$re = '/^(?<serialCode>[a-zA-Z0-9]{0,3})(?:(?<serialMarket>[a-zA-Z]{1,2})(?<serialSuffix>(?<=^.{5})[a-zA-Z0-9]*)?)?/m';
$str = 'abcfobar
abc33bar
abca3bar
abc3abar
ab3abar
c3abar
3abar
bar
ab3a3ar
c3ab4r
3aba4
bar
234f22fsdf
a23a3ar
c3ab4r
3aba4
bar
@saff
a@
4@
ab@
abc@
abcd@f
avcde@
abcdef@
abcdefg@';
preg_match_all($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