Very close. Try this instead:

foreack $k (keys %$hash) {
    print "$k => $hash->{$k}\n";
    print "$k => $$hash{$k}\n";   # equivalent
}
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The code you have above is for a hash named %hash, not a reference to a hash contained in a scalar $hash. Notice that in the code above, the sigil preceding the variable is always a $.

For more info on references in general, take a look at perlref and perlreftut.