Looking for an easier regex check...

Does anybody know of a good way to make sure that a string contains ONLY certain characters. I tried using ereg("[~`!@#$%^&*(){}-+=|\\/.,<>'\":;\[\]]", $string); but I get parse errors. Besides that I only want the characters A-Za-z0-9_ in $string. Is there is simpler way to ensure this rather than checking to see if any of the characters I don't want are in there? Thank you for your help in advance. -- Joshua E Minnie/CIO josh@acsurf.net Phone: 616.276.9690 Fax: 616.342.8750 Nextel: 616.862.2847 "Don't work for recognition, but always do work worthy of recognition."