$re = '/(?<=OH_|ma)(\w)+/';
$str = 'OH_OrderItemStatusChanged
Style1PS1A1OH_OrderItemStatusSpacerOH_OrderItemStatusID_2
(OH_OrderItemSentTo ) (OH_SalesRep )OH_OH_OH_SalesRepSalesRepSalesRep
OH_OH_maSalesRepSalesRepSalesRep';
preg_match_all($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