Your question seems (the way it is phrased) to be a part of either 1) homework 2) Job question

I think Zaxo has given you enough information to read to do the task at hand

Monks, FWIW-found this link that contains the same similar question!(from 2001)

http://bbs.myonehost.com/cgi-bin/bbscon?board=unix&file=M.988731311.A&num=37