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NAME

       bash - GNU Bourne-Again SHell


SYNOPSIS

       bash [options] [command_string | file]


COPYRIGHT

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


DESCRIPTION

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

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


OPTIONS

       All of the single-character shell options documented in the description
       of the set builtin command, including -o, can be used as  options  when
       the  shell  is  invoked.   In  addition,  bash interprets the following
       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  $0  and any remaining arguments are assigned to
                 the positional parameters.  The assignment  to  $0  sets  the
                 name  of  the  shell, which is used in warning and error 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 or when reading input
                 through a pipe.
       -D        A list of all double-quoted strings preceded by $ is  printed
                 on  the standard output.  These are the strings that are sub-
                 ject to language translation when the current locale is not C
                 or  POSIX.   This  implies the -n option; no commands will be
                 executed.
       [-+]O [shopt_option]
                 shopt_option is one of the  shell  options  accepted  by  the
                 shopt   builtin  (see  SHELL  BUILTIN  COMMANDS  below).   If
                 shopt_option is present, -O sets the value of that option; +O
                 unsets  it.   If  shopt_option is not supplied, the names and
                 values of the shell options accepted by shopt are printed  on
                 the  standard  output.   If  the invocation option is +O, the
                 output is displayed in a format that may be reused as  input.
       --        A  --  signals the end of options and disables further option
                 processing.  Any arguments after the -- are treated as  file-
                 names and arguments.  An argument of - is equivalent to --.

       Bash  also  interprets  a  number  of  multi-character  options.  These
       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,  $0 is set to the name of the file, and the positional parame-
       ters are set to the remaining arguments.  Bash reads and executes  com-
       mands  from this file, then exits.  Bash's exit status is the exit sta-
       tus of the last command executed in the script.   If  no  commands  are
       executed,  the  exit status is 0.  An attempt is first made to open the
       file in the current directory, and, if no file is found, then the shell
       searches the directories in PATH for the script.


INVOCATION

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

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

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

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

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

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

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

       If the shell is started with the effective user (group) id not equal to
       the real user (group) id, and the -p option is not supplied, no startup
       files are read, shell functions are not inherited from the environment,
       the  SHELLOPTS,  BASHOPTS,  CDPATH,  and  GLOBIGNORE variables, if they
       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 command (see SHELL GRAMMAR below), the third word of a
       case or select command (only in is valid), or the third word of  a  for
       command (only in and do are valid):

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


SHELL GRAMMAR

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

   Simple Commands
       A  simple  command  is a sequence of optional variable assignments fol-
       lowed by blank-separated words and redirections, and  terminated  by  a
       control operator.  The first word specifies the command to be executed,
       and is passed as argument zero.  The  remaining  words  are  passed  as
       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]] [ ! ] command1 [ [|||&] command2 ... ]

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

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

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

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

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

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

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

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

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

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

              command1 && command2

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

       An OR list has the form

              command1 || command2

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

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

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

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

       ((expression))
              The  expression  is  evaluated  according to the rules described
              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.  The expression undergoes the same expansions as if
              it  were  within  double  quotes, but double quote characters in
              expression are not treated specially and are removed.

       [[ expression ]]
              Return a status of 0 or 1 depending on  the  evaluation  of  the
              conditional  expression expression.  Expressions are composed of
              the primaries described  below  under  CONDITIONAL  EXPRESSIONS.
              The  words  between  the [[ and ]] do not undergo word splitting
              and pathname expansion.  The  shell  performs  tilde  expansion,
              parameter  and variable expansion, arithmetic expansion, command
              substitution, process substitution, and quote removal  on  those
              words  (the  expansions  that  would  occur  if  the  words were
              enclosed in double quotes).  Conditional operators  such  as  -f
              must be unquoted to be recognized as primaries.

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

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

              An  additional  binary operator, =~, is available, with the same
              precedence as == and !=.  When it is used,  the  string  to  the
              right  of  the  operator  is considered a POSIX extended regular
              expression and matched accordingly (using the POSIX regcomp  and
              regexec  interfaces  usually described in regex(3)).  The return
              value is 0 if the string matches the pattern, and  1  otherwise.
              If the regular expression is syntactically incorrect, the condi-
              tional expression's return value is 2.  If the nocasematch shell
              option  is enabled, the match is performed without regard to the
              case of alphabetic characters.  If any part of  the  pattern  is
              quoted,  the  quoted  portion  is matched literally.  This means
              every character in the quoted portion matches itself, instead of
              having  any special pattern matching meaning.  If the pattern is
              stored in a  shell  variable,  quoting  the  variable  expansion
              forces  the  entire  pattern  to  be  matched  literally.  Treat
              bracket expressions in regular expressions carefully, since nor-
              mal  quoting  and pattern characters lose their meanings between
              brackets.

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

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

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

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

       for name [ [ in [ word ... ] ] ; ] do list ; done
              The list of words following in is expanded, generating a list of
              items.  The variable name is set to each element of this list in
              turn,  and  list is executed each time.  If the in word is omit-
              ted, the for command executes  list  once  for  each  positional
              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,  and the set of expanded words is printed on the standard
              error, each preceded by a number.  If the in  word  is  omitted,
              the  positional  parameters  are printed (see PARAMETERS below).
              select then displays the PS3 prompt and reads a  line  from  the
              standard  input.  If the line consists of a number corresponding
              to one of the displayed words, then the value of name is set  to
              that  word.  If the line is empty, the words and prompt are dis-
              played again.  If EOF is read, the select command completes  and
              returns  1.  Any other value read causes name to be set to null.
              The line read is saved in the variable REPLY.  The list is  exe-
              cuted  after  each  selection until a break command is executed.
              The exit status of select is the exit status of the last command
              executed in list, or zero if no commands were executed.

       case word in [ [(] pattern [ | pattern ] ... ) list ;; ] ... esac
              A case command first expands word, and tries to match it against
              each pattern in turn, using the matching rules  described  under
              Pattern Matching below.  The word is expanded using tilde expan-
              sion, parameter and variable  expansion,  arithmetic  expansion,
              command  substitution,  process  substitution and quote removal.
              Each pattern examined is expanded using tilde expansion, parame-
              ter  and  variable expansion, arithmetic expansion, command sub-
              stitution, process substitution,  and  quote  removal.   If  the
              nocasematch  shell  option  is  enabled,  the match is performed
              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  pat-
              terns.   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,  continuing the case
              statement execution as if the pattern list had not matched.  The
              exit status is zero if no pattern matches.  Otherwise, it is the
              exit status of the last command executed in 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 syntax for a coprocess is:

              coproc [NAME] command [redirections]

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

       The recommended form to use for a coprocess is

              coproc NAME { command [redirections]; }

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

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

       When  the  coprocess  is  executed, the shell creates an array variable
       (see Arrays below) named NAME in the context of  the  executing  shell.
       The  standard  output  of  command  is  connected  via a pipe to a file
       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.  Other than those created to execute  command
       and  process  substitutions,  the file descriptors are not available in
       subshells.

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

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

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

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


COMMENTS

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


QUOTING

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

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

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

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

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

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

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

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

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

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

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


PARAMETERS

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

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

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

              name=[value]

       If value is not given, the variable is assigned the null  string.   All
       values  undergo tilde expansion, parameter and variable expansion, com-
       mand substitution, arithmetic expansion, and quote removal (see  EXPAN-
       SION below).  If the variable has its integer attribute set, then value
       is evaluated as an arithmetic expression even if the $((...)) expansion
       is not used (see Arithmetic Expansion below).  Word splitting and path-
       name expansion are  not  performed.   Assignment  statements  may  also
       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 using or changing the nameref attribute
       itself),  the operation is actually performed on the variable specified
       by the nameref variable's value.  A nameref  is  commonly  used  within
       shell functions to refer to a variable whose name is passed as an argu-
       ment to the function.  For instance, if a variable name is passed to  a
       shell function as its first argument, running
              declare -n ref=$1
       inside  the  function creates a nameref variable ref whose value is the
       variable name passed as the first argument.  References and assignments
       to  ref,  and  changes  to  its  attributes, are treated as references,
       assignments, and attribute modifications to the variable whose name was
       passed  as  $1.   If the control variable in a for loop has the nameref
       attribute, the list of words can be a list of shell  variables,  and  a
       name  reference 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 "$1c$2c...", where c
              is the first character of the value of the IFS variable.  If IFS
              is  unset,  the  parameters  are separated by spaces.  If IFS is
              null, the parameters are joined without intervening  separators.
       @      Expands  to  the  positional  parameters, starting from one.  In
              contexts where word splitting is performed,  this  expands  each
              positional  parameter  to  a separate word; if not within double
              quotes, these words are subject to word splitting.  In  contexts
              where  word splitting is not performed, this expands to a single
              word with each positional parameter separated by a space.   When
              the  expansion  occurs  within  double  quotes,  each  parameter
              expands to a separate word.  That is, "$@" is equivalent to "$1"
              "$2"  ...   If the double-quoted expansion occurs within a word,
              the expansion of the first parameter is joined with  the  begin-
              ning  part  of  the original word, and the expansion of the last
              parameter is joined with the last part  of  the  original  word.
              When  there  are no positional parameters, "$@" and $@ expand to
              nothing (i.e., they are removed).
       #      Expands to the number of positional parameters in decimal.
       ?      Expands to the 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).
       0      Expands  to  the name of the shell or shell script.  This is set
              at shell initialization.  If bash is invoked with a file of com-
              mands,  $0  is set to the name of that file.  If bash is started
              with the -c option, then $0 is set to the first  argument  after
              the  string to be executed, if one is present.  Otherwise, it is
              set to the filename used to invoke bash, as  given  by  argument
              zero.

   Shell Variables
       The following variables are set by the shell:

       _      At  shell  startup, set to the pathname used to invoke the shell
              or shell script being executed as passed in the  environment  or
              argument  list.   Subsequently,  expands to the last argument to
              the previous simple command executed in  the  foreground,  after
              expansion.   Also  set  to the full pathname used to invoke each
              command executed and placed in the environment exported to  that
              command.   When  checking mail, this parameter holds the name of
              the mail file currently being checked.
       BASH   Expands to the full filename used to  invoke  this  instance  of
              bash.
       BASHOPTS
              A  colon-separated  list of enabled shell options.  Each word in
              the list is a valid argument for the  -s  option  to  the  shopt
              builtin command (see SHELL BUILTIN COMMANDS below).  The options
              appearing in BASHOPTS are those reported as  on  by  shopt.   If
              this  variable  is  in the environment when bash starts up, each
              shell option in the list will  be  enabled  before  reading  any
              startup files.  This variable is read-only.
       BASHPID
              Expands  to  the  process  ID of the current bash process.  This
              differs from $$ under certain circumstances, such  as  subshells
              that  do  not require bash to be re-initialized.  Assignments to
              BASHPID have no effect.  If BASHPID is unset, it loses its  spe-
              cial properties, even if it is subsequently reset.
       BASH_ALIASES
              An  associative  array  variable whose members correspond to the
              internal list of aliases as maintained  by  the  alias  builtin.
              Elements  added to this array appear in the alias list; however,
              unsetting array elements currently does not cause aliases to  be
              removed from the alias list.  If BASH_ALIASES is unset, it loses
              its special properties, even if it is subsequently reset.
       BASH_ARGC
              An array variable whose values are the number of  parameters  in
              each frame of the current bash execution call stack.  The number
              of parameters to  the  current  subroutine  (shell  function  or
              script  executed  with  . or source) is at the top of the stack.
              When a subroutine is executed, the number of  parameters  passed
              is pushed onto BASH_ARGC.  The shell sets BASH_ARGC only when in
              extended debugging mode (see the  description  of  the  extdebug
              option  to the shopt builtin below).  Setting extdebug after the
              shell has started to execute a script, or referencing this vari-
              able  when  extdebug is not set, may result in inconsistent val-
              ues.
       BASH_ARGV
              An array variable containing all of the parameters in  the  cur-
              rent bash execution call stack.  The final parameter of the last
              subroutine call is at the top of the stack; the first  parameter
              of the initial call is at the bottom.  When a subroutine is exe-
              cuted, the parameters supplied are pushed onto  BASH_ARGV.   The
              shell  sets  BASH_ARGV only when in extended debugging mode (see
              the description of the extdebug  option  to  the  shopt  builtin
              below).  Setting extdebug after the shell has started to execute
              a script, or referencing this variable when extdebug is not set,
              may result in inconsistent values.
       BASH_ARGV0
              When  referenced, this variable expands to the name of the shell
              or shell script (identical to $0; see the description of special
              parameter  0  above).  Assignment to BASH_ARGV0 causes the value
              assigned to also be assigned to $0.  If BASH_ARGV0 is unset,  it
              loses  its special properties, even if it is subsequently reset.
       BASH_CMDS
              An associative array variable whose members  correspond  to  the
              internal  hash  table  of  commands  as  maintained  by the hash
              builtin.  Elements added to this array appear in the hash table;
              however,  unsetting array elements currently does not cause com-
              mand names to be removed from the hash table.  If  BASH_CMDS  is
              unset,  it  loses  its  special properties, even if it is subse-
              quently reset.
       BASH_COMMAND
              The command currently being executed or about  to  be  executed,
              unless the shell is executing a command as the result of a trap,
              in which case it is the command executing at  the  time  of  the
              trap.   If  BASH_COMMAND  is unset, it loses its special proper-
              ties, even if it is subsequently reset.
       BASH_EXECUTION_STRING
              The command argument to the -c invocation option.
       BASH_LINENO
              An array variable whose members are the line numbers  in  source
              files  where  each corresponding member of FUNCNAME was invoked.
              ${BASH_LINENO[$i]}  is  the  line  number  in  the  source  file
              (${BASH_SOURCE[$i+1]})  where  ${FUNCNAME[$i]}  was  called  (or
              ${BASH_LINENO[$i-1]} if referenced within  another  shell  func-
              tion).  Use LINENO to obtain the current line number.
       BASH_LOADABLES_PATH
              A  colon-separated  list of directories in which the shell looks
              for dynamically loadable builtins specified by the  enable  com-
              mand.
       BASH_REMATCH
              An  array  variable  whose members are assigned by the =~ binary
              operator to the [[ conditional command.  The element with  index
              0  is  the  portion  of  the  string matching the entire regular
              expression.  The element with index n  is  the  portion  of  the
              string matching the nth parenthesized subexpression.
       BASH_SOURCE
              An  array  variable whose members are the source filenames where
              the corresponding shell function names  in  the  FUNCNAME  array
              variable  are  defined.   The  shell function ${FUNCNAME[$i]} is
              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.  If BASH_SUBSHELL is unset, it loses its spe-
              cial properties, even if it is subsequently reset.
       BASH_VERSINFO
              A readonly array variable whose members hold version information
              for  this  instance  of  bash.  The values assigned to the array
              members are as follows:
              BASH_VERSINFO[0]        The major version number (the  release).
              BASH_VERSINFO[1]        The  minor version number (the version).
              BASH_VERSINFO[2]        The patch level.
              BASH_VERSINFO[3]        The build version.
              BASH_VERSINFO[4]        The release status (e.g., beta1).
              BASH_VERSINFO[5]        The value of MACHTYPE.
       BASH_VERSION
              Expands to a string describing the version of this  instance  of
              bash.
       COMP_CWORD
              An  index  into ${COMP_WORDS} of the word containing the current
              cursor position.  This variable is available only in shell func-
              tions  invoked  by  the  programmable completion facilities (see
              Programmable Completion below).
       COMP_KEY
              The key (or final key of a key sequence) used to invoke the cur-
              rent completion function.
       COMP_LINE
              The  current  command  line.  This variable is available only in
              shell functions  and  external  commands  invoked  by  the  pro-
              grammable  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  pro-
              grammable  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  pro-
              grammable  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.
       EPOCHREALTIME
              Each time this parameter is referenced, it expands to the number
              of  seconds  since  the  Unix  Epoch (see time(3)) as a floating
              point  value  with  micro-second  granularity.   Assignments  to
              EPOCHREALTIME  are ignored.  If EPOCHREALTIME is unset, it loses
              its special properties, even if it is subsequently reset.
       EPOCHSECONDS
              Each time this parameter is referenced, it expands to the number
              of  seconds  since the Unix Epoch (see time(3)).  Assignments to
              EPOCHSECONDS are ignored.  If EPOCHSECONDS is  unset,  it  loses
              its special properties, even if it is subsequently reset.
       EUID   Expands  to  the effective user ID of the current user, initial-
              ized at shell startup.  This variable is readonly.
       FUNCNAME
              An array variable containing the names of  all  shell  functions
              currently in the execution call stack.  The element with index 0
              is the name of any currently-executing shell function.  The bot-
              tom-most  element  (the  one  with the highest index) is "main".
              This variable exists only when a shell  function  is  executing.
              Assignments  to  FUNCNAME have no effect.  If FUNCNAME is unset,
              it loses its special properties,  even  if  it  is  subsequently
              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.   Assignments  to  HISTCMD  are ignored.  If HISTCMD is
              unset, it loses its special properties, even  if  it  is  subse-
              quently reset.
       HOSTNAME
              Automatically set to the name of the current host.
       HOSTTYPE
              Automatically  set  to a string that uniquely describes the type
              of machine on which bash is executing.  The default  is  system-
              dependent.
       LINENO Each  time this parameter is referenced, the shell substitutes a
              decimal number representing the current sequential  line  number
              (starting  with  1)  within a script or function.  When not in a
              script or function, the value substituted is not  guaranteed  to
              be meaningful.  If LINENO is unset, it loses its special proper-
              ties, even if it is subsequently reset.
       MACHTYPE
              Automatically set to a string that fully  describes  the  system
              type  on  which  bash is executing, in the standard GNU cpu-com-
              pany-system format.  The default is system-dependent.
       MAPFILE
              An array variable (see Arrays below) created to  hold  the  text
              read by the mapfile builtin when no variable name is supplied.
       OLDPWD The previous working directory as set by the cd command.
       OPTARG The  value  of the last option argument processed by the getopts
              builtin command (see SHELL BUILTIN COMMANDS below).
       OPTIND The index of the next argument to be processed  by  the  getopts
              builtin command (see SHELL BUILTIN COMMANDS below).
       OSTYPE Automatically  set to a string that describes the operating sys-
              tem on which bash is executing.  The  default  is  system-depen-
              dent.
       PIPESTATUS
              An  array  variable (see Arrays below) containing a list of exit
              status values from the processes in  the  most-recently-executed
              foreground pipeline (which may contain only a single command).
       PPID   The  process  ID  of the shell's parent.  This variable is read-
              only.
       PWD    The current working directory as set by the cd command.
       RANDOM Each time this parameter is referenced, it expands to  a  random
              integer  between  0 and 32767.  Assigning a value to RANDOM ini-
              tializes (seeds) the sequence of random numbers.  If  RANDOM  is
              unset,  it  loses  its  special properties, even if it is subse-
              quently reset.
       READLINE_ARGUMENT
              Any numeric argument  given  to  a  readline  command  that  was
              defined  using "bind -x" (see SHELL BUILTIN COMMANDS below) when
              it was invoked.
       READLINE_LINE
              The contents of the readline line buffer, for use with "bind -x"
              (see SHELL BUILTIN COMMANDS below).
       READLINE_MARK
              The position of the mark (saved insertion point) in the readline
              line buffer, for use with "bind -x" (see SHELL BUILTIN  COMMANDS
              below).  The characters between the insertion point and the mark
              are often called the region.
       READLINE_POINT
              The position of the insertion point in the readline line buffer,
              for use with "bind -x" (see SHELL BUILTIN COMMANDS below).
       REPLY  Set  to  the line of input read by the read builtin command when
              no arguments are supplied.
       SECONDS
              Each time this parameter is referenced, it expands to the number
              of  seconds  since  shell invocation.  If a value is assigned to
              SECONDS, the value returned upon subsequent  references  is  the
              number  of seconds since the assignment plus the value assigned.
              The number of seconds at shell invocation and the  current  time
              are  always determined by querying the system clock.  If SECONDS
              is unset, it loses its special properties, even if it is  subse-
              quently reset.
       SHELLOPTS
              A  colon-separated  list of enabled shell options.  Each word in
              the list is a valid argument  for  the  -o  option  to  the  set
              builtin command (see SHELL BUILTIN COMMANDS below).  The options
              appearing in SHELLOPTS are those reported as on by set  -o.   If
              this  variable  is  in the environment when bash starts up, each
              shell option in the list will  be  enabled  before  reading  any
              startup files.  This variable is read-only.
       SHLVL  Incremented by one each time an instance of bash is started.
       SRANDOM
              This variable expands to a 32-bit pseudo-random number each time
              it is referenced. The random number generator is not  linear  on
              systems   that  support  /dev/urandom  or  arc4random,  so  each
              returned number has no relationship to the numbers preceding it.
              The  random number generator cannot be seeded, so assignments to
              this variable have no effect.  If SRANDOM is unset, it loses its
              special properties, even if it is subsequently reset.
       UID    Expands to the user ID of the current user, initialized at shell
              startup.  This variable is readonly.

       The 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
              SHELL COMPATIBILITY MODE below for a description of the  various
              compatibility levels and their effects.  The value may be a dec-
              imal number (e.g., 4.2) or an integer (e.g.,  42)  corresponding
              to  the desired compatibility level.  If BASH_COMPAT is unset or
              set to the empty string, the compatibility level is set  to  the
              default  for  the  current  version.  If BASH_COMPAT is set to a
              value that is not one of the  valid  compatibility  levels,  the
              shell  prints  an error message and sets the compatibility level
              to the default for the current version.  The valid values corre-
              spond  to  the  compatibility levels described below under SHELL
              COMPATIBILITY MODE.  For example, 4.2 and 42  are  valid  values
              that correspond to the compat42 shopt option and set the compat-
              ibility level to 42.  The current version is also a valid value.
       BASH_ENV
              If  this parameter is set when bash is executing a shell script,
              its value is interpreted as a filename  containing  commands  to
              initialize the shell, as in ~/.bashrc.  The value of BASH_ENV is
              subjected to  parameter  expansion,  command  substitution,  and
              arithmetic  expansion  before  being  interpreted as a filename.
              PATH is not used to search for the resultant filename.
       BASH_XTRACEFD
              If set to an integer corresponding to a valid  file  descriptor,
              bash  will  write  the  trace  output  generated  when set -x is
              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    Expanded and executed  similarly  to  BASH_ENV  (see  INVOCATION
              above) when an interactive shell is invoked in posix mode.
       EXECIGNORE
              A  colon-separated list of shell patterns (see Pattern Matching)
              defining the list of filenames to be ignored by  command  search
              using  PATH.  Files whose full pathnames match one of these pat-
              terns are not considered executable files for  the  purposes  of
              completion and command execution via PATH lookup.  This does not
              affect the behavior of the [, test, and [[ commands.  Full path-
              names  in  the command hash table are not subject to EXECIGNORE.
              Use this variable to ignore shared library files that  have  the
              executable  bit  set, but are not executable files.  The pattern
              matching honors the setting of the extglob shell option.
       FCEDIT The default editor for the fc builtin command.
       FIGNORE
              A colon-separated list of suffixes  to  ignore  when  performing
              filename completion (see READLINE below).  A filename whose suf-
              fix matches one of the entries in FIGNORE is excluded  from  the
              list of matched filenames.  A sample value is ".o:~".
       FUNCNEST
              If  set  to  a  numeric  value greater than 0, defines a maximum
              function nesting level.  Function invocations that  exceed  this
              nesting level will cause the current command to abort.
       GLOBIGNORE
              A  colon-separated  list  of  patterns  defining the set of file
              names to be ignored by  pathname  expansion.   If  a  file  name
              matched  by a pathname expansion pattern also matches one of the
              patterns in GLOBIGNORE, it is removed from the list of  matches.
       HISTCONTROL
              A  colon-separated  list  of values controlling how commands are
              saved on the history list.   If  the  list  of  values  includes
              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.   The  pattern
              matching honors the setting of the extglob shell option.
       HISTSIZE
              The  number  of commands to remember in the command history (see
              HISTORY below).  If the value is 0, commands are  not  saved  in
              the history list.  Numeric values less than zero result in every
              command being saved on the history list  (there  is  no  limit).
              The  shell  sets  the  default  value  to  500 after reading any
              startup files.
       HISTTIMEFORMAT
              If this variable is set and not null, its value  is  used  as  a
              format string for strftime(3) to print the time stamp associated
              with each history entry displayed by the  history  builtin.   If
              this  variable  is  set,  time stamps are written to the history
              file so they may be preserved across shell sessions.  This  uses
              the  history  comment  character  to distinguish timestamps from
              other history lines.
       HOME   The home directory of the current user; the default argument for
              the cd builtin command.  The value of this variable is also used
              when performing tilde expansion.
       HOSTFILE
              Contains the name of a file in the  same  format  as  /etc/hosts
              that should be read when the shell needs to complete a hostname.
              The list of possible hostname completions may be  changed  while
              the  shell  is  running;  the  next  time hostname completion is
              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).
       INSIDE_EMACS
              If this variable appears  in  the  environment  when  the  shell
              starts,  bash  assumes  that it is running inside an Emacs shell
              buffer and may disable line editing, depending on the  value  of
              TERM.
       LANG   Used  to  determine  the  locale  category  for any category not
              specifically selected with a variable starting with LC_.
       LC_ALL This variable overrides the value of  LANG  and  any  other  LC_
              variable specifying a locale category.
       LC_COLLATE
              This  variable  determines the collation order used when sorting
              the results of pathname expansion, and determines  the  behavior
              of   range   expressions,  equivalence  classes,  and  collating
              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.
       LC_TIME
              This variable determines the locale category used for  data  and
              time formatting.
       LINES  Used  by  the  select  compound  command to determine the column
              length for printing selection lists.  Automatically set  if  the
              checkwinsize  option  is enabled or in an interactive shell upon
              receipt of a SIGWINCH.
       MAIL   If this parameter is set to a file or  directory  name  and  the
              MAILPATH  variable  is  not  set,  bash  informs the user of the
              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  can be configured to supply a default value for this vari-
              able (there is no value by default), but  the  location  of  the
              user  mail  files  that  it  uses  is  system  dependent  (e.g.,
              /var/mail/$USER).
       OPTERR If set to the value 1, bash displays error messages generated by
              the  getopts builtin command (see SHELL BUILTIN COMMANDS below).
              OPTERR is initialized to 1 each time the shell is invoked  or  a
              shell script is executed.
       PATH   The  search  path for commands.  It is a colon-separated list of
              directories in which the shell looks for commands  (see  COMMAND
              EXECUTION  below).   A  zero-length (null) directory name in the
              value of PATH indicates the current directory.  A null directory
              name  may  appear  as  two  adjacent colons, or as an initial or
              trailing colon.  The default path is  system-dependent,  and  is
              set by the administrator who installs bash.  A common value is
              ``/usr/local/bin:/usr/local/sbin:/usr/bin:/usr/sbin:/bin:/sbin''.
       POSIXLY_CORRECT
              If  this  variable  is  in the environment when bash starts, the
              shell enters posix mode before reading the startup files, as  if
              the  --posix  invocation option had been supplied.  If it is set
              while the shell is running, bash enables posix mode, as  if  the
              command  set  -o posix had been executed.  When the shell enters
              posix mode, it sets this variable if it was not already set.
       PROMPT_COMMAND
              If this variable is set, and is an array, the value of each  set
              element  is  executed as a command prior to issuing each primary
              prompt.  If this is set but not an array variable, its value  is
              used as a command to execute instead.
       PROMPT_DIRTRIM
              If  set  to a number greater than zero, the value is used as the
              number of trailing directory components to retain when expanding
              the  \w  and  \W  prompt  string  escapes (see PROMPTING below).
              Characters removed are replaced with an ellipsis.
       PS0    The value of this parameter is expanded  (see  PROMPTING  below)
              and  displayed by interactive shells after reading a command and
              before the command is executed.
       PS1    The value of this parameter is expanded  (see  PROMPTING  below)
              and  used  as  the  primary prompt string.  The default value is
              ``\s-\v\$ ''.
       PS2    The value of this parameter is expanded as with PS1 and used  as
              the secondary prompt string.  The default is ``> ''.
       PS3    The value of this parameter is used as the prompt for the select
              command (see SHELL GRAMMAR above).
       PS4    The value of this parameter is expanded  as  with  PS1  and  the
              value  is  printed  before  each command bash displays during an
              execution trace.  The first character of the expanded  value  of
              PS4 is replicated multiple times, as necessary, to indicate mul-
              tiple levels of indirection.  The default is ``+ ''.
       SHELL  This variable expands to the full pathname to the shell.  If  it
              is  not  set  when the shell starts, bash assigns to it the full
              pathname of the current user's login shell.
       TIMEFORMAT
              The value of this parameter is used as a format string  specify-
              ing  how  the timing information for pipelines prefixed with the
              time reserved word should be displayed.  The % character  intro-
              duces  an  escape  sequence  that is expanded to a time value or
              other information.  The escape sequences and their meanings  are
              as follows; the braces denote optional portions.
              %%        A literal %.
              %[p][l]R  The elapsed time in seconds.
              %[p][l]U  The number of CPU seconds spent in user mode.
              %[p][l]S  The number of CPU seconds spent in system mode.
              %P        The CPU percentage, computed as (%U + %S) / %R.

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

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

              If this variable is not set, bash acts as if it  had  the  value
              $'\nreal\t%3lR\nuser\t%3lU\nsys\t%3lS'.   If  the value is null,
              no timing information is displayed.  A trailing newline is added
              when the format string is displayed.
       TMOUT  If  set  to  a  value greater than zero, TMOUT is treated as the
              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=(value1 ... valuen), where each value may be  of  the  form  [sub-
       script]=string.   Indexed array assignments do not require anything but
       string.  Each value in the list is expanded using all the shell  expan-
       sions  described  below  under  EXPANSION.   When  assigning to indexed
       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 words in a compound assign-
       ment may be either assignment statements, for which  the  subscript  is
       required,  or  a  list  of  words  that is interpreted as a sequence of
       alternating keys and values:  name=(  key1  value1  key2  value2  ...).
       These  are  treated  identically  to name=( [key1]=value1 [key2]=value2
       ...).  The first word in the list determines how  the  remaining  words
       are  interpreted;  all  assignments in a list must be of the same type.
       When using key/value pairs, the keys may not be  missing  or  empty;  a
       final missing value is treated like the empty string.

       This  syntax is also accepted by the declare builtin.  Individual array
       elements may be assigned  to  using  the  name[subscript]=value  syntax
       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.

       The  +=  operator will append to an array variable when assigning using
       the compound assignment syntax; see PARAMETERS above.

       Any element of an array may  be  referenced  using  ${name[subscript]}.
       The braces are required to avoid conflicts with pathname expansion.  If
       subscript is @ or *, the word expands to all members  of  name.   These
       subscripts  differ only when the word appears within double quotes.  If
       the word is double-quoted, ${name[*]} expands to a single word with the
       value  of each array member separated by the first character of the IFS
       special variable, and ${name[@]} expands each element of name to a sep-
       arate  word.   When  there  are no array members, ${name[@]} expands to
       nothing.  If the double-quoted expansion  occurs  within  a  word,  the
       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, for both indexed and
       associative arrays.  Negative subscripts to indexed arrays  are  inter-
       preted  as  described  above.   Unsetting  the last element of an array
       variable does not unset the variable.  unset name,  where  name  is  an
       array,  removes  the  entire  array.  unset name[subscript], where sub-
       script is * or @, behaves differently depending on whether name  is  an
       indexed  or  associative  array.  If name is an associative array, this
       unsets the element with subscript * or @.  If name is an indexed array,
       unset removes all of the elements but does not remove the array itself.

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

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

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

       Only  brace  expansion,  word  splitting,  and  pathname  expansion can
       increase 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[@]}",  and,  in  most  cases,  $*  and
       ${name[*]} as explained above (see PARAMETERS).

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

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

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

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

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

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

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

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

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

       If the tilde-prefix is a `~+', the value  of  the  shell  variable  PWD
       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.

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

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

       When braces are used, the matching ending brace is the  first  `}'  not
       escaped  by  a  backslash  or within a quoted string, and not within an
       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 indirection.  Bash
       uses the value formed by expanding the rest of  parameter  as  the  new
       parameter;  this is then expanded and that value is used in the rest of
       the expansion, rather than the expansion  of  the  original  parameter.
       This  is  known  as  indirect expansion.  The value is subject to tilde
       expansion, parameter expansion, command  substitution,  and  arithmetic
       expansion.   If parameter is a nameref, this expands to the name of the
       parameter referenced by parameter instead of  performing  the  complete
       indirect  expansion.   The  exceptions  to  this  are the expansions of
       ${!prefix*} and ${!name[@]} described  below.   The  exclamation  point
       must  immediately  follow the left brace in order to introduce indirec-
       tion.

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

       When  not  performing  substring  expansion, using the forms documented
       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 @ or *, 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 @ or *, the result is length positional parame-
              ters beginning at offset.  A negative offset is  taken  relative
              to  one  greater  than  the greatest positional parameter, so an
              offset of -1 evaluates to the last positional parameter.  It  is
              an  expansion  error  if  length evaluates to a number less than
              zero.

              If parameter is an indexed array name subscripted by @ or *, the
              result  is  the  length  members  of  the  array  beginning with
              ${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, $0 is prefixed to the list.

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

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

       ${#parameter}
              Parameter  length.   The  length  in  characters of the value of
              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, and matched against the
              expanded value of parameter using the rules described under Pat-
              tern  Matching  below.   If the pattern matches the beginning of
              the value of parameter, then the result of the expansion is  the
              expanded  value  of parameter with the shortest matching pattern
              (the ``#'' case) or the longest  matching  pattern  (the  ``##''
              case)  deleted.   If  parameter  is  @ or *, the pattern removal
              operation is applied to each positional parameter in  turn,  and
              the  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 expan-
              sion is the resultant list.

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

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

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

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

       ${parameter^pattern}
       ${parameter^^pattern}
       ${parameter,pattern}
       ${parameter,,pattern}
              Case  modification.   This expansion modifies the case of alpha-
              betic characters in parameter.  The pattern is expanded to  pro-
              duce a pattern just as in pathname expansion.  Each character in
              the expanded value of parameter is tested against pattern,  and,
              if  it  matches the pattern, its case is converted.  The pattern
              should not attempt to match more  than  one  character.   The  ^
              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:

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

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

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

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

              $(command)
       or
              `command`

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

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

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

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

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

              $((expression))

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

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

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

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

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

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

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

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

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

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

       Pattern Matching

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

       The special pattern characters have the following meanings:

              *      Matches any string, including the null string.  When  the
                     globstar  shell  option  is  enabled,  and * is used in a
                     pathname expansion context, two adjacent  *s  used  as  a
                     single  pattern  will  match  all  files and zero or more
                     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, and the characters included
                     in the range, are determined by the  current  locale  and
                     the  values  of the LC_COLLATE or LC_ALL shell variables,
                     if set.  To  obtain  the  traditional  interpretation  of
                     range  expressions,  where [a-d] is equivalent to [abcd],
                     set value of the LC_ALL shell variable to  C,  or  enable
                     the  globasciiranges shell option.  A - may be matched by
                     including it as the first or last character in  the  set.
                     A ] may be matched by including it as the first character
                     in the set.

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

                     Within  [  and  ],  an equivalence class can be specified
                     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, the
       shell recognizes several extended pattern matching operators.   In  the
       following description, a pattern-list is a list of one or more patterns
       separated by a |.  Composite patterns may be formed using one  or  more
       of the following sub-patterns:

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

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

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

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

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


REDIRECTION

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

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

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

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

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

              ls > dirlist 2>&1

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

              ls 2>&1 > dirlist

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

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

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

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

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

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

       The general format for redirecting input is:

              [n]<word

   Redirecting Output
       Redirection  of  output  causes  the  file  whose name results from the
       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 part  of
       word  is  quoted, the delimiter is the result of quote removal on word,
       and the lines in the  here-document  are  not  expanded.   If  word  is
       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 tilde expansion, parameter and variable expansion,
       command substitution, arithmetic expansion, and quote  removal.   Path-
       name  expansion  and  word  splitting are not performed.  The result is
       supplied as a single string, with a newline appended, to the command on
       its standard input (or file descriptor n if n is specified).

   Duplicating File Descriptors
       The redirection operator

              [n]<&word

       is used to duplicate input file descriptors.  If word expands to one or
       more digits, the file descriptor denoted by n is made to be a  copy  of
       that  file  descriptor.   If  the  digits in word do not specify a file
       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, use a shell function (see FUNCTIONS below).

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

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

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


FUNCTIONS

       A shell function, defined  as  described  above  under  SHELL  GRAMMAR,
       stores  a  series  of commands for later execution.  When the name of a
       shell function is used as a simple command name, the list  of  commands
       associated with that function name is executed.  Functions are executed
       in the context of the current shell;  no  new  process  is  created  to
       interpret  them  (contrast  this with the execution of a shell script).
       When a function is executed, the arguments to the function  become  the
       positional parameters during its execution.  The special parameter # is
       updated to reflect the change.  Special parameter 0 is unchanged.   The
       first  element of the FUNCNAME variable is set to the name of the func-
       tion while the function is executing.

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

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

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

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

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

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

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

       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 child shell processes (those created when exe-
       cuting a separate shell invocation)  automatically  have  them  defined
       with the -f option to the export builtin.  A function definition may be
       deleted using the -f option to the unset builtin.

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


ARITHMETIC EVALUATION

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

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

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

       Integer constants follow the C language definition, without suffixes or
       character constants.  Constants with a leading  0  are  interpreted  as
       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, if a non-digit is required, the digits greater than 9 are
       represented by the lowercase letters, the uppercase letters, @, and  _,
       in  that  order.   If  base  is less than or equal to 36, lowercase and
       uppercase letters may be  used  interchangeably  to  represent  numbers
       between 10 and 35.

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


CONDITIONAL EXPRESSIONS

       Conditional  expressions  are  used  by the [[ compound command and the
       test and [ builtin commands to test file attributes and perform  string
       and  arithmetic  comparisons.   The test and [ commands determine their
       behavior based on the number of  arguments;  see  the  descriptions  of
       those commands for any other command-specific actions.

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

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

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

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

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

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

       string1 < string2
              True if string1 sorts before string2 lexicographically.

       string1 > string2
              True if string1 sorts after string2 lexicographically.

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


SIMPLE COMMAND EXPANSION

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

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

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

       3.     Redirections are performed as described above under REDIRECTION.

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

       If no command name results, the variable assignments affect the current
       shell  environment.   In  the case of such a command (one that consists
       only of assignment statements and redirections), assignment  statements
       are  performed before redirections.  Otherwise, the variables are added
       to the environment of the executed command and do not affect  the  cur-
       rent shell environment.  If any of the assignments attempts to assign a
       value to a readonly variable, an error occurs, and  the  command  exits
       with a non-zero status.

       If  no  command  name  results,  redirections are performed, but do not
       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
       in a separate execution environment with the original command  and  the
       original  command's arguments as its arguments, and the function's exit
       status becomes the exit status of that subshell.  If that  function  is
       not defined, the shell prints an error message and returns an exit sta-
       tus of 127.

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

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

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


COMMAND EXECUTION ENVIRONMENT

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

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

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

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

       o      current traps set by trap

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

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

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

       o      options enabled by shopt

       o      shell aliases defined with alias

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

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


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

       o      the current working directory

       o      the file creation mode mask

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

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

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

       A subshell is a copy of the shell process.

       Command  substitution, commands grouped with parentheses, and asynchro-
       nous commands are invoked in a subshell environment that is a duplicate
       of  the  shell  environment,  except that traps caught by the shell are
       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.

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

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


SIGNALS

       When bash is interactive, in the  absence  of  any  traps,  it  ignores
       SIGTERM (so that kill 0 does not kill an interactive shell), and SIGINT
       is caught and handled (so that the wait builtin is interruptible).   In
       all  cases,  bash  ignores  SIGQUIT.  If job control is in effect, bash
       ignores SIGTTIN, SIGTTOU, and SIGTSTP.

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

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

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

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

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

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

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

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


JOB CONTROL

       Job control refers to the ability to  selectively  stop  (suspend)  the
       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 ^Z, Control-Z) while a process is running causes that process to
       be  stopped  and  returns  control to bash.  Typing the delayed suspend
       character (typically ^Y, Control-Y) causes the process  to  be  stopped
       when  it  attempts  to  read input from the terminal, and control to be
       returned to bash.  The user may then manipulate the state of this  job,
       using  the  bg command to continue it in the background, the fg command
       to continue it in the foreground, or the kill command to kill it.  A ^Z
       takes effect immediately, and has the additional side effect of causing
       pending output and typeahead to be discarded.

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

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

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

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


PROMPTING

       When executing interactively, bash displays the primary prompt PS1 when
       it  is  ready  to  read a command, and the secondary prompt PS2 when it
       needs more input to complete a command.  Bash  displays  PS0  after  it
       reads  a  command  but  before  executing  it.   Bash  displays  PS4 as
       described above before tracing each  command  when  the  -x  option  is
       enabled.   Bash allows these prompt strings to be customized by insert-
       ing a number of backslash-escaped special characters that  are  decoded
       as follows:
              \a     an ASCII bell character (07)
              \d     the  date  in "Weekday Month Date" format (e.g., "Tue May
                     26")
              \D{format}
                     the format is passed to strftime(3)  and  the  result  is
                     inserted  into the prompt string; an empty format results
                     in a locale-specific time representation.  The braces are
                     required
              \e     an ASCII escape character (033)
              \h     the hostname up to the first `.'
              \H     the hostname
              \j     the number of jobs currently managed by the shell
              \l     the basename of the shell's terminal device name
              \n     newline
              \r     carriage return
              \s     the  name  of  the shell, the basename of $0 (the portion
                     following the final slash)
              \t     the current time in 24-hour HH:MM:SS format
              \T     the current time in 12-hour HH:MM:SS format
              \@     the current time in 12-hour am/pm format
              \A     the current time in 24-hour HH:MM format
              \u     the username of the current user
              \v     the version of bash (e.g., 2.00)
              \V     the release of bash, version + patch level (e.g., 2.00.0)
              \w     the  value  of  the PWD shell variable ($PWD), with $HOME
                     abbreviated  with  a  tilde  (uses  the  value   of   the
                     PROMPT_DIRTRIM variable)
              \W     the basename of $PWD, with $HOME abbreviated with a tilde
              \!     the history number of this command
              \#     the command number of this command
              \$     if the effective UID is 0, a #, otherwise a $
              \nnn   the character corresponding to the octal number nnn
              \\     a backslash
              \[     begin a sequence of non-printing characters, which  could
                     be  used  to  embed  a terminal control sequence into the
                     prompt
              \]     end a sequence of non-printing characters

       The command number and the history number are  usually  different:  the
       history  number of a command is its position in the history list, which
       may include commands  restored  from  the  history  file  (see  HISTORY
       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).   This  can  have  unwanted  side
       effects if escaped portions of the string appear within command substi-
       tution or contain characters special to word expansion.


READLINE

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

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

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

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

   Readline Initialization
       Readline  is  customized  by putting commands in an initialization file
       (the inputrc file).  The name of this file is taken from the  value  of
       the  INPUTRC  variable.   If  that  variable  is  unset, the default is
       ~/.inputrc.  If that file  does not exist or cannot be read, the  ulti-
       mate  default  is /etc/inputrc.  When a program which uses the readline
       library starts up, the initialization file is read, and the  key  bind-
       ings  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 $ indi-
       cate conditional constructs.  Other lines denote key bindings and vari-
       able settings.

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

       For example, placing

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

              set variable-name value
       or using the bind builtin command (see SHELL BUILTIN COMMANDS below).

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

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

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

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

              mode   The mode= form of the  $if  directive  is  used  to  test
                     whether  readline  is  in  emacs or vi mode.  This may be
                     used in conjunction with  the  set  keymap  command,  for
                     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.

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

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

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

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

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

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

              $include  /etc/inputrc

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

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

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

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

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

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

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

   Commands for Manipulating the History
       accept-line (Newline, Return)
              Accept the line regardless of where the cursor is.  If this line
              is  non-empty, add it to the history list according to the state
              of the HISTCONTROL variable.  If the line is a modified  history
              line, then restore the history line to its original state.
       previous-history (C-p)
              Fetch the previous command from the history list, moving back in
              the list.
       next-history (C-n)
              Fetch the next command from the history list, moving forward  in
              the list.
       beginning-of-history (M-<)
              Move to the first line in the history.
       end-of-history (M->)
              Move  to  the end of the input history, i.e., the line currently
              being entered.
       operate-and-get-next (C-o)
              Accept the current line for execution and fetch  the  next  line
              relative  to  the  current line from the history for editing.  A
              numeric argument, if supplied, specifies the  history  entry  to
              use instead of the current line.
       fetch-history
              With  a numeric argument, fetch that entry from the history list
              and make it the current line.  Without an argument, move back to
              the first entry in the history list.
       reverse-search-history (C-r)
              Search  backward  starting  at  the current line and moving `up'
              through the  history  as  necessary.   This  is  an  incremental
              search.
       forward-search-history (C-s)
              Search  forward  starting  at the current line and moving `down'
              through the  history  as  necessary.   This  is  an  incremental
              search.
       non-incremental-reverse-search-history (M-p)
              Search backward through the history starting at the current line
              using a non-incremental search for  a  string  supplied  by  the
              user.
       non-incremental-forward-search-history (M-n)
              Search  forward  through  the  history  using  a non-incremental
              search for a string supplied by the user.
       history-search-forward
              Search forward through the history for the string of  characters
              between  the start of the current line and the point.  This is a
              non-incremental search.
       history-search-backward
              Search backward through the history for the string of characters
              between  the start of the current line and the point.  This is a
              non-incremental search.
       history-substring-search-backward
              Search backward through the history for the string of characters
              between  the  start  of  the current line and the current cursor
              position (the point).  The search string may match anywhere in a
              history line.  This is a non-incremental search.
       history-substring-search-forward
              Search  forward through the history for the string of characters
              between the start of the current line and the point.  The search
              string  may  match  anywhere  in a history line.  This is a non-
              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.
       edit-and-execute-command (C-x C-e)
              Invoke  an  editor  on the current command line, and execute the
              result as shell commands.   Bash  attempts  to  invoke  $VISUAL,
              $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, 1, !, ...)
              Insert the character typed.
       transpose-chars (C-t)
              Drag the character before point forward over  the  character  at
              point,  moving point forward as well.  If point is at the end of
              the line, then this transposes the two characters before  point.
              Negative arguments have no effect.
       transpose-words (M-t)
              Drag  the  word  before  point past the word after point, moving
              point over that word as well.  If point is at  the  end  of  the
              line, this transposes the last two words on the line.
       upcase-word (M-u)
              Uppercase  the  current  (or  following)  word.  With a negative
              argument, uppercase the previous word, but do not move point.
       downcase-word (M-l)
              Lowercase the current (or  following)  word.   With  a  negative
              argument, lowercase the previous word, but do not move point.
       capitalize-word (M-c)
              Capitalize  the  current  (or  following) word.  With a negative
              argument, capitalize the previous word, but do not move point.
       overwrite-mode
              Toggle overwrite mode.  With an explicit positive numeric  argu-
              ment, switches to overwrite mode.  With an explicit non-positive
              numeric argument, switches to insert mode.  This command affects
              only  emacs mode; vi mode does overwrite differently.  Each call
              to readline() starts in insert mode.  In overwrite mode, charac-
              ters  bound to self-insert replace the text at point rather than
              pushing the text  to  the  right.   Characters  bound  to  back-
              ward-delete-char  replace  the  character  before  point  with a
              space.  By default, this command is unbound.

   Killing and Yanking
       kill-line (C-k)
              Kill the text from point to the end of the line.
       backward-kill-line (C-x Rubout)
              Kill backward to the beginning of the line.
       unix-line-discard (C-u)
              Kill backward from point to the  beginning  of  the  line.   The
              killed text is saved on the kill-ring.
       kill-whole-line
              Kill  all  characters on the current line, no matter where point
              is.
       kill-word (M-d)
              Kill from point to the end of the current word,  or  if  between
              words,  to  the  end  of the next word.  Word boundaries are the
              same as those used by forward-word.
       backward-kill-word (M-Rubout)
              Kill the word behind point.  Word boundaries  are  the  same  as
              those used by backward-word.
       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-lowercase-version (M-A, M-B, M-x, ...)
              If the metafied character x is uppercase, run the  command  that
              is bound to the corresponding metafied lowercase character.  The
              behavior is undefined if x is already lowercase.
       prefix-meta (ESC)
              Metafy the next character typed.  ESC f is equivalent to Meta-f.
       undo (C-_, C-x C-u)
              Incremental undo, separately remembered for each line.
       revert-line (M-r)
              Undo  all changes made to this line.  This is like executing the
              undo command enough times to return  the  line  to  its  initial
              state.
       tilde-expand (M-&)
              Perform tilde expansion on the current word.
       set-mark (C-@, M-<space>)
              Set  the  mark to the point.  If a numeric argument is supplied,
              the mark is set to that position.
       exchange-point-and-mark (C-x C-x)
              Swap the point with the mark.  The current  cursor  position  is
              set  to the saved position, and the old cursor position is saved
              as the mark.
       character-search (C-])
              A character is read and point is moved to the next occurrence of
              that  character.   A  negative  argument  searches  for previous
              occurrences.
       character-search-backward (M-C-])
              A character is read and point is moved to  the  previous  occur-
              rence  of that character.  A negative argument searches for sub-
              sequent occurrences.
       skip-csi-sequence
              Read enough characters to consume a multi-key sequence  such  as
              those  defined for keys like Home and End.  Such sequences begin
              with a Control Sequence Indicator (CSI), usually ESC-[.  If this
              sequence  is  bound  to "\[", keys producing such sequences will
              have no effect unless explicitly bound to  a  readline  command,
              instead  of  inserting stray characters into the editing buffer.
              This is unbound by default, but usually bound to ESC-[.
       insert-comment (M-#)
              Without a numeric argument,  the  value  of  the  readline  com-
              ment-begin  variable is inserted at the beginning of the current
              line.  If a numeric argument is supplied, this command acts as a
              toggle:  if  the  characters at the beginning of the line do not
              match the value of comment-begin, the value is inserted,  other-
              wise the characters in comment-begin are deleted from the begin-
              ning of the line.  In either case, the line is accepted as if  a
              newline  had  been  typed.   The  default value of comment-begin
              causes this command to make the current line  a  shell  comment.
              If  a  numeric  argument  causes  the  comment  character  to be
              removed, the line will be executed by the shell.
       spell-correct-word (C-x s)
              Perform spelling correction on the current word, treating it  as
              a  directory  or  filename, in the same way as the cdspell shell
              option.   Word  boundaries  are  the  same  as  those  used   by
              shell-forward-word.
       glob-complete-word (M-g)
              The  word  before  point  is  treated  as a pattern for pathname
              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  pro-
       grammable completion facilities are invoked.

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

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

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

       Any completions specified by a pathname expansion  pattern  to  the  -G
       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  ($1)  is  the  name of the command whose arguments are
       being completed, the second argument ($2) is the word being  completed,
       and  the  third argument ($3) is the word preceding the word being com-
       pleted on the current command line.  No filtering of the generated com-
       pletions against the word being completed is performed; the function or
       command has complete freedom in generating the matches.

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

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

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

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

       If  the previously-applied actions do not generate any matches, and the
       -o dirnames option was supplied  to  complete  when  the  compspec  was
       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 fol-
       lowing history line.  These timestamps are optionally displayed depend-
       ing  on  the  value  of the HISTTIMEFORMAT variable.  When a shell with
       history enabled exits, the last $HISTSIZE lines  are  copied  from  the
       history  list  to $HISTFILE.  If the histappend shell option is enabled
       (see the description of shopt under SHELL BUILTIN COMMANDS below),  the
       lines  are  appended to the history file, otherwise the history file is
       overwritten.   If  HISTFILE  is  unset,  or  if  the  history  file  is
       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, and is performed on each
       line  individually  without  taking  quoting  on  previous  lines  into
       account.  It takes place in two parts.  The first is to determine which
       line from the history list to use during substitution.  The  second  is
       to  select  portions  of  that line for inclusion into the current one.
       The line selected from the history is the event, and  the  portions  of
       that  line that are acted upon are words.  Various modifiers are avail-
       able to manipulate the selected words.  The line is broken  into  words
       in  the same fashion as when reading input, so that several metacharac-
       ter-separated words surrounded by quotes are considered one word.  His-
       tory  expansions are introduced by the appearance of the history expan-
       sion character, which is ! by default.  Only backslash (\)  and  single
       quotes  can  quote  the  history  expansion  character, but the history
       expansion character is also treated as quoted if  it  immediately  pre-
       cedes 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.   If
              string  is  missing,  the  string from the most recent search is
              used; it is an error if there is no previous search string.
       ^string1^string2^
              Quick substitution.   Repeat  the  previous  command,  replacing
              string1  with  string2.  Equivalent to ``!!:s^string1^string2^''
              (see Modifiers below).
       !#     The entire command line typed so far.

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

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

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

   Modifiers
       After  the optional word designator, there may appear a sequence of one
       or more of the following modifiers, each preceded by a `:'.  These mod-
       ify, or edit, the word or words selected from the history event.

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


SHELL BUILTIN COMMANDS

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

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

       alias [-p] [name[=value] ...]
              Alias with no arguments or with the -p option prints the list of
              aliases in the form alias name=value on standard  output.   When
              arguments  are supplied, an alias is defined for each name whose
              value is given.  A trailing space in value causes the next  word
              to be checked for alias substitution when the alias is expanded.
              For each name in the argument list for which no  value  is  sup-
              plied,  the  name  and  value  of  the  alias is printed.  Alias
              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
       bind readline-command-line
              Display current readline key and function bindings, bind  a  key
              sequence  to  a  readline  function  or macro, or set a readline
              variable.  Each non-option argument is a  command  as  it  would
              appear  in  a readline initialization file such as .inputrc, but
              each binding or command must be passed as a  separate  argument;
              e.g.,  '"\C-x\C-r":  re-read-init-file'.   Options, if supplied,
              have the following meanings:
              -m keymap
                     Use keymap as the keymap to be affected by the subsequent
                     bindings.  Acceptable keymap names are emacs, emacs-stan-
                     dard, emacs-meta, emacs-ctlx,  vi,  vi-move,  vi-command,
                     and  vi-insert.   vi is equivalent to vi-command (vi-move
                     is also a synonym); emacs is  equivalent  to  emacs-stan-
                     dard.
              -l     List the names of all readline functions.
              -p     Display  readline  function  names and bindings in such a
                     way that they can be re-read.
              -P     List current readline function names and bindings.
              -s     Display readline key sequences bound to  macros  and  the
                     strings  they  output  in such a way that they can be re-
                     read.
              -S     Display readline key sequences bound to  macros  and  the
                     strings they output.
              -v     Display  readline variable names and values in such a way
                     that they can be re-read.
              -V     List current readline variable names and values.
              -f filename
                     Read key bindings from filename.
              -q function
                     Query about which keys invoke the named function.
              -u function
                     Unbind all keys bound to the named function.
              -r keyseq
                     Remove any current binding for keyseq.
              -x keyseq:shell-command
                     Cause shell-command to be  executed  whenever  keyseq  is
                     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 and READLINE_MARK
                     variables to the current location of the insertion  point
                     and  the  saved insertion point (the mark), respectively.
                     The shell assigns any numeric argument the user  supplied
                     to the READLINE_ARGUMENT variable.  If there was no argu-
                     ment, that variable is not set.  If the executed  command
                     changes   the   value  of  any  of  READLINE_LINE,  READ-
                     LINE_POINT, or READLINE_MARK, those new  values  will  be
                     reflected in the editing state.
              -X     List  all  key  sequences bound to shell commands and the
                     associated commands in a format that  can  be  reused  as
                     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.  The  vari-
              able CDPATH defines the search path for the directory containing
              dir: each directory name in CDPATH is searched for dir.   Alter-
              native  directory  names in CDPATH are separated by a colon (:).
              A null directory name in CDPATH  is  the  same  as  the  current
              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 sym-
              bolic links to be followed by resolving the link after  process-
              ing  instances  of  .. in dir.  If .. appears in dir, it is pro-
              cessed by removing the immediately previous  pathname  component
              from  dir,  back  to a slash or the beginning of dir.  If the -e
              option is supplied with -P, and the  current  working  directory
              cannot  be  successfully determined after a successful directory
              change, cd will return an unsuccessful status.  On systems  that
              support it, the -@ option presents the extended attributes asso-
              ciated with a file as a directory.  An argument  of  -  is  con-
              verted  to $OLDPWD before the directory change is attempted.  If
              a non-empty directory name from CDPATH is used, or if -  is  the
              first  argument,  and  the  directory  change is successful, the
              absolute pathname of the new working directory is written to the
              standard output.  If the directory change is successful, cd sets
              the value of the PWD environment variable to the  new  directory
              name,  and  sets the OLDPWD environment variable to the value of
              the current working directory before  the  change.   The  return
              value  is  true if the directory was successfully changed; false
              otherwise.

       command [-pVv] command [arg ...]
              Run command with args  suppressing  the  normal  shell  function
              lookup.  Only builtin commands or commands found in the PATH are
              executed.  If the -p option is given, the search for command  is
              performed  using  a default value for PATH that is guaranteed to
              find all of the standard utilities.  If  either  the  -V  or  -v
              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 pro-
              grammable completion code had generated  them  directly  from  a
              completion specification with the same flags.  If word is speci-
              fied, only those completions matching word will be displayed.

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

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

              The process of applying  these  completion  specifications  when
              word  completion  is  attempted  is  described  above under Pro-
              grammable 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.  Arguments
                      are passed as with the -F option.
              -F function
                      The shell function function is executed in  the  current
                      shell  environment.   When the function is executed, the
                      first argument ($1) is the name  of  the  command  whose
                      arguments  are being completed, the second argument ($2)
                      is the word being completed, and the third argument ($3)
                      is  the  word  preceding the word being completed on the
                      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.  Shell quoting is honored within wordlist,
                      in order to provide a mechanism for the words to contain
                      shell  metacharacters or characters in the value of IFS.
                      The possible completions are the members of  the  resul-
                      tant list which match the word being completed.
              -X filterpat
                      filterpat  is  a pattern as used for pathname expansion.
                      It is applied to the list of possible completions gener-
                      ated  by  the  preceding options and arguments, and each
                      completion matching filterpat is removed from the  list.
                      A  leading  !  in filterpat negates the pattern; in this
                      case, any completion not matching filterpat is  removed.

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

       compopt [-o option] [-DEI] [+o option] [name]
              Modify  completion  options  for  each  name  according  to  the
              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  other  supplied
              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 other
              supplied options should apply to ``empty''  command  completion;
              that  is,  completion  attempted on a blank line.  The -I option
              indicates that other supplied options should apply to completion
              on  the initial non-assignment word on the line, or after a com-
              mand delimiter such as ; or |, which  is  usually  command  name
              completion.

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

       continue [n]
              Resume the next iteration of the enclosing for, while, until, or
              select loop.  If n is specified, resume  at  the  nth  enclosing
              loop.   n  must  be  >=  1.   If n is greater than the number of
              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 [-aAfFgiIlnrtux] [-p] [name[=value] ...]
       typeset [-aAfFgiIlnrtux] [-p] [name[=value] ...]
              Declare variables and/or give them attributes.  If no names  are
              given  then display the values of variables.  The -p option will
              display the attributes and values of each name.  When -p is used
              with  name  arguments, additional options, other than -f and -F,
              are ignored.  When -p is supplied  without  name  arguments,  it
              will  display  the attributes and values of all variables having
              the attributes specified by the additional options.  If no other
              options   are   supplied  with  -p,  declare  will  display  the
              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  -I
              option  causes local variables to inherit the attributes (except
              the nameref attribute) and value of any existing  variable  with
              the  same  name at a surrounding scope.  If there is no existing
              variable, the local variable is initially unset.  The  following
              options  can  be  used  to restrict output to variables with the
              specified attribute or to give variables attributes:
              -a     Each name  is  an  indexed  array  variable  (see  Arrays
                     above).
              -A     Each  name  is  an associative array variable (see Arrays
                     above).
              -f     Use function names only.
              -i     The variable is treated as an integer; arithmetic evalua-
                     tion  (see ARITHMETIC EVALUATION above) is performed when
                     the variable is assigned a value.
              -l     When the variable is assigned  a  value,  all  upper-case
                     characters  are  converted to lower-case.  The upper-case
                     attribute is disabled.
              -n     Give each name the nameref attribute, making  it  a  name
                     reference  to  another  variable.  That other variable is
                     defined by the value of name.   All  references,  assign-
                     ments,  and attribute modifications to name, except those
                     using or changing the -n attribute itself, are  performed
                     on  the variable referenced by name's value.  The nameref
                     attribute cannot be applied to array variables.
              -r     Make names readonly.  These names cannot then be assigned
                     values by subsequent assignment statements or unset.
              -t     Give  each  name  the  trace attribute.  Traced functions
                     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 and +A may not be used to  destroy  array
              variables  and  +r will not remove the readonly attribute.  When
              used in a function, declare and typeset make each name local, as
              with  the local command, unless the -g option is supplied.  If a
              variable name is followed by =value, the value of  the  variable
              is  set  to value.  When using -a or -A and the compound assign-
              ment syntax to create array variables, additional attributes  do
              not  take effect until subsequent assignments.  The return value
              is 0 unless an invalid option is encountered, an attempt is made
              to define a function using ``-f foo=bar'', an attempt is made to
              assign a value to a readonly variable, an  attempt  is  made  to
              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 ... | pid ... ]
              Without options, remove each jobspec from the  table  of  active
              jobs.   If jobspec is not present, and neither the -a nor the -r
              option is supplied, the current job is used.  If the  -h  option
              is  given,  each  jobspec  is not removed from the table, but is
              marked so that SIGHUP is not  sent  to  the  job  if  the  shell
              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
              \0nnn  the eight-bit character whose value is  the  octal  value
                     nnn (zero to three octal digits)
              \xHH   the  eight-bit  character  whose value is the hexadecimal
                     value HH (one or two hex digits)
              \uHHHH the Unicode (ISO/IEC 10646) character whose value is  the
                     hexadecimal value HHHH (one to four hex digits)
              \UHHHHHHHH
                     the  Unicode (ISO/IEC 10646) character whose value is the
                     hexadecimal value HHHHHHHH (one to eight hex digits)

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

       eval [arg ...]
              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.  A subshell exits unconditionally if
              exec fails.  If command is not specified, any redirections  take
              effect  in  the  current  shell, and the return status is 0.  If
              there is a redirection error, the return status is 1.

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

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

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

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

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

              If the first form is used, the  return  value  is  0  unless  an
              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 [arg ...]
              getopts  is used by shell procedures to parse positional parame-
              ters.  optstring contains the option  characters  to  be  recog-
              nized;  if  a  character  is  followed by a colon, the option is
              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 supplied  as  arg  values,  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 -d start-end
       history -anrw [filename]
       history -p arg [arg ...]
       history -s arg [arg ...]
              With no options, display the command history list with line num-
              bers.  Lines listed with a * have been modified.  An argument of
              n lists only the last n lines.  If the shell variable  HISTTIME-
              FORMAT  is  set  and not null, it is used as a format string for
              strftime(3) to display the time stamp associated with each  dis-
              played  history  entry.  No intervening blank is printed between
              the formatted time stamp and the history line.  If  filename  is
              supplied,  it  is  used as the name of the history file; if not,
              the value of HISTFILE is used.  Options, if supplied,  have  the
              following meanings:
              -c     Clear the history list by deleting all the entries.
              -d offset
                     Delete  the  history entry at position offset.  If offset
                     is negative, it is interpreted as relative to one greater
                     than the last history position, so negative indices count
                     back from the end of the history,  and  an  index  of  -1
                     refers to the current history -d command.
              -d start-end
                     Delete  the  range  of  history entries between positions
                     start and end, inclusive.  Positive and  negative  values
                     for start and end are interpreted as described above.
              -a     Append  the  ``new''  history  lines to the history file.
                     These are history lines entered since  the  beginning  of
                     the current bash session, but not already appended to the
                     history file.
              -n     Read the history lines not already read from the  history
                     file  into  the  current  history  list.  These are lines
                     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 following history entry.  The return value is
              0 unless an invalid option is encountered, an error occurs while
              reading  or writing the history file, an invalid offset or range
              is supplied as an argument to -d, or the history expansion  sup-
              plied as an argument to -p fails.

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

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

              If the -x option is supplied, jobs replaces any jobspec found in
              command or args with the corresponding  process  group  ID,  and
              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.
              The restore is effected as if a series of set commands were exe-
              cuted to restore the values that were in place before the  func-
              tion.   With no operands, local writes a list of local variables
              to the standard output.  It is an error to use  local  when  not
              within  a function.  The return status is 0 unless local is used
              outside a function, an invalid name is supplied, or  name  is  a
              readonly variable.

       logout Exit a login shell.

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

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

              If  not  supplied  with  an  explicit origin, mapfile will clear
              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 [-n] [+n] [-n]
              Removes entries from the directory stack.  The elements are num-
              bered  from  0  starting  at the first directory listed by dirs.
              With no arguments, popd  removes  the  top  directory  from  the
              stack, and changes to the new top directory.  Arguments, if sup-
              plied, have the following meanings:
              -n     Suppresses the normal change of directory  when  removing
                     directories  from  the  stack,  so that only the stack is
                     manipulated.
              +n     Removes the nth entry counting from the left of the  list
                     shown  by  dirs, starting with zero, from the stack.  For
                     example: ``popd +0'' removes the first directory,  ``popd
                     +1'' the second.
              -n     Removes the nth entry counting from the right of the list
                     shown by dirs, starting with zero.  For  example:  ``popd
                     -0''  removes the last directory, ``popd -1'' the next to
                     last.

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

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

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

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

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

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

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

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

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

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

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

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

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

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

       readonly [-aAf] [-p] [name[=word] ...]
              The given names are marked readonly; the values of  these  names
              may  not  be changed by subsequent assignment.  If the -f option
              is supplied, the functions corresponding to  the  names  are  so
              marked.   The  -a  option  restricts  the  variables  to indexed
              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] [+o option-name] [--] [-] [arg ...]
              Without  options, display the name and value of each shell vari-
              able in a format that can be reused  as  input  for  setting  or
              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
              $1,  $2,  ...   $n.   Options,  if specified, have the following
              meanings:
              -a      Each variable or function that is created or modified is
                      given  the export attribute and marked for export to the
                      environment of subsequent commands.
              -b      Report the status of terminated background jobs  immedi-
                      ately, rather than before the next primary prompt.  This
                      is effective only when job control is enabled.
              -e      Exit immediately if a pipeline (which may consist  of  a
                      single  simple  command),  a list, or a compound command
                      (see SHELL GRAMMAR above), exits with a non-zero status.
                      The  shell  does  not  exit if the command that fails is
                      part of the command list immediately following  a  while
                      or  until  keyword, part of the test following the if or
                      elif reserved words, part of any command executed  in  a
                      &&  or || list except the command following the final &&
                      or ||, any command in a pipeline but the last, or if the
                      command's  return  value is being inverted with !.  If a
                      compound command other than a subshell  returns  a  non-
                      zero  status because a command failed while -e was being
                      ignored, the shell does not exit.  A  trap  on  ERR,  if
                      set,  is  executed  before the shell exits.  This option
                      applies to the shell environment and each subshell envi-
                      ronment  separately  (see  COMMAND EXECUTION ENVIRONMENT
                      above), and may cause subshells to exit before executing
                      all the commands in the subshell.

                      If  a  compound  command or shell function executes in a
                      context where -e is being ignored, none of the  commands
                      executed  within  the  compound command or function body
                      will be affected by the -e setting, even if  -e  is  set
                      and  a  command returns a failure status.  If a compound
                      command or shell function sets -e while executing  in  a
                      context  where -e is ignored, that setting will not have
                      any effect until the compound  command  or  the  command
                      containing the function call completes.
              -f      Disable pathname expansion.
              -h      Remember  the location of commands as they are looked up
                      for execution.  This is enabled by default.
              -k      All arguments in the form of assignment  statements  are
                      placed  in the environment for a command, not just those
                      that precede the command name.
              -m      Monitor mode.  Job control is enabled.  This  option  is
                      on  by  default  for  interactive shells on systems that
                      support it (see JOB CONTROL above).  All  processes  run
                      in a separate process group.  When a background job com-
                      pletes, the shell prints a line containing its exit sta-
                      tus.
              -n      Read commands but do not execute them.  This may be used
                      to check a shell script  for  syntax  errors.   This  is
                      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.
              -r      Enable restricted shell mode.   This  option  cannot  be
                      unset once it has been set.
              -t      Exit after reading and executing one command.
              -u      Treat unset variables and parameters other than the spe-
                      cial parameters "@" and "*",  or  array  variables  sub-
                      scripted  with  "@"  or "*", as an error when performing
                      parameter expansion.  If expansion is  attempted  on  an
                      unset  variable  or parameter, the shell prints an error
                      message, and, if not interactive, exits with a  non-zero
                      status.
              -v      Print shell input lines as they are read.
              -x      After  expanding  each simple command, for command, case
                      command, select command, or arithmetic for command, dis-
                      play  the expanded value of PS4, followed by the command
                      and its expanded arguments or associated word list.
              -B      The shell performs brace expansion (see Brace  Expansion
                      above).  This is on by default.
              -C      If  set,  bash  does not overwrite an existing file with
                      the >, >&, and <> redirection operators.   This  may  be
                      overridden when creating output files by using the redi-
                      rection operator >| instead of >.
              -E      If set, any trap on ERR is inherited by shell functions,
                      command  substitutions,  and commands executed in a sub-
                      shell environment.  The ERR trap is normally not  inher-
                      ited in such cases.
              -H      Enable !  style history substitution.  This option is on
                      by default when the shell is interactive.
              -P      If set, the shell does not resolve symbolic  links  when
                      executing  commands  such  as cd that change the current
                      working  directory.   It  uses  the  physical  directory
                      structure instead.  By default, bash follows the logical
                      chain of  directories  when  performing  commands  which
                      change the current directory.
              -T      If  set,  any traps on DEBUG and RETURN are inherited by
                      shell functions,  command  substitutions,  and  commands
                      executed  in  a  subshell  environment.   The  DEBUG and
                      RETURN traps are normally not inherited in such cases.
              --      If no arguments follow this option, then the  positional
                      parameters are unset.  Otherwise, the positional parame-
                      ters are set to the args, even if  some  of  them  begin
                      with a -.
              -       Signal  the  end of options, cause all remaining args to
                      be assigned to the positional parameters.  The -x and -v
                      options are turned off.  If there are no args, the posi-
                      tional parameters remain unchanged.

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

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

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

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

              complete_fullquote
                      If set, bash quotes all shell  metacharacters  in  file-
                      names  and  directory  names when performing completion.
                      If not set, bash removes metacharacters such as the dol-
                      lar  sign from the set of characters that will be quoted
                      in completed filenames when these metacharacters  appear
                      in  shell  variable references in words to be completed.
                      This means that dollar  signs  in  variable  names  that
                      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
                      buffer.   If not set, bash attempts to preserve what the
                      user typed.

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

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

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

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

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

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

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

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

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

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

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

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

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

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

              force_fignore
                      If  set,  the  suffixes  specified  by the FIGNORE shell
                      variable cause words to be ignored when performing  word
                      completion even if the ignored words are the only possi-
                      ble  completions.   See  SHELL  VARIABLES  above  for  a
                      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 b will  not  col-
                      late  between  A  and  B,  and upper-case and lower-case
                      ASCII characters will collate together.

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

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

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

              histappend
                      If set, the history list is appended to the  file  named
                      by  the  value  of  the HISTFILE variable when the shell
                      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.

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

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

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

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

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

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

              login_shell
                      The shell sets this option if it is started as  a  login
                      shell  (see  INVOCATION  above).   The  value may not be
                      changed.

              mailwarn
                      If set, and a file that bash is checking  for  mail  has
                      been  accessed  since  the last time it was checked, the
                      message ``The mail in mailfile has been read''  is  dis-
                      played.

              no_empty_cmd_completion
                      If  set,  and  readline  is  being  used,  bash will not
                      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.

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

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

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

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

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

              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.

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

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

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

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

              Expressions may  be  combined  using  the  following  operators,
              listed  in  decreasing  order  of  precedence.   The  evaluation
              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 -a expr2
                     True if both expr1 and expr2 are true.
              expr1 -o expr2
                     True if either expr1 or expr2 is true.

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

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

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

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

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

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

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

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

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

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


SHELL COMPATIBILITY MODE

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

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

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

       Bash-4.3 introduced a  new  shell  variable:  BASH_COMPAT.   The  value
       assigned  to  this  variable  (a decimal version number like 4.2, or an
       integer corresponding to the compatNN option, like 42)  determines  the
       compatibility level.

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

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

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

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

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

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

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

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

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

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

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

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


RESTRICTED SHELL

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

       o      changing directories with cd

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

       o      specifying command names containing /

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

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

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

       o      importing function definitions from  the  shell  environment  at
              startup

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

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

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

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

       o      using  the  enable  builtin  command  to  enable  disabled shell
              builtins

       o      specifying the -p option to the command builtin command

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

       These restrictions are enforced after any startup files are read.

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


SEE ALSO

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


FILES

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


AUTHORS

       Brian Fox, Free Software Foundation
       bfox@gnu.org

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


BUG REPORTS

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

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

       ALL bug reports should include:

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

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

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


BUGS

       It's too big and too slow.

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

       Aliases are confusing in some uses.

       Shell builtin commands and functions are not stoppable/restartable.

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

       Array variables may not (yet) be exported.

       There may be only one active coprocess at a time.



GNU Bash 5.2                   2022 September 19                       bash(1)

bash 5.2.9 - Generated Fri Nov 11 05:33:00 CST 2022
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