<?php $usernames = array('asdasd123', 'asdas_asdasd123', 'asdsad--asdsa123123', 'asdasd<><><>'); foreach($usernames as $u) { if(preg_match('([A-Za-z0-9\-\_]+)', $u) { echo $u.' is totally valid'; } else { echo $u. 'is not valid'; } }
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