$re = '/\]\s*(AN|AV)\s+1\s+([\w\s]+)\s+2\s+([\w\s]+)\s+3\s+((?=.*\bda cui\b)|(?!=.*\bda cui\b).*)/m';
$str = '] AN 1 campo 2 prato con penna B sps a 1 3 campo con penna C as a 1 cfr Nota filologica
] AN 1 campo 2 prato con penna B sps a 1 3 da cui campo con penna C as a 1 cfr Nota filologica
] AN 1 campo 2 prato con penna B sps a 1 3 da cuio campo con penna C as a 1 cfr Nota filologica
';
preg_match_all($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