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539.

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]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
[tab][tab]NCHARS 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
[tab][tab]delimiter
-p prompt[tab]output the string PROMPT without a trailing newline before
[tab][tab]attempting to read
-r[tab]do not allow backslashes to escape any characters
-s[tab]do not echo input coming from a terminal
-t timeout[tab]time out and return failure if a complete line of
[tab][tab]input is not read within TIMEOUT seconds. The value of the
[tab][tab]TMOUT variable is the default timeout. TIMEOUT may be a
[tab][tab]fractional number. If TIMEOUT is 0, read returns
[tab][tab]immediately, without trying to read any data, returning
[tab][tab]success only if input is available on the specified
[tab][tab]file descriptor. The exit status is greater than 128
[tab][tab]if the timeout is exceeded
-u fd[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
(in which case it's greater than 128), a variable assignment error occurs,
or an invalid file descriptor is supplied as the argument to -u.

540.

Return from a shell function.

Causes a function or sourced script to exit with the return value
specified by N. If N is omitted, the return status is that of the
last command executed within the function or script.

Exit Status:
Returns N, or failure if the shell is not executing a function or script.

541.

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 resolve symbolic links when executing commands
such as cd which change the current directory.
-T If set, the DEBUG and RETURN traps are 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.

542.

Unset values and attributes of shell variables and functions.

For each NAME, remove the corresponding variable or function.

Options:
-f[tab]treat each NAME as a shell function
-v[tab]treat each NAME as a shell variable
-n[tab]treat each NAME as a name reference and unset the variable itself
[tab][tab]rather than the variable it references

Without options, unset first tries to unset a variable, and if that fails,
tries to unset a function.

Some variables cannot be unset; also see `readonly'.

Exit Status:
Returns success unless an invalid option is given or a NAME is read-only.

543.

Set export attribute for shell variables.

Marks each NAME for automatic export to the environment of subsequently
executed commands. If VALUE is supplied, assign VALUE before exporting.

Options:
-f[tab]refer to shell functions
-n[tab]remove the export property from each NAME
-p[tab]display a list of all exported variables and functions

An argument of `--' disables further option processing.

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

544.

Mark shell variables as unchangeable.

Mark each NAME as read-only; the values of these NAMEs may not be
changed by subsequent assignment. If VALUE is supplied, assign VALUE
before marking as read-only.

Options:
-a[tab]refer to indexed array variables
-A[tab]refer to associative array variables
-f[tab]refer to shell functions
-p[tab]display a list of all readonly variables or functions,
[tab][tab]depending on whether or not the -f option is given

An argument of `--' disables further option processing.

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

545.

Shift positional parameters.

Rename the positional parameters $N+1,$N+2 ... to $1,$2 ... If N is
not given, it is assumed to be 1.

Exit Status:
Returns success unless N is negative or greater than $#.

546.

Execute commands from a file in the current shell.

Read and execute commands from FILENAME in the current shell. The
entries in $PATH are used to find the directory containing FILENAME.
If any ARGUMENTS are supplied, they become the positional parameters
when FILENAME is executed.

Exit Status:
Returns the status of the last command executed in FILENAME; fails if
FILENAME cannot be read.

547.

Suspend shell execution.

Suspend the execution of this shell until it receives a SIGCONT signal.
Unless forced, login shells cannot be suspended.

Options:
-f[tab]force the suspend, even if the shell is a login shell

Exit Status:
Returns success unless job control is not enabled or an error occurs.

548.

Evaluate conditional expression.

Exits with a status of 0 (true) or 1 (false) depending on
the evaluation of EXPR. Expressions may be unary or binary. Unary
expressions are often used to examine the status of a file. There
are string operators and numeric comparison operators as well.

The behavior of test depends on the number of arguments. Read the
bash manual page for the complete specification.

File operators:

-a FILE True if file exists.
-b FILE True if file is block special.
-c FILE True if file is character special.
-d FILE True if file 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 is set-group-id.
-h FILE True if file is a symbolic link.
-L FILE True if file is a symbolic link.
-k FILE True if file has its `sticky' bit set.
-p FILE True if file is a named pipe.
-r FILE True if file is readable by you.
-s FILE True if file exists and is not empty.
-S FILE True if file is a socket.
-t FD True if FD is opened on a terminal.
-u FILE True if the file is set-user-id.
-w FILE True if the file is writable by you.
-x FILE True if the file is executable by you.
-O FILE True if the file is effectively owned by you.
-G FILE True if the file is effectively owned by your group.
-N FILE True if the file has been modified since it was last read.

FILE1 -nt FILE2 True if file1 is newer than file2 (according to
modification date).

FILE1 -ot FILE2 True if file1 is older than file2.

FILE1 -ef FILE2 True if file1 is a hard link to file2.

String operators:

-z STRING True if string is empty.

-n STRING
STRING True if string is not empty.

STRING1 = STRING2
True if the strings are equal.
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.

Other operators:

-o OPTION True if the shell option OPTION is enabled.
-v VAR True if the shell variable VAR is set.
-R VAR True if the shell variable VAR is set and is a name
reference.
! EXPR True if expr is false.
EXPR1 -a EXPR2 True if both expr1 AND expr2 are true.
EXPR1 -o EXPR2 True if either expr1 OR expr2 is true.

arg1 OP arg2 Arithmetic tests. OP is one of -eq, -ne,
-lt, -le, -gt, or -ge.

Arithmetic binary operators return true if ARG1 is equal, not-equal,
less-than, less-than-or-equal, greater-than, or greater-than-or-equal
than ARG2.

Exit Status:
Returns success if EXPR evaluates to true; fails if EXPR evaluates to
false or an invalid argument is given.