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BASH(1)                    General Commands Manual                   BASH(1)

NAME         top

       bash - GNU Bourne-Again SHell

SYNOPSIS         top

       bash [options] [command_string | file]

COPYRIGHT         top

       Bash is Copyright (C) 1989-2013 by the Free Software Foundation, Inc.

DESCRIPTION         top

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

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

OPTIONS         top

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

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

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

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

       --login
              Equivalent to -l.

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

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

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

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

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

       --verbose
              Equivalent to  -v.

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

ARGUMENTS         top

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

INVOCATION         top

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

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

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

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

       When a login shell exits, bash reads and executes commands from the
       file ~/.bash_logout, if it exists.

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

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

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

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

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

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

DEFINITIONS         top

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

RESERVED WORDS         top

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

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

SHELL GRAMMAR         top

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

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

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

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

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

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

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

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

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

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

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

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

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

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

              command1 && command2

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

       An OR list has the form

              command1 || command2

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

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

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

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

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

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

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

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

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

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

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

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

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

       The format for a coprocess is:

              coproc [NAME] command [redirections]

       This creates a coprocess named NAME.  If NAME is not supplied, the
       default name is COPROC.  NAME must not be supplied if command is a
       simple command (see above); otherwise, it is interpreted as the first
       word of the simple command.  When the 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.  The file descriptors are not available in subshells.
       The process ID of the shell spawned to execute the coprocess is
       available as the value of the variable NAME_PID.  The wait builtin
       command may be used to wait for the coprocess to terminate.

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

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

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

COMMENTS         top

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

QUOTING         top

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

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

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

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

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

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

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

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

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

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

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

PARAMETERS         top

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

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

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

              name=[value]

       If value is not given, the variable is assigned the null string.  All
       values undergo tilde expansion, parameter and variable expansion,
       command substitution, arithmetic expansion, and quote removal (see
       EXPANSION below).  If the variable has its integer attribute set,
       then value is evaluated as an arithmetic expression even if the
       $((...)) expansion is not used (see Arithmetic Expansion below).
       Word splitting is not performed, with the exception of "$@" as
       explained below under Special Parameters.  Pathname expansion is not
       performed.  Assignment statements may also appear as arguments to the
       alias, declare, typeset, export, readonly, and local builtin
       commands.  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.  When += is
       applied to a variable for which the integer attribute has been set,
       value is evaluated as an arithmetic expression and added to the
       variable's current value, which is also evaluated.  When += is
       applied to an array variable using compound assignment (see Arrays
       below), the variable's value is not unset (as it is when using =),
       and new values are appended to the array beginning at one greater
       than the array's maximum index (for indexed arrays) or added as
       additional key-value pairs in an associative array.  When applied to
       a string-valued variable, value is expanded and appended to the
       variable's value.

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

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

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

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

   Shell Variables
       The following variables are set by the shell:

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

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

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

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

              The optional p is a digit specifying the precision, the number
              of 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 is of the form
       [subscript]=string.  Indexed array assignments do not require
       anything but string.  When assigning to indexed arrays, if the
       optional brackets and subscript are supplied, that index is assigned
       to; otherwise the index of the element assigned is the last index
       assigned to by the statement plus one.  Indexing starts at zero.

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

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

       Any element of an array may be referenced using ${name[subscript]}.
       The braces are required to avoid conflicts with pathname expansion.
       If subscript is @ or *, the word expands to all members of name.
       These subscripts differ only when the word appears within double
       quotes.  If the word is double-quoted, ${name[*]} expands to a single
       word with the value of each array member separated by the first
       character of the IFS special variable, and ${name[@]} expands each
       element of name to a separate word.  When there are no array members,
       ${name[@]} expands to nothing.  If the double-quoted expansion occurs
       within a word, the expansion of the first parameter is joined with
       the beginning part of the original word, and the expansion of the
       last parameter is joined with the last part of the original word.
       This is analogous to the expansion of the special parameters * and @
       (see Special Parameters above).  ${#name[subscript]} expands to the
       length of ${name[subscript]}.  If subscript is * or @, the expansion
       is the number of elements in the array.  Referencing an array
       variable without a subscript is equivalent to referencing the array
       with a subscript of 0.  If the subscript used to reference an element
       of an indexed array evaluates to a number less than zero, it is
       interpreted as relative to one greater than the maximum index of the
       array, so negative indices count back from the end of the array, and
       an index of -1 references the last element.

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

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

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

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

EXPANSION         top

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

       ${parameter:-word}
              Use Default Values.  If parameter is unset or null, the
              expansion of word is substituted.  Otherwise, the value of
              parameter is substituted.
       ${parameter:=word}
              Assign Default Values.  If parameter is unset or null, the
              expansion of word is assigned to parameter.  The value of
              parameter is then substituted.  Positional parameters and
              special parameters may not be assigned to in this way.
       ${parameter:?word}
              Display Error if Null or Unset.  If parameter is null or
              unset, the expansion of word (or a message to that effect if
              word is not present) is written to the standard error and the
              shell, if it is 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.  If the
              pattern matches the beginning of the value of parameter, then
              the result of the expansion is the expanded value of parameter
              with the shortest matching pattern (the ``#'' case) or the
              longest matching pattern (the ``##'' case) deleted.  If
              parameter is @ or *, the pattern removal operation is applied
              to each positional parameter in turn, and the expansion is the
              resultant list.  If parameter is an array variable subscripted
              with @ or *, the pattern removal operation is applied to each
              member of the array in turn, and the expansion is the
              resultant list.

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

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

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

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

              $(command)
       or
              `command`

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

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

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

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

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

              $((expression))

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

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

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

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

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

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

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

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

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

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

       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

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

REDIRECTION         top

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

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

       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:

              /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 for a command.

       The format of here-documents is:

              <<[-]word
                      here-document
              delimiter

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

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

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

              <<<word

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

   Duplicating File Descriptors
       The redirection operator

              [n]<&word

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

       The operator

              [n]>&word

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

   Moving File Descriptors
       The redirection operator

              [n]<&digit-

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

       Similarly, the redirection operator

              [n]>&digit-

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

   Opening File Descriptors for Reading and Writing
       The redirection operator

              [n]<>word

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

ALIASES         top

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

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

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

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

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

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

FUNCTIONS         top

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

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

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

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

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

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

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

ARITHMETIC EVALUATION         top

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

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

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

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

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

CONDITIONAL EXPRESSIONS         top

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

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

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

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

SIMPLE COMMAND EXPANSION         top

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

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

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

       3.     Redirections are performed as described above under
              REDIRECTION.

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

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

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

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

COMMAND EXECUTION         top

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

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

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

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

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

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

COMMAND EXECUTION ENVIRONMENT         top

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

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

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

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

       ·      current traps set by trap

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

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

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

       ·      options enabled by shopt

       ·      shell aliases defined with alias

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

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

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

       ·      the current working directory

       ·      the file creation mode mask

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

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

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

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

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

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

ENVIRONMENT         top

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

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

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

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

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

EXIT STATUS         top

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

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

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

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

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

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

SIGNALS         top

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

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

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

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

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

JOB CONTROL         top

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

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

              [1] 25647

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

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

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

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

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

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

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

PROMPTING         top

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

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

READLINE         top

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

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

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

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

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

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

       For example, placing

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

              set variable-name value

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

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

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

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

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

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

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

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

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

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

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

              $include  /etc/inputrc

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

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

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

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

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

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

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

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

   Commands for Changing Text
       end-of-file (usually C-d)
              The character indicating end-of-file as set, for example, by
              ``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 (M-d)
              Kill from point to the end of the current word, or if between
              words, to the end of the next word.  Word boundaries are the
              same as those used by shell-forward-word.
       shell-backward-kill-word (M-Rubout)
              Kill the word behind point.  Word boundaries are the same as
              those used by shell-backward-word.
       unix-word-rubout (C-w)
              Kill the word behind point, using white space as a word
              boundary.  The killed text is saved on the kill-ring.
       unix-filename-rubout
              Kill the word behind point, using white space and the slash
              character as the word boundaries.  The killed text is saved on
              the kill-ring.
       delete-horizontal-space (M-\)
              Delete all spaces and tabs around point.
       kill-region
              Kill the text in the current region.
       copy-region-as-kill
              Copy the text in the region to the kill buffer.
       copy-backward-word
              Copy the word before point to the kill buffer.  The word
              boundaries are the same as backward-word.
       copy-forward-word
              Copy the word following point to the kill buffer.  The word
              boundaries are the same as forward-word.
       yank (C-y)
              Yank the top of the kill ring into the buffer at point.
       yank-pop (M-y)
              Rotate the kill ring, and yank the new top.  Only works
              following yank or yank-pop.

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

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

   Keyboard Macros
       start-kbd-macro (C-x ()
              Begin saving the characters typed into the current keyboard
              macro.
       end-kbd-macro (C-x ))
              Stop saving the characters typed into the current keyboard
              macro and store the definition.
       call-last-kbd-macro (C-x e)
              Re-execute the last keyboard macro defined, by making the
              characters in the macro appear as if typed at the keyboard.
       print-last-kbd-macro ()
              Print the last keyboard macro defined in a format suitable for
              the inputrc file.

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

       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.

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

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

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

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

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

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

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

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

HISTORY         top

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

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

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

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

HISTORY EXPANSION         top

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

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

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

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

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

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

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

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

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

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

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

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

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

SHELL BUILTIN COMMANDS         top

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

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

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

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

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

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

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

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

              Other options, if specified, have the following meanings.  The
              arguments to the -G, -W, and -X options (and, if necessary,
              the -P and -S options) should be quoted to protect them from
              expansion before the complete builtin is invoked.
              -o comp-option
                      The comp-option controls several aspects of the
                      compspec's behavior beyond the simple generation of
                      completions.  comp-option may be one of:
                      bashdefault
                              Perform the rest of the default bash
                              completions if the compspec generates no
                              matches.
                      default Use readline's default filename completion if
                              the compspec generates no matches.
                      dirnames
                              Perform directory name completion if the
                              compspec generates no matches.
                      filenames
                              Tell readline that the compspec generates
                              filenames, so it can perform any
                              filename-specific processing (like adding a
                              slash to directory names, quoting special
                              characters, or suppressing trailing spaces).
                              Intended to be used with shell functions.
                      noquote Tell readline not to quote the completed words
                              if they are filenames (quoting filenames is
                              the default).
                      nospace Tell readline not to append a space (the
                              default) to words completed at the end of the
                              line.
                      plusdirs
                              After any matches defined by the compspec are
                              generated, directory name completion is
                              attempted and any matches are added to the
                              results of the other actions.
              -A action
                      The action may be one of the following to generate a
                      list of possible completions:
                      alias   Alias names.  May also be specified as -a.
                      arrayvar
                              Array variable names.
                      binding Readline key binding names.
                      builtin Names of shell builtin commands.  May also be
                              specified as -b.
                      command Command names.  May also be specified as -c.
                      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.  The possible completions are the
                      members of the resultant list which match the word
                      being completed.
              -X filterpat
                      filterpat is a pattern as used for pathname expansion.
                      It is applied to the list of possible completions
                      generated by the preceding options and arguments, and
                      each completion matching filterpat is removed from the
                      list.  A leading ! in filterpat negates the pattern;
                      in this case, any completion not matching filterpat is
                      removed.

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

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

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

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

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

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

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

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

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

       echo [-neE] [arg ...]
              Output the args, separated by spaces, followed by a newline.
              The return status is 0 unless a write error occurs.  If -n is
              specified, the trailing newline is suppressed.  If the -e
              option 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.  If command is not specified, any redirections take
              effect in the current shell, and the return status is 0.  If
              there is a redirection error, the return status is 1.

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

              The return status is 0 unless no command matches pattern.

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

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

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

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

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

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

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

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

       logout Exit a login shell.

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

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

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

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

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

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

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

              The format is a character string which contains three types of
              objects: plain characters, which are simply copied to standard
              output, character escape sequences, which are converted and
              copied to the standard output, and format specifications, each
              of which causes printing of the next successive argument.  In
              addition to the standard printf(1) format specifications,
              printf interprets the following extensions:
              %b     causes printf to expand backslash escape sequences in
                     the corresponding argument (except that \c terminates
                     output, backslashes in \', \", and \? are not removed,
                     and octal escapes beginning with \0 may contain up to
                     four digits).
              %q     causes printf to output the corresponding argument in a
                     format that can be reused as shell input.
              %(datefmt)T
                     causes printf to output the date-time string resulting
                     from using datefmt as a format string for strftime(3).
                     The corresponding argument is an integer representing
                     the number of seconds since the epoch.  Two special
                     argument values may be used: -1 represents the current
                     time, and -2 represents the time the shell was invoked.
                     If no argument is specified, conversion behaves as if
                     -1 had been given.  This is an exception to the usual
                     printf behavior.

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

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

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

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

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

       read [-ers] [-a aname] [-d delim] [-i text] [-n nchars] [-N nchars]
       [-p prompt] [-t timeout] [-u fd] [name ...]
              One line is read from the standard input, or from the file
              descriptor fd supplied as an argument to the -u option, and
              the first word is assigned to the first name, the second word
              to the second name, and so on, with leftover words and their
              intervening separators assigned to the last name.  If there
              are fewer words read from the input stream than names, the
              remaining names are assigned empty values.  The characters in
              IFS are used to split the line into words 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.
              -e     If the standard input is coming from a terminal,
                     readline (see READLINE above) is used to obtain the
                     line.  Readline uses the current (or default, if line
                     editing was not previously active) editing settings.
              -i text
                     If readline is being used to read the line, text is
                     placed into the editing buffer before editing begins.
              -n nchars
                     read returns after reading nchars characters rather
                     than waiting for a complete line of input, but honor a
                     delimiter if fewer than nchars characters are read
                     before the delimiter.
              -N nchars
                     read returns after reading exactly nchars characters
                     rather than waiting for a complete line of input,
                     unless EOF is encountered or read times out.  Delimiter
                     characters encountered in the input are not treated
                     specially and do not cause read to return until nchars
                     characters are read.
              -p prompt
                     Display prompt on standard error, without a trailing
                     newline, before attempting to read any input.  The
                     prompt is displayed only if input is coming from a
                     terminal.
              -r     Backslash does not act as an escape character.  The
                     backslash is considered to be part of the line.  In
                     particular, a backslash-newline pair may not be used as
                     a line continuation.
              -s     Silent mode.  If input is coming from a terminal,
                     characters are not echoed.
              -t timeout
                     Cause read to time out and return failure if a complete
                     line of input (or a specified number of characters) is
                     not read within timeout seconds.  timeout may be a
                     decimal number with a fractional portion following the
                     decimal point.  This option is only effective if read
                     is reading input from a terminal, pipe, or other
                     special file; it has no effect when reading from
                     regular files.  If read times out, read saves any
                     partial input read into the specified variable name.
                     If timeout is 0, read returns immediately, without
                     trying to read any data.  The exit status is 0 if input
                     is available on the specified file descriptor, non-zero
                     otherwise.  The exit status is greater than 128 if the
                     timeout is exceeded.
              -u fd  Read input from file descriptor fd.

              If no names are supplied, the line read is assigned to the
              variable REPLY.  The return code is zero, unless end-of-file
              is encountered, read times out (in which case the return code
              is greater than 128), a variable assignment error (such as
              assigning to a readonly variable) occurs, or an invalid file
              descriptor is supplied as the argument to -u.

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

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

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

                      If a compound command or shell function executes in a
                      context where -e is being ignored, none of the
                      commands executed within the compound command or
                      function body will be affected by the -e setting, even
                      if -e is set and a command returns a failure status.
                      If a compound command or shell function sets -e while
                      executing in a context where -e is ignored, that
                      setting will not have any effect until the compound
                      command or the command containing the function call
                      completes.
              -f      Disable pathname expansion.
              -h      Remember the location of commands as they are looked
                      up for execution.  This is enabled by default.
              -k      All arguments in the form of assignment statements are
                      placed in the environment for a command, not just
                      those that precede the command name.
              -m      Monitor mode.  Job control is enabled.  This option is
                      on by default for interactive shells on systems that
                      support it (see JOB CONTROL above).  All processes run
                      in a separate process group.  When a background job
                      completes, the shell prints a line containing its exit
                      status.
              -n      Read commands but do not execute them.  This may be
                      used to check a shell script for syntax errors.  This
                      is ignored by interactive shells.
              -o option-name
                      The option-name can be one of the following:
                      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.  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:

              autocd  If set, a command name that is the name of a directory
                      is executed as if it were the argument to the cd
                      command.  This option is only used by interactive
                      shells.
              cdable_vars
                      If set, an argument to the cd builtin command that is
                      not a directory is assumed to be the name of a
                      variable whose value is the directory to change to.
              cdspell If set, minor errors in the spelling of a directory
                      component in a cd command will be corrected.  The
                      errors checked for are transposed characters, a
                      missing character, and one character too many.  If a
                      correction is found, the corrected filename is
                      printed, and the command proceeds.  This option is
                      only used by interactive shells.
              checkhash
                      If set, bash checks that a command found in the hash
                      table exists before trying to execute it.  If a hashed
                      command no longer exists, a normal path search is
                      performed.
              checkjobs
                      If set, bash lists the status of any stopped and
                      running jobs before exiting an interactive shell.  If
                      any jobs are running, this causes the exit to be
                      deferred until a second exit is attempted without an
                      intervening command (see JOB CONTROL above).  The
                      shell always postpones exiting if any jobs are
                      stopped.
              checkwinsize
                      If set, bash checks the window size after each command
                      and, if necessary, updates the values of LINES and
                      COLUMNS.
              cmdhist If set, bash attempts to save all lines of a multiple-
                      line command in the same history entry.  This allows
                      easy re-editing of multi-line commands.
              compat31
                      If set, bash changes its behavior to that of version
                      3.1 with respect to quoted arguments to the [[
                      conditional command's =~ operator and locale-specific
                      string comparison when using the [[ conditional
                      command's < and > operators.  Bash versions prior to
                      bash-4.1 use ASCII collation and strcmp(3); bash-4.1
                      and later use the current locale's collation sequence
                      and strcoll(3).
              compat32
                      If set, bash changes its behavior to that of version
                      3.2 with respect to locale-specific string comparison
                      when using the [[ conditional command's < and >
                      operators (see previous item).
              compat40
                      If set, bash changes its behavior to that of version
                      4.0 with respect to locale-specific string comparison
                      when using the [[ conditional command's < and >
                      operators (see description of compat31) and the effect
                      of interrupting a command list.  Bash versions 4.0 and
                      later interrupt the list as if the shell received the
                      interrupt; previous versions continue with the next
                      command in the list.
              compat41
                      If set, bash, when in posix mode, treats a single
                      quote in a double-quoted parameter expansion as a
                      special character.  The single quotes must match (an
                      even number) and the characters between the single
                      quotes are considered quoted.  This is the behavior of
                      posix mode through version 4.1.  The default bash
                      behavior remains as in previous versions.
              compat42
                      If set, bash does not process the replacement string
                      in the pattern substitution word expansion using quote
                      removal.
              complete_fullquote
                      If set, bash quotes all shell metacharacters in
                      filenames and directory names when performing
                      completion.  If not set, bash removes metacharacters
                      such as the dollar sign from the set of characters
                      that will be quoted in completed filenames when these
                      metacharacters appear in shell variable references in
                      words to be completed.  This means that dollar signs
                      in variable names that expand to directories will not
                      be quoted; however, any dollar signs appearing in
                      filenames will not be quoted, either.  This is active
                      only when bash is using backslashes to quote completed
                      filenames.  This variable is set by default, which is
                      the default bash behavior in versions through 4.2.
              direxpand
                      If set, bash replaces directory names with the results
                      of word expansion when performing filename completion.
                      This changes the contents of the readline editing
                      buffer.  If not set, bash attempts to preserve what
                      the user typed.
              dirspell
                      If set, bash attempts spelling correction on directory
                      names during word completion if the directory name
                      initially supplied does not exist.
              dotglob If set, bash includes filenames beginning with a `.'
                      in the results of pathname expansion.
              execfail
                      If set, a non-interactive shell will not exit if it
                      cannot execute the file specified as an argument to
                      the exec builtin command.  An interactive shell does
                      not exit if exec fails.
              expand_aliases
                      If set, aliases are expanded as described above under
                      ALIASES.  This option is enabled by default for
                      interactive shells.
              extdebug
                      If set, behavior intended for use by debuggers is
                      enabled:
                      1.     The -F option to the declare builtin displays
                             the source file name and line number
                             corresponding to each function name supplied as
                             an argument.
                      2.     If the command run by the DEBUG trap returns a
                             non-zero value, the next command is skipped and
                             not executed.
                      3.     If the command run by the DEBUG trap returns a
                             value of 2, and the shell is executing in a
                             subroutine (a shell function or a shell script
                             executed by the . or source builtins), a call
                             to return is simulated.
                      4.     BASH_ARGC and BASH_ARGV are updated as
                             described in their descriptions above.
                      5.     Function tracing is enabled:  command
                             substitution, shell functions, and subshells
                             invoked with ( command ) inherit the DEBUG and
                             RETURN traps.
                      6.     Error tracing is enabled:  command
                             substitution, shell functions, and subshells
                             invoked with ( command ) inherit the ERR trap.
              extglob If set, the extended pattern matching features
                      described above under Pathname Expansion are enabled.
              extquote
                      If set, $'string' and $"string" quoting is performed
                      within ${parameter} expansions enclosed in double
                      quotes.  This option is enabled by default.
              failglob
                      If set, patterns which fail to match filenames during
                      pathname expansion result in an expansion error.
              force_fignore
                      If set, the suffixes specified by the FIGNORE shell
                      variable cause words to be ignored when performing
                      word completion even if the ignored words are the only
                      possible completions.  See SHELL VARIABLES above for a
                      description of FIGNORE.  This option is enabled by
                      default.
              globasciiranges
                      If set, range expressions used in pattern matching
                      bracket expressions (see Pattern Matching above)
                      behave as if in the traditional C locale when
                      performing comparisons.  That is, the current locale's
                      collating sequence is not taken into account, so b
                      will not collate between A and B, and upper-case and
                      lower-case ASCII characters will collate together.
              globstar
                      If set, the pattern ** used in a pathname expansion
                      context will match all files and zero or more
                      directories and subdirectories.  If the pattern is
                      followed by a /, only directories and subdirectories
                      match.
              gnu_errfmt
                      If set, shell error messages are written in the
                      standard GNU error message format.
              histappend
                      If set, the history list is appended to the file named
                      by the value of the HISTFILE variable when the shell
                      exits, rather than overwriting the file.
              histreedit
                      If set, and readline is being used, a user is given
                      the opportunity to re-edit a failed history
                      substitution.
              histverify
                      If set, and readline is being used, the results of
                      history substitution are not immediately passed to the
                      shell parser.  Instead, the resulting line is loaded
                      into the readline editing buffer, allowing further
                      modification.
              hostcomplete
                      If set, and readline is being used, bash will attempt
                      to perform hostname completion when a word containing
                      a @ is being completed (see Completing under READLINE
                      above).  This is enabled by default.
              huponexit
                      If set, bash will send SIGHUP to all jobs when an
                      interactive login shell exits.
              interactive_comments
                      If set, allow a word beginning with # to cause that
                      word and all remaining characters on that line to be
                      ignored in an interactive shell (see COMMENTS above).
                      This option is enabled by default.
              lastpipe
                      If set, and job control is not active, the shell runs
                      the last command of a pipeline not executed in the
                      background in the current shell environment.
              lithist If set, and the cmdhist option is enabled, multi-line
                      commands are saved to the history with embedded
                      newlines rather than using semicolon separators where
                      possible.
              login_shell
                      The shell sets this option if it is started as a login
                      shell (see INVOCATION above).  The value may not be
                      changed.
              mailwarn
                      If set, and a file that bash is checking for mail has
                      been accessed since the last time it was checked, the
                      message ``The mail in mailfile has been read'' is
                      displayed.
              no_empty_cmd_completion
                      If set, and readline is being used, bash will not
                      attempt to search the PATH for possible completions
                      when completion is attempted on an empty line.
              nocaseglob
                      If set, bash matches filenames in a case-insensitive
                      fashion when performing pathname expansion (see
                      Pathname Expansion above).
              nocasematch
                      If set, bash matches patterns in a case-insensitive
                      fashion when performing matching while executing case
                      or [[ conditional commands.
              nullglob
                      If set, bash allows patterns which match no files (see
                      Pathname Expansion above) to expand to a null string,
                      rather than themselves.
              progcomp
                      If set, the programmable completion facilities (see
                      Programmable Completion above) are enabled.  This
                      option is enabled by default.
              promptvars
                      If set, prompt strings undergo parameter expansion,
                      command substitution, arithmetic expansion, and quote
                      removal after being expanded as described in PROMPTING
                      above.  This option is enabled by default.
              restricted_shell
                      The shell sets this option if it is started in
                      restricted mode (see RESTRICTED SHELL below).  The
                      value may not be changed.  This is not reset when the
                      startup files are executed, allowing the startup files
                      to discover whether or not a shell is restricted.
              shift_verbose
                      If set, the shift builtin prints an error message when
                      the shift count exceeds the number of positional
                      parameters.
              sourcepath
                      If set, the source (.) builtin uses the value of PATH
                      to find the directory containing the file supplied as
                      an argument.  This option is enabled by default.
              xpg_echo
                      If set, the echo builtin expands backslash-escape
                      sequences by default.

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

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

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

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

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

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

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

RESTRICTED SHELL         top

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

       ·      changing directories with cd

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

       ·      specifying command names containing /

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

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

       ·      importing function definitions from the shell environment at
              startup

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

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

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

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

       ·      using the enable builtin command to enable disabled shell
              builtins

       ·      specifying the -p option to the command builtin command

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

       These restrictions are enforced after any startup files are read.

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

SEE ALSO         top

       Bash Reference Manual, Brian Fox and Chet Ramey
       The Gnu Readline Library, Brian Fox and Chet Ramey
       The Gnu History Library, Brian Fox and Chet Ramey
       Portable Operating System Interface (POSIX) Part 2: Shell and
       Utilities, IEEE --
              http://pubs.opengroup.org/onlinepubs/9699919799/
       http://tiswww.case.edu/~chet/bash/POSIX -- a description of posix
       mode
       sh(1), ksh(1), csh(1)
       emacs(1), vi(1)
       readline(3)

FILES         top

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

AUTHORS         top

       Brian Fox, Free Software Foundation
       bfox@gnu.org

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

BUG REPORTS         top

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

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

       ALL bug reports should include:

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

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

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

BUGS         top

       It's too big and too slow.

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

       Aliases are confusing in some uses.

       Shell builtin commands and functions are not stoppable/restartable.

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

       Array variables may not (yet) be exported.

       There may be only one active coprocess at a time.

COLOPHON         top

       This page is part of the bash (Bourne again shell) project.
       Information about the project can be found at 
       ⟨http://www.gnu.org/software/bash/⟩.  If you have a bug report for
       this manual page, see ⟨http://www.gnu.org/software/bash/⟩.  This page
       was obtained from the project's upstream Git repository 
       ⟨git://git.savannah.gnu.org/bash.git⟩ on 2016-08-07.  If you discover
       any rendering problems in this HTML version of the page, or you
       believe there is a better or more up-to-date source for the page, or
       you have corrections or improvements to the information in this
       COLOPHON (which is not part of the original manual page), send a mail
       to man-pages@man7.org

GNU Bash 4.3                   2014 February 2                       BASH(1)