Your code is not doing what you think it's doing. You should change the code from -

print Dumper(%$hash{'output'});
[download]

to

print Dumper(%{$hash{'output'}});
[download]

Because in the original code you were actually dereferencing %{$hash}{'output'}, where the $hash variable was not defined (you defined %hash earlier, but not $hash).

Add use strict; to the start of your code and you will get a compilation error.