$re = '/vars\/(prod\S*|stage\S*)\/(mysql|keys).yml/';
$str = 'vars/prod-region1/mysql.yml
vars/prod-region1/keys.yml
vars/prod-region1/test.yml
vars/stage-region2/mysql.yml
vars/stage-region2/keys.yml
vars/stage-region2/test.yml
vars/local/mysql.yml
vars/local/test.yml';
preg_match_all($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