if(preg_match('(.*)^[A-Za-z0-9]+', $_POST['username']) !== 0) { echo "<p style=\"color:red;font-weight:bold;margin-left:95px\">"; echo "Username must only contain A-Z and 0-9</p>"; include("register.html"); exit; } I used the code above but I now get this error message Warning: preg_match() [function.preg-match]: Unknown modifier '^' in C:\Documents and Settings\iceweasel\Desktop\XAMPP\relik.ath.cx\forum\register.php on line 2 I don't like to run php with errors off so I wanna ask how I can fix this.