First, you have nested your loops so you are comparing each element of the first array against all of the elements of the second array. Unless all of your hashes are identical (rather than just each pair), most of them will be reported as "changed".

Second, = is an assignment operator. Perhaps that was just a typo and you meant == which does a numeric comparison. But you should really use eq which is much more general (compares strings).

Here is some code. I'm not sure I correctly deciphered what you want to do when you find a difference.

#!/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 );
[download]

The $diff[$i]= { %{$array1[$i]} }; bit copies the entire anonymous hash into a new anonymous hash and stores a reference to it into @diff.

The $diff[$i]->{CHANGED}= delete $diff[$i]->{$key}; bit deletes the changed key and the delete operator returns the associated value so that you can associate with the new key, "CHANGED".

This code prints out:

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

        - tye (but my friends call me "Tye")