If the exit statement is used with a value, then gawk exits with
the numeric value given to it.
Otherwise, if there were no problems during execution, gawk exits
with the value of the C constant EXIT_SUCCESS. This is usually
zero.
If an error occurs, gawk exits with the value of the C constant
EXIT_FAILURE. This is usually one.
If gawk exits because of a fatal error, the exit status is 2. On
non-POSIX systems, this value may be mapped to EXIT_FAILURE.
