#!/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;