You're right, it doesn't work.

Seriously, %hash is a lexical variable. The whole point of lexical variables is that they're not available outside of their scopes. %hash is scoped to the enclosing file.

The quick and dirty solution is to make %hash a global variable, probably with the vars pragma. I take issue with this comment, though:

But this is not possible in our real code.

It's just software. I change software all the time.