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468.

Set variable values and attributes.

Declare variables and give them attributes. If no NAMEs are given,
display the attributes and values of all variables.

Options:
-f[tab]restrict action or display to function names and definitions
-F[tab]restrict display to function names only (plus line number and
[tab]source file when debugging)
-p[tab]display the attributes and value of each NAME

Options which set attributes:
-a[tab]to make NAMEs indexed arrays (if supported)
-A[tab]to make NAMEs associative arrays (if supported)
-i[tab]to make NAMEs have the `integer' attribute
-l[tab]to convert NAMEs to lower case on assignment
-r[tab]to make NAMEs readonly
-t[tab]to make NAMEs have the `trace' attribute
-u[tab]to convert NAMEs to upper case on assignment
-x[tab]to make NAMEs export

Using `+' instead of `-' turns off the given attribute.

Variables with the integer attribute have arithmetic evaluation (see
the `let' command) performed when the variable is assigned a value.

When used in a function, `declare' makes NAMEs local, as with the `local'
command.

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

488.

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..

489.

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
-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.

491.

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.
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.

498.

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 as well, and numeric comparison operators.

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.
! 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.

501.

Trap signals and other events.

Defines and activates handlers to be run when the shell receives signals
or other conditions.

ARG is a command to be read and executed when the shell receives the
signal(s) SIGNAL_SPEC. If ARG is absent (and a single SIGNAL_SPEC
is supplied) or `-', each specified signal is reset to its original
value. If ARG is the null string each SIGNAL_SPEC is ignored by the
shell and by the commands it invokes.

If a SIGNAL_SPEC is EXIT (0) ARG is executed on exit from the shell. If
a SIGNAL_SPEC is DEBUG, ARG is executed before every simple command.

If no arguments are supplied, trap prints the list of commands associated
with each signal.

Options:
-l[tab]print a list of signal names and their corresponding numbers
-p[tab]display the trap commands associated with each SIGNAL_SPEC

Each SIGNAL_SPEC is either a signal name in <signal.h> or a signal number.
Signal names are case insensitive and the SIG prefix is optional. A
signal may be sent to the shell with "kill -signal $$".

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

518.

Resume job in foreground.

Equivalent to the JOB_SPEC argument to the `fg' command. Resume a
stopped or background job. JOB_SPEC can specify either a job name
or a job number. Following JOB_SPEC with a `&' places the job in
the background, as if the job specification had been supplied as an
argument to `bg'.

Exit Status:
Returns the status of the resumed job.

520.

Execute conditional command.

Returns a status of 0 or 1 depending on the evaluation of the conditional
expression EXPRESSION. Expressions are composed of the same primaries used
by the `test' builtin, and may be combined using the following operators:

( EXPRESSION )[tab]Returns the value of EXPRESSION
! EXPRESSION[tab][tab]True if EXPRESSION is false; else false
EXPR1 && EXPR2[tab]True if both EXPR1 and EXPR2 are true; else false
EXPR1 || EXPR2[tab]True if either EXPR1 or EXPR2 is true; else false

When the `==' and `!=' operators are used, the string to the right of
the operator is used as a pattern and pattern matching is performed.
When the `=~' operator is used, the string to the right of the operator
is matched as a regular expression.

The && and || operators do not evaluate EXPR2 if EXPR1 is sufficient to
determine the expression's value.

Exit Status:
0 or 1 depending on value of EXPRESSION.

526.

Formats and prints ARGUMENTS under control of the FORMAT.

Options:
-v var[tab]assign the output to shell variable VAR rather than
[tab][tab]display it on the standard output

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 format specifications described in printf(1)
and printf(3), printf interprets:

%b[tab]expand backslash escape sequences in the corresponding argument
%q[tab]quote the argument in a way that can be reused as shell input

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

527.

Specify how arguments are to be completed by Readline.

For each NAME, specify how arguments are to be completed. If no options
are supplied, existing completion specifications are printed in a way that
allows them to be reused as input.

Options:
-p[tab]print existing completion specifications in a reusable format
-r[tab]remove a completion specification for each NAME, or, if no
[tab]NAMEs are supplied, all completion specifications

When completion is attempted, the actions are applied in the order the
uppercase-letter options are listed above.

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