Unknown modifier in regular expression [duplicate]

Answer 1

You did not escape your "/" and you didn't complete your if statements either, please try this:

        function checkFBDateFormat($date) {
        if(preg_match("/^([0-9]{2})\/([0-9]{2})\/([0-9]{4})$/", $date, $parts)){
            if(checkdate($parts[2],$parts[1],$parts[3])) {
                return true;
            } else {
                return false;
            }
        } else {
            return false;
        }
    }

echo var_dump(checkFBDateFormat('08/09/2012'));