$re = '/^([A-Za-z]{2}[0-9*]{0,6}|\*)$/m';
$str = 'RIGHT:
*
DE*
de*
GB5*
gb5*
DE*123
DE**123
de*123
DE123456
WRONG:
**
*DE
*de
D
D*
D**
d*
DE
DE123
DE123**
de
D1*
1
1*
123*
1234
DE1234567
DE123456*';
preg_match_all($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