$re = '/^(?=^[^\d]*\d[^\d]*\d[^\d]*$)(?=.*[a-z])(?=.*[A-Z]).{8,}$/m';
$str = '123456789
abcdefghi
ABCDEFGHI
abcdABC12
abcdABC121
.12nabdh#A
Abc4k9h2L
Abc4k9hL+
Abc4l@s$kl4 ';
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