$re = '/\s*(?:\/\*).*?(?:\*\/)/s';
$str = 'asdfk /* ad kj */
/*
#someOldCSS {
display: none;
}
*/
asdf /* tesat */
asdf/* tesat */
asdf / tesat */
/*
#someOldCSS {
display: none;
}
#someOldCSS {
display: none;
}
*/';
preg_match_all($re, $str, $matches, PREG_SET_ORDER, 0);
// Print the entire match result
var_dump($matches);
Please keep in mind that these code samples are automatically generated and are not guaranteed to work. If you find any syntax errors, feel free to submit a bug report. For a full regex reference for PHP, please visit: http://php.net/manual/en/ref.pcre.php