BASH(1)                     General Commands Manual                    BASH(1)

NAME
       bash - GNU Bourne-Again SHell

SYNOPSIS
       bash [options] [command_string | file]

COPYRIGHT
       Bash is Copyright (C) 1989-2025 by the Free Software Foundation, Inc.

DESCRIPTION
       Bash is a command language interpreter that executes commands read from
       the standard input, from a string, or from a file.  It is a reimplemen-
       tation  and  extension of the Bourne shell, the historical Unix command
       language interpreter.  Bash also incorporates useful features from  the
       Korn and C shells (ksh and csh).

       POSIX  is  the  name for a family of computing standards based on Unix.
       Bash is intended to be a conformant implementation  of  the  Shell  and
       Utilities  portion  of  the  IEEE  POSIX  specification  (IEEE Standard
       1003.1).  Bash POSIX mode (hereafter referred to as posix mode) changes
       the shell's behavior where its default operation differs from the stan-
       dard to strictly conform to the standard.  See SEE  ALSO  below  for  a
       reference  to a document that details how posix mode affects bash's be-
       havior.  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, the shell reads commands 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        Print  a  list  of all double-quoted strings preceded by $ on
                 the standard output.  These are the strings that are  subject
                 to  language  translation when the current locale is not C or
                 POSIX.  This implies the -n option; no commands will be  exe-
                 cuted.

       [-+]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, bash prints the
                 names and values of the shell options accepted  by  shopt  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 a
                 shell script filename (see below)  and  arguments  passed  to
                 that script.  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"
              (portable 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
              Enable posix mode; change the behavior of bash where the default
              operation differs from the POSIX standard to match the standard.

       --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 treated as the  name
       of a file containing shell commands (a shell script).  When bash is in-
       voked in this fashion, $0 is set to the name of the file, and the posi-
       tional  parameters  are set to the remaining arguments.  Bash reads and
       executes commands from this file, then exits.  Bash's  exit  status  is
       the exit status of the last command executed in the script.  If no com-
       mands  are executed, the exit status is 0.  Bash first attempts to open
       the file in the current directory, and, if no file is  found,  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, and whose standard in-
       put  and  standard error are both connected to terminals (as determined
       by isatty(3)), or one started with the -i option.  Bash sets PS1 and $-
       includes i if the shell is interactive, so a shell script or a  startup
       file can 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.  The
       --norc option inhibits this behavior.  The --rcfile file option  causes
       bash to use 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 does not use the value of the PATH variable 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 inhibits this behav-
       ior.  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 execute commands  from
       any  other startup files, the --rcfile option has no effect.  A non-in-
       teractive shell invoked with the name sh does not attempt to  read  any
       other startup files.

       When  invoked  as  sh, bash enters posix mode after reading the startup
       files.

       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 read and execute com-
       mands 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
       and  rarely-seen 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.  Bash does not read this file  if  invoked
       as  sh.  The --norc option inhibits this behavior, and the --rcfile op-
       tion makes bash use a different file instead of ~/.bashrc, 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.
       whitespace
              A character belonging to the space character class in  the  cur-
              rent locale, or for which isspace(3) returns true.
       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 the
       pipeline operator, command1's standard error, in addition to its  stan-
       dard  output,  is  connected  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 redirec-
       tions specified by command1.

       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.  If a pipeline is executed synchronously, the  shell  waits  for
       all commands in the pipeline to terminate before returning a value.

       If  the  time  reserved word precedes a pipeline, the shell reports the
       elapsed as well as user and system time consumed by its execution  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
       recognize  time as a reserved word if the next token begins with a "-".
       The value of the TIMEFORMAT variable is a format string that  specifies
       how  the timing information should be displayed; see the description of
       TIMEFORMAT below under Shell Variables.

       When the shell is in posix mode, time may appear by itself as the  only
       word  in  a simple command.  In this case, the shell displays the total
       user and system time consumed by the shell and its children.  The TIME-
       FORMAT variable specifies 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), and job control  is  not  active,
       the last element of a pipeline may be run by the shell process.

   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 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  re-
              served  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 arithmetic expression is evaluated according  to  the  rules
              described  below  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 ex-
              pansions as if it were within double quotes, but unescaped  dou-
              ble quote characters in expression are not treated specially and
              are  removed.   Since  this  can  potentially  result  in  empty
              strings, this command treats those as expressions that  evaluate
              to 0.

       [[ expression ]]
              Evaluate the conditional expression expression and return a sta-
              tus  of  zero  (true) or non-zero (false).  Expressions are com-
              posed of the primaries described below under CONDITIONAL EXPRES-
              SIONS.  The words between the [[ and  ]]  do  not  undergo  word
              splitting  and pathname expansion.  The shell performs tilde ex-
              pansion, parameter and variable expansion, arithmetic expansion,
              command substitution, process substitution, and quote removal on
              those words.  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.  If  any  part  of  the
              pattern  is  quoted,  the quoted portion is matched as a string:
              every character in the quoted portion matches itself, instead of
              having any special pattern matching meaning.

              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,  as  above.   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 normal quoting and pattern
              characters lose their meanings between brackets.

              The match succeeds if  the  pattern  matches  any  part  of  the
              string.  Anchor the pattern using the ^ and $ regular expression
              operators to force it to match the entire string.

              The  array  variable  BASH_REMATCH  records  which  parts of the
              string matched the pattern.  The element  of  BASH_REMATCH  with
              index  0  contains the portion of the string matching the entire
              regular expression.  Substrings matched by parenthesized  subex-
              pressions within the regular expression are saved in the remain-
              ing  BASH_REMATCH indices.  The element of BASH_REMATCH with in-
              dex n is the portion of the string matching  the  nth  parenthe-
              sized  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
              First, expand The list of words following in, generating a  list
              of  items.   Then,  the  variable name is set to each element of
              this list in turn, and list is executed each time.   If  the  in
              word is omitted, the for command executes list once for each po-
              sitional  parameter that is set (see PARAMETERS below).  The re-
              turn status is the exit status of the  last  command  that  exe-
              cutes.  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, evaluate the arithmetic expression expr1 according to the
              rules described below under ARITHMETIC  EVALUATION.   Then,  re-
              peatedly evaluate the arithmetic expression expr2 until it eval-
              uates  to  zero.  Each time expr2 evaluates to a non-zero value,
              execute list and evaluate the arithmetic expression  expr3.   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 non-zero if any of the expressions is in-
              valid.

              Use the break and continue builtins (see SHELL BUILTIN  COMMANDS
              below) to control loop execution.

       select name [ in word ] ; do list ; done
              First,  expand the list of words following in, generating a list
              of items, and print the set of expanded words the  standard  er-
              ror,  each  preceded  by  a  number.  If the in word is omitted,
              print the positional parameters (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 select sets the value of name to  that
              word.   If  the  line  is  empty,  select displays the words and
              prompt again.  If EOF is read, select completes and  returns  1.
              Any  other  value  sets name to null.  The line read is saved in
              the variable REPLY.  The list is executed after  each  selection
              until a break command is executed.  The exit status of select is
              the exit status of the last command executed in list, or zero if
              no commands were executed.

       case word in [ [(] pattern [ | pattern ] ... ) list ;; ] ... esac
              A case command first expands word, and tries to match it against
              each  pattern  in turn, proceeding from first to last, using the
              matching rules described under Pattern Matching below.   A  pat-
              tern  list  is  a set of one or more patterns separated by , and
              the ) operator terminates the pattern list.   The  word  is  ex-
              panded  using tilde expansion, parameter and variable expansion,
              arithmetic expansion, command substitution, process substitution
              and quote removal.  Each  pattern  examined  is  expanded  using
              tilde  expansion,  parameter  and variable expansion, arithmetic
              expansion, command substitution, process substitution, and quote
              removal.  If the nocasematch shell option is enabled, the  match
              is  performed  without  regard to the case of alphabetic charac-
              ters.  A clause is a pattern list and an associated list.

              When a match is found, case executes the corresponding list.  If
              the ;; operator terminates the case  clause,  the  case  command
              completes after the first match.  Using ;& in place of ;; causes
              execution  to  continue  with  the list associated with the next
              pattern list.  Using ;;& in place of ;; causes the shell to test
              the next pattern list in the statement, if any, and execute  any
              associated  list  if  the  match  succeeds,  continuing the case
              statement execution 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
              the last list executed.

       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 preferred because simple commands result in the  coprocess
       always  being  named COPROC, and it is simpler to use and more complete
       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  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) specified when a  function  is
       defined are performed when the function is executed.

       The  exit status of a function definition is zero unless a syntax error
       occurs or a readonly function with the same name already exists.   When
       executed,  the exit status of a function is the exit status of the last
       command executed in the body.  (See FUNCTIONS below.)

COMMENTS
       In a non-interactive shell, or an interactive shell in which the inter-
       active_comments option to the  shopt  builtin  is  enabled  (see  SHELL
       BUILTIN  COMMANDS below), a word beginning with # introduces a comment.
       A word begins at the beginning of a line, after unquoted whitespace, or
       after an operator.  The comment 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  enabled  by  default  in  interactive
       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 four quoting mechanisms: the escape character, single quotes,
       double quotes, and dollar-single quotes.

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

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

       Enclosing characters in double quotes preserves the  literal  value  of
       all  characters  within the quotes, with the exception of $, `, \, and,
       when history expansion is enabled, !.  When the shell is in posix mode,
       the ! has no special meaning within double quotes,  even  when  history
       expansion  is  enabled.   The  characters  $ and ` retain their special
       meaning within double quotes.  The backslash retains its special  mean-
       ing  only when followed by one of the following characters: $, `, ", \,
       or <newline>.  Backslashes preceding characters without a special mean-
       ing are left unmodified.

       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 back-
       slash 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.

   Translating Strings
       A double-quoted string preceded by a dollar sign ($"string") causes the
       string to be translated according to the current locale.   The  gettext
       infrastructure  performs  the lookup and translation, using the LC_MES-
       SAGES, 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, and the string is
       treated  as double-quoted as described above.  This is a form of double
       quoting, so the string remains double-quoted by default, whether or not
       it is translated and replaced.  If the noexpand_translation  option  is
       enabled  using  the shopt builtin, translated strings are single-quoted
       instead of double-quoted.  See the description  of  shopt  below  under
       SHELL BUILTIN COMMANDS.

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  Para-
       meters.  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).
       The export and readonly builtins assign specific attributes.

       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 is assigned to using 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 appends to or adds to
       the variable's previous value.  This includes arguments to  declaration
       commands  such as declare that accept assignment statements.  When "+="
       is applied to a variable for which the integer attribute has been  set,
       the variable's current value and value are each evaluated as arithmetic
       expressions,  and  the sum of the results is assigned as the variable's
       value.  The current value is usually an integer constant, but may be an
       expression.  When "+=" is applied to an array variable  using  compound
       assignment (see Arrays below), the variable's value is not unset (as it
       is when using and new values are appended to the array beginning at one
       greater than the array's maximum index (for indexed arrays) or added as
       additional  key-value pairs in an associative array.  When applied to a
       string-valued variable, value is expanded and  appended  to  the  vari-
       able'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 local nameref variable ref whose value is
       the variable name passed as the first argument.  References and assign-
       ments to ref, and changes to its attributes, are treated as references,
       assignments, and attribute modifications to the variable whose name was
       passed  as  $1.   If the control variable in a for loop has the nameref
       attribute, the list of words can be a list of shell  variables,  and  a
       name  reference is established for each word in the list, in turn, when
       the loop is executed.  Array variables cannot be given the nameref  at-
       tribute.   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 is unset.

       When  the  shell  starts,  it reads its environment and creates a shell
       variable from each environment variable that has a valid name,  as  de-
       scribed below (see ENVIRONMENT).

   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).  Without
       braces, a digit following $ can only refer to one of the first nine po-
       sitional parameters ($1-$9) or the special parameter $0 (see  the  next
       section).

   Special Parameters
       The  shell  treats  several parameters specially.  These parameters may
       only be referenced; assignment to them is not allowed.  Special parame-
       ters are denoted by one of the following characters.

       *      ($*) Expands to the positional parameters,  starting  from  one.
              When  the expansion is not within double quotes, each positional
              parameter expands to a separate word.  In  contexts  where  word
              expansions  are  performed,  those  words are subject to further
              word splitting and pathname expansion.  When the  expansion  oc-
              curs  within double quotes, it expands to a single word with the
              value of each parameter separated by the first character of  the
              IFS variable.  That is, "$*" 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, such as the value portion
              of  an  assignment statement, this expands to a single word with
              each positional parameter separated by a space.  When the expan-
              sion occurs within double quotes, and  word  splitting  is  per-
              formed,  each  parameter  expands  to a separate word.  That is,
              "$@" is equivalent to "$1" "$2" ...  If the double-quoted expan-
              sion occurs within a word, the expansion of the first  parameter
              is joined with the expansion of the beginning part of the origi-
              nal word, and the expansion of the last parameter is joined with
              the expansion of the last part of the original word.  When there
              are  no  positional  parameters,  "$@"  and $@ expand to nothing
              (i.e., they are removed).
       #      ($#) Expands to the number of positional parameters in decimal.
       ?      ($?) Expands to the exit status of the  most  recently  executed
              command.
       -      ($-) Expands to the current option flags as specified upon invo-
              cation,  by  the  set builtin command, or those set by the shell
              itself (such as the -i option).
       $      ($$) Expands to the process ID of the shell.  In a subshell,  it
              expands to the process ID of the parent 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      ($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
              commands, $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 argu-
              ment zero.

   Shell Variables
       The shell sets following variables:

       _      ($_, an underscore) This has a number of meanings  depending  on
              context.  At shell startup, _ is set to the pathname used to in-
              voke  the  shell or shell script being executed as passed in the
              environment or argument list.  Subsequently, it expands  to  the
              last  argument  to  the  previous simple command executed in the
              foreground, after expansion.  It is also set to the  full  path-
              name  used to invoke each command executed and placed in the en-
              vironment exported to that command.  When checking mail, $_  ex-
              pands to 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, the
              shell enables each option in the list before reading any startup
              files.  If this variable is exported, child shells  will  enable
              each option in the list.  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 remove aliases  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.  Assignments to BASH_ARGC have no effect, and it may not be
              unset.
       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 shell pushes the supplied parameters onto  BASH_ARGV.
              The  shell  sets  BASH_ARGV only when in extended debugging mode
              (see the description of the extdebug option to the shopt builtin
              below).  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.   Assignments  to  BASH_ARGV
              have no effect, and it may not be unset.
       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).  Assigning a value to BASH_ARGV0 sets $0  to
              the  same  value.   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.  Adding elements to this array makes them appear in the
              hash table; however, unsetting array elements currently does not
              remove command names from the hash table.  If BASH_CMDS  is  un-
              set, it loses its special properties, even if it is subsequently
              reset.
       BASH_COMMAND
              Expands  to  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
              properties, 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.  Assign-
              ments to BASH_LINENO have no effect, and it may not be unset.
       BASH_LOADABLES_PATH
              A colon-separated list of directories in which the  enable  com-
              mand looks for dynamically loadable builtins.
       BASH_MONOSECONDS
              Each  time  this variable is referenced, it expands to the value
              returned by the system's monotonic clock, if one  is  available.
              If  there is no monotonic clock, this is equivalent to EPOCHSEC-
              ONDS.  If BASH_MONOSECONDS is unset, it loses its special  prop-
              erties, even if it is subsequently reset.
       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]}.   Assignments  to  BASH_SOURCE have no ef-
              fect, and it may not be unset.
       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_TRAPSIG
              Set  to the signal number corresponding to the trap action being
              executed during its execution.  See the description of trap  un-
              der  SHELL  BUILTIN  COMMANDS below for information about signal
              numbers and trap execution.
       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., beta).
              BASH_VERSINFO[5]        The value of MACHTYPE.
       BASH_VERSION
              Expands  to  a string describing the version of this instance of
              bash (e.g., 5.2.37(3)-release).
       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.  This variable is  available  only  in
              shell  functions and external commands invoked by the programma-
              ble completion facilities (see Programmable Completion below).
       COMP_LINE
              The current command line.  This variable is  available  only  in
              shell  functions and external commands invoked by the programma-
              ble 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 programma-
              ble completion facilities (see Programmable Completion below).
       COMP_TYPE
              Set to an integer value corresponding to the type  of  attempted
              completion  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  programma-
              ble 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.  Assigning to this  vari-
              able  does 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 have no effect.  If HISTCMD is
              unset, it loses its special properties, even  if  it  is  subse-
              quently 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 commands in the most-recently-executed
              foreground pipeline, which may consist of only a simple  command
              (see SHELL GRAMMAR above).  Bash sets PIPESTATUS after executing
              multi-element  pipelines,  timed  and  negated pipelines, simple
              commands, subshells created with the ( operator, the [[  and  ((
              compound commands, and after error conditions that result in the
              shell aborting command execution.
       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.   Seeding  the
              random  number  generator  with the same constant value produces
              the same sequence of values.  If RANDOM is unset, it  loses  its
              special properties, even if it is subsequently 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 at one-second
              resolution.  If SECONDS is unset, it loses its  special  proper-
              ties, even if it is subsequently reset.
       SHELLOPTS
              A  colon-separated  list of enabled shell options.  Each word in
              the list is a valid argument  for  the  -o  option  to  the  set
              builtin command (see SHELL BUILTIN COMMANDS below).  The options
              appearing  in  SHELLOPTS are those reported as on by set -o.  If
              this variable is in the environment when  bash  starts  up,  the
              shell enables each option in the list before reading any startup
              files.   If  this variable is exported, child shells will enable
              each option in the list.  This variable is read-only.
       SHLVL  Incremented by one each time an instance of bash is started.
       SRANDOM
              Each time it is referenced, this variable expands  to  a  32-bit
              pseudo-random number.  The random number generator is not linear
              on  systems  that support /dev/urandom or arc4random(3), so each
              returned 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  shell  uses the following variables. In some cases, bash assigns a
       default value to a variable; these cases are noted below.

       BASH_COMPAT
              The value is used to set the shell's compatibility  level.   See
              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.  A subset of  the  valid
              values  correspond  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 compatibility 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 expanded value is interpreted as a filename containing  com-
              mands  to initialize the shell before it reads and executes com-
              mands from the script.  The value of BASH_ENV  is  subjected  to
              parameter expansion, command substitution, and arithmetic expan-
              sion  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  writes the trace output generated when "set -x" is enabled
              to that file descriptor, instead of  the  standard  error.   The
              file  descriptor  is  closed  when BASH_XTRACEFD is unset or as-
              signed 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 stan-
              dard error being closed.
       CDPATH The search path for the cd command.  This is  a  colon-separated
              list of directories where the shell looks for directories speci-
              fied  as  arguments  to  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  set  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 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.
              The pattern matching honors the setting of the extglob shell op-
              tion.
       GLOBSORT
              Controls  how the results of pathname expansion are sorted.  The
              value of this variable specifies the sort criteria and sort  or-
              der  for the results of pathname expansion.  If this variable is
              unset or set to the null string,  pathname  expansion  uses  the
              historical  behavior  of  sorting  by name, in ascending lexico-
              graphic order as determined by the LC_COLLATE shell variable.

              If set, a valid value begins with an optional +,  which  is  ig-
              nored, or -, which reverses the sort order from ascending to de-
              scending,  followed  by a sort specifier.  The valid sort speci-
              fiers are name, numeric, size, mtime, atime, ctime, and  blocks,
              which sort the files on name, names in numeric rather than lexi-
              cographic  order, file size, modification time, access time, in-
              ode change time, and number of blocks, respectively.  If any  of
              the  non-name  keys compare as equal (e.g., if two files are the
              same size), sorting uses the name as a secondary sort key.

              For example, a value of -mtime sorts the results  in  descending
              order by modification time (newest first).

              The  numeric  specifier treats names consisting solely of digits
              as numbers and sorts them using  their  numeric  value  (so  "2"
              sorts before "10", for example).  When using numeric, names con-
              taining  non-digits  sort  after all the all-digit names and are
              sorted by name using the traditional behavior.

              A sort specifier of nosort disables sorting completely; bash re-
              turns the results in the order they are read from the file  sys-
              tem, ignoring any leading -.

              If  the  sort  specifier  is  missing, it defaults to name, so a
              value of + is equivalent to the null string, and a  value  of  -
              sorts  by  name in descending order.  Any invalid value restores
              the historical sorting behavior.
       HISTCONTROL
              A colon-separated list of values controlling  how  commands  are
              saved  on  the  history  list.   If  the list of values includes
              ignorespace, lines which begin with a space  character  are  not
              saved  in  the history list.  A value of ignoredups causes lines
              matching the previous history entry not to 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, bash saves  all  lines
              read  by  the  shell  parser on the history list, subject to the
              value of HISTIGNORE.  If the first line of a multi-line compound
              command was saved, the  second  and  subsequent  lines  are  not
              tested,  and are added to the history regardless of the value of
              HISTCONTROL.  If the first line was not saved,  the  second  and
              subsequent lines of the command are not saved either.
       HISTFILE
              The name of the file in which command history is saved (see HIS-
              TORY  below).   Bash assigns a default value of ~/.bash_history.
              If HISTFILE is unset or null, the shell does not save  the  com-
              mand history when it 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 or by
              the history builtin.  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.  If  a  command  line
              matches  one  of  the patterns in the value of HISTIGNORE, it is
              not saved on the history list.  Each pattern is anchored at  the
              beginning  of  the  line  and must match the complete line (bash
              does not  implicitly append a  "*").   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.  A backslash  es-
              capes  the  "&";  the  backslash  is removed before attempting a
              match.  If the first line of a multi-line compound  command  was
              saved,  the  second and subsequent lines are not tested, and are
              added to the history regardless of the value of HISTIGNORE.   If
              the first line was not saved, the second and subsequent lines of
              the  command  are not saved either.  The pattern matching honors
              the setting of the extglob shell option.
              HISTIGNORE subsumes some of the function of HISTCONTROL.  A pat-
              tern of "&" is identical to "ignoredups", and a  pattern  of  "[
              ]*"  is  identical  to  "ignorespace".  Combining these two pat-
              terns, separating them with a colon, provides the  functionality
              of "ignoreboth".
       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, the shell writes time stamps to the his-
              tory 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, bash clears the hostname list.
       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.  Word splitting is described below under EXPAN-
              SION.  The default value is "<space><tab><newline>".
       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
              is set but does not have a numeric value, or the value is  null,
              the  default value is 10.  If it is unset, 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 the value is set to a file or directory name and the MAILPATH
              variable  is  not  set,  bash informs the user of the arrival of
              mail in the specified file or Maildir-format 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, $_ expands to the
              name of the current mailfile.  For example:
              MAILPATH='/var/mail/bfox?"You have mail":~/shell-mail?"$_ has mail!"'
              Bash can be configured to supply a default value for this  vari-
              able  (there  is  no  value by default), but the location of the
              user  mail  files  that  it  uses  is  system  dependent  (e.g.,
              /var/mail/$USER).
       OPTERR If set to the value 1, bash displays error messages generated by
              the  getopts builtin command (see SHELL BUILTIN COMMANDS below).
              OPTERR is initialized to 1 each time the shell is invoked  or  a
              shell script is executed.
       PATH   The  search  path for commands.  It is a colon-separated list of
              directories in which the shell looks for commands  (see  COMMAND
              EXECUTION  below).   A  zero-length (null) directory name in the
              value of PATH indicates the current directory.  A null directory
              name may appear as two adjacent colons,  or  as  an  initial  or
              trailing  colon.   The  default path is system-dependent, and is
              set by the administrator who installs bash.  A common value is
                   /usr/local/bin:/usr/local/sbin:/usr/bin:/usr/sbin:/bin:/sbin
       POSIXLY_CORRECT
              If this variable is in the environment  when  bash  starts,  the
              shell  enters posix mode before reading the startup files, as if
              the --posix invocation option had been supplied.  If it  is  set
              while  the  shell is running, bash enables posix mode, as if the
              command "set -o posix" had been executed.  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 brackets 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.  time prints at most
              six digits after the decimal point; values of p greater  than  6
              are changed to 6.  If p is not specified, time prints three dig-
              its after the decimal point.

              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,
              bash  does  not display any timing information.  A trailing new-
              line is added when the format string is displayed.
       TMOUT  If set to a value greater than zero, the read builtin  uses  the
              value  as its default timeout.  The select command terminates if
              input does not arrive after TMOUT seconds when input  is  coming
              from  a  terminal.  In an interactive shell, the value is inter-
              preted as the number of seconds to wait for a line of input  af-
              ter  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, simple commands  consist-
              ing  of only a single word, without redirections, are treated as
              candidates for resumption of an existing stopped job.  There  is
              no  ambiguity  allowed;  if there is more than one job beginning
              with or containing the word, this selects the most recently  ac-
              cessed  job.  The name of a stopped job, in this context, is the
              command line used to start it, as displayed by jobs.  If set  to
              the  value  exact, the word must match the name of a stopped job
              exactly; if set to substring, the word needs  to  match  a  sub-
              string  of  the name of a stopped job.  The substring value pro-
              vides functionality analogous to the %?  job identifier (see JOB
              CONTROL below).  If set to any other value (e.g.,  prefix),  the
              word  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,
              quick  substitution, and tokenization (see HISTORY EXPANSION be-
              low).  The first character is the history  expansion  character,
              the  character  which  begins a history expansion, normally "!".
              The second character is the quick substitution  character,  nor-
              mally  "^".  When it appears as the first character on the line,
              history substitution repeats the previous command, replacing one
              string with another.  The optional third character is  the  his-
              tory  comment character,  normally "#", which indicates that the
              remainder of the line is a comment when it appears as the  first
              character  of  a  word.   The history comment character disables
              history substitution 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  ex-
       plicitly  declares  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 arithmetic expressions
       that must expand to an integer (see ARITHMETIC  EVALUATION  below)  and
       are  zero-based;  associative  arrays  are  referenced  using arbitrary
       strings.  Unless otherwise noted, indexed array indices  must  be  non-
       negative integers.

       The  shell performs parameter and variable expansion, arithmetic expan-
       sion, command substitution, and quote removal  on  indexed  array  sub-
       scripts.  Since this can potentially result in empty strings, subscript
       indexing treats those as expressions that evaluate to 0.

       The  shell  performs tilde expansion, parameter and variable expansion,
       arithmetic expansion, command substitution, and quote removal on  asso-
       ciative  array subscripts.  Empty strings cannot be used as associative
       array keys.

       Bash automatically creates an indexed array if any variable is assigned
       to using the syntax
              name[subscript]=value .
       The subscript is treated as an arithmetic expression that must evaluate
       to a number greater than or equal to zero.  To  explicitly  declare  an
       indexed array, use
              declare -a name
       (see SHELL BUILTIN COMMANDS below).
              declare -a name[subscript]
       is also accepted; the subscript is ignored.

       Associative arrays are created using
              declare -A name
       .

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

       Arrays are assigned using compound assignments of the form name=(value1
       ...  valuen),  where  each value may be of the form [subscript]=string.
       Indexed array assignments do not require  anything  but  string.   Each
       value  in the list is expanded using the shell expansions described be-
       low under EXPANSION, but values that are valid variable assignments in-
       cluding the brackets and subscript do not undergo brace  expansion  and
       word splitting, as with individual variable assignments.

       When  assigning  to  indexed  arrays, if the optional brackets and sub-
       script 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 subscripted by a nega-
       tive 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 appends to an array variable when assigning using the
       compound assignment syntax; see PARAMETERS above.

       An  array  element  is 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, unless noted in the
       description  of  a  builtin or word expansion.  These subscripts differ
       only when the word appears within double quotes.  If the word  is  dou-
       ble-quoted,  ${name[*]} expands to a single word with the value of each
       array member separated by the first character of the IFS special  vari-
       able,  and  ${name[@]} expands each element of name to a separate word.
       When there are no array members, ${name[@]} expands to nothing.  If the
       double-quoted expansion occurs within a  word,  the  expansion  of  the
       first  parameter  is joined with the beginning part of the expansion of
       the original word, and the expansion of the last  parameter  is  joined
       with  the  last  part  of  the expansion of the original word.  This is
       analogous to the expansion of the special parameters * and @ (see  Spe-
       cial 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 eval-
       uates 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 valid; bash creates an array if necessary.

       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] un-
       sets  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] behaves differently de-
       pending on whether name is an indexed or associative  array  when  sub-
       script is * or @.  If name is an associative array, this unsets the el-
       ement  with  subscript  * or @.  If name is an indexed array, unset re-
       moves 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, (e.g., unset a[4]), the argument is subject to  pathname
       expansion.   Quote  the  argument  if pathname expansion is not desired
       (e.g., unset 'a[4]').

       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.   Other
       builtins  accept  array name arguments as well (e.g., mapfile); see the
       descriptions of individual builtins below for details.  The shell  pro-
       vides a number of builtin array variables.

EXPANSION
       Expansion is performed on the command line after it has been split into
       words.  The shell performs these expansions: brace expansion, tilde ex-
       pansion, parameter and variable expansion, command substitution, arith-
       metic expansion, word splitting, pathname expansion, and quote removal.

       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; pathname  expansion;
       and quote removal.

       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.

       Quote  removal  is  always performed last.  It removes quote characters
       present in the original word, not ones resulting from one of the  other
       expansions, unless they have been quoted themselves.

       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 to generate arbitrary strings sharing a
       common prefix and suffix, either of which can be empty.  This mechanism
       is similar to pathname expansion, but the filenames generated need  not
       exist.   Patterns to be brace expanded are formed from an optional pre-
       amble, followed by either a series of comma-separated strings or a  se-
       quence  expression  between  a  pair of braces, followed 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; brace expansion preserves left to right order.  For ex-
       ample, 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.  If either x or y begins with a
       zero, each generated term will contain the same number of digits, zero-
       padding where necessary.  When letters are supplied, the expression ex-
       pands to each character lexicographically between x and  y,  inclusive,
       using  the  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  ap-
       propriate.

       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 Q , may be quoted with a backslash to prevent its  being  con-
       sidered  part of a brace expression.  To avoid conflicts with parameter
       expansion, the string "${" is not considered eligible for brace  expan-
       sion, 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.  Bash outputs that word as "file1 file2" after brace expan-
       sion.   Start  bash  with the +B option or disable brace expansion with
       the +B option to the set command (see SHELL BUILTIN COMMANDS below) for
       strict sh compatibility.

   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 tilde expands
       to the home directory of the user executing the shell 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 shell sub-
       stitutes  the value of the shell variable OLDPWD, if it is set.  If the
       characters 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 characters following the
       tilde in the tilde-prefix as an argument.  If the characters  following
       the tilde in the tilde-prefix consist of a number without a leading "+"
       or "-", tilde expansion assumes "+".

       The  results  of tilde expansion are treated as if they were quoted, so
       the replacement is not subject to word splitting  and  pathname  expan-
       sion.

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

       Bash checks each variable assignment for unquoted tilde-prefixes  imme-
       diately  following  a : or the first =, and performs tilde expansion in
       these cases.  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.

       The basic form of parameter expansion is

       ${parameter}

       which substitutes the value of parameter.  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 new parameter 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 expansion,  parameter  expansion,  command  substitution,  and
       arithmetic  expansion.   If parameter is a nameref, this expands to the
       name of the parameter referenced by parameter instead of performing the
       complete indirect expansion, for compatibility.  The exceptions to this
       are the expansions of ${!prefix*} and ${!name[@]} described below.  The
       exclamation point must immediately follow the left brace  in  order  to
       introduce indirection.

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

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

       ${parameter:-word}
              Use Default Values.  If parameter is unset or null,  the  expan-
              sion  of word is substituted.  Otherwise, the value of parameter
              is substituted.

       ${parameter:=word}
              Assign Default Values.  If parameter is unset or null,  the  ex-
              pansion  of  word is assigned to parameter, and the expansion is
              the final value of parameter.  Positional parameters and special
              parameters may not be assigned in this way.

       ${parameter:?word}
              Display Error if Null or Unset.  If parameter is null or  unset,
              the shell writes the expansion of word (or a message to that ef-
              fect if word is not present) to the standard error and, if it is
              not  interactive,  exits with a non-zero status.  An interactive
              shell does not exit, but does not execute the command associated
              with the expansion.  Otherwise, the value of parameter  is  sub-
              stituted.

       ${parameter:+word}
              Use  Alternate Value.  If parameter is null or unset, nothing is
              substituted, otherwise the expansion  of  word  is  substituted.
              The value of parameter is not used.

       ${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 (the first form above),
              this expands to the substring of the value of parameter starting
              at the character specified by offset and extending to the end of
              the value.  If offset is omitted, it is treated as 0.  If length
              is omitted, but the colon after offset is present, it is treated
              as 0.  length and offset are arithmetic expressions (see  ARITH-
              METIC 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 (or 0 if
              there  are  no positional parameters).  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 ${para-
              meter[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.   Substitutes the length in characters of the
              expanded value of parameter.  If parameter is * or @, the  value
              substituted  is the number of positional parameters.  If parame-
              ter is an array name subscripted by * or @,  the  value  substi-
              tuted  is  the number of elements in the array.  If parameter is
              an indexed array name subscripted by  a  negative  number,  that
              number  is interpreted as relative to one greater than the maxi-
              mum index of parameter, so negative indices count back from  the
              end  of  the  array, and an index of -1 references the last ele-
              ment.

       ${parameter#word}
       ${parameter##word}
              Remove matching prefix pattern.  The word is expanded to produce
              a pattern just as in pathname expansion, 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  operation
              is  applied to each positional parameter in turn, and the expan-
              sion is the resultant list.  If parameter is an  array  variable
              subscripted  with  @  or *, the pattern removal operation is ap-
              plied 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  pattern
              (the  "%%"  case)  deleted.  If parameter is @ or *, the pattern
              removal operation is applied to  each  positional  parameter  in
              turn,  and the expansion is the resultant list.  If parameter is
              an array variable subscripted with @ or *, the  pattern  removal
              operation  is  applied  to each member of the array in turn, and
              the expansion is the resultant list.

       ${parameter/pattern/string}
       ${parameter//pattern/string}
       ${parameter/#pattern/string}
       ${parameter/%pattern/string}
              Pattern substitution.  The pattern is expanded to produce a pat-
              tern and matched against the expanded value of parameter as  de-
              scribed under Pattern Matching below.  The longest match of pat-
              tern  in the expanded value is replaced with string.  string un-
              dergoes  tilde  expansion,  parameter  and  variable  expansion,
              arithmetic  expansion,  command  and  process  substitution, and
              quote removal.

              In the first form above, only the first match is  replaced.   If
              there are two slashes separating parameter and pattern (the sec-
              ond  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 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 escapes & in string; the backslash
              is removed in order to permit a literal  &  in  the  replacement
              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  interac-
              tions  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 instances of &
              they want to be replaced are unquoted.

              Like  the  pattern  removal operators, double quotes surrounding
              the replacement string quote the expanded characters, while dou-
              ble quotes enclosing the entire parameter substitution  do  not,
              since  the expansion is performed in a context that doesn't take
              any enclosing double quotes into account.

              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.  First, the pattern  is  expanded
              to  produce a pattern as described below under Pattern Matching.
              Bash then examines characters in the expanded value of parameter
              against pattern as described below.  If a character matches  the
              pattern,  its case is converted.  The pattern should not attempt
              to match more than one character.

              Using "^" converts lowercase letters matching pattern to  upper-
              case; "," converts matching uppercase letters to lowercase.  The
              ^  and  ,  variants  examine the first character in the expanded
              value and convert its case if it matches pattern; the ^^ and  ,,
              variants  examine  all characters in the expanded value and con-
              vert each one that matches pattern.  If pattern is  omitted,  it
              is treated like a ?, which matches every character.

              If  parameter  is @ or *, the case modification operation is ap-
              plied to each positional parameter in turn, and the expansion is
              the resultant list.  If parameter  is  an  array  variable  sub-
              scripted with @ or *, the case modification operation is applied
              to  each  member  of the array in turn, and the expansion is the
              resultant list.

       ${parameter@operator}
              Parameter transformation.  The expansion is either a transforma-
              tion of the value of parameter or  information  about  parameter
              itself,  depending on the value of operator.  Each operator is a
              single letter:
              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, recre-
                     ates parameter with its attributes and value.
              K      Produces a possibly-quoted version of the value of  para-
                     meter,  except  that  it prints the values of indexed and
                     associative arrays as  a  sequence  of  quoted  key-value
                     pairs (see Arrays above).  The keys and values are quoted
                     in a format that can be reused as input.
              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 itself.  There are two standard forms:

              $(command)
       or (deprecated)
              `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).

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

       There is an alternate form of command substitution:

              ${c command;}

       which executes command in the current execution  environment  and  cap-
       tures its output, again with trailing newlines removed.

       The character c following the open brace must be a space, tab, newline,
       or  |,  and the close brace must be in a position where a reserved word
       may appear (i.e., preceded by a command terminator such as  semicolon).
       Bash allows the close brace to be joined to the remaining characters in
       the  word without being followed by a shell metacharacter as a reserved
       word would usually require.

       Any side effects of command take effect immediately in the current exe-
       cution environment and persist in the  current  environment  after  the
       command completes (e.g., the exit builtin exits the shell).

       This  type of command substitution superficially resembles executing an
       unnamed shell function: local variables are created  as  when  a  shell
       function  is  executing,  and the return builtin forces command to com-
       plete; however, the rest of the execution  environment,  including  the
       positional parameters, is shared with the caller.

       If  the  first character following the open brace is a |, the construct
       expands to the value of the REPLY shell  variable  after  command  exe-
       cutes,  without removing any trailing newlines, and the standard output
       of command remains the same as in the calling shell.  Bash creates  RE-
       PLY as an initially-unset local variable when command executes, and re-
       stores  REPLY to the value it had before the command substitution after
       command completes, as with any local variable.

       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, bash does not perform
       word splitting and pathname expansion on the results.

   Arithmetic Expansion
       Arithmetic expansion evaluates an arithmetic expression and substitutes
       the result.  The format for arithmetic expansion is:

              $((expression))

       The expression undergoes the same expansions as if it were within  dou-
       ble quotes, but unescaped double quote characters in expression are not
       treated  specially  and  are removed.  All tokens in the expression un-
       dergo parameter and variable expansion, command substitution, and quote
       removal.  The result is treated as  the  arithmetic  expression  to  be
       evaluated.   Since  the  way Bash handles double quotes can potentially
       result in empty strings, arithmetic expansion treats those  as  expres-
       sions that evaluate to 0.  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
       to standard error indicating failure, does not  perform  the  substitu-
       tion, and does not execute the command associated with the expansion.

   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  provides  input  for
       list.  If the <(list) form is used, reading the file obtains the output
       of list.  No space may appear between the < or > and the left parenthe-
       sis, otherwise the construct would be interpreted as a redirection.

       Process  substitution  is supported on systems that support 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.  Words that were not expanded are not split.

       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.

       An IFS whitespace character is whitespace as defined above (see Defini-
       tions) that appears in the value of IFS.  Space, tab, and  newline  are
       always  considered IFS whitespace, even if they don't appear in the lo-
       cale's space category.

       If  IFS  is  unset,  field  splitting  acts  as  if  its   value   were
       <space><tab><newline>,  and  treats these characters as IFS whitespace.
       If the value of IFS is null, no word  splitting  occurs,  but  implicit
       null arguments (see below) are still removed.

       Word  splitting  begins by removing sequences of IFS whitespace charac-
       ters from the beginning and end of the results of the  previous  expan-
       sions, then splits the remaining words.

       If  the value of IFS consists solely of IFS whitespace, any sequence of
       IFS whitespace characters delimits a field,  so  a  field  consists  of
       characters that are not unquoted IFS whitespace, and null fields result
       only from quoting.

       If  IFS  contains a non-whitespace character, then any character in the
       value of IFS that is not IFS whitespace, along with  any  adjacent  IFS
       whitespace characters, delimits a field.  This means that adjacent non-
       IFS-whitespace  delimiters  produce  a  null  field.  A sequence of IFS
       whitespace characters also delimits a field.

       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.  Expanding a
       parameter with no value within double quotes  produces  a  null  field,
       which 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, word splitting removes the null argument portion,  leaving
       the  non-null  expansion.   That is, the word "-d''" becomes "-d" after
       word splitting and null argument removal.

   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 a sorted list of filenames matching the pattern (see Pat-
       tern Matching below) subject to the value of the GLOBSORT  shell  vari-
       able.

       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,  bash  prints  an  error
       message  and does not execute the command.  If the shell option nocase-
       glob is enabled, the match is performed without regard to the  case  of
       alphabetic characters.

       When a pattern is used for pathname expansion, the character "." at the
       start  of  a  name or immediately following a slash must be matched 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 en-
       abled, the filenames . and .. never match, even if the  pattern  begins
       with  a  ".".   When  not  matching pathnames, the "." character is not
       treated specially.

       When matching a pathname, 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 GLOBIGNORE is set
       and  not null.  However, setting GLOBIGNORE to a non-null value has the
       effect of enabling the dotglob shell option, so all other filenames be-
       ginning with a "." match.  To get the old behavior  of  ignoring  file-
       names  beginning  with a ".", make ".*"  one of the patterns in GLOBIG-
       NORE.  The dotglob option is disabled when GLOBIGNORE  is  unset.   The
       GLOBIGNORE pattern matching honors the setting of the extglob shell op-
       tion.

       The  value  of  the GLOBSORT shell variable controls how the results of
       pathname expansion are sorted, as described  above  under  Shell  Vari-
       ables.

       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 match all files and zero or more directo-
                     ries and subdirectories.  If followed by a /,  two  adja-
                     cent *s match only directories and subdirectories.
              ?      Matches any single character.
              [...]  Matches  any  one  of the characters enclosed between the
                     brackets.  This is known  as  a  bracket  expression  and
                     matches  a  single character.  A pair of characters sepa-
                     rated by a hyphen denotes a range expression; any charac-
                     ter that falls between those two  characters,  inclusive,
                     using the current locale's collating sequence and charac-
                     ter set, matches.  If the first character following the [
                     is  a  !   or a ^ then any character not within the range
                     matches.  To match a -, include it as the first  or  last
                     character  in  the  set.  To match a ], include it as the
                     first character in the set.

                     The sorting order of characters in range expressions, and
                     the characters included in the range, are  determined  by
                     the  current  locale  and the values of the LC_COLLATE or
                     LC_ALL shell variables, if set.   To  obtain  the  tradi-
                     tional  interpretation  of range expressions, where [a-d]
                     is equivalent to [abcd], set the value of the  LC_COLLATE
                     or  LC_ALL  shell variables to C, or enable the globasci-
                     iranges shell option.

                     Within a bracket expression,  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  a bracket expression, an equivalence class can be
                     specified using the syntax [=c=], which matches all char-
                     acters with the same collation weight (as defined by  the
                     current locale) as the character c.

                     Within   a  bracket  expression,  the  syntax  [.symbol.]
                     matches the collating 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.

       The extglob 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 "." un-
       less the pattern or sub-pattern begins with a ".".  If the globskipdots
       shell  option  is  enabled,  the filenames . and .. never appear in the
       set.  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.   When used with the exec builtin, redirections modify file
       handles in the current  shell  execution  environment.   The  following
       redirection  operators  may  precede or appear anywhere within a simple
       command or may follow a command.  Redirections are processed in the or-
       der 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 allocates a
       file descriptor greater than or equal to 10 and assigns it to  varname.
       If {varname} precedes >&- or <&-, the value of varname defines the file
       descriptor  to  close.   If {varname} is supplied, the redirection per-
       sists beyond the scope of the command, which allows the shell  program-
       mer to manage the file descriptor's lifetime manually without using the
       exec builtin.  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
       redirection  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.

       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  directed  to the standard output before the standard output
       was redirected to dirlist.

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

              /dev/fd/fd
                     If fd is a valid integer, duplicate file descriptor fd.
              /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
       Redirecting input opens the file whose name results from the  expansion
       of  word  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
       Redirecting output opens the file whose name results from the expansion
       of word 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  command  has  been  enabled, the redirection fails 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 is not  enabled,  bash
       attempts the redirection even if the file named by word exists.

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

       The general format for appending output is:

              [n]>>word

   Redirecting Standard Output and Standard Error
       This  construct  redirects both the standard output (file descriptor 1)
       and the standard error output (file descriptor 2)  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 appends both the standard output (file descriptor 1) and
       the standard error output (file descriptor 2) 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 it reads a line containing only delimiter (with no
       trailing  blanks).   All of the lines read up to that point then become
       the standard input (or file descriptor n if n is specified) for a  com-
       mand.

       The format of here-documents is:

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

       The  shell  does  not perform parameter and variable expansion, command
       substitution, arithmetic expansion, or pathname expansion on word.

       If any part of word is quoted, the delimiter is the result of quote re-
       moval on word, and the lines in the here-document are not expanded.  If
       word is unquoted, the delimiter is word itself, and  the  here-document
       text  is  treated similarly to a double-quoted string: all lines of the
       here-document are subjected to parameter expansion,  command  substitu-
       tion,  and  arithmetic  expansion, the character sequence \<newline> is
       treated literally, and \ must be used to quote the characters \, $, and
       `; however, double quote characters have no special meaning.

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

       If the delimiter is not quoted, the \<newline> sequence is treated as a
       line  continuation:  the two lines are joined and the backslash-newline
       is removed.  This happens while reading the here-document,  before  the
       check for the ending delimiter, so joined lines can form the end delim-
       iter.

   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, file descriptor n is made to be a copy of  that  file  de-
       scriptor.  It is a redirection error if the digits in word do not spec-
       ify a file descriptor open for input.  If word evaluates to -, file de-
       scriptor  n  is  closed.  If n is not specified, this uses the standard
       input (file descriptor 0).

       The operator

              [n]>&word

       is used similarly to duplicate output file descriptors.  If  n  is  not
       specified,  this uses the standard output (file descriptor 1).  It is a
       redirection error if the digits in word do not specify a file  descrip-
       tor  open  for  output.   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 -, this redirects the standard output and
       standard error 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

       opens the file whose name is the expansion of word for both reading and
       writing on file descriptor n, or on file descriptor 0 if n is not spec-
       ified.  If the file does not exist, it is created.

ALIASES
       Aliases allow a string to be substituted for a word that is in a  posi-
       tion  in  the input where it can be the first word of a simple command.
       Aliases have names and corresponding values that are set and unset  us-
       ing  the alias and unalias builtin commands (see SHELL BUILTIN COMMANDS
       below).

       If the shell reads an unquoted word in the right  position,  it  checks
       the  word to see if it matches an alias name.  If it matches, the shell
       replaces the word with the alias value, and reads that value as  if  it
       had been read instead of the word.  The shell doesn't look at any char-
       acters following the word before attempting alias substitution.

       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, the  shell  checks
       the next command word following the alias 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)  in-
       stead.

       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 shell reads the next line of input, and an alias defi-
       nition  in  a  compound  command  does  not take effect until the shell
       parses and executes the entire compound command.  The commands  follow-
       ing  the  alias  definition  on that line, or in the rest of a compound
       command, are not affected by the new alias.  This behavior is  also  an
       issue  when  functions are executed.  Aliases are expanded when a func-
       tion definition is read, not when the function is executed,  because  a
       function definition is itself a command.  As a consequence, aliases de-
       fined in a function are not available until after that function is exe-
       cuted.   To  be  safe, always put alias definitions on a separate line,
       and do not use alias in compound commands.

       For almost every purpose, shell functions are preferable to aliases.

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 shell executes the
       list of commands associated with that function name.  Functions are ex-
       ecuted in the context of the calling shell; there  is  no  new  process
       created  to interpret them (contrast this with the execution of a shell
       script).

       When a function is executed, the arguments to the function  become  the
       positional parameters during its execution.  The special parameter # is
       updated  to reflect the new positional parameters.  Special parameter 0
       is unchanged.  The first element of the FUNCNAME variable is set to the
       name of the function 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 are 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.   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 variables with the same name declared at previous scopes, includ-
       ing  global  variables:  references  and assignments refer to the local
       variable, leaving the variables at previous  scopes  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  resolve  to the local variable var from func1, shadowing
       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 unsets  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  remains
       so  (appearing  as  unset) until it is reset in that scope or until the
       function returns.  Once the function returns, any instance of the vari-
       able at a previous scope becomes visible.  If the unset acts on a vari-
       able at a previous scope, any instance of a  variable  with  that  name
       that  had been shadowed becomes visible (see below how the localvar_un-
       set 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.  If return is supplied a numeric argument, that is the func-
       tion's return status; otherwise the function's  return  status  is  the
       exit  status  of the last command executed before the return.  Any com-
       mand associated with the RETURN trap is executed before  execution  re-
       sumes.  When a function completes, the values of the positional parame-
       ters  and  the  special parameter # are restored to the values they had
       prior to the function's execution.

       The -f option to the declare or typeset builtin commands lists function
       names and definitions.  The -F option to declare or typeset  lists  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  executing  a  separate
       shell invocation) automatically have them defined with the -f option to
       the export builtin.  The -f option to the unset builtin deletes a func-
       tion definition.

       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, bash imposes no limit on the  number  of
       recursive calls.

ARITHMETIC EVALUATION
       The  shell allows arithmetic expressions to be evaluated, under certain
       circumstances (see the let and declare builtin commands,  the  ((  com-
       pound  command, the arithmetic for command, the [[ conditional command,
       and Arithmetic Expansion).

       Evaluation is done in the largest fixed-width integers available,  with
       no  check  for overflow, though division by 0 is trapped and flagged as
       an error.  The operators and their precedence, associativity, and  val-
       ues are the same as in the C language.  The following list of operators
       is  grouped  into levels of equal-precedence operators.  The levels are
       listed in order of decreasing precedence.

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

       Shell variables are allowed as operands; parameter  expansion  is  per-
       formed before the expression is evaluated.  Within an expression, shell
       variables  may  also  be referenced by name without using the parameter
       expansion syntax.  This means you can use "x", where x is a shell vari-
       able name, in an arithmetic expression, and the shell will evaluate its
       value as an expression and use the result.  A shell  variable  that  is
       null or unset evaluates to 0 when referenced by name in an expression.

       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 precedence order.  Sub-expressions in paren-
       theses 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 unary or binary primaries listed below.
       Unary  expressions  are  often  used to examine the status of a file or
       shell variable.  Binary operators are used  for  string,  numeric,  and
       file attribute comparisons.

       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 bash checks  file  descriptor  n.
       If  the  file  argument  to  one of the primaries is one of /dev/stdin,
       /dev/stdout, or /dev/stderr, bash checks file descriptor 0,  1,  or  2,
       respectively.

       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 [[, or when the shell is in posix mode, the < and > op-
       erators sort lexicographically using  the  current  locale.   When  the
       shell  is  not in posix mode, the test command sorts using ASCII order-
       ing.

       -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  ac-
              cessed.
       -O file
              True if file exists and is owned by the effective user id.
       -S file
              True if file exists and is a socket.
       -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).  If varname is  an  indexed  array  variable  name  sub-
              scripted  by  @ or *, this returns true if the array has any set
              elements.  If varname is an associative array variable name sub-
              scripted by @ or *, this returns true if an  element  with  that
              key is set.
       -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.

       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.

       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).  Since the expansions the [[ command performs
              on arg1 and arg2 can potentially result in empty strings, arith-
              metic  expression  evaluation  treats  those as expressions that
              evaluate to 0.

SIMPLE COMMAND EXPANSION
       When the shell executes a simple command, it 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 zero sta-
       tus.

COMMAND EXECUTION
       After a command has been split into words, if it results  in  a  simple
       command  and an optional list of arguments, the shell performs the fol-
       lowing actions.

       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).  Bash performs a full search of the directo-
       ries in PATH 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 com-
       mand 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 re-
       turns an exit status of 127.

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

       If  this  execution fails because the file is not in executable format,
       and the file is not a directory, it is assumed to be a shell script,  a
       file containing shell commands, and the shell creates a new instance of
       itself  to  execute  it.  Bash tries to determine whether the file is a
       text file or a binary, and will not execute files it determines  to  be
       binaries.  This subshell reinitializes itself, so that the effect is as
       if  a  new shell had been invoked to handle the script, with the excep-
       tion 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,  except
       possibly  in  the  last  element depending on the value of the lastpipe
       shell option, are also executed in  a  subshell  environment.   Changes
       made  to  the  subshell environment cannot affect the shell's execution
       environment.

       When the shell is in posix mode, subshells spawned to  execute  command
       substitutions  inherit  the  value  of  the -e option from their parent
       shell.  When not in posix mode, bash clears the -e option in such  sub-
       shells.   See the description of the inherit_errexit shell option below
       for how to control this behavior when not in posix mode.

       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
       processes.  Executed commands inherit the environment.  The export, de-
       clare  -x,  and  unset  commands  modify  the environment by adding and
       deleting parameters and functions.  If the value of a parameter in  the
       environment  is  modified,  the new value automatically becomes part of
       the environment, replacing the old.  The environment inherited  by  any
       executed  command  consists  of  the shell's initial environment, whose
       values may be modified in the shell, less any pairs removed by the  un-
       set  or  export  -n commands, plus any additions via the export and de-
       clare -x commands.

       If any parameter assignments, as described above in PARAMETERS,  appear
       before a simple command, the variable assignments are part of that com-
       mand's environment for as long as it executes.  These assignment state-
       ments  affect  only the environment seen by that command.  If these as-
       signments precede a call to a shell function, the variables  are  local
       to the function and exported to that function's children.

       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 pathname 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.  So while 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
       catches and handles SIGINT (so that the wait builtin is interruptible).
       When  bash  receives  SIGINT, it breaks out of any executing loops.  In
       all cases, bash ignores SIGQUIT.  If job control is in effect, bash ig-
       nores SIGTTIN, SIGTTOU, and SIGTSTP.

       The trap builtin modifies the shell's signal handling, as described be-
       low.

       Non-builtin commands bash executes have signal handlers set to the val-
       ues inherited by the shell from its parent, unless trap sets them to be
       ignored, in which case the child process  will  ignore  them  as  well.
       When  job control is not in effect, asynchronous commands ignore SIGINT
       and SIGQUIT in addition to these inherited handlers.  Commands run as a
       result of command substitution ignore the keyboard-generated  job  con-
       trol signals SIGTTIN, SIGTTOU, 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.   The  shell sends SIGCONT to stopped jobs to ensure that they
       receive the SIGHUP (see JOB CONTROL below for  more  information  about
       running  and stopped jobs).  To prevent the shell from sending the sig-
       nal to a particular job, remove it from the jobs table with the  disown
       builtin  (see  SHELL  BUILTIN COMMANDS below) or mark it not to receive
       SIGHUP using disown -h.

       If the huponexit shell option has been set using 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, it will not execute the trap until the  com-
       mand completes.  If bash is waiting for an asynchronous command via the
       wait  builtin,  and it receives a signal for which a trap has been set,
       the wait builtin will return immediately with an  exit  status  greater
       than 128, immediately after which the shell executes the trap.

       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
       processes in that process group.  Since bash does not enable  job  con-
       trol  by  default  when  the shell is not interactive, this scenario is
       most common in non-interactive shells.

       When job control is enabled, and bash is waiting for a foreground  com-
       mand  to  complete,  the shell does not receive keyboard-generated sig-
       nals, because it is not in the same  process  group  as  the  terminal.
       This scenario is most common in interactive shells, where bash attempts
       to  enable  job control by default.  See JOB CONTROL below for more in-
       formation about process groups.

       When job control is not enabled, and bash receives SIGINT while waiting
       for a foreground command, it waits until that foreground command termi-
       nates 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 send the SIGINT to the shell as well, and acts
              on the SIGINT (e.g., by running a SIGINT trap, exiting a non-in-
              teractive shell, or returning to the top level  to  read  a  new
              command).

       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.

       When job control is enabled, bash does not  receive  keyboard-generated
       signals  such  as  SIGINT while it is waiting for a foreground command.
       An interactive shell does not pay attention to the SIGINT, even if  the
       foreground  command  terminates as a result, other than noting its exit
       status.  If the shell is not interactive, and  the  foreground  command
       terminates  due to the SIGINT, bash pretends it received the SIGINT it-
       self (scenario 1 above), 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 dri-
       ver and bash.

       The shell associates a job with each pipeline.  It  keeps  a  table  of
       currently  executing  jobs,  which the jobs command will display.  Each
       job has a job number, which jobs displays between brackets.   Job  num-
       bers  start  at 1.  When bash starts a job asynchronously (in the back-
       ground), 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,
       each process has a process group ID, and the operating system maintains
       the notion of a current  terminal  process  group  ID.   This  terminal
       process group ID is associated with the controlling terminal.

       Processes  that  have  the same process group ID are said to be part of
       the same process  group.   Members  of  the  foreground  process  group
       (processes  whose  process  group  ID  is equal to the current terminal
       process group ID) receive keyboard-generated signals  such  as  SIGINT.
       Processes  in  the  foreground  process group are said to be foreground
       processes.  Background processes are those whose process group ID  dif-
       fers from the controlling terminal's; such processes are immune to key-
       board-generated signals.  Only foreground processes are allowed to read
       from or, if the user so specifies with "stty tostop", write to the con-
       trolling  terminal.   The  system  sends  a SIGTTIN (SIGTTOU) signal to
       background processes which attempt to read from (write to when "tostop"
       is in effect) the terminal, 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 stops that process and
       returns  control  to bash.  Typing the delayed suspend character (typi-
       cally ^Y, Control-Y) causes the process stop when it attempts  to  read
       input  from  the  terminal, and returns control to bash.  The user then
       manipulates 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.  The suspend character takes effect  imme-
       diately,  and  has the additional side effect of discarding any pending
       output and typeahead.  To force a background process to stop, or stop a
       process that's not associated with the current terminal  session,  send
       it the SIGSTOP signal using kill.

       There are a number of ways to refer to a job in the shell.  The % char-
       acter 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 job whose
       command name begins with ce.  Using %?ce, on the other hand, refers  to
       any job containing the string ce in its command line.  If the prefix or
       substring matches more than one job, bash reports an error.

       The  symbols  %% and %+ refer to the shell's notion of the current job.
       A single % (with no accompanying job specification) also refers to  the
       current  job.  %- refers to the previous job.  When a job starts in the
       background, a job stops while in the foreground, or a job is resumed in
       the background, it becomes the current job.  The job that was the  cur-
       rent  job  becomes  the previous job.  When the current job terminates,
       the previous job becomes the current job.  If there is  only  a  single
       job,  %+  and %- can both be used to refer to that job.  In output per-
       taining to jobs (e.g., the output of the jobs command), the current job
       is always marked with a +, and the previous job with a -.

       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, equiva-
       lent to "bg %1".

       The shell learns immediately whenever a job changes  state.   Normally,
       bash  waits  until  it  is about to print a prompt before notifying the
       user about changes in a job's status so as to not interrupt  any  other
       output,  though  it  will  notify  of changes in a job's status after a
       foreground command in a list completes, before executing the next  com-
       mand  in  the list.  If the -b option to the set builtin command is en-
       abled, bash reports status changes immediately.  Bash executes any trap
       on SIGCHLD for each child that terminates.

       When a job terminates and bash notifies the user about it, bash removes
       the job from the table.  It will not appear in jobs  output,  but  wait
       will  report  its  exit status, as long as it's supplied the process ID
       associated with the job as an argument.  When the table is  empty,  job
       numbers start over at 1.

       If  a  user  attempts  to  exit bash 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 the user immediately attempts
       to exit again, without an intervening command, bash does not print  an-
       other warning, and terminates any stopped jobs.

       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 examines the value of the array variable PROMPT_COMMAND  just  be-
       fore  printing  each primary prompt.  If any elements in PROMPT_COMMAND
       are set and non-null, Bash executes each value, in numeric order,  just
       as  if  it had been typed on the command line.  Bash displays PS0 after
       it reads a command but before executing it.

       Bash displays PS4 as described above before tracing each  command  when
       the -x option is enabled.

       Bash allows the prompt strings PS0, PS1, PS2, and PS4, 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  (e.g.,
                     "ttys0").
              \n     A newline.
              \r     A carriage return.
              \s     The  name  of  the shell: the basename of $0 (the portion
                     following the final slash).
              \t     The current time in 24-hour HH:MM:SS format.
              \T     The current time in 12-hour HH:MM:SS format.
              \@     The current time in 12-hour am/pm format.
              \A     The current time in 24-hour HH:MM format.
              \u     The username of the current user.
              \v     The bash version (e.g., 2.00).
              \V     The bash release, version + patch level (e.g., 2.00.0)
              \w     The value of the PWD shell variable  ($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 supplied at shell invoca-
       tion.  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 edit-
       ing  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
       This section uses Emacs-style editing concepts and  uses  its  notation
       for  keystrokes.   Control  keys  are denoted by C-key, e.g., C-n means
       Control-N.  Similarly, meta keys are denoted by  M-key,  so  M-x  means
       Meta-X.  The Meta key is often labeled "Alt" or "Option".

       On  keyboards  without a Meta key, M-x means ESC x, i.e., press and re-
       lease the Escape key, then press and release the x  key,  in  sequence.
       This  makes  ESC the meta prefix.  The combination M-C-x means ESC Con-
       trol-x: press and release the Escape key, then press and hold the  Con-
       trol key while pressing the x key, then release both.

       On  some  keyboards, the Meta key modifier produces characters with the
       eighth bit (0200) set.  You can use  the  enable-meta-key  variable  to
       control  whether  or  not  it does this, if the keyboard allows it.  On
       many others, the terminal or terminal emulator  converts  the  metafied
       key  to a key sequence beginning with ESC as described in the preceding
       paragraph.

       If your Meta key produces a key sequence with the ESC meta prefix,  you
       can  make M-key key bindings you specify (see Readline Key Bindings be-
       low) do the same thing by setting the force-meta-prefix variable.

       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) makes that command  act
       in  a backward direction.  Commands whose behavior with arguments devi-
       ates from this are noted below.

       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.  Readline has the concept of an active region: when the re-
       gion  is  active,  readline  redisplay  highlights the region using the
       value of the active-region-start-color variable.  The enable-active-re-
       gion variable turns this on and off.  Several commands set  the  region
       to active; those 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 accumulate  the  deleted  text  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 shell variable.  If that variable is unset, the default is
       ~/.inputrc.  If that file  does not exist or cannot be  read,  readline
       looks  for /etc/inputrc.  When a program that uses the readline library
       starts up, readline reads the initialization  file  and  sets  the  key
       bindings and variables found there, before reading any user input.

       There  are  only  a  few  basic constructs allowed in the inputrc 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 in this section may be changed using key bind-
       ing commands in the inputrc file.  Programs that use the  readline  li-
       brary, including bash, 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.

       Key bindings may contain the following symbolic character  names:  DEL,
       ESC,  ESCAPE,  LFD,  NEWLINE,  RET, RETURN, RUBOUT (a destructive back-
       space), SPACE, SPC, 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).  The differ-
       ence  between a macro and a command is that a macro is enclosed in sin-
       gle or double quotes.

   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 key  sequence  may
       be  specified in one of two ways: as a symbolic key name, possibly with
       Meta- or Control- prefixes, or as a key sequence  composed  of  one  or
       more  characters  enclosed in double quotes.  The key sequence and name
       are separated by a colon.  There can be no whitespace between the  name
       and the colon.

       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
       none of the symbolic character names are 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 available when speci-
       fying key sequences is
              \C-    A control prefix.
              \M-    Adding the meta prefix or converting the following  char-
                     acter  to  a  meta  character,  as  described below under
                     force-meta-prefix.
              \e     An escape character.
              \\     Backslash.
              \"     Literal ", a double quote.
              \'     Literal ', a single quote.

       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.   The backslash escapes described above are expanded in the
       macro body.  Backslash quotes any other character in  the  macro  text,
       including " and '.

       Bash  will display or modify the current readline key bindings with the
       bind builtin command.  The -o emacs or -o vi options to the set builtin
       (see SHELL BUILTIN COMMANDS below) change the editing mode  during  in-
       teractive use.

   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 readline reads a variable value, empty or null values, "on" (case-
       insensitive),  and  "1"  are  equivalent  to  On.  All other values are
       equivalent to Off.

       The bind -V command lists the current readline variable names and  val-
       ues (see SHELL BUILTIN COMMANDS below).

       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
              that  are  treated  specially by the kernel's terminal driver to
              their readline equivalents.  These override the default readline
              bindings described here.  Type "stty -a" at a bash prompt to see
              your current terminal settings, including  the  special  control
              characters (usually cchars).
       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  the  readline insert-comment command inserts.
              This command is bound to M-# in emacs mode and to # in  vi  com-
              mand 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
              causes 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  maximum length in characters of the common prefix of a list
              of possible completions that is displayed without  modification.
              When  set to a value greater than zero, readline replaces common
              prefixes longer than this value with an ellipsis when displaying
              possible completions.  If a completion begins with a period, and
              eadline is completing filenames, it uses three  underscores  in-
              stead of an ellipsis.
       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
              asks whether or not the user  wishes  to  view  them;  otherwise
              readline  simply lists them 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 converts characters it  reads  that  have
              the  eighth  bit  set  to  an ASCII key sequence by clearing the
              eighth bit and prefixing it with an escape character (converting
              the character to have the meta prefix).  The default is On,  but
              readline  sets it to Off if the locale contains characters whose
              encodings may include bytes with the eighth bit set.  This vari-
              able is dependent on  the  LC_CTYPE  locale  category,  and  may
              change  if  the  locale changes.  This variable also affects key
              bindings; see the description of force-meta-prefix below.
       disable-completion (Off)
              If set to On, readline  inhibits  word  completion.   Completion
              characters are 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 uses a set of key bindings similar  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.  The \1 and \2 es-
              capes 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)
              When this variable is set to On, readline  allows  certain  com-
              mands to designate the region as active.  When the region is ac-
              tive, readline highlights the text in the region using the value
              of the active-region-start-color variable, which defaults to the
              string  that  enables  the terminal's standout mode.  The active
              region shows the text inserted by bracketed-paste and any match-
              ing  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 is called bracketed-paste mode; it  prevents
              readline  from  executing  any editing commands bound to key se-
              quences appearing in the pasted text.
       enable-keypad (Off)
              When set to On, readline tries  to enable the application keypad
              when it is called.  Some systems need this to enable  the  arrow
              keys.
       enable-meta-key (On)
              When  set  to On, readline tries to enable any meta modifier key
              the terminal claims to support.  On many terminals, the Meta key
              is used to send eight-bit characters; this variable  checks  for
              the  terminal  capability that indicates the terminal can enable
              and disable a mode that sets  the  eighth  bit  of  a  character
              (0200)  if the Meta key is held down when the character is typed
              (a meta character).
       expand-tilde (Off)
              If set to On, readline performs tilde expansion when it attempts
              word completion.
       force-meta-prefix (Off)
              If set to On, readline modifies its behavior  when  binding  key
              sequences  containing  \M-  or Meta- (see Key Bindings above) by
              converting a key sequence of the form \M-C or Meta-C to the two-
              character  sequence  ESC  C  (adding  the  meta   prefix).    If
              force-meta-prefix is set to Off (the default), readline uses the
              value  of the convert-meta variable to determine whether to per-
              form this conversion: if convert-meta is On,  readline  performs
              the  conversion described above; if it is Off, readline converts
              C to a meta character by setting the eighth bit (0200).
       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,  bash
              sets  the  maximum number of history entries to the value of the
              HISTSIZE shell variable.  Setting history-size to a  non-numeric
              value will set the maximum number of history entries to 500.
       horizontal-scroll-mode (Off)
              Setting this variable 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 enables eight-bit input (that is, it does
              not clear the eighth bit in the characters it reads), regardless
              of what the terminal claims it can support.  The default is Off,
              but readline sets it to On if  the  locale  contains  characters
              whose encodings may include bytes with the eighth bit set.  This
              variable  is  dependent on the LC_CTYPE locale category, and its
              value may change if the locale changes.  The name meta-flag is a
              synonym for input-meta.
       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 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 readline does not
              receive any input within the timeout, it uses  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 waits  un-
              til  another key is pressed to decide which key sequence to com-
              plete.
       mark-directories (On)
              If set to On, completed directory names have a slash appended.
       mark-modified-lines (Off)
              If set to On, readline displays history  lines  that  have  been
              modified 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, forces readline  to  match  files
              whose  names  begin  with  a "."  (hidden files) when performing
              filename completion.  If set to Off, the user must  include  the
              leading "."  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 displays characters with the  eighth  bit
              set  directly  rather  than  as a meta-prefixed escape sequence.
              The default is Off, but readline sets it to  On  if  the  locale
              contains  characters  whose encodings may include bytes with the
              eighth bit set.  This variable is dependent on the LC_CTYPE  lo-
              cale category, and its value may change if the locale changes.
       page-completions (On)
              If set to On, readline uses an internal pager resembling more(1)
              to display a screenful of possible completions at a time.
       prefer-visible-bell
              See bell-style.
       print-completions-horizontally (Off)
              If  set to On, readline displays 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 executing accept-line.  By default, his-
              tory lines may be modified  and  retain  individual  undo  lists
              across calls to readline.
       search-ignore-case (Off)
              If  set to On, readline performs incremental and non-incremental
              history list searches in a case-insensitive fashion.
       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.
              The \1 and \2 escapes begin and end  sequences  of  non-printing
              characters,  which  can  be used to embed a terminal control se-
              quence 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.
              The \1 and \2 escapes begin and end  sequences  of  non-printing
              characters,  which  can  be used to embed a terminal control se-
              quence 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 available.

       $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 char-
              acters 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  xterm  to  match both xterm and
                     xterm-256color, 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 defaults to  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.  String  and  boolean  variables
                     may  be tested.  Boolean variables must be tested against
                     the values on and off.

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

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

       $include
              This directive takes a single filename as an argument and  reads
              commands and key bindings from that file.  For example, the fol-
              lowing 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.  When using emacs editing
       mode, type C-r to search backward  in  the  history  for  a  particular
       string.   Typing C-s searches forward through the history.  The charac-
       ters present in the value of the isearch-terminators variable are  used
       to  terminate an incremental search.  If that variable has not been as-
       signed a value, ESC and  C-j  terminate  an  incremental  search.   C-g
       aborts  an incremental search and restores 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 C-r or C-s as
       appropriate.  This searches backward or forward in the history for  the
       next  entry matching the search string typed so far.  Any other key se-
       quence bound to a readline command terminates the search  and  executes
       that  command.   For  instance, a newline terminates the search and ac-
       cepts the line, thereby executing the command from the history list.  A
       movement command will terminate the search, make the  last  line  found
       the current line, and begin editing.

       Readline remembers the last incremental search string.  If two C-rs are
       typed  without any intervening characters defining a new search string,
       readline uses any remembered search string.

       Non-incremental searches read the entire search string before  starting
       to search for matching history entries.  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 descriptions, point refers to the current cursor posi-
       tion, and mark refers to a cursor position saved by the  set-mark  com-
       mand.   The  text  between the point and mark is referred to as the re-
       gion.  Readline has the concept of an active region: when the region is
       active, readline redisplay highlights the region using the value of the
       active-region-start-color variable.  The enable-active-region  readline
       variable turns this on and off.  Several commands set the region to ac-
       tive; those are noted below.

   Commands for Moving
       beginning-of-line (C-a)
              Move  to  the start of the current line.  This may also be bound
              to the Home key on some keyboards.
       end-of-line (C-e)
              Move to the end of the line.  This may also be bound to the  End
              key on some keyboards.
       forward-char (C-f)
              Move  forward  a character.  This may also be bound to the right
              arrow key on some keyboards.
       backward-char (C-b)
              Move back a character.  This may also be bound to the left arrow
              key on some keyboards.
       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 (M-C-f)
              Move  forward  to the end of the next word.  Words are delimited
              by non-quoted shell metacharacters.
       shell-backward-word (M-C-b)
              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  ef-
              fect 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  a  numeric  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 and HISTIGNORE variables.  If the line  is  a
              modified  history line, 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.  This may also be bound to the up arrow  key  on  some
              keyboards.
       next-history (C-n)
              Fetch  the next command from the history list, moving forward in
              the list.  This may also be bound to the down arrow key on  some
              keyboards.
       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 as if a newline  had  been
              entered,  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.  This command sets the region to the  matched  text  and
              activates the region.
       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.   This  command  sets the region to the matched text and
              activates the region.
       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.  The search string may match anywhere in a history line.
       non-incremental-forward-search-history (M-n)
              Search  forward  through  the  history  using  a non-incremental
              search for a string supplied by the user.  The search string may
              match anywhere in a history line.
       history-search-backward
              Search backward through the history for the string of characters
              between the start of the current line and the point.  The search
              string must match at the beginning of a history line.  This is a
              non-incremental search.  This may be bound to the Page Up key on
              some keyboards.
       history-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 must match at the beginning of a history line.  This is a
              non-incremental  search.  This may be bound to the Page Down key
              on some keyboards.
       history-substring-search-backward
              Search backward 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.
       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, this uses the history expansion fa-
              cilities to extract the nth word, as if the "!n" history  expan-
              sion 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).  This uses the history expansion facilities
              to extract the last word, as if the "!$" history  expansion  had
              been specified.
       shell-expand-line (M-C-e)
              Expand  the line by performing shell word expansions.  This per-
              forms alias and history expansion, $'string' and $"string" quot-
              ing, tilde expansion, parameter and variable  expansion,  arith-
              metic  expansion,  command and process substitution, word split-
              ting, and quote removal.  An explicit argument  suppresses  com-
              mand  and process substitution.  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(1).  If this character is read when there are no characters
              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.  This may also be bound to the Delete key
              on some keyboards.
       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.
       bracketed-paste-begin
              This function is intended to be bound to the  "bracketed  paste"
              escape  sequence  sent  by some terminals, and such a binding is
              assigned by default.  It allows readline to  insert  the  pasted
              text  as  a single unit without treating each character as if it
              had been read from the keyboard.  The pasted characters are  in-
              serted  as  if each one was bound to self-insert instead of exe-
              cuting any editing commands.
              Bracketed paste sets the region to the inserted text  and  acti-
              vates the region.
       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  past  that  word  as well.  If point is at the end of the
              line, this transposes the last two words on the line.
       shell-transpose-words (M-C-t)
              Drag the word before point past the  word  after  point,  moving
              point  past that word as well.  If the insertion point is at the
              end of the line, this transposes the last two words on the line.
              Word  boundaries  are  the  same   as   shell-forward-word   and
              shell-backward-word.
       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, characters bound to self-insert replace the
              text at point rather than pushing the text to the right.   Char-
              acters  bound  to backward-delete-char replace the character be-
              fore point with a space.  By default, this command  is  unbound,
              but may be bound to the Insert key on some keyboards.

   Killing and Yanking
       kill-line (C-k)
              Kill the text from point to the end of the current line.  With a
              negative  numeric argument, kill backward from the cursor to the
              beginning of the line.
       backward-kill-line (C-x Rubout)
              Kill backward to the beginning of the current line.  With a neg-
              ative numeric argument, kill forward from the cursor to the  end
              of the line.
       unix-line-discard (C-u)
              Kill  backward  from  point to the beginning of the line, saving
              the killed text on the kill-ring.
       kill-whole-line
              Kill all characters on the current line, no matter  where  point
              is.
       kill-word (M-d)
              Kill  from  point  to the end of the current word, or if between
              words, to the end of the next word.   Word  boundaries  are  the
              same as those used by forward-word.
       backward-kill-word (M-Rubout)
              Kill  the  word  behind  point.  Word boundaries are the same as
              those used by backward-word.
       shell-kill-word (M-C-d)
              Kill from point to the end of the current word,  or  if  between
              words,  to  the  end  of the next word.  Word boundaries are the
              same as those used by shell-forward-word.
       shell-backward-kill-word
              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, saving the killed text on the kill-ring.
       unix-filename-rubout
              Kill the word behind point, using  white  space  and  the  slash
              character  as the word boundaries, saving the killed text 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,  so  it  can  be
              yanked immediately.
       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 by first checking for any programmable  com-
              pletions  for  the command word (see Programmable Completion be-
              low), otherwise treating the text as a variable (if the text be-
              gins with $), username (if the text begins with ~), hostname (if
              the text begins with @), or command  (including  aliases,  func-
              tions,  and  builtins)  in  turn.   If  none of these produces a
              match, it falls back to filename completion.
       possible-completions (M-?)
              List the possible completions of the text  before  point.   When
              displaying completions, readline sets the number of columns used
              for  display to the value of completion-display-width, the value
              of the shell variable COLUMNS, or the screen width, in that  or-
              der.
       insert-completions (M-*)
              Insert  all completions of the text before point that would have
              been generated by possible-completions, separated by a space.
       menu-complete
              Similar to complete, but replaces the word to be completed  with
              a  single  match from the list of possible completions.  Repeat-
              edly executing menu-complete steps through the list of  possible
              completions,  inserting  each  match in turn.  At the end of the
              list of completions, menu-complete rings the  bell  (subject  to
              the  setting  of bell-style) and restores the original text.  An
              argument of n moves n positions forward in the list of  matches;
              a  negative argument moves 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.
       export-completions
              Perform completion on the word before point as  described  above
              and  write the list of possible completions to readline's output
              stream using the following format, writing information on  sepa-
              rate lines:

              o      the number of matches N;
              o      the word being completed;
              o      S:E,  where  S and E are the start and end offsets of the
                     word in the readline line buffer; then
              o      each match, one per line

              If there are no matches, the first line will be  "0",  and  this
              command  does  not  print any output after the S:E.  If there is
              only a single match, this prints a single  line  containing  it.
              If  there  is more than one match, this prints the common prefix
              of the matches, which may be empty, on the first line after  the
              S:E, then the matches on subsequent lines.  In this case, N will
              include the first line with the common prefix.

              The user or application should be able to accommodate the possi-
              bility of a blank line.  The intent is that the user or applica-
              tion  reads  N lines after the line containing S:E to obtain the
              match list.  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).  At the end of the line,
              it 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 history list entries 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,
              set the mark to that position.
       exchange-point-and-mark (C-x C-x)
              Swap the point with the mark.  Set the current  cursor  position
              to the saved position, then set the mark to the old cursor posi-
              tion.
       character-search (C-])
              Read  a  character and move point to the next occurrence of that
              character.  A negative argument  searches  for  previous  occur-
              rences.
       character-search-backward (M-C-])
              Read  a  character  and move point to the previous occurrence of
              that character.  A negative argument searches for subsequent oc-
              currences.
       skip-csi-sequence
              Read enough characters to consume a multi-key sequence  such  as
              those  defined  for keys like Home and End.  CSI sequences begin
              with a Control Sequence Indicator (CSI), usually ESC [.  If this
              sequence is bound to "\e[", keys producing CSI sequences have no
              effect unless explicitly bound to a readline command, instead of
              inserting stray characters into the editing buffer.  This is un-
              bound by default, but usually bound to ESC [.
       insert-comment (M-#)
              Without a numeric argument, insert the  value  of  the  readline
              comment-begin variable 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, insert the value; otherwise delete the
              characters in comment-begin from the beginning of the line.   In
              either  case,  the  line  is  accepted  as if a newline had been
              typed.  The default value of comment-begin causes  this  command
              to make the current line a shell comment.  If a numeric argument
              causes the comment character to be removed, the line will be ex-
              ecuted 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)
              Treat the word before point as a pattern for pathname expansion,
              with an asterisk implicitly appended, then use  the  pattern  to
              generate a list of matching file names for possible completions.
       glob-expand-word (C-x *)
              Treat the word before point as a pattern for pathname expansion,
              and  insert the list of matching file names, replacing the word.
              If a numeric argument is supplied, append a  *  before  pathname
              expansion.
       glob-list-expansions (C-x g)
              Display the list of expansions that would have been generated by
              glob-expand-word  and redisplay the line.  If a numeric argument
              is supplied, append a * 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 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.
       execute-named-command (M-x)
              Read a bindable readline command name from the input and execute
              the  function  to  which  it's  bound, as if the key sequence to
              which it was bound appeared in the input.  If this  function  is
              supplied with a numeric argument, it passes that argument to the
              function it executes.
       display-shell-version (C-x C-v)
              Display version information about the current instance of bash.

   Programmable Completion
       When  a user attempts word completion for a command or an argument to a
       command for which a completion specification (a compspec) has been  de-
       fined  using  the  complete builtin (see SHELL BUILTIN COMMANDS below),
       readline invokes the programmable completion facilities.

       First, bash identifies the command name.  If a compspec  has  been  de-
       fined  for  that  command, the compspec is used to generate the list of
       possible completions for the word.  If the command word  is  the  empty
       string  (completion  attempted at the beginning of an empty line), bash
       uses any compspec defined with the -E option to complete.  The  -I  op-
       tion  to  complete indicates that the command word is the first non-as-
       signment word on the line, or after a command delimiter such as ; or |.
       This usually indicates command name completion.

       If the command word is a full pathname, bash searches  for  a  compspec
       for  the  full  pathname  first.   If there is no compspec for the full
       pathname, bash attempts to find a compspec for  the  portion  following
       the  final slash.  If those searches do not result in a compspec, or if
       there is no compspec for the command word, bash uses any  compspec  de-
       fined  with  the  -D option to complete as the default.  If there is no
       default compspec, bash performs alias expansion on the command word  as
       a  final  resort,  and attempts to find a compspec for the command word
       resulting from any successful expansion.

       If a compspec is not found, bash performs its default completion as de-
       scribed above under Completing.  Otherwise, once a  compspec  has  been
       found, bash uses it to generate the list of matching words.

       First,  bash performs the actions specified by the compspec.  This only
       returns matches which are prefixes of the word being  completed.   When
       the  -f or -d option is used for filename or directory name completion,
       bash uses the shell variable FIGNORE to filter the matches.

       Next, programmable completion generates matches specified by a pathname
       expansion pattern supplied as an argument to the -G option.  The  words
       generated by the pattern need not match the word being completed.  Bash
       uses  the  FIGNORE variable to filter the matches, but does not use the
       GLOBIGNORE shell variable.

       Next, completion considers the string specified as the argument to  the
       -W  option.   The string is first split using the characters in the IFS
       special variable as delimiters.  This honors shell quoting  within  the
       string,  in order to provide a mechanism for the words to contain shell
       metacharacters or characters in the value of IFS.  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
       possible completions.

       After these matches have been generated, bash executes any shell  func-
       tion or command specified with the -F and -C options.  When the command
       or   function  is  invoked,  bash  assigns  values  to  the  COMP_LINE,
       COMP_POINT, COMP_KEY, and COMP_TYPE variables as described above  under
       Shell  Variables.  If a shell function is being invoked, bash also sets
       the COMP_WORDS and COMP_CWORD variables.  When the function or  command
       is  invoked,  the  first argument ($1) is the name of the command whose
       arguments are being completed, the second argument ($2) is the word be-
       ing completed, and the third argument ($3) is the  word  preceding  the
       word  being completed on the current command line.  There is no filter-
       ing of the generated completions against the word being completed;  the
       function  or command has complete freedom in generating the matches and
       they do not need to match a prefix of the word.

       Any function specified with -F is invoked first.  The function may  use
       any of the shell facilities, including the compgen and compopt builtins
       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 will  es-
       cape  a  newline, if necessary.  These are added to the set of possible
       completions.

       After generating all of the possible completions, bash applies any fil-
       ter specified with the -X option to the completions in the  list.   The
       filter  is a pattern 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 is removed  from  the
       list.   A  leading ! negates the pattern; in this case bash removes any
       completion that does not match the pattern.  If the  nocasematch  shell
       option  is  enabled, bash performs the match without regard to the case
       of alphabetic characters.

       Finally, programmable completion adds any prefix and  suffix  specified
       with  the  -P and -S options, respectively, to each completion, and re-
       turns the result to readline 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, bash attempts directory name completion.

       If the -o plusdirs option was supplied to complete  when  the  compspec
       was  defined,  bash  attempts  directory  name  completion and adds any
       matches to the set of possible completions.

       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 and the readline default of  filename  comple-
       tion  are  disabled.  If the -o bashdefault option was supplied to com-
       plete when the compspec was defined,  and  the  compspec  generates  no
       matches,  bash  attempts its default completions.  If the compspec and,
       if attempted, the default bash completions generate no matches, and the
       -o default option was supplied to complete when the  compspec  was  de-
       fined, programmable completion performs readline's default completion.

       The  options  supplied to complete and compopt can control how readline
       treats the completions.  For instance, the -o  fullquote  option  tells
       readline  to  quote the matches as if they were filenames.  See the de-
       scription of complete below for details.

       When a compspec indicates that it wants directory name completion,  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 set-
       ting 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  functions  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 can be  used  to
       build  a  set  of  completions  dynamically as completion is attempted,
       rather than loading them 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 shell saves  the  text  of  the
       last HISTSIZE commands (default 500).  The shell stores each command in
       the  history list prior to parameter and variable expansion (see EXPAN-
       SION above) but after history expansion is performed,  subject  to  the
       values of the shell variables HISTIGNORE and HISTCONTROL.

       On  startup,  bash  initializes the history list by reading history en-
       tries  from  the  file  named  by  the   HISTFILE   variable   (default
       ~/.bash_history).   That  file is referred to as the history file.  The
       history file is truncated, if necessary, to contain no  more  than  the
       number  of  history  entries specified by the value of the HISTFILESIZE
       variable.  If HISTFILESIZE is unset, or  set  to  null,  a  non-numeric
       value, or a numeric value less than zero, the history file is not trun-
       cated.

       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 line.  These timestamps are optionally dis-
       played depending on the value of  the  HISTTIMEFORMAT  variable.   When
       present,  history timestamps delimit history entries, making multi-line
       entries possible.

       When a shell with history enabled exits, bash copies the last $HISTSIZE
       entries from the history list to $HISTFILE.  If  the  histappend  shell
       option  is  enabled  (see  the description of shopt under SHELL BUILTIN
       COMMANDS below), bash appends the entries to the history  file,  other-
       wise  it overwrites the history file.  If HISTFILE is unset or null, or
       if the history file is unwritable, the history  is  not  saved.   After
       saving  the history, bash truncates the history file to contain no more
       than HISTFILESIZE lines as described above.

       If the HISTTIMEFORMAT variable is set, the shell writes  the  timestamp
       information  associated  with  each  history entry to the history file,
       marked with the history comment character, so timestamps are  preserved
       across shell sessions.  This uses the history comment character to dis-
       tinguish  timestamps  from  other  history lines.  As above, when using
       HISTTIMEFORMAT, the timestamps delimit multi-line history entries.

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

       The shell allows control over which commands are saved on  the  history
       list.  The HISTCONTROL and HISTIGNORE variables are used to save only a
       subset  of  the  commands  entered.  If the cmdhist shell option is en-
       abled, the shell attempts 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  modifies  cmdhist  by
       saving  the  command with embedded newlines instead of semicolons.  See
       the description of the shopt builtin below under SHELL BUILTIN COMMANDS
       for information on setting and unsetting shell options.

HISTORY EXPANSION
       The shell supports a history expansion feature that is similar  to  the
       history  expansion in csh.  This section describes what syntax features
       are available.

       History expansion is enabled by default for interactive shells, and can
       be disabled using the +H option to the set builtin command  (see  SHELL
       BUILTIN COMMANDS below).  Non-interactive shells do not perform history
       expansion by default, but it can be enabled with "set -H".

       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.  The shell attempts to inform the history  expansion
       functions about quoting still in effect from previous lines.

       It  takes  place in two parts.  The first is to determine which history
       list entry to use during substitution.  The second is  to  select  por-
       tions of that entry to include into the current one.

       The  entry  selected from the history is the event, and the portions of
       that entry that are acted upon are words.  Various modifiers are avail-
       able to manipulate the selected words.  The entry is split  into  words
       in  the same fashion as when reading input, so that several metacharac-
       ter-separated words surrounded by quotes are considered one word.   The
       event  designator  selects  the event, the optional word designator se-
       lects words from the event, and various optional modifiers  are  avail-
       able to manipulate the selected words.

       History  expansions are introduced by the appearance of the history ex-
       pansion character, which is ! by default.  History expansions  may  ap-
       pear anywhere in the input, but do not nest.

       Only  backslash  (\)  and single quotes can quote the history expansion
       character, but the history  expansion  character  is  also  treated  as
       quoted if it immediately precedes the closing double quote in a double-
       quoted string.

       Several  characters inhibit history expansion if found immediately fol-
       lowing the history expansion character, even if it is unquoted:  space,
       tab,  newline,  carriage  return, =, and the other shell metacharacters
       defined above.

       There is a special abbreviation for substitution, active when the quick
       substitution character (described above under histchars) is  the  first
       character on the line.  It selects the previous history list entry, us-
       ing  an  event  designator equivalent to !!, and substitutes one string
       for another in that entry.  It is described below under Event  Designa-
       tors.   This is the only history expansion that does not begin with the
       history expansion character.

       Several shell options settable with the shopt builtin will modify  his-
       tory  expansion  behavior (see the description of the shopt builtin be-
       low).and If the histverify shell option is enabled, and readline is be-
       ing used, history substitutions are not immediately passed to the shell
       parser.  Instead, the expanded line is reloaded into the readline edit-
       ing buffer for further modification.  If readline is  being  used,  and
       the  histreedit  shell option is enabled, a failed history substitution
       is reloaded into the readline editing buffer for correction.

       The -p option to the history builtin command shows what a  history  ex-
       pansion  will do before using it.  The -s option to the history builtin
       will add commands to the end of the history list without actually  exe-
       cuting 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 an entry in the history list.
       The event designator consists of the portion of the word beginning with
       the history expansion character and ending with the word designator  if
       present,  or  the  end  of the word.  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 history list entry n.
       !-n    Refer to the current entry minus n.
       !!     Refer to the previous entry.  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, this uses the string  from  the  most  recent
              search; 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.  They
       are optional; if the word designator isn't supplied, the history expan-
       sion uses the entire 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 in-
       serted into the current line separated by single spaces.

       0 (zero)
              The zeroth word.  For the shell, this is the command word.
       n      The nth word.
       ^      The first argument: 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.  By default, searches begin at the end of  each  line  and
              proceed  to  the beginning, so the first word matched is the one
              closest to the end of the line.
       x-y    A range of words; "-y" abbreviates "0-y".
       *      All of the words but the zeroth.  This is a synonym  for  "1-$".
              It  is  not  an  error to use * if there is just one word in the
              event; it expands to the empty string in that case.
       x*     Abbreviates x-$.
       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, equivalent to !!.

   Modifiers
       After  the  optional  word  designator, the expansion may include a se-
       quence of one or more of the following modifiers, each  preceded  by  a
       ":".   These  modify, or edit, the word or words selected from the his-
       tory event.

       h      Remove a trailing pathname component, leaving only the head.
       t      Remove all leading pathname 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; expansion uses the last one supplied.
       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.  A single backslash quotes the delimiter in  old
              and  new.  If & appears in new, it is replaced with old.  A sin-
              gle backslash quotes the &.  If old is null, it is  set  to  the
              last  old  substituted, or, if no previous history substitutions
              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.

       . [-p path] filename [arguments]
       source [-p path] filename [arguments]
              The  . command (source) reads and execute commands from filename
              in the current shell environment and returns the exit status  of
              the last command executed from filename.

              If filename does not contain a slash, . searches for it.  If the
              -p  option  is supplied, . treats path as a colon-separated list
              of directories in which to find filename; otherwise, . uses  the
              entries  in  PATH  to  find  the  directory containing filename.
              filename does not need to be executable.  When bash  is  not  in
              posix mode, it searches the current directory if filename is not
              found  in  PATH, but does not search the current directory if -p
              is supplied.  If the sourcepath option to the shopt builtin com-
              mand is turned off, . does not search PATH.

              If any arguments are supplied, they become the positional  para-
              meters  when filename is executed.  Otherwise the positional pa-
              rameters 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 executes.  If -T
              is not set, and the sourced file changes the DEBUG trap, the new
              value persists after . completes.  The return status is the sta-
              tus of the last command executed from filename (0 if no commands
              are  executed),  and non-zero if filename is not found or cannot
              be read.

       alias [-p] [name[=value] ...]
              With no arguments or with the -p option, alias prints  the  list
              of  aliases  in  the  form  alias name=value on standard output.
              When arguments are supplied, define an alias 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
              during command parsing.  For each name in the argument list  for
              which  no  value  is  supplied,  print the name and value of the
              alias name.  alias returns true unless a name is given  (without
              a corresponding =value) 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
              uses its notion of the current job.  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] [-lsvSVX]
       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] -p|-P [readline-command]
       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 to a shell  command,
              or  set  a readline variable.  Each non-option argument is a key
              binding or command as it would appear in a readline  initializa-
              tion  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'.    In  the  following  descriptions,  output
              available to be re-read is formatted as commands that would  ap-
              pear in a readline initialization file or that would be supplied
              as  individual  arguments  to  a bind command.  Options, if sup-
              plied, 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 used as an argument to a  subsequent
                     bind  command  or  in a readline initialization file.  If
                     arguments remain after  option  processing,  bind  treats
                     them  as  readline  command names and restricts output to
                     those names.
              -P     List current readline function names  and  bindings.   If
                     arguments  remain  after  option  processing, bind treats
                     them as readline command names and  restricts  output  to
                     those names.
              -s     Display  readline  key  sequences bound to macros and the
                     strings they output in such a way that they can  be  used
                     as an argument to a subsequent bind command or in a read-
                     line initialization file.
              -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 used as an argument to a subsequent bind
                     command or in a readline initialization file.
              -V     List current readline variable names and values.
              -f filename
                     Read key bindings from filename.
              -q function
                     Display  key  sequences  that  invoke  the named readline
                     function.
              -u function
                     Unbind all key sequences  bound  to  the  named  readline
                     function.
              -r keyseq
                     Remove any current binding for keyseq.
              -x keyseq[: ]shell-command
                     Cause shell-command to be executed whenever keyseq is en-
                     tered.  The separator between keyseq and shell-command is
                     either  whitespace  or  a  colon  optionally  followed by
                     whitespace.  If the separator is  whitespace,  shell-com-
                     mand  must  be enclosed in double quotes and readline ex-
                     pands any of its special backslash-escapes in  shell-com-
                     mand  before saving it.  If the separator is a colon, any
                     enclosing double quotes are optional, and  readline  does
                     not  expand  the  command string before saving it.  Since
                     the entire key binding expression must be a single  argu-
                     ment,  it  should  be  enclosed  in  single quotes.  When
                     shell-command is  executed,  the  shell  sets  the  READ-
                     LINE_LINE  variable  to the contents of the readline 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  an
                     argument to a subsequent bind command.

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

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

       builtin shell-builtin [arguments]
              Execute the specified shell builtin  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 functionality of the builtin within the function.
              The cd builtin is commonly redefined this way.  The return  sta-
              tus 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).

              Without  expr,  caller displays the line number and source file-
              name of the current subroutine call.  If a non-negative  integer
              is supplied as expr, caller displays the line number, subroutine
              name, and source file corresponding to that position in the cur-
              rent  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] [-@] [dir]
       cd -P [-e] [-@] [dir]
              Change the current directory to dir.  if dir  is  not  supplied,
              the  value of the HOME shell variable is used as dir.  The vari-
              able CDPATH exists, and dir does not begin with a slash (/),  cd
              uses it as a search path: the shell searches each directory name
              in  CDPATH  for  dir.  Alternative directory names in CDPATH are
              separated by a colon (:).  A null directory name  in  CDPATH  is
              the same as the current directory, i.e., ".".

              The  -P option causes cd to use the physical directory structure
              by resolving symbolic links while traversing dir and before pro-
              cessing instances of .. in dir (see also the -P  option  to  the
              set builtin command).

              The  -L  option  forces cd to follow symbolic links by resolving
              the link after processing instances of .. in dir.  If .. appears
              in dir, cd processes it by  removing  the  immediately  previous
              pathname component from dir, back to a slash or the beginning of
              dir,  and  verifying that the portion of dir it has processed to
              that point is still a valid directory name  after  removing  the
              pathname component.  If it is not a valid directory name, cd re-
              turns  a  non-zero status.  If neither -L nor -P is supplied, cd
              behaves as if -L had been supplied.

              If the -e option is supplied with -P, and cd cannot successfully
              determine the current working directory after a  successful  di-
              rectory change, it returns a non-zero status.

              On  systems that support it, the -@ option presents the extended
              attributes associated with a file as a directory.

              An argument of - is converted to $OLDPWD before  attempting  the
              directory change.

              If  cd  uses  a non-empty directory name from CDPATH, or if - is
              the first argument, and the directory change is  successful,  cd
              writes the absolute pathname of the new working directory 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 ...]
              The command builtin runs command with args suppressing the  nor-
              mal shell function lookup for command.  Only builtin commands or
              commands  found  in the PATH named command are executed.  If the
              -p option is supplied, the search for command is performed using
              a default value for PATH that is guaranteed to find all  of  the
              standard utilities.

              If  either the -V or -v option is supplied, command prints a de-
              scription of command.  The -v option displays a single word  in-
              dicating  the command or filename used to invoke command; the -V
              option produces a more verbose description.

              If the -V or -v option is supplied, the exit status is  zero  if
              command  was  found,  and non-zero if not.  If neither option is
              supplied and an error occurred or command cannot be  found,  the
              exit  status  is 127.  Otherwise, the exit status of the command
              builtin is the exit status of command.

       compgen [-V varname] [option] [word]
              Generate possible completion matches for word according  to  the
              options,  which  may  be  any  option  accepted  by the complete
              builtin with the exceptions of -p, -r, -D, -E, and -I, and write
              the matches to the standard output.

              If the -V option is supplied, compgen stores the generated  com-
              pletions  into  the  indexed  array  variable varname instead of
              writing them to the standard output.

              When using the -F or -C options, the various shell variables set
              by the programmable completion facilities, while available, will
              not have useful values.

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

              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 globpat] [-W wordlist] [-F function] [-C command]
              [-X filterpat] [-P prefix] [-S suffix] 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 or names are sup-
              plied,  print  existing  completion specifications in a way that
              allows them to be reused as input.  The -r option removes a com-
              pletion specification for each name, or, if no  names  are  sup-
              plied, all completion specifications.

              The  -D option indicates that other supplied options and actions
              should apply to the "default" command completion; that is,  com-
              pletion  attempted on a command for which no completion has pre-
              viously been defined.  The -E option indicates that  other  sup-
              plied  options  and actions should apply to "empty" command com-
              pletion; 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 usu-
              ally 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 at-
              tempting  word completion  is described above under Programmable
              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  (such as adding a slash to directory
                              names, quoting special characters, or  suppress-
                              ing  trailing  spaces).   This is intended to be
                              used with shell functions.
                      fullquote
                              Tell readline to quote all the  completed  words
                              even if they are not filenames.
                      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 generating  any  matches  defined  by  the
                              compspec,  attempt directory name completion and
                              add any matches to the results of the other  ac-
                              tions.
              -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 and directory names, similar to  readline's
                              filename  completion.   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 function finishes, programmable
                      completion retrieves the possible completions  from  the
                      value of the COMPREPLY array variable.
              -G globpat
                      Expand  the pathname expansion pattern globpat to gener-
                      ate the possible completions.
              -P prefix
                      Add prefix to the beginning of each possible  completion
                      after all other options have been applied.
              -S suffix
                      Append  suffix  to  each  possible  completion after all
                      other options have been applied.
              -W wordlist
                      Split the wordlist using the characters in the IFS  spe-
                      cial  variable  as delimiters, and expand each resulting
                      word.  Shell quoting is honored within wordlist, in  or-
                      der  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 a prefix of the  word  being  com-
                      pleted.
              -X filterpat
                      filterpat  is  a pattern as used for pathname expansion.
                      It is applied to the list of possible completions gener-
                      ated by the preceding options and  arguments,  and  each
                      completion  matching filterpat is removed from the list.
                      A leading ! in filterpat negates the  pattern;  in  this
                      case, any completion not matching filterpat is removed.

              The  return  value is true unless an invalid option is supplied,
              an option other than -p, -r, -D, -E, or -I is supplied without a
              name argument, an attempt is made to remove a completion  speci-
              fication for a name for which no specification exists, or an er-
              ror 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 supplied,  display  the  completion
              options  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 options should apply
              to  the  "default"  command  completion; the -E option indicates
              that other supplied options should apply to "empty" command com-
              pletion; and the -I option indicates that other supplied options
              should apply to completion on the  initial  word  on  the  line.
              These are determined in the same way as the complete builtin.

              If multiple options are supplied, the -D option takes precedence
              over -E, and both take precedence over -I.

              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]
              continue resumes the next iteration of the enclosing for, while,
              until, or select loop.  If n is specified, bash resumes the  nth
              enclosing  loop.  n must be >= 1.  If n is greater than the num-
              ber of enclosing loops, the shell  resumes  the  last  enclosing
              loop  (the "top-level" loop).  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 or functions.  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, declare will display
              the attributes and values of all variables having the attributes
              specified  by  the  additional options.  If no other options are
              supplied with -p, declare will display the attributes and values
              of all shell variables.  The -f option restricts the display  to
              shell functions.

              The -F option inhibits the display of function definitions; only
              the  function  name and attributes are printed.  If the extdebug
              shell option is enabled using shopt, the source  file  name  and
              line  number  where  each name is defined are displayed as well.
              The -F option implies -f.

              The -g option forces variables to be created or modified at  the
              global scope, even when declare is executed in a shell function.
              It is ignored when declare is not executed in a shell function.

              The  -I  option causes local variables to inherit the attributes
              (except the nameref attribute) and value of any  existing  vari-
              able  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  vari-
              ables  with the specified attribute or to give variables attrib-
              utes:
              -a     Each name  is  an  indexed  array  variable  (see  Arrays
                     above).
              -A     Each  name  is  an associative array variable (see Arrays
                     above).
              -f     Each name refers to a shell function.
              -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 each name for export to subsequent commands via  the
                     environment.

              Using  "+"  instead of "-" turns off the specified attribute in-
              stead, with the exceptions that +a and +A may not be used to de-
              stroy array variables and +r will not remove  the  readonly  at-
              tribute.

              When  used in a function, declare and typeset make each name lo-
              cal, as with the local command, unless the  -g  option  is  sup-
              plied.   If  a variable name is followed by =value, the value of
              the variable is set to value.  When using -a or -A and the  com-
              pound  assignment  syntax  to create array variables, additional
              attributes do not take effect until subsequent assignments.

              The return value is 0 unless an invalid option  is  encountered,
              an  attempt  is made to define a function using "-f foo=bar", an
              attempt is made to assign a value to a readonly variable, an at-
              tempt is made to assign a value to an array variable without us-
              ing the compound assignment syntax (see Arrays  above),  one  of
              the names is not a valid shell variable name, an attempt is made
              to  turn off readonly status for a 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, display the list of currently remembered direc-
              tories.   The default display is on a single line with directory
              names separated by spaces.  Directories are added  to  the  list
              with  the  pushd  command; the popd command removes entries from
              the list.  The current directory is always the  first  directory
              in the stack.

              Options, if supplied, have the following meanings:
              -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] [id ...]
              Without options, remove each id from the table of  active  jobs.
              Each  id may be a job specification jobspec or a process ID pid;
              if id is a pid, disown uses the job containing pid as jobspec.

              If the -h option is supplied, disown does not  remove  the  jobs
              corresponding  to  each id from the jobs table, but rather marks
              them so the shell does not send SIGHUP to the job if  the  shell
              receives a SIGHUP.

              If  no id is supplied, the -a option means to remove or mark all
              jobs; the -r option without an id argument removes or marks run-
              ning jobs.  If no id is supplied, and neither the -a nor the  -r
              option is supplied, disown removes or marks the current job.

              The return value is 0 unless an id 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 not printed.

              If  the  -e option is given, echo interprets the following back-
              slash-escaped characters.  The -E option disables interpretation
              of these escape characters, even on systems where they  are  in-
              terpreted  by  default.   The  xpg_echo  shell option determines
              whether or not echo interprets any options and expands these es-
              cape characters.  echo does not interpret -- to mean the end  of
              options.

              echo interprets the following escape sequences:
              \a     alert (bell)
              \b     backspace
              \c     suppress further output
              \e
              \E     an escape character
              \f     form feed
              \n     new line
              \r     carriage return
              \t     horizontal tab
              \v     vertical tab
              \\     backslash
              \0nnn  The  eight-bit  character  whose value is the octal value
                     nnn (zero to three octal digits).
              \xHH   The eight-bit character whose value  is  the  hexadecimal
                     value HH (one or two hex digits).
              \uHHHH The  Unicode (ISO/IEC 10646) character whose value is the
                     hexadecimal value HHHH (one to four hex digits).
              \UHHHHHHHH
                     The Unicode (ISO/IEC 10646) character whose value is  the
                     hexadecimal value HHHHHHHH (one to eight hex digits).

              echo  writes  any  unrecognized backslash-escaped characters un-
              changed.

       enable [-a] [-dnps] [-f filename] [name ...]
              Enable and disable builtin shell commands.  Disabling a  builtin
              allows  an  executable  file  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 files.

              If  -n  is supplied, each name is disabled; otherwise, names are
              enabled.  For example, to use the test binary found  using  PATH
              instead of the shell builtin version, run "enable -n test".

              If  no  name arguments are supplied, or if the -p option is sup-
              plied, print a list of shell builtins.  With no other option ar-
              guments, the list consists of all enabled shell builtins.  If -n
              is supplied, print only disabled builtins.  If -a  is  supplied,
              the  list  printed  includes all builtins, with an indication of
              whether or not each is enabled.  The -s option means to restrict
              the output to the POSIX special builtins.

              The -f option means to load the new builtin  command  name  from
              shared object filename, on systems that support dynamic loading.
              If filename does not contain a slash, Bash will use the value of
              the  BASH_LOADABLES_PATH  variable  as a colon-separated list of
              directories in which to search for filename.   The  default  for
              BASH_LOADABLES_PATH  is system-dependent, and may include "." to
              force a search of the current directory.   The  -d  option  will
              delete  a builtin previously loaded with -f.  If -s is used with
              -f, the new builtin becomes a POSIX special builtin.

              If no options are supplied 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 ...]
              Concatenate  the args together into a single command, separating
              them with spaces.  Bash then reads and execute this command, and
              returns its exit status as the return status 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 without creating
              a new process.  command cannot be a shell builtin  or  function.
              The arguments become the arguments to command.  If the -l option
              is supplied, the shell places a dash at the beginning of the ze-
              roth  argument  passed  to command.  This is what login(1) does.
              The -c option causes command to be executed with an empty  envi-
              ronment.  If -a is supplied, the shell passes name as the zeroth
              argument to the executed command.

              If command cannot be executed for some reason, a non-interactive
              shell  exits,  unless  the execfail shell option is enabled.  In
              that case, it returns a non-zero status.  An  interactive  shell
              returns  a  non-zero  status  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  redi-
              rection 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.  Any  trap
              on EXIT is executed before the shell terminates.

       export [-fn] [name[=value]] ...
       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.

              The  -n  option unexports, or removes the export attribute, from
              each name.  If no names are given, or if the -p option  is  sup-
              plied,  export  prints a list of names of all exported variables
              on the standard output.

              export allows the value of a variable to be set when it  is  ex-
              ported or unexported by following the variable name with =value.
              This sets the value of the variable to value while modifying the
              export  attribute.  export returns an exit status of 0 unless an
              invalid option is encountered, one of the names is not  a  valid
              shell variable name, or -f is supplied with a name that is not a
              function.

       false  Does nothing; returns a non-zero status.

       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); oth-
              erwise 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.

              If  the  -l  option  is supplied, the commands are listed on the
              standard output.  The -n option suppresses the  command  numbers
              when listing.  The -r option reverses the order of the commands.

              Otherwise,  fc  invokes the editor named by ename on a file con-
              taining those commands.  If ename is not supplied, fc  uses  the
              value  of the FCEDIT variable, and the value of EDITOR if FCEDIT
              is not set.  If neither variable is set, fc uses vi. When  edit-
              ing  is  complete,  fc reads the file containing the edited com-
              mands and echoes and executes them.

              In the second form, fc re-executes command after replacing  each
              instance  of  pat  with rep.  Command is interpreted the same as
              first above.

              A useful alias to use with fc 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 zero unless an
              invalid option is encountered or first or last  specify  history
              lines  out  of  range.   When editing and re-executing a file of
              commands, the return value is the value of the last command exe-
              cuted or failure if an error occurs with the temporary file.  If
              the second form is used, the return status is that of the re-ex-
              ecuted command, unless cmd does not specify a valid history  en-
              try, in which case fc returns a non-zero status.

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

       getopts optstring name [arg ...]
              getopts is used by shell scripts and functions  to  parse  posi-
              tional  parameters and obtain options and their arguments.  opt-
              string contains the option characters to  be  recognized;  if  a
              character is followed by a colon, the option is expected to have
              an  argument,  which should be separated from it by white space.
              The colon and question mark characters may not be used as option
              characters.

              Each time it is invoked, getopts places the next option  in  the
              shell variable name, initializing name if it does not exist, and
              the index of the next argument to be processed into the variable
              OPTIND.   OPTIND  is  initialized  to 1 each time the shell or a
              shell script is invoked.  When an option requires  an  argument,
              getopts places that argument into the variable OPTARG.

              The  shell does not reset OPTIND automatically; it must be manu-
              ally reset between multiple calls to  getopts  within  the  same
              shell invocation to use a new set of parameters.

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

              getopts  normally  parses the positional parameters, but if more
              arguments are 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, getopts uses  silent  error  reporting.
              In  normal operation, getopts prints diagnostic messages when it
              encounters invalid options or missing option arguments.  If  the
              variable  OPTERR is set to 0, getopts does not display any error
              messages, even if the first character  of  optstring  is  not  a
              colon.

              If getopts detects an invalid option, it places ? into name and,
              if  not  silent,  prints an error message and unsets OPTARG.  If
              getopts is silent, it assigns the option character found to  OP-
              TARG and does not print a diagnostic message.

              If  a required argument is not found, and getopts is not silent,
              it sets the value of name to a question mark (?), unsets OPTARG,
              and prints a diagnostic message.  If getopts is silent, it  sets
              the  value  of name to a colon (:) and sets OPTARG 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, it remembers the full pathname of the
              command  name  as  determined  by  searching  the directories in
              $PATH.  Any previously-remembered pathname associated with  name
              is  discarded.  If the -p option is supplied, hash uses filename
              as the full pathname of the command.

              The -r option causes the shell to forget  all  remembered  loca-
              tions.   Assigning  to  the PATH variable also clears all hashed
              filenames.  The -d option causes the shell to forget the  remem-
              bered location of each name.

              If the -t option is supplied, hash prints the full pathname cor-
              responding  to  each  name.  If multiple name arguments are sup-
              plied with -t, hash prints the  name  before  the  corresponding
              hashed full pathname.  The -l option displays output in a format
              that may be reused as input.

              If  no  arguments  are  given,  or  if only -l is supplied, hash
              prints information about remembered commands.  The -t,  -d,  and
              -p  options (the options that act on the name arguments) are mu-
              tually exclusive.  Only one will be active.  If more than one is
              supplied, -t has higher priority than -p, and both  have  higher
              priority than -d.

              The  return  status is zero unless a name is not found or an in-
              valid 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 as described below; otherwise it displays a list of  all
              the builtins and shell compound commands.

              Options, if supplied, have the follow meanings:

              -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

              If  pattern  contains  pattern  matching characters (see Pattern
              Matching above) it's treated as a shell pattern and help  prints
              the description of each help topic matching pattern.

              If  not,  and  pattern exactly matches the name of a help topic,
              help prints the description associated with that topic.   Other-
              wise,  help performs prefix matching and prints the descriptions
              of all matching help topics.

              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  numbers.
              Entries  prefixed with a * have been modified.  An argument of n
              lists only the last n entries.  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.  If history uses HISTTIMEFORMAT, it does
              not print an intervening space between the formatted time  stamp
              and the history entry.

              If filename is supplied, history uses it as the name of the his-
              tory  file;  if not, it uses the value of HISTFILE.  If filename
              is not supplied and HISTFILE is unset or null, the -a,  -n,  -r,
              and -w options have no effect.

              Options, if supplied, have the following meanings:
              -c     Clear the history list by deleting all the entries.  This
                     can be used with the other options to replace the history
                     list.
              -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 and add them to the current history list.  These are
                     lines appended to the history file since the beginning of
                     the current bash session.
              -r     Read the history file and append its contents to the cur-
                     rent history list.
              -w     Write the current history list to the history file, over-
                     writing the history file.
              -p     Perform history substitution on the  following  args  and
                     display  the result on the standard output, without stor-
                     ing 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
                     adding the args.

              If  the  HISTTIMEFORMAT variable is set, history writes the time
              stamp information associated with each history entry to the his-
              tory file, marked with the  history  comment  character  as  de-
              scribed  above.   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 supplied as an argument to -p fails.

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

              If jobspec is supplied, jobs  restricts  output  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] id [ ... ]
       kill -l|-L [sigspec | exit_status]
              Send  the signal specified by sigspec or signum to the processes
              named by each id.  Each id may be a job specification jobspec or
              a process ID pid.  sigspec is either a  case-insensitive  signal
              name  such as SIGKILL (with or without the SIG prefix) or a sig-
              nal number; signum is a signal number.  If sigspec is  not  sup-
              plied, then kill sends SIGTERM.

              The -l option lists the signal names.  If any arguments are sup-
              plied when -l is given, kill lists the names of the signals cor-
              responding  to  the  arguments, and the return status is 0.  The
              exit_status argument to -l is a number specifying either a  sig-
              nal  number or the exit status of a process terminated by a sig-
              nal; if it is supplied, kill prints the name of the signal  that
              caused the process to terminate.  kill assumes that process exit
              statuses are greater than 128; anything less than that is a sig-
              nal number.  The -L option is equivalent to -l.

              kill  returns true if at least one signal was successfully sent,
              or false if an error occurs or an invalid option is encountered.

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

       local [option] [name[=value] ... | - ]
              For each argument, create a local variable named name and assign
              it value.  The option can be any of the options accepted by  de-
              clare.   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.   It is an error to use local when not
              within a function.

              If name is -, it makes the set of shell  options  local  to  the
              function  in  which  local is invoked: any shell options changed
              using the set builtin inside the function after the call to  lo-
              cal  are restored to their original values when the function re-
              turns.  The restore is performed as if a series of set  commands
              were  executed  to  restore the values that were in place before
              the function.

              With no operands, local writes a list of local variables to  the
              standard output.

              The  return status is 0 unless local is used outside a function,
              an invalid name is supplied, or name is a readonly variable.

       logout [n]
              Exit a login shell, returning a status of n to the shell's  par-
              ent.

       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, or from file descriptor fd
              if the -u option is supplied, into the  indexed  array  variable
              array.   The variable MAPFILE is the default array.  Options, if
              supplied, have the following meanings:
              -d     Use the first character of delim to terminate each  input
                     line, rather than newline.  If delim is the empty string,
                     mapfile will terminate a line when it reads a NUL charac-
                     ter.
              -n     Copy at most count lines.  If count is 0, copy all lines.
              -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 zero 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]
              Remove entries from the directory stack.  The elements are  num-
              bered  from 0 starting at the first directory listed by dirs, so
              popd is equivalent to "popd +0."  With no  arguments,  popd  re-
              moves  the  top directory from the stack, and changes to the new
              top directory.  Arguments, if supplied, have the following mean-
              ings:
              -n     Suppress the normal change of directory when removing di-
                     rectories from the stack, only manipulate the stack.
              +n     Remove 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     Remove 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 supplied,
              the directory stack is empty, or n specifies a non-existent  di-
              rectory stack entry.

              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 assigns the output to  the
              variable var rather than printing it 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(3)  format  characters  cCsS-
              ndiouxXeEfFgGaA, printf interprets the following additional for-
              mat specifiers:
              %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 and %Q  use
                     the  $''  quoting style if any characters in the argument
                     string require it, and backslash quoting  otherwise.   If
                     the  format  string uses the printf alternate form, these
                     two  formats  quote  the  argument  string  using  single
                     quotes.
              %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.  This format specifier
                     recognizes two special argument values: -1 represents the
                     current time, and -2 represents the time  the  shell  was
                     invoked.  If no argument is specified, conversion behaves
                     as  if -1 had been supplied.  This is an exception to the
                     usual printf behavior.

              The %b, %q, and %T format specifiers all use the field width and
              precision arguments from the format specification and write that
              many bytes from (or use that wide a field for) the expanded  ar-
              gument,  which  usually contains more characters than the origi-
              nal.

              The %n format specifier accepts a corresponding argument that is
              treated as a shell variable name.

              The %s and %c format specifiers accept  an  l  (long)  modifier,
              which forces them to convert the argument string to a wide-char-
              acter string and apply any supplied field width and precision in
              terms of characters, not bytes.  The %S and %C format specifiers
              are equivalent to %ls and %lc, respectively.

              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 numeric value of the following character, using the cur-
              rent locale.

              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 if an invalid option is sup-
              plied or a write or assignment error occurs.

       pushd [-n] [+n] [-n]
       pushd [-n] [dir]
              Add a directory to the top of the directory stack, or rotate the
              stack, making the new top of the stack the current  working  di-
              rectory.   With  no  arguments, pushd exchanges the top two ele-
              ments of the directory stack.  Arguments, if supplied, have  the
              following meanings:
              -n     Suppress  the normal change of directory when rotating or
                     adding directories to  the  stack,  only  manipulate  the
                     stack.
              +n     Rotate 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 zero un-
              less the directory stack is empty.  When rotating the  directory
              stack, pushd returns zero unless the directory stack is empty or
              n specifies a non-existent directory stack element.

              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 [-Eers] [-a aname] [-d delim] [-i text] [-n nchars] [-N nchars]
       [-p prompt] [-t timeout] [-u fd] [name ...]
              Read one line from the standard input, or from the file descrip-
              tor  fd  supplied as an argument to the -u option, split it into
              words as described above under Word Splitting,  and  assign  the
              first  word  to  the  first  name, the second word to the second
              name, and so on.  If there are more words than  names,  the  re-
              maining  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 the value of the IFS variable  are  used
              to split the line into words using the same rules the shell uses
              for expansion (described above under Word Splitting).  The back-
              slash  character  (\)  removes  any special meaning for the next
              character read and is used 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 terminates the input 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, read
                     uses readline (see READLINE above) to  obtain  the  line.
                     Readline  uses  the  current (or default, if line editing
                     was not previously active)  editing  settings,  but  uses
                     readline's default filename completion.
              -E     If  the  standard  input  is coming from a terminal, read
                     uses readline (see READLINE above) to  obtain  the  line.
                     Readline  uses  the  current (or default, if line editing
                     was not previously active)  editing  settings,  but  uses
                     bash's default completion, including programmable comple-
                     tion.
              -i text
                     If  readline  is being used to read the line, read places
                     text into the editing buffer before editing begins.
              -n nchars
                     read returns after reading nchars characters rather  than
                     waiting  for  a complete line of input, unless it encoun-
                     ters EOF or read times out, but honors a delimiter if  it
                     reads fewer than nchars characters before the delimiter.
              -N nchars
                     read  returns  after  reading  exactly  nchars characters
                     rather than waiting for a complete line of input,  unless
                     it encounters EOF or read times out.  Any delimiter char-
                     acters  in the input are not treated specially and do not
                     cause read to return until it has read nchars characters.
                     The result is not split on the characters in IFS; the in-
                     tent is that the variable is assigned exactly the charac-
                     ters 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, but 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 it does  not
                     read  a  complete line of input (or a specified number of
                     characters) within timeout seconds.   timeout  may  be  a
                     decimal  number  with  a fractional portion following the
                     decimal 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, it saves any partial input read into
                     the specified variable  name,  and  the  exit  status  is
                     greater  than 128.  If timeout is 0, read returns immedi-
                     ately, without trying to read any data.   In  this  case,
                     the  exit status is 0 if input is available on the speci-
                     fied file descriptor, or the read will return  EOF,  non-
                     zero otherwise.
              -u fd  Read  input  from file descriptor fd instead of the stan-
                     dard input.

              Other than the case where delim is the empty  string,  read  ig-
              nores any NUL characters in the input.

              If  no  names  are supplied, read assigns the line read, without
              the ending delimiter but otherwise unmodified, to  the  variable
              REPLY.

              The exit status is zero, unless end-of-file is encountered, read
              times  out  (in  which  case  the status is greater than 128), a
              variable assignment error (such as assigning to a readonly vari-
              able) 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 or unset.  If the -f
              option is supplied, each name refers to a shell  function.   The
              -a  option restricts the variables to indexed arrays; the -A op-
              tion restricts the variables to associative arrays.  If both op-
              tions are supplied, -A takes precedence.  If no  name  arguments
              are  supplied,  or if the -p option is supplied, print a list of
              all readonly names.  The other options may be used  to  restrict
              the output to a subset of the set of readonly names.  The -p op-
              tion displays output in a format that may be reused as input.

              readonly  allows  the  value of a variable to be set at the same
              time the readonly attribute is changed by following the variable
              name with =value.  This sets the value of  the  variable  is  to
              value while modifying the readonly attribute.

              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]
              Stop  executing  a shell function or sourced file and return the
              value specified by n to its caller.  If n is omitted, the return
              status is that of the last command executed.  If return is  exe-
              cuted  by a trap handler, the last command used to determine the
              status is the last command executed before the trap handler.  If
              return is executed during a DEBUG trap, the last command used to
              determine the status is the last command executed  by  the  trap
              handler before return was invoked.

              When return is used to terminate execution of a script being ex-
              ecuted  by  the .  (source) command, it causes the shell to stop
              executing that script and return either n or the exit status  of
              the  last  command executed within the script as the exit status
              of the script.  If n is supplied, the return value is its  least
              significant 8 bits.

              Any  command  associated with the RETURN trap is executed before
              execution resumes after the function or script.

              The return status is non-zero if return is  supplied  a  non-nu-
              meric argument, or is used outside a function and not during ex-
              ecution of a script by . or source.

       set [-abefhkmnptuvxBCEHPT] [-o option-name] [--] [-] [arg ...]
       set [+abefhkmnptuvxBCEHPT] [+o option-name] [--] [-] [arg ...]
       set -o
       set +o 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 or af-
                      ter a foreground command terminates.  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  reserved word, 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 fi-
                      nal && or ||, any command in a  pipeline  but  the  last
                      (subject  to the state of the pipefail shell option), 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
                              "IGNOREEOF=10"  had  been  executed  (see  Shell
                              Variables above).
                      keyword Same as -k.
                      monitor Same as -m.
                      noclobber
                              Same as -C.
                      noexec  Same as -n.
                      noglob  Same as -f.
                      nolog   Currently ignored.
                      notify  Same as -b.
                      nounset Same as -u.
                      onecmd  Same as -t.
                      physical
                              Same as -P.
                      pipefail
                              If set, the return value of a  pipeline  is  the
                              value  of  the  last (rightmost) command to exit
                              with a non-zero status, or zero if all  commands
                              in  the pipeline exit successfully.  This option
                              is disabled by default.
                      posix   Enable posix mode; change the behavior  of  bash
                              where  the  default  operation  differs from the
                              POSIX standard to match the standard.   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, set prints the
                      current shell option settings.  If +o is  supplied  with
                      no  option-name,  set prints a series of set commands to
                      recreate the current option  settings  on  the  standard
                      output.
              -p      Turn  on  privileged mode.  In this mode, the shell does
                      not read the $ENV and $BASH_ENV files,  shell  functions
                      are  not  inherited  from the environment, and the SHEL-
                      LOPTS, BASHOPTS, CDPATH, and  GLOBIGNORE  variables,  if
                      they  appear  in  the  environment, are ignored.  If the
                      shell is started with the effective user (group) id  not
                      equal  to the real user (group) id, and the -p option is
                      not supplied, these actions are taken and the  effective
                      user id is set to the real user id.  If the -p option is
                      supplied at startup, the effective user id is not reset.
                      Turning  this  option  off causes the effective user and
                      group ids to be set to the real user and group ids.
              -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, to
                      the standard error.
              -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.   Using  the
                      redirection  operator >| instead of > will override this
                      and force the creation of an output file.
              -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, unset the positional
                      parameters.  Otherwise, set the positional parameters to
                      the args, even if some of them begin with a -.
              -       Signal the end of options, and assign all remaining args
                      to the positional parameters.  The -x and -v options are
                      turned off.  If there are no args, the positional  para-
                      meters 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 zero unless an invalid option  is  encoun-
              tered.

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

       shopt [-pqsu] [-o] [optname ...]
              Toggle the values of settings controlling optional shell  behav-
              ior.   The settings can be either those listed below, or, if the
              -o option is used, those available with the -o option to the set
              builtin command.

              With no options, or with the -p option, display a  list  of  all
              settable  options,  with an indication of whether or not each is
              set; if any optnames are supplied, the output is  restricted  to
              those options.  The -p option displays output in a form that may
              be reused as input.

              Other options have the following meanings:
              -s     Enable (set) each optname.
              -u     Disable (unset) each optname.
              -q     Suppresses  normal output (quiet mode); the return status
                     indicates whether the optname is set or unset.  If multi-
                     ple optname arguments are supplied with  -q,  the  return
                     status is zero if all optnames are enabled; non-zero oth-
                     erwise.
              -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:

              array_expand_once
                      If set, the shell suppresses multiple evaluation of  as-
                      sociative and indexed array subscripts during arithmetic
                      expression evaluation, while executing builtins that can
                      perform   variable   assignments,  and  while  executing
                      builtins that perform array dereferencing.
              assoc_expand_once
                      Deprecated; a synonym for array_expand_once.
              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.
              bash_source_fullpath
                      If set, filenames added to the BASH_SOURCE  array  vari-
                      able  are  converted  to full pathnames (see Shell Vari-
                      ables above).
              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, the cd command attempts to correct minor  errors
                      in  the spelling of a directory component.  Minor errors
                      include transposed characters, a missing character,  and
                      one extra character.  If cd corrects the directory name,
                      it  prints  the corrected filename, and the command pro-
                      ceeds.  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, bash performs a normal path
                      search.
              checkjobs
                      If set, bash lists the status of any stopped and running
                      jobs before exiting an interactive shell.  If  any  jobs
                      are running, bash defers the exit until a second exit is
                      attempted  without  an intervening command (see JOB CON-
                      TROL above).  The shell always postpones exiting 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, using the file descriptor
                      associated with the standard error if it is a  terminal.
                      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
                      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
                      buffer.  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.  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,  enable  the extended pattern matching features
                      described above under Pathname Expansion.
              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, pattern matching does not  take  the
                      current  locale's  collating sequence 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, the  user  is  given
                      the  opportunity  to  re-edit a failed history substitu-
                      tion.
              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
                      In an interactive shell, a word beginning with #  causes
                      that  word  and all remaining characters on that line to
                      be ignored, as in a non-interactive shell (see  COMMENTS
                      above).  This option is enabled by default.
              lastpipe
                      If  set,  and  job control is not active, the shell runs
                      the last command of a pipeline not executed in the back-
                      ground in the current shell environment.
              lithist If set, and the cmdhist option  is  enabled,  multi-line
                      commands are saved to the history with embedded newlines
                      rather than using semicolon separators where possible.
              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, bash
                      displays the message "The  mail  in  mailfile  has  been
                      read".
              no_empty_cmd_completion
                      If set, and readline is being used, bash does not search
                      PATH  for  possible  completions  when completion is at-
                      tempted 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, pathname expansion patterns which match no files
                      (see Pathname Expansion above) expand to nothing and are
                      removed, rather than expanding to 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,  enable  the programmable completion facilities
                      (see Programmable Completion above).  This option is en-
                      abled 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  when  the -p option is not supplied.  This op-
                      tion is enabled by default.
              varredir_close
                      If set, the shell automatically closes file  descriptors
                      assigned  using  the  {varname}  redirection syntax (see
                      REDIRECTION above) instead of leaving them open when the
                      command completes.
              xpg_echo
                      If set, the echo builtin  expands  backslash-escape  se-
                      quences  by  default.  If the posix shell option is also
                      enabled, echo does not interpret any options.

       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 will 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  sup-
              plied.

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

              Expressions  may  be  combined  using  the  following operators,
              listed in decreasing order of precedence.   The  evaluation  de-
              pends on the number of arguments; see below.  test uses operator
              precedence 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
                     normal operator precedence.
              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.  If the first argument is exactly  (  and  the
                     fourth argument is exactly ), the result is the two-argu-
                     ment  test of the second and third arguments.  Otherwise,
                     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 the shell is in posix mode, or if the expression is part of
              the [[ command, the < and > operators sort using the current lo-
              cale.  If the shell is not in posix mode, the test  and  [  com-
              mands sort lexicographically using ASCII ordering.

              The  historical operator-precedence parsing with 4 or more argu-
              ments can lead to ambiguities when it  encounters  strings  that
              look  like  primaries.  The POSIX standard has deprecated the -a
              and -o primaries and enclosing expressions  within  parentheses.
              Scripts  should  no longer use them.  It's much more reliable to
              restrict test invocations to a single primary,  and  to  replace
              uses of -a and -o with the shell's && and || list operators.

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

       trap [-lpP] [[action] sigspec ...]
              The action is a command that is read and executed when the shell
              receives any of the signals sigspec.  If action is  absent  (and
              there is a single sigspec) or -, each specified sigspec is reset
              to  the  value  it had when the shell was started.  If action is
              the null string the signal specified by each sigspec is  ignored
              by the shell and by the commands it invokes.

              If  no arguments are supplied, trap displays the actions associ-
              ated with each trapped signal as a set of trap commands that can
              be reused as shell input to restore the current signal  disposi-
              tions.   If  -p  is  given, and action is not present, then trap
              displays the actions associated with each sigspec  or,  if  none
              are supplied, for all trapped signals, as a set of trap commands
              that  can be reused as shell input to restore the current signal
              dispositions.  The -P option  behaves  similarly,  but  displays
              only  the actions associated with each sigspec argument.  -P re-
              quires at least one sigspec argument.  The -P or -p options  may
              be  used  in a subshell environment (e.g., command substitution)
              and, as long as they are used before trap is used  to  change  a
              signal's handling, will display the state of its parent's traps.

              The  -l  option  prints  a list of signal names and their corre-
              sponding numbers.  Each sigspec is either a signal name  defined
              in <signal.h>, or a signal number.  Signal names are case insen-
              sitive  and  the SIG prefix is optional.  If -l is supplied with
              no sigspec arguments, it prints a list of valid signal names.

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

              If a sigspec is ERR, action  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 reserved word, part of the test in an if state-
              ment, part of a command executed in a && or || list  except  the
              command  following the final && or ||, any command in a pipeline
              but the last (subject to the state of  the  pipefail  shell  op-
              tion),  or if the command's return value is being inverted using
              !.  These are the same conditions obeyed by the errexit (-e) op-
              tion.

              When the shell is not interactive, signals ignored upon entry to
              the shell cannot be trapped or reset.  Interactive shells permit
              trapping signals ignored on entry.  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.

       true   Does nothing, returns a 0 status.

       type [-aftpP] name [name ...]
              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 executable file,  re-
              spectively.   If  the name is not found, type prints nothing and
              returns a non-zero exit status.

              If the -p option is used, type either returns  the  pathname  of
              the  executable  file that would be found by searching $PATH for
              name or nothing if "type -t name" would not return file.  The -P
              option forces a PATH search for each  name,  even  if  "type  -t
              name" would not return file.  If name is present in the table of
              hashed  commands, -p and -P print the hashed value, which is not
              necessarily the file that appears first in PATH.

              If the -a option is used, type prints all  of  the  places  that
              contain  a  command named name.  This includes aliases, reserved
              words, functions, and builtins, but the path search options  (-p
              and  -P)  can  be  supplied to restrict the output to executable
              files.  type does not consult the table of hashed commands  when
              using -a with -p, and only performs a PATH search for name.

              The -f option suppresses shell function lookup, as with the com-
              mand  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 it starts, on systems that allow such control.

              The  -H and -S options specify whether 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, ulimit sets both the soft and hard limits.

              The value of limit can be a number in the unit specified for the
              resource  or one of the special values hard, soft, or unlimited,
              which stand for the current hard limit, the current soft  limit,
              and  no limit, respectively.  If limit is omitted, ulimit prints
              the current value of the soft limit of the resource, 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 options are interpreted as follows:
              -a     Report all current limits; 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 supplied, and the -a option is not  used,  limit  is
              the  new  value of the specified resource.  If no option is sup-
              plied, 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]
              Set  the user file-creation mask to mode.  If mode begins with a
              digit, it is interpreted as an octal number; otherwise it is in-
              terpreted as a symbolic mode mask similar to  that  accepted  by
              chmod(1).  If mode is omitted, umask prints the current value of
              the mask.  The -S option without a mode argument prints the mask
              in a symbolic format; 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 zero
              if the mode was successfully changed or if no mode argument  was
              supplied, and non-zero otherwise.

       unalias [-a] [name ...]
              Remove  each  name  from  the list of defined aliases.  If -a is
              supplied, remove all alias definitions.   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.  If -f  is  specified,  each  name
              refers  to  a shell function, and the function definition is re-
              moved.  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.   Read-only  variables and functions may not be unset.
              When variables or functions are removed, they are  also  removed
              from  the  environment passed to subsequent commands.  If no op-
              tions are supplied, each name refers to a variable; if there  is
              no  variable by that name, a function with that name, if any, is
              unset.  Some shell variables  may  not  be  unset.   If  any  of
              BASH_ALIASES,  BASH_ARGV0,  BASH_CMDS,  BASH_COMMAND,  BASH_SUB-
              SHELL,  BASHPID,   COMP_WORDBREAKS,   DIRSTACK,   EPOCHREALTIME,
              EPOCHSECONDS,  FUNCNAME,  GROUPS,  HISTCMD, LINENO, RANDOM, SEC-
              ONDS, or SRANDOM are unset, they lose their special  properties,
              even  if  they  are subsequently reset.  The exit status is true
              unless a name is readonly or may not be unset.

       wait [-fn] [-p varname] [id ...]
              Wait for each specified child process id and return the termina-
              tion status of the last id.  Each id may be a process ID pid  or
              a  job  specification  jobspec;  if  a jobspec is supplied, wait
              waits for all processes in the job.

              If no options or ids are supplied, 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  any  one  of  the
              given ids or, if no ids are supplied, any job or process substi-
              tution, to complete and returns its exit status.  If none of the
              supplied  ids is a child of the shell, or if no ids are supplied
              and the shell has no unwaited-for children, the exit  status  is
              127.

              If  the  -p  option is supplied, wait assigns the process or job
              identifier of the job for which the exit status is  returned  to
              the  variable  varname  named by the option argument.  The vari-
              able, which cannot be readonly, will be unset initially,  before
              any  assignment.   This is useful only when used with the -n op-
              tion.

              Supplying the -f option, when job  control  is  enabled,  forces
              wait  to wait for each id to terminate before returning its sta-
              tus, instead of returning when it changes status.

              If none of the ids specify  one  of  the  shell's  active  child
              processes,  the return status is 127.  If wait is interrupted by
              a signal, any varname will remain unset, and the  return  status
              will  be  greater  than  128,  as described under SIGNALS above.
              Otherwise, the return status is the exit status of the last id.

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, com-
       pat40,  compat41,  and so on).  There is only one current compatibility
       level -- each option is mutually exclusive.  The compatibility level is
       intended to allow users to select behavior from previous versions  that
       is  incompatible  with newer versions while they migrate scripts to use
       current features and behavior.  It's intended to be a  temporary  solu-
       tion.

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

       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 began deprecating older compatibility lev-
       els.  Eventually, the options will be removed in favor of BASH_COMPAT.

       Bash-5.0 was the final version for which there was an individual  shopt
       option  for the previous version.  BASH_COMPAT is the only mechanism to
       control the compatibility level in versions newer than bash-5.0.

       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      The < and > operators to the [[ command do  not  consider
                     the current locale when comparing strings; they use ASCII
                     ordering.

       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      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 en-
                     abled.
              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 compatibil-
                     ity 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.
              o      Arithmetic commands ( ((...)) ) and the expressions in an
                     arithmetic for statement can be expanded more than once.
              o      Expressions  used as arguments to arithmetic operators in
                     the [[ conditional command  can  be  expanded  more  than
                     once.
              o      The  expressions  in  substring parameter brace expansion
                     can be expanded more than once.
              o      The expressions in the $((...)) word expansion can be ex-
                     panded more than once.
              o      Arithmetic expressions used as indexed  array  subscripts
                     can be expanded more than once.
              o      test  -v,  when  given an argument of A[@], where A is an
                     existing associative array, will return true if the array
                     has any set elements.  Bash-5.2 will look for and  report
                     on a key named @.
              o      The  ${parameter[:]=value}  word  expansion  will  return
                     value, before any variable-specific transformations  have
                     been performed (e.g., converting to lowercase).  Bash-5.2
                     will return the final value assigned to the variable.
              o      Parsing  command substitutions will behave as if extended
                     globbing (see the description of the shopt builtin above)
                     is enabled, so that parsing a command  substitution  con-
                     taining an extglob pattern (say, as part of a shell func-
                     tion)  will  not fail.  This assumes the intent is to en-
                     able extglob before the command is executed and word  ex-
                     pansions  are  performed.  It will fail at word expansion
                     time if extglob hasn't been enabled by the time the  com-
                     mand is executed.

       compat52
              o      The  test  builtin uses its historical algorithm to parse
                     parenthesized subexpressions when given five or more  ar-
                     guments.
              o      If  the  -p or -P option is supplied to the bind builtin,
                     bind treats any arguments remaining after option process-
                     ing as bindable command names, and displays any  key  se-
                     quences  bound to those commands, instead of treating the
                     arguments as key sequences to bind.

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      Using  the  -p  option  to  the  .  builtin command to specify a
              search path.

       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 values of BASHOPTS and SHELLOPTS from the shell en-
              vironment at startup.

       o      Redirecting output using the >, >|, <>, >&, &>, and >>  redirec-
              tion 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/9799919799/
       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!  You may send suggestions and "philosophical" bug
       reports to bug-bash@gnu.org  or  post  them  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 behavior
       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 lists of the form "a ; b  ;  c"  are  not
       handled  gracefully  when  combined  with  process  suspension.  When a
       process is stopped, the shell immediately executes the next command  in
       the  list  or breaks out of any existing loops.  It suffices to enclose
       the command in parentheses to force it into a subshell,  which  may  be
       stopped  as a unit, or to start the command in the background and imme-
       diately bring it into the foreground.

       Array variables may not (yet) be exported.

GNU Bash 5.3                   2025 February 24                        BASH(1)
