So I have done the following sub:

    foreach my $dir (@{$dirs})
    {
        decode($dir.".data.json",%data); # will change name
        my $final_href = 
        {
            data => { ( %{$final_href->{data} },%{ $data{data} } ) },
            total => do
            {
                my %total;
                for my $href ( $final_href->{total}, $data{total} ) {
                    $total{$_} += $href->{total}{$_} for keys %{ $href
+->{total} };
                }
            \%total;
            }
        };
[download]

But it will fail because at start $final_href->{data} is not defined. How to make it work even if its not defined (in that case I should just get the $data{$data}