open DIFF, $diff_file or die $!;
OUTER:
    while (<DIFF>) {
        if (/Cluster (\d+)/) {
            my $num = $1;
            foreach my $c (1 .. 6) { 
                last OUTER unless defined ($_ = <DIFF>);
            }
            $clust_hash {$num} = $_;
        }
    }