#!/usr/bin/perl -w
use strict;
use Data::Dumper;

my @array1= ( {a=>1,b=>2,c=>3,d=>4}, {w=>0,x=>1,y=>2,z=>3} );
my @array1= ( {a=>1,b=>2,c=>3,d=>4}, {w=>0,x=>4,y=>2,z=>3} );
my @diff;
foreach  my $i  (  0..$#array1  ) {
    foreach  my $key  (  keys %{$array1[$i]}  ) {
        if(  $array1[$i]->{$key} ne $array2[$i]->{$key}  ) {
            $diff[$i]= { %{$array1[$i]} };
            $diff[$i]->{CHANGED}= delete $diff[$i]->{$key};
            last;
        }
    }
}
print Dumper( \@diff );

##</code><code>##

$VAR1 = [
          undef,
          {
            'w' => 0,
            'CHANGED' => 1,
            'y' => 2,
            'z' => 3
          }
        ];