument, a local variable named name is  created,  and
              assigned  value.   The option can be any of the options accepted
              by declare.  When local is used within a function, it causes the
              variable  name  to have a visible scope restricted to that func-
              tion and its children.  If name is -, the set of  shell  options
              is  made  local to the function in which local is invoked: shell
              options changed using the set builtin inside  the  function  are
              restored  to  their  original  values when the function returns.
              The restore is effected as if a series of set commands were exe-
              cuted  to restore the values that were in place before the func-
              tion.  With no operands, local writes a list of local  variables
              to  the  standard  output.  It is an error to use local when not
              within a function.  The return status is 0 unless local is  used
              outside  a  function,  an invalid name is supplied, or name is a
              readonly variable.

       logout Exit a login shell.

       mapfile [-d delim] [-n count] [-O origin] [-s count] [-t] [-u  fd]  [-C
       callback] [-c quantum] [array]
       readarray [-d delim] [-n count] [-O origin] [-s count] [-t] [-u fd] [-C
       callback] [-c quantum] [array]
              Read lines from the standard input into the indexed array  vari-
              able  array, or from file descriptor fd if the -u option is sup-
              plied.  The variable MAPFILE is the default array.  Options,  if
              supplied, have the following meanings:
              -d     The  first  character  of delim is used to terminate each
                     input line, rather than newline.  If delim is  the  empty
                     string, mapfile will terminate a line when it reads a NUL
                     character.
              -n     Copy at most count lines.  If count is 0, all  lines  are
                     copied.
              -O     Begin  assigning  to  array at index origin.  The default
                     index is 0.
              -s     Discard the first count lines read.
              -t     Remove a trailing delim (default newline) from each  line
                     read.
              -u     Read  lines  from file descriptor fd instead of the stan-
                     dard input.
              -C     Evaluate callback each time quantum lines are read.   The
                     -c option specifies quantum.
              -c     Specify  the  number  of  lines read between each call to
                     callback.

              If -C is specified without -c,  the  default  quantum  is  5000.
              When callback is evaluated, it is supplied the index of the next
              array element to be assigned and the line to be assigned to that
              element  as  additional  arguments.  callback is evaluated after
              the line is read but before the array element is assigned.

              If not supplied with an explicit origin, mapfile will clear  ar-
              ray before assigning to it.

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

       popd [-n] [+n] [-n]
              Removes entries from the directory stack.  The elements are num-
              bered from 0 starting at the first  directory  listed  by  dirs.
              With  no  arguments,  popd  removes  the  top directory from the
              stack, and changes to the new top directory.  Arguments, if sup-
              plied, have the following meanings:
              -n     Suppresses  the  normal change of directory when removing
                     directories from the stack, so that only the stack is ma-
                     nipulated.
              +n     Removes  the nth entry counting from the left of the list
                     shown by dirs, starting with zero, from the  stack.   For
                     example:  ``popd +0'' removes the first directory, ``popd
                     +1'' the second.
              -n     Removes the nth entry counting from the right of the list
                     shown  by  dirs, starting with zero.  For example: ``popd
                     -0'' removes the last directory, ``popd -1'' the next  to
                     last.

              If  the  top element of the directory stack is modified, and the
              -n option was not supplied, popd uses the cd builtin  to  change
              to the directory at the top of the stack.  If the cd fails, popd
              returns a non-zero value.

              Otherwise, popd returns false if an invalid  option  is  encoun-
              tered, the directory stack is empty, or a non-existent directory
              stack entry is specified.

              If the popd command is successful, bash runs dirs  to  show  the
              final  contents of the directory stack, and the return status is
              0.

       printf [-v var] format [arguments]
              Write the formatted arguments to the standard output  under  the
              control  of  the  format.  The -v option causes the output to be
              assigned to the variable var rather than being  printed  to  the
              standard output.

              The  format  is a character string which contains three types of
              objects: plain characters, which are simply copied  to  standard
              output,  character  escape  sequences,  which  are converted and
              copied to the standard output, and format  specifications,  each
              of  which  causes  printing of the next successive argument.  In
              addition to the standard printf(1) format specifications, printf
              interprets the following extensions:
              %b     causes printf to expand backslash escape sequences in the
                     corresponding argument in the same way as echo -e.
              %q     causes printf to output the corresponding argument  in  a
                     format that can be reused as shell input.
              %Q     like  %q, but applies any supplied precision to the argu-
                     ment before quoting it.
              %(datefmt)T
                     causes printf to output the  date-time  string  resulting
                     from  using  datefmt  as a format string for strftime(3).
                     The corresponding argument is an integer representing the
                     number  of seconds since the epoch.  Two special argument
                     values may be used: -1 represents the current  time,  and
                     -2  represents the time the shell was invoked.  If no ar-
                     gument is specified, conversion behaves as if -1 had been
                     given.   This  is an exception to the usual printf behav-
                     ior.

              The %b, %q, and %T directives all use the field width and preci-
              sion arguments from the format specification and write that many
              bytes from (or use that wide a field for) the expanded argument,
              which usually contains more characters than the original.

              Arguments  to non-string format specifiers are treated as C con-
              stants, except that a leading plus or minus sign is allowed, and
              if  the leading character is a single or double quote, the value
              is the ASCII value of the following character.

              The format is reused as necessary to consume all  of  the  argu-
              ments.  If the format requires more arguments than are supplied,
              the extra format specifications behave as if  a  zero  value  or
              null  string,  as  appropriate,  had  been supplied.  The return
              value is zero on success, non-zero on failure.

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

              After the stack has been modified, if the -n option was not sup-
              plied,  pushd  uses the cd builtin to change to the directory at
              the top of the stack.  If the cd fails, pushd returns a non-zero
              value.

              Otherwise,  if no arguments are supplied, pushd returns 0 unless
              the directory stack  is  empty.   When  rotating  the  directory
              stack,  pushd returns 0 unless the directory stack is empty or a
              non-existent directory stack element is specified.

              If the pushd command is successful, bash runs dirs to  show  the
              final contents of the directory stack.

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

       read [-ers] [-a aname] [-d delim] [-i text] [-n nchars] [-N nchars] [-p
       prompt] [-t timeout] [-u fd] [name ...]
              One line is read from the standard input, or from the  file  de-
              scriptor fd supplied as an argument to the -u option, split into
              words as described above under Word  Splitting,  and  the  first
              word  is assigned to the first name, the second word to the sec-
              ond name, and so on.  If there are more words  than  names,  the
              remaining words and their intervening delimiters are assigned to
              the last name.  If there are fewer words  read  from  the  input
              stream  than  names, the remaining names are assigned empty val-
              ues.  The characters in IFS are used  to  split  the  line  into
              words  using  the  same  rules the shell uses for expansion (de-
              scribed above under Word Splitting).   The  backslash  character
              (\) may be used to remove any special meaning for the next char-
              acter read and for line  continuation.   Options,  if  supplied,
              have the following meanings:
              -a aname
                     The words are assigned to sequential indices of the array
                     variable aname, starting at 0.  aname is unset before any
                     new  values  are  assigned.  Other name arguments are ig-
                     nored.
              -d delim
                     The first character of delim is used to terminate the in-
                     put  line,  rather  than  newline.  If delim is the empty
                     string, read will terminate a line when it  reads  a  NUL
                     character.
              -e     If the standard input is coming from a terminal, readline
                     (see READLINE above) is used to obtain the  line.   Read-
                     line  uses  the  current (or default, if line editing was
                     not previously active) editing settings, but  uses  read-
                     line's default filename completion.
              -i text
                     If  readline  is  being  used  to  read the line, text is
                     placed into the editing buffer before editing begins.
              -n nchars
                     read returns after reading nchars characters rather  than
                     waiting for a complete line of input, but honors a delim-
                     iter if fewer than nchars characters are read before  the
                     delimiter.
              -N nchars
                     read  returns  after  reading  exactly  nchars characters
                     rather than waiting for a complete line of input,  unless
                     EOF  is encountered or read times out.  Delimiter charac-
                     ters encountered in the input are not  treated  specially
                     and  do  not cause read to return until nchars characters
                     are read.  The result is not split on the  characters  in
                     IFS;  the intent is that the variable is assigned exactly
                     the characters read (with the exception of backslash; see
                     the -r option below).
              -p prompt
                     Display prompt on standard error, without a trailing new-
                     line, before attempting to read any input.  The prompt is
                     displayed only if input is coming from a terminal.
              -r     Backslash does not act as an escape character.  The back-
                     slash is considered to be part of the line.  In  particu-
                     lar,  a  backslash-newline pair may not then be used as a
                     line continuation.
              -s     Silent mode.  If input is coming from a terminal, charac-
                     ters are not echoed.
              -t timeout
                     Cause  read  to time out and return failure if a complete
                     line of input (or a specified number  of  characters)  is
                     not  read within timeout seconds.  timeout may be a deci-
                     mal number with a fractional portion following the  deci-
                     mal  point.   This  option  is  only effective if read is
                     reading input from a terminal,  pipe,  or  other  special
                     file;  it  has no effect when reading from regular files.
                     If read times out, read saves any partial input read into
                     the  specified  variable name.  If timeout is 0, read re-
                     turns immediately, without trying to read any data.   The
                     exit  status  is 0 if input is available on the specified
                     file descriptor, or the read will  return  EOF,  non-zero
                     otherwise.   The  exit  status is greater than 128 if the
                     timeout is exceeded.
              -u fd  Read input from file descriptor fd.

              If no names are supplied, the line read, without the ending  de-
              limiter  but  otherwise  unmodified, is assigned to the variable
              REPLY.  The exit status is zero, unless end-of-file  is  encoun-
              tered,  read times out (in which case the status is greater than
              128), a variable assignment error (such as assigning to a  read-
              only variable) occurs, or an invalid file descriptor is supplied
              as the argument to -u.

       readonly [-aAf] [-p] [name[=word] ...]
              The given names are marked readonly; the values of  these  names
              may  not  be changed by subsequent assignment.  If the -f option
              is supplied, the functions corresponding to  the  names  are  so
              marked.   The  -a  option restricts the variables to indexed ar-
              rays; the -A option restricts the variables to  associative  ar-
              rays.  If both options are supplied, -A takes precedence.  If no
              name arguments are given, or if the -p  option  is  supplied,  a
              list of all readonly names is printed.  The other options may be
              used to restrict the output to a subset of the set  of  readonly
              names.   The -p option causes output to be displayed in a format
              that may be reused as input.  If a variable name is followed  by
              =word,  the  value  of  the variable is set to word.  The return
              status is 0 unless an invalid option is encountered, one of  the
              names is not a valid shell variable name, or -f is supplied with
              a name that is not a function.

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

       set [-abefhkmnptuvxBCEHPT] [-o option-name] [--] [-] [arg ...]
       set [+abefhkmnptuvxBCEHPT] [+o option-name] [--] [-] [arg ...]
              Without  options, display the name and value of each shell vari-
              able in a format that can be reused as input for setting or  re-
              setting the currently-set variables.  Read-only variables cannot
              be reset.  In posix mode, only shell variables are listed.   The
              output  is sorted according to the current locale.  When options
              are specified, they set or unset shell  attributes.   Any  argu-
              ments  remaining  after  option processing are treated as values
              for the positional parameters and are assigned, in order, to $1,
              $2,  ...   $n.   Options, if specified, have the following mean-
              ings:
              -a      Each variable or function that is created or modified is
                      given  the export attribute and marked for export to the
                      environment of subsequent commands.
              -b      Report the status of terminated background jobs  immedi-
                      ately, rather than before the next primary prompt.  This
                      is effective only when job control is enabled.
              -e      Exit immediately if a pipeline (which may consist  of  a
                      single  simple  command),  a list, or a compound command
                      (see SHELL GRAMMAR above), exits with a non-zero status.
                      The  shell  does  not  exit if the command that fails is
                      part of the command list immediately following  a  while
                      or  until  keyword, part of the test following the if or
                      elif reserved words, part of any command executed  in  a
                      &&  or || list except the command following the final &&
                      or ||, any command in a pipeline but the last, or if the
                      command's  return  value is being inverted with !.  If a
                      compound command other than a subshell  returns  a  non-
                      zero  status because a command failed while -e was being
                      ignored, the shell does not exit.  A  trap  on  ERR,  if
                      set,  is  executed  before the shell exits.  This option
                      applies to the shell environment and each subshell envi-
                      ronment  separately  (see  COMMAND EXECUTION ENVIRONMENT
                      above), and may cause subshells to exit before executing
                      all the commands in the subshell.

                      If  a  compound  command or shell function executes in a
                      context where -e is being ignored, none of the  commands
                      executed  within  the  compound command or function body
                      will be affected by the -e setting, even if  -e  is  set
                      and  a  command returns a failure status.  If a compound
                      command or shell function sets -e while executing  in  a
                      context  where -e is ignored, that setting will not have
                      any effect until the compound  command  or  the  command
                      containing the function call completes.
              -f      Disable pathname expansion.
              -h      Remember  the location of commands as they are looked up
                      for execution.  This is enabled by default.
              -k      All arguments in the form of assignment  statements  are
                      placed  in the environment for a command, not just those
                      that precede the command name.
              -m      Monitor mode.  Job control is enabled.  This  option  is
                      on  by  default  for  interactive shells on systems that
                      support it (see JOB CONTROL above).  All  processes  run
                      in a separate process group.  When a background job com-
                      pletes, the shell prints a line containing its exit sta-
                      tus.
              -n      Read commands but do not execute them.  This may be used
                      to check a shell script for syntax errors.  This is  ig-
                      nored by interactive shells.
              -o option-name
                      The option-name can be one of the following:
                      allexport
                              Same as -a.
                      braceexpand
                              Same as -B.
                      emacs   Use  an  emacs-style command line editing inter-
                              face.  This is enabled by default when the shell
                              is interactive, unless the shell is started with
                              the --noediting option.  This also  affects  the
                              editing interface used for read -e.
                      errexit Same as -e.
                      errtrace
                              Same as -E.
                      functrace
                              Same as -T.
                      hashall Same as -h.
                      histexpand
                              Same as -H.
                      history Enable command history, as described above under
                              HISTORY.  This option is on by default in inter-
                              active shells.
                      ignoreeof
                              The  effect  is  as  if  the shell command ``IG-
                              NOREEOF=10'' had been executed (see Shell  Vari-
                              ables above).
                      keyword Same as -k.
                      monitor Same as -m.
                      noclobber
                              Same as -C.
                      noexec  Same as -n.
                      noglob  Same as -f.
                      nolog   Currently ignored.
                      notify  Same as -b.
                      nounset Same as -u.
                      onecmd  Same as -t.
                      physical
                              Same as -P.
                      pipefail
                              If  set,  the  return value of a pipeline is the
                              value of the last (rightmost)  command  to  exit
                              with  a non-zero status, or zero if all commands
                              in the pipeline exit successfully.  This  option
                              is disabled by default.
                      posix   Change  the  behavior  of bash where the default
                              operation differs from  the  POSIX  standard  to
                              match  the  standard (posix mode).  See SEE ALSO
                              below for a reference to a document that details
                              how posix mode affects bash's behavior.
                      privileged
                              Same as -p.
                      verbose Same as -v.
                      vi      Use  a  vi-style command line editing interface.
                              This also affects the editing interface used for
                              read -e.
                      xtrace  Same as -x.
                      If -o is supplied with no option-name, the values of the
                      current options are printed.  If +o is supplied with  no
                      option-name,  a  series  of set commands to recreate the
                      current option settings is  displayed  on  the  standard
                      output.
              -p      Turn  on  privileged  mode.   In this mode, the $ENV and
                      $BASH_ENV files are not processed, shell  functions  are
                      not  inherited  from the environment, and the SHELLOPTS,
                      BASHOPTS, CDPATH, and GLOBIGNORE variables, if they  ap-
                      pear  in  the environment, are ignored.  If the shell is
                      started with the effective user (group) id not equal  to
                      the  real user (group) id, and the -p option is not sup-
                      plied, these actions are taken and the effective user id
                      is  set  to  the real user id.  If the -p option is sup-
                      plied at startup, the effective user id  is  not  reset.
                      Turning  this  option  off causes the effective user and
                      group ids to be set to the real user and group ids.
              -r      Enable restricted shell mode.  This option cannot be un-
                      set once it has been set.
              -t      Exit after reading and executing one command.
              -u      Treat unset variables and parameters other than the spe-
                      cial parameters "@" and "*",  or  array  variables  sub-
                      scripted  with  "@"  or "*", as an error when performing
                      parameter expansion.  If expansion is  attempted  on  an
                      unset  variable  or parameter, the shell prints an error
                      message, and, if not interactive, exits with a  non-zero
                      status.
              -v      Print shell input lines as they are read.
              -x      After  expanding  each simple command, for command, case
                      command, select command, or arithmetic for command, dis-
                      play  the expanded value of PS4, followed by the command
                      and its expanded arguments or associated word list.
              -B      The shell performs brace expansion (see Brace  Expansion
                      above).  This is on by default.
              -C      If  set,  bash  does not overwrite an existing file with
                      the >, >&, and <> redirection operators.   This  may  be
                      overridden when creating output files by using the redi-
                      rection operator >| instead of >.
              -E      If set, any trap on ERR is inherited by shell functions,
                      command  substitutions,  and commands executed in a sub-
                      shell environment.  The ERR trap is normally not  inher-
                      ited in such cases.
              -H      Enable !  style history substitution.  This option is on
                      by default when the shell is interactive.
              -P      If set, the shell does not resolve symbolic  links  when
                      executing  commands  such  as cd that change the current
                      working  directory.   It  uses  the  physical  directory
                      structure instead.  By default, bash follows the logical
                      chain of  directories  when  performing  commands  which
                      change the current directory.
              -T      If  set,  any traps on DEBUG and RETURN are inherited by
                      shell functions, command substitutions, and commands ex-
                      ecuted  in a subshell environment.  The DEBUG and RETURN
                      traps are normally not inherited in such cases.
              --      If no arguments follow this option, then the  positional
                      parameters are unset.  Otherwise, the positional parame-
                      ters are set to the args, even if  some  of  them  begin
                      with a -.
              -       Signal  the  end of options, cause all remaining args to
                      be assigned to the positional parameters.  The -x and -v
                      options are turned off.  If there are no args, the posi-
                      tional parameters remain unchanged.

              The options are off by default unless otherwise noted.  Using  +
              rather  than  -  causes these options to be turned off.  The op-
              tions can also be specified as arguments to an invocation of the
              shell.   The current set of options may be found in $-.  The re-
              turn status is always true unless an invalid option  is  encoun-
              tered.

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

       shopt [-pqsu] [-o] [optname ...]
              Toggle  the values of settings controlling optional shell behav-
              ior.  The settings can be either those listed below, or, if  the
              -o option is used, those available with the -o option to the set
              builtin command.  With no options, or with the -p option, a list
              of  all  settable  options  is  displayed, with an indication of
              whether or not each is set; if optnames are supplied, the output
              is  restricted to those options.  The -p option causes output to
              be displayed in a form that may be reused as input.   Other  op-
              tions have the following meanings:
              -s     Enable (set) each optname.
              -u     Disable (unset) each optname.
              -q     Suppresses  normal output (quiet mode); the return status
                     indicates whether the optname is set or unset.  If multi-
                     ple  optname arguments are given with -q, the return sta-
                     tus is zero if all optnames are enabled; non-zero  other-
                     wise.
              -o     Restricts  the  values of optname to be those defined for
                     the -o option to the set builtin.

              If either -s or -u is used  with  no  optname  arguments,  shopt
              shows  only  those options which are set or unset, respectively.
              Unless otherwise noted, the shopt options are  disabled  (unset)
              by default.

              The  return  status when listing options is zero if all optnames
              are enabled, non-zero otherwise.  When setting or unsetting  op-
              tions,  the  return  status  is  zero unless an optname is not a
              valid shell option.

              The list of shopt options is:

              assoc_expand_once
                      If set, the shell suppresses multiple evaluation of  as-
                      sociative  array subscripts during arithmetic expression
                      evaluation, while executing builtins  that  can  perform
                      variable  assignments, and while executing builtins that
                      perform array dereferencing.
              autocd  If set, a command name that is the name of  a  directory
                      is  executed  as  if it were the argument to the cd com-
                      mand.  This option is only used by interactive shells.
              cdable_vars
                      If set, an argument to the cd builtin  command  that  is
                      not  a directory is assumed to be the name of a variable
                      whose value is the directory to change to.
              cdspell If set, minor errors in the spelling of a directory com-
                      ponent  in  a  cd command will be corrected.  The errors
                      checked for are transposed characters, a missing charac-
                      ter,  and  one  character  too many.  If a correction is
                      found, the corrected filename is printed, and  the  com-
                      mand  proceeds.  This option is only used by interactive
                      shells.
              checkhash
                      If set, bash checks that a command found in the hash ta-
                      ble  exists  before  trying  to execute it.  If a hashed
                      command no longer exists, a normal path search  is  per-
                      formed.
              checkjobs
                      If set, bash lists the status of any stopped and running
                      jobs before exiting an interactive shell.  If  any  jobs
                      are running, this causes the exit to be deferred until a
                      second exit is attempted without an intervening  command
                      (see JOB CONTROL above).  The shell always postpones ex-
                      iting if any jobs are stopped.
              checkwinsize
                      If set, bash checks the window size after each  external
                      (non-builtin)  command  and,  if  necessary, updates the
                      values of LINES and COLUMNS.  This option is enabled  by
                      default.
              cmdhist If  set,  bash attempts to save all lines of a multiple-
                      line command in the same  history  entry.   This  allows
                      easy  re-editing of multi-line commands.  This option is
                      enabled by default, but only has an  effect  if  command
                      history is enabled, as described above under HISTORY.
              compat31
              compat32
              compat40
              compat41
              compat42
              compat43
              compat44
              compat50
                      These  control aspects of the shell's compatibility mode
                      (see SHELL COMPATIBILITY MODE below).

              complete_fullquote
                      If set, bash quotes all shell  metacharacters  in  file-
                      names  and  directory  names when performing completion.
                      If not set, bash removes metacharacters such as the dol-
                      lar  sign from the set of characters that will be quoted
                      in completed filenames when these metacharacters  appear
                      in  shell  variable references in words to be completed.
                      This means that dollar signs in variable names that  ex-
                      pand  to  directories  will  not be quoted; however, any
                      dollar signs appearing in filenames will not be  quoted,
                      either.   This  is  active only when bash is using back-
                      slashes to quote completed filenames.  This variable  is
                      set  by  default,  which is the default bash behavior in
                      versions through 4.2.

              direxpand
                      If set, bash replaces directory names with  the  results
                      of  word  expansion when performing filename completion.
                      This changes the contents of the readline  editing  buf-
                      fer.   If  not  set,  bash attempts to preserve what the
                      user typed.

              dirspell
                      If set, bash attempts spelling correction  on  directory
                      names  during word completion if the directory name ini-
                      tially supplied does not exist.

              dotglob If set, bash includes filenames beginning with a `.'  in
                      the  results of pathname expansion.  The filenames ``.''
                      and ``..''  must always be matched explicitly,  even  if
                      dotglob is set.

              execfail
                      If set, a non-interactive shell will not exit if it can-
                      not execute the file specified as  an  argument  to  the
                      exec  builtin  command.   An  interactive shell does not
                      exit if exec fails.

              expand_aliases
                      If set, aliases are expanded as  described  above  under
                      ALIASES.  This option is enabled by default for interac-
                      tive shells.

              extdebug
                      If set at shell invocation, or in a shell startup  file,
                      arrange to execute the debugger profile before the shell
                      starts, identical to the --debugger option.  If set  af-
                      ter  invocation,  behavior intended for use by debuggers
                      is enabled:

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

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

                      3.     If the command run by the DEBUG  trap  returns  a
                             value  of 2, and the shell is executing in a sub-
                             routine (a shell function or a shell script  exe-
                             cuted  by  the  .  or source builtins), the shell
                             simulates a call to return.

                      4.     BASH_ARGC and BASH_ARGV are updated as  described
                             in their descriptions above).

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

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

              extglob If set, the extended pattern matching features described
                      above under Pathname Expansion are enabled.

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

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

              force_fignore
                      If  set,  the  suffixes  specified  by the FIGNORE shell
                      variable cause words to be ignored when performing  word
                      completion even if the ignored words are the only possi-
                      ble completions.  See SHELL VARIABLES above  for  a  de-
                      scription  of  FIGNORE.   This  option is enabled by de-
                      fault.

              globasciiranges
                      If set,  range  expressions  used  in  pattern  matching
                      bracket  expressions (see Pattern Matching above) behave
                      as if in the traditional C locale when  performing  com-
                      parisons.   That  is, the current locale's collating se-
                      quence is not taken into account, so b will not  collate
                      between  A  and  B,  and upper-case and lower-case ASCII
                      characters will collate together.

              globskipdots
                      If set, pathname expansion will never  match  the  file-
                      names ``.''  and ``..'', even if the pattern begins with
                      a ``.''.  This option is enabled by default.

              globstar
                      If set, the pattern ** used in a pathname expansion con-
                      text  will  match all files and zero or more directories
                      and subdirectories.  If the pattern is followed by a  /,
                      only directories and subdirectories match.

              gnu_errfmt
                      If set, shell error messages are written in the standard
                      GNU error message format.

              histappend
                      If set, the history list is appended to the  file  named
                      by the value of the HISTFILE variable when the shell ex-
                      its, rather than overwriting the file.

              histreedit
                      If set, and readline is being used, a user is given  the
                      opportunity to re-edit a failed history substitution.

              histverify
                      If  set, and readline is being used, the results of his-
                      tory substitution are  not  immediately  passed  to  the
                      shell  parser.   Instead,  the  resulting line is loaded
                      into the readline editing buffer, allowing further modi-
                      fication.

              hostcomplete
                      If set, and readline is being used, bash will attempt to
                      perform hostname completion when a word containing  a  @
                      is   being  completed  (see  Completing  under  READLINE
                      above).  This is enabled by default.

              huponexit
                      If set, bash will send SIGHUP to all jobs when an inter-
                      active login shell exits.

              inherit_errexit
                      If  set,  command substitution inherits the value of the
                      errexit option, instead of unsetting it in the  subshell
                      environment.   This option is enabled when posix mode is
                      enabled.

              interactive_comments
                      If set, allow a word beginning with # to cause that word
                      and  all remaining characters on that line to be ignored
                      in an interactive shell (see COMMENTS above).  This  op-
                      tion is enabled by default.

              lastpipe
                      If  set,  and  job control is not active, the shell runs
                      the last command of a pipeline not executed in the back-
                      ground in the current shell environment.

              lithist If  set,  and  the cmdhist option is enabled, multi-line
                      commands are saved to the history with embedded newlines
                      rather than using semicolon separators where possible.

              localvar_inherit
                      If set, local variables inherit the value and attributes
                      of a variable of the same name that exists at a previous
                      scope before any new value is assigned.  The nameref at-
                      tribute is not inherited.

              localvar_unset
                      If set, calling unset on  local  variables  in  previous
                      function  scopes  marks  them so subsequent lookups find
                      them unset until that function returns. This is  identi-
                      cal  to the behavior of unsetting local variables at the
                      current function scope.

              login_shell
                      The shell sets this option if it is started as  a  login
                      shell  (see  INVOCATION  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 at-
                      tempt to search the PATH for possible  completions  when
                      completion is attempted on an empty line.

              nocaseglob
                      If  set,  bash  matches  filenames in a case-insensitive
                      fashion when performing pathname expansion (see Pathname
                      Expansion above).

              nocasematch
                      If  set,  bash  matches  patterns  in a case-insensitive
                      fashion when performing matching while executing case or
                      [[ conditional commands, when performing pattern substi-
                      tution word expansions, or when filtering possible  com-
                      pletions as part of programmable completion.

              noexpand_translation
                      If  set,  bash encloses the translated results of $"..."
                      quoting in single quotes instead of double  quotes.   If
                      the string is not translated, this has no effect.

              nullglob
                      If  set,  bash allows patterns which match no files (see
                      Pathname Expansion above) to expand to  a  null  string,
                      rather than themselves.

              patsub_replacement
                      If set, bash expands occurrences of & in the replacement
                      string of pattern substitution to the  text  matched  by
                      the  pattern,  as  described  under  Parameter Expansion
                      above.  This option is enabled by default.

              progcomp
                      If set, the programmable completion facilities (see Pro-
                      grammable Completion above) are enabled.  This option is
                      enabled by default.

              progcomp_alias
                      If set, and programmable  completion  is  enabled,  bash
                      treats  a command name that doesn't have any completions
                      as a possible alias and attempts alias expansion. If  it
                      has  an alias, bash attempts programmable completion us-
                      ing the command word resulting from the expanded alias.

              promptvars
                      If set, prompt strings undergo parameter expansion, com-
                      mand  substitution,  arithmetic expansion, and quote re-
                      moval after being expanded  as  described  in  PROMPTING
                      above.  This option is enabled by default.

              restricted_shell
                      The  shell  sets  this  option  if  it is started in re-
                      stricted 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.

              varredir_close
                      If  set, the shell automatically closes file descriptors
                      assigned using the {varname} redirection syntax (see RE-
                      DIRECTION  above)  instead of leaving them open when the
                      command completes.

              xpg_echo
                      If set, the echo builtin  expands  backslash-escape  se-
                      quences by default.

       suspend [-f]
              Suspend  the execution of this shell until it receives a SIGCONT
              signal.  A login shell, or a shell without job control  enabled,
              cannot  be suspended; the -f option can be used to override this
              and force the suspension.  The return status  is  0  unless  the
              shell  is  a login shell or job control is not enabled and -f is
              not supplied.

       test expr
       [ expr ]
              Return a status of 0 (true) or 1 (false) depending on the evalu-
              ation of the conditional expression expr.  Each operator and op-
              erand must be a separate argument.  Expressions are composed  of
              the  primaries  described  above  under CONDITIONAL EXPRESSIONS.
              test does not accept any options, nor does it accept and  ignore
              an argument of -- as signifying the end of options.

              Expressions  may  be  combined  using  the  following operators,
              listed in decreasing order of precedence.   The  evaluation  de-
              pends  on  the  number of arguments; see below.  Operator prece-
              dence is used when there are five or more arguments.
              ! expr True if expr is false.
              ( expr )
                     Returns the value of expr.  This may be used to  override
                     the normal precedence of operators.
              expr1 -a expr2
                     True if both expr1 and expr2 are true.
              expr1 -o expr2
                     True if either expr1 or expr2 is true.

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

              0 arguments
                     The expression is false.
              1 argument
                     The expression is true if and only if the argument is not
                     null.
              2 arguments
                     If the first argument is !, the expression is true if and
                     only if the second argument is null.  If the first  argu-
                     ment  is  one  of  the unary conditional operators listed
                     above under CONDITIONAL EXPRESSIONS,  the  expression  is
                     true if the unary test is true.  If the first argument is
                     not a valid unary conditional operator, the expression is
                     false.
              3 arguments
                     The following conditions are applied in the order listed.
                     If the second argument is one of the  binary  conditional
                     operators listed above under CONDITIONAL EXPRESSIONS, the
                     result of the expression is the result of the binary test
                     using  the first and third arguments as operands.  The -a
                     and -o operators are  considered  binary  operators  when
                     there  are  three arguments.  If the first argument is !,
                     the value is the negation of the two-argument test  using
                     the second and third arguments.  If the first argument is
                     exactly ( and the third argument is exactly ), the result
                     is  the one-argument test of the second argument.  Other-
                     wise, the expression is false.
              4 arguments
                     The following conditions are applied in the order listed.
                     If the first argument is !, the result is the negation of
                     the three-argument expression composed of  the  remaining
                     arguments.   the  two-argument  test using the second and
                     third arguments.  If the first argument is exactly (  and
                     the  fourth argument is exactly ), the result is the two-
                     argument test of the second and third arguments.   Other-
                     wise, the expression is parsed and evaluated according to
                     precedence using the rules listed above.
              5 or more arguments
                     The expression  is  parsed  and  evaluated  according  to
                     precedence using the rules listed above.

              When  used  with  test  or [, the < and > operators sort lexico-
              graphically using ASCII ordering.

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

       trap [-lp] [[arg] sigspec ...]
              The  command  arg  is to be read and executed when the shell re-
              ceives signal(s) sigspec.  If arg is absent (and there is a sin-
              gle  sigspec) or -, each specified signal is reset to its origi-
              nal 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 com-
              mands associated with each signal.  The  -l  option  causes  the
              shell  to  print  a list of signal names and their corresponding
              numbers.  Each sigspec is either a signal name defined in  <sig-
              nal.h>,  or  a signal number.  Signal names are case insensitive
              and the SIG prefix is optional.

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

              If  a  sigspec  is  ERR,  the command arg is executed whenever a
              pipeline (which may consist of a single simple command), a list,
              or a compound command returns a non-zero exit status, subject to
              the following conditions.  The ERR trap is not executed  if  the
              failed command is part of the command list immediately following
              a while or until keyword, part of the test in an  if  statement,
              part of a command executed in a && or || list except the command
              following the final && or ||, any command in a pipeline but  the
              last,  or  if the command's return value is being inverted using
              !.  These are the same conditions obeyed by the errexit (-e) op-
              tion.

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

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

       ulimit [-HS] -a
       ulimit [-HS] [-bcdefiklmnpqrstuvxPRT [limit]]
              Provides  control  over the resources available to the shell and
              to processes started by it, on systems that allow such  control.
              The -H and -S options specify that the hard or soft limit is set
              for the given resource.  A hard limit cannot be increased  by  a
              non-root  user  once it is set; a soft limit may be increased up
              to the value of the hard limit.  If neither -H nor -S is  speci-
              fied, both the soft and hard limits are set.  The value of limit
              can be a number in the unit specified for the resource or one of
              the special values hard, soft, or unlimited, which stand for the
              current hard limit, the current soft limit, and  no  limit,  re-
              spectively.   If limit is omitted, the current value of the soft
              limit of the resource is printed, unless the -H option is given.
              When  more  than  one  resource is specified, the limit name and
              unit, if appropriate, are printed before the value.   Other  op-
              tions are interpreted as follows:
              -a     All current limits are reported; no limits are set
              -b     The maximum socket buffer size
              -c     The maximum size of core files created
              -d     The maximum size of a process's data segment
              -e     The maximum scheduling priority ("nice")
              -f     The  maximum  size  of files written by the shell and its
                     children
              -i     The maximum number of pending signals
              -k     The maximum number of kqueues that may be allocated
              -l     The maximum size that may be locked into memory
              -m     The maximum resident set size (many systems do not  honor
                     this limit)
              -n     The maximum number of open file descriptors (most systems
                     do not allow this value to be set)
              -p     The pipe size in 512-byte blocks (this may not be set)
              -q     The maximum number of bytes in POSIX message queues
              -r     The maximum real-time scheduling priority
              -s     The maximum stack size
              -t     The maximum amount of cpu time in seconds
              -u     The maximum number of processes  available  to  a  single
                     user
              -v     The  maximum  amount  of  virtual memory available to the
                     shell and, on some systems, to its children
              -x     The maximum number of file locks
              -P     The maximum number of pseudoterminals
              -R     The maximum time  a  real-time  process  can  run  before
                     blocking, in microseconds
              -T     The maximum number of threads

              If  limit  is given, and the -a option is not used, limit is the
              new value of the specified resource.  If  no  option  is  given,
              then  -f is assumed.  Values are in 1024-byte increments, except
              for -t, which is in seconds; -R, which is in  microseconds;  -p,
              which  is  in  units of 512-byte blocks; -P, -T, -b, -k, -n, and
              -u, which are unscaled values; and, when in posix mode,  -c  and
              -f,  which  are  in 512-byte increments.  The return status is 0
              unless an invalid option or argument is supplied,  or  an  error
              occurs while setting a new limit.

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

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

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

       wait [-fn] [-p varname] [id ...]
              Wait for each specified child process and return its termination
              status.  Each id may be a process ID or a job specification;  if
              a  job  spec  is given, all processes in that job's pipeline are
              waited for.  If id is not given,  wait  waits  for  all  running
              background  jobs  and the last-executed process substitution, if
              its process id is the same as $!, and the return status is zero.
              If  the  -n option is supplied, wait waits for a single job from
              the list of ids or, if no ids are supplied, any job, to complete
              and  returns its exit status.  If none of the supplied arguments
              is a child of the shell, or if no arguments are supplied and the
              shell  has no unwaited-for children, the exit status is 127.  If
              the -p option is supplied, the process or job identifier of  the
              job  for  which  the  exit status is returned is assigned to the
              variable varname named by the  option  argument.   The  variable
              will  be unset initially, before any assignment.  This is useful
              only when the -n option is supplied.  Supplying the  -f  option,
              when  job control is enabled, forces wait to wait for id to ter-
              minate before returning its status, instead of returning when it
              changes  status.  If id specifies a non-existent process or job,
              the return status is 127.  If wait is interrupted by  a  signal,
              the  return  status will be greater than 128, as described under
              SIGNALS above.  Otherwise, the return status is the exit  status
              of the last process or job waited for.

SHELL COMPATIBILITY MODE
       Bash-4.0  introduced the concept of a shell compatibility level, speci-
       fied as a set of options to the shopt  builtin  (  compat31,  compat32,
       compat40,  compat41, and so on).  There is only one current compatibil-
       ity level -- each option  is  mutually  exclusive.   The  compatibility
       level  is intended to allow users to select behavior from previous ver-
       sions that is incompatible  with  newer  versions  while  they  migrate
       scripts  to  use  current  features and behavior. It's intended to be a
       temporary solution.

       This section does not mention behavior that is standard for a  particu-
       lar  version  (e.g., setting compat32 means that quoting the rhs of the
       regexp matching operator quotes special regexp characters in the  word,
       which is default behavior in bash-3.2 and subsequent versions).

       If  a  user enables, say, compat32, it may affect the behavior of other
       compatibility levels up to  and  including  the  current  compatibility
       level.   The  idea  is  that each compatibility level controls behavior
       that changed in that version of bash, but that behavior may  have  been
       present  in  earlier versions.  For instance, the change to use locale-
       based comparisons with the [[ command came  in  bash-4.1,  and  earlier
       versions used ASCII-based comparisons, so enabling compat32 will enable
       ASCII-based comparisons as well.  That granularity may  not  be  suffi-
       cient  for  all uses, and as a result users should employ compatibility
       levels carefully.  Read the documentation for a particular  feature  to
       find out the current behavior.

       Bash-4.3  introduced  a new shell variable: BASH_COMPAT.  The value as-
       signed to this variable (a decimal version number like 4.2, or an inte-
       ger  corresponding to the compatNN option, like 42) determines the com-
       patibility level.

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

       Bash-5.0 is the final version for which there  will  be  an  individual
       shopt  option for the previous version. Users should use BASH_COMPAT on
       bash-5.0 and later versions.

       The following table describes the behavior changes controlled  by  each
       compatibility level setting.  The compatNN tag is used as shorthand for
       setting the compatibility level to NN using one of the following mecha-
       nisms.   For versions prior to bash-5.0, the compatibility level may be
       set using the corresponding compatNN shopt option.   For  bash-4.3  and
       later  versions,  the  BASH_COMPAT variable is preferred, and it is re-
       quired for bash-5.1 and later versions.

       compat31
              o      quoting the rhs of the [[ command's regexp matching oper-
                     ator (=~) has no special effect

       compat32
              o      interrupting  a  command  list such as "a ; b ; c" causes
                     the execution  of  the  next  command  in  the  list  (in
                     bash-4.0  and later versions, the shell acts as if it re-
                     ceived the interrupt, so interrupting one  command  in  a
                     list aborts the execution of the entire list)

       compat40
              o      the  <  and > operators to the [[ command do not consider
                     the current locale when comparing strings; they use ASCII
                     ordering.  Bash versions prior to bash-4.1 use ASCII col-
                     lation and strcmp(3); bash-4.1 and later use the  current
                     locale's collation sequence and strcoll(3).

       compat41
              o      in  posix mode, time may be followed by options and still
                     be recognized as a reserved word (this is POSIX interpre-
                     tation 267)
              o      in posix mode, the parser requires that an even number of
                     single quotes occur in the  word  portion  of  a  double-
                     quoted  parameter expansion and treats them specially, so
                     that characters within the single quotes  are  considered
                     quoted (this is POSIX interpretation 221)

       compat42
              o      the replacement string in double-quoted pattern substitu-
                     tion does not undergo quote removal, as it does  in  ver-
                     sions after bash-4.2
              o      in  posix mode, single quotes are considered special when
                     expanding the word portion of a  double-quoted  parameter
                     expansion  and  can  be  used to quote a closing brace or
                     other special character (this is part of POSIX  interpre-
                     tation  221);  in  later  versions, single quotes are not
                     special within double-quoted word expansions

       compat43
              o      the shell does not print a warning message if an  attempt
                     is  made  to use a quoted compound assignment as an argu-
                     ment to declare (e.g., declare  -a  foo='(1  2)').  Later
                     versions warn that this usage is deprecated
              o      word  expansion  errors  are  considered non-fatal errors
                     that cause the current command to  fail,  even  in  posix
                     mode  (the  default behavior is to make them fatal errors
                     that cause the shell to exit)
              o      when  executing  a  shell  function,   the   loop   state
                     (while/until/etc.)  is not reset, so break or continue in
                     that function will break or continue loops in the calling
                     context.  Bash-4.4 and later reset the loop state to pre-
                     vent this

       compat44
              o      the shell sets  up  the  values  used  by  BASH_ARGV  and
                     BASH_ARGC  so  they  can expand to the shell's positional
                     parameters even if extended debugging mode is not enabled
              o      a subshell inherits loops from  its  parent  context,  so
                     break  or  continue  will  cause  the  subshell  to exit.
                     Bash-5.0 and later reset the loop state  to  prevent  the
                     exit
              o      variable  assignments  preceding builtins like export and
                     readonly that set attributes continue to affect variables
                     with the same name in the calling environment even if the
                     shell is not in posix mode

       compat50
              o      Bash-5.1 changed the way $RANDOM is generated  to  intro-
                     duce slightly more randomness. If the shell compatibility
                     level is set to 50 or lower, it  reverts  to  the  method
                     from  bash-5.0 and previous versions, so seeding the ran-
                     dom number generator by assigning a value to RANDOM  will
                     produce the same sequence as in bash-5.0
              o      If  the  command hash table is empty, bash versions prior
                     to bash-5.1 printed an informational message to that  ef-
                     fect,  even  when  producing output that can be reused as
                     input. Bash-5.1 suppresses that message when the  -l  op-
                     tion is supplied.

       compat51
              o      The  unset  builtin  treats  attempts to unset array sub-
                     scripts @ and * differently depending on whether the  ar-
                     ray  is  indexed  or associative, and differently than in
                     previous versions.

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:

       o      changing directories with cd

       o      setting or unsetting the values of SHELL, PATH,  HISTFILE,  ENV,
              or BASH_ENV

       o      specifying command names containing /

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

       o      specifying a filename containing a slash as an argument  to  the
              history builtin command

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

       o      importing function definitions from  the  shell  environment  at
              startup

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

       o      redirecting output using the >, >|, <>, >&, &>, and >> redirect-
              ion operators

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

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

       o      using  the  enable  builtin  command  to  enable  disabled shell
              builtins

       o      specifying the -p option to the command builtin command

       o      turning off  restricted  mode  with  set  +r  or  shopt  -u  re-
              stricted_shell.

       These restrictions are enforced after any startup files are read.

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

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

FILES
       /bin/bash
              The bash executable
       /etc/profile
              The systemwide initialization file, executed for login shells
       ~/.bash_profile
              The personal initialization file, executed for login shells
       ~/.bashrc
              The individual per-interactive-shell startup file
       ~/.bash_logout
              The individual login shell cleanup file, executed when  a  login
              shell exits
       ~/.bash_history
              The  default value of HISTFILE, the file in which bash saves the
              command history
       ~/.inputrc
              Individual readline initialization file

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

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

BUG REPORTS
       If you find a bug in bash, you should report it.  But first, you should
       make  sure  that  it really is a bug, and that it appears in the latest
       version  of  bash.   The  latest  version  is  always  available   from
       ftp://ftp.gnu.org/pub/gnu/bash/          and          http://git.savan-
       nah.gnu.org/cgit/bash.git/snapshot/bash-master.tar.gz.

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

       ALL bug reports should include:

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

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

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

BUGS
       It's too big and too slow.

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

       Aliases are confusing in some uses.

       Shell builtin commands and functions are not stoppable/restartable.

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

       Array variables may not (yet) be exported.

       There may be only one active coprocess at a time.



GNU Bash 5.2                   2022 September 19                       BASH(1)
