#!perl -l

use strict;
use warnings;

my %ref = qw(a 1 b 2 c 3 d 4);
my %raw = qw(a 1 b 2 c 4 e 4);
my %keys;

@keys{keys %ref, keys %raw} = 0;

for (keys %keys) {
    unless (defined $raw{$_} && defined $ref{$_} && $raw{$_} eq $ref{$
+_}) {
        my $vraw = defined $raw{$_} ? $raw{$_} : "undef";
        my $vref = defined $ref{$_} ? $ref{$_} : "undef";
        print "$_: $vraw, $_: $vref";
    }
}
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