$re = '/\b(?<!num{)(?<!SI{)\d+,\d+/m';
$str = '2,47
12,67
\\mathbf{12,76}
\\num{2,76}
\\num{12,76}';
preg_match_all($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