$re = '/(?<edition>\d{1,8}-\d{1,8})?_?(?<name>[^_.]+)_?(?<artist>[^_.]+)?.(?<extension>[\S]{1,8})?$/m';
$str = '2-13_oops-i-did-it-again_britney-spears.mp3
3-13_toxic_britney-spears.vaw
hold-it-against-me_britney-spears.flac
unknown.mp3';
preg_match_all($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