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566.

Execute commands based on pattern matching.

Selectively execute COMMANDS based upon WORD matching PATTERN. The
`|' is used to separate multiple patterns.

Exit Status:
Returns the status of the last command executed.

567.

Execute commands based on conditional.

The `if COMMANDS' list is executed. If its exit status is zero, then the
`then COMMANDS' list is executed. Otherwise, each `elif COMMANDS' list is
executed in turn, and if its exit status is zero, the corresponding
`then COMMANDS' list is executed and the if command completes. Otherwise,
the `else COMMANDS' list is executed, if present. The exit status of the
entire construct is the exit status of the last command executed, or zero
if no condition tested true.

Exit Status:
Returns the status of the last command executed.

568.

Execute commands as long as a test succeeds.

Expand and execute COMMANDS as long as the final command in the
`while' COMMANDS has an exit status of zero.

Exit Status:
Returns the status of the last command executed.

569.

Execute commands as long as a test does not succeed.

Expand and execute COMMANDS as long as the final command in the
`until' COMMANDS has an exit status which is not zero.

Exit Status:
Returns the status of the last command executed.

570.

Create a coprocess named NAME.

Execute COMMAND asynchronously, with the standard output and standard
input of the command connected via a pipe to file descriptors assigned
to indices 0 and 1 of an array variable NAME in the executing shell.
The default NAME is "COPROC".

Exit Status:
The coproc command returns an exit status of 0.

571.

Define shell function.

Create a shell function named NAME. When invoked as a simple command,
NAME runs COMMANDs in the calling shell's context. When NAME is invoked,
the arguments are passed to the function as $1...$n, and the function's
name is in $FUNCNAME.

Exit Status:
Returns success unless NAME is readonly.

572.

Group commands as a unit.

Run a set of commands in a group. This is one way to redirect an
entire set of commands.

Exit Status:
Returns the status of the last command executed.

573.

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.

574.

Evaluate arithmetic expression.

The EXPRESSION is evaluated according to the rules for arithmetic
evaluation. Equivalent to "let EXPRESSION".

Exit Status:
Returns 1 if EXPRESSION evaluates to 0; returns 0 otherwise.

575.

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.