sh

BASH(1)                     General Commands Manual                    BASH(1)



NAME
       bash - GNU Bourne-Again SHell

SYNOPSIS
       bash [options] [file]

COPYRIGHT
       Bash is Copyright (C) 1989-2011 by the Free Software Foundation, Inc.

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

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

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

       -c string If the -c option is present, then commands are read from
                 string.  If there are arguments after the string, they are
                 assigned to the positional parameters, starting with $0.
       -i        If the -i option is present, the shell is interactive.
       -l        Make bash act as if it had been invoked as a login shell (see
                 INVOCATION below).
       -r        If the -r option is present, the shell becomes restricted
                 (see RESTRICTED SHELL below).
       -s        If the -s option is present, or if no arguments remain after
                 option processing, then commands are read from the standard
                 input.  This option allows the positional parameters to be
                 set when invoking an interactive shell.
       -D        A list of all double-quoted strings preceded by $ is printed
                 on the standard output.  These are the strings that are
                 subject to language translation when the current locale is
                 not C or POSIX.  This implies the -n option; no commands will
                 be executed.
       [-+]O [shopt_option]
                 shopt_option is one of the shell options accepted by the
                 shopt builtin (see SHELL BUILTIN COMMANDS below).  If
                 shopt_option is present, -O sets the value of that option; +O
                 unsets it.  If shopt_option is not supplied, the names and
                 values of the shell options accepted by shopt are printed on
                 the standard output.  If the invocation option is +O, the
                 output is displayed in a format that may be reused as input.
       --        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).

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

       --rpm-requires
              Produce the list of files that are required for the shell script
              to run.  This implies '-n' and is subject to the same
              limitations as compile time error checking checking; Command
              substitutions, Conditional expressions and eval builtin are not
              parsed so some dependencies may be missed.

       --verbose
              Equivalent to  -v.

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

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

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

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

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

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

       When a login shell exits, bash reads and executes commands from the
       files ~/.bash_logout and /etc/bash.bash_logout, if the files 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 file
       name.

       If bash is invoked with the name sh, it tries to mimic the startup
       behavior of historical versions of sh as closely as possible, while
       conforming to the POSIX standard as well.  When invoked as an
       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 rshd does not generally invoke the shell with
       those options or allow them to be specified.

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

              command1 && command2

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

       An OR list has the form

              command1 || command2

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

   Compound Commands
       A compound command is one of the following:

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

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

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

       [[ expression ]]
              Return a status of 0 or 1 depending on the evaluation of the
              conditional expression expression.  Expressions are composed of
              the primaries described below under CONDITIONAL EXPRESSIONS.
              Word splitting and pathname expansion are not performed on the
              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.  If the shell
              option nocasematch is enabled, the match is performed without
              regard to the case of alphabetic characters.  The return value
              is 0 if the string matches (==) or does not match (!=) the
              pattern, and 1 otherwise.  Any part of the pattern may be quoted
              to force it to be matched as a string.

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

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

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

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

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

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

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

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

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

       while list-1; do list-2; done
       until list-1; do list-2; done
              The while command continuously executes the list list-2 as long
              as the last command in the list list-1 returns an exit status of
              zero.  The until command is identical to the while command,
              except that the test is negated; list-2 is executed as long as
              the last command in list-1 returns a non-zero exit status.  The
              exit status of the while and until commands is the exit status
              of the last command executed in list-2, or zero if none was
              executed.

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

       The format for a coprocess is:

              coproc [NAME] command [redirections]

       This creates a coprocess named NAME.  If NAME is not supplied, the
       default name is COPROC.  NAME must not be supplied if command is a
       simple command (see above); otherwise, it is interpreted as the first
       word of the simple command.  When the coproc 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.  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.

       The return status of a coprocess is the exit status of command.

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

       name () compound-command [redirection]
       function name [()] compound-command [redirection]
              This defines a function named name.  The reserved word function
              is optional.  If the function reserved word is supplied, the
              parentheses are optional.  The body of the function is the
              compound command compound-command (see Compound Commands above).
              That command is usually a list of commands between { and }, but
              may be any command listed under Compound Commands above.
              compound-command is executed whenever name is specified as the
              name of a simple command.  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, !.  The characters $ and ` retain
       their special meaning within double quotes.  The backslash retains its
       special meaning only when followed by one of the following characters:
       $, `, ", \, or <newline>.  A double quote may be quoted within double
       quotes by preceding it with a backslash.  If enabled, history expansion
       will be performed unless an !  appearing in double quotes is escaped
       using a backslash.  The backslash preceding the !  is not removed.

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

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

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

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

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

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

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

              name=[value]

       If value is not given, the variable is assigned the null string.  All
       values undergo tilde expansion, parameter and variable expansion,
       command substitution, arithmetic expansion, and quote removal (see
       EXPANSION below).  If the variable has its integer attribute set, then
       value is evaluated as an arithmetic expression even if the $((...))
       expansion is not used (see Arithmetic Expansion below).  Word splitting
       is not performed, with the exception of "$@" as explained below under
       Special Parameters.  Pathname expansion is not performed.  Assignment
       statements may also appear as arguments to the alias, declare, typeset,
       export, readonly, and local builtin commands.

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

   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 occurs within double quotes, it expands to a
              single word with the value of each parameter separated by the
              first character of the IFS special variable.  That is, "$*" is
              equivalent to "$1c$2c...", where c is the first character of the
              value of the IFS variable.  If IFS is unset, the parameters are
              separated by spaces.  If IFS is null, the parameters are joined
              without intervening separators.
       @      Expands to the positional parameters, starting from one.  When
              the expansion occurs within double quotes, each parameter
              expands to a separate word.  That is, "$@" is equivalent to "$1"
              "$2" ...  If the double-quoted expansion occurs within a word,
              the expansion of the first parameter is joined with the
              beginning part of the original word, and the expansion of the
              last parameter is joined with the last part of the original
              word.  When there are no positional parameters, "$@" and $@
              expand to nothing (i.e., they are removed).
       #      Expands to the number of positional parameters in decimal.
       ?      Expands to the exit status of the most recently executed
              foreground pipeline.
       -      Expands to the current option flags as specified upon
              invocation, by the set builtin command, or those set by the
              shell itself (such as the -i option).
       $      Expands to the process ID of the shell.  In a () subshell, it
              expands to the process ID of the current shell, not the
              subshell.
       !      Expands to the process ID of the most recently executed
              background (asynchronous) command.
       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 file name used to invoke bash, as given by
              argument zero.
       _      At shell startup, set to the absolute pathname used to invoke
              the shell or shell script being executed as passed in the
              environment or argument list.  Subsequently, expands to the last
              argument to the previous command, after expansion.  Also set to
              the full pathname used to invoke each command executed and
              placed in the environment exported to that command.  When
              checking mail, this parameter holds the name of the mail file
              currently being checked.

   Shell Variables
       The following variables are set by the shell:

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

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

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

       BASH_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 file name.
              PATH is not used to search for the resultant file name.
       BASH_XTRACEFD
              If set to an integer corresponding to a valid file descriptor,
              bash will write the trace output generated when set -x is
              enabled to that file descriptor.  The file descriptor is closed
              when BASH_XTRACEFD is unset or assigned a new value.  Unsetting
              BASH_XTRACEFD or assigning it the empty string causes the trace
              output to be sent to the standard error.  Note that setting
              BASH_XTRACEFD to 2 (the standard error file descriptor) and then
              unsetting it will result in the standard error being closed.
       CDPATH The search path for the cd command.  This is a colon-separated
              list of directories in which the shell looks for destination
              directories specified by the cd command.  A sample value is
              ".:~:/usr".
       COLUMNS
              Used by the select compound command to determine the terminal
              width when printing selection lists.  Automatically set 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).
       EMACS  If bash finds this variable in the environment when the shell
              starts with value "t", it assumes that the shell is running in
              an Emacs shell buffer and disables line editing.
       ENV    Similar to BASH_ENV; used when the shell is invoked in POSIX
              mode.
       FCEDIT The default editor for the fc builtin command.
       FIGNORE
              A colon-separated list of suffixes to ignore when performing
              filename completion (see READLINE below).  A filename whose
              suffix matches one of the entries in FIGNORE is excluded from
              the list of matched filenames.  A sample value is ".o:~".
       FUNCNEST
              If set to a numeric value greater than 0, defines a maximum
              function nesting level.  Function invocations that exceed this
              nesting level will cause the current command to abort.
       GLOBIGNORE
              A colon-separated list of patterns defining the set of filenames
              to be ignored by pathname expansion.  If a filename matched by a
              pathname expansion pattern also matches one of the patterns in
              GLOBIGNORE, it is removed from the list of matches.
       HISTCONTROL
              A colon-separated list of values controlling how commands are
              saved on the history list.  If the list of values includes
              ignorespace, lines which begin with a space character are not
              saved in the history list.  A value of ignoredups causes lines
              matching the previous history entry to not be saved.  A value of
              ignoreboth is shorthand for ignorespace and ignoredups.  A value
              of erasedups causes all previous lines matching the current line
              to be removed from the history list before that line is saved.
              Any value not in the above list is ignored.  If HISTCONTROL is
              unset, or does not include a valid value, all lines read by the
              shell parser are saved on the history list, subject to the value
              of HISTIGNORE.  The second and subsequent lines of a multi-line
              compound command are not tested, and are added to the history
              regardless of the value of HISTCONTROL.
       HISTFILE
              The name of the file in which command history is saved (see
              HISTORY below).  The default value is ~/.bash_history.  If
              unset, the command history is not saved when an interactive
              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, by removing the oldest entries, to
              contain no more than that number of lines.  The default value is
              500.  The history file is also truncated to this size after
              writing it when an interactive shell exits.
       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.
       HISTSIZE
              The number of commands to remember in the command history (see
              HISTORY below).  The default value is 500.
       HISTTIMEFORMAT
              If this variable is set and not null, its value is used as a
              format string for strftime(3) to print the time stamp associated
              with each history entry displayed by the history builtin.  If
              this variable is set, time stamps are written to the history
              file so they may be preserved across shell sessions.  This uses
              the history comment character to distinguish timestamps from
              other history lines.
       HOME   The home directory of the current user; the default argument for
              the cd builtin command.  The value of this variable is also used
              when performing tilde expansion.
       HOSTFILE
              Contains the name of a file in the same format as /etc/hosts
              that should be read when the shell needs to complete a hostname.
              The list of possible hostname completions may be changed while
              the shell is running; the next time hostname completion is
              attempted after the value is changed, bash adds the contents of
              the new file to the existing list.  If HOSTFILE is set, but has
              no value, or does not name a readable file, bash attempts to
              read /etc/hosts to obtain the list of possible hostname
              completions.  When HOSTFILE is unset, the hostname list is
              cleared.
       IFS    The Internal Field Separator that is used for word splitting
              after expansion and to split lines into words with the read
              builtin command.  The default value is
              ``<space><tab><newline>''.
       IGNOREEOF
              Controls the action of an interactive shell on receipt of an EOF
              character as the sole input.  If set, the value is the number of
              consecutive EOF characters which must be typed as the first
              characters on an input line before bash exits.  If the variable
              exists but does not have a numeric value, or has no value, the
              default value is 10.  If it does not exist, EOF signifies the
              end of input to the shell.
       INPUTRC
              The filename for the readline startup file, overriding the
              default of ~/.inputrc (see READLINE below).
       LANG   Used to determine the locale category for any category not
              specifically selected with a variable starting with LC_.
       LC_ALL This variable overrides the value of LANG and any other LC_
              variable specifying a locale category.
       LC_COLLATE
              This variable determines the collation order used when sorting
              the results of pathname expansion, and determines the behavior
              of range expressions, equivalence classes, and collating
              sequences within pathname expansion and pattern matching.
       LC_CTYPE
              This variable determines the interpretation of characters and
              the behavior of character classes within pathname expansion and
              pattern matching.
       LC_MESSAGES
              This variable determines the locale used to translate double-
              quoted strings preceded by a $.
       LC_NUMERIC
              This variable determines the locale category used for number
              formatting.
       LINES  Used by the select compound command to determine the column
              length for printing selection lists.  Automatically set 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 file names to be checked for mail.
              The message to be printed when mail arrives in a particular file
              may be specified by separating the file name from the message
              with a `?'.  When used in the text of the message, $_ expands to
              the name of the current mailfile.  Example:
              MAILPATH='/var/mail/bfox?"You have mail":~/shell-mail?"$_ has
              mail!"'
              Bash supplies a default value for this variable, but the
              location of the user mail files that it uses is system dependent
              (e.g., /var/mail/$USER).
       OPTERR If set to the value 1, bash displays error messages generated by
              the getopts builtin command (see SHELL BUILTIN COMMANDS below).
              OPTERR is initialized to 1 each time the shell is invoked or a
              shell script is executed.
       PATH   The search path for commands.  It is a colon-separated list of
              directories in which the shell looks for commands (see COMMAND
              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/gnu/bin:/usr/local/bin:/usr/ucb:/bin:/usr/bin''.
       POSIXLY_CORRECT
              If this variable is in the environment when bash starts, the
              shell enters posix mode before reading the startup files, as if
              the --posix invocation option had been supplied.  If it is set
              while the shell is running, bash enables posix mode, as if the
              command set -o posix had been executed.
       PROMPT_COMMAND
              If set, the value is executed as a command prior to issuing each
              primary prompt.
       PROMPT_DIRTRIM
              If set to a number greater than zero, the value is used as the
              number of trailing directory components to retain when expanding
              the \w and \W prompt string escapes (see PROMPTING below).
              Characters removed are replaced with an ellipsis.
       PS1    The value of this parameter is expanded (see PROMPTING below)
              and used as the primary prompt string.  The default value is
              ``\s-\v\$ ''.
       PS2    The value of this parameter is expanded as with PS1 and used as
              the secondary prompt string.  The default is ``> ''.
       PS3    The value of this parameter is used as the prompt for the select
              command (see SHELL GRAMMAR above).
       PS4    The value of this parameter is expanded as with PS1 and the
              value is printed before each command bash displays during an
              execution trace.  The first character of PS4 is replicated
              multiple times, as necessary, to indicate multiple levels of
              indirection.  The default is ``+ ''.
       SHELL  The full pathname to the shell is kept in this environment
              variable.  If it is not set when the shell starts, bash assigns
              to it the full pathname of the current user's login shell.
       TIMEFORMAT
              The value of this parameter is used as a format string
              specifying how the timing information for pipelines prefixed
              with the time reserved word should be displayed.  The %
              character introduces an escape sequence that is expanded to a
              time value or other information.  The escape sequences and their
              meanings are as follows; the braces denote optional portions.
              %%        A literal %.
              %[p][l]R  The elapsed time in seconds.
              %[p][l]U  The number of CPU seconds spent in user mode.
              %[p][l]S  The number of CPU seconds spent in system mode.
              %P        The CPU percentage, computed as (%U + %S) / %R.

              The optional p is a digit specifying the precision, the number
              of 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%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 input
              after issuing the primary prompt.  Bash terminates after waiting
              for that number of seconds if input does not arrive.
       TMPDIR If set, bash uses its value as the name of a directory in which
              bash creates temporary files for the shell's use.
       auto_resume
              This variable controls how the shell interacts with the user and
              job control.  If this variable is set, single word simple
              commands without redirections are treated as candidates for
              resumption of an existing stopped job.  There is no ambiguity
              allowed; if there is more than one job beginning with the string
              typed, the job most recently accessed is selected.  The name of
              a stopped job, in this context, is the command line used to
              start it.  If set to the value exact, the string supplied must
              match the name of a stopped job exactly; if set to substring,
              the string supplied needs to match a substring of the name of a
              stopped job.  The substring value provides functionality
              analogous to the %?  job identifier (see JOB CONTROL below).  If
              set to any other value, the supplied string must be a prefix of
              a stopped job's name; this provides functionality analogous to
              the %string job identifier.
       histchars
              The two or three characters which control history expansion and
              tokenization (see HISTORY EXPANSION below).  The first character
              is the history expansion character, the character which signals
              the start of a history expansion, normally `!'.  The second
              character is the quick substitution character, which is used as
              shorthand for re-running the previous command entered,
              substituting one string for another in the command.  The default
              is `^'.  The optional third character is the character which
              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.

       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.  If subscript
       evaluates to a number less than zero, it is used as an offset from one
       greater than the array's maximum index (so a subcript of -1 refers to
       the last element of the array).  To explicitly declare an indexed
       array, use declare -a name (see SHELL BUILTIN COMMANDS below).  declare
       -a name[subscript] is also accepted; the subscript is ignored.

       Associative arrays are created using declare -A name.

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

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

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

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

       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.  Referencing an array variable without
       a subscript is equivalent to referencing the array with a subscript of
       0.

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

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

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

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

       The order of expansions is: brace expansion, tilde expansion,
       parameter, variable and 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.

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

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

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

       A sequence expression takes the form {x..y[..incr]}, where x and y are
       either integers or single characters, and incr, an optional increment,
       is an integer.  When integers are supplied, the expression expands to
       each number between x and y, inclusive.  Supplied integers may be
       prefixed with 0 to force each term to have the same width.  When either
       x or y begins with a zero, the shell attempts to force all generated
       terms to contain the same number of digits, zero-padding where
       necessary.  When characters are supplied, the expression expands to
       each character lexicographically between x and y, inclusive.  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.

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

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

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

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

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

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

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

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

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

       ${parameter}
              The value of parameter is substituted.  The braces are required
              when parameter is a positional parameter with more than one
              digit, or when parameter is followed by a character which is not
              to be interpreted as part of its name.

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

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

       When not performing substring expansion, using the forms documented
       below, 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
              parameter starting at the character specified by offset.  If
              length is omitted, expands to the substring of parameter
              starting at the character specified by offset.  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 from the end of the value of
              parameter.  If length evaluates to a number less than zero, and
              parameter is not @ and not an indexed or associative array, it
              is interpreted as an offset from the end of the value of
              parameter rather than a number of characters, and the expansion
              is the characters between the two offsets.  If parameter is @,
              the result is length positional parameters beginning at offset.
              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.
              Substring expansion applied to an associative array produces
              undefined results.  Note that a negative offset must be
              separated from the colon by at least one space to avoid being
              confused with the :- expansion.  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.

       ${#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.

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

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

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

       ${parameter^pattern}
       ${parameter^^pattern}
       ${parameter,pattern}
       ${parameter,,pattern}
              Case modification.  This expansion modifies the case of
              alphabetic characters in parameter.  The pattern is expanded to
              produce a pattern just as in pathname expansion.  The ^ operator
              converts lowercase letters matching pattern to uppercase; the ,
              operator converts matching uppercase letters to lowercase.  The
              ^^ and ,, expansions convert each matched character in the
              expanded value; the ^ and , expansions match and convert only
              the first character in the expanded value.  If pattern is
              omitted, it is treated like a ?, which matches every character.
              If parameter is @ or *, the case modification operation is
              applied to each positional parameter in turn, and the expansion
              is the resultant list.  If parameter is an array variable
              subscripted with @ or *, the case modification operation is
              applied to each member of the array in turn, and the expansion
              is the resultant list.

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

              $(command)
       or
              `command`

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

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

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

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

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

              $((expression))

       The expression is treated as if it were within double quotes, but a
       double quote inside the parentheses is not treated specially.  All
       tokens in the expression undergo parameter expansion, string expansion,
       command substitution, and quote removal.  Arithmetic expansions may be
       nested.

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

   Process Substitution
       Process substitution is supported on systems that support named pipes
       (FIFOs) or the /dev/fd method of naming open files.  It takes the form
       of <(list) or >(list).  The process list is run with its input or
       output connected to a FIFO or some file in /dev/fd.  The name of this
       file is passed as an argument to the current command as the result of
       the expansion.  If the >(list) form is used, writing to the file will
       provide input for list.  If the <(list) form is used, the file passed
       as an argument should be read to obtain the output of list.

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

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

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

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

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

   Pathname Expansion
       After word splitting, unless the -f option has been set, bash scans
       each word for the characters *, ?, and [.  If one of these characters
       appears, then the word is regarded as a pattern, and replaced with an
       alphabetically sorted list of file names matching the pattern.  If no
       matching file names are found, and the shell option nullglob is not
       enabled, the word is left unchanged.  If the nullglob option is set,
       and no matches are found, the word is removed.  If the failglob shell
       option is set, and no matches are found, an error message is printed
       and the command is not executed.  If the shell option nocaseglob is
       enabled, the match is performed without regard to the case of
       alphabetic characters.  When a pattern is used for pathname expansion,
       the character ``.''  at the start of a name or immediately following a
       slash must be matched explicitly, unless the shell option dotglob is
       set.  When matching a pathname, the slash character must always be
       matched explicitly.  In other cases, the ``.''  character is not
       treated specially.  See the description of shopt below under SHELL
       BUILTIN COMMANDS for a description of the nocaseglob, nullglob,
       failglob, and dotglob shell options.

       The GLOBIGNORE shell variable may be used to restrict the set of 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.  The file names ``.''  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 file names beginning with a ``.''  will
       match.  To get the old behavior of ignoring file names beginning with a
       ``.'', make ``.*''  one of the patterns in GLOBIGNORE.  The dotglob
       option is disabled when GLOBIGNORE is unset.

       Pattern Matching

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

       The special pattern characters have the following meanings:

              *      Matches any string, including the null string.  When the
                     globstar shell option is enabled, and * is used in a
                     pathname expansion context, two adjacent *s used as a
                     single pattern will match all files and zero or more
                     directories and subdirectories.  If followed by a /, two
                     adjacent *s will match only directories and
                     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 sorts 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 value of the LC_COLLATE shell
                     variable, if set.  A - may be matched by including it as
                     the first or last character in the set.  A ] may be
                     matched by including it as the first character in the
                     set.

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

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

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

       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

       If the extglob shell option is enabled using the shopt builtin,
       following pattern matching operator is recognized as well:

              !(pattern-list)
                     Matches anything except one of the given patterns

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

REDIRECTION
       Before a command is executed, its input and output may be redirected
       using a special notation interpreted by the shell.  Redirection may
       also be used to open and close files for 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 10 and assign it to varname.  If >&- or
       <&- is preceded by {varname}, the value of varname defines the file
       descriptor to close.

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

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

              /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 a TCP connection to the corresponding 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 a UDP connection to the corresponding socket.

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

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

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

       The general format for redirecting input is:

              [n]<word

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

       The general format for redirecting output is:

              [n]>word

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

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

       The general format for appending output is:

              [n]>>word

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

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

              &>word
       and
              >&word

       Of the two forms, the first is preferred.  This is semantically
       equivalent to

              >word 2>&1

   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

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

       The format of here-documents is:

              <<[-]word
                      here-document
              delimiter

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

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

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

              <<<word

       The word is expanded and supplied to the command on its standard input.

   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.  As a special case, if n is omitted, and word
       does not expand to one or more digits, the standard output and standard
       error are redirected as described previously.

   Moving File Descriptors
       The redirection operator

              [n]<&digit-

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

       Similarly, the redirection operator

              [n]>&digit-

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

   Opening File Descriptors for Reading and Writing
       The redirection operator

              [n]<>word

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

       -a file
              True if file exists.
       -b file
              True if file exists and is a block special file.
       -c file
              True if file exists and is a character special file.
       -d file
              True if file exists and is a directory.
       -e file
              True if file exists.
       -f file
              True if file exists and is a regular file.
       -g file
              True if file exists and is set-group-id.
       -h file
              True if file exists and is a symbolic link.
       -k file
              True if file exists and its ``sticky'' bit is set.
       -p file
              True if file exists and is a named pipe (FIFO).
       -r file
              True if file exists and is readable.
       -s file
              True if file exists and has a size greater than zero.
       -t fd  True if file descriptor fd is open and refers to a terminal.
       -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).
       -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.

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

       string1 < string2
              True if string1 sorts before string2 lexicographically.

       string1 > string2
              True if string1 sorts after string2 lexicographically.

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

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

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

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

       3.     Redirections are performed as described above under REDIRECTION.

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

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

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

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

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

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

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

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

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

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

COMMAND EXECUTION ENVIRONMENT
       The shell has an execution environment, which consists of the
       following:

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

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

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

       ·      current traps set by trap

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

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

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

       ·      options enabled by shopt

       ·      shell aliases defined with alias

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

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


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

       ·      the current working directory

       ·      the file creation mode mask

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

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

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

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

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

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

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

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

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

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

       When bash invokes an external command, the variable _ is set to the
       full file name 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.

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

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

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

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

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

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

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

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

              [1] 25647

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

       For example, placing

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

              set variable-name value

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

       bell-style (audible)
              Controls what happens when readline wants to ring the terminal
              bell.  If set to none, readline never rings the bell.  If set to
              visible, readline uses a visible bell if one is available.  If
              set to audible, readline attempts to ring the terminal's bell.
       bind-tty-special-chars (On)
              If set to On, readline attempts to bind the control characters
              treated specially by the kernel's terminal driver to their
              readline equivalents.
       comment-begin (``#'')
              The string that is inserted when the readline insert-comment
              command is executed.  This command is bound to M-# in emacs mode
              and to # in vi command mode.
       completion-ignore-case (Off)
              If set to On, readline performs filename matching and completion
              in a case-insensitive fashion.
       completion-prefix-display-length (0)
              The length in characters of the common prefix of a list of
              possible completions that is displayed without modification.
              When set to a value greater than zero, common prefixes longer
              than this value are replaced with an ellipsis when displaying
              possible completions.
       completion-query-items (100)
              This determines when the user is queried about viewing the
              number of possible completions generated by the
              possible-completions command.  It may be set to any integer
              value greater than or equal to zero.  If the number of possible
              completions is greater than or equal to the value of this
              variable, the user is asked whether or not he wishes to view
              them; otherwise they are simply listed on the terminal.
       convert-meta (On)
              If set to On, readline will convert characters with the eighth
              bit set to an ASCII key sequence by stripping the eighth bit and
              prefixing an escape character (in effect, using escape as the
              meta prefix).
       disable-completion (Off)
              If set to On, readline will inhibit word completion.  Completion
              characters will be inserted into the line as if they had been
              mapped to self-insert.
       editing-mode (emacs)
              Controls whether readline begins with a set of key bindings
              similar to Emacs or vi.  editing-mode can be set to either emacs
              or vi.
       echo-control-characters (On)
              When set to On, on operating systems that indicate they support
              it, readline echoes a character corresponding to a signal
              generated from the keyboard.
       enable-keypad (Off)
              When set to On, readline will try to enable the application
              keypad when it is called.  Some systems need this to enable the
              arrow keys.
       enable-meta-key (On)
              When set to On, readline will try to enable any meta modifier
              key the terminal claims to support when it is called.  On many
              terminals, the meta key is used to send eight-bit characters.
       expand-tilde (Off)
              If set to On, tilde expansion is performed when readline
              attempts word completion.
       history-preserve-point (Off)
              If set to On, the history code attempts to place point at the
              same location on each history line retrieved with previous-
              history or next-history.
       history-size (0)
              Set the maximum number of history entries saved in the history
              list.  If set to zero, the number of entries in the history list
              is not limited.
       horizontal-scroll-mode (Off)
              When set to On, makes readline use a single line for display,
              scrolling the input horizontally on a single screen line when it
              becomes longer than the screen width rather than wrapping to a
              new line.
       input-meta (Off)
              If set to On, readline will enable eight-bit input (that is, it
              will not strip the high bit from the characters it reads),
              regardless of what the terminal claims it can support.  The name
              meta-flag is a synonym for this variable.
       isearch-terminators (``C-[C-J'')
              The string of characters that should terminate an incremental
              search without subsequently executing the character as a
              command.  If this variable has not been given a value, the
              characters ESC and C-J will terminate an incremental search.
       keymap (emacs)
              Set the current readline keymap.  The set of valid keymap names
              is emacs, emacs-standard, emacs-meta, emacs-ctlx, vi,
              vi-command, and vi-insert.  vi is equivalent to vi-command;
              emacs is equivalent to emacs-standard.  The default value is
              emacs; the value of editing-mode also affects the default
              keymap.
       mark-directories (On)
              If set to On, completed directory names have a slash appended.
       mark-modified-lines (Off)
              If set to On, history lines that have been modified are
              displayed with a preceding asterisk (*).
       mark-symlinked-directories (Off)
              If set to On, completed names which are symbolic links to
              directories have a slash appended (subject to the value of
              mark-directories).
       match-hidden-files (On)
              This variable, when set to On, causes readline to match files
              whose names begin with a `.' (hidden files) when performing
              filename completion.  If set to Off, the leading `.' must be
              supplied by the user in the filename to be completed.
       menu-complete-display-prefix (Off)
              If set to On, menu completion displays the common prefix of the
              list of possible completions (which may be empty) before cycling
              through the list.
       output-meta (Off)
              If set to On, readline will display characters with the eighth
              bit set directly rather than as a meta-prefixed escape sequence.
       page-completions (On)
              If set to On, readline uses an internal more-like pager to
              display a screenful of possible completions at a time.
       print-completions-horizontally (Off)
              If set to On, readline will display completions with matches
              sorted horizontally in alphabetical order, rather than down the
              screen.
       revert-all-at-newline (Off)
              If set to On, readline will undo all changes to history lines
              before returning when accept-line is executed.  By default,
              history lines may be modified and retain individual undo lists
              across calls to readline.
       show-all-if-ambiguous (Off)
              This alters the default behavior of the completion functions.
              If set to On, words which have more than one possible completion
              cause the matches to be listed immediately instead of ringing
              the bell.
       show-all-if-unmodified (Off)
              This alters the default behavior of the completion functions in
              a fashion similar to show-all-if-ambiguous.  If set to On, words
              which have more than one possible completion without any
              possible partial completion (the possible completions don't
              share a common prefix) cause the matches to be listed
              immediately instead of ringing the bell.
       skip-completed-text (Off)
              If set to On, this alters the default completion behavior when
              inserting a single match into the line.  It's only active when
              performing completion in the middle of a word.  If enabled,
              readline does not insert characters from the completion that
              match characters after point in the word being completed, so
              portions of the word following the cursor are not duplicated.
       visible-stats (Off)
              If set to On, a character denoting a file's type as reported by
              stat(2) is appended to the filename when listing possible
              completions.

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

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

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

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

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

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

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

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

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

              $include  /etc/inputrc

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

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

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

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

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

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

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

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

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

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

   Numeric Arguments
       digit-argument (M-0, M-1, ..., M--)
              Add this digit to the argument already accumulating, or start a
              new argument.  M-- starts a negative argument.
       universal-argument
              This is another way to specify an argument.  If this command is
              followed by one or more digits, optionally with a leading minus
              sign, those digits define the argument.  If the command is
              followed by digits, executing universal-argument again ends the
              numeric argument, but is otherwise ignored.  As a special case,
              if this command is immediately followed by a character that is
              neither a digit or minus sign, the argument count for the next
              command is multiplied by four.  The argument count is initially
              one, so executing this function the first time makes the
              argument count four, a second time makes the argument count
              sixteen, and so on.

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

   Keyboard Macros
       start-kbd-macro (C-x ()
              Begin saving the characters typed into the current keyboard
              macro.
       end-kbd-macro (C-x ))
              Stop saving the characters typed into the current keyboard macro
              and store the definition.
       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.

   Miscellaneous
       re-read-init-file (C-x C-r)
              Read in the contents of the inputrc file, and incorporate any
              bindings or variable assignments found there.
       abort (C-g)
              Abort the current editing command and ring the terminal's bell
              (subject to the setting of bell-style).
       do-uppercase-version (M-a, M-b, M-x, ...)
              If the metafied character x is lowercase, run the command that
              is bound to the corresponding uppercase character.
       prefix-meta (ESC)
              Metafy the next character typed.  ESC f is equivalent to Meta-f.
       undo (C-_, C-x C-u)
              Incremental undo, separately remembered for each line.
       revert-line (M-r)
              Undo all changes made to this line.  This is like executing the
              undo command enough times to return the line to its initial
              state.
       tilde-expand (M-&)
              Perform tilde expansion on the current word.
       set-mark (C-@, M-<space>)
              Set the mark to the point.  If a numeric argument is supplied,
              the mark is set to that position.
       exchange-point-and-mark (C-x C-x)
              Swap the point with the mark.  The current cursor position is
              set to the saved position, and the old cursor position is saved
              as the mark.
       character-search (C-])
              A character is read and point is moved to the next occurrence of
              that character.  A negative count searches for previous
              occurrences.
       character-search-backward (M-C-])
              A character is read and point is moved to the previous
              occurrence of that character.  A negative count searches for
              subsequent occurrences.
       skip-csi-sequence
              Read enough characters to consume a multi-key sequence such as
              those defined for keys like Home and End.  Such sequences begin
              with a Control Sequence Indicator (CSI), usually ESC-[.  If this
              sequence is bound to "\[", keys producing such sequences will
              have no effect unless explicitly bound to a readline command,
              instead of inserting stray characters into the editing buffer.
              This is unbound by default, but usually bound to ESC-[.
       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 file names 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 file names is inserted,
              replacing the word.  If a numeric argument is supplied, an
              asterisk is appended before pathname expansion.
       glob-list-expansions (C-x g)
              The list of expansions that would have been generated by
              glob-expand-word is displayed, and the line is redrawn.  If a
              numeric argument is supplied, an asterisk is appended before
              pathname expansion.
       dump-functions
              Print all of the functions and their key bindings to the
              readline output stream.  If a numeric argument is supplied, the
              output is formatted in such a way that it can be made part of an
              inputrc file.
       dump-variables
              Print all of the settable readline variables and their values to
              the readline output stream.  If a numeric argument is supplied,
              the output is formatted in such a way that it can be made part
              of an inputrc file.
       dump-macros
              Print all of the readline key sequences bound to macros and the
              strings they output.  If a numeric argument is supplied, the
              output is formatted in such a way that it can be made part of an
              inputrc file.
       display-shell-version (C-x C-v)
              Display version information about the current instance of bash.

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

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

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

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

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

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

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

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

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

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

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

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

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

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

       There is some support for dynamically modifying completions.  This is
       most useful when used in combination with a default completion
       specified with complete -D.  It's possible for shell functions executed
       as completion handlers to indicate that completion should be 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


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.  When the
       history file is read, lines beginning with the history comment
       character followed immediately by a digit are interpreted as timestamps
       for the preceding history line.  These timestamps are optionally
       displayed depending on the value of the HISTTIMEFORMAT variable.  When
       an interactive shell 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 not set, no truncation is performed.

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

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

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

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

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

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

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

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

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

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

   Word Designators
       Word designators are used to select desired words from the event.  A :
       separates the event specification from the word designator.  It may be
       omitted if the word designator begins with a ^, $, *, -, or %.  Words
       are numbered from the beginning of the line, with the first word being
       denoted by 0 (zero).  Words are inserted into the current line
       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 argument.
       %      The word matched by the most recent `?string?' search.
       x-y    A range of words; `-y' abbreviates `0-y'.
       *      All of the words but the zeroth.  This is a synonym for `1-$'.
              It is not an error to use * if there is just one word in the
              event; the empty string is returned in that case.
       x*     Abbreviates x-$.
       x-     Abbreviates x-$ like x*, but omits the last word.

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

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

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

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

        .  filename [arguments]
       source filename [arguments]
              Read and execute commands from filename in the current shell
              environment and return the exit status of the last command
              executed from filename.  If filename does not contain a slash,
              file names in PATH are used to find the directory containing
              filename.  The file searched for in PATH need not be executable.
              When bash is not in posix mode, the current directory is
              searched if no file is found in PATH.  If the sourcepath option
              to the shopt builtin command is turned off, the PATH is not
              searched.  If any arguments are supplied, they become the
              positional parameters when filename is executed.  Otherwise the
              positional parameters are unchanged.  The return status is the
              status of the last command exited within the script (0 if no
              commands are executed), and false if filename is not found or
              cannot be read.

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

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

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

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

       break [n]
              Exit from within a for, while, until, or select loop.  If n is
              specified, break n levels.  n must be ≥ 1.  If n is greater than
              the number of enclosing loops, all enclosing loops are exited.
              The return value is non-zero when n is ≤ 0; Otherwise, break
              returns 0 value.

       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.  The variable HOME is the
              default dir.  The variable CDPATH defines the search path for
              the directory containing 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 says to use the physical directory structure instead of
              following symbolic links (see also the -P option to the set
              builtin command); the -L option forces symbolic links to be
              followed.  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.  An argument of - is equivalent to $OLDPWD.  If a non-
              empty directory name from CDPATH is used, or if - is the first
              argument, and the directory change is successful, the absolute
              pathname of the new working directory is written to the standard
              output.  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 file name
              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.

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

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

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

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

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

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

       continue [n]
              Resume the next iteration of the enclosing for, while, until, or
              select loop.  If n is specified, resume at the nth enclosing
              loop.  n must be ≥ 1.  If n is greater than the number of
              enclosing loops, the last enclosing loop (the ``top-level''
              loop) is resumed.  When continue is executed inside of loop, the
              return value is non-zero when n is ≤ 0; Otherwise, continue
              returns 0 value. When continue is executed outside of loop, the
              return value is 0.

       declare [-aAfFgilrtux] [-p] [name[=value] ...]
       typeset [-aAfFgilrtux] [-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 are ignored.  When -p is
              supplied without name arguments, it will display the attributes
              and values of all variables having the attributes specified by
              the additional options.  If no other options are supplied with
              -p, declare will display the attributes and values of all shell
              variables.  The -f option will restrict the display to shell
              functions.  The -F option inhibits the display of function
              definitions; only the function name and attributes are printed.
              If the extdebug shell option is enabled using shopt, the source
              file name and line number where the function is defined are
              displayed as well.  The -F option implies -f.  The -g option
              forces variables to be created or modified at the global scope,
              even when declare is executed in a shell function.  It is
              ignored in all other cases.  The following options can be used
              to restrict output to variables with the specified attribute or
              to give variables attributes:
              -a     Each name is an indexed array variable (see Arrays
                     above).
              -A     Each name is an associative array variable (see Arrays
                     above).
              -f     Use function names only.
              -i     The variable is treated as an integer; arithmetic
                     evaluation (see ARITHMETIC EVALUATION above) is performed
                     when the variable is assigned a value.
              -l     When the variable is assigned a value, all upper-case
                     characters are converted to lower-case.  The upper-case
                     attribute is disabled.
              -r     Make names readonly.  These names cannot then be assigned
                     values by subsequent assignment statements or unset.
              -t     Give each name the trace attribute.  Traced functions
                     inherit the DEBUG and RETURN traps from the calling
                     shell.  The trace attribute has no special meaning for
                     variables.
              -u     When the variable is assigned a value, all lower-case
                     characters are converted to upper-case.  The lower-case
                     attribute is disabled.
              -x     Mark names for export to subsequent commands via the
                     environment.

              Using `+' instead of `-' turns off the attribute instead, with
              the exceptions that +a may not be used to destroy an array
              variable and +r will not remove the readonly attribute.  When
              used in a function, makes 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.
              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 [+n] [-n] [-clpv]
              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.
              +n     Displays the nth entry counting from the left of the list
                     shown by dirs when invoked without options, starting with
                     zero.
              -n     Displays the nth entry counting from the right of the
                     list shown by dirs when invoked without options, starting
                     with zero.
              -c     Clears the directory stack by deleting all of the
                     entries.
              -l     Produces a longer listing; 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.

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

       disown [-ar] [-h] [jobspec ...]
              Without options, each jobspec is removed from the table of
              active jobs.  If jobspec is not present, and neither -a nor -r
              is supplied, the shell's notion of 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 present, and
              neither the -a nor the -r option is supplied, the current job is
              used.  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 always 0.  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)

       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 shell option execfail is enabled, in which
              case it returns failure.  An interactive shell returns failure
              if the file cannot be executed.  If command is not specified,
              any redirections take effect in the current shell, and the
              return status is 0.  If there is a redirection error, the return
              status is 1.

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

       export [-fn] [name[=word]] ...
       export -p
              The supplied names are marked for automatic export to the
              environment of subsequently executed commands.  If the -f option
              is given, the names refer to functions.  If no names are given,
              or if the -p option is supplied, a list of all names that are
              exported in this shell 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]
              Fix Command.  In the first form, a range of commands from first
              to last is selected from the history list.  First and last may
              be specified as a string (to locate the last command beginning
              with that string) or as a number (an index into the history
              list, where a negative number is used as an offset from the
              current command number).  If last is not specified it is set to
              the current command for listing (so that ``fc -l -10'' prints
              the last 10 commands) and to first otherwise.  If first is not
              specified it is set to the previous command for editing and -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.  A useful alias to use with this is
              ``r="fc -s"'', so that typing ``r cc'' runs the last command
              beginning with ``cc'' and typing ``r'' re-executes the last
              command.

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

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

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

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

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

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

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

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

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

       hash [-lr] [-p filename] [-dt] [name]
              Each time hash is invoked, the full pathname of the command name
              is determined by searching the directories in $PATH and
              remembered.  Any previously-remembered pathname is discarded.
              If the -p option is supplied, no path search is performed, and
              filename is used as the full file name 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 -anrw [filename]
       history -p arg [arg ...]
       history -s arg [arg ...]
              With no options, display the command history list with line
              numbers.  Lines listed with a * have been modified.  An argument
              of n lists only the last n lines.  If the shell variable
              HISTTIMEFORMAT is set and not null, it is used as a format
              string for strftime(3) to display the time stamp associated with
              each displayed history entry.  No intervening blank is printed
              between the formatted time stamp and the history line.  If
              filename is supplied, it is used as the name of the history
              file; if not, the value of HISTFILE is used.  Options, if
              supplied, have the following meanings:
              -c     Clear the history list by deleting all the entries.
              -d offset
                     Delete the history entry at position offset.
              -a     Append the ``new'' history lines (history lines entered
                     since the beginning of the current bash session) to the
                     history file.
              -n     Read the history lines not already read from the history
                     file into the current history list.  These are lines
                     appended to the history file since the beginning of the
                     current bash session.
              -r     Read the contents of the history file and use them as the
                     current history.
              -w     Write the current history to the history file,
                     overwriting the history file's contents.
              -p     Perform history substitution on the following args and
                     display the result on the standard output.  Does not
                     store the results in the history list.  Each arg must be
                     quoted to disable normal history expansion.
              -s     Store the args in the history list as a single entry.
                     The last command in the history list is removed before
                     the args are added.

              If the HISTTIMEFORMAT variable is set, the time stamp
              information associated with each history entry is written to the
              history file, marked with the history comment character.  When
              the history file is read, lines beginning with the history
              comment character followed immediately by a digit are
              interpreted as timestamps for the previous history line.  The
              return value is 0 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     Restrict output to running jobs.
              -s     Restrict output to stopped jobs.

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

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

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

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

       local [option] [name[=value] ...]
              For each argument, a local variable named name is created, and
              assigned value.  The option can be any of the options accepted
              by declare.  When local is used within a function, it causes the
              variable name to have a visible scope restricted to that
              function and its children.  With no operands, local writes a
              list of local variables to the standard output.  It is an error
              to use local when not within a function.  The return status is 0
              unless local is used outside a function, an invalid name is
              supplied, or name is a readonly variable.

       logout Exit a login shell.

       mapfile [-n count] [-O origin] [-s count] [-t] [-u fd] [-C callback]
       [-c quantum] [array]
       readarray [-n count] [-O origin] [-s count] [-t] [-u fd] [-C callback]
       [-c quantum] [array]
              Read lines from the standard input into the indexed array
              variable array, or from file descriptor fd if the -u option is
              supplied.  The variable MAPFILE is the default array.  Options,
              if supplied, have the following meanings:
              -n     Copy at most count lines.  If count is 0, all lines are
                     copied.
              -O     Begin assigning to array at index origin.  The default
                     index is 0.
              -s     Discard the first count lines read.
              -t     Remove a trailing newline from each line read.
              -u     Read lines from file descriptor fd instead of the
                     standard input.
              -C     Evaluate callback each time quantum lines are read.  The
                     -c option specifies quantum.
              -c     Specify the number of lines read between each call to
                     callback.

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

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

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

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

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

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

              The format is a character string which contains three types of
              objects: plain characters, which are simply copied to standard
              output, character escape sequences, which are converted and
              copied to the standard output, and format specifications, each
              of which causes printing of the next successive argument.  In
              addition to the standard printf(1) format specifications, printf
              interprets the following extensions:
              %b     causes printf to expand backslash escape sequences in the
                     corresponding argument (except that \c terminates output,
                     backslashes in \', \", and \? are not removed, and octal
                     escapes beginning with \0 may contain up to four digits).
              %q     causes printf to output the corresponding argument in a
                     format that can be reused as shell input.
              %(datefmt)T
                     causes printf to output the date-time string resulting
                     from using datefmt as a format string for strftime(3).
                     The corresponding argument is an integer representing the
                     number of seconds since the epoch.  Two special argument
                     values may be used: -1 represents the current time, and
                     -2 represents the time the shell was invoked.

              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.

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

              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.

       read [-ers] [-a aname] [-d delim] [-i text] [-n nchars] [-N nchars] [-p
       prompt] [-t timeout] [-u fd] [name ...]
              One line is read from the standard input, or from the file
              descriptor fd supplied as an argument to the -u option, and the
              first word is assigned to the first name, the second word to the
              second name, and so on, with leftover words and their
              intervening separators assigned to the last name.  If there are
              fewer words read from the input stream than names, the remaining
              names are assigned empty values.  The characters in IFS are used
              to split the line into words.  The backslash character (\) may
              be used to remove any special meaning for the next character
              read and for line continuation.  Options, if supplied, have the
              following meanings:
              -a aname
                     The words are assigned to sequential indices of the array
                     variable aname, starting at 0.  aname is unset before any
                     new values are assigned.  Other name arguments are
                     ignored.
              -d delim
                     The first character of delim is used to terminate the
                     input line, rather than newline.
              -e     If the standard input is coming from a terminal, readline
                     (see READLINE above) is used to obtain the line.
                     Readline uses the current (or default, if line editing
                     was not previously active) editing settings.
              -i text
                     If readline is being used to read the line, text is
                     placed into the editing buffer before editing begins.
              -n nchars
                     read returns after reading nchars characters rather than
                     waiting for a complete line of input, but honor a
                     delimiter if fewer than nchars characters are read before
                     the delimiter.
              -N nchars
                     read returns after reading exactly nchars characters
                     rather than waiting for a complete line of input, unless
                     EOF is encountered or read times out.  Delimiter
                     characters encountered in the input are not treated
                     specially and do not cause read to return until nchars
                     characters are read.
              -p prompt
                     Display prompt on standard error, without a trailing
                     newline, before attempting to read any input.  The prompt
                     is displayed only if input is coming from a terminal.
              -r     Backslash does not act as an escape character.  The
                     backslash is considered to be part of the line.  In
                     particular, a backslash-newline pair may not be used as a
                     line continuation.
              -s     Silent mode.  If input is coming from a terminal,
                     characters are not echoed.
              -t timeout
                     Cause read to time out and return failure if a complete
                     line of input 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 timeout is 0, read returns success if
                     input is available on the specified file descriptor,
                     failure otherwise.  The exit status is greater than 128
                     if the timeout is exceeded.
              -u fd  Read input from file descriptor fd.

              If no names are supplied, the line read is assigned to the
              variable REPLY.  The return code is zero, unless end-of-file is
              encountered, read times out (in which case the return code is
              greater than 128), 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 exit with the return value specified by n.
              If n is omitted, the return status is that of the last command
              executed in the function body.  If 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 used outside a
              function and not during execution of a script by ., the return
              status is false.  Any command associated with the RETURN trap is
              executed before execution resumes after the function or script.

       set [--abefhkmnptuvxBCEHPT] [-o option-name] [arg ...]
       set [+abefhkmnptuvxBCEHPT] [+o option-name] [arg ...]
              Without options, the name and value of each shell variable are
              displayed in a format that can be reused as input for setting or
              resetting the currently-set variables.  Read-only variables
              cannot be reset.  In posix mode, only shell variables are
              listed.  The output is sorted according to the current locale.
              When options are specified, they set or unset shell attributes.
              Any arguments remaining after option processing are treated as
              values for the positional parameters and are assigned, in order,
              to $1, $2, ...  $n.  Options, if specified, have the following
              meanings:
              -a      Automatically mark variables and functions which are
                      modified or created for export to the environment of
                      subsequent commands.
              -b      Report the status of terminated background jobs
                      immediately, rather than before the next primary prompt.
                      This is effective only when job control is enabled.
              -e      Exit immediately if a pipeline (which may consist of a
                      single simple command),  a subshell command enclosed in
                      parentheses, or one of the commands executed as part of
                      a command list enclosed by braces (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 !.  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.
              -f      Disable pathname expansion.
              -h      Remember the location of commands as they are looked up
                      for execution.  This is enabled by default.
              -k      All arguments in the form of assignment statements are
                      placed in the environment for a command, not just those
                      that precede the command name.
              -m      Monitor mode.  Job control is enabled.  This option is
                      on by default for interactive shells on systems that
                      support it (see JOB CONTROL above).  Background
                      processes run in a separate process group and a line
                      containing their exit status is printed upon their
                      completion.
              -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
                              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).
                      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,
                      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 follow 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 variables controlling optional shell
              behavior.  With no options, or with the -p option, a list of all
              settable options is displayed, with an indication of whether or
              not each is set.  The -p option causes output to be displayed in
              a form that may be reused as input.  Other options have the
              following meanings:
              -s     Enable (set) each optname.
              -u     Disable (unset) each optname.
              -q     Suppresses normal output (quiet mode); the return status
                     indicates whether the optname is set or unset.  If
                     multiple optname arguments are given with -q, the return
                     status is zero if all optnames are enabled; non-zero
                     otherwise.
              -o     Restricts the values of optname to be those defined for
                     the -o option to the set builtin.

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

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

              The list of shopt options is:

              autocd  If set, a command name that is the name of a directory
                      is executed as if it were the argument to the cd
                      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 file name is printed, and the
                      command proceeds.  This option is only used by
                      interactive shells.
              checkhash
                      If set, bash checks that a command found in the hash
                      table exists before trying to execute it.  If a hashed
                      command no longer exists, a normal path search is
                      performed.
              checkjobs
                      If set, bash lists the status of any stopped and running
                      jobs before exiting an interactive shell.  If any jobs
                      are running, this causes the exit to be deferred until a
                      second exit is attempted without an intervening command
                      (see JOB CONTROL above).  The shell always postpones
                      exiting if any jobs are stopped.
              checkwinsize
                      If set, bash checks the window size after each command
                      and, if necessary, updates the values of LINES and
                      COLUMNS.
              cmdhist If set, bash attempts to save all lines of a multiple-
                      line command in the same history entry.  This allows
                      easy re-editing of multi-line commands.
              compat31
                      If set, bash changes its behavior to that of version 3.1
                      with respect to quoted arguments to the [[ conditional
                      command's =~ operator.
              compat32
                      If set, bash changes its behavior to that of version 3.2
                      with respect to locale-specific string comparison when
                      using the [[ conditional command's < and > operators.
                      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).
              compat40
                      If set, bash changes its behavior to that of version 4.0
                      with respect to locale-specific string comparison when
                      using the [[ conditional command's < and > operators
                      (see previous item) and the effect of interrupting a
                      command list.
              compat41
                      If set, bash, when in posix mode, treats a single quote
                      in a double-quoted parameter expansion as a special
                      character.  The single quotes must match (an even
                      number) and the characters between the single quotes are
                      considered quoted.  This is the behavior of posix mode
                      through version 4.1.  The default bash behavior remains
                      as in previous versions.
              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.
              execfail
                      If set, a non-interactive shell will not exit if it
                      cannot execute the file specified as an argument to the
                      exec builtin command.  An interactive shell does not
                      exit if exec fails.
              expand_aliases
                      If set, aliases are expanded as described above under
                      ALIASES.  This option is enabled by default for
                      interactive shells.
              extdebug
                      If set, behavior intended for use by debuggers is
                      enabled:
                      1.     The -F option to the declare builtin displays the
                             source file name and line number corresponding to
                             each function name supplied as an argument.
                      2.     If the command run by the DEBUG trap returns a
                             non-zero value, the next command is skipped and
                             not executed.
                      3.     If the command run by the DEBUG trap returns a
                             value of 2, and the shell is executing in a
                             subroutine (a shell function or a shell script
                             executed by the . or source builtins), a call to
                             return is simulated.
                      4.     BASH_ARGC and BASH_ARGV are updated as described
                             in their descriptions above.
                      5.     Function tracing is enabled:  command
                             substitution, shell functions, and subshells
                             invoked with ( command ) inherit the DEBUG and
                             RETURN traps.
                      6.     Error tracing is enabled:  command substitution,
                             shell functions, and subshells invoked with (
                             command ) inherit the ERR trap.
              extglob If set, the extended pattern matching features described
                      above under Pathname Expansion are enabled.
              extquote
                      If set, $'string' and $"string" quoting is performed
                      within ${parameter} expansions enclosed in double
                      quotes.  This option is enabled by default.
              failglob
                      If set, patterns which fail to match filenames during
                      pathname expansion result in an expansion error.
              force_fignore
                      If set, the suffixes specified by the FIGNORE shell
                      variable cause words to be ignored when performing word
                      completion even if the ignored words are the only
                      possible completions.  See SHELL VARIABLES above for a
                      description of FIGNORE.  This option is enabled by
                      default.
              globstar
                      If set, the pattern ** used in a pathname expansion
                      context will match all files and zero or more
                      directories and subdirectories.  If the pattern is
                      followed by a /, only directories and subdirectories
                      match.
              gnu_errfmt
                      If set, shell error messages are written in the standard
                      GNU error message format.
              histappend
                      If set, the history list is appended to the file named
                      by the value of the HISTFILE variable when the shell
                      exits, rather than overwriting the file.
              histreedit
                      If set, and readline is being used, a user is given the
                      opportunity to re-edit a failed history substitution.
              histverify
                      If set, and readline is being used, the results of
                      history substitution are not immediately passed to the
                      shell parser.  Instead, the resulting line is loaded
                      into the readline editing buffer, allowing further
                      modification.
              hostcomplete
                      If set, and readline is being used, bash will attempt to
                      perform hostname completion when a word containing a @
                      is being completed (see Completing under READLINE
                      above).  This is enabled by default.
              huponexit
                      If set, bash will send SIGHUP to all jobs when an
                      interactive login shell exits.
              interactive_comments
                      If set, allow a word beginning with # to cause that word
                      and all remaining characters on that line to be ignored
                      in an interactive shell (see COMMENTS above).  This
                      option is enabled by default.
              lastpipe
                      If set, and job control is not active, the shell runs
                      the last command of a pipeline not executed in the
                      background in the current shell environment.
              lithist If set, and the cmdhist option is enabled, multi-line
                      commands are saved to the history with embedded newlines
                      rather than using semicolon separators where possible.
              login_shell
                      The shell sets this option if it is started as a login
                      shell (see INVOCATION above).  The value may not be
                      changed.
              mailwarn
                      If set, and a file that bash is checking for mail has
                      been accessed since the last time it was checked, the
                      message ``The mail in mailfile has been read'' is
                      displayed.
              no_empty_cmd_completion
                      If set, and readline is being used, bash will not
                      attempt to search the PATH for possible completions when
                      completion is attempted on an empty line.
              nocaseglob
                      If set, bash matches filenames in a case-insensitive
                      fashion when performing pathname expansion (see Pathname
                      Expansion above).
              nocasematch
                      If set, bash matches patterns in a case-insensitive
                      fashion when performing matching while executing case or
                      [[ conditional commands.
              nullglob
                      If set, bash allows patterns which match no files (see
                      Pathname Expansion above) to expand to a null string,
                      rather than themselves.
              progcomp
                      If set, the programmable completion facilities (see
                      Programmable Completion above) are enabled.  This option
                      is enabled by default.
              promptvars
                      If set, prompt strings undergo parameter expansion,
                      command substitution, arithmetic expansion, and quote
                      removal after being expanded as described in PROMPTING
                      above.  This option is enabled by default.
              restricted_shell
                      The shell sets this option if it is started in
                      restricted mode (see RESTRICTED SHELL below).  The value
                      may not be changed.  This is not reset when the startup
                      files are executed, allowing the startup files to
                      discover whether or not a shell is restricted.
              shift_verbose
                      If set, the shift builtin prints an error message when
                      the shift count exceeds the number of positional
                      parameters.
              sourcepath
                      If set, the source (.) builtin uses the value of PATH to
                      find the directory containing the file supplied as an
                      argument.  This option is enabled by default.
              xpg_echo
                      If set, the echo builtin expands backslash-escape
                      sequences by default.

       suspend [-f]
              Suspend the execution of this shell until it receives a SIGCONT
              signal. When the suspended shell is a background process, it can
              be restarted by the fg command. For more information, read the
              JOB CONTROL section. The suspend command can not suspend the
              login shell. However, when -f option is specified, suspend
              command can suspend even login shell.  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 or 1 depending on the evaluation of the
              conditional expression expr.  Each operator and operand must be
              a separate argument.  Expressions are composed of the primaries
              described above under CONDITIONAL EXPRESSIONS.  test does not
              accept any options, nor does it accept and ignore an argument of
              -- as signifying the end of options.

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

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

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

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

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

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

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

              If a sigspec is ERR, the command arg is executed whenever a
              simple command has 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, or if the
              command's return value is being inverted via !.  These are the
              same conditions obeyed by the errexit option.

              Signals ignored upon entry to the shell cannot be trapped, reset
              or listed.  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, not
              necessarily the file that appears first in PATH.  If the -a
              option is used, type prints all of the places that contain an
              executable named name.  This includes aliases and functions, if
              and only if the -p option is not also used.  The table of hashed
              commands is not consulted when using -a.  The -f option
              suppresses shell function lookup, as with the command builtin.
              type returns true if all of the arguments are found, false if
              any are not found.

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

              If limit is given, it is the new value of the specified resource
              (the -a option is display only).  If no option is given, then -f
              is assumed.  Values are in 1024-byte increments, except for -t,
              which is in seconds, -p, which is in units of 512-byte blocks,
              and -T, -b, -n, and -u, which are unscaled values.  The return
              status is 0 unless an invalid option or argument is supplied, or
              an error occurs while setting a new limit.  In POSIX Mode
              512-byte blocks are used for the `-c' and `-f' options.

       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] [name ...]
              For each name, remove the corresponding variable or function.
              If no options are supplied, or the -v option is given, each name
              refers to a shell variable.  Read-only variables may not be
              unset.  If -f is specified, each name refers to a shell
              function, and the function definition is removed.  Each unset
              variable or function is removed from the environment passed to
              subsequent commands.  If any of COMP_WORDBREAKS, RANDOM,
              SECONDS, LINENO, HISTCMD, FUNCNAME, GROUPS, or DIRSTACK are
              unset, they lose their special properties, even if they are
              subsequently reset.  The exit status is true unless a name is
              readonly.

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

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

       ·      changing directories with cd

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

       ·      specifying command names containing /

       ·      specifying a file name containing a / as an argument to the .
              builtin command

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

       ·      importing function definitions from the shell environment at
              startup

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

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

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

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

       ·      using the enable builtin command to enable disabled shell
              builtins

       ·      specifying the -p option to the command builtin command

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

       These restrictions are enforced after any startup files are read.

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

SEE ALSO
       Bash Reference Manual, Brian Fox and Chet Ramey
       The Gnu Readline Library, Brian Fox and Chet Ramey
       The Gnu History Library, Brian Fox and Chet Ramey
       Portable Operating System Interface (POSIX) Part 2: Shell and
       Utilities, IEEE
       sh(1), ksh(1), csh(1)
       emacs(1), vi(1)
       readline(3)

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

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

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

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

       Once you have determined that a bug actually exists, use the bashbug
       command (from the source package) 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

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

BUGS
       It's too big and too slow.

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

       Aliases are confusing in some uses.

       Shell builtin commands and functions are not stoppable/restartable.

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

       Array variables may not (yet) be exported.

       There may be only one active coprocess at a time.



GNU Bash-4.2                   2010 December 28                        BASH(1)