$re = '/^\d+[a-z\d]$/m';
$str = '29c
29
a
2
2425315651252fsaw
24241jl.421c
29c is fine
29 is fine
2425315651252fsaw fails
24241jl.421c fails';
preg_match_all($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