FW: Eregi question

Hi, Hopefully this is my last question so I can put this site to bed. Is there a good article that explains how to do the patterns for eregi. I have read tons of articles, but none really explains what everything means. Like why some things have square brackets and some have round, what does the * and $ do? Etc. i.e. "^[_+a-z0-9-]+(\.[_+a-z0-9-]+)*@[a-z0-9-]+(\.[a-z0-9-]{1,})*\.([a-z]{2,}){1} $" The problem I am having is I'm trying to create a small function to validate a web address. i.e. www.site.com (no http://). I have tried "[a-z0-9]+.[a-z0-9]+.[a-z0-9]", but it only works partially. If I input www.bob I get an error - www.bob.com I get no error, but it doesn't stop. www.bob.com.bob.bob.bob also produces no error. How do I stop it after it matches the 3 patterns? Thanks