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 BASH(1)                        GNU Bash 4.3                         BASH(1)
                               2014 February 2



 NAME
      bash - GNU Bourne-Again SHell

 SYNOPSIS
      bash [options] [command_string | file]

 COPYRIGHT
      Bash is Copyright (C) 1989-2013 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
      incorporates useful features from the Korn and C shells (ksh and csh).

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

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

      -c        If the -c option is present, then commands are read from the
                first non-option argument command_string.  If there are
                arguments after the command_string, they are assigned to the
                positional parameters, starting with $0.
      -i        If the -i option is present, the shell is interactive.
      -l        Make bash act as if it had been invoked as a login shell
                (see INVOCATION below).
      -r        If the -r option is present, the shell becomes restricted
                (see RESTRICTED SHELL below).
      -s        If the -s option is present, or if no arguments remain after
                option processing, then commands are read from the standard
                input.  This option allows the positional parameters to be
                set when invoking an interactive shell.
      -D        A list of all double-quoted strings preceded by $ is printed
                on the standard output.  These are the strings that are
                subject 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.



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      --        A -- signals the end of options and disables further option
                processing.  Any arguments after the -- are treated as
                filenames 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
           (portable object) file format.
      --dump-strings
           Equivalent to -D.
      --help
           Display a usage message on standard output and exit successfully.
      --init-file file
      --rcfile file
           Execute commands from file instead of the standard personal
           initialization 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.





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

      --verbose
           Equivalent to  -v.

      --version
           Show version information for this instance of bash on the
           standard 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
      parameters are set to the remaining arguments.  Bash reads and
      executes commands from this file, then exits.  Bash's exit status is
      the exit status of the last command executed in the script.  If no
      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 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
      Expansion in the EXPANSION section.

      When bash is invoked as an interactive login shell, or as a non-
      interactive shell with the --login option, it first reads and executes
      commands 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 a login shell exits, 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



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      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 command were executed:

           if [ -n "$BASH_ENV" ]; then . "$BASH_ENV"; fi
      but the value of the PATH variable is not used to search for the
      filename.

      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
      interactive login shell, or a non-interactive shell with the --login
      option, it first attempts to read and execute commands from
      /etc/profile and ~/.profile, in that order.  The --noprofile option
      may be used to 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 execute commands from any other startup files, the
      --rcfile option has no effect.  A non-interactive shell invoked with
      the name sh does not attempt to read any other startup files. When
      invoked as sh, bash enters posix mode after the startup files are
      read.

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

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

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



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      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
      document.
      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
           underscores, and beginning with an alphabetic character or an
           underscore.  Also referred to as an identifier.
      metacharacter
           A character that, when unquoted, separates words.  One of the
           following:
           |  & ; ( ) < > space tab
      control operator
           A token that performs a control function.  It is one of the
           following symbols:
           || & && ; ;; ( ) | |& <newline>

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

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

 SHELL GRAMMAR
    Simple Commands
      A simple command is a sequence of optional variable assignments
      followed by blank-separated words and redirections, and terminated by
      a control operator.  The first word specifies the command to be
      executed, and is passed as argument zero.  The remaining words are
      passed as arguments to the invoked command.

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

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

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

      The standard output of command is connected via a pipe to the standard
      input of command2.  This connection is performed before any



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

      The return status of a pipeline is the exit status of the last
      command, unless the pipefail option is enabled.  If pipefail is
      enabled, the pipeline's return status is the value of the last
      (rightmost) command to exit with a non-zero status, or zero if all
      commands exit successfully.  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
      recognize time as a reserved word if the next token begins with a `-'.
      The TIMEFORMAT variable may be set to a format string that specifies
      how the timing information should be displayed; see the description of
      TIMEFORMAT under Shell Variables below.

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

      Each command in a pipeline is executed as a separate process (i.e., in
      a subshell).

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

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

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

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




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

           command1 && command2

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

      An OR list has the form

           command1 || command2

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

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

      (list)
           list is executed in a subshell environment (see COMMAND EXECUTION
           ENVIRONMENT below).  Variable 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
           expression is non-zero, the return status is 0; otherwise the
           return status is 1.  This is exactly equivalent to let
           "expression".

      [[ expression ]]
           Return a status of 0 or 1 depending on the evaluation of the
           conditional expression expression.  Expressions are composed of
           the primaries described below under CONDITIONAL EXPRESSIONS.
           Word splitting and pathname expansion are not performed on the



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           words between the [[ and ]]; tilde expansion, parameter and
           variable expansion, arithmetic expansion, command substitution,
           process substitution, and quote removal are performed.
           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 extglob
           shell option were enabled.  The = operator is equivalent to ==.
           If the shell option nocasematch is enabled, the match is
           performed without regard to the case of alphabetic characters.
           The return value is 0 if the string matches (==) or does not
           match (!=) the pattern, and 1 otherwise.  Any part of the pattern
           may be quoted to force the quoted portion to be matched as a
           string.

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

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

           ( expression )
                Returns the value of expression.  This may be used to
                override the normal precedence of operators.
           ! expression
                True if expression is false.




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           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 omitted,
           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
           expressions is invalid.

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

      case word in [ [(] pattern [ | pattern ] ... ) list ;; ] ... esac
           A case command first expands word, and tries to match it against
           each pattern in turn, using the same matching rules as for
           pathname expansion (see Pathname Expansion below).  The word is
           expanded using tilde expansion, parameter and variable expansion,
           arithmetic substitution, command substitution, process



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           substitution and quote removal.  Each pattern examined is
           expanded using tilde expansion, parameter and variable expansion,
           arithmetic substitution, command substitution, and process
           substitution.  If the shell option nocasematch 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 patterns.  Using ;;& in place of ;; causes the shell
           to test the next pattern list in the statement, if any, and
           execute any associated list on a successful match.  The exit
           status is zero if no pattern matches.  Otherwise, it is the exit
           status of the last command executed in list.

      if list; then list; [ elif list; then list; ] ... [ else list; ] fi
           The if list is executed.  If its exit status is zero, the then
           list is executed.  Otherwise, each elif list is executed in turn,
           and if its exit status is zero, the corresponding then list is
           executed and the command completes.  Otherwise, the else list is
           executed, if present.  The exit status is the exit status 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
           executed.

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

      The format for a coprocess is:

           coproc [NAME] command [redirections]

      This creates a coprocess named NAME.  If NAME is not supplied, the
      default name is COPROC.  NAME must not be supplied if command is a
      simple command (see above); otherwise, it is interpreted as the first
      word of the simple command.  When the coprocess is executed, the shell
      creates an array variable (see Arrays below) named NAME in the context
      of the executing shell.  The standard output of command is connected
      via a pipe to a file descriptor in the executing shell, and that file



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      descriptor is assigned to NAME[0].  The standard input of command is
      connected via a pipe to a file descriptor in the executing shell, and
      that file descriptor is assigned to NAME[1].  This pipe is established
      before any redirections specified by the command (see REDIRECTION
      below).  The file descriptors can be utilized as arguments to shell
      commands and redirections using standard word expansions.  The file
      descriptors are not available in subshells.  The process ID of the
      shell spawned to execute the coprocess is available as the value of
      the variable 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:

      name () compound-command [redirection]
      function name [()] compound-command [redirection]
           This defines a function named name.  The reserved word function
           is optional.  If the function reserved word is supplied, the
           parentheses are optional.  The body of the function is the
           compound 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.
           compound-command is executed whenever name is specified as the
           name of a simple command.  When in posix mode, name may not be
           the name of one of the POSIX special builtins.  Any redirections
           (see REDIRECTION below) specified when a function is defined are
           performed when the function is executed.  The exit status of a
           function definition is zero unless a syntax error occurs or a
           readonly function with the same name already exists.  When
           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
      interactive_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
      interactive shells.

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



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      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
      HISTORY EXPANSION below), the history expansion character, usually !,
      must be quoted to prevent history expansion.

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

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

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

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

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

      Words of the form $string are treated specially.  The word expands to
      string, with backslash-escaped characters replaced as specified by the
      ANSI C standard.  Backslash escape sequences, if present, are decoded
      as follows:
           \a   alert (bell)
           \b   backspace
           \e
           \E   an escape character
           \f   form feed
           \n   new line
           \r   carriage return
           \t   horizontal tab
           \v   vertical tab
           \\   backslash




                                   - 12 -          Formatted:  June 25, 2018






 BASH(1)                        GNU Bash 4.3                         BASH(1)
                               2014 February 2



           \    single quote
           \    double quote
           \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)
           \uHHHH
                the Unicode (ISO/IEC 10646) character whose value is the
                hexadecimal value HHHH (one to four hex digits)
           \UHHHHHHHH
                the Unicode (ISO/IEC 10646) character whose value is the
                hexadecimal value HHHHHHHH (one to eight hex digits)
           \cx  a control-x character
      The expanded result is single-quoted, as if the dollar sign had not
      been present.

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

 PARAMETERS
      A parameter is an entity that stores values.  It can be a name, a
      number, or one of the special characters listed below under Special
      Parameters.  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,
      command substitution, arithmetic expansion, and quote removal (see
      EXPANSION below).  If the variable has its integer attribute set, then
      value is evaluated as an arithmetic expression even if the $((...))
      expansion is not used (see Arithmetic Expansion below).  Word
      splitting is not performed, with the exception of "$@" as explained
      below under Special Parameters.  Pathname expansion is not performed.
      Assignment statements may also appear as arguments to the alias,
      declare, typeset, export, readonly, and local builtin 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.




                                   - 13 -          Formatted:  June 25, 2018






 BASH(1)                        GNU Bash 4.3                         BASH(1)
                               2014 February 2



      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.  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 variable.  This allows variables to be manipulated indirectly.
      Whenever the nameref variable is referenced or assigned to, the
      operation is actually performed on the variable specified by the
      nameref variable's value.  A nameref is commonly used within shell
      functions to refer to a variable whose name is passed as an argument
      to the function.  For instance, if a variable name is passed to a
      shell function as its first argument, running

           declare -n ref=$1
      inside the function creates a nameref variable ref whose value is the
      variable name passed as the first argument.  References and
      assignments to ref are treated as references and assignments 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 -n 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).





                                   - 14 -          Formatted:  June 25, 2018






 BASH(1)                        GNU Bash 4.3                         BASH(1)
                               2014 February 2



    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$2c...", where c is
           the first character of the value of the IFS variable.  If IFS is
           unset, the parameters are separated by spaces.  If IFS is null,
           the parameters are joined without intervening separators.
      @    Expands to the positional parameters, starting from one.  When
           the expansion occurs within double quotes, each parameter expands
           to a separate word.  That is, "$@" is equivalent to "$1" "$2" ...
           If the double-quoted expansion occurs within a word, the
           expansion of the first parameter is joined with the beginning
           part of the original word, and the expansion of the last
           parameter is joined with the last part of the original word.
           When there are no positional parameters, "$@" 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
           foreground pipeline.
      -    Expands to the current option flags as specified upon invocation,
           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 subshell.
      !    Expands to the process ID of the job most recently placed into
           the background, whether executed as an asynchronous command or
           using the bg builtin (see JOB CONTROL below).
      0    Expands to the name of the shell or shell script.  This is set at
           shell initialization.  If bash is invoked with a file of
           commands, $0 is set to the name of that file.  If bash is started
           with the -c option, then $0 is set to the first argument after
           the string to be executed, if one is present.  Otherwise, it is
           set to the filename used to invoke bash, as given by argument
           zero.
      _    At shell startup, set to the absolute 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 command, after expansion.  Also set to the full
           pathname used to invoke each command executed and placed in the
           environment exported to that command.  When checking mail, this
           parameter holds the name of the mail file currently being
           checked.





                                   - 15 -          Formatted:  June 25, 2018






 BASH(1)                        GNU Bash 4.3                         BASH(1)
                               2014 February 2



    Shell Variables
      The following variables are set by the shell:

      BASH Expands to the full filename used to invoke this instance of
           bash.
      BASHOPTS
           A colon-separated list of enabled shell options.  Each word in
           the list is a valid argument for the -s option to the shopt
           builtin command (see SHELL BUILTIN COMMANDS below).  The options
           appearing in BASHOPTS are those reported as on by shopt.  If this
           variable is in the environment when bash starts up, each shell
           option in the list will be enabled before reading any startup
           files.  This variable is read-only.
      BASHPID
           Expands to the process ID of the current bash process.  This
           differs from $$ under certain circumstances, such as subshells
           that do not require bash to be re-initialized.
      BASH_ALIASES
           An associative array variable whose members correspond to the
           internal list of aliases as maintained by the alias builtin.
           Elements added to this array appear in the alias list; unsetting
           array elements cause aliases to be removed from the alias list.
      BASH_ARGC
           An array variable whose values are the number of parameters in
           each frame of the current bash execution call stack.  The number
           of parameters to the current subroutine (shell function or script
           executed with . or source) is at the top of the stack.  When a
           subroutine is executed, the number of parameters passed is pushed
           onto BASH_ARGC.  The shell sets BASH_ARGC only when in extended
           debugging mode (see the description of the extdebug option to the
           shopt builtin below)
      BASH_ARGV
           An array variable containing all of the parameters in the current
           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
           executed, the parameters supplied are pushed onto BASH_ARGV.  The
           shell sets BASH_ARGV only when in extended debugging mode (see
           the description of the extdebug option to the shopt builtin
           below)
      BASH_CMDS
           An associative array variable whose members correspond to the
           internal hash table of commands as maintained by the hash
           builtin.  Elements added to this array appear in the hash table;
           unsetting array elements cause commands to be removed from the
           hash table.
      BASH_COMMAND
           The command currently being executed or about to be executed,
           unless the shell is executing a command as the result of a trap,
           in which case it is the command executing at the time of the
           trap.



                                   - 16 -          Formatted:  June 25, 2018






 BASH(1)                        GNU Bash 4.3                         BASH(1)
                               2014 February 2



      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
           function).  Use LINENO to obtain the current line number.
      BASH_REMATCH
           An array variable whose members are assigned by the =~ binary
           operator to the [[ conditional command.  The element with index 0
           is the portion of the string matching the entire regular
           expression.  The element with index n is the portion of the
           string matching the nth parenthesized subexpression.  This
           variable is read-only.
      BASH_SOURCE
           An array variable whose members are the source filenames where
           the corresponding shell function names in the FUNCNAME array
           variable are defined.  The shell function ${FUNCNAME[$i]} is
           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 initial
           value is 0.
      BASH_VERSINFO
           A readonly array variable whose members hold version information
           for this instance of bash.  The values assigned to the array
           members are as follows:

           BASH_VERSINFO[0]        The major version number (the release).
           BASH_VERSINFO[1]        The minor version number (the version).
           BASH_VERSINFO[2]        The patch level.
           BASH_VERSINFO[3]        The build version.
           BASH_VERSINFO[4]        The release status (e.g., beta1).
           BASH_VERSINFO[5]        The value of MACHTYPE.
      BASH_VERSION
           Expands to a string describing the version of this instance of
           bash.
      COMP_CWORD
           An index into ${COMP_WORDS} of the word containing the current
           cursor position.  This variable is available only in shell
           functions 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
           current completion function.
      COMP_LINE
           The current command line.  This variable is available only in
           shell functions and external commands invoked by the programmable



                                   - 17 -          Formatted:  June 25, 2018






 BASH(1)                        GNU Bash 4.3                         BASH(1)
                               2014 February 2



           completion facilities (see Programmable Completion below).
      COMP_POINT
           The index of the current cursor position relative to the
           beginning 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 programmable
           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
           successive tabs, !, for listing alternatives on partial word
           completion, @, 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 programmable
           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
           subsequently reset.
      COMP_WORDS
           An array variable (see Arrays below) consisting of the individual
           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 functions
           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
           contents 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
           directories already in the stack, but the pushd and popd builtins
           must be used to add and remove directories.  Assignment to this
           variable will not change the current directory.  If DIRSTACK is
           unset, it loses its special properties, even if it is
           subsequently reset.
      EUID Expands to the effective user ID of the current user, initialized
           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
           bottom-most element (the one with the highest index) is "main".
           This variable exists only when a shell function is executing.



                                   - 18 -          Formatted:  June 25, 2018






 BASH(1)                        GNU Bash 4.3                         BASH(1)
                               2014 February 2



           Assignments to FUNCNAME have no effect and return an error
           status.  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 information.
      GROUPS
           An array variable containing the list of groups of which the
           current user is a member.  Assignments to GROUPS have no effect
           and return an error status.  If GROUPS is unset, it loses its
           special properties, even if it is subsequently reset.
      HISTCMD
           The history number, or index in the history list, of the current
           command.  If HISTCMD is unset, it loses its special properties,
           even if it is subsequently reset.
      HOSTNAME
           Automatically set to the name of the current host.
      HOSTTYPE
           Automatically set to a string that uniquely describes the type of
           machine on which bash is executing.  The default is system-
           dependent.
      LINENO
           Each time this parameter is referenced, the shell substitutes a
           decimal number representing the current sequential line number
           (starting with 1) within a script or function.  When not in a
           script or function, the value substituted is not guaranteed to be
           meaningful.  If LINENO is unset, it loses its special properties,
           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-
           company-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 system
           on which bash is executing.  The default is system-dependent.




                                   - 19 -          Formatted:  June 25, 2018






 BASH(1)                        GNU Bash 4.3                         BASH(1)
                               2014 February 2



      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 readonly.
      PWD  The current working directory as set by the cd command.
      RANDOM
           Each time this parameter is referenced, a random integer between
           0 and 32767 is generated.  The sequence of random numbers may be
           initialized by assigning a value to RANDOM.  If RANDOM is unset,
           it loses its special properties, even if it is subsequently
           reset.
      READLINE_LINE
           The contents of the readline line buffer, for use with "bind -x"
           (see SHELL BUILTIN COMMANDS below).
      READLINE_POINT
           The position of the insertion point in the readline line buffer,
           for use with "bind -x" (see SHELL BUILTIN COMMANDS below).
      REPLY
           Set to the line of input read by the read builtin command when no
           arguments are supplied.
      SECONDS
           Each time this parameter is referenced, the number of seconds
           since shell invocation is returned.  If a value is assigned to
           SECONDS, the value returned upon subsequent references is the
           number of seconds since the assignment plus the value assigned.
           If SECONDS is unset, it loses its special properties, even if it
           is subsequently reset.
      SHELLOPTS
           A colon-separated list of enabled shell options.  Each word in
           the list is a valid argument for the -o option to the set builtin
           command (see SHELL BUILTIN COMMANDS below).  The options
           appearing in SHELLOPTS are those reported as on by set -o.  If
           this variable is in the environment when bash starts up, each
           shell option in the list will be enabled before reading any
           startup files.  This variable is read-only.
      SHLVL
           Incremented by one each time an instance of bash is started.
      UID  Expands to the user ID of the current user, initialized at shell
           startup.  This variable is readonly.

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

      BASH_COMPAT
           The value is used to set the shell's compatibility level.  See
           the description of the shopt builtin below under SHELL BUILTIN
           COMMANDS for a description of the various compatibility levels
           and their effects.  The value may be a decimal number (e.g., 4.2)
           or an integer (e.g., 42) corresponding to the desired
           compatibility level.  If BASH_COMPAT is unset or set to the empty



                                   - 20 -          Formatted:  June 25, 2018






 BASH(1)                        GNU Bash 4.3                         BASH(1)
                               2014 February 2



           string, the compatibility level is set to the default for the
           current version.  If BASH_COMPAT is set to a value that is not
           one of the valid compatibility levels, the shell prints an error
           message and sets the compatibility level to the default for the
           current version.  The valid compatibility levels correspond to
           the compatibility options accepted by the shopt builtin described
           below (for example, compat42 means that 4.2 and 42 are valid
           values).  The current version is also a valid value.
      BASH_ENV
           If this parameter is set when bash is executing a shell script,
           its value is interpreted as a filename containing commands to
           initialize the shell, as in ~/.bashrc.  The value of BASH_ENV is
           subjected to parameter expansion, command substitution, and
           arithmetic expansion before being interpreted as a filename.
           PATH is not used to search for the resultant filename.
      BASH_XTRACEFD
           If set to an integer corresponding to a valid file descriptor,
           bash will write the trace output generated when set -x is enabled
           to that file descriptor.  The file descriptor is closed when
           BASH_XTRACEFD is unset or assigned a new value.  Unsetting
           BASH_XTRACEFD or assigning it the empty string causes the trace
           output to be sent to the standard error.  Note that setting
           BASH_XTRACEFD to 2 (the standard error file descriptor) and then
           unsetting it will result in the standard error being closed.
      CDPATH
           The search path for the cd command.  This is a colon-separated
           list of directories in which the shell looks for destination
           directories specified by the cd command.  A sample value is
           ".:~:/usr".
      CHILD_MAX
           Set the number of exited child status values for the shell to
           remember.  Bash will not allow this value to be decreased below a
           POSIX-mandated minimum, and there is a maximum value (currently
           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
           completion facility (see Programmable Completion below).  Each
           array element contains one possible completion.
      EMACS
           If bash finds this variable in the environment when the shell
           starts with value "t", it assumes that the shell is running in an
           Emacs shell buffer and disables line editing.
      ENV  Similar to BASH_ENV; used when the shell is invoked in POSIX
           mode.



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 BASH(1)                        GNU Bash 4.3                         BASH(1)
                               2014 February 2



      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
           suffix matches one of the entries in FIGNORE is excluded from the
           list of matched filenames.  A sample value is ".o:~".
      FUNCNEST
           If set to a numeric value greater than 0, defines a maximum
           function nesting level.  Function invocations that exceed this
           nesting level will cause the current command to abort.
      GLOBIGNORE
           A colon-separated list of patterns defining the set of filenames
           to be ignored by pathname expansion.  If a filename matched by a
           pathname expansion pattern also matches one of the patterns in
           GLOBIGNORE, it is removed from the list of matches.
      HISTCONTROL
           A colon-separated list of values controlling how commands are
           saved on the history list.  If the list of values includes
           ignorespace, lines which begin with a space character are not
           saved in the history list.  A value of ignoredups causes lines
           matching the previous history entry to not be saved.  A value of
           ignoreboth is shorthand for ignorespace and ignoredups.  A value
           of erasedups causes all previous lines matching the current line
           to be removed from the history list before that line is saved.
           Any value not in the above list is ignored.  If HISTCONTROL is
           unset, or does not include a valid value, all lines read by the
           shell parser are saved on the history list, subject to the value
           of HISTIGNORE.  The second and subsequent lines of a multi-line
           compound command are not tested, and are added to the history
           regardless of the value of HISTCONTROL.
      HISTFILE
           The name of the file in which command history is saved (see
           HISTORY 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 truncated,
           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 complete
           line (no implicit `*' is appended).  Each pattern is tested
           against the line after the checks specified by HISTCONTROL are



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                               2014 February 2



           applied.  In addition to the normal shell pattern matching
           characters, `&' matches the previous history line.  `&' may be
           escaped using a backslash; the backslash is removed before
           attempting a match.  The second and subsequent lines of a multi-
           line compound command are not tested, and are added to the
           history regardless of the value of HISTIGNORE.
      HISTSIZE
           The number of commands to remember in the command history (see
           HISTORY below).  If the value is 0, commands are not saved in the
           history list.  Numeric values less than zero result in every
           command being saved on the history list (there is no limit).  The
           shell sets the default value to 500 after reading any startup
           files.
      HISTTIMEFORMAT
           If this variable is set and not null, its value is used as a
           format string for strftime(3) to print the time stamp associated
           with each history entry displayed by the history builtin.  If
           this variable is set, time stamps are written to the history file
           so they may be preserved across shell sessions.  This uses the
           history comment character to distinguish timestamps from other
           history lines.
      HOME The home directory of the current user; the default argument for
           the cd builtin command.  The value of this variable is also used
           when performing tilde expansion.
      HOSTFILE
           Contains the name of a file in the same format as /etc/hosts that
           should be read when the shell needs to complete a hostname.  The
           list of possible hostname completions may be changed while the
           shell is running; the next time hostname completion is attempted
           after the value is changed, bash adds the contents of the new
           file to the existing list.  If HOSTFILE is set, but has no value,
           or does not name a readable file, bash attempts to read
           /etc/hosts to obtain the list of possible hostname completions.
           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><newline>''.
      IGNOREEOF
           Controls the action of an interactive shell on receipt of an EOF
           character as the sole input.  If set, the value is the number of
           consecutive EOF characters which must be typed as the first
           characters on an input line before bash exits.  If the variable
           exists but does not have a numeric value, or has no value, the
           default value is 10.  If it does not exist, EOF signifies the end
           of input to the shell.
      INPUTRC
           The filename for the readline startup file, overriding the
           default of ~/.inputrc (see READLINE below).
      LANG Used to determine the locale category for any category not
           specifically selected with a variable starting with LC_.




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      LC_ALL
           This variable overrides the value of LANG and any other LC_
           variable specifying a locale category.
      LC_COLLATE
           This variable determines the collation order used when sorting
           the results of pathname expansion, and determines the behavior of
           range expressions, equivalence classes, and collating sequences
           within pathname expansion and pattern matching.
      LC_CTYPE
           This variable determines the interpretation of characters and the
           behavior of character classes within pathname expansion and
           pattern matching.
      LC_MESSAGES
           This variable determines the locale used to translate double-
           quoted strings preceded by a $.
      LC_NUMERIC
           This variable determines the locale category used for number
           formatting.
      LINES
           Used by the select compound command to determine the column
           length for printing selection lists.  Automatically set if the
           checkwinsize option is enabled or in an interactive shell upon
           receipt of a SIGWINCH.
      MAIL If this parameter is set to a file or directory name and the
           MAILPATH variable is not set, bash informs the user of the
           arrival of mail in the specified file or Maildir-format
           directory.
      MAILCHECK
           Specifies how often (in seconds) bash checks for mail.  The
           default is 60 seconds.  When it is time to check for mail, the
           shell does so before displaying the primary prompt.  If this
           variable is unset, or set to a value that is not a number greater
           than or equal to zero, the shell disables mail checking.
      MAILPATH
           A colon-separated list of filenames to be checked for mail. The
           message to be printed when mail arrives in a particular file may
           be specified by separating the filename from the message with a
           `?'.  When used in the text of the message, $_ expands to the
           name of the current mailfile. Example:
           MAILPATH=/var/mail/bfox?"You have mail":~/shell-mail?"$_ has
           mail!"
           Bash supplies a default value for this variable, but the 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



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           EXECUTION below).  A zero-length (null) directory name in the
           value of PATH indicates the current directory.  A null directory
           name may appear as two adjacent colons, or as an initial or
           trailing colon.  The default path is system-dependent, and is set
           by the administrator who installs bash.  A common value is
           ``/usr/local/bin:/usr/local/sbin:/usr/bin:/usr/sbin:/bin:/sbin''.
      POSIXLY_CORRECT
           If this variable is in the environment when bash starts, the
           shell enters posix mode before reading the startup files, as if
           the --posix invocation option had been supplied.  If it is set
           while the shell is running, bash enables posix mode, as if the
           command set -o posix had been executed.
      PROMPT_COMMAND
           If set, the value is executed as a command prior to issuing each
           primary prompt.
      PROMPT_DIRTRIM
           If set to a number greater than zero, the value is used as the
           number of trailing directory components to retain when expanding
           the \w and \W prompt string escapes (see PROMPTING below).
           Characters removed are replaced with an ellipsis.
      PS1  The value of this parameter is expanded (see PROMPTING below) and
           used as the primary prompt string.  The default value is
           ``\s-\v\$ ''.
      PS2  The value of this parameter is expanded as with PS1 and used as
           the secondary prompt string.  The default is ``> ''.
      PS3  The value of this parameter is used as the prompt for the select
           command (see SHELL GRAMMAR above).
      PS4  The value of this parameter is expanded as with PS1 and the value
           is printed before each command bash displays during an execution
           trace.  The first character of PS4 is replicated multiple times,
           as necessary, to indicate multiple levels of indirection.  The
           default is ``+ ''.
      SHELL
           The full pathname to the shell is kept in this environment
           variable.  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 specifying
           how the timing information for pipelines prefixed with the time
           reserved word should be displayed.  The % character introduces 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



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           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
           terminates 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
           commands without redirections are treated as candidates for
           resumption of an existing stopped job.  There is no ambiguity
           allowed; if there is more than one job beginning with 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
           analogous 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,
           substituting one string for another in the command.  The default
           is `^'.  The optional third character is the character which



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           indicates that the remainder of the line is a comment when found
           as the first character of a word, normally `#'.  The history
           comment 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
      contiguously.  Indexed arrays are referenced using integers (including
      arithmetic expressions)  and are zero-based; associative arrays are
      referenced 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 COMMANDS below).  declare -a name[subscript] is also accepted;
      the subscript is ignored.

      Associative arrays are created using declare -A name.

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

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

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

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

      Any element of an array may be referenced using ${name[subscript]}.
      The braces are required to avoid conflicts with pathname expansion.
      If subscript is @ or *, the word expands to all members of name.
      These subscripts differ only when the word appears within double



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      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 separate word.  When there are no array members,
      ${name[@]} expands to nothing.  If the double-quoted expansion occurs
      within a word, the expansion of the first parameter is joined with the
      beginning part of the original word, and the expansion of the last
      parameter is joined with the last part of the original word.  This is
      analogous to the expansion of the special parameters * and @ (see
      Special Parameters above).  ${#name[subscript]} expands to the length
      of ${name[subscript]}.  If subscript is * or @, the expansion is the
      number of elements in the array.  Referencing an array variable
      without a subscript is equivalent to referencing the array with a
      subscript of 0.  If the subscript used to reference an element of an
      indexed array evaluates to a number less than zero, it is interpreted
      as relative to one greater than the maximum index of the array, so
      negative indices count back from the end of the array, and an index of
      -1 references the last element.

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

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

      The unset builtin is used to destroy arrays.  unset name[subscript]
      destroys the array element at index subscript.  Negative subscripts to
      indexed arrays are interpreted as described above.  Care must be taken
      to avoid unwanted side effects caused by pathname expansion.  unset
      name, where name is an array, or unset name[subscript], where
      subscript is * or @, removes the entire array.

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

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

      The order of expansions is: brace expansion; tilde expansion,
      parameter and variable expansion, arithmetic expansion, and command



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      substitution (done in a left-to-right fashion); word splitting; and
      pathname expansion.

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

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

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

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

      A sequence expression takes the form {x..y[..incr]}, where x and y are
      either integers or single characters, and incr, an optional increment,
      is an integer.  When integers are supplied, the expression expands to
      each number between x and y, inclusive.  Supplied integers may be
      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 characters are supplied, the expression expands
      to each character lexicographically between x and y, inclusive, using
      the default C locale.  Note that both x and y must be of the same
      type.  When the increment is supplied, it is used as the difference
      between each term.  The default increment is 1 or -1 as appropriate.

      Brace expansion is performed before any other expansions, and any
      characters 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



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      considered part of a brace expression.  To avoid conflicts with
      parameter expansion, the string ${ is not considered eligible for
      brace expansion.

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

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

      Brace expansion introduces a slight incompatibility with historical
      versions of sh.  sh does not treat opening or closing braces specially
      when they appear as part of a word, and preserves them in the output.
      Bash removes braces from words as a consequence of brace expansion.
      For example, a word entered to sh as file{1,2} appears identically in
      the output.  The same word is output as file1 file2 after expansion by
      bash.  If strict compatibility with sh is desired, start bash with the
      +B option or disable brace expansion with the +B option to the set
      command (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
      directory of the user executing the shell is substituted instead.
      Otherwise, 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
      characters following the tilde in the tilde-prefix consist of a number
      N, optionally prefixed by a `+' or a `-', the tilde-prefix is replaced
      with the corresponding element from the directory stack, as it would
      be displayed by the dirs builtin invoked with the tilde-prefix as an
      argument.  If the characters following the tilde in the tilde-prefix
      consist 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
      immediately 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.



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    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 (!), it
      introduces a level of variable indirection.  Bash uses the value of
      the variable formed from the rest of parameter as the name of the
      variable; this variable is then expanded and that value is used in the
      rest of the substitution, rather than the value of parameter itself.
      This is known as indirect expansion.  The exceptions to this are the
      expansions of ${!prefix*} and ${!name[@]} described below.  The
      exclamation point must immediately follow the left brace in order to
      introduce indirection.

      In each of the cases below, word is subject to tilde expansion,
      parameter 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 expansion
           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
           parameter 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



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           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 offset.
           If parameter is @, an indexed array subscripted by @ or *, or an
           associative array name, the results differ as described below.
           If length is omitted, expands to the substring of the value of
           parameter starting at the character specified by offset and
           extending to the end of the value.  length and offset are
           arithmetic expressions (see ARITHMETIC EVALUATION below).

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

           If parameter is @, the result is length positional parameters
           beginning at offset.  A negative offset is taken relative to one
           greater than the greatest positional parameter, so an offset of
           -1 evaluates to the last positional parameter.  It is an
           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 parameters
           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



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           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 parameter
           is an array name subscripted by * or @, the value substituted is
           the number of elements in the array.  If parameter is an indexed
           array name subscripted by a negative number, that number is
           interpreted as relative to one greater than the maximum index of
           parameter, so negative indices count back from the end of the
           array, and an index of -1 references the last element.

      ${parameter#word}
      ${parameter##word}
           Remove matching prefix pattern.  The word is expanded to produce
           a pattern just as in pathname expansion.  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
           expansion is the resultant list.

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

      ${parameter/pattern/string}
           Pattern substitution.  The pattern is expanded to produce a



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           pattern just as in pathname expansion.  Parameter is expanded and
           the longest match of pattern against its value is replaced with
           string.  If pattern begins with /, all matches of pattern are
           replaced with string.  Normally only the first match is replaced.
           If pattern begins with #, it must match at the beginning of the
           expanded value of parameter.  If pattern begins with %, it must
           match at the end of the expanded value of parameter.  If string
           is null, matches of pattern are deleted and the / following
           pattern may be omitted.  If parameter is @ or *, the substitution
           operation is applied to each positional parameter in turn, and
           the expansion is the resultant list.  If parameter is an array
           variable subscripted with @ or *, the substitution operation is
           applied to each member of the array in turn, and the expansion is
           the resultant list.

      ${parameter^pattern}
      ${parameter^^pattern}
      ${parameter,pattern}
      ${parameter,,pattern}
           Case modification.  This expansion modifies the case of
           alphabetic characters in parameter.  The pattern is expanded to
           produce 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
           uppercase; the , operator converts matching uppercase letters to
           lowercase.  The ^^ and ,, expansions convert each matched
           character in the expanded value; the ^ and , expansions match and
           convert only the first character in the expanded value.  If
           pattern is 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 subscripted with @ or *, the case modification operation
           is applied to each member of the array in turn, and the expansion
           is the resultant list.

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

           $(command)
      or
           `command`

      Bash performs the expansion by executing command 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 command substitution
      $(cat file) can be replaced by the equivalent but faster $(< file).



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      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
      substitution.  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
      expansion is:

           $((expression))

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

      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
      substitution, 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



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      field terminators.  If IFS is unset, or its value is exactly
      <space><tab><newline>, the default, then sequences of <space>, <tab>,
      and <newline> at the beginning and end of the results of the previous
      expansions are ignored, and any sequence of IFS characters not at the
      beginning or end serves to delimit words.  If IFS has a value other
      than the default, then sequences of the whitespace characters space
      and tab are ignored at the beginning and end of the word, as long as
      the whitespace character is in the value of IFS (an IFS whitespace
      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.  Unquoted implicit null
      arguments, resulting from the expansion of parameters that have no
      values, are removed.  If a parameter with no value is expanded within
      double quotes, a null argument results and is retained.

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

    Pathname Expansion
      After word splitting, unless the -f option has been set, bash scans
      each word for the characters *, ?, and [.  If one of these characters
      appears, then the word is regarded as a pattern, and replaced with an
      alphabetically sorted list of filenames matching the pattern (see
      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 performed
      without regard to the case of alphabetic characters.  When a pattern
      is used for pathname expansion, the character ``.'' at the start of a
      name or immediately following a slash must be matched explicitly,
      unless the shell option dotglob is set.  When matching a pathname, the
      slash character must always be matched explicitly.  In other cases,
      the ``.'' character is not treated specially.  See the description of
      shopt below under SHELL BUILTIN COMMANDS for a description of the
      nocaseglob, nullglob, failglob, and dotglob shell options.

      The GLOBIGNORE shell variable may be used to restrict the set of
      filenames matching a pattern.  If GLOBIGNORE is set, each matching
      filename that also matches one of the patterns in GLOBIGNORE is
      removed from the list of matches.  The filenames ``.'' and ``..'' are
      always ignored when GLOBIGNORE is set and not null.  However, setting
      GLOBIGNORE to a non-null value has the effect of enabling the dotglob
      shell option, so all other filenames beginning with a ``.'' will
      match.  To get the old behavior of ignoring filenames beginning with a
      ``.'', make ``.*'' one of the patterns in GLOBIGNORE.  The dotglob
      option is disabled when GLOBIGNORE is unset.




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      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 subdirectories.
           ?    Matches any single character.
           [...]
                Matches any one of the enclosed characters.  A pair of
                characters separated by a hyphen denotes a range expression;
                any character that falls between those two characters,
                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 character not enclosed is
                matched.  The sorting order of characters in range
                expressions is determined by the current locale and the
                values of the LC_COLLATE or LC_ALL shell 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 collating



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                symbol symbol.

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

    Quote Removal
      After the preceding expansions, all unquoted occurrences of the
      characters \,  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
      operators may precede or appear anywhere within a simple command or
      may follow a command.  Redirections are processed in the order they
      appear, from left to right.

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

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

      The word following the redirection operator in the following
      descriptions, unless otherwise noted, is subjected to brace expansion,
      tilde expansion, parameter and variable expansion, command



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      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
      output was redirected to dirlist.

      Bash handles several filenames specially when they are used in
      redirections, as described in the following table:

           /dev/fd/fd
                If fd is a valid integer, file descriptor fd is duplicated.
           /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
      internally.

    Redirecting Input
      Redirection of input causes the file whose name results from the
      expansion 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:




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           [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 redirection 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
      equivalent 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.




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    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 for a command.

      The format of here-documents is:

           <<[-]word
                   here-document
           delimiter

      No parameter and variable expansion, command substitution, arithmetic
      expansion, or pathname expansion is performed on word.  If any
      characters in word are quoted, the delimiter is the result of quote
      removal on word, and the lines in the here-document are not expanded.
      If word is unquoted, all lines of the here-document are subjected to
      parameter expansion, command substitution, and arithmetic expansion,
      the character 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:

           <<<word

      The word undergoes brace expansion, tilde expansion, parameter and
      variable expansion, command substitution, arithmetic expansion, and
      quote removal.  Pathname expansion and word splitting are not
      performed.  The result is supplied as a single string to the command
      on its standard input.



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    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
      evaluates to -, file descriptor n is closed.  If n is not specified,
      the standard input (file descriptor 0) is used.

      The operator

           [n]>&word

      is used similarly to duplicate output file descriptors.  If n is not
      specified, the standard output (file descriptor 1) is used.  If the
      digits in word do not specify a file descriptor open for output, a
      redirection 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



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

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

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

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

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

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

 FUNCTIONS
      A shell function, defined as described above under SHELL GRAMMAR,
      stores a series of commands for later execution.  When the name of a
      shell function is used as a simple command name, the list of commands
      associated with that function name is executed.  Functions are
      executed in the context of the current shell; no new process is
      created to interpret them (contrast this with the execution of a shell
      script).  When a function is executed, the arguments to the function



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      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 function while the function is executing.

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

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

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

      If the builtin command return is executed in a function, the function
      completes and execution resumes with the next command after the
      function 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
      typeset will list the function names only (and optionally the source
      file and line number, if the extdebug shell option is enabled).
      Functions may be exported so that subshells automatically have them
      defined with the -f option to the export builtin.  A function
      definition may be deleted using the -f option to the unset builtin.
      Note that shell functions and variables with the same name may result
      in multiple identically-named entries in the environment passed to the
      shell's children.  Care should be taken in cases where this may cause
      a problem.

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

 ARITHMETIC EVALUATION
      The shell allows arithmetic expressions to be evaluated, under certain
      circumstances (see the let and declare builtin commands and Arithmetic
      Expansion).  Evaluation is done in fixed-width integers with no check



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      for overflow, though division by 0 is trapped and flagged as an error.
      The operators and their precedence, associativity, and values are the
      same as in the C language.  The following list of operators is grouped
      into levels of equal-precedence operators.  The levels are listed in
      order of decreasing precedence.

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

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

      Constants with a leading 0 are interpreted as octal numbers.  A
      leading 0x or 0X denotes hexadecimal.  Otherwise, numbers take the
      form [base#]n, where the optional base is a decimal number between 2
      and 64 representing the arithmetic base, and n is a number in that
      base.  If base# is omitted, then base 10 is used.  When specifying n,
      the digits greater< than 9 are represented by the lowercase letters,



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      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.  Expressions are formed from the following
      unary or binary primaries.  If any file argument to one of the
      primaries 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
      symbolic 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.



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      -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
           numbers.
      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
           reference.
      -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
           Commands).

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




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      string1 < string2
           True if string1 sorts before string2 lexicographically.

      string1 > string2
           True if string1 sorts after string2 lexicographically.

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

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

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

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

      3.   Redirections are performed as described above under REDIRECTION.

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

      If no command name results, the variable assignments affect the
      current shell environment.  Otherwise, the variables are added to the
      environment of the executed command and do not affect the current
      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
      expansions 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.




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                               2014 February 2



 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
      containing an executable file by that name.  Bash uses a hash table to
      remember the full pathnames of executable files (see hash under SHELL
      BUILTIN COMMANDS below).  A full search of the directories in PATH is
      performed only if the command is not found in the hash table.  If the
      search is unsuccessful, the shell searches for a defined shell
      function named command_not_found_handle.  If that function exists, it
      is invoked with the original command and the original command's
      arguments as its arguments, and the function's exit status becomes the
      exit status of the shell.  If that function is not defined, the shell
      prints an error message and returns an exit status of 127.

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

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

      If the program is a file beginning with #!, the remainder of the first
      line specifies an interpreter for the program.  The shell executes the
      specified interpreter on operating systems that do not handle this
      executable 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
      following:





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                               2014 February 2



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

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

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

      +    current traps set by trap

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

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

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

      +    options enabled by shopt

      +    shell aliases defined with alias

      +    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
      consists of the following.  Unless otherwise noted, the values are
      inherited from the shell.


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

      +    the current working directory

      +    the file creation mode mask

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

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

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

      Command substitution, commands grouped with parentheses, and
      asynchronous commands are invoked in a subshell environment that is a



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      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 invocation.  Builtin commands that are invoked as part of a
      pipeline are also executed in a subshell environment.  Changes made to
      the subshell environment 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 processes.  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 environment 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 modified 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
      environment 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
      environment.

 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



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      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.

      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 substitution ignore the keyboard-generated job control signals
      SIGTTIN, SIGTTOU, and SIGTSTP.

      The shell exits by default upon receipt of a SIGHUP.  Before exiting,
      an interactive shell resends the SIGHUP to all jobs, running or
      stopped.  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.





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      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
      command 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 status greater than 128, immediately after which the trap is
      executed.

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

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

           [1] 25647

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

      To facilitate the implementation of the user interface to job control,
      the operating system maintains the notion of a current terminal
      process group ID.  Members of this process group (processes whose
      process group ID is equal to the current terminal process group ID)
      receive keyboard-generated signals such as SIGINT.  These processes
      are said to be in the foreground.  Background processes are those
      whose process group ID differs from the terminal's; such processes are
      immune to keyboard-generated 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
      (typically ^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



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      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
      character % 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 ce job.  If
      a prefix matches more than one job, bash reports an error.  Using
      %?ce, on the other hand, refers to any job containing the string ce in
      its command line.  If the substring matches more than one job, bash
      reports an error.  The symbols %% and %+ refer to the shell's notion
      of the 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,
      running), the shell prints a warning message, and, if the checkjobs
      option is enabled, lists the jobs and their statuses.  The jobs
      command may then be used to inspect their status. If a second attempt
      to exit is made without an intervening command, the shell does not
      print another warning, and any stopped jobs are terminated.

 PROMPTING
      When executing interactively, bash displays the primary prompt PS1
      when it is ready to read a command, and the secondary prompt PS2 when
      it needs more input to complete a command.  Bash allows these prompt
      strings to be customized by inserting a number of backslash-escaped
      special characters that are decoded as follows:
           \a   an ASCII bell character (07)
           \d   the date in "Weekday Month Date" format (e.g., "Tue May 26")
           \D{format}
                the format is passed to strftime(3) and the result is
                inserted into the prompt string; an empty format results in
                a locale-specific time representation.  The braces are



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

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

 READLINE
      This is the library that handles reading input when using an
      interactive 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.




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    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.  Similarly, meta keys are denoted by M-key, so M-x means
      Meta-X.  (On keyboards without a meta key, M-x means ESC x, i.e.,
      press the Escape key then the x key.  This makes ESC the meta prefix.
      The combination M-C-x means ESC-Control-x, or press the Escape key
      then hold the Control key while pressing the x key.)

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

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

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

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

      For example, placing

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



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    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
      specified 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




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           \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
      function 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
      modified with the bind builtin command.  The editing mode may be
      switched during interactive use by using the -o option to the set
      builtin command (see SHELL BUILTIN COMMANDS below).

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

           set variable-name value

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

      bell-style (audible)
           Controls what happens when readline wants to ring the terminal
           bell.  If set to none, readline never rings the bell.  If set to
           visible, readline uses a visible bell if one is available.  If
           set to audible, readline attempts to ring the terminal's bell.
      bind-tty-special-chars (On)
           If set to On, readline attempts to bind the control characters
           treated specially by the kernel's terminal driver to their
           readline equivalents.
      colored-stats (Off)
           If set to On, readline displays possible completions using
           different colors to indicate their file type. The color
           definitions are taken from the value of the LS_COLORS environment
           variable.
      comment-begin (``#'')
           The string that is inserted when the readline insert-comment
           command is executed.  This command is bound to M-# in emacs mode
           and to # in vi command mode.
      completion-ignore-case (Off)
           If set to On, readline performs filename matching and completion
           in a case-insensitive fashion.



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      completion-prefix-display-length (0)
           The length in characters of the common prefix of a list of
           possible completions that is displayed without modification.
           When set to a value greater than zero, common prefixes longer
           than this value are replaced with an ellipsis when displaying
           possible completions.
      completion-query-items (100)
           This determines when the user is queried about viewing the number
           of possible completions generated by the possible-completions
           command.  It may be set to any integer value greater than or
           equal to zero.  If the number of possible completions is greater
           than or equal to the value of this variable, the user is asked
           whether or not he wishes to view them; otherwise they are simply
           listed on the terminal.
      convert-meta (On)
           If set to On, readline will convert characters with the eighth
           bit set to an ASCII key sequence by stripping the eighth bit and
           prefixing an escape character (in effect, using escape as the
           meta prefix).
      disable-completion (Off)
           If set to On, readline will inhibit word completion.  Completion
           characters will be inserted into the line as if they had been
           mapped to self-insert.
      editing-mode (emacs)
           Controls whether readline begins with a set of key bindings
           similar to Emacs or vi.  editing-mode can be set to either emacs
           or vi.
      echo-control-characters (On)
           When set to On, on operating systems that indicate they support
           it, readline echoes a character corresponding to a signal
           generated from the keyboard.
      enable-keypad (Off)
           When set to On, readline will try to enable the application
           keypad when it is called.  Some systems need this to enable the
           arrow keys.
      enable-meta-key (On)
           When set to On, readline 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-
           history or next-history.
      history-size (0)
           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



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           number of history entries is not limited.
      horizontal-scroll-mode (Off)
           When set to On, makes readline use a single line for display,
           scrolling the input horizontally on a single screen line when it
           becomes longer than the screen width rather than wrapping to a
           new line.
      input-meta (Off)
           If set to On, readline will enable eight-bit input (that is, it
           will not strip the high bit from the characters it reads),
           regardless of what the terminal claims it can support.  The name
           meta-flag is a synonym for this variable.
      isearch-terminators (``C-[C-J'')
           The string of characters that should terminate an incremental
           search without subsequently executing the character as a command.
           If this variable has not been given a value, the characters 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-command,
           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 displayed
           with a preceding asterisk (*).
      mark-symlinked-directories (Off)
           If set to On, completed names which are symbolic links to
           directories 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



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           through the list.
      output-meta (Off)
           If set to On, readline will display characters with the eighth
           bit set directly rather than as a meta-prefixed escape sequence.
      page-completions (On)
           If set to On, readline uses an internal more-like pager to
           display 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,
           history 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 possible
           partial completion (the possible completions don't share a common
           prefix) cause the matches to be listed immediately instead of
           ringing the bell.
      show-mode-in-prompt (Off)
           If set to On, add a character to the beginning of the prompt
           indicating the editing mode: emacs (@), vi command (:) or vi
           insertion (+).
      skip-completed-text (Off)
           If set to On, this alters the default completion behavior when
           inserting a single match into the line.  It's only active when
           performing completion in the middle of a word.  If enabled,
           readline does not insert characters from the completion that
           match characters after point in the word being completed, so
           portions of the word following the cursor are not duplicated.
      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
           completions.

    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.





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      $if  The $if construct allows bindings to be made based on the editing
           mode, the terminal being used, or the application using readline.
           The text of the test extends to the end of the line; no
           characters are required to isolate it.

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

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

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

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

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

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

      $include
           This directive takes a single filename as an argument and reads
           commands and bindings from that file.  For example, the following
           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.



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      Incremental searches begin before the user has finished typing the
      search string.  As each character of the search string is typed,
      readline 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
      terminate 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
      accompanying key sequence are unbound by default.  In the following
      descriptions, 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).



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      shell-forward-word
           Move forward to the end of the next word.  Words are delimited by
           non-quoted shell metacharacters.
      shell-backward-word
           Move back to the start of the current or previous word.  Words
           are delimited by non-quoted shell metacharacters.
      clear-screen (C-l)
           Clear the screen leaving the current line at the top of the
           screen.  With an argument, refresh the current line without
           clearing the screen.
      redraw-current-line
           Refresh the current line.

    Commands for Manipulating the History
      accept-line (Newline, Return)
           Accept the line regardless of where the cursor is.  If this line
           is non-empty, add it to the history list according to the state
           of the HISTCONTROL variable.  If the line is a modified history
           line, then restore the history line to its original state.
      previous-history (C-p)
           Fetch the previous command from the history list, moving back in
           the list.
      next-history (C-n)
           Fetch the next command from the history list, moving forward in
           the list.
      beginning-of-history (M-<)
           Move to the first line in the history.
      end-of-history (M->)
           Move to the end of the input history, i.e., the line currently
           being entered.
      reverse-search-history (C-r)
           Search backward starting at the current line and moving `up'
           through the history as necessary.  This is an incremental search.
      forward-search-history (C-s)
           Search forward starting at the current line and moving `down'
           through the history as necessary.  This is an incremental search.
      non-incremental-reverse-search-history (M-p)
           Search backward through the history starting at the current line
           using a non-incremental search for a string supplied by the user.
      non-incremental-forward-search-history (M-n)
           Search forward through the history using a non-incremental search
           for a string supplied by the user.
      history-search-forward
           Search forward through the history for the string of characters
           between the start of the current line and the point.  This is a
           non-incremental search.
      history-search-backward
           Search backward through the history for the string of characters
           between the start of the current line and the point.  This is a
           non-incremental search.




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      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
           history expansion as well as all of the shell word expansions.
           See HISTORY EXPANSION below for a description of history
           expansion.
      history-expand-line (M-^)
           Perform history expansion on the current line.  See HISTORY
           EXPANSION below for a description of history expansion.
      magic-space
           Perform history expansion on the current line and insert a space.
           See HISTORY EXPANSION below for a description of history
           expansion.
      alias-expand-line
           Perform alias expansion on the current line.  See ALIASES above
           for a description of alias expansion.
      history-and-alias-expand-line
           Perform history and alias expansion on the current line.
      insert-last-argument (M-., M-_)
           A synonym for yank-last-arg.
      operate-and-get-next (C-o)
           Accept the current line for execution and fetch the next line
           relative to the current line from the history for editing.  Any
           argument is ignored.
      edit-and-execute-command (C-xC-e)
           Invoke an editor on the current command line, and execute the
           result as shell commands.  Bash attempts to invoke $VISUAL,
           $EDITOR, and emacs as the editor, in that order.

    Commands for Changing Text
      end-of-file (usually C-d)
           The character indicating end-of-file as set, for example, by



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           ``stty''.  If this character is read when there are no characters
           on the line, and point is at the beginning of the line, Readline
           interprets it as the end of input and returns EOF.
      delete-char (C-d)
           Delete the character at point.  If this function is bound to the
           same character as the tty EOF character, as C-d commonly is, see
           above for the effects.
      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
           cursor 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
           argument, switches to overwrite mode.  With an explicit non-
           positive numeric argument, switches to insert mode.  This command
           affects only emacs mode; vi mode does overwrite differently.
           Each call to readline() starts in insert mode.  In overwrite
           mode, characters bound to self-insert replace the text at point
           rather than pushing the text to the right.  Characters bound to
           backward-delete-char replace the character before point with a
           space.  By default, this command is unbound.





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    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 (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 shell-forward-word.
      shell-backward-kill-word (M-Rubout)
           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 boundary.
           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
           boundaries 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 following
           yank or yank-pop.





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    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
           followed 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 or 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 argument
           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.




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      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
           completions 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.



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      call-last-kbd-macro (C-x e)
           Re-execute the last keyboard macro defined, by making the
           characters in the macro appear as if typed at the keyboard.
      print-last-kbd-macro ()
           Print the last keyboard macro defined in a format suitable for
           the inputrc file.

    Miscellaneous
      re-read-init-file (C-x C-r)
           Read in the contents of the inputrc file, and incorporate any
           bindings or variable assignments found there.
      abort (C-g)
           Abort the current editing command and ring the terminal's bell
           (subject to the setting of bell-style).
      do-uppercase-version (M-a, M-b, M-x, ...)
           If the metafied character x is lowercase, run the command that is
           bound to the corresponding uppercase character.
      prefix-meta (ESC)
           Metafy the next character typed.  ESC f is equivalent to Meta-f.
      undo (C-_, C-x C-u)
           Incremental undo, separately remembered for each line.
      revert-line (M-r)
           Undo all changes made to this line.  This is like executing the
           undo command enough times to return the line to its initial
           state.
      tilde-expand (M-&)
           Perform tilde expansion on the current word.
      set-mark (C-@, M-<space>)
           Set the mark to the point.  If a numeric argument is supplied,
           the mark is set to that position.
      exchange-point-and-mark (C-x C-x)
           Swap the point with the mark.  The current cursor position is set
           to the saved position, and the old cursor position is saved as
           the mark.
      character-search (C-])
           A character is read and point is moved to the next occurrence of
           that character.  A negative count searches for previous
           occurrences.
      character-search-backward (M-C-])
           A character is read and point is moved to the previous occurrence
           of that character.  A negative count searches for subsequent
           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-[.




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      insert-comment (M-#)
           Without a numeric argument, the value of the readline
           comment-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,
           otherwise the characters in comment-begin are deleted from the
           beginning of the line.  In either case, the line is accepted as
           if a newline had been typed.  The default value of comment-begin
           causes this command to make the current line a shell comment.  If
           a numeric argument causes the comment character to be removed,
           the line will be executed by the shell.
      glob-complete-word (M-g)
           The word before point is treated as a pattern for pathname
           expansion, with an asterisk implicitly appended.  This pattern is
           used to generate a list of matching filenames for possible
           completions.
      glob-expand-word (C-x *)
           The word before point is treated as a pattern for pathname
           expansion, and the list of matching filenames is inserted,
           replacing the word.  If a numeric argument is supplied, an
           asterisk is appended before pathname expansion.
      glob-list-expansions (C-x g)
           The list of expansions that would have been generated by
           glob-expand-word is displayed, and the line is redrawn.  If a
           numeric argument is supplied, an asterisk is appended before
           pathname expansion.
      dump-functions
           Print all of the functions and their key bindings to the 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-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
      programmable completion facilities are invoked.




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

      Once a compspec has been found, it is used to generate the list of
      matching words.  If a compspec is not found, the default bash
      completion 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
      considered.  The string is first split using the characters in the IFS
      special 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 completed on the current command line.  No filtering of the
      generated completions 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



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      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
      environment 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
      specified with the -X option is applied to the list.  The filter is a
      pattern as used for pathname expansion; a & in the pattern is replaced
      with the text of the word being completed.  A literal & may be escaped
      with a backslash; the backslash is removed before attempting a match.
      Any completion that matches the pattern will be removed from the list.
      A leading ! negates the pattern; in this case any completion not
      matching the pattern will be removed.

      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
      supplied to complete when the compspec was defined, the bash default
      completions 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
      specified with complete -D.  It's possible for shell functions
      executed as completion handlers to indicate that completion should be



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      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 commands (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
      variable 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
      HISTFILESIZE 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 followed immediately by a digit are interpreted as
      timestamps for the preceding history line.  These timestamps are
      optionally displayed depending 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 sessions.  This uses the history comment
      character to distinguish timestamps from other history lines.  After
      saving the history, the history file is truncated to contain no more



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      than HISTFILESIZE lines.  If HISTFILESIZE is unset, or set to null, a
      non-numeric value, or a numeric value less than zero, the history file
      is not truncated.

      The builtin command fc (see SHELL BUILTIN COMMANDS below) may be used
      to list or edit and re-execute a portion of the history list.  The
      history 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
      command (see SHELL BUILTIN COMMANDS below).  Non-interactive shells do
      not perform history expansion by default.

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

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

      Several characters inhibit history expansion if found immediately
      following the history expansion character, even if it is unquoted:



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      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 history timestamps when writing the history file.

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

      !    Start a history substitution, except when followed by a blank,
           newline, carriage return, = or ( (when the extglob shell option
           is enabled using the shopt builtin).
      !n   Refer to command line n.
      !-n  Refer to the current command minus n.
      !!   Refer to the previous command.  This is a synonym for `!-1'.
      !string
           Refer to the most recent command preceding the current position
           in the history list starting with string.
      !?string[?]
           Refer to the most recent command preceding the current position
           in the history list containing string.  The trailing ? may be
           omitted if string is followed immediately by a newline.

      ^string1^string2^
           Quick substitution.  Repeat the previous command, replacing
           string1 with string2.  Equivalent to ``!!:s/string1/string2/''
           (see Modifiers below).
      !#   The entire command line typed so far.

    Word Designators
      Word designators are used to select desired words from the event.  A :
      separates the event specification from the word designator.  It may be
      omitted if the word designator begins with a ^, $, *, -, or %.  Words
      are numbered from the beginning of the line, with the first word being


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      denoted by 0 (zero).  Words are inserted into the current line
      separated by single spaces.

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

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

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

      h    Remove a trailing filename component, leaving only the head.
      t    Remove all leading filename components, leaving the tail.
      r    Remove a trailing suffix of the form .xxx, leaving the basename.
      e    Remove all but the trailing suffix.
      p    Print the new command but do not execute it.
      q    Quote the substituted words, escaping further substitutions.
      x    Quote the substituted words as with q, but break into words at
           blanks and newlines.
      s/old/new/
           Substitute new for the first occurrence of old in the event line.
           Any delimiter can be used in place of /.  The final 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 substitutions took place,
           the last string in a !?string[?] search.
      &    Repeat the previous substitution.
      g    Cause changes to be applied over the entire event line.  This is
           used in conjunction with `:s' (e.g., `:gs/old/new/') or `:&'.  If
           used with `:s', any delimiter can be used in place of /, and the
           final delimiter is optional if it is the last character of the
           event line.  An a may be used as a synonym for g.
      G    Apply the following `s' modifier once to each word in the event
           line.





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 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,
      break, continue, 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 interpretation.

      : [arguments]
           No effect; the command does nothing beyond expanding arguments
           and performing any specified redirections.  A zero exit code is
           returned.

       .  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
           executed from filename.  If filename does not contain a slash,
           filenames in PATH are used to find the directory containing
           filename.  The file searched for in PATH need not be executable.
           When bash is not in posix mode, the current directory is searched
           if no file is found in PATH.  If the sourcepath option to the
           shopt builtin command is turned off, the PATH is not searched.
           If any arguments are supplied, they become the positional
           parameters when filename is executed.  Otherwise the positional
           parameters are unchanged.  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
           supplied, 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.




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

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




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      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
           functionality 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
           function or a script executed with the . or source builtins).
           Without expr, caller displays the line number and source filename
           of the current subroutine call.  If a non-negative integer is
           supplied as expr, caller displays the line number, subroutine
           name, and source file corresponding to that position in the
           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 subroutine call or expr does not correspond to a valid position
           in the call stack.

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



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           successful, the absolute pathname of the new working directory is
           written to the standard output.  The return value is true if the
           directory was successfully changed; false otherwise.

      command [-pVv] command [arg ...]
           Run command with args suppressing the normal shell function
           lookup. Only builtin commands or commands found in the PATH are
           executed.  If the -p option is given, the search for command is
           performed using a default value for PATH that is guaranteed to
           find all of the standard utilities.  If either the -V or -v
           option is supplied, a description of command is printed.  The -v
           option causes a single word indicating the command or filename
           used to invoke command to be displayed; the -V option produces a
           more verbose description.  If the -V or -v option is supplied,
           the exit status is 0 if command was found, and 1 if not.  If
           neither option is supplied and an error occurred or command
           cannot be found, the exit status is 127.  Otherwise, the exit
           status 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
           programmable completion code had generated them directly from a
           completion specification with the same flags.  If word is
           specified, only those completions matching word will be
           displayed.

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

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



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           apply to ``empty'' command completion; that is, completion
           attempted on a blank line.

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

           Other options, if specified, have the following meanings.  The
           arguments to the -G, -W, and -X options (and, if necessary, the
           -P and -S options) should be quoted to protect them from
           expansion before the complete builtin is invoked.
           -o comp-option
                   The comp-option controls several aspects of the
                   compspec's behavior beyond the simple generation of
                   completions.  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 compspec
                           generates no matches.
                   filenames
                           Tell readline that the compspec generates
                           filenames, so it can perform any
                           filename-specific processing (like adding a slash
                           to directory names, quoting special characters,
                           or suppressing 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).
                   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.




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                   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
                           specified as -v.
           -C command
                   command is executed in a subshell environment, and its
                   output is used as the possible completions.
           -F function
                   The shell function function is executed in the current
                   shell environment.  When the function is executed, the
                   first argument ($1) is the name of the command whose
                   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 COMPREPLY
                   array variable.
           -G globpat
                   The pathname expansion pattern globpat is expanded to
                   generate the possible completions.
           -P prefix
                   prefix is added at the beginning of each possible
                   completion after all other options have been applied.



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           -S suffix
                   suffix is appended to each possible completion after all
                   other options have been applied.
           -W wordlist
                   The wordlist is split using the characters in the IFS
                   special variable as delimiters, and each resultant word
                   is expanded.  The possible completions are the members of
                   the resultant list which match the word being completed.
           -X filterpat
                   filterpat is a pattern as used for pathname expansion.
                   It is applied to the list of possible completions
                   generated 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 argument,
           an attempt is made to remove a completion specification for a
           name for which no specification exists, or an error occurs adding
           a completion specification.

      compopt [-o option] [-DE] [+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 the remaining
           options should apply to the ``default'' command completion; that
           is, completion attempted on a command for which no completion has
           previously been defined.  The -E option indicates that the
           remaining options should apply to ``empty'' command completion;
           that is, completion attempted on a blank line.

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

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

      declare [-aAfFgilnrtux] [-p] [name[=value] ...]
      typeset [-aAfFgilnrtux] [-p] [name[=value] ...]
           Declare variables and/or give them attributes.  If no names are



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           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 the
           function 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 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 evaluation
                (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 and
                assignments to name, except for changing the -n attribute
                itself, are performed on the variable referenced by name's
                value.  The -n attribute cannot be applied to array
                variables.
           -r   Make names readonly.  These names cannot then be assigned
                values by subsequent assignment statements or unset.
           -t   Give each name the trace attribute.  Traced functions
                inherit the DEBUG and RETURN traps from the calling shell.
                The trace attribute has no special meaning for variables.
           -u   When the variable is assigned a value, all lower-case
                characters are converted to upper-case.  The lower-case
                attribute is disabled.
           -x   Mark names for export to subsequent commands via the
                environment.

           Using `+' instead of `-' turns off the attribute instead, with
           the exceptions that +a may not be used to destroy an array
           variable 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



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           variable name is followed by =value, the value of the variable is
           set to value.  When using -a or -A and the compound assignment
           syntax to create array variables, additional attributes do not
           take effect until subsequent assignments.  The return value is 0
           unless an invalid option is encountered, an attempt is made to
           define a function using ``-f foo=bar'', an attempt is made to
           assign a value to a readonly variable, an attempt is made to
           assign a value to an array variable without using the compound
           assignment syntax (see Arrays above), one of the names is not a
           valid shell variable name, an attempt is made to turn off
           readonly status for a readonly variable, an attempt is made to
           turn off array status for an array variable, or an attempt is
           made to display a non-existent function with -f.

      dirs [-clpv] [+n] [-n]
           Without options, 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.
           -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, prefixing
                each entry with its index in the stack.
           +n   Displays the nth entry counting from the left of the list
                shown by dirs when invoked without options, starting with
                zero.
           -n   Displays the nth entry counting from the right of the list
                shown by dirs when invoked without options, starting with
                zero.

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

      disown [-ar] [-h] [jobspec ...]
           Without options, remove each jobspec from the table of active
           jobs.  If jobspec is not present, and neither the -a nor the -r
           option is supplied, the current job is used.  If the -h option is
           given, each jobspec is not removed from the table, but is marked
           so that SIGHUP is not sent to the job if the shell receives a
           SIGHUP.  If no jobspec is supplied, the -a option means to remove
           or mark all jobs; the -r option without a jobspec 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



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           is given, interpretation of the following backslash-escaped
           characters is enabled.  The -E option disables the interpretation
           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.
           The -d option will delete a builtin previously loaded with -f.
           If no name arguments are given, or if the -p option is supplied,
           a list of shell builtins is printed.  With no other option
           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.  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.




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      eval [arg ...]
           The args are read and concatenated together into a single
           command.  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
           beginning 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
           cannot be executed for some reason, a non-interactive shell
           exits, unless the execfail shell option is enabled.  In that
           case, it returns failure.  An interactive shell returns failure
           if the file cannot be executed.  If command is not specified, any
           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
           environment 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
           supplied with a name that is not a function.

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



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           -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.  Otherwise,
           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
           complete, the edited commands are echoed and executed.

           In the second form, command is re-executed after each instance of
           pat is replaced by rep.  Command is intepreted the same as first
           above.  A useful alias to use with this is ``r="fc -s"'', so that
           typing ``r 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-
           executed, 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 specify a
           valid job or jobspec specifies a job that was started without job
           control.

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



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

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

           getopts can report errors in two ways.  If the first character of
           optstring is a colon, silent error reporting is used.  In normal
           operation, diagnostic messages are printed when invalid options
           or missing option arguments are encountered.  If the variable
           OPTERR is set to 0, no error messages will be displayed, 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
           remembered.  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
           arguments are supplied with -t, the name is printed before the
           hashed full pathname.  The -l option causes output to be
           displayed in a format that may be reused as input.  If no
           arguments are given, or if only -l is supplied, information about
           remembered commands is printed.  The return status is true unless
           a name is not found or an invalid option is supplied.

      help [-dms] [pattern]
           Display helpful information about builtin commands.  If pattern
           is specified, help gives detailed help on all commands matching
           pattern; otherwise help for all the builtins and shell control
           structures is printed.



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           -d   Display a short description of each pattern
           -m   Display the description of each pattern in a manpage-like
                format
           -s   Display only a short usage synopsis for each pattern

           The return status is 0 unless no command matches pattern.

      history [n]
      history -c
      history -d offset
      history -anrw [filename]
      history -p arg [arg ...]
      history -s arg [arg ...]
           With no options, display the command history list with line
           numbers.  Lines listed with a * have been modified.  An argument
           of n lists only the last n lines.  If the shell variable
           HISTTIMEFORMAT is set and not null, it is used as a format string
           for strftime(3) to display the time stamp associated with each
           displayed history entry.  No intervening blank is printed between
           the formatted time stamp and the history line.  If filename is
           supplied, it is used as the name of the history file; if not, the
           value of HISTFILE is used.  Options, if supplied, have the
           following meanings:
           -c   Clear the history list by deleting all the entries.
           -d offset
                Delete the history entry at position offset.
           -a   Append the ``new'' history lines (history lines entered
                since the beginning of the current bash session) 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,
                overwriting 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 information
           associated with each history entry is written to the history
           file, marked with the history comment character.  When the
           history file is read, lines beginning with the history comment
           character followed immediately by a digit are interpreted as
           timestamps for the previous history line.  The return value is 0



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           unless an invalid option is encountered, an error occurs while
           reading or writing the history file, an invalid offset is
           supplied as an argument to -d, or the history expansion supplied
           as an argument to -p fails.

      jobs [-lnprs] [ jobspec ... ]
      jobs -x command [ args ... ]
           The first form lists the active jobs.  The options have the
           following 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 [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.  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
           ARITHMETIC 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 function
           and its children.  With no operands, local writes a list of local
           variables to the standard output.  It is an error to use local



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           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.

 quantum] [array]
      mapfile [-n count] [-O origin] [-s count] [-t] [-u fd] [-C callback] [-c
 quantum] [array]
      readarray [-n count] [-O origin] [-s count] [-t] [-u fd] [-C callback] [-c
           Read lines from the standard input into the indexed array
           variable array, or from file descriptor fd if the -u option is
           supplied.  The variable MAPFILE is the default array.  Options,
           if supplied, have the following meanings:
           -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 newline from each line read.
           -u   Read lines from file descriptor fd instead of the standard
                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.  With no arguments,
           removes the top directory from the stack, and performs a cd to
           the new top directory.  Arguments, if supplied, 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.  For example: ``popd +0''



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                removes the first directory, ``popd +1'' the second.
           -n   Removes the nth entry counting from the right of the list
                shown by dirs, starting with zero.  For example: ``popd -0''
                removes the last directory, ``popd -1'' the next to last.

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

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

           The format is a character string which contains three types of
           objects: plain characters, which are simply copied to standard
           output, character escape sequences, which are converted and
           copied to the standard output, and format specifications, each of
           which causes printing of the next successive argument.  In
           addition to the standard printf(1) format specifications, printf
           interprets the following extensions:
           %b   causes printf to expand backslash escape sequences in the
                corresponding argument (except that \c terminates output,
                backslashes in \, \", and \? are not removed, and octal
                escapes beginning with \0 may contain up to four digits).
           %q   causes printf to output the corresponding argument in a
                format that can be reused as shell input.
           %(datefmt)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.

           Arguments to non-string format specifiers are treated as C
           constants, 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
           arguments.  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.




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      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, exchanges the top two directories
           and returns 0, unless the directory stack is empty.  Arguments,
           if supplied, have the following meanings:
           -n   Suppresses the normal change of directory when adding
                directories to the stack, so that only the stack is
                manipulated.
           +n   Rotates the stack so that the nth directory (counting from
                the left of the list shown by dirs, starting with zero) is
                at the top.
           -n   Rotates the stack so that the nth directory (counting from
                the right of the list shown by dirs, starting with zero) is
                at the top.
           dir  Adds dir to the directory stack at the top, making it the
                new current working directory as if it had been supplied as
                the argument to the cd builtin.

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

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

 prompt] [-t timeout] [-u fd] [name ...]
      read [-ers] [-a aname] [-d delim] [-i text] [-n nchars] [-N nchars] [-p
           One line is read from the standard input, or from the file
           descriptor fd supplied as an argument to the -u option, and the
           first word is assigned to the first name, the second word to the
           second name, and so on, with leftover words and their intervening
           separators assigned to the last name.  If there are fewer words
           read from the input stream than names, the remaining names are
           assigned empty values.  The characters in IFS are used to split
           the line into words using the same rules the shell uses for
           expansion (described above under Word Splitting).  The backslash
           character (\) may be used to remove any special meaning for the
           next character read and for line continuation.  Options, if
           supplied, have the following meanings:




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           -a aname
                The words are assigned to sequential indices of the array
                variable aname, starting at 0.  aname is unset before any
                new values are assigned.  Other name arguments are ignored.
           -d delim
                The first character of delim is used to terminate the input
                line, rather than newline.
           -e   If the standard input is coming from a terminal, readline
                (see READLINE above) is used to obtain the line.  Readline
                uses the current (or default, if line editing was not
                previously active) editing settings.
           -i text
                If readline is being used to read the line, text is placed
                into the editing buffer before editing begins.
           -n nchars
                read returns after reading nchars characters rather than
                waiting for a complete line of input, but honor a delimiter
                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 characters
                encountered in the input are not treated specially and do
                not cause read to return until nchars characters are read.
           -p prompt
                Display prompt on standard error, without a trailing
                newline, 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
                backslash is considered to be part of the line.  In
                particular, a backslash-newline pair may not be used as a
                line continuation.
           -s   Silent mode.  If input is coming from a terminal, characters
                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 decimal number
                with a fractional portion following the decimal point.  This
                option is only effective if read is reading input from a
                terminal, pipe, or other special file; it has no effect when
                reading from regular files.  If read times out, 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 specified file descriptor, non-zero otherwise.  The
                exit status is greater than 128 if the timeout is exceeded.
           -u fd
                Read input from file descriptor fd.




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           If no names are supplied, the line read is assigned to the
           variable REPLY.  The return code is zero, unless end-of-file is
           encountered, read times out (in which case the return code is
           greater than 128), a variable assignment error (such as assigning
           to a readonly 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
           specified 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 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 command
           associated with the RETURN trap is executed before execution
           resumes after the function or script.

      set [--abefhkmnptuvxBCEHPT] [-o option-name] [arg ...]
      set [+abefhkmnptuvxBCEHPT] [+o option-name] [arg ...]
           Without options, the name and value of each shell variable are
           displayed in a format that can be reused as input for setting or
           resetting the currently-set variables.  Read-only variables
           cannot be reset.  In posix mode, only shell variables are listed.
           The output is sorted according to the current locale.  When
           options are specified, they set or unset shell attributes.  Any
           arguments remaining after option processing are treated as values
           for the positional parameters and are assigned, in order, to $1,
           $2, ... $n.  Options, if specified, have the following meanings:




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           -a      Automatically mark variables and functions which are
                   modified or created for export to the environment of
                   subsequent commands.
           -b      Report the status of terminated background jobs
                   immediately, 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 environment
                   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 completes,
                   the shell prints a line containing its exit status.
           -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:




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                   allexport
                           Same as -a.
                   braceexpand
                           Same as -B.
                   emacs   Use an emacs-style command line editing
                           interface.  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
                           interactive 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.




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                   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
                   supplied, these actions are taken and the effective user
                   id is set to the real user id.  If the -p option is
                   supplied at startup, the effective user id is not reset.
                   Turning this option off causes the effective user and
                   group ids to be set to the real user and group ids.
           -t      Exit after reading and executing one command.
           -u      Treat unset variables and parameters other than the
                   special parameters "@" and "*" as an error when
                   performing parameter expansion.  If expansion is
                   attempted on an unset variable or parameter, the shell
                   prints an error message, and, if not interactive, exits
                   with a non-zero status.
           -v      Print shell input lines as they are read.
           -x      After expanding each simple command, for command, case
                   command, select command, or arithmetic for command,
                   display 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
                   redirection operator >| instead of >.
           -E      If set, any trap on ERR is inherited by shell functions,
                   command substitutions, and commands executed in a
                   subshell environment.  The ERR trap is normally not
                   inherited 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



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                   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
                   parameters 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
                   positional 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 encountered.

      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
           behavior.  The settings can be either those listed below, or, if
           the -o option is used, those available with the -o option to the
           set builtin command.  With no options, or with the -p option, a
           list of all settable options is displayed, with an indication of
           whether or not each is set.  The -p option causes output to be
           displayed in a form that may be reused as input.  Other options
           have the following meanings:
           -s   Enable (set) each optname.
           -u   Disable (unset) each optname.
           -q   Suppresses normal output (quiet mode); the return status
                indicates whether the optname is set or unset.  If multiple
                optname arguments are given with -q, the return status is
                zero if all optnames are enabled; non-zero otherwise.
           -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



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           default.

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

           The list of shopt options is:

           autocd  If set, a command name that is the name of a directory is
                   executed as if it were the argument to the cd command.
                   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
                   component in a cd command will be corrected.  The errors
                   checked for are transposed characters, a missing
                   character, and one character too many.  If a correction
                   is found, the corrected filename is printed, and the
                   command proceeds.  This option is only used by
                   interactive shells.
           checkhash
                   If set, bash checks that a command found in the hash
                   table exists before trying to execute it.  If a hashed
                   command no longer exists, a normal path search is
                   performed.
           checkjobs
                   If set, bash lists the status of any stopped and running
                   jobs before exiting an interactive shell.  If any jobs
                   are running, this causes the exit to be deferred until a
                   second exit is attempted without an intervening command
                   (see JOB CONTROL above).  The shell always postpones
                   exiting if any jobs are stopped.
           checkwinsize
                   If set, bash checks the window size after each command
                   and, if necessary, updates the values of LINES and
                   COLUMNS.
           cmdhist If set, bash attempts to save all lines of a multiple-
                   line command in the same history entry.  This allows easy
                   re-editing of multi-line commands.
           compat31
                   If set, bash changes its behavior to that of version 3.1
                   with respect to quoted arguments to the [[ conditional
                   command's =~ operator and locale-specific string
                   comparison when using the [[ conditional command's < and
                   > operators.  Bash versions prior to bash-4.1 use ASCII
                   collation and strcmp(3); bash-4.1 and later use the
                   current locale's collation sequence and strcoll(3).




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           compat32
                   If set, bash changes its behavior to that of version 3.2
                   with respect to locale-specific string comparison when
                   using the [[ conditional command's < and > operators (see
                   previous item).
           compat40
                   If set, bash changes its behavior to that of version 4.0
                   with respect to locale-specific string comparison when
                   using the [[ conditional command's < and > operators (see
                   description of compat31) and the effect of interrupting a
                   command list.  Bash versions 4.0 and later interrupt the
                   list as if the shell received the interrupt; previous
                   versions continue with the next command in the list.
           compat41
                   If set, bash, when in posix mode, treats a single quote
                   in a double-quoted parameter expansion as a special
                   character.  The single quotes must match (an even number)
                   and the characters between the single quotes are
                   considered quoted.  This is the behavior of posix mode
                   through version 4.1.  The default bash behavior remains
                   as in previous versions.
           compat42
                   If set, bash does not process the replacement string in
                   the pattern substitution word expansion using quote
                   removal.
           complete_fullquote
                   If set, bash quotes all shell metacharacters in filenames
                   and directory names when performing completion.  If not
                   set, bash removes metacharacters such as the dollar 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 backslashes 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
                   initially supplied does not exist.
           dotglob If set, bash includes filenames beginning with a `.' in
                   the results of pathname expansion.




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           execfail
                   If set, a non-interactive shell will not exit if it
                   cannot 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
                   interactive shells.
           extdebug
                   If set, 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 subroutine (a
                        shell function or a shell script executed by the .
                        or source builtins), a call to return is simulated.
                   4.   BASH_ARGC and BASH_ARGV are updated as described in
                        their descriptions above.
                   5.   Function tracing is enabled:  command substitution,
                        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
                   possible 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
                   comparisons.  That is, the current locale's collating



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                   sequence is not taken into account, so b will not collate
                   between A and B, and upper-case and lower-case ASCII
                   characters will collate together.
           globstar
                   If set, the pattern ** used in a pathname expansion
                   context 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
                   history substitution are not immediately passed to the
                   shell parser.  Instead, the resulting line is loaded into
                   the readline editing buffer, allowing further
                   modification.
           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
                   interactive login shell exits.
           interactive_comments
                   If set, allow a word beginning with # to cause that word
                   and all remaining characters on that line to be ignored
                   in an interactive shell (see COMMENTS above).  This
                   option is enabled by default.
           lastpipe
                   If set, and job control is not active, the shell runs the
                   last command of a pipeline not executed in the background
                   in the current shell environment.
           lithist If set, and the cmdhist option is enabled, multi-line
                   commands are saved to the history with embedded newlines
                   rather than using semicolon separators where possible.
           login_shell
                   The shell sets this option if it is started as a login
                   shell (see INVOCATION above).  The value may not be
                   changed.
           mailwarn
                   If set, and a file that bash is checking for mail has
                   been accessed since the last time it was checked, the



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                   message ``The mail in mailfile has been read'' is
                   displayed.
           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.
           nullglob
                   If set, bash allows patterns which match no files (see
                   Pathname Expansion above) to expand to a null string,
                   rather than themselves.
           progcomp
                   If set, the programmable completion facilities (see
                   Programmable Completion above) are enabled.  This option
                   is enabled by default.
           promptvars
                   If set, prompt strings undergo parameter expansion,
                   command 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 discover 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
                   parameters.
           sourcepath
                   If set, the source (.) builtin uses the value of PATH to
                   find the directory containing the file supplied as an
                   argument.  This option is enabled by default.
           xpg_echo
                   If set, the echo builtin expands backslash-escape
                   sequences by default.

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



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

           Expressions may be combined using the following operators, listed
           in decreasing order of precedence.  The evaluation depends on the
           number of arguments; see below.  Operator precedence 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 argument
                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.  Otherwise, the expression is
                false.



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           4 arguments
                If the first argument is !, the result is the negation of
                the three-argument expression composed of the remaining
                arguments.  Otherwise, the expression is parsed and
                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
                lexicographically 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
           corresponding 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 executed
           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
           finishes executing.

           If a sigspec is ERR, the command arg is executed whenever a a
           pipeline (which may consist of a single simple command), a list,
           or a compound command returns a non-zero exit status, subject to
           the following conditions.  The ERR trap is not executed if the
           failed command is part of the command list immediately following
           a while or until keyword, part of the test in an if statement,
           part of a command executed in a && or || list except the command



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           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 specified 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 necessarily 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 [-HSTabcdefilmnpqrstuvx [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 specified, both
           the soft and hard limits are set.  The value of limit can be a
           number in the unit specified for the resource or one of the
           special values hard, soft, or unlimited, which stand for the
           current hard limit, the current soft limit, and no limit,
           respectively.  If limit is omitted, the current value of the soft
           limit of the resource is printed, unless the -H option is given.
           When more than one resource is specified, the limit name and unit
           are printed before the value.  Other options are interpreted as
           follows:
           -a   All current limits are reported
           -b   The maximum socket buffer size
           -c   The maximum size of core files created




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           -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
           -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
           -T   The maximum number of threads

           If limit is given, and the -a option is not used, limit is the
           new value of the specified resource.  If no option is given, then
           -f is assumed.  Values are in 1024-byte increments, except for
           -t, which is in seconds; -p, which is in units of 512-byte
           blocks; and -T, -b, -n, and -u, which are unscaled values.  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 symbolic
           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 function, and the



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           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 variable by that name,
           any function with that name is unset.  Each unset variable or
           function is removed from the environment passed to subsequent
           commands.  If any of COMP_WORDBREAKS, RANDOM, SECONDS, LINENO,
           HISTCMD, FUNCNAME, GROUPS, or DIRSTACK are unset, they lose their
           special properties, even if they are subsequently reset.  The
           exit status is true unless a name is readonly.

      wait [-n] [n ...]
           Wait for each specified child process and return its termination
           status.  Each n may be a process ID or a job specification; if a
           job spec is given, all processes in that job's pipeline are
           waited for.  If n is not given, all currently active child
           processes are waited for, and the return status is zero.  If the
           -n option is supplied, wait waits for any job to terminate and
           returns its exit status.  If n specifies a non-existent process
           or job, the return status is 127.  Otherwise, the return status
           is the exit status of the last process or job waited for.

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

      +    changing directories with cd

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

      +    specifying command names containing /

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

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

      +    importing function definitions from the shell environment at
           startup

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

      +    redirecting output using the >, >|, <>, >&, &>, and >>
           redirection operators




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

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

      +    using the enable builtin command to enable disabled shell
           builtins

      +    specifying the -p option to the command builtin command

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

      These restrictions are enforced after any startup files are read.

      When a command that is found to be a shell script is executed (see
      COMMAND 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
 IEEE --
      Portable Operating System Interface (POSIX) Part 2: Shell and Utilities,
           http://pubs.opengroup.org/onlinepubs/9699919799/
      http://tiswww.case.edu/~chet/bash/POSIX -- a description of posix mode
      sh(1), ksh(1), csh(1)
      emacs(1), vi(1)
      readline(3)

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

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





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

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

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

      ALL bug reports should include:

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

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

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

 BUGS
      It's too big and too slow.

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

      Aliases are confusing in some uses.

      Shell builtin commands and functions are not stoppable/restartable.

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

      Array variables may not (yet) be exported.

      There may be only one active coprocess at a time.





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