bash

BASH(1)                      General Commands Manual                     BASH(1)



NAME
       bash - GNU Bourne-Again SHell

SYNOPSIS
       bash [options] [command_string | file]

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

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

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

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

       -c        If the -c option is present, then commands are read from the
                 first non-option argument command_string.  If there are
                 arguments after the command_string, the first argument is
                 assigned to $0 and any remaining arguments are assigned to the
                 positional parameters.  The assignment to $0 sets the name of
                 the shell, which is used in warning and error messages.
       -i        If the -i option is present, the shell is interactive.
       -l        Make bash act as if it had been invoked as a login shell (see
                 INVOCATION below).
       -r        If the -r option is present, the shell becomes restricted (see
                 RESTRICTED SHELL below).
       -s        If the -s option is present, or if no arguments remain after
                 option processing, then commands are read from the standard
                 input.  This option allows the positional parameters to be set
                 when invoking an interactive shell or when reading input
                 through a pipe.
       -D        A list of all double-quoted strings preceded by $ is printed on
                 the standard output.  These are the strings that are subject to
                 language translation when the current locale is not C or POSIX.
                 This implies the -n option; no commands will be executed.
       [-+]O [shopt_option]
                 shopt_option is one of the shell options accepted by the shopt
                 builtin (see SHELL BUILTIN COMMANDS below).  If shopt_option is
                 present, -O sets the value of that option; +O unsets it.  If
                 shopt_option is not supplied, the names 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
       If arguments remain after option processing, and neither the -c nor the
       -s option has been supplied, the first argument is assumed to be the name
       of a file containing shell commands.  If bash is invoked in this fashion,
       $0 is set to the name of the file, and the positional parameters are set
       to the remaining arguments.  Bash reads and executes commands from this
       file, then exits.  Bash's exit status is the exit status of the last
       command executed in the script.  If no commands are executed, the exit
       status is 0.  An attempt is first made to open the file in the current
       directory, and, if no file is found, then the shell searches the
       directories in PATH for the script.

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

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

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

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

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

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

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

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

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

   Pipelines
       A pipeline is a sequence of one or more commands separated by one of 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
       In a non-interactive shell, or an interactive shell in which the
       interactive_comments option to the shopt builtin is enabled (see SHELL
       BUILTIN COMMANDS below), a word beginning with # causes that word and all
       remaining characters on that line to be ignored.  An interactive shell
       without the interactive_comments option enabled does not allow comments.
       The interactive_comments option is on by default in interactive shells.

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

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

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

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

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

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

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

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

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

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

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

PARAMETERS
       A parameter is an entity that stores values.  It can be a name, a number,
       or one of the special characters listed below under Special 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
       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
       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
       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
       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
       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
       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
       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
       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
       The shell has an execution environment, which consists of the following:

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

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

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

       •      current traps set by trap

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

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

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

       •      options enabled by shopt

       •      shell aliases defined with alias

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

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


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

       •      the current working directory

       •      the file creation mode mask

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

              [1] 25647

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

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

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

       There are a number of ways to refer to a job in the shell.  The character
       % introduces a job specification (jobspec).  Job number n may be referred
       to as %n.  A job may also be referred to using a prefix of the name used
       to start it, or using a substring that appears in its command line.  For
       example, %ce refers to a stopped 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
       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
       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
       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
       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
       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
       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
       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
       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
       /bin/bash
              The bash executable
       /etc/profile
              The systemwide initialization file, executed for login shells
       ~/.bash_profile
              The personal initialization file, executed for login shells
       ~/.bashrc
              The individual per-interactive-shell startup file
       ~/.bash_logout
              The individual login shell cleanup file, executed when a login
              shell exits
       ~/.inputrc
              Individual readline initialization file

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

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

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

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

       ALL bug reports should include:

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

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

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

BUGS
       It's too big and too slow.

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

       Aliases are confusing in some uses.

       Shell builtin commands and functions are not stoppable/restartable.

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

       Array variables may not (yet) be exported.

       There may be only one active coprocess at a time.



GNU Bash 5.1                     2020 October 29                         BASH(1)