$re = '/\b\d\d(?=\S*?[A-Z]\S*?\s)[A-Z0-9]{4}\s/m';
$str = 'AT exempt acc to §§ 4 Nr. 1A UStG iVm 6 USTG
254,49/100L 977,23
159C5F Magnatec St-St 0W-30 D, 20L E4 0,00%
Commodity Code :
159C5F Magnatec St-St 0W-30 D, 20L E4
159432 Magnatec St-St 0W-30 D, 20L E4 --> Number only.
1AAAAA Magnatec St-St 0W-30 D, 20L E4 --> Starts with one digit.';
preg_match_all($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