Actually, in any POSIX/UNIX conforming shell,

Code:

exit 0

is not the always the same as

Code:

exit

When exit is called with no operands, the rules are:
Thus, if the success or failure of a shell script is determined by the last command the script executes, calling exit without an exit status returns the exit status of that command. So, the code sequences:

Code:

awk '<some awk program>'
exit

Code:

awk '<some awk program>'
exit $?

Code:

awk '<some awk program>'
status=$?
if [ $status != 0 ]
then {
    printf "$0: awk failed\nTerminating unsuccessfully at %s\n" "$0" "$(date)"
    exit $status
}
printf "$0: Terminating successfully at %s\n" "$0" "$(date)"
exit $status

in a script all provide the same exit status to the invoking shell.

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This has been edited, I originally screwed up the test for success.