$re = '/^(.+?),\s*(?:(.+?),)?\s*(.+?)$/m';
$str = 'city, state, country
city, country
Baltimore, MD, USA
Baltimore, Maryland, United States
Milan, Italy
Paris, France
Calgary, Alberta, Canada
Example Bad';
preg_match_all($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