     BASH(1)                        GNU Bash 5.1                         BASH(1)
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     NAME
          bash - GNU Bourne-Again SHell

     SYNOPSIS
          bash [options] [command_string | file]

     COPYRIGHT
          Bash is Copyright (C) 1989-2020 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, including -o, can be used as
          options when the shell is invoked.  In addition, bash interprets the
          following options when it is invoked:

          -c        If the -c option is present, then commands are read from the
                    first non-option argument command_string.  If there are
                    arguments after the command_string, the first argument is
                    assigned to $0 and any remaining arguments are assigned to
                    the positional parameters.  The assignment to $0 sets the
                    name of the shell, which is used in warning and error
                    messages.
          -i        If the -i option is present, the shell is interactive.
          -l        Make bash act as if it had been invoked as a login shell
                    (see INVOCATION below).
          -r        If the -r option is present, the shell becomes restricted
                    (see RESTRICTED SHELL below).
          -s        If the -s option is present, or if no arguments remain after
                    option processing, then commands are read from the standard
                    input.  This option allows the positional parameters to be
                    set when invoking an interactive shell or when reading input
                    through a pipe.
          -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

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                    and values of the shell options accepted by shopt are
                    printed on the standard output.  If the invocation option is
                    +O, the output is displayed in a format that may be reused
                    as input.
          --        A -- signals the end of options and disables further option
                    processing.  Any arguments after the -- are treated as
                    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

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               SEE ALSO below for a reference to a document that details how
               posix mode affects bash's behavior.

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

          --verbose
               Equivalent to -v.

          --version
               Show version information for this instance of bash on the
               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
          (unless -s is specified) and without the -c option whose standard
          input and error are both connected to terminals (as determined by
          isatty(3)), or one started with the -i option.  PS1 is set and $-
          includes i if bash is interactive, allowing a shell script or a
          startup file to test this state.

          The following paragraphs describe how bash executes its startup files.
          If any of the files exist but cannot be read, bash reports an error.
          Tildes are expanded in filenames as described below under Tilde
          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 an interactive login shell exits, or a non-interactive login
          shell executes the exit builtin command, bash reads and executes

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          commands from the file ~/.bash_logout, if it exists.

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

          When bash is started non-interactively, to run a shell script, for
          example, it looks for the variable BASH_ENV in the environment,
          expands its value if it appears there, and uses the expanded value as
          the name of a file to read and execute.  Bash behaves as if the
          following 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.

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

     DEFINITIONS
          The following definitions are used throughout the rest of this
          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 newline
          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 command (see SHELL GRAMMAR below), the
          third word of a case or select command (only in is valid), or the
          third word of a for command (only in and do are valid):

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

     SHELL GRAMMAR
        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

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

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

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

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          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.  These
          are referred to as asynchronous commands.  Commands separated by a ;
          are executed sequentially; the shell waits for each command to
          terminate in turn.  The return status is the exit status of the last
          command executed.

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

               command1 && command2

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

          An OR list has the form

               command1 || command2

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

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

          (list)
               list is executed in a subshell environment (see COMMAND 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.

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          ((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
               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 nocasematch shell option is enabled, the match is
               performed without regard to the case of alphabetic characters.
               The return value is 0 if the string matches (==) or does not
               match (!=) the pattern, and 1 otherwise.  Any part of the pattern
               may be quoted to force the quoted portion to be matched as a
               string.

               An additional binary operator, =~, is available, with the same
               precedence as == and !=.  When it is used, the string to the
               right of the operator is considered a POSIX extended regular
               expression and matched accordingly (using the POSIX regcomp and
               regexec interfaces usually described in regex(3)).  The return
               value is 0 if the string matches the pattern, and 1 otherwise.
               If the regular expression is syntactically incorrect, the
               conditional expression's return value is 2.  If the nocasematch
               shell option is enabled, the match is performed without regard to
               the case of alphabetic characters.  Any part of the pattern may
               be quoted to force the quoted portion to be matched as a string.
               Bracket expressions in regular expressions must be treated
               carefully, since normal quoting characters lose their meanings
               between brackets.  If the pattern is stored in a shell variable,
               quoting the variable expansion forces the entire pattern to be
               matched as a string.

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

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               to force it to match the entire string.  The array variable
               BASH_REMATCH records which parts of the string matched the
               pattern.  The element of BASH_REMATCH with index 0 contains the
               portion of the string matching the entire regular expression.
               Substrings matched by parenthesized subexpressions within the
               regular expression are saved in the remaining BASH_REMATCH
               indices. The element of BASH_REMATCH with index n is the portion
               of the string matching the nth parenthesized subexpression.

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

               ( expression )
                    Returns the value of expression.  This may be used to
                    override the normal precedence of operators.
               ! expression
                    True if expression is false.
               expression1 && expression2
                    True if both expression1 and expression2 are true.
               expression1 || expression2
                    True if either expression1 or expression2 is true.  The &&
                    and || operators do not evaluate expression2 if the value of
                    expression1 is sufficient to determine the return value of
                    the entire conditional expression.

          for name [ [ in [ word ... ] ] ; ] do list ; done
               The list of words following in is expanded, generating a list of
               items.  The variable name is set to each element of this list in
               turn, and list is executed each time.  If the in word is 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

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               PS3 prompt is then displayed and a line read from the standard
               input.  If the line consists of a number corresponding to one of
               the displayed words, then the value of name is set to that word.
               If the line is empty, the words and prompt are displayed again.
               If EOF is read, the command completes.  Any other value read
               causes name to be set to null.  The line read is saved in the
               variable REPLY.  The list is executed after each selection until
               a break command is executed.  The exit status of select is the
               exit status of the last command executed in list, or zero if no
               commands were executed.

          case word in [ [(] pattern [ | pattern ] ... ) list ;; ] ... esac
               A case command first expands word, and tries to match it against
               each pattern in turn, using the matching rules described under
               Pattern Matching below.  The word is expanded using tilde
               expansion, parameter and variable expansion, arithmetic
               expansion, command substitution, process substitution and quote
               removal.  Each pattern examined is expanded using tilde
               expansion, parameter and variable expansion, arithmetic
               expansion, command substitution, and process substitution.  If
               the nocasematch shell option is enabled, the match is performed
               without regard to the case of alphabetic characters.  When a
               match is found, the 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, continuing the case statement
               execution as if the pattern list had not matched.  The exit
               status is zero if no pattern matches.  Otherwise, it is the exit
               status of the last command executed in list.

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

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

          fname () compound-command [redirection]
          function fname [()] compound-command [redirection]
               This defines a function named fname.  The reserved word function
               is optional.  If the function reserved word is supplied, the
               parentheses are optional.  The body of the function is the
               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, with one
               exception: If the function reserved word is used, but the
               parentheses are not supplied, the braces are required.
               compound-command is executed whenever fname is specified as the
               name of a simple command.  When in posix mode, fname must be a
               valid shell name and may not be the name of one of the POSIX

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               special builtins.  In default mode, a function name can be any
               unquoted shell word that does not contain $.  Any redirections
               (see REDIRECTION below) specified when a function is defined are
               performed when the function is executed.  The exit status of a
               function definition is zero unless a syntax error occurs or a
               readonly function with the same name already exists.  When
               executed, the exit status of a function is the exit status of the
               last command executed in the body.  (See FUNCTIONS below.)

     COMMENTS
          In a non-interactive shell, or an interactive shell in which the
          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
          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, !.  When the shell is in posix
          mode, the ! has no special meaning within double quotes, even when
          history expansion is enabled.  The characters $ and ` retain their
          special meaning within double quotes.  The backslash retains its
          special meaning only when followed by one of the following characters:

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          $, `, ", \, or <newline>.  A double quote may be quoted within double
          quotes by preceding it with a backslash.  If enabled, history
          expansion will be performed unless an ! appearing in double quotes is
          escaped using a backslash.  The backslash preceding the ! is not
          removed.

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

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

          A double-quoted string preceded by a dollar sign ($string) will cause
          the string to be translated according to the current locale.  The
          gettext infrastructure performs the message catalog lookup and
          translation, using the LC_MESSAGES and TEXTDOMAIN shell variables.  If
          the current locale is C or POSIX, or if there are no translations
          available, 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

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          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
          (declaration commands).  When in posix mode, these builtins may appear
          in a command after one or more instances of the command builtin and
          retain these assignment statement properties.

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

          A variable can be assigned the nameref attribute using the -n option
          to the declare or local builtin commands (see the descriptions of
          declare and local below) to create a nameref, or a reference to
          another variable.  This allows variables to be manipulated indirectly.
          Whenever the nameref variable is referenced, assigned to, unset, or
          has its attributes modified (other than using or changing the nameref
          attribute itself), the operation is actually performed on the variable
          specified by the nameref variable's value.  A nameref is commonly used
          within shell functions to refer to a variable whose name is passed as

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          an argument to the function.  For instance, if a variable name is
          passed to a shell function as its first argument, running

               declare -n ref=$1
          inside the function creates a nameref variable ref whose value is the
          variable name passed as the first argument.  References and
          assignments to ref, and changes to its attributes, are treated as
          references, assignments, and attribute modifications to the variable
          whose name was passed as $1.  If the control variable in a for loop
          has the nameref attribute, the list of words can be a list of shell
          variables, and a name reference will be established for each word in
          the list, in turn, when the loop is executed.  Array variables cannot
          be given the nameref attribute.  However, nameref variables can
          reference array variables and subscripted array variables.  Namerefs
          can be unset using the -n option to the unset builtin.  Otherwise, if
          unset is executed with the name of a nameref variable as an argument,
          the variable referenced by the nameref variable will be unset.

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

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

        Special Parameters
          The shell treats several parameters specially.  These parameters may
          only be referenced; assignment to them is not allowed.
          *    Expands to the positional parameters, starting from one.  When
               the expansion is not within double quotes, each positional
               parameter expands to a separate word.  In contexts where it is
               performed, those words are subject to further word splitting and
               pathname expansion.  When the expansion occurs within double
               quotes, it expands to a single word with the value of each
               parameter separated by the first character of the IFS special
               variable.  That is, "$*" is equivalent to "$1c$2c...", where c is
               the first character of the value of the IFS variable.  If IFS is
               unset, the parameters are separated by spaces.  If IFS is null,
               the parameters are joined without intervening separators.
          @    Expands to the positional parameters, starting from one.  In
               contexts where word splitting is performed, this expands each
               positional parameter to a separate word; if not within double
               quotes, these words are subject to word splitting.  In contexts
               where word splitting is not performed, this expands to a single
               word with each positional parameter separated by a space.  When
               the expansion occurs within double quotes, each parameter expands

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               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.

        Shell Variables
          The following variables are set by the shell:

          _    At shell startup, set to the pathname used to invoke the shell or
               shell script being executed as passed in the environment or
               argument list.  Subsequently, expands to the last argument to the
               previous simple command executed in the foreground, after
               expansion.  Also set to the full pathname used to invoke each
               command executed and placed in the environment exported to that
               command.  When checking mail, this parameter holds the name of
               the mail file currently being checked.
          BASH Expands to the full filename used to invoke this instance of
               bash.
          BASHOPTS
               A colon-separated list of enabled shell options.  Each word in
               the list is a valid argument for the -s option to the shopt
               builtin command (see SHELL BUILTIN COMMANDS below).  The options
               appearing in BASHOPTS are those reported as on by shopt.  If this
               variable is in the environment when bash starts up, each shell
               option in the list will be enabled before reading any startup
               files.  This variable is read-only.
          BASHPID
               Expands to the process ID of the current bash process.  This
               differs from $$ under certain circumstances, such as subshells
               that do not require bash to be re-initialized.  Assignments to

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                                   2020 October 29

               BASHPID have no effect.  If BASHPID is unset, it loses its
               special properties, even if it is subsequently reset.
          BASH_ALIASES
               An associative array variable whose members correspond to the
               internal list of aliases as maintained by the alias builtin.
               Elements added to this array appear in the alias list; however,
               unsetting array elements currently does not cause aliases to be
               removed from the alias list.  If BASH_ALIASES is unset, it loses
               its special properties, even if it is subsequently reset.
          BASH_ARGC
               An array variable whose values are the number of parameters in
               each frame of the current bash execution call stack.  The number
               of parameters to the current subroutine (shell function or script
               executed with . or source) is at the top of the stack.  When a
               subroutine is executed, the number of parameters passed is pushed
               onto BASH_ARGC.  The shell sets BASH_ARGC only when in extended
               debugging mode (see the description of the extdebug option to the
               shopt builtin below).  Setting extdebug after the shell has
               started to execute a script, or referencing this variable when
               extdebug is not set, may result in inconsistent values.
          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).  Setting extdebug after the shell has started to execute
               a script, or referencing this variable when extdebug is not set,
               may result in inconsistent values.
          BASH_ARGV0
               When referenced, this variable expands to the name of the shell
               or shell script (identical to $0; see the description of special
               parameter 0 above).  Assignment to BASH_ARGV0 causes the value
               assigned to also be assigned to $0.  If BASH_ARGV0 is unset, it
               loses its special properties, even if it is subsequently reset.
          BASH_CMDS
               An associative array variable whose members correspond to the
               internal hash table of commands as maintained by the hash
               builtin.  Elements added to this array appear in the hash table;
               however, unsetting array elements currently does not cause
               command names to be removed from the hash table.  If BASH_CMDS is
               unset, it loses its special properties, even if it is
               subsequently reset.
          BASH_COMMAND
               The command currently being executed or about to be executed,
               unless the shell is executing a command as the result of a trap,
               in which case it is the command executing at the time of the
               trap.  If BASH_COMMAND is unset, it loses its special properties,
               even if it is subsequently reset.

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          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_LOADABLES_PATH
               A colon-separated list of directories in which the shell looks
               for dynamically loadable builtins specified by the enable
               command.
          BASH_REMATCH
               An array variable whose members are assigned by the =~ binary
               operator to the [[ conditional command.  The element with index 0
               is the portion of the string matching the entire regular
               expression.  The element with index n is the portion of the
               string matching the nth parenthesized subexpression.
          BASH_SOURCE
               An array variable whose members are the source filenames where
               the corresponding shell function names in the FUNCNAME array
               variable are defined.  The shell function ${FUNCNAME[$i]} is
               defined in the file ${BASH_SOURCE[$i]} and called from
               ${BASH_SOURCE[$i+1]}.
          BASH_SUBSHELL
               Incremented by one within each subshell or subshell environment
               when the shell begins executing in that environment.  The initial
               value is 0.  If BASH_SUBSHELL is unset, it loses its special
               properties, even if it is subsequently reset.
          BASH_VERSINFO
               A readonly array variable whose members hold version information
               for this instance of bash.  The values assigned to the array
               members are as follows:

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

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               current completion function.
          COMP_LINE
               The current command line.  This variable is available only in
               shell functions and external commands invoked by the programmable
               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.
          EPOCHREALTIME
               Each time this parameter is referenced, it expands to the number
               of seconds since the Unix Epoch (see time(3)) as a floating point
               value with micro-second granularity.  Assignments to

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               EPOCHREALTIME are ignored.  If EPOCHREALTIME is unset, it loses
               its special properties, even if it is subsequently reset.
          EPOCHSECONDS
               Each time this parameter is referenced, it expands to the number
               of seconds since the Unix Epoch (see time(3)).  Assignments to
               EPOCHSECONDS are ignored.  If EPOCHSECONDS is unset, it loses its
               special properties, even if it is subsequently reset.
          EUID Expands to the effective user ID of the current user, 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.
               Assignments to FUNCNAME have no effect.  If FUNCNAME is unset, it
               loses its special properties, even if it is subsequently reset.

               This variable can be used with BASH_LINENO and BASH_SOURCE.  Each
               element of FUNCNAME has corresponding elements in BASH_LINENO and
               BASH_SOURCE to describe the call stack.  For instance,
               ${FUNCNAME[$i]} was called from the file ${BASH_SOURCE[$i+1]} at
               line number ${BASH_LINENO[$i]}.  The caller builtin displays the
               current call stack using this information.
          GROUPS
               An array variable containing the list of groups of which the
               current user is a member.  Assignments to GROUPS have no effect.
               If GROUPS is unset, it loses its special properties, even if it
               is subsequently reset.
          HISTCMD
               The history number, or index in the history list, of the current
               command.  Assignments to HISTCMD are ignored.  If HISTCMD is
               unset, it loses its special properties, even if it is
               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.

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          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.
          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, it expands to a random
               integer between 0 and 32767.  Assigning a value to RANDOM
               initializes (seeds) the sequence of random numbers.  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_MARK
               The position of the mark (saved insertion point) in the readline
               line buffer, for use with "bind -x" (see SHELL BUILTIN COMMANDS
               below).  The characters between the insertion point and the mark
               are often called the region.
          READLINE_POINT
               The position of the insertion point in the readline line buffer,
               for use with "bind -x" (see SHELL BUILTIN COMMANDS below).
          REPLY
               Set to the line of input read by the read builtin command when no
               arguments are supplied.
          SECONDS
               Each time this parameter is referenced, 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.
               The number of seconds at shell invocation and the current time is
               always determined by querying the system clock.  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

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               the list is a valid argument for the -o option to the set builtin
               command (see SHELL BUILTIN COMMANDS below).  The options
               appearing in SHELLOPTS are those reported as on by set -o.  If
               this variable is in the environment when bash starts up, each
               shell option in the list will be enabled before reading any
               startup files.  This variable is read-only.
          SHLVL
               Incremented by one each time an instance of bash is started.
          SRANDOM
               This variable expands to a 32-bit pseudo-random number each time
               it is referenced. The random number generator is not linear on
               systems that support /dev/urandom or arc4random, so each returned
               number has no relationship to the numbers preceding it.  The
               random number generator cannot be seeded, so assignments to this
               variable have no effect.  If SRANDOM is unset, it loses its
               special properties, even if it is subsequently reset.
          UID  Expands to the user ID of the current user, initialized at shell
               startup.  This variable is readonly.

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

          BASH_COMPAT
               The value is used to set the shell's compatibility level.  See
               SHELL COMPATIBILITY MODE below for a description of the various
               compatibility levels and their effects.  The value may be a
               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 string, the compatibility level is set to the
               default for the current version.  If BASH_COMPAT is set to a
               value that is not one of the valid compatibility levels, the
               shell prints an error message and sets the compatibility level to
               the default for the current version.  The valid values correspond
               to the compatibility levels described below under
               BSHELLCOMPATIBILITYMODE.  For example, 4.2 and 42 are valid
               values that correspond to the compat42 shopt option and set the
               compatibility level to 42.  The current version is also a valid
               value.
          BASH_ENV
               If this parameter is set when bash is executing a shell script,
               its 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

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               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  Expanded and executed similarly to BASH_ENV (see INVOCATION
               above) when an interactive shell is invoked in posix mode.
          EXECIGNORE
               A colon-separated list of shell patterns (see Pattern Matching)
               defining the list of filenames to be ignored by command search
               using PATH.  Files whose full pathnames match one of these
               patterns are not considered executable files for the purposes of
               completion and command execution via PATH lookup.  This does not
               affect the behavior of the [, test, and [[ commands.  Full
               pathnames in the command hash table are not subject to
               EXECIGNORE.  Use this variable to ignore shared library files
               that have the executable bit set, but are not executable files.
               The pattern matching honors the setting of the extglob shell
               option.
          FCEDIT
               The default editor for the fc builtin command.
          FIGNORE
               A colon-separated list of suffixes to ignore when performing
               filename completion (see READLINE below).  A filename whose
               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

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               function nesting level.  Function invocations that exceed this
               nesting level will cause the current command to abort.
          GLOBIGNORE
               A colon-separated list of patterns defining the set of file names
               to be ignored by pathname expansion.  If a file name matched by a
               pathname expansion pattern also matches one of the patterns in
               GLOBIGNORE, it is removed from the list of matches.
          HISTCONTROL
               A colon-separated list of values controlling how commands are
               saved on the history list.  If the list of values includes
               ignorespace, lines which begin with a space character are not
               saved in the history list.  A value of ignoredups causes lines
               matching the previous history entry to not be saved.  A value of
               ignoreboth is shorthand for ignorespace and ignoredups.  A value
               of erasedups causes all previous lines matching the current line
               to be removed from the history list before that line is saved.
               Any value not in the above list is ignored.  If HISTCONTROL is
               unset, or does not include a valid value, all lines read by the
               shell parser are saved on the history list, subject to the value
               of HISTIGNORE.  The second and subsequent lines of a multi-line
               compound command are not tested, and are added to the history
               regardless of the value of HISTCONTROL.
          HISTFILE
               The name of the file in which command history is saved (see
               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
               applied.  In addition to the normal shell pattern matching
               characters, `&' matches the previous history line.  `&' may be
               escaped using a backslash; the backslash is removed before
               attempting a match.  The second and subsequent lines of a multi-
               line compound command are not tested, and are added to the
               history regardless of the value of HISTIGNORE.  The pattern
               matching honors the setting of the extglob shell option.
          HISTSIZE
               The number of commands to remember in the command history (see

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               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).
          INSIDE_EMACS
               If this variable appears in the environment when the shell
               starts, bash assumes that it is running inside an Emacs shell
               buffer and may disable line editing, depending on the value of
               TERM.
          LANG Used to determine the locale category for any category not
               specifically selected with a variable starting with LC_.
          LC_ALL
               This variable overrides the value of LANG and any other LC_
               variable specifying a locale category.

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          LC_COLLATE
               This variable determines the collation order used when sorting
               the results of pathname expansion, and determines the behavior of
               range expressions, equivalence classes, and collating sequences
               within pathname expansion and pattern matching.
          LC_CTYPE
               This variable determines the interpretation of characters and the
               behavior of character classes within pathname expansion and
               pattern matching.
          LC_MESSAGES
               This variable determines the locale used to translate double-
               quoted strings preceded by a $.
          LC_NUMERIC
               This variable determines the locale category used for number
               formatting.
          LC_TIME
               This variable determines the locale category used for data and
               time formatting.
          LINES
               Used by the select compound command to determine the column
               length for printing selection lists.  Automatically set if the
               checkwinsize option is enabled or in an interactive shell upon
               receipt of a SIGWINCH.
          MAIL If this parameter is set to a file or directory name and the
               MAILPATH variable is not set, bash informs the user of the
               arrival of mail in the specified file or Maildir-format
               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 can be configured to supply a default value for this
               variable (there is no value by default), but the location of the
               user mail files that it uses is system dependent (e.g.,
               /var/mail/$USER).
          OPTERR
               If set to the value 1, bash displays error messages generated by
               the getopts builtin command (see SHELL BUILTIN COMMANDS below).
               OPTERR is initialized to 1 each time the shell is invoked or a
               shell script is executed.

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          PATH The search path for commands.  It is a colon-separated list of
               directories in which the shell looks for commands (see COMMAND
               EXECUTION below).  A zero-length (null) directory name in the
               value of PATH indicates the current directory.  A null directory
               name may appear as two adjacent colons, or as an initial or
               trailing colon.  The default path is system-dependent, and is set
               by the administrator who installs bash.  A common value is
               ``/usr/local/bin:/usr/local/sbin:/usr/bin:/usr/sbin:/bin:/sbin''.
          POSIXLY_CORRECT
               If this variable is in the  environment  when  bash  starts,  the
               shell  enters  posix mode before reading the startup files, as if
               the --posix invocation option had been supplied.  If  it  is  set
               while  the  shell  is running, bash enables posix mode, as if the
               command set -o posix had been executed.  When  the  shell  enters
               posix mode, it sets this variable if it was not already set.
          PROMPT_COMMAND
               If this variable is set, and is an array, the value of  each  set
               element  is  executed  as a command prior to issuing each primary
               prompt.  If this is set but not an array variable, its  value  is
               used as a command to execute instead.
          PROMPT_DIRTRIM
               If set to a number greater than zero, the value is  used  as  the
               number  of trailing directory components to retain when expanding
               the \w and  \W  prompt  string  escapes  (see  PROMPTING  below).
               Characters removed are replaced with an ellipsis.
          PS0  The value of this parameter is expanded (see PROMPTING below) and
               displayed  by  interactive  shells  after  reading  a command and
               before the command is executed.
          PS1  The value of this parameter is expanded (see PROMPTING below) and
               used  as  the  primary  prompt  string.   The  default  value  is
               ``\s-\v\$ ''.
          PS2  The value of this parameter is expanded as with PS1 and  used  as
               the secondary prompt string.  The default is ``> ''.
          PS3  The value of this parameter is used as the prompt for the  select
               command (see SHELL GRAMMAR above).
          PS4  The value of this parameter is expanded as with PS1 and the value
               is  printed before each command bash displays during an execution
               trace.  The first character of  the  expanded  value  of  PS4  is
               replicated  multiple  times,  as  necessary, to indicate multiple
               levels of indirection.  The default is ``+ ''.
          SHELL
               This variable expands to the full pathname to the shell.   If  it
               is  not  set  when  the shell starts, bash assigns to it the full
               pathname of the current user's login shell.
          TIMEFORMAT
               The value of this parameter is used as a format string 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.

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               %%        A literal %.
               %[p][l]R  The elapsed time in seconds.
               %[p][l]U  The number of CPU seconds spent in user mode.
               %[p][l]S  The number of CPU seconds spent in system mode.
               %P        The CPU percentage, computed as (%U + %S) / %R.

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

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

               If this variable is not set, bash acts as if  it  had  the  value
               $\nreal\t%3lR\nuser\t%3lU\nsys\t%3lS.   If  the value is null, no
               timing information is displayed.  A  trailing  newline  is  added
               when the format string is displayed.
          TMOUT
               If set to a value greater than zero,  TMOUT  is  treated  as  the
               default  timeout  for  the  read  builtin.   The  select  command
               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

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               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
               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  may  be  of  the form
          [subscript]=string.  Indexed array assignments do not require anything
          but  string.   Each  value in the list is expanded using all the shell
          expansions described below under EXPANSION.  When assigning to indexed
          arrays,  if  the  optional  brackets  and subscript are supplied, that
          index is assigned to; otherwise the index of the element  assigned  is
          the last index assigned to by the statement plus one.  Indexing starts
          at zero.

          When assigning to an  associative  array,  the  words  in  a  compound
          assignment   may  be  either  assignment  statements,  for  which  the
          subscript is required, or a list of words that  is  interpreted  as  a
          sequence  of  alternating  keys  and  values:  name=( key1 value1 key2
          value2 ...).  These are treated identically  to  name=(  [key1]=value1

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          [key2]=value2  ...).   The  first  word in the list determines how the
          remaining words are interpreted; all assignments in a list must be  of
          the  same  type.   When  using  key/value  pairs,  the keys may not be
          missing or empty; a final missing value  is  treated  like  the  empty
          string.

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

          Referencing an array variable without a  subscript  is  equivalent  to
          referencing  the  array  with  a  subscript  of 0.  Any reference to a
          variable using a valid subscript is legal, and  bash  will  create  an
          array if necessary.

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

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

          The unset builtin is used to destroy  arrays.   unset  name[subscript]
          destroys  the  array  element at index subscript, for both indexed and

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          associative  arrays.   Negative  subscripts  to  indexed  arrays   are
          interpreted  as  described  above.   Unsetting  the last element of an
          array variable does not unset the variable.  unset name, where name is
          an array, or unset name[subscript], where subscript is * or @, removes
          the entire array.

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

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

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

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

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

        Brace Expansion
          Brace expansion is a mechanism  by  which  arbitrary  strings  may  be
          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

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

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

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

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

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        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.

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

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

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

          ${parameter}
               The value of parameter is substituted.  The braces  are  required
               when  parameter  is  a  positional  parameter  with more than one

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               digit, or when parameter is followed by a character which is  not
               to  be interpreted as part of its name.  The parameter is a shell
               parameter as described above PARAMETERS) or  an  array  reference
               (Arrays).

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

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               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
               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.

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          ${#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, and matched against the
               expanded value of  parameter  using  the  rules  described  under
               Pattern  Matching below.  If the pattern matches the beginning of
               the value of parameter, then the result of the expansion  is  the
               expanded  value  of  parameter with the shortest matching pattern
               (the ``#'' case) or the  longest  matching  pattern  (the  ``##''
               case)  deleted.   If  parameter  is  @  or *, the pattern removal
               operation is applied to each positional parameter  in  turn,  and
               the  expansion  is  the resultant list.  If parameter is an array
               variable subscripted with @ or *, the pattern  removal  operation
               is applied to each member of the array in turn, and the expansion
               is the resultant list.

          ${parameter%word}
          ${parameter%%word}
               Remove matching suffix pattern.  The word is expanded to  produce
               a  pattern just as in pathname expansion, and matched against the
               expanded value of  parameter  using  the  rules  described  under
               Pattern  Matching  below.   If  the  pattern  matches  a trailing
               portion of the expanded value of parameter, then  the  result  of
               the  expansion  is  the  expanded  value  of  parameter  with the
               shortest  matching  pattern  (the  ``%''  case)  or  the  longest
               matching 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
               pattern  just as in pathname expansion, Parameter is expanded and
               the longest match of pattern against its value is  replaced  with
               string.   The  match is performed using the rules described under
               Pattern Matching below.  If pattern begins with /, all matches of
               pattern  are replaced with string.  Normally only the first match
               is replaced.  If pattern begins with #,  it  must  match  at  the

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               beginning  of the expanded value of parameter.  If pattern begins
               with %, it must match  at  the  end  of  the  expanded  value  of
               parameter.  If string is null, matches of pattern are deleted and
               the / following pattern may be omitted.  If the nocasematch shell
               option  is  enabled, the match is performed without regard to the
               case of alphabetic characters.  If  parameter  is  @  or  *,  the
               substitution operation is applied to each positional 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.

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

               U    The expansion is a string that is  the  value  of  parameter
                    with lowercase alphabetic characters converted to uppercase.
               u    The expansion is a string that is  the  value  of  parameter
                    with  the  first  character converted to uppercase, if it is
                    alphabetic.
               L    The expansion is a string that is  the  value  of  parameter
                    with uppercase alphabetic characters converted to lowercase.
               Q    The expansion is a string that is  the  value  of  parameter
                    quoted in a format that can be reused as input.

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               E    The expansion is a string that is  the  value  of  parameter
                    with  backslash escape sequences expanded as with the $'...'
                    quoting mechanism.
               P    The expansion is a string that is the  result  of  expanding
                    the  value  of  parameter as if it were a prompt string (see
                    PROMPTING below).
               A    The expansion is a string  in  the  form  of  an  assignment
                    statement  or  declare  command  that,  if  evaluated,  will
                    recreate parameter with its attributes and value.
               K     Produces  a  possibly-quoted  version  of  the   value   of
                    parameter,  except  that it prints the values of indexed and
                    associative arrays as a sequence of quoted  key-value  pairs
                    (see Arrays above).
               a     The  expansion  is  a  string  consisting  of  flag  values
                    representing parameter's attributes.

               If parameter is  @  or  *,  the  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 operation is applied to each member of the array in turn, and
               the expansion is the resultant list.

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

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

               $(command)
          or
               `command`

          Bash performs  the  expansion  by  executing  command  in  a  subshell
          environment  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).

          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.

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        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 allows a process's input or output to be referred
          to  using  a  filename.  It takes the form of <(list) or >(list).  The
          process list is run asynchronously, and its input or output appears as
          a  filename.   This  filename  is passed as an argument to the current
          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.   Process  substitution is supported on systems that
          support named pipes (FIFOs) or  the  /dev/fd  method  of  naming  open
          files.

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

        Word Splitting
          The  shell  scans  the  results  of   parameter   expansion,   command
          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
          field  terminators.   If  IFS  is  unset,  or  its  value  is  exactly
          <space><tab><newline>,  the default, then sequences of <space>, <tab>,
          and <newline> at the beginning and end of the results of the  previous
          expansions  are ignored, and any sequence of IFS characters not at the
          beginning or end serves to delimit words.  If IFS has  a  value  other
          than  the  default, then sequences of the whitespace characters space,
          tab, and newline are ignored at the beginning and end of the word,  as
          long  as  the  whitespace  character  is  in  the value of IFS (an IFS
          whitespace  character).   Any  character  in  IFS  that  is  not   IFS
          whitespace,   along  with  any  adjacent  IFS  whitespace  characters,

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          delimits a field.  A sequence of IFS  whitespace  characters  is  also
          treated  as  a  delimiter.   If  the  value  of  IFS  is null, no word
          splitting occurs.

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

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

        Pathname Expansion
          After word splitting, unless the -f option has been  set,  bash  scans
          each  word for the characters *, ?, and [.  If one of these characters
          appears, and is not quoted, then the word is regarded  as  a  pattern,
          and  replaced with an alphabetically sorted list of filenames matching
          the pattern (see Pattern Matching below).  If  no  matching  filenames
          are  found,  and the shell option nullglob is not enabled, the word is
          left unchanged.  If the nullglob option is set,  and  no  matches  are
          found,  the word is removed.  If the failglob shell option is set, and
          no matches are found, an error message is printed and the  command  is
          not executed.  If the shell option nocaseglob is enabled, the match is
          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.  The filenames
          ``.'' and ``..'' must always be matched explicitly, even if dotglob is
          set.   In  other  cases, the ``.'' character is not treated specially.
          When matching a pathname, the slash character must always  be  matched
          explicitly  by  a slash in the pattern, but in other matching contexts
          it can be matched by a special pattern character  as  described  below
          under  Pattern  Matching.   See  the  description of shopt below under
          SHELL BUILTIN COMMANDS for a description of the nocaseglob,  nullglob,
          failglob, and dotglob shell options.

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

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          extglob shell option.

          Pattern Matching

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

          The special pattern characters have the following meanings:

               *    Matches any string, including the  null  string.   When  the
                    globstar  shell  option  is  enabled,  and  *  is  used in a
                    pathname expansion context, two adjacent *s used as a single
                    pattern  will  match  all files and zero or more directories
                    and subdirectories.  If followed by a  /,  two  adjacent  *s
                    will match only directories and 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.

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                    Within [ and ], the syntax [.symbol.] matches the  collating
                    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

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

        Quote Removal
          After the  preceding  expansions,  all  unquoted  occurrences  of  the
          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.   If  {varname} is
          supplied, the redirection persists beyond the scope  of  the  command,
          allowing the shell programmer to manage the file descriptor himself.

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          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
          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.  If the operating
          system on which bash is running provides  these  special  files,  bash
          will  use  them;  otherwise  it  will emulate them internally with the
          behavior described below.

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

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          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:

               [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:

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               &>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.

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

          The format for appending standard output and standard error is:

               &>>word

          This is semantically equivalent to

               >>word 2>&1

          (see Duplicating File Descriptors below).

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

          The format of here-documents is:

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

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

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

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

               [n]<<<word

          The word undergoes tilde expansion, parameter and variable  expansion,
          command   substitution,   arithmetic  expansion,  and  quote  removal.
          Pathname expansion and word splitting are not performed.   The  result
          is  supplied  as  a  single  string,  with  a newline appended, to the
          command  on  its  standard  input  (or  file  descriptor  n  if  n  is
          specified).

        Duplicating File Descriptors
          The redirection operator

               [n]<&word

          is used to duplicate input file descriptors.  If word expands  to  one
          or  more digits, the file descriptor denoted by n is made to be a copy
          of that file descriptor.  If the digits in word do not specify a  file
          descriptor  open  for  input,  a  redirection  error  occurs.  If word
          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.

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          Similarly, the redirection operator

               [n]>&digit-

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

        Opening File Descriptors for Reading and Writing
          The redirection operator

               [n]<>word

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

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

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

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

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

          The rules concerning the definition and use of  aliases  are  somewhat
          confusing.  Bash always reads at least one complete line of input, and
          all lines that make up a compound command, before executing any of the
          commands  on  that line or the compound command.  Aliases are expanded
          when a command is read, not when it is executed.  Therefore, an  alias
          definition appearing on the same line as another command does not take
          effect until the next line of input is read.  The  commands  following

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          the  alias  definition on that line are not affected by the new alias.
          This behavior is also an issue when functions are  executed.   Aliases
          are expanded when a function definition is read, not when the function
          is executed, because a function definition is itself a command.  As  a
          consequence,  aliases  defined  in  a function are not available until
          after that function  is  executed.   To  be  safe,  always  put  alias
          definitions  on  a  separate  line,  and  do not use alias in compound
          commands.

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

     FUNCTIONS
          A shell function, defined as  described  above  under  SHELL  GRAMMAR,
          stores  a  series of commands for later execution.  When the name of a
          shell function is used as a simple command name, the list of  commands
          associated  with  that  function  name  is  executed.   Functions  are
          executed in the context of  the  current  shell;  no  new  process  is
          created to interpret them (contrast this with the execution of a shell
          script).  When a function is executed, the arguments to  the  function
          become  the  positional  parameters during its execution.  The special
          parameter # is updated to reflect the change.  Special parameter 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.  If a variable  is  declared  local,  the
          variable's  visible  scope  is  restricted  to  that  function and its
          children (including the functions it calls).  Local variables "shadow"
          variables  with  the  same  name  declared  at  previous  scopes.  For
          instance, a local variable declared  in  a  function  hides  a  global
          variable  of  the  same  name: references and assignments refer to the
          local variable, leaving the  global  variable  unmodified.   When  the
          function returns, the global variable is once again visible.

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

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          This is also the value that a local  variable  declaration  "shadows",
          and the value that is restored when the function returns.

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

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

          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.

          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, the ((
          compound command, and Arithmetic Expansion).  Evaluation  is  done  in
          fixed-width  integers with no check for overflow, though division by 0
          is  trapped  and  flagged  as  an  error.   The  operators  and  their
          precedence,  associativity,  and  values  are  the  same  as  in the C
          language.  The following list of operators is grouped into  levels  of
          equal-precedence  operators.   The  levels  are  listed  in  order  of

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          decreasing precedence.

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

          Shell variables  are  allowed  as  operands;  parameter  expansion  is
          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.

          Integer constants follow the C language definition,  without  suffixes
          or character constants.  Constants with a leading 0 are interpreted as
          octal numbers.  A leading 0x or 0X  denotes  hexadecimal.   Otherwise,
          numbers  take  the form [base#]n, where the optional base is a decimal
          number between 2 and 64 representing the arithmetic base, and n  is  a
          number in that base.  If base# is omitted, then base 10 is used.  When
          specifying n, if a non-digit is required, the digits  greater  than  9
          are  represented  by  the lowercase letters, the uppercase letters, @,
          and _, in that order.  If base is less than or equal to 36,  lowercase
          and uppercase letters may be used interchangeably to represent numbers

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          between 10 and 35.

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

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

          Expressions are formed from the following unary or  binary  primaries.
          Bash  handles  several  filenames  specially  when  they  are  used in
          expressions.  If  the  operating  system  on  which  bash  is  running
          provides  these  special  files, bash will use them; otherwise it will
          emulate them internally with this behavior: If any  file  argument  to
          one  of the 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).

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          -r file
               True if file exists and is readable.
          -s file
               True if file exists and has a size greater than zero.
          -t fd
               True if file descriptor fd is open and refers to a terminal.
          -u file
               True if file exists and its set-user-id bit is set.
          -w file
               True if file exists and is writable.
          -x file
               True if file exists and is executable.
          -G file
               True if file exists and is owned by the effective group id.
          -L file
               True if file exists and is a symbolic link.
          -N file
               True if file exists and has been modified since it was last read.
          -O file
               True if file exists and is owned by the effective user id.
          -S file
               True if file exists and is a socket.
          file1 -ef file2
               True if file1 and file2  refer  to  the  same  device  and  inode
               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,

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               this performs  pattern  matching  as  described  above  (Compound
               Commands).

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

          string1 < string2
               True if string1 sorts before string2 lexicographically.

          string1 > string2
               True if string1 sorts after string2 lexicographically.

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

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

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

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

          3.   Redirections are performed as described above under REDIRECTION.

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

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          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.

     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 in a  separate  execution  environment  with  the  original
          command and the original command's arguments as its arguments, and the
          function's exit status becomes the exit status of that  subshell.   If
          that  function  is  not defined, the shell prints an error message and
          returns an exit 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

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          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:

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

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

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

          o    current traps set by trap

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

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

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

          o    options enabled by shopt

          o    shell aliases defined with alias

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

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

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

          o    the current working directory

          o    the file creation mode mask

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

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

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

          Command  substitution,  commands   grouped   with   parentheses,   and
          asynchronous  commands are invoked in a subshell environment that is a
          duplicate of the shell environment, except that traps  caught  by  the
          shell are reset to the values that the shell inherited from its parent
          at 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.

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          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
          values  above  125  specially.   Exit statuses from shell builtins and
          compound commands are also  limited  to  this  range.   Under  certain
          circumstances,  the shell will use special values to indicate specific
          failure modes.

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

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

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

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

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

     SIGNALS
          When bash is interactive, in the absence  of  any  traps,  it  ignores
          SIGTERM  (so  that  kill  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

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          the  SIGHUP.   To  prevent  the  shell  from  sending  the signal to a
          particular job, it should be removed from  the  jobs  table  with  the
          disown  builtin  (see  SHELL  BUILTIN COMMANDS below) or marked to not
          receive SIGHUP using disown -h.

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

          If bash is waiting for a command to complete and receives a signal for
          which  a  trap  has  been set, the trap will not be executed until the
          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

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

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

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

          If an attempt to exit bash is made while jobs are stopped (or, if  the
          checkjobs  shell  option  has  been  enabled  using the shopt builtin,
          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.

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

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          terminates before returning.

     PROMPTING
          When executing interactively, bash displays  the  primary  prompt  PS1
          when  it is ready to read a command, and the secondary prompt PS2 when
          it needs more input to complete a command.  Bash displays PS0 after it
          reads  a  command  but  before  executing  it.   Bash  displays PS4 as
          described above before tracing each command  when  the  -x  option  is
          enabled.   Bash  allows  these  prompt  strings  to  be  customized by
          inserting a number of backslash-escaped special  characters  that  are
          decoded as follows:
               \a   an ASCII bell character (07)
               \d   the date in "Weekday Month Date" format (e.g., "Tue May 26")
               \D{format}
                    the format is  passed  to  strftime(3)  and  the  result  is
                    inserted  into the prompt string; an empty format results in
                    a  locale-specific  time  representation.   The  braces  are
                    required
               \e   an ASCII escape character (033)
               \h   the hostname up to the first `.'
               \H   the hostname
               \j   the number of jobs currently managed by the shell
               \l   the basename of the shell's terminal device name
               \n   newline
               \r   carriage return
               \s   the name of the shell,  the  basename  of  $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

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          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).  This can  have  unwanted
          side  effects  if escaped portions of the string appear within command
          substitution or contain characters special to word expansion.

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

        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.   If  that  file   does  not  exist or cannot be read, the
          ultimate default is /etc/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

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          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).

        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

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          re-read-init-file, and ESC [ 1  1  ~  is  bound  to  insert  the  text
          ``Function Key 1''.

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

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

          When entering the text of a macro, single or  double  quotes  must  be
          used to indicate a macro definition.  Unquoted text is assumed to be a
          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
          or using the bind builtin command (see SHELL BUILTIN COMMANDS below).

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

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          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.
          blink-matching-paren (Off)
               If set to On, readline attempts to briefly move the cursor to  an
               opening parenthesis when a closing parenthesis is inserted.
          colored-completion-prefix (Off)
               If set to On, when listing  completions,  readline  displays  the
               common  prefix  of  the  set  of  possible  completions  using  a
               different color.  The color definitions are taken from the  value
               of the LS_COLORS environment variable.
          colored-stats (Off)
               If set  to  On,  readline  displays  possible  completions  using
               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-display-width (-1)
               The number of screen columns used  to  display  possible  matches
               when  performing  completion.  The value is ignored if it is less
               than 0 or greater than the terminal screen width.  A value  of  0
               will  cause  matches  to  be displayed one per line.  The default
               value is -1.
          completion-ignore-case (Off)
               If set to On, readline performs filename matching and  completion
               in a case-insensitive fashion.
          completion-map-case (Off)
               If set to On, and  completion-ignore-case  is  enabled,  readline
               treats  hyphens  (-)  and  underscores  (_)  as  equivalent  when
               performing case-insensitive filename matching and completion.
          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,  readline  will  ask

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               whether  or  not the user wishes to view them; otherwise they are
               simply listed on the terminal.
          convert-meta (On)
               If set to On, readline will convert characters  with  the  eighth
               bit  set to an ASCII key sequence by stripping the eighth bit and
               prefixing an escape character (in effect,  using  escape  as  the
               meta prefix).  The default is On, but readline will set it to Off
               if the locale contains eight-bit characters.
          disable-completion (Off)
               If set to On, readline will inhibit word completion.   Completion
               characters  will  be  inserted  into the line as if they had been
               mapped to self-insert.
          echo-control-characters (On)
               When set to On, on operating systems that indicate  they  support
               it,  readline  echoes  a  character  corresponding  to  a  signal
               generated from the keyboard.
          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.
          emacs-mode-string (@)
               If the show-mode-in-prompt variable is enabled,  this  string  is
               displayed  immediately before the last line of the primary prompt
               when emacs editing mode is active.  The value is expanded like  a
               key  binding,  so  the standard set of meta- and control prefixes
               and backslash escape sequences is available.  Use the \1  and  \2
               escapes  to  begin  and end sequences of non-printing characters,
               which can be used to embed a terminal control sequence  into  the
               mode string.
          enable-bracketed-paste (On)
               When set to On, readline will configure the  terminal  in  a  way
               that  will enable it to insert each paste into the editing buffer
               as a single  string  of  characters,  instead  of  treating  each
               character  as  if  it  had been read from the keyboard.  This can
               prevent pasted  characters  from  being  interpreted  as  editing
               commands.
          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.

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          history-size (unset)
               Set the maximum number of history entries saved  in  the  history
               list.   If  set to zero, any existing history entries are deleted
               and no new entries are saved.  If set to a value less than  zero,
               the  number  of  history entries is not limited.  By default, the
               number of history entries is set to the  value  of  the  HISTSIZE
               shell  variable.   If an attempt is made to set history-size to a
               non-numeric value, the maximum number of history entries will  be
               set to 500.
          horizontal-scroll-mode (Off)
               When set to On, makes readline use a  single  line  for  display,
               scrolling  the input horizontally on a single screen line when it
               becomes longer than the screen width rather than  wrapping  to  a
               new line.  This setting is automatically enabled for terminals of
               height 1.
          input-meta (Off)
               If set to On, readline will enable eight-bit input (that  is,  it
               will  not  strip  the  eighth  bit from the characters it reads),
               regardless of what the terminal claims it can support.  The  name
               meta-flag  is  a  synonym for this variable.  The default is Off,
               but readline will set it to On if the locale  contains  eight-bit
               characters.
          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 (*).

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          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
               through the list.
          output-meta (Off)
               If set to On, readline will display characters  with  the  eighth
               bit  set directly rather than as a meta-prefixed escape sequence.
               The default is Off, but readline will set it to On if the  locale
               contains eight-bit characters.
          page-completions (On)
               If set to On,  readline  uses  an  internal  more-like  pager  to
               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  string  to  the  beginning  of  the  prompt
               indicating  the editing mode: emacs, vi command, or vi insertion.
               The mode strings are user-settable (e.g., emacs-mode-string).
          skip-completed-text (Off)
               If set to On, this alters the default  completion  behavior  when
               inserting  a  single  match into the line.  It's only active when
               performing completion in the  middle  of  a  word.   If  enabled,
               readline  does  not  insert  characters  from the completion that

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               match characters after point in  the  word  being  completed,  so
               portions of the word following the cursor are not duplicated.
          vi-cmd-mode-string ((cmd))
               If the show-mode-in-prompt variable is enabled,  this  string  is
               displayed  immediately before the last line of the primary prompt
               when vi editing mode is active and in command mode.  The value is
               expanded  like  a  key  binding, so the standard set of meta- and
               control prefixes and backslash  escape  sequences  is  available.
               Use  the  \1  and  \2  escapes to begin and end sequences of non-
               printing characters, which  can  be  used  to  embed  a  terminal
               control sequence into the mode string.
          vi-ins-mode-string ((ins))
               If the show-mode-in-prompt variable is enabled,  this  string  is
               displayed  immediately before the last line of the primary prompt
               when vi editing mode is active and in insertion mode.  The  value
               is  expanded like a key binding, so the standard set of meta- and
               control prefixes and backslash  escape  sequences  is  available.
               Use  the  \1  and  \2  escapes to begin and end sequences of non-
               printing characters, which  can  be  used  to  embed  a  terminal
               control sequence into the mode string.
          visible-stats (Off)
               If set to On, a character denoting a file's type as  reported  by
               stat(2)  is  appended  to  the  filename  when  listing  possible
               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.

          $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, after any comparison operator,
                extends to the end of  the  line;  unless  otherwise  noted,  no
               characters are required to isolate it.

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

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

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

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

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

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

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

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

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

               $include  /etc/inputrc

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

          Incremental searches begin before the user  has  finished  typing  the
          search  string.   As  each  character  of  the search string is typed,
          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.

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          forward-word (M-f)
               Move forward to the end of the next word.  Words are composed  of
               alphanumeric characters (letters and digits).
          backward-word (M-b)
               Move back to the start of the current or  previous  word.   Words
               are composed of alphanumeric characters (letters and digits).
          shell-forward-word
               Move forward to the end of the next word.  Words are delimited by
               non-quoted shell metacharacters.
          shell-backward-word
               Move back to the start of the current or  previous  word.   Words
               are delimited by non-quoted shell metacharacters.
          previous-screen-line
               Attempt to move point to the same physical screen column  on  the
               previous  physical  screen  line.  This will not have the desired
               effect if the current Readline line does not take  up  more  than
               one  physical  line or if point is not greater than the length of
               the prompt plus the screen width.
          next-screen-line
               Attempt to move point to the same physical screen column  on  the
               next  physical screen line. This will not have the desired effect
               if the current Readline line does  not  take  up  more  than  one
               physical  line  or  if the length of the current Readline line is
               not greater than the length of the prompt plus the screen width.
          clear-display (M-C-l)
               Clear the screen and,  if  possible,  the  terminal's  scrollback
               buffer, then redraw the current line, leaving the current line at
               the top of the screen.
          clear-screen (C-l)
               Clear the screen, then  redraw  the  current  line,  leaving  the
               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

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               being entered.
          reverse-search-history (C-r)
               Search backward starting at the  current  line  and  moving  `up'
               through the history as necessary.  This is an incremental search.
          forward-search-history (C-s)
               Search forward starting at the current  line  and  moving  `down'
               through the history as necessary.  This is an incremental search.
          non-incremental-reverse-search-history (M-p)
               Search backward through the history starting at the current  line
               using a non-incremental search for a string supplied by the user.
          non-incremental-forward-search-history (M-n)
               Search forward through the history using a non-incremental search
               for a string supplied by the user.
          history-search-forward
               Search forward through the history for the string  of  characters
               between  the  start of the current line and the point.  This is a
               non-incremental search.
          history-search-backward
               Search backward through the history for the string of  characters
               between  the  start of the current line and the point.  This is a
               non-incremental search.
          history-substring-search-backward
               Search backward through the history for the string of  characters
               between  the  start  of  the  current line and the current cursor
               position (the point).  The search string may match anywhere in  a
               history line.  This is a non-incremental search.
          history-substring-search-forward
               Search forward through the history for the string  of  characters
               between  the start of the current line and the point.  The search
               string may match anywhere in a history  line.   This  is  a  non-
               incremental search.
          yank-nth-arg (M-C-y)
               Insert the first argument to the previous  command  (usually  the
               second  word on the previous line) at point.  With an argument n,
               insert the nth word from the previous command (the words  in  the
               previous command begin with word 0).  A negative argument inserts
               the nth word from the end of  the  previous  command.   Once  the
               argument  n is computed, the argument is extracted as if the "!n"
               history expansion had been specified.
          yank-last-arg (M-., M-_)
               Insert the last argument to the previous command (the  last  word
               of  the previous history entry).  With a numeric argument, behave
               exactly like yank-nth-arg.   Successive  calls  to  yank-last-arg
               move  back  through the history list, inserting the last word (or
               the word specified by the argument to the  first  call)  of  each
               line  in turn.  Any numeric argument supplied to these successive
               calls determines the direction to move through  the  history.   A
               negative  argument  switches  the  direction  through the history
               (back or forward).  The history expansion facilities are used  to
               extract  the last word, as if the "!$" history expansion had been
               specified.

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          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.  A
               numeric argument, if supplied, specifies the history entry to use
               instead of the current line.
          edit-and-execute-command (C-x C-e)
               Invoke an editor on the current command  line,  and  execute  the
               result  as  shell  commands.   Bash  attempts  to invoke $VISUAL,
               $EDITOR, and emacs as the editor, in that order.

        Commands for Changing Text
          end-of-file (usually C-d)
               The character indicating end-of-file  as  set,  for  example,  by
               ``stty''.  If this character is read when there are no 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.

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          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.

        Killing and Yanking
          kill-line (C-k)
               Kill the text from point to the end of the line.
          backward-kill-line (C-x Rubout)
               Kill backward to the beginning of the line.
          unix-line-discard (C-u)
               Kill backward from point to  the  beginning  of  the  line.   The
               killed text is saved on the kill-ring.
          kill-whole-line
               Kill all characters on the current line, no  matter  where  point
               is.
          kill-word (M-d)
               Kill from point to the end of the current  word,  or  if  between
               words, to the end of the next word.  Word boundaries are the same
               as those used by forward-word.
          backward-kill-word (M-Rubout)
               Kill the word behind point.  Word  boundaries  are  the  same  as
               those used by backward-word.
          shell-kill-word
               Kill from point to the end of the current  word,  or  if  between

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               words, to the end of the next word.  Word boundaries are the same
               as those used by shell-forward-word.
          shell-backward-kill-word
               Kill the word behind point.  Word  boundaries  are  the  same  as
               those used by shell-backward-word.
          unix-word-rubout (C-w)
               Kill the word behind point, using white space as a word 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.

        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 nor minus sign, the argument count for  the  next
               command  is  multiplied by four.  The argument count is initially
               one, so executing this function the first time makes the 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

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               begins with $), username (if the text begins  with  ~),  hostname
               (if  the  text  begins with @), or command (including aliases and
               functions) in turn.  If none of these produces a match,  filename
               completion is attempted.
          possible-completions (M-?)
               List the possible completions of the text before point.
          insert-completions (M-*)
               Insert all completions of the text before point that  would  have
               been generated by possible-completions.
          menu-complete
               Similar to complete, but replaces the word to be completed with a
               single  match  from  the  list of possible completions.  Repeated
               execution of menu-complete steps through  the  list  of  possible
               completions,  inserting  each  match  in turn.  At the end of the
               list of completions, the bell is rung (subject to the setting  of
               bell-style)  and the original text is restored.  An argument of n
               moves n positions forward in the  list  of  matches;  a  negative
               argument  may  be  used  to move backward through the list.  This
               command is intended to  be  bound  to  TAB,  but  is  unbound  by
               default.
          menu-complete-backward
               Identical to menu-complete, but moves backward through  the  list
               of  possible  completions,  as  if menu-complete had been given a
               negative argument.  This command is unbound by default.
          delete-char-or-list
               Deletes the character under the cursor if not at the beginning or
               end  of  the line (like delete-char).  If at the end of the line,
               behaves identically to  possible-completions.   This  command  is
               unbound by default.
          complete-filename (M-/)
               Attempt filename completion on the text before point.
          possible-filename-completions (C-x /)
               List the possible completions of the text before point,  treating
               it as a filename.
          complete-username (M-~)
               Attempt completion on the text before point,  treating  it  as  a
               username.
          possible-username-completions (C-x ~)
               List the possible completions of the text before point,  treating
               it as a username.
          complete-variable (M-$)
               Attempt completion on the text before point,  treating  it  as  a
               shell variable.
          possible-variable-completions (C-x $)
               List the possible completions of the text before point,  treating
               it as a shell variable.
          complete-hostname (M-@)
               Attempt completion on the text before point,  treating  it  as  a
               hostname.
          possible-hostname-completions (C-x @)
               List the possible completions of the text before point,  treating

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               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.
          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-lowercase-version (M-A, M-B, M-x, ...)
               If the metafied character x is uppercase, run the command that is
               bound  to  the  corresponding  metafied lowercase character.  The
               behavior is undefined if x is already lowercase.
          prefix-meta (ESC)
               Metafy the next character typed.  ESC f is equivalent to Meta-f.
          undo (C-_, C-x C-u)
               Incremental undo, separately remembered for each line.

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          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-[.
          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.

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          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.

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

          Once a compspec has been found, it is used to  generate  the  list  of
          matching  words.   If  a  compspec  is  not  found,  the  default bash
          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.

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          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
          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.  If the nocasematch shell option
          is enabled, the match is performed  without  regard  to  the  case  of
          alphabetic characters.

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          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
          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

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     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  following  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
          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

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          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, and is performed on each
          line individually  without  taking  quoting  on  previous  lines  into
          account.   It  takes  place  in  two parts.  The first is to determine
          which line from the history list  to  use  during  substitution.   The
          second  is  to  select  portions  of  that line for inclusion into the
          current one.  The line selected from the history is the event, and the
          portions  of  that  line  that  are  acted  upon  are  words.  Various
          modifiers are 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, but the history expansion  character  is  also  treated  as
          quoted  if  it  immediately  precedes  the  closing  double quote in a
          double-quoted string.

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

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

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          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.   If
               string  is  missing,  the  string  from the most recent search is
               used; it is an error if there is no previous search string.

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

        Word Designators
          Word designators are used to select desired words from the event.  A :
          separates the event specification from the word designator.  It may be
          omitted if the word designator begins with a ^, $, *, -, or %.   Words
          are numbered from the beginning of the line, with the first word being
          denoted by 0  (zero).   Words  are  inserted  into  the  current  line
          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 first word matched by the most recent `?string?'  search,  if
               the search string begins with a character that is part of a word.
          x-y  A range of words; `-y' abbreviates `0-y'.

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          *    All of the words but the zeroth.  This is a  synonym  for  `1-$'.
               It  is  not  an  error  to use * if there is just one word in the
               event; the empty string is returned in that case.
          x*   Abbreviates x-$.
          x-   Abbreviates x-$ like x*, but  omits  the  last  word.   If  x  is
               missing, it defaults to 0.

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

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

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

     SHELL BUILTIN COMMANDS
          Unless otherwise  noted,  each  builtin  command  documented  in  this
          section  as  accepting options preceded by - accepts -- to signify the
          end of the options.  The :, true, false, and test/[  builtins  do  not
          accept  options  and  do  not  treat  -- specially.  The exit, logout,
          return, break, 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

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          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.  The return status is
               zero.

           .  filename [arguments]
          source filename [arguments]
               Read and execute commands from  filename  in  the  current  shell
               environment  and  return  the  exit  status  of  the last command
               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.  If the -T option  is  enabled,  source
               inherits  any  trap on DEBUG; if it is not, any DEBUG trap string
               is saved and restored around  the  call  to  source,  and  source
               unsets  the  DEBUG trap while it executes.  If -T is not set, and
               the sourced file  changes  the  DEBUG  trap,  the  new  value  is
               retained  when source completes.  The return status is the status
               of the last command exited within the script (0  if  no  commands
               are  executed),  and  false if filename is not found or cannot be
               read.

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

          bind [-m keymap] [-lpsvPSVX]
          bind [-m keymap] [-q function] [-u function] [-r keyseq]

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          bind [-m keymap] -f filename
          bind [-m keymap] -x keyseq:shell-command
          bind [-m keymap] keyseq:function-name
          bind [-m keymap] keyseq:readline-command
               Display current readline key and function bindings,  bind  a  key
               sequence  to  a  readline  function  or  macro, or set a readline
               variable.  Each non-option argument is  a  command  as  it  would
               appear in .inputrc, but each binding or command must be passed as
               a  separate  argument;  e.g.,  '"\C-x\C-r":   re-read-init-file'.
               Options, if supplied, have the following meanings:
               -m keymap
                    Use keymap as the keymap to be affected  by  the  subsequent
                    bindings.     Acceptable    keymap    names    are    emacs,
                    emacs-standard,   emacs-meta,   emacs-ctlx,   vi,   vi-move,
                    vi-command,  and  vi-insert.  vi is equivalent to vi-command
                    (vi-move  is  also  a  synonym);  emacs  is  equivalent   to
                    emacs-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 and READLINE_MARK variables to
                    the current location of the insertion point  and  the  saved
                    insertion  point  (the mark), respectively.  If the executed
                    command  changes  the  value  of   any   of   READLINE_LINE,
                    READLINE_POINT,  or  READLINE_MARK, those new values will be
                    reflected in the editing state.
               -X   List all key sequences  bound  to  shell  commands  and  the
                    associated commands in a format that can be reused as input.

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

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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]
          complete [-abcdefgjksuv] [-o comp-
               option] [-DEI] [-A action]  [-G  globpat]
               [-F function] [-C command] [-X filterpat] [-P prefix] [-S suffix]
               name [name ...]
          complete -pr [-DEI] [name ...]
               Specify how arguments to each name should be completed.   If  the
               -p  option  is  supplied, or if no options are supplied, existing
               completion specifications are printed in a way that  allows  them
               to  be  reused  as  input.   The  -r  option removes a completion
               specification for each name, or, if no names  are  supplied,  all
               completion  specifications.   The  -D option indicates that other
               supplied 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

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               option  indicates  that other supplied options and actions should
               apply  to  ``empty''  command  completion;  that  is,  completion
               attempted  on  a  blank line.  The -I option indicates that other
               supplied options and actions should apply to  completion  on  the
               initial  non-assignment  word  on  the  line,  or after a command
               delimiter  such  as  ;  or  |,  which  is  usually  command  name
               completion.   If  multiple  options  are  supplied, the -D option
               takes precedence over -E, and both take precedence over  -I.   If
               any  of  -D, -E, or -I are supplied, any other name arguments are
               ignored; these completions only apply to the  case  specified  by
               the option.

               The process of applying these completion specifications when word
               completion  is  attempted  is  described above under 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).
                       nosort  Tell readline not to sort the  list  of  possible
                               completions alphabetically.
                       nospace Tell readline not to append a space (the default)
                               to words completed at the end of the line.
                       plusdirs
                               After any matches defined  by  the  compspec  are
                               generated, directory name completion is attempted
                               and any matches are added to the results  of  the
                               other actions.

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               -A action
                       The action may be one of the following to generate a list
                       of possible completions:
                       alias   Alias names.  May also be specified as -a.
                       arrayvar
                               Array variable names.
                       binding Readline key binding names.
                       builtin Names of shell builtin  commands.   May  also  be
                               specified as -b.
                       command Command names.  May also be specified as -c.
                       directory
                               Directory names.  May also be specified as -d.
                       disabled
                               Names of disabled shell builtins.
                       enabled Names of enabled shell builtins.
                       export  Names of exported shell variables.  May  also  be
                               specified as -e.
                       file    File names.  May also be specified as -f.
                       function
                               Names of shell functions.
                       group   Group names.  May also be specified as -g.
                       helptopic
                               Help topics as accepted by the help builtin.
                       hostname
                               Hostnames, as taken from the  file  specified  by
                               the HOSTFILE shell variable.
                       job     Job names, if job control is active.  May also be
                               specified as -j.
                       keyword Shell reserved words.  May also be  specified  as
                               -k.
                       running Names of running jobs, if job control is active.
                       service Service names.  May also be specified as -s.
                       setopt  Valid arguments for the  -o  option  to  the  set
                               builtin.
                       shopt   Shell option  names  as  accepted  by  the  shopt
                               builtin.
                       signal  Signal names.
                       stopped Names of stopped jobs, if job control is active.
                       user    User names.  May also be specified as -u.
                       variable
                               Names  of  all  shell  variables.   May  also  be
                               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)

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                       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.
               -S suffix
                       suffix is appended to each possible completion after  all
                       other options have been applied.
               -W wordlist
                       The wordlist is split using the  characters  in  the  IFS
                       special  variable  as delimiters, and each resultant word
                       is expanded.  Shell quoting is honored  within  wordlist,
                       in  order to provide a mechanism for the words to contain
                       shell metacharacters or characters in the value  of  IFS.
                       The possible completions are the members of the 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] [-DEI] [+o option] [name]
               Modify completion options for each name according to the options,
               or  for  the  currently-executing  completion  if  no  names  are
               supplied.  If  no  options  are  given,  display  the  completion
               options  for  each  name or the current completion.  The possible
               values of  option  are  those  valid  for  the  complete  builtin
               described  above.   The  -D  option indicates that other supplied
               options should apply to the ``default'' command completion;  that
               is, completion attempted on a command for which no completion has
               previously been defined.  The  -E  option  indicates  that  other
               supplied  options  should  apply to ``empty'' command completion;
               that is, completion attempted on a blank  line.   The  -I  option
               indicates  that other supplied options should apply to completion
               on the initial non-assignment  word  on  the  line,  or  after  a
               command  delimiter  such as ; or |, which is usually command name

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               completion.

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

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

          declare [-aAfFgiIlnrtux] [-p] [name[=value] ...]
          typeset [-aAfFgiIlnrtux] [-p] [name[=value] ...]
               Declare variables and/or give them attributes.  If no  names  are
               given  then  display the values of variables.  The -p option will
               display the attributes and values of each name.  When -p is  used
               with  name  arguments,  additional options, other than -f and -F,
               are ignored.  When -p is supplied without name arguments, it will
               display  the  attributes  and  values of all variables having the
               attributes specified by the  additional  options.   If  no  other
               options are supplied with -p, declare will display the attributes
               and values of all shell variables.  The -f option  will  restrict
               the  display  to  shell  functions.   The  -F option inhibits the
               display of function  definitions;  only  the  function  name  and
               attributes  are printed.  If the extdebug shell option is enabled
               using shopt, the source file name and line number where each name
               is defined are displayed as well.  The -F option implies -f.  The
               -g option forces variables to  be  created  or  modified  at  the
               global  scope, even when declare is executed in a shell function.
               It is ignored in all other cases.  The  -I  option  causes  local
               variables   to   inherit   the  attributes  (except  the  nameref
               attribute) and value of any existing variable with the same  name
               at  a  surrounding  scope.  If there is no existing variable, the
               local variable is initially unset.  The following options can  be
               used to restrict output to variables with the specified attribute
               or to give variables attributes:
               -a   Each name is an indexed array variable (see Arrays above).
               -A   Each name is  an  associative  array  variable  (see  Arrays
                    above).
               -f   Use function names only.
               -i   The variable is treated as an integer; arithmetic 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

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

               Using `+' instead of `-' turns off the  attribute  instead,  with
               the  exceptions  that  +a and +A may not be used to destroy array
               variables and +r will not remove the  readonly  attribute.   When
               used  in a function, declare and typeset make each name local, as
               with the local command, unless the -g option is supplied.   If  a
               variable name is followed by =value, the value of the variable is
               set to value.  When using -a or -A and  the  compound  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.   The  current  directory  is  always  the  first
               directory in the stack.
               -c   Clears the directory stack by deleting all of the entries.
               -l   Produces a listing using full pathnames; the default listing
                    format uses a tilde to denote the home directory.
               -p   Print the directory stack with one entry per line.
               -v   Print the directory stack with one entry per line, 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.

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               -n   Displays the nth entry counting from the right of  the  list
                    shown  by  dirs  when invoked without options, starting with
                    zero.

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

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

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          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.

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

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

          export [-fn] [name[=word]] ...
          export -p
               The supplied  names  are  marked  for  automatic  export  to  the

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               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).  When listing, a first or last
               of 0 is equivalent to -1 and -0  is  equivalent  to  the  current
               command (usually the fc command); otherwise 0 is equivalent to -1
               and -0 is invalid.  If last is not specified, it is  set  to  the
               current  command  for  listing  (so that ``fc -l -10'' prints the
               last 10 commands) and  to  first  otherwise.   If  first  is  not
               specified,  it is set to the previous command for editing and -16
               for listing.

               The -n option suppresses the command numbers when  listing.   The
               -r  option  reverses the order of the commands.  If the -l option
               is given, the commands are listed on standard output.  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 interpreted the same as first
               above.  A useful alias to use with this is ``r="fc -s"'', so that
               typing  ``r  cc'' runs the last command beginning with ``cc'' and
               typing ``r'' re-executes the last command.

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

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          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 [arg ...]
               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.

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

               getopts normally parses the positional parameters,  but  if  more
               arguments  are  supplied  as  arg  values,  getopts  parses those
               instead.

               getopts can report errors in two ways.  If the first character of
               optstring  is a colon, silent error reporting is used.  In normal
               operation, diagnostic messages are printed when  invalid  options
               or  missing  option  arguments  are encountered.  If the variable
               OPTERR is set to 0, no error messages will be 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.

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

               The return status is 0 unless no command matches pattern.

          history [n]
          history -c
          history -d offset
          history -d start-end
          history -anrw [filename]
          history -p arg [arg ...]
          history -s arg [arg ...]
               With no options, display  the  command  history  list  with  line
               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:

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               -c   Clear the history list by deleting all the entries.
               -d offset
                    Delete the history entry at position offset.  If  offset  is
                    negative,  it is interpreted as relative to one greater than
                    the last history position, so negative  indices  count  back
                    from  the  end  of the history, and an index of -1 refers to
                    the current history -d command.
               -d start-end
                    Delete the history entries between positions start and  end,
                    inclusive.   Positive  and negative values for start and end
                    are interpreted as described above.
               -a   Append the ``new'' history lines to the history file.  These
                    are history lines entered since the beginning of the current
                    bash session, but not already appended to the history file.
               -n   Read the history lines not already  read  from  the  history
                    file  into  the  current  history  list.   These  are  lines
                    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 following history entry.  The return value is
               0 unless an invalid option is encountered, an error occurs  while
               reading  or  writing  the  history  file,  an  invalid  offset is
               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.

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               -s   Display only stopped jobs.

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

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

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

          let arg [arg ...]
               Each arg  is  an  arithmetic  expression  to  be  evaluated  (see
               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.  If name is -, the set of shell options is made
               local  to  the  function in which local is invoked: shell options
               changed using the set builtin inside the function are restored to
               their  original values when the function returns.  The restore is
               effected as if a series of set commands were executed to  restore
               the  values  that  were  in  place  before the function.  With no
               operands, local writes a list of local variables to the  standard
               output.   It is an error to use local when not within a function.
               The return status is 0 unless local is used outside  a  function,
               an invalid name is supplied, or name is a readonly variable.

          logout
               Exit a login shell.

     callback] [-c quantum] [array]
          mapfile [-d delim] [-n count] [-O origin]  [-s  count]  [-t]  [-u  fd]  [-C

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     callback] [-c quantum] [array]
          readarray  [-d  delim]  [-n  count] [-O origin] [-s count] [-t] [-u fd] [-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:
               -d   The first character of delim is used to terminate each input
                    line,  rather  than  newline.  If delim is the empty string,
                    mapfile will terminate a line when it reads a NUL character.
               -n   Copy at most count lines.  If count  is  0,  all  lines  are
                    copied.
               -O   Begin assigning to array at index origin.  The default index
                    is 0.
               -s   Discard the first count lines read.
               -t   Remove a trailing delim (default  newline)  from  each  line
                    read.
               -u   Read lines from file descriptor fd instead of  the  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''
                    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.

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               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 in the same way as echo -e.
               %q   causes printf to output  the  corresponding  argument  in  a
                    format that can be reused as shell input.
               %(datefmt)T
                    causes printf to output the date-time string resulting  from
                    using  datefmt  as  a  format  string  for strftime(3).  The
                    corresponding argument is an integer representing the number
                    of seconds since the epoch.  Two special argument values may
                    be used: -1 represents the current time, and  -2  represents
                    the   time  the  shell  was  invoked.   If  no  argument  is
                    specified, conversion behaves as if -1 had been given.  This
                    is an exception to the usual printf behavior.

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

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

               If the pushd command is successful, a dirs is performed as  well.
               If  the  first form is used, pushd returns 0 unless the cd to dir
               fails.   With  the  second  form,  pushd  returns  0  unless  the
               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,  split
               into words as described above under Word Splitting, and the first
               word is assigned to the first name, the second word to the second
               name,  and  so  on.   If  there  are  more  words than names, the
               remaining words and their intervening delimiters are assigned  to
               the  last  name.   If  there  are fewer words read from the input
               stream than names, the remaining names are assigned empty 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

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               meanings:
               -a aname
                    The words are assigned to sequential indices  of  the  array
                    variable  aname,  starting  at 0.  aname is unset before any
                    new values are assigned.  Other name arguments are ignored.
               -d delim
                    The first character of delim is used to terminate the  input
                    line,  rather  than  newline.  If delim is the empty string,
                    read will terminate a line when it reads a NUL character.
               -e   If the standard input is coming from  a  terminal,  readline
                    (see  READLINE  above) is used to obtain the line.  Readline
                    uses the current  (or  default,  if  line  editing  was  not
                    previously  active)  editing  settings,  but uses Readline's
                    default filename completion.
               -i text
                    If readline is being used to read the line, text  is  placed
                    into the editing buffer before editing begins.
               -n nchars
                    read returns after reading  nchars  characters  rather  than
                    waiting for a complete line of input, but honors a 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.
                    The result is not split on the characters in IFS; the intent
                    is that the variable is assigned exactly the characters read
                    (with the exception of backslash; see the -r option below).
               -p prompt
                    Display  prompt  on  standard  error,  without  a   trailing
                    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 then 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

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                    read  any  data.  The exit status is 0 if input is available
                    on the specified file descriptor, non-zero  otherwise.   The
                    exit status is greater than 128 if the timeout is exceeded.
               -u fd
                    Read input from file descriptor fd.

               If no names are supplied,  the  line  read,  without  the  ending
               delimiter  but  otherwise unmodified, is assigned to the variable
               REPLY.   The  exit  status  is  zero,   unless   end-of-file   is
               encountered,  read times out (in which case the status is greater
               than 128), a variable assignment error (such as  assigning  to  a
               readonly  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  executed  by a trap handler, the last command used to
               determine the status is the last command executed before the trap
               handler.   If  return  is  executed during a DEBUG trap, the last
               command used to determine the status is the last command executed
               by the trap handler before return was invoked.  If return is used
               outside a function, but during execution of a  script  by  the  .
               (source)  command,  it  causes  the  shell to stop executing that
               script and return either n or the exit status of the last command
               executed  within the script as the exit status of the script.  If
               n is supplied, the return value is its least significant 8  bits.
               The return status is non-zero if return is supplied a non-numeric
               argument, or is used outside a function and not during  execution
               of  a  script  by  .  or source.  Any command associated with the
               RETURN trap  is  executed  before  execution  resumes  after  the
               function or script.

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          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:
               -a      Each variable or function that is created or modified  is
                       given  the  export attribute and marked for export to the
                       environment of subsequent commands.
               -b       Report  the  status  of   terminated   background   jobs
                       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.

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               -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:
                       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

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                               is disabled by default.
                       posix   Change the behavior of  bash  where  the  default
                               operation  differs  from  the  POSIX  standard to
                               match the standard (posix mode).   See  SEE  ALSO
                               below  for a reference to a document that details
                               how posix mode affects bash's behavior.
                       privileged
                               Same as -p.
                       verbose Same as -v.
                       vi      Use a vi-style command  line  editing  interface.
                               This  also affects the editing interface used for
                               read -e.
                       xtrace  Same as -x.

                       If -o is supplied with no option-name, the values of  the
                       current  options  are printed.  If +o is supplied with no
                       option-name, a series of set  commands  to  recreate  the
                       current  option  settings  is  displayed  on the standard
                       output.
               -p      Turn on privileged mode.  In  this  mode,  the  $ENV  and
                       $BASH_ENV  files  are  not processed, shell functions are
                       not inherited from the environment,  and  the  SHELLOPTS,
                       BASHOPTS,  CDPATH,  and  GLOBIGNORE  variables,  if  they
                       appear in the environment, are ignored.  If the shell  is
                       started  with  the effective user (group) id not equal to
                       the real user (group)  id,  and  the  -p  option  is  not
                       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,

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                       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
                       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; if optnames are supplied, the output
               is restricted to those options.  The -p option causes  output  to
               be  displayed  in  a  form  that  may  be reused as input.  Other
               options have the following meanings:
               -s   Enable (set) each optname.

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               -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
               default.

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

               The list of shopt options is:

               assoc_expand_once
                       If set,  the  shell  suppresses  multiple  evaluation  of
                       associative array subscripts during arithmetic expression
                       evaluation, while executing  builtins  that  can  perform
                       variable  assignments,  and while executing builtins that
                       perform array dereferencing.
               autocd  If set, a command name that is the name of a directory is
                       executed  as  if  it were the argument to the cd 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

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                       exiting if any jobs are stopped.
               checkwinsize
                       If set, bash checks the window size after  each  external
                       (non-builtin)  command  and,  if  necessary,  updates the
                       values of LINES and COLUMNS.  This option is  enabled  by
                       default.
               cmdhist If set, bash attempts to save all lines  of  a  multiple-
                       line command in the same history entry.  This allows easy
                       re-editing  of  multi-line  commands.   This  option   is
                       enabled  by  default,  but  only has an effect if command
                       history is enabled, as described above under HISTORY.
               compat31
               compat32
               compat40
               compat41
               compat42
               compat43
               compat44
                       These control aspects of the shell's  compatibility  mode
                       (see SHELL COMPATIBILITY MODE below).

               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.  The filenames ``.''
                       and ``..'' must always be  matched  explicitly,  even  if
                       dotglob is set.

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

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

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

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

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

                       5.   Function tracing is enabled:  command  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.

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               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
                       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).

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                       This is enabled by default.

               huponexit
                       If set, bash  will  send  SIGHUP  to  all  jobs  when  an
                       interactive login shell exits.

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

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

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

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

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

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

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

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               no_empty_cmd_completion
                       If set, and readline is being used, bash will not attempt
                       to   search   the  PATH  for  possible  completions  when
                       completion is attempted on an empty line.

               nocaseglob
                       If set, bash  matches  filenames  in  a  case-insensitive
                       fashion  when performing pathname expansion (see Pathname
                       Expansion above).

               nocasematch
                       If set,  bash  matches  patterns  in  a  case-insensitive
                       fashion  when performing matching while executing case or
                       [[  conditional   commands,   when   performing   pattern
                       substitution  word expansions, or when filtering possible
                       completions as part of programmable completion.

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

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

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

               promptvars
                       If  set,  prompt  strings  undergo  parameter  expansion,
                       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.

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               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.

          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

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                    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.
               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

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

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

          type [-aftpP] name [name ...]
               With no options, indicate how each name would be  interpreted  if
               used  as a command name.  If the -t option is used, type prints a
               string which is one of alias, keyword, function, builtin, or file
               if  name  is an alias, shell reserved word, function, builtin, or
               disk file, respectively.  If the name is not found, then  nothing
               is  printed,  and an exit status of false is returned.  If the -p
               option is used, type either returns the name  of  the  disk  file
               that  would be executed if name were 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 [-HS] -a
          ulimit [-HS] [-bcdefiklmnpqrstuvxPRT [limit]]
               Provides control over the resources available to the shell and to
               processes started by it, on systems that allow such control.  The

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               -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,  if  appropriate,  are  printed  before  the  value.  Other
               options are interpreted as follows:
               -a   All current limits are reported; no limits are set
               -b   The maximum socket buffer size
               -c   The maximum size of core files created
               -d   The maximum size of a process's data segment
               -e   The maximum scheduling priority ("nice")
               -f   The maximum size of files  written  by  the  shell  and  its
                    children
               -i   The maximum number of pending signals
               -k   The maximum number of kqueues that may be allocated
               -l   The maximum size that may be locked into memory
               -m   The maximum resident set size (many  systems  do  not  honor
                    this limit)
               -n   The maximum number of open file descriptors (most systems do
                    not allow this value to be set)
               -p   The pipe size in 512-byte blocks (this may not be set)
               -q   The maximum number of bytes in POSIX message queues
               -r   The maximum real-time scheduling priority
               -s   The maximum stack size
               -t   The maximum amount of cpu time in seconds
               -u   The maximum number of processes available to a single user
               -v   The maximum amount of virtual memory available to the  shell
                    and, on some systems, to its children
               -x   The maximum number of file locks
               -P   The maximum number of pseudoterminals
               -R    The  maximum  time  a  real-time  process  can  run  before
                    blocking, in microseconds
               -T   The maximum number of threads

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

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          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
               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,
               a function with that name, if any, is unset.  Each unset variable
               or function is removed from the environment passed to  subsequent
               commands.    If   any  of  BASH_ALIASES,  BASH_ARGV0,  BASH_CMDS,
               BASH_COMMAND, BASH_SUBSHELL, BASHPID, COMP_WORDBREAKS,  DIRSTACK,
               EPOCHREALTIME,  EPOCHSECONDS,  FUNCNAME, GROUPS, HISTCMD, LINENO,
               RANDOM, SECONDS, or SRANDOM are unset, they  lose  their  special
               properties, even if they are subsequently reset.  The exit status
               is true unless a name is readonly.

          wait [-fn] [-p varname] [id ...]
               Wait for each specified child process and return its  termination
               status.  Each id may be a process ID or a job specification; if a
               job spec is given, all  processes  in  that  job's  pipeline  are
               waited  for.   If  id  is  not  given, wait waits for all running
               background jobs and the last-executed  process  substitution,  if
               its  process id is the same as $!, and the return status is zero.
               If the -n option is supplied, wait waits for a  single  job  from
               the  list of ids or, if no ids are supplied, any job, to complete
               and returns its exit status.  If none of the  supplied  arguments
               is  a child of the shell, or if no arguments are supplied and the
               shell has no unwaited-for children, the exit status is  127.   If
               the  -p  option is supplied, the process or job identifier of the
               job for which the exit status is  returned  is  assigned  to  the
               variable varname named by the option argument.  The variable will

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               be unset initially, before any assignment.  This is  useful  only
               when  the  -n  option is supplied.  Supplying the -f option, when
               job control is enabled, forces wait to wait for id  to  terminate
               before returning its status, instead of returning when it changes
               status.  If id specifies  a  non-existent  process  or  job,  the
               return  status  is 127.  Otherwise, the return status is the exit
               status of the last process or job waited for.

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

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

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

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

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

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

          The following table describes the behavior changes controlled by  each
          compatibility  level  setting.   The compatNN tag is used as shorthand
          for setting the compatibility level to NN using one of  the  following

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          mechanisms.   For  versions prior to bash-5.0, the compatibility level
          may be set using the corresponding compatNN shopt option.   For  bash-
          4.3  and later versions, the BASH_COMPAT variable is preferred, and it
          is required for bash-5.1 and later versions.

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

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

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

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

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

          compat43
               o    the shell does not print a warning message if an attempt  is
                    made  to  use a quoted compound assignment as an argument to
                    declare (declare -a foo='(1 2)'). Later versions  warn  that
                    this usage is deprecated
               o    word expansion errors are considered non-fatal  errors  that
                    cause  the  current command to fail, even in posix mode (the

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                    default behavior is to make them fatal errors that cause the
                    shell to exit)
               o     when  executing  a   shell   function,   the   loop   state
                    (while/until/etc.)  is  not  reset,  so break or continue in
                    that function will break or continue loops  in  the  calling
                    context.  Bash-4.4 and later reset the loop state to prevent
                    this

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

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

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

          o    changing directories with cd

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

          o    specifying command names containing /

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

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     BASH(1)                        GNU Bash 5.1                         BASH(1)
                                   2020 October 29

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

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

          o    importing function definitions  from  the  shell  environment  at
               startup

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

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

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

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

          o    using  the  enable  builtin  command  to  enable  disabled  shell
               builtins

          o    specifying the -p option to the command builtin command

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

          These restrictions are enforced after any startup files are read.

          When a command that is found to be a shell  script  is  executed  (see
          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

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                                   2020 October 29

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

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

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

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

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

          ALL bug reports should include:

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

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

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

     BUGS
          It's too big and too slow.

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

          Aliases are confusing in some uses.

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                                   2020 October 29

          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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