my @GRD = split /,/;
    warn "line $.: wrong number of attributes\n"
        unless @GRD == 6;
    check($GRD[0], 1, @GRDF1);
    check($GRD[1], 2, @GRDF2);
    ...
    check($GRD[5], 6, @GRDF6);


    sub check (
        my($GRD, $col, $@GRDF) = @_;
        return if grep { $GRD eq $_ } @GRDF;
        print "line $.: \"$GRD\" is invalid in column $col\n";
    }