BASH(1)



BASH(1)                     General Commands Manual                    BASH(1)

NAME
       bash - GNU Bourne-Again SHell

SYNOPSIS
       bash [options] [command_string | file]

COPYRIGHT
       Bash is Copyright (C) 1989-2018 by the Free Software Foundation, Inc.

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

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

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

       -c        If the -c option is present, then commands are read from  the
                 first non-option argument command_string.  If there are argu-
                 ments after the command_string, the  first  argument  is  as-
                 signed  to $0 and any remaining arguments are assigned to the
                 positional parameters.  The assignment to $0 sets the name of
                 the shell, which is used in warning and error messages.
       -i        If the -i option is present, the shell is interactive.
       -l        Make bash act as if it had been invoked as a login shell (see
                 INVOCATION below).
       -r        If the -r option is present,  the  shell  becomes  restricted
                 (see RESTRICTED SHELL below).
       -s        If  the -s option is present, or if no arguments remain after
                 option processing, then commands are read from  the  standard
                 input.   This  option  allows the positional parameters to be
                 set when invoking an interactive shell or when reading  input
                 through a pipe.
       -v        Print shell input lines as they are read.
       -x        Print commands and their arguments as they are executed.
       -D        A  list of all double-quoted strings preceded by $ is printed
                 on the standard output.  These are the strings that are  sub-
                 ject to language translation when the current locale is not C
                 or POSIX.  This implies the -n option; no  commands  will  be
                 executed.
       [-+]O [shopt_option]
                 shopt_option  is  one  of  the  shell options accepted by the
                 shopt  builtin  (see  SHELL  BUILTIN  COMMANDS  below).    If
                 shopt_option is present, -O sets the value of that option; +O
                 unsets it.  If shopt_option is not supplied,  the  names  and
                 values  of the shell options accepted by shopt are printed on
                 the standard output.  If the invocation  option  is  +O,  the
                 output is displayed in a format that may be reused as input.
       --        A  --  signals the end of options and disables further option
                 processing.  Any arguments after the -- are treated as  file-
                 names and arguments.  An argument of - is equivalent to --.

       Bash  also  interprets  a number of multi-character options.  These op-
       tions must appear on the command line before the  single-character  op-
       tions to be recognized.

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

       --login
              Equivalent to -l.

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

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

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

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

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

       --verbose
              Equivalent to -v.

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

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

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

       An interactive shell is one started without non-option  arguments  (un-
       less  -s  is  specified) and without the -c option whose standard input
       and error are both connected to terminals (as determined by isatty(3)),
       or  one  started  with  the -i option.  PS1 is set and $- includes i if
       bash is interactive, allowing a shell script or a startup file to  test
       this state.

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

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

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

       When an interactive shell that is not a login shell  is  started,  bash
       reads  and  executes  commands  from /etc/bash.bashrc and ~/.bashrc, if
       these files exist.  This may be inhibited by using the  --norc  option.
       The  --rcfile  file option will force bash to read and execute commands
       from file instead of /etc/bash.bashrc and ~/.bashrc.

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

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

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

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

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

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

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

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

SHELL GRAMMAR
   Simple Commands
       A simple command is a sequence of optional  variable  assignments  fol-
       lowed  by  blank-separated  words and redirections, and terminated by a
       control operator.  The first word specifies the command to be executed,
       and  is passed as argument zero.  The remaining words are passed as 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]] [ ! ] command [ [|||&] command2 ... ]

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

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

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

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

       Each command in a pipeline is executed as a separate process (i.e.,  in
       a  subshell).  See COMMAND EXECUTION ENVIRONMENT for a description of a
       subshell environment.  If the lastpipe  option  is  enabled  using  the
       shopt builtin (see the description of shopt below), the last element of
       a pipeline may be run by the shell process.

   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 environment (see  COMMAND  EXECU-
              TION  ENVIRONMENT below).  Variable assignments and builtin com-
              mands that affect the shell's environment do not remain  in  ef-
              fect after the command completes.  The return status is the exit
              status of list.

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

       ((expression))
              The expression is evaluated according to the rules described be-
              low under ARITHMETIC EVALUATION.  If the value of the expression
              is non-zero, the return status is 0; otherwise the return status
              is 1.  This is exactly equivalent to let "expression".

       [[ expression ]]
              Return a status of 0 or 1 depending on  the  evaluation  of  the
              conditional  expression expression.  Expressions are composed of
              the primaries described  below  under  CONDITIONAL  EXPRESSIONS.
              Word  splitting  and pathname expansion are not performed on the
              words between the [[ and  ]];  tilde  expansion,  parameter  and
              variable  expansion, arithmetic expansion, command substitution,
              process substitution, and quote removal are  performed.   Condi-
              tional operators such as -f must be unquoted to be recognized as
              primaries.

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

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

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

       An  additional  binary operator, =~, is available, with the same prece-
       dence as == and !=.  When it is used, the string to the  right  of  the
       operator  is considered a POSIX extended regular expression and matched
       accordingly (as in regex(3)).  The return value  is  0  if  the  string
       matches  the  pattern,  and  1 otherwise.  If the regular expression is
       syntactically incorrect, the conditional expression's return  value  is
       2.   If the nocasematch shell option is enabled, the match is performed
       without regard to the case of alphabetic characters.  Any part  of  the
       pattern  may  be  quoted to force the quoted portion to be matched as a
       string.  Bracket expressions in regular  expressions  must  be  treated
       carefully,  since normal quoting characters lose their meanings between
       brackets.  If the pattern is stored in a shell  variable,  quoting  the
       variable expansion forces the entire pattern to be matched as a string.
       Substrings matched by parenthesized subexpressions within  the  regular
       expression  are  saved in the array variable BASH_REMATCH.  The element
       of BASH_REMATCH with index 0 is the portion of the string matching  the
       entire regular expression.  The element of BASH_REMATCH with index n is
       the portion of the string matching the nth parenthesized subexpression.

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

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

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

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

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

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

       case word in [ [(] pattern [ | pattern ] ... ) list ;; ] ... esac
              A case command first expands word, and tries to match it against
              each  pattern  in turn, using the matching rules described under
              Pattern Matching below.  The word is expanded using tilde expan-
              sion,  parameter  and  variable expansion, arithmetic expansion,
              command substitution, process substitution  and  quote  removal.
              Each pattern examined is expanded using tilde expansion, parame-
              ter and variable expansion, arithmetic expansion,  command  sub-
              stitution,  and  process substitution.  If the nocasematch shell
              option is enabled, the match is performed without regard to  the
              case  of alphabetic characters.  When a match is found, the cor-
              responding list is executed.  If the ;;  operator  is  used,  no
              subsequent  matches are attempted after the first pattern match.
              Using ;& in place of ;; causes execution to  continue  with  the
              list  associated  with  the  next set of patterns.  Using ;;& in
              place of ;; causes the shell to test the next  pattern  list  in
              the statement, if any, and execute any associated list on a suc-
              cessful match.  The exit status is zero if no  pattern  matches.
              Otherwise, it is the exit status of the last command executed in
              list.

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

       while list-1; do list-2; done
       until list-1; do list-2; done
              The while command continuously executes the list list-2 as  long
              as the last command in the list list-1 returns an exit status of
              zero.  The until command is identical to the while command,  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 format for a coprocess is:

              coproc [NAME] command [redirections]

       This  creates a coprocess named NAME.  If NAME is not supplied, the de-
       fault name is COPROC.  NAME must not be supplied if command is a simple
       command  (see above); otherwise, it is interpreted as 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  descriptor in the executing shell, and that file de-
       scriptor is assigned to NAME[0].  The standard input of command is con-
       nected via a pipe to a file descriptor in the executing shell, and that
       file descriptor is assigned to NAME[1].  This pipe is  established  be-
       fore 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 ex-
       ecute the coprocess is available as the value of the variable NAME_PID.
       The  wait builtin command may be used to wait for the coprocess to ter-
       minate.

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

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

       name () compound-command [redirection]
       function name [()] compound-command [redirection]
              This defines a function named name.  The reserved word  function
              is  optional.   If  the  function reserved word is supplied, the
              parentheses are optional.  The body of the function is the  com-
              pound  command  compound-command  (see Compound Commands above).
              That command is usually a list of commands between { and },  but
              may  be  any  command listed under Compound Commands above, with
              one exception: If the function reserved word is  used,  but  the
              parentheses  are  not  supplied,  the braces are required.  com-
              pound-command is executed whenever name is specified as the name
              of  a  simple  command.  When in posix mode, name may not be the
              name of one of the POSIX  special  builtins.   Any  redirections
              (see REDIRECTION below) specified when a function is defined are
              performed when the function is executed.  The exit status  of  a
              function  definition  is  zero unless a syntax error occurs or a
              readonly function with the same name already exists.  When  exe-
              cuted,  the  exit status of a function is the exit status of the
              last command executed in the body.  (See FUNCTIONS below.)

COMMENTS
       In a non-interactive shell, or an interactive shell in which the inter-
       active_comments  option  to  the  shopt  builtin  is enabled (see SHELL
       BUILTIN COMMANDS below), a word beginning with # causes that  word  and
       all  remaining  characters  on that line to be ignored.  An interactive
       shell without the interactive_comments option enabled  does  not  allow
       comments.  The interactive_comments option is on by default in interac-
       tive shells.

QUOTING
       Quoting is used to remove the special meaning of certain characters  or
       words  to  the shell.  Quoting can be used to disable special treatment
       for special characters, to prevent reserved words from being recognized
       as such, and to prevent parameter expansion.

       Each  of  the metacharacters listed above under DEFINITIONS has special
       meaning to the shell and must be quoted if it is to represent itself.

       When the command history expansion facilities are being used (see  HIS-
       TORY EXPANSION below), the history expansion character, usually !, must
       be quoted to prevent history expansion.

       There are  three  quoting  mechanisms:  the  escape  character,  single
       quotes, and double quotes.

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

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

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

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

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

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

       A double-quoted string preceded by a dollar sign ($"string") will cause
       the  string  to  be translated according to the current locale.  If the
       current locale is C or POSIX, the  dollar  sign  is  ignored.   If  the
       string is translated and replaced, the replacement is double-quoted.

PARAMETERS
       A  parameter is an entity that stores values.  It can be a name, a num-
       ber, or one of the special characters listed below under Special Param-
       eters.   A variable is a parameter denoted by a name.  A variable has a
       value and zero or more attributes.  Attributes are assigned  using  the
       declare builtin command (see declare below in SHELL BUILTIN COMMANDS).

       A parameter is set if it has been assigned a value.  The null string is
       a valid value.  Once a variable is set, it may be unset only  by  using
       the unset builtin command (see SHELL BUILTIN COMMANDS below).

       A variable may be assigned to by a statement of the form

              name=[value]

       If  value  is not given, the variable is assigned the null string.  All
       values undergo tilde expansion, parameter and variable expansion,  com-
       mand  substitution, arithmetic expansion, and quote removal (see EXPAN-
       SION below).  If the variable has its integer attribute set, then value
       is evaluated as an arithmetic expression even if the $((...)) expansion
       is not used (see Arithmetic Expansion below).  Word  splitting  is  not
       performed,  with the exception of "$@" as explained below under Special
       Parameters.  Pathname expansion is not  performed.   Assignment  state-
       ments  may also appear as arguments to the alias, declare, typeset, ex-
       port, readonly, and  local  builtin  commands  (declaration  commands).
       When in posix mode, these builtins may appear in a command after one or
       more instances of the  command  builtin  and  retain  these  assignment
       statement properties.

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

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

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

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

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

   Shell Variables
       The following variables are set by the shell:

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

              This variable can be  used  with  BASH_LINENO  and  BASH_SOURCE.
              Each   element   of   FUNCNAME  has  corresponding  elements  in
              BASH_LINENO and BASH_SOURCE to describe the call stack.  For in-
              stance,    ${FUNCNAME[$i]}    was    called    from   the   file
              ${BASH_SOURCE[$i+1]} at  line  number  ${BASH_LINENO[$i]}.   The
              caller builtin displays the current call stack using this infor-
              mation.
       GROUPS An array variable containing the list of  groups  of  which  the
              current user is a member.  Assignments to GROUPS have no effect.
              If GROUPS is unset, it loses its special properties, even if  it
              is subsequently reset.
       HISTCMD
              The history number, or index in the history list, of the current
              command.  If HISTCMD is unset, it loses its special  properties,
              even if it is subsequently reset.
       HOSTNAME
              Automatically set to the name of the current host.
       HOSTTYPE
              Automatically  set  to a string that uniquely describes the type
              of machine on which bash is executing.  The default  is  system-
              dependent.
       LINENO Each  time this parameter is referenced, the shell substitutes a
              decimal number representing the current sequential  line  number
              (starting  with  1)  within a script or function.  When not in a
              script or function, the value substituted is not  guaranteed  to
              be meaningful.  If LINENO is unset, it loses its special proper-
              ties, even if it is subsequently reset.
       MACHTYPE
              Automatically set to a string that fully  describes  the  system
              type  on  which  bash is executing, in the standard GNU cpu-com-
              pany-system format.  The default is system-dependent.
       MAPFILE
              An array variable (see Arrays below) created to  hold  the  text
              read by the mapfile builtin when no variable name is supplied.
       OLDPWD The previous working directory as set by the cd command.
       OPTARG The  value  of the last option argument processed by the getopts
              builtin command (see SHELL BUILTIN COMMANDS below).
       OPTIND The index of the next argument to be processed  by  the  getopts
              builtin command (see SHELL BUILTIN COMMANDS below).
       OSTYPE Automatically  set to a string that describes the operating sys-
              tem on which bash is executing.  The  default  is  system-depen-
              dent.
       PIPESTATUS
              An  array  variable (see Arrays below) containing a list of exit
              status values from the processes in  the  most-recently-executed
              foreground pipeline (which may contain only a single command).
       PPID   The  process  ID  of the shell's parent.  This variable is read-
              only.
       PWD    The current working directory as set by the cd command.
       RANDOM Each time this parameter is referenced, a random integer between
              0 and 32767 is generated.  The sequence of random numbers may be
              initialized by assigning a value to RANDOM.  If RANDOM is unset,
              it  loses its special properties, even if it is subsequently re-
              set.
       READLINE_LINE
              The contents of the readline line buffer, for use with "bind -x"
              (see SHELL BUILTIN COMMANDS below).
       READLINE_POINT
              The position of the insertion point in the readline line buffer,
              for use with "bind -x" (see SHELL BUILTIN COMMANDS below).
       REPLY  Set to the line of input read by the read builtin  command  when
              no arguments are supplied.
       SECONDS
              Each  time  this  parameter is referenced, the number of seconds
              since shell invocation is returned.  If a value is  assigned  to
              SECONDS,  the  value  returned upon subsequent references is the
              number of seconds since the assignment plus the value  assigned.
              If SECONDS is unset, it loses its special properties, even if it
              is subsequently reset.
       SHELLOPTS
              A colon-separated list of enabled shell options.  Each  word  in
              the  list  is  a  valid  argument  for  the -o option to the set
              builtin command (see SHELL BUILTIN COMMANDS below).  The options
              appearing  in  SHELLOPTS are those reported as on by set -o.  If
              this variable is in the environment when bash  starts  up,  each
              shell  option  in  the  list  will be enabled before reading any
              startup files.  This variable is read-only.
       SHLVL  Incremented by one each time an instance of bash is started.
       UID    Expands to the user ID of the current user, initialized at shell
              startup.  This variable is readonly.

       The following variables are used by the shell.  In some cases, bash as-
       signs a default value to a variable; these cases are noted below.

       BASH_COMPAT
              The value is used to set the shell's compatibility  level.   See
              the  description  of the shopt builtin below under SHELL BUILTIN
              COMMANDS for a description of the various  compatibility  levels
              and  their  effects.   The  value may be a decimal number (e.g.,
              4.2) or an integer (e.g., 42) corresponding to the desired  com-
              patibility  level.   If BASH_COMPAT is unset or set to the empty
              string, the compatibility level is set to the  default  for  the
              current  version.   If BASH_COMPAT is set to a value that is not
              one of the valid compatibility levels, the shell prints an error
              message  and sets the compatibility level to the default for the
              current version.  The valid compatibility levels  correspond  to
              the  compatibility  options  accepted  by  the shopt builtin de-
              scribed below (for example, compat42 means that 4.2 and  42  are
              valid values).  The current version is also a valid value.
       BASH_ENV
              If  this parameter is set when bash is executing a shell script,
              its value is interpreted as a filename  containing  commands  to
              initialize the shell, as in ~/.bashrc.  The value of BASH_ENV is
              subjected to  parameter  expansion,  command  substitution,  and
              arithmetic  expansion  before  being  interpreted as a filename.
              PATH is not used to search for the resultant filename.
       BASH_XTRACEFD
              If set to an integer corresponding to a valid  file  descriptor,
              bash  will  write  the trace output generated when set -x is en-
              abled to that file descriptor.  The file  descriptor  is  closed
              when  BASH_XTRACEFD is unset or assigned a new value.  Unsetting
              BASH_XTRACEFD or assigning it the empty string causes the  trace
              output  to  be  sent  to  the standard error.  Note that setting
              BASH_XTRACEFD to 2 (the standard error file descriptor) and then
              unsetting it will result in the standard error being closed.
       CDPATH The  search  path for the cd command.  This is a colon-separated
              list of directories in which the shell looks for destination di-
              rectories  specified  by  the  cd  command.   A  sample value is
              ".:~:/usr".
       CHILD_MAX
              Set the number of exited child status values for  the  shell  to
              remember.   Bash will not allow this value to be decreased below
              a POSIX-mandated minimum, and there is  a  maximum  value  (cur-
              rently  8192)  that  this  may not exceed.  The minimum value is
              system-dependent.
       COLUMNS
              Used by the select compound command to  determine  the  terminal
              width  when  printing selection lists.  Automatically set if the
              checkwinsize option is enabled or in an interactive  shell  upon
              receipt of a SIGWINCH.
       COMPREPLY
              An array variable from which bash reads the possible completions
              generated by a shell function invoked by the  programmable  com-
              pletion  facility (see Programmable Completion below).  Each ar-
              ray element contains one possible completion.
       EMACS  If bash finds this variable in the environment  when  the  shell
              starts  with  value "t", it assumes that the shell is running in
              an Emacs shell buffer and disables line editing.
       ENV    Similar to BASH_ENV; used when the shell  is  invoked  in  posix
              mode.
       EXECIGNORE
              A  colon-separated list of shell patterns (see Pattern Matching)
              defining the list of filenames to be ignored by  command  search
              using  PATH.  Files whose full pathnames match one of these pat-
              terns are not considered executable files for  the  purposes  of
              completion and command execution via PATH lookup.  This does not
              affect the behavior of the [, test, and [[ commands.  Full path-
              names  in  the command hash table are not subject to EXECIGNORE.
              Use this variable to ignore shared library files that  have  the
              executable  bit  set, but are not executable files.  The pattern
              matching honors the setting of the extglob shell option.
       FCEDIT The default editor for the fc builtin command.
       FIGNORE
              A colon-separated list of suffixes  to  ignore  when  performing
              filename completion (see READLINE below).  A filename whose suf-
              fix matches one of the entries in FIGNORE is excluded  from  the
              list of matched filenames.  A sample value is ".o:~" (Quoting is
              needed when assigning a value to this variable,  which  contains
              tildes).
       FUNCNEST
              If  set  to  a  numeric  value greater than 0, defines a maximum
              function nesting level.  Function invocations that  exceed  this
              nesting level will cause the current command to abort.
       GLOBIGNORE
              A  colon-separated  list  of  patterns  defining the set of file
              names to be ignored by  pathname  expansion.   If  a  file  name
              matched  by a pathname expansion pattern also matches one of the
              patterns in GLOBIGNORE, it is removed from the list of matches.
       HISTCONTROL
              A colon-separated list of values controlling  how  commands  are
              saved  on  the history list.  If the list of values includes ig-
              norespace, lines which begin with  a  space  character  are  not
              saved  in  the history list.  A value of ignoredups causes lines
              matching the previous history entry to not be saved.  A value of
              ignoreboth is shorthand for ignorespace and ignoredups.  A value
              of erasedups causes all previous lines matching the current line
              to  be  removed from the history list before that line is saved.
              Any value not in the above list is ignored.  If  HISTCONTROL  is
              unset,  or does not include a valid value, all lines read by the
              shell parser are saved on the history list, subject to the value
              of  HISTIGNORE.  The second and subsequent lines of a multi-line
              compound command are not tested, and are added  to  the  history
              regardless of the value of HISTCONTROL.
       HISTFILE
              The name of the file in which command history is saved (see HIS-
              TORY below).  The default value is ~/.bash_history.   If  unset,
              the command history is not saved when a shell exits.
       HISTFILESIZE
              The maximum number of lines contained in the history file.  When
              this variable is assigned a value, the  history  file  is  trun-
              cated,  if  necessary,  to  contain  no more than that number of
              lines by removing the oldest entries.  The history file is  also
              truncated  to this size after writing it when a shell exits.  If
              the value is 0, the history file  is  truncated  to  zero  size.
              Non-numeric  values  and  numeric  values less than zero inhibit
              truncation.  The shell sets the default value to  the  value  of
              HISTSIZE after reading any startup files.
       HISTIGNORE
              A  colon-separated list of patterns used to decide which command
              lines should be saved on the history list.  Each pattern is  an-
              chored  at the beginning of the line and must match the complete
              line (no implicit `*' is  appended).   Each  pattern  is  tested
              against  the  line after the checks specified by HISTCONTROL are
              applied.  In addition to the normal shell pattern matching char-
              acters,  `&'  matches the previous history line.  `&' may be es-
              caped using a backslash; the backslash  is  removed  before  at-
              tempting  a  match.  The second and subsequent lines of a multi-
              line compound command are not tested, and are added to the  his-
              tory  regardless of the value of HISTIGNORE.  The pattern match-
              ing honors the setting of the extglob shell option.
       HISTSIZE
              The number of commands to remember in the command  history  (see
              HISTORY  below).   If  the value is 0, commands are not saved in
              the history list.  Numeric values less than zero result in every
              command  being  saved  on  the history list (there is no limit).
              The shell sets the  default  value  to  500  after  reading  any
              startup files.
       HISTTIMEFORMAT
              If  this  variable  is  set and not null, its value is used as a
              format string for strftime(3) to print the time stamp associated
              with  each  history  entry displayed by the history builtin.  If
              this variable is set, time stamps are  written  to  the  history
              file  so they may be preserved across shell sessions.  This uses
              the history comment character  to  distinguish  timestamps  from
              other history lines.
       HOME   The home directory of the current user; the default argument for
              the cd builtin command.  The value of this variable is also used
              when performing tilde expansion.
       HOSTFILE
              Contains  the  name  of  a file in the same format as /etc/hosts
              that should be read when the shell needs to complete a hostname.
              The  list  of possible hostname completions may be changed while
              the shell is running; the next time hostname completion  is  at-
              tempted  after  the  value is changed, bash adds the contents of
              the new file to the existing list.  If HOSTFILE is set, but  has
              no  value,  or  does  not name a readable file, bash attempts to
              read /etc/hosts to obtain the list of possible hostname  comple-
              tions.  When HOSTFILE is unset, the hostname list is cleared.
       IFS    The Internal Field Separator that is used for word splitting af-
              ter expansion and to  split  lines  into  words  with  the  read
              builtin  command.   The  default  value  is  ``<space><tab><new-
              line>''.
       IGNOREEOF
              Controls the action of an interactive shell on receipt of an EOF
              character as the sole input.  If set, the value is the number of
              consecutive EOF characters which must  be  typed  as  the  first
              characters  on an input line before bash exits.  If the variable
              exists but does not have a numeric value, or has no  value,  the
              default  value  is  10.  If it does not exist, EOF signifies the
              end of input to the shell.
       INPUTRC
              The filename for the readline startup file, overriding  the  de-
              fault of ~/.inputrc (see READLINE below).
       INSIDE_EMACS
              If  this  variable  appears  in  the  environment when the shell
              starts, bash assumes that it is running inside  an  Emacs  shell
              buffer  and  may disable line editing, depending on the value of
              TERM.
       LANG   Used to determine the  locale  category  for  any  category  not
              specifically selected with a variable starting with LC_.
       LC_ALL This  variable  overrides  the  value  of LANG and any other LC_
              variable specifying a locale category.
       LC_COLLATE
              This variable determines the collation order used  when  sorting
              the  results  of pathname expansion, and determines the behavior
              of range expressions, equivalence  classes,  and  collating  se-
              quences within pathname expansion and pattern matching.
       LC_CTYPE
              This  variable  determines  the interpretation of characters and
              the behavior of character classes within pathname expansion  and
              pattern matching.
       LC_MESSAGES
              This  variable  determines  the locale used to translate double-
              quoted strings preceded by a $.
       LC_NUMERIC
              This variable determines the locale  category  used  for  number
              formatting.
       LC_TIME
              This  variable  determines the locale category used for data and
              time formatting.
       LINES  Used by the select compound  command  to  determine  the  column
              length  for  printing selection lists.  Automatically set if the
              checkwinsize option is enabled or in an interactive  shell  upon
              receipt of a SIGWINCH.
       MAIL   If  this  parameter  is  set to a file or directory name and the
              MAILPATH variable is not set, bash informs the user of  the  ar-
              rival of mail in the specified file or Maildir-format directory.
       MAILCHECK
              Specifies  how often (in seconds) bash checks for mail.  The de-
              fault is 60 seconds.  When it is time to  check  for  mail,  the
              shell  does  so  before  displaying the primary prompt.  If this
              variable is unset, or set to  a  value  that  is  not  a  number
              greater than or equal to zero, the shell disables mail checking.
       MAILPATH
              A colon-separated list of filenames to be checked for mail.  The
              message to be printed when mail arrives in a particular file may
              be  specified by separating the filename from the message with a
              `?'.  When used in the text of the message, $_  expands  to  the
              name of the current mailfile.  Example:
              MAILPATH='/var/mail/bfox?"You  have  mail":~/shell-mail?"$_  has
              mail!"'
              Bash can be configured to supply a default value for this  vari-
              able  (there  is  no  value by default), but the location of the
              user  mail  files  that  it  uses  is  system  dependent  (e.g.,
              /var/mail/$USER).
       OPTERR If set to the value 1, bash displays error messages generated by
              the getopts builtin command (see SHELL BUILTIN COMMANDS  below).
              OPTERR  is  initialized to 1 each time the shell is invoked or a
              shell script is executed.
       PATH   The search path for commands.  It is a colon-separated  list  of
              directories  in  which the shell looks for commands (see COMMAND
              EXECUTION below).  A zero-length (null) directory  name  in  the
              value of PATH indicates the current directory.  A null directory
              name may appear as two adjacent colons,  or  as  an  initial  or
              trailing  colon.   The  default path is system-dependent, and is
              set by the administrator who installs bash.  A common value is
              ``/usr/local/bin:/usr/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 set, the value is executed as a command prior to issuing each
              primary prompt.
       PROMPT_DIRTRIM
              If set to a number greater than zero, the value is used  as  the
              number of trailing directory components to retain when expanding
              the \w and \W  prompt  string  escapes  (see  PROMPTING  below).
              Characters removed are replaced with an ellipsis.
       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  The full pathname to the shell is kept in this environment vari-
              able.  If it is not set when the shell starts, bash  assigns  to
              it the full pathname of the current user's login shell.
       TIMEFORMAT
              The  value of this parameter is used as a format string specify-
              ing how the timing information for pipelines prefixed  with  the
              time  reserved word should be displayed.  The % character intro-
              duces an escape sequence that is expanded to  a  time  value  or
              other  information.  The escape sequences and their meanings are
              as follows; the braces denote optional portions.
              %%        A literal %.
              %[p][l]R  The elapsed time in seconds.
              %[p][l]U  The number of CPU seconds spent in user mode.
              %[p][l]S  The number of CPU seconds spent in system mode.
              %P        The CPU percentage, computed as (%U + %S) / %R.

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

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

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

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

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

       Associative arrays are created using declare -A name.

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

       Arrays   are  assigned  to  using  compound  assignments  of  the  form
       name=(value1 ... valuen),  where  each  value  is  of  the  form  [sub-
       script]=string.   Indexed array assignments do not require anything but
       string.  When assigning to indexed arrays, if the optional brackets and
       subscript  are supplied, that index is assigned to; otherwise the index
       of the element assigned is the last index assigned to by the  statement
       plus one.  Indexing starts at zero.

       When assigning to an associative array, the subscript is required.

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

       Any  element  of  an  array may be referenced using ${name[subscript]}.
       The braces are required to avoid conflicts with pathname expansion.  If
       subscript  is  @  or *, the word expands to all members of name.  These
       subscripts differ only when the word appears within double quotes.   If
       the word is double-quoted, ${name[*]} expands to a single word with the
       value of each array member separated by the first character of the  IFS
       special variable, and ${name[@]} expands each element of name to a sep-
       arate word.  When there are no array  members,  ${name[@]}  expands  to
       nothing.   If the double-quoted expansion occurs within a word, the ex-
       pansion of the first parameter is joined with the beginning part of the
       original  word,  and the expansion of the last parameter is joined with
       the last part of the original word.  This is analogous to the expansion
       of  the  special  parameters  *  and  @ (see Special Parameters above).
       ${#name[subscript]} expands to the length  of  ${name[subscript]}.   If
       subscript is * or @, the expansion is the number of elements in the ar-
       ray.  If the subscript used to reference an element of an indexed array
       evaluates  to a number less than zero, it is interpreted as relative to
       one greater than the maximum index of the array,  so  negative  indices
       count back from the end of the array, and an index of -1 references the
       last element.

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

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

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

       The unset builtin is used to destroy arrays.  unset name[subscript] de-
       stroys the array element at index subscript, for both indexed and asso-
       ciative  arrays.  Negative subscripts to indexed arrays are interpreted
       as described above.  Unsetting the last element of  an  array  variable
       does  not  unset  the variable.  unset name, where name is an array, or
       unset name[subscript], where subscript is * or @,  removes  the  entire
       array.

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

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

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

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

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

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

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

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

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

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

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

       A  correctly-formed  brace  expansion must contain unquoted opening and
       closing braces, and at least one unquoted comma or a valid sequence ex-
       pression.  Any incorrectly formed brace expansion is left unchanged.  A
       { or , may be quoted with a backslash to prevent its  being  considered
       part  of  a brace expression.  To avoid conflicts with parameter expan-
       sion, the string ${ is not considered eligible for brace expansion, and
       inhibits brace expansion until the closing }.

       This construct is typically used as shorthand when the common prefix of
       the strings to be generated is longer than in the above example:

              mkdir /usr/local/src/bash/{old,new,dist,bugs}
       or
              chown root /usr/{ucb/{ex,edit},lib/{ex?.?*,how_ex}}

       Brace expansion introduces a  slight  incompatibility  with  historical
       versions  of sh.  sh does not treat opening or closing braces specially
       when they appear as part of a word, and preserves them in  the  output.
       Bash  removes  braces  from  words as a consequence of brace expansion.
       For example, a word entered to sh as file{1,2} appears  identically  in
       the  output.  The same word is output as file1 file2 after expansion by
       bash.  If strict compatibility with sh is desired, start bash with  the
       +B option or disable brace expansion with the +B option to the set com-
       mand (see SHELL BUILTIN COMMANDS below).

   Tilde Expansion
       If a word begins with an unquoted tilde character  (`~'),  all  of  the
       characters  preceding  the  first unquoted slash (or all characters, if
       there is no unquoted slash) are considered a tilde-prefix.  If none  of
       the  characters  in  the tilde-prefix are quoted, the characters in the
       tilde-prefix following the tilde are treated as a possible login  name.
       If  this  login name is the null string, the tilde is replaced with the
       value of the shell parameter HOME.  If HOME is unset, the  home  direc-
       tory  of  the  user executing the shell is substituted instead.  Other-
       wise, the tilde-prefix is replaced with the home  directory  associated
       with the specified login name.

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

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

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

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

   Parameter Expansion
       The `$' character introduces parameter expansion, command substitution,
       or arithmetic expansion.  The parameter name or symbol to  be  expanded
       may  be enclosed in braces, which are optional but serve to protect the
       variable to be expanded from characters immediately following it  which
       could be interpreted as part of the name.

       When  braces  are  used, the matching ending brace is the first `}' not
       escaped by a backslash or within a quoted string, and not within an em-
       bedded  arithmetic expansion, command substitution, or parameter expan-
       sion.

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

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

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

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

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

              If offset evaluates to a number less than  zero,  the  value  is
              used as an offset in characters from the end of the value of 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  @, the result is length positional parameters
              beginning at offset.  A negative offset is taken relative to one
              greater  than the greatest positional parameter, so an offset of
              -1 evaluates to the last positional parameter.  It is an  expan-
              sion error if length evaluates to a number less than zero.

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

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

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

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

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

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

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

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

       ${parameter/pattern/string}
              Pattern substitution.  The pattern is expanded to produce a pat-
              tern just as in pathname expansion, Parameter  is  expanded  and
              the  longest match of pattern against its value is replaced with
              string.  The match is performed using the rules described  under
              Pattern  Matching  below.  If pattern begins with /, all matches
              of pattern are replaced with string.  Normally  only  the  first
              match  is  replaced.  If pattern begins with #, it must match at
              the beginning of the expanded value of  parameter.   If  pattern
              begins with %, it must match at the end of the expanded value of
              parameter.  If string is null, matches of  pattern  are  deleted
              and  the / following pattern may be omitted.  If the nocasematch
              shell option is enabled, the match is performed  without  regard
              to  the  case of alphabetic characters.  If parameter is @ or *,
              the substitution operation is applied to each positional parame-
              ter in turn, and the expansion is the resultant list.  If param-
              eter is an array variable subscripted with @ or *, the substitu-
              tion  operation  is applied to each member of the array in turn,
              and the expansion is the resultant list.

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

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

              Q      The expansion is a string that is the value of  parameter
                     quoted in a format that can be reused as input.
              E      The  expansion is a string that is the value of parameter
                     with backslash escape  sequences  expanded  as  with  the
                     $'...' quoting mechanism.
              P      The expansion is a string that is the result of expanding
                     the value of parameter as if it were a prompt string (see
                     PROMPTING below).
              A      The  expansion  is  a string in the form of an assignment
                     statement or declare command  that,  if  evaluated,  will
                     recreate parameter with its attributes and value.
              a      The  expansion is a string consisting of flag values rep-
                     resenting parameter's attributes.

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

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

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

              $(command)
       or
              `command`

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

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

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

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

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

              $((expression))

       The  old  format $[expression] is deprecated and will be removed in up-
       coming versions of bash.

       The expression is treated as if it were within  double  quotes,  but  a
       double  quote inside the parentheses is not treated specially.  All to-
       kens in the expression undergo parameter and variable  expansion,  com-
       mand  substitution,  and  quote  removal.  The result is treated as the
       arithmetic expression to be evaluated.  Arithmetic  expansions  may  be
       nested.

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

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

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

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

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

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

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

   Pathname Expansion
       After  word  splitting,  unless  the -f option has been set, bash scans
       each word for the characters *, ?, and [.  If one of  these  characters
       appears,  then  the word is regarded as a pattern, and replaced with an
       alphabetically sorted list of filenames matching the pattern (see  Pat-
       tern  Matching  below).   If  no  matching filenames are found, and the
       shell option nullglob is not enabled, the word is left  unchanged.   If
       the  nullglob  option is set, and no matches are found, the word is re-
       moved.  If the failglob shell option is set, and no matches are  found,
       an  error  message  is printed and the command is not executed.  If the
       shell option nocaseglob is enabled, the match is performed without  re-
       gard  to the case of alphabetic characters.  Note that when using range
       expressions like [a-z] (see below), letters of the other  case  may  be
       included,  depending  on  the setting of LC_COLLATE.  When a pattern is
       used for pathname expansion, the character ``.''  at  the  start  of  a
       name  or  immediately following a slash must be matched explicitly, un-
       less the shell option dotglob is set.  The filenames ``.''  and  ``..''
       must  always  be  matched explicitly, even if dotglob is set.  In other
       cases, 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 Match-
       ing.  See the description of shopt below under SHELL  BUILTIN  COMMANDS
       for  a  description  of the nocaseglob, nullglob, failglob, and dotglob
       shell options.

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

       Pattern Matching

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

       The special pattern characters have the following meanings:

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

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

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

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

       If the extglob shell option is enabled using the shopt builtin, several
       extended  pattern  matching operators are recognized.  In the following
       description, a pattern-list is a list of one or more patterns separated
       by a |.  Composite patterns may be formed using one or more of the fol-
       lowing sub-patterns:

              ?(pattern-list)
                     Matches zero or one occurrence of the given patterns
              *(pattern-list)
                     Matches zero or more occurrences of the given patterns
              +(pattern-list)
                     Matches one or more occurrences of the given patterns
              @(pattern-list)
                     Matches one of the given patterns
              !(pattern-list)
                     Matches anything except one of the given patterns

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

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

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

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

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

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

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

              ls > dirlist 2>&1

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

              ls 2>&1 > dirlist

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

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

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

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

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

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

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

       The general format for redirecting input is:

              [n]<word

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

       The general format for redirecting output is:

              [n]>word

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

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

       The general format for appending output is:

              [n]>>word

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

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

              &>word
       and
              >&word

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

              >word 2>&1

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

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

       The format for appending standard output and standard error is:

              &>>word

       This is semantically equivalent to

              >>word 2>&1

       (see Duplicating File Descriptors below).

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

       The format of here-documents is:

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

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

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

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

              [n]<<strftime(3) and the result is in-
                     serted into the prompt string; an empty format results in
                     a  locale-specific  time  representation.  The braces are
                     required
              \e     an ASCII escape character (033)
              \h     the hostname up to the first `.'
              \H     the hostname
              \j     the number of jobs currently managed by the shell
              \l     the basename of the shell's terminal device name
              \n     newline
              \r     carriage return
              \s     the name of the shell, the basename of  $0  (the  portion
                     following the final slash)
              \t     the current time in 24-hour HH:MM:SS format
              \T     the current time in 12-hour HH:MM:SS format
              \@     the current time in 12-hour am/pm format
              \A     the current time in 24-hour HH:MM format
              \u     the username of the current user
              \v     the version of bash (e.g., 2.00)
              \V     the release of bash, version + patch level (e.g., 2.00.0)
              \w     the  current  working  directory,  with $HOME abbreviated
                     with a tilde (uses the value of the PROMPT_DIRTRIM  vari-
                     able)
              \W     the basename of the current working directory, with $HOME
                     abbreviated with a tilde
              \!     the history number of this command
              \#     the command number of this command
              \$     if the effective UID is 0, a #, otherwise a $
              \nnn   the character corresponding to the octal number nnn
              \\     a backslash
              \[     begin a sequence of non-printing characters, which  could
                     be  used  to  embed  a terminal control sequence into the
                     prompt
              \]     end a sequence of non-printing characters

       The command number and the history number are  usually  different:  the
       history  number of a command is its position in the history list, which
       may include commands restored from the history file  (see  HISTORY  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).

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

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

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

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

   Readline Initialization
       Readline  is  customized  by putting commands in an initialization file
       (the inputrc file).  The name of this file is taken from the  value  of
       the INPUTRC variable.  If that variable is unset, the default is ~/.in-
       putrc.  When a program which uses the readline library starts  up,  the
       initialization  file  is  read,  and the key bindings and variables are
       set.  There are only a few basic constructs  allowed  in  the  readline
       initialization  file.  Blank lines are ignored.  Lines beginning with a
       # are comments.  Lines beginning with a  $  indicate  conditional  con-
       structs.  Other lines denote key bindings and variable settings.

       The  default  key-bindings  may be changed with an inputrc file.  Other
       programs that use this library may add their own commands and bindings.

       For example, placing

              M-Control-u: universal-argument
       or
              C-Meta-u: universal-argument
       into the inputrc would make M-C-u execute the readline command  univer-
       sal-argument.

       The  following  symbolic  character  names are recognized: RUBOUT, DEL,
       ESC, LFD, NEWLINE, RET, RETURN, SPC, SPACE, and TAB.

       In addition to command names, readline allows keys to  be  bound  to  a
       string that is inserted when the key is pressed (a macro).

   Readline Key Bindings
       The  syntax for controlling key bindings in the inputrc file is simple.
       All that is required is the name of the command or the text of a  macro
       and a key sequence to which it should be bound.  The name may be speci-
       fied in one of two ways: as a symbolic key name, possibly with Meta- or
       Control- prefixes, or as a key sequence.

       When using the form keyname:function-name or macro, keyname is the name
       of a key spelled out in English.  For example:

              Control-u: universal-argument
              Meta-Rubout: backward-kill-word
              Control-o: "> output"

       In the above example, C-u is bound to the function  universal-argument,
       M-DEL  is bound to the function backward-kill-word, and C-o is bound to
       run the macro expressed on the right hand side (that is, to insert  the
       text ``> output'' into the line).

       In  the  second  form,  "keyseq":function-name or macro, keyseq differs
       from keyname above in that strings denoting an entire key sequence  may
       be  specified  by  placing the sequence within double quotes.  Some GNU
       Emacs style key escapes can be used, as in the following  example,  but
       the symbolic character names are not recognized.

              "\C-u": universal-argument
              "\C-x\C-r": re-read-init-file
              "\e[11~": "Function Key 1"

       In this example, C-u is again bound to the function universal-argument.
       C-x C-r is bound to the function re-read-init-file, and ESC [ 1 1 ~  is
       bound to insert the text ``Function Key 1''.

       The full set of GNU Emacs style escape sequences is
              \C-    control prefix
              \M-    meta prefix
              \e     an escape character
              \\     backslash
              \"     literal "
              \'     literal '

       In  addition  to  the GNU Emacs style escape sequences, a second set of
       backslash escapes is available:
              \a     alert (bell)
              \b     backspace
              \d     delete
              \f     form feed
              \n     newline
              \r     carriage return
              \t     horizontal tab
              \v     vertical tab
              \nnn   the eight-bit character whose value is  the  octal  value
                     nnn (one to three digits)
              \xHH   the  eight-bit  character  whose value is the hexadecimal
                     value HH (one or two hex digits)

       When entering the text of a macro, single or double quotes must be used
       to indicate a macro definition.  Unquoted text is assumed to be a func-
       tion name.  In the macro body, the backslash  escapes  described  above
       are  expanded.   Backslash  will quote any other character in the macro
       text, including " and '.

       Bash allows the current readline key bindings to be displayed or  modi-
       fied  with  the bind builtin command.  The editing mode may be switched
       during interactive use by using the -o option to the set  builtin  com-
       mand (see SHELL BUILTIN COMMANDS below).

   Readline Variables
       Readline has variables that can be used to further customize its behav-
       ior.  A variable may be set in the inputrc file with a statement of the
       form

              set variable-name value

       Except  where  noted,  readline variables can take the values On or Off
       (without regard to case).  Unrecognized  variable  names  are  ignored.
       When  a variable value is read, empty or null values, "on" (case-insen-
       sitive), and "1" are equivalent to On.  All other values are equivalent
       to Off.  The variables and their default values are:

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

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

       $if    The $if construct allows bindings to be made based on the  edit-
              ing  mode,  the  terminal  being  used, or the application using
              readline.  The text of the test, after any comparison operator,
               extends to the end of the  line;  unless  otherwise  noted,  no
              characters are required to isolate it.

              mode   The  mode=  form  of  the  $if  directive is used to test
                     whether readline is in emacs or vi  mode.   This  may  be
                     used  in conjunction with the set keymap command, for in-
                     stance,  to  set  bindings  in  the  emacs-standard   and
                     emacs-ctlx  keymaps  only  if readline is starting out in
                     emacs mode.

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

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

              application
                     The application construct is used to include application-
                     specific settings.  Each program using the  readline  li-
                     brary  sets  the  application name, and an initialization
                     file can test for a particular value.  This could be used
                     to  bind key sequences to functions useful for a specific
                     program.  For instance, the following command adds a  key
                     sequence  that  quotes  the  current  or previous word in
                     bash:

                     $if Bash
                     # Quote the current or previous word
                     "\C-xq": "\eb\"\ef\""
                     $endif

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

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

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

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

              $include  /etc/inputrc

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

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

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

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

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

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

   Commands for Moving
       beginning-of-line (C-a)
              Move to the start of the current line.
       end-of-line (C-e)
              Move to the end of the line.
       forward-char (C-f)
              Move forward a character.
       backward-char (C-b)
              Move back a character.
       forward-word (M-f)
              Move forward to the end of the next word.  Words are composed of
              alphanumeric characters (letters and digits).
       backward-word (M-b)
              Move  back  to the start of the current or previous word.  Words
              are composed of alphanumeric characters (letters and digits).
       shell-forward-word
              Move forward to the end of the next word.  Words  are  delimited
              by non-quoted shell metacharacters.
       shell-backward-word
              Move  back  to the start of the current or previous word.  Words
              are delimited by non-quoted shell metacharacters.
       previous-screen-line
              Attempt to move point to the same physical screen column on  the
              previous  physical  screen  line. This will not have the desired
              effect if the current Readline line does not take up  more  than
              one  physical line or if point is not greater than the length of
              the prompt plus the screen width.
       next-screen-line
              Attempt to move point to the same physical screen column on  the
              next physical screen line. This will not have the desired effect
              if the current Readline line does not  take  up  more  than  one
              physical  line  or if the length of the current Readline line is
              not greater than the length of the prompt plus the screen width.
       clear-screen (C-l)
              Clear the screen leaving the current line  at  the  top  of  the
              screen.   With  an  argument,  refresh  the current line without
              clearing the screen.
       redraw-current-line
              Refresh the current line.

   Commands for Manipulating the History
       accept-line (Newline, Return)
              Accept the line regardless of where the cursor is.  If this line
              is  non-empty, add it to the history list according to the state
              of the HISTCONTROL variable.  If the line is a modified  history
              line, then restore the history line to its original state.
       previous-history (C-p)
              Fetch the previous command from the history list, moving back in
              the list.
       next-history (C-n)
              Fetch the next command from the history list, moving forward  in
              the list.
       beginning-of-history (M-<)
              Move to the first line in the history.
       end-of-history (M->)
              Move  to  the end of the input history, i.e., the line currently
              being entered.
       reverse-search-history (C-r)
              Search backward starting at the current  line  and  moving  `up'
              through  the  history  as  necessary.   This  is  an incremental
              search.
       forward-search-history (C-s)
              Search forward starting at the current line  and  moving  `down'
              through  the  history  as  necessary.   This  is  an incremental
              search.
       non-incremental-reverse-search-history (M-p)
              Search backward through the history starting at the current line
              using  a  non-incremental  search  for  a string supplied by the
              user.
       non-incremental-forward-search-history (M-n)
              Search forward  through  the  history  using  a  non-incremental
              search for a string supplied by the user.
       history-search-forward
              Search  forward through the history for the string of characters
              between the start of the current line and the point.  This is  a
              non-incremental search.
       history-search-backward
              Search backward through the history for the string of characters
              between the start of the current line and the point.  This is  a
              non-incremental search.
       history-substring-search-backward
              Search backward through the history for the string of characters
              between the start of the current line and the current cursor po-
              sition  (the  point).  The search string may match anywhere in a
              history line.  This is a non-incremental search.
       history-substring-search-forward
              Search forward through the history for the string of  characters
              between the start of the current line and the point.  The search
              string may match anywhere in a history line.  This is a  non-in-
              cremental search.
       yank-nth-arg (M-C-y)
              Insert  the  first argument to the previous command (usually the
              second word on the previous line) at point.  With an argument n,
              insert  the nth word from the previous command (the words in the
              previous command begin with word 0).  A  negative  argument  in-
              serts  the  nth word from the end of the previous command.  Once
              the argument n is computed, the argument is extracted as if  the
              "!n" history expansion had been specified.
       yank-last-arg (M-., M-_)
              Insert  the last argument to the previous command (the last word
              of the previous history entry).  With a numeric argument, behave
              exactly  like  yank-nth-arg.   Successive calls to yank-last-arg
              move back through the history list, inserting the last word  (or
              the  word  specified  by the argument to the first call) of each
              line in turn.  Any numeric argument supplied to these successive
              calls  determines  the direction to move through the history.  A
              negative argument switches the  direction  through  the  history
              (back or forward).  The history expansion facilities are used to
              extract the last word, as if the "!$" history expansion had been
              specified.
       shell-expand-line (M-C-e)
              Expand the line as the shell does.  This performs alias and his-
              tory expansion as well as all of the shell word expansions.  See
              HISTORY EXPANSION below for a description of history expansion.
       history-expand-line (M-^)
              Perform  history expansion on the current line.  See HISTORY EX-
              PANSION below for a description of history expansion.
       magic-space
              Perform history expansion on  the  current  line  and  insert  a
              space.  See HISTORY EXPANSION below for a description of history
              expansion.
       alias-expand-line
              Perform alias expansion on the current line.  See ALIASES  above
              for a description of alias expansion.
       history-and-alias-expand-line
              Perform history and alias expansion on the current line.
       insert-last-argument (M-., M-_)
              A synonym for yank-last-arg.
       operate-and-get-next (C-o)
              Accept  the  current  line for execution and fetch the next line
              relative to the current line from the history  for  editing.   A
              numeric  argument,  if  supplied, specifies the history entry to
              use instead of the current line.
       edit-and-execute-command (C-x C-e)
              Invoke an editor on the current command line,  and  execute  the
              result as shell commands.  Bash attempts to invoke $VISUAL, $ED-
              ITOR, and emacs as the editor, in that order.

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

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

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

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

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

   Miscellaneous
       re-read-init-file (C-x C-r)
              Read in the contents of the inputrc file,  and  incorporate  any
              bindings or variable assignments found there.
       abort (C-g)
              Abort  the  current editing command and ring the terminal's bell
              (subject to the setting of bell-style).
       do-lowercase-version (M-A, M-B, M-x, ...)
              If the metafied character x is uppercase, run the  command  that
              is bound to the corresponding metafied lowercase character.  The
              behavior is undefined if x is already lowercase.
       prefix-meta (ESC)
              Metafy the next character typed.  ESC f is equivalent to Meta-f.
       undo (C-_, C-x C-u)
              Incremental undo, separately remembered for each line.
       revert-line (M-r)
              Undo all changes made to this line.  This is like executing  the
              undo  command  enough  times  to  return the line to its initial
              state.
       tilde-expand (M-&)
              Perform tilde expansion on the current word.
       set-mark (C-@, M-<space>)
              Set the mark to the point.  If a numeric argument  is  supplied,
              the mark is set to that position.
       exchange-point-and-mark (C-x C-x)
              Swap  the  point  with the mark.  The current cursor position is
              set to the saved position, and the old cursor position is  saved
              as the mark.
       character-search (C-])
              A character is read and point is moved to the next occurrence of
              that character.  A negative count searches for  previous  occur-
              rences.
       character-search-backward (M-C-])
              A  character  is  read and point is moved to the previous occur-
              rence of that character.  A negative count searches  for  subse-
              quent occurrences.
       skip-csi-sequence
              Read  enough  characters to consume a multi-key sequence such as
              those defined for keys like Home and End.  Such sequences  begin
              with a Control Sequence Indicator (CSI), usually ESC-[.  If this
              sequence is bound to "\[", keys producing  such  sequences  will
              have  no  effect  unless explicitly bound to a readline command,
              instead of inserting stray characters into the  editing  buffer.
              This is unbound by default, but usually bound to ESC-[.
       insert-comment (M-#)
              Without  a  numeric  argument,  the  value  of the readline com-
              ment-begin variable is inserted at the beginning of the  current
              line.  If a numeric argument is supplied, this command acts as a
              toggle: if the characters at the beginning of the  line  do  not
              match  the value of comment-begin, the value is inserted, other-
              wise the characters in comment-begin are deleted from the begin-
              ning  of the line.  In either case, the line is accepted as if a
              newline had been typed.   The  default  value  of  comment-begin
              causes  this  command  to make the current line a shell comment.
              If a numeric argument causes the comment  character  to  be  re-
              moved, the line will be executed by the shell.
       glob-complete-word (M-g)
              The  word  before point is treated as a pattern for pathname ex-
              pansion, with an asterisk implicitly appended.  This pattern  is
              used  to generate a list of matching filenames for possible com-
              pletions.
       glob-expand-word (C-x *)
              The word before point is treated as a pattern for  pathname  ex-
              pansion, and the list of matching filenames is inserted, replac-
              ing the word.  If a numeric argument is supplied, an asterisk is
              appended before pathname expansion.
       glob-list-expansions (C-x g)
              The  list  of  expansions  that  would  have  been  generated by
              glob-expand-word is displayed, and the line is  redrawn.   If  a
              numeric  argument  is  supplied,  an asterisk is appended before
              pathname expansion.
       dump-functions
              Print all of the functions and their key bindings to  the  read-
              line output stream.  If a numeric argument is supplied, the out-
              put is formatted in such a way that it can be made  part  of  an
              inputrc file.
       dump-variables
              Print all of the settable readline variables and their values to
              the readline output stream.  If a numeric argument is  supplied,
              the  output  is formatted in such a way that it can be made part
              of an inputrc file.
       dump-macros
              Print all of the readline key sequences bound to macros and  the
              strings  they  output.   If  a numeric argument is supplied, the
              output is formatted in such a way that it can be made part of an
              inputrc file.
       display-shell-version (C-x C-v)
              Display version information about the current instance of bash.

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

       The shell allows control over which commands are saved on  the  history
       list.  The HISTCONTROL and HISTIGNORE variables may be set to cause the
       shell to save only a subset of the commands entered.  The cmdhist shell
       option,  if enabled, causes the shell to attempt to save each line of a
       multi-line command in the same history entry, adding  semicolons  where
       necessary  to preserve syntactic correctness.  The lithist shell option
       causes the shell to save the command with embedded newlines instead  of
       semicolons.  See the description of the shopt builtin below under SHELL
       BUILTIN COMMANDS for information on setting  and  unsetting  shell  op-
       tions.

HISTORY EXPANSION
       The  shell  supports a history expansion feature that is similar to the
       history expansion in csh.  This section describes what syntax  features
       are  available.   This  feature  is  enabled by default for interactive
       shells, and can be disabled using the +H option to the set builtin com-
       mand (see SHELL BUILTIN COMMANDS below).  Non-interactive shells do not
       perform history expansion by default.

       History expansions introduce words from the history list into the input
       stream,  making  it  easy to repeat commands, insert the arguments to a
       previous command into the current input line, or fix errors in previous
       commands quickly.

       History  expansion  is  performed  immediately after a complete line is
       read, before the shell breaks it into words, and is performed  on  each
       line  individually  without  taking  quoting on previous lines into ac-
       count.  It takes place in two parts.  The first is to  determine  which
       line  from  the history list to use during substitution.  The second is
       to select portions of that line for inclusion  into  the  current  one.
       The  line  selected  from the history is the event, and the portions of
       that line that are acted upon are words.  Various modifiers are  avail-
       able  to  manipulate the selected words.  The line is broken into words
       in the same fashion as when reading input, so that several  metacharac-
       ter-separated words surrounded by quotes are considered one word.  His-
       tory expansions are introduced by the appearance of the history  expan-
       sion  character,  which is ! by default.  Only backslash (\) and single
       quotes can quote the history expansion character, but the  history  ex-
       pansion  character is also treated as quoted if it immediately precedes
       the closing double quote in a double-quoted string.

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

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

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

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

       !      Start a history substitution, except when followed by  a  blank,
              newline,  carriage return, = or ( (when the extglob shell option
              is enabled using the shopt builtin).
       !n     Refer to command line n.
       !-n    Refer to the current command minus n.
       !!     Refer to the previous command.  This is a synonym for `!-1'.
       !string
              Refer to the most recent command preceding the current  position
              in the history list starting with string.
       !?string[?]
              Refer  to the most recent command preceding the current position
              in the history list containing string.  The trailing  ?  may  be
              omitted if string is followed immediately by a newline.
       ^string1^string2^
              Quick  substitution.   Repeat  the  previous  command, replacing
              string1 with string2.  Equivalent  to  ``!!:s/string1/string2/''
              (see Modifiers below).
       !#     The entire command line typed so far.

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

       0 (zero)
              The zeroth word.  For the shell, this is the command word.
       n      The nth word.
       ^      The first argument.  That is, word 1.
       $      The last word.  This is usually the last argument, but will  ex-
              pand to the zeroth word if there is only one word in the line.
       %      The word matched by the most recent `?string?' search.
       x-y    A range of words; `-y' abbreviates `0-y'.
       *      All  of  the words but the zeroth.  This is a synonym for `1-$'.
              It is not an error to use * if there is just  one  word  in  the
              event; the empty string is returned in that case.
       x*     Abbreviates x-$.
       x-     Abbreviates x-$ like x*, but omits the last word.

       If  a  word  designator is supplied without an event specification, the
       previous command is used as the event.

   Modifiers
       After the optional word designator, there may appear a sequence of  one
       or more of the following modifiers, each preceded by a `:'.

       h      Remove a trailing filename component, leaving only the head.
       t      Remove all leading filename components, leaving the tail.
       r      Remove a trailing suffix of the form .xxx, leaving the basename.
       e      Remove all but the trailing suffix.
       p      Print the new command but do not execute it.
       q      Quote the substituted words, escaping further substitutions.
       x      Quote  the  substituted words as with q, but break into words at
              blanks and newlines.
       s/old/new/
              Substitute new for the first occurrence  of  old  in  the  event
              line.   Any  delimiter can be used in place of /.  The final de-
              limiter is optional if it is the last  character  of  the  event
              line.   The delimiter may be quoted in old and new with a single
              backslash.  If & appears in new, it is replaced by old.  A  sin-
              gle  backslash  will  quote the &.  If old is null, it is set to
              the last old substituted, or, if no previous  history  substitu-
              tions took place, the last string in a !?string[?]  search.
       &      Repeat the previous substitution.
       g      Cause changes to be applied over the entire event line.  This is
              used in conjunction with `:s' (e.g.,  `:gs/old/new/')  or  `:&'.
              If  used with `:s', any delimiter can be used in place of /, and
              the final delimiter is optional if it is the last  character  of
              the event line.  An a may be used as a synonym for g.
       G      Apply  the following `s' modifier once to each word in the event
              line.

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

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

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

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

       bind [-m keymap] [-lpsvPSVX]
       bind [-m keymap] [-q function] [-u function] [-r keyseq]
       bind [-m keymap] -f filename
       bind [-m keymap] -x keyseq:shell-command
       bind [-m keymap] keyseq:function-name
       bind [-m keymap] keyseq:readline-command
              Display  current  readline key and function bindings, bind a key
              sequence to a readline function or  macro,  or  set  a  readline
              variable.  Each non-option argument is a command as it would ap-
              pear in .inputrc, but each binding or command must be passed  as
              a separate argument; e.g., '"\C-x\C-r": re-read-init-file'.  Op-
              tions, if supplied, have the following meanings:
              -m keymap
                     Use keymap as the keymap to be affected by the subsequent
                     bindings.  Acceptable keymap names are emacs, emacs-stan-
                     dard, emacs-meta, emacs-ctlx,  vi,  vi-move,  vi-command,
                     and  vi-insert.   vi is equivalent to vi-command (vi-move
                     is also a synonym); emacs is  equivalent  to  emacs-stan-
                     dard.
              -l     List the names of all readline functions.
              -p     Display  readline  function  names and bindings in such a
                     way that they can be re-read.
              -P     List current readline function names and bindings.
              -s     Display readline key sequences bound to  macros  and  the
                     strings  they  output  in such a way that they can be re-
                     read.
              -S     Display readline key sequences bound to  macros  and  the
                     strings they output.
              -v     Display  readline variable names and values in such a way
                     that they can be re-read.
              -V     List current readline variable names and values.
              -f filename
                     Read key bindings from filename.
              -q function
                     Query about which keys invoke the named function.
              -u function
                     Unbind all keys bound to the named function.
              -r keyseq
                     Remove any current binding for keyseq.
              -x keyseq:shell-command
                     Cause shell-command to be executed whenever keyseq is en-
                     tered.   When  shell-command  is executed, the shell sets
                     the READLINE_LINE variable to the contents of  the  read-
                     line  line  buffer and the READLINE_POINT variable to the
                     current location of the insertion point.  If the executed
                     command  changes  the  value  of  READLINE_LINE  or READ-
                     LINE_POINT, those new values will  be  reflected  in  the
                     editing state.
              -X     List  all  key  sequences bound to shell commands and the
                     associated commands in a format that can be reused as in-
                     put.

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

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

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

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

       cd [-L|[-P [-e]] [-@]] [dir]
              Change  the  current  directory to dir.  if dir is not supplied,
              the value of the HOME shell variable is the default.  Any  addi-
              tional arguments following dir are ignored.  The variable CDPATH
              defines the search path for the directory containing  dir:  each
              directory  name  in CDPATH is searched for dir.  Alternative di-
              rectory names in CDPATH are separated by a colon  (:).   A  null
              directory  name  in CDPATH is the same as the current directory,
              i.e., ``.''.  If dir begins with a slash (/), then CDPATH is not
              used.   The  -P  option  causes cd to use the physical directory
              structure by resolving symbolic links while traversing  dir  and
              before processing instances of .. in dir (see also the -P option
              to the set builtin command); the -L option forces symbolic links
              to  be followed by resolving the link after processing instances
              of .. in dir.  If .. appears in dir, it is processed by removing
              the  immediately previous pathname component from dir, back to a
              slash or the beginning of dir.  If the  -e  option  is  supplied
              with  -P,  and  the current working directory cannot be success-
              fully determined after a successful directory  change,  cd  will
              return  an unsuccessful status.  On systems that support it, the
              -@ option presents the extended  attributes  associated  with  a
              file  as  a directory.  An argument of - is converted to $OLDPWD
              before the directory change is attempted.  If a non-empty direc-
              tory  name  from  CDPATH is used, or if - is the first argument,
              and the directory change is successful, the absolute pathname of
              the  new  working  directory  is written to the standard output.
              The return value is  true  if  the  directory  was  successfully
              changed; false otherwise.

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

       compgen [option] [word]
              Generate  possible  completion matches for word according to the
              options, which may  be  any  option  accepted  by  the  complete
              builtin  with  the exception of -p and -r, and write the matches
              to the standard output.  When using the -F or  -C  options,  the
              various  shell  variables set by the programmable completion fa-
              cilities, while available, will not have useful values.

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

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

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

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

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

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

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

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

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

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

              Using  `+'  instead of `-' turns off the attribute instead, with
              the exceptions that +a and +A may not be used to  destroy  array
              variables  and  +r will not remove the readonly attribute.  When
              used in a function, declare and typeset make each name local, as
              with  the local command, unless the -g option is supplied.  If a
              variable name is followed by =value, the value of  the  variable
              is  set  to value.  When using -a or -A and the compound assign-
              ment syntax to create array variables, additional attributes  do
              not  take effect until subsequent assignments.  The return value
              is 0 unless an invalid option is encountered, an attempt is made
              to define a function using ``-f foo=bar'', an attempt is made to
              assign a value to a readonly variable, an attempt is made to as-
              sign a value to an array variable without using the compound as-
              signment syntax (see Arrays above), one of the names  is  not  a
              valid  shell variable name, an attempt is made to turn off read-
              only status for a readonly variable, an attempt is made to  turn
              off array status for an array variable, or an attempt is made to
              display a non-existent function with -f.

       dirs [-clpv] [+n] [-n]
              Without options, displays the list of currently  remembered  di-
              rectories.   The default display is on a single line with direc-
              tory names separated by spaces.  Directories are  added  to  the
              list  with  the  pushd command; the popd command removes entries
              from the list.  The current directory is always the first direc-
              tory in the stack.
              -c     Clears  the  directory  stack  by deleting all of the en-
                     tries.
              -l     Produces a listing  using  full  pathnames;  the  default
                     listing format uses a tilde to denote the home directory.
              -p     Print the directory stack with one entry per line.
              -v     Print  the  directory stack with one entry per line, pre-
                     fixing each entry with its index in the stack.
              +n     Displays the nth entry counting from the left of the list
                     shown by dirs when invoked without options, starting with
                     zero.
              -n     Displays the nth entry counting from  the  right  of  the
                     list shown by dirs when invoked without options, starting
                     with zero.

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

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

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

       enable [-a] [-dnps] [-f filename] [name ...]
              Enable  and disable builtin shell commands.  Disabling a builtin
              allows a disk command which has the same name as a shell builtin
              to  be  executed without specifying a full pathname, even though
              the shell normally searches for builtins before  disk  commands.
              If  -n  is used, each name is disabled; otherwise, names are en-
              abled.  For example, to use the test binary found via  the  PATH
              instead  of  the  shell builtin version, run ``enable -n test''.
              The -f option means to load the new builtin  command  name  from
              shared object filename, on systems that support dynamic loading.
              The -d option will delete a builtin previously loaded  with  -f.
              If no name arguments are given, or if the -p option is supplied,
              a list of shell builtins is printed.  With no other option argu-
              ments,  the  list consists of all enabled shell builtins.  If -n
              is supplied, only disabled builtins are printed.  If -a is  sup-
              plied,  the  list printed includes all builtins, with an indica-
              tion of whether or not each is enabled.  If -s is supplied,  the
              output  is restricted to the POSIX special builtins.  The return
              value is 0 unless a name is not a shell builtin or there  is  an
              error loading a new builtin from a shared object.

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

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

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

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

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

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

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

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

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

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

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

              getopts  normally  parses the positional parameters, but if more
              arguments are given in args, getopts parses those instead.

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

              If an invalid option is seen, getopts places ? into name and, if
              not silent, prints an  error  message  and  unsets  OPTARG.   If
              getopts  is  silent, the option character found is placed in OP-
              TARG and no diagnostic message is printed.

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

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

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

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

              The return status is 0 unless no command matches pattern.

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

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

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

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

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

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

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

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

       logout Exit a login shell.

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

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

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

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

       popd [-n] [+n] [-n]
              Removes  entries  from  the directory stack.  With no arguments,
              removes the top directory from the stack, and performs a  cd  to
              the new top directory.  Arguments, if supplied, have the follow-
              ing meanings:
              -n     Suppresses the normal change of directory  when  removing
                     directories from the stack, so that only the stack is ma-
                     nipulated.
              +n     Removes the nth entry counting from the left of the  list
                     shown  by  dirs, starting with zero.  For example: ``popd
                     +0'' removes the first directory, ``popd +1'' the second.
              -n     Removes the nth entry counting from the right of the list
                     shown  by  dirs, starting with zero.  For example: ``popd
                     -0'' removes the last directory, ``popd -1'' the next  to
                     last.

              If  the popd command is successful, a dirs is performed as well,
              and the return status is 0.  popd returns false  if  an  invalid
              option is encountered, the directory stack is empty, a non-exis-
              tent directory stack entry is specified, or the directory change
              fails.

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

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

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

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

       pushd [-n] [+n] [-n]
       pushd [-n] [dir]
              Adds  a  directory to the top of the directory stack, or rotates
              the stack, making the new top of the stack the  current  working
              directory.   With  no arguments, pushd exchanges the top two di-
              rectories and returns 0, unless the directory  stack  is  empty.
              Arguments, if supplied, have the following meanings:
              -n     Suppresses  the  normal change of directory when rotating
                     or adding directories to the  stack,  so  that  only  the
                     stack is manipulated.
              +n     Rotates  the  stack  so  that the nth directory (counting
                     from the left of the list shown by  dirs,  starting  with
                     zero) is at the top.
              -n     Rotates  the  stack  so  that the nth directory (counting
                     from the right of the list shown by dirs,  starting  with
                     zero) is at the top.
              dir    Adds dir to the directory stack at the top, making it the
                     new current working directory as if it had been  supplied
                     as the argument to the cd builtin.

              If the pushd command is successful, a dirs is performed as well.
              If the first form is used, pushd returns 0 unless the cd to  dir
              fails.   With the second form, pushd returns 0 unless the direc-
              tory stack is empty, a non-existent directory stack  element  is
              specified,  or the directory change to the specified new current
              directory fails.

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

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

              If no names are supplied, the line read is assigned to the vari-
              able  REPLY.  The exit status is zero, unless end-of-file is en-
              countered, read times out (in which case the status  is  greater
              than  128),  a variable assignment error (such as assigning to a
              readonly variable) occurs, or an invalid file descriptor is sup-
              plied as the argument to -u.

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

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

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

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

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

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

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

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

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

              The list of shopt options is:

              assoc_expand_once
                      If  set, the shell suppresses multiple evaluation of as-
                      sociative array subscripts during arithmetic  expression
                      evaluation,  while  executing  builtins that can perform
                      variable assignments, and while executing builtins  that
                      perform array dereferencing.
              autocd  If  set,  a command name that is the name of a directory
                      is executed as if it were the argument to  the  cd  com-
                      mand.  This option is only used by interactive shells.
              cdable_vars
                      If  set,  an  argument to the cd builtin command that is
                      not a directory is assumed to be the name of a  variable
                      whose value is the directory to change to.
              cdspell If set, minor errors in the spelling of a directory com-
                      ponent in a cd command will be  corrected.   The  errors
                      checked for are transposed characters, a missing charac-
                      ter, and one character too many.   If  a  correction  is
                      found,  the  corrected filename is printed, and the com-
                      mand proceeds.  This option is only used by  interactive
                      shells.
              checkhash
                      If set, bash checks that a command found in the hash ta-
                      ble exists before trying to execute  it.   If  a  hashed
                      command  no  longer exists, a normal path search is per-
                      formed.
              checkjobs
                      If set, bash lists the status of any stopped and running
                      jobs  before  exiting an interactive shell.  If any jobs
                      are running, this causes the exit to be deferred until a
                      second  exit is attempted without an intervening command
                      (see JOB CONTROL above).  The shell always postpones ex-
                      iting if any jobs are stopped.
              checkwinsize
                      If  set, bash checks the window size after each external
                      (non-builtin) command and,  if  necessary,  updates  the
                      values  of LINES and COLUMNS.  This option is enabled by
                      default.
              cmdhist If set, bash attempts to save all lines of  a  multiple-
                      line  command  in  the  same history entry.  This allows
                      easy re-editing of multi-line commands.  This option  is
                      enabled  by  default,  but only has an effect if command
                      history is enabled, as described above under HISTORY.
              compat31
                      If set, bash changes its behavior to that of version 3.1
                      with  respect  to quoted arguments to the [[ conditional
                      command's =~ operator and locale-specific string compar-
                      ison when using the [[ conditional command's < and > op-
                      erators.  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).
              compat32
                      If set, bash changes its behavior to that of version 3.2
                      with  respect  to locale-specific string comparison when
                      using the [[ conditional command's  <  and  >  operators
                      (see  previous  item)  and  the effect of interrupting a
                      command list.  Bash versions 3.2  and  earlier  continue
                      with  the  next command in the list after one terminates
                      due to an interrupt.
              compat40
                      If set, bash changes its behavior to that of version 4.0
                      with  respect  to locale-specific string comparison when
                      using the [[ conditional command's  <  and  >  operators
                      (see  description  of compat31) and the effect of inter-
                      rupting a command list.  Bash versions 4.0 and later in-
                      terrupt the list as if the shell received the interrupt;
                      previous versions continue with the next command in  the
                      list.
              compat41
                      If  set, bash, when in posix mode, treats a single quote
                      in a double-quoted  parameter  expansion  as  a  special
                      character.   The  single quotes must match (an even num-
                      ber) and the characters between the  single  quotes  are
                      considered  quoted.   This is the behavior of posix mode
                      through version 4.1.  The default bash behavior  remains
                      as in previous versions.
              compat42
                      If  set, bash does not process the replacement string in
                      the pattern substitution word expansion using quote  re-
                      moval.
              compat43
                      If  set, bash does not print a warning message if an at-
                      tempt is made to use a quoted compound array  assignment
                      as  an  argument to declare, makes word expansion errors
                      non-fatal errors that cause the current command to  fail
                      (the  default behavior is to make them fatal errors that
                      cause the shell to exit), and does not  reset  the  loop
                      state  when  a  shell  function is executed (this allows
                      break or continue in a shell function to affect loops in
                      the caller's context).
              compat44
                      If   set,   bash  saves  the  positional  parameters  to
                      BASH_ARGV and BASH_ARGC before they are used, regardless
                      of whether or not extended debugging mode is enabled.
              complete_fullquote
                      If  set,  bash  quotes all shell metacharacters in file-
                      names and directory names  when  performing  completion.
                      If not set, bash removes metacharacters such as the dol-
                      lar sign from the set of characters that will be  quoted
                      in  completed filenames when these metacharacters appear
                      in shell variable references in words to  be  completed.
                      This  means that dollar signs in variable names that ex-
                      pand to directories will not  be  quoted;  however,  any
                      dollar  signs appearing in filenames will not be quoted,
                      either.  This is active only when bash  is  using  back-
                      slashes  to quote completed filenames.  This variable is
                      set by default, which is the default  bash  behavior  in
                      versions through 4.2.
              direxpand
                      If  set,  bash replaces directory names with the results
                      of word expansion when performing  filename  completion.
                      This  changes  the contents of the readline editing buf-
                      fer.  If not set, bash attempts  to  preserve  what  the
                      user typed.
              dirspell
                      If  set,  bash attempts spelling correction on directory
                      names during word completion if the directory name  ini-
                      tially supplied does not exist.
              dotglob If  set, bash includes filenames beginning with a `.' in
                      the results of pathname expansion.  The filenames  ``.''
                      and  ``..''   must always be matched explicitly, even if
                      dotglob is set.
              execfail
                      If set, a non-interactive shell will not exit if it can-
                      not  execute  the  file  specified as an argument to the
                      exec builtin command.  An  interactive  shell  does  not
                      exit if exec fails.
              expand_aliases
                      If  set,  aliases  are expanded as described above under
                      ALIASES.  This option is enabled by default for interac-
                      tive shells.
              extdebug
                      If  set  at shell invocation, arrange to execute the de-
                      bugger profile before the shell starts, identical to the
                      --debugger  option.   If  set after invocation, behavior
                      intended for use by debuggers is enabled:
                      1.     The -F option to the declare builtin displays the
                             source file name and line number corresponding to
                             each function name supplied as an argument.
                      2.     If the command run by the DEBUG  trap  returns  a
                             non-zero  value,  the next command is skipped and
                             not executed.
                      3.     If the command run by the DEBUG  trap  returns  a
                             value  of 2, and the shell is executing in a sub-
                             routine (a shell function or a shell script  exe-
                             cuted  by  the  .  or source builtins), the shell
                             simulates a call to return.
                      4.     BASH_ARGC and BASH_ARGV are updated as  described
                             in their descriptions above.
                      5.     Function  tracing  is  enabled: command substitu-
                             tion, shell functions, and subshells invoked with
                             ( command ) inherit the DEBUG and RETURN traps.
                      6.     Error  tracing  is enabled: command substitution,
                             shell functions, and  subshells  invoked  with  (
                             command ) inherit the ERR trap.
              extglob If set, the extended pattern matching features described
                      above under Pathname Expansion are enabled.
              extquote
                      If set, $'string' and  $"string"  quoting  is  performed
                      within   ${parameter}   expansions  enclosed  in  double
                      quotes.  This option is enabled by default.
              failglob
                      If set, patterns which fail to  match  filenames  during
                      pathname expansion result in an expansion error.
              force_fignore
                      If  set,  the  suffixes  specified  by the FIGNORE shell
                      variable cause words to be ignored when performing  word
                      completion even if the ignored words are the only possi-
                      ble completions.  See SHELL VARIABLES above  for  a  de-
                      scription  of  FIGNORE.   This  option is enabled by de-
                      fault.
              globasciiranges
                      If set,  range  expressions  used  in  pattern  matching
                      bracket  expressions (see Pattern Matching above) behave
                      as if in the traditional C locale when  performing  com-
                      parisons.   That  is, the current locale's collating se-
                      quence is not taken into account, so b will not  collate
                      between  A  and  B,  and upper-case and lower-case ASCII
                      characters will collate together.
              globstar
                      If set, the pattern ** used in a pathname expansion con-
                      text  will  match all files and zero or more directories
                      and subdirectories.  If the pattern is followed by a  /,
                      only directories and subdirectories match.
              gnu_errfmt
                      If set, shell error messages are written in the standard
                      GNU error message format.
              histappend
                      If set, the history list is appended to the  file  named
                      by the value of the HISTFILE variable when the shell ex-
                      its, rather than overwriting the file.
              histreedit
                      If set, and readline is being used, a user is given  the
                      opportunity to re-edit a failed history substitution.
              histverify
                      If  set, and readline is being used, the results of his-
                      tory substitution are  not  immediately  passed  to  the
                      shell  parser.   Instead,  the  resulting line is loaded
                      into the readline editing buffer, allowing further modi-
                      fication.
              hostcomplete
                      If set, and readline is being used, bash will attempt to
                      perform hostname completion when a word containing  a  @
                      is   being  completed  (see  Completing  under  READLINE
                      above).  This is enabled by default.
              huponexit
                      If set, bash will send SIGHUP to all jobs when an inter-
                      active login shell exits.
              inherit_errexit
                      If  set,  command substitution inherits the value of the
                      errexit option, instead of unsetting it in the  subshell
                      environment.   This option is enabled when posix mode is
                      enabled.
              interactive_comments
                      If set, allow a word beginning with # to cause that word
                      and  all remaining characters on that line to be ignored
                      in an interactive shell (see COMMENTS above).  This  op-
                      tion is enabled by default.
              lastpipe
                      If  set,  and  job control is not active, the shell runs
                      the last command of a pipeline not executed in the back-
                      ground in the current shell environment.
              lithist If  set,  and  the cmdhist option is enabled, multi-line
                      commands are saved to the history with embedded newlines
                      rather than using semicolon separators where possible.
              localvar_inherit
                      If set, local variables inherit the value and attributes
                      of a variable of the same name that exists at a previous
                      scope before any new value is assigned.  The nameref at-
                      tribute is not inherited.
              localvar_unset
                      If set, calling unset on  local  variables  in  previous
                      function  scopes  marks  them so subsequent lookups find
                      them unset until that function returns. This is  identi-
                      cal  to the behavior of unsetting local variables at the
                      current function scope.
              login_shell
                      The shell sets this option if it is started as  a  login
                      shell  (see  INVOCATION  above).   The  value may not be
                      changed.
              mailwarn
                      If set, and a file that bash is checking  for  mail  has
                      been  accessed  since  the last time it was checked, the
                      message ``The mail in mailfile has been read''  is  dis-
                      played.
              no_empty_cmd_completion
                      If  set,  and  readline is being used, bash will not at-
                      tempt to search the PATH for possible  completions  when
                      completion is attempted on an empty line.
              nocaseglob
                      If  set,  bash  matches  filenames in a case-insensitive
                      fashion when performing pathname expansion (see Pathname
                      Expansion above).
              nocasematch
                      If  set,  bash  matches  patterns  in a case-insensitive
                      fashion when performing matching while executing case or
                      [[ conditional commands, when performing pattern substi-
                      tution word expansions, or when filtering possible  com-
                      pletions as part of programmable completion.
              nullglob
                      If  set,  bash allows patterns which match no files (see
                      Pathname Expansion above) to expand to  a  null  string,
                      rather than themselves.
              progcomp
                      If set, the programmable completion facilities (see Pro-
                      grammable Completion above) are enabled.  This option is
                      enabled by default.
              progcomp_alias
                      If  set,  and  programmable  completion is enabled, bash
                      treats a command name that doesn't have any  completions
                      as  a possible alias and attempts alias expansion. If it
                      has an alias, bash attempts programmable completion  us-
                      ing the command word resulting from the expanded alias.
              promptvars
                      If set, prompt strings undergo parameter expansion, com-
                      mand substitution, arithmetic expansion, and  quote  re-
                      moval  after  being  expanded  as described in PROMPTING
                      above.  This option is enabled by default.
              restricted_shell
                      The shell sets this option  if  it  is  started  in  re-
                      stricted  mode  (see RESTRICTED SHELL below).  The value
                      may not be changed.  This is not reset when the  startup
                      files  are  executed, allowing the startup files to dis-
                      cover whether or not a shell is restricted.
              shift_verbose
                      If set, the shift builtin prints an error  message  when
                      the shift count exceeds the number of positional parame-
                      ters.
              sourcepath
                      If set, the source (.) builtin uses the value of PATH to
                      find  the  directory  containing the file supplied as an
                      argument.  This option is enabled by default.
              xpg_echo
                      If set, the echo builtin  expands  backslash-escape  se-
                      quences by default.

       suspend [-f]
              Suspend  the execution of this shell until it receives a SIGCONT
              signal.  A login shell cannot be suspended; the -f option can be
              used to override this and force the suspension.  The return sta-
              tus is 0 unless the shell is a login shell and -f  is  not  sup-
              plied, or if job control is not enabled.

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

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

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

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

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

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

       trap [-lp] [[arg] sigspec ...]
              The command arg is to be read and executed when  the  shell  re-
              ceives signal(s) sigspec.  If arg is absent (and there is a sin-
              gle sigspec) or -, each specified signal is reset to its  origi-
              nal  disposition  (the value it had upon entrance to the shell).
              If arg is the null string the signal specified by  each  sigspec
              is  ignored by the shell and by the commands it invokes.  If arg
              is not present and -p has been supplied, then the trap  commands
              associated with each sigspec are displayed.  If no arguments are
              supplied or if only -p is given, trap prints the  list  of  com-
              mands  associated  with  each  signal.  The -l option causes the
              shell to print a list of signal names  and  their  corresponding
              numbers.   Each sigspec is either a signal name defined in <sig-
              nal.h>, or a signal number.  Signal names are  case  insensitive
              and the SIG prefix is optional.

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

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

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

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

       ulimit [-HSabcdefiklmnpqrstuvxPT [limit]]
              Provides control over the resources available to the  shell  and
              to  processes started by it, on systems that allow such control.
              The -H and -S options specify that the hard or soft limit is set
              for  the  given resource.  A hard limit cannot be increased by a
              non-root user once it is set; a soft limit may be  increased  up
              to  the value of the hard limit.  If neither -H nor -S is speci-
              fied, both the soft and hard limits are set.  The value of limit
              can be a number in the unit specified for the resource or one of
              the special values hard, soft, or unlimited, which stand for the
              current  hard  limit,  the current soft limit, and no limit, re-
              spectively.  If limit is omitted, the current value of the  soft
              limit of the resource is printed, unless the -H option is given.
              When more than one resource is specified,  the  limit  name  and
              unit  are  printed  before  the value.  Other options are inter-
              preted as follows:
              -a     All current limits are reported
              -b     The maximum socket buffer size
              -c     The maximum size of core files created
              -d     The maximum size of a process's data segment
              -e     The maximum scheduling priority ("nice")
              -f     The maximum size of files written by the  shell  and  its
                     children
              -i     The maximum number of pending signals
              -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
              -T     The maximum number of threads

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

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

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

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

       wait [-fn] [id ...]
              Wait for each specified child process and return its termination
              status.   Each id may be a process ID or a job specification; if
              a job spec is given, all processes in that  job's  pipeline  are
              waited for.  If id is not given, all currently active child pro-
              cesses are waited for, and the return status is zero.  If the -n
              option  is supplied, wait waits for any job to terminate and re-
              turns its exit status.  If the -f option is  supplied,  and  job
              control is enabled, wait forces id to terminate before returning
              its status, instead of returning when it changes status.  If  id
              specifies  a  non-existent  process or job, the return status is
              127.  Otherwise, the return status is the  exit  status  of  the
              last process or job waited for.

RESTRICTED SHELL
       If bash is started with the name rbash, or the -r option is supplied at
       invocation, the shell becomes restricted.  A restricted shell  is  used
       to  set  up an environment more controlled than the standard shell.  It
       behaves identically to bash with the exception that the  following  are
       disallowed or not performed:

       o      changing directories with cd

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

       o      specifying command names containing /

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

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

       o      importing  function  definitions  from  the shell environment at
              startup

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

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

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

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

       o      using the  enable  builtin  command  to  enable  disabled  shell
              builtins

       o      specifying the -p option to the command builtin command

       o      turning off restricted mode with set +r or set +o restricted.

       These restrictions are enforced after any startup files are read.

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

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

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

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

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

BUG REPORTS
       If you find a bug in bash, you should report it.  But first, you should
       make  sure  that  it really is a bug, and that it appears in the latest
       version  of  bash.   The  latest  version  is  always  available   from
       ftp://ftp.gnu.org/pub/gnu/bash/.

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

       ALL bug reports should include:

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

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

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

BUGS
       It's too big and too slow.

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

       Aliases are confusing in some uses.

       Shell builtin commands and functions are not stoppable/restartable.

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

       Array variables may not (yet) be exported.

       There may be only one active coprocess at a time.

GNU Bash 5.0                    2018 December 7                        BASH(1)

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