The exit operation terminates the pipeline and returns an integer status
code. It takes zero or one argument. When no argument is provided, it exits
with status code 1. When an argument is provided, you must supply an explicit
destination slot (an identifier or _) to receive the exit code, and that code
is used as the status.
The syntax of the exit operation is:
[ $destination ] exit [ statusCode ]
When called without any arguments, exit is equivalent to:
_ exit 1
terminating the pipeline with status code 1 and binding 1 to _. When you
supply a statusCode argument, you must also provide a $destination
identifier:
_ exit 2
This binds the integer 2 to _ and then immediately terminates the pipeline
with status code 2. If you bind to a named identifier, for example:
$code exit 3
then 3 is bound to code before the pipeline exits with status 3.
Once an exit instruction runs, no further operations are executed. If the
argument is missing or not an integer, the pipeline fails to parse or execute
before performing the exit.