| my $f1=shift;
| my $f2=shift;
| open (F1,$f1)||die;
| open (F2,$f2)||die;
| my @accn1=<F1>;
| my @accn2=<F2>;
| my @unique1;
| foreach my $accn (@accn1) {
| push @unique1,$accn unless (grep(/$accn/, at accn2));
| }
This also just does one half (F1-F2). You need to add F2-F1 to it.
T