anonymonk, please read writeup formatting tips the next time you post. We don't use bbcode type formatting here.

To answer your question, you can use exists:

for my $key (keys %{$hash->{$a}{$b}}) {
   unless (exists $hash2->{$d}{$e}{$key}) {
      die "Key $key not found in hash2";
   }
}
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If this is not what you mean, you'd probably have to explain why $c and $f are not the same value in your post, and how $a,$b,$d and $e are determined.