To rewind a file to beginning use seek FILE,0,0. Read the seek for more info on how this works.

Update:Also spotted why you're losing data.. the while (<DATA2>) reads in one line itself into $_, and then you read in a second into $line with $line= <DATA2>, with the result that half the lines are entirely ignored. A better way would be while (my $line= <DATA2>) instead of either of both of the other lines.