It partly depends on what your script is doing: CGI scripts usually run very quickly but frequently, while serious text-processing scripts may just suck up CPU cycles. The latter is much easier to monitor. The ps command is standard on every Unix system I've ever used, and you should be able to find a version of top for your platform for roughly realtime statistics. Execution time you can track by checking the system time at the beginning and end of your scripts, though this isn't very reliable for short-lived scripts.
in reply to Testing Efficiency