$re = '/^\d{5}.*[a-zA-Z]{5}$/m';
$str = '12345some textqwert
12345some text qwer
1234some textqwert
Force the first 5 digits to be only numbers and the last 5 digits to be only letters?';
preg_match_all($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