$re = '/(?<=^Total revenue for )(?=\d+[-_]?\d+)[\d_-]{6,7}(?!\S)/m';
$str = 'Total revenue for 2016-03 is 3000 €
Total revenue for 2016_03 is 3000 €
Total revenue for 201603 is 3000 €
Total revenue for 2016-03 is 3000 €
Total revenue for 2016_03 is 3000 €
Total revenue for 201603 is 3000 €
Total revenue for 032016 is 3000 €
Total revenue for 03_2016 is 3000 €
Total revenue for 03-2016 is 3000 €
Total revenue for 3000 is 3000 €
Total revenue for 30-00100-1010101 is 3000 €
';
preg_match_all($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