$re = '/some-page\/(\d+)\/([^\/\n]+)(?:\/(?!registration-form$).*)?$/m';
$str = '/some-page/12/any-string
/some-page/12/any-string/
/some-page/12/any-string/some-string
/some-page/12/any-string/some-string/
/some-page/12/
/some-page/245/any-string/registration-form
';
preg_match_all($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