You probably wouldn't consider this a gracious way, but... 
use strict;
use warnings;
use Data::Dumper;

my %new_values;
$new_values{MachineType}{Blue_machine}{Unit}{1}{Channel}{0}{Value}{15}
+ = 1;
$new_values{MachineType}{Blue_machine}{Unit}{1}{Channel}{1}{Value}{22}
+ = 2;
$new_values{MachineType}{Blue_machine}{Unit}{2}{Channel}{0}{Value}{19}
+ = 3;
$new_values{MachineType}{Red_machine}{Unit}{1}{Channel}{0}{Value}{22} 
+= 4;

my %old_values;
$old_values{MachineType}{Blue_machine}{Unit}{1}{Channel}{0}{Value}{14}
+ = 5;
$old_values{MachineType}{Blue_machine}{Unit}{1}{Channel}{1}{Value}{22}
+ = 6;
$old_values{MachineType}{Blue_machine}{Unit}{2}{Channel}{0}{Value}{21}
+ = 7;

# Now find the difference
if (my $end_values = hash_keydiff(\%new_values, \%old_values)) {
    print Dumper($end_values);
}

# level by level hash key compare
# NOTE: at no time is the final hash value compared, only keys!!
# returns 0 (no differences)
# or a hash ref of the differences
sub hash_keydiff {
    my ($hash1_ref, $hash2_ref) = @_;
    if (ref($hash1_ref) eq 'HASH') {
        return $hash1_ref unless ref($hash2_ref) eq 'HASH';

        # iterate over hash1_ref keys
        my %return;
        foreach (keys %$hash1_ref) {
            if (defined $hash2_ref->{$_}) {
                # matching keys, dig to the next level
                if (my $result = 
                    hash_keydiff($hash1_ref->{$_}, $hash2_ref->{$_})
                    ) {
                    $return{$_} = $result;
                }
            }
            else { $return{$_} = $hash1_ref->{$_} }
        }
       # iterate over hash2_ref keys
       # NOTE: we've already covered the matching keys above
        foreach (keys %$hash2_ref) {
            $return{$_} = $hash2_ref->{$_}
                unless defined $hash1_ref->{$_};
        }

        return (keys %return) ? \%return : 0;
    }
    return (ref($hash2_ref) eq 'HASH') ? $hash2_ref : 0;
}

[download]
BTW your example result is missing some differences:

$end_values{MachineType}{Blue_machine}{Unit}{1}{Channel}{0}{Value}{15}
$end_values{MachineType}{Blue_machine}{Unit}{2}{Channel}{0}{Value}{21}

In reply to Re: Get the difference between 2 Hashes by ruzam
in thread Get the difference between 2 Hashes by emat

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