I have just received gv data capture device what if I extended
beyond 49 ft with rs232 cable would it work as I am 5 to 6 ft short

The spec for DB-9/RS232 is 50 ft. And I really wouldn't go beyond that. It's not a shielding issue so much as a voltage signal drop. You might try doing this: RS-232->RS-485->RS-232 using a pair of converters.

Many softwrae POS packages now use Geo for example quest is a hardware software POS package that integrates with Geo but only needs ethernet access so you can achieve much longer runs