$re = '/\?([а-яёa-z0-9_]{0,100})/iu';
$str = 'http://мой-адрес.рф/?чтото&what=whatsuuuuup-man!!!';
preg_match($re, $str, $matches, PREG_OFFSET_CAPTURE, 0);
// Print the entire match result
var_dump($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