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489.

Enable and disable shell builtins.

Enables and disables builtin shell commands. Disabling allows you to
execute a disk command which has the same name as a shell builtin
without using a full pathname.

Options:
-a[tab]print a list of builtins showing whether or not each is enabled
-n[tab]disable each NAME or display a list of disabled builtins
-p[tab]print the list of builtins in a reusable format
-s[tab]print only the names of Posix `special' builtins

Options controlling dynamic loading:
-f[tab]Load builtin NAME from shared object FILENAME
-d[tab]Remove a builtin loaded with -f

Without options, each NAME is enabled.

To use the `test' found in $PATH instead of the shell builtin
version, type `enable -n test'.

Exit Status:
Returns success unless NAME is not a shell builtin or an error occurs.

491.

Parse option arguments.

Getopts is used by shell procedures to parse positional parameters
as options.

OPTSTRING contains the option letters to be recognized; if a letter
is followed by a colon, the option is expected to have an argument,
which should be separated from it by white space.

Each time it is invoked, getopts will place 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 shell
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 shell variable OPTARG.

getopts reports errors in one of two ways. If the first character
of OPTSTRING is a colon, getopts uses silent error reporting. In
this mode, no error messages are printed. If an invalid option is
seen, getopts places the option character found into OPTARG. If a
required argument is not found, getopts places a ':' into NAME and
sets OPTARG to the option character found. If getopts is not in
silent mode, and an invalid option is seen, getopts places '?' into
NAME and unsets OPTARG. If a required argument is not found, a '?'
is placed in NAME, OPTARG is unset, and a diagnostic message is
printed.

If the shell variable OPTERR has the value 0, getopts disables the
printing of error messages, even if the first character of
OPTSTRING is not a colon. OPTERR has the value 1 by default.

Getopts normally parses the positional parameters ($0 - $9), but if
more arguments are given, they are parsed instead.

Exit Status:
Returns success if an option is found; fails if the end of options is
encountered or an error occurs.

492.

Replace the shell with the given command.

Execute COMMAND, replacing this shell with the specified program.
ARGUMENTS become the arguments to COMMAND. If COMMAND is not specified,
any redirections take effect in the current shell.

Options:
-a name[tab]pass NAME as the zeroth argument to COMMAND
-c[tab][tab]execute COMMAND with an empty environment
-l[tab][tab]place a dash in the zeroth argument to COMMAND

If the command cannot be executed, a non-interactive shell exits, unless
the shell option `execfail' is set.

Exit Status:
Returns success unless COMMAND is not found or a redirection error occurs.

498.

Remember or display program locations.

Determine and remember the full pathname of each command NAME. If
no arguments are given, information about remembered commands is displayed.

Options:
-d[tab][tab]forget the remembered location of each NAME
-l[tab][tab]display in a format that may be reused as input
-p pathname[tab]use PATHNAME is the full pathname of NAME
-r[tab][tab]forget all remembered locations
-t[tab][tab]print the remembered location of each NAME, preceding
[tab][tab]each location with the corresponding NAME if multiple
[tab][tab]NAMEs are given
Arguments:
NAME[tab][tab]Each NAME is searched for in $PATH and added to the list
[tab][tab]of remembered commands.

Exit Status:
Returns success unless NAME is not found or an invalid option is given.

500.

Display or manipulate the history list.

Display the history list with line numbers, prefixing each modified
entry with a `*'. An argument of N lists only the last N entries.

Options:
-c[tab]clear the history list by deleting all of the entries
-d offset[tab]delete the history entry at offset OFFSET.

-a[tab]append history lines from this session to the history file
-n[tab]read all history lines not already read from the history file
-r[tab]read the history file and append the contents to the history
[tab]list
-w[tab]write the current history to the history file
[tab]and append them to the history list

-p[tab]perform history expansion on each ARG and display the result
[tab]without storing it in the history list
-s[tab]append the ARGs to the history list as a single entry

If FILENAME is given, it is used as the history file. Otherwise,
if $HISTFILE has a value, that is used, else ~/.bash_history.

If the $HISTTIMEFORMAT 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 displayed history entry. No time stamps are printed otherwise.

Exit Status:
Returns success unless an invalid option is given or an error occurs.

501.

Display status of jobs.

Lists the active jobs. JOBSPEC restricts output to that job.
Without options, the status of all active jobs is displayed.

Options:
-l[tab]lists process IDs in addition to the normal information
-n[tab]list only processes that have changed status since the last
[tab]notification
-p[tab]lists process IDs only
-r[tab]restrict output to running jobs
-s[tab]restrict output to stopped jobs

If -x is supplied, COMMAND is run after all job specifications that
appear in ARGS have been replaced with the process ID of that job's
process group leader.

Exit Status:
Returns success unless an invalid option is given or an error occurs.
If -x is used, returns the exit status of COMMAND.

503.

Send a signal to a job.

Send the processes identified by PID or JOBSPEC the signal named by
SIGSPEC or SIGNUM. If neither SIGSPEC nor SIGNUM is present, then
SIGTERM is assumed.

Options:
-s sig[tab]SIG is a signal name
-n sig[tab]SIG is a signal number
-l[tab]list the signal names; if arguments follow `-l' they are
[tab]assumed to be signal numbers for which names should be listed

Kill is a shell builtin for two reasons: it allows job IDs to be used
instead of process IDs, and allows processes to be killed if the limit
on processes that you can create is reached.

Exit Status:
Returns success unless an invalid option is given or an error occurs.

504.

Evaluate arithmetic expressions.

Evaluate each ARG as an arithmetic expression. Evaluation is done in
fixed-width integers with no check for overflow, though division by 0
is trapped and flagged as an error. The following list of operators is
grouped into levels of equal-precedence operators. The levels are listed
in order of decreasing precedence.

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

Shell variables are allowed as operands. The name of the variable
is replaced by its value (coerced to a fixed-width integer) within
an expression. The variable need not have its integer attribute
turned on to be used in an expression.

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

Exit Status:
If the last ARG evaluates to 0, let returns 1; let returns 0 otherwise.

505.

Read a line from the standard input and split it into fields.

Reads a single line from the standard input, or from file descriptor FD
if the -u option is supplied. The line is split into fields as with word
splitting, and the first word is assigned to the first NAME, the second
word to the second NAME, and so on, with any leftover words assigned to
the last NAME. Only the characters found in $IFS are recognized as word
delimiters.

If no NAMEs are supplied, the line read is stored in the REPLY variable.

Options:
-a array[tab]assign the words read to sequential indices of the array
[tab][tab]variable ARRAY, starting at zero
-d delim[tab]continue until the first character of DELIM is read, rather
[tab][tab]than newline
-e[tab][tab]use Readline to obtain the line in an interactive shell
-i text[tab]Use TEXT as the initial text for Readline
-n nchars[tab]return after reading NCHARS characters rather than waiting
[tab][tab]for a newline, but honor a delimiter if fewer than NCHARS
[tab][tab]characters are read before the delimiter
-N nchars[tab]return only after reading exactly NCHARS characters, unless
[tab][tab]EOF is encountered or read times out, ignoring any delimiter
-p prompt[tab]output the string PROMPT without a trailing newline before
[tab][tab]attempting to read
-r[tab][tab]do not allow backslashes to escape any characters
-s[tab][tab]do not echo input coming from a terminal
-t timeout[tab]time out and return failure if a complete line of input is
[tab][tab]not read withint TIMEOUT seconds. The value of the TMOUT
[tab][tab]variable is the default timeout. TIMEOUT may be a
[tab][tab]fractional number. If TIMEOUT is 0, read returns success only
[tab][tab]if input is available on the specified file descriptor. The
[tab][tab]exit status is greater than 128 if the timeout is exceeded
-u fd[tab][tab]read from file descriptor FD instead of the standard input

Exit Status:
The return code is zero, unless end-of-file is encountered, read times out,
or an invalid file descriptor is supplied as the argument to -u.

507.

Set or unset values of shell options and positional parameters.

Change the value of shell attributes and positional parameters, or
display the names and values of shell variables.

Options:
-a Mark variables which are modified or created for export.
-b Notify of job termination immediately.
-e Exit immediately if a command exits with a non-zero status.
-f Disable file name generation (globbing).
-h Remember the location of commands as they are looked up.
-k All assignment arguments are placed in the environment for a
command, not just those that precede the command name.
-m Job control is enabled.
-n Read commands but do not execute them.
-o option-name
Set the variable corresponding to option-name:
allexport same as -a
braceexpand same as -B
emacs use an emacs-style line editing interface
errexit same as -e
errtrace same as -E
functrace same as -T
hashall same as -h
histexpand same as -H
history enable command history
ignoreeof the shell will not exit upon reading EOF
interactive-comments
allow comments to appear in interactive commands
keyword same as -k
monitor same as -m
noclobber same as -C
noexec same as -n
noglob same as -f
nolog currently accepted but ignored
notify same as -b
nounset same as -u
onecmd same as -t
physical same as -P
pipefail the return value of a pipeline is the status of
the last command to exit with a non-zero status,
or zero if no command exited with a non-zero status
posix change the behavior of bash where the default
operation differs from the Posix standard to
match the standard
privileged same as -p
verbose same as -v
vi use a vi-style line editing interface
xtrace same as -x
-p Turned on whenever the real and effective user ids do not match.
Disables processing of the $ENV file and importing of shell
functions. Turning this option off causes the effective uid and
gid to be set to the real uid and gid.
-t Exit after reading and executing one command.
-u Treat unset variables as an error when substituting.
-v Print shell input lines as they are read.
-x Print commands and their arguments as they are executed.
-B the shell will perform brace expansion
-C If set, disallow existing regular files to be overwritten
by redirection of output.
-E If set, the ERR trap is inherited by shell functions.
-H Enable ! style history substitution. This flag is on
by default when the shell is interactive.
-P If set, do not follow symbolic links when executing commands
such as cd which change the current directory.
-T If set, the DEBUG trap is inherited by shell functions.
-- Assign any remaining arguments to the positional parameters.
If there are no remaining arguments, the positional parameters
are unset.
- Assign any remaining arguments to the positional parameters.
The -x and -v options are turned off.

Using + rather than - causes these flags to be turned off. The
flags can also be used upon invocation of the shell. The current
set of flags may be found in $-. The remaining n ARGs are positional
parameters and are assigned, in order, to $1, $2, .. $n. If no
ARGs are given, all shell variables are printed.

Exit Status:
Returns success unless an invalid option is given.