$re = '/(?=.*\d)[A-Za-z0-9]{1,11}/m';
$str = 'a1
12345678901
a1b2c3d4e56
432432324ll
k343242432k
kkkkkkkkkkk
2342343249
asdmsd1kfds';
preg_match_all($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