PHP Manual . ... 3.0.9 - 3.0.18 only, PHP 4 >= 4.0.0) preg_match -- Perform a regular expression match . int preg_match ( string pattern, string subject [, array matches]) . ... Example 1. ... the "i" after the pattern delimiter indicates a case-insensitive search if (preg_match ("/php/i", "PHP is the web scripting language of choice.")) { print "A match was found."; } else { print "A match was not found." ... domain name is: php.net See also preg_match_all() , preg_replace() , and preg_split() . ...