Are you trying to do something like this?

#!/usr/bin/perl

# https://perlmonks.org/?node_id=1228412

use strict;
use warnings;

my $one =
  {
  data  => {
             dir1 => {
                       fileA => { pid => { 61781 => 1 }, total => 13 }
+,
                       fileB => { pid => { 61799 => 1 }, total => 12 }
+,
                     },
             dir2 => {
                       fileA => { pid => { 61439 => 1 }, total => 5 },
                       fileC => { pid => { 12345 => 1 }, total => 10 }
+,
                     },
           },
  total => { fileA => 18, fileB => 12, fileC => 10 },
  };

my $two =
  {
  data  => {
             dir3 => {
                       fileA => { pid => { 616161 => 1 }, total => 6 }
+,
                       fileD => { pid => { 54321 => 1 }, total => 12 }
+,
                     },
             dir4 => {
                       fileA => { pid => { 1718 => 1 }, total => 2 },
                       fileE => { pid => { 15151 => 1 }, total => 3 },
                     },
           },
  total => { fileA => 8, fileD => 12, fileE => 3 },
  };

sub combinemanyhashes
  {
  my $newhash = 
    {
    data => { map %{ $_->{data} // {} }, @_ },
    total => do
      {
      my %total;
      for my $href ( @_ )
        {
        $total{$_} += $href->{total}{$_} for keys %{ $href->{total} //
+ {} };
        }
      \%total;
      }
    };
  return $newhash;
  }

my $totalhashref = {};

$totalhashref = combinemanyhashes( $totalhashref, $one, $two );

use Data::Dump 'dd'; dd $totalhashref;
[download]

Not quite but thank you for the reply. I have created the following sub:


    my ($name,$dirs,$final_href) = @_;
    my %data;
    foreach my $dir (@{$dirs})
    {

        decode($dir."/".$name,%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 won't work because when I pass $final_href to this sub, it is empty, so it will fail "Can't use an undefined value as a HASH reference"
. I tried to add:


$files_href->{data} = ();
$files_href->{total} = ();
[download]

But it also does not work. it wants a real hash (because we do dereferencing with %{$final_href->{data}).
Any ideas how to solve it?

That's not a sub.

Posting incomplete code will cause an incomplete an

In the code you've posted -- now twice -- the answer is staring you in the face. LanX was trying to help you learn how to debug your own code by giving hints, and asking you to research declarations. Since that apparently wasn't enough, my advice to you (HINT: note the link I just embedded) is to look at lines 1 and 7 in the code I am replying to, and maybe study more about "perl scope" as well.

Try and see what happens