BASH(1)                     General Commands Manual                    BASH(1)



NAME
       bash - GNU Bourne-Again SHell

SYNOPSIS
       bash [options] [command_string | file]

COPYRIGHT
       Bash is Copyright (C) 1989-2015 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 can be used as options  when  the  shell  is
       invoked.  In addition, bash interprets the following options 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
                 assigned  to  $$00  and any remaining arguments are assigned to
                 the positional parameters.  The assignment  to  $$00  sets  the
                 name  of  the  shell, which is used in warning and error mes-
                 sages.
       -i        If the -i option is present, the shell is interactive.
       -l        Make bash act as if it had been invoked as a login shell (see
                 INVOCATION below).
       -r        If  the  -r  option  is present, the shell becomes restricted
                 (see RESTRICTED SHELL below).
       -s        If the -s option is present, or if no arguments remain  after
                 option  processing,  then commands are read from the standard
                 input.  This option allows the positional  parameters  to  be
                 set when invoking an interactive shell.
       -D        A  list of all double-quoted strings preceded by $$ is printed
                 on the standard output.  These are the strings that are  sub-
                 ject to language translation when the current locale is not CC
                 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  ++OO,  the
                 output is displayed in a format that may be reused as input.
       ----        A  ----  signals the end of options and disables further option
                 processing.  Any arguments after the ---- are treated as  file-
                 names and arguments.  An argument of -- is equivalent to ----.

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

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

       --login
              Equivalent to -l.

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

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

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

       --posix
              Change the behavior of bash where the default operation  differs
              from the POSIX standard to match the standard (posix mode).  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,  $$00 is set to the name of the file, and the positional parame-
       ters are set to the remaining arguments.  Bash reads and executes  com-
       mands  from this file, then exits.  Bash's exit status is the exit sta-
       tus of the last command executed in the script.   If  no  commands  are
       executed,  the  exit status is 0.  An attempt is first made to open the
       file in the current directory, and, if no file is found, then the shell
       searches the directories in PATH for the script.

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

       An interactive  shell  is  one  started  without  non-option  arguments
       (unless -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 ii if
       bash is interactive, allowing a shell script or a startup file to  test
       this state.

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

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

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

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

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

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

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

       Bash attempts to determine when it is being run with its standard input
       connected to a 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, if that file exists and is readable.  It  will  not  do
       this  if  invoked as sh.  The --norc option may be used to inhibit this
       behavior, and the --rcfile option may be used to force another file  to
       be  read,  but  neither  rshd  nor sshd generally invoke the shell with
       those options or allow them to be specified.

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

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

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

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

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

       The  standard output of command is connected via a pipe to the standard
       input of command2.  This connection is performed  before  any  redirec-
       tions specified by the command (see REDIRECTION below).  If ||&& is used,
       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 22>>&&11 ||.  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).

   Lists
       A list is a sequence of one or more pipelines separated by one  of  the
       operators ;;, &&, &&&&, or ||||, and optionally terminated by one of ;;, &&, or
       <newline>.

       Of these list operators, &&&& and |||| have equal precedence, followed by ;;
       and &&, which have equal precedence.

       A  sequence  of  one or more newlines may appear in a list instead of a
       semicolon to delimit commands.

       If a command is terminated by the control operator &&,  the  shell  exe-
       cutes  the command in the background in a subshell.  The shell does not
       wait for the command to finish, and the return status is  0.   Commands
       separated  by  a  ;; are executed sequentially; the shell waits for each
       command to terminate in turn.  The return status is the exit status  of
       the last command executed.

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

              command1 &&&& command2

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

       An OR list has the form

              command1 |||| command2

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

   Compound Commands
       A compound command is one of the following.  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
              effect after the command completes.  The return  status  is  the
              exit status of list.

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

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

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

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

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

              An  additional  binary operator, ==~~, is available, with the same
              precedence as ==== and !!==.  When it is used,  the  string  to  the
              right  of the operator is considered an extended regular expres-
              sion and matched accordingly (as in regex(3)).  The return value
              is 0 if the string matches the pattern, and 1 otherwise.  If the
              regular expression is syntactically incorrect,  the  conditional
              expression's return value is 2.  If the 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
              parameter that is set (see PARAMETERS below).  The return status
              is  the  exit  status of the last command that executes.  If the
              expansion of the items following in results in an empty list, no
              commands are executed, and the return status is 0.

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

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

       case word in [ [(] pattern [ || pattern ] ... ) list ;; ] ... esac
              A case command first expands word, and tries to match it against
              each pattern in turn, using the same matching rules as for path-
              name expansion (see Pathname  Expansion  below).   The  word  is
              expanded  using  tilde  expansion, parameter and variable expan-
              sion, arithmetic expansion, command substitution,  process  sub-
              stitution  and quote removal.  Each pattern examined is expanded
              using tilde expansion, parameter and variable expansion,  arith-
              metic expansion, command substitution, and process substitution.
              If the nocasematch shell option is enabled, the  match  is  per-
              formed  without  regard  to  the  case of alphabetic characters.
              When a match is found, the corresponding list is  executed.   If
              the  ;;;;  operator  is  used, no subsequent matches are attempted
              after the first pattern match.  Using ;;&& in place of  ;;;;  causes
              execution to continue with the list associated with the next set
              of patterns.  Using ;;;;&& in place of ;;;; causes the shell to  test
              the  next pattern list in the statement, if any, and execute any
              associated list on a successful match.  The exit status is  zero
              if  no pattern matches.  Otherwise, it is the exit status of the
              last command executed in list.

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

       while list-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,
              except  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 exe-
              cuted.

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

       The format for a coprocess is:

              coproc [NAME] command [redirections]

       This creates a coprocess named NAME.  If  NAME  is  not  supplied,  the
       default name is COPROC.  NAME must not be supplied if command is a sim-
       ple command (see above); otherwise, it is interpreted as the first word
       of  the simple command.  When the coprocess is executed, the shell cre-
       ates an array variable (see Arrays below) named NAME in the context  of
       the executing shell.  The standard output of command is connected via a
       pipe to a file  descriptor  in  the  executing  shell,  and  that  file
       descriptor  is  assigned  to NAME[0].  The standard input of command is
       connected via a pipe to a file descriptor in the executing  shell,  and
       that  file descriptor is assigned to NAME[1].  This pipe is established
       before any redirections  specified  by  the  command  (see  REDIRECTION
       below).   The  file  descriptors  can be utilized as arguments to shell
       commands and redirections using standard  word  expansions.   The  file
       descriptors  are  not  available  in  subshells.  The process ID of the
       shell spawned to execute the coprocess is available as the value of the
       variable  NAMEPID.   The  wait builtin command may be used to wait for
       the coprocess to terminate.

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

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

       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
       itself quoted, the \\<newline> is treated as a line  continuation  (that
       is, it is removed from the input stream and effectively ignored).

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

       Enclosing  characters  in  double quotes preserves the literal value of
       all characters within the quotes, with the exception of $$, ``,  \\,  and,
       when  history  expansion  is enabled, !!.  The characters $$ and `` retain
       their special meaning within double quotes.  The backslash retains  its
       special  meaning only when followed by one of the following characters:
       $$, ``, "", \\, or <newline>.  A double quote may be quoted  within  double
       quotes by preceding it with a backslash.  If enabled, history expansion
       will be performed unless an !!  appearing in double  quotes  is  escaped
       using a backslash.  The backslash preceding the !!  is not removed.

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

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

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

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

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

              name=[value]

       If  value  is not given, the variable is assigned the null string.  All
       values undergo tilde expansion, parameter and variable expansion,  com-
       mand  substitution, arithmetic expansion, and quote removal (see EXPAN-
       SION below).  If the variable has its integer attribute set, then value
       is evaluated as an arithmetic expression even if the $((...)) expansion
       is not used (see Arithmetic Expansion below).  Word  splitting  is  not
       performed,  with the exception of ""$$@@"" as explained below under Special
       Parameters.  Pathname expansion is not  performed.   Assignment  state-
       ments  may  also  appear  as  arguments to the alias, declare, typeset,
       export, readonly, and local builtin  commands  (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
       expression  and  added  to  the variable's current value, which is also
       evaluated.  When += is applied to  an  array  variable  using  compound
       assignment (see Arrays below), the variable's value is not unset (as it
       is when using =), and new values are appended to the array beginning at
       one  greater  than  the  array's  maximum index (for indexed arrays) or
       added as additional key-value pairs  in  an  associative  array.   When
       applied  to a string-valued variable, value is expanded and appended to
       the variable's value.

       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
       attributes  modified  (other  than  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 argument 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,
       assignments, and attribute modifications to the variable whose name was
       passed as $$11.  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
              parameter  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
              parameter  separated  by  the first character of the IFS special
              variable.  That is, "$$**" is equivalent to "$$11_c$$22_c......",  where  _c
              is the first character of the value of the IFS variable.  If IFS
              is unset, the parameters are separated by  spaces.   If  IFS  is
              null, the parameters are joined without intervening separators.
       @@      Expands  to  the positional parameters, starting from one.  When
              the  expansion  occurs  within  double  quotes,  each  parameter
              expands to a separate word.  That is, "$$@@" is equivalent to "$$11"
              "$$22" ...  If the double-quoted expansion occurs within  a  word,
              the  expansion  of the first parameter is joined with the begin-
              ning part of the original word, and the expansion  of  the  last
              parameter  is  joined  with  the last part of the original word.
              When there are no positional parameters, "$$@@" and $$@@  expand  to
              nothing (i.e., they are removed).
       ##      Expands to the number of positional parameters in decimal.
       ??      Expands  to  the exit status of the most recently executed fore-
              ground pipeline.
       --      Expands to the current option flags as  specified  upon  invoca-
              tion,  by  the  set  builtin  command, or those set by the shell
              itself (such as the -i option).
       $$      Expands to the process ID of the shell.  In a  ()  subshell,  it
              expands  to  the  process  ID of the current shell, not the sub-
              shell.
       !!      Expands to the process ID of the job most recently  placed  into
              the  background,  whether executed as an asynchronous command or
              using the bg builtin (see JOB CONTROL below).
       00      Expands to the name of the shell or shell script.  This  is  set
              at shell initialization.  If bash is invoked with a file of com-
              mands, $$00 is set to the name of that file.  If bash  is  started
              with  the  -c option, then $$00 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
              argument  to the previous command, after expansion.  Also set to
              the full pathname used  to  invoke  each  command  executed  and
              placed in the environment exported to that command.  When check-
              ing mail, this parameter holds the name of the  mail  file  cur-
              rently being checked.

   Shell Variables
       The following variables are set by the shell:

       BASH   Expands  to  the  full  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.
       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; unsetting
              array elements cause aliases to be removed from the alias list.
       BASH_ARGC
              An  array  variable whose values are the number of parameters in
              each frame of the current bash execution call stack.  The number
              of  parameters  to  the  current  subroutine  (shell function or
              script executed with .. or source) is at the top  of  the  stack.
              When  a  subroutine is executed, the number of parameters passed
              is pushed onto BASH_ARGC.  The shell sets BASH_ARGC only when in
              extended  debugging  mode  (see  the description of the extdebug
              option to the shopt builtin below)
       BASH_ARGV
              An array variable containing all of the parameters in  the  cur-
              rent bash execution call stack.  The final parameter of the last
              subroutine call is at the top of the stack; the first  parameter
              of the initial call is at the bottom.  When a subroutine is exe-
              cuted, the parameters supplied are pushed onto  BASH_ARGV.   The
              shell  sets  BASH_ARGV only when in extended debugging mode (see
              the description of the extdebug  option  to  the  shopt  builtin
              below)
       BASH_CMDS
              An  associative  array  variable whose members correspond to the
              internal hash table  of  commands  as  maintained  by  the  hash
              builtin.  Elements added to this array appear in the hash table;
              unsetting array elements cause commands to be removed  from  the
              hash table.
       BASH_COMMAND
              The  command  currently  being executed or about to be executed,
              unless the shell is executing a command as the result of a trap,
              in  which  case  it  is the command executing at the time of the
              trap.
       BASH_EXECUTION_STRING
              The command argument to the -c invocation option.
       BASH_LINENO
              An array variable whose members are the line numbers  in  source
              files  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
              expression.  The element with index _n  is  the  portion  of  the
              string matching the _nth parenthesized subexpression.  This vari-
              able is read-only.
       BASH_SOURCE
              An array variable whose members are the source  filenames  where
              the  corresponding  shell  function  names in the FUNCNAME array
              variable are defined.  The  shell  function  ${FUNCNAME[_$_i]]}}  is
              defined   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:
              BBAASSHH__VVEERRSSIINNFFOO[[0]]        The major version number (the release).
              BBAASSHH__VVEERRSSIINNFFOO[[1]]        The minor version number (the version).
              BBAASSHH__VVEERRSSIINNFFOO[[2]]        The patch level.
              BBAASSHH__VVEERRSSIINNFFOO[[3]]        The build version.
              BBAASSHH__VVEERRSSIINNFFOO[[4]]        The release status (e.g., beta1).
              BBAASSHH__VVEERRSSIINNFFOO[[5]]        The value of MACHTYPE.
       BASH_VERSION
              Expands to a string describing the version of this  instance  of
              bash.
       COMP_CWORD
              An  index  into ${COMP_WORDS} of the word containing the current
              cursor position.  This variable is available only in shell func-
              tions  invoked  by  the  programmable completion facilities (see
              Programmable Completion below).
       COMP_KEY
              The key (or final key of a key sequence) used to invoke the cur-
              rent completion function.
       COMP_LINE
              The  current  command  line.  This variable is available only in
              shell functions and external commands invoked  by  the  program-
              mable completion facilities (see Programmable Completion below).
       COMP_POINT
              The  index of the current cursor position relative to the begin-
              ning of the current command.  If the current cursor position  is
              at the end of the current command, the value of this variable is
              equal to ${#COMP_LINE}.  This  variable  is  available  only  in
              shell  functions  and  external commands invoked by the program-
              mable completion facilities (see Programmable Completion below).
       COMP_TYPE
              Set to an integer value corresponding to the type of  completion
              attempted  that  caused a completion function to be called: TAB,
              for normal completion, _?, for listing completions after  succes-
              sive  tabs,  _!, for listing alternatives on partial word comple-
              tion, _@, to list completions if the word is not  unmodified,  or
              _%,  for  menu  completion.   This  variable is available only in
              shell functions and external commands invoked  by  the  program-
              mable completion facilities (see Programmable Completion below).
       COMP_WORDBREAKS
              The  set  of characters that the readline library treats as word
              separators when performing word completion.  If  COMP_WORDBREAKS
              is  unset, it loses its special properties, even if it is subse-
              quently reset.
       COMP_WORDS
              An array variable (see Arrays below) consisting of the  individ-
              ual  words  in the current command line.  The line is split into
              words as readline  would  split  it,  using  COMP_WORDBREAKS  as
              described above.  This variable is available only in shell func-
              tions invoked by the  programmable  completion  facilities  (see
              Programmable Completion below).
       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
              unset, it loses its special properties, even  if  it  is  subse-
              quently reset.
       EUID   Expands  to  the effective user ID of the current user, initial-
              ized at shell startup.  This variable is readonly.
       FUNCNAME
              An array variable containing the names of  all  shell  functions
              currently in the execution call stack.  The element with index 0
              is the name of any currently-executing shell function.  The bot-
              tom-most  element  (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
              reset.

              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
              instance,   ${FUNCNAME[_$_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
              reset.
       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
       assigns a default value to a variable; these cases are noted below.

       BASH_COMPAT
              The  value  is used to set the shell's compatibility level.  See
              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
              described 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
              enabled  to that file descriptor.  The file descriptor is closed
              when BASH_XTRACEFD is unset or assigned a new value.   Unsetting
              BASH_XTRACEFD  or assigning it the empty string causes the trace
              output to be sent to the  standard  error.   Note  that  setting
              BASH_XTRACEFD to 2 (the standard error file descriptor) and then
              unsetting it will result in the standard error being closed.
       CDPATH The search path for the cd command.  This is  a  colon-separated
              list  of  directories  in  which the shell looks for destination
              directories specified by the cd  command.   A  sample  value  is
              ".:~:/usr".
       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
              array 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 extended glob  patterns  (see  Pattern
              Matching)  defining  the list of filenames to be ignored by com-
              mand search.  Files whose full pathnames match one of these pat-
              terns  are  not  considered executable files for the purposes of
              completion and command execution.   This  does  not  affect  the
              behavior  of the [[, test, and [[[[ commands.  Use this variable to
              ignore shared library files that have the  executable  bit  set,
              but are not executable files.
       FCEDIT The default editor for the fc builtin command.
       FIGNORE
              A  colon-separated  list  of  suffixes to ignore when performing
              filename completion (see READLINE below).  A filename whose suf-
              fix  matches  one of the entries in FIGNORE is excluded from the
              list of matched filenames.  A sample value is ".o:~".
       FUNCNEST
              If set to a numeric value greater  than  0,  defines  a  maximum
              function  nesting  level.  Function invocations that exceed this
              nesting level will cause the current command to abort.
       GLOBIGNORE
              A colon-separated list of patterns defining the set of filenames
              to be ignored by pathname expansion.  If a filename matched by a
              pathname expansion pattern also matches one of the  patterns  in
              GLOBIGNORE, it is removed from the list of matches.
       HISTCONTROL
              A  colon-separated  list  of values controlling how commands are
              saved on the history list.   If  the  list  of  values  includes
              ignorespace,  lines  which  begin with a space character are not
              saved in the history list.  A value of ignoredups  causes  lines
              matching the previous history entry to not be saved.  A value of
              ignoreboth is shorthand for ignorespace and ignoredups.  A value
              of erasedups causes all previous lines matching the current line
              to be removed from the history list before that line  is  saved.
              Any  value  not in the above list is ignored.  If HISTCONTROL is
              unset, or does not include a valid value, all lines read by  the
              shell parser are saved on the history list, subject to the value
              of HISTIGNORE.  The second and subsequent lines of a  multi-line
              compound  command  are  not tested, and are added to the history
              regardless of the value of HISTCONTROL.
       HISTFILE
              The name of the file in which command history is saved (see HIS-
              TORY  below).   The default value is ~/.bash__history.  If unset,
              the command history is not saved when 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
              anchored at the beginning of the line and must  match  the  com-
              plete  line  (no  implicit  `**'  is  appended).  Each pattern is
              tested against the line after the checks specified  by  HISTCON-
              TROL  are  applied.   In  addition  to  the normal shell pattern
              matching characters, `&&' matches the previous history line.  `&&'
              may  be  escaped  using  a  backslash;  the backslash is removed
              before attempting a match.  The second and subsequent lines of a
              multi-line compound command are not tested, and are added to the
              history regardless of the value of HISTIGNORE.
       HISTSIZE
              The number of commands to remember in the command  history  (see
              HISTORY  below).   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
              attempted  after the value is changed, bash adds the contents of
              the new file to the existing list.  If HOSTFILE is set, but  has
              no  value,  or  does  not name a readable file, bash attempts to
              read /etc/hosts to obtain the list of possible hostname  comple-
              tions.  When HOSTFILE is unset, the hostname list is cleared.
       IFS    The  Internal  Field  Separator  that is used for word splitting
              after expansion and to split lines  into  words  with  the  read
              builtin  command.   The  default  value  is  ``<space><tab><new-
              line>''.
       IGNOREEOF
              Controls the action of an interactive shell on receipt of an EOF
              character as the sole input.  If set, the value is the number of
              consecutive EOF characters which must  be  typed  as  the  first
              characters  on an input line before bash exits.  If the variable
              exists but does not have a numeric value, or has no  value,  the
              default  value  is  10.  If it does not exist, EOF signifies the
              end of input to the shell.
       INPUTRC
              The filename for  the  readline  startup  file,  overriding  the
              default of ~/.inputrc (see READLINE below).
       LANG   Used  to  determine  the  locale  category  for any category not
              specifically selected with a variable starting with LC_.
       LC_ALL This variable overrides the value of  LANG  and  any  other  LC_
              variable specifying a locale category.
       LC_COLLATE
              This  variable  determines the collation order used when sorting
              the results of pathname expansion, and determines  the  behavior
              of   range   expressions,  equivalence  classes,  and  collating
              sequences within pathname expansion and pattern matching.
       LC_CTYPE
              This variable determines the interpretation  of  characters  and
              the  behavior of character classes within pathname expansion and
              pattern matching.
       LC_MESSAGES
              This variable determines the locale used  to  translate  double-
              quoted strings preceded by a $$.
       LC_NUMERIC
              This  variable  determines  the  locale category used for number
              formatting.
       LINES  Used by the select compound  command  to  determine  the  column
              length  for  printing selection lists.  Automatically set if the
              checkwinsize option is enabled or in an interactive  shell  upon
              receipt of a SIGWINCH.
       MAIL   If  this  parameter  is  set to a file or directory name and the
              MAILPATH variable is not set,  bash  informs  the  user  of  the
              arrival  of  mail in the specified file or Maildir-format direc-
              tory.
       MAILCHECK
              Specifies how often (in seconds)  bash  checks  for  mail.   The
              default  is  60 seconds.  When it is time to check for mail, the
              shell does so before displaying the  primary  prompt.   If  this
              variable  is  unset,  or  set  to  a  value that is not a number
              greater than or equal to zero, the shell disables mail checking.
       MAILPATH
              A colon-separated list of filenames to be checked for mail.  The
              message to be printed when mail arrives in a particular file may
              be specified by separating the filename from the message with  a
              `?'.   When  used  in the text of the message, $$__ expands to the
              name of the current mailfile.  Example:
              MAILPATH='/var/mail/bfox?"You  have  mail":~/shell-mail?"$_  has
              mail!"'
              Bash  supplies  a default value for this variable, but the loca-
              tion of the user mail files that it  uses  is  system  dependent
              (e.g., /var/mail/$USER).
       OPTERR If set to the value 1, bash displays error messages generated by
              the getopts builtin command (see SHELL BUILTIN COMMANDS  below).
              OPTERR  is  initialized to 1 each time the shell is invoked or a
              shell script is executed.
       PATH   The search path for commands.  It is a colon-separated  list  of
              directories  in  which the shell looks for commands (see COMMAND
              EXECUTION below).  A zero-length (null) directory  name  in  the
              value of PATH indicates the current directory.  A null directory
              name may appear as two adjacent colons,  or  as  an  initial  or
              trailing  colon.   The  default path is system-dependent, and is
              set by the administrator who installs bash.  A common  value  is
              ``/usr/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.
       PROMPT_COMMAND
              If set, the value is executed as a command prior to issuing each
              primary prompt.
       PROMPT_DIRTRIM
              If  set  to a number greater than zero, the value is used as the
              number of trailing directory components to retain when expanding
              the  \w  and  \W  prompt  string  escapes (see PROMPTING below).
              Characters removed are replaced with an ellipsis.
       PS1    The value of this parameter is expanded  (see  PROMPTING  below)
              and  used  as  the  primary prompt string.  The default value is
              `\s-\v\$ ''.
       PS2    The value of this parameter is expanded as with PS1 and used  as
              the secondary prompt string.  The default is ``>> ''.
       PS3    The value of this parameter is used as the prompt for the select
              command (see SHELL GRAMMAR above).
       PS4    The value of this parameter is expanded  as  with  PS1  and  the
              value  is  printed  before  each command bash displays during an
              execution trace.  The first character of PS4 is replicated  mul-
              tiple  times, as necessary, to indicate multiple levels of indi-
              rection.  The default is ``++ ''.
       SHELL  The full pathname to the shell is kept in this environment vari-
              able.   If  it is not set when the shell starts, bash assigns to
              it the full pathname of the current user's login shell.
       TIMEFORMAT
              The value of this parameter is used as a format string  specify-
              ing  how  the timing information for pipelines prefixed with the
              time reserved word should be displayed.  The %% character  intro-
              duces  an  escape  sequence  that is expanded to a time value or
              other information.  The escape sequences and their meanings  are
              as follows; the braces denote optional portions.
              %%%%        A literal %%.
              %%[[_p]][[ll]]RR  The elapsed time in seconds.
              %%[[_p]][[ll]]UU  The number of CPU seconds spent in user mode.
              %%[[_p]][[ll]]SS  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 ll specifies a longer format, including minutes,  of
              the  form  _M_Mm_S_S._F_Fs.   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
              default timeout for the read builtin.  The select command termi-
              nates if input does not arrive after TMOUT seconds when input is
              coming from a terminal.  In an interactive shell, the  value  is
              interpreted as the number of seconds to wait for 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=((value_1  ...  value_n)),  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
       introduced 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
       expansion  of  the first parameter is joined with the beginning part of
       the original word, and the expansion of the last  parameter  is  joined
       with  the  last  part  of  the original word.  This is analogous to the
       expansion of the special parameters ** and  @@  (see  Special  Parameters
       above).   ${#name[subscript]}  expands  to  the  length  of ${name[sub-
       script]}.  If subscript is ** or @@, the expansion is the number of  ele-
       ments  in  the array.  If the subscript used to reference an element of
       an indexed array evaluates to a number less than  zero,  it  is  inter-
       preted  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]
       destroys  the array element at index subscript.  Negative subscripts to
       indexed arrays are interpreted as described above.  Care must be  taken
       to  avoid  unwanted  side  effects caused by pathname expansion.  unset
       name, where name is an array, or unset name[subscript], where subscript
       is ** or @@, removes the entire array.

       The  declare,  local,  and readonly builtins each accept a -a option to
       specify an indexed array and a -A  option  to  specify  an  associative
       array.   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.

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

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

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

       A  sequence expression takes the form {{_x...._y[[....incr]]}}, where _x and _y are
       either integers or single characters, and incr, an optional  increment,
       is  an  integer.  When integers are supplied, the expression expands to
       each number between _x and _y, inclusive.  Supplied integers may be  pre-
       fixed  with _0 to force each term to have the same width.  When either _x
       or _y begins with a zero, the shell  attempts  to  force  all  generated
       terms  to  contain the same number of digits, zero-padding where neces-
       sary.  When characters are supplied, the  expression  expands  to  each
       character  lexicographically  between  _x  and  _y,  inclusive, using the
       default 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
       expression.   Any incorrectly formed brace expansion is left unchanged.
       A {{ or ,, may be quoted with a backslash to prevent its being considered
       part  of  a brace expression.  To avoid conflicts with parameter expan-
       sion, the string $${{ is not considered eligible for brace expansion.

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

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

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

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

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

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

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

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

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

       ${parameter}
              The value of parameter is substituted.  The braces are  required
              when  parameter  is  a  positional  parameter with more than one
              digit, or when parameter is followed by a character which is not
              to be interpreted as part of its name.  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 variable  indirec-
       tion.   Bash  uses  the  value  of the variable formed from the rest of
       parameter as the name of the variable; this variable is  then  expanded
       and that value is used in the rest of the substitution, rather than the
       value of parameter itself.  This is known as  indirect  expansion.   If
       parameter is a nameref, this expands to the name of the variable refer-
       enced by parameter instead of performing the complete  indirect  expan-
       sion.   The  exceptions  to  this are the expansions of ${!!prefix**} and
       ${!!name[_@]} described below.  The exclamation  point  must  immediately
       follow the left brace in order to introduce indirection.

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

       When not performing substring expansion,  using  the  forms  documented
       below  (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
       unset.

       ${parameter::--word}
              Use  Default  Values.  If parameter is unset or null, the expan-
              sion of word is substituted.  Otherwise, the value of  parameter
              is substituted.
       ${parameter::==word}
              Assign  Default  Values.   If  parameter  is  unset or null, the
              expansion of word is assigned to parameter.  The value of param-
              eter  is  then  substituted.   Positional parameters and special
              parameters may not be assigned to in this way.
       ${parameter::??word}
              Display Error if Null or Unset.  If parameter is null or  unset,
              the  expansion  of  word (or a message to that effect if word is
              not present) is written to the standard error and the shell,  if
              it is not interactive, exits.  Otherwise, the value of parameter
              is substituted.
       ${parameter::++word}
              Use Alternate Value.  If parameter is null or unset, nothing  is
              substituted, otherwise the expansion of word is substituted.
       ${parameter::offset}
       ${parameter::offset::length}
              Substring  Expansion.  Expands to up to length characters of 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
              parameter.  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
              expansion  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 ::-- expan-
              sion.

              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
              ${parameter[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
              undefined results.

              Substring indexing is zero-based unless the  positional  parame-
              ters  are  used,  in  which  case  the  indexing  starts at 1 by
              default.  If offset is 0,  and  the  positional  parameters  are
              used, $$00 is prefixed to the list.

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

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

       ${##parameter}
              Parameter  length.   The  length  in  characters of the value of
              parameter is substituted.  If parameter is **  or  @@,  the  value
              substituted  is the number of positional parameters.  If parame-
              ter is an array name subscripted by ** or @@,  the  value  substi-
              tuted  is  the number of elements in the array.  If parameter is
              an indexed array name subscripted by  a  negative  number,  that
              number  is interpreted as relative to one greater than the maxi-
              mum index of parameter, so negative indices count back from  the
              end  of  the  array, and an index of -1 references the last ele-
              ment.

       ${parameter##word}
       ${parameter####word}
              Remove matching prefix pattern.  The word is expanded to produce
              a pattern just as in pathname expansion.  If the pattern matches
              the beginning of the value of parameter, then the result of  the
              expansion  is  the expanded value of parameter with the shortest
              matching pattern (the ``##'' case) or the longest  matching  pat-
              tern  (the  ``####''  case)  deleted.  If parameter is @@ or **, the
              pattern removal operation is applied to each positional  parame-
              ter in turn, and the expansion is the resultant list.  If param-
              eter is an array variable subscripted with @@ or **,  the  pattern
              removal  operation  is  applied  to  each member of the array in
              turn, and the expansion is the resultant list.

       ${parameter%%word}
       ${parameter%%%%word}
              Remove matching suffix pattern.  The word is expanded to produce
              a pattern just as in pathname expansion.  If the pattern matches
              a trailing portion of the expanded value of parameter, then  the
              result  of the expansion is the expanded value of parameter with
              the shortest matching pattern (the ``%%'' case)  or  the  longest
              matching  pattern  (the ``%%%%'' case) deleted.  If parameter is @@
              or **, the pattern removal operation is  applied  to  each  posi-
              tional  parameter  in  turn,  and the expansion is the resultant
              list.  If parameter is an array variable subscripted with  @@  or
              **,  the  pattern  removal operation is applied to each member of
              the array in turn, and the expansion is the resultant list.

       ${parameter//pattern//string}
              Pattern substitution.  The pattern is expanded to produce a pat-
              tern  just  as in pathname expansion.  Parameter is expanded and
              the longest match of pattern against its value is replaced  with
              string.   If  pattern  begins with //, all matches of pattern are
              replaced  with  string.   Normally  only  the  first  match   is
              replaced.  If pattern begins with ##, it must match at the begin-
              ning of the expanded value of parameter.  If pattern begins with
              %%,  it must match at the end of the expanded value of parameter.
              If string is null, matches of pattern are deleted and the // fol-
              lowing  pattern may be omitted.  If 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 parameter in  turn,  and
              the  expansion  is the resultant list.  If parameter is an array
              variable subscripted with @@ or **, the substitution operation  is
              applied  to  each member of the array in turn, and the expansion
              is the resultant list.

       ${parameter^^pattern}
       ${parameter^^^^pattern}
       ${parameter,,pattern}
       ${parameter,,,,pattern}
              Case modification.  This expansion modifies the case  of  alpha-
              betic  characters in parameter.  The pattern is expanded to pro-
              duce a pattern just as in pathname expansion.  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 ^^
              operator converts lowercase letters matching pattern  to  upper-
              case; the ,, operator converts matching uppercase letters to low-
              ercase.  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
              omitted,  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  sub-
              scripted with @@ or **, the case modification operation is applied
              to each member of the array in turn, and the  expansion  is  the
              resultant list.

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

              QQ      The expansion is a string that is the value of  parameter
                     quoted in a format that can be reused as input.
              EE      The  expansion is a string that is the value of parameter
                     with backslash escape  sequences  expanded  as  with  the
                     $$''......'' quoting mechansim.
              PP      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).
              AA      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.
              aa      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 case modification 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 and replacing the com-
       mand  substitution  with  the  standard output of the command, with any
       trailing newlines deleted.  Embedded newlines are not deleted, but they
       may  be  removed during word splitting.  The command substitution $(cat
       file)) can be replaced by the equivalent but faster $$((<< file)).

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

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

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

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

              $$((((expression))))

       The expression is treated as if it were within  double  quotes,  but  a
       double  quote  inside  the  parentheses  is not treated specially.  All
       tokens in the expression undergo parameter 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  is supported on systems that support named pipes
       (FIFOs) or the /dev/fd method of naming open files.  It takes the  form
       of  <<((list)) or >>((list)).  The process list is run with its input or out-
       put connected to a FIFO or some file in /dev/fd.  The name of this file
       is  passed  as  an argument to the current command as the result of the
       expansion.  If the >>((list)) form is used, writing to the file will  pro-
       vide  input  for list.  If the <<((list)) form is used, the file passed as
       an argument should be read to obtain the output of list.

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

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

       The shell treats each character of IFS as a delimiter, and  splits  the
       results  of  the  other expansions into words 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 and
       tab are ignored at the beginning and end of the word, as  long  as  the
       whitespace  character is in the value of IFS (an IFS whitespace charac-
       ter).  Any character in IFS that is not IFS whitespace, along with  any
       adjacent  IFS  whitespace  characters, delimits a field.  A sequence of
       IFS whitespace characters is also treated as a delimiter.  If the value
       of IFS is null, no word splitting occurs.

       Explicit  null  arguments  (""""  or '''') are retained.  Unquoted implicit
       null arguments, resulting from the expansion of parameters that have no
       values,  are  removed.  If a parameter with no value is expanded within
       double quotes, a null argument results and is retained.

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

   Pathname Expansion
       After word splitting, unless the -f option has  been  set,  bash  scans
       each  word  for the characters **, ??, and [[.  If one of these characters
       appears, then the word is regarded as a pattern, and replaced  with  an
       alphabetically  sorted list of 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
       removed.   If  the  failglob  shell  option  is set, and no matches are
       found, an error message is printed and the command is not executed.  If
       the  shell option nocaseglob is enabled, the match is performed without
       regard to the case of alphabetic characters.  When a  pattern  is  used
       for  pathname expansion, the character ````..''''  at the start of a name or
       immediately following a slash must be matched  explicitly,  unless  the
       shell option dotglob is set.  When matching a pathname, the slash char-
       acter must always be matched explicitly.  In  other  cases,  the  ````..''''
       character is not treated specially.  See the description of shopt below
       under SHELL BUILTIN COMMANDS for a description of the nocaseglob, null-
       glob, 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 filename
       that also matches one of the patterns in GLOBIGNORE is removed from the
       list of matches.  If the nocaseglob option is set, the matching against
       the  patterns  in  GLOBIGNORE is performed without regard to case.  The
       filenames ````..''''  and ````....''''  are always ignored when GLOBIGNORE is  set
       and  not null.  However, setting GLOBIGNORE to a non-null value has the
       effect of enabling the dotglob shell option,  so  all  other  filenames
       beginning  with a ````..''''  will match.  To get the old behavior of ignor-
       ing filenames beginning with a ````..'''', make ````..**''''  one of the  patterns
       in  GLOBIGNORE.   The  dotglob  option  is  disabled when GLOBIGNORE is
       unset.

       Pattern Matching

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

       The special pattern characters have the following meanings:

              **      Matches any string, including the null string.  When  the
                     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
                     directories 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
                     sequence and character set, is  matched.   If  the  first
                     character following the [[ is a !!  or a ^^ then any charac-
                     ter not enclosed is matched.  The sorting order of  char-
                     acters  in range expressions is determined by the current
                     locale and the values of the LC_COLLATE or  LC_ALL  shell
                     variables, if set.  To obtain the traditional interpreta-
                     tion of range expressions, where [a-d] is  equivalent  to
                     [abcd],  set  value of the LC_ALL shell variable to CC, 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
                     using the syntax [[==_c==]], which matches all characters with
                     the same collation weight  (as  defined  by  the  current
                     locale) 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

   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.

       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:

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

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

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

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

       The general format for redirecting input is:

              [_n]<<word

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

       The general format for redirecting output is:

              [_n]>>word

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

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

       The general format for appending output is:

              [_n]>>>>word

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

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

              &&>>word
       and
              >>&&word

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

              >>word 2>>&&1

       When  using  the second form, word may not expand to a number or --.  If
       it does,  other  redirection  operators  apply  (see  Duplicating  File
       Descriptors 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  charac-
       ters  in  word are quoted, the delimiter is the result of quote removal
       on word, and the lines in the here-document are not expanded.  If  word
       is  unquoted, all lines of the here-document are subjected to parameter
       expansion, command substitution, and arithmetic expansion, the  charac-
       ter  sequence  \<newline>  is  ignored, and \\ must be used to quote the
       characters \\, $$, and ``.

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

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

              [_n]<<<<<<word

       The  word  undergoes  brace  expansion,  tilde expansion, parameter and
       variable expansion, command  substitution,  arithmetic  expansion,  and
       quote  removal.   Pathname  expansion  and  word splitting are not per-
       formed.  The result is supplied as a single string to  the  command  on
       its standard input (or file descriptor _n if _n is specified).

   Duplicating File Descriptors
       The redirection operator

              [_n]<<&&word

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

       The operator

              [_n]>>&&word

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

   Moving File Descriptors
       The redirection operator

              [_n]<<&&digit--

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

       Similarly, the redirection operator

              [_n]>>&&digit--

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

   Opening File Descriptors for Reading and Writing
       The redirection operator

              [_n]<<>>word

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

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

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

       There is no mechanism for using arguments in the replacement text.   If
       arguments  are  needed,  a shell function should be used (see FUNCTIONS
       below).

       Aliases are not expanded when the shell is not interactive, unless  the
       expand_aliases  shell option is set using shopt (see the description of
       shopt under SHELL BUILTIN COMMANDS below).

       The rules concerning the definition and use  of  aliases  are  somewhat
       confusing.   Bash  always  reads  at  least  one complete line of input
       before executing any  of  the  commands  on  that  line.   Aliases  are
       expanded  when  a command is read, not when it is executed.  Therefore,
       an alias definition appearing on the same line as another command  does
       not  take  effect  until  the next line of input is read.  The commands
       following the alias definition on that line are not affected by the new
       alias.   This  behavior  is  also an issue when functions are executed.
       Aliases are expanded when a function definition is read, not  when  the
       function  is  executed,  because a function definition is itself a com-
       mand.  As a consequence, aliases defined in a function are  not  avail-
       able  until  after  that  function is executed.  To be safe, always put
       alias definitions on a separate line, and do not use alias in  compound
       commands.

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

FUNCTIONS
       A  shell  function,  defined  as  described  above under SHELL GRAMMAR,
       stores a series of commands for later execution.  When the  name  of  a
       shell  function  is used as a simple command name, the list of commands
       associated with that function name is executed.  Functions are executed
       in  the  context  of  the  current  shell; no new process is created to
       interpret them (contrast this with the execution of  a  shell  script).
       When  a  function is executed, the arguments to the function become the
       positional parameters during its execution.  The special parameter ## is
       updated  to reflect the change.  Special parameter 00 is unchanged.  The
       first element of the FUNCNAME variable is set to the name of the  func-
       tion while the function is executing.

       All  other  aspects  of  the  shell execution environment are identical
       between a function and its caller with these exceptions: the DEBUG  and
       RETURN  traps  (see  the  description  of  the trap builtin under SHELL
       BUILTIN COMMANDS below) are not inherited unless the function has  been
       given  the  trace attribute (see the description of the declare builtin
       below) or the -o functrace shell option has been enabled with  the  set
       builtin  (in  which  case  all  functions  inherit the DEBUG and RETURN
       traps), and the ERR trap is not inherited unless the -o errtrace  shell
       option has been enabled.

       Variables  local to the function may be declared with the local builtin
       command.  Ordinarily, variables and their values are shared between the
       function and its caller.

       The  FUNCNEST  variable,  if  set  to  a  numeric value greater than 0,
       defines a maximum function nesting level.   Function  invocations  that
       exceed the limit cause the entire command to abort.

       If  the  builtin command return is executed in a function, the function
       completes and execution resumes with the next command after  the  func-
       tion  call.   Any  command  associated with the RETURN trap is executed
       before execution resumes.  When a function completes, the values of the
       positional  parameters  and the special parameter ## are restored to the
       values they had prior to the function's execution.

       Function names and definitions may be listed with the -f option to  the
       declare or typeset builtin commands.  The -F option to declare or type-
       set will list the function names only (and optionally the  source  file
       and  line  number, if the extdebug shell option is enabled).  Functions
       may be exported so that subshells automatically have them defined  with
       the  -f  option  to  the  export builtin.  A function definition may be
       deleted using the -f option to the  unset  builtin.   Note  that  shell
       functions and variables with the same name may result in multiple iden-
       tically-named entries in the environment passed to  the  shell's  chil-
       dren.  Care should be taken in cases where this may cause a problem.

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

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

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

       Shell  variables  are  allowed as operands; parameter expansion is per-
       formed before the expression is evaluated.  Within an expression, shell
       variables  may  also  be referenced by name without using the parameter
       expansion syntax.  A shell variable that is null or unset evaluates  to
       0 when referenced by name without using the parameter expansion syntax.
       The value of a variable is evaluated as an arithmetic  expression  when
       it  is  referenced, or when a variable which has been given the integer
       attribute using declare -i is assigned a value.  A null value evaluates
       to  0.   A shell variable need not have its integer attribute turned on
       to be used in an expression.

       Constants with a leading 0 are interpreted as octal numbers.  A leading
       0x  or  0X  denotes  hexadecimal.   Otherwise,  numbers  take  the form
       [base#]n, where the optional base is a decimal number between 2 and  64
       representing  the  arithmetic base, and _n is a number in that base.  If
       base# is omitted, then base 10 is used.  When specifying _n, the  digits
       greater  than 9 are represented by the lowercase letters, the uppercase
       letters, @, and _, in that order.  If base is less than or equal to 36,
       lowercase  and  uppercase letters may be used interchangeably to repre-
       sent numbers between 10 and 35.

       Operators are evaluated in order  of  precedence.   Sub-expressions  in
       parentheses  are  evaluated first and may override the precedence rules
       above.

CONDITIONAL EXPRESSIONS
       Conditional expressions are used by the [[[[  compound  command  and  the
       test  and [[ builtin commands to test file attributes and perform string
       and arithmetic comparisons.  Expressions are formed from the  following
       unary  or  binary  primaries.   If any file argument to one of the pri-
       maries is of the form /dev/fd/n, then file descriptor _n is checked.  If
       the  file  argument  to  one  of  the  primaries  is one of /dev/stdin,
       /dev/stdout, or /dev/stderr, file descriptor 0, 1, or 2,  respectively,
       is checked.

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

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

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

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

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

       string1 << string2
              True if string1 sorts before string2 lexicographically.

       string1 >> string2
              True if string1 sorts after string2 lexicographically.

       arg1 OP arg2
              OP  is one of -eq, -ne, -lt, -le, -gt, or -ge.  These arithmetic
              binary operators return true if arg1 is equal to, not equal  to,
              less  than, less than or equal to, greater than, or greater than
              or equal to arg2, respectively.  Arg1 and arg2 may  be  positive
              or negative integers.

SIMPLE COMMAND EXPANSION
       When  a  simple  command  is executed, the shell performs the following
       expansions, assignments, and redirections, from left to right.

       1.     The words that the parser has  marked  as  variable  assignments
              (those  preceding  the  command name) and redirections are saved
              for later processing.

       2.     The words that are not variable assignments or redirections  are
              expanded.   If  any words remain after expansion, the first word
              is taken to be the name of the command and the  remaining  words
              are the arguments.

       3.     Redirections are performed as described above under REDIRECTION.

       4.     The text after the == in each variable assignment undergoes tilde
              expansion, parameter expansion, command substitution, arithmetic
              expansion,  and quote removal before being assigned to the vari-
              able.

       If no command name results, the variable assignments affect the current
       shell  environment.  Otherwise, the variables are added to the environ-
       ment of the executed command and do not affect the current shell  envi-
       ronment.   If  any  of  the assignments attempts to assign a value to a
       readonly variable, an error occurs, and the command exits with  a  non-
       zero status.

       If  no  command  name  results,  redirections are performed, but do not
       affect the current shell environment.  A redirection error  causes  the
       command to exit with a non-zero status.

       If  there is a command name left after expansion, execution proceeds as
       described below.  Otherwise, the command exits.  If one of  the  expan-
       sions  contained a command substitution, the exit status of the command
       is the exit status of the  last  command  substitution  performed.   If
       there were no command substitutions, the command exits with a status of
       zero.

COMMAND EXECUTION
       After a command has been split into words, if it results  in  a  simple
       command  and  an  optional list of arguments, the following actions are
       taken.

       If the command name contains no slashes, the shell attempts  to  locate
       it.   If  there  exists a shell function by that name, that function is
       invoked as described above in FUNCTIONS.  If the name does not match  a
       function,  the shell searches for it in the list of shell builtins.  If
       a match is found, that builtin is invoked.

       If the name is neither a shell function nor a builtin, and contains  no
       slashes,  bash  searches  each element of the PATH for a directory con-
       taining an executable file by that name.  Bash uses  a  hash  table  to
       remember  the  full pathnames of executable files (see hash under SHELL
       BUILTIN COMMANDS below).  A full search of the directories in  PATH  is
       performed  only  if the command is not found in the hash table.  If the
       search is unsuccessful, the shell searches for a defined shell function
       named command_not_found_handle.  If that function exists, it is invoked
       with the original command and the original command's arguments  as  its
       arguments,  and  the  function's exit status becomes the exit status of
       the shell.  If that function is not defined, the shell prints an  error
       message and returns an exit status of 127.

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

       If this execution fails because the file is not in  executable  format,
       and  the file is not a directory, it is assumed to be a shell script, a
       file containing shell commands.  A subshell is spawned to  execute  it.
       This  subshell  reinitializes itself, so that the effect is as if a new
       shell had been invoked to handle the script, with  the  exception  that
       the  locations  of  commands  remembered  by the parent (see hash below
       under SHELL BUILTIN COMMANDS) are retained by the child.

       If the program is a file beginning with ##!!, the remainder of the  first
       line  specifies an interpreter for the program.  The shell executes the
       specified interpreter on operating systems that do not handle this exe-
       cutable format themselves.  The arguments to the interpreter consist of
       a single optional argument following the interpreter name on the  first
       line  of  the program, followed by the name of the program, followed by
       the command arguments, if any.

COMMAND EXECUTION ENVIRONMENT
       The shell has an execution environment, which consists of  the  follow-
       ing:

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

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

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

       +o      current traps set by trap

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

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

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

       +o      options enabled by shopt

       +o      shell aliases defined with alias

       +o      various  process  IDs,  including  those of background jobs, the
              value of $$$$, and the value of PPID

       When a simple command other than a builtin or shell function is  to  be
       executed,  it  is invoked in a separate execution environment that con-
       sists of the following.  Unless otherwise noted, the values are  inher-
       ited from the shell.


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

       +o      the current working directory

       +o      the file creation mode mask

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

       +o      traps caught by the shell are reset to the values inherited from
              the shell's parent, and traps ignored by the shell are ignored

       A command invoked  in  this  separate  environment  cannot  affect  the
       shell's execution environment.

       Command  substitution, commands grouped with parentheses, and asynchro-
       nous commands are invoked in a subshell environment that is a duplicate
       of  the  shell  environment,  except that traps caught by the shell are
       reset to the values that the shell inherited from its parent at invoca-
       tion.  Builtin commands that are invoked as part of a pipeline are also
       executed in a subshell environment.  Changes made to the subshell envi-
       ronment cannot affect the shell's execution environment.

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

       If  a  command  is  followed  by a && and job control is not active, the
       default standard input for the command is  the  empty  file  /dev/null.
       Otherwise,  the  invoked  command  inherits the file descriptors of the
       calling shell as modified by redirections.

ENVIRONMENT
       When a program is invoked it is given an array of  strings  called  the
       environment.   This  is  a  list  of  name-value  pairs,  of  the  form
       name=value.

       The shell provides several ways  to  manipulate  the  environment.   On
       invocation, the shell scans its own environment and creates a parameter
       for each name found, automatically marking it for export to child  pro-
       cesses.   Executed  commands  inherit  the environment.  The export and
       declare -x commands allow parameters and functions to be added  to  and
       deleted from the environment.  If the value of a parameter in the envi-
       ronment is modified, the new value becomes  part  of  the  environment,
       replacing  the  old.  The environment inherited by any executed command
       consists of the shell's initial environment, whose values may be  modi-
       fied  in  the  shell, less any pairs removed by the unset command, plus
       any additions via the export and declare -x commands.

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

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

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

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

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

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

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

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

       Bash  itself  returns  the  exit  status  of the last command executed,
       unless a syntax error occurs, in which case it exits  with  a  non-zero
       value.  See also the exit builtin command below.

SIGNALS
       When  bash  is  interactive,  in  the  absence of any traps, it ignores
       SIGTERM (so that kill 00 does not kill an interactive shell), and SIGINT
       is  caught and handled (so that the wait builtin is interruptible).  In
       all cases, bash ignores SIGQUIT.  If job control  is  in  effect,  bash
       ignores SIGTTIN, SIGTTOU, and SIGTSTP.

       Non-builtin commands run by bash have signal handlers set to the values
       inherited by the shell from its parent.  When job  control  is  not  in
       effect,  asynchronous commands ignore SIGINT and SIGQUIT in addition to
       these inherited handlers.  Commands run as a result of command  substi-
       tution ignore the keyboard-generated job control signals SIGTTIN, SIGT-
       TOU, and SIGTSTP.

       The shell exits by default upon receipt of a SIGHUP.   Before  exiting,
       an  interactive  shell  resends  the  SIGHUP  to  all  jobs, running or
       stopped.  Stopped jobs are sent SIGCONT to ensure that they receive the
       SIGHUP.   To  prevent the shell from sending the signal to a particular
       job, it should be removed from the jobs table with the  disown  builtin
       (see  SHELL  BUILTIN  COMMANDS  below)  or marked to not receive SIGHUP
       using disown -h.

       If the huponexit shell option has been set with  shopt,  bash  sends  a
       SIGHUP to all jobs when an interactive login shell exits.

       If  bash is waiting for a command to complete and receives a signal for
       which a trap has been set, the trap will not be executed until the com-
       mand  completes.   When bash is waiting for an asynchronous command via
       the wait builtin, the reception of a signal for which a trap  has  been
       set will cause the wait builtin to return immediately with an exit sta-
       tus greater than 128, immediately after which the trap is executed.

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

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

              [1] 25647

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

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

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

       There are a number of ways to refer to a job in the shell.  The charac-
       ter  %%  introduces  a job specification (jobspec).  Job number _n may be
       referred to as %%nn.  A job may also be referred to using a prefix of the
       name used to start it, or using a substring that appears in its command
       line.  For example, %ce refers to  a  stopped  ce  job.   If  a  prefix
       matches  more  than one job, bash reports an error.  Using %?ce, on the
       other hand, refers to any job containing the string ce in  its  command
       line.   If  the  substring  matches  more than one job, bash reports an
       error.  The symbols %%%% and %%++ refer to the shell's notion of  the  cur-
       rent  job, which is the last job stopped while it was in the foreground
       or started in the background.  The previous job may be referenced using
       %%--.  If there is only a single job, %%++ and %%-- can both be used to refer
       to that job.  In output pertaining to jobs (e.g.,  the  output  of  the
       jobs command), the current job is always flagged with a ++, and the pre-
       vious job with a --.  A single % (with no  accompanying  job  specifica-
       tion) also refers to the current job.

       Simply  naming a job can be used to bring it into the foreground: %%11 is
       a synonym for ``fg %%11'''', bringing job 1 from the  background  into  the
       foreground.   Similarly,  ````%%11  &&''''  resumes  job  1 in the background,
       equivalent to ``bg %%11''''.

       The shell learns immediately whenever a job changes  state.   Normally,
       bash waits until it is about to print a prompt before reporting changes
       in a job's status so as to not interrupt any other output.  If  the  -b
       option to the set builtin command is enabled, bash reports such changes
       immediately.  Any trap on SIGCHLD  is  executed  for  each  child  that
       exits.

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

PROMPTING
       When executing interactively, bash displays the primary prompt PS1 when
       it is ready to read a command, and the secondary  prompt  PS2  when  it
       needs  more  input  to  complete  a  command.  Bash allows these prompt
       strings to be customized by inserting  a  number  of  backslash-escaped
       special characters that are decoded as follows:
              \a     an ASCII bell character (07)
              \d     the  date  in "Weekday Month Date" format (e.g., "Tue May
                     26")
              \D{format}}
                     the format is passed to strftime(3)  and  the  result  is
                     inserted  into the prompt string; an empty format results
                     in a locale-specific time representation.  The braces are
                     required
              \e     an ASCII escape character (033)
              \h     the hostname up to the first `.'
              \H     the hostname
              \j     the number of jobs currently managed by the shell
              \l     the basename of the shell's terminal device name
              \n     newline
              \r     carriage return
              \s     the  name  of  the shell, the basename of $$00 (the portion
                     following the final slash)
              \t     the current time in 24-hour HH:MM:SS format
              \T     the current time in 12-hour HH:MM:SS format
              \\@@     the current time in 12-hour am/pm format
              \A     the current time in 24-hour HH:MM format
              \u     the username of the current user
              \v     the version of bash (e.g., 2.00)
              \V     the release of bash, version + patch level (e.g., 2.00.0)
              \w     the current working  directory,  with  $HOME  abbreviated
                     with  a tilde (uses the value of the PROMPT_DIRTRIM vari-
                     able)
              \W     the basename of the current working directory, with $HOME
                     abbreviated with a tilde
              \\!!     the history number of this command
              \\##     the command number of this command
              \\$$     if the effective UID is 0, a ##, otherwise a $$
              \\nnn   the character corresponding to the octal number nnn
              \\\\     a backslash
              \\[[     begin  a sequence of non-printing characters, which could
                     be used to embed a terminal  control  sequence  into  the
                     prompt
              \\]]     end a sequence of non-printing characters

       The  command  number  and the history number are usually different: the
       history number of a command is its position in the history list,  which
       may  include  commands  restored  from  the  history  file (see HISTORY
       below), while the command number is the position  in  the  sequence  of
       commands  executed  during the current shell session.  After the string
       is decoded, it is expanded via parameter expansion,  command  substitu-
       tion,  arithmetic expansion, and quote removal, subject to the value of
       the promptvars shell option (see the description of the  shopt  command
       under SHELL BUILTIN COMMANDS below).

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

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

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

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

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

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

       For example, placing

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

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

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

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

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

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

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

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

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

       In this example, C-u is again bound to the function universal-argument.
       C-x  C-r is bound to the function re-read-init-file, and ESC _[ _1 _1 _~ is
       bound to insert the text ``Function Key 1''.

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

       In addition to the GNU Emacs style escape sequences, a  second  set  of
       backslash escapes is available:
              \a     alert (bell)
              \b     backspace
              \d     delete
              \f     form feed
              \n     newline
              \r     carriage return
              \t     horizontal tab
              \v     vertical tab
              \\nnn   the  eight-bit  character  whose value is the octal value
                     nnn (one to three digits)
              \\xx_H_H   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.
       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-ignore-case (Off)
              If set to On, readline performs filename matching and completion
              in a case-insensitive fashion.
       completion-prefix-display-length ((00))
              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 ((110000))
              This determines when the user is queried about viewing the  num-
              ber  of  possible  completions generated by the possible-comple-
              tions command.  It may be set to any integer value greater  than
              or  equal  to  zero.   If  the number of possible completions is
              greater than or equal to the value of this variable, the user is
              asked  whether or not he wishes to view them; otherwise they are
              simply listed on the terminal.
       convert-meta (On)
              If set to On, readline will convert characters with  the  eighth
              bit set to an ASCII key sequence by stripping the eighth bit and
              prefixing an escape character (in effect, using  escape  as  the
              meta prefix).
       disable-completion (Off)
              If set to On, readline will inhibit word completion.  Completion
              characters will be inserted into the line as if  they  had  been
              mapped to self-insert.
       editing-mode (emacs)
              Controls whether readline begins with a set of key bindings sim-
              ilar to Emacs or vi.  editing-mode can be set to either emacs or
              vi.
       echo-control-characters (On)
              When  set to On, on operating systems that indicate they support
              it, readline echoes a character corresponding to a signal gener-
              ated from the keyboard.
       enable-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
              arrow keys.
       enable-meta-key (On)
              When set to On, readline will try to enable  any  meta  modifier
              key  the  terminal claims to support when it is called.  On many
              terminals, the meta key is used to send eight-bit characters.
       expand-tilde (Off)
              If set  to  On,  tilde  expansion  is  performed  when  readline
              attempts word completion.
       history-preserve-point (Off)
              If  set  to  On, the history code attempts to place point at the
              same location on each history line retrieved with  previous-his-
              tory or next-history.
       history-size (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 not limited.
       horizontal-scroll-mode (Off)
              When  set  to  On, makes readline use a single line for display,
              scrolling the input horizontally on a single screen line when it
              becomes  longer  than the screen width rather than wrapping to a
              new line.
       input-meta (Off)
              If set to On, readline will enable eight-bit input (that is,  it
              will  not  strip  the  high  bit  from the characters it reads),
              regardless of what the terminal claims it can support.  The name
              meta-flag is a synonym for this variable.
       isearch-terminators (``C-[C-J'')
              The  string  of  characters that should terminate an incremental
              search without subsequently executing the character  as  a  com-
              mand.   If this variable has not been given a value, the charac-
              ters ESC and C-J will terminate an incremental search.
       keymap (emacs)
              Set the current readline keymap.  The set of valid keymap  names
              is  emacs,  emacs-standard,  emacs-meta, emacs-ctlx, vi, vi-com-
              mand, and vi-insert.  vi is equivalent to vi-command;  emacs  is
              equivalent  to  emacs-standard.  The default value is emacs; the
              value of editing-mode also affects the default keymap.
       emacs-mode-string ((@@))
              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 con-
              trol sequence into the mode string.
       keyseq-timeout ((550000))
              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
              received 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-directories).
       match-hidden-files (On)
              This  variable,  when  set to On, causes readline to match files
              whose names begin with a  `.'  (hidden  files)  when  performing
              filename  completion.   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.
       page-completions (On)
              If  set to On, readline uses an internal more-like pager to dis-
              play a screenful of possible completions at a time.
       print-completions-horizontally (Off)
              If set to On, readline will  display  completions  with  matches
              sorted  horizontally in alphabetical order, rather than down the
              screen.
       revert-all-at-newline (Off)
              If set to On, readline will undo all changes  to  history  lines
              before returning when accept-line is executed.  By default, his-
              tory lines may be modified  and  retain  individual  undo  lists
              across calls to readline.
       show-all-if-ambiguous (Off)
              This  alters  the  default behavior of the completion functions.
              If set to On, words which have more than one possible completion
              cause  the  matches  to be listed immediately instead of ringing
              the bell.
       show-all-if-unmodified (Off)
              This alters the default behavior of the completion functions  in
              a fashion similar to show-all-if-ambiguous.  If set to On, words
              which have more than one possible completion without any  possi-
              ble  partial  completion (the possible completions don't share a
              common prefix)  cause  the  matches  to  be  listed  immediately
              instead of ringing the bell.
       show-mode-in-prompt (Off)
              If  set  to  On,  add a character to the beginning of the prompt
              indicating the editing mode: emacs (@), vi  command  (:)  or  vi
              insertion (+).
       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))
              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 control sequence into the mode string.
       vi-ins-mode-string ((ins))
              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 control 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 extends to the end of the line;
              no characters are required to isolate it.

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

              term   The  term=  form may be used to include terminal-specific
                     key bindings, perhaps to bind the key sequences output by
                     the terminal's function keys.  The word on the right side
                     of the == is tested against 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.

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

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

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

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

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

              $include  /etc/inputrc

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

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

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

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

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

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

   Commands for Moving
       beginning-of-line (C-a)
              Move to the start of the current line.
       end-of-line (C-e)
              Move to the end of the line.
       forward-char (C-f)
              Move forward a character.
       backward-char (C-b)
              Move back a character.
       forward-word (M-f)
              Move forward to the end of the next word.  Words are composed of
              alphanumeric characters (letters and digits).
       backward-word (M-b)
              Move back to the start of the current or previous  word.   Words
              are composed of alphanumeric characters (letters and digits).
       shell-forward-word
              Move  forward  to the end of the next word.  Words are delimited
              by non-quoted shell metacharacters.
       shell-backward-word
              Move back to the start of the current or previous  word.   Words
              are delimited by non-quoted shell metacharacters.
       clear-screen (C-l)
              Clear  the  screen  leaving  the  current line at the top of the
              screen.  With an argument,  refresh  the  current  line  without
              clearing the screen.
       redraw-current-line
              Refresh the current line.

   Commands for Manipulating the History
       accept-line (Newline, Return)
              Accept the line regardless of where the cursor is.  If this line
              is non-empty, add it to the history list according to the  state
              of  the HISTCONTROL variable.  If the line is a modified history
              line, then restore the history line to its original state.
       previous-history (C-p)
              Fetch the previous command from the history list, moving back in
              the list.
       next-history (C-n)
              Fetch  the next command from the history list, moving forward in
              the list.
       beginning-of-history (M-<)
              Move to the first line in the history.
       end-of-history (M->)
              Move to the end of the input history, i.e., the  line  currently
              being entered.
       reverse-search-history (C-r)
              Search  backward  starting  at  the current line and moving `up'
              through the  history  as  necessary.   This  is  an  incremental
              search.
       forward-search-history (C-s)
              Search  forward  starting  at the current line and moving `down'
              through the  history  as  necessary.   This  is  an  incremental
              search.
       non-incremental-reverse-search-history (M-p)
              Search backward through the history starting at the current line
              using a non-incremental search for  a  string  supplied  by  the
              user.
       non-incremental-forward-search-history (M-n)
              Search  forward  through  the  history  using  a non-incremental
              search for a string supplied by the user.
       history-search-forward
              Search forward through the history for the string of  characters
              between  the start of the current line and the point.  This is a
              non-incremental search.
       history-search-backward
              Search backward through the history for the string of characters
              between  the start of the current line and the point.  This is a
              non-incremental search.
       yank-nth-arg (M-C-y)
              Insert the first argument to the previous command  (usually  the
              second word on the previous line) at point.  With an argument _n,
              insert the _nth word from the previous command (the words in  the
              previous  command  begin  with  word  0).   A  negative argument
              inserts the _nth word from the end of the previous command.  Once
              the  argument _n is computed, the argument is extracted as if the
              "!_n" history expansion had been specified.
       yank-last-arg (M-., M-_)
              Insert the last argument to the previous command (the last  word
              of the previous history entry).  With 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
              EXPANSION below for a description of history expansion.
       magic-space
              Perform  history  expansion  on  the  current  line and insert a
              space.  See HISTORY EXPANSION below for a description of history
              expansion.
       alias-expand-line
              Perform  alias expansion on the current line.  See ALIASES above
              for a description of alias expansion.
       history-and-alias-expand-line
              Perform history and alias expansion on the current line.
       insert-last-argument (M-., M-_)
              A synonym for yank-last-arg.
       operate-and-get-next (C-o)
              Accept the current line for execution and fetch  the  next  line
              relative  to the current line from the history for editing.  Any
              argument is ignored.
       edit-and-execute-command (C-xC-e)
              Invoke an editor on the current command line,  and  execute  the
              result  as  shell  commands.   Bash  attempts to invoke $VISUAL,
              $EDITOR, and emacs as the editor, in that order.

   Commands for Changing Text
       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, 11,, !!,, ......))
              Insert the character typed.
       transpose-chars (C-t)
              Drag  the  character  before point forward over the character at
              point, moving point forward as well.  If point is at the end  of
              the  line, then this transposes the two characters before point.
              Negative arguments have no effect.
       transpose-words (M-t)
              Drag the word before point past the  word  after  point,  moving
              point  over  that  word  as well.  If point is at the end of the
              line, this transposes the last two words on the line.
       upcase-word (M-u)
              Uppercase the current (or  following)  word.   With  a  negative
              argument, uppercase the previous word, but do not move point.
       downcase-word (M-l)
              Lowercase  the  current  (or  following)  word.  With a negative
              argument, lowercase the previous word, but do not move point.
       capitalize-word (M-c)
              Capitalize the current (or following)  word.   With  a  negative
              argument, capitalize the previous word, but do not move point.
       overwrite-mode
              Toggle  overwrite mode.  With an explicit positive numeric argu-
              ment, switches to overwrite mode.  With an explicit non-positive
              numeric argument, switches to insert mode.  This command affects
              only emacs mode; vi mode does overwrite differently.  Each  call
              to readline() starts in insert mode.  In overwrite mode, charac-
              ters bound to self-insert replace the text at point rather  than
              pushing  the  text  to  the  right.   Characters  bound to back-
              ward-delete-char replace  the  character  before  point  with  a
              space.  By default, this command is unbound.

   Killing and Yanking
       kill-line (C-k)
              Kill the text from point to the end of the line.
       backward-kill-line (C-x Rubout)
              Kill backward to the beginning of the line.
       unix-line-discard (C-u)
              Kill  backward  from  point  to  the beginning of the line.  The
              killed text is saved on the kill-ring.
       kill-whole-line
              Kill all characters on the current line, no matter  where  point
              is.
       kill-word (M-d)
              Kill  from  point  to the end of the current word, or if between
              words, to the end of the next word.   Word  boundaries  are  the
              same as those used by forward-word.
       backward-kill-word (M-Rubout)
              Kill  the  word  behind  point.  Word boundaries are the same as
              those used by backward-word.
       shell-kill-word
              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
              numeric argument, but is otherwise ignored.  As a special  case,
              if  this  command is immediately followed by a character that is
              neither 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
              argument  may  be  used to move backward through the list.  This
              command 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-uppercase-version (M-a, M-b, MM--_x,, ......))
              If  the  metafied character _x is lowercase, run the command that
              is bound to the corresponding uppercase character.
       prefix-meta (ESC)
              Metafy the next character typed.  ESC ff is equivalent to Meta-f.
       undo (C-_, C-x C-u)
              Incremental undo, separately remembered for each line.
       revert-line (M-r)
              Undo all changes made to this line.  This is like executing  the
              undo  command  enough  times  to  return the line to its initial
              state.
       tilde-expand (M-&)
              Perform tilde expansion on the current word.
       set-mark (C-@, M-<space>)
              Set the mark to the point.  If a numeric argument  is  supplied,
              the mark is set to that position.
       exchange-point-and-mark (C-x C-x)
              Swap  the  point  with the mark.  The current cursor position is
              set to the saved position, and the old cursor position is  saved
              as the mark.
       character-search (C-])
              A character is read and point is moved to the next occurrence of
              that character.  A negative count searches for  previous  occur-
              rences.
       character-search-backward (M-C-])
              A  character  is  read and point is moved to the previous occur-
              rence of that character.  A negative count searches  for  subse-
              quent occurrences.
       skip-csi-sequence
              Read  enough  characters to consume a multi-key sequence such as
              those defined for keys like Home and End.  Such sequences  begin
              with a Control Sequence Indicator (CSI), usually ESC-[.  If this
              sequence is bound to "\[", keys producing  such  sequences  will
              have  no  effect  unless explicitly bound to a readline command,
              instead of inserting stray characters into the  editing  buffer.
              This is unbound by default, but usually bound to ESC-[.
       insert-comment (M-#)
              Without  a  numeric  argument,  the  value  of the readline com-
              ment-begin variable is inserted at the beginning of the  current
              line.  If a numeric argument is supplied, this command acts as a
              toggle: if the characters at the beginning of the  line  do  not
              match  the value of comment-begin, the value is inserted, other-
              wise the characters in comment-begin are deleted from the begin-
              ning  of the line.  In either case, the line is accepted as if a
              newline had been typed.   The  default  value  of  comment-begin
              causes  this  command  to make the current line a shell comment.
              If a  numeric  argument  causes  the  comment  character  to  be
              removed, the line will be executed by the shell.
       glob-complete-word (M-g)
              The  word  before  point  is  treated  as a pattern for pathname
              expansion, with an asterisk implicitly appended.   This  pattern
              is  used  to  generate a list of matching filenames for possible
              completions.
       glob-expand-word (C-x **))
              The word before point is  treated  as  a  pattern  for  pathname
              expansion,  and  the  list  of  matching  filenames is inserted,
              replacing the word.  If  a  numeric  argument  is  supplied,  an
              asterisk is appended before pathname expansion.
       glob-list-expansions (C-x g)
              The  list  of  expansions  that  would  have  been  generated by
              glob-expand-word is displayed, and the line is  redrawn.   If  a
              numeric  argument  is  supplied,  an asterisk is appended before
              pathname expansion.
       dump-functions
              Print all of the functions and their key bindings to  the  read-
              line output stream.  If a numeric argument is supplied, the out-
              put is formatted in such a way that it can be made  part  of  an
              inputrc file.
       dump-variables
              Print all of the settable readline variables and their values to
              the readline output stream.  If a numeric argument is  supplied,
              the  output  is formatted in such a way that it can be made part
              of an inputrc file.
       dump-macros
              Print all of the readline key sequences bound to macros and  the
              strings  they  output.   If  a numeric argument is supplied, the
              output is formatted in such a way that it can be made part of an
              inputrc file.
       display-shell-version (C-x C-v)
              Display version information about the current instance of bash.

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

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

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

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

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

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

       After  these matches have been generated, any shell function or command
       specified with the -F and -C options is invoked.  When the  command  or
       function is invoked, the COMP_LINE, COMP_POINT, COMP_KEY, and COMP_TYPE
       variables are assigned values as described above under Shell Variables.
       If  a  shell  function  is being invoked, the COMP_WORDS and COMP_CWORD
       variables are also set.  When the function or command is  invoked,  the
       first  argument  ($$11)  is  the  name of the command whose arguments are
       being completed, the second argument ($$22) is the word being  completed,
       and  the  third argument ($$33) 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
       defined, directory name completion is attempted.

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

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

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

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

       _completion_loader()
       {
            . "/etc/bash_completion.d/$1.sh" >/dev/null 2>&1 && return 124
       }
       complete -D -F _completion_loader -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 pre-
       ceding 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
       unwritable,  the  history is not saved.  If the HISTTIMEFORMAT variable
       is set, time stamps are written to the history file,  marked  with  the
       history  comment  character, so they may be preserved across shell ses-
       sions.  This uses the history comment character  to  distinguish  time-
       stamps from other history lines.  After saving the history, the history
       file is truncated to contain no more than HISTFILESIZE lines.  If HIST-
       FILESIZE  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
       manipulate  the  history file.  When using command-line editing, search
       commands are available in each editing mode that provide access to  the
       history list.

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

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

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

       History expansion is performed immediately after  a  complete  line  is
       read,  before  the  shell  breaks it into words.  It takes place in two
       parts.  The first is to determine which line from the history  list  to
       use during substitution.  The second is to select portions of that line
       for inclusion into the current one.  The line selected from the history
       is  the  event,  and  the portions of that line that are acted upon are
       words.  Various modifiers are  available  to  manipulate  the  selected
       words.  The line is broken into words in the same fashion as when read-
       ing input, so that several metacharacter-separated words surrounded  by
       quotes  are  considered one word.  History expansions are introduced by
       the appearance of the  history  expansion  character,  which  is  !!  by
       default.   Only  backslash  (\\) and single quotes can quote the history
       expansion character,  but  the  history  expansion  character  is  also
       treated  as  quoted if it immediately precedes the closing double quote
       in a double-quoted string.

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

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

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

   Event Designators
       An event designator is a reference to a command line entry in the  his-
       tory  list.   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.

       00 (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
              expand 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 xx**, 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 `:'.

       hh      Remove a trailing filename component, leaving only the head.
       tt      Remove all leading filename components, leaving the tail.
       rr      Remove a trailing suffix of the form .xxx, leaving the basename.
       ee      Remove all but the trailing suffix.
       pp      Print the new command but do not execute it.
       qq      Quote the substituted words, escaping further substitutions.
       xx      Quote  the  substituted words as with qq, but break into words at
              blanks and newlines.
       ss//old//new//
              Substitute new for the first occurrence  of  old  in  the  event
              line.   Any  delimiter  can  be  used  in place of /.  The final
              delimiter is optional if it is the last character of  the  event
              line.   The delimiter may be quoted in old and new with a single
              backslash.  If & appears in new, it is replaced by old.  A  sin-
              gle  backslash  will  quote the &.  If old is null, it is set to
              the last old substituted, or, if no previous  history  substitu-
              tions took place, the last string in a !!??string[[??]]  search.
       &&      Repeat the previous substitution.
       gg      Cause changes to be applied over the entire event line.  This is
              used in conjunction with `::ss' (e.g.,  `:gs/old//new//')  or  `::&&'.
              If  used with `::ss', 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 aa may be used as a synonym for gg.
       GG      Apply  the following `ss' 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
              environment  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
              positional 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
              returns  true unless a name is given for which no alias has been
              defined.

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

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

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

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

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

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

       cd [-L|[-P [-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
              directory  names in CDPATH are separated by a colon (:).  A null
              directory name in CDPATH is the same as the  current  directory,
              i.e., ``..''.  If dir begins with a slash (/), then CDPATH is not
              used.  The -P option 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
              option 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
              facilities, while available, will not have useful values.

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

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

       complete  [-abcdefgjksuv]  [-o comp-option] [-DE] [-A action] [-G glob-
       pat] [-W wordlist] [-F function] [-C command]
              [-X filterpat] [-P prefix] [-S suffix] name [name _._._.]
       complete -pr [-DE] [name ...]
              Specify how arguments to each name should be completed.  If  the
              -p  option  is supplied, or if no options are supplied, existing
              completion specifications are printed in a way that allows  them
              to be reused as input.  The -r option removes a completion spec-
              ification for each name, or, if no names are supplied, all  com-
              pletion  specifications.   The  -D  option  indicates  that  the
              remaining options and actions should apply  to  the  ``default''
              command  completion;  that is, completion attempted on a command
              for which no completion has previously  been  defined.   The  -E
              option  indicates  that the remaining options and actions should
              apply to  ``empty''  command  completion;  that  is,  completion
              attempted on a blank line.

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

              Other  options,  if specified, have the following meanings.  The
              arguments to the -G, -W, and -X options (and, if necessary,  the
              -P  and -S options) should be quoted to protect them from expan-
              sion before the complete builtin is invoked.
              -o comp-option
                      The comp-option controls several aspects  of  the  comp-
                      spec's  behavior beyond the simple generation of comple-
                      tions.  comp-option may be one of:
                      bashdefault
                              Perform the rest of the default bash completions
                              if the compspec generates no matches.
                      default Use  readline's  default  filename completion if
                              the compspec generates no matches.
                      dirnames
                              Perform directory name completion if  the  comp-
                              spec generates no matches.
                      filenames
                              Tell  readline that the compspec generates file-
                              names, so it can perform  any  filename-specific
                              processing  (like  adding  a  slash to directory
                              names, quoting special characters, or  suppress-
                              ing  trailing spaces).  Intended to be used with
                              shell functions.
                      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
                              default) to words completed at the  end  of  the
                              line.
                      plusdirs
                              After  any  matches  defined by the compspec are
                              generated,   directory   name   completion    is
                              attempted  and  any  matches  are  added  to the
                              results of the other actions.
              -A action
                      The action may be one of the  following  to  generate  a
                      list of possible completions:
                      alias   Alias names.  May also be specified as -a.
                      arrayvar
                              Array variable names.
                      binding Readline key binding names.
                      builtin Names  of  shell  builtin commands.  May also be
                              specified as -b.
                      command Command names.  May also be specified as -c.
                      directory
                              Directory names.  May also be specified as -d.
                      disabled
                              Names of disabled shell builtins.
                      enabled Names of enabled shell builtins.
                      export  Names of exported shell variables.  May also  be
                              specified as -e.
                      file    File names.  May also be specified as -f.
                      function
                              Names of shell functions.
                      group   Group names.  May also be specified as -g.
                      helptopic
                              Help topics as accepted by the help builtin.
                      hostname
                              Hostnames,  as  taken from the file specified by
                              the HOSTFILE shell variable.
                      job     Job names, if job control is active.   May  also
                              be specified as -j.
                      keyword Shell  reserved words.  May also be specified as
                              -k.
                      running Names of running jobs, if job control is active.
                      service Service names.  May also be specified as -s.
                      setopt  Valid arguments for the -o  option  to  the  set
                              builtin.
                      shopt   Shell  option  names  as  accepted  by the shopt
                              builtin.
                      signal  Signal names.
                      stopped Names of stopped jobs, if job control is active.
                      user    User names.  May also be specified as -u.
                      variable
                              Names of all shell variables.  May also be spec-
                              ified as -v.
              -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 ($$11) is the name  of  the  command  whose
                      arguments  are being completed, the second argument ($$22)
                      is the word being completed, and the third argument ($$33)
                      is  the  word  preceding the word being completed on the
                      current command line.  When it  finishes,  the  possible
                      completions  are retrieved from the value of the COMPRE-
                      PLY 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.   The possible completions are the members
                      of the resultant list which match the  word  being  com-
                      pleted.
              -X filterpat
                      filterpat  is  a pattern as used for pathname expansion.
                      It is applied to the list of possible completions gener-
                      ated  by  the  preceding options and arguments, and each
                      completion matching filterpat is removed from the  list.
                      A  leading  !!  in filterpat negates the pattern; in this
                      case, any completion not matching filterpat is removed.

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

       compopt [-o option] [-DE] [++oo option] [name]
              Modify  completion  options  for  each  name  according  to  the
              options,  or  for the currently-executing completion if no names
              are supplied.  If no options are given, display  the  completion
              options  for  each name or the current completion.  The possible
              values of option  are  those  valid  for  the  complete  builtin
              described  above.   The  -D  option indicates that the remaining
              options should apply to the ``default'' command completion; that
              is,  completion  attempted  on a command for which no completion
              has previously been defined.  The -E option indicates  that  the
              remaining  options should apply to ``empty'' command completion;
              that is, completion attempted on a blank line.

              The return value is true unless an invalid option  is  supplied,
              an attempt is made to modify the options for a name for which no
              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
              enclosing  loops,  the  last  enclosing  loop (the ``top-level''
              loop) is resumed.  The return value is 0 unless _n is not greater
              than or equal to 1.

       declare [-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
              attributes  and  values  of  all shell variables.  The -f option
              will restrict the display to shell  functions.   The  -F  option
              inhibits  the display of function definitions; only the function
              name and attributes are printed.  If the extdebug  shell  option
              is  enabled  using  shopt,  the source file name and line number
              where each name is defined are displayed as well.  The -F option
              implies  -f.   The  -g  option forces variables to be created or
              modified at the global scope, even when declare is executed in a
              shell  function.  It is ignored in all other cases.  The follow-
              ing 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  for
                     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
                     inherit  the  DEBUG  and  RETURN  traps  from the calling
                     shell.  The trace attribute has no  special  meaning  for
                     variables.
              -u     When  the  variable  is  assigned a value, all lower-case
                     characters are converted to upper-case.   The  lower-case
                     attribute is disabled.
              -x     Mark  names  for  export  to  subsequent commands via the
                     environment.

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

       dirs [-clpv] [[++_n]] [[--_n]]
              Without  options,  displays  the  list  of  currently remembered
              directories.  The default display  is  on  a  single  line  with
              directory  names  separated by spaces.  Directories are added to
              the list with  the  pushd  command;  the  popd  command  removes
              entries  from  the  list.   The  current directory is always the
              first directory in the stack.
              -c     Clears  the  directory  stack  by  deleting  all  of  the
                     entries.
              -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 ...]
              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
              receives  a  SIGHUP.   If  no jobspec is supplied, the -a option
              means to remove or mark all jobs; the -r option without  a  job-
              spec  argument  restricts operation to running jobs.  The return
              value is 0 unless a jobspec does not specify a valid job.

       echo [-neE] [arg ...]
              Output the args, separated by spaces,  followed  by  a  newline.
              The  return  status  is 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
              escape characters by default.  echo does  not  interpret  ----  to
              mean  the  end of options.  echo interprets the following escape
              sequences:
              \a     alert (bell)
              \b     backspace
              \c     suppress further output
              \e
              \E     an escape character
              \f     form feed
              \n     new line
              \r     carriage return
              \t     horizontal tab
              \v     vertical tab
              \\\\     backslash
              \\00nnn  the eight-bit character whose value is  the  octal  value
                     nnn (zero to three octal digits)
              \\xx_H_H   the  eight-bit  character  whose value is the hexadecimal
                     value HH (one or two hex digits)
              \\uuHHHH the Unicode (ISO/IEC 10646) character whose value is  the
                     hexadecimal value HHHH (one to four hex digits)
              \\UUHHHHHHHH
                     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
              enabled.  For example, to use the test binary found via the PATH
              instead of the shell builtin version, run  ``enable  -n  test''.
              The  -f  option  means to load the new builtin command name from
              shared object filename, on systems that support dynamic loading.
              The  -d  option will delete a builtin previously loaded with -f.
              If no name arguments are given, or if the -p option is supplied,
              a list of shell builtins is printed.  With no other option argu-
              ments, the list consists of all enabled shell builtins.   If  -n
              is  supplied, only disabled builtins are printed.  If -a is sup-
              plied, the list printed includes all builtins, with  an  indica-
              tion  of whether or not each is enabled.  If -s is supplied, the
              output is restricted to the POSIX special builtins.  The  return
              value  is  0 unless a name is not a shell builtin or there is an
              error loading a new builtin from a shared object.

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

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

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

       export [-fn] [name[=word]] ...
       export -p
              The  supplied names are marked for automatic export to the envi-
              ronment of subsequently executed commands.  If the -f option  is
              given,  the names refer to functions.  If no names are given, or
              if the -p option is supplied, a list of 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 intepreted the same as
              first above.  A useful alias to use with this is ``r="fc  -s"'',
              so  that  typing  ``r  c' runs the last command beginning with
              `c' and typing ``r'' re-executes the last command.

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

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

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

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

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

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

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

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

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

       hash [-lr] [-p filename] [-dt] [name]
              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
              option causes the shell to forget  the  remembered  location  of
              each  name.   If the -t option is supplied, the full pathname to
              which each name corresponds is printed.  If multiple name  argu-
              ments  are  supplied  with  -t,  the  name is printed before the
              hashed full pathname.  The -l option causes output  to  be  dis-
              played in a format that may be reused as input.  If no arguments
              are given, or if only -l is supplied, information  about  remem-
              bered  commands  is printed.  The return status is true unless a
              name is not found or an invalid option is supplied.

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

              The return status is 0 unless no command matches pattern.

       history [[_n]]
       history -c
       history -d offset
       history -anrw [filename]
       history -p arg [arg _._._.]
       history -s arg [arg _._._.]
              With no options, display the command history list with line num-
              bers.  Lines listed with a ** have been modified.  An argument of
              _n lists only the last _n lines.  If the shell variable  HISTTIME-
              FORMAT  is  set  and not null, it is used as a format string for
              strftime(3) to display the time stamp associated with each  dis-
              played  history  entry.  No intervening blank is printed between
              the formatted time stamp and the history line.  If  filename  is
              supplied,  it  is  used as the name of the history file; if not,
              the value of HISTFILE is used.  Options, if supplied,  have  the
              following meanings:
              -c     Clear the history list by deleting all the entries.
              -d offset
                     Delete the history entry at position offset.
              -a     Append  the  ``new''  history  lines 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
                     appended 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 previous history line.  The return value is 0
              unless an invalid option is encountered, an error  occurs  while
              reading  or  writing the history file, an invalid offset is sup-
              plied as an argument to -d, or the history expansion supplied as
              an argument to -p fails.

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

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

       local [option] [name[=value] ... | - ]
              For each argument, a local variable named name is  created,  and
              assigned  value.   The option can be any of the options accepted
              by declare.  When local is used within a function, it causes the
              variable  name  to have a visible scope restricted to that func-
              tion and its children.  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.
              -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
              array before assigning to it.

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

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

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

       printf [-v var] format [arguments]
              Write  the  formatted arguments to the standard output under the
              control of the format.  The -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 (except that \c terminates output,
                     backslashes in \\'', \\"", and \\?? are not removed, and  octal
                     escapes beginning with \\00 may contain up to four digits).
              %q     causes  printf  to output the corresponding argument in a
                     format that can be reused as shell input.
              %%((datefmt))TT
                     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
                     argument is specified, conversion behaves as  if  -1  had
                     been  given.   This  is  an exception to the usual printf
                     behavior.

              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
              directories and returns 0, unless the directory stack is  empty.
              Arguments, if supplied, have the following meanings:
              -n     Suppresses  the  normal change of directory when 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
              invalid option is supplied.

       read [-ers] [-a aname] [-d delim] [-i text] [-n nchars] [-N nchars] [-p
       prompt] [-t timeout] [-u fd] [name ...]
              One  line  is  read  from  the  standard input, or from the file
              descriptor fd supplied as an argument to the -u option, and  the
              first word is assigned to the first name, the second word to the
              second name, and so on, with leftover words and their  interven-
              ing  separators  assigned  to the last name.  If there are fewer
              words read from the input stream than names, the remaining names
              are  assigned  empty  values.  The characters in IFS are used to
              split the line into words using the same rules  the  shell  uses
              for expansion (described above under Word Splitting).  The back-
              slash character (\\) may be used to remove  any  special  meaning
              for the next character 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
                     ignored.
              -d delim
                     The  first  character  of  delim is used to terminate the
                     input line, rather than newline.
              -e     If the standard input is coming from a terminal, readline
                     (see  READLINE  above) is used to obtain the line.  Read-
                     line uses the current (or default, if  line  editing  was
                     not previously active) editing settings.
              -i text
                     If  readline  is  being  used  to  read the line, text is
                     placed into the editing buffer before editing begins.
              -n nchars
                     read returns after reading nchars characters rather  than
                     waiting for a complete line of input, but 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 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
                     returns immediately, without trying  to  read  any  data.
                     The  exit status is 0 if input is available on the speci-
                     fied file descriptor, non-zero otherwise.  The exit  sta-
                     tus 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
              encountered, 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
              arrays; the -A option restricts  the  variables  to  associative
              arrays.   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
              return  is  executed by a trap handler, the last command used to
              determine the status is the last  command  executed  before  the
              trap  handler.   if  return is executed during a DEBUG trap, the
              last command used to determine the status is  the  last  command
              executed  by  the  trap  handler  before return was invoked.  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
              significant  8 bits.  The return status is non-zero if return is
              supplied a non-numeric argument, or is used outside  a  function
              and  not  during execution of a script by .. or source.  Any com-
              mand associated with the RETURN trap is executed  before  execu-
              tion resumes after the function or script.

       set [--abefhkmnptuvxBCEHPT] [-o option-name] [arg ...]
       set [+abefhkmnptuvxBCEHPT] [++oo 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
              options are specified, they set or unset shell attributes.   Any
              arguments  remaining after option processing are treated as val-
              ues for the positional parameters and are assigned, in order, to
              $$11,  $$22,  ......   $$_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
                      ignored by interactive shells.
              -o option-name
                      The option-name can be one of the following:
                      allexport
                              Same as -a.
                      braceexpand
                              Same as -B.
                      emacs   Use  an  emacs-style command line editing inter-
                              face.  This is enabled by default when the shell
                              is interactive, unless the shell is started with
                              the --noediting option.  This also  affects  the
                              editing interface used for read -e.
                      errexit Same as -e.
                      errtrace
                              Same as -E.
                      functrace
                              Same as -T.
                      hashall Same as -h.
                      histexpand
                              Same as -H.
                      history Enable command history, as described above under
                              HISTORY.  This option is on by default in inter-
                              active shells.
                      ignoreeof
                              The   effect   is   as   if  the  shell  command
                              ``IGNOREEOF=10'' had been  executed  (see  Shell
                              Variables above).
                      keyword Same as -k.
                      monitor Same as -m.
                      noclobber
                              Same as -C.
                      noexec  Same as -n.
                      noglob  Same as -f.
                      nolog   Currently ignored.
                      notify  Same as -b.
                      nounset Same as -u.
                      onecmd  Same as -t.
                      physical
                              Same as -P.
                      pipefail
                              If  set,  the  return value of a pipeline is the
                              value of the last (rightmost)  command  to  exit
                              with  a non-zero status, or zero if all commands
                              in the pipeline exit successfully.  This  option
                              is disabled by default.
                      posix   Change  the  behavior  of bash where the default
                              operation differs from  the  POSIX  standard  to
                              match  the  standard (posix mode).  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
                      appear in the environment, are ignored.  If the shell is
                      started with the effective user (group) id not equal  to
                      the  real user (group) id, and the -p option is not sup-
                      plied, these actions are taken and the effective user id
                      is  set  to  the real user id.  If the -p option is sup-
                      plied at startup, the effective user id  is  not  reset.
                      Turning  this  option  off causes the effective user and
                      group ids to be set to the real user and group ids.
              -t      Exit after reading and executing one command.
              -u      Treat unset variables and parameters other than the spe-
                      cial  parameters "@" and "*" as an error when performing
                      parameter expansion.  If expansion is  attempted  on  an
                      unset  variable  or parameter, the shell prints an error
                      message, and, if not interactive, exits with a  non-zero
                      status.
              -v      Print shell input lines as they are read.
              -x      After  expanding  each simple command, for command, case
                      command, select command, or arithmetic for command, dis-
                      play  the expanded value of PS4, followed by the command
                      and its expanded arguments or associated word list.
              -B      The shell performs brace expansion (see Brace  Expansion
                      above).  This is on by default.
              -C      If  set,  bash  does not overwrite an existing file with
                      the >>, >>&&, and <<>> redirection operators.   This  may  be
                      overridden when creating output files by using the redi-
                      rection operator >>|| instead of >>.
              -E      If set, any trap on ERR is inherited by shell functions,
                      command  substitutions,  and commands executed in a sub-
                      shell environment.  The ERR trap is normally not  inher-
                      ited in such cases.
              -H      Enable !!  style history substitution.  This option is on
                      by default when the shell is interactive.
              -P      If set, the shell does not 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
                      executed  in  a  subshell  environment.   The  DEBUG and
                      RETURN traps are normally not inherited in such cases.
              ----      If no arguments follow this option, then the  positional
                      parameters are unset.  Otherwise, the positional parame-
                      ters are set to the args, even if  some  of  them  begin
                      with a --.
              --       Signal  the  end of options, cause all remaining args to
                      be assigned to the positional parameters.  The -x and -v
                      options are turned off.  If there are no args, the posi-
                      tional parameters remain unchanged.

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

       shift [_n]
              The  positional  parameters  from _n+1 ... are renamed to $$11 ........
              Parameters represented by the numbers  $$##  down  to  $$##-_n+1  are
              unset.   _n  must  be a non-negative number less than or equal to
              $$##.  If _n is 0, no parameters are changed.  If _n is  not  given,
              it  is assumed to be 1.  If _n is greater than $$##, the positional
              parameters are not changed.  The return status is  greater  than
              zero if _n is greater than $$## or less than zero; otherwise 0.

       shopt [-pqsu] [-o] [optname ...]
              Toggle  the values of settings controlling optional shell behav-
              ior.  The settings can be either those listed below, or, if  the
              -o option is used, those available with the -o option to the set
              builtin command.  With no options, or with the -p option, a list
              of  all  settable  options  is  displayed, with an indication of
              whether or not each is set.  The -p option causes output  to  be
              displayed  in a form that may be reused as input.  Other options
              have the 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
              options, the return status is zero unless an optname  is  not  a
              valid shell option.

              The list of shopt options is:

              autocd  If  set,  a command name that is the name of a directory
                      is executed as if it were the argument to  the  cd  com-
                      mand.  This option is only used by interactive shells.
              cdable_vars
                      If  set,  an  argument to the cd builtin command that is
                      not a directory is assumed to be the name of a  variable
                      whose value is the directory to change to.
              cdspell If set, minor errors in the spelling of a directory com-
                      ponent in a cd command will be  corrected.   The  errors
                      checked for are transposed characters, a missing charac-
                      ter, and one character too many.   If  a  correction  is
                      found,  the  corrected 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
                      exiting if any jobs are stopped.
              checkwinsize
                      If  set,  bash checks the window size after each command
                      and, if necessary, updates the values of LINES and  COL-
                      UMNS.
              cmdhist If  set,  bash attempts to save all lines of a multiple-
                      line command in the same  history  entry.   This  allows
                      easy re-editing of multi-line commands.
              compat31
                      If set, bash changes its behavior to that of version 3.1
                      with respect to quoted arguments to the  [[[[  conditional
                      command's ==~~ operator and locale-specific string compar-
                      ison when using the [[[[ conditional  command's  <<  and  >>
                      operators.   Bash  versions  prior to bash-4.1 use ASCII
                      collation and strcmp(3); bash-4.1 and later use the cur-
                      rent 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).
              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
                      interrupt  the  list as if the shell received the inter-
                      rupt; 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
                      removal.
              compat43
                      If  set,  bash  does  not  print a warning message if an
                      attempt is made to use a quoted compound  array  assign-
                      ment as an argument to declare, and 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).
              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
                      expand  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.
              execfail
                      If set, a non-interactive shell will not exit if it can-
                      not execute the file specified as  an  argument  to  the
                      exec  builtin  command.   An  interactive shell does not
                      exit if exec fails.
              expand_aliases
                      If set, aliases are expanded as  described  above  under
                      ALIASES.  This option is enabled by default for interac-
                      tive shells.
              extdebug
                      If set,  behavior  intended  for  use  by  debuggers  is
                      enabled:
                      11..     The -F option to the declare builtin displays the
                             source file name and line number corresponding to
                             each function name supplied as an argument.
                      22..     If  the  command  run by the DEBUG trap returns a
                             non-zero value, the next command is  skipped  and
                             not executed.
                      33..     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.
                      44..     BASH_ARGC  and BASH_ARGV are updated as described
                             in their descriptions above.
                      55..     Function tracing is  enabled:  command  substitu-
                             tion, shell functions, and subshells invoked with
                             (( command )) inherit the DEBUG and RETURN traps.
                      66..     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
                      description of  FIGNORE.   This  option  is  enabled  by
                      default.
              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
                      sequence  is  not taken into account, so bb will not col-
                      late between AA and  BB,  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
                      exits, rather than overwriting the file.
              histreedit
                      If  set, and readline is being used, a user is given the
                      opportunity to re-edit a failed history substitution.
              histverify
                      If set, and readline is being used, the results of  his-
                      tory  substitution  are  not  immediately  passed to the
                      shell parser.  Instead, the  resulting  line  is  loaded
                      into the readline editing buffer, allowing further modi-
                      fication.
              hostcomplete
                      If set, and readline is being used, bash will attempt to
                      perform  hostname  completion when a word containing a @@
                      is  being  completed  (see  Completing  under   READLINE
                      above).  This is enabled by default.
              huponexit
                      If set, bash will send SIGHUP to all jobs when an inter-
                      active login shell exits.
              interactive_comments
                      If set, allow a word beginning with ## to cause that word
                      and  all remaining characters on that line to be ignored
                      in an interactive  shell  (see  COMMENTS  above).   This
                      option is enabled by default.
              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.
              login_shell
                      The  shell  sets this option if it is started as a login
                      shell (see INVOCATION above).   The  value  may  not  be
                      changed.
              mailwarn
                      If  set,  and  a file that bash is checking for mail has
                      been accessed since the last time it  was  checked,  the
                      message  ``The  mail in mailfile has been read'' is dis-
                      played.
              no_empty_cmd_completion
                      If set, and  readline  is  being  used,  bash  will  not
                      attempt to search the PATH for possible completions when
                      completion is attempted on an empty line.
              nocaseglob
                      If set, bash matches  filenames  in  a  case-insensitive
                      fashion when performing pathname expansion (see Pathname
                      Expansion above).
              nocasematch
                      If set, bash  matches  patterns  in  a  case-insensitive
                      fashion when performing matching while executing case or
                      [[[[ conditional commands, 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.
              promptvars
                      If set, prompt strings undergo parameter expansion, com-
                      mand   substitution,  arithmetic  expansion,  and  quote
                      removal after being expanded as described  in  PROMPTING
                      above.  This option is enabled by default.
              restricted_shell
                      The   shell  sets  this  option  if  it  is  started  in
                      restricted mode (see RESTRICTED SHELL below).  The value
                      may  not be changed.  This is not reset when the startup
                      files are executed, allowing the startup files  to  dis-
                      cover whether or not a shell is restricted.
              shift_verbose
                      If  set,  the shift builtin prints an error message when
                      the shift count exceeds the number of positional parame-
                      ters.
              sourcepath
                      If set, the source (..) builtin uses the value of PATH to
                      find the directory containing the file  supplied  as  an
                      argument.  This option is enabled by default.
              xpg_echo
                      If   set,  the  echo  builtin  expands  backslash-escape
                      sequences by default.

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

       test expr
       [[ expr ]]
              Return a status of 0 (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
              depends  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 -aa expr2
                     True if both expr1 and expr2 are true.
              expr1 -oo 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
              receives signal(s) sigspec.  If arg is absent (and  there  is  a
              single  sigspec)  or  --,  each  specified signal is reset to its
              original disposition (the value it  had  upon  entrance  to  the
              shell).   If arg is the null string the signal specified by each
              sigspec is ignored by the shell and by the commands it  invokes.
              If  arg  is  not present and -p has been supplied, then the trap
              commands associated with each  sigspec  are  displayed.   If  no
              arguments  are  supplied or if only -p is given, trap prints the
              list of commands associated with each  signal.   The  -l  option
              causes  the shell to print a list of signal names and their cor-
              responding numbers.   Each  sigspec  is  either  a  signal  name
              defined  in  <signal.h>,  or  a signal number.  Signal names are
              case insensitive and the SIG prefix is optional.

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

              If  a  sigspec  is ERR, the command arg is executed whenever a 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)
              option.

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

       type [-aftpP] name [name ...]
              With  no options, indicate how each name would be interpreted if
              used as a command name.  If the -t option is used, type prints a
              string  which  is  one  of alias, keyword, function, builtin, or
              file if  name  is  an  alias,  shell  reserved  word,  function,
              builtin,  or disk file, respectively.  If the name is not found,
              then nothing  is  printed,  and  an  exit  status  of  false  is
              returned.   If  the  -p  option is used, type either returns the
              name of the disk file that would be executed if name were speci-
              fied as a command name, or nothing if ``type -t name'' would not
              return file.  The -P option forces a PATH search for each  name,
              even if ``type -t name'' would not return file.  If a command is
              hashed, -p and -P print the hashed value, 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,
              respectively.   If  limit  is  omitted, the current value of the
              soft limit of the resource is printed, unless the -H  option  is
              given.  When more than one resource is specified, the limit name
              and unit are printed before the value.  Other options are inter-
              preted as follows:
              -a     All current limits are reported
              -b     The maximum socket buffer size
              -c     The maximum size of core files created
              -d     The maximum size of a process's data segment
              -e     The maximum scheduling priority ("nice")
              -f     The  maximum  size  of files written by the shell and its
                     children
              -i     The maximum number of pending signals
              -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 [-aa] [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] [-nn] [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 [-n] [_n _._._.]
              Wait for each specified child process and return its termination
              status.  Each _n may be a process ID or a job specification; if a
              job  spec  is  given,  all  processes in that job's pipeline are
              waited for.  If _n is not given, all currently active child  pro-
              cesses are waited for, and the return status is zero.  If the -n
              option is supplied, wait waits for  any  job  to  terminate  and
              returns  its exit status.  If _n specifies a non-existent process
              or job, the return status is 127.  Otherwise, the return  status
              is the exit status of the last process or job waited for.

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

       +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
       ~/.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 4.4                    2015 October 2                         BASH(1)
