$re = '/\b(?=(?:\w*\d){2}\w*)(?=(?:\w*[A-Za-z]){2}\w*)\w{8}\b/';
$str = 'yi12345678
i1234567
i12345u8
12345678
papave23 ciao il mio pin papaver1 è reeredji332ji con vaff8loe 1234567o 123t123t papavero 9o 123t123y
dssdsdsffvdffvdfv
389223897894237234894722348972348924
';
preg_match_all($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