Thanks all! From your replies I understand that $1 , $2 type of variables will not contain any value or contain only, old match values of first or second paranthesis from any previous regex matching , unless the pattern matching is complete and if that matching is successful. Opposed to this is \1 which stores first paranthesis value even before the entire pattern is matched , so that it has a defined value in the matching pattern itself and hence provides expected results. Hope my understanding is correct. Correct me if any concerns for you...!!!