I don't think so.

Well, yes, I know anything is possible, especially in perl. But when you are using threads, you are still within the same program, and within the scope of the same program. When it comes to global data, think of the thread as any ordinary sub routine. If you change %ENV from the sub routine, it will change for the whole program no matter if it is a threaded sub or not.

The only difference is that you can change it in several places simultaneously if you are not careful. :)

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You have moved into a dark place.
It is pitch black. You are likely to be eaten by a grue.