my %total_col; for my $i (keys %from_to_bytes) { for my $j (keys %{ $from_to_bytes{$i} }) { $total_col{$j} += $from_to_bytes{$i}->{$j}; } } print " " x 11; for my $i (sort keys %total_col) { printf " %10s", "$total_col{$i}"; } print "\n";