bash(1) — Linux manual page

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BASH(1)                  General Commands Manual                 BASH(1)

NAME         top

       bash - GNU Bourne-Again SHell

SYNOPSIS         top

       bash [options] [command_string | file]

COPYRIGHT         top

       Bash is Copyright (C) 1989-2020 by the Free Software Foundation,
       Inc.

DESCRIPTION         top

       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         top

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

       -c     If the -c option is present, then commands are read from
              the first non-option argument command_string.  If there
              are arguments after the command_string, the first argument
              is assigned to $0 and any remaining arguments are assigned
              to the positional parameters.  The assignment to $0 sets
              the name of the shell, which is used in warning and error
              messages.
       -i     If the -i option is present, the shell is interactive.
       -l     Make bash act as if it had been invoked as a login shell
              (see INVOCATION below).
       -r     If the -r option is present, the shell becomes restricted
              (see RESTRICTED SHELL below).
       -s     If the -s option is present, or if no arguments remain
              after option processing, then commands are read from the
              standard input.  This option allows the positional
              parameters to be set when invoking an interactive shell or
              when reading input through a pipe.
       -D     A list of all double-quoted strings preceded by $ is
              printed on the standard output.  These are the strings
              that are subject to language translation when the current
              locale is not C or POSIX.  This implies the -n option; no
              commands will be executed.
       [-+]O [shopt_option]
              shopt_option is one of the shell options accepted by the
              shopt builtin (see SHELL BUILTIN COMMANDS below).  If
              shopt_option is present, -O sets the value of that option;
              +O unsets it.  If shopt_option is not supplied, the names
              and values of the shell options accepted by shopt are
              printed on the standard output.  If the invocation option
              is +O, the output is displayed in a format that may be
              reused as input.
       --     A -- signals the end of options and disables further
              option processing.  Any arguments after the -- are treated
              as filenames and arguments.  An argument of - is
              equivalent to --.

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

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

       --login
              Equivalent to -l.

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

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

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

       --posix
              Change the behavior of bash where the default operation
              differs from the POSIX standard to match the standard
              (posix mode).  See SEE ALSO below for a reference to a
              document that details how posix mode affects bash's
              behavior.

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

       --verbose
              Equivalent to -v.

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

ARGUMENTS         top

       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         top

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

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

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

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

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

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

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

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

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

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

       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         top

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

RESERVED WORDS         top

       Reserved words are words that have a special meaning to the
       shell.  The following words are recognized as reserved when
       unquoted and either the first word of a command (see SHELL
       GRAMMAR below), the third word of a case or select command (only
       in is valid), or the third word of a for command (only in and do
       are valid):

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

SHELL GRAMMAR         top

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

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

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

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

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

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

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

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

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

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

              command1 && command2

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

       An OR list has the form

              command1 || command2

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

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

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

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

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

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

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

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

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

              The pattern will match if it matches any part of the
              string.  Anchor the pattern using the ^ and $ regular
              expression operators to force it to match the entire
              string.  The array variable BASH_REMATCH records which
              parts of the string matched the pattern.  The element of
              BASH_REMATCH with index 0 contains the portion of the
              string matching the entire regular expression.  Substrings
              matched by parenthesized subexpressions within the regular
              expression are saved in the remaining BASH_REMATCH
              indices. The element of BASH_REMATCH with index n is the
              portion of the string matching the nth parenthesized
              subexpression.

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

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

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

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

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

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

       case word in [ [(] pattern [ | pattern ] ... ) list ;; ] ... esac
              A case command first expands word, and tries to match it
              against each pattern in turn, using the matching rules
              described under Pattern Matching below.  The word is
              expanded using tilde expansion, parameter and variable
              expansion, arithmetic expansion, command substitution,
              process substitution and quote removal.  Each pattern
              examined is expanded using tilde expansion, parameter and
              variable expansion, arithmetic expansion, command
              substitution, and process substitution.  If the
              nocasematch shell option is enabled, the match is
              performed without regard to the case of alphabetic
              characters.  When a match is found, the corresponding list
              is executed.  If the ;; operator is used, no subsequent
              matches are attempted after the first pattern match.
              Using ;& in place of ;; causes execution to continue with
              the list associated with the next set of patterns.  Using
              ;;& in place of ;; causes the shell to test the next
              pattern list in the statement, if any, and execute any
              associated list on a successful match, continuing the case
              statement execution as if the pattern list had not
              matched.  The exit status is zero if no pattern matches.
              Otherwise, it is the exit status of the last command
              executed in list.

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

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

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

       The format for a coprocess is:

              coproc [NAME] command [redirections]

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

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

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

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

COMMENTS         top

       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         top

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

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

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

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

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

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

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

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

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

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

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

PARAMETERS         top

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

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

       A variable can be assigned the nameref attribute using the -n
       option to the declare or local builtin commands (see the
       descriptions of declare and local below) to create a nameref, or
       a reference to another variable.  This allows variables to be
       manipulated indirectly.  Whenever the nameref variable is
       referenced, assigned to, unset, or has its attributes modified
       (other than using or changing the nameref attribute itself), the
       operation is actually performed on the variable specified by the
       nameref variable's value.  A nameref is commonly used within
       shell functions to refer to a variable whose name is passed as an
       argument to the function.  For instance, if a variable name is
       passed to a shell function as its first argument, running
              declare -n ref=$1
       inside the function creates a nameref variable ref whose value is
       the variable name passed as the first argument.  References and
       assignments to ref, and changes to its attributes, are treated as
       references, assignments, and attribute modifications to the
       variable whose name was passed as $1.  If the control variable in
       a for loop has the nameref attribute, the list of words can be a
       list of shell variables, and a name reference will be established
       for each word in the list, in turn, when the loop is executed.
       Array variables cannot be given the nameref attribute.  However,
       nameref variables can reference array variables and subscripted
       array variables.  Namerefs can be unset using the -n option to
       the unset builtin.  Otherwise, if unset is executed with the name
       of a nameref variable as an argument, the variable referenced by
       the nameref variable will be unset.

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

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

   Special Parameters
       The shell treats several parameters specially.  These parameters
       may only be referenced; assignment to them is not allowed.
       *      Expands to the positional parameters, starting from one.
              When the expansion is not within double quotes, each
              positional parameter expands to a separate word.  In
              contexts where it is performed, those words are subject to
              further word splitting and pathname expansion.  When the
              expansion occurs within double quotes, it expands to a
              single word with the value of each parameter separated by
              the first character of the IFS special variable.  That is,
              "$*" is equivalent to "$1c$2c...", where c is the first
              character of the value of the IFS variable.  If IFS is
              unset, the parameters are separated by spaces.  If IFS is
              null, the parameters are joined without intervening
              separators.
       @      Expands to the positional parameters, starting from one.
              In contexts where word splitting is performed, this
              expands each positional parameter to a separate word; if
              not within double quotes, these words are subject to word
              splitting.  In contexts where word splitting is not
              performed, this expands to a single word with each
              positional parameter separated by a space.  When the
              expansion occurs within double quotes, each parameter
              expands to a separate word.  That is, "$@" is equivalent
              to "$1" "$2" ...  If the double-quoted expansion occurs
              within a word, the expansion of the first parameter is
              joined with the beginning part of the original word, and
              the expansion of the last parameter is joined with the
              last part of the original word.  When there are no
              positional parameters, "$@" and $@ expand to nothing
              (i.e., they are removed).
       #      Expands to the number of positional parameters in decimal.
       ?      Expands to the exit status of the most recently executed
              foreground pipeline.
       -      Expands to the current option flags as specified upon
              invocation, by the set builtin command, or those set by
              the shell itself (such as the -i option).
       $      Expands to the process ID of the shell.  In a () subshell,
              it expands to the process ID of the current shell, not the
              subshell.
       !      Expands to the process ID of the job most recently placed
              into the background, whether executed as an asynchronous
              command or using the bg builtin (see JOB CONTROL below).
       0      Expands to the name of the shell or shell script.  This is
              set at shell initialization.  If bash is invoked with a
              file of commands, $0 is set to the name of that file.  If
              bash is started with the -c option, then $0 is set to the
              first argument after the string to be executed, if one is
              present.  Otherwise, it is set to the filename used to
              invoke bash, as given by argument zero.

   Shell Variables
       The following variables are set by the shell:

       _      At shell startup, set to the pathname used to invoke the
              shell or shell script being executed as passed in the
              environment or argument list.  Subsequently, expands to
              the last argument to the previous simple command executed
              in the foreground, after expansion.  Also set to the full
              pathname used to invoke each command executed and placed
              in the environment exported to that command.  When
              checking mail, this parameter holds the name of the mail
              file currently being checked.
       BASH   Expands to the full filename used to invoke this instance
              of bash.
       BASHOPTS
              A colon-separated list of enabled shell options.  Each
              word in the list is a valid argument for the -s option to
              the shopt builtin command (see SHELL BUILTIN COMMANDS
              below).  The options appearing in BASHOPTS are those
              reported as on by shopt.  If this variable is in the
              environment when bash starts up, each shell option in the
              list will be enabled before reading any startup files.
              This variable is read-only.
       BASHPID
              Expands to the process ID of the current bash process.
              This differs from $$ under certain circumstances, such as
              subshells that do not require bash to be re-initialized.
              Assignments to BASHPID have no effect.  If BASHPID is
              unset, it loses its special properties, even if it is
              subsequently reset.
       BASH_ALIASES
              An associative array variable whose members correspond to
              the internal list of aliases as maintained by the alias
              builtin.  Elements added to this array appear in the alias
              list; however, unsetting array elements currently does not
              cause aliases to be removed from the alias list.  If
              BASH_ALIASES is unset, it loses its special properties,
              even if it is subsequently reset.
       BASH_ARGC
              An array variable whose values are the number of
              parameters in each frame of the current bash execution
              call stack.  The number of parameters to the current
              subroutine (shell function or script executed with . or
              source) is at the top of the stack.  When a subroutine is
              executed, the number of parameters passed is pushed onto
              BASH_ARGC.  The shell sets BASH_ARGC only when in extended
              debugging mode (see the description of the extdebug option
              to the shopt builtin below).  Setting extdebug after the
              shell has started to execute a script, or referencing this
              variable when extdebug is not set, may result in
              inconsistent values.
       BASH_ARGV
              An array variable containing all of the parameters in the
              current bash execution call stack.  The final parameter of
              the last subroutine call is at the top of the stack; the
              first parameter of the initial call is at the bottom.
              When a subroutine is executed, the parameters supplied are
              pushed onto BASH_ARGV.  The shell sets BASH_ARGV only when
              in extended debugging mode (see the description of the
              extdebug option to the shopt builtin below).  Setting
              extdebug after the shell has started to execute a script,
              or referencing this variable when extdebug is not set, may
              result in inconsistent values.
       BASH_ARGV0
              When referenced, this variable expands to the name of the
              shell or shell script (identical to $0; see the
              description of special parameter 0 above).  Assignment to
              BASH_ARGV0 causes the value assigned to also be assigned
              to $0.  If BASH_ARGV0 is unset, it loses its special
              properties, even if it is subsequently reset.
       BASH_CMDS
              An associative array variable whose members correspond to
              the internal hash table of commands as maintained by the
              hash builtin.  Elements added to this array appear in the
              hash table; however, unsetting array elements currently
              does not cause command names to be removed from the hash
              table.  If BASH_CMDS is unset, it loses its special
              properties, even if it is subsequently reset.
       BASH_COMMAND
              The command currently being executed or about to be
              executed, unless the shell is executing a command as the
              result of a trap, in which case it is the command
              executing at the time of the trap.  If BASH_COMMAND is
              unset, it loses its special properties, even if it is
              subsequently reset.
       BASH_EXECUTION_STRING
              The command argument to the -c invocation option.
       BASH_LINENO
              An array variable whose members are the line numbers in
              source files where each corresponding member of FUNCNAME
              was invoked.  ${BASH_LINENO[$i]} is the line number in the
              source file (${BASH_SOURCE[$i+1]}) where ${FUNCNAME[$i]}
              was called (or ${BASH_LINENO[$i-1]} if referenced within
              another shell function).  Use LINENO to obtain the current
              line number.
       BASH_LOADABLES_PATH
              A colon-separated list of directories in which the shell
              looks for dynamically loadable builtins specified by the
              enable command.
       BASH_REMATCH
              An array variable whose members are assigned by the =~
              binary operator to the [[ conditional command.  The
              element with index 0 is the portion of the string matching
              the entire regular expression.  The element with index n
              is the portion of the string matching the nth
              parenthesized subexpression.
       BASH_SOURCE
              An array variable whose members are the source filenames
              where the corresponding shell function names in the
              FUNCNAME array variable are defined.  The shell function
              ${FUNCNAME[$i]} is defined in the file ${BASH_SOURCE[$i]}
              and called from ${BASH_SOURCE[$i+1]}.
       BASH_SUBSHELL
              Incremented by one within each subshell or subshell
              environment when the shell begins executing in that
              environment.  The initial value is 0.  If BASH_SUBSHELL is
              unset, it loses its special properties, even if it is
              subsequently reset.
       BASH_VERSINFO
              A readonly array variable whose members hold version
              information for this instance of bash.  The values
              assigned to the array members are as follows:
              BASH_VERSINFO[0]
                     The major version number (the release).
              BASH_VERSINFO[1]
                     The minor version number (the version).
              BASH_VERSINFO[2]
                     The patch level.
              BASH_VERSINFO[3]
                     The build version.
              BASH_VERSINFO[4]
                     The release status (e.g., beta1).
              BASH_VERSINFO[5]
                     The value of MACHTYPE.
       BASH_VERSION
              Expands to a string describing the version of this
              instance of bash.
       COMP_CWORD
              An index into ${COMP_WORDS} of the word containing the
              current cursor position.  This variable is available only
              in shell functions invoked by the programmable completion
              facilities (see Programmable Completion below).
       COMP_KEY
              The key (or final key of a key sequence) used to invoke
              the current completion function.
       COMP_LINE
              The current command line.  This variable is available only
              in shell functions and external commands invoked by the
              programmable completion facilities (see Programmable
              Completion below).
       COMP_POINT
              The index of the current cursor position relative to the
              beginning of the current command.  If the current cursor
              position is at the end of the current command, the value
              of this variable is equal to ${#COMP_LINE}.  This variable
              is available only in shell functions and external commands
              invoked by the programmable completion facilities (see
              Programmable Completion below).
       COMP_TYPE
              Set to an integer value corresponding to the type of
              completion attempted that caused a completion function to
              be called: TAB, for normal completion, ?, for listing
              completions after successive tabs, !, for listing
              alternatives on partial word completion, @, to list
              completions if the word is not unmodified, or %, for menu
              completion.  This variable is available only in shell
              functions and external commands invoked by the
              programmable completion facilities (see Programmable
              Completion below).
       COMP_WORDBREAKS
              The set of characters that the readline library treats as
              word separators when performing word completion.  If
              COMP_WORDBREAKS is unset, it loses its special properties,
              even if it is subsequently reset.
       COMP_WORDS
              An array variable (see Arrays below) consisting of the
              individual words in the current command line.  The line is
              split into words as readline would split it, using
              COMP_WORDBREAKS as described above.  This variable is
              available only in shell functions invoked by the
              programmable completion facilities (see Programmable
              Completion below).
       COPROC An array variable (see Arrays below) created to hold the
              file descriptors for output from and input to an unnamed
              coprocess (see Coprocesses above).
       DIRSTACK
              An array variable (see Arrays below) containing the
              current contents of the directory stack.  Directories
              appear in the stack in the order they are displayed by the
              dirs builtin.  Assigning to members of this array variable
              may be used to modify directories already in the stack,
              but the pushd and popd builtins must be used to add and
              remove directories.  Assignment to this variable will not
              change the current directory.  If DIRSTACK is unset, it
              loses its special properties, even if it is subsequently
              reset.
       EPOCHREALTIME
              Each time this parameter is referenced, it expands to the
              number of seconds since the Unix Epoch (see time(3)) as a
              floating point value with micro-second granularity.
              Assignments to EPOCHREALTIME are ignored.  If
              EPOCHREALTIME is unset, it loses its special properties,
              even if it is subsequently reset.
       EPOCHSECONDS
              Each time this parameter is referenced, it expands to the
              number of seconds since the Unix Epoch (see time(3)).
              Assignments to EPOCHSECONDS are ignored.  If EPOCHSECONDS
              is unset, it loses its special properties, even if it is
              subsequently reset.
       EUID   Expands to the effective user ID of the current user,
              initialized at shell startup.  This variable is readonly.
       FUNCNAME
              An array variable containing the names of all shell
              functions currently in the execution call stack.  The
              element with index 0 is the name of any currently-
              executing shell function.  The bottom-most element (the
              one with the highest index) is "main".  This variable
              exists only when a shell function is executing.
              Assignments to FUNCNAME have no effect.  If FUNCNAME is
              unset, it loses its special properties, even if it is
              subsequently reset.

              This variable can be used with BASH_LINENO and
              BASH_SOURCE.  Each element of FUNCNAME has corresponding
              elements in BASH_LINENO and BASH_SOURCE to describe the
              call stack.  For instance, ${FUNCNAME[$i]} was called from
              the file ${BASH_SOURCE[$i+1]} at line number
              ${BASH_LINENO[$i]}.  The caller builtin displays the
              current call stack using this information.
       GROUPS An array variable containing the list of groups of which
              the current user is a member.  Assignments to GROUPS have
              no effect.  If GROUPS is unset, it loses its special
              properties, even if it is subsequently reset.
       HISTCMD
              The history number, or index in the history list, of the
              current command.  Assignments to HISTCMD are ignored.  If
              HISTCMD is unset, it loses its special properties, even if
              it is subsequently reset.
       HOSTNAME
              Automatically set to the name of the current host.
       HOSTTYPE
              Automatically set to a string that uniquely describes the
              type of machine on which bash is executing.  The default
              is system-dependent.
       LINENO Each time this parameter is referenced, the shell
              substitutes a decimal number representing the current
              sequential line number (starting with 1) within a script
              or function.  When not in a script or function, the value
              substituted is not guaranteed to be meaningful.  If LINENO
              is unset, it loses its special properties, even if it is
              subsequently reset.
       MACHTYPE
              Automatically set to a string that fully describes the
              system type on which bash is executing, in the standard
              GNU cpu-company-system format.  The default is system-
              dependent.
       MAPFILE
              An array variable (see Arrays below) created to hold the
              text read by the mapfile builtin when no variable name is
              supplied.
       OLDPWD The previous working directory as set by the cd command.
       OPTARG The value of the last option argument processed by the
              getopts builtin command (see SHELL BUILTIN COMMANDS
              below).
       OPTIND The index of the next argument to be processed by the
              getopts builtin command (see SHELL BUILTIN COMMANDS
              below).
       OSTYPE Automatically set to a string that describes the operating
              system on which bash is executing.  The default is system-
              dependent.
       PIPESTATUS
              An array variable (see Arrays below) containing a list of
              exit status values from the processes in the most-
              recently-executed foreground pipeline (which may contain
              only a single command).
       PPID   The process ID of the shell's parent.  This variable is
              readonly.
       PWD    The current working directory as set by the cd command.
       RANDOM Each time this parameter is referenced, it expands to a
              random integer between 0 and 32767.  Assigning a value to
              RANDOM initializes (seeds) the sequence of random numbers.
              If RANDOM is unset, it loses its special properties, even
              if it is subsequently reset.
       READLINE_LINE
              The contents of the readline line buffer, for use with
              "bind -x" (see SHELL BUILTIN COMMANDS below).
       READLINE_MARK
              The position of the mark (saved insertion point) in the
              readline line buffer, for use with "bind -x" (see SHELL
              BUILTIN COMMANDS below).  The characters between the
              insertion point and the mark are often called the region.
       READLINE_POINT
              The position of the insertion point in the readline line
              buffer, for use with "bind -x" (see SHELL BUILTIN COMMANDS
              below).
       REPLY  Set to the line of input read by the read builtin command
              when no arguments are supplied.
       SECONDS
              Each time this parameter is referenced, the number of
              seconds since shell invocation is returned.  If a value is
              assigned to SECONDS, the value returned upon subsequent
              references is the number of seconds since the assignment
              plus the value assigned.  The number of seconds at shell
              invocation and the current time is always determined by
              querying the system clock.  If SECONDS is unset, it loses
              its special properties, even if it is subsequently reset.
       SHELLOPTS
              A colon-separated list of enabled shell options.  Each
              word in the list is a valid argument for the -o option to
              the set builtin command (see SHELL BUILTIN COMMANDS
              below).  The options appearing in SHELLOPTS are those
              reported as on by set -o.  If this variable is in the
              environment when bash starts up, each shell option in the
              list will be enabled before reading any startup files.
              This variable is read-only.
       SHLVL  Incremented by one each time an instance of bash is
              started.
       SRANDOM
              This variable expands to a 32-bit pseudo-random number
              each time it is referenced. The random number generator is
              not linear on systems that support /dev/urandom or
              arc4random, so each returned number has no relationship to
              the numbers preceding it.  The random number generator
              cannot be seeded, so assignments to this variable have no
              effect.  If SRANDOM is unset, it loses its special
              properties, even if it is subsequently reset.
       UID    Expands to the user ID of the current user, initialized at
              shell startup.  This variable is readonly.

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

       BASH_COMPAT
              The value is used to set the shell's compatibility level.
              See SHELL COMPATIBILITY MODE below for a description of
              the various compatibility levels and their effects.  The
              value may be a decimal number (e.g., 4.2) or an integer
              (e.g., 42) corresponding to the desired compatibility
              level.  If BASH_COMPAT is unset or set to the empty
              string, the compatibility level is set to the default for
              the current version.  If BASH_COMPAT is set to a value
              that is not one of the valid compatibility levels, the
              shell prints an error message and sets the compatibility
              level to the default for the current version.  The valid
              values correspond to the compatibility levels described
              below under BSHELLCOMPATIBILITYMODE.  For example, 4.2 and
              42 are valid values that correspond to the compat42 shopt
              option and set the compatibility level to 42.  The current
              version is also a valid value.
       BASH_ENV
              If this parameter is set when bash is executing a shell
              script, its value is interpreted as a filename containing
              commands to initialize the shell, as in ~/.bashrc.  The
              value of BASH_ENV is subjected to parameter expansion,
              command substitution, and arithmetic expansion before
              being interpreted as a filename.  PATH is not used to
              search for the resultant filename.
       BASH_XTRACEFD
              If set to an integer corresponding to a valid file
              descriptor, bash will write the trace output generated
              when set -x is enabled to that file descriptor.  The file
              descriptor is closed when BASH_XTRACEFD is unset or
              assigned a new value.  Unsetting BASH_XTRACEFD or
              assigning it the empty string causes the trace output to
              be sent to the standard error.  Note that setting
              BASH_XTRACEFD to 2 (the standard error file descriptor)
              and then unsetting it will result in the standard error
              being closed.
       CDPATH The search path for the cd command.  This is a colon-
              separated list of directories in which the shell looks for
              destination directories specified by the cd command.  A
              sample value is ".:~:/usr".
       CHILD_MAX
              Set the number of exited child status values for the shell
              to remember.  Bash will not allow this value to be
              decreased below a POSIX-mandated minimum, and there is a
              maximum value (currently 8192) that this may not exceed.
              The minimum value is system-dependent.
       COLUMNS
              Used by the select compound command to determine the
              terminal width when printing selection lists.
              Automatically set if the checkwinsize option is enabled or
              in an interactive shell upon receipt of a SIGWINCH.
       COMPREPLY
              An array variable from which bash reads the possible
              completions generated by a shell function invoked by the
              programmable completion facility (see Programmable
              Completion below).  Each array element contains one
              possible completion.
       EMACS  If bash finds this variable in the environment when the
              shell starts with value "t", it assumes that the shell is
              running in an Emacs shell buffer and disables line
              editing.
       ENV    Expanded and executed similarly to BASH_ENV (see
              INVOCATION above) when an interactive shell is invoked in
              posix mode.
       EXECIGNORE
              A colon-separated list of shell patterns (see Pattern
              Matching) defining the list of filenames to be ignored by
              command search using PATH.  Files whose full pathnames
              match one of these patterns are not considered executable
              files for the purposes of completion and command execution
              via PATH lookup.  This does not affect the behavior of the
              [, test, and [[ commands.  Full pathnames in the command
              hash table are not subject to EXECIGNORE.  Use this
              variable to ignore shared library files that have the
              executable bit set, but are not executable files.  The
              pattern matching honors the setting of the extglob shell
              option.
       FCEDIT The default editor for the fc builtin command.
       FIGNORE
              A colon-separated list of suffixes to ignore when
              performing filename completion (see READLINE below).  A
              filename whose suffix matches one of the entries in
              FIGNORE is excluded from the list of matched filenames.  A
              sample value is ".o:~".
       FUNCNEST
              If set to a numeric value greater than 0, defines a
              maximum function nesting level.  Function invocations that
              exceed this nesting level will cause the current command
              to abort.
       GLOBIGNORE
              A colon-separated list of patterns defining the set of
              file names to be ignored by pathname expansion.  If a file
              name matched by a pathname expansion pattern also matches
              one of the patterns in GLOBIGNORE, it is removed from the
              list of matches.
       HISTCONTROL
              A colon-separated list of values controlling how commands
              are saved on the history list.  If the list of values
              includes ignorespace, lines which begin with a space
              character are not saved in the history list.  A value of
              ignoredups causes lines matching the previous history
              entry to not be saved.  A value of ignoreboth is shorthand
              for ignorespace and ignoredups.  A value of erasedups
              causes all previous lines matching the current line to be
              removed from the history list before that line is saved.
              Any value not in the above list is ignored.  If
              HISTCONTROL is unset, or does not include a valid value,
              all lines read by the shell parser are saved on the
              history list, subject to the value of HISTIGNORE.  The
              second and subsequent lines of a multi-line compound
              command are not tested, and are added to the history
              regardless of the value of HISTCONTROL.
       HISTFILE
              The name of the file in which command history is saved
              (see HISTORY below).  The default value is
              ~/.bash_history.  If unset, the command history is not
              saved when a shell exits.
       HISTFILESIZE
              The maximum number of lines contained in the history file.
              When this variable is assigned a value, the history file
              is truncated, if necessary, to contain no more than that
              number of lines by removing the oldest entries.  The
              history file is also truncated to this size after writing
              it when a shell exits.  If the value is 0, the history
              file is truncated to zero size.  Non-numeric values and
              numeric values less than zero inhibit truncation.  The
              shell sets the default value to the value of HISTSIZE
              after reading any startup files.
       HISTIGNORE
              A colon-separated list of patterns used to decide which
              command lines should be saved on the history list.  Each
              pattern is anchored at the beginning of the line and must
              match the complete line (no implicit `*' is appended).
              Each pattern is tested against the line after the checks
              specified by HISTCONTROL are applied.  In addition to the
              normal shell pattern matching characters, `&' matches the
              previous history line.  `&' may be escaped using a
              backslash; the backslash is removed before attempting a
              match.  The second and subsequent lines of a multi-line
              compound command are not tested, and are added to the
              history regardless of the value of HISTIGNORE.  The
              pattern matching honors the setting of the extglob shell
              option.
       HISTSIZE
              The number of commands to remember in the command history
              (see HISTORY below).  If the value is 0, commands are not
              saved in the history list.  Numeric values less than zero
              result in every command being saved on the history list
              (there is no limit).  The shell sets the default value to
              500 after reading any startup files.
       HISTTIMEFORMAT
              If this variable is set and not null, its value is used as
              a format string for strftime(3) to print the time stamp
              associated with each history entry displayed by the
              history builtin.  If this variable is set, time stamps are
              written to the history file so they may be preserved
              across shell sessions.  This uses the history comment
              character to distinguish timestamps from other history
              lines.
       HOME   The home directory of the current user; the default
              argument for the cd builtin command.  The value of this
              variable is also used when performing tilde expansion.
       HOSTFILE
              Contains the name of a file in the same format as
              /etc/hosts that should be read when the shell needs to
              complete a hostname.  The list of possible hostname
              completions may be changed while the shell is running; the
              next time hostname completion is attempted after the value
              is changed, bash adds the contents of the new file to the
              existing list.  If HOSTFILE is set, but has no value, or
              does not name a readable file, bash attempts to read
              /etc/hosts to obtain the list of possible hostname
              completions.  When HOSTFILE is unset, the hostname list is
              cleared.
       IFS    The Internal Field Separator that is used for word
              splitting after expansion and to split lines into words
              with the read builtin command.  The default value is
              ``<space><tab><newline>''.
       IGNOREEOF
              Controls the action of an interactive shell on receipt of
              an EOF character as the sole input.  If set, the value is
              the number of consecutive EOF characters which must be
              typed as the first characters on an input line before bash
              exits.  If the variable exists but does not have a numeric
              value, or has no value, the default value is 10.  If it
              does not exist, EOF signifies the end of input to the
              shell.
       INPUTRC
              The filename for the readline startup file, overriding the
              default of ~/.inputrc (see READLINE below).
       INSIDE_EMACS
              If this variable appears in the environment when the shell
              starts, bash assumes that it is running inside an Emacs
              shell buffer and may disable line editing, depending on
              the value of TERM.
       LANG   Used to determine the locale category for any category not
              specifically selected with a variable starting with LC_.
       LC_ALL This variable overrides the value of LANG and any other
              LC_ variable specifying a locale category.
       LC_COLLATE
              This variable determines the collation order used when
              sorting the results of pathname expansion, and determines
              the behavior of range expressions, equivalence classes,
              and collating sequences within pathname expansion and
              pattern matching.
       LC_CTYPE
              This variable determines the interpretation of characters
              and the behavior of character classes within pathname
              expansion and pattern matching.
       LC_MESSAGES
              This variable determines the locale used to translate
              double-quoted strings preceded by a $.
       LC_NUMERIC
              This variable determines the locale category used for
              number formatting.
       LC_TIME
              This variable determines the locale category used for data
              and time formatting.
       LINES  Used by the select compound command to determine the
              column length for printing selection lists.  Automatically
              set if the checkwinsize option is enabled or in an
              interactive shell upon receipt of a SIGWINCH.
       MAIL   If this parameter is set to a file or directory name and
              the MAILPATH variable is not set, bash informs the user of
              the arrival of mail in the specified file or Maildir-
              format directory.
       MAILCHECK
              Specifies how often (in seconds) bash checks for mail.
              The default is 60 seconds.  When it is time to check for
              mail, the shell does so before displaying the primary
              prompt.  If this variable is unset, or set to a value that
              is not a number greater than or equal to zero, the shell
              disables mail checking.
       MAILPATH
              A colon-separated list of filenames to be checked for
              mail.  The message to be printed when mail arrives in a
              particular file may be specified by separating the
              filename from the message with a `?'.  When used in the
              text of the message, $_ expands to the name of the current
              mailfile.  Example:
              MAILPATH='/var/mail/bfox?"You have mail":~/shell-mail?"$_
              has mail!"'
              Bash can be configured to supply a default value for this
              variable (there is no value by default), but the location
              of the user mail files that it uses is system dependent
              (e.g., /var/mail/$USER).
       OPTERR If set to the value 1, bash displays error messages
              generated by the getopts builtin command (see SHELL
              BUILTIN COMMANDS below).  OPTERR is initialized to 1 each
              time the shell is invoked or a shell script is executed.
       PATH   The search path for commands.  It is a colon-separated
              list of directories in which the shell looks for commands
              (see COMMAND EXECUTION below).  A zero-length (null)
              directory name in the value of PATH indicates the current
              directory.  A null directory name may appear as two
              adjacent colons, or as an initial or trailing colon.  The
              default path is system-dependent, and is set by the
              administrator who installs bash.  A common value is
              ``/usr/local/bin:/usr/local/sbin:/usr/bin:/usr/sbin:/bin:/sbin''.
       POSIXLY_CORRECT
              If this variable is in the environment when bash starts,
              the shell enters posix mode before reading the startup
              files, as if the --posix invocation option had been
              supplied.  If it is set while the shell is running, bash
              enables posix mode, as if the command set -o posix had
              been executed.  When the shell enters posix mode, it sets
              this variable if it was not already set.
       PROMPT_COMMAND
              If this variable is set, and is an array, the value of
              each set element is executed as a command prior to issuing
              each primary prompt.  If this is set but not an array
              variable, its value is used as a command to execute
              instead.
       PROMPT_DIRTRIM
              If set to a number greater than zero, the value is used as
              the number of trailing directory components to retain when
              expanding the \w and \W prompt string escapes (see
              PROMPTING below).  Characters removed are replaced with an
              ellipsis.
       PS0    The value of this parameter is expanded (see PROMPTING
              below) and displayed by interactive shells after reading a
              command and before the command is executed.
       PS1    The value of this parameter is expanded (see PROMPTING
              below) and used as the primary prompt string.  The default
              value is ``\s-\v\$ ''.
       PS2    The value of this parameter is expanded as with PS1 and
              used as the secondary prompt string.  The default is ``>
              ''.
       PS3    The value of this parameter is used as the prompt for the
              select command (see SHELL GRAMMAR above).
       PS4    The value of this parameter is expanded as with PS1 and
              the value is printed before each command bash displays
              during an execution trace.  The first character of the
              expanded value of PS4 is replicated multiple times, as
              necessary, to indicate multiple levels of indirection.
              The default is ``+ ''.
       SHELL  This variable expands to the full pathname to the shell.
              If it is not set when the shell starts, bash assigns to it
              the full pathname of the current user's login shell.
       TIMEFORMAT
              The value of this parameter is used as a format string
              specifying how the timing information for pipelines
              prefixed with the time reserved word should be displayed.
              The % character introduces an escape sequence that is
              expanded to a time value or other information.  The escape
              sequences and their meanings are as follows; the braces
              denote optional portions.
              %%     A literal %.
              %[p][l]R
                     The elapsed time in seconds.
              %[p][l]U
                     The number of CPU seconds spent in user mode.
              %[p][l]S
                     The number of CPU seconds spent in system mode.
              %P     The CPU percentage, computed as (%U + %S) / %R.

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

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

              If this variable is not set, bash acts as if it had the
              value $'\nreal\t%3lR\nuser\t%3lU\nsys\t%3lS'.  If the
              value is null, no timing information is displayed.  A
              trailing newline is added when the format string is
              displayed.
       TMOUT  If set to a value greater than zero, TMOUT is treated as
              the default timeout for the read builtin.  The select
              command terminates if input does not arrive after TMOUT
              seconds when input is coming from a terminal.  In an
              interactive shell, the value is interpreted as the number
              of seconds to wait for a line of input after issuing the
              primary prompt.  Bash terminates after waiting for that
              number of seconds if a complete line of input does not
              arrive.
       TMPDIR If set, bash uses its value as the name of a directory in
              which bash creates temporary files for the shell's use.
       auto_resume
              This variable controls how the shell interacts with the
              user and job control.  If this variable is set, single
              word simple commands without redirections are treated as
              candidates for resumption of an existing stopped job.
              There is no ambiguity allowed; if there is more than one
              job beginning with the string typed, the job most recently
              accessed is selected.  The name of a stopped job, in this
              context, is the command line used to start it.  If set to
              the value exact, the string supplied must match the name
              of a stopped job exactly; if set to substring, the string
              supplied needs to match a substring of the name of a
              stopped job.  The substring value provides functionality
              analogous to the %?  job identifier (see JOB CONTROL
              below).  If set to any other value, the supplied string
              must be a prefix of a stopped job's name; this provides
              functionality analogous to the %string job identifier.
       histchars
              The two or three characters which control history
              expansion and tokenization (see HISTORY EXPANSION below).
              The first character is the history expansion character,
              the character which signals the start of a history
              expansion, normally `!'.  The second character is the
              quick substitution character, which is used as shorthand
              for re-running the previous command entered, substituting
              one string for another in the command.  The default is
              `^'.  The optional third character is the character which
              indicates that the remainder of the line is a comment when
              found as the first character of a word, normally `#'.  The
              history comment character causes history substitution to
              be skipped for the remaining words on the line.  It does
              not necessarily cause the shell parser to treat the rest
              of the line as a comment.

   Arrays
       Bash provides one-dimensional indexed and associative array
       variables.  Any variable may be used as an indexed array; the
       declare builtin will explicitly declare an array.  There is no
       maximum limit on the size of an array, nor any requirement that
       members be indexed or assigned contiguously.  Indexed arrays are
       referenced using integers (including arithmetic expressions) and
       are zero-based; associative arrays are referenced using arbitrary
       strings.  Unless otherwise noted, indexed array indices must be
       non-negative integers.

       An indexed array is created automatically if any variable is
       assigned to using the syntax name[subscript]=value.  The
       subscript is treated as an arithmetic expression that must
       evaluate to a number.  To explicitly declare an indexed array,
       use declare -a name (see SHELL BUILTIN COMMANDS below).  declare
       -a name[subscript] is also accepted; the subscript is ignored.

       Associative arrays are created using declare -A name.

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

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

       When assigning to an associative array, the words in a compound
       assignment may be either assignment statements, for which the
       subscript is required, or a list of words that is interpreted as
       a sequence of alternating keys and values: name=( key1 value1
       key2 value2 ...).  These are treated identically to name=(
       [key1]=value1 [key2]=value2 ...).  The first word in the list
       determines how the remaining words are interpreted; all
       assignments in a list must be of the same type.  When using
       key/value pairs, the keys may not be missing or empty; a final
       missing value is treated like the empty string.

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

       Any element of an array may be referenced using
       ${name[subscript]}.  The braces are required to avoid conflicts
       with pathname expansion.  If subscript is @ or *, the word
       expands to all members of name.  These subscripts differ only
       when the word appears within double quotes.  If the word is
       double-quoted, ${name[*]} expands to a single word with the value
       of each array member separated by the first character of the IFS
       special variable, and ${name[@]} expands each element of name to
       a separate word.  When there are no array members, ${name[@]}
       expands to nothing.  If the double-quoted expansion occurs within
       a word, the expansion of the first parameter is joined with the
       beginning part of the original word, and the expansion of the
       last parameter is joined with the last part of the original word.
       This is analogous to the expansion of the special parameters *
       and @ (see Special Parameters above).  ${#name[subscript]}
       expands to the length of ${name[subscript]}.  If subscript is *
       or @, the expansion is the number of elements in the array.  If
       the subscript used to reference an element of an indexed array
       evaluates to a number less than zero, it is interpreted as
       relative to one greater than the maximum index of the array, so
       negative indices count back from the end of the array, and an
       index of -1 references the last element.

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

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

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

       The unset builtin is used to destroy arrays.  unset
       name[subscript] destroys the array element at index subscript,
       for both indexed and associative arrays.  Negative subscripts to
       indexed arrays are interpreted as described above.  Unsetting the
       last element of an array variable does not unset the variable.
       unset name, where name is an array, or unset name[subscript],
       where subscript is * or @, removes the entire array.

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

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

EXPANSION         top

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

       The order of expansions is: brace expansion; tilde expansion,
       parameter and variable expansion, arithmetic expansion, and
       command substitution (done in a left-to-right fashion); word
       splitting; and pathname expansion.

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

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

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

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

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

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

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

       A correctly-formed brace expansion must contain unquoted opening
       and closing braces, and at least one unquoted comma or a valid
       sequence expression.  Any incorrectly formed brace expansion is
       left unchanged.  A { or , may be quoted with a backslash to
       prevent its being considered part of a brace expression.  To
       avoid conflicts with parameter expansion, the string ${ is not
       considered eligible for brace expansion, and inhibits brace
       expansion until the closing }.

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

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

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

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

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

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

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

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

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

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

       ${parameter}
              The value of parameter is substituted.  The braces are
              required when parameter is a positional parameter with
              more than one digit, or when parameter is followed by a
              character which is not to be interpreted as part of its
              name.  The parameter is a shell parameter as described
              above PARAMETERS) or an array reference (Arrays).

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

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

       When not performing substring expansion, using the forms
       documented below (e.g., :-), bash tests for a parameter that is
       unset or null.  Omitting the colon results in a test only for a
       parameter that is unset.

       ${parameter:-word}
              Use Default Values.  If parameter is unset or null, the
              expansion of word is substituted.  Otherwise, the value of
              parameter is substituted.
       ${parameter:=word}
              Assign Default Values.  If parameter is unset or null, the
              expansion of word is assigned to parameter.  The value of
              parameter is then substituted.  Positional parameters and
              special parameters may not be assigned to in this way.
       ${parameter:?word}
              Display Error if Null or Unset.  If parameter is null or
              unset, the expansion of word (or a message to that effect
              if word is not present) is written to the standard error
              and the shell, if it is not interactive, exits.
              Otherwise, the value of parameter is substituted.
       ${parameter:+word}
              Use Alternate Value.  If parameter is null or unset,
              nothing is substituted, otherwise the expansion of word is
              substituted.
       ${parameter:offset}
       ${parameter:offset:length}
              Substring Expansion.  Expands to up to length characters
              of the value of parameter starting at the character
              specified by offset.  If parameter is @, an indexed array
              subscripted by @ or *, or an associative array name, the
              results differ as described below.  If length is omitted,
              expands to the substring of the value of parameter
              starting at the character specified by offset and
              extending to the end of the value.  length and offset are
              arithmetic expressions (see ARITHMETIC EVALUATION below).

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

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

              If parameter is an indexed array name subscripted by @ or
              *, the result is the length members of the array beginning
              with ${parameter[offset]}.  A negative offset is taken
              relative to one greater than the maximum index of the
              specified array.  It is an expansion error if length
              evaluates to a number less than zero.

              Substring expansion applied to an associative array
              produces undefined results.

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

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

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

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

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

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

       ${parameter/pattern/string}
              Pattern substitution.  The pattern is expanded to produce
              a pattern just as in pathname expansion, Parameter is
              expanded and the longest match of pattern against its
              value is replaced with string.  The match is performed
              using the rules described under Pattern Matching below.
              If pattern begins with /, all matches of pattern are
              replaced with string.  Normally only the first match is
              replaced.  If pattern begins with #, it must match at the
              beginning of the expanded value of parameter.  If pattern
              begins with %, it must match at the end of the expanded
              value of parameter.  If string is null, matches of pattern
              are deleted and the / following pattern may be omitted.
              If the nocasematch shell option is enabled, the match is
              performed without regard to the case of alphabetic
              characters.  If parameter is @ or *, the substitution
              operation is applied to each positional parameter in turn,
              and the expansion is the resultant list.  If parameter is
              an array variable subscripted with @ or *, the
              substitution operation is applied to each member of the
              array in turn, and the expansion is the resultant list.

       ${parameter^pattern}
       ${parameter^^pattern}
       ${parameter,pattern}
       ${parameter,,pattern}
              Case modification.  This expansion modifies the case of
              alphabetic characters in parameter.  The pattern is
              expanded to produce a pattern just as in pathname
              expansion.  Each character in the expanded value of
              parameter is tested against pattern, and, if it matches
              the pattern, its case is converted.  The pattern should
              not attempt to match more than one character.  The ^
              operator converts lowercase letters matching pattern to
              uppercase; the , operator converts matching uppercase
              letters to lowercase.  The ^^ and ,, expansions convert
              each matched character in the expanded value; the ^ and ,
              expansions match and convert only the first character in
              the expanded value.  If pattern is omitted, it is treated
              like a ?, which matches every character.  If parameter is
              @ or *, the case modification operation is applied to each
              positional parameter in turn, and the expansion is the
              resultant list.  If parameter is an array variable
              subscripted with @ or *, the case modification operation
              is applied to each member of the array in turn, and the
              expansion is the resultant list.

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

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

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

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

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

              $(command)
       or
              `command`

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

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

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

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

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

              $((expression))

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

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

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

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

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

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

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

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

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

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

       Pattern Matching

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

       The special pattern characters have the following meanings:

              *      Matches any string, including the null string.
                     When the globstar shell option is enabled, and * is
                     used in a pathname expansion context, two adjacent
                     *s used as a single pattern will match all files
                     and zero or more directories and subdirectories.
                     If followed by a /, two adjacent *s will match only
                     directories and subdirectories.
              ?      Matches any single character.
              [...]  Matches any one of the enclosed characters.  A pair
                     of characters separated by a hyphen denotes a range
                     expression; any character that falls between those
                     two characters, inclusive, using the current
                     locale's collating sequence and character set, is
                     matched.  If the first character following the [ is
                     a !  or a ^ then any character not enclosed is
                     matched.  The sorting order of characters in range
                     expressions is determined by the current locale and
                     the values of the LC_COLLATE or LC_ALL shell
                     variables, if set.  To obtain the traditional
                     interpretation of range expressions, where [a-d] is
                     equivalent to [abcd], set value of the LC_ALL shell
                     variable to C, or enable the globasciiranges shell
                     option.  A - may be matched by including it as the
                     first or last character in the set.  A ] may be
                     matched by including it as the first character in
                     the set.

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

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

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

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

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

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

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

REDIRECTION         top

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

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

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

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

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

              ls > dirlist 2>&1

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

              ls 2>&1 > dirlist

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

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

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

       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

       When using the second form, word may not expand to a number or -.
       If it does, other redirection operators apply (see Duplicating
       File Descriptors below) for compatibility reasons.

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

       The format for appending standard output and standard error is:

              &>>word

       This is semantically equivalent to

              >>word 2>&1

       (see Duplicating File Descriptors below).

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

       The format of here-documents is:

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

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

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

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

              [n]<<<word

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

   Duplicating File Descriptors
       The redirection operator

              [n]<&word

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

       The operator

              [n]>&word

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

   Moving File Descriptors
       The redirection operator

              [n]<&digit-

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

       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         top

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

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

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

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

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

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

FUNCTIONS         top

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

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

       Variables local to the function may be declared with the local
       builtin command.  Ordinarily, variables and their values are
       shared between the function and its caller.  If a variable is
       declared local, the variable's visible scope is restricted to
       that function and its children (including the functions it
       calls).  Local variables "shadow" variables with the same name
       declared at previous scopes.  For instance, a local variable
       declared in a function hides a global variable of the same name:
       references and assignments refer to the local variable, leaving
       the global variable unmodified.  When the function returns, the
       global variable is once again visible.

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

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

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

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

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

       Function names and definitions may be listed with the -f option
       to the declare or typeset builtin commands.  The -F option to
       declare or typeset will list the function names only (and
       optionally the source file and line number, if the extdebug shell
       option is enabled).  Functions may be exported so that subshells
       automatically have them defined with the -f option to the export
       builtin.  A function definition may be deleted using the -f
       option to the unset builtin.

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

ARITHMETIC EVALUATION         top

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

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

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

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

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

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

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

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

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

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

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

       string1 < string2
              True if string1 sorts before string2 lexicographically.

       string1 > string2
              True if string1 sorts after string2 lexicographically.

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

SIMPLE COMMAND EXPANSION         top

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

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

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

       3.     Redirections are performed as described above under
              REDIRECTION.

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

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

       If no command name results, redirections are performed, but do
       not affect the current shell environment.  A redirection error
       causes the 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         top

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

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

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

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

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

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

       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         top

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

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

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

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

       When bash invokes an external command, the variable _ is set to
       the full filename of the command and passed to that command in
       its environment.

EXIT STATUS         top

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

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

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

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

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

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

SIGNALS         top

       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         top

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

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

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

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

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

PROMPTING         top

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

       The command number and the history number are usually different:
       the history number of a command is its position in the history
       list, which may include commands restored from the history file
       (see HISTORY below), while the command number is the position in
       the sequence of commands executed during the current shell
       session.  After the string is decoded, it is expanded via
       parameter expansion, command substitution, arithmetic expansion,
       and quote removal, subject to the value of the promptvars shell
       option (see the description of the shopt command under SHELL
       BUILTIN COMMANDS below).  This can have unwanted side effects if
       escaped portions of the string appear within command substitution
       or contain characters special to word expansion.

READLINE         top

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

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

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

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

   Readline Initialization
       Readline is customized by putting commands in an initialization
       file (the inputrc file).  The name of this file is taken from the
       value of the INPUTRC variable.  If that variable is unset, the
       default is ~/.inputrc.  If that file  does not exist or cannot be
       read, the ultimate default is /etc/inputrc.  When a program which
       uses the readline library starts up, the initialization file is
       read, and the key bindings and variables are set.  There are only
       a few basic constructs allowed in the readline initialization
       file.  Blank lines are ignored.  Lines beginning with a # are
       comments.  Lines beginning 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
       or using the bind builtin command (see SHELL BUILTIN COMMANDS
       below).

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

       bell-style (audible)
              Controls what happens when readline wants to ring the
              terminal bell.  If set to none, readline never rings the
              bell.  If set to visible, readline uses a visible bell if
              one is available.  If set to audible, readline attempts to
              ring the terminal's bell.
       bind-tty-special-chars (On)
              If set to On, readline attempts to bind the control
              characters treated specially by the kernel's terminal
              driver to their readline equivalents.
       blink-matching-paren (Off)
              If set to On, readline attempts to briefly move the cursor
              to an opening parenthesis when a closing parenthesis is
              inserted.
       colored-completion-prefix (Off)
              If set to On, when listing completions, readline displays
              the common prefix of the set of possible completions using
              a different color.  The color definitions are taken from
              the value of the LS_COLORS environment variable.
       colored-stats (Off)
              If set to On, readline displays possible completions using
              different colors to indicate their file type.  The color
              definitions are taken from the value of the LS_COLORS
              environment variable.
       comment-begin (``#'')
              The string that is inserted when the readline
              insert-comment command is executed.  This command is bound
              to M-# in emacs mode and to # in vi command mode.
       completion-display-width (-1)
              The number of screen columns used to display possible
              matches when performing completion.  The value is ignored
              if it is less than 0 or greater than the terminal screen
              width.  A value of 0 will cause matches to be displayed
              one per line.  The default value is -1.
       completion-ignore-case (Off)
              If set to On, readline performs filename matching and
              completion in a case-insensitive fashion.
       completion-map-case (Off)
              If set to On, and completion-ignore-case is enabled,
              readline treats hyphens (-) and underscores (_) as
              equivalent when performing case-insensitive filename
              matching and completion.
       completion-prefix-display-length(0)
              The length in characters of the common prefix of a list of
              possible completions that is displayed without
              modification.  When set to a value greater than zero,
              common prefixes longer than this value are replaced with
              an ellipsis when displaying possible completions.
       completion-query-items (100)
              This determines when the user is queried about viewing the
              number of possible completions generated by the
              possible-completions command.  It may be set to any
              integer value greater than or equal to zero.  If the
              number of possible completions is greater than or equal to
              the value of this variable, readline will ask whether or
              not the user wishes to view them; otherwise they are
              simply listed on the terminal.
       convert-meta (On)
              If set to On, readline will convert characters with the
              eighth bit set to an ASCII key sequence by stripping the
              eighth bit and prefixing an escape character (in effect,
              using escape as the meta prefix).  The default is On, but
              readline will set it to Off if the locale contains eight-
              bit characters.
       disable-completion (Off)
              If set to On, readline will inhibit word completion.
              Completion characters will be inserted into the line as if
              they had been mapped to self-insert.
       echo-control-characters (On)
              When set to On, on operating systems that indicate they
              support it, readline echoes a character corresponding to a
              signal generated from the keyboard.
       editing-mode (emacs)
              Controls whether readline begins with a set of key
              bindings similar to Emacs or vi.  editing-mode can be set
              to either emacs or vi.
       emacs-mode-string (@)
              If the show-mode-in-prompt variable is enabled, this
              string is displayed immediately before the last line of
              the primary prompt when emacs editing mode is active.  The
              value is expanded like a key binding, so the standard set
              of meta- and control prefixes and backslash escape
              sequences is available.  Use the \1 and \2 escapes to
              begin and end sequences of non-printing characters, which
              can be used to embed a terminal control sequence into the
              mode string.
       enable-bracketed-paste (On)
              When set to On, readline will configure the terminal in a
              way that will enable it to insert each paste into the
              editing buffer as a single string of characters, instead
              of treating each character as if it had been read from the
              keyboard.  This can prevent pasted characters from being
              interpreted as editing commands.
       enable-keypad (Off)
              When set to On, readline will try to enable the
              application keypad when it is called.  Some systems need
              this to enable the arrow keys.
       enable-meta-key (On)
              When set to On, readline will try to enable any meta
              modifier key the terminal claims to support when it is
              called.  On many terminals, the meta key is used to send
              eight-bit characters.
       expand-tilde (Off)
              If set to On, tilde expansion is performed when readline
              attempts word completion.
       history-preserve-point (Off)
              If set to On, the history code attempts to place point at
              the same location on each history line retrieved with
              previous-history or next-history.
       history-size (unset)
              Set the maximum number of history entries saved in the
              history list.  If set to zero, any existing history
              entries are deleted and no new entries are saved.  If set
              to a value less than zero, the number of history entries
              is not limited.  By default, the number of history entries
              is set to the value of the HISTSIZE shell variable.  If an
              attempt is made to set history-size to a non-numeric
              value, the maximum number of history entries will be set
              to 500.
       horizontal-scroll-mode (Off)
              When set to On, makes readline use a single line for
              display, scrolling the input horizontally on a single
              screen line when it becomes longer than the screen width
              rather than wrapping to a new line.  This setting is
              automatically enabled for terminals of height 1.
       input-meta (Off)
              If set to On, readline will enable eight-bit input (that
              is, it will not strip the eighth bit from the characters
              it reads), regardless of what the terminal claims it can
              support.  The name meta-flag is a synonym for this
              variable.  The default is Off, but readline will set it to
              On if the locale contains eight-bit characters.
       isearch-terminators (``C-[C-J'')
              The string of characters that should terminate an
              incremental search without subsequently executing the
              character as a command.  If this variable has not been
              given a value, the characters ESC and C-J will terminate
              an incremental search.
       keymap (emacs)
              Set the current readline keymap.  The set of valid keymap
              names is emacs, emacs-standard, emacs-meta, emacs-ctlx,
              vi, vi-command, and vi-insert.  vi is equivalent to
              vi-command; emacs is equivalent to emacs-standard.  The
              default value is emacs; the value of editing-mode also
              affects the default keymap.
       keyseq-timeout (500)
              Specifies the duration readline will wait for a character
              when reading an ambiguous key sequence (one that can form
              a complete key sequence using the input read so far, or
              can take additional input to complete a longer key
              sequence).  If no input is received within the timeout,
              readline will use the shorter but complete key sequence.
              The value is specified in milliseconds, so a value of 1000
              means that readline will wait one second for additional
              input.  If this variable is set to a value less than or
              equal to zero, or to a non-numeric value, readline will
              wait until another key is pressed to decide which key
              sequence to complete.
       mark-directories (On)
              If set to On, completed directory names have a slash
              appended.
       mark-modified-lines (Off)
              If set to On, history lines that have been modified are
              displayed with a preceding asterisk (*).
       mark-symlinked-directories (Off)
              If set to On, completed names which are symbolic links to
              directories have a slash appended (subject to the value of
              mark-directories).
       match-hidden-files (On)
              This variable, when set to On, causes readline to match
              files whose names begin with a `.' (hidden files) when
              performing filename completion.  If set to Off, the
              leading `.' must be supplied by the user in the filename
              to be completed.
       menu-complete-display-prefix (Off)
              If set to On, menu completion displays the common prefix
              of the list of possible completions (which may be empty)
              before cycling through the list.
       output-meta (Off)
              If set to On, readline will display characters with the
              eighth bit set directly rather than as a meta-prefixed
              escape sequence.  The default is Off, but readline will
              set it to On if the locale contains eight-bit characters.
       page-completions (On)
              If set to On, readline uses an internal more-like pager to
              display a screenful of possible completions at a time.
       print-completions-horizontally (Off)
              If set to On, readline will display completions with
              matches sorted horizontally in alphabetical order, rather
              than down the screen.
       revert-all-at-newline (Off)
              If set to On, readline will undo all changes to history
              lines before returning when accept-line is executed.  By
              default, history lines may be modified and retain
              individual undo lists across calls to readline.
       show-all-if-ambiguous (Off)
              This alters the default behavior of the completion
              functions.  If set to On, words which have more than one
              possible completion cause the matches to be listed
              immediately instead of ringing the bell.
       show-all-if-unmodified (Off)
              This alters the default behavior of the completion
              functions in a fashion similar to show-all-if-ambiguous.
              If set to On, words which have more than one possible
              completion without any possible partial completion (the
              possible completions don't share a common prefix) cause
              the matches to be listed immediately instead of ringing
              the bell.
       show-mode-in-prompt (Off)
              If set to On, add a string to the beginning of the prompt
              indicating the editing mode: emacs, vi command, or vi
              insertion.  The mode strings are user-settable (e.g.,
              emacs-mode-string).
       skip-completed-text (Off)
              If set to On, this alters the default completion behavior
              when inserting a single match into the line.  It's only
              active when performing completion in the middle of a word.
              If enabled, readline does not insert characters from the
              completion that match characters after point in the word
              being completed, so portions of the word following the
              cursor are not duplicated.
       vi-cmd-mode-string ((cmd))
              If the show-mode-in-prompt variable is enabled, this
              string is displayed immediately before the last line of
              the primary prompt when vi editing mode is active and in
              command mode.  The value is expanded like a key binding,
              so the standard set of meta- and control prefixes and
              backslash escape sequences is available.  Use the \1 and
              \2 escapes to begin and end sequences of non-printing
              characters, which can be used to embed a terminal control
              sequence into the mode string.
       vi-ins-mode-string ((ins))
              If the show-mode-in-prompt variable is enabled, this
              string is displayed immediately before the last line of
              the primary prompt when vi editing mode is active and in
              insertion mode.  The value is expanded like a key binding,
              so the standard set of meta- and control prefixes and
              backslash escape sequences is available.  Use the \1 and
              \2 escapes to begin and end sequences of non-printing
              characters, which can be used to embed a terminal control
              sequence into the mode string.
       visible-stats (Off)
              If set to On, a character denoting a file's type as
              reported by stat(2) is appended to the filename when
              listing possible completions.

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

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

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

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

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

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

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

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

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

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

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

              $include  /etc/inputrc

   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.
       previous-screen-line
              Attempt to move point to the same physical screen column
              on the previous physical screen line. This will not have
              the desired effect if the current Readline line does not
              take up more than one physical line or if point is not
              greater than the length of the prompt plus the screen
              width.
       next-screen-line
              Attempt to move point to the same physical screen column
              on the next physical screen line. This will not have the
              desired effect if the current Readline line does not take
              up more than one physical line or if the length of the
              current Readline line is not greater than the length of
              the prompt plus the screen width.
       clear-display (M-C-l)
              Clear the screen and, if possible, the terminal's
              scrollback buffer, then redraw the current line, leaving
              the current line at the top of the screen.
       clear-screen (C-l)
              Clear the screen, then redraw the current line, leaving
              the current line at the top of the screen.  With an
              argument, refresh the current line without clearing the
              screen.
       redraw-current-line
              Refresh the current line.

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

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

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

   Numeric Arguments
       digit-argument (M-0, M-1, ..., M--)
              Add this digit to the argument already accumulating, or
              start a new argument.  M-- starts a negative argument.
       universal-argument
              This is another way to specify an argument.  If this
              command is followed by one or more digits, optionally with
              a leading minus sign, those digits define the argument.
              If the command is followed by digits, executing
              universal-argument again ends the numeric argument, but is
              otherwise ignored.  As a special case, if this command is
              immediately followed by a character that is neither a
              digit nor minus sign, the argument count for the next
              command is multiplied by four.  The argument count is
              initially one, so executing this function the first time
              makes the argument count four, a second time makes the
              argument count sixteen, and so on.

   Completing
       complete (TAB)
              Attempt to perform completion on the text before point.
              Bash attempts completion treating the text as a variable
              (if the text 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.
       print-last-kbd-macro ()
              Print the last keyboard macro defined in a format suitable
              for the inputrc file.

   Miscellaneous
       re-read-init-file (C-x C-r)
              Read in the contents of the inputrc file, and incorporate
              any bindings or variable assignments found there.
       abort (C-g)
              Abort the current editing command and ring the terminal's
              bell (subject to the setting of bell-style).
       do-lowercase-version (M-A, M-B, M-x, ...)
              If the metafied character x is uppercase, run the command
              that is bound to the corresponding metafied lowercase
              character.  The behavior is undefined if x is already
              lowercase.
       prefix-meta (ESC)
              Metafy the next character typed.  ESC f is equivalent to
              Meta-f.
       undo (C-_, C-x C-u)
              Incremental undo, separately remembered for each line.
       revert-line (M-r)
              Undo all changes made to this line.  This is like
              executing the undo command enough times to return the line
              to its initial state.
       tilde-expand (M-&)
              Perform tilde expansion on the current word.
       set-mark (C-@, M-<space>)
              Set the mark to the point.  If a numeric argument is
              supplied, the mark is set to that position.
       exchange-point-and-mark (C-x C-x)
              Swap the point with the mark.  The current cursor position
              is set to the saved position, and the old cursor position
              is saved as the mark.
       character-search (C-])
              A character is read and point is moved to the next
              occurrence of that character.  A negative count searches
              for previous occurrences.
       character-search-backward (M-C-])
              A character is read and point is moved to the previous
              occurrence of that character.  A negative count searches
              for subsequent occurrences.
       skip-csi-sequence
              Read enough characters to consume a multi-key sequence
              such as those defined for keys like Home and End.  Such
              sequences begin with a Control Sequence Indicator (CSI),
              usually ESC-[.  If this sequence is bound to "\[", keys
              producing such sequences will have no effect unless
              explicitly bound to a readline command, instead of
              inserting stray characters into the editing buffer.  This
              is unbound by default, but usually bound to ESC-[.
       insert-comment (M-#)
              Without a numeric argument, the value of the readline
              comment-begin variable is inserted at the beginning of the
              current line.  If a numeric argument is supplied, this
              command acts as a toggle: if the characters at the
              beginning of the line do not match the value of
              comment-begin, the value is inserted, otherwise the
              characters in comment-begin are deleted from the beginning
              of the line.  In either case, the line is accepted as if a
              newline had been typed.  The default value of
              comment-begin causes this command to make the current line
              a shell comment.  If a numeric argument causes the comment
              character to be removed, the line will be executed by the
              shell.
       glob-complete-word (M-g)
              The word before point is treated as a pattern for pathname
              expansion, with an asterisk implicitly appended.  This
              pattern is used to generate a list of matching filenames
              for possible completions.
       glob-expand-word (C-x *)
              The word before point is treated as a pattern for pathname
              expansion, and the list of matching filenames is inserted,
              replacing the word.  If a numeric argument is supplied, an
              asterisk is appended before pathname expansion.
       glob-list-expansions (C-x g)
              The list of expansions that would have been generated by
              glob-expand-word is displayed, and the line is redrawn.
              If a numeric argument is supplied, an asterisk is appended
              before pathname expansion.
       dump-functions
              Print all of the functions and their key bindings to the
              readline output stream.  If a numeric argument is
              supplied, the output is formatted in such a way that it
              can be made part of an inputrc file.
       dump-variables
              Print all of the settable readline variables and their
              values to the readline output stream.  If a numeric
              argument is supplied, the output is formatted in such a
              way that it can be made part of an inputrc file.
       dump-macros
              Print all of the readline key sequences bound to macros
              and the strings they output.  If a numeric argument is
              supplied, the output is formatted in such a way that it
              can be made part of an inputrc file.
       display-shell-version (C-x C-v)
              Display version information about the current instance of
              bash.

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

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

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

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

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

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

       After these matches have been generated, any shell function or
       command specified with the -F and -C options is invoked.  When
       the command or function is invoked, the COMP_LINE, COMP_POINT,
       COMP_KEY, and COMP_TYPE variables are assigned values as
       described above under Shell Variables.  If a shell function is
       being invoked, the COMP_WORDS and COMP_CWORD variables are also
       set.  When the function or command is invoked, the first argument
       ($1) is the name of the command whose arguments are being
       completed, the second argument ($2) is the word being completed,
       and the third argument ($3) is the word preceding the word being
       completed on the current command line.  No filtering of the
       generated completions against the word being completed is
       performed; the function or command has complete freedom in
       generating the matches.

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

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

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

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

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

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

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

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

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

       For instance, assuming that there is a library of compspecs, each
       kept in a file corresponding to the name of the command, the
       following default completion function would load completions
       dynamically:

       _completion_loader()
       {
            . "/etc/bash_completion.d/$1.sh" >/dev/null 2>&1 && return
       124
       }
       complete -D -F _completion_loader -o bashdefault -o default

HISTORY         top

       When the -o history option to the set builtin is enabled, the
       shell provides access to the command history, the list of
       commands previously typed.  The value of the HISTSIZE variable is
       used as the number of commands to save in a history list.  The
       text of the last HISTSIZE commands (default 500) is saved.  The
       shell stores each command in the history list prior to parameter
       and variable expansion (see EXPANSION above) but after history
       expansion is performed, subject to the values of the shell
       variables HISTIGNORE and HISTCONTROL.

       On startup, the history is initialized from the file named by the
       variable HISTFILE (default ~/.bash_history).  The file named by
       the value of HISTFILE is truncated, if necessary, to contain no
       more than the number of lines specified by the value of
       HISTFILESIZE.  If HISTFILESIZE is unset, or set to null, a non-
       numeric value, or a numeric value less than zero, the history
       file is not truncated.  When the history file is read, lines
       beginning with the history comment character followed immediately
       by a digit are interpreted as timestamps for the following
       history line.  These timestamps are optionally displayed
       depending on the value of the HISTTIMEFORMAT variable.  When a
       shell with history enabled exits, the last $HISTSIZE lines are
       copied from the history list to $HISTFILE.  If the histappend
       shell option is enabled (see the description of shopt under SHELL
       BUILTIN COMMANDS below), the lines are appended to the history
       file, otherwise the history file is overwritten.  If HISTFILE is
       unset, or if the history file is unwritable, the history is not
       saved.  If the HISTTIMEFORMAT variable is set, time stamps are
       written to the history file, marked with the history comment
       character, so they may be preserved across shell sessions.  This
       uses the history comment character to distinguish timestamps from
       other history lines.  After saving the history, the history file
       is truncated to contain no more than HISTFILESIZE lines.  If
       HISTFILESIZE is unset, or set to null, a non-numeric value, or a
       numeric value less than zero, the history file is not truncated.

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

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

HISTORY EXPANSION         top

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

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

       History expansion is performed immediately after a complete line
       is read, before the shell breaks it into words, and is performed
       on each line individually without taking quoting on previous
       lines into account.  It takes place in two parts.  The first is
       to determine which line from the history list to use during
       substitution.  The second is to select portions of that line for
       inclusion into the current one.  The line selected from the
       history is the event, and the portions of that line that are
       acted upon are words.  Various modifiers are available to
       manipulate the selected words.  The line is broken into words in
       the same fashion as when reading input, so that several
       metacharacter-separated words surrounded by quotes are considered
       one word.  History expansions are introduced by the appearance of
       the history expansion character, which is ! by default.  Only
       backslash (\) and single quotes can quote the history expansion
       character, but the history expansion character is also treated as
       quoted if it immediately precedes the closing double quote in a
       double-quoted string.

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

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

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

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

       !      Start a history substitution, except when followed by a
              blank, newline, carriage return, = or ( (when the extglob
              shell option is enabled using the shopt builtin).
       !n     Refer to command line n.
       !-n    Refer to the current command minus n.
       !!     Refer to the previous command.  This is a synonym for
              `!-1'.
       !string
              Refer to the most recent command preceding the current
              position in the history list starting with string.
       !?string[?]
              Refer to the most recent command preceding the current
              position in the history list containing string.  The
              trailing ? may be omitted if string is followed
              immediately by a newline.  If string is missing, the
              string from the most recent search is used; it is an error
              if there is no previous search string.
       ^string1^string2^
              Quick substitution.  Repeat the previous command,
              replacing string1 with string2.  Equivalent to
              ``!!:s^string1^string2^'' (see Modifiers below).
       !#     The entire command line typed so far.

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

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

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

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

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

SHELL BUILTIN COMMANDS         top

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

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

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

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

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

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

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

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

       caller [expr]
              Returns the context of any active subroutine call (a shell
              function or a script executed with the . or source
              builtins).  Without expr, caller displays the line number
              and source filename of the current subroutine call.  If a
              non-negative integer is supplied as expr, caller displays
              the line number, subroutine name, and source file
              corresponding to that position in the current execution
              call stack.  This extra information may be used, for
              example, to print a stack trace.  The current frame is
              frame 0.  The return value is 0 unless the shell is not
              executing a subroutine call or expr does not correspond to
              a valid position in the call stack.

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

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

       compgen [option] [word]
              Generate possible completion matches for word according to
              the options, which may be any option accepted by the
              complete builtin with the exception of -p and -r, and
              write the matches to the standard output.  When using the
              -F or -C options, the various shell variables set by the
              programmable completion facilities, while available, will
              not have useful values.

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

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

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

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

              Other options, if specified, have the following meanings.
              The arguments to the -G, -W, and -X options (and, if
              necessary, the -P and -S options) should be quoted to
              protect them from expansion before the complete builtin is
              invoked.
              -o comp-option
                      The comp-option controls several aspects of the
                      compspec's behavior beyond the simple generation
                      of completions.  comp-option may be one of:
                      bashdefault
                              Perform the rest of the default bash
                              completions if the compspec generates no
                              matches.
                      default Use readline's default filename completion
                              if the compspec generates no matches.
                      dirnames
                              Perform directory name completion if the
                              compspec generates no matches.
                      filenames
                              Tell readline that the compspec generates
                              filenames, so it can perform any
                              filename-specific processing (like adding
                              a slash to directory names, quoting
                              special characters, or suppressing
                              trailing spaces).  Intended to be used
                              with shell functions.
                      noquote Tell readline not to quote the completed
                              words if they are filenames (quoting
                              filenames is the default).
                      nosort  Tell readline not to sort the list of
                              possible completions alphabetically.
                      nospace Tell readline not to append a space (the
                              default) to words completed at the end of
                              the line.
                      plusdirs
                              After any matches defined by the compspec
                              are generated, directory name completion
                              is attempted and any matches are added to
                              the results of the other actions.
              -A action
                      The action may be one of the following to generate
                      a list of possible completions:
                      alias   Alias names.  May also be specified as -a.
                      arrayvar
                              Array variable names.
                      binding Readline key binding names.
                      builtin Names of shell builtin commands.  May also
                              be specified as -b.
                      command Command names.  May also be specified as
                              -c.
                      directory
                              Directory names.  May also be specified as
                              -d.
                      disabled
                              Names of disabled shell builtins.
                      enabled Names of enabled shell builtins.
                      export  Names of exported shell variables.  May
                              also be specified as -e.
                      file    File names.  May also be specified as -f.
                      function
                              Names of shell functions.
                      group   Group names.  May also be specified as -g.
                      helptopic
                              Help topics as accepted by the help
                              builtin.
                      hostname
                              Hostnames, as taken from the file
                              specified by the HOSTFILE shell variable.
                      job     Job names, if job control is active.  May
                              also be specified as -j.
                      keyword Shell reserved words.  May also be
                              specified as -k.
                      running Names of running jobs, if job control is
                              active.
                      service Service names.  May also be specified as
                              -s.
                      setopt  Valid arguments for the -o option to the
                              set builtin.
                      shopt   Shell option names as accepted by the
                              shopt builtin.
                      signal  Signal names.
                      stopped Names of stopped jobs, if job control is
                              active.
                      user    User names.  May also be specified as -u.
                      variable
                              Names of all shell variables.  May also be
                              specified as -v.
              -C command
                      command is executed in a subshell environment, and
                      its output is used as the possible completions.
              -F function
                      The shell function function is executed in the
                      current shell environment.  When the function is
                      executed, the first argument ($1) is the name of
                      the command whose arguments are being completed,
                      the second argument ($2) is the word being
                      completed, and the third argument ($3) is the word
                      preceding the word being completed on the current
                      command line.  When it finishes, the possible
                      completions are retrieved from the value of the
                      COMPREPLY array variable.
              -G globpat
                      The pathname expansion pattern globpat is expanded
                      to generate the possible completions.
              -P prefix
                      prefix is added at the beginning of each possible
                      completion after all other options have been
                      applied.
              -S suffix
                      suffix is appended to each possible completion
                      after all other options have been applied.
              -W wordlist
                      The wordlist is split using the characters in the
                      IFS special variable as delimiters, and each
                      resultant word is expanded.  Shell quoting is
                      honored within wordlist, in order to provide a
                      mechanism for the words to contain shell
                      metacharacters or characters in the value of IFS.
                      The possible completions are the members of the
                      resultant list which match the word being
                      completed.
              -X filterpat
                      filterpat is a pattern as used for pathname
                      expansion.  It is applied to the list of possible
                      completions generated by the preceding options and
                      arguments, and each completion matching filterpat
                      is removed from the list.  A leading ! in
                      filterpat negates the pattern; in this case, any
                      completion not matching filterpat is removed.

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

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

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

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

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

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

       dirs [-clpv] [+n] [-n]
              Without options, displays the list of currently remembered
              directories.  The default display is on a single line with
              directory names separated by spaces.  Directories are
              added to the list with the pushd command; the popd command
              removes entries from the list.  The current directory is
              always the first directory in the stack.
              -c     Clears the directory stack by deleting all of the
                     entries.
              -l     Produces a listing using full pathnames; the
                     default listing format uses a tilde to denote the
                     home directory.
              -p     Print the directory stack with one entry per line.
              -v     Print the directory stack with one entry per line,
                     prefixing each entry with its index in the stack.
              +n     Displays the nth entry counting from the left of
                     the list shown by dirs when invoked without
                     options, starting with zero.
              -n     Displays the nth entry counting from the right of
                     the list shown by dirs when invoked without
                     options, starting with zero.

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

       disown [-ar] [-h] [jobspec ... | pid ... ]
              Without options, remove each jobspec from the table of
              active jobs.  If jobspec is not present, and neither the
              -a nor the -r option is supplied, the current job is used.
              If the -h option is given, each jobspec is not removed
              from the table, but is marked so that SIGHUP is not sent
              to the job if the shell receives a SIGHUP.  If no jobspec
              is supplied, the -a option means to remove or mark all
              jobs; the -r option without a jobspec argument restricts
              operation to running jobs.  The return value is 0 unless a
              jobspec does not specify a valid job.

       echo [-neE] [arg ...]
              Output the args, separated by spaces, followed by a
              newline.  The return status is 0 unless a write error
              occurs.  If -n is specified, the trailing newline is
              suppressed.  If the -e option is given, interpretation of
              the following backslash-escaped characters is enabled.
              The -E option disables the interpretation of these escape
              characters, even on systems where they are interpreted by
              default.  The xpg_echo shell option may be used to
              dynamically determine whether or not echo expands these
              escape characters by default.  echo does not interpret --
              to mean the end of options.  echo interprets the following
              escape sequences:
              \a     alert (bell)
              \b     backspace
              \c     suppress further output
              \e
              \E     an escape character
              \f     form feed
              \n     new line
              \r     carriage return
              \t     horizontal tab
              \v     vertical tab
              \\     backslash
              \0nnn  the eight-bit character whose value is the octal
                     value nnn (zero to three octal digits)
              \xHH   the eight-bit character whose value is the
                     hexadecimal value HH (one or two hex digits)
              \uHHHH the Unicode (ISO/IEC 10646) character whose value
                     is the hexadecimal value HHHH (one to four hex
                     digits)
              \UHHHHHHHH
                     the Unicode (ISO/IEC 10646) character whose value
                     is the hexadecimal value HHHHHHHH (one to eight hex
                     digits)

       enable [-a] [-dnps] [-f filename] [name ...]
              Enable and disable builtin shell commands.  Disabling a
              builtin allows a disk command which has the same name as a
              shell builtin to be executed without specifying a full
              pathname, even though the shell normally searches for
              builtins before disk commands.  If -n is used, each name
              is disabled; otherwise, names are enabled.  For example,
              to use the test binary found via the PATH instead of the
              shell builtin version, run ``enable -n test''.  The -f
              option means to load the new builtin command name from
              shared object filename, on systems that support dynamic
              loading.  The -d option will delete a builtin previously
              loaded with -f.  If no name arguments are given, or if the
              -p option is supplied, a list of shell builtins is
              printed.  With no other option arguments, the list
              consists of all enabled shell builtins.  If -n is
              supplied, only disabled builtins are printed.  If -a is
              supplied, the list printed includes all builtins, with an
              indication of whether or not each is enabled.  If -s is
              supplied, the output is restricted to the POSIX special
              builtins.  The return value is 0 unless a name is not a
              shell builtin or there is an error loading a new builtin
              from a shared object.

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

       hash [-lr] [-p filename] [-dt] [name]
              Each time hash is invoked, the full pathname of the
              command name is determined by searching the directories in
              $PATH and remembered.  Any previously-remembered pathname
              is discarded.  If the -p option is supplied, no path
              search is performed, and filename is used as the full
              filename of the command.  The -r option causes the shell
              to forget all remembered locations.  The -d option causes
              the shell to forget the remembered location of each name.
              If the -t option is supplied, the full pathname to which
              each name corresponds is printed.  If multiple name
              arguments are supplied with -t, the name is printed before
              the hashed full pathname.  The -l option causes output to
              be displayed in a format that may be reused as input.  If
              no arguments are given, or if only -l is supplied,
              information about remembered commands is printed.  The
              return status is true unless a name is not found or an
              invalid option is supplied.

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

              The return status is 0 unless no command matches pattern.

       history [n]
       history -c
       history -d offset
       history -d start-end
       history -anrw [filename]
       history -p arg [arg ...]
       history -s arg [arg ...]
              With no options, display the command history list with
              line numbers.  Lines listed with a * have been modified.
              An argument of n lists only the last n lines.  If the
              shell variable HISTTIMEFORMAT is set and not null, it is
              used as a format string for strftime(3) to display the
              time stamp associated with each displayed history entry.
              No intervening blank is printed between the formatted time
              stamp and the history line.  If filename is supplied, it
              is used as the name of the history file; if not, the value
              of HISTFILE is used.  Options, if supplied, have the
              following meanings:
              -c     Clear the history list by deleting all the entries.
              -d offset
                     Delete the history entry at position offset.  If
                     offset is negative, it is interpreted as relative
                     to one greater than the last history position, so
                     negative indices count back from the end of the
                     history, and an index of -1 refers to the current
                     history -d command.
              -d start-end
                     Delete the history entries between positions start
                     and end, inclusive.  Positive and negative values
                     for start and end are interpreted as described
                     above.
              -a     Append the ``new'' history lines to the history
                     file.  These are history lines entered since the
                     beginning of the current bash session, but not
                     already appended to the history file.
              -n     Read the history lines not already read from the
                     history file into the current history list.  These
                     are lines appended to the history file since the
                     beginning of the current bash session.
              -r     Read the contents of the history file and append
                     them to the current history list.
              -w     Write the current history list to the history file,
                     overwriting the history file's contents.
              -p     Perform history substitution on the following args
                     and display the result on the standard output.
                     Does not store the results in the history list.
                     Each arg must be quoted to disable normal history
                     expansion.
              -s     Store the args in the history list as a single
                     entry.  The last command in the history list is
                     removed before the args are added.

              If the HISTTIMEFORMAT variable is set, the time stamp
              information associated with each history entry is written
              to the history file, marked with the history comment
              character.  When the history file is read, lines beginning
              with the history comment character followed immediately by
              a digit are interpreted as timestamps for the following
              history entry.  The return value is 0 unless an invalid
              option is encountered, an error occurs while reading or
              writing the history file, an invalid offset is supplied as
              an argument to -d, or the history expansion supplied as an
              argument to -p fails.

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

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

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

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

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

       local [option] [name[=value] ... | - ]
              For each argument, a local variable named name is created,
              and assigned value.  The option can be any of the options
              accepted by declare.  When local is used within a
              function, it causes the variable name to have a visible
              scope restricted to that function and its children.  If
              name is -, the set of shell options is made local to the
              function in which local is invoked: shell options changed
              using the set builtin inside the function are restored to
              their original values when the function returns.  The
              restore is effected as if a series of set commands were
              executed to restore the values that were in place before
              the function.  With no operands, local writes a list of
              local variables to the standard output.  It is an error to
              use local when not within a function.  The return status
              is 0 unless local is used outside a function, an invalid
              name is supplied, or name is a readonly variable.

       logout Exit a login shell.

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

       readonly [-aAf] [-p] [name[=word] ...]
              The given names are marked readonly; the values of these
              names may not be changed by subsequent assignment.  If the
              -f option is supplied, the functions corresponding to the
              names are so marked.  The -a option restricts the
              variables to indexed arrays; the -A option restricts the
              variables to associative arrays.  If both options are
              supplied, -A takes precedence.  If no name arguments are
              given, or if the -p option is supplied, a list of all
              readonly names is printed.  The other options may be used
              to restrict the output to a subset of the set of readonly
              names.  The -p option causes output to be displayed in a
              format that may be reused as input.  If a variable name is
              followed by =word, the value of the variable is set to
              word.  The return status is 0 unless an invalid option is
              encountered, one of the names is not a valid shell
              variable name, or -f is supplied with a name that is not a
              function.

       return [n]
              Causes a function to stop executing and return the value
              specified by n to its caller.  If n is omitted, the return
              status is that of the last command executed in the
              function body.  If return is executed by a trap handler,
              the last command used to determine the status is the last
              command executed before the trap handler.  If return is
              executed during a DEBUG trap, the last command used to
              determine the status is the last command executed by the
              trap handler before return was invoked.  If return is used
              outside a function, but during execution of a script by
              the .  (source) command, it causes the shell to stop
              executing that script and return either n or the exit
              status of the last command executed within the script as
              the exit status of the script.  If n is supplied, the
              return value is its least significant 8 bits.  The return
              status is non-zero if return is supplied a non-numeric
              argument, or is used outside a function and not during
              execution of a script by . or source.  Any command
              associated with the RETURN trap is executed before
              execution resumes after the function or script.

       set [--abefhkmnptuvxBCEHPT] [-o option-name] [arg ...]
       set [+abefhkmnptuvxBCEHPT] [+o option-name] [arg ...]
              Without options, the name and value of each shell variable
              are displayed in a format that can be reused as input for
              setting or resetting the currently-set variables.  Read-
              only variables cannot be reset.  In posix mode, only shell
              variables are listed.  The output is sorted according to
              the current locale.  When options are specified, they set
              or unset shell attributes.  Any arguments remaining after
              option processing are treated as values for the positional
              parameters and are assigned, in order, to $1, $2, ...  $n.
              Options, if specified, have the following meanings:
              -a      Each variable or function that is created or
                      modified is given the export attribute and marked
                      for export to the environment of subsequent
                      commands.
              -b      Report the status of terminated background jobs
                      immediately, rather than before the next primary
                      prompt.  This is effective only when job control
                      is enabled.
              -e      Exit immediately if a pipeline (which may consist
                      of a single simple command), a list, or a compound
                      command (see SHELL GRAMMAR above), exits with a
                      non-zero status.  The shell does not exit if the
                      command that fails is part of the command list
                      immediately following a while or until keyword,
                      part of the test following the if or elif reserved
                      words, part of any command executed in a && or ||
                      list except the command following the final && or
                      ||, any command in a pipeline but the last, or if
                      the command's return value is being inverted with
                      !.  If a compound command other than a subshell
                      returns a non-zero status because a command failed
                      while -e was being ignored, the shell does not
                      exit.  A trap on ERR, if set, is executed before
                      the shell exits.  This option applies to the shell
                      environment and each subshell environment
                      separately (see COMMAND EXECUTION ENVIRONMENT
                      above), and may cause subshells to exit before
                      executing all the commands in the subshell.

                      If a compound command or shell function executes
                      in a context where -e is being ignored, none of
                      the commands executed within the compound command
                      or function body will be affected by the -e
                      setting, even if -e is set and a command returns a
                      failure status.  If a compound command or shell
                      function sets -e while executing in a context
                      where -e is ignored, that setting will not have
                      any effect until the compound command or the
                      command containing the function call completes.
              -f      Disable pathname expansion.
              -h      Remember the location of commands as they are
                      looked up for execution.  This is enabled by
                      default.
              -k      All arguments in the form of assignment statements
                      are placed in the environment for a command, not
                      just those that precede the command name.
              -m      Monitor mode.  Job control is enabled.  This
                      option is on by default for interactive shells on
                      systems that support it (see JOB CONTROL above).
                      All processes run in a separate process group.
                      When a background job completes, the shell prints
                      a line containing its exit status.
              -n      Read commands but do not execute them.  This may
                      be used to check a shell script for syntax errors.
                      This is ignored by interactive shells.
              -o option-name
                      The option-name can be one of the following:
                      allexport
                              Same as -a.
                      braceexpand
                              Same as -B.
                      emacs   Use an emacs-style command line editing
                              interface.  This is enabled by default
                              when the shell is interactive, unless the
                              shell is started with the --noediting
                              option.  This also affects the editing
                              interface used for read -e.
                      errexit Same as -e.
                      errtrace
                              Same as -E.
                      functrace
                              Same as -T.
                      hashall Same as -h.
                      histexpand
                              Same as -H.
                      history Enable command history, as described above
                              under HISTORY.  This option is on by
                              default in interactive shells.
                      ignoreeof
                              The effect is as if the shell command
                              ``IGNOREEOF=10'' had been executed (see
                              Shell Variables above).
                      keyword Same as -k.
                      monitor Same as -m.
                      noclobber
                              Same as -C.
                      noexec  Same as -n.
                      noglob  Same as -f.
                      nolog   Currently ignored.
                      notify  Same as -b.
                      nounset Same as -u.
                      onecmd  Same as -t.
                      physical
                              Same as -P.
                      pipefail
                              If set, the return value of a pipeline is
                              the value of the last (rightmost) command
                              to exit with a non-zero status, or zero if
                              all commands in the pipeline exit
                              successfully.  This option is disabled by
                              default.
                      posix   Change the behavior of bash where the
                              default operation differs from the POSIX
                              standard to match the standard (posix
                              mode).  See SEE ALSO below for a reference
                              to a document that details how posix mode
                              affects bash's behavior.
                      privileged
                              Same as -p.
                      verbose Same as -v.
                      vi      Use a vi-style command line editing
                              interface.  This also affects the editing
                              interface used for read -e.
                      xtrace  Same as -x.
                      If -o is supplied with no option-name, the values
                      of the current options are printed.  If +o is
                      supplied with no option-name, a series of set
                      commands to recreate the current option settings
                      is displayed on the standard output.
              -p      Turn on privileged mode.  In this mode, the $ENV
                      and $BASH_ENV files are not processed, shell
                      functions are not inherited from the environment,
                      and the SHELLOPTS, BASHOPTS, CDPATH, and
                      GLOBIGNORE variables, if they appear in the
                      environment, are ignored.  If the shell is started
                      with the effective user (group) id not equal to
                      the real user (group) id, and the -p option is not
                      supplied, these actions are taken and the
                      effective user id is set to the real user id.  If
                      the -p option is supplied at startup, the
                      effective user id is not reset.  Turning this
                      option off causes the effective user and group ids
                      to be set to the real user and group ids.
              -t      Exit after reading and executing one command.
              -u      Treat unset variables and parameters other than
                      the special parameters "@" and "*" as an error
                      when performing parameter expansion.  If expansion
                      is attempted on an unset variable or parameter,
                      the shell prints an error message, and, if not
                      interactive, exits with a non-zero status.
              -v      Print shell input lines as they are read.
              -x      After expanding each simple command, for command,
                      case command, select command, or arithmetic for
                      command, display the expanded value of PS4,
                      followed by the command and its expanded arguments
                      or associated word list.
              -B      The shell performs brace expansion (see Brace
                      Expansion above).  This is on by default.
              -C      If set, bash does not overwrite an existing file
                      with the >, >&, and <> redirection operators.
                      This may be overridden when creating output files
                      by using the redirection operator >| instead of >.
              -E      If set, any trap on ERR is inherited by shell
                      functions, command substitutions, and commands
                      executed in a subshell environment.  The ERR trap
                      is normally not inherited in such cases.
              -H      Enable !  style history substitution.  This option
                      is on by default when the shell is interactive.
              -P      If set, the shell does not resolve symbolic links
                      when executing commands such as cd that change the
                      current working directory.  It uses the physical
                      directory structure instead.  By default, bash
                      follows the logical chain of directories when
                      performing commands which change the current
                      directory.
              -T      If set, any traps on DEBUG and RETURN are
                      inherited by shell functions, command
                      substitutions, and commands executed in a subshell
                      environment.  The DEBUG and RETURN traps are
                      normally not inherited in such cases.
              --      If no arguments follow this option, then the
                      positional parameters are unset.  Otherwise, the
                      positional parameters are set to the args, even if
                      some of them begin with a -.
              -       Signal the end of options, cause all remaining
                      args to be assigned to the positional parameters.
                      The -x and -v options are turned off.  If there
                      are no args, the positional parameters remain
                      unchanged.

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

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

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

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

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

              The list of shopt options is:

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

              complete_fullquote
                      If set, bash quotes all shell metacharacters in
                      filenames and directory names when performing
                      completion.  If not set, bash removes
                      metacharacters such as the dollar sign from the
                      set of characters that will be quoted in completed
                      filenames when these metacharacters appear in
                      shell variable references in words to be
                      completed.  This means that dollar signs in
                      variable names that expand to directories will not
                      be quoted; however, any dollar signs appearing in
                      filenames will not be quoted, either.  This is
                      active only when bash is using backslashes to
                      quote completed filenames.  This variable is set
                      by default, which is the default bash behavior in
                      versions through 4.2.

              direxpand
                      If set, bash replaces directory names with the
                      results of word expansion when performing filename
                      completion.  This changes the contents of the
                      readline editing buffer.  If not set, bash
                      attempts to preserve what the user typed.

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

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

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

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

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

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

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

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

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

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

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

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

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

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

              force_fignore
                      If set, the suffixes specified by the FIGNORE
                      shell variable cause words to be ignored when
                      performing word completion even if the ignored
                      words are the only possible completions.  See
                      SHELL VARIABLES above for a description of
                      FIGNORE.  This option is enabled by default.

              globasciiranges
                      If set, range expressions used in pattern matching
                      bracket expressions (see Pattern Matching above)
                      behave as if in the traditional C locale when
                      performing comparisons.  That is, the current
                      locale's collating sequence is not taken into
                      account, so b will not collate between A and B,
                      and upper-case and lower-case ASCII characters
                      will collate together.

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

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

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

              histreedit
                      If set, and readline is being used, a user is
                      given the opportunity to re-edit a failed history
                      substitution.

              histverify
                      If set, and readline is being used, the results of
                      history substitution are not immediately passed to
                      the shell parser.  Instead, the resulting line is
                      loaded into the readline editing buffer, allowing
                      further modification.

              hostcomplete
                      If set, and readline is being used, bash will
                      attempt to perform hostname completion when a word
                      containing a @ is being completed (see Completing
                      under READLINE above).  This is enabled by
                      default.

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

              promptvars
                      If set, prompt strings undergo parameter
                      expansion, command substitution, arithmetic
                      expansion, and quote removal after being expanded
                      as described in PROMPTING above.  This option is
                      enabled by default.

              restricted_shell
                      The shell sets this option if it is started in
                      restricted mode (see RESTRICTED SHELL below).  The
                      value may not be changed.  This is not reset when
                      the startup files are executed, allowing the
                      startup files to discover whether or not a shell
                      is restricted.

              shift_verbose
                      If set, the shift builtin prints an error message
                      when the shift count exceeds the number of
                      positional parameters.

              sourcepath
                      If set, the source (.) builtin uses the value of
                      PATH to find the directory containing the file
                      supplied as an argument.  This option is enabled
                      by default.

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

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

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

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

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

              0 arguments
                     The expression is false.
              1 argument
                     The expression is true if and only if the argument
                     is not null.
              2 arguments
                     If the first argument is !, the expression is true
                     if and only if the second argument is null.  If the
                     first argument is one of the unary conditional
                     operators listed above under 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 pipeline (which may consist of a single simple command),
              a list, or a compound command returns a non-zero exit
              status, subject to the following conditions.  The ERR trap
              is not executed if the failed command is part of the
              command list immediately following a while or until
              keyword, part of the test in an if statement, part of a
              command executed in a && or || list except the command
              following the final && or ||, any command in a pipeline
              but the last, or if the command's return value is being
              inverted using !.  These are the same conditions obeyed by
              the errexit (-e) option.

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

       type [-aftpP] name [name ...]
              With no options, indicate how each name would be
              interpreted if used as a command name.  If the -t option
              is used, type prints a string which is one of alias,
              keyword, function, builtin, or file if name is an alias,
              shell reserved word, function, builtin, or disk file,
              respectively.  If the name is not found, then nothing is
              printed, and an exit status of false is returned.  If the
              -p option is used, type either returns the name of the
              disk file that would be executed if name were specified as
              a command name, or nothing if ``type -t name'' would not
              return file.  The -P option forces a PATH search for each
              name, even if ``type -t name'' would not return file.  If
              a command is hashed, -p and -P print the hashed value,
              which is not necessarily the file that appears first in
              PATH.  If the -a option is used, type prints all of the
              places that contain an executable named name.  This
              includes aliases and functions, if and only if the -p
              option is not also used.  The table of hashed commands is
              not consulted when using -a.  The -f option suppresses
              shell function lookup, as with the command builtin.  type
              returns true if all of the arguments are found, false if
              any are not found.

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

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

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

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

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

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

SHELL COMPATIBILITY MODE         top

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

RESTRICTED SHELL         top

       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, HISTFILE,
              ENV, or BASH_ENV

       •      specifying command names containing /

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

       •      specifying a filename containing a slash as an argument to
              the history 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         top

       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 --
              http://pubs.opengroup.org/onlinepubs/9699919799/
       http://tiswww.case.edu/~chet/bash/POSIX -- a description of posix
       mode
       sh(1), ksh(1), csh(1)
       emacs(1), vi(1)
       readline(3)

FILES         top

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

AUTHORS         top

       Brian Fox, Free Software Foundation
       bfox@gnu.org

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

BUG REPORTS         top

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

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

       ALL bug reports should include:

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

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

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

BUGS         top

       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.

COLOPHON         top

       This page is part of the bash (Bourne again shell) project.
       Information about the project can be found at 
       ⟨http://www.gnu.org/software/bash/⟩.  If you have a bug report for
       this manual page, see ⟨http://www.gnu.org/software/bash/⟩.  This
       page was obtained from the project's upstream Git repository
       ⟨git://git.savannah.gnu.org/bash.git⟩ on 2021-08-27.  (At that
       time, the date of the most recent commit that was found in the
       repository was 2021-05-04.)  If you discover any rendering
       problems in this HTML version of the page, or you believe there
       is a better or more up-to-date source for the page, or you have
       corrections or improvements to the information in this COLOPHON
       (which is not part of the original manual page), send a mail to
       man-pages@man7.org

GNU Bash 5.1                 2020 October 29                     BASH(1)

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