$re = '/,([a-zA-Z].*?)(?=,[a-zA-Z]|$)/m';
$str = 'a=b,1,2,3,4,c=34,76,67,54,bc=78,45,h=565,64';
preg_match_all($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