$re = '/^(?:.+\\\\*)([0-9]{8})(?:.+)(?:\.)(?:.+)$/';
$str = '"C:\\\\Users\\\\username\\\\C-Sharp\\\\Project\\\\12345678_X\\\\Folder\\\\56781234_01.itm"';
preg_match($re, $str, $matches, PREG_OFFSET_CAPTURE, 0);
// Print the entire match result
var_dump($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