$re = '/^(?:|(https?:\/\/)?(|www)[.]?((t|telegram)\.me)\/)[a-zA-Z0-9_]{5,32}$/m';
$str = 'https://telegram.me/opensid
http://telegram.me/opensid
www.telegram.me/opensid
telegram.me/opensid
www.t.me/opensid
t.me/opensid
';
preg_match_all($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