I don't know if you are permitted to use modules (i fear not).

But if so if you are - and if i where in your shoes i would consider using IO::All and then apply a set operation using Set::Scalar to check for uniqueness.

N.B.: Assuming that i guessed your specs right.

As some of my predecessors already pointed out, it would be helpful if you provide some more details to avoid unnecessary reverse engineering ;-)

Update: tried to fix bad English.

Regards, Karl