$re = '/\.([^.]+)$/m';
$str = '804269_General Motors Financial Company Inc._02-05-2020_10-K_0000804269-20-000006.txt.txt';
preg_match_all($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