$re = '/(data-(?:[a-zA-Z0-9-]+))(?=[a-zA-Z0-9]*)(?:=[\"|\'](.*?)[\"|\'])?/ms';
$str = '<input data-group-validate="true" data-attr=\'what\' data-id/>
';
preg_match_all($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